Carbon fiber-containing paint and machine parts coated therewith

Abstract

To provide a coating in which carbon fiber is blended into a solution composition having fluororesin and polyimide precursor as a main resin component, and a coating film has excellent sliding property, and a light-weight machine component in which the coating film of the above coating is formed on the surface of a substrate made of a carbon material.SOLUTION: Disclosed is coating in which carbon fiber is blended into a solution composition having fluororesin and polyimide precursor as a main resin component by 3 to 30 mass%. Further, also disclosed is a machine component on which a coating film, in which carbon fiber-containing coating formed by blending carbon fiber into a solution composition having fluororesin and polyimide precursor as a main resin component by 3 to 30 mass% is coated on a part or the entire face of a surface of a substrate made of a carbon material, is formed.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a paint comprising a solution composition containing a fluororesin and a polyimide precursor blended with carbon fiber as main resin components, and a machine part having a coating film formed by applying the paint to the surface of a carbon material.

Background Art

[0002] Conventionally, a coating film formed by applying a paint composed of a fluororesin and a polyimide resin has electrical properties such as excellent dielectric breakdown resistance, low dielectric constant, and low dielectric tangent, and is suitable for use in electronic parts such as circuit boards. Furthermore, since it has high heat resistance and mechanical properties, and has characteristics such as high water repellency and oil repellency, it is used in a wide range of applications. Such a solution composition mainly composed of a fluororesin and a polyimide precursor is disclosed in, for example, Patent Documents 1 and 2.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] On the other hand, a coating film formed by applying a solution composition (paint) composed of the above-mentioned fluororesin and polyimide precursor has problems in sliding properties such as lubricity and wear resistance. Therefore, in order to exhibit excellent performance in machine parts including sliding parts such as rod packing, piston rings, labyrinth seals, bearings, vanes, seal rings, rotary joint seals, valve seats, and parts for flow meters, it is necessary to improve the sliding properties.

[0005] Furthermore, in mechanical parts such as those described above, it is often required to be lightweight, and carbon materials, which can be cited as lightweight materials, have come to be widely used in mechanical parts. Therefore, there has been a demand for mechanical parts having a coating film with even better sliding characteristics on the surface of the carbon material, the coating film mainly comprising a fluororesin and a polyimide resin as resin components.

[0006] An object of the present invention is to provide a paint in which carbon fibers are blended in a solution composition mainly comprising a fluororesin having excellent sliding characteristics and a polyimide precursor as main resin components, and further to provide a lightweight mechanical part in which a coating film of the above paint is formed on the surface of a base material made of a carbon material.

Means for Solving the Problems

[0007] The carbon fiber-containing paint of the first invention is characterized in that 3 to 30% by mass of carbon fibers are blended in a solution composition mainly comprising a fluororesin and a polyimide precursor Particles of tourmaline (3 to 20% by mass) and as main resin components.

[0008] The first invention may adopt the following forms. In the first form, the carbon fibers are isotropic pitch-based carbon fibers and the number average length is 30 to 100 μm.

[0009]

[0010] The mechanical part of the second invention is characterized in that a carbon fiber-containing paint in which 3 to 30% by mass of carbon fibers are blended in a solution composition mainly comprising a fluororesin and a polyimide precursor Particles of tourmaline (3 to 20% by mass) and as main resin components is applied to a part or the whole of the surface of a base material made of a carbon material to form a coating film.

[0011] The second invention may adopt the following forms. In the first form, the carbon fibers are isotropic pitch-based carbon fibers and the number average length is 30 to 100 μm.

[0012]

[0013] In the form of 2 the carbon material is artificial graphite.

Advantages of the Invention

[0014] According to the carbon fiber-containing paint of the first invention, since it is a paint in which 3 to 30% by mass of carbon fiber is blended in a solution composition mainly composed of a fluororesin and a polyimide precursor, the heat resistance, low dielectric constant, high adhesion, and insulation resistance, which are the characteristics of the paint film formed by applying the paint composed of the solution composition, can be maintained, and the sliding characteristics (slip properties and abrasion resistance) can be greatly improved by the carbon fiber.

[0015] In particular, since carbon fiber has functional groups with positive and negative charges derived from dangling bonds, it can enhance the dispersibility of fluororesin powder and carbon fiber, and enhance the adhesion of the paint film by the electric force of carbon fiber. Moreover , in the solution composition 3 to 20% by mass of Since fine particles of tourmaline are mixed, when this paint is applied to the metal surface, the adhesion to the metal surface having a positive charge is significantly enhanced by the negative charge of tourmaline.

[0016] Since the paint film of the above paint is formed on a part or all of the surface of the base material made of a carbon material, the mechanical part for a machine according to the second invention can obtain a lightweight mechanical part on which a paint film having heat resistance, high adhesion, insulation resistance, low dielectric constant, and excellent sliding characteristics (slip properties and abrasion resistance) is formed. And , in the solution composition 3 to 20% by mass of Since fine particles of tourmaline are mixed, the adhesion between the surface of the base material made of a carbon material and the paint film is enhanced by the negative charge of tourmaline.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3

Mode for Carrying Out the Invention

[0018] Hereinafter, the mode for carrying out the present invention will be described. However, the present invention is not limited to the following embodiments.

[0019] The solution composition constituting the carbon fiber-containing paint of the present invention uses a fluororesin and a polyimide precursor as main resin components, and the components may be adjusted or commercially available products may be used. This solution composition may be an organic solvent-based solution or an aqueous solution, but an aqueous solution is preferable in terms of excellent handleability considering safety and equipment costs.

[0020] As the fluororesin, a commercially available fluororesin-based micropowder can be used. A typical fluororesin-based micropowder is polytetrafluoroethylene (PTFE). In addition, known ones such as ethylene-propylene fluoride copolymer, perfluoroalkoxy polymer, chlorotrifluoroethylene, vinylidene fluoride, and vinyl fluoride can be used. One type of micropowder may be used, or two or more types may be mixed and used.

[0021] The polyimide precursor is most commonly polyamic acid. For the preparation of the polyimide precursor solution, a known method can be adopted. Examples of the organic solvent (non-aqueous system) solvent include n-methyl-2-pyrrolidone, n-acetyl-2-pyrrolidone, formamide, acetanilide, etc., but known suitable solvents can be used. In the case of water-based paints (aqueous solutions), a mixture of a polyimide precursor and a water-dispersed fluororesin powder has also been commercialized.

[0022] The carbon fiber-containing paint of the present invention is a solution composition mainly composed of a fluororesin and a polyimide precursor. As an additive for improving sliding characteristics such as lubricity and abrasion resistance, various carbon powders such as carbon black, ceramic powders such as alumina, carbon fibers, etc. can be blended. Among these, it is particularly preferable to use carbon fibers. Examples of carbon fibers include isotropic pitch-based carbon fibers, anisotropic pitch-based carbon fibers, PAN-based carbon fibers, rayon-based carbon fibers, etc. In particular, it is preferable to use isotropic pitch-based carbon fibers.

[0023] Anisotropic pitch-based carbon fibers and PAN-based carbon fibers have too high mechanical strength and hardness, so they tend to damage the mating material when used as sliding materials. Rayon-based carbon fibers have a directionality in the arrangement of crystallites, so it is considered that the formation of the sliding film is slightly inferior compared to isotropic pitch-based carbon fibers. On the other hand, isotropic pitch-based carbon fibers have small crystallites composed of carbon hexagonal net planes and are randomly arranged, so their mechanical strength and hardness are relatively low. Therefore, a high-quality sliding film containing the crystallites of carbon fibers can be formed.

[0024] The number average length of the isotropic pitch-based carbon fibers is preferably 30 to 100 μm. More preferably, it is 30 to 50 μm. If the number average length is shorter than 30 μm, the aspect ratio becomes too small, and the arrangement direction of the carbon fibers in the coating film tends to be random, making it difficult to fully exhibit the performance as carbon fibers. If the number average length is longer than 100 μm, it becomes difficult to uniformly mix into the paint.

[0025] The blending amount of the carbon fibers is preferably 3 to 30% by mass in the paint. More preferably, it is 5 to 20% by mass. If the blending amount of the carbon fibers is less than 3% by mass, the improvement of the sliding characteristics is reduced, and if it is more than 30% by mass, it becomes difficult to uniformly mix into the paint.

[0026] In addition, among carbon fibers, there are those with different crystallinities of graphite depending on the heat treatment temperature. Generally, carbon fibers with low graphite crystallinity are heat-treated at a lower temperature (for example, 800 to 1500 °C) and are sometimes called carbonaceous materials.

[0027] And carbon fibers with high graphite crystallinity are heat-treated at a higher temperature (for example, 2000 to 3000 °C) and are sometimes called graphitic materials. Either carbonaceous or graphitic materials can be used. Although it also varies depending on the type of carbon fiber, in the case of isotropic pitch-based carbon fibers, carbonaceous ones are preferred. To blend carbon fibers, there are many functional groups with positive and negative charges on the carbon fiber surface, making it easier for the carbon fibers to be uniformly dispersed in the solution composition. Mixing of carbon fibers into a solution composition mainly composed of a fluororesin and a polyimide precursor is carried out according to a conventional method, for example, by adding carbon fibers to the solution composition and stirring using a mixer.

[0028] In order to strengthen the adhesion between the coating film and the substrate and to enhance the dispersibility of carbon fibers in the solution composition, it is preferable to mix ores having a negative charge or generating negative ions. Examples of such ores include tourmalines having a negative charge such as black tourmaline, pink tourmaline, and hexagonite (registered trademark). The particle size of the tourmaline is preferably about 3 μm or less, and the mixing amount of the tourmaline is preferably 2 to 20% by mass based on the solution composition. More preferably, it is 5 to 15% by mass. This is because if it is less than 2% by mass, the dispersibility of the carbon fibers becomes poor, and if it exceeds 20% by mass, the proportion of tourmaline becomes too large.

[0029] By using various metal materials such as stainless steel, carbon steel, copper and copper alloys, aluminum and aluminum alloys as substrates and applying the carbon fiber-containing paint of the present invention to form a coating film, machine parts having a coating film with excellent sliding characteristics can be obtained. However, when the above metal material is used as the base material, the bulk density becomes high and it is difficult to reduce the weight. Therefore, when used for mechanical parts that require weight reduction, it is preferable to adopt a base material made of a carbon material.

[0030] On the other hand, in the case of a base material made of a carbon material, weight reduction can be achieved. However, generally, the surface of the carbon material has pores and is not smooth. Therefore, it is considered difficult to apply the carbon fiber-containing paint compared to the metal material. Here, examples of the carbon material include carbon fiber composite materials such as artificial graphite, carbon materials for machinery, brush materials, and C / C composite materials. Artificial graphite has the advantage of good workability and can be made into precision processed products of various sizes.

[0031] Generally, artificial graphite includes extruded products, molded products, cold isostatic pressing (CIP) molded products, etc. Any of them can be used as the base material for applying the carbon fiber-containing paint of the present invention. It is desirable to select the base material according to the purpose and use of the mechanical parts. The bulk density of the artificial graphite block is generally in the range of 1.3 - 2.0 g / cm 3 and commercially available products are in this range, but those with a density of 1.5 - 2.0 g / cm 3 are preferred, and more preferably 1.7 - 1.9 g / cm 3 . The smaller the bulk density, the more pores there are and the more difficult it is to apply the paint. This is because those with a bulk density exceeding 1.9 g / cm 3 have limitations such as limited size.

[0032] Next, a sliding test was conducted to examine that the base material coated with the carbon fiber-containing paints A, B, and C of the present invention to form a coating film has excellent slidability as a mechanical part. In Examples 1 - 4 and Comparative Examples 1 - 6, artificial graphite, which is one of the lightweight materials among carbon materials, was used as the base material, and a sliding test was conducted as described later, and the results are shown in Tables 1 and 2.

Examples

[0033] As the base paint, a solution composition having a fluororesin and a polyimide precursor as main resin components, in which PTFE fine particles are uniformly dispersed in polyamic acid, water is used as a solvent, and 5 mass% of tourmaline fine particles having a particle size of 3 μm or less are mixed, a high-functional water-soluble paint Y (manufactured by Japan Mattex Co., Ltd., trade name: QUATLON (ordinary product)) was used.

[0034] Anisotropic pitch-based carbon fiber mild (manufactured by Osaka Gas Chemical Co., Ltd., trade name: Donacarb, product number: S-2404N) was blended with the high-functional water-soluble paint Y. The carbon fiber mild has a number average fiber length of 40 μm and an aspect ratio of 3. Note that this carbon fiber is so-called carbonaceous.

[0035] After putting 475 g of the high-functional water-soluble paint Y into a stainless steel container, 25 g of this carbon fiber mild was put therein and stirred for 30 minutes using a stirrer to prepare a carbon fiber-containing paint A (high-functional water-soluble paint Y + 5 mass% carbon fiber). At this time, stirring was performed using a commercially available stirrer of the type in which metal blades rotate.

[0036] Commercially available artificial graphite A (isotropic graphite manufactured by Ibiden Co., Ltd., product number: EX-60) was used as the coating substrate. The bulk density of the artificial graphite A was 1.80 g / cm 3 It was. From the material block of the artificial graphite A, artificial graphite substrates having sizes of 30×30×3 (mm), 50×50×5 (mm), and 180×100×5 (mm) were cut out by milling.

[0037] Before applying the carbon fiber-containing paint, the artificial graphite substrate was degreased by wiping with acetone. Then, it was preheated at 30 to 40 °C for 10 minutes or more using a dryer. After preheating, air was blown onto the surface of the artificial graphite substrate using an air gun. At this time, the air pressure of the air gun was about 0.15 MPa. The adjustment of the carbon fiber-containing paint A before application was performed by passing it through a 90-mesh strainer.

[0038] The carbon fiber-containing paint A passed through a strainer was applied to a graphite substrate using a commercially available air spray gun with a nozzle diameter of 1.3 mm. The spraying air pressure at this time was about 0.2 MPa. Also, while changing the direction of the graphite substrate, the application was repeated about three times so that the thickness of the coating film after heat treatment would be 40 μm or more. At this time, the application was performed on the largest surface or the entire surface of the test piece. The one with the carbon fiber-containing paint A applied to the graphite substrate was placed on a stainless steel net, placed in a dryer, and dried at 120 °C for 30 minutes in an air atmosphere to disperse most of the solvent.

[0039] Thereafter, the temperature was raised to 380 °C at a rate of about 8 °C / min in the air in the same manner and held at that temperature for 15 minutes. As a result, the curing of the resin component of the paint was completed. Thereafter, the graphite substrate coated with the carbon fiber-containing paint A was rapidly cooled by immersing it in water from the state of 380 °C. After immersing in water for 10 minutes or more, the water adhering to the applied graphite was wiped off with a cloth, air-dried, and then dried at 120 °C for 20 minutes.

[0040] Note that since the high-functional water-soluble paint Y generally loses about 57% of its mass due to the dispersion of the solvent until curing, the carbon fiber content in the coating film formed by applying the carbon fiber-containing paint A to the graphite substrate is about 11% by mass. The coating film of each test piece had a film thickness of 90 μm, had no unevenness or cracks, and had a good appearance. The method of the sliding test common to each example is as described later, and the film thickness and the results of the sliding test of each example are as shown in Tables 1 and 2.

[0041]

Table 1

Examples

[0042] In the preparation of the carbon fiber-containing paint A of Example 1, the compounding ratio of the carbon fiber milled product was set to 10% by mass of carbon fiber. That is, after putting 450 g of the high-functional water-soluble paint Y into a stainless steel container, 50 g of this carbon fiber milled product was put therein to obtain a carbon fiber-containing paint B (high-functional water-soluble paint Y + 10% by mass of carbon fiber) containing 10% by mass of carbon fiber. Except for the compounding of the carbon fiber milled product, it was carried out in the same manner as in Example 1. The carbon fiber content in the coating film was about 21% by mass. Also in Example 2, in any of the test pieces, the coating film had a film thickness of 60 μm, had no unevenness or cracks, and had a good appearance. The results of the film thickness and sliding test are shown in Table 1 above.

[0043] Here, a coating film formed by applying the carbon fiber-containing paint A to a graphite substrate was photographed using a scanning electron microscope (JEOL JSM-6010LA). A surface photograph (scanning electron microscope image) of the coating film is shown in Fig. 2, and a cross-sectional photograph (backscattered electron image) of the coating film is shown in Fig. 3. From Fig. 2, it can be seen that the carbon fiber milled product compounded in the carbon fiber-containing paint A is uniformly dispersed and the coating film is formed, and from Fig. 3, it can be seen that the thickness of the coating film is uniformly formed.

Example

[0044] In the preparation of the carbon fiber-containing paint A of Example 1, the compounding ratio of the carbon fiber milled product was set to 20% by mass of carbon fiber. That is, after putting 400 g of the high-functional water-soluble paint Y into a stainless steel container, 100 g of this carbon fiber milled product was put therein to obtain a carbon fiber-containing paint C (high-functional water-soluble paint Y + 20% by mass of carbon fiber) containing 20% by mass of carbon fiber. Except for the compounding of the carbon fiber milled product, it was carried out in the same manner as in Example 1. The carbon fiber content in the coating film was about 37% by mass. Also in Example 3, in any of the test pieces, the coating film had a film thickness of 100 μm, had no unevenness or cracks, and had a good appearance. The results of the film thickness and sliding test are shown in Table 1 above.

Example

[0045] The coated substrate was changed from the artificial graphite substrate of Example 2 to commercially available artificial graphite B (isotropic graphite, product number: 2124, manufactured by Mersen). Except for the coated substrate, the same method as in Example 2 was used. The bulk density of artificial graphite B was 1.85 g / cm 3 . The carbon fiber content in the coating film was also 10% by mass of carbon fiber, the same as in Example 2. Also in Example 4, for all test pieces, the coating film had a film thickness of 140 μm, no unevenness or cracks, and had a good appearance. Here, Table 2 shows the results of the film thickness and sliding test using artificial graphite B as the coated substrate.

[0046]

Table 2

Example

[0047] Commercially available artificial graphite C (extruded graphite, product number: PSG-12, manufactured by SEC Carbon Co., Ltd.) was used as the coated substrate. The bulk density of artificial graphite C was 1.74 g / cm 3 . In the preparation of the carbon fiber-containing paint D, the blending of the carbon fiber mild was set to 30% by mass of carbon fiber. That is, after putting 350 g of the high-functional water-soluble paint Y into a stainless steel container, 150 g of this carbon fiber mild was put into it to obtain a carbon fiber-containing paint D containing 30% by mass of carbon fiber (high-functional water-soluble paint Y + 30% by mass of carbon fiber). Except for using the above substrate and the carbon fiber-containing paint D containing 30% by mass of carbon fiber, the same method as in Example 1 was used. The carbon fiber content in the coating film was about 50% by mass. Also in Example 5, for all test pieces, the coating film had no unevenness or cracks and had a good appearance.

Example

[0048] Except for using stainless steel (SUS304, size: 100×100×2 (mm)) as the coated substrate, the same method as in Example 1 was used. The coating film had a film thickness of 40 - 50 μm, no unevenness or cracks, and had a good appearance.

Example

[0049] The experiment was carried out in the same manner as in Example 2, except that stainless steel (SUS304, size: 100×100×2 (mm)) was used as the coating substrate. The coating film had a thickness of 40 - 50 μm, with no unevenness or cracks and had a good appearance.

Example

[0050] The experiment was carried out in the same manner as in Example 3, except that stainless steel (SUS304, size: 100×100×2 (mm)) was used as the coating substrate. The coating film had a thickness of 40 - 50 μm, with no unevenness or cracks and had a good appearance.

Example

[0051] The experiment was carried out in the same manner as in Example 5, except that stainless steel (SUS304, size: 100×100×2 (mm)) was used as the coating substrate. The coating film had a thickness of 40 - 50 μm, with no unevenness or cracks and had a good appearance.

[0052] (Comparative Example 1) Graphite substrates with sizes of 30×30×3 (mm), 50×50×5 (mm), and 180×100×5 (mm) were cut out from a stock block of artificial graphite A by milling. Coating of the paint was not performed. The results of the sliding test are shown in Table 1 above.

[0053] (Comparative Example 2) The high - performance water - soluble paint Y of Example 1 was used. After putting 500 g of the high - performance water - soluble paint Y without carbon fiber mild into a stainless - steel container, the paint for coating was prepared by stirring it for 30 minutes using a stirrer. At this time, the stirring was carried out using a stirrer of the type in which commercially available metal blades rotate. Commercially available artificial graphite A was used as the coating substrate. Graphite substrates with sizes of 30×30×3 (mm), 50×50×5 (mm), and 180×100×5 (mm) were cut out from a stock block of artificial graphite A by milling.

[0054] Before coating, the artificial graphite substrate was degreased by wiping with acetone. Then, it was preheated at 30 - 40 °C for 10 minutes or more using a dryer. After preheating, air was blown onto the surface of the artificial graphite substrate using an air gun. At this time, the air pressure of the air gun was about 0.15 MPa. The adjustment of the paint before coating was carried out by passing it through a 140 - mesh strainer.

[0055] The paint passed through the strainer was applied to the artificial graphite substrate using a commercially available air spray gun with a nozzle diameter of 0.8 mm. The spraying air pressure at this time was about 0.2 MPa. Also, while changing the direction of the artificial graphite substrate, the coating was repeated about 3 times so that the thickness of the coating film after heat treatment would be about 10 μm. At this time, the coating was applied to the largest - area side or the entire surface of the test piece. The artificial graphite substrate coated with the paint was placed on a stainless - steel net and arranged in a dryer, and a drying treatment was carried out at 120 °C for 30 minutes in an air atmosphere to disperse most of the solvent.

[0056] After that, the temperature was raised to 380 °C at a rate of about 8 °C / min in the air in the same way and held at that temperature for 15 minutes. As a result, the curing of the resin component of the paint was completed. Then, it was rapidly cooled. The rapid cooling was carried out by immersing the coated graphite in water from the state of 380 °C. After immersing in water for 10 minutes or more, the water adhering to the coated graphite was wiped off with a cloth, air - dried, and then dried at 120 °C for 20 minutes. The coating films of all the test pieces had a good appearance without unevenness or cracks. The film thickness and the results of the sliding test are shown in Table 1 above.

[0057] (Comparative Example 3) A high - performance water - soluble paint Ya (trade name: QUATLON (black product), manufactured by Japan Mattex Co., Ltd.), which is a paint with a solution composition mainly composed of a fluororesin and a polyimide precursor, was used, and the same method as in Comparative Example 2 was carried out except for this. QUATLON (black product) is obtained by adding about 13 mass% of carbon black to the high - performance water - soluble paint Y. The coating films of all the test pieces had a good appearance without unevenness or cracks. The film thickness and the results of the sliding test are shown in Table 1 above.

[0058] (Comparative Example 4) High-functional water-soluble paint Y was used as a base paint for a solution composition mainly composed of a fluororesin and a polyimide precursor resin component. To this base paint, 15% by mass of tourmaline fine particles with a particle size of 3 μm or less were mixed to obtain high-functional water-soluble paint Yb. Except for using high-functional water-soluble paint Yb as the paint, it was carried out in the same manner as in Comparative Example 2. The coating films of all test pieces had a good appearance without unevenness or cracks. The film thickness and the results of the sliding test are shown in Table 1 above.

[0059] (Comparative Example 5) From the material block of artificial graphite B, artificial graphite base materials with sizes of 30×30×3 (mm), 50×50×5 (mm), and 180×100×5 (mm) were cut out by milling. Coating was not performed. The coating films of all test pieces had a good appearance without unevenness or cracks. The film thickness and the results of the sliding test are shown in Table 2 above.

[0060] (Comparative Example 6) It was carried out in the same manner as in Comparative Example 2 except that commercially available artificial graphite B (isotropic graphite manufactured by Nippon Carbon Co., Ltd., product number: 2124) was used as the coating base material. The coating films of all test pieces had a good appearance without unevenness or cracks. The film thickness and the results of the sliding test are shown in Table 2.

[0061] (Evaluation of Coating Film Adhesion) The evaluation of the coating film adhesion was carried out in accordance with the adhesion (cross-cut method) JIS K 5600-5-6. The coating film adhesion was evaluated according to the classification table "Table 1 Classification of Test Results" shown in the said JIS. Classification 0 in this classification table has the highest adhesion, indicating that the adhesion decreases as the numerical value increases. Using a guide, a predetermined blade was applied perpendicular to the coating film to make a cut.

[0062] When six cuts were made at intervals of 1 mm, six cuts perpendicular to the 90° direction were then made. A transparent pressure-sensitive adhesive tape was attached to the cut portion of the coating film lattice, and the tape was firmly rubbed with a finger so that the coating film could be seen through. Within 5 minutes after adhesion, it was pulled off firmly at an angle close to 60° in 0.5 to 1.0 seconds and compared and judged with the classification table. Classification 0 in the classification table is the state where "the cut edge is completely smooth and there is no peeling off in any grid mesh". In the cases of Examples 1 to 5 and Comparative Examples 2, 3, 4, and 6, test pieces of 50×50×5 (mm) were used. In the cases of Examples 6 to 9, test pieces of 100×100×2 (mm) were used. In all of Examples 1 to 9 and Comparative Examples 2, 3, 4, and 6, the coating film adhered well to Classification 0.

[0063] (Sliding test) A schematic diagram related to the sliding test is shown in FIG. 1. The sliding test was carried out in accordance with JIS K7218 Method A. Using a commercially available friction and wear tester (MODEL EFM-III-H manufactured by A&D Co., Ltd.), a PV test was performed by changing P (pressure) while keeping V (sliding speed) constant in a ring-on-disk method.

[0064] As shown in FIG. 1, a coated surface 2a coated with a carbon fiber-containing paint on the surface (30×30 mm) of a test piece 2 with a size of 30×30×3 (mm) was brought into contact with a SUS304 ring 3 (area: 2 cm 2 , center line average surface roughness Ra: about 0.1 μm) as the mating material. The test piece 2 was rotated, the sliding speed was set to 0.5 m / s, the initial load was 50 N (pressure 250 kPa), and the load was increased by 50 N (pressure 250 kPa) every 10 minutes. The test environment was a room temperature of 25°C ± 5°C and a humidity of 50% RH ± 5% RH. The wear depth, friction coefficient, and temperature near the sliding surface of the test piece 2 were measured.

[0065] Note that the wear depth of the test piece 2 was obtained by detecting the displacement between the test piece 2 and a metal plate (not shown) attached to the torque shaft holding the test piece 2 with an eddy current displacement sensor. The temperature near the sliding surface was measured with a thermocouple 4 inserted into a through hole 3a formed in a part of the mating material ring 3.

[0066] In the examples and comparative examples, in the increase of the pressure P, a phenomenon was observed that at a certain point, the value of the wear depth suddenly increased. Therefore, in this test, the PV value, which is the product of P and V before the wear depth suddenly increases, was defined as the limiting PV value. Tables 1 and 2 show the limiting PV value, the coefficient of friction at the limiting PV value, and the temperature near the sliding surface as the results of the sliding test. It can be seen that for the test pieces coated with the carbon fiber-containing paints of Examples 1 to 4, high PV limit values and low coefficients of friction were obtained.

[0067] According to the carbon fiber-containing paint described above, since it is a paint in which 3 to 30% by mass of carbon fiber is blended in a solution composition mainly composed of a fluororesin and a polyimide precursor, while maintaining the heat resistance, low dielectric constant, high adhesion, and electrical insulation resistance, which are the characteristics of the paint film formed by applying the paint composed of the solution composition, the sliding characteristics (slip properties and abrasion resistance) can be greatly improved by the carbon fiber.

[0068] In particular, since carbon fiber has functional groups with positive and negative charges derived from dangling bonds, it can enhance the dispersibility of the fluororesin powder and the carbon fiber, and improve the adhesion of the paint film by the electric force of the carbon fiber. Moreover, when fine particles of tourmaline are mixed in the solution composition, when this paint is applied to a metal surface, the adhesion to the metal surface having a positive charge is remarkably enhanced by the negative charge of the tourmaline.

[0069] When a paint film of the above paint is formed on a part or all of the surface of a base material made of a carbon material among the mechanical parts described above, a lightweight mechanical part with a paint film having heat resistance, high adhesion, electrical insulation resistance, low dielectric constant, and excellent sliding characteristics (slip properties and abrasion resistance) can be obtained. Moreover, when fine particles of tourmaline are mixed in the solution composition, the adhesion between the surface of the base material made of a carbon material and the paint film is enhanced by the negative charge of the tourmaline.

[0070] In addition, those skilled in the art can implement the above embodiments in various modified forms without departing from the spirit of the present invention, and the present invention encompasses such modified forms.

Explanation of Reference Signs

[0071] 2: Specimen 2a: Coating Surface 3: Ring 3a: Through-Hole 4: Thermocouple

Claims

1. A carbon fiber-containing paint, comprising: a solution composition containing a fluororesin, a polyimide precursor, and fine tourmaline particles in an amount of 3 to 20% by mass; and 3 to 30% by mass of carbon fibers.

2. The carbon fiber-containing paint according to claim 1, wherein the carbon fibers are isotropic pitch-based carbon fibers and have a number average length of 30 to 100 μm.

3. A mechanical part, characterized in that a coating film is formed by applying a carbon fiber-containing paint, comprising: a solution composition containing a fluororesin, a polyimide precursor, and fine tourmaline particles in an amount of 3 to 20% by mass; and 3 to 30% by mass of carbon fibers, to a part or the whole of the surface of a substrate made of a carbon material.

4. The mechanical part according to claim 3, wherein the carbon fibers are isotropic pitch-based carbon fibers and have a number average length of 30 to 100 μm.

5. The mechanical part according to claim 3, wherein the carbon material is artificial graphite.

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