Patent GB-1310474-A (GB)
Title: Reticulate sheet material
IPC: B29D28/00
Filed: 1971-07-15
Abstract: 1310474 Reticulated films JOHNSON & JOHNSON 15 July 1971 [15 July 1970 (2)] 33210/71 Heading B5B [Also in Division D1] A reticulate polymer sheet material comprises intersecting molecularly oriented filaments, said filaments being integral at the intersections, said filaments between intersections having a molecular orientation function of at least 0À75 and said filaments at said intersections having a molecular orientation of at least 75% of the molecular orientation of the filaments between intersections. Preferably, the filaments between intersections have a molecular orientation function of at least 0À8, and the filaments at intersections have a molecular orientation of at least 85% of the molecular orientation of the filaments between intersections, especially of at least 0À7. The intersecting filaments may form a pattern of rectangular openings, especially square openings, and the oriented filaments may be uniaxially oriented in the direction of their length. Such material may be made by embossing a film so as to form a net-like structure of substantially unoriented ribs and junctures which define the uniform pattern of openings throughout the structure, said ribs and junctures having substantially uniform cross-sectional areas throughout the structure, and stretching the structure in the longitudinal direction at a ratio of at least 3 : 1 and in the transverse direction at a ratio of at least 4 : 1 so that the total area stretch of the structure is from 12 : 1 to 40 : 1, whereby the ribs and junctures are substantially uniformly molecularly oriented throughout the sheet material. The structure may be heated to a temperature of from 270‹ to 320‹ F. during the stretching operations. Preferably, initial stretching is in the longitudinal direction. The structure may be stretched longitudinally at a ratio of at least 4 : 1, and is preferably stretched in a longitudinal direction as a ratio of at least 3À6 : 1 and in the transverse direction at a ratio of at least 8 : 1. Figs. 4, 5 and 6 show various embodiments of the types of junctures or intersections of a reticulated sheet material. In Fig. 4, a pair of longitudinal filaments 27 and 28 and a pair of transverse filaments 29 and 30 enter the juncture 31. The longitudinal filament 27 splits into a pair of smaller filaments 32 and 33 which merge into the transverse filaments 29 and 30. The longitudinal filament 28 also splits into a pair of smaller filaments 34 and 35 which merge into the transverse filaments 29 and 30. The smaller filaments 32, 33, 34 and 35 are highly oriented and bound an area 36 which is a highly oriented thin film. The film area is thought to be uniaxially oriented with the direction of orientation changing over the area 36, since when stress is placed on a transverse filament 29 and 30, the film area orientation is also transverse; but when stress is placed on longitudinal filaments 27, 28, the molecules of the film area 36 re-orient themselves to a certain degree in the longitudinal direction. In Fig. 5, the opposed transverse filament 43 stretches into three smaller filaments 48, 49 and 47. The filaments form two triangular shaped areas 51 and 52. These areas are covered by a thin film which is also highly uniaxially oriented and aids in taking up any stresses placed on the juncture. Fig. 6 shows another type of juncture which may be present in the reticulate materials. Specified materials include polyolefines, polyesters, and polyamides. Especially suitable materials are isotactic polypropylene and high density polyethylene. Fig. 11 shows a suitable apparatus for making the reticulate sheet material. Film 102 passes via rollers 103 and 105 to heated roll 106 and is embossed at the nip between 106 and embossing roll 107. It is allowed to cool, and then passes to nip rolls 109 and 110 and thence to tenter frame 111, enclosed in oven 117. After transverse stretching the film passes through nip rolls 119 and 120 to a conventional longitudinal stretching apparatus 121, which may be enclosed in an oven, and the oriented net so made is wound up at 128.