TPR foaming material and preparation method thereof

Abstract

The invention discloses a TPR foam material and a preparation method thereof, and belongs to the field of elastic materials. The material comprises the following components: 25%-75% of an ethylene-propylene-diene terpolymer; 5%-40% of poly (butylene adipate); 2%-15% of nano silicon oxide with the particle size smaller than 50 nanometers; 0.5%-6% of a thermally stable coated azodicarbonamide foaming agent; 1%-12% of a foaming aid composed of a calcium magnesium organic acid salt and a nonionic surfactant; and 3%-18% of a plasticizer. The method comprises the following steps: S1, premixing under the conditions of 120 to 140 DEG C and 100 to 150 rpm; s2, mixing the foaming agent and the auxiliary agent for 10-15 minutes at 140-160 DEG C and 180-250 rpm (revolutions per minute); s3, foaming and forming in a mold head in a temperature zone of 130-165 DEG C; s4, cooling and shaping at the speed of 20-40 DEG C / min; the temperature areas of the extruder are set to be 130 DEG C, 135 DEG C, 150-160 DEG C and 165 DEG C in sequence. The method has the beneficial effects that the material prepared by the method is uniform in cell and stable in performance.

Description

Technical Field

[0001] The present invention relates to the field of elastic materials, and more particularly to a TPR foam material and a preparation method thereof. Background Art

[0002] Thermoplastic rubber (TPR) foam, combining the elasticity of rubber with the processability of thermoplastic materials, is widely used in footwear, shock absorption, sealing, and other fields. Early TPR foams were primarily based on SBS elastomers. While these elastomers offered ease of processing, they suffered from poor foaming stability and insufficient aging resistance. The subsequent introduction of blends such as SEBS and EPDM improved heat resistance and resilience, but the foaming process still faced challenges such as coarse cells, uneven structure, and dimensional instability.

[0003] With the increasing demand for refined materials, the industry is gradually introducing nanofillers, chemical cross-linking technology, and controlled foaming systems to improve cell refinement and structural uniformity. However, existing foaming agents often suffer from narrow decomposition temperature ranges, prone to premature decomposition during mixing, and a lack of coordinated design of additive system ratios, resulting in low foaming efficiency and large fluctuations in material properties. Furthermore, traditional fillers suffer from weak interfacial bonding, which affects mechanical properties. Summary of the Invention

[0004] The present invention aims to provide a TPR foam material and a method for its preparation to address the issues raised in the aforementioned background art. However, existing foaming agents often suffer from a narrow decomposition temperature range and are prone to premature decomposition during mixing. Furthermore, the additive system lacks a coordinated design, resulting in low foaming efficiency and large fluctuations in material properties. Furthermore, conventional fillers exhibit weak interfacial bonding, which impacts mechanical properties.

[0005] Technical solution: A TPR foam material, calculated by mass percentage, includes the following components: Ethylene-propylene-diene terpolymer 25% to 75%; thermoplastic polyester elastomer 5% to 40%, wherein the thermoplastic polyester elastomer is polybutylene adipate; nano-silica filler with a particle size less than 50 nanometers 2% to 15%; heat-stable coated azodicarbonamide foaming agent 0.5% to 6%; two-component foaming agent system 1% to 12%, including calcium magnesium organic acid salt and non-ionic surfactant; plasticizer 3% to 18%.

[0006] Preferably, the ethylene-propylene-diene terpolymer has a diene content of 4-8 wt % and a melt index of 1.5-4.0 g / 10 min.

[0007] Preferably, the ester content of the thermoplastic polyester elastomer is more than 85% of the total mass, and the melting point is 110-125°C.

[0008] Preferably, the nano-silicon oxide filler is prepared by a gas phase method, has a uniform particle size distribution, a maximum particle size of no more than 50 nanometers, and a BET specific surface area of ​​180 to 230 m 2 / g.

[0009] Preferably, the heat-stable coated azodicarbonamide foaming agent is polymer-coated, the coating layer thickness is 50-150 nanometers, and the thermal decomposition temperature range is 145-165°C.

[0010] Preferably, the mass of the calcium and magnesium organic acid salt in the two-component foaming auxiliary agent system accounts for 60% to 80% of the auxiliary agent system, and the HLB value of the non-ionic surfactant is 12-14.

[0011] Preferably, the method for preparing a TPR foam material comprises the following steps: S1. The ethylene-propylene-diene terpolymer, thermoplastic polyester elastomer, nano-silica filler and plasticizer were pre-mixed in a twin-screw extruder at 120-140 ° C and a speed of 100-150 rpm; S2. Add heat-stable coated azodicarbonamide foaming agent and two-component foaming agent system to the premix, increase the speed to 180-250rpm in the range of 140-160 ° C, and continue mixing for 10 to 15 minutes to ensure uniform dispersion of the components; S3 extruded the mixture, and foamed by die molding, the molding temperature gradient was set to 130-165 ℃; S4. After foaming, the product is cooled and set at 20-40°C / min.

[0012] Preferably, the temperatures of different sections of the barrel of the twin-screw extruder are set as follows: 130° C. in the mixing zone, 135° C. in the feeding zone, 150-160° C. in the foaming zone, and 165° C. in the die zone, so as to control the thermal decomposition curve of the foaming agent.

[0013] Preferably, the two-component foaming agent system is prepared in advance, and the calcium magnesium organic acid salt and the non-ionic surfactant are mixed uniformly in a weight ratio of 3:1 and then dried to ensure that the particle size distribution of the agent is 5-20 microns.

[0014] Preferably, the nano-silica filler is obtained by a process combining spray drying and air flow pulverization to ensure the filler's dispersibility and its interface bonding strength with the elastomer matrix.

[0015] Compared with the prior art, the advantages of the present invention are: (1) Improve the control accuracy of thermal decomposition temperature to avoid premature decomposition of traditional foaming agents during the mixing process; achieve a more uniform and stable foam structure and improve the dimensional consistency of the foamed product.

[0016] (2) By compounding calcium magnesium organic acid salts with non-ionic surfactants, the foaming efficiency and the degree of cell refinement can be improved; the auxiliary agent ratio and the HLB value of the surfactant can be clearly controlled to effectively improve the cell distribution and density.

[0017] (3) Improve the interfacial bonding force between TPR matrix and filler, enhance mechanical properties and thermal stability; the powder is prepared by gas phase method + spray drying + air flow crushing to improve dispersibility and pore uniformity.

[0018] (4) Finely set the temperature gradient and screw speed of each zone to enhance the mixing and dispersion process; ensure that different components are fully integrated and the foaming agent is decomposed within the specified temperature range to improve molding consistency.

[0019] (5) By setting a cooling rate of 20–40°C / min, the foam collapse and shrinkage are suppressed; the dimensional stability and surface quality of the final foamed material are improved.

[0020] (6) Combining the high flexibility of thermoplastic elastomers with the ductility of biodegradable polyesters to achieve better overall performance; improving the shortcomings of traditional TPR materials in low temperature resistance and fatigue resistance.

[0021] (7) Through full-link control of parameters such as particle size, melt index, melting point, specific surface area, and additive particle size, the scientificity and repeatability of the formula are improved; and the problem of unstable performance between material batches in existing technologies is overcome. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a schematic diagram of the overall process of a method for preparing a TPR foam material according to the present invention; DETAILED DESCRIPTION

[0023] Example Examples 1-4 Example 1. A TPR foam material, comprising the following components by mass percentage: Ethylene-propylene-diene terpolymer 25% to 75%; thermoplastic polyester elastomer 5% to 40%, thermoplastic polyester elastomer is polybutylene adipate; nano-silica filler with particle size less than 50 nanometers 2% to 15%; heat-stable coated azodicarbonamide foaming agent 0.5% to 6%; two-component foaming agent system 1% to 12%, including calcium magnesium organic acid salt and non-ionic surfactant; plasticizer 3% to 18%.

[0024] The diene content of the ethylene-propylene-diene terpolymer is 4-8wt%, and the melt index is 1.5-4.0g / 10min.

[0025] The ester content of the thermoplastic polyester elastomer accounts for more than 85% of the total mass, and the melting point is 110-125°C.

[0026] Nano-silica filler is prepared by gas phase method, with uniform particle size distribution, the maximum particle size does not exceed 50 nanometers, and the BET specific surface area is 180-230m 2 / g.

[0027] The heat-stable coated azodicarbonamide foaming agent is processed by polymer coating, the coating layer thickness is 50-150 nanometers, and the thermal decomposition temperature range is 145-165°C.

[0028] The mass of calcium and magnesium organic acid salts in the two-component foaming additive system accounts for 60% to 80% of the additive system, and the HLB value of the non-ionic surfactant is 12-14.

[0029] A method for preparing a TPR foam material comprises the following steps: S1. The ethylene-propylene-diene terpolymer, thermoplastic polyester elastomer, nano-silica filler and plasticizer were pre-mixed in a twin-screw extruder at 120-140 ° C and a speed of 100-150 rpm; S2. Add heat-stable coated azodicarbonamide foaming agent and two-component foaming agent system to the premix, increase the speed to 180-250rpm in the range of 140-160 ° C, and continue mixing for 10 to 15 minutes to ensure uniform dispersion of the components; S3 extruded the mixture, and foamed by die molding, the molding temperature gradient was set to 130-165 ℃; S4. After foaming, the product is cooled and set at 20-40°C / min.

[0030] The temperatures of different sections of the barrel of the twin-screw extruder were set as follows: 130°C in the mixing zone, 135°C in the feeding zone, 150-160°C in the foaming zone, and 165°C in the die zone to control the thermal decomposition curve of the foaming agent.

[0031] A two-component foaming agent system is prepared in advance. Calcium magnesium organic acid salt and non-ionic surfactant are mixed evenly in a weight ratio of 3:1 and then dried to ensure that the particle size distribution of the agent is 5-20 microns.

[0032] Nano-silica filler is obtained by combining spray drying and air flow milling to ensure the dispersion of filler and the interface bonding strength with the elastomer matrix.

[0033] Example 2. The difference from Example 1 is that the mass parts of each component are as follows: Ethylene-propylene-diene terpolymer (EPDM): 60 parts Polybutylene adipate (PBAT): 25 parts Nano silicon oxide: 8 parts Coated azodicarbonamide: 3 parts Calcium magnesium organic acid salt: 3 parts Nonionic surfactant (HLB=13): 2 parts Plasticizer (dioctyl phthalate): 10 parts The preparation steps are as follows: S1. Premix EPDM, PBAT, nanosilica, and plasticizer in a twin-screw extruder at 130°C, 120 rpm, for 8 minutes. S2. Add the blowing agent and additive system, raise the temperature to 155°C, increase the speed to 200 rpm, and continue mixing for 12 minutes; S3 extrusion temperature is set to 160 ℃, die temperature 165 ℃, complete foaming; S4. The cooling rate is set to 30°C / min, and the foamed material is formed.

[0034] Example 3. The difference from Example 1 is that the mass parts of each component are as follows: EPDM: 55 parts PBAT: 30 parts Nano silicon oxide: 6 parts Coated azodicarbonamide: 2.5 parts Calcium magnesium organic acid salt: 2 parts Nonionic surfactant (HLB=12.5): 2.5 parts Plasticizer: 15 parts The preparation steps are the same as in Example 2.

[0035] Example 4. The difference from Example 1 is that the mass parts of each component are as follows: EPDM: 50 parts PBAT: 35 parts Nano silicon oxide: 5 parts Coated azodicarbonamide: 4 parts Calcium magnesium organic acid salt: 2.5 parts Nonionic surfactant (HLB=14): 2.5 parts Plasticizer: 12 parts During the preparation, the temperature gradient of the twin-screw extruder was set to: 130°C → 145°C → 160°C → 165°C, the rotation speed was 220 rpm, and the cooling rate was controlled at 25°C / min.

[0036] Comparative Example Comparative Examples 1-4 Comparative Example 1: No coated foaming agent was used The components by mass are as follows: EPDM: 60 parts PBAT: 25 parts Nano silicon oxide: 8 parts Uncoated azodicarbonamide: 3 parts Calcium magnesium organic acid salt: 3 parts Nonionic surfactant: 2 parts Plasticizer: 10 parts Comparison of results: During the mixing process, conventional foaming agents decompose prematurely, resulting in coarse and unevenly distributed cells, and local collapse and pore wall rupture in the molded products.

[0037] Comparative Example 2: No two-component foaming agent system was used The components by mass are as follows: EPDM: 60 parts PBAT: 25 parts Nano silicon oxide: 8 parts Coated azodicarbonamide: 3 parts Only calcium and magnesium organic acid salts added: 5 parts No surfactant used Plasticizer: 10 parts Comparison of results: The foaming rate decreased, the cell structure was rough and uneven, the surface showed shrinkage marks, and the cell closure rate was significantly reduced.

[0038] Comparative Example 3: Using ordinary inorganic fillers The components by mass are as follows: EPDM: 60 parts PBAT: 25 parts Ordinary precipitated silica (particle size about 200nm): 8 parts Coated azodicarbonamide: 3 parts Calcium magnesium organic acid salt: 3 parts Nonionic surfactant: 2 parts Plasticizer: 10 parts Comparison of results: The filler is poorly dispersed, agglomerates are formed, defective areas appear around the cells, the mechanical strength decreases, and the foaming uniformity deteriorates.

[0039] Comparative Example 4: Uncontrolled cooling rate The components are the same as those in Example 2, but the product is cooled naturally without constant cooling control.

[0040] Comparison of results: During the cooling process, the foam material suffers from severe local shrinkage and deformation, cell collapse, decreased surface flatness, and poor dimensional stability.

[0041] In order to determine the difference in foaming structure uniformity between the embodiment and the comparative example, the following comparative experiment was designed. The experimental steps are as follows: The purpose is to verify whether the uniformity and stability of the pore structure of the present invention using the coated foaming agent and the two-component foaming aid system are significantly better than those of the comparative material using the traditional process.

[0042] The experimental subjects are as follows: Example 2 Comparative Example 1 (no coated foaming agent used) Comparative Example 2 (without using a two-component foaming agent system) The experimental equipment and materials are as follows: Main equipment: Twin-screw extrusion granulation system (temperature control accuracy ±1°C) Hot pressing equipment (die head temperature control range: room temperature ~ 200℃) High-resolution cell analyzer (freeze section + SEM scanning device) Cooling rate control device (range 20~40℃ / min) Auxiliary equipment: precision electronic balance Standard slicing utensils Drying oven (80°C) Materials: All components required for the examples and comparative examples were prepared in advance and stored in a dry environment for later use.

[0043] The template size was set to 100 mm × 100 mm × 10 mm for uniform cell observation samples.

[0044] The specific experimental steps are as follows: Step 1: Prepare foamed samples of Example 2, Comparative Example 1 and Comparative Example 2 respectively according to their respective process parameters, and use a unified mold for hot pressing to ensure consistent thickness.

[0045] Step 2: Example 2 was cooled at a set rate of 30°C / min, and Comparative Examples 1 and 2 also used this rate to eliminate the interference of the cooling rate on the structural uniformity.

[0046] Step 3: Cut a central area slice from the middle of each foaming sample with a uniform size of 20mm×10mm×2mm.

[0047] Step 4: Freeze the slice in liquid nitrogen for 30 minutes and then break it to obtain the internal cross-sectional structure of the original pores.

[0048] Step 5: Use SEM to observe the freeze fracture surface at 500× and 1000× magnifications, and record the bubble diameter, number, and uniformity distribution data.

[0049] Step 6: Count the average diameter, pore distribution density, coefficient of variation (CV) and other indicators of the bubbles in each sample image.

[0050] The experimental data are shown in Table 1:

[0051] Table 1 Experimental Conclusion Analysis: The results show that Example 2 significantly outperforms Comparative Examples 1 and 2 in terms of cell uniformity, density, and closed-cell ratio. The use of an encapsulated foaming agent significantly reduces the risk of premature decomposition, making cell size more controllable and reducing the coefficient of variation to 7.8%. The introduction of a two-component foaming aid system optimizes the balance between gas release rate and surface tension, increasing the number of cell nucleations, resulting in the highest and most uniform cell distribution density and a closed-cell ratio of 93.2%.

[0052] In the comparative example, the lack of a foaming agent resulted in uneven cell expansion, larger particle size, and uneven distribution; in the absence of a dual-auxiliary system, foaming was insufficient, the closed-cell rate decreased, and the structural stability was insufficient.

[0053] In order to determine the difference in mechanical properties between the examples and the comparative examples, the following comparative experiment was designed, and the experimental steps are as follows: The improvement effect of Example 2 of the present invention on the mechanical properties such as tensile strength, tear strength, and compression set rate of the TPR foam material after using nano-silica filler and optimizing the twin-screw processing parameters was evaluated, and compared and analyzed with the control examples using ordinary fillers or unoptimized processes.

[0054] The experimental subjects are as follows: Example 2, Comparative Example 3 (using conventional precipitated silica), Comparative Example 4 (not controlling the cooling rate and not optimizing the extrusion temperature zone) The experimental equipment and materials are as follows: Main equipment: Electronic universal material testing machine (maximum load 5kN) High-precision tear testing machine Compression deformation measurement device (constant temperature compression fixture) CNC cutting machine Auxiliary equipment: constant temperature box (room temperature ~ 150℃, used for compression deformation maintenance) Standard thickness gauge Digital caliper, constant weight drying oven Material preparation: According to the formula and process conditions described in each embodiment and comparative example, prepare and cut the same batch of foam material samples Sample product size: tensile strip sample (dumbbell type), tear sample (right angle cut type), compression sample (cylindrical Φ20×10mm) The specific experimental steps are as follows: Step 1: According to the specific formulas and molding process parameters of Example 2, Comparative Examples 3 and 4, complete foam material sample plates were prepared respectively, and after drying for 24 hours, they were cut into various standard test samples.

[0055] Step 2: Use an electronic universal testing machine to perform a tensile test according to GB / T528-2009 standard, and record the ultimate tensile strength and elongation at break.

[0056] Step 3: Use the right-angle tear method in accordance with GB / T529-2008 to measure the tear strength.

[0057] Step 4: Place the cylindrical sample in a constant temperature fixture, compress it to 50% of its initial thickness, maintain it at a constant temperature of 70°C for 22 hours, take it out after cooling, measure its compression permanent set, and calculate the compression set rate.

[0058] Step 5: Test each indicator in no less than 5 groups, take the average value as the valid data, and use the statistical standard deviation to evaluate stability.

[0059] The experimental data are shown in Table 2:

[0060] Table 2 Experimental Conclusion Analysis: Experimental data shows that Example 2 outperforms Comparative Examples 3 and 4 in all mechanical performance indicators. The use of nano-silica fillers with a particle size of less than 50 nm significantly improves the interfacial bonding between the filler and the TPR matrix, enhancing both tensile and tear strength. Furthermore, due to their excellent dispersibility, the internal structural continuity is superior to that of Comparative Example 3, which uses traditional silica. Optimizing the twin-screw temperature zone control and cooling rate (Comparative Example 4) further reduces microcracks and bubble collapse, improving the structural integrity of the material and achieving a compression set as low as 18.6%, demonstrating excellent deformation recovery and longevity potential.

[0061] The above shows and describes the basic principles, main features and advantages of the present invention; those skilled in the art should understand that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only preferred examples of the present invention and are not intended to limit the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of the present invention to be protected; the scope of protection claimed in the present invention is defined by the attached claims and their equivalents.

Claims

1. A TPR foam material, characterized in that: Calculated by mass percentage, it includes the following components: Ethylene-propylene-diene terpolymer 25% to 75%; thermoplastic polyester elastomer 5% to 40%, wherein the thermoplastic polyester elastomer is polybutylene adipate; nano-silica filler with a particle size less than 50 nanometers 2% to 15%; heat-stable coated azodicarbonamide foaming agent 0.5% to 6%; two-component foaming agent system 1% to 12%, including calcium magnesium organic acid salt and non-ionic surfactant; plasticizer 3% to 18%.

2. A TPR foam material according to claim 1, characterized in that: The ethylene-propylene-diene terpolymer has a diene content of 4-8 wt % and a melt index of 1.5-4.0 g / 10 min.

3. The TPR foam material according to claim 1, characterized in that: The ester content of the thermoplastic polyester elastomer accounts for more than 85% of the total mass, and the melting point is 110-125°C.

4. The TPR foam material according to claim 1, characterized in that: The nano-silicon oxide filler is prepared by a gas phase method, has a uniform particle size distribution, a maximum particle size of no more than 50 nanometers, and a BET specific surface area of ​​180 to 230 m 2 / g.

5. The TPR foam material according to claim 1, characterized in that: The heat-stable coated azodicarbonamide foaming agent is polymer-coated, the coating layer has a thickness of 50-150 nanometers, and the thermal decomposition temperature ranges from 145-165°C.

6. The TPR foam material according to claim 5, characterized in that: The mass of the calcium and magnesium organic acid salt in the two-component foaming auxiliary agent system accounts for 60% to 80% of the auxiliary agent system, and the HLB value of the non-ionic surfactant is 12-14.

7. A method for preparing a TPR foam material, characterized in that: The method for preparing a TPR foam material comprises the following steps: S1. The ethylene-propylene-diene terpolymer, thermoplastic polyester elastomer, nano-silica filler and plasticizer were pre-mixed in a twin-screw extruder at 120-140 ° C and a speed of 100-150 rpm; S2. Add heat-stable coated azodicarbonamide foaming agent and two-component foaming agent system to the premix, increase the speed to 180-250rpm in the range of 140-160 ° C, and continue mixing for 10 to 15 minutes to ensure uniform dispersion of the components; S3 extruded the mixture, and foamed by die molding, the molding temperature gradient was set to 130-165 ℃; S4. After foaming, the product is cooled and set at 20-40°C / min.

8. The method for preparing a TPR foam material according to claim 7, characterized in that: The temperatures of different sections of the barrel of the twin-screw extruder are set to: 130° C. in the mixing zone, 135° C. in the feeding zone, 150-160° C. in the foaming zone, and 165° C. in the die zone, so as to control the thermal decomposition curve of the foaming agent.

9. The method for preparing a TPR foam material according to claim 8, characterized in that: The two-component foaming agent system is prepared in advance, and the calcium magnesium organic acid salt and the non-ionic surfactant are mixed uniformly in a weight ratio of 3:1 and then dried to ensure that the particle size distribution of the agent is 5-20 microns.

10. A method for preparing a TPR foam material according to any one of claims 7 to 9, characterized in that: The nano silicon oxide filler is obtained by combining spray drying with air flow pulverization to ensure the filler's dispersibility and the interface bonding strength with the elastomer matrix.

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