Analysis of washing color fastness performance of indigo knitted denim fabric

Denim clothing is famous in the world for its special style of partial fading and distressing, and is favored by consumers. With the continuous expansion of the consumer market, the requirements for more varieties and colors of denim fabrics are becoming stronger and stronger. Knitted denim fabrics are highly sought after by consumers due to their unique knitted characteristics, such as elasticity, softness, air permeability, etc. Before the knitted denim garments are treated with whitening, matte, distressed and other styles, how to Accurate control of its color fastness to washing has become a property worth studying. The color fastness tester to washing is a test instrument for measuring the color fastness to washing of printed and dyed fabrics. Indigo yarns are usually dyed with vat dyes. These dyes are insoluble in water and contain carbonyl groups in their molecular structure. When dyeing, they need to be reduced to soluble leuco in an alkaline medium with insurance powder to dye the fibers. After oxidation It is fixed in the fiber as an insoluble dye. The dyeing process goes through four steps of dye reduction and dissolution, leuco dyeing, leuco oxidation, and post-processing. Knitted denim fabric is a yarn-dyed knitted fabric woven by indigo cotton yarn and pure white cotton yarn. Therefore, washing has become an important factor affecting the color fastness of indigo knitted denim fabrics. The structure of the sample: In order to make the test have universal significance, three kinds of commonly used weft knitting structures were selected, namely, large terry, small terry, and twill. The relevant parameters of the samples are shown in Table 1. They are all weft-knitted products with indigo yarn, white yarn and spandex yarn as raw materials. Most of the indigo blue is displayed on the front side of the fabric, and the reverse side is white. changes. The floating color of dyed yarn and grey fabric is caused by proper treatment. After the second washing, the color fastness level of the fabric is significantly improved, which can fully meet the color fastness level of denim fabrics. The changing law of lightness difference: The magnitude of the absolute value of lightness difference indicates the degree of change in the depth of the color, a negative value indicates a darker color, and a positive value indicates a lighter color. It can be seen from the change of the lightness difference of the fabric after three washings that the color of the fabric becomes slightly lighter, and the absolute value of the lightness difference shows a decreasing trend, indicating that the color fastness of the fabric gradually increases and tends to be stable. The changing law of chromaticity difference A* and b* represent chromaticity, the positive direction of a* represents red, the negative direction represents green; the positive direction of b* represents yellow, and the negative direction represents blue. It can be seen from Table 2 that after washing, the chromaticity of the three fabrics is significantly reduced, and the chromaticity is slightly deviated, but it is still within a certain color latitude, and has little effect on the total color difference value.

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