US3666502A - Lithographic inks and solutions for treating lithographic plates - Google Patents

Abstract

TRIACETIN AND HEXYLENE GLYCOL ADDITIVES ELIMINATE PROBLEMS OF SCUMMING AND GREASING WITH LIGHOGRAPHIC INKS IN CONNECTION WITH ALL TYPES OF LITHOGRAPHIC PLATES. THESE ADDITIVES IMPROVE DIFFERENTIAL INKABILITY THUS GIVING SHARPER IMAGES AND HIGH RESOLUTION WITHOUT SACRIFICING FULLNESS OF PRINT.

Description

United States Patent 01 :"fice US. Cl. 106-22 6 Claims ABSTRACT OF THE DISCLOSURE Triacetin and hexylene glycol additives eliminate problems of scumming and greasing with lithographic inks in connection with all types of lithographic plates. These additives improve differential inkability thus giving sharper images and high resolution without sacrificing fullness of print.

BACKGROUND OF THE INVENTION The instant application is a continuation-in-part application of Ser. No. 752,443, filed July 19, 1968, which in turn, is a continuation application of Ser. No. 456,557, filed May 17, 196-5, now abandoned. The instant invention relates specifically to a composition for a lithographic ink containing an additive to eliminate problems of scumming and greasing, to permit printing with a relatively dry litho plate, and to improve, magnify and exaggerate the differential inkability near the boundary line between the aqueous and oil phases present on a lithographic plate so as to transfer a sharp image to the printing surface. The instant additives in a litho ink permit higher resolution in excess of about 200 lines per inch at the same time eliminating problems of scumming or greasing.

There are four distinct printing systems for transferring ink to paper or other surfaces: (1) letterpress or relief printing, in which the type or illustrations are above the surface to receive the ink from distributing rollers (2) lithiography or planographic printing, in which ink is transferred from a level or plane surface (3) intaglio or gravure, in which ink is transferred from a depressed surface and (4) screen printing in which a roller squeezes ink through a piece of screen stretched on a frame. Each system requires different inks for different presses and papers, thus the printing-ink industry is generally a custom prescription one. This requires a formula made for the particular transfer method, vehicles adapted for specific press operations, and pigment colorants chosen for particular reasons. The formula is carefully recorded, by weight of the ingredients, and is given a number. Repeat orders for additional or later runs must be exact to the smallest tolerance (see McGraw-Hill Encyclopedia of Science and Technology, vol. 7, pp. 112 et seq.).

In lithographic printing, a plate is employed having a surface which is water receptive. The information ultimately to be printed is then coated onto this water-receptive surface using a coating which is water repellent and oil receptive. In the printing process, the plates are placed on a machine which first attempts to wet the entire surface with a water solution but which, in fact, wets only the water-receptive surface, leaving the oil-receptive surface free of water. In other words, one area must receive the printing ink and the other must repel it. When this type of inked plate is pressed against a sheet of paper or metal or other surface, the ink from the ink-receptive area is transferred to the surface on which a print appears. To make it difficult for the ink to mix mechanically with the water, the aqueous and non-aqueous phases should be of widely different viscosities. Thus, high vis- 3,666,502 Patented May 30, 1972 cosity inks that are insoluble in water are ideal lithographing inks. The solvents used in moisture-set inks are soluble in water and, therefore, these inks cannot be used. (See Industrial Printing Iinks by Louis M. Larsen, Reinhold Publishing Corporation, New York, 1962.) However, an ink should not be too viscous for then it tends to pick the paper surface and the distribution on the ink rollers is poor. Also, fast printing requires a softer ink body than does slow printing. In any event, because of the frequent contact of the ink with the fountain solution, there will 'be some degree of absorption of the fountain solution by the ink. This normally yields a water-inoil type emulsion. The ink body becomes lower in tack and has less flow. Thus, depending upon the particular need of the printer, the ink manufacturer supplies a particularly compounded ink.

In the text entitled Ink and Paper in the Printing Process Interscience Publishers, New York, 1952, by Andries Voet, in the chapter on Properties of Lithographic Inks at p. 23, it is stated The intimate contact with water or with aqueous solutions results in a complex set of requirements for a lithographic ink. It is perfectly obvious that the ink constituents, such as pigment, vehicle, and drier, must not dissolve or disperse in water, neither in mere contact nor when subjected to shear, since ink and water are continuously brought together under shear by the rapidly rotating plates and rollers. Ink and water films in intimate contact under shear will always show a certain amount of emulsification. As long as the emulsion is of the water-in-oil type it will generally not prevent the proper functioning of the lithographic ink.

The problem of scumming has become particularly serious when using silver halide photographic lithographic plates commonly called, Photo Direct Plates as described in U.S. Pats. Nos. 3,146,104 and 3,146,105. In such plates, photosensitive materials are embedded in a gelatinous film on the surface of the plate. This plate is then placed in a camera and then exposed to the printed material which it is desired to reproduce. The plate is then developed so as to have a positive image thereon. The characteristics of the plate are such that the image area is water repellent and oil receptive; the background area is water receptive and oil repellent. But the contrast in these photodirect plates is much less than in a conventional litho plate, so they tend to scum more easily.

Since the additives triacetin (common name for glyceryl triacetate) and hexylene glycol have been discovered virtually to eliminate scumming in litho inks, together with imparting magnified difierential inkability in lithographic printing, it would be well to consider what the undesirable characteristics of scumming or greasing are. Scumming is a peculiar phenomenon. Even today, after well-nigh a century, the exact mechanism of its cause and the varying degrees in which scumming is exhibited with different inks, depending upon their composition and the conditions under which they are run, is not fully understood. The fundamental causes of scumming in lithography are still under investigation. (Printing Ink- Manual, p. 722 edited by Bowles, Askew et al., published by W. Heifer and Sons Ltd., Cambridge, 1961.) Briefly, when an ink is being run on a lithographic press, particularly an offset lithopress, and it shows a tendency to scum, the scumming can usually be avoided by increasing the amount of water. A printing press is said to be catching up when non-image areas of the plate get inked. Increase of water tends to chase out the ink and clear up the scumming. However, where the scumming has already progressed to the point where the ink has attached itself to the edge portions of the image on the plate which have lost their repellency to ink, then scumming cannot be cleared up by increasing the Water. Note that where an effort is made to overcome scumming by addition of water, one runs the risk of having too much water, so that the ink tends to emulsify. Thus it might be that, for a particular ink, the plate is run so wet that there is very little latitude between scumming and emulsification of the ink.

During the preparation of the lithographic plate, there is formed on the surface of the non-image areas a film that is receptive to water but not to ink. If this film is worn off by abrasion, the damaged areas can become receptive to ink and greasing or scumming will result. The abrasion on the plate can be due to improper roller settings, too much pressure between the plate and the blanket, and to abrasive particles in the ink or in the coated paper. Should the dampening rollers be covered with areas of dried ink, the fountain solution cannot be evenly distributed on these rollers. The result is insufiicient moisture on the corresponding plate areas and, as a result, they receive ink, which gives rise to greasing or scumming. If insufficient water is transferred to the plate, the entire plate will receive ink and this, of course, is to be avoided. The instant invention permits the use of a relatively dry plate and, in general, a correspondingly lower amount of ink feed so that a full and sharp image is printed despite the fact that the plate runs relatively dry. Surprisingly, these advantages are gained with a broadening of the latitude within which the conditions of ink and water may be adjusted for a successful run on the press, which, again permits a wider choice of printing inks, Without having to set up the press very critically, as the ink on the press is changed from one ink to another.

Lithographic printing plates are normally etched with phosphoric acid, chromic acid, and other acids which form metal salts on the surface of the plate, which salts are highly hydrophilic yet which have very low solubility in water. It stands to reason that if the etched surface were soluble in the aqueous fountain solution, the etch would disappear rapidly and the surface would be highly inked. Lithographic plates are often sponged over with a concentrated solution of gum arabic or similar material and dried, an operation which desensitizes the surface further so that the non-image areas will no longer ac cept ink provided they are kept damp. With the use of the instant additives in the ink and/or in the water fountain solution, there is no necessity for using a gum arabic coating.

Voet, in his discussion of lithographic printing problems, states Unlike tinting; greasing is not an overall effect on the lithographic plate, but is characterized by the formation of ink-receptive centers on water receptive areas of the plate. Greasing cannot be removed without injury to the plate. According to Zettlemeyer greasing is caused by a migration of surface-active agents from the ink to the nonwork area. If a surface-active agent of the proper structure migrates from the ink, it may be absorbed by the zinc (or aluminum) salt coating with its polar group orientated toward the plate. The hydrophobic non-polar part will then create an ink-receptive center in an ink-repellent area, resulting in greasing A proper lithographic ink must be made up from ingredients which are water resistant. It must not show tinting or greasing. Its tinctorial strength must be higher than used in typographic inks. (Our emphasis.)

It is a particular facet of this invention that sponging with a solution containing one or both of the additives is unnecessary, since the problem of scumming can be eliminated merely by the addition of the instant additives to the ink, and/or the water fountain solution. Specifically, the problem of scumming with either metallic or silver halide lithographic plates has been entirely eliminated even to the point that if the water-transfer-roll is removed from contact with the plate for a short time, or if the roll is allowed to go dry, such that ink is transferred to the entire plate and then to the paper being printed, when the transfer roll is again placed in contact with the plate or is again moistened, the background area very quickly clears up and it is entirely scum free, if either one or both additives are dissolved in the water fountain solution.

In the text on Industrial Printing Inks by Larsen, Reingold Publishing Company, London, 1962, in the chapter on Printing and Drying Methods, the following comment on the lithographic printing system is made: The best Way to prevent the ink from adhering to the non-printing area is to wet this area with a liquid that does not dissolve the ink and will not readily mix with it mechanically. Such a liquid can be water, which is used commercially Thus high viscosity inks that are insoluble in water are ideal lithographic inks. The solvents used in moisture-set inks are soluble in the water and therefore these inks cannot be used. (Our emphasis.) Accordingly, all efforts have been directed to formulating inks so as to make them more and more water repellent, and to deliberately avoid any ingredient which might transfer into the aqueous phase. Yet it is a critical requirement of the instant composition that the additives triacetin and hexylene glycol be at least partially soluble in water, which would be expected to have the opposite effect from making the ink more water repellent.

The use of triacetin as a plasticizer is known, when the printing is to be done on plastic films of synthetic resinous materials. It is well recognized in the art that such printing is a very particular art far removed from lithopress printing on paper. This is evidenced by the following statement: When printing on films of such materials as cellulose acetate or polyvinyl chloride, it is desirable to incorporate some solvent which will slightly attack the film and provide a key. This is sound in principle, but difiicult in practice, because most of the useful solvents are too volatile for use on letter press or lithographic machines, and the highly non-volatile ones may have an oxidation-retarding or film-softening effect. It is usually possible, however, to add small quantities of plasticizers such as tritolyl phosphate or dibutyl phthalate with useful eifects. Regenerated cellulose (cellophane, etc.) and similar transparent films are not, if it can be avoided, printed by sheet-fed letter press or offset because they are very difiicult to feed in sheet form, due not only to their flimsy nature but also to static electricity. They are usually, therefore, printed from the web, by gravure or aniline. Printing Ink Manual, top of p. 383.)

Plasticizers do not belong in litho inks. The use of plasticizers in inks (in general) is distinct from and particularly distinguishable from the use of an additive for the magnfication and exaggeration of differential inkability. For example, in the discussion of plasticizers in Larsen, it is stated Plasticizers are incorporated into plastics to promote their flexibility. Cellophane is a typical example Many plastics upon ageing fail in this manner because their plasticizer is removed in some manner, possibly by evaporation or migration. Plasticizers are incorporated into printing inks to yield flexibility of the resultant films and also to promote adhesion to the surfaces printed. If a pigmented nitrocellulose-solvent ink is printed on a supercalendered paper, the dried ink film can be removed from the paper easily by simply bending and shaking it. The addition of 3 percent dibutyl phthalate to this ink increases the adhesion so that the dried ink adheres well to the paper. (Bottom of page 128.)

It is to be noted that plasticizers are defined as being materials added to a plastic to facilitate compounding and improve flexibility and other properties of the finished product. (The Condensed Chemical Dictionary, Reinhold Publishing Corp., New York.) It is diflicult to conceive how vehicles used in lithographic inks can be termed plastics, and therefore the use of an additive in a litho ink cannot possibly have a plasticizing function. lncidentally, it will be noted that the first industrial plasticizer was camphor, used to make celluloid from nitrocellulose. At present, the important plasticizers are nonvolatile organic liquids or low melting solids, especially the phthalate, adipate and sebacate esters and aryl phosphate esters.

Larsen also states one of the problems in the use of plasticizers for resin-solvent inks is the possibility that the plasticizer may leave the ink film. This can happenby slow evaporation at room temperature or by migration into surrounding areas. Dibutyl phthalate evaporates very slowly, upon aging, and eventually the ink film becomes brittle and loses its adhesion. However, if the printed matter is soon discarded, not only can dibutyl phthalate be used but also dimethyl phthalate, which evaporates perceptibly faster. Thus evaporation at room temperature must be considered in choosing a plasticizer. (Bottom of page 129.) Under the same subheading of plasticizers, Larsen states The plasticizer selected must not be removed by contact with other surfaces, nor leached outby water or by solvents that can come in contact with the printed film. Plasticizers have to fill many dlfferent kind of needs and are derived from many sources and represent diverse types of properties. Here are some of the plasticizers. Triacetin, caster oil and blown castor oil are among the plasticzers listed. (Bottom of page 130.) Clearly the choice of a plasticizer in a litho ink would be inapposite; and if, arguendo, one were chosen, it would not be one that was leachable and at least partially soluble in water. Particularly noteworthy is the statement in the Printing Ink Manual in the chapter on Regenerated Cellulose Film it is stated that As far as is known, the lithographic process is never used on cellulose film probably because fairly transparent inks are normally used and a white background is essentially. (Page 131.)

It is well known that in moisture-setting inks, the liquid in the varnish is almost invariably a glycol. Ethylene, diethylene, propylene, and dipropylene glycols are prominently used, as solvents for shellac, unmodified alkyds, resole-type alkali catalyzed phen-olics, and resin-modified maleic and fumaric resins. Other materials used as binders include certain cellulose derivatives ineluding cellulose nitrate, and protein-like substances such as zein. (Printing Ink Manual, middle of page 389.) Moisture set inks are used on letterpress cylinder presses and rotary presses, not on lithographic offset presses, and one skilled in the art would not take ingredients which are specifically designed for use in an aqueous-based ink and transfer them to a litho ink which is essentially nonaqueous and water repellent.

U.S. Pat. No. 2,165,499 discloses the use of triacetin as a plasticizer for a cellulose acetate, based ink, in at least 500% of the total weight of the plasticizable material present in the composition which additionally contains large quantities of acetone and alcohol (23% in Example 1, 33.7% in Example 2). One skilled in the art would not seriously consider such inks as litho inks, and would immediately recognize that any ink with such large quantities of water-soluble materials would never run on a litho press. The disclosure also contains an example of a suitable lacquer for backing a printed cellulose acetatebased film.

Lacquers are used for a completely diiferent function as compared with inks. For example, lacquers are used for moisture-proofing film, particularly viscose film which is greatly benefited by a coating of a moisture-proofing lacquer, and on metallic foils which are to be subsequently inked, as for example aluminum foil which is extensively used in packaging. In the case of viscose film, the traditional lacquers used were composed of nitrocellulose, resins, plasticizers and waxes. The printing of these films by photogravure and fiexographic methods does not present serious problems, provided due regard is given to consideration of the nature of the coating lacquer. Metal foils are coated by the use of overprint varnishes with the desired physical and chemical characteristics. The varnishes generally consist of plasticized solutions of resins such as vinyl acetate, cellulose nitrate, ethyl cellulose, etc. For metal foils resins and binders must be used which will give rise to flexible films, and most fiexographic and gravure inks are therefore based on the ceHulose derivatives combined with resins with good adhesion properties such as the rosin esters, shellac, etc. suitably plasticized. Since in many instances the package will be sealed by heat, the inks must be resistant to high temperatures and excess of plasticizer, and resins of too low melting point must be avoided. Solvents will be chosen according to the binders used and both alcohol and hydrocarbon systems may be used. (Printing Manual, page 484.) Lacquers which include a water phase are not known.

The characteristic of inks used for printing metallic surfaces such as tin plate is that they dry by oxidation, polymerization, evaporation or by any combination of these three since they cannot dry by penetration and absorption into the substratum. Considerable polymerization is desirable for obtaining suitable hardness. On the other hand, the ink vehicle when dry must also be quite flexible since the tin plate is printed while it is flat and subsequently formed to make the final product, such as a can, lid, or cap for a bottle. Therefore, the vehicle is usually an alkyd type which possesses stretchability, flexibility, seratchproofness as well as hardness. Generally the tin plate is coated with a lacquer or a white undercoat, which is dried before printing the various colored inks. The latter are printed from a one color or a two color lithographic ofl'set press. The sheets are dried before printing the various colored inks. The overcoating varnish is applied either over the dried ink films or over the last colored ink while it is still wet. The ink films and the varnish are dried in a gas fired oven at a high temperature, frequently over 300 F. for about 10 minutes; thus the importance of heat stability, resistance to oxidative chemical change, and a requirement of low vapor pressure. It is for these specific conditions that triacetin has been disclosed in the prior art as a plasticizer, and the concentration used, in comparison with the concentrations used in the instant application, is clearly dispositive of the difference in the function of the compound.

US. Pat. 1,924,961 discloses triacetin as a low vapor pressure solvent for cellulose lacquer types of bonding mediums. It is also said to serve as a disperse medium for a suspension of (sic) emulsion according to the nature of the bonding medium (pg. 4, col. 1, lines 67-70). The bonding medium incorporated solvents and it was the purpose of the invention to effect a union between prehardened decorations and base materials by a method involving the use of low vapor pressure solvents in the bonding medium for the decoration. Several compositions are listed for bonding mediums. They contain butyl carbinol, butanol benzyl alcohol, acetone, methyl Cellosolve, diacetone alcohol, butyl Cellosolve which are highly water soluble solvents and volatile. Other constituents are toluol, benzol, Varnolene, and turpentine which are highly volatile, low flash-point solvents. The compositions are highly solvent-extended glues which are totally unsuitable for printing of any kind.

Another suprising discovery is that aqueous solutions of triacetin and hexylene glycol are excellent desensitizers. A particularly good desensitizer is hexylene glycol in water whether or not a primary alcohol is present. In general, Dahlgren presses and modifications thereof are run with up to 25% alcohol in the water to prevent scumming. However, when every four gallons of fountain solution contains more than a gallon of isopropyl alcohol, for example, so much alcohol is volatilized that in a big printing room the fumes from the solution are not only hazardous to health, but are a fire hazard. Use of triacetin or hexylene glycol in the aqueous fountain solution permits eliminating or at least cutting down the concentration of alcohol in the Dahlgren press to the point where the problem of noxious vapors is eliminated.

SUMMARY OF THE INVENTION It has been discovered that triacetin and hexylene glycol are additives which, when employed in the critical range of from .5 to by weight of a conventional lithographic ink, effectively eliminate problems of scumming or greasing of plates, at the same time permitting magnified differential inkability so as to permit sharpness of image without sacrificing fullness. It has also been discovered that an aqueous solution of either or both additives, when used in the water fountain of a litho press, effectively eliminates scumming and allows the litho press to be run with a less wet plate utilizing less water as feed to the plate with concomitant consumption of less ink and operation of the press under a wider range of conditions without sacrificing any quality in the finished product.

It is an object of the instant invention to provide two additives: the first, triacetin, is slightly soluble in water at ambient temperatures; and the other, hexylene glycol, is completely soluble in water at ambient temperatures, so that when at least one of the additives is incorporated into a conventional lithographic printing ink which is essentially immiscible in water, a lithographic printing press may be operated over a wide range of settings for ink and water feed, without danger of tinting, scumming or greasmg.

It is another object of the instant invention to provide a method for preventing scumming or greasing, by treating the litho plate with a solution of glycerol triacetate or hexylene glycol when a lithographic printing press displays symptoms of catching up when normal amounts of water are fed to the plate.

It is still another object of the instant invention to provide a composition which might be added to a litho ink on a litho press in operation on a conventional litho press, so that addition of said composition will rectify the catching up or greasing of a litho press to normal, scumfree operation.

It is still another object in the instant invention to provide a method for operating a litho printing press with a variety of conventional lithographic printing inks feeding much less water to the plate, by incorporating a critical amount of triacetin in the litho printing ink and/ or hexylene glycol in the water fountain of the litho press to prevent scumming or greasing.

It is still another object of the instant invention to provide a method of operating a Dahlgren-modified printing press in which triacetin or hexylene glycol, or both, are dissolved in the fountain solution.

PREFERRED EMBODIMENT OF THE INVENTION In the preferred embodiment of the instant invention, triacetin is incorporated into the lithographic ink in an amount from about 0.5 to about 10% by weight of the ink. Triacetin is partially soluble in water to the extent of about 5.8% by weight at 25 C. It is a colorless liquid with slight fatty odor and a bitter taste. Its specific gravity is about 1.160 C.), and it has a boiling point of about 258260 C. It is very soluble in alcohol, ether, and other organic solvents. It is obtained by the action of acetic acid on glycerol, and is a bulk chemical. It is used as a camphor substitute in pyroxylin industries, as a plasticizer, as a fixative in perfumery, in the manufacture of cosmetics, and as a specialty solvent. It is also used as a component in binders for rocket fuels, as well as for a plasticizer for cellulosic material and, particularly, to plasticize cellulose acetate tow in cigarette filters. Commercially available glyceryl triacetate, employed in accordance with the present invention, is supplied by Union Carbide Corporation and is described in their bulletin F-41l52, dated November 1964. So far as I know triacetin has never been employed in a lithographic ink prior to my discovery of its unique property of preventing scumming.

Hexylene glycol is a colorless, nearly odorless liquid. It is slightly less dense than Water, has a boiling point of 198.3 C., and is essentially completely miscible with water. It is used for hydraulic brake fluids because of its low freezing point and as a solvent-coupler, particularly in castor oil fluids. It is also commonly used in steamset or moisture-set inks. In this application, the binder is precipitated when hexylene glycol absorbs moisture. Unexpectedly, its peculiar effect in a litho ink is unique to this particular glycol. Other glycols with somewhat similar properties do not show this particular ability to prevent scumming. For example, ethylene, diethylene, triethylene, tetraethylene, propylene, and dipropylene glycols do not exhibit this anti-scumming action in a lithographic ink.

Surprisingly, the chemical structures of the instant additives are totally unrelated and it appears that the solubility characteristics in water of each additive are not dispositive of the function of the additive in this particular function. The most one can say, is that one additive is a glycol with six carbon atoms, and the other is a glycerol ester with nine carbon atoms. If, perchance, there were anything to indicate that either compound might be useful to prevent scumming, there would be no way to predict that the other compound might also be similarly effective.

In the preferred embodiment, triacetin is used in the lithographic ink, while hexylene glycol is dissolved in the water fountain solution. It is possible to use a mixture of both additives either in the lithographic ink or in the water solution, or in both, but this would entail the expense of precisely weighing out two additives rather than just one, Without a proportionate economic benefit in the effectiveness of the mixture.

The instant additives may be used with any conventional lithographic ink. Such inks include the usual vehicles or varnishes in amounts from about 20 to about by weight, toners or tinctorial agents in amounts of from about 5 to about 50%, and wetting agents such as lecithin or the like in amounts of from about 1 to about 5% Further, in accordance with the instant invention, a method is provided of reducing scnmming in litho printing presses by adding triacetin to the water solution used to coat the litho plate prior to the application of the ink thereto, the triacetin being employed in an amount up to the maximum soluble in the water at the temperature in the water fountain solution.

In accordance with the instant invention, a lithographic ink which may be run on a press without the danger of scumming, over a wide range of feed rates for both ink and water, is formulated as follows:

EXAMPLE 1 Parts by weight Lithographic vehicle or varnish 20 to 80 Toners or tinctorial agents 5 to 50' Lecithin l to 5 T riacetin 1 to 10 Lithographic ink varnishes are well known to the trade. They usually comprise a base capable of fluid flow. The base may be a bodied oil, such as linseed oil, or a hydrocarbon, or an oil-modified synthetic resin such as oil-modified alkyd resin or an oil-modified phenol formaldehyde resicrli. The following are classes of varnishes which can be use Linseed modified phenol formaldehyde varnish Bodied linseed oil varish Maleic-alkyd varnish 1 Phthalic-alkyd varnish 2 Pentaerythritol alkyd varnish Hydrocarbon varnish Quick-set varnish Rubber-based varnish.

) {See Printing Ink Manual, by R. U. Boles ct :tl., W. l-Ieltur 6.: 5,0118 Limited, Cambridge, 1961, pages 302 and 565.

- See Printing Ink Manual, supra, pages 307 and 575.

It is preferred to make use of a varnish having a high degree of water repellency. Suitable varnishes are manufactured by the Sherwin-Williams Company as lithographic varnishes of varying viscosities. Also, suitable varnishes are manufactured and sold by the American Lithovarnish Company, and many others.

The toner comprises a tinctorial agent to impart a desired shade and readability to the copy. Use can be made of such conventional toners or pigments as carbon black, lamp black, alkali blue, iron blue, and other water-insoluble pigments. They may be incorporated as a dry pigment or as a dispersion in varnish oils for introduction into the composition. The surface active agent functions also as a wetting agent for the pigment, and for wet-out of the surface upon which the ink is deposited in printing to produce a full and complete image. For this purpose, best use can be made of a lecithin. A suitable material (soybean lecithin) is marketed by American Lecithin Company, Long Island City, N.Y., under the trade name Alcolec 41ON though several other surface active agents are also useful.

The following are further examples of lithographic ink compositions prepared in accordance with the instant invention:

EXAMPLE 2 Parts by weight Linseed modified phenol formaldehyde varnish 60 Carbon black 20 Alkali blue toner (flushed in litho varnish) 10 Woolgrease Triacetin 5 If desired, various driers can be employed such as cobalt, manganese or lead linoleates, resinates, octoates or napthenates.

A further specific example is as follows:

EXAMPLE 3 Parts by weight Pentaerythritol alkyd varnish 1 40 Linseed oil Barium lithol toner 30 Alumina hydrate Lecithin 2 Triacetin 3 1 See Printing Ink Technology, by E. A. Apps, Leonard Hill (Bgoks) Limited, London, NW. 1, 1958, pages 64, 317, and 31 A further example is:

Driers as required.

1 See Printing Ink Manual, by R. F. Boles et :11. W. Heifer &- Sons, Limited, Cambridge, 1961, page 307.

The materials may be incorporated in any order, but it is best to mix all of the ingredients and then grind the material in conventional machines for the preparation of an ink.

In numerous experiments that were run, the addition of triacetin in the critical range from about 0.5 to about 10% by weight in conventional lithographic inks, immediately cleared up problems of scumming. Greater amounts of triacetin when incorporated in inks will tend to emulsify the ink. Amounts of triacetin less than 0.5% do not have any noticeable effect on the scum-free operability of the press. When triacetin is added to the water fountain, saturating the solution, despite the relatively poor solubility of the triacetin, the impact on the operation of the press is dramatic. A press that is catching-up will immediately start to chase out the ink from the nonprinting areas and the scumming will be eliminated despite the fact that water is cut back rather than increased, which is what is normally done to chase out scum.

Still further examples of lithographic inks embodying the present invention are as follows:

EXAMPLE 5 Parts by weight Bodied linseed oil varnish 60 Carbon black 18' Dry iron blue 10 Lecithin 2 Alkali blue toner (flushed in alkyd varnish) 8 Triacetin 2 EXAMPLE 6 Parts by weight Quick-set varnish (Diamond Magink #19) Alkyd varnish #3, phthalicpentaerythritol 20 Alkali-blue toner (flushed in linseed or alkyd) 20 Dry talc 5 Cobalt octoate drier 2 Hypothiolate 2 Lecithin 2 Diamond scratchproof wax compound #845 5 Carbon black-longflow 44 Triacetin 5 EXAMPLE 7 Parts by weight Quick-set varnish (Diamond Magink #2) 78 Alkyd #3 phthalicpentaerythritol 34 Flushed alkali blue toner 18 Longfiow carbon black 37 Dried talc 9 Diamond scratchproof wax compound 9 Triacetin 12 Cobalt naphthenate drier 4 EXAMPLE 8 Parts by weight Super Magink #50 (Diamond Varnish) 24 Phthalocyanin blue 13 Talc 4 Aluminum hydrate 4 Polyethylene wax compound #845 4 Lecithin 2 Triacetin 3 EXAMPLE 9 Parts by weight Rubber-based vehicle Super Magink #86 (Dia- Phthalic-pentaerythritol (Alkyd #3 Diamond Varnish Co.) 8 Flushed alkali blue 5 Polyethylene wax compound 2 Talc 2 Longflow carbon black 12 Cobalt octoate 2.5 Triacetin 3 Having thus described my invention, I claim:

1. In a water repellent lithographic ink of conventional composition, containing 20-80 wt. percent of a water repellent lithographic varnish, 5-50 wt. percent of a material selected from the group consisting of water repel lent toners and tinctorial agents and 1-5 wt. percent of Water repellent lecithin, the improvement, characterized by a reduced propensity of the ink to scum or grease in a lithographic printing process, consisting essentially of the inclusion in said conventional composition as the sole water soluble ingredient therein, of from 0.5 to 10 wt. percent of a compound selected from the group consisting of glyceryl triacetate and hexylene glycol.

2. The lithographic ink as defined in claim 1, wherein said compound is glyceryl triacetate.

3. The lithographic ink as defined in claim 1, wherein said compound is hexylene glycol.

4. In a Water repellent lithographic ink of conventional composition, containing 20-80 wt. percent of water repellent lithographic varnish, 5-50 wt. percent of water repellent tinctorial agent and 1-5 wt. percent of water repellent surfactant, the improvement, characterized by a reduced propensity of the ink to scum or grease in a lithographic printing process, consisting essentially of the inclusion in said conventional composition as the sole water soluble ingredient thereof, of from 0.5 to 10 wt. percent of a compound selected from the group consisting of glyceryl triacetate and hexylene glycol.

12 5. The lithographic ink as defined in claim 4, wherein said compound is glyceryl triacetate.

6. The lithographic ink as defined in claim 4, wherein said compound is hexylene glycol.

References Cited UNITED STATES PATENTS JOAN B. EVANS, Primary Examiner US. Cl. X.R.

10l465 R; 10629 R, 31, 32, 224, 228, 253, 272; 26038, 40 R, 41 C