JP2011037975A - Grease composition and machine part - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a grease composition having excellent fretting resistance in a temperature range from a normal temperature to a low temperature (e.g. -50°C, preferably nearly -40°C). <P>SOLUTION: In the grease composition containing a base oil, a thickener and an additive, the base oil has 50 to 200 mm<SP>2</SP>/s kinematic viscosity at 40°C, the thickener contains a diurea compound represented by general formula (I): R<SP>1</SP>-NHCONH-R<SP>2</SP>-NHCONH-R<SP>3</SP>(in the formula, R<SP>2</SP>denotes a 6-15C bivalent aromatic hydrocarbon group, R<SP>1</SP>and R<SP>3</SP>denote the same or different groups and denote a cyclohexyl group and a 8-22C linear or branched alkyl group) and the additive is at least one selected from the group consisting of a naphthenic acid metal salt, a salt of a 6-10C fatty acid and a 6-10C aliphatic amine, and an organic sulfonic acid metal salt. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a grease composition and a machine part, and more particularly to a lubricating grease composition having excellent fretting resistance from room temperature to low temperature and a machine part such as a bearing in which the grease composition is sealed.

Automobiles, electrical products, various machine parts and products are often transported by rail or truck. During this transportation, fretting occurs in the lubricated parts to which grease is applied due to vibration caused by rail joints and rough roads. It is said that fretting is a surface damage that occurs under a minute amplitude, and generates oxidized wear powder in the atmosphere and often causes severe wear due to its abrasive action (Non-Patent Document 1).
Countermeasures include: (1) reducing relative slip, (2) separation of both surfaces, prevention of direct contact, (3) contact surfaces such as phosphate coatings, or between surfaces by supplying lubricating oil / grease Prevention of adhesion of the like has been proposed (Non-Patent Document 1).

Grease with excellent actual fretting resistance is often developed and studied in the technical field of grease for automotive wheel bearings. For example, it has been reported that the use of aromatic diurea as a thickening agent and softening of the consistency has significantly improved fretting resistance compared to greases using lithium soap as a conventional thickening agent. (Non-patent document 2).
Thus, in reality, measures such as changing the type of thickener and softening the consistency to improve the inflow of grease have been taken.

However, aromatic diurea is inferior in fluidity, and when used in a bearing, for example, a deep groove ball bearing has a long life, but an angular ball bearing has a drawback that the lubrication life is short due to insufficient inflow to the lubrication part, The bearings that can be used are limited. Thus, the improvement by changing the thickener has a problem that the obtained grease lacks versatility.
Further, if the consistency is made soft, a problem of leakage occurs and it cannot be used in a place where leakage is a problem. Therefore, this also lacks versatility as a grease.
However, these are all countermeasures against fretting that occurs at room temperature, and there are few reports that fretting that occurs at low temperatures can be prevented.

  Furthermore, since the inflow property of the grease decreases as the viscosity of the base oil increases at a low temperature, the ability to prevent adhesion between the surfaces due to the supply of the grease (3) decreases. Therefore, it is possible to use a base oil mainly composed of expensive synthetic oil in order not to cause an increase in the viscosity of the base oil at a low temperature. There is a drawback of incurring soaring.

Yuji Yamamoto et al .: Tribology, Science and Engineering, November 25, 1999, pages 201-203 T.Endo: Eurogrease, November / December (1997) 25-40

An object of the present invention is to provide a grease composition having excellent fretting resistance.
Another object of the present invention is excellent in fretting resistance from room temperature to low temperature (for example, about −50 ° C., preferably about −40 ° C.) without depending on a base oil mainly composed of expensive synthetic oil. A grease composition is provided.
Still another object of the present invention is to provide a machine part using the above grease composition.

The present invention provides the following grease composition and machine part.
1. In a grease composition containing a base oil, a thickener and an additive,
The base oil has a kinematic viscosity at 40 ° C. of 50 to 200 mm ² / s,
The thickener contains a diurea compound represented by the following general formula (I):
General formula ^{(I): R 1 -NHCONH-} R 2 -NHCONH-R 3
Wherein R ² is a divalent aromatic hydrocarbon group having 6 to 15 carbon atoms, R ¹ and R ³ are the same or different groups, a cyclohexyl group, a linear or branched alkyl group having 8 to 22 carbon atoms. Is shown.)
The additive is at least one selected from the group consisting of a metal salt of naphthenic acid, a salt of a fatty acid having 6 to 10 carbon atoms and an aliphatic amine having 6 to 10 carbon atoms, and a metal salt of an organic sulfonic acid. Grease composition.
2. The metal salt of naphthenic acid is at least one selected from the group consisting of zinc cyclopentanoate and zinc cyclohexane acid, and the amine salt is a linear fatty acid having 6 to 10 carbon atoms and a linear aliphatic group having 6 to 10 carbon atoms. A salt of an amine, and the organic sulfonate is at least one selected from the group consisting of dinonylnaphthalenesulfonate calcium salt, dinonylnaphthalenesulfonate zinc salt, and dinonylnaphthalenesulfonate barium salt. The grease composition as described in 1 above.
3. In the grease composition, the content of the naphthenic acid metal salt is 0.5 to 5.0% by mass, the content of the amine salt is 1.5 to 5.0% by mass, The grease composition as described in 1 or 2 above, wherein the content is from 1.5 to 5.0% by mass.
4). A machine part comprising the grease composition according to any one of the above items 1 to 3.

  The grease composition of the present invention is excellent in fretting resistance. Therefore, the grease composition of the present invention can be used for lubricating various machine parts. The target mechanical parts are not particularly limited. For example, rolling bearings, ball screws, linear motion guide bearings, various gears, cams, constant velocity joints, journal bearings (sliding bearings), pistons, screws, ropes, chains, etc. Is mentioned. Particularly suitable for rolling bearings.

The base oil used in the grease composition of the present invention is not particularly limited as long as it has a kinematic viscosity at 40 ° C. of 50 to 200 mm ² / s. If the kinematic viscosity at 40 ° C. is less than 50 mm ² / s, the oil film tends to be thin and a sufficient oil film thickness may not be ensured. If it exceeds 200 mm ² / s, the viscosity resistance tends to increase. .
Mineral oil is most preferred from the viewpoint of cost and performance. Mineral oil or synthetic oil can be mixed and used as necessary.
Synthetic oils include, for example, ester-based synthetic oils typified by diesters and polyol esters, poly-alpha olefins, synthetic hydrocarbon oils typified by polybutene, alkyl-diphenyl ethers, ether-based synthetic oils typified by polypropylene glycol, and silicone oils. Various synthetic oils can be used, and these may be used alone or in admixture of two or more.
However, from the viewpoint of cost and performance, the content of mineral oil in the base oil is preferably 70% by mass or more, more preferably 80 to 100% by mass, and most preferably 100% by mass.

The thickener used in the grease composition of the present invention contains a specific diurea compound represented by the general formula (I).
The content of the diurea compound in the grease composition of the present invention is such an amount that the consistency of the grease composition is preferably 235 to 325, more preferably 280 to 325. Specifically, it is preferably 5 to 15% by mass, more preferably 8 to 12% by mass, based on the entire grease composition.
If the amount is less than 5% by mass, the grease softens when the shear is applied, and the grease easily leaks from the machine parts. If the amount is 15% by mass or more, the inflow property of the grease may be reduced.
On the other hand, a grease using a metal soap such as lithium soap as a thickening agent cannot provide sufficient fretting resistance.

The additive used in the grease composition of the present invention is selected from the group consisting of metal salts of naphthenic acid, salts of fatty acids having 6 to 10 carbon atoms and aliphatic amines having 6 to 10 carbon atoms, and metal salts of organic sulfonic acids. Contains at least one.
Examples of the metal of the naphthenic acid metal salt include zinc, magnesium, calcium, and aluminum. Of these, zinc salts are particularly excellent.
The fatty acid having 6 to 10 carbon atoms constituting the amine salt may be a linear or branched fatty acid. Also, the aliphatic amine having 6 to 10 carbon atoms constituting the amine salt may be a linear or branched aliphatic amine. Preferably, it is a salt of a linear fatty acid having 6 to 10 carbon atoms and a linear aliphatic amine having 6 to 10 carbon atoms, more preferably a salt of a linear fatty acid having 8 carbon atoms and a linear aliphatic amine having 8 carbon atoms. .

Examples of the organic sulfonic acid constituting the organic sulfonic acid metal salt include petroleum sulfonate, dinonylnaphthalene sulfonic acid, and heavy alkylbenzene sulfonic acid obtained by sulfonation of aromatic hydrocarbon components in the lubricating oil fraction. A sulfonic acid is mentioned.
Examples of the metal of the organic sulfonic acid metal salt include calcium, zinc, barium, and sodium. The organic sulfonic acid calcium salt may be a neutral or highly basic salt. For example, a calcium salt having a base number of about 50 to 500 mgKOH / g is used.
Preferred are metal salts of dinonylnaphthalenesulfonic acid, and particularly preferred are calcium, zinc and barium salts of dinonylnaphthalenesulfonic acid.

In the grease composition of the present invention, the content of the naphthenic acid metal salt is preferably 0.5 to 5.0% by mass, particularly preferably 1.0 to 5.0% by mass.
The content of the salt of a fatty acid having 6 to 10 carbon atoms and an aliphatic amine having 6 to 10 carbon atoms is preferably 1.5 to 5.0% by mass, particularly preferably 2.0 to 5.0% by mass. .
The content of the organic sulfonic acid metal salt is preferably 1.5 to 5.0% by mass, particularly preferably 2.0 to 5.0% by mass.
What is necessary is just to adjust content suitably, when using 2 or more types together.
If the content is less than the above, there is an effect as a rust inhibitor, but the effect of preventing fretting generated from room temperature to low temperature is insufficient, and even if added in an amount of 5.0% by mass or more, no further effect of addition is recognized. It is uneconomical.

Naphthenic acid metal salts, fatty acid amine salts, and organic sulfonates used as additives in the grease composition of the present invention are commonly used as rust inhibitors for lubricating oils and are used in a wide range of applications. It is used as an agent.
However, there is no report / disclosure that the naphthenic acid metal salt, amine salt, and organic sulfonic acid metal salt are effective in preventing fretting that occurs from room temperature to low temperature.

If necessary, other general-purpose additives other than the naphthenic acid metal salt, amine salt, and organic sulfonic acid metal salt may be added to the grease composition of the present invention. For example, the additive shown below is mentioned.
Antioxidants Amines: Phenyl α-naphthylamine, alkylated phenyl α-naphthylamine, alkylated diphenylamine, etc. Phenols: 2,6-di-tert-butyl-p-cresol, pentaerythrityl tetrakis [3- (3,5 -Di-t-butyl-4-hydroxyphenyl) propionate], hindered phenols such as octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, etc. Quinoline series: 2, 2, 4 -Trimethyl-1, 2 dihydroquinoline polymer, etc.-Rust inhibitor Carboxylic acid and its derivatives: alkenyl succinic anhydride, alkenyl succinic ester, alkenyl succinic acid half ester Carboxylate: fatty acid, dibasic acid, lanolin fatty acid, alkenyl Metal salts such as succinic acid (C , Ba, Mg, Al, Zn, Na, etc.) or amine salts Passivating agent: Na nitrite, Na molybdate, etc. Ester: Sorbitan trioleate, sorbitan monooleate, etc. Metal corrosion inhibitor: Benzotriazole or its derivatives, oxidation Zinc and other extreme pressure agents Phosphorus compounds: tricresyl phosphate, tri-2-ethylhexyl phosphate, etc. Sulfur compounds: dibenzyl disulfide, various polysulfides, etc. Sulfur-phosphorus compounds: triphenyl phosphorothionate Organometallic electrode Pressure agent: Zn, Mo, Sb, Bi, etc. of dialkyldithiophosphate, Zn, Mo, Sb, Ni, Cu, Bi, etc. of dialkyldithiocarbamate, etc. Others, ashless dithiocarbamate, ashless dithiophosphate carbamate, etc.・ Solid lubricant: Mori disulfide Buden, graphite, PTFE, MCA, etc.

Fretting prevention at room temperature can be dealt with by changing the type of thickener (the effect of (2) above by the aromatic urea film) and softening the consistency (improving the inflow of grease) (described later). Comparative Examples 6 to 10, Comparative Examples 19 and 20).
However, the effect of preventing fretting by supplying grease cannot be expected due to a decrease in grease inflow at low temperatures.

The grease composition of the present invention contains a specific additive (a metal salt of naphthenic acid, a salt of a fatty acid having 6 to 10 carbon atoms and an aliphatic amine having 6 to 10 carbon atoms, or a metal salt of an organic sulfonic acid). For this reason, when this is used for a bearing, for example, the strong adsorption force of the additive to the member surface exerts an adhesive action at the interface between the diurea grease and the balls and the inner and outer ring races, thereby reducing the grease inflow property. Underneath, it is considered that fretting at low temperatures can be prevented by sufficiently separating both surfaces and preventing direct contact.
The effect of the present invention that the fretting resistance from room temperature to low temperature can be improved by the addition of a specific additive cannot be easily predicted by those skilled in the art.

<Examples 1-14, Comparative Examples 1-17>
In the base oil, a predetermined amount was reacted at a ratio of 2 mol of the raw material amine to 1 mol of the raw material isocyanate, and a predetermined amount of the additive was added and adjusted to a specified consistency with a three roll mill.

<Comparative Example 18>
A predetermined amount of lithium hydroxystearate was mixed and dissolved in a predetermined amount of base oil by heating, and after cooling, a predetermined amount of additive was added and adjusted to a specified consistency with a three-roll mill.

<Test method>
・ Mixing penetration: JIS K 2220.7
・ Fafnir friction oxidation test (ADTM D 4170 compliant)
・ Standard test for evaluating fretting resistance Apply test grease to the following two test thrust bearings, perform the specified swing operation, and determine the amount of wear (weight loss due to fretting wear).
[Test conditions]
Bearing: ANDREWS W 5/8
Load: 2450N (550 lbf) (surface pressure: 1861 MPa)
Oscillation angle: 0.21 rad (12 °)
Oscillation cycle: 25Hz
Time: 22h
Temperature: 25 ° C, -30 ° C
Grease filling amount: 1.0 g per pair of bearings
Abrasion amount: Reduced race mass per set of bearings (total reduced test bearing race mass / 2)
[Judgment]
A: Wear amount of 2.0 mg or less (fretting resistance: very large)
○: Wear amount exceeding 2.0 and less than 5.0 mg (fretting resistance: high)
Δ: Amount of wear more than 5.0 and less than 15.0 mg (fretting resistance: a little)
×: Wear amount of 15.0 mg or more (fretting resistance: none)
Antirust test: ASTM D1743-73 Bearing antirust test [judgment]
○: No rust
X: Rust is shown in Tables 1-5.

* 1; Diphenylmethane diisocyanate
* 2: Metal salt of naphthenic acid based on zinc cyclopentanoate * 3; Salt of linear fatty acid with 8 carbon atoms and linear aliphatic amine with 8 carbon atoms * 4; Calcium dinonylnaphthalenesulfonate * 5; Zinc dinonyl naphthalene sulfonate * 6; Barium dinonyl naphthalene sulfonate * 7; Mixture of alkyl phosphorothionate compound and amine compound Product name HITEC 833 (manufactured by Afton Chemical)
* 8; Calcium carbonate * 9; Zinc stearate * 10; Trade name MOLYVAN A (manufactured by RTVANDERBILT)
* 11: Product name LUBRIZOL 1395 (manufactured by Nippon Lubrizol)
ODA: Octadecylamine CHA: Cyclohexylamine OA: Octylamine PAO: Poly-α-olefin In the table, * 2 to * 6, * 8, * 9 () in the total amount of grease in parentheses: mass% is added Represents the active ingredient concentration of the agent.
In addition, * 7, * 10, and * 11 in the table indicate the amount of addition to the total amount of grease in parentheses: mass% represents the concentration of the product.

The grease compositions of Examples 1 to 14 to which a naphthenic acid metal salt, a fatty acid having 6 to 10 carbon atoms and a salt of an aliphatic amine having 6 to 10 carbon atoms, or an organic sulfonic acid metal salt are added as an additive are Without softening, the amount of wear is small and the fretting resistance is excellent at room temperature and low temperature, and the antirust property is also excellent.
The grease compositions of Comparative Examples 1, 9, and 10 that do not contain the specific additive of the present invention have a large amount of wear and poor fretting resistance at room temperature and low temperature, and also have poor rust prevention properties.
The grease compositions of Comparative Examples 2, 4, 11, and 13 containing an additive different from the specific additive of the present invention have a small amount of wear at room temperature, but a large amount of wear at low temperatures and poor fretting resistance. In addition, the rust resistance is inferior.
The grease compositions of Comparative Examples 3, 5, 6, 12, 14, and 15 containing an additive different from the specific additive of the present invention have a large amount of wear and poor fretting resistance at room temperature and low temperature, and Rust prevention is also poor.
The grease compositions of Comparative Examples 7 and 16 using a base oil having a low kinematic viscosity have a little amount of wear at room temperature, but have a large amount of wear at low temperatures and inferior fretting resistance and inferior rust resistance. Yes.
The grease compositions of Comparative Examples 8 and 17 in which the content of the thickener is reduced have a high miscibility and a slight amount of wear at room temperature, but a large amount of wear at low temperatures and poor fretting resistance, and Rust prevention is also poor.
The grease composition of Comparative Example 18 using lithium soap as a thickener is excellent in rust prevention, but has a large amount of wear and inferior fretting resistance at room temperature and low temperature.

Claims (4)

In a grease composition containing a base oil, a thickener and an additive,
The base oil has a kinematic viscosity at 40 ° C. of 50 to 200 mm ² / s,
The thickener contains a diurea compound represented by the following general formula (I):
General formula ^{(I): R 1 -NHCONH-} R 2 -NHCONH-R 3
Wherein R ² is a divalent aromatic hydrocarbon group having 6 to 15 carbon atoms, R ¹ and R ³ are the same or different groups, a cyclohexyl group, a linear or branched alkyl group having 8 to 22 carbon atoms. Is shown.)
The additive is at least one selected from the group consisting of a metal salt of naphthenic acid, a salt of a fatty acid having 6 to 10 carbon atoms and an aliphatic amine having 6 to 10 carbon atoms, and a metal salt of an organic sulfonic acid. Grease composition.   The metal salt of naphthenic acid is at least one selected from the group consisting of zinc cyclopentanoate and zinc cyclohexane acid, and the amine salt is a straight chain fatty acid having 6 to 10 carbon atoms and a straight chain aliphatic group having 6 to 10 carbon atoms. A salt of an amine, and the organic sulfonate is at least one selected from the group consisting of dinonylnaphthalenesulfonate calcium salt, dinonylnaphthalenesulfonate zinc salt, and dinonylnaphthalenesulfonate barium salt. The grease composition according to claim 1.   In the grease composition, the content of the naphthenic acid metal salt is 0.5 to 5.0% by mass, the content of the amine salt is 1.5 to 5.0% by mass, The grease composition according to claim 1 or 2, wherein the content is from 1.5 to 5.0% by mass.   A machine part formed by enclosing the grease composition according to any one of claims 1 to 3.