GREASE COMPOSITION

Abstract

 Provided herein is a grease composition of excellent lubricity containing a novel additive for grease. The grease composition includes a lubricant base oil, a thickener, and a sulfolane derivative represented by the following general formula (1). In the formula, R¹ represents a hydrocarbon group of 1 to 20 carbon atoms, and R² and R³ each represent hydrogen, or a hydrocarbon group of 1 to 20 carbon atoms.

Description

Technical Field

[0001] The present invention relates to a grease composition having excellent lubricity.

Background Art

[0002] Grease is typically used for sliding surfaces where moving contact surfaces make it difficult to keep a lubricant film adhered to the lubricated surfaces, for example, such as in sliding portions and rotors of mechanisms. In recent years, there is an increasing trend of smaller, lighter, higher-output, and longer-life devices along with the advancement of machine technology in products such as automobiles and electrical devices, and these products are used under ever demanding operating conditions. This has created a demand for higher performance in the lubricity or other properties of greases used in devices.

[0003] In order to improve the lubricity of grease, it has been proposed to select a base oil, a thickener, and additives. For example, it is known to add a specific phosphite ester (PTL 1), or incorporate organic molybdenum, zinc dithiophosphate, a polysulfide, and a triglyceride (PTL 2).

[0004] However, for further improvement of lubricity, there is a need for development of a novel additive for grease.

Citation List

Patent Literature

[0005] 

PTL 1: JP-A-2012-057134

PTL 2: JP-A-2014-043526

Summary of Invention

Technical Problem

[0006] The present invention has been made to provide a solution to the foregoing problem, and is intended to provide a grease composition of excellent lubricity containing a novel additive for grease.

Solution to Problem

[0007] The present inventors conducted intensive studies to develop a grease composition of excellent lubricity, and found, rather by chance, that a specific sulfolane derivative is effective as an additive for grease. It was confirmed that the sulfolane derivative has synergy with other additives under specific conditions.

[0008] The present invention is based on these findings, and includes the following.

[1] A grease composition comprising a lubricant base oil, a thickener, and a sulfolane derivative represented by the following general formula (1).


(In the formula, R¹ represents a hydrocarbon group of 1 to 20 carbon atoms, and R² and R³ each represent hydrogen, or a hydrocarbon group of 1 to 20 carbon atoms.)

[2] The grease composition according [1], wherein the sulfolane derivative of the general formula (1) is one in which R¹ is an alkyl group of 4 to 18 carbon atoms, and R² and R³ are each hydrogen, or a hydrocarbon group of 1 to 8 carbon atoms.

[3] The grease composition according to above-described [1] or [2], wherein the sulfolane derivative is contained in a content of 0.2 to 10 mass%.

[4] The grease composition according to any one of above-described [1] to [3], further comprising at least one of a phosphorus-containing organic compound, a sulfur-containing organic compound, and a phosphorus-sulfur-containing organic compound.

Advantageous Effects of Invention

[0009] The grease composition of the present invention has distinguishing effects including a low coefficient of friction, high load bearing characteristics, and excellent lubricity.

Description of Embodiments

Lubricant Base Oil

[0010] A lubricant base oil of the present invention may be any of a mineral oil, a synthetic oil, an animal and vegetable oil, or a mixture thereof, provided that it is a lubricant base oil for common lubricants.

[0011] The lubricant base oil has a kinetic viscosity at 100°C of preferably 1 to 200 mm²/s, more preferably 5 to 50 mm²/s.

[0012] The content of the lubricant base oil is preferably 50 mass% or more, more preferably 60 mass% or more with respect to the total amount of the grease composition. Typically, the upper limit of the content is preferably 95 mass% or less, more preferably 85 mass% or less, accounting for the balance.

[0013] Mineral oil-type base oils for lubricant are generally prepared by distilling crude oil under atmospheric pressure, optionally further distilling the atmospheric residual oil under reduced pressure, refining the resulting distillate oil by various refining processes to obtain a lubricating oil fraction. The fraction is used as a base oil, as it is, or a base oil is prepared by blending various additives to the fraction. examples of the above refining processes include hydrotreating, solvent extraction, solvent dewaxing, hydrodewaxing, sulfuric acid washing, and a clay treatment. A mineral oil-type base oil for lubricant suitable for the present invention can be obtained by combining these processes in an appropriate order and submitting thereto. A mixture of two or more refined oils having different properties obtained by processing different crude oils or different distillate oils in combination with different processes, or in different orders may also be used as a suitable base oil.

[0014] For safety of handling, the mineral oil-type base oil for lubricant is preferably one with an aromatic content of 20% or less.

[0015]  Examples of the synthetic oil-type base oil for lubricant include poly α-olefin (PAO), a low-molecular copolymer of ethylene and α-olefin, high-molecular polymers such as polybutene and polyisobutene, oxygen-containing synthetic oils such as ester oils and ether oils, silicone oils, fluorinated oils, and alkylnaphthalene. These may be used either alone or in combination.

[0016] Preferred examples of the animal and vegetable oil-type base oils for lubricant include milkfat, beef tallow, lard (pig fat), mutton tallow, whale oil, salmon oil, bonito oil, herring oil, cod oil, soy oil, canola oil, sunflower oil, safflower oil, peanut oil, corn oil, cottonseed oil, rice bran oil, sesame oil, olive oil, linseed oil, castor oil, cacao butter, palm oil, coconut oil, hempseed oil, rice oil, and tea seed oil.

Thickener

[0017] The thickener used in the present invention may be, for example, a metal soap- or urea-based thickener commonly used for grease compositions, or an organic synthetic resin powder, an inorganic powder, a gelatinizer made from an amide compound, or a wax.

[0018] The metal soap-based thickener is a metal carboxylate (metal soap), and may be, for example, a sodium soap, a calcium soap, an aluminum soap, or a lithium soap, of which the lithium soap is preferred.

[0019] Examples of the carboxylic acids that form the soap include fatty acids, and aliphatic divalent carboxylic acids. The metal soap may be a so-called composite metal soap.

[0020] Examples of the urea-based thickener include urea compounds such as diurea compounds, triurea compounds, tetraurea compounds, polyurea compounds (excluding diurea compounds, triurea compounds, and tetraurea compounds), urethane compounds such as urea-urethane compounds, and diurethane, and mixtures thereof. Preferred are diurea compounds, urea-urethane compounds, diurethane compounds, and mixtures thereof.

[0021] Examples of the organic synthetic resin powder include fluororesin particles (particularly, polytetrafluoroethylene resin particles).

[0022] Examples of the inorganic powder include metal oxide such as silica, metal carbonates such as calcium carbonate, metal sulfates such as calcium sulfate, and nitrides such as h-BN (atmospheric-phase boron nitride). The inorganic powder also may be, for example, a mineral-derived metal oxide such as bentonite.

[0023] Examples of the gelatinizer made from amide compounds include monoamides, bisamides, and triamides. Preferred are aliphatic monoamides, and aliphatic bisamides.

[0024] Examples of the wax include petroleum waxes, synthetic waxes, and natural resin waxes.

[0025] The thickener content is preferably 3 to 45 mass%, more preferably 5 to 30 mass% with respect to the total amount of the grease composition.

Sulfolane Derivative

[0026] The sulfolane derivative of the present invention is a compound represented by the following general formula (1).

[0027] In the formula, R¹ represents a hydrocarbon group of 1 to 20 carbon atoms, and R² and R³ each represent hydrogen, or a hydrocarbon group of 1 to 20 carbon atoms.

[0028] The sulfolane derivative is preferably one in which R¹ in the general formula (1) is an alkyl group of 4 to 18 carbon atoms, more preferably one in which R¹ is an alkyl group of 6 to 16 carbon atoms, and R² and R³ are each hydrogen or a hydrocarbon group of 1 to 8 carbon atoms. More preferably, R² and R³ are both hydrogens.

[0029] The sulfolane compound is commercially available as a seal-swell agent, and may be produced by, for example, the method described in JP-A-2006-206580.

[0030] The content of the sulfolane derivative is preferably 0.2 to 10 mass%, more preferably 0.5 to 5 mass% with respect to the total amount of the grease composition.

Second Additive

[0031] In the present invention, it is preferable to add a second additive, which is at least one compound selected from a phosphorus-containing organic compound, a sulfur-containing organic compound, and a phosphorus-sulfur-containing organic compound, in addition to the lubricant base oil, the thickener, and the sulfolane derivative. The phosphorus-containing organic compound, the sulfur-containing organic compound, and the phosphorus-sulfur-containing organic compound may be those commonly used as additives for lubricants.

[0032] Examples of the phosphorus-containing organic compound include phosphate esters, phosphite esters, and acidic phosphate esters, including amine salts, and ammonium salts thereof. Preferred are diphenyl hydrogen phosphite, and tricresyl phosphate.

[0033] Examples of the sulfur-containing organic compound include polysulfides, sulfurized olefins, sulfurized fat, and molybdenum dithiocarbamate (MoDTC).

[0034] Examples of the phosphorus-sulfur-containing organic compound include zinc dithiophosphate (ZnDTP), and molybdenum dithiophosphate (MoDTP).

[0035] The content of the second additive is preferably 0.1 to 10 mass%, more preferably 0.2 to 5 mass% with respect to the total amount of the grease composition. The content of the phosphorus element is preferably 0.01 to 1 mass%, more preferably 0.02 to 0.5 mass% with respect to the total amount of the grease composition. The content of the sulfur element is preferably 0.01 to 1 mass%, more preferably 0.02 to 0.5 mass% with respect to the total amount of the grease composition.

Other Additives

[0036] The grease composition of the present invention may also contain known additives, other than the second additive. Examples of such additives include phenol- or amine-based antioxidants; anti-rusting agents such as carboxylates, and sulfonates; antiwear agents such as polyalkylene glycol, and glycerine; extreme-pressure agents such as chlorinated paraffins; oiliness improvers such as higher fatty acids, and synthetic esters; and solid lubricants such as graphite, and molybdenum disulfide. These may be added either alone or in a combination of two or more.

Preparation and Properties of Grease

[0037] The grease composition of the present invention may be prepared by using a common grease preparation method, specifically by blending the thickener with the lubricant base oil to produce a base grease, and blending and mixing the additives to the base grease. Alternatively, the grease composition of the present invention may be prepared by blending and mixing the lubricant base oil, the thickener, and the additives at once.

[0038] The grease composition of the present invention is semi-solid or solid at room temperature, and has a consistency of 000 to 6 in terms of a JIS K2220 consistency number.

Examples

[0039] The thickener shown in Table 1 was added to the lubricant base oil, and the additives were added to make the compositions shown in Table 1. The mixture was stirred, and passed through a roller mill to obtain grease compositions of Examples and Comparative Examples.

[0040] Here, "PAO" is poly α-olefin (kinetic viscosity at 40°C: 48 mm²/s).

[0041] "Mineral oil 1" is a highly-refined mineral oil (kinetic viscosity at 40°C: 38 mm²/s) obtained through hydrocracking of a crude oil-derived component.

[0042] "Mineral oil 2" is a solvent-refining paraffinic mineral oil (kinetic viscosity at 40°C: 100 mm²/s).

[0043] "Urea" in "Thickener" is a urea-based thickener obtained through reaction of diphenylmethane-4,4'-diisocyanate (MDI) and monoamine which is a mixture of 2 mole parts of p-toluidine and 8 mole parts of cyclohexylamine.

[0044] "Li soap" in "Thickener" is lithium stearate.

[0045] "phosphite ester" is diphenyl hydrogen phosphite.

[0046] "Phosphate ester" is tricresyl phosphate.

[0047] "Sulfur compound" is polysulfide (sulfur element content of 40%).

[0048] "Sulfolane derivative" is a compound of the general formula (1) in which R¹ is an alkyl group of 8 carbon atoms, and R² and R³ are hydrogens.

[0049] ZnDTP (zinc dithiophosphate) have alkyl group of 6 carbon atoms, and a Zn element content of 8.7 mass%.

[0050] MoDTC (molybdenum dithiocarbamate) have alkyl group of 4-12 carbon atoms, and a Mo element content of 10.0 mass%.

[0051] The friction characteristics were determined by conducting a ball/disc SRV test, in which the grease composition was subjected to friction for 5 min at a frequency of 50 Hz, an amplitude of 1.0 mm, and a temperature of 40°C under a load of 50 N using a 10-mm ball. The friction test was continued for the next 5 min under an increased load of 100 N, and for another 5 min under 200 N. Subsequently, the load was increased in an increment of 100 N, and the coefficient of friction was measured for each load until 600 N.

[0052] The load at which the coefficient of friction showed an abrupt increase to 0.3 or higher, and a burn occurred was measured as the burn load (load bearing characteristics) . The burn load was measured to be 600 N or higher when burns did not occur under 600 N.

[0053] The coefficient of friction under 50 N was determined as a measure of friction characteristics because the friction characteristics under a light load are important for saving energy in an actual use environment such as in bearings.

[0054] The SRV test used ASTM D5706 testing equipment, and used an SUJ-2 ball and disc.

[0055] The results are presented in Table 1.

[0056] As is clear from these results, the grease compositions with the addition of the sulfolane derivative had greatly improved load bearing characteristics compared to the traditional grease compositions that contained a phosphite ester or a phosphate ester.

[Table 1]

		Exa.1	Exa.2	Exa.3	Exa.4	Exa.5	Exa.6	Exa.7	Exa.8	Exa.9	Exa.10	C.Exa.1	C.Exa.2	C.Exa.3
Base Oil	PAO	83			83	80	82	82	82	82	82	85	83	83
	Mineral oil 1		83
	Mineral oil 2			83
Thickener	Urea	15	15	15
	Li soap				15	15	15	15	15	15	15	15	15	15
Additives	Sulfolane derivative	2	2	2	2	5	2	2	2	2	2
	Phosphite ester						1						2
	Phosphate ester							1						2
	Polysulfide								1
	ZnDTP									1
	MoDTC										1
Consistency		300	300	300	300	310	305	305	305	305	305	295	300	300
SRV lubrication test	Burn load (N)	600 or higter	601 or higter	602 or higter	603 or higter	604 or higter	605 or higter	606 or higter	607 or higter	608 or higter	609 or higher	100	500	500
	Coefficient of friction	0.16	0.16	0.16	0.16	0.17	0.14	0.15	0.16	0.16	0.16	0.17	0.15	0.17

Industrial Applicability

[0057] The grease composition of the present invention has a small coefficient of friction, and high load bearing characteristics, and excels in lubricity. The grease composition of the present invention has use as a lubricant for, for example, sliding portions or rotors of automobiles and electrical devices.

Claims

1. A grease composition comprising a lubricant base oil, a thickener, and a sulfolane derivative represented by the following general formula (1)

wherein R¹ represents a hydrocarbon group of 1 to 20 carbon atoms, and R² and R³ each represent hydrogen, or a hydrocarbon group of 1 to 20 carbon atoms.

2. The grease composition according claim 1, wherein the sulfolane derivative of the general formula (1) is one in which R¹ is an alkyl group of 4 to 18 carbon atoms, and R² and R³ are each hydrogen, or a hydrocarbon group of 1 to 8 carbon atoms.

3. The grease composition according to claim 1 or 2, wherein the sulfolane derivative is contained in a content of 0.2 to 10 mass%.

4. The grease composition according to any one of claims 1 to 3, further comprising at least one of a phosphorus-containing organic compound, a sulfur-containing organic compound, and a phosphorus-sulfur-containing organic compound.