Shoe-Sole and Method for Making the Same

The invention relates to a shoe-sole consisting at least partially of plastic.

The invention is further concerned with a method for making such a shoe-sole. As a plastic material for instance foamed polyurethane, soft-PVC, ethylene-vinyl-acetate or thermoplastic caoutchouc may be used.

It is already known to make shoe-soles from plastic, as from foamed polyurethane, because such shoe-soles prop the foot softly and elastically and cause an agreeable feeling during walking. The fixing of the uppers to such shoe-soles of hard foamed polyurethane has been accomplished heretofore by nailing, screwing or clipping whereby the uppers in general are fastened laterally on the shoe-sole. With this fixing method the fixing elements frequently pluck out so that then the uppers separate themselves from the sole.

For soles of soft foam of polyurethane it is already known to fasten the uppers to the sole with an adhesive. This procedure is very laborious and expensive whereby nevertheless a satisfactory connection between sole and uppers is not ensured.

It is an object of the present invention to provide a shoe-sole consisting at least partially of plastic with which a simple and secure fixing of the uppers is possible.

It is a further object of the invention to provide a shoe-sole consisting at least partially of plastic by which damaging of the shoe-sole during walking, particularly by the tension forces thereby exerted by the uppers to the shoe-sole, is avoided.

It is another object of the invention to provide a shoe-sole with which a connection between the shoe-sole and the uppers can be made in such a way that the connection has a certain elasticity taking bendings and twistings of the shoe-sole, as occurring during walking. This elasticity shall thereby suitably be adapted to the properties of the material of the sole.

A further object of the present invention is to form the shoe-sole in such a manner that the uppers may be fixed quickly and with less expenditure of work. Moreover, a good anchoring of the joint members within the shoe-sole shall be ensured.

In the following the invention will be described with reference to the drawings showing various embodiments of the invention.

FIG. 1 shows a cross-sectional view of a sole formed in accordance with the invention in a plane parallel to the walking surface of the sole wherein two differently formed sprayed die castings are provided; FIG. 2 illustrates the sprayed die castings in their preferred embodiment, wherein a grating is formed; and

FIG. 3 shows a cross-section along the line III--III of FIG. 2 together with a pin.

A sole 1, illustrated in FIG. 1, is thought for a sandal, wherein the uppers consist only of a loop. Therefore, merely two sprayed die castings 2 of plastic are represented within the range of the ball of this sole 1. Normally however, even then, if only a loop forms the uppers, more than two of such sprayed die castings will be provided, for instance three or four sprayed die castings.

Furthermore, in FIG. 1 an embodiment is shown wherein only two opposite fastening points for the uppers form a common sprayed die casting. The upper sprayed die casting 2 of FIG. 1 consists of two sockets 3 interconnected by a longitudinal strap 4 of smaller cross-section than the sockets. Moreover, this sprayed die casting is provided with wing-like protrusions 5 by which the position of the sprayed die casting within the sole is fixed. Pins 6 may be inserted into the sockets 3 in a manner described later in detail for holding uppers 7.

The lower sprayed die casting 2 of FIG. 1 consists of a tube 8 extending over the whole width of the sole and having wing-like protrusions 5'. For fixing the uppers 7 either equally pins 6 may be inserted on both sides or a seem material can be pulled through used for fixing the uppers. Then, the attachment of the uppers 7 on the sole 1 presents a decorative aspect.

As may be seen from the drawings, the free ends of the sockets 3 as well as of the tube 8 project over the lateral surface of the sole to such an extent that these ends can penetrate into openings of corresponding width of the uppers 7. In this way, an additional fixing of the uppers 7 is achieved, thereby facilitating the assembly of the same, since a prefixing of the uppers 7 is caused by pulling the latter over the projecting free ends 9 of the sprayed die castings 2.

A preferred embodiment is illustrated by FIGS. 2 and 3 where only one sprayed die casting is shown as inserted into a mold for making the sole. As apparent, here the sockets 3 opposite to each other are not only interconnected by longitudinal straps 4 but also by transverse straps 10, thus forming a grating adapted to be inserted into the old as a whole. The number of sockets 3 corresponds to the number of the necessary fastening points of the uppers 7 to the sole 1. The grating is inserted into the mold in such a manner that the free ends 9 of the sockets 3 projecting then from the lateral surface of the sole fit into corresponding recesses of the mold, said recesses being located within the range of the separating line of the bipartite mold. In this way the grating is positively secured within the mold without any additional measures necessary. The required spacing of the grating to the bottom of the mold is ensured by studs 11 (vide FIG. 3) protruding from the bottom side of the grating and resting on the bottom of the mold.

It is obvious that also in a grating-like embodiment according to FIG. 2 instead of sockets 3 tubes 8 may be provided replacing likewise the longitudinal straps 4. Further it is obvious, that the longitudinal straps 3 too can be interconnected by the transversed straps 10.

Such a grating-like embodiment has numerous advantages. Thus, the inserting of the sprayed die castings 2 into the mold can be effected for all fastening points of the uppers to the sole 1 by a single manipulation, since all sprayed die castings are interconnected by the grating. In this way an important saving ot time and work is achieved, and the output of the sole produced by one mold is increased. Furthermore, a mutual anchoring of the individual fastening points is obtained by the grating so that partial peak loads can be absorbed by the grating without damaging the sole 1, Particularly with a thin sole, a tearing out of the sprayed die castings 2 is prevented by the grating structure. The grating-like embodiment enables the use of cheaper foams of lower specific density, thereby not only reducing the costs but also diminishing the weight of the sole and thus that of the shoe in a desirable manner, still ensuring a secure anchoring of the uppers on the sole 1.

The pins 6 have a head 12 of a suitable formed decorative aspect.

Preferably the diameter of the pins 6 corresponds to the inner diameter of the sockets 3 or of the tubes 8, or it exceeds the same only insignificantly. In this way it is ensured that with insertion of the pins 6 the latters are in fact well anchored within the sockets 3 or the tubes 8, but there is no important supersession of the material within the sprayed die castings 2 by which the same and consequently also the sole 1 could be damaged. For instance, the pins 6 may be provided with screw threads screwed into an internal thread of the sockets 3 or of the tubes 8. It is, however, also possible to provide the pins 6 with barbs cooperating with projections within the interior of the sockets 3 or the tubes 8. Whereas in the first case a turning movement is necessary for inserting the pins 6, it is sufficient in the second case to push the pins 6 into the holes of the sockets 3 or the tubes 8.

The pins 6 may be of metal, but this is disadvantageous because in this case the pins 6 are not flexible and are not able to follow the movements of the sprayed die castings. Moreover, there is the danger of oxidation whereby the aspect of the finished shoe would be affected. Therefore, it is advantageous, if the pins 6 consist of plastic, preferably dyed through, so that they have likewise a certain flexibility. Furthermore, the pins 6 can be made in a color matching to the sole material whereby in case of pins dyed through this color is maintained even when the surface, for instance of the head of the pins, is damaged.

In case the sockets 3 are interconnected by tubular longitudinal straps 4, or if instead of the sockets 3 continuous tubes 8 are provided at all, as represented in the lower part of FIG. 1, then the uppers may be sewed as though onto the sole 1 because in such a case the sewing material can be passed through the tube from one lateral surface of the sole to the opposite one. The uppers have then a kind of seem within the fastening range to the sole whereby a decorative effect is achieved.

The sprayed die castings 2 shall have a certain elasticity in order that they are able to follow the movements of the shoe-sole 1 during walking and not to tear out in virtue of their rigidity in case of bendings or twistings of the shoe-sole and not to cause a damaging of this shoe-sole. These sprayed die castings 2 consist therefore suitably of a plastic material, the mechanical and physical properties of which being similar to those of the sole material, i.e. when a foamed sole material is used: to the properties of the same unfoamed sole material.

In order that the sprayed die castings 2 have the required properties, the sprayed die castings 2 embedded into a sole 1 of foamed soft-polyurethane consist of soft polymers, such as injectable caoutchouc with a hardness of 36 shore A to 98 shore D, and the sprayed die castings 2 embedded into a sole 1 of foamed semihard polyurethane consist of injectable harder polymers, such as polyamide, with a hardness of 65 shore A to 88 shore D. Thus, when a soft polyurethane foam is used as a sole material also soft sprayed die castings are employed whereas when semihard polyurethane is utilized for the sole material also the sprayed die castings are harder.

Particularly when semihard foamed polyurethane is used as a sole material, it is suitable, if the sprayed die castings 2 are not rigidly connected with the polyurethane but are able to move to some extent within the polyurethane in order not to be embarrassing to the rolling motion of the foot during walking. In order to prevent that the sole material would be damaged by such small relative movements between the sole and the sprayed die castings that could lead subsequently to a fissure in the sole material, the sprayed die castings 2 have a rounded cross-section, for instance a circular or an oval-shaped cross-section. Since in this way edges are avoided, local stresses of the sole material otherwise occurring within the range of these edges are prevented, such local stresses provoking a destruction of the sole, especially when they occur again and again.

When making a sole according to the invention, first the grating shown in FIGS. 2 and 3 is inserted in the above-mentioned manner into the mold. Afterwards, polyurethane-forming material is poured or injected into the mold either before or after the mold is closed, and is let solidify in the mold for forming the sole 1. At last the mold is opened and the sole 1 provided with the sprayed die castings 2 is released.

The sprayed die castings 2 of plastic have mechanical and physical properties matching to the corresponding properties of the sole 1 of foamed polyurethane so that they follow the movements of this sole 1 during walking on the one hand without a destruction of the sole at the location of the insertion of the sprayed die castings whereas on the other hand a secure anchoring of the uppers to the sole is ensured.

When semihard foamed polyurethane is used as a sole material, a rigid connection between the sole material and the sprayed die castings is not desirable in order that the latters can better follow the movements of the sole during walking. In such a case it is suitable to use a polyamide as a material for the sprayed die castings because polyamide does not form a firm bonding with the polyurethane.

The mold for carrying out the procedure is substantially characterized in that it is divided within the range of the lateral surface of the sole and that in at least one mold part recesses are provided along the separating line for receiving the free ends of the sprayed die castings. In this way the sprayed die castings 2 are easily fixed in the mold and are held in position without for instance pins being necessary for this purpose and being anchored within the mold which have to be inserted into openings of the sprayed die castings for fixing the same and which have to be withdrawn separately for releasing the sole from the mold. The free ends of the sprayed die castings 2 supported within the recesses of the mold project then from the lateral surface of the sole in the above-mentioned favourable manner after releasing from the mold.