Patent ID: 6881442

Claim:
A continuous two-stage process for preparing solvent-free polyacrylate hot melt pressure sensitive adhesives which is gentle on the polymer and reemploys the solvent used in the process, and which comprises the following steps: a) polymerizing a composition comprising one or more monomers selected from the group consisting of acrylic acid, mathacrylic acid, acrylate monomers and methacrylate monomers and/or comprising one or more oligomers and/or prepolymers comprising one or more of said monomers, in a solvent or solvent mixture having a vapor pressure temperature at 100 Pas of less than −10° C. to a monomer conversion of >99% to form a polymer solution; b) continuously mixing the polymer solution with additives and auxiliaries and preheating the mixture under superatmospheric pressure; c) concentrating the polymer solution to a residual solvent content of less than 0.1% by weight in a first extruder, under the effect of reduced pressure and increased extruder temperatures to form a pressure sensitive adhesive, the specific drive energy for the polyacrylate pressure sensitive adhesives produced, having an average molecular mass M w of from 600 000 to 900 000 g/mol, being less than 0.18 kWh/kg, while maintaining a temperature of the adhesive at the outlet of the extruder of not more than 135° C.; d) condensing, collecting, and re-using in step a) the solvent stripped off in the extruder, in a proportion of more than 80% of the amount used in step a); e) compounding the solvent-freed pressure sensitive adhesive with tackifying resins, fillers, stabilizers, crosslinkers or other additives in a second extruder with a specific drive energy of less than 0.05 kWh/kg while maintaining a temperature of the adhesive at the outlet of the extruder of not more than 125° C.; and f) transferring the compounded solvent-free pressure sensitive adhesive to a downstream coating unit.