GB2166747A - Composition for coating lithographic substrate plates - Google Patents

Description

1 GB 2 166 747 A 1

SPECIFICATION

Composition for coating lithographic substrate plates This invention relates to a composition for coating lithographic substrate plates; once applied as a coat- 5 ing, and hardened, a photosensitive resin layer can be applied thereon.

Lithography is a printing method which utilizes the repulsion between water and oil on the upper sur face of a plate for printing. A presensitized plate for use in lithography comprises a supporting plate (B) comprising a layer (A) of the type provided by the invention and a substrate plate (C); a photosensitive resin layer is disposed on the surface of the layer (A), and this forms an image.

Aluminium plates have been widely used as the substrata plate (C). For this purpose, aluminium plate has been subjected to various treatments. For instance, in order to strengthen the adhesiveness between the aluminium plate and the photosensitive resin layer, one of the surfaces of the aluminium plate is chemically or mechanically ground, thereby forming microscopic unevenness thereon, and the treated surface is subjected to anodic oxidation, to harden the surface, and then treatment with, say, an aqueous 15 silicate solution, to improve the desired hydrophilicity of the surface. Such treatments cause problems of stability of the quality of the supporting plate (B), difficulty in maintaining complete quality control, and high costs of installation and maintenance.

Plastics or paper sheets are generally unsatisfactory for use as the substrate plate (C).

A first aqueous solution according to the invention comprises a methylo [melamine, a hardening cata- 20 lyst therefor, polyvinyl alcohol, zirconium nitrate and, in dispersion, a water-insoluble inorganic material.

In a second aqueous solution according to the invention, the hardening catalyst, polyvinyl alcohol and zirconium nitrate of the first solution are replaced, as essential components, by an epoxy compound.

A solution according to the invention can be used to give a coating on the surface of the substrate (C), only one layer of which is satisfactory for the given purposes, and irrespective of the material of the substrate.

A solution of the invention can be prepared by dissolving the soluble components in water, and then dispersing therein the water-insoluble inorganic material in powdery form. Optional components, e.g. a metal-chelating agent, pigment, dyestuff andlor viscosity-raising agent, can then be added. The aqueous system should then be vigorously stirred, and air bubbles removed.

The methylolmelamine used in the invention is preferably dimethylolmelamine, trimethylolmelamine or a mixture thereof.

The hardening catalyst is, for example, an ammonium salt such as ammonium chloride, diammonium hydrogen phosphate or ammonium sulfamate, an inorganic salt such as MgC1,, ZnCl, or ZnSO,, or, pref erably, an amine salt such as dimethylaniline hydrochloride, pyridine hydrochloride, pycoline monochlo roacetate or guanidine suffamate.

The polyvinyl alcohol is preferably water-soluble and has a degree of saponification higher than 85%.

The epoxy compound is preferably soluble in water, has two or more 1,2epoxy groups and 8 to 50 carbon atoms. Examples are ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propyl ene glycol diglycidyl ether, polypropylene glycol cliglycidyl ether, glycerol polyglycidyl ether, phenol pol- 40 yethylene glycol diglycidyl ether (as available from Nagase Sangyo Co., Ltd. under the trade name Denacol and under the indices EX-81 0 and 811, EX-851, 830 and 832, EX-91 1, EX-941, 920 and 921, EX 313 and 314, and EX-145, respectively.

The water-insoluble inorganic material is, for example, hydrophilic and either insoluble or poorly solu ble in water or an aqueous alkaline solution. Examples of particular such materials are oxides of metals 45 such as zinc, aluminium, antimony, calcium, chromium, tin, titanium, iron, copper, lead, bismuth, magne sium or manganese, salts such as calcium carbonate or calcium sulfate, silicon compounds such as col loidal silica, natural pigments such as kaolin, bentonite or clay, and metals such as aluminium, iron or zinc. Colloidal silica is particularly suitable for the purposes of the present invention.

Preferably, the maximum particle size of the water-insoluble inorganic material is 43 Vm. Finer particles 50 are more preferred.

The epoxy compound not only provides a hydrophilic property to the layer (A) of the supporting plate (B), but also acts as a hardener of methylolmelamines; it is therefore unnecessary to add any separate hardening catalyst to a novel composition containing an epoxy compound, but ammonium chloride, an aminoalcohol or another hardening catalyst can be used, if desired.

In a novel composition containing polyvinyl alcohol, the weight ratio between the components of the present composition is 2 to 10 parts, preferably 4 to 7 parts of zirconium nitrate, 50 to 200 parts, prefera bly 80 to 180 parts of methylolmelamines, 50 - 200 parts, preferably 70 to 150 parts of the water-insoluble inorganic powdery material and 0.5 - 10 parts of the hardening catalyst of methylolmelamines to 100 parts of polyvinyl alcohol, respectively.

In the case where the amount of zirconium nitrate is below 2 parts by weight to 100 parts by weight of polyvinyl alcohol, the insolubilization of the thus used polyvinyl alcohol to water is incomplete after the thermal treatment, and on the other hand, in the case of over 10 parts by weight to 100 parts by weight of polyvinyl alcohol, there is a tendency the non picture-image parts hold printing ink to cause the so called ground blur on the surface of printing plate due to insufficient hydrophilicity of the surface of the 65 j5 n GB 2 166 747 A 2 layer (A).

In the case where the amount of methylolmelamines is below 50 parts by weight to 100 parts by weight of polyvinyl alcohol, there is a tendency of reducing the adhesion between the substrative plate (C) and the layer (A), and on the other hand, in the case of over 200 parts by weight to 100 parts by weight of polyvinyl alcohol, there is a tendency of causing so-called ground blur on the surface of print- 5 ing plate due to the insufficient hydrophilicity of the surface of the layer (A).

In the case where the amount of the water-insoluble inorganic powdery material is below 50 parts by weight to 100 parts by weight of polyvinyl alcohol, there is a high tendency of causing irregular distribu tion of unevenness on the surface of the layer (A) resulting in the poor reproducibility of net points of the picture-image parts, and on the other hand, in the case of over 200 parts by weight to 100 parts by weight of polyvinyl alcohol, the permeated amount of the solution of the photosensitive resin into the layer (A) is increased resulting in the increase of the amount of the solution of photosensitive resin used and accordingly, the case of over 200 parts becomes noneconomical.

On the other hand, in the present composition containing epoxy compound, the weight ratio between the components of the present composition is 25 to 50 parts, preferably 30 to 40 parts of epoxy com- 15 pound and 50 to 200 parts, preferably 70 to 150 parts of the water- insoluble inorganic powdery material to 100 parts of methylolmelamines, respectively.

In the case where the amount of the water-insoluble inorganic powdery material is below 50 parts by weight to 100 parts by weight of methylolmelamines, there is a high tendency of causing irregular distribution of unevenness on the surface of the layer (A) resulting in the poor reproducibility of net points of 20 the picture-image parts.

On the other hand, in the case of over 200 parts by weight to 100 parts by weight of methylolmelamines, the solution of photosensitive resin permeates into the layer (A) resulting in the increase of the amount of the photosensitive resin used for preparing the printing plate, and accordingly, the case of over 200 parts becomes noneconomical.

As the substrative plate (C) of the supporting plate (B), to which the present composition is applied on the surface thereof, every material which is inexpensive and fulfills the performances required for the plate for lithography may be used and for instance, foils or plates of a metal such as aluminium, iron, copper, tin, zinc, lead, etc., or alloys thereof, plastic films or sheets of polyester, polypropylene, polyi- mide, polyacrylonitrile, polycarbonate, polyamide, polyvinyl chloride, polyvinylidene chloride, polystyrene, polyethylene, etc., synthetic papers, art papers, coated papers, cardboards, thin papers, etc. may be exemplified. Of the metals, aluminium, zinc, iron, etc. are suitable, and of the plastic materials, those of relatively high in dimensional stability such as polyester, polyimide and polycarbonate are suitable.

Of the paper materials, synthetic paper, art paper, coated paper, cardboard, etc. are suitable.

In the case of applying the present composition on the surface of a metal plate for substrative plate (C), 35 a metal-chelating agent such as 5-suifosalicylic acid, ethyl en ed iam i ne-tetraa cetic acid, trans-cyclohexane 1,2-diaminetetraacetic acid, etc. may be added to the present composition for the purpose of reinforcing the adhesion of the layer (A) formed from the present composition to the substrative plate (C).

It is not necessary to carry out a specific treatment of the substrative plate (C) before the application of the present composition thereonto as far as the surface thereof is not polluted by oil substance.

However, the physical treatment of the surface of the substrative plate (C) such as wet- or dry honing, ball-grinding and brush-grinding andior the chemical treatment by acid(s) or alkali(s) may be effected in order to broaden the specific surface area thereof.

The printing plate for use in lithography can be prepared by using the present composition as follows.

For instance, the present composition is applied on the surface of the substrative plate (C) by a bar 45 coater, etc., and the thus treated plate is subjected to thermal treatment for 0.5 to 6 min at a temperature of 120 to 250'C, thereby hardening the thus applied present composition on the plate (thickness: 2 to 5 gm).

In the case where the composition containing polyvinyl alcohol is used, both of polyvinyl alcohol and methylolmelamines are hardened to form a membrane firmly adhering to the surface of the substrative 50 plate (C) by the action of zirconium nitrate and hardening catalyst, respectively, during the thermal treat ment. Particularly, polyvinyl alcohol is insolubilized to water and at the same, fixes a substance having the residual hydrophilic group(s) on the surface of the thus formed membrane, thereby exhibiting the performance of retaining the hydrophilicity required for the layer (A) of the supporting plate (B) for a long time period. On the other hand, it is considered that the water- insoluble inorganic powdery material 55 forms a suitable unevenness on the surface of the layer (A) of the supporting plate (B), as the result, the layer (A) adheres firmly to the layer of the photosensitive resin which is to be applied thereon by the physical adhesive function of the thus formed unevenness.

In the case where the composition containing the epoxy compound is used, the epoxy compound acts as a cross-linking agent of methylolmelamines during the thermal treatment and as a result, a membrane 60 firmly adhering to the surface of the substrative plate (C). Moreover, the epoxy compound fixes a sub stance having the residual hydrophilic group(s) on the surface of the thus formed membrane, thereby exhibiting the performance of retaining the hydrophilicity required for the layer (A) of the supporting plate (B) for a long term. On the other hand, it is considered that the water-insoluble inorganic powdery material forms a suitable unevenness on the surface of the layer (A) of the supporting plate (B), as the 65 3 GB 2 166 747 A 3 result, the layer (A) adheres firmly to the layer of the photosensitive resin which is to be applied thereon by the physical adhesive function of the thus formed unevenness.

After applying a solution of a photosensitive resin on the surface of the thus formed layer (A) of the supporting plate (B) according to a conventional manner, the thus treated supporting plate B is dried, thereby obtaining a pre-sensitised plate (hereinafter referred to as a 'PS plate') having a layer of the 5 photo-sensitive resin thereon. By exposing such a PS plate to light, and developing the exposed PS plate, a lithographic printing plate is produced.

Composition of the present invention can be satisfactorily used in onestep application. Conventional surface treatments such as surface grinding, anodic oxidation and hydrophilisation are unnecessary.

The following Examples illustrate the invention.

Examples 1 to 7 Methylol melamine (made by Nippon Carbide Incl. Co., Ltd. under the trade name Nicaresin) was dis- solved in water, and guanidine sulfamate was added as a hardener. Another aqueous solution, contain ing 5% by weight polyvinyl alcohol (made by Shin-Etsu Chem. Incl. Co., Ltd., grade C-17) and 0.05 to 0.5%15 by weight zirconium nitrate, was then added. After the further addition of colloidal silica (made by Nippon Earojil Ind. Co., Ltd. grade COK 84), the mixture was stirred for about 2 hours, thereby dispersing the colloidal silica and removing air bubbles. Seven compositions were prepared in this way, as shown in Table 1 (amounts in parts by weight).

TABLE 1

Example 1 2 3 4 5 6 7 Polyvinyl alcohol 100 100 100 100 100 100 100 Zirconium nitrate 6 6 6 6 3 4 10 25 Methylolmelamine 50 100 150 180 150 150 150 Colloidal silica 100 100 100 100 50 75 150 Guanidine sulfamate 1.5 1.0 1.5 1.8 1.5 1.5 1.5 30 Examples 8 to 11 Four compositions, having the components shown in Table 2, were prepared by the procedure of Example 1.

TABLE 2 35

Example Components of Composition (1) Weight ratio of (1) No. A 8 C D E A:B:C:D:E 408 Polyvinyl Zirconium Methlylol- Ammonium Titanium oxide 40 alcohol nitrate melamine chloride 1:0.05:1.3:0.01:0,7 9 Polyvinyl Zirconium Methylol- Ammonium Clay 1:0.05:1.4:0.02:0.5 alcohol nitrate melamine sulfamate Polyvinyl Zirconium Methylol- Dimethyl- Barium sulfate 1:0.04:1.5:0.03:0. 4 alcohol nitrate melamine aniline 11 Polyvinyl Zirconium Methylol- Magnesium Kaolin 1:0.07:1.6:0.04:0.6 alcohol nitrate melamine chloride 50 Examples 12 to 17 Two aqueous solutions, one of 5 g methylol melamine in 30 g water, the other containing 0.5 to 3.5 g of an epoxy compound (Denacol EX-313) were mixed. 1.25 to 5 g of the colloidal silica used in Example 1 55 and 1.25 to 5 titanium oxide (made by Teikoku Chem. Incl. Co., Ltd. grade MT-600B) were added, to ob tain six compositions having the components shown in Table 3 (in parts by weight).

TABLE 3

Example 12 13 14 15 16 17 60 Methylolmelamine 100 100 100 100 100 100 Epoxy compound 25 25 25 50 50 50 Colloidal silica 37.5 50 75 37.5 50 75 Titanium oxide 37.5 50 75 37.5 50 75 65 4 GB 2 166 747 A Examples 18 to 21 Four compositions were prepared by the procedure of Example 1, but using the components shown in Table 4 (in parts by weight).

4 TABLE 4 5

Example 18 19 20 21 Polyvinyl alcohol 5 7 6 8 Zirconium nitrate 0.5 0.5 0.12 0.3 Methyl ol melamine 8 10 6 5 10 Guanidine sulfamate 0.07 0.05 0.06 0.05 Colloidal silica 5 1 - 1 Kaolin - 3 - - Calcium sulfate - - 2 Titanium oxide - - 2 15 Calcium carbonate - - - 1 Aluminium oxide - - - 2 Water 100 100 100 100 Examples 22 and 23 Two compositions were prepared by the procedure of Example 12, but using the components shown in Table 5 (in parts by weight). The respective epoxy compounds were propylene glycol diglycidyl ether (Denacol EX-91 1) and polyethylene glycol diglycidyl ether (Denacol EX-832).

TABLE 5

Example 22 23

Methylol melamine 10 10 Guanidine sulfamate 0.05 - 30 Epoxy compound 5 2.5 Colloidal silica 4 4 Aluminium oxide - 5 Kaolin 3 - Ammonia liquor (10%) 0.2 35 Water 150 150 Test examples 1 to 11:

Tests on the printing plates prepared by using the present composition Supporting plates for use in lithography were prepared by applying each one of the present composi tions produced in Examples 1 to 11 on a surface of each one of the de- fatted aluminum thin plates (Japa nese Industrial Standards A-1100) of 200 m/m in length, 300 m/m in width and 0.15 m/m in thickness while using a 46 bar-coater and the thus coated composition was hardened by heating for 3 min in a hot wind drier at a temperature of 180'C and, after applying a solution of a negative type photosensitive 45 resin on the thus coated surface of each of the thus obtained supporting plate, the thus coated plate were dried in a hot wind drier at 1120'C for one min to obtain the presensitized plate (PS plate).

After placing a negative film (test pattern of 175 lines with the area of net points of from 3 to 97%) on the surface of the photosensitive resin layer of each one of the PS plates and setting the thus treated PS plate in a vacuum printing frame in a usual manner, the PS plate was exposed to ultraviolet rays from a 50 hyperpressure mercury lamp (made by OOKU Works, 4 kW) at a distance of 1 m for 30 sec. By develop ing the thus exposed PS plate while using a liquid developer, printing plates for lithography were ob tained.

After washing the printing plates with water and draining off water thereon by using a squeezer, inking was carried out on the printing plate by pouring a protect ink on the thus treated surface thereof while 55 using a sponge. Thereafter, the degree of the adhesion of the ink to the picture-image parts was ob served.

After washing the printing plates again with water, draining off water thereon by using the squeezer and drying the printing plates, the printing plates were subjected to the following tests.

Adhesion of the picture-image parts to the supporting plate was judged on the basis of the degree of 60 exfoliation of the net points after 1000 times of abrasion while using a Taber rotary abrader (truck wheel:

CS-17 type, load of 1000 g).

Reproducibility of the image was judged by the reproducibility of the test pattern (175 lines, the area of net points of 3 to 97%).

Sensitivity was judged by the number of steps of the step tablet (made by Kodak Co., No. 2 provided 65 GB 2 166 747 A 5 with 21 steps).

Hydrophilicity of the non-picture image parts was judged by (1) the state of spoiling by the protect ink after the inking thereof and (2) the yes or no of coming off of the offset ink by pouring water after applying the offset ink directly on the non-picture image parts.

The results of the tests are shown in Table 6.

Test examples 12 to 17:

In the same manner as in TEST EXAMPLE 1 except for using each of the composition obtained in EXAMPLES 12 to 17 and hardening the coated composition by heating for one min at a temperature of 230'C, each of the printing plates were prepared.

Each of the thus prepared printing plates were subjected to the same tests as in TEST EXAMPLE 1, the results being also shown in Table 6.

Comparative test example:

In the same manner as in TEST EXAMPLE 1 except for using a composition containing 100 parts by weight of methylolmela mines and 100 parts by weight of colloidal silica instead of the present composition in TEST EXAMPLE 1, a printing plate was prepared and it was subjected to the same tests as in TEST EXAMPLE 1, the results being also shown in Table 6.

TABLE 6 20

TEST Specific Properties of Printing Plate EXAMPLE Adhesion of Adhesion of Reproduci- Sensi- Hydrophi Nos. ink to pic- picture- bility of tivity licity of ture-image image parts image non-pic- 25 parts ture image parts 1 A A A A A 30 2 A A A A A 3 A A A A A 4 A A A A A A B A A A 6 A A A A A 35 7 A A A A A 8 A A A A A 9 A A A A A A A A A A 11 A A A A A 40 12 A A A A A 13 A A A A A 14 A A A A A A A A A A 16 A A A A A 45 17 A A A A A COMPARA TIVE TEST A A A A c 50 EXAMPLE

Note: Evaluated by the following criteria: A: excellent, B: good, C: poor.

Printing test example 1:

A supporting plate (B) for use in lithography was prepared by continuously applying the composition of Example 3 at a velocity of 30 m/min onto a de-fatted surface of aluminum foil (Japanese Industrial Standard A-1 100) of 500 m/m in width and 0.15 m/m in thickness while using a reverse coater and hard ening the thus coated composition at 23WC.

A presensitized plate (PS plate) was prepared by applying a solution of negative-type photosensitive 60 resin onto the surface of the thus hardened layer in a usual manner and drying thereof.

After cutting off a piece from the thus obtained PS plate, a negative image film was placed on the photosensitive resin layer of the piece, and the PS plate was exposed by ultraviolet light from a hyper pressure mercury lamp of 4 kW at a distance of 1 m for 40 sec. After subjecting the thus exposed PS plate to development by a developing liquid (Nippaku PS developer NN-221) and washing the developed 65 6 GB 2 166 747 A PS plate with water, the washed PS plate was dried to obtain a printing plate for use in lithography.

Printing was carried out on sheets of high quality paper by using the thus obtained printing plate and a printing machine (Heidel KORD). More than 50,000 sheets could be printed without any trouble.

Printing test example 2:

In the same manner as in Printing Test Example 1 except for using the composition obtained in Example 15 instead of that obtained in Example 3, a printing test was carried out. As a result, more than 50,000 sheets could be printed without any trouble.

Printing test example 3:

A PS plate was prepared by applying a solution of positive-type photosensitive resin on the surface of the hardened layer of the supporting plate (B) prepared in the same manner as in Printing Test Example 1, and drying the thus coated supporting plate (B). After placing a positive image film on the PS plate, the thus treated PS plate was exposed by ultraviolet light from a hyper pressure mercury lamp of 4 kW from the distance of 1 m for 50 sec. After subjecting the thus exposed PS plate to development by a positive-type developer (made by OHKA Ind. Co., Ltd., under the index of PL-101) and washing the thus developed PS plate with water, the washed PS plate was dried to obtain a printing plate for use in lithography.

Printing was carried out by using the thus prepared printing plate in the same manner as in Printing Test Example 1. More than 50,000 sheets could be printed without any trouble.

Printing test example 4:

By using the supporting plate (B) obtained in the same manner as in Printing Test Example 2, a printing plate was prepared and a printing test was carried out in the same manner as in Printing Test Exam- pie 3. As a result, more than 50,000 sheets could be printed without any trouble.

Printing test example 5:

By using the compositions obtained in Example 8, a printing plate was prepared in the same manner as in Printing Test Example 1, and as a result of carrying out the printing, more than 50,000 sheets could be printed without any trouble.

Printing test example 6:

A supporting plate was prepared by applying the composition obtained in Example 19 on the surface of a polyester film of 100 lim in thickness, the surface having been blasted preliminarily by air-honing, and hardening the thus coated composition by heating for 1 min at 23WC.

A printing plate was prepared by using the thus obtained supporting plate in the same manner as in Printing Test Example 1, and the thus obtained printing plate was used for printing.

As a result, more than 50,000 sheets of paper could be printed with the thus prepared printing plate without any trouble.

Printing test example 7:

In the same manner as in Printing Test Example 6 except for using the composition obtained in Example 22 and hardening the coated composition by heating for 10 min at 1140'C, printing was carried out. As a result, more than 50,000 sheets could be printed without any trouble.

6 Printing test example 8:

Onto the surface of a preliminarily de-fatted aluminum foil of 25 Km in thickness which had been stuck onto a synthetic paper of 0.2 m/m in thickness, the composition obtained in Example 18 was applied, and the thus coated composition was hardened by heating for 1 min at 23WC to obtain a supporting plate.

By using the thus obtained supporting plate, a printing plate was prepared in the same manner as in 50 Printing Test Example 1 and subjected to printing. As a result, more than 50,000 sheets could be printed without any trouble.

Printing test examples 9 and 10: 55 Each of supporting plates was prepared by applying each of the compositions obtained in Examples 20 55 and 213 on the surface of an iron foil of 50 Rm in thickness, the surface having been subjected to defatting treatment, and hardening the thus coated composition by heating for 1 min at 20WC. Two printing plates were prepared by using each of the thus obtained supporting plates in the same manner as in Printing Test Example 1, and the thus prepared printing plates were used for printing.

60In both the cases, more than 50,000 sheets of paper could be printed without any trouble.

Printing test example 11:

A supporting plate for use in lithography was obtained by applying the composition obtained in Exam ple 21 on the surface of a substrative plate prepared by sticking polycarbonate film of 25 Vm in thickness onto the both surfaces of a de-fatted iron foil of 50 I.Lm in thickness, and hardening the thus coated corn- 65 7 GB 2 166 747 A 7 position by heating for 3 min at 17WC.

A printing plate for use in lithography was prepared by using the thus obtained supporting plate in the same manner as in Printing Test Example 1, and subject to printing.

As a result, more than 50,000 sheets of paper could be printed without any trouble.

Claims (13)

1. An aqueous solution containing a methylol melamine, a hardening catalyst therefor and, dispersed in the solution, a water-insoluble inorganic material, provided that, if the catalyst is not an epoxy compound, polyvinyl alcohol and zirconium nitrate are present.

2. A solution according to Claim 1, wherein the methylolmelamine is dimethylolmelamine, trimethylolmelamine or a mixture thereof.

3. A solution according to Claim 1 or Claim 2, which comprises a watersoluble epoxy compound having 8 to 50 carbon atoms and two 11,2-epoxy groups.

4. A solution according to Claim 3, wherein the epoxy compound is selected from ethylene glycol 15 digylcidyl ether, polyethylene glycol digylcidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, glycerol polyglycidyl ether and phenol polyethylene glycol diglycidyl ether.

5. A solution according to any preceding claim, wherein the catalyst is an ammonium salt, a hydrochloride or sulfamate of an aminoalcohol, an inorganic or organic acid salt of an amine, or an inorganic metal salt.

6. A solution according to Claim 5, wherein the catalyst is selected from ammonium chloride, diammonium hydrogen phosphate, ammonium sulfamate, dimethylaniline hydrochloride, pyridine hydrochloride, pycoline monochloroacetate, guanidine sulfamate, magnesium chloride, zinc chloride and zinc sulfate.

7. A solution according to any preceding claim, which comprises watersoluble polyvinyl alcohol hav- 25 ing a degree of saponification of more than 85%.

8. A solution according to any preceding claim, wherein the waterinsoluble inorganic material is se lected from the oxides of zinc, aluminium, antimony, calcium, chromium, tin, titanium, iron, copper, lead, bismuth, magnesium and manganese, calcium carbonate, calcium sulfate, colloidal silica, kaolin, benton ite, clay, aluminium, iron and zinc.

9. A solution according to any preceding claim, which comprises 100 parts by weight polyvinyl alco hol, 50 to 200 parts by weight methylolmelamine, 2 to 10 parts by weight zirconium nitrate, 50 to 200 parts by weight of the inorganic material and 0.5 to 10 parts by weight of the hardening catalyst.

10. A solution according to any preceding claim, which comprises 100 parts by weight methylolme lamina, 25 to 50 parts by weight epoxy compound and 50 to 200 parts by weight of the inorganic mate- 35 rial.

11. A solution according to Claim 1, substantially as described in any of the Examples.

12. A process for preparing a solution according to any preceding claim, which comprises forming an aqueous solution of the water-soluble components; dispersing the water- insoluble inorganic powdery material into the solution; vigorously stirring the dispersion; and removing air bubbles.

13. A method for producing a pre-sensitised plate for use in lithography, which comprises applying a solution according to any of Claims 1 to 11 on to the surface of a substrate, forming a hardened coating on the substrate from the solution, and applying a photo-sensitive resin on the surface of the hardened layer.

Printed in the UK for HMSO, D8818935, 186, 7102.

Published by The Patent Office, 25 Southampton Buildings, London, WC2A lAY, from which copies may be obtained.

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