JP2000239689A - Lubricating grease composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a lubricating grease composition suitable for decreasing the noise of a bearing and increasing the life of it by compounding a base oil with a thickener containing lithium hydroxystearate and a lithium salt of a 6-11C fatty acid. SOLUTION: This composition contains a base oil and 5-40 mass % (based on the composition) thickener which comprises 5-95 mol% lithium hydroxystearate and 95-5 mol% lithium salt of a 6-11C fatty acid. The base oil is a carbonic ester compound, a synthetic ester oil (e.g. a polyol ester), a synthetic ether oil (e.g. an alkyl diphenyl ether), a synthetic hydrocarbon oil (e.g. a poly-α-olefin), a mineral oil (e.g, a paraffinic mineral oil) or the like, preferably contains 10 mass % or higher ester oil, and preferably has a kinematic viscosity (40 deg.C) of 5-20 mm2/s.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a lubricating grease composition, and more particularly to a grease for a ball bearing.

2. Description of the Related Art Conventionally, greases for ball bearings, especially for ball bearings for spindle motors of recording devices such as hard disks and CD-ROMs of computers, are based on ester oils such as dioctyl sebacate and pentaerythritol ester. Those using thickeners such as stearate and lithium hydroxystearate are used. However, in recent years, with an increase in recording density, a shortage in acoustic life of the bearing has been observed due to an increase in operating temperature due to an improvement in bearing accuracy and an increase in the number of revolutions.

[0002]

SUMMARY OF THE INVENTION An object of the present invention is to provide a lubricating grease composition suitable for lowering the acoustic characteristics of a bearing and extending its life.

[0003]

SUMMARY OF THE INVENTION The present invention provides a grease composition containing a base oil and a thickener, wherein the thickener comprises:
(a) a lithium salt of hydroxystearic acid, (b) C ₆ ~
There is provided a lubricating grease composition which comprises a lithium salt of a fatty acid of C _14.

[0004]

DETAILED DESCRIPTION OF THE INVENTION The present inventors have found that the object of the present invention is achieved by using a soap having a very homogeneous fiber structure as a thickener. Such a soap having a very homogeneous fiber structure is obtained by combining (a) a lithium salt of hydroxystearic acid (eg, 12-hydroxystearic acid) with (b) a lithium salt of a C ₆ -C ₁₄ fatty acid. It is formed by doing. Incidentally, the purity of what is generally commercially available as hydroxystearic acid or fatty acid C ₆ -C ₁₄ are varied, those impure contains fatty acids of different fatty acids and unsaturation carbon atoms. If the content of fatty acids other than the target fatty acid increases, the properties of grease obtained using the same become unstable. Thus, in the present invention, hydroxystearic acid (eg, 12-hydroxystearic acid), C
_{As the 6 to} C ₁₄ fatty acids, those having a purity of 80% (mass%) or more are used.

The fatty acid lithium salt of the component (b) has 6 to 14 carbon atoms. Lithium salts of fatty acids having 5 or less carbon atoms have low solubility in base oils and must be heated to 260 ° C. or higher to dissolve soap. However, many of them are less than this, which is not preferable because it involves danger during production.
Lithium salts of fatty acids having 15 or more carbon atoms are similar in property to the lithium salts of hydroxystearic acid, which is the main fatty acid, and the effect when mixed is not recognized so much, there is no need to dare to mix, Especially 20 carbon atoms
If it exceeds, because the solubility in the base oil is too good, the thickening ability is inferior, the amount of soap required to obtain the desired consistency is compared to the case where 100% of the lithium salt of hydroxystearic acid is used. This is not preferable in terms of cost because it is extremely large.

The molar ratio of (a) the lithium salt of hydroxystearic acid to (b) the lithium salt of a C ₆ to C ₁₄ fatty acid is preferably from 5 to 95:95 to 5, more preferably from 10 to 9
5: 90-5. The kinematic viscosity of the base oil at 40 ° C. is preferably 5
200200 mm ² / s, more preferably 10-100 mm ² / s.
Examples of the base oil of the lubricating grease composition of the present invention include carbonate compounds, ester synthetic oils such as polyol ester oils, ether synthetic oils such as alkyl diphenyl ether, synthetic hydrocarbon oils such as polyalpha-olefins, and paraffinic mineral oils. And other mineral oils.

A particularly preferred base oil is 10% by mass.
Above, more preferably 50% by mass or more of ester oil. The content of the thickener is preferably 5 to 40% by mass, more preferably 7 to 20% by mass, based on the whole composition.

Hereinafter, the present invention will be described in detail with reference to examples. Example 1 As a base oil, pentaerythritol ester oil (40 ° C .: 33
mm ² / s), a fatty acid and lithium hydroxide were reacted in a base oil as follows to prepare a grease composition (200 g each). The amount of fatty acid was increased by 10% by mass, and the amount of lithium hydroxide was increased by 5% from the measured saponification value. Fatty acids having a purity of 80% or more were used. a) A beaker containing a mixture of a base oil and a fatty acid is heated to about 80 ° C. and dissolved in the base oil. b) Warm a beaker containing a mixture of lithium hydroxide and 5 times distilled water to about 80 ° C. c) Charge b into a at a stretch and let it react for about 5 minutes. d) Warming is performed after the reaction, the soap is dissolved in oil (maximum temperature 235 ° C.), cooled as it is to room temperature, and kneaded once through a three-roll mill to obtain a predetermined grease (clearance 10 to 20 μm). ).

Example 2 As a base oil, pentaerythritol ester oil (40 ° C .: 3
3mm ² / s) and use the grease composition (200
g) was prepared. The amount of soap was 10% by mass. a) Weigh the base oil and lithium soap into one beaker,
Heat to 35 ° C. b) After dissolving the soap in oil, cool it to room temperature,
The mixture was passed through the roll mill once and kneaded to obtain a predetermined grease (clearance: 10 to 20 μm).

[0010] Sound life test method After operating for a certain period of time under the following conditions, an Anderon tester
Using (AD-SN-4 manufactured by Sugawara Laboratories), the amount of anderon (volume) and the degree of noise were scored to obtain standard products (Sample 10 of Comparative Example 1, Sample 11 of Comparative Example 2, or Reference Example). Sample 16) was compared. (1) Test conditions Bearing type: 608 VV Test temperature: 100 ° C Rotation speed: 1800 rpm Test time: 500 h Grease filling amount: 0.35 ml (about 40% of bearing space volume) (2) Anderon test (measures anderon amount and noise) ) Number of revolutions: 1800 rpm Test time: 120 seconds Evaluation A standard product was judged according to the following criteria. A: More than 1.1 times the standard product B: 0.9 to 1.1 times the standard product C: Less than 0.9 times the standard product

[0011]

[How to check the length and width of soap fiber] To check the length and width of soap fiber, use an electron microscope (Akashi Seisakusho Co., Ltd .;
LEM-2000). The obtained grease is diluted with petrolatum to 5 to 20 times the sample, and this is applied on a metal mesh for an electron microscope. Next, a metal mesh is placed on a petri dish containing a solvent (such as n-hexane), and oil components are removed from the grease. The metal mesh is taken out of the solvent, dried, set on an electron microscope, and the soap fiber is observed. The measurement magnification is 6000 times, and the length and width of five points of fibers of a typical size that occupy the mainstream of one field of view are measured,
Find the average. The results are shown in the table below.

[0012]

[Table 1]

[0013]

[Table 2] The "-" in the columns of compatibility penetration, dropping point and acoustic life means that the test was not performed.

The hydroxystearic acid used in Example 1 and Comparative Example 1 was 12-hydroxystearic acid (purity 8
5%). The purity of the other fatty acids used is 90% or more. As for the size of the soap fiber, the samples 1 to 9 and 11 were thinner and shorter than the sample 10;
2 was equivalent to sample 10.

[0015]

[Table 3]

[0016]

[Table 4] "-" In the columns of the penetration and acoustic life means that the test was not performed.

The lithium hydroxystearate used in Example 2 and Comparative Example 2 is lithium 12-hydroxystearate (85% purity). The purity of the other fatty acids used is 90% or more. Sample 16 of the reference example used lithium 12-hydroxystearate having a purity of about 70%, and used pentaerythritol ester oil and diester oil at a weight ratio of 80:20 as base oils. The kinematic viscosity of the base oil was 26.0 mm ² / s at 40 ° C, and the drop point of the grease composition was 190 ° C. The size of the soap fiber is from sample 1
Sample 10 was thinner and shorter than sample 11, but samples 13, 14, and 16 were equivalent to sample 11, and sample 15 was thicker and longer than sample 11.

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Claims (5)

[Claims] 1. A grease composition comprising a base oil and a thickener, wherein the thickener comprises (a) a lithium salt of hydroxystearic acid and (b) a lithium salt of a C ₆ -C ₁₄ fatty acid. A lubricating grease composition comprising: 2. A lithium salt (a) of hydroxystearic acid, the molar ratio of the lithium salt of (b) C ₆ ~C _{1 4} fatty acid, 5-95: 95-5 lubricating of claim 1, wherein Grease composition. 3. The lubricating grease composition according to claim 1, wherein the kinematic viscosity at 40 ° C. of the base oil is 5 to 200 mm ² / s. 4. The lubricating grease composition according to claim 1, wherein the base oil contains at least 10% by mass of an ester oil. 5. The lubricating grease composition according to claim 1, wherein the content of the thickener is 5 to 40% by mass based on the whole composition.