Patent GB-481426-A (GB)
Title: Improvements in or relating to compositions for forming flexible sheets, films or coatings, the sheets, films or coatings resulting therefrom, and methods of preparing the compositions and forming the sheets, films or coatings
IPC: D21H11/06
Filed: 1936-06-06
Abstract: 481,426. Rubber compositions. BURGESS, A. F. (Marathon Paper Mills Co.) June 6,1936, No. 15907. [Class 70] [Also in Group VIII] A thermoplastic composition is prepared by dissolving rubber, guttapercha or the like in a molten bath of wax or asphalt or the like under agitation and such control of the heat treatment that the resultant composition is suitable for conversion into flexible self-sustaining films of a thickness not exceeding substantially ten thousandths of an inch, and has a viscosity of at least 16,000 centipoises at 90‹ C., i.e. 8,000 seconds when measured by the Scott viscosimeter. The preferred proportions are between 6 and 30 per cent rubber and 94 and 70 per cent wax, although compositions containing over 50 per cent of rubber or guttapercha may be employed. The viscosity of the composition is preferably considerably above the lower limit, e.g. between 300,000 and 1,000,000 seconds Scott. The wax may be paraffin, beeswax, or spermaceti and may be replaced in part by a hydrogenated vegetable oil, e.g. cottonseed oil, petrolatum or aluminium stearate or by a gum or resin such as rosin. Pigments and fillers and other ingredients, e.g. titanium dioxide, calcium or barium sulphate, aluminium powder, du Pont Red RL or TX zinc oxide (or when a more translucent mixture is desired, zinc carbonate) sodium benzoato or salicylate; accelerators, e.g. zinc dibutyl dithiocarbamate, zinc dimethyl dithiocarbamate, the reaction product of carbon disulphide and methylene dipiperidine, zinc butyl xanthate, or piperidine pentamethylenedithiocarbamate ; anti-oxidants even when no vulcanization is effected, e.g. hydroquinone, pyrogallol, p-hydroxyphenylmorpholine, sym. di-#-naphthyl-p-phenylene diamine or aniline-#-naphthol may be incorporated. The composition may or may not be vulcanized. When unvulcanized, a sheet ofthe composition has good heat sealing properties without tackiness at ordinary temperatures. When super accelerators are incorporated the accelerator may be in one master batch of rubber-wax and the vulcanizing agent in another, the master batches being mixed with separate main batches which are then admixed when required. Thin sheets may be made from compositions containing 6 to 15 per cent rubber by sheeting on a chilled roll 15, by means of a heated doctor blade 10, Fig. 1. When using compositions containing 6 to 25 per cent rubber, the doctor blade may be replaced by a heated doctor roll and a heated feeding hopper, and for compositions having 25 to 50 per cent rubber calender rolls may be employed as in Figs. 2 to 4 and 6 (not shown). Sheets may also be made by extrusion into a cooling liquid. Webs, as of paper, may be coated by means of similar apparatus, Figs. 7 to 13 (not shown), into which a web of material is also fed, and a laminated material may be made, Fig. 14, by feeding webs 65, 66 through the nip of heated rolls 68, 69 together with the composition 67 and cooling the product on chilled rolls 71, 72.