Abstract

A study of the emulsification process of lithographic ink and water was conducted to investigate methods for determining the water content of lithographic ink and water emulsions. Experiments using infra-red spectroscopy and analysis of the hydroxyl and carbonyl absorption bands revealed several variables which must be considered when attempting to use infra-red spectroscopic methods for the determination of the water content of ink emulsions. These factors include the choice of pigment, (either transparent or opaque), the type of cell medium, and methods for dispersing added water into an ink. The initial problem encountered was a lack of reproducibility when attempting to construct a calibration system. The carbonyl absorption band at 1745cm^-1 was shown to vary with each sample of emulsion. The intensity of the hydroxyl absorption band at 1645cm^-1 was discovered to be erratic between differing samples of ink and water emulsions. This resulted in hydroxyl contents which appeared to be inconsistent with known concentrations of water. The simulation of "on-press" emulsification, as it occurs in the lithographic process on an offset press, is a very important factor. The importance of added water attaining the internal phase of the lithographic emulsion is the prime criterion for valid and reproducible data obtained from infra-red spectroscopic analysis. This is accomplished by applying sufficient forces to generate an adequate rate of shear on the ink as added water is introduced into the emulsification process. The two modes of vibration of a water molecule were studied utilizing data obtained from infra-red spectra. The O-H stretching mode exhibited at 3400cm^-1 proved to be more sensitive to changes in water content of an ink than the bending mode exhibited at 1645cm^-1. Valid data used to construct a calibration system for water content determination of lithographic emulsions relies on the elimination of any moisture contamination of the cell medium used in the optics system of an infra-red spectrophotometer. Likewise, use of a transparent pigmented ink yields a continuous spectra. An opaque pigmented ink causes excessive light scattering resulting in off-scale deflections of absorption bands. Present methods of laboratory simulation of the emulsification of water into an ink were investigated to determine the optimum system which would yield stable ink and water emulsions in which the added water would assume the internal phase of the lithographic emulsion. Factors such as the rate of shear and time of dispersion were studied and found to significantly influence the formation of stable lithographic emulsions. Finally, the behavior of added water on the tack of an ink was also investigated. The tack values of a "dry" ink were closely monitored for extended periods of time. Immediate changes in tack were noted and recorded upon the addition of water. The addition of water to an ink in which the tack had apparently stabilized, effectively lowered the tack to the point where a homogeneous, stable emulsion was possible.

Library of Congress Subject Headings

Printing ink--Testing; Emulsions

Publication Date

6-1-1976

Document Type

Thesis

Department, Program, or Center

School of Media Sciences (CIAS)

Advisor

Silver, Julius

Advisor/Committee Member

Lippert, J. L.

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: Z247.S22

Campus

RIT – Main Campus

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