Lubricant composition for brake system

Abstract

A lubricant composition for a brake system having excellent high-temperature operability, the lubricant composition comprising: 85 wt% to 95 wt% of a polyalkylene glycol base oil; 1% to 5% by weight of an antioxidant; 1% to 5% by weight of a first antiwear extreme pressure additive; and 1% to 5% by weight of a second anti-wear extreme pressure additive wherein the antioxidant comprises an amine compound, the first anti-wear extreme pressure additive comprises an amine salt of a phosphate ester, and the second anti-wear extreme pressure additive comprises a nanodiamond dispersion.

Description

[0001] Cross Reference to Related Applications

[0002] This application claims priority to Korean Patent Application No. 10-2024-0045236, filed on April 3, 2024, the entire contents of which are incorporated herein by reference for all purposes. TECHNICAL FIELD

[0003] The present invention relates to a lubricant composition suitable for an electronic parking brake and having excellent high-temperature running properties. BACKGROUND

[0004] Since noise and vibration of a vehicle have a negative impact on the performance of vehicle parts and cause passenger fatigue, solutions to reduce them are being continuously researched. In general, grease or lubricant is used to reduce noise caused by friction between vehicle parts.

[0005] Currently, in a vehicle brake system, various types of lubricants such as grease and compounds, and brake fluid are used depending on the performance requirements of each part. As a part of a vehicle brake system, a parking brake has been changed from a past manual lever operation to an electric motor-driven electronic parking brake (EPB), which requires grease and lubricants having different properties compared to existing lubricants.

[0006] In the case of an EPB lubricant, not only lubricating properties such as wear resistance, friction resistance, and extreme pressure, but also low-temperature properties and high-temperature stability are required. Therefore, grease containing a mixture of poly-alpha olefin (PAO)-based base oil and a thickener in the form of a lithium fatty acid salt has been used. Thereafter, EPB parts have also been variously changed depending on the size of the vehicle, and now large vehicles such as pickup trucks adopt independent EPB parts for parking brakes only. In the case of independent EPB, considering compatibility with brake fluid, a dual synthetic rubber (EPDM: ethylene propylene diene rubber) is adopted as a sealing material, but the use of PAO-based grease is limited due to the problem of compatibility with EPDM rubber.

[0007] When PAO-based lubricants come into contact with a dual synthetic rubber (EPDM) as a sealing material, they chemically attack the rubber, eventually damaging the sealing material. In addition, although glycol-based brake fluid has excellent low-temperature and normal-temperature properties, there is a fatal problem that lubricity is significantly reduced at high temperatures due to low kinematic viscosity.

[0008] Therefore, there is a need to develop an EBP lubricant having excellent compatibility with EPDM rubber and excellent high-temperature running properties. SUMMARY

[0009] An object of the present invention is to provide a lubricant composition for a brake system having excellent lubricity and excellent wear resistance and extreme pressure properties.

[0010] The present application also aims to provide a polyalkylene glycol lubricant composition having excellent compatibility with a double synthetic rubber as a sealing material and improved high-temperature running properties.

[0011] According to an aspect of the present application, there is provided a lubricant composition comprising, based on the total weight of the lubricant composition: 85 to 95 wt% of a polyalkylene glycol base oil; 1 to 5 wt% of an antioxidant; 1 to 5 wt% of a first anti-wear extreme pressure additive; and 1 to 5 wt% of a second anti-wear extreme pressure additive, wherein the antioxidant comprises an amine compound, the first anti-wear extreme pressure additive comprises an amine salt of a phosphate ester, and the second anti-wear extreme pressure additive comprises a nanodiamond dispersion.

[0012] The polyalkylene glycol base oil can have a kinematic viscosity at 40°C of 30 to 40 cSt.

[0013] The polyalkylene glycol base oil can include a polyoxypropylene glycol, such as a butyloxy polypropylene glycol.

[0014] The amine compound can include an alkyl diphenylamine.

[0015] The amine salt of a phosphate ester can include an amine salt of a dihexyl phosphate ester, and the first anti-wear extreme pressure additive can further include a monohexyl phosphate ester.

[0016] The nanodiamond dispersion can have a concentration of 0.05 to 1 wt% based on the total weight of the nanodiamond dispersion, and can include nanodiamond particles having an average particle diameter of 3.0 to 10 nm.

[0017] The lubricant composition of embodiments of the present application can have a kinematic viscosity at 40°C of 30 to 40 cSt, as measured by the ASTM D 7042 test method.

[0018] The lubricant composition of embodiments of the present application can have a four-ball wear of 0.35 to 0.40 kgf, as measured by the ASTM D 2266 test method.

[0019] The lubricant composition of embodiments of the present application can have a four-ball extreme pressure of 160 to 200 kgf, as measured by the ASTM D 2596 test method.

[0020] The lubricant composition of embodiments of the present application can be applied to an electronic parking brake (EPB). BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1FIG. 1 is a graph showing the change rate of operating force of the lubricant composition of Example 1. DETAILED DESCRIPTION

[0022] Hereinafter, the present application will be described in greater detail with reference to the embodiments and the accompanying drawings. However, the following embodiments are provided as examples to help understanding of the present application, and the scope of the present application is not limited thereto. Various modifications can be made to the present application, and the present application can be embodied in many different forms, and it is to be understood that all such modifications and variations that do not depart from the spirit and technical scope of the present application are encompassed in the present application.

[0023] The terms used in the present specification are merely used to describe particular embodiments and are not intended to limit the present application.

[0024] Unless otherwise defined, all terms used in the present application, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art. Terms defined in a commonly used dictionary are to be interpreted as having a meaning that is consistent with its meaning in the context of the relevant art and is not to be interpreted in an idealized or overly formal sense unless otherwise defined herein.

[0025] In addition, the terms used in the embodiments of the present application are used to describe the embodiments and are not intended to limit the present application.

[0026] In the present specification, unless the phrase explicitly states otherwise, a singular expression can include a plural expression, and the expression "at least one of A, B, and C" or "one or more of A, B, and C" can mean one or more of all possible combinations of A, B, and C.

[0027] In addition, in the description of components in the embodiments of the present application, terms such as first, second, A, B, (a), and (b) can be used.

[0028] These terms are used only to distinguish one component from another component, and the nature, order, or sequence of the component is not limited by these terms.

[0029] The lubricant composition of one embodiment comprises: 85 to 95 wt% of a polyalkylene glycol base oil; 1 to 5 wt% of an antioxidant; 1 to 5 wt% of a first anti-wear extreme pressure additive; and 1 to 5 wt% of a second anti-wear extreme pressure additive, wherein the antioxidant can comprise an amine compound, the first anti-wear extreme pressure additive can comprise an amine salt of a phosphate ester, and the second anti-wear extreme pressure additive can comprise a nanodiamond dispersion.

[0030] The components of the lubricant composition are described in detail below.

[0031] < Polyalkylene glycol base oil >

[0032] The base oil accounts for 85 to 95 wt% of the lubricant composition. When a polyalphaolefin (PAO)-based lubricant used in a conventional brake system comes into contact with EPDM, which is a di-synthetic rubber used as a sealing material, it chemically attacks the rubber, causing damage to the sealing material, and the lubricating performance of the glycol-based brake fluid is maintained at low and normal temperatures, but the lubricity significantly decreases at high temperatures due to low kinematic viscosity.

[0033] To solve these problems, in one embodiment, the following antioxidant and anti-wear extreme pressure additive are added to the polyalkylene glycol-based lubricant composition to improve high-temperature running properties, lubricity, and durability.

[0034] The polyalkylene glycol that can be used as a base oil of the lubricant composition can be a copolymer of an alcohol having 3 to 20 carbon atoms and propylene oxide, or a polyoxypropylene glycol. For example, butyloxy polypropylene glycol has a molecular weight of 790, a kinematic viscosity of 33 cSt at 40°C, a specific gravity of 0.98, and a flash point of 208°C, making it suitable as a lubricant base oil for a brake system.

[0035] < Antioxidant >

[0036] In general, a lubricant deteriorates due to temperature, metal catalysts, and oxygen, generating organic acids, which cause corrosion of metals. The antioxidant added to the lubricant composition of the present invention can deactivate the radicals generated early, making them no longer participate in the growth reaction, or decompose the oxidation products already generated, thereby preventing their conversion into stable compounds or as catalysts for metal oxidation.

[0037] An amine compound can be used as an antioxidant. Specifically, the amine compound can be a diphenylamine compound or a naphthylamine compound. For example, examples of the amine compound can include at least one compound selected from the group consisting of dioctyl diphenylamine, butyl diphenylamine, dinonyl diphenylamine, N-phenyl-1,2-phenylenediamine, N-phenyl-1,4-phenylenediamine, N-phenyl-α-naphthylamine, 4,4'-dibutyl diphenylamine, 4,4'-dipentyl diphenylamine, 4,4'-dihexyl diphenylamine, 4,4'-diheptyl diphenylamine, 4,4'-dioctyl diphenylamine, 4,4'-dinonyl diphenylamine, α-naphthylamine, phenyl-α-naphthylamine, butylphenyl-α-naphthylamine, pentylphenyl-α-naphthylamine, hexylphenyl-α-naphthylamine, heptylphenyl-α-naphthylamine, octylphenyl-α-naphthylamine, and nonylphenyl-α-naphthylamine. In addition, in addition to the amine compound, a phenolic antioxidant or a quinoline antioxidant can be used.

[0038] The content of the amine compound used as the antioxidant can be 1 to 5% by weight of the total lubricant composition. When the content of the antioxidant is less than the above range, there is little antioxidant effect, and when the content of the antioxidant is more than the above range, it is not preferred because it is uneconomical and there is a risk of metal corrosion.

[0039] <Anti-wear extreme pressure additive>

[0040] The lubricant composition of one embodiment of the present application includes a mixture of two additives to enhance anti-wear and extreme pressure properties.

[0041] The anti-wear additive is used to prevent surface wear during metal working. When a metal surface is subjected to high pressure / high load, an extreme pressure (EP) additive can prevent surface damage by suppressing metal wear due to oil film rupture.

[0042] A phosphoric acid amine compound can be used as a first anti-wear extreme pressure additive contained in the lubricant composition. Specifically, examples of the phosphoric acid amine compound include alkyl amine salts of monohexyl phosphate and dihexyl phosphate, preferably, in the compound, the content of nitrogen can be about 2.5% by weight, and the content of phosphorus can be about 4.7% by weight.

[0043] In addition, a nanodiamond dispersion can be used as a second anti-wear extreme pressure additive contained in the lubricant composition. The nanodiamond particles are spherical, and preferably, the average diameter of the particles can be 3 to 10 nm.

[0044] The dispersion solvent of the nanodiamond dispersion can be Group 5 lubricating base oil, and the concentration of the dispersion is suitably 0.05 to 1% by weight. When the concentration of the nanodiamond dispersion is lower than the above range, the lubricity and durability effects are minimal, and when the concentration of the nanodiamond dispersion is higher than the above range, there is a possibility that sedimentation can occur later. In addition, when the average diameter of the nanodiamond particles is greater than the above range, long-term dispersion stability can become problematic.

[0045] The lubricant composition of one embodiment of the present application can include each 1 to 5% by weight of a first anti-wear extreme pressure additive and a second anti-wear extreme pressure additive based on the total weight of the composition.

[0046] The kinematic viscosity at 40°C of the lubricant composition of one embodiment, measured by the ASTM D 7042 test method, is 30 to 40 cSt, indicating excellent high-temperature running properties.

[0047] The four-ball wear of the lubricant composition of one embodiment, measured by the ASTM D 2266 test method, is 0.35 to 0.40 kgf, and the four-ball extreme pressure, measured by the ASTM D 2596 test method, is 160 to 200 kgf, indicating excellent anti-wear and extreme pressure properties.

[0048] Accordingly, the lubricant composition of the embodiments has excellent high-temperature running properties and excellent anti-wear properties, making it suitable for use in electronic parking brakes (EPB).

[0049] <Example>

[0050] The base oil and additives were prepared according to the composition of Table 1 below, thereby preparing the lubricant compositions of the examples and comparative examples.

[0051] [Table 1]

[0052]

[0053] <Experimental Example 1>

[0054] The properties of the lubricant compositions of the examples and comparative examples were measured according to the following measurement methods, and the results are shown in Table 2.

[0055] (1) Kinematic Viscosity

[0056] The kinematic viscosity was measured using a viscometer (Stabinger viscometer) according to ASTM D 7042 at 40°C. The viscometer is a device that measures the viscosity or specific gravity of oil filled in a cylinder by the rotation of an outer cylinder (pipe) and an inner cylinder (rotor), and can measure in the range of -56 to 105°C, requiring about 2.5 ml of sample.

[0057] (2) Copper strip corrosion

[0058] The copper strip corrosion degree was measured according to ASTM D 4048 and KS M 2088 test methods. A copper plate having a size of 76 mm x 12.7 mm x 1.0 mm was polished and inserted into a lubricant filled in a prescribed container, and then whether the copper plate was discolored or not was checked after a prescribed time (3 hours) at a prescribed temperature (100°C). The sulfur component in the known oil is a cause of copper corrosion.

[0059] (3) Pour point

[0060] The pour point was measured according to ASTM D 97 and KS M ISO 3016 test methods. The pour point is the lowest temperature at which an oil flows without stirring when cooled, and is expressed as an integer multiple of 2.5°C from 0°C.

[0061] After cooling 45 ml of a sample in a test tube, whenever the sample temperature decreases by 2.5°C, the test tube was taken out of the cooling bath, the temperature at which the sample did not move at all for 5 seconds was read, and the result obtained by adding 2.5 to this value was determined as the pour point.

[0062] (4) Flash point

[0063] The flash point was measured according to ASTM D 92 and KS M ISO 2592 test methods. The flash point is the lowest temperature at which a fire occurs when a flame approaches the vapor of a sample and is on the liquid surface under prescribed conditions at an atmospheric pressure of 101.3 KPa. The sample was filled into a sample cup to a prescribed liquid level. Initially, the temperature of the sample was rapidly increased, and then was slowly increased at regular intervals as it approached the flash point. A small test flame was passed through the sample cup at a prescribed temperature interval, and the lowest temperature at which the test flame ignited the vapor above the liquid surface was determined as the flash point under the ambient atmospheric pressure. The flash point measured under the atmospheric pressure was corrected to a standard atmospheric pressure using a formula.

[0064] The measurement results of the kinematic viscosity, copper strip corrosion, four-ball wear, four-ball extreme pressure (EP) of the lubricant compositions of the examples and comparative examples are shown in Table 2.

[0065] [Table 2]

[0066]

[0067] [Table 3]

[0068]

[0069] <Experimental Example 2>

[0070] A brake fluid conventionally used was prepared according to the composition of the following Table 4 as Comparative Example 3.

[0071] [Table 4]

[0072] Comparative Example 3 CAS No Content (wt%) Polyethylene glycol methyl ether 9004-74-4 5～10 Polyethylene glycol monobutyl ether 9004-77-7 1～10 Triethylene glycol monomethyl ether 112-35-6 25-40 n-Boric acid tris[2-[2-(2-methoxyethoxy)ethoxy]ethyl] ester 30989-05-0 45-60 Other additives up to 5

[0073] The rate of change of operating force of the electronic parking brake system using the lubricants of Example 1 and Comparative Example 3 was measured according to the following test method, and the results thereof were compared.

[0074] 1) Test Mode 1

[0075] The test was conducted under two conditions (stages): a room temperature condition test; and a voltage / temperature specific condition test. The room temperature condition test was conducted to measure the operating force after three cycles of operation at 12V and at room temperature, and the voltage / temperature specific condition test was conducted to measure the operating force after three cycles of operation at 12V and at each temperature (including -40℃, -20℃, 0℃, 20℃, 80℃, 100℃, and 120℃), and three cycles of operation at 9V and 16V under the same temperature conditions.

[0076] 2) Test Mode 2 (Thermal Shock Durability)

[0077] The thermal shock durability was tested by a total of 100,000 cycles of operation with the temperature varying between -20℃ and 85℃.

[0078] 3) Test Mode 3 (High Temperature and High Humidity)

[0079] The high temperature and high humidity durability was measured by placing at a temperature of 85℃ and a humidity of 85% for a total of 240 hours. 47 hours of non-operation and 1 hour of operation were defined as one cycle (48 hours), and this cycle was repeated 5 times, indicating that it was placed for 240 hours.

[0080] 4) Test Mode 4 (Thermal Shock)

[0081] Placing at each temperature of 40℃ and 115℃ for 30 minutes was defined as one cycle, and this cycle was repeated 200 times.

[0082] Figure 1 is a graph showing the rate of change of the operating force of the brake system using the lubricants of Example 1 and Comparative Example 3 under each test mode. Figure 1 In the graph, the left graph shows the operating force of the brake system using the existing lubricant of Comparative Example 3 before (A-1) and after (A-2) Test Mode 1, and the right graph shows the operating force of the brake system using the lubricant of Example 1 of the present application before (B-1) and after (B-2) Test Mode 1. These results show that the performance of the brake system using the lubricant composition of Example 1 is significantly improved due to the reduction in the change in operating force.

[0083] The moisture content of each of the lubricant compositions of Comparative Example 3 and Example 1 before and after ES was measured, and the results are shown in Table 5 below. As can be seen, the moisture content of the lubricant composition of Example 1 is less than that of the conventional brake fluid lubricant of Comparative Example 3, which indicates that the performance of the lubricant is improved.

[0084] [Table 5]

[0085]

[0086] The operating force of each of the lubricants of Example 1 and Comparative Example 3 after Test Mode 2 was measured, and the results are shown in Table 6. The test was performed based on the operating force required for a 30% slope of SPOT, and was evaluated at an input current value of 10 A. The change rate of the operating force compared to room temperature is expressed in minimum / average / maximum. As can be seen from the measurement results, the lubricant composition of Example 1 has very excellent performance at high temperatures compared to the conventional brake fluid of Comparative Example 3.

[0087] [Table 6]

[0088]

[0089] The polyalkylene glycol-based lubricant composition of the embodiments of the present application has excellent compatibility with a synthetic rubber (EPDM) as a sealing material for a brake system, excellent lubricity, and excellent durability. The polyalkylene glycol-based lubricant composition contains polyalkylene glycol as a base oil, which is maintained in a liquid state different from grease, and thus, not only has excellent low-temperature performance, but also exhibits a high viscosity index, indicating excellent high-temperature stability, compared to conventional glycol-based brake fluids. In addition, the lubricant composition of the embodiments contains an antioxidant and two anti-wear extreme pressure additives, and thus, can have excellent durability, and can improve the operating performance of an electronic parking brake in a variety of temperature ranges.

[0090] In the foregoing, although the present application has been described with reference to preferred embodiments, it will be understood by those skilled in the art that various changes in form and details can be made therein without departing from the spirit and scope of the present application as defined by the appended claims.

Claims

1. A lubricant composition, comprising, based on the total weight of the lubricant composition: 85 to 95 weight percent polyalkylene glycol base oil; 1 to 5 wt% of an antioxidant; 1 wt % to 5 wt % of a first antiwear extreme pressure additive; and 1 to 5 wt% of a second antiwear extreme pressure additive, in, The antioxidant comprises an amine compound, The first antiwear extreme pressure additive comprises an amine salt of a phosphate ester, and The second antiwear extreme pressure additive comprises a nanodiamond dispersion.

2. The lubricant composition according to claim 1, wherein The polyalkylene glycol base oil has a kinematic viscosity at 40° C. of 30 cSt to 40 cSt.

3. The lubricant composition according to claim 2, wherein The polyalkylene glycol base oil comprises butoxypolypropylene glycol.

4. The lubricant composition according to claim 1, wherein The amine compound comprises alkyldiphenylamine.

5. The lubricant composition according to claim 1, wherein The amine salt of phosphoric acid ester includes an amine salt of dihexyl phosphate, and the first anti-wear extreme pressure additive further includes monohexyl phosphate.

6. The lubricant composition according to claim 1, wherein The concentration of the nano-diamond dispersion is 0.05 wt% to 1 wt% based on the total weight of the nano-diamond dispersion, and the nano-diamond dispersion comprises nano-diamond particles having an average particle size of 3.0 nm to 10 nm.

7. The lubricant composition according to claim 1, wherein The lubricant composition has a kinematic viscosity at 40° C. measured by ASTM D 7042 test method of 30 cSt to 40 cSt.

8. The lubricant composition according to claim 1, wherein The lubricant composition has a four-ball wear of 0.35 kgf to 0.40 kgf as measured by ASTM D 2266 test method.

9. The lubricant composition according to claim 1, wherein The lubricant composition has a four-ball extreme pressure measured by ASTM D2596 test method of 160 kgf to 200 kgf.

10. The lubricant composition according to claim 1, wherein The lubricant composition is applied to an electronic parking brake (EPB).

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