US2750881A - Lithographic plate process - Google Patents

Description

. June 19, 1956 c, @5555 2,750,881

LITHOGRAPHIC PLATE PROCESS Filed Aug. 15, 1952 Z4 22 Z2 Z2 N4 2 4 2/ 2/ A INVENTOR Charles E yeese ATTOR s United States Patent LiTHOGRAPHIC PLATE PROCESS Charles F. Geese, Old Greenwich, Greenwich, Conn., as-

Sig or to Steel Dot Corporation, Old Greenwich, Conn., a corporat on f Conne ticu Arp sti n A gust 15. 1. .2, erial No- 30 8 1 Claim. (Cl. 101.-149.2)

Thi inv ntion re ates to h omi m. plat d m t l Pla es, particularly plates which are useful'in lithography, to methods of making such plates, to lithographic plates, and to the a of itho p y l 'th rsph o P ng a h gr phic pl te whi h m y be e ther stone or 'metal has a printing image reproduced on its surface s9. that an oil base ink preferentially adheres to the image, and moisture preferentially adheres to the intervening surfaces. For example, treated alu; minnm plates or treated zinc plates have been employed for such printing. Also, plates with plated coatings such as chrome plated copper on inc, copper on stainless steel, and chrome on copper on steel have been used. These known plates not only are relatively expensive but are capable of printing only a limited number of impressions, for example, of the order of one or two hund d th u an impressions P r plate.

It is an object of the present invention to overcome the difficulties and disadvantages of prior lithographic plates and methods of manufacture and to provide plates which are made ef inexpensive materials, which have excellent printing characteristics, which resist wear and corrosive deterioration, which may be manufactured without difiiculty and, importantly which are capable of malging several million printing impressions. Other objects and advantages of the invention will be made apparent by the following description.

In one of its broader aspects the invention may be said to lie in providing a lithographic plate wherein the image is produced in fine grainy steel (such as low carbpn steel of the low SAE 1000 series) and wherein the nonprinting or open, surfaces are coyered with passivated chromium which is substantially non-porous and will not accept ink and retains suflicient moisture to repel grease and ink. In another aspect the invention may be said o. i in a ch omium p a ed steel i h graphic p a Wher xpos v e l r ima e P r ion h reof h s ee so treated hat a hi hly tenac u ond o att acti n. e is s between the rubbed-in ink and the steel image. In still another aspect of the invention, it may be said to lie in providing a substantially non-porous chrominum plating over ordinary steel or iron without the interposition of another plating material and in a relatively rapid manner by high current density.

The features of the invention may perhaps best be appreciated by reference to the accompanying drawing, and subsequent description wherein:

Figure l is a diagrammatic, simplified view of an offset printing press showing the relative positioning of the plate roll, the rubber blanket roll and the impression roll.

Figure 2 is a fragmentary cross-sectional view of a low carbon steel plate.

Figure 3 a cross-sectional view of the steel plate shown in Figure 1 after it has been chrome plated according to the invention.

Figure 4 is a cross-sectional view of the plate of Figure 3 after a light sensitive bichromate gel coating has been placed over the chrome plate.

F re. 5 s a view of he pl te. of F gu e 4 an illustrates diagrammatically he. ex stence of ligh -ha ned areas on he gel a d s t ge ar as after a p o og aphic imag h s been veloped on h gel- Figure 6 is a view .of the same plate after it has been etched so that the image is reprgduced in steel, the overlying chrome plate in such areas having been dissolved away y th h n solu i n.

Figure 7 is a iew of the plate. sh n in Fi e. 6 after the gel coating has been washed off, exposing the steel p nt ng urfaces and the hrome-plate n n-p i s rfac F nre 8 s agramma ic vi w of th Pl te f F gu e wh h i u r tes he. acti a i n. of th steel P nt n surfaces and the passivation of the chrome or waterwettable surfaces.

Referring more particularly to Figure 1, the ofiset printing press 11 is shown as comprised of plate press roll 12 which receives. ink from fonnt 13. by means of transfer r lls .14. and water from fount 15. by transfer rolls 16. R bber blanket roll 17 picks. up the. ink impression from press .roll 12. Paper 19., carried by rollers 20 passes be ween blanket roll 17 and impression roll 18, thereby receiving the printing impressions.

Now referring more particularly to Figures 28 which show the plate th low ar on steel pla e 2.1 of Figur is firs scrubbed thoroughly wi h. a weak. s l ti n of phosphoric acid and pumice to clean it, orgiven a pickling trea men ina ly ashed with w t h p n. the cleaned p te 2 is mm sed in a. hromium plat n h h (n t h n.) h ehi of standar c mp si o o x mple. h plating ba h may c ntain ab ut 30 to 5.0 o nces of oh oini d p r ga lon and. about 0.3 t 0- oun e lfuric acid per gallon. so. ha the ohro na sulfate ratio is about :1. Some 6 to 8 volts are applied an re en i y of appr x mately 1% amp r s P squa e nch of steel is maintained. h Plat ng h is held at temp r ture o a ou 10 o 1 0 F- and p ating; cont n ed for abou 3 to 4 inuteses ont on y l d r r l on the s eel, a hi hly dhes e r me pla 2, Wh s r lati e y non-p r us. an hi h is l o 0.90005. inch th k- It is to b un r d th aria ns in t e. plat n cond ion may he m e h n he so... of t e invention. F r examp e, ne.- may hrome. plate steel plates which have previously been polished or nspec d t nsure ha ho es an oth r urface efe are absen Additionally. one. may o d ct e hr me Plat s ep as a s b t nt ally contin ous perat on where the teel p ate is. ntrodnoed: o the. p ating bath. as a lon s rip thereaft r being out into he d s redsizes.

Pl te :1 with. i s ch me c ating 22.- is next coated With a layer of; light-amena le gum. or g latin potassium bichromate gum, and dried as in the preparation of known lithographers plates. Next, the gum coated plate 21 is exposed and developed by placing over the light sensitive gum coating 23 a photographic film which bears the non-transparent half-tone image to be imprinted. Plate 21 and the film (not shown) are placed in a vacuum holder under a strong light such as a mercury arc so that the parts 23a of gum coating 23 in register with the light transparent parts of the film are light hardened. The plate 21 is removed from the holder and the unhardened areas of gum coating 23 washed away by warm water. The image areas 24 of plate 21 which were under the soft gum sections are then etched with a standard etching solution for chrome plate, e. g. hydrochloric acid or calcium chloride mixtures, to remove the exposed chrome plate and yield the desired image etched to expose the grainy steel surface.

Upon completion of the etching step, the plate is next washed free of the remaining gum or gelatine which protected the non-printing chrome surfaces 23, by immersing the plate in a hot alkali-type detergent solution which advantageously contains synthetic organic detergents such as organic-sodium wetting agents. I have had good results using either Oakite #27, a proprietary product presently available from Oakite Products, Inc., of New York, New York, and which is believed to be a heavy duty alkaline type metal cleaner. After the detergent wash, the etched plate is rinsed with water, and traces of oxidation on the front of the plate removed with a weak solution of orthophosphoric acid which not only cleans steel surfaces 24 but also renders chrome plate surfaces 23 passive and leaves it in a condition to accept a moisture film, whereby to make it repellent to oily or greasy substances such as ink.

Next the exposed steel surfaces 24 are to be rendered permanently ink receptive. I accomplish this by applying with soft rags a blueing solution which attacks the steel only. A representative formulation of this solution is made by mixing:

Formula A Oz. Bismuth chloride 1 Sodium hyposulfate 2 Copper chloride 1 Hydrochloric acid 6 Alcohol (ethyl) Water 64 to yield a solution which in turn is mixed with, in equal parts, a hydrocarbon base liquid detergent. I use liquid detergents which have a hydrocarbon base and contain small amounts of wetting agents and soaps. Particularly good results have been achieved with a mixture of equal parts of kerosene and the liquid detergent known as Oakite #96, which is also available from Oakite Products, Inc., and which is an emulsion type cleaner comprised of various wetting agents with organic and hydrocarbon materials.

In place of Formula A other equivalent solutions or mixes which blacken steel may be used so long as they do not contain such an excessive proportion of hydrogen sulfide forming components as to be deemed objectionable as health hazards. Next, I wash off the steel blueing-detergent mixture with water and, while the odor of hydrogen sulfide is still detectible on the plate, I activate the blackened steel surfaces 24 with a dilute (e. g. solution of orthophosphoric acid by spreading on the solution with a cloth.

After activation and while the plate is still wet I apply a standard rub-in ink to the steel image thereby forming a very tenacious bond between the steel and the ink. The moisture on the chrome surfaces tends to repel the ink, and the ink is thus preferentially applied to the activated steel portions of the plate. If the plate is not to be used immediately, a gum arabic or similar protective coating is i preferably applied to the treated plate to protect it until needed in service.

By my invention there are produced lithographic plates which are inexpensive, strongly resistant to abrasion and wear of the non-printing or chrome plated surfaces and which are permanently ink receptive in the activated steel areas. Additionally, the tenacious ink to steel bond protects the steel printing surfaces from oxidation and corrosion.

Although in the foregoing specification I have given various examples of my invention and have suggested certain modifications and alternatives, these are not intended to be exhaustive of my invention but on the contrary are selected and presented with a view to illustrating and explaining the invention, the principles thereof and the best manner of applying it in practical use in order that others skilled in the art may be enabled to practice the invention and apply it under various circumstances and in various ways, and with modifications, each as may be best suited to the conditions of a particular use.

I claim:

In the process of making a chrome-on-steel lithographic plate whereon an image has been etched on steel, the steps of passivating chrome plated areas of the plate with dilute phosphoric acid, then rendering the etched steel portions of the plate ink receptive by treating said plate with a water-oil-detergent-acidic-metallic chemical blueing solution which evolves hydrogen sulfide on contact with steel, said blueing solution comprising (a) about one part of a mixture of equal parts of kerosene and a hydrocarbon base liquid detergent, and (b) about one part of a solution comprised of approximately 64 ounces of water, 5 ounces of alcohol, 6 ounces of hydrochloric acid, 1 ounce of copper chloride, 2 ounces of sodium hyposulfite and 1 ounce of bismuth chloride, next treating the plate with a dilute solution of phosphoric acid, and then applying rub-in ink to the plate while the plate is still moist.

References Cited in the file of this patent UNITED STATES PATENTS 773,368 Bower et a1 Oct. 25, 1904 951,103 Cornwall Mar. 8, 1910 2,042,003 Huebner May 26, 1936 2,203,849 Trist June 11, 1940 2,289,443 Mange July 14, 1942 2,302,669 Batcheller Nov. 24, 1942 2,519,672 Lawless Aug. 22, 1950 2,527,232 Scroxton Oct. 24, 1950 FOREIGN PATENTS 29,507 Great Britain June 16, 1910 OTHER REFERENCES Modern Electroplating. Special volume, 2d ptg., August 1942. The Electrochemical Society, N. Y. Only pp. 119 and 122 cited. (Copy available in Div. 56.)

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