Chapter 2 - Thermal Transfer Printing

Abstract

This chapter discusses thermal transfer printing, which utilizes heat as its energy source. This forms one of the two main aspects of the broader technology area of thermal printing known as thermography and direct thermal printing. Thermal transfer printing can be subdivided into dye diffusion thermal transfer (D2T2) and thermal melt transfer (thermal wax transfer, thermoplastic transfer). The development of thermal wax transfer technique offered several advantages over direct thermal printing: The need for especially coated papers was eliminated, archival storage was greatly improved, and perhaps most importantly, full color imaging became possible. After that, the introduction of dye diffusion thermal transfer printing produced the next change in thermal printing, bringing the possibility of high quality photographic-like reproduction from electronically captured/generated images. As a general rule, direct thermal printing represents the lower quality, lowest cost technology, while D2T2 provides higher quality, but at a higher price. Thermal melt transfer lies between these two extremes. To acknowledge the existence of direct thermal printing and its position in relation to thermal transfer printing, the chapter concentrates on thermal transfer printing. The presence of α-branched groups in the N,N-dialkylamino substituents of range chromophores improves the light fastness properties of D2T2 dyes. However, this simple structural modification has little or no effect on the absorption maximum of the dye and, therefore, has negligible effect on shade. The photofading products are in agreement with the fading of D2T2 dyes via an oxidative dealkylation process. It is believed that the probable reason for this effect is that the branched group sterically hinders attack of singlet oxygen on the nitrogen atom or hinders abstraction of a proton from the α-carbon atom at a later stage in the mechanism