Soaping fastness refers to the degree of fading of dyed fabrics after soaping in soap solution under specified conditions. It includes the original fading and white cloth staining. Original fading refers to the fading of printed and dyed fabrics before and after soaping. White cloth staining is a situation in which white cloth and dyed fabric are stitched together, and after soaping, the white cloth is stained due to the fading of the dyed fabric. Soaping and fading of dyed fabric refers to the extent to which the dye on the fabric is destroyed by the action of external force and detergent in the soap solution, which causes the dye to fall off the fabric.
The soaping fastness is related to the chemical structure of the dye. The soaping fastness of water-soluble dyes containing hydrophilic groups is lower than that of dyes without hydrophilic groups. For example, acidic and direct dyes have low soaping fastness because they contain more water-soluble groups, while dyes that do not contain water-soluble groups, such as reduced, vulcanized, and insoluble azo dyes, have higher soaping fastness.
Soaping fastness is also related to the combination of dyes and fibers. For example, acid mordant dyes and direct copper salt dyes, due to the chelation of the dye and metal ions, the dye molecules increase, the water solubility is reduced, and the soaping fastness is improved; the reactive dye and the fiber are covalently bonded, and the dye and the fiber become one. Therefore, the soaping fastness is also better.
The soaping fastness of the same dye on different fibers is different. For example, the soaping fastness of disperse dyes on polyester is higher than that on nylon. This is because the structure of polyester is tighter than that of nylon and has strong hydrophobicity. The soaping fastness is closely related to the dyeing process. Poor dyeing and improper removal of floating colors will cause the soaping fastness to decrease. The temperature, pH value and mixing conditions of the soaping liquid also have an effect.
The influence of dyeing concentration on soaping fastness is generally small. Sometimes the soaping fastness of light-colored products is higher than that of dense-colored products. The dye concentration is high, and the combination with the fiber is supersaturated, and it is easy to fall off under the action of external force. The test method for soaping fastness is to treat the dyed material under the specified conditions. After the treatment is completed, use the ministry-issued gray "color fastness fading sample card" or the ministry-issued gray "dye fastness staining sample card" for comparison and rating .
The soaping fastness is divided into 5 grades. Grade 1 is the worst, with serious fading; Grade 5 is the best, with no change in color after soaping under specified conditions. The staining is also divided into 5 levels. Grade 1 staining is the most serious, and Grade 5 is non-staining.