JP2001003074A - Grease to be filled into ball-and-roller bearing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a grease improved in cleanness and quietness by compounding a synthetic oil mixture comprising a synthetic ester oil and a synthetic poly-α-olefin oil in a specified ratio with a thickener mixture comprising a higher fatty acid sodium salt and a higher fatty acid lithium salt, an antioxidant, and an additive to reduce the boundary lubrication state. SOLUTION: An ester oil is mixed with a synthetic poly-α-olefin oil having a pour point of -40 deg.C or lower, a flash point of 200 deg.C or higher, a viscosity index of 100 or higher, and a viscosity (40 deg.C) of 40-300 cSt in a wt. ratio of (5:2)-(1:4). The resultant synthetic oil mixtuer is compounded with 15-35 wt.% thickener mixture prepared by mixing a higher fatty acid sodium salt and a higher fatty acid lithium salt in a wt. ratio of (2:5)-(5:2), 0.3-8.0 wt.% antioxidant prepared by mixing an aminic antioxidant and a phenolic antioxidant in a wt. ratio of (3:10)-(10:3), and 0.5-7.0 wt.% additive to reduce the boundary lubrication state.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rolling bearing, and more particularly to a hard disk drive (hereinafter referred to as an HDD).
Roller bearing sealing grease suitable for use in electronic equipment such as a video tape recorder (hereinafter abbreviated as VTR) and a laser beam printer (hereinafter abbreviated as LBP).

[0002]

2. Description of the Related Art Rolling bearings used in the above-mentioned electronic equipment and the like are, for example, so-called miniatures in which a steel inner ring, an outer ring, a rolling element (ball), a synthetic resin or a steel crown holder are combined. It uses a deep groove type ball bearing and encapsulates grease as a lubricant.

Here, as a sealing device for preventing dust and lubricating oil from scattering outside the bearing, there are a non-contact type sealing device and a contact type sealing device. The former has a narrow gap between the shaft and the bearing, and this gap is filled with grease.
It is superior to the latter in quietness during rotation and simplicity of the structure. In recent years, demands for electronic devices such as HDDs, VTRs, and LBPs have become increasingly sophisticated, and there has been a demand for higher precision and smaller sizes. There is a need for quietness and cleanliness. This is because, in electronic equipment such as HDDs, VTRs and LBPs, if fine oil particles such as grease for enclosing bearings or contaminant particles such as dusts enter the used atmosphere, head damage or reading may occur in HDDs or VTRs. This is because problems such as occurrence of an error / write error and a decrease in the reflectance of the optical reflection surface in LBP are likely to occur.

[0004] To cope with this problem, the amount of grease enclosed is reduced, but in some cases, problems such as insufficient lubrication and reduced lubrication durability arise. In order to mechanically avoid such a situation, there is known a method of attaching a magnetic fluid sealing device instead of or together with a non-contact type sealing device for a bearing. In this magnetic fluid seal, a magnet member is fixed to opposing end faces of a holding member of a bearing rolling element, and a magnetic fluid is gathered between the end faces to improve sealing performance.

[0005] By the way, as a conventional grease for encapsulating rolling bearings, a metal soap having a salt of lithium, calcium and sodium is used as a base oil of mineral oil and ester synthetic oil having relatively low viscosity. An agent having a general composition as an agent was used.

[0006]

In recent years, HDDs, VTs
Demands for electronic equipment such as R and LBP have become increasingly sophisticated, and higher accuracy and smaller size have been demanded. Along with this, the use conditions such as high-speed rotation and use in high-temperature environments have become severe for miniature-type rolling bearings used in electronic equipment such as HDDs, VTRs, and LBPs. There is a demand for longer life and longer life. Further, in order to reduce the production cost, it is required that a rolling bearing not using a magnetic fluid sealing system also satisfy quietness and cleanliness.

As described above, miniature type rolling bearings used in electronic equipment such as HDDs, VTRs, and LBPs are required to operate at higher speeds and to cope with high-temperature environments in the future. No grease for bearing encapsulation was satisfactory in terms of grease oxidation stability and lubrication life. If the grease is oxidized and deteriorated, properties such as dropping point, shear stability, consistency, oil release characteristics, and the like change greatly, and grease leaks from the bearing or the life of the bearing is extremely reduced. Furthermore, if the base oil, which plays a major role in lubrication, is oxidized and deteriorated, deterioration phenomena such as an increase in the amount of base oil evaporated, a decrease in base oil components, formation of sludge, and an increase in viscosity occur. Lubrication is lost. Further, in some cases, corrosion of the bearing is caused by organic acids and the like generated by oxidative deterioration of the base oil. Therefore, it is important to suppress the oxidative deterioration of the grease in order to improve the oxidation stability and the life of the grease.

By the way, as described above, HDD, VT
Since miniature type rolling bearings used for electronic equipment such as R and LBP will be used in higher speed and higher temperature environments in the future, "dragging phenomenon" of grease by rolling elements (balls) tends to occur. Due to the `` dragging phenomenon '' of grease, the grease between the rolling element and the bearing ring is easily cut off, and the rolling element and the bearing ring are in direct contact between the rolling element and the metal of the bearing ring without the lubricating film of the grease, that is, , And a boundary lubrication state may occur. When direct contact between the rolling element and the metal of the raceway occurs (boundary lubrication state), the raceway surface of the rolling element and the raceway becomes extremely worn, damaged and easily roughened.
This leads to an increase in vibration and noise, greatly deteriorating the acoustic characteristics, and significantly shortening the life of the bearing, which is extremely harmful and problematic for electronic equipment.

Conventionally used mineral oil-metal soap based grease, ester synthetic oil-metal soap based grease, etc., cause deterioration of grease characteristics and life problem at high temperature and high speed rotation, and deterioration of grease performance at low temperature. In addition, there were problems such as dust generation. As ester-based synthetic oils conventionally generally used as grease base oils, there are diesters and polyol esters. These ester-based synthetic oils are excellent in fluidity and heat resistance at a low temperature, and have excellent characteristics that a change in viscosity with a change in temperature is small. However, the ester-based synthetic oil having excellent low-temperature performance has a drawback that the amount of evaporation at a high temperature is large.
For this reason, many attempts have been made to add various antioxidants to the ester-based synthetic oil in order to improve the performance at high temperatures. However, nonetheless, it has not been possible to sufficiently improve the characteristics at high temperatures and extend the life.

[0010] Further, the use of only an ester-based synthetic oil as a base oil has a disadvantage that it is difficult to form an oil film on a rotating body or a bearing member because the affinity for a metal is insufficient. For this reason, especially at the time of starting or stopping, there is a problem that an oil film is easily contacted between the rotating body and the bearing member, a boundary lubrication state is apt to occur, and lubrication is apt to be insufficient. Accordingly, the present invention provides a grease for enclosing a rolling bearing, which realizes the anti-oxidation stability and long life of the grease, further improves the lubricity between the rolling elements and the races, and improves the initial lubrication. In addition to excellent performance, it suppresses the generation of vibration and noise to improve the acoustic performance of the bearing, and also improves the performance at low temperatures, and extends the life of the rolling bearing in high-speed rotation and high-temperature environments.
Further, the present invention provides a grease for sealing a rolling bearing for the purpose of reducing dust generation and the like.

At the same time, unless a conventional grease is provided with a magnetic fluid seal that is complicated in structure, fine grease particles and other contaminant particles such as dust generated from the grease during rotation of the bearing cause a clean atmosphere. To solve the problem of not being able to maintain quietness, a grease for sealing rolling bearings that satisfies the above cleanliness and quietness has been adopted for rolling bearings equipped with a non-contact type sealing device that does not use a magnetic fluid sealing method. It is intended to provide.

[0012]

In order to achieve the above object, the present invention provides a mixed oil comprising a mixture of an ester-based synthetic oil and a poly-α-olefin-based synthetic oil in a specific ratio, as a base oil, A mixed thickener in which a sodium salt and a higher fatty acid lithium salt were mixed at a specific ratio was used, and a specific antioxidant and an additive for reducing boundary lubrication were blended as essential components.

The poly-α-olefin synthetic oil has a pour point of −40 ° C. or less, a flash point of 200 ° C. or more, a viscosity index of 100 or more, and a viscosity at 40 ° C. of 40 to 300 cSt. Further, the mixing ratio of the mixed synthetic oil of the ester-based synthetic oil and the poly-α-olefin-based synthetic oil is represented by weight ratio,
Ester type: poly-α-olefin type = 5: 2 to 1: 4.

Further, the mixed thickener of the higher fatty acid sodium salt and the higher fatty acid lithium salt was blended in an amount of 15 to 35% by weight based on the total amount of the grease composition. The mixing ratio of the mixing thickener is expressed in terms of weight ratio as sodium salt:
Lithium salt system: 2: 5 to 5: 2. The specific antioxidant is a mixed antioxidant of an amine-based antioxidant and a phenol-based antioxidant, and is included in an amount of 0.3 to 8.0% by weight based on the total amount of the grease components. . Also, the mixing ratio of this mixed antioxidant is expressed by weight ratio,
Amine: phenol = 3: 10 to 10: 3.

Further, the additive for reducing the specific boundary lubrication state is added in an amount of 0.1% based on the total amount of the grease composition components.
5 to 7.0% by weight was blended. As described above, when a mixed synthetic oil in which an ester-based synthetic oil and a poly-α-olefin-based synthetic oil are blended in a specific ratio is used as a base oil, a grease base oil having both high-temperature performance and low-temperature performance is obtained. Can be
In particular, it is preferable that the mixing ratio of the ester-based synthetic oil and the poly-α-olefin-based synthetic oil is 5: 2 to 1: 4 in terms of a weight ratio. More preferably, ester type: poly-α-olefin type = 2: 1 to 1
A range of 1: 3 is good.

Further, by employing a mixed thickener in which a higher fatty acid sodium salt and a higher fatty acid lithium salt are blended in a specific ratio, the rolling having both the smooth rotation of the rolling bearing and the low dust generation performance is provided. A grease for bearing encapsulation is obtained. In particular, the mixing ratio of the mixed thickener is preferably in the range of 15 to 35% by weight based on the total amount of the grease composition. Further, it is preferable that the mixing ratio of the higher fatty acid sodium salt and the higher fatty acid lithium salt is in a weight ratio of sodium salt: lithium salt = 2: 5 to 5: 2.

Further, by employing a mixed antioxidant in which an amine antioxidant and a phenolic antioxidant are mixed in a specific ratio, the antioxidant effect of grease is improved,
The acoustic characteristics in high-speed rotation and high-temperature environments can be improved. In particular, the mixing ratio of the amine-based antioxidant and the phenol-based antioxidant is preferably amine: phenol-based = 3: 10 to 10: 3 by weight. It should be noted that only one of the amine-based antioxidant and the phenol-based antioxidant cannot provide an excellent improvement in the acoustic effect in high-speed rotation and high-temperature environments as compared with the mixed antioxidant.

Further, an additive for reducing a specific boundary lubrication state is used in an amount of 0.5 w
By adding in the range of t% to 7.0 wt%,
"Grease drag phenomenon" occurs when used in high-speed rotation and high-temperature environments, and instantaneous excellent reduction is achieved when the rolling element and the metal of the bearing ring come into direct contact with each other, that is, in the case of boundary lubrication. It is possible to form a film exhibiting a frictional action. The formation of this coating can prevent direct contact between the rolling element and the metal of the bearing ring, so that friction and wear in the boundary lubrication state can be reduced to the utmost and the generation of wear fine powder can be suppressed.

The grease for rolling bearing encapsulation, which contains the above-mentioned specific mixed synthetic base oil, mixed thickener, mixed antioxidant, and additive for reducing the boundary lubrication state as essential components, has antioxidant and stable properties. It has excellent lubricity and lubrication life, and has improved lubrication between the rolling elements and the bearing rings, has excellent initial lubrication, and suppresses the generation of vibration and noise to improve the acoustic performance of the bearing. Furthermore, it is possible to have both low-temperature performance and high-temperature performance, and the life of the bearing in high-speed rotation and high-temperature environments is improved. In addition, it has made it possible to reduce dust generation.

At the same time, unless the conventional grease is provided with a magnetic fluid seal having a complicated structure, fine grease and other contaminant particles, such as dust, generated from the grease during rotation of the bearing cause a clean atmosphere. Solving the problem that quietness cannot be maintained, even for rolling bearings equipped with a non-contact type sealing device that does not use a magnetic fluid sealing method,
The above cleanliness and quietness can be satisfied.

The grease for enclosing a rolling bearing of the present invention may contain an oily agent, a viscosity index improver, a rust inhibitor,
Various additives such as a solid lubricant can be added.

[0022]

Embodiments of the present invention will be described below. FIG. 3 is an explanatory diagram of various lubricating states in the relationship between the pressure of the fluid lubricant and friction. Generally, the lubricant such as grease is applied to two divided sliding surfaces of a solid that move relative to each other, as shown in FIG. 3 (a fluid lubrication region, a quasi-fluid lubrication region, a boundary lubrication region). ). In the fluid lubrication region, the lubrication mode is such that the thickness of the lubricant such as grease between the friction surfaces is much larger than the surface roughness of the friction surfaces, and the friction surfaces are completely separated by the lubricant film. In this case, the viscosity of a lubricant such as grease is greatly related to lubrication. The quasi-fluid lubrication region is a lubrication mode that takes into account that the sliding surface of two relatively moving solids under load is deformed by a large load. In addition to the viscosity of lubricant such as grease, The elastic modulus of the sliding surface is relevant. In this case, the thickness of the lubricant such as grease existing between the two solid sliding surfaces is slightly thicker than the surface roughness of the friction surface. In the boundary lubrication region, since the thickness of the lubricant such as grease interposed between the friction surfaces is smaller than the surface roughness of the friction surfaces, the protrusions of the friction surfaces of the two solid sliding surfaces come into direct contact with each other. In the lubrication mode with the largest friction coefficient. Most of the load is supported by the direct contact portions (true contact surfaces) between the convex portions of the narrow friction surface. In this direct contact portion (true contact surface), large friction is generated and adhesion and deformation occur, and cannot be explained only by the viscosity of the lubricant like fluid lubrication, and the state of the two solid surfaces is deeply related. This is a complicated lubrication mode.

Here, it is generally known that in grease lubrication, the oil film thickness formed on the bearing lubrication surface is smaller than in oil lubrication. Therefore, under the conditions of high speed rotation and high temperature environment for miniature type rolling bearings, which will become more and more demanding in the future, the lubrication surface of the rolling bearings may cause the `` grease drag phenomenon '' and the like. The boundary lubrication state where the metals are in direct contact with each other is likely to occur, and wear and friction are more likely to occur.

The use of the grease for encapsulating rolling bearings, in which the specific mixed synthetic base oil, the mixed thickener, the mixed antioxidant, and the additive for reducing the boundary lubrication state of the present invention are blended as essential components. Direct contact between rolling element and raceway metal due to "grease drag phenomenon", which tends to occur when used in high-speed rotation and high-temperature environments.
That is, friction and wear in the boundary lubrication state can be reduced to the utmost, and the generation of wear fine powder can be suppressed. As a result, the lubricity between the rolling elements and the races is greatly improved,
In addition to being excellent in initial lubricity, the generation of vibration and noise is suppressed, and the acoustic performance and lubrication life of the bearing are improved.

[0025]

The present invention will be described below in detail with reference to examples and comparative examples. FIG. 1 is a sectional view of a rolling bearing (a deep groove ball bearing). As shown in FIG. 1, the rolling bearing includes an inner ring 3, an outer ring 1, a spherical rolling element 2, and a cage 4.
And grease as a lubricant not shown.

The inner race 3, the outer race 1, and the rolling elements 2 are formed of a metal material. Examples of the metal material include high carbon chromium bearing steel such as JIS SUJ2. If corrosion resistance is required, use JIS
A metal material obtained by subjecting a martensitic stainless steel such as SUS440C or the like and a precipitation hardening stainless steel such as JIS SUS630 to a suitable hardening heat treatment is preferable. In light load applications, for example, JIS SU
Austenitic stainless steel such as S304 can be used.

The retainer 4 is made of a synthetic resin material in addition to mild steel such as SPCC material. As a synthetic resin material,
In addition to a general polyamide resin (nylon 66), a thermoplastic resin having heat resistance, for example, a fluorine-based resin such as polytetrafluoroethylene (PRFE) or ethylenetetrafluoroethylene (ETFE), or a polyetheretherketone ( Engineering plastics such as PEEK), polyphenylene sulfide (PPS), polyether sulfone (PES), and nylon 46 can also be used. As the type of the retainer, a waveform, a crown shape, or the like is used.

The grease for enclosing a rolling bearing of the present invention comprises:
A mixed synthetic oil in which an ester-based synthetic oil and a poly-α-olefin-based synthetic oil are mixed in a specific ratio is used as a base oil, and a mixed thickener in which a higher fatty acid sodium salt and a higher fatty acid lithium salt are mixed in a specific ratio is used. Further, a grease containing a specific antioxidant and an additive for reducing boundary lubrication as essential components.

As the base oil of the grease for enclosing the rolling bearing of the present invention, ester-based synthetic oil and poly-α are used in consideration of lubricating performance while having both high-temperature performance and low-temperature performance.
A mixed synthetic oil in which olefin-based synthetic oil is blended at a specific ratio is adopted as the base oil. The poly-α-olefin synthetic oil preferably has a pour point of −40 ° C. or less, a flash point of 200 ° C. or more, a viscosity index of 100 or more, and a viscosity at 40 ° C. of 40 to 300 cSt.

When the pour point is higher than -40 ° C., the low-temperature performance as a lubricating base oil is not satisfied even when mixed with an ester synthetic oil. On the other hand, at the time of grease production, it is often heated to 180 ° C. or higher in order to achieve uniform mixing, and if the flash point is lower than 200 ° C., it is very dangerous. When the viscosity index is low, the viscosity index at 10 ° C. is inevitable because the viscosity at low temperature is inevitable and the torque at low temperature is increased.
It must be 0 or more.

With regard to viscosity, when the viscosity at 40 ° C. is 40 cSt or less, the average molecular weight of the poly-α-olefin synthetic oil becomes too small, and it is not suitable for grease using ester synthetic oil as a sole base oil. As a result, evaporation loss at a high temperature is high, and it is difficult to obtain satisfactory performance at a high temperature.
Conversely, if the viscosity at 40 ° C. is 300 cSt or more, the viscosity of the mixed base oil becomes considerably high even when mixed with a low-viscosity ester-based synthetic oil, resulting in an increase in bearing rotation torque.

Therefore, the viscosity at 40 ° C. is from 40 cSt to 40 cSt.
A range of 300 cSt is preferred. More preferably, 50
The range is from cSt to 200 cSt. The poly-α-olefin synthetic oil preferably has 7 to 12 carbon atoms and is synthesized by polymerizing an α-olefin monomer. More preferably, it is a polyalphaolefin synthetic oil having 8 to 10 carbon atoms.
The poly-α-olefin synthetic oil obtained by polymerizing an α-olefin monomer having 5 or less carbon atoms and 14 or more carbon atoms has a pour point, a flash point,
It is difficult to satisfy viscosity index and viscosity conditions.

As the ester-based synthetic lubricating oil, the general formula R
₁ OOC (CH ₂₎ diester represented by nCOOR _2,
Or the general formula C (CH ₂ OOR) ₄ or C ₂ H ₅ C (C
(H ₂ OOCR) ₃ . With respect to these ester-based synthetic oils, when the number of carbon atoms is small, there is a disadvantage that the evaporation loss at a high temperature becomes large and the life of the bearing at a high temperature becomes short. On the other hand, if the number of carbon atoms is too large, the low-temperature performance deteriorates, and the required performance of the present invention cannot be satisfied.

The diester is synthesized by reacting a dibasic acid with an alcohol having one active hydroxyl group. The value of n is preferably 3 to 12, and R ₁ and R ₂ are preferably an aliphatic hydrocarbon group having 3 to 18 carbon atoms.
The acid used mainly is adipic acid (n =
4), azelaic acid (n = 7), sebacic acid (n = 8)
and so on. The alcohol used is 2-
Ethyl hexyl alcohol (R _x = 8), trimethyl hex alcohol (R _x = 9), isodecyl alcohol (R _x = 9), tridecyl alcohol (R _x = 13)
and so on. Diesters are characterized by excellent cold flow properties and extremely low pour points. It also has good lubrication performance, good thermal and oxidative stability, and lower volatility as compared to mineral oils of similar viscosity. The viscosity index is relatively high and the shear stability is also good.

The polyol ester is synthesized by reacting a monohydric alcohol with two or more hydroxyl groups or by reacting a polyhydric alcohol with a monobasic acid. The polyols used are trimethylolpropane and pentaerythritol. R is preferably an aliphatic hydrocarbon group having 5 to 10 carbon atoms. Polyol esters are superior to diesters in terms of high temperature stability and have relatively low viscosity indices. Volatility is equal to or lower than diester.

Examples of the ester synthetic oil satisfying the above-mentioned conditions include di-2-ethylhexyl sebacate, di-3-
Methylbutyl adipate, diisooctyl sebacate,
Dioctyl azelate, diisodecyl adipate, di-
Examples thereof include 2-ethylhexyldecanoedioate and pentaerythritol tetraamyl ester. As described above, as the base oil of the grease for enclosing the rolling bearing of the present invention, a mixture of an ester-based synthetic oil and a poly-α-olefin-based synthetic oil having both high-temperature performance and low-temperature performance and taking into consideration lubrication performance and the like. The mixing ratio of the synthetic base oil is expressed in terms of weight ratio: ester type: poly-α-olefin type = 5: 2-1:
4 is preferred.

Here, regarding the mixing ratio, poly-
When the blending ratio of the α-olefin synthetic oil is too large, the solubility of various additives such as an antioxidant and a rust inhibitor deteriorates. In particular, the solubility of the antioxidant is poor, and the additive precipitates at low temperatures, and the precipitated and agglomerated crystalline particles impede the smooth rotation of the bearing and cause uneven rotation and abnormal noise. If the amount of various additives such as an antioxidant is reduced to eliminate this adverse effect, the oxidation stability at high temperatures and the life of the bearing are deteriorated, and the performance of the grease is reduced.

On the other hand, although the blending ratio of the poly-α-olefin-based synthetic oil is too small, and the bearing life at high temperatures is slightly improved and extended as compared with the case where the ester-based synthetic oil is used as the sole base oil, it is sufficiently satisfactory. Long bearing life cannot be obtained. For the reasons described above, the mixing ratio of the poly-α-olefin-based synthetic oil and the ester-based synthetic oil is set to be a polymerization mixing ratio, and ester-based: poly-α-olefin-based is 5: 2 to 1: 4.
Is more preferable, and more preferably, the range of ester type: poly-α-olefin type is 2: 1 to 1: 3.

As the thickener for the grease for enclosing the rolling bearing of the present invention, a mixed thickener prepared by mixing a higher fatty acid sodium salt and a higher fatty acid lithium salt in a specific ratio is used. The alkali metal soap used for this mixed thickener is
It is a higher fatty acid having 10 or more carbon atoms or a hydroxyaliphatic alkali metal salt having 10 or more carbon atoms having one or more hydroxyl groups. Examples of fatty acids having 10 or more carbon atoms or hydroxy fatty acids include, for example, myristic acid, balmitic acid, stearic acid, 12-hydroxystearic acid,
Oleic acid and the like.

It is not preferable to use a metal soap other than an alkali metal salt (an alkali metal soap such as a higher fatty acid sodium salt and a higher fatty acid lithium salt) since the bearing life at high temperatures is deteriorated. Here, the smoothness of rotation of the rolling bearing is greatly affected by the fiber structure of the grease. That is, the rolling of the rolling bearing using the grease having the short fiber fiber structure becomes smoother than the rolling bearing using the grease having the long fiber fiber structure.

Further, the generation of dust from the rolling bearing is greatly affected by the fiber structure of the grease. That is, the rolling bearing using the grease having the short fiber fiber structure generates more dust from the rolling bearing than the rolling bearing using the grease having the long fiber fiber structure. Incidentally, sodium soap-based grease has a long fiber fiber structure, and lithium soap-based grease has a short fiber fiber structure.

Further, lithium soap-based grease has relatively excellent properties such as thermal oxidation stability, shear stability, and retention of lubricating base oil as compared with sodium soap-based grease. Therefore, by adopting a mixed thickener in which a higher fatty acid sodium salt and a higher fatty acid lithium salt are blended in a specific ratio, the smoothness of rotation of the rolling bearing, the oxidation stability in a high-temperature environment, the low dust generation, etc. A grease for rolling bearing encapsulation having excellent performance as described above can be obtained. In particular,
The mixing ratio of the mixing thickener is preferably in the range of 15 to 35% by weight based on the total amount of the grease composition components. Further, it is preferable that the mixing ratio of the higher fatty acid sodium salt and the higher fatty acid lithium salt is in a weight ratio of sodium salt: lithium salt = 2: 5 to 5: 2.

The antioxidant of the grease for enclosing a rolling bearing of the present invention improves the oxidation resistance of the grease and improves the stability of the grease such as dropping point, shear stability, consistency and oil release characteristics. In order to achieve this, a mixed antioxidant obtained by mixing an amine antioxidant and a phenol antioxidant in a specific ratio is used. By using this mixed antioxidant, the antioxidant stability of the grease is improved, and the properties of the grease such as dropping point, shear stability, consistency, oil release characteristics, and the like are obtained. In addition, the lubrication life and acoustic characteristics of the rolling bearing in a high-temperature environment can be significantly improved.

This mixed antioxidant is preferably added in an amount of 0.3 to 8% by weight based on the total amount of the grease composition. More preferably, it is 0.5 to 7% by weight. If the addition ratio of the mixed antioxidant is less than 0.3% by weight, the antioxidant effect of the grease is reduced, and sufficient lubricity cannot be maintained. Further, even if it is added in an amount of 8% by weight or more, the antioxidant effect of the lubricant cannot be expected in accordance with an increase in the amount of addition, which is disadvantageous in terms of cost and also causes a problem of solubility in base oil.

Further, the mixing ratio of the amine antioxidant and the phenolic antioxidant in the mixed antioxidant is preferably amine: phenol type = 3: 10 to 10: 3. Within this range, the effect of preventing grease from being oxidized is greatly improved, and the lubrication life and acoustic characteristics of the rolling bearing in high-speed rotation and high-temperature environments can be significantly improved.
It should be noted that only one of the amine-based antioxidant and the phenol-based antioxidant cannot provide superior lubrication life and improved acoustic characteristics as compared with the mixed antioxidant.

As the amine-based antioxidant, alkyldiphenylamine (trade name: Irganox L01,
L06, L57, etc.), phenyl α-naphthylamine (trade name: Irganox L05, etc.), phenylenediamine, oleylamideamine, phenothiazine and the like are used. In addition, from the viewpoint of evaporation characteristics and compatibility with the base oil,
Alkyldiphenylamine is preferred.

The phenolic antioxidants include:
2,6-di-tert-butylenephenol (trade name:
Ethyl 701, Irganox L108, etc.), 4,4 '
-Methylenebis (2,6-di-tert-butylphenol, trade name: ethyl 702, Irganox L109
2,6-di-tert-butyl-4-ethylphenol (trade name: ethyl 724, etc.), 2,6-di-te
rt-4-n-butylphenol (trade name: ethyl 74
4) are used. From the viewpoint of evaporation characteristics and compatibility with the base oil, 4,4'-methylenebis (2,6-di-t
tert-butylphenol) is preferred.

Further, an additive for reducing the boundary lubrication state is added as a component of the grease for sealing a rolling bearing of the present invention. The additive amount of this additive is 0.5 wt% to 7.0 wt% based on the total amount of the grease composition components. By the way, miniature type rolling bearings used in electronic equipment such as HDDs, VTRs, and LBPs will be used in increasingly high-speed and high-temperature environments in the future. Therefore, "dragging phenomenon" of grease by rolling elements (balls) will occur. It is easy to occur. The grease is scraped from the contact area between the rolling element and the bearing ring due to the occurrence of the "dragging phenomenon" of the grease, and the grease between the rolling element and the bearing ring is easily cut off. May come into direct contact between the rolling element and the metal of the bearing ring without the intermediary of the grease lubricating film, that is, a boundary lubrication state may occur. When direct contact between the rolling element and the metal of the bearing ring (boundary lubrication state) occurs,
The rolling elements and the raceway surfaces of the races are remarkably worn, damaged and easily roughened, leading to an increase in vibration and noise. Such vibrations and noises are extremely harmful and problematic for electronic equipment.

Therefore, in the present invention, in order to solve the problem of the boundary lubrication state caused by such a grease drag phenomenon, an additive for reducing the boundary lubrication state is added as a component of the grease for enclosing the rolling bearing. . This additive has a special effect on the contact points (parts in the boundary lubrication state) where the rolling elements and the metal of the raceway do not pass through the lubricating film of the grease caused by the grease drag phenomenon, etc. Form a film that exhibits excellent anti-friction action.

That is, the additive for reducing the boundary lubrication state is formed by the ultrafine metal wear fine powder generated from the frictional contact between the rolling element and the metal of the raceway and the sliding energy (friction heat energy, etc.). An eutectic film is fixedly formed at the portion of the frictional contact between the metals by instantaneous activation and eutectic action. The eutectic film formed in this way has 1
It has a thickness of about 0000 ° to 250,000 °, is extremely strong in load resistance, and can maintain high lubrication performance without being peeled or broken by pressure. Due to the formation of this eutectic coating, the rolling element and the raceway come into contact via the eutectic coating and do not come into direct contact with each other, thereby suppressing the generation of wear fine powder and minimizing friction and wear. it can. Therefore, the friction surfaces of the rolling elements and the races do not need to be worn or damaged, and are not roughened. As a result, the lubricity between the rolling elements and the races is improved, the initial lubricity is excellent, vibration and noise are suppressed, and the acoustic performance and lubrication life of the bearing are improved.

Specific examples of the additive for reducing the boundary lubrication state include, for example, “NNL-690” and “NNL-690G” (trade names, Power Up Co., Canada). The amount of the additive that reduces this boundary lubrication state is
0.5 wt% to 7.0 wt% based on the total amount of the grease composition
%. 0.5wt of this additive
%, It becomes difficult to form a eutectic film sufficient to exhibit high lubrication performance. On the other hand, if the amount of the additive is more than 7% by weight, the formation of a eutectic film sufficient for exhibiting high lubrication performance is in a saturated state, which is meaningless and disadvantageous in cost.

The grease evaluation test method is described below. (1) Bearing acoustic test: An Anderon meter was used to measure the acoustic characteristics of the bearing. Sealed rolling bearing 6 provided with a non-contact type sealing device (nitrile rubber LB seal) on both sides
95 (inner diameter 5 mm, outer diameter 13 mm, width 4 mm) was filled with 17 mg of the grease composition, and test conditions were: a thrust load of 2 k
gf, rotation speed 7200r. p. The acoustic characteristics of the bearing were measured at a temperature of 80 ° C. and a temperature of 80 ° C. The pass / fail judgment of the acoustic test was performed by comparing the bearing anderon value at the start of the acoustic test (initial anderon value) with the bearing anderon value after 5000 hours of rotation (5000 Hr anderon value) and determining that the rise value was 1.0 or less. Passed. Here, the rise value from the initial anderon value is indicated by the following symbols in FIGS.

○: 1.0 or less Pass Δ: 1.1 to 2.0 Slightly unacceptable ×: 3.0 or more Fail (2) Torque test The torque is measured by a bearing torque measuring device schematically shown in FIG. Was performed. Test sealed rolling bearing 11 provided with non-contact type sealing device (nitrile rubber LB seal) on both sides
(Inner diameter 5 mm, outer diameter 13 mm, width 4 mm) is filled with 17 mg of the grease composition, and the test conditions are: 2 kg of thrust load
f, rotation speed 7200r. p. m, and rotated at a temperature of 80 ° C., the torque value measured using the strain gauge 12 was recorded on a recorder, and the value (initial torque) when the torque after 15 minutes of rotation was almost stabilized was adopted. At the end of the acoustic test, the torque (torque at the end of the test) was measured in the same manner. In addition, the pass / fail judgment of the torque is performed when the initial value is 14 g · c.
m or less, and if the value at the end of the test is 17 g · cm or less, it was judged as pass. Here, in the figure, reference numeral 13 is an air spindle, 14 is an arbor, 15 is an aluminum cap,
16 is an air bearing. The measurement results are shown in FIGS.

(3) High temperature life test Sealed rolling bearing 695 (inner diameter 5 mm, outer diameter 1) provided with a non-contact type sealing device (nitrile rubber LB seal) on both sides
3 gm, width 4 mm) and 17 mg of grease composition,
Test conditions: Thrust load 2 kgf, number of revolutions 10000
r. p. m, the life time was measured at a temperature of 140 ° C. In addition, the pass judgment of the high temperature life test is that the life time is 300 hours.
If it was 0 hours or more, it was judged as passed. The measurement results are shown in FIGS.

(4) Low Temperature (−40 ° C.) Torque Test The low temperature (−40 ° C.) torque was measured by a bearing torque measuring device schematically shown in FIG. Test sealed rolling bearing 11 provided with a non-contact type sealing device (nitrile rubber LB seal) on both sides (inner diameter 5 mm, outer diameter 13 mm, width 4 m)
m) was filled with 17 mg of the grease composition, and the test conditions were: a thrust load of 2 kgf, a rotation speed of 3600 r. p. m, rotating at a temperature of −40 ° C., recording a torque value measured using a strain gauge 21 on a recorder, and adopting a value when the torque was almost stabilized 15 minutes after the rotation. The pass / fail judgment of the torque is that the starting torque is 100 g · cm or less,
If the dynamic torque was 70 g · cm or less, it was judged as acceptable. The measurement results are shown in FIGS.

(5) Measurement of the amount of dust generated The bearing was rotated at 7,200 rpm in a sealed container, and the number of dust generated at that time was measured by an out-particle counter to determine the amount of generated dust. The amount of dust is 0.1cf
(Cubic feet), the number of dust particles having a particle size of 0.1 μm or more was counted, and the amount of dust generated after 1 hour passed was determined to be 400 or less. The measurement results are shown in FIGS. (Example 1) Poly-α-olefin synthetic oil having physical properties of viscosity = 100 cSt (at 40 ° C.), viscosity index = 132, pour point = −54 ° C., flash point = 230 ° C. and a mixed thickener (higher fatty acid sodium salt) And a mixture of a higher fatty acid lithium salt) in a ratio shown in FIG. After heating and dissolving, add ester-based synthetic oil at about 200 ° C. in the ratio shown in FIG. 4 and dissolve with stirring, cool with further stirring. And a mixture of an amine-based antioxidant) at the ratio shown in FIG.
An additive NNL-690 (Power Up Co., Ltd.) for reducing the boundary lubrication state is added at the ratio shown in FIG. 4 and uniformly dissolved with stirring. After cooling, the mixture was homogenized with a three-roll mill to obtain grease.

The mixing ratio of the ester-based synthetic oil of the base oil and the poly-α-olefin-based synthetic oil is such that ester-based: poly-α-olefin-based is about 1: 1. This grease was sealed in the test rolling bearing, and under the various test conditions described above, a high-temperature life test, an acoustic test, a torque test, a low-temperature torque test,
Measurement of the amount of generated dust was performed. FIG. 4 shows the measurement results. (Example 2) Poly-α-olefin synthetic oil having physical properties of viscosity = 150 cSt (at 40 ° C.), viscosity index = 125, pour point = −45 ° C., flash point = 256 ° C. and a mixed thickener (higher fatty acid sodium salt) And a mixture of a higher fatty acid lithium salt) in a ratio shown in FIG. After heating and dissolving, add ester-based synthetic oil at about 200 ° C. in the ratio shown in FIG. 4 and dissolve with stirring, cool with further stirring. And a mixture of an amine-based antioxidant) at the ratio shown in FIG.
An additive NNL-690 (Power Up Co., Ltd.) for reducing the boundary lubrication state is added at the ratio shown in FIG. 4 and uniformly dissolved with stirring. After cooling, the mixture was homogenized with a three-roll mill to obtain grease.

The mixing ratio of the ester-based synthetic oil of the base oil and the poly-α-olefin-based synthetic oil is ester: poly-α-olefin = about 2: 1. This grease was sealed in the test rolling bearing, and under the various test conditions described above, a high-temperature life test, an acoustic test, a torque test, a low-temperature torque test,
Measurement of the amount of generated dust was performed. FIG. 4 shows the measurement results. (Example 3) Viscosity = 70 cSt (at 40 ° C), viscosity index = 128, pour point = -57 ° C, flash point = 228 ° C. Mixture of higher fatty acid lithium salts)
Are mixed in the ratio shown in FIG. 4 and dissolved by heating while stirring.
After heating and dissolving, add ester-based synthetic oil at about 200 ° C. in the ratio shown in FIG. 4 and dissolve with stirring, cool with further stirring. And an amine-based antioxidant in a ratio shown in FIG. 4 and dissolved while stirring, and then an additive NNL-690 (Power Up Co., Ltd.) for reducing boundary lubrication is added in a ratio shown in FIG. 4 and stirred. While dissolving uniformly. After cooling, the mixture was homogenized with a three-roll mill to obtain grease.

The mixing ratio of the ester-based synthetic oil of the base oil and the poly-α-olefin-based synthetic oil is about 1: 2 (ester-based: poly-α-olefin-based). This grease was sealed in the test rolling bearing, and under the various test conditions described above, a high-temperature life test, an acoustic test, a torque test, a low-temperature torque test,
Measurement of the amount of generated dust was performed. FIG. 4 shows the measurement results. (Example 4) Poly-α-olefin synthetic oil having physical properties of viscosity = 45 cSt (at 40 ° C.), viscosity index = 127, pour point = −58 ° C., flash point = 224 ° C. and a mixed thickener (higher fatty acid sodium salt) And a higher fatty acid lithium salt) in a ratio shown in FIG. After heating and dissolving, add ester-based synthetic oil at about 200 ° C. in the ratio shown in FIG. 4 and dissolve with stirring, cool with further stirring. And a mixture of an amine-based antioxidant) at the ratio shown in FIG.
An additive NNL-690 (Power Up Co., Ltd.) for reducing the boundary lubrication state is added at the ratio shown in FIG. 4 and uniformly dissolved with stirring. After cooling, the mixture was homogenized with a three-roll mill to obtain grease.

The mixing ratio of the ester-based synthetic oil of the base oil and the poly-α-olefin-based synthetic oil is about 1: 3 (ester-based: poly-α-olefin-based). This grease was sealed in the test rolling bearing, and under the various test conditions described above, a high-temperature life test, an acoustic test, a torque test, a low-temperature torque test,
Measurement of the amount of generated dust was performed. FIG. 4 shows the measurement results. (Comparative Example 1) Poly-α-olefin synthetic oil having physical properties of viscosity = 100 cSt (at 40 ° C.), viscosity index = 132, pour point = −54 ° C., flash point = 230 ° C. and a mixed thickener (higher fatty acid sodium salt) And a mixture of a higher fatty acid lithium salt) in a ratio shown in FIG. After heating and dissolving, the ester synthetic oil is added at about 200 ° C. in the ratio shown in FIG. 5 and dissolved while stirring, and further cooled while stirring. And a mixture of an amine-based antioxidant) in the ratio shown in FIG.
An additive NNL-690 (Power Up Co., Ltd.) for reducing the boundary lubrication state is added at the ratio shown in FIG. 5 and uniformly dissolved with stirring. After cooling, the mixture was homogenized with a three-roll mill to obtain grease.

Incidentally, Comparative Example 1 is out of the scope of the present invention because the mixing ratio of the mixed thickener (mixture of higher fatty acid sodium salt and higher fatty acid lithium salt) to the total amount of grease is "7 wt%". . This grease was sealed in the test rolling bearing, and a high-temperature life test, an acoustic test, a torque test, a low-temperature torque test, a measurement of dust generation, and the like were performed under the various test conditions described above. FIG. 5 shows the measurement results. (Comparative Example 2) Poly-α-olefin synthetic oil having physical properties of viscosity = 100 cSt (at 40 ° C.), viscosity index = 132, pour point = −54 ° C., flash point = 230 ° C. and a mixed thickener (higher fatty acid sodium salt) And a mixture of a higher fatty acid lithium salt) in a ratio shown in FIG. After heating and dissolving, the ester synthetic oil is added at about 200 ° C. in the ratio shown in FIG. 5 and dissolved while stirring, and further cooled while stirring. And a mixture of an amine-based antioxidant) in the ratio shown in FIG.
An additive NNL-690 (Power Up Co., Ltd.) for reducing the boundary lubrication state is added at the ratio shown in FIG. 5 and uniformly dissolved with stirring. After cooling, the mixture was homogenized with a three-roll mill to obtain grease.

The comparative example 2 is out of the scope of the present invention because the mixing ratio of the mixed thickener (a mixture of the higher fatty acid sodium salt and the higher fatty acid lithium salt) to the total amount of the grease is “12 wt%”. This grease is sealed in the test rolling bearing, and an acoustic test, a low-temperature torque test,
A torque test, a high temperature life test, a low temperature life test, a measurement of the amount of generated dust, and the like were measured under the test conditions described above. FIG. 5 shows the measurement results. Comparative Example 3 An ester-based synthetic oil and a mixed thickener (a mixture of a higher fatty acid sodium salt and a higher fatty acid lithium salt) were blended in the ratio shown in FIG.
The mixture was cooled to about 100 ° C., and a mixed antioxidant (a mixture of a phenolic antioxidant and an amine antioxidant) was added at the ratio shown in FIG. 5 and stirred. Then, an additive NNL-690 (Power Up Co., Ltd.) for reducing the boundary lubrication state is added at a ratio shown in FIG. 5 and uniformly dissolved with stirring. After cooling, the mixture was homogenized with a three-roll mill to obtain grease.

The comparative example 3 is out of the scope of the present invention because no poly-α-olefin synthetic oil is used.
This grease was sealed in the test rolling bearing, and a high-temperature life test, an acoustic test, a torque test, a low-temperature torque test, a measurement of dust generation, and the like were performed under the various test conditions described above. FIG. 5 shows the measurement results. (Comparative Example 4) A mineral oil having a viscosity of about 100 cSt at 40 ° C and a viscosity index of 132 was mixed with an ester-based synthetic oil in the ratio shown in Fig. 5, and a mixture thickener (a sodium salt of a higher fatty acid and a lithium salt of a higher fatty acid) was added. The mixture was mixed at the ratio shown in FIG. 5, heated and dissolved with stirring, heated to 200 ° C., then cooled while stirring, and when the temperature reached about 100 ° C., the mixed antioxidant (phenolic antioxidant) And a mixture of an amine-based antioxidant) at the ratio shown in FIG. 5 and dissolving while stirring, and then an additive NNL-69 for reducing the boundary lubrication state.
0 (Power Up Co., Ltd.) is added at the ratio shown in FIG. 5 and uniformly dissolved with stirring. After cooling, the mixture was homogenized with a three-roll mill to obtain grease.

The comparative example 4 is outside the scope of the present invention because a mineral oil is used instead of the poly-α-olefin synthetic oil. This grease was sealed in the test rolling bearing, and a high-temperature life test, an acoustic test, a torque test, a low-temperature torque test, a measurement of dust generation, and the like were performed under the various test conditions described above. FIG. 5 shows the measurement results. (Comparative Example 5) Poly-α-olefin synthetic oil having physical properties of viscosity = 45 cSt (at 40 ° C.), viscosity index = 127, pour point = −58 ° C., flash point = 224 ° C. and a mixing thickener (higher fatty acid sodium salt) And a mixture of higher fatty acid lithium salts) in a ratio shown in FIG. 5 and heat-melting with stirring, heating to about 200 ° C., and then cooling with stirring. An antioxidant (a mixture of a phenolic antioxidant and an amine antioxidant) is added at the ratio shown in FIG. 5 and dissolved while stirring, and then an additive NNL-690 (Power Up Co., Ltd.) for reducing boundary lubrication is illustrated. Add at the ratio shown in 5 and dissolve uniformly with stirring. After cooling, the mixture was homogenized with a three-roll mill to obtain grease.

Incidentally, Comparative Example 5 is out of the scope of the present invention since no ester synthetic oil was used as the base oil. This grease was sealed in the test rolling bearing, and a high-temperature life test, an acoustic test, a torque test, a low-temperature torque test, a measurement of dust generation, and the like were performed under the various test conditions described above. FIG. 5 shows the measurement results. (Example 6) Poly-α-olefin synthetic oil having physical properties of viscosity = 200 cSt (at 40 ° C.), viscosity index = 123, pour point = −42 ° C., flash point = 260 ° C. and mixed thickener (higher fatty acid sodium salt) And a mixture of a higher fatty acid lithium salt) in a ratio shown in FIG. After heating and dissolving, the ester synthetic oil is added at about 200 ° C. in the ratio shown in FIG. 5 and dissolved while stirring, and further cooled while stirring. When the temperature reaches about 100 ° C., the mixed antioxidant (phenolic antioxidant And a mixture of an amine-based antioxidant) in the ratio shown in FIG.
An additive NNL-690 (Power Up Co., Ltd.) for reducing the boundary lubrication state is added at the ratio shown in FIG. 5 and uniformly dissolved with stirring. After cooling, the mixture was homogenized with a three-roll mill to obtain grease.

In Comparative Example 6, since the mixing ratio of the ester-based synthetic oil of the base oil and the poly-α-olefin-based synthetic oil was about 3: 1 (ester: poly-α-olefin), Out of range. This grease was sealed in the test rolling bearing, and a high-temperature life test, an acoustic test, a torque test, a low-temperature torque test, a measurement of dust generation, and the like were performed under the various test conditions described above. FIG. 5 shows the measurement results. (Example 7) Poly-α-olefin synthetic oil having physical properties of viscosity = 100 cSt (at 40 ° C.), viscosity index = 132, pour point = −54 ° C., flash point = 230 ° C. and a mixed thickener (higher fatty acid sodium salt) And a mixture of a higher fatty acid lithium salt) in a ratio shown in FIG. After heating and dissolving, the ester-based synthetic oil is added at about 200 ° C. in the ratio shown in FIG. 6, dissolved while stirring, and further cooled while stirring. When cooled to about 100 ° C., a mixed antioxidant (a mixture of a phenolic antioxidant and an amine antioxidant) was added at the ratio shown in FIG. 6 and dissolved with stirring. After cooling, the mixture was homogenized with a three-roll mill to obtain grease.

The comparative example 7 is outside the scope of the present invention because the additive NNL-690 (Power Up Co., Ltd.) for reducing the boundary lubrication state is not used. This grease was sealed in the test rolling bearing, and a high-temperature life test, an acoustic test, a torque test, a low-temperature torque test, a measurement of dust generation, and the like were performed under the various test conditions described above. Fig. 6 shows the measurement results.
Shown in (Example 8) Poly-α-olefin synthetic oil having physical properties of viscosity = 100 cSt (at 40 ° C.), viscosity index = 132, pour point = −54 ° C., flash point = 230 ° C. and a mixing thickener (higher fatty acid lithium salt) Only) in the ratio shown in FIG. 6 and dissolve by heating while stirring. After heating and melting, about 200 ° C
Then, the ester-based synthetic oil is added at the ratio shown in FIG. 6 and dissolved while stirring, and further cooled while stirring. When the temperature reaches about 100 ° C., the mixed antioxidant (a phenolic antioxidant and an amine 6) is added at the ratio shown in FIG. 6 and dissolved with stirring. Then, an additive NNL-690 (Power Up Co., Ltd.) for reducing the boundary lubrication state is added at the ratio shown in FIG. 6 and uniformly dissolved with stirring. After cooling, the mixture was homogenized with a three-roll mill to obtain grease.

In Comparative Example 8, the mixing ratio of the mixed thickener (a mixture of the higher fatty acid sodium salt and the higher fatty acid lithium salt) is out of the range of the present invention. This grease,
It was sealed in the test rolling bearing and subjected to a high-temperature life test, an acoustic test, a torque test, a low-temperature torque test, a measurement of dust generation, and the like under the above-described various test conditions. FIG. 6 shows the measurement results. (Example 9) Poly-α-olefin synthetic oil having physical properties of viscosity = 100 cSt (at 40 ° C.), viscosity index = 132, pour point = −54 ° C., flash point = 230 ° C. and a mixed thickener (higher fatty acid sodium salt) Only) are mixed in the ratio shown in FIG. 6 and dissolved by heating while stirring. After heating and melting, about 20
At 0 ° C., an ester-based synthetic oil was added at the ratio shown in FIG. 6 and dissolved with stirring.
, A mixed antioxidant (a mixture of a phenolic antioxidant and an amine antioxidant) is added at the ratio shown in FIG. 6 and dissolved while stirring, and then an additive NNL-690 (which reduces the boundary lubrication state) is used. (Power-up Co., Ltd.) at the ratio shown in FIG. After cooling, the mixture was homogenized with a three-roll mill to obtain grease.

In Comparative Example 9, the mixing ratio of the mixing thickener (a mixture of the higher fatty acid sodium salt and the higher fatty acid lithium salt) was out of the scope of the present invention. This grease,
It was sealed in the test rolling bearing and subjected to a high-temperature life test, an acoustic test, a torque test, a low-temperature torque test, a measurement of dust generation, and the like under the above-described various test conditions. FIG. 6 shows the measurement results. (Comparative Example 10) Viscosity = 100 cSt (at 40 ° C), viscosity index = 132, pour point = -54 ° C, flash point = 230 ° C
A poly-α-olefin synthetic oil having the following physical properties and a mixture thickener (a mixture of a higher fatty acid sodium salt and a higher fatty acid lithium salt) are blended in the ratio shown in FIG. 6 and heated and dissolved with stirring. After heating and dissolving, the ester-based synthetic oil is added at about 200 ° C. in the ratio shown in FIG. 6 and dissolved while stirring, and further cooled while stirring, and when the temperature reaches about 100 ° C., an additive NNL that reduces the boundary lubrication state -690 (Power Up Co., Ltd.) is added at the ratio shown in FIG. 6 and uniformly dissolved with stirring. After cooling, the mixture was homogenized with a three-roll mill to obtain grease.

This Comparative Example 10 is out of the scope of the present invention because it does not contain a mixed antioxidant (a mixture of a phenolic antioxidant and an amine antioxidant).
This grease was sealed in the test rolling bearing, and a high-temperature life test, an acoustic test, a torque test, a low-temperature torque test, a measurement of dust generation, and the like were performed under the various test conditions described above. FIG. 6 shows the measurement results. (Comparative Example 11) Polybutene having a viscosity of about 70 cSt at a temperature of 40 ° C and a viscosity index of 48, and a mixture thickener (a mixture of a sodium salt of a higher fatty acid and a lithium salt of a higher fatty acid) were blended in the ratio shown in Fig. 6 and heated while stirring. Dissolve. After heating and dissolving, the ester-based synthetic oil was added at about 200 ° C. in the ratio shown in FIG. 6 and dissolved with stirring.
When the temperature reaches 0 ° C., a mixed antioxidant (a mixture of a phenolic antioxidant and an amine antioxidant) is added at the ratio shown in FIG. 6 and dissolved while stirring. 690 (Power Up Co., Ltd.) at the ratio shown in FIG. After cooling,
The grease was homogenized with a three-stage roll mill to obtain grease.

The comparative example 11 is outside the scope of the present invention because polybutene is used in place of the poly-α-olefin synthetic oil specified in the present invention. This grease was sealed in the test rolling bearing, and a high-temperature life test, an acoustic test, a torque test, a low-temperature torque test, a measurement of dust generation, and the like were performed under the various test conditions described above. FIG. 6 shows the measurement results. Example 12 Viscosity = 45 cSt (at 40 ° C.), viscosity index = 127, pour point = −58 ° C., flash point = 224 ° C. Polyalphaolefin synthetic oil having physical properties and Al-stearate as a thickener It is blended in the ratio shown in FIG. 6 and dissolved by heating while stirring. After heating and dissolving, the ester synthetic oil was added at about 200 ° C. in the ratio shown in FIG.
A mixed antioxidant (a mixture of a phenolic antioxidant and an amine antioxidant) is added at the ratio shown in FIG. 6 and dissolved while stirring, and then an additive NNL for reducing the boundary lubrication state.
-690 (Power Up Co., Ltd.) is added at the ratio shown in FIG. 6 and uniformly dissolved with stirring. After cooling, the mixture was homogenized with a three-roll mill to obtain grease.

In Comparative Example 12, Al-stearate was used instead of the mixed thickener (mixture of higher fatty acid sodium salt and higher fatty acid lithium salt) specified in the present invention. It is outside the scope of the invention. This grease was sealed in the test rolling bearing, and a high-temperature life test, an acoustic test, a torque test, a low-temperature torque test, a measurement of dust generation, and the like were performed under the various test conditions described above. FIG. 6 shows the measurement results.

As is clear from the test results shown in FIGS.
The grease for sealing rolling bearings shown in Examples 1 to 4 is:
Satisfactory results were obtained in all tests such as high-temperature life test, acoustic test, torque test, low-temperature torque test, and measurement of dust generation, and lubrication life, acoustic characteristics, low-temperature torque characteristics, high-temperature resistance, low It was confirmed that it was excellent over all properties such as dust generation.

On the other hand, as shown in Comparative Examples 1 to 12, those having grease components and compounding ratios which do not satisfy the ranges specified in the present invention were subjected to a high-temperature life test, an acoustic test, a torque test, and a low-temperature torque test. In any of the tests, such as measurement of the amount of dust generated, the results were unsatisfactory, and any one of the properties such as lubrication life, acoustic characteristics, low temperature torque characteristics, high temperature resistance, and low dust generation was obtained. Was found to be inferior in characteristics.

[0075]

As described above, the grease for enclosing a rolling bearing of the present invention has a specific mixed synthetic base oil as described above,
Mixing thickeners, mixed antioxidants and additives that reduce boundary lubrication as essential components provide excellent grease antioxidant stability and lubrication life. The lubrication of the bearing was improved, the initial lubrication was excellent, the generation of vibration and noise was suppressed, and the acoustic performance of the bearing was improved. Further, both low-temperature performance and high-temperature performance can be provided, and the life of the bearing in a high-speed rotation and high-temperature environment can be improved. In addition, dust generation can be reduced.

The use of the grease for sealing a rolling bearing of the present invention greatly reduces the amount of dust generated from the rolling bearing. Therefore, the present invention provides a rolling bearing having a non-contact type sealing device without using a magnetic fluid sealing system. On the other hand, quietness can be maintained without polluting the clean atmosphere. Therefore, since components related to the magnetic fluid seal can be omitted, the size of the apparatus can be reduced and the manufacturing cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a sectional view of a rolling bearing (a deep groove ball bearing).

FIG. 2 is a schematic diagram of a bearing torque measuring device.

FIG. 3 is an explanatory diagram of various lubricating states in a relationship between pressure and friction of a fluid lubricant.

FIG. 4 is a chart showing a component composition table and various test result data of an example of a grease for sealing a rolling bearing of the present invention.

FIG. 5 is a chart showing a component composition table and various test result data of a comparative example of the grease for sealing a rolling bearing of the present invention.

FIG. 6 is a chart showing a component composition table and data of various test results of a comparative example of the grease for sealing a rolling bearing of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Outer ring 2 Rolling element 3 Inner ring 4 Cage 11 Sealing rolling bearing for test 12 Strain gauge 13 Air spindle 14 Arbor 15 Aluminum cap 16 Air bearing

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (Reference) C10M 117/04 C10M 117/04 129/10 129/10 133/12 133/12 133/16 133/16 135 / 32 135/32 171/02 171/02 // C10N 10:02 20:00 20:02 30:00 30:08 30:10 40:02 40:06 50:10 F term (reference) 4H104 BA07A BB05C BB17B BB19B BB33A BB34A BE07C BE11C BG17C CA01A EA02A EA04A EB09 EB20 FA01 LA04 LA05 LA20 PA01 PA04 QA18

Claims (8)

[Claims] Claims: 1. A mixed oil comprising a mixture of an ester-based synthetic oil and a poly-α-olefin-based synthetic oil in a specific ratio as a base oil, and a higher fatty acid sodium salt and a higher fatty acid lithium salt mixed in a specific ratio. A grease for sealing rolling bearings, characterized in that a thickener, an antioxidant and an additive for reducing boundary lubrication are blended in the base oil. 2. The poly-α-olefin synthetic oil has a pour point of −40 ° C. or lower, a flash point of 200 ° C. or higher, and a viscosity index of 100.
The grease according to claim 1, wherein the viscosity at 40C is 40 to 300 cSt. 3. The mixing ratio of the mixed synthetic base oil of the ester-based synthetic oil and the poly-α-olefin-based synthetic oil is expressed in a weight ratio of ester: poly-α-olefin = 5: 2 to 1: 4.
The grease for sealing a rolling bearing according to claim 1 or 2, wherein: 4. The grease for sealing a rolling bearing according to claim 1, wherein the mixed thickener is incorporated in an amount of 15 to 35% by weight based on the total amount of the grease composition components. 5. The mixing ratio of the higher fatty acid sodium salt and the higher fatty acid lithium salt in the mixed thickener is sodium salt: lithium salt = 2: 5 to 5: 2 in weight ratio.
The grease for sealing a rolling bearing according to claim 1 or 4, wherein: 6. The antioxidant is a mixed antioxidant in which an amine antioxidant and a phenolic antioxidant are mixed at a specific ratio, and is 0.3 to 8 based on the total amount of the grease component. 2. The grease according to claim 1, wherein the grease is contained in an amount of 0.0% by weight. 7. The mixing ratio of the amine-based antioxidant and the phenol-based antioxidant is, in terms of weight ratio, amine-based: phenol-based = 3: 10 to 10: 3. Grease for enclosing rolling bearings as described. 8. An additive for reducing the boundary lubrication state, wherein the additive is used in an amount of 0.5 to 7.
The grease for sealing a rolling bearing according to claim 1, wherein the grease is blended at 0% by weight.