GB1588063A - Method for the preparation of a planographic printing plate - Google Patents

Description

(54) METHOD FOR THE PREPARATION OF A PLANOGRAPHIC PRINTING PLATE (71) We, DAI NIPPON PRINTING CO., LTD., a Japanese company, of 12 Kagacho 1-chome, Ichigaya, Shinjuku-ku, Tokyo, Japan, and SHIN-ETSU CHEMICAL CO. LTD., a Japanese company, of 6-1, Otemachi 2-chome, Chiyodaku, Tokyo, Japan, do hereby declare the invention for which we pray that a patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to the preparation of a printing plate for use in dry planography in the absence of dampening water.

In the prior art, various types of planographic printing plates for use in a dampening water-free printing process have been proposed. Those printing plates have drawbacks, such as, for example, poor performance as a printing plate and a complicated process of manufacture.

As an example, a method was proposed in which a planographic printing plate is prepared by coating an aluminum base with multiple diazo type photosensitive layers formed of a diazo type photosensitive composition and an overlying layer formed of dimethylpolysiloxane gum, then subjecting the thus coated aluminum base to exposure to light through an overlaid positive transparency to insolubilize the diazo layer in the exposed areas, dissolving out the diazo layer in the unexposed areas in the developing process, and subsequently stripping the dimethylpolysiloxane layer off the unexposed areas (see Japanese Patent Puiblication 44-23042).

As a further example, a planographic printing plate was prepared by coating an aluminum base with a diazo layer, a layer of an adhesive and a layer of a silicone rubber successively, then subjecting the thus coated aluminum base to exposure to light through an overlaid negative transparency, allowing the photosensitive layer in the exposed areas to photodecompose for development, and stripping the silicone layer off the exposed areas (see U.S. Patent 3,511,178).

In the above two methods wherein the layer of non-photosensitive silicone gum or rubber is present between the diazo photosensitive layer and the positive or negative transparency, any image patterns on the positive or negative transparency cannot be reproduced with high fidelity on the plate and, since the stripping of the silicone layer is carried out by utilizing the change of the solubility of the photosensitive layer in the solvent, the edges of the image areas formed can not have clear-cut sharpness.

Further, the plate making process of the dry planographic printing plate proposed in the prior art is handicapped by the complicated successive steps of providing multiple layers on the base plate, exposure to light and development.

As a solution of the above-described problems encountered in the prior art, the inventors of the present invention have recently proposed a method in which image areas are formed by exposing the bare surface of the base plate after removal of uncured silicone resin on the areas unexposed to light of a plate having a layer of a photosensitive or photocurable silicone resin on the surface (see U.S. Patent 3,86.5,588).

The above methods of making printing plates are defective because of the complexity of the processes in which the removal of the silicone layer from the image areas is performed by the wet process using an organic solvent after exposure to light.

Apart from the above-described wet processes, dry processes are known for the preparation of a dry planographic printing plate. In most of the dry processes, the image areas of the plate are formed with a toner by electrophotography on the surface of a layer of a cured silicone covering the base plate. This dry process, however, is defective because of difficulty in obtaining sufficiently strong adhesion between the toner laid imagewise and the surface of the cured silicone, the resultant printing plates having poor durability and unsatisfactory printability.

For example, Japanese Patent Disclosure 48-19305 discloses a process in which a dry planographic printing plate is prepared by forming thermally fused toner images for adherence to a cured overcoating layer of a silicone on a layer of an electrostatic latent image-forming substance which has been applied on a base plate and dried.

This method of plate making is not free from the above described problem, namely, poor adhesion of the toner to the silicone, since the silicone has been cured when the toner image is formed on it, resulting in poor printing durability of the plate.

Various attempts have been made to improve adhesion between the toner and the surface of the silicone layer. However, no successful results have been obtained.

For example, Japanese Patent Disclosure 49-21204 discloses a method in which the toner images formed on the electrophotographic layer are transferred on to the surface of a layer of a composition composed of a silicone gum and a resin, followed by bonding with thermal fusion to produce a planographic printing plate. The printing plate thus prepared has the disadvantage of poor link-repellency because of the resin component included in the composition to improve adhesion between the toner and the silicone layer.

Further, Japanese Patent Disclosures 50-71405 and 50-71406 disclose a method directed to the improvement of adhesion between the toner and the layer of the silicone wherein the toner is transferred and bonded by thermal fusion to the surface of a silicone layer formed by coating the base plate with an uncured or semi-cured silicone resin, followed by curing of the silicone to produce a finished planographic printing plate. The storability of the plate before curing is insufficient because of the thermosetting silicone resin used. In order to remove the problem of such storability, there was proposed a complicated process in which a solution of a curing catalyst is applied on the layer of the uncured silicone resin after the toner images are formed on the surface of the silicone layer, and then the silicone layer is cured.

Japanese Patent Disclosure 51-16105 discloses a method for the preparation of a master for a planographic printing plate which comprises forming on a base plate a coating layer of a silicone rubber composition containing two kinds of curing catalysts, then photosensitizing one of the catalysts, and thermally activating the other catalyst to cure the silicone rubber composition. This method is also defective in the complexity of formulating the curing catalysts, one being a photosensitive compound, such as an azide compound, and the other being a compound capable of being thermally activated, such as an organic peroxide, as well as the poor storability of the silicone rubber composition admixed with such a catalyst system and the necessity of a heating step for sufficiently curing the silicone rubber composition.

Japanese Patent Disclosure 51-134204 discloses a method for the preparation of a planographic printing plate which comprises sandwiching a layer of photocurable silicone rubber between two base plates to form a complex laminate, then exposing the complex laminate to light through a transparency overlaid thereon, and splitting the base plates to produce the desired printing plate. In this method, the photocurable silicone rubber composition has an addition-polymensable ethylenical monomer or oligomer as a crosslinking agent. Thus, the composition is quite limited with respect to the compatibility of the silicone rubber component and the crosslinking agent as well as with respect to the storability of the composition before it is used.

The method of the present invention for the preparation of a dry planographic printing plate comprises the following steps (not necessarily in the listed order): (a) coating one surface of a substrate which is transparent to ultraviolet light with an uncured photocurable silicone, (b) bringing the surface of the substrate thus coated into direct contact with an optionally coated surface of a base plate to form a laminate, (c) providing or contacting the other surface of the substrate with an image pattern made of a material which is opaque to ultraviolet light.

(d) irradiating the laminate with ultraviolet light from the side of the image pattern, and (e) separating the substrate from the base plate so that a photocured portion of the silicone layer is transferred to the surface of the base plate (to form a non-image area), and an uncured portion of the silicone layer stays in situ on the surface of the substrate (corresponding to the image pattern on the surface of the substrate).

Thus a planographic printing plate prepared by the method of the present invention has a base plate whose surface consists of a plurality of bared image areas and a plurality of photocured silicone non-image areas.

Each of Figs. 1 to 4 is a cross sectional view of a plate illustrating the steps of the process for the preparation of the planographic printing plate in accordance with the method of the present invention; in these Figures, 1 is a substrate which is transparent to ultraviolet light; 2 is uncured photocurable silicone; 2' is photocured silicone; 3 is a layer of a surface treatment agent; 4 is a base plate; 5 is an image pattern formed with a material which is opaque to ultraviolet light; 6 is a base sheet transparent to ultraviolet light; 7 is an original transparency; and 8 denotes beams of ultraviolet light.

The dry planographic printing plate prepared by the method of the present invention is shown in Fig. 4. The printing plate is composed of base plate 4 provided, optionally with a layer of surface treatment agent 3, and with an ink repellent layer 2' forming non-image areas of photocured silicone, the image areas being formed with the layer of surface treatment agent 3 laid stare.

Now referring to Fig. 1, one surface of the substrate 1 is provided with the layer 2 of photocurable but uncured silicone in adhesive contact, and the layer surface is brought into direct contact with the surface of base plate 4 which has optionally been coated with the surface treatment agent 3, with pressing to form a laminate.

Care must be taken in the lamination to use a sufficient pressing force to avoid the formation of bubbles between layer 2 and base plate 4. For example, the lamination is performed either by pressing the assembly of the substrate and the base plate using a roller or, more efficiently, by passing the assembly through a laminating roll or a calendering roll.

Layer 2 of the photocurable silicone is formed on the surface of the substrate 1 by uniformly applying a solution of the silicone, which may optionally be diluted with an organic solvent to have a suitable viscosity, by means of brush coating, rotary coating, rod coating, roll coating, or the like, followed by evaporation of the solvent and drying. The thickness of the photocurable silicone layer is preferably in the range from 2 to 15 zm as dried.

The organic solvents suitable for the above purpose are exemplified by ketone solvents, such as methylethyl ketone and methyl isobutyl ketone; aromatic hydrocarbon solvents, such as benzene, toluene, and xylene; halogenated hydrocarbon solvents, such as trichloroethylene and tetrachloroethylene; alcohol solvents, such as isopropyl alcohol and octyl alcohol; and ester solvents, such as methyl acetate and ethyl acetate.

Substrate 1 may be a film or sheet of plastics having a high transmission of ultraviolet light, such as polypropylene, saturated polyester, cellulose triacetate, cellulose diacetate, polyvinyl chloride, polyvinylidene chloride, polystyrene, acrylic resins, and polycarbonate resins.

It is recommended to use a material having a sufficiently high heat resistance, such as saturated polyester and cellulose triacetate, as the substrate, when the image pattern is provided directly by electrophotography in which toner lis adhesively bonded to the surface by heat fusion.

As will be evident from the description given later with reference to Fig. 3, the material of substrate 1 is required to have a surface such that the uncured photocurable silicone can easily spread over and stick to the surface but the cured areas d the silicone can be readily peeled off and removed from the surface. The surface of substrate 1 is preferably as smooth as possible since a matt surface makes the surface of the cured silicone rough, and adversely influences the ink repellency of the surface.

Base plate 4 is made of a metal, e.g. copper, steel, aluminum, stainless steel, or zinc; plastics, e.g. polypropylene, saturated polyester, cellulose triacetate, cellulose diacetate, polyvinyl chloride, p olyvinylidene chloride, polystyrene, acrylic reins, and polycarbonate resins; resin-coated paper; or metal foil-paper laminate. It is desirable to clean the surface of the base metal prior to application.

It may be added that the material of the base plate is preferably a material having sufficient heat resistance when the toner images are provided on the surface of the substrate by electrophotography after the substrate has been adhered to the base plate.

The image patterns are formed with a material which is opaque to ultraviolet light placed on the surface of substrate 1 (which is transparent to ultraviolet light).

One recommended method is the method as shown in Fig. 2(a) which illustrates the direct formation of image patterns with a material opaque to ultraviolet light. Accord ing to this method, image patterns 5 are formed on substrate 1 either by reproducing the original patterns by an electrophotographic copying machine with a toner or by manual writing with a writing link which is not transparent to ultraviolet light. The formation of the image patterns on the substrate may be carried out either before or after the substrate is adhered to the base plate.

In an alternative and preferred method for providing image patterns 5, a transparency 7 bearing the image patterns opaque to ultraviolet light is brought into direct contact with the surface of substrate 1 as shown in Fig. 2(b). The transparency may ;be either a positive or a negative Ibearing image patterns 5 opaque to ultraviolet light on the surface of a base sheet 6 transparent to ultraviolet light. The image-forming material of the image patterns may be a silver salt or a non-silver salt.

The above step is followed by exposing and irradiating the laminate to and with light from the side of image patterns 5 as shown in Figs. 2(a) and 2(b).

The photocurable silicone is cured by the irradiation on the non-image areas whereby the cured silicone is adhesively bonded to the surface of base plate 4. In order to obtain a stronger bonding of the cured silicone to base plate 4 it is preferred to have the surface of base plate 4 matt or treated in advance with a primer, or more preferably to treat the matt surface with the primer; Illustrative of the primers suitable for the purpose are vinyl tris(2-methoxyethoxy) silane, 3-glycidoxypropyl trimethoxy silane, N-(trimethoxysilylpropyl) ethylenediamine, 3 -methacryloxypropyl trimethoxy silane, 3-aminopropyltriethoxy silane, mixtures thereof, and partial (co)hydrolyzates thereof. The primer is applied to the surface by a conventional method, for example, rotary coating, rod coating, brush coating, or spray coating.

On the other hand, the photocurable silicone on the image areas is left uncured even after exposure to ultraviolet light, since the light is absorbed in the material opaque to ultraviolet light forming the image patterns on substrate 1 before reaching the silicone layer. The light source of ultraviolet light is exemplified by xenon lamps and low-, medium- and high-pressure mercury lamps.

After completion of the step of exposure to light, substrate 1 is peeled off base plate 4 as shown in Figs. 3(a) or 3(b). Image patterns 5 are removed together with substrate 1. When transparency 7 is used as the original to provide thereon image patterns 5, transparency 7 and, consequently, image patterns 5 are naturally removed together with substrate 1 in a similar manner. It is also possible that the removal of transparency 7 and, consequently, image patterns 5 after exposure to light precedes the peeling of substrate 1 as shown in Fig. 3(b).

In the peeling of substrate 1 from base plate 4, the cured photocurable silicone is left on the surface of base plate 4, strongly adhered to the non-image areas, while the uncured photocurable silicone on the image areas is removed together with sub strate 1, since it adheres more strongly to the substrate than to the base plate. Thus, the desired printing plate can be formed as shown in Fig. 4.

The exact mechanism by which the desired planographic printing plate is ob tained in an advantageous manner by the method of the present invention is not well understood, but it may be that the transfer of the cured layer of the photocurable silicone from the surface of substrate 1 to the surface of base plate 4 takes place since the surfaces have a different bonding strength to the silicone cured by exposure to light. In contrast, as the unexposed or uncured silicone on the image areas is removed by adhering to substrate 1, it has a stronger adhesion to the substrate than to the base plate. This lis because the silicone is applied to the surface of the substrate in the form of solution, resulting in a better adhesion than when contacted with the primer-treated base plate by dry lamination.

The photo curable silicone suitable for the preparation of the dry planographic printing plate in accordance with the method of the present invention is readily cured by irradiation with ultraviolet light. Examples of suitable silicones are the following.

(1) An organopolysiloxane, as disclosed in U.S. Patent 4,019,904, containing in a molecule at least one maleimido group-containing organosiloxane unit expressed by the formula

where R1 is an aromatic ring residue or a heterocyclic ring residue, R2 is a hydrogen atom, halogen atom, cyano group or a monovalent hydrocarbon group having 1 to 4 carbon atoms, R; is a divalent hydrocarbon group having 1 to 10 carbon atoms, R4 is a monovalent hydrocarbon group, X is a hydroxy group or a hydrolyzable monovalent atom or group, a is 0 or 1, Ob1, Oc3 and 0~d~3 with the proviso that O < b + c + d, or by the formula

where R1, R2 and R3 have the same meaning as in formula (I) above, R4 is a methyl or a trifluoropropyl group, a and b are each 0 or 1, and 1, m and n are each positive integers, n being not smaller than 25, with the proviso that n/l is from 25 to 2,000 and n/m is from 2.5 to 50.

(2) An organopolysiloxane containing in a molecule at least one acryloxy group containing organosiloxane unit expressed by the following formula as disclosed in British Patent 1,323,869:

where R' is a hydrogen atom, phenyl group or a halogenated phenyl group, R2 is a hydrogen atom or a methyl group, RA is a divalent hydrocarbon group or a halogenated divalent hydrocarbon group having 1 to 10 carbon atoms, R4 is a monovalent hydrocarbon group or a halogenated hydrocarbon group having 1 to 10 carbon atoms, X is a hydroxy group or an alkoxy group having 1 to 4 carbon atoms, a is 0 or 1 and b is 0, 1 or 2 with the proviso that al+ b is 0, 1 or 2, or by the formula as disclosed in Japanese Patent Disclosure No. 521113805:

where Rl, R2 and R have the same meaning as in formula (III) above, R4 is a methyl group or a trifluoropropyl group, a is 0 or 1, and 1, m and n are each positive integers, n being not smaller than 100, with the proviso that n/l is from 35 to 2,000 and n/m is from 4 to 40.

(3) A mixture of an organopolysiloxane containing in a molecule at least one mercapto group-containing organosiloxane unit and an organopolysiloxane containing in a molecule at least one vinyl group-containing organosiloxane unit as disclosed in Japanese Patent Application No. 51-91069.

(4) A mixture of an organopolysiloxane containing in a molecule at least one vinyl group-containing organosiloxane unit and an organohydrogenpolysiloxane as disclosed in Japanese Patent Application No. 51-90719.

The above-mentioned organopolysiloxanes or mixtures of organopolysiloxanes may be mixed with photosensitizers, inhibitors for thermal polymerization, fillers, and other conventional ingredients.

The method of the present invention is a method to produce dry planographic printing plates with a high printing durability in the absence of dampening water in a completely dry process. In particular, no transparency of the original iis required when the image patterns are formed on the substrate by the technique of electrophotography using a non-transparent original. Thus, the plate making processes can be curtailed to a great extent, and, in addition, the preferred photocurable silicones used in the present invention are different from the silicones conventionally used in the prior art and have photocurability in the molecules themselves, giving much greater freedom in the formulation of the photosensitive compositions, and the possibility of enhanoing the printing durability of the plate by using an organopolysiloxane having a larger molecular weight.

This invention will now be further illustrated by the following Examples. In the examples Me and Ph denote a methyl group and a phenyl group, respectively, and parts and percentages are all by weight.

Example 1.

A solution of 260 g of dimethyldichlorosilane and 50 g of phenyltrichlorosilane in 1,000 g of toluene was added dropwise to 1,100 g of water kept at 250C so as to cohydrolyze the silanes. The resulting cohydrolyzate was subjected to washing with water, neutralization and dehydration, and a toluene solution containing a copolymeric organopolysiloxane at a concentration of 15% was obtained.

A mixture of 1,000 g of the above-o btained toluene solution and 56 g of 3aminopropyl triethoxysilane was admixed with 0.2 g of dibutyltin dioctoate, to produce a toluene solution of a 3-aminopropyl group-containing organopolysiloxane as the reaction product of the dethanolation condensation, expressed by the following average unit formula: (Me,SiO)200(PhSiO1.)24(H2NC,HSiO1.5)2.2 Into the thus produced toluene solution of 3-aminopropyl group-containing organopolysiloxane was added dropwise a solution of 3.94 g of a-phenylmaleic anhydride in 10 ml of dimethylformamide at 20"C, the amount of the tt-phenylmaleic anhydride being equivalent to the 3-aminopropyl groups. The reaction between the er-phenyl- maleic anhydride and the 3-aminopropyl groups was conducted at 250C for 1 hour and then by heating at llO"C for 4 hours, while removing the condensation water produced by the reaction continuously out of the reaction vessel. As a result, a maleimido group-containing organopolysiloxane expressed by the following average unit formula as identified by the infrared absorption spectral analysis was obtained.

(Me,SiO)200(PhSiO1.5)24(QC,H6SiO'1.5)2., where Q is a phenyl-substituted maleimido group expressed by the following formula:

The organopolysiloxane thus obtained was solid at room temperature, its softening temperature being in the range from 110 to 1200 C.

Then, a 15% toluene solution of the above maleimido group-containing organopolysiloxane was applied over a polypropylene film 9 jtm thick to form a layer of the organopolysiloxane 5 ,am (as dried) thick.

Separately, a saturated polyester sheet 100 Fm thick, one of the surfaces of which was matt, was coated with N-(trimethoxysilylpropyl)ethylenediamine, to form a coating film 0.5 elm thick (as dried) on the matt surface. On this coating film on the polyester sheet was put the above polypropylene film with the surfaces directly contacting each other and the sheets were pressed to form a laminate. On the surface of the polypropylene film of the laminate image patterns were formed by writing manually with a felt pen using a writing ink which is opaque to ultraviolet light, followed by irradiation with ultraviolet light of 365 nm wavelength at an intensity of 80 Wlmz for 45 seconds of exposure time. Thereupon the polypropylene film and the polyester sheet were separated.

Upon separation, it was observed that the photo cured organopolysiloxane layer on the areas exposed to light through the non-image areas on the polypropylene film had been transferred onto the surface of the polyester sheet leaving the uncured organopolysiloxane layer on the polypropylene film corresponding to the unexposed areas.

The thus obtained polyester sheet was mounted as a printing plate in an offset printing press (manufactured by A. B. Dick Co., U.S.A.), and a printing test was performed, without dampening water, to give more than 10,000 printed copies with satisfactory sharpness.

Example 2.

The same procedure as in Example 1 was repeated except that the imagewise exposure to ultraviolet light was conducted through a positive litho film overlaid on the polypropylene film instead of image patterns hand-written on the polypropylene film.

The performance and durability of the thus prepared printing plate were as good as in Example 1.

Example 3.

A mixture of 247 g of a 15% toluene solution, of an a,w-dihydroxydimethylpoW siloxane expressed by the average formula H04-Me2SiO4700H and 60 g of a 15% toluene solution of a hydrolyzate of phenyltrichlorosilane was added to 0.25 g of 3-methacryloxypropyl trimethoxysilane, 0.01 g of dibutyl hydroxytoluene and 0.1 g of dibutyltin dilaurate. The resulting mixture was heated under toluene refiux for 8 hours while continuously removing the condensation water produced. As a result, a toluene solution of a copolymeric organopolysiloxane having a 15% solid content and a viscosity of 28.5 centistokes at 25"C was obtained as the condensation product.

A coating composition was prepared by blending 100 parts of the above-obtained solution of the photopolymerizable organopolysiloxane with 5 parts of 4-trimethylsilyl benzophenone and 900 parts of toluene. The thus prepared coating composition was applied on a polyester film 6 m thick, using a roll coater, to form a coating film 7 lym thick (as dried).

Separately, an aluminum plate 200.elm thick having a matt surface was roll-coated with 3-methacryloxypropyl trimethoxysilane as a primer on the matt surface in a coating amount to give a 0.2 m thick (as dried) coating layer.

Subsequently, the lamination, exposure and separation procedures were performed in the same manner as in Example 1 to finally obtain a planographic printing plate.

The thus prepared printing plate was subjected to the same printing test as in Example 1 and, as a result, more than 15,000 printed copies with satisfactory sharpness were produced.

Example 4.

The same procedure as in Example 3 was repeated except that the means for forming the image patterns on the polyester film opaque to ultraviolet light was the same as in Example 2. The results of a printing test performed with the thus prepared printing plate were as good as in Example 3.

Example 5.

A solution of 258 g of dimethyldichlorosilane and 53 g of phenyltrichlorosilane in 1,022 g of toluene was added dropwise to 1,124 g of water kept at a temperature not exceeding 2S"C for hydrolyzation. The resultant organic solution was washed wlith water, neutralized and dehydrated, to obtain a 15% toluene solution of a copolymeric organopolysiloxane as the hydrolysis product.

To 1,200 g of the above-obtained solution were added 7.4 g of 3-methacryloxypropyl methyldimethoxysilane, 6.0 g of 4dimethylaminoA'trimethoxysi

Claims (16)

**WARNING** start of CLMS field may overlap end of DESC **. Example 5. A solution of 258 g of dimethyldichlorosilane and 53 g of phenyltrichlorosilane in 1,022 g of toluene was added dropwise to 1,124 g of water kept at a temperature not exceeding 2S"C for hydrolyzation. The resultant organic solution was washed wlith water, neutralized and dehydrated, to obtain a 15% toluene solution of a copolymeric organopolysiloxane as the hydrolysis product. To 1,200 g of the above-obtained solution were added 7.4 g of 3-methacryloxypropyl methyldimethoxysilane, 6.0 g of 4dimethylaminoA'trimethoxysilylethyl)- dimethylsilyl benzophenone, 0.1 g of methoxy hydroquinone and 0.4 g of butyltin dioctoate. The resultant solution was heated under toluene reflux for S hours to prepare a toluene solution of a condensation product having a 15 /o solid content and a viscosity of 20.1 centistokes at 25or. A 12 llm thick saturated polyester film was coated with the thus prepared solution of the self-sensitizing photo-curable organopolysiloxane in a coating amount to give a thickness of 7 Fm (as dried). Separately, an aluminum plate 150 Fm thick having a matt surface was rollcoated with 3-methacryloxypropyl trimethoxysilane to form a 0.5 Fm thick (as dried) coating film. The aluminum plate and the polyester film were laminated in the same manner as in Example 1 and the image patterns on the polyester film were formed by a plane paper copying machine (Model 1200, product of Richo Co., Japan), to manufacture the desired printing plate. The printing test undertaken with this printing plate gave results as good as in Example 1. Example 6. The same procedure as in Example 5 was repeated except that the means for forming the image patterns was the same as in Example 2 instead of being formed by the plane paper copying machine. The results of the printing test performed with the printing plate thus obtained were as good as in Example 5. Example 7. The same prcedures as in Examples 5 and 6 were repeated except that the solution of the photopolymerizable organopolysiloxane was prepared by dissolving 100 parts of an organopolysiloxane having a block structure expressed by the following average formula (Me,SiO)400(PhSiO1.5)(CH2 = CH - C3HsSiOi.5)4 and 5 parts of tetra(3-mercaptopropyl) tetramethyl cyclotetrasiloxane and 2 parts of 4,4'-bis(dimethylamino) benzophenone in 900 parts of toluene. The same printing test as in Example 1 was undertaken with a printing plate prepared as in this example. The results were the same as in Example 1. Example 8. The same procedure as in Example 7 was repeated except that the coating solution of the organopolysiloxane was prepared with tetramethyltetrahydrogen cyclotetrasiloxane, instead of tetra(3-mercaptopropyl) tetramethyl cyclotetrasiloxane, in the same amount. The same printing test as in Example 1 was undertaken with the printing plate so prepared. The results were the same as in Example 1. WHAT WE CLAIM IS:-

1. A method for the preparation of a dry planographic printing plate com- prising the following steps (not necessarily in the listed order): (a) coating one surface of a substrate which is transparent to ultraviolet light with an uncured photocurable silicone, (b) bringing the surface of the substrate thus coated into direct contact with an optionally coated surface of a base plate to form a laminate, (c) providing or contacting the other surface of the substrate with an image pattern made of a material which is opaque to ultraviolet light, (d) irradiating the laminate with ultraviolet light from the side of the image pattern, and (e) separating the substrate from the base plate so that a photocured portion of the silicone layer is transferred to the surface of the base plate, and an uncured portion of the silicone layer stays in situ on the surface of the substrate.

2. The method as claimed in claim 1 wherein step (c) is carried out by bringing

a transparency made of a material which is transparent to ultraviolet light and bearing the image pattern of a material which is opaque to ultraviolet light into direct contact with the surface of the substrate.

3. The method as claimed in claim 1 wherein step (c) is carried out by putting a material which is opaque to ultraviolet light imagewise on the surface of the substrate.

4. The method as claimed in claim 1, 2 or 3 wherein the photocurable silicone is an organopolysiloxane containing in its molecule at least one maleimido groupcontaining organosiloxane unit.

5. The method as claimed in claim 1, 2 or 3 wherein the photocurable silicone is an organopolysiloxane expressed by the formula

where R1 is an aromatic ring residue or a heterocyclic ring residue, R2 is a hydrogen atom, halogen atom, cyano group or a monovalent hydrocarbon group having 1 to 4 carbon atoms, R is a divalent hydrocarbon group having 1 to 10 carbon atoms, R4 is a monovalent hydrocarbon group, X is a hydroxy group or a hydrolyzable monovalent atom or group, a is 0 or 1, 0 < lb < 1, 0~c < 3 and Od3 with the proviso that 0 < b + c + doc4.

6. The method as claimed in claim 1, 2 or 3 wherein the photocurable silicone is an organopolysiloxane containing in its molecule at least one acryloxy group-containing organosiloxane unit.

7. The method as claimed in claim 1, 2 or 3 wherein the photocurable silicone is an organopolysiloxane containing at least one organosiloxane unit expressed by the formula

where Rl is a hydrogen atom, phenyl group or a halogenated phenyl group, R2 is a hydrogen -atom or a methyl group, Ri is a divalent hydrocarbon group or a halogenated divalent hydrocarbon group having 1 to 10 carbon atoms, R4 is a monovalent hydrocarbon group or a halogenated hydrocarbon group having 1 to 10 carbon atoms, X is a hydroxy group or an alkoxy group having 1 to 4 carbon atoms, a is 0 or 1 and b is 0, 1 or 2 with the proviso that a + b is 0, 1 or 2.

8. The method as claimed in any preceding claim wherein the coating layer of the photocurable silicone formed on the substrate has a thickness in the range from 2 to 15 Fm as dried.

9. The method as claimed in any preceding claim wherein the base plate is made of a material selected from metals, plastics, resin coated paper, and metal foil-paper laminate.

10. The method as claimed in any preceding claim wherein the surface of the base plate is matt.

11. The method as claimed in any one of claims 1 to 9 wherein the surface of th.e base plate is treated with a primer.

12. The method as claimed in any one of claims 1 to 9 wherein the surface of the base plate is matt and treated with a primer.

13. The method as claimed in any preceding claim wherein the substrate is made of a material selected from polypropylene, saturated polyester, cellulose triacetate, cellulose diacetate, polyvinyl chloride, polyvinylidene chloride, polystyrene, acrylic resins, and polycarbonate resins.

14. The method as claimed in claim 11 or 12 wherein the primer is one selected from vinyl tris(2-methoxyethoxy) silane, 3-glycidoxypropyl trimethoxy silane, N-(trimethoxysilylpropyl) ethylene-diamine, 3-methacryloxypropyl trimethoxy silane, 3aminopropyltriethoxy silane, mixtures thereof, and, partial (co)hydrolyzates thereof.

15. The method as claimed in claim 1, substantially as described in any of the Examples.

16. A planographic printing plate when prepared by a method as claimed in any preceding claim.