GB1583329A - Process for preparing printing forms and forms produced thereby - Google Patents

Abstract

Method of producing planographic printing forms by irradiating a recording material having a base made of anodised aluminium having at least 3 g of oxide per m<2> and of a recording layer containing a light-curable diazo compound and an amine resin, with laser radiation and washing out the unirradiated layer regions.

Description

(54) PROCESS FOR PREPARING PRINTING FORMS, AND FORMS PRODUCED THEREBY (71) We, HOECHST AKTIENGESELL- SCHAFT, a Body Corporate organised according to the laws of the Federal Republic of Germany, of 6230 Frankfurt/Main 80, Postfach 80 03 20, Federal Republic of Germany, 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 a process for the preparation of a planographic printing form, wherein an aluminum support covered by a recording layer comprising a diazonium com pound is image-wise irradiated with a laser beam, whereby insoluble image areas are produced in the recording layer. The invention also relates to printing forms produced by the process.

U.S. Patent No. 3,664,737 discloses a printing plate comprising a W-light sensitive layer, pre ferably a diazo layer, on an aluminum support and which is irradiated with a laser beam.

German Patent No. 2,448,325 and German Offenlegunsschrift No. 25 43 820 (British Application No. 40404/76 (Serial No.

1 ,563 ,829)) disclose processes for the manufac ture of a printing plate by irradiating a non-light sensitive recording layer with a laser beam, the irradiated areas of the recording layer being made permanently oleophilic or, if an already oleophilic layer is used, insoluble in a suitable developer liquid. Anodized aluminum is among the supports mentioned as suitable.

It has been suggested in German Patent Application P 27 25 308 to use a laser beam for imaging a presensitized printing plate which comprises a support of optionally anodized aluminum and a light-sensitive layer containing a negative-working diazonium compound.

Application No. 7190/77 (Serial No.

1,578,591) relates to a process for the prepara tion of a planographic printing form wherein a printing plate comprising a support of ano dically oxidized aluminum carrying a recording layer disposed on the oxide layer is image-wise irradiated with a laser-beam, thus rendering the irradiated portions of the recording layer oleophilic and/or insoluble, and the non irradiated portions of the recording layer are then removed, where desired or necessary, by washing with a developer liquid, in which a sup port is used which has an oxide layer weighing at least 3 grams per square meter.

The present invention is concerned with improving the sensitivity towards a laser beam of the light-sensitive printing plate of Applica tion No.7190/77 (Serial No. 1,578,591) and/or increasing the length of the printing runs of printing forms prepared from it.

The present invention provides a process of the preparation of a planographic printing form wherein a printing plate comprising a support having thereon a recording layer comprising a light-hardenable diazo compound and an amino resin is image-wise irradiated with a laser beam to render the irradiated portions of the recording layer insoluble in a selected developer and, where desired or necessary, the non-irradiated portions of the recording layer are then removed by treatment with said developer, the support comprising aluminium, the or each supporting surface of which has been anodically oxidized so that the oxide layer weighs at least 3 grams per square meter. A light-hardenable compound is a compound that is hardenable by incoherent actinic light. Such a compound is of course also hardenable by coherent actinic light (laser light).

Preferred negative-working, light-hardenable diazo compounds are diazonium salt condensa tion products, also called diazo resins. Suitable condesnation products are obtained by conden sation of aromatic diazonium salts, preferably optionally substituted diphenylamine-4 diazonium salts, with active carbonyl compounds preferably formaldehyde, in a strongly acid medium.

Products of this type have been disclosed, for example, in German Patents No. 1,214,086 and No. 1,292,001. Particularly preferred are mixed condensation products containing dia zonium salt units and units of non-light-sensitive second components cable of condensation, such, for example, as aromatic amines, phenols, thiophenols, phenol ethers, aromatic thioethers, aromatic hydrocarbons, aromatic heterocyclic compounds, and organic acid amides.

Condensation products of this type are disclosed in U.S. Patents Nos. 3,849,392 and 3,867,147. Negative-working diazo compounds of the p-benzoquinone diazide type and amino quinone diazides, such as those described, for example, in German Patent No. 1,104,824, are also suitable.

As amino resins, amino-formaldehyde resins are preferred which are obtained by condensation of formaldehyde with urea, urethanes (carbamide acid esters), aniline, or melamine.

Such condensation products are known and are commercially available in many forms. Suitable compounds are described , e.g., in "Kunststoff Handbuch" (Plastics Manual), vol. X, published by Vieweg and Becker, Carl Hauser Verlag, Munich,1968.

For the preparation of the laser-sensitive recording layer, the amino resin is added to a solution which contains a diazo compound. The quantity of resin added may vary within wide limits. As a rule, it ranges from 0.1 to 10 parts by weight of resin per part by weight of the diazo compound used. Particularly favorable results are obtained with a resin addition in the range from about 0.6 to 6.0 parts by weight per part by weight of the diazo compound.

The support may be prepared in any suitable manner, many of which are known per se. Prior to anodic oxidation, the aluminum is preferably roughened by mechanical, chemical, or electrochemical means. A combination of electrolytic roughening with anodic oxidation has been found to be particularly advantageous for a continuous process. Roughening is advantageously performed in a bath containing a dilute aqueous mineral acid, e.g. hydrochloric acid or nitric acid, with the simultaneous application of direct or alternating current.

Anodization may be carried out in an aqueous acid bath, for example in a sulphuric acid or phosphoric acid bath, preferably with simultaneous application of direct current, current densities and anodizing times being so adjusted that an oxide layer is obtained of a thickness corresponding to at least 3 grams per square meter. The upper limit for the layer thickness is not critical, but normally no further improvement is obtained by providing a layer weighing more than 15 grams per square meter. If the layer is substantially thicker, i.e. above about 3p grams per square meter, there is the additional risk that cracks will form in the oxide layer when it is bent.

Oxide layers weighing between about 5 and 12 grams per square meter are preferred.

After irradiation with a laser beam, the light.

sensitive diazo layer is advantageously developed with aqueous alkaline or acid solutions, or with water. A lacquer emulsion or a lacquer of the type used for planographic printing plates may also be used. The lacquer emulsion or lacquer may be applied, in one operation, for development and lacquering, or after development with an aqueous solution or water.

An appropriately powered relatively shortwave laser, for example an argon or krypton laser may be used for the process of the present invention, having a radiation output from about 0.5 to about 2.5 watts in the UV range, or of about 1 to 25 watts in the visible range, depending on the type of mirror used. A dyestuff, e.g., a rhodamine, triphenyl methane dye, such as crystal violet, astrazon orange, eosin, or methylene blue, which absorbs strongly within the emitted range and has a sensitizing effect, may be added to the layer used in the process according to the invention. The irradiated areas are oleophilic and insoluble in a selected devel piper.

The laser beam may be controlled by means of a programmed lined and screen movement.

Any process and device for controlling a laser beam by means of computers and bundling, modulation, or deflection of laser beams may be used in the process of the present invention such processes are described in various publications, for example German Offenlegungsschrifte No. 23 18 133 (pages 3 et seq.), No. 23 44 233 (Pages 8 et seq.), and in U.S. Patents No.

3,751,587, No. 3,745,586, No. 3,747,117, No.

3,475,760, No. 3,506,779 and No. 3,664,737.

Preferably, the layer is image-wise irradiated with an argon laser of between 1 and 10 watts.

Speeds of up to and even exceeding 110 m per second can be achieved, depending on the sensitivity and absorption capacity of the layer used. By focussing the laser beam with a lens, hardened spots of less than 50 urn diameter may be produced on the layer.

By the process according to the invention, a very durable oleophilization of the surface is achieved, so that long runs can be printed.

Further, the recording materials used are distinguished in that their sensitivity towards laser beams is especially high.

The following examples illustrate the invention. Unless otherwise stated, all percentages are by weight. The relationship to parts by weight to parts by volume is that of the gram to the milliliter.

EXAMPLE 1 A roll of bright rolled aluminum is electrolytically roughened in a continuous process, and is then anodically oxidized for 75 seconds, at 40"C with a 9A/dm2 direct current in an aqueous bath containing 150 grams of sulphuric acid per liter. An anodic oxide layer weighing 5 grams per square meter is thus produced. The layer is then treated for 30 seconds, at 700C, with a 0.25 per cent aqueous solution of polyvinyl phosphonic acid and dried. The plate is then sensitized with a solution containing 0.4 per cent of a diazo polycondensate (obtained by condensing 1 mole of 3-methoxy-diphenylamine4-diazonium sulphate with 1 mole of 4A'-bis-methoxymethyl-diphen0yl ether in 85 per cent phosphoric acid at 40 C and separating the reaction product in the fonn of the methane sulphonate), 0.72 per cent of a highly reactive, unplasticized urea-formaldehyde condensation resin with a dynamic viscosity in a 60 per cent solution in isobutanol of about 2500 mPas (cP) at 20"C and an acid number below 2 (resin I), and 0.4% of Rhodamine 6 GDN (Color Index No. 45,160) dissolved in ethylene glycol monoethyl ether.

The plate is irradiated with an argon laser which emits in the W range, mainly at wave lengths 363 and 351 nm, the radiation output being 0.8 watt and the recording speed being 100 m/sec. The areas of the layer not struck by the laser beam are decoated with an aqueous solution containing 0.65 per cent of sodium metasilicate 9 H2 0 and 3.8 per cent of benzyl alcohol. The irradiated, hardened areas are oleophilic and accept greasy ink. More than 85,000 copies of good quality can be printed in an offset printing machine.

Similar results are obtained if the above mentioned urea resin is replaced by the same quantity of one of the following unplasticized urea resins: Resin II acid number below 3; dynamic vis cosity in a 65 per cent solution in butanol/xylene, at 200 C, of approxi mately 6,000 mPas (cP).

Resin III acid number below 3, dynamic vis cosity in a 60 per cent solution in isobutanol, at 200 C, of approxi mately 650 mPas (cP).

EXAMPLE 2 An aluminum plate with an anodic oxide layer weighing 3 grams per square meter, which has been pre-treated with polyvinyl phosphonic acid, is coated with a solution containing 1.0 per cent of the diazo polycondensate used in Example 1, but isolated in the form of the mesitylene sulphonate, 1.8 per cent of Resin II, and 0.4 per cent of crystal violet dissolved in ethylene glucol monomethyl ether.

The plate is irradiated with an argon laser emitting in the visible range, mainly at wave lengths 488 and 514 nm, and having a radiation output of 5 watts and a recording speed of 50 m per second. The areas of the layer not struck by the laser beam are decoated with an aqueous solution containing 6 per cent of magnesium sulphate .7 He 0, 20 per cent of n-propanol, and 0.7 per cent of a non-ionogeni wetting agent (alkylphenol-polyglycol ether). The irradiated areas accept greasy ink in an offset printing machine and allow long printing runs.

EXAMPLE 3 An aluminum plate having an anodic oxide layer weighing 10 grams per square meter is coated with a solution of the following composition: 2 p.b.w. of 1-(4'-methyl-benzene-sulfonyl- imino)-2(2", 5 "-dimethyl-phenylamino- sulfonyl)-benzo.quinone-( 1 ,4)-diazide-(4) and 0.7 p.b.w. of an unplasticized, highly reactive melamine resin with a dynamic viscosity in a 50% solution in ethanol at 20 C of about 450 mPas (cP) and an acid number below 1 (Resin IV) in 80 p.b.w. of ethyleneglycol monomethyl ether and 20 p.b.w. of butyl acetate.

The material is irradiated with a Kryptonion-laser emitting in the W-range, mainly at wave lengths 406 and 423 nm, which has a radiation output of 0.9 watt and a recording speed of 80 m per second. Then the plate is decoated with a solution of 1.3 per cent of anhydrous sodium silicate and 1.2 per cent of anhydrous trisodium phosphate in water.

Long printing runs can be obtained.

EXAMPLE 4 An aluminum plate with an anodic oxide layer weighing 5 grams per square meter is coated with a solution of 0.4 part by weight of a crude condensation product of paraformal- dehyde and diphenylamine-4-diazonium chloride, (prepared in 85% phosphoric acid), 1 part by weight of a liquid urethane resin obtained from butylurethane and formaldehyde and having a density of 1.1 at 20 C and a dynamic viscosity at 20 C of from 6 to 20 mPas (cP), and 0.2 gram of Astrazon Orange (C.I. 48,040) dissolved in a mixture of 50 parts by weight of tetrahydrofuran, 40 parts by weight of ethyleneglycol monomethyl ether, and 10 parts by weight of butyl acetate.

The plate is irradiated with an argon laser emitting in the visible range, which has a radiation output of 5 watts and a recording speed of 60 m per second, and is then decoated with water.

WHAT WE CLAIM IS: 1. A process for the preparation of a planographic printing form wherein a printing plate comprising a support having thereon a recording layer comprising a light-hardenable diazo compound and an amino resin is imagewise irradiated with a laser beam to render the irradiated portions of the recording layer insoluble in a selected developer and, where desired or necessary, the non-irradiated portions of the recording layer are then removed by treatment with said developer, the support comprising aluminium, the or each supporting surface of which has been anodically oxidized so that the oxide layer weighs at least 3 grams per square meter.

2. A process as claimed in Claim 1, wherein the oxide layer weighs from 5 to 12 grams per square meter.

3. A process as claimed in Claim 1 or Claim 2, wherein the recording layer comprises 0.6 to 6 parts by weight of the amine resin per part by weight of the diazo compound.

4. A process as claimed in any one of Claim 1 to 3, wherein there is used a printing plate, the or each supporting surface of which, prior

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (9)

**WARNING** start of CLMS field may overlap end of DESC **. 4A'-bis-methoxymethyl-diphen0yl ether in 85 per cent phosphoric acid at 40 C and separating the reaction product in the fonn of the methane sulphonate), 0.72 per cent of a highly reactive, unplasticized urea-formaldehyde condensation resin with a dynamic viscosity in a 60 per cent solution in isobutanol of about 2500 mPas (cP) at 20"C and an acid number below 2 (resin I), and 0.4% of Rhodamine 6 GDN (Color Index No. 45,160) dissolved in ethylene glycol monoethyl ether. The plate is irradiated with an argon laser which emits in the W range, mainly at wave lengths 363 and 351 nm, the radiation output being 0.8 watt and the recording speed being 100 m/sec. The areas of the layer not struck by the laser beam are decoated with an aqueous solution containing 0.65 per cent of sodium metasilicate 9 H2 0 and 3.8 per cent of benzyl alcohol. The irradiated, hardened areas are oleophilic and accept greasy ink. More than 85,000 copies of good quality can be printed in an offset printing machine. Similar results are obtained if the above mentioned urea resin is replaced by the same quantity of one of the following unplasticized urea resins: Resin II acid number below 3; dynamic vis cosity in a 65 per cent solution in butanol/xylene, at 200 C, of approxi mately 6,000 mPas (cP). Resin III acid number below 3, dynamic vis cosity in a 60 per cent solution in isobutanol, at 200 C, of approxi mately 650 mPas (cP). EXAMPLE 2 An aluminum plate with an anodic oxide layer weighing 3 grams per square meter, which has been pre-treated with polyvinyl phosphonic acid, is coated with a solution containing 1.0 per cent of the diazo polycondensate used in Example 1, but isolated in the form of the mesitylene sulphonate, 1.8 per cent of Resin II, and 0.4 per cent of crystal violet dissolved in ethylene glucol monomethyl ether. The plate is irradiated with an argon laser emitting in the visible range, mainly at wave lengths 488 and 514 nm, and having a radiation output of 5 watts and a recording speed of 50 m per second. The areas of the layer not struck by the laser beam are decoated with an aqueous solution containing 6 per cent of magnesium sulphate .7 He 0, 20 per cent of n-propanol, and 0.7 per cent of a non-ionogeni wetting agent (alkylphenol-polyglycol ether). The irradiated areas accept greasy ink in an offset printing machine and allow long printing runs. EXAMPLE 3 An aluminum plate having an anodic oxide layer weighing 10 grams per square meter is coated with a solution of the following composition: 2 p.b.w. of 1-(4'-methyl-benzene-sulfonyl- imino)-2(2", 5 "-dimethyl-phenylamino- sulfonyl)-benzo.quinone-( 1 ,4)-diazide-(4) and 0.7 p.b.w. of an unplasticized, highly reactive melamine resin with a dynamic viscosity in a 50% solution in ethanol at 20 C of about 450 mPas (cP) and an acid number below 1 (Resin IV) in 80 p.b.w. of ethyleneglycol monomethyl ether and 20 p.b.w. of butyl acetate. The material is irradiated with a Kryptonion-laser emitting in the W-range, mainly at wave lengths 406 and 423 nm, which has a radiation output of 0.9 watt and a recording speed of 80 m per second. Then the plate is decoated with a solution of 1.3 per cent of anhydrous sodium silicate and 1.2 per cent of anhydrous trisodium phosphate in water. Long printing runs can be obtained. EXAMPLE 4 An aluminum plate with an anodic oxide layer weighing 5 grams per square meter is coated with a solution of 0.4 part by weight of a crude condensation product of paraformal- dehyde and diphenylamine-4-diazonium chloride, (prepared in 85% phosphoric acid), 1 part by weight of a liquid urethane resin obtained from butylurethane and formaldehyde and having a density of 1.1 at 20 C and a dynamic viscosity at 20 C of from 6 to 20 mPas (cP), and 0.2 gram of Astrazon Orange (C.I. 48,040) dissolved in a mixture of 50 parts by weight of tetrahydrofuran, 40 parts by weight of ethyleneglycol monomethyl ether, and 10 parts by weight of butyl acetate. The plate is irradiated with an argon laser emitting in the visible range, which has a radiation output of 5 watts and a recording speed of 60 m per second, and is then decoated with water. WHAT WE CLAIM IS:

1. A process for the preparation of a planographic printing form wherein a printing plate comprising a support having thereon a recording layer comprising a light-hardenable diazo compound and an amino resin is imagewise irradiated with a laser beam to render the irradiated portions of the recording layer insoluble in a selected developer and, where desired or necessary, the non-irradiated portions of the recording layer are then removed by treatment with said developer, the support comprising aluminium, the or each supporting surface of which has been anodically oxidized so that the oxide layer weighs at least 3 grams per square meter.

2. A process as claimed in Claim 1, wherein the oxide layer weighs from 5 to 12 grams per square meter.

3. A process as claimed in Claim 1 or Claim 2, wherein the recording layer comprises 0.6 to 6 parts by weight of the amine resin per part by weight of the diazo compound.

4. A process as claimed in any one of Claim 1 to 3, wherein there is used a printing plate, the or each supporting surface of which, prior

to anodization, has been roughened.

5. A process as claimed in Claim 4, wherein the or each surface has been electrolytically roughened prior to anodization.

6. A process as claimed in any one of Claims 1 to 5, wherein anodization has been effected in a sulphuric or phosphoric acid electrolyte.

7. A process as claimed in any one of Claims 1 to 5, wherein the diazonium salt condensation product.

8. A process as claimed in Claim 1, carried out substantially as described in any one of the Examples herein.

9. A printing form whenever prepared by a process as claimed in any one of Claims 1 to 8.