Waterborne polyurethane water resistance

　　Speed out of the past pungent odor and contains harmful substances paint. Then by a brief introduction to let everyone know the history of the evolution of waterborne polyurethane products.

　　Most water-based PU is mainly prepared by the self-emulsifying, containing hydrophilic groups of PU as the main curing component, when dried coating if a hydrophilic component can not effectively enter the crosslinked network formed by drying the coating film case Easy water swelling. In addition to its lack of crosslink density and high molecular weight as a two-component solvent-based PU coating can get, thus these aqueous dispersion coating water resistance, solvent resistance, heat resistance and gloss poor, serious It limits the scope of its use.

　　In order to improve the water resistance of the product often used:

　　First, a method to improve the crosslinking density of a coating film

　　Commonly used cross-linking in two ways: one is in the synthesis of PU prepolymer polyol added functionality greater than 2, directly crosslinked PU prepolymers, said prepolymer is well dispersed in water and a macromolecular chain, and finally form an emulsion. This method is also called pre-cross-linking method, the disadvantage is easy to make the prepolymer viscosity increases, more difficult to disperse in water, affecting the stability of the emulsion. In recent years, new cross-linking agent and Screening and synthesis of polyfunctional chain extender is very active, has become one of the main ways to improve the water-based PU physical mechanical properties and water resistance. 

　　Second, the cross-linking method

　　Anionic PU emulsion with a crosslinked carboxymethylcellulose, a crosslinking reaction takes place in PU molecular carboxylic you have aziridine, carbodiimide compounds and metal salts, cross-linking at room temperature. Such cross-linking agent is generally in the use of PU emulsion was added, because the crosslinking reaction rate is very fast, short gelation and emulsion breaking. Cross-linking method can be successfully resolved hydrophilic PU emulsion coating problems, but additional crosslinking agent to form a two-component coating agent to the construction inconvenience, this method uses less.

　　For water resistance, the aqueous polyurethane is particularly prominent. Currently researches are focused on waterborne polyurethane modified it in its functional, modified by increasing the water resistance, solvent resistance and other performance materials. The main physical and chemical modification by two means, by grafting, block, internal, external crosslinking other polymeric materials, blends or interpenetrating polymer network formation methods such as modified.