JP2006292083A - Grease seal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a grease seal which does not precipitate a yellow fixed material on the lip surface, using a nitrile rubber as a rubber-made seal lip material in a rotating bearing grease seal such as an industrial robot or the like which repeats positive and reverse rotations/stops and when a material blending a Mo dialkyl sufide dithiocarbamate [MoDTC] as a grease is used, precipitation of the yellow fixed material is generated on the lip surface and, based on a knowledge that the yellow fixed material causes grease leakage, in the grease including MoDTC and the grease seal using the nitrile rubber as the rubber-made seal lip material. <P>SOLUTION: Material hardness (durometer A) is 60-80 and roughness of the sliding surface has a center line average roughness Ra 0.5-0.65 μm, and a nitrile rubber-made seal lip having characteristics of a ten-point average roughness Rz 1.5-2.5 μm is provided and the grease seal is used for a grease bearing using the grease including 0.5% or more of MoDTC, by weight. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a grease seal. More specifically, the present invention relates to a grease seal that is suitably used for a rotary sliding bearing that can be repeatedly rotated and stopped repeatedly.

  Grease is used for mechanical elements such as rotary bearings of industrial robots for the purpose of maintaining low friction and wear characteristics and preventing foreign matter from entering. A grease seal is used to hold it on the machine element. Nitrile rubber or the like is generally used as a seal lip constituting material of the grease seal.

  And there exists a correlation between the sealing performance of a seal | sticker, and the surface roughness of a seal | sticker, Therefore The predetermined fillers, such as a talc, are mix | blended in order to provide the sealing performance to a seal | sticker. The filler also has a rubber reinforcing effect and contributes to an improvement in the durability of the seal.

On the other hand, grease is sometimes mixed with solid or liquid molybdenum dialkyldithiocarbamate (MoDTC) for the purpose of improving extreme pressure (see Patent Document 1), but solid or liquid MoDTC is sometimes used. When grease containing about 0.5 to 5% by weight is sealed with a seal made of nitrile rubber highly filled with a filler such as talc, there is no problem with constant sliding rotation. Under operating conditions such as a rotary bearing of an industrial robot that continuously repeats the stop, yellow sticking matter may be deposited on the surface of the rubber seal lip, thereby reducing the grease sealing performance.
JP 2003-314369 A

  As described above, in the grease seal, a filler such as talc is blended in an amount of about 100 parts by weight per 100 parts by weight of nitrile rubber for the purpose of imparting the necessary reinforcing properties and the necessary roughness for the sealing performance. However, when such a filler is used to seal the grease containing MoDTC, yellow sticking matter precipitates on the lip surface, which may cause grease leakage.

The occurrence of such yellow sticking matter is not observed in the case of monotonous unidirectional rotational sliding, but is observed only in the case of grease when forward / reverse rotation and stop are repeated. In addition, there is no occurrence even in systems containing MoDTC. Here, MoDTC has the general formula [(R) ₂ NC (S) S] ₂ MO ₂ O _x S _y
Specifically, the following compounds are shown.

  An object of the present invention is to use a nitrile rubber as a rubber seal lip material and a molybdenum dialkyldithiocarbamate molybdenum (MoDTC) as a grease in a rotary bearing grease seal for an industrial robot etc. where forward / reverse rotation / stop is repeated. Based on the knowledge that yellow sticking precipitates on the lip surface and causes grease leakage when used, grease containing MoDTC and nitrile rubber as a rubber seal lip material are used. It is an object of the present invention to provide a grease seal that exhibits the surface characteristics of the seal lip sufficiently and does not deposit yellow sticking matters that cause grease leakage on the lip surface.

  The object of the present invention is that the material hardness (durometer A) is 60 to 80, the roughness of the sliding surface is centerline average roughness Ra is 0.5 to 0.65 μm, and 10-point average roughness Rz is 1.5 to 2.5 μm. This is achieved by a grease seal that is used for a grease bearing having a nitrile rubber seal lip having characteristics and containing 0.5% by weight or more of molybdenum dialkyldithiocarbamate. This grease seal is used as a rotary sliding bearing that repeats forward and reverse rotations and stops repeatedly, such as a rotary sliding bearing for an industrial robot.

  The grease seal according to the present invention is used as, for example, a rubber seal lip material in a rotary bearing grease seal that is used for a motor or gear part of a joint part of an arm of an industrial robot. Even when nitrile rubber is used and grease containing MoDTC is used, it shows good initial sealability and the effect of suppressing precipitation of yellow sticking matter on the sliding surface, so it contains 0.5% by weight or more of MoDTC. It can be suitably used for a grease seal using grease.

  Nitrile rubber seal lip has material hardness (durometer A) of 60-80, sliding surface roughness of centerline average roughness Ra of 0.5-0.65μm, 10 point average roughness Rz of 1.5-2.5μm What has is used. If the hardness falls outside this range, the moldability of the lip seal becomes a problem, and if the surface roughness is less than both Ra and Rz, the required sealability for rotating and sliding seals cannot be obtained. If the value is higher than this value, precipitation of yellow sticking matter occurs.

Here, the centerline average roughness Ra is extracted from the roughness curve by the reference length in the direction of the average line, the X-axis is provided in the direction of the extracted portion, the Y-axis is provided in the direction of the vertical magnification, and y = f ( When expressed by x), it means the value obtained by the following formula.
The 10-point average roughness Rz is extracted from the roughness curve by the reference length in the direction of the average line, measured in the direction of the vertical magnification from the average value of the extracted portion, and the highest peak from the highest peak to the fifth peak. The average value of the absolute values of the altitude (Yp) and the average value of the absolute values of the altitudes (Yv) of the bottom valley from the lowest valley bottom to the fifth are calculated, and the sum of these is calculated. (Refer to JIS B0601-1982)

  As the nitrile rubber, any of medium nitrile content (CN: 25-30%), medium-high nitrile content (CN: 31-35%) and high nitrile content (CN: 36-42%) can be used. A medium or high nitrile content is used, and vulcanization is generally performed by a vulcanization system using a combination of sulfur or a sulfur-donating compound and a general-purpose vulcanization accelerator such as a sulfenamide or thiuram compound. Is called. Organic peroxide crosslinking is also possible. Examples of organic peroxides include tertiary butyl peroxide, dicumyl peroxide, tertiary butyl cumyl peroxide, and 1,1-di (tertiary butyl peroxy) -3. , 3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di (tert-butylperoxy) hexane, 2,5-dimethyl-2,5-di (tert-butylperoxy) hexyne-3, 1,3-di (tert-butylperoxyisopropyl) benzene, 2,5-dimethyl-2,5-di (benzoylperoxy) hexane, tert-butylperoxybenzoate, tert-butylperoxyisopropyl carbonate, n- Commonly used materials such as butyl-4,4-di (tert-butylperoxy) valerate are used. When crosslinking organic peroxides, multifunctional unsaturated compounds such as triallyl isocyanurate, triallyl cyanurate, triallyl trimellitate, trimethylolpropane trimethacrylate, N, N'-m-phenylenebismaleimide Etc. are preferably used in combination.

  A nitrile rubber seal lip having such properties includes a nitrile rubber seal lip having a talc average particle size of 10 to 20 μm, an average particle size of 1 to 10 μm silicate and an average particle per 100 parts by weight of nitrile rubber. It is obtained as a vulcanized molded product of a nitrile rubber composition to which 5 to 50 parts by weight, preferably 20 to 40 parts by weight of a filler consisting of at least one cellulose powder having a diameter of 10 to 50 μm is added. As the silicate, clay, talc or the like is used. The average particle size of the filler is measured using a laser diffraction scattering method (HRA manufactured by Microtrack). If the addition ratio of the filler is less than this, the lip surface roughness as described above required for maintaining the sealing property cannot be imparted, resulting in a problem in the sealing property. On the other hand, when the filler is added at a rate higher than this, a yellow sticking matter is formed on the lip surface, and the subsequent sealing performance is lowered. Further, if the average particle diameter of these fillers is out of this range, an appropriate lip surface roughness for maintaining the sealing property cannot be imparted.

  This nitrile rubber composition includes other general compounding agents such as zinc oxide, hydrotalcite, etc. within a range that does not impair the surface properties of the seal lip in addition to the vulcanizing system such as a vulcanizing agent. It can be used by adding an acid acceptor such as amine, an anti-aging agent such as amine, a lubricant such as stearic acid, etc., and kneading it with a closed kneader such as an intermix, a Banbury mixer, a kneader or an open roll. The kneaded product is vulcanized by general vulcanization conditions for nitrile rubber, for example, by heat vulcanization at about 190 to 200 ° C. for about 2 to 4 minutes.

  Seal lips vulcanized and molded, for example, as oil seal seal lips by injection molding, compression molding, etc., are suitably used as components of rotary sliding bearings, such as industrial robot rotary sliding bearings. .

  Next, the present invention will be described with reference to examples.

Example 1
Medium-to-high nitrile rubber (Nippon ZEON product DN212; CN content 31-35% by weight) 100 parts by weight Talc (Asada milled product talc H; average particle size 14μm) 30 〃
Zinc oxide 10 〃
Stearic acid 1 〃
Glycol-based compound (n-butyl methylenebisthioglycolate) 5 〃
Sulfur 1 〃
Sulfenamide compounds (Ouchi Emerging Chemicals Noxeller CZ) 4 〃
Thiuram compounds (Noxeller TT, the company's product) 4 〃

  The above components are kneaded using a biaxial open roll, and the kneaded product (nitrile rubber composition) is vulcanized at 200 ° C. for 2 minutes using a press molding machine. Each seal was molded.

  The surface roughness of these vulcanized molded products was measured by using a contact-type roughness meter (Surfcom, manufactured by Tokyo Seimitsu Co., Ltd.), sliding a thin contact on the rubber surface, and recording the top and bottom. The measurement conditions are a measurement length of 1.5 mm and a cut-off wavelength (a curve obtained by removing a wavelength component longer than the cut-off wavelength from the cross-sectional curve is 0.08 mm).

  The test piece was subjected to a sliding test using the apparatus shown in FIG. Here, reference numeral 1 indicates a pin test piece, 2 indicates rubber, 3 indicates a carbon steel ring, 4 indicates an oil tank, and 5 indicates a load. Here, as the grease I, a grease having a composition comprising 94% by weight of poly α-olefin oil (Essomobile product SHF 41), 4% by weight of lithium stearate, and 2% by weight of solid MoDTC was used.

  The sliding test using a pin test piece is performed 20000 times with a cycle pattern of stop state → forward rotation (6m / s) 2 seconds-stop 1 second-reverse rotation (6m / s) 2 seconds → stop 1 second → It was broken. The sliding test conditions were a shaft peripheral speed of 6 m / sec, a sliding distance of 480 km, a surface pressure of 0.6 MPa, a natural temperature rise, a sliding contact width of 3 mm, and a counterpart carbon steel ring.

  For the lip seal, a sliding test (1) was performed using an oil seal tester shown in FIG. Here, reference numeral 11 denotes an oil seal, 12 denotes an oil tank, 13 denotes a test shaft, and 14 denotes a motor. Grease I was used as the grease.

  The sliding test using the lip seal is performed 10,000 times with a cycle pattern of stop state → forward rotation (6m / s) 4 seconds-stop 1 second-reverse rotation (6m / s) 4 seconds → stop 1 second → It was. The sliding test conditions were a shaft peripheral speed of 6 m / sec, a sliding distance of 480 km, a surface pressure of 0.6 MPa, a natural temperature rise, a sliding contact width of 0.5 mm, and a counterpart carbon steel.

Comparative Example 1 (ac)
In the nitrile rubber composition of Example 1, the amount of talc was changed to 100 parts by weight (Comparative Example 1a). In addition to the sliding test (1) performed in Comparative Example 1a, the sliding test (2) in which the lip seal was rotated in one direction was also performed (Comparative Example 1b). The test conditions are the same as in the sliding test (1). In addition to the grease I, the sliding test (1) was also performed on grease II composed of 96% by weight of poly α-olefin oil and 4% by weight of lithium stearate (Comparative Example 1c).

Comparative Example 2
In the nitrile rubber composition of Example 1, the amount of talc was changed to 70 parts by weight.

Comparative Example 3
In the nitrile rubber composition of Example 1, talc was not used.

The results obtained in the above Examples and Comparative Examples are shown in the following Table 1 (hardness, surface roughness) and Table 2 (sliding test).
Table 1
Example Talc blending amount (parts) Hardness A Ra (μm) Rz (μm)
Example 1 30 67 0.63 2.32
Comparative Example 1 100 76 0.71 2.64
〃 2 70 69 0.91 3.28
〃 3 0 63 0.21 0.84
Table 2
Pin specimen lip seal sliding test
Yellow solid Gli Sliding Yellow solid
Examples of precipitation over precipitation grease leakage of the scan test <br/> Example 1 None I (1) None (Fig 3-a) None
Comparative Example 1a Yes I (1) Yes (Figure 3-b) Yes
B 1b Yes I (2) No No
〃 1c Yes II (1) No No
〃 2 Yes I (1) Yes (Figure 3-c) Yes
３ 3 No I (1) No Yes

From the above results and the results in Table 3 below, the following can be said.
(1) In the nitrile rubber vulcanized molded product (pin test piece and lip seal) sliding test according to the present invention, no yellow sticking matter was deposited on the lip surface, and no grease leakage was observed after the test.
(2) In samples that have a large surface roughness and deviate from the category of the nitrile rubber composition of the present invention, in the grease containing MoDTC, precipitation of yellow sticking matter occurred in the forward / reverse rotation / stop sliding test. Seal leakage occurred due to the upper sliding test.
(3) In samples with large Ra and Rz, precipitation of yellow sticking matter and seal leakage are observed.
(4) For samples with low hardness A or low Ra and Rz, there is a problem with sealing performance.

Example 2
In the nitrile rubber composition of Example 1, 10 parts by weight of cellulose powder (average particle size of 32 μm) was used instead of talc. In addition, the sliding test was performed only about the pin test piece.

Comparative Example 4
In the nitrile rubber composition of Example 1, 100 parts by weight of finely powdered talc (average particle size 0.2 μm) was used instead of talc. In addition, the sliding test was performed only about the pin test piece.

Comparative Example 5
In the nitrile rubber composition of Example 1, 100 parts by weight of magnesium carbonate (average particle size 12 μm) was used instead of talc. In addition, the sliding test was performed only about the pin test piece.

The results obtained are shown in Table 3 below.
Table 3
Sliding test
Example Hardness A Ra (μm) Rz (μm) Precipitation of yellow sticky matter Example 2 75 0.55 2.01 None
Comparative Example 4 84 0.15 0.59 None
５ 5 85 0.45 3.14 Yes

It is a schematic diagram of the sliding test about a pin test piece. It is a schematic diagram of the sliding test about a lip seal. It is a microscope picture which shows the cross section of the seal lip | rip part after the sliding test in Example 1 (a), Comparative example 1a (b), and Comparative example 2 (c).

Claims (4)

  Nitrile rubber seal with material hardness (durometer A) of 60 to 80, sliding surface roughness of centerline average roughness Ra of 0.5 to 0.65 μm, 10 point average roughness Rz of 1.5 to 2.5 μm Grease seal used for grease bearings with a lip and grease containing 0.5% by weight or more of molybdenum dialkyldithiocarbamate.   The nitrile rubber seal lip is made of at least one kind of talc having an average particle diameter of 10 to 20 μm, silicate having an average particle diameter of 1 to 10 μm and cellulose powder having an average particle diameter of 10 to 50 μm per 100 parts by weight of nitrile rubber. The grease seal according to claim 1, which is a vulcanized molded product of a nitrile rubber composition to which 5 to 50 parts by weight of a filler is added.   The grease seal according to claim 1 or 2, wherein the grease seal is used for a rotary sliding bearing in which forward and reverse rotation and stop are repeated.   4. The grease seal according to claim 3, which is used for a rotary sliding bearing of an industrial robot.