GB2043281A - Producing photosensitive lithographic printing plates - Google Patents

Abstract

A photosensitive lithographic printing plate consists of a support bearing a layer comprising a continuous phase of photosensitive material having fine particles of resin dispersed therein. The layer is formed by coating with a solution containing the components of the continuous phase and the resin. The solvent is a mixture of a first solvent which is a solvent for the components of the continuous phase and a non-solvent for the resin and a second solvent which is a solvent for the resin, has a faster evaporation rate than the first solvent and is compatible therewith. When the coating is dried the second solvent evaporates preferentially causing the resin to flocculate to form a hard particulate precipitate dispersed in the continuous phase.

Description

SPECIFICATION Producing photosensitive lithographic printing plates This invention relates to a process for producing photosensitive lithographic printing plates containing a non-continuous phase of fine particles dispersed in a photosensitive layer.

The image of an early type of photosensitive lithographic plate comprising a combination of a bichromate salt as a photosensitive material and a water-soluble colloidal material such as egg white, albumin or polyvinyl alcohol is hydrophobic and cannot receive an oily ink. For this reason after-treatments are required for rendering the image area oleophilic as is the case with a surface plate which is obtained by coating a fatty ink over the entire surface after exposure but before development, and then removing the unexposed areas (see Surface Plates, Chapter 10, page 26, No. 6 of The Lithographers' Manual, published by the Graphic Arts Technical Foundation, Inc.), ora deep etch plate obtained by removing the unexposed areas, coating a hydrophobic resin from an organic solvent, drying the coating, and peeling off a resist formed by imagewise exposure (see Deep Etch Plates, Chapter 10, page 28, No. 7, "The Lithographers' Manual", supra). Various modifications have been made in such after-treatments and the subsequent technological advance has enabled the use of hydrophobic photosensitive materials. This technique has made it possible to obtain hydrophobic images directly by exposure and development and, at the same time, the stability of the light sensitive layer has been improved.The striking improvement in stability under high humidity conditions led to the mass-production of such lithographic plates which have gained rapid acceptance as presensitized lithographic printing plates (to be referred to as PS plates).

Atypical PS plate is composed of a support having formed thereon a photosensitive layer consisting of a mixture of a photosensitive diazo compound and a resin. The resin is used to give the image area (an area which repels water and receives a printing ink) a higher affinity to oils (the property of recieving a printing ink), and so that the lithographic printing plate obtained may yield more printed copies. Since the photosensitive layer is coated from a suitable solvent, this resin should be soluble in organic solvents and the organic solvents should also dissolve the photosensitive diazo compound. Furthermore, this resin should not degrade the stability of the photosensitive diazo compound during mixing.

Furthermore, the developer used to remove the unexposed areas from the exposed PS plate is desirably an aqueous based developer from the standpoint of safety, etc. However, it is difficult in practice to find resins which satisfy all these requirements. For example, when a photosensitive composition which can be developed with a developer having a composition close to that of pure water is desired, the resin must for the most part by hydrophilic. Accordingly, such a resin will yield an image area having insufficient affinity for oils in the form of oil-based printing inks.

U.S. Patent 3,136,637 discloses a PS plate obtained by forming a photosensitive diazo compound layer and a hydrophobic, solvent-softenable, developer-permeable and actinic light-permeable resin layer in this order on a support. In the PS plate of this structure the resin used in the resin layer is limited, and because the resin layer must be permeable to the developing solution the developer must have a special composition.

British Patent 1,548,764 discloses a PS plate prepared by coating a support with a mixture of a water-soluble diazo compound with a polymer emulsion to provide a photosensitive layer. In the photosensitive layer the photosensitive diazo compound forms a continuous phase together with the protective colloid of the polymer emulsion, and independent particles of the emulsion are dispersed in the continuous phase. In the resulting coated film, the continuous phase is photosensitive and developable and the dispersed particles of the polymer emulsion improve printing characteristics such as ink receptivity and printing durability. Accordingly, the resulting PS plate can give an ink-receptive image upon development with water after imagewise exposure.However, because a polymer emulsion is used, the photosensitive material is substantially limited to water-soluble diazo resins. Thus, this PS plate has the defect that it is susceptible to moisture and has poor storage stability (storage stability is the property of the PS plate to retain the characteristics of the PS plate immediately after production, even after storage for a certain period of time).

Furthermore, when a light-sensitive printing plate is exposed to light through through an original, the light-sensitive printing plate and the original have hitherto been interposed between a rubber sheet and a pressure glass, and the clearance between the rubber sheet and the pressure glass has been evacuated so that the original comes into intimate contact with the surface of a light-sensitive layer of the light-sensitive printing plate, or in the case that a resin layer is provided on the light-sensitive layer of the light-sensitive printing plate, into intimate contact with the surface of the resin layerIhereinafter both are merely referred to as the surface of the light-sensitive printing plate"). This method is hereinafter called a "vacuum contact method".

However, since conventional light-sensitive printing plates have smooth surfaces, when an original is brought into intimate contact with a light-sensitive printing plate by the vacuum adhesion method, adhesion is gradually achieved by suction from the edge of the original, and extremely long periods of time have been required for the original to be brought in complete intimate contact with the whole surface of the light-sensitive printing plate. The fact that a long period of time is required for adhesion reduces the efficiency of plate-making operations and is very uneconomical. Moreover, if image-wise exposure is applied when adhesion is incomplete, a sharp image cannot be obtained at the areas where adhesion is incomplete, and sharp prints cannot be obtained. Thus, shortening the time required for adhesion has been an important object of the art.

It is an object of this invention to provide a process for producing a photosensitive lithographic printing plate which can be developed with a developer consisting essentially of water, and can give a lithographic plate having the desired ink respectivity.

Another object of this invention is to provide a process for producing a photosensitive lithographic printing plate having excellent storage stability, good printing durability, and which is excellent for use in vacuum contact exposure.

The present invention provides a process for producing a photosensitive lithographic printing plate composed of a support having formed thereon a photosensitive layer containing phase of photosensitive material and, dispersed in said continuous phase, a non-continuous phase of fine particles, which process comprises (1) coating a uniform solution on said support, said solution containing a continuous phase component (A) and a non-continuous phase component (B) dissolved in a solvent mixture consisting of a solvent (a) which dissolves component (A) but does not substantially dissolve component (B) and a solvent (b) which is compatible with said solvent (a), has a higher evaporation rate that the solvent (a) and which dissolves component (B); and (2) drying the resulting coating such that the solvent (b) evaporates before solvent (a) causing component (B) to flocculate and precipitate in the form of hard particles.

Throughout this specification, the term "Component A" refers to the materials making up the continuous phase of the photosensitive layer formed in accordance with the present invention. More specifically, the term "Component A" refers to the photosensitive material and to its binder, if present. Furthermore, the term includes any other additives conventionally added to a photosensitive layer in order to improve sensitivity, storage stability, etc.

In addition, throughout the specification the term "component (B)" or "Resin (B)" refers to the material which ultimately forms the fine particles dispersed in the photosensitive layer as a non-continuous phase.

A representative embodiment of the process of this invention comprises the steps of: (1) mixing a solution of the component (A) in a solvent (a) which dissolves the components (A) but does not dissolve the component (B) with a solution of the component (B) in a solvent (b) which dissolves the component (B) and has a higher evaporation rate that the solvent (a), solvent (b) being soluble in the solvent (a), to form a uniform solution, (2) coating the resulting solution on a support, and (3) evaporating the solvents so that solvent (b) is the first substantially evaporated.

More specifically, the present invention comprises the steps of (1) dissolving a photosensitive material (e.g., a diazo compound) and a binder as Component (A) in a solvent (a), (2) dissolving the Resin (B) which is hydrophobic and abrasion-resistant in the solvent (b) having a higher evaporation rate than the solvent (a), (3) mixing the solutions prepared in (1) and (2) to form a uniform solution, (4) coating the resulting solution on the surface of a support by known means such as doctor coating, roller coating, gravure coating, bead coating, or dip coating, and (5) evaporating the solvents so that solvent (b) is first evaporated causing the Resin (B) to flocculate and precipitate in the form of fine particles, and solvent (a) is evaporated slowly to form a continuous phase of photosensitive material and binder which adheres to the support in a manner to envelop the hydrophobic Resin (B).

Such a novel method for forming a coating can be used to produce PS plates of both the negative working type and positive working type.

More specific examples of the materials forming Component (A) can be classified into the following four groups: (1) A diazo resin and a binder:- As negative working photosensitive diazo compounds, a condensation product between diphenylamine-pdiazonium salt and formaldehyde (so-called photosensitive diazo resin), which is formed by reacting a diazonium salt and an organic condensing agent having a reactive carbonyl group such as an aldol or acetal, as disclosed, for example, in U.S. Patents Nos. 2,063,631 and 2,667,415, are conveniently used. Other useful condensed diazo-compounds are disclosed, for example, in British Patents, 1,312,925 and 1,312,926 and U.S.

Patent 3,679,419. These photosensitive diazo compounds are normally obtained in the form of water-soluble inorganic salts, and therefore, can be coated from aqueous solutions.

It is possible to react these water-soluble diazo compounds with aromatic or aliphatic compounds containing at least one phenolic hydroxyl group or a sulfo group, or both by the method disclosed in British Patent 1,280,885, and to use the resulting substantially water-insoluble photosensitive diazo resins.

Examples of the compounds having a phenolic hydroxyl group include diphenolic acids such as hydroxybenzophenones, 4,4-bis(4'-hydroxyphenyl)-pentanoic acid, resorcinol, and diresorcinol. They may further be substituted. The hydroxybenzophenones include 2,4-dihydroxybenzophenone, 2-hydroxy-4- methoxybenzophenone, 2,2'-dihydroxy-4,4'-dimethoxybenzophenone and 2,2',4,4'tetrahydroxybenzophenone. Examples of preferred sulfonic acids includes aromatic sulfonic acids such as benzene-, toluene-, xylene-, naphthalene-, phenol-, naphthol- and benzophenone-sulfonic acids, and soluble salts thereof such as their ammonium or alkali metal salts. The suifo-containing compounds may generally be substituted with a lower alkyl group, a nitro group, a halo group, and/or an additional sulfo group.

Examples of preferred sulfo-containing compounds include benzenesulfonic acid, toluenesulfonic acid, naphthalenesulfonic acid, 2,5-dimethylbenzenesulfonic acid, sodium benzenesulfonate, naphthalene-2sulfonic acid, 1-naphthal-2-(or 4)-sulfonic acid, 2,4-dinitro-1 -naphthol-7-sulfonic acid, 2-hydroxy-4- methoxybenzophenone-5-sulfonic acid, sodium m-(p'-anilinophenylazo)-benzenesulfonate, alizarinesulfonic acid, o-toludine-m-sulfonic acid and ethanesulfonic acid. Sulfonic acid esters of alcohols and salts thereof are also useful and usually available readily as anionic surface-active agents. Examples are ammonium or alkali metal salts of lauryl sulfate, alkylaryl sulfates such as p-nonylphenyl sulfate, 2-phenylethyl sulfate and isooctylphenoxydiethoxyethyl sulfate.These substantially water-insoluble photosensitive diazo resins are isolated as precipitates by mixing water-soluble photosensitive diazo resins and aqueous solutions of the aforesaid aromatic or aliphatic compounds preferably in almost equal proportions.

The diazo resins described in British Patent No. 1,312,925 are also preferred.

The most suitable diazo resin is the 2-methoxy-4-hydroxy-5-benzoyl benzonesulfonate of a condensation product between p-diazodiphenylamine and formaldehyde.

The suitable amount of the diazo resin is 5 to 50% by weight based on the photosensitive layer. If the amount of the diazo resin is small, the sensitivity of the layer naturally increases, but the stability of the photosensitive layer is reduced with time. The most suitable amount of the diazo resin is about 8 to 20% by weight Various polymeric compounds can be used as the binder. In the present invention, those containing hydroxy, amino, carboxy, amido, sulfonamido, active methylene, thioalcohol, and epoxy groups are desirable. Such preferred binders include shellac as described in British Patent No. 1,350,521,the polymers containing hydroxyethyl acrylate units or hydroxyethyl methacrylate units as the principal recurring unit as described in British Patent No. 1,460,978 and U.S.Patent No.4,123,276, the polyamide resins described in U.S. Patent No. 3,751,257, the phenolic resins disclosed in British Patent 1,074,392 and polyvinyl acetals such as polyvinyl formal resin and polyvinyl butyral resin, and linear polyurethane resin as described in U.S.

Patent No. 3,660,097, polyvinyl alcohol phthalate, an epoxy resin resulting from the condensation of bisphenol A and epichlorohydrin, amino-containing polymers such as polyaminostyrene or polyamylamino(meth)acrylate, and cellulose derivatives such as cellulose acetate, cellulose alkyl ethers and cellulose acetate phthalate.

The composition comprising the diazo resin and the binder may further contain additives such as phosphoric acid and the dyes described in U.S. Patent No. 3,236,646 and pH indicators described in British Patent No. 1,041,463.

(2) An o-quinonediazide compound Especially preferred o-quinonediazide compounds are o-naphthoquinonediazide compounds disclosed, for example, in U.S. Patents Nos. 2,766,118; 2,767,092; 2,772,972; 2,859,112; 2,907,665; 3,046,110; 3,046,1.11; 3,046,115; 3,046,118; 3,046,119; 3,046,120; 3,046,121; 3,046,122; 3,046,123; 3,061,430; 3,012,809, 3,106,465; 3,635,709; and 3,647,443; and in may other publications. Among these, o- naphthoquinonediazidosulfonic acid esters or o-naphthoquinonediazidocarboxylic acid esters of aromatic hydroxy compounds, and o-naphthoquinonediazidosulfonic acid amides or o- naphthoquinonediazidocarboxylic acid amides of aromatic amino compounds are preferred.Specifically, the reaction product obtained by esterifying a condensation product between pyrogallol and acetone with o-naphthoquinonediazidosulfonic acid as disclosed in U.S. Patent No. 3,635,709, the reaction product obtained by esterifying a hydroxyl-terminated polyester with o-naphthoquinonediazidosulfonic acid or o-naphthoquinonediazidecarboxylic acid as disclosed in U.S.Patent 4,028,111, the reaction product obtained by esterifying a homopolymer of p-hydroxystyrene or a copolymer of which another copolymerizable monomer with o-naphthoquinonediazidosulfonic acid of o-naphthoquinonediazidocarboxylic acid as described in British Patent No. 1,494,043, and the reaction product obtained by amidating a copolymer of p-aminostyrene with another monomer copolymerizable with it with o-naphthoquinonediazidosulfonic acid or o-naphthoquinonediazidocarboxylic acid as disclosed in U.S. Patent No. 3,759,711 are very superior.

These o-quinonediazide compounds can be used alone, but are preferably used in combination with alkali-soluble resins. Suitable alkali-soluble resins are novolactype phenolic resins such as phenol/ formaldehyde resin, o-cresol/formaldehyde resin, and m-cresol/formaldehyde resin. Furthermore, as disclosed in U.S. Patent No. 4,123,279, the joint use of the aforesaid phenolic resins with condensation products between phenol or cresol substituted by an alkyl group having 3 to 8 carbon atoms and formaldehyde, such as t-butylphenol/formaldehyde resin, is preferred. The alkali-soluble resin is incorporated in an amount of about 50 to about 85% by weight, preferably 60 to 80% by weight, based on the weight of the entire composition which constitutes the photosensitive layer.

The photosensitive composition comprising the o-quinonediazide compound, if required, may contain dyes, plasticizers, and additives such as components which impart print-out properties as described in British Patents Nos. 1,041,463 and 1,039,475, and U.S. Patent No.3,969,118.

(3) An azide compound and a binder (polymer) Representative compositions comprise the azide compounds described in British Patents Nos. 1,235,281 and 1,495,861 and Japanese PatentApplication (OPI) Nos. 32331/76 and 36128/76 (The term "OPI" as used herein refers to a "published unexamined Japanese patent application".) and water-soluble or alkali-soluble polymeric compounds; and compositions composed of polymers containing an azide group described, for example, in Japanese Patent Application (OPI) Nos. 5102/75,84032/75, 84303/75 and 12984/78 and polymeric compounds as a binder.

(4) Photosensitive resins other than (l)-(3) above These include, for example, polyesters, polycarbonates, and polysulfonates containing the following photosensitive group

as the essential moiety in the polymer main chain such as described in U.S. Patents 3,030,208; 3,453,237 and 3,622,320; and polycarbonate resins such as described in Canadian Patent No. 696,996; the polyvinyl cinnamate-type resins described in British Patents Nos. 1,112,277, 1,313,390, 1,341,004, and 1,377,747, and the photopolymerizable photopolymer compositions described in U.S. Patents Nos. 4,072,528 and 4,072,527.

Component (B) is a resin which is substantially insoluble or difficult to dissolve in the solvent (a), and is desirably hydrophobic and abrasion-resistant. The specific properties required for the resin vary depending upon the purpose. For example, for the purpose of obtaining complete contact within a relatively short period of time by the vacuum contact method, a hardness which withstands the forces which arise in production and processing (cutting, packaging, etc.) is required. For the purpose of improving the ink-receptive property (affinity to greasy ink), a resin having a high oleophilicity and a high abrasion resistance is required. In either case, the molecular weight of resin can range from about 5,000 to 500,000.

Preferred as such as resin are polyurethanes, polyesters, ABS resin which is a terpolymer of styrene/butadiene/acrylonitrile, chlorinated rubber, chlorinated polyethylene, polyvinyl formal which is the polymerization reaction product of polyvinyl alcohol and formaldehyde, and cellulose acetate.

The solvent (a) which dissolves the photosensitive components and binder has a lower rate of evaporation than the solvent (b) which dissolves Resin (B), and is compatible with the solvent (b) to form a homogenous solution. Generally solvent (a) is a solvent having a boiling point in the range of about 90 to 1800C, preferably about 120 to 155 C. Examples of the solvent (a) include 2-methoxyethanol, 2-ethoxyethanol, 2-methoxyethyl acetate, 2-ethoxyethyl acetate, dimethylformamide, methanol-ethylene dichloride, and mixtures of these. In the methanol-ethylene dichloride mixture, methanol may be replaced by ethanol, n-propanol, isopropanol, or a mixture thereof, and ethylene dichloride may be replaced by methylene chloride, trichloroethane, monochlorobenzene or a mixture thereof.

The solvent (b) can be selected, for example, from ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone, esters such as methyl acetate, ethyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate, and methylamyl acetate, and chlorine-containing solvents such as methylene chloride, methylene dichloride, and trichloroethane. Generally, the solvent (b) will have a boiling point of about 50 to 120 C, preferably about 55 to 118 C. Strictly speaking, however, it is not appropriate to define solvent (a) and solvent (b) by the difference in their boiling points. The solvents are more accurately defined by their relative evaporation rate.Taking the evaporation rate of n-butyl acetate at 250C as 100, the relative evaporation rate of solvent (a) should be about 100 and the relative evaporation rate of solvent (b) should be 150 to 1200.

Relative evaporation rates can be determined by the method well known in the art, as described in E.G. Shur, Office Dig. Federation Paint Varnish Prod. Clubs, Vol. 28, No.382, page 1060 ~ (1956) "Comparative Evaporation Rates of Paint Solvents II", and W. W. Reynolds and H. J. Gebhart, Office Dig. Federation Soc.

Paint Technol. Vol. 32, No. 428, page 1146 ~ (1960) "The Calculation of the Evaporation Rate of Hydrocarbon Solvents from A.S.T.M. Distillation Data". The relative evaporation rates can be calculated by reference to the evaporation rate of n-butyl acetate.

The two solutions can be mixed by any known means. Another solvent may additionally be incorporated in the solution of Component (A) in solvent (a), the solution of Resin (B) in solvent (b) of the final coating solution. For example, when Component (A) is a system in which clouding (formation of insoluble matter) does not take place upon the inclusion of a tiny amount of water, the addition of water is very effective for controlling the particle diameter of the flocculated precipitate.

The coating can be performed by known means such as doctor coating, roller coating, gravure coating, bead coating, and dip coating.

The solvent compositions and combinations should be selected such that after coating on a support, solvent (b) is substantially completely evaporated before solvent (a) begins to evaporate, or such that in the early stages of drying, the evaporation of solvent (b) advances before the viscosity of the solution (a) becomes relatively high and such that the component (B) is dissolved in the solvent (b) and also stably dissolved in the mixed solvent of (a) and (b) such that upon removing solvent (b) it forms a flocculated precipitate. The solvents can be evaporated at room temperature or at elevated temperatures. Drying at high temperature can be performed by using a known tunnel type dryer, etc. The preferred range of the drying temperature is 20 to 120 C and the more preferred range is 50 to 1 200C.

Below, examples of suitable solvent combinations for some typical resin compositions are provided.

(i) Diazo Resins: In the case of the composition comprising water-soluble diazo resins and hydroxyalkylmethacrylatecopolymers are disclosed, for example, in U.S. Patent 4,123,276, the following solvent and Resin B combinations are illustrative.

Solvent (a) (b) Resin (B) 2-Methoxyethanol Methyl ethyl ketone Polyurethanes 2-Methoxyethanol Ethylene dichloride Polychlorinated polyethylene 2-Methoxyethanol Ethanol Alcohol-soluble linear polyamide (ii) o-Quinonediazide Compounds: Using an o-naphthoquinone diazide sulfonic ester of an pyrozallol-acetone resins and cresolformaldehyde novolac resins as disclosed in, for example, in U.S. Patent 3,635,709 for Component (A) the following combinations can be exemplified.

Solvent (a) (b) Resin (B) 2-Methoxyethanol Methyl ethyl ketone Polyurethanes 2-Methoxyethanol Ethylene dichloride Polychlorinated polyethylene 2-Methoxyethanol Ethanol Alcohol-soluble linear polyamide Amylacetate Methyl ethyl ketone Polyurethane Amylacetate Ethylene dichloride Polyvinyl formal (iii) An azide compound and binder In the case of the composiions comprising, for example, 2,6-di-(4'azidobenzal)-4-methylcyclohexanone and epoxy resins, the following combinations can be exemplified.

Solvent (a) (b) Resin (B) 2-Methoxyethanol Methyl ethyl ketone Polyurethane 2-Methoxyethyl acetate Ethylene dichloride Polyvinyl formal (iv) Photosensitive resins other than the above When Component (A) is a polyester prepared by condensation of p-phenylene-di-ethoxyacrylate and an equimolar amount of 1 ,4-p-hydrnxyethoxycyclohexane and a photosensitizer as disclosed in, for example, U.S. Patent 3,030,208, a preferred combination comprises monochlorobenzene as solvent (a), methyl ethyl ketone as solvent (b) and a polyurethane as Resin (B).

Also, in the case of the composition comprising polyvinyl cinnamate and a photbsenskizer, a preferred combination comprises 2-methoxyethyl acetate as solvent (a), ethylene dichloride as solvent (b) and ABS resin.

Photosensitive compositions other than those above can be easily determined by those skilled in the art by reference hereto.

The solvent system in accordance with this invention is used to coat a solution comprising photosensitive components, a binder, and a resin which forms a flocculated precipitate in the coated film on the surface of a suitable support as a unitary composition, to thereby provide a photosensitive material such as a PS plate, a photosensitive material for use in color proof, and a printed circuit.

The effective proportion of Resin (B) in the non-continuous phase of the photosensitive layer is about 2 to 95% by weight based on the total weight of the photosensitive layer. It is preferably about 5 to 60% weight, most preferably about 10 to 45% by weight.

The particle size of the Resin (B) may vary depending on the use of the material. For example, the upper limit of the particle diameter of (B) is that of the Resin (B) which is flocculated and precipitated in the photosensitive layer in order to roughen the surface of the photosensitive layer and thereby to improve vacuum adhesion of the photosensitive layer with an image-bearing film at the time of exposure. When the Resin (B) is to be flocculated and precipitated in the photosensitive layer in order to improve printing durability, oil receptivity, etc., its particle diameter can be selected from a wide range.Accordingly, the particle diameter of the Resin (B) used in this invention is not more than about 70 cm, preferably about 0.05 Rm to 40 Zm, more preferably about 0.2 um to 1 Sum.

Typically the weight ratio of solvent (a) to (b) is about 10:90 to 95:5, preferably about 50:50 to 90:10. The ratio between the solvents (a) and (b) for the formation of the aforesaid particle diameter can be easily determined by routine experiment and will be evident from the Examples given hereinbelow.

Supports which are used in this invention are, for example, metal plates such as aluminum (including aluminum alloys), zinc, iron, and copper, and plastic sheets having such metals laminated thereto or vacuum-deposited thereon. Al aluminum plate is most preferred. Supports having a metal surface, especially an aluminum surface, are preferably surface-treated by known means, such as graining, dipping in aqueous solutions of sodium silicate, potassium fluorozirconate, phosphate salts, etc., or anodization (anodic oxidation). Furthermore, an aluminum surface which has been grained and then dipped in an aqueous solution of sodium silicate as disclosed in U.S. Patent No.2,714,066, and an aluminum plate which has been anodized and then dipped in an aqueous solution of an alkali metal silicate as disclosed in U.S.

Patent No.3,181,461 can also be used conveniently. The anodization is carried out by passing an electric current through an aluminum plate in one or more aqueous solutions or non-aqueous solutions of inorganic acids such as phosphoric acid, chromic acid, sulfuric acid or boric acid or organic acids such as oxalic acid or sulfamic acid, or salts of these, preferably in an aqueous solution of phosphoric acid, or sulfuric acid or a mixture of these. Silicate electrodeposition as disclosed in U.S. Patent No.3,658,662 is also effective.

Another preferred support is an aluminum plate which is obtained by electrolyzing an aluminum plate in a hydrochloric acid electrolyte solution under an alternating current, and then anodizing it is a sulfuric acid electrolyte solution as described in British Patent No. 1,208,224. Provision of a subbing layer of a cellulosic resin containing a water-soluble salt of a metal such as zinc is preferred in order to prevent scum at the time of printing.

The amount of the photosensitive layer formed on such a support is about 0.1 to about 7 glum2, preferably about 0.5 to 4 g/m2.

The PS plate produced by the process of this invention is imagewise exposed, and then subjected to conventional treatments including development to form a resin pattern. For example, a PS plate having a photo-sensitive layer (1) composed of a diazo resin and a binder is exposed imagewise, and then the unexposed portions of the photosensitive layer are removed by development to obtain a lithographic printing plate. A.PS plate having a photosensitive layer (2) is imagewise exposed, and then washed with an aqueous alkaline solution, whereby the exposed portions are removed and a lithographic printing plate is obtained. The developer solution used for this purpose has a composition which is conductive to dissolving or swelling (A). Since Resin (B) is dispersed in Component (A), it is removed at the same time as the removal of Component (A) from the support.

A conventional homogeneous photosensitive composition should provide a difference in solubility or swellability between an image area and a non-image area at the time of development after exposure, and should have printing characteristics, such as ink receptivity or printing durability, required of the desired images. In contrast, in the heterogeneous photosensitive composition for PS plates produced in accordance with this invention, Component (A) is responsible for photosensitivity and developability, and Resin (B) is responsible for printing characteristics. Accordingly, there is a wide range of tolerance for the selection of materials. Thus, a highly safe developer composed mainly of water can be selected, and a lithographic printing plate of high quality can be easily made.

Furthermore, the present invention can give a photosensitive lithographic printing plate which has superior vacuum adhesion to a transparent image-bearing film in a vacuum printing frame during exposure.

The following Examples illustrate the present invention more specifically. All percentages in these examples are by weight.

Example 1 In a stream of nitrogen, 300 g of dioxane was heated to 100 C, and a mixture of 150 g of 2-hydroxyethyl methacrylate, 60 g of acrylonitrile, 79.5 g of methyl methacrylate,10.5 g of methacrylic acid and 1.2 g of benzoyl peroxide was added dropwise over the course of 2 hours. After the addition, the mixture was diluted with methanol, and poured into water to precipitate the resulting copolymer, followed by drying in vacuo at 70 C. The resulting 2-hydroxyethyl methacrylate copolymer (I) had an acid value of 20, and a viscosity, measured at 250C with a 33% ethylene glycol monomethyl ether solution, of 4,500 centipoises.

An aluminum plate (2S) having a thickness of 0.15 mm was dipped for 30 seconds in a 10% aqueous solution of soidum tertiary phosphate maintained at 80 C to degrease it. The surface of the aluminum plate was grained with a nylon brush while flowing a pumice slurry over the aluminum plate, then etched for 10 seconds with an aqueous sodium aluminate solution at 60 C, and subsequently washed with a 3% aqueous solution of sodium hydrogen sulfate. The treated aluminum plate was anodized for 2 minutes in 20% sulfuric acid at a current density of 2A/dm2, and in a subsequent step, was treated for 1 minute with a 2.5% aqueous solution of sodium silicate at 70 C. to prepare an anodized aluminum plate (I).

A photosensitive solution of the following formulation was coated on the aluminum plate (I), and dried at 1000for 2 minutes.

2-Hydroxyethyl methacrylate copolymer (I) 0.87 g 2-Methoxy-4-hydroxy-5-benzoyl benzenesulfonic acid salt of a p-diazodiphenylamine/ paraformaldehyde condensate 0.1 g Oil Blue #603 (a product of Orient Chemical Co., Ltd.) 0.03g 2-Methoxyethanol 6 g Methanol 6 g Ethylene dichloride 6 g A solution was prepared from the above components, and a separately prepared solution of 0.3 g of polyurethane resin (Estane 5715, a product of Goodrich Company) and 5 g of methyl ethyl ketone was added with stirring to form a uniform solution which was then filtered.

The amount of the coating after drying was 2.1 g/m2. Examination of the photosensitive layer by a metal surface microscope showed that fine particles having a particle diameter of about 0.5 ~lm were uniformly dispersed in the coated film. Since the polyurethane resin had good dyeability, the dispersed particles were colored in a high density, thus making the observation easier. The resulting PS plate was imagewise exposed for 30 second by means of a Berky printer having a 2 KV metal halide light source, and developed with a developer of the following formulation.

Sodium Sulfite 3 9 Benzyl Alcohol 30g Triethanolamine 20 g Monoethanolamine 59 Pelex NBL (Sodium t-butyl naphthalenesulfonate, a product of Kao-Atlas Co., Ltd.) 30g Water 1000 me The developed printing plate was coated with an aqueous solution of gum arabic (7 Bye), and operated on a Heidel GTO printing press.

The printing plate had better ink receptivity and printing durability than a printing plate prepared from a similar composition not containing polyurethane resin.

Example 2 Chlorinated polyethylene 0.5g Ethylene dichloride 5g A solution of the above ingredients was prepared, and added instead of the polyurethane resin solution used in Example 1 to form a uniform solution. Pure water (0.5 g) was added to the resulting solution, and the mixture was stirred and filtered in a customary manner. The resulting coating solution was coated and dried in the same way as in Example 1. The dry weight of the coated film was 1.98 g/m2.

The particles in the photosensitive layer which were formed by flocculation and precipitation had an average particle diameter of about 7um, and the surface of the photosensitive layer was a roughened surface of a fine texture.

The PS plate was associated with a transparent negative film, and set in a vacuum printing frame. A vacuum pump was switched on, and the time which elapsed unit the film completely adhered to the PS plate even at its center was measured. Complete adhesion could be obtained in a time about 3/5 of that required with a PS plate prepared without the addition of chlorinated polyethylene. It was found therefore that this PS plate could drastically shorten the working time for exposure in one step by a multiple printing frame.

The PS plate to which the negative film has been adhered in vacuum was exposed for 50 seconds to a 2KW metal halide light source disposed at a distance of 1 m and then used for printing. The printing durability of the lithographic printing plate was almost the same as that of a PS plate made without using chlorinated polyethylene but has better ink receptivity than the latter.

Example 3 An aluminum plate (2S) mechanically grained by the method described in Japanese Patent Application (OPI) No.33911/73 was dipped for 1 minute in a 2% aqueous solution of sodium hydroxide maintained at 400C to etch a part of its surface. After washing with water, the plate was dipped for about 1 minute in a mixture of sulfuric acid and chromic acid to reveal the surface of pure aluminum. The treated aluminum plate was dipped in 20% sulfuric acid maintained at 30 C, and anodized for 2 minutes by applying a DC voltage of 1.5 V at a current density of 3 A/dm2. It was then washed with water, and dried.A photosensitive coating solution of the following formulation was continuously coated on the surface of the plate by a roll coater so that the dry weight of the coating became about 2 g/m2.

Naphthoquinone-1,2-diazide (2)-2-sulfonic acid ester of acetone-pyrogallol resin (synthesized bythe method of Example 1 of U.S. Patent No. 3,635,709) 5g RP-50530 (tert.butyl phenol/formaldehyde resin, a product of Sumitomo-Durez Ca., Ltd) 0.5g Hitanol #3110 cresol/formaldehyde resin, a product of Hitachi Chemical Co., Ltd) 5 g 2-Methoxyethanol 80g Asolution was prepared from the above ingredients, and separately a solution of 5 g of polyvinyl formal in 20 g of ethylene dichloride was prepared. With stirring, the two solutions were mixed to form a uniform solution, and filtered in a customary manner.

The plate obtained by drying the coating at 1 000C for 2 minutes had properties suitable as a PS plate, and when it was stored for one year in a cold dark place, it still showed satisfactory properties in use. A transparent positive film was superimposed on the resulting photosensitive lithographic printing plate in a vacuum printing frame and a vacuum pump was operated. The time which elapsed until the film completely adhered to the plate even at its center was measured. Complete adhesion was obtained in a time about 1/3 of that required in the case of photosensitive lithographic printing plate obtained by coating a solution not containing polyvinyl formal.Subsequently, the photosensitive lithographic printing plate was exposed for 30 seconds to Fuji Film PS light (having a light source of Toshiba Metal Halide Lamp MU 2000-2-OLtype 3 KW, and sold by Fuji Shashin Film Co., Ltd) disposed at a distance of 1 meter.

The exposed plate was developed with a developer solution having the following formulation.

Sodium silicate (JIS #1) 109 Sodium metasilicate 5g Pure water 180 my Subsequently, a 140 Bé gum arabic solution was coated on the surface of the plate, and buff dried. The finished printing plate was stored for 3 days, and then operated on a Heidel GTO type printing press. The printing durability of the printing plate was about 1.5 times as great as that of a plate produced by using a coating composition not containing polyvinyl formal.

Example 4 An aluminum plate (2S) was dipped for 1 minute in a 10% aqueous solution of sodium tertiary phosphate (kept at 70 C) to wash its surface. At this stage, gray impurities were adhering to the surface of the aluminum plate and could not be removed by washing with water. Then, the aluminum plate was dipped for 1 minute at room temperature in 70% nitric acid to reveal the surface of the pure aluminum. The aluminum plate having a pure aluminum surface was dipped in 20% sulfuric acid kept at 20 C, and anodized for 5 minutes by applying a DC voltage of 12 V at a current density of 2A/dm2. The plate was washed water, and dipped for 3 minutes in a 30% aqueous solution of phosphoric acid kept at 50 C. It was washed with water and dried.

Then, the phosphoric acid radical contained in the surface of the aluminum plate was-measured by using a fluorescent X-ray analysis device. Itwas found that about 80 mg/m2, calculated as phosphoric acid, of the phosphoric acid radical existed on the surface of the aluminum plate. The aluminum plate was then coated with a solution ofthefollowing solution and then dried at 100 Cfor2 minutes.

Polyvinyl Alcohol (GL-05 a product of Nihon Gosei Kagaku Kabushiki Kaisha) 0.1 g Methanol 50 my Water 50 mt Subsequently, a solution of the following formulation was coated.

Polyvinyl Cinnamate ("KPR" solution 20 g- marketed by Eastman Kodak Company) 2-Methoxyethanol 10g 2-Methoxyethyl acetate 10g A solution of the above ingredients was prepared and mixed with a separately prepared solution of the following formulation to form a uniform solution.

ABS resin (acrylonitrile/butadiene/styrene terpolymer) 0.8g Ethylene dichloride 5g The uniform solution was coated on a support coated with polyvinyl alcohol. Then, the coated was dried.

The plate was exposed and dried in a customary manner, and used in printing. It was found that the time required for adhesion in vacuo at the time of exposure was shortened, and its printing durability on a high-speed offset press was improved.

The developer used at this time has the following formulation.

2-Methoxyethyl acetate 8909 Glycerol 9 Water 20g Acetic acid 50 g

Claims (23)

1. A process for producing a photosensitive lithographic printing plate composed of a support bearing a photosensitive layer containing a continuous phase of a photosensitive material and, dispersed in said continuous phase, a non-continuous phase of fine particles which process comprises: (1) coating a uniform solution on said support, said solution containing a continuous phase component (A) and a non-continuous phase component (B) dissolved in a solvent mixture consisting of a solvent (a) which dissolves component (A) but does not substantially dissolve component (B) and a solvent (b) which is compatible with said solvent (a), has a higher evaporation rate than the solvent (a) and which dissolves component (B);; and (2) drying the resulting coating such that the solvent (b) evaporates before solvent (a) causing the component (B) to flocculate and precipitate in the form of hard particles.

2. A process as claimed in Claim 1, wherein solvent (a) has a higher boiling point than solvent (b).

3. A process as claimed in Claim 1 or 2, wherein said solvent (a) has a boiling point of from 90 to 180 C.

4. A process as claimed in any preceding Claim, wherein said solvent (a) is selected from 2-methoxyethanol, 2-ethoxyethanol, 2-methoxyethyl acetate, 2-ethoxyethyl acetate, dimethylformamide, methanolethylene dichloride series solvents and mixtures thereof.

5. A process as claimed in any preceding Claim, wherein said solvent (b) has a boiling point of from 50 to 120 C.

6. A process as claimed in any preceding Claim, wherein said solvent (b) is selected from ketones, esters, and chlorine-containing solvents.

7. A process as claimed in any preceding Claim, wherein taking the evaporation rate of n-butyl acetate at 250C as 100, solvent (a) has a relative evaporation rate of from 5 to 100 and solvent (b) has a relative evaporation rate of from 150 to 1200.

8. A process as claimed in any preceding Claim, wherein water is present in said uniform solution.

9. A process as claimed in any preceding Claim, wherein component (A) comprises a diazo resin and a binder.

10. A process as claimed in any one of Claims 1 to 8, wherein component (A) comprises an o-quinonediazide compound.

11. A process as claimed in any one of Claims 1 to 8, wherein component (A) comprises an azide compound and a binder.

12. A process as claimed in any one of Claims 1 to 8, wherein component (A) comprises a photosensitive polyester compound.

13. A process as claimed in any preceding Claim, wherein component (B) is hydrophobic resin.

14. A process as claimed in Claim 13, wherein the fine particles formed from component (B) are abrasion resistant.

15. A process as claimed in Claim 13 or 14, wherein component (B) is selected from polyurethanes, polyesters, styrene/butadiene/acrylonitrile copolymers, chlorinated rubbers, chlorinated polyethylenes, polyvinyl formal and cellulose acetate.

16. A process as claimed in any preceding Claim, wherein component (B) is present in an amount of from 2 2to 95% by weight based on the total weight of the photosensitive layer.

17. A process as claimed in any preceding Claim, wherein the particles formed by component (B) have a particle size not greater than 70 y.

18. A process as claimed in any preceding Claim, wherein the drying is carried out at a temperature of from 20to 1500C.

19. A process as claimed in any preceding Claim, wherein said support has an aluminum surface which is grained and/or anodized.

20. A process as claimed in Claim 1 and substantially as herein described.

21. A process for producing a lithographic printing plate substantially as herein described with reference to any one of Examples 1 to 4.

22. A lithographic printing plate when produced by a process as claimed in any preceding Claim.

23. The features as herein disclosed, or their equivalents, in any novel selection.