| 摘要 |
An extrudable polyvinyl chloride composition suitable for use in making dilatable sealing elements is made by mixing polyvinyl chloride with a temporary plasticizer comprising a solvent and a non-solvent for the resin, heating with continuous mixing until the mass becomes a stiff gel, then cooling with further mixing, so that it is broken up into small rubbery curds. Specified solvents are isophorone, mesityl oxide, fenchone, cyclohexanone, methyl butyl ketone, methyl isobutyl ketone, methyl amyl ketone, methyl isoamyl ketone, ethyl amyl ketone. Specified non-solvents are xylene, dichlorbenzene, monochlorotoluene, diethylbenzene, chlorinated xylenes. The mixture may also contain fillers and pigments such as zinc oxide and green chrome oxide, organic dyes, stabilizers, e.g. litharge or lead silicate, and small quantities of high boiling plasticizers, e.g. tricresyl phosphate, dioctyl phthalate. The rubbery curds may be extruded into tubes, sleeves, and the tubes formed into cap sealing elements. The sealing of the opening is effected by placing the element in a liquid which dilates it, applying it to the opening and removing the liquid by evaporation at room or elevated temperatures. The liquid may consist of a solvent and non-solvent for the polyvinyl plastic. Specified solvents are acetone, methyl ethyl ketone, and isophorone. Specified non-solvents are benzene, toluene, xylene, ethyl benzene, and cumene. The elements may be used for connecting lengths of plastic materials, or glass or metal; or for closing the ends of lengths of tubing; or for closures for bottles. |
