[acs symposium series] radiation curing of polymeric materials volume 417 || novel photoinitiator...

Chapter 8

Novel Photoinitiator for Modern Technology

V. Desobry, K. Dietliker, R. Hüsler, L. Misev, M. Rembold, G. Rist, and W. Rutsch

Additive Research, Ciba-Geigy Ltd., CH-1701 Fribourg, Switzerland

2-Benzyl-2-dimethylamino-1-(4-morpholinophenyl)-bu-tanone-1 (BDMB) has been synthesized and shown to be an efficient photoinitiator for UV curing applications. Photochemical and CIDNP investigations suggest that photochemical decomposition occurs mainly via α-cleavage. In comparison with other photoinitiators, BDMB provided superior results in pigmented systems and imaging applications.

Advances i n the f i e l d of UV-curing n e c e s s a r i l y engender the development of s p e c i a l i z e d p h o t o i n i t i a t o r s that meet the s p e c i f i c needs of new a p p l i c a t i o n s . Whereas the prepolymer determines many p h y s i c a l c h a r a c t e r i s t i c s of the cured f i l m such as g l o s s , hardness, solvent and scratch r e s i s t a n c e , e t c . , the p h o t o i n i t i a t o r must ensure the proper c u r i n g of the f i l m . The s e l e c t i o n of the p h o t o i n i t i a t o r i s espec i a l l y important when absorbing species such as pigments or s t a b i l i zers are added to the prepolymer.

Our research i n t h i s area has focused upon the t a i l o r i n g of the p h o t o i n i t i a t o r not only to the formulation but a l s o to the c u r r e n t l y a v a i l a b l e l i g h t sources. In a preceeding p u b l i c a t i o n [ 1_], we d i s c u s sed the s p e c i f i c a p p l i c a t i o n s of three s t r u c t u r a l l y d i s t i n c t photo-i n i t i a t o r s . We now present a new alpha-cleavage p h o t o i n i t i a t o r 2-benzyl -2-dimethylamino -1-(4-morpholinophenyl)-butanone -1 (BDMB) which promises great u t i l i t y i n various branches of the graphic a r t s and p r i n t i n g technology.

Synthesis and Prope r t i e s of BDMB

Synthesis. The synthesis of BDMB and i t s analogs re q u i r e s an e f f i c i e n t strategy f o r the co n s t r u c t i o n of the amino-substituted quater-

0097-6156/90/0417-0092$06.00/0 ο 1990 American Chemical Society

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

8. DESOBRY ET AL. Novel Photoinitiator for Modern Technology 93

nary center, οό ,οό - D i s u b s t i t u t e d amine-ketones cannot be prepared by the simple r e a c t i o n of amines with the corresponding oL -bromoketones. While db , cC-dimethyl d e r i v a t i v e s are e a s i l y obtained by the a d d i t i o n of morpholine to intermediate epoxyether [,2] [3], t h i s transformation f a i l s when the epoxyether i s s u b s t i t u t e d with s t e r i c a l l y demanding a l k y l groups. To circumvent t h i s problem, we employed the intramolec u l a r Stevens rearrangement [4^ [5] to create the quaternary center, thereby gaining access to a great v a r i e t y of h i g h l y s u b s t i t u t e d aC -aminoketones (see Figure 1) [6^.

Absorption C h a r a c t e r i s t i c s . C l e a r l y , only compounds having strong absorptions i n the emission range of the l i g h t source can serve as e f f i c i e n t p h o t o i n i t i a t o r s . This allows the d i r e c t e x c i t a t i o n of the p h o t o i n i t i a t o r to an e x c i t e d s t a t e where i t s e f f i c i e n t conversion to r e a c t i v e species ( r a d i c a l s i n the case of alpha-cleavage type photo-i n i t i a t o r s ) i s e s s e n t i a l . The absorption spectra of two commercial p h o t o i n i t i a t o r s BDK (I) and MMMP (II) [J] as wel l as BDMB are reproduced i n Figure 2. I t i s apparent that BDMB, which e x h i b i t s a strong absorption at 322 nm., 16 nanometers higher than the s t r u c t u r a l l y r e l a t e d I I , i s the p h o t o i n i t i a t o r which best matches the emission l i n e s of the medium pressure mercury lamp. These absorption c h a r a c t e r i s t i c s a l s o allow i t s a p p l i c a t i o n i n the curin g of pigmented systems as wel l as i n r e s i s t formulations and flex o g r a p h i c p r i n t i n g p l a t e s .

Photochemi s t r y

The photochemistry of οί> -amino acetophenone d e r i v a t i v e s has been shown by various groups to be st r o n g l y dependent upon the oC -carbon and nitrogen s u b s t i t u e n t s . Unsubstituted oC -(dialkylamino)-acetophe-nones (-CO-CH^-Nialkyl) 2) undergo an e f f i c i e n t e l i m i n a t i o n r e a c t i o n upon i r r a d i a t i o n (Figure 3a) to a f f o r d acetophenone and imines as the sole products [8] [9] [103.

However, when the lone p a i r on the amine i s a par t of a 7T-sy-stem (N-Acyl [8] [1J_] [ 1_2], N-Tosyl [V2] or N-Phenyl [1_3] M 4 ] ) 3 " a z e t i d i n o l s are obtained, v i a c y c l i z a t i o n of an intermediate 1,4-di-r a d i c a l , unless s t e r i c f a c t o r s prevent the formation of the four-mem-bered r i n g (Figure 3b).

These r e s u l t s , and the observation that the photoelimination of où-(dialkylamino)acetophenones i s not suppressed by the standard t r i p l e t quenchers can be explained by a mechanism i n v o l v i n g e l e c t r o n t r a n s f e r from the amine to the carbonyl group [8] (Figure 3a). Lower i n g the i o n i z a t i o n p o t e n t i a l of the amine, i . e . by a c e t y l a t i o n , s u l -f o n y l a t i o n , e t c . , d i s f a v o r s the e l e c t r o n t r a n s f e r pathway and r e s u l t s i n y-hydrogen a b s t r a c t i o n .

I r r a d i a t i o n of N-phenylacetophenones (Figure 3c) furnishes products r e s u l t i n g from d i r e c t ^ - c l e a v a g e [j_3] [J_4]. Geminally disub-s t i t u t e d d e r i v a t i v e s (R* = CH^) undergo p h o t o l y t i c decomposition v i a both oC - and β -cleavage pathways [V3]. Predominant où -cleavage i s observed upon p h o t o l y s i s of II [_3] [15]. This trend i n r e a c t i v i t y can be explained by the i n t e r p l a y of two f a c t o r s :

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RADIATION CURING OF POLYMERIC MATERIALS

Figure 1. Synthesis of BDMB.

Abeocbance

10H

0 ^

BDK MMMP

BDMB

2Ô0 300 Γ So (0.001% in MeOH) (nm)

Figure 2. Absorption spectra of benzildimethylketal (BDK), 4-methyl-thiophenyl-2-morpholino-2-methyl-propanone-l (MMMP) and BDMB (concentration: 0,001 % in methanol).

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DESOBRY ET AL. Novel Photoinitiator for Modem Technology

Ar-C-CH,. -N 2 W

Γ A r — C

X H H

/?-Cleavage || χ Γ χ > Ar-C-CH 3 + R

Ar-C-CH„-N_ 2 \

OH Ar-C N - ®

Ar-C-C-N R< \ > h e n y l

? I ^ Ar-C-

CH. Phenyl

R'-H « s, Ar-C-CH 2- + -N

Ο CH. Il ' 3

Ar-C-4' CH.

I products

\ Phenyl

R

Phenyl

products

Figure 3. Photochemical r e a c t i o n pathways of cù -amino acetophenones.

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96 RADIATION CURING OF POLYMERIC MATERIALS

1 . i n c r e a s i n g s u b s t i t u t i o n at the cC -carbon favors $6 -cleavage due to the weakening of the acyl-οί-carbon bond [_^6] ; and

2 . e l e c t r o n donating groups (alkoxy, amino, etc.) i n the ^ - p o s i t i o n can s t a b i l i z e the t r a n s i t i o n s t a t e of où -cleavage by i n t e r a c t i o n of a lone p a i r of ele c t r o n s with the breaking carbon-carbon bond [ J_7 ] .

In view of the continuum of r e a c t i v i t y e x h i b i t e d by t h i s c l a s s of compounds, the photochemistry of BDMB was i n v e s t i g a t e d .

CIDNP Spectrum of BDMB. The CIDNP technique can provide much u s e f u l information on processes i n which r a d i c a l species are formed and has been used to determine the species r e s p o n s i b l e f o r the i n i t i a t o r act i v i t y of compounds such as I and II [2] [3] [Ji_8] [ J _ 9 ]. The NMR spectrum taken during p h o t o l y s i s of BDMB was obtained under s i m i l a r cond i t i o n s as employed f o r the study of I and II [ ^ 0 ] [ 21_ ]. The enhanced s i n g l e t absorption at 9 , 6 3 ppm (Figure 4 ) i s assigned to 4-morpho-linobenzaldehyde I I I which must r e s u l t from an i n i t i a l oi -cleavage of BDMB to engender a benzoyl and aminoalkyl r a d i c a l p a i r (Figure 5 ) . The aldehyde p o l a r i z a t i o n , according to Kaptein's r u l e s [ 2 ! 2], and the ESR parameters f o r these two r a d i c a l s are i n f u l l agreement with a t r i p l e t s t a t e precursor. By comparing the spectra obtained i n d i f f e r e n t solvents, i t was determined that the r a d i c a l p a i r i s formed ess e n t i a l l y v i a an unimolecular process, thus r u l i n g out the p h o t o l y t i c decomposition of BDMB v i a intermolecular e l e c t r o n t r a n s f e r or other bimolecular r e a c t i o n s . The two quartets at 4 . 4 6 and 4 . 6 2 ppm which e x h i b i t enhanced absorptions are assigned to the o l e f i n i c protons of IVa and b. The s i n g l e t s a t 5 . 2 8 ppm (emission) and 5 . 3 3 ppm (enhanced absorption) are a t t r i b u t e d to the o l e f i n i c protons i n Va and b. The pattern of these s i g n a l s i s due to the combination of cage r e a c t i o n s l e a d i n g to products e x h i b i t i n g absorption p o l a r i z a t i o n and escape r e actions f u r n i s h i n g the same products but e x h i b i t i n g emission pol a r i z a t i o n . The spectrum i n deuterated cyclohexane (Figure 4 ) and the CIDNP experiments i n other solvents lead to the conclusion that the formation of Va and b occurs p r e f e r e n t i a l l y v i a escape r e a c t i o n s whereas f o r the p o l a r i z a t i o n s of IVa and b the c o n t r i b u t i o n of the cage r e a c t i o n i s s l i g h t l y l a r g e r .

Preparative Photochemistry. I r r a d i a t i o n of BDMB on a preparative scale [23^] leads to a product mixture that would be expected based upon the r e s u l t s of the CIDNP experiments (Figure 6 ) . In benzene, the main photoproducts are 4-morpholinobenzaldehyde I I I ( 2 1 %) and 1-phenyl-butan - 2-one VII ( 3 2 % ) . The l a t t e r compound i s be l i e v e d to a r i s e from h y d r o l y s i s of the i n i t i a l l y formed enamines during workup. On the basis of our experiments, however, other pathways f o r i t s formation cannot be completely r u l e d out. The deaminated d e r i v a t i v e VIII was al s o i s o l a t e d i n 11 % y i e l d i n d i c a t i n g t h a t competing react i o n s - i . e . N o r r i s h type II or d i r e c t -cleavage - a l s o take place. S u r p r i s i n g l y N,N-dimethyl -4-morpholinobenzamid VI was i s o l a t e d i n 1 9 %. The mechanism of the formation of VI w i l l be the subject of subsequent i n v e s t i g a t i o n s . I r r a d i a t i o n of BDMB i n isopropanol a f f o r d s the same products a l b e i t i n s l i g h t l y d i f f e r e n t r a t i o s .

Dodecanthiol IX has been o f t e n used as a scavenger f o r non-cage benzoyl r a d i c a l s [ 2 £ ] [ 2 5 J . I r r a d i a t i o n of BDMB i n benzene with a

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8. DESOBRY ET AL. Novel Photoinitiator for Modem Technology 97

4.46/4.62 ppm.q

V C H ,

BDMB

CH, hv

CH,

CH, CH,

CH, CH.

^ ^ 9 IVa, b Q ^ j H y K - H *

III / 9.63 ppm.8

5.32 ppm.8 Λ^0*** 5.28 ppm.8 I ι

CH.CH,

V

Figure 5. Decomposition products of BDMB detected by CIDNP.

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large excess of IX afforded I I I i n 88 % y i e l d (Figure 7) as well as products r e s u l t i n g from the r e a c t i o n of the benzoyl r a d i c a l with 1-dodecanthiyl r a d i c a l s (X, 6 % ) . The trapping product of the ̂ -aminoalkyl r a d i c a l was a l s o obtained (XI, 50 %).

The decomposition of various p h o t o i n i t i a t o r s i n t o carbon centered r a d i c a l s has a l s o been i l l u s t r a t e d by Hageman [25] who used TMPO ( 2 , 2 , 6 , 6-tetramethylpiperidinoxyl) as a trapping agent. A d d i t i o n of a t h r e e f o l d excess of TMPO to a s o l u t i o n of BDMB r e s u l t s i n the f o r mation of XII i n high y i e l d (91 %) (Figure 8). VII could a l s o be i s o l a t e d . This product may a r i s e from an i n s t a b l e primary a d d i t i o n product (XIII) of TMPO and the où -amino-alky1 r a d i c a l which i s hydroly-sed during work-up. These r e s u l t s a l s o confirm t h a t the dominant pathway of decomposition i s t h a t of où -cleavage.

Trapping Reactions with 2 - t - B u t y l a c r y l i c A c i d Methylester XIV. This trapping r e a c t i o n , which mimics the i n i t i a t i o n step of the polymeris a t i o n process, has been used to obtain information on the r e a c t i v i t y of the primary r a d i c a l s formed upon i r r a d i a t i o n [J_] [_26 ]. P h o t o l y s i s of BDMB i n the presence of a t h r e e f o l d excess of XIV a f f o r d s the benz o y l d e r i v a t i v e XV i n 87 % y i e l d (Figure 9). Again VII was a l s o i s o l a t e d (64 % ) , whereas no st a b l e a d d i t i o n product of cC -aminoalkyl r a d i c a l could be i d e n t i f i e d . This r e s u l t suggests that the benzoyl r a d i c a l i s mainly r e s p o n s i b l e f o r the polymerisation of v i n y l i c monomers and i s i n agreement with previous studies on b e n z i l k e t a l s and benzoin ethers [27]. But, as où -aminoalkyl r a d i c a l s have a l s o been shown t o i n i t i a t e a c r y l a t e polymerization [28], f u r t h e r i n v e s t i g a t i o n s w i l l be devoted to the e l u c i d a t i o n of the r o l e of t h i s primary photoproduct i n the o v e r a l l polymerisation process.

A p p l i c a t i o n Studies with BDMB

White Pigmented Lacquer. BDMB was incorporated i n t o the formulation at concentration l e v e l s up to 5 %, and the r e s u l t i n g low v i s c o s i t y lacquer was ap p l i e d to an aluminium f o i l t o form a 30 g/m f i l m . Cur i n g was achieved by passing the sample through a conveyor system equipped with two 80 watt/cm medium pressure mercury lamps. The react i v i t y of the UV-curable coating was q u a n t i f i e d i n terms of the maximum conveyor b e l t speed y i e l d i n g s u f f i c i e n t cure. The l a t t e r i s determined by the r e s i s t a n c e of the coating against rubbing with t i s s u e paper.

As demonstrated i n Figure 10, BDMB markedly exceeds i t s s t r u c t u r a l analog II i n photopolymerization r e a c t i v i t y . Even though a d d i t i o n of an e f f i c i e n t t r i p l e t s e n s i t i z e r , isopropyl-thioxanthone (ITX) boosts the performance of the l a t t e r by a f a c t o r of s i x , i t s r e a c t i v i t y i s s t i l l i n f e r i o r to th a t of BDMB. Th i s observation can be r a t i o n a l i z e d by comparing the absorption spectra of BDMB, I I , ITX and titanium d i o x i d e . While II i s e f f i c i e n t l y screened from i n c i d e n t UV r a d i a t i o n by titanium d i o x i d e , BDMB s t i l l absorbs above the c u t - o f f wavelength of titan i u m d i o x i d e . The marked increase i n r e a c t i v i t y of II i n the presence of ITX r e s u l t s from t r i p l e t s e n s i t i z a t i o n by ITX [26] which a l s o absorbs a t longer wavelength than titanium d i o x i d e .

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DESOBRY ET AL. Novel Photoinitiator for Modem Technology

<QhQ-%m 21 %

I

0 Ο ν

BDMB 32 %

VI

0 ^ { H 11%

VI

Figure 6 . Preparative p h o t o l y s i s of BDMB.

^CH. CH^SH

^CH,

Χ e%

< Q - @ £ « III 8 8 %

.CH, CH. BDMB ix -CH.

Figure 7. P h o t o l y s i s of BDMB: Trapping with Η-donor.

» 60%

Figure 8. P h o t o l y s i s of BDMB: Trapping with TMPO.

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COOCH,

V C H , \ (

BDMB xiv

COOCH,

J O

CH,

XV

CH, • 1^/CH,

CH, \ H , CH, ^CH,

Η,Ο j 0}

VII Figure 9. Pho t o l y s i s of BDMB: Trapping with a non-polymerisable a e r y l a t e .

Photoinitiators Maximum belt speed (m/min)

2%

-

2% 0.5 ITX mmm eo

V C H , V C H , V C H , 170

Figure 10. Comparison of BDMB and II i n a white pigmented l a c quer. Dry f i l m thickness: 15 microns Radiation source: 2 χ 80 W/cm medium pressure Hg lamps.

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8. DESOBRYETAL. Novel Photoinitiator for Modern Technology 101

O f f s e t P r i n t i n g Inks. BDMB a l s o proved to be s l i g h t l y more e f f i c i e n t than II i n the UV-curing of urethane based blue pigmented systems (Figure 11).

The high performance of these oC -amino s u b s t i t u t e d acetophenone p h o t o i n i t i a t o r s i s best explained by the f a c t t h a t both possess suff i c i e n t absorption i n the region where the i n c i d e n t l i g h t i s not f i l t e r e d by the pigment.

R e s i s t Formulations. In t h i s study we used two aqueous r e s i s t systems, an etch and a solder mask. Both are based on polymeric a c r y l a -te r e s i n s with c a r b o x y l i c groups and m u l t i f u n c t i o n a l a c r y l a t e monomers as c r o s s l i n k i n g agents. The a c i d numbers of the etch and the solder formulation are 90 and 45 mg KOH/g r e s p e c t i v e l y .

The s e n s i t i v i t y to photopolymerisation was determined by the highest step on an o p t i c a l density wedge a t which complete c u r i n g of the formulation was observed. Results are g r a p h i c a l l y represented i n Figure 12. Here BDMB i s compared to I, a b e n z i l k e t a l widely used f o r t h i s a p p l i c a t i o n . While the performance of the two p h o t o i n i t i a t o r s i s comparable i n the etch r e s i s t , use of BDMB i n the solder r e s i s t r e s u l t s i n e f f i c i e n t c u r i n g 7 density steps higher than I. This corresponds to an approximate 11-fold increase i n r e a c t i v i t y i n t h i s l e s s a c i d i c formulation. This observation and f u r t h e r i n v e s t i g a t i o n s i n d i c a t e that the r e a c t i v i t y of BDMB i s impaired i n an a c i d i c e n v i ronment due to protonation of the t e r t i a r y amine sub s t i t u e n t où to the keto group.

Flexographic P r i n t i n g P l a t e . This photoimaging system i s based on a styrene butadiene copolymer and a m u l t i f u n c t i o n a l a c r y l a t e monomer as a c r o s s l i n k i n g agent. P r i o r to exposure of the f r o n t s i d e to near UV r a d i a t i o n through a negative photomask, the reverse side i s e n t i r e l y exposed to form a s o l i d base. Again, as with the aforementioned r e s i s t formulation we chose to compare BDMB with I since the l a t t e r i s widely used i n flexography p r i n t i n g p l a t e s . As shown i n Figure 1 3 a cured product of better q u a l i t y can be obtained u t i l i z i n g lower conc e n t r a t i o n s of BDMB.

These r e s u l t s can be e a s i l y explained by examining Figure 14 and 15. The f i r s t f i g u r e shows the overlap between the emission band of the BASF N y l o p r i n t bulb (a l i g h t source commonly employed i n p r i n t i n g p l a t e technology) and the absorption bands of BDMB, I and I I . The l a t t e r two e x h i b i t a small overlap, whereas BDMB can absorb a s i g n i f i c a n t p a r t of the emitted l i g h t . In other words BDMB (Figure 14) having a much l a r g e r e x t i n c t i o n c o e f f i c i e n t at 366 nm can be employed at lower concentrations a f f o r d i n g a formulation of high o p t i c a l d e n s i t y .

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Photoinitiators Maximum belt speed (m/min)

0 CH,

CH,

3%

PPP «H 130 60

O P CH

V C H ,

3%

111 If

70 1 6 0

S B Surface cure • Body cure

Figure 11. Comparison of BDMB and II i n a blue o f f s e t p r i n t i n g ink. Dry f i l m thickness: 1,5 microns Radiation source: 80 W/cm medium pressure Hg lamp.

Photoinitiator Sensitivity on 21 step density wedge

ο O C H*

OCH,

2%

• I 8

14

Etch resist Solder resist

Figure 12. Comparison of BDMB and I i n two r e s i s t formulations (exposure d i s t a n c e : 30 cm).

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DESOBRY ET AL. Novel Photoinitiator for Modern Technology

0.5% 1.2% ® - " - Η § > OCH,

Reverse side exposure/min

Tonal value 2% 3%

Mechanical rigidity At time of 2% tonal value Hole depth/um Relief depth/Mm

40 450

1.5 6

3 4

3 5

Β 35 380 J

Figure 13. Comparison of BDMB and I in a flexographic printing plate (radiation source: BASF Nyloprint bulb, 350-400 nm).

BDK 0.05% MMMP 0.05% BDMB 0.05%

100

g 80

I 6 0

CO 1 40

20

0

i

/ g- Λ Â 300 350 400

5 0 0 J 400 -S

300 J 200 §

100 Ι S ο

0 S 450 Wavelength

Figure 14. Emission spectrum of a riASF N y l o p r i n t bulb vs. absor p t i o n of BDK ( I ) , MMMP (II) and BDMB.

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BDK BDMB

CO c φ Ο β .9 ο. Ο

3.0

2.5

2.0

1.5

1.0

0.5

0.0 **"

3.0 2.5 2.0 1.5 1.0 0.5 0.0

0.0 0.4 0.8 1.2 1.6 Photoinitiator concentration (%)

2.0

Figure 15. Influence of the i n i t i a t o r concentration on the opt i c a l d e n s i t y at 370 run f o r a r e l i e f height of 600 microns.

Literature Cited

1. Desobry, V.; Dietliker, K.; Hüsler, R.; Rutsch, W.; Loeliger, H. Polym. Paint J. 1988, (Suppl.), 125.

2. Kirchmayr, R.; Berner, G.; Hüsler, R.; Rist, G. Farbe und Lack 1982, 88, 910.

3. Rutsch, W.; Berner, G.; Kirchmayr, R.; Hüsler, R.; Rist, G.; Bühler, N. In Organic Coatings - Science and Technology Vol 8; Parfitt, G; Patsis, Α., Eds.; M. Dekker: New York, 1986; p. 175.

4. Stevens, T.S.; Creighton, E.M.; Gordon, A.B.; MacNicol, M. J. Chem. Soc. 1928, 3193; Stevens, T.S. ibid. 1930, 2107; Stevens, T.S.; Snedden, W.W.; Stiller, E.T.; Thomson, T. ibid. 1930, 2119; Thomson, T.; Stevens, T.S. ibid. 1932, 55; Dunn, J.L.; Stevens, T.S. ibid. 1932, 1926; Thomson, T.; Stevens, T.S. ibid. 1932, 1932.

5. Chantrapromma, K.; Ollis, W.D.; Sutherland, I.O. J. Chem. Soc. Chem. Commun. 1978, 670, and references cited therein.

6. Desobry, V.; Dietliker, K.; Hüsler, R.; Rembold, M.; Sitek, F. Eur. Patent Appl. 284561, 1987.

7. I and II are products of CIBA-GEIGY Ltd., commercialized under the names IRGACURE 651 and 907 respectively.

8. Padwa, Α.; Eisenhardt, W.; Gruber, R.; Pashayan, D. J. Am. Chem. Soc. 1971, 93, 6998.

9. Wagner, P.J.; Kemppainen, A.E.; Jellinek, T. J. Am. Chem. Soc. 1972, 94, 7512.

10. Hyatt, J.A. J. Org. Chem. 1972, 37, 1254. 11. Gramain, J.-C.; Ouazzani-Chahdi, L.; Troin, Y. Tetrahedron

Lett. 1981, 22, 3185. 12. Gold, E.H. J. Am. Chem. Soc. 1971, 93, 2793. 13. Allworth, K.L.; El-Hamamy, A.A.; Hesabi, M.M.; Hill, J.

J. Chem. Soc. Perkin Trans. I 1980, 1671. 14. Hill, J.; Zakaria, M.M.; Mumford, D. J. Chem. Soc. Perkin

Trans. I 1983, 2455. 15. Meier, K.; Rembold, M.; Rutsch, W.; Sitek, F. In Radiation

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8. DESOBRY ET AL. Novel Photoinitiator for Modern Technology 105

Curing of Polymers; Randell, D.R., Ed.; Special Publication No 64. Royal Society of Chemistry: London 1987; p 196.

16. Turro, N.J. Modern Molecular Photochemistry: Benjamin/Cum-mings: Menlo Park, CA 1978; p. 528.

17. Heine, H.-G.; Traenker, H.-J. Progr. Org. Coat. 1975, 3, 115. 18. Borer, A.; Kirchmayr, R.; Rist, G. Helv. Chim. Acta 1978, 61,

305; Kirchmayr, R.; Berner, G.; Rist, G. Farbe und Lack 1980, 86, 224.

19. Yankelevich, A.Z.; Potapov, V.K.; Hageman, H.-J.; Kuznets, V.M.; Pershin, A.D.; Buchachenko, A.L. Izv. Akad. Nauk. SSSR, Ser. Khim. 1982, 513; Chem. Abstr. 1982, 96, 217061u.

20. BDMB was dissolved in perdeuterated solvents (C6D6, C6D12, CD3CN, (CD3)2CDOD).

21. CIDNP spectra were recorder using a varian XL 100 spectrometer. In situ irradiation was effected with UV light (1 kw -high pressure Hg lamp - Philips SP-1000). To avoid IR or visible components, an aqueous filter solution of NiSO4 and CoSO4

was employed. 22. Kaptein, R. J. Chem. Soc. Chem. Commun. 1971, 732; Kaptein, R.

J. Am. Chem. Soc. 94, 6251 (1972). 23. 10-2M solutions of BDMB in benzene or isopropanol were irra

diated with a Philips HPK 125 mercury lamp located centrally in water cooled Pyrex Finger. Irradiation was continued until disappearance of the starting material. After evaporation of reaction solvent, the products were separated using column chromatography on silicagel.

24. Lewis, F.D.; Magyar, J.G. J. Am. Soc. 1973, 95, 5973. 25. Hageman, H.J.; Overeem, T. Makromol. Chem., Rapid Commun. 1981

2, 719. 26. Dietliker, K.; Rembold, M.; Rist, G.; Rutsch, W.; Sitek, F.

Radcure Europe 87, Conf. Proc. 3th; 3/37; Assoc. Finish. Processes SME: Dearborn, MI, 1987.

27. Groeneborn, C.J.; Hageman, H.-J.; Overeem, T.; Weber, A.J.M. Makromol. Chem. 1982, 183, 281.

28. Hageman, H.-J. Progr. Org. Coat. 1985, 13, 123.

RECEIVED September 13, 1989

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