Patent NZ-701479-A (NZ)
Title: Molding apparatus, molded articles, and methods of molding
Inventor: DUBINION W SIDNEY
IPC: B29C70/44
Filed: 2014-03-18
Abstract: The present invention relates to methods of molding articles from engineering thermoplastics such as polycarbonate. The present invention further relates to post-molding treatment processes. While certain engineering thermoplastics, such as polycarbonate, have highly desirable material properties in theory, standard molding processes do not work to form articles from these materials wherein these properties are translated satisfactorily to the finished article. In particular, the formation of complex articles present a challenge for such materials. The present invention aims to address the problems of the prior art by providing a mold assembly used to make thermoplastic articles, wherein the mold assembly comprises first and second electrically conductive mold shell sections adapted to be connected to form a mold shell defining a cavity; and a reversibly pressurized electrically conductive inner membrane fluidly connected to a source of pressure, wherein the assembly is formed by disposing the inner membrane within the cavity such that the cavity defines the outer boundary of an article to be molded, and the pressurized inner membrane defines the inner boundary of the article to be molded. In addition, the present invention provides a method of molding an article, the method comprising: adding a thermoplastic material to a first electrically conductive mold shell section and/or a second electrically conductive mold shell section, each mold shell section defining a portion of a cavity; disposing an electrically conductive, reversibly pressurized inner membrane proximal to at least the first mold shell section; attaching the first and second mold shell sections to form a mold assembly defining a cavity, wherein the inner membrane is disposed within the cavity; applying an electrical current to the inner membrane to raise the temperature of the thermoplastic material to between the Tg and Tm of the material, or above the Tm of the material, while maintaining or increasing pressure to the inner membrane; and reducing the temperature while maintaining or increasing pressure to the inner membrane. Furthermore, the present invention provides a mold assembly used to make thermoplastic articles, wherein the mold assembly comprises first and second electrically conductive mold shell sections adapted to be connected to form a mold shell defining a cavity; and a reversibly pressurized electrically conductive inner membrane fluidly connected to a source of pressure, wherein the assembly is formed by disposing the inner membrane within the cavity such that the cavity defines the outer boundary of an article to be molded, and the pressurized inner membrane defines the inner boundary of the article to be molded, and wherein an electrical current is applied to the inner membrane to raise the temperature of the thermoplastic material to between the Tg and Tm of the material, or above the Tm of the material, while maintaining or increasing pressure to the inner membrane; and reducing the temperature while maintaining or increasing pressure to the inner membrane.