Method for producing shoe soles by injection-molding

Abstract: Method for producing soles (4) for shoes (1), which initially includes the production, by molding, of a sole (4) that has a perimetric ridge (5) that protrudes downwards. The sole is then placed on a plunger of a mold that has a head which is shaped complementarily with respect to the lower surface of the sole and with respect to the ridge and in which there is a recess for containing the ridge and a gap for the intended flow of a second material to be injected. The last step consists in trimming the flash, which has an intended consistency.

Description: The present invention relates to a method for producing shoe soles by injection-molding. It is known to produce, by virtue of appropriate molds, the sole of a shoe by placing a tread in a mold. The tread is made of an adapted material, such as for example rubber, adapted to provide greater grip on the ground. The tread has a perimetric ridge that protrudes at an angle of approximately 90° with respect to the lateral surface of the sole and constitutes a confinement barrier for the subsequent injection-molding of thermoplastic materials. A second material, such as for example polyurethane, is then injection-molded to obtain a collar that constitutes the shell for anchoring the upper to the tread. In these conventional molds, closure occurs on a horizontal plane, so that the injection of polyurethane forms, along the ridge of the tread, flash of considerable thickness and possibly discontinuous, which protrudes laterally to the upper end of the sole that does not interact with the ground. The presence of the flash constitutes a considerable drawback as regards the overall time and cost for producing the finished sole. The lateral flash must in fact be removed and this requires trimming it in an optimum manner, since in order to allow the subsequent anchoring, for example of the polyurethane, the sole must then be treated by washing, chlorination, and gluing. Difficulties have in fact been found, in the prior art, specifically as regards controlling the chlorination of the sole, especially at its lateral edge from which the flash protruded. It has in fact been observed that perimetric separation, for example of the polyurethane injection-molded over the tread, can occur; this entails either the rejection of the product during quality control or, as an even worse drawback, perimetric separation on the first time the product is used, i.e. when the first stress is applied to the sole. Another drawback that has been observed in the prior art consists of the fact that molding in place, for example of the polyurethane, on the rubber tread is not always easy, because the tread can shift inside the mold as there are no locator points for its position. GB-A-1 435 837 discloses a footwear manufacture method which includes a first step of forming an outer sole layer (13,13b) in a mould (16) between a bottom plunger (17,17b) and an upper plunger (18,18b), by injecting material laterally through a first lower opening (22,22b) of the mould, whereby a material filler piece (28) is formed on the outer sole layer extending circumferentially and protruding downward from the bottom surface of the outer sole layer and abutting against the bottom plunger. Subsequently, a last (15,15b) with an upper (10,10b) is placed in the mould distally from the outer sole layer, and an inner sole layer (12,12b) is formed between the upper and the lower sole layer by injecting material laterally through a second upper opening (24,24b) of the mould, whereby the inner sole layer has an extended welt part (14,14b) drawn upwards on the upper and drawn downwards over the edge of the outer sole layer. In one embodiment (Figs. 1-4) the bottom plunger (17) is moved vertically during the method steps, while in another embodiment (Figs. 11-12) the bottom plunger (17b) remains stationary. The material filler piece (28) extending circumferentially downward on the outer sole layer is removed after completion of the multi-layered sole. The aim of the present invention is to solve the described technical problems, eliminating the drawbacks of the cited prior art by providing a method that allows to produce soles for shoes by injection-molding and allows high production with low costs. Within the scope of this aim, an important object is to provide a method that allows to considerably reduce the number of rejects, eliminating the possibility of mutual separation of the two components that are injection-molded to form the sole. An important object is to provide a method that allows to obtain a product whose processing and finishing is simple and quick and can also be performed with adapted machines. Another important object is to provide a method that can be repeated without changes over time, in that it is possible to optimally injection-mold in place a second material on a previously formed sole, keeping constant over time technical characteristics such as thicknesses and/or distances between the two materials. Another object is to provide a method that allows to facilitate and easily control steps such as the chlorination of the sole, so as to further contain production costs. In accordance with the invention, there is provided a method for producing shoes as defined in the appended claims. The characteristics and advantages of the invention will become apparent from the detailed description of a particular but not exclusive embodiment, illustrated only by way of non-limitative example in the accompanying drawings, wherein: Fig. 1 is a schematic view of the mold, of the sole, and of an upper with a last; Fig. 2 is a view, similar to Fig. 1, of the sole arranged on the plunger; Fig. 3 is a view, similar to Fig. 2, of the lowering of the last; Fig. 4 is a view, similar to Fig. 3, of the movement of the shells toward the last; Fig. 5 is a view, similar to Fig. 4, of the injection of the material that constitutes the collar; Fig. 6 is a view, similar to Fig. 5, of the rise of the plunger; Fig. 7 is a view, similar to Fig. 6, of the opening of the shells of the mold; Fig. 8 is a view, similar to Fig. 7, of the extraction of the last from the mold; Fig. 9 is a view, similar to Fig. 8, of the extraction of the last from the shoe; Fig. 10 is a transverse sectional view of the shoe after the flash and the material flowed thereon have been cut; Fig. 11 is a perspective view, taken from below, of the shoe in the step shown in Fig. 9; Fig. 12 is a view, similar to Fig. 10, of the finished shoe; Fig. 13 is a detail view of the configuration of the head of the plunger, illustrating the recess for containing the ridge and the gap for the controlled flow of the material that constitutes the collar. With reference to the above figures, the reference numeral 1 designates a shoe constituted by an upper 2, which is associated at an adapted collar 3 that is rigidly coupled to a sole 4. The method for producing the sole and the collar of the shoe initially comprises molding the sole 4 in an adapted mold, for example by vulcanizing rubber, so as to form, during this molding, a ridge 5 which protrudes perimetrically and downwards with respect to the ground resting plane of the sole. This perimetric ridge is obtained so that it forms an angle β, with respect to the plane of arrangement of the lower surface 7 of the sole 4, of 90° to 180°. The production of this ridge, with this specific location and angle, allows on one hand to quickly and simply perform its chlorination for the subsequent injection-molding in place of material and on the other hand constitutes a precise locator element for the mold used for this subsequent step. The method in fact entails placing the sole 4 thus obtained at an adapted plunger 8, which has a head 9 that is shaped complementarily to the lower surface 7 of the sole 4 and to the ridge 5, so as to allow a correct and stable placement of said sole, which during the subsequent injection step does not move despite the internal pressures generated by the expansion of the material. The head 9 of the plunger 8 also has another feature, i.e., it has a gap 10 between said head 9 and the ridge 5 and the facing surface of the rings lla and 11b of the mold 12, between which the upper 2 is also closed with an adapted last 13 preinserted therein. The rings lla and 11b of course have surfaces that allow the injection of a second material, such as for example polyurethane, to produce the collar 3. Indeed, as shown in figures 2 to 5, once the rings have been closed around the upper and the plunger, the material that subsequently constitutes the collar 3 is injected; by means of the gap 10, said material affects, with intended thicknesses, the lateral surface of the ridge 5; a controlled flow is thus achieved, for example of polyurethane, at the ridge 5. Said flow is facilitated, during injection, by the rise of the plunger 8, as shown in Fig. 6. Once the materials have been cooled, the shells have been opened, the shoe has been extracted and the last has been extracted from the upper, the shoe of Fig. 11 is obtained. In the shoe, the ridge 5 protrudes below the sole but the material injected in place has an intended consistency besides having an optimum mutual coupling of the materials. Finally, the method comprises cutting the ridge and the material that has flowed thereon. This cutting can also be performed automatically with adapted machines, in view of the desired consistency that can be given to the ridge and of the ease of the cutting operation, which does not occur laterally to the sole but below it. It has thus been observed that the invention has achieved the intended aim and objects, a method having been provided which allows to achieve an optimum coupling between the two materials constituted by the sole and by the collar, in practice eliminating production rejects and thus considerably increasing production. The production costs are also reduced by the simplicity of the intermediate operations, such as for example cleaning and chlorination, at the same time increasing the quality of the product, since the sole, during the injection-molding in place of the material that constitutes the collar, is fixed in position and is not subject to movement caused by the expansion of the product. The resulting product is also aesthetically pleasant, since the coupling of the two products is visible only below the sole and therefore in a region that is not visible during use. The method according to the invention is susceptible of numerous modifications and variations, all of which are within the scope of the appended claims. Likewise, the materials may also be the most pertinent according to the specific requirements. Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly, such reference signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference signs.

Claims: Method for producing soles for shoes by injection-molding, comprising the following steps: a) molding said sole (4) with a perimetric ridge (5) that protrudes below the ground resting surface at least along a portion of the perimeter of said sole, said ridge (5) constituting a precise locator for the placement of said sole (4) on a mold for the subsequent step of the method; b) placing said sole on a plunger (8) with a complementarily-shaped head (9) that has a recess for containing said ridge (5) and a gap (10) that allows the controlled flow of material injected subsequently so as to form a collar (3) and/or a shell for connection to an upper, said sole being placed at said adapted plunger (8), which has said head (9) that is shaped complementarily to the lower surface (7) of said sole and to said ridge, said head of said plunger also having said lateral gap (10) between said head and said ridge and the facing surface of adapted rings (11a, 11b) of said mold (12), between which said upper is also closed with an appropriate last (13) preinserted therein to perform the injection of a second material, such as for example polyurethane, to obtain said collar; c) cutting off said ridge (5) and said flowed material thereon. Method for producing shoes constituted by an upper (2) associated at an adapted collar (3) that is rigidly coupled to a sole (4), comprising: molding said sole (4) in an adapted mold, preferably by a vulcanization of rubber, so as form a ridge (5) that protrudes perimetrically and downwards with respect to the ground resting surface of said sole, said ridge (5) constituting a precise locator for the placement of said sole (4) on a mold for the subsequent step of the method; and placing said sole on a plunger (8) with a complementarily-shaped head (9) that has a recess for containing said ridge and a gap (10) that allows the controlled flow of material injected subsequently so as to form a collar (3) and/or a shell for connection to an upper, said sole being placed at said adapted plunger (8), which has said head (9) that is shaped complementarily to the lower surface (7) of said sole and to said ridge, said head of said plunger also having said lateral gap (10) between said head and said ridge and the facing surface of adapted rings (11a, 11b) of said mold (12), between which said upper is also closed with an appropriate last (13) preinserted therein to perform the injection of a second material, such as for example polyurethane, to obtain said collar; cutting off said ridge (5) and said flowed material thereon. Method according to either claims 1 or 2, characterized in that said perimetric ridge (5) forms an angle b, with respect to the plane of arrangement of its lower surface, of 90° to 180°. Method according to claim 3, characterized in that once said rings (11a, 11b) have been closed on said upper and on said plunger, the material that subsequently constitutes said collar is injected, said material affecting, by means of said gap, the lateral surface of said ridge with desired thicknesses. Method according to claim 4, characterized in that said flow is facilitated, during injection, by the rise of said plunger (8).

Inventors: FOFFANO MASSIMO, PEROTTO RICCARDO, FOFFANO, MASSIMO
Applicants: BENETTON SPA, BENETTON GROUP S.P.A.
Application year: 1997
Main classification: B29D31
IPC codes: B29D35