1. The high-thermal-conductivity polyimide nano friction material is characterized in that the polyimide nano composite material is prepared from the following raw materials in parts by weight: 100 parts of polyimide, 0.5-2 parts of graphene, 0.5-1 part of multi-walled carbon nanotube and 0.1-1 part of nano copper powder.

2. The high thermal conductivity polyimide nanocomposite as claimed in claim 1, wherein the polyimide is a micron-sized molding powder, has an average particle size of 75 μm, has stable properties, and is very suitable for nano modification and hot press molding.

3. The polyimide nanocomposite as claimed in claim 1, wherein the graphene has a size of 1 to 5 μm and a thickness of 0.8 to 1.2nm, and is a material having the highest thermal conductivity up to the present, and the high temperature wear resistance of the polyimide can be greatly improved by adding the polyimide.

4. The polyimide nanocomposite material according to claim 1, wherein the size of the copper nanoparticles is less than 100nm, the copper powder and the stator of the ultrasonic motor belong to the same material, and friction heat can be timely derived when the copper powder and the stator phosphor bronze are subjected to butt-grinding after the friction material is added, so that the high-temperature wear resistance of the friction material can be further improved.

5. The polyimide nanocomposite as claimed in claim 1, wherein the multi-walled carbon nanotubes have a diameter of 8 to 15nm and a length of 10 to 50 μm, have good mechanical properties and thermal conductivity, and are ideal materials for improving the strength and thermal conductivity of polyimide.

6. A preparation method of a high-thermal-conductivity polyimide composite material sequentially comprises the following steps:

1) ultrasonically dispersing graphene, a multi-walled carbon nanotube and nano copper powder in acetone for 30min, adding polyimide powder, and ball-milling for 4 hours by using a ball mill;

2) drying at 80 deg.C in a vacuum drying oven, pulverizing, and sieving to obtain mixed powder;

3) hot-pressing the mixed powder under the pressure of 10-20 MPa; preserving heat for 1-2 hours at 375-390 ℃, and cooling along with the furnace to prepare the composite material;

4) and (4) slicing, sticking and surface treating the polyimide nano composite material prepared in the step (3) for the rotor of the ultrasonic motor.

7. The method of claim 6, wherein the slice has a thickness of 0.25 mm.

8. The method of claim 6, wherein the surface treatment is by mechanical grinding to a surface roughness of less than 0.1 μm.

Background

With the continuous development of ultrasonic motor technology and the expansion of application range, the requirements on the performance of rotor friction materials are higher and higher, and especially under the harsh working conditions of vacuum, high temperature, high load, high speed and the like, the traditional polyimide-based composite material has the defects of low mechanical strength, small hardness, poor wear resistance, short service life and the like, so that the urgent requirements in the fields of aerospace and the like are difficult to meet. Therefore, the problem that an advanced friction material with excellent high-temperature wear resistance is sought to be solved urgently by the ultrasonic motor is solved.

The friction material used by the prior rotary ultrasonic motor mainly has two problems: the most outstanding problems are that the abrasion is serious under the dry friction condition, the service life is short, the continuous long-life work cannot be met, the service life is shorter under the harsh working conditions of vacuum, high temperature, low temperature and the like, and the use requirements of complex environments such as aerospace and the like cannot be met; secondly, along with the accumulation of friction heat in the running process of the motor, the abrasion is more serious, and the output stability of the motor is reduced due to the reduction of generated abrasive dust and pre-pressure. At present, no friction material can completely solve the two problems in China. Therefore, the finding of a friction material with high temperature resistance, high thermal conductivity and ultra-low wear is a difficult problem to be solved urgently by the ultrasonic motor.

The polyimide is selected as a polymer matrix, and is a high polymer material with excellent comprehensive properties such as high temperature resistance, wear resistance and mechanical properties, but the pure polyimide has high wear rate under the condition of high-frequency micro-vibration, and is difficult to meet the use requirement of the ultrasonic motor under complex working conditions. Therefore, modification of polyimide is the most effective method for improving mechanical, thermodynamic and tribological properties. According to the invention, based on the modification of the nano copper powder, the advanced nano modification technology is utilized, and the graphene and the multi-walled carbon nano tube with excellent thermal conductivity, mechanical property and wear resistance are selected for modification, so that the mechanical strength, heat resistance, thermal conductivity and wear resistance of the polyimide nano composite material can be greatly improved, the environmental adaptability of the ultrasonic motor can be improved, and the service life of the ultrasonic motor can be prolonged.

And secondly, according to different addition ratios of the nano modifier, the preparation method is optimized so as to prepare the high-performance friction material suitable for the ultrasonic motor.

Disclosure of Invention

The invention aims to solve the problem of the friction material of the ultrasonic motor used at present, and provides a polyimide nano composite material more suitable for the ultrasonic motor and a preparation method thereof.

In order to achieve the purpose, the technical scheme of the invention is as follows:

the high-thermal-conductivity polyimide composite material is characterized by comprising polyimide, nano copper powder, graphene and multi-walled carbon nanotubes: the weight parts of the components are as follows: 100 parts of polyimide, 0.5-2 parts of graphene, 0.5-1 part of multi-walled carbon nanotube and 0.1-1 part of nano copper powder.

Preferably, the polyimide is micron-sized mold pressing powder, the average particle size of the mold pressing powder is 75 microns, the performance is stable, and the polyimide is very suitable for inorganic particle filling and hot press molding.

Preferably, the size of the graphene is 1-5 μm, the thickness of the graphene is 0.8-1.2nm, strong intermolecular force exists between the surface active functional group of the graphene and polyimide molecules, and the interface bonding force can be improved, so that the wear resistance of the polyimide is greatly improved; the graphene has good dispersibility in acetone, avoids agglomeration and improves the dispersibility in polyimide.

Preferably, the size of the nano copper powder is less than 100nm, and the nano copper powder can be well dispersed with graphene, polyimide and multi-walled carbon nanotubes in acetone to play a role in synergistic modification.

Preferably, the polyimide composite material is characterized in that the diameter of the multi-walled carbon nanotube is 8-15nm, the length of the multi-walled carbon nanotube is 10-50 μm, and the multi-walled carbon nanotube has good mechanical property and is an ideal reinforcing material for improving the strength of a polymer.

The preparation method of the polyimide friction material comprises the following steps:

1) ultrasonically dispersing graphene, a multi-walled carbon nanotube and nano copper powder in acetone for 30min, adding polyimide powder, and ball-milling for 4 hours by using a ball mill;

2) drying at 80 deg.C in a vacuum drying oven, pulverizing, and sieving to obtain mixed powder;

3) hot-pressing the mixed powder under the pressure of 10-20 MPa; keeping the temperature at 375 plus 390 ℃ for 1-2h, and cooling along with the furnace to obtain the composite material.

4) And (4) carrying out slicing, pasting and surface grinding treatment on the polyimide nano composite material prepared in the step (3) and then supplying the polyimide nano composite material to an ultrasonic motor rotor.

The invention has the beneficial effects that:

(1) according to the invention, polyimide with very good comprehensive performance is selected as a substrate, and the heat conductivity of the material is improved by adding graphene, wherein the graphene is the material with the best heat conductivity at present, so that the heat accumulation of a friction interface in a thermal vacuum environment can be reduced, and the wear resistance of the friction material of the ultrasonic motor can be improved;

(2) the invention selects the cheap nano copper powder with obvious modification effect, and the nano copper powder and the stator phosphor bronze contain the same elements, so that the heat conductivity is good in the friction process, the friction interface temperature is reduced, and the high-temperature wear resistance of the friction material of the ultrasonic motor is improved.

(3) The invention selects the multi-walled carbon nano-tube with excellent mechanical property, heat resistance and thermal conductivity as the modifier, which not only can increase the mechanical property of the polyimide, but also can improve the thermal conductivity in the friction process, thereby being beneficial to improving the wear resistance.

(4) The hot-press forming method selected by the invention has the advantages of reliable process, simple equipment and low cost, and is suitable for industrial production and utilization.

Drawings

FIG. 1 is a thermal conductivity test chart of the material prepared in the embodiment of the present invention.

FIG. 2 is a graph showing the temperature rise due to friction of the material prepared in the embodiment of the present invention.

Detailed Description

The present invention will be described in further detail with reference to the following detailed description of the drawings, and it should be understood that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments, and all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without any inventive work are within the scope of the present invention.

The polyimide nano composite material with high thermal conductivity is mainly used as a friction material in a rotary ultrasonic motor, the average particle size of the polyimide selected in the following examples is 75 micrometers, and the polyimide is purchased from Shanghai synthetic resin research institute; the nanometer copper powder is less than 100nm in size and purchased from Shanghai Allantin Biotechnology GmbH; the graphene is high-purity reagent-grade graphene powder, the purity is more than 99%, the size is 1-5 mu m, the thickness is 0.8-1.2nm, and the graphene is purchased from Nanjing Jicang nanometer technology Co., Ltd; the multi-wall carbon nano-tube has the diameter of 8-15nm and the length of 10-50 mu m, and is purchased from Chengdu organic chemistry GmbH of Chinese academy of sciences.

Example 1

For comparison of the modification effect, the examples tested the thermal conductivity of pure polyimide.

The preparation method comprises the following specific steps:

1) pouring the pure polyimide mould pressing powder into a mould, and hot-pressing and molding the mixed powder under the pressure of 10-20 MPa; keeping the temperature at 375 plus 390 ℃ for 1-2h, and cooling along with the furnace to obtain the composite material.

2) And (3) slicing, sticking and surface treating the polyimide material prepared in the step (1) for the rotor of the ultrasonic motor.

The thermal conductivity of the pure polyimide prepared by the embodiment is 0.35W/m.K, and after the pure polyimide and phosphor bronze are ground for 30 minutes under the conditions of 1MPa and 200r/min at room temperature, the temperature rise in the stable stage is 45 ℃.

Example 2

The high-thermal-conductivity polyimide composite material added with the nano copper powder comprises the following components in parts by weight: 100g of polyimide and 1g of nano copper powder.

The preparation method comprises the following specific steps:

1) ultrasonically dispersing the nano copper powder in acetone for 30min, adding polyimide powder, and ball milling for 4 h by using a ball mill;

2) drying at 80 deg.C in a vacuum drying oven, pulverizing, and sieving to obtain mixed powder;

3) pouring the mixed powder of the polyimide mould pressing powder and the nano copper powder into a mould, and carrying out hot press molding on the mixed powder under the pressure of 10-20 MPa; keeping the temperature at 375 plus 390 ℃ for 1-2h, and cooling along with the furnace to obtain the composite material.

4) And (4) slicing, pasting and surface treating the polyimide and nano copper powder composite material prepared in the step (3) for the rotor of the ultrasonic motor.

The thermal conductivity of the polyimide and nano copper powder composite material prepared by the embodiment is 56W/m.K, and after the composite material is ground with phosphor bronze under the conditions of 1MPa and 200r/min at room temperature for 30 minutes, the temperature rise at the stable stage is 40 ℃.

Example 3

The multi-walled carbon nanotube high-thermal conductivity polyimide composite material comprises the following components in parts by weight: 100g of polyimide and 1g of multi-walled carbon nanotube.

The preparation method comprises the following specific steps:

1) ultrasonically dispersing the multi-walled carbon nano tube in acetone for 30min, adding polyimide powder, and ball-milling for 4 hours by using a ball mill;

2) drying at 80 deg.C in a vacuum drying oven, pulverizing, and sieving to obtain mixed powder;

3) pouring the mixed powder of the polyimide molding powder and the multi-walled carbon nano-tubes into a mould, and carrying out hot-press molding on the mixed powder under the pressure of 10-20 MPa; keeping the temperature at 375 plus 390 ℃ for 1-2h, and cooling along with the furnace to obtain the composite material.

4) And (3) slicing, sticking and carrying out surface treatment on the polyimide and multi-walled carbon nanotube composite material prepared in the step (3) for the rotor of the ultrasonic motor.

The thermal conductivity of the polyimide and multi-walled carbon nanotube composite material prepared by the embodiment is 270W/m.K, and the temperature rise in the stable stage is 31 ℃ after 30 minutes of opposite grinding with phosphor bronze under the conditions of 1MPa and 200r/min at room temperature.

Example 4

The graphene high-thermal-conductivity polyimide composite material comprises the following components in parts by weight: 100g of polyimide and 2g of graphene.

The preparation method comprises the following specific steps:

1) ultrasonically dispersing graphene in acetone for 30min, adding polyimide powder, and ball-milling for 4 hours by using a ball mill;

2) drying at 80 deg.C in a vacuum drying oven, pulverizing, and sieving to obtain mixed powder;

3) pouring the mixed powder of the polyimide molding powder and the graphene into a mold, and carrying out hot press molding on the mixed powder under the pressure of 10-20 MPa; keeping the temperature at 375 plus 390 ℃ for 1-2h, and cooling along with the furnace to obtain the composite material.

4) And (4) carrying out slicing, pasting and surface treatment on the polyimide and graphene composite material prepared in the step (3) for the rotor of the ultrasonic motor.

The thermal conductivity of the polyimide and graphene composite material prepared by the embodiment is 800W/m.K, and after the composite material is ground with phosphor bronze under the conditions of 1MPa and 200r/min at room temperature for 30 minutes, the temperature rise at the stable stage is 12 ℃.

Example 5

The high-thermal-conductivity polyimide composite material added with the three compounds of the nano copper powder, the multi-walled carbon nanotube and the graphene comprises the following components in parts by weight: 100g of polyimide, 2g of graphene, 1g of multi-walled carbon nanotube and 1g of nano copper powder.

The preparation method comprises the following specific steps:

1) ultrasonically dispersing graphene, multi-walled carbon nanotubes and nano copper powder in acetone for 30min, adding polyimide powder, and ball-milling for 4 hours by using a ball mill;

2) drying at 80 deg.C in a vacuum drying oven, pulverizing, and sieving to obtain mixed powder;

3) pouring mixed powder of polyimide mould pressing powder, graphene, multi-walled carbon nanotubes and nano copper powder into a mould, and carrying out hot press molding on the mixed powder under the pressure of 10-20 MPa; keeping the temperature at 375 plus 390 ℃ for 1-2h, and cooling along with the furnace to obtain the composite material.

4) And (4) slicing, sticking and carrying out surface treatment on the polyimide, graphene, multi-walled carbon nanotubes and nano copper powder composite material prepared in the step (3) for the rotor of the ultrasonic motor.

The thermal conductivity of the polyimide and graphene composite material prepared by the embodiment is 1200W/m.K, and after the composite material is ground with phosphor bronze under the conditions of 1MPa and 200r/min for 30 minutes at room temperature, the temperature rise at a stable stage is 8 ℃.

The foregoing is only a preferred embodiment of this invention and it should be noted that modifications can be made by those skilled in the art without departing from the principle of the invention and these modifications should also be considered as the protection scope of the invention.