Silicone rubber composition having excellent resistance to brake fluid and brake caliper piston bush manufactured using same

Abstract

The present application relates to a silicone rubber composition having excellent brake fluid resistance and a brake caliper piston bush manufactured using the same. Provided is a silicone rubber composition comprising 30 to 50 parts by weight of a reinforcing filler, 5 to 10 parts by weight of silicone oil, and 1 to 5 parts by weight of a hydrophobic surface modifier, based on 100 parts by weight of silicone rubber; and a brake caliper piston bush which is manufactured by molding the silicone rubber composition and has excellent resistance to brake fluid.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to and the benefit of Korean Patent Application No. 2023-0083440, filed on June 28, 2023, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0003] The present invention relates to a silicone rubber composition having excellent brake fluid resistance and a brake caliper piston sleeve produced by molding the silicone rubber composition. Background Art

[0004] The brake caliper piston sleeve serves as a dust cover to prevent contact with the outside or inflow of foreign matter when the brake caliper piston is operating.

[0005] The caliper piston sleeve requires brake fluid resistance due to its role as the outer seal of the brake caliper and its role in maintaining the hydraulic pressure of the internal brake fluid. In addition, depending on the caliper system, the seal structure is different, and there are also specifications for inserting a metal ring. For this reason, the rubber material must have excellent adhesion to the metal ring during molding and running.

[0006] The silicone rubber (VMQ) used previously was filled with silica and inorganic fillers to increase the density, thereby inhibiting the penetration of hydrophobic oil (IRM902, IRM903, engine oil, etc.) into the rubber matrix and improving oil resistance.

[0007] This is effective when silicone rubber is immersed in hydrophobic oil, but when it is immersed in a liquid containing ethylene glycol (C4H4(OH)2) as a main component such as brake fluid, it is ineffective in suppressing penetration, and problems such as reduction in mechanical strength or volume expansion of the rubber occur. In addition, in severe cases, the mechanical strength of silicone rubber may be reduced, resulting in damage such as breakage of the molded test piece.

[0008] Furthermore, in order to suppress the penetration of silicone rubber (VMQ), a method of increasing the density of the resin matrix by post-adding (filling) an inorganic filler is generally used, but this cannot effectively suppress the penetration in the case of hydrophilic oil.

[0009] In the compounding process (which is a silicone rubber manufacturing process), a portion of the surface of silica used as a reinforcing filler can be modified to be hydrophobic by adding silicone oil, but when a large amount of oil is added, the plasticity decreases and the product is manufactured in a softened state to the extent that post-processing cannot be performed, so there is a limitation in improving the hydrophobicity.

[0010] On the other hand, fluorine-based silicone rubber (FVMQ) can effectively suppress reduction in mechanical strength, volume expansion and component damage by suppressing penetration even when immersed in a liquid containing ethylene glycol (C4H4(OH)2) as a main component, such as brake fluid, due to its excellent oil resistance and chemical resistance. However, since the price is 5 to 10 times higher than that of general silicone rubber (VMQ), there is a problem of deterioration in marketability when using fluorine-based silicone rubber (FVMQ) to mold parts.

[0011] Furthermore, the EPDM material has excellent brake fluid resistance, but its heat resistance is inferior, so there is a problem that it is inferior to silicon at high temperatures.

[0012] As described above, in the case of using a piston sleeve made of ordinary silicone material, the silicone rubber material is softened by ethylene glycol, which is the main component of brake fluid, which causes cracks in the molded material or deterioration of its physical properties. Therefore, it is necessary to develop a brake caliper piston sleeve made of silicone with improved brake fluid tolerance. Summary of the invention

[0013] The present invention relates to a silicone rubber composition having excellent brake fluid resistance and a brake caliper piston sleeve produced by molding the silicone rubber composition.

[0014] One aspect of the present invention provides a silicone rubber composition, which comprises 30 to 50 parts by weight of a reinforcing filler, 5 to 10 parts by weight of silicone oil and 1 to 5 parts by weight of a hydrophobic surface modifier based on 100 parts by weight of silicone rubber.

[0015] According to one embodiment, the hydrophobic surface modifier may be a trialkoxysilane, such as phenyltrialkoxysilane.

[0016] According to one embodiment, the reinforcing filler may be dry silica or wet silica, and the specific surface area of ​​the dry silica is preferably 100 m 2 / g to 300m 2 / g.

[0017] According to one embodiment, the silicone rubber composition may further include one or more additives selected from the group consisting of an antioxidant, a rust inhibitor, a surfactant, a dispersant, a thickener, and a defoaming agent.

[0018] Another aspect of the present invention provides a caliper piston sleeve, which comprises a cured product of the silicone rubber composition.

[0019] According to one embodiment, a brake caliper piston sleeve manufactured by molding the silicone rubber composition is characterized in that, as a brake fluid tolerance test, the hardness difference before and after immersion in brake fluid at 150° C. for 70 hours is 8 or less.

[0020] According to one embodiment, a brake caliper piston sleeve manufactured by molding the silicone rubber composition is characterized in that, as a brake fluid tolerance test, the tensile strength before and after immersion in brake fluid at 150°C for 70 hours differs by less than 30%; and as a brake fluid tolerance test, the elongation before and after immersion in brake fluid at 150°C for 70 hours differs by less than 30%.

[0021] According to one embodiment, a brake caliper piston sleeve manufactured by molding the silicone rubber composition is characterized in that, as a brake fluid tolerance test, the volume difference before and after immersion in brake fluid at 150° C. for 70 hours is less than 5%. DETAILED DESCRIPTION

[0022] Hereinafter, the present invention will be described in more detail by embodiments. The following embodiments are provided as examples to help understand the present invention, and the scope of the present invention is not limited thereto. It should be understood that the present invention can be modified and implemented in various forms, and the present invention includes all modifications, equivalents or replacements that fall within the spirit and scope of the present invention.

[0023] The terms used in this application are only used to describe specific embodiments and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this application, the term "including" or "having" is intended to indicate the presence of the features, quantities, steps, operations, constituent elements, parts or any combination thereof described in the specification, but it should be understood that the possibility of the presence or addition of one or more other features or quantities, steps, operations, constituent elements, parts or any combination thereof is not excluded.

[0024] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention belongs. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with the meaning in the context of the relevant art, and should not be interpreted as an ideal or overly formal meaning unless explicitly defined in this application.

[0025] The silicone rubber composition according to one embodiment comprises silicone rubber as a crystalline base resin. Common silicone rubber (VMQ) is a compound prepared by mixing a linear siloxane polymer, a reinforcing filler and silicone oil. Silicone rubber has excellent heat resistance, cold resistance and electrical properties, and is molded and used for various purposes. In addition, by applying a small amount of additives such as antioxidants, rust inhibitors, surfactants, dispersants, thickeners and defoamers to existing compounds, various properties can be exhibited.

[0026] The silicone rubber composition according to one embodiment of the present invention may include 30 to 50 parts by weight of reinforcing filler, 5 to 10 parts by weight of silicone oil, and 1 to 5 parts by weight of hydrophobic surface modifier based on 100 parts by weight of silicone rubber. Detailed description of each component and material is as follows.

[0027] <Silicone Rubber>

[0028] The linear siloxane polymer applied to the solid silicone rubber is called silicone gum (GUM), and is a compound having a structure shown in the following Chemical Formula 1.

[0029] [Chemical formula 1]

[0030]

[0031] In the above formula, R1 to R 10 are the same or different organic functional groups, and n and m are the same or different integers of 1 to 10,000. 10 are the same or different and are each independently selected from the group consisting of hydrogen, halogen, substituted or unsubstituted C1-C 30 Alkyl, substituted or unsubstituted C2-C 30 Alkenyl, substituted or unsubstituted C2-C 24 Alkynyl, substituted or unsubstituted C2-C 30 Heteroalkyl, substituted or unsubstituted C6-C 30 Arylalkyl, substituted or unsubstituted C5-C 30 Aryl, substituted or unsubstituted C2-C 30 Heteroaryl, substituted or unsubstituted C3-C 30 Heteroarylalkyl, substituted or unsubstituted C3-C 20 Cycloalkyl, substituted or unsubstituted C3-C 20 Heterocycloalkyl, substituted or unsubstituted C3-C 20 Cycloalkenyl, substituted or unsubstituted C3-C 30 Heteroaralkyl and substituted or unsubstituted C1-C 20 Heteroalkenyl.

[0032] At least one of R2, R3, R7 and R8 is selected from methyl or vinyl.

[0033] <Reinforcement filler>

[0034] The reinforcing filler is silica and is used by selecting dry silica or wet silica. Among them, it is preferred to use silica with a specific surface area of ​​100 m 2 / g to 300m 2 / g of dry silica.

[0035] Based on 100 parts by weight of the silicone rubber, the silicone rubber composition according to one embodiment may include 30 to 50 parts by weight of a reinforcing filler. When the content of the reinforcing filler is less than 30 parts by weight, the mechanical strength of the composition is low, and the composition becomes soft, resulting in problems of poor elasticity and restoring force; and when the content exceeds 50 parts by weight, the filler cannot be well kneaded and agglomerated when kneaded with the silicone resin, resulting in an uneven composition with poor mechanical properties, so it is appropriate to use a filler within the above range.

[0036] <Silicone oil>

[0037] The silicone oil used in the embodiment is an organopolysiloxane oil, which is a compound having the following structure, and acts as a silica surface treatment agent, which inhibits the silica filler from forming hydrogen bonds with moisture in the air, thereby correcting plasticity, and improving mixing and dispersibility.

[0038] [Chemical formula 2]

[0039]

[0040] In the above formula, R 11 To R 18 are the same or different organic functional groups, and l and o are the same or different integers from 1 to 10,000. Specifically, R 11 To R 18 are the same or different and are each independently selected from the group consisting of hydrogen, halogen, substituted or unsubstituted C1-C 30 Alkyl, substituted or unsubstituted C2-C 30 Alkenyl, substituted or unsubstituted C2-C 24 Alkynyl, substituted or unsubstituted C2-C 30 Heteroalkyl, substituted or unsubstituted C6-C 30 Arylalkyl, substituted or unsubstituted C5-C 30 Aryl, substituted or unsubstituted C2-C 30 Heteroaryl, substituted or unsubstituted C3-C 30 Heteroarylalkyl, substituted or unsubstituted C3-C 20 Cycloalkyl, substituted or unsubstituted C3-C 20 Heterocycloalkyl, substituted or unsubstituted C3-C 20 Cycloalkenyl, substituted or unsubstituted C3-C 30 Heteroaralkyl and substituted or unsubstituted C1-C 20 Heteroalkenyl.

[0041] R 12 , R 13 , R 16 and R 17 At least one of the following is selected from methyl or vinyl.

[0042] The silicone rubber composition according to one embodiment may include 5 to 10 parts by weight of silicone oil based on 100 parts by weight of silicone raw rubber. When the content of silicone oil is less than 5 parts by weight, the mixing and dispersibility of the silica filler treated with silica surface is reduced, resulting in increased plasticity and an uneven composition, which causes poor mechanical properties; and when the content exceeds 10 parts by weight, unreacted oil remains in the composition, which reduces plasticity and mechanical strength, softens the composition and reduces elasticity and restoring force, so it is appropriate to use it within the above range.

[0043] <Hydrophobic Surface Modifier>

[0044] In an embodiment, a large number of hydrophobic functional groups are imparted to the surface of silica used as a reinforcing filler in the preparation of silicone rubber to effectively prevent ethylene glycol (C2H4(OH)2), a main component of brake fluid, from penetrating into the silicone rubber matrix.

[0045] Specifically, trialkoxysilane represented by the following Chemical Formula 3 may be used as a hydrophobic surface modifier for silica.

[0046] [Chemical formula 3]

[0047]

[0048] In the above formula, R 19 To R 22 are the same or different and may be independently selected from methyl, ethyl and phenyl. 19 can be selected from methyl or phenyl, and R 20 To R 22 At least one of may be selected from a methyl group or an ethyl group.

[0049] Specific examples of the alkyltrialkoxysilane described below include methyltrimethoxysilane, methyltriethoxysilane, phenyltrimethoxysilane, and phenyltriethoxysilane.

[0050]

[0051] Among trialkoxysilanes, phenylalkoxysilane has excellent water resistance and can effectively prevent the brake fluid from penetrating into the matrix. Even when the addition amount is increased to provide a large amount of hydrophobic functional groups, it does not affect the plasticity, and can maintain favorable plasticity during the post-processing and molding of the parts, making it suitable for use as a surface modifier for silicone rubber compositions.

[0052] The silicone rubber composition according to one embodiment may include 1 to 5 parts by weight of a hydrophobic modifier based on 100 parts by weight of the silicone rubber. When the content of the hydrophobic modifier is less than 1 part by weight, there is a problem that sufficient hydrophobic functional groups cannot be provided to prevent the brake fluid from penetrating into the matrix; and when the content exceeds 5 parts by weight, there is a problem of reduced mechanical properties due to excessive unreacted modifiers and increased product prices due to expensive raw materials, which reduces marketability, so it is appropriate to use it within the above range.

[0053] The silicone rubber composition according to one embodiment may include 30 to 50 parts by weight of a reinforcing filler, 5 to 10 parts by weight of silicone oil, and 1 to 5 parts by weight of a hydrophobic surface modifier, based on 100 parts by weight of the silicone rubber.

[0054] The hydrophobic surface modifier may be a trialkoxysilane, such as phenyltrialkoxysilane.

[0055] The reinforcing filler can be dry silica or wet silica, and the specific surface area of ​​the dry silica is preferably 100 m 2 / g to 300m 2 / g.

[0056] The silicone rubber composition may further include one or more additives selected from antioxidants, rust inhibitors, surfactants, dispersants, thickeners, and defoamers.

[0057] A caliper piston sleeve having excellent brake fluid resistance can be produced by molding the silicone rubber composition.

[0058] The caliper piston sleeve manufactured by molding the silicone rubber composition is characterized by a hardness change rate of 8 or less and a volume change rate of 3% or less as a result of a brake fluid resistance test measured after immersion in brake fluid at 150° C. for 70 hours.

[0059] Furthermore, a caliper piston sleeve manufactured by molding the silicone rubber composition is characterized in that, as a result of a brake fluid resistance test measured after immersion in brake fluid at 150° C. for 70 hours, a tensile strength change rate and an elongation change rate are 20% or less.

[0060] The present invention will be described in more detail below through Examples and Test Examples.

[0061] <Example>

[0062] Preparation of silicone rubber composition

[0063] Based on 100 parts by weight of silicone rubber, 30 to 50 parts by weight of silica as a reinforcing filler, 5 to 10 parts by weight of silicone oil and 1 to 5 parts by weight of phenylalkoxysilane as a hydrophobic surface modifier are mixed to prepare a silicone rubber composition for manufacturing a brake caliper piston sleeve.

[0064] <Comparative Example 1>

[0065] A silicone rubber composition containing only silicone rubber, silicone oil and silica filler but not containing a surface modifier is prepared.

[0066] <Comparative Example 2>

[0067] An oil-resistant silicone rubber composition was prepared by adding inorganic fillers such as alumina (Al2O3) and quartz powder and silica as a reinforcing filler to the resin composition of Comparative Example 1.

[0068] <Comparative Example 3>

[0069] The silicone rubber composition is prepared using fluorine-based silicone rubber.

[0070] <Test example>

[0071] Evaluation of physical properties of molded products

[0072] After each uncured silicone rubber composition prepared according to the above embodiment is fully plasticized in a double-roll mill, 1 part by weight of an organic peroxide (2,5-dimethyl-2,5-tert-butylhexane peroxide, 45% paste) is added and fully dispersed based on 100 parts by weight of the uncured silicone rubber composition. Then, the preformed part that has undergone the defoaming process is pressed in a forming mold at 170°C for 10 minutes to form a sheet with a thickness of 2mm, and cured in a hot air circulation oven at 200°C for 4 hours to produce a cured rubber product. The following physical properties are evaluated for the resulting cured product and are shown in Table 1.

[0073] -Hardness: measured with Shore A durometer according to ASTM D 2240 or with IRHD durometer according to ISO 48-2

[0074] -Tensile strength: measured according to ASTM D 412 standard

[0075] - Elongation: measured according to ASTM D 412

[0076] - Mooney viscosity: measured at 50°C for 6 minutes

[0077] -Curing time: 10 minutes at 170°C

[0078] -Brake oil immersion (DOT) test: Prepare standard test pieces (25×50×2.0±0.01mm) and measure the volume change rate according to the test method of ASTMD471. After immersing in DOT3 oil at 150℃ for 70 hours, take out the test pieces and measure the hardness change, tensile strength, elongation and volume change rate.

[0079] [Table 1]

[0080]

[0081] [Table 2]

[0082]

[0083] According to the embodiment, the silicone rubber composition including the hydrophobic modifier has a high level of excellent mechanical strength due to its excellent resistance to penetration into the silicone rubber matrix even after being immersed in a hydrophilic solution such as ethylene glycol (C2H4(OH)2) which is a main component of brake fluid.

[0084] Furthermore, by adding a silica hydrophobic modifier during the compounding process, a large amount of hydrophobic functional groups can be provided without increasing the amount of commonly used silicone oil, thereby preventing the reduction in plasticity due to silicone oil and preventing the reduction in workpiece properties during processing.

[0085] Furthermore, it can be confirmed that the silicone rubber composition of the example is economical because it can provide water resistance at a low production cost, and is suitable for manufacturing a brake caliper piston sleeve because it has excellent brake fluid resistance and mechanical properties.

[0086] The brake caliper piston sleeve manufactured by molding the silicone rubber composition of the present invention has excellent heat resistance and improved brake fluid tolerance by applying a silicone material. In other words, the piston sleeve has excellent resistance to brake fluid (DOT) infiltration and can maintain mechanical properties even after infiltration.

[0087] Furthermore, since an excessive amount of silicone oil is not added, it has an advantage of being able to correct plasticity to suit workability during processing and molding.

[0088] Meanwhile, the effects of the present invention are not limited to the above-mentioned effects, and other effects that are not mentioned will be clearly understood by those skilled in the art from the above description.

Claims

1. A silicone rubber composition, based on 100 parts by weight of silicone rubber, comprising: 30 to 50 parts by weight of reinforcing filler; 5 to 10 parts by weight of silicone oil; and 1 to 5 parts by weight of a hydrophobic surface modifier.

2. The silicone rubber composition according to claim 1, wherein the hydrophobic surface modifier is a trialkoxysilane. The silicone rubber composition according to claim 2 , wherein the trialkoxysilane is phenyltrialkoxysilane.

4. The silicone rubber composition according to claim 1, wherein the reinforcing filler is dry silica or wet silica.

5. The silicone rubber composition as claimed in claim 4, wherein the specific surface area of ​​the dry silicon dioxide is 100 m 2 / g to 300m 2 / g.

6. The silicone rubber composition according to claim 1, further comprising one or more additives selected from the group consisting of antioxidants, rust inhibitors, surfactants, dispersants, thickeners and defoamers. 7 . A caliper piston sleeve comprising a cured product of the silicone rubber composition according to claim 1 .

8. The caliper piston sleeve according to claim 7, wherein: As a brake fluid tolerance test, the hardness difference before and after immersion in brake fluid at 150°C for 70 hours was less than 8.

9. The caliper piston sleeve according to claim 7, wherein: As a brake fluid tolerance test, the difference in tensile strength before and after immersion in brake fluid for 70 hours at 150°C is less than 30%; And as a brake fluid tolerance test, the elongation before and after immersion in brake fluid at 150°C for 70 hours differed by less than 30%.

10. The caliper piston sleeve according to claim 7, wherein: As a brake fluid tolerance test, the volume difference before and after immersion in brake fluid at 150°C for 70 hours is less than 5%.

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