Patent GB-712052-A (GB)
Title: A method and apparatus for making footwear with rubber soles and footwear made thereby
IPC: B29D35/10
Filed: 1951-10-23
Abstract: 712,052. Moulding rubber soles on to shoe uppers. UNITED STATES RUBBER CO. Oct. 23,1951 [Oct. 25, 1950; Oct. 25, 1950]. No. 24668/51. Class 87 (2) [Also in Group VII] A method of casting a rubber outsole on to the bottom of a footwear sole foundation comprises the steps of pouring a rubber latex containing vulcanizing and gelling agents into an open .footwear sole mould cavity, suspending in the latex the bottom of the sole foundation in spaced relation to the wall and base of the mould cavity, allowing the latex to gel. separating the foundation with the gelled latex thereon from the mould cavity and drying and. vulcanizing the latex. An insole is first secured to an upper on a special last and the last 24 is then fixed to the arm 38 of a jig 26 by a screw 43, associated with locating pins 46<1>, operable by a hand-wheel 39. The arm 38 is mounted on a member 46 slidable on a block 49 and under the control of a hand-wheel 50 to give raising and lowering adjustment. The mounting of the arm 38 is pivotal, about a stud 71, and allows lateral adjustment by screws 69. The block 49 is fixed to a shaft 52 journalled in brackets 53 and having attached to it' an operating arm 54 whereby the last may be raised and lowered 'and which may be held in one of several positions by a spring-pressed detent 56 engaging one of notches 57. The handle 63 by which the detent is released is near the handle 62 of the operating arm so that both may be gripped by one hand. A stop screw 64 on the arm 54 adjusts the slope of the last when in its lowered position. The mould 28 is held in a frame 83 clamped by bars 84, 85 to a plate 73 which may be levelled by screws 74 and adjusted laterally by screws 76 which rest in wide notches to permit latitude of movement. The clamping screws for the bars 84, 85 pass through slots to provide further adjustability. The mould 28 is of flexible material, e.g. a polysulphide synthetic rubber compound with a lead peroxide curing agent and an organic peroxide catalyst and is first made by placing a model of a soled shoe on the last 24, lowering it, suitably adjusting it in a box similar to the frame 83 but with a depth equal to the overall height of the mould, and pouring in moulding compound which is allowed to set. The mould having been made, the insole and upper, carried on the last 24, are positioned in the mould cavity and sufficient latex composition is poured in to produce an outsole 19 of the desired thickness and a foxing 20 of the desired height. As a result of the gelling the outsole and foxing are bonded to the upper and the last is then raised, the flexibility of the mould walls preventing injury to the gelled latex. The last is removed from the jig and passed through a vulcanizer, where the cast latex sole and foxing are simultaneously dried and vulcanized. The insole 18 is provided with perforations 21, conical in shape with their apices pointing upwards so that latex composition enters at the bottom of the perforations and strengthens the bond between outsole and insole but does not pass through the small holes at the top which, however, permit the discharge of air and prevent the formation of blisters between outsole and insole. The latex composition shrinks after it has been dried and vulcanized, and to allow for this the last 24 has a convex bottom 33 and the mould 28 has a concave surface 34. Before pouring in the latex composition the walls of the mould are coated with a lubricant which prevents the composition from sticking to the cavity and acts as a welting agent, a suitable lubricant being the sodium salt of the di-octyl ester of sulfonated succinic acid, preferably mixed with petrol in the proportion 100 : 315. The latex composition may be compounded from concentrated natural rubber latex by adding (1) a paste of vulcanizing ingredients, e.g. sulphur, zinc oxide, ultra-accelerators, and antioxidant dispersed in water containing a dispersing agent and (2) a gelling agent, e.g. an aqueous dispersion containing sodium silicofluoride sodium fluoride and a colloidal clay. A particular example is given of a suitable latex composition. Before adding the gelling agent the latex is preferably de-aerated and partially vulcanized.