US2569488A - Method of continuously renewing lithographic printing surfaces by means of the fountain fluid - Google Patents

Description

Patenterl Oct. 2, 1951 METHOD OF CONTINUOUSLY RENEWING LITHOGRAPBIC PRINTING SURFACES BY MEANS OF THE FOUNTAIN FLUID 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 March 11, 1947. Serial No. 733.993

This invention relates to improvements in aqueous fountain fluids which are employed in the process of planograyhic printing.

Planographic printing involves the preparation of a master plate having water-receptive nonprint portions and water-repellent ink-receptive portions, constituting an image to be reproduced. The plate is moistened with an aqueous fountain fluid, repelled by the image, to render and maintain the non-print portions of the plate inkrepellent, and is then inked with printing ink to deposit the same on the ink-receptive image portions. The ink is then transferred from the image. usually by an offset blanket to a copy sheet, to form an impression of the image thereon. The molstening, inking and transfer operations are successively repeated for the production of large numbers of copies.

Plates to be employed in planographic print ing are provided with a surface which is adapted to constitute the non-print background, and likewise adapted to receive and retain an inkreceptive water-repellent image. The latter is formed by inscribing the plate with an oleophilic image-forming composition, or by photographic processes, for example, by sensitizing the plate with a light-sensitive gelatin-bichromate coating which, upon exposure to light under a photographic negative is insoluhilized and rendered ink-receptive. whereupon the unexposed watersoluble portions are washed away, exposing the underlying plate surface constituting the nonprint background. The said plates can be made of a metal. such as zinc or aluminum of which the surface is modified as by etching or graining to render them water-receptive; or of materials such as vegetable parchment, which possesses the desired hydrophilic as well as image-retaining properties: or the surface may be made of a hydrophilic insoluble colloid coating. such as casein-formaldehyde, insolubilized polyvinyl alcohol, or insolubilized carboxymethyl cellulose compounds.

In using the aforesaid plates for planographic printing, an aqueous solution, often referred to as an etch. is initially applied to the plate. said solution containing ingredients adapted to moisten the non-print background portions of the plate and render them ink-repellent. A similar solution is employed in the fountain of the printing press or molstening the plate before each inking operation, the solution being compounded to maintain the non-print background of the plate ink-repellent and toprevent spreading of the image. while at the same time avoiding undermining of the image. The useful life of the plate for printing copies is largely dependent upon the maintenance by the action of the foun- 4 Claims. (Cl. Mil-149.2)

tain fluid of a balance between the ink-receptive image portions and water-receptive non-print background portions so as to prevent encroachment of either upon the other. Solutions heretofore employed for molstening the plates, both as etch and as fountain solutions, ordinarily included a colloid thickener such as gum arable, gum tragacanth, or the like to impart desired properties, such as adherence to the plate without undermining the image. Moreover, they usually contain ingredients such as wetting agents. butters, hygroscopic agents and the like, to maintain the desired acidity. to prevent drying out, and to accomplish other specific purposes with reference to the nature of the surface on which they are used.

Sometimes it is desired to compound the plate moistening or fountain solutions so as to permit plates moistened therewith to be dried. stored and later re-used for printing, without deleterious effect upon the hydrophilic properties of the background areas and without injury to the image.

The colloidal thickeners commonly employed in such solutions, e. g. gum arabic, gum tragecanth, soluble starch and the like constitute excellent media in the aqueous mixtures in which they are employed, for the growth of molds, bacteria and the like, which alter the properties of the solutions and render them useless for the intended purpose. Thus if solutions which have soured or spoiled are applied to a printing plate, they can ruin the plate for further use, causing serious losses in time. effort and expense. While the solutions can be manufactured and distributed in sealed containers under sterile conditions, they are subject to contamination as soon as they are opened and exposed to the air, necessitating constant use of fresh containers and discarding of unused solution.

In order to prevent such deterioration of thickened plate molstening solutions, it has been attempted to include therein a preservative, such as phenol or a phenolic compound, or cyclic organic acids or their salts such as benzoates, salicylates, and the like. However, these materials to be effective must be present in a concentration of the order of one per cent or more in the solution, and when used in these concentrstions, the preservative rapidly destroys the image on the plate. Accordingly, in practice. a fresh batch of fountain solution must be frequently used, and large amounts of solution must be discarded. This involves considerable inconvenience, waste and expens I have discovered that aqueous plate dampening solutions which contain carboxymethyl cellulose or its salts or other compounds as 001- loidal thickeners, instead of the vegetable gums heretofore employed, are highly effective as etch and fountain solutions in planographic printing. Thus, they maintain the desired balance between the hydrophilic properties of the non-print background area and the ink-receptive water-repellent properties of the image over long periods. The carboxymethyl cellulose compounds when used in such solutions are compatible with all of the other desired or usual ingredients, such as hygroscopic agents, buffering salts and other ma terials, ordinarily employed in etch or fountain solutions. Moreover, in addition to these advantages, carbogrymethyl cellulose compounds are relatively resistant to the deleterious effect of molds, bacteria and the like. Thus. I have found that planographic etch and fountain solutions containing a carboxymethyl cellulose compound as the thickening agent can be rendered immune under ordinary conditions of use to spoilage from mold or bacteria by addition of minute amounts of preservatives in concentrations which have no effect upon the life of the image on the plate. Thus, I have found that concentrations of the order of about 0.1 per cent of the usual preservatives, such as phenols, benzoates, salicylates, formaldehyde and the like, are effective to prevent spoilage of fountain solutions prepared in accordance with my invention when stored in containers and handled for use without any precautions to maintain the solutions sterile. Moreover, the aforesaid preservatives when used in concentrations not exceeding 0.5% have no effect upon the printing image.

when planographic plates moistened with fountain solutions containing a carboxymethyl cellulose compound as the thickening agent are dried, the carboxymethyl cellulose forms a protective film overlying the plate capable of maintaining the plate insensitive to soiling by casual contact with other objects, which would otherwise form smudges or impressions, adapted to pick up ink during'subsequent printing operations and to transfer impressions thereof to the copies. The carboxymethyl cellulose coating has, in effect, the desired properties of a pianographic plate surface, so that upon remoistening the plate with fountain fluid, the background portions have the desired ink-repellent hydrophilic properties. Moreover. the surface formed on the plate when the fountain solutions of my invention are dried thereon is receptive to additional image-forming matter, so that the dried plate can be inscribed with an additional image to be reproduced on copies subsequently printed therefrom.

Planographic plate moistening solutions of my invention are illustrated by the following examples, wherein parts and proportions are by weight.

Example 1 A planographic plate moistening solution was prepared by mixing the following ingredients in the proportions indicated:

Water Crude glycerine i2 Giycerine (C. P.) 48 Sodium carboxymethyl cellulose (low viscosity) The sodium carboxymethyl cellulose is dissolved in the water, and the acid ammonium phosphate, glycerine and phenol are added thereto. The resulting solution is suitable for useas an etch on coated plates having, for example, an insolubilized carboxymethyl cellulose printing surface. as well as on metal and parchment plates. It was further found that this composition can be allowed to stand exposed to air under conditions of use without special precautions to maintain its sterility, and without danger of spoilage from bacteria, molds or ferments.

The solution of this example can also be used as a fountain solution in the aforesaid plates. However, depending upon the type of plate employed, it is generally advantageous to dilute the solution with water for this purpose. For example, in the case of metal plates, the solution when used in the fountain is advantageously diluted with 20 to 40 parts of water to 1 part of solution; while in the case of coated or parchment plates, the solution can be used undiluted or may be diluted with up to 20 parts of water for use in the fountain.

Instead of phenol, a. similar quantity of formaldehyde can be used in this example.

Example 2 A fountain solution was prepared as in Example 1 containing the following ingredients in the proportions indicated:

Grams Water 69.8 Crude glycerin 6 Glycerin (C. P.) 12 Sodium carboxymethyl cellulose (low viscosity) 0.6 NH4H2PO4 4-4 Phenol 0.1

The composition of this example differs from that of Example 1. mainly in that it contains a relatively smaller proportion of glycerine. Like the composition of Example 1, the composition of this example was likewise immune to the action of ferments, molds. or bacteria, under usual conditions of use and storage. The solution of this example can be used in the same manner as the composition of Example 1. as an etch or fountain solution.

The composition of both of the foregoing examples are highly effective for maintaining the non-print background portions of a planographlc plate ink-repellent and water-receptive, and at the same time, preserving the ink-receptive water-repellent image unchanged throughout the use of the plate for printing copies.

Instead of the phenol, employed as a. preservative in the foregoing examples, other preservitives can be similarly used. Such materials are other cyclic organic salt-forming compounds such as other phenols or phenolic compounds, or cyclic organic compounds containing salt-forming groups, particularly carboxylic or sulfonic acid groups, such compounds being usually employed in the form of their water soluble salts. Thus, suitable preservatives include sodium benzoate, sodium salicylate and organic preservatives sold under trade-names such as "Moldex or "Dowicide." The cyclic compounds employed are usually aromatic compounds. Formaldehyde can likewise be used as the preservative. All of these materials can be used in minimum proportions of about 0.1% to provide a solution substantially immune to injury from i'erments, molds, or bacteria. Moreover, in general. these preservatives can be used in concentrations up to 0.5 per cent by weight without deleterious effect upon the image on plates to which the solutions are applied.

Instead of the sodium salt of carboxymethyl cellulose, employed in the foregoing examples, other water-soluble salts thereof can be used; for example, the potassium or ammonium salt or the ammonium-aluminum salt. Moreover, solutions made up with such salts, and acidified to liberate the carboxymethyl cellulose in free acid form can be used. In this case, the carboxymethyl cellulose remains in solution until the solution is dried to form a film, whereupon it becomes substantially insoluble in water. The amount of carboxymethyl cellulose employed in the solutions of my invention is such as to yield the desired viscosity in the plate moistening solution, and generally varies from 0.5 to 1.5 per cent by weight. The presence of vegetable gums or other colloidal materials supporting growth of mold or bacteria is avoided, the carboxymethyl cellulose compound constituting essentially the sole colloidal thickening agent employed.

The ammonium acid phosphate in the above examples acts as a buffering agent to establish and maintain mild acidity in the solution. However. other buffering agents can be employed, preferably yielding a pH within the range of 3.5 to 5. Sometimes, salts heretofore used in fountain solutions were found undesirable in that they blackened or corroded metal printing plates, or metal portions of the printing machinery. Inasmuch as ammonium acid phosphate does not have this effect, it is particularly desirable for use in my compositions. Moreover, this salt does not interfere with properties of the carboxymethyl cellulose compound as a protective film, when a plate moistened with the solutions of this invention is dried. Ammonium acid phosphate can be added, as illustrated in the foregoing examples, in proportions amounting to about per cent by weight.

The glycerine employed in the foregoing examples serves as a hygroscopic agent to prevent drying of the solution on the plate during use. It can be employed in a. relatively wide range of concentrations, as for example, between and 40 per cent by weight. Instead of glycerlne other hygroscopic materials, such as ethylene glycol or other hygroscopic polyhydric alcohols can be used in similar proportions.

When the solutions of my invention are to be used specifically for forming a protective film on a planographic plate after use, so that the plate can be conveniently stored for reuse, the concentration of glycerine or other hygroscopic agent is advantageously reduced by replacing it with water. Thus, the glycerine concentration can be reduced to about 5% or less in the foregoing examples. Despite the lowered concentration of hygroscopic agent, the resulting solution still yields satisfactory results as an etch or fountain solution.

By virtue of the fact that the plate moistening solutions of my invention preserve the balance between the hydrophilic non-printing background of the plate and the water-repellent inkreceptive printing image, planographic plates moistened therewith can be used to produce five to ten thousand or more copies, without substantial deterioration of the image reproduced on the will.

The solutions are universally effective. regardless whether the surface of the plate on which they are employed is of metal or parchment, or is coated with aniusoluble colloidal coating. It is however, particularly advantageous to use the solutions of my invention in conjunction with plates having an insolubllized carboxymethyl cellulose coating, inasmuch as the solution itself tends to renew any portions of the coating which might be removed or worn away during use of the plate. without essentially changing the nature of the plate surface. Furthermore, when used on a carboxymethyl cellulose-coated plate and the plate is dried for storage and subsequent use. the film formed by the solution of my invention is of substantially the same nature as the original coating. The surface thus formed is insensitive to injury by casual smudging. At the same time, it is adapted to receive additional image-forming inscriptions for reproduction on copies subsequently made therewith.

When used on other types of plates. the solutions of my invention can also be dried and yield films which protect the surface of the plate, and at the same time maintain the hydrophilic properties of the non-print background unchanged for subsequent printing operations. The dried solution forms a surface lacking the tacky properties of gum compositions, heretofore used, and this facilitates storage of the plates for later use.

As stated above. the solutions of my invention containing preservatives in concentrations of the order of 0.1 per cent, and not more than 0.5 per cent, are completely resistant to spoilage by fermentation and require no special precautions when the containers in which they are kept have been opened for use. Thus, they avoid the necessity of the printer making up a new etch or fountain solution each time the press is to be used and cleaning the press of used fountain solution whenever the press is shut down, while at the same time they present no danger of ruining the plates from which copies are to be printed.

Variations and modifications may be made within the scope of this invention and portions of the improvements may be used without others.

I claim:

1. The process of planographic printing which comprises forming an ink-receptive water-repellent image on a planographic plate having its printing surface coated with a water-insoluble carboxymethyl cellulose compound, dampening said plate with an aqueous fluid comprising water and a colloidal thickener consisting essentially of a carboxymethyl cellulose compound dissolved therein in an amount yielding the desired viscosity, inking said plate to deposit ink on the image portions thereof, transferring the ink from said image to a copy sheet, and successively repeating said dampening inking and transfer operations.

2. The process of planographie printing which comprises forming an ink-respective water-repellent printing image on the surface of a pianographic plate having a hydrophilic surface for forming non-print background areas, dampening said plate with an aqueous fluid comprising water and a colloidal thickener consisting essentially of a carboxymethyl cellulose compound dissolved therein in an amount yielding the desired viscosity. inking said plate to deposit ink on the image portions thereof, transferring the ink from said image to a copy sheet. dryin said plate withil lt otherwi e "mam! Mid fluid. iuscribinl additional image-forming matter directly on the surface oi said plate as dried, and subsequently repeating said dampening, inking and transfer operations for reproduction of the original image together with the subsequently inscribed image.

3. The process of planographic printing which comprises forming an ink-receptive water-repellent image on a planographic plate having its printing suriace coated with a water-insoluble carboxymethyl cellulose compound. dampening said plate with an aqueous fluid comprising water and a colloidal thickener consisting essentially of a carboxymethyl cellulose compound dissolved therein in an amount yielding the desired viscosity. inking said plate to deposit ink on the image portions thereof, transferring the ink from said image to a copy sheet, drying said plate, inscribing additional image-forming matter on the surface thereof. and subsequently repeating said dampening, inking and transfer operations for reproduction of the original image together with said subsequently inscribed image.

4. The process oi planographic printing which comprises forming an ink-receptive, water-repellent image on the surface of a pianographic plate of which the surface is coated with a water-insoluble carboxymethyl cellulose compound, damp- REFERENCES CITED The following references are of record in the tile of this patent:

UNITED STATES PATENTS Number Name Date 2,003,268 Wescott May 28, 1935 2,060,190 Foster Nov. 10, 1936 2,186,846 Wood Jan. 16, 1940 2,240,486 Beckley May 6, 1941 2,331,245 Stockmayer Oct. 5, 1943 2,393,875 Van Dusen Jan. 29, 1946 OTHER REFERENCES Sodium carboxymethylceliulose Products Dept., Wilmington, Delaware. Cellulose Products Dept, Hercules (4 pages).

Claims (1)

1. THE PROCESS OF PLANOGRAPHIC PRINTING WHICH COMPRISES FORMING AN INK-RECEPTIVE WATER-REPELLENT IMAGE ON A PLANOGRAPHIC PLATE HAVING ITS PRINTING SURFACE COATED WITH A WATER-INSOLUBLE CARBOXYMETHYL CELLULOSE COMPOUND, DAMPENING SAID PLATE WITH AN AQUEOUS FLUID COMPRISING WATER AND A COLLOIDAL THICKENER CONSISTING ESSENTIALLY OF A CARBOXYMETHYL CELLULOSE COMPOUND DISSOLVED THEREIN IN AN AMOUNT YIELDING THE DESIRED VISCOSITY, INKING SAID PLATE TO DEPOSIT INK ON THE IMAGE PORTION THEREOF, TRANSFERRING THE INK FROM SAID IMAGE TO A COPY SHEET, AND SUCCESSIVELY REPEATING SAID DAMPENING INKING AND TRANSFER OPERATIONS.