Patent GB-164770-A (GB)
Title: Improvements in and relating to vulcanisation of rubber, and treatment of vulcanisedrubber
IPC: C08J3/24
Filed: 1919-10-06
Abstract: 164,770. Stevens, H. P. Oct. 6, 1919. India-rubber solutions; vulcanizing.-Solutions or spreadable doughs of undeteriorated vulcanized rubber suitable for waterproofing fabrics &c. are obtained by vulcanizing rubber in the presence of a solvent under suitably regulated conditions as regards (a) concentration of the rubber solution, (b) the amount of vulcanizing agent added, (c) mastication. If the concentration of the solution is low, say ¢-2¢ per cent, the final product does not exhibit the properties of vulcanized rubber, but remains soluble in benzene. If the solution is too concentrated, an unworkable jelly is obtained. A suitable solution contains 10, or even 5, per cent of rubber. The quantity of vulcanizing agent should be limited, the final product preferably containing 1-4 per cent combined sulphur. In all cases the rubber should be masticated, either before or during treatment with the solvent, or, should a gel be produced by vulcanization in the presence of additional solvent, when the jelly can be broken down. The vulcanization may be effected in the following ways : (1) by heating solutions of rubber and sulphur, with or without other ingredients such as accelerators, in solvents having a higher boiling point than the temperature normally used for vulcanization; (2) by heating solutions having a low boiling point in a closed vessel; (3) by partially vulcanizing rubber and heating it with a solvent; or (4) by adding a limited amount of sulphur chloride, e.g. 1 per cent, and masticating. Numerous examples are given in the Specification of which the following are typical. Smoked sheet is broken down, mixed with one-ninth its weight of sulphur, and sheeted. One-half part aldehyde ammonia, is dissolved in 500 volumes of crude benzene and 50 parts by weight of the sheeted mixture is added, the whole is placed in a sealed vessel, and air is exhausted. The vessel is heated to 135‹ for 2 hours. On cooling the viscous liquid is poured off and may be mixed with mineral fillers and diluted with further solvent if necessary, and used for proofing fabric in the usual way. According to another example 9 parts rubber and 1 part sulphur is vulcanized for 1¢ hours at 35 lbs. pressure. Two grammes of this rubber are placed in a tube with 20 cc. benzene, air is exhausted, and the tube is sealed. When the benzene is absorbed, the tube is heated for 3 hours to 135‹ C. In a third example, 600 parts by weight of rubber which has been masticated for 1-3 hours on cooled rollers is placed in a Pfleiderer machine and 1550 parts by weight solvent naphtha (B.P. 138‹-140‹ C.) added. 6.7 parts by weight of sulphur chloride are mixed with 520 parts naphtha and gradually added to the rubber solution with constant stirring. Mastication continues for 4-6 hours. With insufficient mastication or excess of sulphur chloride, the mass stiffens and breaks into crumbs. Films of rubber left after evaporation of the solvent improve on "ageing." A solution may gel on exposure to light but return to the liquid state on being placed in the dark. Suitable solvents are benzene, toluene, xylene, chloroform, dichlorethylene, trichlorethylene, monochlorbenzene, petroleum of low boiling-point.