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US 5,394,595 AGranted
Method and apparatus for shrinking biaxially stretched thermoplastic films
AssigneeLindauer Dornier GmbH
InventorAndreas Rutz
Life of this patent
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AssigneeLindauer Dornier GmbH
InventorAndreas Rutz
Estimating the term…
A thermoplastic film web is subjected to a defined shrinking in a treatment apparatus with two mirror-symmetrically arranged tentering chains. For this purpose, each chain is equipped with tentering clamps that have a variable on-center spacing or pitch in the travel direction of the tentering chains, and which additionally are position adjustable in a direction other than the travel direction. The entire clamp body or clamp elements may be position variable in a direction other than the travel direction. In operation, the pitch is first reduced in the inlet and/or heating zone of the treatment apparatus. Simultaneously, the clamping position of the individual clamps or clamping element is changed, e.g. by tilting or lifting. The clamp position change takes up extra film web length resulting from the pitch change, whereby the film web assumes throughout its width a corrugated configuration. Then, the film web is cross-stretched. Then the position of the clamps or clamp elements is changed in the setting zone of the apparatus so that the film web is plane again, whereby the shrinking takes up the corrugations. Then, the clamps release the film web and thereafter the original longer pitch is restored.
A method for shrinking a biaxially stretched thermoplastic film in a treatment apparatus having two tentering chains arranged in a common plane, said tentering chains defining an inlet zone, a heating zone, a stretching zone, a setting zone, and an outlet zone in that order as viewed in the travel direction of said thermoplastic film, said tentering chains carrying tentering clamps for gripping an edge of said thermoplastic film as it enters said inlet zone and for carrying said thermoplastic film through said treatment apparatus, said method comprising the following steps:
An apparatus for shrinking a biaxially stretched thermoplastic film in a treatment apparatus, comprising two tentering chains arranged in a common plane, said tentering chains defining an inlet zone, a heating zone, a stretching zone, a setting zone, and an outlet zone in that order as viewed in a film travel direction of said thermoplastic film, said tentering chains carrying tentering clamps for gripping each edge of said thermoplastic film as it enters said inlet zone and for carrying said thermoplastic film through said treatment apparatus, said apparatus further comprising first means for varying a pitch between neighboring tentering clamps, whereby a first on-center spacing (T) between neighboring tentering clamps is reduced in said travel direction to a second on-center spacing (t), second means for simultaneously varying a starting position of said tentering clamps in a positional change direction other than said film travel direction whereby said tentering clamps assume a varied position so that an excess film length is provided that is defined in its size and position, third means for cross-stretching said thermoplastic film in said stretching zone, fourth means for changing said varied position of said tentering clamps back to said starting position in said setting zone, fifth means for releasing said thermoplastic film from said tentering clamps, and sixth means for returning said second on-center spacing (t) back to said first on-center spacing (T).
Dependencies are inferred from the claim text.