Patent GB-904172-A (GB)
Title: Self-sealing metallic overwrap and method for producing the same
IPC: B65D75/26
Filed: 1958-12-24
Abstract: 904,172. Laminates; perforating-apparatus. REYNOLDS METALS CO. Dec. 24, 1958 [Jan. 7, 1958], No. 41638/58. Classes 31 (2) and 140. [Also in Group XVII] A laminated sheet material, for use in wrapping, e.g. bread, comprises a layer of metal foil, e.g. aluminium, and a layer of paper, thicker than the metallic layer, and a layer of thermoplastic adhesive, e.g. microcrystalline wax, between the metallic and paper layers, two bands of perforations being formed in the metallic layer, along two parallel edges of the sheet, each band comprising a plurality of spaced rows of perforations which pass through the metal layer but not substantially into the paper layer and are spaced far enough apart to prevent their acting as tear-strips during normal wrapping and sealing operations. Each band of perforations is big enough to provide within its confines a substantial area of metal-to-metal contact. Such material may be made by moving a laminated web comprising a layer of metal foil a layer of paper, thicker than the metal foil, and a thermoplastic adhesive between the metal and the paper, continuously under tension through a skip-score perforating step, applying a variable cutting pressure to web-perforating blades rotatably engaging the metallic side of the moving web to form two bands of perforations in the metallic layer, extending one along each of two parallel edges of the web, the depth of penetration of the blade being regulated by causing the pressure to diminish as the blade cuts more deeply into the web, whereby each perforation penetrates the metallic layer fully, but does not penetrate the paper layer substantially. As shown, web material from a roll 28 is drawn, metal side up, through a perforating apparatus and re-reeled at 23. A backing roll 39 is supported by stub shafts in recesses 36, and is a hollow tube of metal having a resilient covering, e.g. of rubber. An adjustable shaft 41 has a handle 50 rigidly fixed to it. Perforating assemblies 51, 52, 53 and 54 are mounted on this shaft. Each comprises a yoke member having spaced arms 60 and 61, joined at one end by a cylindrical spacer that is a close but freely movable fit on the shaft 41. Attached to this spacer is a plate 63. Beside the yoke member is an L-shaped spring backboard member 68 clamped by a cap member 69 and two bolts to the shaft 41. A compression-spring between the other end of this backboard member and the plate 63 urges them apart. Between the arms of the yoke are perforating blades 74, 75, 76, 77 and 78, mounted to rotate independently on a pin between the sides of the yoke. Each blade has a series of sharp bevelled teeth spaced from each other by undercuts. As the web is drawn through the apparatus, it causes the blades, which are pressed on to it by the compression-springs, to rotate independently of one another, and so to perforate the upper, metallic layer of the web. The resilient surface of the backing roll then absorbs the residual energy of the spring before the blades penetrate substantially into the paper layer. The position in which the members 68 and 69 are clamped on the shaft may be adjusted to give the desired depth of cut.