Shock-absorbing EVA supercritical foaming material and preparation process thereof

Abstract

The invention discloses a shock-absorbing EVA supercritical foaming material and a preparation process thereof, and relates to the technical field of foaming material products, and the preparation process comprises the steps of raw material preparation, raw material mixing, supercritical foaming treatment, structure post-treatment and finished product material preparation. The preparation method has the advantages that the supercritical nitrogen and supercritical carbon dioxide mixed foaming agent, the nano shock absorption particles A and the nano shock absorption particles B with special structures and functions are used, and the steps of magnetic field induced directional arrangement and the like are combined; the problems that an existing EVA foaming material is residual in foaming agent, uneven in foam structure, insufficient in shock absorption performance and the like are effectively solved, nano shock absorption particles B are added into the EVA foaming material, so that the EVA foaming material can form a stripping or intercalation structure in an EVA matrix, the barrier property of the material is improved, energy transfer is reduced, a lamellar structure can serve as a physical cross-linking point, and the foaming performance of the EVA foaming material is improved. The overall strength and stability of the material are improved.

Description

Technical Field

[0001] The invention relates to the technical field of foamed material products, in particular to a shock-absorbing EVA supercritical foamed material and a preparation process thereof. Background Art

[0002] Ethylene-vinyl acetate copolymer (EVA) foam materials have been widely used in many fields due to their good elasticity, flexibility, impact resistance and easy processing, such as sports shoes, sports protective gear, packaging materials, toys, etc. Traditional EVA foam materials are usually foamed with chemical foaming agents, such as azodicarbonamide (AC). During the preparation process, EVA resin is mixed with chemical foaming agents, cross-linking agents, lubricants, fillers and other additives in an internal mixer or an open mixer, and then through molding processes such as molding and extrusion, under certain temperature and pressure conditions, the chemical foaming agent is decomposed by heat to produce gas, so that the EVA material foams to form a porous structure; It is difficult for chemical foaming agents to completely decompose and release gases during the foaming process, and some foaming agents often remain inside the foaming material. These residual foaming agents may gradually migrate to the surface of the material during subsequent use, which will not only affect the appearance quality of the foaming material, such as surface frosting, causing the surface of the material to become white and lose its luster, but also may cause potential harm to human health and the environment. For example, some decomposition products of foaming agents may have certain toxicity or irritating odors. When they are in long-term contact with the human body or released into the air under specific environmental conditions, they will cause adverse effects on the respiratory tract, skin, etc. At the same time, they do not meet the increasingly stringent environmental protection regulations. The uniformity of the pore structure of EVA foaming materials prepared with chemical foaming agents is difficult to control. Since the dispersibility of chemical foaming agents in the EVA matrix is ​​limited, and the foaming process is greatly affected by various factors such as temperature, pressure, and the uniformity of material mixing, it is easy to cause pores of different sizes. The uneven pore structure will cause large fluctuations in the mechanical properties of the foamed material, and the local stress concentration phenomenon is obvious, which reduces the overall strength and stability of the material. For example, in the application of sports shoes, the uneven pore structure may cause the sole to deform too much locally when subjected to force, affecting the comfort of wearing and the service life of the sole. Although the traditional EVA foam material has a certain shock absorption ability, its shock absorption performance still needs to be improved for some special application fields with high requirements for shock absorption performance, such as high-end sports shoes, sports protective gear and precision instrument packaging. The pore morphology and structure of the EVA material prepared by chemical foaming are relatively fixed, and it is difficult to further optimize its shock absorption characteristics through conventional processes. It cannot effectively meet the needs of energy absorption and buffering in high-impact and high-frequency vibration environments, which limits its application in high-performance shock-absorbing products. For this reason, we propose a shock-absorbing EVA supercritical foam material and its preparation process. Summary of the invention

[0003] The purpose of the present invention is to provide a shock-absorbing EVA supercritical foaming material and a preparation process thereof.

[0004] In order to solve the problems raised in the above background technology, the present invention provides the following technical solutions: a process for preparing a shock-absorbing EVA supercritical foaming material, including raw material preparation, raw material mixing, supercritical foaming treatment, structural post-treatment and preparation of finished materials. The specific steps of the process for preparing a shock-absorbing EVA supercritical foaming material are as follows: Step 1: Select EVA resin, supercritical foaming agent, cross-linking agent and antioxidant as basic reaction materials, and prepare nano shock-absorbing particles A and nano shock-absorbing particles B as additive materials; Step 2: Add EVA resin, crosslinking agent, antioxidant, nano shock-absorbing particles A and nano shock-absorbing particles B into an internal mixer step by step for mixing, and prepare a mixed rubber after the materials are evenly dispersed; Step 3: Transfer the rubber mixture to a high-pressure reactor and evacuate the mixture, inject a mixed gas component of supercritical nitrogen and supercritical carbon dioxide into the high-pressure reactor to infiltrate the rubber mixture, and after the infiltration is completed, place the reactor in an external magnetic field to stabilize the supercritically treated mixed colloid for standby use; Step 4: transferring the stable mixed colloid into an oven for vulcanization and cross-linking treatment, and after the treatment is completed, transferring it into a magnetic field generating device for magnetization treatment to obtain a finished mixed rubber product; Step 5: Transfer the finished rubber mixture into a slipper stamping die for stamping and forming. After the stamping is completed, the formed slippers are trimmed, and the slippers are tested for appearance quality and performance. After passing the test, they are put into use.

[0005] As a further scheme of the present invention: in the step 1, the EVA resin is selected from EVA resin with a vinyl acetate content of 18wt%-25wt%, the supercritical foaming agent is a mixed gas of supercritical nitrogen and supercritical carbon dioxide, the volume ratio of supercritical nitrogen to supercritical carbon dioxide is 1:3-5, the cross-linking agent is di-tert-butyl peroxide isopropylbenzene, and the addition amount is 0.8%-1.5% of the total mass of the EVA resin, and the antioxidant is hindered phenol antioxidant 1010, and the usage amount is 0.1%-0.3% of the total mass of the EVA resin.

[0006] As a further solution of the present invention: in the step 1, the nano shock absorbing particle A is a nanoparticle with a core-shell structure, the core is a magnetic iron oxide nanoparticle with a particle size of 10n-20nm, and the shell is a polydopamine layer. The preparation process of the nano shock absorbing particle A is to synthesize Fe by coprecipitation method. 3 O 4Nanoparticles, ferric chloride and ferrous chloride are dissolved in water at a molar ratio of 2:1, ammonia water is added under nitrogen protection, the pH is adjusted to 9-10, the reaction temperature is controlled at 60℃-70℃, the reaction is carried out for 1h-2h, and Fe 3 O 4 The nanoparticles are washed and dried, dispersed in a Tris-HCl buffer solution containing dopamine monomer at pH 8.5, and stirred at room temperature for 24h-48h to obtain nano shock-absorbing particles A. For nano shock-absorbing particles B, montmorillonite is dispersed in water, long-chain alkyl quaternary ammonium salt is added, and stirred at a temperature of 60°C-80°C for 3h-6h. After completion, the particles are taken out and washed and dried for 3-4 times to obtain organic modified montmorillonite, which is nano shock-absorbing particles B.

[0007] As a further solution of the present invention: in the step 2, the internal mixer is preheated to 90°C, EVA resin is added thereto, and the EVA resin is initially plasticized at a stirring rate of 30 r / min-40 r / min for 2 min-5 min, and the crosslinking agent di-tert-butyl peroxide is added thereto, and the stirring rate is 50 r / min-80 r / min for 1 min-2 min, and the crosslinking agent di-tert-butyl peroxide is evenly dispersed in the initially plasticized EVA resin. After the dispersion is completed, an antioxidant hindered phenol antioxidant is added thereto for 10 10. Stir at a stirring rate of 30r / min-40r / min for 2min-3min. After stirring, add nano shock absorbing particles A, and increase the stirring rate to 60r / min-80r / min. After stirring for 3min-4min, add nano shock absorbing particles B, keep the speed at 60r / min-80r / min, and continue stirring for 4min-5min to obtain a rubber compound. When adding each component to an internal mixer for mixing, control the temperature in the internal mixer cavity between 90℃-110℃. During the mixing process, the following reactions occur:

[0008] Amino groups in the polydopamine layer With the ester group in EVA resin Hydrogen bonding occurs to produce , which is a hydrogen bond product.

[0009] As a further scheme of the present invention: in the step 3, the rubber mix is ​​transferred to a high-pressure reactor, and the high-pressure reactor is vacuumed for 15min-20min to reduce the pressure in the high-pressure reactor to 0.01MPa-0.05MPa. After the treatment is completed, a mixed gas of supercritical nitrogen and supercritical carbon dioxide is injected into the high-pressure reactor, and the injection speed is controlled to be 2L / min-3L / min, and the pressure in the high-pressure reactor is increased to 20MPa-30MPa, and the temperature is controlled between 45°C and 55°C. During the injection of the mixed gas, the mixed gas penetrates into the rubber mix, and the penetration time is set to 40min-80min. After the penetration is completed, the reactor is placed in an external magnetic field with a magnetic field strength of 0.5T-1.5T, and the direction of the magnetic field is set according to the direction of the required shock absorption performance. The reaction is carried out for 20min-30min under the action of the magnetic field, and the magnetic iron oxide in the nano shock-absorbing particles A With supercritical carbon dioxide Adsorption and electron transfer occur:

[0010] in Indicates the number of supercritical carbon dioxide molecules adsorbed.

[0011] As a further solution of the present invention: in the step 4, the mixed colloid after supercritical foaming treatment and stabilization in a magnetic field is quickly transferred to an oven preheated to 130°C for vulcanization and crosslinking treatment. During the vulcanization and crosslinking process, the oven temperature is first increased from 130°C to 150°C at a heating rate of 2°C / min, and maintained at this temperature for 10min-15min to allow the crosslinking reaction to proceed fully. The reaction equation is as follows:

[0012]

[0013]

[0014] During the reaction, the crosslinking agent di-tert-butyl peroxide isopropylbenzene decomposes to produce free radicals, which trigger the crosslinking reaction between EVA molecular chains.

[0015] As a further solution of the present invention: in the step 4, the reaction equation of the layer structure of the organically modified montmorillonite in the EVA matrix is ​​as follows:

[0016] The above is the entanglement interaction between the long-chain alkyl on the surface of the organic modified montmorillonite layer and the EVA molecular chain, where is the carbon number of the long chain alkyl group.

[0017] As a further solution of the present invention, in the step 5, the finished rubber mixture is placed in a special slipper stamping mold, and the surface of the mold cavity is finely polished to control the surface roughness to Ra0.8um-1.6um. The stamping equipment adopts a hydraulic stamping machine, and its stamping pressure can be accurately controlled between 150-300MPa, and the stamping speed is set to 15-25mm / s. After the stamping is completed, a high-precision CNC cutting device is used to remove the overflow and burrs on the edge of the slipper, and the cutting accuracy is controlled within ±0.2mm. After completion, the surface of the slipper is finely polished using a grinding process to make the surface smooth and flat. During the grinding process, the sandpaper particle size gradually transitions from 200 mesh to 800 mesh. After the grinding is completed, the appearance quality of the slippers is inspected, including the shape integrity, surface flatness, color uniformity and presence of obvious defects of the slippers, and the shape of the slippers is scanned and analyzed using a three-dimensional profile scanner, and compared with the standard model, and the deviation is controlled within ±0.5mm; A drop hammer impact tester is used to test the shock absorption performance of the slippers. A drop hammer with a mass of 5kg-10kg is dropped from a height of 0.8m-1.2m to impact the sole of the slippers. A sensor is used to record the impact force-time curve and the shock absorption rate is calculated. The shock absorption rate is required to reach 65%-85%. At the same time, a universal material testing machine is used to test the tensile, compression and bending performance of the soles of the slippers. The tensile strength is not less than 2.5MPa, the elongation at break is between 350%-550%, and the compression permanent deformation rate is less than 35%. Slippers that pass both appearance quality and performance tests are put into use.

[0018] A shock-absorbing EVA supercritical foaming material is prepared by mixing EVA resin, di-tert-butyl peroxide isopropylbenzene, hindered phenol antioxidant 1010, nano shock-absorbing particles A and nano shock-absorbing particles B, and then infiltrating a mixed gas component of supercritical nitrogen and supercritical carbon dioxide.

[0019] By adopting the above technical solution, compared with the prior art, the beneficial effects of the present invention are: The present invention uses supercritical nitrogen and supercritical carbon dioxide to mix a foaming agent, nano shock-absorbing particles A and nano shock-absorbing particles B with special structures and functions, and combines steps such as magnetic field-induced directional arrangement, thereby effectively solving the problems of foaming agent residue, uneven cell structure, and insufficient shock-absorbing performance in existing EVA foaming materials. By adding nano shock-absorbing particles B to the EVA foaming material, a peeling or intercalation structure can be formed in the EVA matrix, thereby increasing the barrier performance of the material and reducing energy transfer. The sheet structure can be used as a physical cross-linking point to improve the overall strength and stability of the material. By using the mixed gas as a supercritical foaming agent, supercritical nitrogen can increase the gas diffusion rate in the foaming process, and synergize with supercritical carbon dioxide to make the cell formation more uniform. The nano-shock-absorbing particles A interact with the EVA resin to help the nano-shock-absorbing particles A to disperse stably in the EVA matrix. When the material is impacted by external forces, the nano-shock-absorbing particles A can dissipate energy by destroying and rebuilding hydrogen bonds, thereby improving the shock absorption performance of the material. At the same time, due to the effect of the magnetic iron oxide in the inner core of the nano-shock-absorbing particles A, the nano-shock-absorbing particles A can interact with the external magnetic field in the subsequent magnetic field treatment process, thereby improving the shock absorption performance of the prepared slippers. By subjecting the high-pressure reactor to magnetic field treatment, the nano-shock-absorbing particles A in the mixed rubber can be gradually arranged in a directional manner along the direction of the magnetic field under the action of the magnetic field, thereby making the arrangement of the particles more regular and orderly, thereby enhancing the shock absorption performance of the material in a specific direction. The present invention further optimizes the directional arrangement of the nano shock-absorbing particles A by performing magnetic field treatment again after vulcanization and cross-linking, and promotes the EVA molecular chains to perform directional arrangement to a certain extent under the action of the magnetic field. After the first magnetic field treatment, the nano shock-absorbing particles A have preliminarily achieved directional arrangement. The second magnetic field treatment can further adjust and optimize the arrangement direction and degree of the nano particles, making them more regular and orderly, thereby further enhancing the shock absorption performance and anisotropic mechanical properties of the material in the direction of the magnetic field in terms of microstructure. At the same time, the orientation effect of the magnetic field on the EVA molecular chains can also make the molecular chains arrange along the magnetic field direction to a certain extent, increase the orderliness and interaction between the molecular chains, and enable the material to more effectively resist external force deformation in this direction. At the same time, the impact force can be transmitted and dissipated more quickly during the shock absorption process, further improving the shock absorption efficiency and stability of the material. The surface of the mold cavity after polishing treatment is smooth, and in the stamping molding process, the mixed rubber can better fit the mold surface, and the surface of the formed slippers is smoother and flawless. The smooth surface not only improves the aesthetics of the product, making it more attractive in the market, but also reduces the friction resistance with the skin or other objects. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1This is a schematic diagram of the process of preparing slippers from EVA supercritical foaming material in an embodiment of the present invention. DETAILED DESCRIPTION

[0021] The specific embodiments of the present invention are further described below in conjunction with the accompanying drawings. It should be noted that the description of these embodiments is used to help understand the present invention, but does not constitute a limitation of the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0022] The present invention discloses a process for preparing a shock-absorbing EVA supercritical foam material, which comprises raw material preparation, raw material mixing, supercritical foaming treatment, structural post-treatment and preparation of finished materials. The specific steps of the process for preparing a shock-absorbing EVA supercritical foam material are as follows: Step 1: Select EVA resin, supercritical foaming agent, cross-linking agent and antioxidant as basic reaction materials, and prepare nano shock-absorbing particles A and nano shock-absorbing particles B as additive materials; Step 2: Add EVA resin, crosslinking agent, antioxidant, nano shock-absorbing particles A and nano shock-absorbing particles B into an internal mixer step by step for mixing, and prepare a mixed rubber after the materials are evenly dispersed; Step 3: Transfer the rubber mixture to a high-pressure reactor and evacuate the mixture, inject a mixed gas component of supercritical nitrogen and supercritical carbon dioxide into the high-pressure reactor to infiltrate the rubber mixture, and after the infiltration is completed, place the reactor in an external magnetic field to stabilize the supercritically treated mixed colloid for standby use; Step 4: transferring the stable mixed colloid into an oven for vulcanization and cross-linking treatment, and after the treatment is completed, transferring it into a magnetic field generating device for magnetization treatment to obtain a finished mixed rubber product; Step 5: Transfer the finished rubber mixture into a slipper stamping die for stamping and forming. After the stamping is completed, the formed slippers are trimmed, and the slippers are tested for appearance quality and performance. After passing the test, they are put into use.

[0023] In one embodiment of the present invention: in step one, the EVA resin is selected from EVA resin with a vinyl acetate content of 18wt%-25wt%, the supercritical foaming agent is a mixed gas of supercritical nitrogen and supercritical carbon dioxide, the volume ratio of supercritical nitrogen to supercritical carbon dioxide is 1:3-5, the cross-linking agent is di-tert-butyl peroxide isopropylbenzene, and the addition amount is 0.8%-1.5% of the total mass of the EVA resin, and the antioxidant is hindered phenol antioxidant 1010, and the usage amount is 0.1%-0.3% of the total mass of the EVA resin.

[0024] In one embodiment of the present invention, in step 1, the nano-shock absorbing particle A is a nano-particle with a core-shell structure, wherein the core is a magnetic iron oxide nano-particle with a particle size of 10n-20nm and the shell is a polydopamine layer. The preparation process of the nano-shock absorbing particle A is to synthesize Fe by coprecipitation method. 3 O 4 Nanoparticles, ferric chloride (FeCl 3 ) and ferrous chloride (FeCl 2 ) was dissolved in water at a molar ratio of 2:1, and ammonia water was added under nitrogen protection, the pH was adjusted to 9-10, the reaction temperature was controlled at 60℃-70℃, and the reaction was carried out for 1h-2h to generate Fe 3 O 4 The nanoparticles are washed and dried, dispersed in a Tris-HCl buffer solution containing dopamine monomer at pH 8.5, and stirred at room temperature for 24h-48h to obtain nano shock-absorbing particles A. For nano shock-absorbing particles B, montmorillonite is dispersed in water, long-chain alkyl quaternary ammonium salt is added, and stirred at a temperature of 60°C-80°C for 3h-6h. After completion, the particles are taken out and washed and dried for 3-4 times to obtain organic modified montmorillonite, which is nano shock-absorbing particles B.

[0025] In one embodiment of the present invention, in step 2, the internal mixer is preheated to 90° C., EVA resin is added thereto, stirred at a stirring rate of 30 r / min-40 r / min for 2 min-5 min, the EVA resin is preliminarily plasticized, di-tert-butyl peroxide isopropylbenzene is added thereto as a crosslinking agent, stirred at a stirring rate of 50 r / min-80 r / min for 1 min-2 min, the crosslinking agent di-tert-butyl peroxide isopropylbenzene is evenly dispersed in the preliminarily plasticized EVA resin, and after the dispersion is completed, an antioxidant hindered phenol antioxidant is added thereto for 10 10. Stir at a stirring rate of 30r / min-40r / min for 2min-3min. After stirring, add nano shock absorbing particles A, and increase the stirring rate to 60r / min-80r / min. After stirring for 3min-4min, add nano shock absorbing particles B, keep the speed at 60r / min-80r / min, and continue stirring for 4min-5min to obtain a rubber compound. When adding each component to an internal mixer for mixing, control the temperature in the internal mixer cavity between 90℃-110℃. During the mixing process, the following reactions occur:

[0026] Amino groups in the polydopamine layer With the ester group in EVA resin Hydrogen bonding occurs to produce , which is a hydrogen bond product.

[0027] In one embodiment of the present invention: in step three, the rubber mix is ​​transferred to a high-pressure reactor, and the high-pressure reactor is vacuumed for 15 minutes to 20 minutes to reduce the pressure in the high-pressure reactor to 0.01MPa-0.05MPa. After the treatment is completed, a mixed gas of supercritical nitrogen and supercritical carbon dioxide is injected into the high-pressure reactor, and the injection speed is controlled to be 2L / min-3L / min. The pressure in the high-pressure reactor is increased to 20MPa-30MPa, and the temperature is controlled between 45°C and 55°C. During the injection of the mixed gas, the mixed gas penetrates into the rubber mix, and the penetration time is set to 40min-80min. After the penetration is completed, the reactor is placed in an external magnetic field with a magnetic field strength of 0.5T-1.5T, and the direction of the magnetic field is set according to the direction of the required shock absorption performance. The reaction is carried out for 20min-30min under the action of the magnetic field, and the magnetic iron oxide in the nano shock-absorbing particles A With supercritical carbon dioxide Adsorption and electron transfer occur:

[0028] in Indicates the number of supercritical carbon dioxide molecules adsorbed.

[0029] In one embodiment of the present invention: in step 4, the mixed colloid after supercritical foaming treatment and stabilization in a magnetic field is quickly transferred to an oven preheated to 130°C for vulcanization and crosslinking treatment. During the vulcanization and crosslinking process, the oven temperature is first increased from 130°C to 150°C at a heating rate of 2°C / min, and maintained at this temperature for 10min-15min to allow the crosslinking reaction to proceed fully. The reaction equation is as follows:

[0030]

[0031]

[0032] During the reaction, the crosslinking agent di-tert-butyl peroxide isopropylbenzene decomposes to produce free radicals, which trigger the crosslinking reaction between EVA molecular chains.

[0033] In one embodiment of the present invention: in step 4, the reaction equation of the layer structure of organically modified montmorillonite in the EVA matrix is ​​as follows:

[0034] The above is the entanglement interaction between the long-chain alkyl on the surface of the organic modified montmorillonite layer and the EVA molecular chain, where is the carbon number of the long chain alkyl group.

[0035] In one embodiment of the present invention: in step five, the finished rubber mixture is placed in a special slipper stamping die, and the surface of the mold cavity is finely polished to control the surface roughness to Ra0.8um-1.6um. The stamping equipment uses a hydraulic stamping machine, and its stamping pressure can be accurately controlled between 150-300MPa, and the stamping speed is set to 15-25mm / s. After the stamping is completed, a high-precision CNC cutting device is used to remove the overflow and flash on the edge of the slipper, and the cutting accuracy is controlled within ±0.2mm. After completion, the surface of the slipper is finely polished using a grinding process to polish the surface smooth and flat. During the grinding process, the sandpaper particle size gradually transitions from 200 mesh to 800 mesh. After the grinding is completed, the appearance quality of the slippers is inspected, including the shape integrity, surface flatness, color uniformity and presence of obvious defects of the slippers, and the shape of the slippers is scanned and analyzed using a three-dimensional profile scanner, and compared with the standard model, and the deviation is controlled within ±0.5mm; A drop hammer impact tester is used to test the shock absorption performance of the slippers. A drop hammer with a mass of 5kg-10kg is dropped from a height of 0.8m-1.2m to impact the sole of the slippers. A sensor is used to record the impact force-time curve and the shock absorption rate is calculated. The shock absorption rate is required to reach 65%-85%. At the same time, a universal material testing machine is used to test the tensile, compression and bending performance of the soles of the slippers. The tensile strength is not less than 2.5MPa, the elongation at break is between 350%-550%, and the compression permanent deformation rate is less than 35%. Slippers that pass both appearance quality and performance tests are put into use.

[0036] The invention discloses a shock-absorbing EVA supercritical foaming material, which is prepared by mixing EVA resin, di-tert-butyl peroxide isopropylbenzene, hindered phenol antioxidant 1010, nano shock-absorbing particles A and nano shock-absorbing particles B, and then infiltrating a mixed gas component of supercritical nitrogen and supercritical carbon dioxide.

[0037] In one embodiment of the present invention: in step 1, dopamine is in Fe 3 O 4 The surface self-polymerizes to form a PDA layer. This nanoparticle utilizes Fe 3 O 4 The magnetism can be induced to align in a directional manner by an external magnetic field during the foaming process, thus enhancing the shock absorption performance of the material in a specific direction. At the same time, the PDA layer has good adhesion and damping properties, and can effectively dissipate energy.

[0038] In one embodiment of the present invention: in step 1, the EVA resin material can be Elvax260 produced by DuPont and 7350MEVA resin produced by Formosa Plastics Corporation.

[0039] In one embodiment of the present invention: in step three, the adsorption effect causes the concentration of supercritical carbon dioxide to increase locally on the surface of the magnetic iron oxide. In the subsequent foaming process, when the pressure is released, these adsorbed supercritical carbon dioxide are more inclined to form bubbles near the magnetic iron oxide, further improving the uniformity and controllability of bubble formation, and due to the special distribution relationship between the bubbles and the magnetic iron oxide, when subjected to external force impact, the energy can be better dissipated through the deformation, rupture of the bubbles and the interaction with the magnetic iron oxide, thereby improving the overall shock absorption performance of the material.

[0040] In one embodiment of the present invention: in step five, during the stamping process, the rubber mix is ​​subjected to pressure in the mold cavity, the pore structure inside the material will be deformed and rearranged to a certain extent, and the nano shock-absorbing particles A and nano shock-absorbing particles B will also adjust their positions and orientations accordingly. Example

[0041] Raw materials preparation: EVA resin: 7350MEVA resin produced by Formosa Plastics Corporation is used, and its vinyl acetate content is about 21%; Supercritical foaming agent: a mixed gas of supercritical nitrogen and supercritical carbon dioxide is used, with a volume ratio of 1:4; Cross-linking agent: Di-tert-butyl peroxide isopropylbenzene, and the addition amount is 1.2% of the total mass of EVA resin; Antioxidant: Hindered phenol antioxidant 1010 is used, and the dosage is 0.2% of the total mass of EVA resin; Nano shock-absorbing particles A: First, prepare magnetic iron oxide nanoparticles. Dissolve ferric chloride and ferrous chloride in water at a molar ratio of 2:1. Add ammonia water under nitrogen protection, adjust the pH to 9.5, control the reaction temperature to 65°C, and react for 1.5 hours to generate Fe 3 O 4 The nanoparticles were washed and dried thoroughly, and then dispersed in a Tris-HCl buffer solution containing dopamine monomers at pH 8.5. The reaction was stirred at room temperature for 36 hours to allow dopamine to react with Fe 3 O 4 The surface self-polymerizes to form a polydopamine layer to obtain nano shock-absorbing particles A; Nano shock-absorbing particles B: Disperse montmorillonite in water, add an appropriate amount of long-chain alkyl quaternary ammonium salt, stir and react at 70°C for 4.5 hours, take it out and wash and dry it three times to obtain organic modified montmorillonite, which is nano shock-absorbing particles B; Preheat an internal mixer to 90°C, add EVA resin thereto, stir at a stirring rate of 35 r / min for 3.5 min to preliminarily plasticize the EVA resin, add a crosslinking agent di-tert-butyl peroxide isopropylbenzene to the preliminarily plasticized EVA resin, stir at a stirring rate of 65 r / min for 1.5 min to uniformly disperse the crosslinking agent therein, add an antioxidant hindered phenol antioxidant 1010 after dispersion, stir at a stirring rate of 35 r / min for 2.5 min, add nano shock absorbing particles A after stirring, increase the stirring rate to 70 r / min, continue stirring for 3.5 min, then add nano shock absorbing particles B, keep the speed at 70 r / min, continue stirring for 4.5 min to obtain a rubber compound, and during the mixing process, control the temperature in the internal mixer cavity between 90°C and 110°C, at which time the amino group in the polydopamine layer and the ester group in the EVA resin undergo hydrogen bond interaction to form a hydrogen bonded product; The rubber compound is transferred into a high-pressure reactor, and the high-pressure reactor is vacuumed for 18 minutes to reduce the pressure in the high-pressure reactor to 0.03MPa. After the treatment, a mixed gas of supercritical nitrogen and supercritical carbon dioxide is injected into the high-pressure reactor, and the injection speed is controlled to be 2.5L / min. The pressure in the high-pressure reactor is increased to 25MPa, and the temperature is controlled between 50°C. During the injection of the mixed gas, the mixed gas penetrates into the rubber compound, and the penetration time is set to 60min. After the penetration is completed, the reactor is placed in an external magnetic field with a magnetic field strength of 1.0T. The direction of the magnetic field is set according to the front and rear direction of the sole, and the reaction is carried out under the action of the magnetic field for 25min. During this process, the magnetic iron oxide in the nano shock-absorbing particles A and the supercritical carbon dioxide undergo adsorption and electron transfer, and the concentration of the supercritical carbon dioxide on the surface of the magnetic iron oxide increases locally. In the subsequent foaming process, when the pressure is released, these adsorbed supercritical carbon dioxide are more inclined to form bubbles near the magnetic iron oxide. The mixed colloid that has been subjected to supercritical foaming treatment and stabilized in a magnetic field is quickly transferred to an oven preheated to 130°C for vulcanization and crosslinking treatment. During the vulcanization and crosslinking process, the oven temperature is first increased from 130°C to 150°C at a heating rate of 2°C / min, and maintained at this temperature for 13 minutes to allow the crosslinking reaction to proceed fully. During the reaction, the crosslinking agent di-tert-butyl peroxide isopropylbenzene decomposes to produce free radicals, which trigger the crosslinking reaction between the EVA molecular chains. At the same time, the lamellar structure of the organically modified montmorillonite interacts with the EVA molecular chains in the EVA matrix. After the vulcanization and crosslinking treatment is completed, the material is immediately transferred to a magnetic field generating device, the magnetic field strength is adjusted to 1.5T, and the magnetization treatment is performed for 38 minutes; The finished rubber compound is placed in a special slipper stamping die, and the surface of the mold cavity is finely polished to control the surface roughness to Ra1.2um. The stamping equipment uses a hydraulic stamping machine, and its stamping pressure can be accurately controlled between 225MPa. The stamping speed is set to 20mm / s. During the stamping process, the rubber compound is subjected to pressure in the mold cavity, and the pore structure inside the material will undergo a certain degree of deformation and rearrangement. The nano shock-absorbing particles A and nano shock-absorbing particles B will also adjust their positions and orientations accordingly, so that the material can better adapt to external forces after molding and exert shock-absorbing performance. After the stamping is completed, high-precision CNC cutting equipment is used to remove the overflow and burrs on the edge of the slippers, and the cutting accuracy is controlled at ±0.2mm. After completion, the surface of the slippers is finely polished using a grinding process to make the surface smooth and flat. During the grinding process, the sandpaper particle size gradually transitions from 200 mesh to 800 mesh. After the grinding is completed, the slippers are quality inspected; Shock absorption performance test, A drop weight impact tester was used to test multiple pairs of slippers according to the set conditions (a drop weight of 7.5 kg fell from a height of 1.0 m to impact the sole of the slipper), and the shock absorption rate was calculated by recording the impact force-time curve through a sensor. After multiple tests, the average shock absorption rate reached 72%, meeting the set requirements of 65%-85%. This shows that the slippers can effectively absorb and dissipate energy and reduce the impact on the feet when subjected to a large impact force. In the actual wearing experience, users can clearly feel that the impact force from the ground is well buffered during activities such as walking and jumping, and the fatigue of the foot is significantly reduced, especially when walking or exercising for a long time, which plays a good protective role on the foot joints and muscles; 2. Mechanical properties test, Tensile strength: The slipper soles were subjected to tensile tests using a universal material testing machine. The results showed that the average tensile strength was 3.0MPa, which is higher than the set standard of no less than 2.5MPa. This means that the slipper soles have good resistance to tensile forces and are not prone to cracking or deformation. This ensures that even if the soles are stretched during daily wear, the soles can maintain their intact structure and maintain their normal use functions and appearance. Elongation at break: The average elongation at break obtained from the test is 420%, which is within the set range of 350%-550%. This shows that the sole material has good flexibility and elasticity. After being stretched to a certain extent, it can still recover to its original shape or maintain a small residual deformation. In actual wear, when the foot performs various movements in the shoe, the sole can deform moderately with the movement of the foot, providing a comfortable fit, and recover quickly after the movement is over, without affecting the wearing experience or causing damage to the sole due to excessive deformation; Compression permanent deformation rate: The test shows that the average compression permanent deformation rate is 28%, which is lower than the set requirement of 35%. This means that after the slippers are under pressure for a long time, the deformation of the sole can be mostly restored after the pressure is removed, and there will be no serious collapse or deformation. After a day of normal wear, the shape of the slippers' soles can still be maintained in a good state without obvious flatness, ensuring the long-term comfort and durability of the slippers. 3. Appearance quality and durability test, In terms of appearance quality inspection, the shapes of multiple pairs of slippers were scanned and analyzed by a 3D profile scanner, and the surface flatness, color uniformity and obvious defects were checked manually. The results showed that the shape deviation of all the tested slippers was controlled within ±0.3mm (better than the set ±0.5mm), the surface flatness was good, there was no obvious unevenness, the color was uniform, and no problems such as color difference and color spots were found. There were no obvious defects such as degumming, open lines, and material peeling. This shows that in the production process, from mold processing to material molding and the final finishing process, they have been effectively controlled to ensure that the product has a high appearance quality; In the durability test, various daily wear conditions were simulated, including walking on cement floors, wooden floors, tile floors, going up and down stairs, jumping on the spot, running in a small range, etc. After 3 consecutive months of testing, the overall structure of the slippers remained intact, and the decline in the shock absorption and mechanical properties of the soles were within an acceptable range (the shock absorption rate decreased by about 5%, the tensile strength decreased by about 8%, the elongation at break decreased by about 10%, and the compression permanent deformation rate increased by about 5%). The appearance quality also had only slight scratches on the surface of the sole and slight stains on the upper, which did not affect normal use. This proves that the slippers have good durability and can meet the needs of daily use for a long time.

[0042] According to the above embodiments and the quality inspection of the finished slippers, it is shown that the EVA supercritical foaming material is feasible for preparing slippers, and the prepared slippers have the property of shock absorption.

[0043] The embodiments of the present invention are described in detail above with reference to the accompanying drawings, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions and variations of these embodiments are made without departing from the principles and spirit of the present invention, and still fall within the scope of protection of the present invention.

[0044] In the description of the specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0045] The above contents are merely examples and explanations of the present invention. Various modifications or additions to the specific embodiments described or replacements in similar ways by technicians in the technical field shall fall within the protection scope of the present invention as long as they do not deviate from the invention or exceed the scope defined by the claims.

[0046] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A process for preparing a shock-absorbing EVA supercritical foaming material, comprising raw material preparation, raw material mixing, supercritical foaming treatment, structural post-treatment and preparation of finished material, characterized in that: The specific steps of the preparation process of the shock-absorbing EVA supercritical foaming material are as follows: Step 1: Select EVA resin, supercritical foaming agent, cross-linking agent and antioxidant as basic reaction materials, and prepare self-made nano shock-absorbing particles A and nano shock-absorbing particles B as additive materials; Step 2: Add EVA resin, crosslinking agent, antioxidant, nano shock-absorbing particles A and nano shock-absorbing particles B into an internal mixer step by step for mixing, and prepare a mixed rubber after the materials are evenly dispersed; Step 3: Transfer the rubber mixture to a high-pressure reactor and evacuate the mixture, inject a mixed gas component of supercritical nitrogen and supercritical carbon dioxide into the high-pressure reactor to infiltrate the rubber mixture, and after the infiltration is completed, place the reactor in an external magnetic field to stabilize the supercritically treated mixed colloid for standby use; Step 4: transferring the stable mixed colloid into an oven for vulcanization and cross-linking treatment, and after the treatment is completed, transferring it into a magnetic field generating device for magnetization treatment to obtain a finished mixed rubber product; Step 5: Transfer the finished rubber mixture into a slipper stamping die for stamping and forming. After the stamping is completed, the formed slippers are trimmed, and the slippers are tested for appearance quality and performance. After passing the test, they are put into use.

2. The process for preparing a shock-absorbing EVA supercritical foam material according to claim 1, characterized in that: In the step 1, the EVA resin is selected from EVA resin with a vinyl acetate content of 18wt%-25wt%, the supercritical foaming agent is a mixed gas of supercritical nitrogen and supercritical carbon dioxide, the volume ratio of supercritical nitrogen to supercritical carbon dioxide is 1:3-5, the cross-linking agent is di-tert-butyl peroxide isopropylbenzene, and the addition amount is 0.8%-1.5% of the total mass of the EVA resin, and the antioxidant is a hindered phenol antioxidant 1010, and the usage amount is 0.1%-0.3% of the total mass of the EVA resin.

3. The process for preparing a shock-absorbing EVA supercritical foam material according to claim 2, characterized in that: In the step 1, the nano-shock-absorbing particle A is a nano-particle with a core-shell structure, wherein the core is a magnetic iron oxide nano-particle with a particle size of 10n-20nm, and the shell is a polydopamine layer. The preparation process of the nano-shock-absorbing particle A is to synthesize Fe3O4 nano-particles by a coprecipitation method, dissolve ferric chloride and ferrous chloride in water at a molar ratio of 2:1, add ammonia water under nitrogen protection, adjust the pH to 9-10, control the reaction temperature to 60°C-70°C, react for 1h-2h, generate Fe3O4 nano-particles, wash and dry them, disperse them in a Tris-HCl buffer solution containing dopamine monomer at a pH of 8.5, stir and react at room temperature for 24h-48h, and obtain the nano-shock-absorbing particle A. For the nano-shock-absorbing particle B, montmorillonite is dispersed in water, a long-chain alkyl quaternary ammonium salt is added, and the reaction is stirred at a temperature of 60°C-80°C for 3h-6h. After completion, the nano-shock-absorbing particle is taken out and washed and dried for 3-4 times to obtain an organic modified montmorillonite, i.e., the nano-shock-absorbing particle B.

4. The process for preparing a shock-absorbing EVA supercritical foaming material according to claim 3, characterized in that: In the step 2, the internal mixer is preheated to 90°C, EVA resin is added thereto, and the mixture is stirred at a stirring rate of 30 r / min-40 r / min for 2 min-5 min to preliminarily plasticize the EVA resin, and di-tert-butyl peroxide isopropylbenzene is added thereto as a crosslinking agent, and the mixture is stirred at a stirring rate of 50 r / min-80 r / min for 1 min-2 min to uniformly disperse the crosslinking agent di-tert-butyl peroxide isopropylbenzene in the preliminarily plasticized EVA resin. After the dispersion is completed, an antioxidant hindered phenol antioxidant 1010 is added thereto, and the mixture is stirred at a stirring rate of 30 r / min-40 r / min for 1 min-2 min to uniformly disperse the crosslinking agent di-tert-butyl peroxide in the preliminarily plasticized EVA resin. The mixture was stirred at a stirring rate of r / min-40r / min for 2min-3min. After the stirring was completed, nano shock absorbing particles A were added, and the stirring rate was increased to 60r / min-80r / min. After continuous stirring for 3min-4min, nano shock absorbing particles B were added, and the speed was maintained at 60r / min-80r / min. The mixture was stirred for 4min-5min to obtain a rubber compound. When each component was added to the internal mixer for mixing, the temperature in the internal mixer cavity was controlled between 90℃-110℃. During the mixing process, the following reactions occurred: ； Amino groups in the polydopamine layer With the ester group in EVA resin Hydrogen bonding occurs to produce , which is a hydrogen bond product.

5. The process for preparing a shock-absorbing EVA supercritical foaming material according to claim 4, characterized in that: In the step three, the rubber mix is ​​transferred to a high-pressure reactor, and the high-pressure reactor is vacuumed for 15 minutes to 20 minutes to reduce the pressure in the high-pressure reactor to 0.01MPa-0.05MPa. After the treatment is completed, a mixed gas of supercritical nitrogen and supercritical carbon dioxide is injected into the high-pressure reactor, and the injection speed is controlled to be 2L / min-3L / min. The pressure in the high-pressure reactor is increased to 20MPa-30MPa, and the temperature is controlled to be between 45°C and 55°C. During the injection of the mixed gas, the mixed gas penetrates into the rubber mix, and the penetration time is set to 40min-80min. After the penetration is completed, the reactor is placed in an external magnetic field with a magnetic field strength of 0.5T-1.5T, and the direction of the magnetic field is set according to the direction of the required shock absorption performance. The reaction is carried out for 20min-30min under the action of the magnetic field, and the magnetic iron oxide in the nano shock-absorbing particles A With supercritical carbon dioxide Adsorption and electron transfer occur: ； in Indicates the number of supercritical carbon dioxide molecules adsorbed.

6. The process for preparing a shock-absorbing EVA supercritical foaming material according to claim 5, characterized in that: In the step 4, the mixed colloid after supercritical foaming treatment and stabilization in the magnetic field is quickly transferred to an oven preheated to 130°C for vulcanization and crosslinking treatment. During the vulcanization and crosslinking process, the oven temperature is first increased from 130°C to 150°C at a heating rate of 2°C / min, and maintained at this temperature for 10min-15min to allow the crosslinking reaction to proceed fully. The reaction equation is as follows: ； ； ； During the reaction, the crosslinking agent di-tert-butyl peroxide isopropylbenzene decomposes to produce free radicals, which trigger the crosslinking reaction between EVA molecular chains.

7. The process for preparing a shock-absorbing EVA supercritical foaming material according to claim 6, characterized in that: In the step 4, the reaction equation of the lamellar structure of the organically modified montmorillonite in the EVA matrix is ​​as follows: ； The above is the entanglement interaction between the long-chain alkyl on the surface of the organic modified montmorillonite layer and the EVA molecular chain. is the carbon number of the long chain alkyl group.

8. The process for preparing a shock-absorbing EVA supercritical foaming material according to claim 7, characterized in that: In the step 5, the finished rubber mixture is placed in a special slipper stamping die, and the surface of the die cavity is finely polished to control the surface roughness to Ra0.8um-1.6um. The stamping equipment adopts a hydraulic stamping machine, and its stamping pressure can be accurately controlled between 150-300MPa. The stamping speed is set to 15-25mm / s. After the stamping is completed, the overflow and burrs on the edge of the slipper are removed by using a high-precision CNC cutting device, and the cutting accuracy is controlled within ±0.2mm. After completion, the surface of the slipper is finely polished using a grinding process to make the surface smooth and flat. During the grinding process, the sandpaper particle size gradually transitions from 200 mesh to 800 mesh. After the grinding is completed, the appearance quality of the slippers is inspected, including the shape integrity, surface flatness, color uniformity and presence of obvious defects of the slippers, and the shape of the slippers is scanned and analyzed using a three-dimensional profile scanner, and compared with the standard model, and the deviation is controlled within ±0.5mm; A drop hammer impact tester is used to test the shock absorption performance of the slippers. A drop hammer with a mass of 5kg-10kg is dropped from a height of 0.8m-1.2m to impact the sole of the slippers. A sensor is used to record the impact force-time curve and the shock absorption rate is calculated. The shock absorption rate is required to reach 65%-85%. At the same time, a universal material testing machine is used to test the tensile, compression and bending performance of the soles of the slippers. The tensile strength is not less than 2.5MPa, the elongation at break is between 350%-550%, and the compression permanent deformation rate is less than 35%. Slippers that pass both appearance quality and performance tests are put into use.

9. A shock-absorbing EVA supercritical foam material suitable for use in any one of claims 1 to 8, characterized in that: The shock-absorbing EVA supercritical foaming material is prepared by mixing EVA resin, di-tert-butyl peroxide isopropylbenzene, hindered phenol antioxidant 1010, nano shock-absorbing particles A and nano shock-absorbing particles B, and then infiltrating a mixed gas component of supercritical nitrogen and supercritical carbon dioxide.

Images