UV Cure of Epoxysiloxanes and Epoxysilicones - ACS Symposium

Chapter 27

UV Cure of Epoxysiloxanes and Epoxysilicones Richard P. Eckberg and Karen D. Riding

Downloaded by COLUMBIA UNIV on January 2, 2017 | http://pubs.acs.org Publication Date: December 28, 1990 | doi: 10.1021/bk-1990-0417.ch027

Silicone Products Division, General Electric Company, Waterford, NY 12188

Polydimethylsiloxanes, commonly referred to as silicones, are unique materials with a broad range of applications in industrial, consumer, and cosmetic products and processes. There are excellent opportunities for silicone suppliers to take advantage of growing market demand for radiation-curable silicone coatings used for release of pressure-sensitive adhesives, conformal coatings, and other diverse applications which combine unique silicone properties with low-temperature processing, high speed through-put, and the low energy and environmental impact of radiation processing. Among the most successful of the new radiation-curable silicone coating systems are compositions incorporating cycloaliphatic epoxy-functional silicone polymers with compatible iodonium salt photocatalysts (1 - 5). The syntheses, structures, UV cure response, and other properties of these materials and some of their derivatives and monomeric homologs are discussed in the balance of this chapter. Their specific application for release coatings has been described in great detail elsewhere (5,6) and is not the subject of this paper. A handy shorthand system of abbreviating silicone polymer structures has been developed by the industry and will be used herein. Chainstopper siloxy groups are designated "M" (monofunctional). Superscripts refer to organic functionality other than methyl, i.e.

Siloxane units making up linear polysiloxane molecules are designated "D" (difunctional), and are superscripted in the same fashion as above; subscripts refer to chainlength of linear polymers. 0097-6156/90/0417-0382$06.00/0 ©1990 American Chemical Society Hoyle and Kinstle; Radiation Curing of Polymeric Materials ACS Symposium Series; American Chemical Society: Washington, DC, 1990.

27. ECKBERG & RIDING

D =

UVCure of Epoxysiloxanes and Epoxysilicones 383

CH, 3

H

SiO

SiO

CH

CH. 3

3

CH, 3

D

=

( S i l i c o n i n s i l i c o n e polymers i s always c o n s i d e r e d

SiO

4-coordinate).


EPOXYSILICONES P l a t i n u m - c a t a l y s e d r e a c t i o n o f o l e f i n e p o x i d e s t o S i H compounds, o r h y d r o s i l a t i o n , i s an e l e g a n t and c o n v e n i e n t means o f s y t h e s i z i n g e p o x y - f u n c t i o n a l s i l i c o n e s and s i l o x a n e s (7.) . The b a s i c r e a c t i o n i s p r e s e n t e d as e q u a t i o n ^ ! : HSiH

+

(1)

Two o l e f i n e p o x i d e s , a l l y l g l y c i d y l e t h e r and 4 - v i n y l c y c l o h e x e n e o x i d e (VCHO), a r e c o m m e r c i a l l y a v a i l a b l e t o the e x t e n t t h a t l a r g e scale production of their siloxane derivatives i s f e a s i b l e :

Since extremely f a s t - c u r i n g UV-sensitive s i l i c o n e m a t e r i a l s are d e s i r e d by t h e r e l e a s e c o a t i n g i n d u s t r y , e p o x y s i l i c o n e s d e r i v e d f r o m VCHO were chosen f o r development, s i n c e c a t i o n i c UV c u r e o f c y c l o a l i p l i a t i c e p o x i e s i s known t o be much f a s t e r than t h a t o f analogous g l y c i d y l e t h e r s ( 8 ) . Two c l a s s e s o f c y c l o a l i p h a t i c epoxy c o n t a i n i n g m a t e r i a l s have emerged from e a r l y r e s e a r c h e f f o r t s : e p o x y s i l i c o n e p o l y m e r s and e p o x y s i l o x a n e monomers ( o r o l i g o m e r s ) . E p o x y s i l i c o n e polymers s u i t a b l e f o r r a d i a t i o n - c u r e r e l e a s e c o a t i n g a p p l i c a t i o n s have t o s a t i s f y an i m p o r t a n t r e q u i r e m e n t i n o r d e r t o be u s e f u l : they must be c o a t a b l e by t h r e e r o l l o f f s e t g r a v u r e ( o r o t h e r m u l t i r o l l t e c h n i q u e ) c o a t e r s d e s i g n e d to p r o v i d e complete coverage o f s u b s t r a t e a t low c o a t w e i g h t s ( t y p i c a l l y 1 gram/meter o r l e s s ) w i t h o u t b e n e f i t o f s o l v e n t . Since v i s c o s i t y of such m a t e r i a l s i s c o n s t r a i n e d w i t h i n 200-2000 c e n t i s t o k e ( c s t k ) , w i t h 200-500 c s t k p r e f e r r e d , t h e m o l e c u l a r w e i g h t o f t h e s i l i c o n e used must be t i g h t l y c o n t r o l l e d , as w e l l , and i s n o r m a l l y between 500010,000 D a l t o n s , o r about 60 t o 150 d i m e t h y l s i l o x y (D) u n i t s . Two methods t o p r o d u c e such polymers have been e s t a b l i s h e d : (a) h y d r o s i l a t i o n a d d i t i o n o f VCHO t o an S i H - f u n c t i o n a l polymer p r e formed (by means o f a c i d e q u i l i b r a t i o n ) t o t h e d e s i r e d m o l e c u l a r w e i g h t and S i H c o n t e n t and (b) b a s i c e q u i l i b r a t i o n o f a l k o x y s i l a n e VCHO a d d u c t s w i t h o t h e r s i l o x a n e s (2). Since the t r i m e t h o x y s i l a n e (MeO) Si3

Hoyle and Kinstle; Radiation Curing of Polymeric Materials ACS Symposium Series; American Chemical Society: Washington, DC, 1990.

384

RADIATION CURING OF POLYMERIC MATERIALS

i s the o n l y such s i l a n e c o m m e r c i a l l y a v a i l a b l e (as A-186, trademark of Union C a r b i d e C o . ) , the former approach has p r o v e n to be the most v e r s a t i l e , and most r e a d i l y t r a n s l a t e d t o l a r g e s c a l e p r o d u c t i o n . T y p i c a l l i n e a r e p o x y s i l i c o n e polymers m a n u f a c t u r e d i n t h i s manner a r e r e p r e s e n t e d below: E

M D

E 5

D

9 5

M

m

\ F

(C H Ph) ISbF^

800

396

160

65

CY 179 ( C i b a - G e i g y )

2000

370

Epon 825 ( S h e l l )

4000

1460

/\^^J^

where Ε =

Limonenedioxide =

θ ζ ^ \ )

/

-^XJ^XÎO

CÏ179 Epon 825 =

E

E

The h i g h Tg o b s e r v e d f o r M M a n d i t s a n a l o g s might r e f l e c t t h e r m a l c u r e t a k i n g p l a c e d u r i n g t h e DSC measurements t h e m s e l v e s ; f u r t h e r a n a l y s i s i s required to resolve p o s s i b l e ambiguities. However, even r e l a t i v e l y low m o l e c u l a r weight W D ^ T type p o l y s i l o x a n e o l i g o m e r s ' cured f i l m p r o p e r t i e s resemble t h o s e o f conv e n t i o n a l c u r e d d i m e t h y l s i l i c o n e s , which r e t a i n t h e i r p r o p e r t i e s a t v e r y low t e m p e r a t u r e . EPOXYSILOXANES AND POLYOLS A l c o h o l s , p h e n o l s , and p o l y o l s r e a c t w i t h e p o x i e s under cat i o n i c UV-cure c o n d i t i o n s : 1

R R-OH

+

θ φ ^

OR

R

«


6

UV Cure of Epoxysiloxanes and Epoxysilicones


ECKBERG & RIDING


393


394 Table VI.

Approximate; Tg o f U V - c r o s s i i n k e d F i l m s * Tg,

Monomer

C

165-195 (broad

transition)

30-70

4

M W

(9-40 @-100


Ε-S iMe

200-215

iMe ~ E 2

190-195

E-SiMe CH CH SiMe -E 2

2

2

2

E - S i M e ^ 0 - < ^ SiMe -E

180-190

CY179

143

Epon 825

132

2

* 0.5 wt % ( C

2

1 2

H

2 5

Ph)

2

ISbF , 6

2j/cm

2

UV

flux

Numerous p u b l i s h e d r e p o r t s d e s c r i b e how p o l y o l o r a l c o h o l a d d i t i v e s improve e l o n g a t i o n , impact r e s i s t a n c e , and g e n e r a l toughness o f b r i t t l e , i n f l e x i b l e UV-cured c y c l o a l i p h a t i c epoxy r e s i n s (16,17). We endeavored t o determine i f f i l m p r o p e r t i e s o f t h e s e b r i t t l e UVc u r e d e p o x y s i l o x a n e s can be improved by h y d r o x y - f u n c t i o n a l a d d i t i v e s . I n i t i a l s t u d i e s were l i m i t e d t o t h e system M D ^ M / 2 - e t h y l - l , 3 h e x a n e d i o l (EHDO) w h i c h p r o v e d m i s c i b l e when χ = 0, 4, and 10, w i t h 0.5 wt % iodonium c a t a l y s t B. We i n v e s t i g a t e d t h e e f f e c t o f EHDO on epoxysiloxane cure response, w i t h r e s u l t s g r a p h i c a l l y d e p i c t e d i n F i g u r e 4. P o l y o l s a c t as c h a i n t r a n s f e r agents which a s s i s t UV c u r e o f c a t i o n i c epoxy systems. Our r e s u l t s w i t h EHDO and M DJMT d i d n o t i l l u s t r a t e t h i s e f f e c t , perhaps because a l l components o f these blends are d i f u n c t i o n a l * We r e p e a t e d t h i s experiment by d e t e r m i n i n g UV c u r e response o f wn/l,2,6-trihydroxyhexane mixture u s i n g the same iodonium c a t a l y s t and c o n c e n t r a t i o n . These r e s u l t s a r e l i s t e d i n Table V I I . Table V I I .

UV Cure Response, M ^ / T r i o l System 2

OH/Epoxy Mole R a t i o 1.00 0.75 0.5 0.25 0

UV F l u x f o r Cure,

MJ/cm

212 70 32 30 15


ECKBERG & RIDING

UVCure of Epoxysiloxanes and Epoxysilicones


300


395

396


S o l u b i l i t y of 1,2,6-trihydroxyhexane in was l i m i t e d , but t h i s t r i o l formed c l e a r b l e n d s w i t h M M and o c t a n o l . An 8:1:1 (wt:wt:wt) mix o f M M : t r i o l : o c t a n o l curbed t o a tough, t r a n s p a r e n t 2 m i l f i l m on i r r a d i a t i o n w i t h 70 MJ/cm UV energy i n the p r e s e n c e o f 0.5% iodonium s a l t B, s u g g e s t i n g t h a t b l e n d s o f v a r i o u s a l c o h o l s and p o l y o l s may be used w i t h e p o x y s i l o x a n e s o r e p o x y s i l i c o n e s to o v e r come s o l u b i l i t y c o n s t r a i n t s . M o n o f u n c t i o n a l a l c o h o l s may a l s o be c u r e d w i t h e p o x y s i l o x a n e s , a l t h o u g h t h e y a c t as c h a i n t e r m i n a t o r s and slow UV c u r e a s O H / o x i r a n e r a t i o s approach 1. T h i s e f f e c t i s i l l u s t r a t e d f o r the Μ *M / o c t a n o l system i n T a b l e V I I I below: E

Table V I I I .

UV

Cure Response, M V / N - o c t a n o l


2 OH/oxirane mole r a t i o

UV

f l u x f o r Cure, MJ/cm 2

1.0 0.75 0.5 0.25 0

No

c u r e a t 5000 MJ/cm 2700 140 70 15

P h y s i c a l p r o p e r t y measurement o f t h i c k s e c t i o n - U V c u r e d epoxys i l o x a n e / a l c o h o l b l e n d s were d i f f i c u l t t o o b t a i n b e c a u s e many o f the c u r e d f i l m s ( l i k e u n m o d i f i e d e p o x y s i l i c o n e s ) p r o v e d too weak and b r i t t l e to t e s t . S e l e c t e d r e s u l t s a r e d e p i c t e d i n T a b l e IX f o r 20 m i l f i l m s UV c u r e d w i t h 0.5 wt% (C. H -Ph) ISbF,. by e x p o s u r e t o 2 J/cm t o t a l UV f l u x . ^ 9

i

T a b l e IX. Mole R a t i o , 0 H / 0 x i r a n e E

EHD0/M M

Cured

?1

Film Properties

Peak T e n s i l e , p s i

E l o n g a t i o n a t Break, %

E

1.0 0.8 0.6 0.4

( v e r y low) 111 643 (very high) E

O c t a n o l /M M 0.5 0.4 0.33 0.25 EHDO/MVM

17 36.5 130 159

14 22.5 26 23

9 18 17 28

20 19 14.5 10.5

5 4 28

16 9 L8

5

0.83 0.66 0.5

iU

100 62 29 5

E

Γ7(Γ

EHDO/^D 1.0 0.75

?

Z

M

E


27. ECKBERG & RIDING

UV Cure of Epoxysiloxanes and Epoxysilicones

397

W h i l e most o f t h e s e f i l m s a r e c l e a r l y low-modulus m a t e r i a l s , they p o s s e s s p r o p e r t i e s u s e f u l f o r such r a d i a t i o n - c u r e c o a t i n g a p p l i c a t i o n s as c o n f o r m a i c o a t i n g s , e l e c t r o n i c e n c a p s u l e n t g e l s , o r f i b e r o p t i c c o a t i n g s , p a r t i c u l a r l y where such a p p l i c a t i o n s demand silicones b r o a d o p e r a t i o n a l temperature range. 1


SUMMARY E p o x y s i l i c o n e s r a n g i n g from l o w - m o l e c u l a r w e i g h t s i l o x a n e monomers t o h i g h m o l e c u l a r w e i g h t polymers have been d e v e l o p e d f o r a wide range of r a d i a t i o n - c u r a b l e c o a t i n g a p p l i c a t i o n s . M o d i f i c a t i o n s o f iodonium p h o t o c a t a l y s t s and o f e p o x y - f u n c t i o n a l d i m e t h y l s i l i c o n e s make t h e c a t a l y s t s and r e s i n s m u t u a l l y c o m p a t i b l e , thus r e n d e r i n g t h e s e systems c o m m e r c i a l l y f e a s i b l e . D i - c y c l o a l i p h a t i c epoxy-terminated s i l o x a n e monomers and o l i g o m e r s d i s p l a y e x t r e m e l y f a s t UV c u r e r e s ponse and c a n be used t o a c c e l e r a t e c u r e o f o r g a n i c epoxy r e s i n s . P h y s i c a l p r o p e r t i e s o f UV c u r e d e p o x y s i l o x a n e s a r e r e a d i l y m o d i f i e d by c o - c u r e w i t h a l c o h o l s and p o l y o l s .

REFERENCES 1. 2. 3. 4.

R.P. Eckberg and R.W. LaRochelle, U.S. 4,279,717 (7/21/81). R.P. Eckberg and R.W. LaRochelle, U.S. 4,421,904 (12/20/83). R.P. Eckberg, U.S. 4,547,431 (10/15/85). R.P. Eckberg, Radcure '84 Conference Proceedings, Atlanta, Georgia, pg. 2-1. 5. R.P. Eckberg, Radtech '88 North America Conference Proceedings, New Orleans, pp. 576-586. 6. Chemical & Engineering News, Nov 28, pg 32 (1988). 7. R.D. Mendecino, U.S. Pat. 4,046,930 (4/11/78). 8. J.V. Crivello, UV Curing: Science & Technology, (Ed. S. Peter Pappas), pp 24-77, Technology Marketing Corporation, (1978). 9. I. Yilgor and J.E. McGrath, Adv. Polymer Science, 86, 1-86 (1988) and references therein. 10. F.M. Beringer, M. Drexler, E.M. Gindler, and C.C. Lumpkin, J. Amer. Chem. Soc., 73, 2705 (1953). 11. F.M. Beringer, R.A Falk, M. Karmal, J. Lillien, G. Masullo, M. Mausner, and E. Sommer, J. Amer. Chem.Soc.,81,342 (1959). 12. G.F. Koser, R.H. Wettack, and C.S. Smith, J. Org. Chem., 45, 1543 (1980). 13. X. Coqueret, A. Lablache-Combier, and C. Loucheux, Eur. Polym. J., 24, 713-718 (1988). 14. R.P. Eckberg, U.S. 4,558,082 (12/16/85). 15. E.P. Plueddemann and G. Fanger, J. Amer. Chem.Soc.,81, 2632 (1959). 16. G.H. Smith, U.S. 4,256,828 (3/17/81). 17. J.V. Koleski, Radtech '88 North American Conference Proceedings, New Orleans, pp 353-371. RECEIVED September 13,

1989


UV Cure of Epoxysiloxanes and Epoxysilicones - ACS Symposium

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