WO2024008818A1

WO2024008818A1 - Midsole for shoe

Info

Publication number: WO2024008818A1
Application number: PCT/EP2023/068598
Authority: WO
Inventors: Enrick BOISDUR; David Gonzalez
Original assignee: Cockcinel
Priority date: 2022-07-06
Filing date: 2023-07-05
Publication date: 2024-01-11
Also published as: FR3137543A1

Abstract

The present invention relates to a shoe midsole (2, 3), formed by a three-dimensional structure formed by a polymer expanded to form closed cavities, characterized in that the copolymer is a single copolymer for the entirety of the three-dimensional structure, and has a density decreasing continuously in a direction perpendicular to a reference median transverse surface, and in that the three-dimensional structure has a plurality of inner walls extending between two opposite surfaces in directions predominantly inclined at an angle of between 2° and 30°, preferably between 2° and 20°, to the reference median transverse surface.

Description

MIDSOLE FOR SHOE

Field of the invention

The present invention relates to the field of soles and midsoles (in English “midsole”) of shoes.

The 1970s saw the explosion of running success among the general public. A sport previously practiced mainly by an elite of good-level runners, the discipline has seen the arrival of numerous runners with very diverse levels of training and practice. This influx of new practitioners has been accompanied by an increase in the number of injuries linked to the practice. The focus of sports equipment manufacturers of the time then evolved: historically very focused on the creation of shoes aimed at maximum performance, manufacturers began to pay more and more attention to the comfort and protection of the runner in their new models. Although the race for revolutionary foam began in earnest in 2013 to meet athletes' expectations for durability, resilience and rebound with the first shoe equipped with "ADIDAS" (registered trademark) "BOOST" (registered trademark) , and the recognized performance of “NIKE” (registered trademark) has changed the game, with cushioning technology in thermoplastic polyurethane TPU foam or Polyether amide block (PEBA) designed to restore maximum energy.

The development of soles also focused on the use of expanded foams using the technique consisting of injecting into a mold a mixture of copolymer and chemical foaming agent molecular nitrogen N2, carbon dioxide CO2, are found in the form gas.

State of the art

In particular, patent application WO2019178154A1 is known in the state of the art describing various foams and foam components, in particular foam components for footwear and sports equipment. The articles include a composition having a foam structure, the composition comprising a thermoplastic copolyester elastomer comprising: (a) a plurality of first segments, each first segment being derived from a dihydroxy-terminated polydiol; (b) a plurality of second segments, each second segment being derived from a diol; and (c) a plurality of third segments, each third segment being derived from an aromatic dicarboxylic acid. This document also relates to methods of manufacturing the compositions and foams, as well as methods of manufacturing an article of footwear comprising at least one of the foam components. In some aspects, the foams and foam components may be manufactured by extrusion or injection molding to foam the polymer composition, or by extrusion or injection molding to foam the polymer composition followed by compression molding of the foam.

Patent application WO2017006273 describes another system for molding a vulcanized foam rubber sole for shoes, comprising the phases consisting of preparing a rubber in the form of a strip, preform and/or granules, mixing said rubber inside it. 'a loading and mixing chamber, prepare a mold for molding a shoe sole, said mold defining a molding chamber in counter-shape with respect to a shoe sole, transport the mixed material inside said molding chamber and molding the shoe sole inside the molding chamber, removing the shoe sole from said mold. Advantageously, the rubber comprises a foaming agent capable of generating an expansion of the material inside the molding chamber during molding, so as to uniformly fill said molding chamber with the foam rubber; furthermore, the method includes the phase of vulcanization of the foam material inside the molding chamber.

We also know the patent application US2018345575 which proposes an additive manufacturing process consisting of increasing the temperature of a plurality of foam particles by means of actinic radiation under conditions effective for fusing a part of the plurality of foam particles comprising at least one thermoplastic elastomer. Increasing the temperature of the foam particles can be done once or repeatedly. These methods can be implemented to manufacture articles having sub-areas having differing degrees of fusion between foam particles, resulting in sub-areas having different properties, such as density, resilience. and/or the flexural modulus.

Patent CN111150173 describes a shock-absorbing sole and shock-absorbing shoes, which are characterized in that they include dilatant components. The cushioning insole and cushioning shoes have good cushioning performance because the sole contains the dilating assembly, greater impact force can be absorbed in the movement process, discomfort or discomfort. Damages that may occur in the process of movement of a human body are effectively reduced, and the defect that the cushioning effect of existing cushioning shoes (soles) is poor is overcome.

Patent application US2019039309 relates to the printing of materials, using three-dimensional printing and other printing techniques, including the use of one or more mixing nozzles, and/or remote control. multiple axes on the translation and/or rotation of the print head or the substrate on which materials are printed. In some embodiments, a material may be prepared by extruding a material through a print head including a nozzle, such as a microfluidic printing nozzle, which may be used to mix materials therein. of the nozzle and to direct the product thus obtained onto a substrate. The print head and/or substrate may be configured to be translated and/or rotated, for example, using a computer or other control device, to control the deposition of material onto the substrate.

Disadvantages of the prior art

The solutions proposed in the prior art are generally of the two-component type with a rigid skin containing a compressible foam. The result is a sole inside which the materials work partly in shear and in compression, which causes accelerated aging during use. Furthermore, the orientation of the local elastic modulus is isotropic and leads to an uncontrolled deformation of the shape of the sole.

Solutions using the polyether amide block polymer PEBA or TPU are not satisfactory due to poor aging, particularly in flexion and compression, and their very hydrophilic nature.

These solutions also require a connection with the other elements of the shoe by gluing or welding, which introduces inhomogeneities and fragile areas.

Finally, the use of different materials, in particular those based on EVA, makes the sole difficult to recycle because it is often a composition with more than 2 ingredients and sometimes vulcanized.

It should be noted that there is suspicion of EVA as to its carcinogenic nature and its probable inclusion on the California 65 and Reach lists. This is why it is very difficult and expensive to make EVA parts in countries with modern labor regulations.

In addition, most of the compositions used to make these foamed articles include additives for different functions such as foaming, anti-ozone, anti-UV, stiffening, fatigue resistance, softening, etc.

Solution provided by the invention

In order to respond to these drawbacks, the invention concerns, in its most general sense, an intermediate sole of

intermediate shoe formed by a three-dimensional structure formed by an expanded polymer to form closed cavities, characterized in that said copolymer is a single copolymer for the entirety of said three-dimensional structure, and has a density continuously decreasing in a direction perpendicular to a surface median transverse reference surface, and in that said three-dimensional structure has a plurality of interior walls extending between two opposite surfaces in directions predominantly inclined at an angle between 2° and 30° relative to said median transverse reference surface and preferably from 2° to 20°.

By “single copolymer” we mean a material formed by a single type of macromolecule constituted by two or more kinds of monomer units, excluding mixtures of copolymers.

Preferably, said increasing local density varies continuously between a maximum value at the exterior surfaces, and a minimum value at the heart of said sole at the level of said median transverse reference surface.

By “local density” is meant the average density in a representative elementary volume D _V that is statistically homogeneous with regard to the rate and section of the cavities resulting from foaming.

This volume D _V must contain sufficient cavities to be representative of the microstructure. The medium will be said to be homogeneous, or more precisely statistically homogeneous if the neighborhoods D _V at the same distance from the median transverse reference surface measured along an axis normal to said median transverse reference surface and passing through D _V are similar or statistically indistinguishable ( in other words, same “number” of cavities, same average shape of the cavities). The volume D _V is therefore an elementary volume representative of the expanded material. It is small enough compared to the thickness of the three-dimensional structure in order to be able to establish the differential calculation rules and verify that on a sliding window along a normal to the median transverse reference surface, the value of D _V is continuously increasing in the direction of said reference median transverse surface and does not present a singular value.

Preferably, said single copolymer has a density of between 0.9 and 1.15.

Advantageously, said three-dimensional structure has a continuously increasing local density between a value between 0.15 and 0.8 at the level of the transverse surfaces, and a minimum value at the heart of said sole at the level of said median transverse reference surface. The values are determined according to the intended use.

Preferably, said single copolymer has a resilience greater than 65% and a maximum deformation greater than 450%.

According to a first variant, said single copolymer is a polyester-polyether copolymer.

According to a second variant, said single copolymer is a polyether/polyether copolymer

The invention also relates to a method of manufacturing a sole mentioned above, characterized in that an expanded polymer is prepared in an extrusion chamber extended by a mixing chamber opening into a mold via of a controlled valve, the method comprising an injection step at a flow rate greater than that of the supply of said mixing chamber, by at least one injection point configured to ensure the supply of the mold according to a flow presenting a main propagation direction in said transverse middle surface.

Detailed description of a non-limiting example of carrying out the invention

The present invention will be described in more detail with reference to non-limiting examples of embodiment specifying the advantages and considerations mentioned above. A more particular description of the invention briefly described above:

there represents an exploded view of a shoe

there represents a sectional view of a peripheral part of the sole according to the invention

there represents a sectional view of a central part of the sole according to the invention

there represents a sectional view of equipment for manufacturing a sole according to the invention

General principle

Une plaque (1) optionnelle en fibre de carbone intégrée
Un ou plusieurs éléments de semelle intermédiaire (2, 3) objet de la présente invention
Un corps chaussant (4)
Des éléments de semelle inférieure (5, 6).

There represents a general view of a shoe composed of:

One (1) optional integrated carbon fiber plate
One or more midsole elements (2, 3) object of the present invention
A fitting body (4)
Lower sole elements (5, 6).

The carbon fiber plate (1) is optional. It extends over the entire length to increase the longitudinal bending rigidity of the shoe. The carbon fiber plate (1) stiffens the metatarsophalangeal joint and acts as a lever to reduce the work rate at the ankle

In the state of the art, the midsole (2, 3) is made of “PEBAX” foam (registered trademark) for recent sports shoes. “PEBAX” (registered trademark) is a polyamide block elastomer (PEBA) commonly used as a rigid plastic in the outsoles of shoes. When made from foam, it has two advantages over traditional ethylene-vinyl acetate (EVA) or thermoplastic polyurethane (TPU) midsoles.

The invention relates to the structure of the midsoles (2, 3) and its manufacturing method, as well as to the production of a shoe including all of the flexible components, namely the footwear body (4), the midsoles (2, 3) and the elements of the lower sole (5, 6), and any additional parts such as the interlayer fabrics in a single polymer to allow recycling without dismantling for the separation of the different parts of the shoe.

Midsole structure

The midsole (2, 3) consists of a microstructured body of polymer and preferably a polyester-polyether copolymer or a polyether-polyether copolymer or a polyester-polyester copolymer.

We will distinguish the foamed bodies, formed of solidified polymer in the form of microbubbles, with a spongy and elastic consistency, formed of a cluster of bubbles separated by isotropic solid walls, and the microstructured body according to the invention, where the solid polymer forms a matrix with a continuously variable distribution of microcavities from the outer surface to the center, these microcavities having a size also continuously varying from the outer surface to the center. The polymer matrix has preferential planes where the walls separating the microcavities form walls oriented not only along the transverse plane, but with an inclination ensuring the restitution of forces in the direction of travel, with an inclination of 2° to 30° relative to the transverse plane.

The solid parts delimited by the microcavities define walls inclined with respect to the transverse planes, these walls being mainly inclined at an angle of between 2° and 30°, and advantageously 2° and 20° with respect to said median transverse reference surface. These orientations can be observed by a transverse section plane along the longitudinal axis.

On an INSTRON series 55 or Shimadzu AG-Xplus or ZwickRoell Proline dynamometer, a fine, half-spherical indenter is mounted on the moving part of the machine on the sensor line. The tested sample is placed on a support plate that can be rotated from 0° to 60° relative to the ground. The observation of the round-trip force curves differ between a moment where the shoe is vertical and a moment where the shoe is vertical on the way out and inclined on the way back. A test condition is for example, a speed of 20mm/min with a desired crush of 50 kg regulated then a relaxation at the initial point of initial displacement of the test.

The microstructured body has cavities whose average size is not constant but evolves increasingly from the surface of the midsole to reach the maximum section in the central part of the midsole (2, 3) with a density gradient decreasing towards the center of the intermediate sole, and a preferential orientation of the walls of the closed cells in transverse planes so as to form anisotropic flexible stiffeners oriented according to the direction of the forces.

There represents a sectional view of a peripheral portion of the sole, close to the skin of the sole. We observe a skin (10) formed by the local fusion of the microstructured copolymer injected into the mold then a part (11) where the microcavities begin to appear and a third zone (12) where the closed microcavities become larger and more numerous.

There represents another view, of a central portion of the sole, where we observe in the middle part (13) the greatest density of microcavities, with microcavities of the largest size, with a reduction in the number and the size of the microcavities in the zones (12) further from the center.

We also observe that, apart from the surface where a skin is formed by contact with the hot mold, there appears no rupture or singular surface where the density of microgravities or their sizes varies suddenly, but on the contrary a continuous in the variations of sizes and number of microcavities.

Manufacturing process

The sole according to the invention is manufactured with equipment illustrated by the .

The aim of the process is to form a body not like a foam with final properties imposed by the means of obtaining it, but like a plastic matrix with initial properties which we will seek to lighten by adding CO ² gas. or N ² in supercritical conditions by a “MUCELL” type process (registered trademark). The “MUCELL” process (registered trademark) allows the formation of very small cells, from 5 to 50 micrometers in diameter. The general principle is described in patent US5516067 describing a process for producing an expanded semi-crystalline polymer material containing uniform closed-cell microcellular voids, comprising the steps, carried out in the following order, consisting of:

a) firstly, heating a semi-crystalline or non-semi-crystalline polymer material to a temperature equal to or greater than the melting temperature of the material to thereby melt the polymer material;

b) second, saturating the molten polymer material at an elevated pressure equal to or above the melting temperature with a uniform concentration of gas;

c) third, shaping the gas-saturated polymer material in a cavity, mold or die at a high pressure to substantially prevent cell nucleation within the material;

d) fourthly, initiating the formation of uniform bubbles in the shaped polymer material, in the absence of sonic vibrations, by reducing the pressure and supersaturating the shaped polymer material with gas, resulting in a uniform nucleated shaped polymer material having closed-cell microcellular voids below approximately 100 microns in diameter in said polymer material; And

e) fifth, lowering the temperature below the melting point of said polymeric material to prevent further cell growth.

The micro cellular foam produced using this “MUCELL” (registered trademark) process invented at MIT is a polymer foam with cell sizes less than about 100 micrometers (μm) and ideally in the range of about 5 to about 25 μm. These void diameters appear to be small enough to improve or at least maintain the mechanical properties of the parent polymer.

In the “MUCELL” (registered trademark) injection, carbon dioxide plays the role of expanding agent. Injected in the liquid state, it dissolves in the material before being transformed by sublimation upon arriving in the injection mold, resulting in a weight gain of 10 to 30% depending on the material and the part. These bubbles inside the matrix are delimited by walls which constitute, in a way, the inclined walls of the body of the sole.

All of this geometry has properties which are defined by the entry of a known matrix which will see its physicochemical properties become the properties of the unitary wall. The sequence of these walls and their orientations are defined according to the property we want to obtain. The matrix is preferably made of thermoplastic, with an elastomeric character, selected from Polyether/polyester or polyester/polyester or Polyether/polyether copolymers, and more particularly made up of ether-ester block copolymer COPE (Copolyester Thermoplastic Elastomers)

The matrix includes additives where necessary to ensure protection against UV, O3, humidity, alkaline and/or salty environment aging.

The matrix is judiciously selected by those skilled in the art to ensure increased resistance to external attacks due to its intrinsic chemical properties such as: UV, O3, humidity, alkaline and/or salty environment.

Déformation élastique > 5%
Résilience entre 65% et 100%
% humidité absorbé max <0.85%
Déformation max >450%
Densité 0.9-1.15.

The matrix must have the following physical characteristics:

Elastic deformation > 5%
Resilience between 65% and 100%
% moisture absorbed max <0.85%
Max deformation >450%
Density 0.9-1.15.

The resilience expressed as a percentage of an elastomer subjected to periodic forces is equal, according to the ASTM standard, to the ratio of the energy restored after deformation, to the energy supplied to deform the elastomer.

A schematic representation of a system for forming a microstructured cell from crystalline polymers is illustrated by the . It comprises equipment formed by a cylindrical body (20) defining a supply chamber (21) and an injection chamber (22) separated by a transverse piston (23). An extruder screw (30) is loaded with polymer pellets from a feed hopper (40). These pellets are heated to a temperature above their melting point and forced through the extrusion chamber (21) by the screw (30). The molten polymer is forced by the extrusion screw (30) into an injection chamber (22) opening into an injection die (24) the outlet is closed by a valve (25).

The melting screw (30) has temperatures regulated by zone according to an increasing gradient from the supply (40) towards the injection point (23).

The body (20) has a feed conduit (45), through which high pressure gas can be injected into the molten polymer entrained by the screw (30) to enable interaction between the polymer and the gas at the same time. polymer/gas interface. At this interface, the gas dissolves in the polymer liquid. The polymer is then compressed in the injection chamber (22) where it homogenizes and cools to stop foaming.

The gas is injected at a pressure between 2.5 and 100MPa.

The injection press can be hydraulic or electric and horizontal or vertical.

When the compression chamber (22) is filled, the screw (30) is no longer moved in pure rotation but in translation to inject the contents of the compression chamber (22) into the mold (50), by one or more injectors (24) opening into a central surface (51) of the mold (50). The injection of the polymer material into the mold (50) produces a transverse progression front, progressing in the longitudinal direction of the sole to be molded, with a pressure gradient on either side of the injection axis ( 41). The injection front is not a transverse plane but a convex surface presenting tangents, at the level of the walls of the mold, slightly inclined, which leads to preferential structuring axes which are not completely transverse, but have a component longitudinal.

The mold (50) is machined from a metal with an anti-scratch and smooth surface treatment obtained by milling and grinding or by dipping bath or by surface treatment.

Optionally, the mold will have a surface appearance to obtain textured parts (shot blasting, laser, sandblasting, acid attack, etc.)

The mold (50) is thermostatically controlled, and maintained at a lower temperature at least 130°C colder than the hottest point of the feed screw (30).

Temperature profile

For example, the rear part of the body (20) where the polymer granules are introduced has a temperature between 160 and 180 °C. In the central extrusion section of the body (20), the temperature increases slightly to reach between 170° and 190°C then, at the level of the injection chamber (22), a temperature of 180°C to 200°C. At the injectors (24), the temperature is 190°C to 210°C. The mold (50) is maintained at a significantly lower temperature, of the order of 20°C to 50°C.

Claims

Intermediate shoe sole (2, 3) formed by a three-dimensional structure formed by an expanded polymer to form closed cavities, characterized in that said copolymer is a single copolymer for the entirety of said three-dimensional structure, and has a continuously decreasing density in a direction perpendicular to a median transverse reference surface, and in that said three-dimensional structure has a plurality of interior walls extending between two opposite surfaces in directions predominantly inclined at an angle between 2° and 30° relative to said reference median transverse surface and preferably from 2° to 20°.
Intermediate shoe sole (2, 3) according to claim 1 characterized in that said three-dimensional structure has a continuously increasing local density without a singular surface.
Intermediate shoe sole (2, 3) according to claim 1 characterized in that said single copolymer has a density of between 0.9 to 1.15 g/cm 3 .
Intermediate shoe sole (2, 3) according to claim 1 characterized in said three-dimensional structure has a local density continuously increasing between a value between 0.15 to 0.8 g/cm 3 at the level of the transverse surfaces, and a minimum value at the core of said sole at said median transverse reference surface.
Intermediate shoe sole (2, 3) according to claim 1 characterized in that said unique copolymer has a resilience greater than 65% and a maximum deformation greater than 450%.
Intermediate shoe sole (2, 3) according to claim 1 characterized in that said single copolymer is a polyester-polyether copolymer.
Intermediate shoe sole (2, 3) according to claim 1 characterized in that said single copolymer is a polyether/polyether copolymer.
Method of manufacturing a sole (2, 3) in accordance with claim 1 characterized in that an expanded polymer is prepared in an extrusion chamber extended by a mixing chamber opening into a mold by via a controlled valve, the method comprising an injection step at a flow rate greater than that of the supply of said mixing chamber, by at least one injection point configured to ensure the supply of the mold according to a flow having a main propagation direction in said transverse middle surface.