US2291854A - Lithographic plate and method of producing it - Google Patents

Description

-Aug. 4, 1 942. WHYZMUZIS Y 2,291,854

LITHOGRAPHIG PLATEAND METHOD onrgonucme IT Filed Feb. 28, 1940 PHOTOGRAPH IC POSITIVE l5 f N; STEEL mum l COPPER-K .3

F I G. 2 INKATTRACTIVE WATING FIG.3

CHROMIU GRAINED INVENTOR PAUL. WHYZMUZIS BY W W ATTORNEY Patented Aug. 4;, 1942 LITHOGRAPHIC PLATE AND METHOD OF PRODUCING IT Paul Whyzmuzis, New York, N. Y., assignor to Intel-chemical Corporation, New York, N. Y., a

corporation of Ohio Application February 28, 1940, Serial No. 321,205

3 Claims. (01. 41-415) This invention relates to planographic printing plates for wet offset printing, and particularly to planog'raphic printing plates highly resistant to wear, having copper printing areas, and waterreceptive chromium non-printing areas. The invention also relates to improved methods for producing such plates, and to a desensitizing etch particularly useful in said methods.

Planographic printing plates are generally produced on rather soft materials such as stone, zinc or aluminum. Other metals such as copper and stainless steel have been tried. The surface is divided into the printing areas, which repel water and thus'att'ract ink, and into non-printing areas which are treated to attract water, and which repel ihk when wet; in printing the plate is wet, and then inked, the ink being attracted only to the printing areas, and the design is transferred to an ofiset blanket from which the actual printing is done. with ordinary lithographic deep etch metal plates, the surface is ordinarily grained; the plate is then coated with a light sensitive gelatin or gum arabic film, which is developed into a resist, and the plate is then etched to produce the ink receiving portions. The plate is then inked, the remainder of the resist stripped, and the uninked portions of the plate treated to be water attracting, and so ink repellant when wet.

The principal advantage of conventional lithographic, plates is their low cost, as compared to either typographic or intaglio plates. This advantage of economy is lost, however, in long runs, since new plates must ordinarily be prepared somewhere betweeif 5,000 and 100,000 impressions, due to rapid wearing of the image areas of the plates. The worn plate must then be regrained to remove the design, and an entirely new printing surface produced. A great deal of work has been done in attempting to overcome this rapid effect on the exposed portion of the light sensiwearing of planographic plates, by using harder metals such as copper, stainless steel and even chromium; but hard plates comparable in cost with ordinary soft planographic plates have not been made heretofore.

I have discovered a very cheap and economical method of producing planographic printing plates with hard surfaces. My method comprises graining a base metal plate or cylinder, plating the grained base with copper, preferably to a depth tive coating. The etch is washed off with anhydrous alcohol and dried; the entire plate coated with a water resistant coating, which is dried; a developing ink is applied and dried; the remainder of the lightsensitive coating is then strippedwith water or an aqueous solution, and

the chromium etched with a desensitizlng solution, to make it water receptive and grease repellant. The plate is then ready for printing.

My new plate is a hard grained surface having a copper printing layer, covered by a water receptive chromium layer in all but the printing areas.

When a run is over, the chromium can be dissolved with the same etching material used in the plate making operation, and the cleaned plate need only be chromium plated again to have a surface available for a new plate. Because of the low cost of the base plate, the resultant finished plate compares very favorably in costwith conventional soft planographic plates.

The steps in my process can perhaps be best understood by referring to the accompanying drawing, in whichs Fig. 1 is a cross-sectional view of a plate just after exposure, with the photographic positive in place.

Fig. 2 is a cross-sectional view of the plate after etching, and after application of the ink attractive coating.

Fig. 3 is a cross sectional view of the finished plate.

As shown in the drawing, the planographic plate comprises a base member I I, preferably of steel or the like, which is grained in conventional fashion by a graining machine. The grained base member is then copper plated to yield a grained copper layer l2, and a smooth back copper layer II, which protects the plate against rusting. Over this layer is plated a deposit ll of chromium. A sensitized coating II is then laid down on the chromium, and exposed to light in conventional fashion through a positive transparency II.

This light sensitive coating can be prepared in any desired manner. A typical solution comprises It is preferably coated on the plate by spinning.

After exposure, the positive is removed, and the imperfections in the non-printing areas of the plate are painted out with lacquer in conventional fashion. The plate is then treated in conventional fashion with a developing solution to remove the unexposed light sensitive coating, leaving the resist on the portions of the plate where it has been hardened by the light passing through the positive. A satisfactory developing solution comprises 950 cc. of 40 Baum calcium chloride solution and 50 cc. of 85% lactic acid sy p, fl lusted with water to 37 Baum.

The plate, having bare metal in desired spots, is now etched with a fluid which dissolves chromium, but does not attack copper or the hardened light sensitive coating. A satisfactory solution comprises 3 volumes of propylene glycol to 1 of 37% hydrochloric acid. This makes an exceptionally good deep etch solution for stainless steel plates as well as for my new plate; the solution has a fast action on stainless steel and chromium without affecting copper or the developed resist.

The plate is then washed with anhydrous alcohol, which removes the lacquer, together with the deep etch solution. The entire plate is then coated with a thin film of liquid asphaltum, or varnish ll, shown in Fig. 2.

A typical varnish is 70 grams phenol aldehyde resin grams dimethyl phthalate 95 grams furfural 25 grams benzaldehyde 1 ounce of a solution of-- 40 grams basic chromium sulfate 12 grams phosphoric acid 85% 500 cc. water and 8 ounces of 14 Baum gum arabic solution.

The solution is then dried, leaving the plate as shown in Fig. 3, comprising the grained base Ii, the copper layer l2, covered with the chromium layer it in the non-printing areas, and with the varnish I1, and with ink II in the printing areas.

accuses WhileIhave shown mes-cameramcal solutions to perform various steps in'the process, these solutions may in general be replaced by others. The light sensitive coating may be of any conventional type; and the solutionusedtodevelopthecoatingandremovsthe unexposed portions must bi chosen so as to dissolve only the unexposed portion of the particular coating; the type of solution used is well known to the art.

Any solution which attacks chromium without affecting the resist or copper may be used for etching to the copper. Mixture of aqueous hydrochloric acid with completely water-miscible glycols give. a satisfactory etch, provided the glycol contains more carbon atoms than hydroxyl groups (e. g. propylene glycol, diethylene glycol), and provided the volume ratio of glycol to aqueous acid is between about 6 to 1 and 3 to 1.

The coating varnish and developing ink may be varied as desired, and so may the final desensitizing etch. However, my desensitizing etch makes possible the elimination of one conventional operation. In ordinary practice, the plate is etched, the etching solution removed, and the etched surface coated with a layer of gum arabic. By using a mixture of basic chromium sulfate and phosphoric acid, together with a gum arabic solution, both operations may'be combined.

The desensitizing solution may be varied over that shown above, while retaining the desirable properties of yielding both a desensitizing etch and a coating, provided the following range of proportions is observed:

% to 1% volumes of solution of- 40-80 grams basic chromium sulfate 6-18 grams phosphoric acid 500 cc. water 4 to 12 volumes of 14 Baum gum arabic solution (at 25 C.)

Other variations may of course be made in my invention without departing from the scope of my invention, which is described in the claims.

I claim:

1. A planographic printing plate comprising a grained copper surface, coated with a waterreceptive chromium layer in the non-printing areas the copper being exposed in the printing as: to act as the ink-bearing portion of the p 2. A planographic printing plate comprising a grained base plate carrying a coating of copper of uniform thickness over the entire surface thereof, and a layer of water-receptive chromium of uniform thickness over the non-printing areas of the plate, the copper being exposed in the printing areas.

3. The method of making a planographic printing plate, which comprises chromium plating a grained copper surface, coating said chromium with a light sensitive coating, exposing said coating to light through a transparency carrying a design, developing the coating to remove the unhardenedportions thereof, etching the plate with a solution which dissolves chromium but does not affect copper or the resist, removing the etch solution, coating the plate with a developing varnish, inking the plate, removing the hardened light sensitive coating and making the chromium surface water attracting.

PAUL WHYZMUZIS.

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