ADDITIVE TO GREASE AND GREASE COMPOSITION

Abstract

Provided is an additive to grease comprising a salt including a silicon-containing phosphoric acid ester anion represented by the following formula (1). In the formula, R1 to R3 are independently alkyl groups having 1-4 carbon atoms. R4 is an alkyl group having 1-8 carbon atoms. n is an integer of 1-8.

Description

TECHNICAL FIELD

The present invention relates to a grease additive and a grease composition.

BACKGROUND ART

Grease compositions are used as lubricants on rolling bearings and sliding members in various types of industrial machinery. As industrial machinery has become more compact and higher performing, the service environment of grease compositions has become more demanding. Hence, there exists a desire to enhance the performance of greases.

SUMMARY OF INVENTION

Technical Problem

In light of the above circumstances, the object of the present invention is to provide an additive which can improve the friction performance of greases.

Solution to Problem

The inventor has conducted intensive investigations in order to achieve this object and discovered as a result that the friction performance of greases can be enhanced by using a salt which contains a given silicon atom-containing phosphate ester anion (also referred to below as a “silicon-containing phosphate ester salt”) as a grease additive. This discovery has ultimately led to the present invention.

Accordingly, this invention provides the following grease additive and grease composition.

1. A grease additive comprising a salt which includes a silicon-containing phosphate ester anion of formula (1) below.

wherein R¹ to R³ are each independently an alkyl group of 1 to 4 carbon atoms, R⁴ is an alkyl group of 1 to 8 carbon atoms, and n is an integer from 1 to 8.
2. The grease additive of 1 above, wherein R¹ to R³ are identical groups.
3. The grease additive of 2 above, wherein R¹ to R³ are all methyl groups.
4. The grease additive of any of 1 to 3 above, wherein R⁴ is an alkyl group of 1 to 4 carbon atoms.
5. The grease additive of any of 1 to 4 above, wherein n is an integer from 2 to 4.
6. The grease additive of 5 above, wherein n is 3.
7. The grease additive of any of 1 to 6 above, wherein the salt includes an organic cation as the cation.
8. The grease additive of any of 1 to 7 above, wherein the salt includes a phosphorus atom-containing cation as the cation.
9. A grease composition comprising a base oil, a thickener and the grease additive of any of 1 to 8 above.
10. The grease composition of 9 above, wherein the thickener is a fluoropolymer.

ADVANTAGEOUS EFFECTS OF INVENTION

By using the above silicon-containing phosphate ester salt as a grease additive, the coefficient of friction can be made smaller and the coefficient of friction can be maintained even in a high-load region.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is schematic diagram of the grease caliper used in Examples 2-1 to 2-3 and Comparative Examples 2-1 and 2-2.

FIG. 2 is a graph showing the results of friction tests in Examples 2-1 to 2-3 and Comparative Examples 2-1 and 2-2.

DESCRIPTION OF EMBODIMENTS

[Grease Additive]

The grease additive of the invention comprises a salt which includes a silicon-containing phosphate ester anion of formula (1) below.

In formula (1), R¹ to R³ are each independently an alkyl group of 1 to 4 carbon atoms. The alkyl groups of 1 to 4 carbon atoms may be linear, branched or cyclic. Specific examples include methyl, ethyl, n-propyl, isopropyl, cyclopropyl, n-butyl, s-butyl, isobutyl, t-butyl and cyclobutyl groups. Of these, R¹ to R³ are preferably alkyl groups of 1 to 3 carbon atoms, more preferably linear alkyl groups of 1 to 3 carbon atoms, even more preferably methyl or ethyl groups, and most preferably methyl groups. Also, R¹ to R³ are preferably all identical groups, and are most preferably all methyl groups.

In formula (1), R⁴ is an alkyl group of 1 to 8 carbon atoms. The alkyl group of 1 to 8 carbon atoms may be linear, branched or cyclic. Specific examples include, in addition to the groups mentioned above as alkyl groups of 1 to 4 carbon atoms: n-pentyl, n-hexyl and n-octyl groups. Of these, R⁴ is preferably an alkyl group of 1 to 4 carbon atoms, more preferably a linear alkyl group of 1 to 4 carbon atoms, even more preferably a methyl or ethyl group, and most preferably a methyl group.

In formula (1), n is an integer from 1 to 8, preferably an integer from 2 to 4, and more preferably 3.

The cation included in the silicon-containing phosphate ester salt of the invention may be, without particular limitation, monovalent or polyvalent, although one that is monovalent or divalent is preferred, and one that is monovalent is more preferred. The cation may be an inorganic cation or an organic cation.

Examples of inorganic cations include alkali metal ions such as sodium, potassium and lithium ions; and metal ions such as silver, zinc, copper, calcium, magnesium, barium and aluminum ions.

Phosphorus atom-containing cations and nitrogen atom-containing cations are preferred as the organic cations. Specific examples include quaternary phosphonium ions, ammonium ions, imidazolium ions, pyridinium ions, pyrrolidinium ions and piperidinium ions.

The phosphorus atom-containing cation is preferably, for example, a quaternary phosphonium ion of formula (2) below.

In formula (2), R¹¹ is an alkyl group of 1 to 20 carbon atoms. The alkyl group of 1 to 20 carbon atoms may be linear, branched or cyclic. Specific examples include, in addition to the above-mentioned alkyl groups of 1 to 4 carbon atoms: n-pentyl, cyclopentyl, n-hexyl, cyclohexyl, n-heptyl, n-octyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, n-tridecyl, n-tetradecyl, n-pentadecyl, n-hexadecyl, n-heptadecyl, n-octadecyl, n-nonadecyl and n-eicosyl groups.

In formula (2), R¹² is an alkyl group of 1 to 20 carbon atoms or an alkoxyalkyl group represented by —(CH₂)_k—OR. Here, k is 1 or 2, and R is a methyl or ethyl group. The alkyl group of 1 to 20 carbon atoms is exemplified by the same groups as mentioned in the explanation of R¹¹. Examples of the alkoxyalkyl group include methoxymethyl, ethoxymethyl, methoxyethyl and ethoxyethyl groups. Of these alkoxyalkyl groups, a methoxymethyl or methoxyethyl group is preferred.

Of the quaternary phosphonium ions of formula (2), those in which R¹² is an alkoxyalkyl group represented by —(CH₂)_k—OR readily form ionic liquids. When R¹² is an alkyl group, quaternary phosphonium ions in which R¹¹ and R¹² have differing structures readily form ionic liquids. In this case, the difference in the number of carbon atoms is preferably one or more, more preferably 3 or more, and even more preferably 5 or more.

The above nitrogen atom-containing cation is preferably one of formula (3) below.

In formula (3), R²¹ R²⁴ are each independently a hydrogen atom, an alkyl group of 1 to 20 carbon atoms, or an alkoxyalkyl group represented by —(CH₂)_k—OR, where k is 1 or 2 and R is a methyl or ethyl group. The alkyl group of 1 to 20 carbon atoms and the alkoxyalkyl group are exemplified by the same groups as those mentioned in the explanation of formula (2). In cases where R²¹ to R²⁴ are all alkyl groups, nitrogen-containing cations in which at least one of these has a structure differing from the others readily form ionic liquids. In this case, the difference in the number of carbon atoms is preferably one or more, more preferably 3 or more, and even more preferably 5 or more.

Any two of R²¹ to R²⁴ may mutually bond to form a ring together with the nitrogen to which they are bonded. Moreover, the remaining two may also mutually bond to form a spiro ring in which the nitrogen atom serves as a spiro atom. In this case, the ring is exemplified by aziridine, azetidine, pyrrolidine, piperidine, azepane, imidazolidine and morpholine rings. Pyrrolidine and morpholine rings are preferred; a pyrrolidine ring is more preferred. A 1,1′-spirobipyrrolidine ring is especially preferred as the spiro ring.

Specific examples of the nitrogen atom-containing cation of formula (3) include quaternary ammonium ions of formula (3-1) or (3-2) below, and pyrrolidinium ions of formula (3-3) or (3-4) below.

In formulas (3-1) to (3-4), R and k are as defined above, R²⁰¹ to R²⁰⁴ are each independently an alkyl group of 1 to 4 carbon atoms, and R²⁰⁵ and R²⁰⁶ are each independently an alkyl group of 1 to 4 carbon atoms and may mutually bond to form a ring together with the nitrogen to which they are bonded.

Imidazolium ions of formula (4) below are also preferred as the nitrogen atom-containing cation.

In formula (4), R³¹ and R³² are each independently a hydrogen atom, an alkyl group of 1 to 20 carbon atoms, or an alkoxyalkyl group represented by —(CH₂)_k—OR. Here, R and k are as defined above. The alkyl group of 1 to 20 carbon atoms and the alkoxyalkyl group are exemplified by the same groups as mentioned in the explanation of formula (2). In this case, imidazolium ions in which R³¹ and R³² are differing groups readily form ionic liquids.

Pyridinium ions of formula (5) below are also preferred as the nitrogen atom-containing cation.

In formula (5), R⁴¹ is an alkyl group of 1 to 8 carbon atoms or an alkoxyalkyl group represented by —(CH₂)_k—OR. Here, R and k are as defined above. The alkyl group of 1 to 8 carbon atoms may be linear, branched or cyclic. Specific examples include methyl, ethyl, n-propyl, isopropyl, cyclopropyl, n-butyl, s-butyl, isobutyl, t-butyl, cyclobutyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, cyclopentyl and cyclohexyl groups. The alkoxyalkyl group is exemplified by the same groups as mentioned above in the explanation of formula (2).

The silicon-containing phosphate ester salt may be synthesized by a known method. For example, it may be synthesized according to the method described in WO 2018/105482 A1.

[Grease Composition]

The grease composition of the invention includes a base oil, a thickener and an additive including the above silicon-containing phosphate ester salt.

Any hitherto known base oil may be used without particular limitation as the base oil. Mineral oils, synthetic oils and mixtures thereof are especially preferred as the base oil.

The mineral oil may be paraffinic or naphthenic. A base oil belonging to any of Groups I, II and II of the American Petroleum Institute (API) may be used as the mineral oil; base oils belonging to Group II or III are preferred, and base oils belonging to Group III are more preferred.

Exemplary synthetic oils include hydrocarbon-based synthetic oils such as poly(α-olefins) (PAOs), polybutene, alkylbenzenes and alkylnaphthalenes; ester-based synthetic oils such as dioctyl sebacate (DOS), polyol esters and polyalkylene glycol esters; ether-based synthetic oils such as polyalkylene glycol and polyphenyl ether; phosphorus compounds; silicon compounds; and halogen compounds.

The preferred viscosity index of the base oil varies according to the type of base oil and the intended use, and so cannot be strictly specified. For example, although not particularly limited, the preferred viscosity index is from 80 to 119 for base oils belonging to API Groups I and II, and is 120 and above for base oils belong to Group III. The preferred kinematic viscosity of the base oil likewise varies according to the type of base oil and the intended use, and so cannot be strictly specified, although base oils having a kinematic viscosity at 40° C. in the range of from 1.98 to 3,520 mm²/s are generally preferred. The viscosity index and kinematic viscosity can be measured in accordance with JIS K 2283.

The base oil may be of one type used alone, or two or more may be used in combination.

The thickener is used so as to semi-solidify or solidify the base oil. A hitherto known thickener may be used for this purpose. Exemplary thickeners include fluoropolymers, metal soaps, urea compounds, bentonite, mica, silica gel, copper phthalocyanine and sodium terephthalamate.

Examples of the fluoropolymers include polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymers, tetrafluoroethylene-hexafluoropropylene copolymers, tetrafluoroethylene-ethylene copolymers, polyvinylidene fluoride and polychlorotrifluoroethylene.

Examples of the metal soaps include lithium soaps, lithium complex soaps, sodium soaps, calcium soaps, calcium complex soaps, aluminum soaps and aluminum complex soaps.

Examples of the urea compounds include diurea compounds, tetraurea compounds and polyurea compounds.

Of these, the thickener is preferably a fluoropolymer. By using a fluoropolymer, oxidative degradation and the like can be prevented, making it possible to exhibit a stable performance over an extended period of time.

The content of the thickener in the grease composition is preferably from 3 to 70 wt %, and more preferably from 5 to 50 wt %. The thickener may be of one type used alone, or two or more may be used in combination.

The grease composition of the invention includes an additive which is the above-described silicon-containing phosphate ester salt. In cases where the silicon-containing phosphate ester salt is one that has a quaternary phosphonium ion of formula (2) and is an ionic liquid, the friction performance and wear performance-improving effects are especially high. The content of the additive which is the silicon-containing phosphate ester salt in the grease composition of the invention is preferably from 0.1 to 10 wt %, and more preferably from 0.5 to 5 wt %. The additive which is the silicon-containing phosphate ester salt may be of one type used alone or two or more types may be used in combination.

The grease composition of the invention may include additives other than the above silicon-containing phosphate ester salt (also referred to below as “other additives”). Additives that are commonly used as grease additives may be used as such other additives. Examples include solid lubricants, antioxidants, antifoaming agents, demulsifying agents, emulsifying agents, preservatives, viscosity index improvers, pour point depressants, oiliness agents, anti-wear additives, extreme pressure agents, friction modifiers, detergents, dispersants, rust inhibitors, corrosion inhibitors, colorants and scents.

Examples of the solid lubricants include molybdenum disulfide, graphite, melamine cyanurate, boron nitride and mica. When a solid lubricant is included, the content thereof in the grease composition is preferably from 0.1 to 10 wt %.

Examples of the antioxidants include phenol derivatives, aromatic amine derivatives, organosulfur compounds, organophosphorus compounds, zinc dithiophosphate and hindered amines. When an antioxidant is included, the content thereof in the grease composition is preferably from 0.1 to 10 wt %.

Examples of the antifoaming agents include organopolysiloxanes (dimethylpolysiloxane, etc.) and polyacrylate derivatives. When an antifoaming agent is included, the content thereof in the grease composition is preferably from 0.1 to 10 wt %.

Examples of demulsifying agents include polymers of ethylene oxide and propylene oxide, ether-based surfactants and ester-based surfactants. When a demulsifying agent is included, the content thereof in the grease composition is preferably from 0.1 to 10 wt %.

Examples of emulsifying agents include metal salts such as sulfonates and surfactants such as fatty acid amine salts. When an emulsifying agent is included, the content thereof in the grease composition is preferably from 0.1 to 10 wt %.

Examples of preservatives include formaldehyde-releasing agents, pyridine-type compounds and phenolic compounds. When a preservative is included, the content thereof in the grease composition is preferably from 0.1 to 10 wt %.

Examples of viscosity index improvers include polyalkyl methacrylates, olefin copolymers (ethylene-propylene copolymers, etc.), polyisobutylene, styrene-butadiene block copolymers, graft polymers of polyalkyl methacrylates and olefin copolymers, and hydrogenated radial isoprene polymers. When a viscosity index improver is included, the content thereof in the grease composition is preferably from 0.1 to 10 wt %.

Examples of pour point depressants include alkylated aromatic compounds such as polyalkyl methacrylates, polyalkyl acrylates and alkyl naphthalenes; fumaric acid ester-vinyl acetate copolymers, styrene-maleic anhydride ester copolymers and ethylene-vinyl acetate copolymers. When a pour point depressant is included, the content thereof in the grease composition is preferably from 0.1 to 10 wt %.

Examples of oiliness agents include alcohols, long-chain fatty acids, alkyl amines, ester compounds and amide compounds. When an oiliness agent is included, the content thereof in the grease composition is preferably from 0.1 to 10 wt %.

Examples of anti-wear additives include zinc dithiophosphate and organophosphorus compounds. When an anti-wear additive is included, the content thereof in the grease composition is preferably from 0.1 to 10 wt %.

Examples of extreme pressure agents include organosulfur compounds and phosphate ester amine salts. When an extreme pressure agent is included, the content thereof in the grease composition is preferably from 0.1 to 10 wt %.

Examples of friction modifiers include esters of long-chain fatty acids such as oleic acid (glycerol monooleate, etc.), long-chain amide compounds and organomolybdenum compounds such as molybdenum dithiocarbamate. When a friction modifier is included, the content thereof in the grease composition is preferably from 0.1 to 10 wt %.

Examples of detergents include neutral, superbasic metal salts (calcium salts, magnesium salts, barium salts, etc.) such as alkylbenzene sulfonates, alkyl phenates and alkyl salicylates. When a friction modifier is included, the content thereof in the grease composition is preferably from 0.1 to 10 wt %.

Examples of dispersants include succinimides having a lipophilic group and a polar group, such as polybutenyl succinimide, succinic acid esters, benzylamines and polyamines. When a dispersant is included, the content thereof in the grease composition is preferably from 0.1 to 10 wt %.

Examples of rust inhibitors include metal salts such as sulfonates, carboxylate esters of polyhydric alcohols, phosphate ester compounds, alkenyl succinic acid derivatives, carboxylic acid salts and amine compounds. When a rust inhibitor is included, the content thereof in the grease composition is preferably from 0.1 to 10 wt %.

Examples of corrosion inhibitors include benzotriazole derivatives and thiadiazole derivatives. When a corrosion inhibitor is included, the content thereof in the grease composition is preferably from 0.1 to 10 wt %.

Examples of colorants include oil-soluble colorants. When a colorant is included, the content thereof in the grease composition is preferably from 0.1 to 10 wt %.

Examples of scents include oil-soluble scents. When a scent is included, the content thereof in the grease composition is preferably from 0.1 to 10 wt %.

Other additives may be used singly or two or more may be used in combination. When a plurality of such other additives are included, the sum thereof is preferably not more than 30 wt % of the grease composition.

EXAMPLES

The invention is illustrated more fully below by way of Examples and Comparative Examples, although the invention is not limited by these Examples.

[1] Synthesis of Additives

[Example 1-1] Synthesis of BDDP·SiC3P

BDDP·SiC3P was synthesized according to the method of Example 2 in WO 2018/105482 A1.

[Example 1-2] Synthesis of BHDP·SiC3P

BHDP·SiC3P was synthesized according to the method of Example 3 in WO 2018/105482 A1.

[Example 1-3] Synthesis of HTDP·SiC3P

Aside from replacing tributyldodecylphosphonium bromide with trihexyltetradecylphosphonium chloride (Tokyo Chemical Industry Co., Ltd.), HTDP·SiC3P was synthesized by a method similar to the method of Example 2 in WO 2018/105482 A1.

[Comparative Example 1-1] Synthesis of HTDP·TMSES

HTDP·TMSES was synthesized according to the method of Synthesis Example 5 in WO 2016/181726 A1.

[2] Friction Test 1

Examples 2-1 to 2-3, Comparative Examples 2-1 and 2-2

Greases composed of, in admixture, the base oil PAO4 (SpectraSyn4, from Nippon Chemicals Sales Co., Ltd.), the thickener Dyneon PTFE Micropowder TF9207Z (Sumitomo 3M Limited) and various silicon-containing phosphate ester salts were prepared.

In the blank (Comparative Example 2-1) alone, the mixing ratio of the ingredients was set to a weight ratio of the base oil to the thickener of 7:3. In the other examples, the mixing ratio of the base oil to the thickener to the silicon-containing phosphate ester salt was set to 7:3:0.1. Mixture was carried out using the P-7 planetary ball mill (Fritsch GmbH). The mixing conditions in all the examples were as follows: 300 rpm; every 5 minutes the direction of rotation was reversed, this being done 8 times; total mixing time was 40 minutes.

Example 2-1 used BDDP·SiC3P, Example 2-2 used BHDP·SiC3P, Example 2-3 used BHDP·SiC3P and Comparative Example 2-2 used BHDP·SiC3P as the silicon-containing phosphate ester salt.

The friction tests were performed using the high-speed, high-temperature reciprocating friction tester SRV4 (Optimol Instruments) as the test apparatus and with steel (SUJ2) ball (10 mm diameter)—steel (SUJ2) plate (steel ball-steel plate) contact. Specifically, using a grease caliper like that in FIG. 1 at room temperature and under a load of from 100 N to 1,000 N, with the load being increased 100 N at a time after 10 minutes at each load level, the prepared grease was applied in each case onto a 9.0 mm diameter by 1.15 mm region and the change over time in the coefficient of friction at a stroke of 1 mm and a frequency of 25 Hz was tracked. Destabilization of the stroke and a rise in the coefficient of friction (when it exceeded 0.2) were judged to be seizure and the test was stopped after several seconds (about 5 seconds). The results are shown in FIG. 2.

As is apparent from FIG. 2, the initial coefficient of friction in each of Examples 2-1 to 2-3 was lower than in Comparative Examples 2-1 and 2-2. The load capacity too was better in Examples 2-1 to 2-3 than in Comparative Examples 2-1 and 2-2.

Claims

1. A grease additive comprising a salt which includes a silicon-containing phosphate ester anion of formula (1) below wherein R1 to R3 are each independently an alkyl group of 1 to 4 carbon atoms, R4 is an alkyl group of 1 to 8 carbon atoms, and n is an integer from 1 to 8.

2. The grease additive of claim 1, wherein R1 to R3 are identical groups.

3. The grease additive of claim 2, wherein R1 to R3 are all methyl groups.

4. The grease additive of claim 1, wherein R4 is an alkyl group of 1 to 4 carbon atoms.

5. The grease additive of claim 1, wherein n is an integer from 2 to 4.

6. The grease additive of claim 5, wherein n is 3.

7. The grease additive of claim 1, wherein the salt includes an organic cation as the cation.

8. The grease additive of claim 1, wherein the salt includes a phosphorus atom-containing cation as the cation.

9. A grease composition comprising a base oil, a thickener and the grease additive of claim 1.

10. The grease composition of claim 9, wherein the thickener is a fluoropolymer.