The present invention relates to a footwear sole construction as pre¬ sented in the preamble of the accompanying claim 1.

In the soles of the footwear, air-containing porous plastic has been used as heat-insulating material, which plastic has poor thermal con¬ ductivity and which therefore serves as an insulator. The construction of the insulator is so dense that the convection, i.e., in this case the air flow through the insulator, is prevented. A material of this type is most commonly of foamed polyurethane, EVA (ethylene-vinylacetate) foam or latex foam. Another generally used solution is to "lighten" the some¬ what thick sole construction by shaping projections on the sole surface which is against the foot, between which projections there is left mate- rial and weight saving air pocket which, at the same time, is a heat- insulating construction.

Due to the cellular construction of the plastic used, the proportion of the heat radiation in the heat transfer increases, because the heat radiation penetrates easily the gas pore or the air pocket, although conductivity and convection are insignificant. To prevent the heat loss caused by heat radiation, a reflective Iayer can have been glued on the surface of the insulating Iayer, which reflective Iayer is most commonly a thin metal film, e.g. a lustrous aluminium foil. A lustrous metal surface well reflects the heat radiation coming via the insulating Iayer and it should thus prevent heat loss by radiation.

In prior art solutions, the reflective Iayer is attached to the insulating Iayer by gluing. Although the glue Iayer is thin (0.02 — 0.03 mm) and e.g. visually seen it is transparent, it can affect the heat-insulating prop¬ erties. Many materials used as a glue absorb well heat radiation in the wavelength area of 8 to 15 μm, and the quantity that is absorbed can well exceed even 80 %. Also the radiation reflecting back from the re¬ flecting surface of the reflective Iayer is absorbed when returning to the glue Iayer, so that over 95 % of the heat radiation can be absorbed even to a thin glue Iayer. The quantity of the heat radiation returning to the insulating Iayer can thus be very small. Hence, the problem is that the materials of the reflective Iayer also conduct well heat, wherein

when the heat is transferred by conducting from the glue Iayer to the reflective Iayer, heat is transferred out exactly due to the good heat conductivity of the reflective Iayer, e.g. to the glue Iayer on the opposite side of the reflective Iayer.

These problems are present both in situations in which it is desired to protect the foot in the footwear against cold or against heat surrounding the sole from below. In the former case, the heat should be prevented from transferring out from the interior of the footwear, and in the latter case from outside into the footwear. A metal foil glued to the insulating Iayer does not operate, i.e., reflect heat radiation, as planned.

British Patent application GB-A-2137866 discloses a separate insole in which a surface which is facing the inner sole is made of polyester coated with a metal film, and between the outermost metal surface and the inner sole there is an additional intermediate Iayer, having a thick¬ ness of 1 mm, attached to the metal surface, perforated and made of polyethylene. The polyester Iayer (PET) on the side of the foot behaves in the same manner as the glue Iayer; it conducts well heat, and the openness of the intermediate Iayer facing the inner sole subjects the metal Iayer to mechanical damages and the heat is capable of transfer¬ ring partially by convection through holes, particularly in the case of a separate insole, which will move during the use.

The object of the invention is to eliminate the above mentioned disad¬ vantages and to present a sole construction with improved heat insula¬ tion properties, the sole construction being most commonly an insole used between the inner lining and the wear sole. To attain this object the sole construction is mainly characterized in what is presented in the characterizing portion of the accompanying claim 1. The reflective surface of the reflective Iayer is attached directly to the material of the insulating Iayer without an intermediate absorbent glue Iayer. The sig¬ nificance of this construction has until now remained undiscovered, but it can be proved that the advantage achieved by means of it is distinctly to be noticed in connection with insulating layers permeable to heat radiation.

In the following, the invention will be described in more detail with refer¬ ence to the accompanying drawings, wherein

Fig. 1 illustrates a cross section of a conventional construction and phenomena taking place therein,

Fig. 2 illustrates a cross section of a construction in accordance with the invention and phenomena taking place therein,

Fig. 3 shows how the construction in accordance with the invention is located in the footwear, and

Fig. 4 shows a second altemative of the sole construction.

In Fig. 1 the reference numeral 1 refers generally to an insulating Iayer having the predominant task of preventing heat transfer from taking place by conduction. The insulating layers employed advantageously in the construction of the invention are discussed later. To this Iayer there is attached, by using a glue Iayer 2, a reflective Iayer 3 made of such material that its surface reflects more than 90 %, preferably more than 95 % of the heat radiation coming thereto in the wave-length area of 8 to 15 μm. Such materials include metals, and the most employed mate¬ rial is aluminium. The reflective Iayer 3 can be further attached to its other side to another construction by means of a glue Iayer 2. The above described heat transfer phenomena are further illustrated sche¬ matically by arrows, of which an arrow 6 refers to incoming heat radia¬ tion, an arrow 7 to reflected heat radiation, arrows 8 to absorbed heat radiation and arrows 9 to heat transfer taking place between the layers by means of conduction.

Fig. 2 illustrates a construction according to the invention, in which, as in Fig. 1 , the thickness of the layers has been exaggerated for the sake of clarity. The insulating Iayer 1 is generally of plastic material with good heat-radiation permeability but poor heat conductivity being char- acterized in the employed Iayer thickness by a heat-radiation perme¬ ability of 40 to 90 % taken as average in a wavelength area of 8 to 15 μ m, particularly in the wavelength range between 9 and 10 μm, which corresponds to foot temperature. Furthermore, a material of this type is

characterized by the fact that, particularly compared to an ordinary polyethylene-terephthalate (polyester) of the same thickness, it is in the employed Iayer thickness characterized by at least twice, preferably at least three times, higher heat-radiation permeability in the wavelength range of 9 to 10 μm. The material is advantageously of some expanded polyolefin having a cellular construction brought about by orientation. Most advantageously suitable are such films which have a thickness not exceeding 0.1 mm, and most commonly in an area between 0.025 and 0.06 mm and having a closed-cell cellular construction brought about by cavitation technique. One suitable film material is polypropylene, and applicable for this purpose is e.g. a commercial OPP-film, which is known from other contexts. A reflective Iayer 4 is attached directly on the surface of the insulating Iayer 1 , wherein a re¬ flective surface 4a crucial to the heat-insulation has a direct contact with the material of the insulating Iayer 1. It is important that the inter¬ face is sharp so that the material having the above mentioned proper¬ ties of the insulating Iayer 1 changes at the interface Iayer to the material of the reflective Iayer 4 without an intermediate Iayer having distinctly different properties from those of the insulating Iayer. Non- glue attachment of this kind to the insulating Iayer can be obtained e.g. by vacuum evaporating the material of the reflective Iayer 4 onto the surface of the insulating Iayer 1 , and this can be obtained by a known vacuum evaporation technique of metals, by which technique plastic materials are metallized. Also other methods can be considered for attaching the film directly onto the surface of the insulating Iayer, e.g. a closed cellular construction could be formed directly on top of the metal film.

Due to this construction the heat radiation (arrow 6) is reflected almost entirely (arrow 7) from the reflective surface 4a, because there exists no heat-absorbing material between the insulating Iayer 1 and the re¬ flective Iayer 4, and only the portion (arrow 8) determined by the prop¬ erties of the material of the reflective Iayer 4 is absorbed and is trans¬ ferred away by conducting. E.g. the emission coefficient of a vacuum- evaporated aluminium film is 0.04 at temperature of 20°C, which corre¬ sponds to a reflectivity of 96 %.

The thickness of the reflective Iayer 4 is most advantageously not more than 50 nm, which is a relatively thick Iayer in vacuum-evaporation technique, corresponding to a basis weight of 0.15 g/m ² for aluminium.

Further, the insulating Iayer 1 is characterized by the fact that it is a film having a uniform macroscopic construction and covering the reflective Iayer 4, i.e., it is closed having no holes in the middle through which the heat could pass through the film by convection, the air operating as the medium, and through which the reflective Iayer would be subject to damages.

The above mentioned layers constitute the minimum conditions for the invention to be functional. Provided that it is desired to maintain heat in the interior of the footwear, the insulating Iayer 1 is in the insole on the side of the inner lining and the reflective Iayer 4a faces consequently the inner linings. In case it is desired to protect the foot from hot sur¬ roundings, e.g. the footwear being intended for walking on hot grounds, the insulating Iayer 1 is positioned in the insole on the side of the wear sole and the reflective surface 4a of the reflective Iayer faces conse- quently the wear sole. However, Fig. 2 shows at the same time a two- sided construction according to the invention which construction can be used for preventing the heat from transferring from both sides. In this case the construction has a second insulating Iayer 1 and a reflective Iayer 4 attached directly thereon, the layers being situated in a mirror symmetrical manner in relation to the first layered construction in a manner that the reflective layers 4 are situated in the middle of the construction and their reflective surfaces 4a reflecting heat radiation are facing to the opposite directions towards their own insulating layers 1. These layered constructions comprising an insulating Iayer 1 and a reflective Iayer 4 can be attached together by attaching the reflective layers 4 at their free surfaces together, e.g. by means of an intermedi¬ ate glue Iayer 2, which has no disadvantageous effect in this position. Also in case of the two-sided construction only a small proportion of the heat radiation coming through one insulation Iayer 1 is transferred by conducting away through the reflective layers 4 and the glue Iayer 2 and is radiated to a second insulating Iayer (arrow 10). Fig. 2 further shows how the insulating layers 1 are joined at their outer surfaces to the rest of the sole construction 5, e.g. to an ordinary insole material,

and at this point a glue line also can be used for joining. The inner lining can serve as the Iayer 5 above, and beneath there can be the upper¬ most blank piece of the insole, having the size of the shoe sole. As for the use and manufacturing, the two-layer construction includes the advantage that the inner thin reflective layers 4 are well protected and the outermost insulating layers 1 function as attachment surfaces with the other layers. Particularly in the insole, but also elsewhere in the shoe sole, the thin Iayer 4 is not subject to bending to the degree that it would be damaged.

The insulating Iayer 1 can be used for separating the reflective Iayer 4a from such layers of the sole construction which have a distinctly poorer heat-radiation permeability than the insulating Iayer 1 or which are practically non-permeable to heat radiation.

The above-mentioned two-sided protection can also be obtained by means of a construction having the reflective Iayer 4 attached on both sides of the insulating Iayer 1 in accordance with the invention, wherein on both sides of the insulating Iayer there is a reflective surface 4a di- rectly against it, which reflective surface is capable of receiving the heat radiation coming through the insulating Iayer 1 without intermediate absorbent material. The glue line is also in this situation elsewhere than between the reflecting surface and the insulating Iayer. On the other hand, the heat radiation in this construction is low as such, because the reflective Iayer 4 has a poor emissivity and it does not radiate much when warmed up.

Fig. 3 shows a cross section of a footwear in which the sole construc¬ tion is situated. The construction is most advantageously a layered construction situated close to the interior of the footwear, in the exam¬ ple of Fig. 3 a fixed insole 11 , to which the vamp or upper 12 is attached by using methods generally known in footwear industry. An outsole to which the ready-made vamp part is connected by means of a soling method is denoted by reference numeral 13, and the filling which is left between the insole 11 and the outsole 3 is denoted by reference numeral 14. The entity constituted of one or several insulating layers 1 and reflective layers 4 is placed to a correct position in relation to the

direction of the incoming heat radiation, preferably in the middle of the insole, wherein they are supported and protected by its layers.

Fig. 4 shows yet another sole construction, i.e., a separate insole 15 or insert positioned on top of the inner sole (interior bottom) of the foot¬ wear. Also here the layered construction composed of the insulating Iayer 1 and the reflective Iayer 2, most advantageously the two-sided construction of Fig. 2, is situated preferably in the middle, wherein on its other side there is a Iayer having the suitable properties and placed against the foot sole, and on the other side there is a Iayer placed against the inner sole.

The invention is further illustrated with the following two Examples, which are not to restrict the scope of protection.

Example 1.

The effect of the glue Iayer on heat reflection was measured by means of a long-wave camera. The test included three samples, the order of the samples from the top to the bottom being:

Sample 1 : OPP-film — vacuum-evaporated aluminium Iayer — glue Iayer — OPP-film.

Sample 2: OPP-film — glue Iayer — vacuum-evaporated aluminium Iayer — OPP-film.

Sample 3: OPP-film — glue Iayer — OPP-film.

The OPP-film is a biaxially oriented polypropylene film. The samples were placed side by side on a surface of room temperature (23°C). On the other side of the samples a vessel of warm water (36°C) was placed to serve as the heat source and on the other side a heat camera was placed by which the temperatures of the heat source and the sam- pie surfaces were measured. The surface of the sample 1 showed a temperature of 27°C and the surfaces of the samples 2 and 3 both showed a temperature of 25°C and the surface below showed a tem¬ perature of 23°C. According to the measurement, the glue Iayer

between the OPP-film and the aluminium surface prevented the heat- reflecting effect of the aluminium and the reflectivity showed the same value as the sample without the aluminium Iayer.

Example 2.

Various insoles were manufactured for tests. The basic materials were common commercial insole materials. An element according to the invention was laminated to a part of the samples. The warmth of the different solutions were measured by employing a device in which the sample to be measured was pressed against an aluminium surface in a cold weather room ( — 10°C) by means of a heating element constructed for this purpose. The heating element was heated at a constant power and the temperature was measured on the surface of the sample after the stabilization time of two hours. The better the insulation was, the higher the temperature that was measured. In the test, the insole pro¬ vided with the element of the invention was 2°C warmer than a corre¬ sponding construction without the element (8.9°C versus 10.8°C). When a construction corresponding to the element and having the same thickness but having no reflective Iayer was laminated to a corresponding insole construction, the insulation properties were improved but distinctively less than when the construction was provided with a reflective Iayer.