Patent ID: 8535588

Claim:
A sheet or film oblique stretching method comprising: feeding a sheet or film to a preheating zone, a stretching zone and a heat-treating zone while keeping opposite side edge parts of the sheet or film clipped by first and second clip arrays composed of pitch-variable clips having clip pitches, each pitch being a distance between adjacent clips, in a moving direction of the sheet or film, the pitches being variable in the moving direction of the sheet or film; having, with respect to the moving direction of the sheet or film, a position for the first clip array to initiate enlargement of clip pitch different from a position for the second clip array to initiate enlargement of clip pitch in the stretching zone; and enlarging clip pitches of the first and second clip arrays along with the travel of the first and second clip arrays to thereby make an oblique stretch of the sheet or film in the stretching zone.