Teijin Limited

Teitin Limited

Yasuji Hirabayashi

Hiroo Inata

Takanori Urasaki

Makoto Ogasawara

Tugusi Yoshida

A wholly aromatic copolyester composed mainly of isophthalic acid units and hydroquinone units, the total proportion of said isophthalic acid units and hydroquinone units being at least about 80 mole % based on the entire units, said wholly aromatic copolyester having a terminal carboxyl group concentration, measured by the method described in the specification, of not more than about 90 eq/10.sup.6 g and a reduced viscosity, determined at 35.degree. C. in a mixed solvent of phenol and tetrachloroethane in a weight ratio of 4:6 in a concentration of 1.2 g/dl of at least about 0.6 and being substantially linear and melt-shapable and substantially free from a halogen atom bonded to the molecular chain, and a film prepared therefrom by melt shaping.

Novel wholly aromatic copolyester, process for production thereof, and

A melt-molded film of a wholly aromatic polyester, said film having in its plane two perpendicularly crossing directions in each of which the Young's modulus and strength of the film at 25.degree. C. are at least about 200 kg/mm.sup.2 and at least about 5 kg/mm.sup.2 respectively, the product of the Young's moduli of the film in the two directions being at least 8.times.10.sup.4 (kg/mm.sup.2).sup.2, and said wholly aromatic polyester being substantially linear, having a melt viscosity at about its melting point of at least about 10000 poises, and being composed substantially of recurring units derived from p-hydroxybenzoic acid, recurring units derived from a m- or p-oriented aromatic dicarboxylic acid and recurring units derived from a m- or p-oriented aromatic dihydroxy compound, the proportion of said recurring units derived from p-hydroxybenzoic acid being about 30 to about 70 mole % based on the entire recurring units. This invention provides also a process for producing said film which comprises heating aforesaid wholly aromatic polyester to a temperature above a point at which the polyester is extrusion-moldable and extruding the heated polyester through a slit; and either (i) orienting the extruded film in the extruding direction or machine direction and a direction perpendicular thereto while the heated aromatic polyester resides in said slit or after it has left the slit but before it is cooled to the glass transition temperature of the polyester, of (ii) orienting the extruded film substantially only in the extruding direction or machine direction while the polyester heated at said temperature resides in the slit, or after it has left the slit but before it is cooled to the glass transition temperature of the polyester, and then re-heating the film to a temperature higher than the glass transition temperature of the polyester, and orienting the film in a direction perpendicular to the machine direction.

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Hachioji, Japan

Yasuji Hirabayashi