Technical Field
[0001] The present invention relates to a grease composition.
Background Art
[0002] Conventionally, a grease has been used as a lubricant in a bearing, a constant velocity
joint and the like with which an apparatus such as a driving force transmission mechanism
is provided.
[0003] In recent years, the apparatus such as a driving force transmission mechanism has
tended to be increasingly advanced, higher in performance, higher in speed, smaller
in size and longer in lifetime, and a bearing, a constant velocity joint and the like
have been used under a high load condition. Therefore, in order to maintain stable
lubrication characteristics for a long period of time, levels required for characteristics
of a grease, in particular, stability and lubricity as basic performances have been
further higher.
[0004] In addition, in an apparatus with a large number of bearing systems rotated at a
relatively low speed and bearing positions, the energy saving effect due to a reduction
in friction is high. Then, a measure by a reduction in viscosity of a base oil for
use in a grease is studied. The reduction in viscosity, however, deteriorates oil
film formability in a lubrication part, and thus has limitations with the occurrence
of a lubrication failure in mind.
[0005] From the above, a grease that is superior in stability and lubricity and exhibits
low friction characteristics is demanded.
[0006] With respect to the enhancement in stability of a grease, Patent Literature 1 discloses
a grease in which a thickener, (A) a dialkyldithiocarbamate and (B) an aromatic amine
compound are added to a base oil with a polyol ester and an alkyl phenyl ether mixed,
Patent Literature 2 discloses a grease composition in which a base oil includes a
polyoxyalkylene glycol ether and an additive includes a quinoline type compound and
a benzotriazole type compound, Patent Literature 3 discloses a grease in which a base
oil is a specific condensed phosphoric acid ester and a specific thickener such as
organic bentonite is blended therewith, Patent Literature 4 discloses a lubricant
containing in a base oil, fluorinated calcium phosphate also having a thickening effect,
Patent Literature 5 discloses a lubricant composition containing a thickener and trimagnesium
phosphate in a base oil, Patent Literature 6 discloses a grease containing a thickener
and a base oil including a specific poly-α-olefin and a specific ethylene-α-olefin
copolymer, and Patent Literature 7 discloses a grease in which a base oil is a specific
perfluoropolyether, respectively.
[0007] With respect to the enhancement in lubricity of a grease, Patent Literature 8 discloses
a grease containing a powdery oxymolybdenum dithiocarbamate sulfide composition of
a specific structure, Patent Literature 9 discloses a conductive grease composition
having good lubricity, including an ionic liquid, an alkaline earth metal salt of
a higher fatty acid, and a dispersant, Patent Literature 10 discloses a grease mixed
with a particulate thickening substance whose rate of increase in viscosity can satisfy
the condition expressed by a specific expression, Patent Literature 11 discloses a
grease containing a thickener, a specific polytetrafluoroethylene resin powder and
a specific zinc dialkyldithiophosphate in a synthetic base oil, Patent Literature
12 discloses a grease in which a base oil is a perfluoropolyether and a thickener
is a specific fluororesin, and Patent Literature 13 discloses a grease composition
containing a silicone oil, a polyurethane powder and synthetic mica, respectively.
Citation List
Patent Literature
[0008]
[Patent Literature 1] Japanese Patent Application Laid-Open No. 9-3468
[Patent Literature 2] Japanese Patent Application Laid-Open No. 2006-249376
[Patent Literature 3] Japanese Patent Application Laid-Open No. 2010-174209
[Patent Literature 4] Japanese Patent Application Laid-Open No. 2011-21149
[Patent Literature 5] Japanese Patent Application Laid-Open No. 2011-57762
[Patent Literature 6] Japanese Patent Application Laid-Open No. 2011-148908
[Patent Literature 7] Japanese Patent Application Laid-Open No. 2011-256397
[Patent Literature 8] Japanese Patent Application Laid-Open No. 2004-2872
[Patent Literature 9] Japanese Patent Application Laid-Open No. 2007-99826
[Patent Literature 10] Japanese Patent Application Laid-Open No. 2007-231207
[Patent Literature 11] Japanese Patent Application Laid-Open No. 2008-101122
[Patent Literature 12] Japanese Patent Application Laid-Open No. 2010-65171
[Patent Literature 13] Japanese Patent Application Laid-Open No. 2010-138320
Summary of Invention
Technical Problem
[0009] According to studies by the present inventor, however, the greases described in Patent
Literatures 1 to 13 above cannot be said to be necessarily sufficient in terms of
stability and lubricity under severe use conditions, and have room for improvement
in simultaneously satisfying these characteristics and friction characteristics.
[0010] The present invention has been made in view of the problems of the prior art above,
and an object thereof is to provide a grease composition that is good in stability,
lubricity and friction characteristics and excellent in long-term reliability even
under severe use conditions as compared with a conventional grease.
Solution to Problem
[0011] The present inventors have found that the above problems are solved by blending a
thickener, an epoxy compound and an antiwear additive with a specific base oil in
respective specific proportions to thereby result in improvements in stability, lubricity
and friction characteristics of a grease, leading to completion of the present invention.
[0012] That is, the present invention provides grease compositions according to the following
[1] to [10].
[0013] [1] A grease composition comprising at least one base oil selected from a mineral
oil and a synthetic oil, and, based on the total amount of the grease composition,
2 to 35% by mass of a thickener, 0.05 to 5% by mass of an epoxy compound and 0.1 to
20% by mass of an antiwear additive.
[0014] [2] The grease composition according to [1], wherein the epoxy compound is at least
one selected from a phenyl glycidyl ether type epoxy compound, an alkyl glycidyl ether
type epoxy compound, a glycidyl ester type epoxy compound, an alicyclic epoxy compound,
an epoxidized aliphatic monoester and an epoxidized vegetable oil.
[0015] [3] The grease composition according to [2], wherein the epoxy compound is an alkyl
glycidyl ether represented by the following formula (1):

wherein R represents a linear or branched alkyl group having 6 to 20 carbon atoms.
[0016] [4] The grease composition according to [3], wherein the epoxy compound is at least
one selected from octyl glycidyl ether, 2-ethylhexyl glycidyl ether, nonyl glycidyl
ether, decyl glycidyl ether, undecyl glycidyl ether and dodecyl glycidyl ether.
[0017] [5] The grease composition according to any one of [1] to [3], wherein the antiwear
additive is at least one selected from an oxygen-containing compound, a nitrogen-containing
compound, an organophosphorus compound, an organosulfur compound, an organomolybdenum
compound, an alkaline earth metal compound and an organozinc compound.
[0018] [6] The grease composition according to [5], wherein the oxygen-containing compound
is at least one selected from an ester, an alcohol, an ether and a carboxylic acid;
the nitrogen-containing compound is at least one selected from an aliphatic amine,
an aliphatic amide and an aliphatic imide; the organophosphorus compound is at least
one selected from a phosphoric acid ester, a phosphorous acid ester and an acidic
phosphoric acid ester amine salt; the organosulfur compound is at least one selected
from a sulfide compound, and sulfurized fat and oil; the organomolybdenum compound
is at least one selected from molybdenum dithiocarbamate and molybdenum dithiophosphate;
the alkaline earth metal compound is at least one selected from alkaline earth metal
sulfonate salt, phenate salt and salicylate salt; and the organozinc compound is at
least one selected from a zinc dialkyl, a zinc dialkyldithiophosphate and a zinc dialkyldithiocarbamate.
[0019] [7] The grease composition according to any one of [1] to [3], wherein the antiwear
additive is a solid lubricant.
[0020] [8] The grease composition according to [7], wherein the solid lubricant is at least
one selected from molybdenum disulfide, graphite, a tetrafluoroethylene resin powder
and boron nitride.
[0021] [9] The grease composition according to any one of [1] to [8], wherein the synthetic
oil is at least one selected from a hydrocarbon oil, a diester, a polyol ester and
a polyalkylene glycol compound.
[0022] [10] The grease composition according to any one of [1] to [8], wherein the thickener
is at least one selected from lithium soaps, calcium soaps, aluminum soaps and a urea
compound.
[0023] [11] The grease composition according to [5], containing, as the antiwear additive,
an organomolybdenum compound and an organozinc compound.
[0024] [12] The grease composition according to [5], containing, as the antiwear additive,
an organomolybdenum compound, an organozinc compound and an organosulfur compound.
Advantageous Effects of Invention
[0025] According to the present invention, it is possible to provide a grease composition
that is good in stability, lubricity and friction characteristics and excellent in
long-term reliability even under severe use conditions as compared with a conventional
grease.
Description of Embodiments
[0026] Hereinafter, a preferred embodiment of the present invention is described in detail.
[0027] A grease composition according to an embodiment of the present invention comprises
at least one base oil selected from a mineral oil and a synthetic oil, and based on
the total amount of the grease composition, 2 to 35% by mass of a thickener, 0.05
to 5% by mass of an epoxy compound and 0.1 to 20% by mass of an antiwear additive.
[Base oil]
[0028] As the base oil in the present embodiment, a mineral oil and/or a synthetic oil for
use in a lubricating oil may be used.
[0029] The mineral oil includes a paraffinic base oil, a naphthenic base oil and a mixed
base oil. These are each a refined lubricating oil fraction obtained by subjecting
a crude oil to distillation at ordinary pressure and further distillation at reduced
pressure and treating the resulting lubricating oil fraction by an appropriate combination
of lubricating oil-refining procedures such as solvent deasphalting, solvent extraction,
hydrorefining, hydrocracking, solvent dewaxing, hydrodewaxing and a clay treatment,
and may be suitably used. In particular, a step of controlling the composition corresponds
to solvent extraction, hydrorefining and hydrocracking, a step of controlling low
temperature characteristics such as a pour point corresponds to solvent dewaxing and
hydrodewaxing for removal of the wax content, and a clay treatment is a step of removing
the nitrogen content mainly to enhance the stability of the base oil.
[0030] In addition, examples include a lubricating base oil such as a wax-cracked/isomerized
mineral oil obtained by hydrocracking and/or isomerizing a raw material containing
a wax mainly including n-paraffins, such as a slack wax or GTL WAX (gas to liquid
wax) produced by a Fischer-Tropsch process or the like. A refined lubricating oil
fraction having a different property, obtained from a combination of various raw materials
and various refining procedures, may be used singly or in combinations of two or more,
and is a suitable base oil.
[0031] In addition, the synthetic oil includes esters such as monoesters, diesters and polyol
esters, ethers such as polyoxyalkylene glycols, polyvinyl ethers, dialkyl diphenyl
ethers and polyphenylethers, and hydrocarbon oils such as poly-α-olefins (PAO), an
ethylene-α-olefin oligomer, alkylbenzenes and alkylnaphthalenes.
[0032] Esters are compounds having various molecular structures, and each of them has particular
viscosity characteristics and low temperature characteristics and is a base oil that
is characterized by being high in flash point as compared with a hydrocarbon type
base oil whose viscosity is the same. Esters may be each obtainable by a dehydration
condensation reaction of an alcohol with a carboxylic acid such as a fatty acid, but,
in the present invention, a suitable base oil component includes diesters of dibasic
acids and monohydric alcohols, polyol esters of polyols (in particular, neopentyl
polyol) and monovalent fatty acids, or complex esters of polyols, polyvalent basic
acids and monohydric alcohols (or monovalent fatty acids) in terms of chemical stability.
[0033] Dibasic acids include adipic acid, azelaic acid, sebacic acid and dodecanedioic acid,
and monohydric alcohols include, as linear monohydric alcohols, butanol, pentanol,
hexanol, octanol and decanol, and, as branched monohydric alcohols, 2-ethylhexanol,
3,5,5-trimethylhexanol and isodecanol.
[0034] Among monovalent fatty acids, specifically, linear fatty acids include butanoic acid,
pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid and oleic
acid, and branched fatty acids include branched butanoic acid, branched pentanoic
acid, branched hexanoic acid, branched heptanoic acid, branched octanoic acid and
branched nonanoic acid. Specifically, α- and/or β-branched fatty acids include isobutanoic
acid, 2-methylbutanoic acid, 2-methylpentanoic acid, 2-methylhexanoic acid, 2-ethylpentanoic
acid, 2-methylheptanoic acid, 2-ethylhexanoic acid and 3,5,5-trimethylhexanoic acid.
As monovalent fatty acids, saturated fatty acids having 4 to 18 carbon atoms, preferably
6 to 12 carbon atoms, can be used.
[0035] As polyhydric alcohols, polyhydric alcohols having 2 to 6 hydroxyl groups, polyhydric
alcohols having 4 to 12 carbon atoms, are preferably used. Specifically, polyhydric
alcohols include hindered alcohols such as neopentyl glycol, trimethylolethane, trimethylolpropane,
trimethylolbutane, di-(trimethylolpropane), pentaerythritol and di-(pentaerythritol).
[0036] Ethers include polyalkylene glycols, polyvinyl ethers and dialkyl diphenyl ethers.
Polyalkylene glycols include polypropylene glycol, polyethylene glycol, and a copolymer
of propylene oxide and ethylene oxide. A compound, in which the hydroxyl group at
one end is etherified and the hydroxyl group at the remaining end remains as it is,
is commonly used, but a compound in which the hydroxyl groups at both ends are etherified
is preferable because of being low in hygroscopicity, and the backbone thereof is
more preferably an oxypropylene type than an oxyethylene type high in hygroscopicity.
In the present embodiment, a polyalkylene glycol compound may be suitably used.
[0037] Among hydrocarbon oils, poly-α-olefins (PAOs) are widely used, and are polymers of
α-olefins and thus are characterized by the degree of polymerization. While alkylbenzenes
and alkylnaphthalenes are used in the field of a specific lubricating oil, they are
classified to a linear type and a branched type depending on the structure of the
alkyl group and are different in terms of characteristics, and thus are used depending
on the purpose.
[0038] Among these base oils, a mineral oil, diesters, polyol esters, a polyalkylene glycol
compound or poly-α-olefins may be preferably used.
[0039] In the present embodiment, one of the mineral oil or one of the synthetic oil may
be used singly. In addition, two or more selected from the group consisting of the
mineral oil and the synthetic oil may be appropriately combined and blended in appropriate
proportions so as to satisfy various performances required depending on the application.
Herein, a plurality of the mineral oil type base oils and a plurality of the synthetic
oil type base oils may be each used.
[0040] The kinematic viscosity of the base oil at 40°C is preferably 3 to 2000 mm
2/s, more preferably 5 to 1000 mm
2/s and further preferably 8 to 500 mm
2/s in order that the grease composition maintains an appropriate viscous property.
[0041] The content of the base oil is preferably 60% by mass or more and more preferably
70% by mass or more based on the total amount of the grease composition. In addition,
the content of the base oil is preferably 95% by mass or less and more preferably
90% by mass or less based on the total amount of the composition. If the content is
within this range, lubricity is excellent and it is possible to stably provide a grease.
[Thickener]
[0042] The thickener for use in the grease composition according to the present embodiment
is not particularly limited, and all thickeners usually used for a grease composition
may be used. Examples of the thickener include metal soaps including lithium, calcium,
sodium or aluminum, a urea compound, an imide compound, Bentone, silica gel, a non-soap
thickener such as a fluorinated thickener typified by polytetrafluoroethylene, and
furthermore an amide compound that is liquid at a temperature equal to or higher than
the melting point of the compound and is a gel-like grease at room temperature. Among
them, metal soaps and a urea compound are preferable. In addition, among metal soaps,
lithium soaps are particularly preferable.
[0043] Lithium soaps include lithium soaps and lithium complex soaps. Lithium soaps include
lithium metal soaps such as lithium 12-hydroxystearate and lithium stearate, and lithium
complex soaps include lithium soaps with a mixture of a monovalent carboxylic acid
and a polyvalent carboxylic acid (preferably, divalent carboxylic acid), specifically,
a mixture of a reaction product of 12-hydroxystearic acid and lithium hydroxide and
a reaction product of azelaic acid and lithium hydroxide, and the like.
[0044] The urea compound includes a diurea compound, and in particular, examples of the
diurea compound include a diurea compound obtained by reacting an aromatic amine,
an aliphatic amine, an alicyclic amine or a mixture of two or more of them with an
aromatic diisocyanate. Examples of the aromatic diisocyanate include tolylene diisocyanate,
diphenylmethane diisocyanate and naphthalene diisocyanate, examples of the aromatic
amine include p-toluidine, aniline and naphthylamine, examples of the aliphatic amine
include octylamine, nonylamine, decylamine, undecylamine, dodecylamine, tridecylamine
and tetradecylamine, and examples of the alicyclic amine include cyclohexylamine and
methylcyclohexylamine.
[0045] These thickeners are thickeners that are balanced in terms of characteristics and
suitable for practical use in terms of availability and cost. In the present embodiment,
the thickener may be used singly or in combinations of two or more. The content of
the thickener can be appropriately selected so as to be necessary for achieving required
consistency, but is preferably 2 to 35% by mass, preferably 5 to 30% by mass and further
preferably 5 to 25% by mass based on the total amount of the grease composition.
[Epoxy compound]
[0046] The grease composition according to the present embodiment comprises an epoxy compound.
In the present embodiment, the epoxy compound and an antiwear additive are used in
combination while the base oil and the thickener are combined, thereby enabling to
enhance stability and wear resistance, and also to simultaneously satisfy these characteristics
and friction characteristics. Herein, the epoxy compound itself does not usually exhibit
the effect of enhancing wear resistance. In addition, the present inventor has confirmed
that the grease composition according to the present embodiment is excellent in wear
resistance as compared with the case where no epoxy compound is used and the antiwear
additive is used singly. It is thus found that the above effect by the grease composition
according to the present embodiment is a synergetic effect by use of the epoxy compound
and the antiwear additive in respective specific contents in combination, and a special
effect that is not exerted by a conventional grease composition.
[0047] The type of the epoxy compound includes an alkyl glycidyl ether type epoxy compound,
a phenyl glycidyl ether type epoxy compound, a glycidyl ester type epoxy compound,
an alicyclic epoxy compound, an epoxidized fatty acid monoester and an epoxidized
vegetable oil.
[0048] The alkyl glycidyl ether type epoxy compound specifically includes hexyl glycidyl
ether, octyl glycidyl ether, 2-ethylhexyl glycidyl ether, nonyl glycidyl ether, decyl
glycidyl ether, undecyl glycidyl ether, dodecyl glycidyl ether, tridecyl glycidyl
ether, tetradecyl glycidyl ether, oleyl glycidyl ether, neopentyl glycol diglycidyl
ether, trimethylolpropane triglycidyl ether, pentaerythritol tetraglycidyl ether,
1,6-hexanediol diglycidyl ether, sorbitol polyglycidyl ether, polyalkylene glycol
monoglycidyl ether and polyalkylene glycol diglycidyl ether.
[0049] The phenyl glycidyl ether type epoxy compound includes phenyl glycidyl ether, methylphenyl
glycidyl ether, ethylphenyl glycidyl ether, propylphenyl glycidyl ether and butylphenyl
glycidyl ether.
[0050] The glycidyl ester type epoxy compound specifically includes phenyl glycidyl esters,
alkyl glycidyl esters and alkenyl glycidyl esters, and examples include glycidyl-2,2-dimethyl
octanoate, glycidyl benzoate, glycidyl acrylate and glycidyl methacrylate. Examples
include alkyl glycidyl esters in which the number of carbon atoms in the alkyl group
is 4 to 18, in particular, 6 to 12.
[0051] The alicyclic epoxy compound specifically includes 1,2-epoxycyclohexane, 1,2-epoxycyclopentane,
3,4-epoxycyclohexyl methyl-3',4'-epoxycyclohexane carboxylate, bis(3,4-epoxy-6-methylcyclohexyl
methyl)adipate, 2-(7-oxabicyclo[4,1,0]hept-3-yl)-spiro(1,3-dioxane-5,3'-[7]oxabicyclo[4
,1,0]heptane, 4-(1'-methylepoxyethyl)-1,2-epoxy-2-methylcyclohexane and 4-epoxyethyl-1,2-epoxycyclohexane.
Examples include derivatives of epoxycycloalkanes having 5 to 7 carbon atoms.
[0052] Epoxidized fatty acid monoesters include esters of epoxidized fatty acids having
12 to 20 carbon atoms and alcohols having 1 to 8 carbon atoms, or phenols or alkyl
phenols, and examples include butyl, hexyl, benzyl, cyclohexyl, methoxyethyl, octyl,
phenyl and butyl phenyl esters of epoxy stearic acid.
[0053] The epoxidized vegetable oil includes an epoxy compound of a vegetable oil such as
a soybean oil, a flaxseed oil or a cotton seed oil.
[0054] In the present embodiment, the epoxy compound incorporates a carboxylic acid or the
like produced along with degradation of the grease into the molecule to stabilize
the carboxylic acid or the like, and thus suppresses production of a component that
causes corrosion wear and suppresses degradation of the additive to thereby contribute
to an enhancement in lubricity.
[0055] Furthermore, the present inventor has found that alkyl glycidyl ethers among the
epoxy compounds exhibit a different behavior from other types of epoxy compounds,
and result in not only an enhancement in lubricity by stabilization but also a significant
increase in the effect of the antiwear additive. In particular, an alkyl glycidyl
ether represented by the following formula (1) is preferable because of resulting
in not only an enhancement in stability but also a large effect of increasing wear
resistance, and furthermore an alkyl glycidyl ether in which R in the formula (1)
represents an alkyl group having 8 to 12 carbon atoms is more preferable.

[wherein R represents a linear or branched alkyl group having 6 to 20 carbon atoms.]
[0056] Preferred alkyl glycidyl ethers include octyl glycidyl ether, 2-ethylhexyl glycidyl
ether, nonyl glycidyl ether, decyl glycidyl ether, undecyl glycidyl ether and dodecyl
glycidyl ether.
[0057] In the present embodiment, the epoxy compound may be used singly or may be used in
combinations of two or more.
[0058] The content of the epoxy compound is 0.05 to 5% by mass, preferably 0.1 to 3% by
mass and more preferably 0.1 to 2% by mass based on the total amount of the grease
composition. If the content is low, no effect of enhancing stability and wear resistance
is exerted, and if the content is too high, characteristics as the grease are not
balanced, for example, an organic material in a mechanical system is swollen.
[Antiwear additive]
[0059] The grease composition according to the present-embodiment comprises an antiwear
additive. A preferred antiwear additive includes an oxygen-containing compound, a
nitrogen-containing compound, an organophosphorus compound, an organosulfur compound,
an organomolybdenum compound, a calcium compound and an organozinc compound. In addition,
a solid lubricant may also be preferably used. Herein, the antiwear additive may be
classified to an oiliness agent, an antiwear agent and an extreme pressure agent,
but such classification is not necessarily critical. In addition, one antiwear additive
may correspond to two or three of an oiliness agent, an antiwear agent and an extreme
pressure agent. The epoxy compound for use in the present invention is excluded from
the antiwear additive in the present invention.
[0060] Among the antiwear additives, the oxygen-containing compound includes higher fatty
acids such as oleic acid and stearic acid, higher alcohols such as oleyl alcohol,
esters such as glycerol monooleate, and ethers such as glycerol monooleyl ether. These
oxygen-containing compounds are typically configured from an oxygen-containing polar
group such as a hydroxyl group, a carboxylic acid group, an ether group or an ester
group and a saturated or unsaturated hydrocarbon group having 12 to 24 carbon atoms.
It is expected in these oxygen-containing compounds that the polar group adsorbs to
the surface of a metal sliding portion and the hydrocarbon group forms an oil film
to enhance wear resistance. Examples include partial esters in which a hydroxyl group
remains, in particular, glycerol partial esters with fatty acids having 12 to 24 carbon
atoms.
[0061] In addition, the nitrogen-containing compound includes aliphatic amines such as oleylamine
and dodecylamine, aliphatic amides and aliphatic imides. These nitrogen-containing
compounds are typically configured from a nitrogen-containing polar group such as
an amine group, an amide group or an imide group and a hydrocarbon group having a
saturated or unsaturated bond and having 12 to 24 carbon atoms. It is expected in
these nitrogen-containing compounds that the polar group adsorbs to the surface of
a metal sliding portion and the hydrocarbon group forms an oil film to enhance wear
resistance. In particular, examples include aliphatic amines having 12 to 24 carbon
atoms.
[0062] In addition, the organophosphorus compound includes phosphoric acid esters, phosphorous
acid esters and an acidic phosphoric acid ester amine salt. In the present invention,
it is to be noted that a compound containing nitrogen or the like, in addition to
phosphorus, as a constituent element, is included in the organophosphorus compound.
The organophosphorus compound is typically one having one or more hydrocarbon groups
having 6 to 24 carbon atoms. Such a hydrocarbon group includes a linear hydrocarbon
group, a branched hydrocarbon group and an aromatic group. The salt compound in the
organophosphorus compound includes a compound completely neutralized or a compound
partially neutralized. It is expected in such an organophosphorus compound that a
lubricant film of iron phosphate or the like is formed on the surface of a metal sliding
portion to enhance wear resistance. Examples of phosphoric acid esters include those
having an aromatic group, and typically include triaryl phosphates.
[0063] The organosulfur compound includes a monosulfide compound, a disulfide compound,
a polysulfide compound, sulfurized fat and oil and sulfurized olefins. It is expected
in such an organosulfur compound that a lubricant film of iron sulfide or the like
is formed on the surface of a metal sliding portion to enhance wear resistance. Examples
include diaryl sulfides, dialkyl sulfides and dialkenyl sulfides. The sulfur element
content in the organosulfur compound can be, for example, 2 to 70% by mass, in particular,
5 to 60% by mass.
[0064] The organomolybdenum compound includes molybdenum dithiocarbamate and molybdenum
dithiophosphate. In the present invention, it is to be noted that a compound containing
sulfur or the like, in addition to molybdenum, as a constituent element, is included
in the organomolybdenum compound. It is expected in such an organomolybdenum compound
that a lubricant film made of molybdenum disulfide is formed on the surface of a metal
sliding portion to enhance wear resistance. Examples include molybdenum dialkyldithiocarbamates
and molybdenum dialkyldithiophosphates in which the number of carbon atoms in an alkyl
group is 4 to 12.
[0065] The alkaline earth metal compound includes alkaline earth metal sulfonate salt, phenate
salt and salicylate salt. The alkaline earth metal may be selected from calcium, magnesium
and barium. In the present invention, it is to be noted that a compound containing
sulfur or the like, in addition to the alkaline earth metal, as a constituent element
is included in the alkaline earth metal compound. In addition, the calcium compound
may include a basic component such as calcium carbonate.
[0066] The organozinc compound includes organozinc compounds such as zinc dialkyls, zinc
dialkyldithiophosphates and zinc dialkyldithiocarbamates. In the present invention,
it is to be noted that a compound containing sulfur, phosphorus or the like, in addition
to zinc, as a constituent element is included in the organozinc compound. The organozinc
compound typically has one or more linear, branched or aromatic hydrocarbon groups
having 6 to 24 carbon atoms. Examples include zinc dialkyldithiophosphates in which
the number of carbon atoms in an alkyl group is 4 to 12.
[0067] In addition, a solid lubricant may also be applied to the grease being a semi-solid
lubricant. The solid lubricant is an additive that is used in the form of a powder
or thin film in order to prevent the surface of a sliding material from being damaged
or in order to reduce friction/wear, and includes molybdenum disulfide, tungsten disulfide,
graphite, graphite fluoride, melamine cyanurate, a tetrafluoroethylene (PTFE) resin
powder, a polyimide resin powder, a high-density polyethylene resin powder, boron
nitride, a copper powder, a nickel powder, a tin powder and a silver powder.
[0068] In particular, molybdenum disulfide, graphite, a tetrafluoroethylene resin powder
and boron nitride may be suitably used in the present invention.
[0069] In the present embodiment, the antiwear additive may be used singly or may be used
in combinations of two or more. The content of the antiwear additive is 0.1 to 20%
by mass, preferably 0.2 to 20% by mass, more preferably 0.2 to 7% by mass and further
preferably 0.3 to 5% by mass based on the total amount of the grease composition.
If the content is too low, no effect of wear-resistance is exerted, and if the content
is too high, the stability of the lubricating oil is deteriorated.
[0070] It is preferable to contain the organomolybdenum compound and the organozinc compound
as the antiwear additive. The mass ratio of the content of the organomolybdenum compound
to the content of the organozinc compound may be, for example, 0.2 to 10 : 1, in particular,
1 to 5 : 1. In this case, it is possible to use a lithium complex soap as the thickener.
[0071] It is preferable to contain the organomolybdenum compound, the organozinc compound
and the organosulfur compound as the antiwear additive. The mass ratio of the content
of the organomolybdenum compound to the content of the organozinc compound may be,
for example, 1 to 10 : 1, in particular, 1 to 5 : 1, and the mass ratio of the content
of the organozinc compound to the content of the organosulfur compound may be, for
example, 0.2 to 2 : 1, in particular, 0.5 to 2 : 1. In this case, it is possible to
use a lithium soap as the thickener. It is possible to use a dialkyl sulfide having
alkyl having 4 to 18, in particular, 6 to 10 carbon atoms as the organosulfur compound.
[Other additives]
[0072] The grease composition according to the present embodiment may contain, in order
to improve its performance, additives such as an antioxidant, an antirust agent, a
metal deactivator, a corrosion inhibitor, a viscosity index improver, a pour point
depressant, a detergent dispersant, an emulsifier and an antifoamer that have been
conventionally used for a lubricating oil, as long as the object of the present invention
is not impaired.
[0073] The antioxidant includes a phenol type compound like di-tert-butyl-p-cresol, and
an amine type compound like alkyl diphenyl amines, the antirust agent includes alkenyl
succinic acid esters or partial esters thereof, the metal deactivator includes benzotriazole
and gallic acid esters, the corrosion inhibitor includes thiadiazole, the viscosity
index improver includes polymethacrylate and polyisobutylene, the pour point depressant
includes polyalkylacrylate and polyalkylstyrene, the detergent dispersant includes
succinic imide and phosphonates, the emulsifier includes a fatty acid soap and a long-chain
alcohol sulfate ester salt, and the antifoamer includes a silicone compound and a
polyester compound, respectively.
Examples
[0074] Hereinafter, the present invention is described in more detail based on Examples
and Comparative Examples, but the present invention is not limited to such Examples.
[Examples 1 to 28, Comparative Examples 1 to 17]
[0075] In Examples 1 to 28 and Comparative Examples 1 to 17, respective base oils, thickeners
and additives shown below were used to prepare respective grease compositions having
composition shown in Tables 1 to 6.
(A) Base oil
[0076]
(A-1) Mineral oil: paraffinic refined mineral oil (kinematic viscosity at 40°C: 93.3
mm2/s; viscosity index: 95; pour point: -15°C; flash point: 260°C)
(A-2) Polyol ester (POE): ester of pentaerythritol and a mixed acid of 2-ethylhexanoic
acid and 3,5,5-trimethylhexanoic acid in a mass ratio of 5 : 5 (kinematic viscosity
at 40°C: 66.7 mm2/s; viscosity index: 92; pour point: -40°C; flash point: 248°C)
(A-3) Polyalkylene glycol (PAG): polyoxypropylene in which both ends were blocked
by a methyl group (weight average molecular weight: 1000; kinematic viscosity at 40°C:
46.0 mm2/s; viscosity index: 190; pour point: -45°C; flash point: 218°C)
(A-4) Poly-α-olefin (PAO): polymer of 1-dodecene (kinematic viscosity at 40°C: 100
mm2/s; viscosity index: 140; pour point: -40°C; flash point: 260°C)
Herein, the kinematic viscosity and the viscosity index of each of the base oils were
measured according to JIS K2283, the pour point thereof was measured according to
JIS K2269, and the flash point thereof was measured according to JIS K2265.
(B) Thickener
[0077]
(B-1) Lithium soap grease: lithium 12-hydroxystearate (10% by mass) was blended and
stirred with any of the base oils, uniformly dissolved therein at about 200°C and
then cooled, and additive (C or D) was added thereto at about 80°C to provide a grease.
This lithium soap grease was allowed to pass through a roll mill and tested as the
grease composition.
(B-2) Urea grease: one in which diphenylmethane-4,4'-diisocyanate was dissolved in
any of the base oils (about 80°C) and one in which cyclohexylamine and octadecylamine
were dissolved in any of the base oils (about 80°C) were prepared (mass ratio of diphenylmethane-4,4'-diisocyanate/cyclohexylamine/octadecylamine:
9/6/4), both of them were mixed and stirred for reaction (160°C, 30 minutes) and cooled,
and thereafter an additive (C or D) was added thereto at about 80°C to provide a urea
grease (5% by mass as diurea). This urea grease was allowed to pass through a roll
mill and tested as the grease composition.
(B-3) Lithium complex soap grease: 12-hydroxystearic acid and azelaic acid, and lithium
hydroxide were blended and stirred with any of the base oils in 10% by mass relative
to the total amount of the grease composition, uniformly dissolved therein at about
200°C and then cooled, and additive (C or D) was added thereto at about 80°C to provide
a grease. This lithium complex soap grease was allowed to pass through a roll mill
and tested as the grease composition.
(C) Epoxy compound
[0078]
(C-1) 2-Ethylhexyl glycidyl ether
(C-2) Dodecyl glycidyl ether
(C-3) Glycidyl-2,2-dimethyl octanoate
(C-4) 3,4-Epoxycyclohexylmethyl-3',4'-epoxycyclohexane carboxylate
(D) Antiwear additive
[0079]
(D-1) Oxygen-containing compound: glycerol monooleate
(D-2) Nitrogen-containing compound: oleylamine
(D-3) Organophosphorus compound: tricresyl phosphate
(D-4) Organosulfur compound A: dibenzyl disulfide
(D-5) Organomolybdenum compound A: molybdenum dialkyldithiophosphate [Mo element content:
8.0% by mass]
(D-6) Alkaline earth metal compound: overbasic Ca sulfonate, [TBN (ASTM D2895): 325
mgKOH/g; Ca: 12.7% by mass; S: 2% by mass]
(D-7) Organozinc compound: zinc dioctyl dithiophosphate
(D-8) Solid lubricant: graphite (average particle size: 10 µm)
(D-9) Organomolybdenum compound B: molybdenum dialkyldithiocarbamate [Mo element content:
10.0% by mass]
(D-10) Organosulfur compound B: dioctyl polysulfide [sulfur element content: 39% by
mass]
[0080] With respect to each of the grease compositions in Examples 1 to 28 and Comparative
Examples 1 to 17, the following tests were performed.
[SRV test]
[0081] A ball/disc reciprocating kinematic friction/wear test machine, SRV test machine
(Optimol Instruments, Instrument SRV), was used to perform seizure load and wear coefficient
measurements according to ASTM D5706.
[0082] SUJ2 was used for materials of the ball and disc of the SRV test. The test was started
at a temperature of 80°C, an amplitude of 1 mm, a frequency of 50 Hz and a load of
50 N, and the load was increased by 100 N every 2 minutes to perform the operation
until seizure occurred (the maximum load set was 2000 N).
[0083] In this test, the seizure load, and the friction coefficient at each load before
the seizure can be measured. Tables 1 to 6 show the seizure load, and the friction
coefficient at a load lower than the seizure load by 200 N in the test in which each
of the grease compositions was used. Herein, "Unstable" in the column "Friction coefficient"
in Tables means that the friction coefficient varied between 0.08 and 0.18 and the
value could not be read.
[Oxidation stability test]
[0084] A sample pressurized to 755 KPa by an oxygen tank was heated to 99°C and the pressure
drop after a lapse of 100 hours was measured according to the grease oxidation stability
test method of JIS K2220. The results obtained are shown in Tables 1 to 3. JIS K2220
defines Class 3 grease for rolling bearing (oxidation stability is good over a wide
temperature range) as having a reduction in oxygen pressure of 49 KPa or less, and
the oxidation stability of each of the grease compositions can be rated based on the
definition.
[Table 1]
|
Example 1 |
Comparative Example 1 |
Comparative Example 2 |
Comparative Example 3 |
Example 2 |
Comparative Example 4 |
Example 3 |
Comparative Example 5 |
Base oil |
|
|
|
|
|
|
|
|
Type |
A-1 |
A-1 |
A-1 |
A-1 |
A-1 |
A-1 |
A-1 |
A-1 |
Content (% by mass) |
Balance |
Balance |
Balance |
Balance |
Balance |
Balance |
Balance |
Balance |
Thickener (% by mass) |
|
|
|
|
|
|
|
|
B-1 |
10.0 |
10.0 |
10.0 |
10.0 |
10.0 |
10.0 |
- |
- |
B-2 |
- |
- |
- |
- |
- |
- |
5.0 |
5.0 |
Epoxy compound (% by mass) |
|
|
|
|
|
|
|
|
C-1 |
0.5 |
- |
0.5 |
- |
0.2 |
- |
- |
- |
C-2 |
- |
- |
- |
- |
- |
- |
0.3 |
- |
C-3 |
- |
- |
- |
- |
- |
- |
- |
- |
C-4 |
- |
- |
- |
- |
- |
- |
- |
- |
Antiwear additive (% by mass) |
|
|
|
|
|
|
|
|
D-1 |
1.0 |
- |
- |
1.0 |
- |
- |
- |
- |
D-2 |
- |
- |
- |
- |
0.5 |
0.5 |
- |
- |
D-3 |
- |
- |
- |
- |
- |
- |
1.5 |
1.5 |
D-4 |
- |
- |
- |
- |
- |
- |
- |
- |
D-5 |
- |
- |
- |
- |
- |
- |
- |
- |
D-6 |
- |
- |
- |
- |
- |
- |
- |
- |
D-7 |
- |
- |
- |
- |
- |
- |
- |
- |
D-8 |
- |
- |
- |
- |
- |
- |
- |
- |
SRV test |
|
|
|
|
|
|
|
|
Seizure load (N) |
700 |
200 |
200 |
400 |
700 |
400 |
800 |
500 |
Friction coefficient |
0.07 |
Unstable |
Unstable |
0.10 |
0.08 |
0.11 |
0.10 |
0.13 |
Oxidation stability test |
|
|
|
|
|
|
|
|
Amount of reduction in oxygen pressure (KPa) |
35 |
85 |
38 |
75 |
39 |
70 |
25 |
73 |
[Table 2]
|
Example 4 |
Comparative Example 6 |
Example 5 |
Comparative Example 7 |
Example 6 |
Comparative Example 8 |
Example 7 |
Comparative Example 9 |
Base oil |
|
|
|
|
|
|
|
|
Type |
A-1 |
A-1 |
A-1 |
A-1 |
A-1 |
A-1 |
A-1 |
A-1 |
Content (% by mass) |
Balance |
Balance |
Balance |
Balance |
Balance |
Balance |
Balance |
Balance |
Thickener (% by mass) |
|
|
|
|
|
|
|
|
B-1 |
10.0 |
10.0 |
- |
- |
10.0 |
10.0 |
10.0 |
10.0 |
B-2 |
- |
- |
5.0 |
5.0 |
- |
- |
- |
- |
Epoxy compound (% by mass) |
|
|
|
|
|
|
|
|
C-1 |
- |
- |
- |
- |
2.0 |
- |
0.2 |
- |
C-2 |
- |
- |
- |
- |
- |
- |
- |
- |
C-3 |
1.0 |
- |
- |
- |
- |
- |
- |
- |
C-4 |
- |
- |
0.5 |
- |
- |
- |
- |
- |
Antiwear additive (% by mass) |
|
|
|
|
|
|
|
|
D-1 |
- |
- |
- |
- |
- |
- |
- |
- |
D-2 |
- |
- |
- |
- |
- |
- |
- |
- |
D-3 |
- |
- |
- |
- |
- |
- |
- |
- |
D-4 |
1.0 |
1.0 |
- |
- |
- |
- |
- |
- |
D-5 |
- |
- |
1.0 |
1.0 |
- |
- |
- |
- |
D-6 |
- |
- |
- |
- |
3.0 |
3.0 |
- |
- |
D-7 |
- |
- |
- |
- |
- |
- |
0.5 |
0.5 |
D-8 |
- |
- |
- |
- |
- |
- |
- |
- |
SRV test |
|
|
|
|
|
|
|
|
Seizure load (N) |
700 |
500 |
700 |
500 |
1100 |
700 |
900 |
500 |
Friction coefficient |
0.11 |
0.13 |
0.07 |
0.09 |
0.08 |
0.11 |
0.08 |
0.11 |
Oxidation stability test |
|
|
|
|
|
|
|
|
Amount of reduction in oxygen pressure (KPa) |
32 |
76 |
35 |
80 |
28 |
92 |
22 |
68 |
[Table 3]
|
Example 8 |
Comparative Example 10 |
Example 9 |
Comparative Example 11 |
Example 10 |
Comparative Example 12 |
Example 11 |
Comparative Example 13 |
Base oil |
|
|
|
|
|
|
|
|
Type |
A-1 |
A-1 |
A-2 |
A-2 |
A-3 |
A-3 |
A-1 |
A-1 |
Content (% by mass) |
Balance |
Balance |
Balance |
Balance |
Balance |
Balance |
Balance |
Balance |
Thickener (% by mass) |
|
|
|
|
|
|
|
|
B-1 |
10.0 |
10.0 |
10.0 |
10.0 |
10.0 |
10.0 |
10.0 |
10.0 |
B-2 |
- |
- |
- |
- |
- |
- |
- |
- |
Epoxy compound (% by mass) |
|
|
|
|
|
|
|
|
C-1 |
- |
- |
0.15 |
- |
0.1 |
- |
0.3 |
- |
C-2 |
0.3 |
- |
- |
- |
- |
- |
- |
- |
C-3 |
- |
- |
- |
- |
- |
- |
- |
- |
C-4 |
- |
- |
- |
- |
- |
- |
- |
- |
Antiwear additive (% by mass) |
|
|
|
|
|
|
|
|
D-1 |
- |
- |
0.2 |
0.2 |
- |
- |
- |
- |
D-2 |
- |
- |
- |
- |
- |
- |
|
- |
D-3 |
- |
- |
1.0 |
1.0 |
- |
- |
- |
- |
D-4 |
- |
- |
- |
- |
0.5 |
0.5 |
- |
- |
D-5 |
- |
- |
- |
- |
0.1 |
0.1 |
1.0 |
1.0 |
D-6 |
2.0 |
2.0 |
- |
- |
- |
- |
2.0 |
2.0 |
D-7 |
1.5 |
1.5 |
- |
- |
- |
- |
1.5 |
1.5 |
D-8 |
1.0 |
1.0 |
- |
- |
- |
- |
- |
- |
SRV test |
|
|
|
|
|
|
|
|
Seizure load (N) |
1500 |
1100 |
1100 |
700 |
1000 |
700 |
1500 |
1200 |
Friction coefficient |
0.07 |
0.10 |
0.07 |
0.10 |
0.07 |
0.10 |
0.06 |
0.09 |
Oxidation stability test |
|
|
|
|
|
|
|
|
Amount of reduction in oxygen pressure (KPa) |
20 |
60 |
38 |
75 |
39 |
70 |
21 |
65 |
[Table 4]
|
Example 12 |
Example 13 |
Example 14 |
Example 15 |
Example 16 |
Example 17 |
Example 18 |
Example 19 |
Base oil |
|
|
|
|
|
|
|
|
Type |
A-1 |
A-1 |
A-1 |
A-1 |
A-1 |
A-4 |
A-1 |
A-1 |
Content (% by mass) |
Balance |
Balance |
Balance |
Balance |
Balance |
Balance |
Balance |
Balance |
Thickener (% by mass) |
|
|
|
|
|
|
|
|
B-1 |
- |
10.0 |
- |
- |
- |
- |
- |
- |
B-3 |
10.0 |
- |
10.0 |
10.0 |
10.0 |
10.0 |
10.0 |
10.0 |
Epoxy compound (% by mass) |
|
|
|
|
|
|
|
|
C-1 |
0.5 |
0.5 |
- |
- |
- |
0.5 |
1.0 |
0.5 |
C-2 |
- |
- |
0.5 |
- |
- |
- |
- |
- |
C-3 |
- |
- |
- |
0.5 |
- |
- |
- |
- |
C-4 |
- |
- |
- |
- |
0.5 |
- |
- |
- |
Antiwear additive (% by mass) |
|
|
|
|
|
|
|
|
D-5 |
1.0 |
1.0 |
1.0 |
1.0 |
1.0 |
1.0 |
5.0 |
1.0 |
D-7 |
1.0 |
1.0 |
1.0 |
1.0 |
1.0 |
1.0 |
5.0 |
- |
D-9 |
1.0 |
1.0 |
1.0 |
1.0 |
1.0 |
1.0 |
5.0 |
- |
SRV test |
|
|
|
|
|
|
|
|
Seizure load (N) |
1500 |
1400 |
1400 |
1400 |
1400 |
1500 |
1700 |
1200 |
[Table 5]
|
Example 20 |
Comparative Example 14 |
Comparative Example 15 |
Comparative Example 16 |
Comparative Example 17 |
Base oil |
|
|
|
|
|
Type |
A-1 |
A-1 |
A-1 |
A-1 |
A-1 |
Content (% by mass) |
Balance |
Balance |
Balance |
Balance |
Balance |
Thickener (% by mass) |
|
|
|
|
|
B-1 |
- |
- |
- |
- |
10.0 |
B-3 |
10.0 |
10.0 |
10.0 |
10.0 |
- |
Epoxy compound (% by mass) |
|
|
|
|
|
C-1 |
0.5 |
- |
0.5 |
- |
- |
C-2 |
- |
- |
- |
- |
- |
C-3 |
- |
- |
- |
- |
- |
C-4 |
- |
|
- |
- |
- |
Antiwear additive (% by mass) |
|
|
|
|
|
D-5 |
- |
1.0 |
- |
- |
0.5 |
D-7 |
1.0 |
1.0 |
- |
- |
1.0 |
D-9 |
- |
1.0 |
- |
- |
3.0 |
D-10 |
- |
-- |
- |
- |
1.0 |
SRV test |
|
|
|
|
|
Seizure load (N) |
1100 |
800 |
400 |
400 |
800 |
Friction coefficient |
- |
- |
- |
- |
0.07 |
[Table 6]
|
Example 21 |
Example 22 |
Example 23 |
Example 24 |
Example 25 |
Example 26 |
Example 27 |
Example 28 |
Base oil |
|
|
|
|
|
|
|
|
Type |
A-1 |
A-1 |
A-1 |
A-1 |
A-1 |
A-2 |
A-1 |
A-1 |
Content (% by mass) |
Balance |
Balance |
Balance |
Balance |
Balance |
Balance |
Balance |
Balance |
Thickener (% by mass) |
|
|
|
|
|
|
|
|
B-1 |
10.0 |
- |
10.0 |
10.0 |
10.0 |
10.0 |
10.0 |
10.0 |
B-2 |
- |
10.0 |
- |
- |
- |
- |
- |
- |
Epoxy compound (% by mass) |
|
|
|
|
|
|
|
|
C-1 |
0.5 |
0.5 |
- |
- |
- |
0.5 |
1.0 |
0.5 |
C-2 |
- |
- |
0.5 |
- |
- |
- |
- |
- |
C-3 |
- |
- |
- |
0.5 |
- |
- |
- |
- |
C-4 |
- |
- |
- |
- |
0.5 |
- |
- |
- |
Antiwear additive (% by mass) |
|
|
|
|
|
|
|
|
D-5 |
0.5 |
0.5 |
0.5 |
0.5 |
0.5 |
0.5 |
2.0 |
- |
D-7 |
1.0 |
1.0 |
1.0 |
1.0 |
1.0 |
1.0 |
3.0 |
1.0 |
D-9 |
3.0 |
3.0 |
3.0 |
3.0 |
3.0 |
3.0 |
5.0 |
3.0 |
D-10 |
1.0 |
1.0 |
1.0 |
1.0 |
1.0 |
1.0 |
3.0 |
1.0 |
SRV test |
|
|
|
|
|
|
|
|
Seizure load (N) |
1600 |
1500 |
1500 |
1500 |
1500 |
1600 |
1700 |
1400 |
Friction coefficient |
0.04 |
0.05 |
0.05 |
0.05 |
0.05 |
0.04 |
0.04 |
0.04 |
Industrial Applicability
[0085] The grease composition of the present invention is a grease that is significantly
improved in terms of stability, lubricity and friction characteristics and that is
excellent in reliability so that the initial characteristics may be maintained and
the effect of wear-resistance may be kept even under severe lubrication conditions,
as compared with a conventional grease. Accordingly, the grease composition of the
present invention may be suitably used as a lubricant for various machines, vehicles,
driving force transmission mechanisms and the like that are required to have anti-wear
performance and energy saving performance.
1. A grease composition comprising:
at least one base oil selected from a mineral oil and a synthetic oil; and
based on the total amount of the grease composition,
2 to 35% by mass of a thickener;
0.05 to 5% by mass of an epoxy compound; and
0.1 to 20% by mass of an antiwear additive.
2. The grease composition according to claim 1, wherein the epoxy compound is at least
one selected from a phenyl glycidyl ether type epoxy compound, an alkyl glycidyl ether
type epoxy compound, a glycidyl ester type epoxy compound, an alicyclic epoxy compound,
an epoxidized aliphatic monoester and an epoxidized vegetable oil.
3. The grease composition according to claim 2, wherein the epoxy compound is an alkyl
glycidyl ether represented by the following formula (1):

wherein R represents a linear or branched alkyl group having 6 to 20 carbon atoms.
4. The grease composition according to claim 3, wherein the epoxy compound is at least
one selected from octyl glycidyl ether, 2-ethylhexyl glycidyl ether, nonyl glycidyl
ether, decyl glycidyl ether, undecyl glycidyl ether and dodecyl glycidyl ether.
5. The grease composition according to any one of claims 1 to 3, wherein the antiwear
additive is at least one selected from an oxygen-containing compound, a nitrogen-containing
compound, an organophosphorus compound, an organosulfur compound, an organomolybdenum
compound, an alkaline earth metal compound and an organozinc compound.
6. The grease composition according to claim 5, wherein
the oxygen-containing compound is at least one selected from an ester, an alcohol,
an ether and a carboxylic acid,
the nitrogen-containing compound is at least one selected from an aliphatic amine,
an aliphatic amide and an aliphatic imide,
the organophosphorus compound is at least one selected from a phosphoric acid ester,
a phosphorous acid ester and an acidic phosphoric acid ester amine salt,
the organosulfur compound is at least one selected from a sulfide compound, and sulfurized
fat and oil,
the organomolybdenum compound is at least one selected from molybdenum dithiocarbamate
and molybdenum dithiophosphate,
the alkaline earth metal compound is at least one selected from alkaline earth metal
sulfonate salt, phenate salt and salicylate salt, and
the organozinc compound is at least one selected from a zinc dialkyl, a zinc dialkyldithiophosphate
and a zinc dialkyldithiocarbamate.
7. The grease composition according to any one of claims 1 to 3, wherein the antiwear
additive is a solid lubricant.
8. The grease composition according to claim 7, wherein the solid lubricant is at least
one selected from molybdenum disulfide, graphite, a tetrafluoroethylene resin powder
and boron nitride.
9. The grease composition according to any one of claims 1 to 8, wherein the synthetic
oil type is at least one selected from a hydrocarbon oil, a diester, a polyol ester
and a polyalkylene glycol compound.
10. The grease composition according to any one of claims 1 to 8, wherein the thickener
is at least one selected from lithium soaps, calcium soaps, aluminum soaps and a urea
compound.
11. The grease composition according to claim 5, containing, as the antiwear additive,
an organomolybdenum compound and an organozinc compound.
12. The grease composition according to claim 5, containing, as the antiwear additive,
an organomolybdenum compound, an organozinc compound and an organosulfur compound.