US3690878A - Planographic printing element having carboxylic acid treated image areas - Google Patents

Abstract

A PLANOGRAPHIC PRINTING PLATE IS PROVIDED HAVING IMAGE AREAS FORMED BY TREATMENT WITH A CARBOXYLIC ACID AS A MARKING INK, THE ACID HAVING FROM ABOUT 12 CARBON ATOMS TO ABOUT 22 CARBON ATOMS. THE PLATE IS PREFERABLY A PAPERBASED, ELECTROPHOTOSENSITIVE SHEET BUT CAN COMPRISE OTHER BACKING MEMBERS AND OTHER IMAGE-RECEPTIVE PRINTING SURFACES.

Description

United States Patent O 3,690,878 PLANOGRAPHIC PRINTING ELEMENT HAVING CARBOXYLIC ACID TREATED IMAGE AREAS William H. Tandy, Mentor, Ohio, assignor to Addressograph-Multigraph Corporation, Cleveland, Ohio No Drawing. Filed Jan. 9, 1970, Ser. No. 1,887 Int. Cl. (203g /00, 13/00 US. CI. 96-13 11 Claims ABSTRACT OF THE DISCLOSURE A planographic printing plate is provided having image areas formed by treatment with a carboxylic acid as a marking ink, the acid having from about 12 carbon atoms to about 22 carbon atoms. The plate is preferably a paperbased, electrophotosensitive sheet but can comprise other backing members and other image-receptive printing surfaces.

BACKGROUND OF THE INVENTION In planographic printing, that is, printing from a plane surface, the plate must readily accept a Water-repellent, ink-receptive image which is then tenaciously held by the plate. The non-image areas must be readily wetted by and retain a -1film of the aqueous lithographic solutions while rejecting the printing ink.

[Metal masters have been partially supplanted by nonmetallic carrier sheets coated with a film capable of accepting and holding an oleophilic image, or having an area chemically transformed into an ink receptive image area.

Lithographic ink is a grease type, and the master coatings will accept lithographic ink. But if areas of the coating are covered with hydrophobic material such as typewriter ink, crayons, etc., and then the entire master surface treated with a conversion solution, the covered areas are not converted.

Phosphate acids are used, for example, to convert the zinc oxide coated plates to a hydrophilic oleophobic condition. The covered areas remain oleophilic. These areas will pick up lithographic ink and transfer ink replicas of the image in the lithographic printing technique.

Sometimes it is desired to ad image areas to a master after it is prepared. For example, it is common practice to print masters of commonly used forms. A pen is used to apply a protective coating of imaging ink to create an image for data which must be added to a pre-printed planographic master, such as order numbers, shipping weights, addresses of receivers, etc., so that a suitable number of duplicate copies can then be printed for distribution to those involved. This type of planographic master is relatively rough and porous as compared to other types of masters. Prior to this invention, available imaging inks have been susceptible to the penetration and running of the imaging ink beyond the edges of the actual printing areas. Existing imaging inks quickly penetrate the porous surface of direct-image planographic masters, leaving no oleophilic film in the image areas to accept the lithographic ink. Moreover, in some cases, pen tips used in direct imaging scratch the surface of the plate, thereby facilitating penetration of the lithographic solution and accelerating its spread into the plate.

It would therefore, advance the art if a marking ink were developed which was capable of forming ink-receptive image areas on planographic masters which held fast and resisted penetration of and spreading by the imaging ink.

SUMMARY OF THE INVENTION In accordance with the present invention, the image areas of a planographic printing element are formed by contact with a marking ink comprising carboxylic acid having from about 12 carbon atoms to about 22 carbon atoms.

The preferred embodiment comprises a base sheet, preferably a paper base resin coated to provide wet strength, and a water insoluble, film-forming coating overlying and adhered to the base sheet. The coating comprises photoconductive material, such as zinc oxide bonded to the base sheet, to provide a plate, especially an electrostatic plate. The carboxylic acid reacts with the zinc oxide to form a securely bonded, oleophilic film comprising the water insoluble, ink receptive zinc salt of the acid. In this case the zinc oxide is naturally ink receptive, and the usual practice has been to apply an oil base marking fluid to prevent later application of conversion solution from reaching the naturally ink receptive image. However, typical base marking fluids do gradually soak into the supporting base and expose the zinc oxide. The zinc oxide is gradually converted by fountain solution, with resultant shortened image life. This invention operates on the premise of converting the zinc oxide to a more resistant zinc salt, usually of a fatty acid. The surface around the image is thereafter converted to a hydrophilic phosphate without affecting the image. The resistant Zinc salt remains as a master image for the life of a paper-based sheet when used as on an offset duplicator.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The preferred backing member or base sheet of a planographic master used in accordance with the present invention is paper, such as kraft paper, because of its relative low cost, strength, and desired flexibiilty. The paper may weigh from about 15 to 40 pounds per thousand square feet and be suitably resin treated to provide additional strength, especially wet strength, with such resins as ureaformaldehyde, melamine-formaldehyde, and the like. The paper may also be conventionally sized if desired.

Other base sheets can also be used. For example, the base may comprise cellulosic material, such as cellophane or cellulose acetate. 01', the base can be metallic, preferably in foil form, and comprise such metals as aluminum, copper or brass. Still further, although not as desirable, the base sheet can be relatively inflexible, such as a glass or mica sheet.

In the preferred form, the water insoluble, film-forming coating which overlies the base sheet comprises a phootconductive zinc oxide. However, almost any photo-- conductor having sufiiciently high value of surface photoconductivity may be used in the coating, for example, anthracene, the photoconductive oxides, sulfides, selenides, tellurides and iodides of cadmium, mercury, antimony, bismuth, thallium, molybdenum, lead or zinc, especially when chemically reactive with the carboxylic acid used. The manner of preparing a base sheet having a coating of photoconductive material is well known in the art. US. Pat. Nos. 2,993,787 to Sugarman and 3,010,884 to Johnson et al., for example, described the preparation of such plates. In general, the zinc oxide or equivalent is mixed with a film-forming resinous vehicle, such as polyvinyl alcohol, and a solvent, and then coated by conventional means on the selected backing. After drying, the master is then cut or punched to a desired shape and size.

In place of the polyvinyl alcohol, other materials may be used such as hydroxyethyl cellulose, carboxymethyl cellulose, gum arabic, guar gum, and the like. Such a film-forming vehicle must be electrically-insulating and is applied with the photoconductive material from a suitable liquid medium, such as an aqueous dispersion. As a rule, the amount of photoconductor material used may range from about parts to 900 parts per 100 parts by weight of the film-forming vehicle. A plasticizer may be used with the vehicle to vary the physical properties of the final coating.

However, the coating forming the image receptive printing surface need not be of the photoconductive type. The present invention also contemplates a planographic master having a coating comprising a finely divided filler or pigment material and an adhesive hydrophilic colloid which serves as a binder. These masters are often referred to as direct image masters. The filler may comprise clay, such as Georgia clay or kaolin, blanc fixe, calcium sulfate, talc, titanium dioxide, and other equivalent finely divided mineral pigments. The hydrophilic colloid may be any of a large number of colloidal materials. In some cases, a colloid hardening agent may be used, such as formaldehyde. Exemplary colloids include: gums such as arabic, mesquite, karaya, locust bean, guar, and the various alginates such as sodium alginate and ammonium alginate; proteins such as casein, soya bean, zein, animal glue, gelatin and egg and blood albumin; still other hydrophilic colloidal materials such as starch, dextrin, pectins and derivatives thereof including fibrous sodium pectate; and synthetic hydrophilic colloidal materials, such as carboxymethyl cellulose, sodium polyacrylate, methyl cellulose, hydroxyethyl cellulose, and polyvinyl alcohol. The hydrophilic colloid is used in an amount of about 15 parts to about 30 parts per 100 parts by weight of the filler or pigment, and the mixture applied from a suitable liquid carrier such as an aqueous dispersion.

Whether applied with an electroconductive material or a pigment colloid admixture, the base sheet of the present planographic master may be coated by any convenient method. For example, the coating may be sprayed on or flowed on, or the base sheet may be dipped into the mixtures. Following the coating step, the assembly is dried. The drying temperature is not critical, but it should be sufficiently high to evaporate the liquid carrier but not so high as to burn or char the backing or constituents of the coating.

The coatings may be of any convenient thickness. In flexible embodiments of the invention, a paper backing, for example, may weigh from about 15 to about 40 pounds per one thousand square feet. A layer of the photoconductive material may have a thickness of about 0.3 to about 2.0 mils, with a coating of about 0.5 mil in thickness being preferred. A suitable weight of pigmented colloid coating may be from about 3 to about pounds per side (more than one side can be coated) per one thousand square feet of base sheet. The laminated assembly is cut into sheets of suitable size to be used as plates in duplicating or other planographic printing machines.

Carboxylic acids useful in accordance with the present invention are those having from about 12 carbon atoms to about 22 carbon atoms. Carboxylic acids having less carbon atoms tend to have sufficient water solubility to be unsuited for the purpose intended. Carboxylic acids having more carbon atoms have too high molecular weights to be easily and conveniently employed. Within the range indicated, both saturated and unsaturated acids are contemplated, as well as both monocarboxylic and dicarboxylic acids, although monocarboxylic acids are preferable. The predominantly greasy acids are desired. Oleic acid is preferred, although stearic and isostearic acids provide excellent results. Isostearic acid is preferred to staric acid, since isostearic acid is liquid at room temperatures. Highly acceptable results are also obtained with eurcic and linoleic acids. Mixtures of acids may also be used.

The acid may be applied to a planographic master in any convenient form. Usually an organic solvent medium is used such as methylethyl ketone, carbon tetrachloride, naphtha, etc., and especially aromatic solvents such as toluene, xylene, benzene, and benzaldehyde. Mixtures of solvents can also be used. The amount of acid dissolved in the organic solvent is not at all critical, since the purpose is merely to apply some of the acid onto a plate.

Solvents or diluents are preferably used in an amount to give desired flow properties for a specific pen or for other means by which the acid solution is applied. In general, the acid may comprise from about 25 percent to about 75 percent by weight of the solution. If desired for legibility, easy proofreading, or a lingering record if the master is not to be used immediately, the solution can also contain a water insoluble dye such as indulin, nigrosine (Nubian Resin Black available from Allied Chemical and Dye Corporation) and the like. A black or dark blue dye is preferred for legibility.

The application of the acid-organic solvent mixture, which is in the nature of a marking ink, can be carried out by any tool capable of depositing the solution as desired onto a plate. Any relatively sharp pointed instrument can be used for this purpose, such as a stylus, fiber tipped pens, dip pens, ball point pens, rubber stamps, etc.

The carboxylic acid does not run on the plate, but, to the contrary, acts as a fixative. When a photoconductive material reactive with the marking ink is used, such as zinc oxide, the reaction is between the zinc oxide and the carboxylic group of the acid to form a permanent, chemically-bonded, water insoluble, oleophilic image consisting essentially of the zinc salt of the acid or acids used. When the ink receptive, image reproducing surface comprises a pigment-hydrophilic colloid combination, the marking ink sticks to the area to which it is applied, probably by a mechanical, physical adhesive bond, although there may well be other forces not readily understood which contribute to the desired result.

The following examples are intended to illustrate the invention and should not be construed as limiting the claims.

Example 1 A mixture of the following compositions was prepared: Ingredient: Amount Polyvinyl alcohol grams 5 Methanol ml 60 Distilled water ml 40 Photoconductive zinc oxide grams The polyvinyl alcohol was dissolved in a mixture of the water and methanol, after which the zinc oxide was dispersed in the mixture by blending for five minutes on a high speed blender. The blended mixture was then coated on a paper backing to a thickness to provide a final dry coating of about 0.5 mil in thickness. The coat- 1ng was then dried and the assembly cut or punched to a desired shape and size. The product was an electrophotographic recording element especially adapted for use in electrostatic printing.

A marking ink was then prepared by admixing the ingredients of the following formula:

Ingredient: Weight percent Oleic acid 65 Toluene 25 Nigrosine base dye 10 By means of a stylus, some of the marking ink was applied in direct imaging over an area of the electrostatic master initially prepared. Wherever the marking ink touched the plate, a deposit of zinc oleate formed even at room temperatures. When the resulting plate was attached to and operated on a conventional duplicating ma chine, the zinc oleate remained chemically bonded to the plaltle, did not run, and reproduced the image exceptionally we Example 2 A coating composition was prepared by first mixing together 640 grams of photoconductive zinc oxide, 533 grams of a 30 percent solution of 30:70 copolymer butadiene and styrene in toluene, and 353 grams of acetone. The mixture was ball milled for about eight hours. The resulting slurry or suspension was thick and viscous but flowed readily and could be spread with a coating knife to form a smooth, uniform coating. The suspension was coated on a clean surface of thin aluminum foil and the solvent removed by evaporation to provide a smooth, uniform dried coating of about 0.8 mil in thickness. The resulting sheet was flexible, and the coating remained bonded to the metal.

A marking ink was then prepared by admixing the following ingredients.

Ingredient: Weight percent Isostearic acid 43.4 Benzaldehyde 30 Toluene 16.6 Nigrosine base dye When a dip pen transferred some of the marking ink onto the plate initially prepared, an ink reproducing area formed consisting essentially of zinc isostearate which ran well without toning in the non-image areas of an offset printing machine.

Example 3 Example 4 A wet strength paper was coated with a layer containing parts of casein, 10 parts of gum arabic, 100 parts of clay, and parts of a 40 percent aqueous formaldehyde solution, all by weight. The paper was then dried and calendered.

A solution of mixed carboxylic acids was prepared consisting essentially of the following:

Ingredient: Weight percent Linoleic acid 20.1 Oleic acid 22.3 Stearic acid 1.0 Benzaldehyde Toluene 16.6 Nigrosine base dye 10 This marking ink was applied by a pen to the planographic printing element first prepared and found to provide image areas which also held fast, did not permit excessive penetration by a printing ink, and reproduced well.

The present invention makes possible the addition of handwritten or typewritten information to planographic masters for later duplication, especially such addition to the various direct image masters including those of the photoconductive type, such as a zinc oxide electrostatic master. It is unexpected that the defined carboxylic acids would be so easily suitable for this purpose and particularly that the acids would react at room temperatures with a photoconductive metal compound like zinc oxide.

Although the foregoing describes several embodiments of the present invention, it is understood that the invention may be practiced in still other forms within the scope of the following claims.

What is claimed is:

1. A planographic printing plate prepared for printing comprising a base sheet, a layer of a water-insoluble, film-forming material coating the base sheet selected from the group consisting of a photoconductive material, and an ink-receptive, image reproducing area on said layer formed by treating said area with a carboxylic acid having from about 12 carbon atoms to about 22 carbon atoms.

2. In a process for preparing for printing a planographic printing plate comprising a base sheet and a layer of a water-insoluble, film-forming material overlying the base sheet; the improvements comprising forming said film-forming layer from a material selected from the group consisting of a photoconductive material, and contacting a portion of said layer with a carboxylic acid having from about 12 carbon atoms to about 22 carbon atoms to form an ink-receptive, image reproducing area from said portion.

3. An electrostatic master prepared for printing comprising a base sheet, a layer of a water-insoluble, filmforming material coating the base sheet comprising a metal-containing photoconductive material, an ink-receptive, electrostatically produced first image area of said layer, and an ink-receptive, chemically-produced second image area of said layer comprising the reaction product of said metal-containing photoconductive material and a carboxylic acid having from about 12 carbon atoms to about 22 carbon atoms.

4. The electrostatic master of claim 3 wherein said photoconductive material comprises photoconductive zinc oxide, and said second image area comprises an oleophilic zinc salt of said carboxylic acid.

5. The electrostatic master of claim 3 wherein said carboxylic acid includes saturated and unsaturated carboxylic acids having from about 12 carbon atoms to about 22 carbon atoms.

6. The electrostatic master of claim 3 wherein said carboxylic acid includes monocarboxylic and dicarboxylic acids having from about 12 carbon atoms to about 22 carbon atoms.

7. A process for preparing for printing an electrostatic master comprising a base sheet and a layer of a waterinsoluble, film-forming material overlying the base sheet comprising a metal-containing photoconductive material, said process comprising electrostatically producing one image area on said layer, and chemically producing another image area on said layer by contacting the metalcontaining photoconductive material of said another image area with a carboxylic acid having from about 12 carbon atoms to about 22 carbon atoms.

8. The process of claim 7 wherein contacting said second image area with said carboxylic acid comprises reacting the metal of said photoconductive material with said acid.

9. The process of claim 7 wherein said photoconductive material contains photoconductive zinc oxide, and contacting said second image area with said carboxylic acid forms an oleophilic zinc salt of said carboxylic acid.

10. The process of claim 7 wherein said carboxylic acid includes saturated and unsaturated carboxylic acids having from about 12 carbon atoms to about 22 carbon atoms.

11. The process of claim 7 wherein said carboxylic acid includes monocarboxylic and dicarboxylic acids having from about 12 carbon atoms to about 22 carbon atoms.

References Cited UNITED STATES PATENTS 437,780 10/ 1890 Higgins 10627 X 2,357,809 9/ 1944 Carlson 96l.5 X 2,427,921 9/1947 Pfaelzer 10627 X 2,624,652 1/ 1953 Carlson 96-1 X 683,161 9/1901 White et al. 10614.5 2,138,836 12/1938 Brower 10627 X OTHER REFERENCES Carman: Theory of the Printing of Lithographic Inks Part II, American Ink Maker, March 1950, pp. 36-38 and 65.

GEORGE F. LESMES, Primary Examiner J. R. MH.LER, Assistant Examiner US. Cl. X.R.

96-15; l01--460, 466, Digest 13