| 摘要 |
Expandable plastic compositions for the production of foam plastics comprise a vinyl cyclohexane polymer, the molecular weight of which is more than 10,000, preferably 50,000 to 1,000,000, which has been obtained by hydrogenation (and preferably perhydrogenation) of a styrene polymer, or copolymer containing at least 50% by weight of styrene in polymerized form, and which contains at least 20% by weight of cyclohexyl radicals, and 2 to 20%, preferably 5 to 10%, by weight, with reference to the vinyl cyclohexane polymer, of an organic compound whose boiling point is lower than the softening point of the polymer and which does not dissolve the polymer, as an expanding agent. The foam plastic is obtained by heating the expandable plastic composition above its softening point. Suitable vinylcyclohexane polymers are those which have been obtained by hydrogenation of polystyrene, and copolymers of styrene containing at least 50% by weight of styrene, and up to 50% by weight of a -methyl styrene or nuclear-substituted methylstyrene, in polymerized form. The styrene polymers may also contain up to 5% by weight of other monomers, e.g. acrylonitrile, esters of acrylic and methacrylic acid with alcohols having one to eight carbon atoms or vinyl carbazole, in polymerized form. In perhydrogenated styrene polymers and copolymers, all the phenyl radicals have been converted into cyclohexyl radicals. Hydrogenation of the styrene polymers may be carried out in liquid phase with hydrogen in the presence of catalysts. The polymers may be hydrogenated in molten condition or dissolved in inert organic solvents, e.g. a mixture of cyclohexane and tetrahydrofuran. Hydrogen pressures of more than 170 atmospheres may be used. Suitable catalysts are nickel, cobalt or the metals of the platinum group, in finely powdered or colloidally dispersed distribution, and they may be supported on porous substances, e.g. carbon, aluminium oxide, pumice or di-atomaceous earth. Suitable expanding agents are volatile hydrocarbons, e.g. propane, butane, pentane, hexane, cyclopentane or cyclohexane; volatile halo-hydrocarbons, e.g. methylene chloride or dichlorodifluoro methane; or volatile or alkyl ethers, e.g. dimethyl ether. Homogeneous mixtures of the vinylcyclohexane polymers and expanding agents may be obtained by various means, e.g. mechanical mixing, adding expanding agent to a solution of the plastic and removing the solvent, suspending the polymer in finely divided form in water, and treated with expanding agent under pressure while stirring or by pouring solutions of the polymer and expanding agent into water containing a suspension agent while stirring, and removing the solvent while continuing the stirring. Foamed mouldings from the finely divided plastic compositions containing expanding agent may be prepared in one operation, by expanding and sintering the particles by heating them in moulds, e.g. with superheated steam, infra-red radiation or in a high frequency field, which are not gas-tight when closed. Extrusion techniques may also be employed to prepare foamed shapes continuously. The foams have high thermal stability under load, good mechanical strength and a low bulk density. They absorb practically no water owing to their closed cell structure. |
