Studies on High Fastness to Light in Coloring Matters in Hydrophobic Substrates

Disperse dyes C. I. 12770, 61100, and 61105, have been applied to disoriented polyester film, oriented polyester film and fiber (Terylene), and to cellulose secondary acetate and triacetate (films and fibers). Some control tests with a direct cotton dye (C. I. 24410) on regenerated cellulose films (normal and gel state) have been included. Spectral absorption (x- and y-baud) and lightfastness (fading rate and CF curve) measurements have been made in dry and damp atmospheres. The dyes become increasingly aggregated with rise in concentration, in each substrate, and also with rise in porosity (i.e., moisture regain) of all the substrates. The results show that if the adsorbed dye were freely accessible to water vapor and air, lightfastness would in all cases follow the normal rule and increase with the degree of aggregation of the dye, and thus with the moisture regain of the substrate. In substrates of very low regain, however, i.e., polyesters, fading is retarded by the "diffusion-restriction effect," i.e., the restricted access of, probably, water vapor and air to the dye particles. Lightfastness of disperse dyes on polyesters is thus higher than would be expected, and in one case (C. 1. 61100) it is better on Terylene fiber than on cellulose acetates. In films lightfastness rises in the order: disoriented polyester < oriented polyester < cellu lose triacetate < cellulose secondary acetate. A hydrogen-bonding carrier (4-hydroxydiphenyl) reduces the degree of aggregation of a disperse dye in polyester film. This effect probably accounts for its deleterious effect on the lightfastness of disperse dyes on Terylene fiber. The results agree with published data on lightfastness of disperse dye on cellulose acetate and polyester fibers. In agreement with Color Index data, the present results appear to show that sym metry of substitution in anthraquinone disperse dyes favors the diffusion-restriction effect in polyester fibers and thus tends to raise lightfastness.