US2927858A - Method of producing printing surfaces - Google Patents

Description

March 8, 1960 1.. MAYR 2,927,858

METHOD OF PRODUCING PRINTING SURFACES Filed May 9, 1957 INVENTOR 1. up we MA YR ATTORNEY United States PatentO 2,927,858 METHOD OF PRODUCING PRINTING SURFACES- Imdwig;Mayr, Munich, Germany,assignor to Wolfgang Muth, Munich-501b,. Bavaria, Germany Application May 9, 1 951, SerialNo. 658,090 7 priority, application Germany May 11, 1956 1. Claim. (Cl. v96+ 35) fixed. material, are. carried. out. alternately and repeatedly.-

2,927,858 Patented 8 196i) M ICE (uj 'lreatingthe fixed photograph material with aqueous solutions or organic or inorganic acids. and/or salts of such acids in'the presence of hydrogen peroxide,and

-(b-) Subsequently drying without intermediate hardening. g

The effect. of this procedure is, two-fold: the gelatine is loosened and made adequately availablefor the buildup of printing elements-and in addition excess gelatine is disintegrated. Informer processes this excess gelatine remained in the material due to the intermediate hardening operation and'the smaller printing elements were; urged outwardly of the surface resulting in the rapid wear of the-formedrelief block as noted hereinbefore.

Accordinglyby the practice of the present invention it has become possible to influence the size of the printing elements and to, in addition, obtain a coarsening or diminution of grain by the addition of appropriate chemi In yet another process, the reproduction of an. objectis. made by exposure in a. camera on a gelatine-silver halide film, andthe. film is subsequently developed in a tanning developer. The film is then partially dried, squeezed: face down on a. stable support and subjected to a. washing in a warm; water: solution containing agents which retard. the swelling of the .gela-tine and which'preventfurther photographic development. This results in the establishment on. thestable support. ofbare and cov-. ered spots, the covered support port-ions representing an image; of the. object in relief, the. covered spots. being formed: with gelatine- Subsequently the gelatine. forming the. image is hardenedzby' treatment withfa solution containing formaldehyde tannic acid and glycerine. .Such a process is described in U.S. Pate nt No. 2,532,390.

A major drawback of prior art processes however has been that due toilrarderiing. of theravailable silver-free 'gelatinesuch gelatinecannot adequately contribute'to a suflicient buildup of the printingel enaents which on their outer surfaces are of silverjconsequentlyalso such silver halide film' is exposed to light under a screen negative, light rays penetrate into the film to'dilterent degrees of depth depending upon the intensity of the light and the toning permeability of the negative. Depending upon toning value larger or smaller screen points are found to be distributed on and in the gelatine layer of the film; therefore the mass of silver-free gelatine between the screen elements is large or small.

In the process of chemical relief formation, on those areas where there are many screen points and silver-free gelatine is thus present in greater concentration, a greater expansion of the gelatine will take place. This silverfree expanded gelatine protrudes more or less from the film surface and if not sufiiciently reduced it will be attracted by the silver of the screen points and will become molded. The small screen points then become elevated out of proportion, and in the case of a line block, for example, the printing element is worn out rapidly.

a The present invention contemplates the provision of a process which overcomes the above noted drawbacks by providing for the disintegration of the unhardened expanded gelatine to such an extent that the small screen elements do not protrude but are slightly depressed. This is achieved in the practice of the invention by:

of salts is utilized for optimum control.

cal compounds to the solution. For example, Farmer's Reducer maybe employed for this purpose. 7

Reliefs produced in accordance with the principles of the present invention are immediately usablefor printing. The appropriate adjustment of the temperature and makeup of the treating solution permits the disintegration of silver-free gelatine tosuch extent that the small printing elements do not protrude but are slightly recessed as will be noted more particularly hereinafter.

The solution with which the fixed, unhardened photographic material is treated suitably contains an acid to provide'a pH below that of the isoelectric point of the gelatine. In addition a salt is included to provide for controlled swelling of the gelatine and suitablya mixture To further enhance pH control of the solution a buffer acid may be introduced. The solution rate is materiallyaided in an. eflfective controlled" manner by the hydrogen peroxide which functions in thev disintegration of the gelatine Whil e numerous: modifications may be made in the componentspf the bath, the temperatnrepf'thebath. and time of .exposureto thebath, and whileruchwill. depend upon properties of the photographic material such as film thickness, density and the like, conditions may be regulated to provide for the disintegration action in a desired manner and the functioning of the hydrogen peroxide.

The procedure of' the improved process is diagrammatically illustrated in the accompanying drawings wherein:

Figure 1 represents a positive printed through a cross line screen and fixed without hardening;

Figure 2 represents the positive of Figure stage in the swelling of the gelatine;

Figure 3 indicates the positive in a swollen condition; and

lat a first Figure 4 illustrates the processed photographic mate- Acetic acid grams 10 Sodium sulfate (crystalline) do Ferric sulfate (crystalline) do 30 Water cc 9.00

When the above ingredients have been thoroughly dissolved, the solution may be passed through a filter and 50 cc. of concentrated sulfuric acid is added to the clear solution while stirring well. The solution which contains the agents to induce gelatine swelling, is then'cooled to room temperature and reacted with about IO'grams of hydrogen peroxide. The addition of the hydrogen peroxide may suitably be in the solid-form, that is, in the form of tablets containing H and urea, for example. The solution thus prepared is preferably permitted to stand over night before treating the photographic material.

A bath of the treating solution having a temperature of about 15' C. (59 F.) is prepared and the photographic material bearing a positive image copied through the point screen (Figure 1) is immersed for about minutes. During the treatment the photographic mate rial may be lightly rinsed in clear water. The immersion ence of the aqueous solution containing a large amount of water the life will be longer.

In the described treatment the hydrogen peroxide functions to insure the disintegration of the gelatine excess. The sulfuric acid and acetic acid provide the pH ,at a potential below the isoelectric point to insureswelling of the gelling-for this purpose other inorg'anic'and organic acids,'including nitric, hydrochloric, phosphoric, may be employed. The ionizable salts, ferric sulfate and sodium sulfate exert control over the swelling; other trivalent and divalent ionizable salts maybe employed.

In general the ionizable salts and the acid "concentration for combination with the hydrogen peroxide may be time will depend to some extent upon the thickness of the photographic material as well as the toning value thereof-but in general an original thickness of 30 microns will increase to about 100 microns. The swollen film (Figure 2) will in the course of action raise the silver or screen elements (Figure 3); the gelatine in the areas of higher gelatine concentration will disintegrate to a greater degree however and the smaller screen elements in the product of the treatment will be somewhat recessed below the print plane (Figure 4).

The product of the treatment with the noted solution is rinsed well in clear water and dried in a circulating current of warm air. When dry the product is ready for printing. 7

If desired a solution of the agents which induce the swelling and which contain the peroxide may also include Farmers Reducer as referred to hercinbcfore. A suitable Farmers reducing solution is:

Ferricyanide stock solution (30%):

Potassium Ferricyanide oz 12 Water 07 28 Hypo stock solution: Sodium thiosulphate Baum 35 It is to be noted that when the above two solutions are combined they may lose their activity at room temperature in a short period of time; however, in the presreadily selected to produce controlled swelling and partial disintegration of the gelatine.

It will be understood that this invention is susceptible to modification in order to adapt it to different usages and conditions and accordingly, it is desired to comprehend such modifications within this invention as may fall within the scope of the appended claim.

/ I claim: 7

In a process of preparing a printing block from photographic film comprising a light-sensitive layer of silver halide gelatin emulsion and bearing a positive image thereon copied through a screen, developed and fixed so that the gelatin is substantially unhardened; the steps of subjecting the fixed and unhardened photographic film to an aqueous relief forming solution to eifect swelling'of the gelatin substantially without hardening the gelatin with said solution comprising 10 grams of acetic acid, 90 grams of crystalline sodium sulfate, 30 grams of ferric sulfate, cc. of concentrated sulfuric acid, and about 10 grams of hydrogen peroxide for every 900 cc. of water and the treatment being effective to swell and partially disintegratethe gelatin; rinsing the photographic film in clear water; and subsequently drying the photographic film without intermediate hardening of the gelatin therein.

References Cited in the file of this patent UNITED STATES PATENTS 2,178,338 Frankenburger et al Oct. 31,v 1939 2,772,160 Hepher Nov. 27,1956

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