Process of preparing polyurethane elastomer foam

Abstract

This invention provides a method for preparing polyurethane elastomer foam, the polyurethane elastomer foam prepared by the method, and the uses of the polyurethane elastomer foam.

Description

[Technical Field]

[0001] This invention relates to the field of polyurethane elastomer foaming technology, and specifically to a method for preparing polyurethane elastomer foaming materials and the products thereof. [Previous Technology]

[0002] Utilizing foaming technology to form a large number of air bubbles inside polyurethane (PU) materials, creating a porous polyurethane foam material, is an effective means to achieve lightweight products and save materials. The presence of a large number of air bubbles can also endow the material with excellent thermal insulation, damping and cushioning, noise reduction and sound absorption properties.

[0003] Traditional polyurethane foaming mainly includes three processes: (1) Prepolymer method, which is to first mix polyol (white material) and isocyanate (black material) to form a prepolymer, and then add foaming agent, catalyst, surfactant, other additives, etc. to the prepolymer and mix and foam under high speed stirring. After curing, it is cured at a certain temperature to obtain the finished product; (2) Semi-prepolymer method, which is to first mix polyol (white material) and isocyanate (black material) to form a prepolymer, and then add another polyether or polyester polyol and isocyanate, water, catalyst, surfactant, other additives, etc., and mix and foam under high speed stirring; and (3) One-step method, which is to add polyether or polyester polyol (white material) and polyisocyanate (black material), water, catalyst, surfactant, foaming agent, other additives, etc. in one step and mix and foam under high speed stirring.

[0004] However, it is difficult for polyurethane foam produced by this type of process to simultaneously achieve low density and good mechanical properties, because a high foaming ratio usually leads to reduced mechanical properties and poor skin quality.

[0005] Continuous extrusion and injection molding are important methods for continuous foaming molding. However, these methods require molten polymer raw materials for foaming, making them unsuitable for industrial mass production. Solid-state foaming can effectively solve the problem of foaming polymer materials with low melt strength. In solid-state foaming, the polymer matrix filled with a foaming agent is heated to a softening zone close to its melting point for foaming. For example, when using physical foaming agents such as supercritical N2 or CO2, the supercritical fluid dissolves in the polymer matrix. After a rapid increase in temperature, the fluid reaches a supersaturated state. After depressurization, it induces cell nucleation and promotes cell growth, thus achieving polymer material foaming. Solid-state foaming allows for control of cell size by controlling the temperature, making it suitable for producing polymer foam materials with special pore sizes, such as microporous foams.

[0006] CN105829417A discloses a method for preparing expanded thermoplastic elastomer beads, including an impregnation step, an expansion step, and a fusion step selected as needed. The resulting thermoplastic elastomer beads have a continuous skin, low density, and uniform pore distribution. The bead expansion and forming process can be carried out in one operation and one device.

[0007] CN110126171A discloses an integrated foaming molding process for polymer particles, comprising the following steps: 1) preparing polymer particles coated with a high-melting-point polymer resin by a low-melting-point polymer resin; 2) foaming the polymer particles in one step to obtain a foamed product. By preparing polymer particles with a core-shell structure of a low-melting-point polymer resin coated with a high-melting-point polymer resin, during the foaming process, the foaming temperature is below the melting point of the core resin, allowing the particle core to form foam beads, while the foaming temperature is higher than the melting point of the shell resin, and the surface is in a molten state. When the particles expand and squeeze each other, the molten shell resin fuses the particles together; at the same time, the particles are in a fluidized state during the foaming process, and all particles are at the same temperature, ensuring that the particles do not stick together prematurely, and the internal fusion is uniform and consistent when expansion occurs, avoiding filling defects.

[0008] Supercritical foaming process is commonly used for foaming thermoplastic elastomers, such as thermoplastic polyurethane elastomers (TPU). However, as described in the above-disclosed patent application, this method usually requires the thermoplastic polyurethane elastomer to be prepared into particles by an extruder or other processes before being foamed and molded. The overall process involves many steps and is complex.

[0009] Therefore, a new foaming process is needed that can take into account both the high performance requirements of polyurethane foam products and the need for a simple and efficient production process. [Summary of the Invention]

[0010] The present invention provides a polyurethane foaming process that can overcome the technical problems existing in the prior art and produce low-density polyurethane foam products with good physical properties, while also having a simple and efficient production process.

[0011] Therefore, the present invention adopts the following technical solution:

[0012] This invention provides a method for preparing polyurethane elastomer foam, comprising the following steps: a) premixing a polyol with additives selected as needed to obtain a mixed component A; b) mixing component B containing isocyanate with component A and adding it into a mold, closing the mold, and allowing it to react to obtain a polyurethane preform; c) placing the polyurethane preform in a sealed cavity, introducing fluid into the sealed cavity until the sealed cavity reaches a pressure P, and simultaneously raising the temperature to a first temperature T1, so that the fluid in the cavity reaches a supercritical or near-supercritical state to impregnate the polyurethane preform, wherein the temperature T1 is 80 °C to 190 °C, preferably 90 °C to 160 °C, the pressure P is 5 MPa to 50 MPa, and the impregnation time is 3 minutes to 6 hours; and d) after reaching the impregnation time, depressurizing the sealed cavity, and obtaining a polyurethane elastomer foam material from the polyurethane preform, wherein the depressurization rate is 3 MPa / s to 500 MPa / s.

[0013] Preferably, the polyol in component A in step a) above can be a polyether polyol, a polyester polyol, or a mixture of the two.

[0014] The polyether polyols used to prepare polyurethanes are obtained by known methods, for example by anionic polymerization of olefin oxides in the presence of a catalyst, with the addition of at least one initiator molecule containing 2-8, preferably 2-6, reactive hydrogen atoms in a bonded form. As catalysts, alkali metal hydroxides such as sodium hydroxide or potassium hydroxide, or alkali metal alkoxides such as sodium methoxide, sodium ethoxide, potassium ethoxide, or potassium isopropoxide, or in the case of cationic polymerization, Lewis acids such as antimony pentachloride, boron trifluoride ethers, or bleaching earth are used as catalysts. Furthermore, bimetallic cyanides, known as DMC catalysts, can also be used as catalysts.

[0015] As an olefin oxide, one or more compounds having 2-4 carbon atoms in an alkylene group are preferred, such as ethylene oxide, 1,2-propylene oxide, tetrahydrofuran, 1,2- or 2,3-butene oxide, in each case alone or in mixtures, preferably ethylene oxide and / or 1,2-propylene oxide.

[0016] Possible initiator molecules include, for example, ethylene glycol (MEG), diethylene glycol, glycerol, trimethylolpropane (TMP), pentaerythritol, sugar derivatives such as sucrose, sugar alcohols such as sorbitol, methylamine, ethylamine, isopropylamine, butylamine, aniline, toluidine, toluenediamine, naphthylamine, ethylenediamine, diethylenetriamine, 4,4'-methylenediphenylamine, 1,3-propanediamine, 1,6-hexanediamine, ethanolamine, diethanolamine, triethanolamine, and other di- or polyols, or monofunctional or polyfunctional amines.

[0017] In a preferred embodiment, the polyether polyol also comprises polytetrahydrofuran.

[0018] Polyester polyols are typically prepared by condensing a polyol having 2-12 carbon atoms, such as ethylene glycol, diethylene glycol, butanediol (BDO), trimethylolpropane, glycerol, or pentaerythritol, with an isomer or anhydride of a polycarboxylic acid having 2-12 carbon atoms, such as succinic acid, glutaric acid, adipic acid, octanoic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, maleic acid, fumaric acid, phthalic acid, isophthalic acid, terephthalic acid, or naphthalenedicarboxylic acid. Polycarboxylic acids also include other sources of dicarboxylic acids, such as dimethyl terephthalate (DMT), polyethylene terephthalate (PET), etc.

[0019] The polyols used in this invention further include bio-based polyether and polyester polyols. These include, but are not limited to, polyether polyols made from castor oil, palm oil, olive oil, soybean oil, etc.; polyether polyols made from seaweed, lignin, etc.; and bio-based dicarboxylic acids, such as sebacic acid and succinic acid, and polyester polyols made from bio-based polyols, such as ethylene glycol, butanediol, propylene glycol, etc.

[0020] Furthermore, the polyether polyol or polyester polyol used in this invention has a hydroxyl value of about 20 to about 270 mg KOH / g, preferably about 28 to about 200 mg KOH / g, more preferably about 28 to about 150 mg KOH / g, even more preferably about 28 to about 100 mg KOH / g, and most preferably about 28 to about 80 mg KOH / g.

[0021] The molecular weight of the polyether polyol or polyester polyol is from about 500 to about 10,000, preferably from about 600 to about 6,000, and more preferably from about 1,000 to about 2,500. Furthermore, the polydispersity index of the polyether polyol or polyester polyol is within a specific range, for example, from about 0.8 to about 1.3, preferably from about 0.9 to about 1.2, and more preferably from about 0.95 to about 1.1.

[0022] Component A may further contain a crosslinking agent and / or a chain extender.

[0023] As a crosslinking agent and / or chain extender, a difunctional or higher-functional amine or alcohol, or a mixture thereof, is used, particularly a difunctional or trifunctional amine or alcohol, especially a diol, a triol, or a mixture thereof, in each case having a molecular weight of less than 350, preferably 60-300, and particularly 60-250. Here, the difunctional compound is referred to as a chain extender, and the trifunctional or higher-functional compound is referred to as a crosslinking agent. Aliphatic, alicyclic, and / or aromatic diols having 2-14, preferably 2-10, carbon atoms, such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-pentanediol, 1,3-pentanediol, 1,10-decanediol, 1,2-dihydroxycyclohexane, 1,3-dihydroxycyclohexane, 1,4-dihydroxycyclohexane, diethylene glycol and triethylene glycol, dipropylene glycol and tripropylene glycol, 1,4-butanediol, 1,6-hexanediol, and bis(2-hydroxyethyl)hydroquinone, can be used. Triols, such as 1,2,4-trihydroxycyclohexane, 1,3,5-trihydroxycyclohexane, glycerol, and trimethylolpropane, and hydroxyl-containing low molecular weight polyoxyethylenes based on ethylene oxide and / or propylene oxide and the above-mentioned diols and / or triols as initiator molecules, can also be used.

[0024] The chain extender may be a single compound or a mixture thereof. Preferred chain extenders include propylene glycol, dipropylene glycol, tripropylene glycol and / or 2,3-butanediol, either alone or as a mixture of each other or a mixture with other chain extenders, as needed.

[0025] The crosslinking agent is preferably 1,2,4-trihydroxycyclohexane, 1,3,5-trihydroxycyclohexane, glycerol and / or trimethylolpropane, alone or in mixtures thereof as needed.

[0026] According to the present invention, the reaction to form polyurethane is carried out in the presence of a catalyst, which may be added to component A or component B as needed.

[0027] As catalysts, all compounds that promote the isocyanate-polyol reaction can be used. Such compounds are known and described, for example, in "Kunststoff Handbuch, Volume VII, PU", Carl Hanser-Verlag, 3rd edition, 1993, Chapter 3.4.1. These include amine-based catalysts and organometallic compound-based catalysts.

[0028] As a catalyst based on organometallic compounds, organotin compounds such as tin(II) salts of organic carboxylic acids, such as tin(II) acetate, tin(II) octoate, tin(II) ethylhexanoate, and tin(II) laurate, and dialkyltin(IV) salts of organic carboxylic acids, such as dibutyltin diacetate, dibutyltin dilaurate, dibutyltin maleate, and dioctyltin diacetate, as well as bismuth(III) carboxylic acids, bismuth 2-ethylhexanoate, and bismuth octoate, or alkali metal salts of carboxylic acids, such as potassium acetate or potassium formate, can be used.

[0029] Amine-based catalysts may include bis(2-dimethylaminoethyl) ether, N,N,N',N'',N''-pentamethyldiethylenetriamine, 2-(2-diethylaminoethoxy)ethanol, dimethylcyclohexylamine, dimethylbenzylamine, triethylamine, triethylenediamine, pentamethyldipropylenetriamine, dimethylethanolamine, N-methylimidazole, N-ethylimidazole, tetramethylhexamethylenediamine, tris(dimethylaminopropyl)hexahydrotriazine, dimethylaminopropylamine, N-ethylmorpholine, diazabicycloundecene, and diazabicyclononene.

[0030] In component A of the present invention, those skilled in the art may add any auxiliaries and / or additives as needed, including but not limited to pore conditioners, fillers, pigments, dyes, antioxidants, hydrolytic stabilizers, antistatic agents, bactericides and bacteriostatic agents, etc.

[0031] Component B containing isocyanates in step b) of the present invention includes diisocyanates or polyisocyanates, and may be any aliphatic, alicyclic or aromatic isocyanate known for the preparation of polyurethanes, including but not limited to diphenylmethane 2,2'-, 2,4'- and 4,4'- diisocyanates, mixtures of monomeric diphenylmethane diisocyanate (MDI) and diphenylmethane diisocyanate homologues (polymeric MDI) having more rings, isophorone diisocyanate (IPDI) or oligomers thereof, toluene diisocyanate (TDI), such as toluene diisocyanate isomers such as toluene 2,4- or 2,6-diisocyanate or mixtures thereof, tetramethylene diisocyanate or oligomers thereof, hexamethylene diisocyanate (HDI) or oligomers thereof, naphthalene diisocyanate (NDI) or mixtures thereof.

[0032] The diisocyanate or polyisocyanate used preferably includes isocyanates based on diphenylmethane diisocyanate, particularly including polymeric MDI. The functionality of the diisocyanate or polyisocyanate is preferably 2.0 to 2.9, and particularly preferably 2.1 to 2.8.

[0033] Diisocyanates and polyisocyanates can also be used in the form of prepolymers. These prepolymers can be obtained by reacting an excess of the above-mentioned diisocyanates and / or polyisocyanates with a compound having at least two groups reactive to isocyanates at a temperature of, for example, 30 to 100 °C, preferably 80 °C. The NCO content of the diisocyanate prepolymers and / or polyisocyanate prepolymers of the present invention is preferably 10 to 33% by weight, particularly preferably 15 to 28% by weight.

[0034] In this invention, neither component A nor component B contains any additional foaming agent.

[0035] In step b) of the present invention, the polyurethane preform can be injection molded or cast. The mixture of component A and component B is added to the mold by injection or casting. Compared with the granulation process of thermoplastic polyurethane, the polyurethane preform used in the present invention is directly molded after liquid mixing, which makes the processing technology more flexible and simple, and the production efficiency higher.

[0036] In a preferred embodiment of the present invention, the hardness of the polyurethane preform obtained in step b) is not greater than 80 Shore A, preferably 10 to 80 Shore A, more preferably 20 to 80 Shore A, and even more preferably 45 to 75 Shore A.

[0037] In step c) of the present invention, the preferred sealed cavity is a pressure vessel resistant to high temperature and pressure, such as an autoclave reactor. The required pressure and the necessary temperature depend on the polyurethane preform used, the auxiliary materials used, the fluid used, and the mixing ratio between the components.

[0038] Any fluid known to those skilled in the art can be used for impregnation, preferably an inert gas such as argon, nitrogen or carbon dioxide, and particularly preferably carbon dioxide or nitrogen or mixtures thereof.

[0039] The fluid used as a blowing agent is preferably a mixture of CO2 and N2. In principle, any mixing ratio of CO2 and N2 is acceptable. For example, a blowing agent comprising 50% to 100% by weight of carbon dioxide and 0% to 50% by weight of nitrogen is preferred. Particularly preferred blowing agents contain only CO2, N2, or a mixture of these two gases and no other blowing agents. Alternatively, a blowing agent comprising 50% to 100% by weight of nitrogen and 0% to 50% by weight of carbon dioxide is preferred.

[0040] In step c) of this invention, the temperature is set to 80 °C to 190 °C, and the pressure P is 5 MPa to 50 MPa, so that the fluid in the cavity reaches a supercritical or near-supercritical state to impregnate the polyurethane preform. The impregnation of the polyurethane preform by the fluid can reach saturation. Impregnation saturation refers to impregnation in a high-pressure fluid atmosphere until the high-pressure fluid and the polyurethane preform reach a dissolution equilibrium. The impregnation time is usually 3 minutes to 6 hours.

[0041] In a preferred embodiment, the pressure P is set to 10 MPa to 18 MPa, and the immersion time is 3 minutes to 2 hours, preferably 30 minutes to 90 minutes.

[0042] In step d) of the present invention, the preform is foamed and molded by depressurization, and the depressurization rate is from 3 MPa / s to 500 MPa / s. A preferred rate is from 4 MPa / s to 100 MPa / s, and more preferably from 5 MPa / s to 30 MPa / s.

[0043] Optionally, after depressurization in step d), step e) further includes cooling at a temperature of 0 to 25 °C.

[0044] Optionally, the polyurethane elastomer foam material obtained in step d) or e) is placed in a mold for further hot pressing and shaping.

[0045] Optionally, the polyurethane elastomer foam material obtained in step d) or e) may be further cut to the desired size.

[0046] In a preferred embodiment of the method, the foaming of the polyurethane preform in step d) is partial, which means that the pressure at the first temperature T1 is reduced to a pressure higher than the ambient pressure, and the density of the partially foamed polyurethane preform is greater than the density of the polyurethane elastomer foam that can be obtained by reducing the pressure to the ambient pressure.

[0047] Preferably, in the further foaming step d2), a portion of the foamed polyurethane preform subsequently expands completely at a second temperature T2, thereby reducing the pressure at the second temperature T2 until the desired density is obtained. The desired density is preferably obtained when the pressure at the second temperature T2 is reduced to ambient pressure. The foaming step d2) can be performed in the same or a different apparatus than the foaming step d2).

[0048] In this invention, supercritical fluid foaming is performed by injecting fluid into a closed cavity containing polyurethane preform material. After reaching a certain temperature and pressure, the material reaches a supercritical or near-supercritical state. This state is maintained for a certain period of time, allowing the supercritical / near-supercritical fluid to permeate into the interior of the polyurethane preform, forming a polymer / fluid homogeneous system. By using a pressure reduction method at a certain rate, the equilibrium state of the polymer / fluid homogeneous system inside the material is disrupted, causing bubble nuclei to form inside the material and grow and solidify, thus obtaining a foamed material. Increasing the pressure can improve the solubility of the fluid in the polymer, thereby increasing the number of bubble nuclei and the cell density. The greater the pressure drop, the faster the bubble nucleation rate and the more bubble nuclei there are. The fluid concentration gradient inside and outside the bubble or the pressure difference inside and outside is the driving force for cell growth. The depressurization rate directly affects the acceleration of cell growth. Increasing the depressurization rate is beneficial to reducing the cell diameter and increasing the cell density. Above the glass transition temperature, the lower the saturation temperature, the higher the solubility of the fluid in the polymer, the higher the nucleation rate, and the greater the nucleation density. The final product meets lightweight requirements, with a density ranging from 0.05 g / cm³ to 0.50 g / cm³, preferably from 0.10 g / cm³ to 0.35 g / cm³. The resulting foam has a hardness of 10 to 70 Asker C, preferably 10 to 65 Asker C, further preferably 10 to 50 Asker C, and even more preferably 20 to 45 Asker C.

[0049] The present invention also provides the use of polyurethane elastomer foam.

[0050] Preferably, the polyurethane elastomer foam is used in the fields of transportation vehicles, furniture, sports products or footwear materials.

[0051] Preferably, polyurethane elastomer foam is used for the seat.

[0052] Preferably, polyurethane elastomer foam is used for the sole.

[0053] This invention uses the above-described preparation method to produce a foamed material from a polyurethane elastomer preform via a supercritical fluid foaming molding process. The resulting foamed material, at the same density, possesses superior physical properties compared to polyurethane foam foamed with chemical foaming agents. It can be used in the transportation sector, such as vehicle seats, automotive interiors, and armrests, as well as in the furniture sector, such as padding materials and various laminated composite materials. It can also be used as sound insulation materials, filter materials, decorative materials, shock-absorbing materials, packaging materials, and thermal insulation materials. Furthermore, it can be used in sporting goods and footwear applications, such as helmets, protective gear, shoe soles, insoles, and sports assistive devices. When used in the preparation of footwear products, especially shoe sole materials, it results in shoes with lighter weight, higher resilience, and superior physical properties, providing wearers with a better comfort experience. Simultaneously, this preparation method is simpler, milder, has a shorter production process, higher efficiency, and is environmentally friendly compared to the pre-granulation and post-foaming process for thermoplastic polyurethane, making it suitable for large-scale industrial production.

Implementation Method

[0055] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described herein, nor do they constitute a limitation on the content and scope of protection of the present invention. The scope of protection of the present invention still extends to the technical solutions claimed in the claims of the present invention and any adjustments and modifications thereto that conform to the present invention.

[0056] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate orientations or positional relationships only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0057] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0058] Where specific experimental steps or conditions are not specified in the embodiments, they can be performed according to the conventional experimental steps or conditions described in the literature in this field. Raw materials or instruments used without specified manufacturers are all commercially available conventional products.

[0059] The test methods used in this invention are as follows: Density (g / cm3): ISO 1183-1; Hardness (Asker C): JIS S 6050; Hardness (Shore A): DIN ISO 7619-1; Tensile strength (MPa): DIN 53504; Elongation at break (%): DIN 53504; Tear strength (kg / cm): ISO 1183-1; Delamination tear (kg / cm): SATRA TM 411; Resilience (%): ASTM D 2632

[0060] Among the raw materials used, the isocyanate prepolymers are as follows: Table 1 Element Isocyanate monomers polyols NCO weight % Isocyanate prepolymer 1 MDI Polyester polyol 1, polyester polyol 2 18.9 Isocyanate prepolymer 2 MDI Polyether polyol 1 18.2 Isocyanate prepolymer 3 MDI Polyether polyol 1 26.2 Isocyanate prepolymer 4 MDI Polyester polyol 1, polyester polyol 2 12 Isocyanate prepolymer 5 MDI Polyether polyol 1 29.5

[0061] Polyols are as follows: Table 2 Element monomer Weight-average molecular weight (g / mol) sensibility Polyester polyol 1 Diethylene glycol, ethylene glycol, adipic acid 1400 2 Polyester polyol 2 Ethylene glycol, glycerol, adipic acid 2500 2.6 Polyether polyol 1 Tetrahydrofuran 2000 2

[0062] The amine catalyst is Dabco EG, purchased from Evonik.

[0063] The tin catalyst is Fomorez UL-28, purchased from Huntsman.

[0064] The silicone oil was Dabco DC 193, purchased from Evonik. Example 1

[0065] Component A Table 3 Element Number of portions (by weight) Polyester polyol 1 85 Polyester polyol 2 10 BDO 4.5 Amine catalysts 0.495 Tin catalysts 0.005

[0066] Component B: Isocyanate prepolymer 1

[0067] Component A and component B are thoroughly mixed at a weight ratio of 100:52, poured into a mold, reacted for 10 minutes, and then demolded to obtain a non-foamed polyurethane preform with a hardness of 55 Shore A. The obtained polyurethane preform is placed in a sealed cavity, and carbon dioxide gas is introduced into the sealed cavity until it reaches 10 MPa, while the temperature is simultaneously raised to 120 °C, so that the supercritical carbon dioxide in the cavity impregnates the polyurethane preform for 60 minutes. After the impregnation time is reached, the pressure is released, and expansion foaming molding is performed to obtain a polyurethane foam material, wherein the pressure release rate is 10 MPa / s. Comparative Example 1

[0068] Component A Table 4 Element Number of portions (by weight) Polyester polyol 1 83.6 Polyester polyol 2 9.9 BDO 4.4 Water (foaming agent) 1.3 Amine catalysts 0.495 Tin catalysts 0.005 Silicon oil 0.3

[0069] Component B: Isocyanate prepolymer 1

[0070] After thoroughly mixing component A and component B at a weight percentage of 100:83.1, the mixture is poured into a mold, reacted for 10 minutes, and then demolded to obtain polyurethane foam material. Table 5 Example 1 Comparative Example 1 Density (g / cm³) 3 ) 0.19-0.21 0.19-0.22 Hardness (Asker C) 20-28 20-28 Tensile strength (MPa) 3.5 0.8 Elongation (%) 460 160 Tear rate (kg / cm) 12 5 Delamination tear (kg / cm) 3.2 0.5 Rebound (%) 55 40 Example 2

[0071] Component A Table 6 Element Number of portions (by weight) Polyether polyol 1 97 MEG 2 Amine catalysts 1.0

[0072] Component B: Isocyanate prepolymer 2

[0073] Component A and component B were thoroughly mixed at a weight percentage of 100:37.7, poured into a mold, reacted for 10 minutes, and then demolded to obtain a non-foamed polyurethane preform with a hardness of 63 Shore A. The obtained polyurethane preform was placed in a sealed cavity, and carbon dioxide gas was introduced into the sealed cavity until it reached 12 MPa, while the temperature was simultaneously raised to 140 °C, so that the supercritical carbon dioxide in the cavity impregnated the polyurethane preform for 60 minutes. After the impregnation time was reached, the pressure was released, and expansion foaming molding was performed to obtain a polyurethane foam material, wherein the pressure release rate was 10 MPa / s. Comparative Example 2

[0074] Component A Table 7 Element Number of portions (by weight) Polyether polyol 1 95.1 MEG 1.9 Water (foaming agent) 1.7 Amine catalysts 1.0 Silicon oil 0.3

[0075] Component B: Isocyanate prepolymer 2

[0076] After thoroughly mixing component A and component B at a weight percentage of 100:80.1, the mixture is poured into a mold, reacted for 10 minutes, and then demolded to obtain polyurethane foam material. Table 8 Example 2 Comparative Example 2 Density (g / cm³) 3 ) 0.15-0.16 0.15-0.16 Hardness (Asker C) 40-41 40-41 Tensile strength (MPa) 3.2 1.5 Elongation (%) 470 390 Tear rate (kg / cm) 11 6 Delamination tear (kg / cm) 2.5 1.3 Rebound (%) 70 50 Appearance Good skin texture, no peeling. Peeling Example 3

[0077] Component A Table 9 Element Number of portions (by weight) Polyether polyol 1 91.5 MEG 4 PDO 3 TMP 0.45 Amine catalysts 1.0 Tin catalysts 0.05

[0078] Component B: Isocyanate prepolymer 3

[0079] Component A and component B were thoroughly mixed at a weight percentage of 100:52.8, poured into a mold, reacted for 15 minutes, and then demolded to obtain a non-foamed polyurethane preform with a hardness of 80 Shore A. The obtained polyurethane preform was placed in a sealed cavity, and carbon dioxide gas was introduced into the sealed cavity until it reached 12 MPa, while the temperature was simultaneously raised to 140 °C, so that the supercritical carbon dioxide in the cavity impregnated the polyurethane preform for 60 minutes. After the impregnation time was reached, the pressure was released, and expansion foaming molding was performed to obtain a polyurethane foam material, wherein the pressure release rate was 10 MPa / s. Comparative Example 3

[0080] Component A Table 10 Element Number of portions (by weight) Polyether polyol 1 89 MEG 4 BDO 3 TMP 0.45 water 2.0 Amine catalysts 1.0 Tin catalysts 0.05 Silicon oil 0.5

[0081] Component B: Isocyanate prepolymer 3

[0082] After thoroughly mixing component A and component B at a weight percentage of 100:91.5, the mixture is poured into a mold, reacted for 15 minutes, and then demolded to obtain polyurethane foam material. Table 11 Example 3 Comparative Example 3 Density (g / cm³) 3 ) 0.18-0.20 0.18-0.20 Hardness (Asker C) 43-44 43-44 Tensile strength (MPa) 3.6 1.7 Elongation (%) 430 370 Tear rate (kg / cm) 12 6.5 Delamination tear (kg / cm) 3.4 1.5 Rebound (%) 65 40 Appearance Good skin texture, no peeling. Peeling Example 4

[0083] Component A Table 12 Element Number of portions (by weight) Polyester polyol 1 88.5 Polyester polyol 2 10 BDO 1 Amine catalysts 0.495 Tin catalysts 0.005

[0084] Component B: Isocyanate prepolymer 4

[0085] Component A and component B are thoroughly mixed at a weight ratio of 100:45, poured into a mold, reacted for 10 minutes, and then demolded to obtain a non-foamed polyurethane preform with a hardness of 25 Shore A. The obtained polyurethane preform is placed in a sealed cavity, and carbon dioxide gas is introduced into the sealed cavity until it reaches 10 MPa, while the temperature is simultaneously raised to 120 °C, so that the supercritical carbon dioxide in the cavity impregnates the polyurethane preform for 60 minutes. After the impregnation time is reached, the pressure is released, and expansion foaming molding is performed to obtain polyurethane foam material, wherein the pressure release rate is 10 MPa / s. Comparative Example 4

[0086] Component A Table 13 Element Number of portions (by weight) Polyester polyol 1 86.8 Polyester polyol 2 9.9 BDO 1 Water (foaming agent) 1.5 Amine catalysts 0.495 Tin catalysts 0.005 Silicon oil 0.3

[0087] Component B: Isocyanate prepolymer 4

[0088] After thoroughly mixing component A and component B at a weight percentage of 100:100, the mixture is poured into a mold, reacted for 10 minutes, and then demolded to obtain polyurethane foam material. Table 14 Example 4 Comparative Example 4 Density (g / cm³) 3 ) 0.19-0.21 0.19-0.22 Hardness (Asker C) 10-15 12-16 Tensile strength (MPa) 3.5 0.8 Elongation (%) 310 105 Tear rate (kg / cm) 6 2.5 Delamination tear (kg / cm) 2.2 0.5 Rebound (%) 45 35 Comparative Example 5

[0089] Component A Table 15 Element Number of portions (by weight) Polyether polyol 1 89.5 MEG 7 BDO 2 TMP 0.45 Amine catalysts 1.0 Tin catalysts 0.05

[0090] Component B: Isocyanate prepolymer 5

[0091] Component A and component B are thoroughly mixed at a weight ratio of 100:50, poured into a mold, reacted for 15 minutes, and then demolded to obtain a non-foamed polyurethane preform with a hardness of 90 Shore A. The obtained polyurethane preform is placed in a sealed cavity, and carbon dioxide gas is introduced into the sealed cavity until it reaches 12 MPa, while the temperature is simultaneously raised to 140 °C, so that the supercritical carbon dioxide in the cavity impregnates the polyurethane preform for 60 minutes. After the impregnation time is reached, the pressure is released, and expansion foaming molding is performed to obtain polyurethane foam material, wherein the pressure release rate is 10 MPa / s. Table 16 Comparative Example 5 Density (g / cm³) 3 ) 0.55 Hardness (Asker C) 65-75 Foaming characteristics Poor foaming

[0092] Table 17 shows that the polyurethane preforms in Examples 1 to 4 had a hardness below 80, resulting in foams with uniform cell structure and relatively stable production. In contrast, the preform in Comparative Example 5 had a hardness exceeding Shore A 80, exhibiting poor foaming performance, uneven cell structure, and unstable production. Table 17 Example 1 Example 2 Example 3 Example 4 Comparative Example 5 Shore A (Prep body hardness) 55 63 80 25 90 Foaming density (g / cm³) 3 ) 0.19-0.21 0.15-0.16 0.18-0.20 0.19-0.21 0.55 Foam hardness (Asker C) 20-28 40-41 43-44 10-15 65-75 Cell uniformity uniform uniform uniform uniform Uneven Production stability Relatively stable Stablize Stablize Relatively stable Unstable [Simplified Explanation of the Diagram]

[0054] None

Claims

1. A method for preparing polyurethane elastomer foam, comprising the following steps: a) premixing a polyol with additives selected as needed to obtain a mixed component A; b) mixing component B containing isocyanate with component A and adding it to a mold, closing the mold, and allowing it to react to obtain a polyurethane preform; c) placing the polyurethane preform in a sealed cavity, introducing fluid into the sealed cavity until the sealed cavity reaches a pressure P, and simultaneously heating it to a first temperature T1, so that the fluid in the cavity reaches a supercritical or near-supercritical state to impregnate the polyurethane preform, wherein the temperature T1 is 80 °C to 190 °C, the pressure P is 5 MPa to 50 MPa, and the impregnation time is 3 minutes to 6 hours; and d) after reaching the impregnation time, depressurizing the sealed cavity to obtain a polyurethane elastomer foam material from the polyurethane preform, wherein the depressurization rate is 3 MPa / s to 500 MPa / s; wherein the hardness of the polyurethane preform is not greater than 80 Shore A.

2. The method for preparing polyurethane elastomer foam according to claim 1, characterized in that the pressure P is 10 MPa to 18 MPa and the impregnation time is 3 minutes to 2 hours.

3. The method for preparing polyurethane elastomer foam according to claim 1, wherein the depressurization rate is 4 MPa / s to 100 MPa / s.

4. The method for preparing polyurethane elastomer foam according to claim 1, wherein the fluid contains at least one of nitrogen and carbon dioxide.

5. The method for preparing polyurethane elastomer foam according to claim 4, wherein the nitrogen in the fluid is not less than 50% by weight.

6. The method for preparing polyurethane elastomer foam according to claim 1, characterized in that the mixture of component A and component B is added to the mold by injection or casting.

7. The method for preparing polyurethane elastomer foam according to claim 1, characterized in that neither component A nor component B contains any additional foaming agent.

8. A method for preparing polyurethane elastomer foam according to any one of claims 1 to 7 of the patent application, characterized in that after depressurization in step d), it further includes step e) cooling at a temperature of 0 to 25 °C.

9. The method for preparing polyurethane elastomer foam according to claim 8, characterized in that the polyurethane elastomer foam material obtained in step d) or e) is placed in a mold for further hot pressing and shaping.

10. The method for preparing polyurethane elastomer foam according to claim 8, characterized in that the polyurethane elastomer foam material obtained in step d) or e) is further cut into the required size.

11. The method for preparing polyurethane elastomer foam according to any one of claims 1 to 7 of the patent application, characterized in that the foaming of the non-foamed polyurethane preform in step d) is partial, wherein the pressure at the first temperature T1 drops to a pressure higher than the ambient pressure, and the density of the partially foamed polyurethane preform is greater than the density that can be obtained by depressurizing to the ambient pressure.

12. The method for preparing polyurethane elastomer foam according to claim 11, characterized in that it further includes a foaming step d2), wherein a portion of the foamed polyurethane preform subsequently expands at a second temperature T2, and the pressure inside the cavity is reduced to such a degree that the pressure at the second temperature T2 is reduced until the desired density is obtained.

13. The method for preparing polyurethane elastomer foam according to claim 12, characterized in that the foaming step d2) is carried out in the same or a different device than the foaming step d2).

14. A polyurethane elastomer foam prepared by the method for preparing polyurethane elastomer foam according to any one of claims 1 to 13 of the patent application.

15. Use of the polyurethane elastomer foam as described in claim 14.

16. Use of the polyurethane elastomer foam according to claim 15, wherein the polyurethane elastomer foam is used in the fields of vehicles, furniture, sporting goods or footwear.

17. Use of the polyurethane elastomer foam according to claim 16, wherein the polyurethane elastomer foam is used for a seat.

18. Use of the polyurethane elastomer foam according to claim 16, wherein the polyurethane elastomer foam is used for shoe soles.