CA1153236A - Long-running water developable printing plates and compositions - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

Water developable planographic printing plates comprising a substrate having a water developable photocurable coating layer thereon can have a long press life in the water softenable binder components comprises less than 10% by weight of the coating layer, at least 50%
by weight of all ethylenically unsaturated monomers comprise oligomeric materials having a molecular weight in excess of 500 and more than two ethylenically unsaturated groups, and is the ratio of ethylenically unsaturated materials with a molecular weight of less than 500 to organic solvent soluble film forming binder in the composition is less than 1/0.6.

Description

`" 1153236 LONG-RUNNING WATER DEVELOPABLE
PRINTING PLATES AND COMPOSI~IONS

Background of the Invention Planographic printing plates function by 5 providing dif~erential ink adsorptivity between exposed and non-exposed areas after development. This is ordinarily effected by coating a hydrophilic substrate (e.g., an oligomeric diazonium resin coated aluminum sheet) with a photocurable composition. `When the photo-10 curable composition is exposed to light, it hardens. Thesubsequent application of an appropriate solvent washes away unhardened, non-light exposed areas without removing the photocured areas on the substrate. The hardened areas will accept ink while the washed away areas with the hydro-15 philic background areas will repell ink. This wouldtherefore provide a good planographic printing plate.
The expense, inconvenience, and even the possibility of fire hazards in having to store developing solutions have been recently overcome by the development 20 of a truly pure water developable lithographic printing plate as described in copending Canadian Patent Applica-tion Serial No. 346,444, filed 26 February, 1980. This technology is a substantial advance in the art, but does have its limitations, particularly in the running life of ; 25 the printing p~ate.
It is one aspect of the present invention to improve the press life of water developable printing plates.
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Summary of the Invention The present invention relates to water developable printing plate compositions and printing plates which have a longer press life than previous water developable plates and compositions. It has been found that the use of high amounts of oligomeric ethylenically 35 unsaturated components, wbile maintaining no more than a j .

1153Z3~i maximum ratio of low molecular weight ethylenically unsaturated materials to film forming resins, enables the use of lower amounts of water-softenable binder ~aterials which provides a water developable printing plate with longer press life capabilities.
The compositions useful according to the present invention comprise a homogeneous mixture of:
A. 0.9 to less than lO percent by weight of a water softenable polymeric binder, B. 30 to 70 percent by weight of at least diethylenically unsaturated polymericable materials of which at least 50 percent by weight of these materials have more than two ethylenically unsaturated groups and a molecular weight greater than 500, C. 0.01 to 10 percent by weight of a free radical photo-initiator system, D. lO to 40 percent by weight of an organic solvent soluble film forming binder, and E. preferably 1 to 20% by weight of an oligomeric, photosensitive, organic solvent soluble diazonium resin, wherein the ratio of at least diethylenically unsaturated monomers having a molecular weight of less than or equal to 500 to the total amount of film forming binders (A plus D) is less than l/0.6.

Detailed Description of the Invention As noted above, there are at least five different components in the present invention, the water softenable binder, the organic solvent soluble film forming binder, the ethylenically unsaturated materials, the photoinitiator system, and the solvent soluble oligomeric diazonium resin. Each of these materials will be described in their turn.

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~lS3Z36 The Oligomeric Diazonium Re The photoreactive solvent soluble oligomeric resin component which is optionally, but preferably used iR the present invention is a diazo resin. These resins must be organic solvent soluble, but may also be somewhat water soluble and are known in the art as represented by U.S. Patent Nos. 4,104,072; 3,933,499; 3,837,858; and 3,899,332. Examples of diazos useful in forming such resins, which resins are generally known in the art, are:

4-diazo-diphenylamine, 1-diazo-4-N,N-dimethylamino-benzene, l-diazo-4-N,N-diethylamino-benzene, l-diazo-4-N-ethyl-N-hydroxyethylamino-benzene, l-diazo-4-N-methyl-N-hydroxyethylamino-benzene, 1-diazo-2,5-diethoxy-4-benzoylamino-benzene, l-diazo-4-N-benzylamino-benzene, l-diazo-4-N,N-dimethylamino-benzene l-diazo-4-morpholino-benzene, l-diazo-2,5-dimethoxy-4-p-tolylmercaptobenzene, 1-diazo-2-ethoxy-4-N,N-dimethylaminobenzene, p-diazo-dimethyl aniline, l-diazo-2,5-dibutoxy-4-morpholino-benzene, l-diazo-2,5-diethoxy-4-morpholino-benzene, l-diazo-2,5-dimethoxy-4-morpholino-benzene, 1-diazo-2,5-diethoxy-4-morpholino-benzene, l-diazo~2,5-diethoxy-4-p-tolylmercapto-benzene, l-diazo-3-ethoxy-4-N-methyl-N-benzylamino-benzene, l-diazo-3-chloro-4-N,N-diethylamino-benzene, l-diazo-3-methyl-4-pyrrolidino-benzene, l-diazo-2-chloro-4-N,N-dimethylamino-5-methoxy-ben2ene, and l-diazo-3-methoxy-4-pyrrolidino benzene.

These diazos are organic solvent soluble when an appropriate anion is selected, for example from amongst those known in the art, such as tetrafluoroborate, ~iS3Z36 triisopropylonapthalene sul~onate, p-toluene sulfonate, lauryl sulfate, hexafluorophosphate, 2-naphthalene sulfonate, etc. These resins, as noted in the list above, are organic solvent soluble, light-sensitive, negative working aromatic diazo resins. The diazo resins are generally useful as 1-20% by weight of active ingredients in the printing composition. Preferably they are present as 3-8% by weight of the composition. The preparation of these resins is generally described in U.S. Patent No.

2,714,066. It must be noted that the diazo resins used in the practice of the present invention is not synonymous with or inclusive of diazonium salts as known in the art.
Diazo resins have more than one diazonium group in the molecule. Diazo resins comprise a number of salts, at least two, covalently bonded together. For example, a useful diazo resin can be represented by the formula 1-- ~ --N2 ~n r ~ 3 wherein n is about 4 or 5.

It is interesting to note that polymerization does not necessarily occur through generation of a Lewis acid from the anion. The anion shown above does not form or generate a Lewis acid when the diazo resin is photo-initiated. Lewis acids may be generated in other diazo resins, but non-Lewis acid generating resins are useful in the present invention.

_e Organic Solvent Soluble Resin 3a The binder resin component, which is an organic solvent soluble film forming resin, is generally known in the art. It is preferably selected from epoxy resins, polyesters, polyallyl orthophthalate prepolymers, pollyallyl isophthalate prepolymers, polyvinyl formals, liS3236 polyurethanes, polyvinyl butyrals, polyoxyethylene oxides, polyvinyl hydrogen phthalates, polyacrylates, polymethacrylates, cellulose acetate esters, and polyvinyl chlorides. Some of these resins are disclosed as useful in plate compositions in U.S. Patent Nos. 4,104,072;

3,899,332; 3,837,858; and 3,933,499. These binder resins may or may not enter into the polymerization which occurs upon exposure to radiation. Prepolymers or fully polymerized materials may be useful as long as they are capable of orming a film with sufficient structural integrity to be self-supporting. These resins are generally useful as 10-40% by weight of the printing composition, excluding solvents and other non-functional additives. Preferably 15-35% by weight solid ingredients are binder resin. A minimum molecular weight of at least 1,000, preferably 2000, and most preferably 3500 is desired. There is no required upper limit for the molecular weight. Molecular weights of 2,000,000 or 3,000,000 are known in the art and are useful. The use of binders having a molecular weight less than 200,000 and preferably less than 100,000 appears to make the compositions more readily developable. It is preferred that these resins be more oleophilic than hydrophilic.
When the binder resin is selected so that it is a prepolymer capable of independently crosslinking or polymerizing upon heating (which can be readily determined outside of the compositions of the present invention), the plate on which the composition is coated can be post-heated (i.e., after development) to control the dot size of the image on the plate and also to strengthen the integrity of the image. This would improve press life.
Because the dots are given more structural integrity by post-heating, underexposure during imaging may be used to produce dots with fine resolution. These dots would ordinarily be removed in development or on the press, but post-heating with these particular types of binder resins would make the dots secure to the printing plate. This is llS3236 believed to be unique in negative acting water developable plates. It is preferred that such crosslinking or polymerizable can be initiated at a temperature of at least 100C. Higher polymerization temperatures are also advantageous. Examples of this class of binder are polyallyl isophthalate and polyallylorthophthalate prepolymers such as ,~C-O-CH2-CH-CH2 0 . I ~ CH- CH2- 0- C
C O-CI~2-C~ H2 \13--C-o-C~2-CIi=C}~2¦

'. _ 10 The Ethylenically Unsaturated Materials The polyfunctional unsaturated monomer or oligomer component useful in the present invention is a free radical polymerizable polyethylenically unsaturated compound. These compounds may be true monomers or dimers, trimers, oligomers, or polymers having at least 2, preferably 2 to 12, and most preferably 2 to 5 ethylenically unsaturated groups such as acrylate, methacrylate, vinyl, acrylamide and allyl. Preferred are compounds having multiple acrylate and methacrylate groups such as acrylic and methacrylic esters of polyols.
Examples of these materials are trimethylolpropane triacrylate, pentaerythritol tetraacrylate, pentacry-thritol triacrylate, ethylene glycol diacrylate, ethylene glycol dimethaorylate, pentaerythritol tetramethacrylate, diallyl phthalate, diallyl adipate, diallyl succinate, etc. Suitable ethyleneically unsaturated, free-radical initiated, chain-propagating addition polymerizable compounds include alkylene or polyalkylene glycol diacrylates, e.g., diethylene glycol diacrylate, glycerol diacrylate, glycerol triacrylate, l,3-propanediol dimethacrylate, 1,2,4-butanetriol trimethacrylate, .
, llS3236 1,4-cyclohexanediol diacrylate, sorbitol hexaacrylate; bis[l-(3-acryloxy-2-hydroxy)]p-ethoxy-phenyl-dimethylmethane, tris-hydroxethylisocyanurate trimeth-acrylate, the bis-acrylates and bis-methacrylates of polyethylene glycols of molecular weight 200-500 and the like; unsaturated amides, c.g., methylene bis-acrylamide, methylene bis-methacrylamide, 1,6-hexamethylene bisacrylamide, diethy-lene triamine trisacrylamide, B-methacrylaminoethyl methacrylate; vinyl esters such as divinyl succinate, divinyl adipate, and divinyl phthalate. Mixtures of these esters may also be used as well as mixtures of these compounds with alkyl esters of acrylic acid and methacrylic acid including such esters as methyl acrylate, methyl methacrylate, ethyl acrylate, isopropyl methacrylate, n-hexl acrylate, stearyl acrylate, allyacrylate, styrene, diallyl phthalate and the like. These compounds are generally known in the art, as, for example, in British Patent No. 1,482,953 and United States Patent Nos. 3,954,475 and 3,905,815. The polyfunctional unsaturated materials are generally useful as 30-70% by weight of active ingredients in the printing composition. Preferably they are present as 40-60% by weight of the composition.
The oligomeric materials having molecular weights in excess of 500 are, by themselves, well known in the art. They may have essentially linear backbones which are terminated by a multiplicity of ethylenically unsaturated-groups such as those disclosed in United States Patent No. 4,316,949, filed 14 December, 1979 or they may be highly branched with ethylenically unsaturated groups randomly pendant from the backbone, as dlsclosed in United States Patent No. 4,228,232, (which issued to patent from the continuation-in-part of United States Serial No.
15,586, filed 27 February, 1979). Other examples are included in United States Patents 3,700,643; 4,065,587i and 4,153,778. Many other highly polymerizable oligomers are known in the art. The ethylenically unsaturated materials dis-closed in Canadian Serial No. 352,477, filed May 22, 1980 and United States Patent No. 4,316,949 are preferred.

llS3Z36 The Free-Radical Photoinitiator System _ _ The free-radical photoinitiator systems of the present invention are generally known. They are compounds which absorb radiation, generally actinic radiation, and are activated to become agents which abstract hydrogens from hydrogen donors. There may also be or may need to be sensitizers present to enable the compounds to be photoactivated. Examples of these materials are the benzoins, acetophenones, naphthoquinones and benzophenones (as disclosed in British Patent No. 1,4~2,953), vinyl substituted halomethyl-s-tr~azine compounds (as disclosed in U.S. Patent No. 3,954,475), and aromatic onium compounds (as disclosed in U.S. Patents Nos. 4,058,400;

4,058,401). Other desirable photoinitiator systems are generally known in the prior art such as in U.S. Patent Nos. 3,775,113; 3,887,450; 3,895,949; and 4,043,819. The photoinitiator systems are generally useful as 0.01-10% by weight of active ingredients in the printing composition.
Preferably they are present as 1-6% by weight of the composition. When needed, spectral sensitizers are usually included at a level of about 10 to 70~ by weight of the photoinitiator.

The ~ater Softenable Binder _ The water-softenable polymer of this invention is a water soluble or at least water softenable polymer which is also soluble in organic solvent systems. By water softenable it is meant that the ~oung's modulus of the polymer decrea~es in the presence of water. Thi~
modulus can be measured on commercially available equipment such as the "Rheovibron"*model D-DV-II-C
manufactured by Toyo Baldwin Co., ~td. A polymer which formed a molecular suspension in water would be one example of a non-soluble (in water) polymer that was water softenable. Another exàmple of a water softenable polymer is a polymer in which a portion of the bonds within or without (e.g., hydrogen bondings) the polymers are broken * Trade Mark r~

llS;~236 in the presence of water. Specific examples of these polymers include polyvinyl pyrrolidone, partially hydrolyzed polyvinyl acetate, poly(vinylpyrrolidone/vinyl acetate copolymer), hydroxyalkyl cellulose resins (e.g., hydroxypropyl cellulose), alkyl vinyl ethers maleicanlydride copolymers, and organic solvent soluble polyvinyl alcohol derivatives or copolymers. These materials are generally well known in the art. British Patent No. 1,482,953 discloses the use of photopolymeric compositions suitable for the preparation of relief plates developable with water which contain amino-substituted hydroxyalkyl cellulose resins which would also be useful and are a species of hydroxyalkyl cellulose resins. The term water-softenable as used in the practice of the present invention includes water soluble resins unless otherwise stated. The water- softenable resins are generally useful as 0.9-10% by weight of solid ingredients in the printing composition. Preferably they are present as 5-10% by weight of the composition.
The su~strates of the present invention may be any substrate, including metal, polymer and paper surfaces. Cnly when the coated article is to be used as a lithographic printing plate must the substrates be hydrophilic on their surfaces. The substrate for a printing plate may be any material which may be coated on at least one surface thereof to provide this hydrophilic property. The substrates normally used for lithographic plates, such as those of U.S. Patent Nos. 556,3807 2,100,063t 2,251,181; 3,181,461; 2,373,357; and 4,116,695 30 are useful in the practice of the present invention.
Preferred are polymeric or metal substrates. Particularly desirable are aluminum and zinc substrates. Most preferred are aluminum substrates which have a permanent hydrophilic coating reacted onto the surface thereof by 35 reaction of an aqueous solution of a soluble silicate as in U.S. Patent No. 2,714,066. This form of aluminum or zinc substrate is referred to as smooth, grained, or ~iS3236 grained and anodized. A variety of alloys may be used with the aluminum, as is known in the prior art such as U.S. Patent No. 4,116,695. When the term aluminum substrate or aluminum plate is used in the art, it is understood that the material is predominantly but not necessarily exclusively aluminum.
over this substrate is usually applied another coating which comprises a water-soluble light-sensitive diazo resin which may be the same as some of those described above as part of the photoreactive composition.
These resins are well known in the art and are also disclosed in U.S. Patent Nos. 2,714,066 and 3,905,815.
In a preferred practice of the present invention, a sixth component may be added or a particular organic solvent soluble resin selected. This component is an oleophilic polymer which is added to the composition to improve its ink receptivity. As the printing plates operate to provide an image by having areas of ink receptivity (oleophilic areas) and non-ink receptivity (oleophobic areas) in a subtractive development process, enhanced ink reception in the imaged areas where the composition is retained on the plate is desirable. Some of the binder resins listed above ~re also oleophilic, and resins in that list which are oleophilic may be added to the composition so that more than one organic solvent soluble resin is present. The oleophilic resin need not be a film forming resin, as structural integrity is provided by other components, but it i9 preferred that the oleophilic re~in i9 a film forming polymer. Any compatible ~ilm forming oleophilic resin i9 useful, and cellulose acetate esters such as cellulose acetate butyrate and cellulose acetate propionate have been found to be particularly desirable. This ingredient shows useful effects in weight percentages of from O.S to 40% of the composition (the maximum is where it also constitutes the binder resin).

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There are numerous other additives which may be desirably added to these compositions. It is generally desirable to have a solvent system in the compositions when they are applied to the substrate. These solvents of course tend to evaporate out of the composition after it has been coated out. These solvent systems may comprise one or more solvents to keep all of the ingredients compatable. The solvents are usually organic polar solvents but some minor amount (e.g., up to about 25% by weight) of non-polar solvents may be included.
Particularly desirable solvents include methylethyl ketone (and other ketones such as cyclohexanone and acetone), amides tsuch as dimethyl- formamide), chlorinated hydrocarbons (such as ethylene dichloride), 2-nitropropane, diacetone alcohol, and short chain (e.g., 1 to 5 carbons) aliphatic alcohols. Many of these materials are disclosed in British Patent No. 1,447,142.
These are the types of organic solvents from amongst which all materials previously referred to as organic solvent soluble can find a solvent system of one or more solvents.
Dyes or pigments may also be used in the printing compositions. Acutance dyes would also be useful in compositions of the present invention. Many of these materials are disclosed in British Patent No. 1,~47,142 for printing compositions.
For the purpose of inhibiting premature polymeri-zation and reducing any polymerization in non-imaged areas from scattered light, the incorporation of stabilizer~
such as phenothiazine and phenolic stabilizers may be useful. These materials are well known in the art and are exemplified by di-t-butyl-p-cresol, hydroquinone, quinone, hydroquinone monomethyl ether, amyl quinone, n-butyl phenol etc. These stabilizers are usually present in amounts from 0.0002 to 1 percent by weight of the solids in the composition.
The compositions may also contain inert particulate filler which is transmissive or transparent to actinic light. The particles may also be so small as to not interrupt light transmission. Organophilic silicas, bentonites and powdered glass are examples of these materials. All should be smaller than 10 microns, preferably smaller than 1 micron, and most preferably smaller than 0.1 microns.
Flow control agents, viscosity modifiers, and surfactants may also be useful in the present compositions.
The following examples will further enable an understanding of the present invention. All percentages are by weight unless otherwise stated. All plates were treated with commercially available diazo desensitizing compositions after development.

Example l A homogeneous mixture comprising 9.8 by weight of polyvinylpyrolidone, 10% by weight of the polyalkyl phthalate prepolymer described above by structural formula, 5% cellulose acetate butyrate, 6% of the fluoroborate salt of the condensation product of paraformaldehyde a p-diazo diphenylamine, 12% of a dispersion (50/50 weight percent) of a red pigment in a copolymer ~86/14) of vinyl chloride and vinyl acetate, 2%
of 2-(p-methoxystyryl)-4,6-bis-(tri-chloromethyl)-s-Z5 triazine, and 55.2% by weight of a mixture of polyethylen-ically unsaturated materials comprising 70~ by welght of an oligomer (OL-I) of the formula:

llS3Z;~6 CH2=CH--O-C--CH2 Il I ~C~
CH =CH-O-C-CH -C-CH2-0-~H-CH2-N N
CH2=CH--O--C--CH2 OH C--C--CH3 ll 2 CH O CH2--C--CH2--C--O--CH=CH
OH CH --C--O--CH=CH2 2 il and 30 percent pentaerythritol tetraacrylate. This was brought to a solution in a blend of 60% ethyleneglycol 15 monomethyl ether, 27% dimethyl formamide, and 13% methyl ethyl ketone and coated onto anodized, silicated aluminum which had been squeeze roll coated with a water soluble, light sensitive p-diazodiphenylamine-formaldehyde resin from a 2 . 5% aqueous solution. The plate was air dried at 20 about 80C.
The dried plate was exposed to a carbon arc source of ultraviolet radiation for 100 seconds at 1.37 meters. The exposed sheet was developed with tap water with a few seaonds o$ gentle scrubbing with a soft cloth.
25 The plate was then treated with a commercially available aqueous desensitizing and gumming ~olution, then buf~ed dry and mounted on a llthographic printing press. In an accelerated abrasion press test condition, the plate ran for about 10,000 impressions without loss of detail. The 30 plates faithfully reproduced 150 line screens cantaining 3% high light dots and 97% shadows.
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,' ~53236 Examples 2-6 These examples show that press life is highly dependent upon maintain-ing less than 10 percent by weight of water softenable binder.
The following materials were used in preparing the compositions used in these examples.
Polyvinyl Pyrrolidone (PVP) 2,6-bis-trichloromethyl-4-p-methoxystyryl-s-triazine (TMT) Oligomer of Example 1 (OL-I) Oligomer of Example 1 of United States Patent No. 4,316,949 (OL-II) Pentaerythritol Triacrylate (PETA) Cellulose Acetate Butyrate (CAB) Diallyl Phthalate Resin of Example 1 ~DPR) Diazonium Resin of Example 1 (DZR) Perylene Red Pigment dispersion (50/50) in Vinyl Acetate/Vinyl Chloride (86/14) Copolymer (PRAC) All compositions contained 450 ppm of phenothiazine based on the combined weight of ethylenically unsaturated materials.
These compositions were dissolved in the solvent mixture of Example 1 as 10% solids and coated at 250 mg/ft2 on an aluminum substrate, dried, exposed, developed, desensitized, and placed on press as in Example 1. The number of prints under accelerated abrasion press test conditions was recorded. The results are shown in Table 1, .

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Table 1 Example 2 3 4 5 b PVP 4.82 9.65 14.47 19.31 24.15 TMT 1.93 1.93 1.93 1.93 1.93 CAB 2.90 2.90 2.90 2.90 2~90 DPR 14.47 14.47 14.47 14.47 14.47 OLrI 16.90 15.20 13.52 11.82 10.13 OLrII 23.64 21.96 20.27 18.58 16.88 PETA 17.38 15.93 14.48 13.03 11.58 DZR 5.80 5.80 5.80 5.80 5.80 PRAC 12.16 12.16 12.16 12.16 12.16 rmpressions (X1000) 16 11 7 7 6 As can be seen from these Examples, the press life falls 15 off rather significantly with more than 10% by weiqht of water-softenable binder.

Examples 7 and 8 A comparison was made between a plate having only low molecular weight ethylenically unsaturated 20 materials and one having a high proportion of oligomeric ethylenically unsaturated materials. Amongst additional materials in the composition were the triacrylate of trihydroxy ethyl isocyanurate (TTEI) and an insert polyurethane binder (PUB).

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liS3236 Table 2 Example 7 8 PVP 19.88 9.84 TMT 1.99 1.97 CAB 0.99 0.98 DPR 23.86 9.84 TTCI 29.82 PETA ----- 17.72 OL-II ----- 41.34 PRAC 12.52 12.40 DZR 5.96 5.91 PU~ 4.98 ----These compositions were dissolved as 10% solids in the solvent mixture of Example 1, coated at 250 mg/ft2, dried, exposed, developed and placed on press as in Example 1. Under accelerated abrasion press test conditions the first plate broke down at 3500 impressions while the second plate broke down after 7000 impressions.
These examples show the improved press life available from practice of the present invention as compared to the technology of Canadian Serial No. 346,444 filed 26 February 1980.
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ExampIes 9, 10 and 11 ~: The following compositions were prepared for evaluation.

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Table 3 Example 9 10 11 PVP 4.92 5.00 0.96 TMT 1.97 2.00 1.91 CAB 0.98 3.00 2.87 DPR 24.61 6.00 14.34 OL-I 34.45 21.00 18.40 OL-II --- 28.00 25.10 PETA 14.76 21~00 19.54 DZR 5.91 4.00 5.74 PRAC 12.40 10.00 12.04 These compositions were dissolved, coated, dried, exposed, developed, desensitized and mounted on press as in Example 1. All plates provided at least 7,000 impressions before being damaged~

15One other aspect of the present invention is the fact that the coatings of the present invention, in spite of the high concentration of ethylenically unsaturated materials, are non-tacky compositions with as high a level of monomeric unsaturated materials as are allowable in the 20: practice of the present invention are usually so tacky ~ that the composition could be pulled off the substrate :~ ~from contact with another }ayer. This did not occur in ~ any of the above examples.

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Claims (8)

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

1. A water-developable planographic printing plate comprising a substrate having a hydrophilic surface and as a coating over said hydrophilic surface a coating comprising a homogeneous mixture of:
A) 0.9 to less than 10% by weight of a water-softenable polymeric binder B) 30 to 70% by weight of at least diethylenically unsaturated polymer-izable materials of which at least 50% by weight of these materials have more than two ethylenically unsaturated groups and a molecular weight greater than 500.
C) 0.01 to 10% by weight of a free-radical photoinitiator system, and D) 10 to 40% by weight of an organic solvent soluble film forming polymeric binder wherein the ratio of diethylenically unsaturated monomers having a molecular weight of less than or equal to 500 to the combined weight of A) plus D) is less than 1/0.6.

2. The printing plate of claim 1 wherein said at least diethylenically unsaturated monomers are selected from the class of acrylic and methacrylic monomers.

3. The printing plate of claim 1 wherein said composition contains from 1 to 20% by weight of a solvent soluble oligomeric diazonium resin.

4. The printing plate of claim 2 wherein said composition contains from 1 to 20% by weight of a solvent soluble oligomeric diazonium resin.

5. The printing plate of claim 1, 2 or 3 wherein said substrate comprises anodized and silicated aluminum.

6. The printing plate of claim 1, 2 or 3 wherein said water-softenable binder is selected from the group consisting of polyvinyl pyrrolidone, poly(vinyl pyrrolidone/vinyl acetate copolymers), alkyl vinyl ether-maleic anhydride copoly-mers, and polymers or copolymers of polyvinyl alcohol.

7. The printing plate of claim 1, 2 or 3 wherein said water-softenable binder comprises from 5 to less than 10% by weight of said mixture and said substrate comprises anodized and silicated aluminum.

8. The printing plate of claim 1, 2 or 3 wherein said water-softenable bonder is selected from the group consisting of polyvinyl pyrrolidone, poly (vinyl pyrrolidone/vinyl acetate copolymers), alkyl vinyl ether-maleic anhydride copolymers, and polymers or copolymers of polyvinyl alcohol and comprises from 5 to less than 10% by weight of said mixture.