Low chemical crosslinking degree thermoplastic polyurethane and preparation method thereof

Abstract

The present invention provides a thermoplastic polyurethane with a low chemical crosslinking degree, comprising, by weight, 10-45 parts of a diisocyanate, 40-80 parts of an oligomeric diol, 1-15 parts of a diol chain extender, 0.5-5 parts of dihydroxyitaconamide, 0.1-3 parts of a crosslinker, and 0.1-2 parts of a thermal initiator (DCP). Dihydroxyitaconamide is a co-chain extender prepared by reacting itaconic acid or an itaconate ester with an alcoholamine. The present invention also provides a method for preparing the thermoplastic polyurethane with a low chemical crosslinking degree, comprising premixing the diol chain extender with dihydroxyitaconamide, adding the diisocyanate and the oligomeric diol to a prepolymer obtained by reaction, curing the mixture at 105-115°C for 12-24 hours, and aging the mixture at room temperature for 7 days to obtain a TPU polymer matrix. The advantages of the present invention are that diol itaconamide is introduced into polyurethane as a co-chain extender to produce a low-crosslinked TPU elastomer, which not only improves the processability of the TPU elastomer, but also enhances the mechanical properties of TPU, thereby producing a shoe midsole material with lower density, higher resilience and higher tear resistance.

Description

Technical Field

[0001] The invention belongs to the technical field of foaming materials, and in particular relates to a thermoplastic polyurethane with a low chemical crosslinking degree and a preparation method thereof. Background Art

[0002] As the most fundamental piece of athletic equipment, athletic shoes are the subject of much attention and anticipation from consumers looking for improvements and upgrades to their performance. The wearing experience provided by athletic shoes is inextricably linked to the physical properties of the midsole, with the performance of the midsole material directly impacting both the comfort and functionality of the shoe.

[0003] Among them, thermoplastic polyurethane (TPU) is widely used in the field of sports shoes due to its excellent mechanical properties, easy processing and molding, environmentally friendly and reusable materials. TPU is a type of block copolymer composed of diisocyanate, chain extender and polyol. The hard segment composed of diisocyanate and chain extender gives the material hardness and rigidity, while the soft segment of polyol makes the material flexible and tough. The regular hard segment undergoes microphase separation from the soft segment after crystallization, and the hard crystalline phase is evenly dispersed in the continuous rubber phase composed of the soft segment. Therefore, TPU exhibits high tensile strength, high elongation at break, and excellent rebound performance.

[0004] For example, BASF has developed non-cross-linked TPU foam beads (E-TPU) using supercritical foaming technology, using TPU as raw material. This material has been successfully applied to running shoe midsoles. With the continuous advancement and innovation of supercritical foaming technology, TPU midsoles produced using sheet and embryo foaming processes are also gradually being used in high-end footwear. TPU produced using this supercritical foaming process has a microporous structure with low density, high specific strength, excellent rebound and shock absorption properties, and is environmentally friendly, making it adopted by many well-known sports footwear brands.

[0005] The basic physical properties of shoe midsoles, such as density, strength, elasticity, shock absorption and durability, are mainly determined by the molecular chain structure and molecular chain cohesion state of the materials used in the shoe midsole.

[0006] With the development of the sports shoe industry, midsoles require lighter density, higher elasticity, and greater tear resistance. Therefore, TPU's strength and expansion ratio need to be further improved. Patent application CN115197392A discloses a dual-soft segment TPU modified with organic peroxide micro-crosslinking and a preparation method, which improves the hardness and tensile strength of TPU. Patent application CN117801214A introduces a hydroxyl / amine isopropylaniline chain extender crosslinker into TPU, improving the material's strength, wear resistance, and heat resistance. While the solutions in these patents can improve the mechanical properties of TPU to a certain extent, they do not consider the impact on TPU's foaming performance. Based on the macrostructural changes in TPU during supercritical foaming, it is clear that comprehensively improving the performance of TPU foam materials requires not only increasing the mechanical strength of the TPU itself but also increasing its melt strength during foaming, ensuring the expansion ratio, and maintaining the crystallization properties and microphase separation of the TPU after micro-crosslinking. This is the only way to ensure the processability of TPU and enhance the performance of the foamed midsole.

[0007] However, the micro-cross-linked TPU reported so far cannot meet the requirements of improving mechanical properties, processing properties and foaming properties at the same time. Summary of the Invention

[0008] In view of the problem that the micro-crosslinked TPU in the prior art cannot simultaneously meet the requirements of improving mechanical properties, processing properties and foaming properties, the present invention provides a thermoplastic polyurethane with a low chemical crosslinking degree and a preparation method thereof.

[0009] The technical solution of the present invention is as follows: a thermoplastic polyurethane with a low chemical crosslinking degree, comprising, by mass: 10 to 45 parts of diisocyanate, 40 to 80 parts of oligomeric diol, 1 to 15 parts of diol chain extender, 0.5 to 5 parts of dihydroxyitaconamide, 0.1 to 3 parts of crosslinking agent, and 0.1 to 2 parts of thermal initiator DCP;

[0010] The dihydroxyitaconamide is a co-chain extender, and its general structural formula is as follows:

[0011]

[0012] Wherein, n is any integer from 1 to 5.

[0013] Furthermore, the diisocyanate includes at least one of methylene diphenyl diisocyanate, toluene diisocyanate, p-phenylene diisocyanate, xylylene diisocyanate, hexamethylene diisocyanate, methylene dicyclohexyl diisocyanate, isophorone diisocyanate, and cyclohexane dimethyl diisocyanate.

[0014] Furthermore, the diol chain extender includes at least one of ethylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,5-pentanediol, and 1,6-hexanediol.

[0015] Furthermore, the cross-linking agent includes any one of divinyl ether, ethylene glycol divinyl ether, diethylene glycol divinyl ether, polyethylene glycol divinyl ether, ethylene glycol diacrylate, butanediol diacrylate, hexanediol diacrylate, and polyethylene glycol diacrylate.

[0016] Furthermore, the molecular weight of the oligomer diol is 1,000 to 3,000.

[0017] Preferably, the diisocyanate includes at least one of methylene diphenyl diisocyanate and hexamethylene diisocyanate.

[0018] Furthermore, dihydroxyitaconamide is prepared by reacting itaconic acid or itaconate with an alcoholamine, and the alcoholamine is any one of ethanolamine, propanolamine, butanolamine, pentanolamine and hexanolamine.

[0019] Preferably, the crosslinking agent is any one of diethylene glycol divinyl ether, hexanediol diacrylate, and diethylene glycol diacrylate.

[0020] Preferably, the weight of the diol chain extender is 3.5 to 4.5 parts, the weight of the dihydroxyitaconamide is 2 to 2.5 parts, the weight of the crosslinking agent is preferably 1.5 to 2.8 parts, and the weight of the thermal initiator DCP is preferably 0.8 to 1.2 parts.

[0021] The present invention also provides a method for preparing a thermoplastic polyurethane with a low chemical crosslinking degree, which is used to prepare the above-mentioned thermoplastic polyurethane with a low chemical crosslinking degree, comprising the following steps:

[0022] S1. Add diisocyanate and oligomer diol according to corresponding parts by weight into a reaction kettle, add a catalyst, and heat to 80°C. Stir under nitrogen for 2-3 hours, and cool to room temperature to obtain a prepolymer.

[0023] S2. Degas the prepolymer obtained in step S1 under vacuum at 80° C. for 1 to 2 hours, add a premix of a diol chain extender and dihydroxyitaconamide, stir at high speed for 2 to 3 minutes, pour into a mold, cure at 105 to 115° C. for 12 to 24 hours, and mature at room temperature for 7 days to obtain a TPU polymer matrix;

[0024] S3. The TPU polymer matrix obtained in step S1 is uniformly mixed with a crosslinking agent and a thermal initiator DCP in corresponding proportions, and the mixture is pelletized after twin-screw extrusion or injection molded by a twin-screw injection molding machine to obtain a TPU elastomer with a low chemical crosslinking degree.

[0025] The advantages of the present invention are that diol itaconamide is introduced into polyurethane as a co-chain extender to produce a low-crosslinked TPU elastomer, which not only improves the processability of the TPU elastomer, but also enhances the mechanical properties of TPU, thereby producing a shoe midsole material with lower density, higher resilience and higher tear resistance. DETAILED DESCRIPTION

[0026] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0027] The low-chemically crosslinked thermoplastic polyurethane of the present invention utilizes a certain amount of itaconic acid derivatives, along with a diol, as chain extenders to introduce unsaturated bonds into the side chains of the TPU molecules. Flexible long-chain reactive monomers are then added to react with the unsaturated bonds to form a TPU with a low chemical crosslinking degree. This improves the TPU's foaming properties and maintains its crystallization and microphase separation after micro-crosslinking. The itaconic acid derivative acts as a co-chain extender, preferably in the form of dihydroxyitaconamide, to extend the chain.

[0028] Specifically, the low chemical crosslinking thermoplastic polyurethane includes, by weight, 10 to 45 parts of diisocyanate, 40 to 80 parts of oligomer diol, 1 to 15 parts of diol chain extender, 0.5 to 5 parts of dihydroxyitaconamide, 0.1 to 3 parts of crosslinking agent, and 0.1 to 2 parts of thermal initiator DCP.

[0029] The diisocyanate includes at least one of methylene diphenyl diisocyanate (MDI), toluene diisocyanate (TDI), p-phenylene diisocyanate (PPDI), xylene diisocyanate (XDI), hexamethylene diisocyanate (HDI), methylene dicyclohexyl diisocyanate (HMDI), isophorone diisocyanate (IPDI), and cyclohexane dimethyl diisocyanate.

[0030] At least one of methylene diphenyl diisocyanate (MDI) and hexamethylene diisocyanate (HDI) is preferred.

[0031] The molecular weight of the oligomer diol is 1000 to 3000, preferably 1000 to 2000, more preferably 2000; and its mass fraction is preferably 55 to 75 parts.

[0032] The diol chain extender includes at least one of ethylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,5-pentanediol, and 1,6-hexanediol; the weight proportion is preferably 3.5 to 4.5 parts.

[0033] Dihydroxyitaconamide is a co-chain extender with the following general structure:

[0034]

[0035] wherein n=1-5, and the structure is prepared by reacting itaconic acid or an itaconate with an alcoholamine, wherein the alcoholamine is any one of ethanolamine, propanolamine, butanolamine, pentanolamine, and hexanolamine. Preferably, the alcoholamine is any one of ethanolamine, butanolamine, and hexanolamine. The mass fraction of dihydroxyitaconamide is preferably 2-2.5 parts.

[0036] The crosslinking agent includes any one of divinyl ether, ethylene glycol divinyl ether, diethylene glycol divinyl ether, polyethylene glycol divinyl ether, ethylene glycol diacrylate, butanediol diacrylate, hexanediol diacrylate, and polyethylene glycol diacrylate. Diethylene glycol divinyl ether, hexanediol diacrylate, and diethylene glycol diacrylate are preferred. The crosslinking agent is preferably present in an amount of 1.5 to 2.8 parts by weight; the thermal initiator DCP is preferably present in an amount of 0.8 to 1.2 parts by weight.

[0037] The present invention also provides a method for preparing the above-mentioned thermoplastic polyurethane with low chemical crosslinking degree, comprising the following steps:

[0038] S1. Add diisocyanate and oligomer diol according to corresponding parts by weight into a reaction kettle, add a catalyst, and heat to 80°C. Stir under nitrogen for 2-3 hours, and cool to room temperature to obtain a prepolymer.

[0039] S2. Degas the prepolymer obtained in step S1 under vacuum at 80° C. for 1 to 2 hours, add a premix of a diol chain extender and dihydroxyitaconamide, stir at high speed for 2 to 3 minutes, pour into a mold, cure at 105 to 115° C. for 12 to 24 hours, and mature at room temperature for 7 days to obtain a TPU polymer matrix;

[0040] S3. The TPU polymer matrix obtained in step S1 is uniformly mixed with a crosslinking agent and a thermal initiator DCP in a certain proportion, and the mixture is pelletized after twin-screw extrusion or injection molded by a twin-screw injection molding machine to obtain a TPU elastomer with a low chemical crosslinking degree.

[0041] The low chemical crosslinking TPU elastomer obtained by the above method has a bulk hardness of 30 to 48D, preferably 40 to 45D, and a melting temperature of 120 to 180°C, preferably 120 to 150°C. The low chemical crosslinking TPU elastomer obtained by the present invention has a lower hardness than ordinary TPU elastomers (the aliphatic TPU elastomers commonly used in shoe soles have a bulk hardness of 85 to 90A and a melting temperature of 160 to 190°C). The melting temperature range is lower and wider, which is fully compatible with the supercritical foaming process and has higher melt strength.

[0042] When the above-mentioned low chemical cross-linking TPU elastomer is used for foaming, the steps and process parameters involved in the foaming method need to fully conform to the low-crosslinking structural characteristics of the thermoplastic TPU elastomer. The foaming temperature is related to the melting point of the obtained TPU elastomer. The prepared shoe midsole has light weight, high elasticity and high tear resistance.

[0043] The supercritical foaming method of thermoplastic polyurethane with low chemical crosslinking degree proposed by the present invention comprises:

[0044] S1. Weigh a low chemical crosslinking TPU elastomer, an antioxidant, and a nucleating agent in certain parts by weight, and dry the weighed low chemical crosslinking TPU elastomer in an oven at 90-100° C. for 4 hours for later use;

[0045] S2, after the raw materials in step S1 are mixed evenly with a high-speed stirring device, they are sent to a twin-screw extruder for extrusion granulation, and the particle size is controlled at 1-3 mm. The prepared pellets are stored in a dry and ventilated environment for standby use; or after the raw materials are mixed evenly, they are sent to a twin-screw injection molding machine for injection molding, and the body thickness is 3-10 mm. The injection-molded small embryos are stored in a dry and ventilated environment for standby use;

[0046] S3. Place the masterbatch or embryo obtained in step S2 into an autoclave, turn on the temperature controller, set the temperature in the autoclave to 100-140° C., and after the temperature reaches the set temperature and stabilizes, introduce nitrogen or carbon dioxide into the autoclave and adjust the gas pressure in the autoclave to 15-60 MPa. When the gas in the autoclave is in a supercritical state, maintain constant temperature and pressure for 0.5-4 hours, then quickly release the pressure to normal pressure, place the autoclave containing the sample in ice water and cool it to room temperature. After waiting for a certain period of time, open the autoclave to obtain foamed beads or embryos.

[0047] S4. Add the foamed beads obtained in step S3 to a pre-opened sole mold, introduce water vapor to bond and form, during this process, maintain the gas pressure in the mold at 1-3 bar, the molding time is 180-300 seconds, and after demolding, dry at 50-60° C. for 1-5 hours, and cool to obtain the finished foamed midsole of sports shoes; for the foamed embryo form, place the foamed embryo obtained in step S3 in a mold for hot pressing molding, the molding time is 180-300 seconds, and demold after cooling to obtain the finished foamed midsole of sports shoes.

[0048] The specific properties of the thermoplastic polyurethane with low chemical crosslinking degree of the present invention are further illustrated by several groups of specific examples below.

[0049] Example 1

[0050] The low chemical crosslinking thermoplastic polyurethane includes, in parts by mass: 25 parts of methylene diphenyl diisocyanate (MDI), 70 parts of polytetramethylene ether glycol, 4 parts of 1,4-butanediol, 2 parts of dihydroxyethyl itaconamide, 1.5 parts of crosslinking agent ethylene glycol divinyl ether, and 0.8 parts of thermal initiator DCP.

[0051] The raw materials were used according to the above preparation method to prepare a low chemical cross-linking TPU elastomer with a bulk hardness of 38D and a melting temperature of 135°C.

[0052] The low chemical cross-linking TPU elastomer is then foamed according to the above-mentioned supercritical foaming method, wherein the specific parameters of the supercritical foaming are: a twin-screw injection molding machine is used to inject into a small embryo form, the mold thickness is 5mm, the foaming agent is CO2, the foaming temperature is 137°C, the pressure in the autoclave is 25Mpa, the constant temperature and pressure are maintained for 120min, the pressure is released to normal pressure and then cooled to obtain a foamed embryo, which is hot pressed in a sole mold into a sports shoe foam midsole test piece.

[0053] The performance test of the obtained sports shoe foam midsole test piece was carried out, and the test results were: hardness 40C, density 0.09g / cm 3 , tensile strength 3.2MPa, elongation at break 360%, energy rebound 79.5%, impact peak acceleration (PeakG) 10.27, 180-degree tear 3.3kg / cm, yellowing resistance grade 3-4.

[0054] Example 2

[0055] The low chemical crosslinking thermoplastic polyurethane includes, in parts by mass: 35 parts of toluene diisocyanate (TDI), 60 parts of polybutylene adipate diol, 3.5 parts of 1,4-butanediol, 2 parts of dihydroxyethyl itaconamide, 1.8 parts of crosslinking agent ethylene glycol divinyl ether, and 1.0 part of thermal initiator DCP.

[0056] The raw materials were used according to the above preparation method to prepare a low chemical cross-linking TPU elastomer with a bulk hardness of 42D and a melting temperature of 137°C.

[0057] The low chemical cross-linking TPU elastomer is then foamed according to the above-mentioned supercritical foaming method, wherein the specific parameters of the supercritical foaming are: using a twin-screw extruder to extrude beads, the beads have a particle size of 3 mm, the foaming agent is CO2, the foaming temperature is 134°C, the pressure in the autoclave is 20 MPa, the constant temperature and pressure are maintained for 90 minutes, the pressure is released to normal pressure and then cooled to obtain foamed beads, which are molded into sports shoe foam midsole test pieces in a sole mold.

[0058] The performance test of the obtained sports shoe foam midsole test piece was carried out, and the test results were: hardness 43C, density 0.07g / cm 3, tensile strength 3.6MPa, elongation at break 320%, energy rebound 82.5%, impact peak acceleration (PeakG) 11.33, 180-degree tear 3.7kg / cm, yellowing resistance grade 3-4.

[0059] Example 3

[0060] The low chemical crosslinking thermoplastic polyurethane includes, in parts by mass: 15 parts of methylene diphenyl diisocyanate (MDI), 25 parts of hexamethylene diisocyanate (HDI), 55 parts of polytetramethylene ether glycol, 4.5 parts of 1,4-butanediol, 2.2 parts of dihydroxybutyl itaconamide, 2.5 parts of crosslinking agent diethylene glycol diacrylate, and 0.8 parts of thermal initiator DCP.

[0061] The raw materials were used according to the above preparation method to prepare a low chemical cross-linking TPU elastomer with a bulk hardness of 41D and a melting temperature of 139°C.

[0062] The low chemical cross-linking TPU elastomer is then foamed according to the above-mentioned supercritical foaming method, wherein the specific parameters of the supercritical foaming are: injection molding into a small embryo form using a twin-screw injection molding machine, the mold thickness is 5 mm, the foaming agent is CO2, the foaming temperature is 137°C, the pressure in the autoclave is 25 MPa, the constant temperature and pressure are maintained for 120 minutes, the pressure is released to normal pressure and then cooled to obtain a foaming mold base, which is hot-pressed in a sole mold to form a sports shoe foam midsole test piece.

[0063] The performance test of the obtained sports shoe foam midsole test piece was carried out, and the test results were: hardness 41C, density 0.06g / cm 3 , tensile strength 4.0MPa, elongation at break 290%, energy rebound 82.2%, impact peak acceleration (PeakG) 12.56, 180-degree tear 4.1kg / cm, yellowing resistance grade 3-4.

[0064] Example 4

[0065] The low chemical crosslinking thermoplastic polyurethane includes, in parts by mass: 45 parts of hexamethylene diisocyanate (HDI), 60 parts of polytetramethylene ether glycol, 4 parts of 1,4-hexanediol, 2.5 parts of dihydroxyethyl itaconamide, 2.8 parts of crosslinking agent ethylene glycol divinyl ether, and 1.2 parts of thermal initiator DCP.

[0066] The raw materials were used according to the above preparation method to prepare a low chemical cross-linking TPU elastomer with a bulk hardness of 45D and a melting temperature of 148°C.

[0067] The low chemical cross-linking TPU elastomer is then foamed according to the above-mentioned supercritical foaming method, wherein the specific parameters of the supercritical foaming are: a twin-screw injection molding machine is used to inject into a small embryo form, the mold thickness is 8mm, the foaming agent is CO2, the foaming temperature is 145°C, the pressure in the autoclave is 35Mpa, the constant temperature and pressure are maintained for 180min, the pressure is released to normal pressure and then cooled to obtain a foamed embryo, which is hot pressed in a sole mold into a sports shoe foam midsole test piece.

[0068] The performance test of the obtained sports shoe foam midsole test piece was carried out, and the test results were: hardness 46C, density 0.05g / cm 3 , tensile strength 4.5MPa, elongation at break 265%, energy rebound 84.6%, impact peak acceleration (PeakG) 13.27, 180-degree tear 4.5kg / cm, yellowing resistance grade 3-4.

[0069] In Examples 1-4, the specific types and weight fractions of isocyanate, oligomeric diol, and dihydroxyitaconamide as co-chain extenders vary within the scope of the present invention, but it can be seen that the basic density of the low chemical cross-linking degree TPU midsole foam shoe material obtained is less than 0.1 g / cm 3 , energy rebound is greater than 79%, and tear resistance is not less than 3.3kg / cm.

[0070] Example 5

[0071] The low chemical crosslinking thermoplastic polyurethane includes, in parts by mass: 32 parts of hexamethylene diisocyanate (HDI), 63 parts of polybutylene adipate diol, 3 parts of 1,4-hexanediol, 2 parts of dihydroxyethyl itaconamide, 2.4 parts of crosslinking agent ethylene glycol divinyl ether, and 0.8 parts of thermal initiator DCP.

[0072] The raw materials are prepared into a low chemical cross-linking TPU elastomer according to the above preparation method, and then the low chemical cross-linking TPU elastomer is foamed according to the above supercritical foaming method, wherein the specific parameters of the supercritical foaming are: a twin-screw injection molding machine is used to injection mold the elastomer into a small embryo form, the body thickness is 5 mm, the foaming agent is CO2, and the foaming temperature is 142°C; the pressure in the autoclave is 25 MPa, the constant temperature and pressure are maintained for 120 minutes, the pressure is released to normal pressure, and then cooled to obtain a foamed embryo body, which is hot-pressed in a sole mold to form a sports shoe foam midsole test piece.

[0073] The performance test of the obtained sports shoe foam midsole test piece was carried out, and the test results were: hardness 46C, density 0.06g / cm 3 , energy rebound 81.6%, 180 degree tear 4.2kg / cm, yellowing resistance grade 3-4.

[0074] Example 6

[0075] The low chemical crosslinking thermoplastic polyurethane includes, in parts by mass: 32 parts of hexamethylene diisocyanate (HDI), 63 parts of polybutylene adipate diol, 3 parts of 1,4-hexanediol, 2 parts of dihydroxybutyl itaconamide, 2.4 parts of crosslinking agent ethylene glycol divinyl ether, and 0.8 parts of thermal initiator DCP.

[0076] The raw materials are prepared into a low chemical cross-linking TPU elastomer according to the above-mentioned preparation method, and then the low chemical cross-linking TPU elastomer is foamed according to the above-mentioned supercritical foaming method, wherein the specific parameters of the supercritical foaming are: a twin-screw injection molding machine is used to injection mold the elastomer into a small embryo form, the body thickness is 5 mm, the foaming agent is CO2, and the foaming temperature is 144°C; the pressure in the autoclave is 25 MPa, the constant temperature and pressure are maintained for 120 minutes, the pressure is released to normal pressure, and then cooled to obtain a foamed embryo body, which is hot-pressed in a sole mold to form a sports shoe foam midsole test piece.

[0077] The performance test of the obtained sports shoe foam midsole test piece was carried out, and the test results were: hardness 45C, density 0.07g / cm 3 , energy rebound 83.2%, 180 degree tear 3.8kg / cm, yellowing resistance grade 3-4.

[0078] Example 7

[0079] The low chemical crosslinking thermoplastic polyurethane includes, in parts by mass: 32 parts of hexamethylene diisocyanate (HDI), 63 parts of polybutylene adipate diol, 3.5 parts of 1,4-hexanediol, 1.5 parts of dihydroxyethyl itaconamide, 2.4 parts of crosslinking agent ethylene glycol divinyl ether, and 0.8 parts of thermal initiator DCP.

[0080] The raw materials are prepared into a low chemical cross-linking TPU elastomer according to the above preparation method, and then the low chemical cross-linking TPU elastomer is foamed according to the above supercritical foaming method, wherein the specific parameters of the supercritical foaming are: a twin-screw injection molding machine is used to injection mold the elastomer into a small embryo form, the body thickness is 5 mm, the foaming agent is CO2, and the foaming temperature is 140°C; the pressure in the autoclave is 25 MPa, the constant temperature and pressure are maintained for 120 minutes, the pressure is released to normal pressure, and then cooled to obtain a foamed embryo body, which is hot-pressed in a sole mold to form a sports shoe foam midsole test piece.

[0081] The performance test of the obtained sports shoe foam midsole test piece was carried out, and the test results were: hardness 45C, density 0.06g / cm 3 , energy rebound 81.9%, 180 degree tear 4.1kg / cm, yellowing resistance grade 3-4.

[0082] Example 8

[0083] The low chemical crosslinking thermoplastic polyurethane includes, in parts by mass: 32 parts of hexamethylene diisocyanate (HDI), 63 parts of polybutylene adipate diol, 4 parts of 1,4-hexanediol, 1 part of dihydroxyethyl itaconamide, 2.4 parts of crosslinking agent ethylene glycol divinyl ether, and 0.8 part of thermal initiator DCP.

[0084] The raw materials are prepared into a low chemical cross-linking TPU elastomer according to the above preparation method, and then the low chemical cross-linking TPU elastomer is foamed according to the above supercritical foaming method, wherein the specific parameters of the supercritical foaming are: a twin-screw injection molding machine is used to injection mold the elastomer into a small embryo form, the body thickness is 5 mm, the foaming agent is CO2, and the foaming temperature is 138°C; the pressure in the autoclave is 25 MPa, the constant temperature and pressure are maintained for 120 minutes, the pressure is released to normal pressure, and then cooled to obtain a foamed embryo body, which is hot-pressed in a sole mold to form a sports shoe foam midsole test piece.

[0085] The performance test of the obtained sports shoe foam midsole test piece was carried out, and the test results were: hardness 44C, density 0.08g / cm 3 , energy rebound 82.4%, 180 degree tear 3.9kg / cm, yellowing resistance grade 3-4.

[0086] Comparative Example 1

[0087] The thermoplastic polyurethane includes, by mass, 32 parts of hexamethylene diisocyanate (HDI), 63 parts of polybutylene adipate diol, and 5 parts of 1,4-hexanediol.

[0088] The raw materials are made into a TPU elastomer, and then subjected to supercritical foaming, wherein the specific parameters of the supercritical foaming are: injection molding into a small embryo form with a twin-screw injection molding machine, the body thickness is 5 mm, the foaming agent is CO2, and the foaming temperature is 135°C; the pressure in the autoclave is 25 MPa, the constant temperature and pressure are maintained for 120 minutes, the pressure is released to normal pressure, and then cooled to obtain a foamed embryo body, which is hot-pressed in a sole mold to form a sports shoe foam midsole test piece.

[0089] The performance test of the obtained sports shoe foam midsole test piece was carried out, and the test results were: hardness 42C, density 0.11g / cm 3 , energy rebound 76.4%, 180 degree tear 2.8kg / cm, yellowing resistance grade 3-4.

[0090] Comparative Example 2

[0091] The thermoplastic polyurethane includes, by mass, 32 parts of hexamethylene diisocyanate (HDI), 63 parts of polybutylene adipate diol, 5 parts of 1,4-hexanediol, 2.4 parts of a cross-linking agent, ethylene glycol divinyl ether, and 0.8 parts of a thermal initiator, DCP.

[0092] The raw materials were made into a TPU elastomer and then subjected to supercritical foaming. The specific supercritical foaming parameters were: injection molding into a small embryonic form with a thickness of 5mm using a twin-screw injection molding machine, using CO2 as the blowing agent, and a foaming temperature of 135°C. The pressure in the autoclave was 25 MPa, and the temperature and pressure were maintained constant for 120 minutes. After depressurization to atmospheric pressure, the foamed embryonic form was cooled to obtain a foamed embryonic form, which was then hot-pressed in a sole mold to form a sports shoe foam midsole test piece.

[0093] The performance test of the obtained sports shoe foam midsole test piece was carried out, and the test results were: hardness 42C, density 0.11g / cm 3 , energy rebound 74.2%, 180 degree tear 3.2kg / cm, yellowing resistance grade 3-4.

[0094] In Examples 5-8, the types and mass fractions of isocyanate, oligomeric diol, crosslinker, and thermal initiator, as well as the supercritical foaming conditions, were fixed, with only the mass fractions of chain extender and co-chain extender varying. It can be seen that within the mass range of the present invention, differences in the type and content of the co-chain extender have little impact on the performance of the final midsole product. However, in Comparative Examples 1 and 2, the omission of the co-chain extender, diol itaconamide, significantly impacts the performance of the final shoe midsole, resulting in higher density, poorer resilience, and lower tear resistance.

[0095] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as above in terms of a preferred embodiment, it is not intended to limit the present invention. Any technician familiar with this patent can make slight changes or modifications to equivalent embodiments using the above technical content without departing from the scope of the technical solution of the present invention. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the solution of the present invention.

Claims

1. A thermoplastic polyurethane with low chemical crosslinking degree, characterized in that: The composition comprises, by mass: 10-45 parts of diisocyanate, 40-80 parts of oligomer diol, 1-15 parts of diol chain extender, 0.5-5 parts of dihydroxyitaconamide, 0.1-3 parts of crosslinking agent, and 0.1-2 parts of thermal initiator DCP; The dihydroxyitaconamide is a co-chain extender, and its general structural formula is as follows: Where n is any integer from 1 to 5; The cross-linking agent includes any one of divinyl ether, ethylene glycol divinyl ether, diethylene glycol divinyl ether, ethylene glycol diacrylate, butanediol diacrylate, and hexanediol diacrylate.

2. The low chemical crosslinking thermoplastic polyurethane according to claim 1, characterized in that: The diisocyanate includes at least one of methylene diphenyl diisocyanate, toluene diisocyanate, p-phenylene diisocyanate, xylylene diisocyanate, hexamethylene diisocyanate, methylene dicyclohexyl diisocyanate, isophorone diisocyanate, and cyclohexane dimethyl diisocyanate.

3. The low chemical crosslinking thermoplastic polyurethane according to claim 1, characterized in that: The diol chain extender includes at least one of ethylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,5-pentanediol, and 1,6-hexanediol.

4. The low chemical crosslinking thermoplastic polyurethane according to claim 1, characterized in that: The molecular weight of the oligomer diol is 1000~3000.

5. The low chemical crosslinking thermoplastic polyurethane according to claim 2, characterized in that: The diisocyanate includes at least one of methylene diphenyl diisocyanate and hexamethylene diisocyanate.

6. The low chemical crosslinking thermoplastic polyurethane according to claim 1, characterized in that: Dihydroxyitaconamide is prepared by reacting itaconic acid or itaconate with an alcoholamine, wherein the alcoholamine is any one of ethanolamine, propanolamine, butanolamine, pentanolamine and hexanolamine.

7. The low chemical crosslinking thermoplastic polyurethane according to claim 1, characterized in that: The crosslinking agent is any one of diethylene glycol divinyl ether, hexanediol diacrylate, and diethylene glycol diacrylate.

8. The low chemical crosslinking thermoplastic polyurethane according to any one of claims 2 to 4, characterized in that: 3.5-4.5 parts by mass of diol chain extender, 2-2.5 parts by mass of dihydroxyitaconamide, 1.5-2.8 parts by mass of crosslinking agent, and 0.8-1.2 parts by mass of thermal initiator DCP.

9. A method for preparing a thermoplastic polyurethane with a low chemical crosslinking degree, for preparing the thermoplastic polyurethane with a low chemical crosslinking degree according to any one of claims 1 to 8, characterized in that: The steps include: S1. Add diisocyanate and oligomer diol according to corresponding parts by weight into a reaction kettle, add a catalyst, and heat to 80°C. Stir under nitrogen for 2-3 hours, and cool to room temperature to obtain a prepolymer. S2. Degas the prepolymer obtained in step S1 under vacuum at 80° C. for 1-2 h, add a premix of a diol chain extender and dihydroxyitaconamide, stir at high speed for 2-3 min, pour into a mold, cure at 105-115° C. for 12-24 h, and mature at room temperature for 7 days to obtain a TPU polymer matrix; S3. The TPU polymer matrix obtained in step S1 is uniformly mixed with a crosslinking agent and a thermal initiator DCP in corresponding proportions, and the mixture is pelletized after twin-screw extrusion or injection molded by a twin-screw injection molding machine to obtain a thermoplastic polyurethane with a low chemical crosslinking degree.

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