Patent GB-1051125-A (GB)
IPC: C09J7/02
Abstract: 1,051,125. Pressure sensitive adhesive tape. MINNESOTA MINING & MANUFACTURING CO. Jan. 29, 1964, No. 3908/64. Addition to 948,051. Heading B2E. A pressure sensitive adhesive tape comprises (i) a water-insoluble and hydrocarbon oilinsoluble film backing comprising a stable blend of (a) a film forming polymer of monomers containing at least a major proportion of vinyl polymer, and (b) substantially non- volatile plasticizing material therefor in an amount of 45 or more parts by weight per 100 parts by weight of the polymer providing a plasticized film backing having at -20‹C. a modulus at 50% elongation of less than 5000 p.s.i., and further having a brittleness which at -20‹C. is not more than twice the value at 0‹C.; and (ii) a coating of pressure sensitive adhesive united to one face of the plasticized film backing and comprising an elastomeric rubber material and a compatible resinous tackifier therefor, the combined rubbery and resinous ingredients of the adhesive having a low cohesive energy density (defined); the adhesive tape being originally stretchable in widths of one inch to at least 100% at normal room temperatures and being substantially completely retractable from an elongation of 50%. The plasticizing material may be present in an amount from 45 to 75 parts by weight per 100 parts by weight of the polymer. The plasticizing material may have a number average molecular weight (defined) of 500 to 3500. The plasticized film backing, at -20‹C., may have an elongation at break of at least 165%. The combined rubbery and resinous ingredients of the adhesive may be resinant to softening by the plasticizing material and the cohesive energy density thereof is less than 75 calories per c.c. The primary constituent of the plasticizing material may be a polyester having a number average molecular weight of 500 to 3500 and where below 750 the material has substantially no molecules of less than about 500; the polyester may comprise ester groups connected by hydrocarbon chains, e.g. alkylene chains, containing an average of 4 to 8 carbon atoms and being terminated by acyl chains, the hydrocarbon chain portions of the acyl chain containing 2 to 18 carbon atoms, the average number of carbon atoms in individual connecting and terminating chains considered together being 5 to 9; the polyester may have an open-chain molecular structure and an average of at least 4 ester groups per molecule, substantially all the molecules having a molecular weight of 500 to 1000. The polyester may be an acylated polyester of a glycol and a saturated aliphatic dibasic carboxylic acid. The glycol may be selected from at least one of 1,2-propylene glycol, 1,4-butane diol, and 1,6-hexane diol, but not more than 65 mol per cent of the glycol being 1,2-propylene glycol. The acid may be selected from at least one of the saturated aliphatic dibasic acids having alkylene chains of 3 to 8 carbon atoms. The selected glycol may constitute 90 mol per cent of the total glycol and the selected dibasic acid may constitute 90 mol per cent of the total dibasic acid. The film backing may comprise a stable blend of (a) 100 parts by weight of a polymer comprising at least 90% vinyl chloride and (b) 45 to 75 parts by weight of plasticizer comprising an acylated polyester of glycol and saturated aliphatic dibasic acid, the skeletal backbone of which consists of ester groups connected by alkylene chains containing an average of 4 to 7 carbon atoms, counting branch carbons, and is terminated by acyl chains, the hydrocarbon chain portions of the acyl radical containing 2 to 18 carbon atoms and on the average at least 8 carbon atoms. The polyester may be liquid and is present in the film backing as 1/3 to 3/4 of the amount of the vinyl polymer, the liquid polyester being compatible with the vinyl polymer in this amount and stable against exudation from the vinyl polymer. The vinyl polymer of the film backing may include 3 to 5% vinyl acetate copolymerized with 97 to 95% vinyl chloride. The vinyl polymer may contain up to 10% vinyl acetate. The total plasticizer of the film backing may have an acid number not exceeding 8. The adhesive coating may comprise a homogeneous blend of (a) 40 to 60 parts by weight of natural rubber, (b) correspondingly 60 to 40 parts by weight of butadiene-styrene synthetic rubber, (c) 60 to 150 parts by weight of pure hydrocarbon thermoplastic terpene resin having a low acid number and a melting point of at least 60‹C., and (d) 3 to 16 parts by weight of a compatible, oil soluble, heat reactive phenol-aldehyde resin. A primer coating may be applied to the inner face of the film backing to increase the anchorage of the adhesive coating subsequently applied thereto. The plasticizing material in the film backing may be in permanent equilibrium with the adhesive coating so as to avoid pastiness or loss of tack of the adhesive coating while still maintaining good flexibility and retractability of the film backing over the range of subfreezing temperatures to 50‹C. The film backing may have a dielectric strength sufficient to provide effective electrical insulation of splices and of wires over a temperature range of 20 to 87‹C.