Patent GB-426226-A (GB)
Title: Improvements in or relating to a process for making rubber thread
IPC: B29D99/00
Filed: 1934-01-04
Abstract: In the manufacture of articles of or containing rubber or similar material from aqueous dispersions thereof by known operations such as mass moulding, dipping, spreading, extrusion, or coating, a predetermined quantity of an aqueous dispersion containing one or more reagents substantially inactive either in cold or on heating is admixed with an aqueous medium of one or more reagents which are also by themselves similarly inactive towards the dispersions but which by chemical reaction either in the cold or on heating with the reagent or reagents first referred to produce one or more substances in situ which function as active coagulating or gelling agents.  By this means the difficulty operating with concentrated aqueous dispersions which have been treated, for example, according to the methods described in Specifications 284,608 and 292,964, [both in Class 70], that progressive thickening of the dispersion may occur, with consequent shortening of the desired definite time interval in which coagulation of gelling is intended to take place, is avoided.  The process is applicable to the production of goods of compact, cellular, spongy, porous, or microporous rubber. Examples of reagents which can be admixed with the dispersions are oxide and hydroxides of divalent metals such as zinc or magnesium and of trivalent metals such as aluminium, chromium, and iron. Insoluble salts such as the carbonates and borates of lead or zinc can also be used.  Examples of reagents which can be added to the aqueous medium are sulphates, chlorides, nitrates, and acetates of the alkali metals including ammonium.  The aqueous medium may be either water, an aqueous solution of soluble material or an aqueous dispersion of rubber or the like.  The aqueous dispersion and/or the aqueous medium may be conditioned to alkalinity by the addition of caustic soda, ammonia, a strong organic base, piperidine, diethylamine, or the like.  The process may be carried out by coating a mould or former with the aqueous medium referred to, preferably heating the mould or former, and contacting it with latex containing one or more reagents such as zinc oxide. Alternatively a former coated with latex containing zinc oxide may be introduced into a solution of ammonium sulphate or into latex containing ammonium sulphate.  The process may also be applied to the production of play balls &c. by internal or mass moulding, the moulds being subjected to rotation about a variable axis and heated to effect total gelling, after adding preferably predetermined amounts of aqueous medium containing ammonium sulphate to the dispersion containing zinc oxide or like reagent in the mould. Permeable or semi-permeable material can be coated with rubber, or articles comprising such materials can be coated on both sides with stout rubber walls, for example, by dipping a woven fabric container nearly filled with a rubber latex composition containing ammonium sulphate into a hot latex composition containing zinc oxide.  In making filaments, threads, or bands by extrusion, the coagulable rubber dispersion containing one or more inactive reagents is preferably passed through a nozzle into the aqueous medium containing the other reagents, and the coagulated filament afterwards hardened by means of a further setting or coagulating treatment.  The aqueous dispersions which can be employed are those of rubber, guttapercha, balata or similar vegetable resins naturally occurring or obtained artificially, including coagulated, vulcanized, or synthetic rubber, vulcanized latices, waste or reclaim, alone or in admixture with one another and, if desired, containing the usual compounding ingredients and/or being in concentrated form. Concentrates obtained by the methods described in Specifications 219,635 and 290,313, [both in Class 70], may be used.  Examples are given.