GB2075702A - Photosensitive printing plate precursor - Google Patents

Abstract

A support (e.g. of plastics, paper or metal) is coated with a layer of photosensitive composition (e.g. of a diazo resin, o-quinone diazide or photosensitive azide or addition- polymerizable unsaturated compound or polymer containing -C=CH-CO- group), in which is uniformly dispersed particles, of average size 1 to 17 mu m, in amount of 0.01 to 20% by weight, of a phenolic resin (novalak or resol type) which was normally hardened. The number of the resin particles may be 50 to 500,000 per cm<2>. Other organic or inorganic particles may also be present. The resin particles act as matting agents and given good vacuum adhesion to an original for imagewise exposure of the precursor, without impairing the image. The exposed precursor is developed to make a lithographic, relief or intaglio printing plate.

Description

SPECIFICATION Photosensitive printing plate precursor The present invention relates to photosensitive printing plate precursors.

When making a photosensitive printing plate, it is usual before the imagewise exposure to bring the printing plate precursor into close contact with an original superposed thereon so as to form (after development) a clear image on the printing plate precursor. Therefore, the so-called vacuum contact exposure process has been adopted. In this process, the printing plate precursor is brought into close contact with the original by putting the printing plate precursor and the original between a rubber sheet and a pressing glass plate.

However, with conventional printing plate' precursors, when the original is put on the printing plate precursor to eliminate any space between them and create suction by vacuum, there is close adherence between them from the circumference, beacuse the surface of the printing plate precursor is smooth. As a result, close adherence between all parts of the surfaces can not be attained by a brief period of suction, because the air in the central part is difficult to remove.

Therefore, the use of vacuum suction requires a considerably long time and does not improve the efficiency of the plate making operation. It would, therefore, be desirable to shorten the operation time for vacuum suction.

In order to shorten the time for vacuum adherence, there has been proposed the use of photosensitive printing plate precursors having a finely roughened surface and processes for producing them. One such process comprises providing a mat (matt) layer which can be removed by development as a top layer of the printing plate precursor, as described in British Patents 1,495,361 and 1,512,080 an U.S. Patents 4,126,460 and 4,216,289. However, in order to produce printing plate precursors having such a construction, separate steps of applying the mat layer and drying it are needed. Furthermore, it is necessary to use a coating apparatus for providing the mat layer. Consequently, the cost of production is high compared with a process which does not use the mat layer.Another process for matting the surface of printing plate precursors comprises incorporating a mafting agent in a photosensitive layer, as described in Japanese Patent Application (OPI) No. 12905/79 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application"). In addition, it has been proposed in British Patent 2,046,461A to add a fine powder such as talc, glass, clay, starch or corn to a photo-sensitive layer. In such processes which comprise incorporating the matting agent in the photosensitive layer, the matting agent is dispersed in a solution of components for the photosensitive layer in a solvent and the resulting dispersion is applied to a base and then dried.

However, when the matting agent has been thus incorporated in the photosensitive layer, it has been found that the following phenomena often occur: Namely, (1) the matting agent is not dispersed in the solution of composition for the photosensitive layer in a solvent (coating solution) or it is difficult to keep a stable dispersion of the matting agent; (2) a photosensitive layer having the matting agent uniformly dispersed cannot be obtained, because the uniform dispersion of the matting agent is destroyed during the steps of applying the coating solution in which the matting agent is dispersed and drying it, so as to cause agglomeration of the matting agent; (3) the photosensitive layer becomes coarse in outward appearance, for example, parts where the matting agent is contained become highly swollen or the circumference thereof becomes pitted; (4) the printing plate has inferior tone reproduction; and (5) the parts where the matting agent agglomerates cause inferior development. Particularly, when the dyes or pigments are contained in the photosensitive layer, the photosensitive layer develops an obviously uneven appearance due to color irregularity.

An object of the present invention is to uniformly disperse a finely divided powder in a photosensitive layer and thus provide a photosensitive printing plate precursor with a surface having uniform and minute uneveness. The photosensitive printing plate precursors have the advantages they do not cause deterioration of tone reproduction or inferior development and their vacuum adherence time is remarkably shortened because they have a photosensitive layer having a mat surface.

The present invention provides photosensitive printing plate precursors comprising a support having a layer of a photosensitive composition in which are dispersed particles of average size 1 to 17 micrometres (um) of a phenol resin which has been thermally hardened.

The printing plate precursors of the invention include photosensitive printing plate precursors used for producing lithographic printing plates, relief printing plates and intaglio plates.

Preferred photosensitive printing plate precursors are those which are used for producing lithographic printing plates and intaglio plates.

The support or base is composed of a dimensionally stabilized material, which is generally a plate. Materials used heretofore as a base of printing plates can be suitably used in the present invention.

Examples of useful materials include paper, paper laminated with plastics (for example, polyethylene, polpropylene or polystyrene), metal plates of, for example, aluminum (including aluminum alloy), zinc, iron or copper, plastic films of, for example, various cellulose resins, polyethylene terephthalate or polycarbonate and paper or plastics films to which the abovedescribed metal is applied by lamination or vacuum evaporation. A suitable base is selected from these bases according to the form of the printing plate. For example, in case of photosensitive lithographic printing plates, it is preferred to use compound sheets wherein an aluminum sheet is bonded to a polyethylene terephthalate film described in Japanese Patent Publication No. 18327/73.In case of photosensitive relief printing plates, it is preferred to use polyethylene terephthalate film, aluminum plates and iron plates.

If necessary, the base is subjected to a surface treatment. In case of a photosensitive lithographic printing plate, for example, a surface of the base is process so as to have a hydrophilic property or a subbing layer is applied to the platic base after it is subjected to a surface treatment. This treatment for giving a hydrophilic property is carried out not only for forming a hydrophilic surface but also for preventing an injurious reaction with the photosensitive composition provided thereon or for improving adhesion to the photosensitive layer.

The photosensitive composition which comprises the photosensitive layer possesses solubility or swelling ability in the developing solution which varies after exposure to light. Typical examples thereof are illustrated below.

(1) Composition comprising diazo reins Diazo resins represented by condensates of Rdiazodiphenyl and paraformaldehyde may be soluble in water or may be insoluble in water, but diazo resins which are insoluble in water and soluble in conventional organic solvents are preferably used. Particularly preferred diazo compounds include compounds having two or more diazo groups in the molecule, such as a phenol salt or sulfonic acid salt of a condensate of Rdiazodiphenylamine and formaldehyde.

Although diazo resins may be used alone, it is preferable to use them together with a binder.

Useful binders include various kinds of known high molecular compounds. The amount of the binder in the photosensitive layer is 40 to 95% by weight. If the amount of the binder increases (namely, the amount of the diazo resin decreases), the sensitivity naturally increases; however, stability deteriorates with the lapse of time. An optimum amount of the binder is about 70 to 90% by weight.

(2) Composition comprising oquinonediazide compounds Particularly preferred & uinonediazide compounds are known & aphthoquinonediazide compounds which are useful in the invention. Although these o-quinonediazide compounds may be used alone, it is preferable to use them together with an alkali-soluble resin as a binder. Useful alkali-soluble resins include novolak phenol resins and t-butylphenol formaldehyde resins. The binder is included in the photosensitive layer in an amount of about 50 to 80% by weight.

Detailed description of the composition appears in U.S. Patent 4,259,434.

(3) Composition comprising photosensitive azide compounds Suitable photosensitive azide compounds include aromatic azide compounds wherein an azide group is bonded to an aromatic ring directly or through a carbonyl group or a sulfonyl group.

The azide group in these compounds is decomposed by light to form a nitrene which causes various reactions rendering them insoluble. Useful photosensitive azide compounds include a number of known compounds which are generally used in combination with a binder for preparing a composition in a manner similar to the preparation of other photosensitive resins.

Useful photosensitive compositions include high molecular weight compounds having the group -CH = CH-CO- in the main chain or side chain thereof and photopolymerizable compositions comprising addition-polymerizable unsaturated compounds, which can be used for the present invention. These photosensitive compositions have been described in the prior art references, for example, U.S. Patents 2,927,022, 3,030,208, 3,453,237 and 3,511,661.

At least one powdered hardened phenolic reins is uniformly dispersed in the photosensitive composition described above. Thus the coating solution is produced which forms a mat surface having uniformly dispersed minute unevenness when applied to the support to form the photosensitive layer. The phenol resin used can be novolak type (two-step) phenol resins (prepared by condensing phenols with aldehydes with an acid after the addition of a hardening agent) or resol type (one-step) phenol resins (prepared by condensing phenols and aldehydes with an alkali). These are hardened by heating, which serves to cross-link the resin.

Useful phenols include phenol, cresol, xylenol and resorcinol. Useful aldehydes include formaldehyde, acetaldehyde and furfural. By combining these raw materials, it is possible to obtain various kinds of resins such as phenol-formaldehyde resin, phenol-furfural resin or resorcinol-formaldehyde resin. Many of these useful resins are commercially available and can be used in the present invention. These raw materials have been extensively analyzed in the past with respect to the conditions of their production and processing; those which can be classified as a "thermally hardened phenol resin" can be suitably used in the present invention. A mixture of two or more hardened phenolic resins may be used.

The hardened phenolic resin is finely crushed by, for example, a ball mill or a jet mill. The particles having an average size of 1 to 17 ym are separated for use. If the particles are too small, the effect of shortening the vacuum adherence time becomes inferior. If the particles are too large, the dispersion stability, quality of the coated surface and reproduction of halftones deteriorates. When the particle size is in the above-described range, the vacuum adhesion is satisfactorily carried out and the dispersion stability, quality of the coated surface and reproduction of half-tones are not adversely affected even though the amount of the thermally hardened phenol resins is comparatively small. The shape of the particles is not especially restricted, and spherical particles may be used or crushed particles having complicated shape may be used directly.

The finely divided powder of the thermally hardened phenol resin may be merely added to the coating solution of a photosensitive composition in order to distribute the powder in the photosensitive layer. However, in order to more uniformly disperse the finely divied powder, it may be added to the coating solution together with, for example, a surface active agent, fine particles of inorganic materials such as silica, zinc oxide, titanium oxide, zirconium oxide, alumina, calcium carbonate or talc, fine organic particles such as latexes or fine particles described in Japanese Patent Application No. 136728/79 which corresponds to U.S. Patent Application Serial No. 199,123, filed October 23, 1980.

The number of the particles of thermally hardened phenol resin on the surface of the photosensitive layer of the photosensitive lithographic printing plate is selected generally in the range from 50/cm2 to 500,000/cm2, more preferably the range of 1,000 to 100,000/cm2.

Usually, an optimum range is determined by carrying out many test experiments using various amounts of thermally hardened phenol resin, and the number of particles can be determined, after coating on the plate, by microscopically observing the surface of photosensitive layer using a scanning electron microscope.

The amount of the thermally hardened phenol resin dispersed in the coating solution (in the abovedescribed range) varies depending upon the amount of coating for the photosensitive layer. The amount of coating is in the range of 0.01% by weight to 20% by weight, preferably 0.1 to 10% by weight, based on the solid content in the coating solution (namely, the amount of the coating solution excepting the solvent).

The coating solution containing the dispersed thermally hardened phenol resin can be applied to the base by various methods, for example, doctor coating, roller coating, bead coating or dip coating.

Further, drying of the coating solution can be carried out as usual by evaporating the solvent at a room temperature or a high temperature. Preferred drying temperature is in the range from about 20 C to about 1 50 C, more preferably in the range of from 50 to 1 20 C.

The photosensitive layer preferably has a weight after drying in the range from 0.1 g/m2 to 7 g/m2, more preferably 0.5 to 4 g/mg', in case of, for example, a photosensitive lithographic printing plate.

Since the finely divided powder is uniformly distributed in the photosensitive layer, the photosensitive layer does not have an inferior outward appearance such as uneven coloring caused by agglomeration of the finely divided powder in the coating solution and deterioration of properties such as inferior development.

Further, the present invention has a characteristic that the vacuum adherence time is remarkably shortened due to the formation of a mat surface having minute uniform unevenness.

Accordingly, the production of printing plates and the plate making operation can be efficiently carried out.

Examples of the present invention as well as Comparative Examples are shown below. Unless otherwise indicated, all parts, percents and ratios are by weight.

Example 1 and Comparative Examples (a) to (d) and (x) An aluminum plate having a thickness of 0.24 mm was degreased by dipping in a 7% aqueous solution of sodium tertiary phosphate (liquid temperature: 60 C) for 3 minutes. After washing with water, the surface was rubbed by a nylon brush with flowing an aqueous suspension of pumice to take place graining. After washing with water, it was dipped in a 5% aqueous solution of sodium silicate JIS No. 3 [ SiO2/Na2O = 3.1 to 3.3 (molar ratio) ] (liquid temperature: 70 C) for 30 to 60 seconds. It was then sufficiently washed with water and dried.

Coating solutions consisting of "Composition A" having the following composition were prepared.

Composition A: Ester compound of naphthoquinone 1 ,2-diazide-5-sulfonyl chloride and pyrogallol acetone resin (Note 1) 0.9 9 Cresol-formaldehyde resin 2.0 9 t-Butylphenol-formaldehyde rein (Note 2) 0.05 9 Naphthoquinone- ,2-diazide-4-sulfonyl chloride 0.03 9 "Oil Blue 603" (trade name, Note 3) 0.02 9 Methyl ethyl ketone 89 2-Methoxyethyl acetate 1 5 9 Finely divided powdery material (Note 4) 0.03 g Note 1: Resin described in Example 1 of U.S. Patent 3,635,709 (polyhydroxyphenyl-2-diazo1 -naphthol-5-sulfonate).

Note 2: Resin described in U.S. Patent 4,123,279 (PR50530 (tert-butylphenol-formaldehyde resin; melting point, 62-72 C; viscosity (10 9 in 1,000 ml of ethanol), 1.85-2.10; produced by Sumitomo-Durez Co., Ltd.].

Note 3: Blue dye produced by Orient Kagaku Kogyo Co. (C.l. 74350) represented by the formula:

X : acid anion Note 4: Finely divided powdery material Example 1: Thermally hardened phenol resin (average particle size: 5 ELm; novolak type cresolformaldehyde resin was hardened by adding hexamethylenetetramine and heating, and then it was crushed by a jet mill) Comparative Example (a): Glass beads (average particle size: 10 ym) Comparative Example (b): Syloid (trade name; silica gel produced by Fuji Davison Co.; average particle size: 10 tlm) Comparative Example (c): Pumice (average particle size: 10 clam) Comparative Example (d): Polyethylene powder (average particle size: 10 clam) Comparative Example (x):No addition In preparation of the above-described coating solutions, dispersibility of the finely divided powdery material in the coating solution and stability after dispersion were excellent when using the thermally hardened phenol resin powder in Example 1 as compared with cases of using other finely divided powders.

The coating solutions prepared as described above were applied to the above-described aluminium plate and dried to form a photosensitive layer, which was used to produce the photosensitive lithographic printing plate precursors in Example 1 and Comparative Examples (a) to (d) and (x), respectively. The photosensitive layer was 1.8 g/m2. When the outward appearance of the photosensitive layer in each printing plate was compared, the photosensitive layer in Example 1 and Comparative Example (x) had a uniform color, whereas the photosensitive layer in other examples had remarkably inferior uneven coloring around the finely divided powder. When vacuum adhesion of each printing plate was carried out by superposing an original film, the time required for vacuum adhesion was the longest in case of Comparative Example (x). The time required in the other examples was fairly shorter and was about 1/2 to 1/3 times. Each plate in the state of vacuum adhesion was then exposed to light at a distance of 1 m from a metal halide lamp for 40 seconds. Subsequently, each printing plate was developed for 60 seconds with a 5.26% aqueous solution of sodium silicate having SiO2/Na2O: 1.74 (molar ratio) (pH: 12.7, liquid temperature: 25on) to produce a printing plate. When the surface and printing property of the resulting printing plates were examined, prints having good tone reproduction were obtained from those in Example 1 and Comparative Example (x), but prints obtained from those in the other examples had inferior tone reproduction.

Example 2 A grained aluminum plate having a thickness of 0.3 mm was subjected to anodic oxidation in sulfuric acid to form an oxide film of about 2 g/m2. After sufficiently washing, it was dried.

On the other hand, a coating solution consisting of "Composition B" having the following composition was prepared. This coating solution was applied to the above-described aluminium plate and dried to form a photosensitive layer having about 2.5 g/m2 of the weight which was used to produce a photosensitive printing plate precursor.

Composition B: The same composition as Composition A in Example 1 except that the following two materials were used as the finely divided powdery material was prepared.

Thermally hardened phenol powder (average particle size: 10 ym; resol type cresol-formaldehyde resin obtained by crushing by means of a jet mill after heating) 0.06 g "Aerosil R 972" (trade name; silica powder produced by Nippon Aerosil Co.; average particle size: 16 ym) 0.06 g In preparation of the above-described coating solution, dispersion of "Aerosil R 972" was carried out by ultrasonic waves. Dispersibility of the finely divided powdery material in the coating solution after preparation was excellent, as was the dispersion stability.

Outward appearance, vacuum adherence time and tone reproduction of the photosensitive layer of the resulting photosensitive printing plate precursor were excellent and comparable to results obtained with Example 1.

Example 3 and Comparative Example (e) Photosensitive printing plate precursors were produced in the same manner as described in Example 1, except that the composition of the coating solution was substituted with the following Composition C.

Composition C: 2-Hydroxyethyl methacrylate copolymer (I) (Note 1) 0.87 g 2-Methoxy-4-hyd roxy-5-benzoylbenzene sulfonate of p-diazodiphenylamine paraformaldehyde condensate 0.1 g "Oil Blue #603" 0.03 g Methanol 6g 2-Methoxyethanol 6g Finely divided powdery material: Thermally hardened phenol resin (Note 2) 0.049 Note1: Resin described in Example 1 of U.S. Patent 4,123,276 (prepared from a mixture of 2-hydroxyethyl methacrylate, acrylonitrile, methyl methacrylate, methacrylic acid and benzoyl peroxide).

Note 2: The same as that used in Example 2. In case of Comparative Example (e), this finely divided powdery material was not added.

The coating amount of the photosensitive layer after drying was 1.0 g/m2 in both Example 3 and Comparative Example (e). The outward appearance, vacuum adherence time and tone reproduction of the photosensitive layer of each printing plate, as well as the outward appearance and the tone reproduction of the photosensitive layer were excellent in both cases.

However, the vacuum adherence time in Example 3 was about 1/3 of that in Comparative Example (e).

In both cases, vacuum adherence exposure of the printing plates was carried out in the same manner as in Example 1. After exposure, they were dipped in a developing solution having the following composition for 1 minute. The surface of the photosensitive layer was softly rubbed by absorbent cotton to carry out development by removing the nonexposed part, washed with water and dried.

Composition of developing solution: Benzyl alcohol 3.0 g Sodium isopropylnaphthalenesulfonate 1.0 9 40% aqueous solution of sodium silicate 1.0 g Water 95 9

Claims (9)

1. Aphotosensitive printing plate precursor which comprises a support having thereon a layer of a photosensitive composition in which are dispersed particles, of average size 1 to 17 ,um, of a phenol resin which has been thermally hardened.

2. A photosensitive printing plate precursor as claimed in Claim 1, wherein said hardened resin constitutes 0.01 to 20% by weight of said layer.

3. A photosensitive printing plate precursor as claimed in Claim 1 or 2; wherein the number of particles of hardened resin is 50 to 500,000 per square centimetre of the surface layer.

4. A photosensitive printing plate precursor as claimed in Claim 3, wherein said number is 1000 to 100,000/cm2.

5. A photosensitive printing plate precursor as claimed in any preceding claim, wherein the resin has been prepared by condensing phenol, cresol, xylenol or resorcinol with formaldehyde, acetaldehyde or furfural together with an acid or alkali.

6. A photosensitive printing plate precursor as claimed in any preceding claim, wherein said photosensitive layer has a dry weight of from 0.5 to 4 grams per square metre.

7. A photosensitive printing plate precursor as claimed in any preceding claim, wherein said photosensitive composition comprises a diazo resin, an bquinonediazide compound, a photosensitive azide compound, a photosensitive composition including a high molecular weight compound having the group -CH = CH-CO- in the main chain or side chain thereof or a photopolymerizable composition comprising an addition-polymerizable unsaturated compound.

8. A photosensitive printing plate precursor, substantially as hereinbefore described with reference to Example 1. 2 or 3.

9. A method of making a printing plate which comprises imagewise vacuum contact exposure and development of a precursor as claimed in any preceding claim.