US2382674A - Method of making images on metal plates - Google Patents

Description

C. J. STAUD METHOD OF MAKING IMAGES ON METAL PLATES Filed Aug. 27, 1942 K l 1 GLASS PLATE 3 LAYERW/7'H :K' I I '41 SILVER/MAG? wvsm. HATE SENSITIVE LAYER A T'TORNE YS Patented Aug. 14, 1945 METHOD OF MAKING IMAGES N METAL PLATES Cyril J. Stand, Rochester, N. Y., assignor to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey Application August 27, 1942, Serial No. 456,372

2 Claims.

This invention relates to a method of makin images on metal plates, more particularly useful as a step in the making of relief images in zinc plates by a process involving etching through a relief image.

Ordinarily the plates are coated with a gelatin or albumen layer sensitized with potassium dichromate and exposed under a negative carried on clear glass or film, the exposure being prolonged because of low sensitivity of the material.

It is well known that in making gelatin relief images on glass, it is customary and desirable that exposures be made through the support, thus hardening the gelatin nearest to the support preliminary to washing off the unaffected soft gelatin. This has not been possible with an opaque metal plate, and it has accordingly been necessary that the exposure be prolonged to make certain that exposure at all points is complete. This restricts the latitude of exposure and tends to obliterate detail.

I propose to overcome this difiiculty by utilizing X-rays to make exposures through the zinc plate and through a metal image having a greater opacity to X-rays than the metal of the plate.

Reference is made to the diagrammatic figure of the accompanying drawing.

The metal plate I, usually of zinc, can be coated with an unhardened, photographic gelatino silver halide emulsion layer 2 in any suitable way. A most convenient method is by means of a transfer film from which the emulsion layer alone is stripped and transferred to the metal plate. Such a film and a method for transferring it are disclosed in the patent of Gale F. Nadeau, No. 2,326,048, of August 3, 1943, and the pending application of Victor N. Gioseffi, Serial No. 452,928, filed July 30, 1942.

Against the back or unsensitized surface of the zinc plate is placed a line negative or half-tone screen glass negative 3 bearing a layer 4 containing a silver image. For the sake of clearness, plates I and 3 are shown as slightly spaced. This is then exposed to X-rays from tube 5 which pass in succession through the negative or image, the zinc plate and the photographic emulsion. Because of the greater density to X-rays of silver than zinc, an image is formed in the sensitive layer. This is developed in a tanning developer, of a well known type, and the unaffected and still unhardened gelatin washed off in warm water leaving a gelatin relief image. Other known means of obtaining the relief image could be used.

This process depends on the fact that absorption of X-rays by silver is many times that of zinc. To maintain the difierential the zinc plate would be no thicker than practical requirements necessitate. The silver image could be converted by known methods to uranium, platinum, or gold, which would ive even greater differential absorption than silver; and hence, greater contrast in the resultant image and, of course, other metals, readily permeable to X-rays, could be used instead of zinc, where suitable for the process proposed.

Further control of contrast could be obtained by selection of suitable voltages on the X-ray tube. In general, moderate voltages are most suitable.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. The method of making a relief image on a metal plate that comprises coating one surface of said plate with a sensitive layer, placing on the other side of the metal plate a layer transparent to X-rays carrying an image consisting of a metal more absorptive of X-rays than is the metal of the plate, passing X-rays through said image and the metal plate to the sensitive layer and processing the sensitive layer to form a relief image therefrom.

2. The method of making a relief image oh a zinc plate that comprises coating one surface thereof with an unhardened, sensitive, gelatinosilver halide layer, placing on the other side of the zinc plate a support transparent to X-rays and carrying a silver photographic image, passing X-rays through said image and said zinc plate to the sensitive layer to form a latent image therein, developing said latent image in a developer that acts to tan the gelatin and washing oif the untanned gelatin to form a relief image.

CYRIL J. STAUD.

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