JP2001226688A - Low dusting lubricating grease and rolling bearing and direct-acting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new low dusting lubricating grease by improving the shape of fiber of thickener, to provide a low dusting rolling bearing, and to provide a low dusting rolling bearing or low dusting direct-acting device to be used in a clean room or the like. SOLUTION: This low dusting lubricating grease prepared by dispersing a fibrous thickener having a length of <=2 μm in a base oil having a surface tension of >=25 mN/m at 25 deg.C and preferably adjusting the worked penetration (JIS K2220) of the grease to 180 to 260. The thickener having a fine short fiber structure is homogeneously dispersed in the base oil to give the excellent homogenous and low dusting lubricating grease. When a fatty acid lithium salt not containing a hydroxyl group in the chemical structure is adopted, the fibrous thickener is surely and homogeneously dispersed. A low dusting rolling bearing or low dusting direct-acting device in which the low dusting lubricating grease is sealed in the rolling bearing has an excellent low dusting characteristic.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low power generation lubricant applied to a bearing device or a linear motion device such as a ball screw used in a clean room, such as a semiconductor manufacturing facility or a liquid crystal manufacturing facility. The present invention relates to a dust-type lubricating grease, a low-dust-generating rolling bearing, and a linear motion device.

[0002]

2. Description of the Related Art In the manufacturing process of semiconductors and liquid crystals, air conditioning in a manufacturing facility is controlled so that the amount of suspended particulate matter in the air that comes into contact with products and parts thereof is below a specified level. The room managed by the atmosphere is called a clean room. The reason why the air conditioning is controlled in the manufacturing facility is to prevent fine dust from adhering to products and the like and impairing their operation reliability, to increase manufacturing efficiency, and to increase product yield.

[0003] Linear motion devices such as rolling bearings, ball screws, and linear guides used in such clean rooms are filled with lubricating grease so that these devices and components can operate smoothly and accurately. In particular, lubricating grease having low scattering properties is sealed so as not to generate the fine droplets.

[0004] In an information recording device such as a hard disk of an electronic computer, a malfunction may occur even if fine dust adheres to the surface of a recording medium. Therefore, a bearing used in or near the information recording device. Adopts a low-dust-generating rolling bearing that employs grease that does not generate droplets of lubricating grease (fine droplets in the form of mist).

As low-dust-generating grease sealed in conventional rolling bearings for clean rooms and linear motion devices, fluorine-based grease having a large specific gravity is known, and a typical example thereof is based on perfluoropolyether (PFPE). Oil and
There is one using polytetrafluoroethylene (PTFE) as a thickener.

However, fluorine-based greases do not have sufficient lubricating properties, so that the torque of a rolling bearing cannot be sufficiently reduced to a required level in some cases.

[0007] In some cases, grease for electronic computers uses Andok C (trade name) and other sodium soap-based grease using mineral oil as a base oil and sodium complex soap (composite sodium soap) as a thickener.

However, since this grease has high water absorption, the properties of the grease change with time, so that lubrication failure is likely to occur. Further, since the acoustic performance is not good, the grease is particularly used for applications where low noise and low vibration are important. Was inappropriate.

Japanese Patent Application Laid-Open No. Hei 5-9489 discloses a grease composition for a bearing of an electronic computer, which comprises at least one group selected from the group consisting of mineral oil, synthetic hydrocarbon oil and polyphenyl ether oil. A composition containing 20 to 30% by weight of an oil and a lithium salt of a higher fatty acid having 12 to 24 carbon atoms not containing a hydroxyl group is described.

JP-A-6-330070 discloses a grease composition for bearings of electronic computers, comprising at least one base oil selected from mineral oil and synthetic hydrocarbon oil, and a high-grade base oil having 12 to 24 carbon atoms. 2 thickeners consisting of lithium salt of fatty acid and lithium salt of higher hydroxy fatty acid
A grease composition containing 0 to 30% by weight is described. JP-A-8-270747 describes a low-dusting linear motion device in which the grease composition is sealed in a ball screw device or a linear guide device. ing.

[0011]

However, the above-mentioned conventional low-dust-generating lubricating grease merely employs a type of thickener in order to improve the low-dust-generating property.
Nothing is said about the relationship between certain physical properties of the thickener and low dusting properties.

Thus, the invention according to each claim of the present application is:
The relationship between the length of the fiber shape of the thickener and the dust generation is based on the fact that the inventors of the present application have found a predetermined correspondence.

In addition, the mixing consistency of grease in the conventional low-dust-generating rolling bearing is not adjusted to ensure low-dust-generating properties, and soft ones excessively soften when subjected to shearing force. There is also a problem that fine particles are easily formed and scattered.

A metal soap comprising a lithium salt of a higher fatty acid having 12 to 24 carbon atoms and a lithium salt of a higher hydroxy fatty acid is a thickener having excellent heat resistance. However, when filled in a rolling bearing, grease is sprayed. There was also a problem that it easily occurred.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention according to each claim of the present application is to solve the above problems and to provide a low-dust-generating rolling bearing by specifying the fiber form of the thickener in the best condition. To provide a novel low-dust-generating lubricating grease.

Another problem to be solved in the invention according to each claim of the present application is that a lubricating grease having excellent heat resistance, and that even when used continuously for a long time, droplets such as base oil are generated. Low dusting lubricating grease,
It is another object of the present invention to provide a low-dust-generating rolling bearing or a low-dust-generating linear motion device which is used in a clean room by enclosing the same.

[0017]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the invention of a low-dust-generating lubricating grease according to the present invention provides a low-dust lubricating grease having a length of 2 μm or less dispersed in a base oil. It is dusty lubricating grease.

The lubricating grease of the present invention configured as described above is a lubricating grease excellent in homogeneity and low dusting property, in which a thickening agent having a fine short fiber structure is uniformly dispersed in a base oil. become.

As such a fibrous thickener having a length of 2 μm or less, a fatty acid lithium salt having no hydroxyl group in the chemical structural formula can be employed.

Lithium soap having a hydroxyl group in the chemical structural formula has a long fiber structure elongated by twisting, and it is difficult to uniformly disperse it. However, the lithium soap-based thickener comprising a lithium salt of a fatty acid not containing a hydroxyl group used in the present invention stabilizes grease consistency at high temperatures, and has a spindle-shaped short rod-like fiber structure forming micelles. For this reason, it is finely dispersed as compared with a long-fiber thickener such as a lithium salt of a higher hydroxy fatty acid containing a hydroxyl group in the chemical structural formula.

The low-dusting lubricating grease in which the mixing consistency is adjusted to a predetermined range maintains the predetermined consistency even when it is agitated and subjected to shearing in the rolling bearing, so that it does not easily scatter outside the bearing. . Therefore, the above-mentioned low-dust-generating lubricating grease ensures low dust-generation.

The base oil, which is the main component of the lubricating grease, is preferably a base oil having a surface tension of 25 mN / m or more at 25 ° C. in order to ensure low dusting of the prepared lubricating grease. .

The lubricating grease composition in which the dense micelles are dispersed as described above has a low oil separation even when the sealed bearing is rotated for a long time, and the base oil is not excessively separated and scattered. Even when rotated at high temperature for a long time, the amount of dust generated from the enclosed device is reduced.

As a suitable target device for exhibiting low dust generation by enclosing the lubricating grease as described above, a linear motion device such as a rolling bearing or a ball screw or a linear guide is suitable.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The grease base oil used in the claimed invention is one which is collected without any limitation, but preferably has a surface tension of 25 m at 25 ° C.
N / m or more base oil.

Examples of the base oil having a surface tension of 25 mN / m or more include those using one or more lubricating oils selected from mineral oils, synthetic hydrocarbon oils and ether oils, or mixed oils of any mixing ratio.

Such a base oil has a kinematic viscosity at 40 ° C. of 1
It is preferably from 0 to ²⁰⁰ mm ² / s. This is because a lubricating grease using a base oil having a kinematic viscosity (40 ° C.) of less than 10 mm ² / s has a large evaporation amount and a short life. A lubricating grease using a base oil having a kinematic viscosity (40 ° C.) of more than 200 mm ² / s has a large resistance when subjected to a shearing force, and preferably has a large rotational torque when sealed in a rolling bearing. Absent. For these reasons, a more preferable kinematic viscosity (40 ° C.) of the base oil is 20 to
100 mm ² / s.

The mineral oil used as the base oil is preferably a highly refined oil derived from petroleum in order to stabilize the lubricating performance, and a naphthenic mineral oil is more preferable than a paraffinic mineral oil.

Specific examples of the synthetic hydrocarbon oil used as the base oil include poly-α-olefin oil, synthetic oligomer of poly-α-olefin and ethylene, olefin polymerized oil such as liquid polybutene, and alkyl aromatic oil. . Among them, 1-decene (CH ₃ (CH ₂ ) ₇ CH
= CH ₂ ), or a synthetic oil composed of a copolymer of poly α-olefin and ethylene.

Specific examples of the ether oil used as the base oil include commercially available ether oils having 2 to 5 aromatic rings. However, as the number of rings in the chemical structure of the ether oil increases, the lower the temperature in the low temperature range. Performance degrades and becomes expensive. Therefore, diphenyl number aromatic rings to improve the low temperature performance by a alkyl substituent 2-4 ring, triphenyl, C ₁₂ of -C ₂₀ (di) phenyl ether oil in which the alkyl group is introduced tetra phenyl Preferred and more preferred are alkyl diphenyl ether oils.

The thickener used in the present invention has a length of 2 μm.
m or less as long as it is a fibrous thickener, and known short fibrous thickeners can be used. Among them, lithium soap having good heat resistance, particularly lithium soap containing no hydroxyl group in its chemical structural formula, is more suitable. It is something.

Specific examples of lithium soap include lithium laurate (C ₁₂ ), lithium myristate (C ₁₄ ), lithium palmitate (C ₁₆ ), and margaric acid (C ₁₆ ).
₁₇₎ Lithium stearate (C ₁₈₎ lithium, arachidic acid (C ₂₀₎ lithium, behenic acid (C ₂₂₎ lithium,
Examples include lithium lignoceric acid (C ₂₄ ), lithium tallow fatty acid, lithium ricinoleate, and lithium ricinoelaidate. Among them, particularly preferred lithium soap is lithium stearate (CH ₃ (CH ₂ ) ₁₆
It is clear from the examples described below that these are COOLi), and these are short rod-shaped fibers having a spindle-shaped fiber structure forming micelles and having a length of 2 μm or less.

Such a short fibrous thickener is prepared by mixing a lubricating grease with a penetration (JIS K2220) (40).
C) may be adjusted to 180 to 260,
It is difficult to clearly limit the lower limit of the fiber length due to the relationship with the mixing ratio.

Incidentally, lithium soap containing a hydroxyl group such as lithium 9-hydroxystearate, lithium 10-hydroxystearate, lithium 12-hydroxystearate and lithium 9,10-hydroxystearate is twisted to a length exceeding 2 μm. It cannot be used in the present invention because it has a long fiber structure and does not have the desired uniform dispersibility.

The mixing penetration (JIS K2220) of the lubricating grease of the present invention is preferably in the range of 180 to 260 in order to suppress dust generation as described above. If the mixing penetration is less than 180, the bearing torque of the rolling bearing increases, making it difficult to seal the bearing in a small-diameter bearing. Also,
When the penetration exceeds 260, the amount of dust generated by scattering increases, and when the rotor rotates at a high speed, insufficient lubrication occurs in the rolling bearing, and noise may occur in the rolling bearing.

The mixing ratio of the thickener is 15% by weight or more so that the lubricating grease is adjusted to a predetermined mixing consistency. If the mixing ratio is less than 15% by weight, the consistency becomes insufficient, and the grease becomes soft and easily scattered. Although the upper limit of the mixing ratio of the predetermined lithium soap-based thickener in the grease may be adjusted according to a practical limit, there is little need to particularly limit the mixing ratio.
If the content is more than the weight%, the consistency becomes too small, and the encapsulation work in a lubricating device such as a bearing becomes difficult.

Also, lubricating greases include well-known rust inhibitors, antioxidants, extreme pressure additives, wear inhibitors, oil agents, corrosion inhibitors, pour point depressants, so as not to impair the intended purpose.
Viscosity index improvers, structural stabilizers, thickeners, antistatic agents, emulsifiers, coloring agents, and the like may be added.

The type of the rolling bearing in the present invention is as follows.
It may be a rolling bearing with a retainer, or may be a total ball rolling bearing in which a plurality of balls are incorporated between a pair of races consisting of an inner ring and an outer ring without regulating the circumferential interval of the raceway. Good. The ball row of the rolling bearing may be either a single row or a double row, and is applicable to a deep groove type rolling bearing and an angular type radial ball bearing. Further, the present invention can be applied to a thrust ball bearing, and may be a cylindrical roller bearing or a tapered roller bearing.

The low-dust-generating linear motion device according to the invention of the present application is a ball screw which is a transmission device for mutual conversion between rotary motion and linear motion, or a linear guide such as used for an XY table of a precision positioning unit. This is a so-called linear motion device.

Incidentally, in the ball screw, a number of balls are interposed between the screw shaft and the nut, and the balls circulate while rolling on a circulation path provided inside or outside the screw groove and the nut, and are rotated. This is a well-known transmission that converts rotational movement into linear movement in the screw axis direction.

Such a low-dust-generating rolling bearing or a low-dust-generating linear motion device is, for example, a device in a clean room where fine dust is not allowed to float, such as a semiconductor manufacturing device or a liquid crystal manufacturing device. It is applied to.

[0042]

Examples and Comparative Examples [Examples 1 to 7, Comparative Examples 1 to
6] A lubricating grease was prepared by mixing a base oil and a thickener in the mixing ratio shown in Table 1 or 2. In addition, each compounding ratio shown in the table was shown by weight%.

The grease is prepared by mixing a base oil, a thickener and other additives while heating in a container, and pouring the mixture in a completely dissolved state into a stainless steel pad whose bottom is cooled with ice water. Then, the mixture was rapidly cooled to obtain a grease-like composition.

The obtained grease-like composition was used as a test bearing [deep groove ball bearing (inner diameter 8 mm, outer diameter 22 mm, width 7 mm, with nylon cage, 7 balls)] or test ball screw [shaft diameter φ14 mm , Lead 4mm, BCD1
4.3mm, ball diameter φ 2.381mm, lead angle 5 °
50 ', circulation system: guide plate system, number of turns: 3.7
0.1 g each in a single row of rolls, material: SUS440C), and a dust generation amount measurement test shown below was performed. The results are also shown in Table 1 or Table 2.

[Measurement Test of Particle Generation of Bearing (1)] As shown in FIG. 1, a schematic diagram of the test apparatus, two test bearings 3 are mounted on a rotating shaft 2 passing through a test table 1. The jig 4 is mounted side by side, a thrust load is applied to the two test bearings via the coil spring 5 on the clamp jig 4, and the clamp jig 4 is not rotated by the lock 6 fixed on the test table 1. Fixed.

A box-shaped airtight cover 7 is provided on the upper surface of the test table 1 so as to cover the clamp-type jig 4. The airtight cover 7 has clean air (clean air containing no dust). Connecting the introduction duct 8 and the exhaust duct 9 of
The exhaust duct 9 is a dust counter 1 with a built-in intake pump.
0 (also called a particle counter). The rotating shaft 2 was rotated by an electric motor 11, and the test stand 1 and the rotating shaft 2 were sealed with a magnetic fluid seal 12.

The test conditions were as follows: the thrust load on the test bearing was 10 N, and the rotation speed of the rotating shaft was 1500 revolutions /
The test is carried out continuously for 1000 hours in a room temperature environment, and the particle size (diameter) is 0.1
The number of collected suspended particles (μm or more) (pieces / cf) was measured.

[Ball Screw Dust Generation Measurement Test (2)] FIG.
As shown in the figure, the test apparatus fixed the substrate 14 on the upper part of the frame 13, provided the rotating shaft 15 penetrating the substrate 14, and fixed the upper part of the rotating shaft 15 on the uppermost part of the frame 13. Rotated by an electric motor 16, the lower part of the rotating shaft 15 is connected via a joint to a ball screw shaft 17 having a helical ball screw groove on the outer peripheral surface, and a ball nut 18 is attached to the ball screw shaft 17. And has a structure for supporting the ball screw 19.

The rotating shaft 15 is provided on the lower surface of the substrate 14.
An airtight cover 20 is attached so as to cover the lower part and the ball screw 19, and the cover 20 is provided with air introduced from an unillustrated air clean unit (clean air from which dust of φ0.1 μm or more has been removed by 95% or more). The air filter (φ
(100% of dust of 0.05μm or more can be removed) 2
1 is connected to a clean air introduction duct 22 that is introduced while passing through the exhaust gas duct 1, and an exhaust duct 23 is connected to the dust counter 10.

The substrate 14 and the rotating shaft 15 are hermetically sealed by a magnetic fluid seal 24, and the ball nut 18 is vertically movable while being prevented from rotating by a vertically arranged guide rail (not shown). .

The test conditions were as follows: the rotation speed of the ball screw shaft 17 was 1500 rpm, the stroke length of the ball nut 18 on the ball screw shaft 17 was 150 mm, the acceleration / deceleration time was 0.05 seconds, and the stroke of the ball screw shaft 17 was The operation conditions were such that the intermittent reciprocating movement was performed so that the stop time was 1 second at both ends of the length. At this time, the number of dust particles was measured while introducing clean air at a flow rate of 28.3 liters / minute for 1 minute, and then the cycle of stopping the air introduction for 20 minutes was repeated for 300 hours. The total number of collected suspended particles having a diameter (diameter) of 0.1 μm or more (pieces / cf) was measured.

[0052]

[Table 1]

[0053]

[Table 2]

As is clear from the results shown in Tables 1 and 2, the rolling bearings and ball screws of Comparative Examples 1 to 6 in which lubricating grease having a fiber length of the thickener exceeding 2 μm was filled were subjected to the dust generation test (1). In (2) and (2), a large number of dust particles were counted. In particular, the thickener consisted of PTFE, and the number of dust particles in Comparative Example 5 in which the fiber was considerably longer than 2 μm was remarkably large.

On the other hand, the fiber length of the thickener was 2 μm.
m or less, the mixing consistency is 180 to 260, and the surface tension of the base oil is 31.7 to 48 mN / m. The amount of screw dust generated is 580-790 (pcs / c).
f) The latter was a small amount of 190 to 340 (pieces / cf), and was a low-dust-generating lubricating grease, a rolling bearing, or a ball screw with extremely low dust generation.

In Examples 1 to 7, lithium stearate having no hydroxyl group was used as a thickener.
Although the number of particles generated from the rolling bearing or the ball screw was small, in Comparative Examples 3 and 4 using a thickener containing a hydroxyl group, the number of particles generated from both the rolling bearing and the ball screw was large.

[0057]

As described above, the lubricating grease having a low dust generation is obtained by dispersing a fibrous thickener having a predetermined length or less in a base oil, as described above. Therefore, by improving the fiber shape of the thickener, it is possible to provide a low-dust-generating lubricating grease in which the dust-generating properties are reliably suppressed to a low level regardless of the type of the base oil.

Further, the low-dusting lubricating grease in which the mixing consistency is adjusted to a predetermined range maintains the predetermined consistency even when subjected to shearing by being stirred in the rolling bearing. There is an advantage to surely get.

A lubricating grease in which a fibrous thickener comprising a fatty acid lithium salt having no hydroxyl group in the chemical structural formula is dispersed has a stable grease consistency at a high temperature, and a fiber structure for forming micelles has a spindle type. It has a short rod-like shape, and has the advantage of ensuring low dust generation because it is uniformly dispersed in the base oil.

The dust generated from the lubricating grease is considered to be deformed or separated by the force applied at the rolling portion, and the separated particles are considered to be generated.
A lubricating grease using a base oil of 5 mN / m or more has a high resistance to separation of a lubricant, so that low dust generation becomes more reliable.

When low-lubricating lubricating grease is used for a low-dust-generating rolling bearing used in a clean room, etc., in addition to the above-mentioned advantages, floating particulates such as grease droplets and mist may be present in an atmosphere in which a rolling bearing such as a clean room is used. It does not pollute the atmosphere.

Further, if the low-dust-generating lubricating grease is used by enclosing it in a low-dust-generating linear motion device such as a ball screw device or a ball screw support bearing, in addition to the above-mentioned advantages, the external environment of the linear motion device can be improved. Can minimize the amount of dust generated.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view of a dust test apparatus for a rolling bearing.

FIG. 2 is a schematic explanatory view of a dust test apparatus for a ball screw.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Test stand 2, 15 Rotation axis 3 Test bearing 4 Clamp type jig 5 Coil spring 6 Locking tool 7 Airtight cover 8, 22 Introductory duct 9, 23 Exhaust duct 10 Duct counter 11, 16 Electric motor 12, 24 Magnetic Fluid seal 13 Frame with stand 14 Board 17 Ball screw shaft 18 Ball nut 19 Ball screw 20 Cover 21 Air filter

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) C10N 20:02 C10N 20:02 20:06 20:06 B 30:00 30:00 Z 40:02 40: 02 50:10 50:10 F term (reference) 3J101 EA63 FA60 GA55 4H104 BB17B DA02A EA01A EA01Z EA10B EB02 FA01 LA15 PA01 QA18

Claims (6)

[Claims] 1. A low dusting lubricating grease comprising a base oil and a fibrous thickener having a length of 2 μm or less dispersed therein. 2. The low-dust-generating lubricating grease according to claim 1, wherein the mixing consistency (JIS K2220) is adjusted to 180 to 260. 3. A fibrous thickener having a length of 2 μm or less,
The lubricating grease with low dust generation according to claim 1 or 2, which is a lithium salt of a fatty acid containing no hydroxyl group in the chemical structural formula. 4. The base oil has a surface tension of 25 m at 25 ° C.
The low-dusting lubricating grease according to any one of claims 1 to 3, which is a base oil of N / m or more. 5. A low-dust-generating rolling bearing in which the low-dust-generating lubricating grease according to claim 1 is sealed in a rolling bearing. 6. A low-dusting linear motion device in which the low-dusting lubricating grease according to claim 1 is enclosed in a device.