JPH06330070A - Grease composition for bearing of electronic computer - Google Patents

Abstract

PURPOSE:To provide a grease composition for bearing of electronic computer having excellent noise and torque properties and scatterability especially at a high temperature. CONSTITUTION:A grease is imparted with a close and homogeneously stabilized short-fiber structure of soap by the grease composition compounded with a thickener consisting of a lithium soap having no hydroxy group in the chemical configuration and a lithium soap having hydroxy groups in the chemical configuration. A mineral oil and a synthetic hydrocarbon oil are used as the base oil. Thus obtained grease is capable of reducing its scattering in the range between ordinary and high temperatures and improving the noise and torque properties of a bearing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a grease composition for electronic computer bearings, and more particularly to improvement of grease scattering properties, friction torque performance and acoustic performance.

[0002]

2. Description of the Related Art Required performances of a grease composition for a computer bearing include a small amount of scattering, a small torque, and an excellent acoustic performance. The most required performance among these is that the amount of grease scattered from the bearing is small. This is to prevent the recording medium from being contaminated with the scattered grease and causing an error.

As a conventional grease composition for computer bearings, a sodium soap type grease well known as Undock C (trade name) (sodium complex soap using mineral oil as a base oil and sodium complex soap as a thickener) is known. -Mineral oil type grease) has been used almost exclusively for more than 20 years since its splattering property was evaluated.

Further, as a recent representative prior art,
There is one disclosed in Japanese Patent Laid-Open No. 5-9489.

[0005]

However, the sodium complex soap-mineral oil type grease has poor dispersion of soap in the grease and is not homogeneous, so that the acoustic / vibration performance at the initial stage of bearing rotation is not good. Further, sodium complex soap has a strong water absorption property, and the grease hardens with the passage of time to deteriorate the fluidity in the bearing, resulting in poor lubrication, and the bearing noise of the bearing is likely to occur. there were.

Therefore, especially when low noise and low vibration are emphasized, low noise and low noise represented by lithium soap-ester type grease are used. Low torque grease is used. However, this lithium soap-ester type grease has a problem that it is easily scattered, and if used as it is, there is a great risk of contaminating the recording medium. It is also used together with a magnetic fluid seal in order to prevent the scattering, but it is expensive and increases the cost of the product, and a mounting space for the magnetic fluid seal is required, which hinders miniaturization.

The technique disclosed in Japanese Patent Laid-Open No. 5-9489 is at least one base oil selected from the group consisting of mineral oil, synthetic hydrocarbon oil and polyphenyl ether oil having a kinematic viscosity of 8 to 180 cSt at 40 ° C. 70-80 wt%
And 20 to 30 wt% of a lithium salt of a C _{12 to} C ₂₄ higher fatty acid having no hydroxyl group in the chemical structural formula, and a specific rust inhibitor is added to the grease composition for a computer. However, although this technique exhibits excellent scattering properties at room temperature, it has a drawback that the amount of scattering increases at a high temperature of about 70 ° C., which is the maximum operating temperature of bearings for electronic computers.

Therefore, the present invention is a grease composition for a computer which maintains the excellent splattering property at room temperature in the prior art, has a small splattering amount even at a high temperature of about 70 ° C., and has excellent acoustic characteristics and torque performance. The purpose is to provide things.

[0009]

The grease composition of the present invention comprises at least one base oil 70 selected from the group consisting of mineral oils and synthetic hydrocarbon oils having a kinematic viscosity of 8 to 180 cSt at 40 ° C. and 80 wt%, characterized by containing a thickener 20-30 wt-% consisting of higher hydroxy fatty acid lithium salt C ₁₂ -C lithium salt and C ₁₂ -C ₂₄ higher fatty acid of _24.

In the grease composition of the present invention, the content of the higher hydroxy fatty acid lithium salt in the thickener is 10 to 40 wt%, and the resulting grease has an impregnated consistency of 190 to 250. It is a composition for use.

[0011]

The grease composition of the present invention uses lithium soap as a thickener. Among the thickeners, lithium soap has relatively good lubricity, and by uniformly and sufficiently dispersing it in grease, excellent acoustic performance and torque performance of the bearing can be obtained. In addition, the thickener has a short-fiber structure and does not contain a hydroxyl group in the chemical structural formula (hereinafter referred to as lithium soap (A)) and a lithium soap containing a hydroxyl group in the chemical structural formula (hereinafter referred to as lithium). Soap (B) is used as a mixture. Therefore, the micelle structure of the lithium soap and the base oil is more stabilized and a dense structure is obtained, so that the oil separation degree of the grease can be reduced.
As a result, the amount of grease scattered was reduced. But,
Lithium soap (A) even if the degree of oil separation is small
It was found that the amount of scattering under the temperature condition of 70 ° C. does not decrease significantly unless the mixing ratio of the lithium soap (B) and the lithium soap (B) is within the predetermined range.

In particular, when the mixing ratio of lithium soap (B) in the thickener increases, the consistency yield increases and hard grease is produced, which causes problems in acoustic and torque performance. The present inventors have found that it is effective to increase the thickening agent amount of lithium soap grease more than usual and to have a short fiber structure.
By using lithium soap (A) and lithium soap (B) as a thickener and mineral oil and synthetic hydrocarbon oil or a mixed oil thereof as a base oil, the grease composition of the present invention excellent in scattering property at high temperature Came to.

As the base oil used in the grease composition of the present invention, mineral oil and synthetic hydrocarbon oil may be used alone or in combination. When both are mixed and used, the grease scattering property is improved especially at high temperature. The mixing ratio of both is preferably 30 to 70 wt% for mineral oil and about 50 for mineral oil.
Most preferably, it is wt%. The mineral oil is preferably a highly refined oil derived from so-called petroleum, but the viscosity index does not matter. As the synthetic hydrocarbon oil, any of olefin polymerization oil such as poly-α-olefin, liquid polybutene and alkyl aromatic oil can be used. Among them, polyα-olefins such as 1-Decene (CH ₃ (CH ₂ ) ₇ CH═CH ₂ ) oligomers and copolymers of ethylene and poly-α-olefins are preferable.

Regarding the viscosity of the base oil used in the grease composition of the present invention, those having a kinematic viscosity of 8 to 180 cSt at 40 ° C. can be used. If it is less than 8 cSt, it tends to evaporate at a high temperature and it is difficult to produce grease. On the other hand, if it exceeds 180 cSt, not only the friction torque is increased but also the amount of scattering is increased, which is not preferable. According to the research conducted by the present inventors, it has been confirmed that a rather low base oil viscosity is advantageous in terms of splattering property. Considering this point, the viscosity at 40 ° C. is 16 to 100.
It can be said that cSt is preferable.

The thickener used in the grease composition of the present invention has good dispersibility easy to obtain good acoustic performance C ₁₂
Is a lithium salt of a C ₂₄ higher fatty acid. Examples of the higher fatty acid salt include lithium soap (A) having no hydroxyl group in its chemical structural formula such as lithium stearate and beef tallow fatty acid lithium salt, and lithium soap having a hydroxyl group such as lithium 12-hydroxystearate ( It is necessary to mix B) with B in a predetermined ratio. The reason for this is that by using lithium stearate and lithium 12-hydroxystearate in an appropriate combination in the range of a predetermined mixing ratio, the amount of scattering at high temperatures can be considerably reduced. When the mixing ratio of the lithium soap (B) containing a hydroxyl group becomes too large, the amount of scattering at a high temperature remarkably increases.

C _{12 to} C used in the grease composition of the present invention
_With regard to the thickener composed of ₂₄ higher fatty acid lithium salts, the compounding amount with respect to the base oil affects the scattering property of the grease composition. In the conventional lithium soap type grease, the compounding amount of the thickener is generally 8 to 18 wt%. On the other hand, in the case of the present invention, the compounding amount of the thickener is set in the range of 20 to 30 wt% based on the experimental result. It is preferably 23 to 27% by weight. For example, when the amount of the thickener mixed is more than 30 wt% or less than 20 wt%, the scattering property at high temperature becomes poor. Furthermore, the blending amount of the lithium soap thickener is an important factor not only for the scattering property of the grease composition, but also for improving the sound and torque performance.

Grease scattering is a dispersion of fine particles of grease generated by the rotation of the bearing, and a grease having an appropriate hardness is required to improve the scattering property. On the other hand, if the grease is too hard, the fluidity inside the bearing will decrease, and the cage noise will be adversely affected. In other words, the hardness of grease is also a factor that is very related to the scattering property and the acoustic performance. Therefore, the inventors of the present invention also investigated the consistency of the grease composition, and found that the immiscible consistency was 1
It was concluded that the range of 90 to 250 is desirable. If the immiscible consistency is less than 190, the hardness and sound / torque performance are significantly deteriorated. On the other hand, the consistency is 25
If it exceeds 0, the amount of scattering increases and the recording medium of the electronic computer is contaminated.

[0018]

EXAMPLES Next, examples of the present invention and comparative examples will be described. Using the grease compositions of Examples 1 to 18 shown in Tables 1 and 2 and the grease compositions of Comparative Examples 1 to 15 shown in Table 3, the consistency, scattering amount, bearing sound, torque, etc. were measured.

[0019]

[Table 1]

[0020]

[Table 2]

[0021]

[Table 3]

The penetration was measured according to JIS K2220 (5.3), and the oil separation was measured according to JIS K2220 (5.7). To measure the physical properties of the amount of scattering, bearing acoustics, and torque, 19 mg of the grease composition of the sample was enclosed in a single-row deep groove ball bearing with an inner diameter of 5 mm and an outer diameter of 14 mm, which was completely degreased with an organic solvent. It was carried out under conditions of room temperature (about 25 ° C.) and 70 ° C. (scattering amount only) with a preload of 1.5 Kgf.

FIG. 1 shows an outline of the scattering amount measuring device. This device is placed at room temperature or 70 ° C., and while the bearing A in which the grease composition is enclosed is rotated at 3600 rpm for 20 minutes, clean air is flown into the container B of FIG. 1 for every 0.01 cf volume of air. The number of scattered particles of 0.3 μm or more contained therein was measured using a particle counter. Table 1, Table 2 and Table 3 show the amount of scattering after 20 minutes of rotation of the bearing.

For the acoustic measurement of the bearing, an Anderon meter was used to auditorily determine the presence or absence of cage noise when the bearing was rotated at 1800 rpm. The judgment result is indicated by O when the cage sound is not generated, Δ when it is hardly generated, and X when it is occasionally or constantly generated. An outline of the torque measuring device is shown in FIG. Specimen bearing A
Was rotated at 3600 rpm, the torque value measured using the strain gauge C was recorded on the recorder, and the values when the torque was substantially stable after 10 minutes of rotation were shown in Table 1, Table 2 and Table 3.
It was shown to. In FIG. 2, D is an air spindle,
E is an arbor, F is an aluminum cap, and G is an air bearing.

All of the grease compositions of Examples 1 to 18 were good in both scattering property and acoustic performance, whereas the greases of Comparative Examples 1 to 15 were at least one of scattering property and acoustic performance. I had a problem with. Below, we will compare and examine the data in each table regarding the relationship between thickener, kinematic viscosity of base oil, type of base oil, ratio of base oil and thickener, consistency, etc. and grease composition. .

Regarding the thickener, Comparative Examples 1, 4, 7, 8, 10, and 11 in which lithium stearate and lithium 12-hydroxystearate were used alone and Examples 1 to 1 in which both were mixed were used. Comparing No. 18 with Example 18, the amount of scattering at 70 ° C. is considerably smaller in Example than in Comparative Example. Particularly, in Comparative Example 4 in which lithium 12-hydroxystearate was used alone, the amount of scattering at 25 ° C. was much larger, and it is not suitable to use it alone.
Further, as the proportion of lithium 12-hydroxystearate in the thickener increases, the amount of scattering increases, and in Comparative Examples 2 and 3 in which this proportion in the thickener is 70%, Examples 1, 4,
Compared with 7, 8 and 13, the oil separation degree is small, but the amount of scattering at 70 ° C increases and increases. In addition, by mixing lithium stearate and lithium 12-hydroxystearate at a mixing ratio within a certain range and using them,
It was possible to reduce the amount of scattering at. It is considered that this is because a dense and stable grease structure was obtained by appropriately mixing the lithium soap (A) and the lithium soap (B).

Regarding the kinematic viscosity of the base oil, Examples 1 to 8 having a kinematic viscosity at 40 ° C. of 8 to 180 cSt and 40
Comparing with Comparative Example 5 in which the kinematic viscosity at 200C was increased to 200 cSt, the oil separation degree of the Comparative Example was small, but the amount of scattering at 70 ° C was large, and the acoustic / torque performance was also inferior to the Examples. Regarding the type of base oil, Examples 1 to 18 using a mineral oil, a poly-α-olefin oil, or a mixture thereof, show a good amount of scattering under normal temperature and 70 ° C temperature conditions. Even when compared with Comparative Examples 14 and 15 in which the diester oil and the polyol ester oil were used, it was found that the Example shows a far superior scattering amount. From this result, it was found that it is effective to use the mineral oil, the poly-α-olefin oil or the mixed oil thereof for the base oil as well as the thickener for reducing the scattering amount.

Regarding the ratio between the base oil and the thickener, comparing Examples 12 and 13 with Comparative Examples 6 to 9, lithium stearate and lithium 12-hydroxystearate were used as the thickener. However, Comparative Example 6 in which the amount of the thickening agent in the grease is 35 wt% has a problem in acoustic and torque performance, while Comparative Example 9 in which the amount of the thickening agent is 10 wt% has a problem in scattering. From this result, it is understood that the amount of the thickener in the grease is important for improving the scattering, sound and torque performance.

Mineral oil and poly-α-olefin are used as the base oil,
In Examples 14 to 18 in which lithium stearate and lithium 12-hydroxystearate were used as thickeners, respectively, the amount of scattering at 70 ° C was particularly small. Concerning the consistency, comparing Example 15 having a consistency of 190 to 250 and Comparative Example 12 having a consistency of 250 or more and Comparative Example 13 having a consistency of 180 or less, Comparative Example 12 It can be seen that the amount of scattering at 70 ° C. increases, and the sound / torque performance of Comparative Example 13 deteriorates.

[0030]

As described above, the grease composition for a computer bearing of the present invention exhibits excellent scattering properties not only at room temperature but also at a higher temperature of 70 ° C., and the acoustic torque performance of the bearing. To obtain effective results.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a scattering amount measuring device.

FIG. 2 is a schematic view of a torque measuring device.

[Explanation of symbols]

 A (for inspection) bearing

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location C10M 117: 04) C10N 10:02 20:02 40:02 50:10 (72) Inventor Kenichi Iso 2590-1 Fukuda, Yamato City, Kanagawa Prefecture (72) Inventor Tetsuo Tsuchiya 3-5 Kasumigaseki, Chiyoda-ku, Tokyo Awa Shell Oil Co., Ltd. (72) Inventor Yukihiro Ozaki 3-5-5 Kasumigaseki, Chiyoda-ku, Tokyo No. Showa Shell Sekiyu Co., Ltd.

Claims (3)

[Claims] 1. At least one base oil 70-80 wt% selected from a mineral oil and a synthetic hydrocarbon oil having a kinematic viscosity of 8 to 180 cSt at 40 ° C., and a lithium salt of a C _{12 to} C ₂₄ higher fatty acid. 20 to 30% by weight of a thickener comprising a C _{12 to} C ₂₄ higher hydroxy fatty acid lithium salt
A grease composition for a computer bearing, which comprises: 2. A C _{12 to} C ₂₄ containing a hydroxyl group in its chemical structural formula.
A thickener containing 10 to 40 wt% of a higher fatty acid lithium salt and 60 to 90 wt% of a C _{12 to} C ₂₄ higher fatty acid lithium salt containing no hydroxyl group in the chemical structural formula.
The grease composition for a computer bearing according to claim 1, which contains 0 to 30 wt%. 3. The grease composition for a computer bearing according to claim 2, which has an immiscibility of 190 to 250.