Textile Color Fastness and Dyeing and Finishing Production Process

The color fastness of textiles usually includes resistance to soaping, rubbing, light, bleaching or oxidation (reducing agent), ironing, perspiration and perspiration. Among them, soaping resistance, friction resistance, light resistance, water resistance and perspiration resistance are several color fastness indicators that most buyers pay more attention to in actual production and trade.

Color fastness ratings are: Level 1, Level 1-2, Level 2, Level 2-3, Level 3, Level 3-4, Level 4, Level 4-5, Level 5. 5th grade 9th grade. Level 1 is the worst, Level 3 is basic, and Level 5 is the highest, but almost impossible. Level 3 can only be a basic level, an intermediate level.

1. Test method for color fastness to soaping

Soaping color fastness is one of the most common color fastness assessment items. Soaping color fastness refers to the degree of fading of colored fabrics after soaping under specified conditions, which includes two evaluation contents: original fading and white cloth staining. As-is fading refers to the fading of colored fabrics before and after soaping; white cloth staining refers to the situation that white cloth and colored fabrics are sewn and stacked together in a certain way, and after soaping, the white cloth is stained due to fading of colored fabrics. The degree of fading or staining should be tested under the specified light source and graded on a standard gray card. The results are divided into 5 grades, with 5 being the best and 1 being the worst.

2. Relationship between dye structure, dyeing and post-treatment process and color fastness to soaping

In daily tests, a considerable number of textiles, including cotton, wool, polyester, nylon and their blends, as well as spandex-containing elastic fabrics, stained at or below grade 3 to nylon and acetate backings. Although the dyes and printing and dyeing processes used in different fiber materials are different, the problems that arise are quite similar. This is mainly related to the floating color of the cloth surface and the transfer of some colored nits, so it is also related to the type of dye used, the dyeing process and the post-treatment process.

3. The soaping fastness of reactive dyeing products depends on the unfixed dyes

Taking reactive dyes as an example, in theory, due to the covalent bond between dyes and fibers, washing with water cannot easily cause dye desorption, fading and bleeding. Therefore, the color fastness of reactive dyes to soaping depends on Quantity of unfixed dyes (hydrolyzed dyes and small amounts of unreacted dyes). If the hydrolyzed dye cannot be completely removed by soaping, the subsequent washing will continue to fade. Soaping fastness is also related to the bond-forming stability of bond dyes, and bond-breaking dyes will also be washed out with water.

Therefore, the most important factors affecting the color fastness to soaping are the dye structure and properties, followed by the dyeing and post-dyeing processes. Reactive dyes have high fixation rate, or slow hydrolysis rate, less hydrolyzed dyes, and less dyes to be removed by washing. Unfixed dyes and hydrolyzed dyes have low directness, good water solubility, not easy to stain, and easy to wash off. However, with high dye concentration and a large amount of residual dye, it is not easy to wash off.

4. Soaping fastness is also closely related to the dyeing process

In addition, soaping fastness is also closely related to the dyeing process. The dye adsorption and diffusion are sufficient, the fixation rate is high, the residual dye and hydrolyzed dye are less, and it is easy to wash off. The dyeing process is reasonable, the covalent bond between the dye and the fiber is not easy to break during dyeing and post-treatment, and the color fastness to soaping is good.