Wilson Hurst

Abstract

One of the most attractive attributes of the gravure process is its ability to print a variable ink film by virtue of cell depth variation. This cell depth variation is achieved through the use of a diffusion resist. All diffusion resists are negative-working and, after exposure, require transfer to plate or cylinder. A "negative-working" resist is one where the emulsion becomes insoluble to the developing solution in those areas struck by actinic radiation. Presently available resists, which are directly applied to plate or cylinder prior to exposure, are not capable of controlling cell depth variation. Thus, the tone range obtainable in the print is limited. This sacrifice has been justified by advantages inherent in the direct system, such as ease of application and seamless image capability. It has long been recognized, however, that a direct system capable of variable cell depth control would be most advantageous. The purpose of this study is to examine the possible application of a radiation-sensitive/positive-working iron salt system for use as a direct diffusion resist. "Positive-working" refers to an emulsion which becomes soluble in those areas struck by actinic radiation. The is sensitized by immersing it in a potassium dichromate solution, and is then dried in the dark. The concentration of dichromate ranges from 2.5 to 5 percent. The time of immersion varies with the temperature, the pH, and the strength of the bath. The water content of the gelatin before sensitizing is also most important. In general practice, gravure tissues are immersed in the dichromate bath for approximately three minutes. "Carbon tissue is a long-scale process which can accurately reproduce a tone range of 1.30 to as much as 1.50 without going into the under- or over-exposed regions of the 2 photographic reproduction curve." Despite many disadvan tages associated with the instability of dichromated colloid layers, no other radiation-sensitive material has been found, up to the present, which can do the job so well. The sensitized and dried pigment paper is then exposed behind a photogravure screen which consists of opaque squares separated by narrow, clear lines (about 150 to 175 lines to the inch). The clear lines are usually about 1/3 the width of the opaque squares which they separate. The effect of this screen exposure is to form a network of insoluble lines of hardened gelatin. The next step is to print the screened tissue behind a continuous- tone positive transparency. This results in a negative resist in which the shadows are represented by gelatin hardened to only a historical roots of this concept are explored and the results of empirical tests explained. It is concluded that the relief characteristics of such a resist system are manifest in the solarization region of the characteristic curve.

Library of Congress Subject Headings

Intaglio printing; Photoresists

Publication Date

9-1-1982

Document Type

Thesis

Department, Program, or Center

School of Print Media (CIAS)

Advisor

Silver, Julius

Advisor/Committee Member

Hill, Tom

Comments

Note: imported from RIT’s Digital Media Library running on DSpace to RIT Scholar Works. Physical copy available through RIT's The Wallace Library at: Z252.5.I5 H87

Campus

RIT – Main Campus

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