Fluororubber composition and seal for electric vehicle

Abstract

The purpose of the present invention is to provide a fluorine rubber composition that exhibits excellent roll machining properties and electrical conductivity.　The fluorine rubber composition contains a peroxide-vulcanized fluorine rubber and 16-26 mass% of a conductive agent.

Description

[Technical Field]

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

[0002] Fluororubber compositions have excellent oil and fuel resistance and are used as sealing materials for oil seals, O-rings, packings, and other applications in a wide range of fields, including automobiles and industrial machinery. In recent years, electric vehicles (hereinafter sometimes referred to as "EVs") have begun to become popular, and as a result, the prime mover has shifted from engines to motors. In EVs, a seal is installed between the motor, which is the prime mover, and the reducer.

[0003] Patent Document 1 (Japanese Patent No. 6288398) discloses Tecnoflon BR9151 and BR9171 as rubbers that do not deteriorate due to reactions with additives in oil. Patent Document 2 (WO 2014 / 175079) discloses a fluororubber made of a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene-ethylene-perfluoro(methyl vinyl ether) pentagonal copolymer, and discloses Tecnoflon BR9151 and BR9171 as specific examples of such fluororubber.

[0004] In technical fields such as automobiles equipped with conventional engines, insulating fluororubber compositions are generally used as sealing materials. However, unlike automobiles equipped with conventional engines, in new technical fields such as electric vehicles (EVs), if seals are made of insulating fluororubber compositions, the seals may become charged and generate potential differences, raising concerns about electrolytic corrosion in the vehicle interior. Furthermore, electromagnetic waves generated by the charged seals may cause radio noise. In response to this issue, conventional EVs prevent charging and electrolytic corrosion in the vehicle interior by connecting conductive components such as carbon earth brushes and knuckle earths to the reducer or body ground. However, implementing such measures increases the number of components within the EV, requiring additional space for the components, raising concerns about potential problems such as increased costs. On the other hand, there is a concern that changing the composition of a fluororubber composition from a conventional one to impart the desired conductivity to the fluororubber composition may reduce the roll processability of the fluororubber composition.

[0005] Thus, conventional fluororubber compositions have been desired to have excellent roll processability as well as excellent electrical conductivity from the viewpoint of preventing static electricity and electrolytic corrosion. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 6288398 [Patent Document 2] International Publication No. 2014 / 175079 Summary of the Invention [Problem to be solved by the invention]

[0007] Therefore, the present inventors have discovered that excellent roll processability and electrical conductivity can be achieved by preparing a fluororubber composition containing a specific type of fluororubber and a predetermined content of a conductive agent, and have completed the present invention. That is, the present invention provides a fluororubber composition having excellent roll processability and electrical conductivity. [Means for solving the problem]

[0008] The gist and configuration of the present invention are as follows. [1] A fluororubber composition containing a peroxide-vulcanized fluororubber and 16 to 26 mass % of a conductive agent. [2] The fluororubber composition according to [1] above, which has a volume resistivity of 1.0 Ω·cm or less. [3] A seal for an electric vehicle, comprising the fluororubber composition according to [1] or [2] above. [Effects of the Invention]

[0009] It is possible to provide a fluororubber composition having excellent roll processability and electrical conductivity. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram illustrating a sealing device having a conductive part containing a vulcanized fluororubber composition according to one embodiment as a seal. DETAILED DESCRIPTION OF THE INVENTION

[0011] The vulcanized fluororubber composition of the present invention contains a peroxide-vulcanized fluororubber and 16 to 26% by mass of a conductive agent. The peroxide-vulcanized fluororubber improves the elongation of the fluororubber composition, thereby improving the roll processability of the fluororubber composition. A conductive agent content of 16% by mass or more in the fluororubber composition ensures excellent electrical conductivity. Furthermore, a conductive agent content of 26% by mass or less in the fluororubber composition ensures that the fluororubber composition has appropriate hardness and viscosity, improving the roll processability of the fluororubber composition. For example, when shaft seals, packing seals, etc. are made from the fluororubber composition of the present invention vulcanized in an EV, the seals themselves have excellent electrical conductivity, eliminating the need for extra components such as earth brushes and knuckle earths found in conventional EVs, thereby saving space within the EV. Furthermore, while rotating shafts and other such components generate heat due to their high rotational speeds, seals made from the fluororubber composition of the present invention have excellent heat resistance, allowing them to maintain excellent electrical conductivity and sealing properties even when used at high temperatures as seals for rotating shafts, etc. Furthermore, in the fluororubber composition of the present invention, it is not necessary to increase the content of a processing aid in order to improve roll processability. The fluororubber composition is preferably a fluororubber composition for shaft seals or packing seals, and more preferably a fluororubber composition for seals such as shafts and packings of electric vehicles.

[0012] The volume resistivity of the fluororubber composition after vulcanization is preferably 1.0 Ω·cm or less, more preferably 0.5 Ω·cm or less, and even more preferably 0.3 Ω·cm or less. To measure the volume resistivity of a fluororubber composition, a sample of the vulcanized fluororubber composition measuring 140 mm x 100 mm x 2 mm is used. This sample is prepared by preparing the fluororubber composition, first vulcanizing it in a molding press at 160-200°C for 3-30 minutes to reduce it to 140 mm x 100 mm x 2 mm, and then post-vulcanizing it in a thermostatic oven at 150-250°C for 0.5-24 hours. It has been confirmed through preliminary testing 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 is measured according to the four-probe method in accordance with JIS K7194:1994, using a Hioki Milliohm High Tester 3540 (product name) manufactured by Hioki E.E. Corporation as the measuring device, and the measurement is performed at room temperature by the parallel terminal electrode method.

[0013] Each component constituting the fluororubber composition of the present invention will be described in detail below. (Fluorine rubber) The fluororubber is not particularly limited as long as it is a peroxide-vulcanized fluororubber after vulcanization, but homopolymers or copolymers of one or more fluorine-containing olefins can be used. Examples of fluorine-containing olefins include vinylidene fluoride, hexafluoropropylene, pentafluoropropylene, trifluoroethylene, trifluorochloroethylene, tetrafluoroethylene, vinyl fluoride, perfluoroacrylic esters, perfluoroalkyl acrylates, perfluoromethyl vinyl ether, perfluoroethyl vinyl ether, and perfluoropropyl vinyl ether. These fluorine-containing olefins can be used alone or in combination of two or more. Examples of fluorine-containing rubbers include vinylidene fluoride-hexafluoropropylene binary copolymers, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene terpolymers, and vinylidene fluoride-hexafluoropropylene-perfluoroalkyl vinyl ether terpolymers.

[0014] Fluororubber may be obtained by solution polymerization, suspension polymerization, or emulsion polymerization, or may be commercially available. Examples of commercially available fluororubbers include Chemours' VITON® GBL-600S and VITON® GLT-600S products, and Daikin Industries' Dai-el® GBR-6002 and Dai-el® G-901 products. The fluororubber may be a peroxide-vulcanized fluororubber vulcanized with peroxide. Peroxide-vulcanized fluororubber is a polymer based on a vulcanization reaction in which a cure site such as Br or I is introduced to the molecular chain end during polymerization. Peroxide-vulcanized fluororubber can be confirmed by, for example, (a) detecting Br or I in the fluororubber by elemental analysis using XRF (X-ray fluorescence analysis), or (b) detecting no elements derived from acid acceptors such as Mg or Ca in the molded fluororubber composition by elemental analysis. Since peroxide-vulcanized fluororubber does not require an acid acceptor compared with polyol-vulcanized fluororubber, the fluororubber composition can achieve excellent roll processability. Therefore, in a preferred embodiment of the present invention, the fluororubber composition does not contain an acid acceptor.

[0015] (Conductive agent) The fluororubber composition after vulcanization contains 16 to 26% by mass of a conductive agent. By containing 16 to 26% by mass of a conductive agent, the fluororubber composition can have excellent conductivity and roll processability. 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 18 to 26% by mass, more preferably 20 to 26% by mass, and even more preferably 22 to 26% by mass. By keeping the content of the conductive agent in the fluororubber composition within the above ranges, it is possible to maintain excellent conductivity and roll processability while adjusting other physical properties to desired ranges. The fluororubber composition may contain one type of conductive agent or two or more types.

[0016] (processing aids) The fluororubber composition may further contain a processing aid. The processing aid is not particularly limited, but is preferably at least one material selected from the group consisting of vegetable wax, polyester, and fluoropolyether derivatives. The content of the processing aid in the fluororubber composition is preferably 3 to 14 mass%, more preferably 6 to 10 mass%, and even more preferably 6 to 7 mass%.

[0017] (Other additives) The fluororubber composition of the present invention contains a fluororubber and a conductive agent, and the fluororubber composition may further contain, as components other than the fluororubber and the conductive agent, an antioxidant; a thermoplastic resin; a plasticizer; a softener; a foaming agent; a foaming aid; a colorant; a dispersant; a flame retardant; a tackifier; a release agent; various metal powders, etc.

[0018] (Method of producing fluororubber composition) The fluororubber composition can be obtained by kneading 16 to 26% by mass of a conductive agent, a peroxide-vulcanized fluororubber, and, if necessary, processing aids and other materials using kneading equipment (rolls, kneaders, etc.). The vulcanized fluororubber composition of the present invention can be obtained by adding a vulcanizing agent to the fluororubber composition obtained as described above, and then heating the resulting mixture in a predetermined shape. Known manufacturing equipment can be used to obtain the desired molded product by molding and vulcanizing the fluororubber composition. For example, the fluororubber composition can be introduced 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, the fluororubber composition may be pressed into a predetermined shape and subjected to primary vulcanization, and the fluororubber composition after primary vulcanization may then be subjected to secondary vulcanization.

[0019] (Molded product of fluororubber composition) As described above, molded articles of desired shapes can be produced by molding and vulcanizing the fluororubber composition. The product containing the fluororubber composition is preferably a seal such as a shaft seal or a packing seal for an electric vehicle. The conductivity of the entire seal for an electric vehicle is preferably 10 Ω or less, more preferably 9 Ω or less, and even more preferably 5 Ω or less. The conductivity of the entire seal can be evaluated by placing the seal between the shaft and housing of a rotation testing machine, and then contacting the shaft and housing with a conductor, using an impedance analyzer (IM3570 (device name), manufactured by Hioki E.E. Corporation) to measure the electrical resistance at 500 kHz / 5 V.

[0020] FIG. 1 is a diagram showing a sealing device of one embodiment having a conducting part 120 containing the vulcanized fluororubber composition of the present invention as a seal, and shows a schematic cross-sectional view (schematic cross-sectional view) of a rotating shaft 20 and a housing 38 of the sealing device 40, taken along a plane including the axis ω of the rotating shaft 20.

[0021] As shown in FIG. 1, the sealing device 40 is disposed in a gap 107 between the outer surface 20s of the rotating shaft 20 and the inner surface 38s that constitutes the axial hole in the housing 38 having the axial hole into which the rotating shaft 20 is inserted.

[0022] As described above, the rotating shaft 20 may be, for example, a motor shaft of a drive motor in an EV (Electric Vehicle) or HEV (Hybrid Electric Vehicle). The rotating shaft 20 is usually rod-shaped (cylindrical), and its cross section is usually circular. The housing 38 is usually grounded.

[0023] <Sheath pipe part> The following describes the sheath pipe portion 110 of the sealing device 40 shown in Fig. 1. The sheath pipe portion 110 is an annular portion that is directly or indirectly fixed to the outer surface 20s of the rotating shaft 20. The sheath pipe portion 110 is directly fixed to the outer surface 20s of the rotating shaft 20. There are no particular limitations on the means for fixing the sheath pipe portion 110 to the outer surface 20s of the rotating shaft 20. For example, the sheath pipe portion 110 may be fixed to the outer surface 20s of the rotating shaft 20 by fitting the sheath pipe portion 110 and the outer surface 20s of the rotating shaft 20 using an interference fit method. Alternatively, the sheath pipe portion 110 may be fixed to the outer surface 20s of the rotating shaft 20 using an adhesive or the like.

[0024] The sleeve tube portion 110 includes a fixed portion 110a extending in a direction parallel to the axis ω of the rotating shaft 20, and a support portion 110b connecting to an end of the fixed portion 110a and extending toward the inner surface 38s of the housing 38. The fixed portion 110a and the support portion 110b are preferably plate-shaped. That is, the fixed portion 110a is preferably cylindrical, and the support portion 110b is preferably disk-shaped with a through-hole in the center. Furthermore, the fixed portion 110a and the support portion 110b are substantially perpendicular to each other in a cross section obtained by cutting the sleeve tube portion 110 along a plane including the axis ω of the rotating shaft 20. Therefore, the sleeve tube portion 110 has a substantially L-shaped cross section. Here, "substantially perpendicular" means that the cross section does not have to be completely perpendicular. That is, it is preferable that the angle between the fixed portion 110a and the support portion 110b is 90 degrees, but this angle may be 75 to 105 degrees (preferably 80 to 100 degrees, and more preferably 85 to 95 degrees).

[0025] The sheath tube portion 110 is preferably made of a metal, and more preferably a metal having electrical conductivity. Examples of such metals include stainless steel, cold-rolled steel (SPCC), brass, and aluminum. The sheath tube portion 110 does not have to be made of a metal. For example, it may be made of a resin. The sheath tube portion 110 can be formed by press working or forging.

[0026] <Conductive part> The following describes the conductive portion 120 of the sealing device 40 shown in FIG. 1. The conductive portion 120 is ring-shaped, with an outer peripheral portion 120a of the ring contacting the inner surface 38s of the housing 38 and a main surface 120s fixed to the sleeve pipe portion 110. The main surface 120s of the conductive portion 120 is fixed to the support portion 110b of the sleeve pipe portion 110. The conductive portion 120 functions as a seal containing the vulcanized fluororubber composition of the present invention and is sheet- or plate-shaped. The conductive portion 120 in FIG. 1 is deformed so that its cross section is approximately L-shaped, and the main surface 120s of the conductive portion 120 contacts the main surface of the plate-shaped support portion 110b of the sleeve pipe portion 110. Here, it is preferable that the main surface 120s of the conductive portion 120 is in close contact with the main surface of the support portion 110b.

[0027] A main surface 120s of the ring outer peripheral portion 120a contacts the inner surface 38s of the housing 38. When the rotating shaft 20 rotates, centrifugal force is applied to the sealing device 40, and it is preferable that the main surface 120s of the ring outer peripheral portion 120a come into close contact with the inner surface 38s of the housing 38. In the conductive portion 120 that has been deformed so that its cross section is approximately L-shaped, the ring outer peripheral portion 120a is cylindrical, and the remaining portion is disk-shaped with a through-hole in the center. Due to centrifugal force F generated by the rotation of the rotating shaft 20, the force that presses the conductive portion 120 against the inner surface 38s of the housing 38 increases compared to before the rotating shaft 20 rotates.

[0028] When the rotating shaft 20 rotates, centrifugal force F is applied to the conductive part 120, and the ring outer periphery 120a of the conductive part 120 is pressed against the inner surface 38s of the housing 38. As a result, the ring outer periphery 120a of the conductive part 120 is stably brought into close contact with the inner surface 38s of the housing 38, ensuring electrical continuity between the rotating shaft 20 and the housing 38.

[0029] There are no particular limitations on the method for fixing the main surface 120s of the conductive portion 120 to the main surface of the support portion 110b of the sheath pipe portion 110, and they can be fixed using an adhesive, for example. However, if they are fixed using metal bolts and nuts without using an adhesive, electrical continuity between the conductive portion 120 and the sheath pipe portion 110 is more easily ensured, which is preferable because it results in easier electrical continuity between the rotating shaft 20 and the housing 38. [Example]

[0030] Next, examples will be described to further clarify the effects of the present invention, but the present invention is not limited to these examples.

[0031] (Examples 1 to 5, Comparative Examples 1 to 10) In each example, a fluororubber composition was produced by kneading materials according to the formulation shown in Table 1. The names of the materials used in each example are shown below. Type 1 (ASTM) fluororubber: VITON (registered trademark) A-500 (manufactured by Chemours) Type 2 (ASTM) fluoroelastomer: VITON (registered trademark) B-600 (manufactured by Chemours) Type 3 (ASTM) fluororubber: VITON (registered trademark) GLT-600S (manufactured by Chemours) Type 6 (ASTM) fluororubber: Daiel (registered trademark) GBR-6002 (manufactured by Daikin Industries, Ltd.) Ketjenblack A: KETJENBLACK EC600JD (Lion Specialty Chemicals) Ketjen Black B: Denka Black (manufactured by Denka Co., Ltd.) Graphite: A-0 (manufactured by Higashi Nippon Carbon Co., Ltd.) Carbon fiber: S-241 (Osaka Gas Chemicals) Carbon nanotubes: Lucan CP1001M (LG Chem) Clay: NN kaolin clay (Takehara Chemical Co., Ltd.) Silica: NIPSIL (registered trademark) ER (manufactured by Tosoh Silica Corporation) Vegetable wax: VPA#2 (Chemours) Polyester: SYNCROFLEX 3142 (CRODA) [Table 1]

[0032] The fluororubber compositions produced as described above were evaluated for hardness (Durometer A hardness), hardness (IRHD (International Rubber Hardness Degree) hardness), volume resistivity, seal conductivity, and roll processability. The preparation and measurement methods for the samples for each evaluation are described below.

[0033] (1) Hardness (Durometer A 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 2 mm thick sample. The Durometer A hardness of this sample was then measured at room temperature using a constant pressure rubber hardness tester P1-A (device name) manufactured by Kobunshi Keiki Co., Ltd. in accordance with JIS K6253-2:2012. (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 measuring 140mm x 100mm x 2mm. The IRHD hardness of this sample was then measured under IRHD (micro) conditions using a Digitest II (device name) manufactured by Burleith in accordance with JIS K6253-2:2012. (3) 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 140mm x 100mm x 2mm. Next, this sample was measured according to the four-probe method in accordance with JIS K7194:1994, and the volume resistivity was measured at room temperature using a Milliohm High Tester 3540 (device name) manufactured by Hioki E.E. Corporation by the parallel terminal electrode method.

[0034] (4) Seal conductivity: 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 placed between the shaft and housing of a rotation testing machine, and the shaft and housing were connected with a conductor, and the electrical resistance was measured at 500 kHz / 5 V using an impedance analyzer (IM3570 (device name), manufactured by Hioki E.E. Corporation). (5) Roll processability: A fluororubber composition before vulcanization was kneaded in a kneader to prepare a dough, and then a vulcanizing agent was added to the fluororubber composition dough using a roll. The ability of the fluororubber composition to wrap around the roll when the vulcanizing agent was added was evaluated. When evaluating the ability of the fluororubber composition to wrap around the roll, two rolls were rotated and the gap between the two rolls was adjusted to about 5 mm, so that the thickness of the dough made of the fluororubber composition was 5 mm. At this time, the evaluation was performed visually. If the dough made of the fluororubber composition separated from the surfaces of the two rolls, the rolling process was completed and it would be dangerous when cutting the dough with a knife, so it was marked as "X." If the dough made of the fluororubber composition did not separate from the surfaces of the two rolls, it was marked as "O." The evaluation items measured as described above are shown in Table 1 above.

[0035] As shown in Examples 1 to 5 in Table 1, the fluororubber compositions of the present invention had a volume resistivity of 0.3 Ω·cm or less, a seal conductivity of 9 Ω or less, and roll processability was also rated "Good." On the other hand, as shown in Comparative Examples 1 to 10 in Table 1, the fluororubber compositions of the comparative examples all had very high volume resistivities and seal conductivity values, or the fluororubber compositions could not be kneaded, or the roll processability was rated "Poor." From the above, it was confirmed that the present invention can provide a fluororubber composition having excellent conductivity and roll processability. [Explanation of symbols]

[0036] 20 Rotation axis 20s Outer surface of rotating shaft 38 Housing 38s Housing inner surface 40 Sealing device 107 Gap 110 Sheath pipe section 110a: Fixing portion in sheath tube portion 110b Support portion in sheath tube portion 120 Conductive part 120a: Ring outer periphery in conductive portion 120s Main surface of conductive part ω Axis center of the rotating shaft

Claims

1. The adhesive tape contains a peroxide-vulcanized fluororubber and 16 to 26 mass % of a conductive agent, The fluororubber composition further comprises 3 to 14 mass % of at least one processing aid selected from the group consisting of vegetable waxes and fluoropolyether derivatives.

2. The fluororubber composition according to claim 1, which has a volume resistivity of 1.0 Ω·cm or less.

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

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