CA2006074C

CA2006074C - Photopolymerizable mixture and photopolymerizable copying material containing same

Info

Publication number: CA2006074C
Application number: CA002006074A
Authority: CA
Inventors: Hartmut Steppan; Hans-Dieter Frommeld
Original assignee: Morton International LLC
Current assignee: Eternal Technology Corp
Priority date: 1988-12-22
Filing date: 1989-12-20
Publication date: 1998-12-08
Anticipated expiration: 2009-12-20
Also published as: DE3843204A1; CA2006074A1; AU4698989A; EP0374704B1; JPH02226148A; EP0374704A3; EP0374704A2; JP2821463B2; DE58909630D1

Abstract

A photopolymerizable mixture is described which contains a polymeric binder, a polymerizable compound and an acridine compound of the general formula I

(see fig. I) as photoinitiator, in which R1 denotes an optionally substituted alkyl or acyl group, R2, R3 are identical or different and denote and R4 hydrogen or halogen atoms or optionally substituted alkyl or acyl groups, R5, R6 are identical or different and denote and R7 hydrogen or halogen atoms or optionally substituted alkyl, aryl or acyl groups, or groups of the formula II

(see fig. II) The photoinitiators yield a mixture having high photosensitivity and have a lower tendency to diffusion than the known 9-phenylacridine.

Description

PHOTOPOLYMERIZA~LE MIXTURE ~ND
PHOTOPOLYMERIZABLE COPYING MATERIAL CONTAINING SAME

Backqround of the Invention The invention relates to a photopolymerizable mixture. More particularly, the invention relates to a mixture which comprises a polymeric binder, a polymerizable compound having at least one terminal olefinic double bond and having a boiling point above 100~C at normal pressure, and a 9-arylacridine compound as photoinitiator.
DE-C-2,027,467 discloses photopolymerizable mixtures of the composition specified above which contain derivatives of acridine and phenazine as photoinitiators. Some representatives of this class of compound, for example 9-phenylacridine, are notable for a high photosensitivity. The preferred representatives have the disadvantage that they tend to migrate out of photopolymerizable coatings which are in contact with polyethylene films into said films and through them. As a result, the coating becomes depleted of initiator and loses sensitivity.

2~

The initiator may also migrate out of photocured photoresist coatings into certain treatment baths, for example acidic ele~troplating baths and produce a troublesome yellow coloration therein.

Summary of the Invention Accordingly, it is an object o~ the present invention to provide a photopolymerizable mixture having a photosensitivity and image reproduction as good as the preferred known mixtures, but with photoinitiators having a lesser tendency to migrate out of the photopolymerizable or photopolymerized coating.
In accomplishing the foregoing objectives, there has been provided, in accordance with one aspect of the present invention, a photopolymerizable mixture which comprises a polymeric binder, a polymerizable compound having at least one terminal olefinic double bond and having a boiling point above 100~C at normal pressure, and a 9-phenylacridine compound as photoinitiator, wherein the acridine compound conforms to the general formula I
R6 = - 2i ~ - ~ ) (I) ,,~..~1 7~L

in which R1 denotes an optionally substituted alkyl . or acyl group, R , R are identical or different and denote and R4 hydrogen or halogen atoms or optionally substituted alkyl or acyl groups, ~5, R6 are identical or different and denote and R7 hydrogen or halogen atoms or optionally substituted alkyl, aryl or acyl groups, or groups of the formula II

R~ (II) In accordance with another aspect of the present invention, there is provided a photopolymerizable copying material which comprises a coating base and a photopolymerizable layer comprising the photopolymerizable mixture defined above.
Other objects, features and advantages of the present invention will become apparent to those skilled in the art from the following detailed description. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the p-esent inven~ion, are given by way of illustration and not limitation. Many changes and modifications within ~he scope of the present invention may be made without departing from the spirit thereof, and ~he inventlon includes all such modifications.

Detailed Description of Preferred ~mbodiments In the compounds of the general formula I, Rl is an alkyl group containing preferably 1 to 10 carbon atoms, an aliphatic acyl group containing 2 to 10 carbon atoms or an aromatic acyl group containing 7 to 15 carbon atoms.
These groups may be substituted by halogen atoms, in particular fluorine, chlorine or bromine, hydroxyl groups, alkoxy groups, alkoxycarbonyl groups, alkyl groups, aryl groups, aryloxy groups, acyl groups, acyloxy groups, primary, secondary or tertiary amino groups, alkoxycarbonylamino groups or alkylaminocarbonyloxy groups. In g~neral R1 has a molecular weight of about 15 to 200, preferably of 60 to 150. R2 is a hydrogen or halogen atom or a group having the meaning of Rl.
Preferably R2 is a group having the meaning of R1, it being possible for R1 and R~ to be identical or different.
; R3 and R4 have the same general meaning as R2, but preferably at least one of these radicals is a hydrogen atom.
Rs, R6 and R7 may have the same meaning as R3 and R4 and may additionally be aryl groups or groups 7~

of the formula II, in particular halogen atoms (especially fluorine, chlorine or bromine) or alkyl groups. Preferably, at least one of these radicals is a hydrogen atom.
In general, the radicals R1 to R7 contain in total at least S, preferably 12 to 40 carbon atoms.
The molecular weight of the compound-of the formula I is increased by these substituents in general by 60 to 800, preferably by 100 to 700, in particular by 200 to 600, compared with 9-phenylacridine.
Compounds in which at least one of the radicals Rl to R7 is or contains an aromatic group are preferred. In general, at least one of the radicals R2 to R7 is different from hydrogen, and preferably it is the radical R2. Advantageously, compounds are also used which contain a halogen atom, in particular a fluorine, chlorine or bromine atom, in at least one of the substituents R1 to R4.
Preferably, those substituents are used which contain (optionally in addition to the aromatic group) at least one oxygen atom which may be an ethereal, carbonyl or ester oxygen atom.
The compounds of the formula I may be present and be used in pure form or as mixtures with one another, for example as substance mixtures ~hich are produced during the synthesis. Mixtures of this type usually have the advantage of a better solubility than the pure compounds in the coating solvents.
Some of the compounds of the formula I are already known, for example 2,7-dibenzoyl-9-7~

phenylacridine from J. Org. Chem. 29, 2857 (1964) or from J. Chem. Soc. (London) C 1967, 2071 and 1968, 2900. No usability as photoinitiators is mentioned therein.
The compounds of the formula I are synthesized by reacting diphenylamine or its simple substitution products, for e~ample 4,4'-dimethyl-diphenylamine, 3-methyldiphenylamine or ~-chloro-diphenylamine, with benzoic acid or simple benzoic acid derivatives, for example tert-butylbenzoic acid, benzophenone-4-carboxylic acid, diphenyl-4-carboxylic acid, 4-aminomethylbenzoic acid or terephthalic acid in a suitable reaction medium such as polyphosphoric acid at about 150 - 200~C.
With diphenylamine, acridine compounds of the formula I are obtained in which R1 is an optionally substituted benzoyl group whose carbonyl group can be further reacted, for example, reduced to the -CHOH group with sodium boranate.A multiplicity of further derivatives is possible in the sequence:
reaction of the OH group with acid anhydrides, isocyanates, condensation reactions with phenols or esterifications.
Examples of suitable compounds of the formula I are 2,7-dibenzoyl-9-phenylacridine, 2,7-bis(~-hydrcxybenzyl)-g-phenylacridine, 2,7-bis (Q-acetoxybenzyl)-g-phenylacridine, 2,7-dimethyl-9-(4-methylphenyl)acridine, 2,7-dimethyl-9-phenyl-acridine, 2,7-bis(3,4-dimethylbenzoyl)-9-(3,4-dimethylphenyl)acridine~ 2,7-bis(~-acetoxy-4-tert-butylbenzyl)-9-(4-tert-butylphenyl)acridine, 2,7-6C37~L

dimethyl-9-(3,4-dichlorophenyl)acridine, 2,7-dimethyl-9-(~-benzoylphenyl)acridine, 2,7-bis~2-chlorobenzoyl)-9-(2-chlorophenyl~acridine, 2~
hydroxy-3-bromoben~yl)-6-methyl-9-(3-bromophenyl)-acridine, 2,5-bis(4-tert-butylbenzoyl)-9-(4-tert-butylphenyl)acridine, 1,4-bis(2,7-dimethyl-9-acridinyl)benzene, 2,7-bis(~-phenylaminocarbonyloxy-3,4-dimethylbenzyl)-9-(3,4- dimethylphenyl~acridine and 2,7-bis(3,5-dimethyl-4-hydroxy-4'-fluorodi-phenylmethyl)-9-(4-fluorophenyl)acridine.
The quantitative proportion of the compounds of the formula I in the mixture according to the invention is in general about 0.01 to 10, preferably 0.1 to 5% by weight, based on the nonvolatil~
constituents.
For the purposes of the invention, suitable polymerizable compounds are known and are described, for example, in US-A 2,760,863 and 3,060,023.
Preferred examples are acrylic acid esters and methacrylic acid esters of monohydric or polyhydric, preferably at least dihydric alcohols such as ethylene glycol diacrylate, polyethylene glycol dimethacrylate, acrylates and methacrylates of trimethylolethane, trimethylolpropane, pentaery-thritol and dipentaerythritol and of polyhydricalicyclic alcohols or N-substituted acrylic acid amides and methacrylic acid amides. Advantageously, reaction products of mono- or diisocyanates with partial esters of polyhydric alcohols are also used.
Monomers of this type are described in DE-A
2,064,079, 2,361,0~1 and 2,822,190. The 2~ 37~

quantitative proportion of monomers in the coating is in general about 10 to 80, preferably 20 to 60%
by weight.
The mixture also contains, in addition, a polymeric binder. A multiplicity of so]uble organic polymers can be used as binder.
As examples, mention may be made of polyamides, polyvinyl esters, polyvinyl acetals, polyvinyl ethers, epoxy resins, polyacrylic acid esters, polymethacrylic acid esters, polyesters, alkyd resins, polyacrylamide, polyvinyl alcohol, polyethylene oxide, polydimethylacrylamide, polyvinyl pyrrolidone, polyvinylmethylformamide, polyvinylmethyl acetamide and also copolymers of the monomers which form the homopolymers listed.
Furthermore, natural substances or modified natural substances, for example gelatin and cellulose ethers,are possible as binders.
The use of binders which are water-insoluble but are soluble, or at least swellable, in aqueous alkaline solutions is particularly advantageous since coatings containing such binders can be developed with the preferred aqueous alkaline developers. Such binders may contain, for example, the following groups: -COOH, PO3H2, -SO3H, -SO2NH-, -SO2-NH-SO2- and -SO2-NH-CO-.
As examples thereof, mention may be made of maleate resins, polymers of~-(methacryloyloxy)ethyl N-(p-tolylsulfonyl)carbamate and copolymers of the latter and similar monomers with other monomers, and also vinyl acetate/crotonic anhydride and styrene/maleic anhydride copolymers. Alkyl methacrylate/methacrylic acid copolymers and copolymers of methacrylic acid, higher al,;yl methacrylates and methyl methacrylate and/or styrene, acrylonitrile etc., such as are described in DE-A 2,064,080 and 2,363,806, are preferred.
The quantity of binder is in general about ~0 to 90, preferably 40 to 80% by weight of the constituents of the coating.
Depending on the planned application and depending on the desired properties, the photopolymerizable mixtures may contain diverse substances as additives.
Examples are: inhibitors for preventing thermal polymerization of the monomers, hydrogen donors, substances which modify the spectral photosensitivity of coatings of thls type, dyestuffs, colored and colorless pigments, color formers, indicators, and plasticizers, for example polyglycols or esters of p-hydroxybenzoic acid.
These constituents are advantageously chosen in a manner such that they have as little absorption as possible in the actinic radiation range which is important for the initiation process.
For the purpose of this description, actinic - radiation shall be understood to mean any radiation whose energy is equivalent at least to that of short wave visible light. Longwave UV radiation and also electron radiation, X-ray radiation and laser radiation are suitable.

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The photopolymerizable mixture may be used for a wide variety of applications, for e~ample to produce safety glass, lacquers which are cured by light or corpuscular beams, for example electron beams, in the field of dentistry and, in particular, as a photosensitive copying material in the field of reproduction.
The detailed description of the invention is restricted to the latter field of application, but the invention is not restricted thereto. As possible applications in this field, mention may be made of copying rnaterials for the photomechanical production of print forms for letterpress printing, lithographic printir,g, gra~ure printing,screen printing, of relief images, for example production of texts in Braille, of single copies,tanned images, pigment images, etc. Furthermore, the mixtures may be used for the photomechanical production of etch resists, for example for manufacturing nameplates, printed circuits and for chemical milling. The mixtures according to the invention are particularly important as copying materials for the photo-mechanical production of lithographic print forms and for the photoresist techniques.
For the said application purposes, the mixture can be utilized commercially in the form of a liquid solution or dispersion, for example as a photoresist solution, which is applied by the user himself to an individual base, for example for chemical milling, for the production of prin~ed circuits, of screen printing stencils 6~

and the llke. The mixture may also take the form of a solid photosensitive coating on a suitable base in the form of a storable precoated photosensitive copying material, for example for production of print forms. It is also suitable for the production of dry resist.
It is in general beneficial to largely exclude the mixtures from the influence of atmospheric oxygen during the photopolymerization.
If the mixture is used in the form of thin copying coatings, it is advisable to apply a suitable top coat which has low permeability to oxygen. The latter may be .$elf-supporting and may be peeled off before the copying coating is developed. Polyester films, for example, are suitable for this purpose.
The top coat may also be composed of a material which dissolves in the developer liquid or may be removed at least at the noncured points during development. Suitable materials for this purpose are, for example, waxes, polyvinyl alcohol, polyphosphates, sugar etc.
Suitable coating bases for copying materials produced with the mixture according to the invention are, for example, aluminum, steel, zinc, copper and plastic films, for example made of polyethylene terephthalate or cellulose acetate, and also screen printing bases such as perlon gauze.
The photosensitive materials using the mixture according to the invention are produced in a known manner.

Thus, the mixture can ~ taken up in a solvent and the solution or dispersion may be applied bv pouring, spraying, immersion, application with rollers, etc.
as a film to the base provided and then dried.
Thick coatings (for example of 250 ~Lm and over) are advantageously produced by extrusion or pressing as a self-supporting film which is then possibly laminated onto the base. In the case of dry resist, solutions of the mixture are applied to transparent temporary bases and dried. The photosensitive coatin~s (thickness approY.imately between 10 and 100 ~m) are then laminated onto the desired final substrate, together with the temporary base.

The processing of the materials is carried out in a known manner. For the purpose of development, they are treated with a suitable developer solution, preferably a wea~ly al~aline aqueous solution, in which process the unexposed portions of the coating are removed and the exposed regions of the copying coating remain behind on the base.
The copying materials according to the invention are notable for a lower loss in photosensitivity during storage. This advantage is effected apparently by a higher resistance to diffusion of the initiators in the photopoly-merizable coating compared with unsubstituted 9-phenylacridine. The diffusion resistance increases with increasing molecular weight. In this connection, it is essential that the substituents 7~L

are in the 2-position or pre~erably in the 2,7-position of the acridine nucleus. The initiators also do not migrate, or migrate to a substanti,ally lesser extent than known initiators, out of the photocured coating.
Examples oE the mixture according to the invention are given below. Here the preparation of compounds of the formula I is first described.
Then Table I specifies photoinitiators which are used in the photopolymerizable mixtures of the application examples.
In the examples, parts by weight (pbw) and parts by volume ~pbv) are in the ratio of g to ccm.
~nless otherwise specified, percentages and quantity ratios are understood in units of weight.

Preparation examples 1. 2,7-Dibenzoyl-9-phenylacridine~ (compound 1) 1 pbw of diphenylamine and 15 pbw of polyphosphoric acid are heated to 100~C while stirring. After adding 2.5 pbw of benzoic acid, heating of the mixture is continued at 200~C for 45 minutes. After cooling to lOODC, the mixture is poured into 70 pbw of water, the product is filtered off and purified (m.p. 210~C).

)6~)7~

2. 2,7-Bis(~-hYdroxybenzyl)-9-phenylacridine (compound 2) 1 pbw of 2,7-dibenzoyl-9-phenylacridine is suspended in 4 pbw of ethanol and re~uced by adding 0.1 pbw of sodium boranate in portions at 20-50~C. After 24 hours, the reaction product is precipitated with water, purified and dried (m.p. above 280~C).

3. 2~7-Bis(~-acetoxybenzyl)-s-phenylacridine (compound 3) 1 pbw of 2,7-bis(~-hydroxybenzyl)-9-phenylacridine is suspended in 4 pbw of acetone and heated for 1 hour under reflux with 0.8 pbw of acetic anhydride and 0.001 pbw of 4-dimethylaminopyridine. Water is then added to the mixture and the product is filtered off.

4. 2,7-Dimethyl-9-(p-tolyl)acridine(compound4) l mol of 4,4'-dimethyldiphenylamine and 1 mol of 4-methylbenzoic acid are heated for 1 hour at 200~C in 5000 g of polyphosphoric acid.
After cooling, water and ammonia are added to the reaction mixture and the product is filtered off by suction and purified (m.p.
210-211~C).

2~6~i7~

Table Compounds of the formula I having R3 = R4 = R7 = H

Compound R1 ~2 R5 R6 1 Benzoyl Benzoyl H H
2 ~ Hydroxybenzyl ~-Hydroxybenzyl H H
3 ~-Acetoxybenzyl ~-Acetoxybenzyl H H
4 Methyl Methyl 4-Methyl H
Methyl Methyl H H
6 3,4-Dimethyl~ 3,4-Dimethyl- 4-Methyl 3-Methyl benzoyl benzoyl 7 ~-Acetoxy-p- ~-Acetoxy-p- 4-tert- H
tert-butyl tert-butyl- butyl benzyl benzyl Application example l The following three coating solutions were prepared from pbw of a terpolymer of methyl methacrylate, n-hexylmethacrylate and methacrylic acid (5:60:35) with a mean molecular weight M~ =
70,000, 11 pbw of the diurethane formed from 2 mol of hydroxyethyl methacrylate and 1 mol of 2,2,4-trimethylhexamethylene diisocyanate, 39 pbw of the reaction product formed from 1 mol of hydroxyethyl acrylate, 2 mol of capro-lactone and l mol of n-butyl isocyanate.
0.1 pbw of the blue dyestuff 1,4-bis-iSO
butylamino-anthraquinone (C.I. 61551), 160 pbw of butanone and pbw o~ ethanol, to which a 0.51 pbw of 9-phenylacridine (molecular weight 255, comparison) b 0.926 pbw of compound 1 (molecular weight 464), or c 1.102 pbw of compound 3 (molecular weight 552) were added as photoinitiator.
The solutions were applied to biaxially oriented and heat-set polyethylene terephthalate films having a thickness of 25 ~m in a manner such that a coating weight of 45 g/m2 was always obtained after drying at 100~C.
To protect the dry resist coatings from contamination with dust and against damage, they were clad with a 23 ~m thick polyethyl~ne top film and rolled up. They can then be stored with light excluded for a prolonged period of time. The rolls ~polyethylene film outwards) were fastened with a commercial adhesive tape.
After the rolls had been stored for 24 hours at 40~C, the resists were processed.
On peeling off the adhesive tape it was found that, although separated from the resist by the polyethylene top film, the tape was colored light blue by anthraquinone dyestuff which had diffused.
In order to test whether the adhesive tape also )66~7~

contained traces of photolnitiators, a UV spectrum was recorded at 350-450 nm usin~ a spectrophoto-meter, tvpe Perkin-Elmer Lambda 3. Compared with a comparison sample, the adhesive tape of sample a exhibited a peak (extinction = 0.12) at 358 nm. The light blue adhesive tapes b and c exhibited no additional extinction between 350 and 450 nm. They did not contain any photoinitiator.
The dry resist films were laminated in a commercial laminating apparatus at 115~C onto phenolic laminate panels clad with copper foil having a thickness of 35 ~m and were exposed for 4 seconds by means of a 5 kW metal halide lamp with a distance of 110 cm between lamp and vacuum copying frame. The master used was a 13-step exposure wedge which contained density increments of 0.15. In this operation, the exposure wedge was sited so that it was positioned on the parts which had originally been covered by polyethylene film and adhesive tape.
After exposure, the polyester films were peeled off and the coatings were developed with a 1%-strength sodium carbonate solution in a spray development apparatus in the course of 60 s.
The sample a was underexposed, the resist being cured only up to step 5; lines reproduced were 10~ too narrow. The step wedge of samples b and c, on the other hand, was fully cured up to step 6. A
test master having 80 ~m wide clear and dark lines was reproduced true to scale as a raised image.

2~6~1i7~

Application example 2 a 0.70 pbw of 9-~3,4-dimethylphenyl)acridine (molecular weight 283, comparison), b 0.70 pbw of compound 5 (molecular weight 283), or c 1.35 pbw of compound 6 (molecular weight 547) were dissolved as photoinitiators in coating solutions composed of pbw of a copolymer of methyl methacrylate and methacrylic acid (acid number 115), pbw of trimethylolpropane triacrylate and 0.5 pbw of Disperse Blue 134 (C.I. 61551) in 520 pbw of 2-methoxyethanol.

~he solutions were applied by spinning to 15 electrolytically roughened 0.3 mm thick aluminum which had been hardened by anodizing. The coating was dried for 2 minutes at 100~C, a coating weight of 2.4 g/m~ being obtained.
For the purpose of protection against contamination, the coated, slightly sticky photosensitive panels were clad at room temperature with a 20 ~m thick polyethylene film.
The printing plates thus obtained were exposed for 15 seconds with a 5 kW metal halide lamp at a distance of 110 cm under a negative master .~

together wlth a 13-step exposure wedge which contained density increments of 0.15.
The parts no~ cured by light were removed by wiping over with a developer solution of the following composition:

3 pbw of sodium metasilicate nonahydrate, 0.05 ~pbw of strontium chloride, 0.03 pbw of nonionogenic wetting agent (coconut butter alcohol/polyoxyethylene ether containing approx. 8 oxyethylene units), 0.003 pbw of antifoaming agent, lO0 pbw of demineralized water.

The number of completely cured steps of the exposure wedge provides a coefficient of measurement for the photosensitivity. The values are listed under (A) in the table below.
In order to elucidate the diffusion of the initiator through the polyethylene film, a commercial colorless transparent adhesive tape was pressed onto the polyethylene film on one sample panel in each case and the composite was stored for 24 hours at room temperature (23~C). The adhesive film was then peeled off again and (B) the increase in the optical density at 358 nm was measured. The exposure test wedge having 13 gray steps was furthermore placed at the position where the adhesive film had been removed (experiment C), and the printing plate was exposed for 15 seconds and then developed just as described above.
The results listed in the following table show that the initiator diffuses most strongly out of the sample a, to a markedly lesser extent out of sample b and does not diffuse out of sample c.

(A) Wedge (B) Density(C) Wedge steps differencestep a 6 0~17 2 b 7 0.11 4 c 7 0 7 Example 3 a l pbw of compound 7 or b 1 pbw of isopropylthioxanthone and 2 pbw of p-dimethylaminobenzoate (initiator mixture of a commercial photoresist) were added as initiators to coating solutions composed of:

pbw of a copolymer of methyl methacrylate, butyl acrylate, styrene and methacrylic acid (35:40:5:20), pbw of trimethylolpropane triacrylate, l pbw of leuco crystal violet and 0.05 pbw of crystal violet in pbw of butanone and Z0~961~

75 pbw of ethanol.

The solutions were applied tO polyethylene terephthalate film as in ~xample 1, dried, laminated onto copper foil, e~posed and developed. Then the optimum exposure time was determined.
In a further experiment,boards produced and developed as above were rinsed for 30 s with tap water, incipiently etched for 30 s in a 15~ strength ammonium pero~odisulfate solution, rinsed with water again, immersed for 30 s in 10%-strength sulfuric acid and then electroplated consecutively in the following electrolyte baths.

1~ 60 minutes in copper electrolyte bath supplied by Schloetter, Geislingen/Steige, "bright copper bath" type current density: 2.5 A/dm2 metal buildup: approx. 30 ~m temperature: room temperature 2. 15 minutes in a lead-tin bath LA supplied by Schloetter, Geislingen/Steige, current density: 2 A/dm2 metal buildup: 15 ~m temperature: room temperature The plates did not exhibit any undercuttingor damage.
To test whether the resist constituents diffuse into the electroplating baths, 0.075m 2 -21~

~6~7a~

~lass plates were coated with resist (45~/m2) and immersed for one hour in one liter of 20%-strength sulfuric acid.
In both cases the sulfuric acid remained colorless:
a U~7 spectrum (200 - 800 nm) of both sulfuric acid extractC war then recorded with the spectrophotometer (1 cm cell); b sho~!ed a di.stinct peak at 225 nm (extinction = 0.9'5), some of the initiator system having migrated into the sulfuric acid; a showed no contamination.

Claims

1. A photopolymerizable mixture which comprises:
a) a polymeric binder, b) a polymerizable compound having at least one terminal olefinic double bond and having a boiling point above 100°C at normal pressure, and c) a 9-arylacridine compound as photoinitiator, wherein the acridine compound conforms to the general formula (I) in which R1 denotes an optionally substituted alkyl or acyl group, R2, R3 and R4 are identical or different and denote hydrogen or halogen atoms or optionally substituted alkyl or acyl groups, R5, R6 and R7 are identical or different and denote hydrogen or halogen atoms or optionally substituted alkyl, aryl or acyl groups, or groups of the formula II

2. A photopolymerizable mixture as claimed in claim 1, wherein R1 is an alkyl group containing 1 to 10 carbon atoms, an aliphatic acyl group containing 2 to 10 carbon atoms or an aromatic acyl group containing 7 to 15 carbon atoms.

3. A photopolymerizable mixture as claimed in claim 1, wherein R3, R4 and R5 are hydrogen atoms.

4. A photopolymerizable mixture as claimed in claim 1, wherein the radicals R1 to R7 together contain at least 6 carbon atoms.

5. A photopolymerizable mixture as claimed in claim 1, wherein at least one of the radicals to R7 contains an aromatic group.

6. A photopolymerizable mixture as claimed in claim 1, wherein at least one of the radicals R2 to R7 is different from hydrogen.

7. A photopolymerizable mixture as claimed in claim 1, wherein the radicals R1 to R7 together increase the molecular weight of the compound of the formula I by about 60 to 800.

8. A photopolymerizable mixture as claimed in claim 7, wherein the radicals R1 to R7 together increase the molecular weight of the compound of the formula I by 100 to 700.

9. A photopolymerizable mixture as claimed in claim 1, wherein at least one of the radicals R1 to R7 contains an oxygen atom.

10. A photopolymerizable mixture as claimed in claim 1, wherein the binder is insoluble in water and soluble in aqueous alkaline solutions.

11. A photopolymerizable mixture as claimed in claim 1, wherein the photopolymerizable compound is an ester of acrylic acid or methacrylic acid with an aliphatic alcohol.

12. A photopolymerizable mixture as claimed in claim 1, wherein the proportion of the compounds of the formula I is about 0.01 to 10 wt%, based on the nonvolatile constituents of the mixture.

13. A photopolymerizable copying material comprising a coating base and a photopolymerizable coating, wherein the coating comprises a mixture as claimed in claim 1.

14. A photopolymerizable copying material as claimed in claim 12, further comprising a layer having a low permeability to oxygen disposed on top of said photopolymerizable coating.