Patent GB-963361-A (GB)
Title: Improvements in adhesive tapes
IPC: C09J7/26
Filed: 1961-07-10
Abstract: 963,361. Making perforated plastic films. KENDALL CO. July 10, 1961 [Aug. 8, 1960], No. 24919/61. Heading B5A. [Also in Divisions A5 and B2] An adhesive tape comprises a backing 41 constituted by a thermoplastic film having therein a multiplicity of small perforations 42, each perforation being surrounded at one side of the film by a raised bead 43 of thermoplastic material integral with the body of the film, and a coating 49 of adhesive on the beaded side of the film which is confined to the areas 48 of film between the beads and does not overlap the beads. The beads 43 may have substantially level surfaces 44 which are substantially free of adhesive. The exposed surface of the coating may be substantially coplanar with the surfaces 44 of the beads. The outer edges 47 of the surfaces 44 of the beads may project outwardly beyond the portions of the beads which extend upwardly from the film. The adhesive coating abuts against the upwardly extending portions 46 of the beads and against the undersurfaces of the outwardly projecting edges of the beads. The perforations in the film have an area equivalent to that of a circular opening of diameter between 10 and 60 mils. The film may be of polyethylene, polyethylene terephthalate or a vinyl polymer, a vinylidene chloride-vinyl chloride or a vinyl chloride-vinyl acetate copolymer or polyvinyl chloride, and the adhesive may be pressure sensitive and may contain butadiene-styrene pale crepe rubber, tackifier resins, e.g. a blend of a polyterpene resin, glycerol esters of hydrogenated rosin, dimerized abietic acid and/or pentaerythritol ester of hydrogenated rosin. As shown in Fig. 4, the adhesive tape may have an absorbent pad 54 positioned substantially medially on the adhesive surface 51 of the tape and a releasable facing sheet, e.g. of polyethylene, covering the adhesive surface of the tape to constitute a sterilized perforated adhesive bandage. The adhesive tape may be produced by subjecting an imperforate thermoplastic film 41, having on one surface thereof a coating 49 of adhesive extending over the whole of the surface and faced with a releasable facing sheet 67, to heat and pressure at discrete areas to melt the adhesive, displace portions of the film into openings produced in the adhesive coating as the result of melting thereof and finally to melt the displaced portions of the film and accumulate the molten portions of the film to form raised beads extending through the adhesive coating and surrounding the perforations formed in the film as the result of the melting of the displaced portions. The film and facing sheet may be passed through a nip between a heated smooth roll 60 and a cool knurled roll 61 with the facing sheet in contact with the smooth roll. A back-up sheet 66 may be fed through the nip in contact with the surface of the film facing the knurled roll. The facing sheet may be a " Cellophane " (Registered Trade Mark) film and the back-up sheet may consist of newsprint or glassine paper, high and low density polyethylene, "Cellophane" (Registered Trade Mark), non-woven and woven fabrics, polyurethane foam rubber, and soft rubber. An apparatus for the manufacture of the adhesive tape comprises a smooth heated roll 60 and a co-operating knurled roll 61 having raised bosses 62, the rolls providing a nip for the passage of the tape so that as the rolls rotate in opposite directions, with the tape passing between them with its backing facing the knurled roll, the bosses on the knurled roll will penetrate the backing and perforate the tape. The knurled roll may be driven and the smooth roll rotates as the result of frictional engagement with the material passing through the nip. The bosses on the knurled roll may have flat end faces 63 and may be thermally insulated, for example, by a coating of a material of low thermal conductivity such as an oil, a grease or a resin. The smooth roll may be made of metal and the knurled roll of a hard non-thermoplastic resin. Specifications 851,473 and 951,468 are referred to.