US2655864A - Method of making planographic plates - Google Patents

Description

' Patented Oct. 20, 1953 METHOD OF MAKING PLAN OGRAPHIC PLATES Douglas A. Newman, Port Washington, N. Y., assignor to Columbia Ribbon and Carbon Manufacturing Company, Inc., Glen Cove, N. Y., a

corporation of New York No Drawing. Application December 22, 1945, Serial No. 637,088

Claims. (Cl. 101-149.2)

This invention relates to the manufacture of planographic printing plates, suitable for use in planographic printing processes in which the surface of a plate on which an image is formed of ink-receptive material (usually a greasy ink) is wetted with an aqueous ink-repelling fountain fluid, then inked over to deposit ink only on the image, the latter being then transferred to a sheet of paper, usually by way of a blanket as in offset printing, the image being repeatedly reinked and the foundation being maintained wet or ink-repellent as repeated copies are printed.

More specifically, this invention relates to planographic printing plates having a paper foundation which can be inscribed with an oleophilic image-forming material for use in a planographic printing process of the aforesaid type,

it receives and holds the image-forming material 0 and printing ink, and hydrophilic to a degree where it will receive and hold sufiicient aqueous ink-repellent fountain solution to limit the reinking of the plate to the image. Heretofore,

many proposals have been made to meet these requirements by making the plates of special materials, or impregnating or coating the plates with various films or surface strata, so that they could be inscribed or printed with ink when dry, and then wetted to render the background around the image ink-repellent. Such proposals include, for example, impregnation and coating of plates with vinyl alcohols or their polymers or derivatives, urea-aldehyde condensation products, casein and other binders, with and without fillers. These proposals have been only partially successful, by reason of the fact that the plates are unstable or variable, and change their properties, especially the optimum balance of the hydrophilic and oleophilic properties required in a satisfactory planographic printing plate. Thus, plates prepared according to prior art methods change before use by aging, and also while prints are being made.

Often the surface of planographic printing 2 plates heretofore known, when too water absorptive, permitted the wetting solution to undermine and invade the image with the result that the image was gradually reduced or lost. When the surface was not sufficiently water absorptive, it failed to retain suflicient wetting solution from the fountain to repel. particles of ink used to print duplicates, and the ink was deposited on the background portions of the plate, producin specks which multiplied as the plates were repeatedly inked, resulting in a splotchy and objectionable background in the prints. Excessive water absorption by the plates during use weakened the plates so that they stretched and buckled, causing distortion of the image. Moreover, in the use of many types of plates heretofore proposed, consistently satisfactory results could not be obtained from the beginning to the end of the run, due to the fact that the coating or impregnating solution varied in concentration and character while the run was being made.

Thus, the results obtained heretofore, for reasons above stated and others, are not uniformly satisfactory or reliable, and plates apparently made or constituted in the same manner ave vastly different results, so far as fidelity of the prints to the original was concerned, and the number of prints which could be made before the quality fell below an acceptable standard.

A further deficiency in plates heretofore known lay in the fact that the special coatings provided thereon for retaining the fountain fluid so as to render the background ink-repellent, would not sustain erasure without so injuring the coating surface as to render the master copy useless, or at best usable for only a few copies. In order to make a correction, it was necessary to make a new master copy, or to repair the erased surface by applying a repair solution or coating to the erased areas, before inserting the correction. Such repaired areas had to be dried before reinscription, rendering correction of an error a time-consuming and inconvenient operation. As a result, the user, in preparing a master copy, generally found it more expedient to work at much reduced speed in order to insure absence of errors and thus avoid the necessity for making corrections or retyping the master copy.

Often the surface of planographic plates heretofore used were sensitive to soiling with finger prints or the like which were reproduced on the printed copies. Such plates therefore required inordinate care in handling during preparation of a master copy, and up to the time they were used for printing.

I have discovered that if a paper printing plate is provided on its printing surface with a film or coating of a water-insoluble carboxy-methyl cellulose compound (1. e., a carboxymethyl ether of cellulose or a salt or other derivative thereof) especially a water-insoluble metal derivative or salt of carboxy-methyl cellulose, the coating remains stable and does not change during storage,

nor while the paper is being used. When dry,

the surface of the plate is sufficiently oleophilic to receive an ink-receptive image, and to retain the image tenaciously during use; while the background is sufliciently hydrophilic to absorb water from the fountain solution and repel ink applied during printing. The absorption of water from the fountain solution employed in printing is retarded and reduced by the coatings provided in accordance with my invention, so that troubles heretofore experienced involving reduction or loss of the image do not occur. At the same time, the background portion of the plate consistently maintains its hydrophilic ink-repellent character, preventing background specks from forming, and consistently retains a true image applied to it on the surface of the coating.

I have found that planographic printing plates having a paper foundation, and a coating on the printing surface thereof of a water insoluble metal derivative or salt of a carboxy-methyl cellulose, particularly a copper salt or derivative of carboxymethyl cellulose, or a mixture of the copper salt or derivative with such other salts or derivatives as those of aluminum, iron and chromium have especially desirable properties. Such plates, when dried, are adapted to receive an image inscribed or imprinted thereon with an oleophilic image-forming medium, and to retain the image tenaciously during printing; while the uninscribed background, which moistened Iith an aqueous fountain solution, consistently repels the printing ink yielding clear backgrounds. even when used for printing an exceedingly large number of copies. Such plates are not subject to aging, and do not change their characteristics when stored for an indefinitely long period.

Plates prepared in accordance with my invention are very clean to handle so that they do not show thumb prints or finger marks, which usually appear on metal plates or other coated lithographic plates. In addition errors may be easily deleted with a pencil eraser, several times at the same point on the sheet if necessary, without injuringthe ink-repellent or image-receptive properties of the background, and without causing any perceptible change in the resulting copies after the correction is made. This is especially advantageous, in that a typist can prepare master copies at normal speed, since minor errors can be readily corrected and do not necessitate retyping or reprinting the entire copy. or a tedious repair operation after erasure.

Planogra-phic plates can be prepared in accordance with my invention in a number of ways. The simplest, and therefore the preferred method involves coating the paper with an aqueous composition containing a water soluble carboxymethyl cellulose salt or compound dissolved therein, drying the coating, and then insolubilizing the resulting film by treatment with a solution of a precipitant or coagulant reagent, particularly a coagulant metal compound.

The coating composition is applied to the paper preferably in the form of a continuous web from which the plates can be later cut, for example, by

brushcoating or tub-sizing methods. It is desir-- able to apply the coating of water-soluble carboxy-methyl cellulose compound in more than one laye in order to insure sealing pin holes which may occur in the surface if the coating is applied in a single operation. Thus, paper which has been brush-coated with the carboxy-methyl cellulose solution and dried is preferably given a second coating with a similar composition, and again dried before subjecting it to treatment with the coagulant or precipitant metal compound. The insolubilizing solution is applied to the carboxymethyl cellulose coated paper as' a wash (e. g. by coating devices or by tub-sizing) and the paper is then dried and calendered.

Before coating or after the intermediate or final drying, or after calendering, the sheet may be provided with a water-resistant backing, for example, by coating with a solution of a waterrepellent, resinous or plastic material in a volatile organic solvent, e. g. a solution of Polystyron (i. e. a resinous styrene polymer) in ethyl acetate. A Polystyron backing has been found especially satisfactory in that it not only Waterproofs the back of the plate, but gives it additional body without too much stiffness which would interfere with convenient handling of the .plate in a typewriter or printing machine.

The coating composition employed in accordance with my invention preferably contains, in addition to a water-soluble carboxy-methyl cellulose compound, an inert filler such as colloidal clay, barium sulphate, calcium carbonate or the like, to provide a surface having a substantial tooth, which possesses improved holdingpower for the ink applied to the image. Moreover, plasticizers such as glycerine can be included in the composition to insure or maintain the pliability of the film. Readily volatile alcohols such as methanol or ethanol can also be included in the mixture to accelerate drying of the film.

In making a planographic plate for commercial use, it is desirable that the foundation sheet be made of paper having relatively high wet strength, so that the plate will have sufiicient body to be conveniently handled and applied to the printing press, and will have sumcient resistance to mechanical abrasion in use. To provide such a foundation sheet or continuous strip from which the sheet may be cut, a water leaf strip from a paper-making machine may be passed through a size tub containing a solution for increasing the wet strength of the paper. Preferably, however, a fiber-bonding, absorptionlimitingmaterial is included in the pulp and the paper is formed as a wet-strength, limited-absorption paper. Thus, as set forth in my copending application, Serial Number 586,825, a material such as a melamine or urea-formaldehyde resin, or a reaction product of these materials with a carboxy-methyl cellulose compound can be incorporated in the paper as a fiber-bonding, water-absorption-limiting material, either by addition to the pulp before the paper is prepared, or by impregnation after the paper is formed. When the web thus prepared is heated and dried, the aforesaid materials become coagulated or hardened and the paper foundation has its fibers bonded together and rendered resistant to penetration by'water.

The following examples, wherein parts and percentages are by weight, will serve to illustrate planographic printing plates made in accordance with my invention.

Example 1 Calendered water leaf sheets, prepared from long-fibered pulp to which a melamine resin is added during manufacture to improve the wet strength of the resulting paper, is brush-coated with a composition made by dissolving the aluminum salt of carboxy-methyl cellulose in aqueous ammonia, adding a plasticizer and a lower alcohol, and mixing colloidal clay with the resulting solution until a uniform slurry is obtained. The mixture has the following composition:

180 parts of the aluminum salt of oarboxy-methyl cellulose 463 parts of methyl alcohol 90 parts of aqueous ammonia (containing about 28 /2% of NI-la) 5238 parts of water 180 parts of colloidal clay After coating the paper with the foregoing composition, it is dried and calendered. The paper is again brush-coated with the same composition, redried, and again calendered. The sheet is then tub-sized with an aqueous metal salt solution having the following composition:

3% of copper sulphate (CuSO4) 1% of aluminum sulphate (Al2(SO4)a) /2% of ferric chloride (FeCla) /2% of chromium trioxide (Cl'Oa) After drying and calendering, the back of the sheet is advantageously coated with a 20% solution of Polystyron in ethyl acetate.

Example 2 Paper suitable for the foundation of a planographic printing plate, e. g., paper of the type employed in Example 1 is brush-coated with a uniform slurry composed of:

100 parts of a 5% aqueous solution of low viscosity sodium carboxy-methyl cellulose parts of china clay 3 parts of glycerine After drying and calendering the sheet, it is again brush-coated with the same composition and again dried and calendered. The paper is then tub-sized with a 5% aqueous solution of copper sulphate to insolubilize the coating, then dried and calendered. The sheet thus prepared is likewise advantageously provided, as in Example 1 with a water-resistant backing of Polystyron.

Instead of using copper sulphate in the foregoing example, or the mixture of metal compounds disclosed in Example 1, to insolubilize the carboxy-methyl cellulose coating on the paper, mixtures of metallic compounds, advantageously having a total concentration of about 5% can be used to obtain planographic plates having similarly advantageous properties. For example, solutions containing 5% of copper sulphate and /2% of chromium trioxide; or 2 of copper sulphate and 2 /2% of aluminum sulphate have been found satisfactory.

Variations and modifications can be made in the foregoing examples without departing from the scope of the invention, as will be obvious to those skilled in the art. Thus, other soluble salts of carboxy-methyl cellulose, such as the ammonium, calcium or magnesium salt, can be used instead of the sodium or ammonium-aluminum salt in preparing the initial coating composition for the paper. The penetration-re- Polystyron) can be applied either before or after the carboxy methyl cellulose coating is formed on the printing surfaceof the paper.

The concentration of carboxy-methyl cellulose compound in the aqueous solution employed to form the coating composition is preferably about 3 to 5% in the case of the sodium compound, or about 1 to 3% in the case of the aluminum compound (which is dissolved in aqueous ammonia or other aqueous alkaline solution). The coating on the paper preferably amounts to about 8 to 9 lbs. or more, per ream of 24" x 38" sheets. The amount of coating can be readily controlled by adjusting the proportions of ingredients in the coating composition, varying the number of coatings, or the amount of composition applied in each coating treatment. In the foregoing examples, each brush-coated treatment results in formation of a coating of about 4 pounds per ream so that the two treatments described produce a coating on the finished sheets of about 8 lbs. per ream.

Desired variations in the character of the insolubilized carboxy-"nethyl cellulose film can be obtained by varying the type of coagulant or precipitant employed in the process as illustrated in Examples 1 and 2. When a single metal compound is employed, it has been found that copper salts produce the most satisfactory film for most purposes, the copper compound of carboxy-methyl cellulose having a gelatinous nature, and yielding a coating of especially desirable properties. Thus, when mixtures of coagulant metal compounds are employed, they preferably include a cop er salt such as copper sulphate. The coagulan is advantageously used in a concentration of about 5%, although the concentration may be varied over a relatively wide range.

High wet-strength paper for use as a foundation for the plates of my invention can be advantageously made as disclosed in my copending application, Serial Number 586,825, by combining a concentrated melamine resin preparation (e. g. the product commercially available under the name of Melmac No. 7278) with a 2% aqueous solution of the sodium salt of a carboxymethyl cellulose; grinding the resulting precipitate to a colloidal slurry, adding the slurry to the paper pulp so as to incorporate it inthe paper, or impregnating the paper as it leaves the paper machine by applying the slurry thereto in a size tub, and drying and heating the paper to cause bonding of the fibres by the added material, thus forming paper of high wet strength and resistance to water absorption. Instead of using a precipitate of melamine-carboxy-methyl cellulose, a solution formed by mixing other melamine resins (e. g. Melmac No. 7277 which do not form a precipitate with dilute carboxy-methyl cellulose salt solutions with a 2%solution of sodium carboxy-methyl cellulose can be added to the paper pulp or used to impregnate the paper from a size tub. Methylolurea or lower urea-formaldehyde polymers can be used instead of melamine resins.

When the plate is to be used, its coated surface is typed, imprinted or inscribed with the desired image, using an oleophilic, ink-retaining, water-repellent, image-forming medium. The plate is then fastened on the cylinder of a planographic printingmachine, and wetted with the aqueous wetting solution employed in the fountain of the machine. No reagent capable sistant backing of waterproofing plastic (e. g., of reacting with the coating on the plate is required in the fountain solution, and accordingly the latter does not change its composition during use. Water alone can be used; or water containing such non-reactive materials as gum thickeners, wetting agents or buflers, generally'used in fountain solutions, can be employed. In the course of the printing, oleous ink is applied from an inking roller to the image-bearing surface of the plate, the ink adhering only to those portions of the plate which are inscribed with the oleous image, while being repelled by the background portions of the plate constituted by the coating moistened with the aqueous fountain solution. The inked image is then transferred to a printing blanket, used in offset printing and then applied to the sheet on which the copy of the image is to be made. Planographic plates prepared in accordance with this invention can be employed for making 6000 to 10,000 copies without substantial deterioration in 'the quality of the duplicate copies of the image. If desired, the inked plate can also be applied for direct printing of copies, the image in this case being the reverse of the matter to be duplicated on the copies.

If desired, the paper foundation can be printed or inscribed with an oleous image-forming medium to produce a water-repellent image before application of the soluble carboxy-methyl cellulose solution, the latter being repelled by the image and thus coating only the uninscribed portion of the plate. After drying, the coating of carboxy-methyl cellulose is converted to an insoluhie metal derivative as described above, and the plate is dried and calendered. The uninscribed portions of the plate can then be inscribed with an image-forming medium, and the plate can be used to make copies of the pre-formed as well as the later-formed image.

Moreover, if desired, plates prepared according tomy invention can be dried after use for duplicating an image inscribed thereon, a further inscription made on the background, and the plate used to make duplicate copies bearing the original as well as the later inscribed image. If desired, the filler and/or plasticizer can be omitted in preparing the surface of a pianographic plate in accordance with my invention, the paper foundation being coated one or more times with an aqueous solution of a water-soluble carboxymethyl cellulose compound having a concentration, for example of about 1% to 5%, the coating being dried to form a film after each application, and the film being insolubilized in the manner described above by conversion to a waterinsoluble metal derivative or salt or carboxymethyl cellulose.

I claim:

1. In the art of planographic printing, the process of preparing a master which comprises coating the surface of a paper foundation with a composition comprising an aqueous solution of a water-soluble carboxymethyl cellulose compound; drying the resulting coating; treating said coating with an aqueous solution of metal compounds consisting essentially of copper salts and aluminum salts in about equal parts by weight to coagulate the carboxymethyl cellulose; drying the coagulated coating; and inscribing an ink-receptive, water-repellent image on the surface of said coating.

2. In the art of planographic printing, the process of preparing a master which comprises coating the surface of a paper foundation with a composition comprising an aqueous solution of a water-soluble carboxymethyl cellulose compound; drying the resulting coating; treating said coating with an aqueous solution of metal compounds consisting essentially of copper salts and chromium salts in the ratio by weight of about 10:1 respectively to coagulate the carboxymethyl cellulose; drying the coagulated coating; and inscribing an ink-receptive, water-repellent image on the surface of said coating.

3. In the art of planographic printing, the process of preparing a master which comprises coating the surface of a paper foundation with a composition comprising an aqueous solution of a water-soluble carboxymethyl cellulose compound; drying the resulting coating; treating said coating with an aqueous solution of metal compounds consisting essentially of copper salts, aluminum salts, iron salts and chromium compounds in the ratio by weight of about 6:2:1:1 respectively to coagulate the carboxymethyl cellulose;

drying the coagulated coating; and inscribing an ink-receptive, water-repellent image on the surface of said coating.

4. In the art of planographic printing, the process of preparing a master which comprises coating the surface of a paper foundation with a composition comprising an aqueous solution of a water-soluble carboxymethyl cellulose compound; drying the resulting coating; treating said coating with an aqueous solution of metal compounds consisting essentially of copper sulphate, aluminum sulphate, ferric chloride and chromium trioxide in the ratio by weight of about 6:2:1:1 respectively to coagulate the 'carboxymethyl cellulose; drying the coagulated coating; and inscribing an ink-receptive, water-repellent image on the surface of said coating.

5. In the art of planographic printing, the process of preparing a master which comprises coating the surface of a paper foundation with a composition comprising an aqueous solution of a water-soluble carboxymethyl cellulose compound, and colloidal clay suspended therein as a filler; drying the resulting coating, the amount of said composition being such as to yield a dry coating of about 4 lbs. per ream of 24" x 38" sheets; repeating the foregoing coating and drying operations so as to form a coating of about 8 to 9 lbs. per ream of 24" x 38" sheets; treating said coating with an aqueous solution of metal compounds consisting essentially of copper sulphate, aluminum sulphate, ferric chloride and chromium trioxide in the ratio by weight of about 6:2:1:1 respectively; and forming an ink-receptive, water-repellent image on the surface of the resulting coating.

DOUGLAS A. NEWMAN.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,625,714 De Sperati Apr. 19, 1927 2,130,241 MacLaurin Sept. 13, 1938 2,214,565 Montgomery et al. Sept. 10, 1940 2,230,981 Toland Feb, 4, 1941 2,236,545 Maxwell Apr. 1, 1941 2,302,816 Toland Nov. 24, 1942 2,331,858 Freeman et a1 Oct. 12, 1943 2,370,517 Bass Feb. 27, 1945 2,373,287 Bassist Apr. 10, 1945 2,542,784 Van Dusen Feb. 20, 1951 OTHER REFERENCES Sodium Carboxymethylcellulose, Hercules Powder 00., Wilmington, Delaware. Copy in Div. 64.

Claims (1)

1. 5. IN THE ART OF PLANOGRAPHIC PRINTING, THE PROCESS OF PREPARING A MASTER WHICH COMPRISES COATING THE SURFACE OF A PAPER FOUNDATION WITH A COMPOSITION COMPRISING AN AQUEOUS SOLUTION OF A WATER-SOLUBLE CARBOXYMETHYL CELLULOSE COMPOUND, AND COLLIDAL CLAY SUSPENDED THEREIN AS A FILLER; DRYING THE RESULTING COATING, THE AMOUNT OF SAID COMPOSITION BEING SUCH AS TO YIELD A DRY COATING OF ABOUT 4 LBS. PER REAM OF 24" X 38" SHEETS; REPEATING THE FOREGOING COATING AND DRYING OPERATIONS SO AS TO FORM A COATING OF ABOUT 8 TO 9 LBS. PER REAM OF 24" X 38" SHEETS; TREATING SAID COATING WITH AN AQUEOUS SOLUTION OF METAL COMPOUNDS CONSISTING ESSENTIALLY OF COPPER SULPHATE, ALUMIONUM SULPHATE, FERRIC CHLORIDE AND CHROMIUM TRIOXIDE IN THE RATION BY WEIGHT OF ABOUT 6:2:1:1 RESPECTIVELY; AND FORMING AN INK-RECEPTIVE, WATER-REPELLENT IMAGE ON THE SURFACE OF THE REULTING COATING.