Technology has been developed to enable efficient manufacture of electrical articles, such as power accessories, using a thermoplastic molding approach followed by an off-mold, latent cure (as opposed to standard in-mold vulcanization). Many design variations exist, but generally these articles comprise three-layers, i.e., (a) an inner semi-conductive sleeve referred to as the faraday cage, (b) an outer semi-conductive layer referred to as the jacket, and (c) a thick layer in between the two semi-conductive (a) and (b) layers, this thick layer made of an electrically insulating material and referred to as the insulation layer.
The new technology allows for the article to be molded in a standard thermoplastic injection molding process, and then cured off-mold at ambient conditions. Since not cured in the mold, one important requirement during the molding operation is to cool these thick articles enough to achieve geometrical integrity prior to demolding. The molding cycle is thus controlled by the efficiency of cooling the article inside the mold and achieving appropriate green strength for demolding. For this to work, the operation typically uses a chilled mold, one that is maintained below the melting temperature of the polymer(s) from which the article is made. This is very different from conventional in-mold vulcanization in which the material is injected and cured in a high temperature mold.
This off-mold cure method poses unique challenges including material solidification in undesired location, air entrapment, etc., which can results in article defects. In addition, given the typically elastomeric nature of the materials used, issues exist regarding layer deformation during injection and these, in turn, can lead to unacceptable article quality. This invention pertains to a molding method to solve the problem and enable the production of defect-free parts.