A preparation method and application of microporous EPDM rubber foam material

Abstract

The invention relates to the technical field of rubber foaming materials, and discloses a preparation method and application of a microporous EPDM rubber foaming material. The anti-aging co-crosslinking agent structure contains a multi-maleimide group, which can generate chemical crosslinking with the EPDM rubber, and the crosslinking activity of the molecular chain is enhanced, so that the carbon dioxide dissolved in the matrix is ​​not easy to diffuse out of the matrix, and the nucleation sites are gradually increased, which can support the formation of the pore structure and maintain the integrity of the pore structure, so as to form a dense microporous structure; the imide heterocycle, triazine ring and benzene ring in the anti-aging co-crosslinking agent have strong high temperature resistance. In the rubber vulcanization process, the double bonds are opened to participate in the crosslinking reaction, and free radical active species are formed, which undergo a co-crosslinking reaction with the EPDM rubber, improve the crosslinking network structure, improve the heat air aging resistance and salt spray aging resistance of the EPDM rubber, and enhance the elastic recovery ability of the rubber.

Description

Technical Field

[0001] The invention relates to the technical field of rubber foam materials, in particular to a preparation method of a microporous EPDM rubber foam material and application thereof. Background Art

[0002] EPDM is a terpolymer of ethylene, propylene and non-conjugated dienes. Because its main chain is composed of chemically stable saturated hydrocarbons and only contains unsaturated double bonds in the side chains, it has excellent aging resistance such as ozone resistance, heat resistance, weather resistance, etc., and can be widely used in automotive parts, building waterproof materials, wire and cable sheaths, heat-resistant hoses, tapes, automotive seals and other fields; foam rubber has the ability to adapt to large deformations, and foam rubber sealing products can be widely used in transportation industry and special equipment and other fields. However, due to defects inside the rubber material, under the influence of these environmental factors, physical or chemical changes will occur inside the material, resulting in cross-linking hardening or degradation softening, and powdering or cracking on the surface, which will lead to damage to the material from the inside out, causing a series of safety problems. Therefore, the aging problem of rubber materials in various harsh environments such as hot air and salt spray has become a research hotspot in related fields.

[0003] Traditional EPDM rubber foaming materials are usually prepared by sulfur or peroxide vulcanization and chemical foaming. The current method for preparing EPDM rubber foam materials is mainly chemical foaming, in which an organic foaming agent is evenly mixed with EPDM rubber, and then the organic foaming agent undergoes thermal decomposition during the high-temperature vulcanization process of the rubber to produce gas to foam the rubber matrix. Since the foaming process and the vulcanization process are carried out simultaneously, and a large amount of compounding agents such as vulcanizers and accelerators need to be added, the vulcanization rate and the foaming rate are difficult to match, so a uniform and fine pore structure cannot be obtained. The pore structure is difficult to control and the experimental repeatability is low. As a green, efficient and environmentally friendly process, the supercritical foaming process separates the rubber vulcanization process and the foaming process, and the pore structure can be controlled by changing the foaming pressure and the foaming temperature.

[0004] The present invention synthesizes polymaleimide in the structure of the anti-aging auxiliary cross-linking agent, which can generate chemical cross-linking with EPDM rubber during the mixing and vulcanization process, thereby increasing the cross-linking density and being beneficial to improving the anti-aging performance of the EPDM rubber material; adopts a green and environmentally friendly supercritical CO2 process to regulate the pore structure of the EPDM rubber, and prepares a microporous foam material with a smaller pore size and a larger pore density, which has a simple process and a wide range of applications. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a method for preparing a microporous EPDM rubber foam material and its application, thereby solving the problems of irregular pore structure and poor aging resistance of the existing EPDM rubber foam material.

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] A method for preparing a microporous EPDM rubber foam material comprises the following steps:

[0008] (1) EPDM rubber is mixed in an internal mixer at a temperature of 50-70°C and a rotation speed of 80-100 r / min until it reaches a viscous flow state, and white carbon black and a structural formula of Anti-aging auxiliary cross-linking agent, stearic acid, zinc oxide and diisopropylbenzene peroxide are mixed for 20-40 minutes, and then sulfur and accelerator AG-60 are added and mixed on an open mixing mill. After mixing evenly, thin sheets are passed through. After the mixed rubber is left for 16-24 hours, it is placed on the molding plate of a high-temperature vulcanizer for vulcanization to obtain an anti-aging EPDM rubber material.

[0009] (2) The aging-resistant EPDM rubber material is cut into strips and foamed using a supercritical foaming device. When the foaming temperature reaches a set value, the rubber strips are added into the cavity of the supercritical foaming device, and carbon dioxide is introduced to replace the air in the cavity. The cavity is pressurized to a set pressure value, and the pressure is released after being fully saturated for 30-50 minutes to obtain a microporous EPDM rubber foam material.

[0010] Furthermore, in step (1), the ratio of EPDM rubber, white carbon black, anti-aging co-crosslinking agent, stearic acid, zinc oxide, dicumyl peroxide, sulfur, and accelerator AG-60 is 100g:(10-25)g:(2-10)g:(1-2.5)g:(1.8-3.5)g:(2-4)g:(1-3)g:(0.5-1.2)g.

[0011] Furthermore, in step (1), the vulcanization temperature is 140-160° C., the vulcanization pressure is 60-80 kN, and the vulcanization time is 20-60 min.

[0012] Furthermore, in step (2), the foaming temperature setting value is 45-65°C.

[0013] Furthermore, in step (2), the pressure setting value is 10-20 MPa.

[0014] Furthermore, the preparation method of the anti-aging auxiliary cross-linking agent in step (1) comprises the following steps: adding 2,4,6-tris(4-aminophenyl)-1,3,5-triazine and a solvent to a reaction container under a nitrogen atmosphere, stirring evenly, adding maleic anhydride, acetic anhydride and sodium acetate, stirring for reaction, cooling to room temperature after the reaction is completed, adding methanol for precipitation, filtering, and drying to obtain an anti-aging auxiliary cross-linking agent. The preparation reaction formula is as follows:

[0015]

[0016] Furthermore, the solvent is any one of N,N-dimethylformamide, N,N-dimethylacetamide or N-methylpyrrolidone.

[0017] Furthermore, the ratio of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine, maleic anhydride, acetic anhydride and sodium acetate is 1 mol:(6.5-9) mol:(8-10) mol:(1.5-3) mol.

[0018] Furthermore, the reaction temperature is 60-80°C, and the reaction time is 16-24h.

[0019] By adopting the above technical solution, the beneficial effects of the present invention are:

[0020] The invention firstly reacts 2,4,6-tris(4-aminophenyl)-1,3,5-triazine with maleic anhydride to obtain an anti-aging auxiliary cross-linking agent, then mixes and vulcanizes with EPDM rubber, white carbon black and auxiliary agents to obtain an anti-aging type EPDM rubber material, and then uses a supercritical CO2 process for physical foaming to obtain a microporous EPDM rubber foaming material.

[0021] The anti-aging co-crosslinking agent contains multiple maleimide groups in its structure, which can produce chemical crosslinking with EPDM rubber, so that the crosslinking activity of the molecular chain is enhanced, the degree of crosslinking is gradually increased, and the free activity space between the molecular chains is gradually reduced, so that the carbon dioxide dissolved in the matrix is ​​not easy to diffuse out of the matrix, the nucleation sites are gradually increased, and the pore density increases accordingly; at the same time, the benzene ring and the imide five-membered ring in its structure have a certain rigidity strength, which can support the formation of the pore structure and maintain the integrity of the pore structure, can stabilize the pore structure, and can ensure sufficient CO2 intake, which is conducive to the preparation of microporous EPDM rubber foam material with small pore size, high pore density, good pore continuity and uniform pore structure, so that the pores in the foam material develop in the direction of more regular shape, smaller size and higher density.

[0022] The aging-resistant co-crosslinking agent contains heat-resistant groups such as imide heterocycles, triazine rings and benzene rings, and has strong high-temperature resistance. During the rubber vulcanization process, the double bonds of polymaleimide open to participate in the cross-linking reaction, forming free radical active species. This active species can undergo co-cross-linking reaction with EPDM rubber, increasing the number of cross-linking bonds, further improving the cross-linking network structure, and improving the tensile strength. In addition, a small amount of unreacted maleimide in the rubber can terminate the free radicals generated during the aging of some rubbers, avoiding the occurrence of aging chain growth reactions, thereby improving the heat-resistant air aging performance of EPDM rubber to a certain extent.

[0023] The cross-linking density between the aging-resistant co-crosslinking agent and EPDM rubber increases, which significantly reduces the pore size and improves the distribution uniformity. A large number of dense microporous structures appear, which can effectively hinder the infiltration of external corrosion ions, thereby improving the corrosion resistance of the rubber foam material. In addition, because the imide heterocycle and triazine groups with good temperature resistance are introduced into the cross-linking network, the degradation and destruction of the rubber molecular segments are reduced, and "bridge bond" cross-linking is formed with the EPDM rubber to form a cross-linked network structure, which improves the compatibility between the two, thereby enhancing the elastic recovery ability and salt spray aging resistance of the rubber. DETAILED DESCRIPTION

[0024] In order to more clearly understand the above-mentioned purpose, features and advantages of the present invention, the present invention is further described in detail below in conjunction with specific embodiments. It should be noted that the embodiments of the present application and the features in the embodiments can be combined with each other without conflict.

[0025] Example 1

[0026] (1) Under a nitrogen atmosphere, 15 mmol of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine and 150 mL of N,N-dimethylformamide were added to a reaction container, and after stirring, 120 mmol of maleic anhydride, 135 mmol of acetic anhydride and 37.5 mmol of sodium acetate were added, and the mixture was reacted at 70° C. for 20 h. The mixture was cooled to room temperature, and methanol was added for precipitation. The mixture was filtered and dried to obtain an anti-aging auxiliary cross-linking agent.

[0027] (2) 100 g of EPDM rubber was mixed in an internal mixer at a temperature of 60°C and a speed of 90 r / min until it reached a viscous flow state. 15 g of white carbon black, 2 g of an anti-aging co-crosslinking agent, 1.3 g of stearic acid, 2.2 g of zinc oxide and 3 g of diisopropylbenzene peroxide were added in sequence and mixed for 30 min. Then, 2 g of sulfur and 0.8 g of accelerator AG-60 were added and mixed on an open mixer. After mixing evenly, the mixture was thinly passed through 5 times and then placed on a sheet. After the mixed rubber was left for 24 h, it was placed on a mold plate of a high-temperature vulcanizer for vulcanization at a vulcanization temperature of 150°C, a vulcanization pressure of 70 kN and a vulcanization time of 30 min to obtain an anti-aging EPDM rubber material.

[0028] (3) The aging-resistant EPDM rubber material is cut into strips and foamed using a supercritical foaming device. When the foaming temperature reaches 50°C, the rubber strips are added into the cavity of the supercritical foaming device, and carbon dioxide is introduced to replace the air in the cavity. The cavity is pressurized to 15 MPa, and the pressure is released after being fully saturated for 40 minutes to obtain a microporous EPDM rubber foam material.

[0029] Example 2

[0030] (1) Under a nitrogen atmosphere, 26 mmol of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine and 208 mL of N,N-dimethylacetamide were added to a reaction container, and after stirring, 169 mmol of maleic anhydride, 208 mmol of acetic anhydride and 39 mmol of sodium acetate were added, and the mixture was reacted at 80° C. for 16 h. The mixture was cooled to room temperature, and methanol was added for precipitation. The mixture was filtered and dried to obtain an aging-resistant co-crosslinking agent.

[0031] (2) 100 g of EPDM rubber was mixed in an internal mixer at a temperature of 70°C and a rotation speed of 100 r / min until it reached a viscous flow state. Then, 20 g of white carbon black, 4 g of an anti-aging co-crosslinking agent, 1 g of stearic acid, 3.5 g of zinc oxide and 2 g of diisopropylbenzene peroxide were added in sequence and mixed for 20 min. Then, 1 g of sulfur and 1.2 g of accelerator AG-60 were added and mixed on an open mixer. After mixing evenly, the mixture was thinly passed 5 times and then placed on a sheet. After the mixed rubber was left for 16 h, it was placed on a mold plate of a high-temperature vulcanizer for vulcanization at a vulcanization temperature of 160°C, a vulcanization pressure of 80 kN and a vulcanization time of 20 min to obtain an anti-aging EPDM rubber material.

[0032] (3) The aging-resistant EPDM rubber material is cut into strips and foamed using a supercritical foaming device. When the foaming temperature reaches 65°C, the rubber strips are added into the cavity of the supercritical foaming device, and carbon dioxide is introduced to replace the air in the cavity. The cavity is pressurized to 20 MPa, and the pressure is released after being fully saturated for 30 minutes to obtain a microporous EPDM rubber foam material.

[0033] Example 3

[0034] (1) Under a nitrogen atmosphere, 45 mmol of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine and 540 mL of N-methylpyrrolidone were added to a reaction container, and after stirring, 405 mmol of maleic anhydride, 450 mmol of acetic anhydride and 135 mmol of sodium acetate were added, and the mixture was reacted at 60° C. for 24 h. The mixture was cooled to room temperature, and methanol was added for precipitation. The mixture was filtered and dried to obtain an anti-aging auxiliary cross-linking agent.

[0035] (2) 100 g of EPDM rubber was mixed in an internal mixer at a temperature of 50°C and a rotation speed of 80 r / min until it reached a viscous flow state. 18 g of white carbon black, 6 g of an aging-resistant co-crosslinking agent, 2.5 g of stearic acid, 1.8 g of zinc oxide and 4 g of diisopropylbenzene peroxide were added in sequence and mixed for 40 min. Then, 3 g of sulfur and 0.5 g of accelerator AG-60 were added and mixed on an open mixer. After mixing evenly, the mixture was thinly passed through 5 times and then placed on a sheet. After the mixed rubber was left for 24 h, it was placed on a mold plate of a high-temperature vulcanizer for vulcanization at a vulcanization temperature of 140°C, a vulcanization pressure of 60 kN and a vulcanization time of 60 min to obtain an aging-resistant EPDM rubber material.

[0036] (3) The aging-resistant EPDM rubber material is cut into strips and foamed using a supercritical foaming device. When the foaming temperature reaches 45°C, the rubber strips are added into the cavity of the supercritical foaming device, and carbon dioxide is introduced to replace the air in the cavity. The cavity is pressurized to 10 MPa, and the pressure is released after being fully saturated for 50 minutes to obtain a microporous EPDM rubber foam material.

[0037] Example 4

[0038] (1) Under a nitrogen atmosphere, 12 mmol of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine and 132 mL of N,N-dimethylformamide were added to a reaction container, and after stirring, 102 mmol of maleic anhydride, 90 mmol of acetic anhydride and 30 mmol of sodium acetate were added, and the mixture was reacted at 75° C. for 18 h. The mixture was cooled to room temperature, and methanol was added for precipitation. The mixture was filtered and dried to obtain an anti-aging auxiliary cross-linking agent.

[0039] (2) 100 g of EPDM rubber was mixed in an internal mixer at a temperature of 65°C and a rotation speed of 90 r / min until it reached a viscous flow state. 15 g of white carbon black, 8 g of an aging-resistant co-crosslinking agent, 2 g of stearic acid, 2.5 g of zinc oxide and 3.5 g of diisopropylbenzene peroxide were added in sequence and mixed for 35 min. Then, 1.3 g of sulfur and 1.1 g of accelerator AG-60 were added and mixed on an open mixer. After mixing evenly, the mixture was thinly passed through 5 times and then placed on a sheet. After the mixed rubber was left for 18 h, it was placed on a mold plate of a high-temperature vulcanizer for vulcanization at a vulcanization temperature of 145°C, a vulcanization pressure of 75 kN and a vulcanization time of 35 min to obtain an aging-resistant EPDM rubber material.

[0040] (3) The aging-resistant EPDM rubber material is cut into strips and foamed using a supercritical foaming device. When the foaming temperature reaches 50°C, the rubber strips are added into the cavity of the supercritical foaming device, and carbon dioxide is introduced to replace the air in the cavity. The cavity is pressurized to 12 MPa, and the pressure is released after being fully saturated for 45 minutes to obtain a microporous EPDM rubber foam material.

[0041] Example 5

[0042] (1) Under a nitrogen atmosphere, 20 mmol of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine and 190 mL of N,N-dimethylacetamide were added to a reaction container, and after stirring, 176 mmol of maleic anhydride, 160 mmol of acetic anhydride and 45 mmol of sodium acetate were added, and the mixture was reacted at 80° C. for 24 h. The mixture was cooled to room temperature, and methanol was added for precipitation. The mixture was filtered and dried to obtain an anti-aging auxiliary cross-linking agent.

[0043] (2) 100 g of EPDM rubber was mixed in an internal mixer at a temperature of 70°C and a speed of 100 r / min until it reached a viscous flow state. 10 g of white carbon black, 10 g of an anti-aging co-crosslinking agent, 2.2 g of stearic acid, 1.8 g of zinc oxide and 2.5 g of diisopropylbenzene peroxide were added in sequence and mixed for 25 min. Then, 2.1 g of sulfur and 0.9 g of accelerator AG-60 were added and mixed on an open mixer. After mixing evenly, the mixture was thinly passed 5 times and then placed on a sheet. After the mixed rubber was left for 16 h, it was placed on a mold plate of a high-temperature vulcanizer for vulcanization at a vulcanization temperature of 155°C, a vulcanization pressure of 75 kN and a vulcanization time of 30 min to obtain an anti-aging EPDM rubber material.

[0044] (3) The aging-resistant EPDM rubber material is cut into strips and foamed using a supercritical foaming device. When the foaming temperature reaches 60°C, the rubber strips are added into the cavity of the supercritical foaming device, and carbon dioxide is introduced to replace the air in the cavity. The cavity is pressurized to 15 MPa, and the pressure is released after being fully saturated for 40 minutes to obtain a microporous EPDM rubber foam material.

[0045] Comparative Example 1

[0046] (1) 100 g of EPDM rubber was mixed in an internal mixer at a temperature of 60°C and a speed of 90 r / min until it reached a viscous flow state, and 15 g of white carbon black and 2 g of trimethylolpropane trimethacrylate (structural formula: CAS No. 3290-92-4), 1.3g stearic acid, 2.2g zinc oxide and 3g diisopropylbenzene peroxide, mix for 30min, then add 2g sulfur and 0.8g accelerator AG-60 and mix on an open mill. After mixing evenly, thin pass 5 times and sheet. After the mixed rubber is left for 24h, it is placed on the mold plate of a high-temperature vulcanizer for vulcanization at a vulcanization temperature of 150°C, a vulcanization pressure of 70kN and a vulcanization time of 30min to obtain an EPDM rubber material.

[0047] (2) The EPDM rubber material is cut into strips and foamed using a supercritical foaming device. When the foaming temperature reaches 50°C, the rubber strips are added into the cavity of the supercritical foaming device, and carbon dioxide is introduced to replace the air in the cavity. The cavity is pressurized to 15 MPa, and the pressure is released after being fully saturated for 40 minutes to obtain an EPDM rubber foam material.

[0048] Comparative Example 2

[0049] (1) 100 g of EPDM rubber was mixed in an internal mixer at a temperature of 60°C and a rotation speed of 90 r / min until it reached a viscous flow state, and 15 g of white carbon black, 1.3 g of stearic acid, 2.2 g of zinc oxide and 3 g of diisopropylbenzene peroxide were added in sequence and mixed for 30 min. Then, 2 g of sulfur and 0.8 g of accelerator AG-60 were added and mixed on an open mixer. After mixing evenly, the mixture was thinly passed through 5 times and then placed on a sheet. After the mixed rubber was left for 24 h, it was placed on a mold plate of a high-temperature vulcanizer for vulcanization at a vulcanization temperature of 150°C, a vulcanization pressure of 70 kN and a vulcanization time of 30 min to obtain an EPDM rubber material.

[0050] (2) The EPDM rubber material is cut into strips and foamed using a supercritical foaming device. When the foaming temperature reaches 50°C, the rubber strips are added into the cavity of the supercritical foaming device, and carbon dioxide is introduced to replace the air in the cavity. The cavity is pressurized to 15 MPa, and the pressure is released after being fully saturated for 40 minutes to obtain an EPDM rubber foam material.

[0051] Cell density and average pore size test: Scanning electron microscopy was used to characterize the cell morphology and structure, and the SEM image of the foam material cells was obtained. ImageJ software was used to count the pore size and number of the cells in the image, and then the pore density was calculated based on the number of pores per unit area. The calculation formula is pore density = (n / A) 3 / 2 , where n is the number of cells in the SEM image; A is the area of ​​the counting region in the SEM image (cm 2 ). The test results are shown in Table 1.

[0052] Table 1 Cell performance test

[0053] Average cell diameter (μm) <![CDATA[Cell density (cells / cm 3 )]]> Example 1 4.15 <![CDATA[2.25×10 10 ]]> Example 2 3.76 <![CDATA[9.12×10 10 ]]> Example 3 3.03 <![CDATA[1.87×10 11 ]]> Example 4 2.19 <![CDATA[3.68×10 11 ]]> Example 5 1.25 <![CDATA[8.06×10 11 ]]> Comparative Example 1 3.96 <![CDATA[1.93×10 10 ]]> Comparative Example 2 7.23 <![CDATA[1.52×10 9 ]]>

[0054] Generally speaking, the greater the density of the pores and the smaller the average pore size, the better the performance of the microporous foamed material. It can be seen from the test results in the above table that with the increase of the content of the aging-resistant cross-linking agent, the average pore size of the microporous EPDM rubber foamed material gradually decreases and the pore density gradually increases. The average particle size of the pores in Example 5 is only 1.25 μm, and the pore density is 8.06×10 11 Pieces / cm 3 , indicating that the pores in the foamed material are developing towards a more regular shape, smaller size and higher density; this is because the anti-aging co-crosslinking agent contains multiple maleimide groups in its structure, which can produce chemical crosslinking with EPDM rubber, thereby enhancing the crosslinking activity of the molecular chain, gradually increasing the degree of crosslinking, and gradually reducing the free activity space between the molecular chains, making it difficult for the carbon dioxide dissolved in the matrix to diffuse out of the matrix, and the nucleation sites gradually increase, and the pore density increases accordingly. At the same time, the benzene ring and the five-membered heterocyclic ring of imide in its structure have a certain rigidity strength, which can support the formation of the pore structure and maintain the integrity of the pore structure, which can not only stabilize the pore structure, but also ensure sufficient CO2 intake, which is conducive to the preparation of microporous EPDM rubber foamed materials with small pore size, high pore density, good pore continuity and uniform pore structure.

[0055] The comparative example adds a common cross-linking agent, which can produce a certain cross-linking density with the EPDM rubber, and the average particle size of the bubbles is 3.96μm. However, the strength of the cross-linking agent is too low, and there is not enough strength to support the bubble structure, and the regularity of the bubbles cannot be controlled; Comparative Example 2 is pure EPDM rubber, without the addition of a cross-linking agent, the bubble wall is easy to collapse, the bubbles are interconnected, the CO2 gas cannot be retained, and the gas overflows from the matrix, resulting in an increase in the bubble diameter and a decrease in the bubble density, and the bubble performance is poor.

[0056] Hot air aging performance test: The test was conducted in accordance with the standard GB / T 3512-2001. The aging conditions were placed in a hot air aging box at 150°C for 240 hours. According to the standard GB / T 528-1998, the tensile strength before and after aging was tested on an electronic tensile machine. The test results are shown in Table 2.

[0057] Table 2 Hot air aging resistance test

[0058]

[0059] It can be seen from the test results in the above table that with the increase of the content of the aging-resistant co-crosslinking agent, the tensile strength of the microporous EPDM rubber foam material gradually increases. The tensile strength in Example 4 reaches 3.84MPa. After being placed at 150°C for 120h, the tensile strength value does not change significantly, indicating that the addition of the aging-resistant co-crosslinking agent is effective in improving the hot air aging resistance of the EPDM rubber. This may be due to the participation of the multi-maleimide in the aging-resistant co-crosslinking agent in the crosslinking reaction, which increases the pore density of the foam material and makes the material structure compact, effectively improving the material's ability to resist high temperature degradation, thereby increasing the foam material. The tensile strength of the material is improved; in the cross-linked network structure of the rubber, there are heat-resistant groups such as imide heterocycles, triazine rings and benzene rings, which have strong high temperature resistance; at the same time, the double bonds of maleimide are opened during the vulcanization process to form free radical active species, which can undergo co-cross-linking reaction with EPDM rubber, increasing the number of cross-linking bonds, further improving the cross-linked network structure, and improving the tensile strength; in addition, a small amount of unreacted maleimide in the rubber can terminate the free radicals generated during the aging of some rubbers, avoiding the occurrence of aging chain growth reactions, thereby improving the heat air aging resistance of EPDM rubber to a certain extent.

[0060] Corrosion resistance test: The test was conducted in a salt spray corrosion cycle test chamber, using a continuous spray method, the chamber temperature was 35°C, the mass fraction of the sodium chloride solution was 5%, the aging time was 240h, and the Shore hardness before and after corrosion was tested using a Shore hardness tester. The test results are shown in Table 3.

[0061] Table 3 Corrosion resistance test

[0062]

[0063] It can be seen from the test results in the above table that with the increase of the content of the anti-aging co-crosslinking agent, the hardness and corrosion resistance of the microporous EPDM rubber foam material are enhanced. This is because the crosslinking density between the anti-aging co-crosslinking agent and the EPDM rubber increases, which significantly reduces the pore size and improves the distribution uniformity. A large number of dense microporous structures appear, which can effectively hinder the infiltration of external corrosive ions, thereby improving the corrosion resistance of the rubber foam material; and because the imide heterocycle, triazine and benzene ring groups with good temperature resistance are introduced into the crosslinking network, the degradation and destruction of the rubber molecular segments are reduced, thereby enhancing the salt spray aging resistance of the rubber.

[0064] Compression set test: The test was conducted in accordance with the standard GB / T 1683-1981, and the experimental conditions were compression for 64 hours at 25°C and 100°C respectively. The test results are shown in Table 4.

[0065] Table 4 Anti-deformation performance test

[0066]

[0067] Generally speaking, the smaller the compression permanent deformation rate of rubber, the better the resilience of the rubber material and the stronger the deformation resistance. It can be seen from the test results in the above table that with the increase of the content of the anti-aging co-crosslinking agent, the compression permanent deformation rate of the EPDM rubber foam material gradually decreases. This is because the multi-maleimide group in the structure of the anti-aging co-crosslinking agent has more double bond functional groups with higher activity. During the mixing and vulcanization process with the EPDM rubber, the active double bonds are opened and form "bridge bonds" with the EPDM rubber to form a cross-linked network structure, which improves the compatibility between the two and enhances the elastic recovery ability of the rubber. The above is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various changes and variations. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a microporous EPDM rubber foam material, characterized in that: The preparation method comprises the following steps: (1) Knead EPDM rubber in an internal mixer at a temperature of 50-70°C and a speed of 80-100 r / min until it reaches a viscous flow state, and add white carbon black and the structural formula The aging-resistant auxiliary cross-linking agent, stearic acid, zinc oxide and dicumyl peroxide are mixed for 20-40 minutes, and then sulfur and accelerator AG-60 are added and mixed on an open mill. After mixing evenly, thin sheets are passed through. After the mixed rubber is left for 16-24 hours, it is placed on a molded plate of a high-temperature vulcanizer for vulcanization to obtain an aging-resistant EPDM rubber material. (2) Cutting the aging-resistant EPDM rubber material into strips, foaming it using a supercritical foaming device, and when the foaming temperature reaches a set value, adding the rubber strips into the cavity of the supercritical foaming device, introducing carbon dioxide to replace the air in the cavity, pressurizing it to a set pressure value, fully saturating it for 30-50 minutes, and then releasing the pressure to obtain a microporous EPDM rubber foam material; In the step (1), the ratio of EPDM rubber, white carbon black, anti-aging co-crosslinking agent, stearic acid, zinc oxide, diisopropylbenzene peroxide, sulfur, and accelerator AG-60 is 100g: 15g: 8g: 2g: 2.5g: 3.5g: 1.3g: 1.1g. The preparation method of the anti-aging co-crosslinking agent in the step (1) comprises the following steps: adding 2,4,6-tris(4-aminophenyl)-1,3,5-triazine and solvent to a reaction container under a nitrogen atmosphere, stirring evenly, adding maleic anhydride, acetic anhydride and sodium acetate, stirring for reaction, cooling to room temperature after the reaction is completed, adding methanol for precipitation, filtering, and drying to obtain the anti-aging co-crosslinking agent; the ratio of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine, maleic anhydride, acetic anhydride, and sodium acetate is 12mmol: 102mmol: 90mmol: 30mmol, Alternatively, in step (1), the ratio of EPDM rubber, white carbon black, anti-aging co-crosslinking agent, stearic acid, zinc oxide, dicumyl peroxide, sulfur, and accelerator AG-60 is 100g: 10g: 10g: 2.2g: 1.8g: 2.5g: 2.1g: 0.9g, wherein the preparation method of the anti-aging auxiliary cross-linking agent in step (1) comprises the following steps: under a nitrogen atmosphere, adding 2,4,6-tris(4-aminophenyl)-1,3,5-triazine and a solvent into a reaction container, stirring evenly, adding maleic anhydride, acetic anhydride and sodium acetate, stirring for reaction, cooling to room temperature after the reaction is completed, adding methanol for precipitation, filtering, and drying to obtain an anti-aging auxiliary cross-linking agent; the ratio of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine, maleic anhydride, acetic anhydride and sodium acetate is 20mmol:176mmol:160mmol:45mmol.

2. The method for preparing a microporous EPDM rubber foam material according to claim 1, characterized in that: In the step (1), the vulcanization temperature is 140-160° C., the vulcanization pressure is 60-80 kN, and the vulcanization time is 20-60 min.

3. The method for preparing a microporous EPDM rubber foam material according to claim 1, characterized in that: The foaming temperature setting value in step (2) is 45-65°C.

4. The method for preparing a microporous EPDM rubber foam material according to claim 1, characterized in that: The pressure setting value in step (2) is 10-20 MPa.

5. The method for preparing a microporous EPDM rubber foam material according to claim 1, characterized in that: The solvent is any one of N,N-dimethylformamide, N,N-dimethylacetamide or N-methylpyrrolidone.

6. The method for preparing a microporous EPDM rubber foam material according to claim 1, characterized in that: The reaction temperature is 60-80°C, and the reaction time is 16-24h.

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