KR20240165366A - Greek composition - Google Patents

Abstract

The present invention relates to a grease composition containing a base oil, a thickener, and an additive, wherein the base oil is at least one selected from the group consisting of polyoxyalkylene, ether derivatives of polyoxyalkylene, and mixtures thereof, and the additive includes polytetrafluoroethylene as a first solid lubricant, and at least one selected from the group consisting of calcium carbonate, calcium oxide, tricalcium phosphate, and calcium salts of fatty acids as a second solid lubricant, wherein the content of the second solid lubricant is 0.5 mass% or more based on the total mass of the composition.

Description

Greek composition

This invention relates to a grease composition that can be suitably used in machine parts requiring peeling resistance, such as reducers and ball screws.

Recently, machine parts are required to be miniaturized and have higher output for weight reduction. Therefore, grease used in the lubricating part of such machine parts is required to respond to more stringent usage environments than before, such as high speeds, high surface pressures, and expansion of the usage temperature range to the high temperature side. In particular, extending the life of grease used in parts under high temperature and high surface pressure is becoming one of the important technical tasks.

The longevity of grease can be achieved by suppressing the peeling of machine parts. It has been known so far that the peeling life of grease can be extended by including a so-called reactive anti-peeling additive, such as amine phosphate or dialkyl dithiolic acid zinc, in the grease (Patent Document 1). The reactive anti-peeling additive plays a role by reacting on the metal surface to form a protective film.

However, nitrile rubber (NBR) is widely used as a sealant for machine parts due to reasons such as oil resistance, wear resistance, heat resistance, processability, and low price. However, there are cases where the sealant deteriorates due to low temperatures in winter or heat damage in tropical climates. Deterioration of the sealant also occurs when the base oil contained in the grease that comes into contact with the sealant swells the sealant. Therefore, if a machine part equipped with a sealant is used for a long period of time, there is a concern that foreign substances from the outside may be allowed to enter, causing lubrication failure, and reducing the life of the machine part. As a countermeasure for this problem, an approach has been taken from two viewpoints: selection of the sealant and selection of the base oil of the grease. That is, if ethylene propylene rubber (EPDM), which has better heat resistance, cold resistance, weather resistance, and water resistance than NBR, is used as a sealant, the life of the machine part can be extended. In machine parts where EPDM or natural rubber is used as a sealant for a lubricating portion or its surrounding members, swelling of the EPDM or natural rubber can be suppressed by using polyoxyalkylene or a polyoxyalkylene derivative as the base oil of the grease (Patent Document 2).

Japanese Patent No. 6268642 Japanese Patent No. 2960561

Under these circumstances, there is a demand for a grease composition containing polyoxyalkylene or a polyoxyalkylene derivative as a base oil that can be applied to machine parts in which EPDM or natural rubber is used as a sealing member by having excellent suitability as a rubber, thereby inhibiting the occurrence of peeling of machine parts even under high temperatures or high surface pressure, thereby extending the life of machine parts.

By including a reaction-type anti-stripping additive in a grease using polyoxyalkylene or a polyoxyalkylene derivative as a base oil, swelling of EPDM or natural rubber and stripping of machine parts can be suppressed. However, when this grease is used at high temperatures, there is a problem in that the decomposition of the polyoxyalkylene or a polyoxyalkylene derivative is accelerated by the acid component generated when the reaction-type anti-stripping additive forms a reaction film on the metal surface.

In addition, the anti-stripping additive of the reaction system effectively exerts a stripping inhibition effect in base oils that do not have polarity, such as polyalphaolefin. However, in the case of polarity, such as polyoxyalkylene or polyoxyalkylene derivatives, it is difficult to disperse in the base oil and adsorb in the lubrication field, so there is also a problem that it is difficult to obtain a stripping inhibition effect.

Instead of a reactive anti-stripping additive, if a solid lubricant, i.e. a non-reactive anti-stripping additive, such as polytetrafluoroethylene (PTFE) or melamine cyanurate is used, the decomposition of the base oil can be suppressed. A non-reactive anti-stripping additive (solid lubricant) plays a role by adhering to a metal surface and preventing contact between metals, but since the anti-stripping property is significantly inferior to that of a reactive anti-stripping additive, the resulting grease lacks general purpose.

In this technical flow, the problem that the present invention seeks to solve is to improve the peeling resistance of a grease composition using polyoxyalkylene or a polyoxyalkylene derivative as a base oil, even under high temperature or high surface pressure, without using an anti-peeling additive in the reaction system, and also to suppress thermal deterioration of the base oil.

The inventors of the present invention have solved the problem of improving the above-mentioned peeling resistance by using a non-reactive solid lubricant in combination. That is, the present invention provides the following grease composition.

1. A grease composition containing base oil, thickener, and additives,

The base oil is at least one selected from the group consisting of polyoxyalkylene, ether derivatives of polyoxyalkylene, and mixtures thereof,

A grease composition, wherein the additive comprises polytetrafluoroethylene as a first solid lubricant and at least one selected from the group consisting of calcium carbonate, calcium oxide, tricalcium phosphate and calcium salts of fatty acids as a second solid lubricant, and the content of the second solid lubricant is 0.5 mass% or more based on the total mass of the composition.

2. A grease composition according to claim 1, wherein the content of the first solid lubricant is 0.5 to 20 mass% based on the total mass of the composition.

3. A grease composition according to item 1 or 2, wherein the content of the second solid lubricant is 0.5 to 10 mass% based on the total mass of the composition.

4. A grease composition according to any one of claims 1 to 3, wherein the second solid lubricant is calcium carbonate.

5. A grease composition according to any one of claims 1 to 4, comprising first and second solid lubricants in a ratio of 1 to 3 mass% of the second solid lubricant relative to 10 mass% of the first solid lubricant.

6. A machine part to which a grease composition described in any one of items 1 to 5 above has been applied.

According to the present invention, even under high temperature or high surface pressure, the peeling resistance and heat resistance of a grease composition can be improved without using an anti-peeling additive in a reaction system and without promoting the decomposition of polyoxyalkylene and/or ether derivatives of polyoxyalkylene.

<Oil>

The base oil used in the grease composition of the present invention is an ether derivative of polyoxyalkylene and/or polyoxyalkylene. The ether derivative of polyoxyalkylene and/or polyoxyalkylene has a low adverse effect on rubber, which is a sealing material. The ether derivative of polyoxyalkylene and/or polyoxyalkylene is represented by the following formula (1).

[Fire 1]

Polyoxyalkylene or an ether derivative thereof is a compound in which R ₁ and R ₃ in formula (1) are each independently hydrogen or an alkyl group having 1 to 6 carbon atoms such as a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a pentyl group, a hexyl group, etc., R ₂ is hydrogen or an alkyl group having 1 to 2 carbon atoms, and n represents a number of 5 to 55.

Polyoxyalkylene is a diol obtained by ring-opening polymerization of alkylene oxides such as ethylene oxide and propylene oxide. Its ether derivatives are monoethers in which either R ₁ or R ₃ is an alkyl group having 1 or more carbon atoms, or diethers in which both R ₁ and R ₃ are alkyl groups having 1 or more carbon atoms.

Specific examples of polyoxyalkylenediols include polyoxyethylene, polyoxypropylene, poly(oxypropyleneoxyethylene), poly(oxybutyleneoxyethylene), poly(oxybutyleneoxypropylene), poly(oxypentyleneoxyethylene), and poly(oxypentyleneoxypropylene).

Specific examples of the ether derivatives of polyoxyalkylene include polyoxypropylene monopropylene ether, polyoxypropylene monobutyl ether, polyoxybutylene monobutyl ether, polyoxyethylene oxypropylene monopropylene ether, polyoxyethylene oxypropylene monobutyl ether, and polyoxyethylene oxypropylene monopentyl ether.

And, among these, polyoxyethylene, poly(oxypropyleneoxyethylene) and ether derivatives thereof are water-soluble, so greases using them as base oils have poor water resistance. Therefore, what is suitable as the base oil of the present invention is a polyoxyalkylene or an ether derivative thereof in which R ₂ is an alkyl group having 1 or more carbon atoms, preferably polyoxypropylene monobutyl ether, particularly preferably polyoxypropylene monobutyl ether in which n is 10 to 25, and still more particularly preferably polyoxypropylene monobutyl ether in which n is 10 to 22.

The base oil of the present invention may be so-called biomass oil, which is manufactured using biological resources derived from plants and animals as raw materials.

The base oil of the present invention preferably has a kinematic viscosity of 2 to 100㎟/s at 100℃. Thereby, it has excellent low-temperature properties. The kinematic viscosity at 100℃ is more preferably 2 to 50㎟/s, further preferably 2 to 20㎟/s, and particularly preferably 6 to 19㎟/s.

The base oil of the present invention preferably has a pour point of -10°C or lower. This provides excellent low-temperature properties. The pour point is more preferably -20°C or lower, more preferably -30°C or lower, and particularly preferably -35°C or lower.

As the base oil of the present invention, polyoxypropylene monobutyl ether having a kinematic viscosity of 6 to 19 mm2/s at 100°C and a pour point of -35°C or lower, and wherein n is 10 to 22 in formula (1), is most preferable.

The content of base oil in the grease composition of the present invention is preferably 60 to 90 mass%, for example, and more preferably 60 to 80 mass%.

<Solid lubricant>

The first solid lubricant in the present invention is polytetrafluoroethylene.

The content of the first solid lubricant is preferably 0.5 mass% or more based on the total mass of the composition. This provides excellent load-bearing properties. It is more preferably 1 mass% or more. From the viewpoint of grease inflow, the upper limit is preferably 20 mass% or less, and more preferably 15 mass% or less.

The second solid lubricant in the present invention is at least one selected from the group consisting of calcium carbonate, calcium oxide, tricalcium phosphate, and calcium salts of fatty acids. Among these, calcium carbonate is preferable from the viewpoint of peeling resistance. As the fatty acid constituting the calcium salt of fatty acids, a fatty acid having 1 to 22 carbon atoms is preferable, and a fatty acid having 16 to 20 carbon atoms is more preferable.

From the viewpoint of improving peeling resistance through combined use, the particle size of the second solid lubricant is preferably larger than that of the first solid lubricant, PTFE.

The content of the second solid lubricant is 0.5 mass% or more based on the total mass of the composition. Thereby, the peeling resistance is excellent. It does not have to be the same as the content of the first solid lubricant. It is more preferably 1 mass% or more. From the viewpoint of the influx of grease, the upper limit is preferably 10 mass% or less, and more preferably 5 mass% or less.

Regardless of the type of the second solid lubricant, if the second solid lubricant is included in an amount of 1 to 3 parts by mass relative to 10 parts by mass of PTFE, the peeling resistance of the grease composition is particularly excellent. Therefore, from the viewpoint of peeling resistance, it is particularly preferable to include calcium carbonate having a larger particle diameter than PTFE in an amount of 1 to 3 parts by mass relative to 10 parts by mass of PTFE.

The total amount of the first solid lubricant and the second solid lubricant in the grease composition of the present invention is preferably 1 to 20 mass%, more preferably 5 to 15 mass%. When the total amount of the first solid lubricant and the second solid lubricant is within this range, the influence of the grease's influx on the performance is small, which is preferable.

Since the first and second solid lubricants of the present invention do not have polarity, even if included in polyoxyalkylene and/or an ether derivative of polyoxyalkylene, the peeling resistance can be improved without being affected by the base oil.

Although not bound by any theory, it is thought that by intervening in the lubricating field with polytetrafluoroethylene having a smaller particle diameter than the second solid lubricant, it becomes possible to stably supply the second solid lubricant to the lubricating field while improving the peeling resistance, thereby significantly improving the peeling resistance.

<Theme>

As the thickener of the grease of the present invention, there are no particular restrictions. Specifically, soap-based thickeners such as Li soap or Li complex soap, urea-based thickeners such as diurea, inorganic thickeners such as organic bentonite or silica, and organic thickeners such as sodium terephthalate can be mentioned.

Among these, Li soap and diurea compounds are preferable because they are practical thickeners with few defects and are inexpensive.

As for Li soap, lithium 12-hydroxystearate (Li-(12OH)St) or lithium stearate (Li-St) is preferable. They have excellent lubricating properties.

Li complex soaps include complexes of lithium salts of aliphatic carboxylic acids such as stearic acid or 12-hydroxystearic acid and lithium salts of dibasic acids. Examples of the dibasic acids include succinic acid, malonic acid, adipic acid, pimelic acid, azelaic acid, and sebacic acid. Azelaic acid and sebacic acid are preferred. In particular, Li complex soaps which are mixtures of salts of azelaic acid and lithium hydroxide and salts of 12-hydroxystearic acid and lithium hydroxide are preferred.

Diurea compounds are generally represented by the following formula (2).

R ₄ -NHCONH-R ₅ -NHCONH-R ₆ (2)

(In the formula, R ₄ and R ₆ may be the same or different and represent a C6-30 alkyl group, a C5-8 cycloalkyl group, or a C6-10 aryl group, and R ₅ represents a C6-15 divalent aromatic hydrocarbon group.)

As the diurea compound, an aliphatic diurea in which R ₄ and R ₆ are a C6-30 alkyl group which may be the same or different, an alicyclic aliphatic diurea in which one of R ₄ and R ₆ is a C5-8 cycloalkyl group and the other is a C6-30 alkyl group, or an aromatic diurea in which R ₄ and R ₆ are a C6-10 aryl group which may be the same or different are preferable.

As the aliphatic diurea, an aliphatic diurea in which both R ₄ and R ₆ are C8 alkyl groups, an aliphatic diurea in which both R ₄ and R ₆ are C18 alkyl groups, and an aliphatic diurea in which one of R ₄ and R ₆ is a C8 alkyl group and the other is a C18 alkyl group are more preferable. An aliphatic diurea in which one of R ₄ and R ₆ is a C8 alkyl group and the other is a C18 alkyl group is particularly preferable. An aliphatic diurea in which the ratio of the number of moles of the C8 alkyl group to the total number of moles of the C8 alkyl group and the C18 alkyl group is 30 to 70 mol% is particularly more preferable.

As the alicyclic aliphatic diurea, an alicyclic aliphatic diurea in which one of R ₄ and R ₆ is a cyclohexyl group and the other is a C18 alkyl group is more preferable. An alicyclic aliphatic diurea in which the ratio of the number of moles of cyclohexyl groups to the total number of moles of cyclohexyl groups and C18 alkyl groups is 30 to 90 mol% is particularly preferable.

As an aromatic diurea, an aromatic diurea in which both R ₄ and R ₆ are p-toluyl groups is particularly preferable.

The content of the thickener in the grease composition of the present invention is preferably 4 to 25 mass%, for example, and more preferably 5 to 20 mass%. When the content of the thickener is within this range, the grease has an appropriate hardness and prevents leakage from the lubricating portion, which is preferable.

<Other additives>

The grease composition of the present invention may optionally contain any additives generally used in grease compositions. Examples thereof include antioxidants, rust inhibitors, corrosion inhibitors, oil-based agents, and viscosity index improvers. It is preferable to contain an antioxidant and/or a rust inhibitor. However, it is preferable not to contain a reaction system additive (i.e., an additive that reacts on a lubricating surface to generate a component that decomposes the base oil, such as molybdenum disulfide, amine phosphate, zinc dialkyldithiolinate, and molybdenum dialkyldithiocarbamate).

As antioxidants, amine-based, phenol-based, quinoline-based, sulfur-based, etc. can be mentioned, but amine-based and quinoline-based antioxidants are preferable.

Examples of rust inhibitors include zinc-based, carboxylic acid-based, carboxylate-based, succinic acid-based, amine-based, sulfonate-based, and naphthenic acid-based. Amine-based and naphthenic-based are preferred. Mixtures of these are more preferred.

Examples of corrosion inhibitors include thiadiazole, benzimidazole, and benzotriazole.

Examples of lubricants include fatty acids, fatty acid esters, and phosphate esters.

When the grease composition of the present invention contains other additives, the content thereof is usually 0.5 to 10 mass%, preferably 0.5 to 5 mass%, based on the total amount of the grease composition.

[Consistency]

The viscosity of the grease composition of the present invention is adjusted according to the intended use, but is preferably 235 to 370. By setting the viscosity to 235 or more, a grease composition having excellent low-temperature properties can be obtained, and by setting it to 370 or less, a grease composition having excellent adhesion to machine parts can be obtained. In addition, in this specification, the term "push viscosity" refers to 60-times mixed viscosity. The viscosity can be measured according to JIS K2220 7.

The use of the grease composition of the present invention, i.e., the type of machine part to which the grease composition is applied, is irrelevant. Examples thereof include rolling bearings, ball screws, linear guide bearings, reducers, injection molding machines, linear guides, machine tools, various gears, cams, constant velocity joints, journal bearings (slide bearings), pistons, screws, ropes, chains, and the like. Among these, reducers, ball screws, and the like require strict levels of heat resistance and load resistance, but the grease composition of the present invention can satisfy even such high requirements.

The type of sealant used in machine parts is not particularly limited, and examples include NBR, EPDM, and natural rubber.

[Example]

The Greek compositions of examples and comparative examples were prepared using the following ingredients.

<Oil>

·PPG: Polyoxypropylene monobutyl ether (product name "Unilube MB-7", manufactured by NOF Corporation, propylene oxide addition mole number 12, average molecular weight 700, kinematic viscosity at 40℃: 32.8㎟/s, kinematic viscosity at 100℃: 6.7㎟/s, pour point: -47.5℃)

<Theme>

·Lithium soap: lithium 12-hydroxystearate

·Aliphatic diurea: Reaction product of diphenylmethane diisocyanate, octylamine and stearylamine (molar ratio of octylamine and stearylamine is 5:5)

·Alicyclic aliphatic diurea: reaction product of diphenylmethane diisocyanate, cyclohexylamine, and stearylamine (molar ratio of cyclohexene and stearylamine is 7:1)

·Aromatic diurea: reaction product of diphenylmethane diisocyanate and p-toluidene

<First and second solid lubricants>

·PTFE: Polytetrafluoroethylene (solid)

·Calcium carbonate (solid)·Calcium oxide (solid)

·Tricalcium phosphate (solid)

·Calcium stearate (solid)

·MoDTC: MoDTC: Molybdenum dithiocarbamate (liquid)

·MoS ₂ : molybdenum disulfide (solid)

·ZnDTP: Zinc dithiophosphate (liquid)

·Amine phosphate (liquid)

And, MoDTC, MoS ₂ and ZnDTP and amine phosphate are the anti-exfoliation additives of the reaction system for comparison.

<Other additives>

· Antioxidant: 2,2,4-trimethyl-1,2-dihydroquinoline polymer

·Anti-rust agent

<Test Greece>

Preparation Example 1 Test grease composition in which the thickener is a diurea compound

Among base oils, 2 moles of a given amine was reacted with 1 mole of 4.4'-diphenylmethane diisocyanate, cooled, and made into a base grease.

To the above base grease, additives were mixed in the proportions shown in Table 1, additional base oil was added so as to have the amount of thickener in the proportions shown in Table 1, and a test grease composition was prepared by dispersing using a 3-roll mill. The consistency of the test grease composition was 280.

Preparation Example 2 Test grease composition with lithium soap as thickener

Among the base oils, lithium 12-hydroxystearate was added, stirred, and then heated to 230°C. After that, it was cooled to below 100°C while stirring, and used as a base grease.

To the above base grease, additives were mixed in the proportions shown in Tables 1 and 2, additional base oil was added so as to have an amount of thickener in the proportions shown in Tables 1 and 2, and dispersion was performed using a 3-roll mill to prepare a test grease composition. The consistency of the test grease composition was 280.

The mass % of each component in each test grease composition is as shown in Tables 1 and 2.

And, the kinematic viscosity of the base oil at 100℃ was measured according to JIS K2220 23. The pour point of the base oil was measured according to JIS K2269. The consistency of the grease composition was measured according to JIS K 2220 7.

The Greek composition obtained above was tested and evaluated by the method shown below.

<Test method>

·Evaluation of heat resistance by high-temperature thin film test

Grease is applied to the steel plate below, and after being placed in a constant temperature bath at a specified temperature for a specified period of time, gel permeation chromatography analysis is performed to check whether or not decomposition of the base oil occurs.

[Test conditions]

Steel plate: SPCC-SD 80mm×60mm×1mm

Temperature: 120℃

Time: 1152h

Coating thickness: 2mm

GPC measurement solvent: Chloroform

GPC Detector: RI Detector

[metewand]

No decomposition of oil… ○(Pass)

There is decomposition of oil… ×(Fail)

·Evaluation of peeling resistance by rolling 4-ball test Prepare three φ15mm bearing steel balls, place them in a cylindrical container with an inner diameter of 40mm and a height of 14mm, and fill them with about 20g of test grease. Place one φ5/8 inch bearing steel ball in contact with these three steel balls, and rotate them at a predetermined rotational speed, so that the three balls on the lower side rotate and revolve. This is continuously rotated until peeling occurs on the surface of the balls.

※ Peeling occurs between balls, which have the highest surface pressure.

※ The lifespan is the number of times the upper ball comes into contact with the lower ball at the point where peeling occurs. The peeling resistance was evaluated based on the lifespan.

[Test conditions]

Test ball: φ5/8in, Ra 0.45㎛ bearing ball (rotating ball)

φ15mm steel ball for bearing (follower ball)

Test load: 400kgf(6.5GPa)

Rotation speed: 1200rpm

Evaluation criteria: 150,000 times or more… ◎(Pass)

100,000 times or more but less than 150,000 times… ○(Pass)

50,000 or more to less than 100,000 times… △(Failed)

Less than 50,000 times… ×(Failed)

The results are shown in Tables 1 and 2.

[Table 1]

[Table 2]

Examples 1 to 15, which used a first solid lubricant, polytetrafluoroethylene, and a second solid lubricant, at least one selected from calcium carbonate, calcium oxide, tricalcium phosphate, and calcium salts of fatty acids, as additives, have excellent peeling resistance compared to Comparative Examples 1 to 6, 9, and 10. Examples 1 to 15 have excellent heat resistance compared to Comparative Examples 7 to 10. In general, the heat resistance of grease differs depending on the type of thickener, but the improvement in heat resistance in the examples is recognized for both Li soap and urea-based thickeners. Therefore, by using the first solid additive and the second solid additive specified herein in combination as additives, it is possible to improve the peeling resistance and heat resistance of the grease even under high temperature or high surface pressure, without using an anti-peeling additive in the reaction system or selecting a thickener.

Claims (6)

A grease composition containing base oil, thickener, and additives,
At least one selected from the group consisting of base oil, polyoxyalkylene, ether derivatives of polyoxyalkylene, and mixtures thereof;
The additive comprises polytetrafluoroethylene as a first solid lubricant and at least one selected from the group consisting of calcium carbonate, calcium oxide, tricalcium phosphate and calcium salts of fatty acids as a second solid lubricant, and the content of the second solid lubricant is 0.5 mass% or more based on the total mass of the composition.
Greek composition. In the first paragraph,
A grease composition having a content of the first solid lubricant of 0.5 to 20 mass% based on the total mass of the composition. In paragraph 1 or 2,
A grease composition having a content of a second solid lubricant of 0.5 to 10 mass% based on the total mass of the composition. In any one of claims 1 to 3,
A grease composition wherein the second solid lubricant is calcium carbonate. In any one of claims 1 to 4,
A grease composition comprising first and second solid lubricants in a ratio of 1 to 3 mass% of the second solid lubricant relative to 10 mass% of the first solid lubricant. A machine part to which a grease composition according to any one of claims 1 to 5 has been applied.