JP2008274021A - Grease composition and rolling apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem that stable removal of electricity is difficult since the number of revolution is usually several hundreds to several thousands per minute in a motor for household electric equipment having an inverter control circuit (a fan motor, a cleaner motor and a washing machine motor), a fan motor for a clean room, a motor for a ventilation fan and a motor for a hot water supply unit. <P>SOLUTION: A grease composition containing 0.1 mass% to 20 mass% of dielectric ceramics having relative permittivity of 3 or higher is filled in the rolling device. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a rolling device in which a grease composition is enclosed, and more particularly to a rolling bearing capable of preventing electrolytic corrosion that can prevent electrolytic corrosion generated between a race and a rolling element due to an electrostatic phenomenon. .

Conventionally, this type of rolling bearing is a relatively small motor such as a motor for household appliances (fan motor, cleaner motor, washing machine motor), fan motor for clean room, motor for ventilation fan, motor for water heater, etc. Used in motors with circuits.
In the above applications, there is a problem that high-frequency current is generated from the inverter circuit, and this current flows between the inner ring, ball, and outer ring in the bearing and generates electrolytic corrosion on the rolling surface (race surface). It was.

As a countermeasure, for example, a rolling bearing capable of preventing electrolytic corrosion in which a resin sleeve made of an insulating material is attached to the outer diameter of the outer ring has been proposed (Patent Documents 1 and 2, etc.).
A rolling bearing has been proposed in which ceramics for the purpose of insulation and long life are used as rolling elements, and the residual austenite of one or both of the bearing rings is 2% by volume or less (Patent Document 3).
In office machine bearings, a bearing provided with an energizing brush may be used (Patent Document 4).
Japanese Utility Model Publication No. 5-89953 JP-A-6-229425 JP 2001-41248 A Utility model registration No. 582960

  Usually, since the rotation speed of the bearing for office machines is about several tens to several hundreds of revolutions per minute, it is possible to cope with such measures. On the other hand, motors for home appliances having an inverter control circuit (fan motors, cleaner motors, washing machine motors), fan motors for clean rooms, motors for ventilation fans, motors for water heaters, etc. are usually several hundred to several thousand revolutions per minute. Therefore, it is difficult to remove static electricity stably. Further, as an important function, it is desirable that the bearing torque is small, and it is preferable that the charge is gently removed through grease.

In order to achieve the above object, the present invention provides a grease composition containing 0.1 to 20% by mass of a dielectric ceramic and having a relative dielectric constant of 3 or more.
The grease composition of the present invention preferably contains either or both of an ionic liquid and conductive carbon black as an additive.
The present invention also provides a rolling device enclosing the grease of the present invention.
In the rolling device of the present invention, it is preferable that the value of “relative dielectric constant / oil film parameter” is 0.8 or more. The oil film parameter is “EHL oil film thickness / synthetic surface roughness”.

In the rolling device of the present invention, a grease composition having a high relative dielectric constant is enclosed, so that even if static electricity is generated between the inner and outer rings, it can be easily mitigated, effectively preventing the occurrence of electrolytic corrosion. it can.
Furthermore, by specifying the impedance characteristics and relative permittivity related to the frequency instead of the DC current resistivity, it is possible to effectively prevent the electrolytic corrosion due to the high frequency noise of the inverter control drive motor. .

Hereinafter, embodiments of the present invention will be described.
In the present invention, there are no restrictions on the type of rolling device and its structure, but the various rolling devices and inverter control drive motors mentioned above are the main targets. In these rolling devices, a grease composition containing 0.1 to 20% by mass of dielectric ceramics and having a relative dielectric constant of 3 or more is used. Further, the value of “relative dielectric constant / oil film parameter” is 0.8 or more.

[Base oil]
The base oil of the grease composition is not particularly limited as long as the relative dielectric constant of the grease composition satisfies 3 or more, but an oil containing a polar group is more preferable.
Usually, all the oils used as the base oil of the lubricating oil can be used. Preferably, the kinematic viscosity at 40 ° C. is preferably 5 mm ² / sec or more and less than 300 mm ² / sec, more preferably 10 mm, from the viewpoint of noise generation at low temperature startup due to insufficient low temperature fluidity and heat resistance at high temperatures. ^A base oil that is ² / sec or more and less than 100 mm ² / sec is desirable.

Specific examples include mineral oil-based, synthetic oil-based, and natural oil-based lubricating oils. As the mineral oil-based lubricating oil, it is possible to use a refined oil obtained by appropriately combining mineral oil under reduced pressure distillation, oil removal, solvent extraction, hydrocracking, solvent dewaxing, sulfuric acid washing, white clay purification, hydrorefining, etc. it can.
Examples of the synthetic oil-based lubricating base oil include hydrocarbon oils, aromatic oils, ester oils, ether oils, polyglycol oils, and the like. Examples of the hydrocarbon oil include normal paraffin, isoparaffin, polybutene, polyisobutylene, 1-decene oligomer, poly-α-olefin such as 1-decene and ethylene co-oligomer, and hydrides thereof.

Examples of the aromatic oil include alkylbenzenes such as monoalkylbenzene and dialkylbenzene, and alkylnaphthalenes such as monoalkylnaphthalene, dialkylnaphthalene and polyalkylnaphthalene.
Preferred examples of the ester oil include a diester oil obtained from a reaction between a dibasic acid and a branched alcohol, and a neopentyl type polyol ester oil obtained from a reaction between a monobasic acid and a polyhydric alcohol. These may be used alone or in combination.

  To disclose specific examples, diesters include dioctyl adipate (DOA), diisobutyl adipate (DIBA), dibutyl adipate (DBA), dibutyl sebacate (DBS), dioctyl sebacate (DOS), methyl acetylricinolate (MAR-). N). Examples of the aromatic ester oil include trioctyl trimellitate (TOTM), tridecyl trimellitate, tetraoctyl pyromellitate and the like. The neopentyl polyol ester is made by reacting a neopentyl polyol having 5 to 12 carbon atoms, preferably 5 to 9 carbon atoms, and an organic acid having 4 to 18 carbon atoms, preferably 6 to 12 carbon atoms.

  The above neopentyl type polyol is a polyhydric alcohol having a neopentyl structure. For example, 2,2-dimethyl-propane-1,3-diol (that is, neopentyl glycol), 2-ethyl-2-butyl-propane- 1,3-diol, 2,2-diethyl-propane-1,3-diol, 2-methyl-2-butyl-propane-1,3-diol, trimethylolethane, trimethylolpropane, trimethylolbutane, pentaerythritol Etc. can be used. Preferred are 2,2-dimethyl-propane-1,3-diol, 2-methyl-2-butyl-propane-1,3-diol, trimethylolpropane and pentaerythritol, particularly preferably 2,2-dimethyl- Propane-1,3-diol, trimethylolpropane, and pentaerythritol.

  Examples of the organic acid include n-butanoic acid, i-butyric acid, n-pentanoic acid, i-valeric acid, n-hexanoic acid, 2-ethylbutanoic acid, i-hexanoic acid, hexahydrobenzoic acid, n -Heptanoic acid, i-heptanoic acid, methylhexahydrobenzoic acid, n-octanoic acid, dimethylhexanoic acid, 2-ethylhexanoic acid, 2,4,4-trimethylpentanoic acid, i-octanoic acid, 3,5,5 5-Trimethylhexanoic acid, n-nonanoic acid, i-nonanoic acid, i-decanoic acid, i-undecanoic acid, 2-butyloctanoic acid, tridecanoic acid, tetradecanoic acid, hexadecanoic acid, octadecanoic acid and the like can be used. Preferred are n-heptanoic acid, n-octanoic acid, dimethylhexanoic acid and 2-ethylhexanoic acid.

The synthesis of neopentyl polyol ester from these organic acids and neopentyl polyol can be carried out by a conventionally known method, for example, dehydration condensation in the presence of an acidic catalyst.
The neopentyl type polyol ester in the composition of the present invention (hereinafter, neopentyl glycol is abbreviated as NPG, trimethylolpropane is abbreviated as TMP, pentaerythritol is abbreviated as PE), for example, NPG di- (heptanoate), NPG di- (2 -Ethyl butyrate), NPG.di- [mixed (hexanoate, heptanoate)], TMP.tri- (pentanoate), TMP.tri- (hexanoate), TMP.tri- [mixed (butyrate, octadecanoate)] , TMP • tri- [mixed (hexanoate, heptanoate, octanoate)], PE • tetra (pentanoate), an ester of PE and a mixture of a linear or branched carboxylic acid having 4 to 8 carbon atoms, and the like.

Also, neopentyl polyols other than NPG, TMP and PE, that is, 2-methyl-2-propyl-1,3-diol, 2,2-dimethyl-propane-1,3-diol, trimethylolethane, trimethylolhexane, Examples thereof include neopentyl type polyol esters with the above organic acids alone or in a mixture.
In order to maintain the intramolecular electric polarity, the base oil preferably has a relatively short hydrocarbon chain length and a small molecular weight. Furthermore, the complex ester oil etc. which are oligoesters of a polyhydric alcohol and the mixed fatty acid of a dibasic acid and a monobasic acid are mentioned.

  Examples of the ether oil include polyglycols such as polyethylene glycol, polypropylene glycol, polyethylene glycol monoether, and polypropylene glycol monoether, or monoalkyl triphenyl ether, alkyl diphenyl ether, dialkyl diphenyl ether, pentaphenyl ether, tetraphenyl ether, and monoalkyl. Examples thereof include phenyl ether oils such as tetraphenyl ether and dialkyl tetraphenyl ether. Other synthetic lubricating base oils include tricresyl phosphate, silicone oil, perfluoroalkyl ether and the like.

Examples of the polyglycol oil include polyethylene glycol, polypropylene glycol, and polyoxyalkylene glycol obtained by copolymerizing propylene oxide and ethylene oxide. Polyglycol oil can be adjusted to be water-soluble or oil-soluble by changing the polymerization ratio of polyethylene glycol and propylene glycol.
Examples of the natural oil-based lubricating base oil include beef tallow, lard, soybean oil, rapeseed oil, rice bran oil, coconut oil, palm oil, palm kernel oil, and other oils and hydrides thereof.

In order to increase the relative dielectric constant of the grease, ester-based oils, ether-based oils and the like in which polar groups are contained in the base oil are more preferable.
These base oils can be used alone or as a mixture, and are adjusted to the above-mentioned preferable kinematic viscosity.

[Thickener]
The thickener is not particularly limited as long as it has a relative dielectric constant of 3 or more as a grease composition and has the ability to retain the above base oil in the gel structure. For example, metal soaps made of Li, Na, etc., metal soaps such as composite metal soaps selected from Li, Na, Ba, Ca, etc., benton, silica gel, conductive carbon, urea compounds, urea / urethane compounds, urethane compounds Non-soaps such as these can be selected and used as appropriate, but considering the heat resistance of the grease, a urea compound, a urea-urethane compound, a urethane compound, or a mixture thereof is preferable.

  Specific examples of the urea compound, urea / urethane compound, and urethane compound include diurea compounds, triurea compounds, tetraurea compounds, polyurea compounds, urea / urethane compounds, diurethane compounds, and mixtures thereof. Among these, diurea compounds , Urea / urethane compounds, diurethane compounds or mixtures thereof are more preferred. In view of heat resistance, it is more desirable to add a diurea compound.

In order to increase the relative dielectric constant as in the present invention, it is preferable to use a thickener containing a metal element such as a metal soap or a metal composite soap. As the fatty acid, C6 to C18 are preferable. Among them, 12-hydroxystearic acid and stearic acid which is beef tallow fatty acid can be exemplified. Among these, lithium 12-hydroxystearate is desirable, and lithium stearate soap improves and promotes fretting resistance and wear resistance. Lithium composite soap is preferable because it has a high dropping point of grease and excellent heat resistance.
The total amount of the thickener is not particularly limited to obtain an appropriate grease consistency, but is about 2 to 30% by mass.

[Dielectric ceramics]
Dielectric ceramics added to increase the relative permittivity of grease include group 4 elements, lanthanoid elements, and group 2 elements alone or in combination. Specific examples of Group 4 elements and lanthanoid elements include titanium (Ti), zirconium (Zr), hafnium (Hf), rutherfordium (Rf), lanthanum (La), cerium (Ce), prasedium (Pr), neodymium (Nd). ), Promethium (Pm), samarium (Sm), and europium (Eu). Specific examples of Group 2 elements include beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra), and Ca, Sr, and Ba are particularly preferable. . Other than the above elements, tin (Sn), antimony (Sb), tellurium (Te), and bismuth (Bi) are suitable.

Specific examples of the dielectric ceramic include barium titanate, strontium titanate, lead zirconate titanate (PZT), lanthanum-lead titanate (PLZT), and lead titanate.
The dielectric ceramic is powdered and added to the grease. The average primary particle diameter of the powder is preferably 2 μm or less. If the grease contains a powder exceeding 2 μm, it is not preferable because it may cause vibration of the bearing.
Along with dielectric ceramics, conductive carbon black is preferred. Specifically, Ketjen Black (Lion), # 3350B, # 3050B, # 3030B (Mitsubishi Chemical), etc. have both conductivity and thickening, so they can be combined with base oils with low relative permittivity. It is suitable for.

[Additive]
(Antioxidant)
An antioxidant is used to prevent oxidation of the grease, and examples thereof include amine-based and phenol-based compounds and zinc dithiocarbamate.
(Rust preventive agent, oil-based agent)
Although overlapping with the surfactants exemplified above, for example, fatty acids such as oleic acid and stearic acid, fatty acid alcohols such as oleyl alcohol, fatty acid esters such as polyoxyethylene stearic acid ester, tricresyl phosphate, lauric acid ester, Phosphoric acid esters such as polyoxyethylene oleyl ether phosphoric acid can be used.

  As a rust preventive agent, oil-soluble sulfonates are often used in metal systems, and examples thereof include barium salts, calcium salts, magnesium salts, sodium salts, zinc salts, aluminum salts, and lithium salts of (petroleum) sulfonates. Other examples of phenates, salicylates, phosphonates, and ashless systems include succinimide, benzylamine, succinic acid ester, succinic acid half ester, polymethacrylate, polybutene, and polycarboxylic acid ammonium salt.

(Antiwear agent)
In order to enhance the load bearing performance, the following additives can be added as needed. For example, dithiocarbamate such as zinc, molybdenum, tellurium, antimony, selenium, iron, copper and combinations thereof, zinc, molybdenum, dithiophosphate such as antimony, etc., iron octylate, copper naphthenate, dibutyltin sulfide, phenate, Organometallic compounds such as phosphate can be used as needed.

(Other additives)
It is effective to add a surfactant, and a liquid one is particularly preferable. Surfactants include sulfonic acid types such as alcohol sulfate, alcohol ethoxy sulfate, alcohol ether sulfate, aromatic ether sulfate, phosphate ester types such as aromatic phosphate ester, aliphatic phosphate ester, sorbidan fatty acid ester, glycerin fatty acid ester, Examples include polyoxyethylene alkyl ether and imidazoline type. As disclosed in Japanese Patent Application Laid-Open No. 2003-42166, metal oxide particles can microscopically smooth an oxide film due to abrasion and unevenness due to electric corrosion, so that a stable function can be maintained for a long time. The total amount of these additives is preferably 10% by mass or less.

  As for the grease used in the present invention, an antioxidant, an oily agent, and an antiwear agent are appropriately added as long as the effect is not impaired. In particular, a viscous liquid at room temperature is preferable because it does not affect the sound and vibration of the bearing when sealed. Further, the additive preferably has an intramolecular polarity, and the additive can increase the electrical orientation in the grease and increase the conductivity.

The additive can enhance various functions of the grease, but may adversely affect the grease properties such as consistency, and the total amount of other additives is preferably less than 10% by mass.
An ionic liquid exhibiting high dielectric properties can be used as an additive. The ionic liquid is also called a room temperature molten salt and is in a liquid state and forms an ionic bond. Specifically, aliphatic amines, alicyclic amines, imidazoliums, pyridines, and the like can be cited as cations. Anions (X ⁻ ) include BF ₄ ⁻ , PF ₆ ⁻ , [(CF ₃ SO ₂ ) ₂ N] ⁻ , Cl ⁻ , Br ^{− and the} like.

An ionic liquid forming an ionic bond is preferable because of its high relative dielectric constant.
The grease consistency is not particularly limited, but NLGI is preferably No. 1 to 4 (mixing consistency 340 to 175). More preferably, about 220-295 is preferable. If the grease is too hard, there is a problem with torque stability, which is not preferable. On the other hand, if it is too soft, grease leaks from the coated part and a sufficient effect cannot be obtained, which is not preferable.

Hereinafter, the present invention will be further described with reference to examples and comparative examples, but the present invention is not limited thereto.
A 6201 type deep groove ball bearing made of bearing steel (SUJ2) (inner diameter 12 mm, outer diameter 32 mm, width 10 mm) was filled with lubricating grease equivalent to 30% of the space volume, and a shield plate was attached. A leakage current from the inverter was passed through the bearing (similar to Japanese Patent Laid-Open No. 2004-92750). The inverter carrier frequency in this example was 16 kHz.

At room temperature, the shaft is supported by another bearing, connected to the motor via a joint, and a leakage current from the inverter is passed through the bearing of this embodiment.
Axial load 39.2N A test was performed at a predetermined rotational speed and time (number of tests n = 3). After the test, using an Anderon device (acoustic measuring device), the increase in the Anderon value before and after the test was less than 3, “◎”, 3 to 5 or less “◯”, 5 to 20 or less “ “Δ”, 20 or more “×”. The table shows the tested grease composition and representative properties.

Although not described in the table, 1% of an amine-based antioxidant and 1% of zinc sulfonate as an antirust agent are added to all examples and comparative examples.
The resistance of the grease was measured with an insulation resistance meter, and the volume low efficiency due to direct current was converted and listed as a reference value. The structural formula of the ionic liquid used is shown below.

<Grease LCR meter measurement>
Grease the electrodes (diameter: 38 mm, thickness: 0.3 mm), connect an LCR meter, and in an atmosphere of 25 ° C., impedance Z (Ω), phase angle θ (°), capacitance C _p (F ), Resistance R _p (Ω) was measured. The measured impedance value was converted to volume resistivity from the cross-sectional area and thickness of the measurement electrode.
The frequency was measured in the range of 50 Hz to 1 MHz. The inverter carrier frequency was evaluated as 16 kHz.

The relative dielectric constant was obtained by substituting into the following equation.
Dielectric constant: εr = √ [(εr ′) ² + (εr ″) ² ]
εr ′: real part of complex permittivity = C _p / C ₀
εr ″: Imaginary part of complex dielectric constant = 1 / (2πf × C ₀ × R _P )
f: Frequency (Hz)
C _p : Capacitance (F) of sample grease
C ₀ : Capacitance (F) of air (with grease removed)
R _P : Resistance of sample grease (Ω)

  In the bearing determination test in the present application, a value of “relative dielectric constant / oil film parameter” is 0.8 or more, and a good value is obtained.

Claims (4)

  A grease composition containing 0.1 to 20% by weight of dielectric ceramics and having a relative dielectric constant of 3 or more.   The grease composition according to claim 1, comprising either or both of an ionic liquid and conductive carbon black as an additive.   A rolling device in which the grease according to claim 1 is enclosed.   The rolling device according to claim 3, wherein the value of “relative permittivity / oil film parameter” is 0.8 or more.