GB2293019A - Photosensitive printing plate - Google Patents

Abstract

A photosensitive lithographic printing plate comprises an aluminum support having a hydrophilic surface having thereon a photosensitive layer, wherein two sides facing with each other or four sides of the aluminum support are downwardly curved and the curved lateral side of the photosensitive layer face is subjected to desensitizing treatment. The printing plate produced from the photosensitive lithographic printing plate of the present invention does not suffer from any generation of scum on the printed paper corresponding to the edge part of the printing plate. <IMAGE>

Description

PHOTOSENSITIVE LITHOGRAPHIC PRINTING PLATE FIELD OF THE INVENTION The present invention relates to a photosensitive lithographic printing plate, more specifically, to a photosensitive lithographic printing plate capable of providing a printing plate free of generation of scum in the edge part.

BACKGROUND OF THE INVENTION A photosensitive lithographic printing plate comprising a support of an aluminum plate is commercially available and widely used. The method for producing such a photosensitive lithographic printing plate is usually conducted such that an aluminum plate in the form of a sheet or a coil is subjected to various surface treatments such as graining, anodic oxidation and chemical conversion treatment, which may be applied individually or in an appropriate combination, then thereon a photosensitive solution is coated and dried and the plate is cut into a desired size.

When printing is carried out using a printing plate obtained by processing, for example imagewise exposing and developing such a photosensitive lithographic printing plate, if the printing is made on a paper smaller in size than the printing plate as done by a printing machine for printing normal sheets of paper, there arises no problem since the portion corresponding to the edge part of the printing plate does not serve as a print face, but if the printing is continuously made on a rolled paper using a rotary press as in the newspaper printing, the portion corresponding to the edge part of the printing plate comes into contact with the rolled paper to play as a print face and as a result, the ink attached to the edge part is also printed to leave scum, which gives rise to the outstanding damage in the commercial value of the printed matter.

In order to prevent scum at the edge part of the printing plate, for example, JP-B-57-46754 (the term 'JP-B" as used herein means an "examined Japanese patent publication") discloses a method where the edge face of an aluminum support is cut at an angle of from 100 to 45" to the aluminum surface. However, according to this method, the ink is accumulated on the edge part upon printing of 10,000 sheets or more to generate scum.Also, JP-B-62-61946 discloses a method where the edge face of an aluminum support is subjected to desensitizing treatment and JP-A-63-256495 (the term "JP-A" as used herein means an unexamined published Japanese patent application") discloses the edge face of the printing plate comprising an aluminum support is in advance subjected to hydrophilic treatment, however, the effects thereof are yet insufficient and further improvements have been demanded.

SUMMARY OF THE INVENTION An object of the present invention is to provide an improved photosensitive lithographic printing plate capable of providing a lithographic printing plate free from generation of scum at the edge part.

The above-described object of the present invention can be achieved by a photosensitive lithographic printing plate comprising an aluminum support having a hydrophilic surface having thereon a photosensitive layer, wherein two sides facing with each other or four sides of the aluminum support are downwardly curved and the curved lateral side of the photosensitive layer face is subjected to desensitizing treatment.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a cross sectional view showing the cutting part of a slitter; Fig. 2 shows a first embodiment of the shape of the tip of the lower cutting blade according to the present invention; Fig. 3 shows the edge part 30a of an aluminum sheet 30; Fig. 4 shows a second embodiment of the shape of the tip of the lower cutting blade; Fig. 5 shows the edge part 35a of an aluminum sheet 35; and Fig. 6 is an example of the edge part of a photosensitive lithographic printing plate according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION The photosensitive printing plate according to the present invention can be produced, for example, by providing a photosensitive layer on an aluminum support having a hydrophilic surface, curving downwardly and cutting the edge parts of two sides facing with each other or four sides of the aluminum support and then subjecting the lateral side of the photosensitive layer face to desensitizing treatment.

More specifically, a coil-form aluminum plate is degreased and cleaned by various methods and grained by various methods. Then, after removing the residue, if desired, anodic oxidation treatment and hydrophilic treatment are applied to the plate and a photosensitive solution is coated thereon and dried. Thereafter, the plate is slit into a size (corresponding to the edge face of an aluminum support to be put into contact with paper in printing) fitted to a desired printing machine and at this time, the edge parts are downwardly curved to form the edge part of the photosensitive lithographic printing plate of the present invention.

Still more specifically, the plate is slit at a cutting part of a slitter shown in Fig. 1 by means of lower cutting blades shown in Fig. 2 or Fig. 4 to have a shape as shown in Fig. 3 or Fig. 5 where the edge part is downwardly curved.

Fig. 1 is a cross sectional view showing the cutting part of a slitter. In the slitter, a pair of up and down cutting blades 10 and 20 is provided at the left and right sides. The cutting blades 10 and 20 each comprises a disklike round blade and the upper cutting blades l0a and 10b or the lower cutting blades 20a and 20b are held on the same shaft, namely the shaft 11 or the shaft 21, respectively.

The upper cutting blades 10a and lOb are rotated in the reverse direction to that where the lower cutting blades 20a and 20 are rotated. An aluminum sheet 30 is passed through the upper cutting blades 10a, lOb and the lower cutting blades 20a, 20b and slit to a predetermined width.

Fig. 2 shows a first embodiment of the shape of the tip of the lower cutting blade according to the present invention. The lower cutting blade 20 is chamfered so that the lateral side and the outer peripheral side are cut by X and Y, respectively. The aluminum sheet 30 which is slit by means of the chamfered lower cutting blade 20 has a shape such that the edge part 30a is downwardly curved as shown in Fig. 3.

Fig. 4 shows a second embodiment of the shape of the tip of the lower cutting blade. The lower cutting blade 25 has a step notched by X on the lateral side and by ',' on the outer peripheral side. The aluminum sheet 35 which is slit by means of the lower cutting blade 25 with a step has an edge part 35a curved downwardly and at the same time, a flat part 35b is formed at the bottom-side edge part of the curved part 35a as shown in Fig. 5.

In Figs. 3 and 5, X is in the range of preferably from 10 to 200 zm, more preferably from 30 to 200 zm. In Figs. 3 and 5, Y is in the range of preferably from 20 to 3,000 zm, more preferably from 50 to 3,000 Hm. The X/Y ratio is preferably 1/2 or less. In Fig. 5, Z may vary depending upon the size of Y but it is in the range of preferably from 5 to 2,000 gum, more preferably from 20 to 2,000 zm.

In Figs. 3 and 5, if X is less than 10 zm and Y is less than 20 gum, scum is generated at the edge part. In Figs. 3 and 5, if X exceeds 200 um, transportation failure is readily caused in an automatic plate making machine. In Figs. 3 and 5, if Y exceeds 3,000 zm, the press life of the image part near the edge part is reduced. If X/Y exceeds 1/2, scum is generated in the neighborhood of the curved part. In Fig. 5, if Z is less than 5 um, scum may be generated at the edge part in a printing condition such that the amount of fountain solution is reduced and the amount of ink is increased, whereas if Z exceeds 2,000 pm, the ink density of the image part is reduced in the neighborhood of the edge part.

After forming the edge part of a photosensitive lithographic printing plate into a downwardly curved shape, by subjecting the lateral side of the photosensitive layer to desensitizing treatment, unexpectedly, scum at the edge part is greatly improved. As the desensitizing solution used in the desensitizing treatment,-a desensitizing solution used in the desensitizing treatment of a lithographic printing plate comprising a support of an aluminum plate can be effectively used. A preferred example of the desensitizing solution is an aqueous solution containing at least one of a hydrophilic organic polymer compound, a hexametaphosphoric acid and a salt thereof, and a phytic acid and a salt thereof.

Specific examples of the hydrophilic organic polymer compound include gum arabic, dextrin, alginate such as sodium alginate, a water-soluble cellulose such as carboxymethyl cellulose, hydroxyethyl cellulose and hydroxypropylmethyl cellulose, polyvinyl alcohol, polyvinyl pyrrolidone, polyacrylamide, a water-soluble copolymer containing an acrylamide unit, polyacrylic acid, a copolymer containing an acrylic acid unit, polymethacrylic acid, a copolymer containing a methacrylic acid unit, a copolymer of vinyl methyl ether and maleic anhydride, a copolymer of vinyl acetate and maleic anhydride and phosphoric acid-modified starch. Of these, gum arabic is preferred because of its strong desensitizing effect. These hydrophilic polymer compounds can be used in combination of two or more, if desired, and they are used at a concentration of from about 1 to 40 wt%, preferably from 3 to 30 wt%.

Specific examples of the hexametaphosphate include an alkali metal salt and an ammonium salt of hexametaphosphoric acid. Examples of the hexametaphosphoric acid alkali metal salt or ammonium salt include sodium hexametaphosphate, potassium hexametaphosphate and ammonium hexametaphosphate.

Specific examples of the phytic acid or a salt thereof include an alkali metal salt such as sodium salt, potassium salt and lithium salt, an ammonium salt and an amine salt. Examples of the amine salt include salts of diethylamine, triethylamine, n-propylamine, di-n-propylamine, tri-n-propylamine, n-butylamine, n-amylamine, n-hexylamine, laurylamine, ethylenediamine, trimethylenediamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, ethanolamine, diethanolamine, triethanolamine, allylamine and aniline. The phytate may be in any form of a normal salt with all hydrogens in twelve acids being substituted, a hydrogen salt (acid salt) with a part of hydrogens in acids being substituted, a simple salt comprising a salt of one kind of base and a double salt containing two or more kinds of bases as a component.These compounds can be used either individually or in combination of two or more of them.

The desensitizing solution used in the present invention preferably further contains a strongly acidic metal salt to increase the desensitizing effect. Specific examples of the strongly acidic metal salt include a sodium salt, a potassium salt, a magnesium salt, a calcium salt and a zinc salt of nitric acid, a sodium salt, a potassium salt, a magnesium salt, a calcium salt and a zinc salt of sulfuric acid, a sodium salt, a potassium salt, a magnesium salt, a calcium salt and a zinc salt of chromic acid, and sodium fluoride and potassium fluoride. These strongly acidic metal salts can be used in combination of two or more thereof and they are used in an amount of from about 0.01 to 5 wt% based on the entire weight of the desensitizing solution.

The desensitizing solution used in the present invention has a pH in an acid region and the pH is more preferably adjusted to from 1 to 5, most preferably from 1.5 to 4.5. Accordingly, when the pH of the aqueous phase is not acidic, an acid is further added to the aqueous phase.

Examples of the acid added as a pH adjuster include a mineral acid such as phosphoric acid, sulfuric acid and nitric acid, and an organic acid such as citric acid, tannic acid, malic acid, glacial acid, lactic acid, oxalic acid, p-toluenesulfonic acid and organic phosphonic acid. Among these the phosphoric acid is particularly superior because it not only functions 2S a pH adjuster but also acts to intensify the desensitizing effect. The phosphoric acid is preferably contained in an amount of from 0.01 to 20 wt%, most preferably from 0.1 to 10 wt%, based on the entire weight of the desensitizing solution.

The desensitizing solution used in the present invention preferably contains a wetting agent and/or a surface active agent to improve the coatability of the desensitizing solution. Specifically, the wetting agent is preferably a lower polyhydric alcohol and examples thereof include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, butylene glycol, pentanediol, hexylene glycol, tetraethylene glycol, polyethylene glycol, dipropylene glycol, tripropylene glycol, glycerine, sorbitol and pentaerythritol, with glycerine being particularly preferred.

Examples of the surface active agent include a nonionic surface active agent such as a polyoxyethylene alkylphenyl ether and a polyoxyethylene polyoxypropylene block copolymer, an anionic surface active agent such as fatty acid salts, alkylsulfuric esters, alkylbenzenesulfonates, alkylnaphthalenesulfonates, dialkylsulfosuccinates, alkylsuccinic esters, alkylphosphonic esters and naphthalenesulfonic acid formalin condensate, and an amphoteric surface active agent such as betaine type, glycine type, alanine type and sulfobetaine type anphoteric surface active agents.

The wetting agent and/or the surface active agent is contained in an amount of from about 0.5 to 10 wt%, preferably from 1 to 5 wt%, based on the entire weight of the desensitizing solution.

The desensitizing solution used in the present invention can further contain a filler such as silicon dioxide, talc and clay in an amount up to 2 wt%, or a dyestuff or a pigment in an amount up to 1 wt%.

The desensitizing solution used in the present invention comprises a hydrophilic aqueous solution as described above, but in considering adverse effects on the photosensitive layer of the PS plate, an emulsion type desensitizing solution as described, for example in U.S.

Patents 4,253,999, 4,268,613 and 4,348,954 can also be used.

In effecting desensitizing treatment on the edge face of the PS plate with the above-described desensitizing solution, the desensitizing solution may be coated sheet by sheet on the edge face of the PS place but in a preferred embodiment, the PS plate is stacked in a plurality (for example, 1,000 sheets) and the solution is coated on the edge face of the stacked plates. In this case, the coating can be carried out while interposing interleaving sheet as described, for example, in JP-B-57-23259 and JP-A-57-99647 between the plates. Further, a method where immediately after continuous cutting by a slitter of the present invention, the coating is carried out by means of a molleton roll impregnated with the desensitizing solution of the present invention is also preferred.The coating amount of the desensitizing solution on the edge face is in terms of a dry weight from 0.001 to 50 g/m2, preferably from 0.01 to 10 g/m2, more preferably from 0.05 to 5 g/m2. If it is less than 0.001 g/m2, scum is generated at the edge part, whereas if it exceeds 50 g/m2, the plates adhere with each other to readily cause transportation failure in an automatic plate making machine.

The photosensitive layer of a photosensitive lithographic printing plate to which the present invention can be applied includes various kinds of layers, for example, the layer is formed by applying a negative photosensitive composition comprising a diazo resin and a hydrophobic resin, a positive photosensitive composition comprising an o- quinonediazide compound and a novolak resin, an addition polymerizable unsaturated monomer, a photopolymerization composition comprising a photopolymerization initiator and an organic polymer compound as a binder or a photosensitive resin having a -CH=CH-CO- bond in the molecule and capable of causing photocrosslinking reaction.

A representative negative photosensitive composition comprises a diazo resin and a binder. The diazo resin is represented by a condensate of an aromatic diazonium salt with an active carbonyl group-containing compound such as formaldehyde.

Examples of the diazo resin include an organic solvent-soluble diazo resin inorganic salt as a reaction product of a condensate of a p-diazodiphenylamine with an aldehyde such as formaldehyde or acetaldehyde with a hexafluorophosphate or tetrafluoroborate and an organic solvent-soluble diazo resin organic salt as a reaction product of the above-described condensate with a sulfonate such as p-toluenesulfonic acid or a salt thereof, propylnaphthalenesulfonic acid or a salt thereof, butylnaphthalenesulfonic acid or a salt thereof, dodecylbenzenesulfonic acid or a salt thereof, or 2-hydroxy4-methoxybenzophenone-5-sulfonic acid or a salt thereof described in JP-B-47-1167. In particular, a high molecular diazo compound containing 20 mole% or more of a hexamer or greater polymer described in JP-A-59-78340 is preferred.

Also, 3-methoxy-4-diazo-diphenylamine converted into a mesitylenesulfonate resulting from condensation with 4,4'bis-methoxy-methyl-diphenyl ether described in JP-A-58-27141 is suitable.

Further, a polycondensate containing an aromatic compound having at least one of a carboxyl group, a sulfonic acid group, a sulfinic acid group, an oxygen acid group of phosphorus and a hydroxyl group, and a diazonium compound, preferably an aromatic diazonium compound, as constituent units is preferred.

The binder is an organic polymer compound having an acid content of from 0.1 to 3.0 meq/g, preferably from 0.2 to 2.0 meqg, being substantially water insoluble (namely, insoluble in a neutral or acidic aqueous solution) and having a film-forming property but preferably, it can dissolve or swell in an aqueous alkali solution type developer and at the same time, is photocured in the co-presence of the abovedescribed photosensitive diazo resin to become insoluble or non-swelable in the above-described developer. If the acid content is less than 0.1 meq/g, the development is difficult, whereas if it exceeds 3.0 meq/g, the image strength at the development is conspicuously weakened.

Examples of the particularly preferred binder include copolymers containing an acrylic acid, a methacrylic acid, a crotonic acid or a maleic acid as an essential component, such as a polyphyletic copolymer of 2-hydroxyethylacrylate or 2-hydroxyethylmethacrylate, acrylonitrile or methacrylonitrile, acrylic acid or methacrylic acid and, if desired, other copolymerizable monomer as described in JP-A50-118802, a polyphyletic copolymer with the terminal being a hydroxyl group and consisting of an acrylic acid or a methacrylic acid esterified by a group containing a dicarboxylic ester residue, an acrylic acid or a methacrylic acid and, if desired, other copolymerizable monomer as described in JP-A-53-120903, a polyphyletic copolymer of a monomer with the terminal being an aromatic hydroxyl group (e.g., N-(4-hydroxyphenyl)methacrylamide), an acrylic acid or a methacrylic acid and, if desired, other copolymerizable monomer as described in JP-A-54-98614, and a polyphyletic copolymer of alkylacrylate, acrylonitrile or methacrylonitrile and an unsaturated carboxylic acid as described in JP-A-56-4144. In addition, an acid polyvinyl alcohol derivative and an acid cellulose derivative are useful. Further, binders resulting from alkali-solubilizing polyvinyl acetal or polyurethane described in JP-B-54-19773, JP-A-57-94747, JP-A-60-182437, JP-A-62-58242 and JP-A-62123453 are also useful. Furthermore, a photocrosslinking polymer having a maleimide group on the side chain described in JP-B-5-2227 is also useful.

The photosensitive layer of the photosensitive lithographic printing plate preferably has a diazo resin content of from 3 to 30 wt% and a binder content of from 70 to 97 wt%, based on the total amount of the diazo resin and the binder. Although as the diazo resin content is smaller, the sensitivity is higher, if it is less than 3 wt%, the photocuring of the binder is insufficient and as a result, the photocured layer swells by the developer at the development to weaken the layer. On the other hand, if the diazo resin content exceeds 30 wt%, the sensitivity is reduced to cause difficulties in practical use. Accordingly, more preferably, the diazo content is from 5 to 25 wt% and the binder content is from 75 to 95 wt%.

An example of the photosensitive compound for the positive photosensitive composition is an o-quinonediazide compound and a representative example thereof is an o- naphthoquinonediazide compound.

The o-naphthoquinonediazide compound is preferably an ester of 1,2-diazonaphthoquinonesulfonic chloride with a pyrogallol-acetone resin described in JP-B-43-28403. Other suitable orthoquinonediazide compounds include an ester of 1,2-diazonaphthoquinone-5-sulfonic acid chloride with a phenol-formaldehyde resin described in U.S. Patents 3,046,120 and 3,188,210 and an ester of 1,2-diazonaphthoquinone-4sulfonic acid chloride with a phenol-formaldehyde resin described in JP-A-2-96163, JP-A-2-96165 and JP-A-2-96761.

Other useful o-naphthoquinonediazide compounds include those described and known in many patents, for example, those described in JP-A-47-5303, JP-A-48-63802, JP-A-48-63803, JP A-48-96575, JP-A-49-38701, JP-A-48-13354, JP-B-37-18015, JP B-41-11222, JP-B-45-9610, JP-B-49-17481, U.S. Patents 2,797,213, 3,454,400, 3,544,323, 3,573,917, 3,674,495 and 3,785,825, British Patents 1,227,602, 1,251,345, 1,267,005, 1,329,888 and 1,330,932 and German Patent 854,890.

A photosensitive compound which acts on positive materials without using an o-naphthoquinonediazide compound, for example, a polymer compound having an orthonitrocarbinol ester group described in JP-B-56-2696 may also be used in the present invention.

Further, a combination system of a compound which generates an acid on photolysis with a compound having a -C O-C group or a -C-O-Si group and dissociative by an acid can also be used in the present invention.

Examples of the combination include combinations of a compound which generates an acid on photolysis with acetal or an O,N-acetal compound (see, JP-A-48-89003), with orthoester or an amideacetal compound (see, JP-A-51-120714), with a polymer having acetal or ketal group on the main chain (see, JP-A-53-133429), with an enol ether compound (see, JP-A-5512995), with an N-acyliminocarbon compound (see, JP-A-55126236), with a polymer having an orthoester group on the main chain (see JP-A-56-17345), with a silylester compound (see, JP-A-60-10247) and with a silylether compound (see, JP A-60-37549, JP-A-60-121446).

The photosensitive substance used in the photosensitive composition of the present invention suitably comprises as a main component a photosensitive polymer containing -CH=CH-CO- as a photosensitive group on the polymer main chain or side chain, such as a polyester, a polyamide or a polycarbonate. Examples thereof include a photosensitive polyester obtained by the condensation of phenylenediethylacrylate with hydrogenated bisphenol A and triethylene glycol described in JP-A-55-40415 and a photosensitive polyester derived from a (2propenylidene)malonic acid compound such as cinnamylidenemalonic acid and a bifunctional glycol described in U.S. Patent 2,956,878.

The photosensitive substance used in the photosensitive composition of the present invention also includes an aromatic azide compound in which the azide group is bonded to the aromatic ring directly or via a carbonyl group or a sulfonyl group. Examples thereof include polyazidostyrene, polyvinyl-p-azidobenzoate and polyvinyl-p-azidobenzal described in U.S. Patent 3,096,311, a reaction product of azidoarylsulfanyl chloride with an unsaturated hydrocarbonbased polymer described in JP-B-45-9613, and a polymer having sulfonylazide or carbonylazide described in JP-B-43-21067, JP-B-44-229, JP-B-44-22954 and JP-B-45-24915.

Further, as the photosensitive substance used in the photosensitive composition of the present invention, a photopolymerizable composition comprising an addition polymerizable unsaturated compound can also be used.

Furthermore, a photosensitive composition used in the printing plate in an electrophotographic system can also be used in the present invention. Examples thereof include a photosensitive composition comprising an electron-donating compound, a phthalocyanine-based pigment and a phenol resin for use in a printing plate using an electrophotography described in JP-A-55-161250.

The photosensitive composition is dissolved in the coating solvent of the present invention and coated and dried on an aluminum support having a hydrophilic surface to give a dry coated amount of from 0.3 to 5.0 g/m2, preferably from 0.5 to 3.5 g/m2 to thereby obtain a photosensitive lithographic printing plate. The solid concentration in the photosensitive composition on coating is suitably from 1.0 to 50 wt%, preferably from 2.0 to 30 wt%. The photosensitive composition can be coated on a support by a conventional known method such as roll coating, bar coating, spray coating, curtain coating or rotary coating. The coated photosensitive composition solution is preferably dried at a temperature of from 50 to 1500C.The drying can be effected either by a method comprising initial preparatory drying at a low temperature and then drying at a high temperature or a method comprising direct drying at a high temperature.

The support is preferably aluminum or a composite support covered by aluminum, more preferably an 1S aluminum plate containing from 0.1 to 0.5 wt% of iron, from 0.03 to 0.3 wtZ of silicon, from 0.001 to 0.03 wtt of copper and from 0.002 to 0.1 wt% of titanium.

The surface of the aluminum member is preferably subjected to surface treatment for the purpose of increasing water receptivity and improving adherence to the photosensitive layer. The surface may also preferably be etched by dipping it in a 1 to 30 wt% aqueous solution of an alkali, preferably, of sodium hydroxide, potassium hydroxide, sodium carbonate or sodium silicate, at a temperature of from 20 to 800C for from 5 to 250 seconds. To the etching bath, an aluminum ion may be added in an amount about 1/5 of the alkali. The aluminum member is dipped in a 10 to 30 wt% aqueous nitric or sulfuric solution at a temperature of from 20 to 700C for from 5 to 25 seconds and after alkali etching, subjected to neutralization and removal of smuts.Examples of the graining include commonly known brushing, ball polishing, electrolytic etching, chemical etching, liquid honing, sandblasting and a combination of these. Among these, brushing, electrolytic etching, chemical etching and liquid honing are preferred and in particular, graining including the use of electrolytic etching is preferred.

Also, a method comprising brushing and then electrolytic etching described in JP-A-54-63902 is preferred.

The electrolytic bath used in the electrolytic etching is an aqueous solution containing an acid, an alkali or a salt thereof or an aqueous solution containing an organic solvent and in particular, an electrolytic solution containing hydrochloric acid, nitric acid or a salt thereof is preferred.

The brushing preferably uses pumice stone-water suspension and a nylon brush and gives an average surface roughness preferably of from 0.25 to 0.9 zm.

The electrolytic solution used in the electrolytic etching is an aqueous solution of hydrochloric acid or nitric acid and it is used at a concentration of preferably from 0.01 to 3 wt%, more preferably from 0.05 to 2.5 wt%.

The electrolytic solution may contain, if desired, a corrosion inhibitor (or a stabilizer) such as nitrate, chloride, monoamine, diamine, aldehyde, phosphoric acid, chromic acid, boric acid or ammonium oxalate, and a uniformalizing agent of graining. Also, the electrolytic solution may contain an appropriate amount (from 1 to 10 g/C) of aluminum ions.

The electrolytic etching is usually conducted at an electrolyte temperature of from 10 to 600C. The alternating current used at this time may be in any of rectangular waveform, trapezoidal waveform and sinusoidal waveform as long as positive and negative polarities are exchanged alternately, and single-phase and three-phase alternating currents commonly in a commercial use may be used. The processing is preferably conducted at a current density of from 5 to 100 A/dm2 for from 10 to 300 seconds.

The surface roughness of the aluminum alloy support of the present invention is adjusted by the quantity of electricity to from 0.2 to 0.8 zm.

Further, the aluminum plate subjected to graining treatment is, if desired, subjected to desmutting treatment with an acid or alkali aqueous solution.

The thus grained aluminum alloy is preferably subjected to the removal of smuts attached to the surface thereof and etching (preferably in the range of from 0.01 to 2.0 g/m2) with a 10 to 50 wt% heat sulfuric acid (from 40 to 600C) or a diluted alkali (e.g., sodium hydroxide). If the removal of smuts and etching are effected by an alkali, the plate is subsequently cleaned by dipping it in an acid (nitric acid or sulfuric acid) to neutralize.

After the removal of smuts on the surface, an anodic oxidation film is provided thereon. The anodic oxidation may be made according to conventionally well known methods but, the most useful electrolytic solution here is sulfuric acid.

The phosphoric acid is the next useful electrolytic solution.

Further, a mixed acid of sulfuric acid and phosphoric acid described in JP-A-55-28400 is also useful.

In the sulfuric acid method, a direct current is usually used 1n the processing but an alternating current may be used. The electrolysis is effected using a sulfuric acid in a concentration of from 5 to 30 wt% at a temperature of from 20 to 600C for from 5 to 250 seconds to provide an oxidation film of from 1 to 10 g/m2 on the surface. The electrolytic solution preferably contains an aluminum ion.

At this time, the current density is preferably from 1 to 20 A/dm2.

In the phosphoric acid method, the processing is conducted using a phosphoric acid in a concentration of from 5 to 50 wt% at a temperature of from 30 to 600C for from 10 to 300 seconds at a current density of from 1 to 15 A/dm2.

Further, the aluminum plate is particularly preferably subjected, if desired, to silicate (e.g., sodium silicate, potassium silicate) treatment described in U.S.

Patents 2,714,066 and 3,181,461, potassium zirconium fluoride treatment described in U.S. Patent 2,946,638, phosphomolybdate treatment described in U.S. Patent 3,201,247, alkyl titanate treatment described in British Patent 1,108,559, polyacrylic acid treatment described in German Patent 1,091,433, polyvinylphosphonic acid treatment described in German Patent 1,134,093 and British Patent 1,230,447, phosphonic acid treatment described in JP-B-446409, phytic acid described in U.S. Patent 3,307,951, treatment with a salt of a hydrophilic organic polymer compound with a divalent metal described in JP-A-58-16893 and JP-A-58-18291, hydrophilic treatment by applying an undercoat of a water-soluble polymer having a sulfonic acid group described in JP-A-59-101651, or coloration by an acid dye described in JP-A-60-64352.

In addition, the hydrophilic treatment can be effected by silicate electrodeposition described in U.S.

Patent 3,658,662.

The aluminum plate is also preferably subjected to sealing after the graining and the anodic oxidation. The sealing is conducted by dipping the plate in a hot water or a hydrothermal solution containing an inorganic salt or an organic salt or by means of a steam bath.

Further, an undercoat may be provided on the aluminum support.

Examples of preferred compounds used in the undercoating include carboxymethyl cellulose, dextrin, gum arabic, phosphonic acids having an amino group such as 2aminoethylphosphonic acid, a phenylphosphonic acid which may have a substituent, a naphthylphosphonic acid, an alkylphosphonic acid, a glycerophosphonic acid, an organic phosphonic acid such as methylenediphosphonic acid and an ethylenediphosphonic acid, a phenylphosphoric acid which may have a substituent, an organic phosphoric acid such as naphthylphosphoric acid, an alkylphosphoric acid and a glycerophosphoric acid, a phenylphosphinic acid which may have a substituent, a naphthylphosphinic acid, an organic phosphinic acid such as alkylphosphinic acid and glycerophosphinic acid, amino acids such as glycine and ss- alanine, a hydrochloride of an amine having a hydroxyl group such as hydrochloride of triethanolamine, a water-soluble polymer having a sulfonic acid group described in JP-A-59101651 and an acid dye described in JP-A-60-64352.

The undercoat layer can be provided by dissolving the above-described compound in water, methanol, ethanol, methyl ethyl ketone or a mixed solvent of these, coating the solution on a support and drying it. A yellow dye may be added thereto for improving tone reproducibility of the photosensitive lithographic printing plate.

The undercoat layer has a dry coverage suitably of from 2 to 200 mg/m2, preferably from 5 to 100 mg/m2.

The photosensitive layer preferably has thereon a matting layer composed of protrusions provided independently from each other. The matting layer is provided to improve the vacuum contact between the negative image film and the photosensitive lithographic printing plate at the contact exposure to thereby reduce the vacuum length time and also to prevent plugging of fine dots at the exposure due to poor contact.

The matting layer may be coated either by a method described in JP-A-55-12974 where solid powder after powdering is heat welded or a method described in JP-A-58-182636 where a polymer-containing water is sprayed and dried. The matting layer preferably comprises a material which dissolves in an aqueous developer containing substantially no organic solvent or can be removed therefrom.

The photosensitive lithographic printing plate comprising a photosensitive composition layer coated and dried on a grained aluminum plate is developed after imagewise exposure with an alkali aqueous solution-based developer to obtain a relief. Examples of the light source suitable for the exposure include carbon arc lamp, mercury lamp, xenon lamp, metal halide lamp, stroboscope, ultraviolet rays and laser beams.

The alkali aqueous solution-based developer used for the development of a negative photosensitive lithographic printing plate includes developers described in JP-A-5177401, JP-A-51-80228, JP-A-53-44202 and JP-A-55-52054 and it preferably has a pH of from 8 to 13 and contains water in an amount of 75 wt% or more.The above-described developer may contain, if desired, an organic solvent having a solubility in water at room temperature of 10 wt% or less (e.g., benzyl alcohol, ethylene glycol monophenyl ether), an alkali agent (e.g., triethanolamine, diethanolamine, monoethanolamine, sodium phosphate, sodium carbonate), an anionic surface active agent (e.g., aromatic sulfonate, dialkylsulfosuccinate, alkylnaphthalenesulfonate, fatty acid salt, alkylsulfuric ester), a nonionic surface active agent (e.g., polyoxyethylene alkyl ether, polyoxyethylene alkylaryl ether, polyoxyethylene polyoxypropylene block polymer), a scumming inhibitor (e.g., sodium sulfite, sodium salt of sulfopyrazolone) or a hard water softening agent (e.g., tetrasodium ethylenediaminetetraacetate, trisodium nitrotriacetate).

However, if the developer contains an organic solvent, there arise a hygienic problem such as toxicity and odor at the operation, a safety problem such as fire and gas explosion, an operability problem such as generation of bubbles, a problem such as public nuisance due to waste solution and a problem in the cost, and thus, the developer further preferably contains substantially no organic solvent.

The aqueous alkali developer containing substantially no organic solvent includes a developer composition used in developing, after imagewise exposure, a positive lithographic printing plate described, for example, in JP-A-59-84241, JP A-57-192952 and JP-A-62-24263.

The photosensitive lithographic printing plate of the present invention may be subjected to plate making processing according to the methods described in JP-A-54-8002, JP-A-55115045 and JP-A-59-58431. More specifically, after development, desensitizing treatment following water washing, desensitizing treatment with no intervening processing, treatment with an aqueous solution containing an acid or desensitizing treatment following treatment with an aqueous solution containing an acid may be applied thereto.

In the development of this kind of photosensitive lithographic printing plate, the processing ability is reduced because the alkali aqueous solution is consumed according to the processing amount to lower the alkali concentration or the alkali concentration is lowered due to the air in a prolonged operation of an automatic developing machine. In this case, in order to recover the processing ability,-a replenisher may be used as described in JP-A-5462004 and there, the replenishment is preferably conducted according to the method described in U.S. Patent 4,882,246.

The above-described plate making is preferably conducted in an automatic developing machine as described in JP-A-2-7054 and JP-A-2-32357.

The desensitizing gum which is coated, if desired, at the final step of the plate making processing include, as preferred examples, those described in JP-B-62-16834, JP-B62-25118, JP-B-63-52600, JP-A-62-7595, JP-A-62-11693 and JP A-62-83194.

After the processing with a developer, unnecessary portions in the image area can be, if desired, deleted by a commercially available deletion fluid for negative materials or scrubbed off by a stone stick.

The developer used in the development of a positive photosensitive lithographic printing plate is preferably an alkaline aqueous solution containing substantially no organic solvent and specific examples of the suitable aqueous solution include sodium silicate, potassium silicate, sodium hydroxide, potassium hydroxide, lithium hydroxide, sodium tertiary phosphate, sodium secondary phosphate, ammonium tertiary phosphate, ammonium secondary phosphate, sodium metasilicate, sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate and aqueous ammonia. The aqueous solution is added to give a concentration of from 0.1 to 10 wt%, preferably from 0.5 to 5 wt%.

In particular, a developer containing an alkali silicate such as potassium silicate, lithium silicate or sodium silicate is preferred because scum is hardly generated at the printing and the developer preferably has an alkali silicate composition of [SiO2]/[M] = from 0.5 to 2.5 by mole (where [SiO2] and [M] indicate a molarity of SiO2 and a molarity of the entire alkali metals, respectively) and contains from 0.8 to 8 wt% of SiO2. The above-described developer may also contain, for example, a water-soluble sulfite such as sodium sulfite, potassium sulfite and magnesium sulfite, resorcin, methylresorcin, hydroquinone or thiosalicylic acid. Such a compound is contained in the developer in an amount of from 0.002 to 4 wt%, preferably from 0.01 to 1 wt%.

Also, the developer preferably contains an anionic surface active agent and an amphoteric surface active agent described in JP-A-50-51324 and JP-A-59-84241, at least one of nonionic surface active agents described in JP-A-59-75255, JP-A-60-111246 and JP-A-60-213943, or a polymer electrolyte described in JP-A-55-95946 and JP-A-56-142528 because thereby the wettability to the photosensitive composition is increased or the stability of development (development latitude) is enhanced. Such a surface active agent is added in an amount of preferably from 0.001 to 2 wt%, more preferably from 0.003 to 0.5 wt%.As the alkali metal in the alkali silicate, potassium is preferably contained in an amount of 20 mole% or more, more preferably 90 mole% or more, most preferably 100 mole%, based on the entire alkali metals, because insoluble matters are less generated in the development.

Further, the developer used in the present invention may contain an organic solvent such as a slight amount of alcohol, a chelating agent described in JP-A-58-190952, a metal salt described in JP-B-1-30139 or an anti-foam fluid such as an organic silane compound.

In the case when the photosensitive lithographic printing plate of the present invention is imagewise exposed, developed and washed or rinsed and then the unnecessary image area is deleted, a deletion fluid as described in JP-B-213293 is preferably used. Further, the desensitizing gum which is coated, if desired, at the final step of the plate making processing include, as preferred examples, those described in JP-B-62-16834, JP-B-62-25118, JP-B-63-52600, JP A-62-7595, JP-A-62-11693 and JP-A-62-83194.

Furthermore, in the case when the photosensitive lithographic printing plate of the present invention is imagewise exposed, developed, washed or rinsed and then, if desired, subjected to deletion operation, washing and burning, the plate is preferably processed before burning with a burning conditioner described in JP-B-61-2518, JP-B55-28062, JP-A-62-31859 and JP-A-61-159655.

SYNTHESIS EXAMPLE 1 29.4 g of 4-diazodiphenylamine sulfate (purity: 99.5%) was gradually added at 250C to 70 ml of 96% sulfuric acid and stirred for 20 minutes. 3.26 g of paraformaldehyde (purity 92%) was gradually added thereto over about 10 minutes and the mixture was stirred at 300C for 4 hours to advance the condensation reaction. The condensation molar ratio of the diazo compound and the formaldehyde above was 1:1. The reaction product was poured into 2 c of ice water while stirring and treated with a cold thick aqueous solution having dissolved therein 130 g of zinc chloride. The precipitate was recovered by suction filtration and the partially dried solid was dissolved in 1 Q of water, filtered, ice cooled and treated with an aqueous solution having dissolved therein 23 g of potassium hexafluorophosphate.The precipitate was recovered and air dried to obtain 30.3 g of Polymer Group Diazo Compound (1).

The resulting Diazo Compound (1) was coupled with 1phenyl-3-methyl-5-pyrazolone in methyl cellosolve to obtain a dye. The resulting dye had a weight-average molecular weight (determined by means of a light scattering photometer for low angle measurement) of 16,500 which corresponded to about tetracopentamer.

Further, the dye was measured on the-weight molecular weight distribution by gel permeation chromatography (GPC) and found to contain decamer or greater polymers in an amount of about 30 mole%.

The present invention will be described below in greater detail with reference to the examples, but the present invention should not be construed as being limited thereto.

EXAMPLE 1 A 0.30 mm-thick rolled plate made of JIS A1050 aluminum material containing 99.5 wt% of aluminum, 0.01 wt% of copper, 0.03 wt% of titanium, 0.3 wt% of iron and 0.1 t of silicon was grained on the surface thereof using a 20 wt% aqueous suspension of 400-mesh pumice stone (produced by Kyoritsu Yogyo KK.) and a rotary nylon brush (6,10-nylon) and then well washed with water.

The resulting plate was dipped in an aqueous solution of 15 wt% sodium hydroxide (containing 4.5 wt% of aluminum) to etch it until the dissolved amount of aluminum reached 5 g/m2 and then washed with flowing water. Thereafter, the plate was neutralized with 1 wt% nitric acid and then subjected to electrolytic graining in a 0.7 wt% aqueous nitric solution (containing 0.5 wt% of aluminum) using a rectangular wave alternating waveform voltage (current ratio r=0.90, current waveform described in the example of JP-B-585796) able to supply an anode time voltage of 10.5 V and a cathode time voltage of 9.3 V, at an anode time power of 160 Coulomb/dm2. After water washing, the grained plate was dipped in an aqueous solution of 10 wt% sodium hydroxide to etch it until the dissolved amount of aluminum reached 1 g/m2 and then washed with water.Thereafter, the etched plate was dipped in a 30 wt% aqueous sulfuric solution at 50"C to desmut and then washed with water.

Further, the plate was subjected to porous anodic oxidation film formation treatment in a 20 wt% aqueous sulfuric solution at 35"C (containing 0.8 wt% of aluminum) using a direct current. More specifically, the electrolysis was conducted at a current density of 13 A/dm2 and the anod;e oxidation film weight was set to 2.7 g/m2 by controlling the electrolysis time.

For the preparation of a negative photosensitive lithographic printing plate using a diazo resin and a binder, the support obtained as above was washed with water, dipped in a 3 wt% aqueous solution of sodium silicate at 700C for 30 seconds, washed with water and dried.

The thus-obtained aluminum support was measured by a Macbeth RD 920 reflection densitometer and found to have a reflection density of 0.30 and a center line average roughness of 0.58 pm.

Then, a 1.0 wt% aqueous solution of a methyl methacrylate/ethyl acrylate/sodium 2-acrylamide-2-methyl propanesulfonate copolymer (average molecular weight: about 60,000) (molar ratio: 50/30/20) was coated on the support obtained above by a roll coater to give a coated amount after drying of 0.05 g/m2.

Further, the following Photosensitive Solution 1 was coated thereon using a bar coater and dried at 1100C for 45 seconds. The dry coated amount was 2.0 g/m2.

Photosensitive Solution-1 Diazo resin in Synthesis Example 1 0.50 g Binder-l 5.00 g Styrite HS-2 (produced by Daido Kogyo KK) 0.10 g Victoria Pure Blue BOH 0.15 a Tricresyl phosphate 0.50 g Dipicolinic acid 0.20 g FC-430 (surface active agent, produced by 0.05 g 3M Co.) Solvent l-Methoxy-2-propanol 25.00 g Methyl lactate 12.00 g Methanol 30.00 g Methyl ethyl ketone 30.00 g Water 3.00 g Binder-1 is a 2-hydroxyethylmethacrylate/acrylonitrile/methyl methacrylate/methacrylic acid copolymer (weight ratio: 50/20/26/4, average molecular weight: 75,000, acid content: 0.4 meq/g) which is a water-insoluble and alkali water-soluble film-forming polymer.

Styrite HS-2 (produced by Daido Kogyo KK) is a styrene/maleic acid mono-4-methyl-2-pentyl ester (molar ratio: 50/50) copolymer having an average molecular weight of about 100,000 which is a polymer having an ink-receptivity higher than that of the binder.

The thus-obtained coil-form photosensitive lithographic printing plate having a thickness of 0.3 mm and a width of 800 mm was continuously slit to a width of 398 mm and to have a shape such that the edge part was downwardly curved as shown in Fig. 3 (X=100 pm, Y=500 pm) using a lower cutting blade shown in Fig. 2 (X=100 pm, i=500 pom).

Thereafter, on the lateral side of the curved aluminum support, an aqueous solution comprising 5 g of sodium hexametaphosphate and 95 g of pure water was continuously coated as a desensitizing solution by molleton roller to have a dry weight of 0.1 g/m2, the coating obtained was continuously cut to a length of 560 mm, and 1,000 sheets were stacked and packaged.

After one week, the photosensitive lithographic printing plate cut into a sheet was imagewise exposed and developed with a 1:1 diluted solution of DN-3C (an alkali aqueous solution-based developer, produced by Fuji Photo Film Co., Ltd.) with water in 800H (an automatic developing machine, manufactured by Fuji Photo Film Co., Ltd) and immediately thereafter, a 1:1 diluted solution of FN-2 (a gum solution, produced by Fuji Photo Film Co., Ltd.) with water was coated thereon and dried.

Next day, the printing plate was printed on 20,000 sheets using an ink for newspapers produced by Sakata Ink KK and TOYO ALKY fountain solution produced by Toyo Ink KK at a speed of 100,000 sheets/hour in an offset rotary press. No scum was generated on the printed paper corresponding to the edge part of the printing plate.

EXAMPLE 2 A coil-form photosensitive lithographic printing plate was prepared in the same manner as in Example 1. This coil-form photosensitive lithographic printing plate was continuously slit to have a shape such that the edge part was downwardly curved as shown in Fig. 5 and a flat part was formed on the bottom-side edge part of the curved part (X=100 pm, Y=500 um, Z=50 pm) using a lower cutting blade shown in Fig. 4 (X=100 pm, Y=500 pom).

Thereafter, a desensitizing solution was applied to the lateral side of the aluminum support in the same manner as in Example 1 and then, the plate making and the printing were conducted in the same manner as in Example 1. No scum was generated on the edge face.

EXAMPLES 3 TO 25 A coil-formed photosensitive lithographic printing plate was prepared in the same manner as in Example 1. This photosensitive lithographic printing plate was slit into photosensitive lithographic printing plates with X, Y and Z as shown in Fig. 3 and Fig. 5 being varied using various types of lower blades. The example numbers are shown in Table 1.

Thereafter, a desensitizing solution was applied to the lateral side of the aluminum support in the same manner as in Example 1 and the plate making and the printing were conducted in the same manner as in Example 1. In any level, no scum was generated on the edge face.

In particular, in Examples 15, 16, 17, 18, 20, 21, 22, 23, 24 and 25, no scum was generated on the edge face even in a printing condition such that the amount of fountain solution was reduced and the ink amount was increased.

TABLE 1 X ( m) Y Z ( m) ( m) 20 50 200 Example No.

3 - - 40 0 4 5 - 100 0 6 7 8 500 0 - 9 10 2,000 0 11 - - 40 10 12 13 - 100 10 14 15 16 500 10 - 17 18 2,000 10 19 20 21 500 100 - 22 23 2,000 100 - 24 25 2,000 1,000 EXAMPLES 26 TO 35 A coil-form photosensitive lithographic printing plate was prepared in the same manner as in Example 2 and continuously slit to have the same edge face shapes as in Example 2.

Thereafter, desensitizing solutions shown in Table 2 were applied to the lateral side of the aluminum support and then, the plate making and the printing were conducted in the same manner as in Example 1.

In any case, no scum was generated on the edge face.

TABLE 2 Example Coating Solution Coated Dry Coated No. on Lateral Side Amount Amount (g) (g/m2) 26 Sodium hexametaphosphate 1 0.02 Pure water 99 27 Sodium hexametaphosphate 20 0.40 Pure water 80 28 Sodium hexametaphosphate 5 0.10 Pure water 94 Phosphoric acid (85 wt% aq. 1 soln.) 29 Sodium hexametaphosphate 5 0.30 Pure water 85 Phosphoric acid (85 wt% aq. 10 soln.) 30 Phytic acid (30 wt% aq. 3 0.02 soln.) Pure water 97 31 Phytic acid (30 wt% aq. 15 0.10 soln.) Pure water 85 32 Gum arabic (30 wt% aq. 3 0.02 soln.) Pure water 97 33 Gum arabic (30 wt% aq. 15 0.10 soln.) Pure water 85 34 Sodium hexametaphosphate 5 0.15 Pure water 91 Phosphoric acid (85 wt% aq. 1 soln.) Gum arabic (30 wt% aq. 3 soln.) 35 Phytic acid (30 wt% aq. 15 0.12 soln.) Pure water 82 Gum arabic (30 wt% aq. 3 soln.) COMPARATIVE EXAMPLES 1 AND 2 A coil-form photosensitive lithographic printing plate was coated by a photosensitive layer, dried and slit into 398 mm in the same manner as in Example 1 and then continuously slit in the same manner as in Examples 1 and 2 The plate of Example 1 to which the desensitizing solution was not applied was used for Comparative Example 1 and the plate of Example 2 to which the desensitizing solution was not applied was used for Comparative Example 2 Thereafter, the plate making and the printing were conducted in the same manner as in Example 1.

Either in Comparative Example 1 or Comparative Example 2, thin linear scum was generated in the printed paper corresponding to the edge part of the printing plate.

In particular, thick linear scum was generated in the conditions such that the amount of fountain solution was reduced, the ink amount was increased, or the amount of fountain solution was reduced and the ink amount was increased.

COMPARATIVE EXAMPLES 3 TO 6 A coil-form photosensitive lithographic printing plate was prepared in the same manner as in Example 1 and continuously slit using a conventional lower cutting blade having no step differently from those shown in Fig. 2 and Fig. 4.

Thereafter, the desensitizing solutions shown in Table 3 were applied to the lateral side of the aluminum support and then, the plate making and the printing were conducted in the same manner as in Example 1.

In any case, thin linear scum was generated on the printed paper corresponding to the edge part of the printing plate. In particular, thick linear scum was generated in the conditions such that the amount of fountain solution was reduced, the ink amount was increased, or the amount of fountain solution was reduced and the ink amount was increased.

TABLE 3 Comparat ive Example Coating Solution Coated Dry Coated No. on Lateral Side Amount Amount (g) (g/m2) 3 Sodium hexametaphosphate 5 0.10 Pure water 95 4 Sodium hexametaphosphate 5 0.30 Pure water 85 Phosphoric acid (85 wt% 10 aq. soln.) 5 Phytic acid (30 wt% aq. 15 0.10 soln.) Pure water 85 6 Gum arabic (30 wt% aq. 15 0.10 soln.) Pure water 85 COMPARATIVE EXAMPLE 7 A coil-form photosensitive lithographic printing plate was prepared in the same manner as in Example 1 and continuously slit using the same conventional lower cutting blade as in Comparative Examples 3 to 6.

Thereafter, without applying a desensitizing solution to the lateral side of the aluminum support, the plate making and the printing were conducted in the same manner as in Example 1.

Thick linear scum was generated on the printed paper corresponding to the edge part of the printing plate.

As clearly seen from the foregoing Examples, the printing plate produced from the photosensitive lithographic printing plate of the present invention does not suffer from any generation of scum on the printed paper corresponding to the edge part of the printing plate.

While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.

Claims (4)

WHAT IS CLAIMED IS:

1. A photosensitive lithographic printing plate comprising an aluminum support having a hydrophilic surface having thereon a photosensitive layer, wherein two sides facing with each other or four sides of said aluminum support are downwardly curved and said curved lateral side of the photosensitive layer face is subjected to desensitizing treatment.

2. The photosensitive lithographic printing plate as claimed in claim 1, wherein the downwardly protruded edge of said curved side has a flat part in parallel to the bottom face.

3. The photosensitive lithographic printing plate as claimed in claim 1, wherein the solution for said desensitizing treatment contains at least one of a hydrophilic organic polymer compound, a hexametaphosphoric acid and a salt thereof, and a phytic acid and a salt thereof.

4. A photosensitive lithographic printing plate substantially as herein described with reference to the Examples.