The Status And Development Of Waterborne Polyurethane Finishing Agent

PU leather finishing can be divided into two basic types, one is an organic solvent-media systems (solvent-based PU) and the other is based on system of water as the medium (emulsion, water and solvent-based PU). Solvent-based PU due to organic solvents (such as ethyl acetate and methyl dimethyl formamide, tetrahydrofuran, cyclohexyl ketone, toluene, etc) as a dispersion medium, inflammable, explosive, toxic, environmental pollution, high cost disadvantages. Water-based PU compared, is based on the water as the medium, when using non-toxic, pollution-free, non-burning, low priced, but still has a general solvent-based on the performance of the PU high gloss, high wear resistance, high elasticity, high adhesion, water resistance, weatherability, chemical resistance, and on a variety of substrate adhesion properties such as good, which to a large extent replaced the solvent-based PU, is an extremely promising "Green materials".

?

First, the types and preparation of water-based PU coating

　　 According to the different preparation method of PU dispersions, water-based PU can be divided into two types of water-soluble emulsion type PU and PU.

　　 1, emulsion type PU

　　 PU dispersions usually contain emulsifiers are called emulsion type PU, or call out emulsion PU. It is the use of methods of applied emulsifier, under high shear stress, PU resin production dispersed in water, depending on your choice of different types of emulsifiers, emulsion-type PU can be divided into anionic, cationic and nonionic PU. Emulsion type PU has a very good film. In the course of filming, water after they have been excluded, PU between molecular chains of ionic groups are regularly arranged, hydrogen bonds not only exist, generate static functions.

　　 The results will form a very strong and flexible, stable film effects on the water, on the leather has a strong bond. General preparation method is: first, was dissolved in non-polar or relatively weakly polar solvents of low molecular weight polymers with 2%~5% free-NCO groups, and then by mechanical mixing effect of strong, this polymer emulsion in water containing emulsifiers in solution, and then add a chain Extender chain, resulting in PU emulsion containing emulsifiers.

　　 However, emulsion type PU belonging to the system of thermodynamic instability, emulsion stability of difference, the storage time is short. And made of PU emulsion particle size larger, because a hydrophilic emulsifier is added to the product, in the course of using these emulsifiers residues in products, colour as well as water resistance and mechanical properties of resin surface damage, these effects are widely used for emulsion type PU and performance. Therefore, emulsion type PU was subsequently gradually evolved from "emulsification" replaced by a system an aqueous solution of PU.

　　 2, water soluble type PU

　　 Typically do not contain emulsifiers for water-soluble polyurethane dispersions are called PU, water soluble PU by "emulsification in", also known as self emulsified type PU. It is in the chain of hydrophobic PU primary chain introduced water-based so that it does not have external emulsifier and high shear

?