CA1270089A

CA1270089A - Photopolymerizable composition

Info

Publication number: CA1270089A
Application number: CA000514865A
Authority: CA
Inventors: Masami Kawabata; Koichi Kimoto; Yasuyuki Takimoto
Original assignee: Nippon Paint Co Ltd
Current assignee: Nippon Paint Co Ltd
Priority date: 1985-08-01
Filing date: 1986-07-29
Publication date: 1990-06-05
Anticipated expiration: 2007-06-05
Also published as: DE3677276D1; AU6075786A; EP0211615B1; AU590305B2; EP0211615A2; EP0211615A3; US4766055A

Abstract

Abstract:
The invention relates to a photopolymerizable composition which is very sensitive to visible light.
The composition comprises a polymerizable compound and a photopolymerization initiator. The photopolymerization initiator comprises (a) a xanthene or thioxanthene dye-stuff having a particular formula, (b) a photosensitizer selected from the group consisting of N-phenylglycine, 2,4,6-tris(trichloromethyl)-1,3,5-triazine, and a mixture of p-dimethylaminobenzoic acid isopentyl ester and 2,4-diisopropylthioxanthone, and (c) a peroxide.

Description

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Photopolymerizable composltion The present invention relates to a photopoly-merizable composition which is cured by exposure to light sources containing visible light or ultraviolet light.
More particularly, the present invention relates to a photopolymerizable composition which can be used for the formation of litho printing plates, resists for producing printed circuit boards, or original editions for preparing mother plates for rainbow holograms.
Photosensitive compositions comprising a photosensitive component, such as a diazonium salt, an azide or a quinonediazide, or photohardening compositions comprising a photocrosslinkable component are used in photographic techniques for image formation. Most of these compositions are sensitive to ultraviolet light but not sensitive to visible light. This is a problem because it is often desired to carry out the printing by exposure to visible light instead of ultraviolet light.
Scanning exposure techniques employing laser beams have recently advanced and it is possible that these techniques may be applied to imaging procedures. If so, the use of a visible light laser, such as an argon laser, -is more desirable than an ultraviolet laser because of the lower energy and equipment costs. Accordingly, a composition which is sensitive to visible light is strongly desired.
Japanese Patent Publication No. 114139/1982 and .
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Japanese Patent Application Ser. No. 170599/1985 disclose a photopolymerizable composition sensitive to visible light having a wavelength of 400 to 700 nm, wherein a dyestuff is combined with a photosensitizer. These photopolymeriz-able compositions still have low sensitivity to visiblelight and, therefore, require the use of a high output laser when applied to imaging techniques using laser scanning systems. Accordingly, further improvements of the sensitivity are required.
It has now been found that certain kinds of xanthene or thioxanthene dyestuffs are very sensitive to visible light when combined with a polymerizable monomer, a photosensitizer and an organic peroxide. It also has been found that the resulting cured composition exhibits good physical properties for the uses mentioned above.

According to the invention, there is provided a photopolymerizable composition which is sensitive to visible light. The composition comprises a polymerizable compound and a photopolymerization initiator wherein the photopolymerization initiator comprises:

(a) a xanthene or thioxanthene dyestuff having the following formula;

> ~ ~ R2 ~I) X

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~27~)~89 wherein A represents an oxygen atom or a sulfur atom, X represents a hydrogen atom or a halogen atom, Y
represents a carbon atom or a nitrogen atom (provided that when Y represents a carbon atom, the bond with an adjacent S carbon atom, which is shown by a dotted line, is a double bond and when Y represents a nitrogen atom, the bond with the adjacent carbon atom is a single bond), Z represents an oxygen atom wherein the bond with an adjacent carbon atom is a double bond, a lower alkoxy group or a lower alkanoyloxy group, Rl represents a lower alkyl group, a lower alkoxy lower alkyl group, a hydroxy-lower alkyl group, di-(lower) alkylamino lower alkyl group or an aryl group, R2 represents a hydrogen atom, a lower alkoxy group or di-(lower) alkylamino group, wherein in some cases Z and Rl together represent the formula;

-N

(b) a photosensitizer selected from the group consisting of N-phenylglycine, 2,4,6-tris(trichloromethyl)-1j3,5-triazine, and a mixture of p-dimethylaminobenzoic acid isopentyl ester and 2,4-diisopropylthiozanthone, and (c) a peroxide.
The polymerizable compound of the present invention is usually a monomer having an ethylenically ~ ~.

127t~(~!89 unsaturated bond which enables an addition polymerization to occur during curing. The compound pre~erably has a boiling point of at least 100C.
Typical examples of the polymerizable compounds are unsaturated carboxylic acids, esters of unsaturated carboxylic acids and polyhydroxy compounds, and the like.
Suitable polyhydroxy compounds include aliphatic or arom-atic polyhydroxy compounds, and mixtures thereof. A poly-carboxylic acid which does not have an unsaturated bond can be mixed with the unsaturated carboxylic acid, if desired. Examples of suitable unsaturated carboxylic acids are acrylic acid, methacrylic acid, itaconic acid, crotonic acid, maleic acid and the like. Examples of aliphatic polyhydroxy compounds are diols, e.g. ethylene glycol, diethylene glycol, triethylene glycol, tetra-ethylene glycol, neopentyl glycol, propylene glycol, 1,2-butanediol and the like; triols, e.g. trimethylol-ethane, trimethylolpropane, glycerol and the like; higher polyols, e.g pentaerythritol, tripentaerythritol and the like; and polyhydroxycarboxylic acids. Examples of aromatic polyhydroxy compounds are hydroquinone, resorcin, catechol, pyrogallol and the like. Examples of polycarboxylic acids having no r~
.

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unsaturated bond are phthalic acid9 isophthalic acid, terephthalic acid, tetrachlorophthalic ~cid, trimellitic a~id, pyromellitic acid, benzophenone dicarboxylic acid, glutaric acid, adipic acid, sebacic acid, tetrahydroph~halic acid and the like.
Examples of esters of aliphatic polyhydroxy compounds and unsaturated carboxylic acids are acrylates, e.~. ethylene glycol diacrylate, triethylene glycol diacrylate, tetramethylene glycol diacrylate, trimethylolpropane triacrylate, trimethylolethane trlacrylate, pentaerythrltol dlacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, dipentaerythritol tetraacrylate, dipentaerythritol pentaacrylate, dipentaerythritol hexaacrylate, tripentaerythritol octaacrylate, glycerol diacrylate;
methacrylate~, e.g. triethylene glycol dimethacrylate, tetramethylene glycol dimethacrylate, trimethylolpropane trimethacrylate, trimethylolethane trimethacrylate, pentaerythritol dlmethacrylate, pentaerythritol trlmethacrylate, pentaerythritol tetramethacrylate, dipentaerythritol dimethacrylate, dipentaerythritol trimethacrylate, dipentaerythritol tetramethacrylate, tripentaerythritol octamethacrylate, ethylene glycol dimethacrylate, 1,2-butanediol dimethacrylate, solbitol tetramethacrylate and the like; itaconates, e.g. ethylene glycol diitaconate, propylene glycol diitaconate, 1,2-butanediol diitaconate, tetramethylene glycol diitaconate, ~ . . .

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pentaerythritol triitaconate and the like; crotonates e.g.
ethylene glycol dicrotonate, diethylene glycol dicrotonate, pentaerythritol tetracrotonate and the like;
and maleates, e.g. ethylene glycol dimaleate, triethylene glycol dimaleate, pentaerythritol dimaleate and the like.
Examples of esters of unsaturated carboxylic acids and aromatic polyhydroxy compounds are hydroquinone diacrylate, hydroquinone dimethacrylate, resorcinol diacrylate, resorcinol dimethacrylate, pyrogallol triacrylate and the like. The esters which are obtained by an esterification of polyhydroxy compounds and a mixture of unsaturated carboxylic acids and polyhydric carboxylic acids are not always a single compound and may include the following:

Z ' -OC2H4-OOC-C6H4-COO-C2H40-Z
Z'-(OC2H4)2-OOC-(CH2)4-COO-(C2H40)2 Z
Z'-(OC2H4)~-OOC-CH-CH-COO-(C2H40)3-Z ' Z~-(c2H4)2-c ~ COO-(c2H4O)2 Z
z'-(OC2H4)2-0OC ~

Z ' -OCH2 ~C2H5 C2H5 C ~CH20 Z
Z'-OCH2''' \ CH2ooo-c6H4-coocH2~ CH2o-Z ' -OCH2 ~CH2 Z
. - CH-OOC-CH=CH-COO-CH
Z ' -OCH2~ \CH20-Z ' zl_Oc2H4-ooc-c6H4-coo-c2H4 OH

Z ' -OCH2~ ~CH2 Z
Z ' -OCH2--C-CH200C-C6H4 -COOCH2-C~OHH20-ZH

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~27(~ 85 Z ' -OCH2 ~ , OH20-Z ' Z'-OCH2- C-CH20OC-CH~CH-COOCH2-C- OH2O-Z' Z ' -OCH2-- ~OH20-Z ' z~-0C2H4-00c-(cH2)4-coo-lH2 z ~ -OC2H4-00C-(cH2)4-cOo-f~2 z-_0c2H4-OOC-(cH2)4-coo-cH2 S wherein Z' represents an acryloyl group or methacryloyl group.
Beside above compounds, the polymerizable compounds include acrylamides, e.g. acrylamide, ethylene-bis-acrylamide, hexamethylene-bis-acrylamide and the like; methacrylamides, e-g- ethylene-bis-methacrylamide, hexamethylene-bis-methacrylamide and the like; allyl ester~, e-g- diallyl phthalate, diallyl malonate, diallyl fumarate, triallyl isocyanurate; and vinyl-conta$ning co~pounds, e.g. divinyl adipate, divinyl phthalate, ethyleneglycol divinyl ether and the like.
The polyermizable compound may be a polymer having an unsaturated bond therein, in which case the unsaturated bond may be contained either in a main chain or a branched chain. Examples of polymers having an ethylen-ically unsaturated bond in the main chain include a poly-ester obtained from a condensation reaction of an unsatur-ated dicarboxylic acid and a dihydroxy compound, and a polyamide obtained from a condensation polymerization of an " ~.C,., ;. - '"' ~ ' unsaturated dicarboxylic acid and a diamine. Examples of unsaturated dicarboxylic acids are maleic acid, fumaric acid and the like. Examples of polymers having an ethylenically unsaturated bond in a branched chain are a polyester pre-pared from a condensation reaction of a dicarboxylic acid having an unsaturated bond in a branched and a dihydroxy compound, a polyamide prepared from a condensation reaction of the dicarboxylic acid havin~ an unsaturated bond in a branched chain and a diamine and the like. Examples of the dicarboxylic acids having an unsaturated bond are itaconic acid, ~-methylitaconic acid, ~-methylitaconic acid, propylidenesuccinic acid, ~-ethylideneglutaric acid, ethylidenemalonic acid, propylidenemalonic acid and the like. The polymer having an unsaturated bond in a branched chain can be prepared by introducing unsaturated groups in-to a polymer having at least one reactive functional group, e.g. hydroxy or halogenated alkyl. Examples of the polymers having functional group~ are polyvinyl alcohol; a copolymer of polyvinyl alcohol and a copolymerizable monomer e.g.
acrylonitrll, vinyl chloride, styrene, vinylidene chloride and the llke; polyepichlorohydrin ; a copolymer Or 2-hydroxyethyl methacrylate with acrylonitri~
methylmethacrylate, butyl methacrylate, styrene, vinylidene chloride, vinyl acetate and the like; a polyether prepared from the reaction of epichlorohydrin and 2,2-bis(4-hydroxyphenyl)-propane, poly(4-hydroxystyrene), poly(N-methylolacrylamide) and the like. The compound for ~.

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, ~27~ 89 g introducing the unsaturated groups may be acrylic acid, methacrylic acid, crotonic acid and the like.
Of the above polymerizabl~ compounds, acrylate monomers and methacrylate monomers are preferred.
According to the present invention, the photopolymerization initiator contains a xanthene or thioxanthene compound (1). In formula (I), a typical example of X ls chlor$ne, bromlne and the like. Examples of the lower alkoxy groups represented by Z are methoxy, ethoxy, propoxy,and the like and the lower alkanoyloxy groups are acetyloxy, propionyloxy, butylyloxy a~nd the like. Examples of R1 are a lower alkyl group, e.g.
methyl, ethyl, propyl, butyl, pentyl, nexyl, heptyl, octyl, nonyl, decyl and the like; a hydroxy lower alkyl group, e-g-hydroxymethyl, hydroxyethyl, hydroxypropyl, hydroxybutyl and the like; a lower alkoxy lower alkyl group, e.g.
methoxymethyl, methoxyethyl, methoxypropyl, ethoxyethyl, ethoxypropyl, ethoxybutyl, propoxyethyl, propoxypropyl and the like; a di-lower alkyl amino lower alkyl group, e.g.
dimethylamino0ethyl, dimethylaminoethyl, dimethylaminopropyl, diethylaminoethyl, diethylaminopropyl, diethylaminobutyl and the like; and an aryl group, e.g.
phenyl, xylyl, tolyl, naphthyl and the like. Examples of R2 are a lower alkoxy group, e.g. methoxy, ethyoxy, propoxy,and the like; di-lower alkylamino group, e.g.
2S dimethylamino, diethylamino and the like. The xanthene or thioxanthene dyestuff (I) is already known in the art.

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In the present invention, the photopolymerization initiator further contains a photosensitizer, by means of which the sensitivity to light sources is enhanced so that curing can be completed in a short period of time. Examples of the photosensitizers are N-phenylglycine, 2,4,6-tris(trichloromethyl)-1,3,5-triazine, and a mixture Or 2,4-dlisopropylthioxantone and p-dimethylaminobenzoic acid lsopentylester.
The photopolymerization initiator Or the present invention contains a peroxide. The pre~erred peroxides are selected from the group consi~ting of ketone peroxides, peroxy ketals, hydroperoxides, dialkyl peroxides, diacyl peroxides, peroxy dicarbonates, peroxy esters and the like. Typical exmaples of the peroxides are methyl ethyl ketone peroxide, cyclohexanone peroxide, 3,3,5-trimethylhexanone peroxide, methylcyclohexanone peroxide, acetylacetone peroxide, l,l-bis(t-butyl peroxy)-3,3,5-trimethylcyclohexane, 1,1-bis(t-butyl peroxy)cyclohexane, n-butyl-4,4-bis(t-butyl peroxy)v~lerate, 2,2-bis(t-butyl peroxy)butane, t-butyl hydroperoxide, cumen hydroperoxide, diisopropylbenzen hydroperoxide, paramenthane hydroperoxide,

2,5-dimethylhexane-2,5-dihydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, di-t-butyl peroxide, t-butyl cumyl peroxide, dicumyl peroxide, ,'-bis(t-butyl peroxy isopropyl)benzene, 2,5-dimethyl-2,5-di(t-butyl ; peroxy)hexane, 2,5-dimethyl-2,5-di(t-butyl peroxy)hexyn-3, acetyl peroxide, isobutylyl peroxide, octanoyl peroxide, ~ .

~Z7(~ 9 ~ecanoyl peroxide, lauroyl peroxide, 3,5,5-trimethyl hexanoyl peroxide, peroxysuccinic acid, benzoyl perox~de, 2,4-dichlorobenzoyl peroxide, m-toluoyl peroxide, diisopropyl peroxy dicarbonate, di-2-ethyl hexyl peroxy ~icarbonate, di-2-ethoxy ethyl peroxy dicarbonate, dimethoxy isopropyl peroxy carbonate, di(3-methyl-3-methoxybutyl)-peroxy dicarbonate, t-butyl peroxy pivalate, t-butyl peroxy neodecanoate, t-butyl peroxy octanoate, t-butyl peroxy-

3,5,5-trimethyl hexa~oate, t-butyl peroxy laurate, t-butyl ~eroxy benzoate, di-t-butyl peroxy isophtharate, 2,5-dimethyl-2,5-di(benzoyl peroxy)hexane, t-butyl peroxy malein, t-butyl peroxy isopropyl carbonate and the like.
The xanthene or thioxanthene dyestuff is preferably present in the composition in an amount of O.OOS to 0.3 part by weight, and more preferably 0.02 to 0.1 part by weight, per part by weight of the polymerizable compound. The amount of the photosensitizer is normally within the range of 0.005 to 0.3 part by weight, and preferably 0.02 to 0.1 part by weight, per part by weight of the polymerizable compound, wherein, when the mixture of p-dimethylaminobenzoic acid isopentyl ester and 2,4-diisopropylthioxantone is employed, the total amount should fall within the above ranges. The mixture is prepared by mixing 0.1 to 1.5 parts by weight, and preferably 0.3 to 1 part by weight, of 2,4-diisopropylthio-xanthone with one part by weight o p-dimethylaminobenzoic acid isopentyl ester. The peroxide is present in the composition in an amount of 0.005 to 0.2 part by weight, and preferably 0.01 to 0.08 part by weight, per part by weight ~ 'U

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of the polymerizable compound. Amounts less than the lower limit of each component do not impart the required photosensitivity to the composition. Amounts more than the upper limit of each component give a cured material of lower molecular weight, which decreases film hardness, solvent-resistance and the like.
The photopolymerizable composition of the present invention may contain polymeric binders, heat-polymeriz-ation inhibitors, plasticizers and coloring agents, if desired. The polymeric binders may improve compatibility, film-forming ability, developing capability, and adhesive properties. Typical examples of such polymeric binders are acrylic acid copolymers; methacrylic acid copolymers;

itaconic acid copolymers; partially esterified maleic acid copolymers; modified acidic cellulose having a branched carboxyl group; polyethylene oxide; polyvinylpyrolidone;
polyethers of epichlorohydrin and 2,2-bis(4-hydroxyphenyl) propane; polyamides; alkyl polytmeth)acrylates e.g. poly (methyl(meth)acrylate); copolymers of an alkyl acrylate with acrylonitrile, acrylic acid, methacrylic acid, vinyl chloride, vinylidene chloride, styrene and the like;
copolymers of acrylonitrile with vinyl chloride, or vinyl-idene chloride; copolymers of vinyl acetate with vinylidene chloride, a chlorinated polyolefin, or vinyl chloride;
polyvinyl acetate; styrene-acrylonitrile copolymers;

ABS, polyvinyl alkyl ethers, polyvinyl alkyl ketones, polystyrenes, polyamides, polyurethanes, polyethylene ~i lZ'~C~089 terephthalates, polyethylene isophthalates, acetylcellu-loses, polyvinyl butyral and the like. The binder may be present in the composition in an amount of not more than 10 parts by weight, and preferably 0.5 to 3 parts by weight, per part by weight of the polymerizable compound.
The heat polymerization inhibitor may be, for example, hydroquinone, p-methoxyphenol, pyrogallol, catechol, 2,6-di-t-butyl-cresol, ~ naphthol and the like.
These inhibitors are present in amounts of 0.01 to 3 parts by weight based on the total amount of the polymerizable compound and the polymeric binder.
The coloring agents include pigments e.g.
phthalocyanine pigments, azo pigments, carbon black, titanium oxides, and the like; and dyes e.g. triphenyl-methane dyes, azo dyes, and anthraquinone dyes. Thesecoloring agents are normally present in an amount of 0.001 to 10 parts by weight of the total amount of the polymer-izable compound and the polymeric binder.

The plasticizers which may be contained in the photopolymerizable composition of the present invention includes dioctyl phthalate, didodecyl phthalate, dibutyl-phthalate, butylbenzyl phthalate, triethyleneglycol dicaprylate, dimethylglycol phthalate, tricresyl phosphate, dioctyl adipate, dibutyl adipate, dibutyl sebacate, dibutyl maleate, triacetylglycerol and the like. The amount of the plasticizer is normally up to 5 ~ by weight based on the total amount of the polymerizable compound and the polymeric binder.

'`' -, 1270(~89 In order to form a photosensitive resin layer on a substrate from the photopolymerizable composition mentioned above, the composition can be applied on the substrate directly or after it has been dissolved in a suitable solvent followed by drying. Suitable solvents are methyl ethyl ketone, acetone, cyclohexane, ethyl acetate, butyl acetate, amyl acetate, ethyl propionate, toluene, xylene, benzene, monochlorobenzene, chloroform, carbon tetrachloride, tri-chloroethylene, trichloroethane, dimethylformamide, methyl cellosolve, ethyl cellosolve, tetrahydrofuran, pentoquinone, methanol, ethanol, propanol and the like.
The photosensitive resin layer is optionally subjected to a known treatment in order to prevent decline of sensitivity and storage stability due to oxygen. For example, the resin layer may be covered by a removable transparent sheet or provided with a coating of wax having low oxygen permeability or of a water-soluble or alkaline water-soluble polymer.
The photosensitive resin layer can be exposed to a conventional light source containing ultraviolet or visible light having a wave length of at least 180 nm, e.g. light from a carbon arc, a high pressure mercury lamp, a xenon lamp, a metal halide lamp, a fluorescent lamp, a tungsten lamp, an argon ion laser, a helium-cadmium laser, a crypton laser and the like. The use of lasers is preferred because they can simultaneously carry out image formation and curing. Development after curing may be carried out by ;

127C~( 18~

dissolving an uncured portion of the composition with a developing solution which can be selected depending on the kind of the photosensitive resin layer.
Examples The present invention is illustrated by the following Examples, but it should not be construed as limited thereto.
Example 1 Preparation of photopolymerizable composition One gram of a copolymer of methyl methacrylate and methacrylic acid (available from Mitsubishi Rayon Co., Ltd.
as BR-77) was dissolved in 10 g of methyl ethyl ketone, followed by the addition of 1.0 g of pentaerythritol triacrylate (available from Osaka Organic Chemical Inc.
Ltd.) to form a first solution. Next, 60 mg of a thioxanthene dyestuff (A=S; X=H; Y=C; Z=OC2H5; Rl=C6H5;
R =H), 60 mg of di-t-butyl peroxy isophthalate, 30 mg of N-phenylglycine and 10 mg of methoquinone(p-methoxyphenol) were dissolved in 3 g of methyl cellosolve to form a second solution. The first and second solutions were mixed to form a photopolymerizable composition.
Preparation of photosensitive resin layer (test panel) The composition obtained above was coated on an aluminum substrate in an amount of 2 g/m2 by means of a bar coater and dried at 60C for three minutes to provide a photosensitive layer on the substrate having a thickness of .. ... . .

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2.0~ m. An overcoat layer having a thickness of 2.0~ m was for~ed on the photosensitive layer by coating a 5~
solution of polyvinyl alcohol (saponification degree 88%;
polymerization degree 500) with a bar coater.
Photosensitivity The resulting panels were piled with Kodak Step Tablet No.2 ~21 steps) followed by exposure for ten seconds to light having a wavelength of around 490 nm and a light intensity of 4.0 mW/cm , provided by a xenon lamp of 150 W
(available from Ushio Electric Co. Ltd.) through a filter.
The panels were then developed with a developing solution containing 10 parts by weight of sodium hydrogencarbonate, 50 parts by weight of butyl cellosolve, 3 parts by weight of a surfactant and 1,000 parts by weight of water, to result in 15 steps being cured. As appeared from the above result, it has been found that the tested panel can form cured images with an exposure of 0.3 mJ/cm2.
Arqon ion laser sensitivity The resulting panels were spot exposed by changing ; 20 the intensity and exposure period of an argon ion laser having a wavelength of 488 nm and a beam diameter of 1.25 mm, followed by developing the panels with the developing solu-tion mentioned above. The laser sensitivity of this panel was 0.65 mJ/cm2. By laser sensitivity herein is meant the energy required to obtain a spot having a diameter of 1.25 mm.
Next, the test panel was exposed by cylindrically scanning the laser light (488 nm) while modulating it by a ;~
:

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lZ7C1~89 modulator (1,000 rpm, 600 lines/inch), wherein the laser light was condensed into a beam having a diameter of 20 from a 0.5 w argon ion laser light source through an optical system. The plate was then developed with the developing solution to form a clear image.
Comparative Example 1-1 A photopolymerizable composition was prepared as generally described in Example 1 with the exception that the ~-phenylglycine was not employed. The photosensitivity was measured as generally described in Example 1 and it was found that 11 steps were cured. From this it has been found that the plate can form images with an exposure of 1.1 mJ/cm2.

The laser sensitivity of the plate was 2.80 mJ/cm2. An image obtained by cylindrical scanning of the argon laser as described in Example 1 was less clear than the plate of Example 1.
Comparative Example 1-2 A photopolymerizable composition was prepared ; 20 as generally described in Example 1 with the exception that the 60 mg of di-t-butyl peroxy isophthalate was not employed. The photosensitivity was measured as generally described in Example 1 to find that 10 steps was cured. From this it has been found that the plate can form images with an exposure of 1.6 mJ/cm2.

The laser sensitivity of the plate was 2.94 mJ/cm . An image obtained by cylindrical scanning of the , . ~- .

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: -- : . .
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argon laser as described in Example 1 was less clear than the plate of Example 1.
Comparative Exam~le 1-3 A photopolymerizable composition was prepared as generally described in Example 1 with the exception that 90 mg of di-t-butyl peroxy isophthalate was employed instead of 60 mg and N-phenylglycine was not employed.
The photosensitivity was measured as generally described in Example 1 to find that 11 steps was cured.
From this it has been found that the plate can form images with an exposure of 1.1 mJ/cm2.
The laser sensitivity of the plate was 2.95 mJ/cm2. An image obtained by cylindrical scanning of the argon laser as described in Example 1 was less clear than the plate of Example 1.
ComParative Example 1-4 A photopolymerizable composition was prepared as generally described in Example 1 with the exception that the 60 mg of di-t-butyl peroxy isophthalate was not employed and 90 mg of N-phenylglycine was employed instead of 30 mg. The photosensitivity was measured as generally described in Example 1 to find that 10-11 steps was cured. From this it has been found that the plate can form images with an exposure of 1.4 mJ/cm2.
The laser sensitivity of the plate was 2.90 mJ/cm2. An image obtained by cylindrical scanning of the ~B argon laser as described in Example 1 was less clear than , `

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1~7(~(J8S~
_ 19 _ the plate of Example 1.
Example 2 A sample panel was obtained as generally described with the exception that 60 mg of a xanthene dyest~f~ (A=0;
X=Cl; YeN; zso; R1-C2H50(CH2)3; R2=N(C2H5)2) was employed as the dyestuff. Photosensitivity was measured as generally described in Example 1 to find that 16 steps was cured. From the result of it, it has been found that the plate can form images with an exposure of 0.2 mJ/cm2.
The laser sensitivity of the plate was 0.60 mJ~cm2. An image obtained by cylindrical scanning of the argon laser as described in Example 1 was as clear as the plate of Example 1.
Comparative Example 2-1 A photopolymerizable composition was prepared as generally described in Example 2 with the exception that the N-phenylglycine was not employed. The photosensitivity was measured as generally described in Bxample 2 and it was found that 12 steps was cured. From this, it has been found that the plate can form images with an exposure of 0.8 mJ/cm2.
The laser sensitivity of the plate was 2.52 mJ/cm2. An image obtained by cylindrical scanning of the argon laser as described in Example ? was less clear than the plate of Example 2.
Comparative Example 2-2 A photopolymer.izable composition was prepared as ~.~B. . .
, ,~ .
.
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, ' "' . ,.:-:., ',," :'' 12~0Q~g ( generally described în Example 2 with the exception that the 60 mg of di-t-butyl peroxy isophthalate was not employed. The photosensitivity was measured as generally described in Example 2 and it was found that 11 steps was cured. From this, it has been found that the plate can form images with an exposure of 1.1 mJ/cm2.
The laser sensitivity of the plate was 2.80 mJ/cm2. An image obtained by cylindrical scanning of the argon laser as described in Example 2 was less clear than the plate of Example 2.
Example 3 and Comparative Example 3 A test panel was prepared as generally described in Example 1 with the exception that 30 mg of 2,4,6-tris (trichloromethyl)-1,3,5-triazine was employed instead of the N-phenylglycine. The photosensitivity was measured as generally described in Example 1 and it was found that 15 steps was cured. From this it has been found that the plate can form images with an exposure of 0.3 mJ/cm2.
The laser sensitivity of the plate was 0.72 mJ/cm2.
An image obtained by cylindrical scanning of the argon laser as described in Example 1 was as clear as the plate of Example 1.
For comparison, a photopolymerizable composition was prepared as generally described in Example 1 with the exception that the di-t-butyl peroxy isophthalate was not employed. The photosensitivity was measured as generally l.~

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,, " ~ ' ~27(~(~89 ! described in Example 1 and it was found that 11 steps was cured. From this it has been found that the plate can form images with an exposure of 1.12 mJ/cm2.
The laser sensitivity of the plate was 2.80 mJ/cm . An image obtained by cylindrical scanning of the argon laser as described in Example 3 was less clear than the plate of Example 3.
Example 4 and Comparative Example 4 A test panel was prepared as generally described in Example 1 with the exception that 30 mg of p-dimethyl-aminobenzoic acid isopentyl ester and 15 mg of 2,4-diiso-propylthioxanthone were employed instead of the N-phenyl-glycine. The photosensitivity was measured as generally described in Example 1 and it was found that 14 steps was cured. From this it has been found that the plate can form images with an exposure of 0.4 mJ/cm2.
The laser sensitivity of the plate was 1.08 mJ/cm2.
An image obtained by cylindrical scanning of the argon laser as described in Example 1 was slightly less clear than the plate of Example 1, but it was in usable condition.
For comparison, a photopolymerizable composition was prepared as generally described and mentioned above with the exception that di-t-butyl peroxy isophthalate was not employed. The photosensitivity was measured as generally described in Example 1 to find that 9 steps was cured. From this, it has been found that the plate can form ; images with an exposure of 2.24 mJ/cm2.
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~'~'7~8 The laser sensitivity of the plate was 4.35 mJ/cm2.
An image obtained by cylindrical scanning of the argon laser as described in Example 4 was less clear than the plate of Example 4.
Example 5 and Comparative Example 5 A photopolymerizable composition was prepared as generally described in Example 1 with the exception that 60 mg of 2,5-dimethyl-2,5-di(benzoyl peroxy)hexane was employed instead of the di-t-butyl peroxy isophthalate. The photo-sensitivity was measured as generally described in Example 1 and it was found that 16 steps was cured. From this, it has been found that the plate can form images with an exposure of 0.2 mJ~cm2.
The laser sensitivity of the plate was 0.65 mJ/cm2.
An image obtained by cylindrical scanning of the argon laser as described in Example 1 was as clear as the plate of Example 1.
For comparison, a photopolymerizable composition was prepared as generally described in the above Example 5 with the exception that the N-phenylglycine was not employed.
The photosensitivity was measured as generally described in Example 1 and it was found that 12 steps was optionally cured. From this, it has been found that the plate can form ~ images with an exposure of 0.8 mJ/cm2.
; 25 The laser sensitivity of the plate was 2.41 mJ/cm2.
~ An image obtained by cylindrical scanning of the argon laser . .

lZ~7C!~8~

as described in Example S was less clear than the plate of Example 5.
ExamPle 6 A test panel was prepared as generally described S in Example 1 with the exception that 60 mg of N-phenylglyciné
was employed. The photosensitivity was measured as generally described in Example 1 and it was found that 15 steps was cured. From this, it has been found that the plate can form images with an exposure of 0.3 mJ/cm2.
The laser sensitivity of the plate was 0.83 mJ/cm2.
An image obtained by cylindrical scanning of the argon laser as described in Example i was as clear as the plate of Example 1.

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.

Claims

Claims:

1. A photopolymerizable composition comprising a polymerizable compound and a photopolymerization initiator, wherein the photopolymerization initiator comprises:
(a) a xanthene or thioxanthene dyestuff having the following formula:

(I) wherein A represents an oxygen atom or a sulfur atom, X represents a hydrogen atom or a halogen atom, Y
represents a carbon atom or a nitrogen atom (provided that when Y represents a carbon atom, the bond with an adjacent carbon atom, which is shown by a dotted line, is a double bond and when Y represents a nitrogen atom, the bond with the adjacent carbon atom is a single bond), Z represents an oxygen atom wherein the bond with an adjacent carbon atom is a double bond, a lower alkoxy group or a lower alkanoyloxy group, R1 represents a lower alkyl group, a lower alkoxy lower alkyl group a hydroxy-loweralkyl group, di-(lower) alkylamino lower alkyl group or an aryl group, R2 represents a hydrogen atom, a lower alkoxy group or di-(lower) alkylamino group, wherein in some cases z and R1 together represent the formula:

(b) a photosensitizer selected from the group consisting of N-phenylglycine, 2,4,6-tris(trichloromethyl)-1,3,5-triazine, and a mixture of p-dimethylaminobenzoic acid isopentyl ester and 2,4-diisopropylthioxanthone, and (c) a peroxide.

2. A composition according to claim 1 wherein the photosensitizer is N-phenylglycine.

3. A composition according to claim 1 wherein the photosensitizer is 2,4,6-tris(trichloromethyl)-1,3,5-triazine.

4. A composition according to claim 1 wherein the photosensitizer is a mixture of p-dimethylaminobenzoic acid isopentyl ester and 2,4-diisopropylthioxanthone.

5. A composition according to claim 1 wherein the dyestuff is present in the composition in an amount of 0.005 to 0.3 part by weight per part by weight of the polymerizable compound.

6. A composition according to claim 1 wherein the peroxide is present in the composition in an amount of 0.005 to 0.2 part by weight per part by weight of the polymerizable compound.

7. A composition according to claim 1 wherein the polymerizable compound has two ethylenically unsaturated bonds per molecule.

8. A composition according to claim 7 wherein the polymerizable compound has a boiling point of at least 100°C.

9. A composition according to claim 1 wherein the composition further comprises a polymeric binder.