JP2017200981A - Grease composition and rolling bearing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a grease composition capable of achieving lower torque in comparison with hitherto, while suppressing decline of heat resistance and long-term lubrication; and to provide a rolling bearing having the grease composition included therein.SOLUTION: A grease composition (G) includes a base oil, a thickener containing a diurea compound, and an additive containing organic fibers, in which the organic fibers contain cellulose fibers. The cellulose fiber may contain a short fiber having a length of 0.1-2 mm and/or a long fiber having a length of 2-5 mm.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a grease composition and a rolling bearing in which the grease composition is enclosed.

In recent years, as a characteristic of a grease for a bearing, a reduction in bearing rotational torque has been demanded in order to meet the needs for energy saving and high efficiency. On the other hand, urea greases with excellent heat resistance and long-term lubrication characteristics are mainly used because there is a strong demand for improving heat resistance and extending the service life as well as reducing bearing rotational torque.
As a urea-based grease composition, Patent Document 1 discloses, for example, a grease composition containing a base oil and a thickener, wherein the base oil is a mineral oil, and the thickener is a mixture of TDI, oleylamine, and octadecylamine. A grease composition is disclosed which is a diurea compound comprising a reaction product with an amine.

Patent Document 2 is, for example, a grease composition containing a base oil, a thickener and a wax, wherein the base oil is PAO, the thickener is aliphatic diurea, and the wax is a polyethylene wax. And a grease composition that is a mixture of montan wax.
Patent Document 3 is a grease composition containing, for example, a base oil and a thickener, wherein the base oil is a mixture of an alkylated diphenyl ether, a polyol ester and a complex type polyol ester, and the thickener is N A grease composition is disclosed which is a mixture of substituted sodium terephthalate and alicyclic diurea.

Japanese Patent Laid-Open No. 03-243696 International Publication No. 2004/081156 JP 2011-46898 A

By the way, the characteristics affecting the bearing rotational torque are mainly (1) stirring resistance of enclosed grease, (2) rolling viscosity resistance, (3) sliding friction resistance between ball / resin cage, and (4). There is sliding frictional resistance between balls / tracks. Since grease is semi-solid, among these, (1) it is considered that the influence of stirring resistance is large.
In order to reduce the stirring resistance, it is necessary to improve the channeling property of the grease so as not to hinder the progress of the balls. In this respect, the channeling property is expected to be improved by shortening the carbon chain length of the thickener (diurea). However, if the carbon chain length is too short, the heat resistance is reduced, and the low torque and long life It becomes difficult to achieve both.

  Accordingly, an object of the present invention is to provide a grease composition capable of realizing a lower torque than conventional ones while suppressing a decrease in heat resistance and long-term lubrication characteristics, and a rolling bearing in which the grease composition is enclosed. .

The grease composition of the present invention for solving the above-mentioned problems contains a base oil, a thickener containing a diurea compound, and an additive containing organic fibers, and the organic fibers contain cellulose fibers. (Claim 1).
In the grease composition of the present invention, the cellulose fiber may include a short fiber having a length of 0.1 mm to 2 mm and / or a long fiber having a length of 2 mm to 5 mm (Claim 2).

The grease composition of the present invention may contain 1 to 5% by mass of short fibers having a length of 0.1 mm to 2 mm as the cellulose fibers (Claim 3).
The grease composition of the present invention may contain 3 to 10% by mass of long fibers having a length of 2 mm to 5 mm as the cellulose fibers (Claim 4).
In the grease composition of the present invention, the thickener may contain an aliphatic diurea having a carbon chain length of C12 or less (Claim 5).

In the grease composition of the present invention, the base oil may contain a synthetic hydrocarbon oil (Claim 6).
The grease composition (G) of the present invention is enclosed in the rolling bearing (1) of the present invention (Claim 7).

  According to the grease composition of the present invention, it is possible to improve the channeling property of the grease and reduce the rotational torque of the bearing by containing the cellulose fiber. In addition, since the cellulose fiber has a relatively high melting point and has sufficient heat resistance, it can be suppressed that the lubrication life of the grease composition is reduced by addition.

FIG. 1 is a cross-sectional view showing a rolling bearing according to an embodiment of the present invention. FIG. 2 is a diagram showing the relationship between the viscosity lowering energy and the rotational torque. FIG. 3 is a diagram illustrating measurement results of the rotational torques of the example and the comparative example. FIG. 4 is a diagram showing the amount of grease attached to the seal in Examples and Comparative Examples.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a cross-sectional view showing a rolling bearing 1 according to an embodiment of the present invention.
The rolling bearing 1 rolls with respect to the inner ring 3 and the outer ring 4 as a pair of race members that define an annular region 2 between them, and the races 13 and 13 of the inner ring 3 and the outer ring 4 that are arranged in the region 2. A plurality of balls 5 as rolling elements, a cage 6 disposed in the region 2 and holding each ball 5, a grease G filled in the region 2, and a pair of sliding contacts with the inner ring 3 fixed to the outer ring 4 Annular seal members 7 and 8 are provided.

Each of the seal members 7 and 8 has an annular core metal 9 and 9 and an annular rubber body 10 and 10 baked on the core metal 9 and 9. Each of the seal members 7 and 8 has an outer peripheral portion fitted into and fixed to groove portions 11 and 11 formed on both end surfaces of the outer ring 4, and an inner peripheral portion formed on the groove portions 12 and 12 formed on both end surfaces of the inner ring 3. It is fitted and fixed.
The grease G is sealed so as to be almost full in the region 2 defined by the pair of seal members 7 and 8 between the two wheels 3 and 4.

Next, the grease composition constituting the grease G will be described in detail.
The grease composition of the present invention contains an additive containing a base oil, a thickener, and organic fibers. The blending amounts of the base oil and the thickener may be 75% by mass to 90% by mass, 10% by mass to 25% by mass, respectively, with respect to the total amount of the grease composition.
As the base oil, for example, synthetic oil and mineral oil can be used, but preferably synthetic oil is used. Synthetic oils can improve the lubrication performance of the grease composition because impurities are not mixed or are small even if they are mixed. In addition, the kinematic viscosity and pour point of the base oil can be selected in a wide range according to the molecular weight and molecular structure.

  Synthetic oils include, for example, synthetic hydrocarbon oil, ester oil, silicone oil, fluorine oil, phenyl ether oil, polyglycol oil, alkylbenzene oil, alkylnaphthalene oil, biphenyl oil, diphenylalkane oil, di (alkylphenyl) alkane oil. , Fluorine compounds such as polyglycol oil, polyphenyl ether oil, perfluoropolyether, and fluorinated polyolefin. Of these, synthetic hydrocarbon oils are preferably used.

  More specifically, examples of the synthetic hydrocarbon oil include those obtained by polymerizing α-olefins produced by using ethylene, propylene, butene, and derivatives thereof as raw materials alone or in combination of two or more. As the α-olefin, those having 6 to 20 carbon atoms are preferably used, and more preferably, poly-α-olefin (PAO) which is an oligomer of 1-decene or 1-dodecene is used.

(According to JIS K 2283) kinematic viscosity of the base oil is not particularly limited, for ^example, a ^{20mm 2 / s~50mm 2 / s (} 40 ℃).
Further, the solubility parameter (SP value) of the base oil is not particularly limited, but is, for example, 8 (cal / cm ³ ) ^{1/2 to} 9 (cal / cm ³ ) ^1/2 .
As the thickener, a urea compound is preferably used. Examples of the urea thickener include urea compounds such as diurea compounds, triurea compounds, tetraurea compounds, polyurea compounds (excluding diurea compounds, triurea compounds, tetraurea compounds), urethane compounds such as urea / urethane compounds, diurethanes, and the like. And the like. Of these, a diurea compound is preferably used, and an aliphatic diurea compound obtained by reacting an aliphatic amine with a diisocyanate compound is more preferably used. However, the thickener is not limited to aliphatic diurea but may be composed of aromatic diurea, alicyclic diurea, and combinations thereof.

  Examples of the aliphatic amine include those having a carbon chain length of C12 or less. Examples include hexylamine (C6), heptylamine (C7), octylamine (C8), nonylamine (C9), decylamine (C10), undecylamine (C11), dodecylamine (also known as laurylamine C12). . The aliphatic amine is preferably one having a carbon chain length of C8 or more. If the carbon chain length of the aliphatic amine constituting the diurea compound is C8 or more, the heat resistance of the thickener can be kept relatively high.

  Examples of the diisocyanate compound include aliphatic diisocyanate, alicyclic diisocyanate, and aromatic diisocyanate. Examples of the aliphatic diisocyanate include diisocyanates having a saturated and / or unsaturated linear or branched hydrocarbon group. Specific examples include octadecane diisocyanate, decane diisocyanate, and hexane diisocyanate (HDI). Is mentioned. Examples of the alicyclic diisocyanate include cyclohexyl diisocyanate and dicyclohexylmethane diisocyanate. Moreover, as aromatic diisocyanate, phenylene diisocyanate, tolylene diisocyanate (TDI), diphenyl diisocyanate, diphenylmethane diisocyanate (MDI) etc. are mentioned, for example. Of these, aromatic diisocyanates are preferably used, and diphenylmethane diisocyanate (MDI) is more preferably used. That is, an aliphatic diurea comprising a combination of an aliphatic amine (carbon chain length of C8 to C12) and an aromatic diisocyanate (particularly diphenylmethane diisocyanate (MDI)) is preferably used as the thickener.

  The amine and diisocyanate compound can be reacted under various methods and conditions. Since a diurea compound having a high uniform dispersibility of the thickener is obtained, the reaction is preferably carried out in a base oil. The reaction may be performed by adding a base oil in which a diisocyanate compound is dissolved in a base oil in which an amine is dissolved, or by adding a base oil in which an amine is dissolved in a base oil in which a diisocyanate compound is dissolved. You may go. The temperature and time in these reactions are not particularly limited, and may be the same as those of ordinary reactions of this type. The reaction temperature is preferably 60 ° C. to 170 ° C. from the viewpoint of solubility and volatility of amine and diisocyanate. The reaction time is preferably 0.5 to 2.0 hours from the viewpoint of completing the reaction between the amine and the diisocyanate and improving efficiency by shortening the production time.

The average particle size of the thickener may be, for example, 10 μm or less, preferably 5 μm to 8 μm. The average particle diameter of the thickener may be measured by a known measuring method such as a laser diffraction method, a dynamic light scattering method, an image imaging method, or a gravity sedimentation method.
Further, the solubility parameter (SP value) of the thickener is not particularly limited, and is, for example, 9.5 (cal / cm ³ ) ^{1/2 to} 10.5 (cal / cm ³ ) ^1/2 . The difference between the solubility parameter of the base oil and the solubility parameter of the thickener is preferably 1.3 (cal / cm ³ ) ^{1/2 to} 1.7 (cal / cm ³ ) ^1/2 .

The organic fiber includes a cellulose fiber. Cellulose fibers are, for example, wood pulp fibers refined from the bark of wood trunk, and may be either short fibers or long fibers, both of which are contained in the grease composition. Also good.
The short fiber is obtained from a broad-leaved tree (L material), and examples thereof include those derived from eucalyptus from beech, birch, maple, willow, and myrtaceae. The short fiber has a length of 0.1 mm to 2 mm, for example. Moreover, 10 micrometers-30 micrometers may be sufficient as the width | variety (fiber diameter) of a short fiber, for example.

On the other hand, long fibers are obtained from softwood (N material) as a raw material, and examples thereof include those derived from firaceae and pineaceae. The long fiber has a length of 2 mm to 5 mm, for example. Moreover, 40 micrometers-60 micrometers may be sufficient as the width | variety (fiber diameter) of a long fiber, for example.
The blending amount of cellulose fibers is preferably 1 to 5% by mass in the case of short fibers, and preferably 3 to 10% by mass in the case of long fibers. By blending the cellulose fiber in the above range, the rotational torque of the bearing can be reduced satisfactorily. For example, it can be reduced to 10 mN · m or less.

Moreover, the solubility parameter (SP value) of the cellulose fiber is not particularly limited, but is, for example, 15 (cal / cm ³ ) ^{1/2 to} 16 (cal / cm ³ ) ^1/2 . The difference between the solubility parameter of the base oil and the solubility parameter of the cellulose fiber is preferably 6.5 (cal / cm ³ ) ^{1/2 to} 7.5 (cal / cm ³ ) ^1/2 .
In addition, the grease composition of the present invention includes, as other additives, for example, extreme pressure agents, oil agents, rust inhibitors, antioxidants, antiwear agents, dyes, hue stabilizers, thickeners, and structural stabilizers. Further, it may contain a metal deactivator, a viscosity index improver and the like.

In order to produce the grease composition of the present invention, for example, first, base oil, thickener and cellulose fiber are mixed and stirred. Next, the mixture is rolled (rolled) by passing it through a roll mill or the like. Through the above steps, the above grease composition can be obtained.
According to this embodiment, the grease G enclosed in the rolling bearing 1 contains cellulose fibers, so that the channeling property of the grease G can be improved and the rotational torque of the rolling bearing 1 can be reduced. More specifically, since the organic fiber (cellulose fiber) larger than the thickener is contained, the thickener is placed in a place where the movement of the balls 5 and the cage 6 is not hindered, such as the seal members 7 and 8. It can be held firmly. As a result, the channeling property of the grease G can be improved.

Moreover, since it is an organic fiber, the base oil can be appropriately supplied to the tracks 13 and 13 from the gap between the organic fibers when heat and shear are applied. Therefore, it is possible to maintain good lubricity.
Further, since the organic fiber is sufficiently larger than the thickener particles, it hardly flows between the ball 5 and the tracks 13 and 13. Therefore, it is possible to prevent the ball 5 from climbing on the organic fiber and moving up and down, and the acoustic value of the bearing is increased due to the vibration. Even if the ball 5 climbs onto the organic fiber, the organic fiber is soft and the acoustic value does not increase significantly. As a result, if the grease G is used, it is possible to ensure the quietness of the rolling bearing 1.

In addition, since the cellulose fiber has a relatively high melting point and has sufficient heat resistance, it is possible to suppress a decrease in the lubrication life of the grease G due to the addition.
In addition, this invention is not restrict | limited to said embodiment, It can also implement in other embodiment.
For example, in the above embodiment, the example in which the grease (G) is enclosed in the rolling bearing 1 constituted by the (double row) ball bearing has been described. However, the bearing in which the grease made of the grease composition of the present invention is enclosed. These may be other rolling bearings such as needle bearings, roller bearings or the like in which other than balls are used as rolling elements.

Moreover, the rolling bearing of this invention is suitable also for uses other than an automotive use.
In addition, various design changes can be made within the scope of matters described in the claims.

Next, although this invention is demonstrated based on an Example and a comparative example, this invention is not restrict | limited by the following Example.
1. Selection of Base Grease First, in performing the examples and comparative examples, a grease capable of expressing a relatively low rotational torque was selected. Specifically, test grease compositions U1 to U4 were prepared by blending a base oil and a thickener at a blending ratio shown in Table 1 below and roll-processing.

Next, as a method for evaluating the thixotropy of the obtained grease composition for test, evaluation based on a hysteresis loop was performed. In the hysteresis loop measurement, when the shear rate is increased linearly from 0 to 9000 s ⁻¹ , an accelerated flow curve with shearing is obtained. Since the grease network structure is destroyed at this high shear rate, the shear stress decreases. Further, when the shear rate is linearly reduced to 0, a deceleration flow curve is obtained. Since the area surrounded by the speed increasing flow curve and the speed reducing flow curve corresponds to the energy used to destroy the thickener, the thixotropy of the grease was evaluated using this “viscosity reducing energy”. . The measurement conditions are shown in Table 2 below.

  The viscosity decreasing energy of each of the greases U1 to U4 obtained by the evaluation of the thixotropy is as shown in Table 3 below.

  Moreover, the bearing rotational torque of each grease U1-U4 was measured according to the conditions of Table 4 below.

FIG. 2 shows the relationship between the viscosity lowering energy of each of the greases U1 to U4 and the bearing rotational torque obtained by the above measurement.
From FIG. 2, it was confirmed that the rotational torque tends to be lower as the viscosity decreasing energy is larger, that is, as the grease has better thixotropy. Therefore, the grease U1 having the lowest rotational torque was selected as the base grease used in the following examples and comparative examples.
2. Examples 1 to 9 and Comparative Example 1
<Grease formulation>
For each example and each comparative example, a test grease composition was prepared by blending a base oil, a thickener, and an additive (cellulose fiber) at the blending ratio shown in Table 5 and Table 6 and rolling. . The following evaluation was performed on the obtained grease composition for test. The evaluation results are shown in Table 5, Table 6, FIG. 3 and FIG.

<Evaluation>
(I) Bearing rotation torque (mN · m)
According to the conditions in Table 4 above, the bearing rotational torque of each example and each comparative example was measured.
(II) Amount of grease adhering to seal member (mg)
After measuring the bearing rotational torque, the rolling bearing used for the measurement was disassembled, and the weight of the grease composition adhering to the seal member was measured.
(III) Bearing sound (vibration acceleration: VG)
The bearing acoustic value was evaluated by bearing vibration acceleration. Specifically, grease was sealed in a bearing (62022RU) so that the space volume ratio was 35%. Then, the vibration acceleration in the radial direction of the outer ring when the inner ring was rotated at 1800 min ⁻¹ was measured with a piezoelectric acceleration sensor (measurement time: 1 min).
(IV) Bearing life test A bearing life test was conducted according to the conditions shown in Table 7 below.

(V) Consideration As is clear from Tables 5 and 6 and FIG. 3, in Examples 1 to 9, the rotation torque is in the range of 5 to 12 mN · m, and the rotation torque is 14 mN · m. It was reduced in comparison. In particular, Examples 1 to 3 in which short fibers (fiber A) were blended at a ratio of 1 to 5% by mass and Examples 7 to 9 in which long fibers (fiber B) were blended at a ratio of 3 to 10% by mass The lower rotational torque can be realized.

Further, as is apparent from Tables 5 and 6 and FIG. 4, in Examples 1 to 9, the grease is less likely to interfere with the movement of the ball and cage of the rolling bearing compared to Comparative Example 1, and the inner wall of the seal member. Many were attached. That is, in Examples 1-9, as a result of improving the channeling property of grease, a relatively large amount adhered to the inner wall of the seal member.
Further, from Tables 5 and 6, it was confirmed that the bearing acoustic characteristics of Examples 1 to 9 were slightly lowered as compared with Comparative Example 1 due to the addition of cellulose fibers, but this was not a practically problematic level.

  Furthermore, as a representative example, the bearing life test was conducted only in Example 3. As shown in Table 5, no significant reduction in the lubrication life was observed.

  1 ... Rolling bearing, G ... Grease

Claims (7)

Base oil,
A thickener containing a diurea compound;
Containing additives including organic fibers,
The said organic fiber is a grease composition containing a cellulose fiber.   The grease composition according to claim 1, wherein the cellulose fibers include short fibers having a length of 0.1 mm to 2 mm and / or long fibers having a length of 2 mm to 5 mm.   The grease composition according to claim 1, wherein the cellulose fiber contains 1 to 5 mass% of short fibers having a length of 0.1 mm to 2 mm.   The grease composition according to claim 1, wherein the cellulose fiber contains 3 to 10% by mass of a long fiber having a length of 2 mm to 5 mm.   The said thickener is a grease composition as described in any one of Claims 1-4 containing the aliphatic diurea which has C12 or less carbon chain length.   The grease composition according to any one of claims 1 to 5, wherein the base oil includes a synthetic hydrocarbon oil.   A rolling bearing in which the grease composition according to claim 1 is encapsulated.

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