A high-air-tightness supercritical foaming sole material and a preparation method and application thereof

Abstract

The application discloses a kind of high air-tightness supercritical foaming shoe sole material and preparation method, application, belong to footwear parts field.The preparation method includes: the mixing material is sequentially carried out injection molding, irradiation crosslinking, supercritical foaming and mould pressing, and high air-tightness supercritical foaming shoe sole material is obtained;The mixing material includes: ethylene-vinyl acetate 40-55 parts, polyolefin POE elastomer 10-20 parts, styrene elastomer 10-20 parts, linear polymer elastomer 10-25 parts, ethylene-vinyl alcohol copolymer 5-10 parts, acrylate rubber 5-10 parts, copolymer tackifying resin 2-4 parts, carboxymethyl cellulose 3-5 parts, crosslinking agent 0.4-0.6 parts, irradiation sensitizer 0.3-1 part, lubricant 0.8-1.1 part.The supercritical foaming shoe sole material provided has high air-tightness, still has good performance stability under satisfying density, elasticity and other physical properties.

Description

Technical Field

[0001] This invention relates to the field of footwear components technology, and in particular to a high airtightness supercritical foamed sole material, its preparation method, and its application. Background Technology

[0002] Currently, the emerging supercritical physical foaming technology in the footwear industry mainly uses N2 or CO2 supercritical foaming technology. Due to the superior performance of its sole materials and the absence of chemical foaming agents and odorless residue, it has become a new favorite in the industry. As consumers' demands for physical properties increase, the industry typically strives to make supercritical foamed soles extremely lightweight, extremely elastic, and extremely soft. In published patents and literature, efforts have been made to achieve a weight of 0.10±0.03 g / cm³ for EVA-based supercritical foamed soles. 3 Properties such as resilience ≥65% are typically achieved by introducing one of the following into the formulation: nylon elastomer PEBAX, polyester elastomer TPEE, or polyurethane elastomer TPU. The process mainly involves a single injection molding process, supercritical foaming in an autoclave, and a second molding process.

[0003] However, such supercritical foam soles have a fatal flaw: their hardness drops significantly after 1-2 months. This is because as the density decreases, the foaming ratio increases, the cell walls become thinner, and the low hardness reduces cell stability. Therefore, during the storage of mass-produced soles or during consumer use, the gas inside the foam sole will slowly escape, causing a significant decrease in hardness and creating a risk of trampling after wearing. Summary of the Invention

[0004] In view of this, the present invention provides a high airtightness supercritical foamed shoe sole material, its preparation method and application. The provided supercritical foamed shoe sole material has high airtightness and good performance stability while meeting the physical property indicators such as density and elasticity.

[0005] This invention provides a method for preparing a high airtightness supercritical foamed shoe sole material, comprising the following steps: sequentially subjecting the mixed materials to injection molding, irradiation crosslinking, supercritical foaming, and compression molding to obtain a high airtightness supercritical foamed shoe sole material;

[0006] By weight, the compound comprises: 40-55 parts ethylene-vinyl acetate, 10-20 parts polyolefin POE elastomer, 10-20 parts styrene elastomer, 10-25 parts linear polymer elastomer, 5-10 parts ethylene-vinyl alcohol copolymer, 5-10 parts acrylate rubber, 2-4 parts copolymer tackifying resin, 3-5 parts carboxymethyl cellulose, 0.4-0.6 parts crosslinking agent, 0.3-1 part radiation sensitizer, and 0.8-1.1 parts lubricant;

[0007] The linear polymer elastomer is one or more of nylon elastomers, polyurethane elastomers, and polyester elastomers.

[0008] The preparation and implementation method of this invention can yield a supercritical foamed shoe sole material with good physical properties, stability, and high airtightness.

[0009] like Figure 1 As shown, in this embodiment of the invention, the ingredients are weighed separately according to the weight ratio of the formula components, and then mixed to obtain the mixed material.

[0010] In terms of formulation, the matrix components of the compound in this embodiment of the invention include: 40-55 parts by weight of ethylene-vinyl acetate, 10-20 parts by weight of polyolefin elastomer (POE), 10-20 parts by weight of styrene elastomer, and 10-25 parts by weight of linear polymer elastomer; wherein the linear polymer elastomer is one or more of nylon elastomer, polyurethane elastomer, and polyester elastomer. In this invention, the use of ethylene-vinyl acetate, polyolefin elastomer, styrene elastomer, nylon elastomer, polyurethane elastomer, or polyester elastomer mainly achieves the lightweight, softness, resilience, and compressibility of the foamed shoe sole.

[0011] Specifically, ethylene-vinyl acetate (EVA) is a plastic resin copolymerized from ethylene and vinyl acetate (VA). The higher the VA content, the better its elasticity and other properties. The resin raw materials used in this invention include EVA with VA content of 18%-40%, with EV303 being a preferred variety; its weight parts can be 40 parts, 45 parts, 50 parts, 52 parts, 55 parts, etc.

[0012] The polyolefin POE elastomer (which may be represented as polyolefin elastomer POE, etc.) is preferably an ethylene-octene random copolymer with a hardness of 60-90A. Further preferred varieties include Dow's Engage 8180, with a hardness of 63-80A, but it is not limited to this specific commercially available product. In some embodiments, the POE weight parts may be 10 parts, 11 parts, 14 parts, 15 parts, etc.

[0013] The styrene elastomer is primarily a linear triblock copolymer (SEBS) with polystyrene as the end block and ethylene-butene copolymer (obtained by hydrogenating polybutadiene) as the middle elastic block. It exhibits excellent aging resistance and other properties. Preferably, it is a styrene-butadiene-styrene block copolymer with a hardness of 45-80A, specifically SEBS P1083 (Asahi Kasei Corporation). In some embodiments, the weight parts of the styrene elastomer may be 10 parts, 11 parts, 12 parts, 15 parts, etc.

[0014] Furthermore, the linear polymer elastomer described in the embodiments of the present invention is one or more of nylon elastomer, polyurethane elastomer, and polyester elastomer; specifically, it is nylon elastomer PEBAX, polyurethane elastomer TPU, or polyester elastomer TPEE, and the weight parts can be 10 parts, 15 parts, 18 parts, 20 parts, etc.

[0015] In a preferred embodiment of the present invention, the nylon elastomer comprises a block polyether amide elastomer with a hardness of 35-45D, such as 40D or 45D, with KHX7040 (Xinyuan Chemical (Shandong) Co., Ltd.) being a preferred variety. The polyurethane elastomer comprises an aliphatic polyether polyurethane elastomer with a hardness of 37-45D, with EZ32-5-A (Lubrizol) being a preferred variety. The polyester elastomer comprises a linear block copolymer of PBT (polybutylene terephthalate) polyester hard segments and aliphatic polyether soft segments with a hardness of 37-47D, with Hytrel 4058 (Celanis) being a preferred variety.

[0016] Secondly, this invention employs high-viscosity materials such as acrylic rubber, copolymer tackifying resin, and carboxymethyl cellulose. Utilizing the hydrogen bonding and ionic crosslinking properties between their polymer chains, these materials enhance the matrix viscosity and effectively trap the gases (N2 or CO2) generated during the foaming process. Furthermore, the carboxymethyl cellulose acts as a nucleating agent, reducing the Gibbs free energy of bubble formation during foaming, lowering the nucleation energy barrier of the cells, effectively promoting bubble nucleation, reducing the difficulty of supercritical foaming, and improving the compressibility of the foamed material. Finally, this invention uses a high-barrier material, ethylene-vinyl alcohol copolymer, to reduce gas escape in the later stages of mass production of foamed shoe soles, enhance gas retention capacity, and improve the long-term stability of physical properties. This, in turn, improves the stability and safety of the product while meeting consumers' demands for lightweight, soft, and elastic sole properties.

[0017] The compounding formulation described in this embodiment of the invention includes: 5-10 parts of ethylene-vinyl alcohol copolymer; 5-10 parts of acrylate rubber; 2-4 parts of copolymer tackifying resin; and 3-5 parts of carboxymethyl cellulose.

[0018] The ethylene-vinyl alcohol copolymer, abbreviated as EVOH, is obtained by copolymerizing ethylene and vinyl acetate, followed by hydrolysis. Combining the processability of the ethylene-structured polymer with the barrier properties of the vinyl alcohol polymer, EVOH exhibits excellent processing performance and superior barrier properties against gases, odors, fragrances, and solvents. EVOH copolymers are highly crystalline (e.g., EVOH crystallinity is 30%-50%), and its properties primarily depend on the relative concentration of its comonomers; as the ethylene content decreases, the gas barrier performance improves. EVOH resin possesses high mechanical strength, elasticity, surface hardness, abrasion resistance, and weather resistance, as well as strong antistatic properties. The hydroxyl groups in the EVOH molecular structure give it extremely high barrier properties against gases such as oxygen and carbon dioxide, with an oxygen permeability coefficient as low as 4, which is 100 times that of PA and 10,000 times that of PE or PP. This characteristic allows it to effectively suppress the escape of gases (such as N2 or CO2) during supercritical foaming, maintaining the stability of the cell structure. Specifically, the preferred variety is EVOH F101A (Kuraray Co., Ltd., Japan), which can be in parts by weight of 5, 8, or 10.

[0019] The acrylate rubber, abbreviated as ACM, refers to a copolymer of alkyl acrylate monomers and a small amount of monomers with crosslinking active groups. Its main chain is a saturated carbon chain, and its side groups are polar ester groups, which impart high viscosity to ACM. Preferably, ACM includes acrylate rubber with a vulcanization point of ethyl feldspar monoester. A further preferred variety is ACM-2212 (Jiujiang Duwei Rubber Technology Co., Ltd.), with a Mooney viscosity of 40±5 [ML(1+4)*100℃] and a gel content ≤5%. Its weight parts can be 5, 6, 7, 8, or 10 parts. Due to its polar groups, some ACM rubbers exhibit significant sticking to rollers and molds during processing, indicating high viscosity.

[0020] The aforementioned copolymer tackifying resin is primarily an isoprene-styrene copolymer resin. This resin can be synthesized through strict block copolymerization or random copolymerization, and its polar molecular structure gives it excellent tackifying properties. Styrene enhances the flexibility of the molecular chain and its compatibility with other polymers, such as EVA, POE, and SEBS, significantly improving the adhesion and cohesive strength of the polymer matrix. Furthermore, a preferred copolymer tackifying resin is Escorez 5690 (ExxonMobil), with a styrene content of 10-15% by mass.

[0021] The carboxymethyl cellulose described in this invention is a fibrous powder containing carboxymethyl functional groups. Its carboxyl groups endow cellulose with excellent surface activity and polarity, increasing its viscosity. They can also undergo covalent reactions with other substances or through electrostatic adsorption. The carboxyl groups form strong chemical bonds with ester groups of ethylene-vinyl acetate, ester groups of acrylate rubber (ACM), and hydroxyl groups of ethylene-vinyl alcohol copolymers, resulting in excellent compatibility and effectively binding non-polar and polar polymers, thus enhancing the strength of the foam cells. Furthermore, carboxymethyl cellulose can reduce the Gibbs free energy of bubble nuclei during foaming, lowering the nucleation energy barrier of the foam cells, effectively promoting bubble nucleation, reducing the difficulty of supercritical foaming, and improving the compressibility of the foamed material. The degree of substitution (DS) of the carboxymethyl cellulose is ≤0.8; a preferred variety is CM-22 (Shanghai Bangjing Industrial Co., Ltd.).

[0022] Meanwhile, the supercritical foaming formulation of this invention includes 0.4-0.6 parts of crosslinking agent, 0.3-1 parts of radiation sensitizer, and 0.8-1.1 parts of lubricant. Preferably, the crosslinking agent is a peroxide crosslinking agent. By introducing an appropriate amount of crosslinking agent into the formulation, this invention allows for micro-crosslinking of EVA / POE / SEBS during the injection molding of the shoe sole preform. This not only increases the viscosity of the blend but also facilitates the formation of a network crosslinked structure during high-temperature, high-pressure foaming in the supercritical autoclave, thereby controlling the pore size and reducing the shrinkage of the foamed shoe sole. Specifically, the preferred peroxide crosslinking agent is 1,4-di-tert-butylperoxyisopropylbenzene (BIBP).

[0023] PEBAX / TPEE / TPU are all linear polymers. Without modification, they cannot be directly crosslinked using peroxides, resulting in poor melt strength under high temperature and pressure. Simply adding compatibilizers cannot achieve satisfactory results. This invention uses 0.3-1 parts by weight of an irradiation sensitizer (more preferably 0.5-0.7 parts), preferably an amide or ester. Specifically, the irradiation sensitizer for the nylon elastomer is preferably N,N'-methylenebisacrylamide, the irradiation sensitizer for the polyurethane elastomer is preferably triallyl isocyanurate, and the irradiation sensitizer for the polyester elastomer is preferably trimethylolpropane triacrylate.

[0024] In addition, the lubricant may include stearic acid, with stearic acid 1801 being a preferred variety.

[0025] In this embodiment of the invention, BIBP, stearic acid, and radiation sensitizer are weighed as the first group; ethylene-vinyl alcohol copolymer, acrylate rubber, copolymer tackifying resin, and carboxymethyl cellulose are weighed as the second group; and the remaining materials are weighed as the third group. First, the third group of materials is poured into the internal mixer and the machine is turned on. When the temperature rises to between 100±10℃, the second group of materials is poured in; when the temperature rises to between 110±10℃, the first group of materials is poured in; when the temperature rises to between 110-120℃, the mixed material is poured out.

[0026] After mixing, the present invention embodiment performs granulation: the mixed material is poured into the granulator, and the temperatures of the first, second, third and fourth zones are adjusted to 95℃, 100℃, 105℃ and 110℃ respectively, and the screw speed is adjusted to 40-50 rpm and the cutting speed is adjusted to 15-20 rpm.

[0027] In this embodiment of the invention, the granules obtained from the material preparation process are sequentially subjected to preform injection molding, irradiation crosslinking, supercritical autoclaving foaming, and MD secondary molding to obtain a high-airtightness supercritical foamed shoe sole material. Prior to the supercritical physical foaming process, this embodiment of the invention mainly involves preform injection molding and irradiation crosslinking processes, as detailed below:

[0028] IP injection molding, also known as preform injection, involves pouring the prepared granules into the IP one-time injection foaming molding machine. The temperatures of the first, second, third, and fourth feeding zones are set to 94, 96, 98, and 100℃, respectively; the injection speed is 50(±2)-45(±2)-40(±2)-35(±2)-30(±2)%; the injection pressure is 90(±5)-90(±5)-90(±5)-90(±5)-90(±5)bar; the vacuuming time is 80±20 seconds; and the mold temperatures of the upper and lower mold plates are set to 175±3℃ and 173±5℃, respectively.

[0029] The material quantity is set according to the mold requirements (mold size 18cm*10cm*1cm, material quantity can be set to 90±10g based on a foaming ratio of 1.5), the injection time is 150±20 seconds, and the vulcanization time is 450±30 seconds. Then, the small rough shoe sole blank is taken out and allowed to cool naturally for 2 hours to set. In this embodiment of the invention, a certain proportion of crosslinking agent is added during the single injection cold blank process, which achieves micro-crosslinking. This is beneficial for the formation of a network crosslinked structure in the polymer matrix during high-temperature and high-pressure foaming, thereby improving the strength of the foamed structure and avoiding local melting and collapse during the foaming process.

[0030] The irradiation crosslinking process includes: placing the IP-injected preform into an irradiation crosslinking machine, irradiating it with a high-energy electron beam of 6-10 MeV, a dose of 25±10 kGy, a temperature of 25±2℃, and an irradiation time of 20±10 minutes. Nylon elastomers, polyurethane elastomers, or polyester elastomers are linear polymers and cannot be directly crosslinked using peroxides; therefore, electron beam irradiation crosslinking is employed. The process includes: energy of 6-10 MeV, dose of 25±10 kGy, temperature of 25±2℃, and irradiation time of 20±10 minutes, selectively irradiating and crosslinking the linear elastomers (such as nylon elastomers, polyurethane elastomers, or polyester elastomers), thereby increasing the melt viscosity and cell wall strength, enabling stable foam growth without bursting.

[0031] The supercritical physical foaming process is autoclave supercritical foaming: A small rough blank, after being left to stand for 24 hours, is placed in an autoclave supercritical physical foaming tank. The supercritical N2 pressure is 24±6 MPa, the foaming temperature is 120±10℃, and the holding time is 120±30 min. Then, a staged depressurization method is used (slow first, then fast: slow depressurization rate 0.1~0.5 MPa / s, time 10-60s; fast depressurization rate 3~10 MPa / s, time 0.5-6s). The foamed shoe sole is then removed and cooled to room temperature. In this embodiment of the invention, the autoclave supercritical foaming process sets the supercritical foaming pressure to 24±6 MPa, the saturation temperature to 120±10℃, the holding time to 120±30 min, and employs a staged depressurization method to induce uniform foaming and reduce gas escape.

[0032] Finally, the molding process is the secondary molding of the supercritical foam: the supercritical foam semi-finished product, which has been left to stand for 48-72 hours, is placed into a flat molding die to complete the molding of the finished product. Preferably, the hot pressing temperature is 170±5℃; the hot pressing time is 700±30 seconds; the cooling water temperature is 25±3℃; and the cooling time is 700±30 seconds. This embodiment of the invention, through the secondary molding process, facilitates the formation of a dense skin on the surface of the supercritical micro-foamed sole, improving gas sealing and optimizing the appearance, thus better preventing gas escape from the foamed sole.

[0033] This invention provides a high airtightness supercritical foamed shoe sole material obtained by the preparation method described above, and provides the application of the high airtightness supercritical foamed shoe sole material in shoemaking.

[0034] This invention features significant improvements in formulation design, achieving a comprehensive enhancement of sole material performance through the combination of multiple high-performance materials, including: ① Combining with basic performance providers: ethylene-vinyl acetate, polyolefin elastomers, styrene elastomers, nylon elastomers, polyurethane elastomers, or polyester elastomers; these materials collectively impart lightweight, softness, resilience, and compressibility to the foamed sole. ② Introducing gas-locking reinforcing agents: high-viscosity materials such as acrylate rubber, copolymer tackifying resins, and carboxymethyl cellulose; through hydrogen bonding and ionic crosslinking between their molecular chains, these effectively lock in gases (such as N2 or CO2) generated during the foaming process; moreover, carboxymethyl cellulose can reduce the Gibbs free energy of bubble nuclei during foaming, lowering the nucleation energy barrier of the cells, effectively promoting bubble nucleation, reducing the difficulty of supercritical foaming, and improving the compressibility of the foamed material. ③ Ensuring long-term stability: Using ethylene-vinyl alcohol copolymers, a high-barrier material, can significantly reduce gas escape from the foamed sole in the later stages of mass production, thereby improving the long-term stability and safety of the product. Through the above-mentioned innovative formula, the embodiments of the present invention not only meet consumers' demands for lightweight, soft, and elastic physical properties of shoe soles, but also significantly improve the stability and safety of the products.

[0035] Based on the existing three-step process flow (first-stage cold preform injection, supercritical foaming under pressure, and secondary molding), this invention adds an irradiation crosslinking step and systematically optimizes each step, as follows: ① First-stage cold preform injection (referred to as preform injection): A certain proportion of crosslinking agent is added at this stage to achieve micro-crosslinking. This step helps to form a network crosslinked structure during high-temperature and high-pressure foaming, thereby improving the strength of the foam structure and avoiding local melting and collapse. ② Irradiation crosslinking step: To address the problem that the linear polymer cannot be directly crosslinked using peroxides, electron beam irradiation crosslinking technology is adopted. On the one hand, it improves the melt viscosity and cell wall strength of the overall formulation, ensuring stable foam growth without bursting; on the other hand, electron beams have higher energy transfer efficiency, which, combined with irradiation sensitizers, can further improve irradiation efficiency and shorten irradiation time. Moreover, the crosslinking agent promotes uniform crosslinking of molecular chains, making it suitable for mass production. ③ Supercritical foaming under pressure: The supercritical foaming pressure is set to 24±6 MPa, the saturation temperature to 120±10℃, and the holding time to 120±30 min. Simultaneously, a staged depressurization method (slow first, then fast) is adopted to induce uniform foaming and reduce gas escape. ④ Secondary molding process: A dense skin is formed on the surface of the supercritical micro-foamed sole, which further improves gas sealing and optimizes the appearance, thereby better preventing gas escape from the foamed sole.

[0036] This invention innovatively monitored the hardness changes of foamed shoe soles for up to two months. By enhancing the strength of the foam cells and the angle of gas retention, and through dual innovation in formulation and process, it successfully broke through the technical bottleneck of synergistic improvement of material crosslinking / foaming and gas retention capabilities, and solved the core problem of the difficulty in balancing the pursuit of lightness, softness and elasticity with other performance stability in foamed shoe soles. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the preparation process according to an embodiment of the present invention. Detailed Implementation

[0038] The technical solutions in the embodiments of this application are described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application. The embodiments of the present invention are further illustrated below, but the present invention is not limited to these embodiments.

[0039] Example 1

[0040] Weighing: Based on the dosage of the formula in Table 1, weigh BIBP, stearic acid, and radiation sensitizer as the first group; weigh ethylene-vinyl alcohol copolymer, acrylate rubber, copolymer tackifying resin, and carboxymethyl cellulose as the second group; weigh the remaining materials as the third group.

[0041] Mixing: First, pour the third batch of material into the internal mixer and turn on the machine. When the temperature rises to between 100±10℃, pour in the second batch of material. When the temperature rises to between 110±10℃, pour in the first batch of material. When the temperature rises to between 110-120℃, pour out the mixed material.

[0042] Material preparation: Pour the mixed material into the material preparation machine. Set the temperatures of the first, second, third, and fourth zones to 95, 100, 105, and 110℃ respectively. Adjust the screw speed to 40-50 rpm and the cutting speed to 15-20 rpm.

[0043] IP Injection Preform: Pour the prepared granules into the IP one-time injection foaming molding machine. Adjust the temperatures of the first, second, third, and fourth feeding zones to 94, 96, 98, and 100℃ respectively; the injection speed to 50(±2)-45(±2)-40(±2)-35(±2)-30(±2)%; the injection pressure to 90(±5)-90(±5)-90(±5)-90(±5)-90(±5)bar; the vacuuming time to 80±20 seconds; and adjust the upper and lower mold temperatures to 175±3℃ and 173±5℃ respectively. Set the material quantity according to the mold quantity (mold size 18cm*10cm*1cm, material quantity can be set to 90±10g based on foaming ratio of 1.5), injection time is 150±20 seconds, vulcanization time is 450±30 seconds, then take out the small rough shoe sole blank and let it cool naturally for 2 hours to set.

[0044] Irradiation crosslinking: The IP-injected embryo is placed in an irradiation crosslinking machine and irradiated with a high-energy electron beam of 6-10 MeV, with a dose of 25±10 kGy, a temperature of 25±2℃, and an irradiation time of 20±10 minutes.

[0045] Supercritical foaming under pressure: After standing for 24 hours, the small rough blank is placed in a supercritical physical foaming tank under pressure. The supercritical N2 pressure is 24±6 MPa, the foaming temperature is 120±10℃, and the holding time is 120±30min. Then, the pressure is released in stages (slow first, then fast: slow release rate is 0.3~0.5 MPa / s, time is 36-60s; fast release rate is 4~6MPa / s, time is 3.5-6s). The foamed shoe sole is then removed and cooled to room temperature.

[0046] Compression molding: The supercritical foamed semi-finished product, which has been left to stand for 48-72 hours, is placed into a flat molding die to complete the molding of the finished product. The hot pressing temperature is 170±5℃; the hot pressing time is 700±30 seconds; the cooling water temperature is 25±3℃; and the cooling time is 700±30 seconds.

[0047] Examples 2-8

[0048] The procedure is the same as in Example 1, and the specific formulations are shown in Table 1.

[0049] Table 1. Formulations and tests of the examples:

[0050]

[0051]

[0052] Comparative Examples 1-7

[0053] The operation is basically the same as or different from that in Example 1. For specific formulations, please refer to Table 2.

[0054] Table 2 Comparative Examples: Formulations and Tests

[0055]

[0056]

[0057] The contents of each raw material are as follows:

[0058] EV 303: VA content is 18%, hardness is 88A (34D), melt index is 3.0 g / 10 min, melting point is 82℃, and tensile strength is 19 MPa.

[0059] Engage 8180: Hardness 63A (16D), melt flow index 0.5 g / 10 min, melting point 44 °C, Dow Chemical Company.

[0060] SBBS P1083: Hardness 56A, S content 20%, melt flow index 3.0g / 10min, tensile strength 9MPa, Asahi Kasei Corporation.

[0061] KHX7040: Hardness 40D, melting point 162℃, melt index 10.0g / 10min, tensile strength 25MPa, Xinyuan Chemical (Shandong) Co., Ltd.

[0062] EZ32-5-A: Hardness 37D, Melting point 127℃, Melt flow index 5.0g / 10min, Tensile strength 40MPa, Lubrizol Corporation.

[0063] Hytrel 4058: Hardness 37D, Melting point 152℃, Melt index 5.6g / 10min, Tensile strength 60MPa, Celanese Corporation.

[0064] ACM-2212: Mooney viscosity 40±5 [ML(1+4)*100℃], gel content ≤5%, Jiujiang Duwei Rubber Technology Co., Ltd.

[0065] Escorez 5690: softening point 90.5℃, styrene content 10-15%, ExxonMobil.

[0066] CM-22: Molecular weight 250,000, degree of substitution DS≤0.8, particle size 50um, Shanghai Bangjing Industrial Co., Ltd.

[0067] BIBP: AkzoNobel.

[0068] N,N'-Methylenebisacrylamide: Melting point 185℃, Suzhou Yake Technology Co., Ltd.

[0069] Triallyl isocyanurate: Melting point 26-28℃, Shandong Guohua Chemical Co., Ltd.

[0070] Trimethylolpropane triacrylate: Shandong Guohua Chemical Co., Ltd.

[0071] Stearic acid 1801: Dukuda, Indonesia.

[0072] EVOH F101A: Melting point 183℃, hardness 115A, tensile strength 34.0 MPa, elongation 15%, melt index 1.6 g / 10 min, ethylene content 32 wt%, crystallinity 42%, Kuraray Co., Ltd., Japan.

[0073] The comparative data from Examples 1-4 show that as the amount of nylon elastomer added increases, the rebound rate gradually increases and the compression deformation rate gradually decreases, indicating that nylon elastomer is beneficial to improving the rebound performance and compression performance of foamed shoe soles.

[0074] The comparative data from Examples 2, 7, and 8 show that when the amount of nylon elastomer, polyurethane elastomer, or polyester elastomer added is 15 parts, it is beneficial to improve the rebound and compression performance of foamed shoe soles, with nylon elastomer being the best and polyester elastomer being the second best.

[0075] The test data from Examples 1-8 show that when the formulation of the foamed shoe sole is adjusted to include 40-55 parts ethylene-vinyl acetate, 10-20 parts polyolefin POE elastomer, 10-20 parts styrene elastomer, 10-25 parts nylon elastomer, polyurethane elastomer, or polyester elastomer, 5-10 parts ethylene-vinyl alcohol copolymer, 5-10 parts acrylate rubber, 2-4 parts copolymer tackifying resin, 3-5 parts carboxymethyl cellulose, 0.4-0.6 parts crosslinking agent, 0.3-1 part radiation sensitizer, and 1 part lubricant, a density of 0.12 ± 0.02 g / cm³ can be obtained. 3 Foamed shoe sole material with a hardness of 42±3C, a rebound rate of ≥70%, a compression deformation of ≤32%, and a shock absorption G-value of ≤10, and a retention rate of ≥93% for all physical properties such as density, hardness, rebound, compression deformation, and shock absorption G-value within 60 days.

[0076] The comparative data from Comparative Example 1 and Example 2 show that when the other components and contents of Example 2 remain unchanged, and no ethylene-vinyl alcohol copolymer is added, the initial properties of the foamed shoe sole change significantly compared to those of Example 2. The rebound / compression performance deteriorates noticeably, and the retention rate of various properties is ≤90% after 30 days of standing and ≤85% after 60 days of standing. This indicates that the high-barrier ethylene-vinyl alcohol copolymer reduces gas escape in the later stages of mass production of foamed shoe soles, enhances gas retention capacity, and improves the long-term stability of physical properties.

[0077] Comparative data from Comparative Examples 2, 3, 5, and Example 2 show that when other components and contents of Example 2 remain unchanged, and no acrylate rubber or copolymer tackifying resin is added, or neither is added, the initial physical properties of the foamed sole show a decrease in rebound / compression performance compared to the initial physical properties of Example 2. Furthermore, the retention rate of various physical properties is ≤90% after 30 days of standing and ≤85% after 60 days of standing. This indicates that the polarity and viscosity of acrylate rubber or copolymer tackifying resin can improve the overall viscosity and cohesive strength of the foaming formulation, effectively locking in the gases (N2 or CO2) generated during the foaming process, and enhancing the overall performance of the foamed sole.

[0078] Comparative data from Comparative Example 4 and Example 2 show that when other components and contents of Example 2 remain unchanged, but carboxymethyl cellulose is not added, the initial properties of the foamed shoe sole show a slight decrease in resilience and a significant deterioration in compression performance compared to the initial properties of Example 2. Furthermore, the retention rate of various properties after 30 days of standing is ≤90%, and after 60 days of standing, the retention rate is ≤85%. This indicates that carboxymethyl cellulose not only has high viscosity, but its carboxyl groups also form strong chemical bonds with the ester groups of ethylene-vinyl acetate, acrylate rubber (ACM), and hydroxyl groups of ethylene-vinyl alcohol copolymer, playing an excellent compatibility role. This effectively binds non-polar and polar polymers together, enhancing the strength of the foam cells. On the other hand, carboxymethyl cellulose lowers the Gibbs free energy of bubble nuclei during foaming, reducing the nucleation energy barrier of the cells, effectively promoting bubble nucleation, reducing the difficulty of supercritical foaming, and improving the compression performance of the foamed material.

[0079] The comparative data from Comparative Example 6 and Example 2 show that when the other components and contents of Example 2 remain unchanged, and ethylene-vinyl alcohol copolymer / acrylate rubber / copolymer tackifying resin / carboxymethyl cellulose are not added, the initial physical properties of the foamed shoe sole are significantly worse than those of Example 2 in terms of resilience and compression performance, and the retention rate of various physical properties after standing for 60 days is ≤80%. This indicates that adding the above materials can improve the stability and safety of the product while meeting consumers' demands for lightweight, soft, and elastic physical properties.

[0080] Comparative data from Comparative Example 7 and Example 2 show that when other components and their contents remain unchanged in Example 2, no radiation sensitizer is added, and the preform is injected without undergoing radiation crosslinking, supercritical foaming is performed directly. This invention uses electron beam irradiation crosslinking to selectively crosslink the linear elastomer, thereby increasing melt viscosity and cell wall strength, thus maintaining stable foam growth, producing uniform and dense cells, reducing gas escape, and improving the resilience and compression properties of the foamed shoe sole.

[0081] As can be seen from the above embodiments, the embodiments of the present invention are prepared by combining ethylene-vinyl acetate, polyolefin elastomer, styrene elastomer, nylon elastomer or polyurethane elastomer or polyester elastomer, ethylene-vinyl alcohol copolymer, acrylate rubber, copolymer tackifying resin, carboxymethyl cellulose and crosslinking agent, radiation sensitizer, lubricant, etc., and by a process of one-time injection cold preform, radiation crosslinking, supercritical foaming in autoclave, and two-time molding, finally obtaining a material with a density of 0.12±0.02 g / cm³. 3 This is a high-airtightness supercritical foamed shoe sole material with a hardness of 42±3C, a resilience of ≥70%, a compression set of ≤32%, a shock absorption G-value of ≤10, and a property retention rate of ≥93% within 60 days. This foamed shoe sole material further enhances the viscosity of the matrix by using high-viscosity materials such as acrylic rubber, copolymer tackifying resin, and carboxymethyl cellulose, effectively locking in gas during the foaming process. The use of ethylene-vinyl alcohol copolymer, a high-barrier material, reduces gas escape in the later stages of mass production, enhancing gas retention capacity and improving long-term stability of physical properties. Irradiation crosslinking technology increases the melt viscosity of each matrix and the strength of the cell walls during foaming, enhancing foam stability and facilitating its application in shoe manufacturing.

[0082] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing a high-airtightness supercritical foamed shoe sole material, characterized in that, Includes the following steps: The mixed materials are sequentially subjected to injection molding, irradiation crosslinking, supercritical foaming and compression molding to obtain a high airtight supercritical foamed shoe sole material. By weight, the compound comprises: 40-55 parts ethylene-vinyl acetate, 10-20 parts polyolefin POE elastomer, 10-20 parts styrene elastomer, 10-25 parts linear polymer elastomer, 5-10 parts ethylene-vinyl alcohol copolymer, 5-10 parts acrylate rubber, 2-4 parts copolymer tackifying resin, 3-5 parts carboxymethyl cellulose, 0.4-0.6 parts crosslinking agent, 0.3-1 part radiation sensitizer, and 0.8-1.1 parts lubricant; The linear polymer elastomer is one or more of nylon elastomer, polyurethane elastomer, and polyester elastomer; the nylon elastomer is a block polyether amide elastomer with a hardness of 35-45D; the polyurethane elastomer is an aliphatic polyether polyurethane elastomer with a hardness of 37-45D; and the polyester elastomer is a linear block copolymer of butylene terephthalate polyester hard segment and aliphatic polyether soft segment with a hardness of 37-47D. The VA content of the ethylene-vinyl acetate is 18-40% by mass; the polyolefin POE elastomer is an ethylene-octene random copolymer with a hardness of 60-90A; the styrene elastomer is a styrene-butadiene-styrene block copolymer with a hardness of 45-80A. The acrylate rubber contains a monomer structure with a vulcanization point of itaconic acid monoester; the copolymer tackifying resin is mainly an isoprene-styrene copolymer resin.

2. The preparation method according to claim 1, characterized in that, The oxygen permeability coefficient of the ethylene-vinyl alcohol copolymer is less than 4.

3. The preparation method according to claim 1, characterized in that, The degree of substitution of the carboxymethyl cellulose is ≤0.

8.

4. The preparation method according to claim 1, characterized in that, The crosslinking agent is a peroxide crosslinking agent; the radiation sensitizer is an amide or ester substance; and the lubricant is stearic acid.

5. The preparation method according to claim 1, characterized in that, The irradiation crosslinking is electron beam irradiation crosslinking with an energy of 6~10MeV and a dose of 15~35kGy; the supercritical foaming pressure is 18~30MPa and the temperature is 110~130℃.

6. The high airtightness supercritical foamed shoe sole material obtained by the preparation method according to any one of claims 1-5.

7. The application of the high airtightness supercritical foamed sole material as described in claim 6 in shoe manufacturing.

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