WO2016128818A1

WO2016128818A1 - Forming process and mould for a shoe sole and shoe sole

Info

Publication number: WO2016128818A1
Application number: PCT/IB2016/000084
Authority: WO
Inventors: Antonio STORTINI
Original assignee: STORTINI, Daniele; STORTINI, Sonia
Priority date: 2015-02-09
Filing date: 2016-02-03
Publication date: 2016-08-18

Abstract

Cast moulding process of a product (1) comprising at least two overlapped layers (10, 11) of expansible plastic materials (Mi, Ms), said plastic materials (Mi, Ms) being cast in a sequence into a mould (2). According to the invention, after the casting of the material (Mi) for the first layer (10; 11) but before the casting of the material (Ms) for the second layer (11) of said product (1), between the first (20; 21) and the second (21) half shell of said mould (2), a junction element (12) retained all about by the edges, clamped to each other, of said half shells (20; 21), is inserted. The junction element (12) is compatible or made compatible for the adhesion to the upper surface of the material (Mi) of the first layer (10; 11) and to that lower of the material (Ms) of the overlying second layer (11) during the curing of said materials (Mi, Ms). Said first layer (10; 11) and second layer (11) are two consecutive and overlapped layers of a possible sequence of two or more layers (10; 11). Among the advantages there is the elimination of part of the moulding equipment and a significant shortening of the forming times. The process is particularly useful for the forming of footwear soles with multiple layers of synthetic material; in particular polyurethane.

Description

FORMING PROCESS AND MOULD FOR A SHOE AND SHOE SOLE

D E S C R I PT I O N

The object of the present invention is an innovative process for the cast moulding of soles for shoes composed of multiple overlapped layers of plastic material, each preferably characterised by different mechanical properties and chemical-physical and/or aesthetic features.

A further object of the present invention is the sole for shoe obtainable by said innovative moulding process and the mould used for its creation.

The invention therefore falls within the footwear field, in particular that of the forming of soles made of plastic material.

Even more precisely, the invention falls within the field of multi-layer sole making, made of materials formable by casting, preferably polyurethane.

However, nothing prevents the possibility of extending the use of this innovative process for making any other object made of plastic material for which, for purely aesthetic or functional reasons, a sequential moulding of multiple layers of material with different properties and aesthetic finishes is required; without any limiting intent, the invention may for example be applied to the field of moulding of household articles made of plastic material, that of the creation of furnishing, automotive or household appliances components or giftware in general.

It is known that some plastic materials (such as polyurethanes) are suitably fluid to be cast in rigid or flexible moulds of which they take the shape defining, once "polymerised", a wide variety of shapes and products.

Cast moulding techniques (conducted with equipment and machines well known to the man skilled in the art and whereon, therefore, there is no need to dwell too much) are widely used in the field of shoe sole making, including those defined as "multi-layer"; i.e., of the type comprising at least a lower layer defining a tread bottom and one or more upper intermediate layers, overlapped to it, for connection to an upper.

To date, such multi-layer soles may be obtained according to different techniques and cast moulding procedures.

For example, a much used technique provides that two layers of sole, one defining the tread bottom the other the intermediate layer, are formed by casting in two different moulds, in substantially simultaneous times. Said materials formed by casting, once poured, expand, polymerise and take a final shape even in a few seconds in a process that is called "curing." Once "cured" and extracted from the relative mould said layers are overlapped and constrained to each other, for example by gluing, so as to form the "multi-layer" sole desired.

Many of these materials, at least the polyurethane ones, adhere tenaciously and indissolubly to the surfaces of other materials (herein referred to as

"compatible") with which they come into contact during the curing.

As known, incompatible materials may be made compatible with such materials in the process of curing in some cases by suitably heating them or even through suitable and well-known surface treatments (mechanical or chemical or coating with primer). A process is also known according to which the tread bottom, once moulded and polymerised inside a first mould is transferred and inserted into a second mould for the overmoulding of at least one intermediate layer.

Of course, the gluing or, alternatively, overmoulding operations may be repeated several times according to the number of layers provided for the sole to be obtained.

It is clear how such known moulding systems and techniques always require the use of at least two moulds (one for the tread and at least one for the intermediate layers), operating in a discontinuous manner.

This inevitably leads to high operating costs, large use of labour and an expansion of production times; we may consider, for example, the need to wait for the substantial polymerisation of the tread bottom before it can be transferred to a second mould for the overmoulding of an intermediate layer or the need to provide and carry out appropriate preparatory operations on the moulded items in order to make them suitable to their subsequent gluing.

Said operations, normally carried out according to a repetitive sequence, may be automated but with high equipment costs compared to the value for the manufactured articles obtained.

Alternative forming techniques in a single mould may be used for making said multi-layer soles comprising, in succession, sequential steps of:

- casting. in a mould of a first material intended to form a first layer of the sole with the relative closing of a first cover removed after the actual curing of the layer.

- casting of a second material for the moulding of a second layer of sole overlying the first and closing the mould with a second different cover until the complete curing thereof.

Such process is obviously repeated as many times as the layers defining the sole to be obtained.

It is clear that, in addition to being particularly slow, said moulding technique of multi-layer soles requires the use of a lot of equipment, in particular as many covers as the layers of the sole to be obtained.

Furthermore, the process is particularly slow because each layer may be applied only after the substantial polymerisation of the underlying layer.

The sequential introduction into the mould of said covers and their subsequent removal is carried out by automatic machines particularly expensive and complex with an inevitable and consequent increase in production costs.

The plants using the "RPU technology" (also called "with sprayed polyurethane") are known as well to the man skilled in the art (and whereon, therefore, it is not necessary to dwell too much), however, suitable for making moulded items of reduced thickness and not always capable of uniformly covering all the zones of the mould with the moulding material.

Such a moulding technique finally provides very high production times and costs with inevitable negative consequences on the final price of the sole.

The main object of the present invention is to eliminate at least part of the above listed drawbacks of the prior art, by designing an innovative moulding process of multi-layer products made of plastic materials, in particular soles for shoes, comprising at least two or more overlapped layers, each preferably characterised by different mechanical properties and/or aesthetic features, capable of reducing the production times, economically advantageous, and employing the lesser number of equipment.

A further object of the present invention is to provide an innovative moulding process of multi-layer soles made of plastic material, preferably polyurethane, which makes use for most part of already existing and normally used equipment, substantially without the need for modifications or adaptations thereof.

A further object of the present invention is to provide a multi-layer sole for shoes obtained according to the forming process object of the invention and the relative mould used for its creation.

These and other objects, which shall appear clear hereinafter, are achieved with a forming process of multi-layer soles according to claim 1 , as illustrated in the following description and in the annexed claims, which constitute an integral part of the description itself.

Further features of the present invention shall be better highlighted by the following description of a preferred embodiment, in accordance with the patent claims and illustrated in the enclosed drawing tables. Such figures should be considered as having an illustrative and non-limiting purpose, in which:

- figs, la and lb schematically show an exploded view of possible intermediate layers and possible treads of a multi-layer sole according to two known possible constructive variants; - figs. 2a and 2b schematically show an exploded view of the multi-layer sole of the invention according to two possible constructive variants;

- fig. 3 schematically shows an exploded view of the mould for making the multi-layer sole of fig. 2a;

- figs. 4a and 4b show the mould of fig. 3 according to the section A-A, respectively, in non-operating and operating condition;

- figs. 5a, 5b, 5c, 5d, 5e, 5f schematically show the steps of the forming process of multi-layer soles for shoes according to the invention.

The elements of the apparatus according to the invention are now described using the references contained in the annexed figures. It should be noted that any dimensional and spatial term (such as "lower", "upper", "right", "left" and the like) refers, unless otherwise indicated, to the position according to which the object of the invention is shown in the drawings which not necessarily coincides with the position of the finding in operating conditions.

With the purpose of highlighting some features instead of others, not necessarily what described in the annexed drawings is perfectly to scale.

It is also noted that, in the description, all that shall be said with reference to a sole for shoes may be extended, as already anticipated, to any other product or object obtained, for functional and/or aesthetic reasons, through a sequential moulding of multiple layers of polymeric material, such as giftware and household articles, furnishing, automotive or household appliances components. As shown in figs, la- lb and 2a-2b, reference numeral 1 globally indicates two types of multi-layer soles.

More precisely, in the examples in the figure, said sole 1 comprises two "layers", a lower one defining a tread bottom 10, an upper one, constrained to it in the manners that shall be seen hereinafter, defining an intermediate layer 1 1 for connection to an upper (not shown).

The tread 10 may be a single block piece (see fig. lb or 2a) or, alternatively, "fractionated" into several parts such as to identify at least a heel 10a and a zone 10b defining the tip of the sole 1 (see figs, lb and 2b). In the description, the general term "tread" 10 shall identify without distinction both variants indicated with 10 or with 10a + 10b just described above as well as any other known configuration thereof.

It is useful to clarify that the multi-layer sole 1 shown in the annexed figures is applicable on any type of shoe (e.g., woman, man or child), including the work and safety ones. It may of course also provide for a larger number of "layers" overlapped and/or having different geometries, shapes and aesthetic finishes. It is also noted that the polymeric materials preferably used in the cast moulding according to the invention are of the family of polyurethane materials.

Hereinafter, in the description the term "moulding" will refer, for simplicity, to "cast moulding".

Preferably, the layers 10, 11 of the sole 1 can have different and peculiar physical properties and/or aesthetic features depending on the specific functions that they have to ensure and/or in order to meet the most various "tastes" of the future users of the shoe.

For example, without any limiting intent, the overlapped layers of the multi-layer sole 1 of the invention may have different colours and/or density and/or stiffness/softness and/or flexibility and/or aesthetic finishes etc. Without any limiting intent, it may be useful to ensure cushioning and/or anti-slip properties or wear resistance to the tread 10 while it may be desirable to have one or more intermediate layers 1 1 characterised by a greater structural stiffness so as to offer a more stable and comfortable support to the foot arches.

The choice of plastic materials for the forming of each layer 10, 11 of the sole 1 is therefore normally made on the basis of the properties and peculiar characteristics to be ensured to them.

Said materials may therefore belong to the same "family" (e.g., that of polyurethane materials) but have different and specific chemical "formulations" or be "heterogeneous" to each other but compatible for the subsequent coupling of the layers 10, 11 of sole 1 resulting therefrom.

A sole 1 as shown in the embodiments of fig. l a and lb is normally known as "bicomponent sole" or "two-tone" (depending on the different properties of each layer).

Nothing prevents, of course, the possibility to mould sequentially and in succession more than two overlapped layers qualitatively and aesthetically the equal or different to each other.

According to the invention, each layer 10, 11 of the sole 1 is firmly "bound" to the one immediately overlying by means of the interposition of an intermediate junction element 12, suitably applied between two subsequent layers during the moulding process object of the invention (and that shall be referred to hereinafter) where such two subsequent layers may be either the tread bottom 10 and the subsequent and optionally single intermediate layer 11 or two subsequent generic intermediate layers 11.

For the reasons that shall be seen hereinafter, the respective contact surfaces of two overlapped layers 10, 11 are capable of adhering on said junction element 12, binding them reciprocally; that is, with reference to the example of fig. 2a- 2b, the upper surface 100 of the expanding material Mi defining the tread bottom 10 will adhere to a first face 120 thereof, while on the opposite one 121 the lower surface 1 10 of the expanding material Ms intended to form the overlying intermediate layer 11 , following the respective profiles and patterns thereof. Not necessarily, therefore, said junction element 12 is forced to lie on a flat surface and even less such surface is necessarily horizontal being, on the contrary, capable of coupling and adapting even to curved and/or irregular surfaces 100, 1 10 of said layers 10, 1 1.

Said junction element 12 may be without distinction a stretched or flexible membrane while any convexities, concavities and/or curvatures thereof shall be determined from the amount of material Mi, Ms cast in the mould 2.

Such configuration is, for example, clearly shown in fig. 2a or 2b.

According to a preferred embodiment of the invention, said junction element 12 is a membrane (or film) made of synthetic material so thin to be imperceptible between the two overlapped layers 10, 1 1 of the sole 1 once its protruding edges are trimmed.

Without any limiting intent, said membrane 12 made of synthetic material may belong to the same family of materials used for the forming of the sole 1 (e.g., it may be a plastic film, in particular of the family of polyurethanes) although nothing prevents the possibility of using other materials suitable for the purpose such as, by way of an example, films of graphene or other carbon compounds (characterised, as known, by high sturdiness and flexibility).

According to another variant of the invention, said junction element 12 may consist of sheets of natural material suitably pre-treated externally to perform the same "binding" function of the plastic films 12 previously described.

More in detail, said sheets 12 may consist of sheets of leather, cork, cardboard, fabric or similar materials coated with adhesive substances and binders such as mastics or adhesives so as to adhere in a secure and lasting manner to the layers 10, 11 of the sole 1 which connects.

Said sheets 12 may have such thicknesses as to..remain deliberately visible between the two layers 10, 11 that they bind contributing to define the final aesthetics of the sole 1.

At this point, forming techniques and process of the sole 1 of the invention widely described just above shall be described that, even if using equipment for most part substantially known and pre-existing to the introduction of the innovation, are particularly innovative.

It is useful to immediately specify that said forming process may be conducted using conventional moulds 2 (shown in schematic form in Fig. 3) comprising at least a first 20 and second half shell 21 for the moulding, respectively, of a first and second layer 10, 11 of sole 1, overlapped to each other, and a cover 22 for closing the same mould 2.

In figures 3-4a-4b, in particular a mould 2 is shown comprising a first shell 20 defining a base 20 for the moulding the tread bottom 10 and at least a second half shell 21 consisting of an intermediate ring 21 for making an overlying intermediate layer 11. Of course, said mould 2 may comprise as many intermediate rings 21, closable one on the other, also different in shape and size to each other, as the intermediate layers 11 that are wished to be sequentially overmoulded.

Said moulds 2 are falling in the "open moulds" type, that is, able to receive by casting moulding materials of any formulation and property (e.g., one- or two- tone, one- or two-density, etc.).

For greater accuracy, the base 20 of the mould 2 carries at least one cavity 200 with the imprint of the tread bottom 10 to be obtained.

Said cavity 200 may be a single cavity 200 in case soles 1 of the type shown in fig. la or 2a are wished to be obtained or, on the contrary, be fractionated into several discontinuous and separated portions for the forming of treads 10 of the type shown in fig. lb-2b.

The profile of said imprint 200 may also be substantially flat (e.g., in case "wedge" type soles are wished to be obtained) or, as shown in the non-limiting example of fig. 3, follow a "curved" pattern towards the tip zone of the sole 1 and/or heel; that is, in general, said imprint 200 shall be shaped and outlined according to the shape that is wished to be given, for aesthetic and/or functional reasons, to the tread 10 of the sole 1 , without any limitation of shape of the part that will remain visible at least with respect to what possible today with the known technologies.

On the base 10 of the mould 2 the intermediate ring 11 comprising a through opening 210 that defines the moulding chamber 21 1 of a first intermediate layer 1 1 , overlying the tread 10, is capable of closing.

The cover 22 of the mould 2 is finally suitably shaped so that, as shall be seen, closing on the underlying ring 21 and "pressing", prior to their complete polymerisation, on the tread 10 and/or the intermediate layer 11 it can suitably model and define the final shape of the intermediate layer 11.

Without any limiting intent (see fig. 3), said cover 22 may comprise for example a curvilinear "last profile" 220 to define sole zones with different thicknesses (greater, for example, in the proximity of the heel for comfort requirements, smaller at the tip) and/or include "projections" and "ribs" or "bosses" 221 , 222 defining, in at least a portion of the sole 1 , recesses and/or lightening grooves or any other device aimed at least at improving and making more comfortable and safe the walking activity of a user of the shoe.

For this purpose, in the example of fig. 3, the cover 22 comprises one or more pins 221 and/or bosses 222 adapted to define at least in the intermediate layer 11, in the support zone of the heel and in the proximity of the tip, respectively, specific lightening channels (not shown in the annexed figs.).

Although this function is ensured, at least in part, by the pins 221 , said bosses 222, preferably obtained on the front convex . stretch of the inner profile 220 of the cover 22, are suitably shaped and sized to also act as thrust members 222 contributing, at the time of closing of the mould 2, to push the moulding materials cast into it even in those zones of its relative casting cavities 200, 21 1 more difficult to reach, distributing them uniformly (for example in the tip or heel zone where the creation of "fins", also quite thin, capable of being glued directly to the upper may be required).

Of mould 2, the "vents" required for the expulsion of any air bubbles that might remain trapped in its interior during the castings of the moulding material with the risk of compromising the functionality of the sole 1 shall not be described (not shown either in figure 3 or in the relevant sections of fig. 4a, 4b) being well known to the man skilled in the art.

In such description, the machinery and equipment set up for obtaining said castings in the mould shall not be discussed any further being substantially those commonly long been used.

At this point, the process of forming in the mould 2 a multi-layer sole 1 of the invention shall be described in detail.

To this end, reference shall be made to figs. 5a to 5f in which at least the main steps of said process are schematically and symbolically shown.

In very general terms, said forming process of a multi-layer sole 1 provides that immediately after the casting of the material for a first layer 10 of said sole 1 and immediately before the casting of the second layer 11 (coinciding with the first and possibly only one intermediate layer 1 1), to be overlapped to the first, the said junction element 12 is inserted between the first half shell 20 and second half shell 21 of the mould 2, capable of mutually binding them.

Said junction element 12, retained all about by the edges, clamped to each other, of said first 20 and second 21 half shell of the mould 2, therefore:

- closes at the top said first shell 20 in which a material Mi for said first lower layer 10 is cast and within which it starts to expand

- defines the "bottom" of the overlying half shell 21 positioned over the first and capable of receiving a material Ms for said second layer 11 of sole 1.

Upon the closure of the cover 22 on the second half shell 21, as already partly anticipated, the above optional bosses 222 formed on its inner profile 220 (and at least in part the said optional pins 221) press on the material Ms of the second layer 11 capable, in turn, of pressing on the underlying material Mi pushing and distributing it also towards the zones that are narrower and more difficult to reach of said first half shell 20 of said mould 2.

According to the invention, said first half shell 20 may consist of the base 20 of the mould 2 suitable for making a tread 10 while said second half shell 21 is an intermediate ring 21 for the moulding of an overlying intermediate layer 11 ; of course they may consist, as will be seen, even of two overlapped consecutive intermediate rings 21. In the first case, therefore, said junction element 12 will indissolubly constrain the tread bottom 10 and the overlying intermediate layer 11 to each other, in the second case two consecutive intermediate layers 1 1. With reference to the example of figures 5a to 5f, said forming process of the multi-layer sole 1 may comprise, in more detail:

a) a first step (fig. 5a-5b) during which the first plastic material Mi intended to form a first layer 10, for example a tread 10, is cast in the cavity 200 of the base 20;

b) a second step (fig. 5c-5d) during which the junction element 12 is first . positioned on the base 20 of the mould 2 and then a first intermediate ring 21 is lowered that locks all the outline thereof against the base 20 and "pushes" it towards the material Mi in the process of expansion with which it is intended to "bind" (see fig. 5d);

c) a third step (fig. 5e) during which a second material Ms is cast in the moulding chamber 211 of the intermediate ring 21 for the creation of an intermediate layer 11 overlying said first layer 10, said material Ms substantially covering the upper face 121 of said junction element 12;

d) a fourth step (fig. 5f) of closing the mould 2 by means of said cover 22 that defines, as anticipated, the final shape and outline of said at least intermediate layer 11 ; that is, the inner profile 220 of said cover 22 being modelled to generate in the sole 1, with reference to the example examined, appropriate and desired curvatures, identifying areas with greater thickness, usually at its rear part, and other progressively thinner towards its tip.

Obviously, a last step will follow (not shown) of opening the mould 2 for the extraction of the multi-layer sole 1 that has now reached the complete "curing". Of course, as already partly anticipated, the moulding in sequence of further intermediate layers 1 1 overlapped to the first will require the use of as many intermediate rings 11, each couplable each time on that immediately below subsequent to interposition of a junction element 12 and capable of receiving the specific moulding material Ms.

Between each pair of intermediate rings the relative junction element 12 is therefore positioned and tightened in the manners already described. In such a case, therefore, said junction element 12 will act as a closing element of the moulding chamber 21 1 of the lower ring 1 1 and as the bottom for that immediately overlying, constraining two overlapped intermediate layers 1 1. The adhesion between said junction element 12 and said overlapped layers 10, 1 1 may be obtained in various ways separately or also, in the measure of one or more, jointly usable to one another.

For example, the adhesion can be firm and spontaneous because, as already mentioned, inherent in the characteristics of the materials Mi, Ms that in the "curing" step naturally adhere to other compatible materials among which the junction element 12 must be suitably chosen (e.g. all of the family of polyurethanes).

In this regard it shall be specified that, as well known, substantially all the expanding polyurethane materials (and still others) currently used for the manufacture of soles for shoes or various giftware have such a feature of spontaneous adhesion on many other materials during the curing. Therefore, the choice of materials compatible to each other to be used in the process according to the invention substantially does not pose renunciations to materials in use today. In other words, the process according to the invention allows to continue using most of the materials already known and well-accepted to the end-users without the technology according to the invention to obligatorily change the appearance or performance of the manufactured article.

However, it has already been said that the adhesion may be favoured or promoted by appropriate temperatures with which the above materials Mi, Ms are cast in the mould 2; in fact, said temperatures may be such as to cause a momentary partial softening of the junction element 12 and its consequent substantial welding to the surfaces 100, 1 10 of said layers 10, 11 where of course the method is applicable if the junction element 12 consists of a plastic sheet 12 capable of softening by the effect of heat.

Or still adhesion may be favoured or promoted by appropriate treatments or coatings of the surfaces of the junction element 12 (e.g., grinding or mastics or primers or other similar substances or treatments) where of course the applicable treatment depends on the nature of the same junction element 12.

In any case, it has been discovered that a pre-heating of the surface against which the material cures improves the compatibility.

The junction element 12 may for example be suitably pre-heated before being inserted, manually or by means of automatic machines, inside the mould 2.

Of course, one or more of these devices or still other may be jointly used to extend the possibilities of choice of materials. At the end of the polymerisation process of the sole 1, the junction element 12 will therefore remain securely constrained to its overlapped layers 10, 11, binding them indissolubly.

Finally, nothing prevents the possibility of providing on said junction element 12, preferably at the central zone thereof, a plurality of slots or holes (not shown in the annexed figures) so as to define contact and direct adhesion zones between the overlapped layers 10, 11, strengthening their coupling.

Thus, the materials Mi, Ms used in the making of the layers 10, 1 1 of a multilayer sole 1 may be different from one another provided that they are compatible or made compatible to "bind" with the said junction element 12. They may belong to the same "family" but characterised by different chemical formulations, attributing peculiar and specific functional and/or aesthetic properties to each layer of the sole 1.

Preferably, said materials Mi, Ms may belong to the family of polyurethanes, for example polyester- or polyether-based.

For the purposes of the invention, instead, it is not necessary to dwell in the description of the subsequent processing and finishing steps of the sole 1 thus obtained being substantially similar to those of the prior art and well known to the man skilled in the art; the only step of carding (or die cutting) of burrs and protruding edges 122 of the junction element 12 that, as shown in figs. 5d, 5e, 5f, protrude from the mould 2 and, consequently, at the end of the forming process of the sole 1 are herein mentioned.

The sole 1 thus obtained may therefore be applied permanently to the upper of the shoe, in particular to its bottom, for example by means of known gluing techniques, as is also possible, at least in principle, that also the upper is formed on the underlying layers with the method according to the invention.

It has been said that the process according to the invention may use most part of pre-existing moulds. This is possible, for example, when the known technology provides a moulding process of each layer over the subsequent using, for each layer to be moulded, a specific ring and a corresponding cover. In such case it is very likely that all the rings are directly or with few modifications usable as intermediate rings 21 for the process according to the invention.

It is clear that the process according to the invention may be applied in conjunction with the known moulding technologies. Nothing prevents, in fact, that layers employing, instead, covers of the prior art may be interposed to layers

10, 11 obtained according to the invention with the aid of the junction element

12.

However, it is clear that in the practical embodiment of the invention numerous modifications and further variants may be provided, all falling within the same inventive concept.

Nothing prevents, for example, that, at least for some types of sole 1 , the above cover 22 may consist, actually, of an upper previously mounted on a last and capable of being positioned with its bottom inside said moulding chamber 21 1 of at least one intermediate layer 11 such upper being made of material compatible with the expanding material Ms cast in said intermediate layer 11. According to this variant, not shown in the annexed figures, it is therefore possible to mould the multi-layer sole 1 of the invention directly on the upper, actually eliminating the final step of gluing of which it has been briefly discussed.

Moreover, nothing prevents to insert, during the forming process according to the invention, anti-puncture steel plates for safety shoes. Indeed, in principle one of the junction elements 12 may itself consist of a steel plate possibly suitably pre-formed before being clamped between the base 20 of the mould 2 and first intermediate ring 1 1 or between two consecutive intermediate rings 1 1.

From the above description the advantages attainable with the present invention appear clear, in particular the possibility of making multi-layer soles made of plastic material (e.g., polyurethane) in a single mould without the need of having to wait for the "curing" of each individual layer for the overmoulding of the next. This results in a considerable shortening of production times.

The use of the junction element 12 of the invention, in its many variants, also allows a considerable reduction of equipment and machinery needed for the making of multi-layer soles 1, said junction element 12 replacing, in fact, the plurality of covers "lowered" in succession in the mould as the existing and known sequential moulding techniques provide.

According to the process of the invention, it is therefore possible to mould substantially simultaneously multiple overlapped layers of sole being no longer necessary to wait, unlike the techniques of the prior art, for their curing and the removal of each single cover served to their moulding.

Even when junction elements 12 of high flexibility and elasticity are used, their uncontrolled deformation is impossible both due to the fact that the above materials Mi and Ms are cast in the appropriate quantities and appropriate distributions and because they, expanding almost simultaneously, act as a contrast to one another. The above process may also be fully automated, requiring less labour.

Claims

1. Forming process of a product (1) comprising at least two overlapped layers (10, 1 1) of plastic materials (Mi, Ms), said plastic materials (Mi, Ms) being cast in a sequence into a mould (2) comprising at least:

- a first half shell (20; 21) for the moulding of a first layer (10; 11) of said product (1)

- at least a second half shell (21) for the subsequent moulding of at least a second layer (11) of said product (1) said at least second layer (11) being overlapped ed to the first (10; 1 1)

- at least a cover (22) for closing said mould (2)

characterised in that after the casting of the material (Mi) for said first layer (10; 1 1) but before the casting of the material (Ms) for said at least one second layer (1 1) of said product (1) a junction element (12) is inserted between said first (20; 21) and second (21) half shell of said mould (2), said junction element (12) being retained all about by the edges, clamped to each other, of said half shells (20; 21),

said junction element (12) being compatible or made compatible for the adhesion to the upper surface of the material (Mi) of said first layer (10; 11) and to that lower of the material (Ms) of said overlying second layer (11) during the curing of said materials (Mi, Ms)

said first layer (10; 1 1) and second layer (11) being two consecutive and overlapped layers of a possible sequence of two or more layers (10; 11).

2. Forming process of a multi-layer product (1) according to claim 1,

characterised in that said compatibility between said materials (Mi, Ms) and said junction element (12) is obtained at least with the suitable choice of said materials (Mi, Ms) and the material of said junction element (12) among those per se compatible to each other where in particular said compatibility is due to belonging to the same chemical family.

3. Forming process of a multi-layer product (1) according to any previous claim, characterised in that said compatibility between said materials (Mi, Ms) and said junction element (12) is obtained at least through suitable treatments or coatings of the surfaces of the junction element (12).

Forming process of a multi-layer product (1) according to any previous claim,

characterised in that said compatibility between said materials (Mi, Ms) and said junction element (12) is obtained at least by casting said materials (Mi, Ms) in said mould (2) at such temperatures as to cause a partial temporary softening of the said junction element (12), where said junction element (12) is of such physical nature as to be able to come to the softening.

Forming process of a multi -layer product (1) according to any previous claim,

characterised in that said junction element (12) may be provided with holes or slots so as to define zones of direct contact between said materials (Mi, Ms) of said two overlapped layers (10, 1 1).

Forming process of a multi-layer product (1) according to any previous claim and

characterised in that before its insertion in the mould (2) said junction element (12) may be subjected to pre-heating at a sufficient temperature to improve the compatibility of said junction element (12) with said at least two overlapped layers (10, 11).

Forming process of a multi-layer product (1) according to any previous claim,

characterised in that it comprises a step of pressure on the material (Ms) of said second layer (1 1) of said multi-layer product (1) cast in said mould (2), said material (Ms) being in turn capable of pressing on said underlying material (Mi) pushing and distributing it towards the zones that are narrower and more difficult to reach of said first half shell (20; 21) of said mould (2).

8. Forming process of a multi-layer product (1) according to any previous claim,

characterised in that it comprises in detail at least the following steps: a) a first step during which said first plastic material (Mi) intended to form a first layer (10; 11) is cast in said first half shell (20; 21) of said first mould (2)

b) a second step during which said junction element (12) is firstly positioned over said first half shell (20; 21) of said mould (2) and then said at least one second half shell (21) is lowered, said second half shell (21) locking all the outline of said junction element (12) on said first half shell (21) and pushing it towards said material (Ms), in the process of expansion, to which it is intended to bind,

c) a third step during which a second material (Ms) is cast in said first half shell (21) for the creation of a second layer (11) overlying said first layer (10; 11), said material (M2) substantially covering the upper face (121) of said junction element (12).

d) a fourth step of closing said mould (2) by means of said cover (22), said cover (22) defining final shape and outline of said at least two overlapped layers (10, 11) of said product (1).

9. Forming process of a multi-layer product (1) according to the previous claim,

characterised in that

the moulding of further intermediate layers (1 1) overlapped to said second layer (11) overlying said first layer (10; 11), requires the use of a corresponding half shell (21) couplable to the half shell (21) immediately below subsequent to interposition between said two half shells (21) of a corresponding junction element (12) and the casting in said corresponding half shell (21) of the specific moulding material (Ms) of the corresponding of said intermediate layers (1 1).

10. Forming process of a multi-layer product (1) according to any previous claim,

characterised in that said multi-layer product (1) formed is a multi-layer sole (1) for shoes.

11. Forming process of a multi-layer product (1) according to the previous claim,

characterised in that said first (10; 11) and second (1 1) overlapped layers form respectively the tread (10) and an upper intermediate layer (1 1) of said sole (1).

12. Forming process of a multi-layer sole (1) according to any claim from 10 onwards,

characterised in that said first (10; 11) and second (11) overlapped layers form two overlapped intermediate layers (11) of said sole (1), said multilayer sole (1) comprising more of two overlapped layers.

13. Forming process of a multi-layer sole (1) according to any claim from 10 onwards,

characterised in that an upper of a shoe is made to adhere directly on said sole (1), said upper being fitted on a last and acting as a cover (22) of said mould (2).

14. Multi-layer sole (1) for shoes comprising at least two overlapped layers (10, 11) of plastic materials (Mi, Ms) cast in a mould (2) according to the forming process of one or more of the claims 1 to 13,

characterised in that a junction element (12) is interposed between a layer (10) of said sole (1) and that (11) immediately overlying, said junction element (12) being made of material compatible or made compatible with the material (Mi) of said first layer (10) and the material (Ms) of said overlying second layer (11).

15. Multi-layer sole (1) according to the previous claim,

characterised in that said junction element (12) is a membrane of synthetic material, said membrane (12) being sufficiently thin so as to be imperceptible between said overlapped layers (10, 11).

16. Multi-layer sole (1) according to the previous claim,

characterised in that said membrane (12) is a membrane of plastic material or graphene or any other known material suitable for the purpose.

17. Multi-layer sole ( 1 )^' according to claim 13 ,

characterised in that said junction element (12) is a sheet (12) of natural material externally coated with adhesive substances and binders that make it compatible with said materials (Mi, Ms) of said overlapped layers (10, 11).

18. Multi-layer sole (1) according to the previous claim,

characterised in that said sheet (12) of natural materials is a sheet made of hide or cork or cardboard or textile fibres or similar materials, said sheet (12) having such a thickness as to remain visible between said at least two overlapped layers (10, 1 1) of said sole (1).

19. Multi-layer sole (1) according to any claim from 13 onwards,

characterised in that said at least two overlapped layers (10, 1 1) consist of, respectively, a bottom provided with a tread (10) and an overlying intermediate layer (11) for connection to an upper.

20. Multi-layer sole (1) according to the previous claim,

characterised in that it comprises multiple intermediate layers (1 1) overlapped to each other.

21. Multi-layer sole (1) according to any claim from 14 onwards,

characterised in that said two or more overlapped layers (10, 11) may have thicknesses or be qualitatively and/or aesthetically similar or different to each other.

22. Multi-layer sole (1) according to any previous claim,

characterised in that it comprises recesses and or lightening grooves.

23. Mould for forming a multi-layer product (1) according to one or more of the claims 14 to 22 and according to the procedure of claims 1 to 13 comprising:

at least: - a base (20) comprising at least a cavity (200) for the moulding of a first layer (10) of said product (1)

- at least an intermediate ring (21) defining with said base (20) a moulding chamber (211) of- at least one second layer (1 1) of said product (1), overlapped to the first

- at least one cover (22) for closing said mould (2), characterised in that said cover (22) comprises a shaped inner profile

(220) adapted to press against said sole (1) before the complete polymerisation thereof, modelling the shape of at least said second layer (11).

24. Mould (2) according to the previous claim,

characterised in that one or more thrust members (221, 222) may be provided on said inner profile (220) of said cover (22), said thrust members (221, 222) being capable of pressing on the material (Ms) of the second layer (11) capable, in turn; of pressing on the underlying material (Mi) of the first layer (10) pressing and distributing it also towards the zones that are narrower and more difficult to reach of said cavity (200) of the base (20) of the mould (2).

25. Mould (2) according to the previous claim,

characterised in that said thrust members (221 , 222) consist of one or more bosses (222) specially obtained in the front convex stretch of said profile (220) of said cover (22).

26. Mould (2) according to any previous claim from 24 onwards,

characterised in that said cover (22) comprises one or more "projections"

(221) suitable for defining recesses and/or lightening grooves on at least one of said layers (10, 1 1) of said sole (1), said projections also being able to act as thrust members (221).

27. Mould (2) according to any previous claim from 24 onwards,

characterised in that it comprises multiple intermediate rings (1 1) superimposable and closable one on the other.

28. Mould (2) according to any previous claim from 23 onwards,

characterised in that said cavity (200) of said base (20) may be a single cavity (200) or be divided into multiple separate portions.