Sole structure for a shoe

Abstract

The invention relates to a sole structure (1) for a shoe, comprising: a sole (2) having a lower portion including a lower surface (6) adapted for ground contact, and an upper portion extending from the lower portion and which includes at least one shock-absorbing portion (5), and at least one stabilizing element (3) constrained to the at least one shock-absorbing portion (5), wherein the at least one shock-absorbing portion (5) is made of a foam material obtained by means of a fluid in supercritical state, wherein the at least one stabilizing element (3) has at least one exposed surface (8) facing from the at least one shock-absorbing portion (5), and wherein the at least one stabilizing element (3) has density greater than the density of the at least one shock- absorbing portion (5).

Description

SOLE STRUCTURE FOR A SHOE***DESCRIPTIONField of the InventionThe present invention relates to the field of shoes and, in particular, relates to a sole structure for a shoe.State of the artGenerally speaking, a footwear article comprises a sole structure placed below the footwear article when the latter is in use arrangement and adapted to support a user's foot by allowing the user's weight to be discharged to the ground while allowing stresses transmitted to the foot by the ground to be mitigated, and an upper assembly which is placed above and wraps around the foot and is joined to the sole structure which, in turn, may be monolithic, meaning that it is made in one piece, or may comprise a tread joined to a midsole.In the case of tread joined to the midsole, the former is adapted for ground contact while the midsole is interposed between the tread and the upper assembly, wherein the tread generally consists of a relatively compact material such as rubber or thermoplastic polyurethane (TPU) with density greater than 1 g / cm3, and the midsole consists of a relatively foamed material such as polyurethane (PU) or ethylene vinyl acetate (EVA) with density less than 1 g / cm3.In general, a material can expand through so-called chemical route by using foaming agents that generate, possibly by a heat-facilitated chemical reaction, gas bubbles that are then trapped in the finished piece, the foaming agents being inserted into the mixture that makes up the material or, alternatively, the material can be expanded through so-called physical route by using a supercritical fluid.In the specific case of footwear articles, generally speaking, in order to obtain by physical expansion the desired midsole, it is preferred to first mold asemi-finished product with limited expansion, starting in particular from a mixture in which foaming agents are present (first chemical expansion), and then subject the semi-finished product to additional expansion in a designated container (e.g., an autoclave), inside which the fluid, typically a gas such as nitrogen (N2) or carbon dioxide (CO2) (second physical expansion), is inserted.Therefore, the size of the semi-finished product after the first expansion is smaller than that the midsole reaches at the end of the second expansion.In detail, the aforesaid fluid is brought to a supercritical condition, i.e. , to relatively high pressure and temperature values, so that it is in a phase almost intermediate between liquid and gas.In the supercritical condition, the fluid becomes highly soluble and is able to easily penetrate the semi-finished product.Subsequently, the pressure is lowered, thus returning the fluid, particularly that which has penetrated the semi-finished product, to the gaseous phase with the formation of gas bubbles within the semi-finished product, thus causing the latter to expand.To sum up, a semi-finished product that can be defined "partially expanded" is first obtained through the aforesaid so-called chemical route, thanks to the use of a "chemical" foaming agent typical of traditional molding processes, for example EVA, which releases gas during the molding step itself, the semi-finished product is subsequently "super-expanded" by means of a "mechanical" expanding agent (the fluid in supercritical condition) thus obtaining the desired midsole.As an alternative to the above-described process (first process) for making a midsole that involves a first partial expansion and a second superexpansion, the known art provides a second process in which a fluid in supercritical condition is directly combined with the initial mixture via appropriate injectors before molding the midsole, i.e. while the mixture is still in the extruder that guides it to the injector which directs it into a mold.According to the aforesaid second process, the midsole comes out of themold already super-expanded, and this expansion has been achieved only by means of a mechanical agent (the fluid in supercritical condition).In accordance with the above, to make a midsole, the known art also provides processes that employ chemical foaming agents only, although operating by chemical route only is not currently a preferred solution due to the drawbacks involved, as will appear in more detail below.It should also be specified that, in the case of a midsole obtained by the aforesaid first process, an amount of chemical foaming agents equal to a maximum of 5% of the amount of chemical foaming agents used in processes that operate an expansion solely by chemical route is generally used for the initial chemical expansion.EP 580777 B1 describes the making of a midsole both through the aforesaid first process, specifically in paragraphs

[0021] -

[0022] , and through the aforesaid second process, specifically in paragraphs

[0029] -

[0039] ,Document WO 2022 / 157582 A1 describes a footwear article comprising a sole structure having a tread and a midsole that is substantially a shockabsorbing element, wherein the midsole is obtained by means of a fluid in supercritical condition (supercritical state).In general, the use of a fluid in supercritical condition to obtain the expansion of a polymer material results in a midsole with a highly uniform microcellular structure, with gas bubbles distributed with good uniformity within the polymer material and having smaller size than the size of gas bubbles that are formed by foaming processes using only chemical agents. The above characteristics promote both high elastic recovery of the midsole, which in practice returns to the user part of the effort he / she makes thus reducing their fatigue, and a high absorption of stresses that would otherwise burden the user's foot.Disadvantageously, however, a midsole of the type considered above is not without drawbacks, including causing the user to feel unstable.Indeed, since the relatively low density of this midsole reduces themodulus of elasticity, even if the midsole improves the absorption of stresses acting on the foot, it exhibits relatively high deformability to both orthogonal stresses and shear stresses, which results in the aforesaid feeling of instability.Figure 1 shows, in magnified manner, the orthogonal and transverse deformation experienced by a generic sole structure comprising a tread and a midsole at a generic cross section when subjected to a stress having normal component F1 and tangential component F2 or F3.Considering an infinitesimal portion of midsole, such as a cube of side Zo, called 0 an infinitesimal angular deformation caused by the shear stress T to which this portion is subjected, the following relation applies:T=G y, where y=tg 0=Ay / Zo.In other words, for the same shear stress (T), there is greater tangential deformation (Ay) when G is smaller, where G is the tangential modulus of elasticity.The same reasoning can be made when considering the normal modulus of elasticity (or Young's modulus) E.Indeed, considering the aforesaid infinitesimal portion of midsole, called £ its infinitesimal axial deformation (measured as the ratio of the change in length AZ to the rest length Zo) caused by the normal stress o to which this portion is subjected, the following relation applies:O=E'£, where£ = AZ / ZoSimilarly to the above, with the same compression stress (o), there is greater deformation (£) when E is lower, where E is the normal modulus of elasticity.Since the deformability of the midsole, and thus the aforesaid feeling of instability, is the higher the lower the value of the tangential G and normal Eelasticity moduli, and the latter are (as shown by experimental evidence) directly proportional to the density p according to an equation of the type: y=C*pnwhere p is the density, while C and n are two constants that depend on the material and in particular its microstructure, it can be stated that a material with higher density has higher tangential modulus of elasticity and a higher normal modulus of elasticity and, as a result, under the same applied stress, has less deformation and causes lower feeling of instability as well.Thus, in general, expansion by means of a fluid in supercritical conditions allows high uniformity of gas bubbles to be obtained compared to the relative non-uniformity of gas bubbles generated during chemical foaming. In addition, expansion by means of a fluid in supercritical condition makes it possible to obtain gas bubbles with a smaller size, and lower density of the expanded material, than the bubble size and density of the expanded material obtained by chemical foaming.In this regard, it should also be noted that regions with larger gas bubbles are structurally weaker than those with smaller gas bubbles because they offer less mechanical resistance to bending and twisting. Similarly, substantially with the same bubble size, regions with higher bubble concentration are structurally weaker than regions with lower bubble concentration.Moreover, for a manufactured article, in this case a midsole, density is inversely proportional to the expansion ratio, i.e., the ratio between final size, i.e., after expansion, and initial size, i.e., within the mold.In detail, we can talk about foaming ratio in the process or the material known as IP EVA (injection-phylon EVA or injection-molded EVA) in which chemical expansion takes place outside the mold when the mold is opened and the manufactured article comes out "exploding" (in this case, only a chemical expansion is involved), and in processes with physical expansion in accordance with the aforesaid first process, essentially due to the fact that there is no mold to somehow "limit" the expansion to keep the manufactured article within certaindimensional tolerances.Conversely, in cases where expansion is provided almost exclusively within the mold, such as in Pll or CM EVA (compression molded EVA), or in the case of physical expansion through the aforesaid second process, it makes no sense to speak of initial and final dimensions because they are nearly coincident.In general, in accordance with the above, the terms IP EVA and CM EVA mean both a process and the material obtained by that process.It should be added that in the case of foaming by solely chemical route, due to the aforesaid unevenness of gas bubbles, it may be risky to decrease the density below 0.5 g / cm3, especially in the aforesaid IP EVA processes.It should also be added that a high expansion ratio typical of sole structures equipped with a midsole expanded by means of a fluid in supercritical condition necessarily amplifies any sizing errors, which increase the percentage of discarded product.In this regard it should be mentioned that, in general, a manufactured article must meet certain dimensional tolerances, and that the dimensional error (or tolerance) is directly proportional to the expansion ratio. It is therefore not uncommon to find manufactured articles that are too long or too short, too wide or too narrow, their number increasing as the expansion ratio increases.Disadvantageously, therefore, in sole structures according to known art described above, it is difficult to keep dimensional tolerance within certain values. For example, if, in order not to affect the aesthetics or functionality of a shoe, a tolerance of 1 mm for the length of the sole or midsole is established, as the expansion ratio increases, the detected tolerance may instead increase up to 2 mm, for example. This means that it is no longer possible to restrain the tolerance below 1 mm, consequently increasing the number of soles or midsoles that are discarded.Summary of the inventionThe technical problem underlying the present invention was to provide asole structure having characteristics able to overcome one or more of the drawbacks mentioned above with reference to the known art.According to the invention, the aforesaid problem is solved by a sole structure for a shoe, comprising a sole having, when the shoe is in use arrangement, a lower portion including a lower surface adapted for ground contact, and an upper portion extending from the aforesaid lower portion and which includes at least one shock-absorbing portion, and at least one stabilizing element constrained to the aforesaid sole at the aforesaid at least one shock-absorbing portion, wherein the aforesaid at least one shock-absorbing portion is made of a foam material obtained by means of a fluid in supercritical state, wherein the aforesaid at least one stabilizing element has at least one exposed surface facing from the aforesaid at least one shock-absorbing portion, and wherein the aforesaid at least one stabilizing element has density greater than the density of the aforesaid at least one shock-absorbing portion.According to the invention, the aforesaid sole structure is capable of satisfactorily absorbing the stresses acting on a user's foot, while providing a high degree of stability during walking.Preferably, the difference between the density of the aforesaid stabilizing element and the density of the aforesaid shock-absorbing portion is at least 10%, more preferably at least 20%, even more preferably at least 30%.Preferably, the aforesaid at least one stabilizing element has hardness greater than the hardness of the aforesaid at least one shock-absorbing portion.Preferably, the difference between the hardness of the aforesaid stabilizing element and the hardness of the aforesaid shock-absorbing portion is at least 10 points, more preferably at least 20 points.Preferably, the aforesaid at least one stabilizing element has density between 0.23 and 0.60 g / cm3, more preferably between 0.30 and 0.50 g / cm3.Preferably, the aforesaid at least one stabilizing element has hardness between 45 and 70 Asker C, more preferably between 50 and 60 Asker C.Preferably, the aforesaid at least one stabilizing element is made of cork, a polymer material or a foam material obtained by means of a fluid in supercritical state, wherein said material is preferably ethylene vinyl acetate (EVA) or polyurethane (PU).Preferably, the aforesaid at least one exposed surface of the aforesaid at least one stabilizing element faces from an upper surface and / or a side surface of the aforesaid at least one shock-absorbing portion.Preferably, the aforesaid at least one stabilizing element comprises at least two portions having different hardness between them, wherein more preferably the hardness of the aforesaid at least one stabilizing element is greater at the foot inside and lesser at the foot outside of the aforesaid sole and / or wherein the hardness of the aforesaid at least one stabilizing element is greater at the hindfoot and lesser at the forefoot of the aforesaid sole.In accordance with the invention and the above, more than one stabilizing element can also be provided, therefore stabilizing elements having different hardness among them can be provided, possibly according to the preferences set forth above with reference to a stabilizing element having two or more portions having different hardness among them. Furthermore, in case more than one stabilizing element is provided, each of them can have a different thickness from the others. In particular, stabilizing elements of different thicknesses can be provided, which are obtained by blanking EVA sheets normally available on the market.Preferably, the aforesaid at least one shock-absorbing portion has density between 0.10 and 0.25 g / cm3, more preferably between 0.12 and 0.20 g / cm3Preferably, the aforesaid at least one shock-absorbing portion has hardness between 30 and 50 Asker C, more preferably between 35 and 45 Asker C.Preferably, the aforesaid at least one shock-absorbing portion is made of ethylene vinyl acetate or polyurethane.Preferably, the aforesaid at least one shock-absorbing portion and the aforesaid at least one stabilizing element are made of the same material, more preferably ethylene vinyl acetate.Preferably, the aforesaid at least one shock-absorbing portion has an upper surface with curved section.Preferably, the ratio of the thickness of the aforesaid at least one stabilizing element to the usable thickness of the aforesaid at least one shockabsorbing portion is between 0.3 and 0.6, wherein "usable thickness" means the thickness that provides the greatest contribution to the shock absorption of the sole structure, being calculated net of tread reliefs which inevitably reduce their contribution over time, as they are worn due to abrasion caused by the ground, and net of any midsole ends that wrap the upper assembly below and whose contribution is almost irrelevant.It should be noted that, preferably, the aforesaid thickness of the at least one stabilizing element remains almost constant from the hindfoot toward the forefoot, however, the possibility of providing a variable thickness or multiple stabilizing elements having different thickness among them as previously stated is not excluded.In accordance with the invention, the aforesaid lower portion and the aforesaid upper portion of the aforesaid sole may be made in one piece and thus be integral with each other, or alternatively, the aforesaid sole may comprise a tread and a midsole constrained to each other, wherein the aforesaid tread substantially coincides with the aforesaid lower portion and the aforesaid midsole substantially coincides with the aforesaid upper portion of the sole.According to the invention, the aforesaid problem is further solved by a process of making the aforesaid sole structure, comprising the steps of: providing at least one first blank of a stabilizing element, whereinpreferably the aforesaid at least one first blank is made of cork, a polymer material or a foam material obtained by means of a fluid in supercritical state, wherein, more preferably, the aforesaid material is preferably ethylene vinyl acetate or polyurethane, providing at least one second blank of a shock-absorbing portion, made of a foam material obtained by means of a fluid in supercritical state (superexpanded blank), inserting the aforesaid at least one second blank of the shock-absorbing portion or super-expanded blank, the aforesaid at least one first blank of the stabilizing element and possibly a tread into a mold of a shoe sole, so that the aforesaid at least one first blank of the stabilizing element has at least one exposed surface facing from the aforesaid at least one second blank of the shock-absorbing portion, co-molding together the aforesaid at least one second blank of the shock-absorbing portion, the aforesaid at least one first blank of the stabilizing element and possibly the aforesaid tread.Preferably, the aforesaid fluid in supercritical state is nitrogen (N2).Preferably, the aforesaid at least one second blank, so-called superexpanded, is obtained by expanding, up to 4-4.5 times, at least one initial blank of the shock-absorbing portion having thickness of about 2 cm.Preferably, the aforesaid at least one initial blank of the shock-absorbing portion is made of IP EVA.Preferably, the aforesaid at least a first blank of the stabilizing element is made of CM EVA or lP EVA.In accordance with the invention, a cost-effective sole structure is thus obtained through a reliable process that advantageously employs known techniques.In accordance with the above, therefore, the present invention provides embodiments of the present sole structure in which both the aforesaid shockabsorbing portion and the aforesaid stabilizing element are made of a foammaterial, possibly the same one, which is obtained by means of a fluid in supercritical state, and embodiments in which only the aforesaid shockabsorbing portion is made of a foam material which is obtained by means of a fluid in supercritical state whereas the aforesaid stabilizing element is obtained without using a fluid in supercritical state.In each case, the aforesaid shock-absorbing portion and the aforesaid stabilizing element are made separately from each other and are subsequently joined together with a permanent constraint, wherein the individual realization of the shock-absorbing portion and the stabilizing element determines in their union, and particularly at the constraint area, an interface between the mutually contacting surfaces. The aforesaid interface constitutes a discontinuity in the sole structure in accordance with the present invention, which is basically always found in the same sole structure, i.e. in the finished product.Brief description of the figuresFurther characteristics and advantages of the invention will be more evident from the review of the following description of some preferred, but not exclusive, embodiments depicted for illustration purposes only and without limitation, with the aid of the attached drawings, wherein:- Figure 1 shows schematically and in magnified manner the normal deformation and transverse deformation experienced at a generic cross section by a generic sole structure comprising a tread and midsole, according to known art, when subjected to a stress having normal component F1 and tangential component F2 or F3;- Figure 2 schematically shows a bottom view of a sole structure comprising a sole having a tread and a midsole or shock-absorbing portion, according to the present invention;- Figure 3 schematically shows a top view of the sole structure of Figure 2 in which a stabilizing element combined with the aforesaid sole is visible at the aforesaid midsole or shock-absorbing portion;- Figure 4 schematically shows a cross-sectional view of the solestructure of Figures 2 and 3, which is taken where the aforesaid tread and the aforesaid midsole are simultaneously present;- Figure 5 schematically shows a cross-sectional view of the sole structure of Figures 2 and 3, which is taken where the aforesaid tread and the aforesaid midsole are simultaneously present, according to an embodiment variant of the invention;- Figure 6 schematically shows a comparison of an initial blank and a so- called super-expanded blank obtained from the aforesaid initial blank of the aforesaid shock-absorbing portion, as well as a blank of the aforesaid stabilizing element, of the sole structure of Figures 2 and 3;- Figure 7 schematically shows the parameters a), b), d) and e) acquired by a baropodometric platform during a test performed on a sample of nine people (users), with a shoe comprising a stabilizing element according to the present invention (shoe 2), and with a similar shoe without the stabilizing element (shoe 1 );- Figure 8 is a graph illustrating the trends superimposed of the parameter a) of Figure 7 (area of the ellipse resulting from all displacements of the center of pressure--COP), of the users of the aforesaid shoe 1 and the aforesaid shoe 2;- Figure 9 shows, in a respective table, the mean values of parameter c) related to the mean center of pressure (COP) displacement velocity, as a result of an acquisition similar to that related to the aforesaid parameters of Figure 7, for the right foot, RH - col. "E," and for the left foot, LH - col. "F" for each user, as well as the mean value RH+LH- col. "G," for each user.Detailed description of the inventionReferring to the example in Figures 2, 3 and 4, a sole structure for a shoe according to the present invention is generally denoted by 1.The sole structure 1 essentially comprises a sole 2 and a stabilizing element 3 combined with the sole 2 which, in accordance with the aforesaid figures, comprises a tread 4 and a midsole or shock-absorbing portion 5constrained to each other, in particular in which the tread 4 is joined at the bottom to the midsole, i.e. , at a lower surface 5a of the latter, so that in shoe use arrangement of the sole structure, the lower surface of the tread 4 contacts the ground, although the possibility of providing a one-piece sole, with tread and midsole or shock-absorbing portion integral with each other, is not excluded.In this regard, it can therefore be said that, generally speaking, in use arrangement, the sole 2 comprises a lower portion that includes a lower surface 6 adapted for ground contact, and an upper portion which extends from the aforesaid lower portion and which includes a midsole, i.e. the aforesaid shockabsorbing portion 5 to which the stabilizing element is constrained 3.In practice, in a shoe, the shock-absorbing portion 5 is interposed between the tread or in any case between the lower surface adapted for ground contact and an upper assembly with which the sole structure according to the invention is intended to be combined.In detail, the tread 4 comprises a plurality of portions 7 not connected to each other, although it is not excluded that a tread comprising portions connected to each other may be provided to form, in practice, a single portion that can extend over all or part of the lower surface of the midsole which, in turn, is made as a bas-relief with respect to the tread 4 so that in use arrangement it does not touch the ground, except to a limited extent.In any case, the aforesaid tread is preferably made of polymer material, more preferably rubber or thermoplastic polyurethane, with hardness preferably between 45 and 65 Shore A.With regard again to the aforesaid shock-absorbing portion, as an alternative to what shown in the aforesaid figures in which it extends from the forefoot area to the hindfoot area, it must be said that a shock-absorbing portion limited, for example, to either the hindfoot or the forefoot, can be provided, or more than one shock-absorbing portion can be provided, for example a shockabsorbing portion in the forefoot and one in the hindfoot, each with its own stabilizing element constrained thereto.Therefore, the aforesaid stabilizing element may also extend substantially along the entire length of the aforesaid sole, as shown in the example of the aforesaid figures, or it may only extend along part of the sole, being for example limited to the forefoot or the hindfoot, more than one stabilizing element being possible to provideIn accordance with the invention, the stabilizing element 3 has an exposed surface 8 facing from the shock-absorbing portion 5.In practice, in the example of the aforesaid figures, the shock-absorbing portion 5 wraps around a large part of the stabilizing element 3 which has only its own upper surface not wrapped by the shock-absorbing portion 5, which is therefore exposed and intended to face toward the upper assembly of the shoe, in particular is intended to contact the insole of the upper assembly.In any case, in the present sole structure, a stabilizing element may be provided with a different surface not wrapped by the shock-absorbing portion and therefore exposed, i.e. which faces from the shock-absorbing portion, such as a side surface, or a front surface or even a rear surface, as described in more detail below.Generalizing the above it can be said that, in accordance with the present invention, the aforesaid stabilizing element, which has a substantially rectangular section, has at least one exposed surface facing from an upper surface 5b and / or from a side surface 5c of the aforesaid shock-absorbing portion.In accordance with the invention, the stabilizing element 3, which preferably is made of cork, a polymer material or a foam material obtained by means of a fluid in supercritical state, wherein more preferably the aforesaid material is ethylene vinyl acetate or polyurethane, has density greater than the density of the shock-absorbing portion 5 which is made of foam material obtained by means of a fluid in supercritical state.In case both the aforesaid stabilizing element and the aforesaid shockabsorbing portion are made of a foam material obtained by means of a fluid insupercritical state, the aforesaid density difference can be maintained by appropriately setting the density of the respective starting blanks, or by calibrating the expansion process by means of the fluid in supercritical state, such as by decreasing its duration to increase the final density.This embodiment is advantageous because the interface between the stabilizing element and the shock-absorbing portion is made up of materials having an expanded structure that is more “similar” to each other. In particular, it should be noted that, in this case, the surface of the stabilizing element does not have, or has in a limited way, the typical "film" (which is stiffer than the rest of the material of which the stabilizing element is made) that is obtained instead when it is made, for example, of CM EVA. Thanks to this, it is possible to achieve a reduction in the noise that occurs in certain sole structures during use and that is caused by the “vibration” of aforesaid "film" due to the stresses acting on the sole structure. In order to mitigate or eliminate such vibrations and the resulting noise that can be a source of annoyance to the user and / or those around him or her, the thickness of this film has to be partially or completely decreased. In case of manufacturing by CM EVA, the film is formed at the parts of the stabilizing element that directly contact the mold walls and practically results in a sharp decrease in gas bubbles within the polymer material. In the case of expansion achieved by means of a fluid in supercritical state, however, this decrease in gas bubbles occurs to a lesser extent.Particularly in the case of a first chemical expansion and a second expansion by fluid in supercritical state, the smaller decrease in gas bubbles occurs because the so-called super expansion does not occur within a mold.In the case of expansion by supercritical state fluid alone, the smaller decrease in gas bubbles occurs because, while expanding within a mold, the presence already at the start of a single phase consisting of the fluid in supercritical state and the polymer material allows a more homogeneous distribution of gas bubbles than would be the case in chemical expansion (CM EVA) where there are two distinct phases at the start: polymer material on oneside and gas produced by the chemical foaming agent on the other.In detail, the stabilizing element 3 has density preferably between 0.23 and 0.60 g / cm3, more preferably between 0.30 and 0.50 g / cm3.Furthermore, the stabilizing element 3 has hardness preferably between 45 and 70 Asker C, more preferably between 50 and 60 Asker C which, preferably, is greater than the hardness of the shock-absorbing portion 5.It should be particularly said that the difference between the hardness of the stabilizing element and the hardness of the shock-absorbing portion is preferably at least 10 points, more preferably at least 20 points.In accordance with the invention, a stabilizing element of the aforesaid type can also be provided, which comprises at least two portions having different hardness between them, this embodiment not being illustrated in the figures.In a first case of stabilizing element comprising at least two portions having different hardness between them, it should be said that a stabilizing element with higher hardness at the foot inside and lower hardness at the foot outside of the aforesaid sole is preferably provided. This way, the foot support can be increased at the inside of the foot, where, due to its own anatomy, the yielding property can be greater thus resulting in a tendency to pronate (indeed, during walking the foot rests on the outside).In a second case of stabilizing element comprising at least two portions having different hardness between them, as an alternative or in combination with the aforesaid first case, it should be said that a stabilizing element with higher hardness at the hindfoot and lower hardness at the forefoot of the aforesaid sole is preferably provided. This embodiment allows the feeling of "falling backward," which is also responsible for the sense of instability of some known sole structures, to be reduced or even eliminated.If more than one stabilizing element is provided, as described above, stabilizing elements having different hardness between them can be provided, possibly according to the preferences set forth above with reference to astabilizing element having two or more portions with different hardness between them. Furthermore, in case more than one stabilizing element is provided, each of them can have a different thickness from the thickness of the other stabilizing elements. In particular, stabilizing elements of different thicknesses can be provided, which are obtained by blanking EVA sheets normally available on the market, instead of making a mold intended for forming a single stabilizing element.Still regarding the shock-absorbing portion 5 it should be said that it is preferably made of ethylene vinyl acetate or polyurethane.Moreover, the shock-absorbing portion 5 has density preferably between 0.10 and 0.25 g / cm3, more preferably between 0.12 and 0.20 g / cm3.Furthermore, the shock-absorbing portion 5 has hardness preferably between 30 and 50 Asker C, more preferably between 35 and 45 Asker C.In accordance with the invention and the above, it should be added that, preferably, the difference between the density of the aforesaid stabilizing element and the density of the aforesaid shock-absorbing portion is at least 10%, more preferably at least 20%, even more preferably at least 30%.In accordance with the above it should be also noted that, in a particularly preferred embodiment of the invention, the aforesaid shockabsorbing portion and the aforesaid stabilizing element are made, albeit with different densities, of the same material, preferably ethylene vinyl acetate. This is advantageous because it allows the shock-absorbing portion and the stabilizing element to be joined in a more stable and durable manner, without the need to use chemicals, such as so-called cleaners, to prepare the respective surfaces for gluing. Furthermore, the sorting of materials at the end of the shoe life cycle is advantageously simplified.In accordance with a further preferred characteristic of the invention not shown in the examples of the aforesaid figures, it should be said that the aforesaid shock-absorbing portion may have an upper surface with curved section which, there is to be said, is compatible with the characteristic of havingthe aforesaid stabilizing element preferably with substantially rectangular section.In case of curved section of the upper surface of the aforesaid shockabsorbing portion, the point considered to define the usable thickness of the same shock-absorbing portion is basically taken at the centerline.In this regard, the ratio of the thickness of the stabilizing element 3 to the usable thickness of the shock-absorbing portion 5 is preferably between 0.2 and 0.8 and remains almost constant from the hindfoot toward the forefoot, even though embodiments where the thickness of the stabilizing element has a higher value at the hindfoot and a lower value at the forefoot are not excluded. This occurs, for example, in sole structures that have a significant difference in overall thickness between the forefoot and hindfoot.The aforesaid usable thickness is calculated as follows:- starting from the lower surface 5a of the shock-absorbing portion 5 in contact with the tread 4 to the upper surface 5b of the shock-absorbing portion 5, thus in the case of separate tread and midsole; or- starting from the lower surface of the shock-absorbing portion net of the reliefs constituting the tread to the upper surface of the shock-absorbing portion, in the case of a sole comprising tread and midsole in one single indivisible piece.It should be added that, still regarding the dimensional aspects of the present sole structure, depending on actual requirements, the size of the cross section of the stabilizing element 3 can be set at any point, so that the corresponding section of the shock-absorbing portion 5 has as uniform a thickness as possible.In other words, wherever possible, an attempt is made to minimize the difference between the distance, denoted by s1, between the stabilizing element 3 and the side surface 5c of the shock-absorbing portion 5, and the distance, denoted by s2, between the stabilizing element 3 and the lower surface 5a of the shock-absorbing element 5. This is advantageous in thatallows greater uniformity of the shock-absorbing portion 5 during the expansion process by fluid in supercritical state.It should also be noted that the thickness of the stabilizing element 3 is selected in proportion to the total thickness of the shock-absorbing portion 5 and that, preferably, it is between 10% and 60% of the total thickness of the shock-absorbing portion 5.In this regard it should be said that, from the implementation point of view, the shock-absorbing portion 5 and the stabilizing element 3 are made separately and then joined together, as described below.Specifically, in accordance with the above and with reference to the example in Figure 6, the sole structure according to the present invention is made by a process that comprises the steps of: providing at least one first blank of a stabilizing element preferably made of polymer material, which in the example of Figure 6 is denoted by 23, providing at least one second blank of a shock-absorbing portion made of a foam material obtained by means of a fluid in supercritical state (superexpanded blank), which in the example of Figure 6 is denoted by 25, inserting the at least one second blank of the shock-absorbing portion 25 or super-expanded blank, the at least one first blank of the stabilizing element 23 and possibly a tread into a mold of a sole for shoes, so that the aforesaid at least one first blank of the stabilizing element has at least one exposed surface facing from the aforesaid at least one second blank of the shock-absorbing portion, co-molding together the at least one second blank of the shockabsorbing portion 25, the at least one first blank of the stabilizing element 23 and possibly the aforesaid tread.The shock-absorbing portion and the stabilizing element are then joined by thermoforming, even though they can be joined also by, or only by, gluing.In this regard, it should be noted that thermoforming promotes adhesion between the shock-absorbing portion and the stabilizing element by promotingfurther crosslinking of the polymer material, particularly in case they are both made of EVA.In any case, it should be pointed out that the stabilizing element is permanently constrained to the shock-absorbing portion. This is advantageous because it prevents relative movements between stabilizing element and shockabsorbing portion, which could cause noise and / or rubbing between the respective contact surfaces resulting in wear and / or breakage.Where a tread is present, it can be joined to the shock-absorbing portion at the bottom by thermoforming, as set forth above, and / or by gluing.Therefore, in case a thermoforming process is carried out, the tread, shock-absorbing portion and stabilizing element can be joined together in a single step.Regarding in detail the making of the aforesaid blanks, it should be said that the so-called super-expanded blank (second blank) is preferably formed by expanding, up to 4-4.5 times, an initial blank of the shock-absorbing portion denoted by the numeral reference 35, having a thickness of about 2 cm.In this regard, the expansion of the aforesaid initial blank of the shockabsorbing portion 35 is achieved by using nitrogen (N2) as a fluid in supercritical state, whereas the initial blank of the shock-absorbing portion 35 is made of IP EVA with a much smaller amount of chemical foaming agent than the amount of chemical foaming agent used in a molding process of a "finished" sole, i.e. , a sole that does not undergo subsequent "physical" expansion, the aforesaid amount being at most 5%. Actually, it is necessary to operate with liquefied material instead of pellets (as is the case with CM EVA) in order to obtain a homogeneous blank.Therefore, the aforesaid shock-absorbing portion, in accordance with the present invention, is preferably made by means of a first chemical expansion and a subsequent second physical expansion, although the possibility of providing only a physical expansion by means of a fluid in supercritical state is not excluded.The blank of the stabilizing element 23 (first blank) is preferably made of IP EVA or CM EVA starting from EVA pellets with a chemical foaming agent which are placed inside a mold that has the final shape. The latter process is more economical than IP EVA due to the lower cost of the mold and the lower cost of the molding machines, and, compared to IP EVA, it also makes it rather easier to form differentiated hardness zones. The stabilizing element can also be made by using an EVA blank formed by blanking a sheet of EVA normally available on the market.To sum up, in accordance with an embodiment of the present invention, it should be said that the aforesaid stabilizing element is molded almost already of the final size, that is, it comes out of the mold and is not subjected to further expansion after a so-called chemical expansion, although there is the possibility, in accordance with a variant embodiment of the invention, to make the aforesaid stabilizing element in an expanded material obtained by means of a fluid in supercritical state, in accordance with the above to which reference is made.The aforesaid shock-absorbing portion, on the other hand, is preferably made through an initial chemical expansion (which can be exactly the same as the chemical expansion implemented to make the aforesaid stabilizing element), thus obtaining the aforesaid initial blanks which, subsequently, undergoes a second so-called physical or mechanical expansion through the aforesaid fluid in supercritical state, thus obtaining the aforesaid superexpanded blank. In this case, the shock-absorbing portion has an expansion ratio of about 4-4.5.Specifically, the expansion by means of the fluid in supercritical state takes place in a special container, for example an autoclave at a temperature, for example, of about 120°C, and pressure for example of about 10 bars, for a time for example of two hours (2h), to expand up to 4-4.5 times an initial blank having a thickness of about 2 cm. Therefore, the blank exiting the autoclave, after the temperature and pressure have been restored to ambient conditions,e.g., 20°C and 1 bar, have dimensions equal to the final dimensions or slightly larger. In this regard, its dimensions can be stabilized in a stabilization oven and / or by using templates according to known processes applied to manufactured articles made of IP EVA, for example.Optionally, it is also possible to smooth, e.g., by sanding, any irregularities in the blank coming out of the autoclave or stabilization oven.Alternatively, and in accordance with the present invention, the shockabsorbing portion can be obtained through only one expansion by means of a fluid in supercritical state. In this case it has, at the exit of the mold, dimensions equal to the final dimensions or slightly larger. In this case too, its dimensions can be stabilized in a stabilization oven and / or by using templates according to known processes applied to manufactured articles made of IP EVA, for example.In any case, the aforesaid stabilizing element, which, as mentioned above, has a lower expansion ratio or coefficient than the aforesaid shockabsorbing portion, exhibits less amplification of dimensional tolerances and therefore, advantageously, contributes to reducing the overall dimensional tolerance of the sole structure according to the present invention.In addition to the above unless otherwise stated, what previously set forth in relation to the aforesaid sole structure applies to the aforesaid stabilizing element and the aforesaid shock-absorbing portion in relation to the aforesaid process.The example in Figure 5 shows a sole structure 100 that is very similar to the sole structure 1 described above with reference to Figures 2-4, whose reference numerals are maintained for the corresponding elements and to whose description reference is made, except that the exposed surface of the stabilizing element 3 is a side surface 3c thereof which faces from the side surface 5c of the shock-absorbing portion 5.It should be noted that the section plan A-A depicted in the example in Figure 5, which is perpendicular to the ground in use arrangement, interceptsthe stabilizing element 3 which, as mentioned, has higher density than the density of the shock-absorbing portion 5 and, therefore, this embodiment also overcomes the drawbacks previously mentioned with reference to the known art.Therefore, generally speaking, it can be said that the stabilizing element of the sole structure according to the present invention has a width from foot outside to foot inside, that is, a length in a direction substantially perpendicular to the longitudinal extent direction of the aforesaid sole, thus of the respective shoe and foot of a user, preferably extending at least over half the width of the shock-absorbing portion or extending essentially from the foot inside to the foot outside.It should also be noted that the embodiment of the example in Figure 5 allows the stability of the sole structure according to the present invention to be increased and the yielding properties thereof to be decreased only in predetermined areas, for example at the foot outer or the foot inner.The above has also been demonstrated by studies conducted by the Applicant.Specifically, the Applicant had a shoe according to the invention tested, also identified as "shoe 2," and a similar shoe without the stabilizing element, also identified as "shoe 1".The tests were carried out on a sample of nine people who wore the shoes on a baropodometric platform.For each person, five acquisitions were made with left shoe and five acquisitions were made with right shoe with "shoe 1" and as many with "shoe 2," wherein each acquisition involved a single leg stance lasting twenty seconds to simulate an unipedal posture with the counter-lateral leg flexed at 45°.This simulation represented well the possible difficulty in walking and in particular the muscle fatigue required for holding the position for twenty seconds on a relatively soft surface.Acquisitions were carried out on an initial group of five people whereeach person performed the left-right sequence five times, alternating a two- minute break between each sequence, first with "shoe 1" and, after a five- minute break, repeating the sequence with "shoe 2".A second group of four people reversed the acquisitions by starting with "shoe 2" and then continuing with "shoe 1" following the same pattern.Figure 7 shows an example of the acquisitions of the right shoe (the acquisitions of the left shoe being quite similar), where the platform recorded five parameters in the acquisitions: a) Area of the ellipse resulting from all displacements of the center of pressure - COP. The larger the aforesaid area, the greater the difficulty in maintaining balance. The ellipse is obtained at the area with the highest concentration of points detected by the platform. b) Length of the path of the center of pressure in its displacements during the twenty seconds (this path resembles a ball of yarn). c) Mean velocity of COP displacement: the higher it is, the greater the difficulty (and consequently the effort) in maintaining balance. d) Length of the first axis: highlights the maximum left / right displacement. e) Second axis length: highlights the maximum forward / backward displacement.These five parameters were statistically analyzed by a two-sample T-test to examine whether the mean values of the two independent groups, i.e. , "shoe 1" and "shoe 2," were significantly different from each other.Without going too deep into theory, for a two-tailed test with an alpha level of 0.05 at 89 degrees of freedom (considering 90 values for "shoe 1" and 90 for "shoe 2" you have in fact 90-1 =89 degrees of freedom) the critical value is 1.98698. The difference between the mean values of the areas of the aforesaid ellipse and the difference between the mean values of the second axes showed a T-stat value > critical value: meaning that these values aresignificantly different from each other. In other words, the improvement achieved by "shoe 2" over "shoe 1" is significant.The difference between the mean values of the first axis then showed a T-stat value just below the critical value (specifically, the difference between T- stat and the critical value is less than 10%): this means at least a tendency, albeit less significant than that of the two parameters examined earlier, of "shoe 2" to show a shorter first axis than that of "shoe 1 ".These results make it possible to state that a user of "shoe 1" needs a larger area to stay balanced (ellipse area), as well as larger oscillations (first and second axes). In other words, a user of "shoe 1" encounters more instability than a user of "shoe 2".For completeness, Figure 8 depicts a graph showing, the superimposed trends of the area of the ellipse in the users of "shoe 1" and "shoe 2", and Figure 9 depicts a table showing the mean values of the aforesaid parameter c) related to the mean velocity of COP displacement, for the right foot, RH - col. "E," and for the left foot, LH - col. "F" for each user, as well as the mean value RH+LH- col. "G," for each user.The advantages of the present invention, which have become apparent in the course of the description set forth above, may be summarized by pointing out that a sole structure that is capable of absorbing the stresses acting on a user's foot in a satisfactory manner is provided, while providing a high degree of stability during walking, through a reliable process that advantageously employs known techniques and, therefore, at low cost.A further advantage of the sole structure according to the present invention is that the shock-absorbing portion is made with reduced thickness at the stabilizing element, which thickness, if there were no stabilizing element, would be greater and thus would slow down productivity. Indeed, the process of expanding the shock-absorbing portion, especially when carried out by a first expansion with chemical foaming reagent and a second expansion with fluid in supercritical state (first process according to previously described known art),requires a process time exponentially proportional to the thickness of the manufactured article to be made. By reducing the thickness of the shockabsorbing portion, and more generally its volume, the process time can be reduced, making the aforesaid first process attractive as well. To the present invention, in the embodiments illustrated and described, in order to satisfy contingent and specific needs, a person skilled in the art may make numerous variations and modifications, all of which are included within the scope of protection of the invention as defined by the following claims.

Claims

1. CLAIMS1. Sole structure (1 ) for a shoe, comprising: a sole (2) having a lower portion including a lower surface (6) adapted for ground contact, and an upper portion extending from said lower portion and which includes at least one shock-absorbing portion (5), and at least one stabilizing element (3) constrained to said sole at said at least one shock-absorbing portion (5), wherein said at least one shock-absorbing portion (5) is made of a foam material obtained by means of a fluid in supercritical state, wherein said at least one stabilizing element (3) has at least one exposed surface (8) facing from said at least one shock-absorbing portion (5), and wherein said at least one stabilizing element (3) has density greater than the density of said at least one shock-absorbing portion (5).

2. Sole structure according to claim 1 , wherein said at least one stabilizing element (3) has hardness greater than the hardness of said at least one shock-absorbing portion (5).

3. Sole structure according to claim 1 or 2, wherein said at least one stabilizing element (3) has density between 0.23 and 0.60 g / cm3, preferably between 0.40 and 0.50 g / cm3.

4. Sole structure according to claim 1 , 2 or 3, wherein said at least one stabilizing element (3) has hardness between 45 and 70 Asker C, preferably between 50 and 60 Asker C.

5. Sole structure according to any one of the preceding claims, wherein said at least one stabilizing element (3) is made of cork, a polymer material or a foam material obtained by means of a fluid in supercritical state, wherein the aforesaid material is preferably ethylene vinyl acetate (EVA) or polyurethane (PU).

6. Sole structure according to any one of the preceding claims, wherein said at least one exposed surface (8) of said at least one stabilizing element (3) faces from an upper surface (5b) and / or from a side surface (5c) of said at leastone shock-absorbing portion (5).

7. Sole structure according to any one of the preceding claims, wherein said at least one stabilizing element (3) comprises at least two portions of different hardness.

8. Sole structure according to claim 7, wherein the hardness of said at least one stabilizing element is greater at the foot inside and lesser at the foot outside of said sole (2) and / or wherein the hardness of said at least one stabilizing element is greater at the hindfoot and lesser at the forefoot of said sole (2).

9. Sole structure according to any one of the preceding claims, wherein said at least one shock-absorbing portion (5) has density between 0.10 and 0.25 g / cm3, preferably between 0.12 and 0.20 g / cm3.

10. Sole structure according to any one of the preceding claims, wherein said at least one shock-absorbing portion (5) has hardness between 30 and 50 Asker C, preferably between 35 and 45 Asker C.

11. Sole structure according to any one of the preceding claims, wherein said at least one shock-absorbing portion (5) is made of ethylene vinyl acetate (EVA) or polyurethane (PU).

12. Sole structure according to any one of the preceding claims, wherein said at least one shock-absorbing portion (5) and said at least one stabilizing element (3) are made of the same material, preferably ethylene vinyl acetate (EVA).

13. Sole structure according to any one of the preceding claims, wherein the ratio of the thickness of said at least one stabilizing element (3) to the usable thickness of said at least one shock-absorbing portion (5) is between 0.3 and 0.6, wherein preferably said thickness of said at least one stabilizing element is essentially constant along said sole.

14. Sole structure according to any one of the preceding claims, wherein said lower portion and said upper portion of said sole (2) are made in one piece being integral with each other.

15. Sole structure according to any one of claims 1-13, comprising a tread (4) and a midsole, wherein said tread (4) coincides with said lower portion and said midsole coincides with said upper portion and with said shockabsorbing portion (5) of said sole (2).

16. Process of making a sole structure according to any one of the preceding claims, comprising the steps of: providing at least one first blank of a stabilizing element (23) made of cork or a polymer material, providing at least one second blank of a shock-absorbing portion (25) made of a foam material obtained by means of a fluid in supercritical state (super-expanded blank), inserting said at least one second blank of the shock-absorbing portion (25), said at least one first blank of the stabilizing element (23) and possibly a tread (4) into a mold of a sole for shoes, so that said at least one first blank of the stabilizing element (23) has at least one exposed surface (8) facing from said at least one second blank of the shock-absorbing portion (25), co-molding together said at least one second blank of the shockabsorbing portion (25), said at least one first blank of the stabilizing element (23) and possibly said tread (4).

17. Process according to claim 16, wherein said fluid in supercritical state is nitrogen (N2).

18. Process according to claim 16 or 17, wherein said at least one first blank of the stabilizing element (23) is made of CM EVA, IP EVA or by means of a fluid in supercritical state.

19. Process according to any one of claims 16-18, wherein said at least one second blank of the shock-absorbing portion (25) is obtained by expanding, up to 4-4.5 times, at least one initial blank of the shock-absorbing portion (35) having thickness of about 2 cm.

20. Process according to claim 19, wherein said at least one initial blank of the shock-absorbing portion (35) is made of IP EVA.

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