Modern container coatings

Modern Container Coatings In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Wa...

Author: Robert C. Strand

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Modern Container Coatings

In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.


Modern Container Coatings Robert C . Strand, EDITOR American Can Company

A symposiu the Division of Organic Coatings and Plastics Chemistry at the 174th Meeting of the American Chemical Society, Chicago, IL, August 2 9 September 2, 1977.

78

ACS SYMPOSIUM SERIES

AMERICAN

CHEMICAL

SOCIETY

WASHINGTON, D. C. 1978


Library of Congress CIP Data Modern container coatings. (ACS symposium series; 78. ISSN 0097-6156) Bibliography: p. 124 + ix. Includes index. 1. Containers—Congresses. 2. Coatings—Congresses. I. Strand, Robert C., 1925. II. American Chemical Society. Division of Organic Coatings and Plastics Chemistry. III. Series: American Chemical Society. ACS symposium series; 78. TS198.3.C6M63 ISBN 0-8412-0446-2

621.7'57 ACSMC8

78-14801 78 1-124 1978

Copyright © 1978 American Chemical Society All Rights Reserved. The appearance of the code at the bottom of the first page of each article in this volume indicates the copyright owner's consent that reprographic copies of the article may be made for personal or internal use or for the personal or internal use of specific clients. This consent is given on the condition, however, that the copier pay the stated per copy fee through the Copyright Clearance Center, Inc. for copying beyond that permitted by Sections 107 or 108 of the U.S. Copyright Law. This consent does not extend to copying or transmission by any means—graphic or electronic—for any other purpose, such as for general distribution, for advertising or promotional purposes, for creating new collective works, for resale, or for information storage and retrieval systems. The citation of trade names and/or names of manufacturers in this publication is not to be construed as an endorsement or as approval by ACS of the commercial products or services referenced herein; nor should the mere reference herein to any drawing, specification, chemical process, or other data be regarded as a license or as a conveyance of any right or permission, to the holder, reader, or any other person or corporation, to manufacture, reproduce, use, or sell any patented invention or copyrighted work that may in any way be related thereto. PRINTED IN THE UNITED STATE OF AMERICA

American Chemical

Society Library

1158Container 16th St. N.W.Strand, R.; In Modern Coatings; ACS Symposium Series; American Chemical Washington, D. C. Society: 20036 Washington, DC, 1978.

ACS Symposium Series Robert F. G o u l d , Editor

Advisory Board Kenneth B. Bischoff

Nina I. McClelland

Donald G . Crosby

John B. Pfeiffer

Jeremiah P. Freeman

Joseph V . Rodricks

E. Desmond Goddard

F. Sherwood Rowland

Jack Halpern

Alan C. Sartorelli

Robert A . Hofstader

Raymond B. Seymour

James P. Lodge

Roy L. Whistler

John L. Margrave

Aaron Wold


FOREWORD The ACS SYMPOSIUM SERIES was founded in 1974 to provide

a medium for publishin format of the SERIES parallels that of the continuing ADVANCES IN CHEMISTRY SERIES except that in order to save time the papers are not typeset but are reproduced as they are submitted by the authors in camera-ready form. As a further means of saving time, the papers are not edited or reviewed except by the symposium chairman, who becomes editor of the book. Papers published in the ACS SYMPOSIUM SERIES are original contributions not published elsewhere in whole or major part and include reports of research as well as reviews since symposia may embrace both types of presentation.


PREFACE Containers—metal, glass, and more recently plastic—are an essential part of our food and beverage distribution system. The technology of these containers, particularly metal cans, has developed steadily over the past 75 years. A key to the success of the metal container has been the development and availability of organic coatings which offer a wide range of performance properties. Early coating materials such as C-enamel, which is used in corn cans, were relatively simple to manufacture and apply. They did not represent a high level o for a specific packaging need. Once a coating was developed, it tended to remain in use for many years because there generally was little reason to change it. With the advent of newer can-making technology such as the drawing-redrawing and the drawing and ironing processes, newer and more sophisticated coating materials were needed. Environmental concerns and energy conservation pressures also have contributed to the demand for new and different coating materials. This trend is seen also in the glass container industry where safety coatings for beverage bottles are now in use. Much of the change in coating technology has taken place within the past four to five years and brings the latest, most modern coating technology to the container industry. That segment of the coating industry which serves the packaging business is characterized by vigorous competition among suppliers and the use of extensive proprietary know-how. For these reasons it is difficult for coating chemists to discuss their company products or processes. For example, there are no papers in this symposium on the wash coating of two-piece beverage cans because the process involves proprietary technology on the part of several companies. Despite these problems, this symposium succeeds in surveying the main areas of coating development and analysis currently used in the rigid packaging industry. I would like to thank the authors whose time and effort contributed to the success of this symposium. American Can Company,

ROBERT C. STRAND

Barrington Technical Center, Barrington, IL May 31, 1978 ix In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

1 Waterborne Spray Can Coatings DAVID Ο. LAWSON PPG Industries, Delaware, OH 43015

In preparing to cove was difficult to determin coatings and the reasons for their increased interest in the industrial coatings field. Other presentations here have and w i l l mention some of the areas I wish to review. However, for understanding of water borne spray can coatings, we will explain the purpose of spraying the interior of metal cans, review why the various legislative actions of recent years have stimulated development of water borne sprays, give a general insight into coating formulations, and relate field experience with coating handling and equipment operation. From this, we will be able to have some feeling for the future of water borne spray can coatings. The metal can industry supplies the major share of its pro duction for the beer and soft drink markets. With calculations from various industry figures, this highly specialized business today is producing in the range of 45 to 50 b i l l i o n cans annually. The three-piece can is produced from decorated flat stock, which has undergone a number of coatings operations. Handling of sheets through the coating stages and subsequent can forming oper ations can be expected to damage the interior basecoat through abrasion and scratching. Complete protection and coverage must be achieved with the steel substrates used for three-piece cans, because of the delicate flavor properties of beer and the corrosiveness, as well as taste considerations, of carbonated soft drink products. The interior spray, then is actually a repair coating and is the last operation in coating of the can body. Two -piece cans are taking over the major share of the beverage can market and are produced in the integral form of the drawn cup. Both aluminum and tinplated steel substrates are used today, and again protection of beverages from the metal and of metal from the product to be packaged requires the inside spray coating. For some years, the interior sprays have been familiar or ganic coating types with organic solvents as the transport media. Reduction of organic solvent emissions from such coatings has 0-8412-0446-2/78/47-078-001$05.00/0 © 1978 American Chemical Society In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

MODERN CONTAINER COATINGS

2

been a goal f o r some time and e f f o r t s i n c r e a s e d w i t h the advent of the famous Los Angeles Rule 66. Here i t was proposed to a l l o w s o l v e n t emissions i f s o - c a l l e d Rule 66 exempt s o l v e n t s were used. F i v e to s i x years l a t e r , other s e c t i o n s of the country had adopted Rule 66 and even added some more s t r i n g e n t requirements to attempt meeting governmental A i r Q u a l i t y Standards. Again, Los Angeles l e d the way w i t h a modified Rule 66, but we i n the coatings i n d u s t r y were given the opportunity to proceed w i t h water borne coatings which, along w i t h high s o l i d s c o a t i n g s , were made exempt from any requirements of i n c i n e r a t i o n of v o l a t i l e s . You should be aware that important progress was made i n the development and c o m m e r c i a l i z a t i o n of water r e d u c i b l e e l e c t r o c o a t ings i n the e a r l y 1960 s. This c o m m e r c i a l i z a t i o n and some b e t t e r understanding of how to formulate water r e d u c i b l e polymers to meet the demands of i n d u s t r i a l a p p l i c a t i o n s took p l a c e before the l e g i s l a t i v e pressures askin emissions. We were working c l o s e l y w i t h major can companies to see what place could be found f o r the e f f i c i e n t e l e c t r o d e p o s i t i o n process. This l e d to spray a p p l i c a t i o n s of the water r e d u c i b l e polymer systems that were e v o l v i n g f o r i n t e r i o r beer and s o f t d r i n k cont a c t . I t was recognized that the spray a p p l i c a t i o n area i n can p l a n t s i s a source of h i g h emissions, because of the spray opera t i o n and the use of low s o l i d s content c o a t i n g s . The i n d u s t r y was moved toward changing to water borne i n t e r i o r sprays because s o l v e n t emissions could be reduced by as much as 70 to 80% over the low s o l i d s , organic s o l v e n t c o n t a i n i n g c o n v e n t i o n a l systems. Remember, t h i s c o a t i n g o p e r a t i o n takes place f o r every beer and s o f t d r i n k can manufactured . As f u r t h e r i n c e n t i v e , the avenue of water borne spray o f f e r s continued use of e x i s t i n g equipment, which represents extremely high c a p i t a l investment i n the can industry. The f i r s t challenge from these m a t e r i a l s , then, i s to spray apply on the v a r i o u s types of a i r and a i r l e s s spray equipment i n the many can producing p l a n t s . The coatings are a l s o t a i l o r e d to meet cure c o n d i t i o n s d i c t a t e d by the v a r i o u s s u b s t r a t e s , s i d e seam c o n s t r u c t i o n , and oven designs i n use i n the i n d u s t r y . Of major importance, of course, i s meeting the h i g h e r temperature, s h o r t e r time c y c l e of the two-piece can cure. The f i n a l measure of a c c e p t a b i l i t y f o r a can l i n e r i n contact w i t h beer and s o f t d r i n k products i s to meet the performance and f l a v o r c h a r a c t e r i s t i c requirements expected. Much of the s u c c e s s f u l a p p l i c a t i o n to date i n v o l v e s a c r y l i c and epoxy chemistry, and we w i l l d i r e c t our b r i e f review f o r t h i s p r e s e n t a t i o n to those types of thermosetting m a t e r i a l s . These coatings are processed v i a an a d d i t i o n a l p o l y m e r i z a t i o n of monomers i n i t i a t e d by thermal decomposition of a f r e e r a d i c a l i n i t i a t o r . P o l y m e r i z a t i o n i n a batch r e a c t o r uses a c o u p l i n g s o l v e n t and chain t r a n s f e r s o l v e n t s to c o n t r o l molecular weight. Following proper p o l y m e r i z a t i o n , a p o r t i o n of the organic a c i d groups f

1


1.

LAWSON

Waterborne

Spray Can

Coatings

3

along the polymer backbone are converted to amine s a l t s , u s i n g an a p p r o p r i a t e amine, t o render the polymer r e d u c i b l e i n water. As i n many polymer systems, s t r i c t a t t e n t i o n i s given t o raw materi a l s , t h e i r p r o p o r t i o n s and a d d i t i o n r a t e s , times, temperatures, and s p e c i f i c process check p o i n t s . A m u l t i t u d e of p r o c e s s i n g f a c t o r s a f f e c t s u c c e s s f u l manufacture of product, and each i n t u r n would i n v o l v e d e t a i l e d study o f engineering parameters. I w i l l simply mention these f o r our purposes as: proper s e l e c t i o n and p r e p a r a t i o n o f equipment, c a r e f u l c o n t r o l o f p o l y m e r i z a t i o n c o n d i t i o n s , and m a i n t a i n i n g awareness o f how such f a c t o r s a f f e c t polymer molecular weight, p a r t i c l e s i z e , e t c . The performance of the water borne spray c o a t i n g so produced i s extremely dependent on p r o c e s s i n g procedures. As we work w i t h water borne spray c o a t i n g s , our b i g g e s t challenge comes from the rheology and s u r f a c e w e t t i n g c h a r a c t e r i s t i c s that are so predominantl Coated, as w e l l as bar problems. I n the area o f spray, of course, behavior o f the coating m a t e r i a l upon a t o m i z a t i o n through spray n o z z l e s has a great b e a r i n g on the w e t t i n g and coverage a l s o . Experience has been g e n e r a l l y good i n the h a n d l i n g o f these coatings through convent i o n a l equipment. Some reeducation i s r e q u i r e d i n the a c t u a l s e l e c t i o n o f spray nozzles because newer coatings cannot necessari l y have the exact same s o l i d s , v i s c o s i t y , and rheology propert i e s o f the c o n v e n t i o n a l coatings they r e p l a c e . O v e r a l l , recognize the f a c t t h a t l i n e c o n d i t i o n s vary w i d e l y i n the i n d u s t r y . Such f a c t o r s as temperature, type spray machine, can c o n f i g u r a t i o n , pressure a v a i l a b l e , can r o t a t i o n speeds, and many more can and must be d e a l t w i t h . To d i s c u s s these t o any degree would consume a great deal o f the time to which we are l i m i t e d f o r one p r e s e n t a t i o n . I b e l i e v e other speakers w i l l b e t t e r d e s c r i b e some equipment d e t a i l s . We are meeting these challenges and through experience the use of water borne spray coatings i s becoming more f a m i l i a r t o the i n d u s t r y . With these low s o l v e n t coatings h e l p i n g to meet A i r Q u a l i t y Standards, and the recognized s a f e t y aspects o f storage and h a n d l i n g , we can c e r t a i n l y expect t h i s technology t o enjoy a great growth p a t t e r n and a long and u s e f u l l i f e c y c l e . RECEIVED MAY 22, 1978.


2 Fast-Cure Epoxy Powders as Beer and Beverage Can Interior Lacquers PETER H. SCOTT, DONALD C. CLAGETT, and KENNETH V. FISCHER Dewey and Almy Chemical Division, W. R. Grace & Co., 55 Hayden Avenue, Lexington, MA 02173

The Clean Air Act the coatings industry t coatings (1, 2). These alternatives include waterborne coatings, powder coatings, non-aqueous dispersions, radiation cured total solids, and electrodeposition. Relative to coating the interior of beer/beverage cans with a solvent-free material, the Dewey and Almy Chemical Division of W. R. Grace & Co. has elected to pursue development of a powdered lacquer. Powdered coatings contain l i t t l e or no volatile effluents and require low energy consumption for application and cure. DISCUSSION Any acceptable beer/beverage can coating must meet several general requirements. It must be formulated exclusively of materials approved for this use by the FDA (3). It must not affect the taste of the beverage packed in the can. It must be coated at low film weights (thin films) to minimize coating expense, and when used in a two-piece can it must cure within two minutes at a maximum temperature of 400°F to meet existing line specifications. Other powder properties necessary to economically coat beer/beverage cans are: 1. Fine particle size powders on the order of 5-8 micron mean diameter. 2. Good bulk flow and fluidization such that the powder does not cake or cause blockage inside the application tubing. This is critical when dealing with very fine particle powders.

0-8412-0446-2/78/47-078-004$05.00/0 © 1978 American Chemical Society In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

2.

s e o i r ET AL.

Fast-Cure

Epoxy

Powders

3.

Minimal overspray and high t r a n s f e r e f f i c i e n c i e s .

4.

The powdered m a t e r i a l must be formulated such that i t does not b u i l d up (impact fuse) on moving machinery p a r t s i n s i d e the a p p l i c a t i o n device.

5

To meet the above requirements thermosetting epoxies and epoxy/phenolics were chosen f o r powder c o a t i n g development a t Grace. These r e s i n s have had a h i s t o r y of s u c c e s s f u l use as solvent base m a t e r i a l s and thus the p o t e n t i a l f o r o b t a i n i n g a powder w i t h the p r o p e r t i e s needed f o r an i n t e r i o r can c o a t i n g was high. T y p i c a l epoxy powder f o r m u l a t i o n s t e s t e d contained a b i s - p h e n o l A type epoxy r e s i n , c u r i n g agent ( a c i d i c or b a s i c ) , l e v e l i n g agent, w e t t i n g agent and c a t a l y s t (4, 5 ) . I n i t i a l t e s t r e s u l t s i n our l a b o r a t o r y showed that coatings w i t h acceptable p h y s i c a cure times a t 400°F wer (Table 1). This was a key problem s i n c e an oven residence time of two minutes or l e s s i s a n e c e s s i t y on a commercial beer^ beverage can l i n e . I n c r e a s i n g oven temperatures above 400 F was one obvious o p t i o n f o r reducing cure time, but that o p t i o n was r u l e d out because of increased energy consumption and other commercial c o n s t r a i n t s . Therefore, we screened a v a r i e t y of formulations to s e l e c t c u r i n g systems w i t h exotherms a t or below 400°F as determined u s i n g d i f f e r e n t i a l scanning c a l o r i m e t r y (DSC). Samples were prepared by m i c r o m i l l i n g raw m a t e r i a l m i x t u r e s , and DSC scans were made u s i n g a duPont 990 instrument. The sample s i z e was 17 -1 mg., and the samples were heated i n a n i trogen atmosphere at 0.3 mm p o s i t i v e pressure. Our i n i t i a l work showed that standard mixtures of epoxy and c u r i n g agent had exotherms a t or above 400°F (Figures 1 and 2 ) . Both a c i d and base c a t a l y s t , however, gave i n i t i a l exotherms s i g n i f i c a n t l y lower than obtained w i t h the uncatalyzed systems (Figure 3). U n f o r t u n a t e l y , many of these f o r m u l a t i o n s degraded other necessary p r o p e r t i e s , and some i n f a c t r e s u l t e d i n unstable powder f o r m u l a t i o n s . The survey revealed f i n a l l y that t r i m e l l i c t i c anhydride (TMA) cured epoxy powders could be c a t a l y z e d using e i t h e r stannous octoate (Figure 4) or dicyandiamide (DICY) (Figure 5 ) . Based on t h i s technology we have prepared epoxy powders w i t h small p a r t i c l e s i z e and narrow p a r t i c l e s i z e d i s t r i b u t i o n (Figure 6) which meet the requirements f o r an acceptable beer/ beverage can c o a t i n g . The p r o p e r t i e s of a t y p i c a l epoxy powder cured w i t h TMA and c a t a l y z e d w i t h stannous octoate a r e given i n Table I I . I t should be noted that both c a t a l y s t and c u r i n g agent a r e accepted by the FDA f o r use i n can c o a t i n g s as a r e s u l t of s u c c e s s f u l p e t i t i o n s by W. R. Grace & Co. and Sherwin W i l l i a m s Co.



100

—I·— 150

Temperature Figure 1.

100

150

—h250

200

300

C

DSC scan of Τ M A/epoxy

200

250

300

Temperature °C Figure 2.

DSC scan of DICY/epoxy


SCOTT ET AL.

Figure 4.

Fast-Cure

Epoxy

Powders

DSC scan of TMA/epoxy with stannous octoate catalyst



Figure 5.

DSC scan of TMA/epoxy with DICY catalyst


2.

s e o i r ET AL.

Fast-Cure

Epoxy

9

Powders

TABLE I EFFECT OF CURING AGENT TYPE ON THE CURE: EPOXY/CURING AGENT RATIO = 1.5/1

AGENT

CURE TIME (minutes)

T r i m e l l i t i c Anhydride

4

P o l y a z e l a i c Polyanhydride

5

P h t h a l i c Anhydride

7

Dicyandiamide

8

XD 8038

1

C i t r i c Acid

Variable

Phosphoric A c i d

Variable

TABLE I I PROPERTIES OF DEWEY AND ALMY POWDERED CAN LACQUER FOR TWO-PIECE BEER/BEVERAGE CANS PROPERTY Cross Hatch Adhesion i n B o i l i n g Water

PERFORMANCE pass

Reverse Impact on Parker Panels (160 i n . l b . )

pass

P a s t e u r i z a t i o n Resistance (212°F/10 minutes)

pass

Flexibility (1/8 i n c h c o n i c a l mandrel)

pass

Beverage Pack Resistance (beer and s o f t d r i n k )

>1 month @ 100°F

Flavor P r o f i l e Testing

pass

Enamel Rater (WACO)

pass

I r o n Pick-up

pass



10

As of now, equipment f o r a p p l y i n g Grace powders to twopiece can i n t e r i o r s i s i n commercial development a t Coors i n Golden,Colorado. We have succeeded i n powder c o a t i n g q u a l i t y cans at commercial l i n e speeds w i t h no impact f u s i o n and good transfer e f f i c i e n c i e s . SUMMARY In c o n c l u s i o n , W. R. Grace & Co. has succeeded i n develop ing a i r p o l l u t i o n - f r e e powdered epoxy can lacquers whose r e a c t i v i t y a l l o w s c u r i n g a t current commercial r a t e s using e x i s t i n g can-maker ovens and s e t t i n g s . I t i s very l i k e l y that these powdered coatings w i l l a l s o a l l o w r e d u c t i o n i n energy input as compared to that r e q u i r e d f o r solvent c o a t i n g s . Grace's developing powder technology represents an imme d i a t e s o l u t i o n to th emissions and conservin

REFERENCES CITED 1.

Gardon, J . L. and Prane, J . W., Non-polluting Coatings and Coatings Processes, Plenum Press, New York, New York, 1973, pp 1-13.

2.

Cole, J r . , G. E . , Plastics Raw Materials to End Products and Coatings, American Chemical Society, Division of Chemical Marketing and Economics, 1974, pp 168-9.

3.

Code of Federal Regulations, Title 21, paragraph 175.300.

4.

Talen, H. and Teringa, P. Μ., Powder Coating, Elsevier Sequoia Patent Report No. 4, Elsevier Sequoia, S. Α., Lausanne, Switzerland, 1974, pp 3-13.

5.

Miller, E. P. and Taft, D. D., Fundamentals of Powder Coating, Society of Manufacturing Engineers, Dearborn, MI, 1974, pp 16 and 162, 211-220.

6.

Zorll, Ü., Progress in Organic Coatings, 4, pp 124-125, (1976).

RECEIVED M A Y 22,

1978.


3 Waterborne Two-Piece Body Spray L. A. WATSON Technical Coatings Co., North & 25th Avenues, Melrose Park, IL 60160

The epoxy resins have served the container coatings industry well for many years. Solvent based epoxy systems have been designed for utilization in almost every segment of canclosure manufacture. If not as the basic backbone (component) of the coating system, the epoxy resin found merit as a modifier for other resinious materials. With the increased emphasis for ecologically acceptable coating, epoxy chemistry has been directed toward meaningful water borne systems. New water borne epoxy ester coatings have been developed in recent years which are fairly equivalent, in performance, to their solvent counterpart. Film integrity, such as fabrication, steam processing and moderate corrosion resistance can be maintained. Applied cost of the water borne systemVSi t s solvent counterpart is lower mainly because of the restricted use of expensive solvents. Recent developments have produced interior can coatings which meet the FDA requirements as per Regulation 121.2514, now 175.300. Formulating latitude with the water borne epoxy systems have allowed the chemist to circumvent the problems of taste, odor and turbidity when exposed to beer packaging. Application of spray linings can be tailored to provide adequate coverage over both steel and aluminum D&I containers. Commercial acceptance of epoxy water borne spray lining for the beer and beverage container is on the rise. This article w i l l relate to the interior spray application.

0-8412-0446-2/78/47-078-011$05.00/0 © 1978 American Chemical Society In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.


12

DISCUSSION: Water borne epoxy i n t e r i o r c o a t i n g s can be c l a s s i f i e d i n t o three d i f f e r e n t groups: a) b) c)

Water D i s p e r s i b l e Epoxy Coatings Water Epoxy Emulsion Coatings Water Borne Epoxy C o a t i n g s - S o l u t i o n Type

From the above c l a s s i f i c a t i o n s the chemist must survey the known data f o r the necessary p h y s i c a l parameter conducive toward the proposed end use ( i n t e r i o r spray l i n i n g i n t h i s c a s e ) . Negative aspects sometimes p l a y the more aggressive r o l e i n the choice of v e h i c l e development GROUP A - WATER DISPERSIBLE EPOXY COATINGS In water d i s p e r s i b l e epoxy c o a t i n g s , the epoxy r e s i n i s d i s p e r s e d w i t h the a i d of a s u i t a b l e d i s p e r s i n g agent. These systems are heterogeneous i n nature and have s e v e r a l d i s t i n c t disadvantages : 1.

The d i s p e r s a n t must be h e l d to an a b s o l u t e minimum because of p o s s i b l e f l a v o r contamination i n packaged beer or beverage.

2.

Solvent t o l e r a n c e of dispersion i s rather extremely c r i t i c a l . factor separation i s

3.

Extended storage g e n e r a l l y produces s e t t l i n g w i t h i n the f i n i s h e d goods (product).

4.

Spray a p p l i c a t i o n of the epoxy d i s p e r s i o n systems i s extremely d i f f i c u l t . (Poor s u b s t r a t e w e t t i n g ) .

the r e s u l t a n t l i m i t e d and Because of t h i s g e n e r a l l y noted.

GROUP Β - WATER EMULS IF TABLE EPOXY SYSTEMS 1.

S i m i l a r t o the epoxy d i s p e r s i o n f a m i l y , but much more complex.

2.

Need f o r an e m u l s i f y i n g agent and other s u r f a c e a c t i v e agents t o p r o t e c t the encapsulated p a r t i c l e .


3.

WATSON

Waterborne

Two-Piece

Body Spray

The n e c e s s i t y f o r such a d d i t i v e s , to maintain s i o n system, i n c r e a s e s b i l i t y of f l a v o r o f f the packed media.

13

additional the emulthe p o s s i notes of

3.

P o s s i b i l i t y of water s e n s i t i v i t y g e n e r a l l y caused by the presence of the v a r i o u s surface a c t i v e agents.

4.

Lowest g l o s s f a c t o r of the three v a r i a b l e s under c o n s i d e r a t i o n .

5.

Spray a p p l i c a t i o the epoxy d i s p e r s i o n system.

GROUP C - WATER BORNE EPOXY SOLUTION SYSTEMS The s o l u t i o n type water borne epoxy coatings a r e g e n e r a l l y epoxy r e s i n s e s t e r i f i e d w i t h d i f f e r e n t a c i d s . These e s t e r s a r e subsequently n e u t r a l i z e d w i t h amines. Water and a s u i t a b l e c o s o l v e n t a r e then added t o reduce the polymer t o the d e s i r e d n o n - v o l a t i l e content. Curing agents of v a r i o u s types (such as Melamines, Urea-Formaldehyde o r P h e n o l i c s ) may then be added t o optimize the system. The r e s u l t a n t epoxy system e x h i b i t s exc e l l e n t g l o s s , f l o w and f i l m formation. This type of c o a t i n g system i s very comparable t o s o l v e n t based epoxy coatings even i n product r e s i s t a n c e . Having resigned o u r s e l v e s to concentrate on the development of the s o l u t i o n type water borne epoxy, s e v e r a l major parameters must be s a t i s f i e d . These a r e : 1.

Taste and Odor P r o f i l e - (The c o a t i n g m a t e r i a l should n e i t h e r impart or d i s t r a c t any f l a v o r connotations from the packaged media).

2.

T u r b i d i t y Resistance - (Maintain the d e s i r e d c l a r i t y of the packaged goods).

3.

Application - (Sprayability).

4.

Shelf S t a b i l i t y - ( H y d r o l i t i c stability).


14


EXPERIMENTAL DETAILS A l l c o a t i n g systems were evaluated over the 12 oz. (211 χ 413) two p i e c e aluminum c o n t a i n e r (D&I). The treatment on these c o n t a i n e r s were both A l o d i n e 401-45 and 404. The s t e e l D&I can was a l s o i n c l u d e d i n our i n v e s t i g a t i o n . Dry f i l m depo s i t i o n f o r the aluminum c o n t a i n e r was 120-140 mgs./can and the s t o v i n g c y c l e 2 minutes @ 400 F. For the s t e e l c o n t a i n e r the f i l m weights were increased to 180-200 mgs./can and cured 2 minutes @ 400°F. The coated c o n t a i n e r s were evaluated f o r beer and water p a s t e u r i z a t i o n at 160 F. f o r 30 minutes. Taste and odor pro f i l e s were generated as w e l l as beer t u r b i d i t y d e f i n i t i o n . The attached dat water borne coatings evaluate TABLE I Having e s t a b l i s h e d a v a i l i d coatings candidate ( s o l u t i o n water borne epoxy) our next step was to d e f i n e r e p r o d u c i b i l i t y and s t o v i n g l a t i t u d e . TABLE I I I n d i c a t e s our f i n d i n g s w i t h System A - Laboratory Β - 1st P i l o t Batch.

Batch:

TABLE I I I Represents our t a s t e and odor c h a r a c t e r i z a t i o n s . Having s u c c e s s f u l l y demonstrated the v a l i d i t y of our approach u t i l i z i n g the s o l u t i o n type epoxy, one major h u r d l e remained: That being a p p l i c a t i o n . Because of v a r i o u s p r o f i l e s of the D&I c o n t a i n e r being used i n the i n d u s t r y , s p r a y a b i l i t y (uniform coverage) can be very e v a s i v e . A s s i s t a n c e from the spray equipment people was e n l i s t e d to maximize our e f f o r t s . C o l l e c t i v e l y , we were able to achieve good f i l m d i s t r i b u t i o n of s i d e w a l l coverage from 3.0 to 3.5 mgs./4 i n . ^ and y i e l d enamel r a t e r readings of an average of 5 ma. Total f i l m weight i n the container was roughly 120 mgs. Temperature, pressure and s o l v e n t balance seemed to have more i n f l u e n c e on our m a t e r i a l than d i d i n i t i a l v i s c o s i t y . B e t t e r a t o m i z a t i o n at the lower f l u i d volume output seems to be the key.



ok

ok

Vinyl

Epoxy/ Acrylic Emulsion

Epoxy Disper sion

Epoxy Solu tion Type

Coating A

Coating Β

Coating C

Coating D

ok

ok

>100

>100

>50

10-15

SI.Blush

ok

MEK Rubs

Beer Past. 160°F. 30 Min.

ok

ok

ok

ok

ok

Excellent

ok

ok

ok

Satisfactory

Adhesion

ok

ok

Taste

Turbidity Resistance A f t e r 3 Mos. @ 105°F.

*Coating A & Β gave i n f e r i o r r e s u l t s on s t e e l cans compared to aluminum. However, coating C and Coating D has equivalent performance on both aluminum and s t e e l cans.

ok

SI.Blush

Type

System

Water Past. 160°F. 30 Min.

TABLE I. WATER BORNE COATINGS

ok

ok

Not Satis factory

ok

Flavor

ok

ok

ok

Not S a t i s f a c t o r y

Application Characteristic

ok

ok

ok

Satis factory

Stability 6 Months 9 77°F.

MODERN CONTAINER

16

COATINGS

TABLE I I

H 0 Past. 30 @ 160°F. X Scotch Tape 2

f

Beer P a s t . 30 @ 160°F. X Scotch Tape T

404 Alumn.

2

@ 360°F.

A

0-0

0-0

401 Alumn.

2' @ 360°F.

A

10-10

8-2

Steel

2' @ 360°F.

A

10-10

0-0

404 Alumn.

2

1

@ 360°F.

Β

10-8

9-8

401 Alumn.

2

f

@ 360°F

Steel

V

404 Alumn.

V

1

@ 360°F.

Β

@ 385°F.

A

10-10

10-9

401 Alumn.

2

@ 385°F.

A

10-10

10-8

Steel

2' @ 400°F.

A

10-10

10-10

404 Alumn.

2

@ 385°F.

Β

10-10

10-10

401 Alumn.

V

@ 385°F.

Β

10-10

10-10

Steel

2

@ 400°F.

Β

10-10

10-10

1

?

1

Lab Batch O r i g . A 1st P i l o t Batch - Β Legend:

0 - Complete F a i l u r e 10 - P e r f e c t


3.

WATSON

Waterborne

Two-Piece

17

Body Spray

TABLE I I I

A l l samples and the c o n t r o l were prepared u s i n g unpasteur i z e d beer. The samples were then p a s t e u r i z e d and h e l d f o r approximately 30 days before the f l a v o r e v a l u a t i o n was conducted. The t a s t e panel c o n s i s t e d of 8 p a n e l i s t s . CODE SHEET Lab Number C o n t r o l (Blank) Sample A Sample Β Sample C (Solvent base epoxy c o n t r o l )

C o l l e c t i v e Panel R a t i n g +1.3 +1.4

Distribution* 7/0/1 8/0/0

*In the r a t i n g d i s t r i b u t i o n , the f i r s t f i g u r e i n d i c a t e s how many panel members gave a p l u s (+) o p i n i o n ; the second f i g u r e i n d i c a t e s how many gave a zero ( 0 ) ; the t h i r d f i g u r e s i g n i f i e s how many gave a minus (-) r a t i n g . COMMENTS CONTROL SAMPLE D u l l aroma. Reasonably f r e s h . Rather f u l l i n body and f l a v o r . A t r a c e of harshness. The hop b i t t e r and a f t e r t a s t e are of average i n t e n s i t y . The f l a v o r i s moderately aromatic and malty, r a t h e r d r y and e s t e r y , s l i g h t l y a s t r i n g e n t w i t h a g r a i n y note. Good d r i n k i n g q u a l i t y . SAMPLE A S l i g h t l y f r e s h e r t a s t i n g and smoother p a l a t e than the Con t r o l Sample. Very good d r i n k a b i l i t y . SAMPLE Β Smoother p a l a t e and diminished d r y overtones. acceptance.

Good panel

SAMPLE C (Solvent Base Epoxy C o n t r o l ) A t r i f l e f r e s h e r t a s t i n g w i t h smoother p a l a t e and lessened dry notes. Reasonably good d r i n k i n g q u a l i t y .



18

SUMMARY While other approaches d i r e c t e d toward the i n t e r i o r spray a p p l i c a t i o n of the D&I c o n t a i n e r have m e r i t , we f e e l that the water borne s o l u t i o n epoxy o f f e r s the best l a t i t u d e . Coating systems based on t h i s technology r e q u i r e very l i t t l e d e v i a t i o n from the norm w i t h r e s p e c t t o r e s i n manufacture and subsequent letdown. This i s a v e r y prominent f a c t o r t o consider because most of the previous knowledge of s o l v e n t type epoxy systems can be r e a d i l y a p p l i e d . I n d i c a t i o n s are that some energy cons e r v a t i o n and improved economics can a l s o be achieved. ACKNOWLEDGMENT Many thanks t o D opment input and Herb Goldt f o r h i s meticulous l a b o r a t o r y i n v e s t i g a t i o n . Thanks a l s o t o the Nordson people f o r t h e i r valuable contribution. RECEIVED JUNE 12,

1978.


4 Container Coatings Based on Dispersions of Epoxy Resins in Water FRANK N. JONES, THOMAS H. GLADNEY, WILLIAM T. SOLOMON, JOHN R. GREENWALD, JOHN E. MASTERS, and DAVID A. SHIMP Celanese Polymer Specialties Co., Technical Center, 9800E Bluegrass Parkway, Louisville, KY 40299

Coatings based o epoxy and beverage containers for over twenty-five years. These coatings are based on blends of resin (idealized structure in Fig.1) with a small proportion of crosslinker, usually an aminoplast which reacts predominately with the secondary hydroxyl groups along the backbone of the resin. Baking produces a film which has much of the toughness and chemical resistance of a thermoset coating yet retains considerable elasticity and is capable of excellent adhesion. These characteristics give epoxy coatings an outstanding combination of properties for container interiors - chemical inertness, physical damage resistance, little or no effect on flavor and the ability to protect metal from contents and vice versa.

Figure 1. Soon after the development of the two-piece drawn and ironed beverage can, epoxies were recognized as a preferred coating. In addition to adhesion and toughness, epoxy coatings are able to overcome a number of irregularities that occasionally arise during two-piece can production. They cover surface scratches well, they protect container contents from substances such as drawing lubricants which are occasionally left on the metal surface, and they are somewhat tolerant of variations in metal pretreatment, application and bake conditions. Most epoxy resins used in container linings are especially tailored for the purpose. Molecular weights are relatively high, ranging from 2500 to 8000 (n = 8 to 27 in Figure 1). 0-8412-0446-2/78/47-078-019$05.00/0 © 1978 American Chemical Society In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.


20

Lower molecular weights are usable, but molecular weights above 2500 impart superior elasticity to the film and are believed to reduce the potential for food or beverage contamination from traces of uncrosslinked substances in the cured film. Epoxy coating technology has not been static. In recent years "low-bake formulations based on specific resins, crosslinkers and solvent blends have been developed. Low-bake coatings can be cured at oven temperatures 20°C. to 40°C.lower than first generation epoxy coatings and they have broader bake latitude. Oven temperatures can vary over a 30°C. range without serious adverse effects. Historically the r e l i a b i l i t y of epoxy container coatings has been superb. Over 1QU cans have been coated, and the frequency of major coating-related problems has been very low. Epoxy coatings have established an excellent reputation among brewers for their abilit and among food canners aggressive contents. Container coatings are usually applied by rollcoating flat stock or by high-speed automatic spray into formed cans. Both methods require the resins to be used as dilute solutions in organic solvents to achieve low viscosity, substrate wetting and film-thickness control. Current formulations usually are sprayed at 20% to 23% solids by weight and are rollcoated at 28% to 42% solids. Application in this form causes air pollution and i t wastes solvents and energy. Therefore, new physical forms for epoxy coatings are needed. The industry is seriously examining coatings based on four technologies : (1) Water-dilutable epoxy resins (2) Emulsions of liquid epoxy resins in water (3) Dispersions of solid epoxy resins in water (4) Epoxy powders Each of these technologies has some attractive features, but each involves major technical problems. Our group has been exploring a l l of them for more than a decade. In recent years we have been working intensively with the third, epoxy dispersions. This paper is a generalized report on how this technology is progressing. CURRENT DISPERSION COATING FORMULATIONS. An epoxy dispersion container coating is based on a small particle size dispersion in water of solid resins and crosslinkers very similar to those used in solvent-borne coatings. Small amounts of dispersants are required to stabilize the dispersion, and other substances are usually added to adjust rheology for application. The total weight of non-volatile additives may be 2% to 8% of the weight of the film. Particle diameter is predominately 0.5ûm to 3jam, although this may not be the optimum range. Spray formulations contain 25% to 30% 11


4.

JONES ET AL.

Container

Coatings

21

s o l i d s by weight; r e l a t i v e l y high s o l i d s are p o s s i b l e because the dispersed r e s i n adds l i t t l e t o the v i s c o s i t y o f the medium. The f o r m u l a t i o n complies w i t h a l l a p p l i c a b l e requirements of S e c t i o n 175.300 of T i t l e 21 of Code o f F e d e r a l Regulations f o r food contact coatings (1). Such coatings have been manufactured i n production equipment. O r i g i n a l l y i t was hoped that such d i s p e r s i o n s could be a p p l i e d on present-day spray equipment w i t h almost t o t a l p o l l u t i o n abatement. However, most c u r r e n t formulations i n c o r p o r a t e 18% to 20% by volume of organic s o l v e n t t o improve s p r a y a b i l i t y and to promote formation o f uniform f i l m s . FILM PROPERTIES OF DISPERSION COATINGS The r e s i n s used i n d i s p e r s i o n coatings a r e B i s p h e n o l - A / e p i c h l o r o h y d r i n types c r o s s l i n k e d w i t h amino r e s i n s , s i m i l a r t o those used i n solvent-borne epox coatings Ther i d reduce the molecular weigh bond s o l u b i l i z i n g groups to make t w a t e r - d i l u t a b l e . Molecula weight i s w i t h i n the 2500 to 8000 range p r e f e r r e d f o r f i l m p h y s i c a l p r o p e r t i e s and f l a v o r . This advantage i s being r e a l i z e d in practice. Industry requirements f o r p r o p e r t i e s such as s o l v e n t r e s i s t a n c e , adhesion, p a s t e u r i z a t i o n r e s i s t a n c e and absence of v o l a t i l e s i n the cured f i l m have been met or exceeded. For example, d i s p e r s i o n coatings r e s i s t the necking and f l a n g i n g of two-piece cans b e t t e r than current coatings based on watersoluble resins. Dozens of beer f l a v o r t e s t s o f v a r i o u s formulat i o n s have given c o n s i s t e n t l y good r e s u l t s , u s u a l l y e q u a l l i n g c o n t r o l s and sometimes surpassing them. Of course, s u b s t a n t i a l e f f o r t was r e q u i r e d to f i n d d i s p e r s a n t s and m o d i f i e r s which do not adversely a f f e c t c o a t i n g p r o p e r t i e s . Crosslinkable modifiers which meet t h i s requirement have been i d e n t i f i e d . METAL PRETREATMENT D i s p e r s i o n coatings have e x c e l l e n t adhesion t o detergentwashed aluminum, to aluminum t r e a t e d w i t h the standard p r e treatments and to most of the surfaces encountered i n s t e e l cans. However, i t i s recommended that i n c o n v e r t i n g to water-borne coatings of any type the i n d u s t r y should take e x t r a care w i t h washing and pretreatment procedures u n t i l the boundaries of acceptable p r a c t i c e can be d e f i n e d . Such care might prevent c o a t i n g f a i l u r e caused by adhesion l o s s o r poor w e t t i n g . Formulators of any water-borne c o n t a i n e r c o a t i n g face an inherent problem: the surfaces t o be coated are designed t o be e a s i l y wetted by solvent-borne coatings whose surface tensions u s u a l l y range from 26 t o 28 dynes/cm. Water has a very high surface t e n s i o n , 72 dynes/cm. at 25°C, and i t w i l l not wet low energy s u r f a c e s . A d d i t i v e s are a v a i l a b l e which are capable of reducing surface t e n s i o n t o about 32 dynes/cm. and which are acceptable f o r use i n food contact c o a t i n g s , but the i d e a l 26 dynes/cm. l e v e l i s d i f f i c u l t t o achieve. Even i f low surface


22


t e n s i o n i s achieved, i t i s d o u b t f u l that water-borne coatings can be as e f f e c t i v e as solvent-borne ones i n " b i t i n g " i n t o o i l contaminated s u r f a c e s . APPLICATION The most troublesome o b s t a c l e s to developing water d i s p e r s i o n coatings l i e i n the a p p l i c a t i o n area. The formulator i s faced w i t h the formidable task of a p p l y i n g a d i s p e r s i o n on equipment designed to s u i t the r h e o l o g i c a l c h a r a c t e r i s t i c s of a s o l u t i o n . The rheology of the d i s p e r s i o n i s g r o s s l y d i f f e r e n t . Further, the d i s p e r s i o n o f f e r s r e l a t i v e l y l i t t l e l a t i t u d e f o r a d j u s t i n g s o l v e n t evaporation r a t e s . In the e a r l y stages of development a p p l i c a t i o n d i f f i c u l t i e s c h a r a c t e r i z e d by poor s u b s t r a t e w e t t i n g , b l i s t e r i n g , poor atomizat i o n during spray, spray n o z z l e p l u g g i n g , i n s t a b i l i t y at elevated temperatures and poor flow during r o l l c o a t i n g were encountered. These problems have bee by a s e r i e s of s u c c e s s f u r e p r e s e n t a t i v e production c o n d i t i o n s . They were solved mainly by f o r m u l a t i o n refinements combined w i t h minor equipment changes. D i s p e r s i o n coatings having e x c e l l e n t a p p l i c a t i o n c h a r a c t e r i s t i c s have r e c e n t l y been formulated. Only minor set-up a d j u s t ments are needed to convert a two-piece can l i n e from s o l v e n t borne to aqueous d i s p e r s i o n spray c o a t i n g s . Beer f i l m weights (90-120 mg./can) can be achieved, and the r e l a t i v e l y high s o l i d s of d i s p e r s i o n coatings are advantageous f o r s o f t - d r i n k f i l m weights (160-220 mg./can). S p e c i a l spray n o z z l e s now being designed e s p e c i a l l y f o r water-borne coatings may o f f e r advantages. To prevent spray n o z z l e plugging a l l s o l i d p a r t i c l e s l a r g e enough to plug a 70 o r i f i c e have been s c r u p u l o u s l y e l i m i n a t e d . P a r t i c l e diameter i s under good c o n t r o l i n the 0.5 ûm to 3 jim range, and few i f any p a r t i c l e s as l a r g e as 10 jam are present i n current formulations. No i n s t a n c e of n o z z l e plugging has occurred i n more than two years of l a b o r a t o r y and production trials. D i s p e r s i o n coatings have s e v e r a l advantageous a p p l i c a t i o n characteristics : (1) Spray l i n e s t a r t up i s easy; the o p a c i t y of the wet c o a t i n g a l l o w s the operator to v i s u a l l y check u n i f o r m i t y of coverage. (2) Clean up i s e a s i e r than w i t h any other c o a t i n g type. (3) Less f i l t e r blockage occurs than w i t h other types of water-borne c o a t i n g s . A l s o , d i s p e r s i o n coatings o f f e r p o t e n t i a l energy savings. Baking temperatures are s i m i l a r to those of "low-bake" epoxy c o a t i n g s , and the cure r a t e i s such t h a t the f i r s t oven zone can be operated at reduced temperature. F u r t h e r , the low p r o p o r t i o n of s o l v e n t could reduce the amount of heated a i r which must be exhausted to stay s a f e l y below the lower e x p l o s i v e l i m i t .



Type

borne,

borne,

borne,

Powder

Resin

dispersed

Water-borne,

dispersed

Water

dilutable

Water

dilutable

Water

resin

resin

resin

resin

Solvent borne, maximum s o l i d s

Solvent borne, standard s o l i d s

Coating

99

38.0

27.5

20.0

20.0

23.0

20.6

% Solids By W e i g h t

95:5

80:20

80:20

70:30

By Volume

Ratio of to O r g a n i c

96:4

83:17

83:17

74:26

By W e i g h t

0.066:1

0.45:1

0.68:1

1.04:1

3.35:1

3.85:1

Weight R a t i o Organic V o l a t i l e s to S o l i d s

99%

98%

88%

82%

73%

13%

Standard

Organic Solvent Reduction

OF SPRAY-TYPE EPOXY INTERIOR CAN COATINGS.

I.

Water Solvent

AIR POLLUTION ABATEMENT POTENTIAL

TABLE


24

Formulations for three-piece cans, end stock and side-seam stripe are not yet as well refined as those for two-piece cans, but we believe that dispersion technology w i l l soon find uses in these areas. AIR POLLUTION ABATEMENT Current dispersion coatings are formulated to meet a l l presert and proposed U.S. environmental regulations. The volatile portion contains at most 20% of organic solvent measured by volume. Current coatings based on water-dilutable epoxy resins are frequently formulated at a 70:30 water : organic solvent volume ratio to meet interim regulations. The proportion of solvent can be reduced, but technical problems multiply as coupling solvent is subtracted. An 80:20 ratio appears feasible, but i t may be near the limit of what can be accomplished without substantial trade off. In contrast, coating potential to far exceed current EPA regulations and to meet the very stringent regulations being proposed abroad. Coatings which are virtually solvent free are possible, and a formulation having a 95:5 water : organic solvent ratio shows considerable promise. However, such formulations cannot be properly applied to two-piece cans using presently available equipment. The application problems could probably be overcome with concentrated engineering effort. Even when formulated at an 80:20 water : solvent ratio, dispersion coatings are ecologically attractive because they can be applied in more concentrated form than water-dilutable types. The situation is summarized in Table I, from which i t can be seen that to apply a given weight of solids from a water-dilutable coating containing 20% solids by weight requires about 50% more solvent than to apply i t from a dispersion coating containing 27.5% solids. This factor is expected to increase in importance in future years. The trend in U.S. regulatory philosophy is toward controlling total organic effluent and away from the less fundamental approach of controlling water : solvent ratio. SUMMARY The feasibility of using epoxy dispersion coatings formulated at an 80:20 water :organic solvent volume ratio for two-piece cans has been firmly established. The technology is expected to be broadly applicable to other container interior uses. It offers a number of advantages including the potential for almost total pollution abatement. In the future, as environmental regulations tighten, the advantages of dispersion technology may become compelling. LITERATURE CITED (1) Title 21 was recently reorganized; the former section 121.2514 is now section 175.300. Federal Register 42, No.50, page 14545 (1977). RECEIVED MAY 23, 1978.


5 Coatings for Drawn Tinplate and Chrome-Coated Steel Food Containers G. W. GERHARDT, K. G. DAVIS, and J. R. HALL Mobil Chemical Co., Packaging Coatings Dept., 2000 Westhall St., Pittsburgh, PA 15233 Drawn container mad fro tinplat d chrome -coated steel are beginnin tration into the food containe market. U t i l i z a t i o n of these substrates for the production of a single draw or draw-redraw container has been prompted primarily by three factors: 1. The success of the drawn aluminum container in this market. 2. The increasing concern with the p o s s i b i l i t y of introducing trace quantities of lead into the packed product when lead-containing solders are used in making three-piece s o l dered side seam containers. 3· The continuing desire by industry to investigate whether better or lower cost containers than those already on the market can be made commercially. The manufacturer of a single or multiple draw container requires coatings which have much better fabr i c a t i o n properties than those commonly used on tinplate and chrome-coated steel three-piece containers where the coating must withstand only a simple forming, or is applied after fabrication of the container. The drawn container is fabricated from precoated metal to yield a container with a wall thickness essentially equal to the thickness of the bottom of the container and, in turn, equal to the thickness of the o r i g i n a l f l a t metal stock. There is very little thinning or thickening of the metal, but the metal is d r a s t i c a l l y reformed, p a r t i c u l a r l y on the sidewall near the top of the can. From a p r a c t i c a l standpoint, the industry would l i k e to form the container to the maximum capability of the metal being used. Thus, i t i s necessary that the coatings industry develop coatings which will perform under severe drawing conditions. Also,to 0-8412-0446-2/78/47-078-025$05.00/0 © 1978 American Chemical Society In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.


26

provide extra strength i n the w a l l of the container, many c a n s h a v e c i r c u m f e r e n t i a l b e a d s i n t h e b o d y . The b e a d i n g o p e r a t i o n i s done a f t e r d r a w i n g o f t h e c a n and thus adds f u r t h e r d e f o r m a t i o n . Coatings f o r food containers, by n e c e s s i t y , must have t h e u l t i m a t e i n p h y s i c a l p r o p e r t i e s . In addition t o t h e r e q u i r e m e n t t h a t t h e c o a t i n g n o t change t h e food I n a n y w a y , t h e c o a t i n g must p o s s e s s a m u l t i t u d e of other r e q u i r e m e n t s . S t e r i l e food packs are produced by p r o c e s s i n g t h e c o n t a i n e r a f t e r p a c k i n g of t h e food or by a s e p t i c a l l y p a c k i n g a s t e r i l e product i n a sterilized container. The e l e v a t e d t e m p e r a t u r e s to which the c o n t a i n e r i s exposed d u r i n g these processes r e q u i r e that the coatings perform under elevated temperatures as w e l l as at normal storage temperatures. The p a r t i c u l a r p r o p e r t i e s w h i c h t h e c o a t i n g s must possess are that the p r o c e s s i n g c y c l e , and t h e c o a t i n g on t h e e x t e r i o r o f the c o n t a i n e r must have e x c e p t i o n a l s c u f f resistance at elevated temperature since that coating i s In direct contact with the s t e r i l i z i n g equipment. A f t e r the container i s f i l l e d and processed, then the o r g a n i c c o a t i n g must p r o t e c t t h e f o o d p r o d u c t d u r i n g s t o r a g e p e r i o d s a s h i g h as 100°F. f o r p e r i o d s a s long as two or three years . Experimental The p r i m a r y p r o b l e m s i n t h e e v a l u a t i o n o f c o a t ings f o r drawn c o n t a i n e r s is to obtain meaningful test results i n a short period of time so that sign i f i c a n t p r o g r e s s c a n be a c h i e v e d rapidly. E a r l y i n o u r w o r k w e f o u n d t h a t we c o u l d n o t d u p l i c a t e the drawing of a c o n t a i n e r by any simple fabrication test. We t h e r e f o r e p r o c u r e d e q u i p m e n t f o r d r a w i n g a 202X200 c a n u t i l i z i n g a 44$ r e d u c t i o n I n t h e f i r s t d r a w a n d 22$ i n t h e s e c o n d d r a w . After we d i d c o n s i d e r a b l e w o r k w i t h t h i s s t r a i g h t - w a l l e d c o n t a i n e r , we f o u n d t h a t i t was n o t q u i t e as severe in f a b r i c a t i o n as commercial c o n t a i n e r s , s o we p r o c u r e d a s e t o f t o o l s w h i c h beads t h e c a n . A deep bead n e a r t h e f l a n g e a r e a g i v e s us a s e x t r e m e fabrication a s we h a v e s e e n o n m o s t c o m m e r c i a l c a n s . A f t e r f a b r i c a t i o n of the container, the cans are p a c k e d , seamed w i t h a n e n d w h i c h has a p r o d u c t resistant c o a t i n g on i t and p r o c e s s e d . We p r e f e r u s i n g a 90 m i n u t e a t 2 5 0 ° F . p r o c e s s , e v e n t h o u g h some p r o d u c t s do n o t r e q u i r e s u c h s t r i n g e n t s t e r i l i z i n g c o n d i t i o n s . After cooling of the containers, the e x t e r i o r and i n t e r i o r a r e examined f o r c o a t i n g performance a n d ,


5.

GERHARDT ET AL.

Coatings

for Food

Containers

27

presuming the coatings pass t h i s i n i t i a l screening, d u p l i c a t e c o n t a i n e r s a r e p l a c e d on s t o r a g e a t room t e m p e r a t u r e a n d a t 120°F. We r e c o g n i z e t h a t n o f o o d p r o d u c t s a r e s t o r e d a t 1 2 0 ° F . , b u t we u s e t h i s temperature t o a c c e l e r a t e breakdown of the coated c a n . The b e s t way o f d e v e l o p i n g a c o a t e d c a n f o r a p a r t i c u l a r p r o d u c t i s t o pack that p r o d u c t under commercial conditions. S i n c e we a r e n o t a l w a y s certain a s t o w h a t p r o d u c t s w i l l b e p a c k e d , we m u s t simulate pack c o n d i t i o n s . Quick tests f o r coating integrity a r e g e n e r a l l y r u n w i t h a s o l u t i o n c o n s i s t i n g o f 10 p a r t s h y d r o c h l o r i c a c i d / 2 0 p a r t s CuS04*5H20/70 p a r t s water. E x p o s u r e t i m e s t o t h i s t e s t s o l u t i o n may v a r y from several minutes t o several hours. This test is simply a screening t e s t t o determine whether the coating has f a b r i c a t e d p r o p e r l y and whether that system s h o u l d be p u t o n l o n t e s t pack r e p r e s e n t i n g v a r i o u s types of foods a r e shown i n T a b l e 1. We d o n o t p a c k f o o d s t h e w a y t h e y w o u l d be p a c k e d c o m m e r c i a l l y ; t h a t i s , from the basic food i n g r e d i e n t s . Our packs a r e a l l a c t u a l l y repacks. We f e e l , however, that by r e p a c k i n g a s t a n d a r d commerc i a l p r o d u c t , we c a n i n s u r e o u r s e l v e s g o o d c o n t r o l o f the c h a r a c t e r i s t i c s of that product without r e q u i r i n g extended food p r e p a r a t i o n time. Results E a r l y i n t h e t e s t w o r k we d e t e r m i n e d t h a t t h e c o a t i n g s w h i c h performed t h e best were those w h i c h showed t h e b e s t i n i t i a l f a b r i c a t i o n . Typical fabric a t i o n and process p r o p e r t i e s of coatings are presented i n Table 2. Of t h o s e w h i c h showed good fabricat i o n , a few were q u i c k l y e l i m i n a t e d because they d i d n o t have t h e r e q u i r e d h y d r o l y t i c s t a b i l i t y o r t h e r e s i s t a n c e t o s o f t e n i n g by f a t s and o i l s that a r e r e q u i r e d o f many f o o d s . The p r i m a r y development work then centered around the f o r m u l a t i o n of p o l y v i n y l d i s p e r s i o n type coatings and epoxy f o r m u l a t i o n s . S i n c e t h e d a t a i n T a b l e 2 shows t h a t t h e PVC d i s p e r s i o n v i n y l s as a r u l e have b e t t e r f a b r i c a t i o n than the epoxies, we t r i e d t o u s e t h e P V C d i s p e r s i o n s o n both the i n t e r i o r and the e x t e r i o r of the c a n . However, i n studying exterior coatings, we d i s c o v e r e d that t h e PVCd i s p e r s i o n s a r e n o t r e a l l y thermosetting; and, consequently, they w i l l resoften s l i g h t l y during processing of the f i l l e d container. A l s o , any movement i n t h e s t e r i l i z e r w i l l a b r a d e t h e P V C d i s p e r s i o n off of the metal. Epoxy coatings which thermoset duri n g t h e bake a r e n o t s u b j e c t t o t h i s t y p e o f a d h e s i o n



28

TABLE

TEST

Type

of

Food

High

acid

1.

MEDIA

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Pea High

sulfur

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Figure 19. Emulsion polymer cured with 20% melamine cross-linker: dynamic me chanical spectra, 120°C -> —180°C -> 204°C -* RT at 2°C/min in He of coating cured 3 min at 19ΓC (40)



78

Journal of Coatings Technology

Figure 20. Commercial emulsion polymer/cross-linker: dynamic mechanical spectra, 120° -180 C -> 204 C -» RT at 2°C/min in He of coating cured 3 min at 191°C (40) e

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8.

ROLLER AND GILLHAM

Dynamic

Mechanical

Testing

79

two systems l i e s i n the bimodel g l a s s t r a n s i t i o n r e g i o n (Tg = 26 and 52°C) o f the commercial product vs. the s i n g l e Tg (39°C) f o r the other. T h i s f e a t u r e has been r e l a t e d t o the presence of phase s e p a r a t i o n (14). S i m i l a r i t i e s i n the low temperature regions and simple c a l c u l a t i o n s o f an average Tg (39°C) f o r equal amounts of the two phases present i n the commercial m a t e r i a l a t t e s t t o these two c o a t i n g s being s i m i l a r i n monomer r e s i d u e composition. The technology r e q u i r e d to produce t h i s type of behavior v i a emulsion p o l y m e r i z a t i o n concerns i t s e l f w i t h the p r o d u c t i o n o f core and s h e l l emulsion p a r t i c l e s as has been d e s c r i b e d (14). The technique should provide rubber-modified, impact r e s i s t a n t c o a t i n g s , wherein the s o f t phase i s t o t a l l y encased i n the hard phase with the domain s i z e d e f i n e d by the p a r t i c l e . T h i s system, i n one c o a t i n g , would d i s p l a y a combination of impact r e s i s t a n c e , hardness, mar r e s i s t a n c e , and adhesion. I n v e s t i g a t i o n of th revealed the c a p a b i l i t q u i r e d c o a t i n g p r o p e r t i e s a t low baking temperatures. T h i s prompted a study of the g e l a t i o n k i n e t i c s of the two systems. F i g u r e 21 shows the Arrhenius s t r a i g h t l i n e p l o t s o f l o g (apparent g e l time) vs. 1/T°K f o r each system. Note t h a t the commercial system gels n e a r l y f o u r times as f a s t as the other at 204°C and n e a r l y 10 times as f a s t a t 100°C. Whether the source of the higher g e l a t i o n r a t e l i e s i n higher f u n c t i o n a l i t y of the r e s i n s and c r o s s l i n k e r s or more e f f i c i e n t c a t a l y s t systems has not been a s c e r tained. Note t h a t i n the case o f these two emulsion polymers the mechanical p r o p e r t i e s do not change a f t e r h e a t i n g to 200°C. Presumably, the room temperature toughness o f these m a t e r i a l s i s r e l a t e d to t h e i r low g l a s s t r a n s i t i o n temperatures. Emulsion p o l y mers develop t h e i r f i n a l Tg values b e f o r e c r o s s l i n k i n g as a consequence o f t h e i r very h i g h molecular weights. The r e l a t i v e l y l i g h t l e v e l s of c r o s s l i n k i n g i n t r o d u c e d t o these m a t e r i a l s p r o v i d e r e q u i r e d r e s i s t a n c e to c o l d flow and s o l v e n t s i n the v i c i n i t y of the g l a s s t r a n s i t i o n which i s c l o s e to room temperature. Comparison of the E f f e c t of C r o s s l i n k i n g Agents The nature of c r o s s l i n k e r s can d r a s t i c a l l y a f f e c t the propert i e s of cured thermosets. F i g u r e s 22-24 are the s p e c t r a of an a c i d f u n c t i o n a l a c r y l i c prepolymer and the same prepolymer cured with two monomeric hexamethoxymethyl melamine (HMMM)-type c r o s s l i n k e r s at the same c o n c e n t r a t i o n . One c r o s s l i n k e r had l e s s than 0.5% f r e e hydroxymethyl and the other had approximately 16% f r e e hydroxymethyl groups. The prepolymer i t s e l f d i s p l a y s a Tg o f 73°C and evidence of flow through both a r e d u c t i o n i n r i g i d i t y and a broad damping maximum above 100°C. The c r o s s l i n k e d systems show d i s t i n c t l y d i f f e r e n t behavior. The < 0.5% f r e e hydroxymethyl system d i s p l a y s a sharp Tg r e g i o n c e n t e r i n g about 79°C. The r i g i d i t y s t a r t s to decrease at 69°C and



80

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84

and l e v e l s o f f near 91°C. The ^16% hydroxymethyl system d i s p l a y s a broad Tg r e g i o n c e n t e r i n g about 87°C. In t h i s case, the r i g i d i t y begins t o decrease a t about 58°C and l e v e l s o f f near 110°C. T h i s behavior bears on the g e n e r a l p r o p e r t i e s o f the f i n a l prod ucts over a wide temperature range. The broad Tg r e g i o n o f the h i g h hydroxymethyl system presumably a r i s e s from the c o n t r i b u t i o n s o f the competing r e a c t i o n s o f the methoxymethyl groups w i t h both a c i d and hydroxymethyl groups which give r i s e t o molecular h e t e r o geneties. A f t e r h e a t i n g t o 204°C, the Tg o f the low hydroxymethyl HMMM i n c r e a s e d 6°C t o 85°C, whereas the Tg o f the 16% hydroxymethyl system i n c r e a s e d 7°C t o 94°C. T h i s behavior i s t y p i c a l o f the response t o f u r t h e r h e a t i n g o f most thermosetting m a t e r i a l s a f t e r t h e i r normal i n d u s t r i a l cure c y c l e s . In the i n t e r e s t o f economy o f time i n d u s t r y tends t o design i t s systems t o have acceptable p r o p e r t i e s i n an undercure Plasticization The a b i l i t y t o examine l i q u i d s by using supported samples permits study o f t r a n s i t i o n s i n the f l u i d s t a t e as w e l l as t r a n s formation of l i q u i d t o s o l i d . The most complete example o f t r a n s i t i o n s i n the f l u i d s t a t e i s the p l a s t i c i z a t i o n o f t h e r m o p l a s t i c p o l y s t y r e n e throughout the range o f composition (15). P o l y s t y r e n e (Mn = 37000, Mw/Mn < 1.1) was homogeneously p l a s t i c i z e d w i t h (CgÔCgHÔ) 2 6 + (which i s a low molecular weight analogue o f polyphenylene o x i d e ) . Dynamic mechanical s p e c t r a f o r the p l a s t i c i z e r / p o l y m e r system are d i s p l a y e d i n F i g u r e 25. Three t r a n s i t i o n s are made apparent, i . e . , Tg, T^£ and T ^ ' , a l l f o l l o w i n g the r e l a t i o n s h i p Τ = A A + B B KW^B is e m p i r i c a l constant, Τ r e p r e s e n t s the t r a n s i t i o n temperature o f the mixture (T) and o f the c o n s t i t u e n t s (^T and β Τ ) , and W and W r e f e r t o the r e s p e c t i v e weight f r a c t i o n s o f the components. Corresponding t r a n s i t i o n s have been noted by us i n low molecular weight thermosetting prepolymers. These t r a n s i t i o n s , which r e l a t e t o flow, bear p a r t i c u l a r l y on p r o c e s s i n g o p e r a t i o n s (see below). c

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Dynamic

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2


86 1

t i o n s w i t h T^£ and T^^ t h a t the l a t t e r l o s s maxima observed i n t h e r m o p l a s t i c s should bear on t h e i r p r o c e s s i n g . I t has a l s o been observed t h a t the temperatures f o r T^£ and T ^ can be s u b s t r a t e (braid) m a t e r i a l and/or geometry dependent (41). D i f f e r e n t t h e r momechanical s p e c t r a have been observed a f t e r c u r i n g i s o t h e r m a l l y at d i f f e r e n t temperatures t o the peak o f the l o s s maximum which has been used t o approximate g e l a t i o n . I t f o l l o w s that t h i s l o s s maximum cannot correspond t o the t h e o r e t i c a l g e l p o i n t which i s d e f i n e d as an i s o c o m p o s i t i o n a l s t a t e . I t can be demonstrated t h a t i f t i as determined by t o r s i o n a l b r a i d a n a l y s i s represents an i s o v i s c o u s s t a t e than an Arrhenius p l o t o f l o g t i v s . 1/T (°K) w i l l g i v e a s t r a i g h t l i n e over a s i g n i f i c a n t temperature range. T h i s has been done by ap p l y i n g an e m p i r i c a l time-temperature-viscosity model (42) t h a t has been used t o p r e d i c t the change i n v i s c o s i t y o f a c u r i n g system. This model reduce by many workers (42). The v i s c o s i t y model i s expressed f o r isothermal c u r i n g con d i t i o n s as f o l l o w s : 1

g

g

In where

e

e

n(t) = In ηoo + ΔΕη/RT + t k oo 7

A

E

k

/

/

R

T

e

η(t) = v i s c o s i t y o f time t (sec) η», = c a l c u l a t e d v i s c o s i t y o f the i n i t i a l m a t e r i a l a t Τ = , cps Τ = temperature °K ΔΕη = Arrhenius a c t i v a t i o n energy f o r the v i s c o s i t y , cal/mole R = gas constant = 1.987 cal/mole °K _^ ko, = c a l c u l a t e d k i n e t i c constant a t Τ = °°, sec ΔΕ]ς = "apparent" k i n e t i c a c t i v a t i o n energy, cal/mole. 00

I f a given i s o v i s c o s i t y l e v e l i s s e l e c t e d and the l o g o f p r e d i c t e d time t o t h a t v i s c o s i t y vs. 1/T (°K) i s p l o t t e d , the data can be f i t t e d w i t h a s t r a i g h t l i n e . Furthermore, the f i t becomes b e t t e r as the v i s c o s i t y range t r a v e r s e d (from zero time t o the end point) increases. This can be accomplished by choosing a higher cure temperature (lower i n i t i a l v i s c o s i t y ) o r a higher v i s c o s i t y end p o i n t . As the f i t improves, the a c t i v a t i o n energy o f l o g t i vs. 1/T curve approaches the "apparent" a c t i v a t i o n energy i n the v i s c o s i t y model. As the temperature f o r isothermal cure i s reduced, the zero time v i s c o s i t y approaches the i s o v i s c o u s l e v e l chosen and " t g i " goes t o zero. At h i g h e r temperatures, " t g i " goes through a maximum and then decreases. I t i s i n t h i s d e c r e a s i n g r e g i o n where the l i n e a r f i t h o l d s . From t h i s a n a l y s i s , i t appears t h a t i f t g ^ i s an i s o v i s c o u s s t a t e , l i n e a r A r r h e n i u s p l o t s can be obtained. Furthermore i f the v i s c o s i t y l e v e l detected f o r t l i s s u f f i c i e n t l y h i g h , i t i s c l o s e enough t o the t r u e g e l p o i n t t o be r e p r e s e n t a t i v e . As with g

e

e

e

g

e


e


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all mechanical measurements of gelation, one depends upon a vis cosity measurement. Rising bubbles, tack tests and viscositytime measurements all provide similar approximations. As a matter of fact, the SPI Prepreg Reinforced Plastics Committee Test Method: Prepreg 3 - Measurement of Gel Time of Preimpregnated Inorganic Reinforcements (New York, May, 1960) was found to pro vide gel times corresponding to 120,000-140,000 cps (42). SUMMARY In this paper the history of dynamic mechanical testing and its past relationship to thermoset and coatings research and de velopment is reviewed. With the introduction of several fully automated systems, the study of thermosetting systems by these techniques will greatly increase. Provided are examples of the use of the technique a behavior of thermosettin of environment, comparison of similar materials, cure, aging of prepolymers, correlation with fabrication, monitoring of phase separation, apparent gelation kinetics, and the influence of gela tion and vitrification on material properties. The article con cludes with recent results which reveal the coincidence of transi tions in thermoplastics observed above the glass transition, and in thermosets during the transformation from fluid to intractible solids; these bear on processing. Now that the difficulties of data reduction have been elimi nated, the future applicability of dynamic mechanical techniques depends only upon the ingenuity of research and development per sonnel. ACKNOWLEDGMENT The authors wish to thank the management of Mobil Chemical Co. for permission to publish this paper. Plastics Analysis Con sultants Inc., P. O. Box 408, Princeton, New Jersey provided thermomechanical TBA plots. LITERATURE CITED (1) (2) (3) (4) (5)

Nielsen, L.E., ASTM Bulletin No. 165, p. 48, April (1950); Rev. Sci. Instr., 22, 690 (1951). Gillham, J.K., A.I.Ch.E. J., 20, 1066 (1974). Blaine, R.L. and Woo, L . , Am. Chem. Soc., Polymer Preprints, 17(2), 1 (1976). Kenyon, A.S., Grote, W. Α., Wallace, D. Α., and Rayford, M. J., ibid., 17(2), 1 (1976). Also J. Macromol. Sci.-Phys. B13(4), 553 (1977). Davis, W.M. and Macosko, C. W., Polymer Eng. Sci., 17(1), 32 (1977).



88

(6) Gillham, J.K. and McPherson, C.A., Preprints of 32nd Annual Tech. Conf., Reinforced Plastics/Composites Institute, SPI, sect. 9-E (1977). (7) Gillham, J.K. and Roller, M.B., Polymer Eng. Sci., 11, 295 (1971). (8) Ozari, Υ., Chow, R. H. and Gillham, J.K., Am. Chem. Soc., Polymer Preprints 18(1), 649 (1977). (9) Roller, M.B., unpublished literature survey. (10) Heijboer, J., Publication P73/28, of Central Laboratories TNO, Delft, The Netherlands, 1973; also "Secondary Loss Peaks in Glassy Amorphous Polymers," presented at 4th Mid land Macromol. Meeting, Midland, Mich. Feb. (1975), Int. J. Polymer Material. 6, 11 (1977). See also Ann. N.Y. Acad. Sci., 279, 104 (1976). (11) Kaelble, D.H., "Physical Chemistry of Adhesion," Wiley Interscience, Ne (12) Babayevsky, P.G 17, 2067 (1973). (13) Gillham, J. K., Glandt, C. Α., and McPherson, C. Α., Am. Chem. Soc., Preprints, Div. Org. Coat. Plastics Chem., 37(1), 195 (1977); also "Chemistry and Properties of Crosslinked Polymers," S.S. Labana, Ed., Academic Press, New York, 1977, p. 491. (14) Manson, J.A. and Sperling, L.H., "Polymer Blends and Com posites," Plenum Press, New York, 1976, Chapters 3, 8 and 13. (15) Gillham, J. Κ., Benci, J.A., and Boyer, R.F., Polymer Eng. Sci., 16(5), 357 (1976). (16) Inoue, Y. and Kobatake, Υ . , Kolloid, Ζ., 159(1), 18 (1958). (17) Inoue, Y. and Kobatake, Υ . , ibid., 160(1), 44 (1958). (18) Yoshino, M. and Takayanagi, Μ., Zairyo Shiken,8, 330 (1959). (19) Lewis, A. F. and Gillham, J. Κ., J. Appl. Polymer Sci., 6, 422 (1962). (20) Zorll, U., Forschungsber. Landes Nordhein-Westfalen, No. 1361, Westdeutschen Verlag Omblt, Köln and Opladen (1962). (21) Hansen,C.M.,Official Digest, 37(480), 57 (1965). (22) Myers, R.R., Klimek, J., and Knauss, C.J., Journal of Paint Technology, 38(500), 479 (1966). (23) Bender, H.S., J. Appl. Polymer Sci., 13, 1253 (1969). (24) Takahashi, Y., Naganuma, S., Onozawa, Κ., and Kishi, Η., Proc. 5th Inter. Cong. Rheology, 1968, p. 485 (1970). (25) Myers, R. R., J. Polymer Sci., Part C 35, 3 (1971). (26) Kollinsky, F., and Markert, G., "Multicomponent Polymer Systems," Advances in Chemistry Series, No. 99, American Chemical Society, Washington, D. C., 1971, p. 175. (27) Naganuma, S., Sakurai, T., Takahashi, Υ . , and Takahashi, S., High Polymer Chemistry (Hobunski Kagaku), 29(322), 105, and (327), 519 (1972). (28) Massa, D. J., J. Appl. Phys., 44, 2595 (1973). (29) Ikeda, S., Prog. Org. Coatings, 1(3), 205 (1972/3). s



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(30) Shimbayama, Κ., ibid., 3(3), 245 (1975). (31) Massa, D. J., Flick, J . R., and Petrie, S.E.B., Am. Chem. Soc. Preprints, Div. Org. Coat. Plastic Chem., 35(1), 371 (1975). (32) Seefried, C.G., Jr. and Koleske, J.V., J. Testing Eval., 4(3), 220 (1976). (33) Ginsberg, T., Merriam, C.N., and Robeson, L.M., J. Oil Col our Chemists' Assoc., 59, 315 (1976). (34) Cowie, J.M.G., Am. Chem. Soc. Preprints, Div. Org. Coat. Plastic Chem., 38(1), 284 (1978). (35) Koleske, J.V. and Faucher, J.A., ibid, 38(1), 355 (1978). (36) MacKnight, W.J., Neuman, R.A. and Senich, G.A.,ibid, 38(1) 360 (1978). (37) Senich, G. A. and MacKnight, W.J., ibid, 38(1), 510 (1978). (38) Hill, D.R.J., ibid, 38(1) 590 (1978) (39) Gillham, J. Κ., Polymer Chem. Soc., Preprints, Org , 38(2), (1978). (40) Roller, M. B. and Gillham, J. Κ., J. Coatings Tech., 50, No. 636, 57 (1978). (41) Schwartz, Β., Ph.D. Thesis, Department of Chemical Engineer ing, Princeton University, 1979. (42) Roller, Μ. Β., Polym. Eng. Sci., 15, 406 (1975). (43) Gillham, J . Κ., Polym. Eng. S c i . , 16, 353 (1976). (44) Gillham, J . Κ., Am. Chem. Soc., Preprints, Div. Org. Coat. Plastics Chem., 38(1), 221 (1978). RECEIVED MAY 22, 1978.


9 Application of Electrochemical Techniques to the Evaluation of the Corrosion Barrier Properties of Modern Container Coatings R. E. BEESE American Can Co., 433 N. Northwest Highway, Barrington, IL 60010 J. C. ALLMAN M&T Chemicals, Inc., 26701

Introduction: Testing programs are required to evaluate the performance of materials considered for the development of new containers to preserve and store foods and beverages. Historically, testing was accomplished by packing fabricated containers with a representative product, storing the packed containers, and periodically evaluating to determine container performance. This lengthy procedure limits the number of variables to be considered and causes development delays. Experience has shown that electrochemical techniques can be used to evaluate the corrosion performance of new containers and coating materials. The electrochemical testing program permits one to evaluate a large number of variables in a short time. We have found that electrochemical tests can readily determine container failure caused by metal dissolution or corrosion for variables which perform poorly. In cases where measured corrosion rates are low, test packs are needed to establish whether or not long -term protection is provided. Application of Electrochemical Technique: We chose to measure the rate of iron dissolution by the slope-intercept technique identified by Stern(1) and formalized by ASTM(2) rather than the polarization resistance technique(3) 0-8412-0446-2/78/47-078-090$05.00/0 © 1978 American Chemical Society In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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which Kleniewski(4) employed t o measure the r e l a t i v e c o r r o s i o n b a r r i e r p r o p e r t i e s o f can c o a t i n g s . P o l a r i z a t i o n r e s i s t a n c e i s i n v e r s e l y p r o p o r t i o n a l t o c o r r o s i o n r a t e provided the nature of t h e anodic and cathodic r e a c t i o n s which account f o r t h e c o r r o s i o n process remain constant; however, t h i s i s not t h e case. Makrides(5) solved t h i s problem by measuring an average c o r r o s i o n r a t e by weight l o s s and then c a l c u l a t i n g an average p r o p o r t i o n a l i t y constant between p o l a r i z a t i o n r e s i s t a n c e and c o r r o s i o n r a t e . This procedure i s not a p p l i c a b l e because the c o r r o s i o n o f i r o n through can coatings cannot be monitored by weight l o s s . Mansfeld(6) p o i n t s out t h a t the IR drop i n the p o t e n t i a l measuring c i r c u i t causes e r r o r s i n t h e e v a l u a t i o n of c o r r o s i o n r a t e from p o l a r i z a t i o n r e s i s t a n c e data. Hausler(7) a l s o discusses f u r t h e r problems a s s o c i a t e d w i t h t h i s technique. The s l o p e - i n t e r c e p t techniqu an a c t u a l c o r r o s i o n r a t c o r r o s i o n performance. While problems a s s o c i a t e d w i t h e r r o r s caused by IR drops i n the p o t e n t i a l measuring c i r c u i t a r e s t i l l w i t h us, the data developed i n both beer and tomato j u i c e provide reasonable estimates o f i r o n c o r r o s i o n r a t e through organic enamel coatings o r a t d i s c o n t i n u i t i e s o r f r a c t u r e s i n organic enamel coatings on t i n p l a t e o r e l e c t r o l y t i c chromium coated s t e e l W h e t h e r the c o r r o s i o n r e a c t i o n occurs by i o n d i f f u s i o n through organic enamel coatings g e n e r a l l y or through coatings a t d i s c r e t e s i t e s caused by f o r e i g n m a t e r i a l as i n d i cated by Koehler(9) or through d i s c o n t i n u i t i e s such as cracks caused by mechanical damage t o the coatings depends on the system under study. Since the s l o p e - i n t e r c e p t technique f o r measuring c o r r o s i o n depends only on the anodic and cathodic r e a c t i o n s ; i . e . , the r a t e o f i r o n d i s s o l u t i o n and hydrogen e v o l u t i o n r e s p e c t i v e l y i n a i r - f r e e systems, the l o c a t i o n o f the r e a c t i o n s i t e s i s not important. Two other problems a s s o c i a t e d w i t h the e l e c t r o c h e m i c a l approach to c o n t a i n e r e v a l u a t i o n need t o be recognized. The b a r r i e r p r o p e r t i e s o f some coatings d i m i n i s h because the coatings a r e degraded by exposure t o aggressive media. This was i l l u s t r a t e d by L e i d h e i s e r 0 - 0 ) i n h i s work w i t h polybutadiene coatings i n aerated sodium c h l o r i d e s o l u t i o n s . Secondly, t h e metal area a t a pore or crack i n the c o a t i n g increases as c o r r o s i o n proceeds; thus, i t i s reasonable t o expect instantaneous c o r r o s i o n r a t e s to i n c r e a s e as c o r r o s i o n proceeds. Test procedures are d e v e l oped t o e s t a b l i s h reasonably steady s t a t e c o n d i t i o n s before making the c o r r o s i o n r a t e measurement. F o r example, c o r r o s i o n i n beer cans can be evaluated a f t e r a 15 minute immersion i n a 150° F water bath t o simulate a p a s t e u r i z a t i o n c y c l e . Tomato j u i c e cans are permitted t o stand two days b e f o r e e v a l u a t i n g c o n t a i n e r performance t o e s t a b l i s h a steady c o r r o s i o n r a t e .



92 Instrumentation

and Test Procedure:

C o r r o s i o n r a t e can be estimated from a p o t e n t i o s t a t i c p o l a r i z a t i o n curve by the s l o p e - i n t e r c e p t technique. The l i n e a r p o r t i o n of the log c u r r e n t - p o t e n t i a l p l o t of a p o l a r i z a t i o n curve; i . e . , the T a f e l l i n e , i s e x t r a p o l a t e d t o the c o r r o s i o n p o t e n t i a l . The c u r r e n t at the i n t e r s e c t i o n of the T a f e l l i n e and the c o r r o s i o n p o t e n t i a l i s the r a t e of the c o r r o s i o n r e a c t i o n . Any q u a l i t y p o t e n t i o s t a t can be used t o c o n t r o l the p o t e n t i a l of a corroding metal sample. The log c u r r e n t - p o t e n t i a l r e l a t i o n s h i p i s a u t o m a t i c a l l y p l o t t e d w i t h an X-Y recorder. The p o t e n t i a l of the corroding metal i s measured w i t h respect t o a reference e l e c t r o d e on the Y a x i s of the r e c o r d e r . The log of the current flow between an a u x i l i a r y platinum e l e c t r o d e and the c o r r o d i n g metal i s recorded on the X a x i s . Examples of cathodic p o l a r i z a t i o Cans or can p a r t s are t e s t e d by f i l l i n g w i t h a r e p r e s e n t a t i v e product and measuring c o r r o s i o n r a t e . Beer i s the t e s t medium f o r beer cans. Tomato j u i c e i s used as a r e p r e s e n t a t i v e moderately c o r r o s i v e m i l d l y a c i d food product. Cans are c l o s e d by s e a l i n g a l u c i t e f i x t u r e t o the can or the can p a r t w i t h an O-ring. Cans f i l l e d w i t h beer are maintained under a carbon d i o x i d e atmosphere and can be given a simulated p a s t e u r i z a t i o n c y c l e by immersing the c l o s e d f i l l e d can i n a 150° F water bath f o r 15 minutes. The can i s s t o r e d overnight at 80° F before t e s t i n g . Cans to be t e s t e d w i t h tomato j u i c e are maintained under a n i t r o g e n gas atmosphere. They are f i l l e d w i t h 190° F tomato j u i c e and stored two days at 80° F before testing. C o r r o s i o n r a t e i s measured by i n s e r t i n g a platinum a u x i l i a r y e l e c t r o d e and a s a t u r a t e d calomel reference e l e c t r o d e i n a 1% sodium c h l o r i d e s a l t b r i d g e i n t o the product through a s i l i c o n e rubber gromet i n the l u c i t e c l o s u r e . The p o t e n t i o s t a t s reference p o t e n t i a l i s set at a p o t e n t i a l a few m i l l i v o l t s anodic t o the c o r r o s i o n p o t e n t i a l . The p o t e n t i o s t a t s reference p o t e n t i a l i s then permitted t o change i n the cathodic d i r e c t i o n ; i . e . , t o more negative p o t e n t i a l s at a r a t e of 5 t o 6 m i l l i v o l t s per minute t o generate the cathodic p o l a r i z a t i o n curve. It i s important t o p o l a r i z e at the slow r a t e t o o b t a i n r e p r o d u c i b l e data. The slow adsorbtion-desorbtion of the c o r r o s i o n i n h i b i t o r systems n a t u r a l l y o c c u r r i n g i n beer and tomato j u i c e on the c o r r o d i n g metal probably e x p l a i n s the need f o r the slow p o l a r ization rate. f

f

A p p l i c a t i o n of P o l a r i z a t i o n Measurements: The f o l l o w i n g three examples of i r o n c o r r o s i o n through organic enamel can coatings i l l u s t r a t e the v a r i o u s mechanisms by which


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AMPERES

Figure 2. Iron corrosion rate for experimental beer cans in 80°F beer: O , #1 211 X 413 cemented can; Δ , #2 211 X 413 cemented can; Q #3 207.5/209 X 504 D&Z can; X , #4 209/211 X 413 Dal can



94

c o r r o s i o n can occur through p r o p e r l y a p p l i e d can c o a t i n g s : A.

Iron C o r r o s i o n Through Breaks i n Coatings: The draw-redraw process f o r the manufacture of two-piece food cans i n v o l v e s the c o a t i n g of e l e c t r o l y t i c chromium coated s t e e l or t i n p l a t e w i t h an organic enamel c o a t i n g and mechanically forming the coated s t e e l i n t o a c y l i n d e r w i t h an i n t e g r a l end. Mechanical damage can occur t o the organic c o a t i n g during the drawing o p e r a t i o n . M i c r o s c o p i c t e a r s occur i n the v i n y l organosol c o a t i n g used on many draw-redraw cans. Draw-redraw cans have been evaluated w i t h tomato j u i c e t o determine the area of metal exposure through the damage t o the organic c o a t i n g of the c o n t a i n e r performanc T y p i c a l p o l a r i z a t i o n curves and c o r r o s i o n r a t e data f o r drawn cans are given i n F i g u r e 1 and i n Table I . The d i f ferences between the c o n t a i n e r s are r e l a t e d t o the area of i r o n exposed. I t should be p o i n t e d out t h a t Table I i n d i c a t e s t h a t the c o r r o s i o n r e a c t i o n through a 21 square i n c h area of v i n y l organosol coated s t e e l was very s m a l l . Since t h i s c o a t i n g provides an e x c e l l e n t b a r r i e r t o c o r r o s i o n before drawing, one must conclude t h a t the observed c o r r o s i o n occurs at s i t e s where the organic c o a t i n g was mechanically damaged by drawing.

B.

I r o n C o r r o s i o n Through a Thick P l a s t i s o l : Experimental easy-open beer ends made from organic enamel coated e l e c t r o l y t i c chromium coated s t e e l were made by p a r t i a l l y c u t t i n g two c i r c u l a r holes through the s t e e l and r e s e a l i n g the p a r t i a l l y cut c i r c l e w i t h a p l a s t i s o l f i l m approximately 10 m i l s t h i c k . The organic enamel coatings on the chromium coated s t e e l p r o v i d e an e x c e l l e n t b a r r i e r t o c o r r o s i o n . The p l a s t i s o l s e a l a n t was designed t o f i l l the crack between the d i s c and the end and t o p r o v i d e a mechanical s e a l . The p r o p e r t i e s of t h i s p l a s t i s o l are unique. I t must p r o v i d e a gas and l i q u i d s e a l and s t i l l be e a s i l y t o r n so t h a t the c o n t a i n e r can be opened. The p l a s t i s o l s e a l provided an e x c e l l e n t p h y s i c a l b a r r i e r ; however, beer t e s t packs i n d i c a t e d t h a t t h i s p l a s t i s o l was a poor b a r r i e r t o i r o n c o r r o s i o n . Reformulation of the p l a s t i s o l improved i t s c o r r o s i o n b a r r i e r p r o p e r t i e s , as i n d i c a t e d i n Table I I . T h i s example d e s c r i b e s an organic m a t e r i a l t h a t o r i g i n a l l y was formulated w i t h very poor c o r r o s i o n b a r r i e r p r o p e r t i e s .


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Properties

TABLE I Representative Iron C o r r o s i o n i n Drawn Cans Made From V i n y l Organosol Coated E l e c t r o l y t i c Chromium Coated S t e e l A f t e r Two Days i n 80° F Tomato J u i c e E l e c t r o c h e m i c a l Data C o r r o s i o n T a f e l C o r r . Iron C o r r . S t e e l P o t e n t i a l Slope Rate Rate Container D e s c r i p t i o n Code mV V jua/Can ppm Fe/Yr. 21 square inches o f enamel coated s t e e l

?

Β

10 mils d i d contain fragments w i t h i n the impact zone. However, transparency was



114

not acceptable and the economics w i t h > 1 0 mil coatings were borderline. To meet program o b j e c t i v e s , 6-8 mil coatings would be r e q u i r e d and low melt index - lower d e n s i t y powders were the obvious t a r g e t s . Several medium d e n s i t y ethylene copolymers produced v i a our v e r s a t i l e p o l y m e r i z a t i o n process e x h i b i t e d s i g n i f i c a n t l y improved transparency and strength with e x c e l l e n t g l a s s r e t e n t i o n at nominal 6 mil coating t h i c k n e s s . SDP-531, a medium d e n s i t y ethylene copolymer, was s u c c e s s f u l l y produced meet ing the targeted p h y s i c a l p r o p e r t i e s : 0.935 d e n s i t y and 5-6 melt index. Beverage b o t t l e coatings obtained with SDP-531 e x h i b i t e d e x c e l l e n t g l a s s r e t e n t i o n , s t r e n g t h , and acceptable transparency: contact c l a r i t y with beverage was e x c e p t i o n a l l y good (Figure 7) and Tables II and III.

MEDIUM DENSIT POLYMER PROPERTIES Property Density, g/cc Melt Index, g/10 Min. Melting P o i n t , °C. (1)

Test Method ASTM-D1505 ASTM-1238 DSCU)

D i f f e r e n t i a l Scanning Elmer C o r p o r a t i o n .

SDP-531 0.935 5.5 122

C a l o r i m e t e r , DSC-1B, P e r k i n -

TABLE III MEDIUM DENSITY POLYETHYLENE GLASS BOTTLE COATING PROPERTIES Thickness, M i l s , Glass R e t e n t i o n , W t . % Transparency (2), % Appearance Coating Elongation ( ) , % Coating T e n s i l e Strength (3), PSI 1 λ

U j

3

(1) (2) (3)

5.5 98.0 91.0 Very S l i g h t Haze 800 3500

Wt. % Retained Within 3' Drop Zone. L i g h t Transmission, Water F i l l e d B o t t l e . ASTM D-638, Type IV M o d i f i e d .

SDP-531 was e x t e n s i v e l y evaluated i n l a b o r a t o r i e s and on p i l o t c o a t i n g l i n e s with the f o l l o w i n g r e s u l t s : A. Glass Retention - >95% @ 5.5 M i l s B. Transparency ->90% L i g h t Transmission C. A l k a l i Resistance - No Change i n Strength or Appear5% Caustic @ 80°C ance A f t e r 16 Hours Immersion


11.

HMiEL

Beverage Bottle Coatings

Figure 7.

Super Dylan SDP-531-coated glass beverage bottle— water cooling (left) vs. air cooling (right)


115


116

D.

Heat Resistance

- No Change in Strength or Appearance A f t e r 4 Hours @ 98°C. In Water E. U. V. S t a b i l i t y - 1000 Hours Fadeometer Exposure. NR g l a s s beverage b o t t l e s have h o t - c o l d end surface treatments to improve o n - l i n e handling and s c r a t c h r e s i s t a n c e . Studies were made varying these treatments as well as using bare ( p r i s t i n e ) g l a s s to determine t h e i r e f f e c t s . SDP-531 coatings performed comparably r e g a r d l e s s of s u r f a c e treatment. Production Coating and Market T r i a l s A s u c c e s s f u l production t r i a l on a commercial coating l i n e was made and the coated beverage b o t t l e s e x h i b i t e d performance c h a r a c t e r i s t i c s comparable to l a b o r a t o r y and p i l o t l i n e coated ware. Normal productio mended c o a t i n g and c o o l i n on a commercial b o t t l i n g l i n e and s u c c e s s f u l l y marketed. The contact c l a r i t y o f f i l l e d b o t t l e s was acceptable to b o t t l i n g and marketing personnel. Returnable Beverage B o t t l e s Glass r e t u r n a b l e b o t t l e s are designed to withstand normal abuse repeatedly through the washing, f i l l i n g , and consumer use c y c l e . The e x c e l l e n t a l k a l i r e s i s t a n c e of SDP-531 c o a t ings suggested p o s s i b l e use on r e t u r n a b l e b o t t l e s with c o r responding reduction i n g l a s s weight. Both l i g h t w e i g h t NR's and r e t u r n a b l e b o t t l e s were coated and tested on a commercial soft drink b o t t l i n g l i n e . The b o t t l e s were washed in a twostage c a u s t i c washer, f i l l e d with carbonated beverage, capped, and d i s t r i b u t e d to s e l e c t e d users. These coated b o t t l e s remained i n t a c t and f u n c t i o n a l through nine complete c y c l e s before a mechanical malfunction terminated the t e s t . These p r e l i m i n a r y r e s u l t s suggest that l i g h t e r weight coated g l a s s b o t t l e s f o r l i m i t e d t r i p r e t u r n a b l e s are a n e a r - f u t u r e possibility. Conclusion A medium d e n s i t y ethylene copolymer powder was s u c c e s s f u l l y developed and scaled up i n production equipment f o r fragment r e t e n t i v e non-returnable beverage b o t t l e coatings with acceptable transparency. T h i s R&D program e s t a b l i s h e d a c o r r e l a t i o n between polymer p r o p e r t i e s and c o a t i n g performance; developed procedures to maximize strength and transparency by water quenching molten coatings and s u c c e s s f u l l y a p p l i e d these c o a t i n g - c o o l i n g procedures on a commercial c o a t i n g l i n e . Current s t u d i e s with our v e r s a t i l e polymerization process are designed to f u r t h e r r e f i n e these " e t h y l e n e " powders f o r even b e t t e r performance as economical, fragment r e t e n t i v e beverage b o t t l e coatings with g l a s s - l i k e transparency. RECEIVED M A Y 31,

1978.


INDEX A Β Accelerator-aged coating 67 Bake cycles, equivalent Accelerator-aged vs. room tempera Basecoat, interior ture-aged unreacted prepolymers 61 Beading Acid functional acrylic polymer 81 Beer hexamethoxymethylmelamine with can interior lacquers < 0.5 % free hydroxymethyl ... 82 cans, corrosion in and hexamethoxymethylmelamine markets with ~ 16% free hydroxy methyl 8 Acids, Lewis 3 Acrylic bottle coatings, glass retentive A, water-dispersed 63 can interior lacquers B, water-dispersed 63 can market C, water-dispersed 64 Blends, structures of materials used in C2, water-dispersed 64 Blushing polymer Body spray, waterborne two-piece acid functional 81 Bottle coating requirements and hexamethoxymethylmelamine Bottles, returnable beverage with < 0.5% free hydroxy methyl, acid functional 82 C and hexamethoxymethylmelamine with ~ 16% free hydroxy methyl, acid functional 83 Can coatings, waterborne spray resins 61 cure, two-piece Adhesion grades 40 production, two-piece Adhesion, pasteurization 42 three-piece Air cooling, melt temperature via IR .... I l lCationic polymerization cooling, water cooling vs 115 Chemically similar coatings, com parison of pollution abatement 24 Chrome-coated steel food containers, potential of spray-type epoxy coatings for interior can coatings 23 Chrome-coated steel, TFS Almy powdered-can lacquer for twopiece beverage cans, properties of 9 Circumferential beads Alodine 401-45 14 Clean Air Act of 1970 Alodine 404 14 Coated bottle performance Aluminum D & I containers 11 bottles, cooling of Application 13 cans for particular products, of container coatings 20 development of problems of high-solid systems 48 cans, performance of Araldite 6004 44 Coating(s) ARCO polymers polymerization accelerator-aged process 105 based on four technologies Arrhenius plot for commercial emul chrome-coated steel food containers sion polymer/cross-linker 80 Arrhenius plot for emulsion polymer comparison of chemically similar .... cured with 2 0 % melamine crosscompatability linker 80 container Automated dynamic mechanical conventional epoxy testing 53 curing of 119 In Modern Container Coatings; Strand, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

35 1 26 4 91 1

105 4 1 41 66 11 106 116

1 2 19 1 38 61 25 36 26 4 113 108 27 36 67 20 25 61 34 19 68 38


120 Coatings (continued) epoxy 19, 27 experimental epoxy 69 exterior 27 fabricable-cured 66 food contact 21 glass retentive beverage bottle 105 high-solids 48 hot mar resistance of exterior 31 interior 27 low-bake 20 for metal substrates, thermoset 66 organic enamel 91 polyethylene fragment retentive 113 polymer properties vs 106 polyvinyl-dispersion-type 27 process 108 properties 106 repair 1 room temperature-aged 6 technology, electrostatic powde thermoset 19 thermosetting 30 vinyl organosol 94 waterborne 15 weight 30 Coefficient fabrication, effect of lubricant level on 32 friction, effect of lubricant level on 32 friction values 30 Cold cure curing systems 49 Colorant, levels of 30 Commercial emulsion polymer/crosslinker 78 Arrhenius plot for 80 Complete cure 73 Container(s) coating(s) 19 application of 20 epoxy dispersion 20 test procedure for 92 draw-redraw 25 drawn 25 and ironed (D&I) 14 linings 19 performance 33 effect of lining coating weight on 33 single-draw 25 Controller data analyzer sequence 60 Cooling of coated bottles 108 Coors 10 Corrosion barrter properties of modern container coatings, application of electromechanical techniques to the evaluation of 90 in beer cans 91 rate measurements 91

Cross-link density Cross-linking agents, comparison of the effect of Cure effect of curing agent type on the .... isothermal time reduction Cured coatings, fabricable Cured epoxy rubber system, effect of environment on the dynamic mechanical spectra of a Curing agent(s) melamine-of-urea type on the cure, effect of of coatings systems cold cure

Cycloaliphatic epoxides

70 79 9 86 5 66 62 13 49 9 38 5 49

40

D Decorated flat stock 1 Deformation 26 Density, polymer properties vs. coating performance 107 Determinants of thermoset material behavior 70 Dewey powdered-can lacquer for twopiece beer cans, properties of 9 D & I ( drawn and ironed ) can, twopiece 19 D & I (drawn and ironed) container .. 14 Diazonium salt, photodecomposition of 39 DICY (dicyandiamide) 5 Dicyandiamide (DICY) 5 epoxy, DSC scan of 6 Dispersion coating(s) 20 adhesion 21 application 22 characteristics 22 film properties of 21 formulations, current 20 Draw-redraw cans 94 Draw-redraw containers 25 Drawn containers 25 iron corrosion in 95 and ironed ( D&I ) container 14 -tinplate food containers, coatings for 25 DSC scan of dicyandiamide/epoxy 6 polyazelaic polyanhydride (PAPA)/ epoxy with dicyandiamide catalyst 7


INDEX

121

DSC scan of (continued) trimellictic anhydride/epoxy with dicyandiamide catalyst with stannous octoate catalyst .... Dynamic mechanical analysis, examples of spectra of a cured epoxy/rubber system, effect of environment on testing (DMT) automated in coatings, development of in thermoset, development of

6 8 7 59 62 53 53 54 54

Ε Electromechanical techniques to the evaluation of the corrosion barrier properties of modern containe coatings, application of 9 Electrocoatings 2 Electrodeposition process 2 Electrostatic powder spray coating technology 108 Electrostatic powder spray, powder application 109 Emissions, procedure for qualitative analysis of 101 Emulsion polymer(s) 73 cross-linker, commercial 78 cured with 20% melamine crosslinker 77 Arrhenius plot for 80 Epoxide coatings for metal containers, photocurable 38 monomers 38 parameters physical property measurements 42 oligomers 38 parameters physical measure ments on 42 resins 40 Epoxy chemistry 11 coating(s) 19,27 conventional 68 disadvantage of water-dispersible 12 experimental 69 technology 20 thermosetting 30 water-dispersible 12 control, solvent-base 17 dispersion container coating 20 ester coatings, waterborne 11 interior coatings groups, waterborne 12 powder(s) fast-cure 4 formulations, typical 5

powders (continued) prepared trimellictic anhydride ( TMA ) cured resins in water, dispersions of solution systems, parameters of waterborne solution systems, waterborne system ( s ) at a constant temperature, me chanical damping vs. time curing cure of an at a constant temperature, me chanical rigidity vs. time curing cure of an rubber-modified solvent-based water-emulsifiabl hot mar resistance of External lubrication

5 5 11 19 13 13

72 72 73 11 2 31 30

F Fabricable cured coatings Fabrication screening test Fast-cure epoxy powders Film integrity properties of coatings, relative properties of dispersion coatings .... Finite vs. infinite shelf-life Flat stock, decorated Flavor evaluation Food contact coatings containers, coatings for chromecoated steel containers, coatings for drawn tinplate packs, sterile Friction values, coefficient of Fuming factors

66 25 27 4 11 29 21 71 1 17 21 25 25 26 30 49

G Gelation 70 kinetics 73 temperature and 71 Glass beverage bottle, Super Dylan SDP-531-coated 115 bottle coating properties, mediumdensity polyethylene 114 retentive beverage bottle coatings .. 105 transition temperature (Tg) 71



122 Glycidyl epoxides Grace powders

40 10 H

High solids application, objective of coatings in the laboratory, visible emis sions from oleo resinous system to heat, viscosity response of systems, application problems of .... thermally cured systems vs. water-based coating Hot mar resistance of exterior coatings Hydrogen evolution Hydroxymethyl system

50 48 99 49 48 48 50 31 91 84

Lubricant level on coefficient of friction, effect on Lubrication, external Lubrication, internal

32 30 30

M Materials used in blends, structures of Measured iron pickup Mechanical damping vs. time-curing cure of an epoxy system at a constant temperature Mechanical rigidity vs. time-curing cure of an epoxy system at constant temperature Medium-density ethylene copolymer, (SDP-513) polyethylene glass bottle coating properties

41 97 72 72 114 114

I Impact properties of thermoplastics .. Interior basecoat coatings groups, waterborne epoxy lacquers, beer can lacquers, beverage can sprays Internal lubrication IR analysis of the emissions from bakes Iron corrosion rate for experimental beer cans .. through breaks in coatings through discrete sites in coatings in drawn cans through organic enamel can coatings, examples of through plastisol, rate of through a thick plastisol dissolution measurement pickup calculated from corrosion rate measurements pickup, measured Isothermal cure Isoviscosity level

70 1 27 12 4 4 1 30 101 95 95 94 97 95 92 95 94 90 97 97 86 86

L Lacquer, powdered Lewis acids Line conditions Los Angeles Rule 66 Low-bake coatings Low-bake formulations Low-melt index powders Lubricant level on coefficient of fabrication, effect of

4 38 2 2 20 20 106 32

index polymer properties vs. coating performance temperature via IR-air cooling transparency, powder fusionMelamine(s) -of-urea curing agents Metal can industry containers, photocurable epoxide coatings for pretreatment substrates, thermoset coatings for .... Monitek slip-stream turbidimeter

106 107 Ill 110 13 49 1 38 21 66 100

Ν Non-drag optical transducer

59

Ο O'Brien/Monitek method of measur ing visible emissions Odor profile Opacity requirements, Ringleman I .... Opacity requirements, Ringleman II .. Optical transducer, non-drag Organic enamel can coatings, examples of iron corrosion through Organic enamel coatings

100 13 51 48 59 92 91

Ρ Particle-size distribution for pow dered-can lacquer Pasteurization adhesion beer water


8 42 14 14

123

INDEX Pencil hardness 31 Phenolics 13 Photocurable epoxide coatings for metal containers 38 Photodecomposition of diazonium salt 39 Plasticization 61, 84 Plastisol, rate of iron corrosion through 95 Plastisol sealant 94 Plate-wetting 48 Polarization measurements, applica tion of 92 Polarization resistance 91 Polyazelaic polyanhydride ( P A P A ) / epoxy with dicyandiamide catalyst 7 Polyethylene fragment retentive coatings 113 Polyethylene powders 105 Polymer(s) properties 106 medium-density polyethylene 114 vs. coating performance density 107 vs. coating performance-melting index 107 vs. coatings 106 emulsion 73 systems, water-reducible 2 Polymerization, cationic 38 Polymerization process, A R C O polymers 105 Polyvinyl dispersion-type coatings 27 Postbake, thermal 40 Post-cure 73 Potentiostatic polarization curve 92 Powder application 108 electrostatic powder spray 109 coating development 5 fusion 108 transparency 110 Powdered-can lacquer particle-size distribution for 8 for two-piece beer cans, properties of Dewey 9 for two-piece beverage cans prop erties of Almy 9 Powdered lacquer 4 Prepolymers, unreacted 66 Processability 84 Production coating and market trials .. 116 Properties of epoxy coatings 19 P V C dispersion G 34 P V C dispersion vehicle 33

R RD-2 blends, properties of Reflow point

43 34

Reformation Repair coating Resins, acrylic Rheometrics mechanical spectrometer Rheovibron Returnable beverage bottles Ringleman I opacity requirements Ringleman II opacity requirements .... Rollcoat application Rollcoating Room temperature-aged coating Rubber-modified epoxy, effect of catalyst level on the cure of Rubber-modified epoxy systems

25 1 61 55 53 116 51 48 49 202 67 74 73

S Schiemann reaction SDP-531 (medium-density ethylene

38

Shelf stability Sherwin-Williams Co. Single-draw container Slope-intercept technique Soft drink markets Softening points Softening temperature Solvent-base epoxy control Solvent-based epoxy systems Scratch tests Spray can coatings, waterborne nozzles plugging -type epoxy interior can coatings, air pollution abatement poten tial of Stannous octoate catalyst, D S C scan of trimellitic anhydride/epoxy with Steel D & I containers Sterile food packs Substrate wetting Super Dvlan high-density poly ethylene production ( H D P E ) .... Super Dylan SDP-531-coated glass beverage bottle

13 5 25 91 1 40 71 17 11 30 1 22 22 23 5 7 11 26 48 105 115

Τ Tack free time Tafel line Taste profile T B A , (torsional braid analysis) Temperature and gelation Test pack foods Testing programs for new containers T F S chrome-coated steel Tg, (glass transition temperature) ....


42 92 13 85 71 28 90 36 71


124 Thermal postbake 40 Thermoplastics, impact properties of .. 70 Thermoset coating(s) 19 for metal substrates 66 development of dynamic mechan ical testing on 54 material behavior, determinants of 70 Thermosetting 27 epoxy coatings 30 systems, time to gel vs. isothermal cure temperature for 74 system, time to vitrify vs. isothermal cure temperature for 74 Three-piece can 1 Three-piece food containers 48 Time to gel vs. isothermal cure temperature for thermosetting systems 74 Time to vitrify vs. isothermal cur temperature for thermosettin system 74 Torsion pendulum automated 58 free-hanging, freely decaying 55 torsional braid analysis 57 characteristics of an automated, free-hanging, freely decaying .. 55 mechanical function of 56 sequence of events of the automated 59 Torsional braid analysis (TBA) 53,85 torsion pendulum (automated) 57 Transparency, water cooling-coated bottle 112 Trimellictic anhydride (TMA) / epoxy with dicyandiamide catalyst, DSC scan of 8 DSC scan of 6 with stannous octoate catalyst, DSC scan of 7 -cured epoxy powders 5 Turbidimeter, Monitek slip-stream .... 100 Turbidity resistance 13 Two-piece beer cans, properties of Dewey powdered-can lacquer for 9 beverage cans, properties of Almy powdered-can lacquer for 9

Two-piece (continued) body spray, waterborne can cure can production D & I can

11 2 19 19

U

Unreacted prepolymers accelerated-aged vs. room tempera ture-aged Urea-formaldehyde UV radiation curing, advantages of V Vinyl organosol coating Viscosity response of high-solids oleoresinous system to heat Visible emission, procedure for measuring Vitrification

66 61 13 38 38 94 49

100 70

W

Water cooling-coated bottle transparency Water cooling vs. air cooling Waterborne coatings epoxy ester coatings interior coatings groups solution systems parameters of spray can coatings two-piece body spray Water-dispersed Acrylic A Β C C2 Water-dispersible epoxy coatings disadvantages of Water-emulsifiable epoxy systems Water pasteurization Water-reducible polymer systems W. R. Grace & Co


112 115 15 11 12 13 13 1 11 63 63 64 64 12 12 12 14 2 5

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