Mold Release Agents in the Rubber Industry

Abstract

Abstract The efficient production of high quality molded products in the rubber industry depends substantially on the use of suitable mold release agents and mold lubricants. Their function is to release even odd shaped articles from the molds. Since the mechanical strength of the stock at curing temperature is only a fraction of the room temperature value mold release agents play an important role in this operation. Effective mold release agents decrease the percentage of rejects and shorten the time between release and injection. A number of additional qualities are required of an “ideal” mold release agent. No decomposition residues should build up on the mold surface, since this would affect the product surface and would require cleaning of the mold after each use. The mold surface should be protected against corrosion, thus a mold release agent should be thermally stable and chemically inert. Furthermore, a mold release agent should produce a good appearance and a convenient finish while avoiding undesired side-effects detrimental to the color, the adhesive properties or the lacquer acceptance of the rubber. The mold release agent should affect neither the aging properties nor the odor and taste of the product and must be nontoxic. In addition, a virtually unlimited shelf life is expected. In view of the multitude of technical requirements it is not surprising that no single compound will combine all these qualities. Practically, a compromise is made and a few shortcomings have to be accepted. The following is an attempt to characterize the most important groups of mold release agents with respect to their technological properties.