Conductive composition containing silicone oil and carbon nanotubes

Abstract

To provide a conductive composition with a low volume resistivity.SOLUTION: The present invention provides a conductive composition that contains a silicone oil as a base oil and carbon nanotubes as a conductive substance, wherein the diameter of the carbon nanotubes is 0.4-5.0 nm and the content of the carbon nanotubes is 0.5-3.0 mass% relative to the total mass of the composition.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an electrically conductive composition that can be used in rolling bearings and the like. [Background technology]

[0002] Electrical damage is known to occur on the lubricating surfaces of steel and steel. For example, in bearings, damage called electrolytic corrosion occurs when a voltage is applied between the rotating shaft and the bearing, causing discharge. In the case of bearings, electrolytic corrosion occurs when there is a potential difference between the inner and outer rings of the bearing, or when a common mode current flows. More specifically, it progresses to electrolytic corrosion when continuous discharge occurs in the lubricating film between the ball and the raceway surface of the bearing.

[0003] The patent document 1 aims to provide a conductive grease that has excellent conductivity and is not likely to decrease over time, and to provide a rolling device that has a small electrical resistance value and is not likely to become charged over a long period of time, and provides a conductive grease that contains carbon nanotubes as a conductivity-imparting additive. The use of this grease reduces the electrical resistance value of bearings. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2002-332490 A Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a conductive composition having a low volume resistivity. [Means for solving the problem]

[0006] The present invention provides the following conductive composition. 1. Contains silicone oil as a base oil and carbon nanotubes as a conductive material. The carbon nanotube has a diameter of 0.4 to 5.0 nm, and A conductive composition, wherein the content of the carbon nanotubes is 0.5 to 3.0% by mass based on the total mass of the composition. 2. The conductive composition according to 1, wherein the carbon nanotubes are single-walled or double-walled. 3. The conductive composition according to 1 or 2, which does not contain a thickener. 4. The conductive composition according to 1 or 2, further comprising a thickener. Effect of the Invention

[0007] According to the present invention, by combining a silicone oil, which has a very high volume resistivity as an insulating oil, with a specific amount of carbon nanotubes of a specific size, the volume resistivity value, which indicates the difficulty of current flow, can be made particularly smaller than when other base oils are used. As a result, the conductive composition can maintain a good electrical conduction state and suppress discharge by making it difficult for charges to accumulate, so the conductive composition of the present invention can suppress the occurrence of electrolytic corrosion. The composition of the present invention can also reduce the dielectric breakdown voltage. [Brief description of the drawings]

[0008] [Figure 1] 1 is a schematic diagram showing the overall structure of a carbon nanotube; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] <Base oil> Specific examples of silicone oils that can be used in the composition of the present invention include dimethyl silicone oil, methyl phenyl silicone oil, methyl hydrogen silicone oil, modified silicone oil, etc. Of these, dimethyl silicone oil is particularly preferred.

[0010] The silicone oil of the present invention may be used alone or in combination of two or more kinds, but does not include base oils other than silicone oil. Kinematic viscosity at 25°C (measured according to JIS K2283) is approximately 5 to 10,000 mm 2 More preferably, the kinetic viscosity is 10 to 1000 mm 2 / s. The kinetic viscosity of the base oil at 25°C is 5mm 2 / s or more is preferable because it tends to suppress evaporation of the base oil and oil separation at high temperatures. 2 / s or less is preferable because it is easier to obtain appropriate fluidity. In addition, silicone oils having a relatively high kinetic viscosity at 25°C, e.g. 2 When a silicone oil having a kinetic viscosity of 100 mm / s or more is used, the conductive composition of the present invention can be made into a paste-like form, which prevents leakage or dripping at the application site and improves usability depending on the application. As will be described later, a thickener and / or a solid lubricant can be added to the conductive composition of the present invention to make it into a solid or semi-solid grease-like form. In this case, a silicone oil having a relatively low kinetic viscosity at 25°C, for example 100 mm / s, is used. 2 It may also be silicone oil having a viscosity of 1 / s or less. The content of the silicone oil in the conductive composition of the present invention is preferably 50 to 99.5 mass %, more preferably 60 to 99.4 mass %, and even more preferably 70 to 99.3 mass %, based on the total mass of the composition. The content of the base oil in such a range is preferable from the viewpoints of fluidity and heat resistance.

[0011] <Carbon nanotubes> Carbon nanotubes are tubes made of stacked graphite-like carbon, with both ends of each layer closed like fullerenes. The overall structure is roughly as shown in Figure 1. The minimum diameter ("D") of carbon nanotubes reported so far is 0.4 nm (Lu-Chang Qin et al., "The smallest carbon nanotube", Nature, 408, 50 (2000)). In the present invention, carbon nanotubes with a diameter of 0.4 nm or more can be used. On the other hand, since the torque increases as the content of carbon nanotubes in the composition increases, it is preferable that the content of carbon nanotubes in the composition is small. By containing carbon nanotubes with a diameter of 5.0 nm or less, a sufficient discharge suppression effect can be exhibited even in a small amount. The composition of the present invention preferably contains carbon nanotubes with a diameter of 0.4 to 5.0 nm, and more preferably contains carbon nanotubes with a diameter of 1.2 to 5.0 nm. On the other hand, in carbon nanotubes with a diameter of more than 5.0 nm, multi-walled carbon nanotubes with three or more walls account for a large proportion, which makes it easy to discharge, so it is preferable that the conductive composition of the present invention does not contain carbon nanotubes with a diameter of more than 5.0 nm.

[0012] The length of the carbon nanotube is not particularly limited. For example, carbon nanotubes having a length of 5 μm or more and 600 μm or less can be used. The diameter of a carbon nanotube refers to the short side in plan view, and the length of a carbon nanotube refers to the long side in plan view, as shown in Figure 1. The diameter and length of a carbon nanotube can be measured using a transmission electron microscope.

[0013] Generally, carbon nanotubes are available in single-wall, double-wall, and triple-wall or more multi-wall configurations, but the carbon nanotubes used in the conductive composition of the present invention are preferably single-wall or double-wall from the viewpoint of discharge suppression effect. From the viewpoint of discharge suppression effect, the conductive composition of the present invention is preferably substantially free of triple-wall or more multi-wall carbon nanotubes. For example, based on the total mass of the composition, the content is preferably 0.5 mass% or less, more preferably 0.2 mass% or less, and even more preferably 0.1 mass% or less. The carbon nanotubes have active sites on the surface, at least a part of which may be modified with OH, CH, CHO, etc. However, as the carbon nanotubes used in the present invention, unmodified ones are preferable because they have a higher affinity with the base oil.

[0014] The content of carbon nanotubes in the conductive composition of the present invention is 0.5 to 3.0 mass% based on the total mass of the composition, preferably 0.6 to 2.0 mass%, more preferably 0.7 to 1.5 mass%. When the content of carbon nanotubes is in such a range, it is preferable because the discharge suppression effect is effectively exhibited. By adding about 0.5% by mass of carbon nanotubes having a diameter of 0.4 to 5.0 nm to the silicone oil, the composition of the present invention has a hardness equivalent to a 60-stroke worked penetration (measured according to JIS K 2220 7.) of about 440 in terms of grease. On the other hand, by adding about 3.0% by mass of carbon nanotubes having a diameter of 0.4 to 5.0 nm, the composition of the present invention has a hardness equivalent to the above-mentioned penetration of about 200. Note that, in the case of grease, a penetration of less than 200 is generally not possible (because if it is too hard, the grease cannot flow into the lubricated part), but the composition of the present invention can be used in places where lubrication is not required as long as prevention of electrolytic corrosion is required. In this case, the hardness may be equivalent to a penetration of less than 200.

[0015] If necessary, the conductive composition of the present invention may further contain a thickener, a solid lubricant, an antioxidant, a rust inhibitor, an extreme pressure agent, an oiliness agent, etc. Among these, it is preferable to contain a thickener from the viewpoint of oil retention and heat resistance.

[0016] <Thickener> By adding a thickener, the conductive composition of the present invention can be made into a grease, which is preferable from the viewpoints of oil retention and heat resistance. The thickener that can be used in the present invention is at least one selected from the group consisting of, for example, soap-based thickeners such as Li soap and Ca soap; complex soap-based thickeners such as Li complex soap, Ca complex soap, Ca sulfonate complex soap, and Al complex soap; urea-based thickeners such as diurea, triurea, and tetraurea; urethane-based thickeners such as urethane; sodium terephthalamate; organo-bentonite; fluorine-based powders such as PTFE (polytetrafluoroethylene); fibrous cellulose; and aramid fibers. When the grease composition of the present invention is used for bearings, particularly motor bearings, from the viewpoint of low torque, the thickener preferably contains a Li soap or a urea compound, and is more preferably a urea compound. Those skilled in the art can appropriately determine the consistency of the grease depending on the application. For example, when applied to bearings, the consistency is typically 220 to 340, and preferably 235 to 325. The content of the thickener is the amount required to obtain this consistency, and is, for example, 1 to 30 mass %, and preferably 5 to 15 mass %, based on the total mass of the grease composition.

[0017] <Solid lubricants> By incorporating a solid lubricant, the conductive composition of the present invention can be made into a grease or a compound. Examples of solid lubricants that can be used in the present invention include melamine cyanurate, graphite, onion-like carbon, nanodiamond, graphite fluoride, silica, black silica, granular polyethylene, granular polypropylene, polyethylene wax, polypropylene wax, oxidized polyethylene wax, ester wax, montanic acid wax, amide wax, spherical alumina, zinc oxide, mica, molybdenum disulfide, tungsten disulfide, calcium carbonate, boron nitride, and metal powders such as copper and nickel. Among these, melamine cyanurate is preferred from the viewpoint of lubricity at high temperatures. The content of the solid lubricant is, for example, 0.01 to 5.0 mass %, and preferably 0.1 to 1.0 mass %, based on the total mass of the composition.

[0018] <Antioxidants> By including an antioxidant, it is possible to suppress the oxidative deterioration of the grease. The antioxidants that can be used in the present invention include phenol-based antioxidants and amine-based antioxidants. Examples of phenol-based 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-butyl-phenol, 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-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate. Of these, octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate is preferred from the viewpoints of volatility and oil resistance. Examples of the amine-based antioxidant include Nn-butyl-p-aminophenol, 4,4'-tetramethyl-di-aminodiphenylmethane, α-naphthylamine, N-phenyl-α-naphthylamine, phenothiazine, alkyldiphenylamines, etc. Among these, alkyldiphenylamines are preferred from the viewpoints of both the effectiveness of suppressing sludge formation and viscosity increase and the cost. The content of the antioxidant is, for example, 0.01 to 5.0 mass %, and preferably 0.1 to 1.0 mass %, based on the total mass of the composition.

[0019] <Rust inhibitor> By including a rust inhibitor, the occurrence of rust on the lubricated surface can be prevented. The rust inhibitors that can be used in the present invention include inorganic rust inhibitors and organic rust inhibitors. Examples of inorganic rust inhibitors include inorganic metal salts such as sodium silicate, lithium carbonate, potassium carbonate, and zinc oxide. Examples of organic rust inhibitors include sodium benzoate, benzoates of lithium benzoate, zinc naphthenate, carboxylates of sodium sebacate, succinic acid, succinic anhydride, succinic acid derivatives of succinic acid half esters, fatty acid amine salts, benzotriazole or derivatives thereof, benzothiazole or derivatives thereof, and thiadiazole or derivatives thereof. Of these, sodium sebacate is preferred because it exerts an excellent effect even in small amounts. The content of the rust inhibitor is, for example, 0.01 to 5.0 mass % and preferably 0.1 to 1.0 mass % based on the total mass of the composition.

[0020] <Extreme pressure agent> By including extreme pressure agents, it acts to reduce friction and wear between two metal surfaces and to prevent seizure. Examples of extreme pressure agents that can be used in the present invention include chlorine compounds such as sulfurized oils and fats, sulfurized olefins, polysulfides, ashless dithiocarbamates, trioctyl phosphate, tricresyl phosphate, triphenyl phosphorothioate, zinc dialkyldithiocarbamates, dialkyldithiocarbamates of molybdenum dialkyldithiocarbamates, zinc dialkyldithiophosphates, dialkyldithiophosphates of molybdenum dialkyldithiophosphates, chlorinated paraffins, and chlorinated diphenyls. Among these, dialkyldithiocarbamates and dialkyldithiophosphates are preferred from the viewpoint of suitability under high temperature and high load conditions. The content of the extreme pressure agent is, for example, 0.01 to 5.0 mass %, and preferably 0.1 to 1.0 mass %, based on the total mass of the composition.

[0021] <Oil-based agent> By including an oily agent, it prevents direct contact between metal and metal, thereby reducing friction and wear. Examples of oiliness agents that can be used in the present invention include fatty acids or their esters, higher alcohols, polyhydric alcohols or their esters, aliphatic esters, aliphatic amines, fatty acid monoglycerides, montan wax, amide waxes, etc. Among these, montan wax is preferred from the viewpoint of suitability under normal temperature and low load conditions. The content of the oily agent is, for example, 0.01 to 5.0 mass %, and preferably 0.1 to 1.0 mass %, based on the total mass of the composition.

[0022] The composition of the present invention can be easily produced by adding silicone oil, carbon nanotubes, and, if necessary, optional components, and mixing them uniformly. Examples of such methods include a method of kneading while heating using a planetary mixer, and then kneading uniformly using a three-roll mixer, and a method of kneading using a mixer that rotates and revolves to knead (hereinafter referred to as a "rotating and revolving mixer"). The composition of the present invention can be used for rolling bearings and the like. EXAMPLES

[0023] The conductive compositions of the examples and comparative examples were prepared as follows. That is, the base oil and carbon nanotubes were placed in a planetary centrifugal mixer "Awatori Rentaro ARE-310" (manufactured by Thinky Corporation) so as to have the components and contents shown in Table 1, and were mixed at 25°C and a revolution speed of 1400 rpm for 10 minutes to prepare the compositions. Then, the volume resistivity of the compositions was measured by the following method.

[0024] Evaluation of electrical properties by volume resistivity measurement Volume resistivity is the ratio of the DC electric field (V / m) applied to a sample at 25°C to the current per unit cross-sectional area applied to the sample at that time, and is equal to the resistance between the opposing faces of a cube of the sample with one side measuring 1 cm. The specific volume resistivity was measured based on the electrical insulating oil test method specified in JIS C2101. The results are shown in Table 1.

[0025] The base oils used in the examples and comparative examples are as follows. Silicone oil: Shin-Etsu Chemical's "KF-96-100cs" PAO: Polyalphaolefin Ether oil: MORESCO "Hi-Lube LB-68D" Ester oil: Kao Corporation's "Kaolube 279" Polyglycol oil: NOF Corp. "Unilube MB-7" The carbon nanotubes used in the examples and comparative examples are as follows.

[0026] [Table A]

[0027] [Table 1]

Claims

1. The silicone oil is used as a base oil, and carbon nanotubes are used as a conductive material. The carbon nanotubes have a diameter of 0.4 to 5.0 nm, and The conductive composition has a carbon nanotube content of 0.5 to 3.0 mass % based on the total mass of the composition.

2. The conductive composition of claim 1 , wherein the carbon nanotubes are single-walled or double-walled.

3. The conductive composition according to claim 1 or 2, which does not contain a thickener.

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

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