Radiation-Induced Cationic Curing of Vinyl-Ether-Functionalized

Chapter 26

Radiation-Induced Cationic Curing of Vinyl-Ether-Functionalized Urethane Oligomers

Downloaded by GEORGETOWN UNIV on August 27, 2015 | http://pubs.acs.org Publication Date: December 28, 1990 | doi: 10.1021/bk-1990-0417.ch026

Stephen C. Lapin Allied-Signal Engineered Materials Research Center, 50 East Algonquin Road, Des Plaines, IL 60017 Vinyl ether terminated urethane (VEU) oligomers were prepared by reacting hydroxy vinyl ethers with isocyanates. These materials were chain extended with polyols and combined with divinyl ether monomers to produce radiation curable coating formulations. Cationic curing was induced by UV or electron beam irradiation in the presence of a triaryl sulfomium salt catalyst. Curing occured at high speeds and produced coatings with desirable physical properties.

R a d i a t i o n c u r a b l e c o a t i n g s c o n s i s t o f monomers a n d o l i g o m e r s w h i c h have f u n c t i o n a l groups i n which p o l y m e r i z a t i o n may be i n d u c e d b y the p r e s e n c e o f UV o r e l e c t r o n beam r a d i a t i o n . The major t y p e s o f systems that have been u s e d include: (1) u n s a t u r a t e d p o l y e s t e r s , (2) t h i o l / e n e s , (3) a c r y l a t e s , and (4) c a t i o n i c a l l y c u r e d e p o x i e s . Each o f t h e s e systems h a s i t s own d i s t i n c t advantages and d i s a d v a n t a g e s . One chooses a system t h a t i s b e s t s u i t e d t o a p a r t i c u l a r a p p l i c a t i o n . A c r y l a t e s a t p r e s e n t a r e b y f a r the most w i d e l y u s e d system. They o f f e r a n e x c e l l e n t c o m b i n a t i o n o f h i g h r e a c t i v i t y and moderate c o s t s . I n a d d i t i o n , t h e r e a r e a wide v a r i e t y o f c o m m e r c i a l l y a v a i l a b l e a c r y l a t e d monomers and o l i g o m e r s w h i c h a l l o w t h e f o r m u l a t i o n o f c o a t i n g s w i t h a wide range o f p h y s i c a l p r o p e r t i e s . A l t h o u g h a c r y l a t e s a r e e x t r e m e l y u s e f u l and v e r s a t i l e m a t e r i a l s , t h e y a l s o have some d i s t i n c t d i s a d v a n t a g e s . One d i s a d v a n t a g e i s the growing c o n c e r n w i t h h e a l t h h a z a r d s t h a t a r e a s s o c i a t e d w i t h the use of acrylates (1-4). Another disadvantage i s that the r a d i c a l p o l y m e r i z a t i o n o f a c r y l a t e s i s i n h i b i t e d b y a t m o s p h e r i c oxygen ( 5 , 6 ) . A system t h a t has r e c e n t l y been r e c e i v i n g a t t e n t i o n i s r a d i a t i o n induced c a t i o n i c curing. The i n t e r e s t i n c a t i o n i c c u r i n g has been i n s p i r e d b y the development o f onium s a l t c a t a l y s t s . S t r o n g a c i d s a r e l i b e r a t e d when the c o a t i n g s a r e i r r a d i a t e d i n the p r e s e n c e o f c e r t a i n onium s a l t s . These a c i d s a r e capable o f c a t a l y z i n g cationic polymerization reactions (7). Onium s a l t s have b e e n u s e d m o s t l y i n UV c u r a b l e systems. However, i t has b e e n shown r e c e n t l y t h a t t h e y may a l s o be u s e d f o r e l e c t r o n beam i n d u c e d c u r i n g ( 8 , 9 ) . Reprinted with permission ©1988 Radtech International

In Radiation Curing of Polymeric Materials; Hoyle, C., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1990.


364

RADIATION CURING OF POLYMERIC MATERIALS

Most o f the work on c a t i o n i c c u r i n g has dealt with the h o m o p o l y m e r i z a t i o n o f e p o x i e s (9,10,11). Epoxy c o a t i n g s a r e w e l l known f o r t h e i r s u p e r i o r a d h e s i o n , toughness, and c h e m i c a l r e s i s t a n c e . This makes r a d i a t i o n c u r a b l e epoxies extremely u s e f u l i n some demanding a p p l i c a t i o n s . A n o t h e r advantage o f e p o x i e s i s t h a t the c a t i o n i c c u r i n g r e a c t i o n i s n o t i n h i b i t e d by a t m o s p h e r i c oxygen. The major d i s a d v a n t a g e o f e p o x i e s i s t h e i r s l o w c u r e speed. One r e a s o n f o r u s i n g r a d i a t i o n c u r i n g i s t o take advantage o f l i n e speeds w h i c h c a n o p e r a t e c o n c u r r e n t l y w i t h o t h e r h i g h speed p r o c e s s i n g steps. E p o x i e s do n o t c u r e f a s t enough t o make them u s e f u l as d i r e c t r e p l a c e m e n t s f o r a c r y l a t e s i n most a p p l i c a t i o n s . Epoxies will c o n t i n u e t o p o l y m e r i z e i n a "dark c u r e " r e a c t i o n l o n g a f t e r t h e y a r e irradiated. T h i s can complicate the h a n d l i n g o f m a t e r i a l s i n a production l i n e . A " t h e r m a l bump" i s o f t e n a p p l i e d f o l l o w i n g the i r r a d i a t i o n s t e p i n o r d e r t o h a s t e n the a t t a i n m e n t o f the final c o a t i n g p r o p e r t i e s ( 9 , 1 0 ) . The use o f t h i s a d d i t i o n a l t h e r m a l c u r i n g s t e p d e f e a t s p a r t o f the purpose o f r a d i a t i o n c u r i n g , and i s g e n e r a l l y c o n s i d e r e d t o be u n a c c e p t a b l e . I t has r e c e n t l y be shown t h a t a l c o h o l s may be added t o the epoxy based formulations. T h i s i n c r e a s e s the c u r e speed o f the c o a t i n g t h r o u g h a c h a i n t r a n s f e r p o l y m e r i z a t i o n r e a c t i o n . The c h a i n t r a n s f e r processes produces coatings w i t h reduced c r o s s l i n k d e n s i t y . This g e n e r a l l y l e a d s t o a r e d u c t i o n i n the m e c h a n i c a l p r o p e r t i e s and the c h e m i c a l r e s i s t a n c e i n the c u r e d c o a t i n g . I t has b e e n s u g g e s t e d t h a t m u l t i f u n c t i o n a l a l c o h o l s may u s e d as c h a i n t r a n s f e r a g e n t s t o h e l p o f f s e t the l o s s o f c r o s s l i n k d e n s i t y ( 1 2 ) . However, much o f the p u b l i s h e d d a t a shows a sharp d e c r e a s e i n T and t e n s i l modulus upon the a d d i t i o n o f p o l y o l s ( 1 3 ) . I n 1982, C r i v e l l o and co-workers p u b l i s h e d a r e p o r t on the UV i n i t i a t e d c a t i o n i c p o l y m e r i z a t i o n o f v i n y l e t h e r monomers u s i n g onium s a l t c a t a l y s t s ( 1 4 ) . V i n y l e t h e r s are among the most r e a c t i v e monomers w h i c h p o l y m e r i z e by a c a t i o n i c mechanism. The r a d i a t i o n i n d u c e d c a t i o n i c c u r i n g o f v i n y l e t h e r s o c c u r s much f a s t e r t h a n the c a t i o n i c c u r i n g o f epoxy c o a t i n g s . I n f a c t , c u r e r a t e s t h a t a r e a t l e a s t as fast as the free radical polymerization of acrylates can be achieved(8,14). A recent report indicates that the cationic p o l y m e r i z a t i o n o f v i n y l e t h e r s can o c c u r even i n the p r e s e n c e o f c e r t a i n p o l a r f u n c t i o n a l groups(15). One way i n w h i c h v i n y l e t h e r monomers may be u s e d i s as r e a c t i v e d i l u e n t s i n epoxy systems. The a d d i t i o n o f a v i n y l e t h e r g r e a t l y i n c r e a s e s the c u r e speed o f the system. The r a p i d change t o a t a c k f r e e s t a t e a p p e a r s t o be the r e s u l t o f the p o l y m e r i z a t i o n o f the v i n y l e t h e r component o f the m i x t u r e . A " t h e r m a l bump" i s s t i l l n e c e s s a r y t o c u r e the epoxy and b r i n g the c o a t i n g t o a f u l l y c u r e d s t a t e ( 1 6 ) . T h e r e i s l i t t l e e v i d e n c e f o r any c o p o l y m e r i z a t i o n o f the v i n y l e t h e r and the epoxy g r o u p s . I n o r d e r t o t a k e f u l l advantage o f the h i g h c u r e speed o f v i n y l e t h e r s , systems a r e needed w h i c h have a c u r i n g mechanism b a s e d t o t a l l y on the p o l y m e r i z a t i o n o f v i n y l e t h e r g r o u p s . A few v i n y l ether monomers a r e now c o m m e r c i a l l y a v a i l a b l e ( 1 7 ) ; however, t h e r e are c u r r e n t l y no s o u r c e s o f v i n y l e t h e r f u n c t i o n a l i z e d o l i g o m e r s . It is d i f f i c u l t t o f o r m u l a t e c o a t i n g s b a s e d on monomers a l o n e . Higher molecular weight m a t e r i a l s are o f t e n r e q u i r e d . O l i g o m e r i c components have more d e s i r a b l e r h e o l o g i c a l p r o p e r t i e s and t h e y a l l o w greater g


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c o n t r o l o f the cured f i l m p r o p e r t i e s . I n t h i s p a p e r we r e p o r t t h e development o f v i n y l e t h e r t e r m i n a t e d o l i g o m e r s . These m a t e r i a l s g r e a t l y widen the scope o f p o t e n t i a l a p p l i c a t i o n s o f r a d i a t i o n i n d u c e d cationic curing. Introduction


V i n y l e t h e r s may be s y n t h e s i z e d b y t h e base c a t a l y z e d r e a c t i o n o f a l c o h o l s w i t h a c e t y l e n e a t e l e v a t e d temperatures and p r e s s u r e s ( 1 8 ) . D i o l s may a l s o be u s e d t o produce d i f u n c t i o n a l v i n y l e t h e r s ( E q u a t i o n 1) T h i s i s most l i k e l y a r e v e r s i b l e r e a c t i o n t h e r e f o r e , a m i x t u r e

KOH HO-R-OH

+

2C H 2

> CH -CH-0-R-0-CH»CH 200°C., p r e s s .

2

2

2

+ CH -CH-0-R-OH 2

(1)

of products i s obtained(18). The m i x t u r e i n c l u d e s t h e d i v i n y l e t h e r a l o n g w i t h a m o n o a c e t y l a t e d p r o d u c t and u n r e a c t e d d i o l . The d i v i n y l e t h e r h a s a b o i l i n g p o i n t w h i c h i s lower t h a n t h e o t h e r p r o d u c t s and may be s e p a r a t e d from t h e m i x t u r e b y f r a c t i o n a l d i s t i l l a t i o n . The d i s t i l l a t i o n a l s o s e r v e s t o s e p a r a t e t h e d i v i n y l e t h e r monomer from the KOH and o t h e r r e a c t i o n b y - p r o d u c t s w h i c h would i n h i b i t c a t i o n i c polymerization. T h i s method has been u s e d t o p r o d u c e d i v i n y l e t h e r s from butane d i o l , d i e t h y l e n e g l y c o l , and t r i e t h y l e n e g l y c o l and 1,4cyclohexane dimethanol(17). The method does n o t l e n d i t s e l f w e l l , however, t o t h e p r o d u c t i o n o f o l i g o m e r i c v i n y l e t h e r s from h i g h e r molecular weight p o l y o l s . I t i s not p r a c t i c a l to p u r i f y higher m o l e c u l a r p r o d u c t s by d i s t i l l a t i o n . I n a d d i t i o n t h e backbone o f t h e o l i g o m e r would be l i m i t e d t o s t r u c t u r e s w h i c h a r e s t a b l e under t h e a c e t y l e n e r e a c t i o n c o n d i t i o n s ( i . e . , 3% KOH and 2 0 0 ° C ) . A n o t h e r method which may be u s e d t o s y n t h e s i z e o l i g o m e r i c v i n y l ethers i s the r e a c t i o n o f c h l o r o e t h y l v i n y l ether with a l c o h o l s ( E q u a t i o n 2) (14,19). The r e a c t i o n i s a i d e d b y t h e a d d i t i o n o f a

CH -CH-0-CH CH -Cl 2

2

2

+

ROH

KOH > PTC

CH =CH-0-CH CH -OR 2

2

2

(2)

phase t r a n s f e r c a t a l y s t . W h i l e t h i s i s good method f o r t h e l a b o r a t o r y s c a l e p r e p a r a t i o n o f c e r t a i n v i n y l e t h e r s , i t does n o t appear t o be commercially attractive. There a r e no commercial sources o f c h l o r o e t h y l v i n y l e t h e r i n t h e U n i t e d S t a t e s , and as w i t h t h e a c e t y l e n e r e a c t i o n , one may have d i f f i c u l t y s e p a r a t i n g t h e d e s i r e d p r o d u c t from t h e r e a c t i o n m i x t u r e on a commercial s c a l e . We have c h o s e n t o u s e h y d r o x y v i n y l e t h e r s (CH2-CH-0-R-0H) as intermediates i n the synthesis of vinyl ether functionalized oligomers. Hydroxy v i n y l e t h e r s a r e e a s i l y o b t a i n e d a s b y - p r o d u c t s o f t h e s y n t h e s i s o f d i v i n y l e t h e r monomers ( E q u a t i o n 1 ) . The h y d r o x y group may be r e a c t e d t o form a l i n k t o t h e o l i g o m e r backbone w h i l e t h e v i n y l e t h e r m o i e t y remains f r e e t o be p o l y m e r i z e d i n a r a d i a t i o n i n d u c e d r e a c t i o n a t a l a t e r time. T h i s p a p e r w i l l f o c u s on v i n y l e t h e r t e r m i n a t e d u r e t h a n e (VEU) oligomers(20,21). VEU o l i g o m e r s may be p r e p a r e d b y r e a c t i n g h y d r o x y


366


v i n y l e t h e r s w i t h compounds c o n t a i n i n g i s o c y a n a t e groups ( E q u a t i o n 3) . The a l c o h o l group o f the h y d r o x y v i n y l ether reacts with the i s o c y a n a t e t o form the d e s i r e d u r e t h a n e l i n k a g e .


R'-NCO

+

H0-R-0-CH-CH

2

>

R'-NH-e-0-R-0-CH-CH

2

(3)

One i n t e r e s t i n g f e a t u r e o f the p r o d u c t i o n o f VEU o l i g o m e r s i s the way t h a t i t may be t i e d t o the i n i t i a l s y n t h e s i s o f the h y d r o x y v i n y l e t h e r . The r e a c t i o n o f a c e t y l e n e w i t h the d i o l p r o d u c e s a m i x t u r e o f the d i v i n y l e t h e r , the h y d r o x y v i n y l e t h e r and the u n r e a c t e d diol (Equation 1). C a r e f u l f r a c t i o n a l d i s t i l l a t i o n can separate the h y d r o x y v i n y l e t h e r f o r use i n VEU o l i g o m e r s ; however, i t may a c t u a l l y be d e s i r a b l e t o use the m i x t u r e o f t h e s e p r o d u c t s , i n c o r p o r a t i n g the d i o l and the d i v i n y l e t h e r i n t o the 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 (Scheme I ) . The d i o l s e r v e s t o c h a i n e x t e n d the r e s i n . Each h y d r o x y l group on the d i o l r e a c t s w i t h a n i s o c y a n a t e group f o r m i n g a h i g h e r m o l e c u l a r w e i g h t m a t e r i a l . The t o t a l c o n c e n t r a t i o n o f h y d r o x y groups from the d i o l and the h y d r o x y v i n y l e t h e r c a n be d e t e r m i n e d and t h e n combined w i t h an e q u i v a l e n t c o n c e n t r a t i o n o f i s o c y a n a t e . The d i v i n y l e t h e r does n o t have f r e e h y d r o x y groups, t h e r e f o r e i t w i l l n o t r e a c t w i t h the d i i s o c y a n a t e . The d i v i n y l e t h e r s e r v e s as a d i l u e n t w h i c h l o w e r s the v i s c o s i t y o f the m i x t u r e d u r i n g the o l i g o m e r s y n t h e s i s . When the m i x t u r e i s f i n a l l y c u r e d , the d i v i n y l e t h e r copolymerizes w i t h the VEU o l i g o m e r , e f f e c t i v e l y i n c r e a s i n g the c r o s s l i n k d e n s i t y o f the f i l m . Experimental S y n t h e s i s o f T r i e t h y l e n e G l y c o l M o n o v i n v l E t h e r (TEGMVE) . T r i e t h y l e n e g l y c o l (250 mL) and ground KOH ((7.5 g) were added t o a 500 mL, 3-neck r o u n d bottom f l a s k e q u i p p e d w i t h a mechanical s t i r r e r , reflux c o n d e n s e r and gas i n l e t tube. The a p p a r a t u s was p l a c e d b e h i n d a p r o t e c t i v e s h i e l d i n a fume hood. The o u t l e t from the c o n d e n s e r was v e n t e d t o the upper a r e a o f t h e hood. The m i x t u r e was h e a t e d t o 190 ± 10°C w h i l e p u r g i n g w i t h n i t r o g e n . A f t e r the t e m p e r a t u r e was s t a b i l i z e d , a c e t y l e n e f l o w was begun ( 1.0 liter/min). The r e a c t i o n was c o n t i n u e d f o r 5 h o u r s . The f l a s k was f i t t e d w i t h a d i s t i l l a t i o n head. The p r o d u c t (125 mL) was c o l l e c t e d w i t h a b o i l i n g range o f 70 t o 84°C a t 0.3 t o r r . Gas c h r o m a t o g r a p h i c a n a l y s i s i n d i c a t e d t h a t the p r o d u c t s were a m i x t u r e o f t r i e t h y l e n e g l y c o l d i v i n y l e t h e r ( 1 4 % ) , t r i e t h y l e n e g l y c o l m o n o v i n y l e t h e r ( 7 8 % ) , and u n r e a c t e d t r i e t h y l e n e g l y c o l ( 7 % ) . R e d i s t i l l a t i o n t h r o u g h a 12 i n c h V i g r e a u x column gave an 85 mL f r a c t i o n t h a t c o n t a i n e d 95% TEGMVE. S y n t h e s i s o f VEU O l i g o m e r s . A number o f d i f f e r e n t VEU o l i g o m e r s was s y n t h e s i z e d . The f o l l o w i n g i s a t y p i c a l p r o c e d u r e : d i p h e n y l m e t h y l e n e d i i s o c y a n a t e (25.58 g, 0.102 moles) was d i s s o l v e d i n 100 mL o f d r y methylene c h l o r i d e i n a 250 mL round b o t t o m f l a s k e q u i p p e d w i t h a r e f l u x c o n d e n s e r and a m a g n e t i c s t i r b a r under a n i t r o g e n atmosphere. TEGMVE (36.02 g, 0.204 mois) was added t o the s o l u t i o n a l o n g w i t h 2 drops o f d i b u t y l t i n d i l a u r a t e . The m i x t u r e began t o r e f l u x w i t h i n 2 to 3 minutes without e x t e r n a l h e a t i n g . A f t e r r e a c t i n g f o r a b o u t 30



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Products

Curing of Vmyl-Ether-Functionalized Urethane Oligomers

( 1 HO-R-OHI 1

jggy^U Reaction Curable Mixture

[

1

HO-R-Q-CH=CH^n

+ OCN-R-NCO

•

/ ^. . . . ^y CH2=CH > R Q CH CH Ο

o

ο

ο

Γ( C H 2 = C H - Q - R - 0 ) - C - N H - R - N H - C - | 0 - R - 0 | - C - t l H - R - N H - C - ( 0 - R - Q - C H = C H 2 ) L + other oligomers V C H 2 = C H - 0 - R - 0 - C H = C H 2 / Scheme I


367

368


m i n u t e s the m i x t u r e began t o c o o l . A t r e g u l a r i n t e r v a l s a few d r o p s o f the r e a c t i o n m i x t u r e were removed f o r i n f r a r e d a n a l y s i s . A f t e r 5 h o u r s , the -NCO band a t 2250 cm" was no l o n g e r d e t e c t a b l e . The s o l v e n t was removed i n a vacuum and the r e s u l t i n g t h i c k l i q u i d p r o d u c t was a n a l y z e d by 1H and 13C NMR. The s p e c t r a were c o n s i s t e n t w i t h the expected product, I. Many VEU o l i g o m e r s were s y n t h e s i z e d u s i n g t r i e t h y l e n e g l y c o l d i v i n y l e t h e r (TEGDVE) as a r e a c t i o n s o l v e n t i n p l a c e o f methylene chloride. The TEGDVE was n o t s e p a r a t e d from the p r o d u c t s . It remained as p a r t o f the p o l y m e r i z a b l e m i x t u r e .


1

Radiation Curing. Samples t o be i r r a d i a t e d were c o a t e d onto e i t h e r Bonderite-40 treated steel test panels (Parker Chemical) or p o l y e t h y l e n e c o a t e d paper b o a r d . An e x c e s s o f the sample was p l a c e d a t one end o f the s u b s t r a t e and a #6 w i r e wound r o d was drawn a c r o s s the s u b s t r a t e w i t h even p r e s s u r e p u s h i n g e x c e s s m a t e r i a l o f f the edge. T h i s method p r o d u c e d c o a t i n g s w i t h a t h i c k n e s s o f 6 t o 12 urn. An RPC model QC-1202 p r o c e s s o r was u s e d f o r UV c u r i n g . The u n i t was e q u i p p e d w i t h two 12 i n c h medium p r e s s u r e mercury a r c lamps and a v a r i a b l e speed conveyor (50 t o 500 f t / m i n ) . O n l y one lamp was u s e d a t a time i n the t e s t i n g ( o p e r a t e d a t 200 w a t t s / i n ) . The UV e n e r g y dosage was measured by p a s s i n g a UV P r o c e s s S u p p l y Compact Radiometer under the lamp on the conveyor b e l t . An Energy S c i e n c e s E l e c t r o c u r t a i n model CB-150 e q u i p p e d w i t h a 15 cm l i n e a r cathode was u s e d f o r EB c u r i n g . E l e c t r o n e n e r g i e s o f 160 KeV were employed. Samples were p l a c e d i n a an aluminum t r a y on a v a r i a b l e speed conveyor (20- 235 f t / m i n ) w i t h i n the CB-150 u n i t . I r r a d i a t i o n o c c u r r e d i n a n i t r o g e n atmosphere. C o a t i n g E v a l u a t i o n The c o a t i n g s were e v a l u a t e d w i t h i n one h o u r a f t e r i r r a d i a t i o n . The c o a t i n g s were examined f o r s o l v e n t r e s i s t a n c e u s i n g methyl e t h y l ketone. The number o f d o u b l e rubs n e c e s s a r y t o b r e a k t h r o u g h the c o a t i n g was r e c o r d e d . R e v e r s e impact was measured on the s t e e l p a n e l s u s i n g a Gardner impact t e s t e r a c c o r d i n g t o ASTM Method D2794. The c o a t i n g e l o n g a t i o n was measured by b e n d i n g the c o a t e d s t e e l p a n e l o v e r a c o n i c a l mandrel a c c o r d i n g t o ASTM Method D522. P e n c i l h a r d n e s s was measured a c c o r d i n g t o ASTM D3363. R e s u l t s and

Discussion

A number o f d i f f e r e n t VEU o l i g o m e r s may be s y n t h e s i z e d from a v a r i e t y o f h y d r o x y v i n y l e t h e r s and i s o c y a n a t e monomers o r p r e p o l y m e r s . T h i s p a p e r w i l l f o c u s on o l i g o m e r s s y n t h e s i z e d from t r i e t h y l e n e g l y c o l monovinyl ether (TEGMVE) and diphenylmethane d i i s o c y a n a t e (MDI). I n i t i a l l y , the UV and EB c u r i n g p a r a m e t e r s were d e t e r m i n e d u s i n g the s i m p l e 2:1 a d d u c t o f TEGMVE and MDI (I). The r e s u l t s were f a i r l y r e p r e s e n t a t i v e o f o t h e r VEU o l i g o m e r s .

2

CH -CH-0- ( C H C H 0 ) - ë - N H - ( O y C H - ( Q y N H - C - 0 - ( C H C H 0 ) - C H - C H 2

2

2

3

2

2

2

3

I


2

26.

369

Curing of Vinyl-Ether-FuncthnatizedUrethaw

LAPIN

The o l i g o m e r , I , was combined w i t h a t r i a r y l s u l f o n i u m s a l t o f h e x a f l u o r o p h o s p h a t e ( G e n e r a l E l e c t r i c UVE-1016), and t h e n was c o a t e d onto t h e s u b s t r a t e . The c u r i n g p r o p e r t i e s were s t u d i e d u s i n g UV and e l e c t r o n beam i r r a d i a t i o n c o n d i t i o n s . T a b l e 1 shows some o f t h e p h y s i c a l p r o p e r t i e s o f t h e c o a t i n g as a f u n c t i o n o f t h e exposure t o t h e UV lamp. A t a c k - f r e e c o a t i n g was o b t a i n e d i m m e d i a t e l y upon i r r a d i a t i o n a t a energy dosages g r e a t e r t h a n 38 mj/cm . The c o a t i n g was u n a f f e c t e d by 100 d o u b l e r u b s w i t h m e t h y l e t h y l k e t o n e (MEK) a f t e r b e i n g exposed a t 60 mj/cm . Coatings c u r e d a t g r e a t e r t h a n 100 mj/cm h a d a n o t i c e a b l e y e l l o w d i s c o l o r a t i o n i m m e d i a t e l y a f t e r i r r a d i a t i o n , and t u r n e d a g r e e n i s h c o l o r upon s t a n d i n g f o r 24 h r s . No a d d i t i o n a l changes i n t h e c o a t i n g p r o p e r t i e s were o b s e r v e d a t h i g h e r UV exposure l e v e l s . 2

2


2

T a b l e 1.

UV C u r i n g

Energy Dose (mj/cm )

o f VEU O l i g o m e r I * R e v e r s e Impact (in-lbs)

MEK Rubs

P e n c i l Hardness

2

38 44 60 89 179 346 *

2 pph UVE-1016, n i t r o g e n

(%) >50 >50 >50 >50 >50 >50

>160 >160 >160 >160 >160 >160

60 80 100 >100 >100 >100

3B HB F 2H 2H 2H

Elongation

atmosphere

T a b l e 2 shows t h e r e s u l t s o f c u r i n g t h e same VEU o l i g o m e r ( I ) , by e l e c t r o n beam i r r a d i a t i o n . No c u r i n g was o b s e r v e d i n t h e absence o f t h e onium s a l t . I n t h e p r e s e n c e o f onium s a l t ( 2 % ) , an e n e r g y dosage o f 0.7 Mrads was r e q u i r e d t o produce a t a c k - f r e e c o a t i n g . A dosage o f 4 Mrads p r o d u c e d a c o a t i n g w h i c h was u n a f f e c t e d b y 100 MEK rubs. The c o a t i n g became n o t i c e a b l y d i s c o l o r e d a t dosages g r e a t e r t h a n 6 Mrads. These EB c u r e speeds were n o t p a r t i c u l a r l y fast compared t o t y p i c a l a c r y l a t e b a s e d c o a t i n g s . However, we have shown p r e v i o u s l y t h a t much h i g h e r EB c u r e speeds may be o b t a i n e d b y u s i n g an iodonium s a l t i n p l a c e o f a s u l f o n i u m s a l t c a t a l y s t . 8

T a b l e 2. EB Dose (Mrads) 0.5 1.0 2.0 4.0 6.0 12.0 a. b.

E l e c t r o n Beam C u r i n g P e n c i l Hardness

NC? 6B 2H 3H 3H 3H

o f VEU I

MEK Rubs

a

R e v e r s e Impact (in-lbs)

Elongation (%)

— >160 >160 >160 >160 >160

>50 >50 >50 >50 >50

~ 4 80 >100 >100 >100

2 pph UVE-1016, n i t r o g e n atmosphere. C o a t i n g remained t a c k y a f t e r i r r a d i a t i o n .



370


The p r o p e r t i e s o f the c o a t i n g s shown i n T a b l e s 1 and 2 f o r UV and EB c u r i n g appear t o be v e r y s i m i l a r . T h i s suggests t h a t s i m i l a r polymer networks were c r e a t e d by the two i r r a d i a t i o n methods. As e x p e c t e d , the c o a t i n g o b t a i n e d by c u r i n g t h i s d i f u n c t i o n a l u r e t h a n e o l i g o m e r was h i g h l y f l e x i b l e . The c o a t i n g s c o u l d n o t be r u p t u r e d by b e n d i n g on a c o n i c a l mandrel o r by r e v e r s e impact up t o 160 i n - l b s . These f l e x u r a l p r o p e r t i e s were a t t r a c t i v e f o r a c o a t i n g t h a t a l s o gave p e n c i l h a r d n e s s v a l u e s o f 2H t o 3H. A s t u d y was done t o d e t e r m i n e the e f f e c t o f the s u l f o n i u m s a l t c o n c e n t r a t i o n on the c u r e speed o f the VEU o l i g o m e r ( I ) . A s e r i e s o f m i x t u r e s was p r e p a r e d c o n t a i n i n g from 0.2% t o 7.7% o f UVE-1016. The e n e r g y dosages f o r b o t h UV and e l e c t r o n beam i r r a d i a t i o n were c o n t r o l l e d by v a r y i n g the sample c o n v e y o r speeds. The minimum e n e r g y dose w h i c h would produce a t a c k - f r e e c o a t i n g was r e c o r d e d . Figure 1 shows the r e s u l t s f o r UV i n d u c e d c u r i n g . The f a s t e s t c u r e speed o c c u r r e d when the c a t a l y s t was p r e s e n t a t a c o n c e n t r a t i o n o f about 1% to 3%. The c u r e speed began t o f a l l v e r y r a p i d l y a t c o n c e n t r a t i o n s below 0.5%. A l o s s o f c u r e speed a l s o o c c u r r e d a t h i g h e r c a t a l y s t concentrations. T h i s was l i k e l y due t o h i g h a b s o r p t i o n o f l i g h t a t the s u r f a c e o f the c o a t i n g by the s u l f onium s a l t . T h i s a l l o w e d l i t t l e l i g h t t o p e n e t r a t e f o r c u r i n g u n d e r n e a t h the s u r f a c e . VEU o l i g o m e r s d e r i v e d from a r o m a t i c i s o c y a n a t e s w i l l absorb l i g h t i n c o m p e t i t i o n with the onium s a l t s . T h i s i s an important consideration i n d e t e r m i n i n g the optimum c a t a l y s t c o n c e n t r a t i o n . F i g u r e 2 shows the e l e c t r o n beam c u r e speed o f the o l i g o m e r ( I ) as a f u n c t i o n o f the s u l f onium s a l t c o n c e n t r a t i o n . A g a i n the c u r e speed began t o drop r a p i d l y a t c o n c e n t r a t i o n s below 0.5%. No s i g n i f i c a n t g a i n i n c u r e speed was a c h i e v e d by i n c r e a s i n g the c a t a l y s t c o n c e n t r a t i o n above about 3%. The e l e c t r o n beam e a s i l y p e n e t r a t e s the e n t i r e c o a t i n g and i s n o t s e l e c t i v e l y a b s o r b e d by the o l i g o m e r o r t h e catalyst, t h e r e f o r e e l e c t r o n beam c u r e d c o a t i n g s a r e much l e s s s e n s i t i v e t o c a t a l y s t c o n c e n t r a t i o n e f f e c t s t h a n UV c u r e d c o a t i n g s . P r o p e r t i e s such as t a c k and MEK rub r e s i s t a n c e c a n g i v e some i n d i c a t i o n o f the degree o f c u r i n g o f a c o a t i n g . I t i s often d e s i r a b l e however, t o use s p e c t r o p s c o p i c methods i n o r d e r t o make a more q u a n t i t a t i v e d e t e r m i n a t i o n . F r e e f i l m s o f the r a d i a t i o n c u r e d o l i g o m e r were a n a l y z e d by i n f r a r e d t r a n s m i t t a n c e . The s p e c t r a were compared t o the u n r e a c t e d s t a r t i n g m a t e r i a l , I , ( F i g u r e 3 ) . The v i n y l e t h e r has C-C a b s o r p t i o n bands a t 1635 and 1616 c m ( 8 ) . While the 1616 cm" band o v e r l a p s w i t h bands a r i s i n g the from the a r o m a t i c r i n g s t r u c t u r e , the 1635 cm" band o c c u r s i n an u n o b s t r u c t e d r e g i o n o f the spectrum. A f t e r UV i r r a d i a t i o n a t 100 mj/cm o r e l e c t r o n beam i r r a d i a t i o n a t 4 Mrads, the v i n y l e t h e r band a t 1635 cm" was no l o n g e r d e t e c t a b l e ( F i g u r e 3 ) . These r e s u l t s i n d i c a t e t h a t r a d i a t i o n c u r i n g l e a d s t o a h i g h c o n v e r s i o n o f the s t a r t i n g m a t e r i a l s . The r e s u l t s do n o t n e c e s s a r i l y i n d i c a t e t h a t a l l o f the v i n y l e t h e r groups have polymerized. O t h e r r e a c t i o n s such as h y d r o l y s i s o r c h a i n t e r m i n a t i o n may o c c u r . _1

1

1

2

1

A mixture o f the p r o d u c t s resulting from the r e a c t i o n o f a c e t y l e n e w i t h a d i o l may be u s e d t o s y n t h e s i z e a v i n y l ether terminated oligomer (Scheme I ) . A VEU o l i g o m e r was p r e p a r e d t o i l l u s t r a t e t h i s process. The c o n c e n t r a t i o n s o f the r e a g e n t s were a d j u s t e d so t h a t e q u i v a l e n t amounts o f h y d r o x y and i s o c y a n a t e groups were r e a c t e d . Thus a m i x t u r e c o n t a i n i n g t r i e t h y l e n e g l y c o l d i v i n y l




LAPIN

F i g u r e 1. on t h e UV

The e f f e c t o f s u l f o n i u m s a l t c o n c e n t r a t i o n c u r e speed o f oligomer I .


371


372


h

10

0

I

Ο

1 2

1 4

1 6

UVE-1016 Concentration

Ι 8 (%)

F i g u r e 2. The e f f e c t o f s u l f o n i u m s a l t on t h e EB c u r e s p e e d o f o l i g o m e r I .

concentration


Curing of Vinyl-Ether-Functionalized Urethane Oligomers 373


LAPIN

" 1690

1658

1626

1594

1562

Wavenumber

F i g u r e 3. Infrared a n a l y s i s of the r a d i a t i o n curing of oligomer I.

induced


374


e t h e r (40.0 g, 0.2 m o l ) , t r i e t h y l e n e g l y c o l m o n o v i n y l e t h e r ( 1 4 . l g , 0.08 m o l ) , and t r i e t h y l e n e g l y c o l (6.0 g, 0.04 mol) was r e a c t e d w i t h diphenylmethane d i i s o c y a n a t e (20.0 g, 0.08 m o l ) . The r e s u l t i n g VEU o l i g o m e r ( I I ) was a c l e a r t h i c k l i q u i d . GPC a n a l y s i s showed a m i x t u r e o f p r o d u c t s w i t h a range o f m o l e c u l a r w e i g h t s (Mn - 462, Mw - 1,464, i n c l u d i n g a c o n t r i b u t i o n from the d i v i n y l e t h e r monomer, 202 g/mol). The o l i g o m e r ( I I ) was combined w i t h a s u l f onium s a l t c a t a l y s t and c u r e d by UV and e l e c t r o n beam i r r a d i a t i o n . The r e s u l t s a r e shown i n T a b l e 3.


T a b l e 3.

R a d i a t i o n C u r i n g o f VEU

Min. Energy Dose f o r T a c k - F r e e Cure

UV EB a. b. c.

100

Mrads

Pencil Hardness

b

>100

Oligomer

3H c

b

3H

II

a

Reverse Impact (in-lbs)

>160 C

Elongation (%)

b

>160

>50 c

b

>50

c

2 pph UVE-1016, n i t r o g e n atmosphere A f t e r UV c u r i n g a t 75 mj/cm A f t e r EB c u r i n g a t 4.0 Mrads 2

The o l i g o m e r I I was c h a i n extended w i t h t r i e t h y l e n e g l y c o l groups w h i c h would t e n d t o produce s o f t e r c o a t i n g s w i t h a lower c r o s s l i n k density. However, the m i x t u r e a l s o c o n t a i n e d 50% o f the TEGDVE monomer w h i c h was i n c o r p o r a t e d d u r i n g the o l i g o m e r s y n t h e s i s . When the m i x t u r e was i r r a d i a t e d the d i v i n y l e t h e r monomer c o p o l y m e r i z e d w i t h o l i g o m e r i c components i n c r e a s i n g the c r o s s l i n k d e n s i t y o f t h e cured f i l m . The n e t r e s u l t s were t h a t the c o a t i n g s had s i m i l a r p r o p e r t i e s t o the c o a t i n g p r o d u c e d from the monodisperse o l i g o m e r I . One i m p o r t a n t d i f f e r e n c e between o l i g o m e r s I and I I was t h a t I gave c o a t i n g s w h i c h were h i g h l y d i s c o l o r e d w h i l e I I p r o d u c e d c o a t i n g s t h a t were n e a r l y c o l o r l e s s . T h i s o b s e r v a t i o n was l i k e l y due t o the f a c t t h a t o l i g o m e r I c o n t a i n e d a much h i g h e r c o n c e n t r a t i o n o f a r o m a t i c u r e t h a n e groups r e l a t i v e t o o l i g o m e r I I . These groups appear t o be a t l e a s t p a r t i a l l y r e s p o n s i b l e f o r c o l o r a t i o n problems. M u l t i f u n c t i o n a l VEUs were p r e p a r e d by i n c o r o r a t i n g t r i m e t h y l o l propane (TMP) i n t o the o l i g o m e r c o m p o s i t i o n s . The o l i g o m e r ( I I I ) was t h e p r o d u c t o f the r e a c t i o n o f TEGMVE and MDI w i t h t r i m e t h y l o l propane (TMP) i n a 3:3:1 mole r a t i o . The p r o d u c t was p r e p a r e d u s i n g methylene c h l o r i d e as a s o l v e n t w h i c h was l a t e r removed a t r e d u c e d p r e s s u r e . I t was a l s o p r e p a r e d u s i n g TEGDVE as a s o l v e n t w h i c h remained i n the m i x t u r e as a r e a c t i v e d i l u e n t . I n the absence o f s o l v e n t the p r o d u c t was a c o l o r l e s s , low m e l t i n g , amorphous s o l i d . The s i m p l e s t s t r u c t u r e t h a t would r e s u l t from a c o m b i n a t i o n o f TEGMVE, MDI and TMP i s shown below. GPC a n a l y s i s i n d i c a t e d t h a t the p r o d u c t ( I I I ) was a c t u a l l y a

CH CH C- [CH -0-C-NH-(( 3

2

2

j)-CH -(( 2

))-NH-C-0-(CH CH 0) -CH-CH ] 2

2

3

III


2

3

26*. LAPIN

Curing of Vinyl-Ether-Functwnalized Urethane Oligomers

mixture o f s e v e r a l d i f f e r e n t oligomers ( F i g u r e 4 ) . The m o l e c u l a r w e i g h t d i s t r i b u t i o n and t h e v i s c o s i t y were c o n t r o l l e d b y a d j u s t i n g the s t o i c h i o m e t r y o f t h e r e a c t a n t s d u r i n g t h e s y n t h e s i s o f t h e o l i g o m e r ( T a b l e 4 ) . A 1:1 mole r a t i o o f h y d r o x y groups t o i s o c y a n a t e groups was m a i n t a i n e d i n t h e t h r e e examples shown i n T a b l e 4. As expected, the v i s c o s i t y and m o l e c u l a r weights o f the products i n c r e a s e d as t h e p r o p o r t i o n o f TMP i n t h e m i x t u r e was i n c r e a s e d . Table

4.

E f f e c t o f Reagent S t o i c h i o m e t r y


Mole R a t i o TEGMVE: MDI: TMP

on VEU O l i g o m e r I I I Molecular Mn

Viscosity* (cps)

3 : 3 : 1 3.5 : 4 : 1.5 4 : 5 : 2

1,273 1,472 1,577

1,130 3,140 8,380

Weight* Mw 3,888 4,861 8,160

* I n c l u d i n g c o n t r i b u t i o n from 50% added TEGDVE monomer (202

g/mol).

The v i s c o s i t y o f t h e o l i g o m e r ( I I I ) was a l s o a d j u s t e d b y v a r y i n g the p r o p o r t i o n o f TEGDVE i n t h e m i x t u r e ( F i g u r e 5 ) . TEGDVE i s a n e f f e c t i v e r e a c t i v e d i l u e n t f o r the oligomer (III). Viscosities s p a n n i n g more t h a n t h r e e o r d e r s o f magnitude were o b t a i n e d b y v a r y i n g the p r o p o r t i o n o f TEGDVE from 20% t o 80%. The m i x t u r e s o f t h e VEU o l i g o m e r I I I and TEGDVE were combined w i t h a t r i a r y l s u l f o n i u m s a l t (UVE-1016, 2 pph) and c o a t e d onto t h e s u b s t r a t e . The p r o p e r t i e s o f the c u r e d c o a t i n g s a r e shown i n T a b l e 5. Table

5.

TEGDVE (%)

R a d i a t i o n C u r i n g o f VEU O l i g o m e r Min Tack- F r e e Dose UV EB (mj/cm ) (Mrads) 2

20 40 50 70 80 100 a. b.

50 >50 30 6

2 pph UVE-1016, n i t r o g e n atmosphere. A f t e r UV c u r i n g a t 75 mj/cm 2

As t h e p r o p o r t i o n o f TEGDVE i n t h e f o r m u l a t i o n was i n c r e a s e d above 50% a d e c r e a s e i n t h e r e v e r s e impact and e l o n g a t i o n p r o p e r t i e s were o b s e r v e d . T h i s was e x p e c t e d due t o t h e i n c r e a s e i n c r o s s l i n k d e n s i t y o f the cured f i l m . A l l o f t h e m i x t u r e s gave c o a t i n g s w h i c h showed good a d h e s i o n t o u n t r e a t e d p o l y e t h y l e n e s u b s t r a t e . Adhesion t o t h e t r e a t e d s t e e l p a n e l s was r e l a t i v e l y p o o r , b u t showed some improvement a t h i g h e r monomer c o n c e n t r a t i o n s . C o a t i n g s p r o d u c e d from m i x t u r e s c o n t a i n i n g a t l e a s t 50% TEGDVE monomer showed v e r y l i t t l e discoloration. O v e r a l l , t h e c o m b i n a t i o n o f t h e m u l t i f u n c t i o n a l VEU


375


376


4 «

F i g u r e 4.

Increasing Molecular

Weight

GPC chromatogram o f o l i g o m e r m i x t u r e I I I .


CuringofVinyl-Ether-FunctwnalwedU


26. LAPIN


377


378


o l i g o m e r I I I and TEGDVE gave a d e s i r a b l e s e t o f p h y s i c a l p r o p e r t i e s (Table 5). These p r o p e r t i e s compared v e r y f a v o r a b l y w i t h c o a t i n g s p r o d u c e d by t y p i c a l a c r y l a t e d u r e t h a n e f o r m u l a t i o n s ( 2 2 ) . C a t i o n i c p o l y m e r i z a t i o n r e a c t i o n s a r e n o t i n h i b i t e d by oxygen. T h i s r e s u l t s i n an enhancement o f the c u r e speeds o f v i n y l e t h e r s compared t o a c r y l a t e b a s e d m a t e r i a l s . A m i x t u r e o f the VEU oligomer I I I and TEGDVE (50%) was c u r e d s i d e - b y - s i d e w i t h some t y p i c a l a c r y l a t e f o r m u l a t i o n s . The samples were exposed t o UV i r r a d i a t i o n i n a d r y a i r atmosphere. The maximum c o n v e y o r speed t h a t would p r o d u c e a t a c k f r e e c o a t i n g was r e c o r d e d . The r e s u l t s a r e shown i n F i g u r e 6. There was a d r a m a t i c d i f f e r e n c e between the v i n y l e t h e r and a c r y l a t e b a s e d formulations. The v i n y l e t h e r r e a c h e d a t a c k - f r e e s t a t e a t the maximum c o n v e y o r speed (500 f t / m i n . , 40 mj/cm2) i n the p r e s e n c e o f less than 1% added p h o t o i n i t i a t o r . When the a c r y l a t e based f o r m u l a t i o n s were c u r e d a t h i g h speeds t h e y t y p i c a l l y formed a f i r m c o a t i n g , b u t showed i n c o m p l e t e c u r i n g a t the s u r f a c e . T h i s was due to oxygen i n h i b i t i o n o f the f r e e r a d i c a l p o l y m e r i z a t i o n r e a c t i o n . When the c o a t i n g s were compared i n a n i t r o g e n atmosphere t h e r e were v e r y few o b s e r v a b l e d i f f e r e n c e s between the v i n y l e t h e r and a c r y l a t e based coatings. A l l o f the f o r m u l a t i o n s c o n t a i n i n g a t l e a s t 1% p h o t o i n i t i a t o r , gave t a c k - f r e e c o a t i n g s a t 500 f t / m i n (40 mj/cm2) i n a n i t r o g e n atmosphere. Oxygen i n h i b i t i o n o f the s u r f a c e c u r e i n the a c r y l a t e b a s e d c o a t i n g s was r e d u c e d s l i g h t l y by i n c r e a s i n g the photoinitiator concentration. Benzophenone/amine i n i t i a t e d a c r y l a t e systems a r e known t o show r e d u c e d oxygen i n h i b i t i o n ( 2 3 ) . This i s c l e a r l y s e e n i n F i g u r e 6 a t i n i t i a t o r c o n c e n t r a t i o n s o f 2 t o 3%. The c u r e speed o b t a i n e d i n the benzophenone/amine i n i t i a t e d s y s t e m was improved; however, i t s t i l l does n o t a p p r o a c h the c u r e speed o b t a i n e d w i t h the v i n y l e t h e r b a s e d c o a t i n g . A l t h o u g h oxygen does n o t appear t o a f f e c t UV i n d u c e d c a t i o n i c p o l y m e r i z a t i o n , i t does have an a f f e c t on e l e c t r o n beam induced c a t i o n i c c u r i n g . We have p r e v i o u s l y s u g g e s t e d t h a t t h e mechanism f o r the a c t i v a t i o n o f the onium s a l t s i s d i f f e r e n t f o r UV and EB irradiation. The EB r e a c t i o n mechanism i n v o l v e s an intermediate r a d i c a l s p e c i e s w h i c h may be quenched by o x y g e n ( 8 ) . The EB c u r i n g o f the VEU o l i g o m e r I I I ( c o n t a i n i n g 50% TEGDVE monomer and 2 pph UVE1016 s u l f o n i u m s a l t ) was compared i n a d r y n i t r o g e n and a d r y a i r atmosphere. A t a c k - f r e e c o a t i n g was o b t a i n e d a t 0.7 Mrads i n n i t r o g e n w h i l e a 1.8 Mrad dose was r e q u i r e d i n d r y a i r . W h i l e t h i s r e p r e s e n t s a s u b s t a n t i a l decrease i n cure speed i t i s s t i l l well within a c c e p t a b l e l i m i t s o f most commercial c u r i n g o p e r a t i o n s . I t i s w e l l known t h a t c a t i o n i c p o l y m e r i z a t i o n may be i n h i b i t e d by n u c l e o p h i l i c s p e c i e s i n the r e a c t i o n m i x t u r e ; however, v i n y l e t h e r s appear t o be l e s s s e n s i t i v e t h a n e p o x i e s t o p r e s e n c e o f n u c l e o p h i l e s . The h i g h r e a c t i v i t y o f the v i n y l e t h e r group w i t h the growing c a t i o n i c c h a i n i s o f t e n f a v o r e d o v e r t e r m i n a t i o n by a n u c l e o p h i l i c s p e c i e s . Water may a c t as a n u c l e o p h i l e and i t has b e e n r e p o r t e d t h a t h i g h atmospheric humidity conditions w i l l i n h i b i t the p h o t o c u r i n g of epoxies(24). We have o b s e r v e d a s i m i l a r e f f e c t on v i n y l e t h e r b a s e d coatings. T a b l e 6 shows the c u r e speed f o r the VEU o l i g o m e r I I I ( w i t h 50% TEGDVE) a t v a r i o u s h u m i d i t y l e v e l s . No d i f f e r e n c e s were o b s e r v e d i n the c u r e d f i l m s a f t e r i r r a d i a t i o n i n d r y n i t r o g e n o r i n a i r a t up t o 34% r e l a t i v e h u m i d i t y . A t 61% r e l a t i v e h u m i d i t y the c u r e speed was



LAPIN

Curing of Vmyl-Ether-Functionalized Urethane Oligomers

Initiator C o n c e n t r a t i o n

(pph)

F i g u r e 6. Maximum t a c k - f r e e c u r e s p e e d s . S a m p l e s UV c u r e d (one 200 w a t t / i n lamp) i n d r y a i r . A = 50% o l i g o m e r I I I , 50% TEGDVE, UVE-1016 # = 50% CMD 6700, 50% EO-TMPTA, I r g a c u r e 184 • = 50% C e l r a d 3700, 50% EO-TMPTA, I r g a c u r e 184 · = 50% 3700, 50% EO-TMPTA, 2 p p h MDEA, b e n z o p h e n o n e


379

380


reduced t o l e s s than h a l f o f i t s o r i g i n a l v a l u e . A t 78% r e l a t i v e h u m i d i t y no c u r i n g appeared t o o c c u r even a t t h e l o w e s t c o n v e y o r s e t t i n g (50 f t / m i n . , 350 mj/cm2). A l t h o u g h t h e c u r i n g was a f f e c t e d by a t m o s p h e r i c h u m i d i t y , t h e f o r m u l a t i o n i t s e l f d i d n o t appear t o be p a r t i c u l a r l y s e n s i t i v e t o t h e a d d i t i o n o f water. The VEU f o r m u l a t i o n u s e d i n T a b l e 6 was s p i k e d w i t h water ( 5 % ) . T h i s m i x t u r e was e a s i l y c u r e d a t 500 f t / m i n (36 mj/cm2) i n a n i t r o g e n atmosphere t o produce a c o a t i n g w h i c h r e s i s t e d g r e a t e r t h a n 100 d o u b l e r u b s w i t h MEK. T a b l e 6. The E f f e c t o f A t m o s p h e r i c H u m i d i t y on t h e UV Cure Speed o f VEU O l i g o m e r I I I a


Relative

Humidity

(%) 0 (dry N ) 0 (dry a i r ) 19 34 61 69 78 2

Max.

Tack-Free (ft/min) >500 >500 >500 >500 200 150 < 50

Speed

MEK

Rubs

b

>100 >100 >100 >100 >100 >100

a. 50% TEGDVE, 2% UVE-1016, p o l y e t h y l e n e s u b s t r a t e , one "00 w / i n lamp. b. A f t e r c u r i n g a t 100 f t / m i n .

I t h a s been shown t h a t t h e e f f e c t o f h u m i d i t y on c a t i o n i c c u r i n g c a n be overcome b y moderate i n c r e a s e s i n t h e t e m p e r a t u r e o f t h e s u b s t r a t e (45°C). T h i s i n c r e a s e i n temperature i s o f t e n a c h i e v e d under commercial UV c u r i n g c o n d i t i o n s due t o t h e h e a t o u t p u t o f t h e lamps. T h i s would t e n d t o o b s c u r e t h e e f f e c t s o f h i g h h u m i d i t y ( 2 5 ) . Conclusions The c o m b i n a t i o n o f v i n y l e t h e r monomers and VEU o l i g o m e r s a l o n g w i t h onium s a l t c a t a l y s t s p r o v i d e s a v e r s a t i l e new r a d i a t i o n c u r a b l e c o a t i n g s system. The c o a t i n g s may be c u r e d a t h i g h speeds u s i n g e i t h e r UV o r EB i r r a d i a t i o n . The UV c u r i n g i s n o t i n h i b i t e d b y oxygen a l t h o u g h i t c a n be a f f e c t e d b y h i g h a t m o s p h e r i c h u m i d i t y . Literature 1. 2.

3. 4.

Cited

Leaf, D. Α., Environmental Protection Agency, Presentation at Radcure 86, Baltimore, 1986. Tu, R. S. In UV Curing: Science and Technology, Vol. II; Pappas, S. P., Ed.; Technology Marketing Corp.: Norwalk, Connecticut, 1985, p. 147. Safe Handling and Use of UV/EB Curable Coatings, National Paint and Coatings Association: Washington, D.C., 1980. Conning, D. M. Radcure 85: Technical Paper, Association for Finishing Processes: Basel, Switzerland, 1985; FC85-442.


26. LAPIN 5.

6. 7. 8. 9.


10. 11. 12.

13. 14.

15. 16.

17. 18. 19. 20. 21. 22.

23.

24. 25.


Decker, C.; Bendaikha, T.; Fizet, M.; Faure, J. Radcure 85: Technical Paper, Association for Finishing Processes: Basel, Switzerland, 1985; FC85-432. Decker, C.; Bendaikha, T. Europ. Polym. J. 1984, 20, 753. For a review see: Crivello, J. V. Advances in Polymer Science, 1984, 62, 1. Lapin, S. C. Radcure 86: Conference Proceedings, Association for Finishing Processes: Baltimore, Maryland, 1986; p. 15-15. Watt, W. R. In UV Curing: Science and Technology, Vol. II, Pappas, S. P., Ed.; Technology Marketing Corp.: Norwalk, Connecticut, 1985; p. 247. Koleske, J. V. Finishing Line, 2, (3), Association for Finishing Processes, 1986. Gaube, H. G. Radcure 86: Conference Proceedings, Association for Finishing Processes: Baltimore, Maryland, 1986; p. 15-27. Crivello, J. V.; Conlon, D. Α.; Olsen, D. R. ; Webb, Κ. K. Radcure Europe '87: Conference Prceedings, Association for Finishing Processes: Munich, 1987; p. 1-27. Koleske, J. V. Radtech '88: Conference Proceedings, Radtech International: New Orleans, 1988; p. 353. Crivello, J. V.; Lee, J. L.; Conlon, D. A. Radiation Curing VI: Conference Proceedings, Association for Finishing Processes: Chicago, 1982; p. 4-28. Higashimura, T.; Aoshima, S.; Sawamoto, M. Makromol. Chem. Symp. 1986, 3, 99. Dougherty, J. Α.; Vara, F. J.; Anderson, L. R. Radcure 86: Conference Proceedings, Association for Finishing Processes: Baltimore, Maryland, 1986; p. 15-1. GAF Corporation, Wayne, New Jersey. Reppe, J. W. Acetylene Chemistry, I.G. Farbenindustrie A.A., Translated from German, Charles A. Meyer Co.: New York; 1949. Gallucci, R. R.; Going, R. C. J. Org. Chem. 1983, 48, 342. Lapin, S. C.; House, D. W. U.S. Patent 4,751,237, 1988. Lapin, S. C. Radtech '88: Conference Proceedings, Radtech International: New Orleans, 1988; p. 395. Christmas, Β. Κ.; Zey, E. G. Radcure 86: Conference Proceedings, Association for Finishing Processes: Baltimore, Maryland, 1986; p. 14-53. Brann, B. L.; Riggs, G. Radcure 86: Conference Proceedings, Association for Finishing Processes: Baltmore, Maryland, 1986; p. 4-57. Watt, W. R. ACS Symposium Series: Epoxy Resin Chemistry, American Chemical Society: 1979, p. 18. Hanrahan, B. D.; Manus, P; Eaton, R. F. Radtech '88: Conference Proceedings, Radtech International: New Orleans, 1988; p. 14.

RECEIVED

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1989


381

Radiation-Induced Cationic Curing of Vinyl-Ether-Functionalized

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