GB2044788A - Photosensitive compositions and articles - Google Patents

Abstract

The compositions comprise a homogeneous mixture of: A. 1 to 75% by weight of organic solvent soluble film forming resin, B. 10 to 65% by weight of free radical polymerizable polyethylenically unsaturated compounds having at least two ethylenically unsaturated groups, C. 0.5 to 15% by weight of a free radical photo-initiator or photoinitiator system, D. 5 to 40% by weight of a water- softenable organic solvent soluble polymer, and E. 1 to 20% by weight of organic solvent soluble diazo resin. The compositions are useful as imageable layers for photoimageable printing systems and as imageable layers in printing plates. The compositions are water developable and can be processed without the use of organic solvents.

Description

SPECIFICATION Photosensitive compositions and articles Field of the Invention The present invention relates to polymerizable compositions and in particular to photoreactive compositions. These compositions are useful as imageable layers for photoimageable printing systems and as imageable layers in printing plates. These compositions are also water developable and can be processed without the use of organic solvents.

Background of the Invention Most negative acting printing plate compositions work in the following manner. A photoreactive composition is applied to a substrate. The coated substrate is imaged by radiation (e.g., visible light, infrared radiation, ultraviolet radiation, etc.), heat or electron beams. Where the radiation or other imaging action has struck the photosensitive coating composition, the photoreactive composition polymerizes. This polymerization in imaged areas renders those areas of the composition less soluble in solvents. When a developer solution is applied to the exposed surface of the coated substrate, the unexposed composition is removed more easily and more rapidly than the exposed composition. Removal of the unexposed composition leaves an ink receptive image in the exposed areas.When used as a printing plate, these coated substrates therefore act as negative acting plates.

These imageable systems operate on a change in solubility, and the unexposed area should dissolve or release easily from the substrate while the exposed area should not be disturbed by the solvent. The more easily the unpolymerized composition is removable by developer solutions and the more resistant the polymerized composition becomes, the better the system is.

Most polymerizable systems require organic solvent developer systems rather than aqueous developer systems as it is easier to formulate printing compositions for organic solvents which are soluble before polymerization and insoluble after polymerization. Organic solvent systems are less desirable than aqueous systems because of the potential for pollution and the higher cost of the organic solvents. However, it has been very difficult to produce aqueous developable systems which have adequate imaging speeds, are easily removed when unexposed, are insoluble when exposed, and are long lasting as a printing plate. Water soluble compositions are disclosed, for example, in U.S. Patent Nos. 3,837,858; 3,899,332; 3,933,499; 4,092,170; and 4,042,386 and British Patent No. 1,447,142.

Those systems which are referred to in the prior art as water developable are not readily water developable and often require the use of additional additives such as surfactants. Some of these prior art systems, such as that of U.S. Patent No. 4,104,072, rely on diazo resins as the photopolymerizable material within the composition and tend to be short-lived on the press.

Other prior art systems, such as that of U.S. Patent No. 3,036,915 use various polyethylenically unsaturated materials as the photopolymerizable component within the composition. These systems tend to be very sensitive to humidity and are not storage stable. The active composition lifts from the surface of the plate, easily abrades from the plate, and suffers from reduced resolution with storage under humid conditions.

Summary of the Invention The present invention relates to polymerizable compositions which are useful as printing plate compositions. The present invention further relates to printing plates having these compositions thereon wherein the compositions are solvent or water developable.

The compositions suitable for use in a printing plate system comprise a homogeneous mixture of an organic solvent soluble photoreactive oligomeric resin, an organic solvent soluble film forming resin with oleophilic properties as a binder, a free radical photoinitiator system, a polyfunctional unsaturated monomer or oligomer, and a water softenable polymer.

The plates of the present invention are presensitized and comprise an oleophobic substrate, a water soluble photoreactive resin on at least one surface of the substrate, and a coating of one of the compositions of the present invention over said resin.

The broadest ranges of components used in the practice of the present invention are as follows: A. 1-75% by weight of organic solvent soluble film forming resin, B. 10-65% by weight of free radical polymerizable polyethylenically unsaturated compounds having at least two ethylenically unsaturated groups, C. 0.5 to 15% by weight of a free radical photo-initiator system, D. 5-40% by weight of a water softenable organic solvent soluble polymer, and E. 1-20% by weight of organic solvent soluble diazo resin.

Preferably the sum of the water softenable and organic film forming resins would be equal to at least 10% by weight of the composition.

The photoreactive solvent soluble oligomeric resin component used in 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, 1 -diazo-4-N, N-diethylamino-benzene, 1 -diazo-4-N-ethyl-N-hyd roxyethylamino-benzene, 1 -diazo-4-N-methyl-N-hydroxyethylamino- benzene, 1 -diazo-2, 5-diethoxy-4-benzoylamino-benzene, 1 -diazo-4-N-benzylamino-benzene, 1-di- azo-4-N, N-dimethylamino-benzene, 1 -diazo-4-morpholino-benzene, 1-diazo-2,5-dimethoxy-4-p-to- lylmercaptobenzene, 1 -diazo-2-ethoxy-4-N, N-dimethylaminobenzene, p-diazo-dimethyl aniline, 1 diazo-2, 5-dibutoxy-4-morpholino-benzene, 1-diazo-2,5-diethoxy-4-morpholino-benzene, 1-diazo- 2, 5-dimethoxy-4-morpholino-benzene, 1 -diazo-2, 5-diethoxy-4-morpholino-benzene, 1 -diazo-2, 5- diethoxy-4-p-tolylmercapto-benzene, 1 -diazo-3-ethoxy-4-N-methyl-N-benzylamino-benzene, 1 -diazo-3-chloro-4-N,N-diethylamino-benzene, 1 -diazo-3-methyl-4-pyrrolidino-benzene, 1 -diazo-2- chloro-4-N, N-dimethylamino-5-methoxy-benzene, and 1 -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, triisopropylonapthalene sulfonate, 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

wherein n is about 4 or 5.

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

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, 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 forming a film with sufficient structural integrity to be selfsupporting.These resins are generally useful as 15-75% by weight of the printing composition, excluding solvents and other non-functional additives. Preferably 30-50% 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 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 100 C. Higher polymerization temperatures are also advantageous. Examples of this class of binder are polyallyl isophthalate and polyallylorthophthalate prepolymers such as

The polyfunctional unsaturated monomer or oligomer component useful in the present invention is a free radical polymerizable polyethylenically unsaturated compound.These com pounds 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, pentacrythritol triacrylate, ethylene glycol diacrylate, ethylene glycol dimethacrylate, pentaerythritol tetrametha crylate, diallyl phthalate, diallyl adipate, diallyl succinate, etc.Suitable ethylenically unsaturated, free-radical initiated, chain-propagating addition polymerizable compounds include alkylene or polyalkylene glycol diacrylates, e.g., diethylene glycol diacrylate, glycerol diacrylate, glycerol triacrylate, 1,3-propanediaol dimethacrylate, 1,3-propanediol dimethacrylate, 1,2,4-butanetriol trimethacrylate, 1,4-cyclohexanediol diacrylate, sorbitol hexaacrylate; bis [ 1 -(3-acry- loxy-2-hyd roxy) ] p-ethoxy-phenyl-d imethyl methane, tris-hydroxyethylisocya nurate tri methacrylate, the bis-acrylates and bis-methacrylates of polyethylene glycols of molecular weight 200-500 and the like; unsaturated amides, e.g., methylene bis-acrylamide, methylene bis-methacrylam ide, 1,6-hexamethylene bisacrylamide, diethylene triamine trisacrylamide, B-methacrylaminoe thyl 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-hexyl acrylate, stearyl acrylate, allyacry late, 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 U.S. Patent Nos. 3,954,475 and 3,905,815. The polyfunctional unsaturated materials are generally useful as 10-60% by weight of active ingredients in the printing composition. Preferably they are present as 20-40% by weight of the composition.

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. 1,482,953), vinyl substituted halomethyl-s-triazine 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 0.5-15% 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 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 Young's modulus of the polymer decreases in the presence of water. This modulus can be measured on commercially available equipment such as the "Rheovibrnn" model D-DV-II-C manufactured by Toyo Baldwin Co., Ltd. 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 example 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 in the presence of water.

Specific examples of these polymers include polyvinyl pyrrolidone, partially hydrolyzed polyvinyl acetate, hydroxyalkyl cellulose resins (e.g., hydroxypropyl cellulose), 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 10-40% by weight of solid ingredients in the printing composition. Preferably they are present as 12-25% by weight of the composition.

The substrates of the present invention may be any substrate, including metal, polymer and paper surfaces. Only when the coated article is to be used as a printing plate must the substrates be oleophobic on their surfaces. They are usually hydrophilic at the same time, but this is not essential. The substrate for a printing plate may be any material which is coated on at least one surface thereof to provide this oleophobic property. The substrates normally used for lithographic plates, such as those of U.S. Patent Nos. 556,380; 2,100,063; 2,251,181; 3,181,461; 2,373,357; and 4,116,695 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 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 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 lightsensitive 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. 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 are 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 is preferred that the oleophilic resin is a film forming polymer.Any compatible film forming oleophilic resin is 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 0.5 to 75% of the composition (the maximum is where it also constitutes the binder resin).

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 (such as dimethyl-formamide), chlorinated hydrocarbons (such as ethylene dichloride), 2nitro-propane, 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. 1,447,142 for printing compositions.

For the purpose of inhibiting premature polymerization and reducing any polymerization in non-imaged areas from scattered light, the incorporation of stabilizers such as phenolic stabilizers may be useful. These materials are well known in the art and are exemplified by di-tbutyl-p-cresol, hydroquinone, quinone, hydroquinone monomethyl ether, amyl quinone, n-butyl phenyl 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.

As noted above, many additional materials may be added to the compositions of the present invention. Some, of course, are more or less desirable than others. Epoxy polymerizable materials are amongst those ingredients which are less preferred or undesirable, unless present in amounts less than 10% by weight of solids in the compositions. Preferably there are no epoxy polymerizable materials present. The presence of the epoxy resins in amounts of 9% by weight or more, as shown in U.S. Patent Application Serial No. 15,585, filed February 27, 1979 in the name of C. Podsiadly and J. Holmes, has been found to contribute only limited capability to water developability.Reduced amounts of epoxy polymerizable materials has been surprisingly found to provide improved properties, even where both ethylenically unsaturated materials and epoxy polymerizable materials were present in that system. In view of the requirement for that minimum amount of epoxy polymerizable components in that system, this was a surprising discovery. An epoxy polymerizable material is defined as any material (monomer, oligomer, prepolymer or polymer) which has polymerizable epoxy groups thereon, particularly those materials with an epoxy equivalent weight between 90 and 10,000.

The following examples will show additional aspects 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 1 A photoreactive composition of the present invention was formulated by sequentially mixing ingredients as follows: diallyl orthophthalate prepolymer (having the structure shown above) as a 25% solution in methylethyl ketone 363 g polyvinylpyrrolidone as a 7% solution in ethyleneglycol monomethyl ether 590 g pentaerythritol tetraacrylate 68.75 g cellulose acetate butyrate 83.75 g polyurethane resins as a 10% solution in dimethylformamide 279 g 2(p-methoxystryl)4,6-bis(trichloromethyl) -s-triazine 5.5 g fluoroborate salt of the condensation product of paraformaldehyde and p-diazo diphenylamine 16.5 g yellow oil soluble dye 2.4 g dispersion of 1 8% Microlith Blue 4GK dye in methylethyl ketone (a copper phthalocyanine pigment) 168 g After homogeneous mixing of these compositions, the final solution was reduced to 8% solids, .

by the addition of 250 g methylethyl ketone, 500 g dimethylformamide and 1293 g of ethyleneglycol monomethyl ether. The polyurethane resin used in this and other examples was a thermoplastic polyurethane having repeating units of the formula:

which has a Shore hardness of 78A, tensile strength of 8900 (p.s.i.), and 300% Modulus at 1490 (psi).

The pigment dispersion in this and other examples was 60% pigment in 40% vinyl copolymer comprising 86% units derived from vinylchloride and 14% units derived from vinyl acetate.

A lithographic support plate structure for use in the examples was prepared according to the example in U.S. Patent No. 2,714,066. A smooth surfaced aluminum sheet was washed with trisodium phosphate, then treated with a nitric acid solution and rinsed in water. The sheet was then treated with an aqueous silicate solution and washed clean of any remaining water-soluble material. An initially water-soluble, light sensitive resin, p-diazodiphenylamine-formaldehyde resin as a 2.5% aqueous solution, was then coated over the silicate treated surface. A dry coating weight of 120-140 mg/ft2 of the above described photoreactive composition was then applied and air dried at 71-88 C.

A portion of this printing plate was exposed to a carbon arc source of ultraviolet radiation for 100 seconds at a distance of 1.37 meters. Development was with tap water and a few seconds of gentle rubbing with a soft cloth. After the coating in the unexposed areas was removed, the entire surface of the plate was treated with an aqueous desensitizing and gumming solution. The plate was buffed dry, mounted on a lithographic printing plate, and in an overpacked condition was run for over 4,000 impressions without loss of detail. Under normal packing conditions 50,000 impressions would be expected when used with fine quality halftone negatives. These plates can faithfully reproduce 176 line screens containing 3% highlight dots and 97% shadows.

The water developed plate required only 3 to 5 paper copies being passed through the press before all light exposed areas would accept ink, being fully converted from a generally hydrophilic surface to a hydrophobic olephilic surface. This compares favorably with organic solvent developed plates.

Example 2 A conventional grained and anodized substrate generally prepared according to the teachings of-U.S. Patents Nos. 3,181,461 and 3,865,700 was first coated with an initially water-soluble light sensitive p-diazodiphenylamine4ormaldehyde resin as a 0.5% aqueous solution and then coated with the following composition at a dry coating weight of 170-200 mg/ft2:: Weight % diallyl orthophthalate prepolymer (having the structure shown above) as a 25% solution in methylethyl ketone 30 g polyvinylpyrrolidone as a 7% solution in ethylenglycol monomethyl ether 16 y pentaerythritol tetraacrylate 24.0 g cellulose acetate butyrate 2.0 g polyurethane resin as a 10% solution in dimethylformamide 5.5 g 2(p-methoxystyryl)4, 6-bis(trichloromethyl) -s-triazine 2.0 g fluoroborate salt of the condensation product of paraformaldehyde and p-diazo diphenylamine 8.0 g yellow oil soluble dye 0.5 g dispersion of 18% Microlith Blue 46K dye in methylethyl ketone 12.0 g After exposure and development as in Example 1, press testing under accelerated conditions indicated an expected durability of about one hundred thousand impressions under normal conditions. Roll-up of the plate required only 5 copies and image quality was believed to be sufficient to develop and hold 176 line screen with 3-97% dots.

Example 3 This example shows the utility of the plates of the present invention for underexposure and post-heating.

A plate as prepared in Example 1 was exposed through a halftone negative in a step and repeat fashion so that different sections of the plate had 1 /4, 1 /2, 3/4, and full exposure as in Example 1. This plate was then developed as in Example 1 with tap water and treated with gum-desensitizer. The plate was then placed in an oven at about 230 C for six minutes which helped to crosslink the underexposed portions of the plate and to preserve the sharp dot structure of the image.

When mounted on a press along with a commercially available solvent developed plate which had a normal full exposure, the underexposed portions of the water developed plates printed with a sharper dot structure and yet the section receiving only one-quarter of its normal exposure time ran equally as long as did the control solvent developed plate.

Example 4 The coating composition of Example 1, without the pentaerythritol tetraacrylate, was coated, exposed, developed and desensitized as in Example 1. The plate showed good dot quality and resolution. The plate, however, showed very poor resistance to contact with solvents, such as might be present in press rooms and in certain conventional inks. This result confirms the necessity of the polyethylenically unsaturated component in the composition and plates of the present invention.

Example 5 When the composition of Example 1, without the organic solvent soluble diazo resin, was coated out on grained and anodized aluminum, no visible image appeared after exposure, although development was good. There was poor adhesion of the coating, however, as the grey scale could be rubbed off almost completely with only water. This shows the independent criticality of the diazo resin to the composition. It is believed that one of the significant aspects of the present invention is the combination of the ethylenically unsaturated component and organic solvent soluble diazo resin into one composition. The combination of these two diverse imaging materials provides a composition of unique quality and performance as a water developable composition.

Examples 6-11 A master batch of photoreactive composition without the organic solvent soluble film forming resin was constituted as follows: diallyl phthalate prepolymer of Example 1 38% polyvinylpyrrolidone 20% pentecrythritol triacrylate 20% cellulose acetate butyrate 5% 2-(p-methoxystyryl)-4, 6-bis(trich loromethyl) -2-trizaine 3% fluoroborate salt of Example 1 6% Yellow oil soluble dye 0.5% To portions of this composition each one of the following resins was added to a 7.5% level to form six different compositions which were coated on grained and anodized aluminum at the weight indicated in parentheses:: 6. no additional film forming resin 7. polyvinylformal (167 mg/ft2) 8. diglycidyl ether of Bisphenol A (M.W. of 1750-2050) (173 mg/ft2) 9. terpolymer of vinyl chloride (86%), vinylacetate (13%), and maleic acid (1%), (183 mg/ft2) 10. the polymer of Example 8, methacrylated by mixing 500 g of the polymer with 8.6 g methacrylic acid, 0.4 g triphenyl antimony and 0.065 g triphenyl phosphorous and heating at 100 C for 24 hours (183 mg/ft2) 11. (poly)ss-methacryloxypropyltrimethoxy silane (198 gm/ft2) These solutions were coated at 8% solids using a #10 wire wound Meyer bar on both smooth and grained aluminum base both of which had been precoated with a 1 % solution of the water soluble diazo resin used as a coating in Example 1.After exposure, development and press mounting, all samples ran for a longer press life than the same composition without polymeric additive. The polyvinylformal and terpolymer appeared to be the most durable compositions of these resins.

Examples 12 and 13 The composition of Example 1 was replicated, once without any cellulose acetate butyrate and once with an equal weight amount of cellulose acetate propionate replacing the butyrate. The cellulose acetate propionate containing film performed in substantially the same fashion as the composition of claims 1 when exposed, developed and placed on press. Both compositions having the cellulose acetate esters retained portions of the ink charge applied to the developed plates by the inking roll more efficiently than the plates without them. This property enables faster roll-up and faster start-ups in the use of presses.

Examples 14-18 A composition having no photoinitiator system therein was prepared having the following ingredients: diallylorthophthalate prepolymer of Example 1 as a 10% solution in methylethyl ketone 13.1% polyvinylpyrrolidone (as a 7% solution in ethylene glycol monomethyl ether 24.7% triacrylate of tris(2-hyd roxyethyl) isocyanurate (as a 50% solution in methylethyl ketone) 30.3% cellulose acetate butyrate (10% in dimethylformamide) 1.2% polyurethane of Example 1 (10% in dimethyl formamide) 6.1% fluoroborate salt of Example 1 7.2% yellow oil soluble dye 0.4% pigment dispersion of Example 1 (32.5 g) 17.0% To this was added 152 g of ethleneglycol monomethyl ether 485 g of methylethyl ketone and 768 g of dimethylformamide.Five portions of 105 g each of this composition were taken and one of the following four photoinitiators were added thereto: 1. 2-(p-methoxystyryl)-4,6-bis (trichloromethyl)-s-triazine 0.4 g 2. 2-chloro-thioxanthone 0.4 g 3. diphenyliodonium hexafluorophosphate (0.4 g) and 4,4-bis(dimethylamino) benzophenone 0.4 g 4. isopropyl benzoin ether (0.4 g) and 4,4'-bis(dimethylamino)benzophenone 0.2 g The fifth portion contained no photoinitiator system. The first portion showed good organic solvent resistance, indicating good crosslinking. The second and third portions showed fair solvent resistance, some of which would be improved by higher intensity exposure. The fourth and fifth samples showed no solvent resistance.In the case of the ether, the glass window of the exposure frame may have acted as a special filter for the peak sensitivity range for that particular well known free radical photoinitiator.

Examples 19-20 To portions of a composition having all of the ingredients of Example 1, except for the polyvinylpyrrolidone, and having the following composition: prepolymer 31%, tetraacrylate 31%, triazine photoinitiator 3%, diazo resin 3%, cellulose acetate butyrate 3%, yellow oil dye 1%, pigment dispersion 9% and dimethylformamide in an amount equal to about 31 times the combined weight of the initiator, diazo resin, butyrate and yellow oil dye were added the following polymers in an amount equal to 19% of the total composition solids (as 10% solutions in dimethylformamide): 1. Low molecular weight hydroxypropyl cellulose.

2. copolymer (50/50) of polyvinyl acetate and polyvinyl alcohol.

Both compositions were coated at a 20% solids level on smooth aluminum base having a coating of water soluble diazo resin thereon. In all cases the predispersed pigment tended to fall out of solution. After exposure through a halftone transparency and tap water development it was noted that the copolymer composition developed easier and the resulting image was tougher than that of the composition with the cellulose. The first composition still developed easily and the image portions accepted ink readily. The use of a higher molecular weight hydroxypropyl cellulose resins caused the composition to develop with more difficulty, but it did develop with tap water and the images accepted the ink after desensitization with conventional lithographic process gum.

Examples 21 and 22 Four portions of composition of Example 1 were duplicated except that the prepolymer was replaced by equal weight portions of two diglycidyl ethers of Bisphenoi A having high (MW 875-1025) and low (MW 450-550) molecular weight, polymethacrylated diglycidyl ether of Bisphenol A, and a polyacrylated polycaprolactone-2,4-toluene diisocyanate-hexane diol oligomer taught in Example 2 of U.S. Patent Application Serial No. 901,480, filed 1 May 1978. The compositions without the acrylate groups either had little solvent and abrasion resistance or developed with difficulty. Both compositions containing the ethylenically unsaturated materials performed well in comparison to the composition of Example 1.

The diglycidyl ether prepolymers had the following structure

wherein n in the low molecular weight prepolymer is about 2.5 and n in the high molecular weight prepolymer is about 6.

Examples 23 to 25 The following Examples investigate the extreme limits of the ranges for certain ingredients. All compositions were formed from the same components: (1) monomer; trishydroxyethylisocyanurate triacrylate (2) water softenable binder: polyvinylpyrrolidone (as a 7% solution in ethyleneglycol monomethyl ether) (3) film forming binders: (a) the polyallylorthophthalate prepolymer the structural formula of which is shown earlier, (b) a copolymer of vinyl acetate and vinyl chloride (14/86), and (c) cellulose acetate butyrate (4) solvent soluble diazo resin: the tetrafluoroborate salt of the condensation product of paraformaldehyde and pdiazo diphenylamine (5) photoinitiator system: 2-(Rmethoxystyryl)-4,4-bis-(trichloromethyl)-s-triazine (6) pigment:Microlith Blue 4GK in methyl ethyl ketone (18% dispersion) The compositions evaluated are shown in percentages by weight in the following table.

Example 23 24 25 Monomer 50 65 65 Water Softenable 30 10 5 Binder Film Forming Binder 5.0a, 3.2b 8a, 3.2b, 2c 9a, 3.2b Diazo 5 5 5 Photoinitiators 2 2 2 Pigment 4.8 4.8 4.8 Each of the compositions were homogeneously mixed and coated at 120-140 mg/ft2 onto separate lithographic support plate structures as recited in Example 1. The plates were then exposed and developed in tap water according to the procedures of Example 1. All plates were developable with water and held ink well. The plate of Example 25 was more difficult to develop (required more scrubbing with water), but did provide a usable plate. The higher amounts of monomer made the plates more tacky, but all performed reasonably well.

The water softenable binder does, in fact, provide some coherent film forming properties to the composition and printing plate in a manner similar to the organic solvent soluble film forming binder. The main requirement for the presence of at least 1 % by weight of the latter is to assist in providing ink receptivity.

Claims (17)

1. A photoreactive composition comprising a homogeneous mixture of: A. 1 to 75% by weight of organic solvent soluble film forming resin, B. 10 to 65% by weight of free radical polymerizable polyethylenically unsaturated compounds having at least two ethylenically unsaturated groups, C. 0.5 to 15% by weight of a free radical photo-initiator system, D. 5 to 40% by weight of a water softenable organic solvent soluble polymer, and E. 1 to 20% by weight of organic solvent soluble diazo resin.

2. A photoreactive composition as claimed in Claim 1 in which the sum of the water softenable and organic film forming resins would be equal to at least 10% by weight of the composition.

3. A photoreactive composition comprising a homogeneous mixture of: A. 15 to 75% by weight of an organic solvent soluble film forming resin, B. 10 to 60% by weight of free radical polymerizable polyethylenically unsaturated compounds having at least two ethylenically unsaturated groups, C. 0.5 to 15% by weight of a free-radical photo-initiator system, D. 10 to 40% by weight of a water-softenable organic solvent soluble polymer, and E. 1 to 20% by weight of organic solvent soluble diazo resin.

4. A composition as claimed in any preceding claim in which at least two of the ethylenically unsaturated groups on said ethylenically unsaturated compounds are selected from the acrylate and methacrylic groups.

5. A composition as claimed in Claim 4 in which the ethylenically unsaturated compounds have from 2 to 5 groups selected from acrylate and methacrylate groups.

6. A composition as claimed in any preceding claim in which the water-softenable polymer is selected from polyvinylpyrrolidone, partially hydrolyzed polyvinyl acetate, hydroxyalkyl cellulose resins and organic solvent soluble polyvinyl alcohol derivatives.

7. A composition as claimed in Claim 6 in which the water-softenable resin comprises polyvinylpyrrolidone.

8. A composition as claimed in any preceding claim in which at least 0.5% by weight of a second film forming resin which is oleophilic is present.

9. A composition as claimed in Claim 8 in which the oleophilic film forming resin is selected from cellulose acetate butyrate and cellulose acetate propionate.

10. A composition as claimed in any preceding claim in which the organic solvent soluble film forming resin is selected from epoxy resins, polyesters, polyallyl orthophthalate prepolymers, polyallyl isophthalate prepolymers, polyvinyl formal, polyurethanes, polyvinylbutyral, polyoxyethylene oxides, polyvinylhydrogen phthalates, polyacrylates, polymethacrylates, cellulose acetate esters, and polyvinyl chloride having a molecular weight of at least 1,000.

11. A composition as claimed in any preceding claim in which the solvent soluble film forming resin is capable of crosslinking or polymerizing by itself when heated to a temperature of at least 100 C.

12. A photoreactive composition as claimed in Claim 1 substantially as herein described with reference to any one of the Examples.

13. An imageable system comprising a substrate having coated on at least one surface thereof the photoreactive composition as claimed in any preceding claim.

14. An imageable system as claimed in Claim 13, in which the substrate comprises aluminium, the coated surface being oleophilic.

15. An imageable system as claimed in Claim 14 in which there is a coating of a water soluble diazo resin on the aluminium surface under the coating of the photoreactive composition.

16. An imageable system as claimed in Claim 12 substantially as herein described with reference to any one of the Examples.

17. A photoreactive composition comprising in homogeneous mixture a diazo resin, a free radical polymerizable polyethylenically unsaturated compound, and a free radical photoinitiator system.