JP2010065171A - Grease composition and rolling device - Google Patents

Abstract

To provide a grease composition excellent in heat resistance, wear resistance and lubricity, and a rolling device excellent in seizure resistance and wear resistance and having a long life.
A deep groove ball bearing includes an inner ring 1 having a raceway surface 1a on an outer peripheral surface, an outer ring 2 having a raceway surface 2a facing the raceway surface 1a on an inner peripheral surface, and rolling between both raceway surfaces 1a and 2a. A plurality of rolling elements 3 that are freely arranged, a cage 4 that holds the plurality of rolling elements 3 between the inner ring 1 and the outer ring 2, and a seal that covers an opening of a gap between the inner ring 1 and the outer ring 2 Sealing devices 5 and 5. Further, a grease composition G for lubricating the deep groove ball bearing is enclosed in a gap formed between the inner ring 1 and the outer ring 2 and provided with the rolling elements 3. The grease composition G contains perfluoropolyether oil, a fluororesin, and inorganic fine particles having a primary particle size of 3 nm to 100 nm.
[Selection] Figure 1

Description

  The present invention relates to a grease composition. The present invention also relates to a rolling device such as a rolling bearing, a ball screw, a linear guide device, and a linear motion bearing.

  In recent years, automobiles (passenger cars) have been required to be reduced in size and weight and expanded in living space, and therefore the engine room space has been reduced. Etc.) are being further reduced in size and weight. In addition to this, since the improvement of silence is desired and the engine room is being sealed, the temperature increase in the engine room is promoted. Therefore, the various parts have been required to have a property to withstand high temperatures.

  The rolling bearings used in the various parts mainly use urea-synthetic oil greases containing synthetic oil as a base oil and a urea compound as a thickener. This urea-synthetic oil-based grease can be used satisfactorily with a long lubricating life of the bearing under conditions where the bearing temperature is 170 to 180 ° C. However, under conditions where the bearing temperature is 200 ° C. or higher, the base oil evaporates, the resulting grease hardens, and the grease softens due to the destruction of the thickener, which may cause seizure early. is there.

For this reason, in order to improve heat resistance, for example, it is known that fluorine-based grease containing perfluoropolyether oil (PFPE) as a base oil and polytetrafluoroethylene (PTFE) as a thickener is enclosed in a rolling bearing. (See Patent Document 1). If this fluorine-based grease is used, the rolling bearing can be sufficiently used even in an environment of 180 ° C. or higher.
JP-A-1-284542 Japanese Patent Laid-Open No. 11-131087 JP-A-10-184706

However, perfluoropolyether oil has a tendency to be inferior in friction and wear characteristics because it is inferior in affinity to bearing materials such as bearing steel SUJ2 and stainless steel SUS440C, as compared with synthetic oil and mineral oil such as ester oil and ether oil. was there. In addition, since it is difficult to add an additive blended in a general grease to a fluorine-based grease, there is a limit to improving the friction and wear characteristics with conventional additives.
A technique for improving the torque life by using a layered mineral powder as a thickener has been disclosed (see Patent Document 2), but considering the recent demand for maintenance-free, a longer life is required. there were.

  In addition, for electronic control motor bearings for automobiles such as electronic control throttle bearings, idle rotation control valve (ISCV) bearings, exhaust gas recirculation device (EGR) bearings, etc., as in the case of the above-mentioned various parts. Since high speed due to downsizing of the bearing and high temperature due to sealing of the engine room are problems, durability in a high temperature environment of 180 ° C. or higher is required. Furthermore, low torque is required for energy loss reduction and operability in a low temperature environment of −30 ° C. or lower, and the ability to quickly stabilize torque is also required (hereinafter, this Such torque performance is referred to as torque stability performance).

Under such circumstances, the above-mentioned lubrication of automobile electronic control motor bearings provides excellent seizure resistance even in a high temperature environment of 180 ° C. or higher, and over a wide temperature range from low temperature to high temperature. Because of its low torque, a fluorine grease using a fluorine oil as a base oil and a fluorine resin as a thickener has been used.
However, when conventional fluorine grease is used, although the seizure resistance and the low torque property as described above are excellent, it cannot be said that the torque stability performance is sufficient, and further performance improvement is required.

  Accordingly, an object of the present invention is to solve the above-described problems of the prior art and to provide a grease composition having excellent heat resistance, wear resistance, and lubricity. Another object is to provide a rolling device that has excellent seizure resistance and wear resistance and has a long life. Furthermore, a grease composition and an electronically controlled motor for automobiles that have excellent seizure resistance even in a high temperature environment of 180 ° C. or higher, low torque over a wide temperature range from low temperature to high temperature, and excellent torque stability performance Another object is to provide a bearing for a vehicle.

  In order to solve the above problems, the present invention has the following configuration. That is, the grease composition of claim 1 according to the present invention is a grease composition containing a base oil and a thickener, wherein the base oil is a perfluoropolyether oil and the thickener is a fluororesin. In addition, inorganic fine particles having a primary particle size of 3 nm to 100 nm are added. Since the grease composition of the present invention is based on perfluoropolyether oil having excellent thermal stability even at high temperatures, the base oil is hardly thermally deteriorated even at a high temperature environment of 180 ° C. or higher, and has excellent heat resistance. Showing gender. Moreover, since this grease composition can keep the base oil viscosity low, it is excellent in low-temperature fluidity. Furthermore, since it contains inorganic fine particles, it is excellent in wear resistance and lubricity.

When the grease composition is used in a rolling device, the inorganic fine particles enter the oil film formed between the rolling contact surfaces (between the raceway surface and the rolling surface of the rolling element), and the rolling contact surface is agglomerated. Since a film having a thickness of about 500 nm or less is formed by adsorbing to the surface, direct contact of the rolling contact surface is suppressed. Therefore, the occurrence of damage such as wear and seizure on the rolling contact surface is suppressed.
Since the inorganic fine particles having a primary particle size of 3 nm or more and 100 nm or less have agglomeration properties, secondary aggregates may be generated in the grease composition. When a large secondary aggregate is generated, it is difficult to enter the oil film formed between the rolling contact surfaces. Therefore, it is preferable that the inorganic fine particles are subjected to a hydrophobic treatment so as to be difficult to aggregate. Hydrophobized inorganic fine particles are difficult to agglomerate and stably disperse in the grease composition, so that they sufficiently penetrate into the oil film formed between the rolling contact surfaces and suppress direct contact of the rolling contact surfaces. In addition, the occurrence of damage such as wear and seizure is sufficiently suppressed.

  In order for the inorganic fine particles to sufficiently enter the oil film formed between the rolling contact surfaces, the primary particle size of the inorganic fine particles needs to be 3 nm or more and 100 nm or less. If the primary particle size exceeds 100 nm, it may be difficult to enter an oil film having a thickness of about 1 μm. On the other hand, if it is less than 3 nm, the aggregation properties of the inorganic fine particles become strong, so that large secondary aggregates are generated, and the inorganic fine particles act as an abrasive to promote wear, and it is difficult to enter the oil film. There is a risk. In order to make such problems less likely to occur, the primary particle size of the inorganic fine particles is preferably 3 nm or more and 50 nm or less, more preferably 3 nm or more and 30 nm or less, and more preferably 3 nm or more and less than 20 nm. Is more preferable. In order for inorganic fine particles to sufficiently enter the oil film formed between the rolling contact surfaces, the aspect ratio (ratio of major axis to minor axis) of the inorganic fine particles is preferably 4 or less.

The grease composition of claim 2 according to the present invention is characterized in that, in the grease composition of claim 1, the content of the inorganic fine particles is 0.001 mass% or more and 5 mass% or less. To do.
If the content of the inorganic fine particles is less than 0.001% by mass, sufficient seizure resistance and wear resistance may not be obtained. On the other hand, if it exceeds 5% by mass, secondary aggregates are likely to be formed in the grease composition, so that it is difficult to enter between the rolling contact surfaces of the rolling device. In order to make such a problem less likely to occur, the content of the inorganic fine particles is more preferably 0.01% by mass or more and 1% by mass or less, and preferably 0.1% by mass or more and 1% by mass or less of the entire grease composition. More preferably, it is less than mass%.

Furthermore, the grease composition of claim 3 according to the present invention is characterized in that, in the grease composition of claim 1 or 2, the dispersion diameter of the inorganic fine particles is 3 nm or more and 200 nm or less.
Since the inorganic fine particles have aggregability, secondary aggregates may be generated in the grease composition. When a large secondary aggregate is generated, it is difficult to enter the oil film formed between the rolling contact surfaces. Therefore, the dispersion diameter of the inorganic fine particles (the diameter of the secondary aggregate) in the grease composition may be 200 nm or less. preferable. More preferably, it is 100 nm or less, More preferably, it is 50 nm or less. Since the lower limit value of the primary particle size of the inorganic fine particles is 3 nm, the lower limit value of the dispersion diameter is also 3 nm.

Furthermore, the grease composition according to claim 4 of the present invention is the grease composition according to any one of claims 1 to 3, wherein the inorganic fine particles are subjected to a surface treatment with an organosilicon compound. It is characterized by being silicon.
Since silicon dioxide has a high affinity for organosilicon compounds such as silane coupling agents and silicon oils, the surface of silicon dioxide can be made hydrophobic with high density by surface treatment with an organosilicon compound. As a result, the effect of adding silicon dioxide, which is an inorganic fine particle, can be greatly enhanced.

Furthermore, the grease composition according to claim 5 of the present invention is the grease composition according to any one of claims 1 to 4, wherein the perfluoropolyether oil is linear. .
Linear perfluoropolyether oil has a high viscosity index (ie, a small change in viscosity with temperature). Therefore, when such a grease composition is used for a rolling device, the rolling device can have a low torque over a wide temperature range.

  Furthermore, a rolling device according to a sixth aspect of the present invention includes an inner member having a raceway surface on an outer surface and a raceway surface facing the raceway surface of the inner member, and is disposed outward of the inner member. In a rolling device, comprising: an outer member that is formed, a plurality of rolling elements that are arranged to roll between the raceway surfaces, and a lubricant that lubricates between the raceway surfaces and the rolling elements. The lubricant composition is the grease composition according to any one of claims 1 to 5.

Such a rolling device is excellent in seizure resistance and wear resistance and has a long life even when used at high temperatures.
Furthermore, the rolling device according to a seventh aspect of the present invention is the rolling device according to the sixth aspect, wherein the rolling device is a rolling bearing incorporated in an electrical component of an automobile or an engine accessory of the automobile.

Such a rolling bearing is excellent in seizure resistance and wear resistance and has a long life even when used at high temperatures. Therefore, it is suitable as a rolling bearing incorporated in an electrical component of an automobile such as an electric cooling fan motor, an electronic control throttle, an idle rotation control valve (ISCV), an exhaust gas recirculation device (EGR), or an engine accessory.
The present invention can be applied to various rolling devices. For example, a rolling bearing, a ball screw, a linear guide device, a linear motion bearing, and the like.

Further, the inner member in the present invention means an inner ring when the rolling device is a rolling bearing, a screw shaft when the ball screw is also used, a guide rail when the linear guide device is used, and a linear motion bearing. Means each axis. The outer member is the outer ring when the rolling device is a rolling bearing, the nut when it is a ball screw, the slider when it is a linear guide device, and the outer cylinder when it is also a linear bearing. Each means.
Furthermore, the grease composition according to claim 8 of the present invention is characterized by containing fluorine oil, a fluororesin, and ultrafine particles having a primary particle size of 50 nm or less.

Such a grease composition is suitable for lubricating a rolling bearing incorporated in an electronic control motor used in an automobile.
Furthermore, an electronic control motor bearing for an automobile according to a ninth aspect of the present invention includes an inner ring having a raceway surface on an outer surface, an outer ring having a raceway surface facing the raceway surface of the inner ring, and a roller between the raceway surfaces. In a rolling bearing incorporated in an electronic control motor used in an automobile, comprising: a plurality of rolling elements arranged freely; and a lubricant that lubricates between both the raceway surfaces and the rolling elements. The agent is a grease composition containing fluorine oil, a fluororesin, and ultrafine particles having a primary particle size of 50 nm or less.

  Since the grease composition as a lubricant contains ultrafine particles having a primary particle size of 50 nm or less, the fluidity is good, and the frictional wear characteristics on both the raceway surfaces and the rolling surfaces of the rolling elements. Forms a strong grease film. Therefore, the electronic control motor bearing for an automobile of the present invention has excellent seizure resistance even in a high temperature environment of 180 ° C. or more, and has low torque and a stable torque over a wide temperature range from low temperature to high temperature. Excellent performance.

  If the primary particle size of the ultrafine particles exceeds 50 nm, the ultrafine particles may act as an abrasive and promote the wear of both the raceway surfaces and the rolling surfaces of the rolling elements. However, when the primary particle size of the ultrafine particles is less than 3 nm, the cohesiveness of the ultrafine particles becomes strong, so that it is difficult to stably exist in the grease composition. In order to make such inconvenience less likely to occur, the primary particle size of the ultrafine particles is preferably 3 nm or more and 30 nm or less. In order to achieve stable torque performance and low torque, the primary particle size of the ultrafine particles is preferably 3 nm or more and less than 20 nm.

The grease composition of the present invention is excellent in heat resistance, wear resistance, and lubricity. Further, the rolling device of the present invention has excellent seizure resistance and wear resistance and a long life.
Furthermore, the grease composition of the present invention and the automotive electronic control motor bearing have excellent seizure resistance even in a high temperature environment of 180 ° C. or higher, and low torque over a wide temperature range from low temperature to high temperature. It has excellent torque stability.

[First embodiment]
An embodiment of a rolling device according to the present invention will be described in detail with reference to the drawings.
FIG. 1 is a longitudinal sectional view showing a structure of a deep groove ball bearing which is an embodiment of a rolling device according to the present invention. This deep groove ball bearing has an inner ring 1 having a raceway surface 1a on the outer peripheral surface, an outer ring 2 having a raceway surface 2a facing the raceway surface 1a on the inner peripheral surface, and a raceway between the raceway surfaces 1a and 2a. A plurality of rolling elements (balls) 3, a cage 4 that holds the plurality of rolling elements 3 between the inner ring 1 and the outer ring 2, and a seal that covers the opening of the gap between the inner ring 1 and the outer ring 2 Sealing devices 5 and 5. Note that the cage 4 and the sealing device 5 may not be provided.

  A grease composition G that lubricates between the raceway surfaces 1a and 2a and the rolling element 3 is disposed in a gap formed between the inner ring 1 and the outer ring 2 in which the rolling element 3 is provided. The base oil of the grease composition G is perfluoropolyether oil (PFPE), the thickener is a fluororesin, and inorganic fine particles having a primary particle size of 3 nm to 100 nm are added. The content of the inorganic fine particles is 0.001% by mass or more and 5% by mass or less of the entire grease composition G. Furthermore, the dispersion diameter of the inorganic fine particles in the grease composition G is 3 nm or more and 200 nm or less.

Below, each component which comprises the grease composition G is demonstrated in detail.
[About fluororesin]
The type of the fluororesin that is a thickener is not particularly limited, but polytetrafluoroethylene (PTFE), tetrafluoroethylene and other ethylenically unsaturated hydrocarbon monomers partially or fluorinated (Hereinafter referred to as tetrafluoroethylene copolymer).

Examples of the tetrafluoroethylene copolymer include those shown in the following (A) to (D).
(A) One or more comonomers of perfluoroalkyl-trifluoroethylene ethers, vinylidene fluoride, hexafluoroisobutene, chlorotrifluoroethylene, perfluoroalkylethylenes (for example, perfluoropropene) are added to PTFE as 0 Modified polytetrafluoroethylene copolymerized by 0.01 to 3 mol%, preferably 0.05 to 0.5 mol%.

  (B) Tetrafluoroethylene (TFE) thermoplastic obtained by copolymerizing 0.5 to 8 mol% of at least one perfluoroalkyl vinyl ether (perfluoroalkyl group has 1 to 6 carbons) Copolymer. Examples include a copolymer of perfluoropropyl vinyl ether and TFE, a copolymer of perfluoromethyl vinyl ether and TFE, a copolymer of perfluoroethyl vinyl ether and TFE, and the like.

(C) A TFE thermoplastic copolymer obtained by copolymerizing 2 to 20 mol% of a perfluoroolefin having 3 to 8 carbons. Examples include a copolymer of hexafluoropropene and TFE. The copolymer may be copolymerized with another comonomer having a trifluoroethylene ether structure as long as it is less than 5 mol%.
(D) perfluoromethyl vinyl ether (0.5 to 13 mol%) and one or more (0.05 to 5 mol%) of fluorine compound monomers of the following formulas (I) to (III): A TFE thermoplastic copolymer.

However, R ₄ in the formula (III) is a perfluoroalkyl group having 1 to 5 carbons, and CF ₃ is preferable. X ₁ and X ₂ are each independently a perfluoroalkyl group having 1 to 3 carbons or F, and CF ₃ is preferred.
Further, R _F in the formulas (I) and (II) is at least one of the following (i) to (iii).
(I) Perfluoroalkyl group having 2 to 12 carbons (ii) A chemical structure represented by the following formula (IV). However, r in Formula (IV) is an integer of 1-4, and r 'is an integer of 0-3.

（iii ）下記式（Ｖ）のような化学構造を有するもの。

(Iii) Those having a chemical structure represented by the following formula (V).

However, the structural units (OCFX) and (OCF ₂ CFY) in the formula (V) are statistically distributed along the chain. T is a perfluoroalkyl group having 1 to 3 carbons, and optionally has one H or Cl. Furthermore, X and Y are F or CF ₃ , and Z is —CFX— or —CF ₂ CFY—. Further, q and q ′ are integers of 0 to 10, which are the same or different from each other, and the number average molecular weight of the fluorine compound monomer in that case is 200 to 2000.

  In addition, in (A) to (D), suitable numerical ranges for the numerical value in the molecular formula, the copolymerization ratio, and the average molecular weight are defined as described above, but these numerical values are less than the lower limit of the above range. In such a case, the tetrafluoroethylene copolymer is not imparted with sufficient thickening property to make the grease composition grease-like. If the upper limit of the above range is exceeded, the grease composition will harden and it will be difficult to exhibit sufficient lubricity.

[About base oil]
The kind of perfluoropolyether oil used in the base oil of the grease composition G is not particularly limited, and it is composed of at least one selected from the following fluorooxyalkylene structural units. preferable. X ₃ in the formula is CF ₃ (CF ₂ ) _n —, where n is an integer of 0-4.

When the perfluoropolyether oil is composed of two or more of the above fluorooxyalkylene structural units, each structural unit is statistically distributed along the chain. Then, the terminal _{group, CF 3 -, C 2 F} 5 -, C 3 F 7 -, CF 2 Cl (CF 3) CF-, CF 3 CFClCF 2 -, CF 2 ClCF 2 -, CF 2 Cl-, A fluoroalkyl group optionally having one H and / or Cl, such as CHF ₂ —, CF ₃ CHF— and the like.
Such perfluoropolyether oils include, for example, linear ones represented by the following chemical formula (VI) and branched ones represented by the following chemical formula (VII), for example. There is.

  Rolling bearings built into automotive electrical components such as electric cooling fan motors, electronically controlled throttles, idle rotation control valves (ISCV), and exhaust gas recirculation devices (EGR), and engine auxiliary machines, are in a high temperature environment of 180 ° C or higher. Excellent durability is required. Further, low torque is required for reduction of energy loss and sufficient operability in a low temperature environment of −30 ° C. or lower.

For the rolling bearing for such use, it is preferable to use a grease composition based on a linear perfluoropolyether oil as represented by the chemical formula (VI) as a lubricant. Since the linear perfluoropolyether oil has a high viscosity index and the change in viscosity with temperature is small, the rolling bearing can have a low torque over a wide temperature range.
In order to suppress the occurrence of abnormal noise at low temperature startup due to insufficient low temperature fluidity of the grease composition and seizure that occurs because an oil film is hardly formed at high temperature, the kinetic viscosity of PFPE at 40 ° C. is 20 to 20 ° C. is preferably 400 mm ² / s, more preferably 30 to 200 mm ² / s.

[Inorganic fine particles]
The type of inorganic fine particles added to the grease composition G is not particularly limited. For example, metal oxides such as SiO ₂ , TiO ₂ , Al ₂ O ₃ , ZnO, SnO ₂ , and CuO, SiC, and TiC , WC and other metal carbides, Si ₃ N ₄ , TiN, AlN and other metal nitrides, carbon black, diamond and other carbon compounds.

Among these inorganic fine particles, SiO ₂ is preferable when the rolling device such as a rolling bearing is made of bearing steel. Since SiO ₂ has high affinity with bearing steel containing silicon and having a surface covered with an oxide film, an SiO ₂ adsorption film is likely to be formed on the surface of the member made of bearing steel. As a result, the adsorption film further suppresses the occurrence of wear and seizure.

The method for producing the inorganic fine particles is not particularly limited, and can be produced by a known method. For example, vapor phase methods such as chemical vapor deposition (CVD) and physical vapor deposition (PVD), and liquid phase methods such as coprecipitation, metal alkoxide, and sol-gel are available.
Further, in order to prevent aggregation of the inorganic fine particles and improve the dispersibility in the grease composition, the inorganic fine particles may be subjected to a hydrophobic treatment to impart hydrophobicity to the surface. By hydrophobizing the surface of the inorganic fine particles, water uptake can be suppressed and base oil can be taken up selectively and efficiently. The type of the hydrophobizing treatment is not particularly limited, but a treatment using a hydrophobizing agent is preferable.

The type of the hydrophobizing agent is not particularly limited, but those that impart hydrophobicity to the inorganic fine particles by chemical adsorption or physical adsorption on the surface of the inorganic fine particles are preferable. In particular, silane coupling agents, titanate coupling agents, aluminum coupling agents, silane compounds (chlorosilane, alkoxysilane, silazane, etc.), silicone oils (modified silicone oil, dimethylpolysiloxane, methylhydrogen polysiloxane, etc.), Higher fatty acids, higher fatty acid salts (wax, higher fatty acid glyceryl, higher fatty acid polyvalent metal salts, etc.), polyvalent metal salts of sulfonic acids having higher aliphatic hydrocarbon groups, higher alcohols, higher alcohol derivatives, and organic fluorine compounds ( Higher fatty acids, higher alcohols and the like partially or wholly fluorinated) are preferred. These may be used alone or in combination of two or more.
Furthermore, silicon dioxide that has been subjected to a hydrophobic treatment with an organosilicon compound such as a silane coupling agent or silicon oil is more preferred. Since the organosilicon compound and silicon dioxide have a high affinity, the surface of the silicon dioxide can be hydrophobized densely by performing a hydrophobization treatment with the organosilicon compound. Therefore, the addition effect of silicon dioxide can be greatly enhanced.

[Additives]
An additive generally used for grease may be added to the grease composition G together with inorganic fine particles. For example, antioxidants, rust inhibitors, antiwear agents, extreme pressure agents, dispersants, metal protective agents, surfactants and the like can be mentioned. Examples of the rust preventive include vaporizable rust preventives such as benzotriazole, dicarboxylates such as sodium sebacate, magnesium oxide, sodium nitrite, and the like. These additives may be used independently and may be used in combination of 2 or more types as appropriate. However, the total content of additives is preferably 15% by mass or less based on the entire grease composition.

  In addition, this embodiment shows an example of this invention and this invention is not limited to this embodiment. For example, in the present embodiment, a deep groove ball bearing has been described as an example of the rolling device, but the present invention can be applied to various types of other rolling bearings. For example, radial rolling bearings such as angular contact ball bearings, self-aligning ball bearings, cylindrical roller bearings, tapered roller bearings, needle roller bearings, and self-aligning roller bearings, and thrust types such as thrust ball bearings and thrust roller bearings This is a rolling bearing. Furthermore, the present invention can be applied not only to rolling bearings but also to various types of various rolling devices. For example, a ball screw, a linear guide device, a linear motion bearing, or the like.

〔Example〕
Hereinafter, the present invention will be described more specifically with reference to examples. Nine types of grease compositions having the compositions shown in Tables 1 and 2 were prepared, and their seizure resistance and wear resistance were evaluated.

First, the grease composition will be described. In any grease composition, a base grease using a perfluoropolyether oil having a side chain (kinematic viscosity at 40 ° C. of 88 mm ² / s) and polytetrafluoroethylene as a thickener is used as an inorganic fine particle. Is added.
As the inorganic fine particles, silica (SiO ₂ ), titanium oxide (TiO ₂ ), zinc oxide (ZnO), copper oxide (CuO), carbon black (CB), and diamond (CD) are used. In this case, it is 0.05% by mass of the entire grease composition.

The inorganic fine particles described in Tables 1 and 2 are as follows.
Silica A: Hydrophobized silica fine particles (primary particle size 12 nm, aspect ratio 1.2)
Silica B: hydrophilic fumed silica (primary particle size 12 nm, aspect ratio 1.3)
Silica C: hydrophobic fumed silica (primary particle size 16 nm, aspect ratio 1.4)
Titanium oxide: manufactured by vapor phase method (primary particle size 35 nm, aspect ratio 1.1)
-Zinc oxide: manufactured by vapor phase method (primary particle size 35nm, aspect ratio 3.3)
Copper oxide: manufactured by a vapor phase method (primary particle size 48 nm, aspect ratio 1.3)
CB: having hollow shell particles (primary particle size 40 nm, aspect ratio 1.7) CD: manufactured by gas phase method (primary particle size 5 nm, aspect ratio 1.1)

  Such a grease composition was produced by adding inorganic fine particles to the base grease and then applying it to three rolls. However, in the case of silica A, a grease composition was produced as follows. A dispersion of silica fine particles in isopropyl alcohol was added to the base grease and heated to 80 ° C. with stirring to evaporate the isopropyl alcohol. And after confirming that the isopropyl alcohol did not remain | survive with a Fourier-transform infrared spectroscopy analyzer, it applied to 3 rolls.

[Evaluation method for seizure resistance]
A test bearing in which 5 g of a grease composition was sealed in a rolling bearing having a nominal number of 6306 VV was prepared. This test bearing was mounted on a test machine similar to the bearing life tester specified in ASTM D1741, and rotated under conditions of a temperature of 220 ° C., a radial load of 686 N, an axial load of 490 N, and a rotational speed of 8000 min ⁻¹ . And the time until the drive motor which rotates a test bearing stops by an overload, or bearing temperature exceeds 230 degreeC was measured. Ten pieces per one test bearing performs rotation test, and the L ₁₀ life and seizure life. The results are shown in Tables 1 and 2. Note that the seizure life shown in Tables 1 and 2 is shown as a relative value when the seizure life of the comparative example to which inorganic fine particles are not added is 1.

[Evaluation method for wear resistance]
Abrasion resistance was evaluated using a tester similar to the high-speed four-ball tester specified in ASTM D 2596. That is, three test balls (SUJ2 steel balls for ball bearings, 1/2 inch in diameter) are arranged and fixed in an equilateral triangle shape so as to contact each other, and one test is performed in a recess formed in the center thereof. A ball was placed. And after apply | coating a grease composition to all the test balls, with the load (surface pressure of 1.5 GPa) loaded, the mounted test balls are kept at a constant speed (sliding speed of 1.5 m / s) for 10 minutes. Rotated. After the rotation, the areas of wear marks generated on three test balls arranged in an equilateral triangle were measured. Such a test was performed 5 times, and the average value of the wear area of a total of 15 test balls was calculated. The results are shown in Tables 1 and 2. The wear areas listed in Tables 1 and 2 are shown as relative values when the wear area of the comparative example to which inorganic fine particles are not added is 1.
As can be seen from Tables 1 and 2, since the grease compositions of Examples 1 to 8 contain inorganic fine particles, they are more resistant to seizure than the grease compositions of Comparative Examples not containing inorganic fine particles. Excellent in wear resistance and wear resistance.

Next, the grease composition of Example 1 was prepared by variously changing the content of the silica fine particles, and the seizure resistance and the wear resistance were evaluated in the same manner as described above. The result is shown in the graph of FIG. The content of silica fine particles is 0.0005% by mass, 0.001% by mass, 0.01% by mass, 0.05% by mass, 0.08% by mass, 0.1% by mass, and 1,5% by mass. 10% by mass. Further, the seizure life and the wear area described in the graph of FIG. 2 are shown as relative values when the seizure life and the wear area of the comparative example to which inorganic fine particles are not added are set to 1.
As can be seen from the graph, when the content of the silica fine particles is 0.001% by mass or more and 5% by mass or less, both seizure resistance and wear resistance are excellent. And when it was 0.01 mass% or more and 0.1 mass% or less, both seizure resistance and abrasion resistance were more excellent.

Next, seven types of grease compositions based on linear perfluoropolyether oil were prepared, and their seizure resistance and torque performance were evaluated. First, the grease composition will be described. In any grease composition, a linear perfluoropolyether oil (kinematic viscosity at 40 ° C. is 85 mm ² / s) is used as a base oil, and polytetrafluoroethylene is used as a thickener. System fine particles are added.
The inorganic fine particles are hydrophobic fumed silica (primary particle size: 12 nm, aspect ratio: 1.3) obtained by subjecting silica to a hydrophobization treatment with dimethyl silicone, and the content thereof is 0% by mass of the entire grease composition. 0.01% by mass, 0.1% by mass, 0.5% by mass, 1% by mass, 5% by mass, and 10% by mass.

[Evaluation method for seizure resistance]
Evaluation of seizure resistance was performed in the same manner as described above. The result is shown in the graph of FIG. Note that the seizure life shown in the graph of FIG. 3 is a relative value when the seizure life of the second base grease to which inorganic fine particles are not added is 1.
[Torque performance evaluation method]
A test bearing in which a grease composition was sealed in a rolling bearing having a nominal number of 608 VV was prepared. The test bearing was rotated under conditions of a temperature of −30 ° C., an axial load of 29.4 N, and a rotational speed of 1800 min ⁻¹ . And the dynamic torque after rotating for 30 minutes on said conditions was measured. The results are shown in the graph of FIG. The dynamic torque described in the graph of FIG. 4 is based on the dynamic torque of the grease composition of the comparative example described above, which is based on perfluoropolyether oil having side chains and does not contain inorganic fine particles. The relative value is shown.

A similar test bearing was rotated under the conditions of room temperature, an axial load of 29.4 N, and a rotational speed of 1800 min ⁻¹ , and the time from the initial rotation to the stabilization of the torque was measured. The results are also shown in the graph of FIG. The torque stabilization time shown in the graph of FIG. 4 is based on the torque stabilization of the grease composition of the above-described comparative example that is based on perfluoropolyether oil having side chains and does not contain inorganic fine particles. The relative value when the time is 1 is shown.

  As can be seen from the graph of FIG. 3, the grease composition containing the linear perfluoropolyether oil as the base oil and containing the inorganic fine particles includes the second base grease containing no inorganic fine particles and In comparison, the seizure resistance was excellent. Further, as can be seen from the graph of FIG. 4, the grease composition containing a linear perfluoropolyether oil as a base oil and containing inorganic fine particles is based on a perfluoropolyether oil having a side chain. The dynamic torque was low and the torque stabilization time was short as compared with the grease composition of the above-mentioned comparative example which was oil and did not contain inorganic fine particles.

[Second Embodiment]
Embodiments of a bearing for an electronic control motor of an automobile according to the present invention will be described in detail with reference to the drawings.
FIG. 5 is a longitudinal sectional view showing the structure of a deep groove ball bearing which is an embodiment of a bearing for an electronic control motor of an automobile according to the present invention. This deep groove ball bearing has an inner ring 1 having a raceway surface 1a on the outer peripheral surface, an outer ring 2 having a raceway surface 2a facing the raceway surface 1a on the inner peripheral surface, and a raceway between the raceway surfaces 1a and 2a. A plurality of rolling elements (balls) 3, a cage 4 that holds the plurality of rolling elements 3 between the inner ring 1 and the outer ring 2, and a sealing device 5 that covers an opening of a gap between the inner ring 1 and the outer ring 2 5 (for example, a contact-type rubber seal or a shield). Note that the cage 4 and the sealing device 5 may not be provided.

In a gap (bearing space) formed between the inner ring 1 and the outer ring 2 in which the rolling element 3 is provided, a grease composition G for lubricating the raceway surfaces 1a, 2a and the rolling element 3 is disposed. Has been. The base oil of this grease composition G is fluoro oil, the thickener is fluoro resin, and ultrafine particles having a primary particle size of 50 nm or less are added.
In such a deep groove ball bearing, since the grease composition G contains ultrafine particles having a primary particle size of 50 nm or less, the torque stability performance compared to the case of using conventional fluorine grease that does not contain ultrafine particles. Is excellent. In addition, the seizure resistance under a high temperature environment of 180 ° C. or higher and the low torque performance over a wide temperature range from low temperature to high temperature have the same or better performance than when using conventional fluorine grease. .
Therefore, the deep groove ball bearing of this embodiment is suitable as a rolling bearing (for example, an electronic control throttle bearing, an ISCV bearing, or an EGR bearing) incorporated in an electronic control motor used in an automobile.

Below, each component which comprises the grease composition G is demonstrated in detail.
[About ultrafine particles]
The type of ultrafine particles is not particularly limited to be contained in the grease composition G, ultrafine particles of an inorganic compound is preferable, for _{example, SiO 2, TiO 2, Al} 2 O 3, ZnO, SnO 2, CuO , etc. Metal carbides such as SiC, TiC and WC, metal nitrides such as Si ₃ N ₄ , TiN and AlN, and carbon compounds such as diamond. Among these, SiO ₂ (silica) is particularly preferable, and hydrophilic silica not subjected to surface treatment or the like is preferable.

  One of the grease characteristics that affects the torque characteristics of rolling bearings is channeling (the groove through which the rolling element passes can be formed on the raceway surface). The higher this channeling ability (the easier the groove through which the rolling element passes). It was found that the torque was stabilized early (that is, the torque stability performance was excellent). It was also found that channeling properties can be improved by strengthening the grease structure and optimizing the flow characteristics of the grease composition. Furthermore, it has been found that by forming a strong grease film with excellent friction and wear characteristics on the raceway surface and the rolling surface of the rolling element, the steady torque is reduced and the wear resistance and seizure resistance are improved.

  The ultrafine particles (preferably silica, more preferably hydrophilic silica) as described above have a strong effect of strengthening the grease structure, and the flow characteristics of the grease composition as described above are optimized and a grease film is formed. Cheap. Therefore, the bearing using the grease composition containing ultrafine particles has excellent torque stability performance. Further, since silica, more preferably hydrophilic silica, has good affinity with the surface of bearing steel such as SUJ2 and stainless steel such as SUS440C, a good film can be formed on the rolling contact surface. It has excellent seizure resistance even under a high temperature environment, and has a low torque over a wide temperature range from low temperature to high temperature.

The production method of the ultrafine particles is not particularly limited, and can be produced by a known method. For example, vapor phase methods such as chemical vapor deposition (CVD) and physical vapor deposition (PVD), and liquid phase methods such as coprecipitation, metal alkoxide, and sol-gel are available.
The content of the ultrafine particles in the grease composition G is not particularly limited, but is preferably 0.01% by mass or more and 5% by mass or less of the entire grease composition G. If the ultrafine particle content is less than 0.01% by mass, a sufficient torque reduction effect may not be obtained. On the other hand, if it exceeds 5% by mass, the ultrafine particles tend to aggregate in the grease composition, which may adversely affect the wear resistance and seizure resistance. In order to make such a problem less likely to occur, the content of the ultrafine particles is more preferably 0.05% by mass or more and 1% by mass or less of the entire grease composition G, and 0.1% by mass or more and 1% or less. More preferably, it is at most mass%.

[About fluororesin]
The type of the fluororesin that is a thickener is not particularly limited, but polytetrafluoroethylene (PTFE), tetrafluoroethylene and other ethylenically unsaturated hydrocarbon monomers partially or fluorinated These copolymers are preferred.
[About base oil]
Although the kind of fluorine oil used as the base oil of the grease composition G is not particularly limited, perfluoropolyether oil (PFPE) is preferable. PFPE includes, for example, a straight chain as represented by the aforementioned chemical formula (VI) and a branched chain as represented by the aforementioned chemical formula (VII).
Since linear PFPE has a high viscosity index and excellent fluidity at extremely low temperatures, it is suitable as a base oil for grease compositions used for bearings for electronic control motors of automobiles.

In order to suppress the generation of noise at low temperature startup due to insufficient low temperature fluidity of the grease composition and seizure that occurs due to the difficulty of forming an oil film at high temperatures, the kinematic viscosity of fluorine oil at 40 ° C. is 20 mm. It is preferably ² / s or more and 400 mm ² / s or less, and more preferably 30 mm ² / s or more and 200 mm ² / s or less. Moreover, in order to ensure the stable fluidity | liquidity over a wide temperature range, it is preferable that the viscosity index of a fluorine oil is 100-400, and it is more preferable that it is 200-400.

[Additives]
To the grease composition G, an additive generally used in the grease composition may be added together with the ultrafine particles. For example, antioxidants, rust inhibitors, metal deactivators, oiliness agents, antiwear agents, extreme pressure agents and the like can be mentioned.
As the rust preventive, it is preferable to select a rust inhibitor that exhibits an effect from a high temperature to a low temperature, or that does not lose its effect even after being exposed to a high temperature. For example, benzotriazole compounds such as benzotriazole, carboxylate compounds such as sodium sebacate, and inorganic salt compounds such as sodium nitrite are preferable. These additives may be used independently and may be used in combination of 2 or more types as appropriate.

  In addition, this embodiment shows an example of this invention and this invention is not limited to this embodiment. For example, in the present embodiment, a deep groove ball bearing has been described as an example of a rolling bearing, but the present invention can be applied to various types of rolling bearings. For example, radial rolling bearings such as angular contact ball bearings, self-aligning ball bearings, cylindrical roller bearings, tapered roller bearings, needle roller bearings, and self-aligning roller bearings, and thrust types such as thrust ball bearings and thrust roller bearings This is a rolling bearing.

〔Example〕
Hereinafter, the present invention will be described more specifically with reference to examples. Three types of grease compositions having the following compositions were prepared, and their torque and seizure resistance were evaluated.
First, the grease composition will be described. The grease compositions of Examples 11 and 12 are base greases using linear PFPE (kinematic viscosity at 40 ° C. of 85 mm ² / s and viscosity index of 286) as a base oil and PTFE as a thickener. (This is referred to as Comparative Example 11) to which 0.5% by mass of ultrafine particles of the entire grease composition is added.

  The ultrafine particles added to the grease composition of Example 11 are hydrophilic silica (fumed silica) having a primary particle size of 12 nm, and the ultrafine particles added to the grease composition of Example 12 are hydrophobic having a primary particle size of 16 nm. Silica (having fumed silica hydrophobized). In addition, the blending degrees of the grease compositions of Examples 11 and 12 and Comparative Example 11 were all 280.

[Torque test at room temperature]
A grease composition is sealed in a deep groove ball bearing with a shield plate having an inner diameter of 8 mm, an outer diameter of 22 mm, and a width of 7 mm, and is rotated under conditions of an inner ring rotational speed of 1800 min ⁻¹ , an ambient temperature of 30 ° C., a radial load of 0 N, and an axial load of 29.4 N. It was. The torque half-time is measured, and the time until the intermediate value between the initial torque value and the steady-state torque value (hereinafter referred to as torque half-life) is measured. Thus, the torque stability performance was evaluated. Note that the amount of the grease composition enclosed is 30% by volume of the bearing space volume.
First, the change over time in the torque value is shown in the graph of FIG. The torque values in this graph are shown as relative values when the initial torque value of the grease composition of Comparative Example 11 is 1. From the graph of FIG. 6, it can be seen that the torques of the grease compositions of Examples 11 and 12 are reduced earlier than the grease composition of Comparative Example 11.

  Next, the measurement result of the torque half-life indicating the degree of decrease in the torque value is shown in the graph of FIG. The torque half-life in this graph is shown as a relative value when the torque half-life of the grease composition of Comparative Example 11 is 1. As can be seen from the graph of FIG. 7, the grease compositions of Examples 11 and 12 containing ultrafine particles had a shorter torque half-life than the grease composition of Comparative Example 11 containing no ultrafine particles. And hydrophilic silica had shorter torque half-life than hydrophobized silica.

[Torque test at low temperature]
The grease composition of Example 11 was prepared by changing the ultrafine particle content from 0.005% by mass to 8% by mass. These grease compositions had a penetration of 220-280. Then, the same amount of grease composition is enclosed in the same deep groove ball bearing as in the torque test at room temperature described above, and the deep groove ball bearing is rotated under the same conditions except that the ambient temperature is −40 ° C. Torque value (low temperature torque) was measured.
The measurement results are shown in the graph of FIG. The low temperature torque in this graph is shown as a relative value when the low temperature torque of the grease composition of Comparative Example 11 is 1. As can be seen from the graph of FIG. 8, the torque at low temperature was low when the content of the ultrafine particles was 0.01 to 5 mass%.

[About seizure test at high temperature]
The grease composition used in the above-mentioned low temperature torque test is sealed in a deep groove ball bearing with a contact type rubber seal having an inner diameter of 17 mm, an outer diameter of 40 mm, and a width of 12 mm, and the inner ring rotational speed is 6000 min ⁻¹ , the bearing outer ring temperature is 200 ° C., and the radial load is It was rotated under conditions of 19.6 N and axial load 196 N, and the time until seizure occurred was measured. Performed 10 test per one bearing calculates the L ₁₀ life was the value as seizure life of the bearing. Note that the amount of the grease composition enclosed is 30% by volume of the bearing space volume.
The results are shown in the graph of FIG. The seizure life in this graph is shown as a relative value when the seizure life of the grease composition of Comparative Example 11 is 1. As can be seen from the graph of FIG. 8, when the content of the ultrafine particles is 0.01 to 5% by mass, the seizure life is excellent.

[Torque test at high temperature]
The grease composition of Example 11 described above was prepared by changing the primary particle size of the ultrafine particles to 7 nm, 12 nm, 16 nm, 20 nm, 30 nm, 50 nm, and 70 nm, respectively. Then, the same amount of grease composition is enclosed in the same deep groove ball bearing as in the torque test at room temperature described above, and the deep groove ball bearing is rotated under the same conditions except that the ambient temperature is 100 ° C. The constant torque value (high temperature torque) was measured.

The measurement results are shown in the graph of FIG. The torque half-life in this graph is shown as a relative value when the torque half-life of the grease composition of Comparative Example 11 is 1. Further, the high temperature torque in this graph is shown as a relative value when the high temperature torque of the grease composition of Comparative Example 11 is 1.
As can be seen from the graph of FIG. 9, when the primary particle size of the ultrafine particles was 50 nm or less, the torque decreased early and the torque at high temperature (torque value under actual use conditions) was low.

  The grease composition and rolling device of the present invention are suitable for use at high temperatures. For example, it can be suitably used for rotating parts and sliding parts of equipment used at high temperatures such as automobile electrical parts such as alternators and electromagnetic clutches and automobile engine accessories such as idler pulleys.

It is a longitudinal cross-sectional view which shows the structure of the deep groove ball bearing which is one Embodiment of the rolling device which concerns on this invention. It is a graph which shows the correlation with content of a silica fine particle, a seizure lifetime, and a wear area. It is a graph which shows the correlation with content of a silica fine particle, and a seizure lifetime. It is a graph which shows the correlation with content of a silica fine particle, dynamic torque, and torque stabilization time. 1 is a longitudinal sectional view showing a structure of a deep groove ball bearing which is an embodiment of a bearing for an electronic control motor of an automobile according to the present invention. It is a graph which shows the result (time-dependent change of a torque value) of the torque test in normal temperature. It is a graph which shows the result (measurement result of a torque half life) of the torque test in normal temperature. It is a graph which shows the correlation with content of an ultrafine particle, low temperature torque, and a seizure lifetime. It is a graph which shows the result of the torque test in high temperature.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Inner ring 1a Raceway surface 2 Outer ring 2a Raceway surface 3 Rolling element G Grease composition

Claims (9)

  A grease composition comprising a base oil and a thickener, wherein the base oil is perfluoropolyether oil, the thickener is a fluororesin, and inorganic fine particles having a primary particle size of 3 nm to 100 nm. A grease composition characterized by being added.   The grease composition according to claim 1, wherein the content of the inorganic fine particles is 0.001% by mass or more and 5% by mass or less.   The grease composition according to claim 1 or 2, wherein a dispersion diameter of the inorganic fine particles is 3 nm or more and 200 nm or less.   The grease composition according to claim 1, wherein the inorganic fine particles are silicon dioxide that has been surface-treated with an organosilicon compound.   The grease composition according to any one of claims 1 to 4, wherein the perfluoropolyether oil is linear.   An inner member having a raceway surface on the outer surface, an outer member having a raceway surface opposite to the raceway surface of the inner member, and arranged on the outer side of the inner member, and rolling between the both raceway surfaces A rolling device comprising a plurality of freely arranged rolling elements, and a lubricant that lubricates between the raceway surface and the rolling elements, wherein the lubricant is any one of claims 1 to 5. A rolling device characterized by comprising the grease composition described in 1.   The rolling device according to claim 6, wherein the rolling device is a rolling bearing incorporated in an electrical component of an automobile or an engine auxiliary machine of the automobile.   A grease composition comprising fluorine oil, a fluororesin, and ultrafine particles having a primary particle size of 50 nm or less. An inner ring having a raceway surface on the outer surface, an outer ring having a raceway surface facing the raceway surface of the inner ring, a plurality of rolling elements arranged to roll between the raceway surfaces, the both raceway surfaces and the rolling surface. A rolling bearing that is incorporated in an electronic control motor used in an automobile.
A bearing for an electronic control motor of an automobile, wherein the lubricant is a grease composition containing fluorine oil, a fluororesin, and ultrafine particles having a primary particle size of 50 nm or less.

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