Patent ID: 8445626

Claim:
A biaxially-oriented film comprising: a nylon film comprising nylon 6 and metaxylylene adipamide, wherein said film has an elongation ratio in each of the machine direction, transverse direction, a 45 degree direction and a 135 degree direction, until a film rupture is 70 percent or more, the elongation ratio being measured in a tensile test, wherein the testing conditions include: a sample width of 15 mm; a distance between gauge points of 50 mm; and a tensile speed of 100 mm/min, and a stress ratio A (σ 1 /σ 2 ) between a tensile stress σ 1 and a tensile stress σ 2 in a stress-strain curve obtained in the tensile test of the film is 2 or more in each of the four directions, the tensile stress σ 1 being a value at a point where the elongation ratio becomes 50 percent while the tensile stress σ 2 being a value at an yield point, wherein said film is made from a film forming material that contains a virgin material and a thermal hysteresis material, the virgin material being formed of nylon 6 and metaxylylene adipamide, the thermal hysteresis material being obtained by melt-kneading nylon 6 and metaxylylene adipamide, and by setting the metaxylylene adipamide to have a melt point of 233 to 238 degrees C., and a hydrothermal shrinkage factor of said film is 3 to 20 percent in each of the machine direction and the transverse direction of said film when said film is retained in hot liquid of 95 degrees C. for thirty minutes, wherein the nylon 6 and metaxylylene adipamide are contained in the virgin material at ratios of 60 to 85 parts by mass and 15 to 40 parts by mass, respectively, and the content of the thermal hysteresis material is 5 to 40 percent by mass of the total amount of the film forming material.