Abstract: A heat sensitive original sheet for stencil printing made of a laminate of a paper sheet and a biaxially oriented polyester film having a melting point of 150.degree. to 240.degree., a thickness of 0.2 to 3 .mu.m, an average refractive index of 1.570 to 1.578, a thermal shrinkage stress of 100 to 800 g/mm.sup.2 after being treated at 80.degree. C. for 10 seconds, a thermal shrinkage factor of 5 to 50% after being treated at 80.degree. C. for 10 minutes, a shrinkage factor of 15% or less after being treated in toluene at 25.degree. C. for 10 minutes, and a center line average surface roughness of 0.02 to 0.3 .mu.m, which original sheet is excellent in a perforation sensitivity, resistance to curling, and resolution and image density of a printed image.

Abstract: Disclosed is a film for high heat-sensitive stencil paper, comprising a biaxially oriented film having a thickness of 0.5 to 6.0 .mu.m and formed from a polyester composition comprising polybutylene terephthalate and another polyester,a ratio of the polybutylene terephthalate in the whole polyester being 20 to 80 wt %, a maximum value of average heat shrinkage stresses in the machine and transverse directions of the film measured at a film temperature of 60.degree. to 140.degree. C. being more than 300 g/mm.sup.2, and a heat shrinkage of the film by treatment at 100.degree. C. for 3 minutes being not less than 20%.

Abstract: A film for heat-sensitive stencil paper comprising a biaxially oriented film having a thickness of 0.5 to 6.0 .mu.m and formed from a polyester composition comprising polybutylene terephthalate and at least one other polyester, the content of the polybutylene terephthalate in the polyester composition being 20 to 80 wt %, the polyester composition has one melting point or a plurality of melting points with a difference of less than 10.degree. C. between the highest melting point and the lowest melting point.

Abstract: A biaxially oriented polyester film containing 0.01 to 4 wt % of multilayered high-molecular particles having a weight-average particle size of 0.05 to 3 .mu.m which comprise core crosslinked high-molecular particles having a glass transition temperature of not lower than 100.degree. C. coated with a crosslinked polymer having a glass transition temperature of lower than 100.degree. C., the ratio Dw/Dn of the weight-average particle size (Dw) and the number-average particle size (Dn) being not more than 1.3 is disclosed. The film of the present invention has excellent running property and wear resistance and is useful as a base film for various products such as magnetic recording media, capacitors, photomechanical plates, electric insulators, heat-sensitive transfer film, packaging film, transfer marks and gold and silver threads. Thus, the present invention has a high industrial value.