An epdm rubber composition for automotive vacuum brake hose and a method for producing the same

Abstract

This invention discloses an EPDM rubber composition for automotive vacuum brake hoses, made from the following raw materials in parts by weight: 100-150 parts EPDM rubber, 8-12 parts zinc oxide, 1-2 parts stearic acid, 2-4 parts antioxidant, 50-80 parts plasticizer, 180-250 parts carbon black, 0.8-1.2 parts sulfur S-80, 7-9 parts crosslinking agent, 1-2 parts co-crosslinking agent, and 90-140 parts inorganic filler; the carbon black is a combination of carbon black N990 and carbon black N550. The rubber composition of this invention possesses excellent fuel resistance, high temperature resistance, and low pressure deformation properties, meeting the stringent requirements of high-end vehicle models and thus adapting to specific operating environments.

Description

Technical Field

[0001] This invention belongs to the fields of rubber composite material processing and automotive vacuum braking systems, and relates to an EPDM rubber composition for automotive vacuum brake hoses and its preparation method. Specifically, it relates to an EPDM rubber composition for preparing an inner rubber layer and an outer rubber layer of an automotive vacuum brake hose, and an automotive vacuum brake hose prepared with the above-mentioned EPDM rubber composition. Background Technology

[0002] With the development of the times, automobiles play an increasingly prominent role in people's production and daily lives. Automotive hoses, as an important component of automotive parts, play a crucial role in automotive braking systems, fuel systems, and cooling systems. With the rapid development of the automotive industry, people increasingly pursue high speed, safety, and comfort in automobiles. The performance requirements for automotive hoses are also upgrading with the increasing demands of use, especially for high-end vehicles where the temperature resistance requirements for vacuum brake hoses are becoming increasingly stringent. However, because the medium inside the hose contains oil and gas, oil resistance is required. Currently, most vacuum brake hoses are made of nitrile rubber, which has good oil resistance, but its temperature resistance, weather resistance, and ozone resistance are poor, failing to meet the requirements of operating conditions. Consequently, EPDM vacuum brake hoses emerged on the market. However, EPDM is a non-polar rubber with less than ideal oil resistance, exhibiting significant swelling in fuel and severely compromising its physical and mechanical properties. Due to the stringent performance requirements of high-end vehicles, some OEMs have set stringent fuel resistance B technical specifications (strength and elongation within ±30%) based on the hose's operating conditions. Even some nitrile rubbers cannot fully meet these specifications, making it extremely challenging for EPDM. Even more difficult is simultaneously achieving high temperature resistance and low-pressure deformation. Currently, the highest temperature resistance of EPDM compounds used in vacuum brake hoses on the market is only 125℃ (125℃~150℃ (instantaneous)), which cannot meet the requirements of higher operating conditions. Summary of the Invention

[0003] The purpose of this invention is to provide an EPDM rubber composition for automotive vacuum brake hoses. This rubber composition has excellent fuel resistance, high temperature resistance (150℃ temperature resistance (125℃~150℃ (instantaneous))), and low pressure deformation performance, which can meet the stringent requirements of high-end models and thus adapt to specific usage environment conditions.

[0004] The objective of this invention is achieved through the following technical solution:

[0005] An EPDM rubber composition for automotive vacuum brake hoses is made from the following raw materials in parts by weight: 100-150 parts EPDM rubber, 8-12 parts zinc oxide, 1-2 parts stearic acid, 2-4 parts antioxidant, 50-80 parts plasticizer, 180-250 parts carbon black, 0.8-1.2 parts sulfur S-80, 7-9 parts crosslinking agent, 1-2 parts co-crosslinking agent, and 90-140 parts inorganic filler; wherein the carbon black is a combination of carbon black N990 and carbon black N550.

[0006] Preferably, the EPDM rubber composition for automotive vacuum brake hoses is made from the following raw materials in parts by weight: 100-150 parts EPDM rubber, 8-12 parts zinc oxide, 2 parts stearic acid, 2-4 parts antioxidant, 50-80 parts plasticizer, 180-250 parts carbon black, 0.8-1.2 parts sulfur S-80, 7-9 parts crosslinking agent, 1-2 parts co-crosslinking agent, and 90-140 parts inorganic filler.

[0007] More preferably, when the EPDM rubber is non-oil-extended EPDM rubber, the EPDM rubber composition for automotive vacuum brake hoses is made from the following raw materials in parts by weight: 100 parts non-oil-extended EPDM rubber, 8-12 parts zinc oxide, 2 parts stearic acid, 2-4 parts antioxidant, 50-80 parts plasticizer, 180-200 parts carbon black, 0.8-1.2 parts sulfur S-80, 7-9 parts crosslinking agent, 1-2 parts co-crosslinking agent, and 90-100 parts inorganic filler.

[0008] When the EPDM rubber is oil-extended EPDM rubber, the EPDM rubber composition for automotive vacuum brake hoses is made from the following raw materials in parts by weight: 100-150 parts oil-extended EPDM rubber, 8-12 parts zinc oxide, 2 parts stearic acid, 2-4 parts antioxidant, 50-80 parts plasticizer, 220-230 parts carbon black, 0.8-1.2 parts sulfur S-80, 7-9 parts crosslinking agent, 1-2 parts co-crosslinking agent, and 120-140 parts inorganic filler.

[0009] The EPDM rubber is an ultra-high Mooney viscosity and ultra-high molecular weight EPDM rubber with a bulk Mooney viscosity of 80-110 at 125°C, an ethylene content of 60%-70%, and a third monomer content of 5.0%-7.0%.

[0010] Preferably, the EPDM rubber is an oil-extended rubber. 10675C or non-oil-extended rubber 8570C.

[0011] The antioxidant is at least one of antioxidant FR, antioxidant RD, and antioxidant MMBI-70, preferably a combination of antioxidant RD and antioxidant MMBI-70 in a weight ratio of 1:2.

[0012] The plasticizer mentioned is paraffin oil 2280.

[0013] The carbon black is a combination of carbon black N990 and carbon black N550 in a weight ratio of 1:1 to 1:1.5, preferably a combination of carbon black N990 and carbon black N550 in a weight ratio of 1:1.2 to 1:1.25.

[0014] The crosslinking agent is KF-B50CC (a mixture of bis(tert-butylperoxyisopropyl)benzene and silica with an active oxygen content of 4.6%).

[0015] The crosslinking agent mentioned is Altermix TAIC-70PD.

[0016] The inorganic filler is calcium carbonate.

[0017] The EPDM rubber composition is an ultra-high filler rubber composition with a rubber content of 17% to 21%.

[0018] Another object of the present invention is to provide a method for preparing the EPDM rubber composition for automotive vacuum brake hoses, comprising the following steps:

[0019] Step (1): Cool the internal mixer with water and control the temperature of the internal mixer chamber to not exceed 50°C. First, mix EPDM rubber, zinc oxide, stearic acid and antioxidant for 20-40 seconds. Then add carbon black N550 and continue mixing for 50-60 seconds. Add carbon black N990, inorganic filler and plasticizer to the above mixture and continue mixing for 50-70 seconds. When the temperature of the mixture in the internal mixer rises to 140-150°C, discharge the rubber and transfer it to an open rubber mixing mill for sheeting. Cool to room temperature and let it stand for 8 hours to obtain EPDM rubber composition material.

[0020] Step (2): Cool the internal mixer with water and control the temperature of the internal mixer chamber to not exceed 50°C. Add the EPDM rubber composition material obtained in step (1) to the internal mixer and mix for 40-50 seconds. Then add sulfur S-80 and continue mixing. When the temperature of the internal mixer rises to 100-105°C, discharge the rubber and transfer it to an open rubber mixing mill for thin sheeting. Cool to room temperature and let it stand for 8 hours to stabilize. Then place it in a flat vulcanizing machine for vulcanization. The vulcanization temperature is 170-175°C and the vulcanization time is 25-30 minutes to obtain the EPDM rubber composition.

[0021] In step (1), the temperature of the water introduced into the internal mixer should not exceed 15℃. Considering that the filler accounts for a very large proportion and is used in large quantities, the filler is added in stages to ensure the uniformity of mixing. Carbon black N550 has a relatively large structure and small particle size, so adding it in advance is more conducive to the uniformity of dispersion.

[0022] In step (2), the temperature of the water introduced into the internal mixer shall not exceed 15°C.

[0023] Another object of the present invention is to provide the application of the EPDM rubber composition in the preparation of automotive vacuum brake hoses.

[0024] An automotive vacuum brake hose is made of rubber material with the EPDM rubber composition for automotive vacuum brake hoses described in this invention as the inner and outer rubber layers of the hose.

[0025] The beneficial effects of this invention are:

[0026] This invention utilizes EPDM rubber with ultra-high Mooney viscosity, ultra-high molecular weight, and higher ethylene content, and forms a high-filler system through a combination of specific fillers to control the rubber content. Combined with an effective vulcanization system and related additives, the EPDM rubber composition possesses excellent fuel resistance, high temperature resistance, and low pressure deformation properties. Its fuel resistance can even rival that of NBR rubber, and its temperature resistance can reach a high temperature resistance of 150℃ (150℃~175℃ (instantaneous)), fully meeting the stringent requirements of high-end vehicles and adapting to specific usage environments, thus breaking through the technical barrier of poor fuel resistance of EPDM.

[0027] This invention uses EPDM rubber of ultra-high Mooney viscosity and ultra-high molecular weight (EPDM rubber with a Mooney viscosity ML(1+4) greater than 100 at 125°C) and is oil-extended. 10675C (to improve its processing performance) enhances the initial mechanical properties, heat resistance, and pressure resistance of the matrix, providing higher initial values ​​for subsequent heat resistance, oil resistance, and pressure resistance processes. This invention employs a peroxide vulcanization system; the crosslinking of peroxides does not require ZnO and stearic acid. Furthermore, this invention effectively improves the heat resistance of the rubber composition by adding zinc oxide, and also improves the solubility and dispersibility of ZnO in the rubber by adding stearic acid. The filler system uses carbon black with different structures and inorganic filler calcium carbonate in combination. By limiting the ratio between materials, the filler content of the composition is greatly increased while ensuring mechanical, pressure resistance, and heat resistance properties. This effectively dilutes the rubber itself, which has poor oil resistance, and significantly improves the EPDM composition's resistance to fuel B. KF-B50CC is used as the crosslinking agent in the peroxide vulcanization system. Compared to DCP, this crosslinking agent does not produce an irritating odor, and the surface of the manufactured hose will not bloom. Its relatively high active oxygen content allows the rubber composition to achieve a higher crosslinking density.

[0028] The innovation of this invention lies in the addition of sulfur S-80 to the peroxide vulcanization system. This enhances the mixing effect, prevents carbon black scorching, and acts as a further crosslinking aid, playing a crucial role in improving the fuel resistance of the EPDM rubber composition. Furthermore, corresponding to the peroxide vulcanization system of this invention, the filler system discards silica and untreated clay, avoiding a reduction in the crosslinking efficiency of the composition and thus affecting its overall performance.

[0029] In summary, compared with the traditional nitrile rubber or EPDM rubber formulations currently used in automotive vacuum brake hoses, the rubber composition of this invention has excellent fuel resistance, high temperature resistance, and low pressure deformation performance, which can meet the stringent requirements of high-end models and thus adapt to specific operating environment conditions. Detailed Implementation

[0030] The technical solution of the present invention will be further described below through specific embodiments.

[0031] Table 1. Formulations (parts by weight) of rubber compositions for Examples 1-4 and Comparative Examples 1-4

[0032]

[0033]

[0034] Note: Crosslinking agent KF-B50CC (manufacturer: Shanghai Kanfeng Chemical Technology Co., Ltd.)

[0035] Example 1

[0036] An EPDM rubber composition for automotive vacuum brake hoses, the raw materials and weight parts of which are shown in Table 1, is prepared according to the following preparation method:

[0037] Step (1): Cool the internal mixer with water, ensuring the cooling water temperature does not exceed 15℃ and controlling the temperature of the internal mixer chamber to not exceed 50℃. First, put the EPDM... Mix 10675C, zinc oxide, stearic acid, and antioxidants (antioxidant RD, antioxidant MMBI-70) for 30 seconds. Then add carbon black N550 and continue mixing for 50 seconds. Add the remaining carbon black N990, inorganic filler (calcium carbonate), and plasticizer (paraffin oil 2280) to the above mixture and continue mixing for 50-70 seconds. When the temperature of the mixture in the internal mixer reaches 145°C, discharge the rubber and transfer it to an open mixing mill for sheeting. Cool to room temperature and let it stand for 8 hours to stabilize.

[0038] Step (2): Cool the internal mixer with water, with the cooling water temperature not exceeding 15°C and the temperature of the internal mixer chamber not exceeding 50°C. Add the EPDM rubber composition material obtained in step (1) to the internal mixer and mix for 50 seconds. Then add the vulcanizing agent and continue mixing. When the internal mixer temperature rises to 100°C, discharge the rubber and transfer it to an open rubber mixing mill for thin sheeting. Cool to room temperature and let it stand for 8 hours to stabilize. Then place it in a flat vulcanizing machine for vulcanization at a vulcanization temperature of 170°C and a vulcanization time of 30 minutes to obtain the EPDM rubber composition.

[0039] Example 2

[0040] The raw materials were weighed according to Table 1, and the EPDM rubber composition was prepared according to the preparation method of Example 1.

[0041] Example 3

[0042] The raw materials were weighed according to Table 1, and the EPDM rubber composition was prepared according to the preparation method of Example 1.

[0043] Example 4

[0044] The raw materials were weighed according to Table 1, and the EPDM rubber composition was prepared according to the preparation method of Example 1.

[0045] Comparative Example 1

[0046] An EPDM rubber composition, the raw materials and their weight parts are shown in Table 1, is prepared according to the following method:

[0047] Step (1): Cool the internal mixer with water, ensuring the cooling water temperature does not exceed 15℃ and controlling the temperature of the internal mixer chamber to not exceed 50℃. First, put the EPDM... Mix 10675C, zinc oxide, stearic acid, and antioxidants (antioxidant RD, antioxidant MMBI-70) for 30 seconds, then add carbon black N550 and continue mixing for 50 seconds. Add carbon black N990, inorganic filler (calcium carbonate), and plasticizer (paraffin oil 2280) to the above mixture and continue mixing for 50-70 seconds. When the temperature of the mixture in the internal mixer reaches 145°C, discharge the rubber and transfer it to an open mixing mill for sheeting. Cool to room temperature and let it stand for 8 hours to stabilize.

[0048] Step (2): Cool the internal mixer with water, ensuring the cooling water temperature is not higher than 15°C and the temperature of the internal mixer chamber is not higher than 50°C. Add the EPDM rubber composition material obtained in step (1) to the internal mixer and mix for 50 seconds. Then add the vulcanizing agent (sulfur S-80), accelerator (accelerator DTDC-80, accelerator TBZTD-70, accelerator CZ, accelerator ZBEC) and continue mixing. When the internal mixer temperature rises to 95°C, discharge the rubber and transfer it to an open mixing mill for thin sheeting. Cool to room temperature and let it stand for 8 hours to stabilize. Then place it in a flat vulcanizing machine for vulcanization at a vulcanization temperature of 160°C and a vulcanization time of 30 minutes to obtain the EPDM rubber composition.

[0049] Comparative Example 2

[0050] An EPDM rubber composition, the raw materials and their weight parts are shown in Table 1, is prepared according to the following method:

[0051] Step (1): Cool the internal mixer with water and control the temperature of the internal mixer chamber to not exceed 50°C. Add raw rubber, antioxidant, zinc oxide and stearic acid, and mix for 60 seconds.

[0052] Step (2): Add paraffin oil 2280, natural gas semi-reinforcing carbon black, carbon black N550, and carbon black N990, and mix for 3 minutes;

[0053] Step (3): Add vulcanizing agent and continue mixing. After the temperature reaches 125℃, discharge the rubber compound.

[0054] Step (4): Transfer the rubber compound to the open mill for thin sheeting and cool it to room temperature.

[0055] Step (5): Place the EPDM rubber composition material obtained in step (4) into a flat vulcanizing machine for vulcanization at a vulcanization temperature of 170°C and a vulcanization time of 30 min to obtain the EPDM rubber composition.

[0056] Comparative Example 3

[0057] The raw materials were weighed according to Table 1, and the rubber compound was prepared by referring to the preparation method of Comparative Example 2.

[0058] Comparative Example 4

[0059] The raw materials were weighed according to Table 1, and the rubber compound was prepared by referring to the preparation method of Comparative Example 2.

[0060] The properties of the rubber compounds prepared in Examples 1-4 and Comparative Examples 1-4 were examined, and the results are shown in Table 2.

[0061] Table 2. Performance parameters of the rubber compositions prepared in Examples 1-4 and Comparative Examples 1-4

[0062]

[0063] It can be seen that, compared with Example 1, Comparative Example 1, with other components remaining the same, only changed the vulcanization system to a sulfur vulcanization system, but its B-type compression set at 125°C was very poor, reaching 65%. Changes in the degree of crosslinking and the type of crosslinking bonds (from a combination of carbon-carbon bonds and a small amount of sulfur crosslinking bonds to pure sulfur crosslinking bonds) also worsened the composition's fuel resistance and heat aging performance. Comparative Example 2 used EPDM rubber with a high Mooney viscosity (ML(1+4) of 80 at 125°C) and an ethylene content of 48%. 8550C, using the same vulcanization system as Example 1, showed a significant improvement in its B-type compression set performance, but its fuel resistance failed to meet the technical specifications. To further improve the fuel resistance of the rubber composition in Comparative Example 2, the inventors used a method combining it with polar rubber (Comparative Example 3 and Comparative Example 4). Through a series of experiments, it was found that while combining it with polar rubber helped improve its fuel resistance, the improvement was not significant due to factors such as compatibility and co-vulcanization effects, falling far short of the technical specifications. Furthermore, it was also observed that the use of NBR or CR rubber resulted in a certain loss in the rubber composition's thermal aging performance and compression set resistance; the higher the proportion of NBR or CR rubber used, the greater the loss, making it impossible to simultaneously achieve excellent fuel resistance, high temperature resistance, and low compression set performance.

Claims

1. An EPDM rubber composition for automotive vacuum brake hoses, characterized in that: It is made from the following raw materials in parts by weight: 100-150 parts EPDM rubber, 8-12 parts zinc oxide, 1-2 parts stearic acid, 2-4 parts antioxidant, 50-80 parts plasticizer, 180-250 parts carbon black, 0.8-1.2 parts sulfur S-80, 7-9 parts crosslinking agent, 1-2 parts co-crosslinking agent, and 90-140 parts inorganic filler; the EPDM rubber is oil-extended rubber Keltan® 10675C or non-oil-extended rubber Keltan® 8570C; the antioxidant is a combination of antioxidant RD and antioxidant MMBI-70 in a weight ratio of 1:2; the plasticizer is paraffin oil 2280; the carbon black is a combination of carbon black N990 and carbon black N550 in a weight ratio of 1:1 to 1:1.5; the crosslinking agent is crosslinking agent KF-B50CC; and the co-crosslinking agent is Altermix. The inorganic filler in TAIC-70PD is calcium carbonate.

2. The EPDM rubber composition for automotive vacuum brake hoses according to claim 1, characterized in that: It is made from the following raw materials in parts by weight: 100-150 parts EPDM rubber, 8-12 parts zinc oxide, 2 parts stearic acid, 2-4 parts antioxidant, 50-80 parts plasticizer, 180-250 parts carbon black, 0.8-1.2 parts sulfur S-80, 7-9 parts crosslinking agent, 1-2 parts co-crosslinking agent, and 90-140 parts inorganic filler.

3. The EPDM rubber composition for automotive vacuum brake hoses according to claim 1, characterized in that: When the EPDM rubber is non-oil-extended EPDM rubber, the EPDM rubber composition for automotive vacuum brake hoses is made from the following raw materials in parts by weight: 100 parts non-oil-extended EPDM rubber Keltan® 8570C, 8-12 parts zinc oxide, 2 parts stearic acid, 2-4 parts antioxidant, 50-80 parts plasticizer, 180-200 parts carbon black, 0.8-1.2 parts sulfur S-80, 7-9 parts crosslinking agent, 1-2 parts co-crosslinking agent, and 90-100 parts inorganic filler; When the EPDM rubber is oil-extended EPDM rubber, the EPDM rubber composition for automotive vacuum brake hoses is made from the following raw materials in parts by weight: 100-150 parts oil-extended EPDM rubber Keltan® 10675C, 8-12 parts zinc oxide, 2 parts stearic acid, 2-4 parts antioxidant, 50-80 parts plasticizer, 220-230 parts carbon black, 0.8-1.2 parts sulfur S-80, 7-9 parts crosslinking agent, 1-2 parts co-crosslinking agent, and 120-140 parts inorganic filler.

4. The EPDM rubber composition for automotive vacuum brake hoses according to claim 1, 2, or 3, characterized in that: The carbon black is a combination of carbon black N990 and carbon black N550 in a weight ratio of 1:1.2 to 1:1.

25.

5. The application of the EPDM rubber composition of claim 1 in the preparation of automotive vacuum brake hoses.

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