Film forming method

A method for manufacturing a film by inflation molding, comprising extruding a thermoplastic polymer capable of forming an optically anisotropic melt phase (hereinafter referred to as a thermotropic liquid crystal polymer), wherein

• said thermotropic liquid crystal polymer having any one of activation energies Ea1 and Ea2 of a melt viscosity being within the range of 30 to 90 kcal/mol, with the ratio (Ea1/Ea2) of the activation energy Ea1 relative to the activation energy Ea2 being within the range of 1 to 1.7;
• said activation energies being measured by a capillary rheometer, including a nozzle of 1 mm in inner diameter and 10 mm in length disposed at an angle of introduction of 90° and a barrel of 9.55 mm in inner diameter, at respective shear rates of 243 seconds −1 and 2432 seconds−1 (the activation energy measured at the shear rate of 243 seconds−1 being referred to as Ea1 while the activation energy measured at the shear rate of 2,432 seconds−1 is referred to as Ea2) under a temperature ranging from a first temperature [(Tm−10)° C.], which is lower by 10° C. than the melting point [(Tm)° C.] of the thermotropic liquid crystal polymer, to a second temperature [(Tm+20)° C.], which is higher by 20° C. than the melting point [(Tm)° C.] of the thermotropic liquid crystal polymer;
• said thermotropic liquid crystal polymer also having a melt viscosity, which, when measured at the shear rate of 2,432 seconds−1 under a temperature ranging from the melting point [(Tm)° C.], of the thermotropic liquid crystal polymer to a third temperature [(Tm +10)° C.], which is higher by 10° C. than the melting point [(Tm)° C.] of the thermotropic liquid crystal polymer, is equal to or higher than 400 poises;
• and
• said extruding of the thermotropic liquid crystal polymer being carried out from a die that is heated to a die temperature [(Td)° C.] adjusted to satisfy the following equation:
• 0≦Tm−Td≦50
• wherein Td represents the die temperature (° C.) and Tm represents the melting point (° C.) of the thermotropic liquid crystal polymer.