High-airtightness supercritical foaming sole material as well as preparation method and application thereof

Abstract

The invention discloses a high-airtightness supercritical foaming sole material as well as a preparation method and application thereof, and belongs to the field of shoe parts. The preparation method comprises the following steps: sequentially carrying out injection molding, irradiation crosslinking, supercritical foaming and compression molding on a mixed material to obtain the high-airtightness supercritical foaming sole material, the mixed material is prepared from 40 to 55 parts of ethylene-vinyl acetate, 10 to 20 parts of polyolefin POE (Polyolefin Elastomer), 10 to 20 parts of styrene elastomer, 10 to 25 parts of linear polymer elastomer, 5 to 10 parts of ethylene-vinyl alcohol copolymer, 5 to 10 parts of acrylate rubber, 2 to 4 parts of copolymerized tackifying resin, 3 to 5 parts of carboxymethylcellulose, 0.4 to 0.6 part of cross-linking agent, 0.3 to 1 part of irradiation sensitizer and 0.8 to 1.1 parts of lubricant. The supercritical foaming sole material provided by the invention has high air tightness, and still has good performance stability under the condition that physical properties such as density and elasticity are met.

Description

Technical Field

[0001] The present invention relates to the technical field of shoe components, and in particular to a high-air-tightness supercritical foaming sole material and a preparation method and application thereof. Background Art

[0002] At present, the emerging supercritical physical foaming technology in the footwear industry is mainly N2 or CO2 supercritical foaming technology. It has become a new favorite in the industry because of its excellent sole material product performance, the fact that it does not use chemical foaming agents, and has no odor residue. As consumers' physical property requirements become increasingly higher, the industry usually makes supercritical foamed soles extremely light, extremely elastic, and ultra-soft. In published patents or literature, in order to make EVA-based supercritical foamed soles reach 0.10±0.03g / cm 3 , rebound rate ≥ 65% and other physical properties, usually one of the nylon elastomer PEBAX or polyester elastomer TPEE or polyurethane elastomer TPU is introduced into the formula, and it is mainly obtained through one-time injection cold embryo, autoclave supercritical foaming and secondary compression molding processes.

[0003] However, such supercritical foaming soles have a fatal flaw: their hardness drops significantly after one to two months of use. This is because as density decreases, the expansion ratio increases, the cell walls become thinner, and the low hardness reduces cell stability. Consequently, during the placement of mass-produced soles or during consumer use, the gas trapped within the foamed soles slowly escapes, causing a significant drop in hardness and creating a risk of being stepped on after wear. Summary of the Invention

[0004] In view of this, the present invention provides a high-air-tightness supercritical foaming sole material and its preparation method and application. The provided supercritical foaming sole material has high air-tightness and still has good performance stability while meeting physical properties such as density and elasticity.

[0005] The present invention provides a method for preparing a high-air-tightness supercritical foamed sole material, comprising the following steps: subjecting a mixed material to injection molding, radiation cross-linking, supercritical foaming, and compression molding in sequence to obtain the high-air-tightness supercritical foamed sole material;

[0006] The mixed material comprises, in parts by weight, 40-55 parts of ethylene vinyl acetate, 10-20 parts of polyolefin POE elastomer, 10-20 parts of styrene elastomer, 10-25 parts of linear polymer elastomer, 5-10 parts of ethylene vinyl alcohol copolymer, 5-10 parts of acrylic rubber, 2-4 parts of copolymerized tackifying resin, 3-5 parts of carboxymethyl cellulose, 0.4-0.6 parts of crosslinking agent, 0.3-1 parts of radiation sensitizer and 0.8-1.1 parts of lubricant;

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

[0008] By means of the preparation and realization method of the present invention, a supercritical foaming sole material with good physical properties, stability and high air tightness can be obtained.

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

[0010] In terms of formulation, the matrix components of the mixed material in the embodiments of the present 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 a linear polymer elastomer; the linear polymer elastomer is one or more of nylon elastomer, polyurethane elastomer, and polyester elastomer. In the present invention, the use of ethylene vinyl acetate, polyolefin elastomer, styrene elastomer, nylon elastomer, polyurethane elastomer, or polyester elastomer primarily achieves the lightweight, soft, resilient, and compressible properties of the foamed shoe sole.

[0011] Specifically, ethylene vinyl acetate (EVA) is a plastic resin formed by the copolymerization of ethylene and vinyl acetate (VA). The higher the VA content, the better its elasticity. The resin raw material used in the embodiments of the present invention includes EVA with a VA content of 18%-40%, with preferred varieties including EV 303. The weight ratios can be 40, 45, 50, 52, or 55 parts, among others.

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

[0013] The styrene elastomer, referred to as SEBS, is a linear triblock copolymer primarily composed of polystyrene as the terminal segments and an ethylene-butylene copolymer derived from hydrogenated 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, a specific example being SEBS P1083 (Asahi Kasei Corporation). In some embodiments, the weight percentage of the styrene elastomer can be 10 parts, 11 parts, 12 parts, 15 parts, etc.

[0014] Moreover, the linear polymer elastomer described in the embodiment of the present invention is one or more of nylon elastomer, polyurethane elastomer and polyester elastomer; specifically, nylon elastomer PEBAX or 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 segmented polyetheramide elastomer with a hardness of 35-45D, such as 40D or 45D, preferably KHX7040 (Xinyuan Chemical (Shandong) Co., Ltd.). The polyurethane elastomer comprises an aliphatic polyether polyurethane elastomer with a hardness of 37-45D, preferably EZ32-5-A (Lubrizol). The polyester elastomer comprises a linear block copolymer of a PBT (polybutylene terephthalate) polyester hard segment and an aliphatic polyether soft segment with a hardness of 37-47D, preferably Hytrel 4058 (Celanese Corporation).

[0016] Secondly, the embodiments of the present invention utilize highly viscous materials such as acrylic rubber, copolymerized tackifying resin, and carboxymethyl cellulose, leveraging hydrogen bonding and ionic crosslinking between polymer chains to enhance matrix viscosity and effectively lock in 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 nucleation during foaming and lowering the cell nucleation barrier, effectively promoting bubble nucleation, reducing the difficulty of supercritical foaming, and improving the compressibility of the foamed material. Finally, the embodiments of the present invention utilize ethylene-vinyl alcohol copolymer, a high-barrier material, to reduce gas escape during the later stages of mass production of foamed soles, enhance gas retention, and improve the long-term stability of physical properties. This, in turn, improves product stability and safety while meeting consumer demand for lightweight, soft, and resilient soles.

[0017] The mixing formula described in the embodiment of the present invention includes: 5-10 parts of ethylene-vinyl alcohol copolymer; 5-10 parts of acrylic rubber; 2-4 parts of copolymerized 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 and then hydrolyzing the resulting copolymer. Combining the processability of ethylene-based polymers with the barrier properties of vinyl alcohol polymers, EVOH not only exhibits excellent processing properties but also demonstrates superior barrier properties against gases, odors, fragrances, and solvents. EVOH copolymers are highly crystalline (e.g., EVOH crystallinity ranges from 30% to 50%). Their properties are primarily determined by the relative concentrations of their comonomers, with gas barrier properties improving as the ethylene content decreases. EVOH resin exhibits high mechanical strength, elasticity, surface hardness, abrasion resistance, weatherability, and strong antistatic properties. The hydroxyl groups in the EVOH molecular structure give it exceptional barrier properties against gases such as oxygen and carbon dioxide. Its oxygen permeability coefficient is as low as 4, 100 times that of PA and 10,000 times that of PE or PP. This property effectively inhibits 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), and the weight parts can be 5 parts, 8 parts, 10 parts, etc.

[0019] Acrylic rubber, abbreviated as ACM, refers to a copolymer composed of an alkyl acrylate monomer and a small amount of monomers with cross-linking active groups. Its backbone is a saturated carbon chain, with pendant polar ester groups. These polar ester groups impart high viscosity to the ACM. Preferred ACMs include acrylate rubbers whose vulcanization monomer is itaconic acid monoester. ACM-2212 (Jiujiang Duwei Rubber Technology Co., Ltd.) is even more preferred, with a Mooney viscosity of 40±5 [ML(1+4)*100°C] and a gel content of ≤5%. ACM rubbers can be prepared in various weight ratios, including 5, 6, 7, 8, and 10 parts. Due to the presence of polar groups, some ACM rubbers can experience significant sticking to the stick and mold during processing, indicating high viscosity.

[0020] The copolymer tackifying resin is primarily a piperylene-styrene copolymer resin. This copolymer can be synthesized through strict block or random copolymerization. Its polar molecular structure provides 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), which contains 10-15% styrene by weight.

[0021] The carboxymethyl cellulose described in the embodiments of the present invention is a fibrous powder containing carboxymethyl functional groups. The carboxyl groups impart excellent surface activity and polarity to the cellulose, increasing its viscosity. They can also react covalently with other substances or through electrostatic adsorption. The carboxyl groups form strong chemical bonds with ester groups in ethylene-vinyl acetate, ester groups in acrylic rubber (ACM), and hydroxyl groups in ethylene-vinyl alcohol copolymers, providing excellent compatibility. They can effectively bond non-polar and polar polymers, enhancing cell strength. Furthermore, carboxymethyl cellulose can reduce the Gibbs free energy of cell nucleation during foaming, lowering the cell nucleation barrier and effectively promoting bubble nucleation. This reduces the difficulty of supercritical foaming and improves the compressibility of the foamed material. The carboxymethyl cellulose has a degree of substitution (DS) of ≤0.8. Preferred varieties include CM-22 (Shanghai Bangjing Industrial Co., Ltd.).

[0022] The supercritical foaming formula of the present embodiment includes 0.4-0.6 parts of a crosslinker, 0.3-1 parts of a radiation sensitizer, and 0.8-1.1 parts of a lubricant. The crosslinker is preferably a peroxide crosslinker. By introducing an appropriate amount of crosslinker into the formula, the EVA / POE / SEBS blend undergoes micro-crosslinking during the injection molding of the shoe sole blank. This not only increases the viscosity of the blend but also facilitates the formation of a network-like crosslinked structure during the high-temperature, high-pressure foaming process in the supercritical autoclave, thereby controlling cell diameter and reducing shrinkage of the foamed shoe sole. Specifically, the preferred peroxide crosslinker is 1,4-bis-tert-butylperoxyisopropylbenzene (BIBP).

[0023] PEBAX / TPEE / TPU are all linear polymers. Without modification, they cannot be directly crosslinked using peroxides. Consequently, their melt strength is poor under high temperature and pressure, and simply adding a compatibilizer cannot achieve good results. However, the present embodiments utilize 0.3-1 parts by weight of a radiation sensitizer (preferably 0.5-0.7 parts), preferably an amide or ester. Specifically, the radiation sensitizer for the nylon elastomer is preferably N,N'-methylenebisacrylamide, the radiation sensitizer for the polyurethane elastomer is preferably triallyl isocyanurate, and the radiation sensitizer for the polyester elastomer is preferably trimethylolpropane triacrylate.

[0024] In addition, the lubricant may include stearic acid, preferably stearic acid 1801.

[0025] In this embodiment of the present invention, BIBP, stearic acid, and radiation sensitizer are weighed as the first group; ethylene-vinyl alcohol copolymer, acrylic rubber, copolymerized 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 reaches between 100±10°C, the second group of materials is poured in. When the temperature reaches 110±10°C, the first group of materials is poured in. When the temperature reaches 110-120°C, the mixed materials are poured out.

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

[0027] In the embodiment of the present invention, the pellets obtained from the material preparation are sequentially subjected to small-pellet injection, radiation cross-linking, supercritical autoclave foaming, and MD secondary compression molding to obtain a high-airtightness supercritical foamed sole material. Before the supercritical physical foaming process, the embodiment of the present invention mainly includes the small-pellet injection and radiation cross-linking steps, which are specifically as follows:

[0028] IP injection small rough blanks are referred to as small blank injection. The prepared pellets can be poured into the IP one-time injection foaming molding machine. The temperatures of the first, second, third and fourth feeding zones are adjusted 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 vacuum time is 80±20 seconds; the temperature of the upper and lower templates of the molding mold are adjusted to: 175±3℃, 173±5℃ respectively.

[0029] The material quantity is set according to the mold size (mold dimensions are 18cm*10cm*1cm. Based on a foaming ratio of 1.5, the material quantity can be set to 90±10g). The injection time is 150±20 seconds, and the curing time is 450±30 seconds. The shoe sole rough blank is then removed and naturally cooled for 2 hours to set the shape. In this embodiment of the present invention, a certain proportion of crosslinking agent is added during the single-shot cold blank injection process to achieve micro-crosslinking. This facilitates the formation of a network-like crosslinked structure in the polymer matrix during high-temperature and high-pressure foaming, enhancing the strength of the foamed structure and preventing localized melt collapse during the foaming process.

[0030] The radiation crosslinking process involves placing the IP-injected embryo into a radiation crosslinking machine and irradiating it with a 6-10 MeV high-energy electron beam at a dose of 25±10 kGy, a temperature of 25±2°C, and an irradiation time of 20±10 minutes. Nylon, polyurethane, or polyester elastomers are linear polymers and cannot be directly crosslinked using peroxides, so electron beam radiation crosslinking is used. The process involves selective radiation crosslinking of linear elastomers (such as nylon, polyurethane, or polyester elastomers) at an energy of 6-10 MeV, a dose of 25±10 kGy, a temperature of 25±2°C, and an irradiation time of 20±10 minutes. This increases melt viscosity and cell wall strength, maintaining stable foam growth and preventing bursting.

[0031] The supercritical physical foaming process described is a supercritical autoclave foaming process: After standing for 24 hours, the rough pieces are placed in an autoclave supercritical physical foaming tank at a supercritical N2 pressure of 24±6 MPa, a foaming temperature of 120±10°C, and a holding time of 120±30 minutes. The foamed soles are then released in stages (slow followed by rapid release: a slow release rate of 0.1-0.5 MPa / s for 10-60 seconds; a rapid release rate of 3-10 MPa / s for 0.5-6 seconds). The foamed soles are then removed and cooled to room temperature. In the autoclave supercritical foaming process of this embodiment of the present invention, a supercritical foaming pressure of 24±6 MPa, a saturation temperature of 120±10°C, a holding time of 120±30 minutes, and a staged pressure release method are used to induce uniform foaming and reduce gas escape.

[0032] Finally, the molding process is the MD secondary molding process: the supercritical foamed semi-finished product that has been left to stand for 48-72 hours is placed in a flat-plate molding mold to complete the molding of the finished product. Preferably, the hot pressing temperature is 170±5°C; the hot pressing time is 700±30 seconds; the cooling water temperature is 25±3°C, and the cooling time is 700±30 seconds. The embodiment of the present invention, through the secondary molding process, is conducive to forming a dense crust on the surface of the supercritical small foam sole, improving gas sealing and optimizing the appearance, and better preventing gas escape from the foamed sole.

[0033] The embodiments of the present invention provide a high-air-tightness supercritical foamed sole material obtained by the preparation method, and provide application of the high-air-tightness supercritical foamed sole material in shoemaking.

[0034] The embodiments of the present invention feature significant improvements in formulation design, achieving comprehensive improvements in the performance of the sole material through the combination of multiple high-performance materials. These include: 1. 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. Gas-locking enhancers: highly viscous materials such as acrylic rubber, copolymerized tackifying resins, and carboxymethyl cellulose; these effectively lock gases (such as N₂ or CO₂) generated during the foaming process through hydrogen bonding and ionic crosslinking between their molecular chains. Furthermore, carboxymethyl cellulose reduces the Gibbs free energy of bubble nucleation during foaming, lowering the cell nucleation barrier and effectively promoting bubble nucleation, reducing the difficulty of supercritical foaming, and improving the compressibility of the foamed material. 3. Long-term stability: The use of ethylene-vinyl alcohol copolymer, a high-barrier material, significantly reduces gas escape during the later stages of mass production, thereby enhancing the long-term stability and safety of the product. The embodiments of the present invention, through the above-mentioned innovative formula, not only meet consumers' demands for physical properties of the soles such as lightness, softness, and elasticity, but also greatly improve the stability and safety of the product.

[0035] Based on the existing three-step process (single-shot cold blank injection, autoclave supercritical foaming, and secondary compression molding), the present invention incorporates a new radiation crosslinking step and systematically optimizes each step as follows: ① Single-shot cold blank injection (referred to as small blank injection): During this stage, a certain proportion of crosslinking agent is added to achieve micro-crosslinking. This step helps form a network of crosslinked structures during high-temperature and high-pressure foaming, thereby enhancing the strength of the foam structure and preventing localized melt collapse. ② Radiation crosslinking: To address the problem of linear polymers being unable to be directly crosslinked using peroxides, electron beam radiation crosslinking technology is employed. This not only improves the melt viscosity of the overall formulation and the strength of the cell walls, ensuring stable foam growth without bursting, but also offers higher energy transfer efficiency. Combined with a radiation sensitizer, this further enhances irradiation efficiency and shortens irradiation time. The crosslinking agent promotes uniform crosslinking of molecular chains, making it suitable for mass production. ③ Autoclave supercritical foaming: The supercritical foaming pressure is set at 24±6 MPa, the saturation temperature is 120±10°C, and the holding time is 120±30 minutes. At the same time, a staged pressure release method (slow first, then fast) is used to induce uniform foaming and reduce gas escape. ④ Secondary compression molding process: A dense crust is formed on the surface of the supercritical small foam sole, further improving gas sealing and optimizing the appearance, thereby better preventing gas escape from the foam sole.

[0036] The embodiment of the present invention pioneered the monitoring of the hardness changes of the foamed sole for up to 2 months. By enhancing the strength of the foam cells and locking the gas, and through dual innovations in formulation and process, it successfully broke through the technical bottleneck of synergistically improving the cross-linking / foaming of materials and the gas retention capacity, and solved the core problem of the foamed sole that is difficult to balance with other performance stability while pursuing lightness, softness and elasticity. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 Schematic diagram of the preparation process of an embodiment of the present invention. DETAILED DESCRIPTION

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

[0039] Example 1

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

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

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

[0043] IP injection molding of small rough blanks: pour the prepared pellets into the IP one-step injection molding machine, and adjust the temperatures of the first, second, third and fourth feeding zones 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 vacuum time is 80±20 seconds; the temperature of the upper and lower templates of the molding mold is adjusted to: 175±3℃, 173±5℃ respectively. Set the material amount according to the mold usage (mold size 18cm*10cm*1cm, according to the foaming ratio of 1.5, the material amount can be set to 90±10g), the injection time is 150±20 seconds, the vulcanization time is 450±30 seconds, and then take out the small rough sole and cool it naturally for 2 hours to set.

[0044] Irradiation cross-linking: Place the IP-ejected embryo into an irradiation cross-linking machine and irradiate with a 6-10 MeV high-energy electron beam, with a dose of 25±10 kGy, a temperature of 25±2°C, and an irradiation time of 20±10 minutes.

[0045] Autoclave supercritical foaming: Place the small rough blank after standing for 24 hours into an autoclave supercritical physical foaming tank, with a supercritical N2 pressure of 24±6 MPa, a foaming temperature of 120±10℃, and a heat preservation and pressure holding time of 120±30min. Then, use the staged pressure release method (slow first and then fast: the pressure release rate is 0.3~0.5 MPa / s and the time is 36-60s when slow; the pressure release rate is 4~6 MPa / s and the time is 3.5-6s when fast). Take out the foamed sole and cool it to room temperature.

[0046] Molding: Place the supercritical foamed semi-finished product, which has been left to rest for 48-72 hours, into a flat-plate molding die to complete the molding process. The hot pressing temperature is 170±5°C, the hot pressing time is 700±30 seconds, the cooling water temperature is 25±3°C, and the cooling time is 700±30 seconds.

[0047] Examples 2-8

[0048] The operation is the same as that in Example 1. For specific formulas, see Table 1.

[0049] Table 1 Formulation and test of embodiment:

[0050]

[0051]

[0052] Comparative Examples 1-7

[0053] The operation is basically the same as or different from that of Example 1. For specific formulas, see Table 2.

[0054] Table 2 Comparative Example Formulation and Test

[0055]

[0056]

[0057] Among them, the contents of each raw material are as follows:

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

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

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

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

[0062] EZ32-5-A: hardness 37D, melting point 127°C, melt index 5.0g / 10min, tensile strength 40MPa, Lubrizol.

[0063] Hytrel 4058: hardness 37D, melting point 152°C, 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°C, styrene content 10-15%, ExxonMobil.

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

[0067] BIBP: Akzo Nobel.

[0068] N,N'-Methylenebisacrylamide: melting point 185°C, Suzhou Yake Technology Co., Ltd.

[0069] Triallyl isocyanurate: melting point 26-28°C, Shandong Guohua Chemical Co., Ltd.

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

[0071] Stearic acid 1801: Indonesian Dukuda.

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

[0073] From the comparative data of Examples 1-4, it can be seen that as the amount of nylon elastomer added increases, the rebound rate gradually increases and the compression deformation rate gradually decreases, indicating that the nylon elastomer is beneficial to improving the rebound and compression properties of the foamed sole.

[0074] From the comparative data of Examples 2, 7, and 8, it can be seen that when the addition amount of nylon elastomer, polyurethane elastomer, or polyester elastomer is 15 parts, it is beneficial to improve the rebound and compression properties of the foamed sole, with nylon elastomer being the best and polyester elastomer being the second.

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

[0076] Comparison of the data between Comparative Example 1 and Example 2 shows that, when the other components and amounts of Example 2 remain unchanged and ethylene-vinyl alcohol copolymer is omitted, the initial physical properties of the foamed sole differ significantly from those of Example 2, with a particularly noticeable deterioration in rebound and compression performance. Furthermore, the retention rates of various physical properties after 30 days of stabilization are ≤90%, and after 60 days of stabilization, the retention rates of various physical properties are ≤85%. This demonstrates that the high-barrier ethylene-vinyl alcohol copolymer reduces gas escape during late-stage mass production of the foamed sole, enhances gas retention, and improves the long-term stability of physical properties.

[0077] Comparison of the data from Comparative Examples 2, 3, and 5 with Example 2 shows that, when the other components and contents of Example 2 are maintained unchanged, without the addition of either the acrylic rubber or the copolymerized tackifying resin, or both, the initial physical properties of the foamed sole deteriorate somewhat compared to those of Example 2, with the rebound and compression properties showing a decrease. Furthermore, the retention rates of these properties after 30 days of standing are ≤90%, and after 60 days of standing are ≤85%. This demonstrates that the polarity and viscosity of the acrylic rubber or copolymerized tackifying resin can improve the overall viscosity and cohesive strength of the foaming formula, effectively trapping the gases (N₂ or CO₂) generated during the foaming process and enhancing the overall performance of the foamed sole.

[0078] From the comparative data of Comparative Example 4 and Example 2, it can be seen that when the other components and contents of Example 2 are kept unchanged and carboxymethyl cellulose is not added, the initial physical properties of the foamed sole show a slight decrease in rebound rate compared to the initial physical properties of Example 2, and the compression performance deteriorates significantly. Moreover, the retention rate of each physical property after standing for 30 days is ≤90%, and the retention rate of each physical property after standing for 60 days is ≤85%. This shows that carboxymethyl cellulose is not only highly viscous, but also forms a strong chemical bond with the carboxyl group of ethylene-vinyl acetate, the ester group of acrylic rubber (ACM), and the hydroxyl group of ethylene-vinyl alcohol copolymer, which plays an excellent compatibility role and can effectively form a bond between non-polar polymers and polar polymers, thereby enhancing the strength of the foam cells. On the other hand, carboxymethyl cellulose reduces the Gibbs free energy of bubble nucleation during the foaming process, lowers the nucleation energy barrier of the foam cells, effectively promotes bubble nucleation, reduces the difficulty of supercritical foaming, and improves the compression performance of the foam material.

[0079] Comparison of the data from Comparative Example 6 and Example 2 shows that, when the other components and contents of Example 2 remain unchanged and the ethylene-vinyl alcohol copolymer / acrylate rubber / copolymerized tackifying resin / carboxymethyl cellulose are omitted, the initial physical properties of the foamed shoe sole deteriorate significantly compared to those of Example 2, with the rebound rate and compression performance significantly deteriorating. Furthermore, after 60 days of standing, the retention rate of each physical property is ≤80%. This demonstrates that the addition of these materials can improve product stability and safety while meeting consumer demand for lightness, softness, and elasticity.

[0080] Comparison of the data from Comparative Example 7 and Example 2 reveals that, when the other components and contents of Example 2 remain unchanged, no radiation sensitizer is added, and the embryos are directly subjected to supercritical foaming after injection without radiation crosslinking, the present invention utilizes electron beam radiation crosslinking to selectively crosslink the linear elastomer, thereby increasing melt viscosity and cell wall strength, thereby maintaining stable foam growth and producing uniform, dense cells, reducing gas escape, and thereby improving the rebound / compression properties of the foamed shoe sole.

[0081] As can be seen from the above embodiments, the embodiments of the present invention are formulated with ethylene-vinyl acetate, polyolefin elastomer, styrene elastomer, nylon elastomer or polyurethane elastomer or polyester elastomer, ethylene-vinyl alcohol copolymer, acrylic rubber, copolymerized tackifying resin, carboxymethyl cellulose and cross-linking agent, radiation sensitizer, lubricant, etc., and are prepared by a single injection cold embryo, radiation cross-linking, autoclave supercritical foaming, and secondary molding process to finally obtain a density of 0.12±0.02g / cm 3 The supercritical foaming sole material has a high airtightness, hardness of 42±3C, rebound rate ≥70%, compression deformation ≤32%, shock absorption G value ≤10, and a physical property retention rate of ≥93% within 60 days. This foaming sole material further enhances the viscosity of the matrix by using high-viscosity materials such as acrylic rubber, copolymerized tackifying resin, and carboxymethyl cellulose, effectively locking the gas during the foaming process; the high-barrier material ethylene-vinyl alcohol copolymer is used to reduce gas escape in the later stage of mass production of the foamed sole, enhance gas retention capacity, and improve the long-term stability of physical properties; and through radiation cross-linking technology, the melt viscosity of each matrix and the strength of the cell wall during foaming are increased, thereby enhancing the stability of the foam and facilitating its application in shoemaking.

[0082] The above embodiments are only intended to help understand the method and core concept of the present invention. It should be noted that, without departing from the principles of the present invention, a number of improvements and modifications may be made to the present invention by those skilled in the art, and such improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a high-air-tightness supercritical foaming sole material, characterized in that: The following steps are involved: The mixed material is sequentially subjected to injection molding, radiation cross-linking, supercritical foaming and compression molding to obtain a high-air-tightness supercritical foamed sole material; The mixed material comprises, in parts by weight, 40-55 parts of ethylene vinyl acetate, 10-20 parts of polyolefin POE elastomer, 10-20 parts of styrene elastomer, 10-25 parts of linear polymer elastomer, 5-10 parts of ethylene vinyl alcohol copolymer, 5-10 parts of acrylic rubber, 2-4 parts of copolymerized tackifying resin, 3-5 parts of carboxymethyl cellulose, 0.4-0.6 parts of crosslinking agent, 0.3-1 parts of radiation sensitizer and 0.8-1.1 parts of lubricant; The linear polymer elastomer is one or more of nylon elastomer, polyurethane elastomer and polyester elastomer.

2. The preparation method according to claim 1, characterized in that The VA mass content of the ethylene-vinyl acetate is 18-40%; the polyolefin POE elastomer is an ethylene-octene random copolymer with a hardness of 60-90A; and the styrene elastomer is a styrene-butadiene-styrene block copolymer with a hardness of 45-80A.

3. The preparation method according to claim 1, characterized in that The nylon elastomer is a block polyetheramide elastomer with a hardness of 35-45D; the polyurethane elastomer is an aliphatic polyether polyurethane elastomer with a hardness of 37-45D; 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.

4. The preparation method according to any one of claims 1 to 3, characterized in that The oxygen permeability coefficient of the ethylene-vinyl alcohol copolymer is lower than 4.

5. The preparation method according to any one of claims 1 to 3, characterized in that The acrylic rubber contains itaconate monoester vulcanization point monomer structure; the copolymerized tackifying resin is mainly isobutylene-styrene copolymer resin.

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

8.

7. The preparation method according to any one of claims 1 to 3, characterized in that The cross-linking agent is a peroxide cross-linking agent; the radiation sensitizer is an amide or ester substance; and the lubricant is stearic acid.

8. The preparation method according to any one of claims 1 to 3, characterized in that The radiation crosslinking is electron beam radiation crosslinking with an energy of 6-10 MeV and a dosage of 15-35 kGy; the supercritical foaming has a pressure of 18-30 MPa and a temperature of 110-130°C.

9. A high-air-tightness supercritical foamed sole material obtained by the preparation method according to any one of claims 1 to 8.

10. Use of the high-air-tightness supercritical foaming sole material according to claim 9 in shoemaking.

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