GB806142A - Improvements in or relating to elastomers - Google Patents

Abstract

Unsupported deposited elastic films are prepared from blends comprising 2.3 to 50 parts of natural rubber per part of a vinyl elastomeric copolymer containing pendent carboxyl groups, the major portion of which consists of at least one 1,3-conjugated diene or halogenated derivative thereof having 4 to 10 carbon atoms, the major portion of the carboxyl groups being cross-linked with a polyvalent metal cation or organic polyvalent basic radical and imparting to the film the property that a cut propagates at the most for a short distance and along a straight line at the end of which is a small arcuate tear transverse to the straight line. The copolymers may be prepared by copolymerizing dienes with unsaturated acids or with esters, e.g. methyl and ethyl acrylates, or nitriles, e.g. acrylonitrile and methacrylonitrile, and hydrolysing. Further carboxyl groups may be introduced by reacting the polymers with maleic or thioglycollic acids. Specified dienes are butadiene, isoprene, 2,3-dimethyl butadiene, 2-neopenthyl butadiene, chloroprene, 1-or 2-cyano butadiene and piperylene. Many unsaturated acids are listed and the copolymerization of methacrylic acid exemplified. Additional comonomers, e.g. styrene, vinyl toluene, vinyl naphthalene, acrylonitrile, methacrylonitrile, alkyl acrylates and alkacrylates, and vinylidene chloride may be employed. Polymerization may be effected in acid aqueous emulsion in the presence of catalysts, e.g. alkali metal persulphates, percarbonates and perborates, benzoyl, acetyl and di-tert.-butyl peroxides and diisopropylbenzene hydroperoxide, emulsifiers, e.g. ethers and esters of polyglycols with aliphalic acids having 10 to 20 carbon atoms, alkyl sulphates and sulphonates and alkaryl sulphonates where the alkyl group has 10 to 20 carbon atoms, alkyl aryl polyether sulphates, sulphated monoglycerides and amine salts of alkylaryl sulphonates, chelating agents, e.g. ethylenediamine tetraacetic acid, and modifiers, e.g. n-dodecyl mercaptan, mixed tertiary mercaptans having 12 to 16 carbon atoms, thiophenol and alpha- and beta-thionaphthols, and the reaction shortstopped by adding 2.5-di-tert.-butyl hydroquinone. The latices so formed may be made alkaline with volatile or unstable monovalent bases, e.g. ammonia, ethylamine, ethanolamine, morpholine and trimethylbenzyl ammonium hydroxide, stabilized, e.g. with sodium lauryl or myristyl sulphate, and blended with alkaline natural rubber latices. Cross-linking may be effected with compounds, e.g. oxides, nitrates, chlorides, sulphates, acetates, and formates, of calcium, barium, magnesium, zinc, tin, iron, lead, cobalt and nickel, or with polyamines such as diethylene triamine, optionally together with sulphur and known accelerators. The cross-linking agents may be added to the latex blend and films deposited on shaped dipping forms, or the forms may be coated, before or after dipping, with an aqueous, alcohol or acetone solution of a polyvalent metal salt, the process being repeated till a film of adequate thickness is obtained. The compositions may contain other polymers, e.g. neoprene, and fillers and pigments, e.g. titanium dioxide, and may be used in the product of gloves, tobacco pouches, overshoes, sheets, shower caps, girdles and baby pants. Specification 464,019, [Group V], is referred to.