JP2020193287A - Conductive grease composition - Google Patents

Abstract

To provide the conductive grease composition that prevents electrolytic corrosion in a rolling bearing and has excellent corrosion resistance.SOLUTION: The problem can be solved by the conductive grease composition comprising 40 to 95 mass% of a lubricating oil base oil, 2 to 40 mass% of a thickener, and 0.1 to 18 mass% of a phosphonium-based ionic liquid.SELECTED DRAWING: None

Description

The present invention relates to a conductive grease composition. The present invention relates in detail to a conductive grease composition capable of preventing electrolytic corrosion in a rolling bearing and further having excellent corrosion resistance. The present invention also relates to a method for preventing electrolytic corrosion in a rolling bearing using a conductive grease composition.

Rolling bearings such as ball bearings and roller bearings are used in electrical components and auxiliary machinery such as automobiles and precision machinery such as copiers. In such a rolling bearing, electrolytic corrosion due to a potential difference may occur between the inner ring and the outer ring, and the surface of the rolling bearing may be damaged.

Grease is mainly used to lubricate rolling bearings. Grease is a lubricant in which a solid thickener having a strong lipophilicity is dispersed in a base oil to make it semi-solid. A technique for preventing electrolytic corrosion of rolling bearings by adding a substance such as carbon black to this grease is known (Patent Document 1).
However, in this technique, with the passage of time, the conductive grease containing carbon black is removed from the contact surface and / or the chain structure of the carbon black particles is destroyed, so that the conductivity decreases with time. Therefore, there is a risk of electrolytic corrosion. It is also possible that carbon black particles cause dust.

Further, since the inside of an automobile or the like or a precision machine is hermetically sealed and becomes hot, a conductive grease having durability and corrosion resistance is required.

Japanese Unexamined Patent Publication No. 2002-53890

The present invention has been made in view of such a situation, and an object of the present invention is to provide a conductive grease composition capable of preventing electrolytic corrosion in a rolling bearing and further having excellent corrosion resistance.

As a result of diligent research to solve this problem, the present inventors surprisingly added a lubricating oil base oil, a thickener, and a phosphonium-based ionic liquid to the grease in a specific ratio. , It has been found that it is possible to provide a conductive grease composition which not only can prevent electrolytic corrosion in rolling bearings but also has excellent corrosion resistance. That is, the present invention has been made based on such findings, and is as follows.

[1] A conductive grease composition containing 40 to 95% by mass of a lubricating oil base oil, 2 to 40% by mass of a thickener, and 0.1 to 18% by mass of a phosphonium-based ionic liquid.
[2] The conductive grease composition according to [1], wherein the cation portion of the phosphonium-based ionic liquid is at least one selected from tributyllaurylphosphonium cation and trihexyltetradecylphosphonium cation.
[3] The conductive grease composition according to [1] or [2], wherein the dielectric breakdown voltage measured in accordance with JIS C 2101 is 32 kV or less.
[4] The conductive grease composition according to any one of [1] to [3], wherein the thickener is a urea-based thickener and / or a metallic soap-based thickener.
[5] A method for preventing electrolytic corrosion in a rolling bearing, which comprises using the conductive grease composition according to any one of [1] to [4].

According to the conductive grease composition of the present invention, even if carbon black is not contained, electrolytic corrosion in the rolling bearing can be prevented, and a conductive grease composition having excellent corrosion resistance can be provided.

[1. Conductive grease composition]
The conductive grease composition of the present invention contains 40 to 95% by mass of a lubricating oil base oil, 2 to 40% by mass of a thickener, and 0.1 to 18% by mass of a phosphonium-based ionic liquid.

[Lubricating oil base oil]
As the lubricating oil base oil of the present invention, the lubricating oil base oil used in ordinary greases can be used, but those having a kinematic viscosity at 40 ° C. of ²⁰ to 500 mm ² / s are preferable, and 50 to 300 mm ² / S is more preferable. By setting the kinematic viscosity at 40 ° C. in the above range, a conductive grease composition having a desired consistency can be easily prepared.

As the lubricating oil base oil, an ether-based base oil is preferably used. The ether-based base oil consists of an ether compound having an ether bond in the molecule. The molecule preferably consists of only carbon, hydrogen and oxygen, and preferably does not contain halogen such as fluorine. As the ether compound, diaryl ether, particularly preferably having 12 to 60 carbon atoms and further preferably 18 to 36 carbon atoms. Such diaryl ethers include diphenyl ethers and alkylated diphenyl ethers in which the hydrogen of the phenyl group is replaced with 1 to 4 linear or branched alkyl groups. A particularly preferred lubricating oil base oil is dialkyldiphenyl ether. Although it may contain a base oil other than the ether-based base oil, it is preferably 30% by mass or less, particularly preferably 10% by mass or less, based on the total base oil.

In the conductive grease composition of the present invention, the content of the lubricating oil base oil is 40 to 95% by mass, preferably 50 to 90% by mass, more preferably 60 to 80% by mass, based on the conductive grease composition. Most preferably, it is 65 to 75% by mass.

[Thickener]
As the thickener of the present invention, any thickener used in ordinary grease can be used without any particular problem, but a metal soap-based thickener and / or a urea-based thickener should be used. Is preferable. The thickener may be used alone or in combination of two or more. The content of the thickener may be such that a desired consistency can be obtained, for example, 2 to 40% by mass, more preferably 5 to 30% by mass, still more preferably 10 to 10% by mass based on the total amount of the conductive grease composition. It is 20% by mass.

Of these, the metal soap-based thickener is a thickener composed of a carboxylic acid metal salt, but the carboxylic acid may be a carboxylic acid derivative having a hydroxy group or the like.
The carboxylic acid may be an aliphatic carboxylic acid such as stearic acid or azelaic acid, or an aromatic carboxylic acid such as terephthalic acid, but a monovalent or divalent aliphatic carboxylic acid, particularly an aliphatic carboxylic acid having 6 to 20 carbon atoms. Carboxylic acid is used. In particular, a monovalent aliphatic carboxylic acid having 12 to 20 carbon atoms and a divalent aliphatic carboxylic acid having 6 to 14 carbon atoms are preferably used. A monovalent aliphatic carboxylic acid containing one hydroxyl group is preferable.
The metal may be an alkali metal such as lithium or sodium, an alkaline earth metal such as calcium, or an amphoteric metal such as aluminum, but an alkali metal, particularly lithium, is preferably used.

This thickener may be blended in the form of metal soap, but carboxylic acid and a metal source (metal salt, metal salt hydroxide, etc.) are blended separately and reacted at the time of grease preparation to form a metal. It may be used as a soap thickener.
Such a carboxylic acid metal salt may be used alone or in admixture of a plurality of types. For example, a mixture of lithium 12-hydroxystearate and lithium azelaate is particularly preferred.

As the thickener added to the conductive grease composition of the present invention, a urea-based thickener can be used.
As the urea-based thickener, for example, a diurea compound obtained by a reaction between diisocyanate and monoamine, a polyurea compound obtained by a reaction between diisocyanate and monoamine, and a diamine can be used.

The diisocyanate is a compound in which two hydrogens of a hydrocarbon are substituted with an isocyanate group, and phenylenediisocyanate, tolylene diisocyanate, diphenyldiisocyanate, diphenylmethanediisocyanate, octadecanediisocyanate, decandiisocyanate, hexanediisocyanate and the like are preferable, and hydrocarbons are used. The hydrogen may be a non-cyclic hydrocarbon or a cyclic hydrocarbon, and may be an aromatic hydrocarbon, an alicyclic hydrocarbon, or an aliphatic hydrocarbon. The carbon number is preferably 4 to 20, particularly 8 to 18.

The monoamine is a compound in which one hydrogen of ammonia is substituted with a hydrocarbon group, and octylamine, dodecylamine, hexadecylamine, stearylamine, oleylamine, aniline, p-toluidine, cyclohexylamine and the like are preferable. The diamine is a compound in which two hydrogens of ammonia are substituted with a hydrocarbon group, and ethylenediamine, propanediamine, butanediamine, hexanediamine, octanediamine, phenylenediamine, tolylenediamine, xylenediamine, diaminodiphenylmethane and the like are preferable. .. The hydrocarbon group of monoamine or diamine may be a non-cyclic hydrocarbon group or a cyclic hydrocarbon group, and may be an aromatic hydrocarbon group, an alicyclic hydrocarbon group, or an aliphatic hydrocarbon group. The carbon number is preferably 2 to 20, particularly preferably 4 to 18.

As the urea-based thickener, a diurea compound, particularly an aromatic hydrocarbon as a diisocyanate, and an alkylenediaryldiisocyanate such as methylene diphenyl diisocyanate are preferable. The carbon number is preferably 12 to 24. Further, as the monoamine, an aromatic amine, an alicyclic amine or an aliphatic amine can be used, and a mixed amine obtained by mixing these can be used. It is preferable to use an alicyclic amine and an aromatic amine in combination, and it is more preferable to use cyclohexylamine and p-toluidine in combination.

The urea-based thickener of the present invention is preferably a diurea compound represented by the formula (2).
R ^11- NHCONH-R ^12- NHCONH-R ¹³ (2)
(In the formula, R ¹¹ and R ¹³ may be the same or different, respectively, and represent a hydrocarbon group having 4 to 20 carbon atoms, and R ¹² is a divalent aromatic hydrocarbon group having 6 to 24 carbon atoms. Show.)

[Ionic liquid]
The conductive grease composition of the present invention contains an ionic liquid, specifically a phosphonium-based ionic liquid. The ionic liquid refers to a substance that becomes liquid at around room temperature (for example, 25 ° C.) even though it is an ionic bonding compound composed of a cation component and an anion component. The content of the phosphonium-based ionic liquid is 0.1 to 18% by mass, preferably 0.1 to 16% by mass, more preferably 0, based on the total amount of the grease composition in consideration of manufacturing cost and corrosion resistance. 1 to 15% by mass, more preferably 0.1 to 12% by mass, and most preferably 0.5 to 12% by mass.
Surprisingly, in the conductive grease composition of the present invention, a sufficient effect of reducing the dielectric breakdown voltage can be obtained even when a small amount of ionic liquid (for example, 1% or 2.5%) is blended. Good corrosion resistance can be achieved.

化１において、式中のＲ、Ｒ’、Ｒ''、Ｒ''' は、水素、炭化水素含有基、又はアルキル基であり、同一でも、それぞれ異なっていてもよい。また、化１においてアニオン成分（Ｘ^- ）としては、ハロゲン化物イオン、ＳＣＮ^-、ＢＦ₄ ^-、ＣｌＯ₄ ^-、ＰＦ₆ ^-、（ＣＦ₃ＳＯ₂）₂Ｎ^-、（ＣＦ₃ＣＦ₂ＳＯ₂）₂Ｎ^-、ＣＦ₃ＳＯ₃ ^-、ＣＦ₃ＣＯＯ^-、Ｐｈ₄Ｂ^-、（ＣＦ₃ＳＯ₂）₃Ｃ^- 、ＰＦ₃（Ｃ₂Ｆ₅）₃ ^- 等が挙げられる。
他のイオン液体（例えば、イミダゾリウム系、ピリジン系等）は腐食性が問題となることも多かった。ホスホニウム系イオン液体を使用することで導電性及び耐腐食性の両方を併せ持つグリースを提供できたことは、驚くべきことである。 In the conductive grease composition of the present invention, a phosphonium-based ionic liquid is used as the ionic liquid. In the present specification, the "phosphonium-based ionic liquid" is an ionic liquid having a quaternary phosphonium cation (see Chemical formula 1 below) as a cation portion. In the conductive grease composition of the present invention, it is preferable to use a phosphonium-based ionic liquid having a tributyllaurylphosphonium cation or a trihexyltetradecylphosphonium cation as a cation moiety, and tributyllaurylphosphonium bis (trifluoromethanesulfonyl) imide and trihexyltetra. It is more preferable to use at least one phosphonium-based ionic liquid selected from decylphosphonium bis (trifluoromethanesulfonyl) imide.

In Chemical formula 1, R, R', R'', and R''' in the formula are hydrogen, hydrocarbon-containing groups, or alkyl groups, and may be the same or different from each other. Further, the anion component in Formula 1 ^- include halide ^{ions, SCN (X) -, BF} 4 -, ClO 4 -, PF 6 -, (CF 3 SO 2) 2 N -, (CF 3 CF 2 SO 2 _{^{) 2 N -, CF 3 SO}} 3 -, CF 3 COO -, Ph 4 B -, (CF 3 SO 2) 3 C -, PF 3 (C 2 F 5) 3 - , and the like.
Corrosion was often a problem for other ionic liquids (for example, imidazolium-based, pyridine-based, etc.). It is surprising that the use of phosphonium-based ionic liquids has provided a grease that is both conductive and corrosion resistant.

[Other additives]
In addition to the above components, the grease composition of the present invention contains, if necessary, a cleaning agent, a dispersant, an anti-wear agent, a viscosity index improver, an antioxidant, and a pole, which are generally used for lubricating oils and greases. A pressure agent, a rust preventive, a corrosion inhibitor and the like can be appropriately added. Examples of the antioxidant include phenolic compounds such as 2,6-di-t-butylphenol and 2,6-di-t-butyl-p-cresol, dialkyldiphenylamine, phenyl-α-naphthylamine, and p-alkylphenyl. Examples thereof include amine compounds such as −α-naphthylamine. Examples of the rust preventive include amines, neutral or hyperbasic petroleum-based or synthetic oil-based metal sulfonates, metal soaps, esters, phosphoric acid, phosphates and the like.

[Dielectric breakdown voltage]
Dielectric breakdown is a phenomenon in which when the voltage applied to an insulator exceeds a certain limit, the insulator is electrically destroyed and loses its insulating property to allow current to flow. The dielectric breakdown voltage is the voltage at which dielectric breakdown occurs in an object. If the breakdown voltage is high, a large current will suddenly flow, which can cause serious electrolytic corrosion. In the conductive grease composition of the present invention, the dielectric breakdown voltage is low, and therefore, electrolytic corrosion of the rolling bearing can be effectively prevented. In the conductive grease composition of the present invention, the dielectric breakdown voltage is preferably 32 kV or less when performed in accordance with JISC 2101.

[2. How to prevent electrolytic corrosion in rolling bearings]
[Rolling bearing]
A rolling bearing is a type of bearing composed of a raceway ring, a rolling element, and a cage. In rolling bearings, electric discharge may occur between the raceway ring and the rolling element, and electrolytic corrosion may occur on the raceway surface and the rolling surface. The electrolytic corrosion generated due to such a cause causes wear on the raceway surface and the rolling surface, causes deterioration of the lubricating oil, and causes an increase in vibration and noise. By using the conductive grease composition of the present invention for lubrication of rolling bearings, electrolytic corrosion of rolling bearings can be effectively prevented. Further, the conductive grease composition of the present invention can be suitably used for preventing electrolytic corrosion inside automobiles and precision machinery.

The present invention will be described below with reference to examples that are embodiments of the present invention. The present invention is not limited to the following embodiments. Unless otherwise specified,% indicates mass%.

[Preparation method]
A grease composition was prepared in which each component was contained according to the blending amount (indicated by mass%) shown in Table 1. The blending amount of the lubricating oil base oil is the balance obtained by removing the components other than the lubricating oil base oil from the grease composition.

The following components were used.
1. 1. Lubricating oil Base oil: Dialkyldiphenyl ether (kinematic viscosity at 40 ° C; 100 mm ² / s)

2. 2. Thickener: Diurea synthesized from monoamines (cyclohexylamine and p-toluidine) and methylene diphenyl diisocyanate was used as the thickener.

3. 3. Ionic liquid:
The following ionic liquids were used.
Imidazole A: IL-IM2 (manufactured by Koei Chemical Industry Co., Ltd.)
Imidazole B: IL-IM9 (manufactured by Koei Chemical Industry Co., Ltd.)
Pyridine-based C: IL-P14 (manufactured by Koei Chemical Industry Co., Ltd.)
Phosphonium D: Tributyllaurylphosphonium bis (trifluoromethanesulfonyl) imide Phosphonium E: Trihexyltetradecylphosphonium bis (trifluoromethanesulfonyl) imide

4. As other additives, antioxidants and the like were added.

[Evaluation of dielectric breakdown voltage]
-The dielectric breakdown voltage test was conducted in accordance with JISC 2101.
Using opposing spherical electrodes with adjusted gaps between the electrodes, the voltage was increased at a rate of about 3 kV per second and the breakdown voltage at the commercial frequency of the sample oil was measured.

[Evaluation of corrosion resistance]
The corrosion resistance of grease prepared using a method according to ASTM D 1743 was evaluated. The bearing filled with grease was allowed to stand under specified conditions (salt water 0.1%, 25 degrees, 24 hours), and the presence or absence of rust was confirmed (tested at N = 3). Those without rust were evaluated as −, those with rust but with a small number of rust occurrence points were evaluated as +, and those with a large number of rust were evaluated as ++.

〔Evaluation results〕
The evaluation results of dielectric breakdown voltage and corrosion resistance are shown in Tables 1 and 2 below.

If the dielectric breakdown voltage of grease is high, a large current may flow when a constant voltage is applied to the grease. In Comparative Example 1 containing no ionic liquid, the dielectric breakdown voltage showed a high value of 38 kV. In Comparative Examples 2 to 4 containing an ionic liquid other than the phosphonium type, the dielectric breakdown voltage was 22 kV to 26 kV, which was lower than that of Comparative Example 1, but slight corrosion was observed.
On the other hand, in each of Examples 1 to 5 containing the phosphonium-based ionic liquid, the insulation voltage was 19 kV to 31 kV, which was lower than that of Comparative Example 1. In Examples 1 to 3, no corrosion was observed, and good corrosion resistance was exhibited. The dielectric breakdown voltage of Example 5 was 19 kV, which was the best result, but slight corrosion was observed.
From the above results, it is considered that the conductive grease compositions of Examples 1 to 5 containing the phosphonium-based ionic liquid can effectively prevent electrolytic corrosion in the rolling bearing. The dielectric breakdown voltage of the conductive grease of Example 5 was 19 kV, which was particularly good. Further, the conductive grease compositions of Examples 1 to 5 had good corrosion resistance.

The conductive grease composition of the present invention has excellent corrosion resistance and can prevent electrolytic corrosion in rolling bearings.

Claims (5)

A conductive grease composition containing 40 to 95% by mass of a lubricating oil base oil, 2 to 40% by mass of a thickener, and 0.1 to 18% by mass of a phosphonium-based ionic liquid. The conductive grease composition according to claim 1, wherein the cation portion of the phosphonium-based ionic liquid is at least one selected from tributyllaurylphosphonium cation and trihexyltetradecylphosphonium cation. The conductive grease composition according to claim 1 or 2, wherein the dielectric breakdown voltage measured according to JIS C2101 is 32 kV or less. The conductive grease composition according to any one of claims 1 to 3, wherein the thickener is a urea-based thickener and / or a metallic soap-based thickener. A method for preventing electrolytic corrosion in a rolling bearing, which comprises using the conductive grease composition according to any one of claims 1 to 4.