LUBRICANT COMPOSITION AND USE OF THE LUBRICANT COMPOSITION IN A ROLLING BEARING

Abstract

Lubricating grease composition, which includes: an ester base oil in an amount of 78 to 88% by mass based on the total amount of the lubricating grease composition; and a thickening agent in an amount of 10 to 17% by mass based on the total amount of the lubricating grease composition, wherein the thickening agent contains diurea, expressed by the following formula (1): R 1 -NHCONH-C6H4-CH2-C6H4-NHCONH-R 2 (1) in which R 1 and R 2 Each independently represent one of the following: (A) a cyclohexyl group A; (B) an octyl group B; and (C) an octadecyl group C, and where the diurea, based on R 1 and R 2overall, is such that the cyclohexyl group A occupies 5 to 35 mol% of it, the octyl group B occupies 50 mol% or more of it, and the octadecyl group C serves as the remainder, occupying 5 to 45 mol% of it.

Description

TECHNICAL AREA

[0001] The present invention relates to a lubricating grease composition and a use of the lubricating grease composition in a rolling bearing. STATE OF THE ART

[0002] In recent years, the demands placed on three-phase motors have increased with regard to higher efficiency, maintenance-free operation, and compliance with energy-saving regulations. Therefore, there is a need for a rolling bearing used in a motor to ensure both low torque characteristics and a long service life.

[0003] For example, JP 2010 - 65 171 A proposes a lubricating grease composition for use in a bearing for an engine. This lubricating grease composition contains a base oil comprising a perfluoropolyether oil, a thickener comprising polytetrafluoroethylene, and silica as inorganic fine particles.

[0004] EP 3 885 425 A1 relates to a lubricating grease composition and a tapered roller bearing in which this lubricating grease composition is used.

[0005] WO 2019 / 083 022 A1 and DE 11 2018 004 265 T5 each relate to a lubricating grease composition suitable for use in rolling bearings and the like. SUMMARY OF THE INVENTIONAL TASK OF THE INVENTION

[0006] A grease composition described in the prior art for use in an engine bearing does not exhibit satisfactory low-torque behavior when enclosed in a rolling bearing. Improvements are needed to achieve low-torque behavior.

[0007] To reduce the torque in a rolling bearing containing the grease, it is considered advantageous to use a grease containing diurea as a thickener with a short-chain aliphatic amine as one of the amine components. However, if such a diurea-containing grease is used in a relatively large rolling bearing, the grease (especially its base oil) can leak out of the bearing due to high shear or centrifugal forces acting upon it. Such oil leakage can lead to a reduction in the bearing's service life.

[0008] Therefore, there is a need for a grease composition that achieves both low torque behavior and resistance to grease leakage, and for the use of the grease composition in a rolling bearing. SOLUTION TO THE TASK

[0009] As a result of serious studies to meet the aforementioned requirement, the present inventors found that a lubricating grease composition containing a mixture of a variety of diuretic variants with predetermined structures as a thickening agent can achieve low torque characteristics and resistance to grease leakage. The present inventors have thus completed the present invention.

[0010] A lubricating grease composition of the present invention comprises: an ester base oil in an amount of 78 to 88% by mass based on the total amount of the lubricating grease composition; and a thickening agent in an amount of 10 to 17% by mass based on the total amount of the lubricating grease composition, wherein the thickening agent contains diurea, expressed by the following formula (1), R 1 -NHCONH-C6H4-CH2-C6H4-NHCONH-R 2 (1) where R 1 and R 2 Each independently represent one of the following: (A) a cyclohexyl group A; (B) an octyl group B; and (C) an octadecyl group C, wherein the diurea, with respect to R 1 and R 2 overall, is such that the cyclohexyl group A occupies 5 to 35 mol% of it, the octyl group B occupies 50 mol% or more of it, and the octadecyl group C serves as the remainder, occupying 5 to 45 mol% of it.

[0011] The lubricating grease composition according to the present invention comprises an ester oil as a base oil and a thickening agent, wherein the thickening agent contains diurea expressed by the aforementioned formula (1). The diurea comprises a plurality of diurea variants having predetermined chemical structures.

[0012] In particular, the thickening agent comprises a mixture of the following diuretics (U1) to (U6) in a predetermined ratio: (U1) Diurea comprising the aforementioned alicyclic group A at each of the opposite ends. (U2) Diurea comprising the aforementioned alicyclic group A at one of the opposite ends and the aforementioned alkyl group B at the other end. (U3) Diurea comprising the aforementioned alicyclic group A at one of the opposite ends and the aforementioned alkyl group C at the other end. (U4) Diurea comprising the aforementioned alkyl group B at each of the opposite ends. (U5) Diurea comprising the aforementioned alkyl group B at one of the opposite ends and the aforementioned alkyl group C at the other end. (U6) Diurea comprising the aforementioned alkyl group C at each of the opposite ends.

[0013] The thickening agent in the lubricating grease composition according to the present invention contains the aforementioned diuretics. When the lubricating grease composition is used as a lubricant for a rolling bearing, it is possible to achieve both low torque characteristics and resistance to grease leakage.

[0014] This reason is assumed to be as follows.

[0015] The aforementioned lubricating grease composition comprises diurea as part of the thickening agent, in which one or each of the terminal functional groups (R) 1 and R 2 ) represents the alkyl group B (with 8 carbon atoms), which has a comparatively short chain. Due to the content of such ureas, a low torque characteristic can be ensured.

[0016] On the other hand, in the case where the diurea forming a component of the thickening agent contains the diurea (U4 mentioned above) in which both terminal functional groups (R 1 and R 2 ) the alkyl group B, the low torque behavior is excellent, however the structure of the diurea is so uniform that the thickening agent forms a long fiber structure.

[0017] If the thickening agent has a long fibrous structure, the contact area between the thickening agent and the base oil decreases, thus reducing the force with which the thickening agent can retain the base oil. Therefore, the lubricating grease (base oil) trapped in a rolling bearing tends to leak out of the bearing.

[0018] In contrast, as in the lubricating grease composition according to the present invention, when using a thickening agent in which a plurality of variants of diureas with different structures with respect to the terminal functional groups (R) are used 1 and R 2 When the components are mixed, the fibers of the thickening agent do not clump together, and the proportion of short fibers in the thickening agent increases. Particularly when using the thickening agent with the composition according to the present invention, the structure of the thickening agent can be micronized. When the structure of the thickening agent is micronized, the contact area between the thickening agent and the base oil increases, thereby improving the force with which the thickening agent can retain the base oil. In this way, the lubricating grease (base oil) trapped in a rolling bearing can be prevented from easily escaping the rolling bearing.

[0019] For the above reason, it is assumed that the lubricating grease composition according to the present invention can achieve both the low torque behavior and the resistance to grease leakage.

[0020] Preferably, the aforementioned grease composition further contains 1 to 10% by mass of an additive, based on the total quantity of the grease composition. In this case, it is possible to further improve the performance of the grease composition while simultaneously ensuring low torque characteristics and resistance to grease leakage.

[0021] According to the invention, the lubricating grease composition according to the present invention is used in a rolling bearing. ADVANTAGES OF INFINDING

[0022] A lubricating grease composition according to the present invention can achieve both low torque behavior and resistance to grease leakage when the lubricating grease composition is enclosed in a rolling bearing.

[0023] When the lubricating grease composition is used in a rolling bearing, the lubricating grease composition contained within it hardly leaks out, so that lubrication can be ensured for a long time and a low torque can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 shows a sectional view of a ball bearing according to an embodiment of the present invention. Fig. Figure 2 is a diagram showing the evaluation results for the bearing torque for each grease produced according to the examples and comparison examples. Fig.Figure 3 is a diagram showing the results of the evaluated oil leakage quantity for each lubricating grease produced according to the examples and the comparison examples. DESCRIPTION OF EXECUTION FORMS

[0024] One embodiment of the present invention is described below with reference to the drawings.

[0025] A rolling bearing according to the present embodiment is a ball bearing in which a lubricating grease is enclosed, which contains a lubricating grease composition according to an embodiment of the present invention.

[0026] Fig. Figure 1 shows a sectional view of a ball bearing according to an embodiment of the present invention.

[0027] A ball bearing 1 comprises an inner ring 2, an outer ring 3 mounted radially outside the inner ring 2, a plurality of balls 4 positioned between the inner ring 2 and the outer ring 3 to serve as rolling elements 4, and a cage 5, which has an annular shape and retains the balls 4. Furthermore, annular shielding plates 6 are provided axially on one and the other side of the ball bearing 1.

[0028] Furthermore, the lubricating grease G, which contains the lubricating grease composition according to the embodiment of the present invention, is enclosed in an annular region 7, which is surrounded by the inner ring 2, the outer ring 3 and the two shielding plates 6.

[0029] An inner raceway surface 21 is formed on the outer circumference of the inner ring 2, on which the balls 4 roll.

[0030] An outer raceway surface 31 is formed on the inner circumference of the outer ring 3, on which the balls 4 roll.

[0031] The majority of the balls 4 are brought between the inner raceway surface 21 and the outer raceway surface 31, so that they roll on the inner raceway surface 21 and the outer raceway surface 31.

[0032] The lubricating grease G enclosed in area 7 is also applied at the points where the balls 4 contact the inner raceway surface 21 of the inner ring 2 and at the points where the balls 4 contact the outer raceway surface 31 of the outer ring 3. The lubricating grease G is otherwise enclosed such that it occupies 20 to 40% by volume of the space bounded by the inner ring 2, the outer ring 3, and the two shielding plates 6, excluding the balls 4 and the cage 5 from this space.

[0033] Each shielding plate 6 is an annular element made of galvanized steel sheet coated with lithium silicate. The shielding plate 6 is attached to the outer ring 3 such that an outer circumferential portion (radially outer part) of the shielding plate 6 is attached to the inner circumferential surface of the outer ring 3. Conversely, an inner circumferential portion (radially inner part) of the shielding plate 6 faces the outer circumferential surface of the inner ring 2, maintaining a small gap between them. The inner circumferential surface forms a labyrinth seal. The shielding plate 6 prevents the enclosed lubricating grease G from escaping to the outside.

[0034] The lubricating grease with a lubricating grease composition according to the embodiment of the present invention, which will be described later, is enclosed as lubricating grease G in the ball bearing 1 thus designed. It is therefore possible to guarantee the low torque of the bearing over a long period of time without any grease leakage (oil leakage).

[0035] The following section describes in detail the composition of the lubricating grease G.

[0036] The lubricating grease composition forming the lubricating grease G is a lubricating grease composition according to the embodiment of the present invention, which contains at least a base oil and a thickening agent.

[0037] One of the technical characteristics of the aforementioned lubricating grease composition is that it contains a specific amount of a particular thickening agent. This technical characteristic makes it possible to achieve the excellent effect described above.

[0038] The aforementioned base oil in the aforementioned lubricating grease composition is an ester oil.

[0039] The lubricating grease G, whose base oil is an ester oil, can be easily adsorbed onto a metal surface due to the high polarity of the ester oil. This allows an oil film to form easily. Another advantage is, for example, that the lubricating grease G can suppress the evaporation of the base oil without increasing its viscosity.

[0040] Examples of ester oils include diester oils such as dibutyl sebacate, dioctyl sebacate, di-2-ethylhexyl sebacate or bis(2-ethylhexyl) sebacate, dioctyl adipate, diisodecyl adipate or bis(8-methylnonyl) adipate, ditridecyl adipate, ditridecyl phthalate, and methyl acetylcinoleate; aromatic ester oils such as trioctyl trimellitate or trioctyl-1,2,4-benzene tricarboxylate, tridecyl trimellitate or tris(decyl)-1,2,4-benzene tricarboxylate, and tetraoctyl pyromellitate or tetraoctyl-1,2,4,5-benzene tetracarboxylate; Polyolester oils such as trimethylolpropane caprylate or 2,2-bis(hydroxymethyl)butyl octanoate, trimethylolpropane pelargonate, pentaerythritol 2-ethylhexanoate, and pentaerythritol pelargonate; carbonate oil; complex ester oil, which is an oligoester of polyhydroxy alcohol and mixed fatty acid, including dibasic and monobasic acid; etc.

[0041] Each of these ester oils can be used alone, or two or more types of them can be used together.

[0042] The kinematic viscosity of the base oil at 40°C is preferably 20 to 30 mm². 2 / s.

[0043] Furthermore, the kinematic viscosity of the base oil at 100°C is preferably 2 to 7 mm. 2 / s.

[0044] When the grease composition containing the base oil with this kinematic viscosity of the base oil is enclosed in the rolling bearing, the grease composition does not so easily cause oil leakage and is suitable for achieving a low torque.

[0045] The kinematic viscosity corresponds to a value according to JIS K 2283 (2000).

[0046] The base oil content is 78 to 88% by mass, based on the total volume of the grease composition. If the base oil content is less than 78% by mass, the thickener content increases relatively to harden the grease more than necessary. Therefore, maintaining low-torque performance can prove difficult. Conversely, if the base oil content exceeds 88% by mass, the proportion of base oil in the grease composition increases, making oil leakage more likely when the grease is contained within the rolling bearing.

[0047] The lubricating grease composition contains diurea, expressed by the following formula (1), as a thickening agent. R 1 -NHCONH-C6H4-CH2-C6H4-NHCONH-R 2 (1) in the formula R 1 and R 2Each independently represents one of (A) a cyclohexyl group A, (B) an octyl group B and (C) an octadecyl group C.

[0048] The thickening agent comprises a variety of diurea variants, expressed by the formula (1) described above.

[0049] In this case, the diurea, based on R 1 and R 2 overall, is such that the cyclohexyl group A occupies 5 to 35 mol% of it, the octyl group B occupies 50 mol% or more of it, and the octadecyl group C serves as the remainder and occupies 5 to 45 mol% of it.

[0050] The thickening agent, which has this configuration, possesses a low fibrous structure. The grease composition containing the thickening agent is suitable for achieving low torque characteristics and resistance to grease leakage.

[0051] In the thickening agent, the alkyl group B is 50 mol% or more, based on R. 1 and R 2 Overall, the low-torque behavior of the grease composition is further improved in this case.

[0052] In the diurea expressed by formula (1), the functional group “-C6H4-CH2-C6H4-” between the two urea bonds preferably comprises two phenylene groups bonded in the para position.

[0053] The diurea contained in the lubricating grease composition is a reactant between a diisocyanate compound and a mixture of a variety of amine compounds (hereinafter also referred to as an amine mixture).

[0054] Examples of the diisocyanate compound include 4,4'-diphenylmethane diisocyanate (4,4'-MDI), 2,4'-diphenylmethane diisocyanate (2,4'-MDI), and 2,2'-diphenylmethane diisocyanate (2,2'-MDI).

[0055] The amine mixture is a mixture of (a) cyclohexylamine, (b) an aliphatic amine with 8 carbon atoms, and (c) an aliphatic amine with 18 carbon atoms. The content of component (a) in the amine mixture is 5 to 35 mol%, the content of component (b) is 50 mol% or more, and the remainder is component (c) at 5 to 45 mol%.

[0056] The aliphatic amine (b) with 8 carbon atoms is preferably 1-aminooctane.

[0057] The aliphatic amine (c) with 18 carbon atoms is preferably 1-aminooctadecane.

[0058] To obtain the aforementioned diurea, the diisocyanate compound and the amine mixture can be reacted under various conditions. The diisocyanate compound and the amine mixture are preferably reacted in the base oil to obtain diurea with high homogeneous dispersibility as a thickening agent.

[0059] Furthermore, the reaction between the diisocyanate compound and the amine mixture can be carried out by adding the base oil in which the diisocyanate compound is dissolved to the base oil in which the amine mixture is dissolved, or by adding the base oil in which the amine mixture is dissolved to the base oil in which the diisocyanate compound is dissolved.

[0060] The temperature and time for the reaction between the amine mixture and the diisocyanate compound are not particularly limited, but can be the same as the conditions commonly used to obtain a diurea that forms a lubricating grease composition.

[0061] With regard to the solubility and volatility of the diisocyanate compound and the amine compounds contained in the amine mixture, the reaction temperature is preferably between 60°C and 170°C.

[0062] The reaction time is preferably 0.5 to 2.0 hours to complete the reaction between the diisocyanate compound and the amine compounds contained in the amine mixture and to shorten the production time for efficient manufacture of the lubricating grease.

[0063] The thickening agent content is 10 to 17% by mass, based on the total amount of the lubricating grease composition.

[0064] If the thickener content is less than 10% by mass, its ability to retain the base oil is low. In this case, the amount of base oil released during the rotation of the rolling bearing increases, leading to oil leakage from the bearing. Conversely, if the thickener content exceeds 17% by mass, the rotation of the rolling bearing can cause relative movement between the inner ring, the outer ring, the balls, and the cage. This increases the rotational resistance caused by the shearing of the lubricating grease and consequently the torque of the rolling bearing.

[0065] The lubricating grease composition may contain additives as optional components.

[0066] Examples of additives include an antioxidant, a high-pressure agent, an oil-based agent, a rust inhibitor, an anti-wear agent, a dye, a color stabilizer, an adhesion promoter, a structural stabilizer, a metal deactivator, a viscosity index improver, and a detergent.

[0067] The additive content is preferably 1 to 10% by mass, based on the total amount of the lubricating grease composition.

[0068] Preferably, the lubricating grease composition contains at least the antioxidant as an additive. The antioxidant contained in the lubricating grease composition can improve the lubrication service life of the grease G.

[0069] The aforementioned antioxidant can be any antioxidant known from the prior art, such as an amine-based or phenol-based antioxidant.

[0070] The lubricating grease composition can be produced using a method known from the prior art.

[0071] As described above, the lubricating grease composition can be prepared, for example, by mixing the base oil in which the diisocyanate compound is dissolved and the base oil in which the amine compounds are dissolved to allow the diisocyanate compound to react with the amine compound, and optional additives are added during the reaction or at a desired time after the reaction.

[0072] According to the embodiment, a composition containing a predetermined thickening agent is used as the lubricating grease composition that forms the lubricating grease G enclosed in the ball bearing 1. Therefore, in the ball bearing 1, as described above, the enclosed lubricating grease G is prevented from easily leaking out, thus ensuring lubrication for a long time and enabling low torque operation.

[0073] The present invention is not limited to the embodiment mentioned above, but can also be implemented by another embodiment.

[0074] The rolling bearing according to the embodiment is not limited to the ball bearing in which the lubricating grease comprising the lubricating grease composition according to the embodiment of the present invention is included. The rolling bearing can be a different rolling bearing, such as a rolling bearing in which rolling elements other than balls are used, as long as the lubricating grease comprising the lubricating grease composition according to the embodiment of the present invention is included therein. EXAMPLE

[0075] The present invention will now be described in more detail using examples. However, the present invention is not limited to these examples. (Examples 1 to 6 and comparative examples 1 to 9)

[0076] A variety of grease compositions were created, and each of these compositions was evaluated. The components of the grease compositions are listed in Table 1, and the evaluation results are presented in Table 1 and the following. Fig. 2 and Fig. 3 shown. (Raw materials of the lubricating grease composition) (1) Base oil Base oil A: Ester oil Polyol ester (kinematic viscosity (40°C) = 25 mm 2 / s, kinematic viscosity (100°C) =4.9 mm 2 / s) Base oil B: Mixed oil of poly-α-olefin and ester oil. Poly-α-olefin (kinematic viscosity (40°C) = 30 mm²). 2 / s, kinematic viscosity (100°C) =5.9 mm 2 / s) Ester oil (kinematic viscosity (40°C) = 30 mm 2 / s, kinematic viscosity (100°C) =5.4 mm 2 / s) Mixing ratio (based on weight): Poly-α-olefin / Ester oil = 80 / 20 (2) Thickening agent: Diurea (reactant between diisocyanate and (Amine compounds) (2-1) Diisocyanate4,4'-Diphenylmethane diisocyanate (4,4'-MDI) (2-2) Amine compounds (a) cyclohexylamine (b) 1-Aminooctane (c) 1-Aminooctadecan (3) Additive: amine-based antioxidant, phenol-based antioxidant (Preparation of the lubricating grease)

[0077] Lubricating greases containing the components listed in Table 1 were prepared as lubricating greases for the examples and comparison examples by the following steps. (1) 4,4'-MDI, cyclohexylamine, 1-aminooctane and 1-aminooctadecane were adjusted so that the sum of cyclohexylamine, 1-aminooctane and 1-aminooctadecane reached 100 mol% based on 50 mol% of 4,4'-MDI. (2) Half the quantity of the base oil, the content of which is 84% ​​by mass of the total quantity of the grease composition, and the quantity of 4,4'-MDI, with which the content of the thickening agent after the reaction is 14% by mass of the total quantity of the grease composition, are placed in a stainless steel vessel A and heated to 60 °C in order to dissolve. (3) Half the quantity of the base oil, the content of which is 84 wt% based on the total quantity of the grease composition, and the quantity of cyclohexylamine, 1-aminooctane and 1-aminooctadecane, with which the content of the thickening agent after the reaction is 14 wt% based on the total quantity of the grease composition, are placed in another stainless steel vessel B and heated to 80 °C in order to dissolve. (4) The solution of the amine mixture in stainless steel vessel B is released into stainless steel vessel A so that it enters the isocyanate solution. (5) After it has been confirmed that the entire quantity of the amine mixture solution has been transferred from stainless steel vessel B to stainless steel vessel A, the solution in stainless steel vessel A is heated to 150 °C. (6) The solution in the stainless steel vessel A is heated while stirring and kept at a temperature of 150 °C for 30 minutes. (7) The heating is stopped, and the quantity of the amine-based antioxidant and the phenol-based antioxidant, each containing 1% by mass of the total quantity of the grease composition, is added while stirring and the mixture is cooled. (8) Following this, a homogenization treatment is carried out using a three-roll mill.

[0078] Each lubricating grease was produced using steps (1) to (8). (Assessment of the lubricating grease)

[0079] Each grease composition according to the examples and comparison examples was evaluated with respect to (1) the bearing torque and (2) the amount of oil leakage. The results are shown in Table 1. Fig. 2 and Fig. 3 shown. [Table 1] Examples Comparative examples 1 2 3 4 5 6 1 2 3 4 5 6 7 8 9 Base oil Art Base oil A (ester oil) Base oil B Content relative to the total amount of the lubricating grease composition 84% by mass Thickener Art R 1 -NHCONH-C6H4-CH2-C6H4-NHCONH-R 2 (NH and CH2 were in first and fourth place relative to C6H4) -NHCONH-C6H4-CH2-C6H4-NHCONH- (mol-%) (NH and CH2 are in first and fourth place relative to C6H4)* 50 R 1 +R 2 * (a) Cyclohexyl group (mol-%) 10 10 20 30 30 10 0 10 10 20 30 10 30 100 10 (b) Octyl group (mol-%) 60 70 60 60 50 50 100 40 30 20 0 90 70 0 90 (c) Octadecyl group (mol-%) 30 20 20 10 20 40 0 50 60 60 70 0 0 0 0 Content relative to the total amount of the lubricating grease composition 14% by mass Additive Type (content based on the total amount of the lubricating grease composition) Amine-based antioxidant (1 wt%), phenol-based antioxidant (1 wt%) Evaluation Bearing torque (mN·m) 7.3 8.8 9.0 8.6 8.7 10.3 6.8 14.3 17.7 15.6 18.4 12.9 16.4 19.1 28.2 Amount of oil spilled (%) 3.3 3.9 3.1 4.5 5.7 5.8 19.5 6.0 8.0 4.2 5.9 9.9 15.6 - - Mol-% of each functional group when R1 and R2 together constitute 100 mol-%

[0080] The evaluations shown in Table 1 were each carried out according to the following evaluation methods. (1) Torque of the bearing

[0081] The bearing torque of each grease produced in the examples and comparison examples was measured using a torque testing device under the following conditions according to Table 2.

[0082] In this test, 0.83 g of each of the greases produced in the examples and comparison examples were enclosed in 62022RU (with non-contact seals on both sides), which was a test bearing. In this application, the amount of enclosed grease reached 40% by volume, based on the volume of a space bounded by an inner ring, an outer ring, and the seals, excluding the balls and a cage.

[0083] The test bearings (two) prepared in this way were inserted into the test device and initially rotated for 60 seconds at 1,800 rpm. -1 The test bearings were then brought to a standstill for 60 seconds and subsequently rotated for 1,800 seconds at 1,800 rpm. -1 The average torque value for the last 60 seconds was defined as the bearing torque. The results are shown in Table 1 and Fig.2 shown (the results of comparison examples 8 and 9 are only given in Table 1).

[0084] Fig. Figure 2 shows the evaluation results for the bearing torque for each of the lubricating greases produced in the examples and comparison examples. The diagram of Fig. 2, in which the ordinate represents the torque of the bearing and the abscissa represents the total molar percentage of the octyl and cyclohexyl groups, each molar percentage of the cyclohexyl groups is shown.

[0085] The torque given as a result is, incidentally, a torque that corresponds to two test bearings.

[0086] Furthermore, in this evaluation, the low torque behavior can be considered good if the torque corresponding to the two test bearings is 14 mN:m or less. [Table 2] Conditions Test bearing (model number) 62022RU Amount of grease included 0.83 g Axial load 77 N Surface pressure (calculated) 0.93 GPa Rotational speed 1,800 min -1 Temperature of the atmosphere 25 °C (room temperature) Length of time 1,800 s (pre-rotation 60 s) measurement Torque (average value of the last 60 s) (2) Quantity of spilled oil

[0087] The amount of oil discharged was measured using a radial grease test rig under the conditions listed in Table 3.

[0088] In this test, 8.2 g of each of the greases produced in the examples and comparative examples were enclosed in 6309ZZ (with shielding plates on both sides), which was a test bearing. In this application, the amount of enclosed grease reached 20% by volume, based on the volume of a space bounded by an inner ring, an outer ring, and the shielding plates, excluding the balls and a cage.

[0089] The two test bearings prepared in this way were inserted into the test device, heated and kept at an outer ring temperature of 150 °C, and rotated for 15 hours at 6,000 min -1 .

[0090] The weight of the test bearings was measured before and after the test on the grease test rig, and the ratio of the weight reduction after the test <([bearing weight before test - bearing weight after test] (g) / [enclosed grease quantity (8.2 g)]) × 100 (%)> was calculated to determine the amount of oil that had leaked out. The results are shown in Table 1 and Fig. 3 shown.

[0091] Fig. Figure 3 is a diagram showing the results of the evaluated oil leakage quantity for each lubricating grease produced in the examples and comparison examples. In the diagram of Fig. 3, in which the ordinate represents the amount of oil leakage and the abscissa represents the total mol percentage of octyl groups and cyclohexyl groups, each mol % of the cyclohexyl groups is plotted.

[0092] In this evaluation, resistance to oil leakage can be rated as good if the amount of oil leakage is 9% or less. [Table 3] Conditions Test bearing (model number) 6309ZZ Amount of grease included 8.2 g Radial loading 0.925 kN Axial load 0.151 kN Rotational speed 6,000 min -1 Outer ring temperature 150 °C Length of time 15 h measurement Oil leakage rate (change in bearing weight)

[0093] As shown in Table 1 and Fig. 2 and Fig. As shown in Figure 3, a low torque characteristic and resistance to grease leakage can be achieved through the lubricating grease composition according to the embodiment of the present invention.

[0094] 1: Ball bearing, 2: Inner ring, 3: Outer ring, 4: Ball, 5: Cage, 6: Shielding plate, 7: Area, G: Grease

Claims

[1] Grease composition comprising: an ester base oil in an amount of 78 to 88% by mass based on the total amount of the lubricating grease composition; and a thickening agent in an amount of 10 to 17% by mass based on the total amount of the lubricating grease composition, wherein the thickening agent contains diurea, expressed by the following formula (1): R 1 -NHCONH-C6H4-CH2-C6H4-NHCONH-R 2 (1) in which R 1 and R 2 Each independently represent one of the following: (A) a cyclohexyl group A; (B) an octyl group B; and (C) an octadecyl group C, and where the diurea, based on R 1 and R 2overall, is such that the cyclohexyl group A occupies 5 to 35 mol% of it, the octyl group B occupies 50 mol% or more of it, and the octadecyl group C serves as the remainder, occupying 5 to 45 mol% of it. [2] Lubricating grease composition according to claim 1, further comprising an additive in an amount of 1 to 10% by mass based on the total amount of the lubricating grease composition. [3] Use of the grease composition according to claim 1 or 2 in a rolling bearing.

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