JP6603592B2 - Grease composition and use thereof - Google Patents

Description

  The present invention relates to a grease composition containing onion-like carbon and use thereof.

Conventionally, attempts have been made to add various additives to grease for the purpose of improving the performance of the grease. For example, a solid lubricant is blended with grease for the purpose of improving wear resistance. As the solid lubricant, molybdenum disulfide, graphite, boron nitride or the like is typically used. In recent years, the use conditions of grease have become increasingly severe, and further improvement in wear resistance by a solid lubricant is desired.
Japanese Unexamined Patent Publication No. 2009-63154 (Patent Document 1) has an object to provide a rolling device that has a friction reducing effect and is excellent in seizure resistance and wear resistance and has a long life, and solves such a problem. Therefore, a rolling device has been proposed that is lubricated with grease containing spherical fine particles having a layered structure as an additive. In the example of Patent Document 1, a test grease is prepared by adding onion-like carbon fine particles and an antioxidant to a base grease made of hydrocarbon oil and urea compound, and the grease is sealed in a bearing, in accordance with ASTM D1741. The torque and seizure life of the bearing are evaluated. However, the wear resistance of the bearing has not been evaluated, and the relationship between grease prescription and wear resistance is not clear.

JP2009-63154A

  In order to improve the wear resistance of a grease composition containing a solid lubricant, the present inventors first examined the reason why the conventional solid lubricant cannot sufficiently exhibit the wear resistance. As a result of various investigations, the inventors of the present invention, as one of the reasons described above, have a conventional primary lubricant such as molybdenum disulfide having a relatively large primary particle size of several hundreds of nanometers to several tens of micrometers. Then, it was thought that the particle size was further increased, and it was difficult for the grease to flow into the lubrication part. Accordingly, the present inventors have come to use a material having a relatively small primary particle size, and pay attention to onion-like carbon from among a large number of candidate materials, and use it as a solid lubricant for grease to provide wear resistance. Tried to improve. That is, an object of the present invention is to provide a grease composition containing onion-like carbon having excellent wear resistance and its use.

As a result of diligent studies to achieve the above-mentioned problems, the present inventors have found that the wear resistance of a grease composition can be remarkably improved by combining an aliphatic diurea compound and onion-like carbon. completed.
That is, the gist of the present invention is as follows.
[1] A grease composition containing (a) a thickener, (b) a base oil, and (c) onion-like carbon, wherein the (a) thickener is represented by the following formula (1):
R ¹ —NHCONH—R ² —NHCONH—R ³ (1)
(In the formula, R ¹ and R ³ may be the same or different, and are a linear or branched alkyl group having 5 to 20 carbon atoms, and R ² is a divalent aromatic system having 6 to 15 carbon atoms. (It is a hydrocarbon group)
The grease composition which is an aliphatic diurea compound represented by these.
[2] The grease composition according to [1], wherein the content of (c) onion-like carbon is 0.05 to 10% by mass with respect to the total mass of the grease composition.
[3] The grease composition according to [1] or [2], wherein the base oil is a mineral oil or a synthetic hydrocarbon oil having a kinematic viscosity at 40 ° C. of 70 to 200 mm ² / s.
[4] The grease composition according to any one of [1] to [3], which is used for bearings, gears, or constant velocity joints.

  According to the present invention, the wear resistance of the grease composition, particularly the wear resistance evaluated by ASTM D2266 (high-speed four-ball wear test) can be remarkably improved.

1 is an optical micrograph (objective lens 40 ×, eyepiece 10 ×, photographing magnification 400 ×, scale shown in the drawing) showing the dispersion state of onion-like carbon in the grease composition of Example 3. FIG.

  The grease composition of the present invention contains (a) a thickener, (b) a base oil, and (c) onion-like carbon. Hereinafter, each component will be described in detail.

(a) Thickener Thickener has the formula (1):
R ¹ —NHCONH—R ² —NHCONH—R ³ (1)
(In the formula, R ¹ and R ³ may be the same or different, and are a linear or branched alkyl group having 5 to 20 carbon atoms, and R ² is a divalent aromatic system having 6 to 15 carbon atoms. (It is a hydrocarbon group)
It is an aliphatic diurea compound represented by these.
Specific examples of R ¹ and R ³ include pentyl, hexyl, heptyl, octyl, 2-ethylhexyl, nonyl, decyl, dodecyl, tetradecyl, hexadecyl, octadecyl, icosyl and the like. Especially, C8-C18 linear alkyl groups, such as octyl, nonyl, decyl, dodecyl, tetradecyl, hexadecyl, octadecyl, are preferable, C8-10 linear alkyl groups are more preferable, and octyl is especially preferable.
Specific examples of R ² include phenylene, naphthylene, diphenylmethanediyl, biphenylene (these groups may be substituted by an alkyl group having 1 to 4 carbon atoms such as methyl). Above all, formulas (A) to (C):
Is preferable, and a group represented by the formula (B) is more preferable.
The thickener is obtained by a reaction between an aliphatic monoamine having 5 to 20 carbon atoms and an aromatic diisocyanate having 6 to 15 carbon atoms. Examples of the monoamine include hexylamine, octylamine, 2-ethylhexylamine, nonylamine, decylamine, dodecylamine, tetradecylamine, hexadecylamine, and octadecylamine. These amines may be used alone or in combination of two or more. Examples of the diisocyanate include xylylene diisocyanate, tolylene diisocyanate, naphthalene diisocyanate, diphenylmethane-4,4′-diisocyanate, and tolidine diisocyanate. These diisocyanates may be used alone or in combination of two or more.
In the reaction, the monoamine may be used in an amount of 2 molar equivalents or more based on the diisocyanate. The reaction may be performed at 10 to 150 ° C. in the presence of a solvent. As the solvent, a volatile solvent may be used, but when a base oil is used, the base grease of the present invention is used as it is.
The content of the thickener is, for example, 3 to 25% by mass, preferably 5 to 20% by mass (particularly 6 to 12% by mass) with respect to the total mass of the grease composition.

(b) Base oil The base oil is not particularly limited, and any kind of base oil can be used. Specific examples of the base oil include mineral oil [for example, paraffinic or naphthenic mineral oil], synthetic hydrocarbon oil [for example, poly α-olefin (polymerized linear α-olefin having 6 to 18 carbon atoms such as 1-decene). Oil obtained by hydrogenation), polybutene, alkylnaphthalene, alkylbenzene, ethylene-α-olefin co-oligomer], ester oil [eg, diester, polyol ester], ether oil [eg, polyalkylene glycol, polyphenyl ether ] Etc. are mentioned. These base oils can be used alone or as various mixed oils.
As the base oil, mineral oil, synthetic hydrocarbon oil (especially poly α-olefin) or a mixed oil thereof is preferable, mineral oil or poly-α olefin is more preferable, and mineral oil (particularly paraffinic mineral oil) is most preferable.
Kinematic viscosity at 40 ° C. of the base oil is, for example, a 30~500mm ² / s, preferably from 50 to 300 mm ² / s, more preferably 70~200mm ² / s (e.g., 90~150mm ² / s ). In addition, said kinematic viscosity is measured by the method based on JISK2283.
The content of the base oil is, for example, 70 to 97% by mass, preferably 80 to 95% by mass, based on the total mass of the grease composition.

(c) Onion-like carbon Onion-like carbon is a nanoparticle in which carbon atoms are layered and overlapped like an onion, and is sometimes called carbon onion, multilayer fullerene, fullerene onion or the like.
The average primary particle size of onion-like carbon is, for example, 5 nm to 100 nm (for example, 10 to 50 nm), preferably 5 nm to 30 nm, and more preferably 5 nm to 15 nm. The specific surface area of the onion-like carbon, for example, 20~150m ² / g, preferably 50~120m ² / g, more preferably from 80~90m ² / g.
Onion-like carbon can be highly dispersed in the grease composition. The minimum particle size of the dispersed onion-like carbon is, for example, 0.5 μm or less, preferably 0.2 to 0.4 μm, and the maximum particle size is, for example, 7 μm or less, preferably 1 to 6 μm (particularly 2 The average particle diameter is, for example, 0.3 to 1.8 μm, and preferably 0.5 to 1.0 μm. In addition, the minimum particle size, the maximum particle size, and the average particle size of the dispersed onion-like carbon are equivalent to the circle of each black particle in the optical micrograph using a conventional image analyzer (for example, LUZEX AP manufactured by Nireco Corporation). The diameter can be calculated by preparing a particle size distribution from the equivalent circle diameter and frequency, and reading the minimum particle size, maximum particle size, and peak particle size (average particle size) from the particle size distribution.
The production method of onion-like carbon is not particularly limited. For example, DLC (Diamond like Carbon) powder from hydrocarbon gas (acetylene gas, etc.) by plasma CVD (Chemical Vapor Deposition) at a predetermined temperature (300 ° C. or less, etc.) The DLC powder is heated at a predetermined temperature (such as 1600 to 2000 ° C.) in a vacuum or in an inert gas atmosphere. For details of the exemplified manufacturing method, Japanese Patent No. 5159960 can be referred to.
The content of onion-like carbon is, for example, 0.05 to 10% by mass, preferably 0.05 to 5% by mass, and more preferably 0.1 to 5% by mass with respect to the total mass of the grease composition. % (Particularly 0.1 to 3% by mass). When the content of onion-like carbon is less than 0.05% by mass, the lubricating effect is reduced, and when it exceeds 10% by mass, the lubricating effect is reduced by aggregation without being dispersed.

The grease composition of the present invention can further contain other additives as required. Specific examples of other additives include antioxidants (for example, phenol-based and amine-based), extreme pressure agents (for example, zinc dithiocarbamate, zinc dithiophosphate, organic molybdenum), and rust inhibitors (for example, zinc naphthenate). Carboxylic acids such as Zn sulfonate and Ca sulfonate), viscosity index improvers, dispersants, combinations thereof, and the like. In the present invention, onion-like carbon can be highly dispersed without adding a dispersant to the grease composition.
When other additives are blended in the grease composition, the blending amount varies depending on the type, but is, for example, 0.1 to 10% by mass, preferably 0.5%, based on the total mass of the grease composition. ˜5 mass%.

  Although the penetration degree of the grease composition of this invention is not specifically limited, For example, it is 280-400, Preferably it is 300-380. In addition, the penetration degree is a value measured immediately after mixing the sample 60 times with a specified mixer as defined in JIS K 2220.

  The method for producing the grease composition of the present invention is not particularly limited. For example, a base grease is prepared by reacting an aliphatic monoamine having 5 to 20 carbon atoms with an aromatic diisocyanate having 6 to 15 carbon atoms in a base oil. And a step of adding onion-like carbon to the base grease. Further, in the method for producing a grease composition of the present invention, it is preferable to carry out a dispersion treatment after the above-mentioned step, for example, a step of dispersing the base grease by a three-roll mill (hand-clamped or hydraulic), It is preferable to include a step of dispersing the mixture of the base grease and the onion-like carbon with a three-roll mill (hand-clamped or hydraulic). By these dispersion treatments, the thickener and onion-like carbon can be highly dispersed in the base oil.

  The grease composition of the present invention is excellent in wear resistance and can be suitably used for various applications such as bearings, gears and constant velocity joints.

  Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

Examples 1-4 and Comparative Examples 1-5
<Raw material of test grease>
[Base oil]
Mineral oil (paraffinic, kinematic viscosity at 40 ° C .: 90 mm ² / s)
PAO (PAO8, kinematic viscosity at 40 ° C .: 48.5 mm ² / s)
〔Additive〕
・ Onion-like carbon (OLC-G manufactured by Shinko Seiki Co., Ltd., primary particle size: 10 nm, specific surface area 86 m ² / g)
・ Graphite (CSP-2 manufactured by Fuji Graphite Industry Co., Ltd., primary particle size: 42 μm or less)
・ Molybdenum disulfide (SF-O manufactured by Daizo Co., Ltd., primary particle size: 0.45 μm)

<Preparation of test grease>
In the base oil, diphenylmethane diisocyanate and octylamine were reacted at a molar ratio of 1: 2, heated and cooled, and then milled with a three-stage roll mill to obtain a base grease (Comparative Example 1). A predetermined amount of the additives shown in Table 1 was mixed with the base grease, milled with a hydraulic three-stage roll mill, and defoamed to obtain grease compositions of Examples 1 to 5 and Comparative Examples 2 to 3.
In the base oil, diphenylmethane diisocyanate, cyclohexylamine, and stearylamine were reacted at a molar ratio of 1: 1: 1. After heating and cooling, milling was performed with a three-stage roll mill to obtain a base grease. A predetermined amount of the following additives was mixed with the base grease, milled with a hydraulic three-stage roll mill, and defoamed to obtain a grease composition of Comparative Example 4.
In the base oil, diphenylmethane diisocyanate and p-toluidine were reacted at a molar ratio of 1: 2, the temperature was raised and cooled, and then milled with a three-stage roll mill to obtain a base grease. A predetermined amount of the following additives was mixed with the base grease, milled with a hydraulic three-stage roll mill, and defoamed to obtain grease compositions of Comparative Examples 5-6.
The base oil was mixed with lithium 12 hydroxystearate, heated and cooled, and then milled with a three-stage roll mill to obtain a base grease. A predetermined amount of the following additive was mixed with the base grease, and after milling with a hydraulic three-stage roll mill, defoaming was performed to obtain a grease composition of Comparative Example 7.

  For the grease composition of Example 3, the average particle size of dispersed onion-like carbon was measured. Specifically, an equivalent circle diameter of each black particle in the optical micrograph shown in FIG. 1 is calculated by an image processing analyzer LUZEX AP manufactured by Nireco Corporation, and a particle size distribution is created from the equivalent circle diameter and frequency. The minimum particle size, maximum particle size, and average particle size (peak particle size) were determined from the particle size distribution. As a result, the minimum particle size was 0.358 μm, the maximum particle size was 4.98 μm, and the average particle size was 0.90 μm.

<Test method, test conditions>
-The penetration was measured according to JIS K2220.7.
-Abrasion resistance was measured according to the following evaluation criteria by measuring the wear diameter according to ASTM D2266 (high-speed four-ball wear test).
○: Pass, wear diameter less than 0.65 mm ×: Fail, wear diameter 0.65 mm or more

In each of Examples 1 to 5 to which aliphatic diurea and onion-like carbon were added, the wear diameter was less than 0.65, and the wear resistance was significantly improved as compared with Comparative Examples 1 to 7.
More specifically, from the comparison between Example 1 and Comparative Example 1, the wear resistance is remarkably improved by the addition of onion-like carbon, and from the comparison between Example 3 and Comparative Examples 2-3, conventional solid lubrication From the comparison of Example 5 and Comparative Examples 4, 6, and 7, onion-like carbon is superior to the agent (graphite, molybdenum disulfide), and the comparison between Example 5 and Comparative Examples 4, 6, and 7, or 12 It can be seen that aliphatic diurea is more excellent in wear resistance than lithium hydroxystearate (Li soap).

Claims (4)

A grease composition containing (a) a thickener, (b) a base oil, and (c) onion-like carbon, wherein the (a) thickener is represented by the following formula (1):
R ¹ —NHCONH—R ² —NHCONH—R ³ (1)
(In the formula, R ¹ and R ³ may be the same or different, and are a linear or branched alkyl group having 5 to 20 carbon atoms, and R ² is a divalent aromatic system having 6 to 15 carbon atoms. (It is a hydrocarbon group)
The grease composition which is an aliphatic diurea compound represented by these.   The grease composition according to claim 1, wherein the content of (c) onion-like carbon is 0.05 to 10% by mass relative to the total mass of the grease composition. (b) The grease composition of Claim 1 or 2 whose kinematic viscosity in 40 degreeC of base oil is 70-200 mm < ² > / s.   The grease composition according to any one of claims 1 to 3, which is used for a bearing, a gear, or a constant velocity joint.