| 摘要 |
<p>Re-using scrap foamed thermoplastic polymer by hot-extruding the previously ground-up scrap as an unfoamed solid containing a foaming agent and quench chilling the solid throughout preferably in a liquid bath such as a water bath. The scrap polymer preferably contains a volatile foaming agent. An optional feature of the invention involves incorporating virgin unfoamed expansible thermoplastic polymer and/or a small amount of make-up foaming agent in the scrap prior to extruding the unfoamed solid as above. The unfoamed extrudate may be in the form of a rod or sheet and is preferably conminuted before being mixed, if desired, with additional volatile liquid foaming agent and passed through a second extruder to form foamed articles such as sheets or tubes with or without unfoamed surface skins. The preferred thermoplastic polymers are polymers of mono-olefines having 2-4 carbon atoms, vinyl chloride resins or styrene resins particularly crystal grade or specified high impact polystyrenes and mixtures thereof normally containing 5 to 95% of crystal grade polystyrene. Other polymers which can be used are cellulose ethers or esters, homo-polymers and interpolymers of monomeric compounds containing the CH2 = C< grouping such as olefines, polyfluoroalkenes, vinyl halides, vinyl ethers, vinyl esters of carboxylic acids, derivatives of acrylic acid and interpolymers of the above monomers with a ,b -unsaturated polycarboxylic acids and derivatives thereof. Polycarbonates, polyoxymethylene, oxymethylene-alkylene oxide copolymers, polyurethanes, polyethylene terephthalates, nylon, A.B.S. terpolymers, chlorinated rubber, bituminous materials and paraffin waxes are also mentioned. The preferred additional foaming agents are volatile liquids such as hydrocarbons, halogenohydrocarbons, alcohols, ethers, esters, ketones or aldehydes normally contained in a solid absorbent such as silica gel, diatomaceous earth, activated alumina or carbon, molecular sieves or a swollen polymer. Conventional nucleating agents which liberate carbon dioxide and solid foaming agents which decompose to form a gas are also specified.</p> |
