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Browse Prior Art Database

Offset Printing Plate for Direct Production of Positive Images

IP.com Disclosure Number: IPCOM000090198D
Original Publication Date: 1969-Mar-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 37K

Publishing Venue

IBM

Related People

Schwartz, PM: AUTHOR

Abstract

Plate 2, drawing A, can be used to fabricate a reversed image offset printing plate. Plate 2 consists of stable hydrophilic substrate 3 such as grained aluminum, decomposable oleophilic intermediate layer 4 such as gelatin or bichromated gelatin, and overcoat 5 of photosensitive material such as silver halide-gelatin emulsion. Plate 2 is exposed to subject 6 having dark and light areas and developed, preferably in a tanning developer, until image areas 7, those exposed to light, are hardened, drawing B. Nonimage areas of layer 5, those not exposed to light, are then removed by washing to produce a negative relief image, drawing C. Plate 2 can then be further stabilized, for example, by baking.

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Offset Printing Plate for Direct Production of Positive Images

Plate 2, drawing A, can be used to fabricate a reversed image offset printing plate. Plate 2 consists of stable hydrophilic substrate 3 such as grained aluminum, decomposable oleophilic intermediate layer 4 such as gelatin or bichromated gelatin, and overcoat 5 of photosensitive material such as silver halide-gelatin emulsion. Plate 2 is exposed to subject 6 having dark and light areas and developed, preferably in a tanning developer, until image areas 7, those exposed to light, are hardened, drawing B. Nonimage areas of layer 5, those not exposed to light, are then removed by washing to produce a negative relief image, drawing C. Plate 2 can then be further stabilized, for example, by baking.

As a next step, the developed plate is briefly immersed in an acid, such as nitric acid. During the plate's immersion in the acid, acid is imbibed in exposed offset portions 7. By rinsing with water, all external traces of acid are removed from the plate. However, the rinse does not remove the acid imbibed in developed portions 7. The acid is imbibed in exposed offset portions 7. By rinsing with water, all external traces of acid are removed from the plate. However, the rinse does not remove the acid imbibed in developed portions 7. The imbibed acid reacts with both developed portions 7 and the portions of oleophilic layer 4 directly supporting them. This reaction can be one of either hydrolysis or oxidation and r...