Wear-resistant polyimide graphite composite material and preparation method thereof

Abstract

The invention discloses a wear-resistant polyimide-graphite composite material and a preparation method thereof, and the wear-resistant polyimide-graphite composite material comprises the following components in percentage by mass: 80-95% of polyimide, 4-18% of graphite and 1-2% of wear-resistant filler, the polyimide is a polyimide terminated polymer containing an aromatic anhydride terminated end. The graphite and the polyimide are combined and then compounded with the wear-resistant filler, so that the dynamic wear resistance and the high temperature resistance are improved; the acid anhydride containing aryl is terminated, so that the polarity of amino-terminated groups is reduced, and the compatibility of polyimide and graphite is improved; generation of bubbles of the composite material is controlled, and the quality and the use performance of the material are improved.

Description

Technical Field

[0001] The invention relates to the technical field of new composite materials for vacuum pumps, and in particular to a wear-resistant polyimide graphite composite material and a preparation method thereof. Background Art

[0002] Vacuum pumps are important production and scientific research equipment, among which rotary vane vacuum pumps account for a large proportion. The rotary vane is an important component in the vacuum pump. There are many common vacuum pump rotary vane materials, generally including graphite carbon sheets (carbon sheets), resin rotary vanes, glass fiber, carbon fiber, aluminum alloy and other materials.

[0003] Technical requirements for the material of the vacuum pump vane: it should have high bending strength and not be easily deformed or bent during startup and operation; its density is smaller than that of iron, so the centrifugal force is small, the wear on the cylinder wall is small, and it will not directly bite the metal; it can withstand high temperatures; its thermal expansion coefficient in the length direction is small, equivalent to that of cast iron, so the tolerance in this direction can be considered according to cast iron parts during design, the expansion coefficient in the thickness direction is large, the hardness is high, the friction coefficient of oil lubrication is small, and it is wear-resistant and durable under the premise of sufficient oil lubrication.

[0004] At present, the main advantages of graphite carbon sheets (carbon sheets) are relatively low price, environmental protection, low noise, and low friction on the pump body. The disadvantages are easy breakage and poor wear resistance. In order to improve the application defects of graphite sheets, wear-resistant composite materials composed of polymer materials and graphite are widely used in the manufacture of air compressors, gasoline engine vacuum pump vanes (scrapers), seals or gaskets. Polyimide (PI for short) has the characteristics of strong corrosion resistance and good thermal stability, and has been widely used in the field of tribology. The wear resistance and abrasion resistance of polyimide can be further improved by composite modification with graphite. Huang Lijian (Journal of Materials Science and Engineering, Vol. 26, No. 2), Yang Tao (Industrial Technology, 2019.01) and others studied the effect of graphite filler on the performance of polyimide composites, and confirmed that the addition of graphite can effectively improve the wear resistance of the material, but the wear rate of the material increases with the further increase of the content. In addition, since polyimide has a linear molecular structure and contains polar terminal carboxyl groups (or terminal anhydride groups) and terminal amino groups at both ends of the molecule, it has poor compatibility with graphite. During the plasticizing and pressing process, polyimide easily aggregates into micelles and cannot be evenly dispersed, affecting the overall high temperature resistance and wear resistance of the composite material, resulting in unstable structure and performance of the composite material. Moreover, polyimide further imides under heating to produce water, which easily causes bubbles in the resin matrix.

[0005] Therefore, the current polyimide graphite composite materials generally have problems such as insufficient wear resistance, poor compatibility between polyimide and graphite, bubbles in the material, unstable performance and structure, and cannot meet the application requirements in vane vacuum pumps or sealing gaskets. Summary of the invention

[0006] In view of the defects of the prior art, the present invention provides a wear-resistant polyimide-graphite composite material, which solves the problems of poor wear resistance and high temperature resistance of the existing composite materials.

[0007] The object of the present invention is also to provide a method for preparing the above-mentioned wear-resistant polyimide graphite composite material;

[0008] The present invention also aims to provide the use of the wear-resistant polyimide graphite composite material in a vane vacuum pump or a sealing gasket.

[0009] In order to achieve the above object, the technical solution of the present invention is implemented as follows: a wear-resistant polyimide graphite composite material, calculated by mass percentage, includes the following components:

[0010] Polyimide 80~95%,

[0011] Graphite 4-18%;

[0012] Wear-resistant filler 1-2%;

[0013] The polyimide is a polyimide-terminated polymer containing aromatic anhydride end-capping, and the wear-resistant filler is at least one of nano-scale or micro-scale white corundum, silicon carbide, and silicon nitride.

[0014] Preferably, the polyimide is at least one of the self-made PI-1, PI-3, and PI-S, wherein the PI-1 is a polymer of 4,4'-oxydiphthalic anhydride and 2,2'-bis[4-(4-aminophenoxy)phenyl]propane; the PI-3 is a polymer of 4,4'-oxydiphthalic anhydride and 4,4'-diaminodiphenyl ether; and the PI-S is a capped polymer of 3,3',4,4'-dibenzophenone tetracarboxylic dianhydride and 4,4'-diaminodiphenyl ether.

[0015] Preferably, the graphite is at least one of high-purity graphite and static-pressure graphite.

[0016] Preferably, the size of the polyimide graphite composite material is 365×245×5.5 mm, and the density is 1.75-1.95 g / cm 3 , linear expansion coefficient ≤1.

[0017] The second technical solution of the present invention is achieved as follows: the preparation method of the above-mentioned polyimide graphite composite material comprises the following steps:

[0018] S1. Mixing polyimide, graphite and wear-resistant filler in a mixer in a weight ratio of (80-95):(4-18):(1-2) to obtain a premix;

[0019] S2, adding the premix obtained in S1 into a mold, hot pressing and then cooling under pressure to obtain a polyimide graphite composite material.

[0020] Preferably, in S1, the particle size of the polyimide is 800-1000 mesh; the particle size of the graphite is 800-1250 mesh.

[0021] Preferably, the rotation speed of the mixer is 15 rpm, and the mixing time is 2 to 4 hours.

[0022] Preferably, the specific method in S2 is:

[0023] S2-1. Take a certain amount of premix and fill it into the mold. Then put the mold with the material into the hot press. After the hot press is heated to 350°C, adjust the pressure of the hot press to 100KN and keep it warm and pressurized for 40 to 45 minutes.

[0024] S2-2, after the mold is heat-insulated and pressure-pressed, the mold is placed in a cold press, the pressure of the cold press is set to 1500KN and pressing is started. After pressing for 5 to 7 minutes, the pressure of the cold press is kept unchanged, and the mold is cooled by air cooling. When the temperature drops to below 200°C, the cold press is depressurized and the mold is taken out;

[0025] S2-3. When the mold is placed at room temperature and naturally cooled to below 50° C., the mold is disassembled to obtain a polyimide graphite composite material.

[0026] The third technical solution of the present invention is achieved as follows: the polyimide graphite composite material is used in a vane vacuum pump or a sealing gasket.

[0027] The principle of the present invention is described as follows:

[0028] The preparation method adds graphite and wear-resistant filler silicon nitride to the polyimide PI matrix, and through hot pressing and cold pressing and holding processes, the wear resistance and self-lubrication of the polyimide and graphite composite material are improved. The mechanical strength of the pressed vacuum pump vane can meet the use requirements.

[0029] The polyimide used in the present invention is a self-made polyimide-terminated polymer, which has good compatibility with graphite. The hot-pressed plate does not bend or warp, and the test indicators of self-lubricity, wear resistance and high temperature resistance are qualified. The customer trial effect is ideal and it has been put into mass production.

[0030] The key technology is to use phthalic acid groups to end-cap the amino groups of polyimide, which reduces the polarity of the polyimide end groups, improves the compatibility with graphite, and reduces the agglomeration of polyimide during the plasticization process; in addition, after the amino groups are end-capped, the water produced by further condensation of polyimide during the thermoplastic process is greatly reduced, the bubbles in the sheet are reduced, and the overall strength, heat resistance and wear resistance of the composite material are improved.

[0031] One of the general structural formulas of the polyimide-terminated polymer containing aromatic anhydride end-capping of the present invention is as follows:

[0032]

[0033] Linear polyimide has excellent thermal stability, good mechanical properties, outstanding radiation resistance and solvent resistance, and also has excellent wear resistance. During dry friction, a transfer film is formed with its opposite surface, which plays a self-lubricating role. However, the polyimide resin itself has a high friction coefficient and generates a large shear force, which causes greater adhesive wear; graphite has the function of a dry friction lubricant due to its unique lamellar crystal structure, and is usually used as a solid lubricant filler for polyimide self-lubricating composite materials. After graphite is added to the resin, the friction properties of the resin are improved. Graphite has a tendency to enrich on the friction opposite surface and form a transfer film, which may cause the friction surface of the sample to be not smooth enough when the graphite content is low, but when the graphite content is high, graphite can form a complete transfer film on the opposite surface and the sample surface, so the friction surface of the sample containing 15% graphite is very smooth.

[0034] The beneficial effects of the present invention are:

[0035] Solid lubricant graphite is combined with PI and then compounded with silicon nitride to form dynamic lubrication performance. Because silicon nitride has good hardness, it can promote the hardness of polyimide graphite material and reduce wear loss. In addition, the sliding friction coefficient of silicon nitride is low, and the dynamic lubrication performance is improved. The most important thing is that it reduces the dynamic wear amount and improves the dynamic wear resistance and high temperature resistance.

[0036] The present invention adopts anhydride end-capping containing aromatic groups to reduce the polarity of the terminal amino group, and the aromatic group (benzene) is similar to the graphite structure, thereby improving the compatibility of the polyimide and the graphite; in addition, after the terminal amino group of the polyimide is end-capped, further imidization reaction of the polyimide is prevented, the generation of condensation water is greatly reduced, the generation of bubbles in the plasticizing process is effectively controlled, and the quality and use performance of the composite material are improved; in addition, the compatibility of the solid lubricant graphite and the polyimide is improved, the continuous phase of the material is evenly distributed, and the wear resistance and high temperature resistance are improved.

[0037] The preparation method of the present invention improves the wear resistance and self-lubricating properties of the polyimide-graphite composite material for a vacuum pump by adding graphite and wear-resistant fillers to a polyimide matrix, and undergoes a hot pressing molding and a cold pressing and holding pressure process. The mechanical strength of the pressed vacuum pump vane or sealing gasket can meet the use requirements. In addition, by using dry powder to press into a rotary vane, the processing technology is simple, the raw materials are easy to purchase, there is no volatile organic compound (VOCs) emission, it is clean and environmentally friendly, and it is convenient for large-scale production. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0039] The present invention provides a wear-resistant polyimide graphite composite material, characterized in that it comprises the following components by mass percentage:

[0040] Polyimide 80~95%,

[0041] Graphite 4-18%,

[0042] Wear-resistant filler 1-2%;

[0043] The polyimide is a polyimide-terminated polymer containing aromatic anhydride end-capping, and the wear-resistant filler is at least one of nano-scale or micro-scale white corundum, silicon carbide, and silicon nitride.

[0044] The polyimide is at least one of the self-made PI-1, PI-3 and PI-S, with a fineness of 800-1000 meshes, the PI-1 is a polymer of 4,4'-oxydiphthalic anhydride and 2,2'-bis[4-(4-aminophenoxy)phenyl]propane; the PI-3 is a polymer of 4,4'-oxydiphthalic anhydride and 4,4'-diaminodiphenyl ether; the PI-S is a capped polymer of 3,3',4,4'-dibenzophenone tetracarboxylic dianhydride and 4,4'-diaminodiphenyl ether; the graphite is at least one of high-purity graphite and statically pressed graphite.

[0045] The present invention also provides a method for preparing a wear-resistant polyimide graphite composite material, which comprises the following steps in sequence:

[0046] S1. Mix polyimide, graphite and wear-resistant filler in a weight ratio of (80-95):(4-18):(1-2) in a V-type mixer at a speed of 15 rpm for 2-4 hours to obtain a premix;

[0047] The particle size of the polyimide is 800-1000 meshes, and it is pre-treated by drying in an oven at 240-260° C. for 5-8 hours before use; the particle size of the graphite is 800-1250 meshes.

[0048] S2, adding the premix obtained in S1 into a mold, hot pressing and then cooling under pressure to obtain a polyimide graphite composite material. Specifically comprising the following steps:

[0049] S2-1, take a certain amount of the premix obtained in S1 and fill it into the mold, then put the mold with the material into the hot press, heat the hot press to 350°C, adjust the pressure of the hot press to 100KN, and keep the temperature and pressure for 40 to 45 minutes;

[0050] S2-2, after the mold is heat-insulated and pressure-pressed, the mold is placed in a cold press, the pressure of the cold press is set to 1500KN and pressing is started. After pressing for 5 to 7 minutes, the pressure of the cold press is kept unchanged, and the mold is cooled by air cooling. When the temperature drops to below 200°C, the cold press is depressurized and the mold is taken out;

[0051] S2-3. When the mold is placed at room temperature and naturally cooled to below 50° C., the mold is disassembled to obtain a polyimide graphite composite material.

[0052] The invention also applies the prepared wear-resistant polyimide graphite composite material to a sliding vane vacuum pump or a sealing gasket.

[0053] Test method:

[0054] 1. Density: GB / T 1033.1-2008 (immersion method);

[0055] 2. Flexural strength and flexural modulus: GB / T 9341-2008 Determination of flexural properties of plastics;

[0056] 3. Compressive strength: GB 8624-2006;

[0057] 4. GB / T 531.1-2008 Test method for indentation hardness of vulcanized rubber or thermoplastic rubber Part 1: Shore hardness tester method (Shore hardness);

[0058] 5. Load thermal deformation temperature: GB / T 1634.2-2004;

[0059] 6. Linear expansion coefficient: GB 1036-89, determination method of linear expansion coefficient of plastics.

[0060] Table 1 Vacuum pump vane detection indicators

[0061] Test items Control indicators <![CDATA[Density (g / cm 3 )]]> 1.75-1.95 Bending strength (MPa) (23±2℃) ≥60 Flexural modulus (MPa) (23℃±2℃) ≥16000 Compressive strength (MPa) (23±2℃) ≥80 Shore Hardness ≥65 <![CDATA[Heat distortion temperature under load (18.6 kg / cm 2 ) °C]]> ≥270 <![CDATA[Coefficient of linear expansion (23 to 200 °C), (10 -5 cm / cm / °C)]]> ≤1

[0062] The following are specific embodiments

[0063] Example 1

[0064] A wear-resistant polyimide-graphite composite material provided in Example 1 of the present invention comprises the following components by mass percentage: 95% polyimide, 4% graphite, and 1% wear-resistant filler; the polyimide is PI-S, and the wear-resistant filler is silicon nitride.

[0065] The method for preparing the polyimide graphite composite material provided in Example 1 of the present invention comprises the following steps in sequence:

[0066] S1, polyimide with a particle size of 800-1000 mesh, pre-treated by drying in an oven at 240° C. for 5 h, high-purity graphite with a particle size of 800-1250 mesh, and wear-resistant filler nano-scale silicon nitride are mixed in a V-type mixer at a weight ratio of 95:4:1, with a rotation speed of 15 rpm and a mixing time of 2 h to obtain a premix;

[0067] S2, adding the premix obtained in S1 into a mold, hot pressing and then cooling under pressure to obtain a polyimide graphite composite material. Specifically comprising the following steps:

[0068] S2-1, take a certain amount of the premix obtained in S1 and fill it into the mold, then put the mold with the material into the hot press, heat the hot press to 350°C, adjust the hot press pressure to 100KN, and keep the temperature and pressure for 40 minutes;

[0069] S2-2, after the mold is heat-insulated and pressure-pressed, the mold is placed in a cold press, the pressure of the cold press is set to 1500KN and pressing begins. After pressing for 5 minutes, the pressure of the cold press is kept unchanged, and the mold is cooled by air cooling. When the temperature drops to below 200°C, the cold press is depressurized and the mold is taken out;

[0070] S2-3. When the mold is placed at room temperature and naturally cooled to below 50° C., the mold is disassembled to obtain a finished polyimide graphite composite material slide.

[0071] Example 2

[0072] Embodiment 2 of the present invention provides a polyimide-graphite composite material, which comprises the following components by mass percentage: 90% polyimide, 9% graphite, and 1% wear-resistant filler; the polyimide is PI-S, and the wear-resistant filler is silicon nitride.

[0073] The method for preparing the polyimide graphite composite material provided in Example 2 of the present invention comprises the following steps in sequence:

[0074] S1, polyimide with a particle size of 800-1000 mesh, pre-treated by drying in an oven at 260° C. for 8 h, high-purity graphite with a particle size of 800-1250 mesh, and wear-resistant filler nano-scale silicon nitride are mixed in a V-type mixer at a weight ratio of 90:9:1, with a rotation speed of 15 rpm and a mixing time of 4 h to obtain a premix;

[0075] S2, adding the premix obtained in S1 into a mold, hot pressing and then cooling under pressure to obtain a polyimide graphite composite material. Specifically comprising the following steps:

[0076] S2-1, take a certain amount of the premix obtained in S1 and fill it into the mold, then put the mold with the material into the hot press, heat the hot press to 350°C, adjust the pressure of the hot press to 100KN, and keep the temperature and pressure for 45 minutes;

[0077] S2-2, after the mold is heat-insulated and pressure-pressed, the mold is placed in a cold press, the pressure of the cold press is set to 1500KN and pressing begins. After pressing for 7 minutes, the pressure of the cold press is kept unchanged, and the mold is cooled by air cooling. When the temperature drops to below 200°C, the cold press is depressurized and the mold is taken out;

[0078] S2-3. When the mold is placed at room temperature and naturally cooled to below 50° C., the mold is disassembled to obtain a finished polyimide graphite composite material slide.

[0079] Example 3

[0080] A wear-resistant polyimide-graphite composite material provided in Example 3 of the present invention comprises the following components, by mass percentage: 85% polyimide, 13% graphite, and 2% wear-resistant filler; the polyimide is PI-S, and the wear-resistant filler is silicon nitride.

[0081] The method for preparing the polyimide graphite composite material provided in Example 3 of the present invention comprises the following steps in sequence:

[0082] S1, mixing polyimide and graphite in a weight ratio of 85:13:2 in a V-type mixer at a speed of 15 rpm for 3 h to obtain a premix;

[0083] S2, adding the premix obtained in S1 into a mold, hot pressing and then cooling under pressure to obtain a polyimide graphite composite material. Specifically comprising the following steps:

[0084] S2-1, take a certain amount of the premix obtained in S1 and fill it into the mold, then put the mold with the material into the hot press, heat the hot press to 350°C, adjust the pressure of the hot press to 100KN, and keep the temperature and pressure for 42 minutes;

[0085] S2-2, after the mold is heat-insulated and pressure-pressed, the mold is placed in a cold press, the pressure of the cold press is set to 1500KN and pressing begins. After pressing for 6 minutes, the pressure of the cold press is kept unchanged, and the mold is cooled by air cooling. When the temperature drops to below 200°C, the cold press is depressurized and the mold is taken out;

[0086] S2-3. When the mold is placed at room temperature and naturally cooled to below 50° C., the mold is disassembled to obtain a finished polyimide graphite composite material slide.

[0087] Example 4

[0088] A wear-resistant polyimide-graphite composite material provided in Example 4 of the present invention comprises the following components by mass percentage: 80% polyimide, 18% graphite, and 2% wear-resistant filler; the polyimide is PI-S, and the wear-resistant filler is silicon nitride.

[0089] The method for preparing the polyimide graphite composite material provided in Example 4 of the present invention comprises the following steps in sequence:

[0090] S1, mixing polyimide and graphite in a weight ratio of 80:18:2 in a V-type mixer at a speed of 15 rpm for 3 h to obtain a premix;

[0091] S2. Same as Example 3.

[0092] Example 5

[0093] Example 5 of the present invention provides a wear-resistant polyimide-graphite composite material, wherein the polyimide is PI-1, the graphite is static-pressure graphite, the wear-resistant filler is micron-grade white corundum, and the rest is the same as Example 1.

[0094] Example 6

[0095] Example 6 of the present invention provides a wear-resistant polyimide-graphite composite material, wherein the polyimide is PI-3, the graphite is static-pressure graphite, the wear-resistant filler is micron-sized silicon carbide, and the rest is the same as Example 2.

[0096] Example 7

[0097] Example 7 of the present invention provides a wear-resistant polyimide graphite composite material, wherein the polyimide is a mixture of PI-1, PI-3, and PI-S, the high-purity graphite is a mixture of static graphite, and the wear-resistant filler is a mixture of nano-grade white corundum, silicon carbide, and silicon nitride, and the rest is the same as Example 1.

[0098] Example 8

[0099] Example 8 of the present invention provides a wear-resistant polyimide graphite composite material, wherein the polyimide is a mixture of PI-1, PI-3, and PI-S, the high-purity graphite is a mixture of static graphite, and the wear-resistant filler is a mixture of micron-grade white corundum, silicon carbide, and silicon nitride, and the rest is the same as Example 2.

[0100] Table 2 Test data of Examples 1-4

[0101]

[0102]

[0103] The following is a comparative example

[0104] The above embodiment is obtained without adding wear-resistant filler silicon nitride to obtain a comparative example, and a comparative example test is carried out, and the data is compared with that of German SGL EK60.

[0105] Table 3 Comparative Examples 1-3 Test Data

[0106]

[0107]

[0108] Comparative Example 1

[0109] The polyimide graphite composite plate material provided in this comparative example 1 includes the following components by weight percentage: 95% polyimide and 5% graphite. The polyimide and graphite are mixed in a V-type mixer at a weight ratio of 95:5, and the other components are the same as those in Example 1.

[0110] Comparative Example 2

[0111] The polyimide graphite composite plate material provided in this comparative example 1 includes the following components by weight percentage: 90% polyimide and 10% graphite. The polyimide and graphite are mixed in a V-type mixer at a weight ratio of 90:10, and the other components are the same as those in Example 1.

[0112] Comparative Example 3

[0113] The polyimide graphite composite plate material provided in this comparative example 1 includes the following components by weight percentage: 85% polyimide and 15% graphite. The polyimide and graphite are mixed in a V-type mixer at a weight ratio of 85:15, and the other components are the same as those in Example 1.

[0114] In Examples 1-4, as the amount of graphite filler increases, the mechanical properties of the composite material gradually decreases. Because graphite, as a self-lubricating filler, has no toughening and strengthening effect on the composite material. Due to the low inherent strength of graphite, the interface strength between the graphite particles and the polyimide PI matrix is ​​not high, and the bonding force (compatibility) is poor, resulting in reduced mechanical properties of the composite material. After the polyimide PI is capped, its compatibility with graphite is improved, and its mechanical properties, heat resistance and wear resistance are all improved. The performance of Example 3 is relatively good.

[0115] In comparative example 1-3, no silicon nitride nanopowder is added. Compared with example 1-3, the hardness is changed, and the changes of other indicators are not significant. After the installation test (1320rmp), the running noise of the rotor blade of example 1-4 is low, and the running condition is relatively good.

[0116] Example 3 was installed and compared with the resin and graphite composite vane EK60 produced by SGL in Germany. The overall performance of EK60, especially the wear resistance, was better than that of Example 3, but the thermal deformation temperature and linear expansion coefficient performance indicators of Examples 1-4 were better than those of SGL vane EK60. Therefore, the composite material composed of polyimide, graphite and silicon nitride has its specific lubrication performance, can meet the performance requirements of high-performance vacuum pump vanes, and has good product space and market prospects.

[0117] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0118] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the attached claims.

Claims

1. A wear-resistant polyimide graphite composite material, characterized in that: Calculated by mass percentage, it includes the following components: Polyimide 80~95%, Graphite 4-18%, Wear-resistant filler 1-2%; The polyimide is a polyimide-terminated polymer containing aromatic anhydride end-capping; the wear-resistant filler is at least one of nano-scale or micro-scale white corundum, silicon carbide, and silicon nitride.

2. A wear-resistant polyimide graphite composite material according to claim 1, characterized in that: The polyimide is at least one of the self-made PI-1, PI-3 and PI-S, wherein the PI-1 is a polymer of 4,4'-oxydiphthalic anhydride and 2,2'-bis[4-(4-aminophenoxy)phenyl]propane; the PI-3 is a polymer of 4,4'-oxydiphthalic anhydride and 4,4'-diaminodiphenyl ether; and the PI-S is a capped polymer of 3,3',4,4'-dibenzophenone tetracarboxylic dianhydride and 4,4'-diaminodiphenyl ether.

3. The wear-resistant polyimide graphite composite material according to claim 1, characterized in that: The graphite is at least one of high-purity graphite and static-pressure graphite.

4. The wear-resistant polyimide graphite composite material according to claim 1, characterized in that: The size of the polyimide graphite composite material is 365×245×5.5 mm, and the density is 1.75-1.95 g / cm 3 , linear expansion coefficient ≤1.

5. A method for preparing the polyimide graphite composite material according to any one of claims 1 to 4, characterized in that: The following steps are involved: S1. Mixing polyimide, graphite and wear-resistant filler in a mixer in a weight ratio of (80-95):(4-18):(1-2) to obtain a premix; S2, adding the premix obtained in S1 into a mold, hot pressing and then cooling under pressure to obtain a polyimide graphite composite material.

6. The method for preparing a wear-resistant polyimide graphite composite material according to claim 5, characterized in that: In S1, the particle size of the polyimide is 800-1000 mesh; the particle size of the graphite is 800-1250 mesh, and the wear-resistant filler is nanometer-level or submicron-level.

7. The method for preparing a wear-resistant polyimide graphite composite material according to claim 5, characterized in that: In S1, the rotation speed of the mixer is 15 rpm, and the mixing time is 2 to 4 hours.

8. The method for preparing a wear-resistant polyimide-graphite composite material according to claim 5, characterized in that: The specific method in S2 is: S2-1. Take a certain amount of premix and fill it into the mold. Then put the mold with the material into the hot press. After the hot press is heated to 350°C, adjust the pressure of the hot press to 100KN and keep it warm and pressurized for 40 to 45 minutes. S2-2, after the mold is heat-insulated and pressure-pressed, the mold is placed in a cold press, the pressure of the cold press is set to 1500KN and pressing is started. After pressing for 5 to 7 minutes, the pressure of the cold press is kept unchanged, and the mold is cooled by air cooling. When the temperature drops to below 200°C, the cold press is depressurized and the mold is taken out; S2-3. When the mold is placed at room temperature and naturally cooled to below 50° C., the mold is disassembled to obtain a polyimide graphite composite material.

9. Use of the polyimide graphite composite material according to any one of claims 1 to 4 in a sliding vane vacuum pump or a sealing gasket.

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