Rolling bearing

Abstract

The purpose of the present invention is to provide a rolling bearing capable of suppressing electrocorrosion and a motor incorporating the bearing. A rolling bearing and a motor including the same, the rolling bearing including: an inner ring; an outer ring disposed on the outer peripheral side of the inner ring so as to be coaxial with the inner ring; a plurality of rolling bodies disposed between the inner ring and the outer ring; the retainer is used for retaining the rolling bodies; and a grease composition held between the inner ring and the outer ring, the grease composition containing a base oil containing an aromatic ester-based base oil, a thickener, and an ionic liquid containing borate anions, the grease composition having an electrode diameter of 10 mm, an electrode pitch of 1 mm, and an electrostatic capacitance of 4.6 pF or more under conditions of a frequency of 10 kHz. Or the loss tangent (tan [delta]), which is represented by the ratio of the storage modulus to the loss modulus at 25 DEG C as measured under the conditions of a film thickness of 0.5 mm, a shear strain of 1%, and a frequency of 100 Hz in dynamic viscoelasticity measurement by a rotary rheometer, is 0.7 or more.

Description

TECHNICAL FIELD

[0001] The present application relates to a rolling bearing in which a grease composition containing an ionic liquid is enclosed, and a motor provided with the rolling bearing. BACKGROUND

[0002] An ionic liquid is a salt in a liquid state composed only of ions (anions, cations). An ionic liquid has characteristics such as low vapor pressure (non-volatile), high thermal stability, flame retardancy, low viscosity, high ionic conductivity, and the like, and in addition, various properties can be designed by the combination of cations and anions, and thus is expected to be applied to various technical fields represented by electrolytic solutions, solvents.

[0003] Due to such characteristics, ionic liquids are also being studied for application to lubricants, greases.

[0004] For example, a lubricant composition obtained by adding an ionic liquid for the purpose of maintaining low friction over a long period under high load conditions has been proposed (Patent Document 1).

[0005] In addition, for example, as a grease composition in which improvement in low friction is sought, a grease composition obtained by combining an ionic liquid as a base oil of a grease with a non-soap thickener has been proposed (Patent Document 2).

[0006] PRIOR ART DOCUMENTS PATENT DOCUMENTS Patent Document 1: Japanese Patent Application Publication No. 2019-065256 Patent Document 2: Japanese Patent Application Publication No. 2019-123846 SUMMARY

[0007] PROBLEMS TO BE SOLVED BY THE INVENTION For example, in a rolling bearing for an electric motor or the like, a potential difference (shaft voltage) is easily generated between an inner ring and an outer ring, and due to this potential difference (shaft voltage), current flows in the bearing to cause electric corrosion, and sometimes damage occurs on the surface of a rolling element and a raceway surface of the rolling bearing. Such damage to the rolling element and the raceway surface can lead to degradation of the rolling bearing and can even cause the rolling bearing to stop, and thus appropriate measures are required.

[0008] An object of the present application is to provide a rolling bearing in which a grease composition containing an ionic liquid is enclosed, in which electric corrosion is suppressed, and a motor in which the bearing is built in.

[0009] SOLUTION TO PROBLEM One aspect of the present application relates to a rolling bearing, including: an inner ring; an outer ring disposed coaxially with the inner ring on an outer peripheral side of the inner ring; a plurality of rolling elements disposed between the inner ring and the outer ring; a retainer that retains the rolling elements; and a grease composition retained between the inner ring and the outer ring, the grease composition including a base oil including an aromatic ester base oil, a thickening agent, and an ionic liquid including a borate anion, the grease composition having an electrostatic capacitance of 4.6 pF or more under conditions of an electrode diameter of 10 mm, an electrode spacing of 1 mm, and a frequency of 10 kHz, and a tan δ of 0.7 or more as a ratio of a storage modulus to a loss modulus at 25°C, measured under conditions of a film thickness of 0.5 mm, a shear strain of 1%, and a frequency of 100 Hz in dynamic viscoelasticity measurement by a rotary rheometer.

[0010] Further, the present application relates to a motor provided with the rolling bearing. BRIEF DESCRIPTION OF DRAWINGS

[0011] Figure 1 is a schematic view illustrating one example of a configuration of a rolling bearing of the present application.

[0012] Figure 2 is a schematic view illustrating one example of a configuration of a motor of the present application.

[0013] Figure 3 is a conceptual view of a test device used for an electric corrosion test. DETAILED DESCRIPTION

[0014] As described above, in a rolling bearing for a motor or the like, an electric current flows in the bearing to generate an electric spark at a rolling element (ball) and a raceway surface, and damage occurs at these surfaces (electric corrosion). The damage caused by the electric spark is at a level of small spots (pits) on the surfaces at an initial stage, but if it progresses further, it becomes a wave-plate-like unevenness (a pumice-like electric corrosion mark), thereby causing abnormal noise, vibration, and degradation (stop) of the bearing.

[0015] As such measures against electric corrosion, there are two considerations of bearing electrification and bearing insulation, and as the former, for example, an electrically conductive grease can be cited, and as the latter, for example, a ceramic bearing that does not electrify can be cited. However, ceramic bearings have problems such as high cost, and their application is limited.

[0016] The present inventors and others have conducted research on a grease in which an ionic liquid that functions as an electrically conductive imparting agent is incorporated, in order to address the problem of suppression of electric corrosion of a rolling bearing, and as a result, it has been found that other grease compositions in combination with the composition of the ionic liquid: in particular, the combination of the ionic liquid and the base oil is effective in suppressing electric corrosion.

[0017] Further research revealed for the first time that in a grease composition using aromatic ester base oil and an ionic liquid containing borate anions, when the electrostatic capacitance of the grease composition is above a certain value and the loss tangent (tanδ) of the grease composition, determined by dynamic viscoelasticity measurement, is above a certain value, the generation of electro-corrosion in rolling bearings can be suppressed.

[0018] Electrostatic capacitance represents the electrical properties of grease and is therefore considered an indicator of electro-corrosion. However, to date, there have been no reports on the threshold of electrostatic capacitance associated with electro-corrosion.

[0019] Furthermore, the dynamic viscoelasticity of grease is an indicator of its flow characteristics and shape stability. For example, it is an effective parameter for understanding the movement of grease inside a rolling bearing during rotation [the ease with which it adheres to rolling elements (balls), etc. (easy to adhere: churning type, difficult to adhere: channeling type)]. However, to date, there are no reports on research into the dynamic viscoelasticity of grease in conjunction with its composition and electrostatic capacitance, considering the generation and suppression of electro-corrosion.

[0020] As the results of the embodiments described later show, for the suppression of electro-corrosion in rolling bearings, both the composition of the grease (base oil, ionic liquid) and the physical properties of the grease (electrostatic capacitance, dynamic viscoelasticity) are important. This is demonstrated by the fact that even greases with the desired electrostatic capacitance and dynamic viscoelasticity can exhibit electro-corrosion in greases with compositions that do not conform to the specified parameters.

[0021] The present invention will now be described in detail.

[0022] [Rolling bearings] First, the preferred embodiments of the rolling bearing of the present invention will be described in detail below with reference to the accompanying drawings. It should be noted that the present invention is not limited to the following embodiments.

[0023] Figure 1 This is a radial cross-sectional view of a rolling bearing 10 according to a preferred embodiment of the present invention. The rolling bearing 10 has the same basic structure as prior art rolling bearings, including an annular inner ring 11, an outer ring 12, a plurality of rolling elements 13, a retainer 14, and a sealing member 15.

[0024] The inner ring 11 is a cylindrical structure coaxially disposed on the outer periphery of the shaft (not shown in the figure) with the central shaft. The outer ring 12 is a cylindrical structure coaxially disposed on the outer periphery of the inner ring 11. Each of the plurality of rolling elements 13 is a ball disposed in a track within an annular bearing space 16 formed between the inner ring 11 and the outer ring 12. That is, the rolling bearing 10 in this embodiment is a ball bearing.

[0025] A retainer 14 is disposed within the track and holds a plurality of rolling elements 13. The retainer 14 is an annular body coaxially arranged with the central axis of the shaft, and has the following structure: on one side in the direction of the central axis, it has a plurality of pockets for holding the rolling elements 13, and the rolling elements 13 are accommodated in each pocket. The rolling elements 13 are held by the retainer 14 at predetermined intervals in the circumferential direction of the inner ring 11 and the outer ring 12, thereby preventing the rolling elements 13 from falling off and preventing contact between adjacent rolling elements 13. It should be noted that the shape (crown-shaped, wave-shaped, etc.) and material (steel plate or resin, etc.) of the retainer 14 are arbitrary and not limited to a specific shape or material.

[0026] The sealing member 15 is fixed to the inner circumferential surface of the outer ring 12 and extends towards the inner ring 11 to seal the bearing space 16. A grease composition G is sealed within the bearing space 16 sealed by the sealing member 15. That is, the grease composition G is held between the inner ring 11 and the outer ring 12. The grease composition G used is one described later. It should be noted that the amount of grease G sealed into the bearing space 16 can, for example, be set to 5% to 50% of the volume of the bearing space 16.

[0027] The sealing member 15 is formed, for example, of steel plate or rubber, and examples include a steel plate shield that does not contact the outer periphery of the inner ring 11, and a non-contact rubber seal that does not contact the outer periphery of the inner ring 11. In this invention, any sealing member from the steel plate shield or the non-contact rubber seal can be used. It should be noted that this figure shows a solution with the sealing member 15, and the rolling bearing of this invention also includes a solution with a rolling bearing that does not have the sealing member.

[0028] In the rolling bearing 10 with the above structure, the grease composition G functions to reduce friction between the rolling elements 13 and the cage 14, and between the rolling elements 13 and the inner ring 11 and even the outer ring 12. By reducing friction, frictional torque is reduced, and the generation of frictional heat is suppressed, promoting smooth rotation of the inner ring 11 and the outer ring 12. Figure 1 As can be seen from the structure shown, the grease composition G sealed in the rolling bearing 10 lubricates the rolling element 13 and the inner ring 11 and even the outer ring 12 when the rolling bearing 10 rotates.

[0029] The rolling bearings in this invention are, for example, rolling bearings with an outer diameter of less than 10 mm or rolling bearings with an outer diameter of more than 50 mm, and there are no particular limitations on their size or usage conditions.

[0030] The rolling bearing of the present invention can be used as a rolling bearing for motors (e.g., fan motors, cleaner motors) used in automobiles, home appliances, information equipment, etc.

[0031] [motor] As an example Figure 2 The present invention will be described in detail with respect to the embodiments of the motor having the rolling bearing of the present embodiment, but the present invention is not limited to the following embodiments.

[0032] Figure 2 This is a cross-sectional view of a motor in the axial direction according to one embodiment of the present invention. The motor 20 has the same basic structure as motors in the prior art, consisting of a housing 21, a stator 22, a coil 23, a rotor magnet 24, a shaft 25, and a rolling bearing 26 supporting the shaft 25.

[0033] As for motor 20, the current supplied by the power source (not shown above) through the drive circuit flows through the coil 23 wound on the stator 22 to generate magnetic force, thereby causing the rotor magnet 24 to rotate and transmitting the rotation to the external rotating body through the shaft 25.

[0034] [Lubricating Grease Composition] The grease composition used in the rolling bearings of the present invention comprises a base oil containing an aromatic ester base oil, a thickener, and an ionic liquid containing borate anions.

[0035] The grease composition encapsulated in the rolling bearing of the present invention will be described below.

[0036] <Base Oils> In the grease composition sealed in the rolling bearing of this embodiment, an aromatic ester base oil is used as the base oil.

[0037] As an aromatic ester base oil, aromatic esters with ester groups as cyclic substituents can be listed, such as esters of aromatic polycarboxylic acids such as phthalic acid, trimellitic acid, and pyromellitic acid with aliphatic monohydric alcohols having 4 to 16 carbon atoms.

[0038] Specifically, examples include: di(tridecyl) phthalate; trioctyl trimellitate and tri-2-ethylhexyl trimellitate, etc., which are 8-carbon trialkyl esters of trimellitic acid; trinonyl trimellitate, etc., which are 9-carbon trialkyl esters of trimellitic acid; tridecyl trimellitate, etc., which are 10-carbon trialkyl esters of trimellitic acid; trialkyl trimellitate, etc., which are 11-carbon trialkyl esters of trimellitic acid; and trialkyl esters of trimellitic acid with 4 to 16 carbon atoms (the alkyl chains of the three alkyl ester groups in a compound can be the same or different, for example, including the following scheme: "alkyl esters of trimellitic acid with (carbon numbers x, y, z)" is an alkyl ester of trimellitic acid with carbon number x, and a alkyl ester of trimellitic acid with carbon number y). A mixture of alkyl esters and alkyl esters of trimellitic acid with carbon atom z (a mixture of esters in which all three alkyl ester groups are the same in a compound); a mixture of alkyl esters of trimellitic acid with carbon atom x (a mixture of esters in which all three alkyl ester groups are the same in a compound) and alkyl esters of trimellitic acid with carbon atom y and carbon atom z (a mixture of esters in which the three alkyl ester groups are different in a compound); or esters of trimellitic acid with carbon atom x, carbon atom y, and carbon atom z (a mixture of esters in which the three alkyl ester groups are different in a compound), etc.); tetraoctyl pyromellitic acid, tetra-2-ethylhexyl pyromellitic acid; or mixtures of two or more of these, etc., but not limited to these.

[0039] Furthermore, the aromatic ester base oil used in this invention can have a dynamic viscosity at 40°C of, for example, 53 to 130 mm. 2 The range is 55–130 mm / s. 2 The range is / s, and also, for example, in the range of 70–130 mm. 2 The range is / s, or for example, in the range of 70–100 mm. 2 Aromatic ester base oils in the range of / s.

[0040] There are no particular limitations on the aromatic ester base oils with dynamic viscosity within the above-mentioned range. For example, aromatic ester compounds with ester groups as substituents on the ring can be listed above, such as esters of aromatic polycarboxylic acids such as phthalic acid, trimellitic acid, and pyromellitic acid with aliphatic monohydric alcohols having 4 to 16 carbon atoms.

[0041] The base oil described above may be contained in a proportion of 70% by mass or more based on the total mass of the grease composition used in this invention. For example, it may be set to contain the base oil in a proportion of 70% to 98% by mass, 70% to 90% by mass, or 80% to 98% by mass based on the total mass of the grease composition.

[0042] <Thickener> In the grease composition used in this invention, the type of thickener is not particularly limited, but urea-based thickeners are preferred.

[0043] Urea compounds exhibit excellent heat and water resistance, especially good stability at high temperatures, making them a preferred choice for use as thickeners in high-temperature environments.

[0044] Urea compounds such as diurea compounds, triurea compounds, and polyurea compounds can be used as urea thickeners.

[0045] As these urea-based thickeners, conventionally known urea compounds can be used.

[0046] As an example of a diurea compound used as a urea-based thickener, a diurea compound represented by the following formula (1) can be listed.

[0047] Equation (1): R 1 -NHCONH-R 2 -NHCONH-R 3 .

[0048] In the above formula (1), R 1 and R 3 Each can independently represent a monovalent aliphatic hydrocarbon group, a monovalent alicyclic hydrocarbon group, or a monovalent aromatic hydrocarbon group, and R 1 and R 3 At least one of them represents a monovalent aliphatic hydrocarbon group or a monovalent alicyclic hydrocarbon group. For example, it can be set as R. 1 and R 3 One side represents an aliphatic hydrocarbon group, and the other side represents a monovalent alicyclic hydrocarbon group or a monovalent aromatic hydrocarbon group, or it can be set as R. 1 and R 3 One side represents an aliphatic hydrocarbon group, and the other side represents a monovalent aromatic hydrocarbon group.

[0049] In addition, R 2 It represents a divalent aromatic hydrocarbon group.

[0050] It should be noted that the scheme shown in formula (1) can also be a mixture of multiple substances for the diurea compound. As an example, it can be set as R. 1 and R 3 These two groups represent compounds with monovalent aliphatic hydrocarbon groups, R 1 and R 3 These two represent compounds with monovalent aromatic hydrocarbon groups and R. 1 and R 3 A scheme for a mixture of compounds in which one side represents an aliphatic hydrocarbon group and the other side represents a monovalent aromatic hydrocarbon group.

[0051] Examples of monovalent aliphatic hydrocarbon groups include, for example, straight-chain or branched saturated or unsaturated alkyl groups with 6 to 26 carbon atoms.

[0052] Examples of monovalent alicyclic hydrocarbon groups include cycloalkyl groups with 5 to 12 carbon atoms.

[0053] In addition, examples of the aforementioned aromatic hydrocarbon groups include monovalent or divalent aromatic hydrocarbon groups with 6 to 20 carbon atoms.

[0054] Urea compounds used as urea-based thickeners can be synthesized using amine compounds and isocyanate compounds.

[0055] Examples of amine compounds include aliphatic amines such as hexylamine, octylamine, dodecylamine, hexadecylamine, octadecylamine (stearylamine), behenamine, and oleylamine, as well as alicyclic amines such as cyclohexylamine, and aromatic amines such as aniline, p-toluidine, and ethoxyphenylamine. Two or more of these amine compounds can also be used in combination during the synthesis of urea compounds.

[0056] In addition, as isocyanate compounds, aromatic diisocyanates such as phenyl diisocyanate, toluene diisocyanate (TDI), diphenyl diisocyanate, diphenylmethane diisocyanate (MDI), and dimethyl biphenyl diisocyanate (TODI) can be used, as well as aliphatic diisocyanates such as octadecane diisocyanate, decane diisocyanate, and hexane diisocyanate.

[0057] It should be noted that when aromatic diurea compounds obtained by using aromatic monoamines and aromatic diisocyanates as amine raw materials are used as urea-based thickeners, abnormal noises may occur, so further research is needed on their use.

[0058] The aforementioned urea-based thickener (urea compound) can be formulated in a manner that is, for example, 10 to 20% by mass relative to the total amount of the grease composition used in this invention.

[0059] <Ionic Liquids> The grease composition used in the rolling bearings of this embodiment comprises an ionic liquid containing borate anions.

[0060] In the past, for grease compositions and lubricants, in order to release the static electricity generated between parts due to rotational friction, conductivity was imparted as needed, and the addition of ionic liquids was studied as one method.

[0061] In this invention, the use of a specific ionic liquid containing borate anions helps to suppress the generation of electro-corrosion in rolling bearings.

[0062] The above-mentioned ionic liquid is not particularly limited as long as it contains borate anions. As an example, it can be configured to have the following cations and anions: as a cation, at least one cation selected from the group consisting of tetraalkylphosphonium cation represented by formula (A) and tetraalkylammonium cation represented by formula (B) described below; as an anion, at least one anion selected from the group consisting of borate anion represented by formula (C-1), borate anion represented by formula (C-2), and borate anion represented by formula (C-3) described below.

[0063] <cation> The tetraalkylphosphonium cation used in the ionic liquid of the present invention is represented by formula (A). In the above formula (A), R 4 R 5 R 6 and R 7 Each can be independently represented as an alkyl group with 1 to 18 carbon atoms, whether straight or branched.

[0064] Preferably, R 4 R 5 R 6 and R 7 Each can be independently represented as an alkyl group with 4 to 18 carbon atoms, whether straight or branched.

[0065] Examples of alkyl groups having 1 to 18 carbon atoms in formula (A) above include: methyl, ethyl, n-propyl, n-butyl, sec-butyl, tert-butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecanyl, octadecyl, etc.

[0066] R in the above formula (A) 4 R 5 R 6 and R 7 Combinations of, for example, can be listed as: R 4 R is an alkyl group with 11 to 18 carbon atoms in a straight or branched structure. 5 ~R 7 Each is an independent combination of alkyl groups having 4 to 10 carbon atoms in a straight-chain or branched structure; or R 4 R is an alkyl group with 12 to 16 carbon atoms in a straight or branched structure. 5 ~R 7 Each is an independent combination of alkyl groups having 4 to 8 carbon atoms in a straight-chain or branched structure; or, R 4 ~R 7 Combinations of alkyl groups with 6 to 12 carbon atoms, each independently having a straight or branched structure.

[0067] Furthermore, R in the above formula (A) 4 R 5 R 6 and R 7 The total number of carbon atoms can be set to, for example, 32.

[0068] As a tetraalkylphosphonium cation represented by formula (A), R can be listed as an example. 1 It is tetradecyl and R 2 ~R 4 It is a hexyl (tetradecyl)tri(hexyl)phosphonium cation, etc.

[0069] Furthermore, the tetraalkylammonium cation is represented by formula (B). In the above formula (B), R 8 R 9 R 10 and R 11 Each can be independently represented as an alkyl group with 1 to 18 carbon atoms, whether straight or branched.

[0070] Preferably, R 8 R 9 R 10 and R 11 Each can be independently represented as an alkyl group with 5 to 18 carbon atoms, whether straight or branched.

[0071] Examples of alkyl groups having 1 to 18 carbon atoms in formula (B) above include: methyl, ethyl, n-propyl, n-butyl, sec-butyl, tert-butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecanyl, octadecyl, etc.

[0072] R in the above equation (B) 8 R 9 R 10 and R 11 Combinations of, for example, can be listed as: R 8 R is an alkyl group with 1 to 4 carbon atoms, either straight or branched. 9 ~R 11 Each is independently a combination of alkyl groups having 6 to 14 carbon atoms, either straight or branched; in addition, R 8 R is an alkyl group with 11 to 16 carbon atoms, either straight or branched. 9 ~R 11 Each is independently a combination of alkyl groups having 6 to 10 carbon atoms, either straight or branched; or, R 8 ~R 11 Combinations of alkyl groups having 6 to 12 carbon atoms, each independently having a straight or branched structure.

[0073] In the above formula (B), R 8 R 9 R 10 and R 11 The total number of carbon atoms can be set to, for example, 24 to 40.

[0074] As a tetraalkylammonium cation represented by formula (B), examples include: R 8 ~R 11 It is a tetrahexylammonium cation of hexyl, R 8 It is methyl and R 9 ~R 11 It is an octylmethyltris(octyl)ammonium cation, R 8 It is tetradecyl and R 9 ~R 11 It is a hexyl (tetradecyl)tri(hexyl)ammonium cation, R 8 ~R 11 It is an octyl tetraoctylammonium cation, R 8 ~R 11 It is a tetradecyl ammonium cation of decyl, etc.

[0075] <Anions> As an example, the anion used in the ionic liquid of the present invention can be selected from the group consisting of the borate anion shown in formula (C-1), the borate anion shown in formula (C-2), and the borate anion shown in formula (C-3). In the above formula (C-1), R 12 and R 14 Each independently represents an alkyl group with 1 to 22 carbon atoms, either straight or branched, or an aryl group with 6 to 10 carbon atoms; R 13 and R 15 Each can be independently represented by a hydrogen atom, an alkyl group with 1 to 22 carbon atoms (straight or branched), or an aryl group with 6 to 10 carbon atoms.

[0076] As mentioned above, R 12 R 13 R 14 and R 15 Alkyl groups having 1 to 22 carbon atoms, for example, include: methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecanyl, octadecyl, nonadecanyl, eicosyl, dodecyl, dodecyl, etc.

[0077] As mentioned above, R 12 R 13 R 14 and R 15 The aryl groups with 6 to 10 carbon atoms mentioned above include, for example, phenyl and naphthyl.

[0078] R in the above equation (C-1) 12 R 13 R 14 and R 15 Combinations of, for example, can be listed as: R 12 ~R 15 Each is independently a combination of alkyl groups having 1 to 6 carbon atoms in a straight-chain or branched structure, or R 12 ~R 15 Combinations consisting entirely of methyl groups, or R 12 and R 14 Each is independently an alkyl group having 1 to 6 carbon atoms in a straight-chain or branched structure and R 13 and R 15 A combination of hydrogen atoms, or R 12 and R 14 Each is independently an aryl group having 6 to 10 carbon atoms and R 13 and R 15 Combinations of hydrogen atoms, etc.

[0079] The ionic liquid used in this invention may, for example, be a combination of cations and anions shown in (i) to (v) below. The total amount of the above-mentioned ionic liquid relative to the lubricating grease composition used in this invention is, for example, in a manner that is 0.1 to 10% by mass.

[0080] <Other Additives> The grease compositions used in this invention may contain additives commonly used in grease compositions, as needed and to a extent that does not impair the effects of this invention.

[0081] Examples of such additives include: antioxidants, extreme pressure agents (extreme pressure additives), metal passivators, anti-friction agents (wear-resistant agents), rust inhibitors, oiliness improvers, viscosity index improvers, and thickeners.

[0082] When these other additives are included, their addition amount (total amount) is typically 0.1 to 10% by mass relative to the total amount of the grease composition.

[0083] For example, examples of antioxidants mentioned above include: octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, pentaerythritol tetra[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 2,4-bis-(n-octylthio)-6-(4-hydroxy-3,5-di-tert-butylaniline)-1,3,5-triazine, 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene, triethylene glycol-bis[3-(3-tert-butyl-5-methyl-4-hydroxyphenyl)propionate], and 1,6-hexanediol-bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]. Hindered phenolic antioxidants include 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, 2,2-thio-diethylethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], N,N'-hexamethylenebis(3,5-di-tert-butyl-4-hydroxy-hydrogenated cinnamicamide), octyl-3,5-di-tert-butyl-4-hydroxy-hydrogenated cinnamic acid ester, etc.; other phenolic antioxidants include 2,6-di-tert-butyl-4-methylphenol and 4,4-methylenebis(2,6-di-tert-butylphenol), etc.; and amine antioxidants include diphenylamine, alkylated diphenylamine, triphenylamine, hindered amines, phenyl-α-naphthylamine, alkylated phenyl-α-naphthylamine, phenothiazine, alkylated phenothiazine, etc.

[0084] In addition, extreme pressure agents include, for example, phosphorus compounds such as phosphate esters, phosphites, and phosphate ester amine salts; sulfur compounds such as thioethers and dithioethers; chlorine compounds such as chlorinated paraffins and chlorinated biphenyls; and metal salts of sulfur compounds such as zinc dialkyl dithiophosphate and molybdenum dialkyl dithiocarbamate.

[0085] Examples of metal passivating agents include: benzotriazole, 1-[N,N-bis(2-ethylhexyl)aminomethyl]-benzotriazole, 1-[N,N-bis(2-ethylhexyl)aminomethyl]-4-methylbenzotriazole and other benzotriazole compounds; thiadiazole, 2-mercaptothiadiazole, 2,5-bis(alkyldithio)-1,3,4-thiadiazole and other thiadiazole compounds; benzimidazole, 2-mercaptobenzimidazole, 2-(decyldithio)-benzimidazole and other benzimidazole compounds; sodium nitrite, etc.

[0086] In addition, anti-friction agents (wear-resistant agents) include tricresyl phosphate and polymeric esters.

[0087] Examples of the aforementioned polymeric esters include, for example, esters of aliphatic monocarboxylic acids and dicarboxylic acids with polyols. Specific examples of the aforementioned polymeric esters include, but are not limited to, the PRIOLUBE (registered trademark) series manufactured by Croda Japan.

[0088] The grease composition used in this invention can be obtained by combining a thickener, an ionic liquid containing borate anions, and other additives as needed with the above-mentioned aromatic ester base oil.

[0089] In addition, for example, a grease composition can be obtained by combining an ionic liquid containing borate anions with other additives as needed in a urea-based grease (base grease) containing the aromatic ester base oil and the urea thickener.

[0090] Typically, the content of thickener relative to the base grease is about 10 to 30% by mass. For example, the content of diurea compound (urea-based thickener) relative to the above-mentioned urea-based grease can be set to about 10 to 25% by mass, or it can be set to about 10 to 20% by mass.

[0091] <Loss Tangent (tanδ) in the Measurement of Electrostatic Capacitance and Dynamic Viscoelasticity> In addition to the above-described components, the grease composition used in this invention also ensures that the electrostatic capacitance and the loss tangent (tanδ) determined by dynamic viscoelasticity measurement are within an appropriate range, thereby suppressing the generation of electro-corrosion in rolling bearings.

[0092] Specifically, the electrostatic capacitance of the grease composition is 4.6 pF or more under the conditions of an electrode diameter of 10 mm, an electrode spacing of 1 mm, and a frequency of 10 kHz. For example, it can be set to 5.0 pF or more, 5.5 pF or more, or 6.0 pF or more. Furthermore, there is no particular upper limit to the electrostatic capacitance, and it can be set to 4.6 pF or more and 15 pF or less, 4.6 pF or more and 10 pF or less, 4.6 pF or more and 8 pF or less, or 4.6 pF or more and 7 pF or less.

[0093] Furthermore, in the grease composition used in this invention, the loss tangent (tanδ), expressed as the ratio of storage modulus (G') to loss modulus (G") at 25°C (G” / G'), is 0.7 or higher, for example, 0.75 or higher, as measured in the dynamic viscoelasticity determination using a rotational rheometer under conditions of 0.5 mm film thickness, 1% shear strain, and 100 Hz frequency. It should be noted that the upper limit of the loss tangent (tanδ) is not particularly limited; for example, it can be set to 0.7 or higher and 1.5 or lower, or, for example, 0.75 or higher and 1.3 or lower.

[0094] This invention is not limited to the embodiments or specific examples described in this specification, and various changes and modifications can be made within the scope of the technical concept described in the claims.

[0095] Example The present invention will be described in more detail below through embodiments. However, the present invention is not limited thereto.

[0096] The grease compositions of Examples 1 to 16 were prepared using the proportions shown in Table 1 below, and various evaluations were performed in the order described below. In the following description, the example numbers of the grease compositions are also treated as example numbers for the evaluation of each test.

[0097] It should be noted that the detailed information and abbreviations of the components used in the preparation of the lubricating grease composition are as follows.

[0098] <Base Oils> • Aromatic ester oil A: A mixture of trioctyl trimellitate (TOTM) and tetraoctyl pyromellitic acid (TOPM) [Dynamic viscosity at 40°C: 100 mm] 2 / s].

[0099] • Aromatic ester oil B: Alkyl ester of trimellitic acid (9, 10, 11 carbon atoms) [Dynamic viscosity at 40°C: 80 mm] 2 / s].

[0100] • Aromatic ester oil C: Alkyl ester of trimellitic acid with 10 carbon atoms [Dynamic viscosity at 40°C: 55 mm] 2 / s].

[0101] • Aromatic ester oil D: Alkyl ester of trimellitic acid with 10 carbon atoms [Dynamic viscosity at 40°C: 52 mm] 2 / s].

[0102] • Aromatic ester oil E: Alkyl ester of trimellitic acid (8, 9, 10 carbon atoms) [Dynamic viscosity at 40°C: 39 mm] 2 / s].

[0103] • Polyalphaolefin (PAO) oil A [Dynamic viscosity at 40°C: 95 mm] 2 / s].

[0104] • Polyalphaolefin (PAO) oil B [Dynamic viscosity at 40°C: 48 mm] 2 / s].

[0105] <Thickener> • Biuret compound 1: Aliphatic-aromatic biuret compound (a biuret compound obtained by reacting a mixture of aliphatic and aromatic amines with a diisocyanate compound).

[0106] • Biuret compound 2: Alicyclic-aliphatic biuret compound (a biuret compound obtained by reacting a mixture of alicyclic and aliphatic amines with a diisocyanate compound).

[0107] <Additives> • Ionic liquid: An ionic liquid comprising a combination of anions and cations shown in the following formulas (i) to (v), (X), (Y), (Z-1), (Z-2). Other additives: Extreme pressure additive: TPPT (triphenyl thiophosphate), manufactured by BASF Japan Co., Ltd. IRGALUBE TPPT.

[0108] Metal passivating agent: benzotriazole compound BT-LX manufactured by Chengbei Chemical Company.

[0109] Antioxidant: IRGANOX L57, a diarylamine antioxidant manufactured by BASF Japan Co., Ltd.

[0110] Other additives are added in such a manner that the above extreme pressure additives, metal passivators, and antioxidants are added in a total of 3% by mass in each grease composition (total mass: 100% by mass).

[0111] <(1) Evaluation of electro-corrosion> use Figure 3 The device shown in the image underwent an electro-corrosion test.

[0112] Figure 3 The attached diagram shows a schematic diagram of the electro-corrosion accelerated testing device 50, which includes: a test motor 51, a lower housing 52, a support bearing unit 53, a test bearing unit 54 (ball bearing 54a for the test object and ball bearing 54b for the non-test object), a metal shaft 55, a connector 56, a resin connector 57, and a pulse oscillator 58.

[0113] In this apparatus 50, in order to prevent current from flowing through components other than the ball bearing 54a of the test object, the peripheral components of the ball bearing 54a of the test object are made of insulating material (resin material). In addition, a ceramic ball bearing is used in the ball bearing 54b of the non-test object, which is insulated from the ball bearing 54a of the test object.

[0114] A grease composition is sealed into the ball bearing 54a (inner diameter 3mm, outer diameter 8mm, width 3mm) of the test object at 25% to 35% of the bearing volume. The ball bearing 54a is installed in the housing to form the test bearing unit 54. After applying a preload of 20N to the outer ring from the axial direction, a metal shaft 55 is inserted into the inner diameter of the bearing. The metal shaft 55 is connected to the rotating shaft of the test motor 51 via resin connectors 57 and 56, and the ball bearing rotates its inner ring.

[0115] In addition, a low-resistance slip ring (not shown) is brought into contact with the front end of the metal shaft 55, and a pulse transmitter 58 is connected between the slip ring and the outer ring housing of the test bearing unit 54 to apply a voltage of 10V.

[0116] Rotate for 100 hours at a test temperature of 25℃ and a rotation speed of 1000 rpm.

[0117] After 100 hours of rotation, the ball bearing 54a was removed from the housing and disassembled. Visual inspection was conducted to check for electro-corrosion marks on the inner ring, outer ring, and balls. The results are shown in Table 1.

[0118] <Judgment Criteria> A: No electrolytic corrosion marks.

[0119] N: There are traces of electro-corrosion.

[0120] <(2) Evaluation of electrostatic capacitance [pF]> For the determination of electrostatic capacitance, a TOYO Tech SH2-Z type four-terminal sample holder with a protective electrode around the lower electrode was used. Each example of the grease composition was clamped with a thickness of 1 mm using an upper electrode of φ25 mm and a lower electrode of φ10 mm. The electrostatic capacitance of each grease composition was measured at a frequency of 10 kHz, a voltage of 5 V, and room temperature using an impedance meter (NF Corporation, LCR Meter ZW2371).

[0121] The results are shown in Table 1.

[0122] <(3) Dynamic viscoelasticity: evaluation of loss tangent (tanδ)> Frequency dispersion was measured using a stress-controlled rotational viscometer (rheometer, trade name MCR302) manufactured by Anton Paar. The storage modulus (G') and loss modulus (G') of each grease composition were determined, and the loss tangent (tanδ) was calculated. The test sample was clamped between the upper and lower plates of a fixture, and the upper plate was subjected to a certain shear strain (1%). The frequency dependence of the responsiveness was evaluated by gradually changing the frequency. The mechanical relaxation time was evaluated based on the time response of the network structure of the test sample.

[0123] Specifically, under the test conditions of a fixture consisting of parallel plates φ25mm (PP25), a plate gap of 0.5mm, a frequency of 100Hz, and a temperature of 25℃, a grease composition of the test object was clamped between the plates, and the storage modulus (G') and loss modulus (G”) were measured. Based on the obtained storage modulus (G') and loss modulus (G”), the loss tangent tanδ was calculated using the following formula.

[0124] Loss tangent tanδ=G” / G' If the value of the loss tangent tanδ is large, the substance (grease composition) is viscous, which can be said to reflect the action of easily flowing into the lubrication area and forming a sufficient oil film (eddy current). On the other hand, if the value of the loss tangent tanδ is small, the substance (grease composition) is elastic, which can be considered to reflect the action of being discharged from the lubrication area over time (channeling). As shown in Table 1, it was confirmed that the generation of electro-corrosion was suppressed in the rolling bearings encapsulated with the grease compositions of Examples 1 to 7. The grease compositions of Examples 1 to 7 contain a base oil containing an aromatic ester base oil, a thickener, an ionic liquid containing borate anions, an electrostatic capacitance of 4.6 pF or more, and a dynamic viscoelasticity: loss tangent (tanδ) of 0.7 or more.

[0125] On the other hand, even when the same ionic liquid (iii) as in Examples 3 to 5 was used, in the grease compositions of Examples 8 and 9, which used polyalphaolefin oil A or B as base oil, the electrostatic capacitance was less than 4.6 pF, and electro-corrosion was also confirmed.

[0126] The dynamic viscoelasticity of the grease compositions in Examples 10 and 11 showed a loss tangent (tanδ) of 0.7 or higher, but an electrostatic capacitance of less than 4.6 pF, confirming the occurrence of electro-corrosion.

[0127] The grease compositions of Examples 12 and 13, which used ionic liquids (Z-1) or (Z-2) containing anions other than borate anions, had an electrostatic capacitance of 4.6 pF or more. In addition, the dynamic viscoelasticity of Example 13 was 0.7 or more, but electro-corrosion was confirmed in both cases.

[0128] Furthermore, the grease compositions of Examples 14 and 15 had an electrostatic capacitance of 4.6 pF or more, but a dynamic viscoelasticity: loss tangent (tanδ) of less than 0.7, confirming the occurrence of electro-corrosion.

[0129] Furthermore, the electrostatic capacitance of the grease composition of Example 16, which does not contain ionic liquids, is less than 4.6 pF, confirming the occurrence of electro-corrosion.

[0130] The preferred embodiments have been described in detail above, but the present invention is not limited to the above embodiments. Modifications and improvements within the scope of achieving the purpose of the present invention are also included in the present invention.

[0131] Explanation of reference numerals in the attached figures 10: Rolling bearing; 11: Inner ring; 12: Outer ring; 13: Rolling element; 14: Cage; 15: Sealing component; 16: Bearing space; 20: Motor; 21: Housing; 22: Stator; 23: Coil; 24: Rotor magnet; 25: Shaft; 26: Bearing; 50: Accelerated electro-corrosion testing device; 51: Test motor; 52: Lower housing; 53: Support bearing unit; 54: Test bearing unit (54a: Ball bearing of the test object; 54b: Ball bearing of the non-test object); 55: Metal shaft; 56: Connector; 57: Resin connector; 58: Pulse transmitter.

Claims

1. A rolling bearing, wherein, Include: Inner circle; The outer ring is coaxially disposed on the outer periphery of the inner ring; Multiple rolling elements are disposed between the inner ring and the outer ring; A retainer, which holds the rolling element; and A grease composition is retained between the inner and outer rings. The grease composition comprises a base oil containing an aromatic ester base oil, a thickener, and an ionic liquid containing borate anions. The electrostatic capacitance of the grease composition under the conditions of an electrode diameter of 10 mm, an electrode spacing of 1 mm, and a frequency of 10 kHz is 4.6 pF or higher, and In dynamic viscoelasticity measurements using a rotary rheometer, the loss tangent tanδ, expressed as the ratio of storage modulus to loss modulus at 25°C, was greater than 0.7, measured under conditions of 0.5 mm film thickness, 1% shear strain, and 100 Hz frequency.

2. The rolling bearing according to claim 1, wherein, The base oil has a dynamic viscosity of 53–130 mmHg at 40°C. 2 / s of aromatic ester base oil.

3. The rolling bearing according to claim 1, wherein, The thickener is a urea-based thickener, which contains a diurea compound represented by the following general formula (1). Equation (1): R 1 -NHCONH-R 2 -NHCONH-R 3 In equation (1), R 1 and R 3 Each can independently represent a monovalent aliphatic hydrocarbon group, a monovalent alicyclic hydrocarbon group, or a monovalent aromatic hydrocarbon group, and R 1 and R 3 At least one of them represents a monovalent aliphatic hydrocarbon group or a monovalent alicyclic hydrocarbon group. R 2 It represents a divalent aromatic hydrocarbon group.

4. The rolling bearing according to claim 3, wherein, The R 1 and R 3 One side represents a monovalent aliphatic hydrocarbon group, and the other side represents a monovalent aromatic monovalent hydrogen group.

5. The rolling bearing according to claim 1, wherein, The ionic liquid is at least one of the five combinations of anions and cations shown in (i) to (v) below. 。 6. A motor comprising a rolling bearing as claimed in any one of claims 1 to 5.

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