GB1041014A - Preparation of expandable thermoplastic particles - Google Patents

Abstract

A blowing agent is uniformly distributed throughout a particulate thermoplastic mass by maintaining the thermoplastic in contact with the blowing agent and a low M.W. material solid at 25 DEG C., the mixture meanwhile being heated to a temperature at which the low M.W. material is fluid, but which is not above the sintering temperature of the thermoplastic and is below the decomposition temperature of the blowing agent, so that the thermoplastic is coated with the other materials, the coating then being allowed to solidify. The low M.W. material may be molten or in solution. 0.1-5% of the blowing agent and 0.1-10% of the low M.W. material may be used. Articles, e.g. wire insulation, shock absorbers, packing material and laminates may be formed from the product at a temperature at which the blowing agent decomposes. Two types of low M.W. materials are specified: (a) Polymers of ethylene, propylene and butene and copolymers of these with styrene and acrylates of 3500-12,000 M.W., prepared either from the monomers or by pyrolysis at 300-600 DEG C. of higher molecular weight polymers. (b) Waxy materials of melting point 25-150 DEG C., insoluble in water, at least partially soluble in alcohol and ether and completely soluble in oils, fats and hydrocarbon solvents. Type (b) is exemplified by petroleum, paraffin and microcrystalline waxes, spermaceti, beeswax, Chinese insect wax, ozokerite, montan, ceresin, carnauba wax, japan wax, bayberry wax and candelilla wax, jojoba wax. Mixtures of low molecular weight materials may be used. Blowing agents specified are carbonates, azo compounds, N-nitroso compounds, sulphonyl hydrazides, aryoyl azides, N-nitro-N1 - cyclohexyl - urea, N,N1 - dinitroethylene urea, nitroguanadine, nitrobiuret, N,N1-dinitro - N,N1 - dimethyl - oxamide, N - nitrophthalimide, N - nitrosuccimide, N,N1 - dinitroso - N,N1 - diacetyl - ethylenediamine and N-nitroxazolidone. Four types of thermoplastics are specified: (i) polymers and copolymers of olefinically unsaturated compounds, e.g. hydrocarbons, dienes, mono and dicarboxylic acids, amides and esters, including glycidyl methacrylate, halides, nitriles, silanes and phosphonates, (ii) polymers derived from ethylene oxide, (iii) condensates of bisphenols with carbonate precursors, e.g. 2,2-bis-(4-hydroxyphenol) propane and dialkyl or diaryl esters of carbonic acid or phosgene; (iv) condensates of bisphenols with epihalohydrins. The thermoplastics may contain as additives fillers, extenders, opacifiers, modifiers and stabilizers. In Examples (1)-(6) low M.W. polythene (1)-(5) or paraffin wax (6) was added to a mixture of polypropylene (1), (4), polyisobutylene (1), polyvinyl chloride (2), polyethylene (3) or 2,2-bis-(4 - hydroxyphenyl) propane / epichlorohydrin condensate (6) and 1,11-azo-bisformamide (1), (3)-(6) or N,N1 - dimethyl - N,N1 - dinitroso-terephthalimide (2) and oxanilide (1), tribasic lead sulphate (2), dioctyl phthalate (2), hydrolysed clay (2) and CaCO3 (2). The mixture was then melted and cooled to solidify. In Examples (13)-(15) the reactants were as in Example (1), but (13) the blowing agent in molten polythene was added to the thermoplastic, (14) the blowing agent and polythene dissolved in toluene were added to the thermoplastic and (15) the polythene dissolved in toluene was added to the blowing agent and the thermoplastic.