Knowledge of fabric color fastness

Color fastness refers to the degree of fading and staining of clothing colors. The mandatory national standard GB18401-2003 "National Basic Safety Technical Specifications for Textile Products" stipulates that the various color fastness indicators of qualified products must be greater than or equal to level 3.

Color fastness ratings are: Grade 1, Grade 1-2, Grade 2, Grade 2-3, Grade 3, Grade 3-4, Grade 4, Grade 4-5, Grade 5. 5 grades and 9 grades, grade 1 is the worst, grade 5 is the best (no fading). Level 3 can only be a basic level, an intermediate level.

Textile color fastness generally includes:

Resistance to soaping, rubbing, light, bleaching or oxidizing agent (reducing agent), ironing resistance, perspiration stain resistance and color fastness to perspiration and light, etc.

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 to soaping

1. Comparison of test methods for color fastness to soaping

Color fastness to soaping is one of the most common color fastness assessment items. Color fastness to soaping refers to the degree of fading of colored fabrics after soaping under specified conditions. It includes two evaluation items: fading as it is and staining of white cloth. Fading as it is refers to the fading of colored fabrics before and after soaping; staining of white cloth means that white cloth and colored fabrics are stitched together in a certain way, and after soaping, the white cloth is stained due to the fading of the colored fabrics. The degree of fading or staining should be tested under the designated light source, and graded by the standard gray card. The results are divided into 5 grades, with grade 5 being the best and grade 1 being the worst.

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

In the daily test, a considerable number of textiles, including cotton, wool, polyester, nylon and their blended fabrics, and spandex-containing elastic fabrics, stained nylon and acetate fiber linings at or below level 3. Although the dyes and dyeing processes used for 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 cellulose particles, so it is also related to the type of dye used, the dyeing process and the post-treatment process.

3. The soaping color fastness of dyed products with reactive dyes depends on the unfixed dyes

Taking reactive dyes as an example, theoretically speaking, due to the formation of covalent bonds 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 The amount of unfixed dye (hydrolyzed dye and a small amount of unreacted dye). If the hydrolyzed dye cannot be completely removed by soaping, the color will continue to fade after subsequent washing. The soaping fastness is also related to the bond stability of the bonded dye, and the bond-broken dye will also fade in water. Therefore, the most important factor affecting the color fastness to soaping is the structure and performance of the dye, followed by the dyeing and post-dyeing processes. Reactive dyes have a high fixation rate, or a slow hydrolysis rate, and the amount of hydrolyzed dye is small, and the amount of dye to be removed by washing is also small. Unfixed dyes and hydrolyzed dyes have low directness, good water solubility, are not easy to stain, and are easy to wash off. However, the concentration of dye is high and the amount of residual dye is large, so it is not easy to wash off.

4. Soaping fastness is also closely related to dyeing process

In addition, the soaping fastness is also closely related to the dyeing process. The dye adsorption and diffusion are sufficient, the color 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.