Continuous two-stage process for the production of solvent-free polyacrylate melting adhesives

摘要

A continuous process for the production of solvent-free polyacrylate hot-melt adhesives involves concentration of the polymer solution under vacuum in a concentrating extruder at a low specific driving energy and with recycling of solvent, followed by compounding the solvent-free product with other components in another extruder. A continuous 2-stage process for the production of solvent-free polyacrylate hot-melt adhesives (I) under conditions which are mild to the polymer and with recycling of the solvent. The process involves (a) polymerisation of polyacrylate material to a monomer conversion of more than 99% in a solvent or solvent mixture with a vapour pressure temperature of below -10[deg]C at 100 Pa, (b) continuous mixing of the polymer solution with additives and auxiliary substances and preheating the mixture under elevated pressure, (c) concentration of the solution to a residual solvent content of less than 0.1 wt% in a first extruder at elevated temperature under vacuum, with a specific driving energy (SDE) of less than 0.18 kWh/kg for the production of (I) with a weight-average mol. wt. (M w) of 600000-900000, giving extruded material at a temperature of not above 135[deg]C, (d) condensation, collection and recycling of the solvent from stage (c) at the rate of more tha n 80% based on the original amount, (e) compounding of the solvent-free material with tackifying resins, fillers, stabilisers, crosslinkers or other additives in a second extruder with an SDE of less than 0.05 kWh/kg, to give extruded material at a temperature of not more than 125[deg]C and (f) transfer to a coating unit.