Effects of the chemical structure of direct dyes on ultraviolet ray shielding efficiency of the fabrics have been studied for the purpose of protecting human bodies from the harmful ultraviolet rays. Five kinds of direct dyes have been examined on (1) molar absorption coefficient at the regions of 700-400nm in wavelength (visible light region: VIS), 400-320nm (UVA) and 320-280nm (UVB) respectively, (2) dye exhaustion (%) on cotton fabrics, and (3) UV ray shielding efficiency (%) of the dyed fabrics.
The results are as follows:
1) Red 28 (C.I.22120) has the highest molar absorption coefficient of dye on UVA/VIS and Red 23 (C.I.29160) has the highest on UVB/VIS.
2) Red 28 shows the excellent dye exhaustion property by reasons of small molecular weight and substantivity. However, Red 28 seems to have no practical use because it is under suspicion of carcinogemicity.
3) Even on dyeing of light color, the dyed fabrics show higher UV-ray shielding properties than undyed fabrics. The UV-ray shielding properties of fabrics increase with decreasing of the lightness of fabrics, by the concentration of dyes on the fabrics.
4) As a whole, Red 23 (C.I. 29160) is recognized as an excellent dye on ultraviolet ray shielding properties.
View full abstract