Electron-Curable Coatings and Adhesives: Formulation Basics and

7 Electron-Curable Coatings and Adhesives: Formulation Basics and Application Technology J. P. GUARINO Mobil Chemical Company, Edison Laboratory, Edison, NJ 08817

Downloaded by UNIV LAVAL on July 12, 2016 | http://pubs.acs.org Publication Date: August 29, 1979 | doi: 10.1021/bk-1979-0107.ch007

E. P. TRIPP Energy Sciences Inc., Woburn, MA 01801

A. Formulation Basics 1. Introduction. Industry-wide concern over natural gas consumption in thermal curing processes and solvent emissions from conventional formulations has generated increasing interest in the use of solvent-free radiation curable coatings and adhesives. In spite of these strong driving forces for the development of such compositions, industrial adoption of radiation curing is growing at a very slow rate at present. Some of the key reasons for this slow growth can be more clearly understood by considering the criteria which must be met by an acceptable radiation curable formulation. These include: a) Efficient conversion at useful line speeds. b) Safety in handling in an industrial environment. c) Smooth application at desired coating weight. d) Acceptable overall economics. e) The necessary physical properties in a final product. Simultaneous satisfaction of a l l of these requirements limits the number of materials which can be used in formulations. The relationships between formulation materials and the above criteria provide the basis for practical radiation curable products. 2. R a d i a t i o n Curable M a t e r i a l s . The exposure of a m a t e r i a l to e l e c t r o n beam (EB) r a d i a t i o n produces f r e e r a d i c a l s randomly by bond breaking. I f components a r e chosen which a r e capable o f undergoing a f r e e r a d i c a l i n i t i a t e d p o l y m e r i z a t i o n , the composit i o n can be r a p i d l y converted from a l i q u i d to a s o l i d polymer f i l m . Although some monofunctional monomers can be converted f a i r l y e f f i c i e n t l y to polymeric m a t e r i a l using EB r a d i a t i o n , the products a r e g e n e r a l l y s o f t f i l m s w i t h poor i n t e g r i t y . On the other hand, m u l t i f u n c t i o n a l m a t e r i a l s , such as d i - o r t r i f u n c t i o n a l monomers o r resinous m a t e r i a l s , w i l l g e n e r a l l y be converted to a hard, b r i t t l e f i l m , with poor adhesion and f l e x i b i l i t y . These m u l t i f u n c t i o n a l m a t e r i a l s g e n e r a l l y provide an excessive

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Vigo and Nowacki; Energy Conservation in Textile and Polymer Processing ACS Symposium Series; American Chemical Society: Washington, DC, 1979.


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amount of c r o s s l i n k i n g when f u l l y cured and monofunctional monomers are r e q u i r e d i n order to reduce t h i s c r o s s l i n k i n g . Such mixtures o f mono- and m u l t i f u n c t i o n a l m a t e r i a l s can provide a wide range o f p h y s i c a l p r o p e r t i e s when p r o p e r l y balanced. Of the many types o f polymerizable m a t e r i a l s which have been s t u d i e d , a c r y l i c f u n c t i o n a l m a t e r i a l s have g e n e r a l l y been found to provide the f a s t e s t cure r a t e s by EB r a d i a t i o n , p a r t i c u l a r l y when exposed i n an atmosphere w i t h a lowered oxygen content. The present d i s c u s s i o n s w i l l g e n e r a l l y r e f e r to such a c r y l a t e - f u n c t i o n a l m a t e r i a l s cured i n an i n e r t atmosphere. A t y p i c a l EB curable formulation w i l l g e n e r a l l y c o n s i s t o f a r e l a t i v e l y high molecular weight s o l i d or s e m i - s o l i d d i f u n c t i o n a l a c r y l i c r e s i n reduced to a p p l i c a t i o n v i s c o s i t y with comb i n a t i o n s of l i q u i d mono- and m u l t i f u n c t i o n a l a c r y l i c monomers. These a c r y l i c monomers, along with a few other s e l e c t e d polymeri z a b l e monomers, serve as r e a c t i v e d i l u e n t s and allow formulation of s o l v e n t - f r e e compositions. U s u a l l y , small amounts o f a d d i t i v e s are a l s o used i n order t o provide s p e c i a l p r o p e r t i e s , such as s l i p . The s e l e c t i o n o f l i q u i d monofunctional monomers f o r use i n EB cure has been a key f a c t o r i n the slow pace o f development of acceptable formulations. These monomers p l a y dominant r o l e s i n determining cure speed, v i s c o s i t y , s a f e t y and c o s t , i n a d d i t i o n to s i g n i f i c a n t c o n t r i b u t i o n s to the p h y s i c a l p r o p e r t i e s of the cured f i l m s . 3. R a d i a t i o n Cure E f f i c i e n c y . The ultimate goal o f r a d i a t i o n cure i s to e l i m i n a t e emissions e n t i r e l y by p r o v i d i n g 100% convers i o n o f a p p l i e d m a t e r i a l t o f i n a l product. For minimizing energy usage, t h i s should be accomplished a t the highest p o s s i b l e l i n e speeds. Thus the d e f i n i t i o n o f r a d i a t i o n cure e f f i c i e n c y must be r e l a t e d to measurements of both the energy input and the convers i o n o f the formulation t o n o n - v o l a t i l e product. Exposure o f a m a t e r i a l t o EB r a d i a t i o n w i l l deposit a measurable amount o f energy, which i s g e n e r a l l y expressed i n the u n i t s o f Megarads, where 1 MR « 2.4 cal/gm. In t y p i c a l a p p l i c a t i o n t e s t s , the dose r e q u i r e d f o r "cure" i s determined observ a t i o n a l l y by running a t various doses and t e s t i n g f o r some p h y s i c a l property. The cure dose f o r coatings o f t e n r e f e r s to the minimum dose needed f o r a t a c k - f r e e s u r f a c e . This procedure i s not meaningful i f one d e s i r e s to produce a f u l l y polymerized m a t e r i a l which i s tacky, such as f o r an adhesive. The exposure o f a given formulation t o EB r a d i a t i o n r e s u l t s i n conversion of some f r a c t i o n o f the sample to a polymerized n o n - v o l a t i l e f i l m . The remainder o f the sample i s p o t e n t i a l l y v o l a t i l e , e i t h e r during the EB exposure o r during subsequent treatment o r usage o f the f i n a l product. A s t r a i g h t f o r w a r d g r a v i m e t r i c technique, i n use i n our l a b o r a t o r y f o r some time to measure the conversion o f a formulation, i s based on weighing the wet c o a t i n g a p p l i e d a t the d e s i r e d weight on a cleaned aluminum



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panel before EB exposure, a f t e r EB exposure, and a f t e r a p o s t bake o f f i v e minutes at 350°F. R e p r o d u c i b i l i t y i s g e n e r a l l y w i t h i n 1%. The EB u n i t i n use a t the Mobil Chemical Company Edison Laboratory i s a c u r t a i n - t y p e l a b o r a t o r y e l e c t r o n processor which r e q u i r e s a w a i t i n g time o f about one minute to reduce the oxygen l e v e l with n i t r o g e n f l u s h i n g . During t h i s n i t r o g e n f l u s h i n g , a l o s s o f v o l a t i l e monomer can occur, which r e f l e c t s a s i m i l a r p o t e n t i a l l o s s on high speed c o a t i n g equipment. Low v o l a t i l i t y monomers give n e g l i g i b l e weight l o s s e s d u r i n g f l u s h i n g and EB exposure, so the measurement o f the f i l m weight i s considered a very u s e f u l screening d e v i c e i n the development o f h i g h convers i o n EB f o r m u l a t i o n s . Separate measurements have a l s o shown that the resinous components are v i r t u a l l y n o n - v o l a t i l e when baked a t 350°F f o r f i v e minutes without EB exposure. However, the l i q u i d monomeric components are completely v o l a t i l i z e d i n the bake, demonstrating that no thermal conversion o c c u r s . Thus, the weight measurements described above provide a measure o f the amounts o f l i q u i d components which are l o s t i n the EB u n i t and, from the post-bake weight, the t o t a l conversion to a n o n - v o l a t i l e f i l m . Measurement o f conversions o f v a r i o u s formulations a t v a r i ous EB doses can be used to rank the r e a c t i v i t y o f the formulat i o n . A p a r t i c u l a r l y u s e f u l procedure has been to prepare a standard mixture of an a c r y l a t e r e s i n w i t h v a r i o u s r e a c t i v e d i l u e n t monomers i n order to compare the v o l a t i l i t y and react i v i t y o f new monomers. For these s t u d i e s , a mixture o f 40 weight % o f a Bis-phenol A epoxy d i a c r y l a t e r e s i n with 60% of the t e s t l i q u i d monomer has proved convenient. A v i s c o s i t y measurement o f the mixture a l s o provides i n f o r m a t i o n on the r e l a t i v e v i s c o s i t y reducing a b i l i t y o f the t e s t monomer. Illustrative examples o f these measurements are shown i n Table I and F i g u r e 1. Note from these examples that a monofunctional monomer, Monomer B*, can be used to provide the low v o l a t i l i t y and high r e a c t i v i t y t y p i c a l o f the m u l t i f u n c t i o n a l monomers, while a l s o s e r v i n g t o reduce the c r o s s l i n k i n g . Many other a v a i l a b l e monofunctional monomers are found to be e i t h e r more v o l a t i l e or l e s s r e a c t i v e than Monomer B. The r e l a t i v e r e a c t i v i t i e s of v a r i o u s other r e s i n s , monomers and combinations o f monomers have been measured i n a s i m i l a r manner. From t h i s i n f o r m a t i o n , i t was learned that many commerc i a l l y a v a i l a b l e monofunctional monomers were not s u i t a b l e f o r use i n r a d i a t i o n c u r a b l e f o r m u l a t i o n s . Mobil Chemical Company has now developed s e v e r a l p r o p r i e t a r y monofunctional monomers which provide low v o l a t i l i t y , high r e a c t i v i t y and s a f e handling p r o p e r t i e s to f u l f i l l these needs. I n a d d i t i o n , other m a t e r i a l s u p p l i e r s have begun to make s u i t a b l e monomers a v a i l a b l e , so the o v e r a l l a v a i l a b i l i t y o f m a t e r i a l s f o r f o r m u l a t i n g has improved g r e a t l y w i t h i n the l a s t few y e a r s . * P r o p r i e t a r y M o b i l monofunctional a c r y l a t e monomer.


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Table I E l e c t r o n Beam Conversions of Standard Formulations Formulation • 40 wt % Dow XD9002 Resin 60 wt % Test Monomer


Monomer TMPTA HDODA Monomer Β IBOA PEA

Vise. CP 1710 75 380 220 125

EB 100 100 100 93 99

5MR Bake 96 99 98 79 93

EB 100 100 100 88 99

2MR Bake 93 92 94 71 77

1MR Bake 90 85 89 69 64

EB 100 100 100 86 98 2

A l l conversions measured f o r t h i n f i l m s (^3mg/in ) on aluminum panels using the Edison Lab c u r t a i n - t y p e l a b o r a t o r y e l e c t r o n processor. EB conversions i n c l u d e ^1 min f l u s h i n g w i t h n i t r o g e n gas. Bake conversion i s a f t e r 5 min a t 350°F. TMPTA » T r i m e t h y l o l propane t r i a c r y l a t e . HDODA - Hexanediol d i a c r y l a t e . Monomer Β • M o b i l a c r y l a t e monomer. IBOA « Isobornyl a c r y l a t e . PEA - Phenoxyethyl a c r y l a t e .


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4. Safe Handling. Most of the handling problems a s s o c i a t e d w i t h e a r l y r a d i a t i o n c u r a b l e formulations have been traced to the l i q u i d monomers i n use. In p a r t i c u l a r , d e r m a t i t i s has been a common complaint. As p a r t of our monomer development program, extensive use of animal t e s t i n g was made to f u r t h e r d e f i n e acceptable monomers. At t h i s time, the t e s t i n g program, along w i t h a l i m i t e d amount of p i l o t and commercial l i n e experience, i n d i c a t e s that the m a t e r i a l s i n use do not appear to pose h e a l t h hazards any greater than the use of conventional c o a t i n g s . However, as w i t h any new technology, s t r i c t a t t e n t i o n should be paid to adequate v e n t i l a t i o n and minimizing of s k i n contact. 5. A p p l i c a t i o n . From a f o r m u l a t i o n point of view, the key a p p l i c a t i o n parameter i s rneology, which can be adjusted by the s e l e c t i o n of r e s i n s and r e a c t i v e d i l u e n t s and t h e i r l e v e l s . EB curable formulations are a v a i l a b l e c o v e r i n g a range of 10 to 50,000 c e n t i p o i s e or h i g h e r . 6. O v e r a l l Economics. Statements are o f t e n made that r a d i a t i o n cure equipment r e q u i r e s too l a r g e a c a p i t a l investment or that c o a t i n g c o s t s are too h i g h . Our own a n a l y s i s of many potent i a l a p p l i c a t i o n areas i n d i c a t e s that r a d i a t i o n cure may be economically favorable f o r higher l i n e speeds, heat s e n s i t i v e subs t r a t e s , replacement of conventional coatings p r e s e n t l y used at l e s s than 30% s o l i d s , and new products which cannot be made conv e n t i o n a l l y . For purposes of i n i t i a l c a l c u l a t i o n s , EB c o a t i n g costs ranging from $1.50 to $2.50 per pound can be used to d e t e r mine economic f e a s i b i l i t y o f p o s s i b l e new a p p l i c a t i o n areas. 7. End Use P r o p e r t i e s . The areas of p o t e n t i a l end use f o r r a d i a t i o n c u r a b l e coatings and adhesives i n i n d u s t r y may be as wide as those using s o l v e n t s or water. In a p p l i c a t i o n s on porous s u b s t r a t e s , such as paper, the r a p i d cure minimizes a b s o r p t i o n i n t o the s u b s t r a t e and can produce e x c e p t i o n a l l y high gloss with a minimum of c o a t i n g usage. Other present commercial a p p l i c a t i o n s i n c l u d e c l e a r and pigmented coatings f o r wood, paper and p l a s t i c f i l m s . Laminating adhesives have a l s o gained acceptance i n s e v e r a l s p e c i a l t y end uses. Coatings f o r metals, p l a s t i c s and t e x t i l e substrates are p r e s e n t l y under development. C o n t r o l o f the EB cured f i l m p r o p e r t i e s through formulation i s the key to meeting s p e c i f i c end use p r o p e r t i e s . A wide range of hardness and f l e x i b i l i t y can be produced by adjustment of c r o s s l i n k d e n s i t y and g l a s s t r a n s i t i o n temperature. Studies on the e f f e c t s of f o r m u l a t i o n v a r i a b l e s on the t e n s i l e e l o n g a t i o n p r o p e r t i e s of f r e e f i l m s have proven e s p e c i a l l y v a l u a b l e i n development of coatings f o r f l e x i b l e s u b s t r a t e s . By c a r e f u l s e l e c t i o n of m a t e r i a l s used i n EB curable formul a t i o n s i t has been found f e a s i b l e to produce a wide range of p h y s i c a l p r o p e r t i e s while maintaining f a s t cure, s a f e t y i n hand l i n g , smooth a p p l i c a t i o n , and reasonable c o s t .


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The advancement of low v i s c o s i t y , r a d i a t i o n curable systems i n the l a s t two years has f o r the f i r s t time made gravure a p p l i c a t i o n of these systems a r e a l i t y . Since many i n d u s t r i a l web processes ( c o a t i n g paper or f i l m , l a m i n a t i n g , metal c o a t i n g , e t c . ) already employ gravure equipment, the a v a i l a b i l i t y of these new systems (1) has had major impact on the i n t e r e s t i n e l e c t r o n c u r i n g technology. P r i o r to the development of low v i s c o s i t y formulations (503000cp, depending upon pigment l e v e l , p r o p e r t i e s d e s i r e d , c o s t , e t c . ) , the handful of a p p l i c a t i o n s i n v o l v i n g r a d i a t i o n cure c o a t ings were performed w i t h non-gravure equipment, i . e . r e v e r s e or d i r e c t r o l l c o a t e r s , c u r t a i n c o a t e r s or k n i f e over r o l l c o a t e r s . For example, most UV curable wood f i l l e r s have been a p p l i e d w i t h d i r e c t r o l l c o a t e r s , reverse r o l l coaters or r e v e r s e r o l l f i l l e r s (2,3). The c o a t i n g o f v i n y l f l o o r t i l e , on the other hand, has t r a d i t i o n a l l y used c u r t a i n c o a t e r s w i t h good r e s u l t s , and a f l o c k i n g o p e r a t i o n employing an e l e c t r o n c u r a b l e adhesive has s u c c e s s f u l l y operated w i t h a k n i f e over p l a t e (or r o l l ) s t a t i o n (4). The use of these a p p l i c a t i o n techniques was g e n e r a l l y necessary both because of the type of product being coated and the r a t h e r high v i s c o s i t y (syrupy) nature of the coatings used. Moreover, some of the coatings r e q u i r e d moderate h e a t i n g to r e duce the v i s c o s i t y to a l e v e l where c o a t i n g smoothness would show optimum r e s u l t s . Now, however, gravure and o f f s e t gravure c o a t i n g appear to be i n c r e a s i n g l y f e a s i b l e f o r a wide v a r i e t y of h i g h speed web processes. Over the past year, many e l e c t r o n curable coatings and adhesives were s u c c e s s f u l l y a p p l i e d and cured on a s p e c i a l l y b u i l t p i l o t c o a t i n g / l a m i n a t i n g l i n e at speeds up to 280 meters/ minute. T h i s l i n e , i n c o r p o r a t i n g a very v e r s a t i l e coater with a c u r t a i n type EB c u r i n g s t a t i o n ( 5 ) , i s capable of a p p l y i n g matr i a l s w i t h d i r e c t gravure, o f f s e t gravure, reverse o f f s e t gravure, as w e l l as reverse r o l l and k n i f e over r o l l . Most of the t r i a l s run to date, however, have u t i l i z e d the f i r s t three techniques. A major c r i t e r i o n f o r a p p l i c a t i o n i s the achievement of a smooth, continuous s u r f a c e , whether i t be f l a t or g l o s s y . Since there are no s o l v e n t s or water i n these m a t e r i a l s f o r l e v e l i n g by surface t e n s i o n , the appearance of the 100% s o l i d s c o a t i n g as i t i s a p p l i e d i s e s s e n t i a l l y the appearance of the cured f i n i s h . To achieve the best f i n i s h , p i l o t experience has shown t h a t o f f s e t gravure w i l l c o n s i s t e n t l y give a smoother s u r f a c e than d i r e c t gravure f o r m a t e r i a l s having v i s c o s i t i e s i n the upper p a r t of the gravure range (^500-3000cp). The d i f f e r e n c e between d i r e c t and o f f s e t gravure i s shown i n F i g u r e 2. The improvement w i t h o f f s e t i s most l i k e l y due to the o f f s e t r o l l both smearing the gravure p a t t e r n ( r o l l s can be operated a t s l i g h t l y d i f f e r e n t speeds) and s p l i t t i n g the c o a t i n g f i l m before i t ' s t r a n s f e r r e d to the s u b s t r a t e . B e t t e r c o a t i n g s u r f a c e s a l s o r e s u l t with o f f s e t



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gravure on many of the lower v i s c o s i t y (*v/500cp or l e s s ) formula t i o n s , but the appearance of " f l o o d i n g " (Figure 3) gives r i s e to s t r e a k i n g problems and thus these m a t e r i a l s cannot be a p p l i e d with o f f s e t gravure. Whether or not such formulations give a s a t i s f a c t o r y s u r f a c e w i t h d i r e c t gravure can only be determined by running them and observing the r e s u l t s . I t has not yet been p o s s i b l e to d i r e c t l y r e l a t e v i s c o s i t y w i t h t h i s f l o o d i n g problem as the o v e r a l l rheology of the m a t e r i a l i s what determines per formance. G e n e r a l l y , however, the higher gravure v i s c o s i t i e s do not show f l o o d i n g , and o f f s e t gravure i s the p r e f e r r e d c o a t i n g technique when the smoothest p o s s i b l e s u r f a c e i s d e s i r e d . Reverse o f f s e t gravure has proven u s e f u l i n a p p l y i n g c e r t a i n coatings where forward o f f s e t gravure has shown problems w i t h surface d e f e c t s , i . e . f i s h eyes, s t r e a k s , p i t s , or roughness. In t h i s case, as with reverse r o l l c o a t i n g , the reverse wiping a c t i o n of the o f f s e t r o l l provides enhanced smoothness. Our experience has shown t h i s technique p a r t i c u l a r l y u s e f u l i n a p p l y i n g h i g h l y pigmented coatings to aluminum r o l l stock. The use of any of these gravure c o a t i n g methods can u s u a l l y be enhanced by the a d d i t i o n of a r o t a t i n g smoothing bar on the s u r f a c e of the coated s u b s t r a t e j u s t p r i o r to cure. T h i s device can smooth out many minor and sometimes major i r r e g u l a r i t i e s i n the surface r e s u l t i n g from c o a t i n g a p p l i c a t i o n . U s u a l l y the smoothing bar i s r o t a t e d i n the reverse or opposite d i r e c t i o n the web i s t r a v e l i n g to provide a wiping a c t i o n . In some unusual cases, however, c e r t a i n pigmented coatings give b e t t e r r e s u l t s when the bar i s r o t a t e d i n the web d i r e c t i o n at approximately the same s u r f a c e speed. Other s i t u a t i o n s may a l s o warrant the use of m u l t i p l e smoothing bars of perhaps d i f f e r i n g s u r f a c e t e x t u r e s . One of the advantages of using gravure or o f f s e t gravure i s the a b i l i t y of the technique to apply coatings of a uniform and c o n s i s t e n t t h i c k n e s s . How much c o a t i n g or adhesive i s a p p l i e d i s p r i m a r i l y determined by the type and depth of the engraving on the gravure c y l i n d e r . Experiments with both d i r e c t and o f f s e t gravure on a wide s e l e c t i o n of coatings i n d i c a t e the f o l l o w i n g thicknesses r e s u l t from quadrangular c e l l (6) engraved r o l l s : 200 Quad - * 2- 4μ c o a t i n g thickness 150 Quad - ^ 5- 8μ c o a t i n g thickness 110 Quad - ^ 8-10μ c o a t i n g t h i c k n e s s 85 Quad - ^12-15μ c o a t i n g thickness The combination of e l e c t r o n c u r i n g with gravure a p p l i c a t i o n technology can o f f e r some r a t h e r unusual b e n e f i t s . One of the most important of these i s the c o n t r o l of c o a t i n g p e n e t r a t i o n i n t o porous s u b s t r a t e s by the very short dwell time between c o a t ing a p p l i c a t i o n and cure. With t y p i c a l dwell times on the order of 0.5 sec or l e s s , coatings can be deposited at minimum t h i c k ness on porous s u b s t r a t e s such as paper while a c h i e v i n g maximum surface smoothness. F i g u r e s 4 and 5 show photomicrographs of a paper s u r f a c e before and a f t e r c o a t i n g by o f f s e t gravure. The EB cured c o a t i n g thickness i s approximately 5μ (150 Quad). Note the



ENERGY

CONSERVATION

Figure 2.

IN TEXTILE

A N DPOLYMER

Gravure application technique

FLOODING Figure 3.

"Flooding" with offset gravue


PROCESSING


7. GUARiNO

A N D TRIPP

Coatings

and Adhesives

Figure 4.

Photomicrograph (7200X) of 28 # clay coated paper surface. Longer of two lines represents 1μ.

Figure 5.

Photomicrograph (7200χ) of same paper coated with approximately 6μ. of an EB cured coating (applied offset gravure)


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ENERGY

80

CONSERVATION

IN TEXTILE

A N D POLYMER

PROCESSING


absence of surface d e f o r m i t i e s i n the c o a t i n g i n s p i t e o f the rough nature of the o r i g i n a l paper s u r f a c e . Since low v i s c o s i t y e l e c t r o n curable systems have only r e c e n t l y become a v a i l a b l e , the a p p l i c a t i o n r e s u l t s presented here do not attempt to give a l l the answers. Each c o a t i n g system has i t s own rheology and only by running a c t u a l c o a t i n g t r i a l s can the performance of the a p p l i c a t i o n technique be evaluated. Perhaps, when enough data has been accumulated, accurate p r e d i c t i o n s on c o a t i n g behavior w i l l be r o u t i n e matters. However, u n t i l that time i s reached, general g u i d e l i n e s such as presented here w i l l h o p e f u l l y prove u s e f u l to those c o n s i d e r i n g the adoption o f e l e c t r o n c u r i n g technology.

References: (1) Gerhardt, G. W., 3rd International Radiation Curing Conference, Session X, Paper FC76-531, Society of Manufacturing Engineers, Chicago, Sept. 28-30, 1976. (2) Ibid, Jones, D. T., Session VII, Paper FC76-537. (3) Ibid, Hodakowski, L. E . , Session V, Paper FC76-502. (4) Ibid, Trask, B. D., Session VIII, Paper FC76-521. (5) Nablo, S. V. and Tripp, E. P., Radiation Physics and Chemistry, 9, 325, (1977). (6) For more information see: Heurich, C. R., Better Ink Transfer Guaranteed by New Engineering Techniques, Report of Proceedings of Flexographic Technical Association Forum, 1966, May 10-11, 1966. RECEIVED

March

1, 1979.


Electron-Curable Coatings and Adhesives: Formulation Basics and

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