Low-water-soluble reactive dyes for application in ultrafine polyamide/polyurethane synthetic leather

Ultrafine polyamide/polyurethane synthetic leather (UP/PSL), with a highly natural leather-like appearance and touch, is widely used in many leather commodities. Generally, acid dyes, which are mostly used for dyeing UP/PSL, exhibit poor colour fastness. While, reactive dyes are well-known for their good colour fastness. However, reactive dyes are not used to dye UP/PSL because they are water-soluble and cannot stain the polyurethane (PU) in UP/PSL. In this study, five low water-soluble reactive dyes with good affinity for both polyamide (PA) and PU were synthesised and characterised using ultraviolet-visible and infrared spectroscopy, and mass spectrometry. All low-water-soluble reactive dyes were monoazo dyes with only one sulfonic group and two different functional groups. The reactive dyes were used to dye UP/PSL at 98 degrees C and fixed at 90 degrees C with 7-azatridecane-1,13-diamine as a crosslinking agent. For comparison, Eriofast Red-2B (ER-2B) was used to dye UP/PSL using a special dyeing procedure. ER-2B showed severe issues related to low utilisation and uneven dyeing, whereas the five low water-soluble reactive dyes exhibited better performance than ER-2B. Both the exhaustion and fixation of dyes 1 and 4 exceeded 90.0% when the dosage was less than 3.0% owf (on weight of fabric). In addition, they exhibited good levelling. The washing fastness of the five reactive dyes was excellent and higher than grade 4. The dry rubbing fastness was higher than grade 3-4. Therefore, UP/PSL can be satisfactorily dyed using the reactive dyes with a solubility of less than 1.0 g/L and meet the requirements of daily life applications.