Patent Description:
The use of particle foam materials, i.e. materials made from individual particles of expanded plastic materials, has found its way into the manufacture of cushioning elements for sports apparel, particularly the manufacture of shoe soles for sports shoes. In particular, the use of particles of expanded thermoplastic polyurethane, eTPU, which are fused at their surfaces by subjecting them to pressurized steam within a mold (often called "steam chest molding" in the art), has been considered for the manufacture of shoe soles.

However, conventional molds for steam chest molding shoe soles are not adapted to the specific requirements of the used materials. For example, the steam chest molding process of a shoe sole made from particles with a conventional mold requires a large amount of energy for heating the mold, as conventional molds typically have a high mass. Moreover, the cooling process of such molds is slow and therefore leads to extended cycle times. Finally, steam chest molding shoe soles from particles requires to uniformly supplying the pressurized steam to the particles in order to achieve a homogeneous interconnection of the particles. Therefore, conventional molds are not adapted to such a uniform medium supply.

Energy carriers other than pressurized steam have also been considered. In particular, a method for the manufacture of a cushioning element for sports apparel that comprises loading a mold with a first material comprising particles of an expanded material and fusing the surfaces of the particles by supplying energy in the form of at least one electromagnetic field has been described in <CIT> and <CIT>. However, these methods leave still room for improvement, because they do not yet take full account of the specific material characteristics of the mold material that, in particular, for the manufacture of modern performance footwear like running shoes are necessary, specifically when it comes to their soles and midsoles.

<CIT> relates to an apparatus for the manufacture of a particle foam component, said apparatus comprising a molding tool limiting a molding space, wherein, adjacent to the molding space, at least two capacitor plates are arranged which are connected to a radiation source for electromagnetic radiation, wherein the radiation source for electromagnetic radiation is designed for emitting electromagnetic radiation, and wherein the molding tool is formed of at least two molding halves, wherein at least one of the molding halves is made from an electrically conducting material and forms one of the capacitor plates.

<CIT> discloses a tool (<NUM>) is made mainly of a thermosetting plastic based on cyanate and/or triazine polymers allowing microwaves to penetrate the tool to heat the molded plastic. An independent claim is made for a process for manufacturing the tool which involves producing a negative pattern of the tool (<NUM>) and locating it in a casting tool, casting fluid mono-, di-, oligo and/or prepolymers and a hardening catalyst around the pattern, and curing the cast tool by heating and then demolding from the casting tool.

<CIT> relates to a mold for relatively uniform heating and molding of a work material to form a workpiece using a microwave oven, includes upper and lower mold members and a sidewall mold member. The mold members are formed from materials selected to have an approximately equal effective thermosensitivity.

<CIT> discloses that molding of expanded plastic material such as dielectric material by microwave radiation is effected in a mold in which the part of the mold which contacts the material to be molded is of a material having high dielectric losses and capable of absorbing microwave radiation. Such mold portion preferably comprises a resin containing a small amount of carbon black.

It is an object underlying the present invention to overcome said disadvantages of the prior art and to provide an improved mold for molding a shoe sole.

This object is accomplished by the teachings of the independent claims. Advantageous embodiments are contained in the dependent claims.

In one embodiment not in accordance with the claimed invention, a mold for molding a component, in particular a piece of sports apparel, comprises (a. ) a mixture of a polymer material and a filler material, (b. ) wherein the filler material is adapted to allow a heating of the component inside the mold by means of an electromagnetic field.

The inventors of the present invention have surprisingly found that such a mold provides an improved approach for molding pieces of sports apparel. By using such a mixture of a polymer material and a filler material the specific characteristics of the mold material can be significantly improved without deteriorating the remaining material characteristics of the mold, e.g. its stability, during the molding process. Moreover, the use of an electromagnetic field, in particular electromagnetic radiation, for heating the piece of sports apparel inside the mold allows the manufacture of components with various thicknesses and complex geometry, too, since the energy for heating is not coupled to any kind of media transport, for example, the introduction of pressurized steam. The electromagnetic radiation may be chosen such that it permeates the mold loaded with the material for the piece of sports apparel essentially homogeneously and supplies an essentially constant amount of energy to all portions of the piece of sports apparel, such that a homogeneous and constant molding is achieved throughout the entire piece of sports apparel and in every depth of the piece of sports apparel.

It is explicitly mentioned at this point that, for clarity reasons, a filler material may be a solid additive incorporated into the polymer material. In this way, the filler material may be a functional filler used to improve the performance of the polymer mold material. In other words, when added to the polymer material, a particular property of the polymer mold material is improved, up to a certain extent, as the amount of filler material increases. Moreover, mixtures of fillers can help to "tailor" the material characteristics and balance mechanical performance with dielectric behaviour of the whole mold. The filler material may be adapted to increase the thermal conductivity of the mold. As a consequence, the loss of heat energy when heating the mold as thermal inflow is significantly increased, because the heat flows away from the mold. Moreover, the increased thermal conductivity of the mold also improves the cooling process as thermal outflow after molding which is further supported by the mixture of a polymer material and a filler material according to the present invention. In addition, there is no further need for additional external or internal cooling of the component so that the whole molding process is simplified. Summarizing, the overall productivity of the manufacturing process for a piece of sports apparel can be increased by such a mold.

The term "thermal conductivity", as used in the present application, refers to the ability of a mold material to conduct heat. In other words, the thermal conduction is defined as the transport of energy due to random molecular motion across a temperature gradient. It is distinguished from energy transport by convection and molecular work in that it does not involve macroscopic flows or work-performing internal stresses. In the International System of Units (SI), the thermal conductivity is measured in watts per meter and kelvin (W/(m·K)).

The filler material is adapted to increase the permittivity of the mold compared to the component. Moreover, the filler material may comprise a dielectric material, in particular, a mixture of at least two inorganic materials, preferably at least one of the following: a metal nitride, a metal oxide, a metal carbide, a metal sulfide, a metal silicate, a silicon carbide and silicon nitride, most preferably boron nitride, BN. The permittivity of the mold has a direct influence on the field strength of the electromagnetic field or electromagnetic radiation inside the mold (for a constant 'external' field being applied to the mold), as the skilled person understands, and will also influence the field distribution (e.g., the local value of the field strength) inside the mold. A further advantage of using an increased permittivity of the mold to influence the electromagnetic field distribution is that filler materials with a wide variety of permittivity-values are known and available, such that a large degree of tuning and adaption is possible in this manner, by choosing and/or combining different filler materials. Moreover, an increased permittivity of the mold may indirectly reduce the loss of heat energy during the molding process, in that the electromagnetic field density is concentrated on the component material - and away from the mold material itself.

Furthermore, the filler material may comprise at least one of the following: a mixture of a carbon material and an inorganic material, carbon fiber, glassy carbon, carbon nanotubes, carbon nanobuds, aerographite, linear acetylenic carbon, q-carbon, graphene, a salt, a monocrystalline powder, a polycrystalline powder, an amorphous powder, a glass fiber. Besides the effects mentioned above, fibers or fiber composite materials are lightweight yet exceptionally strong. In particular, glass or glass fibers are fairly cheap and are moisture resistant as well as have a high strength to weight ratio. Therefore, the mold materials may influence the performance of the whole process and a tailored selection of mold materials of different dielectric properties allows for achieving optimal properties for efficient dielectric heating and subsequent cooling. Moreover, a certain range of electrical resistivity and properties related to mechanical stability may also be considered in the selection of the materials.

All of these described embodiments with different filler materials having different shapes, optical, thermal and electrical properties or material characteristics follow the same idea of achieving optimal properties for efficient molding by dielectric heating of the piece of sports apparel inside the mold and the subsequent cooling of the whole mold. The piece of sports apparel to be molded is a shoe sole, both reduced cycle times when manufacturing the shoe sole and a high quality of the shoe sole may be provided with the mold of the present invention.

The term "sports apparel", as used in the present application, may refer to clothing, including footwear and accessories, worn for sport or physical exercise. Sport-specific clothing or garments may be worn for most sports and physical exercise, for practical, comfort or safety reasons. Typical sport-specific garments may include tracksuits, shorts, T-shirts and polo shirts. Specialized garments may include swimsuits (for swimming), wet suits (for diving or surfing), ski suits (for skiing) and leotards (for gymnastics). Sports footwear may include trainers, football boots, riding boots, and ice skates. Sportswear also may include bikini and some crop tops and undergarments, such as the jockstrap and sports bra. Sportswear may be also at times worn as casual fashion clothing.

The mixture comprises the filler material in an amount of <NUM> to <NUM> % by volume, in particular <NUM> to <NUM> % by volume. The indicated values have been found to provide a reasonable compromise between optimized optical properties for efficient dielectric heating and sufficient thermal properties to provide increased thermal conductivity of the mold for the subsequent cooling.

The polymer material comprises a thermoplastic material, preferably at least one of the following: polyethylene terephthalate, PET, polybutylene terephthalate, PBT, polyoxymethylene, POM, polyamide-imide, PAI, polycarbonate, PC, polyketones, PK, polyether ether ketone, PEEK, or polyethylene, PE. Moreover, the polymer material may comprise a foamed material. These materials have turned out advantageous and may hence be used in the context of the present invention. For example, POM has a dielectric loss factor D of approximately <NUM> for radio frequency radiation. This material may thus be essentially transparent to radio frequency radiation, since it absorbs only a small part of the electromagnetic radiation and may, due to the relatively low loss factor, be formed with a certain thickness.

The polymer material may be adapted to increase the permittivity of the mold compared to the component. For example, certain polymer materials from certain polymer grades may be used due to their high intrinsic permittivity compared to the component material. Therefore, since the permittivity of the mold has a direct influence on the field strength of the electromagnetic field or electromagnetic radiation inside the mold, an optimized thermal inflow and outflow of the mold may be provided in that the electromagnetic field density is concentrated on the component material. Examples may comprise at least one of polyacrylonitrile, PAN, polyamide or polyethylene terephthalate, PET. In preferred embodiments, the mold may comprise a mixture of PET and <NUM> % by volume of Aluminium oxide, Al2O3, or a mixture of POM and titanium dioxide (TiO2).

The polymer material may be adapted to increase the dielectric loss factor of the mold. It is also conceivable that certain portions of the mold may be adapted to increase the dielectric loss factor. Such embodiments allow to selectively introduce excessive heat buildup in the whole mold or only at specific portions within the mold by means of high dielectric loss since the mold material may absorb a high amount of the electromagnetic radiation. Therefore, an optimized thermal inflow and outflow of the mold may also be provided. Examples may comprise at least one of polyketones, PK, polyvinylidene fluoride or polyvinylidene difluoride, PVDF or polyamide-imide, PAI. In a preferred embodiment, the mold may comprise a mixture of POM and titanium dioxide, TiO2.

The mold is a sole mold and the component is a shoe sole, in particular a midsole. The molding process by dielectric heating and the subsequent cooling process of the shoe sole are much faster so that the productivity may be improved. Moreover, the homogeneous and constant molding allows the manufacture of a lightweight, durable shoe sole that offers optimum cushioning properties.

The disclosure further concerns a method for manufacturing a component not in accordance with the claimed invention, in particular a piece of sports apparel, the method comprising the step of (a. ) molding the component using a mold as described herein. Moreover, the method may further comprise at least one of the following steps: (b. ) loading the mold with a first material for the component which comprises particles of an expanded material and (c. ) heating the first material and/or the mixture of the polymer material and the filler material of the mold and/or a susceptor of the mold by means of an electromagnetic field. The susceptor may comprise at least one of the following materials: expanded polypropylene, ePP, polyurethane, PU, polylactide, PLA, polyether-block-amide, PEBA, or polyethylene terephthalate, PET.

The heating step may comprise the step of fusing the surfaces of the particles. As mentioned above, an electromagnetic field, in particular electromagnetic radiation, may be chosen such that it permeates the mold loaded with the particles essentially homogeneously and supplies an essentially constant amount of energy to all particles, such that a homogeneous and constant fusing of the particle surfaces is achieved throughout the entire component and in every depth of the component.

The particles for the component may comprise at least one of the following materials: expanded thermoplastic polyurethane, eTPU, expanded polyamide, ePA, expanded polyetherblockamide, ePEBA, polylactide, PLA, polyether-block-amide, PEBA, polyethylene terephthalate, PET, polybutylene terephthalate, PBT, thermoplastic polyester ether elastomer, TPEE. For example, for use in the manufacture of shoe soles, particles of eTPU, ePEBA and/or ePA have turned out advantageous and may hence be used in the context of the present invention.

The particles may be filled into the mold using conventional techniques known in the art, for example, pressure filling through a filling gate.

The particles may comprise a foamed material. For example, using a foamed material for both the particles and for the surface of the mold leads to a similar loss factor so that a substantially uniform heating of both the particles and the mold may be provided so that a better surface fusion of the component may be obtained.

The electromagnetic field may be in the radio frequency range of <NUM> - <NUM>. The electromagnetic field may, for example, be supplied in the form of radiation in the microwave range, i.e. with a frequency in the range from <NUM> - <NUM>.

Microwave generators are commercially available and may be implemented into a manufacturing device for using an inventive mold with comparatively little effort. In addition, it may be possible to focus the microwave radiation essentially onto a cavity of the mold in which the component material is loaded by a suitable device, such that the energy efficiency of a method using the mold is increased. Furthermore, the intensity and frequency of the microwave radiation may easily be changed and adapted to the respective requirements.

The electromagnetic field may be in the radio frequency range of <NUM> - <NUM>, more preferably in the range of <NUM> - <NUM>, most preferably in the range of <NUM> - <NUM>. In a preferred embodiment, the electromagnetic field may have a frequency in the radio frequency range around <NUM>. It is also conceivable that one or more radio frequencies or radio frequency ranges may be used.

Radio frequency generators are also commercially available and may be easily implemented in a manufacturing device. Moreover, also radio frequency radiation may be focused on the respective parts of the manufacturing device and its intensity and frequency may be adapted to the requirements.

It is further possible that the electromagnetic field, in particular electromagnetic radiation, is supplied in a frequency range different from the frequency ranges mentioned above.

The mold may be further loaded with a second material, which remains essentially unaltered by the electromagnetic field. This may, for example, be a material the electromagnetic field permeates without being absorbed by the material to a noticeable degree. In particular, the second material may be free from electromagnetic field absorbing material. "Essentially unaltered" may mean that the second material does not melt or start melting or become softer or harder.

Possible embodiments of the present invention are further described in the following with reference to the following figures:.

Possible embodiments of the different aspects of the present invention are described in the following detailed description primarily with respect to molds for molding a piece of apparel, in particular a cushioning element such as a midsole. However, it is emphasized, that the present invention is not limited to these embodiments. Rather, it may also be used for different kinds of cushioning elements for sports equipment, for example, knee- or elbow protectors.

Reference is further made to the fact that in the following only individual embodiments of the invention can be described in more detail. However, the skilled person will understand that the optional features and possible modifications described with reference to these specific embodiments may also be further modified and/or combined with one another in a different manner or in different sub-combinations without departing from the scope of the present disclosure. Individual features may also be omitted if they are dispensable to obtain the desired result. In order to avoid redundancies, reference is therefore made to the explanations in the preceding sections, which also apply to the following detailed description.

<FIG> illustrates the surprising effect of a sole mold <NUM> according to the present invention.

The embodiment of <FIG> shows a comparison of simulations for the thermal radiation, i.e. the heat radiation or temperature, of a conventional sole mold of the prior art and the sole mold <NUM> according to the present invention, wherein a shoe sole <NUM>, in particular a midsole <NUM>, is molded inside the two sole molds by dielectric heating and subsequent cooling. The comparison of their heat radiation is simulated after <NUM> minutes of cooling of the two sole molds and the midsole <NUM>.

This comparison between the mold of the prior art and the invention on cooling performance improvement were created using a simulation model where both the dielectric heating phenomenon and the thermodynamic heat conduction were characterized by a fully coupled multiphysics simulation model. The model uses the finite element method for calculation of the thermal energy induced inside of the mold construction during the presence of a radio frequency electric field. Material models represent the dielectric properties of the shoe sole <NUM> and the parts of the sole mold <NUM> construction, and through standard dielectric heating equations the correlation of used materials to induced heating power can be calculated with partial differential equations.

The sole mold <NUM> according to the present invention comprises a mixture of a polymer material and a filler material, wherein the filler material is adapted to allow a heating of the midsole <NUM> inside the sole mold <NUM> by means of an electromagnetic field, in particular radio frequency radiation. As can be seen in <FIG>, the filler material adapted to increase the thermal conductivity of the sole mold <NUM> shows a drastic decrease in cooling time for both the sole mold <NUM> and the midsole <NUM>. Moreover, the inventors have found out that the increased thermal conductivity does not influence the dielectric heating process. The conventional sole mold of the prior art comprises polyethylene terephthalate, PET, and has a thermal conductivity of approx. <NUM> W/m·K.

In the exemplary embodiment of <FIG>, the sole mold <NUM> of the present invention comprises a mixture of polyethylene terephthalate PET and boron nitride, BN, as filler material in an amount of <NUM> % by volume so that the sole mold <NUM> has a thermal conductivity of approx. <NUM> W/m·K, i.e. five times higher than for the conventional sole mold. The inventors have found out that this increased thermal conductivity leads to a significant reduction of the cooling time compared to the conventional sole mold.

In the case shown in <FIG>, the sole mold <NUM> comprises a bottom part 105a, a top part 105b and a side part 105c. For example, the bottom part 105a and the top part 105b of the sole mold <NUM> may be plates having dimensions of <NUM> x <NUM> x <NUM><NUM>. Other mold geometries as well as more or less parts of the sole mold <NUM> are also conceivable.

In another embodiment of the invention being experimentally investigated, the sole mold comprises a mixture of foamed PET and BN as filler material in an amount of <NUM> % by volume, which leads to a thermal conductivity of approx. <NUM> W/m·K. The inventors have found out that this experimentally investigated embodiment leads to a cooling time of approx. <NUM> compared to <NUM> for the conventional sole mold as mentioned above. In other words, the cooling time is approx. reduced by <NUM> %.

The following <FIG> show the analysis of dielectric and thermal properties of different matrix materials comprising corresponding polymer and filler materials.

Values for the (relative) permittivity of materials with polyoxymethylene, POM, and polyethylene terephthalate, PET, over the temperature range from <NUM>° C to <NUM>° C (suitable for use in a sole mold <NUM>), measured at a frequency of approx. <NUM>, are shown in <FIG>:.

Values for the dielectric loss factor of materials with POM and PET together with BN or SILATHERM® as filler materials according to the invention over the temperature range from <NUM>° C to <NUM>° C (suitable for use in a sole mold <NUM>) are shown in <FIG>3d:.

Values for investigating the storage modulus of materials with POM or PET and filler materials according to the invention over the temperature range from <NUM>° C to <NUM>° C are shown in <FIG>:.

Values for investigating the thermal expansion of materials with POM or PET and filler materials according to the invention over the temperature range from <NUM>° C to <NUM>° C are shown in <FIG>. The term "thermal expansion" of a component is composed of the values of the individual materials used and their concentration. Additionally, the thermal expansion is dependent on the temperature applied and is therefore not constant over the whole temperature range.

Values for the thermal conductivity of POM and PET in combination with BN or SILATHERM® as filler materials with different filler concentrations are shown in <FIG>. These values were investigated for the three directions X, Y and Z, wherein X describes an injection direction, Y displays an orthogonal plane direction and Z marks a through plane:.

Next, the improvement of process cycle time by the use of modified mold materials is investigated. Here, unfilled POM and PET were used as mold material. <FIG> shows the temperatures measured inside the welded foam and mold during heating and cooling. All given temperatures are displayed relative to the minimum temperature required for a sufficient fusion Tfuse.

If POM is used as sold mold material (curve <NUM>), the maximum temperature of the foam exceeds Tfuse by <NUM> %. The mold's peak temperature was <NUM> %. The process cycle is finished after <NUM>. For PET as mold material (curve <NUM>), the peak in foam temperature is <NUM> %. The mold reaches a maximum temperature of only <NUM> %. The demolding temperature (curve <NUM>) in the foam is achieved after <NUM>. The maximum temperatures reached in foam (curves <NUM> and <NUM>) and mold (curves <NUM> and <NUM>) are <NUM> % higher for the use of POM. Due to POM's higher thermal conductivity, the foam temperature may be reduced faster in the beginning. As soon as the foam temperature reaches <NUM> % of Tfuse cooling is equal for both mold materials. For lower temperatures, the cooling becomes faster for PET. This may be caused by the higher temperature difference between foam and mold for PET. It could be seen that the largest part of one cycle may be consumed by passive cooling. For the unfilled mold materials cooling takes <NUM> (PET), respectively <NUM> (POM). This may be caused by the low thermal conductivity of foam and mold material. The <NUM> of heating are comparably short, independent of the mold material.

<FIG> show filler concentrations of <NUM> and <NUM> % by volume for BN together with POM or PET. Here, the temperature measured inside the foam and the mold for the modified POM is shown in <FIG>. With increasing filler content, the foam peak temperature (curves <NUM>, <NUM> and <NUM>) is slightly lowered. In comparison to the <NUM> % of Tfuse of unfilled POM (curve <NUM>), <NUM> % and <NUM> % were measured for POM with <NUM> % by volume of BN and for POM with <NUM> % by volume of BN (curves <NUM> and <NUM>). At the same time, the temperature inside the mold is lower (curves <NUM>, <NUM> and <NUM>).

Due to the reduction of dielectric loss factor by the thermal conductive fillers, mold peak temperatures of <NUM> % and <NUM> % (curves <NUM> and <NUM>) of Tfuse may be obtained. The combination of enhanced thermal conductivity and lower temperatures of the mold may lead to a significant shortening of the cooling time. While the processing time for POM with <NUM> % by volume of BN is <NUM>, it is further decreased to <NUM> by the use of <NUM> % by volume of BN. This may mean an effective saving of up <NUM> % respectively <NUM> % of cycle time.

The same analysis was done for PET and <NUM> % by volume of BN in <FIG>. Compared to the results with POM in <FIG>, the peak temperature is similar for filled and unfilled mold material (curves <NUM> and <NUM>). Additionally, the peak temperature of the mold with a mixture of PET and <NUM> % by volume of BN (curve <NUM>) is <NUM> % higher compared to the unfilled mold (curve <NUM>). According to the dielectric characterization, the dielectric loss factor of both materials is quite similar, which might lead to a comparable temperature development. Nevertheless, the enhanced thermal conductivity may result in a faster heat transfer from foam to mold material. This then may result in a higher peak temperature for the thermal conductive mold material. Because of the enhanced thermal conductivity both, foam and mold, may show a faster cooling in the further course. A cycle time of <NUM> may be achieved, which equals a reduction of cycle time by <NUM> %.

The skilled person will understand that other filler material(s) or mixtures as mentioned above are also conceivable. For example, the filler material may comprise a dielectric material, in particular a mixture of at least two inorganic materials, preferably at least one of the following: a metal nitride, a metal oxide, a metal carbide, a metal sulfide, a metal silicate, a silicon carbide and silicon nitride, most preferably boron nitride, BN, SILATHERM® (a mixture of Al2O3 and SiO2) or SILATHERM® Advance. Alternatively or in addition, the filler material comprises at least one of the following: a mixture of a carbon material and an inorganic material, carbon fiber, glassy carbon, carbon nanotubes, carbon nanobuds, aerographite, linear acetylenic carbon, q-carbon, graphene, a salt, a monocrystalline powder, a polycrystalline powder, an amorphous powder, a glass fiber. As discussed above, all of these described embodiments follow the same idea of achieving optimal properties for efficient molding by dielectric heating of the midsole inside the sole mold and the subsequent cooling of the sole mold and the midsole.

Alternatively or in addition, it is also possible to choose a filler material to get defined physical or mechanical properties in different areas of the component, in particular a piece of sports apparel like the midsole <NUM> by the use of an inventive mold according to the present invention. This may include different degrees of fusion in these different areas and thus graded physical or mechanical properties in the midsole <NUM>. For example, different mixtures of the polymer material and the filler material may be used in different areas of the mold. Therefore, such embodiments open up the possibility to provided graded and thus tailored midsole properties in a reproducible manufacturing process.

Claim 1:
A sole mold (<NUM>) for molding a piece of sports apparel, wherein the piece of sports apparel is a shoe sole (<NUM>), the mold (<NUM>) comprising:
a. a mixture of a polymer material and a filler material, wherein the mixture comprises the filler material in an amount of <NUM> to <NUM> % by volume and wherein the polymer material comprises a thermoplastic material,
b. wherein the filler material is adapted to allow a heating of the piece of sports apparel inside the mold (<NUM>) by means of an electromagnetic field; and
c. wherein the filler material is adapted to increase the permittivity of the mold (<NUM>) compared to the piece of sports apparel (<NUM>).