US3309990A

US3309990A - Process for the preparation of printing plates

Info

Publication number: US3309990A
Application number: US162278A
Authority: US
Inventors: Klupfel Kurt-Walter; Tomanek Martha; Endermann Fritz
Original assignee: Azoplate Corp
Current assignee: Azoplate Corp
Priority date: 1961-01-25
Filing date: 1961-12-26
Publication date: 1967-03-21
Anticipated expiration: 1984-03-21
Also published as: SE319084B; LU41142A1; DK104127C; BE613038A; GB979313A; CH393087A; NL273558A; DE1145184B

Description

United States Patent 3,309,990 PROCESS FOR THE PREPARATION OF PRlNTlNG PLATES Kurt-Walter Kliipfel and Martha Tomanek, Wiesbaden- Biebrich, and Fritz Endermann, Wiesbaden, Germany, assignors, by mesne assignments, to Azoplate Corporation, Murray Hill, N5. N0 Drawing. Filed Dec. 26, 1961, Ser. No. 162,278 Claims priority, application Germany, Jan. 25, 1961,

Claims. ((311. 101-1492) It is known, to produce copies ele-ctrophotograiphically as follows: an electrophotographic material is electrically charged and then exposed to light, either by the contact process, in which the light passes through the master, or by episcopic projection; the resultant latent electrostatic image is made visible by powdering over with a pigmented resin powder and then fixed, for example by heating, whereupon the pigmented resin powder becomes irremovably anchored to the support. The electrophotographic material used for this process consists of a support and a photoelectrically conductive insulator coating applied thereto, the latter consisting of or containing a photoelectrically conductive substance.

From copies of this type, obtained by the electrophotographic process, printing plates have been prepared by treatment with a solvent. The coating is removed by the solvent from the support in the image-free areas and, if necessary, the bared parts are rendered water-conductive by suitable means; the image parts are then inked up with greasy ink. Printing plates for the production of prints are thereby obtained. This known process has the disadvantage that to a considerable extent the solvent dissolves away the image-bearing parts of the reproduction coating also, so that printing plates with but inadequate properties are obtained.

Also, lithographic printing plates have been prepared by the application to a support of a coating of a hygroscopic substance which, in turn, is covered by a photoconductor coating. In this process, the disadvantage is that the hygroscopic coating must be applied first and the photoconductor coating afterwards. Furthermore, when the printing plates are being prepared, the hygroscopic coating must be bared in the image-free parts. This coating tends, however, to retain fine particles of the photoconductor coating that is being dissolved away, so that frequently, when printing is performed, prints are obtained which are not free of background, i.e., the prints have traces of ink in these parts.

For the preparation of a water-conductive surface in the image-free parts of a photoelectrically conductive inorganic insulator coating, water-soluble salts of bivalent metals from Groups I, II, IV, VII and VIII of the periodic system have been proposed, e.g., zinc acetate in an aqueous alcoholic solution, and a mixture of zirconyl acetate and sodium acetate in butanol, formaldehyde and water. However, images completely free of background are still not obtained as a result of treatment with these salt solutions.

Solutions of hexacyano-iron acids to which acetic acid, tartaric acid or citric acid has been added have also been disclosed for the conversion of an electrophotographic copy into a printing plate. Coatings treated in this way have, however, the disadvantage that they tend to scum after a few prints have been made and in general give ice only a short printing run as the effect of this mixture is not specific.

The present invention relates to a process for the preparation of printing plates in which the image-free parts of a photoelectrically conductive insulator layer containing inorganic photosemiconductors, on which an image has been produced by electrophotographic methods, are made hydrophilic by treatment with an aqueous solution containing one or more salts of the hexacyano-iron (II)- acid and/or the hexacyano-iron (III)-acid and one or more organic acids of high molecular weight.

The process of the invention has the advantage over the processes hitherto known that it yields printing images that are completely free of background. Considerably longer runs than those hitherto possible can be obtained, no greasy ink being taken up by the image-free parts in any case. With this treatment, the image parts, which are covered with resin powder, remain water-repellent and can be inked up with greasy ink. The process by which the parts are rendered water-accepting with the solution of the invention is performed very easily and very quickly, so that an electrophotographic copy needs only to be set up in an offset printing machine, wiped over with the solution, and in this way made ready for printmg.

As inorganic compounds which can be used as photosemiconductors in the present process, the following are mentioned by way of example: the photoconductive oxides, sulfides, selenides, tellurides and iodides of zinc, bismuth, molybdenum, lead, antimony and cadmium. Also, mixtures of a number of the photosemiconductors mentioned can be employed; further, mixtures of organic photosemiconductors with the inorganic photosemiconductors mentioned above are suitable.

As organic photoelectrically conductive compounds the following are exemplary: oxadiazoles, e.g., 2,5-bis-(4- diethylaminophenyl-( 1) )-l,3,4-oxadiazole, 2,5-bis (4' (n-propylamino)-2'-chlorphenyl-(1) )-1,3,4-oxadiazole or 2,5 bis (4 N-ethyl-N-n-propylaminophenyl-(1') )-1,3, 4-oxadiazole; triaz-oles, e.g., 1 methyl 2,5 bis (4-diethylamino-phenyl (1')) 1,3,4-triazole; imidazoles, e.g., 2- (4-dimethylaminophenyl) -6-methoxy-benzimidazole; oxazoles, e.g., 2-(4-chlorphenyl)-phenanthreno-(9,1 O:4,5) oxazole; thiazoles, e.g., 2-(4-diethylaminophenyl)-benzthiazole; thiophens, e.g., 2,3,5-triphenyl-thiophen; triazines, e.g., 3-(4'-aminophenyl)-5,'6-di-pyridyl-(2)-1,2,4- triazine or 3-(4'-dimethylaminophenyl)-5,6-di-(4-phenoxyphenyl)-1,2,4-triazine; hydrazones, e.g., 4-dimethylaminobenzaldehyde-isonicotinic acid hydrazone; styryl compounds, e.g., 2-(4-dimethylaminostyryl)-6-methy1-4-pyridone or 2(4-dirnethylaminostyryl)-6-methyl-4-pyrone or 2-(4-dimethylaminostyryl) -5-( or 6) -amino-benzimidazole; azomethines, e.g., 4-dimethylaminobenzylidene-{imaphthylamine; amino compounds, e.g., 3-dimethylamino-1,2- benzophenazi-ne; and polyvinylcarbazole.

The photosemiconductors can the applied in known manner to a suitable support as a suspension in .a solution containing a natural or synthetic resin, e.g., silicone resin, acrylic resins, ketone resins, balsam resins, phenol resins modified with colophony, cournarone and indene resins, as Well as processed natural substances such as cellulose ethers, polymers such as polyvinyl chlorides, polyvinyl acetates, polyvinyl alcohols, also polystyrene and isobutylene, polycondensates, such as phthalate resins, alkyd resins, maleinate resins, phenol-formaldehyde resins and polyadducts, e.g., polyurethanes.

To increase the light-sensitivity of the reproduction coating in the visible region of the spectrum, sensitizers are added in small quantities (about 0.001 to 0.5 percent by weight with respect to the quantity of photoconductor employed in the reproduction coating) to the solutions in which the photoconductor is suspended or they are applied by subsequent treatment after the electrocopying material has been prepared. As sensitizers, dyestuffs, the identification number of which is given below under which they are listed in the Schultz Farbstofftabellen (7th edition, 1st vol., 1931), are particularly suitable. Examples of effective sensitizers are: triaryl methane dyestuffs such as Brilliant Green (No. 760, p. 314), Victoria Blue B (No. 822, p. 347), Methyl Violet (No. 783, p. 327), Ethyl Violet (No. 787, p. 331), Crystal Violet (No. 785, p. 329), Acid Violet 63 (No. 831, p. 351); xanthene dyestuffs, more particularly Rhodamines such as Rhodamine B (No. 864, p. 365), Rhodamine 6G (No. 866, p. 366), Rhodamine G Extra (No. 865, p. 366), Sulphorhodamine B (No. 863, p. 364) and Fast Acid Eosin G (No. 870, p. 368), as also phthaleins such as Eosin S (No. 883, p. 376) Eosin A (No. 881, p. 374), Erythrosin (No. 886, p. 376), Phloxin (No. 890, p. 378), Bengal Rose (No. 889, p. 378) and Fluorescein (No. 880, p. 373); thiazine dyestuffs such as Methylene Blue (No. 1038, p. 449); acridine dyestuffs such as Acridine Yellow (No. 901, p. 383), Acridine Orange (No. 908, p. 387) and Trypofiavine (No. 906, p. 386); quinoline dyestuffs such as pinacyanol (No. 924, p. 396) and Cryptocyanine (No. 927, p. 397); quinone dyestuffs and ketone dyestuffs such as Alizarin (No. 1141, p. 499), Alizarin Red S (No. 1145, p. 502) and Quinizarine (No. 1148, p. 504); cyanine dyestuffs, e.g., cyanine (No. 921, p. 394) and chlorophyll.

As the supports for the electrocopying layers, foils made of metals such as aluminum, zinc, copper and brass are preferably employed. Other supports used in electrophotography such as paper, or foils made of paper or plastic with vacuum deposited or laminated metal surfaces can also be used. The papers may, moreover, be provided with a conductive precoat which is resistant to organic solvents, e.g., like that described in U.S. Patents 2,534,650, 2,681,617 or 2,559,610.

In applying the reproduction coatings to the supporting material, the photoconductive substances are suspended in a resin solution by a process of homogenization in a colloid mill and then applied to the support in a thickness of 20-40 grams/square meter, preferably 2835 grams/ square meter. This can be done in known manner by spraying, painting, roller application, immersion in the suspension, or application of the suspension to the rotating supporting material. The coating is then advantageously dried at an elevated temperature to drive off residual solvent.

The preparation of the electrocopies is in known manner, i.e., the electrocopying material described above is charged with a charging device, by means of a corona discharge, and then exposed imagewise by the contact process, the light passing through the master. The material can also be exposed to an episcopic projection or it can be exposed directly in a camera. The latent electrostatic image is then developed in known manner with one of the usual pigmented resin powders, which may in some cases be suspended in a dielectric liquid and the image that becomes visible is fixed, e.g., by heating with an infra-red radiator to about 100-470, preferably 130-160" C., or by treatment with solvents, so that irremovable images are obtained which have good contrast.

In converting the images obtained by the electrophotographic process above described into printing plates, these are contacted with a solution containing water and one or more salts of the hexacyano-iron acid and one or more organic acids of high molecular weight.

The substances included in the term salts of the hexacyano-iron acids are salts which preferably contain as the cationic component alkalis such as sodium and potassium,

but alkaline earths such as calcium and magnesium or other cations can also be used.

As the hexacyano-iron acids of the invention, hexacyano-iron (II) acid, which is represented by the formula H [Fe(CN) and hexacyano-iron (III) acid, which is represented by the formula H [Fe(CN) are contemplated.

Also, mixtures consisting of the salt-forming metals listed above and the two hexacyano-iron acids can be used.

Among the organic acids of high molecular weight which can be used in accordance with the invention, the following are preferable: polymerization products of phosphonic acids which are substituted with organic polymerized residues, e.g., polyvinyl phosphonic acid; moreover polymerization products of substitted or unsubstituted acrylic acids, e.g., polyacrylic acid and polymethacrylic acid are suitable.

The treatment of the image for the purpose of conversion into a printing plate may consist, for example, simply of a wiping over process, e.g., with a wetted cotton pad, or immersion of the foil in the solution imparting hydrophilic properties; the foil may even be first set up in an offset machine and the surface then wiped over with a wetted sponge containing the solution. The image-free parts immediately become Water-conductive so that printing may be immediately effected from the foil. It is advantageous for the printing plate to be Washed down with water after the treatment.

Aqueous solutions containing the salts of hexacyanoiron acids in quantities of from 0.0115%, preferably 15% and polymeric acids in quantities of 0.0110%, preferably 15%, can be utilized in the present process With great success.

Sometimes it is advantageous for up to 10% of organic solvents to be added to the aqueous solutions according to the present invention. As the organic solvents, a wide variety of Water-miscible solvents are suitable. Those that are preferred are, however, those which contain oxygen in the molecule in the form of ether, ketone or alcohol groups; exemplary are cyclic ethers such as dioxane and tetrahydrofuran, lower ketones such as acetone and methyl ethyl ketone, and, in particular, solvents containing alcohol groups, e.g., methanol, ethanol, propanol, isopropanol, ethyleneglycol, polyethyleneglycol, glycerine, ethyleneglycol monomethylether and glycerine monoethyl ether. The multivalent alcohols such as ethyleneglycol, glycerine and polyglycols are particularly favorable. Also, mixtures of solvents can be used.

Further, it is often advantageous for wetting agents and/or thickening agents to be added to the solutions of the invention. As wetting agents, alkali salts of dialkyl naphthalene sulfonic acids, such as diisobutylnaphthalene sulfonic acid sodium salt, sulfonated fatty alcohols, fatty alcohol polyglycol ethers and glycerine are, for example, suitable and, as thickening agents, polyvinyl alcohol, cellulose products, such as carboxymethyl cellulose or alkyl cellulose, silica gel or soluble starch products may be used.

The invention will be further illustrated by reference to the following specific examples:

Example I parts by weight of especially pure zinc oxide, grade A (from the Zinkweiss Handelsgesellschaft, Oberhausen, Germany),

80 parts by weight of Silikonharz K, a methyl silicone resin, (50% solution in toluene) (from the Wacker- Chemie, Burghausen, Germany),

parts by weight of industrial toluene,

25 parts by weight of methanol,

and 0.010.05 part by weight of Rhodamine B extra are homogenized in a colloid mill or in a high-speed rapid mixer. The suspension, now ready for coating, is applied in known manner to a paper foil, to which a thin aluminum foil is laminated, and then dried. For the production of images on the electrocopying material thus produced, the coating is negatively charged by a corona discharge and then given an exposure of 5-30 seconds according to the reproduction scale at stop 9 in the cassette of a document camera fitted with a reversal prism. As a light source, eight 500-watt filament lamps are used. A suitable master is a line drawn with printing on both sides.

The electrostatic image of the master thereby formed on the zinc oxide layer is made visible by dusting over with a resin powder pigmented with carbon black and is fixed, by heating to about 160 C., to give an irremovable copy. The resin powder used for the development consists of the components known as toner and carrier. As the carrier, glass balls or iron powder are used, as in general practice; these, in conjunction with the toner, produce charging as a result of the triboelectric effect, the toner acquiring the opposite charge to that of the carrier. The toner consists of a polystyrene-colophony mixture of low melting point to which carbon black and, advantageously, spirit-soluble nigrosine (Schultz, Farbstofi'tabellen, No. 985), as an organic dyestuff, are added. The components are melted together, the melt is ground and, as a uniform grain size is advantageous for the production of the images, the particles are separated by air sifting. For example, a fraction containing toner particles of a grain size of 2030,u is very suitable.

For the preparation of the printing plates, the image is wiped over with a solution containing 3 parts by weight of the potassium salt of the hexacyano-iron (II) acid (K [Fe(CN 2 parts by weight of polyvinyl phosphonic acid, 0.3 part by weight of diisobutyl naphthalene sulfonic acid sodium salt and 95 parts by volume of water. After brief rinsing with water and inking up of the printing plate with greasy ink, printing can be effected in an offset machine in the usual Way.

Example 11 180 parts by weight of zinc sulfide (a product com mercially available under the name Sachtolith L),

80 parts by weight of Silikonharz K, a methyl silicone resin, (50% in toluene) (from the firm 0f Wacker, Burghausen, Germany),

160 parts by weight of a product available under the name Plexigum, a polymethacrylic acid ester in which the ester component is primarily butyl or isobutyl, (20% in toluene),

200 parts by weight of toluene,

40 parts by weight of methanol,

and 0.01-0.05 part by weight of Bengal Rose N extra are homogenized as described in Example I. This suspension is coated on an aluminum foil made of bright rolled aluminum and is then dried. The electrocopying material prepared in this way is negatively charged with a corona discharge and a leica diapositive is projected thereon with an illumination strength of 3 luxes, in a photographic enlarging apparatus, the exposure being of 40 seconds duration. Development is effected with a developer consisting of a toner and iron powder and fixing is accomplished by brief heating to 100450 C.

For conversion into a printing plate, the image is wiped over with a solution containing 0.5 part by weight of the potassium salt of the hexacyano-iron (III) acid 2 parts by weight of the potassium salt of the hexacyanoiron (II) acid (K [Fe(CN) 1 part by weight of carboxymethyl cellulose, 3 parts by weight of polyacrylic acid and 93.5 parts by weight of water, and it is then inked up with greasy ink.

Example III The procedure of Example I is followed but for the preparation of a printing plate, a solution imparting the property of water acceptance is used which consists of 5 parts by weight of the potassium salt of the hexacyanoiron (II) acid, 3 parts by weight of poly-vinyl phosphonic acid, 10 parts by volume of methanol and 83 parts by volume of water. After the fixed image has been wiped over with the solution, the image-free parts become water conductive and the toner image accepts greasy ink. Prints can be made once the plate has been set up in an offset machine.

Example IV parts by weight of especially pure zinc oxide,

100 parts by Weight of a methyl silicone resin (50% solution in toluene),

parts by weight of toluene of the commercial degree of purity,

1015 parts by weight of 2,5-bis-[4-diethylamino-phenyl- (1) ]-l,3,4-oxadiazole,

10 parts by weight of methanol, and

0.02 part by weight of Rhodamine B extra are together homogenized in a high speed mixer, after dissolving the oxadiazole in toluene. A printing plate is prepared as described in Example I, but the solution imparting the hydrophilic properties has the following composition:

100 parts by volume of a 5% aqueous solution of the potassium salt of hexacyano-iron (II) acid,

100 parts by volume of a 5% aqueous solution of polyvinyl phosphonic acid, and

50 parts by volume of isopropyl alcohol.

It will be obvious to those skilled in the art that many modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications.

What is claimed is:

1. A process for the preparation of a printing plate which comprises treating a photoelectrically conductive insulating layer, containing at least one inorganic photosemiconductor and having a developed and fixed electrostatic image thereon, with an aqueous solution of at least one salt selected from the group consisting of ferrocyanides and ferricyanides, in admixture with polyvinyl phosphonic acid whereby hydrophilic properties are imparted to the image free areas of the layer.

2. A process according to claim 1 in which the aqueous solution contains a water-miscible organic solvent.

3. A process according to claim 1 in which the insulating layer also contains an organic photosemiconductor.

4. A process according to claim 1 in which the insulating layer also contains a dyestuff sensitizer.

5. A process according to claim 1 in which the insulating layer is on a support.

6. A process according to claim 5 in which the support is aluminum.

7. A process according to claim 5 in which the support is paper.

8. A process according to claim 1 in which the salt is an alkali metal salt.

9. A process according to claim 1 in which the aqueous solution contains a wetting agent.

10. A process according to claim 1 in which the aqueous solution contains a thickener.

11. A composition adapted for treatment of photoelectrically conductive insulating layers comprising an aqueous solution of at least one salt selected from the group consisting of ferrocyanides and ferricyanides in admixture with polymerized polyvinyl phosphonic acid.

12. A composition according to claim 11 containing, in addition, a water-miscible organic solvent.

13. A composition according to claim 11 in which the salt is an alkali metal salt.

14. A composition according to claim 11 in which the aqueous solution contains a wetting agent.

15. A composition according to claim 11 in which the 2,988,988 aqueous solution contains a thickener. 2,997,387 3,037,861 References Cited by the Examiner 3,108,53 5 UNITED STATES PATENTS 5 3,211,686

2,186,945 1/1940 Wood 101149.2 2,186,946 1/1940 Wood 101-149.2

Kurz 101-1492 Tanebaum 961 Hocgl et a1 961 Uhlig 101149.2 Uber et a1.

DAVID KLEIN, Primary Examiner.

Claims

1. A PROCESS FOR THE PREPARATION OF A PRINTING PLATE WHICH COMPRISES TREATING A PHOTOELECTRICALLY CONDUCTIVE INSULATING LAYER, CONTAINING AT LEAST ONE INORGANIC PHOTOSEMICONDUCTOR AND HAVING A DEVELOPED AND FIXED ELECTROSTATIC IMAGE THEREON, WITH AN AQUEOUS SOLUTION OF AT LEAST ONE SALT SELECTED FROM THE GROUP CONSISTING OF FERROCYANIDES AND FERRICYANIDES, IN ADMIXTURE WITH POLYVINYL PHOSPHONIC ACID WHEREBY HYDROPHILIC PROPERTIES ARE IMPARTED TO THE IMAGE-FREE AREAS OF THE LAYER.