ABSTRACT
An aromatic polyester is often called one of the third-generation engineering plastics because of its excellent electrical and thermal properties as well as mechanical properties [1]. Vecstar which is a trade name of Kuray Company, Ltd., Japan is an aromatic polyester made from acetoxy benzoic acid and acetoxy naphthoic acid (Fig. 1). Vecstar is fabricated into a sheet form by a blow molding technique, and is commercially available in the form of a film (25 and 50 µm thickness). In the fabrication process, polymer chains near the film surface are oriented in the machine
direction due to its highly crystalline nature and thermotropic liquid-crystalline behavior. As a result, Vecstar film is not homogeneous but has a heterogeneous structure (skin-core structure). The skin-core structure leads to troublesome problems such as fracture from the skin-core interface, curling of the film, etc. when shear stress or heat shock is applied to the films. In order to eliminate the skin-core structure, Vecstar films are subjected to heat treatment for converting into a homogeneous structure. Two types of Vecstar films, Vecstar FA and Vecstar OC, are available in the market. Vecstar FA is a film without the heat treatment, and Vecstar OC is a film which has been subjected to the heat treatment. Essential properties of the Vecstar FA and OC and polyimide are compared in Table 1.
