JP4895926B2 - Silicone grease composition - Google Patents

Description

  The present invention relates to a silicone grease composition that can be used for lubricated parts such as bearings and gears and has excellent fretting damage resistance between steel and steel.

  Silicone oils are widely used as grease base oils by taking advantage of their characteristics because they exhibit excellent performance in viscosity temperature characteristics, thermal oxidation stability, resin resistance, and the like. However, since silicone oil tends to have poor lubricating performance between steel and steel compared to synthetic oil such as mineral oil, PAO, and ester, grease based on silicone oil (hereinafter referred to as silicone grease). In order to improve the lubricating performance, various attempts have been made (see Patent Document 1, Patent Document 2, and Patent Document 3).

JP-A-62-283196 Japanese Patent Laid-Open No. 5-132688 JP-A-5-230486

However, in a steel bearing or the like, when external vibration is applied in a stationary state, a minute slip may occur between the rolling elements and the raceway groove, which may damage the bearing. In general, such surface damage caused by micro reciprocating sliding between two contacting solids is called fretting. However, in silicone grease, improvement of fretting damage resistance between steel and steel is desired.

As a result of intensive studies to achieve the above object, the inventors of the present invention use a dimethyl silicone oil having a kinematic viscosity at 25 ° C. of 1 to 2000 mm ² / s as a base oil, and add a thickener to the base oil. As an aliphatic hydrocarbon group containing at least one selected from lithium soap-based thickeners, complex lithium soap-based thickeners, polyurea and N-substituted terephthalamic acid metal salts, and having 1 to 14 carbon atoms Or a silicone grease composition containing a specific amount of zinc dithiophosphate having at least one selected from aromatic hydrocarbon groups having 6 to 24 carbon atoms, whereby the resistance of the silicone grease between steel and steel is improved. It has been found that fretting damage is greatly improved, and the present invention has been completed.

That is, the present invention relates to a dimethyl silicone oil base oil having a kinematic viscosity at 25 ° C. of 1 to 2000 mm ² / s, a lithium soap thickener, a composite lithium soap thickener, polyurea, and an N-substituted terephthalamic acid metal salt. A zinc dithiophosphate having at least one thickener selected from the group consisting of an aliphatic hydrocarbon group having 1 to 14 carbon atoms or an aromatic hydrocarbon group having 6 to 24 carbon atoms The present invention provides a silicone grease composition characterized by containing 0.5 to 20% by mass of the toner.

  The silicone grease composition of the present invention is excellent in fretting damage resistance of a steel-steel sliding portion. Therefore, the silicone grease composition of the present invention is extremely useful in practice. Particularly, it is suitable for steel bearings and gears having a steel-steel sliding portion.

The base oil used in the present invention is dimethyl silicone oil. Examples of the dimethyl silicone oil include dimethyl silicone oil represented by the general formula (1).
(CH ₃ ) ₃ SiO— [Si (R ¹ ) (R ² ) —O—] _n —Si (CH ₃ ) ₃
... (1)
(In the formula, R ¹ and R ² are methyl groups, and n is an integer of 1 to 2000.)

The dimethyl silicone oil used in the present invention preferably has a kinematic viscosity at 25 ° C. of 1 to 2000 mm ² / s, more preferably 5 to 1500 mm ² / s, and particularly preferably 10 to 1500 mm ² / s. It is. If the kinematic viscosity at 25 ° C. is too small, the fretting damage resistance tends to be low. When the kinematic viscosity at 25 ° C. is too large, the fluidity is deteriorated and the inherent performance of the grease tends to be difficult to be obtained.
Further, the content of dimethyl silicone oil can be appropriately selected according to the required characteristics, but is usually preferably in the range of 55 to 98% by mass, more preferably 65 to 95% by mass with respect to the total amount of silicone grease. It is a range.

The thickener used in the silicone grease composition of the present invention is at least one selected from a lithium soap-based thickener, a composite lithium soap-based thickener, polyurea and a metal salt of N-substituted terephthalamic acid.
Examples of the lithium soap thickener include aliphatic carboxylic acid lithium salts having a hydroxyl group such as lithium-12-hydroxystearate, aliphatic carboxylic acid lithium salts such as lithium stearate, and mixtures thereof.

  Examples of the complex lithium soap thickener include a complex of the above-described aliphatic carboxylic acid lithium salt having a hydroxyl group and a dibasic acid lithium salt. Here, suitable dibasic acids include succinic acid, malonic acid, adipic acid, pimelic acid, azelaic acid, sebacic acid and the like. Particularly preferred are azelaic acid and sebacic acid.

Examples of polyurea include those represented by the following general formula (2).
R ³ -NH- (CONH-R ⁴ -NHCONH-R ⁵ NH) _y -CONH-R ⁴ -NHCONH-R ⁶
... (2)
(Wherein R ³ , R ⁴ , R ⁵ and R ⁶ are hydrocarbon groups having 1 to 30 carbon atoms, and y is an integer of 0 to 3)
In General formula (2), y is an integer of 0-3, Preferably it is 0 or 1, More preferably, it is 0. R ³ and R ⁶ are an aliphatic hydrocarbon group, an alicyclic hydrocarbon group, an aromatic hydrocarbon group or a combination thereof, and preferably have 1 to 30 carbon atoms, more preferably 3 to 22, Preferably it is 6-18. R ⁴ is a hydrocarbon group having 1 to 30 carbon atoms, and R ⁵ is a hydrocarbon group having 1 to 30 carbon atoms. The polyurea of the general formula (2) is usually obtained by the reaction of diamine and diisocyanate.

Examples of the N-substituted terephthalamic acid metal salt include those represented by the general formula (3).

In the general formula (3), R ⁷ is a hydrocarbon group having 4 to 22 carbon atoms, and the carbon number thereof is preferably 8 to 22, more preferably 12 to 22, particularly preferably 14 to 20. is there. If the number of carbon atoms is too small, the thickener is difficult to disperse in the base oil, and the base oil tends to separate. Moreover, when carbon number is too large, there exists a tendency for shear stability to worsen. Examples of R ⁷ include decyl group, tetradecyl group, hexadecyl group, octadecyl group and the like.

M is a metal, and examples thereof include metals of Group I, Group II, Group III, and Group IV. Specific examples of M include lithium, potassium, sodium, magnesium, calcium, barium, zinc, aluminum, lead and the like. Particularly preferred are sodium, barium, lithium and potassium, with sodium being most preferred. x is the same integer as the valence of the metal M.
The above thickeners can be used alone or in combination of two or more.

  The thickener used in the silicone grease composition of the present invention imparts consistency to the present invention, and the preferred content is 1 to 40% by mass, more preferably 2 to 2%, based on the total amount of silicone grease. 20% by mass. When the blending amount is too small, a predetermined consistency is not obtained without becoming a grease. On the other hand, if the amount is too large, the lubricity of the product grease tends to decrease.

In the silicone grease composition of the present invention, zinc dithiophosphate having at least one selected from an aliphatic hydrocarbon group having 1 to 14 carbon atoms or an aromatic hydrocarbon group having 6 to 24 carbon atoms is contained. In zinc dithiophosphate, one of the four substituents may be an aliphatic hydrocarbon group having 1 to 14 carbon atoms or an aromatic hydrocarbon group having 6 to 24 carbon atoms. All of the substituents are preferably an aliphatic hydrocarbon group having 1 to 14 carbon atoms or an aromatic hydrocarbon group having 6 to 24 carbon atoms. Preferred zinc dithiophosphates include those represented by the general formula (4).

（式中、Ｒ^８、Ｒ^９、Ｒ^１０及びＲ^１１は、炭素数が１〜１４の脂肪族炭化水素基、または炭素数６〜２４の芳香族炭化水素基であり、それぞれ同一であっても異なっていてもよい。）

(In the formula, R ⁸ , R ⁹ , R ¹⁰ and R ¹¹ are each an aliphatic hydrocarbon group having 1 to 14 carbon atoms or an aromatic hydrocarbon group having 6 to 24 carbon atoms, and are the same. May be different.)

When R ^{8 to} R ¹¹ of the zinc dithiophosphate in the above formula (4) is an aliphatic hydrocarbon group, the carbon number thereof is 1 to 14, preferably 1 to 12, particularly preferably 2 to 8. The aliphatic hydrocarbon group is preferably a primary or secondary alkyl group, and more preferably a primary alkyl group that is difficult to hydrolyze. When the aliphatic hydrocarbon group is too long, the fretting damage resistance tends to decrease. Further, from the viewpoint of better compatibility with grease and higher resistance to fretting damage, the aliphatic hydrocarbon group preferably has 2 or more carbon atoms. Specific examples of preferable aliphatic hydrocarbon groups include butyl group, pentyl group, hexyl group, heptyl group, octyl group and the like.

On the other hand, when R ^{8 to} R ¹¹ of the zinc dithiophosphate in the above formula (4) is an aromatic hydrocarbon group, the carbon number thereof is 6 to 24, preferably 8 to 24. When the carbon number is too large, the fretting damage resistance tends to be lowered. Specific examples of preferred aromatic hydrocarbon groups include phenyl group, methylphenyl group, nonylphenyl group, decylphenyl group, dodecylphenyl group and the like.
The preferable content of zinc dithiophosphate is 0.5 to 20% by mass, preferably 1.0 to 10% by mass, and particularly preferably 1.5 to 7% by mass. When the content is too small, the predetermined fretting damage resistance tends to be not obtained. If it is too much, the effect tends to be saturated.

The silicone grease composition of the present invention can be produced by blending the thickener, base oil and zinc dithiophosphate of each of the above components, but various additives may be blended as necessary. You can also.
Examples of additives include dispersants such as alkenyl succinimide, alkenyl succinimide boronated modified product, and benzylamine; polymethacrylate, ethylene propylene copolymer, styrene-isoprene copolymer, styrene-isoprene copolymer Viscosity index improvers such as hydride of polymer or polyisobutylene; alkylphenols such as 2,6-di-tert-butyl-p-cresol, 4,4′-methylenebis- (2,6-di-t-butylphenol) ) Phenol compounds such as n-octadecyl-3- (4′-hydroxy-3 ′, 5′-di-tert-butylphenol) propionate, aromatic amine compounds such as naphthylamines and dialkyldiphenylamines, etc. And various antioxidants. An additive can be used individually by 1 type or in combination of 2 or more types.

  Next, the present invention will be specifically described with reference to examples. In addition, this invention is not limited at all by these Examples.

(Examples 1-6 and Comparative Examples 1-4)
In Examples and Comparative Examples, silicone grease compositions containing the following * 1 to * 14 components in the proportions (mass) shown in Tables 1 and 2 were prepared. The thickener of * 1 to * 14 is obtained by mixing the raw material of the thickener with the base oil and reacting the raw material in the base oil to obtain a thickener. As a result, * 1 to * 14 A silicone grease composition containing these components was prepared. The silicone grease composition was prepared by properly mixing the components * 1 to * 14 and milling to uniformly disperse the thickener in the silicone grease.

* 1: Each base oil in the table and lithium-12-hydroxystearate (manufactured by Sakai Chemicals; trade name “S7000H”) are put into a lithium-12-hydroxystearate heat-resistant container and heated to about 200 ° C. Dissolved, added base oil, cooled, and milled to optimize lithium-12-hydroxystearate crystals, and a silicone grease mixed and dispersed in the base oil was prepared.

* 2: Each base oil and lithium stearate (made by Sakai Chemicals; trade name “S7000”) in the table are put into a lithium-stearate heat-resistant container, heated and dissolved at about 200 ° C. After addition, cooling, and milling, the lithium-stearate crystals were optimized and a silicone grease mixed and dispersed in the base oil was prepared.

* 3: Each base oil and diphenylmethane-4,4-diisocyanate in the table are put into an aliphatic diurea heat-resistant container, heated, and then octylamine is added at about 60 ° C. and reacted for about 40 minutes. Thereafter, the mixture was heated to 170 ° C. with stirring, the base oil was added, and after cooling, milling was performed to optimize diurea crystals, and a silicone grease mixed and dispersed in the base oil was prepared.
In the general formula (2), y is 0, R ³ and R ⁶ are aliphatic hydrocarbon groups having 8 carbon atoms, and R ⁴ is an aromatic hydrocarbon group having 13 carbon atoms.

* 4: Each base oil and diphenylmethane-4,4-diisocyanate in the table are put into an alicyclic diurea heat-resistant container, heated, and then cyclohexylamine is added at about 60 ° C and allowed to react for about 40 minutes. Thereafter, the mixture was heated to 110 ° C. with stirring, the base oil was added, and after cooling, milling was performed to optimize diurea crystals, and a silicone grease mixed and dispersed in the base oil was prepared.
In general formula (2), y is 0, R ³ and R ⁶ are alicyclic hydrocarbon groups having 6 carbon atoms, and R ⁴ is an aromatic hydrocarbon group having 13 carbon atoms.

* 5: Sodium N-substituted terephthalate The base oil and methyl ester of N-octadecyl terephthalate are placed in a heat-resistant container, heated and dissolved, then cooled to 100 ° C. or less and added with a 50% by mass aqueous sodium hydroxide solution. N-octadecyl terephthalate obtained by gradually heating with sufficient stirring, sufficiently saponifying, further adding a base oil at 150 ° C. and heating to a maximum temperature of 180 ° C., followed by cooling to 60 ° C. Sodium laminate

* 6: The base oil and 12-hydroxystearate in the table are put into a composite lithium soap heat-resistant container and heated. Next, an aqueous lithium hydroxide solution is added at about 80 ° C., and lithium-12-hydroxystearate is generated by a saponification reaction. Further, lithium hydroxide and azelaic acid are added at about 90 ° C. and reacted for about 2 hours to form lithium complex soap. Thereafter, this is heated, semi-molten and then rapidly cooled to optimize the lithium complex soap crystal, and the resulting lithium-12-hydroxystearate uniformly mixed and dispersed in the base oil / Azelaic acid complex lithium soap

* 7: Silicone oil A
Dimethyl silicone oil having a kinematic viscosity at 25 ° C. of 500 mm ² / s * 8: Silicone oil B
Methylphenyl having a kinematic viscosity at 25 ° C. of 500 mm ² / s, R ¹ and R ² being a mixture of methyl group and phenyl group, and a mixing ratio of methyl group to phenyl group in the structure being 9: 1 Silicone oil

* 9: Zinc dithiophosphate A
In general formula (4), R ⁸ , R ⁹ , R ¹⁰ and R ¹¹ are zinc dithiophosphates that are linear alkyl groups having 4 or 5 carbon atoms * 10: zinc dithiophosphate B
In the general formula (4), R ⁸ , R ⁹ , R ¹⁰ and R ¹¹ are zinc dithiophosphates that are linear alkyl groups having 12 carbon atoms * 11: zinc dithiophosphate C
In the general formula (4), R ⁸ , R ⁹ , R ¹⁰ and R ¹¹ are zinc dithiophosphates (trade name “Oroa 260” manufactured by Chevron Texaco) which is an aromatic hydrocarbon group having 14 to 20 carbon atoms.

* 12: Antioxidant (diphenylamine)
* 13: MoDTC
Molybdenum dithiophosphate (manufactured by Adeka, trade name “Sakura Rube 600”)
* 14: TCP
Tricresyl phosphate (trade name "TCP", manufactured by Akzo Nobel)

(Evaluation test method)
(1) Fretting wear test (between steel and steel)
An SRV friction tester was used. The test conditions were a temperature of 40 ° C., a frequency of 50 HZ, a swing width of 1 mm, a load of 200 N, and a test time of 20 minutes. Moreover, a cylinder and a disk were used for the test piece. In the evaluation, the wear depth was measured using a surface roughness meter for the maximum friction coefficient during the test and the sliding portion of the disc after the test.
The fretting damage resistance was evaluated according to the following criteria.
A: The maximum friction coefficient μ is 0.14 or less.
○: The maximum friction coefficient μ is more than 0.14 and 0.2 or less.
X: The maximum friction coefficient μ exceeds 0.2.

Claims (1)

At least selected from a base oil of dimethyl silicone oil having a kinematic viscosity at 25 ° C. of 1 to 2000 mm ² / s, a lithium soap-based thickener, a composite lithium soap-based thickener, polyurea, and an N-substituted terephthalamic acid metal salt. 0.5 to 0.5% of zinc dithiophosphate having one thickener and at least one selected from an aliphatic hydrocarbon group having 1 to 14 carbon atoms or an aromatic hydrocarbon group having 6 to 24 carbon atoms A silicone grease composition containing 20% by mass.