Fluororubber compositions and seals for electric vehicles

Abstract

The purpose of the present invention is to provide a fluorine rubber composition that exhibits excellent sealing properties and electrical conductivity.　The fluorine rubber composition contains a fluorine rubber, 4-15 mass% of a conductive agent, and 5-15 mass% of an insulating filler, and the total amount of the conductive agent and the insulating filler is 15-25 mass%.

Description

Technical Field

[0001] The present invention relates to a fluororubber composition.

Background Art

[0002] Fluororubber compositions are excellent in oil resistance and fuel resistance, and are used as materials for sealing materials such as oil seals, O-rings, and packings in a wide range of fields such as automobiles and industrial machines. In recent years, electric vehicles (hereinafter sometimes referred to as "EVs") have begun to spread, and along with this, the prime mover has shifted from an engine to a motor. In an EV, a seal is provided between the motor, which is the prime mover, and the speed reducer.

[0003] Patent Document 1 (Japanese Patent No. 6288398) discloses Tecnoflon BR9151 and BR9171 as rubbers that do not deteriorate by reaction with additives in oil. Patent Document 2 (International Publication No. 2014 / 175079) discloses a fluororubber composed of a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene-ethylene-perfluoro(methyl vinyl ether) five-component copolymer, and discloses, for example, Tecnoflon BR9151 and BR9171 as specific examples of such fluororubbers.

[0004] In the field of conventional engine-powered automobiles and other technological fields, insulating fluororubber compositions are generally used as sealing materials. However, unlike conventional engine-powered automobiles, in new technological fields such as electric vehicles (EVs), if seals are made of insulating fluororubber compositions, the seals become charged, creating a potential difference, which raises concerns about galvanic corrosion in the vehicle's internal components. Furthermore, electromagnetic waves generated by the charging of the seals could potentially cause radio noise. In contrast, conventional EVs prevent charging and galvanic corrosion in the vehicle's internal components by connecting conductive parts such as carbon earth brushes and knuckle earths to the gearbox and body earth. However, such measures increase the number of parts in the EV, requiring new space for these parts, which raises concerns about increased costs and other problems.

[0005] Thus, conventional fluororubber compositions were desired to have excellent sealing properties as well as excellent conductivity from the viewpoint of preventing static electricity and galvanic corrosion. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Patent No. 6288398 [Patent Document 2] International Publication No. 2014 / 175079 [Overview of the project] [Problems that the invention aims to solve]

[0007] Therefore, the inventors discovered that excellent sealing properties and conductivity can be achieved by providing a fluororubber composition containing predetermined amounts of a conductive agent and an insulating filler, and in which the total content of the conductive agent and insulating filler is within a predetermined range, and thus completed the present invention. In other words, the present invention provides a fluororubber composition having excellent sealing properties and conductivity. [Means for solving the problem]

[0008] The gist of the present invention is as follows: [1] Fluororubber and 4-15% by mass of conductive agent, 5-15% by mass of insulating filler and It contains, A fluororubber composition in which the total content of the conductive agent and the insulating filler is 15 to 25% by mass. [2] The fluororubber composition according to [1] above, wherein the IRHD hardness after vulcanization is 85 or less. [3] The fluororubber composition according to [1] or [2] above, wherein the volume resistivity after vulcanization is 8 Ω·cm or less. [4] A seal for an electric vehicle comprising the fluororubber composition described in any one of [1] to [3] above. [Effects of the Invention]

[0009] This provides a fluororubber composition with excellent sealing properties and conductivity. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a partial cross-sectional view of a sealing device that includes a fluororubber composition as a seal according to one embodiment. [Figure 2] Figure 2 is a partial perspective view of the sealing device shown in Figure 1. [Modes for carrying out the invention]

[0011] The fluororubber composition of the present invention contains fluororubber, 4 to 15% by mass of a conductive agent, and 5 to 15% by mass of an insulating filler, with the total content of the conductive agent and insulating filler being 15 to 25% by mass. A conductive agent content of 4% by mass or more in the fluororubber composition provides excellent conductivity. Furthermore, a conductive agent content of 15% by mass or less results in an appropriate hardness for the fluororubber composition, and excellent fluidity and moldability. As a result, the fluororubber composition can have excellent sealing properties. A insulating filler content of 5 to 15% by mass in the fluororubber composition provides an appropriate hardness. Additionally, a total content of 15 to 25% by mass of the conductive agent and insulating filler in the fluororubber composition allows for both excellent sealing properties and conductivity. For example, when a seal made of the vulcanized fluororubber composition of the present invention is used in an EV, the seal itself has excellent conductivity and sealing properties, eliminating the need for extra parts such as earth brushes and knuckle earths as in conventional EVs, thus saving space inside the EV. Furthermore, although rotating shafts such as shafts generate heat due to their high rotational speed, seals made from the fluororubber composition of the present invention have excellent heat resistance, so they can maintain excellent conductivity and sealing properties even when used at high temperatures as seals for rotating shafts, etc. The fluororubber composition may be unvulcanized or post-vulcanized, but both the unvulcanized and post-vulcanized fluororubber compositions contain 4 to 15% by mass of a conductive agent and 5 to 15% by mass of an insulating filler based on the entire fluororubber composition, with the total content of the conductive agent and insulating filler being 15 to 25% by mass. The fluororubber composition is preferably a fluororubber composition for sealing, and more preferably a fluororubber composition for sealing in electric vehicles.

[0012] The fluororubber composition preferably has an IRHD (International Rubber Hardness Degree) hardness of 85 or less after vulcanization, more preferably 70 to 80, and even more preferably 70 to 75. An IRHD hardness of 85 or less after vulcanization results in good fluidity of the fluororubber composition, allowing for excellent moldability. For example, the Compression Set (CS) of the fluororubber composition after treatment at 175°C for 22 hours can be reduced to less than 40%. As a result, products such as seals made from the fluororubber composition are less prone to deformation and associated leakage, resulting in highly durable products. To measure the IRHD hardness of the fluororubber composition, a sample of vulcanized fluororubber composition with dimensions of 140 mm × 100 mm × 2 mm is used. This sample is prepared by first vulcanizing a fluororubber composition at 160-200°C for 3-30 minutes using a molding press to achieve dimensions of 140 mm x 100 mm x 2 mm, followed by second vulcanization at 150-250°C for 0.5-24 hours using a constant temperature bath. Prior tests have confirmed that the IRHD hardness of the fluororubber composition does not change within the above temperature and vulcanization time ranges. The IRHD hardness of the fluororubber composition is measured in accordance with JIS K6253-2:2012, using a DigiTest II manufactured by Barleys, under IRHD (micro) conditions.

[0013] The volume resistivity of the fluororubber composition after vulcanization is preferably 8 Ω·cm or less, more preferably 6 Ω·cm or less, and even more preferably 3 Ω·cm or less. For measuring the volume resistivity of the fluororubber composition, a sample consisting of a vulcanized fluororubber composition with dimensions of 140 mm × 100 mm × 2 mm is used. This sample is prepared by first vulcanizing the fluororubber composition at 160-200°C for 3-30 minutes using a molding press to achieve dimensions of 140 mm × 100 mm × 2 mm, followed by second vulcanization at 150-250°C for 0.5-24 hours using a constant temperature bath. Prior tests have confirmed that the volume resistivity of the fluororubber composition does not change within the above temperature and vulcanization time ranges. The volume resistivity of the fluororubber composition was measured according to the four-probe method in accordance with JIS K7194:1994. The measurement device used was a Hioki Milliohm High Tester 3540 (product name), and the measurement was performed at room temperature using the parallel terminal electrode method.

[0014] The Compression Set (CS) of the fluororubber composition is preferably less than 40%, more preferably 35% or less, and even more preferably 30% or less after treatment at 175°C for 22 hours. Preferably, the CS of the fluororubber composition can be reduced to less than 40% by setting the IRHD hardness of the fluororubber composition to 85 or less. The CS of the fluororubber composition is measured using the RSTD Gear Oven 45-P (product name) manufactured by Toyo Seiki Co., Ltd. as the measuring device, and the measurement is performed under conditions of a compression ratio of 25%.

[0015] The following describes in detail each component constituting the fluororubber composition of the present invention. (Fluororubber) While not particularly limited, homopolymers or copolymers of one or more fluorine-containing olefins can be used as fluororubbers. Examples of fluorine-containing olefins include vinylidene fluoride, hexafluoropropylene, pentafluoropropylene, trifluoroethylene, trifluorochloroethylene, tetrafluoroethylene, vinyl fluoride, perfluoroacrylic acid ester, perfluoroalkyl acrylate, perfluoromethyl vinyl ether, perfluoroethyl vinyl ether, and perfluoropropyl vinyl ether. These fluorine-containing olefins can be used individually or in combination of two or more. Examples of fluororubbers include vinylidene fluoride-hexafluoropropylene binary copolymer, vinylidene fluoride-tetral-oroethylene-hexafluoropropylene ternary copolymer, and vinylidene fluoride-hexafluoropropylene-perfluoroalkyl vinyl ether ternary copolymer.

[0016] Fluororubber may be obtained by solution polymerization, turbidity polymerization, or emulsion polymerization, or it may be available as a commercially available product. Examples of commercially available fluororubber products that can be used include Chemours' "VITON® A-500", "VITON® B-600", "VITON® GBL-600S", and "VITON® GLT-600S", and Daikin Industries' "Daiel® G801" and "Daiel® GBR-6002". Furthermore, fluororubber that can be vulcanized with polyols, fluororubber that can be vulcanized with peroxides, etc., can be used.

[0017] (Conductive agent) The fluororubber composition before or after vulcanization contains 4 to 15% by mass of a conductive agent. By containing 4 to 15% by mass of the conductive agent, the fluororubber composition can have excellent conductivity and sealing properties. The conductive agent is not particularly limited as long as it can impart conductivity to the fluororubber composition, but the conductive agent is preferably at least one material selected from the group consisting of Ketjen black, graphite, carbon nanotubes, and carbon fibers. The content of the conductive agent in the fluororubber composition is preferably 5 to 15% by mass, more preferably 5 to 12% by mass. By the content of the conductive agent in the fluororubber composition being within the above range, excellent conductivity and sealing properties can be maintained while other physical properties can be within the desired range. The conductive agent in the fluororubber composition may be one type or two or more types.

[0018] (Insulating filler) The fluororubber composition before or after vulcanization contains 5 to 15% by mass of an insulating filler. By containing 5 to 15% by mass of the insulating filler, the fluororubber composition can have an appropriate hardness. For example, when the vulcanized fluororubber composition is used as a seal, the seal can have excellent sealing performance. The insulating filler is not particularly limited as long as it has insulating properties, but the insulating filler is preferably at least one material selected from the group consisting of wollastonite and clay. Also, the insulating filler preferably has an aspect ratio (L / D) of 2 to 20. The content of the insulating filler in the fluororubber composition is preferably 7 to 15% by mass. By the content of the insulating filler in the fluororubber composition being within the above range, the fluororubber composition can have an appropriate hardness and can achieve both good conductivity and sealing performance. The insulating filler in the fluororubber composition may be one type or two or more types. The total content of the conductive agent and the insulating filler in the fluororubber composition before or after vulcanization is 15 to 25% by mass. By the total content of the conductive agent and the insulating filler in the fluororubber composition being 15 to 25% by mass, both excellent sealing performance and conductivity can be achieved. The total content of the conductive agent and the insulating filler in the fluororubber composition is preferably 18 to 25% by mass, and more preferably 19 to 24% by mass. By the total content of the conductive agent and the insulating filler in the fluororubber composition being within the above range, a product with both excellent sealing performance and conductivity can be obtained.

[0019] (Other additives) The fluororubber composition of the present invention contains a fluororubber and a conductive agent, but the fluororubber composition may further contain, as components other than the fluororubber and the conductive agent, a vulcanizing agent; processing aids such as wax, metal soap, carnauba wax, etc.; acid acceptors such as calcium hydroxide, magnesium oxide, zinc oxide, hydrotalcite, etc.; antioxidants; thermoplastic resins; plasticizers; softeners; foaming agents; foaming aids; colorants; dispersants; flame retardants; tackifiers; mold release agents; various metal powders, etc.

[0020] (Method for producing fluororubber composition) The fluororubber composition before vulcanization of the present invention can be obtained by kneading a material containing 4 to 15% by mass of a conductive agent, 5 to 15% by mass of an insulating filler, and fluororubber, etc., using a kneading facility (roller, kneader, etc.), wherein the total content of the conductive agent and insulating filler is 15 to 25% by mass. The fluororubber composition after vulcanization of the present invention can be obtained by adding a vulcanizing agent to the fluororubber composition obtained as described above, and then heating it in a molded state. When obtaining a desired molded product by molding and vulcanizing the fluororubber composition, known manufacturing equipment can be used. For example, the fluororubber composition can be placed into a cavity of a predetermined shape using an injection molding machine, compression molding machine, etc., and heated under appropriate conditions to obtain a vulcanized fluororubber composition. In this case, vulcanization may be carried out in multiple stages. For example, primary vulcanization may be performed with the fluororubber composition pressed into a predetermined shape, and secondary vulcanization may be performed on the fluororubber composition after primary vulcanization.

[0021] (Molded articles made from fluororubber composition) As described above, molded articles of a desired shape can be produced by molding and vulcanizing a fluororubber composition. The molded article of the fluororubber composition is preferably a seal, and more preferably a seal for electric vehicles. The seal, which is a molded article of the fluororubber composition, preferably has an overall conductivity of 100 Ω or less, more preferably 70 Ω or less, and even more preferably 50 Ω or less. The overall conductivity of the seal can be evaluated as the electrical resistance value obtained by measuring it under conditions of 500 kHz / 5V using an impedance analyzer (IM3570 (device name), manufactured by HIOKI E.E. CORPORATION) with the shaft and housing in contact with a wire after the seal has been installed so as to be fitted between the shaft and housing of a rotary testing machine.

[0022] Figure 1 is a partial cross-sectional view of a sealing device 1 according to one embodiment, which includes the fluororubber composition of the present invention as a seal, and Figure 2 is a partial perspective view of the sealing device 1 shown in Figure 1. In Figure 1, one side of the cross-section (hereinafter also simply referred to as the cross-section) of the sealing device 1 along the axis x is shown with respect to the axis x, and in Figure 2, a part of the sealing device 1 is shown in a state in which it has been cut along the plane along the axis x. The sealing device 1 according to this embodiment is intended to seal an annular space between an inner circumferential member and an outer circumferential member that rotate relative to each other, for example, in electric vehicles (EVs) such as battery electric vehicles (BEVs), hybrid vehicles (HVs), and fuel cell vehicles (FCVs). The inner circumferential member and the outer circumferential member are, for example, members of a drive device equipped with an electric motor, the inner circumferential member is, for example, the rotation shaft of the electric motor, and the outer circumferential member is, for example, the housing of the drive device through which the rotation shaft of the electric motor passes. In this embodiment, the sealing device 1 is designed to seal the annular space 104 between the shaft 101, which is the rotating shaft of the electric motor (not shown) of the drive unit (not shown), and the housing 102 of the drive unit, as shown in Figure 1. However, the application of the sealing device 1 is not limited to such drive units.

[0023] As shown in Figures 1 and 2, the sealing device 1 includes a conductive elastic body portion 2, which is an annular member around an axis x and is made of the vulcanized fluororubber composition of the present invention. The conductive elastic body portion 2 is capable of contacting the shaft 101 and housing 102 of the electric motor. Furthermore, the conductive elastic body portion 2 is capable of forming a conductive circuit 3 between the shaft 101 and housing 102 of the electric motor. For example, the impedance of the conductive circuit 3 during the rotation of the shaft 101 of the electric motor at a peripheral speed of 60 m / s or less is between 0.01 Ω and 100 Ω. The configuration of the sealing device 1 will be described in detail below.

[0024] The conductive elastic body part 2 is designed to maintain electrical contact with the shaft 101 even when subjected to a force that would cause the contact between the conductive elastic body part 2 and the shaft 101 to be lost due to the rotation of the electric motor shaft 101. Conventional conductive lip made of a conductive elastic material of the so-called radial type is subjected to a force from the rotating shaft of the application that causes the contact between the conductive lip and the rotating shaft to be lost when the rotating shaft of the application is rotating at high speed. When the rotating shaft is rotating at a speed of 30 m / s or more, it is thought that the contact area between the conductive lip and the rotating shaft may decrease due to this force that causes the contact to be lost. For this reason, it is thought that when the rotating shaft is rotating at a speed of 30 m / s or more, the conductivity between the conductive lip and the rotating shaft may decrease in conventional radial type conductive lip. The peripheral speed of the rotating shaft is the distance that the outer surface of the rotating shaft moves per unit time. More specifically, the peripheral speed of the rotating shaft is the distance that a point on the outer surface of the rotating shaft moves per unit time.

[0025] In contrast, the sealing device 1 maintains electrical contact between the conductive elastic body part 2 and the shaft 101 even when the shaft 101 rotates at high speed, by interposing a lubricant such as conductive grease G. The impedance of the conductive circuit 3 formed by the conductive elastic body part 2 is set to be, for example, between 0.01Ω and 100Ω even when the shaft 101 of the electric motor rotates at a peripheral speed of 60 m / s or less. Thus, the sealing device 1 can maintain an impedance in the range of, for example, between 0.01Ω and 100Ω even when the shaft 101 of the electric motor rotates at high speed, thereby suppressing a decrease in conductivity.

[0026] As shown in Figures 1 and 2, the sealing device 1 has an annular shape around its axis x and is attached to the annular space 104 between the through hole 103 provided in the housing 102 and the shaft 101 of the electric motor that exits the housing 102 through the through hole 103, thereby sealing the space 104. This prevents the sealed material, such as lubricating oil, inside the housing 102 from leaking to the atmosphere. In the illustrated example, as shown in Figure 1, the side indicated by the symbol I is the side with the material to be sealed, and the side indicated by the symbol O is the side with the atmosphere. Also, as shown in Figure 1, the axis x of the sealing device 1 attached to the space 104 coincides with or approximately coincides with the axis of the shaft 101. In the illustrated example, the axis x of the sealing device 1 coincides with the axis of the shaft 101.

[0027] The sealing device 1 includes a reinforcing ring 10, which is an annular metal member around an axis x, and a conductive elastic body 2, which is a seal body 20 attached to the reinforcing ring 10. The reinforcing ring 10, as shown in Figures 1 and 2, for example, has a cylindrical portion 11 that extends along the axis x, a bent portion 12 that is an annular portion folded back from the atmospheric side O end (end 11a) of the cylindrical portion 11 toward the object to be sealed I, and an annular portion 13 that extends inward from the inner circumference end (end 12a) of the bent portion 12. The cylindrical portion 11, the bent portion 12, and the annular portion 13 are parts of the reinforcing ring 10 integrally formed from the same metal material. The reinforcing ring 10 is formed, for example, by press-forming an annular metal plate. The cylindrical portion 11 is a cylindrical or substantially cylindrical part with axis x as its central axis or substantially as shown in Figure 1, for example, and is shaped to fix the sealing device 1 to the through hole 103 when the sealing device 1 is attached to the through hole 103 of the housing 102. Note that the material of the reinforcing ring 10 is not limited to metal.

[0028] The conductive elastic body portion 2, which serves as the seal body 20, is integrally molded by cross-linking and bonding to the reinforcing ring 10. The conductive elastic body portion 2 is, for example, a molded body obtained by insert molding of the fluororubber composition of the present invention, with the reinforcing ring 10 as an insert component. As shown in Figures 1 and 2, for example, the conductive elastic body portion 2 is attached to the reinforcing ring 10 so as to cover the entire reinforcing ring 10, and has a seal portion 21, a base portion 22, a gasket portion 23, and a cover portion 24. The seal portion 21 has a conductive lip portion 30 and a seal lip portion 40. The seal portion 21, base portion 22, gasket portion 23, and cover portion 24 are integrally formed from the vulcanized fluororubber composition of the present invention and constitute the seal body 20.

[0029] The base portion 22 is located at the inner circumferential end of the annular portion 13 of the reinforcing ring 10 and its vicinity, the gasket portion 23 is the portion that covers the outer circumferential surface 11b of the cylindrical portion 11 of the reinforcing ring 10, and the cover portion 24 is the portion that covers the reinforcing ring 10 between the base portion 22 and the gasket portion 23. The outer diameter of the gasket portion 23 is the same as or larger than the diameter of the inner circumferential surface 103a of the through hole 103 of the housing 102. Therefore, when the sealing device 1 is installed in the space 104 of the housing 102, the gasket portion 23 is compressed radially between the cylindrical portion 11 of the reinforcing ring 10 and the housing 102, fixing the sealing device 1 to the housing 102 and sealing the space between the inner circumferential surface 103a of the through hole 103 of the housing 102 and the sealing device 1.

[0030] As described above, the seal portion 21, as shown in Figures 1 and 2, is a bifurcated portion from the base portion 22 and has a conductive lip portion 30 and a seal lip portion 40 that extend backward from each other along the axis x. The conductive lip portion 30 extends from the atmospheric side O end of the base portion 22 toward the atmospheric side O so as to be able to contact the outer circumferential surface 101a of the shaft 101. The seal lip portion 40 extends from the sealed object side I end of the base portion 22 toward the sealed object side I so as to be able to contact the outer circumferential surface 101a of the shaft 101. The conductive lip portion 30 extends, for example, parallel to or approximately parallel to the axis x, and the seal lip portion 40 extends, for example, parallel to or approximately parallel to the axis x.

[0031] As shown in Figures 1 and 2, the seal lip portion 40 has a seal lip 41 at the end on the side I of the object to be sealed. The seal lip 41 is a portion that extends along an annular or substantially annular ring with axis x as its center or substantially its center, and its cross-sectional shape is a wedge shape that is convex toward the inner circumference. The seal lip portion 40 is configured such that the seal lip 41 contacts the outer circumferential surface 101a of the shaft 101.

[0032] Specifically, for example, as shown in Figure 2, the seal lip 41 has a side surface 42 for the object to be sealed and an atmospheric side surface 43, which form the wedge-shaped cross-section described above. The side surface 42 for the object to be sealed is an annular surface facing the inner circumference and the side I for the object to be sealed, and the atmospheric side surface 43 is an annular surface facing the inner circumference and the side O for the atmosphere. As shown in Figures 1 and 2, the side surface 42 for the object to be sealed and the atmospheric side surface 43 intersect on the inner circumference, forming a ring-shaped or substantially ring-shaped tip 44 at the intersection.

[0033] Multiple screw grooves 45 are provided on the atmospheric side 43 to serve as fluid return sections. These screw grooves 45 are recessed from the atmospheric side 43 and are inclined in the direction of rotation of the shaft 101, starting from the tip 44. As the shaft 101 rotates, the screw grooves 45 generate an airflow from the atmospheric side 43 toward the sealed object side 42, creating a screw pump action that returns the sealed object (not shown) that has seeped out to the atmospheric side O beyond the tip 44 back to the sealed object side I.

[0034] As shown in Figures 1 and 2, the seal lip portion 40 is formed such that the seal lip 41 contacts the outer circumferential surface 101a of the shaft 101 with a predetermined amount of tension at and near the tip 44. A garter spring 47 is also provided on the seal lip portion 40 at a position facing away from the seal lip 41. The garter spring 47 applies a tensioning force to the seal lip portion 40 that pushes the seal lip 41 inward, thereby increasing the tensioning force that presses the seal lip 41 against the outer circumferential surface 101a of the shaft 101.

[0035] The conductive lip portion 30 has a conductive lip 31 at the end facing the atmosphere O, as shown in Figures 1 and 2. The conductive lip 31 is a portion extending along an annular or substantially annular shape with axis x as its center or substantially its center, and its cross-sectional shape is, for example, a rectangular or trapezoidal shape that is convex toward the inner circumference. The conductive lip portion 30 is configured such that the conductive lip 31 contacts the outer circumferential surface 101a of the shaft 101.

[0036] Specifically, for example, the conductive lip 31 has an annular contact surface 32 that forms the rectangular or trapezoidal cross-section described above, as shown in Figures 1 and 2. The contact surface 32 is in surface contact with the outer circumferential surface 101a of the shaft 101, and is, for example, a cylindrical surface or a substantially cylindrical surface with axis x as the central axis or substantially the central axis. The contact surface 32 is not limited to a cylindrical surface or a substantially cylindrical surface, and may be a surface of other shape. The contact surface 32 may be, for example, an annular surface that draws a curved line that is convex on the inner circumferential side in cross-section. In this case, in the operating state, the contact surface 32 deforms along the outer circumferential surface 101a of the shaft 101, thereby expanding or maintaining the contact area with respect to the outer circumferential surface 101a of the shaft 101.

[0037] Furthermore, as shown in Figure 2, multiple communication grooves 34 are provided on the contact surface 32 of the conductive lip 31. The communication grooves 34 are grooves that extend along the axis x over the entire width of the contact surface 32 in the axial direction x, and are recessed outward from the contact surface 32. They intersect and communicate with the grease grooves 33, and connect the space S (see Figure 1) created between the shaft 101, the conductive lip portion 30, and the seal lip portion 40 with the space on the atmospheric side O. The communication grooves 34 extend, for example, parallel or approximately parallel to the axis x, and are provided at equal or approximately equal angular intervals around the axis x.

[0038] As shown in Figures 1 and 2, a garter spring 35 is provided on the conductive lip portion 30 at a position facing away from the conductive lip 31. The garter spring 35 applies a tensioning force to the conductive lip portion 30 that pushes the conductive lip 31 inward, thereby increasing the tensioning force that presses the conductive lip 31 against the outer surface 101a of the shaft 101. [Examples]

[0039] Next, examples will be described to further clarify the effects of the present invention, but the present invention is not limited to these examples.

[0040] (Examples 1-3, Comparative Examples 1-9) In each example, a fluororubber composition before vulcanization was produced by kneading the materials according to the formulations shown in Table 1 below. The names of the materials used in each example are listed below. Fluororubber: VITON (registered trademark) A-500 (manufactured by Chemours) Ketjenblack A: KETJENBLACK EC600JD (manufactured by Lion Specialty Chemicals) Ketjenblack B: Denka Black (manufactured by Denka Co., Ltd.) Graphite: A-0 (manufactured by Higashi Nippon Carbon Co., Ltd.) Carbon fiber: S-241 (manufactured by Osaka Gas Chemical Co., Ltd.) Carbon nanotube: Lucan CP1001M (manufactured by LG Chem) Wollastonite: TREMIN® 283-400 (manufactured by QUARZWERKE) Clay: NN Kaolin Clay (manufactured by Takehara Chemical Co., Ltd.) [Table 1]

[0041] The fluororubber compositions manufactured as described above were evaluated for hardness (durometer A hardness), hardness (IRHD hardness), compression set (CS) after 22 hours at 175°C, volume resistivity, conductivity of the seal, and sealing performance. The methods for preparing and measuring the samples used for each evaluation are shown below.

[0042] (1) Hardness (Durometer A hardness): A fluororubber composition was vulcanized under the conditions of primary vulcanization at 180°C for 4 minutes and secondary vulcanization at 230°C for 9 hours to prepare a sample with dimensions of 2 mm thickness. Then, the Durometer A hardness of this sample was measured at room temperature in accordance with JIS K6253-2:2012 using a constant-pressure rubber hardness tester P1-A (device name) manufactured by Polymer Instruments Co., Ltd. (2) Hardness (IRHD hardness): The fluororubber composition was vulcanized under the conditions of primary vulcanization at 180°C for 4 minutes and secondary vulcanization at 230°C for 9 hours to prepare a sample with dimensions of 140 mm × 100 mm × 2 mm. Then, the IRHD hardness of this sample was measured under IRHD (micro) conditions using a DigiTest II (instrument name) manufactured by Barleys Corporation in accordance with JIS K6253-2:2012. (3) CS (Compression Set) after 22 hours at 175°C: The compression set of the fluororubber composition was measured after 22 hours of heating at 175°C with a compression ratio of 25%. (4) Volume resistivity: The fluororubber composition was vulcanized under the conditions of primary vulcanization at 180°C for 4 minutes and secondary vulcanization at 230°C for 9 hours to prepare a sample with dimensions of 140 mm × 100 mm × 2 mm. The volume resistivity of this sample was then measured at room temperature using the parallel terminal electrode method with a milliohm high tester 3540 (device name) manufactured by HIOKI E. CORPORATION, in accordance with the four-probe method conforming to JIS K7194:1994.

[0043] (5) Conductivity of the seal: The fluororubber composition was vulcanized under the conditions of primary vulcanization at 180°C for 4 minutes and secondary vulcanization at 230°C for 9 hours to form an oil seal with an inner diameter of 85 mm, an outer diameter of 105 mm, and a width of 13 mm. Next, the oil seal was installed so as to fit between the shaft and housing of the rotary testing machine, and with the shaft and housing in contact with a wire, the electrical resistance was measured using an impedance analyzer (IM3570 (device name), manufactured by HIOKI E.E. CORPORATION) under the conditions of 500 kHz / 5V. (6) Sealing performance: The fluororubber composition was vulcanized under the conditions of primary vulcanization at 180°C for 4 minutes and secondary vulcanization at 230°C for 9 hours to form an oil seal with an inner diameter of 85 mm, an outer diameter of 105 mm, and a width of 13 mm. Next, the oil seal was installed so that it was fitted between the shaft and housing of the rotating test machine and the sealing surface of the oil seal faced outwards. After this, a predetermined amount of oil (oil type: SN0W-20 (API standard, ILSAC standard), oil temperature: 120°C) was poured into the rotating test machine so that it reached the center of the shaft, and the shaft was rotated at 5000 rpm. The amount of oil that leaked into the atmosphere during the rotation of the shaft was measured as the suction amount. If the amount of oil leaked per minute was less than 0.2 ml, it was evaluated as "×", and if the amount of oil leaked per minute was 0.2 ml or more, it was evaluated as "○". Note that a larger amount of oil leaking out indicates a larger suction amount, and therefore can be evaluated as having excellent sealing performance. The results of each evaluation measured as described above are shown in Table 1. In Table 1, a "-" indicates that it was not possible to manufacture the oil seal and therefore measurement was not possible.

[0044] As shown in Examples 1-3 of Table 1, the fluororubber compositions of the present invention exhibited excellent conductivity, with a volume resistivity of 8.0 Ω·cm or less and a seal conductivity of 90 Ω or less, and also showed good sealing performance. On the other hand, as shown in Comparative Examples 1-9 of Table 1, the fluororubber compositions of the comparative examples all showed very high values ​​for volume resistivity and seal conductivity, or were unmeasurable, or showed poor sealing performance. From the above, it was confirmed that the present invention can provide fluororubber compositions with excellent conductivity and sealing performance. [Explanation of symbols]

[0045] 1 Sealing device 2 Conductive elastic body 3 Conductive Circuits 10 Reinforcement ring 11 Cylinder part 11a End 11b Outer surface 12. Bending section 12a end 13. Annular section 20 Sticker body 21 Seal part 22 Base 23 Gasket section 30 Conductive lip section 31 Conductive Lip 32 Contact surface 33 Grease groove 34 Connecting groove 35 Garter Spring 40 Seal lip section 41 Seal Lip 42 Side view of the sealed object 43 Atmospheric side 44 Tip 45 thread grooves 47 Garter Spring 101 Shaft 101a Outer surface 102 Housing 103 Through hole 103a Inner surface 104 Space G Grease O Atmospheric side S space x-axis

Claims

1. Fluororubber and 5 to 15% by mass of conductive agent, 5 to 15% by mass of insulating filler and It contains, The conductive agent is at least one material selected from the group consisting of Ketjenblack, graphite, carbon nanotubes, and carbon fibers. The insulating filler is at least one material selected from the group consisting of wollastonite and clay. A fluororubber composition for sealing electric vehicles, wherein the total content of the conductive agent and the insulating filler is 18 to 25% by mass.

2. A fluororubber composition for sealing electric vehicles according to claim 1, wherein the IRHD hardness after vulcanization is 85 or less.

3. A fluororubber composition for sealing electric vehicles according to claim 1 or 2, wherein the volume resistivity after vulcanization is 8 Ω·cm or less.

4. A seal for an electric vehicle comprising the fluororubber composition for sealing an electric vehicle according to claim 1 or 2.

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