JP5931509B2 - Grease composition - Google Patents

Description

  The present invention relates to a grease composition using a metal soap thickener.

  Grease is mainly used for sliding bearings, rolling bearings (bearings), or sliding surfaces where it is difficult to keep the lubricant film attached due to movement of the contact surface. Among these, metal soap thickeners The so-called metal soap grease using water is excellent in water resistance, heat resistance and mechanical stability, and in particular, lithium soap grease is most commonly used as a universal grease and has various sliding parts between steel and resin. It is also used for bearings, gears, ball joints, pinions and the like.

As a grease for resin used in such a steel-resin sliding portion, 3 to 25% by mass of silicone oil and lithium soap thickener, polytetrafluoroethylene resin powder and 1 to 15% by mass of saturated fatty acid amide are contained. A composition has been proposed (Patent Document 1).
However, since this grease composition uses a base oil with a high density called silicone oil, there is a problem that the dispersibility of the solid lubricant is poor, the friction coefficient cannot be lowered sufficiently, and stick slip is likely to occur. there were.

JP 2011-225781 A

  The problem to be solved by the present invention is to provide a grease composition that improves the dispersibility of a solid lubricant, has a sufficiently low coefficient of friction at the sliding portion of steel and resin, and does not cause stick slip. .

As a result of diligent research, the present inventor has improved the dispersibility of the solid lubricant by using a lubricating base oil having a predetermined density, and the sliding of steel and resin. It was found that a grease composition having a sufficiently low coefficient of friction at the part and no stick-slip was obtained.
This invention is made | formed based on this knowledge, and consists of the following.

(1) A grease composition containing a lubricating base oil having a density at 15 ° C. of 0.75 to 0.95 g / cm ³ , an amide compound, a solid lubricant, and a metal soap thickener.
(2) The grease composition as described in (1) above, wherein the solid lubricant is a layered compound or a fluororesin.
(3) The grease composition as described in said (1) or (2) whose amide compound is monoamide or bisamide.

  The grease composition of the present invention has a special effect that the solid lubricant is sufficiently dispersed, the friction coefficient at the sliding portion of steel and resin is low, and stick slip does not occur.

The grease composition of the present invention comprises a lubricating base oil having a density at 15 ° C. of 0.75 to 0.95 g / cm ³ , an amide compound, a solid lubricant, and a metal soap thickener.
[Lubricant base oil]
As the lubricating base oil of the present invention, either mineral oil or synthetic oil can be used, but the lubricating base oil has a density at 15 ° C. in the range of 0.75 to 0.95 g / cm ^3. is there. When the lubricant base oil is out of this range, the dispersibility of the solid lubricant is lowered, and the friction coefficient cannot be sufficiently lowered. This density is particularly preferably from 0.8 to 0.9 g / cm ³ .
Further, those having a kinematic viscosity at 40 ° C. of 1 to 500 mm ² / s are preferred, and 5 to 100 mm ² / s are more preferred. When the kinematic viscosity at 40 ° C. deviates from 1 to 500 mm ² / s, it becomes difficult to easily prepare a grease composition having a desired consistency. Further, in order to prepare a grease having excellent lubricity, the viscosity index is 90 or more, particularly 95 to 250, the pour point is -10 ° C or less, particularly -15 to -70 ° C, and the flash point is 150 ° C. A lubricating base oil having the above physical properties is preferred.

  Examples of the mineral-based lubricating base oil include lubricating oil fractions obtained by purifying distillate obtained by subjecting crude oil to atmospheric distillation or further distillation under reduced pressure by various purification processes. The refining process includes hydrorefining, solvent extraction, solvent dewaxing, hydrodewaxing, sulfuric acid washing, clay treatment, etc., and these can be combined and processed in an appropriate order to obtain the base oil of the present invention. . A mixture of refined oils having different properties, obtained by different crude oils or distillate oils by different process combinations and sequences, is also useful. Any method can be preferably used by adjusting the properties of the obtained base oil so as to satisfy the above-described density.

  As the synthetic lubricant base oil, it is preferable to use a substrate having excellent hydrolysis stability. For example, polyolefins such as poly-α-olefin, polybutene and copolymers of two or more kinds of olefins, polyesters, polyalkylenes Examples thereof include glycol, alkylbenzene, and alkylnaphthalene. Of these, poly-α-olefins are preferable in terms of availability, cost, viscosity characteristics, oxidation stability, and compatibility with system components. The poly-α-olefin is more preferably a polymer such as 1-dodecene or 1-decene in terms of cost.

As the lubricating base oil, the exemplified synthetic systems can be used alone or in admixture of two or more. Furthermore, it can also be used by mixing with the mineral oil system.
When using a mixture of a plurality of lubricating base oils including a synthetic base oil, if the base oil mixture satisfies the above physical properties, the individual base oils before mixing are within the range of physical properties. It can be used even if it is off. Accordingly, the individual synthetic base oils do not necessarily satisfy the above physical properties, but are preferably within the above physical properties.
The content of the lubricating base oil is preferably 50 to 95% by mass, particularly preferably 60 to 85% by mass, based on the total amount of the grease composition. When the content of the lubricating base oil is out of the range of 50 to 95% by mass, it becomes difficult to easily prepare a grease composition having a desired consistency.

[Amide compound]
The amide compound of the present invention is a compound having at least one amide group (-NH-CO-). As the amide compound, a compound containing one amide group (monoamide), a compound containing two amide groups (bisamide) or Any compound (triamide) containing three amide groups can be used. Bisamide and triamide are most preferred because they have the advantage of reducing the frictional resistance of the sliding portion even with a relatively small amount.
The monoamide may be either a monoamine acid amide or a monoacid acid amide, and may be a bisamide, a diamine acid amide, or a diacid acid amide.
The amide compound preferably used is one having a melting point of 40 to 180 ° C., particularly preferably 80 to 180 ° C., more preferably 100 to 170 ° C., and a molecular weight of 242 to 932, particularly preferably 298 to 876.
Monoamide, bisamide, and triamide are represented by the following general formula (1), general formula (2) and (3), and general formula (4), respectively.

R ¹ -CO-NH-R ² (1)
R ¹ -CO-NH-A ¹ -NH-CO-R ² (2)
R ¹ -NH-CO-A ¹ -CO-NH-R ² (3)
R ¹ -M-A ¹ -CH (A ² -M-R ³ ) -A ³ -M-R ² (4)

In each of the above formulas, R ¹ , R ² and R ³ are each independently a hydrocarbon group having 5 to 25 carbon atoms, which is an aliphatic hydrocarbon group, an alicyclic hydrocarbon group or an aromatic hydrocarbon group. Either is acceptable. In the case of the general formula (1), the case where R ² is hydrogen is also included. A ¹ , A ² , and A ³ are each independently an aliphatic hydrocarbon group having 1 to 10 carbon atoms, an alicyclic hydrocarbon group, an aromatic hydrocarbon group, or a combination of these carbon numbers 1-10 divalent hydrocarbon groups, M is an amide group.
In the case of monoamide, R ² is preferably hydrogen or a saturated or unsaturated chain hydrocarbon group having 10 to 20 carbon atoms.
In the case of a diamine acid amide, A ¹ is preferably a divalent saturated chain hydrocarbon group having 1 to 4 carbon atoms.
Furthermore, in the formulas (2) and (3), in the hydrocarbon group represented by R ¹ , R ² , or A ¹ , a part of hydrogen may be substituted with a hydroxyl group (—OH).

In the present specification, an amide compound in which A ¹ , A ² and A ³ are aliphatic hydrocarbon groups is an aliphatic amide, and an amide in which at least one of A ¹ , A ² or A ³ is an aromatic hydrocarbon group The compound is referred to as an aromatic amide, and the amide compound in which at least one of A ¹ , A ^2, or A ³ is an alicyclic hydrocarbon group or an aromatic hydrocarbon group is referred to as a non-aliphatic amide.
In the case of an aliphatic amide, R ¹ , R ² and R ³ are preferably a saturated or unsaturated chain hydrocarbon group having 10 to 20 carbon atoms.
In the case of an aromatic amide, R ¹ , R ² , and R ³ are preferably those having a saturated or unsaturated chain hydrocarbon group having 10 to 20 carbon atoms and an aromatic hydrocarbon group.
As the amide compound, a non-aliphatic amide can be used, but an aliphatic amide is preferred. In the case of a diamine acid amide (general formula (3)), A ¹ is preferably a divalent saturated chain hydrocarbon group having 1 to 4 carbon atoms.

  Specific examples of monoamides include saturated fatty acid amides such as lauric acid amide, palmitic acid amide, stearic acid amide, behenic acid amide, hydroxystearic acid amide, unsaturated fatty acid amides such as oleic acid amide and erucic acid amide, and Examples thereof include substituted amides with saturated or unsaturated long-chain fatty acids and long-chain amines such as stearyl stearamide, oleyl oleate amide, oleyl stearate amide, stearyl oleate amide and the like.

Specific examples of the acid amide of the diamine represented by the formula (2) include ethylene bis stearic acid amide, ethylene bis isostearic acid amide, ethylene bis oleic acid amide, methylene bis lauric acid amide, and hexamethylene bis oleic acid amide. And hexamethylene bishydroxystearic acid amide. Specific examples of the diacid bisamide represented by the formula (3) include N, N′-bisstearyl sebacic acid amide.
Among these bisamides, R ¹ and R ² in formula (2) and formula (3) are each independently an amide compound having a saturated chain hydrocarbon group or unsaturated chain hydrocarbon group having 12 to 20 carbon atoms. It is preferable.

  There are many triamides represented by the general formula (4), and specific examples of compounds that can be suitably used in the present invention include N-acylamino acid diamide compounds. The N-acyl group of this compound is a linear or branched saturated or unsaturated aliphatic acyl group or aromatic acyl group having 1 to 30 carbon atoms, particularly a caproyl group, capryloyl group, lauroyl group, myristoyl group, Those composed of stearoyl groups are preferred, and as amino acids are preferably composed of aspartic acid and glutamic acid, and the amine of the amide group is a linear or branched saturated or unsaturated aliphatic amine having 1 to 30 carbon atoms, In particular, butylamine, octylamine, laurylamine, isostearylamine, stearylamine and the like are preferable. In particular, N-lauroyl-L-glutamic acid-α, γ-di-n-butyramide is preferred as a specific compound.

The amide compounds may be used alone or in combination of two or more. The content of the amide compound is preferably 1 to 50% by mass and more preferably 5 to 30% by mass based on the total amount of the grease composition.
When this amide compound is heated and melted in the presence of a lubricant base oil, the lubricant base oil is held in the amide compound forming a three-dimensional network structure, and the amide compound is simply dispersed in the grease. Compared to the case of mixing, the friction coefficient at the sliding portion of steel and resin is further reduced, and no stick slip occurs.

[Solid lubricant]
The solid lubricant is not particularly limited as long as it is generally used for a lubricant, but it is preferable to use a layered compound or a fluorine resin having excellent lubricity.
As the layered compound, those having a layered crystal structure, for example, melamine cyanurate, molybdenum disulfide, boron nitride, graphite, mica, fluorinated graphite and the like are suitable.
Examples of fluororesins include polytetrafluoroethylene (PTFE), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene / hexafluoropropylene copolymer (FEP), and tetrafluoroethylene / ethylene copolymer. (ETFE), polyvinylidene fluoride (PVDF), polychlorotrifluoroethylene (PCTFE) and the like are suitable.
These solid lubricants can be used alone or as a mixture of two or more thereof, and those having an appropriate particle size can be appropriately selected and used depending on the intended use, but the particle diameter is 0.2 to 50 μm, particularly The thing of 1-10 micrometers is preferable.
The content of the solid lubricant is preferably 0.1 to 10% by mass, particularly 0.2 to 5% by mass, based on the total amount of the grease composition.

[Metal soap thickener]
The metal soap-based thickener is a thickener made of a carboxylic acid metal salt, and the carboxylic acid may be a carboxylic acid derivative having a hydroxy group or the like.
The carboxylic acid may be an aliphatic carboxylic acid such as stearic acid or azelaic acid, or an aromatic carboxylic acid such as terephthalic acid, but a monovalent or divalent aliphatic carboxylic acid, particularly an aliphatic group having 6 to 20 carbon atoms. Carboxylic acid is used. In particular, monovalent aliphatic carboxylic acids having 12 to 20 carbon atoms and divalent aliphatic carboxylic acids having 6 to 14 carbon atoms are preferably used. Monovalent aliphatic carboxylic acids containing one hydroxyl group are preferred.
The metal may be an alkali metal such as lithium or sodium, an alkaline earth metal such as calcium, or an amphoteric metal such as aluminum, but an alkali metal, particularly lithium, is preferably used.

This thickener may be blended in the form of metal soap, but a carboxylic acid and a metal source (metal salt, metal salt hydroxide, etc.) are blended separately and reacted at the time of grease preparation, It may be a soap thickener.
Such carboxylic acid metal salts may be used singly or in combination. For example, a mixture of lithium 12-hydroxystearate and lithium azelate is particularly preferred.
The content of the metal soap thickener may be a desired consistency, and is, for example, preferably 2 to 30% by mass, more preferably 5 to 15%, based on the total amount of the grease composition.

[Other additives]
In addition to the above components, the grease composition of the present invention includes, as necessary, a detergent, a dispersant, an antiwear agent, a viscosity index improver, an antioxidant, an electrode, which are generally used in lubricating oils and greases. A pressure agent, a rust inhibitor, a corrosion inhibitor, and the like can be added as appropriate.

[Preparation method]
The grease composition of the present invention can be produced by a general method for producing grease, but it is preferable to heat the amide compound once after its melting point after mixing.
In other words, the amide compound and the lubricating base oil may be heated to the melting point of the amide compound or higher and cooled, and then physically mixed with a general grease composed of a solid lubricant, a thickener, and a lubricating base oil. Moreover, after mixing all the components including a thickener, it may be cooled by heating above the melting point of the amide compound.

[Lubrication target]
The grease composition of the present invention is suitably used for lubrication of various resin sliding members and metal sliding members. Examples of resin sliding members include nylon resin, polycarbonate (PC) resin, polybutylene terephthalate (PBT) resin, polyacetal (POM) resin, etc., which have a UL standard long-term heat-resistant temperature of 50 to 150 ° C. Suitable for members using nylon PA6 resin, and as metal sliding members, bearing steel, carbon steel, stainless steel (SUS), etc., especially members using bearing steel SUJ-2 It is suitable for.

1. Lubricant base oil (1) Mineral oil base oil / Lubricant base oil obtained by solvent-refining distillate obtained by distillation under reduced pressure from atmospheric distillation residue Kinematic viscosity at 40 ° C; 68 mm ² / s
Density at 15 ° C; 0.87 g / cm ³
Viscosity index: 100
Pour point: -10 ° C
Flash point: 250 ° C

(2) Synthetic lubricating base oil (a) Poly-alpha olefin (Durasyn 170 manufactured by INEOS)
Kinematic viscosity at 40 ° C; 68 mm ² / s
Density at 15 ° C .: 0.83 g / cm ³
Viscosity index; 133
Pour point: -45 ° C
Flash point: 250 ° C
(B) Polydimethylsiloxane (silicone oil; KF-96 50cs, 100cs manufactured by Shin-Etsu Chemical Co., Ltd.)
Kinematic viscosity at 40 ° C; 68 mm ² / s
Density at 15 ° C .: 0.96 g / cm ³
(C) Linear perfluoropolyether (fluorinated oil; FOMBLIN M15 manufactured by Solvay Solexis)
Kinematic viscosity at 40 ° C; 85 mm ² / s
Density at 15 ° C .: 1.83 g / cm ³

2. Amide compound (1) Aliphatic amide (a) Ethylene bis-stearic acid amide (special grade reagent)
(B) Ethylene bisoleic acid amide (special grade reagent)
(C) Stearic acid monoamide (special grade reagent)
(2) Aromatic amide (a) m-xylylene bis-stearic acid amide (special grade reagent)

3. Solid lubricant (1) Melamine cyanurate (MCA, average particle diameter: 4 μm, MELAPUR MC25 manufactured by BASF)
(2) Molybdenum disulfide (average particle size: 0.5 μm, Nichimori M-5 powder manufactured by Daizonitori)
(3) Polytetrafluoroethylene (PTFE, average particle size: 4 μm, KTL-8N manufactured by Kitamura)
(4) Boron nitride (average particle size: 2 μm, HP-P1 manufactured by Mizushima Alloy Iron Company)
(5) Silicon oxide (average particle size: 35 μm, special grade reagent)
The average particle diameter is measured by a laser light diffraction method.

4). Metal soap thickener (1) Lithium 12-hydroxystearate (shown as “lithium stearate” in the table)
(2) Composite of lithium 12-hydroxystearate and lithium azelate (mixing ratio is 2: 1) (shown as “composite lithium soap” in the table)
5. Other additives Diphenylamine was added to all as an antioxidant.

[Preparation method]
Each component was placed in a container at the blending amounts (shown in mass%) shown in Tables 1 and 2, heated to 150 ° C. (above the melting point of the amide), stirred with a magnetic stirrer, and then cooled to room temperature. This was subjected to pressure dispersion treatment with a roller (three rolls) to prepare a grease composition.

〔Evaluation method〕
An evaluation test was conducted with a ball-disk reciprocating friction tester. As the metal sliding member, a 1/4 inch sphere of SUJ-2 diameter and a 6 nylon plate-like member (N6 (NC) manufactured by Toyo Plastic Seiko Co., Ltd.) as a resin sliding member were used.
The test load was 2000 gf, the sliding speed was 10 mm / s, and the amplitude was 20 mm. Grease was applied to the disk, and the presence or absence of stick-slip was evaluated from the friction coefficient and the frictional force waveform when slid. In addition, stick slip occurs when the frictional force during sliding is not constant).

〔Evaluation results〕
When only mineral oil and a lithium soap thickener were blended, the friction coefficient was high and the occurrence of stick-slip was also confirmed (Comparative Example 7).
When only mineral oil, a lithium soap thickener and a solid lubricant were blended, the friction coefficient was slightly reduced and stick slip was slightly reduced, but it was not sufficient (Comparative Example 1-6).
When mineral oil, lithium soap, solid lubricant, and aliphatic amide were blended, the friction coefficient was further reduced, and the occurrence of stick slip was also suppressed (Example 1-12).
When silicone oil or fluorinated oil was used as the base oil, the melted amide compound and the base oil separated into two phases even when heated to a temperature higher than the melting point of the amide compound, and did not dissolve uniformly (Comparative Example 8, 9). For this reason, silicon oxide was added to the silicone oil and polytetrafluoroethylene was added to the fluorinated oil, but the friction test could not be carried out because of non-uniform finish (Comparative Examples 10 and 11).

  In the grease composition of the present invention, the solid lubricant is sufficiently dispersed, the coefficient of friction in the sliding portion of steel and resin is low, and there is no occurrence of stick-slip. For example, it is useful for lubricating various bearings, gears, ball joints, pinions and the like.

Claims (7)

Lubricating base oil density at 15 ℃ is 0.75~0.95g / cm ^3, and containing an aliphatic bisamide, composed of at least one of boron nitride and fluorine resin is et solid lubricant, and metal soaps A grease composition containing a system thickener. The grease composition according to claim 1, wherein the solid lubricant comprises boron nitride . The grease composition according to claim 1, wherein the aliphatic bisamide is any one compound represented by the following general formulas (2) to (3) .
R ¹ —CO—NH—A ¹ —NH—CO—R ² (2)
R ¹ —NH—CO—A ¹ —CO—NH—R ² (3)
(In the above formula, R ¹ and R ² each independently represents a saturated chain hydrocarbon group having 12 to 20 carbon atoms, and A ¹ represents an aliphatic hydrocarbon group having 1 to 10 carbon atoms.) The grease composition according to any one of claims 1 to 3, which is used for lubrication between steel and resin. The grease composition according to any one of claims 1 to 3, which is used for lubrication between steel and nylon resin. The lubrication method which uses the grease composition of any one of Claims 1-3 for lubrication between steel and resin. The lubrication method which uses the grease composition of any one of Claims 1-3 for lubrication between steel and nylon resin.