US3567445A

US3567445A - Presensitized lithographic plate with two differentially spectrally sensitized layers separated by a novolak resin

Info

Publication number: US3567445A
Application number: US676713A
Authority: US
Inventors: Lawrence Atkinson; Leonard Roy Brooker; Brian Ronald David Whitear
Original assignee: Polychrome Corp
Current assignee: Polychrome Corp
Priority date: 1966-10-28
Filing date: 1967-10-20
Publication date: 1971-03-02
Anticipated expiration: 1988-03-02
Also published as: DE1597781A1; CH495567A; BE705781A; GB1187980A; US3471162A

Abstract

THE APPLICATION DESCRIBES A COMPOSITE PRESENSITISED LITHOGRAPHIC PLATE WHICH COMPRISES A HYDROPHILIC-SURFACE SUPPORT BASE AND COATED THEREON, IN ORDER, A FIRST LIGHTSENSITIVE LAYER WHICH IS AN ADHERENT LIGHT-SENSITIVE LAYER OF THE TYPE WHICH IS CAPABE OF BEING USED AS THE LIGHTSENSITIVE LAYER IN A NEGATIVE-WORKING PRESENSITISED LITHOGRAPHIC PLATE, AN INTERMIEDIATE PROTECTIVE LAYER OR LAYERS, THE LAYER OR IF THERE IS MORE THAN ONE LAYER, THE LAYER WHICH IS NEAREST TO THE SAID FIRST LAYER, BEING A NONHARDENABLE RESIN OF THE CONDENSED PHENOL-CARBONYL COMPOUND TYPE, AND A SECOND LIGHT-SENSITIVE LAYER WHICH IS A SILVER HALIDE EMULSION LAYER.

Description

United States Patent ()flice 3,567,445 Patented Mar. 2, 1971 3,567,445 PRESENSITIZED LITHOGRAPHIC PLATE WITH TWO DIFFERENTIALLY SPECTRALLY SENSI- TIZED LAYERS SEPARATED BY A NOVOLAK RESIN Lawrence Atkinson, Leonard Roy Brooker, and Brian Ronald David Whitear, llford, Essex, England, assignors to Polychrome Corporation, Yonkers, N.Y. No Drawing. Filed Oct. 20, 1967, Ser. No. 676,713 Claims priority, application Great Britain, Oct. 28, 1966,

1 48,491/ 66 Int. Cl. G03f 7/02 US. Cl. 96-33 14 Claims ABSTRACT OF THE DISCLOSURE The application describes a composite presensitised lithographic plate which comprises a hydrophilic-surface support base and coated thereon, in order, a first lightsensitive layer which is an adherent light-sensitive layer of the type which is capable of being used as the lightsensitive layer in a negative-working presensitised lithographic plate, an intermediate protective layer or layers, the layer or if there is more than one layer, the layer which is nearest to the said first layer, being a nonhardenable resin of the condensed phenol-carbonyl compound type, and a second light-sensitive layer which is a silver halide emulsion layer.

This invention relates to presensitised lithographic plates and in particular to such plates which are of camera speed.

The term of camera speed indicates that the presensitised lithographic plate is sufliciently fast in the photographic sense to be used in a camera such as a process camera. Most presensitised lithographic plates at present in use commercially are of contact speed, that is to say that a photographic negative has to be used as an image and this is placed in contact With the plate and the plate is exposed to ultra-violet light through the negative. The consequent need to produce a negative when using contact speed plates increases considerably the preparation needed to produce useable plates.

The usual sensitisers for presensitised lithographic plates and in particular negative working plates are diazo compounds or photosensitive polymers such as polyvinyl cinnamates but the photographic speed of these compounds is too slow for plates sensitised therewith to be of camera speed and thus, as previously stated, most presensitised lithographic plates are of contact speed. The most common sensitiser for photographic material of camera speed is silver halide and presensitised lithographic plates have been produced which are silver halide sensitised. However, such plates are comparatively difiicult to process and their printing life, that is to Say the number of prints which can be taken from them, is not very great.

It is the object of the present invention to provide a presensitised lithographic plate which is of camera speed but which is comparatively easy to process and which is capable of producing a plate of relatively long printing life.

According to the present invention there is provided a composite presensitised lithographic plate which comprises a hydrophilic surface support base and coated thereon, in order, a first layer which is an adherent lightsensitive layer of the type which is capable of being used as the light-sensitive layer in a negative-working presensitised lithographic plate, an intermediate protective layer or layers, this layer or if there is more than one layer, the layer which is nearest to the said first layer,

being a nonhardenable resin of the condensed phenolcarbonyl compound type, and a second layer which is a silver halide emulsion layer.

The support base may be any support base commonly used for presensitised lithographic plates, for example, metal plates such as lightly-grained aluminium plates, plastics plates such as polyethylene terephthalate which has been treated so as to make one surface hydrophilic, paper plates or paper impregnated-with-resin plates.

By light-sensitive layer of the type which is capable of being used as the light-sensitive layer in a negativeworking presensitised lithographic plate is meant a layer which can be coated on to the base and which is sensitive to ultra-violet light and when exposed to ultra-violet through a negative in the exposed areas undergoes a chemical reaction which renders the exposed areas insoluble. The layer is developed by removing the unexposed unchanged areas thus leaving the insoluble areas which form a positive image of the original and exposing the hydrophilic base. The insoluble areas are oleophilic either due to the fact that the original layer is oleophilic or because on exposure to light the layer becomes oleo philic. A large number of such photosensitive layers have been proposed and used. Exemplary of such layers are (a) light-sensitive polymers such as polyvinyl cinnamate, polyvinyl-phosphonic monoesters of chalcones, styrene/ maleic anhydride copolymers containing a cinnamoyl or chalcone group, vinyl polymers containing an aromatic azide group, (b) polymers together with a light-sensitive compound which hardens the polymers when exposed to light such as gelatin and bichromate, gelatin and diazo compounds, polyacrylate and diazo compounds, vinyl polymers and p-hydroxybenzal acetophenone, styrene/maleic anhydride copolymers and diazo fiuorborate, (c) photopolymerisable mixtures such as acrylamide plus N,N -methylene-bis-acrylamide plus a catalyst, (d) polymeric diazonium compounds such as the condensate of 4-diazodiphenylamine and formaldehyde, and (e) lightsensitive compounds which can be coated directly on to the support base without any hardenable polymers such as diazo compounds, diazostilbenes, naphthoquinone diazides, methylene fluorene sulphonic acid and cinnamoyl furfurylidene. These latter compounds are usually coated on to the support together with a nonhardenable resin such as novolak resin to prevent them crystallizing on the support.

The preferred photosensitive layers of the first layer are diazo-resin layers and in particular the condensation product of 4-diazodiphenylamine and formaldehyde and lightsensitive polymers containing an unsaturated acyl group such as polyvinyl cinnamate.

The intermediate protective layer or layers are present to prevent the first layer hardening the binder of the silver halide emulsion and to protect the first layer during the processing of the silver halide emulsion.

Particularly useful resins of the condensed phenol-carbonyl compound type are the novalak resins which are condensation products of phenol and formaldehyde. These resins have no reactive groups and they are not photopolymerisable or hardenable by the light-decomposition products of the first layer. The presence of an intermediate layer which comprises a resin of the phenolcarbonyl compound type is a particular feature of the present invention as most of the resins and other polymeric substances tried hardened onto the exposed first layer. Other polymeric substances tried were not filmforming unless plasticisers were present and these plasticisers were found to effect the first layer adversely. Other advantages of using a phenol-carbonyl compound resin are that silver halide emulsions adhere directly thereon and the resins are freely soluble in a number of solvents, e.g., aqueous alkali, ketones and alcohols. However in another embodiment of the invention the intermediate layers may constitute a stripable assembly, in this case the silver halide emulsion is coated on to a support membrane and this membrane is anchored to the first layer by a layer of the phenol carbonyl compound resin. The preferred emulsion support membrane is polyvinyl alcohol. A particularly useful polyvinyl alcohol is Elvanol 73-125 made by the Du Pont Company of the USA.

It is preferred that a gelatino silver halide emulsion is used but other binders for the silver halide such as polyvinyl alcohol or polyvinyl pyrrolidone may be used. Any type of silver halide emulsion may be used depending on the original to be reproduced. The most usual original is a positive photographic print, very often in an enlarger, for this a high contrast silver chloride or chlorobromide emulsion is the most suitable. A direct screened image can be produced by inserting a screen between the original and the plate. For this purpose a lith type emulsion is preferred. The silver halide emulsion may he colour sensitised to enable colour separations to be prepared.

According to another aspect of the present invention there is provided a method of producing a useable printing plate from the presensitised lithographic plate hereinbefore described which comprises exposing the plate to an original, developing the resultant latent image in the silver halide layer, fixing out or stabilising the unexposed silver halide, exposing the plate to an all-over strong light and then removing the silver halide emulsion and the intermediate layer or layers and developing the resultant positive image of the original in the first layer and removing the unexposed light-sensitive material in the first layer.

It is preferred that strong light is ultra-violet light. The method of removing the silver halide and intermediate layer or layers depends on the nature of the intermediate layer or layers, and the method of developing the image in the first layer and removing unexposed photosensitive material therefrom depends on the sensitiser used in the first layer. For example, if the intermediate layer is a single layer of a novolak resin it is possible to remove the silver halide emulsion layer and the intermediate layer in dilute alkali solution or the silver halide emulsion is first removed in hot water, dilute alkali or organic solvent solution and the intermediate layer is then removed in dilute alkali. However, if the first layer is diazo compound sensitised, dilute alkali reacts with the unexposed diazo. In this case, it is preferred to add a coupler, which is capable of reacting with a diazo compound to form a dye, to the dilute alkali solution. The coupler reacts with the unexposed diazo compound to form a dye. This dye, which constitutes a negative image of the original is removed either by subsequent treatment with an organic solvent, such as the organic solvent used in an image lacquering solution or if the coupler which is used contains suitable solubilising groups the dye formed is soluble in dilute alkali and is thus removed in the dilute alkali solution. Alternatively, in some cases it is possible to remove the silver halide emulsion layer, the intermediate layer and the unexposed areas of the first layer by treatment with an organic solvent such as the solvent used in a combined plate cleaner lacquering solution, e.g., cyclohexanone.

On the other hand if the intermediate layer or layers constitute a stripable assembly this assembly can be removed by dissolving the stripable layer in, for example, dilute alkali or an organic solvent and then physically removing the emulsion support membrane with the silver halide coated thereon. Alternatively the emulsion support membrane can be removed by using physical means alone.

The first layer is developed by treating it with water, dilute alkali, dilute acid or an organic solvent to remove the unexposed areas. The choice of solvent depends on the composition of the first layer. Sometimes as hereinbefore described this development step takes place at the same time as the removal of the intermediate layer or layers.

It is preferred that the image is lacquered to increase its oleophilic properties and thus prolong the useable life of the plate.

Thus using the composite presenitised lithographic plate of the present invention a positive printing plate can be produced from an original by exposing the presensitised plate in a camera, the silver halide emulsion being fast enough for this purpose. A silver image is formed which acts as a negative in contact with the light-sensitive first layer. This layer is only fast enough to be affected when exposed by the ultra-violet or other strong light.

The silver halide emulsion layer and intermediate layer are easily removed from the first layer and thus the processing of the composite presensitised lithographic plate of the present invention can be carried out without complicated apparatus.

In another embodiment of the present invention wherein the support base is of transparent material, e.g., when it is cellulose triacetate or polyethylene terephthalate there has been found a process whereby a laterally correct image may be obtained.

According to this aspect of the present invention there is provided a method of producing a useable printing plate from the composite presensitised printing plate hereinbefore described wherein the support base is transparent, which comprises exposing the suitably sensitized silver halide emulsion layer of the plate to an original through the noncoated support base with light of a wave-length to which the first layer is not sensitive, developing the resultant latent image in the silver halide layer, stabilising or fixing out the unexposed silver halide, exposing the plate to an all-over strong light on the silver image side of the base (thus exposing the first layer through the silver image), and then removing the silver halide emulsion and the intermediate layer or layers and developing the resultant positive image of the original in the first layer and removing the unexposed light-sensitive material in the first layer.

It is preferred that the strong light is ultra-violet light.

By use of this method of exposure and subsequent processing of the plate a laterally correct image is obtained without having to use a process camera with an image converter. As the silver halide emulsion is so much faster than the first layer the short initial exposure through the first layer does not cause any significant photochemical reaction therein.

The term suitably-sensitised means that the sensitivity of the silver halide layer is extended so that it is beyond the light absorption of the first layer, e.g., diazo-resin layers absorb all the ultra-violet light and a portion of the blue light.

The following examples will serve to illustrate the invention.

EXAMPLE 1 A negative working faintly grained aluminium plate presensitised with a polymeric diazonium resin was supercoated with a 2% w./v. solution of a novolak resin (believed to be of molecular weight approximately 1200) in isopropyl alcohol. The smooth coating was dried in a Whirler machine.

A high contrast silver halide emulsion was coated thereon and the even coating subsequently dried. The composite plate was exposed in a camera to a positive image, the latent silver image so obtained, developed in a metal hydroquinone based developing solution to a high density black, and the nonexposed portions were made light insensitive in a solution of ammonium thiocyanate. There was thus obtained a negative silver image of the original.

The plate was given a short exposure to ultra-violet light and the plate processed as follows. The silver emulsion and protective interlayer were removed by treatment with a solution of sodium hydroxide (0.5 normal) con taining 0.25% W./V. benzoylacetanilide and ethyl alcohol, which at the same time coupled with the unexposed diazo material to form an azo dye. There was thus produced a hardened positive image of the original and also a negative image composed of azo dye. The plate was then insensitive to light.-The azo dye was removed and the image protected by lacquering with an emulsion containing essentially an organic solvent, cyclohexanone, an epoxy resin, aqueous gum arabic solution and an anionic wetting agent. The azo dye dissolved in the organic phase and the resin lacquered the ink receptive hardened diazo image. The plate was washed with water and placed on an offset printing press, from which prints of a high quality were obtained. Press life of the plate was 20,000 copies.

EXAMPLE 2 The negative working aluminium presensitised plate was coated and exposed as described in Example 1. The silver emulsion and protective interlayers were removed by treatment with a solution of sodium hydroxide (0.5 normal) containing 0.5% w./v. 2-hydroxy naphthalene-3,6-disulphonic acid sodium salt, which at the same time coupled with the unexposed diazo layer to form an azo dye. There was thus produced a hardened positive image of the original and also a negative image composed of azo dye. The negative image was removed by gentle rubbing with dilute alkali and the plate washed with water and placed on an offset printing press. The image was inked-up and from the plate there was obtained positive prints.

EXAMPLE 3 The lithographic plate was prepared and processed as described in Example 2. In this example, however, the image was protected by lacquering with the resin-solvent mix as described in Example 1. Prints were obtained in the usual way.

EXAMPLE 4 A fairly deeply grained aluminium-alloy plate presensitised by a coating of a formaldehyde-diazo diphenylamine resin was supercoated with a 2% W./v. solution of a novolak resin in isopropyl alcohol and the product whirled to a smooth dry finish. The plate was again supercoated with a high contrast silver halide emulsion which was carefully dried. The plate was exposed to a positive original, and a negative silver image obtained by the usual processing conditions, then exposed to ultra- 'violet light.

The silver emulsion, protective interlayer, unexposed diazo resin layer, were all removed and the image given a protective'lacquer by the use of a single suspensionemulsified lacquer, which comprised benzylacetate, cyclohexanone, epoxy resins, red pigment gum arabic in aqueous solution, citric acid and nonionic and anionic wetting agents. The plate was then washed with water, and retreated with the above lacquer wash mix (the silver emulsion and protective interlayer dissolve in the organic solvents, the resins lacquer the ink receptive exposed diazo layer and the various solvents, citric acid and wetting agents remove the unexposed diazo portions and clean the nonimage areas of the grained plate).

The plate thus produced was placed on an off-set printing press and very good quality prints were obtained. The press life of this plate was about 50,000 copies.

EXAMPLE 5 A grained aluminium plate suitable for lithography was coated with a solution of polyvinyl cinnamate in acetone and allowed to dry, then supercoated with a 2% solution of a novolak resin in isopropanol, by submersion in a dish containing the solution, draining and allowing to air dry. The plate was further supercoated with a high contrast silver halide emulsion which was carefully dried. The plate was exposed to a positive original and a negative silver image obtained by development in a metalhydroquinone developer, fixing in a sodium thiosulphate solution and washing to remove the stabilised silver salts, and dried.

The plate was given a short exposure to ultra-violet light and processed as follows. The silver emulsion and protective interlayer were removed and the image given a protective lacquer by the use of a single suspension emulsified lacquer which comprised organic solvents, cyclohexanone and 2-methoxybutylacetate, epoxy resins, gum arabic, red pigment, phosphoric acid and nonionic wetting agents. The plate was washed with water and retreated with the lacquer. The plate thus produced was placed on an offset press and good quality prints obtained from it.

EXAMPLE 6 A plate was prepared as in Example 5 except the polyvinyl cinnamate was replaced by a solution of partially hydrolysed polyvinyl acetate 10% and ammonium dichromate 3.5% in water. The dried coating was supercoated with novolak resin from isopropanol and the plate coated with a silver halide emulsion and processed as previously described.

EXAMPLE 7 A transparent support base of polyethylene terephthalate was suitably subbed and coated with cellulose acetate and the surface hydrolysed with potassium hydroxide solution, treated in an acid stop bath, washed and dried.

The support base thus produced was sensitised with the condensation product of formaldehyde and 4-diazodiphenylamine using a 2% solution in water and dried. The plate was supercoated witha novolak resin (2% solution in isopropanol) and dried. It was further coated with a high contrast silver halide emulsion and dried. The silver halide layer was exposed to a positive original through the transparent base and the latent image developed, fixed and washed in the usual way.

The plate was given an overall exposure to ultra-violet light through the negative silver layer and the plate processed as follows.

The silver emulsion and protective interlayer were removed by treatment with a single suspension emulsified lacquer consisting of cyclohexanone, epoxy resins, red pigment, gum arabic in aqueous solution, citric acid and nonionic and anionic Wetting agents. The plate Was washed with Water and relacquered with the above mixture, and again washed with water. When placed on an offset printing press good quality prints were obtained from it.

EXAMPLE '8 A grained aluminium plate suitable for lithography was sensitised by coating with a diazo resin (the condensate of formaldehyde with 4-diazodiphenylamine) from a 2% aqueous solution and dried, then supercoated with a solution of a novolak resin (2% in isopropanol) and redried.

A stripable layer was coated over the previous layers and was obtained from a 4% solution of a polyvinyl alcohol in water and dried. A high contrast silver halide emulsion containing a developing agent (e.g., hydroquinone) was coated thereon and dried. The silver halide layer was exposed to a positive original and the latent silver image developed in an aqueous alkaline solution and the unexposed portion stabilised with a thiocyanate solution containing an aluminium salt, and dried. The plate was given a short exposure to ultra-violet light and the silver halide layer removed by peeling off the stripable layer. The exposed plate was processed by treating with a combined plate cleaner-lacquer consisting of epoxy resins, cyclohexanone gum arabic in aqueous solution, citric acid, red pigment and anionic and nonionic wetting agents. The plate was washed with water and placed on an offset printing press. Good quality prints were obtained from it.

We claim as our invention:

1. A composite presensitised lithographic plate which comprises a hydrophilic-surface support base and coated thereon, in order, a first light-sensitive layer which is an adherent ultra violet light-sensitive layer of the type which when exposed to ultra-violet light through a negative n the exposed areas undergoes a chemical reaction which renders the said exposed areas insoluble in a developer liquid which subsequently is used to develop the layer by removing the unexposed areas of the layer thus leaving the insoluble areas which form a positive image and exposing the underlying hydrophilic base, the said insoluble areas being oleophilic either because the layer is initially oleophilic or because on exposure to ultra-violet light the layer becomes oleophilic, an intermediate protective layer which is an alkali soluble novolak resin layer and .a second light-sensitive layer which is a silver halide emulsion layer.

2. A composite presensitised lithographic plate according to claim 1 wherein the first layer comprises a diazoresin layer.

3. A composite presensitised lithographic plate according to claim 2 wherein the diazo-resin layer is the con densation product of 4-diazodiphenylamine and formaldehyde.

4. A composite presensitised lithographic plate accord ing to claim 1 wherein the first layer comprises a lightsensitive polymer containing an unsaturated acyl group.

5. A composite presensitised lithographic plate according to claim 4 wherein the light-sensitive polymer con= taining an unsaturated acyl group is polyvinyl cinnamate.

6. A composite presensitised plate according to claim 1 wherein the hydrophilic-surface support base is composed of transparent material.

7. A process for the preparation of a printing plate from a composite presensitised lithographic plate which comprises a hydrophilic-suriace support base and coated thereon, in order, a first light-sensitive layer which is an adherent ultra-violet light sensitive layer of the type which when exposed to ultra-violet light through a negative in the exposed areas undergoes a chemical reaction which renders the said exposed areas insoluble in a developer liquid which subsequently is used to develop the layer by removing the unexposed areas of the layer thus leaving the insoluble areas which form a positive image and exposing the underlying hydrophilic. base, the said insoluble areas being oieophilic either because the layer is initially oleophilic or because on exposure to ultraviolet light the layer becomes oleophilic, an intermediate protection layer which is an alkali soluble novolak resin layer and a second light-sensitive layer which is a silver halide emulsion layer, which comprises exposing the silver halide layer of the presensitised plate to an original, developing the resultant latent. image, stabilising or fixing out the unexposed silver halide, exposing the plate to ultra-violet light and then removing the silver halide emulsion and the intermediate layer and developing the resultant positive image of the original in the first layer by removing the unexposed light-sensitive material therefrom.

8. A process according to claim 7 wherein the first layer comprises a diazo resin, which comprises removing the novolak resin layer and the exposed silver halide layer by treatment with aqueous alkali solution which comprises a diazo cc-iour coupler.

9. A process according to ciaim 7 wherein the first layer comprises either a diazo resin or a polyvinyl cinnamate, which comprises removing the novolak resin layer and the exposed silver halide layer and developing the image in the said first layer by treating the exposed plate with a ketone.

10. A process according to claim 9 wherein the ketone is cyclohexanone.

11. A process for the preparation of a printing plate from a composite presensitised lithographic piate which comprises a transparent hydrophilic-surface support base and coated thereon, in order, a first light-sensitive layer which is an adherent ultra-violet light sensitive layer of the type which when exposed to ultra-violet light through a negative in the exposed areas undergoes a chemical reaction which renders the said exposed areas insoluble in a developer liquid which subsequently is used to develop the layer by removing the unexposed areas of the layer thus leaving the insoluble areas Which form a p sitive image and exposing the underlying hydrophilic base, the said insoluble areas being c-ieophilic either because the layer is initially oleophilic or because on exposure to ultra-violet light the layer becomes oleophilic, an intermediate protective layer which is an alkali soluble novolak resin layer and a second light-sensitive layer which is a silver halide emulsion layer, which comprises exposing the suitably sensitised silver halide emulsion layers of the plate to an original through the noncoated side of the support base with light of wavelength to which the first layer is not sensitive, developing the resultant siiver halide image, stabilising or fixing out the unexposed silver halide, exposing the plate to ultra-violet light on the silver image side of the base (thus exposing the first layer through the silver image) and then removing the silver halide emulsion and the intermediate layer and developing the resultant positive image of the original in the first layer by removing the unexposed light-sensitive material there- Irom.

12. A process according to claim 11 wherein the first layer comprises a diazo resin, which comprises removing the novolak resin layer and the exposed silver halide layer by treatment with aqueous alkali Solution which comprises a diazo colour coupler.

13. A process according to claim 11 wherein the first layer comprises either a diazo resin or a polyvinyl cinnamate, which comprises removing the novolak resin layer and the exposed silver halide layer and developing the image in the said first layer by treating the exposed plate with a ketone.

14. A process according to claim 13 wherein the ketone is cyclohexanone.

References Cited UNITED STATES PATENTS 1,912,693 6/1933 Cornell 9683X 2,140,648 12/1938 Nadeau 959 2,207,388 7/1940 Kujawa 958 3,313,626 4/1967 Whitney no 96-33 NORMAN G. TORCHIN, Primary Examiner W. H. LOUIE, JR., Assistant Examiner US. Cl. 9668,