Preparation method of a polyimide compression material with a packing chain distribution

Abstract

The present invention belongs to the technical field of insulating materials and relates to a preparation method of a polyimide compacting material with a chain-like distribution of fillers, including: S1 raw material pretreatment; S2 mixing and sieving; S3 mold loading and sintering; S4 field-assisted pressing. By utilizing the difference in dielectric constant between the pressure-sensitive filler and the polyimide matrix, an alternating voltage is applied to form an electric field during pressing in the molten state. Under the action of the electric field force, the pressure-sensitive filler presents a chain-like distribution and aggregates to form a chain column, forming a good conductive network and heat conduction network, thereby obtaining a polyimide compacting material with a chain-like distribution of fillers that has excellent non-linear conductivity and good heat conductivity, while minimizing the influence of the filler on the overall performance of the polyimide matrix to the greatest extent.

Description

Technical Field

[0001] The present invention belongs to the technical field of insulating materials, and particularly relates to a preparation method of a polyimide compacting material with a chain-like distribution of fillers. Background Art

[0002] Among numerous polymers, polyimide has extremely outstanding comprehensive properties, including excellent mechanical properties, dielectric properties, heat resistance, and high insulation properties, etc. It is known as "one of the most promising engineering plastics in the 21st century" and can be widely applied in aerospace, electrical and electronics, machinery manufacturing, water conservancy, and other industrial fields.

[0003] In the aerospace field, the main energy source of current spacecraft is solar energy obtained by the solar array drive assembly (SADA), and the drive slip ring is the core component for realizing electrical energy transmission in the SADA. As an insulating material on the slip ring, polyimide ensures the stable operation of the slip ring. However, the space environment is extremely complex, and atomic oxygen, solar electromagnetic radiation, charged particles, etc. existing in space will all affect the performance of insulating materials. Extreme high-energy charged particles will penetrate the aluminum shielding shell and enter the interior of the SADA, and finally deposit in insulating media such as polyimide. Since the polyimide insulating medium has a low conductivity, the deposited electrons are difficult to discharge, and charge accumulation forms inside the medium. The accumulated charge will form local electric field distortion inside the spacecraft drive slip ring. When the electric field strength exceeds the discharge threshold of the insulating medium, electrostatic discharge will be triggered, which will even seriously endanger the safe operation of the spacecraft.

[0004] Polyimide modified with a voltage-sensitive filler has non-linear conductivity characteristics, and its conductivity increases with the increase of the electric field. It can effectively release the accumulated charge at the electric field distortion point, thereby playing a role in uniforming the electric field and improving the electric field distortion. However, according to the actual application scenario, in order to play an effective role in uniforming the electric field, it is often necessary to dope a large amount of voltage-sensitive filler. Relevant research by scholars shows that the improvement of the filler doping content often causes the deterioration of the mechanical properties of the material. Therefore, while ensuring the requirement of electric field uniformity, minimizing the filler content and improving the comprehensive performance of the insulating material is the direction of our further efforts. Summary of the Invention

[0005] In view of the above-mentioned deficiencies in the prior art, the present invention provides a preparation method of a polyimide compacting material with a chain-like distribution of fillers, and the specific technical solution is as follows:

[0006] A preparation method of a polyimide compacting material with a chain-like distribution of fillers includes the following steps:

[0007] S1 Raw material pretreatment: Dry the voltage-sensitive filler and the polyimide molding powder, stir and disperse the voltage-sensitive filler, and then screen the voltage-sensitive filler and the polyimide molding powder respectively;

[0008] S2 Mixing and sieving: After uniformly mixing the pressure-sensitive filler and the polyimide molding powder in a blender, sieve to obtain mixed powder materials;

[0009] S3 Molding and sintering: Load the sieved mixed powder materials into a mold, then place it in a sintering furnace and sinter the mixed powder materials to a molten state;

[0010] S4 Applying electric field and pressing: Apply an alternating voltage above and below the mold containing the molten mixed powder materials, then perform constant-pressure shaping and cooling to room temperature and demold to obtain a compacted material with a chain-like distribution of fillers.

[0011] As Figure 1 is the force analysis diagram of the pressure-sensitive filler particles after applying voltage, showing the principle of the chain-like arrangement of the pressure-sensitive filler. The dielectric constants of the pressure-sensitive filler and the polyimide matrix differ greatly. Under an alternating voltage, the pressure-sensitive filler particles act as dielectric particles, polarize in the electric field, and move under force to form a chain column, thus forming a good conductive network and heat conduction network, enabling the polyimide compacted material with a chain-like distribution of fillers to obtain excellent non-linear conductivity and good thermal conductivity at a lower filler content.

[0012] Furthermore, the particle sizes of the polyimide molding powder and the pressure-sensitive filler are less than 100 mesh.

[0013] Furthermore, the polyimide molding powder is one or more of YS20 molding powder, A-PI-280 molding powder, or cp-8002 molding powder.

[0014] Furthermore, the pressure-sensitive filler is one or more of ZnO, SiC, or carbon nanotubes.

[0015] Furthermore, the pressure-sensitive filler and the polyimide molding powder in step S1 are dried in a blast drying oven at 150 - 250 °C for 1 - 3 h.

[0016] Furthermore, the rotation speed during stirring in step S2 is 8000 - 10000 revolutions per minute, mixing for 5 - 20 min, and stopping stirring and shaking the drum every 2 - 3 s.

[0017] The centrifugal force of high-speed stirring is stronger, which can make the powder materials more uniformly mixed and the required time is shorter. However, high speed will also bring the problem of local overheating and easy carbonization of the powder materials. Therefore, stop stirring and shake the drum every 2 - 3 s to prevent local overheating and carbonization of the powder materials.

[0018] Furthermore, the sintering temperature in step S3 is 375 - 385 °C, and the sintering time is 2 - 2.5 h.

[0019] Further, in step S4, the applied alternating voltage is 60 Hz, and the molten mixture powder is under an electric field strength of 450 - 500 V / mm. The time for applying the alternating voltage is 70 - 90 seconds. rms / mm, and the time for applying the alternating voltage is 70 - 90 seconds.

[0020] Further, in step S4, the pressure of the constant - pressure pressing is 40 - 50 MP, and the time is 30 - 60 min.

[0021] The beneficial effects of the present invention are as follows:

[0022] The present invention utilizes the difference in dielectric constants between the pressure - sensitive filler and the polyimide matrix. When pressing in the molten state, an alternating voltage is applied to form an electric field. Under the action of the electric field force, the pressure - sensitive filler shows a chain - like distribution and aggregates to form chain columns, forming a good conductive network and a good heat - conducting network. Thus, a polyimide compact material with excellent non - linear conductivity and good heat conductivity, while minimizing the influence of the filler on the overall performance of the polyimide matrix, is obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is the force - analysis diagram of the pressure - sensitive filler particles after applying voltage in the present invention;

[0024] Figure 2 It is the preparation flow chart of the polyimide compact material with a chain - like distribution of fillers in the present invention;

[0025] Figure 3 It is the column chart of the DC breakdown field strength of the sample pieces of the examples and comparative examples in the present invention;

[0026] Figure 4 It is the characteristic diagram of the non - linear conductivity of the sample pieces of the examples and comparative examples in the present invention;

[0027] Figure 5 It is the column chart of the thermal conductivity of the sample pieces of the examples and comparative examples in the present invention;

[0028] Figure 6 It is the column chart of the simply - supported beam impact strength (without notch) of the sample pieces of the examples and comparative examples in the present invention. SPECIFIC EMBODIMENTS

[0029] The principles and features of the present invention will be described below in conjunction with examples. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0030] Example 1:

[0031] As Figure 2 shown, a preparation method of a polyimide compact material with a chain - like distribution of fillers includes the following steps:

[0032] S1 Raw material pretreatment: Dry an adequate amount of ZnO varistor microsphere fillers and fusible YS20 polyimide molding powders at 200 °C for 2 h, then use a blender to stir and disperse the ZnO varistor microsphere fillers, and pass the ZnO varistor microsphere fillers and YS20 molding powders through a 100-mesh sieve respectively;

[0033] S2 Mixing and sieving: Weigh 7.00 g of ZnO varistor microsphere fillers and 63.00 g of YS20 molding powders processed in step S1 using a precision balance. Use a clean and dry high-speed tissue blender to mix the ZnO varistor microsphere fillers and YS20 molding powders. Set the blender speed to 10,000 revolutions per minute. Stop stirring and shake the drum every 2 - 3 s. The stirring time is about 10 min. When the ZnO varistor microsphere fillers and YS20 molding powders are evenly mixed, pour the mixed raw materials into a 150-mesh sieve, and pick out the agglomerates to obtain mixed powder materials;

[0034] S3 Molding and sintering: Disperse and lay the sieved mixed powder materials flat in a mold of 101×59×30 mm. The thickness of the powder layer is 15 mm. Then put it into a sintering furnace, set the sintering temperature to 375 °C, and the sintering time to 2.5 h to sinter the mixed powder materials to a molten state;

[0035] S4 Field application and pressing: Place the mold filled with molten mixed powder materials on the hydraulic press platform, apply an AC voltage of 60 Hz above and below to make the mixed materials in an electric field strength of 450 Vrms / mm, and apply the electric field for 90 seconds. Then press with a constant pressure of 40 MPa and hold the pressure for 60 min to completely shape the mixed materials. After taking out the mold and cooling it for 1 h to room temperature, demold to obtain a 90% YS20 + 10% ZnO molded material sample with a filler chain distribution of 101×59×5 mm.

[0036] Example 2:

[0037] A preparation method of a polyimide compacting material with a filler chain distribution, comprising the following steps:

[0038] S1 Raw material pretreatment: Dry an adequate amount of nano-SiC fillers and A-PI-280 polyimide molding powders at 200 °C for 2 h, stir and disperse the nano-SiC fillers, and pass the nano-SiC fillers and A-PI-280 molding powders through a 100-mesh sieve respectively;

[0039] S2 Mixing and sieving: Use a precision balance to weigh 11.00 g of nano-SiC filler and 99.00 g of A-PI-280 molding powder after the treatment in step S1. Use a clean and dry high-speed tissue blender to mix the nano-SiC filler and A-PI-280 molding powder. Set the blender speed to 10,000 revolutions per minute. Stop stirring and shake the drum every 2 - 3 s. The stirring time is about 10 min. After the nano-SiC filler and A-PI-280 molding powder are evenly mixed, pour the mixed raw materials into a 150-mesh sieve, and pick out the lumps to obtain the mixed powder.

[0040] S3 Molding and sintering: Disperse and lay the sieved mixed powder flatly into a mold of 101×59×30 mm. The thickness of the powder laying is 25 mm. Then put it into a sintering furnace. Set the sintering temperature to 385 °C and the sintering time to 2 h to sinter the mixed powder to a molten state.

[0041] S4 Electric field application and pressing: Place the mold containing the molten mixed powder on the hydraulic press platform. Apply a 60 Hz alternating current electric field above and below to make the mixture in an electric field strength of 480 Vrms / mm. The application time of the electric field is 75 s. Then press it at a constant pressure of 50 MPa and hold the pressure for 40 min to completely shape the mixture. After taking out the mold and cooling it to room temperature, the mold can be demolded to obtain a 90% A-PI-280 + 10% SiC molded material sample with a 101×59×5 mm filler chain distribution.

[0042] Comparative example:

[0043] A preparation method of a polyimide compaction material includes the following steps:

[0044] S1 Raw material pretreatment: Dry an adequate amount of ZnO varistor microsphere filler and YS20 fusible polyimide molding powder at 200 °C for 2 h. Then use a blender to stir and disperse the ZnO varistor microsphere filler, and pass the ZnO varistor microsphere filler and YS20 molding powder through a 100-mesh sieve respectively.

[0045] S2 Mixing and sieving: Use a precision balance to weigh 14.00 g of ZnO varistor microsphere filler and 56.00 g of YS20 molding powder after the treatment in step S1. Use a clean and dry high-speed tissue blender to mix the ZnO varistor microsphere filler and YS20 molding powder. Set the blender speed to 10,000 revolutions per minute. Stop stirring and shake the drum every 2 - 3 s. The stirring time is about 10 min. After the ZnO varistor microsphere filler and YS20 molding powder are evenly mixed, pour the mixed raw materials into a 150-mesh sieve, and pick out the lumps to obtain the mixed powder.

[0046] S3 Die loading and sintering: The sieved mixed powder is evenly dispersed and loaded into a mold of 101×59×30 mm. The thickness of the powder laying is 15 mm. Then it is placed in a sintering furnace. The sintering temperature is set at 370 °C and the sintering time is 2.5 h to sinter the mixed powder into a molten state.

[0047] S4 Constant pressure pressing: The mold filled with the molten mixed powder is placed on the platform of a hydraulic press and pressed at a constant pressure of 40 MPa, and the pressure is maintained for 60 min to completely shape the mixture. After taking out the mold and cooling it for 1 h to room temperature, the mold can be demolded to obtain a 101×59×5 mm sample piece of the 80% YS20 + 20% ZnO molded material with uniformly distributed fillers.

[0048] The 90% YS20 + 10% ZnO compacted sample pieces of Example 1 are processed into small sample pieces of 40×40×2 mm and small sample strips of 80×10×4 mm; the 90% A-PI-280 + 10% SiC compacted sample pieces of Example 2 are processed into small sample pieces of 40×40×2 mm and small sample strips of 80×10×4 mm; the 80% YS20 + 20% ZnO compacted sample pieces of the comparative example are processed into small sample pieces of 40×40×2 mm and small sample strips of 80×10×4 mm; and the electrical properties, thermal properties and mechanical properties are tested respectively. Among them, the DC breakdown field strength is tested by a platform built in the laboratory, and the test results are as Figure 3 shown; the volume conductivity is tested according to the three-electrode method, and the test results are as Figure 4 shown; the thermal conductivity is detected by a Hot Disk TPS 3500 thermal conductivity meter, and the test results are as Figure 5 shown; the simply supported beam impact strength (without notch) is tested according to the national standard GB / T1043.1-2008, and the test results are as Figure 6 shown.

[0049] From Figures 3 to 6 data analysis, it can be seen that the 90% YS20 + 10% ZnO molded material sample pieces with chain distribution of fillers in Example 1 are quite close to the 80% YS20 + 20% ZnO molded material sample pieces prepared normally in the comparative example in terms of electrical properties such as DC breakdown field strength and non-linear conductance characteristics. The thermal conductivity is slightly higher than that of the comparative example, while the simply supported beam breakdown strength (without notch) is increased by 28.9% compared with the comparative example; it shows that the preparation method of the present invention can enable the polyimide molded material to form a good conductive network and thermal network at a low filling amount, achieving an effect similar to that of a high filling amount, and at the same time effectively reducing the deterioration effect of the high filling amount on the mechanical properties of the material.

[0050] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a polyimide compression material with a filler chain distribution, characterized in that: The steps include: S1 raw material pretreatment: drying the pressure-sensitive filler and the polyimide molding powder, stirring and breaking up the pressure-sensitive filler, and then sieving the pressure-sensitive filler and the polyimide molding powder respectively; S2 Mixing and sieving: After the pressure-sensitive filler and the polyimide molding powder are mixed evenly in a mixer, the mixed powder is sieved; S3 mold sintering: the sieved mixed powder is loaded into a mold, and then placed in a sintering furnace to sinter the mixed powder into a molten state; S4 field pressing: applying AC voltage to the upper and lower parts of the mold filled with molten mixed powder, and then pressing and shaping at a constant pressure, cooling to room temperature and demolding to obtain a compacted material with chain distribution of fillers; In step S4, the AC voltage applied is 60 Hz, so that the molten mixed powder is in a field strength of 450 to 500 Vrms / mm, and the AC voltage is applied for 70 to 90 seconds; In the step S4, the constant pressure pressing is performed at a pressure of 40 to 50 MPa and a time of 30 to 60 min.

2. The method for preparing a polyimide compression material with a filler chain distribution according to claim 1, characterized in that: The particle sizes of the polyimide molding powder and the pressure-sensitive filler are less than 100 meshes.

3. The method for preparing a polyimide compression material with a filler chain distribution according to claim 1, characterized in that: The polyimide molding powder is one or more of YS20 molding powder, A-PI-280 molding powder or cp-8002 molding powder.

4. The method for preparing a polyimide compression material with a filler chain distribution according to claim 1, characterized in that: The pressure-sensitive filler is one or more of ZnO, SiC or carbon nanotubes.

5. The method for preparing a polyimide compression material with a filler chain distribution according to claim 1, characterized in that: The pressure-sensitive filler and the polyimide molding powder in step S1 are placed in a forced air drying oven at 150-250° C. and dried for 1-3 hours.

6. The method for preparing a polyimide compression material with a filler chain distribution according to claim 1, characterized in that: The stirring speed in step S2 is 8000-10000 rpm, and the mixing is performed for 5-20 min. The stirring is stopped and the drum is shaken every 2-3 s.

7. The method for preparing a polyimide compression material with a filler chain distribution according to claim 1, characterized in that: The sintering temperature in step S3 is 375-385° C., and the sintering time is 2-2.5 hours.

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