GB2046461A - Method for producing photosensitive printing plate precursor - Google Patents

Abstract

A light-sensitive material ("precursor") used to produce a printing plate is known to comprise a support bearing a photosensitive layer and having an outer surface which is matted with particulate matting agent, e.g. silica or glass beads, so as to reduce the time needed for vacuum contacting of the plate made from the precursor before imagewise exposure. According to the present invention, to improve the durability and the quality of reproduction, the outer matted layer is provided by coating a composition in which the particulate matting agent is stably dispersed but has poor affinity for the liquid of the composition so that as the liquid is evaporated the particles are pushed to the surface of the material and are there weakly bonded as minute protrusions; development removes the coatings from the support entirely in non-image areas and removes the protruded particles in image areas. Suitable matting agents are of polyethylene, polypropylene, polyethylene terephthalate, cross- linked vinyl polymers and copolymers of ethylene and propylene or vinyl acetate. Photosensitive compositions can comprise a diazo resin, o-quinone diazide, photosensitive diazide or polymeric compounds.

Description

SPECIFICATION Method for producing photosensitive printing plate precursor This invention relates to a method for producing a photosensitive printing plate. (The term "printing plate" as used herein with respect to unexposed materials is actually a reference to a printing plate precursor, i.e. a photosensitive material which forms a printing plate after imagewise exposure and development).

To obtain perfect contact of the outermost surface of a photosensitive printing plate (which surface may be the photosensitive coating or a resinous top coating overlying the photosensitive coating) with an original for exposure of the photosensitive coating, the two elements have customarily been disposed in superimposed engagement between an elastomer sheet and a pressure glass plate and the intervening space between the elastomer sheet and the glass plate has been evacuated. This procedure has become known as the vacuum contact method. An extraordinarily long evacuation time is sometimes required before perfect contact is realized over the entire surface of the conventional type photosensitive printing plate.Due to the smooth surfaces of the plate and the original and the contact being initiated at the periphery of the surface and only gradually being propagated to the center, the central area is sealed off and evacuation of the central area is seriously impeded. When image exposure is carried out with imperfect contact, the image lacks sharpness, leading to the production of unacceptable printed matter. Since such a time-consuming contacting operation reduces the efficiency of plate fabrication, curtailment of the evacuation period has long been desired.

Photosensitive printing plates and manufacturing methods which can reduce the time of the vacuum contact process are disclosed in British Patents 1,495,361, 1,512,080 and 1,542,131. These patents disclose that by providing on the surface of a photosensitive printing plate a matted layer which is removable upon development one can markedly reduce the time required for vacuum contact. However, to produce such a photosensitive printing plate, additional production steps for coating as well as drying the matted layer are required which are performed with a specially designed coating device. Thus, the resulting plate suffers from increased production costs.

On the other hand, Japanese Patent Application (OPI) No. 12905/79 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application") discloses another type of photosensitive printing plate comprising a photosensitive coating having a matted surface obtained by the incorporation of a matting agent in the coating. This type of plate which can also reduce the vacuum contact time is depicted in the accompanying Figure 1 in which support 10 is provided with photosensitive coating 20, the surface of which is matted with a finely-divided material 50. Though this type of photosensitive printing plate is free of the drawback inherent in the former type of plate, the plate suffers from (1) low printing durability and (2) poor tone reproduction.

A printing plate prepared from a photosensitive lithographic plate of such construction has proved to withstand rather few impressions. Presumably, the finely-divided material incorporated in the photosensitive coating as matting agent and remaining in the image area (the area where the printing ink is accepted as a result of water repulsion) after development will be worn off after some of the impressions, leaving areas which no longer accept ink. As a result, the printing plate exhibits rather poor durability.

As shown in Figure 2 cross-sectionally, the presence of particles 50A and SOB of the matting agent bridging exposed area 20A and unexposed area 20B of a negative type photosensitive lithographic plate original M to active radiation (shown by the arrows) gives rise to an image as illustrated in Figure 3 upon development whereby the unexposed area 20B is removed together with particle SOB leaving the bare surface of support 10 exposed. Occasionally some particles such as 50A remain. As a result, it is apparent that the image area of the finished plate does not correspond to or reproduce the original faithfully.

Accordingly, an object of the present invention is to provide a method for producing photosensitive printing plates having a matted surface without additional coating and drying procedures.

Another object of the present invention is to provide a method for producing photosensitive printing plates with a matted surface without a specialized coating apparatus.

Still another object of the present invention is to provide a method for producing photosensitive printing plates having a matted surface from which one can prepare lithographic printing plates of high durability and unimpaired tone reproduction.

The present invention is a method of producing photosensitive printing plates comprising a photosensitive layer on a support in which the outermost layer is provided by coating and drying a mixture containing a finely-divided material dispersed in a solvent solution of the other ingredients making up the outermost layer and thereby providing a matted surface. The method is characterized by stably dispersing finely-divided material in the coating mixture such that with the evaporation of the solvent, individual particles of the finely-divided material remains on the surface as minute protrusions in the outermost layer.

The invention will be described with reference to the accompanying drawings, wherein: Figure 1 is a cross-sectional view of a conventional photosensitive planographic printing plate.

Figure 2 illustrates imagewise exposure of the plate depicted in Figure 1.

Figure 3 illustrates the same plate (Figure 1) after being developed and converted into a planographic plate.

Figure 4 depicts schematically and cross-sectionally the plate manufactured in accordance with the present invention at each manufacturing step between the spreading of a photosensitive coating fluid over the support and drying, viz., (a) immediately after spreading (b) in the course of drying, and (c) after complete removal of the volatile solvent.

Figure 5 illustrates imagewise exposure of the photosensitive planographic plate of the present invention as shown in Figure 4 (c).

Figure 6 is a cross-sectional view of the plate of Figure 5 after development.

Figure 7 is another embodiment of the present invention in which a non-sensitive coating is applied to the photosensitive coating. Figures 7 (a) and (b) are each cross-sectional views of a coated product, first just after being coated with the coating solution (Figure 7 (a)) and after drying (Figure 7 (b)).

Figure 8 is a cross-sectional view of the planographic printing plate obtained from the photosensitive plate shown in Figure 7 (b) through image exposure and development.

Herein the expression "stably dispersed" implies that the particles of the finely-divided material will not aggregate, precipitate or float during the period between preparation of the coating mixture and coating.

Such periods during which the dispersion state remains unchanged preferably exceed 2 minutes and more preferably 5 minutes. However, in accordance with preferred embodiments of the invention much longer periods of stability are possible.

The production of a negative type photosensitive lithographic plate using a photosensitive diazonium resin will be described with reference to the accompanying drawings.

Figure 4 (a) illustrates by cross-section an aluminum support 10 immediately after coating with a coating mixture comprising a diazonium resin and a binder dissolved in a suitable solvent and a finely-divided material dispersed in the solution (i.e., the coating is not yet dry). At this stage, particles 50 are stably dispersed in the thin layer of the coating mixture 20C.

Figure 4 (c) illustrates the same coated product as in Figure 4 (a) after the coating mixture has dried, wherein particles 50 of the finely-divided material protrude from surface 20S of the photosensitive coating 20, being only tangentially held on the very surface 20S of the coating 20. It should be noted that particles 50 do not substantially exist inside the effective thickness of coating 20. Accordingly, the photosensitive lithographic printing plate prepared in accordance with the present invention has a micro-structure distinctly different from that of the conventional plates in which particles 50 are substantially embedded in the effective thickness of coating 20. Such a structure presumably results when the coated product shown in Figure 4 (a) is dried and the solvent in the coating evaporates.Such a reduction of solvent destroys the dispersion of the finely-divided material in coating mixture 20C. Then, if the affinity or wettability of the finely-divided material to the dissolved ingredients of the coating fluid (i.e., the diazonium resin, the binder and the remaining solvent) is weak, the particles are pushed from the bulk of the coating fluid to the surface.

Figure 4(b) illustrates such a transition wherein fine particles 50 are repelled towards the top surface of the coating fluid layer 20C' which results from the decrease in the solvent content halfway to complete drying.

Hence, as drying proceeds, a photosensitive lithographic printing plate having the cross-sectional structure shown in Figure 4(c) is obtained. This explanation is indicated by a comparison of photosensitive plates fabricated by the same procedures described above and merely changing the chemical species of the matting agent. When the affinity of the matting agent for the other ingredients of the coating mixture (represented by the solvent) is poor, the resulting plate assumes the cross-sectional structure depicted in Figure 4 (c), but when the matting agent has a strong affinity for the other ingredients, printing plates of the type shown in Figure 1 results.

The photosensitive printing plate thus prepared can noticeably reduce the time required to realize perfect contact with the original by the vacuum contact method. Moreover, since none of the finely-divided particles are substantially embedded in the photosensitive coating, the surface roughening is achieved quite effectively. Accordingly, in comparison to conventional photosensitive lithographic plates shown in Figure 1, far smaller particles can provide the surface of the photosensitive coating with an equivalent degree of roughness.

Figure 5 depicts contact exposure of the photosensitive coating 20 of a photosensitive lithographic plate having a cross-sectional structure shown in Figure 4 (c) through original M (exposure is shown by the arrows) wherein the exposed areas of the photosensitive coating are designated 20A and the unexposed areas 20B.

Figure 6 depicts the cross-sectional view of the exposed plate in Figure 5 after development wherein the unexposed area of the photosensitive coating is removed to expose a bare surface of support 10 which constitutes the non-image area of the lithographic plate. On the other hand, the exposed area remains on the support to form an ink-receptive area 20A of the lithographic plate. As is seen in the Figure, no matting agent remains in the image area 20A. The particles have been eliminated by development. Removal of the particles is complete because the particles are only superficially held to the surface and they are not substantially embedded in the coating interior. Accordingly, even after the exposed area of the photo-sensitive coating has been cross-linked, the particles are not held to the surface firmly enough to withstand the development operation. In any event, one can confirm the absence of the particulate material in the image area by the use of a microscope.

The absence of the matting agent at the image area of the finished lithographic plate advantageously eliminates the drawbacks inherent in the conventional lithographic plate shown in Figure 1 (c), i.e., poor printing durability and inferior tone reproduction. The plate of the present invention is also free from another drawback attending the conventional photosensitive printing plate represented by the structure shown in Figure 1, that is, incomplete removal of non-image areas when it is processed with a developer with deteriorated developing activity (a so-called exhausted developer). Moreover, in accordance with the present invention, additional manufacturing procedures are not necessary to roughen the surface of the photosensitive coating.

The photosensitive printing plate prepared by the process of this invention basically comprises a support having a photosensitive layer thereon, and it includes those photosensitive printing plates used for the preparation of a lithographic printing plate, a letterpress printing plate, an intaglio printing plate and other printing plates. Photographic printing plates used for the preparation of a lithographic printing plate and an intaglio printing plate are preferred.

The support is a dimensionally stable sheet-like material as is conventionally used as the support for printing plates. Examples of such a support include paper, paper laminated with plastics (e.g., polyethylene, polypropylene and polystyrene); metal sheets such as aluminum (including aluminum alloys), zinc, iron and copper; plastic films such as cellulose diacetate, cellulose triacetate, cellulose propionate, cellulose butyrate, cellulose acetate butyrate, cellulose nitrate, polyethylene terephthalate, polyethylene, polystyrene, polypropylene, polycarbonate, and polyvinyl acetal; and paper and plastic films which are laminated or metallized with the above indicated metals. A suitable support is selected depending upon the type of printing plate to be prepared.For a photosensitive lithographic printing plate, the aluminum sheet and a composite sheet of the type described in Japanese Patent Publication No. 18327/73 which has a polyethylene terephthalate film combined with an aluminum sheet are particularly preferred. For a photosensitive letterpress printing plate, a polyethylene terephthalate film, an aluminum sheet and an iron sheet are preferred.

The support is subjected to surface treatment as required. For instance, the surface of the support used in the preparation of a photosensitive lithographic printing plate is rendered hydrophilic by various methods. A support having the plastic surface is subjected to surface treatments such as chemical treatment, discharge treatment, flame treatment, U.V. treatment, hig h-frequency wave treatment, glow discharge treatment, active plasma treatment and laser treatment (see, for example, U.S. Patents 2,764,520,3,497,407, 3,145,242, 3,376,208,3,072,483, 3,475,193 and 3,360,448, and British Patent 788,365), or the so treated plastic surface is coated with a subbing layer.

The subbing layer can be applied by two methods. One is the double-layer method which first applies a layer of hydrophobic resin that strongly adheres to plastics and which is highly soluble and then applies a layer of hydrophilic resin, and the other is the single-layer method wherein a layer of resin containing both hydrophobic and hydrophilic layers in the same polymer is applied.

Supports having a metal surface, especially aluminum, are preferably subjected to such surface treatments as graining, immersion in an aqueous solution of sodium silicate, potassium fluorozirconate or phosphate, and anodization. A sheet having an aluminum surface may be grained, followed by immersion in aqueous sodium silicate as described in U.S. Patent 2,714,066, or it may be anodized, followed by immersion in aqueous alkali metal silicate as described in Japanese Patent Publication No.5125/72. Either of these two types of aluminum treatment may be used in this invention with advantage.The above indicated anodization is carried out in an electrolyte composed of one or more aqueous or non-aqueous solutions of inorganic acids such as phosphoric acid, chromic acid, sulfuric acid and boric acid or organic acids such as oxalic acid and sulfamic acid or salts thereof, with an electric current applied through an aluminum anode.

Another effective surface treatment is electrodeposition of silicate as described in U.S. Patent 3,658,662.

The purpose of these surface treatments is not limited to rendering the surface of the support hydrophilic; they are also performed to prevent deleterious reaction with a photosensitive composition disposed on the support as well as to provide intimate contact with the photosensitive layer.

Any material can be used as the photosensitive component of the photosensitive compositions used in the present invention as long as it changes its solubility in a developer or the property of swelling in a developer upon imagewise exposure. Typical examples of such materials are set forth below.

(1) Compositions ofa diazo resin Diazo compounds typified by the condensate of p-diazodiphenylamine and paraformaldehyde may be used with advantage whether they are water-soluble or insoluble, and those which are insoluble in water and soluble in ordinary organic solvents are preferred. Particularly preferred diazo compounds are condensates of p-diazodiphenylamine and formaldehyde or acetaldehyde, and those compounds which contain at least two diazo groups in the molecule such as the salts of p-diazodiphenylamine and phenol, fluorocapric acid, and triisopropyl naphthalenesulfonic acid, 4,4-biphenyldisulfonic acid, 5nitroorthotoluenesulfonic acid, 5-sulfosalicyclic acid, 2,5-dimethylbenzenesulfonic acid, 2 nitrobenzenesulfonic acid, 3-chlorobenzenesulfonic acid, 3-bromobenzenesulfonic acid, 2-chloro-5- nitrobenzenesulfonic acid, 2-fluorocapryl naphthalenesulfonic acid, 1-naphthol-5-sulfonic acid, 2-methoxy-4hydroxy-5-benzoylbenzenesulfonic acid and paratoluenesulfonic acid. Other suitable diazo resins are the condensate of 2,5-dimethoxy-4-p-tolylmercaptobenzene diazonium and formaldehyde, and the condensate of 2,5-dimethoxy-4-morpholinobenzene diazonium and formaldehyde or acetaldehyde, containing the above identified salts.

The diazo resins described in British Patent 1,312,925 are also preferred.

These diazo resins may be used independently as the photosensitive material but they are preferably used together with a binder. Various polymeric compounds may be used as such binder, and preferred polymeric compounds are those which contain hydroxy, amino, carboxylic acid, amide, sulfonamide, active methylene, thio alcohol or epoxy groups. Included within these preferred binders are the shellac described in British Patent 1,350,521, the polymer containing a hydroxyethyl acrylate or hydroxyethyl methacrylate unit as a main recurring unit, as described in British Patent 1,460,078 and U.S. Patent 4,123,276, the polyamide resin described in U.S. Patent 3,751,257, the phenolic resin and polyvinyl acetal resin such as polyvinyl formal resin or polyvinyl butyral resin, as described in British Patent 1,074,392, the linear polyurethane resin described in U.S.Patent 3,660,097, a polyvinyl alcohol resin esterified with phthalic acid, an epoxy resin condensed from bisphenol A and epichlorohydrin, a polymer containing an amino group such as polyaminostyrene or polyalkyl amino(meth)acrylate, and celluloses such as cellulose acetate, cellulose alkyl ether and cellulose acetate phthalate.

The binder is suitably contained in the photosensitive composition in an amount of from 40 to 95 wt% (dried). A high binder content (less diazo resin) naturally results in high sensitivity, but the stability of the composition decreases with time faster than when the binder content is low. An optimum content is in the range of from about 70 to 90 wt%.

The compositions made of diazo resins may further contain the phosphoric acid described in U.S. Patent 3,236,646, and other additives such as dye and pigment.

(2) Compositions of o-quinonediazide compounds Preferred o-quinonediazide compounds are o-naphthoquinonediazide compounds such as those described in U.S. Patents 2,766,118, 2,767,092, 2,772,972, 2,859,112,2,907,665, 3,046,110, 3,046,111, 3,046,115, 3,046,118,3,046,119, 3,046,120,3,046,121, 3,046,122,3,046,123, 3,061,430,3,102,809, 3,106,465,3,635,709 and 3,647,443 and many other prior art references. These compounds can be used in this invention with advantage. Preferred examples are o-naphthoquinonediazide sulfonate ester or o-naphthoquinonediazide carboxylate ester of aromatic hydroxyl compound, and o-naphthoquinonediazide sulfonic acid amide of o-naphthoquinonediazide carboxylic acid amide of aromatic amino compound.Particularly preferred are a pyrogallollacetone condensate which is esterified with o-naphthoquinonediazide sulfonic acid as described in U.S. Patent 3,635,709, a polyester having a terminal hydroxyl group which is esterified with o-naphthoquinonediazide sulfonic acid or o-naphthoquinonediazide carboxylic acid as described in U.S.

Patent 4,028,111, a homopolymer of p-hydroxystyrene or a copolymer thereof with another copolymerizable monomer, which is esterified with o-naphthoquinonediazide sulfonic acid or o-naphthoquinonediazide carboxylic acid, as described in U.S. Patent 4,139,384.

These o-quinonediazide compounds may be used independently, but they are preferably mixed with an alkali-soluble resin. Advantageous alkali-soluble resins include phenolic novolak resins, for example, phenol4ormaldehyde resin, o-cresol-formaldehyde resin m-cresol-formaldehyde resin. More preferably, these phenolic resins may be used in combination with a condensate of alkyl (C3)-substituted phenol or cresol and aldehyde (e.g., t-butylphenolformaldehyde resin), as taught in U.S. Patent 4,123,279. Such alkali-soluble resin is incorporated in the photosensitive resist-forming composition in an amount of from about 50 to about 85 wt%, preferably from 60 to 80 wt%, based on the total weight of the composition.

The photosensitive composition of an o-quinonediazide compound may further contain a pigment, dye, plasticizer and other additives.

(3) Compositions of photosensitive azide compounds Suitable photosensitive azide compounds are aromatic azide compounds wherein an azido group is bonded to an aromatic ring either directly or with an intermediary of a carbonyl or sulfonyl group. Upon exposure to light, the azide group is decomposed to form a nitrene which induces various reactions to render the compounds insoluble.Preferred aromatic azide compounds are those which contain at least one of such groups as azidophenyl, azidostyryl, azidobenzal, azidobenzoyl and azidocinnamoyl groups; examples are 4,4'-diazidochalcone, 4-azido-4'-(4-azido-benzoylethoxy)chalcone, N,N-bis-p-azidobenzal-p phenylenediamine, 1 ,2,6-tri(4'-azidobenzoxy)hexane, 2-azido-3-chlorobenzoquinone, 2,4-diazido-4'- ethoxyazobenzene, 2,6-di(4'-azidobenzal)-4-methylcyclohexanone, 4,4'-diazidobenzophenone, 2,5-diazido- 3,6-dichlorobenzoquinone, 2,5-bis(4-azidostyryl)-1 ,3,4-oxadiazole, 2-(4-azidocinnamoyl )-thiophene, 2,5- di(4'-azidobenzal)cyclohexanone, 4,4'-diazidodiphenylmethane, 1 -(4-azidophenyl)-5-furyl-2-penta-2,4-diene 1-one, 1 -(4-azidophenyl)-5-(4-methoxyphenyl)-penta-1 ,4-diene-3-one, 1 -(4-azidophenyl)-3-(1 -naphthyl )- propene-1 -one, 1 -(4-azidophenyl)-3-(4-dimethylaminophenyl)-propane-1 -one, 1 -(4-azidophenyl)-5-phenyl- 1 ,4-pentadiene-3-one, 1 -(4-azidophenyl )-3-(4-nitrophenyl)-2-propene-1 -one, 1 -(4-azidophenyl )-3-(2-furyl)-2- propene-1 -one, 1 ,2,6-tri(4'-azidobenzoxy)hexane, 2,6-bis(4-azidobenzylidene-p-t-butyl)cyclohexanone, 4,4'- diazidobenzalacetone, 4,4'-diazidostilbene-2,2'-disulfonic acid, 4'-azidobenzalacetophenone-2-sulfonic acid, 4,4'-diazidostil bene-a-carboxylic acid, di(4-azido-2'-hydroxybenzal)acetone-2-sulfonic acid, 4 azidobenzalacetophenone-2-sulfonic acid, 2-azido-1 ,4-dibenzenesulfonylaminonaphthalene, 4,4'-diazido- stilbene-2,2'-disulfoanilide.

Besides these low molecular weight aromatic azide compounds, the azido-containing polymers described in Japanese Patent Publications Nos. 9047/69,31837/69, 9613/70,24915/70, 25713/70 and Japanese Patent Applications (OPI) Nos. 5102/75,84302/75, 84303/75 and 12984/78 are suitable.

These photosensitive azide compounds are preferably used in combination with a polymeric compound used as a binder. Preferred binders are alkali-soluble resins, for example, natural resins such as shellac and rosin; phenolic novolak resins such as phenol-formaldehyde resin and m-cresol-formaldehyde resin: homopolymers of unsaturated carboxylic acids or copolymers thereof with another copolymerizable monomer such as polyacrylic acid, polymethacrylic acid, methacrylic acid/styrene copolymer, methacrylic acid/methyl acrylate copolymer and styrene/maleic anhydride copolymer; resins having acetal groups formed by reacting partially or completely saponified polyvinyl acetate with aldehydes such as acetaldehyde, benzaldehyde, hydroxybenzaldehyde and carboxybenzaldehyde; and polyhydroxystyrene.

Other suitable binders are resins soluble in organic solvents typified by cellulose alkyl ethers such as cellulose methyl ether and cellulose ethyl ether.

The composition composed of a photosensitive azide compound preferably contains such binder in an amount of from about 10 to about 90 wt% based on the total weight of the composition.

The composition composed of a photosensitive azide compound may further contain additives such as a dye; pigment, plasticizer such as phthalate esters, phosphate esters, aliphatic carboxylate esters, glycols, and sulfonamides; and sensitizers such as Michler's ketone, 94luorenone, 1-nitropyrene, 1,8-dinitropyrene, 2-chloro-1 ,2-benzanthraquinone, 2-bromo-1 ,2-benzanthraquinone, pyrene-1,6-quinone,2-chloro-1,8- phthaloylnaphthalene, and cyano-acridine.

(4) Compositions ofpolymeric compounds containing O # -CH=CH-C-group in the main chain or side chain of the polymer These compositions include those mainly consisting of photosensitive polymers such as polyesters, polyamides, and polycarbonates containing a photosensitive-CH=CH-C # O group in the main chain or side chain of the polymer (e.g., the compound described in U.S. Patents 3,030,208,3,707,373 and 3,453,237); those mainly consisting of photosensitive polyesters derived from (2-propylidene)malonic acid compound such as cinnamylidenemalonic acid and bifunctional glycols (e.g., the photosensitive polymers described in U.S.Patents 2,956,878 and 3,173,787); and cinnamate esters of hydroxyl-containing polymers such as polyvinyl alcohol, starch, cellulose and the like (e.g., the photosensitive polymers described in U.S. Patents 2,690,966, 2,752,372 and 2,732,301). These compositions may further contain a sensitizer, stabilizer, plasticizer, pigment and dye.

(5) Photosensitive compositions of addition-polymerizable unsaturated compounds These compositions are preferably composed of (a) a vinyl monomer having at least two terminal vinyl groups, (b) a photopolymerization initiator, and (c) a polymeric compound as a binder.

Illustrative vinyl monomers used as component (a) include acrylate or methacrylate esters of polyols such as diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, pentaerythritol tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, or bis(meth)acrylamides such as methylene bis(meth)acrylamide and ethylene bis(meth)acrylamide, or urethane-containing unsaturated monomers, for example, a reaction product of diol mono(meth)acrylate and diisocyanate, such as di(2'-methacryloxyethyl)-2,4-tolylene diurethane and di(2'-acryloxyethyl)-trimethylene diurethane, as described in Japanese Patent Publication Nos. 5093/60, 14719/60 and 28727/69.

Examples of the photopolymerization initiator or component (b) are the carbonyl compounds listed in Chap. 5 of J. Kosar Light-Sensitive Systems, organic sulfur compounds, peroxides, redox compounds, azo and diazo compounds, halogen compounds and photo-reductive pigments. More specific examples are disclosed in British Patent 1,459,563. Other initiators as recognized in the art can also be used.

Various known polymers may be used as the binder or compound (c). Details of specific binders are given in U.S. Patent 4,072,527. The chlorinated polyolefin described in British Patent 1,459,563 is a particularly preferred binder.

The components (a) and (c) are used in combination in a weight ratio in the range of from 1:9 to 6:4. The component (b) is contained in an amount of from 0.5 to 10 wt% based on the weight of component (a).

The photopolymerizable composition may further contain a thermal polymerization inhibitor, plasticizer, dye and pigment.

The photosensitive printing plate prepared by the method of this invention basically comprises a support having disposed thereon a photosensitive layer composed of the photosensitive material illustrated above, and it may further include a plurality of resin layers as disposed on the photosensitive layer. A specific example is described in U.S. Patent 3,136,637 wherein a support has disposed thereon a photosensitive layer overlaid with layers of lipophilic, hydrophobic, water-insoluble and solvent-softenable resins in that order.

Other examples of the photosensitive printing plates having similar construction are described in British Patents 1,478,333 and 1,478,334 and they are included within the scope of the photosensitive printing plate that is to be prepared by the method of this invention.

For the coating of the photosensitive layer, one can adopt a variety of solvents such as, for example, 2-methoxyethanol, 2-ethoxyethanol, 2-methoxyethyl acetate, Bethoxyethyl acetate, dimethylformamide, methanol/dichloroethylene, and mixtures therebetween. Starting from the above cited methanol/dichloroethylene mixture, one can replace methanol with ethanol, n-propanol, iso-propanol, or with mixtures thereof, and further substitute dichloroethylene with methylene chloride, trichloroethane, monochlorobenzene or with mixtures thereof. Auxiliary solvents can be further added to these systems within a proportion so as not substantially to alter the basic nature of the original mixture.Such auxiliary solvents include, for example, ketones such as acetone, methyl ethyl ketone or methyl isobutyl ketone, esters such as methyl acetate, ethyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate or methylamyl acetate and water.

The practical range of the concentration of the coating fluid containing the photosensitive composition dissolved in such solvent systems lies ordinarily between about 0.1 and about 20% by weight, and more preferably between 1 and 10% by weight.

As was noted previously, the finely-divided material to be incorporated in a dispersed state in the coating fluid must be expelled during the subsequent drying procedure. At the same time, the material should advantageously keep a stable dispersion condition from the preparation of the coating fluid until the coating operation is performed.

Illustrative and preferred fine particulate materials used in this invention include polyethylene particles, polypropylene particles, ethylene-propylene copolymer particles, ethylene-vinyl acetate copolymer particles, polyethylene terephthalate particles and cross-linked vinyl polymer particles. Of these, polyethylene, polypropylene and ethylene-propylene copolymers are preferred.

The cross-linked vinyl polymer particles are prepared by a well known method of suspension polymerization. According to one example, a mixture of a hydrophobic vinyl monomer having one vinyl group (e.g., acrylate esters, methacrylate esters, styrene, styrene derivatives, and acrylonitrile) and 1 to 30 parts by weight of a polyfunctional monomer based on said vinyl monomer (e.g., divinylbenzene, polyethylene glycol diacrylate (the number of ethylenes being 1 to 14), polyethylene glycol dimethacrylate (the number of ethylenes being 1 to 14), trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, pentaerythritol triacrylate, pentaerythritol trimethacrylate, and pentaerythritol tetramethacrylate) is added to an aqueous medium having dissolved therein a dispersant conventionally used for suspension polymerization (e.g., inorganic powders such as zinc oxide, calcium carbonate and talc, and water-soluble polymers such as gelatin and polyvinyl alcohol), the polymerization system is evacuated and purged with nitrogen, and while the temperature is elevated to about 50 to 80 C under stirring, a conventional oil-soluble polymerization initiator (e.g., benzoyl peroxide or azobisisobutyl nitrile) is added to start polymerization that continues for a period of about 2 to 20 hours until a dispersion of cross-linked vinyl polymer particles is obtained. The dispersion is then subjected to solid-liquid separation and drying, thereby to obtain the particles of cross-linked vinyl polymer.

The fine particulate material used in this invention has an average particle size (dia.) which is suitably in the range of from 5 to 40 microns, preferably from 5 to 20 microns.

The amount of the fine particulate material present on the surface of the photosensitive printing plate can be selected from a wide range and, generally, it is about 50 to about 500,000 particles per square centimeter, preferably about 1,000 to 100,000 particles per square centimeter. Usually, an optimum range is determined empirically by repeating trial and error experiments. The amount of the fine particulate material in the coating is adjusted taking into consideration the coating weight of the uppermost layer to provide the desired coverage. If the uppermost layer of the photosensitive printing plate consists of a photosensitive layer, the fine particulate material is typically present in an amount of from about 0.01 to about 20 wt%, preferably about 0.1 to 10 wt%, based on the solid content of the coating liquid (i.e, the amount of the coated layer minus the solvent).

It has been found in accordance with a preferred embodiment of the present invention that the stability and uniformity of the coating dispersion can be enhanced significantly if the dispersion also contains an aqueous polymer latex having an average particle size of 0.001 to 0.1 times the average particle size of the fine particulate material which forms the roughened surface.

Aqueous polymer latexes useful in this invention are well known in the polymer industry, and contain the fine particles of polymer (referred as latex particles) dispersed in an aqueous medium. According to this invention, a stable dispersion of the fine particulate material in an organic solvent is obtained if the latex particles of an aqueous polymer latex have an average particle size (dia.) which is in the range of from one thousandth to one tenth of the average particle size of the fine particulate material. Such aqueous polymer latex can be selected from those having an average particle size in the range of from about 0.01 to about 2 microns, preferably from 0.01 to 1 micron, and more preferably from 0.02 to 0.5 micron.

Such aqueous polymer latexes can be prepared by subjecting a vinyl monomer to emulsion polymerization in water. According to one embodiment of such emulsion polymerization, a vinyl monomer is added to an aqueous medium containing about 0.1 to 20 wt% of a dispersant for emulsion polymerization based on vinyl monomer (generally a surfactant) and about 2 to 50 wt% of water, the polymerization system is drawn under a vacuum and purged with nitrogen. Additives used in conventional emulsion polymerization (e.g., molecular weight modifier and antioxidant) are added as required during emulsification, and finally an emulsion polymerization initiator (e.g., hydrogen peroxide, potassium persulfate) is added and emulsion polymerization is performed in the conventional manner to produce an aqueous polymer latex of vinyl polymer.Any vinyl monomer can be used in the emulsion polymerization without particular limitation, and details of the monomers used in the synthesis of the aqueous polymer latex are given below. For simplicity, the monomers are divided into Group A (hydrophobic monomers), Group B (hydrophilic monomers) and Group C (cross-linkable monomers).

Monomers of Group A: Hydrophobic unsaturated vinyl monomers having one vinyl group such as acrylate esters, methacrylate esters, vinyl esters, styrenes and olefins.

Monomers of Group B: Hydrophilic unsaturated vinyl monomers having one vinyl group such as monomers having such functional groups as an amino group, a carboxyl group, a sulfonic acid group, an amido group and a hydroxyl group.

Monomers of Group C: Monomers having a reactive cross-linkable group (e.g., an epoxide group, a hydroxymethylamide group, an alkoxymethylamide group, an acyloxymethylamide group, and an isocyanate group) and polyfunctional monomers having two or more vinyl groups.

Suitable combinations of these monomers for synthesis of the aqueous polymer latex are: a homopolymer of a monomer of Group A or a copolymer combining at least two monometer of Group A; a copolymer of at least one monomer of Group A and at least one monomer of Group B; a copolymer of at least one monomer of Group A, at least one monomer of Group C, and at least one monomer of Group B; and a copolymer of at least one monomer of Group A and at least one monomer of Group C. Details of the applicable monomers are given below.

The monomers of Group A are hydrophobic vinyl monomers having one vinyl group (by the term "hydrophobic" is meant that not more than 8 wt% of the monomer is soluble in water at 20 C) such as acrylate esters, methacrylate esters, vinyl esters, styrene and a-olefins.

Illustrative acrylate esters include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, sec-butyl acrylate, amyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, octyl acrylate, 2-phenoxyethyl acrylate, 2-chloroethyl acrylate, benzyl acrylate, cyclohexyl acrylate, tetrahydrofurfuryl acrylate, phenyl acrylate, 2-methoxy-ethyl acrylate and 2-ethoxyethyl acrylate.

Illustrative methacrylate esters include methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, sec-butyl methacrylate, amyl methacrylate, hexyl methacrylate, cyclohexyl methacrylate, benzyl methacrylate, acetoacetoxyethyl methacrylate, chlorobenzyl methacrylate, octyl methacrylate, furfuryl methacrylate, tetrahydrofurfuryl methacrylate, phenyl methacrylate, trimethylolpropane monomethacrylate, 2-methoxyethyl methacrylate and 2ethoxyethyl methacrylate.

Illustrative vinyl esters include vinyl acetate vinyl propionate, vinyl butyrate, vinyl chloroacetate, vinyl dichloroacetate, vinyl methoxyacetate, vinyl acetoacetate, vinyl benzoate, vinyl salicylate and vinyl chlorobenzoate.

Illustrative styrenes include styrene, methylstyrene, chloromethylstyrene, trifluoromethylstyrene, acetoxymethylstyrene, methoxystyrene, chlorostyrene, dichlorostyrene, trichlorostyrene and bromostyrene.

Illustrative olefins include butadiene, isoprene, chloroprene, propylene, vinyl chloride, vinyl bromide, vinylidene chloride, vinylidene bromide and vinylidene fluoride.

Another example of a monomer of Group A is acrylonitrile.

The monomers of Group B are hydrophilic vinyl monomers having one vinyl group and a functional group such as an amino group, a carboxyl group, a sulfonic acid group, an amido group or a hydroxyl group. By the term "hydrophilic monomers" is meant those monomers which are so highly soluble in water that they are difficult to emulsion polymerize in water when used alone.

Illustrative Group B monomers having an amino group include dimethylaminomethyl acrylate, dimethylaminomethyl methacrylate, diethylaminomethyl acrylate, diethylaminomethyl methacrylate, diethylaminoethyl acrylate, diethylaminoethyl methacrylate, tert-butylaminoethyl acrylate, and tert butylaminoethyl methacrylate.

Illustrative Group B monomers having a carboxyl group include acrylic acid, methacrylic acid, itaconic acid, maleic acid, crotonic acid, fumaric acid, methylenemalonic acid, monoalkyl itaconate (e.g., monomethyl itaconate, monoethyl itaconate, and monobutyl itaconate), monoalkyl maleate (e.g., monomethyl maleate, monoethyl maleate, monobutyl maleate, monopropyl maleate, and monooctyl maleate), citraconic acid, sodium acrylate, ammonium acrylate, and ammonium methacrylate.

Illustrative Group B monomers having a sulfonic acid group include styrene sulfonic acid, vinylbenzylsulfonic acid, vinylsulfonic acid, acryloyloxyalkylsulfonic acid (e.g., acryloyloxymethylsulfonic acid, acryloyloxy-ethylsulfonic acid, acryloyloxypropylsulfonic acid, and acryloyloxybutylsulfonic acid), methacryloyloxyalkylsulfonic acid (e.g., methacryloyloxymethylsulfonic acid, methacryloyloxyethylsulfonic acid, methacryloyloxypropylsulfonic acid, and methacryloyloxybutylsulfonic acid), acrylamide alkylsulfonic acid (e.g., 2-acrylamide-2-methylethanesulfonic acid, 2-acrylamide-2-methylpropanesu Ifonic acid, and 2acrylamide-2-methylbutanesulfonic acid), and methacrylamide alkylsulfonic acid (e.g., 2-methacrylamide-2- methylethanesulfonic acid, 2-methacrylamide-2-methyl-propanesulfonic acid, and 2-methacrylamide-2methylbutane-sulfonic acid).

Illustrative monomers having an amido group include acrylamide, methylacrylamide and propylacryla mide.

Illustrative monomers having a hydroxyl group include allyl alcohol, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, and allyl ether of polyhydric alcohol.

Other examples of the monomer of Group B are N-acryloyl piperidine, vinyl pyridine, vinyl pyrrolidone and maleic anhydride.

The monomers of Group C are those monomers having a reactive cross-linkable group (e.g., an epoxide group, a hydroxymethylamide group, an alkoxymethylamide group, an acyloxymethylamide group and an isocyanate group) and polyfunctional monomers having two or more vinyl groups. The monomers of Group C C are not used independently, and instead, they are added to monomers of Group A or a mixture of monomers of Group A and Group B for the purpose of synthesizing a cross-linked polymer latex.

Illustrative Group C monomers having an epoxide group include glycidyl acrylate, glycidyl methacrylate, glycidyl p-vinyl benzoate, glycidyl crotonate, diglycidyl itaconate, diglycidyl maleate, diglycidyl methylene malonate, glycidyl vinyl ether, allyl glycidyl ether, and glycidyl a-chloroacrylate.

Illustrative Group C monomers having a hydroxy-methylamide group include hydroxymethylacrylamide and hydroxymethylemethacrylamide.

Illustrative Group C monomers having an alkoxymethylamide group include methoxymethylacrylamide, methoxymethyl methacrylamide, ethoxymethylacrylamide, ethoxymethylmethacrylamide, butoxymethylacrylamide, butoxymethylmethacrylamide, and hexyloxymethylacrylamide.

Illustrative monomers of Group C having an acyloxymethylamide group inlude acetoxymethylacrylamide, acetoxymethylmethacrylamide, and propionyloxymethylacrylamide.

Illustrative Group C monomers having an isocyanate group include vinyl isocyanate and allyl isocyanate.

Illustrative polyfunctional Group C monomers include divinylbenzene, polyethylene glycol diacrylate (the number of ethylenes: 1 to 14), polyethylene glycol dimethacrylate (the number of ethylenes: 1 to 14), trimethylolpropane triacrylate, trimethylolpropane trimethylacrylate, pentaerythritol triacrylate, pentaerythritol trimethacrylate, and pentaerythritol tetramethacrylate. The polymer latex having an epoxide group may be partially hydrolyzed under acidic or alkaline condition so that it may have a dihydroxyl group.

Suitable combinations of monomers that constitute the aqueous polymer latex are a homopolymer of a monomer of Group A or a copolymer of at least two monomers of Group A, a copolymer of at least 50 wt%, preferably at least 80 wt%, of at least one monomer of Group A and at least one monomer of Group B, a terpolymer of at least 50 wt%, preferably at least 80 wt%, of a mixture of at least one monomer of Group A and at least one monomer of Group C and a monomer of Group B, and a copolymer of a monomer of Group A and a monomer of Group C. Generally, hydrophilic monomers of Group B are used to provide improved stability for emulsion polymerization and provide an aqueous polymer latex stable during storage.

It is essential that the particles of an aqueous polymer latex, as dispersed in an organic solvent, be insoluble in the solvent and that they not flocculate in the solvent. Since the latex particles may or may not be soluble or may or may not flocculate depending upon the composition of the organic solvent used, there is no defining a general composition for the monomers of which the latex particles are composed. However, it can be safely said that cross-linked latex polymers are preferred. Thus, preferred latices are a terpolymer of at least 50 wt%, preferably at least 80 wt%, of a mixture of at least one monomer of Group A and at least one monomer of Group C and a monomer of Group B, and a copolymer of at least one monomer of Group A and at least one monomer of Group C. There is no general rule for defining the ratio of a monomer of Group A to a monomer of Group C.

A dispersant for emulsion polymerization may be selected from general anionic, castionic, nonionic and amphoteric surfactants. These surfactants may be used independently or as a mixture. These dispersants for emulsion polymerization are familiar to those skilled in the art. To give a few examples, the anionic surfactant includes sulfate esters of higher alkanols of the formula: R-OSO3M or R4OCH2CH2ieOSO3M (wherein R is an alkyl group having 8 to 30 carbon atoms; M is an alkali metal or ammonium; e is O or an integer of 1 to 30), and alkylbenzenesulfonic acids of the formula:

wherein R' is hydrogen or an alkyl group having 1 to 18 carbon atoms; R" is an alkyl group having 1 to 18 carbon atoms; M is an alkali metal or ammonium; m iso or an integer of 1 to 30; n is any of 0,3 or 4.

Illustrative nonionic surfactants include polyoxyethylene derivatives and higher aliphatic acid esters of saccharides. Illustrative amphoteric surfactants are sulfobetaines and amino acids.

The partidle size of the aqueous pqlymer latex can be adjusted depending upon such factors as the amounts of erhulsion polymerization dispersant, monomers and polymerization initiator, the speed of stirring, and the polymerization temperature.

Various solvents can be used.for-the coating solution from which the uppermost layer of a photosensitive printing plate precursor is applied and, generally, one or more organic solvents may be used. In case of using a polymer latex, it is desired that at least 10 wt% of water be dissolved in the composition at 20 C. To be more specific, if a single organic solvent is used, it is desired that the organic solvent be capable of dissolving at least 1p wt% water at 20 C. If two or more organic solvents are used as a mixture, it is desired that the solvent mixture is capable of dissolving at least 10 wt% water at 20 C.

Illustrative soiveiits or solvent systems are those set forth previously.

In accordance with the preferred embodiment of the invention, the coating liquid for coating the topmost layer of a photosensitive printing plate precursor contains the aqueous polymer latex described above in an amount in the range of from about 0.0001 wt% to about 10 wt% in terms of the solid content basedon the organic solvent described above. The. further below 0.0001 wt% the content is; the lower is the stability of the dispersion of the hydrophobic polymer particles and the sooner the dispersion must be used after preparation. On the other hand, the higher the content is above 10 wt%, the greater is the tendency of the latex particles to cohere whereas there is no improvement in the stability of the dispersion of the fine particulate material.Therefore, the content of the aqueous polymer latex is preferably about 0.005 to 5 wt%, more preferably about 0.01 to 2 wt%, in terms of the solid content based on the organic solvent.

The amount of water contained in the dispersion of this invention as a result of incorporation of the aqueous polymer latex is not more than about 10 wt%, preferably not more than 3 wt%, based on the organic solvent.

The coating liquid containing the fine particulate material and optionally the aqueous polymer latex can be applied to the support by various means, such as doctor coating, roller coating, gravure coating, bead coating and dip coating.

The layer of the coating liquid can be dried in a conventional manner by letting the solvent evaporate at room temperature or an elevated temperature. The drying temperature is preferably about 200C to about 150 C, more preferably about 50 to 1200C. Drying can also be effected using heated air. The air temperature is about 300C to 2000C, in particular, about 400C to 1400C. The drying temperature is not necessarily maintained at one level during drying, but may be stepwise raised. In some cases, favorable results are obtained by removing moisture from the drying air. The heated air is supplied to the coated surface at a rate of about 0.1 m/sec to 30 m/sec, in particular, about 0.5 m/sec to 20 m/sec.

The coating rate (dry) of the thus-prepared photosensitive coating is preferably about 0.1 to about 7 g/m2, and more preferably from 0.5 to 4 g/m2 for the case of planographic printing plate.

The explanations heretofore have been for the layer structure of a photosensitive planographic plate produced in accordance with the present invention wherein the photosensitive coating constitutes the outermost layer (i.e., the surface farthest from the support). The method of the present invention is, however, also applicable to the layer structure set forth in U.S. Patent 3,136,637 comprising a support, a diazo resin layer and an outermost resin layer which is oleophilic, hydrophobic, water-insoluble and swellable with organic solvents, and which surface is roughened by the presence of a matting agent.A cross-sectional view of such a structure is shown in Figures 7 (a) and (b), in which a cross-sectional view of the support 10 and the diazo resin layer 20 on the support are shown having been just provided with a coating fluid comprising an oleophilic, hydrophobic, water-insoluble and solvent-swellable resin such as poly(vinylformal) dissolved in an appropriate solvent and a finely-divided material 50 dispersed in said solution. In the solution, the finely-divided material 50 is stably dispersed, and such a stability is kept even in coating fluid layer 30C spread over the support. The polymer latex is not shown but is present in accordance with the preferred embodiment of the invention.

Figure 7(b) illustrates the cross-sectional view of the same member as shown in Figure 7(a) after evaporation of the volatile ingredient in the fluid wherein finely-divided material 50 is held on the surface of the outermost resin layer 30 with substantially the entire volume of the matting agent being expelled or excluded from the dried layer. When the thus-prepared photosensitive planographic plate is subjected to image-exposure, the exposed area of the photosensitive coating is rendered insoluble in the developer and, at the same time, is firmly bonded to the overlying resin layer. On the other hand, the unexposed area of the photosensitive coating remains unchanged and soluble in the developing fluid.Hence, when the exposed plate is subjected to development, the developer fluid can readily penetrate through the superficial resin layer to reach and dissolve the unexposed area of the photosensitive coating. If one lightly rub the surface of the plate with a piece of, for example, absorbent cotton, the unexposed area is removed with the overlying resin layer, while in the exposed area of the photosensitive coating, the photosensitive coating remains on the support together with the overlying resin layer without being affected by the action of the developer fluid. At such a developing operation, the finely-divided material adhered to the surface of the resin layer is completely removed as is shown in Figure 8, in which, in the exposed areas, the photosensitive coating 20A and the overlying resin layer 30A remain on the support 10.

Preparation of the coating fluid for the surface resin layer of a photosensitive planographic plate can be conducted by methods similar to those adopted and mentioned previously for the preparation of the coating fluid for the photosensitive coating.

Development or processing of the photosensitive printing plate fabricated in accordance with the present invention can be carried out in any one of the conventionally known methods, not requiring any particular modifications.

The present invention is now illustrated in more detail by reference to the following Examples, in which all percentages and parts are by weight unless otherwise indicated.

Example 1 An aluminum plate of 0.24 mm thickness was degreased by immersion into a 7% aqueous solution of trisodium phosphate at 60 C, and after rinsing with water, the surface was grained by rubbing with a nylon brush under a stream of water having pumice suspended therein. After thoroughly rinsing with water, the plate was immersed in a 5% aqueous solution of sodium silicate (SiO2 : Na2O = 3.1 -33 1 1 in mol ratio) of JUST3 grade and=kept at 700Cfor 30 to 60 seconds.

Following thorough rinsing with water and drying, each coating composition shown in the following Table was applied on a piece of the thus-prepared aluminum support.

(At least the diazo condensate and blue dye are (usually) dissolved in the organic solvent for the coating composition, in each example, whilst any matting agent is dispersed but not dissolved.) TABLE 1 Example Coating Composition Comparison Composition C, Example 1 2-Hydroxyethyl methacrylate 0.87 g containing a tetramer of 2 hydroxyethyl methacrylate/ acrylonitrile/methyl methacrylate/ methacrylic acid set forth in Example 1 of U.S.Patent 4,123,276, as Copolymer (I) 2-Methoxy-4-hydroxy-5-benzoyl- 0.1 g benzene sulfonic acid salt of p-diazodiphenylamine/paraform aldehyde condensate Oil Blue 603 (C.l. 74350, a dye 0.03 g product of Orient Chemical Ind., Ltd.) Methanol 6g 2-Methoxyethanol 6g Comparison Composition C2 Example 2 Coating composition C1 109 Glass beads (average diameter 0.03 g 10 microns) Comparison Composition C3 Example 3 Coating composition C1 10g Siloyd (silica gel with an average 0.03 g particle diameter of 10 microns available from Fuji-Davidson Co.) Comparison Composition C4 Example 4 Coating composition C1 10g Pumice (average diameter = 10 0.03 g microns) Comparison Coating Composition C5 Example 5 Composition C1 10g Finely-divided urea/formaldehyde 0.03 g resin (average diameter 10 microns) Example 1 Composition C6 Coating composition C1 10g Particulate polyethylene 0.03 g (average diameter = 10 microns) The coating rate on dry base was 1.0 g/m2 for each example. The photosensitive lithographic plates resulting from coating compositions C1, C2, C3, C4, C5 and C6 are designated as Plates C1, C2, C3, C4, C5 and C6, respectively. Each plate from C2 to C8 required a vacuum contact time shorter than Plate C1 by a factor of from 1/2 to 1/3.Each plate was exposed through a vacuum contacted original image (transparency) to light from a metal halide lamp placed at a distance of 1 m for40 seconds, and then processed by immersion in the following developing fluid for 1 minute at ambient temperature, followed by gentle rubbing with absorbent cotton whereby the unexposed areas of the photosensitive coating were removed.

Developer fluid Benzyl Alcohol 3.0 g Sodium lsopropylnaphthalenesulfonate 1.0 g Sodium Silicate (40% aq. soln.) 1.0 g Water 95g Each processed plate thus prepared was subjected to printing; printing masters obtained from Plates C1 and C6 withstood 50,000 impressions while those obtained from CPI C3, C4 and C5 gave only 20,000 to 30,000 prints.

Printing masters from Plates C1 and C6 produced printed matter with good tone reproduction, while the printed matter produced from Plates C2 to C5 showed poor tone reproduction characteristics. Microscopic observation of the surface of each printing master immediately after development proved the presence of the finely-divided particles in the image area for the masters from Plates CZI C3, C4 and C5, but failed to show fine particles at the image area of the master from Plate C6 (Example 1).

Returning to the photosensitive lithographic plates before processing, their surfaces were carefully examined under a microscope. The examination proved that, for Plates from C2 to C5, the particulate materials were more or less embedded in the photosensitive coating, while for Plate C6 (Example 1) the matting agent substantially protruded from the coating, although it was dispersed non-uniformly.From these observations, it is determined that the particles of glass bead, silica gel, pumice and ureal formaldehyde resin used in coating mixtures C2to C6 had strong affinitiesforthe coating solvent (the mixture of methanol and 2-methoxyethanol) such that they were not expelled to the surface of the coating, while the polyethylene particles which exhibit poor affinity to the mixed solvent cited above were almost completely expelled from the outer surface of the dried coating.

Further, each plate was subjected to development with an exhausted liquid developer of the same composition as cited previously, whereby only the plate C6 prepared according to the present invention (Example 1) was successfully processed, and the remaining plates produced as comparative examples were found to suffer from imperfect dissolution of non-image areas.

Though Example 1 describes the production of a negative type photosensitive lithographic plate using a diazonium resin as photosensitive material, it is evident that the polyethylene matting agent can be used in the manufacture of various other types of photosensitive plate.

Examples 2-5 Following the procedures of Example 1, photosensitive planographic Plates C7 to C10 were fabricated by use of coating fluids C7 to C10 having the following compositions: TABLE 2 Ex. Coating Solid (non-volatile) Ingrdients No. Fluid Solvent Components (common to the four fluids) 2 C7 2-Methoxyethanol 6.0 g 2-Hydroxyethyl Methacrylate Copolymer (1) 0.87 g Used in Example 1 Methanol 6.0 g 2-Methoxy-4-hydroxy-5-benzoylbenzenesulphonic 0.1 g Acid Salt of p-Diazodiphenylamine/Paraform3 C8 2-Methoxyethanol 6.0 g aldehyde Condensate Methyl Ethyl Ketone 6.0 g Oil Blue 603 (C. l. 74350, a product of 0.03 g Orient chemical Ind, Ltd.) 4 C9 2-Methoxyethanol 6.0 g Pulverized Polyethylene with Average 0.03 g Particle Size of 10 Microns Acetonitrile 6.0 g 5 C10 2-Methoxyethanol 6.0 g Methyl Ethyl Ketone 3.0 g Methanol 3.0 g Microscopic examination of the plate surfaces revealed that the polyethylene particles, which were dispersed non-uniformly, existed in the form of minute protrusions with substantially the entire volume thereof being exposed upon drying. The vacuum contact period for each of the plate was measured, and all of the plates exhibited shorter values than Plate C1 of Comparison Example 1, by a factor of from 1/2 to 1/3.

Each plate was subjected to imagewise exposure and development, followed by printing as in Example 1, wherein the durability of all the plates proved equivalent to that of Plate C6 of Example 1, i.e., 50,000 impressions. Furthermore, the tone reproduction characteristics were also equivalent, and polyethylene particles were not observed in the image area of any of the plates after development.

Examples 6-7 The procedures described in Example 1 were repeated using coating fluids C11 and C12 having the following compositions: Example 6 Composition C11 Coating fluid Cl prepared in Ex. 1 109 Pulverized polypropylene (mean 0.O3g particle size = 10 microns) Example 7 Composition C12 Coating fluid C1 prepared in Ex. 1 109 Pulverized ethylene/propylene 0.03 g copolymer (mean particle size = 10 microns) Microscopic observation revealed that each of the photosensitive planographic plates thus prepared had the finely-divided material employed dispersed non-uniformly and bonded to the coating surface of the photosensitive coating in the form of minute protrusions forced out of the coating.The vacuum contact period for each of Plates C11 and C12 was measured, and all of the plates exhibited shorter values than Plate C1 prepared in Example 1 by a factor of from 1/2 to 1/3.

Each plate was subjected to imagewise exposure and development, followed by printing as in Example 1, whereby the durability of all the plates in printing proved equivalent to that of Plate C1, i.e., 50,000 impressions. Further, the tone reproduction characteristics were also equivalent, and finely-divided matting agent was not observed in the image area after development.

Example 8 A 0.3 mm thick, grained aluminum plate was anodized in a sulfuric acid bath to give rise to an oxide surface film at a rate about 2 g/m2. After rinsing and drying, a coating fluid comprising the following ingredients was coated on its surface so as to provide a coating rate of about 2.5 g/m2.

The naphthoquinone-1,2-diazide-5-sulfonic 1 g acid ester of polyhydroxyphenyl (a compound set forth in Example 1, U.S. Patent 3,635,709) Pulverized Polyethylene (mean particle 0.03 g diameter = 10 microns) 2-Methoxyethanol 6g Methanol 6g Microscopic examination of the surface of the photosensitive coating thus-prepared revealed that the polyethylene particles were dispersed non-uniformly and bonded to the surface in the form of minute protrusions extending out of the surface.

Measurement of the vacuum contact time of this photosensitive planographic plate gave a shorter value by a factor of from 1/2 to 1/3 compared to that of a plate obtained by use of a coating fluid not containing the matting agent. After imagewise exposure was performed as in Example 1, the plate was converted into a planographic printing plate by development with a 7% sodium silicate aqueous solution. The resulting plate withstood 60,000 impressions, demonstrating the same durability as the plate obtained using a coating fluid without the matting agent. The tone reproduction characteristics were also equivalent to the comparative plate. Observation of the image area surface with a microscope failed to confirm the presence of the polyethylene particles.

Aqueous polymer latices Aqueous polymer latex I used in the following examples and identified in Table 3 below was prepared in the following manner.

A 10-liter glass sealed reactor equipped with a temperature regulator, stirrer, reflux condenser, heater and gas inlet was purged with nitrogen gas and charged with 7.2 liters of distilled water and 90 g of a surfactant A (indicated below) for emulsion polymerization. The mixture was heated to 600C at which it was stirred to form a solution. Ethylenic unsaturated vinyl monomers (1.1 kg of butyl methacrylate and 0.7 kg of glycidyl methacrylate) were added to the solution which was stirred at 50 to 200 rpm for 30 minutes at 60 C until an emulsion was formed. Polymerization initiators (1.3 g of potassium persulfate and 0.4 g of sodium bisulfite) were added to the emulsion to start polymerization which continued for a period of 5 hours.The temperature of the reaction mixture increased from 60 C to about 75 C due to the heat of polymerization. After the 5-hour polymerization, the reaction product was cooled to 40 C. The resulting aqueous polymer latex I had a particle size of 0.03 to 0.07 micron and its solid content was 20 wt%.

The same procedure was repeated to prepare aqueous polymer latex 11 identified in Table 3. To prepare aqueous polymer latices Ill and IV, 0.36 kg of 1.8 kg of the vinyl monomers was first charged into the reactor and emulsified under stirring, and at the same time as the addition of the polymerization initiators, the remaining 1.44 kg of the monomers was added dropwise to the emulsion to start polymerization.

Dispersants A to E for emulsion polymerization

TABLE 3 Aqueous Surfactant Average Latex for Emulsion Surfactant Particle Polymer Vinyl Monomer Polymerization Content Size (kg) (g) ( m) Butyl Methacrylate 1.1 I A 90 0.03-0.07 Glycidyl Methacrylate 0.7 B/C B: 128 II Ethyl Acrylate 1.8 0.03-0.07 (95/5) C: 7 Styrene 0.72 Butyl Acrylate 0.72 D/E D: 21 III 0.05-0.10 Acrylic Acid 0.09 (70/30/ E: 9 N-Methyloi Acrylamide 0.27 Diethylaminoethyl Methacrylate 1.71 IV D 54 0.06-0.10 Ethylene Glycol Dimethacrylate 0.09 Examples 9 - 13 An aluminum plate 0.24 mm thick was degreased by immersion in a 7% aqueous solution of sodium tertiary phosphate at 60 C, washed with water, and grained with a nylon brush that rubbed the surface of the plate with an aqueous suspension of pumice powder flushed over the plate.After washing with water, the grained plate was immersed for 30 to 60 seconds in a 5% aqueous solution of JIS No.3 sodium silicate (SiO2/Na2O = 3.1 to 3.3 in molar ratio) held at 70 C.

After thorough washing with water and drying, the plate was coated with coating liquids (C13) to (C17) identified in Table 4 below, and dried to provide photosensitive lithographic printing Plates C13 to C17.

TABLE 4 Run No. Formulation of Coating Composition Example 9 Coating Composition (cho3) 2-Hydroxyethyl/methacrylate 0.87g copolymer (described in Example 1 of U.S. Patent 4,123,276) 2-Methoxy-4-hydroxy-5-benzoyl- 0.1 g benzenesulfonic acid salt of p diazophenylamine/paraformaldehyde condensate Oil Blue 603 0.03g (C.l. 74350, manufactured by Orient Chemical Industry Co., Ltd.) 2-Methoxyethanol 12.or Powdered Polyethylene 0.03g (average part. size: 10 ) Example 10 Coating Composition (CJ Coating Composition (C13) 10g Aqueous Polymer Latex I 0.02g Example 11 Coating Composition (C15) Coating Composition (C13) 10g Aqueous Polymer Latex II 0.02 g Example 12 Coating Composition (C16) Coating Composition (C13) 10g Aqueous Polymer Latex lil 0.02 g Example 13 Coating Composition (C17) Coating Composition (C13) 10 g Aqueous Polymer Latex IV 0.02 g Each coating liquid was left to stand for an hour before it was applied to the plate. The dry weight of the coated layer was 1.0 g/m2.Observation of the surfaces of the photosensitive lithographic printing plate precursors C13 to C17 showed that the Plate C13 (Example 9) had fine particles exposed on the surface and that said particles adhered to the surface. However, the individual particles were not dispersed uniformly, and instead, they cohered together. On the other hand, each of the photosensitive lithographic printing plate precursors C14 to C17 (Examples 10-13) had fine particles exposed on the surface, and these particles adhered to the surface and were dispersed uniformly (due to the presence of the polymer latex).

Each of the photosensitive lithographic printing plates was brought into intimate contact with a negative transparent original image by the vacuum contact technique. The time required for achieving the intended contact was from one half to a third of the time required with a photosensitive lithographic printing plate prepared without the fine particles. Each of the plates in close contact with the original was imagewise exposed for 40 seconds to a metal halide lamp positioned 1 m away from the precursor. The plate was then immersed in a developer of the following formulation at room temperature for a minute. Thereafter, the surface of the plate was rubbed with absorbent cotton lightly to remove the unexposed area. Thus, a lithographic printing plate was prepared.

Ben Alcohol 3.09 Sodium lsopropylnaphthalenesulfonate 1.0 g Sodium Silicate (40% aq. soled 1.0 g Water 959 The lithographic printing plates prepared from the photosensitive lithographic printing plates C13 to C17 could print 50,000 reproductions.

Microscopic observation indicated that the fine particles were absent from the surfaces of the image areas of the freshly developed lithographic printing plates prepared from the photosensitive lithographic printing plate precursors C13 to C17.

Examples 14- 79 The procedure of Example 9 was repeated to prepare photosensitive lithographic printing plate precursors C18 to C23 using six coating liquids (C19) to (C231 whereof the solvents and any polymer latex were shown in the following Table 5 and the other, solid, ingredients as shown in Table 2 above: TABLE 5 Run No.Coating Solvent Components Example 14 (C19) 2-Methoxyethanol 6.0 g Methanol 6.0 g Example 15 (C19) 2-Methoxyethanol 6.0 g Methanol 6.0 g Aqueous Polymer Latex I 0.02 g Example 16 (C20) 2-Methoxyethanol 6.0 g Methyl Ethyl Ketone 6.0 g Example 17 (C21) 2-Methoxyethanol 6.0 g Methyl Ethyl Ketone 6.0 g Aqueous Polymer Latex 1 0.02 g Example 18 (C22) 2-Methoxyethanol 6.Og Methyl Ethyl Ketone 3.0 g Methanol 3.0 g Example 19 (C23) 2-Methoxyethanol 6.Og Methyl Ethyl Ketone 3.0 g Methanol 3.0 g Aqueous Polymer Latex I 0.02 g Each coating composition was left to stand for an hour before it was applied to the aluminum plate. The dry weight of the coated photosensitive layer was 1.0 g/m2.Observation of the surfaces of the photosensitive lithographic printing plates showed that each plate had fine particles exposed on the surface of the photosensitive layer and that the particles adhered to the surface. The fine particles were exposed on the surfaces of the photosensitive lithographic printing plate precursors C18, C20 and C22 but they cohered together and were not dispersed uniformly. On the other hand, the photosensitive lithographic printing plate precursors C19, C21 and C23 had a uniform dispersion of the fine particles on the surfaces.

The time required for bringing each of the photosensitive printing plate precursor into intimate contact with a negative original image by the vacuum contact technique was one half to a third of the time required with a photosensitive lithographic printing plates prepared without fine particles.

Each of the plates in close contact with the original image was subjected to imagewise exposure in the same manner as in Example 1. The exposed plate was developed in the same manner as Example 1 to produce a lithographic printing plate. Each plate could print 50,000 reproductions. Observation indicated the absence of fine particles from the surface of the image area of each printing plate.

Examples 20 and 21 The procedure of Example 9 was repeated to prepare photosensitive lithographic printing plate precursors C24 and C25 using two coating liquids C24 and C25 having formulations as shown in the following Table 6: TABLE 6 Dispersed particles used in place Coating of the polyethylene in Composition Run No. Composition C14 (Example 10) Example 20 (C24) Polypropylene Particles 0.03 g (avg. part. size 10,u) Example 21 (C25) Styrene-Divinylbenzene 0.03 g Cross-Linked Particles (avg. part. size: 25 cm) Each coating liquid was left to stand for an hour before it was applied to the aluminum plate. The dry weight of the coated photosensitive layer was 1.0 g/m2. Each of the resulting photosensitive lithographic printing plate precursor had fine particles exposed on the surface of the photosensitive layer; the particles adhered to the surface, and they were uniformly dispersed without cohering together.

Examples 22 to 25 A grained aluminum plate 0.3 mm thick was anodized in sulfuric acid to form an oxide film in an amount of about 2 g/m2. The plate was thoroughly washed with water and dried. Then, it was coated with coating liquids (C26) to (C29) having formulations identified in columns I and ll of the following Table 7. Upon drying, photosensitive lithographic printing plate precursors C26 to C29 were obtained, each having a photosensitive layer the dry weight of which was about 2.5 g/m2.

TABLE 7 Coating Compo- Components particular to each Other Components (common to the four Run No. sition Composition coating compositions) (C26) Example 22 2-Methoxyethanol 6.0 g Naphthoquinone-1,2-diazido-5- 1 g sulfonate Ester of Methanol 6.0 g Polyhydroxyphenyl (described in Example 1 of U.S. Patent 3,635,709) Example 23 (C27) 2-Methoxyethanol 6.0 g Phenolic Novolak- 2 g Methanol 6.0 g Formaldehyde Resin Aqueous Polymer Latex l 0.02 g Polyethylene Particles 0.03 g (avg. part. size 10 ) Example 24 (C28) 2-Methoxy Ethyl 6.0 g Acetate Methyl Ethyl Ketone 6.0 g Example 25 (C29) 2-Methoxy Ethyl 6.0 g Acetate Methyl Ethyl Ketone 6.0 g Aqueous Polymer Latex l 0.02 g Each coating liquid was left to stand for an hour before it was applied to the aluminum plate.Observation of the surface of each photosensitive printing plate precursor showed that the fine particles on C26 and C28 cohered together and were not dispersed uniformly. On the other hand, the fine particles on the surfaces of C27 and C29 were uniformly dispersed. With each of the photosensitive lithographic printing plate precursors, the fine particles were exposed on the surface while adhering to it.

The time required for bringing each photosensitive printing plate precursor into close contact with a positive transparent original image by the vacuum contact technique was one half to a third of the time required with a photosensitive lithographic printing plate precursor prepared in the absence of fine particles.

Each of the precursors was then imagewise exposed in the same manner as in Example 9 and developed with a 7% aqueous solution of sodium silicate to prepare a lithographic printing plate. It could print 60,000 reproductions, and this number was equal to that obtained with a conventional printing plate prepared from a precursor coated with a liquid containing no matting agent. The plates prepared from the precursor of this invention also had tone reproducing property equivalent to that of the conventional plate. Observation of the developed precursors showed that no polyethylene particles were present in the image area of each resulting plate.

Claims (14)

1. A method of producing a photosensitive printing plate precursor comprising a support bearing a photosensitive layer, the outermost surface of which is matted with a finely-divided material, wherein the surface-matted outermost layer is obtained by coating a composition comprising a finely-divided material stably dispersed in a solution of the other ingredients constituting the outermost layer, and during evaporation of solvent from said composition, the dispersion is destroyed and the particles of the finely-divided material are repulsed from the bulk of the layer, thus leaving the particles bonded to the surface of the outermost layer in the form of minute protrusions.

2. A method as claimed in Claim 1, wherein said finely-divided material has an average particle diameter of 5 to 40 microns.

3. A method as claimed in Claim 1 or 2 wherein said finely-divided material is selected from polyethylene particles, polypropylene particles, ethylene-propylene copolymer particles, ethylene-vinyl acetate copolymer particles, polyethylene terephthalate particles and cross-linked vinyl polymer particles.

4. A method as claimed in Claim 1 or 2, wherein said outermost layer is a non-photosensitive resin layer.

5. A method as claimed in Claim 1 or 2, wherein said outermost layer is a non-photosensitive resin layer penetrable by a developer for the light-sensitive layer.

6. A method as claimed in any preceding claim, wherein the photosensitive layer comprises as photosensitive component any of the compositions described hereinbefore under the headings (1) to (5).

7. A method as claimed in any preceding claim, wherein the particles are used in an amount of 50 to 500,000 particles per square centimetre.

8. A method as claimed in any preceding claim, wherein the solvent is evaporated at a temperature of 200 to 1500C.

9. A method as claimed in any preceding claim, wherein said coating composition for the outermost layer additionally contains an aqueous polymer latex, which latex does not flocculate and is insoluble in said solvent for the outermost layer coating composition.

10. A method as claimed in Claim 9, wherein said aqueous polymer latex has an average particle size of 0.001 to 0.1 of the average particle size of said finely-divided material.

11. A method of producing a photosensitive printing plate precursor, substantially as hereinbefore described with reference to any of the Examples 1 to 25.

12. A photosensitive printing plate prepared by the method of any preceding claim.

13. A method of making a printing plate, which comprises imagewise exposing under vacuum contacting and developing a plate as claimed in Claim 12.

14. A method of printing, which comprises printing multiple sheets from an inked plate made by the method of Claim 13.