Conductive composition comprising perfluoropolyether oil and carbon nanotubes

Abstract

According to the present invention, provided is a conductive composition containing a perfluoropolyether oil as a base oil and carbon nanotubes as a conductive substance, the carbon nanotubes having a diameter of 0.4-5.0 nm, and the content of the carbon nanotubes being 0.5-3.0 mass% relative to the total mass of the composition.

Description

Technical Field

[0001] This invention relates to conductive compositions that can be used in rolling bearings and the like. Background Technology

[0002] In recent years, variable-speed operation of rotating electric machines using inverter power supplies has been implemented in fields such as automobiles, railways, and home appliances. However, this has also generated electrical problems associated with inverter drives. For example, in bearings, there is damage known as electro-corrosion, caused by the application of voltage between the rotating shaft and the bearing, resulting in discharge. In the case of bearings, electro-corrosion occurs due to a potential difference or common-mode current flow between the inner and outer rings. Specifically, electro-corrosion progresses due to continuous discharge in the lubricating film between the balls (which are the rolling elements of the bearing) and the bearing's raceway surfaces.

[0003] Patent Document 1 addresses the issue of providing a conductive grease that exhibits good conductivity and good frictional properties, and provides a conductive grease containing a perfluoropolyether oil as a base oil and 0.1 to 20% by weight of carbon nanotubes with a diameter of 40 to 200 nm as a conductivity-imparting substance.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent No. 5747230 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] Patent document 1 evaluates the quality of conductivity by measuring the volume resistivity. Volume resistivity is a value calculated based on DC circuit measurements, but it is more appropriate to evaluate the difficulty of current flow in the inverter circuit that converts DC to AC, which is equivalent to a resistance index, by using impedance, which represents the difficulty of current flow in AC circuits.

[0009] The objective of this invention is to provide a conductive composition with low impedance.

[0010] Methods for solving problems

[0011] According to the present invention, the following conductive composition is provided.

[0012] 1. A conductive composition comprising a perfluoropolyether oil as a base oil and carbon nanotubes as a conductive material, wherein the diameter of the carbon nanotubes is 0.4 to 5.0 nm and the content of the carbon nanotubes is 0.5 to 3.0 by mass relative to the total mass of the composition.

[0013] 2. The conductive composition according to 1, wherein the carbon nanotubes are a single layer or two layers.

[0014] 3. The conductive composition according to 1 or 2, wherein it does not contain a thickener.

[0015] 4. The conductive composition according to 1 or 2, further comprising a thickener.

[0016] Invention Effects

[0017] According to the present invention, by combining perfluoropolyether oil with a specific amount of carbon nanotubes of a specific size, the impedance value, which represents the difficulty of current flow in an AC circuit, can be reduced. Thus, the conductive composition maintains a good energizing state, making charge accumulation difficult and suppressing discharge; therefore, the conductive composition of the present invention can suppress the generation of electro-corrosion. The composition of the present invention can also reduce the insulation breakdown voltage. Attached Figure Description

[0018] Figure 1 This is a schematic diagram showing the overall structure of carbon nanotubes. Detailed Implementation

[0019] <Base Oil>

[0020] Specifically, the perfluoropolyether oil that can be used in the compositions of the present invention can be, for example, the perfluoropolyether oil shown in formulas (1) to (5). Among them, the compound shown in formula (1) is particularly preferred.

[0021] [Chemistry 1]

[0022]

[0023] Where m and n are both numbers greater than or equal to 0.

[0024] The perfluoropolyether oil of the present invention can be used alone or in combination with two or more other types. However, it does not include base oils other than perfluoropolyether oils.

[0025] The kinematic viscosity at 40°C (measured according to JIS K2283) is preferably about 4 to 2000 mm. 2 / s. Further preferred kinematic viscosity is 60~500 mm³ / s. 2 / s. The kinematic viscosity of the base oil at 40°C is 4 mm. 2 At speeds above a certain value, it tends to suppress evaporation and separation of the base oil at high temperatures, and is therefore preferred. On the other hand, a kinematic viscosity of 2000 mm at 40°C is also desirable. 2 When the flow rate is below a certain value, it is easy to obtain adequate fluidity, and therefore preferred.

[0026] Additionally, if a perfluoropolyether oil with a relatively high kinematic viscosity at 40°C is used, such as 400mm... 2 Perfluoropolyether oils with a viscosity of / s or higher can make the conductive composition of the present invention into a paste, thus preventing leakage or dripping at the application site and improving ease of use depending on the application. As described later, thickeners and / or solid lubricants can also be added to the conductive composition of the present invention to form a solid or semi-solid grease. In this case, a perfluoropolyether oil with a relatively low kinematic viscosity at 40°C, such as 400 mm, can also be used. 2 Perfluoropolyether oil with a density of less than 1 / s.

[0027] The content of perfluoropolyether oil in the conductive composition of the present invention is preferably 50 to 99.5% by mass, more preferably 60 to 99.4% by mass, and even more preferably 70 to 99.3% by mass, based on the total mass of the composition. From the viewpoint of fluidity and heat resistance, a base oil content within such a range is preferred.

[0028] Carbon nanotubes

[0029] Carbon nanotubes are tubes made of stacked graphite-like carbon, with each layer forming a closed structure at both ends, similar to fullerenes. Their overall structure is roughly as follows: Figure 1 As shown.

[0030] The smallest reported diameter (“D”) of carbon nanotubes to date is 0.4 nm (Lu-Chang Qin et al., “The smallest carbon nanotube”, Nature, 408, 50 (2000)). In this invention, carbon nanotubes with a diameter of 0.4 nm or more can be used. On the other hand, if the content of carbon nanotubes in the composition increases, the torque increases, so it is preferable that the content of carbon nanotubes in the composition is low. By including carbon nanotubes with a diameter of 5.0 nm or less, even a small amount can achieve a sufficient discharge suppression effect. The composition of this invention preferably includes carbon nanotubes with a diameter of 0.4 to 5.0 nm, and more preferably carbon nanotubes with a diameter of 1.2 to 5.0 nm. On the other hand, in carbon nanotubes with a diameter greater than 5.0 nm, multilayer carbon nanotubes with three or more layers account for a large proportion, which are prone to discharge; therefore, the conductive composition of this invention preferably does not include carbon nanotubes with a diameter greater than 5.0 nm.

[0031] There is no particular limitation on the length of carbon nanotubes. For example, carbon nanotubes with a length greater than 5 μm and less than 600 μm can be used.

[0032] like Figure 1As shown, the diameter of the carbon nanotube refers to the shorter side in the top view, and the length refers to the longer side. The diameter and length of the carbon nanotube can be measured using a transmission electron microscope.

[0033] Typically, carbon nanotubes exist in single-layer, two-layer, or multi-layer (three or more layers). From the viewpoint of discharge suppression, single-layer or two-layer carbon nanotubes are preferred for use in the conductive composition of the present invention. From the viewpoint of discharge suppression, the conductive composition of the present invention preferably does not substantially contain three or more layers of multi-layer carbon nanotubes. For example, based on the total mass of the composition, it is preferably 0.5% by mass or less, more preferably 0.2% by mass or less, and even more preferably 0.1% by mass or less.

[0034] Carbon nanotubes have active sites on their surface, and at least some of them can be modified with OH, CH, CHO, etc. However, as the carbon nanotubes used in this invention, unmodified carbon nanotubes have a high affinity for base oils and are therefore preferred.

[0035] The carbon nanotube content in the conductive composition of the present invention is 0.5 to 3.0% by mass based on the total mass of the composition. Preferably, it is 0.6 to 2.0% by mass, more preferably 0.7 to 1.5% by mass. If the carbon nanotube content is within this range, the discharge suppression effect is well achieved, and therefore it is preferred.

[0036] By containing approximately 0.5% by mass of carbon nanotubes with a diameter of 0.4 to 5.0 nm in the perfluoropolyether oil, the composition of the present invention, in the case of a grease, achieves a hardness of approximately 440 corresponding to a penetration of 60 working cycles (measured according to JIS K 2220 7). On the other hand, by containing approximately 3.0% by mass of carbon nanotubes with a diameter of 0.4 to 5.0 nm, the composition of the present invention achieves a hardness of approximately 200 corresponding to the aforementioned penetration. It should be noted that, in the case of a grease, a penetration of less than 200 is generally not achievable (because if it is too hard, the grease cannot flow into the lubricated area), but the composition of the present invention can be used in areas where electrolytic corrosion prevention is required, even in areas where lubrication is not necessary. In such cases, a hardness of less than 200 corresponding to the aforementioned penetration is also possible.

[0037] The conductive composition of the present invention may be further formulated with thickeners, solid lubricants, antioxidants, rust inhibitors, extreme pressure agents, oiling agents, etc., as needed. From the viewpoint of oil retention and heat resistance, the presence of a thickener is preferred.

[0038] Thickener

[0039] By including a thickener, the conductive composition of the present invention can be formulated into a grease. From the viewpoint of oil retention and heat resistance, it is preferable to formulate it as a grease.

[0040] As a thickener that can be used in this invention, organic or inorganic thickeners commonly used in fluorinated greases can be used. Among them, polytetrafluoroethylene is preferred from the viewpoint of affinity with fluorinated oil.

[0041] Those skilled in the art can appropriately determine the cone penetration of the grease according to its application. For example, when applied to bearings, the cone penetration is typically 220 to 340, preferably 235 to 325. The amount of thickener is the amount required to obtain this cone penetration, for example, 1 to 30% by mass, preferably 5 to 15% by mass, based on the total mass of the grease composition.

[0042] Solid lubricants

[0043] By including a solid lubricant, the conductive composition of the present invention can be made into a grease or a complex.

[0044] Examples of solid lubricants that can be used in this invention include melamine cyanurate, graphite, onion-shaped carbon, nanodiamond, fluorinated graphite, black silica, granular polyethylene, granular polypropylene, polyethylene wax, polypropylene wax, oxidized polyethylene wax, ester wax, lignite wax, amide wax, spherical alumina, zinc oxide, mica, molybdenum disulfide, tungsten disulfide, calcium carbonate, boron nitride, copper, or nickel powders. From the viewpoint of lubricity at high temperatures, melamine cyanurate is preferred.

[0045] The content of solid lubricant is based on the total mass of the composition, for example, 0.01 to 5.0% by mass, preferably 0.1 to 1.0% by mass.

[0046] Antioxidants

[0047] By containing antioxidants, it can inhibit the oxidative deterioration of lubricating grease.

[0048] Examples of antioxidants that can be used in this invention include phenolic antioxidants and amine antioxidants.

[0049] Examples of phenolic antioxidants include 2,6-di-tert-butyl-p-cresol (BHT), 2,2'-methylenebis(4-methyl-6-tert-butylphenol), 4,4'-butylidenebis(3-methyl-6-tert-butylphenol), 2,6-di-tert-butylphenol, 2,4-dimethyl-6-tert-butylphenol, tert-butylhydroxyanisole (BHA), 4,4'-butylidenebis(3-methyl-6-tert-butylphenol), 4,4'-methylenebis(2,3-di-tert-butylphenol), 4,4'-thiobis(3-methyl-6-tert-butylphenol), and octadecyl alcohol ester of 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate. Among these, octadecyl alcohol ester of 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate is preferred from the perspectives of volatility and oil resistance.

[0050] Examples of amine-based antioxidants include N-n-butyl-p-aminophenol, 4,4'-tetramethyl-diaminodiphenylmethane, α-naphthylamine, N-phenyl-α-naphthylamine, phenothiazine, and alkyl diphenylamine. Among these, alkyl diphenylamine is preferred from both the perspectives of inhibiting sludge formation and viscosity increase, and from the perspective of cost.

[0051] The content of antioxidant is based on the total mass of the composition, for example, 0.01 to 5.0% by mass, preferably 0.1 to 1.0% by mass.

[0052] Rust Inhibitor

[0053] By containing rust inhibitors, it can prevent the lubricated surface from rusting.

[0054] Examples of rust inhibitors that can be used in this invention include inorganic and organic rust inhibitors.

[0055] Inorganic rust inhibitors include sodium silicate, Li carbonate, K carbonate, and Zn oxide, among other inorganic metal salts.

[0056] Examples of organic rust inhibitors include benzoic acid (Na), benzoic acid (Li), naphthenic acid (Zn), sebacic acid (Na), succinic acid, succinic anhydride, succinic acid derivatives of succinic acid half-ester, fatty acid amine salts, benzotriazole or its derivatives, benzothiazole or its derivatives, thiadiazole or its derivatives, etc.

[0057] From the viewpoint of demonstrating excellent results with small amounts, Na sebacic acid is preferred.

[0058] The content of the rust inhibitor is based on the total mass of the composition, for example, 0.01 to 5.0% by mass, preferably 0.1 to 1.0% by mass.

[0059] Extreme Pressure Agent

[0060] By containing extreme pressure agents, it can reduce friction and wear between the two sides of the metal and prevent burning and sticking.

[0061] Examples of extreme pressure agents that can be used in this invention include sulfurized oils and fats, sulfurized olefins, polysulfides, ashless dithiocarbamates, trioctyl phosphate, tricresyl phosphate, triphenyl thiophosphate, zinc dialkyl dithiocarbamate, molybdenum dialkyl dithiocarbamate, zinc dialkyl dithiophosphate, molybdenum dialkyl dithiophosphate, chlorinated paraffins, and chlorinated biphenyls, among other chlorinated compounds. From the viewpoint of suitability for high temperature and high load conditions, dialkyl dithiocarbamates and dialkyl dithiophosphates are preferred.

[0062] The content of the extreme pressure agent is based on the total mass of the composition, for example, 0.01 to 5.0% by mass, preferably 0.1 to 1.0% by mass.

[0063] <Oil-based agent>

[0064] By containing an oily agent, it can prevent direct contact between metals, reduce friction and wear.

[0065] Examples of oily agents that can be used in this invention include fatty acids or their esters, higher alcohols, polyols or their esters, aliphatic esters, aliphatic amines, fatty acid monoglycerides, lignite wax, and amide waxes. Among these, lignite wax is preferred from the viewpoint of being suitable for room temperature and low-load conditions.

[0066] The content of the oiliness agent is based on the total mass of the composition, for example, 0.01 to 5.0% by mass, preferably 0.1 to 1.0% by mass.

[0067] The compositions of the present invention can be readily manufactured by adding perfluoropolyether oil, carbon nanotubes, or any desired component and mixing them uniformly. Examples of such methods include mixing while heating using a planetary mixer and further uniformly mixing using a three-roll mill, and mixing using a mixer that mixes while rotating on its own axis and revolving around a point (hereinafter referred to as a "rotation-revolution mixer").

[0068] The compositions of the present invention can be used in rolling bearings, etc.

[0069] Example

[0070] The conductive compositions of the examples and comparative examples were prepared as follows. Specifically, base oil and carbon nanotubes were placed in a rotary mixer, "Defoaming Rentarō ARE-310" (manufactured by THINKY Corporation), and mixed for 10 minutes at 25°C and a rotation speed of 1400 rpm, in the manner shown in Table 1. The impedance of the compositions was then measured using the following method.

[0071] Impedance Measurement

[0072] Impedance was measured using an LCR meter “IM 3536” (manufactured by HIOKI Corporation), and the impedance values ​​at an AC frequency of 100,000 Hz (100 kHz) are shown in Table 1.

[0073] [Measurement Conditions]

[0074] Measurement temperature: 25℃

[0075] AC frequency: 10~1000000(1M)Hz

[0076] Measurement voltage: 0.2V

[0077] Thickness of conductive composition: 2mm

[0078] Diameter of conductive composition: 20mm

[0079] The base oils used in the examples and comparative examples are described below.

[0080] PFPE: Solvay's "Fomblin YPL1500" (kinematic viscosity @ 40℃ = 420 mmHg) 2 / s)

[0081] PAO: Polyalphaolefin (kinematic viscosity @40℃ = 48 mm) 2 / s)

[0082] The carbon nanotubes used in the examples and comparative examples are as follows.

[0083] [Table A]

[0084]

[0085] [Table 1]

[0086]

Claims

1. A conductive composition comprising a perfluoropolyether oil as a base oil and carbon nanotubes as a conductive material. The carbon nanotubes have a diameter of 0.4~5.0 nm, and The content of the carbon nanotubes is 0.5 to 3.0% of the total mass of the composition.

2. The conductive composition according to claim 1, wherein, The carbon nanotubes are single-layered or double-layered.

3. The conductive composition according to claim 1 or 2, wherein, It does not contain thickeners.

4. The conductive composition according to claim 1 or 2, further comprising a thickener.

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