Process and apparatus for compressive transverse stretching of polymeric sheet material
AssigneeOle-Bendt Rasmussen
InventorOle-Bendt Rasmussen
Life of this patent
Estimating the term…
Abstract
Sheet material (4) is stretched transversely into longitudinally extending pleats by passage between intermeshing grooved rollers (A and B) having circularly or helically extending grooves in their surfaces. Each groove is formed of a base (6a,6b) and side walls (5a,5b) inclined outwardly to a peak (7a,7b). Portions of adjacent side walls (5a,5b) are parallel to one another. The peaks are less than about 3 mm apart and the film is stretched by the peaks and is compressed between the side walls by forcing the rollers together. The pleated material is generally then stretched longitudinally substantially to eliminate the pleats and it may then be again stretched transversely between a further set of intermeshing grooved rollers.
Claims20
A process of stretching continuous polymeric sheet material in which the material is subjected to transverse stretching by passing the material between intermeshing grooved rollers in which the grooves extend substantially helically or circularly around each roller and are arranged in alternating valleys and peaks with outwardly inclined side walls that extend between the valleys and the peaks and the sheet material is thereby stretched transversely to increase significantly its transverse dimension and form the same into pleats that extend substantially in the machine direction, wherein the total roller length is at least 50 cm, the pitch between adjacent peaks is less than about 3 mm, the side walls of said intermeshing grooves have portions which are substantially parallel to each other, and the sheet material is compressed between opposed pairs of said substantially parallel side wall portions by forcing the rollers together under a substantially uniform pressure along their axial length of at least 17 kg/cm of said length but not sufficient to rupture said sheet material to a compression position in which the clearance between said substantially parallel side wall portions is smaller than the starting sheet thickness, and then subjecting said sheet material to at least one stretching step sufficient to remove substantially said pleats and impart a generally flat condition to the final sheet material while retaining therein a transverse dimension at least substantially equal to that of the starting sheet material.
Apparatus suitable for biaxial stretching of continuous polymeric sheet material and comprising intermeshing grooved rollers in which the grooves extend substantially helically or circularly around each roller and are arranged in alternating valleys and peaks with inclined side walls that extend between the valleys and the peaks, the total roller length being at least 50 cm, the pitch between adjacent peaks being less than about 3 mm, and the opposed side walls of said intermeshing grooves having portions which are substantially parallel to each other;
- means for passing the sheet material between said rollers;
- means for biasing the rollers together while the sheet material passes therebetween to undergo significant widthwise stretching and arrangement into longitudinally pleated condition, wherein one of the rollers comprises a single elongated roller and the other comprises a plurality of short rollers that are biased by said biasing means toward the elongated roller with substantially equal pressure, so that together they intermesh with said elongated roller over substantially its entire length;
- and downstream of said intermeshing grooved rollers at least one stretching means for stretching the sheet material emerging from said grooved rollers sufficient to remove substantially the pleats from the sheet material and impart a generally flat condition thereto while maintaining a sheet material width at least substantially equal to that of the starting sheet material.
Dependencies are inferred from the claim text.