Method for longitudinal stretching a film in solid state and apparatus to carry out the method

摘要

Method and apparatus for longitudinal orientation of thermoplastic film material (20) comprises a width-reduction zone upstream of the longitudinal stretching zone (9, 10), through which the width of the film is gradually reduced so as to allow longitudinal stretching without necking. The width-reduction zone comprises at least two sets of pleating rollers (7, 1) comprising intermeshing grooves or discs for pleating the material. The downstream (1) rollers comprise a mini-roller defined by the following measures a) the pitch of the corrugations, measured from middle of tip to middle of each neighboring tip is 20 mm or less; b) the perimeter from middle of a tip to the middle of each neighboring tip measured along the corrugated roller surface, divided by the said pitch is in the range between 1.10 and 1.80; and c) the diameter of the mini-roller, measured at the tips of the corrugations, is at the highest 4 times the said pitch. Preferably a pair of mini-roller sets is arranged on opposing sides of the film in reciprocating mounts enabling alternate entwining of the film around one then the other mini-roller. The method allows achievement of high tensile strength, yield point, resistance to tear propagation and puncture resistance, especially for polyethylene and polypropylene films.

主权项

1. A process of supplying a thermoplastic polymer film having longitudinally extending pleats comprising:
stretching the advancing film in the solid state in one or more short zones between or on two or more stretching rollers or partly on and partly between such rollers, and entwining the advancing film in the solid state under longitudinal tension around a grooved mini-roller having corrugations and stretching on a smooth stretching roller, where the mini-roller is mounted upstream of and in close proximity to the smooth stretching roller, where the mini-roller is characterized by having: a) a pitch of the corrugations of 20 mm or less; as measured from a middle of a tip to a middle of each neighboring tip; b) a ratio of a perimeter to the pitch ranging between 1.10 and 1.80, where the perimeter is measured from a middle of a tip to a middle of each neighboring tip along the corrugated roller surface; and c) a diameter of less than or equal to 4 times the pitch, where a width of the film as measured in a straight line from edge to edge is reduced after the stretching and entwining to form a film having a pattern of longitudinally extending pleats.