Patent ID: 8561321

Claim:
A tenter oven comprising: (a) an oven housing having an inlet for a resin film at one end thereof and an outlet for the resin film at the other end, (b) a stretching zone between the inlet and the outlet, wherein the resin film is stretched at least in a direction perpendicular to the direction in which the resin film is carried while the resin film is carried from the inlet toward the outlet, and (c) a heat treatment zone between the inlet and the outlet, wherein air is ejected toward a surface of the resin film and the resin film is heat treated, wherein (d-1) an air ejection nozzle is provided against a passing plane of the resin film with a clearance and ejects air toward the surface of the resin film, (d-2) the air ejection nozzle comprises a nozzle housing, and the nozzle housing has an air supply passage therein, an air ejection face facing the passing plane of the resin film, and many air ejection holes opening to the air supply passage and opening in the air ejection face respectively, (d-3) the many air ejection holes in the air ejection face are circular, (d-4) the many air ejection holes are arranged in the air ejection face in two rows including a first row and a second row in the direction perpendicular to the carrying direction of the resin film, with the air ejection holes of the first row and the air ejection holes of the second row being arranged in a zigzag arrangement, and (d-5) the distance L (mm) between the air ejection face and the passing plane of the resin film, the diameter D (mm) of the respective air ejection holes in the air ejection face, the interval Px (mm) in the carrying direction of the resin film between first air ejection holes aligned in a straight line passing through the centers of the multiple air ejection holes arranged in the first row and second air ejection holes aligned in a straight line passing through the centers of the multiple air ejection holes arranged in the second row, and each interval Py (mm) between the centers of the respectively adjacent air ejection holes in the first air ejection holes aligned straight line and between the centers of the respectively adjacent air ejection holes in the second air ejection holes aligned straight line satisfy the following formulae (1) and (2): 6≦( L/D )/( Px/Py )≦9 formula (1) 4 ≦L/D ≦8 formula (2) (d-6) an air ejection face of the air ejection nozzle is positioned to face the passing plane of the resin film formed between the inlet and the outlet, and (e) the air ejection nozzle is provided in the heat treatment zone in such a manner that the directions of the first row and the second row of the air ejection holes of the air ejection nozzle are kept perpendicular to the carrying direction of the resin film.