Acrylated Melamines in UV-Curable Coatings - ACS Symposium

Chapter 14

Acrylated Melamines in UV-Curable Coatings

Downloaded by UNIV OF PITTSBURGH on May 16, 2016 | http://pubs.acs.org Publication Date: December 28, 1990 | doi: 10.1021/bk-1990-0417.ch014

Joel J. Gummeson Monsanto Chemical Company, 730 Worcester Street, Springfield,MA01151

Acrylated melamines have both acrylic and alkoxy functionality. The acrylate functionality allows the melamine to be UV cured by a free radical mechanism. The alkoxy groups may be cured by a condensation mechanism. The triazine ring has six reactive sites that can be used to prepare materials with a range of unsaturated functionality. The result is that a number of acrylated materials can be prepared to meet a variety of process requirements. This paper demonstrates the utility of incorporating acrylated melamines into UV curable coating formulations. It reports on coating properties obtained by replacement of common acrylated oligomers by acrylated melamines. BACKGROUND Acrylated melamines c a n be made by r e a c t i n g acrylamide with etherified melamine resins thereby incorporating acrylic f u n c t i o n a l i t y onto the t r i a z i n e r i n g . ^ ' Table 1 describes a l l o f t h e A c r y l a t e d Melamine (AM) r e s i n s used i n t h e paper. Some work was done w i t h t h e base r e s i n w i t h o u t s o l v e n t o r d i l u e n t (AM 1-3) and o t h e r work r e f e r s t o t h e d i l u t e d r e s i n (AM 4-10). T a b l e 2 compares t h e p r o p e r t i e s o f two AM r e s i n s . F i g u r e s 1-2 show t y p i c a l s t r u c t u r e s o f t h e s e base r e s i n s . The AM i n f i g u r e 1 has been m o d i f i e d w i t h o l e a m i d e i n a d d i t i o n t o a c r y l a m i d e . These base r e s i n s a r e available in a variety o f d i l u e n t s and s o l v e n t s . F i g u r e 3 shows t h e v i s c o s i t i e s o f t h e s e r e s i n s i n N - v i n y l p y r r o l i d o n e (NVP). The e x p e r i m e n t a l work p r e s e n t e d i n t h i s paper i s i n t e n d e d t o show t h e u t i l i t y o f AM o l i g o m e r s i n UV c u r e f o r m u l a t i o n s and t h e e f f e c t combined a c r y l a m i d e c o n t e n t has on t h e UV c u r e p r o p e r t i e s o f a c r y l a t e d melamines. T h i s work w i l l c o n s i d e r t h r e e c u r e p r o c e s s e s : UV, t h e r m a l , and d u a l c u r e . I n t h i s c a s e d u a l c u r e i s UV f o l l o w e d by a t h e r m a l bump. 1

0097-6156/90/0417-0176$06.00/0 ο 1990 American Chemical Society

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

14. GUMMESON

T a b l e 1.


Reference in Paper

177


Description

Resin Structure

o f a c r y l a t e d melamines used

Moles Acrylamide

Percent AM

Diluent

AM

1

A

2.0

100

None

AM

2

Β

2.5

100

None

AM

None

3

Β

1.5

100

AM 4

Β

0.5

75

TPGDA

AM

5

Β

1.0

75

TPGDA

AM

6

Β

1.5

75

TPGDA

AM

7

Β

2.5

75

TPGDA

AM

8

Α

2.0

75

NVP

AM

9

Β

2.5

75

NVP

2.5

75

Dowanol PM

AM

Β

10

T a b l e 2.

Typical physical properties

Base Resin Molecular Weight (No. Avg.) Average Functionality

AM 1

o f t h e AM

resins

AM 2

1130

970

3.6

4.0

Solution Properties @ 75% Resin Solids in NVP: Density @25 C

1.099

Viscosity @25 C

10,000 C P S

1.093 16,200 C P S


178

RADIATION CURING OF POLYMERIC MATERIALS


-OCH

/

C H

2

NHCCH-CH 2 II 2 Ο

CH «HCCHNCH 2 II 2 Ο Ν NHCH

Η

C 2

H

2

0

R

Η Η (CH ) C»C(CH ) CH 2

F i g u r e 1.

7

2

7

3

Type A a c r y l a t e d melamine t y p i c a l

OCH

CHg—X

CH^HCCHNCH

ϋ

C H OR 2

2

ROCH^

Figure 2

structure.

X

CH NH^CH-CH 2

Type Β a c r y l a t e d melamine

2

typical

structure.


14.

GUMMESON

179

Aerylated Melamines in UV-Curable Coatings

EXPERIMENTAL


A c r y l a t e d Melamine r e s i n s were p r e p a r e d by r e a c t i n g d i f f e r e n t l e v e l s o f a c r y l a m i d e w i t h a f u l l y a l k y l a t e d c o e t h e r i f i e d melamine r e s i n c o n t a i n i n g m e t h y l and b u t y l groups a t an approximate r a t i o o f 1:1. They were p r e p a r e d w i t h 0.5, 1.0, 1.5, and 2.5 moles o f a c r y l a m i d e per t r i a z i n e r i n g . Throughout t h e paper a b i s - p h e n o l A epoxy acrylate resin ( E b e c r y l 3700 from Radcure S p e c i a l t i e s ) and an aliphatic urethane acrylate resin ( E b e c r y l 8800 from Radcure S p e c i a l t i e s ) a r e used as c o n t r o l s . UV Cure. S h r i n k a g e upon UV Cure was d e t e r m i n e d f o r AM 8, AM 9, and t h e epoxy a c r y l a t e , a l l a t 75% i n NVP. S h r i n k a g e was d e t e r m i n e d from t h e d e n s i t y d i f f e r e n c e b e f o r e and a f t e r UV c u r e . The d e n s i t y measurements were made i n pyenometers a t 25° C. AM 8, and AM 9 were e v a l u a t e d i n an overprint varnish f o r m u l a t i o n f o r h i g h speed l i t h o a p p l i c a t i o n s . The v i s c o s i t i e s o f t h e f o r m u l a t i o n s were measured w i t h a B r o o k f i e l d RVT viscometer. C u r i n g was done w i t h an RPC UV p r o c e s s o r w i t h two 200 w a t t / i n c h medium p r e s s u r e Hg vapor lamps o r w i t h a F u s i o n Systems p r o c e s s o r w i t h one 300 w a t t / i n c h "H" b u l b . T h e r m a l Cure. Thermal c u r e o f an AM 10 was compared w i t h t h a t o f Resimene 755 a m e t h y l b u t y l c o e t h e r i f i e d melamine r e s i n Both melamines were f o r m u l a t e d i n a c l e a r t o p c o a t a t 25, 40, and 50% o f t o t a l r e s i n s o l i d s (TRS) w i t h J o n c r y l 500 (S.C. Johnson & Sons) as the p o l y o l coreactant. v

Dual Cure. F i l m s were p r e p a r e d f o r Dynamic M e c h a n i c a l A n a l y s i s (DMA). A l l f i l m s were c a s t on r e l e a s e paper w i t h a 4.5 m i l draw down b a r , and p a r t i a l l y c u r e d w i t h two 200 w a t t / i n c h lamps a t h a l f power and a b e l t speed o f 200 f t / m i n . The f i l m s were i n t e n t i o n a l l y under c u r e d t o f a c i l i t a t e c u t t i n g w i t h minimal f l a w s . A f t e r the f i l m s were c u t i n t o ^ - i n c h t e s t p i e c e s , t h e y were c u r e d w i t h two 200 w a t t / i n c h lamps a t 100 f t / m i n , e q u a l t o 260 m i l l i j o u l e s / c m dose. The i n s t r u m e n t used f o r t h e DMA work was a R h e o m e t r i c s RSA I I S o l i d s A n a l y z e r . A l l t e s t s were made a t a f r e q u e n c y o f 11 hz w i t h a nominal s t r a i n o f 0.05%, under n i t r o g e n . Both temperature scans, at 2°C/minute, and i s o t h e r m a l runs were made. An FTIR was used t o o b s e r v e t h e changes i n UV c u r e d f i l m s . The same c o a t i n g f o r m u l a t i o n s were used f o r t h e epoxy a c r y l a t e and o l e a m i d e m o d i f i e d AM but a l s o i n c l u d e d 3% PTSA. An i n i t i a l s c a n was made f o r t h e s e m a t e r i a l s on s a l t p l a t e s . The p l a t e s were r e s c a n n e d a f t e r a UV e x p o s u r e o f 260 mj/cm and a g a i n as t h e f i l m s were c u r e d a t 150° C. 2

2

RESULTS

UV Cure Viscosity. The v i s c o s i t i e s o f AM r e s i n s d e c r e a s e w i t h d e c r e a s i n g acrylamide content. F i g u r e 4 shows t h e v i s c o s i t y o f t h e 1.5 mole b a s e r e s i n (AM 3) w i t h o u t s o l v e n t o r d i l u e n t . F i g u r e 5 shows t h e




180

Brookfield RVT, Thermosel, #27

Spindle

1000000 =E

1

1000 45

50

1

1

55

» — — 60 65

1

1

70

1

75

1

80

Temperature (Degrees C) F i g u r e 4.

Viscosity

o f AM3 base

resin.


85

14.

GUMMESON


181


v i s c o s i t y o f t h e base r e s i n i n TPGDA (AM 6) as a f u n c t i o n o f r e s i n content. A wide range o f v i s c o s i t i e s i s p o s s i b l e by a d j u s t i n g t h e combined a c r y l a m i d e c o n t e n t and t h e amount o f monomer. However, s o l u b i l i t y i n TPGDA d e c r e a s e s w i t h i n c r e a s i n g a c r y l a m i d e c o n t e n t and r e s i n s w i t h more t h a n 2 moles o f a c r y l a m i d e a r e n o t c o m p l e t e l y soluble. V i s c o s i t i e s o f o v e r p r i n t v a r n i s h f o r m u l a t i o n s c o n t a i n i n g AM o r epoxy a c r y l a t e a r e shown i n T a b l e 3. V i s c o s i t i e s o f t h e AM f o r m u l a t i o n s a r e i n t h e same range as t h a t o f t h e epoxy a c r y l a t e . Shrinkage. The r e s u l t s i n T a b l e 4 show t h a t t h e s h r i n k a g e o f AM r e s i n s i s l e s s t h a n t h e epoxy a c r y l a t e c o n t r o l . I t has been r e p o r t e d t h a t f o r UV C u r a b l e c o a t i n g s used i n m i r r o r c o n s t r u c t i o n , i t i s d e s i r a b l e f o r good a d h e s i o n t o have c o a t i n g s w i t h l e s s t h a n 10 percent shrinkage.^ ) 3

F i l m P r o p e r t i e s . The o v e r p r i n t v a r n i s h f o r m u l a t i o n s o f T a b l e 3 were a p p l i e d t o c l a y c o a t e d paper s t o c k o v e r b l a c k l i t h o g r a p h i c i n k w i t h a #3 r o d and c u r e d w i t h t h e RPC p r o c e s s o r . P r o p e r t i e s e v a l u a t e d one day a f t e r c u r e , a r e shown i n T a b l e 5. The d a t a show t h e epoxy a c r y l a t e c u r e s f a s t e r t h a n t h e AM r e s i n s , and i n t h i s h i g h speed l i t h o g r a p h i c f o r m u l a t i o n c u r e d a t a low energy l e v e l (46 mj/cm ) a h i g h degree o f c r o s s l i n k i n g i s not expected. This i s reflected i n t h e low MEK d o u b l e rubs seen f o r a l l f o r m u l a t i o n s . Even though t h e AM r e s i n s c u r e s l o w e r t h e y s t i l l e x h i b i t i m p r o v e d C r o s s h a t c h and s c r a t c h a d h e s i o n , and improved a b r a s i o n r e s i s t a n c e . More t h r o u g h c u r e c a n be o b t a i n e d w i t h i n c r e a s e d r a d i a t i o n l e v e l s o r i n t h e c a s e o f AM r e s i n s by a d d i t i o n o f t h e r m a l c u r e . In a n o t h e r experiment, f o r m u l a t i o n s w i t h o l i g o m e r s i n TPGDA were c o a t e d o v e r B o n d e r i t e 40 s t e e l as shown i n T a b l e 6. P a n e l s were 2

c u r e d w i t h e x p o s u r e s r a n g i n g from 200 t o 2300 mj/cm with a Fusion "H" lamp. F i g u r e 6 shows t h e average Tukon h a r d n e s s w i t h AM 6 i s h i g h e r t h a n w i t h t h e u r e t h a n e a c r y l a t e b u t s i g n i f i c a n t l y lower t h a n w i t h t h e epoxy a c r y l a t e . The f i l m hardness f o r a l l f i l m s i s v e r y c o n s i s t e n t f o r c u r e s o v e r t h e e n t i r e e x p o s u r e range. Table 6 shows t h e r e s u l t s o f c r o s s h a t c h t a p e a d h e s i o n and mandrel bend t e s t s f o r t h e f i l m s c u r e d w i t h a p p r o x i m a t e l y 2000 mj/cm o f UV energy. Both t h e AM and epoxy f i l m s have good a d h e s i o n . The f l e x i b i l i t y o f t h e AM f i l m i s i n t e r m e d i a t e between t h a t o f t h e u r e t h a n e and epoxy acrylate films. 2

A c c e l e r a t e d Weathering. The c o l o r and Q-U-V a g i n g o f AM 6 was compared w i t h t h e epoxy a c r y l a t e and a l i p h a t i c u r e t h a n e a c r y l a t e . F o r t h i s e v a l u a t i o n a l l r e s i n s were used a t 70% i n TPGDA and f o r m u l a t e d w i t h 4% D a r o c u r 1173 as t h e p h o t o i n i t i a t o r . Formulations were drawn down on w h i t e c l a y c o a t e d b o a r d w i t h a #14 r o d and c u r e d w i t h t h e F u s i o n p r o c e s s o r . The c o l o r o f t h e f i l m s was measured w i t h a D25D2 C o l o r / D i f f e r e n c e meter from H u n t e r l a b . F i g u r e 7 shows i n i t i a l and aged f i l m c o l o r f o r t h e AM i s s i g n i f i c a n t l y lower t h a n t h a t o f t h e u r e t h a n e a c r y l a t e , and f a r lower t h a n t h a t o f t h e epoxy acrylate. Some improvement i n epoxy a c r y l a t e c o l o r c a n be o b t a i n e d by b l e n d i n g w i t h AM 6.



100000


10000 ±

1000 =b

(CPS)

100 40

45

50

55

60

75

65

Percent Resin In TPGDA Figure 5.

Viscosity of AM6 in TPGDA.

Table 3. Overprint varnish formulations containing A M or epoxy acrylate Formulation 3700 @ 75% T R S in NVP (1)32 AM 2 (at 75% in NVP) AM 1 (at 75% in NVP) 36 TMPTA 11 PETA 8 Triethanolamine 6 Benzophenone 5 1173 (2) 2 L - 7 6 0 2 (3) Viscosity (CPS @25 C)

205

32 36 11 8 6 5 2

32 36 11 8 6 5 2

242

188

(1) Ebecryl 3700 from Radcure Specialties (2) Darcur 1173 from EM Industries (3) SILWET L - 7 6 0 2 from Union Carbide


14.

GUMMESON

183

Aerylated Melamines in UV-Curable Coatings

Table 4. Shrinkage of AM resins compared to epoxy acrylate


AM

AM

1

Epoxy Acrylate

2

Sample 1

6.3%

5.8%

6.5%

Sample 2

5.4%

5.1%

8.3%

Sample 3

6.1%

5.8%

6.7%

Average

5.9%

5.6%

7.2%

0.330

0.386

0.806

Std.

Dev.

0.7

0.7

0.7

Variance

The .7% variance was calculated statistically by pooling the standard deviation values for all four experiments and is based on a 95% confidence level.

T a b l e 5.

Cured f i l m p r o p e r t i e s f o r t h e o v e r p r i n t

varnish

formulations III

Formulation Max. Belt Speed (Ft/Min) For Tack Free Surface With 1-200 Watt Lamp

450

(Cured With One 200 MEK

Double R u b s

Cross Hatch Tape Adhesion Over Black Litho Ink

( 1 )

250 Watt/Inch Lamp @ 200

30

2bu Ft/Min)

20

15

No Loss

No Loss

12

50

25

11.8

9.4

10% Loss

Scratch Adhesion Coin Rubs Over Black Litho Ink (2) Taber Abrasion Mg Coating Loss

(1) Coated On White Clay Coated Paper With #3 Rod (2) CS-10 Taber Abrasion Wheel With 500g Weight


184


Table 6. AM and epoxy acrylate based films cured over bonderite 40 steel


Formulation

VIII

75% 8800 in TPGDA 75% 3700 in TPGDA AM 6 TPGDA NVP Darocur 1173 Benzophenone L-7602

75 75

Bend

75 5 10 5 4 1

5 10 5 4 1

5 10 5 4 1

Tape Adhesion (3M #610) Mandrel

X

IX

50% loss

No Loss

Passes 1/8 Inch

Fails 1/2 Inch

No Loss Passes 1/2 Inch

Films applied to Bonderite 40 panels (4 mil dry film) and UV Cured with one 300 watt/inch Fusion "H" bulb at a belt speed providing 2000 mj/sq cm of UV radiation.

500

1000

1500

2000

2500

Energy Mj/Sq Cm —

Figure 6.

AM 6

Ebecryl 8800

Ebecryl 3700

Tukon hardness of AM and epoxy acrylate based films.



GUMMESON


UV Cured Films : 1000 mj/sq cm

14, 12 Η

ίο

3700

75:25

50:50

AM 6

8800

3700/AM 6 •B F i g u r e 7. Color f i l m s compared.

Initial

β

48 Hrs QUV

o f epoxy a e r y l a t e ,

Π3

120 Hrs QUV

urethane

acrylate,


and AM


186


Thermal Cure. S i n c e t h e a l k o x y f u n c t i o n a l i t y o f AM r e s i n s i s s i g n i f i c a n t l y lower t h a n t h a t o f u n m o d i f i e d melamine r e s i n s , a s e r i e s of e x p e r i m e n t s were r u n t o demonstrate t h a t t h e AM r e s i n r e t a i n s t h e a b i l i t y t o c u r e by c o n d e n s a t i o n r e a c t i o n s . F i g u r e 8 compares t h e Tukon hardness o f t h e melamine and AM 10 f i l m s . F i l m s o f each m a t e r i a l were drawn on primed B o n d e r i t e 40 w i t h a #4 b l a d e and c u r e d f o r 30 minutes a t 2 5 0 ° F. Both f o r m u l a t i o n s were c a t a l y z e d w i t h 0.8% PTSA on TRS. F o r t h e melamine c u r e d f i l m s , h a r d n e s s i n c r e a s e s s l i g h t l y as melamine c o n t e n t i s i n c r e a s e d from 25 t o 40%, b u t t h e n i s r e d u c e d a t 50% melamine c o n t e n t , p r o b a b l y due t o p l a s t i c i z a t i o n by u n r e a c t e d e x c e s s melamine f u n c t i o n a l i t y . For the acrylated melamine, hardness increases monotonically, probably b e c a u s e o f t h e lower a l k o x y f u n c t i o n a l i t y and h i g h e r Tg o f t h e AM r e s i n compared t o t h e melamine r e s i n . A t 40% AM t h e Tukon hardness i s s i m i l a r t o t h a t a c h i e v e d w i t h a 25% melamine r e s i n . T a b l e 7 shows a comparison o f o t h e r p r o p e r t i e s between t h e 40% AM and 25% melamine c o n t a i n i n g f i l m s . With t h e e x c e p t i o n o f c o n d e n s i n g h u m i d i t y , t h e AM f i l m has comparable p r o p e r t i e s . The lower h u m i d i t y r e s i s t a n c e o f t h e AM f i l m might be due t o r e s i d u a l unsaturation. I t i s l i k e l y t h a t under t h e r m a l c u r e c o n d i t i o n s and w i t h a l a c k o f f r e e r a d i c a l s t h e r e was l i t t l e r e a c t i o n o f t h e d o u b l e bonds. The p u r p o s e o f t h i s experiment was t o show t h a t c o n d e n s a t i o n c u r e was p o s s i b l e w i t h AM. Under " d u a l c u r e " c o n d i t i o n s an e f f o r t would be made t o c u r e b o t h f u n c t i o n a l i t i e s o f t h e AM.

Dual Cure D e m o n s t r a t i o n o f Dual Cure. To demonstrate t h e r m a l c u r e a f t e r UV c u r e t h r e e s e t s o f f i l m s were p r e p a r e d f o r Dynamic Mechanical A n a l y s i s (DMA). I n t h e f i r s t s e t , f o u r f o r m u l a t i o n s were based on AM 1, AM 2, t h e epoxy a e r y l a t e , and t h e u r e t h a n e a e r y l a t e . Formulations used t h e t e s t r e s i n a t 65% i n TPGDA, and i n c l u d e d 3% D a r o c u r 1173 as a source o f f r e e r a d i c a l s . DMA p l o t s f o r t h e epoxy a c r y l a t e and u r e t h a n e a c r y l a t e a r e shown i n F i g u r e 9. The e l a s t i c o r s t o r a g e modulus (Ε') i n t h e r u b b e r y r e g i o n i s o f t e n used as a measure o f c r o s s l i n k d e n s i t y . The maximum o f t h e t a n d e l t a p l o t , n o t shown, i s t a k e n as t h e T g . I n t h i s c a s e t h e Tg's f o r t h e epoxy a c r y l a t e and u r e t h a n e a c r y l a t e a r e 96 and 7 0 ° C r e s p e c t i v e l y . The DMA p l o t f o r t h e AM i s shown i n F i g u r e 10. I t shows a v e r y b r o a d t r a n s i t i o n , w i t h Tg about 1 2 0 ° C, on t h e f i r s t s c a n . The b r o a d n e s s i s most l i k e l y because t h e f i l m i s c u r i n g d u r i n g t h e s c a n . T h i s c a n be seen from t h e i n c r e a s e i n E ' between 140 and 1 8 0 ° C, and from t h e i n c r e a s e d u r i n g t h e 10 minute i s o t h e r m a l h o l d a t 1 8 0 ° C. The r e s u l t i s a Tg t h a t i s c o n t i n u o u s l y i n c r e a s i n g . When t h e f i l m i s r e s c a n n e d , t h e E ' c u r v e has h i g h e r v a l u e s i n d i c a t i n g an even h i g h e r c r o s s l i n k d e n s i t y . A broad t a n d e l t a peak, n o t shown, g i v e s a Tg o f about 1 6 0 ° C f o r t h e second s c a n . T h i s d e m o n s t r a t e s t h a t t e m p e r a t u r e s c a n n i n g t e c h n i q u e s a r e n o t good t o o l s f o r m e a s u r i n g t h e Tg o f AM films. F i g u r e 11 shows t h a t f o r t h e epoxy and u r e t h a n e a c r y l a t e s t h e e l a s t i c modulus remains c o n s t a n t d u r i n g i s o t h e r m a l DMA runs a t 1 5 0 ° C. However, t h e e l a s t i c m o d u l i o f AM f i l m s i n c r e a s e s i g n i f i c a n t l y for about 30-40 m i n u t e s i n d i c a t i n g t h e r m a l c u r e r e s u l t i n g i n an



GUMMESON

S


25%

40%

50%

% Melamine Based on Total Resin Solids ί F i g u r e 8.

T a b l e 7.

1 Acrylated Melamine

BI1

Melamine

Tukon h a r d n e s s o f melamine and AM10 f i l m s

Properties

o f 40% AM and 25% melamine f i l m s

Acrylated Melamine 40% on TRS (1) Dry Film Thickness

1.30 mil

Melamine 1.30 mil

93

92

Tukon Hardness @ 24 Hours

11.5

10.0

10 Days Condensing Humidity

No Change Slight Haze (2)

compared

25% on T R S (1)

20 Degree Gloss

24 Hr. Condensing Humidity

compared.

No Change No Change

(1) Coreactant is Joncryl 500 From S.C. Johnson & Sons (2) Haze disappears on standing.


188


Epoxy, Urethane Temperature S c a n 10'

1

1

1

1

1

1

1

1

1

1

1

1

—ι— —•— — —ι— — — — —ι— — — — —Γ

-epoxy control (UV cured) : T = 96°C -urethane control (UV cured) : T -= 70°C g


g

10°

50

200

1 50

100

Temperature (°C)

Figure 9. DMA temperature scan for UV cured epoxy and urethane acrylate films.

AM Temperature S c a n , Two Heats 10

τ 1

1

1

. 1 1 1

1

r-

ι 1 1— r

AM/TPGDA UV cured film

, u

10 h

'n

0/

o

X-linking

10*

Figure 10.

50

DMA

100

150

200

Temperature (°C)

temperature scan for a UV cured AM Film.



14. GUMMESON


189

increase i n crosslink density. C a r e must be t a k e n i n i n t e r p r e t i n g t h e magnitude o f t h e i n c r e a s e i n E ' however. Where E ' i s p r o p o r t i o n a l t o c r o s s l i n k d e n s i t y i n t h e rubbery r e g i o n , t h a t i s not t r u e i n t h e g l a s s y r e g i o n . T h e r e f o r e t h e t e m p e r a t u r e chosen f o r t h e i s o t h e r m a l experiment w i l l have a s i g n i f i c a n t e f f e c t on t h e r e s u l t . Whether t h e t e m p e r a t u r e i s above o r below Tg w i l l d e t e r m i n e i f Ε'is b e i n g measured i n t h e r u b b e r y o r g l a s s y r e g i o n . O r d e r o f magnitude i n c r e a s e s i n E' can r e s u l t i f t h e r e a c t i o n d r i v e s t h e f i l m i n t o t h e g l a s s y r e g i o n . I n t h i s experiment one would e x p e c t t h e Tg o f t h e AM f i l m t o be a p p r o a c h i n g 150° C, t h u s moving t h e measurement from t h e rubbery t o the t r a n s i t i o n r e g i o n . F o r t h e second s e t o f f i l m s , b l e n d s o f AM 1 and epoxy a c r y l a t e i n r a t i o s o f 50:50, 20:80, 10:90, and 5:95 were used a t 68% i n TPGDA. F i l m s were p r e p a r e d as above and a n a l y z e d w i t h i s o t h e r m a l DMA r u n s . F i g u r e 12 shows t h a t an 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 c a n be a c h i e v e d w i t h as l i t t l e as 10% AM i n epoxy a c r y l a t e f i l m s . F o r t h e t h i r d s e t o f f i l m s , t h e 0.5, 1.0, and 1.5 mole a c r y l a m i d e r e s i n s a t 70% i n TPGDA were f o r m u l a t e d w i t h 3% D a r o c u r 1173. These f o r m u l a t i o n s a l s o i n c l u d e d 2% CG21-746 UV d e b l o c k a b l e PTSA from C i b a Geigy. F i l m s were p r e p a r e d as above and e v a l u a t e d u s i n g i s o t h e r m a l DMA. F i g u r e 13 shows t h a t as t h e l e v e l o f a c r y l a m i d e f u n c t i o n a l i t y i s i n c r e a s e d from 0.5 t o 1.5 moles t h e i n i t i a l c r o s s l i n k d e n s i t y i s i n c r e a s e d , w i t h t h e l a r g e s t i n c r e a s e between 0.5 and 1.0 moles o f acrylamide. Thermal c u r e o c c u r s w i t h a l l r e s i n s , w i t h t h e f a s t e s t i n c r e a s e i n modulus seen w i t h t h e 0.5 mole AM which has t h e most remaining alkoxy f u n c t i o n a l i t y . FTIR e x p e r i m e n t s show a l o s s o f e t h e r f u n c t i o n a l i t y a t 990 cm" a t 1 5 0 ° C which i s f u r t h e r e v i d e n c e t h a t c o n d e n s a t i o n o f a l k o x y f u n c t i o n a l i t y i s o c c u r r i n g . A l o s s o f a c r y l i c f u n c t i o n a l i t y a t 1640 cm" i s o b s e r v e d f o r t h e AM as w e l l as f o r t h e epoxy a c r y l a t e d u r i n g thermal cure. T h i s may be t h e r e s u l t o f t h e r m a l g e n e r a t i o n o f r a d i c a l s o r of r a d i c a l t r a p p i n q i n t h e photoploymerized acrylic network w h i c h has been r e p o r t e d . 1

1

P r o p e r t i e s o f D u a l Cured F i l m s . The p r o p e r t i e s o f d u a l c u r e d f i l m s c o n t a i n i n g t h e o l e a m i d e m o d i f i e d AM and epoxy a c r y l a t e were compared. The f o r m u l a t i o n s used o l i g o m e r s a t 65% i n TPGDA and i n c l u d e d 3% D a r o c u r 1173 and 3% PTSA. They were a p p l i e d t o c l a y c o a t e d b o a r d o v e r b l a c k l i t h o g r a p h i c i n k w i t h a #3 r o d and c u r e d by a UV e x p o s u r e o f 250 mj/cm f o l l o w e d by a t h e r m a l c u r e o f 5 m i n u t e s a t 150° C. The d a t a i n T a b l e 8 show t h a t t h e 5 minute c u r e a t 1 5 0 ° C i n c r e a s e s MEK r e s i s t a n c e o f t h e AM f o r m u l a t i o n , i n d i c a t i n g a d d i t i o n a l c u r e . Even w i t h i n c r e a s e d c u r e t h e AM f i l m m a i n t a i n s e x c e l l e n t c r o s s h a t c h t a p e adhesion. The epoxy a c r y l a t e f o r m u l a t i o n , i n c o n t r a s t , l o s e s a l l a d h e s i o n d u r i n g t h e t h e r m a l bump. While i t i s r e c o g n i z e d t h a t a 5 minute a t 150° C t h e r m a l c u r e may be i m p r a c t i c a l i n many c a s e s , u s e f u l improvements i n p r o p e r t i e s may be a t t a i n a b l e w i t h lower c u r e s and c a t a l y s i s . 2

Thermal t r e a t m e n t o f UV c u r e d f i l m s was a l s o used t o improve s t a i n r e s i s t a n c e . I n t h i s work t h e u r e t h a n e a c r y l a t e , AM6, and t h e i r b l e n d s were r e d u c e d t o 70% i n TPGDA and f o r m u l a t e d w i t h 4% D a r o c u r 1173 a s t h e p h o t o i n i t i a t o r . The c o a t i n g s were a p p l i e d o v e r w h i t e c l a y c o a t e d b o a r d w i t h a 2 m i l b a r and c u r e d as i n t h e a c c e l e r a t e d weathering study. I n i t i a l c o l o r was d e t e r m i n e d by t h e Hunter


RADIATION CURING O F POLYMERIC MATERIALS

190

1 u 1 0

L


I

ι

ι

«ι

10°

F i g u r e 11.

ι

ι

ι

ι

ι

««ι

20

40

ι

' ι '

'

'

I

'

• • -

I

60

Time (min.)

100

80

120

I s o t h e r m a l s c a n a t 150 d e g r e e s C f o r UV c u r e d

films.

Τ"

Τ"

10

ι

acrylated melamine (AM) epoxy acrylate urethane acrylate

68% ACRYLATED MELAMINE in TPGDA 50/50 AM/EPOXY ACRYLATE; 68% in TPGDA 20/80 AM/EPOXY ACRYLATE; 68% in TPGDA 10/90 AM/EPOXY ACRYLATE; 68% in TPGDA 68% EPOXY ACRYLATE in TPGDA

10

υ

\ ω c

-Θ

io

9

UJ

10

e

20

40

60

Time

80

100

120

(min.)

F i g u r e 12. I s o t h e r m a l s c a n a t 150 d e g r e e s C f o r UV c u r e d o f epoxy a c r y l a t e m o d i f i e d w i t h AM.


films

Acrylamide Mole -ι—ι—ι—ι—ι—ι—ι—ι—ι


10

191


GUMMESON

ι

ι

Models

-

150°C

Γ τ—ι—ι—ι—ι—ι—ι—I

" " '

1.5 mole acrylamide model (all films UV cured) 1.0 mole acrylamide model 0.5 mole acrylamide model

10

υ \

a) -ο

10

9

UJ

10'

•

'

ι

I

20

I

ι—ι—ι—L

40

• • I

60

Time

I

80

I

1—ι—I—ι—ι—L

100

120

(min.)

Figure 13. Isothermal scan at 150 degrees C for UV cured films of AM containing varied levels of combined acrylamide.

Table 8. The effect of a 5 min/150 degree C post UV thermal bump on the film properties of epoxy acrylate and AM Formulation AM 1 (1) Ebecryl 3700 (1) Darocure 1173 40% PTSA

XI 100

— 3 5

— 100 3 5

UV Cured Only Tape Adhesion MEK Double Rubs

0% loss 196

16% loss > 300

UV • Thermal Bump Tape Adhesion MEK Double Rubs

0% loss > 300

100% loss > 300

(1) Used at 68% T R S in TPGDA

UV Cured With Two 200 Watt/Inch lamps & 100 Ft/Min



192

measurement. The c o a t i n g s were t h e n s t a i n e d f o r 2 h o u r s w i t h y e l l o w mustard. A f t e r w i p i n g o f f t h e mustard, t h e r e s i d u a l s t a i n was measured w i t h t h e Hunter meter. F i g u r e 14 shows t h a t a d d i t i o n o f AM 6 t o t h e a l i p h a t i c urethane w i l l significantly r e d u c e mustard s t a i n i n g when a p o s t UV t h e r m a l bump i s u s e d . The r e d u c t i o n i n mustard s t a i n i n c r e a s e s w i t h i n c r e a s i n g l e v e l s o f AM.


35

8800

60:20

40:40

20:60

AM 6

Aliphatic UrethaneiAcrylated Melamine I

I UV Cured

• • UV • 5' e> 150 C

F i g u r e 14. The e f f e c t o f mustard s t a i n i n g on AM m o d i f i e d of urethane a c r y l a t e .

films

CONCLUSIONS A c r y l a t e d melamines have p r o p e r t i e s which make them s u i t a b l e f o r u s e i n UV c u r a b l e c o a t i n g s . P r o p e r t i e s c a n be v a r i e d by a d j u s t i n g t h e combined a c r y l a m i d e c o n t e n t and t h e i n c l u s i o n o f o t h e r m o d i f i e r s . F o r m u l a t i o n v i s c o s i t i e s a r e s a t i s f a c t o r y f o r normal a p p l i c a t i o n methods, and f i l m s c u r e t o a h i g h degree o f h a r d n e s s a t p r a c t i c a l i r r a d i a t i o n l e v e l s . B e n e f i t s demonstrated i n c l u d e improved t a p e and s c r a t c h a d h e s i o n , a b r a s i o n r e s i s t a n c e , c o l o r , and Q-U-V d u r a b i l i t y . A c r y l a t e d melamines c a n a l s o c u r e by c o n d e n s a t i o n r e a c t i o n s . The c o n d e n s a t i o n r e a c t i o n s w i l l p r o c e e d e i t h e r b e f o r e o r a f t e r a UV cure. Use o f a c r y l a t e d melamines i n a d u a l c u r e p r o c e s s a l l o w s a u n i q u e c o m b i n a t i o n o f melamine c o n d e n s a t i o n and a c r y l a t e f r e e r a d i c a l addition chemistries. This can r e s u l t i n increased hardness, improved s t a i n r e s i s t a n c e , and d u r a b i l i t y . ACKNOWLEDGMENTS The a u t h o r w i s h e s t o t h a n k t h e Monsanto P h y s i c a l and A n a l y t i c a l Science Center and P a u l D. G a r r e t t f o r t h e DMA analysis. C o n t r i b u t o n s and i n s i g h t s from L o r e n W. H i l l , R o b e r t T. Jones, D a v i d M. Lademan, N e i l J . M o r e l l i and George E . S h e l d r i c k are also appreciated.


14.

GUMMESON

Literature


Cited

(1) Strazik, W.F.; Leblanc, J.R.; Santer, J.O. U.S Patent 4 293 461, 1980. (2) Resimene Amino Crosslinker Resins for Surface Coatings, Monsanto publication No. 6515D (3) Sirkock, R.J.; Niederst, K.W.; Weissberg, A.B.; Greigger, P.P.; Henning, C.C. U.S. Patent 4 745 003, 1988. (4) Hill, L.W.; Kozlowski, K. J. Coatings Tech 1987, 59, 751. (5) Decker, C.; Moussa, Κ. J. Polym. Sci. 1987, A2, 739. 1989


RECEIVED July 17,


193

Acrylated Melamines in UV-Curable Coatings - ACS Symposium

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