Study On The Preparation Of Polyurethane Dyes Based On Acid Dye Chain Extension And Leather Coloring Properties

There are some defects in the traditional leather dyeing and finishing process.For example,some dyes are carcinogenic when dyeing,some dyes have low dye uptake and poor color fastness;pigment paste commonly used in finishing is not resistant to friction,and metal complex dyes will bring heavy metal pollution.Therefore,in this paper,non-ferrous small molecule dyes are introduced into the main chain of polyurethane to synthesize polyurethane based polymer dyes,which are applied to leather dyeing and finishing processes,so as to play a good reference role in the new methods of dyeing and coating coloring.Firstly,polyurethane prepolymer with isocyanate-terminated group was synthesized from isophorone diisocyanate(IPDI)and polyethylene glycol-800(PEG-800).Then acid dyes(such as Acid Red 122,Acid Orange 95,Acid Green 20 and Acid Brown 5)containing double active groups were used to prepare polyurethane prepolymer with 2,2-dihydroxymethyl butyric acid(DMBA)by the chain extension reaction.Four series of waterborne polyurethane polymer dyes(WPU-Red 122,WPU-Orange 95,WPU-Green 20,WPU-Brown 5)were prepared after neutralization and emulsification.Based on the differences of the principles and methods of leather dyeing and finishing,the dyes suitable for leather dyeing(WPU-D Red 122,WPU-D Orange 95,WPU-D Green 20,WPU-D Brown 5)and finishing dyes(WPU-F Red 122,WPU-F Orange 95,WPU-F Green 20,WPU-F Brown 5)were prepared by adjusting the parameters of the synthesis process.Through FT-IR,UV-vis and TGA analysis,it was found that:small molecule acid dyes were connected to the main chain of polyurethane through urethane and urea bonds;the absorption spectrum of four small molecule dyes and their corresponding four waterborne polyurethane dyes were similar in the whole wavelength range of 200-800nm,which further proves that the low molecule dyes enter into the chain of polyurethane and have color The initial decomposition temperature of series polyurethane dyes is high,which meets the temperature requirements of leather dyeing and finishing.The experimental results showed that the initial R value of WPU-D series polyurethane dyes was 3 the total R value was 1.3;the initial R value of WPU-F series polyurethane dyes was 3,the total R value was 1.2.The traditional wet dyeing process of leather was adopted,and WPU-D series dyes were used for leather dyeing instead of corresponding acid dyes.The results showed that the dye uptake of WPU-D series dyes was 90%?96%,the color fastness to dry and wet rubbing and perspiration of crust leather dyed by WPU-D series dyes was 5,and the color fastness to soaping was 4?5,which was 0.5?1 higher than that of acid dyes,and the color fastness of leather dyed by WPU-D series dyes was 3.The color fastness of acid dyes to dry and wet rubbing and soaping was generally about 2-2.5,and the color fastness to perspiration was only 1.After dyeing with 4 kinds of polyurethane dyes,polyurethane dyes had certain retanning and filling effect on leather,which made the green leather have obvious thickening and soft and full hand.The dyeing properties of WPU-D series dyes were better than those of small molecule dyes.In this paper,WPU-F series dyes was used for leather finishing instead of acid dyes.The results showed that the thermal mobility of the film formed by WPU-F series dyes was 2.5%?5%,and the thermal mobility of the film formed by the physical blending of the corresponding acid dyes and WPU was basically between 10%?20%;the color fastness of the coating colored by WPU-F series dyes to dry and wet rubbing reached grade 5,the color fastness to soap washing and the color fastness to perspiration reached grade 4 and above,and the color fastness to dry and wet rubbing reached grade 4 The staining grade of color fastness and soaping fastness was grade 4,and that of perspiration fastness was grade 2.5?3.The staining grade and fading grade of acid dye crust leather coating were 1?2 lower than those of WPU-F series,especially that of perspiration fastness was only grade 1.The results showed that WPU-F series dyes were better than the small molecule dyes in leather coating.