Stretching webs of sheet material

Claim 1

Apparatus for transversely stretching a travelling web of flexible plastic sheet material comprising a pair of edge-restraining means for gripping the longitudinal margins of the web to prevent substantial lateral inward movement of the web margins, a pair of opposed pressure assemblies between which the web can travel whilst in the grip of the edge-restraining means so that the assemblies cause the web to take up an extended path from margin to margin by applying opposed forces respectively to the opposite surfaces of the web at alternate spaced locations across the width of the web so as to cause the web to stretch transversely, said edge restraining means gripping the longitudinal margin of the web prior to engagement of the web with said pressure assemblies and releasing the web subsequent to the engagement with the pressure assemblies, each pressure assembly comprising a bank of laterally spaced pressure elements, the elements of one bank being laterally staggered in relation to the elements of the other bank and overlapping the elements of the other bank across a plane containing the web margins with a degree of overlap so as to stretch the web transversely into a pleated form without substantial lateral inward movement of the web margins, the pressure elements each having a web engaging peripheral surface of an anti-friction material which permits lateral slippage between the web and said surface and drive means for continuously advancing the web longitudinally through and between said pressure assemblies, whereby said pressure assemblies continuously deform the web.