JP2009235341A - Solid lubricant magnetoattractive onto sliding surface, and lubricating oil composition containing the solid lubricant - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid lubricant high in storage stability in a lubricating oil, and excellent in the friction-reducing effects of various mechanical parts such as of automobiles. <P>SOLUTION: The solid lubricant, which is magnetoattractive onto a sliding surface, contains at least one ferromagnetic powder selected from the group consisting of powders of iron oxide-based ferromagnetic substances, cobalt oxide-based ferromagnetic substances, chromium oxide-based ferromagnetic substances and rare earth-based ferromagnetic substances. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a solid lubricant excellent in friction reduction effect and storage stability in various machine products such as automobiles, and a lubricating oil composition containing the solid powder lubricant.

  Friction exists as a factor that reduces the operating efficiency of many machine products such as automobiles. Normally, lubricating oil is used to reduce friction in machine products. However, since lubricating oil has viscous resistance, friction loss is not eliminated. Also, under the condition of being exposed to high temperature and high pressure as in an engine such as an automobile, a so-called “oil film break” occurs, and the friction loss increases rapidly, and in some cases, the machine itself may be destroyed.

  While liquid lubricants having such problems have been studied, in recent years, solid lubricants (solid lubricants) have been studied (see, for example, Patent Document 1). Solid lubricants do not necessarily have the effect of reducing friction as that of commonly used lubricants, but because the friction reduction mechanism is fundamentally different from that of liquid lubricants, (i) the shear rate of the sliding surface Regardless of the characteristics, a constant friction reducing effect can be obtained, and (ii) the friction characteristics do not deteriorate so much even under high temperature conditions.

  If a solid lubricant and a lubricating oil having such characteristics are used in combination, and if both defects can be complemented well, it is expected that a lubricating oil composition having an excellent friction reducing effect in various machine products can be obtained. Has been.

However, in the prior art, it is difficult to stably hold the powder that can sufficiently exert the effect of the solid lubricant in the lubricating oil. For example, in the automobile industry, for example, the solid lubricant is added to the lubricating oil. And reluctant.
JP 2004-18555 A

  The problem to be solved by the present invention is to provide a solid lubricant that is excellent in storage stability in a lubricating oil and excellent in friction reduction effect of various machine products such as automobiles. Another object of the present invention is to provide a solid lubricant that has little corrosive action on various machine products and can keep the friction loss of lubricating oil low even after long-term use.

As a result of intensive studies to solve the above problems, the present inventors have found that the conventional solid lubricant has the following problems.
(1) Conventionally known solid lubricants are produced with the idea of how to stably “disperse” in a lubricating oil, but many solid lubricants are so-called inorganic powders. However, it is difficult to stably disperse the inorganic powder for a long time in a lubricating oil that is an organic substance.

  (2) It is considered that a conventionally known solid lubricant exhibits a lubricating action by “electrostatically” adsorbing to sliding surfaces of various machine products such as automobiles. However, in such an electrostatic action, it is difficult to maintain the adsorption state stably for a long time due to a change in temperature or a change in characteristics of the powder surface due to wear of the solid lubricant powder.

  Based on the above knowledge, the present inventors have found that the solid lubricant and the lubricating oil can coexist stably and have an excellent friction reducing effect by a mechanism called “magnetization” which is completely different from the conventional solid lubricant. The present invention has been completed. Note that Patent Document 1 describes a lubricant additive containing at least ferrite as ceramics and magnetizing the ferrite. However, the magnetized ferrite is not specifically disclosed, and the effect of being magnetized also relates to dispersibility.

That is, the present invention relates to the following matters.
[1] including at least one ferromagnetic powder selected from the group consisting of iron oxide ferromagnets, cobalt oxide ferromagnets, chromium oxide ferromagnets, and rare earth ferromagnets Solid lubricant that can be magnetically attached to the sliding surface.

  [2] The iron oxide ferromagnet is at least one ferromagnet selected from the group consisting of a barium / ferrite ferromagnet and a strontium / ferrite ferromagnet. The solid lubricant that can be magnetically attached to the sliding surface according to [1].

  [3] The rare earth ferromagnet is at least one ferromagnet selected from the group consisting of a samarium-cobalt ferromagnet and an iron-neodymium ferromagnet [1] ] Or a solid lubricant that can be magnetically attached to the sliding surface according to [2].

  [4] A lubricating oil composition comprising 0.001 to 5% by weight of a solid lubricant that can be magnetically attached to the sliding surface according to any one of [1] to [3].

  ADVANTAGE OF THE INVENTION According to this invention, the solid lubricant which is excellent in storage stability in lubricating oil, and excellent in the friction reduction effect of various machine products, such as a motor vehicle, can be provided. Further, it is possible to provide a solid lubricant that has little corrosive action on various machine products and can keep the friction loss of the lubricating oil low even after long-term use.

  In particular, the effect of the solid lubricant can be maintained stably for a long time only by adding a very small amount of solid lubricant to the lubricating oil as compared with the conventional case.

Next, the solid lubricant that can be magnetically attached to the sliding surface of the present invention and the lubricating oil composition containing the solid lubricant will be specifically described.
[Solid lubricant that can be magnetically attached to the sliding surface]
The solid lubricant that can be magnetically attached to the sliding surface of the present invention is selected from the group consisting of iron oxide ferromagnets, cobalt oxide ferromagnets, chromium oxide ferromagnets, and rare earth ferromagnets And at least one ferromagnetic powder. In the present invention, “magnetization” means that the ferromagnetic powder is attracted to the sliding surface of various mechanical products such as iron by the magnetic force of the ferromagnetic material. Specifically, if the ferromagnetic powder has a magnetic force having a holding force (iHc) of 2000 (Oe) or more, or a maximum energy product (BH product) of 0.5 (MGOE) or more, iron Adsorbs well to various machine products such as

  Examples of the iron oxide ferromagnetic material include barium / ferrite and strontium / ferrite ferromagnetic materials. Examples of the rare earth ferromagnets include samarium-cobalt and iron-neodium ferromagnets. Among these, iron oxide ferromagnets are preferable, and barium / ferrite ferromagnets are particularly preferable.

Further, the solid lubricant of the present invention includes boron nitride (BN) as long as the object of the present invention is not impaired.
, Teflon (registered trademark), alumina, boron oxide (B ₂ O ₃ ), carbon and the like may be contained.

  The average particle size of the primary particles of the ferromagnetic powder used in the present invention is usually 20 μm or less, preferably 0.1 to 3 μm, more preferably 0.5 to 2 μm. When the average particle size of the primary particles of the ferromagnetic powder is in the above range, the particles can easily enter a narrow space, and the function as a solid lubricant is more effectively exhibited even with a small addition amount. In the present invention, the average particle size of the primary particles of the ferromagnetic powder is measured by a laser diffraction / scattering method, and the average particle size is a particle size at a position where the integrated weight of the weight integrated particle size distribution is 50% by weight. Say.

  The average particle size of the primary particles of the ferromagnetic powder is determined by an attrition mill, a ball mill, or other roll type shearing mill including two or three types of ceramic beads or balls as necessary. The above range can be adjusted by wet pulverization using a pulverizer or the like, or dry pulverization such as a jet mill.

  The shape of the ferromagnetic powder used in the present invention is not particularly limited, but the shape of the primary particles observed in an enlarged photograph by a scanning electron microscope (SEM) works well even in a crushed shape, but is substantially a disc. When the shape is substantially spherical or substantially spherical, the function as a solid lubricant is better exhibited.

  In general, it is known that, under conditions where the sliding speed is slow, the pressure generated in the oil film decreases, so that the chances of contact between members of the machine product increase (boundary lubrication). The solid lubricant of the present invention is particularly excellent in the friction reducing effect in the boundary lubrication. As described above, the reason why the solid lubricant containing the ferromagnetic powder in the present invention is excellent in storage stability in the lubricating oil and excellent in the friction reducing effect of various machine products such as automobiles is considered as follows. .

  When the above-mentioned ferromagnetic powder is added singly or in combination of two or more to lubricating oil, and the lubricating oil is used in various mechanical products such as engines, the ferromagnetic powder in the lubricating oil is fast. In the stage, for example, magnetic adhesion, that is, ferromagnetic powder is unevenly distributed on the friction surface on the sliding surface of the A member or B member of the machine product composed of the A member and the B member. Conventionally known solid lubricants are considered to exhibit a lubricating action by “electrostatically” adsorbing to sliding surfaces of various machine products such as automobiles. On the other hand, the solid lubricant of the present invention uses magnetic adhesion, which is a property of the ferromagnetic powder contained in the solid lubricant, so that even if the ferromagnetic powder is worn or at a certain high temperature. Even when exposed, there is little deterioration in properties. In addition, since the ferromagnetic powder is an iron oxide or intermetallic compound, it basically has a low affinity with the iron-based material, does not react with the iron-based material and does not melt, and is a high-hardness powder. is there.

  For the above reasons, it is considered that the friction reducing effect can be maintained for a long time even if the amount of the solid lubricant added in the lubricating oil is extremely small compared to the conventional case. Further, since the amount of the solid lubricant added is extremely small, it is considered that the solid lubricant is excellent in storage stability without aggregation.

[Lubricating oil composition containing solid lubricant magnetically attachable to sliding surface]
The lubricating oil composition of the present invention includes a solid lubricant that can be magnetically attached to the sliding surface and a lubricating oil, and may further include various additives as optional components.

<Solid lubricant that can be magnetically attached to the sliding surface>
The amount of the solid lubricant that can be magnetically adhered to the sliding surface in the lubricating oil composition may be in a very small amount because the lubricating action utilizing the magnetic adhesion is utilized. Although there is an appropriate and economical content depending on the usage conditions of the lubricating oil composition, it can provide a good lubricating effect and cover a wide range of usage conditions. The content of the solid lubricant that can be worn is usually 0.001 to 5% by weight, preferably 0.01 to 0.5% by weight, more preferably 0.02 to 0.1% by weight. If the content of the solid lubricant that can be magnetically attached to the sliding surface is below the above range, the lubricating effect is not sufficient, and if it exceeds the above range, it is difficult to form a uniform suspension and settles upon addition. This causes a problem of remaining on the oil pan and is not preferable from the viewpoint of cost performance.

  The lubricating oil composition is preferably prepared by preliminarily preparing and storing a suspension of solid lubricant that can be magnetically attached to a high concentration sliding surface, and diluted with a lubricating oil so as to obtain a concentration required for use. It is convenient because it is not bulky during transportation or storage.

<Lubricating oil>
The lubricating oil used in the present invention is not particularly limited as long as it is a commonly used lubricating oil. Such lubricating oils include, for example, mineral oils, bright stocks, hydrogen contact refined oils, contact leak-free refined oils, etc .; α-olefin oligomers such as liquid polybutene and liquid decene oligomers, and liquid ethylene / α-olefin co-oligomers Hydrocarbon synthetic oils such as: Dibasic acid esters such as diisooctyl adipate, diisooctyl sebacate, dilauryl sebacate; Polyol ester synthetic oils obtained by esterifying polyols such as trimethylolpropane, pentaerythritol, dipentaerythritol with fatty acids Etc. These can be used alone or in combination of two or more.

<Additives>
As the additive for the lubricating oil used as an optional component in the present invention, various additives can be used according to each purpose. Examples of such additives include load bearing additives, antioxidants, metal deactivators, antifoaming agents, detergent dispersants, antiwear additives, rust inhibitors, corrosion inhibitors, fluidity improvers and the like. Is mentioned. Also, viscosity index improvers such as OCP type represented by hydrogenated poly (meth) acrylate, ethylene-propylene copolymer, styrene-isoprene copolymer; poly (meth) acrylate, styrene-fumarate Pour point depressants such as condensates of naphthalene and chlorinated paraffins; detergents such as sulfonates, salicylates, phenates and naphthenates; antioxidants such as zinc dithiophosphate, amines and hindered phenols Agents: Oil-based agents such as fatty acid-based and fatty acid ester-based materials; Friction / wear adjusting agents such as molybdenum dithiophosphate and molybdenum carbamate; Extreme pressure agents such as sulfur-phosphorus-based and chlor-based materials.

  Since the solid lubricant contained in the lubricating oil of the present invention is extremely small as described above, a stable suspended state can be maintained in the lubricating oil without using a dispersant. However, in general, the ferromagnetic powder contained in the solid lubricant has strong hydrophilicity, and may be aggregated in the lubricating oil as it is. Therefore, it is preferable to impart lipophilicity by adsorbing a dispersant such as a surfactant on the surface of the ferromagnetic powder. Further, if a dispersant is added to the lubricating oil, even if the solid lubricant is settled and separated in the lubricating oil due to a difference in specific gravity with the lubricating oil, it can be easily redispersed.

  Examples of the dispersant include nonionic surfactants, anionic surfactants, cationic surfactants, amphoteric surfactants, and oil-soluble surfactants. Of these, amphoteric surfactants and oil-soluble surfactants are particularly preferable.

[Use]
The solid lubricant or lubricating oil composition of the present invention is used in engine oils for vehicles such as passenger cars, trucks, work vehicles, tractors, and two-wheeled vehicles equipped with gasoline engines and diesel engines, gear oils, automatic transmission oils, and tillers.・ Engine oil for agricultural machinery such as combine, other marine engine oil, shock absorber oil, industrial hydraulic oil, industrial gear oil, vacuum pump oil, bearing oil, and other industrial lubricating oil, generator lubricating oil, compressor It can be used as a lubricant for industrial use and as a lubricant for bearings of artificial satellites. Among these, particularly when added to a fuel-saving automotive engine oil, which has recently been increasing in demand, it exhibits excellent performance.

EXAMPLES Hereinafter, although this invention is demonstrated further more concretely based on an Example, this invention is not limited to these.
FIG. 1 shows a jig used for measuring the frictional force in this example. The jig is composed of four parts: a: rotator, b: stator, c: stage, d: strain gauge, and the whole is placed on a general-purpose drilling machine. A: The rotator has a donut-shaped sliding surface having an outer diameter of φ100, an inner diameter of φ56, and a width of 22 mm. The materials of a: rotator and b: stator are both S45C.

  The above general-purpose drilling machine is combined with an inverter, and the rotational speed can be changed from 5 to 160 rpm, and the tangential speed (sliding speed) of the sliding surface at this time corresponds to 0.04 to 1.28 m / s. .

[Example 1]
Svelt (manufactured by Nippon San Oil Co., Ltd., SAE standard 5W-50) as a lubricant, barium-ferrite powder (manufactured by Toda Kogyo Co., Ltd., GP-500) as a solid lubricant The average particle diameter is 1 μm, the holding power is 2050 (Oe), and the BH product is 0.64 (MG Oe)). The concentration of the solid lubricant in the lubricating oil composition is 4 L in the lubricating oil composition. It prepared so that it might become 2g (0.07 weight%) with respect to it. The average particle diameter is a value measured by a laser diffraction / scattering method.

The lubricating oil composition was poured into a jig shown in FIG. 1, and the coefficient of friction with respect to the sliding speed on the sliding surface was measured under the condition that the temperature of the lubricating oil composition was 40 ° C. The results are shown in FIG.
[Comparative Example 1]
A lubricating oil composition was prepared in the same manner as in Example 1 except that no solid lubricant was added, and the coefficient of friction with respect to the sliding speed on the sliding surface was measured. The results are shown in FIG.

  From the results of Example 1 and Comparative Example 1 (FIG. 2), it can be seen that the friction coefficient is clearly reduced by the addition of the solid lubricant (barium / ferrite powder). In addition, the reduction of the friction coefficient becomes remarkable under the condition that the sliding speed is small. In the result of FIG. 2, since the friction coefficient is more markedly reduced in the region where the sliding speed is low (boundary lubrication), the solid lubricant mainly exhibits the friction (dry friction) value due to contact between solids. It can be interpreted that it is reduced.

  FIG. 3 shows the amount of friction coefficient reduction and the ratio of Example 1 with respect to Comparative Example 1. In Example 1 using the solid lubricant, compared with Comparative Example 1 not using the solid lubricant, an effect of reducing the friction coefficient by 30% or more is obtained in a region where boundary lubrication becomes remarkable.

  In order to clarify the cause of the effect of reducing the friction coefficient, the result of observing the sliding surface using SEM is shown in FIG. It can be seen that many barium / ferrite powders are magnetically attached to the sliding surface, and that even after the sliding test, they are rubbed against the sliding surface and do not collapse or adhere.

As described above, the ferromagnetic powder contained in the solid lubricant of the present invention has a characteristic that it has low hardness and high hardness in addition to magnetism, and therefore has a very small amount with respect to the lubricating oil. Even with the addition of, it is considered that the solid lubricant functioned as a solid lubricant stably for a long time while adsorbing efficiently on a sliding surface such as iron and maintaining the original shape.

Friction test apparatus used in Example 1 and Comparative Example 1 Relationship between sliding speed and friction coefficient (friction force) Reduction amount and improvement rate of friction coefficient by adding solid lubricant (ferromagnetic powder) Observation result of sliding surface after sliding test

Explanation of symbols

a ... rotator b ... stator c ... stage d ... strain gauge

Claims (4)

  Including at least one ferromagnetic powder selected from the group consisting of iron oxide ferromagnets, cobalt oxide ferromagnets, chromium oxide ferromagnets, and rare earth ferromagnets Solid lubricant that can be magnetically attached to the sliding surface.   The iron oxide ferromagnet is at least one ferromagnet selected from the group consisting of a barium / ferrite ferromagnet and a strontium / ferrite ferromagnet. A solid lubricant that can be magnetically attached to the sliding surface.   3. The rare earth ferromagnet is at least one ferromagnet selected from the group consisting of samarium-cobalt ferromagnets and iron-neodymium ferromagnets. A solid lubricant that can be magnetically attached to the sliding surface.   A lubricating oil composition comprising 0.001 to 5% by weight of a solid lubricant that can be magnetically attached to the sliding surface according to any one of claims 1 to 3.