Importance

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Abstract

Method and apparatus for imparting a uniformly apertured three-dimensional pattern to a heated plastic material subjected to a fluid pressure differential while in contact with said forming structure. In a preferred embodiment, said forming structure is created by forming a substantially continuous pattern of apertures in a multiplicity of planar sheets, at least a portion of said sheets having aperture patterns which are concentrically aligned but dissimilar in size to one another. The sheets having said concentrically aligned aperture patterns are thereafter superposed upon one another so as to form a stack exhibiting a three-dimensional continuum of capillary networks. A sufficient number of laminae are employed to ensure that said networks are of greater overall length than the maximum depth to which the plastic film being processed thereon is drawn when subjected to said fluid pressure differential. Said capillary networks exhibit a cross sectional area which reaches a minimum intermediate the uppermost and lowermost surfaces of the stack and thereafter increases in the direction of the lowermost surface of the stack to increase fluid permeability. The superposed sheets are bonded to one another at contact points while in the stacked configuration to form an integral laminate structure. The laminate forming structure is preferably caused to assume a tubular shape and its opposing free edges are secured to one another without disrupting the three-dimensional continuum of capillary networks along its periphery, thereby facilitating continuous plastic web processing against its outermost surface. The tubular laminate forming structure is preferably supported on a cylindrical drum by a multiplicity of radially oriented support members having lands which contact the innermost surface of the tubular member, but which are of insufficient cross-section to obstruct fluid flow through the capillary networks.

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First Claim