Grease composition and rolling bearing

Abstract

To provide a grease composition capable of suppressing occurrence of electrolytic corrosion in a rolling bearing over a long period of time even under high temperature and high speed conditions.SOLUTION: A grease composition comprises: a base oil; a thickener; a conductive additive (A); and an antioxidant (B), wherein the base oil is a trimellitate ester, the thickener is diurea, the conductive additive (A) is a mixture containing sepiolite and bentonite and is an organically modified additive, the antioxidant (B) is 4,4'-bis(α,α-dimethylbenzyl)diphenylamine and / or alkylated diphenylamine, a content of the conductive additive (A) is 3 to 10 mass% with respect to the total mass of the base oil and the thickener, and the content of the antioxidant (B) is 1 to 5 mass% with respect to the total mass of the base oil and the thickener.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a grease composition and a rolling bearing in which the grease composition is packed. [Background technology]

[0002] Bearings for drive motors in electric vehicles (EVs) and hybrid vehicles (HVs) can experience a problem called electrolytic corrosion when an electric current passes through the bearing. When electrolytic corrosion occurs in a bearing, corrugated electrolytic corrosion marks appear on the bearing raceway, creating unevenness that can cause abnormal noise and vibration when the vehicle is running. Furthermore, electrolytic corrosion can lead to early damage to the bearing and adversely affect the unit function of the drive motor.

[0003] To address this issue, measures have been proposed to prevent electrolytic corrosion in bearings, such as using ceramic balls with insulating properties as rolling elements or applying a coating to the outer diameter of the outer ring to give the bearing insulating properties. However, both of these methods have the drawback of being expensive and not suitable for mass production.

[0004] Furthermore, studies are being conducted to provide bearings with resistance to electrolytic corrosion by filling them with a conductive grease composition. Patent Documents 1 and 2 propose grease compositions that use carbon black or an ionic liquid as conductive grease compositions for preventing electrolytic corrosion. Furthermore, Patent Document 3 proposes a grease composition that imparts galvanic corrosion resistance to bearings, and that contains a trimellitic acid ester as a base oil, a thickener, and an organophilic phyllosilicate as a conductive additive. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-329264 [Patent Document 2] Japanese Patent Application Publication No. 2020-193287 [Patent Document 3] International Publication No. 2021 / 034927 Summary of the Invention [Problem to be solved by the invention]

[0006] In recent years, drive motors used in electric and hybrid vehicles are being required to rotate at high speeds in order to achieve both compactness and lightness as well as high output. In addition to this, the grease compositions sealed in the bearings used in the drive motors are required to have not only electrolytic corrosion resistance, but also heat resistance and low torque during high-speed rotation (hereinafter also referred to as high-speed performance).

[0007] However, conventional grease compositions have not been able to fully meet these requirements, and when used under high-temperature and high-speed conditions, they are unable to conduct electricity stably for long periods of time, and their resistance to electrolytic corrosion often quickly deteriorates. [Means for solving the problem]

[0008] Under these circumstances, the present inventors conducted extensive research and discovered that a grease composition containing a specific base oil, thickener, and conductive additive, as well as a specific antioxidant, exhibits good electrical conductivity resistance and can be suitably used even under high-temperature and high-speed conditions, thereby completing the present invention.

[0009] The grease composition of the present invention is a grease composition comprising a base oil, a thickener, a conductive additive (A), and an antioxidant (B), The base oil is a trimellitic acid ester, The thickener is diurea, The conductive additive (A) is a mixture containing sepiolite and bentonite, and is an organically modified additive; The antioxidant (B) is a diphenylamine-based antioxidant, The diphenylamine antioxidant is one or both of 4,4'-bis(α,α-dimethylbenzyl)diphenylamine and alkylated diphenylamine, the content of the conductive additive (A) is 3 to 10 mass % based on the total mass of the base oil and the thickener, The content of the antioxidant (B) is 1 to 5 mass % based on the total mass of the base oil and the thickener.

[0010] The grease composition of the present invention is a grease composition containing a base oil, a thickener, a conductive additive (A), and an antioxidant (B), in which the base oil is a trimellitic acid ester, the conductive additive (A) is a mixture containing sepiolite and bentonite and is an organically modified additive, and the antioxidant (B) is 4,4'-bis(α,α-dimethylbenzyl)diphenylamine and / or an alkylated diphenylamine. A grease composition having such a composition has good electrical conductivity, which can suppress the occurrence of electrolytic corrosion in a rolling bearing in which the grease composition is packed. In addition, the grease composition also has good heat resistance and high-speed properties.

[0011] Furthermore, since the grease composition contains a specific amount of a specific antioxidant (B), it is resistant to deterioration over a long period of time even under high temperature and high speed conditions, and can exhibit stable performance.

[0012] In the grease composition, the diurea is a diurea represented by the following structural formula (1): R 1 -NHCONH-R 2 -NHCONH-R 3 ···(1) (In the formula, R 1 and R 3 are each independently an octyl group or a cyclohexyl group, and R 2 is -C6H4-CH2-C6H4-.) In the entire diurea represented by the structural formula (1), the proportion of the octyl groups is preferably 60 to 80 mol % relative to 100 mol % in total of the octyl groups and the cyclohexyl groups. In this case, the grease composition has better heat resistance, and the rolling bearing packed with this grease composition has even better high speed and leak resistance.

[0013] In the grease composition, the alkylated diphenylamine is preferably a reaction product of N-phenylbenzenediamine with styrene and 2,4,4-trimethylpentane. In the grease composition, the content of the thickener is preferably 10 to 20% by mass with respect to the total mass of the base oil and the thickener. The rolling bearing of the present invention is a rolling bearing in which the grease composition of the present invention is packed. [Effects of the Invention]

[0014] The grease composition of the present invention has good electrical conductivity, and rolling bearings filled with the grease composition are less susceptible to electrolytic corrosion. Furthermore, the grease composition is resistant to deterioration over a long period of time even under high temperature and high speed conditions, and is able to exhibit stable performance. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a cross-sectional view showing a ball bearing according to an embodiment of the present invention. [Figure 2] FIG. 2 is a diagram illustrating a process for preparing a base grease. [Figure 3] 1 is a graph showing the oxidation onset temperatures of grease compositions produced in Examples and Comparative Examples. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The rolling bearing according to the embodiment of the present invention is a ball bearing filled with grease made from the grease composition according to the embodiment of the present invention. FIG. 1 is a cross-sectional view showing a ball bearing according to one embodiment of the present invention. Ball bearing 1 includes an inner ring 2, an outer ring 3 provided radially outward of inner ring 2, a plurality of balls 4 as rolling elements provided between inner ring 2 and outer ring 3, and an annular cage 5 that holds balls 4. Ball bearing 1 is also provided with seals 6 on both sides in the axial direction. Furthermore, an annular region 7 between the inner ring 2 and the outer ring 3 is filled with grease G made of the grease composition according to an embodiment of the present invention.

[0017] The inner ring 2 has an inner raceway surface 21 formed on its outer periphery, on which the balls 4 roll. The outer ring 3 has an outer raceway 31 formed on its inner periphery, on which the balls 4 roll. A plurality of balls 4 are interposed between the inner raceway surface 21 and the outer raceway surface 31 and roll on these inner raceway surface 21 and outer raceway surface 31. The grease G sealed in the region 7 is also present at the contact points between the balls 4 and the inner raceway surface 21 of the inner ring 2, and at the contact points between the balls 4 and the outer raceway surface 31 of the outer ring 3. The grease G is sealed so that it occupies 20 to 40% by volume of the space surrounded by the inner ring 2, the outer ring 3, and the seal 6, excluding the balls 4 and the cage 5. The seal 6 is an annular member comprising an annular metal ring 6a and an elastic member 6b fixed to the metal ring 6a, with its radially outer portion fixed to the outer ring 3 and its radially inner portion with a lip tip attached so as to be able to slide against the inner ring 2. The seal 6 prevents the enclosed grease G from leaking to the outside.

[0018] The ball bearing 1 configured in this manner is filled with grease G, which is made of a grease composition according to an embodiment of the present invention, which will be described later. Therefore, the ball bearing 1 filled with grease G is prevented from generating electrolytic corrosion, and can exhibit stable performance over a long period of time even when used at high temperatures and high speeds.

[0019] Next, the grease composition that constitutes the grease G will be described in detail. The grease composition constituting the grease G is a grease composition according to an embodiment of the present invention, and contains a base oil, a thickener, and at least two types of additives.

[0020] The base oil is a trimellitic acid ester. When used in combination with an organophilic phyllosilicate, the trimellitic acid ester is suitable for imparting good electrical conductivity to Grease G. Furthermore, the use of a trimellitic acid ester as the base oil is also suitable for imparting good heat resistance to Grease G. Furthermore, trimellitic acid esters have polar groups, which give them excellent wettability with metals. Therefore, Grease G has good adhesion to the friction surfaces of rolling bearings and is suitable for suppressing heat generation and wear. Therefore, Grease G, which uses trimellitic acid ester as the base oil, is suitable for maintaining a stable flow of electricity.

[0021] The trimellitic acid ester is preferably a trimellitic acid triester. Examples of the trimellitic acid triester include a reaction product of trimellitic acid with a monoalcohol having 6 to 18 carbon atoms. Among these, a reaction product of trimellitic acid with a monoalcohol having 8 and / or 10 carbon atoms is preferred. Specific examples of the trimellitic acid triester include tri-2-ethylhexyl trimellitate, tri-normal alkyl (C8, C10) trimellitate, triisodecyl trimellitate, and tri-normal octyl trimellitate. The trimellitic acid triesters may be used alone or in combination of two or more.

[0022] The trimellitic acid triester has a base oil kinematic viscosity at 40°C of 37 to 57 mm 2 In this case, it is suitable to reduce the torque of the rolling bearing while ensuring heat resistance. The kinematic viscosity of the base oil is a value in accordance with JIS K 2283.

[0023] The thickener is diurea. The diurea is preferably a diurea represented by the following structural formula (1). R 1 -NHCONH-R 2 -NHCONH-R 3 ···(1) (In the formula, R 1 and R 3 are each independently a hydrocarbon group having 6 to 10 carbon atoms, R 2 is -(CH2)6-, -C6H3(CH3)-, or -C6H4-CH2-C6H4-. where R 2 When R is —C6H3(CH3)—, the phenylene group is preferably bonded at the 2,4 or 2,6 positions relative to the methyl group at the 1 position. 2 When is -C6H4-CH2-C6H4-, both phenylene groups are preferably bonded at the para position. In the above structural formula (1), R 2 is preferably —C6H4—CH2—C6H4—.

[0024] In the above structural formula (1), R 1 and R 3 The hydrocarbon group having 6 to 10 carbon atoms constituting each of the above is preferably an alkyl group having 6 to 10 carbon atoms, a cyclohexyl group, or an alkylcyclohexyl group having 1 to 4 alkyl groups having 1 to 4 carbon atoms (the total number of carbon atoms in the alkyl groups is 4 or less). In this case, a grease composition using the diurea represented by the above structural formula (1) has a high viscosity reduction energy, which is an index of channeling properties, and is suitable for reducing torque. Viscosity reduction energy is an index of thixotropy and can be obtained using a rotational rheometer.

[0025] In the grease composition, the proportion of the thickener relative to the total mass of the base oil and the thickener is preferably 10 to 20% by mass. If the content of the thickener is less than 10% by mass, the ability of the grease G to retain the base oil may decrease, resulting in a large amount of base oil separating from the grease G during rotation of the rolling bearing.On the other hand, if the content of the thickener exceeds 20% by mass, the rotation of the rolling bearing may cause the grease G to shear due to the relative motion of the inner ring, outer ring, balls, and cage, which may increase the stirring resistance and increase the torque of the rolling bearing.The heating of the grease G due to the stirring resistance caused by the shearing of the grease G may also accelerate the oxidation of the grease G, the evaporation of the base oil, and the deterioration of the grease G due to oil separation.

[0026] The diurea represented by the structural formula (1) is more preferably R 1 and R 3 are octyl groups or cyclohexyl groups, respectively, and the diurea as a whole is a mixture of diurea having an octyl group and diurea having a cyclohexyl group. In this case, the diurea used as a thickener in the grease composition contains: (a) R represented by the following structural formula (2) 1 and R 3 Diurea, in which each of the groups is an octyl group, [ka]

[0027] (b) R represented by the following structural formula (3) 1 and R 3 and diurea, in which each of the groups is a cyclohexyl group. [ka]

[0028] (c) R represented by the following structural formula (4) 1 and R 3a diurea in which one of the groups is an octyl group and the other is a cyclohexyl group; [ka] It is more preferable that at least two types of diureas from the above (a) to (c) are contained. In the above structural formulas (2) to (4), R 2 is R in the above structural formula (1). 2 is the same as:

[0029] When the diurea contained in the grease composition is a mixture of at least two types of diurea from (a) to (c) above, the proportion of the octyl groups in the entire diurea is preferably 60 to 80 mol % relative to 100 mol % in total of the octyl groups and the cyclohexyl groups. This ensures good heat resistance and high-speed performance (low torque), and also provides better leakage resistance when filled into a rolling bearing than a grease composition in which the diurea is composed solely of aliphatic diurea.

[0030] On the other hand, if the proportion of octyl groups exceeds 80 mol % (if the proportion of cyclohexyl groups is less than 20 mol %), the effect of improving leak resistance becomes poor. Furthermore, if the proportion of octyl groups is less than 60 mol % (if the proportion of cyclohexyl groups exceeds 40 mol %), the torque reduction effect of a rolling bearing in which the grease composition is enclosed may be reduced, and the grease composition may be more susceptible to thermal degradation due to heat generated when the rolling bearing rotates at high speed.

[0031] The diurea represented by the structural formula (1) is a product formed by the reaction of an amine with a diisocyanate compound. In this case, the amine used is an amine in which one of the hydrogen atoms of ammonia is substituted with a hydrocarbon group having 6 to 10 carbon atoms. Here, the amine and diisocyanate compounds are selected taking into consideration the structure of the resulting diurea. For example, R 1, R 3 To generate a diurea containing an octyl group, use 1-aminooctane as the amine and 1 , R 3 When a diurea containing a cyclohexyl group is to be produced, cyclohexylamine is used as the amine. Also, for example, R 2 When a diurea having the formula -C6H4-CH2-C6H4- is produced, 4,4'-diphenylmethane diisocyanate (MDI) is used as the diisocyanate compound.

[0032] To obtain the diurea represented by the structural formula (1), the amine and the diisocyanate compound can be reacted under various conditions. However, it is preferable to react them in a base oil, since this gives a diurea compound that has high uniform dispersibility as a thickener. The reaction between the amine and the diisocyanate compound may be carried out by adding a base oil in which the diisocyanate compound is dissolved to a base oil in which the amine is dissolved, or by adding a base oil in which the amine is dissolved to a base oil in which the diisocyanate compound is dissolved.

[0033] The temperature and time for the reaction of the amine with the diisocyanate compound are not particularly limited, and conditions similar to those usually employed in this type of reaction may be employed. The reaction temperature is preferably 150°C to 170°C in view of the solubility and volatility of the amine and diisocyanate compound. The reaction time is preferably 0.5 to 2.0 hours from the viewpoint of completing the reaction between the amine and the diisocyanate compound and shortening the production time to efficiently produce the grease composition.

[0034] The two types of additives contained in the grease composition are a conductive additive (A) and an antioxidant (B). The conductive additive (A) is a mixture containing sepiolite and bentonite, and is an organically modified additive, also known as an organophilic phyllosilicate. Sepiolite is a mineral with a chain structure, while bentonite is a mineral with a layered or plate-like structure. The organophilic phyllosilicate, a mineral additive, not only provides electrical conductivity but also improves heat resistance.

[0035] The organophilic phyllosilicate has a three-dimensional network structure in which sepiolite and bentonite are intricately intertwined. The organophilic phyllosilicate has electrical conductivity because the three-dimensional network structure forms a conductive path. Furthermore, the organophilic phyllosilicate has excellent affinity with base oils because it is organically modified. Therefore, by blending the organophilic phyllosilicate, it is possible to impart good electrical conductivity to the grease composition. Furthermore, the organophilic phyllosilicate can improve the channeling properties of the grease composition and contribute to reducing the torque of rolling bearings.

[0036] In the organophilic phyllosilicate, both the sepiolite and the bentonite may be organically modified, or only one of them may be organically modified. The organophilic phyllosilicate is preferably an organically modified sepiolite and an organically modified bentonite, which is more suitable for reducing the torque of a bearing in which the grease composition is packed.

[0037] The above sepiolite or bentonite being organically modified means that it has been treated with a cationic surfactant, for example. Examples of the cationic surfactant include quaternary ammonium salt-type cationic surfactants such as alkyltrimethylammonium chloride, alkyltrimethylammonium bromide, alkyltrimethylammonium iodide, dialkyldimethylammonium chloride, dialkyldimethylammonium bromide, dialkyldimethylammonium iodide, and alkylbenzalkonium chloride; and alkylamine salt-type cationic surfactants such as monoalkylamine salts, dialkylamine salts, and trialkylamine salts. Among these, quaternary ammonium salt type cationic surfactants are preferred.

[0038] As the organically modified mixture containing sepiolite and bentonite (organophilic phyllosilicate), commercially available products can also be used. Specific examples of commercially available products include GARAMITE (registered trademark) 1958 (manufactured by BYK), GARAMITE (registered trademark) 2578 (manufactured by BYK), GARAMITE (registered trademark) 7303 (manufactured by BYK), and GARAMITE (registered trademark) 7305 (manufactured by BYK).

[0039] The content of the organophilic phyllosilicate, which is the conductive additive (A), is 3 to 10% by mass based on the total mass of the base oil, the thickener, and the conductive additive (A). When the content of the conductive additive (A) is within the above range, the grease composition suppresses the occurrence of electrolytic corrosion when filled in a rolling bearing, and is useful for reducing torque. On the other hand, if the content of the conductive additive (A) is less than 3 mass %, the conductivity of the grease composition will not be sufficiently high, and when the grease composition is filled in a rolling bearing, the torque of the rolling bearing may become too high. Furthermore, if the content of the conductive additive (A) exceeds 10% by mass, the grease composition becomes hard, and the torque of a rolling bearing containing the grease composition may become too large. The content of the organophilic phyllosilicate is more preferably 4 to 6 mass % relative to the total amount of the base oil and the thickener.

[0040] The antioxidant (B) is a diphenylamine-based antioxidant. The diphenylamine antioxidant is one or both of 4,4'-bis(α,α-dimethylbenzyl)diphenylamine and alkylated diphenylamine. The alkylated diphenylamine may, for example, be a reaction product of N-phenylbenzenediamine with styrene and 2,4,4-trimethylpentane (CAS Registry Number 68921-45-9).

[0041] As the diphenylamine-based antioxidant, commercially available products can also be used. An example of a commercially available product of the above 4,4'-bis(α,α-dimethylbenzyl)diphenylamine is Nocrac (registered trademark) CD manufactured by Ouchi Shinko Chemical Industry Co., Ltd. An example of a commercially available product of the reaction product of the above-mentioned N-phenylbenzenediamine with styrene and 2,4,4-trimethylpentane is Nocrac (registered trademark) ODA manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0042] The content of the antioxidant (B) is 1 to 5 mass% based on the total mass of the base oil and the thickener. When both 4,4'-bis(α,α-dimethylbenzyl)diphenylamine and alkylated diphenylamine are used in combination as the antioxidant (B), the total mass ratio thereof is 1 to 5 mass% based on the total mass of the base oil and the thickener.

[0043] If the content of the antioxidant (B) is less than 1% by mass, the oxidation inhibitory effect is low, and the grease composition is prone to early deterioration when used under high-temperature and high-speed conditions. On the other hand, even if the content of the antioxidant (B) exceeds 5% by mass, there is no significant improvement in the oxidation inhibitory effect. Furthermore, if the content exceeds 5% by mass, the grease composition softens, and there is a risk of leakage from the rolling bearing in which the grease composition is packed. The preferred content of the antioxidant (B) is 1 to 3 mass % based on the total mass of the base oil and the thickener.

[0044] When both 4,4'-bis(α,α-dimethylbenzyl)diphenylamine and the alkylated diphenylamine are used in combination as the antioxidant (B), the content ratio (by mass) of the two may be the same or different.

[0045] It is important that the grease composition contains a specific amount of a specific diphenylamine-based antioxidant in addition to trimellitic acid as a base oil, diurea as a thickener, and organophilic phyllosilicate as a conductive additive. This composition makes the grease particularly resistant to oxidative degradation and improves heat resistance.

[0046] The grease composition may contain other additives in addition to the conductive additive (A) and the antioxidant (B) as long as the required properties of the grease composition of the present invention are not impaired. Examples of the other additives include rust inhibitors, extreme pressure agents, oiliness agents, anti-wear agents, dyes, color stabilizers, thickeners, structure stabilizers, metal deactivators, and viscosity index improvers. The grease composition preferably does not contain carbon black, in order to avoid black contamination of surrounding components in the event of leakage from the rolling bearing.

[0047] Next, a method for producing the above grease composition will be described. The grease composition can be produced, for example, by first preparing a base grease consisting of a base oil and a thickener, then adding the conductive additive (A), the antioxidant (B), and any optional components to be contained as needed to the obtained base grease, and mixing the components by stirring with a planetary mixer or the like.

[0048] According to this embodiment, the grease G packed in the ball bearing 1 contains a grease composition containing the above-mentioned organophilic phyllosilicate and a specific diphenylamine antioxidant in addition to a trimellitic acid ester as a base oil and diurea as a thickener. By using this type of grease composition, the ball bearing 1 packed with the above-mentioned grease G can suppress the occurrence of electrolytic corrosion over a long period of time, even when used under high-speed and high-temperature conditions. Furthermore, by using the grease G, the torque of the ball bearing 1 can be reduced.

[0049] The present invention is not limited to the above-described embodiments and can be implemented in other embodiments. The rolling bearing according to the embodiment of the present invention is not limited to a ball bearing filled with grease made from the grease composition according to the embodiment of the present invention, and the rolling bearing may be any other rolling bearing, such as a roller bearing, in which something other than balls is used as the rolling element, as long as it is filled with grease made from the grease composition according to the embodiment of the present invention. [Example]

[0050] Next, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples. Here, several grease compositions were prepared and the properties of each grease composition were evaluated. The compositions of each grease composition are shown in Tables 1 and 2.

[0051] The additives used in the examples and comparative examples are as follows. Conductive Additive (A): Organophilic phyllosilicate: BYK-Chemie GARAMITE® 7303

[0052] Antioxidant (B): 4,4'-bis(α,α-dimethylbenzyl)diphenylamine: Nocrac (registered trademark) CD, manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Alkylated diphenylamine: Nocrac® ODA, manufactured by Ouchi Shinko Chemical Industry Co., Ltd. ·2,6-di-tert-butyl-4-(4,6-bis(octylthio)-1,3,5-triazin-2-ylamino)phenol 2-Mercaptomethylbenzimidazole Zinc salt of 2-mercaptobenzimidazole

[0053] (Preparation of base grease A) As base grease A, a grease composition containing a trimellitic acid triester as a base oil and diurea as a thickener was prepared through the following steps. FIG. 2 is a diagram illustrating the process for preparing base grease A.

[0054] (1) Tri-normal alkyl trimellitate (C8, C10), a type of trimellitic triester (manufactured by Kao Corporation, registered trademark Trimex N-08NB), is used as the base oil, and this base oil is heated to 100°C.

[0055] (2) Weigh out the base oil, 1-aminooctane, cyclohexylamine, and 4,4'-diphenylmethane diisocyanate (MDI). At this time, the molar ratio of 1-aminooctane to cyclohexylamine is 1-aminooctane:cyclohexylamine=7:3.

[0056] (3) Put half the amount of base oil (100°C) and MDI into stainless steel container A and stir at 100°C for 30 minutes. (4) Into another stainless steel container B, add the remaining half of the base oil (100°C), 1-aminooctane, and cyclohexylamine, and stir at 100°C for 30 minutes. The above steps (3) and (4) are referred to as the primary step.

[0057] (5) The amine solution in stainless steel container B is dripped into stainless steel container A and gradually poured into the isocyanate solution. At this time, the liquid temperature rises by about 20°C due to the heat of reaction. (6) After confirming that the entire amount of the amine solution in stainless steel container B has been poured into stainless steel container A, the temperature is raised to 170°C. (7) Stir while heating and maintain the temperature at 170°C for 30 minutes. This step (7) is called the secondary step. (8) Stop heating and allow to cool naturally while stirring to 100°C. (9) After confirming that the temperature has dropped below 100°C, stop stirring and allow to cool naturally to room temperature. (10) Homogenization is carried out using a three-roll mill. At this time, the processing conditions are as follows: Roll gap: -50μm Pressure between rolls: 1 MPa Rotation speed: 200 r / min Processing temperature: 25℃ Let's say. Through these steps (1) to (10), a base grease A containing 15 mass % of thickener and 85 mass % of base oil was prepared.

[0058] The thickener of the resulting base grease A is a mixture of diureas represented by structural formulas (5) to (7).

[0059] [ka]

[0060] [ka]

[0061] [ka]

[0062] (Preparation of base grease B) As the base oil, instead of trimellitic triester, PAO8 (manufactured by INEOS Oligomers, Durasyn® 168 Polyalphaolefin, kinematic viscosity (40°C) 45 to 49 mm 2 Base grease B was prepared in the same manner as base grease A, except that a base grease B containing 100% hydroxybenzoates (100%) was used.

[0063] Example 1 A grease composition was prepared by mixing 100 parts by mass of the above base grease, 5 parts by mass of organophilic phyllosilicate, and 1 part by mass of 4,4'-bis(α,α-dimethylbenzyl)diphenylamine in the following manner. Using a planetary centrifugal mixer, the conductive additive and antioxidant were mixed into the base grease at a rotation speed of 2000 rpm for 3 minutes.

[0064] Example 2 A grease composition was prepared in the same manner as in Example 1, except that the blending amount of 4,4'-bis(α,α-dimethylbenzyl)diphenylamine was changed to 2 parts by mass.

[0065] Example 3 A grease composition was prepared in the same manner as in Example 1, except that the blending amount of 4,4'-bis(α,α-dimethylbenzyl)diphenylamine was changed to 3 parts by mass.

[0066] Example 4 A grease composition was prepared in the same manner as in Example 1, except that the blending amount of 4,4'-bis(α,α-dimethylbenzyl)diphenylamine was changed to 5 parts by mass.

[0067] Example 5 A grease composition was prepared in the same manner as in Example 1, except that alkylated diphenylamine (Nocrac ODA) was used as the antioxidant instead of 4,4'-bis(α,α-dimethylbenzyl)diphenylamine.

[0068] Example 6 A grease composition was prepared in the same manner as in Example 5, except that the amount of alkylated diphenylamine was changed to 2 parts by mass.

[0069] Example 7 A grease composition was prepared in the same manner as in Example 5, except that the amount of alkylated diphenylamine was changed to 3 parts by mass.

[0070] Example 8 A grease composition was prepared in the same manner as in Example 5, except that the amount of alkylated diphenylamine was changed to 5 parts by mass.

[0071] Example 9 A grease composition was prepared by mixing 100 parts by mass of the above base grease, 5 parts by mass of organophilic phyllosilicate, 1 part by mass of 4,4'-bis(α,α-dimethylbenzyl)diphenylamine, and 1 part by mass of alkylated diphenylamine (Nocrac ODA) in the same manner as in Example 1.

[0072] (Comparative Example 1) A grease composition was prepared by mixing 100 parts by mass of the above base grease and 5 parts by mass of organophilic phyllosilicate in the same manner as in Example 1.

[0073] (Comparative Example 2) A grease composition was prepared in the same manner as in Example 1, except that the blending amount of 4,4'-bis(α,α-dimethylbenzyl)diphenylamine was changed to 0.5 parts by mass.

[0074] (Comparative Example 3) A grease composition was prepared in the same manner as in Example 5, except that the amount of alkylated diphenylamine was changed to 0.5 parts by mass.

[0075] Comparative Example 4 A grease composition was prepared in the same manner as in Example 2, except that 2,6-di-tert-butyl-4-(4,6-bis(octylthio)-1,3,5-triazin-2-ylamino)phenol was used as the antioxidant instead of 4,4'-bis(α,α-dimethylbenzyl)diphenylamine.

[0076] (Comparative Example 5) A grease composition was prepared in the same manner as in Example 2, except that 2-mercaptomethylbenzimidazole was used as the antioxidant instead of 4,4'-bis(α,α-dimethylbenzyl)diphenylamine.

[0077] (Comparative Example 6) A grease composition was prepared in the same manner as in Example 2, except that a zinc salt of 2-mercaptobenzimidazole was used as the antioxidant instead of 4,4'-bis(α,α-dimethylbenzyl)diphenylamine.

[0078] (Comparative Example 7) A grease composition was prepared in the same manner as in Comparative Example 1, except that base grease B was used instead of base grease A.

[0079] (Comparative Example 8) A grease composition was prepared in the same manner as in Example 2, except that base grease B was used instead of base grease A.

[0080] (Comparative Example 9) A grease composition was prepared in the same manner as in Example 6, except that base grease B was used instead of base grease A.

[0081] (Evaluation of Grease Composition) The grease compositions prepared in the examples and comparative examples were evaluated. Here, the oxidation onset temperature of the grease composition was measured, and the results are shown in Tables 1 and 2 and FIG. The measurement of the oxidation onset temperature was carried out in accordance with ASTM E2009-08(2014) "Standard Test Methods for Oxidation Onset Temperature of Hydrocarbons by Differential Scanning Calorimetry." At this time, the measurement conditions were as follows: Heating rate: 10℃ / min Temperature range: 30~300℃ Oxygen pressure: 3.5MPa Oxygen flow rate: 100mL / min Sample size: approx. 2 mg

[0082] [Table 1]

[0083] [Table 2]

[0084] As shown in Tables 1 and 2 and FIG. 3, the grease composition according to the embodiment of the present invention contains a base oil of trimellitic acid and a specific amount of a specific diphenylamine-based antioxidant, and therefore it has been revealed that the oxidation threshold temperature is exceptionally high and the grease composition has excellent heat resistance. [Explanation of symbols]

[0085] 1: Ball bearing, 2: Inner ring, 3: Outer ring, 4: Ball, 5: Cage, 6: Seal, 7: Area, 100: Rotational rheometer, G: Grease

Claims

1. A grease composition comprising a base oil, a thickener, a conductive additive (A), and an antioxidant (B), the base oil is a trimellitic acid ester, the thickener is diurea, The conductive additive (A) is a mixture containing sepiolite and bentonite, and is an organically modified additive; The antioxidant (B) is a diphenylamine-based antioxidant, The diphenylamine antioxidant is one or both of 4,4'-bis(α,α-dimethylbenzyl)diphenylamine and alkylated diphenylamine, The content of the conductive additive (A) is 3 to 10 mass% based on the total mass of the base oil and the thickener, The grease composition, wherein the content of the antioxidant (B) is 1 to 5 mass % based on the total mass of the base oil and the thickener.

2. The diurea is represented by the following structural formula (1): R １ -NHGNH-R ２ -NHGNH-R ３ ・・・(1) (In the formula, R １ and R ３ are each independently an octyl group or a cyclohexyl group, and R ２ is -C ６ H ４ -CH ２ -C ６ H ４ - is.) 2. The grease composition according to claim 1, wherein in the entire diurea represented by structural formula (1), the proportion of the octyl groups is 60 to 80 mol % relative to 100 mol % of the total of the octyl groups and the cyclohexyl groups.

3. 3. The grease composition according to claim 1, wherein the alkylated diphenylamine is a reaction product of N-phenylbenzenediamine with styrene and 2,4,4-trimethylpentane.

4. The grease composition according to any one of claims 1 to 3, wherein the content of the thickener is 10 to 20 mass% with respect to the total mass of the base oil and the thickener.

5. A rolling bearing in which the grease composition according to any one of claims 1 to 4 is packed.

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