Method and apparatus for biaxially stretching a tubular film

Claim 1

A method of biaxially stretching a tubular thermoplastic polymer film, comprising the steps of: (a) feeding the tubular film in flattened form longitudinally at a first speed; (b) supporting the film while being longitudinally fed at its opposite selvages from inside on a pair of belt means having respective portions disposed within the tubular film in abutment against the selvages thereof; (c) gripping the film selvages between said pair of belt means and the peripheries of a pair of substantially coplanar pulleys disposed outside the film, each of said belt means being trained around one of said pulleys through a substantially semicircular peripheral edge thereof; (d) rotating said pulleys in opposite directions at a peripheral speed greater than said first speed, whereby the film is stretched longitudinally and transversely and is turned inside out and reversed in direction of travel as the film selvages are advanced along a pair of divergent substantially semicircular paths, respectively, between said pulleys and said belt means; (e) heating the film during the longitudinal and transverse stretching thereof; and (f) cutting the stretched film at the selvages into a pair of sheets adjacent to a position where the film is released from the belt means and pulleys at the ends of said divergent substantially semicircular paths.

Claim 2

A method of biaxially stretching a tubular thermoplastic polymer film, comprising the steps of: (a) feeding the tubular film in flattened form longitudinally at a first speed; (b) supporting the film while being longitudinally fed at its opposite selvages from inside on a pair of belt means having respective portions disposed within the tubular film in abutment against the selvages thereof; (c) gripping the film selvages between said pair of belt means and the peripheries of a pair of substantially coplanar pulleys disposed outside the film, each of said belt means being trained around one of said pulleys through a substantially semicircular peripheral edge thereof; (d) rotating said pulleys in opposite directions at a peripheral speed greater than said first speed, whereby the film is stretched longitudinally and transversely and is turned inside out and reversed in direction of travel as the film selvages are advanced along a pair of divergent substantially semicircular paths, respectively, between said pulleys and said belt means; (e) heating the film during the longitudinal and transverse stretching thereof; and (f) cutting the stretched film at the selvages into a pair of sheets adjacent to a position where the film is released from the belt means and pulleys at the ends of said divergent substantially semicircular paths.

Claim 5

An apparatus for biaxially stretching a tubular thermoplastic polymer film, comprising: (a) means for feeding the tubular film in flattened form at a first speed along a longitudinal path; (b) a pair of substantially coplanar pulleys disposed one on each side of said path and rotatable in opposite directions at a peripheral speed greater than said first speed; (c) a pair of endless belt means disposed symmetrically with respect to said path and extending along said longitudinal path between said pulleys for being located within the tubular film in abutment against the opposite selvages thereof, respectively, to support the film at the selvages from inside thereof as it is fed along said longitudinal path, said belt means being trained around said pulleys substantially through their respective substantially semicircular peripheral edges, respectively, for gripping the film at the selvages thereof respectively along a pair of divergent substantially semicircular paths between said pulleys and said belt means, whereby the film is stretched longitudinally and transversely and is turned inside out and reversed in direction of travel upon rotation of said pulleys; (d) means for heating the film during the longitudinal and transverse stretching thereof; and (e) means for cutting the stretched film at the selvages into a pair of sheets adjacent to a position where the film is released from said belt means and pulleys at the ends of said divergent substantially semicircular paths.

Claim 6

An apparatus for biaxially stretching a tubular thermoplastic polymer film, comprising: (a) means for feeding the tubular film in flattened form at a first speed along a longitudinal path; (b) a pair of substantially coplanar pulleys disposed one on each side of said path and rotatable in opposite directions at a peripheral speed greater than said first speed; (c) a pair of endless belt means disposed symmetrically with respect to said path and extending along said longitudinal path between said pulleys for being located within the tubular film in abutment against the opposite selvages thereof, respectively, to support the film at the selvages from inside thereof as it is fed along said longitudinal path, said belt means being trained around said pulleys substantially through their respective substantially semicircular peripheral edges, respectively, for gripping the film at the selvages thereof respectively along a pair of divergent substantially semicircular paths between said pulleys and said belt means, whereby the film is stretched longitudinally and transversely and is turned inside out and reversed in direction of travel upon rotation of said pulleys; (d) means for heating the film during the longitudinal and transverse stretching thereof; and (e) means for cutting the stretched film at the selvages into a pair of sheets adjacent to a position where the film is released from said belt means and pulleys at the ends of said divergent substantially semicircular paths.