Heat Sensitive Paper Views

General Goods

A: Some of the characteristics of our heat sensitive periodic tables are easy to understand and some more challenging. The inks used provide color at lower temperatures and are colorless at higher temperatures. The change over temperature is called the c“critical temperature.l” Adding heat to the paper causes the paper to loose its color, an “endothermic ” reaction. The reverse, going from colorless to colored, is an e“exothermic2” reaction and returns the heat.

Educational Innovations, Inc. was one of the first companies to sell thermochromic paper and drinking cups, over 15 years ago. We followed up on an article about this new discovery in the NY Times. At that time the r“Touch-Itp” paper used two colors of heat sensitive inks: blue and red i– both turning colorless when heated. From those two heat sensitive inks, five colors of paper could be manufactured: red paper which turned colorless; blue paper which turned colorless: orange paper which turned yellow; green paper which turned yellow; and purple paper which turned colorless. For the orange and green paper, the thermochromic inks were printed on yellow paper.

In order to print, thermo-sensitive paper is inserted between the thermal head and the platen. The printer sends an electrical current to the heating elements of the thermal head, which generate heat. The heat activates the thermo-sensitive coloring layer of the thermo-sensitive paper, which changes color where heated. Such a printing mechanism is known as a thermal system or direct system. The heating elements are usually arranged as a matrix of small closely-spaced dots—thermal printers are actually dot-matrix printers, though they are not so called.

Early formulations of the thermo-sensitive coating used in thermal paper were sensitive to incidental heat, abrasion, friction (which can cause heat, thus darkening the paper), light (which can fade printed images), and water. Later thermal coating formulations are far more stable; theoretically, thermally-printed text should remain legible at least 50 years[citation needed].