A shrinkage-resistant macroporous ultralight soft elastic supercritical foaming sole material and preparation method thereof

Abstract

The present invention provides a shrinkage-resistant macroporous ultralight soft elastic supercritical foaming sole material and a preparation method thereof; the foaming sole material improves the flexibility / resilience / compressibility / mechanical strength of the foaming sole by using poly (1,2-butadiene)-b-polyethylene oxide copolymer, improves the cell strength by the double cross-linking effect of ethylene-methacrylic polymer, and effectively disperses ultra-high molecular weight polyethylene micropowder in the matrix and enhances the strength of large-aperture cells with carboxyl polystyrene microspheres, and then selects medium molecular weight polyisobutylene and cross-linking agent micro-cross-linking to further enhance the viscosity and strength of the matrix and effectively lock the gas, not only meeting the physical property requirements of consumers for lightness, softness and elasticity, thereby effectively preventing the shrinkage of the sole under the appearance of large pores, and improving the yield of the product and the stability and safety of mass production. In terms of technology, the ultra-high pressure foaming method is adopted, and the foaming time can be shortened by more than 50% compared with the traditional supercritical autoclave pressure, greatly improving the production efficiency.

Description

Technical Field

[0001] The invention belongs to the technical field of sole materials, and in particular relates to an anti-shrinkage macroporous ultra-light soft elastic supercritical foaming sole material and a preparation method thereof. Background Art

[0002] The traditional chemical foaming method for preparing sports shoe foam midsoles has problems such as harmful additive residues, strong odor, and environmental pollution. The existing physical foaming (mainly N2 or CO2 supercritical foaming technology) has become the new favorite of the industry because of its excellent product performance, no use of chemical foaming agents, and no odorous substance residue. Among them, EVA foam material is the most commonly used polymer matrix in the industry. At present, there are three main processes for EVA-based supercritical foaming, namely two-step kettle compression molding, three-step kettle compression molding or compression supercritical molding. Compression supercritical molding requires the supercritical foaming agent to be passed into each mold in the compression molding machine. The pressure holding time for each pair of soles is as high as 1 to 4 hours, while the foaming time of ordinary chemical foaming compression molding is only 10 minutes. Therefore, the production efficiency of this process is extremely low and cannot be popularized. The two-step autoclave molding or three-step autoclave molding both use a single injection machine to inject the EVA small embryo sole. The difference is that the two-step autoclave molding small embryo already has texture, but after the autoclave tank supercritical foaming, the texture will be unclear, resulting in appearance defects such as rounded corners, and without the third step of molding, the size of the sole is inconsistent, the size and length are different, resulting in a high number of defective products, a high scrap rate, and poor mass production stability. The three-step autoclave molding is currently the most mature process for the EVA-based series. Its process steps are to first use a single injection machine to inject the EVA small embryo sole, then use supercritical autoclave foaming to form a small foamed embryo, and finally use the mold for secondary back pressure shaping to obtain the finished sole. The secondary back pressure shaping can well control the problems of the product's pattern clarity and length, and the finished product has a high yield rate and good mass production stability.

[0003] However, a major drawback of supercritical foaming is that after the cell nucleation and subsequent cell growth, as the supercritical gas continues to diffuse outward from the matrix material, the matrix molecular chain is stretched by the pore wall during the cell growth process, but the molecular chain will curl up and return to its initial state after cooling and reducing pressure, which causes the soles after supercritical foaming to shrink continuously during the subsequent placement process. At present, the industry generally controls the shrinkage of supercritical microporous foamed soles through macro processes such as baking and shaping, but it is difficult to solve the fundamental shrinkage problem of supercritical macroporous / coarse pore foamed soles through baking, shaping and other processes. Summary of the invention

[0004] In view of this, the purpose of the present invention is to provide a shrinkage-resistant large-pore ultra-light soft-elastic supercritical foamed sole material and a preparation method thereof, wherein the sole material has a large-pore / coarse-pore appearance structure, and is light in weight, soft and elastic, high in strength, and shrinkage-resistant.

[0005] The present invention provides a shrinkage-resistant macroporous ultralight soft elastic supercritical foaming sole material, which comprises the following raw materials in parts by weight:

[0006] 50-70 parts of ethylene vinyl acetate (EVA), 10-20 parts of ethylene methacrylic acid polymer (Fusabond), 5-15 parts of hydrogenated styrene-butadiene-styrene copolymer (SEBS), 5-15 parts of poly (1,2-butadiene) - b-polyethylene oxide copolymer (PBD-b-PEO), 3-6 parts of carboxyl polystyrene microspheres, 4-8 parts of polyethylene micropowder with a molecular weight of 2 million to 3 million, 4-6 parts of polyisobutylene with a molecular weight of 45,000 to 65,000, 0.3-0.5 parts of cross-linking agent, and 1 part of lubricant.

[0007] The present invention uses PBD-b-PEO copolymer to blend with EVA, SEBS, and Fusabond for foaming. On the one hand, the poly (1,2-butadiene) in PBD-b-PEO improves the flexibility and resilience of the base material. On the other hand, the polyethylene oxide in PBD-b-PEO has high compatibility with polar groups and can be combined with the ester group in EVA and the carboxyl group of Fusabond to form a strong chemical bond, further improving the strength of the foamed material, thereby maintaining light weight while having good compression performance and mechanical strength. Secondly: the carboxyl polystyrene microsphere dispersant is cleverly selected in the formula, which helps the ultra-high molecular weight polyethylene micropowder to be evenly dispersed in the matrix. The ultra-high molecular weight polyethylene micropowder with small particle size and uniform distribution not only reduces the Gibbs free energy of bubble nucleus embryo formation during supercritical foaming, but also effectively promotes bubble nucleation. While increasing the bubble size and reducing the bubble density, it can also enhance the strength of the large-aperture bubbles in the foamed sole, and effectively reduce the shrinkage of the bubbles. Furthermore, the viscosity of the matrix is ​​further enhanced by medium molecular weight polyisobutylene and the supercritical gas is effectively locked to prevent excessive and rapid gas overflow, thereby effectively preventing the shrinkage of the sole under the large cell structure. Finally, the viscosity of the blend is increased and the cell diameter is controlled by an appropriate amount of cross-linking agent to reduce the shrinkage of the foamed sole. Through the ingenious combination and action of the above materials, a macroporous foam material that is light, soft, elastic, and shrinkage-resistant is finally obtained. The selection of materials and the combination of formulas are pioneering in the industry, and the product has a high yield, high mass production stability and safety, and has a high application prospect.

[0008] The raw materials for preparing the shrinkage-resistant macroporous ultra-light soft elastic supercritical foaming sole material provided by the present invention include 50-70 parts of ethylene-vinyl acetate; the dosage can be specifically 50 parts, 51 parts, 52 parts, 53 parts, 54 parts, 55 parts, 56 parts, 57 parts, 58 parts, 59 parts, 60 parts, 61 parts, 62 parts, 63 parts, 64 parts, 65 parts, 66 parts, 67 parts, 68 parts, 69 parts or 70 parts; the VA content of the ethylene-vinyl acetate is 18-30%; in a specific embodiment, the brand of the ethylene-vinyl acetate is EVA265.

[0009] The raw materials for preparing the shrinkage-resistant macroporous ultra-light soft elastic supercritical foaming sole material provided by the present invention include 10 to 20 parts of ethylene-methacrylic acid polymer; the specific amount can be 10 parts, 11 parts, 12 parts, 13 parts, 14 parts, 15 parts, 16 parts, 17 parts, 18 parts, 19 parts or 20 parts. The methacrylic acid content in the ethylene-methacrylic acid polymer described in the present invention is 5 to 15%; in a specific embodiment, the ethylene-methacrylic acid polymer is Fusabond 514D. The ethylene-methacrylic acid polymer described in the present invention contains carboxyl groups in its molecular structure, and can form a dual effect of peroxide crosslinking and ionic bond crosslinking during the foaming and crosslinking process, forming a higher melt strength under high temperature and high pressure, which is beneficial to enhance the strength of the blend in the molten state and the support pore strength during high-ratio foaming, while reducing the shrinkage rate during subsequent placement.

[0010] The raw materials for preparing the shrinkage-resistant macroporous ultra-light soft elastic supercritical foaming sole material provided by the present invention include 5 to 15 parts of hydrogenated styrene-butadiene-styrene copolymer; the specific amount can be 5 parts, 6 parts, 7 parts, 8 parts, 9 parts, 10 parts, 11 parts, 12 parts, 13 parts, 14 parts or 15 parts; the styrene content in the hydrogenated styrene-butadiene-styrene copolymer is 10 to 30%; in a specific embodiment, the hydrogenated styrene-butadiene-styrene copolymer is YH688.

[0011] The raw materials for preparing the shrinkage-resistant macroporous ultralight soft elastic supercritical foaming sole material provided by the present invention include 5 to 15 parts of poly(1,2-butadiene)-polyethylene oxide copolymer; the specific amount can be 5 parts, 6 parts, 7 parts, 8 parts, 9 parts, 10 parts, 11 parts, 12 parts, 13 parts, 14 parts or 15 parts; the poly(1,2-butadiene)-polyethylene oxide copolymer is a block copolymer formed by copolymerization of 1,2-butadiene and ethylene oxide, and the poly(1,2-butadiene) in its structure has excellent elasticity and toughness, while the polyethylene oxide has excellent mechanical strength, which is beneficial to improving the elasticity and strength of the foaming sole. In the present invention, the polyethylene oxide content in the poly(1,2-butadiene)-polyethylene oxide copolymer is 5 to 10%; in a specific embodiment, the poly(1,2-butadiene)-polyethylene oxide copolymer is PBD-PEO AT300.

[0012] The raw materials for preparing the shrinkage-resistant macroporous ultralight soft-elastic supercritical foamed sole material provided by the present invention include 3 to 6 parts of carboxyl polystyrene microspheres; the dosage can be specifically 3 parts, 3.5 parts, 4 parts, 4.5 parts, 5 parts, 5.5 parts or 6 parts; the carboxyl content in the carboxyl polystyrene microspheres is 1 to 3%, and the carboxyl group gives the polystyrene microspheres excellent surface activity, and can react with other substances by covalent bonds or through electrostatic adsorption. The particle size of the carboxyl polystyrene microspheres is preferably 100-500 nm. The carboxyl polystyrene microspheres with small particle size have a large specific surface area, which increases the contact area with other substances, effectively adsorbs and disperses the ultra-high molecular weight polyethylene micropowder in the matrix, and at the same time, the carboxyl group forms a strong chemical bond with the ester group of ethylene-vinyl acetate, the carboxyl group of ethylene-methacrylic acid, the styrene group of hydrogenated styrene-butadiene-styrene copolymer, and the poly (1,2-butadiene) -polyethylene oxide copolymer, etc., which plays an excellent compatibility role, and can form an effective combination between the non-polar ultra-high molecular weight polyethylene micropowder and the polar polymer, greatly enhancing the strength of the large-aperture pores; that is, the carboxyl polystyrene microspheres play the role of dispersant and compatibilizer, and indirectly play the role of increasing the pore strength, which is achieved through the dual effects of physical dispersion and chemical bonds.

[0013] The raw materials for preparing the shrinkage-resistant macroporous ultralight soft elastic supercritical foaming sole material provided by the present invention include 4 to 8 parts of polyethylene powder with a molecular weight of 2 million to 3 million; the specific amount can be 4 parts, 5 parts, 6 parts, 7 parts or 8 parts; on the one hand, the present invention adopts the above-mentioned ultra-high molecular weight polyethylene powder, which can reduce the Gibbs free energy of bubble nucleus embryo formation during the foaming process, reduce the nucleation barrier of the pores, effectively promote bubble nucleation, and reduce the difficulty of supercritical foaming; at the same time, after adding small-particle ultra-high molecular weight polyethylene powder (average particle size 115 μm, molecular weight 3 million), the pore size can be increased and the pore density can be reduced; on the other hand, the ultra-high molecular weight polyethylene powder has the excellent characteristics of high specific strength and high specific modulus, and its specific strength is more than ten times that of steel wire with the same cross-section, and its specific modulus is second only to special carbon fiber, which is beneficial to improving the pore strength of the coarse pore / macroporous structure, and therefore, it has a dual effect on the foaming effect, and can improve the pore strength under the condition of increasing the pore size. In a specific embodiment, the polyethylene powder is UHMWPE 9030UH, which is in powder form, has a molecular weight of 3 million, an average particle size of 115um, a tensile strength of 40MPa, and a density of 0.935g / cm 3 , Lotte Company of South Korea.

[0014] The raw materials for preparing the shrinkage-resistant macroporous ultralight soft elastic supercritical foaming sole material provided by the present invention include 4 to 6 parts of polyisobutylene with a molecular weight of 45,000 to 65,000; the dosage can be specifically 4 parts, 4.5 parts, 5 parts, 5.5 parts or 6 parts; the polyisobutylene, due to the presence of two substituted methyl groups, leads to slow molecular chain movement and small free volume, thus producing low diffusion coefficient and gas permeability, and thus has excellent air tightness, greatly reducing the overflow of gas after cooling and decompression; and polyisobutylene has viscosity, which can improve the viscosity of the blended matrix, is conducive to enhancing the bonding between the pore walls, and preventing the collapse and shrinkage of large pores. In a specific embodiment of the present invention, the polyisobutylene is PIB HRD-500.

[0015] The raw materials for preparing the shrinkage-resistant macroporous ultra-light soft elastic supercritical foaming sole material provided by the present invention include 0.3 to 0.5 parts of a cross-linking agent; the dosage can be specifically 0.3 parts, 0.35 parts, 0.4 parts, 0.45 parts or 0.5 parts; if the EVA series of foaming soles are not cross-linked, the melt strength of each polymer cannot form a network structure at high temperature and high pressure, and the foam cells are prone to rupture and merge, etc., and the mechanical strength of the final foaming sole is poor; by introducing an appropriate amount of cross-linking agent into the formula, micro-cross-linking is first performed when the sole embryo is ejected, which can not only increase the viscosity of the blend, but also facilitate the formation of a network cross-linked structure during high temperature and high pressure foaming in a supercritical autoclave, thereby controlling the pore size and reducing the shrinkage of the foaming sole. The peroxide cross-linking agent is diisopropylbenzene peroxide and / or 1,4-di-tert-butylperoxyisopropylbenzene. In a specific embodiment, the peroxide cross-linking agent is BIBP. In the present invention, micro cross-linking is achieved through a cross-linking agent, while ordinary chemical foaming requires complete cross-linking. In the present invention, supercritical physical foaming requires the use of an IP injection process to first inject a small embryo, so only micro cross-linking can be achieved. If complete cross-linking is achieved, the foaming effect will be affected during the supercritical autoclave pressure foaming stage, and the foaming ratio will become smaller.

[0016] The raw materials for preparing the shrinkage-resistant macroporous ultralight soft elastic supercritical foamed sole material provided by the present invention include 1 part of lubricant; the lubricant is stearic acid; in a specific embodiment, the lubricant is stearic acid 1801.

[0017] The foamed sole material provided by the present invention improves the flexibility / resilience / compressibility / strength of the foamed sole by adopting poly(1,2-butadiene)-b-polyethylene oxide copolymer; secondly, the strength of the blend in a molten state and the strength of the supporting pores are enhanced by using ethylene-methacrylic acid polymer; furthermore, ultra-high molecular weight polyethylene micropowder is effectively dispersed in a matrix by using carboxyl polystyrene microspheres and the strength of large-aperture pores is enhanced; finally, medium molecular weight polyisobutylene and micro-crosslinking are selected to further enhance the viscosity and strength of the matrix and effectively lock the gas, thereby meeting the consumer's requirements for light, soft and elastic physical properties, thereby effectively preventing the shrinkage of the sole under the appearance of large pores, and improving the product yield and the stability and safety of mass production.

[0018] The present invention provides a method for preparing the shrinkage-resistant macroporous ultralight soft elastic supercritical foamed sole material according to the above technical solution, comprising the following steps:

[0019] The crosslinking agent and the lubricant are mixed to obtain a first group of materials; polyethylene micropowder with a molecular weight of 2 million to 3 million, carboxyl polystyrene microspheres and polyisobutylene with a molecular weight of 45,000 to 65,000 are mixed to obtain a second group of materials; ethylene-vinyl acetate, ethylene-methacrylic acid polymer, hydrogenated styrene-butadiene-styrene copolymer and poly (1,2-butadiene) - polyethylene oxide copolymer are mixed to obtain a third group of materials;

[0020] The third group of materials is heated to 80-85°C and then mixed with the second group of materials; the temperature is further heated to 90-95°C and then mixed with the first group of materials, and the temperature is raised to 100-110°C to obtain a mixed material;

[0021] granulating the mixed material to obtain granules;

[0022] Injection-molding the pellets once to obtain a rough blank;

[0023] Allowing the rough blank to stand for supercritical foaming to obtain a foamed sole;

[0024] The foamed sole is left to stand, then molded and cooled to obtain a shrinkage-resistant macroporous ultralight soft-elastic supercritical foamed sole material.

[0025] The present invention shortens the immersion saturation time of the blended matrix by adopting a high-pressure supercritical foaming method, which can be shortened by more than 50% compared with the foaming time of the traditional supercritical autoclave pressure, greatly improving the production efficiency, and having a good foaming effect and a high yield rate.

[0026] The invention mixes a crosslinking agent and a lubricant to obtain a first group of materials; mixes polyethylene micropowder with a molecular weight of 2 million to 3 million, carboxyl polystyrene microspheres and polyisobutylene with a molecular weight of 45,000 to 65,000 to obtain a second group of materials; and mixes ethylene-vinyl acetate, ethylene-methacrylic acid polymer, hydrogenated styrene-butadiene-styrene copolymer and poly (1,2-butadiene) -polyethylene oxide copolymer to obtain a third group of materials.

[0027] The present invention heats the third group of materials to 80-85° C. and then mixes them with the second group of materials; further heats the third group of materials to 90-95° C. and then mixes them with the first group of materials; and heats the third group of materials to 100-110° C. to obtain a mixed material.

[0028] The present invention granulates the mixed material to obtain granules. The temperatures of the first zone, the second zone, the third zone and the fourth zone used in the granulation are respectively adjusted to 75°C, 80°C, 85°C and 90°C; the screw speed used in the granulation is 40-50rpm, and the cutting speed is 15-20rpm.

[0029] The present invention performs one-time injection molding of the pellets to obtain a rough blank. During one-time injection, the temperatures of the first, second, third and fourth feeding zones are adjusted to 84°C, 86°C, 88°C and 90°C respectively; the injection speed is 50(±2)-45(±2)-40(±2)-35(±2)%; the injection pressure is 90(±5)-90(±5)-90(±5)-90(±5)bar; the vacuuming time is 80±20 seconds; the upper and lower template temperatures of the mold used for molding are 175±5°C and 175±5°C respectively; the one-time injection time is 150±20 seconds, and the vulcanization time is 450±30 seconds.

[0030] After obtaining the rough blank, the present invention allows the rough blank to stand for supercritical foaming to obtain a foamed sole. The rough blank is allowed to stand for 12 to 24 hours. When the foaming temperature is set to 105°C, due to the low temperature, part of the polymer has not completely melted, thus affecting the foaming effect, resulting in a decrease in the foaming ratio of the final foamed material, a high density and hardness, and a decrease in resilience; and when the foaming temperature is set to 125°C, due to the high temperature, the bubble nucleation rate is too fast and too much, and the foamed material finally formed has too large bubbles, a greatly increased shrinkage rate, and poor properties such as compression deformation and tensile strength. Therefore, the foaming temperature is 115±5°C. In specific embodiments, the foaming temperatures are 110°C, 112°C, 115°C, and 120°C;

[0031] The supercritical foaming pressure is 25-55 MPa. The present invention adopts a high-pressure rapid foaming method at 25-55 MPa, which shortens the immersion saturation time of the blended matrix, and can shorten the foaming time by more than 50% compared with the traditional supercritical autoclave pressure, greatly improving the production efficiency, and having a good foaming effect and a high yield rate. In a specific embodiment, the foaming pressure is 25 MPa, 35 MPa, 40 MPa, 45 MPa, 50 MPa or 55 MPa.

[0032] The present invention releases pressure after keeping the temperature and pressure for 20 to 60 minutes, the pressure release rate is 0.3 to 1 MPa / second, and the pressure release time is 50 to 200 seconds; the pressure holding time is specifically 20 minutes, 22 minutes, 25 minutes, 28 minutes, 30 minutes, 40 minutes, 48 ​​minutes, 54 minutes or 60 minutes; in a specific embodiment, the pressure release rate is 0.3 MPa / second, 0.5 MPa / second, 0.8 MPa / second or 1.0 MPa / second; the pressure release time is 50 seconds, 62.5 seconds, 70 seconds, 80 seconds, 90 seconds, 100 seconds, 110 seconds or 167 seconds. Compared with the prior art method of obtaining a microporous supercritical foamed sole by a rapid pressure relief method with a pressure relief time of 10 to 40 seconds, the present invention obtains a large-pore appearance structure by a slow pressure relief method with a pressure relief speed of 0.3 MPa / s to 1.0 MPa / s and a pressure relief time of 50 to 200 seconds, creating a preparation method for a large-pore / coarse-pore appearance structure, and also has excellent mechanical properties and usage performance such as light weight, high strength, and anti-shrinkage.

[0033] The present invention adopts a foaming pressure of 25-50MPa. Increasing the gas pressure and raising the saturation temperature can rapidly increase the solubility of the gas in the polymer, accelerate the rate of bubble nucleation, and then rapidly increase the number of bubble nucleations, greatly shortening the pressure holding time; the pressure difference inside and outside the bubble is the main reason for driving the growth of the pores. The faster the pressure release rate, the smaller the pore diameter and the increased pore density, and only dense pores can be obtained. Slowing down the pressure release rate, the pores slowly grow, which is conducive to the formation of large-diameter pores. Through the special setting of process conditions, a coarse pore / macropore appearance structure different from the traditional dense pore appearance is prepared, and the foaming time can be shortened by more than 50% compared with the traditional supercritical autoclave pressure, which greatly improves the production efficiency.

[0034] In the present invention, the diameter of the pores is 0.5-2.0 mm; in specific embodiments, the diameter of the pores is 0.5-0.6 mm, 0.5-0.7 mm, 0.6-0.8 mm, 0.8-1.0 mm, 1.0-1.2 mm, 1.1-1.3 mm or 1.7-2.0 mm.

[0035] After obtaining the foamed sole, the present invention molds and cools the foamed sole to obtain a shrinkage-resistant macroporous ultralight soft elastic supercritical foamed sole material. The foamed sole is molded after being allowed to stand for 72 to 96 hours; the molding temperature is 165±5° C. and the time is 750±30 seconds. The cooling water temperature used for cooling is 25±3° C. and the cooling time is: 750±30 seconds.

[0036] The foamed sole material provided by the present invention improves the flexibility / resilience / compressibility / mechanical strength of the foamed sole by using poly(1,2-butadiene)-b-polyethylene oxide copolymer, improves the cell strength by the double cross-linking effect of ethylene-methacrylic polymer, and effectively disperses ultra-high molecular weight polyethylene micropowder in the matrix and enhances the strength of large-aperture cells with carboxyl polystyrene microspheres, and then selects medium molecular weight polyisobutylene and micro-cross-linking to further enhance the viscosity and strength of the matrix and effectively lock the gas, which not only meets the consumer's demand for light, soft and elastic physical properties, but also effectively prevents the shrinkage of the sole under the appearance of large cells, and improves the yield of the product and the stability and safety of mass production. At the same time, the foamed sole adopts an ultra-high pressure foaming method in terms of technology, which can shorten the foaming time by more than 50% compared with the traditional supercritical autoclave pressure, greatly improving the production efficiency. DETAILED DESCRIPTION

[0037] In order to further illustrate the present invention, a shrinkage-resistant macroporous ultra-light soft elastic supercritical foamed sole material and a preparation method provided by the present invention are described in detail below in combination with embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0038] The raw materials used in the following examples and comparative examples are:

[0039] EVA 265: hardness 78A, VA content 28%, crystallinity 21.8%, DuPont.

[0040] Fusabond 514D: methacrylic acid content 9%, hardness 53D, crystallinity 50%, DuPont.

[0041] SEBS YH688: styrene content 13%, hardness 43A, molecular weight 150,000, Baling Petrochemical Company.

[0042] PBD-PEO AT300: polyoxyethylene content 10%, hardness 91A, melting point 105°C, crystallinity 29%, tensile strength 21.2MPa, Japan JSR Company.

[0043] Carboxyl polystyrene microspheres: liquid, carboxyl content: polystyrene content = 1%-3%: 97%-99%, particle size 200nm, solid content (carboxyl polystyrene microspheres / (carboxyl polystyrene microspheres + water) 5%.

[0044] UHMWPE 9030UH: powder, molecular weight 3 million, average particle size 115um, tensile strength 40MPa, density 0.935g / cm3, Lotte Company, South Korea.

[0045] PIB HRD-500: molecular weight 50,000, dynamic viscosity 60,000 mPa.s / 150°C, Shandong Hongrui New Material Technology Co., Ltd.

[0046] BIBP: Sinopec.

[0047] Stearic acid 1801: Dukuda, Indonesia.

[0048] The present invention is based on the following supercritical physical foaming process:

[0049] Weighing → mixing → granulation → IP injection of small rough embryos → autoclave supercritical foaming → secondary compression molding;

[0050] Examples and Comparative Examples

[0051] Implementation steps:

[0052] Weighing materials: According to the dosage of the formula (see Table 1, Table 2, Table 3 and Table 4), weigh the crosslinking agent BIBP and stearic acid as the first group; weigh the ultra-high molecular weight polyethylene powder, carboxyl polystyrene microspheres, and medium molecular weight polyisobutylene as the second group; and weigh the remaining materials as the third group.

[0053] Mixing: First, pour the third group of materials into the internal mixer and turn on the machine. Wait until the temperature rises to between 80 and 85°C; then pour in the second group of materials. When the temperature rises to 90 to 95°C, pour in the third group of materials. When the temperature rises to 100 to 110°C, pour out the mixed materials.

[0054] Material making: Pour the mixed material into the material making machine, adjust the temperatures of the first, second, third and fourth zones to 75℃, 80℃, 85℃ and 90℃ respectively, adjust the screw speed to 40~50 rpm, and adjust the cutting speed to 15~20 rpm.

[0055] IP injection of small rough embryos: Pour the prepared pellets into the injection foaming molding machine, and adjust the temperatures of the first, second, third and fourth feeding zones to 84℃, 86℃, 88℃ and 90℃ respectively; the injection speed is 50(±2)-45(±2)-40(±2)-35(±2)%; the injection pressure is 90(±5)-90(±5)-90(±5)-90(±5)bar; the vacuum time is 80±20 seconds; the upper and lower mold temperatures of the molding mold are adjusted to 175±5℃ and 175±5℃ respectively. Set the material quantity according to the mold dosage (the mold size is 18cm×10cm×1cm, and the material quantity can be set to 100±10g according to the foaming ratio of 1.5), the injection time is 150±20 seconds, the vulcanization time is 450±30 seconds, and then take out the small rough embryo of the sole and cool it naturally for 2 hours to finalize.

[0056] Autoclave supercritical foaming: After standing for 12 to 24 hours, the small rough embryo is placed in an autoclave supercritical physical foaming tank for foaming. After heat preservation and pressure maintenance, the pressure is released and the foamed sole is taken out and cooled to room temperature.

[0057] Molding: Place the supercritical foamed semi-finished product that has been standing for 72 to 96 hours into a flat-plate molding mold to complete the finished product molding; the cooling water temperature is: 25±3℃, and the cooling time is: 750±30 seconds.

[0058] Table 1

[0059]

[0060] Table 2

[0061]

[0062] Table 3

[0063]

[0064] Table 4

[0065]

[0066] It can be seen from Tables 1 to 4 that: (1) From the comparison data of Example 5 and Comparative Example 1, it can be seen that the poly (1,2-butadiene)-b-polyethylene oxide copolymer is beneficial to improving the resilience and tensile strength of the foaming material, and reducing the shrinkage and compression deformation;

[0067] (2) From the comparison data of Example 5 and Comparative Example 2, it can be seen that if the carboxyl polystyrene microsphere compatibilizer is removed from the formula, the resilience and tensile strength of the final foamed material decrease, while the shrinkage and compression deformation deteriorate. This shows that the carboxyl polystyrene microsphere compatibilizer can effectively adsorb and disperse the ultra-high molecular weight polyethylene powder in the matrix, and the carboxyl group forms a strong chemical bond with the ester group of EVA, the carboxyl group of ethylene-methacrylic acid, the styrene group of SEBS, poly (1,2-butadiene) -b-polyethylene oxide copolymer, etc., which plays an excellent compatibility role and greatly enhances the strength of large-diameter foams;

[0068] (3) From the comparison data of Example 5 and Comparative Example 3, it can be seen that if the ultra-high molecular weight polyethylene powder is omitted in the formula, the resilience and tensile strength of the final foamed material decrease, while the shrinkage and compression deformation become worse, indicating that the ultra-high molecular weight polyethylene powder with a small particle size has a good dual effect of promoting bubble nucleation and improving cell strength;

[0069] (4) From the comparison data of Example 5 and Comparative Example 4, it can be seen that adding an appropriate amount of medium molecular weight polyisobutylene can increase the viscosity of the blended matrix during foaming, which is beneficial to strengthening the bonding between the cell walls and preventing the collapse and shrinkage of large cells. Ultimately, it is also beneficial to improve the rebound rate and tensile strength of the foamed material and reduce the shrinkage rate and compression deformation rate;

[0070] (5) From the comparison data of Example 5 and Comparative Example 5, it can be seen that if a cross-linking agent is not used for micro-cross-linking, the melt strength of each polymer matrix is ​​low at high temperature and high pressure, and the cells are prone to rupture and merge, resulting in a significant increase in the hardness and density of the final foamed material. Therefore, it is impossible to prepare a foamed material that meets the performance requirements. This shows that an appropriate amount of cross-linking agent can not only increase the viscosity of the blend, but also facilitate the formation of a cross-linked network structure during high temperature and high pressure foaming in a supercritical autoclave, thereby controlling the pore size and reducing the shrinkage of the foamed sole;

[0071] (6) From the comparison data of Example 1, Example 2, Example 3, Example 4, Example 5, Example 6 and Comparative Example 6, Comparative Example 7, Comparative Example 8, it can be seen that: when the foaming formula, supercritical foaming temperature and pressure release rate are fixed; as the foaming pressure of the autoclave increases from 10MPa to 55MPa, the pressure holding time can be gradually shortened from 150 minutes to 20 minutes, indicating that increasing the foaming pressure of the autoclave is beneficial to rapidly increase the solubility of the gas in the polymer, accelerate the rate of bubble nucleation, and rapidly increase the number of bubble nucleations, greatly shortening the pressure holding time and greatly improving production efficiency. For mass production efficiency, the preferred foaming pressure of the autoclave in the present invention is 25~55MPa;

[0072] (7) From the comparison data of Example 5 and Comparative Examples 9 and 10, it can be seen that: when the foaming formula, the foaming pressure and the pressure relief speed of the autoclave are fixed, and the supercritical foaming temperature is adjusted, when the foaming temperature is set to 105°C, due to the low temperature, part of the polymer has not been completely melted, thus affecting the foaming effect, resulting in a decrease in the foaming ratio of the final foaming material, a high density and hardness, and a decrease in the resilience performance; and when the foaming temperature is set to 125°C, due to the high temperature, the bubble nucleation rate is too fast and too much, the bubbles of the final foaming material are too large, the shrinkage rate is greatly increased, and the properties such as compression deformation and tensile strength are deteriorated;

[0073] (8) From the comparison data of Example 5, Example 10, Example 11, Example 12 and Comparative Example 11, Comparative Example 12, Comparative Example 13, Comparative Example 14, Comparative Example 15, it can be seen that: when the foaming formula, the foaming pressure of the autoclave, and the supercritical foaming temperature are fixed, the pressure relief rate is adjusted from 0.3MPa / s to 5MPa / s. As the pressure relief rate increases, the pore diameter gradually decreases, from 1.7~2mm at 0.3MPa / s to less than 0.01mm at 5MPa / s. This shows that slowing down the pressure relief rate is conducive to the gradual growth of the pores, thereby preparing a foam material with a large-diameter pore appearance. The preferred pressure relief rate of the present invention is from 0.3MPa / s to 1.0MPa / s;

[0074] (9) From the comparison data of Example 5, Example 7, Example 8, and Example 9, it can be seen that: when the foaming formula is fixed, the foaming pressure of the autoclave is 50MPa / s and the pressure relief rate is 0.5MPa / s, and the foaming temperature is adjusted between 110℃ and 120℃, the holding time is shortened from 30 minutes to 20 minutes as the temperature increases. This shows that as the foaming temperature increases, the solubility of the supercritical gas in the polymer increases, the nucleation rate increases, and it is also beneficial to shorten the holding time. The properties of the final foamed material, such as the pore diameter, hardness, density, rebound rate, shrinkage rate, compression deformation, and tensile strength, are basically similar, so the preferred foaming temperature is 110℃~120℃;

[0075] (10) From the comparative data of Example 13, Example 14, Example 15 and Example 16, it can be seen that: by fixing the foaming pressure, pressure relief speed and foaming temperature of the autoclave, adjusting the foaming formula to 50-70 parts of ethylene-vinyl acetate, 10-20 parts of ethylene-methacrylic acid polymer, 5-15 parts of hydrogenated styrene-butadiene-styrene copolymer, 5-15 parts of poly(1,2-butadiene)-b-polyethylene oxide copolymer, 3-6 parts of carboxyl polystyrene microspheres, 4-8 parts of polyethylene micropowder with ultra-high molecular weight of 2 million to 3 million, 4-6 parts of polyisobutylene with medium molecular weight of 45,000 to 65,000, and 0.3-0.5 parts of cross-linking agent, it is possible to obtain a foam that meets the requirements of macroporous appearance and various The foaming materials with the performance requirements are explained, which show that the flexibility / resilience / compressibility / strength of the foamed soles are improved by using poly (1,2-butadiene) -b-polyethylene oxide copolymer; the strength of the blend in the molten state and the supporting pore strength are enhanced by using ethylene-methacrylic acid polymers; the ultra-high molecular weight polyethylene micropowder is effectively dispersed in the matrix by carboxyl polystyrene microspheres and the strength of the large-pore pores is enhanced. Finally, medium molecular weight polyisobutylene and micro-crosslinking are selected to further enhance the viscosity and strength of the matrix and effectively lock the gas, which can not only meet the consumers' demand for light, soft and elastic physical properties, but also effectively prevent the shrinkage of the soles under the appearance of large pores, thereby improving the product yield and the stability and safety of mass production.

[0076] It can be seen from the above embodiments that the present invention obtains a shrinkage-resistant macroporous ultra-light soft elastic supercritical foaming sole material by controlling the type and amount of raw materials and adopting high-pressure supercritical foaming and slow pressure release method; its density is 0.13±0.02g / cm 3 , hardness is 43±3C, rebound rate ≥68%, compression deformation ≤35%, pore diameter 0.5~2mm, and shrinkage rate ≤2.0%.

[0077] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A shrinkage-resistant macroporous ultralight soft elastic supercritical foaming sole material, comprising the following raw materials in parts by weight: 50-70 parts of ethylene-vinyl acetate, 10-20 parts of ethylene-methacrylic acid polymer, 5-15 parts of hydrogenated styrene-butadiene-styrene copolymer, 5-15 parts of poly(1,2-butadiene)-b-polyethylene oxide copolymer, 3-6 parts of carboxyl polystyrene microspheres, 4-8 parts of polyethylene micropowder with a molecular weight of 2 million to 3 million, 4-6 parts of polyisobutylene with a molecular weight of 45,000 to 65,000, 0.3-0.5 parts of peroxide crosslinking agent, and 1 part of lubricant.

2. The shrinkage-resistant macroporous ultralight soft elastic supercritical foaming sole material according to claim 1, characterized in that: The VA content of ethylene-vinyl acetate is 18~30mol%; The methacrylic acid content in the ethylene-methacrylic acid polymer is 5-15 mol%; The styrene content in the hydrogenated styrene-butadiene-styrene copolymer is 10-30 mol%; The polyethylene oxide content in the poly(1,2-butadiene)-b-polyethylene oxide copolymer is 5-10 mol%; The carboxyl content in the carboxyl polystyrene microspheres is 1-3 mol%.

3. The shrinkage-resistant macroporous ultralight soft elastic supercritical foaming sole material according to claim 1, characterized in that: The peroxide crosslinking agent is dicumyl peroxide and / or 1,4-di-tert-butyl peroxycumene; The lubricant is selected from stearic acid.

4. A method for preparing the shrinkage-resistant macroporous ultralight soft elastic supercritical foaming sole material according to any one of claims 1 to 3, comprising the following steps: The crosslinking agent and the lubricant are mixed to obtain a first group of materials; polyethylene micropowder with a molecular weight of 2 million to 3 million, carboxyl polystyrene microspheres and polyisobutylene with a molecular weight of 45,000 to 65,000 are mixed to obtain a second group of materials; ethylene-vinyl acetate, ethylene-methacrylic acid polymer, hydrogenated styrene-butadiene-styrene copolymer and poly (1,2-butadiene) - b-polyethylene oxide copolymer are mixed to obtain a third group of materials; The third group of materials is heated to 80-85°C and then mixed with the second group of materials; the temperature is further heated to 90-95°C and then mixed with the first group of materials, and the temperature is raised to 100-110°C to obtain a mixed material; granulating the mixed material to obtain granules; Injection-molding the pellets once to obtain a rough blank; Allowing the rough blank to stand for supercritical foaming to obtain a foamed sole; The foamed sole is allowed to stand for molding and then cooled to obtain a shrinkage-resistant macroporous ultralight soft-elastic supercritical foamed sole material.

5. The preparation method according to claim 4, characterized in that: The temperatures of the first zone, the second zone, the third zone and the fourth zone used in the granulation are adjusted to 75°C, 80°C, 85°C and 90°C respectively; The screw speed used for granulation is 40~50rpm, and the cutting speed is 15~20rpm.

6. The preparation method according to claim 4, characterized in that: During one injection, the temperatures of the first, second, third and fourth feeding zones are adjusted to 84°C, 86°C, 88°C and 90°C respectively; the injection pressure is 90(±5)-90(±5)-90(±5)-90(±5)bar; the vacuuming time is 80±20 seconds; The upper and lower mold plate temperatures of the mold used for molding are 175±5℃ and 175±5℃ respectively; The time for one shot is 150±20 seconds, and the vulcanization time is 450±30 seconds.

7. The preparation method according to claim 4, characterized in that: The rough embryo is left to stand for 12 to 24 hours. The pressure of supercritical foaming is 25~55MPa, the temperature is 115±5℃, and the pressure is released after keeping the temperature and pressure for 20~60min. The pressure release rate is 0.3~1MPa / s.

8. The preparation method according to claim 4, characterized in that: The foamed sole is left to stand for 72-96 hours before molding; The molding temperature is 165±5℃ and the molding time is 750±30s.

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