Rolling bearings

Abstract

To provide a rolling bearing which can suppress dust emission while maintaining the rust prevention performance of grease, can maintain the sealing performance of a seal member for a long period of time, and can obtain low dust emission performance.SOLUTION: A rolling bearing 1 has an inner ring 2, an outer ring 3, a plurality of rolling bodies 4 interposed between the inner ring 2 and the outer ring 3, a seal member 6 fixed to the outer ring 3, contacting with the inner ring 2, and sealing a bearing space, and grease 7 sealed into the bearing space. The grease 7 contains base oil, a thickener and an ester rust prevention agent, the ester rust prevention agent is contained by 0.2 to 0.6 pts. mass with respect to 100 pts. mass of a total amount of the base oil and the thickener. The seal member 6 has a rubber part contacting with a slide face of the inner ring 2, and the rubber part is formed of nitrile rubber containing a trimellitic acid ester plasticizer.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a rolling bearing filled with a grease composition, and in particular to a rolling bearing that supports a rotating shaft in a rotary encoder that detects the rotation angle and rotation speed of a servo motor or a rotating shaft, or in other locations where contamination of the surrounding environment is undesirable. [Background technology]

[0002] Bearings used in the rotation support of electrical machines such as electric motors generally have lubricating grease sealed inside and the lubricating grease sealed with a sealing plate such as a rubber seal made of a rubber material vulcanized and bonded to an iron plate or a core metal. For example, bearings installed on the servo mechanism side of a servo motor or bearings supporting the rotating shaft of an optical rotary encoder may be impaired in function due to dust generated from the bearing. Thus, in places where contamination of the surrounding environment is particularly undesirable, there is a demand for improved low-dust generation grease and improved sealing performance of the sealing plate.

[0003] Dust generation occurs when part of the grease evaporates or scatters and is released outside the bearing due to heat generated by the rotation of the rolling bearing and the increase in pressure inside the bearing. Therefore, in order to suppress dust generation from the bearing, it is considered effective to use a grease with low consistency and a base oil with high viscosity and high surface tension.

[0004] Conventionally, various grease compositions aimed at low dust generation have been studied. For example, Patent Document 1 discloses a grease composition having a kinetic viscosity of 30 mm at 40°C. 2 / s~180mm 2 The proposed grease composition comprises a base oil having a viscosity of 100 / s and containing at least one oil selected from synthetic hydrocarbon oils and ether oils, a thickener made of a urea compound, and further containing an additive made of only non-metallic elements in an amount of 0.1 to 1% by weight of the total amount of the grease.

[0005] In addition, the sealing plate is roughly divided into two types according to the positional relationship between the inner lip of the sealing member and the seal groove provided in the inner ring. Specifically, the type in which the inner lip contacts inside the seal groove is called the contact type (see FIG. 2), and the type in which the inner lip forms a labyrinth gap with the inside of the seal groove and is not in contact is called the non-contact type (see FIG. 4). In places where contamination of the surrounding environment is undesirable, a contact type sealing member is generally used in consideration of sealing performance. For example, the technology of Patent Document 2 is known as a technology for reducing torque loss caused by a contact type sealing member while maintaining sealing performance. In the rolling bearing of Patent Document 2, a contact type sealing member and a non-contact type sealing member are used together in the same bearing, and the contact type sealing member is arranged on the side that should not be contaminated. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 11-166191 [Patent Document 2] JP 2006-316858 A Summary of the Invention [Problem to be solved by the invention]

[0007] In recent years, as motors become smaller and more powerful, the environments in which bearings are used are increasingly becoming hotter, and they are increasingly being used in environments that are unfavorable to dust generation. The grease composition described in Patent Document 1 is for rolling devices used in clean rooms such as semiconductor manufacturing facilities, and dust generation at high temperatures has not been considered, which is a concern. In addition, the rubber seal described in Patent Document 2 may deteriorate at high temperatures, and wear may make it difficult to ensure the required sealing performance.

[0008] Here, in addition to the viscosity of the base oil, the selection of additives such as rust inhibitors and antioxidants, which evaporate more easily than the base oil, is also considered to be important for the dust generation of the grease composition. In particular, since the rust inhibitor acts on the base oil to reduce the surface tension, greases containing a large amount of rust inhibitors may increase dust generation. Considering dust generation, it is preferable to not add rust inhibitors, but there is a risk that the rust prevention performance of the grease itself will be significantly reduced.

[0009] On the other hand, high sealing performance is required for the seal material to prevent the evaporated and scattered grease from being released outside the bearing. Contact type seal material is used to improve the sealing performance, but when used in high temperature environments, the plasticizer added to the rubber material evaporates, hardening the rubber and losing its inherent flexibility, reducing the wear resistance and causing wear powder to be generated. As a result, the contact area between the seal material and the inner ring wears out, making it impossible to ensure the required sealing performance, promoting the generation of dust from inside the bearing, and the evaporated plasticizer and wear powder from the seal material may also be a cause of dust generation and contaminating the surrounding area.

[0010] The present invention has been made in consideration of the above circumstances, and has an object to provide a rolling bearing that can suppress dust generation while maintaining the rust-preventing performance of grease, and can maintain the sealing performance of sealing members for a long period of time, thereby achieving low dust generation. [Means for solving the problem]

[0011] The rolling bearing of the present invention has an inner ring, an outer ring, a plurality of rolling elements interposed between the inner ring and the outer ring, a seal member fixed to one of the inner ring and the outer ring and contacting the other member, which is a mating member, to seal the space within the bearing, and a grease composition sealed within the space within the bearing, wherein the grease composition contains a base oil, a thickener, and an ester-based rust inhibitor, the ester-based rust inhibitor being contained in an amount of 0.2 to 0.6 part by mass per 100 parts by mass of the total amount of the base oil and the thickener, and the seal member has a rubber portion that contacts the sliding surface of the mating member, and the rubber portion is formed of nitrile rubber containing a trimellitate ester-based plasticizer.

[0012] The ester-based rust inhibitor is characterized in that it is at least one selected from sorbitan fatty acid esters and succinic acid esters.

[0013] The base oil is at least one selected from synthetic hydrocarbon oils and ether oils.

[0014] The thickener is a mixture of an aliphatic diurea compound and an alicyclic diurea compound, and is characterized in that the content of the aliphatic diurea compound in the thickener is greater than the content of the alicyclic diurea compound.

[0015] The grease composition is characterized in that it does not contain additives that contain sulfur and phosphorus in their molecular structures.

[0016] The rolling bearing is characterized in that it is a bearing for a rotating electrical machine. Effect of the Invention

[0017] The rolling bearing of the present invention contains a base oil, a thickener, and an ester-based rust inhibitor, and the ester-based rust inhibitor is contained in an amount of 0.2 to 0.6 parts by mass relative to 100 parts by mass of the total amount of the base oil and the thickener, so that the amount of dust generation can be suppressed while maintaining the rust-preventive performance of the grease itself. In addition, the ester-based rust inhibitor has a high affinity with the nitrile rubber applied to the rubber part of the seal member, so that the wear of the rubber part can be suppressed. Furthermore, by using a low-volatility trimellitic acid ester-based plasticizer as a plasticizer for the rubber part, the evaporation of the plasticizer itself can be suppressed, and the low dust generation of the bearing can be improved. As a result, dust generation can be suppressed while maintaining the rust-preventive performance of the grease, and the sealing property of the seal member can be maintained for a long period of time, thereby realizing low dust generation. [Brief description of the drawings]

[0018] [Figure 1] 1 is a cross-sectional view of a deep groove ball bearing which is an example of a rolling bearing according to the present invention. [Diagram 2] FIG. 2 is an enlarged cross-sectional view of the rolling bearing of FIG. [Diagram 3] 1 is a schematic diagram of a servomotor to which a rolling bearing according to the present invention is applied; [Figure 4] FIG. 2 is an enlarged cross-sectional view of a non-contact rolling bearing. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] The grease composition filled in the rolling bearing of the present invention contains a base oil, a thickener, and an ester-based rust inhibitor. The base oil can be any oil that is normally used in rolling bearings, without any particular limitations. Examples of the base oil include mineral oils such as paraffinic mineral oil and naphthenic mineral oil, synthetic hydrocarbon oils such as poly-α-olefin oil (PAO oil) and alkylbenzene oil, ester oil, ether oil, silicone oil, and fluorine oil. These base oils may be used alone or in combination of two or more. Among these, the base oil is preferably at least one selected from synthetic hydrocarbon oils and ether oils, and more preferably a mixed oil of synthetic hydrocarbon oils and ether oils.

[0020] As the synthetic hydrocarbon oil, PAO oil is more preferable. PAO oil is a mixture of α-olefins or isomerized α-olefin oligomers or polymers. Specific examples of α-olefins include 1-octene, 1-nonene, 1-decene, 1-dodecene, 1-tridecene, 1-tetradecene, 1-pentadecene, 1-hexadecene, 1-heptadecene, 1-octadecene, 1-nonadecene, 1-eicosene, 1-docosene, and 1-tetradocosene, and mixtures thereof are usually used.

[0021] Examples of the ether oil include polyphenyl ether oil, alkyl diphenyl ether oil, alkyl triphenyl ether oil, and alkyl tetraphenyl ether oil. Among these, alkyl diphenyl ether oil is preferred from the viewpoint of durability at high temperatures. Examples of the alkyl diphenyl ether oil include monoalkyl diphenyl ether oil, dialkyl diphenyl ether oil, and polyalkyl diphenyl ether oil.

[0022] The kinetic viscosity of the base oil (in the case of a mixed oil, the kinetic viscosity of the mixed oil) is 120 mm at 40°C. 2 / s or more is preferable. More preferably, 120 mm 2 / s~160mm 2 / s, and more preferably 125 mm 2 / s~140mm 2 / s.

[0023] The thickener used in the grease of the present invention is not particularly limited, and may be any commonly used thickener in the field of grease. For example, soap-based thickeners such as metal soaps and complex metal soaps, and non-soap-based thickeners such as bentone, silica gel, diurea compounds, triurea compounds, tetraurea compounds, and urea-urethane compounds may be used. Examples of metal soaps include sodium soaps, calcium soaps, and lithium soaps, and examples of complex metal soaps include complex lithium soaps. Among these, it is preferable to use a diurea compound as the thickener.

[0024] Diurea compounds are obtained by reacting a diisocyanate component with a monoamine component. Examples of diisocyanate components include phenylene diisocyanate, tolylene diisocyanate, diphenyl diisocyanate, diphenylmethane diisocyanate (MDI), octadecane diisocyanate, decane diisocyanate, and hexane diisocyanate. Examples of diurea compounds include aliphatic diurea compounds, alicyclic diurea compounds, and aromatic diurea compounds, which are classified according to the type of substituent of the monoamine component used. In the case of aliphatic diurea compounds, aliphatic monoamines (hexylamine, octylamine, dodecylamine, hexadecylamine, octadecylamine, stearylamine, oleylamine, and the like) are used as the monoamine components. In the case of alicyclic diurea compounds, alicyclic monoamines (cyclohexylamine, and the like) are used as the monoamine components. In the case of aromatic diurea compounds, an aromatic monoamine (such as p-toluidine) is used as the monoamine component.

[0025] As the thickener, it is preferable to use a mixture of an aliphatic diurea compound and an alicyclic diurea compound. In particular, from the viewpoint of dust generation, it is more preferable that the content of the aliphatic diurea compound in the thickener is greater than the content of the alicyclic diurea compound, and it is even more preferable that the content of the aliphatic diurea compound relative to the content of the alicyclic diurea compound is 1.5 to 2 times by mass ratio.

[0026] A base grease is obtained by blending a diurea compound as a thickener with a base oil. The base grease using a diurea compound as a thickener is produced by reacting a diisocyanate component with a monoamine component in the base oil. The thickener is preferably contained in an amount of 12 to 15 parts by mass relative to 100 parts by mass of the total amount of the base oil and the thickener.

[0027] The grease composition contains 0.2 to 0.6 parts by mass of an ester-based rust inhibitor per 100 parts by mass of the total amount of the base oil and the thickener. Examples of the ester-based rust inhibitor include partial esters of polyhydric alcohols such as sorbitan, sorbitol, pentaerythritol, sucrose, and glycerin with carboxylic acids such as oleic acid and lauric acid, and succinic acid half esters. These ester-based rust inhibitors may be used alone or in combination of two or more kinds.

[0028] The ester-based rust inhibitor has a high affinity with the nitrile rubber used in the rubber part of the sealing member described below, and therefore can suppress wear of the rubber part. Specifically, it is thought that the nitrile rubber absorbs the volatilized ester-based rust inhibitor and functions as a plasticizer, thereby maintaining the wear resistance of the rubber part.

[0029] Among the above ester-based rust inhibitors, it is preferable to use at least one selected from sorbitan fatty acid esters and succinic acid half esters. Examples of sorbitan fatty acid esters include sorbitan monolaurate, sorbitan monostearate, sorbitan monooleate, and sorbitan trioleate. Examples of succinic acid half esters include alkyl succinic acid half esters and alkenyl succinic acid half esters.

[0030] The grease composition may further contain an antioxidant. Examples of the antioxidant that can be used include amine-based antioxidants, phenol-based antioxidants, and sulfur-based antioxidants. Among these, it is preferable to use amine-based antioxidants, such as phenyl-1-naphthylamine, diphenyl-p-phenylenediamine, dipyridylamine, phenothiazine, N,N'-diisopropyl-p-phenylenediamine, N-phenyl-N'-isopropyl-p-phenylenediamine, and dialkyldiphenylamine (DDPA).

[0031] In addition, other additives can be added to the grease composition as necessary. For example, an organic acid metal salt can be added. The organic acid metal salt is a salt of an aliphatic compound or aromatic compound having a substituent such as an organic carboxylic acid, an organic sulfonic acid such as an alkylbenzenesulfonic acid, an organic sulfuric acid such as an alkylsulfuric acid, an organic phosphonic acid such as an alkylphosphonic acid, or an organic phosphinic acid such as an alkylphosphinic acid, and a metal ion. The organic acid metal salt preferably has a melting point of more than 20°C, and preferably 100°C or higher. By adding the organic acid metal salt, it is expected that the organic acid metal salt will melt without affecting the surface tension of the base oil, and will protect the steel surface as an extreme pressure agent when the supply of the base oil is insufficient and wear is a concern.

[0032] Specific examples of organic acid metal salts include sodium salts and calcium salts of organic carboxylic acids having 2 to 18 carbon atoms, such as acetic acid, propionic acid, butyric acid, hexanoic acid, lauric acid, myristic acid, palmitic acid, stearic acid, 12-hydroxystearic acid, oleic acid, and linoleic acid. More specifically, it is particularly preferable to use sodium acetate (melting point 324°C), calcium acetate (melting point 160°C), sodium stearate (melting point 220°C), calcium stearate (melting point 179°C), and the like. The amount of the organic acid metal salt to be blended is preferably 0.5 to 5 parts by mass, more preferably 0.5 to 3 parts by mass, and even more preferably 1 to 3 parts by mass, relative to 100 parts by mass of the total amount of the base oil and the thickener.

[0033] In addition, it is preferable that the grease composition used in the present invention does not contain additives containing phosphorus atoms or sulfur atoms in the molecular structure. As shown in the examples described later, the inclusion of these additives results in a decrease in the surface tension of the base oil, which may result in an increase in the amount of dust generation. Examples of such additives include extreme pressure agents such as phosphate esters such as tricresyl phosphate, phosphite esters such as tricresyl phosphite, thiophosphates, thiophosphites, zinc alkyldithiophosphates (ZnDTP), molybdenum alkyldithiophosphates (MoDTP), and zinc dithiocarbamate (ZnDTC).

[0034] Considering dust generation, it is effective to make the worked penetration (JIS K 2220) of the grease composition as low as possible. In other words, it is effective to increase the thickener and reduce the base oil, but if the thickener is increased too much, it will affect the rotation torque and lubrication performance of the bearing, so an appropriate amount is necessary. From this perspective, it is preferable that the worked penetration of the grease is in the range of 200 to 240.

[0035] A rolling bearing filled with the above-mentioned grease composition will be described with reference to FIG. 1. FIG. 1 is a cross-sectional view of a deep groove ball bearing. In the rolling bearing 1, an inner ring 2 having an inner ring raceway surface 2a on its outer circumferential surface and an outer ring 3 having an outer ring raceway surface 3a on its inner circumferential surface are concentrically arranged, and a plurality of rolling elements 4 are arranged between the inner ring raceway surface 2a and the outer ring raceway surface 3a. The rolling elements 4 are held by a cage 5. In addition, openings 8a, 8b at both axial ends of the inner and outer rings are sealed by a seal member 6, and the above-mentioned grease composition 7 is filled at least around the rolling elements 4. The inner ring 2, the outer ring 3 and the rolling elements 4 are made of an iron-based metallic material, and the grease composition 7 is interposed between the raceway surface and the rolling elements 4 to lubricate them.

[0036] In the rolling bearing 1, the iron-based metallic material constituting the bearing components such as the inner ring 2, the outer ring 3, the rolling elements 4, and the cage 5 is any material commonly used as a bearing material, such as high carbon chromium bearing steel (SUJ1, SUJ2, SUJ3, SUJ4, SUJ5, etc.; JIS G 4805), carburized steel (SCr420, SCM420, etc.; JIS G 4053), stainless steel (SUS440C, etc.; JIS G 4303), high speed steel (M50, etc.), cold rolled steel, etc.

[0037] The seal member of the rolling bearing of FIG. 1 will be described with reference to FIG. 2. As shown in FIG. 2, the seal member 6 is composed of a disk-shaped core 10 formed by pressing a cold-rolled steel plate (such as SPCC of the JIS standard) and a rubber portion 9 vulcanized and bonded integrally to the core 10. The rubber portion 9 has a main lip portion 9a formed by bifurcating the tip at the end portion on the inner ring 2 side, and a dust lip portion 9b located on the outer side of the bearing than the main lip portion 9a. The seal member 6 is fitted into a seal groove on the inner circumference of the end portion of the outer ring 3 via the rubber portion 9, and the rubber portion 9 is directly slidably contacted with a seal groove having a substantially U-shaped cross section formed on the outer circumference of the end portion of the inner ring 2. In this way, the seal member 6 is a contact-type seal member. Note that in the rolling bearing, the seal member may be fitted into a seal groove on the outer circumference of the end portion of the inner ring, and the rubber portion may be directly slidably contacted with a seal groove formed on the inner circumference of the end portion of the outer ring.

[0038] In the present invention, the rubber portion 9 of the seal member 6 is formed of nitrile rubber containing a trimellitate ester plasticizer. The trimellitate ester plasticizer is represented by the following formula (1). [ka] In formula (1), R 1 , R 2 , R 3 may be the same or different. Preferably, they are the same. In addition, R 1 , R 2 , R 3 is preferably an aliphatic monohydric alcohol residue having 7 to 9 carbon atoms. This aliphatic monohydric alcohol residue may be a linear alkyl group or a branched alkyl group. Specific examples include tri-n-octyl trimellitate and tri-2-ethylhexyl trimellitate. As the trimellitic acid ester plasticizer, Rheolub LTM, Rheolub TM10 (manufactured by FMC), etc. can be used. The rubber portion 9 may contain other known plasticizers in addition to the trimellitic acid ester plasticizer as a plasticizer, but it is preferable that the trimellitic acid ester plasticizer is the main component (50 mass% or more), and it is more preferable that the trimellitic acid ester plasticizer is the only component.

[0039] In addition to the above-mentioned plasticizer, the rubber portion 9 may also contain various known additives, such as flame retardants, lubricants, stabilizers, fillers, foaming agents, antioxidants, processing aids, neutralizing agents, UV absorbers, pigments, antistatic agents, dispersants, thickeners, metal deterioration inhibitors, anti-mold agents, and flow adjusters, as necessary.

[0040] 1 and 2 show ball bearings as examples of bearings, but the rolling bearing of the present invention can also be used as a cylindrical roller bearing, tapered roller bearing, spherical roller bearing, needle roller bearing, thrust cylindrical roller bearing, thrust tapered roller bearing, thrust needle roller bearing, thrust spherical roller bearing, etc. Furthermore, the sealing member is not limited to the composite of a metal plate and a rubber molded body as shown in Figures 1 and 2, but may be a rubber molded body alone, or a composite of a rubber molded body and a plastic plate or a ceramic plate.

[0041] The configuration in which the rolling bearing of the present invention is applied to a servo motor will be described with reference to Fig. 3. As shown in Fig. 3, servo motor 11 has rotor 12, stator 13, shaft 14, and encoder 15 on the anti-load side of shaft 14 for reading the angle of rotor 12. Shaft 14 is supported by rolling bearing 16 arranged on the load side, and rolling bearing 1 of the present invention arranged on the anti-load side. Although rolling bearing 1 of the present invention is arranged in the vicinity of encoder 15, the amount of dust generated from the bearing is suppressed, so that a decrease in the detection accuracy by encoder 15 can be prevented.

[0042] The rolling bearing of the present invention can be used not only in servomotors but also in other rotating electrical machines that require low dust generation, such as generators and electric motors other than servomotors, such as spindle motors, stepping motors, and fan motors. EXAMPLES

[0043] Grease compositions were prepared according to the compositions shown in Tables 1 and 2. In Tables 1 and 2, the contents of base oil, thickener, and additives are shown as the content (mass%) relative to the base grease (base oil + thickener). The grease compositions of Examples 1 to 6 in Table 1 contain only an ester-based rust inhibitor as an additive. Also, 1) to 6) and a) to e) below in Table 1 are the same in Table 2.

[0044] <Dust generation test> Each grease composition was filled into a deep groove ball bearing 6900 (inner diameter 10 mm × outer diameter 22 mm × width 6 mm) equipped with a contact type seal member to prepare a test bearing. The rubber part of the seal member in Examples 1 to 6 and Comparative Examples 5 to 11 contained a trimellitic acid ester plasticizer (Reolube LTM, manufactured by FMC, kinetic viscosity at 40°C 53 mm 2 The rubber parts of the seal members of Comparative Examples 1 to 4 were made of NBR containing a phthalate ester plasticizer (di-2-ethylhexyl phthalate). The obtained test bearings were subjected to a 6000 min test at an ambient temperature of 120°C. -1 The inner ring was rotated for 200 hours. Glass plates were placed on both axial ends of the test bearing, and the grease composition that had scattered from the bearing was attached to them. The amount of dust generated was determined by subtracting the weight of the glass plate before the test from the weight of the glass plate after the test. The amount of dust generated is evaluated in Tables 1 and 2 with a ◎ mark for 0.6 mg or less, a ○ mark for between 0.6 mg and 1 mg, a △ mark for between 1 mg and 2 mg, and an × mark for more than 2 mg.

[0045] <Rust test> The test conditions were more severe than those for rusting, in accordance with the rusting test method specified in ASTM D 1743. Approximately 2.0 g of each grease composition was packed into the raceway of a tapered roller bearing 30204 that had been degreased with an organic solvent and dried in advance, and then the bearing was run-in for 1 minute at 1,800 revolutions per minute with an axial load of approximately 98 N. Next, the bearing was immersed in 1 wt. % salt water, placed in a sealed high-humidity container that reached the saturated water vapor pressure at 40°C, and left at 40°C for 48 hours, after which the rusting state was checked. The rusting state was determined by dividing the outer race into 32 equal parts in the circumferential direction, counting the number of sections with rust, and calculating the probability of rusting (percentage %). The evaluation of the probability of rusting is shown in Tables 1 and 2 with ◎ for 30% or less, ○ for more than 30% and less than 60%, △ for more than 60% and less than 90%, and × for more than 90%.

[0046] <Wear evaluation of seal materials> The appearance of the rubber part (seal lip) of the seal member after the dust generation test was observed with the naked eye. The wear evaluation is shown in Tables 1 and 2 with a circle indicating no wear, a triangle indicating slight wear, and an x ​​indicating severe wear.

[0047] [Table 1]

[0048] [Table 2]

[0049] Regarding the evaluation of the amount of dust generated in Tables 1 and 2, the amount of dust generated in Examples 2 to 4 and Comparative Example 10 was 0.2 mg or less, and thus the results were superior in terms of dust generation to the other test examples marked with ◎ (Examples 1 and 5).

[0050] As shown in Tables 1 and 2, Examples 1 to 6, which combined a grease composition containing a specified amount of an ester-based rust inhibitor with a sealing member having a rubber portion formed of nitrile rubber containing a trimellitic acid ester-based plasticizer, showed good results in all tests.

[0051] Comparing each Example with Comparative Example 3 and Comparative Example 6, it was found that sulfonates such as Ba sulfonate have lower rust-preventive performance than ester-based rust-preventive agents. In addition, the amount of ester-based rust-preventive agent added must be 0.2 parts by mass or more per 100 parts by mass of the total amount of base oil and thickener in order to maintain the rust-preventive performance of the grease (Comparative Examples 1, 5, 10 to 11), but when it is 0.7 parts by mass or more, the amount of dust generation increases (Comparative Examples 4, 7 to 9).

[0052] In addition, when a trimellitic acid ester-based plasticizer was used as the plasticizer for the rubber part, the wear of the rubber part was significantly improved and the amount of dust generation tended to decrease compared to when a phthalic acid ester-based plasticizer was used (Comparative Examples 1 to 4). Compared to phthalic acid ester-based plasticizers, trimellitic acid ester-based plasticizers have lower volatility (higher boiling point), and as a result, it is considered that the evaporation of the plasticizer itself is suppressed, the deterioration of the rubber part is suppressed, and the amount of dust generation is reduced. In addition, by using a trimellitic acid ester-based plasticizer and adding 0.2 parts by mass or more of an ester-based rust inhibitor to the grease composition, the wear of the rubber part was further improved (Comparative Examples 5, 10 to 11). From this, it was found that the ester-based rust inhibitor not only imparts rust prevention performance but also contributes to improving the wear resistance of the rubber part.

[0053] As for the thickener of the grease composition, when the thickener is a mixture of an aliphatic diurea compound and an alicyclic diurea compound, the dust generation tendency tends to improve as the content of the aliphatic diurea compound is higher than the content of the alicyclic diurea compound (Comparative Examples 10 to 11). Furthermore, as for the aliphatic diurea compound, the dust generation tendency tends to improve when the aliphatic amine is stearylamine rather than octylamine (Examples 1 to 6).

[0054] In addition, a surface tension test was conducted separately in accordance with JIS K2241, and the kinetic viscosity at 40°C was 47 mm 2 The surface tension of the PAO oil alone at 1.0 g / s was 29.8 mN / m, whereas the surface tension of the test oil to which 2 mass% of ZnDTP had been added to the PAO oil was 26 mN / m. Therefore, when considering low dust generation, it can be said that it is preferable for the grease composition to not contain additives that contain phosphorus or sulfur atoms in their molecular structures.

[0055] As described above, the rolling bearings of Examples 1 to 6 can enhance the low dust generation performance of the bearings while maintaining their rust prevention performance by combining a grease composition containing an appropriate amount of a specific ester-based rust inhibitor, such as a sorbitan fatty acid ester, with a sealing member containing a trimellitic acid ester-based plasticizer, in addition to using a base oil with low penetration, high viscosity and high surface tension, which is effective for the low dust generation of the grease. [Industrial Applicability]

[0056] The grease composition of the present invention suppresses dust generation while maintaining the rust-preventing performance of the grease, and can maintain the sealing performance of sealing members for a long period of time, thereby achieving low dust generation. Therefore, the grease composition of the present invention can be particularly suitably used for rolling bearings used in locations where contamination of the surrounding environment is undesirable, such as bearings arranged on the servo mechanism side of a servo motor and bearings supporting the rotating shaft of an optical rotary encoder. [Explanation of symbols]

[0057] 1. Rolling bearings 2. Inner Circle 3 Outer ring 4 Rolling elements 5 Cage 6 Sealing material 7 Grease 8a, 8b opening 9 Rubber part 10 Core wire 11 Servo motor 12 Rotor 13 Stator 14 Shaft 15 Encoders 16 Rolling bearings

Claims

1. A rolling bearing comprising an inner ring, an outer ring, a plurality of rolling elements interposed between the inner ring and the outer ring, a seal member fixed to one of the inner ring and the outer ring and contacting the other member, that is a mating member, for sealing a space within the bearing, and a grease composition sealed within the space within the bearing, The grease composition includes a base oil, a thickener, and an ester-based rust inhibitor, and the ester-based rust inhibitor is included in an amount of 0.2 parts by mass to 0.6 parts by mass per 100 parts by mass of the total amount of the base oil and the thickener, The base oil has a kinematic viscosity at 40°C of 120 mm2 / s or more; The rolling bearing according to claim 1, wherein the sealing member has a rubber portion that contacts the sliding surface of the counter member, the rubber portion being formed from a nitrile rubber containing a trimellitic acid ester-based plasticizer.

2. 2. The rolling bearing according to claim 1, wherein the ester-based rust inhibitor is at least one selected from the group consisting of sorbitan fatty acid esters and succinic acid esters.

3. 3. The rolling bearing according to claim 1, characterized in that the thickener is a mixture of an aliphatic diurea compound and an alicyclic diurea compound, and the content of the aliphatic diurea compound in the thickener is greater than the content of the alicyclic diurea compound.

4. 4. The rolling bearing according to claim 1, wherein the rolling bearing is a bearing for a rotating electrical machine.

5. The base oil is at least one selected from synthetic hydrocarbon oils and ether oils, 5. The rolling bearing according to claim 1, wherein the grease composition does not contain any additive that contains sulfur and phosphorus in its molecular structure.

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