JP5685141B2 - Grease composition, grease-filled bearing, universal joint and linear motion device - Google Patents

Description

  The present invention relates to a grease composition, and a bearing, a universal joint, a ball screw, a linear motion device and the like in which the grease composition is enclosed.

  Conventionally, attempts have been made to improve lubricity by blending various additives in the lubricant for the purpose of improving the performance of the lubricant in the industry. When a bearing or the like is used under high speed and high surface pressure conditions, the lubricating film of the encapsulated grease composition tends to break. When the lubricating film breaks, metal contact occurs, causing a problem that heat generation and frictional wear increase. For this reason, there is a need for a grease composition that exhibits excellent lubricity even under severe conditions such as high speed and high surface pressure. Conventionally, extreme pressure agents such as organometallic compounds have been added to grease compositions in order to reduce friction under such high surface pressure conditions.

  For example, greases for constant velocity joints containing molybdenum compounds such as molybdenum dialkyldithiocarbamate (molybdenum dithiocarbamate) and molybdenum dithiophosphate as organometallic compounds have been proposed (see Patent Document 1 and Patent Document 2). In addition, for the purpose of reducing vibrations generated from constant velocity joints, as an extreme pressure agent, oil-soluble molybdenum dithiocarbamate that dissolves in base oil and non-oil-soluble molybdenum dithiocarbamate that does not dissolve in base oil are used in combination. A grease for a constant velocity joint has been proposed (see Patent Document 3). Further, a grease that does not contain molybdenum disulfide and contains an organic molybdenum compound and Ca sulfonate is disclosed (see Patent Document 4).

Japanese Patent Laid-Open No. 07-197072 JP-A-10-147771 Japanese Patent Laid-Open No. 2003-165988 JP 09-324190 A

  However, for use under severe conditions of high speed and high surface pressure, which have become increasingly severe in recent years, conventional additives are not always sufficient, and further improvement in performance is desired. In addition, the molybdenum compounds described in the above patent documents are PRTR-regulated substances. From the viewpoint of environmental protection, it is desired to reduce the amount of the molybdenum compound used, and the use itself is regarded as a problem. In addition, when the amount of molybdenum is extremely small, it has been difficult to exhibit a sufficiently low friction when used under severe conditions of high speed and high surface pressure. In view of these backgrounds, it is desired to develop a low friction additive that is excellent in low friction characteristics with high speed and high surface pressure while reducing the amount of molybdenum.

  The present invention has been made to cope with such problems, and is excellent in low molybdenum content (0.1% by weight or less) in use under severe sliding conditions such as high speed and high surface pressure. Another object of the present invention is to provide a grease composition capable of realizing low friction, and a bearing, a universal joint, and a linear motion device in which the grease composition is enclosed.

  The grease composition of the present invention is a grease composition containing a base oil, a thickener, and an additive, wherein the additive is an oil-soluble molybdenum dithiocarbamate (hereinafter referred to as MoDTC), carbon And a metal salt of a fatty acid having a number of 2 or more, wherein the molybdenum content in the grease composition is 0.1% by weight or less.

  The fatty acid is a fatty acid having 2 to 18 carbon atoms. The metal of the metal salt is lithium, sodium, or calcium.

  The oil-soluble MoDTC content is 0.5 to 1.6 parts by weight based on 100 parts by weight of the total amount of the base oil and the thickener.

  The content of the metal salt of the fatty acid is 1 to 7 parts by weight with respect to 100 parts by weight of the total amount of the base oil and the thickener.

  The additive includes calcium carbonate (hereinafter referred to as Ca carbonate). The calcium carbonate content is 1 to 7 parts by weight based on 100 parts by weight of the total amount of the base oil and the thickener.

  The base oil is a highly refined oil or mineral oil. The highly refined oil has a sulfur content of less than 0.1% by weight. The thickening agent is a urea compound.

  The grease-enclosed bearing of the present invention is characterized by encapsulating the grease composition of the present invention.

  The universal joint of the present invention is characterized in that the grease composition of the present invention is enclosed.

  The linear motion device of the present invention is characterized by linearly moving along a guide member and enclosing the grease composition of the present invention. The linear motion device includes a screw shaft that is a guide member having a helical thread groove on an outer peripheral surface, a ball screw nut having a helical thread groove corresponding to the screw shaft on the inner peripheral surface, A ball screw including a plurality of balls interposed between screw grooves, wherein the grease composition is sealed around the balls.

  Since the grease composition of the present invention contains oil-soluble MoDTC and a metal salt of a fatty acid having 2 or more carbon atoms as additives, even when used under severe conditions such as high speed and high surface pressure, low molybdenum content (0 .1% by weight or less) exhibiting excellent lubricity, improving wear resistance and reducing friction. Further, the use of Ca carbonate as an additive can further reduce friction.

  By using highly refined oil or mineral oil as the base oil, the cost can be reduced while maintaining lubricity. Further, by using a urea compound as the thickener, the heat resistance and durability are excellent, and the intervention property and adhesion to the sliding portion are also excellent.

  Since the grease-enclosed bearing, universal joint, and linear motion device of the present invention are filled with the grease composition of the present invention, the friction coefficient on the sliding surface is small and wear even when used under high speed and high surface pressure conditions. Can also be suppressed. Moreover, the grease to be enclosed has a low molybdenum content, which is preferable from the viewpoint of environmental protection.

It is sectional drawing which shows a deep groove ball bearing as an example of the grease enclosure bearing of this invention. It is sectional drawing which shows a constant velocity joint as an example of the universal joint of this invention. It is sectional drawing which shows a ball screw as an example of the linear motion apparatus of this invention. It is a figure which shows the relationship between carbon number of the fatty acid which comprises a fatty-acid metal salt, and a friction coefficient.

  The grease composition of the present invention is obtained by adding an additive to a base grease composed of a base oil and a thickener, and includes (1) oil-soluble MoDTC and (2) two or more carbon atoms as additives. It includes a metal salt of a fatty acid, and (3) the molybdenum content in the grease composition is 0.1% by weight or less (not contained (not 0% by weight)). When these are added to the grease composition, it is considered that a molybdenum coating can be formed on the sliding surface while the molybdenum content is small, and this molybdenum coating can improve wear resistance and reduce friction.

  Examples of the MoDTC used in the present invention include oil-soluble ones among molybdenum dialkyldithiocarbamates represented by the following formula (1). By using oil-soluble MoDTC, the molybdenum content is as low as 0.1% by weight or less, so that the heat resistance and durability are excellent, the thermal decomposition does not occur, and the extreme pressure effect is high.

（式中、Ｒ¹ およびＲ² はそれぞれ炭素原子数 1〜24、好ましくは 3〜18 のアルキル基であり、Ｘ+Ｙ＝ 4 の整数であり、かつＸは 0〜3 、Ｙは 4〜1 である。）

Wherein R ¹ and R ² are each an alkyl group having 1 to 24 carbon atoms, preferably 3 to 18 carbon atoms, an integer of X + Y = 4, and X is 0 to 3 and Y is 4 to 4 1)

  The oil-soluble MoDTC used in the present invention is a mixture of 0.5% by weight of MoDTC with respect to the total weight after dissolution added to the base oil used in the grease composition, and this is maintained at 70 ° C. for 24 hours. As a result of visual observation later, it refers to MoDTC in which insoluble components are not precipitated in the base oil. If the insoluble matter is precipitated, the base oil is not transparent, and MoDTC is in a colloidal state or a suspended state, which can be judged visually. As a commercial item of oil-soluble MoDTC, Adeka Co., Ltd .: SakuraLube 100, 165, 200 etc. are mentioned, for example.

  In the grease composition of the present invention, the molybdenum content in the composition is 0.1% by weight or less. More preferably, it is 0.06% by weight or less. In addition, it is preferable not to contain molybdenum-containing compounds other than the oil-soluble MoDTC. The blending ratio of the oil-soluble MoDTC is set to a range that satisfies this.

  The blending ratio (content) of the oil-soluble MoDTC is preferably 0.5 to 1.6 parts by weight with respect to 100 parts by weight of the base grease. If the blending ratio is less than 0.5 parts by weight, there is a possibility that sufficient low friction cannot be achieved under high speed and high surface pressure conditions. If the blending ratio exceeds 1.6 parts by weight, the molybdenum content in the grease composition may exceed 0.1% by weight depending on the type of MoDTC, and the molybdenum content cannot be reduced.

  The additive in the grease composition of the present invention contains, as an essential component, a fatty acid metal salt having 2 or more carbon atoms in addition to the oil-soluble MoDTC. By using a metal salt of a fatty acid in combination, it is possible to improve wear resistance and reduce friction while having a low molybdenum content (0.1% by weight or less).

  Examples of fatty acids that can be used in the present invention include monovalent saturated fatty acids having 2 or more carbon atoms, monovalent unsaturated fatty acids, divalent saturated fatty acids, and divalent unsaturated fatty acids. Moreover, an alicyclic fatty acid and an aromatic fatty acid can also be used. As carbon number of a fatty acid, 2-18 are preferable, 2-8 are more preferable, and 2-4 are especially preferable. Assuming that the metal species of the metal salt are the same, as shown in FIG. 4 described later, the metal salt of a fatty acid having 2 to 8 carbon atoms, which is a lower fatty acid, is lower than the metal salt of a fatty acid having 10 or more carbon atoms. Friction can be achieved, and among these, a metal salt of a fatty acid having 2 to 4 carbon atoms can further reduce friction.

  Fatty acids suitable for the present invention are monovalent saturated fatty acids having 2 to 18 carbon atoms, specifically, acetic acid, propionic acid, butanoic acid (butyric acid), pentanoic acid (valeric acid), hexanoic acid, heptanoic acid, Examples include octanoic acid (caprylic acid), nonanoic acid, decanoic acid, dodecanoic acid, tetradecanoic acid, pentadecanoic acid, hexadecanoic acid, heptadecanoic acid, and octadecanoic acid (stearic acid). Moreover, as a metal which comprises a fatty-acid metal salt, an alkali metal and alkaline-earth metal are mentioned, Among these, lithium, sodium, and calcium are preferable.

  Suitable fatty acid metal salts in the present invention include sodium acetate (C2), sodium butyrate (C4), sodium hexanoate (C6), sodium caprylate (C8), sodium decanoate (C10), and sodium stearate (C18). Etc. The numbers in parentheses indicate the number of carbon atoms in the fatty acid. Among these, sodium acetate (C2) and sodium butyrate (C4) are particularly preferable because of excellent extreme pressure and low friction.

  The blending ratio (content) of the fatty acid metal salt is preferably 1 to 7 parts by weight with respect to 100 parts by weight of the base grease. Particularly preferred is 2 to 6 parts by weight. When the blending ratio is less than 1 part by weight, there is little improvement in the effect of reducing friction. On the other hand, if the blending ratio exceeds 7 parts by weight, the low friction expression of the oil-soluble MoDTC is hindered, and a sufficiently low friction cannot be achieved particularly under a low surface pressure.

  In the present invention, the additive preferably contains Ca carbonate. By including Ca carbonate, the effect of reducing friction on the sliding surface can be further improved. The proportion (content) of Ca carbonate is preferably 1 to 7 parts by weight with respect to 100 parts by weight of the base grease. When the blending ratio is less than 1 part by weight, there is little improvement in the effect of reducing friction. Further, even if the blending ratio exceeds 7 parts by weight, further improvement in the effect of reducing friction by the combined use cannot be expected.

  In the grease composition of the present invention, as an additive, in addition to oil-soluble MoDTC and fatty acid metal salt, which are essential components, in combination with the above-mentioned Ca carbonate, it can be used under severe conditions such as high speed and high surface pressure. Although the molybdenum content is low (0.1 wt% or less), the friction can be reduced in the same manner as when a conventional amount of non-oil soluble molybdenum powder is blended (about 1 to 5 wt%).

  The grease composition of the present invention may contain known additives other than those described above as necessary. Examples of such additives include rust inhibitors such as dinonyl naphthalene sulfonate and sorbitan esters, antioxidants such as amines and phenols, corrosion inhibitors such as sodium nitrite and sodium sebacate, graphite And solid lubricants such as molybdenum disulfide, oily agents such as fatty acid amides, fatty acids, amines and fats, and viscosity index improvements such as polymethacrylate and polystyrene. In addition, these can be added individually or in combination of 2 or more types.

  The base oil of the grease composition of the present invention is not particularly limited, and general oils usually used in the grease field can be used. For example, highly refined oils, mineral oils, animal and vegetable oils, ester synthetic oils, synthetic hydrocarbon oils, phosphate ester oils, silicone oils, fluorine oils, and mixed oils thereof can be used. Among these, in consideration of lubricity and cost, use of highly refined oil or mineral oil is preferable.

  Highly refined oil is obtained by, for example, catalytic hydrothermal decomposition of slag wax obtained from residual oil of vacuum distillation and synthesizing. Moreover, the GTL oil etc. which are synthesize | combined by the Fischer-Tropsch method are mentioned. The highly refined oil preferably has a sulfur content of less than 0.1% by weight, more preferably less than 0.01% by weight. Examples of commercially available highly refined oils include Shell High Back Oils X46 and X68 manufactured by Showa Shell Sekiyu K.K. Further, examples of the mineral oil include spindle oil, refrigerator oil, turbine oil, machine oil, dynamo oil and the like.

  The thickener of the grease composition of the present invention is not particularly limited, and those commonly used in the field of grease can be used. For example, soap-type thickeners such as metal soaps and composite metal soaps, and non-soap-type thickeners such as benton, silica gel, urea compounds and urea / urethane compounds can be used. Examples of the metal soap include sodium soap, calcium soap, aluminum soap, and lithium soap. Examples of the urea compound and urea / urethane compound include diurea compounds, triurea compounds, tetraurea compounds, other polyurea compounds, and diurethane compounds. Among these, it is preferable to use a urea compound that is excellent in heat durability and excellent in intervening property and adhesion to the sliding portion.

  A urea compound is obtained by reacting a polyisocyanate component and a monoamine component. Examples of the polyisocyanate component include phenylene diisocyanate, tolylene diisocyanate, diphenyl diisocyanate, diphenylmethane diisocyanate, octadecane diisocyanate, decane diisocyanate, and hexane diisocyanate. Moreover, an aliphatic monoamine, an alicyclic monoamine, and an aromatic monoamine can be used for a monoamine component. Aliphatic monoamines include hexylamine, octylamine, dodecylamine, hexadecylamine, octadecylamine, stearylamine, oleylamine and the like. Examples of the alicyclic monoamine include cyclohexylamine. Aromatic monoamines include aniline and p-toluidine.

  Among these urea compounds, aromatic diisocyanate is used as the polyisocyanate component, aliphatic monoamine and / or alicyclic as the monoamine component, since the above-mentioned heat resistance and resistance to the sliding portion are particularly excellent. The use of an aliphatic urea compound or an alicyclic urea compound using an aromatic monoamine is particularly preferred.

  A base grease for blending the above-mentioned additives can be obtained by blending a thickener such as a urea compound with the base oil. A base grease using a urea compound as a thickener is prepared by reacting the polyisocyanate component and the monoamine component in a base oil.

  The blending ratio of the thickener in 100 parts by weight of the base grease is 1 to 40 parts by weight, preferably 3 to 25 parts by weight. If the content of the thickener is less than 1 part by weight, the thickening effect is reduced, making it difficult to form a grease. If the content exceeds 40 parts by weight, the obtained base grease becomes too hard and the desired effect is difficult to obtain. Become.

  The grease composition of the present invention can be used as grease to be sealed in mechanical parts used under severe conditions such as high speed and high surface pressure, such as bearings, universal joints, linear motion devices, and ball screws. Hereinafter, these will be described.

  A grease-filled bearing of the present invention will be described with reference to FIG. FIG. 1 is a cross-sectional view of a deep groove ball bearing. In the grease-filled bearing 1, an inner ring 2 having an inner ring rolling surface 2a on the outer peripheral surface and an outer ring 3 having an outer ring rolling surface 3a on the inner peripheral surface are arranged concentrically, and the inner ring rolling surface 2a and the outer ring rolling surface 3a are arranged. A plurality of rolling elements 4 are arranged between the two. The plurality of rolling elements 4 are held by a cage 5. In addition, seal members 6 fixed to the outer ring 3 and the like are provided in the axial both ends openings 8a and 8b of the inner ring 2 and the outer ring 3, respectively. The grease composition 7 of the present invention is enclosed at least around the rolling element 4.

  Ball bearings have been exemplified as the bearings, but the grease composition of the present invention is not limited to the above cylindrical roller bearings, tapered roller bearings, self-aligning roller bearings, needle roller bearings, thrust cylindrical roller bearings, thrust tapered roller bearings, thrust It can also be used as a grease for rolling bearings such as needle roller bearings and thrust spherical roller bearings, or sliding bearings.

  The universal joint of the present invention will be described with reference to FIG. FIG. 2 is a partially cutaway sectional view showing a Rzeppa constant velocity joint as an example of the universal joint of the present invention. As shown in FIG. 2, the constant velocity joint 11 includes six track grooves 14, 15 in the axial direction on the inner surface of an outer member (also referred to as an outer ring) 12 and the outer surface of a spherical inner member (also referred to as an inner ring) 13. Are formed at equal angles, and a torque transmission member (also called a ball) 16 incorporated between the track grooves 14 and 15 is supported by a cage 17, the outer periphery of the cage 17 is a spherical surface 17a, and the inner periphery is an inner member. The spherical surface 17b is adapted to the outer periphery of the 13th. The outer periphery of the outer member 12 and the outer periphery of the shaft 18 are covered with a boot 19, and the outer member 12, the inner member 13, the track grooves 14 and 15, the torque transmission member 16, the cage 17, and the shaft The grease composition 20 of the present invention is enclosed in a space surrounded by 18.

  Although the Zepper type constant velocity joint is exemplified as the universal joint, the grease composition of the present invention includes other fixed type constant velocity joints such as the Barfield type, double offset type, cross groove type, tripod type constant velocity joints, etc. It can also be used as a sealing grease for non-constant universal joints such as slide type constant velocity joints or cross joints.

  The linear motion device of the present invention will be described with reference to FIG. FIG. 3 is a sectional view showing a ball screw which is an example of the linear motion device of the present invention. As shown in FIG. 3, the ball screw of the present invention includes a plurality of screw grooves 22 formed on the outer peripheral surface of the screw shaft 21 that is a guide member and a plurality of screw grooves 24 formed on the inner peripheral surface of the ball nut 23. The ball 25 is interposed, the rotational power of the screw shaft 21 or the ball nut 23 is transmitted to the ball nut 23 (or the screw shaft 21) via the ball 25, and the ball nut 23 is moved in the axial direction. is there. The grease composition of the present invention is enclosed between the screw shaft 21 and the ball nut 23 around the ball 25 and sealed with a ball screw seal member 26.

  The present invention will be specifically described with reference to examples and comparative examples, but is not limited to these examples.

Examples 1 to 17 and Comparative Examples 1 to 8
Base grease obtained by increasing the base oil with a diurea thickener (diurea compound obtained by reacting octylamine and cyclohexylamine with 4,4′-diphenylmethyldiisocyanate) at the ratio shown in Table 1 and Table 2. Obtained. The additives listed in Table 1 and Table 2 were mixed with this base grease, milled with a three-stage roll mill, and then defoamed to obtain a grease composition. In addition, Mo content in a table | surface is molybdenum content (weight%) in the whole grease composition. About the obtained grease composition, it used for the SRV friction abrasion test shown below, and measured the friction coefficient. The results are shown in Tables 1 and 2. Note that 1) to 6) in Tables 2 and 3 are the same as 1) to 6) shown in the lower part of Table 1.

<SRV friction and wear test>
Test piece: Ball diameter 10mm (SUJ2)
Disc plate Diameter 24mm x 7.85mm (SUJ2)
Evaluation conditions: Point contact maximum surface pressure 1.45 GPa, 2.62 GPa
Frequency 10Hz
Amplitude 1.2mm
30 minutes
Test temperature 40 ℃
Measurement item: Coefficient of dynamic friction; average value (value that is constant within the measurement time)

  As shown in Table 1, in each example, by adding oil-soluble MoDTC and metal acetate as an additive, low friction can be achieved while molybdenum content is low (0.1 wt% or less). I understood. Furthermore, it was found that the friction can be further reduced by using Ca carbonate together.

Examples 18 to 23, Comparative Example 9, and Comparative Example 10
A base grease obtained by increasing the base oil with a diurea thickener (diurea compound obtained by reacting octylamine and cyclohexylamine with 4,4′-diphenylmethyldiisocyanate) at the ratio shown in Table 3 was obtained. The additives listed in Table 3 were mixed with this base grease, milled with a three-stage roll mill, and then defoamed to obtain a grease composition. In addition, Mo content in a table | surface is molybdenum content (weight%) in the whole grease composition. The obtained grease composition was subjected to the SRV frictional wear test in the same manner as in Example 1, and the friction coefficient was measured. The results are shown in Table 3 and FIG. In FIG. 4, the horizontal axis represents the carbon number of the fatty acid constituting the fatty acid metal salt, the vertical axis represents the measured friction coefficient, and the carbon number of 0 is the result of Comparative Example 9.

  As shown in Table 3 and FIG. 4, in each example, low molybdenum content (0.1 wt% or less) is obtained by blending oil-soluble MoDTC and a metal salt of a fatty acid having 2 to 18 carbon atoms as additives. However, it was found that low friction can be achieved. Moreover, in each Example, with respect to a fatty acid having 10 or more carbon atoms, a lower fatty acid having 2 to 8 carbon atoms can achieve lower friction, and among them, a fatty acid having 2 to 4 carbon atoms can further reduce friction. I understood that.

  The grease composition of the present invention has excellent lubricity even when used under severe conditions such as high speed and high surface pressure, with low molybdenum content (0.1 wt% or less). For this reason, it can be suitably used as a lubricating grease for use in, for example, a bearing, a universal joint, a linear motion device, a ball screw, etc., used under high speed and high surface pressure conditions.

DESCRIPTION OF SYMBOLS 1 Grease enclosure bearing 2 Inner ring 3 Outer ring 4 Rolling element 5 Cage 6 Seal member 7 Grease composition 8a, 8b Opening 11 Constant velocity joint 12 Outer member (outer ring)
13 Inner member (inner ring)
14, 15 Track groove 16 Torque transmission member (ball)
17 Cage 18 Shaft 19 Boot 20 Grease Composition 21 Screw Shaft 22 Screw Groove 23 Ball Nut 24 Screw Groove 25 Ball 26 Seal Member

Claims (12)

A grease composition comprising a base oil, a thickener, and an additive,
It said additive, and molybdenum dithiocarbamates oil-soluble, and a metal salt of a fatty acid having 2 to 4 carbon atoms, the molybdenum content in the grease composition is Ri der 0.1 wt% or less,
The metal of the metal salt is lithium, sodium, or calcium;
The content of the oil-soluble molybdenum dithiocarbamate is 0.5 to 1.6 parts by weight with respect to 100 parts by weight of the total amount of the base oil and the thickener,
The grease composition , wherein a content of the fatty acid metal salt is 1 to 7 parts by weight with respect to 100 parts by weight of the total amount of the base oil and the thickener . Wherein the fatty acid is acetic acid or grease composition of claim 1, wherein the butyric acid. The grease composition according to claim 1 or 2 , wherein the additive contains calcium carbonate. The grease composition according to claim 3 , wherein the content of the calcium carbonate is 1 to 7 parts by weight with respect to 100 parts by weight of the total amount of the base oil and the thickener. The grease composition according to any one of claims 1 to 4 , wherein the base oil is highly refined oil or mineral oil. 6. The grease composition according to claim 5, wherein the highly refined oil has a sulfur content of less than 0.1% by weight. The grease composition according to any one of claims 1 to 6 , wherein the thickener is a urea compound obtained by reacting a polyisocyanate component and a monoamine component. The grease composition according to claim 7 , wherein the monoamine component is at least one monoamine selected from an aliphatic monoamine and an alicyclic monoamine. A grease-enclosed bearing in which a grease composition is encapsulated, wherein the grease composition is the grease composition according to any one of claims 1 to 8 . A universal joint formed by enclosing a grease composition, wherein the grease composition is the grease composition according to any one of claims 1 to 8 . A linear motion device that linearly moves along a guide member and encloses a grease composition, wherein the grease composition is the grease composition according to any one of claims 1 to 8. A linear motion device characterized by. The linear motion device includes: a screw shaft that is a guide member having a helical thread groove on an outer peripheral surface; a ball screw nut having a helical thread groove corresponding to the screw shaft on an inner peripheral surface; The linear motion device according to claim 11 , wherein the grease composition is a ball screw including a plurality of balls interposed therebetween, and the grease composition is sealed around the balls.

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