EP1828290A1

EP1828290A1 - Polyether block amide foam

Info

Publication number: EP1828290A1
Application number: EP05798154A
Authority: EP
Inventors: Remco Cornelis Willemse; Raphael Dabbous; Armin Fasola; Christophe Lacroix; Muriel Mauger
Original assignee: Arkema France SA; Sekisui Chemical Co Ltd
Current assignee: Arkema France SA; Sekisui Chemical Co Ltd
Priority date: 2004-10-19
Filing date: 2005-10-19
Publication date: 2007-09-05
Also published as: TW200621847A; WO2006045513A1; KR20070092204A; CN101044196A; WO2006045513A8; JP2008517122A; EP1650255A1

Abstract

The present invention concerns a closed cell crosslinked foam of a copolymer having polyamide blocks and polyether blocks and a density from 20 to 700 kg/m3, preferably 20 to 500 kg /m3 , more preferably 40 to 300 kg/m3, as determined according to ISO 845. Preferably the foam is made by a production process that consists of steps such as a) extrusion/kneading with insertion of a blowing agent or an expansion gas, followed by b) chemical or physical crosslinking, and c) foaming either through decomposition of an organic foaming agent added during the first phase, or through return to equilibrium of supersaturated gas added during the first phase, or through expansion of a gas added directly during extrusion (first phase). Preferably the foam does not undergo any further mechanical or thermal treatment.

Description

POLYETHER BLOCK AMIDE FOAM

[Field of the invention]

The present invention concerns a closed-cell crosslinked, polyether block amide foam and more precisely a foam made from a copolymer having polyamide blocks and polyether blocks. The properties of said foam are, among others, high energy return, low density, high fatigue resistance, low compression strength, low dynamic shear modulus, high shape recovery, and high water vapour transmission whilst still being a closed-cell product. Such properties are unique to a closed-cell foam. The present invention also relates to uses of the foam.

[Prior art and technical problem]

The patent US 3711584 describes a process and apparatus for producing a wrinkle- free, highly foamed sheet of an ethylenic resin having a uniform and fine cellular structure by causing a long strip of a sheet-like moulded article of a cross-linked ethylenic resin containing a normally solid organic blowing agent to fall downwardly and continuously transferring it in the falling direction, heating the sheet-like moulded article in transit to a foaming temperature, the heating being controlled so that a starting position of foaming along the widthwise direction of the sheet-like article will not appreciably fluctuate upwards or downwards and extending the foamed sheet-like article in the widthwise direction. Ethylenic resins have the disadvantage of not being permeable for water vapor and are therefore not suitable for applications where water vapor transmission is desired.

The purpose of Japanese patent application JP 56111658 is obtain a foamy body having an excellent cushion quality and a rebounding elasticity with a small quantity of raw material by a method wherein a rubber sheet containing synthetic rubber and a bubbling agent in a specific ratio is filled in a moulding mould, it is blocked with a covering mould to be heated and pressed and then, it is cooled and thereafter, a metallic mould is released. The process of this document results in a foam having a disadvantageously high density.

Patent EP 81069 describes a web of a cross-linked plastic material foamed in a closed-cell structure or configuration, having substantially parallel upper and lower surfaces, wherein canals penetrate the foamed material and extend and open to at least one of said upper and lower surfaces, and wherein substances can be introduced into the canals to impart beneficial properties to the web of foamed material. The plastic material is polyethylene which is not water vapor transmissible.

The patent US 4559190 describes a process for the preparation of bodies of expanded cross-linked polyethylene having closed cells.

The patent EP 0646622 describes a plastic foam material composed of a blended resin composition which includes at least two thermoplastic resins and a silane- modified based resin. The blended resin composition consists essentially of 100 parts by weight of at least two thermoplastic resins, from about 1 to about 50 parts by weight of a silane-modified, cross-linked, thermoplastic resin; from about 0.001 to about 2.5 parts by weight of a crosslinking catalyst for use in a silane compound and from about 1 to about 20 parts by weight of a foaming agent. The thermoplastic resins are polyethylene, polypropylene or polystyrene, which are not water vapor transmissible.

Patent application WO 9512481 describes a bilayer object comprising a lightened thermoplastic elastomer of the polyether amide type adhering by itself on a non lightened thermoplastic selected from polyether amides, polyetheresters, polyurethanes. The bilayer product obtained by moulding the lightened thermoplastic over the compact thermoplastic may be used in the fabrication of shoe soles. The density of the foam is 0.6 and is not crosslinked. A disadvantage is the bϋayer structure which makes the product more difficult to produce. Since the product is not crosslinked the density is unacceptably high for applications such as sports products, e.g. sports shoes.

Patent application WO200402729 describes a waterproof/breathable moisture transfer liner for alpine, snowboard and hiking. It includes an inner liner selected from technically advanced fabrics which are carefully selected. A series of layers are provided outside the inner liner including foam material and insulated nonwoven layers, breathable membranes, a supportive mesh included in a mouldable foam, or mouldable a spacer material and an outer shell fabric. The foam is an open-cell foam. This has disadvantages when it comes to preventing microorganisms from permeating the foam and at the same time enabling the transmission of water vapor.

Patent application JP 60042432 describes foamed particles for the production of a resin moulding, which is a crosslinked product of a block copolymer having crystalline polyamide segments and polyether segments, having a melt index of <40 g/10 min and a hot xylene soluble residue of <60%. When these foamed particles are foamed by in-mould expansion moulding, the resulting foam has rubber elasticity, tensile strength, low temperature properties, resistance to abrasion, chemical, water or heat, adhesiveness, dye affinity, etc. This foam is intended to be used where polyurethiane foams show limitations in their performances for heat insulating materials, clothes, carpets, building materials or automotive supplies. Foams produced by this process, i.e. first producing foamed particles and then foaming the particles by in-mould expansion moulding, are disadvantageous in that these foams do not have a uniform foam structure. These foams rather have areas corresponding to "holes" due to the spacial packing of the foam particles used for their production and are therefore no barrier against microorganisms or liquids such as liquid water.

The purpose of patent application JP 60026029 is obtaining a thermoplastic elastomer resin comprising a crosslinked block copolymer having crystalline polyamide segments and polyether segments. This resin has a melt index > 0.5 g/10 min and can retain melt flowability, therefore it is mouldable, especially expansion-mouldable, has rubber elasticity, tensile strength, low temperature properties, resistance to impact, abrasion, chemical, water and heat. It also has affinity for dyes, hydrophilicity, and can be formed by melt expansion moulding.

Apart from being an expansion moulded foam the density of the described foam is too high.

None of the currently existing closed-cell foams have a sufficiently high rebound height, especially at low temperature, low compressive strength at given density, or a low dynamic shear modulus. Further, they do not have a sufficiently high water vapour transmission whilst having a closed-cell structure which prevents the permeation of microorganisms and contributes to a good recovery of the foam after compression.

It is therefore an object of the present invention to provide foams being water transmissible, but at the same time forming a barrier for microorganisms and liquids such as liquid water. The foams should further have properties such as high energy return, low density, high fatigue resistance, low compression strength, low dynamic shear modulus and high shape recovery. Such properties make the foam ideally suitable for example in the fields of sports articles for breathable and/or resilient materials or in the field of medicine, e.g. in the case of breathable plasters.

The present inventors have now discovered a crosslinked foam made from a copolymer having polyamide blocks and polyether blocks as disclosed in claim 1. Preferred embodiments are described in the following and in the depending claims. The foam of the present invention has unexpected properties, a very regular cell size, uniformity and very low density.

[Description of the invention]

The present invention concerns a closed-cell crosslinked foam of a copolymer having polyamide blocks and polyether blocks and a density from 20 to 700 kg/m³, preferably 20 to 500 kg/m³, more preferably from 40 kg/m³ to 300 kg/m³, the density being measured according to the method ISO 845.

Advantageously the cell size is from 0.05 to 2.0 mm, preferably from 0.1 mm to 1.0 mm. The cell size distribution is very uniform and the foam as a whole has no regions of ununiformity which could permit a transmission of liquid or microorganisms. The cells are closed. Preferably the foam does not undergo any further mechanical or thermal treatment (except to be adhesive bonded or thermoformed).

The term "closed cell", in contrast to "open cell", is known to a skilled person and means that essentially all cell walls of the foam are undamaged. Preferably, at least 90% of the cells have undamaged cell wails, more preferably at least 95%, even more preferably more than 98%. According to the present invention, a closed cell foam with about 98% or more undamaged ceils is generally obtained.

Preferably the foam is made by a production process that consists of steps such as a) extrusion/kneading with insertion of a blowing agent or an expansion gas, followed by b) chemical or physical crosslinking, and c) foaming either through decomposition of an organic foaming agent added during the first step, or through return to equilibrium of supersaturated gas added during the first step, or through expansion of a gas added directly during extrusion (first step). Preferably, the foam does not undergo any further mechanical or thermal treatment.

In this production process the steps of extrusion/kneading, crosslinking and foaming can preferably be clearly separated; i.e. during extrusion preferably no foaming should occur. For this purpose, the extrusion/kneading should be performed at a low temperature.

The foam of the present invention has many advantages :

The compressive strength is from 90 to 170 kPa, preferably from 110 to 150 kPa (measured on foam of 240 kg/m³, at 25% deflection, method according to ISO 844).

The shore hardness 0 is from 20 to 34, preferably from 23 to 32 (measured on foam of 240 kg/m³).

The thermal conductivity is from 0.038 to 0.058 VWm⁰K, preferably from 0.043 to 0.053 VWm⁰K (measured on foam of 240 kg/m³, method according to ISO 2581).

The energy return is 28 to 40 cm, preferably 31 to 37 cm (measured on foam of 240 kg/m³, method according to ISO 8307, falling height 50 cm). Whilst being a closed-cell product, the water vapour transmission is from 100 g/m²/day to 10000 g/m²/day, preferably from 500 to 3500 g/m²/day (method according to ASTM E96 BW) provided there are enough hydrophilic polyether blocks, and the water absorption (dipping in water during one week) is lower than 8% vol.

As regards the copolymer having polyamide blocks and polyether blocks, these result from the copolycondensation of polyamide blocks containing reactive ends with polyether blocks containing reactive ends, such as, inter alia:

1) Polyamide blocks containing diamine chain ends with polyoxyalkylene blocks containing carboxylic chain ends.

2) Polyamide blocks containing dicarboxylic chain ends with polyoxyalkylene blocks containing diamine chain ends obtained by cyanoethylation and hydrogenation of aliphatic dihydroxylated alpha-omega polyoxyalkylenes known as polyether diols.

3) Polyamide blocks containing dicarboxylic chain ends with polyether diols, the products obtained in this particular case being polyetheresteramides. The copolymers used in the present invention are advantageously of this type. The polyamide blocks containing dicarboxylic chain ends are derived, for example, from the condensation of α, ω-aminocarboxylic acids, lactams or dicarboxylic acids and diamines in the presence of a chain-limiting dicarboxylic acid.

The number-average molar mass (Mn) of the polyamide blocks is between 300 and 15 000 and preferably between 600 and 5 000. The mass Mn of the polyether blocks is between 100 and 6000 and preferably between 200 and 3000.

The polymers containing polyamide blocks and polyether blocks may also comprise randomly distributed units. These polymers may be prepared by the simultaneous reaction of the polyether and the polyamide-block precursors. For example, polyetherdiol, a lactam (or an α, ω-amino acid) and a chain-limiting diacid may be reacted in the presence of a small amount of water. A polymer is obtained essentially containing polyether blocks, polyamide blocks of very variable length, and also the various reagents which have reacted randomly and which are distributed randomly in the polymer chain.

Whether these polymers containing polyamide blocks and polyether blocks are derived from the copolycondensation of polyamide and polyether blocks prepared beforehand or from a one-pot reaction, they have, for example,

Shore D hardnesses which may be between 20 and 75 and advantageously between 30 and 70 and an intrinsic viscosity of between 0.8 and 2.5 measured in meta-cresol at 25O⁰C for an initial concentration of 0.8 g/100 ml. The MFIs may be between 5 and 50 (235⁰C for a 1 kg load).

The polyetherdiol blocks are either used without modification and are copolycondensed with polyamide blocks containing carboxylic ends, or they are aminated in order to be converted into polyetherdiamines and condensed with polyamide blocks containing carboxylic ends. They may also be blended with polyamide precursors and a chain limiterto make polymers containing polyamide blocks and polyether blocks with randomly distributed units.

Polymers containing polyamide blocks and polyether blocks are disclosed in patents US 4331 786, US 4 115475, US 4 195015, US 4839441, US 4 864 014, US 4230 838 and US 4332 920.

Three types of copolymer containing polyamide blocks and polyether blocks may be distinguished. According to a first type, the polyamide blocks containing dicarboxylic chain ends are derived, for example, from the condensation of α, ω-aminocarboxylic acids, of lactams or of dicarboxylic acids and diamines in the presence of a chain- limiting dicarboxylic acid. As an example of an α, ω-aminocarboxylic acid, mention may be made of aminoundecanoic acid, as examples of lactams, mention may be made of caprolactam and lauryllactam, as examples of dicarboxylic acids, mention may be made of adipic acid, decanedioic acid and dodecanedioic acid, and as an example of a diamine, mention may be made of hexamethylenediamine.

Advantageously, the polyamide blocks are made of polyamide 12 or of polyamide 6. According to a second type, the polyamide blocks result from the condensation of one or more α, ω-aminocarboxylic acids and/or of one or more lactams containing from 6 to 12 carbon atoms in the presence of a dicarboxylic acid containing from 4 to 12 carbon atoms, and are of low mass, i.e. they have an Mn of from 400 to "1 000. As examples of α, ω-aminocarboxylic acids, mention may be made of aminoundecanoic acid and aminododecanoic acid. As examples of dicarboxylic acids, mention may be made of adipic acid, sebacic acid, isophthalic acid, butanedioic acid, 1,4- cyclohexyldicarboxylic acid, terephthalic acid, the sodium or lithium salt of sulphoisophthalic acid, dimerized fatty acids (these dimerized fatty acids have a dimer content of at least 98% and are preferably hydrogenated) and dodecanedioic acid HOOC-(CH₂)io-COOH.

Examples of lactams which may be mentioned are caprolactam and lauryllactam. Polyamide blocks obtained by qondensation of lauryllactam in the presence of adipic acid or dodecanedioic acid and with an Mn of 750 have a melting point of 127-130⁰C.

According to a third type, the polyamide blocks result from the condensation of at least one α, ω-aminocarboxylic acid (or a lactam), at least one diamine and at least one dicarboxylic acid. The α, ω-aminocarboxylic acid, the lactam and the dicarboxylic acid may be chosen from those mentioned above. The diamine may be an aliphatic diamine containing from 6 to 12 atoms and may be arylic and/or saturated cyclic. Examples which may be mentioned are hexamethylenediamine, piperazJne, 1- aminoethylpiperazine, bisamino-propylpiperazine, tetramethylenediamine, octamethylenediamine, decamethylenediamine, dodecamethylenediamine, 1,5- diaminohexane, 2,2,4-trimethyl-1,6-diaminohexane, diamine polyols, isophoronediamine (IPD), methylpentamethylenediamine (MPDM), bis(aminocyclohexyl)methane (BACM) and bis(3-methyl-4-aminocyclohexyl)methane (BMACM).

In the second and third types, the various constituents of the polyamide block and their proportion may be chosen in order to obtain a melting point of less than 150⁰C and advantageously between 90⁰C and 135⁰C.

Copolyamides with a low melting point are disclosed in patents US 4483 975, DE 3 730 504 and US 5 459 230, and the same proportions of the constituents are adopted for the polyamide blocks. Advantageously the copolymers having polyamide blocks and polyether blocks are made of : PA 12 (PA: polyamide) and PEG (PEG: polyethylene glycol), PA 12 and PTMG (PTMG: polytetramethylene glycol), PA 6 and PTMG, PA 6 and PEG, copolyamide blocks and PEG, copolyamide blocks and PTMG.

The polyether blocks may represent 5% to 85% by weight of the copolymer containing polyamide and polyether blocks. The polyether blocks may contain units other than ethylene oxide units, such as, for example, propylene oxide or polytetrahydrofuran (which leads to polytetramethylene glycol sequences). It is also possible to use simultaneously PEG blocks, i.e. those consisting of ethylene oxide units, PPG blocks, i.e. those consisting of propylene oxide units, and PTMG blocks, i.e. those consisting of tetramethylene glycol units, also known as polytetrahydrofuran. PPG or PTMG blocks are advantageously used. The amount of polyether blocks in these copolymers containing polyamide and polyether blocks is advantageously from10% to 50% by . weight of the copolymer and preferably from 35% to 50%.

The copolymers containing polyamide blocks and polyether blocks may be prepared by any means for attaching the polyamide blocks and the polyether blocks. In practice, two processes are essentially used, one being a 2-step process, the other a one-step process.

The 2-step process consists firstly in preparing polyamide blocks containing carboxylic ends by condensation of the polyamide precursors in the presence of a chain-limiting dicarboxylic acid and then, in a second step, in adding the polyether and a catalyst.

Once the polyamide containing carboxylic acid ends has been prepared, the polyether and a catalyst are then added. The polyether may be added in one or more portions, as may the catalyst.

The catalyst is defined as being any product which facilitates the bonding of the polyamide blocks and the polyether blocks by esterification. The catalyst is advantageously a derivative of a metal (M) chosen from the group formed by titanium, zirconium and hafnium. This process and these catalysts are disclosed in patents US 4332 920, US 4230 838, US 4 331 786 US 4- 252 920 JP 07145368A, JP 06287547A and EP 613919.

As regards the one-step process, all the reagents used in the two-step process, i.e. the polyamide precursors, the chain-limiting dicarboxylic acid, the polyether and the catalyst, are blended. These are the same reagents and the same catalyst as in the two-step process disclosed above. If the polyamide precursors are only lactams, it is advantageous to add a small amount of water.

The copolymer essentially has the same polyether blocks and the same polyamide blocks, but also a small portion of different reagents which have reacted randomly and which are distributed randomly in the polymer chain.

The higher the proportion of PEG blocks the higher the water vapour transmission rate. It would not depart of the scope of the invention to use a blend of (i) a copolymer having polyamide blocks and PEG blocks and (ii) a copolymer having polyamide blocks and PTMG blocks.

It would not depart of the scope of the invention to use a blend of (i) a copolymer having polyamide blocks and polyether blocks and (ii) a polyamide or a copolyamide. Advantageously the polyamide is of the same type as the polyamide of the polyamide block.

It would not depart of the scope of the invention to use a blend of (i) a copolymer having polyamide blocks and polyether blocks and (ii) a polymer or copolymer of polyolefine, preferably of ethylene with acetate or acrylate groups, preferably a copolymer of ethylene and alkyl (meth)acrylate. Eventually (ii) is functionalized. It could be a copolymer of ethylene-alkyl(meth)acrylate-maleic anhydride. This is described in EP 688 826.

As regards the process to make the foam, the following steps are advantageous :

1) Extrusion/kneading:

a) Extrusion and/or calendering as a film or a sheet, with or without cutting of the sheet. b) Mixing/kneading and possibly calendering to a sheet or a felt.

2) Crosslinking:

a) Chemical crosslinking: through addition of peroxide and/or silane during the extrusion/kneading phase.

b) Physical crosslinking: by electron beam or gamma radiation.

Both a) and b) alternatives can contain crosslinking co-agents or promoters as described in the literature to control the crosslinking network and density.

3) Foaming:

a) Through decomposition of an organic foaming agent added during the mixing phase, preferably azodicarbonamide.

b) Through release of supersaturated gas, preferably CO2 or N2, added in a high pressure autoclave, after extrusion but before expansion.

c) Through expansion of gas added directly during extrusion (usually as aid together with organic foaming agent as under a).

4) Expansion process:

a) In a horizontal oven. Free expansion.

b) In a vertical oven. Free expansion.

c) In a low pressure autoclave. Free expansion.

d) In a heated press. Constrained expansion. An in-mould expansion or expansion in a heated press can be performed according to the present invention. The expansion is in this case preferably conducted with an extruded sheet or a kneaded felt cut to the necessary size to fill the mould. Unlike in JP 60042432, however, the expansion is not conducted with foam particles or beads to laminate or sinter in the press or mould.

5) Shape:

a) Roll foams

b) Batch foams

The foam of the present invention can be shaped by pressforming (i.e. by preheating, placing into a mould, closing of the mould, and allowong to cool down in the closed mould), vacuumforming, embossing and/or over-injection.

Uses

As regards the uses, they are connected to the following specific properties and advantages of the foam:

• Softness, low hardness, low compressive modulus

• Low density

• High friction coefficient

• Low compression set

• High thermal insulation (low thermal conductivity)

• Good UV resistance

• Good chemical resistance against a great number of substances • Prominent shape recovery

• Good printing results, even without surface treatment

• Excellent behaviour in ultrasonic and HF welding processes

• High water vapour transmission

• Can be flame laminated, pressformed, vacuumformed

• Can be adhesive coated

• Can be cut or die-cut

• Can be skived; not easy but possible

• Good wash resistance (at least to 60⁰C, incl. tumbler drying) 5

• High energy return (rebound height)

• High abrasion resistance

• Can be over-injected (with non-expanded copolymer having polyamide block and polyether block, or polyamide, or polyurethane or thermoplastic polyurethane) in usual injection moulding process, or in low pressure moulding process (whereby the molten mass is injected in the open mould, and the mould is closed after injection of the partially distributed resin).

• Can be extrusion coated to achieve a stiff/flexible thermoplastic complex.

Possible uses and relevant properties:

Soccer balls: Energy return/Rebound.

Sports gloves padding (goalkeepers, boxing, etc): Antislip, energy return, roll product, easier. Immersion suits: Shape recovery, elasticity, thermal insulation, tear resistance.

Golf clubs (grip): Nice touch, abrasion resistance.

Rebound layer for table tennis rackets (as only layer or in combination with other layers, for instance for protection): excellent grip/antislip (for spin-effect on ball), easy to cut and bond.

Ski poles: As golf clubs.

Sports bat grips: As golf clubs.

Snowboard and windsurf pads: Antislip, surface resistance, easy to stick.

Saddles (for bicycles): Cushioning, comfort, compression set, dynamic properties.

Antislip coated tape (construction or automotive): Antislip property, high surface tension, good touch.

Lingerie articles (bra cup): Elasticity, wash resistance, no crease, breathable.

Parts of ski boots (ankle padding, tongue): Low temperature resistance, flexibility.

Mouse mats: Antislip feature, printability (no need of printed film).

Soft keyboards and buttons: Shape recovery, nice touch, vacuumformability, fatigue resistance.

Trays for objects in cars: Antislip, easy to stick.

Gaskets: Conformability, temp, resistance, vibration damping.

Flexographic printing rolls: Elasticity, energy return, fatigue resistance.

Single and double side adhesive coated tapes: Conformability, elasticity, shape recovery.

Orthopaedic insoles/inlays: Mechanical properties, touch, fatigue resistance. Footwear insoles/insocks: Light weight, compression set, rebound properties.

Footwear midsoles: Light weight, compression set, rebound properties.

Footwear lining: Waterproof, but water vapour breathable, thermoformable, thermal insulation.

Breathable footwear midsole: Waterproof, but water vapour breathable, thermoformable, thermal insulation, cushioning and rebound properties.

Heel inserts: Compression set, fatigue resistance, rebound features.

Inserts for forefoot: Rebound and cushioning.

Transdermal pads Water vapour breathable, skin friendly, elastic.

Woundcare plasters Water vapour breathable, skin friendly, elastic.

Sportswear and garment lining Waterproof but water vapour breathable, thermoformable, thermal insulation, light weight.

Cushioning of seats of ski-lifts Energy return, UV resistance (if not covered), touch.

[Examples]

The Examples of the present invention refer to the following figures:

Fig. 1: An apparatus used for testing the dynamic shear modulus

Fig. 2: A diagram showing the dynamic shear modulus and the density of foams according to the present invention and the prior art.

Fig. 3: A diagram showing the compressive strength and the deflection of foams according to the present invention and the prior art. Fig. 4: A diagram showing the shape recovery (tensile strength and tensile elongation) of foams according to the present invention and the prior art.

Fig. 5: A diagram showing the water absorption as a function of time of a foam according to the present invention.

Fig. 6: A diagram showing the energy return of foams according to the present invention and the prior art.

Fig. 7: A diagram showing the fatigue resistance of foams according to the present invention and the prior art.

Fig.8: Another diagram showing the fatigue resistance of foams according to the present invention and the prior art.

a) Dynamic Shear Modulus of PEBAX® foam

It is very easy to obtain a high elongation and "conformability" with the foams of the present invention. The apparatus shown in Fig. 1 was used to determine the dynamic sheaf modulus. The test method is based on ISO 1922 "Shear strength of rigid cellular foam" modified to fit on soft elastic foams.

In Fig. 2, "PEBAX® FOAM" means a foam according to the invention.

It has been made with a copolymer sold by Arkema (formely ATOFINA) under the trade name PEBAX.

It is obvious that the dynamic shear modulus of the foam according to the invention is lower than that of other closed-cell products, and is in the same region as partly closed-cell foams. Please state which foams in the figure are closed-cell and which are partly closed-cell.

b) Compressive Strength The compressive strength was determined on different foams according to ISO 844. The foam according to the present invention had a density of 240 kg/m³.

Fig. 3 shows that the foam according to the present invention has a lower compressive strength than other known closed-cell products. It is almost as low as the compressive strength of partly closed-cell products. Please state which foams in the figure are closed-cell and which are partly closed-cell.

c) Shape Recovery

The shape recovery was tested performing a tensile test up to 1500 kPa, then returning to 0 kPa and measurement of the remaining length.

Fig. 4 shows that the remaining strain after applying a tensile load up to- 1500 kPa, and releasing it, is much lower for the foam according to this invention, in comparison with polyolefine foams of similar density.

d) Water Vapour Transmission

With the invented foam a material with high water vapour transmission, but still closed- cells, is provided. Depending on the number of hydrophilic polyether blocks, the level of water vapour transmission (WVT) can vary between 100 and 10000 g/m²/day. Examples of results obtained (measured according to ASTM E96E 38°C /90% relative humidity (RH)):

- A foam of a copolymer having PA 12 blocks of Mn 600 and PTMG blocks of Mn 2000 with an area weight of 160 g/m² has a WVT value of 1276 g/m²/day;

- A foam of a copolymer having PA 12 blocks of Mn 1000 and PTMG blocks of Mn 1000 with an area weight of 180 g/m² has a WVT value of 676 g/m²/d;

- A foam of a copolymer having PA 12 blocks of Mn 1500 and PEG blocks of Mn 1500 with an area weight of 460 g/m² has a WVT value of 1400 g/m²/d; - A foam of a copolymer having 6.10 /11 copolyamide blocks and PEG blocks (PEG is 40% by weight of the copolymer) with an area weight of 155 g/m² has a WVT value of 2207 g/m²/d;

- A foam of (i) a copolymer having 6.10 /11 copolyamide blocks and PEG blocks (PEG is 40% by weight of the copolymer) blended with (ii) EVA in a weight ratio 70/30 with an area weight of 185 g/m² has a VWT value of 1730 g/m²/d.

No other closed-cell foam has such high water-vapour transmission values. The combination of such specific characteristics as cushioning, closed-cell structure and water vapour transmission is unique and makes the foam according to this invention a product of high potential for so-called "breathable-waterproof midsoles.

While the water vapour transmission of the foam according to this invention is especially high, its closed-cell structure makes it waterproof, as evidenced by Fig.5. This means that the foam according to this invention is at the same time permeable to water vapour but not to liquid water. Fig. 5 shows the water absorption as a function of time, the uptake of water after immersion of the foam into liquid water was measured.

The foam according to the present invention takes up less than 4 vol% water after dipping for one whole week in water.

e) Energy return, including at low temperature

Measurement procedure (SATRA test method TM 142):

With falling weight onto anvil - The falling weight is dropped onto the anvil on which the sample is placed - A displacement transducer is fixed to the weight so that the acceleration/deceleration can be measured and the rebound height is calculated.

The results are shown in Fig. 6 for a foam according to the invention and polyurethane (PU) foams. The by far highest energy return was observed with PEBAXFOAM® (according to the invention).

Tests run on a pendulum apparatus at low temperature (5°C) have shown that the energy return is retained at a level of 44%. The same tests run on other products (rubber foams, polyurethane-based foams, etc) show strong decrease in energy return between measurement at room temperature and at low temperature.

f) Fatigue resistance

Input: compression 50% at 1 Hz and 10 Hz, at room temperature.

Output: recording of the compressive force, then converted in compressive strength.

As can be seen from Fig. 7, PEBAXFOAM (the foam according to this invention) and Poron 50 (a partly open cell foam of similar hardness) have very different fatigue behaviour. The most obvious difference is the small hysteresis of PEBAXFOAM^®.

Fig. 8 shows the development of fatigue resistance over the number of cycles performed. This chart shows that the foam according to this invention shows the lowest strength loss over a high number of cycles, and has therefore a better fatigue resistance, even better than partly closed-cell foams.

Claims

1. Closed-cell, crosslinked foam of a copolymer having polyamide blocks and polyether blocks, wherein the density of the foam is 20 to 700 kg/m³.

2. Foam according to claim 1 , wherein the foam has a homogenous, smooth skin.

3. Foam according to claim 1 , wherein the density is from 20 to 500 kg/m³, preferably from 40 kg/m³ to 300 kg/m³.

4. Foam according to anyone of the preceding claims obtainable by a prod uction process comprising the steps a) extrusion/kneading with incorporation of a blowing agent or an expansion gas, followed by b) chemical or physical crosslinking, and c) foaming either through decomposition of an organic foaming agent added during step a), or through return to equilibrium of supersaturated gas added during ste>p a), or through expansion of a gas added directly during extrusion (step a)).

5. Foam according to any one of claims 1-4, wherein the cell size is from 0.05 to 2.0 mm, preferably from 0.1 mm to 1.0 mm.

6. Foam according to anyone of the preceding claims not being subjected to a mechanical or thermal treatment.

7. Foam according to claim 1 , wherein the water vapour transmission is from 100 to 10000 g/πvVday, preferably from 500 to 3500 g/m²/day.

8. Foam according to any one of claims 1 to 7, wherein the water absorption after one week dipping at room temperature is lower than 8 vol%.

9. Foam according to anyone of the preceding claims wherein the copolymers having polyamide blocks and polyether blocks are selected from the following combinations: PA 12 and PEG, PA 12 and PTMG, PA 6 and PTMG, PA 6 and PEG, copolyamide blocks and PEG, copolyamide blocks and PTMG.

10. Foam according to anyone of the preceding claims, wherein the copolymers of claim 9 are blended or mixed to a polyolefin homo polymer or copolymer.

11. Foam according to anyone of the preceding claims characterized in that it is shaped by pressforming or vacuumforming.

12. The use of the foam according to anyone of claims 1 to 11 to make soccer balls, sports gloves padding, immersion suits, golf club grips, rebound layer for table tennis rackets, ski poles, sports bat grips, snowboard or Λ/vindsurf pads, saddles, preferably for bicycles, or parts of ski boots.

13. The use of the foam according to anyone of claims 1 to 11 to make antislip coated tapes.

14. The use of the foam according to anyone of claims 1 to 11 to make lingerie articles, preferably bra cups.

15. The use of the foam according to anyone of claims 1 to 11 to make mouse pads, soft keyboards or buttons.

16. The use of the foam according to anyone of claims 1 to 11 to make trays for objects.

17. The use of the foam according to anyone of claims 1 to 11 to make gaskets.

18. The use of the foam according to anyone of claims 1 to 11 to make flexographic printing rolls.

19. The use of the foam according to anyone of claims 1 to 11 to make single or double adhesive coated tapes.

20. The use of the foam according to anyone of claims 1 to 11 to make orthopaedic insoles or inlays; footwear insoles or insocks; footwear midsoles; footwear linings, preferably watertight and water vapour breathable footwear linings; waterproof, breathable insoles or midsoles, footwear shafts or heel inserts.

21. The use of the foam according to anyone of claims 1 to 11 to make transdermal pads or woundcare plasters.

22. The use of the foam according to anyone of claims 1 to 11 to make sportswear garments or linings.

23. The use of the foam according to anyone of claims 1 to 11 to make cushioning of seats of ski lifts.