HIGH SPEED AQUEOUS DEVELOPABLE RADIATION-SENSITIVE COMPOSITION AND PRINTING PLATE CONTAINING SAME

Abstract: A negative-working radiation-sensitive composition, comprising a mixture of a condensation polymer (A) having recurring units derived from (a) 1,4-bis( beta -hydroxyethoxy)cyclohexane and (b) diethyl-p-phenylenediacrylate; and a condensation polymer (B) having recurring units derived from (a), (b) and (c) dimethyl-3,3'-[sodioimino)disulfonyl]dibenzoate present in a weight ratio of A to B of from about 1:1 to about 9:1, and wherein units derived from (c) are present in an amount less that 1 mole % based on the total units in the polymer mixture, is particularly useful in preparing a printing plate which develops cleanly in an aqueous developer and exhibits improved speed and good incubation stability.

Description: HIGH SPEED AQUEOUS DEVELOPABLE RADIATION-SENSITIVE COMPOSITION AND PRINTING PLATE CONTAINING SAME FIELD OF THE INVENTION This invention relates to negative—working radiation—sensitive compositions which are particularly useful in preparing high speed aqueous developable printing plates. BACKGROUND OF THE INVENTION Negative— orking radiation-sensitive compositions can be formed from polymers which crosslink in radiation—exposed areas. A coating is ordinarily formed using an organic solvent as a coating aid. A developer is used in removing the unexposed portions of the coating to form a negative image. Conventionally, organic developers are used with negative—working radiation—sensitive coatings. These organic developers are expensive compared to aqueous alkaline solutions and, moreover, are substantially more burdensome to dispose of after use, because, if untreated, they can be ecologically objectionable. U.S. Pat. No. 3,929,489 describes superior, high speed lithographic printing plates developable with aqueous alcohol comprising a support having thereon a coated layer comprising a radiation—sensitive polyester derived from 1,4-bis(β—hydroxyethoxy)cyclohexane, diethyl p—phenylenediacrylate and dimethyl—3,3 • —[(sodioimino)— disulfonyl]dibenzoate. However, to meet the increasingly demanding requirements of the highly competitive printing and publishing industries, there is a continuing need for printing plates having improved speed and stability and which can be developed in aqueous developers. SUMMARY OF THE INVENTION In accordance with this invention, there is provided a printing plate which develops cleanly in an aqueous developer and which exhibits good incubation stability and improved speed. These features result, more specifically, from a negative—working radiation—sensitive composition which comprises a mixture of a condensation polymer (A) having recurring units derived from (a) 1,4—bis(β—hydroxyethoxy)cyclohexane and (b) diethyl p—phenylenediacrylate; and a condensation polymer (B) having recurring units derived from (a), (b) and (c) dimethyl—3,3'—[(sodioimino)disulfonyl]dibenzoate present in a weight ratio of A to B of from about 1:1 to about 9:1, and wherein units derived from (c) are present in an amount less than 1 mole T» based on the total units in the polymer mixture. The printing plate of this invention comprises the above—noted radiation—sensitive composition coated as a layer on a support. DESCRIPTION OF THE PREFERRED EMBODIMENTS An essential feature of this invention is that the radiation—sensitive composition is soluble in aqueous developers and can be selectively crosslinked to an insoluble form. The radiation—sensitive composition is formed From a mixture of condensation polymers (A) and (B) described above, which are known in the art. The condensation polymers are comprised of repeating units (b) provided for the purpose of introducing crosslinking sites. Repeating units (c) are provided in polymer (B) for the purpose of rendering the radiation—sensitive composition soluble in aqueous alkaline solutions before crosslinking. The repeating units (b) or (b) and (c) are linked into a condensation copolymer by repeating units (a). As is well known, the formation of the polymer by condensation inherently determines that the repeating units (a) will approximately equal on a molar basis the sum of the number of repeating units (b) and (c) present. As a practical matter, it is frequently desirable to utilize an excess of up to about 10 molar percent of the reactant (a). The preparation of the condensation polymers can be accomplished using procedures generally known to those skilled in the art, such as, for example, those preparation procedures described in U.S. Pat. No. 3,929,489 and Research Disclosure. Vol. 207, July 1981, Item 20708, the disclosures of which are hereby incorporated by reference. Typically, the condensa¬ tion copolymers are formed by mixing the reactants in the presence of a catalyst, such as butyl titanate, titanium isopropoxide, antimony oxide, strontium oxide, zinc acetate and the like. The degree and duration of heating can be used to increase the degree of polymerization achieved. Condensation polymer (A) preferably exhibits an inherent viscosity (IV) of 0.2 to 1.0, and most preferably 0.4 to 0.8. The inherent viscosity of polymer (B) can also be from 0.2 to 1.0. However, it is preferred that polymer (B) exhibit an inherent viscosity of from 0.3 to 0.6. It has been found that the inherent viscosity (which is related to the molecular weight distribution) of polymer (A) is the predominant factor in controlling the speed of the composition. On the other hand, it has been found that the inherent viscosity of polymer (B) plays a much smaller role in determining speed, although, incubation stability and developability of the plate are curtailed as the inherent viscosity of polymer (B) increases. Unless otherwise stated, all inherent viscosities are to be understood as being measured in 1:1 phenol: chlorobenzene (volume ratio) at 25 C using 0.25 grams of polymer per deciliter of solution. Prior to this invention it was believed, as is indicated by U.S. Pat. No. 3,929,489, that ionically charged units, such as (c) described above, were required to be present in an amount of at least 1 mole %, based on the total units in the polymer to render the polymer aqueous developable. Thus, it is surprising and unexpected that the composition of this invention comprising a polymer mixture containing units derived from (c) in an amount less than 1 mole % based on the total units present in such mixture develops cleanly in an aqueous developer. The polymers A and B preferably are present in a weight ratio of A to B of from about 1:1 to about 9:1. More preferably, polymers A and B are present in a weight ratio of A to B of from about 4:1 to 8:1. The currently most preferred weight ratio is about 6:1. Printing plates of this invention comprise a support having coated thereon a layer containing the radiation—sensitive composition described above. Such plates can be prepared by forming coatings with the coating composition and removing the solvent by drying at ambient or elevated temperatures. Any one of a variety of conventional coating techniques can be employed, such as hopper coating, doctor—blade coating, spray coating, dip coating, whirl coating, spin coating, roller coating, etc. Coating compositions containing the mixture of crosslinkable polymers of this invention can be prepared by dispersing or dissolving the polymers in any suitable solvent or combination of solvents used in the art to prepare polymer dopes. The solvents are chosen to be substantially unreactive toward the crosslinkable polymers within the time period contemplated for maintaining the solvent and polymer in association and are chosen to be compatible with the substrate employed for coating. While the best choice of solvent will vary with the exact application under consideration, exemplary preferred solvents include alcohols, such as methanol, ethanol, 1-propanol, 2-proρanol, butanol and benzyl alcohol; ketones, such as acetone, 2—butanone and cyclohexanone; ethers, such as tetrahydrofuran and dioxane; 2— ethoxyethyl acetate; N,N'—dimeth lformamide; chlorinated hydrocarbons such as chloroform, trichloroethane, 1,2—dichloroethane, 1,1—dichloroethane, 1,1,2—trichloroethane, dichloromethane, tetrachloroethane, chlorobenzene; and mixtures thereof. Suitable supports can be chosen from among a variety of materials which do not directly chemically react with the coating composition. Such supports include fiber based materials such as paper, polyethylene—coated paper, polypropylene—coated paper, parchment, cloth, etc.; sheets and foils of such materials as aluminum, copper, magnesium, zinc, etc.; glass and glass coated with such metals as chromium alloys, steel, silver, gold, platinum, etc.; synthetic resin and polymeric materials such as poly(alkyl acrylates), e.g. poly(methyl methacrylate), polyester film base, e.g. poly(ethylene terephthalate), poly(vinyl acetals), polyamides, e.g. nylon and cellulose ester film base, e.g. cellulose nitrate, cellulose acetate, cellulose acetate propionate, cellulose acetate butyrate and the like. Preferred support materials include zinc, anodized aluminum, grained aluminum, and aluminum which has been grained and anodized. A preferred support material is described in commonly assigned co—pending U.S. patent application Ser. No. 786,012 filed October 10, 1985, in the names of Miller and Gilson. The support can be treated by any of the methods well known in the art. A useful method of treating an aluminum support is to contact the support with a silicate material. The support can be contacted with an aqueous solution containing metal ions. A particularly useful method of treating an anodized aluminum support is described in commonly assigned co—pending U.S. patent application Ser. No. 786,403 filed October 10, 1985 in the names of Gilson and Miller and comprises the steps of contacting the support with a silicate, and contacting the silicated support with a metal salt solution. The support can be preliminarily coated — i.e., before receipt of the radiation—sensitive coating — with known subbing layers such as copolymers of vinylidene chloride and acrylic monomers — e.g. acrylonitrile, methyl acrylate, etc. and unsaturated dicarboxylic acids such as itaconic acid, etc.; carboxymethyl cellulose, gelatin; polyacrylamide; and similar polymer materials. A preferred subbing composition comprises benzoic acid and is described in commonly assigned, co—pending U.S. patent application Ser. No. 786,013 filed October 10, 1985 in the names of Miller and Gilson. The optimum coating thickness of the radiation—sensitive layer will depend upon such factors as the particular application to which the printing plate will be put, and the nature of other components which may be present in the coating. Typical coating thicknesses can be from about 0.05 to -7- 10.0 microns or greater, with thicknesses of from 0.1 to 2.5 microns being preferred. The printing plate of this invention can be exposed by conventional methods, for example, through a transparency or a stencil, to an imagewise pattern of actinic radiation, preferably rich in ultraviolet light, which crosslinks and insolubilizes the radiation-sensitive polymer in the exposed areas. Suitable light sources include carbon arc lamps, mercury vapor lamps, fluorescent lamps, tungsten filament lamps, "photoflood" lamps, lasers and the like. The exposure can be by contact printing techniques, by lens projection, by reflex, by bireflex, from an image— earing original or by any other known technique. The exposed printing plate of this invention can be developed by flushing, soaking, swabbing or otherwise treating the radiation—sensitive composition with a solution (hereinafter referred to as a developer) which selectively solubilizes (i.e. removes.) the unexposed areas of the radiation—sensitive layer. The developer is preferably an aqueous alkaline solution having a pH in the range of from about 9 to 14. Basicity can be imparted to the developer by the incorporation of soluble inorganic basic compounds such as alkali metal hydroxides, phosphates, sulfates, silicates, carbonates and the like as well as combinations thereof. Alternatively or in combination, basic soluble organic substances such as amines — e.g. triethanol amine, diethylene amine, diethyl amino ethanol, etc. can be incorporated. In a preferred form the developer includes a miscible combination of water and alcohol as a solvent system. The proportions of water and alcohol can be varied widely but are typically within the range of from 40 to 99 percent by volume water and from 1 to 60 percent by volume alcohol. Most preferably, the water content is maintained within the range of from 60 to 90 percent by volume. Any alcohol or combination of alcohols that does not chemically adversely attack the radiation—sensitive layer during development and that is miscible with water in the proportions chosen for use can be employed. Exemplary of useful alcohols are glycerol, benzyl alcohol, 2—phenoxyethanol, 1,2—propanediol, sec—butyl alcohol and ethers derived from alkylene glycols — i.e. dihydroxy poly(alkylene oxides) — e.g. dihydroxy poly(ethylene oxide), dihydroxy poly(propylene oxide), etc . It is recognized that the developer can, optionally, contain additional addenda. For example, the developer can contain dyes and/or pigments. It can be advantageous to incorporate into the developer anti—scumming and/or anti—blinding agents as is well recognized in the art. The printing plate can then be treated in any known manner consistent with its intended use. For example, lithographic printing plates are typically subjected to desensitizing etches. In addition to the photocrosslinkable mixture of polymers, a number of other addenda can be present in the coating composition and ultimately form a part of the completed printing plate. For example, radiation sensitivity of the radiation-sensitive polymeric composition can be enhanced by incorporating therein one or more spectral sensitizers. Suitable spectral sensitizers include enthrones, nitro sensitizers, triphenylmethanes, quinones, cyanine dyes, naphthones, pyrylium and thiapyrylium salts, furanones, anthraquinones, 3—ketocoumarins, thiazoles, thiazolines, naphthothiazolines, quinalizones, and others described in U.S. Pat. No. 4,139,390 and references noted therein. Preferred sensitizers include the 3—ketocoumarins described in U.S. Pat. No. 4,147,552 and the thiazoline sensitizers of U.S. Pat. No. 4,062,686. Such sensitizers can be present in the compositions in effective sensitizing amounts easily determined by one of ordinary skill in the art. The coating composition can contain pigments preferably having a maximum average particle size less than about 3 micrometers. These pigments can provide a visible coloration to an image before or after development of the element. Useful pigments are well known in the art and include titanium dioxide, zinc oxide, copper phthalocyanines halogenated copper phthalocyanines, quinacridine, and colorants such as those sold commercially under such trade names as Monastral Blue and Monastral Red B. The pigments are generally present in the compositions in an amount within the range of from 0 to about 50 percent (by weight) based on the total dry composition weight. Preferred amounts are within the range of from about 5 to about 20 percent (by weight). It is frequently desirable to add print out or indicator dyes to the compositions to provide a colored . print out image prior to development. Useful dyes for such purpose include monoazo, diazo, methine, anthraquinone, triarylmethane, thiazine, xanthene, phthalocyanine, azine, cyanine and leuco dyes as described, for example, in U.S. Pat. Nos. 3,929,489 and 4,139,390 and references noted therein. Such dyes are present in amounts readily determined by a person of ordinary skill in the art. It is recognized that the polymer mixture of this invention can become crosslinked prior to intended exposure if the compositions or printing plates of this invention are stored at elevated temperatures, in areas permitting exposure to some quantity of actinic radiation and/or for extended periods of time. To insure against crosslinking the polymer mixture inadvertently before intended exposure to actinic radiation stabilizers can be incorporated into the radiation—sensitive compositions and printing plates of this invention. Useful stabilizers include piccoline—N—oxide; phenols, such as 2,6—di—tert— ut 1-p—cresol, 2,6—di—tert—but lanisole and p—methoxyphenol; hydroquinones such as hydroquinone, phloroglucinol and 2,5—di—tert—butyIhydroquinone; triphenylmetallics, such as triphenylarsine; triphenylstilbene; and tertiary amines, such as N— ethyldiphenylamine. Still other addenda useful in the printing plates of this invention include antioxidants, surfactants, anti—scumming agents, and others known in the art. Binders or extenders can optionally be incorporated into the radiation—sensitive composition. Such binders or extenders can be present in an amount within the range of from 0 to about 50 percent (by weight) based on total dry composition weight. • Suitable binders include styrene—butadiene copolymers; silicone resins; styrene—alkyd resins; silicone—alkyd resins; soya—alkyd resins; poly(vinyl chloride); poly(vinylidene chloride); vinylidene chloride—acrylonitrile copolymers; poly(vinyl acetate); vinyl acetate—vinyl chloride copolymers; poly(vinyl acetals), such as pol (vinyl butyral); polyacrylic and -methacrylic esters, such as poly(methyl methacrylate), poly(n—butyl methacrylate) and poly(isobutyl methacrylate); polystyrene; nitrated polystyrene; polymethylstyrene; isobutylene polymers; polyesters, such as poly(ethylene—co—alkaryloxy- alkylene terephthalate) ; phenolformaldehyde resins; ketone resins; polyamides; polycarbonates; polythiocarbonates, ρoly(ethylene 4,4'-isopropylidenediphenylene terephthalate); copolymers of vinyl acetate such as poly(vinyl-m-bromobenzoate—co-vinyl acetate); ethyl cellulose, poly(vinyl alcohol), cellulose acetate, cellulose nitrate, chlorinated rubber and gelatin. Methods of making binders or extenders of this type are well known in the prior art. A typical resin of the type contemplated for use is Piccolastic ASO™, commercially available from Hercules, Inc., Wilmington, Del. Other types of binders which can be used include such materials as paraffin and mineral waxes. The radiation-sensitive composition can contain at least one other film—forming polymeric resin in addition to the crosslinkable polymers of this invention. These additional polymeric resins are typically not radiation—sensitive, although mixtures of radiation—sensitive resins can be employed and are usually selected from those resins which are soluble in the coating solvent. The amount of resin employed can be varied, depending upon the resin, the crosslinkable polymer, the coating solvent, and the coating method and application chosen. For optimum performance, however, it is preferred that the radiation—sensitive composition be free of other film-forming resins and binders. Thus, the radiation—sensitive composition preferably comprises a photocrosslinkable polymer which consists essentially of the polymer mixture described above. Exemplary of film-forming resins useful in the compositions of this invention are phenolic resins, such as novolac and resole resins. These resins are particularly useful in improving the resistance of coatings to etchants. Where it is desired to control wear resistance of the coatings, it can be desirable to incorporate resins, such as epoxy. resins; hydrogenated rosin; poly(vinyl acetals); and acrylic polymers and copolymers, such as pol (methyl methacrylate), acrylates of the type disclosed in British Pat. No. 1,108,383, poly(alkylene oxides) and pol (vinyl alcohol). The crosslinkable polymers of this invention are also generally compatible with linear polyesters. Examples The following examples illustrate the invention. Examples 1—2 Demonstration of Improved Speed The following composition was coated at a 2 total dry coverage of 100 mg/ft on an aluminum support grained and anodized as described in U.S. application Ser. No. 786,012 noted above. The support was silicated and treated as described in U.S. application Ser. No. 786,403, and provided with a subbing layer as described in U.S. application Ser. No. 786,013. -13- dichloromethane 318.3 gm polymer A (IV = 0.57) 7.85 polymer B (IV = 0.33) 1.24 2,6-di-t-butyl-p-cresol 0.36 7—diethylamino-3-(4-dimethyl- aminobenzoyl) coumarine 0.394 piccoline-N—oxide 0.575 Monastral Blue (a blue pigment sold by the DuPont Co., 19.7% solids) 3.5 DC-1248 surfactant (a silicon glycol copolymer sold by Dow Corning, 10% solids in dichloromethane) 0.125 Polymer A was derived from (a) l,4-bis(β-hydroxy- ethoxy)cyclohexane (HEC) and (b) diethyl p—phenylenediacrylate (DEBA) present in about equimolar amounts, i.e., (HEC) 5Q (DEBA) 5Q . Polymer B was derived from (a), (b) and (c) dimethyl-3,3'—[(sodioimino)disulfonyl]dibenzoate (CX-5) present in molar amounts of about (HEC) 50 (DEBA 46.5 (CX - 5 3.5' The plate so prepared was exposed to a "blue filtered" 1 kw Tamarack mercury light source contained in an Opti-Copy Image Imposer unit. The exposed plate was processed in aqueous Developer "A" using an Ajax Compact 86 processor at 30 cm/min at 30 C. Developer "A" had the following formula: benzyl alcohol 5.0% *Carbowax 350 15.01 sodium silicate 1.0% polyvinyl pyrrolidone 1.0% water 78.0% *A low molecular weight polyethylene glycol sold by Union Carbide. The plate speed was measured by reflection densitometry using a KODAK T—14 Control scale. The plate speed was compared with the commercially available, high speed KODAK Polymatic™ Litho Plate (PLP) which was exposed to the same light source and processed in accordance with the procedure normally used in the trade. The results are as follows: Example Relative Speed 1 3.5 PLP 1 Example 2 A composition identical to that in Example 1 was prepared except that polymer A having an inherent viscosity of 0.6 was used. The plate was exposed and developed as described above and was found to be 4.9 time faster than the PLP plate. Example 3 Demonstration of Incubation Stability A printing plate prepared as described in Example 1 was incubated at 49 C for 1 week. The plate was then exposed and developed in the Ajax Processor with Developer "A" as described above. Comparison with a second plate, prepared as described in Example 1 except that it was not incubated, revealed that the incubated plate had gained an acceptable 0.15 log E in speed and still developed cleanly.. Comparative Example 1 A composition similar to Example 1 but omitting polymer (B) and using polymer (A) having an inherent viscosity of 0.57 for the total polymer coverage was prepared and coated on an aluminum support as described above. This plate did not develop cleanly, exhibited pigment redeposit, long toes and areas of incomplete cleanout. After 1 week at 49 C, a plate prepared in this manner would not develop at all. Comparative Example 2 A composition similar to Example 1 but this time omitting polymer (A) and using polymer (B) having an inherent viscosity of 0.56 as the only polymer was prepared''and coated on an aluminum support as in Example 1. The plate was exposed and developed in Developer "A" as previously described. However, after 1 week at 49 C the plate did not develop cleanly, thus indicating poor stability. This polymer contained 3.5 mole percent of recurring CX-5 units. The plate of Example 1 of this invention which processed cleanly after incubation at 49 C for 1 week contained a polymer mixture which contained less than 1 mole percent of recurring CX-5 units. Comparative Example 3 A composition similar to Example 1 but this time omitting polymer (A) and using polymer (B) having an inherent viscosity of 0.33 for the total polymer coverage was prepared and coated on an aluminum support, and exposed and developed in Developer "A" as described above. This plate was found to be substantially slower in speed than the PLP plate. The invention has been described in detail with particular reference to preferred embodiments thereof but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

Claims: Claims 1. A negative—working radiation—sensitive composition consisting essentially of a mixture of a condensation polymer (A) consisting essentially of recurring units deriυed from (a) l,4—bis(β—hydroxy— ethoxy)cyclohexane and (b) d ethyl p—phenylene¬ diacrylate; and a condensation polymer (B) consisting essentially of recurring units deriυed from (a), (b) and (c) dimethyl-3, 3 '—[(sodio- imino)disulfonyl]dibenzoate present in a weight ratio of A to B of from about 1:1 to about 9:1, and wherein units deriυed from (c) are present in an amount less than 1 mole % based on the total units in the polymer mixture. 2. The composition of claim 1 wherein said polymers (A) and (B) are present in a weigh ratio of A to B of from 4:1 to 8:1. 3. The composition of claim 1 wherein said polymer (A) has an inherent υiεcosity of from 0.4 to 0.8. 4. A negatiυe— orking printing plate comprising a support haυing thereon a coated layer of a radiation—sensitive composition consisting essentially of a mixture of a condensation polymer (A) consisting essentially of recurring units derived from (a) 1,4—bis(β-hydroxyethoxy)— cyclohexane and (b) diethyl p—phenylene¬ diacrylate; and a condensation polymer (B) consisting essentially of recurring units derived from (a), (b) and (c) dimethyl-3, 3 ' [(sodio- imino)disulfonyl)dibenzoate present in a weight ratio of A to B of from about 1:1 to about 9:1, and wherein units derived from (c) are present in an amount less than 1 mole % based on the total units in the polymer mixture. 5. The printing plate of claim 4 wherein said polymers (A) and (B) are present in a weight ration of A to B of from 4:1 to 8:1. 6. The printing plate of claim 4 wherein said support comprises anodized aluminum. 7. The printing plate of claim 6 further comprising a subbing layer.

Inventors: KAPLAN MARK STEVEN, KAPLAN, MARK, STEVEN
Applicants: EASTMAN KODAK CO, EASTMAN KODAK COMPANY
Application year: 1988
Main classification: G03F7
IPC codes: C08G63, C08L67, G03F7