Patent Description:
Polyurethane (PU) is a polymer composed of organic units joined by carbamate (urethane) links. Polyurethane polymers are typically produced by the reaction of an isocyanate with at least two isocyanate groups with a polyol with at least two hydroxyl groups. Polyurethanes are used in the manufacture of high-resilience foam seating, footwear, rigid foam insulation panels, microcellular foam seals and gaskets, durable elastomeric wheels and tires, automotive suspension bushings, electrical potting compounds, high performance adhesives, surface coatings and surface sealants, synthetic fibers, carpet underlay, hard-plastic parts, hoses and so on.

When polyurethanes are used in the form of foams in applications such as soles for footwear, they could provide light weight with highly abrasion-resistant properties. Applications for such PU foams include a wide range of footwear types such as sports and trekking shoes and boots along with shoes for business and fashion shoe soles, as well as high-quality safety shoes. To achieve light weight soles the PU foam needs to have a low density (e.g., no greater than <NUM> grams/liter). In addition to light weight, the PU foam also needs to have sufficient hardness (e.g., Shore A hardness above <NUM>), high rebound properties (higher than <NUM> %), low compression set (lower than <NUM>%), and good split tear (e.g. split tear is above <NUM> N/mm). Split tear is a highlighted mechanical property of microcellur polyurethane foam for footwear application.

<CIT> discloses a low-density microporous polyurethane elastomer added with a thermal foaming microsphere and a preparation method thereof. By adding the thermal foaming microsphere, the invention prepares a low-density (<NUM>-<NUM>/cm) microporous polyurethane elastomer which is applied to the sole material; the obtained material has excellent additive mechanical property.

<CIT> discloses a polyurethane elastomer foam having improved mechanical properties such as ball rebound prepared using the reaction product of a combination of polytetramethylene ether glycol (polytetrahydrofuran) having a molecular weight of <NUM> to <NUM> and hydroxyl value of <NUM> to <NUM>, and monoethylene glycol, and <NUM>,<NUM>'-diphenylmethane diisocyanate (<NUM>,<NUM>'-MDI) as isocyanate prepolymer.

However, none of these applications describe how to produce a low-density polyurethane foam system with high split tear performance, which could be used as soles for footwear, such as sports and trekking shoes and boots along with shoes for business and fashion shoe soles, as well as high-quality safety shoes.

Embodiments of the present disclosure provide polyurethane foam produced in a "one shot process" that having low density (no greater than <NUM>/L) are semi-hard (Asker C hardness of <NUM> to <NUM>), display a high rebound value (vertical rebound of <NUM>% to <NUM> %) all while providing superior split tear performance. It has been surprisingly found that the use of both water and expandable microspheres as the blowing agent with polytetramethylene ether glycol (PTMEG) as the only polyols provides a polyurethane foam that display the above properties. The polyurethane foam of the present disclosure differs significantly from the prior art polyurethane foam is that, as noted, the blowing agent used in this polyurethane foam is the combination of water and expandable microspheres.

The polyurethane foam of the present disclosure has a density of <NUM> to <NUM>/L measured according to DIN EN ISO <NUM> and is formed by reacting a mixture that includes <NUM> to <NUM> weight percent (wt. %) of a polyol formulation and <NUM> to <NUM> wt. % of an isocyanate prepolymer, where the wt. % is based on the total weight of the mixture. The polyol formulation comprises <NUM> to <NUM> wt. % of a polytetramethylene ether glycol (PTMEG) with a weight average molecular weight (MWw) of <NUM> to <NUM>; a blowing agent combination of <NUM> to <NUM> wt. % of expandable microspheres and <NUM> to <NUM> wt. % of water; where the wt. % values for the polyol formulation are based on the total weight of the polyol formulation.

The polyol formulation further comprises a catalyst, a surfactant, a crosslinking agent, and other optional additives as ingredients in the polyol where the catalyst, the surfactant, the crosslinking agent, and other optional additives together bring the wt. % of the polyol formulation to <NUM> wt.

The isocyanate prepolymer includes <NUM> to <NUM> wt. % of an isocyanate component having at least <NUM> wt. % of <NUM>,<NUM>'-diphenylmethane diisocyanate; and <NUM> to <NUM> wt. % of the PTMEG, based on the total weight of the isocyanate prepolymer, wherein the NCO value of the isocyanate prepolymer is <NUM> to <NUM>. The mixture described herein does not include other polyols in either the polyol formulation or the isocyanate prepolymer. In other words, there is only one polyol PTMEG in the mixture that forms the polyurethane foam of the present disclosure.

For the embodiments, the polyol formulation includes <NUM> to <NUM> wt. % of water. In additional embodiments, the polyol formulation includes <NUM> to <NUM> wt. % of water.

For the embodiments, the polyol formulation includes <NUM> to <NUM> wt. % of expandable microspheres. In additional embodiments, the polyol formulation includes <NUM> to <NUM> wt. % of expandable microspheres.

As mentioned, the polyurethane foam has an Asker C hardness of <NUM> to <NUM> measured according to ASTM D2240. In addition, the polyurethane foam of the present disclosure can preferably have an Asker C hardness of <NUM> to <NUM>, more preferably <NUM>-<NUM>, measured according to ASTM D2240.

As mentioned, the polyurethane foam has a vertical rebound of <NUM>% to <NUM> % measured according to ASTM D2632.

The present disclosure also provides for a method of forming the polyurethane foam. The method includes preparing the polyol formulation by admixing at room temperature (<NUM>) and melting PTMEG at <NUM> overnight and then kept at <NUM>-<NUM> for a better handling and dosing together with other components; heating a polyol formulation to a temperature of <NUM> to <NUM> inside a stirred reactor tank of a polyurethane foam machine, and heating an isocyanate prepolymer to a temperature of <NUM> to <NUM> inside an isocyanate tank of a polyurethane foam machine; admixing the isocyanate prepolymer with the polyol formulation at atmospheric pressure and pour the mixture using the polyurethane foam machine into a heated mold with desired shape, where the mixture has <NUM> to <NUM> weight percent of a polyol formulation and <NUM> to <NUM> wt. % of an isocyanate prepolymer; closing the mold, allowing the reactants to fill the mold and reacting for given demolding time from <NUM> to <NUM> minutes to form a polyurethane foam.

The polyurethane foam of the present disclosure can be used in a "one shot process" to produce a shoe sole, a mid-sole or an insole for a shoe. The shoe sole may be used for forming an outer sole of a sandal type shoe, a midsole of an athletic type shoe, or an insole for insertion into any type of shoe.

Embodiments of the present disclosure provide polyurethane foam produced in a "one shot process" that having low density (no greater than <NUM>/L) are semi-hard (Asker C hardness of <NUM> to <NUM>), display a high rebound value (vertical rebound of <NUM>% to <NUM> %) all while providing superior split tear performance. It has been surprisingly found that the use of both water and expandable microspheres as the blowing agent with polytetramethylene ether glycol (PTMEG) as the only polyol provides a polyurethane foam that display the above properties. The polyurethane foam of the present disclosure differs significantly from the prior art polyurethane foam is that, as noted, the blowing agent used in this polyurethane foam is the combination of water and expandable microspheres.

The polyurethane foam of the present disclosure is ideal for the production of comfortable, single density shoe soles, mid-soles and/or insoles for casual applications, such as athletic or technical shoes. In addition, the polyurethane foam of the present disclosure is superior to other PU foams in terms of rebound and split tear. In addition, the only polyols used in forming the polyurethane foam is PTMEG and the blowing agents used are a combination of water and expandable microspheres. The blowing agent combination of water and expandable microspheres used together with solo polyols (PTMEG) in a "one shot" process of the present disclosure surprising gives a semi-hard PU foam with low density, high resiliency and superior split tear. In addition, the polyurethane foam of the present disclosure has good processing, cures well, has good surface quality and shows minimal shrinkage at demold, although its density is low.

The polyol formulation of the present disclosure includes <NUM>~<NUM> wt. % at least one extra diol chain extender agent, where the wt. % are based on the total weight of the polyol formulation. In additional embodiments, the polyol formulation includes <NUM>~<NUM> wt. % extra diol chain extender agent. Preferably, a mixture used to form the polyurethane foam does not include extra diol chain extender agent in the present disclosure. The extra chain extender agents for polyurethane are usually low molecular weight alcohol or amine compounds with two hydroxyl or amine functional groups. The examples of commonly used diol chain extenders are but not limited to <NUM>,<NUM>-propanediol, <NUM>,<NUM>-propanediol, <NUM>,<NUM>-butanediol (BDO), <NUM>,<NUM>-pentanediol, <NUM>,<NUM>-pentanediol, <NUM>,<NUM>-decanediol, <NUM>,<NUM>-dihydroxycyclohexane, <NUM>,<NUM>-dihydroxycyclohexane, <NUM>,<NUM>-dihydroxycyclohexane, monoethylene glycol (MEG), diethylene glycol and triethylene glycol, dipropylene glycol and tripropylene glycol, <NUM>,<NUM>-hexanediol and bis(<NUM>-hydroxyethyl) hydroquinone.

The polyurethane foam of the present disclosure has a density of <NUM> to <NUM> grams/liter (g/<NUM>) measured according to DIN EN ISO <NUM>. Preferably, the polyurethane elastomer foam of the present disclosure has a density of <NUM>/<NUM> to <NUM>/<NUM> measured according to DIN EN ISO <NUM>. This density of the polyurethane foam means the averaged density over the entire polyurethane foam. The polyurethane foam of the present disclosure also has an Asker C hardness of <NUM> to <NUM>, as measured by ASTM D2240. Preferably, the polyurethane foam of the present disclosure has an Asker C hardness of <NUM> to <NUM> measured according to ASTM D2240. More preferably the polyurethane foam of the present disclosure has an Asker C hardness of <NUM> to <NUM>, measured according to ASTM D2240. The polyurethane foam of the present disclosure also has a vertical rebound of <NUM>% to <NUM> % measured according to ASTM D2632. In addition, the polyurethane foam of the present disclosure preferably targets a compression set of no greater than <NUM>% as measured according to ASTM D <NUM>. Other properties of the polyurethane elastomer foam include a tear strength ranging from <NUM> to <NUM> N/mm measured according to ASTM D624; a tensile strength of <NUM> to <NUM> N/mm<NUM> as measured according to DIN <NUM>; elongation at break of <NUM> to <NUM> % as measured according to DIN <NUM>; The polyurethane foam of the present disclosure also has a split tear in a range of <NUM> to <NUM> N/mm, where the method for measuring the split tear is described in the Examples section below.

The polyurethane foam described herein is formed by reacting a mixture that includes <NUM> to <NUM> weight percent (wt. %) of a polyol formulation and <NUM> to <NUM> wt. % isocyanate prepolymer, where the wt. % is based on the total weight of the mixture. Preferably, the mixture includes <NUM> to <NUM> wt. % of the polyol formulation and <NUM> to <NUM> wt. % isocyanate prepolymer, where the wt. % is based on the total weight of the mixture. More preferably, the mixture includes <NUM> to <NUM> wt. % of the polyol formulation and <NUM> to <NUM> wt. % isocyanate prepolymer, where the wt. % is based on the total weight of the mixture. % of the polyol formulation and the isocyanate pre-polymer forming the mixture can add up to <NUM> wt. % where the wt. % is based on the total weight of the mixture.

The polyol formulation includes <NUM> to <NUM> wt. % of a solo glycol of a polytetramethylene ether glycol (PTMEG) with a weight average molecular weight (MWw) of <NUM> to <NUM>, where the wt. % are based on the total weight of the polyol formulation. The polyol formulation consisting of <NUM> to <NUM> wt. % of the PTMEG described herein is preferred. The polyol formulation consisting of <NUM> to <NUM> wt. % of the PTMEG is more preferred. In one embodiment, the polyol formulation preferably consists of <NUM> wt. % of the PTMEG described herein. In an additional preferred embodiment, the polyol formulation preferably consists of <NUM> wt. % of the PTMEG described herein.

Examples of the PTMEG include TERATHAE® PTMEG <NUM> commercially available from INVISTA. TERATHANE® PTMEG <NUM> has a weight average molecular weight of <NUM> to <NUM> and a hydroxyl number (mg KOH/gm) of <NUM> to <NUM>. Other examples of PTMEG suitable for the present disclosure include PolyTHF <NUM>, commercially available from BASF, which has a weight average molecular weight of <NUM> to <NUM>, and a hydroxyl number (mg KOH/gm) of <NUM> to <NUM>. Other PTMEGs having a MWw of <NUM> to <NUM> and a hydroxyl number of about <NUM> to about <NUM> are commercially available and would be suitable for the present disclosure.

The polyol formulation further includes a blowing agent combination of water and expandable microspheres. For the various embodiments, the water is present in the polyol formulation from <NUM> to <NUM> wt. % and the expandable microspheres are from <NUM> to <NUM> wt. %, where the wt. % are based on the total weight of the polyol formulation. Preferably, the water is present in the polyol formulation from <NUM> to <NUM> wt. More preferably, <NUM> to <NUM> wt. % of the water is present in the polyol formulation. The expandable microspheres are preferably present in the polyol formulation from <NUM> to <NUM> wt. %, more preferably from <NUM> to <NUM> wt. %, where the wt. % are based on the total weight of the polyol formulation.

Expandable microspheres are hollow microbeads comprise a thermoplastic polymer shell (such as polyacrylonitrile or copolymers thereof) encapsulating a hydrocarbon gas. When heated, the thermoplastic shell encapsulating the hydrocarbon gas softens. Concurrent with the softening of the thermoplastic shell, the gas expands and exerts an increasing pressure on the shell resulting in an increase in the volume of the microspheres. The temperature to which the material is exposed during reaction processing causes the plastics shell to soften and simultaneously causes the enclosed gas to expand. The result is that the microspheres expand. The expandability of the microspheres may be described by determining their TMA density [kg/m<NUM>] (Mettler Toledo Stare thermal analysis system; heating rate <NUM>/min). The TMA density here is the minimum achievable density at a certain temperature Tmax at atmospheric pressure prior to collapse of the microspheres. Any thermally expandable microspheres can be used in the present invention. However, microspheres containing hydrocarbons, in particular aliphatic or cycloaliphatic hydrocarbons, are preferred. The term "hydrocarbon" as used herein is intended to include non-halogenated and partially or fully halogenated hydrocarbons. Examples of expandable microspheres suitable for use in this disclosure include without limitation EXPANCEL WU, EXPANCEL DU, EXPANCEL SL and EXPANCEL MB series which are expandable microspheres commercially available from AkzoNobel company and ADVANCELL EM which are expandable microspheres commercially available from Sekisui Chemical Company. Other expandable microspheres that are commercially available or known to one skilled in the art are also suitable for use in this invention.

The polyol formulation further includes a catalyst, a surfactant, a crosslinking agent, and other optional additives as ingredients in the polyol formulation. For the various embodiments, the catalyst, the surfactant, the crosslinking agent, and other optional additives together bring the wt. % of the polyol formulation to <NUM> wt.

As catalysts, it is possible to use all compounds which accelerate the reaction between isocyanate groups and hydroxyl groups. Such compounds are known and are described, for example, in "<NPL>. These compounds include amine-based catalysts, catalysts based on organic metal compounds and tetraalkylstannoxy based catalysts. Examples of amine based catalysts include a triethylendiamine (TEDA) based catalyst, a triethanolamine (TEA) based catalyst, a diisopropylethanolamine (DIEA) based catalyst, a pentamethyldiethylenetriamine based catalyst, a tertamethyl butanediamine based catalyst, a dimethylcyclohexylamine based catalyst, a bis(dimethylaminopropyl)methylamine based catalyst, a bis(<NUM>-dimethylaminoethyl) ether and a <NUM>,<NUM>-Diazabicyclo[<NUM>. <NUM>]undec-<NUM>-ene (DBU) based catalyst. Other examples of suitable catalysts include <NUM>,<NUM>-dimethyl-<NUM>,<NUM>,<NUM>,<NUM>-tetrahydropyrimidine, tertiary amines such as triethylamine, tributylamine, dimethylbenzylamine, N-methyl, N-ethyl, N-cyclohexylmorpholine, N, N, N', N'-tetramethylethylenediamine, N, N, N', N'-tetramethyl-butanediamine, N, N, N ', N'-tetramethyl-hexanediamine, pentamethyl-diethylenetriamine, Tetramethyldiaminoethylether, bis-(dimethylaminopropyl)-urea, N,N-dimethylbenzylamine, dimethylpiperazine, <NUM>,<NUM>-dimethylimidazole, <NUM>-methylimidazole, <NUM>-azabicyclo (<NUM>,<NUM>,<NUM>) octane and preferably <NUM>,<NUM>-diazabicyclo (<NUM>,<NUM>,<NUM>) octane and alkanolamine compounds such as triethanolamine, triisopropanolamine, N-methyl- and N-ethyldiethanolamine and dimethylethanolamine. Examples of organic metal catalyst compounds include zinc salts such as zinc octoate, organic tin compounds such as tin (II) salts of organic carboxylic acids, tin (II) acetate, tin (II) octoate, tin (II) ethylhexanoate and tin (II) laurate, and the dialkyl tin (IV) salts of organic carboxylic acids, dibutyltin diacetate, dibutyltin dilaurate, dibutyltin maleate and dioctyltin diacetate, and also bismuth, such as bismuth (III) neodecanoate, bismuth <NUM>-ethylhexanoate and bismuth octanoate or mixtures thereof. The amine based catalysts can be used alone or in combination with organic metal catalyst compounds. The catalyst may represent from <NUM> wt. % to <NUM> wt. % based on the total weight of the polyol formulation.

Examples of commercially available catalysts include DABCO® EG (EVONIK Nutrition & Care GmbH), DABCO® <NUM> LM (Air Products/ Evonik), MAX™ A-I Catalyst (Momentive Performance Materials Inc. ); FOMREZ™ UL <NUM> (Momentive Performance Materials Inc. ); DABCO® BDMA (Air Products) and DABCO® XD <NUM> (Air Products/Evonik).

Surfactants suitable for the present disclosure include silicone-comprising surfactants such as siloxane-oxyalkylene copolymers and other organopolysiloxanes. Alkoxylation products of fatty alcohols, oxo alcohols, fatty amines, alkylphenols, dialkylphenols, alkylcresols, alkylresorcinol, naphthol, alkylnaphthol, naphthylamine, aniline, alkylaniline, toluidine, bisphenol A, alkylated bisphenol A, polyvinyl alcohol and also further alkoxylation products of condensation products of formaldehyde and alkylphenols, formaldehyde and dialkylphenols, formaldehyde and alkylcresols, formaldehyde and alkylresorcinol, formaldehyde and aniline, formaldehyde and toluidine, formaldehyde and naphthol, formaldehyde and alkylnaphthol and also formaldehyde and bisphenol A or mixtures of two or more of these foam stabilizers can also be used. Examples of such surfactants include DABCO® DC <NUM> (Air Products) and TEGOSTAB™ B <NUM> (EVONIK Nutrition & Care GmbH) and DABCO® DC <NUM> (Air Products). The surfactants may represent from <NUM> wt. % to <NUM> wt. % based on the total weight of the polyol formulation.

Crosslinking agents used for the present disclosure include, but are not limited to, low-molecular weight compounds containing at least two moieties selected from hydroxyl groups, primary amino groups, secondary amino groups, and other active hydrogen-containing groups which are reactive with an isocyanate group. Crosslinking agents include, for example, polyhydric alcohols (especially trihydric alcohols, such as glycerol and trimethylolpropane), polyamines, and combinations thereof. Non-limiting examples of polyamine crosslinking agents include diethyltoluenediamine, chlorodiaminobenzene, diethanolamine, diisopropanolamine, triethanolamine, tripropanolamine, <NUM>,<NUM>-hexanediamine, and combinations thereof. Typical diamine crosslinking agents comprise twelve carbon atoms or fewer, more commonly seven or fewer. Examples of such crosslinking agents include Diethanolamine pure (BASF) or Glycerine (DOW). The crosslinking agents may represent from <NUM> wt. % to <NUM> wt. % based on the total weight of the polyol formulation.

The isocyanate pre-polymer includes <NUM> to <NUM> wt. % of an isocyanate blend having at least <NUM> wt. % of <NUM>,<NUM>'-diphenylmethane diisocyanate, and <NUM> to <NUM> wt. % of the PTMEG, based on the total weight of the isocyanate prepolymer, wherein the NCO value of the isocyanate prepolymer is <NUM> to <NUM>. Preferably, the NCO value of the isocyanate prepolymer the isocyanate prepolymer is <NUM> to <NUM>. Preferably, the isocyanate prepolymer includes <NUM> to <NUM> wt. % of the isocyanate blend and <NUM> to <NUM> wt. % of the PTMEG. Preferably, the isocyanate blend can include <NUM> to <NUM> wt. % of <NUM>,<NUM>'-diphenylmethane diisocyanate and <NUM> to <NUM> wt. % of <NUM>,<NUM>'-MDI, uretonimine or carbodiimide modified <NUM>,<NUM>'-MDI. More preferably, the isocyanate blend can include <NUM> to <NUM> wt. % of <NUM>,<NUM>'-diphenylmethane diisocyanate and <NUM> to <NUM> wt. % of carbodiimide modified <NUM>,<NUM>'-MDI. Example of such isocyanate prepolymer includes Isocyanate prepolymer ISO <NUM>/<NUM> (BASF).

The polyurethane forming composition of the present invention may further comprise one or more additional additives, such as pigments, reinforcing materials such as glass fibers, anti-hydrolysis agents, antistatic agents, flame retardants, anti-oxidants and anti-abrasion agents etc. Each of the additional additives, when present, can be added to either of the polyol formulation or the isocyanate pre-polymer.

The present disclosure also provides for a method of forming the polyurethane foam. The method includes preparing the polyol formulation by admixing at room temperature (<NUM>) and melting PTMEG at <NUM> overnight and then kept at <NUM>-<NUM> for a better handling and dosing together with other components; heating a polyol formulation to a temperature of <NUM> to <NUM>; heating an isocyanate prepolymer to a temperature of <NUM> to <NUM> inside an isocyanate tank of a polyurethane foam machine, and admixing the isocyanate pre-polymer with the polyol formulation at atmospheric pressure and pour the mixture using the polyurethane foam machine into a heated mold with desired shape; closing the mold, allowing the reactants to fill the mold and reacting for given demolding time to form a polyurethane foam. The polyurethane forming composition of the present invention in the method has <NUM> to <NUM> weight percent of a polyol formulation and <NUM> to <NUM> wt. % of an isocyanate prepolymer, wherein the wt. % is based on the total weight of the polyurethane forming composition.

The polyurethane foam according to the present disclosure is preferably produced by the one shot process using a low-pressure or a high-pressure technique in closed mold, advantageously heated molds. The polyurethane elastomer foam according to the present disclosure can also be produced in an open mold using a pouring or casting machine, as are known. The molds are usually metal (e.g., aluminum or steel) and set to a temperature of <NUM> to <NUM>. The demolding time is from <NUM> to <NUM>. Optionally, the forms may already contain other parts of the shoe sole, such as the outer sole or parts of the midsole.

<FIG> Shows a split tear test specimen after preparation for test showing position of splits and mark.

The following examples are provided to illustrate various embodiments. All components purchased from commercial vendors and used as received unless otherwise noted. All percentages are weight percentages (wt. %) based on the total weight of the mixture used to form the polyurethane elastomer foam, unless otherwise noted.

The components used for preparing the polyurethane elastomer foam of the following Examples are listed in Table <NUM>.

Mechanical properties are determined according to the procedure listed in the following standards in Table <NUM>.

The split tear test is based on the SATRA TM65 (<NUM>), keep the same preparation of test specimens according to article <NUM>, while the sample size was modified to a thickness of <NUM>±<NUM> and cutting <NUM> rectangular <NUM>±<NUM>×<NUM>±<NUM> from the sheet material.

Table <NUM> below lists Comparative Examples <NUM>, which include various polyol formulations but exclude expandable microspheres in Comparative Example <NUM>.

To form the polyurethane elastomer foam of Example <NUM>-<NUM>, heat the formulated polyol formulation at their given weight percent (wt. %) to a temperature of <NUM> to <NUM> inside the stirred reactor tank and heat the isocyanate pre-polymer at its given weight percent (wt. %) to a temperature of <NUM> to <NUM> in an isocyanate tank of a low pressure machine (Zhejiang Haifeng Shoemaking Equipment Co. Heat an aluminum mold (test plate mold <NUM> × <NUM> × <NUM>) to a temperature of <NUM>. Admix given parts in the table <NUM> of the isocyanate pre-polymer with <NUM> parts by weight of the polyol formulation at atmospheric pressure and pour the admixture using the low pressure machine into the heated aluminum mold. Close the mold, allow the reactants to fill the mold and react for given demolding time in the table <NUM>.

Open the mold and demold the polyurethane elastomer foam. Allow the polyurethane elastomer foam to cure for <NUM> hours at <NUM> and <NUM> % relative humidity before testing the physical properties of the polyurethane elastomer foam.

Claim 1:
A polyurethane foam having a density of <NUM> to <NUM>/L measured according to DIN EN ISO <NUM>, where the polyurethane foam is formed by reacting a mixture consisting of:
<NUM> to <NUM> weight percent (wt. %) of a polyol formulation and <NUM> to <NUM> wt.% of an isocyanate prepolymer, wherein the wt. % is based on the total weight of the mixture;
wherein the polyol formulation comprises <NUM> to <NUM> wt.% of a polytetramethylene ether glycol (PTMEG) with a weight average molecular weight (MWw) of <NUM> to <NUM>, <NUM> to <NUM> wt. % of expandable microspheres and <NUM> to <NUM> wt. % of water, where the wt.% values for the polyol formulation are based on the total weight of the polyol formulation.