CA1267478A

CA1267478A - Radiation-polymerizable composition

Info

Publication number: CA1267478A
Application number: CA000496896A
Authority: CA
Inventors: John E. Walls; Carlos Tellechea
Original assignee: Hoechst Celanese Corp
Current assignee: CNA Holdings LLC
Priority date: 1984-12-06
Filing date: 1985-12-05
Publication date: 1990-04-03
Also published as: JPS61144640A; EP0184725A2; EP0184725B1; DE3567294D1; EP0184725A3

Abstract

ABSTRACT OF THE DISCLOSURE
This invention relates to a photopolymerizable composition for use in a photographic element such as a lithographic printing plate comprising in admixture a) a polymeric binder;
b) a photoinitiator;
c) a diazonium salt; and d) a polymerizable mixture of i) an acrylic monomer having from 3 to 6 unsaturated groups; and ii) an oligomer which is prepared by reacting one molar equivalent of a substantially linear polymeric compound having an active hydrogen group at each end thereof with at least two molar equivalents of a diisocyanate compound so as to form a prepolymer having an isocyanate group at each end thereof; and subsequently reacting said prepolymer with at least two equivalents of an ethylenically unsaturated compound having an active hydrogen group to provide said prepolymer with unsaturation at each end thereof.

Description

7'~

1 - 20731-92~

The present invention re:lates to a radlation-polymerizable composition. More particularly, this invention relates to a radiation-polymerizable composition which may be employed to produce an improved photographic element such as a lithographic printing plate. The basic difference in the various approaches in the Eormulation of lithographic printing plates from radiation polymerizable compositions has been in the search for a system which is prepared Erom relatively inexpensive ingredients, does not require prolonged imaging cycles (has a high quantum efEiciency), is able to undergo an increased number of press runs and results in the creation of high resolution images within the composition which can be manifested without prolonged and elaborate development.
Most such lithographic printing plates comprise a metal substrate which is coated with a light sensitive diazonium compound in admixture with suitable binding resins, photoinitiators, photopolymerizable compositions, colorants, stabilizers, exposure indicators, surfactants and the like.
Although ~he art is replete with photosensitive compositions which may be used ~or lithographic printing plates, the priar art composition's serviceability is restricted by their limited stability and number of press runs.
This invention relates to a photopolymerizable composition for use in forming photographic elements such as lithographic printing plates, comprising in admixture a) a polymeric binder;
b) a photoinitiator;
c) a dlazonium salt; and d) a polymerizable mixture of i) an acrylic monomer having from 3 to 6 unsaturated groups; and ii) an oligomer which is prepared by reacting one molar

2 2073~ 24 equivalent of a substantlally linear polymeric compound havin~ an active hydrogen group at each end thereof with at least two molar equivalents : of a diisocyanate compound so as to form a prepolymer having an isocyanate group at each end thereof; and subsequently reacting said prepolymer with at least two equivalents of an ethylenically unsaturated compound having an active hydrogen group to provide said prepolymer with unsaturation at each end thereof.
~-~ This invention relates to a radiation~polymerizable composition.
The polymeric binder useful in the practice of this invention is preferably characterized as being a polymer which does not react with ,~

' 7~2J~

itself or oLher compo-mds whell exposed to actinic radiation. The preferred binder resin should be substantially organic solvent soluble and is preferably one which is not substcmtially alkali, acid or water soluble. The binder must have a molecular weight sufficient to provide a tack-free surface when in admixture with the photopolymerizable mixture and to provide a tough cohesive matrix which when used to produce a lithographic printing plate is capable of providing numerous quality impressions. The molecular weight must be low enough, though, to permit solubility in formulation as well as during development. The molecular weight of the binder should be greater than about 20,000, preferably greater than about 30,~0 and, most preferably, greater than about 40,000.
Examples of binders suitable for this invention include epoxy resins, polyvinyl acetate, polyvinyl formals, polyvinyl acetals, ~ b~t rR~
L~ polyvinyl ~ , polyesters, polyamides, polye-thers, polyurethanes and polyacrylic resins which are either homo- or copolymers of acrylates (or methacrylates) and/or acrylic acid (or methacrylic acid) and copolymers or terpolymers of any of the monomers ~orming the above polymers. In the preferred embodiment, the polymeric binder is a terpolymer o~ polyvinyl acetate, polyvinyl alcohol and polyvinyl formal available as Formvar 12/85 commercially from Monsanto of St. Louis, Missouri.
Preferably, the polymeric binder is present in the composition at a percent solids level of from about 20% to about 75~ by weight.
A more preferred range is from about 30% to about 65% by weight and, most pre~erably, the polymeric bincler is present at a percent solids level of from about 35% ~o about 50% by weight.
Suitable pho~oinitiators whlch may be used in this invention are preferably those free-radical pho~oinitiators having an absorption maximum range from about 320 to about ~00nm. Examples include the acetophenones, benzophenones, triazines, benzoins, benzoin ethers, xanthones, thioxanth-ones, acridines and benzoquinones. More preferred of these are the A~ ~r~

7'~

triazines havint~ the Eormula ,CC13 Ar - CH = CH _ ~ C~

N-C
R R2 \CC13 wherein Ar is ~

` ~4 and Rl, ~2' R3 and R4 are, independently, hydrogen, chlorine, bromine, alkoxy or alkyl. The most preferred photoinitiator is 2-stilbenyl-4,6-di(trichloromethyl) triazine.
" The photoinitiator is preferably present in the com-position at a percent solids level of about 1.5% to about 8.~
by weight, more preferably about 2.0 to about 6.0% by welght and is most preferably present at a percent solids level of from about 3.0~ to about 4.~% by weight.
The diazonium salt which is useful in the practice of this invention may be any suitable light-sensitive diazonium polymeric or monomeric compound wh:ich are well known to the skilled artisan although the polymeric diazonium compounds are preferred. Suitable diazonium compounds include those condensed with ~ormaldehyde such as disclosed in United States Patents 2,063,631 and 2,667,415, the polycondensation products such as disclosed in United States Patents 3,849,392 and 3,867,147, and the high speed diazos such as disclosed in United States Patent 4,436,804.
Preferably~the diazonium salt comprises the 1:1 poly-condensation product of 3-methoxy-diphenyl amine-4-diazonium sulEate and 4,4'-bis-methoxYmethyl-diphenyl ether, precipitated as the mesikylene sulfonate, such as is taught in United States .:

3,849,392.

4 -t ~

3 ~L~ 7~

The diazonium ~alt is pre~er~bly present in the composition of the su~ject invention at a percent solids level oE from about 3% to about - 4a -.,, -s ~

7~

2~% by weight. More preEerably it i5 present at about 5% to about 18% by ~eigllt and most preferably the diazonium salt Ls present at a percent solids level of from about 10% to about 15% by weight.
The photopolymerizable mixture of the subject invention is comprised of, in admixture, an acrylic monomer which has Erom 3 to 6 unsaturated groups and a urethane oligomer preferably a diacrylated polyurethane, which is hereinafter described.
The monomer is an ethylenically unsaturated compound having from three to six unsaturated groups and being capable of reacting with the urethane oligomer upon exposure to imaging radiation. Preferably the unsaturated groups are acrylate or methacrylate esters. The preferred monomer is either a solid or liquid having a viscosity of greater than about 7~0 cps (mPa.5~ at 25C, preferably greater than about 2000 cps at 25DC. Most preferably, the monomer has a viscosity of greater than about 4000 cps at 25C.
Examples of compounds which are suitable for use as the monomer of this invention include trimethylolpropane triacrylate and the ethoxylated or propoxylated homologs thereof, trimethylol propane t7~

.

tri-methacrylate and the ethoxylated or propoxylated homolog~
thereof, pentaerythritol triacrylate, pentaerythritol tr-methacrylate, dipentaerythritol monohydroxY pentdacrylate, dipentaerythritol monohydroxy pentamethacrylate, dipentaerythritol hexaacrylate, dipentaerythritol hexamethacrylate, pentaerythritol tetraacrylate and pentaerythritol tetramethacrylate. Preferably, the monomer is dipentaerythritol monohydroxy pentaacrylate, although a combination of suitable monomers is also advantageous.

The monomer is present at a percent solids level which is preferably in the range of from about 1~ to about 35% by weight.
More preferably, the monomer is present at a percent solids level of from about 15% to about 30% by weight and most preferably from about 15~ to about 25~ by weight.

The oligomeric component of the photopolymerizable mixture of the composition of the subject invention is a photocurable oligomer or polymer which is prepared by reacting one molar equivalent of a substantially linear polymeric compound having an active hydrogen group at each end thereof with a least two molar equivalents of a diisocyanate compound so as to form a prepolymer having an isocyanate group at each end thereof; and subsequently reacting said prepolymer with at least two equivalents of an ethylenically unsaturated compound having an active hydrogen group to provide said prepolymer with unsaturation at each end thereof. The preferred oligomer is one havin~ a polyester backbone prepared from an aliphatic dicarboxylic acid and an aliphatic diol. The preferred dicarboxylic acid is linear and has from about 2 to ~ carbon atoms. The polyester is prepared in such a way that the compound is symmetrical and hydroxy-terminated. A procedure for doing so would be known to the skilled artisan, for example as shown in Sandler and Karo, '7~3 Pol~mer Synthesis, Vol. 2, Academic Press 1977, pp 1~167. The pol~ester polyol is in turn reacted with preEerably an aliphatic, more preferably a cyclic aliphatic, diisocyana~.e having from about 2 to 13 carbon atoms. The diisocyanate is reacted with the polyester polyol so that one of the two isocyanate groups is reacted with the terminal hydroxy group on the end of the polyester backbone. The remaining isocyanate group is subsequently reacted with a hydroxy-containing acrylate or methacrylate. For example, 1,6-hexane diol is reacted with adipic acid in a mole ratio of greater than 1:1 to form a polyester and then reacted with dicyclohexyl-methane-4,4'-bis diisocyanate in a 2:1 mole ratio (diisocyanate/polyester). The product is reacted with 2-hydroxy ethyl acrylate in a 2:1 mole ratio (acrylate/diisocyanate-polyester product) to for,m an oligomer useful in this invention.
The oligomer may be characterized as follows:
U-D-R-D-U
wherein:
R prior to the reaction to form the oligomer is an essentially linear polymeric compound having two end groups with active hydrogen functionality, D prior to the reaction to form the oligomer is a diisocyanate compound, and U prior to the reaction to form the oligomer is a compound having ethylenic unsaturation and a group with an active hydrogen.

Examples of compounds which can be used as the ~ group are polyesters obtained by reacting a dicarboxylic acid with a diol in such a fashion that the rnole ratio of diol to dicarboxylic acid is greater than 1:1 so as to have a symmetrical hydroxyl terminated polymer; polyethers obtained by reacting a diol with an alkylene oxide 747~

and epo~ies obtained by reacting a symmetrical diglycidyl compound with a diol in such a fashion that the mole ratio of diol to diglycidyl compound is greater than 1:1 so as to have a symmetrical hydroxyl terminated polymer.

More specifically, R groups which are polyesters are prepared from dicarboxylic acids such as oxalic, malonic, succinic, glutaric, adipic, pimelic, suberic, azelaic and sebacic acids, and from diols such as ethylene glycol, diethylene glycol, neopentyl glycol, propylene glycol, dipropylene glycol, 1,3-butane diol, 1,9-butane diol, 1,6-hexanediol and 2-ethyl-1,6-hexane diol.

. .
R groups which are polye~hers are prepared from diols such as ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, neopentyl glycol, 1,3-butane diol, 1,4-butane diol, 1,6-hexane diol and 2-ethyl-1,6-hexane diol, and alkylene oxides such as ethylene oxide or propylene oxide, or tetrahydrofuran.

R groups which are epoxies are prepared from diols such as ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, neopentyl glycol, 1,3-butane diol, l,~-butane diol, 1,6-hexane diol and 2-ethyl-1,6-hexane diol, and diglycidyls such as diglycidyl iscphthalate, diglycidyl terephthalate, diglycidy phthalate and bisphenol-A diglycidyl ether.

Examples oE compounds which can be used as the D group are ethylene diisocyanate, propylene diisocyanate, tetramethylene diisocyanate, dicyclohexyl-methane-4,~'-diisocyanate, hexamethylene diisocyanate, l-methyl-2,3-diisocyanato-cyclohexane, l-methyl-2,6-diisocyanatocyclohexane, lysine 7~ 3 _ 9 _ di~socyanate, 4,~'-ethylene-bis-(cyclohexyl isocyanate) and isaphorolle diisocyanate.

Ex-mple of compounds which may be used as the U group include hyaroxyethyl acrylate, hydroxypropyl methacrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, 1,3-butane diol acrylate, 1,3-butane diol methacrylate, 2,4-butane diol acrylate, 1,4-butane diol methacrylate, neopentyl glycol acrylate, neopentyl glycol methacrylate, pentaerythritol triacrylate, pen~aerythritol trimethacrylate and the mono acrylate and methacrylate of polyethylene glycol, polypropylene glycol and polycopolymers of ethylene glycol and propylene glycol.

Useful oligomers in the practice of this invention include those oligomers preferably having a molecular weight of from about 1500 to about 4000, more preferably from about 2000 to about 3500 and, most preferably, the oligomer has a molecular weight of about , 3a00. It is desirable that the oligomer be in solid form or semi-solid form, i.e. having a viscosity of greater than about ~8~,0~0 cps at 25C. The composition preferably contains the oligomer at a percent solids level of from about 10~ to about 35 by weight. More preferably the oligomer is present in the radiation polymerizable composition of this invention in an amount of from about 15~ to about 30~ by weight and it is most preferably present at a percent solids level of from about 15% to about 25~ by weight.

One of the 5igniEicant aspects of this invention is that the unique combination of photoinitiator, diazonium salt and photopolymerizable mixture eliminates the need for use of an oxygen barrier layer or the necessity for processing in a nitrogen environment, although the exact mechanism for this in unclear. Among the advantages derived is elimination of i7~'71~

1, the inconvenience of applying a second coating, 2) the concern o~ r thè refractive index and solubility of the oxygen barrier la er, 3) the concern over blinding on a printing press due to residue from the oxygen barrier layer, and ~) the concern over potential image gain due to the oxygen barrier layer.

Other components which may be included in the radiation-polymerizable composition of this invention include acid stabilizers, exposure indicators, plasticizers, photoactivators and colorants.

Suitable acid stabilizers useful within the context of this invention include phosphoric, citric, benzoic, m-nitro benzoict p(p-anilino phenylazo) benzene sulfonic acid, 4,4'-dinitro-2,2'-stilbene disulfonic, ita~onic, tartaric and p-toluene sulfonic acid, and mixtures thereof. Preferably, the acid stabilizer is phosphoric acid. When used, the acid stabilizer is prefera~ly present in the radiation-polymerizable composition in the amount of from about 0.3% to about 2.0~, and most preferably from about ~.75% to about 1.5~, although the skilled artisan may use more or less as desired.

Exposure indicators (or photoimagers) which may be useful in conjunction with the present invention include 4-phenylazodiphenylamine, eosin, azobenzene, CalcozineFuchsine dyes and Crystal Violet and Methylene Blue dyes Preferably, the exposure indicator is 9-phenylazodiphenylamine. The exposure indicator, when one is used, is preferably present in the composition in an arnount ~ from about 0.001~ to about C.0035~ by weight. A more preferred range is from about 0.002~ to about ~. C3~b and, most preferably, the~ exposure indicator is present in an amount of from about 0.005~ to about ~.20~, althou~h the skilled artisan may use more or less)as desired.

7~

Th~ photoactivator which may be included in the composition of this invention should be an amine-containing photoactivator which combines synergistically with the free-radical photoinitiator in order to extend the e~fective half-life of the photoinitiator, which is normally in the approximate ranye of about 10 9 to 10 15 seconds. Suitable photoactivators include 2-(n-butoxy) ethyl-4-dimethylamino benzoate, 2-(dimethylamino) amino benzoate and acrylated amines. Preferably the photoactivator is ethyl-4-dimethylamino benzoate. The photoactivator is preferably present in the composition of this invention in an amount of from about 1.~% to about 4.0% by weight, although the skilled artisan may use more or less as desired.

A plasticizer may also bé included in the composition of this invention to prevent coating brittleness and to keep the composition pliable if desired. Suitable plasticizers include dibutylphthalate, triarylphosphate and, preferably, dioctylphthalate. The plasticizer is preferably present in the composition of this invention in an amount of from about 0.5% to about 1.25~ by weight, although the s~illed artisan may use more or less as desired.

Colorants useful herein include dyes such as Rhodamine, Calcozinej Victoria Blue and methyl violet, and such pigments as the anthraquinone and phthalocyanine types. Generally, the colorant is present in the form of a pigment dispersion which may comprise a mi~ture of one or more pigments and~or one or more dyes dispersed in a suitable solvent or mixture of solvents.
When a colorant is used, it is preferably present in the composition of this invention in~an amount of from about 1.5~ to about 4.0~ by weight, more preferably from about 1.75~ to about 7~

.

3.~% and most preferably from about 2.C~ to about 2.75~, although the s~illed drtisan may use more or less as desired.
.

In order to form a coating composition for the production of lithographic printing plates, the composition of this invention may be dispersed in admixture in a solvent or mixture of solvents to facilitate application of the composition to the substrate.
Suitable solvents for this purpose include tetrahydrofuran, propylene glycol monomethyl ether, butyrolactone, methyl cellosolve, ethylene glycol ethers, alcohols such as ethyl alcohol and n-propanol, and ketones such as methyl ethyl ketone, or mixtures thereof. Preferably, the solvent comprises a mixture of tetrahydrofuran, propylene glycol monomethyl ether and butyrolactone. In general, the solvent system is evaporated from the coating composition o,nce it is applied to an appropriate substrate, however, some insignificant amount of solvent may remain as residue.

Substrates useful for coating with the composition of this invention to form a lithographic printing plate include sheets of transparent films such as polyester, aluminum and its alloys and other metals, silicon and similar materials which are well known in the art. Preferably, the substrate comprises aluminum. ~hè
substrate may first be pretreated by standard graining and/or etching and/or anodizing techniques as are well known in the art, and also may or may not have been treated with a composition such as polyvinyl phosphonic acid, sodium silicate or the li~e suitable for use a~ a hydrophilizing agent.

In the production of photographic elements such as lithographic printing plates, an aluminum substrate is first preferably grained by art recognized methods such as by means of a wire brush, a slurry of particulates or by chemical or electrochemical mear.s, for example in an electrolyte solution comprising hy ochloric acid. The grained plate is preferably th~n an~ized for example in sulfuric or phosphoric acid in a manner well known in the art. The grained and anodized surface is preferably then rendered hydrophilic by treatment with polyvinyl phosphonic acid by means which are also known to the skilled artisan. The thusly prepared plate is then coated with the composition of the present invention, preferably at a coating weight of from about ~.6g/m2 to about 2.5g/m2, more preferably from about 0.8g/m2 to about 2.0g/m2 and most preferably from about 1.2g/m2 to about 1.5g/m2, although these coating weights are not critical to the ?ractice of this invention, and dried.

Preferably the thusly prepared lithographic printing plate is exposed to actinic radiation through a negative test flat so as to yield a solid 6 on a 21 step Stouffer exposure wedge after development. The exposed plate is then developed with a suitable developer composition such as an organic solvent based developer, preferably one comprising 2-propoxyethanol, a nonionic surfactant and an ino~ganic salt such as is disclosed in U.S. Patents 4,3~8,340 and 4,381,340. In conventional use, the developed plate is finished with a subtractive finisher such as a hydrophilic polymer.
Examples include cold water-soluble dextrin and/or polyvinyl pyrrolidone, a nonionic surfactant, a humectant, an inorganic salt and water, as taught by U.S. Patent 4,213,887.

E;or the purpose of improving the press performance of 2 plate prepared as described above, it is kno~n that baking of the exposed and developed plate can result in an increase in the number of quality impressions over that otherwise obtainable. To properly bake the plate, it is first treated with a solution designed to prevent loss of hydrophilicity of the background during baking. ~n example of an effective solution is disclosed 7'~7~

in U.S. Patent ~,355,096. The thusly prepared plate is thcn heat trea.ted by baking at a temperature of from about 18aC up to the annealing temperature of the s~lbstrate, most preferably about 24~C. The effective baking time is inversely proportional to the temperature and averages in the range of from about 2 to about 15 minutes. At 24~C the time is about 7 minutes.

The following examples are illustrative of the invention but it is understood that the invention is not limited thereto. None of the plates prepared in Examples 1-5 have an oxygen barrier layer thereon nor were they processed in a nitrogen environment.
' ' Example 1 An 8" x 25" section of lithographic grade 1100 aluminum alloy is deqreased with an aqueous alkaline degreasing solution and electrochemically grained using 9~0 coulombs of alternating current in a ~edium of nitric acid and aluminum nitrate. The grained plate is well rinsed and anodized in a sulfuric acid bath wherein the aluminum is made anodic. Sufficient current and voltage is used to produce an oxide layer of 2.8g/m2. The anodized plate is well rinsed and hydrophilized by immersing the plate into a solution of polyvinyl phosphonic acid. The plate is well rinsed and dried. The thusly prepared plate is whirler coated with a solution having the followin~ composition:

% w/w A terpolymer of polyvinyl acet~te~ y~ y~ alcohol and polyvinyl formal commercially available as Formvar 12/85 4-59 Dipentaerythritol monohydroxy pe~ntaacrylate 2.01 Diacrylated urethane oligomer formed by reacting 1,6-hexane diol with adipic acid in a mole ratio of greater than 1:1 ' -o form a polyester and then reacting with dicyclohexyl-methane-i7'~

4, '-bis diisocyanate in a 2:1 mole ratio tdiisocyanate/
polyester). The product is then reacted with 2-hydroxy et:-.yl acrylate in a 2:1 mole ratio (acrylate/
diiocyanate polyester product) 2.el Polycondensation product of 3-methoxy~4-diazo-diphenyl amine sulfate and 4,4~bis-methoxy methyl dlphenyl ether isolated as the mesitylene sulfonate 1.22 2-(4-Styryl-phenyl)-4,6-di(trichloromethyl)triazine 3.20 Methyl cellosolve 87.02 The coated and dried plate is exposed to actinic radiation through a negative exposure flat so as to yield a solid seven on a 21 step Stouffer step wedge. The plate is developed using the following composition % w/w 2-propoxy ethanol 14.85 n-propanol 11.15 g 4 7H2O 8.00 NaH2PO4 (anhydrous) 1.50 Polyvinyl pyrrolidone 1.50 Trycol OP-407 ~ 75 polyethylene glycol 20~ 1.00 2 Balance M~'l = 10, 000 **
nonyl phenol polyoxyethylene ether ~ 40 moles ethylene oxide) as a 70% solution in H2O.

and finished with the following composition ~ w/w Dextrin 5.52 sodiu,n octyl sulfate 1.61 ****
Triton X-100 1.00 Givgaurd DXN a.05 3 4 2.37 H2O Balance .

7~

~ ~*
hydrolyzed tapioca dextrin ****
isooctyl phenol polyoxyethylene ether ( ~.5 moles ethylene oxide) **~ **
1,4-dimethyl-6-acetoxy-dioxane and run on a Solna sheet fed press ~sing abrasive ink, over-packing, and a ~ahlgren dampening system until image breakdown is achieved. Under these conditions the plate provides 595,000 acceptable impressions.

Example 2 A lithographic printing plate is prepared and processed as described in Example 1 except that the diacrylated urethane oligomer is omitted. Under these conditions the plate provides only 315,000 acceptable impressions.

Example 3 A lithographic printing plate is prepared and processed as described in Example 1 except that the dipentaerythritol monohydroxy pentaacrylate is omitted. Under these conditions the plate provides only 340,000 acceptable impressions.

Example 4 A lithographic printing plate is prepared and processed as described in Example 1 except that the diazo composition is omitted. Under these conditions the plate provides only 220,t5t50 acceptable impressions.

Example 5 A lithographic printing plate is preparea ana nrocessed as described in Example 1 except that the 2-t4-styryl-phenyl)-4,6-di-(trichloromethyl)triazine is omi~ted. Under these conditions theplate provides only 335,(50a acceptable impressions.

~374'7~

It can be readily observed that plates prepared according to this invention (Example l) show substantially increased press runs.

.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A photopolymerizable composition comprising in admixture a) a polymeric hinder;
b) a photoinitiator;
c) a diazonium salt; and d) a polymerizable mixture of i) an acrylic monomer having from 3 to 6 unsaturated groups; and ii) an oligomer which is prepared by reacting one molar equivalent of a substantially linear polymeric compound having an active hydrogen group at each end thereof with at least two molar equivalents of a diisocyanate compound so as to form a prepolymer having an isocyanate group at each end thereof; and subsequently reacting said prepolymer with at least two equivalents of an ethylenically unsaturated compound having an active hydrogen group.

2. The composition of claim 1, wherein the unsaturated groups of said acrylic monomer are acrylate or methacrylate ester groups.

3. The composition of claim 1 wherein said oligomer is a diacrylated polyurethane.

4. The composition of claim 1 wherein said acrylic monomer is present in said composition in an amount of from about 10% to about 35%
by weight.

5. The composition of claim 1 wherein said oligomer is present in said composition in an amount of from about 10% to about 35% by weight.

\

6. The composition of claim 1 wherein said polymeric binder is selected from the group consisting of epoxy resins, polyvinyl acetates, polyvinyl formals, polyvinyl butyrals, poly-esters, polyamides, polyethers, polyurethanes and polyacrylic resins, and copolymers or terpolymers of any of the monomers forming these polymers.

7. The composition of claim 1 wherein said photoinitiator comprises a bis-trichloromethyl triazine having the formula wherein Ar is and R1, R2, R3 and R4 are, independently, hydrogen, chlorine, bromine, alkoxy, or alkyl.

8. The composition of claim 1 wherein said diazonium salt comprises the condensation product of 3-methoxy-diphenylamine 4-diazonium sulfate and 4,4'-bismethoxymethyl diphenyl ether.

9. The composition of claim 2 wherein said monomer is dipentaerythritol monohydroxy penta-acrylate.

10. The composition of claim 4 wherein said monomer is present in said composition in an amount of from about 15% to about 30% by weight.

11. The composition of claim 5 wherein said oligomer is present in said composition in an amount of from about 15% to about 30% by weight.

12. The composition of claim 6 wherein said polymeric binder comprises a terpolymer of polyvinyl acetate, polyvinyl alcohol and polyvinyl formal.

13. The composition of claim 7 wherein said photoinitiator is 2-stilbenyl-4,6-di(trichloromethyl)triazine.

14. A photographic element comprising a substrate upon which the composition of claim 1 is coated.

15. The photographic element of claim 14 wherein said sub-strate comprises aluminum or an aluminum alloy.

16. The photographic element of claim 14 wherein said sub-strate is selected from the group consisting of aluminum and its alloys, polyester and silicon.