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Summary:
It is known that rubber on contact with ink in the printing process absorbs ink vehicle to a greater or lesser extent. Among the factors determining rate and amount of absorption is the composition of the ink and rubber. This paper describes the techniques developed and used by the Lithographic Technical Foundation to study the rate of ink absorption by rubber of the type used in the manufacture of lithographic blankets. The equipment consisted of an LTF Pick Tester with a strain gauge transducer and electronic components to measure the dynamic signal resulting from ink film splitting. Absorption was determined indirectly by measuring the change in the force required to split the ink film remaining on the surface as time for absorption varied. The rubber studied was molded as well as in the form of a normal litho blanket. The molded form allowed the effect of various typical plasticizers to be studied. A blanket, nylon coated to prevent absorption, was also included. The inks used were conventional litho, quickset litho, and two test inks of differing viscosity. Initially, the ink transfer characteristics of several blankets and inks were also determined gravimetrically for two methods of inking. The paper also presents data and discusses the effect on absorption of rubber plasticizers and previously absorbed ink. While the results show fairly wide differences in absorbency due to the properties of the ink, differences due to plasticizers, while significant, are not comparably as great.