Synthesis Of High Solid Content Polyurethane Dispersion And Its' Application In Membrane Press Adhesive

With the improvement of environmental regulations among different countries and the awareness to environmental protection, traditional solvent-based adhesives become more restricted in use. Polyurethane dispersion (PUD) adhesive, noted for its versatile properties in applications, friendliness to environment and easy adjustment in molecular structure, has for many years become a hotspot in study and widely used in many industries like footwear and woodworking. Nevertheless, the most popular hydrophilic monomer used in waterborne polyurethane is a carboxylic acid type like 2,2-dimethylol propionic acid (DMPA), which is a weak acid and mild base salt with weak hydrophilic property, and not suitable for polymerization of high solid content polyurethane. In addition, the -COOH groups in polyurethane segment accelerate the degradation of polyurethane and reduce its shelf life. Sulfonate, the hydrophilic group of amino-sulphonate, is stronger than carboxylic group, when polymerizing polyurethane at the same hydrophilic level, the consumption of the molar ratio of sulfonate is less than that of carboxylic group. It leads to reducing of ion in the polyurethane chain, weakening of electrostatic repulsion, and making for the preparation of high solid content waterborne polyurethane.In this paper, the synthesis of stable polyurethane dispersions at approx. 50% solid content was made by using N-(2-aminoethyl)-2-aminoethane sulphonic sodium(AAS-Na) as hydrophilic monomers, different types of polyols as soft segments, the mixture of isophorone diisocyanate (IPDI) and hexamethylene diisocyanate (HDI) as hard segments, and ethylene diamine(EDA) as chain extender. Acetone was used as dilute agent in the process. The differences of the molecular structure of PUD impacted to the general properties such as viscosity, particle size and solid content, and the properties in adhesion and thermodynamics had been studied. The result shown that with the increase of the content of AAS-Na, the quality content percentage of PBA or the molar ratio of IPDI/HDI, the PUD viscosity increased and its particle size dropped; the initial tack and peel strength increased with the increase of content of AAS-Na or the quality content percentage of PBA, and dropped with the increase of IPDI/HDI ratio; the activation temperature and heat resistance improved with the increase of PBA quality content percentage or the drop of IPDI/HDI molar ratio, and had no difference when changing the content of AAS-Na. Finally, the appropriate conditions among the content of AAS-Na, the quality content percentage of PBA and the molar ratio of IPDI/HDI were found to synthesize an ideal PUD used for membrane press adhesives. And then, the selected high solid content polyurethane dispersion and VAE emulsion were taken as key raw materials to compound membrane press adhesive. It was used to laminate MDF board and over 35% plasticizer PVC film, and not only achieved satisfied results in different requirements of segmented markets, but also reduced cost.