EP2341121B1

EP2341121B1 - Lubricating grease composition and manufacturing method therefor

Info

Publication number: EP2341121B1
Application number: EP09820564.4A
Authority: EP
Inventors: Takeshi Hishinuma; Tatsuya Hashimoto; Toshio Nitta
Original assignee: Nok Klueber Co Ltd
Current assignee: Nok Klueber Co Ltd
Priority date: 2008-10-17
Filing date: 2009-10-13
Publication date: 2015-05-27
Anticipated expiration: 2029-10-13
Also published as: CN102186958A; JPWO2010044386A1; EP2341121A4; EP2341121A1; CN102186958B; WO2010044386A1; JP5310732B2; US20110218128A1

Description

TECHNICAL FIELD

The present invention relates to a lubricating grease composition and a method for producing the same. More particularly, the present invention relates to a lubricating grease composition comprising a base oil mixture of a non-fluorine-based base oil and a fluorine-based base oil, which are incompatible with each other; and a method for producing the composition.

BACKGROUND ART

Conventional fluorine-based greases comprise a perfluoropolyether oil as a base oil, a homopolymer of tetrafluoroethylene [PTFE], a copolymer of tetrafluoroethylene and hexafluoropropene [HFP], or the like as a thickener, and small amounts of additives, such as rust inhibitors. They are used under severe conditions requiring, for example, low-temperature characteristics, high-temperature durability, oxidation stability, and chemical resistance.
However, the base oil and thickener both contain fluorine, and thus have such problems as high cost; poor compatibility with materials to be lubricated, such as resins, metals, rubber, etc.; failure to form oil films necessary for lubrication under high-load conditions, causing abrasion, and resulting in increased friction coefficients, so that the torque transmission efficiency is lowered; and poor rust prevention and corrosion resistance.
In order to solve these problems, it has been proposed to use a fluorine-based base oil in combination with a non-fluorine-based base oil (e.g., hydrocarbon-based oil) to form a lubricating grease composition, which is thus less expensive and has excellent abrasion resistance to mating materials.
Examples of lubricating grease compositions comprising a base oil mixture of a non-fluorine-based base oil and a fluorine-based base oil are as follows:

(1) Patent Document 1 discloses a grease comprising a hydrogenated mineral oil and/or synthetic lubricating oil, a fluoropolyether oil, and an organic or inorganic thickening agent, wherein the weight ratio of the lubricating oil and the fluoropolyether oil to the thickening agent is 97:3 to 80:20, and the weight ratio of the lubricating oil to the fluoropolyether oil is 95:5 to 60:40. The grease is evaluated for abrasion resistance, load resistance, and bearing durability. In the Examples of Patent Document 1, an ester oil mixed with an aliphatic lithium complex soap (a lithium complex soap of azelaic acid and 12-hydroxystearic acid) is used.
(2) Patent Document 2 discloses a ball-and-roller bearing for an electromagnetic clutch and an idler pulley, the bearing being filled with a grease mixture of a fluorine-based grease comprising a perfluoropolyether oil as a base oil and PTFE as a thickener, and a grease other than fluorine-based grease. The ball-and-roller bearing has a longer seizure life at a high temperature exceeding 180°C and enhanced resistance to rust. Hydrocarbon-based and ester-based oils, etc. are used as the base oil for non-fluorine-based grease, and lithium, sodium, barium, calcium, and other metal complex soaps are used as metal complex soap thickeners. The Examples of Patent Document 2 disclose a method for producing a lithium complex soap thickener by a two-step saponification reaction comprising saponifying 12-hydroxystearic acid and lithium hydroxide, and then adding dibasic acid and lithium hydroxide, followed by saponification.
(3) Patent Document 3 discloses a grease mixture, using for a ball-and-roller bearing, comprising a metal complex soap-based grease and a fluorine-based grease at a specific ratio, the metal complex soap-based grease containing 8 to 35 mass% of thickener, and the fluorine-based grease containing a perfluoropolyether oil as a base oil and 15 to 42.5 mass% of PTFE as a thickener, wherein the total amount of the thickeners is 20 to 30 mass%. Hydrocarbon-based and ester-based oils, etc. are used as the base oil for non-fluorine-based grease, and lithium, sodium, barium, calcium, and other metal complex soaps are used as metal complex soap thickeners. The Examples of Patent Document 3 disclose a method for producing a lithium complex soap thickener by a two-step saponification reaction comprising saponifying 12-hydroxystearic acid and lithium hydroxide, and then adding dibasic acid and lithium hydroxide, followed by saponification.
(4) Patent Document 4 discloses a ball-and-roller bearing for a fuel cell in which a fluorine-based grease comprising a fluorine oil as a base oil and a fluororesin as a thickener, and a grease other than fluorine-based grease are enclosed; and a pressure-feeder for a fuel cell system providing the ball-and-roller bearing. Patent Document 4 merely indicates that hydrocarbon-based and ester-based oils, etc. are used as the base oil for non-fluorine-based grease, and that lithium, sodium, barium, calcium, and other metal complex soaps are used as metal complex soap thickeners.
(5) Patent Document 5, which was filed by the present applicant, discloses a lubricating grease composition comprising a straight-chain perfluoropolyether oil, a synthetic lubricating oil other than the straight-chain perfluoropolyether oil, and a thickener, wherein lithium soaps or lithium complex soaps, such as saturated or unsaturated aliphatic monocarboxylic acid lithium salts or aliphatic dicarboxylic acid lithium salts, are used.
(6) Patent Document 6, which was also filed by the present applicant, discloses a lubricating grease composition comprising a perfluoropolyether oil, and, as a thickener, at least one selected from an aliphatic dicarboxylic acid metal salt, a monoamide monocarboxylic acid metal salt, and a monoester carboxylic acid metal salt. The lubricating grease composition reportedly has excellent abrasion resistance to mating materials, leakage resistance, washing properties, etc., and satisfies the cost requirements.

The monoamide carboxylic acid metal salts used in Patent Document 6 are obtained as amide and metal salt of the each dicarboxylic group of dicarboxylic acids. It is reported that primary, secondary, or unsaturated aliphatic amines are used as amines to be amidated, and Li, Na, K, Ca, Ba, Mg, Cu, Fe, Co, Zn, Al, and other salts are used as metal salts.

PRIOR ART DOCUMENT

PATENT DOCUMENT

Patent Document 1 : JP-A-7-268370
Patent Document 2 : JP-A-2003-239997
Patent Document 3 : JP-A-2004-028326
Patent Document 4 : JP-A-2004-190688
Patent Document 5 : JP-A-2003-096480
Patent Document 6 : JP-A-2001-354986

US 2003/0069144 A1 discloses a grease which is a mixture of at least one of metal complex soap-based grease and urea-based grease, each incorporated with 8 to 35% by mass of thickening agent, and fluorine-based grease comprising perfluoropolyether oil as a base oil incorporated with 15 to 42.5% by mass of polytetrafluoroethylene as a thickening agent, ratio of said at least one of the metal complex soap-based grease and urea-based grease versus said fluorine-based grease being 40 to 80:60 to 20 by mass, and total content of the thickening agents being 20 to 30% by mass.

OUTLINE OF THE INVENTION

PROBLEM TO BE SOLVED BY THE INVENTION

An object of the present invention is to provide a lubricating grease composition prepared by adding a metal soap-based thickener to a fluorine-based base oil, the composition having improved abrasion resistance and ensuring cost reduction; and a method for producing the composition.

MEANS FOR SOLVING THE PROBLEM

The above object of the present invention can be achieved by a lubricating grease composition comprising a complex metal soap thickener of aliphatic dicarboxylic acid and monoamide monocarboxylic acid obtainable by amidation of a monocarboxylic group of a saturated or unsaturated aliphatic dicarboxylic acid having 2 to 20 carbon atoms, and a fluororesin powder contained in a base oil mixture of a non-fluorine-based base oil and a fluorine-based base oil, which are incompatible with each other, i.e. a homogeneous base oil mixture cannot be formed by simply mixing these two base oils, wherein the non-fluorine-based base oil is contained in an amount of 5 to 90 wt.%, wherein the fluorine-based base oil is contained in an amount of 5 to 90 wt.%, wherein the complex metal soap is contained in an amount of 1.5 to 30 wt.% and wherein the fluororesin powder is contained in an amount of 0.1 to 50 wt.% in the lubricating grease composition. The lubricating grease composition can be produced by kneading a non-fluorine-based grease and a fluorine-based grease preferably using a three-roll mill; the non-fluorine-based grease being prepared by stirring a non-fluorine-based base oil, aliphatic dicarboxylic acid, and monoamide monocarboxylic acid obtainable by amidation of a monocarboxylic group of a saturated or unsaturated aliphatic dicarboxylic acid having 2 to 20 carbon atoms under heating, and adding metal hydroxide thereto to form a complex metal soap in the non-fluorine-based base oil; and the fluorine-based grease being prepared from a fluorine-based base oil and a fluororesin powder, wherein the non-fluorine-based base oil is used in an amount of 5 to 90 wt.%, wherein the fluorine-based base oil is used in an amount of 5 to 90 wt.%, wherein the complex metal soap is used in an amount of 1.5 to 30 wt.% and wherein the fluororesin powder is used in an amount of 0.1 to 50 wt.% in the lubricating grease composition. As a complex metal soap, a complex barium metal soap is preferably used.

EFFECT OF THE INVENTION

The lubricating grease composition of the present invention has excellent abrasion resistance, load resistance, heat resistance (degree of oil separation), and shear stability (consistency change). Particularly, compared with the lubricating grease composition disclosed in Patent Document 6, the lubricating grease composition of the present invention has improved abrasion resistance and ensures cost reduction.
More specifically, in abrasion scar diameter measurement using the Shell four-ball test, the lubricating grease composition (perfluoropolyether oil: 80 wt.%, lithium azelate: 15 wt.%, and PTFE: 5 wt.%) of Example 15 of Patent Document 6 has a abrasion scar diameter of 0.9 mm. This value is inferior to the abrasion scar diameter (0.6 mm) of grease compositions of Comparative Examples 2 and 3 of the present specification, described later (poly-α-olefin oil containing a 12-hydroxystearic acid lithium soap or a lithium complex soap of azelaic acid and 12-hydroxystearic acid: 80 wt.%, and PTFE-containing perfluoropolyether oil: 20 wt.%). In contrast, grease compositions of Examples of the present invention have a abrasion scar diameter of 0.4 to 0.8 mm, showing further improved abrasion resistance. Additionally, the expensive fluorine-based base oil is partially substituted by the non-fluorine-based base oil, leading to effective cost reduction.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

Mutual incompatibility between the non-fluorine-based base oil and the fluorine-based base oil means that a homogeneous base oil mixture cannot be formed by simply mixing these two base oils.
The non-fluorine-based base oil is at least one of, for example, synthetic hydrocarbon oils such as poly-α-olefin, ethylene-α-olefin oligomer, polybutene or hydrogenates thereof, alkyl benzene, and alkyl naphthalene; ether-based synthetic oils such as polyalkylene glycol, polyphenyl ether, and alkyl-substituted diphenyl ether; ester-based synthetic oils such as trimellitic acid ester, pyromellitic acid ester, neopentyl glycol ester, trimethylolpropane ester, pentaerythritol ester, and dipentaerythritol ester; synthetic oils such as polyol ester, aromatic polycarboxylic acid ester, aliphatic dibasic acid ester, phosphoric acid ester, phosphorous acid ester, and carbonic acid ester; paraffinic mineral oil, naphthenic mineral oil or purified mineral oils thereof, etc. Preferably, synthetic hydrocarbon oils or ether-based synthetic oils are used.
As such non-fluorine-based base oils, those having a kinematic viscosity at 40°C (according to JIS K2283 corresponding to ASTM D445) of about 5 to 1,500 mm²/sec., preferably about 10 to 500 mm²/sec., are generally used. Non-fluorine-based base oils having a kinematic viscosity of less than this range are largely evaporated, and do not comply with the requirements for the standard of JIS ball-and-roller bearing grease, class 3 specified as heat-resistant grease (i.e., the amount of evaporation is 1.5% or less). Conversely, non-fluorine-based base oils having a kinematic viscosity of more than this range have a pour point (according to JIS K2283) of 10°C or more; bearings cannot be rotated by an ordinary method at the time of low-temperature starting; and they must be heated to make them usable. Thus, such non-fluorine-based base oils cannot suitably be used in general greases.
As fluorine-based base oils, those having a kinematic viscosity at 40°C (according to JIS K2283) of about 10 to 1,500 mm²/sec., preferably about 20 to 500 mm²/sec., are generally used. More specifically, those represented by the general formula:

RfO(CF₂O)_x(C₂F₄O)_y(C₃F₆O)_zRf

are used. Specific examples thereof include those represented by the following general formulae (1) to (4), and one represented by the general formula (5). Rf is perfluoromethyl, perfluoroethyl, perfluoropropyl, or other perfluoro lower alkyl group having 1 to 5 carbon atoms, preferably 1 to 3 carbon atoms.

(1) RfO(CF₂CF₂O)_m(CF₂O)_nRf

wherein m+n is 3 to 200, m:n is 10:90 to 90:10, and CF₂CF₂O group and CF₂O group are randomly bonded to the main chain. This can be obtained by complete fluorination of a precursor produced by photooxidation polymerization of tetrafluoroethylene.

(2) RfO[CF(CF₃)CF₂O)]_m(CF₂O)_nRf

wherein m+n is 3 to 200, m:n is 10:90 to 90:10, and CF(CF₃)CF₂O group and CF₂O group are randomly bonded to the main chain. This can be obtained by complete fluorination of a precursor produced by photooxidation polymerization of hexafluoropropylene.

(3) RfO[CF(CF₃)CF₂O]_p(CF₂CF₂O)_q(CF₂O)_rRf

wherein p+q+r is 3 to 200, q and r may be 0, (q+r)/p is 0 to 2, and CF(CF₃)CF₂O, CF₂CF₂O group and CF₂O group are randomly bonded to the main chain. This can be obtained by complete fluorination of a precursor produced by photooxidation polymerization of hexafluoropropylene and tetrafluoroethylene.

(4) RfO[CF(CF₃)CF₂O]_s(CF₂CF₂O)_tRf

wherein s+t is 2 to 200, t may be 0, t/s is 0 to 2, and CF(CF₃)CF₂O group and CF₂CF₂O group are randomly bonded to the main chain. This can be obtained by complete fluorination of a precursor produced by photooxidation polymerization of hexafluoropropylene and tetrafluoroethylene. Alternatively, it can be obtained by anionic polymerization of hexafluoropropylene oxide or tetrafluoroethylene oxide in the presence of a cesium fluoride catalyst, and then by fluorine gas treatment of the obtained acid fluoride compound having a terminal -CF(CF₃)COF group.

(5) F(CF₂CF₂CF₂O)_2-100C₂F₅

This can be obtained by anionic polymerization of 2,2,3,3-tetrafluorooxetane in the presence of a cesium fluoride catalyst, and then by fluorine gas treatment of the obtained fluorine-containing polyether (CH₂CF₂CF₂O)_n under UV irradiation at about 160 to 300°C.
The non-fluorine-based base oil and fluorine-based base oil are used in such a proportion that the former base oil is generally used at a ratio of about 5 to 95 wt.%, preferably about 10 to 90 wt.%, with respect to about 95 to 5 wt.%, preferably about 90 to 10 wt.%, of the latter base oil. When the proportion of the non-fluorine-based base oil is less than this range, load resistance increases, while abrasion resistance, heat resistance, shear stability, etc. decrease. Conversely, when the proportion is higher than this range, abrasion resistance increases, while heat resistance, load resistance, shear stability, etc. decrease.
The complex metal soap used as a thickener is formed as a complex metal soap of aliphatic dicarboxylic acid and monoamide monocarboxylic acid. The formation of the complex metal soap is carried out during preparation of the lubricating grease composition, as described later.
As aliphatic dicarboxylic acids, saturated or unsaturated dicarboxylic acids having 2 to 20 carbon atoms are used. Examples of saturated dicarboxylic acids include oxalic acid, malonic acid, succinic acid, methylsuccinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, nonamethylenedicarboxylic acid, decamethylenedicarboxylic acid, undecanedicarboxylic acid, dodecanedicarboxylic acid, tridecanedicarboxylic acid, tetradecanedicarboxylic acid, pentadecanedicarboxylic acid, hexadecanedicarboxylic acid, heptadecanedicarboxylic acid, octadecanedicarboxylic acid, etc. Preferably used are adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, nonamethylenedicarboxylic acid, decamethylenedicarboxylic acid, undecanedicarboxylic acid, dodecanedicarboxylic acid, tridecanedicarboxylic acid, tetradecanedicarboxylic acid, pentadecanedicarboxylic acid, hexadecanedicarboxylic acid, heptadecanedicarboxylic acid, octadecanedicarboxylic acid, etc. Examples of unsaturated dicarboxylic acids include maleic acid, fumaric acid, 2-methylenesuccinic acid, 2-ethylenesuccinic acid, 2-methyleneglutaric acid, and other alkenyl succinic acids. These saturated or unsaturated dicarboxylic acids are used singly or in combination of two or more.
Monoamide monocarboxylic acids are obtained by amidation of the monocarboxylic groups of the above dicarboxylic acids. Examples of amines to be amidated include aliphatic primary amines, such as butylamine, amylamine, hexylamine, heptylamine, octylamine, nonylamine, decylamine, laurylamine, myristylamine, palmitylamine, stearylamine, and behenylamine; aliphatic secondary amines, such as dipropylamine, diisopropylamine, dibutylamine, diamylamine, dilaurylamine, monomethyl laurylamine, distearylamine, monomethyl stearylamine, dimyristylamine, and dipalmitylamine; aliphatic unsaturated amines, such as allylamine, diallylamine, oleylamine, and dioleylamine; alicyclic amines, such as cyclopropylamine, cyclobutylamine, cyclopentylamine, and cyclohexylamine; aromatic amines, such as aniline, methylaniline, ethylaniline, benzylamine, dibenzylamine, diphenylamine, and α-naphthylamine; and the like. Preferably used are hexylamine, heptylamine, octylamine, nonylamine, decylamine, laurylamine, myristylamine, palmitylamine, stearylamine, behenylamine, dibutylamine, diamylamine, monomethyl laurylamine, monomethyl stearylamine, oleylamine, etc.
These aliphatic dicarboxylic acids and monoamide monocarboxylic acids are used to form complex metal soaps together with lithium, sodium, potassium, calcium, barium, magnesium, copper, iron, cobalt, zinc, aluminum, and other metals; complex barium soaps are preferred.
Moreover, examples of the fluororesin powder include PTFE powder, HFP powder, perfluoroalkylene resin powder, etc. The fluororesin powder generally has an average primary particle size of about 500 µm or less, preferably about 0.1 to 30 µm.
As for usable PTFE (polytetrafluoroethylene), tetrafluoroethylene is subjected to emulsion polymerization, suspension polymerization, solution polymerization, or like method to produce polytetrafluoroethylene, and the resulting polytetrafluoroethylene is treated by pyrolysis, degradation by electron-beam irradiation, physical pulverization, or like method, so that the number average molecular weight Mn is about 1,000 to 1,000,000. Moreover, as for usable HFP powders, the copolymerization of tetrafluoroethylene and hexafluoropropene and the reduction of molecular weight are carried out in the same manner as with polytetrafluoroethylene, so that the number average molecular weight Mn is about 1,000 to 600,000. The molecular weight can be controlled by a chain transfer agent during copolymerization reaction.
The formation of the complex metal soap and the preparation of the lubricating grease composition are carried out as follows.

(a-1) A non-fluorine-based base oil, aliphatic dicarboxylic acid, and monoamide monocarboxylic acid are placed in a reaction kettle that allows stirring under heating, and the mixture is stirred while heating to about 80 to 180°C, at which stirring is possible, the reaction is efficiently promoted, and the base oil does not deteriorate. To the mixture, metal hydroxide is added to form a complex metal soap in the non-fluorine-based base oil. After cooling, a predetermined amount of amine-based antioxidant, etc. is added thereto, and the mixture is kneaded through a three-roll mill or a high-pressure homogenizer, thereby preparing a non-fluorine-based grease. Prior to kneading, non-fluorine-based base oils other than the non-fluorine-based base oil initially used may be added.
(a-2) A fluorine-based base oil and a fluororesin powder are mixed in a mixing kettle, and the mixture is then kneaded through a three-roll mill or a high-pressure homogenizer, thereby preparing a fluorine-based grease.
(a-3) These two kinds of greases are mixed in a mixing kettle, preferably kneaded by a three-roll mill, thereby preparing a lubricating grease composition. Generally, a hydraulic three-roll mill is used for kneading.

That is, the lubricating grease composition of the present invention can be prepared by mixing two kinds of greases, i.e., a non-fluorine-based grease that is a complex metal soap thickener-containing non-fluorine-based base oil, and a fluorine-based grease that is a fluororesin powder-containing fluorine-based base oil.
(b) The lubricating grease composition of the present invention can also be prepared by adding a fluorine-based base oil and fluororesin to the non-fluorine-based grease prepared in the above manner, and mixing them in a mixing kettle, followed by kneading with a three-roll mill.
In the lubricating grease composition (base grease) comprising the above essential components, the non-fluorine-based base oil is used in an amount of 5 to 90 wt.%, preferably 10 to 80 wt.%, in the base grease; the fluorine-based base oil, which is used together with the non-fluorine-based base oil at the above-described ratio, is used in an amount of 5 to 90 wt.%, preferably 10 to 80 wt.%, in the base grease; the complex metal soap is used in an amount of 1.5 to 30 wt.%, preferably 5 to 25 wt.%, in the base grease; and the fluororesin powder is used in an amount of 0.1 to 50 wt.%, preferably 5 to 35 wt.%, in the base grease.
Compounding of each component in the proportion described above has the following effects:

Non-fluorine-based base oil: thickeners having little or no compatibility with the fluorine-based base oil can be added, thereby resulting in increased abrasion resistance, lower friction coefficient, and improved rust prevention and corrosion inhibition effect.
Fluorine-based base oil: heat resistance is improved.
Complex metal soap: abrasion resistance is improved.
Fluororesin powder: the compatibility between the fluorine-based base oil and the complex metal soap increases.

The lubricating grease composition may contain, if necessary, antioxidants, rust inhibitors, corrosion inhibitors, extreme pressure additives, oiliness agents, solid lubricants, and other additives used in conventional lubricants. Examples of antioxidants include phenol-based antioxidants, such as 2,6-di-tert-butyl-4-methylphenol and 4,4'-methylenebis(2,6-di-tert-butylphenol); amine-based antioxidants, such as alkyl diphenylamine having a C₄-C₂₀ alkyl group, triphenylamine, phenyl-α-naphthylamine, alkylated phenyl-α-naphthylamine, phenothiazine, and alkylated phenothiazine; phosphoric acid-based antioxidants, sulfur-based antioxidants, and the like.
Examples of rust inhibitors include fatty acids, fatty acid metal salts, fatty acid amines, alkylsulfonic acid metal salts, alkylsulfonic acid amine salts, oxided paraffin, polyoxyethylene alkyl ethers, and the like. Examples of corrosion inhibitors include benzotriazole, benzoimidazole, thiadiazole, and the like.
Examples of extreme pressure additives include phosphorus-based compounds, such as phosphoric acid esters, phosphorous acid esters, and phosphoric acid ester amine salts; sulfur-based compounds, such as sulfides and disulfides; sulfur-based compound metal salts, such as dialkyldithiophosphoric acid metal salts and dialkyldithiocarbamic acid metal salts; chlorine-based compounds, such as chlorinated paraffin and chlorinated diphenyl; and the like.
Examples of oiliness agents include fatty acids or esters thereof, higher alcohols, polyhydric alcohols or esters thereof, aliphatic esters, aliphatic amines, fatty acid monoglycerides, montan wax, amide-based wax, and the like. Examples of other solid lubricants include molybdenum disulfide, graphite, boron nitride, silane nitride, melamine cyanurate, and the like. Such other solid lubricants have an average primary particle size of 30 µm or less, preferably 0.1 to 20 µm.
Additionally, other thickeners that have generally been used as thickeners, such as silica, clay, graphite, zinc oxide, urea compounds, polyethylene, polypropylene, polyamide, organic pigments, metal soaps, etc., can be suitably added.

EXAMPLES

The following describes the present invention with reference to Examples.

Reference Example 1

In a poly-α-olefin oil (40°C viscosity: 30 mm²/sec.), a barium complex soap of sebacic acid and sebacic acid monostearylamide, accounting for 30 wt.% of the base grease as a thickener, was synthesized by the process (a-1) described above. To the barium complex soap, 2 wt.% of amine-based antioxidant (NA-LUBE AO-120, a product of King Industries, Inc.; alkyl diphenylamine) was added, and the mixture was kneaded twice by a three-roll mill, thereby producing a grease A.

Reference Example 2

In a poly-α-olefin oil (40°C viscosity: 46 mm²/sec.), a barium complex soap of azelaic acid and azelaic acid monooctylamide, accounting for 25 wt.% of the base grease as a thickener, was synthesized by the process (a-1) described above. To the barium complex soap, 3 wt.% of oiliness agent (trimethylolpropane alkyl ester; 40°C viscosity: 30 mm²/sec.) and 2 wt.% of amine-based antioxidant (NA-LUBE AO-120) were added, and the mixture was kneaded twice by a three-roll mill, thereby producing a grease B.

Reference Example 3

In a diphenyl ether oil (40°C viscosity: 100 mm²/sec.), a barium complex soap of sebacic acid and sebacic acid monostearylamide, accounting for 30 wt.% of the base grease as a thickener, was synthesized by the process (a-1) described above. To the barium complex soap, 2 wt.% of amine-based antioxidant (NA-LUBE AO-120) was added, and the mixture was kneaded twice by a three-roll mill, thereby producing a grease C.

Reference Example 4

In a poly-α-olefin oil (40°C viscosity: 30 mm²/sec.), a lithium soap of 12-hydroxystearic acid, accounting for 10 wt.% of the base grease as a thickener, was synthesized. To the lithium soap, 2 wt.% of amine-based antioxidant (NA-LUBE AO-120) was added, and the mixture was kneaded twice by a three-roll mill, thereby producing a grease D.

Reference Example 5

In a poly-α-olefin oil (40°C viscosity: 46 mm²/sec.), a lithium complex soap of azelaic acid and 12-hydroxystearic acid, accounting for 20 wt.% of the base grease as a thickener, was synthesized. To the lithium complex soap, 3 wt.% of oiliness agent (trimethylolpropane alkyl ester; 40°C viscosity: 30 mm²/sec.) and 2 wt.% of amine-based antioxidant (NA-LUBE AO-120) were added, and the mixture was kneaded twice by a three-roll mill, thereby producing a grease E.

Reference Example 6

A fluorine-based base oil (40°C viscosity: 230 mm²/sec.) having a molecular structure represented by the general formula: RfO[CF(CF₃)CF₂O]_mRf was mixed with a PTFE powder (average particle diameter: 0.3 µm) in an amount accounting for 32 wt.% of the base grease. The mixture was kneaded twice by a three-roll mill, thereby producing a grease I.

Reference Example 7

A fluorine-based base oil (40°C viscosity: 230 mm²/sec.) having a molecular structure represented by the general formula: RfO[CF(CF₃)CF₂O]_mRf was mixed with a PTFE powder (average particle diameter: 0.3 µm) in an amount accounting for 18 wt.% of the base grease. The mixture was kneaded twice by a three-roll mill, thereby producing a grease II.

Reference Example 8

A fluorine-based base oil (40°C viscosity: 85 mm²/sec.) having a molecular structure represented by the general formula: RfO(CF₂CF₂O)_m(CF₂O)_nRf was mixed with a PTFE powder (average particle diameter: 0.3 µm) in an amount accounting for 27 wt.% of the base grease. The mixture was kneaded twice by a three-roll mill, thereby producing a grease III.

Examples 1 to 6 and Comparative Examples 1 to 5

One or two kinds of the non-fluorine-based greases A to E and the fluorine-based greases I and II prepared in the above Reference Examples were mixed at predetermined weight ratios. Each of the resulting mixtures was sufficiently stirred in a mixing kettle, and then kneaded twice by a three-roll mill, thereby producing lubricating grease compositions.
The produced lubricating grease compositions were measured for the following items:

Abrasion resistance: Shell four-ball test, according to ASTM D2266
- Temperature: 75°C
- Number of rotations: 1,200 rpm
- Load: 392 N
- Time: 60 minutes
- The abrasion scar diameter after the test was measured
- (Smaller values indicate better abrasion resistance)
Load resistance (four-ball test): Soda type, according to JIS K2519
- Step pressurization method
- Number of rotations: 750 rpm
- Temperature: room temperature
- (Larger values indicate better load resistance)
Heat resistance (oil separation degree): according to JIS K2220.11
- corresponding to ASTM D6184
- The degree of oil separation after 24 hours at a temperature of 180°C was measured
- (Smaller values indicate better heat resistance)
Shear stability (consistency change): Shell roll test, according to ASTM 1831
- Temperature: 80°C
- Number of rotations: 165 rpm
- Time: 24 hours
- Consistency changes before and after the test were measured
- (Smaller values indicate better shear stability)

The following table shows the measurement results.

Table

	Ex.						Comp. Ex.
	1	2	3	4	5	6	1	2	3	4	5
[Grease]
A (wt.%)	80	60	60	20	-	-	100	-	-	-	-
B (wt.%)	-	-	-	-	80	-	-	-	-	-	-
C (wt.%)	-	-	-	-	-	50	-	-	-	-	-
D (wt.%)	-	-	-	-	-	-	-	80	-	-	-
E (wt.%)	-	-	-	-	-	-	-	-	80	-	-

I (wt.%)	20	40	-	80	20	-	-	20	20	100	-
II (wt.%)	-	-	-	-	-	50	-	-	-	-	-
III (wt.%)	-	-	40	-	-	-	-	-	-	-	100

[Measurement Item]
Abrasion scar diameter (mm)	0.4	0.5	0.5	0.7	0.5	0.6	0.4	0.6	0.6	1.0	1.1
Load resistance (MPa)	0.784	0.833	0.784	0.980	0.735	0.784	0.637	0.294	0.441	0.980	0.980
Oil separation degree (wt.%)	1.1	0.9	0.8	0.5	1.5	1.5	2.4	5.2	3.0	5.5	5.0
Consistency change (-)	44	38	35	30	45	35	50	76	69	30	30

The above results demonstrate that the greases obtained in the Examples of the present invention are obviously superior in load resistance, oil separation degree, and consistency change to the greases of Comparative Examples 2 and 3 prepared using, as a thickening agent, a lithium soap of 12-hydroxystearic acid or a lithium complex soap of azelaic acid and 12-hydroxystearic acid.

INDUSTRIAL APPLICABILITY

The lubricating grease composition of the present invention, which has excellent characteristics as described above, i.e., excellent heat resistance, shear stability, abrasion resistance to mating materials, and load resistance, as well as satisfies the cost requirements, can be suitably used to lubricate and protect the contact portion between individual sliding parts of ball-and-roller bearings, sliding bearings, sintering bearings, gears, valves, cocks, oil seals, electric contacts, etc.
More specifically, the lubricating grease composition can be suitably applied in various parts of various devices, machines, and apparatuses listed below.

Automobiles: ball-and-roller bearings, sliding bearings, or gear parts of electric radiator fan motors, fan couplings, electronically controlled EGR, electronically controlled throttle valves, alternators, idler pulleys, electric brakes, hub units, water pumps, power windows, wipers, electric power steering systems, etc., to which heat resistance and shear stability are required;
electric contact parts of control switches for automatic transmissions, lever control switches, push switches, etc., to which heat resistance, shear stability, and abrasion resistance are required;
rubber sealing parts of X ring parts of viscous couplings, O rings of exhaust brakes, etc., to which heat resistance and shear stability are required; and
ball-and-roller bearings, sliding bearings, gears, sliding parts, etc., of headlights, sheets, ABSs, door locks, door hinges, clutch boosters, two-divided flywheels, window regulators, ball joints, clutch boosters, etc.
Office appliances: ball-and-roller bearings, sliding bearings, sliding parts or gear parts of resin films, etc., of fixing rolls, fixing belts, etc., of copying machines, laser beam printers, etc., to which heat resistance and abrasion resistance are required
Resin manufacturing apparatuses: ball-and-roller bearings, sliding bearings, pins, oil seals, gears, etc., of film tenters, film laminators, Banbury mixers, etc., to which heat resistance and load resistance are required
Paper making devices: ball-and-roller bearings, sliding bearings, pins, oil seals, gears, etc., of corrugate machines etc., to which heat resistance and abrasion resistance are required
Timber processing devices: ball-and-roller bearings, sliding bearings, pins, oil seals, gears, etc., of conch presses etc., to which heat resistance and abrasion resistance are required
Machines for food products: ball-and-roller bearings etc. of linear guides of bread-baking machines, ovens, etc., to which heat resistance and abrasion resistance are required
Ball-and-roller bearings, sliding bearings, etc., in spindles, servomotors, etc., of machine tools, to which a low friction coefficient is required
Sliding parts etc. of hinges of mobile phones, to which shear stability and abrasion resistance are required
Ball-and-roller bearings and gears in vacuum pumps of semiconductor manufacturing apparatuses, liquid crystal manufacturing apparatuses, electron microscopes, etc; and ball-and-roller bearings etc. in breakers of power controlling device
Household electrical/information appliances: ball-and-roller bearings, sliding bearings, oil seals, etc., in cooling fans for personal computers, vacuum cleaners, washing machines, etc

Claims

A lubricating grease composition comprising a complex metal soap thickener of aliphatic dicarboxylic acid and monoamide monocarboxylic acid obtainable by amidation of a monocarboxylic group of a saturated or unsaturated aliphatic dicarboxylic acid having 2 to 20 carbon atoms, and a fluororesin powder contained in a base oil mixture of a non-fluorine-based base oil and a fluorine-based base oil, which are incompatible with each other, i.e. a homogeneous base oil mixture cannot be formed by simply mixing these two base oils, wherein the non-fluorine-based base oil is contained in an amount of 5 to 90 wt.%, wherein the fluorine-based base oil is contained in an amount of 5 to 90 wt.%, wherein the complex metal soap is contained in an amount of 1.5 to 30 wt.% and wherein the fluororesin powder is contained in an amount of 0.1 to 50 wt.% in the lubricating grease composition.
The lubricating grease composition according to claim 1, which comprises a mixture of two kinds of greases, one grease comprising a complex metal soap thickener of aliphatic dicarboxylic acid and monoamide monocarboxylic acid contained in a non-fluorine-based base oil, and the other grease comprising a fluororesin powder contained in a fluorine-based base oil.
The lubricating grease composition according to claim 1, wherein the non-fluorine-based base oil is a synthetic hydrocarbon oil or an ether-based synthetic oil.
The lubricating grease composition according to claim 2, wherein the non-fluorine-based base oil is a synthetic hydrocarbon oil or an ether-based synthetic oil.
The lubricating grease composition according to claim 1, wherein the complex metal soap is a barium complex soap.
The lubricating grease composition according to claim 2, wherein the complex metal soap is a barium complex soap.
The lubricating grease composition according to claim 1, wherein the fluorine-based base oil is used at a ratio of 95 to 5 wt.% with respect to 5 to 95 wt.% of the non-fluorine-based base oil.
The lubricating grease composition according to claim 1, wherein the fluorine-based base oil is used at a ratio of 90 to 10 wt.% with respect to 10 to 90 wt.% of the non-fluorine-based base oil.
A method for producing a lubricating grease composition according to claim 1, the method comprises by kneading a non-fluorine-based grease and a fluorine-based grease; the non-fluorine-based grease being prepared by stirring a non-fluorine-based base oil, aliphatic dicarboxylic acid, and monoamide monocarboxylic acid obtainable by amidation of a monocarboxylic group of a saturated or unsaturated aliphatic dicarboxylic acid having 2 to 20 carbon atoms under heating, and adding metal hydroxide thereto to form a complex metal soap in the non-fluorine-based base oil; and
the fluorine-based grease being prepared from a fluorine-based base oil and a fluororesin powder, wherein the non-fluorine-based base oil is used in an amount of 5 to 90 wt.%, wherein the fluorine-based base oil is used in an amount of 5 to 90 wt.%, wherein the complex metal soap is used in an amount of 1.5 to 30 wt.% and wherein the fluororesin powder is used in an amount of 0.1 to 50 wt.% in the lubricating grease composition.
The method for producing a lubricating grease composition according to claim 9, wherein the non-fluorine-based grease and the fluorine-based grease are each prepared by kneading through a three-roll mill or a high-pressure homogenizer.
The method for producing a lubricating grease composition according to claim 9, wherein the non-fluorine-based grease and the fluorine-based grease are kneaded by a three-roll mill.
The method for producing a lubricating grease composition according to claim 9, wherein a synthetic hydrocarbon oil or an ether-based synthetic oil is used as the non-fluorine-based base oil.
The method for producing a lubricating grease composition according to claim 9, wherein barium hydroxide is used as the metal hydroxide.