Ethylene-propylene rubber insulation material for charging pile cable and preparation method thereof

Abstract

The application discloses an ethylene-propylene rubber insulation material for charging pile cable and a preparation method thereof, and relates to the technical field of cable insulation materials. The insulation material is prepared by mixing and cross-linking of first ethylene-propylene rubber, second ethylene-propylene rubber, liquid ethylene-propylene rubber, flaky calcined kaolin treated by ethenyl trimethoxysilane, white carbon black, anti-oxidant, anti-ozone wax, anti-aging agent, dicumyl peroxide and triallyl isocyanurate. During the preparation, the liquid ethylene-propylene rubber is added into the ethylene-propylene rubber material, and the modified flaky calcined kaolin is mixed under the condition that the white carbon black has not been added, and then the white carbon black is added for further mixing. Finally, the final mixing and cross-linking are completed. The application can reduce the filler interface defects of the material after immersion in a cooling medium and temperature circulation, and improve the insulation performance and the retention ability of the flexibility without excessively increasing the overall cross-linking degree and the initial rigidity.

Description

Technical Field

[0001] This invention relates to the field of cable insulation materials technology, and in particular to an ethylene propylene rubber insulation material for charging pile cables and its preparation method. Background Technology

[0002] With the increase in charging pile power, charging cables need to withstand bending, temperature changes and contact with cooling media during use. EPDM rubber has good electrical insulation, heat resistance and weather resistance. It is usually combined with silica, kaolin, silane treatment agent and peroxide crosslinking system to prepare cable insulation materials. In order to balance processing performance and flexibility, EPDM rubber with different properties and liquid EPDM rubber can also be used.

[0003] However, in EPDM rubber systems containing silica and flake inorganic fillers, when the two types of fillers come into contact with the rubber compound simultaneously or too early during the mixing process, it can easily affect the full mixing of liquid EPDM rubber and modified flake calcined kaolin. After the material is soaked in a cooling medium and subjected to repeated temperature changes, the interface defects between the filler and the rubber are likely to increase. If the stability of the material is improved simply by increasing the overall degree of crosslinking, the stiffness of the material is likely to increase, affecting the flexibility required for charging cables.

[0004] Therefore, how to improve the interfacial stability and insulation performance retention of ethylene propylene rubber after cooling medium and temperature cycling without excessively increasing the overall network constraint and initial stiffness of the ethylene propylene rubber is a problem that existing technologies need to solve. Summary of the Invention

[0005] In a first aspect, the present invention provides an ethylene propylene rubber insulation material for charging pile cables, wherein the ethylene propylene rubber insulation material is obtained by mixing and cross-linking raw materials comprising the following components:

[0006] 100 parts by weight of EPDM rubber and EPDM rubber (total), 6-24 parts by weight of liquid EPDM rubber, 12 parts by weight of flake calcined kaolin surface-treated with vinyltrimethoxysilane, 25 parts by weight of silica, 0.8 parts by weight of antioxidant 1010, 0.6 parts by weight of antioxidant 168, 1.0 part by weight of anti-ozone wax, 0.6 parts by weight of antioxidant 6PPD, 1.8 parts by weight of dicumyl peroxide, and 2.5 parts by weight of triallyl isocyanurate;

[0007] The mass ratio of the first EPDM rubber to the second EPDM rubber is 30:70 to 70:30. The ethylene content of the first EPDM rubber is 68% to 78%, and the Mooney viscosity ML(1+4) at 125°C is 55 to 85. The ethylene content of the second EPDM rubber is 50% to 65%, and the Mooney viscosity ML(1+4) at 125°C is 30 to 55.

[0008] The mixing process involves first introducing the liquid EPDM rubber into a rubber compound containing the first and second EPDM rubbers. Before the addition of silica, the flake-shaped calcined kaolin treated with vinyltrimethoxysilane is added in two batches, 6 parts by weight per batch. After the first batch is added, the mixture is mixed for 1 minute. After the second batch is added, the mixture is further mixed for 4 minutes. After the above mixing process is completed, silica is added and mixed again. The mixture is then crosslinked with dicumyl peroxide and triallyl isocyanurate to form the EPDM rubber insulating material.

[0009] Preferably, the first EPDM rubber, the second EPDM rubber, and the liquid EPDM rubber all use ethylene-neobornene as the third monomer.

[0010] The liquid EPDM rubber has a viscosity of 500–5000 mPa·s at 25°C and a volatile content of no more than 1.0%.

[0011] Preferably, the D50 of the flaky calcined kaolin is 0.5–5 μm, and the mass of vinyltrimethoxysilane added is 0.5%–3.0% of the dry basis mass of the calcined kaolin.

[0012] The BET specific surface area of ​​the silica is 120–250 m² / g.

[0013] Preferably, the first EPDM rubber is 55 parts by weight and the second EPDM rubber is 45 parts by weight.

[0014] The first EPDM rubber has an ethylene content of 72% and a Mooney viscosity ML(1+4) of 70 at 125°C, while the second EPDM rubber has an ethylene content of 58% and a Mooney viscosity ML(1+4) of 40 at 125°C.

[0015] Preferably, the first EPDM rubber, the second EPDM rubber, and the liquid EPDM rubber all use ethylene-neobornene as the third monomer.

[0016] The liquid EPDM rubber is 15 parts by weight, and its viscosity at 25°C is 2000-2400 mPa·s, and its volatile content is not higher than 0.8%.

[0017] The D50 of the flaky calcined kaolin is 1.5 μm, and the mass of vinyltrimethoxysilane added is 1.2% of the dry basis mass of the calcined kaolin.

[0018] The BET specific surface area of ​​the silica is 180 m² / g.

[0019] Secondly, the present invention provides a method for preparing ethylene propylene rubber insulation material for charging pile cables. Based on a total of 100 parts by mass of a first ethylene propylene rubber and a second ethylene propylene rubber, the first ethylene propylene rubber and the second ethylene propylene rubber are mixed. The mass ratio of the first ethylene propylene rubber to the second ethylene propylene rubber is 30:70 to 70:30. The ethylene content of the first ethylene propylene rubber is 68% to 78%, and the Mooney viscosity ML(1+4) at 125°C is 55 to 85. The ethylene content of the second ethylene propylene rubber is 50% to 65%, and the Mooney viscosity ML(1+4) at 125°C is 30 to 55.

[0020] Add 6-24 parts by weight of liquid EPDM rubber and continue mixing;

[0021] Before the addition of silica, 12 parts by weight of flake calcined kaolin treated with vinyltrimethoxysilane were added in two batches of 6 parts by weight each. After the first batch was added, the mixture was kneaded for 1 min, and after the second batch was added, the mixture was kneaded for another 4 min.

[0022] After completing the above-mentioned mixing of the flaky calcined kaolin, add 25 parts by weight of precipitated silica and continue mixing.

[0023] During the masterbatch process, 0.8 parts by weight of antioxidant 1010, 0.6 parts by weight of antioxidant 168, 1.0 part by weight of anti-ozone wax, and 0.6 parts by weight of antioxidant 6PPD are added to complete the masterbatch process;

[0024] After the obtained masterbatch is discharged and cooled, 1.8 parts by weight of dicumyl peroxide and 2.5 parts by weight of triallyl isocyanurate are added for final mixing. The resulting final rubber is then shaped and crosslinked to obtain the ethylene propylene rubber insulation material for charging pile cables.

[0025] Preferably, the first EPDM rubber is 55 parts by weight and the second EPDM rubber is 45 parts by weight.

[0026] The first and second EPDM rubbers were put into a mixer and mixed for 2 minutes at an initial chamber temperature of 70°C and a rotor speed of 45 r / min. Then, 15 parts by mass of liquid EPDM rubber were added within 60 seconds, and mixing was continued for 2 minutes after the addition was completed.

[0027] Preferably, the temperature of the rubber compound during the two batches of calcined kaolin added and mixed is 80-95°C;

[0028] After the second batch of calcined kaolin flakes was added and the mixture was continued for 4 minutes, the rotor speed was adjusted to 50 r / min, 12.5 parts by weight of silica were added and mixed for 90 seconds, and then the remaining 12.5 parts by weight of silica were added and the mixture was continued for 4 minutes.

[0029] Then add 0.8 parts by weight of antioxidant 1010, 0.6 parts by weight of antioxidant 168, 1.0 part by weight of anti-ozone wax and 0.6 parts by weight of antioxidant 6PPD and continue mixing for 1 min. After controlling the temperature of the rubber compound to not exceed 120℃, discharge the rubber.

[0030] Preferably, the obtained masterbatch is made into a sheet with a thickness of 3-5 mm and cooled to a surface temperature not exceeding 65°C. It is then transferred to a two-roll mill with a front and rear roll temperature of 40-50°C and a roll gap of 1.0-1.5 mm. After passing through the mill twice, the dicumyl peroxide and triallyl isocyanurate are added. The milling continues for 3 minutes, and the rubber is alternately cut and turned 6 times. Then, it is passed through the mill 6 more times, and the surface temperature of the rubber compound is kept not exceeding 70°C during the final mixing process.

[0031] Preferably, the positive vulcanization time t90 of the final rubber compound is determined at 170°C using a rotorless vulcanizer. After the final rubber compound is molded, it is crosslinked at 170°C and 10 MPa for 2 min after the positive vulcanization time t90.

[0032] The beneficial effects of this invention are as follows:

[0033] This invention involves first introducing liquid EPDM rubber into the EPDM rubber compound, and then completing the specified mixing of flake calcined kaolin treated with vinyltrimethoxysilane before adding silica. This reduces filler interface defects after medium immersion and temperature cycling, and improves the retention of insulation and flexibility properties without excessively increasing the overall crosslinking degree and initial stiffness of the material. Attached Figure Description

[0034] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1 These are SEM morphology comparison images from Example 2;

[0036] Figure 2 This is a comparison chart of tensile properties in Example 2. Detailed Implementation

[0037] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0038] Unless otherwise stated, the mass fraction of each component is based on a total of 100 parts by mass of the first EPDM rubber and the second EPDM rubber.

[0039] The first EPDM (ethylene propylene diene monomer) has an ethylene content of 68%–78% and a Mooney viscosity (ML(1+4)) of 55–85 at 125°C. The second EPDM has an ethylene content of 50%–65% and a Mooney viscosity (ML(1+4)) of 30–55 at 125°C. Both the first and second EPDMs use ethylene-ide norbornene as the third monomer.

[0040] Liquid ethylene propylene diene monomer (EPDM) rubber, hereinafter referred to as liquid EPDM, uses ethylene-ide norbornene as the third monomer. Its viscosity at 25°C is 500-5000 mPa·s, and its volatile content is not higher than 1.0%.

[0041] The calcined kaolin used is flaky calcined kaolin with a D50 of 0.5–5 μm and is surface treated with vinyltrimethoxysilane. The silica used is precipitated silica with a BET specific surface area of ​​120–250 m² / g.

[0042] Antioxidant 1010 is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]; Antioxidant 168 is tris(2,4-di-tert-butylphenyl) phosphite; Antioxidant 6PPD is N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine; and the ozone-protecting wax is a rubber protective wax with a melting point of 64±2℃.

[0043] Dicumyl peroxide (hereinafter referred to as DCP) and triallyl isocyanurate (hereinafter referred to as TAIC) are used in amounts based on the mass of the active ingredients.

[0044] For each embodiment and comparative example, three independent mixing batches were prepared. Each batch independently completed the weighing of raw materials, internal mixing, final mixing and cross-linking. The test results that required the calculation of standard deviation were used as the final statistical unit.

[0045] Both the calcined kaolin and silica fume were dried at 105℃ for 2 hours before use and then weighed after cooling in a desiccator.

[0046] During internal mixing, select the appropriate internal mixer specifications based on the actual amount of material fed in, keeping the loading coefficient between 0.65 and 0.75. The mixing time for each stage is calculated from the time the corresponding raw material is added and the pressure roller is closed. The temperature of the rubber compound is measured using the internal mixer's built-in temperature detection device.

[0047] After the masterbatch is completed, the rubber compound is made into a sheet with a thickness of 3-5 mm. After the surface temperature of the sheet drops to no higher than 65°C, it is transferred to a two-roll mill. The temperature of the front and rear rolls of the two-roll mill is controlled at 40-50°C, and the roll gap is 1.0-1.5 mm. After the rubber compound is passed through the mill twice, the specified amount of DCP and TAIC are added, and the milling continues for 3 minutes. The rubber is then cut and turned 6 times alternately from left to right, and then passed through the mill 6 more times to ensure that the surface temperature of the rubber compound does not exceed 70°C during the final mixing process. Then the roll gap is adjusted to 2-3 mm and the sheet is cut.

[0048] The positive vulcanization time t90 of each final rubber compound was determined at 170℃ using a rotorless vulcanizer. After the final rubber compound was molded, it was crosslinked at 170℃ and 10 MPa for 2 min at the corresponding t90.

[0049] After all cross-linked test pieces are demolded, they are placed at 23±2℃ and 50%±5% relative humidity for no less than 24 hours before initial performance testing or subsequent media treatment.

[0050] Example 1

[0051] This embodiment uses a premixed adhesive method to prepare ethylene propylene rubber insulation material.

[0052] By weight, the composition includes 55 parts of first EPDM, 45 parts of second EPDM, 15 parts of liquid EPDM, 12 parts of flake calcined kaolin treated with vinyltrimethoxysilane, 25 parts of silica, 0.8 parts of antioxidant 1010, 0.6 parts of antioxidant 168, 1.0 part of anti-ozone wax, 0.6 parts of antioxidant 6PPD, 1.8 parts of DCP, and 2.5 parts of TAIC.

[0053] The first EPDM has an ethylene content of 72% and a Mooney viscosity (ML(1+4)) of 70 at 125°C; the second EPDM has an ethylene content of 58% and a Mooney viscosity (ML(1+4)) of 40 at 125°C; the liquid EPDM has a viscosity of 2200 mPa·s at 25°C and a volatile content of 0.6%; the D50 of the calcined kaolin flakes is 1.5 μm; and the BET specific surface area of ​​the silica is 180 m² / g.

[0054] Take 100 parts of calcined kaolin flakes, dry them at 105℃ for 2 h and cool them to below 40℃.

[0055] Mix 18 parts of anhydrous ethanol and 2 parts of deionized water, adjust the pH to 4.5±0.2 with glacial acetic acid, add 1.2 parts of vinyltrimethoxysilane, and stir for 20 min at 25±2℃ and 300 r / min.

[0056] The dried calcined kaolin flakes were added to a high-speed mixer and mixed for 2 minutes at 45–55°C and 600 r / min. The above-mentioned silane treatment solution was sprayed in within 3 minutes. After the spraying was completed, the speed was increased to 1200 r / min and the mixing continued for 10 minutes.

[0057] The obtained powder was dried at 105℃ for 2 h, then kept at 120℃ for 1 h, cooled and passed through a 100-mesh sieve to obtain modified flaky calcined kaolin.

[0058] Weigh 25 parts of the second EPDM and put them into the internal mixer. Plasticize for 1 min at an initial chamber temperature of 60℃ and a rotor speed of 45 r / min.

[0059] Add 15 parts of liquid EPDM within 60 seconds, and continue mixing for 2 minutes after the addition is complete.

[0060] 12 parts of modified calcined kaolin were added in two batches, 6 parts each. After the first batch was added, the mixture was stirred for 1 minute. Then the second batch was added and stirred for another 4 minutes. No silica was added during this process. The temperature of the rubber compound was controlled to be no higher than 80℃. After the mixture was finished, the rubber was discharged to obtain the premixed rubber.

[0061] The premixed adhesive is made into a film with a thickness of 3 to 5 mm, cooled to a surface temperature of no more than 50°C, and then cut into strips with a width of 10 to 20 mm.

[0062] 55 parts of the first EPDM and 20 parts of the remaining second EPDM were put into an internal mixer and mixed for 2 minutes at an initial chamber temperature of 75°C and a rotor speed of 50 r / min.

[0063] The premixed rubber was added in three batches in equal quantities, with a 60-second interval between each batch. After the third batch was added, the mixture was continued for 3 minutes.

[0064] Add 25 parts of silica in two batches, 12.5 parts each. After the first batch is added, mix for 90 seconds, then add the second batch and continue mixing for 4 minutes.

[0065] After the silica is mixed, add 0.8 parts of antioxidant 1010, 0.6 parts of antioxidant 168, 1.0 part of anti-ozone wax and 0.6 parts of antioxidant 6PPD, and continue mixing for 1 minute. After the rubber compound temperature does not exceed 120℃, discharge the rubber.

[0066] Add 1.8 parts of DCP and 2.5 parts of TAIC according to the aforementioned final mixing conditions, and then complete the crosslinking according to the measured t90 to obtain the ethylene propylene rubber insulation material of Example 1.

[0067] Example 2

[0068] refer to Figure 1 and Figure 2 In this embodiment, the segmented mixing is completed within the same internal mixer.

[0069] The types, weights, and specifications of the raw materials are the same as in Example 1.

[0070] 55 parts of the first EPDM and 45 parts of the second EPDM were put into an internal mixer and mixed for 2 minutes at an initial chamber temperature of 70°C and a rotor speed of 45 r / min.

[0071] Add 15 parts of liquid EPDM within 60 seconds, and continue mixing for 2 minutes after the addition is complete.

[0072] Add 12 parts of modified calcined kaolin in two batches, 6 parts per batch. After the first batch is added, mix for 1 minute, then add the second batch and continue mixing for 4 minutes, keeping the compound temperature at 80-95℃.

[0073] No silica was added during the addition and mixing of the two batches of modified calcined kaolin.

[0074] After the second batch of modified flake calcined kaolin was mixed for another 4 minutes, the rotor speed was adjusted to 50 r / min, 12.5 parts of silica were added and mixed for 90 s, then the remaining 12.5 parts of silica were added and mixed for another 4 minutes.

[0075] After the two inorganic fillers have been mixed as specified, add 0.8 parts of antioxidant 1010, 0.6 parts of antioxidant 168, 1.0 part of anti-ozone wax and 0.6 parts of antioxidant 6PPD, and continue mixing for 1 minute. After the rubber compound temperature does not exceed 120℃, discharge the rubber.

[0076] The obtained masterbatch was processed according to the aforementioned final mixing and crosslinking conditions to obtain the ethylene propylene rubber insulation material of Example 2.

[0077] Examples 3 through 6 all used the same feeding sequence and mixing conditions as Example 2, only changing the test parameters explicitly described in the corresponding examples. Independent reference samples were prepared for each parameter series, and the test results for each series were statistically analyzed independently.

[0078] Example 3

[0079] This embodiment examines the viscosity and dosage of liquid EPDM.

[0080] The liquid EPDM used in samples 3-1, 3-2 and 3-3 all used ethylene norbornene as the third monomer, with an ethylene content of 55% ± 3%, an ethylene norbornene content of 5.0% ± 0.5%, and a volatile content of no more than 0.8%.

[0081] The viscosity of liquid EPDM used in Sample 3-1 at 25℃ was 550±50 mPa·s, and the amount used was 15 parts; the viscosity of liquid EPDM used in Sample 3-2 at 25℃ was 2200±200 mPa·s, and the amount used was 15 parts; the viscosity of liquid EPDM used in Sample 3-3 at 25℃ was 4800±200 mPa·s, and the amount used was 15 parts.

[0082] Samples 3-4 used liquid EPDM of the same specifications as sample 3-2, with a quantity of 6 parts; Samples 3-5 used liquid EPDM of the same specifications as sample 3-2, with a quantity of 24 parts.

[0083] The remaining components and preparation conditions are the same as in Example 2.

[0084] Example 4

[0085] This embodiment examines the amount of vinyltrimethoxysilane added.

[0086] The same batch of calcined kaolin with a D50 of 1.5 μm was used and surface treated according to the method described in Example 1.

[0087] The amount of vinyltrimethoxysilane added in sample 4-1 was 0.5% of the dry basis weight of the calcined kaolin flakes; in sample 4-2 it was 1.2%; and in sample 4-3 it was 3.0%.

[0088] All percentages represent the ratio of the actual mass of vinyltrimethoxysilane fed to the dry basis mass of the calcined kaolin flakes before treatment.

[0089] All three samples used 12 parts of the corresponding modified flaky calcined kaolin, and the remaining components and preparation conditions were the same as in Example 2.

[0090] Example 5

[0091] This embodiment examines the mass ratio of the first EPDM to the second EPDM, Mooney viscosity, and ethylene content.

[0092] The mass fractions of the first EPDM and the second EPDM in samples 5-1, 5-2 and 5-3 are 30:70, 55:45 and 70:30, respectively.

[0093] The Mooney viscosity ML(1+4) at 125℃ of the first EPDM in samples 5-4, 5-2 and 5-5 were 55, 70 and 85 respectively, and the Mooney viscosity of the second EPDM was 40.

[0094] The Mooney viscosity ML(1+4) at 125℃ of the second EPDM in samples 5-6, 5-2 and 5-7 were 30, 40 and 55 respectively, while the Mooney viscosity of the first EPDM was 70.

[0095] The ethylene contents of the first EPDM in samples 5-8, 5-2 and 5-9 were 68%, 72% and 78% respectively, while the ethylene content of the second EPDM was 58% in all samples.

[0096] The ethylene content of the second EPDM in samples 5-10, 5-2 and 5-11 was 50%, 58% and 65% respectively, while the ethylene content of the first EPDM was 72% in all samples.

[0097] In each group of experiments, the EPDM mass fraction, Mooney viscosity, and ethylene content, which were not variables, remained unchanged, while the remaining components and preparation conditions were the same as in Example 2.

[0098] Example 6

[0099] This embodiment examines the particle size of calcined kaolin and the BET specific surface area of ​​silica.

[0100] Samples 6-1, 6-2, and 6-3 were calcined kaolin with D50 values ​​of 0.6 μm, 1.5 μm, and 4.8 μm, respectively. The mass of vinyltrimethoxysilane added in all three samples was 1.2% of the dry weight of the calcined kaolin. The BET specific surface area of ​​the silica in all three samples was 180 m² / g.

[0101] Samples 6-4, 6-5, and 6-6 were all modified calcined kaolin with a D50 of 1.5 μm and a vinyltrimethoxysilane content of 1.2%. The BET specific surface areas of the silica used were 125 m² / g, 180 m² / g, and 245 m² / g, respectively.

[0102] The remaining components and preparation conditions of each sample were the same as in Example 2.

[0103] Comparative Example 1

[0104] Comparative Example 1 used the same types, specifications, and mass fractions of raw materials as Example 2, only changing the feeding time relationship between modified calcined kaolin and silica.

[0105] After mixing the first and second EPDM for 2 minutes, add 15 parts of liquid EPDM within 60 seconds and continue mixing for 2 minutes.

[0106] Subsequently, 12 parts of modified calcined kaolin were added, and within 30 seconds after the addition of the kaolin, 25 parts of silica were added, so that the silica was added into the rubber compound before the modified calcined kaolin had completed the 1 min plus 4 min mixing specified in Example 2.

[0107] After the two inorganic fillers were mixed according to the specified instructions, 0.8 parts of antioxidant 1010, 0.6 parts of antioxidant 168, 1.0 part of anti-ozone wax and 0.6 parts of antioxidant 6PPD were added and mixed for 1 min. The material was then prepared according to the same final mixing and crosslinking conditions as in Example 2.

[0108] Comparative Example 2

[0109] Comparative Example 2 used the same types, specifications, and mass fractions of raw materials as Example 2, only changing the feeding order of the two inorganic fillers.

[0110] After mixing the first and second EPDM for 2 minutes, add liquid EPDM within 60 seconds and continue mixing for 2 minutes.

[0111] First, add 12.5 parts of silica and mix for 90 seconds, then add the remaining 12.5 parts of silica and continue mixing for 4 minutes.

[0112] Then add 6 parts of modified calcined kaolin flakes and mix for 1 min, then add the remaining 6 parts and continue mixing for 4 min.

[0113] After the two inorganic fillers were mixed, 0.8 parts of antioxidant 1010, 0.6 parts of antioxidant 168, 1.0 part of anti-ozone wax and 0.6 parts of antioxidant 6PPD were added and mixed for another 1 min. Then, the final mixing and crosslinking were completed under the same conditions as in Example 2.

[0114] Comparative Example 3

[0115] Comparative Example 3 used the same raw material types, specifications, and mass fractions as Example 2, only changing the feeding sequence of liquid EPDM.

[0116] After mixing the first EPDM and the second EPDM for 2 minutes, the modified calcined kaolin flakes were added in two batches and mixed for 1 minute and 4 minutes respectively.

[0117] The silica was then added in two batches. After the first batch was added, the mixture was kneaded for 90 seconds, and after the second batch was added, the mixture was kneaded for another 4 minutes.

[0118] After the two inorganic fillers are mixed, 15 parts of liquid EPDM are added within 60 seconds and the mixing continues for 2 minutes.

[0119] After the liquid EPDM is fully mixed, add 0.8 parts of antioxidant 1010, 0.6 parts of antioxidant 168, 1.0 part of anti-ozone wax and 0.6 parts of antioxidant 6PPD and mix for 1 min, then perform final mixing and crosslinking.

[0120] Comparative Example 4

[0121] Twelve portions of calcined kaolin, from the same batch as in Example 2 and untreated with vinyltrimethoxysilane, were used to replace the 12 portions of modified calcined kaolin in Example 2.

[0122] The D50 of untreated flaky calcined kaolin is 1.5 μm.

[0123] The other raw materials, feeding sequence, mixing time, final mixing and crosslinking conditions are the same as in Example 2.

[0124] Comparative Example 5

[0125] The first EPDM (55 copies) and the second EPDM (45 copies) in Example 2 were replaced with 100 copies of the second EPDM.

[0126] The second EPDM has an ethylene content of 58% and a Mooney viscosity ML(1+4) of 40 at 125°C.

[0127] The remaining raw materials, mass fractions, and preparation conditions are the same as in Example 2.

[0128] Comparative Example 6

[0129] The masterbatch formula and masterbatch sequence of Comparative Example 6 are the same as those of Comparative Example 1, except that the amount of DCP is increased from 1.8 parts to 2.6 parts, while the amount of TAIC remains at 2.5 parts.

[0130] Each batch of rubber compound has its own vulcanization curve to determine t90, and then crosslinking is completed under the same molding conditions.

[0131] Comparative Example 7

[0132] 15 parts of liquid paraffin were used to replace 15 parts of liquid EPDM in Example 2.

[0133] The kinematic viscosity of liquid paraffin at 40°C is 18.6 mm² / s.

[0134] The remaining raw materials and preparation conditions are the same as in Example 2.

[0135] Comparative Example 8

[0136] No calcined kaolin flakes were added; only 25 parts of silica were retained.

[0137] After the first EPDM, the second EPDM and the liquid EPDM have been mixed according to the specified mixing, they are mixed for another 5 minutes without adding inorganic fillers. Then, 25 parts of silica are added and the mixing is completed according to the silica mixing conditions in Example 2.

[0138] Subsequently, antioxidant 1010, antioxidant 168, anti-ozone wax and anti-aging agent 6PPD were added, and the material was prepared under the same final mixing and crosslinking conditions as in Example 2.

[0139] Comparative Example 9

[0140] The mixture consisted of 100 parts of second EPDM, 15 parts of liquid paraffin, 12 parts of untreated calcined kaolin flakes, and 25 parts of silica.

[0141] The second EPDM used the same batch of raw materials as Comparative Example 5, the liquid paraffin used the same batch of raw materials as Comparative Example 7, and the untreated flaky calcined kaolin used the same batch of raw materials as Comparative Example 4.

[0142] After the second EPDM is mixed for 2 minutes, liquid paraffin is added and the mixture is continued for another 2 minutes.

[0143] Add 12 parts of untreated calcined kaolin flakes, and within 30 seconds after the kaolin is added, start adding 25 parts of silica.

[0144] After the two fillers are mixed, antioxidant 1010, antioxidant 168, anti-ozone wax and anti-aging agent 6PPD are added, and then the final mixing and crosslinking are completed.

[0145] Comparative Example 10

[0146] 15 parts of hydrogenated polyisobutylene were used to replace 15 parts of liquid EPDM in Example 2.

[0147] The dynamic viscosity of hydrogenated polyisobutylene at 25°C is 2250±150 mPa·s, and the volatile matter content is not higher than 0.5%.

[0148] The remaining raw materials and preparation conditions are the same as in Example 2.

[0149] Comparative Example 11

[0150] Twelve parts of spherical fused silica were used to replace twelve parts of the modified flaky calcined kaolin in Example 2.

[0151] The D50 of the spherical fused silica is 1.5 ± 0.2 μm.

[0152] Following the feeding timing of the modified flaky calcined kaolin in Example 2, spherical molten silica was added in two batches, 6 parts per batch. After the first batch was added, the mixture was stirred for 1 minute, and after the second batch was added, the mixture was stirred for another 4 minutes.

[0153] Subsequently, silica was added and the masterbatch, final refining, and crosslinking were completed according to the conditions of Example 2.

[0154] When testing for uncrosslinked rubber is required, prepare a parallel batch with the same formulation and mixing conditions as the corresponding normal batch, and do not draw samples from the rubber compound that will continue to be used for molding and crosslinking.

[0155] Uncrosslinked test samples were obtained at the following time points: except for antioxidant 1010, antioxidant 168, anti-ozone wax, antioxidant 6PPD, DCP and TAIC, all other components in the corresponding masterbatch formulation were sampled after the specified feeding and mixing were completed.

[0156] In Example 2, samples were taken after the second batch of silica had been mixed for 4 minutes and before the addition of antioxidant 1010 and other components; in Comparative Example 3, samples were taken after the addition of liquid EPDM and after the mixing had continued for 2 minutes and before the addition of antioxidant 1010 and other components.

[0157] Three uncrosslinked rubber samples were taken from each independent mixing batch, each sample weighing 0.5000±0.0050 g, and cut into rubber particles smaller than 2 mm.

[0158] Add the sample to 150 mL of toluene and extract at 23±2℃ for 72 h, replacing the toluene every 24 h.

[0159] Insoluble matter was collected using a 0.45 μm polytetrafluoroethylene filter membrane, washed three times with 20 mL of toluene, and then dried under vacuum at 60 °C. The mass was measured every 2 hours. Drying was stopped when the mass change between two consecutive weighings was no more than 0.5% of the previous mass. The mass of the dried residue, m1, was obtained by subtracting the mass of the filter membrane.

[0160] The resulting dried residue was transferred to a constant weight crucible and ashed at 600°C in air to constant weight, yielding inorganic ash mass m2.

[0161] Take untreated flake calcined kaolin and corresponding modified flake calcined kaolin from the same batch, dry them to constant weight at 105℃, and then ashing them to constant weight in air at 600℃.

[0162] The loss on ignition L0 of unmodified flaky calcined kaolin and the loss on ignition L1 of modified flaky calcined kaolin were calculated separately. The difference between L1 and L0 was used as the mass correction ratio cs of the vinyltrimethoxysilane organic part.

[0163] The mass of the rubber, mb, is calculated using the following formula:

[0164] mb = m1 - m2 - m0 × wk × cs;

[0165] Where m0 is the mass of the sample before extraction, and wk is the mass fraction of modified calcined kaolin in the corresponding uncrosslinked sample.

[0166] The relative rubber content B is calculated using the following formula:

[0167] B = mb / (m0×wr)×100%;

[0168] Where wr is the total mass fraction of the first EPDM, the second EPDM, and the liquid EPDM in the corresponding uncrosslinked sample.

[0169] For each mixing batch, the average of the results of three extraction samples is used as the B value for that batch. The overall average and standard deviation are then calculated using the B values ​​of three independent mixing batches.

[0170] Comparative Examples 7 and 9 contain liquid paraffin, and Comparative Example 10 contains hydrogenated polyisobutylene. Considering that the residual behavior of the above non-EPDM liquid components under toluene extraction conditions is different from that of liquid EPDM, the relative content B of the bound rubber in the above three comparative examples is not reported, nor is their B value used for quantitative cross-sectional comparison.

[0171] The final rubber compound was tested at 170°C using a rotorless vulcanizing apparatus to measure the minimum torque ML, maximum torque MH, and t90. The torque difference ΔM was calculated as MH - ML.

[0172] Each independent batch of compounding was tested in parallel three times. The average of the three test results was taken as the result of that batch. The average and standard deviation of the results of the three independent batches were then calculated.

[0173] The equilibrium swelling sample size is 10 mm × 10 mm × 2.0 ± 0.2 mm, and 3 samples are set for each independent mixing batch.

[0174] The sample was dried under vacuum at 50℃ for 4 h, cooled, and weighed. The resulting dry mass was recorded as md.

[0175] The sample was placed in 100 mL of toluene and soaked at 23±2℃, with the toluene being replaced every 24 h.

[0176] The soaking time should be no less than 72 hours. After 72 hours, the sample should be taken out every 24 hours, and the surface toluene should be removed by gently pressing with lint-free absorbent paper. Weighing should be completed within 60 seconds. When the change in wet mass between two consecutive wet mass measurements does not exceed 1% of the previous wet mass, it is considered that swelling equilibrium has been reached. The final wet mass is recorded as ms.

[0177] The equilibrium swelling mass ratio Q is calculated according to the following formula:

[0178] Q = (ms - md) / md;

[0179] For each independent mixing batch, the Q average of 3 samples is used as the result of that batch, and the overall average and standard deviation are calculated based on the results of the 3 independent mixing batches.

[0180] Q is only used as a relative comparative indicator of the overall network constraint degree of different materials.

[0181] Crosslinked test pieces were prepared from three independent mixing batches of each material.

[0182] The sample was completely immersed in liquid nitrogen for 10 minutes and then rapidly fractured along the thickness direction. The fracture surface was treated with carbon coating and observed using a field emission scanning electron microscope and EDS surface scanning.

[0183] Before performing interface size statistics, the image scale of the field emission scanning electron microscope (SEM) was calibrated using a standard sample with a known nominal spacing. The calibration results were verified to be valid according to the calibration procedure of the SEM used. After calibration, SEM images of each sample were acquired at 5000x magnification and the same digital image resolution.

[0184] Based on the Al and Si element distribution obtained from the corresponding EDS surface scan, the region where the flaky calcined kaolin is located is determined, and particles that intersect with the image edge or have incomplete particle boundaries are excluded.

[0185] In the calibrated SEM image, a continuous open region directly connected to the boundary of the flaky calcined kaolin particles is extracted, and the continuous length of the open region along the direction of the kaolin particle boundary is measured according to the image spatial scale recorded in the SEM acquisition file.

[0186] Through cracks directly connected to the outer boundary of the image are not counted as interface openings. When the same sheet-like calcined kaolin particle has at least one continuous interface opening region with a length of not less than 1.0 μm, the particle is counted as having an interface defect.

[0187] At least one brittle fracture sample should be prepared for each independent mixing batch. At least five non-overlapping fields of view should be randomly collected for each sample. At least 100 particles with intact boundaries that can be identified as flaky calcined kaolin by EDS should be counted for each batch. The proportion of interface defects should be calculated based on the number of particles with interface defects and the total number of effectively counted particles.

[0188] The proportion of interface defects in three independent mixing batches was calculated, and then the overall average and standard deviation were calculated based on the results of the three batches.

[0189] The cooling media used were ethylene glycol and deionized water from the same batch. Test solutions were prepared independently for each material at a 50:50 mass ratio; different materials did not share the same test solution.

[0190] The sample was completely immersed in a heat-resistant container equipped with a reflux condenser, with the ratio of the total volume of the cooling medium to the total volume of the sample not less than 15:1, and kept at 80±2℃ for 168 h.

[0191] The sample size for mass and volume changes was 30 mm × 20 mm × 2.0 ± 0.2 mm, and 5 samples were set for each independent mixing batch.

[0192] Weigh the sample in air before immersion, and measure the mass m0.

[0193] Deionized water at 23±1℃ was used as the draining medium. The mass of the sample in the air and the apparent mass when it was completely submerged in deionized water were recorded. After removing air bubbles attached to the sample surface, the initial volume V0 was calculated based on the mass difference between the two and the density of deionized water at 23±1℃.

[0194] After soaking for 168 h, the sample was taken out, rinsed with deionized water for 10 s, and the visible liquid on the surface was removed by gently pressing with lint-free absorbent paper. The mass m1 was measured within 5 min, and the volume V1 was measured by the same liquid drainage method.

[0195] The rate of change in mass is calculated using the following formula:

[0196] (m1-m0) / m0×100%;

[0197] The rate of change of volume is calculated according to the following formula:

[0198] (V1-V0) / V0×100%;

[0199] The media-treated specimens used for electrical, tensile, and compliance tests are independent of the specimens used for mass and volume determination.

[0200] After the above samples were soaked for 168 h, they were rinsed with deionized water for 10 s, and the visible liquid on the surface was removed by gently pressing with lint-free absorbent paper. After being placed in an environment of 23±2℃ for 2 h, the corresponding performance tests were carried out.

[0201] For thermal cycling testing, a separate set of independent samples that had undergone 168 hours of immersion in the cooling medium were used. After rinsing and removing visible liquid from the surface, the samples were transferred to the high and low temperature test chamber within 30 minutes.

[0202] The test chamber is kept at -30±2℃ for 60 min, then raised to 90±2℃ within 15 min and kept at 90±2℃ for 60 min, and then lowered to -30±2℃ within 15 min. This process is counted as one thermal cycle, and a total of 50 cycles are performed.

[0203] After the 50th thermal cycle, the sample was transferred to an environment of 23±2℃ and placed for 2 hours before being tested for volume resistivity, breakdown strength, tensile properties, compliance properties and interface morphology.

[0204] Volume resistivity was determined using cross-linked specimens with a thickness of 1.0 ± 0.1 mm.

[0205] A high-resistance meter with a main electrode, a protection electrode and a high-voltage electrode is used. The effective diameter of the main electrode is 50 mm.

[0206] The test environment was 23±2℃ and 50%±5% relative humidity. A 500 V DC voltage was applied, and the stable resistance was read 60 s after the voltage was applied. The volume resistivity was calculated based on the effective area of ​​the main electrode and the actual thickness of the sample.

[0207] Three independent samples were set up for each independent mixing batch and each treatment state.

[0208] The breakdown strength was measured using a specimen with a thickness of 1.0 ± 0.1 mm.

[0209] The sample was placed in insulating oil at 23±2℃, and a spherical electrode with a diameter of 25 mm was used to continuously increase the voltage at a rate of 2 kV / s until breakdown.

[0210] The breakdown strength is calculated by dividing the breakdown voltage by the actual sample thickness at the breakdown location.

[0211] Breakdowns occurring outside the effective electrode area or that can be confirmed as being caused by mechanical damage to the sample are not included in the valid results, and a corresponding sample is provided.

[0212] For each independent mixing batch and each processing state, at least five valid results should be obtained.

[0213] The tensile specimen thickness is 2.0±0.2 mm, the width of the narrow parallel section is 4.0±0.1 mm, and the initial gauge length is 20 mm.

[0214] The test temperature was 23±2℃, and the tensile speed was 500 mm / min. At least 5 valid test results were obtained for each independent mixing batch and each treatment condition.

[0215] The 100% constant elongation stress M100 is tested using the tensile specimens described above. When the 20 mm gauge length is extended to 40 mm, the load F100 is recorded, and M100 is calculated according to the ratio of F100 to the initial cross-sectional area of ​​the specimen.

[0216] The specified deflection bending force F10 is achieved using a rectangular specimen measuring 80 mm × 10.0 ± 0.1 mm × 2.0 ± 0.2 mm.

[0217] The three-point bending support span is 40 mm, the upper pressure head and the support roller are both 10 mm in diameter, and the upper pressure head descends at a speed of 50 mm / min.

[0218] Displacement is recorded when the load reaches 0.02 N, and load F10 is recorded when the deflection at the middle of the specimen reaches 10.0 mm.

[0219] Five independent samples were set up for each independent mixing batch and each treatment state.

[0220] For volume resistivity, breakdown strength, tensile strength, elongation at break, M100, and F10, the batch average values ​​for the initial state and the corresponding processing state are calculated for each independent mixing batch.

[0221] The performance retention rate Rk of the kth independent compounding batch is calculated according to the following formula:

[0222] Rk = Average value of the processed batch / Average value of the initial state of the same batch × 100%.

[0223] R1, R2 and R3 were obtained for the same material. The arithmetic mean of the retention rates of the three independent compounding batches was used as the final retention rate, and the standard deviation was calculated using R1, R2 and R3.

[0224] For volume change rate and mass change rate, the average of the results of 5 samples was used as the result of each independent mixing batch, and the overall average and standard deviation were calculated using the results of 3 independent mixing batches.

[0225] Table 1 shows the main material condition test results for Examples 1 and 2.

[0226] sample Combined with relative rubber content B / % ΔM / (dN·m) Q Percentage of interface defects after medium + thermal cycling / % Initial M100 / MPa Initial F10 / N Example 1 28.5±1.0 7.60±0.12 1.92±0.05 21.5±2.0 3.17±0.09 1.46±0.05 Example 2 27.4±0.9 7.48±0.12 1.96±0.05 22.7±2.1 3.11±0.08 1.44±0.05

[0227] Table 2 shows the test results for the viscosity and dosage of liquid EPDM.

[0228] sample Liquid EPDM conditions Combined with relative rubber content B / % Percentage of interface defects after medium + thermal cycling / % Medium volume change rate / % Dielectric + Thermal Cycling Breakdown Strength Retention Rate / % Initial M100 / MPa Initial F10 / N 3-1 550±50 mPa·s, 15 parts 25.1±0.9 26.7±2.1 3.01±0.14 84.9±1.5 3.15±0.08 1.46±0.05 3-2 2200±200 mPa·s, 15 parts 27.2±0.9 23.1±2.1 2.61±0.14 87.5±1.5 3.10±0.08 1.44±0.05 3-3 4800±200 mPa·s, 15 parts 26.0±1.0 25.2±1.9 2.83±0.15 85.9±1.6 3.18±0.07 1.47±0.05 3-4 2200±200 mPa·s, 6 parts 24.6±0.9 27.3±2.2 3.06±0.16 84.6±1.7 3.23±0.09 1.51±0.06 3-5 2200±200 mPa·s, 24 parts 26.3±1.1 25.8±2.0 2.90±0.13 86.0±1.3 2.97±0.08 1.35±0.05

[0229] Table 3 shows the test results for the amount of vinyltrimethoxysilane added.

[0230] sample Vinyltrimethoxysilane addition amount / % Combined with relative rubber content B / % Percentage of interface defects after medium + thermal cycling / % Medium volume change rate / % Dielectric + Thermal Cycling Breakdown Strength Retention Rate / % Initial M100 / MPa Initial F10 / N 4-1 0.5 25.3±0.9 27.4±2.2 3.03±0.14 85.0±1.6 3.08±0.07 1.41±0.05 4-2 1.2 27.7±0.8 22.2±2.0 2.54±0.13 88.2±1.3 3.13±0.09 1.42±0.05 4-3 3.0 26.5±1.0 25.0±2.1 2.79±0.15 86.3±1.5 3.21±0.08 1.48±0.05

[0231] Table 4 shows the test results of the parameters of the first and second EPDM.

[0232] sample Examination conditions Combined with relative rubber content B / % Percentage of interface defects after medium + thermal cycling / % Medium volume change rate / % Dielectric + Thermal Cycling Breakdown Strength Retention Rate / % Initial M100 / MPa Initial F10 / N 5-1 First / Second EPDM = 30:70 25.1±0.9 28.1±2.2 3.10±0.15 84.6±1.6 2.96±0.08 1.35±0.05 5-2 First / Second EPDM = 55:45 27.5±1.0 22.6±2.2 2.57±0.15 87.9±1.6 3.11±0.08 1.45±0.06 5-3 First / Second EPDM = 70:30 26.1±1.0 25.5±1.9 2.85±0.14 86.2±1.5 3.35±0.10 1.55±0.06 5-4 First EPDM Mooney 55 26.0±0.9 25.7±2.0 2.90±0.13 85.7±1.6 3.00±0.07 1.38±0.05 5-5 First EPDM Mooney 85 26.7±1.1 24.7±2.1 2.74±0.14 86.8±1.4 3.36±0.10 1.58±0.07 5-6 Second EPDM Mooney 30 26.8±0.9 25.0±1.8 2.77±0.12 86.4±1.5 3.05±0.08 1.40±0.05 5-7 Second EPDM Mooney 55 25.8±1.0 26.2±2.2 2.94±0.15 85.5±1.6 3.26±0.09 1.50±0.06 5-8 First EPDM ethylene 68% 26.3±0.8 25.6±2.1 2.89±0.13 85.8±1.5 3.04±0.07 1.39±0.04 5-9 First EPDM ethylene 78% 26.8±1.0 24.5±1.9 2.73±0.14 86.9±1.4 3.27±0.09 1.53±0.06 5-10 Second EPDM ethylene 50% 26.4±0.9 25.3±2.0 2.82±0.12 86.2±1.5 3.18±0.08 1.46±0.05 5-11 Second EPDM ethylene 65% 25.9±1.1 26.4±2.2 2.96±0.16 85.5±1.7 3.09±0.08 1.42±0.05

[0233] Table 5 shows the test results of particle size of calcined kaolin and BET specific surface area of ​​silica.

[0234] sample Examination conditions Combined with relative rubber content B / % Percentage of interface defects after medium + thermal cycling / % Medium volume change rate / % Dielectric + Thermal Cycling Breakdown Strength Retention Rate / % Initial M100 / MPa Initial F10 / N 6-1 Kaolin D50 = 0.6 μm 26.9±0.9 24.6±2.2 2.75±0.14 86.9±1.5 3.20±0.08 1.47±0.05 6-2 Kaolin D50 = 1.5 μm 27.5±0.9 22.5±2.0 2.57±0.13 87.9±1.4 3.12±0.08 1.44±0.05 6-3 Kaolin D50 = 4.8 μm 25.8±1.0 26.4±2.3 2.96±0.16 85.6±1.6 3.05±0.09 1.40±0.06 6-4 Silica BET = 125 m² / g 26.4±0.8 24.8±2.1 2.84±0.15 86.2±1.5 2.99±0.08 1.37±0.05 6-5 Silica BET = 180 m² / g 27.3±0.9 22.9±2.2 2.61±0.14 87.7±1.5 3.10±0.09 1.43±0.05 6-6 Silica BET = 245 m² / g 26.7±1.0 24.2±2.0 2.78±0.13 86.6±1.4 3.30±0.09 1.55±0.06

[0235] Table 6 shows the material condition test results for the examples and main comparative examples.

[0236] sample Combined with relative rubber content B / % ΔM / (dN·m) Q Percentage of interface defects in kaolin after medium + thermal cycling / % Initial M100 / MPa Initial F10 / N Example 1 28.5±1.0 7.60±0.12 1.92±0.05 21.5±2.0 3.17±0.09 1.46±0.05 Example 2 27.4±0.9 7.48±0.12 1.96±0.05 22.7±2.1 3.11±0.08 1.44±0.05 Comparative Example 1 23.5±1.0 7.43±0.13 2.03±0.06 30.1±2.3 3.09±0.08 1.43±0.05 Comparative Example 2 24.2±0.9 7.50±0.12 2.00±0.05 28.9±2.2 3.13±0.07 1.45±0.05 Comparative Example 3 21.9±1.1 7.31±0.14 2.10±0.07 34.4±2.4 3.05±0.08 1.40±0.05 Comparative Example 4 20.8±0.8 7.33±0.12 2.09±0.06 36.0±2.5 3.00±0.07 1.39±0.05 Comparative Example 5 22.9±0.9 7.20±0.15 2.14±0.07 33.0±2.0 2.88±0.08 1.34±0.05 Comparative Example 6 23.4±0.9 8.28±0.11 1.76±0.05 29.4±1.8 3.53±0.09 1.67±0.06 Comparative Example 7 — 7.37±0.13 2.12±0.07 32.5±2.3 2.94±0.08 1.32±0.05 Comparative Example 8 — 7.27±0.14 2.16±0.08 — 3.18±0.08 1.48±0.05 Comparative Example 9 — 7.06±0.15 2.25±0.08 38.8±2.6 2.76±0.08 1.26±0.05 Comparative Example 10 — 7.40±0.14 2.08±0.06 30.2±2.4 3.01±0.08 1.37±0.06 Comparative Example 11 — 7.31±0.10 2.12±0.07 — 3.16±0.07 1.47±0.05

[0237] In the table, “—” indicates that because the liquid components or inorganic filler composition of the sample are different from those in Example 2, this indicator does not use the same quantitative comparison method as in Example 2.

[0238] Table 7 shows the test results after only immersion in the cooling medium.

[0239] sample Volume change rate / % Quality change rate / % Volume resistivity retention rate / % Breakdown strength retention rate / % Tensile strength retention rate / % Elongation at break retention rate / % Example 1 2.43±0.15 1.77±0.11 91.6±1.4 92.5±1.4 89.3±1.6 85.1±1.8 Example 2 2.58±0.13 1.88±0.10 90.9±1.1 91.9±1.3 88.7±1.5 84.4±1.8 Comparative Example 1 3.12±0.16 2.36±0.10 87.0±1.2 88.6±1.4 86.4±1.6 81.8±1.7 Comparative Example 2 2.99±0.15 2.24±0.11 87.7±1.3 89.1±1.3 86.9±1.5 82.5±1.5 Comparative Example 3 3.46±0.14 2.63±0.09 85.1±1.4 86.5±1.2 84.4±1.5 79.8±1.8 Comparative Example 4 3.67±0.17 2.79±0.12 83.2±1.6 84.9±1.5 83.7±1.7 78.6±1.5 Comparative Example 5 3.30±0.15 2.49±0.10 85.5±1.2 87.0±1.4 84.8±1.4 79.5±1.7 Comparative Example 6 3.07±0.16 2.33±0.11 87.4±1.2 89.3±1.3 87.3±1.4 77.1±2.0 Comparative Example 7 3.50±0.14 2.69±0.10 86.3±1.3 87.9±1.3 85.7±1.6 80.8±1.6 Comparative Example 8 3.74±0.14 2.92±0.13 85.6±1.2 87.2±1.4 84.7±1.5 79.6±1.5 Comparative Example 9 4.10±0.16 3.22±0.14 83.4±1.2 85.6±1.2 82.6±1.5 78.0±1.6 Comparative Example 10 3.29±0.16 2.48±0.11 86.8±1.3 88.2±1.4 85.9±1.5 80.5±1.6 Comparative Example 11 3.33±0.15 2.54±0.12 86.2±1.3 87.5±1.5 85.3±1.5 79.9±1.7

[0240] Table 8 shows the test results after immersion in the cooling medium and 50 thermal cycles.

[0241] sample Volume resistivity retention rate / % Breakdown strength retention rate / % Tensile strength retention rate / % Elongation at break retention rate / % M100 change rate / % F10 change rate / % Example 1 88.6±1.5 88.7±1.5 86.5±1.8 81.7±2.0 5.6±0.7 6.4±0.8 Example 2 87.9±1.6 87.8±1.5 85.7±1.8 80.9±1.8 6.2±0.9 7.1±0.8 Comparative Example 1 83.2±1.6 83.4±1.4 82.0±1.6 76.7±1.9 9.4±0.8 10.6±0.9 Comparative Example 2 84.2±1.4 84.0±1.3 82.8±1.5 77.6±1.8 8.8±0.7 9.7±0.8 Comparative Example 3 80.6±1.7 80.7±1.5 79.2±1.4 74.0±2.0 11.6±0.9 12.8±0.9 Comparative Example 4 78.9±1.4 79.1±1.4 77.8±1.8 72.9±1.6 12.5±0.8 13.9±0.9 Comparative Example 5 81.0±1.3 81.5±1.4 79.9±1.6 73.8±1.8 12.0±0.9 13.4±0.8 Comparative Example 6 83.4±1.4 84.0±1.3 82.4±1.5 72.6±1.5 15.1±0.8 16.2±1.0 Comparative Example 7 82.6±1.6 83.4±1.6 80.9±1.5 75.3±1.8 13.5±0.9 14.8±1.0 Comparative Example 8 81.7±1.5 82.1±1.6 80.2±1.6 74.4±1.7 10.5±0.8 11.7±0.9 Comparative Example 9 79.1±1.4 79.8±1.5 77.3±1.4 71.9±1.7 16.1±0.9 17.5±1.0 Comparative Example 10 83.3±1.5 84.4±1.5 81.7±1.6 75.7±1.8 12.5±0.9 13.6±0.9 Comparative Example 11 82.7±1.4 83.8±1.5 81.0±1.5 75.1±1.8 10.8±0.8 12.1±0.9

[0242] Example 2 and Comparative Example 1 used the same first EPDM, second EPDM, liquid EPDM, modified flake calcined kaolin, silica, antioxidant, anti-ozone wax, anti-aging agent and crosslinking system.

[0243] In Example 2, the modified calcined kaolin was mixed 1 minute after the first batch was added and 4 minutes after the second batch was added, before the silica was added; in Comparative Example 1, silica began to enter the rubber compound within 30 seconds after the modified calcined kaolin was added.

[0244] The ΔM values ​​for Example 2 and Comparative Example 1 are 7.48±0.12 dN·m and 7.43±0.13 dN·m, respectively; the initial M100 values ​​are 3.11±0.08 MPa and 3.09±0.08 MPa, respectively; and the initial F10 values ​​are 1.44±0.05 N and 1.43±0.05 N, respectively. The three indicators are within a similar range.

[0245] The relative content of the bound rubber B in Example 2 and Comparative Example 1 was 27.4 ± 0.9% and 23.5 ± 1.0%, respectively.

[0246] After immersion in the cooling medium and 50 thermal cycles, the proportion of interfacial defects in the sheet-like calcined kaolin of Example 2 was 22.7±2.1%, while that of Comparative Example 1 was 30.1±2.3%; the breakdown strength retention rates were 87.8±1.5% and 83.4±1.4%, respectively.

[0247] In Comparative Example 2, silica was introduced into the rubber compound before modified calcined kaolin flakes. The relative content of B in the bound rubber was 24.2±0.9%, and the proportion of interface defects after medium immersion and thermal cycling was 28.9±2.2%.

[0248] In Comparative Example 3, liquid EPDM was added after the two inorganic fillers were mixed. The relative content of the binding rubber B was 21.9±1.1%, and the proportion of interface defects after medium immersion and thermal cycling was 34.4±2.4%.

[0249] Comparative Example 6 used the same masterbatch formulation and masterbatch sequence as Comparative Example 1, only increasing the amount of DCP. Its ΔM increased to 8.28±0.11 dN·m, Q decreased to 1.76±0.05, while the proportion of interface defects after medium immersion and thermal cycling remained at 29.4±1.8%.

[0250] Meanwhile, the initial M100 and F10 of Comparative Example 6 were 3.53±0.09 MPa and 1.67±0.06 N, respectively, and the change rates of M100 and F10 after medium immersion and thermal cycling were 15.1±0.8% and 16.2±1.0%, respectively.

[0251] Based on the above test results, under the experimental conditions, when the modified calcined kaolin was mixed according to the specified method before the addition of silica, the resulting uncrosslinked rubber had a higher relative content of bound rubber. At the same time, the overall vulcanization torque difference of the crosslinked material and the initial M100 and F10 did not increase significantly. However, after soaking in the cooling medium and thermal cycling, the proportion of interfacial defects in the calcined kaolin decreased and the breakdown strength retention rate increased.

[0252] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. An ethylene propylene rubber insulation material for charging pile cables, characterized in that, The ethylene propylene rubber insulating material is obtained by mixing and cross-linking raw materials comprising the following components: 100 parts by weight of EPDM rubber and EPDM rubber (total), 6-24 parts by weight of liquid EPDM rubber, 12 parts by weight of flake calcined kaolin surface-treated with vinyltrimethoxysilane, 25 parts by weight of silica, 0.8 parts by weight of antioxidant 1010, 0.6 parts by weight of antioxidant 168, 1.0 part by weight of anti-ozone wax, 0.6 parts by weight of antioxidant 6PPD, 1.8 parts by weight of dicumyl peroxide, and 2.5 parts by weight of triallyl isocyanurate; The mass ratio of the first EPDM rubber to the second EPDM rubber is 30:70 to 70:

30. The ethylene content of the first EPDM rubber is 68% to 78%, and the Mooney viscosity ML(1+4) at 125°C is 55 to 85. The ethylene content of the second EPDM rubber is 50% to 65%, and the Mooney viscosity ML(1+4) at 125°C is 30 to 55. The mixing process involves first introducing the liquid EPDM rubber into a rubber compound containing the first and second EPDM rubbers. Before the addition of silica, the flake-shaped calcined kaolin treated with vinyltrimethoxysilane is added in two batches, 6 parts by weight per batch. After the first batch is added, the mixture is mixed for 1 minute. After the second batch is added, the mixture is further mixed for 4 minutes. After the above mixing process is completed, silica is added and mixed again. The mixture is then crosslinked with dicumyl peroxide and triallyl isocyanurate to form the EPDM rubber insulating material.

2. The ethylene propylene rubber insulation material for charging pile cables according to claim 1, characterized in that, The first EPDM rubber, the second EPDM rubber, and the liquid EPDM rubber all use ethylene-ide norbornene as the third monomer; The liquid EPDM rubber has a viscosity of 500–5000 mPa·s at 25°C and a volatile content of no more than 1.0%.

3. The ethylene propylene rubber insulation material for charging pile cables according to claim 1, characterized in that, The D50 of the flaky calcined kaolin is 0.5–5 μm, and the mass of vinyltrimethoxysilane added is 0.5%–3.0% of the dry basis mass of the calcined kaolin. The BET specific surface area of ​​the silica is 120–250 m² / g.

4. The ethylene propylene rubber insulation material for charging pile cables according to claim 1, characterized in that, The first EPDM rubber is 55 parts by weight, and the second EPDM rubber is 45 parts by weight; The first EPDM rubber has an ethylene content of 72% and a Mooney viscosity ML(1+4) of 70 at 125°C, while the second EPDM rubber has an ethylene content of 58% and a Mooney viscosity ML(1+4) of 40 at 125°C.

5. The ethylene propylene rubber insulation material for charging pile cables according to claim 4, characterized in that, The first EPDM rubber, the second EPDM rubber, and the liquid EPDM rubber all use ethylene-ide norbornene as the third monomer. The liquid EPDM rubber is 15 parts by weight, and its viscosity at 25°C is 2000-2400 mPa·s, and its volatile content is not higher than 0.8%. The D50 of the flaky calcined kaolin is 1.5 μm, and the mass of vinyltrimethoxysilane added is 1.2% of the dry basis mass of the calcined kaolin. The BET specific surface area of ​​the silica is 180 m² / g.

6. A method for preparing ethylene propylene rubber insulation material for charging pile cables, characterized in that, Based on a total of 100 parts by weight of the first EPDM rubber and the second EPDM rubber, the first EPDM rubber and the second EPDM rubber are mixed and compounded. The mass ratio of the first EPDM rubber to the second EPDM rubber is 30:70 to 70:

30. The ethylene content of the first EPDM rubber is 68% to 78%, and the Mooney viscosity ML(1+4) at 125°C is 55 to 85. The ethylene content of the second EPDM rubber is 50% to 65%, and the Mooney viscosity ML(1+4) at 125°C is 30 to 55. Add 6-24 parts by weight of liquid EPDM rubber and continue mixing; Before the addition of silica, 12 parts by weight of flake calcined kaolin treated with vinyltrimethoxysilane were added in two batches of 6 parts by weight each. After the first batch was added, the mixture was kneaded for 1 min, and after the second batch was added, the mixture was kneaded for another 4 min. After completing the above-mentioned mixing of the flaky calcined kaolin, add 25 parts by weight of precipitated silica and continue mixing. During the masterbatch process, 0.8 parts by weight of antioxidant 1010, 0.6 parts by weight of antioxidant 168, 1.0 part by weight of anti-ozone wax, and 0.6 parts by weight of antioxidant 6PPD are added to complete the masterbatch process; After the obtained masterbatch is discharged and cooled, 1.8 parts by weight of dicumyl peroxide and 2.5 parts by weight of triallyl isocyanurate are added for final mixing. The resulting final rubber is then shaped and crosslinked to obtain the ethylene propylene rubber insulation material for charging pile cables.

7. The method for preparing ethylene propylene rubber insulation material for charging pile cables according to claim 6, characterized in that, The first EPDM rubber is 55 parts by weight, and the second EPDM rubber is 45 parts by weight; The first and second EPDM rubbers were put into a mixer and mixed for 2 minutes at an initial chamber temperature of 70°C and a rotor speed of 45 r / min. Then, 15 parts by mass of liquid EPDM rubber were added within 60 seconds, and mixing was continued for 2 minutes after the addition was completed.

8. The method for preparing ethylene propylene rubber insulation material for charging pile cables according to claim 7, characterized in that, The temperature of the rubber compound during the two batches of calcined kaolin added and mixed was 80-95℃. After the second batch of calcined kaolin flakes was added and the mixture was continued for 4 minutes, the rotor speed was adjusted to 50 r / min, 12.5 parts by weight of silica were added and mixed for 90 seconds, and then the remaining 12.5 parts by weight of silica were added and the mixture was continued for 4 minutes. Then add 0.8 parts by weight of antioxidant 1010, 0.6 parts by weight of antioxidant 168, 1.0 part by weight of anti-ozone wax and 0.6 parts by weight of antioxidant 6PPD and continue mixing for 1 minute. After controlling the temperature of the rubber compound to not exceed 120℃, discharge the rubber.

9. The method for preparing ethylene propylene rubber insulation material for charging pile cables according to claim 6, characterized in that, The obtained masterbatch is made into a sheet with a thickness of 3-5 mm and cooled to a surface temperature not exceeding 65°C. It is then transferred to a two-roll mill with a front and rear roll temperature of 40-50°C and a roll gap of 1.0-1.5 mm. After passing through the mill twice, the dicumyl peroxide and triallyl isocyanurate are added. The milling continues for 3 minutes, and the rubber is alternately cut and turned 6 times. Then, it is passed through the mill 6 more times, ensuring that the surface temperature of the rubber compound does not exceed 70°C during the final mixing process.

10. The method for preparing ethylene propylene rubber insulation material for charging pile cables according to claim 9, characterized in that, The positive vulcanization time t90 of the final compound was determined at 170°C using a rotorless vulcanizer. After the final compound was molded, it was crosslinked at 170°C and 10 MPa for 2 min after the positive vulcanization time t90.

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