Patent GB-887956-A (GB)
Title: A new or improved flexible material, particularly suitable for use as a protective covering material for packaging and preservation purposes
Inventor: GONDA DESIRE
IPC: B32B15/08
Filed: 1957-01-02
Abstract: 887,956. Laminates. E.P.S. (RESEARCH & DEVELOPMENT) Ltd. Jan. 2, 1958 [Jan. 2, 1957; March 28, 1957], Nos. 220/57 and 10216/57. Classes 42 (1) and 140. [Also in Groups XI, XVII, XXV and XL (a)] A flexible laminate comprises a layer of lead foil having adhered to each side thereof a sheet of fabric impregnated with a flexible, thermoplastic, synthetic resin having a thickness of not less than 0.01 inch. The thermoplastic synthetic resin may be polyvinyl chloride resin or vinyl chloride copolymers or polyethylene or polypropylene, and may be pigmented to render it opaque to ultra-violet rays. The fabric may be woven and may be of cotton, silk or other vegetable or animal fibres, or any other fabric such as rayon or a fabric made from synthetic fibres such as polyethylene terephthalate. The adhesive used to stick this material to the lead foil may have a good preliminary tack and may be a solution of a mixture of a phenolformaldehyde resin and a synthetic rubber. The laminate may be made by combining a woven sheet with a sheet of calendered polyvinyl chloride resin, and sticking the same to lead foil, one sheet on each side of foil, by applying adhesive and pressing together. The adhesive may be applied to either or both of the lead foil and fabric sheets. In an alternative method, the laminate may be formed by coating one side of a sheet of fabric with a paste adapted to form, on the application of heat and pressure, the thermoplastic synthetic resin, applying the adhesive to the fabric side of the coated fabric sheet, and to one side of the lead foil, hot calendering, and repeating the process to apply a second sheet of coated fabric to the other side of the lead foil. Each hot calendering operation may be followed by a cold calendering operation. The paste may comprise polyvinyl chloride and/or a vinyl chloride copolymer mixed with a plasticizer and heat- and lightstabilizers. According to the Provisional Specifications, the laminate may comprise lead foil, to each side of which is secured, by a suitable adhesive, a layer of polyvinyl chloride resin or like flexible corrosion-resistant heat-sealable material, or a sheet of fabric-reinforced polyvinyl chloride or like flexible corrosion-resistant heat-sealable material, e.g. a copolymer of polyvinyl chloride. Seaming of the above material may be carried out by overlapping and heat-sealing, or by joining adjoining edges by means of extruded jointing members of thermoplastic synthetic resin heat-sealable to the laminate, e.g. polyvinyl chloride, the jointing members being provided with grooves. These jointing members may have the forms shown in Figs. 2, 10, 12, 14, 15 or 19; that shown in Fig. 2 being used when the two pieces to be joined are coplanar, Fig. 10 when they are perpendicular to one another, Fig. 12 for joining an edge of the sheet material to a flat surface; the forms of Figs. 14 and 15 can be used for any of these purposes, as shown in Figs. 16, 17 and 18; the form of Fig. 19 is used for joining two sheets located side-byside in the one groove. The pieces of material may be heat-sealed to the jointing members by radio-frequency heating. Shaped articles, e.g. box-like structures, can be made by cutting a plurality of pieces of the laminated material, to form the desired structure, and seaming their edges in this way, meeting jointing members being mitred and joined by being heat-sealed together (Fig. 13). The corners may be reinforced by flexible corner-pieces secured thereover, or moulded corner-jointing members of a mouldable heat-sealable material may be used. As shown in Figs. 5 and 6, an apparatus for heat-sealing comprises a radio-frequency dielectric heating head 6 with two electrode limbs 7 spaced to register with the grooves 5 in a jointing member 4. The apparatus has a handle 8 for manual traversing and application of pressure, and a guard 9 for the head. This guard may be made of transparent material, e.g. polymethylmethacrylate resin, and may be spring-loaded, so that the apparatus can be run over a joint between two jointing members without having to be lifted off the work. The apparatus may include a micro-switch that will only close the circuit when the electrode limbs are in contact with a jointing member. When this apparatus is used, the lead foil 2 acts as a virtual earth, and the high-frequency field is generated between the live electrodes and the foil. As shown in Fig. 21, an apparatus for heat-sealing with jointing members 18 of the kind shown in Fig. 19 comprises two pressuremembers 20 carrying electrodes 21 between which the member 18 may be held. The electrodes may be straight or curved (Figs. 20 and 22, not shown). Their potentials may form a balanced system about earth potential, or the lead foil may be earthed by capacitive coupling, and the radio-frequency generator output connected to the electrodes which are electrically strapped together. The edges of the sheet material of the invention may also be sealed to slide fasteners in the form of two extruded strips having interfitting parts, the strips being formed with grooved parts to form a jointing member. According to the second Provisional Specification, the seaming apparatus, described above, may include also a fractional horse-power motor and driving-wheels by which it may be caused to traverse along the jointing member. Specifications 522,663, 723,998, 731,144 and 868,964 are referred to.