WO2016030808A1

WO2016030808A1 - Multilayer thermoisolating material for footwear and method for its production

Info

Publication number: WO2016030808A1
Application number: PCT/IB2015/056407
Authority: WO
Inventors: Gabriele Diddi
Original assignee: Pranem S.R.L.
Priority date: 2014-08-27
Filing date: 2015-08-24
Publication date: 2016-03-03

Abstract

A heat-insulation multilayer material is made up of three layers: an inner layer (1), in contact with the foot when in use, made of fabric and/or leather and/or imitation leather; an intermediate layer (2) made of needle-punched staple synthetic microfibres and containing expanded microspheres (21); an outer layer (3) which is made of fibres having high moisture absorption power and which, in use, is the furthest from the foot, Some of the fibres of the outer layer extend through the intermediate layer substantially up to the interface with the inner layer to form micro-channels (31) for displacing the moisture from the layer which is in contact with the foot to the outermost layer. The material has a high capacity of transporting moisture outwards, is light in weight and relatively reduced in thickness compared to prior art heat insulation materials. It is not easily compressible, nevertheless having satisfactory breathability, but has an elastic effect which allows it to recover at least 80-90% of its initial thickness.

Description

MULTILAYER THERMOISOLATING MATERIAL FOR FOOTWEAR AND METHOD FOR ITS PRODUCTION

DESCRIPTION

Field of the invention

The invention addresses the footwear industry in general and relates, in particular, to a heat insulation multilayer material with good moisture transportation and elasticity properties to be used especially to make footwear parts and padding fabrics such as hygienic insoles, upper padding and liners, tongue padding, heel cushions and the like.

The invention also relates to a production method for making the aforementioned heat insulation multilayer material.

Background art

Numerous materials which can be used as heat insulation materials in a wide variety of fields are known. In particular, in the footwear sector, it is important for the footwear to provide good heat insulation so as to protect the foot from the cold outside. Some of the materials used for this application are synthetic and/or artificial fibre felts in single and/or multiple layers. In some cases, the layers are coupled to an aluminium foil whose purpose is to create a partial transpiration and air barrier and to reflect, and thereby retain, the heat emitted by the skin. The aluminium foil is coupled to the felt by needle punching, that is to say, a process by which fibres are transported through the aluminium by needles. The holes made by the needles create a passage for the air and thus make the aluminium partly permeable. In order to retain air, which constitutes the insulating element, these materials tend to be very thick and heavy. They have no elasticity or elastic return, which means they rapidly lose their thickness when compressed. They retain moisture, holding it within even on the side which is in contact with the foot.

Synthetic fur materials allow good heat insulation, provided they are relatively thick. For aesthetic reasons, however, they can only be used in some types of footwear.

Some materials are made up of several layers, with an outer layer made of textile fabric, an inner layer of expanded polyurethane foam (MTP), an aluminium foil and, lastly, a felt. Although they provide a degree of insulation which is satisfactory for the purpose, as demonstrated by tests on static footwear (that is to say, footwear not subjected to the bending which occurs when walking), these materials are easily compressed during use, resulting in a significant reduction of their insulating capacity on account of warm air being allowed to escape. Moreover, materials of this type tend to retain moisture in the whole mass of the material, thus further reducing their insulation capacity and lowering the temperature of the footwear.

A greater air retention capacity and hence improved heat insulation properties compared to traditional felts is provided by materials made of nonwoven microfibres. These materials, too, are easily compressed and when walking and even during the footwear production process, they lose their thickness and thus their insulation capacity. They have no elasticity or elastic return. The same applies to synthetic fibre wadding.

For the same applications in the footwear industry, use is also made of other materials consisting of closed-cell foams of polyurethane, ethyl-vinyl acetate copolymer (EVA), EPDM rubbers, polyethylene, acrylonitrile-butadiene rubbers ( BR), and the like, which provide excellent insulation but have no breathability properties, which means that the moisture produced by sweating remains in contact with the foot and thus results in cooling. They are also heavy and make walking more tiring.

Open-cell foams of polyurethane, SBR, polyester and the like have good breathability and elastic return properties and are therefore used to improve footwear comfort. They must, however, be very thick to contain enough air to guarantee satisfactory insulation and they, too, are subject to moisture retention.

In the case of SBRs in particular, and elastomers in general, the effect resulting from the presence of surfactants and mechanical action leads to the production of a foam which, once dry, forms a compact and uniform, spongy material. The indispensable presence of surfactants, however, prevents use of hydrophobic products and/or materials and leads to retention of the moisture produced by the foot.

MTP expanded polyurethane foams have good elasticity and breathability but easily absorb and retain moisture. The "spongy" structure acts as a container for moisture because the cell walls, having no hydrophobic properties, do not create any obstacles to moisture penetration,

To prevent moisture from penetrating the footwear, use can be made of materials consisting of hydrophobic fibre matting materials whose large volumes allow them to retain air and to have an insulating effect. When used in footwear, however, these materials are easily compressed, losing much of their heat insulation properties, and thus limiting their use. Moreover, the total hydrophobicity prevents moisture from penetrating inside but at the same time makes it difficult to carry away the moisture produced by the skin.

From the foregoing it is clear that the footwear industry needs a material which has good heat insulation properties, is light in weight and reduced in thickness, which prevents the build-up of moisture in contact with the foot and which is at once elastic and not easily compressible, while maintaining a satisfactory degree of breathability.

Summary of the invention

The general aim of this invention is to provide a heat insulation multilayer material for use in the footwear industry and which is at once light in weight and reduced in thickness.

A specific aim of this invention is to provide a multilayer material of the aforementioned type which has a high capacity for carrying moisture away from the foot, that is to say, which allows displacing and concentrating the moisture produced by sweating towards the outermost part of the material, that is, furthest away from the part in contact with the foot.

Another specific aim of this invention is to provide a multilayer material of the aforementioned type in which at least 70-90% of the thickness remains dry and does not retain moisture by effect of contact with the foot.

A further specific aim of this invention is to provide a multilayer material of the aforementioned type which maintains limited air breathability in order to prevent the build-up of moisture which would otherwise remain in proximity to the foot.

Yet another specific aim of this invention is to provide a multilayer material of the aforementioned type which is not easily compressible but has an elastic effect which allows it to recover at least 80-90% of its initial thickness.

A yet further specific aim of this invention is to provide a multilayer material of the aforementioned type which is thermoformable, so as to allow the production of thermoformed anatomic insoles. Another aim of this invention is to provide a production method which allows obtaining a heat insulation multilayer material for use in the footwear industry and which is at once light in weight and reduced in thickness, with good moisture transportation properties for carrying the moisture away from the foot and with good elastic return properties.

These aims are achieved by the heat insulation multilayer material for use in the footwear industry and by the method for its production according to this invention whose essential features are set out in claim 1 and in claim 9. Further important features are set out in the dependent claims.

According to an important feature of the invention, the heat insulation multilayer material for use in the footwear industry comprises an inner layer, that is a layer which, in use, remains substantially in contact with the foot, and which is made of fabric and/or leather and/or imitation leather and has hydrophobic properties; an intermediate layer made of hydrophobic needle-punched staple synthetic microfibres containing microspheres filled with a gaseous fluid; an outer layer made of fibres having high moisture absorption power, said layer being, in use, the one furthest from the foot, said fibres extending through said intermediate layer substantially up to the interface with said inner layer to form micro-channels for displacing the moisture from said inner layer to said outer layer.

According to another important feature of the invention, a method is provided for the production of a heat-insulation multilayer material for use in the footwear industry and comprising the following steps:

mechanically bonding staple synthetic microfibres by carding, web forming and needle punching process to form a needle punched nonwoven product;

- preparing a compound by mixing non-expanded microspheres and bonding synthetic resins in an aqueous solution;

mixing said compound with air to form a foam;

applying said foam to the needle punched nonwoven product by total or partial soaking from one side thereof;

- drying the foam applied on said needle punched nonwoven product by heat or IR exposure causing water to evaporate, resins to dry and microspheres to expand; - treating the dried product with hydrophobic agents to provide the fibres and all the nonwoven fabric forming an intermediate layer of said material with moisture repelling properties;

- joining fibres with high moisture absorption power to one side of said intermediate layer by needle punching to form an outer layer of said material and, working with needles, conveying a part of said fibres through said intermediate layer, thus forming micro-channels therethrough;

applying to the other side of said intermediate layer a layer of fabric material and/or leather and/or imitation leather, processed so as to be made hydrophobic, to form an inner layer of said material, said micro-channels extending substantially up to the interface between said intermediate layer and said inner layer.

Brief description of the drawings

These and other features, as well as the advantages, of the heat insulation multilayer material for use in the footwear industry according to this invention will become apparent from the following description of a non-limiting example embodiment of it with reference to the accompanying drawings, in which

Figure 1 shows a schematic cross section of the heat insulation multilayer material according to this invention

Figure 2 graphically compares certain properties of a heat insulation material according to the prior art and a multilayer one according to this invention.

Detailed description of the invention

With reference to Figure 1, the material according to this invention is substantially made up of three layers: an inner layer, labelled 1, which, in use, remains in contact with the foot (not illustrated) and which is made of fabric and/or leather and/or imitation leather; an intermediate layer, labelled 2, which is made of staple synthetic microfibres containing microspheres 21 filled with a gaseous fluid, normally air; and an outer layer, labelled 3, which is made of fibres having high moisture absorption power and which, in use, is the furthest from the foot,

The inner layer 1 is made of textile materials (for example, fabrics, nonwoven fabrics, run-resist fabrics, jersey fabrics and the like) and/or leather and/or imitation leather of various kinds provided they are breathable and treated in such a way as to be "water repellent" (for example, treated with fluorocarbon resins, waxes and the like). Water-repellent finishing makes it possible to avoid absorbing the moisture produced by the foot (sweat) and thus prevents the moisture from remaining in contact with the skin. During use of the footwear, the compressive actions applied to the inner layer 1 allow the sweat to pass through this layer without it absorbing the moisture.

The intermediate layer 2 comprises staple synthetic microfibres such as, for example, polyester, polyolefin and polyamide microfibres. If the material is used to make thermoformed, anatomic, hygienic insoles, the intermediate layer 2 also comprises low-melt (LMP) bicomponent fibres, such as, for example, polyester/polyester, polypropylene/polyethylene and the like, which confer thermoformability on the material. In this case, the staple synthetic microfibres are present in percentage amounts from 50% to 90%, preferably from 60% to 80%, and the low-melt bicomponent fibres in percentage amounts from 10% to 50%, preferably polypropylene/polyethylene from 20%) to 40%) (percentages by weight). The intermediate layer 2 may weigh from 80 g/m² to 400 g/m², the preferred weights being 80 g/m², 120 g/m², and 300 g/m².

Besides the aforestated microfibres and the microspheres 21, the intermediate layer 2 comprises synthetic resins such as, for example, SBR, vinyl resins, EVA, polyurethane resins, acrylic resins and the like, whose purpose is to bond the microspheres to the fibres. The microspheres are made of synthetic resins (SBR, acrylic, polyurethane, vinyl, EVA). Preferably, acrylic based resins can be used.

The outer layer 3, which is made of fibres with high moisture absorption power such as, for example, viscose, superabsorbent fibres (SAF), modified polyester and the like, constitutes the receptacle which receives the moisture. It is located in the outermost zone, furthest away from the foot, but some of the fibres making it up, labelled 31, extend through the intermediate layer 2 substantially up to the interface with the layer 1. This creates microchannels with high moisture absorption power embedded in a material which is hydrophobic. The result is that the moisture (sweat) produced by the foot, besides being partly carried away by the dynamic air component, is absorbed by contact by the aforementioned microchannels and transported by capillary action to the outermost part of the material, to the outer layer 3 whose main property is to absorb moisture and which acts as a receptacle for the moisture.

The weight of the outer layer 3 and the type of fibre it is made of are calculated as a function of the capacity of absorbing the mean daily amount of sweat produced by a human foot. By way of non-limiting example, to absorb all the moisture produced by the feet in 14 hours (length of time the footwear is used in one day), that is, approximately 75 g, the weight must be 150 g/m². Assuming the footwear has an average inside surface of 1200 cm² and the material weighs 150 g/m² with a moisture regain of 450%, we obtain a moisture absorption capacity of 81 g. Obviously, the type of footwear must be taken into account. For example, in the case of ski boots, the absorption capacity should be 100% of the production of sweat because the boot is totally insulated from the outside, whereas in the case of footwear which allows air to be exchanged with the outside, lower weights are possible because some of the moisture evaporates during use. The purpose of this is to maintain the best possible conditions of thermal and moisture comfort in the footwear.

The intermediate layer 2 is the one which gives the multilayer material according to this invention its properties of heat insulation, lightness and compressibility with elastic return and thickness recovery. The method of producing this layer, as described below, is therefore fundamental to obtaining the aforestated properties.

The first step in the method of producing the multilayer material according to the invention involves carding, web forming and needle punching of the staple microfibres which are mechanically bonded. The type of needle used, the bonding punch density per cm² and the depth of penetration of the needles into the fibres are essential conditions to obtain a product with the right density to produce subsequent swelling and increase in thickness. If needle punching is too dense, the fibres would be too close together and would prevent swelling. On the contrary, a material which is loosely bonded would tend to flake during subsequent stages in the process and/or during use of the footwear. It is preferable to work with a punching density of between 100 and 200 punches/cm². A lower density would make the product too limp and not machinable whereas a higher density would prevent the required swelling to increase the thickness. If the multilayer material according to the invention is used to make anatomic insoles by thermoforming, the staple synthetic microfibres are premixed with the low- melt bicomponent resins in the above mentioned percentage amounts.

In the next step, a compound is prepared by mixing the non-expanded microspheres with the resins (EVA or Vinylic or PU) in aqueous solution. The compound thus obtained is then mixed with air to form a foam which is applied to the needle-punched microfibre product in the first stage of the process. Application is done by total impregnation or partial impregnation on one side and the material is then dried by passing it through a drying oven - for example, a plane drying oven, a multilayer drying oven, a stenter, operating either with hot air or infrared radiation - in order to cause the water in the material to evaporate, dry the resins and swell the microspheres. The microspheres contain a gas, such as air, which expands on reaching a certain temperature, thereby increasing the volume of the microspheres. The increase in volume results in an increase in the thickness of the product but not in its weight.

The diameter of the expanded microspheres may vary from 40 to 100 μ. If it is less than this, there is an excessive amount of microspheres and a barrier to the passage of air is created. Larger diameters, on the other hand, cause the microspheres to be separated from the fibres, leading to flaking. Further, owing to the ratio between microsphere volume and area, large microspheres are more easily compressed and liable to break, especially in the case of thermoforming (where heat weakens the walls of the microspheres), thus nullifying the functionality of the whole system.

The purpose of the foam formed by mixing the compound with air is to create a porous network in the compound, preventing the resins from forming a continuous film during subsequent drying. Such a film would cause the product to become excessively stiff, instead of remaining soft and malleable, with the risk of preventing breathability. The foam also allows the microspheres to be kept separate. Otherwise, on swelling during the subsequent stage in the process, they would stick together, forming a dense, compact block, resulting in a hard material preventing air from passing through it.

Next, by means of treatment with hydrophobic agents (for example waxes, fluorocarbon resins and the like) the fibres and all the nonwoven making up the intermediate layer 2 is made resistant to water absorption so that, in use, moisture (sweat) is prevented from spreading into the intermediate layer which is thus kept dry.

The outer layer 3 is then joined to one side of the intermediate layer 2 by needle- punching and, working with needles, a part of the fibres are conveyed through the intermediate layer 2 substantially up to the interface with the inner layer 1 of the material, thus forming the above mentioned micro-channels 31.

The inner layer 1 is joined to the other side of the intermediate layer 2 by known methods - for example, by thermofusion of a web interposed between the two layers, by hot-melt or by flaming using expanded polyurethane foams (MTP).

The walls of the microspheres are elastic, which means they can be compressed and then return to their initial volume. This confers elasticity, cushion effect and thickness recovery of up to 80%-90% of the initial thickness.

The heat insulation effect is obtained as a result of swelling the microspheres. More precisely, where the volume of air present in the material is 100, up to approximately 70% is static air, that is, the air present in the microspheres. During use of the footwear, the air in proximity to the foot is heated, increases in volume, becomes lighter and thus moves outwards and is replaced by cooler air (convective motions). In the case of the multilayer material according to this invention, this movement applies only to the part of the air which is dynamic, that is to say, the air between the fibres, not that inside the microspheres, creating a "thermos flask effect", so to speak.

At the same time, the air in direct contact with the foot is moistened (sweating) and it is therefore necessary that the dynamic air component be able to be moved away from the foot, taking the moisture with it and transferring it towards the outer layer 3. If the moisture remained in contact with the foot, the sweat would, on the contrary, cool the foot.

The use of microfibres instead of traditional fibres allows obtaining a fibre network with a larger number of fibres for the same weight, with the result that the dynamic air component (that is, in a breathable fabric, the air which is subject to convective motions) finds more obstacles in its way and its displacement towards the outside is slower. This enhances the heat insulation effect and also keeps transpiration at a level sufficient to prevent the build-up of moisture and condensation which would remain in proximity to the foot.

The microfibres also have another important function, and that is to provide a larger anchoring surface area for the microspheres 21, which thus remain bonded to the textile.

From the foregoing description it is clear that the multilayer material according to the invention fully achieves the above mentioned aims. More specifically, the multilayer material according to the invention allows obtaining good heat insulation and other distinctive properties in thicknesses of 4 - 5 mm. Prior art materials with similar performance in terms of insulation but not of the other properties, require thicknesses of 7 - 10 mm.

To further demonstrate the advantageous effects of this invention, a material according to this invention (herein called Ela Therm 1300) 5 mm thick and having a unit weight of 450 g/m² was compared with a traditional product used for heat insulation and breathability, made up of two layers of needle-punched nonwovens of polyester fibres with an interposed aluminium foil 10 mm thick and weighing 900 g/m² (herein called Felt + Aluminium).

The degree of heat insulation was measured using the Sweating Guarded-Hotplate Test Method according to UNI-EN 31092, which defines the result in Ret (thermal resistance of the fabric) expressed in m²K/W. The test simulates the amount of heat the human body must generate to keep its temperature at 36°C in the presence of a temperature difference of 15°C, that is, how much energy it must consume to prevent getting cold. The more the material insulates, that is, the higher the value of m²K/W, the higher the level of insulation and the lower the amount of energy to be "consumed".

The results of the test are represented in Figure 2 and clearly show the differences in the performance of the two materials. The material identified by the name ElaTherm 1300 has in insulating power of 0.17, higher than the 0.16 of the Felt+ Aluminium, but with the big advantage of weighing 450 g/m² instead of 900 g/m².

The heat insulation multilayer material for the footwear industry according to this invention and the method for its production can be modified and adapted without thereby departing from the scope of protection provided by the invention as defined in the appended claims.

Claims

1. A heat-insulation multilayer material for use in the footwear field characterized in that it comprises:

- an inner layer (1), substantially in contact with the foot when in use, made of fabric and/or leather and/or imitation leather and having hydrophobic properties;

- an intermediate layer (2) made of hydrophobic needle-punched staple synthetic microfibres containing expanded microspheres (21);

- an outer layer (3) which is made of fibres having high moisture absorption power and which, in use, is the furthest from the foot, said fibres extending through said intermediate layer (2) substantially up to the interface with said inner layer (1) to form micro-channels (31) for displacing the moisture from said inner layer (1) to said outer layer (3).

2. The multilayer material according to claim 1, wherein said intermediate layer (2) further contains synthetic resins serving as a bonding agent for the microspheres.

3. The multilayer material according to claim 2, wherein said synthetic resins and the material of said microspheres (21) are selected from the group consisting of SBR rubbers, vinyl resins, EVA, polyurethane resins, acrylic resins.

4. The multilayer material according to claim 3, wherein said synthetic resins are acrylic resins.

5. The multilayer material according to any one of the preceding claims, wherein said intermediate layer (2) contains low-melt two-component fibres to make said material thermo-formable, in a percent amount of 10-50%, preferably 20-40%, by weight based on the total weight of the microfibre/low-melt two-component fibres.

6. The multilayer material according to claim 5, wherein said low-melt two- component fibres are selected from the group consisting of polyester/polyester, polypropylene/polyethylene, preferably polypropylene/polyethylene.

7. The multilayer material according to any one of the preceding claims, wherein said staple synthetic microfibres are selected from the group consisting of polyester, polyolefin, and polyamide microfibres.

8. The multilayer material according to any one of the preceding claims, wherein the fibres having a high moisture absorption power forming said outer layer (3) are fibres selected from the group consisting of viscose, superabsorbent fibres (SAF), modified polyester.

9. A method for the production of a heat-insulation multilayer material for use in the footwear field characterized in that it comprises the following steps:

- mechanically bonding staple synthetic microfibres by carding, web forming and needle punching process to form a needle punched nonwoven product;

preparing a compound by mixing non-expanded microspheres and bonding synthetic resins in an aqueous solution;

mixing said compound with air to form a foam;

- applying said foam to the needle punched nonwoven product by total or partial soaking from one side thereof;

drying the foam applied on said needle punched nonwoven product by heat or IR exposure causing water to evaporate, resins to dry and microspheres (21) to expand;

- treating the dried product with hydrophobic agents to provide the fibres and all the nonwoven fabric forming an intermediate layer (2) of said material with moisture repelling properties;

- joining fibres with high moisture absorption power to one side of said intermediate layer (2) by needle punching to form an outer layer (3) of said material and, working with needles, conveying a part of said fibres through said intermediate layer (2), thus forming micro-channels (31) therethrough;

applying to the other side of said intermediate layer (2) a layer of fabric material and/or leather and/or imitation leather, processed so as to be made hydrophobic, to form an inner layer (1) of said material, said micro-channels (31) extending substantially up to the interface between said intermediate layer (2) and said inner layer (1).

10. The method according to claim 9, wherein said staple synthetic microfibres are selected from the group consisting of polyester, polyolefin, and polyamide microfibres.

11. The method according to claim 9, wherein said synthetic resins and the material of said microspheres (21) are selected from the group consisting of SBR rubbers, vinyl resins, EVA, polyurethane resins, acrylic resins.

12. The method according to claim 11, wherein said synthetic resins are acrylic resins.

13. The method according to any one of claims 9 to 12, wherein said staple synthetic microfibres are added with low-melt two-component fibres to make said material thermo-formable, in a percent amount of 10-50%, preferably 20-40%, by weight based on the total weight of the microfibre/low-melt two-component fibres.

14. The method according to claim 13, wherein said low-melt two-component fibres are selected from the group consisting of polyester/polyester, polypropylene/polyethylene, preferably polypropylene/polyethylene.

15. The method according to any one of claims 9 to 14, wherein bonding of said staple synthetic microfibres is carried out with a density of between 100 and 200 punches/cm².

16. The method according to any one of the previous claims, wherein said expanded microspheres are between 40 and 100 μ in diameter.