PRESENSITIZED LITHOGRAPHIC PLATE

Abstract: A presensitized lithographic plate is comprised of a sup­ port base such as an aluminum support base with an anodized surface, having a subbing layer positioned thereon which is coated with a light-sensitive layer. The light-sensitive layer comprises a diazo compound and a binder or comprises a photopolymerizable composition. The subbing layer com­ prises a high molecular compound containing sulfonic acid group-containing monomer units as recurring units. The sub­ bing layer provides a lithographic plate with greatly improved shelf life. Moreover, it increases the stability of the lithographic plate such that when the plate is stored it continues to be cap­ able of producing copies which do not have stained back­ ground areas even when the plate is stored under adverse temperature and humidity conditions.

Description: This invention relates to a presensitized lithographic plate. More particularly, it relates to a presensitized lithographic plate having improved develop-ability and resistance with respect to the formation of background stains. One of essential requirements for lithographic printing plates is to provide copies having no background stains. Background stains increase particularly in proportion to the storage period after preparation of the printing plate. Printing plates which have no background stains immediately after their preparation undergo formation of background stains over time. This tendency is conspicuous particularly when printing plates are stored at high temperatures and under high humidity. Therefore, presensitized lithographic plates which resist formation of background stains when stored for a long time, particularly at high temperatures and under high humidity have been desired. Many attempts to obtain such lithographic plates have been conducted. For example, there have been known a presensitized lithographic plate comprising an anodized aluminum plate having provided thereon in sequence a subbing layer composed of polyvinylphosphonic acid and a diazo compound-containing light-sensitive layer (DE-C-1621478) (corresponding to US-A-4153461), a presensitized lithographic plate comprising an aluminum support having provided thereon in sequence a subbing layer of polyacrylic acid or the like and a diazo resin layer DE-C-1091433), a presensitized lithographic plate comprising a polyacrylamide-subbed support having provided thereon a light-sensitive layer US-A-3511661), a technique of adding a high molecular organic acid to a light-sensitive layer of a presensitized lithographic plate containing a diazo compound and an organic high molecular carrier in the light-sensitive layer for the purpose of improving stability with time of the plate and preventing formation of background stains JP-A-107238/81 and the like. However, none of these techniques have exerted satisfactory effects, and, hence, more improvements have been desired. JP-A-5042/82 (corresponding to US-A-4401743) describes a light-sensitive adduct containing a combination of a diazo resin having a plurality of side chain diazonium groups and a sulfonated polymer having a plurality of sulfonato groups (e.g., sulfonated polyurethane or sulfonated polyester) . This adduct, however, fails to attain the effect of preventing formation of background stains and, in addition, performance of a presensitized plate using it is governed by the properties of the sulfonated polyurethane or sulfonated polyester because the adduct is used as a light-sensitive layer itself and, as a result, the applicable scope of the lithographic plate is extremely limited. Further, FR-A-1 551 884 and Research Disclo sure, No. 17712 (January 1979) disclose a light-sensitive lithographic printing plate comprising an anodized aluminum sheet (which has a cellular structure in the former publication and a grained structure in the latter publication) having thereon a subbing layer of a high molecular compound containing sulfonic acid group-containing monomer units as recurring units. This subbing layer is intended to maintain hydrophilicity of non-image area throughout development and press runs and is not provided for improving shelf-life of lithographic printing plates. In fact, in specific examples of the latter publication, a light-sensitive layer comprising poly-1,4-cyclohexylenebis-(oxyethylene)-p-phenylenediacrylate-co-3,3'-[(sodio-iminodisulfonyl)dibenzoate], a dye, a sensitizer and azide for print-out is used, and a plate sample having the light-sensitive layer and having been incubated at 120°F and 50% RH for 2 weeks cannot be developed with a developer to be used for developing fresh plates and is, therefore, developed with dichloroethane having stronger solvent action. In JP-B-39-23982 the subbing layer is applied to an aluminum support which is neither anodized nor treated with sodium silicate. In DE-A-22 48 743 lithographic printing plates are disclosed having an anodized aluminum support the surface of which may further be treated with a polyvinyl benzene sulfonate or, alternatively, with another hydrophilizing agent like sodium silicate. It is, therefore, an object of the present invention to provide a presensitized lithographic plate comprising a support having provided thereon a subbing layer and a light-sensitive layer with comparatively high shelf-life stability and poor liability to form stains in non-image areas such as a light-sensitive layer comprising a diazo compound and a binder, which plate has a subbing layer capable of preventing formation of background stains when printing is conducted using a lithographic printing plate prepared from the presensitized lithographic plate by an imagewise exposure and a development even after having been stored for a long period of time after production of the presensitized lithographic plate or having been stored at high temperature and high humidity. As a result of intensive investigations, the inventors have developed presensitized lithographic plates comprising: an anodized aluminum support treated with an aqueous sodium silicate solution; a subbing layer comprising a high molecular weight compound which contains sulfonic acid group-containing monomer units as recurring units and has a molecular weight in the range of 1,000 to 1,000,000 provided on said support; and a light-sensitive layer comprising a diazo compound and a binder or comprising a photopolymerizable composition provided on said subbing layer. Specific examples of monomer units which have a sulfonic acid group, and are used in the present invention include those derived from such monomers as pstyrenesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, ethylenesulfonic acid, 2-chloroethylenesulfonic acid, ethylenedisulfonic acid, 1-propene-1-sulfonic acid, 1-propene-2-sulfonic acid, 2-methyl-1,3-propenedisulfonic acid, 1-butene-1-sulfonic acid, 1-pentene-1-sulfonic acid, 1-hexene-1-sulfonic acid, 2-phenylethylenesulfonic acid, 1-methyl-2-phenylethylenesulfonic acid, 3-chloroallylsulfonic acid, allylsulfonic acid, 3-chloro-2-butenesulfonic acid, 3-chloromethallylsulfonic acid, methallylsulfonic acid, 3-methyl-2-butene-2-sulfonic acid, 3-phenylallylsulfonic acid, 3-phenylmethallylsulfonic acid, 2-benzylallylsulfonic acid, 2-chloro-4-styrenesulfonic acid, vinyltoluenesulfonic acid, α-methylstyrenesulfonic acids. Of these, pstyrenesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, and ethylenesulfonic acid are particularly preferable monomers. One or more of these monomers are selected and polymerized or copolymerized with other monomers. In conducting copolymerization, any monomer that can be copolymerized with the sulfonic acid group-containing monomer can be used. Particularly preferable examples of such monomers include, for example, alkyl acrylates (e.g., methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, n-amyl acrylate, isoamyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, n-octyl acrylate, n-decyl acrylate, 2-hydroxyethyl acrylate), alkyl methacrylates (e.g., methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-amyl methacrylate, 2-ethylhexyl methacrylate, n-octyl methacrylate, n-decyl methacrylate, 2-hydroxyethyl methacrylate styrenes (e.g., styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, 2,4-dimethylstyrene, 2,5-dimethylstyrene, 3,4-dimethylstyrene, 3,5-dimethylstyrene, 2,4,5-trimethylstyrene, 2,4,6-trimethylstyrene, o-ethylstyrene, o-sec-butylstyrene, o-tert-butylstyrene, p-fluorostyrene, 2,5-difluorostyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, 2,4-dichlorostyrene, 2,5-dichlorostyrene, 2,6-dichlorostyrene, 3,4-dichlorostyrene, p-bromostyrene, p-cyanostyrene, acrylonitrile, methacrylonitrile, acrylamide, N-sec-butylacrylamide, N-tert-butylacryl amide, N,N-dibutylacrylamide, N-tert-butylmethacrylamide, acrylic acid, methacrylic acid, vinyl acetate. The molecular weight of the high molecular compound to be used in the present invention is not limited as long as it is solvent-soluble but, as a general guide, a range of from about 1,000 to about 1,000,000 is suitable, with a range of 2,000 to 100,000 being preferable and a range of 10,000 to 100,000 being most preferable. The content of sulfonic acid group-containing monomer units in the high molecular compound can be selected over a wide range, with a range of about 1 to 100 mol% being suitable and a range of 5 to 100 mol% being more preferable. The high molecular compound of the present invention can be synthesized according to a known process, for example, by conducting polymerization according to a solution polymerization process and, if desired, neutralizing the acid groups of the resulting polymer to form salts thereof, such as alkali metal salts, e.g., sodium salt, potassium salt., ammonium salts and water-soluble amine salts. This solution polymerization process is usually conducted in a solvent capable of dissolving the starting monomer or monomers, such as isopropyl alcohol, in a nitrogen atmosphere in the presence of a polymerization initiator. Alternatively, the starting monomer or monomers may be emulsified in water with the aid of a surfactant and subjected to emulsion polymerization using a polymerization initiator such as potassium persulfate to obtain an aqueous dispersion. The polymer solids may of course be collected as solids. When coating the above-described high molecular compound, it is dissolved in a suitable solvent and coated on a support in a conventionally known manner. The coating amount of the compound depends upon the kind of the high molecular compound to be used, and hence it cannot be set forth unequivocally. However, as a general guide, a coating amount of 0.0001 to 1 g/m² is suitable. If the amount is less than 0.0001 g/m², the effect of depressing formation of background stain becomes insufficient and, if it is more than 1 g/m², there result detrimental influences on durability of the resulting lithographic printing plates, etc. Thus, an amount of 0.0005 to 0.2 g/m² is preferable. The solution for the subbing layer may contain suitable additives such as pH-adjusting agents (e.g., phosphorous acid, oxalic acid, low molecular organic sulfonic acid.) and wetting agents (e.g., saponin). The subbing layer of the present invention is coated on an aluminum plate having been anodized and then treated with a sodium silicate aqueous solution as is disclosed in US-A-3181461. In accordance with the invention, a light-sensitive layer is provided on a support having the above-described subbing layer to obtain a presensitized lithographic plate which undergoes formation of remarkably reduced stain in non-image areas even after being stored for a long time. Examples of useful light-sensitive layers include that containing both a diazo compound and an organic high molecular binder, and a photopolymerizable light-sensitive layer which comprises an addition-polymerizable unsaturated compound, a photopolymerization initiator, and an organic high molecular binder. Of these, the light-sensitive layer containing both a diazo compound and an organic high molecular binder serves to obtain the greatest effect of the present invention. Therefore, this light-sensitive layer will be described in detail below. Particularly preferable diazo compounds are diazo resins which are soluble in an organic solvent and substantially insoluble in water, and diazo resins represented by a condensate between an aromatic diazonium salt and, for example, an active carbonyl-containing compound (particularly, formaldehyde) are useful. Useful diazo resins include Lewis acid salts (such as hexafluorophosphate or tetrafluoroborate) of a condensate between p-diazodiphenylamine and formaldehyde or acetaldehyde (described in, for example, 17602/64 and 98613/79), anionic surfactant salts of a condensate between p-diazodiphenylamine and formaldehyde (described in 6813/66 and 9804/73), phenol salts, fluorocaprates or sulfonates (e.g., triisopropylnaphthalenesulfonate, 4,4'-biphenyldisulfonate, 5-nitro-o-toluenesulfonate, 5-sulfosalicylate, 2,5-dimethylbenzenesulfonate, 2-nitrobenzenesulfonate, 3-chlorobenzenesulfonate, 2-chloro-5-nitrobenzenesulfonate, 2-fluorocaprylnaphthalenesufonate 1-naphthol-5-sulfonate, 2-methoxy-4-hydroxy-5-benzoylbenzenesulfonate, p-toluenesulfonate .) of a condensate between p-diazodiphenylamine and formaldehyde (described in US-A-3300309, JP-A-38302/72, and 44123276), organophosohonates of a condensate between p-diazodiphenylamine and formaldehyde (described in US-A-3404003), aromatic carboxylates of a condensate between p-diazodiphenylamine and formaldehyde (described in 28594/70), and phosphates or oxalates of a condensate between p-diazodiphenylamine and formaldehyde. Other useful diazo resins include a condensate between substituted or unsubstituted diphenylamine-4-diazonium salt and an ether compound (described in US-A-3,679,419). Of these, halogenated Lewis acid salts of a condensate between an aromatic diazonium compound and an active carbonyl compound or active ether compound, especially tetrafluoroborate and hexafluorophosphate, are most preferable as a diazo resin to be used in the present invention. Additionally, the term "substantially water-insoluble" used with the diazo resin of the present invention means a solubility of about 1 wt% or less in water at an ordinary temperature. On the other hand, as the organic high molecular binder to be used in the present invention, those which are substantially water-insoluble and have film-forming properties are preferable, with those having a good compatibility with diazo resin, oleophilic properties, and excellent abrasion resistance being particularly preferable. Specific examples thereof include polystyrene, polyvinyl chloride, polyacrylate or polymethacrylate, polyester, polyamide, polyurethane, polycarbonate, epoxy resin, polyvinyl formal, polyvinyl butyral, and alkylphenol-formaldehyde resin. Of these, polyacrylates or polymethacrylates with an acid value of 10 to 200 are preferable. As particularly preferable examples of the polyacrylates or polymethacrylates with an acid value of 10 to 200, there are illustrated copolymers containing acrylic acid, methacrylic acid, crotonic acid or maleic acid as a necessary ingredient such as multicomponents copolymers comprising 2-hydroxyethyl acrylate or 2-hydroxyethyl methacrylate, acrylonitrile or methacrylonitrile, acrylic or methacrylic acid and, if necessary, other copolymerizable monomer or monomers as described in JP-A-118802/75 (corresponding to US-A-4123276), multicomponents copolymers comprising acrylic or methacrylic acid esterified with a group having a terminal hydroxy group and a dicarboxylic ester residue, acrylic or methacrylic acid and, if necessary, other copolymerizable monomer or monomers as described in JP-A-120903/78, multicomponents copolymers comprising a monomer having an aromatic hydroxy group at the terminus (for example, N-(4-hydroxyphenyl)methacrylamide), acrylic or methacrylic acid and, if necessary, other copolymerizable monomer or monomers as described in JP-A-98614/79, and multicomponents copolymers comprising alkyl acrylate or methacrylate, acrylonitrile or methacrylonitrile, and unsaturated carboxylic acid as described in JP-A-4144/81. In addition, acidic polyvinyl alcohol derivatives and acidic cellulose derivatives are also useful. Additionally, substantially water-insoluble organic high molecular binders to be used in the present invention mean those with a solubility in water of about 1 wt% or less at an ordinary temperature. The contents of the diazo resin and the high molecular compound in the light-sensitive layer are: 3 to 30 wt% of the diazo resin and 97 to 70 wt% of the high molecular compound based on the total weight of the two, with 5 to 20 wt% of the diazo resin and 95 to 80 wt% of the high molecular compound being more preferable. The smaller the content of the diazo resin, the higher the sensitivity but, if the content is less than 3 wt%, photohardening of the high molecular compound becomes so insufficient that photohardened film will be swollen with a developer upon development to undergo weakening of the film. On the other hand, if the content of the diazo resin exceeds 30 wt%, there results such a reduced sensitivity that the product cannot be practically used. The light-sensitive layer is coated in a dry coated amount of about 0.1 to 5 g/m². In making a lithographic printing plate from the presensitized lithographic plate of the present invention, conventionally known procedures can be utilized as such. That is, the presensitized lithographic plate is exposed through a transparency having a line image and/or halftone dot image, then processed with a developer to remove non-image areas of the light-sensitive layer. As suitable light sources to be used for the exposure, a mercury lamp, xenon lamp, chemical lamp, metal halide lamp, strobo, etc., are used. As the developer, a proper one may be used according to the composition of the light-sensitive layer. For example, for a light-sensitive layer comprising a diazo compound and an organic high molecular binder, aqueous alkaline developers described in e.g. US-A-3475171, 3669660 and 4186006 are used. The present invention will now be described in more detail by reference to following non-limiting examples. Percentages in the examples are by weight unless otherwise specified. EXAMPLES 1 TO 4 An aluminum plate was soaked in a 20% sodium phosphate aqueous solution to degrease and, after conducting electrolytic etching, anodized in a sulfuric acid solution, then subjected to pore-sealing treatment in a sodium metasilicate aqueous solution. A light-sensitive solution of the following formulation (b) was coated on the thus treated aluminum plate and dried to form a light-sensitive layer having 2 g/m² of dry weight. Accordingly, a presensitized plate was obtained. This plate was referred to as Comparative Sample (I). On the same aluminum support as used in this Comparative Sample (I) was coated a 1% solution (solvent: water/methanol 50 wt% mixture) of each of the copolymers of the formulations B to E described below. The coating was dried to form a subbing layer, followed by coating the light-sensitive solution of formulation (b) in a dry weight of 2 g/m² to obtain presensitized lithographic plates. These plates were referred to as Samples (I) to (4). In every sample, the dry coated weight of the subbing layer was 0.005 g/m² . Each of these Samples (1) to (4) and Comparative Sample (I) was left for 5 days at 40°C and 80% RH, exposed, and subjected to plate-making procedures in the same manner as in Example 1. When printing was conducted using the thus obtained Lithographic Printing Plates (1) to (4) and (I), Samples (1) to (4) remarkably depressed formation of background stains in comparison with Comparative Sample (I) having no subbing layer, thus fully exerting the effects of the present invention. EXAMPLE 5 A 0.30 mm thick aluminum plate was surface-grained using a nylon brush and an aqueous suspension of 400 mesh pumice and thoroughly washed with water. Then, the aluminum plate was soaked in 10% sodium hydroxide at 70°C for 60 seconds in order to etch the plate. The etched plate was then washed with running water, neutralized with 20% HNO₃, and thoroughly washed with water. The plate was then subjected to electrolytical graining treatment in a 1% nitric acid aqueous solution using sine wave alternating current under the conditions of V A = 12.7 V and an anodic electric amount of 160 coulomb/dm² to attain a surface roughness of 0.6 µ (Ra). Subsequently, the plate was soaked in a 30% H₂SO₄ aqueous solution to desmut at 55°C for 2 minutes, anodized in a 20% H₂SO₄ aqueous solution for 2 minutes at a current density of 2 A/dm² to attain a thickness of 2.7 g/m², and then soaked in a 2.5% sodium silicate aqueous solution at 70°C for 1 minute, washed with water, and dried. A 1% aqueous solution of the copolymer of the following formulation A was coated on the thus treated aluminum plate and dried to form a subbing layer. The dry amount of the coated subbing layer was 0.05 g/m². Formulation A Methyl methacrylate/ethyl acrylate/sodium 2-acryl amido-2-methylpropanesulfonate (50 : 30 : 20 molar ratio) copolymer (mean molecular weight: about 60,000) Light-sensitive solution (1) was then prepared. Additionally, the poly(allyl methacrylate/ methacrylic acid) was synthesized as follows. 1.68 ℓ of a reaction solvent of 1,2-dichloroethane was added to a 3-liter four neck flask equipped with a stirring rod, stirring blade, reflux condenser, dropping funnel, and thermometer and heated to 70°C while replacing the atmosphere with nitrogen. A solution of 100.8 g of allyl methacrylate, 7.6 g of methacrylic acid, and 1.68g of a polymerization initiator of 2,2'-azobis(2,4-dimethylvaleronitrile) in 0.44 liter of 1,2-dichloroethane was placed in the dropping funnel, and the mixture solution was dropwise added to the flask over a period of 2 hours under stirring. After completion of the dropwise addition, the stirring was continued for 5 hours at a reaction temperature of 70°C to complete the reaction. After heating, 0.04 g of p-methoxyphenol was added to the reaction solution, and the solution was concentrated to 500 mℓ. The concentrate was added to 4 liters of hexane to precipitate. Vacuum drying of the precipitate gave 61 g (yield: 56%) of a copolymer. Viscosity: [η] = 0.068 at 30°C in MEK solution. After being filtered, the light-sensitive solution (1) was coated on the foregoing subbed base plate in a dry coated amount of 2.5 g/m² . Drying was conducted at 100°C for 2 minutes. Then, a 3% aqueous solution of polyvinyl alcohol (viscosity: 5.3 + 0.5 m Pa.5 in 4% aqueous solution at 20°C (measured according to Höpler method); saponification degree: 86.5 to 89.0 mol%; polymerization degree: not more than 1,000) was coated on the surface of the above-described light-sensitive layer in a dry amount of 1.0 g/m². The thus obtained presensitized lithographic plate was referred to as Sample (5). For the purpose of comparison, a presensitized lithographic plate was prepared in the same manner as with Sample (5) except for not providing the subbing layer. This was referred to as Comparative Sample (II). These Samples (5) and (II) were stored for 10 days in an atmosphere of 40°C and 80% RH exposed, and developed with the developer of the following formulation to obtain Lithographic Printing Plates (5) and (II). Comparison of the printing plates with each other revealed that Lithographic Printing Plate (5) suffered much less background stains than Lithographic Printing Plate (II).

Claims: A presensitized lithographic plate comprising: an anodized aluminum support treated with an aqueous sodium silicate solution; a subbing layer comprising a high molecular weight compound which contains sulfonic acid group-containing monomer units as recurring units and has a molecular weight in the range of 1,000 to 1,000,000 provided on said support; and a light-sensitive layer comprising a diazo compound and a binder or comprising a photopolymerizable composition provided on said subbing layer. A presensitized lithographic plate as in Claim 1, wherein said monomer units are derived from monomers selected from p-styrenesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, ethylenesulfonic acid, and alkali metal salts, ammonium salts, and water-soluble amine salts thereof. A presensitized lithographic plate as in Claim 1 or 2, wherein said light-sensitive layer contains a substantially water-insoluble and organic solvent-soluble diazo resin and an organic high molecular binder. A presensitized lithographic plate as in Claim 3, wherein the diazo resin is a halogenated Lewis acid salt of a condensate between an aromatic diazonium compound and an active carbonyl compound or an active ether compound. A presensitized lithographic plate as in any of Claims 1-4, wherein the high molecular compound has a molecular weight in the range of 2,000 to 100,000, and preferably 10,000 to 100,000. A presensitized lithographic plate as in any of Claims 1-5, wherein the sulfonic acid group-containing monomer units are present in the high molecular compound in an amount in the range of 1 to 100 mol%, preferably 5 to 100 mol%. A presensitized lithographic plate as in any of Claims 1-6, wherein the high molecular compound of the subbing layer is present on the support base in an amount in the range of 0.0001 to 1 g/m², preferably 0.0005 to 0.2 g/m².

Inventors: SEKIYA, TOSHIYUKI
Applicants: FUJI PHOTO FILM CO., LTD.
Application year: 1983
Main classification: G03F7
IPC codes: G03F7, B41N3