Abstract
Application of basic dyes to acid-modified polyethylene terephthalate fibers offers such attractive features as brightness of shade, excellent color value, and good solvent and sublimation-fastness. Lightfastness studies of basic dyes on this polymeric substrate indicate that the Critical Fading Region (C.F.R.) is a rather narrow spectral region extending from 350 to 425 mμ. Substituted hydroxybenzophenones such as 2,2'-di hydroxy-4,4'-dimethoxybenzophenone (DHDMBP) act as light screeners with many of these dyes in the C.F.R. and extend their lightfastness in dyed fabrics. Many of these screeners can be applied to the fiber by normal dyeing techniques. The requirements for efficient screening ability of these agents are discussed. Photosensitization of dyes by some screeners with a resultant diminution of lightfastness is ascribed to a radiationless transfer of energy from screener to dye by a resonance transfer mechanism. Chemically modified DHDMBP gave improved lightfastness in dark shades utilizing the tinctorially strong triphenylmethane dyes. The lightfastness improvement due to these modifications can be ascribed to their enhanced bathochromic absorption in the C.F.R. relative to the absorption spectrum of DHDMBY.
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