The present invention pertains to a process for preparing resinous products from epoxy-containing materials and materials containing hydroxyl, thiol, carboxyl, isocyanate, thioisocyanate or secondary amine groups or a combination of such groups.
Linear polyhydroxy ether resins, i.e. thermoplastic epoxy resins also known as phenoxy resins and advanced epoxy resins have been produced and sold for a long time. Generally, they are produced and often sold in a solvent (25 or 50% concentrations) to reduce their viscosity. The primary reason for this is that as the molecular weight increases, the viscosity increases significantly. The process commonly used is a batch process using large kettles. Also, with the batch process there is a continuing product reaction such that the first product removed from the kettle will vary from the last thus causing product inconsistencies. The mass of materials in large kettle reactors is further complicated by heat transfer, i.e., the heat of reaction is more difficult to control and localized high heats will cause adverse reactions to occur, i.e., crosslinking. Current commercial processes involving solution processes require substantial capital equipment to reduce the product to a powder or granular product. This involves successive solvent stripping and vacuum devolatilization and, in some cases, salt by-products need to be washed from the product before granulation. Even then the final product contains significant amounts of undesirable solvents, water, and other by-products.
The residual solvents cause numerous problems when the product is fabricated into a usable product, such as a film in coextrusion, or moldings. The residual volatiles require extensive vacuum drying to prevent voids in the film and molded articles. The hazard of solvents being released from a product during fabrication could cause a problem unless proper venting is employed. Solvents may have an adverse effect on polymer properties such as stability, color, haze, etc.
The present invention solves most of the problems associated with the batch solvent process, i.e. less capital requirement, reduced energy requirement, more product consistency and in the case of phenoxy resins, it permits the production of such resins which are higher in molecular weight. The present invention also provides greatly improved temperature control during the reaction which significantly reduces or eliminates undesirable crosslinking.