Grease composition

Abstract

To provide a grease composition exhibiting good wear resistance.SOLUTION: A grease composition comprises: a di-urea compound represented by a structural formula R1-NHCONH-R2-NHCONH-R3 (formula I) or a complex Li soap thickener; a base oil with kinematic viscosity of 4-100 mm2 / s at 40°C; a wax; and at least one of acid phosphate and an amine salt thereof, wherein the grease composition does not contain per-basic Ca sulfonate, and has a worked penetration of 265-385(in the formula I, R1 and R3 are a same or different C8-20 linear alkyl group, C6 or C7 aryl group, or cyclohexyl group, and R2 is a C6-15 aromatic hydrocarbon group).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a grease composition that can be used for a ball screw portion of a rack-assist type electric power steering. [Background technology]

[0002] In recent years, electric power steering has been widely adopted to improve driving comfort in automobiles, due to the need for responsiveness and quietness during steering. Electric power steering is divided into column-assist, pinion-assist, and rack-assist types, and demand for rack-assist types is expected to expand in the electric power steering market due to their high responsiveness and output. Accordingly, greases used in the ball screws in rack-assist electric power steering devices are also required to meet various requirements, such as longer life, lower torque over a wide speed range, and reduced noise and vibration. Patent Document 1 is an example of a prior art grease composition that can be applied to a ball screw portion in a rack-assist type electric power steering device. Patent Document 1 describes a grease composition that uses, as a thickener, a diurea compound having an unsaturated component in the aliphatic portion in combination with a fatty acid metal salt and an amide compound in a predetermined ratio, and uses, as a base oil, a lubricating base oil whose main component is a synthetic hydrocarbon oil and has a pour point of -25°C or lower, and contains predetermined amounts of predetermined additives.It is reported that this grease can significantly reduce irregular friction fluctuations, exhibits low and stable torque characteristics over a wide temperature range, and is a long-life grease that can maintain a sufficient oil film even at high temperatures. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-306275 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to provide a grease composition that exhibits good antiwear properties. [Means for solving the problem]

[0005] As a result of extensive research, the present inventors have found that the use of specific types of additives can improve wear resistance. That is, the present invention provides the following grease composition. 1. A grease composition containing a thickener, a base oil, a wax, and a phosphate ester, but not containing an overbased Ca sulfonate, The thickener is a diurea compound or a complex Li soap represented by the following formula (I), R1-NHCONH-R2-NHCONH-R3(I) (In the formula, R1 and R3 may be the same or different and are a linear alkyl group having 8 to 20 carbon atoms, an aryl group having 6 or 7 carbon atoms, or a cyclohexyl group. R2 is a divalent aromatic hydrocarbon group having 6 to 15 carbon atoms.) The kinematic viscosity of the base oil at 40°C is 4 to 100 mm 2 / s, the phosphate ester is at least one compound selected from the group consisting of acidic phosphate esters and amine salts of acidic phosphate esters, The grease composition as described above, wherein the composition has a worked penetration of 265 to 385. 2. The grease composition according to item 1 above, wherein the wax comprises at least one wax selected from the group consisting of polyethylene wax, oxidized polyethylene wax, and montan wax. 3. The grease composition according to 1 or 2 above, wherein the phosphate ester is tertiary alkylamine dimethyl phosphate. 4. The grease composition according to any one of 1 to 3 above, wherein the base oil contains a poly-α-olefin. 5. The kinematic viscosity of the poly-α-olefin at 40°C is 15 to 70 mm 2 5. The grease composition according to 4 above, wherein the grease composition is / s. 6. The grease composition according to any one of 1 to 5 above, wherein the thickener is a diurea compound of formula (I) in which either R1 or R3 is a linear alkyl group having 8 carbon atoms, and the other is a linear alkyl group having 18 carbon atoms, and R2 is a group derived from diphenylmethane-4,4'-diisocyanate, and / or a compound in which both R1 and R3 are linear alkyl groups having 8 carbon atoms, and R2 is a group derived from diphenylmethane-4,4'-diisocyanate. 7. The grease composition according to any one of 1 to 6 above, which is for use in a ball screw portion of a rack-assist type electric power steering. [Effects of the Invention]

[0006] According to the present invention, it is possible to provide a grease composition that can reduce noise and vibration due to its good wear resistance. Also, according to the present invention, it is possible to provide a grease composition with an extended life. DETAILED DESCRIPTION OF THE INVENTION

[0007] ○Thickener The thickener that can be used in the present invention is a diurea compound and / or a complex Li soap represented by formula (I). R1-NHCONH-R2-NHCONH-R3(I) In the formula, R1 and R3 may be the same or different and are a linear alkyl group having 8 to 20 carbon atoms, an aryl group having 6 or 7 carbon atoms, or a cyclohexyl group, preferably a linear alkyl group having 8 to 18 carbon atoms. R2 is a divalent aromatic hydrocarbon group having 6 to 15 carbon atoms, preferably a group derived from tolylene diisocyanate or diphenylmethane-4,4'-diisocyanate, more preferably a group derived from diphenylmethane-4,4'-diisocyanate. From the viewpoint of torque and torque fluctuation, the diurea of ​​formula (I) most preferably includes a compound in which either R1 or R3 is a linear alkyl group having 8 carbon atoms and the other is a linear alkyl group having 18 carbon atoms, and R2 is a group derived from diphenylmethane-4,4'-diisocyanate. It is also most preferred to include compounds in which, in formula (I), both R1 and R3 are linear alkyl groups having 8 carbon atoms, and R2 is a group derived from diphenylmethane-4,4'-diisocyanate.

[0008] The Li complex soap is preferably composed of a lithium salt of a hydroxy fatty acid having 12 to 24 carbon atoms and one or more hydroxyl groups, and a lithium salt of a fatty acid dicarboxylic acid having 2 to 12 carbon atoms. Examples of the hydroxy fatty acid include 12-hydroxystearic acid, 12-hydroxylauric acid, and 16-hydroxypalmitic acid. Of these, 12-hydroxystearic acid is preferred. Examples of the aliphatic dicarboxylic acid include azelaic acid, sebacic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, undecanedioic acid, and dodecanedioic acid. Azelaic acid is most preferred. From the viewpoint of shear stability, the Li complex soap is most preferably composed of a lithium salt of 12-hydroxystearic acid and a lithium salt of azelaic acid. From the viewpoint of torque and torque fluctuation, the thickener of the present invention is preferably a thickener containing a diurea compound of formula (I) in which one of R1 and R3 is a linear alkyl group having 8 carbon atoms, the other is a linear alkyl group having 18 carbon atoms, and R2 is a group derived from diphenylmethane-4,4'-diisocyanate, or a thickener containing a compound in which both R1 and R3 are linear alkyl groups having 8 carbon atoms, and R2 is a group derived from diphenylmethane-4,4'-diisocyanate. The content of the thickener in the composition of the present invention is an amount that enables the worked penetration of the grease composition of the present invention to be adjusted to the range of 265 to 385, and is usually 4 to 13 mass %, preferably 5 to 12 mass %, and more preferably 6 to 10 mass %, based on the total mass of the composition.

[0009] Base oil The type of base oil for the grease composition of the present invention is not particularly limited. It may be a mineral oil or a synthetic oil. The base oil may be used alone or in combination of two or more types. As the mineral oil, paraffinic mineral oil, naphthenic mineral oil, and mixtures thereof can be used. As synthetic oils, various synthetic oils can be used, such as ester-based synthetic oils represented by diesters and polyol esters; synthetic hydrocarbon oils represented by poly-α-olefins (PAOs) and polybutenes; ether-based synthetic oils represented by alkyldiphenyl ethers and polypropylene glycols; silicone oils; and fluorinated oils. The base oil preferably contains a poly-α-olefin. When the base oil contains a base oil other than a poly-α-olefin, the poly-α-olefin content is preferably 50 mass% or more, more preferably 80 mass% or more, even more preferably 90 mass% or more, and most preferably 100 mass% based on the total mass of the base oil. When the proportion of poly-α-olefin in the base oil is as described above, it is preferable because the low-temperature properties are excellent. The kinematic viscosity of the base oil in the present invention is 4 to 100 mm at 40°C from the viewpoint of low temperature properties and suppressing torque in the high speed range. 2 / s, 10 to 80 mm2 / s is preferable, and 15 to 70 mm 2 In this specification, the kinematic viscosity at 40°C is a value measured in accordance with JIS K 2283. The base oil of the present invention is, in particular, a base oil having a kinematic viscosity at 40°C of 15 to 70 mm 2 / s, especially 20-40mm 2 PAOs with / s are preferred. The content of the base oil in the grease composition of the present invention is the amount normally used to produce grease, for example, 50 to 95.5 mass%, and from the viewpoint of consistency, it is preferably 60 to 94 mass%, more preferably 80 to 90.5 mass%.

[0010] ○Essential additives The grease composition of the present invention contains a wax and, as a phosphoric acid ester, an acid phosphoric acid ester or an acid phosphoric acid ester amine salt. In this specification, wax refers to an organic substance that is solid at room temperature and does not dissolve in base oil at room temperature. That is, when wax is heated in base oil, it dissolves in the base oil, but when cooled and returned to room temperature, it becomes solid again. Therefore, wax is solid even in grease. Examples of waxes include polyethylene wax, oxidized polyethylene wax, montan wax, and mixtures thereof. The waxes may be used alone or in combination of two or more. The polyethylene wax has a weight-average molecular weight of about 1,000 to 20,000, preferably 4,000 to 20,000, and includes high-density types with a density of 0.96 or more, medium-density types with a density of 0.94 to 0.95, and low-density types with a density of 0.93 or less. High-density types have high melting points, softening points, and crystallinity, and are hard. On the other hand, low-density types are characterized by low melting points and softening points and are soft. From the viewpoint of heat resistance, the dropping point is preferably 120°C or higher, and more preferably 130°C or higher. From the viewpoint of solubility in base oil, the dropping point is preferably 150°C or lower, and more preferably 140°C or lower. Commercially available polyethylene waxes include Hiwax 200P, 210P, and NL200 manufactured by Mitsui Chemicals, Inc., and Licowax PE520, PE190, and PE130 manufactured by Clariant Japan KK, among others.

[0011] Examples of oxidized polyethylene wax include those obtained by oxidizing polyethylene wax and those obtained by oxidizing high-density polyethylene resin, and these have a weight-average molecular weight of approximately 3,000 to 12,000. From the viewpoint of heat resistance, the dropping point is preferably 90°C or higher, more preferably 100°C or higher. From the viewpoint of solubility in base oil, the dropping point is preferably 125°C or lower. The acid value is preferably 60 mgKOH / g or lower, more preferably 30 mgKOH / g or lower, and also preferably 15 mgKOH / g or higher, more preferably 20 mgKOH / g or higher. An acid value within this range is preferable because it reduces the effect of oxidation degradation of the grease due to acid components. Examples of commercially available products include Hiwax 210MP, 4051E, and 1105A manufactured by Mitsui Chemicals, Inc., and Licowax PED522 manufactured by Clariant Japan K.K. Montan wax is classified as a mineral oil-based wax and is primarily composed of long-chain esters, free higher alcohols, resins, sulfur compounds, etc. Examples of such waxes include acid waxes with an acid value of 110 to 160 mgKOH / g, ester waxes with both non-polar and polar moieties, partially saponified ester waxes, which are mixtures of montanic acid esters and saponified products with calcium hydroxide, saponified waxes of montanic acid sodium salts and calcium salts, and montan waxes to which ethylene oxide has been added. From the viewpoint of heat resistance, the dropping point is preferably 75°C or higher, more preferably 80°C or higher. From the viewpoint of solubility in base oil, the dropping point is preferably 105°C or lower. The acid value is preferably 0 to 160 mgKOH / g, more preferably 0 to 40 mgKOH / g. An acid value within this range is preferred because it minimizes the impact of oxidative degradation of the grease due to the acid component.

[0012] Commercially available products include Licowax OP, Licowax S, and Licolub WE40 manufactured by Clariant Japan Co., Ltd. In this specification, the dropping point is a value measured according to DIN 51801. The acid value is a value measured according to DIN 53402. The wax used in the present invention is particularly preferably polyethylene wax, and among these, polyethylene wax having a dropping point of 130 to 140°C is preferred. The wax content in the grease composition of the present invention is preferably 0.1 to 10 mass %, more preferably 0.5 to 7 mass %, and even more preferably 3 to 6 mass %. A content within such a range is preferred because wear can be effectively suppressed.

[0013] The phosphate ester used in the present invention is at least one selected from the group consisting of acidic phosphate esters and amine salts thereof. The acidic phosphate ester is preferably a compound represented by formula (1). R 15 O A PO(OH) 3-A (1) (In the formula, R 15 represents a linear or branched alkyl group having 1 to 30 carbon atoms, preferably a linear or branched alkyl group having 1 to 18 carbon atoms, more preferably an alkyl group having 1 to 8 carbon atoms, and particularly preferably an alkyl group having 1 to 4 carbon atoms. A represents 1 or 2, preferably 2. The amine salt of an acidic phosphoric acid ester is preferably an amine salt of a compound represented by the above formula (1). As the amine salt of an acidic phosphoric acid ester, tertiary alkylamine-dimethyl phosphate is particularly preferred. The phosphate ester used in the present invention is preferably an amine salt of an acidic phosphate ester represented by formula (1), and particularly preferably tertiary alkylamine-dimethylphosphate. The content of the acidic phosphate ester and the amine salt of the acidic phosphate ester in the grease composition is preferably 0.01 to 7 mass%, more preferably 0.05 to 5 mass%, and even more preferably 0.1 to 2 mass%. A content within such a range is preferable because wear can be effectively suppressed.

[0014] Worked consistency In this specification, the term "worked penetration" refers to 60-stroke worked penetration, which can be measured in accordance with JIS K2220 7. The worked penetration of the present invention is 265 to 385, and preferably 285 to 340. When the worked penetration is 265 or more, the torque is excellent. When the worked penetration is 385 or less, the scattering resistance and dripping resistance are excellent.

[0015] A particularly preferred embodiment of the present invention is The thickener includes a diurea compound of formula (I) in which either R1 or R3 is a linear alkyl group having 8 carbon atoms and the other is a linear alkyl group having 18 carbon atoms, and R2 is a group derived from diphenylmethane-4,4'-diisocyanate, and / or a compound in which both R1 and R3 are linear alkyl groups having 8 carbon atoms, and R2 is a group derived from diphenylmethane-4,4'-diisocyanate, As a base oil, the kinematic viscosity at 40°C is 20 to 40 mm 2 / s, including PAO, The wax contains polyethylene wax having a dropping point of 130 to 140°C, The phosphate ester contains tertiary alkylamine-dimethyl phosphate, The grease composition has a worked penetration of 285 to 340.

[0016] A further particularly preferred embodiment of the present invention is The thickener comprises 6 to 10 mass% of a diurea compound of formula (I) in which either R1 or R3 is a linear alkyl group having 8 carbon atoms, and the other is a linear alkyl group having 18 carbon atoms, and R2 is a group derived from diphenylmethane-4,4'-diisocyanate, and / or a compound in which both R1 and R3 are linear alkyl groups having 8 carbon atoms, and R2 is a group derived from diphenylmethane-4,4'-diisocyanate, based on the total mass of the composition; As a base oil, the kinematic viscosity at 40°C is 20 to 40 mm 2 / s, based on the total mass of the composition, contains 80 to 90.5 mass% of PAO, The wax contains 3 to 6 mass% of polyethylene wax having a dropping point of 130 to 140°C, based on the total mass of the composition; The composition contains 0.1 to 2 mass% of tertiary alkylamine dimethyl phosphate as a phosphate ester, based on the total mass of the composition; The grease composition has a worked penetration of 285 to 340.

[0017] The grease composition of the present invention may contain additives commonly used in greases, as needed. The content of these additives is typically 0.5 to 35 mass%, preferably 5 to 25 mass%, based on the total amount of the grease composition. Examples of such additives include additives other than the wax and phosphate ester, such as antioxidants, inorganic passivators, rust inhibitors, metal corrosion inhibitors, oiliness agents, anti-wear agents, extreme-pressure agents, and solid lubricants. From the viewpoints of oxidation resistance, rust prevention, boundary lubricity, and durability, it is preferable to include at least one of antioxidants, rust inhibitors, oiliness agents, and extreme-pressure agents. However, the grease composition of the present invention does not contain overbased Ca sulfonates. The inclusion of overbased Ca sulfonates impairs wear resistance. In this specification, overbased Ca sulfonates refer to those having a base number of 50 mgKOH / g or more as measured according to JIS K2501.

[0018] The grease composition of the present invention can be applied to, for example, the ball screw portion of a rack-assist electric power steering system. All elements constituting the ball screw are preferably made of steel. [Example]

[0019] <Test grease> 1 mole of 4',4-diphenylmethane diisocyanate was reacted with 1 mole of octylamine and 1 mole of stearylamine in poly-α-olefin (PAO), the temperature was raised, and the mixture was cooled. After that, additives were added in the proportions shown in Table 1 or Table 2, and the mixture was kneaded in a three-roll mill to obtain the grease compositions of Examples 1 to 4 and Comparative Examples 1 to 5. The grease composition of Example 5 was obtained in the same manner as above, except that 2 moles of octylamine were used instead of 1 mole of octylamine and 1 mole of stearylamine. The mass % in Tables 1 and 2 is based on the total mass of the grease composition.

[0020] <Test Method> [Wear evaluation] Wear was observed using a TE77 testing machine, and the details of the measurement conditions are shown below. Load: 150N Frequency: 2Hz Stroke: 1.1mm Speed: 4.4mm / s Temperature: 80℃ Test time: 20 minutes Upper test piece: Steel ball (φ17.5) Lower test piece: Steel plate (Rz: 0.8 to 1.2 μm)

[0021] [Judgment criteria] ◎: The wear marks are thin and the surface is almost free of roughness. ○: The wear marks are slightly thin and the surface is slightly rough. △: The wear marks are somewhat dark and the surface is rough. ×: Dark wear marks and significant surface roughness are observed.

[0022] [Table 1]

[0023] [Table 2]

[0024] PAO: Kinematic viscosity at 40°C = 30mm 2 / s Wax 1: Polyethylene wax (trade name: Licowax PE190, manufactured by Clariant Japan Co., Ltd., dropping point 132-138°C, acid value 0 mgKOH / g, weight average molecular weight 17,500) Wax 2: Oxidized polyethylene wax (trade name: Licowax PED522, manufactured by Clariant Japan Co., Ltd., dropping point 98-104°C, acid value 22-28 mgKOH / g, weight average molecular weight 3,100) Wax 3: Montan wax (trade name: Licowax OP, manufactured by Clariant Japan Co., Ltd., dropping point 96-102°C, acid value 9-14 mgKOH / g) Wax 4: Montan wax (trade name: Licolub WE40, manufactured by Clariant Japan Co., Ltd., dropping point 73-79°C, acid value 13-26 mgKOH / g) Phosphate ester 1: Amine salt of acidic phosphate ester (trade name: VANLUBE 672, manufactured by Vanderbilt Chemicals, LLC, tertiary alkylamine-dimethyl phosphate) Phosphate ester 2 (for comparison): Phosphite ester (product name: JP-260, manufactured by Johoku Chemical Industry Co., Ltd.) Overbased calcium sulfonate (product name: Bryton C-400CKY, manufactured by Kanematsu Corporation)

Claims

1. A grease composition containing a thickener, a base oil, a wax, and a phosphate ester, and not containing an overbased Ca sulfonate, The thickener is a diurea compound represented by the following formula (I): R 1 -NHGNH-R 2 -NHGNH-R 3 (I) (In the formula, R 1 and R 3 one of which is a linear alkyl group having 8 carbon atoms, and the other is a linear alkyl group having 18 carbon atoms, and R 2 is a group derived from diphenylmethane-4,4'-diisocyanate. and / or A diurea compound represented by the above formula (I) (wherein R 1 and R 3 are both linear alkyl groups having 8 carbon atoms, and R 2 is a group derived from diphenylmethane-4,4'-diisocyanate), The kinematic viscosity of the base oil at 40°C is 4 to 100 mm 2 / s, the phosphate ester is at least one compound selected from the group consisting of acidic phosphate esters and amine salts of acidic phosphate esters, The grease composition as described above, wherein the composition has a worked penetration of 265 to 385.

2. 2. The grease composition according to claim 1, wherein the wax comprises at least one wax selected from the group consisting of polyethylene wax, oxidized polyethylene wax, and montan wax.

3. 3. The grease composition according to claim 1, wherein the phosphate ester is a tertiary alkylamine-dimethyl phosphate.

4. The grease composition according to any one of claims 1 to 3, wherein the base oil contains a poly-α-olefin.

5. The poly-α-olefin has a kinematic viscosity of 15 to 70 mm at 40°C. 2 5. The grease composition according to claim 4, wherein the grease composition is:

6. The grease composition according to any one of claims 1 to 5, which is used for a ball screw portion of a rack-assist type electric power steering.

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