PROCESS FOR PRODUCING NATURAL RUBBER FOR PRESSURE-SENSITIVE ADHESIVE AND NATURAL RUBBER-BASED PRESSURE-SENSITIVE ADHESIVE COMPOSITION

摘要

PURPOSE: To simply obtain a natural rubber having a suitable molecular weight by lowering the molecular weight of an unmasticated natural rubber by the action of a peptizing agent while dissolving it in an organic solvent. CONSTITUTION: The natural rubber is exemplified by SMR, SVR, ribbed smoked sheet No. 1-6, or pale crepe Nos. 1-3. The organic solvent is exemplified by an aromatic hydrocarbon such as toluene or an aliphatic hydrocarbon such as heptane or hexane. The peptizing agent is desirably a mastication accelerator such as a disulfide or a mercaptan such as o,o-dibenzamidodiphenyl disulfide, 2-benzamidothiophenol zinc salt, 2-thionaphthol, thioxylenol, or pentachlorothiophenol. The natural rubber-based tackifier composition comprises a natural rubber having a weight-average molecular weight of at most 700,000 and obtained by the above process. It is desirable in the production of a pressure-sensitive adhesive tape that the composition has a viscosity of at most 80 Pa.s as measured at 30deg.C with a Brookfield viscometer.