Maleic acid additive, grease composition, and rolling bearing

Abstract

A grease composition containing a base oil, a thickener, and a maleic acid additive, the maleic acid additive being a polymer having maleic anhydride and one or both of an acrylic acid derivative and an olefin as monomer components, the content of the maleic acid additive is from 0.10% by mass to 8.10% by mass (inclusive) with respect to the total mass of the thickener and the base oil.

Description

Technical Field

[0001] The present invention relates to a maleic acid additive, a grease composition and a rolling bearing. Background Art

[0002] Demand for electric vehicles (EVs) has rapidly expanded in recent years. This expansion has led to increasingly stringent requirements for rolling bearings used in EVs. Specifically, bearings must be able to withstand the increased rotational speeds and heat generation associated with smaller and higher-output electric motors. In other words, rolling bearings used in EVs and other vehicles must be able to operate under high-temperature and high-speed rotation conditions.

[0003] Rolling bearings used under high temperature and high-speed rotation conditions (hereinafter also referred to as high-temperature and high-speed conditions) are filled with grease suitable for such use environments.

[0004] Patent Document 1 proposes a grease composition having excellent high-temperature and high-speed durability, wherein an additive is added to a base grease containing a base oil and a thickener, wherein a predetermined diurea compound is used as the thickener.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: International Publication No. 2009 / 063839 Summary of the Invention

[0008] Problems to be solved by the invention

[0009] When the rolling bearing containing the grease composition described in Patent Document 1 is used at ultra-high speeds, the grease migrates toward the seal provided in the rolling bearing due to centrifugal force, instantly transitioning to a channeling state. Consequently, the grease composition-enclosed rolling bearing of Patent Document 1 has difficulty supplying oil between the inner ring and the balls, and between the cage and the balls, and may cause premature seizure in the rolling bearing.

[0010] Methods used to solve problems

[0011] The grease composition of the present invention comprises a base oil, a thickener, and a maleic acid additive. The maleic acid additive is a polymer having maleic anhydride and one or both of an acrylic acid derivative and an olefin as monomer components. The content of the maleic acid additive is 0.10% by mass or more and 8.10% by mass or less relative to the total mass of the thickener and the base oil.

[0012] The rolling bearing of the present invention comprises a rolling element, a first raceway component, a second raceway component and grease, wherein the grease comprises the grease composition of the present invention, the first raceway component has a first raceway, the second raceway component has a second raceway, and the grease is sandwiched between the rolling element and the first raceway and between the rolling element and the second raceway and adheres to at least one of a portion of the first raceway component adjacent to the first raceway and a portion of the second raceway component adjacent to the second raceway.

[0013] The maleic acid additive of the present invention is used in a grease composition for rolling bearings and comprises a polymer containing maleic anhydride and one or both of an acrylic acid derivative and an olefin as monomer components.

[0014] Effects of the Invention

[0015] The grease composition of the present invention can improve the bearing lubrication life of a rolling bearing used under high-temperature and high-speed conditions.

[0016] The rolling bearing of the present invention has a long bearing lubrication life.

[0017] According to the maleic acid additive of the present invention, the grease composition of the present invention can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a cross-sectional view showing a ball bearing as an example of the rolling bearing of the present invention.

[0019] 2( a ) and 2 ( b ) are photographs showing the state of an evaluation sample after 120 hours of a bearing lubrication life evaluation test performed using the grease composition of Example 1. FIG.

[0020] 3( a ) and 3 ( b ) are photographs showing the state of an evaluation sample after 30 hours of a bearing lubrication life evaluation test performed using the grease composition of Comparative Example 1. FIG.

[0021] Figure 4 It is a graph showing the evaluation results of the bearing lubrication life. DETAILED DESCRIPTION

[0022] <Overview of Embodiments of the Invention>

[0023] Hereinafter, embodiments of the present invention will be briefly described.

[0024] (1) A grease composition according to one embodiment of the present invention comprises a base oil, a thickener, and a maleic acid additive, wherein the maleic acid additive is a polymer having maleic anhydride and one or both of an acrylic acid derivative and an olefin as monomer components, and the content of the maleic acid additive is 0.10% by mass or more and 8.10% by mass or less relative to the total mass of the thickener and the base oil.

[0025] (2) In the grease composition of (1) above, the content of the maleic acid additive is preferably 0.19% by mass or more and 7.50% by mass or less relative to the total mass of the thickener and the base oil.

[0026] (3) In the grease composition of (1) above, the content of the maleic acid additive is preferably 0.35% by mass or more and 6.20% by mass or less relative to the total mass of the thickener and the base oil.

[0027] (4) In the grease composition of (1) above, the content of the maleic acid additive is preferably 0.47% by mass or more and 5.00% by mass or less relative to the total mass of the thickener and the base oil.

[0028] (5) In the grease composition according to any one of (1) to (4) above, the content of the thickener is preferably 10.0% by mass or more and 20.0% by weight or less relative to the total mass of the base oil and the thickener.

[0029] (6) In the grease composition according to any one of (1) to (5) above, the thickener is preferably diurea.

[0030] (7) In the grease composition according to any one of (1) to (6) above, the base oil preferably contains at least one of poly-α-olefin oil, ester oil, and alkyl diphenyl ether oil.

[0031] (8) A rolling bearing according to one embodiment of the present invention comprises a rolling element, a first raceway member, a second raceway member and grease, wherein the grease comprises the grease composition described in any one of (1) to (7) above, the first raceway member has a first raceway, the second raceway member has a second raceway, and the grease is sandwiched between the rolling element and the first raceway and between the rolling element and the second raceway and adheres to at least one of a portion of the first raceway member adjacent to the first raceway and a portion of the second raceway member adjacent to the second raceway.

[0032] (9) The rolling bearing of (8) above is preferably: the first raceway member is an inner ring, and the second raceway member is an outer ring; or the first raceway member is a shaft ring, and the second raceway member is a seat ring.

[0033] (10) The rolling bearing of (8) or (9) above preferably further comprises at least one of a retainer and a sealing device, and the grease is attached to the above component.

[0034] (11) The maleic acid additive of the present invention is a maleic acid additive for a grease composition for rolling bearings, and comprises a polymer containing maleic anhydride and one or both of an acrylic acid derivative and an olefin as monomer components.

[0035] <Details of Embodiments of the Invention>

[0036] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0037] The rolling bearing according to the embodiment of the present invention is a ball bearing enclosed with grease containing the grease composition according to the embodiment of the present invention.

[0038] Figure 1 This is a cross-sectional view showing a deep groove ball bearing according to one embodiment of the present invention.

[0039] A deep groove ball bearing 1 includes an inner ring 2, an outer ring 3 disposed radially outside the inner ring 2, a plurality of balls 4 serving as rolling elements disposed between the inner ring 2 and the outer ring 3, and an annular retainer 5 that retains the balls 4. In this deep groove ball bearing 1, the inner ring 2 corresponds to the first raceway member, and the outer ring 3 corresponds to the second raceway member.

[0040] Furthermore, the deep groove ball bearing 1 is provided with seals 6 as sealing means on one axial side and the other axial side, respectively.

[0041] Furthermore, grease G containing the grease composition according to the embodiment of the present invention is enclosed in an annular region 7 between the inner ring 2 and the outer ring 3 .

[0042] The inner ring 2 includes an inner raceway surface 21 on its outer periphery, on which the balls 4 roll.

[0043] The outer ring 3 includes an outer raceway surface 31 on its inner periphery on which the balls 4 roll.

[0044] A plurality of balls 4 are interposed between the inner raceway surface 21 and the outer raceway surface 31 , and roll on the inner raceway surface 21 and the outer raceway surface 31 .

[0045] The inner raceway surface 21 of the deep groove ball bearing 1 corresponds to the first raceway, and the outer raceway surface 31 of the deep groove ball bearing 1 corresponds to the second raceway.

[0046] Grease G enclosed in area 7 is located between the contact areas between the ball 4 and the inner raceway 21 of the inner ring 2, and between the contact areas between the ball 4 and the outer raceway 31 of the outer ring 3. Grease G also adheres to both the portion (shoulder) 22 of the inner ring 2 adjacent to the inner raceway 21 and the portion (shoulder) 32 of the outer ring 3 adjacent to the outer raceway 31. Grease G also adheres to the retainer 5 and seal 6. Depending on the situation, grease G may adhere to only one of the portion (shoulder) 22 adjacent to the inner raceway 21 and the portion (shoulder) 32 adjacent to the outer raceway 31.

[0047] The grease G is enclosed so as to occupy 20 to 40 volume % of the 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 .

[0048] The seal 6 is an annular member comprising an annular metal ring 6a and an elastic member 6b fixed to the metal ring 6a. Its radially outer portion is fixed to the outer ring 3, while the tip of its radially inner lip is mounted so as to be in sliding contact with the inner ring 2. The seal 6 prevents leakage of the enclosed grease G.

[0049] The grease G enclosed in the deep groove ball bearing 1 thus constructed is a grease comprising a grease composition according to an embodiment of the present invention, described below. Therefore, when the deep groove ball bearing 1 enclosed with the grease G is used under high-temperature, high-speed conditions, the grease G remains interposed between the contact areas between the balls 4 and the inner raceway 21 of the inner ring 2, the contact areas between the balls 4 and the outer raceway 31 of the outer ring 3, and the contact areas between the balls 4 and the cage 5. Consequently, the deep groove ball bearing 1 is less susceptible to seizure when used under high-temperature, high-speed conditions, enabling extended use.

[0050] Next, the grease composition constituting the grease G will be described in detail.

[0051] The grease composition described above is a grease composition according to an embodiment of the present invention, and contains a base oil, a thickener, and a maleic acid additive.

[0052] The grease G comprising the grease composition containing the maleic acid additive tends to remain adhered to the raceway surface of the inner ring, the raceway surface of the outer ring, and the cage.

[0053] Examples of the base oil include poly-α-olefin (PAO), ester oil, polyalkylene glycol, fluorinated oil, silicone oil, and ether oil such as alkyl diphenyl ether oil, etc. These may be used alone or in combination of two or more.

[0054] The base oil preferably contains at least one of poly-α-olefin (PAO), ester oil, and alkyl diphenyl ether oil.

[0055] More preferably, the base oil is an ether oil or a mixed base oil of poly-α-olefin (PAO) and ester oil.

[0056] Examples of the poly-α-olefin include oligomers or polymers of α-olefins such as 1-hexene, 1-octene, 1-nonene, 1-decene, 1-dodecene, and 1-tetradecene, and hydrogenated α-olefins.

[0057] Preferred poly-α-olefins are PAO4 to PAO8 (PAO4, PAO5, PAO6, PAO7, PAO8) obtained by oligomerizing 1-decene.

[0058] Among the above base oils, the preferred base oil has a dynamic viscosity (40°C) of 30 to 150 mm 2 In this case, the grease G tends to remain attached to the inner ring raceway, the outer ring raceway, and the cage. Therefore, the rolling bearing enclosed with the grease G has a long bearing lubrication life.

[0059] Furthermore, the torque of the rolling bearing filled with the grease G is less likely to become excessive.

[0060] The more preferred base oil dynamic viscosity (40°C) is 30 to 50 mm 2 / s.

[0061] The above-mentioned base oil dynamic viscosity is a value in accordance with JIS K 2283.

[0062] The thickener is not particularly limited, and is, for example, a urea thickener.

[0063] The preferred urea thickener is diurea.

[0064] A preferred diurea is a diurea represented by the following structural formula (1).

[0065] R 1 -NHCONH-R 2 -NHCONH-R 3 …(1)

[0066] (In formula (1), R 1 and R 3 are independently monovalent hydrocarbon groups, R 2 is -(CH2)6-, -C6H3(CH3)- or -C6H4-CH2-C6H4-.)

[0067] Here, in R 2 In the case of -C6H3(CH3)-, the phenylene group is preferably bonded to the 2nd, 4th, or 2nd, 6th positions with the methyl group at the 1st position.2 In the case of -C6H4-CH2-C6H4-, both phenylene groups are preferably bonded at the para position.

[0068] R 2 Preferred is -C6H4-CH2-C6H4-.

[0069] In the diurea represented by the structural formula (1), the hydrocarbon group is an aliphatic hydrocarbon group, an aromatic hydrocarbon group or an alicyclic hydrocarbon group.

[0070] The above-mentioned aliphatic hydrocarbon group is, for example, -C n H 2n＋1 (n is an integer of 6 to 20). The aliphatic hydrocarbon group may be linear or branched.

[0071] The preferred aliphatic hydrocarbon group is octadecyl (-C 18 H 37 ).

[0072] The aromatic hydrocarbon group is, for example, R 4 -C6H4-(R 4 An aromatic hydrocarbon group represented by (an alkyl group having 1 to 12 carbon atoms).

[0073] A preferred aromatic hydrocarbon group is p-tolyl (p-methylphenyl).

[0074] The above-mentioned alicyclic hydrocarbon group is, for example, R 5 -C6H 10 -(R 5 is an alicyclic hydrocarbon group represented by hydrogen, 2-methyl, 3-methyl or 4-methyl).

[0075] The preferred alicyclic hydrocarbon group is cyclohexyl (-C6H 11 ).

[0076] When the thickener is composed of diurea, the thickener may be composed of only one type of diurea or a mixture of two or more types of diureas having different chemical structures.

[0077] In the case where the thickener is composed of a mixture of two or more diureas, the preferred thickener is 1 and R 3 are all octadecyl diureas, in the above structural formula (1), R 1 and R 3 The diurea of cyclohexyl and R in the above structural formula (1) 1 and R 3 A mixture A of bisureas in which one is octadecyl and the other is cyclohexyl.

[0078] The preferred mixture A is composed as follows: 1 and R 3 The total of octadecyl group is 50 to 70 mol%, cyclohexyl group is 30 to 50 mol%, and the sum of octadecyl group and cyclohexyl group is 100 mol%.

[0079] The reasons are as follows. 1 and R 3 Grease G, which contains a grease composition containing octadecyl diurea as a thickener, softens at high temperatures and is prone to leaking from bearings. Grease G, which contains the aforementioned mixture A as a thickener, heat-hardens at high temperatures and is less likely to leak from bearings.

[0080] In addition, other preferred thickeners are those in the above structural formula (1) 1 and R 3 are all diureas of p-tolyl, in the above structural formula (1) R 1 and R 3 The diurea of cyclohexyl and R in the above structural formula (1) 1 and R 3 A mixture B of diureas in which one of the diureas is p-tolyl and the other is cyclohexyl.

[0081] The preferred mixture B is as follows: 1 and R 3 The total of p-tolyl is 60-80 mol%, cyclohexyl is 20-40 mol%, and the sum of p-tolyl and cyclohexyl is 100 mol%.

[0082] The reasons are as follows: Grease G containing the mixture B as a thickener is thermally cured in a high-temperature atmosphere and is less likely to leak from the bearing.

[0083] The reason why the thickener containing the mixture A or the mixture B is preferred is as follows: a rolling bearing enclosing grease G containing the thickener containing the mixture A or the mixture B has an excellent lubrication life in a high-temperature atmosphere.

[0084] The base oil used in combination with the mixture A is preferably a base oil obtained by mixing poly-α-olefin (PAO) and ester oil. The base oil used in combination with the mixture B is preferably an ether oil.

[0085] The diurea represented by the above structural formula (1) is a product formed by the reaction of an amine compound and a diisocyanate compound.

[0086] The above amine compound is an amine compound having the same structure as R 1 and R 3 Amine compounds corresponding to the functional groups.

[0087] The above-mentioned amine compound is an aliphatic amine, an aromatic amine or an alicyclic amine.

[0088] The above-mentioned aliphatic amine is an aliphatic amine having 6 to 20 carbon atoms.

[0089] A preferred aliphatic amine is octadecylamine.

[0090] The above aromatic amine is R 4 -C6H4-NH3(R 4 is an aromatic amine represented by an alkyl group having 1 to 12 carbon atoms).

[0091] A preferred aromatic amine is p-toluidine (1-amino-4-methylbenzene).

[0092] The above alicyclic amine is R 5 -C6H 10 -NH3(R 5 is hydrogen, 2-methyl, 3-methyl or 4-methyl).

[0093] A preferred aromatic amine is cyclohexylamine.

[0094] Examples of the diisocyanate compound include hexamethylene diisocyanate (HDI), 2,4-toluene diisocyanate (2,4-TDI), 2,6-toluene diisocyanate (2,6-TDI), a mixture of 2,4-TDI and 2,6-TDI, and 4,4′-diphenylmethane diisocyanate (4,4′-MDI).

[0095] The diurea represented by the structural formula (1) is obtained by reacting the amine compound with the diisocyanate compound under various conditions. From the perspective of obtaining a diurea compound with high uniform dispersibility as a thickener, the preferred reaction conditions are the reaction in a base oil.

[0096] The reaction of the amine compound and the diisocyanate compound is performed by adding a base oil in which a diisocyanate compound is dissolved to a base oil in which an amine compound is dissolved, or by adding a base oil in which an amine compound is dissolved to a base oil in which a diisocyanate compound is dissolved.

[0097] The temperature and time conditions for the reaction of the aliphatic amine and the diisocyanate compound are not particularly limited, and generally, the same conditions as those used in this reaction can be employed.

[0098] The reaction temperature is preferably 150°C to 170°C from the viewpoint of the solubility and volatility of the amine compound and the diisocyanate compound.

[0099] From the viewpoint of completing the reaction between the amine compound and the diisocyanate compound and shortening the production time to efficiently produce the grease composition, the reaction time is preferably 0.5 to 2.0 hours.

[0100] The preferred content of the thickener is 10.0% to 20.0% by mass relative to the combined mass of the base oil and thickener. In this case, the rolling bearing enclosed with the grease G facilitates the flow of grease G between the inner ring and the balls, and between the cage and the balls. Furthermore, the torque of the rolling bearing enclosed with the grease G is less likely to increase.

[0101] The maleic acid additive is a polymer containing maleic anhydride and one or both of an acrylic acid derivative and an olefin as monomer components.

[0102] That is, the maleic acid additive is a copolymer of maleic anhydride and an acrylic acid derivative, a copolymer of maleic anhydride and an olefin, or a copolymer of maleic anhydride, an acrylic acid derivative and an olefin.

[0103] The maleic acid additives mentioned above include the following products: All of the products are manufactured by DIC Corporation.

[0104] (1) PAD-19 (trade name): Copolymer of maleic anhydride and acrylic acid derivative, weight-average molecular weight 67,000, pale yellow clear liquid dispersion (solids content 24.0-26.0% by mass), viscosity <500 mPa·s, pH 7.0-9.0, acid value 460 (calculated), glass transition temperature 89°C, melting point 143°C, thermal decomposition temperature 326°C

[0105] (2) PAD-21 (trade name): Copolymer of maleic anhydride and acrylic acid derivative, weight-average molecular weight 27,000, pale yellow clear liquid dispersion (solids content 24.0-26.0% by mass), viscosity <300 mPa·s, pH 7.0-9.0, acid value 460 (calculated), glass transition temperature 39°C, melting point 103°C, thermal decomposition temperature 313°C

[0106] (3) PAD-26 (trade name): Copolymer of maleic anhydride and acrylic acid derivative, weight-average molecular weight 19,000, pale yellow transparent liquid dispersion (solids content 24.0-26.0% by mass), viscosity <100 mPa·s, pH 7.0-9.0, acid value 460 (calculated), melting point 52°C, thermal decomposition temperature 358°C

[0107] (4) PAD-30 (trade name): Copolymer of maleic anhydride and acrylic acid derivative, weight-average molecular weight 10,000, pale yellow transparent liquid dispersion (solids content 24.0-26.0% by mass), viscosity <100 mPa·s, pH 7.0-9.0, acid value 460 (calculated), melting point 132°C, thermal decomposition temperature 322°C

[0108] (5) PAD-112 (trade name): Copolymer of maleic anhydride and acrylic acid derivative, weight-average molecular weight 19,000, pale yellow transparent liquid, dispersion (solids content 24.0-26.0% by mass), viscosity <100 mPa·s, pH 7.0-9.0, acid value 610 (calculated value)

[0109] The content of the maleic acid additive is 0.10% by mass or more and 8.10% by mass or less relative to the total amount of the base oil and the thickener.

[0110] In this case, the grease G comprising the grease composition containing the maleic acid additive easily maintains the grease G adhered to the inner ring raceway, the outer ring raceway, and the cage. Therefore, the rolling bearing enclosed with the grease G has a long bearing lubrication life.

[0111] On the other hand, if the content of the maleic acid additive is less than 0.1% by mass, the grease G will have difficulty maintaining its adherence to the inner and outer ring raceways, as well as the cage, and may prematurely migrate from these raceways to other locations (e.g., the seal side). Consequently, rolling bearings enclosed with the grease G do not have a long bearing lubrication life. Furthermore, if the content of the maleic acid additive exceeds 8.10% by mass, the rotational torque of the rolling bearing enclosed with the grease G becomes excessively high, potentially causing rotational failure in the bearing.

[0112] From the viewpoint of extending the bearing lubrication life, the preferred content of the maleic acid additive is 0.19% by mass or more and 7.50% by mass or less relative to the total amount of the base oil and the thickener.

[0113] From the viewpoint of extending the bearing lubrication life, the more preferred content of the maleic acid additive is 0.35% by mass or more and 6.20% by mass or less relative to the total amount of the base oil and the thickener.

[0114] From the viewpoint of further extending the bearing lubrication life, the more preferred content of the maleic acid additive is 0.47% by mass or more and 5.00% by mass or less relative to the total amount of the base oil and the thickener.

[0115] The grease composition may further contain a rust inhibitor or an antioxidant. In this case, the lubrication life of the grease composition can be further improved.

[0116] The grease composition may further contain other additives such as an extreme pressure agent, an oiliness agent, an anti-wear agent, a dye, a color stabilizer, a tackifier, a structure stabilizer, a metal deactivator, and a viscosity index improver.

[0117] Next, a method for producing the above-mentioned grease composition will be described.

[0118] The grease composition can be produced, for example, by first preparing a base grease comprising a base oil and a thickener. The maleic acid additive and other optional additives are then added to the resulting base grease, and the components are mixed by stirring using a planetary centrifugal mixer or the like.

[0119] Therefore, in order to produce the grease composition according to the embodiment of the present invention, the above-mentioned maleic acid additive is used.

[0120] According to this embodiment, a grease composition comprising the aforementioned base oil and thickener and containing a predetermined amount of a maleic acid additive is used as the grease composition constituting the grease G enclosed in the deep groove ball bearing 1. By employing this grease composition, the grease G in the deep groove ball bearing 1 enclosed with the grease G easily remains adhered to the inner ring, outer ring, and cage, ensuring sufficient bearing life when the deep groove ball bearing 1 is used under high-temperature and high-speed conditions.

[0121] The present invention is not limited to the above-described embodiment, and can also be implemented in other embodiments.

[0122] The ball bearings according to embodiments of the present invention are not limited to deep groove ball bearings. They may also be angular contact ball bearings or thrust ball bearings comprising a shaft washer, a raceway, balls, and a cage. In such cases, grease G is applied to the contact areas between the balls and the raceway of the shaft washer, and between the balls and the raceway of the raceway. Grease G also adheres to the cage.

[0123] Furthermore, the rolling bearing according to the embodiment of the present invention may be another rolling bearing such as a roller bearing using objects other than balls as rolling elements.

[0124] Example

[0125] Next, the present invention will be described in further detail based on examples, but the present invention is not limited to these examples.

[0126] As an example, a plurality of grease compositions were prepared and the properties of each grease composition were evaluated. The composition and evaluation results of each grease composition are shown in Table 1.

[0127] (Raw materials of grease composition)

[0128] (1) Base oil

[0129] (1-1) Poly-α-olefin oil (PAO 8): base oil dynamic viscosity (40°C) = 47.5 mm 2 / s, base oil dynamic viscosity (100℃) = 7.8mm 2 / s

[0130] (1-2) Ester oil: base oil dynamic viscosity (40℃) = 27mm 2 / s, base oil dynamic viscosity (100℃) = 6mm 2 / s

[0131] (1-3) Ether oil: base oil dynamic viscosity (40℃) = 100mm 2 / s, base oil dynamic viscosity (100℃) = 13mm 2 / s

[0132] (2) Thickener: diurea (reaction product of amine compound and diisocyanate compound)

[0133] (2-1) Amine compounds

[0134] Aliphatic amine: octadecylamine

[0135] Alicyclic amines: cyclohexylamine

[0136] Aromatic amines: p-toluidine

[0137] (2-2) diisocyanate

[0138] 4,4′-diphenylmethane diisocyanate (4,4′-MDI)

[0139] (3) Additives

[0140] Maleic acid additive: PAD-26 (manufactured by DIC Corporation)

[0141] (Preparation of base grease A)

[0142] (1) 4,4'-MDI, octadecylamine, and cyclohexylamine were weighed so that the amount of octadecylamine was 60 mol% and the amount of cyclohexylamine was 40 mol% relative to 50 mol% of 4,4'-MDI.

[0143] (2) In a stainless steel container A, half of the base oil in an amount such that the blending amount becomes 85% by mass relative to the total amount of the base grease A (the total amount of the base oil and the thickener) and 4,4′-MDI in an amount such that the blending amount of the reacted thickener becomes 15% by mass relative to the total amount of the base grease A were placed, and the mixture was heated to 60° C. to dissolve the mixture.

[0144] (3) In another stainless steel container B, add half of the remaining amount of base oil so that the amount thereof reaches 85% by mass relative to the total amount of base grease A, and octadecylamine and cyclohexylamine so that the amount of thickener thereof after the reaction reaches 15% by mass relative to the total amount of base grease A, and heat to 80°C to dissolve them.

[0145] (4) The amine mixture solution in the stainless steel container B is added dropwise to the stainless steel container A and then introduced into the isocyanate solution.

[0146] (5) After confirming that all the amine mixture solution in the stainless steel container B has been put into the stainless steel container A, the temperature of the isocyanate and amine mixture solution is raised to 150°C.

[0147] (6) The solution of the isocyanate and amine mixture was heated while stirring and the temperature was maintained at 150°C for 30 minutes.

[0148] (7) For the solution of the isocyanate and amine mixture, stop heating and let it cool to room temperature to complete base grease A.

[0149] (Preparation of base grease B)

[0150] (1) 4,4'-MDI, p-toluidine, and cyclohexylamine were weighed so that p-toluidine accounted for 30 mol% and cyclohexylamine accounted for 70 mol% relative to 50 mol% of 4,4'-MDI.

[0151] (2) In a stainless steel container A, half of the base oil in an amount such that the blending amount becomes 85% by mass relative to the total amount of the base grease B (the total amount of the base oil and the thickener) and 4,4′-MDI in an amount such that the blending amount of the reacted thickener becomes 15% by mass relative to the total amount of the base grease B are placed and heated to 60° C. to dissolve them.

[0152] (3) In another stainless steel container B, add half of the remaining base oil so that the amount thereof reaches 85% by mass relative to the total amount of the base grease B, and p-toluidine and cyclohexylamine so that the amount of the reacted thickener reaches 15% by mass relative to the total amount of the base grease B, and heat to 80°C to dissolve them.

[0153] (4) The amine mixture solution in the stainless steel container B is added dropwise to the stainless steel container A and then introduced into the isocyanate solution.

[0154] (5) After confirming that all the amine mixture solution in the stainless steel container B has been put into the stainless steel container A, the temperature of the isocyanate and amine mixture solution is raised to 150°C.

[0155] (6) The solution of the isocyanate and amine mixture was heated while stirring and maintained at 150°C for 30 minutes.

[0156] (7) For the solution of the isocyanate and amine mixture, stop heating and let it cool to room temperature to complete base grease B.

[0157] (Example 1)

[0158] 5 parts by mass of a maleic acid additive were added to 100 parts by mass of base grease A. The base grease A containing the maleic acid additive was mixed using a planetary centrifugal mixer at 2000 rpm for 3 minutes and then homogenized using a three-roll mill to obtain a grease composition.

[0159] (Example 2)

[0160] 1 part by mass of a maleic acid additive was added to 100 parts by mass of base grease A. The base grease A containing the maleic acid additive was mixed using a planetary centrifugal mixer at 2000 rpm for 3 minutes and then homogenized using a three-roll mill to obtain a grease composition.

[0161] (Example 3)

[0162] 0.3 parts by mass of a maleic acid additive was added to 100 parts by mass of base grease A. The base grease A containing the maleic acid additive was mixed using a planetary centrifugal mixer at 2000 rpm for 3 minutes and then homogenized using a three-roll mill to obtain a grease composition.

[0163] (Example 4)

[0164] 0.1 parts by mass of a maleic acid additive was added to 100 parts by mass of base grease A. The base grease A containing the maleic acid additive was mixed using a planetary centrifugal mixer at 2000 rpm for 3 minutes and then homogenized using a three-roll mill to obtain a grease composition.

[0165] (Comparative Example 1)

[0166] The base grease A was homogenized using a three-roll mill to obtain a grease composition of Comparative Example 1.

[0167] (Comparative Example 2)

[0168] 10 parts by mass of a maleic acid additive was added to 100 parts by mass of base grease A. The base grease A containing the maleic acid additive was mixed using a planetary centrifugal mixer at 2000 rpm for 3 minutes and then homogenized using a three-roll mill to obtain a grease composition.

[0169] (Example 5)

[0170] 5 parts by mass of a maleic acid additive were added to 100 parts by mass of base grease B. The base grease B containing the maleic acid additive was mixed using a planetary centrifugal mixer at 2000 rpm for 3 minutes and then homogenized using a three-roll mill to obtain a grease composition.

[0171] (Example 6)

[0172] 1 part by mass of a maleic acid additive was added to 100 parts by mass of base grease B. The base grease B containing the maleic acid additive was mixed using a planetary centrifugal mixer at 2000 rpm for 3 minutes and then homogenized using a three-roll mill to obtain a grease composition.

[0173] (Example 7)

[0174] 0.1 parts by mass of a maleic acid additive was added to 100 parts by mass of base grease B. The base grease B containing the maleic acid additive was mixed using a planetary centrifugal mixer at 2000 rpm for 3 minutes and then homogenized using a three-roll mill to obtain a grease composition.

[0175] (Comparative Example 3)

[0176] The base grease B was homogenized using a three-roll mill to obtain a grease composition of Comparative Example 3.

[0177] (Comparative Example 4)

[0178] 10 parts by mass of a maleic acid additive was added to 100 parts by mass of base grease B. The base grease B containing the maleic acid additive was mixed using a planetary centrifugal mixer at 2000 rpm for 3 minutes and then homogenized using a three-roll mill to obtain a grease composition.

[0179] (Evaluation of Grease Composition)

[0180] The grease compositions prepared as Examples 1 to 7 and Comparative Examples 1 to 4 were evaluated. The evaluation items were the measurement of mixed consistency and the measurement of bearing lubrication life.

[0181] The results are shown in Tables 1, 2, Figure 4 middle. Figure 4 This is a graph that plots the relationship between the content of maleic acid additives and the bearing lubrication life.

[0182]

[0183]

[0184] The evaluation method is as follows.

[0185] (1) Mixing consistency

[0186] The work consistency (60W) of the grease composition of each Example and each Comparative Example was measured by a method in accordance with JIS K 2220-7.

[0187] (2) Bearing lubrication life

[0188] The bearing lubrication life of the grease composition of each example and each comparative example was evaluated.

[0189] The evaluation criteria for bearing lubrication life are the time until the cage of the rolling bearing is damaged.

[0190] The bearing lubrication life test used to evaluate the bearing lubrication life is an air turbine tester.

[0191] The test bearings were 3NC608-2RU, with multiple balls made of silicon nitride. The inner and outer rings were made of quenched and tempered JIS SU J2 steel. Seals were assembled on the outer rings on both axial sides of the multiple balls. The seals were deep groove ball bearings that did not contact the inner ring.

[0192] The test temperature is room temperature (natural heating), the rotation speed is 100,000 minutes -1 , the axial load is 20N.

[0193] The grease composition was enclosed in the test bearing so that its volume became 20% by volume relative to the volume of the space enclosed by the inner ring, outer ring, and two seals, excluding the total volume of all balls and the volume of the cage.

[0194] Malrotation refers to a state in which the test bearing cannot rotate smoothly due to the grease composition being sealed in the test bearing.

[0195] Figures 2(a) and 2(b) are photographs showing the state of an evaluation sample after 120 hours of a bearing lubrication life evaluation test conducted using the grease composition of Example 1. Figure 2(a) is a photograph of a portion of the retainer, and Figure 2(b) is a photograph of a portion of the outer ring.

[0196] Figures 3(a) and 3(b) are photographs showing the state of an evaluation sample 30 hours after a bearing lubrication life evaluation test using the grease composition of Comparative Example 1. Figure 3(a) is a photograph of a portion of the retainer, and Figure 3(b) is a photograph of a portion of the outer ring.

[0197] Evaluation of the bearing lubrication life revealed that the use of the grease composition according to the embodiment of the present invention ensured a long bearing lubrication life even under high-temperature and high-speed conditions.

[0198] As shown in Figures 2 and 3 , it can be seen that the grease composition containing the maleic acid additive tends to remain adhered to the cage and the outer ring raceway surface compared to the grease composition not containing the maleic acid additive.

[0199] Explanation of symbols

[0200] 1: Deep groove ball bearing

[0201] 2: Inner circle

[0202] 3: Outer ring

[0203] 4: Ball

[0204] 5: Cage

[0205] 6: Seals

[0206] 7: Region

[0207] G: Grease

Claims

1. A grease composition comprising a base oil, a thickener and a maleic acid additive, The maleic acid additive is a polymer with maleic anhydride, one or both of acrylic acid derivatives and olefins as monomer components. The content of the maleic acid additive is 0.10% by mass or more and 8.10% by mass or less relative to the total mass of the thickener and the base oil.

2. The grease composition according to claim 1, wherein The content of the maleic acid additive is 0.19% by mass or more and 7.50% by mass or less relative to the total mass of the thickener and the base oil.

3. The grease composition according to claim 1, wherein The content of the maleic acid additive is 0.35% by mass or more and 6.20% by mass or less relative to the total mass of the thickener and the base oil.

4. The grease composition according to claim 1, wherein The content of the maleic acid additive is 0.47% by mass or more and 5.00% by mass or less relative to the total mass of the thickener and the base oil.

5. The grease composition according to claim 1, wherein The content of the thickener is 10.0% by mass or more and 20.0% by weight or less relative to the total mass of the base oil and the thickener.

6. The grease composition according to claim 1, wherein The thickener is diurea.

7. The grease composition according to claim 1, wherein The base oil includes at least one of poly-α-olefin oil, ester oil, and alkyl diphenyl ether oil.

8. A rolling bearing comprising a rolling element, a first raceway member, a second raceway member and grease, The grease comprises the grease composition according to claim 1, The first raceway member has a first raceway, The second raceway member has a second raceway, The grease is interposed between the rolling element and the first raceway and between the rolling element and the second raceway and adheres to at least one of a portion of the first raceway member adjacent to the first raceway and a portion of the second raceway member adjacent to the second raceway.

9. The rolling bearing according to claim 8, wherein: The first raceway member is an inner ring, and the second raceway member is an outer ring; or The first raceway component is a shaft washer, and the second raceway component is a seat washer. 10 . The rolling bearing according to claim 8 , further comprising at least one of a cage and a sealing device, wherein the grease adheres to the at least one member.

11. A maleic acid additive for a grease composition for a rolling bearing, comprising a polymer containing maleic anhydride and one or both of an acrylic acid derivative and an olefin as monomer components.

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