Study On High Solid Content Water-borne Polyurethane Adhesives For Shoes

A water-borne polyurethane(WPU)is defined as a binary colloidal system in which PU particles are dispersed in a continuous aqueous medium.Compared to solvent-based polyurethane,water-borne polyurethane has advantages of being free from toxicity and pollution etc.,and can be used in textile coatings,sizing and adhesives for numbers of polymeric materials,leather surface, etc..However, the drying time of common WPU is longer than that of solvent-based polyurethane due to the high latent heat of water evaporation, which is difficult to meet the technical requirements for the drying properties of adhesives for shoes in fast-paced modern production lines. Increasing the solid content of WPU is one of the most effective methods to improve the drying properties of WPU adhesives for shoes.In this paper, WPU was prepared by using prepolymer dispersion method. Firstly, using diisocyanate (HDI, IPDI), and polyester diol(PBA1000, PBA2000, PBA3000, PCDL2000 and PEBA2000) as the main raw materials, hydrophilic DMPA as chain extender, polyurethane prepolymer was synthesized. Then, the prepolymer was neutralized by using triethylamine, and dispersed in water by force.Finally, using ethylene diamine as chain extenders, the waterborne polyurethane emulsion was obtained. Three types of WPU formulations were studied and the performance of the products were tested and characterized.The three formulas were: WPU made by IPDI / HDI, a single polyester; WPU made by IPDI, a single polyester; WPU made by IPDI, mixing two-component polyester.Each formulation had got a good performance of waterborne polyurethane emulsion.Through the research of the content of the above, some couclusions were drawn. The reaction time is 4 hours for the best.The amount of DMPA decides viscosity and average particle size of WPU. It is used as little as possible under ensuring the emulsion stablility. It is the best that the amount of DMPA is between 3% and 4%. The molar ratio of IPDI and HDI is also important. The experiment would be failed if using too much HDI. The molar ratio of IPDI and HDI is 3:7 best. Soft segment content is 65-70% at best, because WPU is most suitable for adhesive under this value.Through the comparison of the five kinds of WPU which were prepared with five different polyesters, PBA2000 is the best. By the method of mixing two different polyesters, I synthesized a series of WPU with 46~49% solid content, and found that PBA2000 and PCDL2000's mixing effect is the best. In addition, the R value (NCO and OH molar ratio) was also studied, and the emulsion were characterized by GPC test and SEM, TEM spectroscopy.GPC results show that the number average molecular weight of the prepared WPU emulsion reached 10,000 or more and the largest weight average molecular weight was up to 110,000 or more. TEM observations show that the prepared WPU emulsion have a certain distribution of molecular particle size.