Лако-красочные материалы — производство

3.1.3 Introduction

Disperse dyes are colorants with low water solubility that, in their disperse colloi­dal form, are suitable for dyeing and printing hydrophobic fibers and fabrics. Forerunners of the disperse dyes were the ionamine dyes of British Dyestuffs Corp.; these were N-methanesulfonic acids of aminoazo or aminoanthraquinone dyes that released the N -methanesulfonic acid group in the dyeing process and, thereby, precipitated as disperse dyes on the acetate fibers. The understanding of this mechanism in 1923 initiated the development of genuine disperse dyes. Brit­ish Celanese and British Dyestuffs Corp. were the first companies to introduce these dyes into the market for coloring acetate fibers. The dyes were dispersed with sulforicinoleic acid, soap, or Turkey red oil [1].

From 1924 to 1930, products of other companies appeared on the market, initially as pastes; later, when the materials could be dried successfully without interfering with their dispersibility, they were also marketed as powders. Since 1950, the production of disperse dyes has increased sharply, closely following the growth in worldwide production of synthetic fibers, especially polyester [polyethyl­ene terephthalate)] fibers, production ofwhich has grown steadily from ca. 2 x 106 t/a in 1970 to about 16* 106 t/a in 1999 [2]. Furthermore, new dyeing processes necessi­tated the development of special disperse dyes. For instance, dyes characterized by special ease of sublimation are preferred for transfer printing [3]. The demand for new fastness properties such as thermomigration fastness and automotive light fastness [4-7] also led to new dyes, as has the ongoing pressure on market prices.

Models for the dyeing of polyester fibers with disperse dyes have been devel­oped [8]. When the dye is applied from aqueous medium, it is adsorbed from the molecularly dispersed aqueous solution onto the fiber surface and then diffuses into the interior of the fiber. The following parameters determine the rate of dye­ing and, to some extent, the leveling properties: (1) the dissolution rate during the transition from the dispersed crystalline state of the dye into the molecularly dispersed phase, and (2) the diffusion rate at the fiber surface and, especially, in the interior of the fiber. The rates of both processes vary with temperature.

Differences in geometry and polarity of the dye molecules can lead to wide variations in these finishing or dye-specific properties and can have a marked effect on the absorption characteristics of all dyes, irrespective of whether single­component or combination dyeing processes are used. For instance, uneven dye­ing may occur when an unequal distribution of particle size results in insufficient dispersion stability and hence crystal growth and precipitation at the substrate surface.