Powdered polyurethane hot melt adhesive is formulated by mixing thermoplastic polyurethane resin with colorants, plasticizers, stabilizers, curing agents and other additives, providing an economical and low-energy-consuming manufacturing process. The powder mixing process is gentle, maintaining the integrity of the resin structure and stable performance, thereby ensuring its performance. Another advantage of powder is that it has fluidity, which provides convenience for transportation, dispersion and use. Therefore, it does not need the help of other media (such as organic solvents or water), so the powder does not need to be melted to complete transportation and dispersion.
There are three main methods for preparing polyurethane powder:
1. Under oxygen-free conditions (oxygen can cause dust explosion) Milled polyurethane elastomer. If an impact grinder is used, the softer the product to be ground, the lower the operating temperature required. Chilled brine, ice or liquid nitrogen can be used to lower the temperature.
2. Prepare by addition polymerization in solvent, The solvent selected is required to dissolve only one reaction component but not the final polyurethane product (such as hydrocarbons that only dissolve isocyanates). The polyurethane resin produced by this solution polymerization method consumes a lot of energy no matter what method is used to recover the solvent.
3. In the presence of a very small amount of emulsifier or in close proximity When the content of water groups is extremely low, the polyurethane water dispersion is obtained through emulsion polymerization, and is made into powder after demulsification and drying. The manufacturing technology of polyurethane emulsion is complex, and there is a big gap between its product performance and overall polymerization.
In summary, the first method is currently mainly used, mixing granular polyurethane resin with additives, and then extruding it from a twin-screw extruder at a temperature of 80-130°C (extrusion time 0.5-2min). After the extruded material is cooled and cut, it is crushed into particles with an average diameter of 40~60um in a special pulverizer, and coarse particles are removed by screening method. The polyurethane powder prepared by this method has good fluidity and stability (the particles will not stick together when stored at 50°C).
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