Tear-resistant low-density polyurethane foam system

Abstract

The low-density polyurethane foams produced by the "one-shot process" are semi-rigid, exhibit high rebound values, and provide excellent tear resistance. The polyurethane foams of the present disclosure can be used in the "one-shot process" to form shoe soles, midsoles, or insoles for shoes. The shoe soles can be used to form outer soles for sandal-type shoes, midsoles for athletic-type shoes, or insoles for insertion into any type of shoe.

Description

Technical Field

[0001] The present invention relates to a low-density polyurethane foam that is useful for footwear applications and has high tear strength.

Background Art

[0002] Polyurethane (PU) is a polymer composed of organic units linked by carbamate (urethane) linkages. Polyurethane polymers are usually produced by the reaction of an isocyanate having at least two isocyanate groups with a polyol having at least two hydroxy groups. Polyurethane is used in the manufacture of high-resilience foam seats, 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 underlays, rigid plastic parts, hoses, and the like.

[0003] When polyurethane is used in the form of foam for applications such as footwear soles, the polyurethane can provide lightweight with high wear resistance. Such applications of PU foam include a wide range of types of footwear (e.g., business shoes and fashion shoe soles, as well as sports and trekking shoes and boots, and high-quality safety shoes). To achieve a lightweight sole, the PU foam needs to be of low density (e.g., 400 g / L or less). In addition to weight reduction, the PU foam needs to have sufficient hardness (e.g., Shore A hardness of 40 or more), high resilience characteristics (more than 50%), low compression strain (less than 20%), and good tear strength (e.g., tear strength exceeding 1.8 N / mm). Tear strength has been attracting attention as a mechanical property of microcellular polyurethane foam for footwear applications.

[0004] CN101486801B discloses a low-density microporous polyurethane elastomer with added thermo-expandable microspheres and a method for producing the same. This invention produces a low-density (0.28-0.32 g / cm³) microporous polyurethane elastomer by adding thermo-expandable microspheres and applies it as a material for shoe soles. The resulting material has excellent additional mechanical properties.

[0005] WO2018 / 160945A1 discloses a polyurethane elastomer foam with improved mechanical properties (e.g., ball rebound) produced by a reaction product of a combination of polytetramethylene ether glycol (polytetrahydrofuran) with a molecular weight of 1900-2100 and a hydroxyl value of 53-60 and monoethylene glycol, and 4,4'-diphenylmethane diisocyanate (4,4'-MDI) as an isocyanate prepolymer. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] CN101486801B [Patent Document 2] WO2018 / 160945A1 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, these applications do not describe a method for manufacturing a low-density polyurethane foam system having strong tear resistance that can be used as the soles of footwear (for example, business shoes and fashion shoes, as well as sports and trekking shoes and boots, and high-quality safety shoes). [Means for solving the problem]

[0008] Embodiments of this disclosure provide a low-density (400 g / L or less) polyurethane foam manufactured by a "one-shot process" that is semi-rigid (Asker C hardness 25-70), exhibits high rebound value (vertical rebound 55-65%), and has excellent split-tear properties. Surprisingly, it was found that a polyurethane foam exhibiting the above properties can be obtained by using polytetramethylene ether glycol (PTMEG) as the sole polyol and both water and expandable microspheres as blowing agents. What distinguishes the polyurethane foam of this disclosure from the prior art polyurethane foam is, as mentioned above, the combination of water and expandable microspheres as the blowing agent used in this polyurethane foam.

[0009] The polyurethane foams of this disclosure have a density of 150 to 400 g / L as measured in accordance with DIN EN ISO 845 and are formed by reacting a mixture containing 80 to 50 mass percent (mass%) of a polyol formulation with 20 to 50 mass percent (mass%) of an isocyanate prepolymer (mass%) based on the total mass of the mixture. The polyol formulation contains 90 to 98 mass percent of polytetramethylene ether glycol (PTMEG) with a weight-average molecular weight (MWw) of 1800 to 2100, and a combination of 0.1 to 6 mass percent of expandable microspheres and 0.5 to 3 mass percent of water as a blowing agent (the mass percent value of the polyol formulation is based on the total mass of the polyol formulation).

[0010] The polyol formulation further contains a catalyst, surfactant, crosslinking agent, and other optional additives as components of the polyol, and when the catalyst, surfactant, crosslinking agent, and other optional additives are combined, the mass percentage of the polyol formulation becomes 100% by mass.

[0011] The isocyanate prepolymer contains 40-70% by mass of an isocyanate component having at least 92% by mass of 4,4'-diphenylmethane diisocyanate and 30-60% by mass of PTMEG, based on the total mass of the isocyanate prepolymer (the NCO value of the isocyanate prepolymer is 15-22). The mixtures described herein do not contain other polyols in either the polyol formulation or the isocyanate prepolymer. In other words, the mixtures forming the polyurethane foams of this disclosure contain only one polyol, PTMEG.

[0012] In one embodiment, the polyol formulation contains 0.8 to 2% by mass of water. In another embodiment, the polyol formulation contains 1.4 to 2% by mass of water.

[0013] In one embodiment, the polyol formulation contains 0.5 to 5% by mass of expandable microspheres. In an additional embodiment, the polyol formulation contains 1 to 5% by mass of expandable microspheres.

[0014] As described above, the polyurethane foam has an Asker C hardness of 25 to 70 as measured in accordance with ASTM D2240. In addition, the polyurethane foam of this disclosure may preferably have an Asker C hardness of 30 to 55, more preferably 35 to 55, as measured in accordance with ASTM D2240.

[0015] As mentioned above, polyurethane foam has a vertical rebound of 55% to 65% as measured in accordance with ASTM D2632.

[0016] This disclosure also provides a method for forming polyurethane foam. This method is The polyol formulation is prepared by mixing at room temperature (23°C), then melting the PTMEG at 70°C overnight, and then maintaining the PTMEG at 40-50°C for good handling with other components and for adding other components; Heating the polyol formulation to a temperature of 40 to 45 °C in the stirring reaction tank of the polyurethane foam equipment, and heating the isocyanate prepolymer to a temperature of 30 to 45 °C in the isocyanate tank of the polyurethane foam equipment; Mixing the isocyanate prepolymer and the polyol formulation under atmospheric pressure (where the mixture has 50 to 80% by mass of the polyol formulation and 20 to 50% by mass of the isocyanato prepolymer), and injecting the mixture into a heated mold of a desired shape using the polyurethane foam equipment; Closing the mold and reacting the reactants while filling the mold for a predetermined demolding time of 5 to 15 minutes to form a polyurethane foam; including.

Effect of the Invention

[0017] The polyurethane foam of the present disclosure can be used in the "one-shot process" to form shoe soles, midsoles, or insoles for shoes. The shoe sole may be used to form 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.

Brief Description of the Drawings

[0018] [Figure 1] It shows the tearing position and marks on the tear test piece after test preparation.

Modes for Carrying Out the Invention

[0019] Embodiments of this disclosure provide a polyurethane foam manufactured by a "one-shot process" that is low in density (less than 400 g / L), semi-rigid (Asker C hardness 25-70), exhibits high rebound (vertical rebound 55-65%), and provides excellent tear resistance. Surprisingly, it was found that a polyurethane foam exhibiting the above properties could be obtained by using only polytetramethylene ether glycol (PTMEG) as the sole polyol and both water and expandable microspheres as blowing agents. What distinguishes the polyurethane foam of this disclosure from the prior art polyurethane foam is, as mentioned above, the combination of water and expandable microspheres as the blowing agent used in this polyurethane foam.

[0020] The polyurethane foam of this disclosure is ideal for the manufacture of comfortable, single-density soles, midsoles, and / or insoles for casual applications such as athletic or technical shoes. In addition, the polyurethane foam of this disclosure is superior to other PU foams in terms of resilience and tear resistance. Furthermore, the polyol used to form the polyurethane foam is PTMEG only, and the foaming agent used is a combination of water and expandable microspheres. The combination of water and expandable microspheres used as a foaming agent with a single polyol (PTMEG) in the “one-shot” process of this disclosure remarkably gives a semi-rigid PU foam with low density, high resilience, and excellent tear resistance. In addition, despite its low density, the polyurethane foam of this disclosure has good processability, good curability, good surface quality, and exhibits minimal shrinkage upon demolding.

[0021] The polyol formulations of the present disclosure include from 0 to 5% by weight of at least one additional diol chain extender (weight % is based on the total weight of the polyol formulation). In additional embodiments, the polyol formulation includes from 0.5 to 5% by weight of the additional diol chain extender. Preferably, the mixture used to form the polyurethane foam does not include an additional diol chain extender in the present disclosure. Additional chain extenders for polyurethanes are typically low molecular weight alcohol or amine compounds having two hydroxy functional groups or amine functional groups. Examples of commonly used diol chain extenders include, but are not limited to, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol (BDO), 1,2-pentanediol, 1,3-pentanediol, 1,10-decanediol, 1,2-dihydroxycyclohexane, 1,3-dihydroxycyclohexane, 1,4-dihydroxycyclohexane, monoethylene glycol (MEG), diethylene glycol and triethylene glycol, dipropylene glycol and tripropylene glycol, 1,6-hexanediol and bis(2-hydroxyethyl)hydroquinone.

[0022] The polyurethane foams of this disclosure have a density of 150 to 400 grams / liter (g / L) as measured in accordance with DIN EN ISO 845. Preferably, the polyurethane elastomer foams of this disclosure have a density of 250 g / L to 350 g / L as measured in accordance with DIN EN ISO 845. This density of the polyurethane foam refers to the average density throughout the polyurethane foam. The polyurethane foams of this disclosure also have an Asker C hardness of 25 to 70 as measured by ASTM D2240. Preferably, the polyurethane foams of this disclosure have an Asker C hardness of 30 to 55 as measured in accordance with ASTM D2240. More preferably, the polyurethane foams of this disclosure have an Asker C hardness of 35 to 55 as measured in accordance with ASTM D2240. The polyurethane foams of this disclosure also have a vertical rebound of 55% to 65% as measured in accordance with ASTM D2632. Furthermore, the polyurethane foams of this disclosure preferably have a compression set of 20% or less as measured in accordance with ASTM D395. Other properties of the polyurethane elastomer foams include tear strength in the range of 7 to 10 N / mm as measured in accordance with ASTM D624; and tear strength in the range of 1.5 to 3 N / mm as measured in accordance with DIN 53504. 2 The polyurethane foam of this disclosure has a tensile strength of 350-450% elongation at break as measured in accordance with DIN 53504; the split tear of the polyurethane foam of this disclosure also has a split tear of 1.2-5 N / mm, the method for measuring the split tear is described in the Examples section below.

[0023] The polyurethane foam described herein is formed by reacting a mixture containing 80 to 50 mass percent (mass%) of a polyol formulation with 20 to 50 mass percent (mass%) of an isocyanate prepolymer (mass%). Preferably, the mixture contains 70 to 55 mass percent of the polyol formulation and 30 to 45 mass percent of the isocyanate prepolymer (mass%). More preferably, the mixture contains 59 to 57 mass percent of the polyol formulation and 41 to 43 mass percent of the isocyanate prepolymer (mass%). The mass percent of the polyol formulation and isocyanate prepolymer forming the mixture can be increased up to 100 mass percent (mass%).

[0024] The polyol formulation contains 90 to 98% by mass of a single glycol of polytetramethylene ether glycol (PTMEG) having a weight-average molecular weight (MWw) of 1800 to 2100 (mass% is based on the total mass of the polyol formulation). A polyol formulation consisting of 90 to 96% by mass of the PTMEG described herein is preferred. A polyol formulation consisting of 93 to 96% by mass of PTMEG is more preferred. In one embodiment, the polyol formulation preferably consists of 94.8% by mass of the PTMEG described herein. In a further preferred embodiment, the polyol formulation preferably consists of 94.3% by mass of the PTMEG described herein.

[0025] An example of a PTMEG is TERATHAE® PTMEG2000, commercially available from INVISTA. TERATHAE® PTMEG 2000 has a weight-average molecular weight of 1900–2100 and a hydroxyl value of 53.4–59.1 (mgKOH / gm). Another example of a PTMEG suitable for this disclosure is PolyTHF2000, commercially available from BASF, which has a weight-average molecular weight of 1950–2050 and a hydroxyl value of 54.7–57.5 (mgKOH / gm). Other commercially available PTMEGs with MWw of 1800–2100 and a hydroxyl value of approximately 53–60 would also be suitable for this disclosure.

[0026] The polyol formulation further comprises a combination of water and a foaming agent of expandable microspheres. In various embodiments, water is present in the polyol formulation at a concentration of 0.5 to 3% by mass, and expandable microspheres at a concentration of 0.1 to 6% by mass (mass percent is based on the total mass of the polyol formulation). Preferably, water is present in the polyol formulation at a concentration of 0.8 to 2% by mass. More preferably, water is present in the polyol formulation at a concentration of 1.4 to 2% by mass. The expandable microspheres are preferably present in the polyol formulation at a concentration of 0.5 to 5% by mass, more preferably 1 to 5% by mass (mass percent is based on the total mass of the polyol formulation).

[0027] Expandable microspheres are hollow microbeads containing a thermoplastic polymer shell (e.g., polyacrylonitrile or a copolymer thereof) encapsulating hydrocarbon gas. When heated, the thermoplastic resin shell containing the hydrocarbon gas softens. As the thermoplastic shell softens, the gas expands, increasing the pressure on the shell and thus increasing the volume of the microspheres. Depending on the temperature to which the material is exposed during the reaction process, the plastic shell softens and the enclosed gas expands simultaneously. As a result, the microspheres expand. The expandability of the microspheres is expressed as TMA density [kg / m³]. 3 This can be determined by measuring the TMA density (TMA density) at a certain temperature T before the microspheres disintegrate. maxand the minimum density achievable at atmospheric pressure. Any thermally expandable microspheres can be used in the present invention. However, microspheres containing hydrocarbons (particularly aliphatic hydrocarbons or cycloaliphatic hydrocarbons) are preferred. As used herein, the term "hydrocarbon" is intended to include non-halogenated hydrocarbons and partially or fully halogenated hydrocarbons. Examples of expandable microspheres suitable for use in this disclosure include, but are not limited to, the EXPANCEL WU, EXPANCEL DU, EXPANCEL SL and EXPANCEL MB series, which are commercially available from AkzoNobel, and the ADVANCELL EM, which is commercially available from Sekisui Chemical Co., Ltd. Other commercially available expandable microspheres or those known to those skilled in the art are also suitable for use in the present invention.

[0028] The polyol formulation further comprises a catalyst, a surfactant, a crosslinking agent, and other optional additives as components of the polyol formulation. In various embodiments, the catalyst, surfactant, crosslinking agent, and other optional additives together make the mass% of the polyol formulation 100% by mass.

[0029] Any compound that promotes the reaction between an isocyanate group and a hydroxyl group can be used as a catalyst. Such compounds are well known and are described, for example, in "Kunststoffhandbuch, volume 7, Polyurethane," Carl Hanser Verlag, 3rd edition, 1993, Chapter 3.4.1. These compounds include amine catalysts, organometallic compound catalysts, and tetraalkylstanoxy catalysts. Examples of amine catalysts include triethylenediamine (TEDA) catalysts, triethanolamine (TEA) catalysts, diisopropylethanolamine (DIEA) catalysts, pentamethyldiethylenetriamine catalysts, tetramethylbutanediamine catalysts, dimethylcyclohexylamine catalysts, bis(dimethylaminopropyl)methylamine catalysts, bis(2-dimethylaminoethyl) ether, and 1,8-diazabicyclo[5.4.0]-7-undecene (DBU) catalysts. Other examples of suitable catalysts include 2,3-dimethyl-3,4,5,6-tetrahydropyrimidine, tertiary amines such as triethylamine, tributylamine, dimethylbenzylamine, N-methyl, N-ethyl, N-cyclohexylmorpholine, N,N,N',N'-tetramethylethylenediamine, N,N,N',N'-tetramethylbutanediamine, N,N,N',N'-tetramethylhexanediamine, pentamethyldiethylenetriamine, and tetramethyldiaminoe Examples include tyl ethers, bis-(dimethylaminopropyl)-urea, N,N-dimethylbenzylamine, dimethylpiperazine, 1,2-dimethylimidazole, 1-methylimidazole, 1-azabicyclo(3,3,0)octane, preferably 1,4-diazabicyclo(2,2,2)octane, alkanolamine compounds, such as triethanolamine, triisopropanolamine, N-methyl- and N-ethyldiethanolamine, and dimethylethanolamine.Examples of organometallic catalyst compounds include zinc salts, e.g., zinc octate; organotin compounds, e.g., tin(II) salts of organic carboxylic acids, tin(II) acetate, tin(II) octoate, tin(II) ethylhexanoate, tin(II) laurate; dialkyltin(IV) salts of organic carboxylic acids, dibutyltin diacetate, dibutyltin dilaurate, dibutyltin maleate, dioctyltin diacetate; bismuth, e.g., bismuth(III) neodecanoate, bismuth 2-ethylhexanoate, bismuth octanoate, or mixtures thereof. Amine catalysts can be used alone or in combination with organometallic catalyst compounds. The catalyst can be expressed in amounts from 0.01% to 2% by mass, based on the total mass of the polyol formulation. Examples of commercially available catalysts include DABCO®EG (EVONIK Nutrition & Care GmbH), DABCO®33 LM (Air Products / Evonik), MAX®Al Catalyst (Momentive Performance Materials Inc.), FOMREZ®UL 22 (Momentive Performance Materials Inc.), DABCO®BDMA (Air Products), and DABCO®XD 102 (Air Products / Evonik).

[0030] Suitable surfactants for this disclosure include silicone-containing surfactants, such as siloxane-oxyalkylene copolymers and other organopolysiloxanes. Fatty alcohols, oxo alcohols, fatty amines, alkylphenols, dialkylphenols, alkyl cresols, alkyl resorcinols, naphthol, alkyl naphthols, naphthylamines, aniline, alkylaniline, toluidine, bisphenol A, alkylated bisphenol A, alkoxylated products of polyvinyl alcohols; furthermore, alkoxylated products of the following condensation products, condensation products of formaldehyde and alkylphenols, condensation products of formaldehyde and dialkylphenols, condensates of formaldehyde and alkyl cresols, condensation products of formaldehyde and alkyl resorcinols, condensation products of formaldehyde and aniline, condensation products of formaldehyde and toluidine, condensation products of formaldehyde and naphthol, condensation products of formaldehyde and alkylnaphthols, condensation products of formaldehyde and bisphenol A, or mixtures of two or more of these foaming stabilizers can also be used. Examples of such surfactants include DABCO® DC 193 (Air Products), TEGOSTAB® B 2114 (EVONIK Nutrition & Care GmbH), and DABCO® DC 3043 (Air Products). The amount of surfactant can range from 0.05% to 3% by mass, based on the total mass of the polyol formulation.

[0031] Examples of crosslinking agents used in this disclosure include, but are not limited to, low molecular weight compounds comprising at least two moieties selected from hydroxyl groups, primary amino groups, secondary amino groups, and other active hydrogen-containing groups that react with isocyanate groups. Examples of crosslinking agents include polyhydric alcohols (particularly trihydric alcohols, e.g., glycerol, trimethylolpropane), polyamines, and combinations thereof. Non-limiting examples of polyamine crosslinking agents include diethyltoluenediamine, chlorodiaminobenzene, diethanolamine, diisopropanolamine, triethanolamine, tripolanolamine, 1,6-hexanediamine, and combinations thereof. Typical diamine crosslinking agents contain 12 or fewer carbon atoms, more commonly 7 or fewer carbon atoms. Examples of such crosslinking agents include diethanolamine (pure) (BASF) or glycerin (DOW). The amount of crosslinking agent can be 0.05% to 3% by mass, based on the total mass of the polyol formulation.

[0032] The isocyanate prepolymer comprises 40-70% by mass of an isocyanate mixture having at least 92% by mass of 4,4'-diphenylmethane diisocyanate and 30-60% by mass of PTMEG (based on the total mass of the isocyanate prepolymer), and the NCO value of the isocyanate prepolymer is 15-22. Preferably, the NCO value of the isocyanate prepolymer is 18-20. Preferably, the isocyanate prepolymer comprises 60-65% by mass of an isocyanate mixture and 35-40% by mass of PTMEG. Preferably, the isocyanate mixture may contain 93-100% by mass of 4,4'-diphenylmethane diisocyanate and 7-0% by mass of 2,4'-MDI, uretonimine, or carbodiimide-modified 4,4'-MDI. More preferably, the isocyanate mixture may contain 96-98% by mass of 4,4'-diphenylmethane diisocyanate and 4-2% by mass of carbodiimi-modified 4,4'-MDI. An example of such an isocyanate prepolymer is isocyanate prepolymer ISO 136 / 26 (BASF).

[0033] The polyurethane-forming composition of the present invention may further contain one or more additional additives (e.g., pigments, reinforcing materials such as glass fibers, hydrolysis inhibitors, antistatic agents, flame retardants, antioxidants, and abrasion inhibitors). Each of the additional additives, if present, can be added to either the polyol formulation or the isocyanate prepolymer.

[0034] This disclosure also provides a method for forming polyurethane foam. This method is The polyol formulation is prepared by mixing at room temperature (23°C), then melting the PTMEG at 70°C overnight, and then maintaining the PTMEG at 40-50°C for good handling with other components and for adding other components; Heating the polyol-containing material to a temperature of 40-45°C; Heating the isocyanate prepolymer to a temperature of 30-45°C in the isocyanate tank of a polyurethane foaming apparatus; mixing the isocyanate prepolymer and polyol compound under atmospheric pressure; and injecting the mixture into a heated mold of the desired shape using the polyurethane foaming apparatus; The method includes closing the mold and allowing the reaction to proceed for a predetermined demolding time while the reactants remain filled in the mold, thereby forming a polyurethane foam. The polyurethane-forming composition of the present invention in this method comprises 50 to 80% by mass of a polyol compound and 20 to 50% by mass of an isocyanate prepolymer (the mass percentage is based on the total mass of the polyurethane-forming composition).

[0035] The polyurethane foam according to this disclosure is preferably manufactured by a one-shot process using low-pressure or high-pressure techniques in a closed mold (preferably a heated mold). The polyurethane elastomer foam according to this disclosure may also be formed in an open mold using a casting or casting machine, as is known. The mold is usually made of metal (e.g., aluminum or steel) and is set to a temperature of 50-60°C. Demolding time is 5-15 minutes. Optionally, the foam may already contain other parts of a shoe sole (e.g., an outsole or midsole). [Examples]

[0036] The following examples are provided to illustrate various embodiments and are not intended to limit the scope of the claims. All components purchased from the market were used as received, unless otherwise noted. All percentages are mass percentages (mass%) based on the total mass of the mixture used to form the polyurethane elastomer foam, unless otherwise noted. Examples 1, 5, and 6 are for reference only.

[0037] Table 1 shows the components used to prepare the polyurethane elastomer foam in the following examples. PolyTHF® 2000 has a weight-average molecular weight (MWw) between 1950 and 2050.

[0038] [Table 1]

[0039] Mechanical properties are measured according to the procedures described in the standards in Table 2 below.

[0040] [Table 2]

[0041] Tear test method: The tear test was conducted according to SATRA TM65 (1992). Specimen preparation was carried out in the same manner as in Article 5, but the sample size was changed to a thickness of 10 ± 1 mm, and three rectangles measuring 25 ± 1 mm × 160 ± 5 mm were cut from the sheet material.

[0042] The procedure is as follows: 1. Divide one end of each test specimen at a distance of 16 ± 4 mm midway between the top and bottom surfaces. Next, create four consecutive 30 mm sections on the test specimen, as shown in Figure 1. The cutting tools and cutting methods shall be as specified in Sections 6.1 and 6.2.

[0043] 2. Set the jaw separation speed to 100 ± 10 mm / min and operate until the crack propagates or reaches the surface in 4 × 30 mm increments, as indicated by the marks in Figure 1. If the crack does not propagate along the center of the specimen and reaches the surface before reaching the 120 mm (4 × 30 mm) mark, that value is not counted.

[0044] 3. Repeat step 2 above for the remaining two samples.

[0045] Data collection and analysis: 1. Record the lowest values ​​of each of the four parts of each sample. Calculate the average of the four lowest values ​​for each sample and record the result in units of N / mm. 2. Record the average value for each sample.

[0046] Table 3 below shows various polyol formulations, but Comparative Example 1 excludes expandable microspheres. PolyTHF® 2000 has a weight-average molecular weight (MWw) between 1950 and 2050.

[0047] To form the polyurethane elastomer foams of Examples 1-6, a predetermined mass percentage (mass%) of the polyol compound is heated to 40-45°C in a stirred reaction tank, and a predetermined mass percentage (mass%) of the isocyanate prepolymer is heated to 30-35°C in an isocyanate tank of a low-pressure machine (Zhejiang Haifeng Shoemaking Equipment Co., Ltd.). An aluminum mold (test plate mold 200×200×10mm) is heated to 55°C. The predetermined parts of the isocyanate prepolymer shown in Table 3 and 100 parts by mass of the polyol compound are mixed at atmospheric pressure, and the mixture is poured into the heated aluminum mold using the low-pressure machine. The mold is closed, the reactants are filled into the mold, and the reaction is allowed to proceed for the predetermined demolding time shown in Table 3.

[0048] Open the mold and demold the polyurethane elastomer foam. Before testing the physical properties of the polyurethane elastomer foam, cure it at 25°C and 50% relative humidity for 24 hours.

[0049] [Table 3]

[0050] The characteristics of Example 1 and Comparative Example 1 shown in Table 3 demonstrate that the absence of expandable microspheres negatively affects the tearing of polyurethane foam.

Claims

1. A polyurethane foam having a density of 250 to 350 g / L as measured in accordance with DIN EN ISO 845, The polyurethane foam is formed by reacting a mixture consisting of 70 to 55 mass percent (mass%) of a polyol compound and 30 to 45 mass percent (mass%) of an isocyanate prepolymer (mass percent is based on the total mass of this mixture). The polyol formulation comprises 93 to 96% by mass of polytetramethylene ether glycol (PTMEG) having a weight-average molecular weight (MWw) of 1950 to 2050, 1 to 5% by mass of expandable microspheres, and 1.4 to 2% by mass of water (the mass percentage values ​​in the polyol formulation are based on the total mass of the polyol formulation), and the expandable microspheres are hollow microbeads containing a thermoplastic polymer shell with a thermal expansion component enclosed, in a polyurethane foam.

2. The polyol formulation further comprises a catalyst, a surfactant, a crosslinking agent, and other optional additives. The polyurethane foam according to claim 1, wherein the catalyst, the surfactant, the crosslinking agent, and any other additives together give the mass percentage of the polyol formulation 100% by mass.

3. The polyurethane foam according to claim 1 or 2, wherein the component forming the isocyanate prepolymer comprises 40 to 70% by mass of isocyanate component and 30 to 60% by mass of PTMEG, based on the total mass of the isocyanate prepolymer, the isocyanate component has at least 92% by mass of 4,4'-diphenylmethane diisocyanate, and the NCO value (mass %) of the isocyanate prepolymer is 15 to 22.

4. The polyurethane foam according to any one of claims 1 to 3, wherein the polyurethane foam has a vertical rebound of 55% to 65% as measured according to ASTM D2632.

5. The polyurethane foam according to any one of claims 1 to 4, wherein the polyurethane foam has an Asker C hardness of 25 to 70 as measured according to ASTM D2240.

6. A shoe sole, midsole, or insole formed from the polyurethane foam described in any one of claims 1 to 5.

7. A method for forming a polyurethane foam according to any one of claims 1 to 5, i) Prepare the polyol formulation by mixing at room temperature, melting the PTMEG at 70°C overnight, and then maintaining the PTMEG at 40-50°C for proper handling with the other components and for adding the other components. ii) Heat the polyol mixture to a temperature of 40 to 45°C in the stirring reaction vessel of the polyurethane foam equipment. iii) Heating the isocyanate prepolymer to a temperature of 30 to 45°C in the isocyanate tank of the polyurethane foam equipment. iv) Mixing the isocyanate prepolymer and the polyol compound under atmospheric pressure, and injecting the mixture into a heated mold of the desired shape using the polyurethane foaming equipment. v) Close the mold and, with the reactants still filled in the mold, allow the reaction to proceed for a predetermined demolding time to form a polyurethane foam. Methods that include...

8. The method according to claim 7, wherein the foam-forming composition for the polyurethane foam comprises 55 to 70% by mass of a polyol compound and 30 to 45% by mass of an isocyanate prepolymer (the mass percentage is based on the total mass of the foam-forming composition for the polyurethane foam).

9. The method according to claim 7 or 8, wherein the temperature of the heated mold is 50 to 60°C and the demolding time is 5 to 15 minutes.

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