A lightweight, highly elastic modified EVA foam material, its preparation method and application

Abstract

This invention discloses a lightweight, highly elastic modified EVA foam material, comprising the following components in parts by weight: 50-90 parts of ethylene-vinyl acetate copolymer, 10-50 parts of branched polyolefin elastomer, 2-5 parts of foaming agent, 0.5-2 parts of foaming aid, 0.5-2 parts of crosslinking agent, 0.6-3 parts of lubricant, 1-30 parts of filler, and 5-10 parts of compatibilizer. The branched polyolefin elastomer has a long and short branched chain structure, a weight-average molecular weight of 20,000-8,000,000 g / mol, a degree of branching of 50-120 / 1000°C, and a melt index of 0.1-20 g / 10 min at 190°C and a load of 2.16 kg. This invention uses light olefin raw materials to increase the branching degree of the elastomer, thereby improving its toughening performance. Combined with a composite compatibilizer, it improves the compatibility of the melt and further enhances the toughening effect of the branched polyolefin elastomer. It significantly improves the room temperature and low temperature elasticity of the foamed material, thereby improving the comfort and durability of the shoe sole. The hardness change of the foamed material at low temperatures is significantly reduced, making it of great application and promotion value.

Description

Technical Field

[0001] This invention belongs to the field of polymer foaming materials, and in particular relates to a lightweight, highly elastic modified EVA foaming material, its preparation method, and its application. Background Technology

[0002] Athletic shoes, encompassing various recreational and professional competitive sports footwear, protect the feet and enhance athletic performance to some extent. The structure of an athletic shoe includes a textile upper, insole, midsole, and outsole. The upper covers the foot, providing comfort, breathability, and a distinctive appearance. The outsole primarily functions to prevent slipping and provide durability. The midsole, the core of the athletic shoe, is technologically advanced, providing stability, cushioning, and rebound during exercise, absorbing impact and providing energy return.

[0003] Current midsole foam substrates include Peba nylon elastomer (Polyeher block amide), TPEE thermoplastic polyester elastomers, TPU thermoplastic polyurethane elastomers, and EVA (Ethylene vinyl acetate). Among these, TPU-based supercritical foam midsole materials were jointly developed by Adidas and BASF. They possess superior performance characteristics, high resilience, and good durability, but their high density and high price result in a current market share of approximately 5%. Pebax nylon elastomers offer the highest resilience (greater than 80%) and good impact resistance, but currently only Arkema can produce them, resulting in low production volumes, limited product ranges, and high prices, limiting their market share to professional athletic shoes. TPEE thermoplastic polyester elastomers offer high tensile strength, low-temperature impact resistance, tear resistance, durability, and high resilience; however, they are expensive and, as a relatively new material in footwear, have a small market share. EVA-based foam materials are soft and cost-effective, and currently account for more than 90% of the market. However, their cushioning ability is weak, and their resilience is relatively low, about 40-50%. Furthermore, the soles tend to harden after repeated use. Therefore, developing modified EVA midsole materials has strong practical significance and a promising market prospect.

[0004] Currently, EVA midsole material modifiers include POE (Polyolefin elastomer), EPDM (Ethylene Propylene Diene Monomer), and SEBS (Styrene Ethylene Butylene Styrene). Compared to EPDM, POE is available in granular form, eliminating the need for premixing block rubber. POE also offers good processability, excellent mechanical properties, and good weather resistance. Compared to SEBS, POE exhibits lower thermal compression deformation and lower density.

[0005] POE-modified EVA foam materials can be produced using various foaming processes, including compression molding chemical foaming, cross-linking injection foaming, and supercritical foaming. The performance of foamed products is strongly correlated with the formulation and foaming process parameters. Deng Fuquan et al. (Functional Materials 4 (43), 2012, 508-511) explored the influence of the dosage of foaming agent azodicarbonamide (AC), cross-linking agent dicumyl peroxide (DCP), talc, etc., on the performance of POE / EVA composite foam materials. Cheng Bo et al. (Plastics 41 (4), 2012, 52-55) used chemical foaming to study the influence of POE on the foaming behavior and mechanical properties of EVA foam materials. The results showed that with the increase of POE content, on the one hand, the elasticity of the foam material increased and the compression set decreased, but the tensile and tear strength decreased; on the other hand, the cell diameter decreased and the cell density increased. With the increase of POE-g-MAH content, the tensile, tear strength and abrasion resistance of the foamed material are significantly improved on the one hand, and the cell diameter is further reduced and the cell density is increased on the other hand. Liu Wei (Plastics 48(5), 2019, 54-57) prepared POE / EVA composite foamed material by supercritical CO2 assisted foaming. By changing the ratio of POE / EVA, the effects of different ratios of POE / EVA on the macroscopic expansion ratio and microstructure under the same foaming temperature and saturation pressure were studied. The results showed that when the mass fraction of EVA was 40%, the apparent density of the composite foamed material at a saturation pressure of 10 MPa was 0.169 g / cm3, the expansion ratio was 5.3; the cell size was 56 μm, and the cell density was 4.27 × 10⁻⁶. 6 pcs / cm 3 Its cell microstructure is good and the size is uniform. However, the resilience of EVA foam material is still relatively low. It is necessary to further improve its resilience and reduce its compression set to improve the durability of the material.

[0006] In addition, traditional EVA materials have a high glass transition temperature, and their hardness changes greatly at low temperatures, resulting in a significant reduction in resilience and a deterioration in cushioning performance. This leads to poor comfort of the sole in low-temperature environments, and the sole may even break easily, seriously affecting the consumer experience.

[0007] Therefore, it is necessary to improve the low-temperature resilience of EVA foam materials, reduce the hardness change at low temperatures, and provide a low-temperature resistant, lightweight, and highly elastic modified EVA foam material. Summary of the Invention

[0008] In view of this, the purpose of this invention is to overcome the defects and deficiencies in the prior art and provide a lightweight, highly elastic modified EVA foam material modified with branched polyolefin elastomer. The resilience is significantly improved compared with existing materials, the compression set is reduced, and the hardness changes little at low temperatures, making it suitable for cold environments.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0010] A lightweight, highly elastic modified EVA foam material, comprising the following components in parts by weight:

[0011] 50-90 parts of ethylene-vinyl acetate copolymer

[0012] 10-50 parts of branched polyolefin elastomer

[0013] 2-5 parts of foaming agent

[0014] Foaming agent 0.5~2 parts

[0015] Crosslinking agent 0.5~2 parts

[0016] Lubricant 0.6~3 parts

[0017] 1-30 parts of filler

[0018] 5-10 parts compatibilizer.

[0019] The branched polyolefin elastomer has a long and short branched chain structure, a weight-average molecular weight of 20,000-8,000,000 g / mol, a branching degree of 50-120 / 1000 C, and a melt index of 0.1-20 g / 10 min at 190 °C and a load of 2.16 kg.

[0020] Furthermore, the branched polyolefin elastomer is one or more combinations of branched elastomers obtained by solution polymerization of ethylene or ethylene and C3-C5 olefins as raw materials, and the branched polyolefin elastomer is preferably a single ethylene branched polymerization product.

[0021] Furthermore, the branched polyolefin elastomer preferably has a weight-average molecular weight of 50,000 to 500,000 g / mol, a branching degree of 60 to 90 / 1000°C, and a melt index of 0.5 to 10 g / 10 min at 190°C and a load of 2.16 kg.

[0022] Furthermore, the melting point of the branched polyolefin elastomer is in the range of 10°C to 90°C, preferably 10°C to 80°C.

[0023] The crystallinity is 1-20%, preferably 1-10%.

[0024] The preferred lightweight, highly elastic modified EVA foam material comprises the following components in parts by weight:

[0025] 50-70 parts of ethylene-vinyl acetate copolymer

[0026] 30-50 parts of branched polyolefin elastomer

[0027] 2-5 parts of foaming agent

[0028] Foaming agent 0.5~2 parts

[0029] Crosslinking agent 0.5~2 parts

[0030] Lubricant 0.6~3 parts

[0031] 1-10 parts of filler

[0032] 5-10 parts compatibilizer.

[0033] In this invention, the branched polyolefin elastomer can be prepared by the following method:

[0034] Organic solvent, catalyst, and co-catalyst are added to the reactor, the temperature is controlled at 10~100℃, ethylene is introduced into the reactor to carry out the polymerization reaction, the ethylene pressure is 0.1~5MPa, the reaction time is 10~90min, after the reaction is completed, the reaction solution is added to acidified ethanol to terminate the reaction and a solid precipitate is obtained. After washing and drying the solid precipitate, branched polyolefin elastomer is obtained.

[0035] The catalyst is a post-transition metal catalyst.

[0036] The post-transition metal catalyst is a metal complex olefin polymerization catalyst with post-transition metal atoms such as nickel(II), palladium(II), iron(II), cobalt(II), and ruthenium(II) as the active center. The chelating ligand is selected from types such as N^N, P^N, N^O, and P^O. Various post-transition metal catalysts disclosed in the prior art that can catalyze the polymerization of ethylene to prepare branched polyolefins and can obtain the branched polyolefin material parameters specified in this invention are all applicable to this invention.

[0037] Furthermore, the post-transition metal catalyst is a Brookhart catalyst; such as a (α-diimine) nickel / palladium complex; more preferably, an α-diimine nickel catalyst.

[0038] The co-catalyst is one or more of diethylaluminum chloride, diethylaluminum chloride, methylaluminoxane, polymethylaluminoxane, and sesquiethylaluminum chloride (EASC), preferably methylaluminoxane.

[0039] The molar ratio of Al in the co-catalyst to Ni in the α-diimine nickel catalyst is 50~1000:1.

[0040] The polymerization reaction is carried out in an organic solvent, which is one or more of dichloromethane, toluene, and n-hexane.

[0041] In this invention, a branched structure with tunable long and short branch structures is obtained through long-chain branching polymerization in solution using a post-transition metal catalyst. Since this invention involves in-situ polymerization of ethylene, the branches contain both long and short chains, resulting in high branching degree. The long branches also increase the crosslinking points, leading to lower crystallinity and improved elastomer properties.

[0042] Furthermore, the compatibilizer is a mixture of maleic anhydride-grafted EVA and maleic anhydride-grafted POE in a mass ratio of 1:0.1~2.

[0043] In this invention, the VA content in the ethylene-vinyl acetate copolymer is 12-30 mol%.

[0044] Furthermore, in this invention, the foaming agent is AC foaming agent (azodicarbonamide).

[0045] The foaming agent is nano-zinc oxide or nano-zinc acetate. Different particle sizes and distributions of the foaming agent affect its decomposition temperature and gas production. Nano-zinc oxide is commonly used.

[0046] The crosslinking agent is dicumyl peroxide (DCP) or bis-tert-butylperoxide (BIPB). BIPB is preferred. BIPB has a decomposition temperature 10°C higher than DCP, requires approximately 2 / 3 the amount of DCP, and produces odorless foamed products, meeting increasingly stringent environmental protection requirements.

[0047] The lubricant is stearic acid.

[0048] The filler is calcium carbonate or talc.

[0049] Lightweight and highly elastic modified EVA foam material is made by mixing and extruding various raw materials according to a certain ratio, forming them into sheets, and then molding and foaming them.

[0050] This invention also provides a method for preparing the aforementioned lightweight, highly elastic modified EVA foam material, the method comprising:

[0051] Ethylene-vinyl acetate copolymer, branched polyolefin elastomer, and compatibilizer are blended in a mixer at 105-120°C. Then, lubricant, foaming accelerator, and filler are added, and the mixture is cooled to 95-105°C. Foaming agent and crosslinking agent are added, and the mixture is blended. The mixture is then pressed into sheets using a two-roll mill at 85-90°C to obtain sheets. After being cut to appropriate sizes, the sheets are molded and foamed in a flat vulcanizing apparatus to obtain the lightweight, high-elasticity modified EVA foam material.

[0052] The preferred blending time for the ethylene-vinyl acetate copolymer, branched polyolefin elastomer, and compatibilizer is 2-8 minutes, and the internal mixer speed is 40-50 r / min.

[0053] After adding lubricant and foaming accelerator, the preferred mixing time is 2-8 minutes.

[0054] After adding the foaming agent and crosslinking agent, the preferred mixing time is 5-12 minutes.

[0055] Generally speaking, internal mixing has a better effect, while open milling makes it easier to control the melt temperature. The melt blending method can be either internal mixing or open milling, or POE and EVA can be internally mixed first, and then other components can be blended in an open mill and sheeted out.

[0056] The thickness of the sheet is preferably 1 to 15 mm.

[0057] The sheet material is preferably left to stand for 24-48 hours before molding and foaming.

[0058] In the method described above, the molding foaming temperature is generally 180-200 ℃, the pressure is 10-15 MPa, and the time is 10-12 minutes.

[0059] After molding and foaming, the material is cooled and set, and then left at room temperature for 24-48 hours to obtain the lightweight, high-elasticity modified EVA foam material.

[0060] In this invention, the branched polyolefin elastomer has a high degree of branching, maintaining a low melting temperature and crystallinity even with increased molecular weight, and exhibiting excellent toughening properties at both room temperature and low temperatures. Furthermore, this invention combines maleic anhydride-grafted EVA and maleic anhydride-grafted POE as compatibilizers. Maleic anhydride-grafted EVA and EVA have good compatibility, as do maleic anhydride-grafted POE and POE. Moreover, both contain maleic anhydride grafts, resulting in similar polarities and excellent compatibility. This improves the compatibility of the overall EVA and POE melt, further enhancing the toughening properties of the branched polyolefin elastomer. The resilience at room temperature can reach 60%, and the compression set can be as low as 15%. In addition, the branched polyolefin elastomer has large molecular chain entanglement and a low glass transition temperature, thus significantly increasing the low-temperature toughness of the foamed material, reducing hardness changes at low temperatures, and improving elasticity in low-temperature environments. The foamed material of this application still maintains a resilience of over 30% at -15°C, with a hardness change of less than 10.

[0061] The lightweight, highly elastic modified EVA foam material of this invention can be used to prepare highly elastic and cold-resistant shoe soles, which are particularly suitable for cold environments.

[0062] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0063] This invention adds branched polyolefin elastomers with long and short branched chain structures as toughening agents, which can effectively improve the toughening efficiency of the matrix and the filler loading effect, while maintaining good processing stability of the composite material and reducing the defect rate.

[0064] This invention uses light olefin raw materials and solves the technical problem that the toughening performance of ethylene-light olefin copolymers as elastomers is not as good as that of ethylene-octene copolymers by increasing the branching degree of the elastomer. Compared with traditional POE ethylene-octene copolymers, using light olefins as raw materials reduces raw material costs and improves economic efficiency.

[0065] This invention employs a composite compatibilizer, which improves the compatibility of the melt, further enhances the toughening effect of branched polyolefin elastomers, significantly improves the room temperature and low temperature elasticity of foamed materials, enhances the comfort and durability of shoe soles, and significantly reduces the hardness change of foamed materials at low temperatures, thereby increasing the temperature range of the material and making it of great application and promotion value. Detailed Implementation

[0066] Unless otherwise defined, the technical terms used in the following embodiments have the same meanings as commonly understood by those skilled in the art to which this invention pertains. Unless otherwise specified, the experimental reagents used in the following embodiments are conventional biochemical reagents; and the experimental methods described are conventional methods.

[0067] The invention will be described in detail below with reference to specific embodiments.

[0068] Example 1

[0069] In 100 mL of n-hexane solvent, α-diimine nickel catalyst (2 μmol) and sesquiethyl aluminum chloride (2 mmol, Al:Ni molar ratio = 1000) were added. The temperature was controlled at 20-80 °C, and ethylene was introduced to carry out the polymerization reaction. Timing was started after the ethylene pressure stabilized. The ethylene pressure was 0.1-5 MPa, and the reaction time was 10-70 min. After the reaction was completed, the reaction solution was added to 200 mL of acidified ethanol, stirred for 10 h, filtered, washed with ethanol, and vacuum dried to obtain the branched polyolefin material.

[0070] The α-diimine nickel catalyst used in this embodiment was prepared according to the following reaction formula:

[0071]

[0072] In Formula I, R1 is a phenyl or a substituted phenyl, wherein the substituted phenyl is p-aminophenyl, p-methylphenyl, p-methoxyphenyl or p-tert-butylphenyl;

[0073] R2 is a phenyl or a substituted phenyl, wherein the substituted phenyl is p-methylphenyl, p-methoxyphenyl, p-fluorophenyl or p-tert-butylphenyl;

[0074] R3 is a phenyl or a substituted phenyl, wherein the substituted phenyl is p-methoxyphenyl, p-fluorophenyl or p-tert-butylphenyl;

[0075] In toluene solvent, aniline compounds of formula II and dimethyl ethyl ketone are mixed at a molar ratio of 2-2.2:1 and reacted at 60-90°C for 20-24 hours under the catalytic action of p-toluenesulfonic acid. Then, the mixture is separated by water separation and refluxed for 2-3 days to obtain the diimine ligand compound of formula III.

[0076] The diimine ligand compound shown in Formula III and (DME)NiBr2 were mixed at a molar ratio of 1:0.5~2, dissolved in dichloroethane solvent, and stirred under nitrogen protection for 10~24 h to prepare the α-diimine nickel catalyst shown in Formula I.

[0077] In this embodiment, R1, R2, and R3 are all α-diimine nickel catalysts for the preparation of p-tert-butylphenyl, and the specific method is as follows:

[0078] 2,4-Bis(p-tert-butylphenyl)-6-di-p-tert-butylphenylmethylaniline (4 mmol) and dimethylbutane (2 mmol) were dissolved in 100 mL of toluene, and 10 mg of p-toluenesulfonic acid (PTSA) was added. The mixture was stirred and refluxed at 80 °C for 24 h. Then, the mixture was refluxed using a Dean-Stark water separator for 3 days. After the reaction solution was cooled to room temperature, part of the solvent was evaporated under reduced pressure, and a solid precipitated. 400 mL of methanol was added to precipitate the solid product. The product was filtered, and the filter cake was washed with methanol and dried to obtain the diimine ligand compound in 81% yield.

[0079] Under nitrogen protection, a mixture of diimine ligand compound and (DME)NiBr2 (0.2 mmol) and a diimine ligand compound (0.20 mmol) was dissolved in 5 mL of dichloromethane. The mixture was stirred at room temperature for 20 h. After removing the dichloromethane under reduced pressure, diethyl ether was added, and a red solid precipitated. The precipitate was filtered, washed with diethyl ether, and dried to obtain the α-diimine nickel catalyst. The yield was approximately 85%.

[0080] In 100 mL of n-hexane solvent, α-diimine nickel catalyst (2 μmol) and methylaluminoxane (2 mmol, Al:Ni molar ratio = 1000) were added. The temperature was controlled at 20-80 °C, and ethylene was introduced to carry out the polymerization reaction. Timing was started after the ethylene pressure stabilized. The ethylene pressure was 0.1-5 MPa, and the reaction time was 10-70 min. After the reaction was completed, the reaction solution was added to 200 mL of acidified ethanol, stirred for 10 h, filtered, washed with ethanol, and dried under vacuum to obtain branched polyolefin elastomer.

[0081] Using ethylene as raw material, n-hexane as solvent, α-diimine nickel catalyst as catalyst, and methylaluminoxane as co-catalyst, branched elastomers A (reaction temperature 30℃, pressure 0.5MPa, melt index 1.0g / 10min, molecular weight 350,000, branching degree 50 / 1000C, crystallinity 9%, melting point 72℃), B (reaction temperature 45℃, pressure 0.5MPa, melt index 5g / 10min, molecular weight 200,000, branching degree 70 / 1000C, melting point 61℃, crystallinity 5%), and C (reaction temperature 60℃, pressure 1.5MPa, melt index 0.2 g / 10min, molecular weight 520,000, branching degree 115 / 1000C, melting point 10℃, crystallinity 1%) were prepared by adjusting the ratio of main and co-catalysts, process, and product compounding combination.

[0082] Using ethylene and octene as raw materials, alkanes as solvents, and transition metal complex catalysts, branched elastomer D (melt index 1.1 g / 10 min, molecular weight 250,000, branching degree 45 / 1000C, crystallinity 15%, melting point 65℃) was prepared by adjusting the type, ratio, and process of the main catalyst and co-catalyst.

[0083] The EVA used in the examples is Elvax 265: VA molar content is 28%, DuPont.

[0084] The foaming agent is AC foaming agent, the foaming aid is nano zinc oxide, and the crosslinking agent is BIPB. The lubricant is stearic acid. The filler is talc. The compatibilizer is a mixture of EVA-g-MAH and POE-g-MAH in a mass ratio of 1:0.5.

[0085] The formulations for experiments No. 1-4 are shown in Table 1 below:

[0086]

[0087] The process for preparing foamed materials is as follows:

[0088] POE, EVA, and compatibilizer were internally mixed using an RM-200C mixing torque rheometer with the following mixing parameters: temperature 105-120 ℃, rotation speed 40-50 r / s, and mixing time 8 min. Then, stearic acid, nano zinc oxide, and talc were added and mixed for 5 min. The mixture was then cooled to 95-100 ℃, and AC foaming agent and BIPB were added and mixed for 8 min. After internal mixing, the colloid was transferred to an HTR-120 two-roll mill for open melting. The open melting parameters were: two-roll temperature 85-90 ℃, rotation speed 20-30 r / s, and open melting time 5-10 min. The blend system was then formed into 3 mm thick sheets, which were left to stand for at least one day after extrusion.

[0089] Cut the sheet to the appropriate size, place it in a custom foaming mold, put it into a flat vulcanizing machine, control the mold temperature at 180℃, the pressure at 12Mpa, and the time at 10 minutes. After cooling and setting, test it after placing it at room temperature for 3-5 days.

[0090] Performance characterization:

[0091] Resilience: The HMLQ falling ball rebound tester was used. The test standard was GB / T 6670-2008, "Determination of Resilience Performance of Flexible Foam Polymer Materials by Falling Ball Method." The procedure is as follows:

[0092] 1. Cut the product into rectangles with dimensions of 100mm x 100mm and a height of 50mm, with flat top and bottom surfaces;

[0093] 2. Place the sample on the reference surface and adjust it so that the distance from the bottom of the steel ball to the sample surface from the fixed position is 460 mm. Ensure that there is light contact between the tube and the sample without causing any visible pressure.

[0094] 3. Place the steel ball on the release device, then release the ball and record the integer value of the maximum rebound height. If the ball hits the inner wall of the tube during its fall or rebound, the test result is invalid. This mainly occurs because the tube is not perpendicular or the sample surface is uneven. To reduce visual error, the tester's line of sight should be horizontally aligned with the rebound reading scale line on the tube. Trial measurements are necessary to verify the accuracy of the visual level.

[0095] 4. Each sample must yield at least three valid rebound values ​​within one minute;

[0096] 5. The results represent three values ​​measured for each sample. If any value exceeds 20% (one-fifth) of the median, two more tests are conducted to determine the median of the five values. The median of the three samples is then taken as the rebound rate of the sample.

[0097] Compression set: Tested using an ASTM D3574 compression set tester; Test standard: GB / T 6669-2008 Determination of compression set of flexible foam polymer materials; Test procedure:

[0098] The steps are as follows:

[0099] 1. The sample has flat top and bottom surfaces, a length and width of 50 mm, and a thickness of 25 mm;

[0100] 2. Measure the initial thickness H0 of the sample;

[0101] 3. Place the sample between the two plates of the device, compress the sample thickness by 50%, and maintain this state.

[0102] 4. Within 15 minutes, place the compressed sample or stacked sample in an oven at 70 °C and keep it for 22 hours;

[0103] 5. Remove the apparatus from the oven and take out the sample from the apparatus within 1 minute. Place it on the surface of a low thermal conductivity object (such as a wooden board). The surface temperature of the object should be the laboratory temperature.

[0104] 6. Measure the final thickness H of the specimen. Permanent compression deformation: deformation / initial thickness.

[0105] Hardness: The MC010-LX-C microporous material hardness tester was used; the test was conducted according to HG-T 2489-2007, the test method for testing the hardness of microporous materials for footwear. Test steps:

[0106] 1. Raise the sample platform so that the indenter of the hardness tester is in full contact with the sample platform under the action of the fixed weight. At this time, the reading should be 100. When the indenter is completely removed from the sample platform, the reading should be 0.

[0107] 2. Place the sample on the sample platform, ensuring the indenter is at least 10 mm away from the edge of the sample. Slowly raise the platform and smoothly and without impact press the hardness tester against the sample under the specified weight. Once the indenter is in complete contact with the sample and subjected to the test load, take the reading within 1 second.

[0108] 3. Each measurement point is only allowed to be measured once, and there must be no fewer than three measurement points at different locations on the same sample that are more than 10 mm apart;

[0109] Tear strength: Tested using a CMT5000 tensile testing machine; according to GB / T 10808-2006, determination of tear strength of porous polymer elastic materials; test procedure:

[0110] 1. The sample thickness shall not be less than 24 mm;

[0111] 2. At least 5 test samples must be provided, and samples should generally not be used for testing within 72 hours of production;

[0112] 3. The clamp moving speed is 50mm / min to 500mm / min.

[0113] 4. Measure the thickness of the sample;

[0114] 5. Carefully unfold the specimen, place it on the clamp of the testing machine, adjust it to the appropriate position, and apply force to the specimen;

[0115] 6. During the tearing process, if it is necessary to keep the cut of the sample in the center, a sharp tool can be used for auxiliary cutting, such as a single-edged razor.

[0116] 7. When the sample is torn to 25 mm ± 5 mm, record the maximum force value on the display screen or dial, and issue a report based on the tear strength of three samples.

[0117] Density: Determination of apparent density of foamed plastics and rubber in accordance with GB / T 6343-2009.

[0118] Expansion ratio: Density before foaming / Density after foaming.

[0119] The performance test results of EVA foam materials obtained using four different elasticity regimes are shown in Table 2:

[0120]

[0121] Experimental results show that although the degree of branching of the elastomer used in experiments NO 1, 2, 3 and 4 is different, it has little effect on the density and foaming ratio of the foamed material.

[0122] The elastomers of Experiment NO 1, 2, and 3 all had a higher degree of branching than those of Experiment NO 4. In terms of performance, Experiment NO 1, 2, and 3 showed significantly better room temperature and low temperature resilience than Experiment NO 4, with smaller compression set and less increase in hardness at low temperatures, indicating better low-temperature performance.

[0123] Furthermore, experiments NO 1, 2, and 3 showed that the increased branching degree of the elastomers resulted in a decrease in hardness at room temperature, but an increase in resilience. The increase in hardness at low temperatures was reduced, indicating that the increased branching degree is beneficial to improving the resilience and low-temperature performance of the foamed material.

[0124] The elastomer in Experiment NO 4 was an ethylene-octene copolymer, which had the lowest branching degree among the four elastomers. It is a commonly used POE elastomer. However, conventional POE elastomers have limited effect on improving the resilience of foamed materials. This invention, by adjusting the branching degree of the elastomer, found that increasing the branching degree to above 50 / 1000C significantly improved the resilience of the foamed material. It is speculated that this may be because the ethylene copolymer elastomer of this invention has long and short branches, and the side chains form a coiled and entangled structure, which has better toughness or elasticity.

[0125] Example 2

[0126] The formulations for experiments NO 5-8 are shown in Table 3 below. The preparation and testing steps are the same as in Example 1.

[0127]

[0128] The performance test results of EVA foam materials in experiments NO. 5-8 are shown in Table 4:

[0129]

[0130] Table 4 shows that Experiment No. 5, without the addition of a compatibilizer, exhibited poor melt compatibility, resulting in poor resilience, low-temperature performance, and strength. Experiments No. 6 and 7, however, added EVA-g-MAH and POE-g-MAH as single compatibilizers, respectively. EVA-g-MAH showed better compatibility with EVA, leading to higher toughening efficiency than POE-g-MAH in Experiment No. 7. Overall, Experiment No. 8, using a composite compatibilizer, showed a significant improvement in overall performance. This invention is the first to propose that composite compatibilizers are beneficial for improving the toughening efficiency of elastomers and enhancing the resilience and low-temperature performance of foamed materials.

[0131] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A lightweight, highly elastic modified EVA foam material, characterized in that, The components include the following parts by weight: 50-90 parts of ethylene-vinyl acetate copolymer 10-50 parts of branched polyolefin elastomer 2-5 parts of foaming agent Foaming agent 0.5~2 parts Crosslinking agent 0.5~2 parts Lubricant 0.6~3 parts 1-30 parts of filler 5-10 parts compatibilizer The branched polyolefin elastomer has a long and short branched chain structure, a weight-average molecular weight of 50,000 to 500,000 g / mol, a degree of branching of 50 to 120 / 1000 °C, and a melt index of 0.1 to 20 g / 10 min at 190 °C and a load of 2.16 kg. The branched polyolefin elastomer is a branched elastomer obtained by solution polymerization of ethylene. The compatibilizer is a mixture of maleic anhydride-grafted EVA and maleic anhydride-grafted POE in a mass ratio of 1:0.1~2.

2. The lightweight, highly elastic modified EVA foam material as described in claim 1, characterized in that... The branched polyolefin elastomer has a weight-average molecular weight of 50,000~500,000 g / mol, a branching degree of 60~90 / 1000°C, and a melt index of 0.5~10 g / 10 min at 190°C and a load of 2.16 kg.

3. The lightweight, highly elastic modified EVA foam material as described in claim 1, characterized in that... The branched polyolefin elastomer has a melting point in the range of 10℃ to 90℃ and a crystallinity in the range of 1-20%.

4. The lightweight, highly elastic modified EVA foam material as described in claim 1, characterized in that... The branched polyolefin elastomer is prepared by the following method: Organic solvent, catalyst, and co-catalyst are added to the reactor, the temperature is controlled at 10~100℃, ethylene is introduced into the reactor to carry out the polymerization reaction, the ethylene pressure is 0.1~5MPa, the reaction time is 10~90min, after the reaction is completed, the reaction solution is added to acidified ethanol to terminate the reaction and a solid precipitate is obtained. After washing and drying the solid precipitate, branched polyolefin elastomer is obtained. The catalyst is a post-transition metal catalyst.

5. The lightweight, highly elastic modified EVA foam material as described in claim 1, characterized in that... The foaming agent is AC foaming agent, the foaming aid is nano zinc oxide or nano zinc acetate; the crosslinking agent is dicumyl peroxide or bis-tert-butylperoxyisopropylbenzene; the lubricant is stearic acid; and the filler is calcium carbonate or talc.

6. The method for preparing the lightweight, highly elastic modified EVA foam material according to any one of claims 1 to 5, characterized in that... The method is as follows: Ethylene-vinyl acetate copolymer, branched polyolefin elastomer, and compatibilizer are blended in a mixer at 105-120°C. Then, lubricant, foaming accelerator, and filler are added, and the mixture is cooled to 95-105°C. Foaming agent and crosslinking agent are added, and the mixture is blended. The mixture is then pressed into sheets using a two-roll mill at 85-90°C to obtain sheets. After being cut to appropriate sizes, the sheets are molded and foamed in a flat vulcanizing apparatus to obtain the lightweight, high-elasticity modified EVA foam material.

7. The application of the lightweight, high-elasticity modified EVA foam material as described in any one of claims 1 to 5 in the preparation of high-elasticity, cold-resistant shoe soles.

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