Conductive grease composition

Abstract

To provide a grease composition that can impart good conductivity. [Solution] The grease composition according to the present invention is characterized by comprising a base grease containing a base oil and a thickener, and a nonionic surfactant having an HLB value of 10 to 15. The nonionic surfactant is preferably of the alkyl ether or ester type hydrophobic group. Furthermore, the content of the nonionic surfactant is preferably in the range of 0.1% to 10% by mass relative to the total amount of the composition. Moreover, this conductive grease composition is suitable for use in bearings.

Description

Technical Field

[0001] The present invention relates to a conductive grease composition that is particularly suitable for application to bearings.

Background Art

[0002] In a motor operated by frequency control such as an inverter, a common-mode voltage generates a ground-axis voltage between the shaft and the housing due to the capacitance between the rotor and the stator windings. These voltages cause discharge inside the bearing depending on the state of the bearing and lubricity, leading to bearing damage.

[0003] As a method of preventing such bearing damage, in addition to improving lubricity by applying a grease film inside the bearing, a method of imparting conductivity to the grease film to form a path (conductive path) for discharging static electricity is conceivable.

[0004] As a technique for imparting conductivity to a grease film to suppress electrolytic corrosion of a bearing, for example, the techniques described in Patent Documents 1 and 2 have been proposed.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] The present invention has been proposed in view of such circumstances, and an object thereof is to provide a grease composition capable of imparting good conductivity.

Means for Solving the Problems

[0007] The inventors diligently conducted research to solve the above-mentioned problems. As a result, they discovered that good conductivity can be imparted to a grease composition by incorporating a specific HLB nonionic surfactant, and thus completed the present invention.

[0008] (1) The first invention of the present invention is a conductive grease composition comprising a base grease containing a base oil and a thickener, to which a nonionic surfactant having an HLB value of 10 to 15 is blended.

[0009] (2) The second invention of the present invention is a conductive grease composition in which, in the first invention, the nonionic surfactant has an alkyl ether type or ester type hydrophobic group.

[0010] (3) The third invention of the present invention is a conductive grease composition in which, in the first or second invention, the content of the nonionic surfactant is in the range of 0.1% by mass to 10% by mass.

[0011] (4) The fourth invention of the present invention is a conductive grease composition used in bearings, in any of the first to third inventions. [Effects of the Invention]

[0012] According to the present invention, a grease composition that can impart good conductivity can be provided. [Modes for carrying out the invention]

[0013] The following describes in detail specific embodiments of the present invention (hereinafter referred to as "these embodiments"). It should be noted that the present invention is not limited to the following embodiments, and modifications can be made as appropriate without altering the essence of the invention.

[0014] ≪1. Grease Composition≫ The grease composition according to this embodiment comprises a base grease containing a base oil and a thickener, to which a specific nonionic surfactant is blended. Specifically, it is characterized by the blending of a nonionic surfactant having an HLB value in the range of 10 to 15.

[0015] Furthermore, preferably, the nonionic surfactant has a hydrophobic group of the alkyl ether type or ester type.

[0016] Thus, by using a grease composition containing a nonionic surfactant with an HLB value of 10 to 15, conductivity can be imparted to the grease (grease film). As a result, by applying this grease composition to the inside of a bearing in a motor, for example, excellent lubrication is provided to the bearing, improving its sliding characteristics. Furthermore, the grease film acts as a conductive path (conductive pathway) that dissipates static electricity generated by the sliding of the bearing, effectively preventing bearing damage caused by discharge within the bearing.

[0017] As described above, the grease composition according to this embodiment is suitable as a bearing grease composition for forming a grease film inside the bearing. The type of bearing is not particularly limited, and it can be applied to any type, such as rolling bearings or sliding bearings.

[0018] [Base oil] The base oil is the main component of grease and, together with the thickener described later, constitutes the base grease. The base oil imparts good lubricity to the grease.

[0019] The type of base oil is not particularly limited, and those conventionally and commonly used can be used. For example, lubricating oils such as mineral oil, ether oil-based synthetic oil, ester-based synthetic oil, and hydrocarbon synthetic oil, or their synthetic oils can be mentioned. Among them, it is preferable to use ester oil-based synthetic oil and hydrocarbon synthetic oil. Examples of ester oil-based synthetic oil include polyol ester oil, phosphate ester oil, polymer ester oil, aromatic ester oil, carbonate ester oil, diester oil, polyglycol oil, etc. Examples of hydrocarbon-based synthetic oil include polyalpha-olefin (PAO), etc.

[0020] The base oil may be used alone or in combination of two or more. For example, two or more types with different viscosities may be used in combination to form the base oil.

[0021] The content of the base oil in the grease composition is not particularly limited and can be determined in consideration of the blending ratio with the thickener described later that constitutes the base grease. For example, it can be set at a ratio of 50% by mass or more based on the total amount of the grease composition, preferably 60% by mass or more, and more preferably 70% by mass or more. The upper limit is not particularly limited and can be set within a range that does not impair the effects of the blending components described later, for example, about 95% by mass or less.

[0022] [Thickener] The thickener is a material necessary for retaining oil in the grease and constitutes the base grease together with the base oil.

[0023] The type of thickener is not particularly limited, and those conventionally and commonly used can be used.

[0024] Specifically, the thickeners can be broadly classified into soap-based and non-soap-based types. Examples of soap-based thickeners include lithium soap, lithium composite soap, calcium soap, calcium composite soap, aluminum soap, and aluminum composite soap. Examples of non-soap-based thickeners include urea, sodium terephthalate, fluororesin, organic bentonite, silica gel, etc. These thickeners may be used alone or in combination of two or more kinds.

[0025] The content of the thickener in the grease composition is not particularly limited and can be determined in consideration of the blending ratio of the above-mentioned base oil constituting the base grease.

[0026] [Nonionic surfactant] As described above, in the grease composition according to this embodiment, a nonionic surfactant having an HLB value in the range of 10 to 15 is blended. The surfactant can impart conductivity to the grease.

[0027] In the surfactant, "HLB" is a value indicating the balance between hydrophilicity and lipophilicity. When the HLB value is in the range of 10 to 15, excellent conductivity can be imparted to the grease. If the HLB value is less than 10, the conductivity decreases. On the other hand, if the HLB value exceeds 15, the hydrophilicity becomes too high, and it may be difficult to be compatible with the base oil in the grease composition and may not dissolve.

[0028] Also, the HLB value is preferably in the range of 11 to 14, and more preferably in the range of 12 to 13.5. Preferably being in such a range enables good dissolution in the base oil and imparts more excellent conductivity. [[ID=!19]]

[0029] The type of the nonionic surfactant is not particularly limited as long as its HLB value is in the above-mentioned range. Among them, it is preferable that the hydrophobic group is of an alkyl ether type or an ester type.

[0030] Specifically, nonionic surfactants with alkyl ether-type hydrophobic groups are not particularly limited, but examples include polyoxyethylene 2-ethylhexyl ether, polyoxyethylene oleyl ether, polyoxyethylene lauryl ether, polyoxyethylene tridecyl ether, polyoxyethylene castor oil ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether, polyoxyalkylene 2-ethylhexyl ether, polyoxyalkylene nonyl ether, polyoxyalkylene tridecyl ether, and polyoxyethylene polyoxypropylene block copolymer.

[0031] Furthermore, examples of nonionic surfactants with ester-type hydrophobic groups include, but are not limited to, polyoxyethylene fatty acid esters, polyoxyethylene polyhydric alcohol fatty acid esters, propylene glycol fatty acid esters, polyhydric alcohol fatty acid esters, sorbitan esters, glycerin esters, propylene glycol esters, polyethylene glycol fatty acid esters, and others.

[0032] These nonionic surfactants may be used individually or in combination of multiple types.

[0033] The content of nonionic surfactants is not particularly limited, but is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, and especially preferably 0.5% by mass or more, based on the total amount of the grease composition. Furthermore, the content of nonionic surfactants is preferably 10% by mass or less, more preferably 5% by mass or less, and especially preferably 3% by mass or less, based on the total amount of the grease composition. When using multiple nonionic surfactants, it is preferable to blend them so that their total content falls within the above-mentioned range.

[0034] [others] In the grease composition according to this embodiment, in addition to the components described above, various additives commonly used in lubricating oils and greases, such as extreme pressure agents, antioxidants, rust inhibitors, and polymer additives, may be added as needed. Furthermore, additives other than those described above, such as friction modifiers, wear inhibitors, and solid lubricants, may also be added.

[0035] When these additives are included, it is preferable that their content be approximately 0.1% to 10% by mass of the total amount of the grease composition.

[0036] It goes without saying that the additives mentioned above may also be included as components of the base grease, along with the base oil and thickener.

[0037] ≪2. Method for Producing Grease Composition≫ As described above, the grease composition according to this embodiment is obtained by blending a nonionic surfactant having an HLB value in the range of 10 to 15 with a base grease containing a base oil and a thickener. This grease composition can be manufactured by a well-known method, similar to conventional grease compositions.

[0038] Specifically, for example, a base grease is prepared by kneading a base oil with a thickener such as a metal soap, a nonionic surfactant with an HLB value of 10 to 15 is added to this base grease and dispersed, and various additives are added and kneaded as needed to obtain it.

[0039] The mixing process can be carried out using well-known stirring and dispersion equipment such as a three-roll machine, a universal stirrer, a homogenizer, or a colloid mill. Furthermore, the process is not limited to adding each component sequentially as described above; each component may be added and mixed simultaneously. [Examples]

[0040] The present invention will be described in more detail below with reference to examples, but the present invention is not limited in any way to the following examples.

[0041] [Manufacturing of grease compositions] In the examples and comparative examples, grease compositions were prepared by blending additives into the base grease as shown in Table 1 below.

[0042] Specifically, in Examples 1 to 10, first, a fixed amount of base oil and fatty acid was weighed into a beaker and heated while stirring until the fatty acid melted. Primary and secondary saponification reactions were carried out using alkali to completely remove water, and then the mixture was heated to a predetermined temperature and allowed to cool naturally to produce the base grease. Next, the prepared base grease and the nonionic surfactants shown in Table 1 below were weighed and subjected to stirring and dispersion treatments to produce the grease composition. Stirring was performed using a universal stirrer. Dispersion was performed using a three-roll mill.

[0043] Furthermore, mineral oil and polyalphaolefin (PAO) were used as the base oils, and a base grease containing lithium complex soap as a thickener was prepared as described above.

[0044] Comparative Example 1 consisted only of base grease, while Comparative Examples 2 to 7 had the compounds shown in Table 1 below added as additives. Other than this, the procedures were the same as in the Examples.

[0045] [evaluation] The volume resistivity at room temperature was measured for the grease compositions of Examples 1-10 and Comparative Examples 1-7. Volume resistivity (resistance per unit volume) was calculated by applying a constant current between brass plates coated with grease and measuring the potential difference between the electrodes at a distance from each other. The results are shown in Table 1 below.

[0046] [Table 1]

[0047] As shown in the results in Table 1, the grease compositions (Examples 1-10) containing nonionic surfactants with HLB values ​​of 10-15 showed a significant reduction in resistance compared to the comparative grease compositions. In other words, it was found that the grease compositions of the examples can impart excellent conductivity.

Claims

1. A base grease containing a base oil and a thickener, It contains a nonionic surfactant with an HLB value of 10 to 15. Conductive grease composition.

2. The aforementioned nonionic surfactant has a hydrophobic group of the alkyl ether type or ester type. The conductive grease composition according to claim 1.

3. The content of the nonionic surfactant is in the range of 0.1% by mass to 10% by mass. The conductive grease composition according to claim 1 or 2.

4. The conductive grease composition is used in bearings. A conductive grease composition according to any one of claims 1 to 3.

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