Two Steps Crosslinking Water Borne Polyurethane Adhesive

The environmental advantages of water-based adhesive becomes increasingly clear. It has been a important direction of adhesive. In this area, Most of the current research and application is about water-based polyurethane adhesive(WPU). The water-based polyurethane adhesive has the best performance. WPU has better adhesion property to laminated films,not only can satisfy the need of laminated fastness to filems, and its low viscosity, easy to transfer adhesive, spread coating, more and more learners have paid attention to it. Whereas, there are also some problems, such as:low solid content; poor water resistance; worse wetting quality to the substrate.In order to improve the above problems, we drew up a "two-steps crosslinking" research route.we used a three functional macromolecule monomer as raw material, which can intruduce appropriate cross-linked structure to the amino terminal one component(one step crosslinking).Compared with the small molecule three functional crosslinking agent, long chain-chain crosslinking structure can give the molecular chain both appropriate rigidity and flexibility. Further more, the water-soluble epoxy resin was the outer cross-linking agent(two steps crosslinking). TC-WPU was prepared by mixing the epoxy based and amino compound at a certain mole ratio.Epoxy group reacted to primary amine, sec-amine,in order to improve to a further cross-linking degree. Two steps crosslinking structure can substantially increase the water resistance and adhesive cohesion.Based on the above idea, the good stability, high solid content, outstanding water resistance, excellent adhesive strength two-component waterborne polyurethane adhesive was prepare by a two-step method, using toluene diisocyanate (TDI), polyether polyols,2,2-dimethylol propionic acid (DMPA), ethylenediamine, triethylamine, etc. as raw materials.We studied three major sections:phase transformation during the process of pre-polymer synthesis; water absorption of pre-polymer and peel strength of two-component polyurethane adhesive. By infrared spectroscopy, transmission electron microscopy,we characterized chemical structure of the adhesive, morphological changes during the phase transition. We also studied the effect of process conditions, R value, different types of chain and neutralizer, neutralization degree, mounts of three functional macromolecule monomer, amounts of DMPA, etc. on the two-component polyurethane adhesive. We obtained the following results and conclusions:(1)Carboxyl content and neutralization degree have a obvious influence on phase transition and solid content.With the carboxyl content increased, the phase transition point in advanced. The amount of water for phase transition reduced from 139% of the theoretical value to 104%, the solid content increaced from 27.92% to 34.11%.When the neutralization degree is lower, the phase transition occurd more easily. Along with the neutralization degree reduced from 100% to 70%, solid content increased from 35.33% to 45.26%.(2) The value of NCO/OH has a significantly impact on the water absorption. As the value of NCO/OH increased from 1.1 to 1.7, the water absorption decreased from the 23.52% to 15.77%. When the functional groups of FMM:polyether glycol OH increased, the water absorption decreased. When the functional groups of FMM: polyether glycol OH=1:6, the water absorption decreased to 13.84%.(3) The use of amine chain extenders and the neutralizer during prepolymer synthesis will make color yellow, and as the extension of storage time,system colors deepen.(4) with the DMPA content increased, the peel strength of BOPP/PE increased. When the hydroxy mol ratio of polyether glycol:DMPA=1.0:1.4, the peel strength reach a maximum value. The destroyed mode developed from cohesive failure to adhesive material failure.When the functional groups of FMM:polyether glycol OH increased, the peel strength of BOPP/PE, PET/PE showed a continuous increase trend.The mode of failure is adhesive material destruction. With the same thickness of adhesive layer and curing conditions, when used for non-polar/non-polar substrate, the TC-WPU exhibit excellent adhesion Property, the peel strength can reach up to 16.32N/25mm.