Conductive composition comprising silicone oil and carbon nanotubes

Abstract

According to the present invention, provided is a conductive composition containing a silicone 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% with respect 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] Electrically induced damage is known to exist on steel and its lubricated surfaces. For example, in bearings, there exists damage known as electro-corrosion, caused by the application of voltage between the rotating shaft and the bearing, resulting in a 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. More specifically, electro-corrosion progresses due to continuous discharge within the lubricating film between the balls and the bearing's raceway surfaces.

[0003] Patent Document 1 addresses the issue of providing a conductive grease with excellent conductivity and resistance to conductivity degradation over time, as well as a rolling device with low resistance that is not easily charged over long periods. Patent Document 1 provides a conductive grease incorporating carbon nanotubes as a conductivity-enhancing additive. Using this grease reduces the resistance of the bearing.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2002-332490 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] The objective of this invention is to provide a conductive composition with low volume resistivity.

[0009] Methods for solving problems

[0010] According to the present invention, the following conductive composition is provided.

[0011] 1. A conductive composition comprising silicone 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.

[0012] 2. The conductive composition according to 1, wherein the carbon nanotubes are a single layer or two layers.

[0013] 3. The conductive composition according to 1 or 2, wherein it does not contain a thickener.

[0014] 4. The conductive composition according to 1 or 2, further comprising a thickener.

[0015] Invention Effects

[0016] According to the present invention, by combining silicone oil, which itself has a very high volume resistivity as an insulating oil, with a specific amount of carbon nanotubes of a specific size, the volume resistivity, which represents the difficulty of current flow, can be significantly reduced compared to the use of other base oils. As a result, the above-mentioned conductive composition maintains a good energizing state, making it difficult for charge to accumulate, thereby 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

[0017] Figure 1 This is a schematic diagram showing the overall structure of carbon nanotubes. Detailed Implementation

[0018] <Base Oil>

[0019] Specifically, silicone oils that can be used in the compositions of the present invention include, for example, dimethyl silicone oil, methylphenyl silicone oil, methylhydrosilicone oil, modified silicone oil, etc. Among these, dimethyl silicone oil is particularly preferred.

[0020] The silicone oil of this invention can be used alone or in combination with two or more other types. However, it does not contain base oils other than silicone oil.

[0021] The kinematic viscosity at 25°C (measured according to JIS K2283) is preferably about 5 to 10,000 mm⁻¹ 2 / s. Further preferred kinematic viscosity is 10~1000 mm³ / s. 2 / s. If the kinematic viscosity of the base oil at 25°C is 5 mm. 2 A viscosity of 10000 mJ / s or higher tends to suppress evaporation and separation of the base oil at high temperatures, and is therefore preferred. On the other hand, if the kinematic viscosity at 25°C is 10000 mJ / s... 2 For speeds below / s, adequate fluidity is easily obtained, and therefore preferred.

[0022] Additionally, if a silicone oil with a relatively high kinematic viscosity at 25°C is used, such as 100mm... 2 Silicone oil 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 silicone oil with a relatively low kinematic viscosity at 25°C, such as 100 mm, can also be used. 2 Silicone oil with a viscosity of less than / s.

[0023] The content of silicone 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.

[0024] Carbon nanotubes

[0025] 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.

[0026] 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.

[0027] 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.

[0028] like Figure 1 As 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] By containing approximately 0.5% by mass of carbon nanotubes with a diameter of 0.4 to 5.0 nm in the silicone 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.

[0033] 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.

[0034] Thickener

[0035] 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.

[0036] The thickeners that can be used in this invention are, for example, at least one selected from the group consisting of soap-based thickeners such as Li soap and Ca soap, compound soaps such as Li complex soap, Ca complex soap, Ca sulfonate complex soap, Al complex soap, urea-based thickeners such as diurea, triurea, and tetraurea, urethane-based thickeners such as carbamates, sodium terephthalate, organo-modified bentonite, fluorine-based powders represented by PTFE (polytetrafluoroethylene), fibrous cellulose, and aromatic polyamide fibers.

[0037] When the grease composition of the present invention is used in bearings, particularly bearings for electric motors, from the viewpoint of low torque, the thickener preferably contains Li soap or urea compound, more preferably urea compound.

[0038] 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.

[0039] Solid lubricants

[0040] By including a solid lubricant, the conductive composition of the present invention can be made into a grease or a complex.

[0041] Examples of solid lubricants that can be used in this invention include melamine cyanurate, graphite, onion-shaped carbon, nanodiamond, fluorinated graphite, silica, 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.

[0042] 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.

[0043] Antioxidants

[0044] By containing antioxidants, it can inhibit the oxidative deterioration of lubricating grease.

[0045] Examples of antioxidants that can be used in this invention include phenolic antioxidants and amine antioxidants.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] Rust Inhibitor

[0050] By containing rust inhibitors, it can prevent the lubricated surface from rusting.

[0051] Examples of rust inhibitors that can be used in this invention include inorganic and organic rust inhibitors.

[0052] Inorganic rust inhibitors include sodium silicate, Li carbonate, K carbonate, and Zn oxide, among other inorganic metal salts.

[0053] 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.

[0054] From the viewpoint of demonstrating excellent results with small amounts, Na sebacic acid is preferred.

[0055] 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.

[0056] Extreme Pressure Agent

[0057] By containing extreme pressure agents, it can reduce friction and wear between the two sides of the metal and prevent burning and sticking.

[0058] 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.

[0059] 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.

[0060] <Oil-based agent>

[0061] By containing an oily agent, it can prevent direct contact between metals, reduce friction and wear.

[0062] 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.

[0063] 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.

[0064] The compositions of the present invention can be readily manufactured by adding silicone oil, carbon nanotubes, or any other desired components 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").

[0065] The compositions of the present invention can be used in rolling bearings, etc.

[0066] Example

[0067] 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 volume resistivity of the compositions was then measured using the following method.

[0068] Evaluation of electrical properties based on volume resistivity measurements

[0069] Volume resistivity represents the ratio of the DC electric field (V / m) applied to the specimen at 25°C to the current applied per unit cross-sectional area of ​​the specimen at that time, and is equal to the resistance between opposite faces of a cube with one side of 1 cm. The inherent volume resistivity was determined based on the test method for electrical insulating oils specified in JIS C2101. The results are shown in Table 1.

[0070] The base oils used in the examples and comparative examples are described below.

[0071] Silicone oil: Shin-Etsu Chemical Co., Ltd.'s "KF-96-100cs"

[0072] PAO: Polyalphaolefin

[0073] Ether oil: "HILUBE LB-68D" manufactured by MORESCO

[0074] Ester oil: Kao Corporation's "KAOLUBE 279"

[0075] Polyethylene glycol oil: Nippon Oil Company's "UNILUBE MB-7"

[0076] The carbon nanotubes used in the examples and comparative examples are as follows.

[0077] [Table A]

[0078]

[0079] [Table 1]

[0080]

Claims

1. A conductive composition comprising silicone oil as a base oil and carbon nanotubes as a conductive material. The carbon nanotubes have a diameter of 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.

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.

Images