Abstract: A rabbit for radiation formed of an aromatic polyester composed of ethylene-2,6-naphthalenedicarboxylate units as main recurring units and having an intrinsic viscosity of 0.45 to 0.90.

Abstract: A biaxially oriented film of polyethylene-2,6-naphthalate having a Young's modulus of at least 650 kg/mm.sup.2 in a given direction on the film plane and a direction crossing it at right angles, the difference between the Young's moduli in the two directions being at most 200 kg/mm.sup.2, the difference between the thermal shrinkages in the two directions being 0 to 0.1%.

Abstract: A biaxially oriented polyester film formed from an intimate mixture comprising (1) an aromatic polyester, and (2) 0.01 to 4% by weight, based on the aromatic polyester, of spherical fine particles of silica having (a) an average particle diameter of 0.05 to 4 .mu.m, (b) a particle diameter ratio, defined by the ratio of maximum diameter of minimum diameter, of from 1.0 to 1.2, and (c) a relative standard deviation (.sigma.) of particle size, of up to 0.5. A biaxially oriented polyester film formed from an intimate mixture comprising (1) an aromatic polyester, (2) 0.005 to 3% by weight, based on the aromatic polyester, of spherical fine particles of silica having the same properties as the above-mentioned (a), (b) and (c), and (3) 0.005 to 3% by weight, based on the aromatic polyester, of inert fine particles having an average particle diameter of 0.01 to 3 .mu.m and not exceeding the average particle diameter of the spherical fine particles of silica.

Abstract: A biaxially oriented film formed from a intimate mixture comprising (I) an aromatic polyester, (II) 0.005 to 1.0% by weight, based on the aromatic polyester, of fine particles of a silicone resin having (a) a composition represented by the following formula (A)R.sub.x SiO.sub.2-x/2 (A)wherein R represents a hydrocarbon group having 1 to 7 carbon atoms, and x is a number of from 1 to 1.2, (b) a volume shape factor (f), represented by the following formula (B), of more than 0.4 but not exceeding .pi./6f=V/D.sup.3 (B)wherein V is the average volume (.mu.m.sup.3) of the particles and D is the average maximum particle diameter (.mu.m) of the particle, and (c) an average particle diameter of 0.3 to 4 .mu.m. The film optionally contains (III) 0.005 to 1% by weight, based on the aromatic polyester, of inert fine particles having an average particle diameter of 0.01 to 1 .mu.m but being smaller than the average particle diameter of the silicone resin particles.