WO2021103850A1 - Preparation method for modified carbon nanotube and use thereof - Google Patents

Abstract

Disclosed in the present invention are a preparation method for a modified carbon nanotube and use thereof, the preparation method comprising: (1) preparing a surface-carboxylated carbon nanotube; and (2) dissolving the surface-carboxylated carbon nanotube in a mixed solution of water and ethanol, then adding tetraethoxysilane, vinyltriethoxysilane and aqueous ammonia, reacting same to prepare the modified carbon nanotube, the surface of the modified carbon nanotube having a vinyl group. Further disclosed is use of the modified carbon nanotube prepared by the preparation method in a thermally conductive and insulating material. The modified carbon nanotube prepared by the preparation method of the present invention can have the characteristics of high thermal conductivity, low electrical conductivity, and good compatibility with organics; and is thus especially suitable for a thermally conductive and insulating paint.

Description

Preparation method and application of modified carbon nanotube

This application requires the prior patent application of the State Intellectual Property Office of China with the application number of CN 201911170322.X and the filing date of 2019.11.26 as priority, and the content of the prior patent application text is fully incorporated into this patent application by reference in.

Technical field

The invention belongs to the technical field of thermal conductivity and insulation, and specifically relates to a method for preparing modified carbon nanotubes and applications thereof.

Background technique

With the continuous development of motor technology, the power of the motor is continuously increasing, and the power consumption of the motor is also increasing at the same time, which causes the working temperature of the motor to become higher and higher, and the heat dissipation capacity of the motor components, especially the insulating parts, directly affects the temperature of the motor. If the motor temperature rise exceeds the limit, it will cause insulation aging, coil breakdown, and motor burnout. If the insulating varnish has both high thermal conductivity and electrical insulation performance, it can effectively reduce the temperature rise of the motor windings, thereby increasing The output power of the motor, and the insulating paint in the prior art still has the problem that it is difficult to have excellent thermal conductivity, insulation and mechanical properties, which greatly limits the quality and life of the motor. Therefore, the requirements for insulating paint in the prior art are getting higher and higher. In order to solve the above problems, there are generally two ideas. One is to continuously improve the heat resistance level of the insulating paint to adapt to the high working temperature of the motor; the other is to improve the insulation. The thermal conductivity of the paint improves the heat dissipation of the motor, thereby reducing the working temperature of the motor. Compared with improving the heat resistance level, improving the thermal conductivity of the insulating paint has the advantages of reducing the energy consumption of the motor and improving the overall life of the motor.

However, most insulating varnishes nowadays have poor thermal conductivity due to the use of polymer materials. In order to improve the thermal conductivity of insulating varnishes, most researchers use the method of doping with high thermal conductivity materials, but these insulating varnishes are in order to obtain high thermal conductivity. In general, high doping is required for performance, and high doping will affect other mechanical properties of insulating varnish, and there are also problems such as poor compatibility of doped particles with insulating varnish. For example, unsaturated polyester resin, due to its simple production process, easy availability of raw materials, chemical corrosion resistance, excellent mechanical and electrical properties, room temperature curing, good process performance, etc., and then used as the largest variety of thermosetting resins. It is widely used in insulating paint, but it also has the above problems. In order to improve the thermal conductivity, adding highly doped thermally conductive materials, on the one hand, it is difficult to achieve better heat conduction due to uneven dispersion or the defects of the thermally conductive material itself, on the other hand , Due to the incompatibility of the thermal conductive material and the surface interface of the organic matter further restricts its thermal conductivity.

Among them, carbon nanotubes (CNTs) in thermal conductive materials have received extensive attention because of their excellent thermal conductivity, mechanical strength, electrical conductivity and other properties. According to Maxwell’s mixing theory, adding 1% of carbon nanotubes can theoretically improve The thermal conductivity of organic compounds is 50 times, so it is expected to solve the negative effects of high doping mentioned above. For example, high doping reduces the mechanical properties of insulating varnishes; however, for insulating materials, carbon nanotubes have high The high electrical conductivity and incompatibility with the surface and interface of organic matter limit the application of carbon nanotubes as thermally conductive materials in insulating materials.

Summary of the invention

The purpose of the present invention is to overcome the shortcomings of the prior art and provide a new method for preparing modified carbon nanotubes. The modified carbon nanotubes prepared by the method can combine high thermal conductivity, low electrical conductivity, and compatibility with organics. Good characteristics.

The invention also provides an application of the modified carbon nanotube prepared by the above method in a thermally conductive insulating material.

To solve the above technical problems, the present invention adopts the following technical solutions:

A preparation method of modified carbon nanotubes, the preparation method includes the following steps:

(1) Preparation of carbon nanotubes with surface carboxylation;

(2) The surface carboxylated carbon nanotubes prepared in step (1) are dissolved in a mixed solution of water and ethanol, and then ethyl orthosilicate, vinyl triethoxysilane and ammonia are added to react to prepare The modified carbon nanotube is formed, and the surface of the modified carbon nanotube has a vinyl group.

According to the present invention, the modified carbon nanotube produced by the preparation method includes a carbon nanotube core layer and a silica shell layer formed on the surface of the carbon nanotube core layer, the carbon nanotube core layer and Part or all of the silica shell layers are connected by chemical bonds.

According to some preferred aspects of the present invention, in step (2), the reaction is carried out at 30-50°C.

According to some preferred aspects of the present invention, in step (2), the ethyl orthosilicate, the vinyl triethoxy silane and the ammonia are added to the mixed solution in the form of dropwise addition.

According to some specific and preferred aspects of the present invention, in step (2), the step of adding the ethyl orthosilicate, the vinyl triethoxysilane and the ammonia water to the mixed solution is specifically as follows: Part of the mixture of ethyl orthosilicate and the vinyl triethoxy silane is added dropwise to the mixed solution, while a part of the ammonia water is added dropwise to react; then the remaining part of the mixture and the ammonia water are added separately .

According to some preferred aspects of the present invention, in step (2), the feed quality of the surface carboxylated carbon nanotubes, the mixture of the ethyl orthosilicate and the vinyl triethoxysilane, and the ammonia The ratio is 1:0.9-1.2:1-1.2.

According to some preferred aspects of the present invention, in step (2), the feed mass ratio of the water to the ethanol is 1:0.95-1.1.

According to some preferred aspects of the present invention, in step (2), the feed mass ratio of one of the ethyl orthosilicate and the vinyl triethoxysilane relative to the other is controlled to be within 3 times.

According to some specific and preferred aspects of the present invention, in step (1), the surface carboxylated carbon nanotubes are prepared by mixing and reacting carbon nanotubes with a mixed acid at 105-115°C, and the mixed acid is made of Consists of sulfuric acid and nitric acid.

According to some specific and preferred aspects of the present invention, the feed mass ratio of the sulfuric acid to the nitric acid is 2-4:1.

According to some specific and preferred aspects of the present invention, the carbon nanotubes are multi-wall carbon nanotubes and/or single-wall carbon nanotubes.

In the present invention, the mass fraction of sulfuric acid is 80-98%, and the mass fraction of nitric acid is 60-80%.

Another technical solution provided by the present invention: an application of modified carbon nanotubes produced by the above-mentioned method for preparing modified carbon nanotubes in thermally conductive insulating materials.

Due to the implementation of the above technical solutions, the present invention has the following advantages compared with the prior art:

The present invention innovatively adopts a specific method to prepare modified carbon nanotubes with vinyl on the surface, and because the prepared modified carbon nanotubes have a chemical bond between the core layer and the shell layer, the modified carbon nanotubes of the present invention It can exist stably and can be applied to insulating varnish with a small amount of addition, and can participate in the cross-linking network of the unsaturated resin of insulating varnish with vinyl bonds, so that the insulating varnish made can not only have excellent thermal conductivity and insulation It can also obtain excellent mechanical properties, overcome the disadvantages of high doping in the prior art that are not conducive to the common impregnation process and the VPI impregnation process, and the temperature resistance level can reach H level.

Detailed ways

With the continuous development of motor technology, the power of the motor is continuously increasing, and the power consumption of the motor is also increasing at the same time, which causes the working temperature of the motor to become higher and higher, and the heat dissipation capacity of the motor components, especially the insulating parts, directly affects the temperature of the motor. If the motor temperature rise exceeds the limit, it will cause insulation aging, coil breakdown, and motor burnout. If the insulating varnish has both high thermal conductivity and electrical insulation performance, it can effectively reduce the temperature rise of the motor windings, thereby increasing The output power of the motor, and the insulating paint in the prior art still has the problem that it is difficult to have excellent thermal conductivity, insulation and mechanical properties, which greatly limits the quality and life of the motor.

Based on the above problems, the present invention provides a modified carbon nanotube with a specific structure made by a specific method, which allows the modified carbon nanotube to exist in a core-shell structure, and a silica shell is formed on the surface of the carbon nanotube core layer. At the same time, the two layers are connected by a chemical bond to make the bond tighter and stronger, which is conducive to giving full play to the thermal conductivity of carbon nanotubes and inhibiting the conductivity of carbon nanotubes, and also gives the modified carbon nanotube surface ethylene Base, so that the modified carbon nanotubes can participate in the crosslinking network of organic resins such as unsaturated polyester resins, so that on the one hand, it can ensure that the carbon nanotubes are evenly dispersed in the insulating paint, make full use of their thermal conductivity, and also improve The degree of crosslinking of the resin curing, on the other hand, enables the carbon nanotubes of the present invention to be applied to insulating paint with a small amount of addition, and thus does not affect the mechanical properties and electrical properties of the insulating paint.

Specifically, a method for preparing modified carbon nanotubes provided by the present application includes: (1) preparing surface carboxylated carbon nanotubes; (2) preparing the surface carboxylated carbon nanotubes prepared in step (1) The tube is dissolved in a mixed solution of water and ethanol, and then ethyl orthosilicate, vinyl triethoxy silane and ammonia are added to react to form the modified carbon nanotube, the surface of the modified carbon nanotube has Vinyl. According to the present invention, the modified carbon nanotube produced includes a carbon nanotube core layer and a silica shell layer formed on the surface of the carbon nanotube core layer, the carbon nanotube core layer and the dioxide Part or all of the silicon shell layers are connected by chemical bonds.

The present invention will be further described in detail below in conjunction with specific embodiments. It should be understood that these embodiments are used to illustrate the basic principles, main features and advantages of the present invention, but the present invention is not limited by the following embodiments. The implementation conditions used in the examples can be further adjusted according to specific requirements, and implementation conditions not specified are usually conditions in routine experiments. The raw materials used in the examples are all commercially available industrial products.

In the following examples, unless otherwise specified, all raw materials are basically commercially available or prepared by conventional methods in the art. In the following, the mass percentage of concentrated sulfuric acid is 98%, the mass percentage of nitric acid is 68%, the mass percentage of ammonia is 28%, and the multi-walled carbon nanotubes are purchased from (Beijing Deke Island Gold Technology Co., Ltd., CNT106).

Example 1 Preparation of modified carbon nanotubes

(1) Prepare surface carboxylated carbon nanotubes; add 1 part of multi-walled carbon nanotubes to 90 parts of concentrated sulfuric acid to ultrasonically disperse for 30 minutes, then add 30 parts of nitric acid to this solution, and stir at 110°C in an oil bath 6 hours. After the reaction is completed, pour the solution into 1000 parts of water to obtain a yellowish-brown solution, and then centrifuge the solution at a speed of 10000r/min, wash the product with water and continue centrifugation three times to obtain carbon nanotubes with carboxylated surface;

(2) Add 10 parts of surface carboxylated carbon nanotubes prepared in step (1) to a mixture of 50 parts of water and 50 parts of ethanol, and add 5 parts of ethyl orthosilicate and 5 parts of vinyl triethoxy silane Mix and prepare 10 parts ammonia. Place the carboxylated carbon nanotube solution in an oil bath at 35°C and stir, slowly add 1 part of the mixture of 10 parts of ethyl orthosilicate and vinyl triethoxy silane, and then add dropwise to the above mixture. At the same time, slowly add 1 part of ammonia water, and stir for 30 minutes after the addition is complete; then slowly add the remaining 9 parts of ethyl orthosilicate and vinyl triethoxy silane mixture and 9 parts of ammonia dropwise. After the dripping is completed, the reaction After 2 hours, centrifuged at 10000r/min to obtain modified carbon nanotubes.

Example 2 Preparation of modified carbon nanotubes

(1) Prepare surface carboxylated carbon nanotubes; add 1 part of multi-walled carbon nanotubes to 90 parts of concentrated sulfuric acid to ultrasonically disperse for 30 minutes, then add 35 parts of nitric acid to this solution, and stir at 115°C in an oil bath After 6 hours, after the reaction is complete, pour this solution into 1000 parts of water to obtain a yellow-brown solution, and then centrifuge this solution at a speed of 10000r/min. After washing the product with water, continue centrifugation three times to obtain surface carboxylated carbon. nanotube;

(2) Add 10 parts of carbon nanotubes with surface carboxylation prepared in step (1) to a mixture of 50 parts of water and 50 parts of ethanol, and add 2.5 parts of ethyl orthosilicate and 7.5 parts of vinyl triethoxy silane Mix and prepare 10 parts ammonia. Place the carboxylated carbon nanotube solution in an oil bath at 40°C and stir, slowly add 1 part of the mixture of 10 parts of ethyl orthosilicate and vinyl triethoxysilane, and then add dropwise to the above mixture. At the same time, slowly add 1 part of ammonia water, and stir for 30 minutes after the addition is complete; then slowly add the remaining 9 parts of ethyl orthosilicate and vinyl triethoxy silane mixture and 9 parts of ammonia dropwise. After the dripping is completed, the reaction After 2 hours, centrifuged at 10000r/min to obtain modified carbon nanotubes.

Example 3 Preparation of modified carbon nanotubes

(1) Prepare surface carboxylated carbon nanotubes; add 1 part of multi-walled carbon nanotubes to 90 parts of concentrated sulfuric acid to ultrasonically disperse for 30 minutes, then add 30 parts of nitric acid to this solution, and stir at 110°C in an oil bath 6 hours. After the reaction is completed, pour the solution into 1000 parts of water to obtain a yellowish-brown solution, and then centrifuge the solution at a speed of 10000r/min, wash the product with water and continue centrifugation three times to obtain carbon nanotubes with carboxylated surface;

(2) Add 10 parts of surface carboxylated carbon nanotubes prepared in step (1) to a mixture of 50 parts of water and 50 parts of ethanol, and add 7.5 parts of ethyl orthosilicate and 2.5 parts of vinyl triethoxy silane Mix and prepare 10 parts ammonia. Place the carboxylated carbon nanotube solution in an oil bath at 35°C and stir, slowly add 1 part of the mixture of 10 parts of ethyl orthosilicate and vinyl triethoxy silane, and then add dropwise to the above mixture. At the same time, slowly add 1 part of ammonia water, and stir for 30 minutes after the addition is complete; then slowly add the remaining 9 parts of ethyl orthosilicate and vinyl triethoxy silane mixture and 9 parts of ammonia dropwise. After the dripping is completed, the reaction After 2 hours, centrifuged at 10000r/min to obtain modified carbon nanotubes.

Comparative example 1

It is basically the same as Example 1, except that: "5 parts of ethyl orthosilicate and 5 parts of vinyl triethoxysilane" are replaced with 10 parts of ethyl orthosilicate.

Comparative example 2

It is basically the same as Example 1, except that: "5 parts of ethyl orthosilicate and 5 parts of vinyl triethoxy silane" are replaced with 10 parts of vinyl triethoxy silane.

Application Example 1

This example provides a thermally conductive insulating paint. In parts by mass, the raw materials of the thermally conductive insulating paint include: 10 parts of isophthalic anhydride, 22 parts of maleic anhydride, and 23.6 parts of 1,2-propylene glycol. Examples 1. Prepare 4 parts of modified carbon nanotubes, 1 part of dibenzoyl peroxide, 0.05 parts of cobalt naphthenate, 23 parts of styrene, and 0.02 parts of hydroquinone.

The preparation method is as follows: Weigh the raw materials according to the formula, then add isophthalic anhydride, maleic anhydride, 1,2-propanediol, and modified carbon nanotubes into the reaction vessel, under the protection of protective gas, heating and stirring , Raise the temperature to 160°C, keep the reaction until the acid value is 45±1mg KOH/g, raise the temperature to 175°C, keep the reaction to the acid value 35±1mg KOH/g, raise the temperature to 200°C, and keep the reaction to the acid value 12±1mg KOH/g finishes the reaction; then, it is cooled to room temperature, the remaining raw materials are added, and the reaction is mixed to prepare the thermally conductive insulating paint.

Application Example 2

It is basically the same as Application Example 1, except that the modified carbon nanotubes prepared in Example 1 are added in 2 parts.

Application Example 3

It is basically the same as Application Example 1, except that the modified carbon nanotube prepared in Example 1 is added in an amount of 8 parts.

Application Example 4

It is basically the same as Application Example 1, except that the preparation method is different. The specific preparation method is as follows: Weigh each raw material according to the formula, and then add isophthalic anhydride, maleic anhydride, and 1,2-propanediol into the reaction vessel , Under the protection of protective gas, heat up and stir, heat up to 160°C, heat up the reaction to an acid value of 45±1mg KOH/g, heat up to 175°C, heat up the reaction to an acid value of 35±1mg KOH/g, heat up to 200°C , Heat preservation reaction to an acid value of 12±1 mg KOH/g to complete the reaction; then cool to room temperature, add the remaining raw materials, mix and react to prepare the thermally conductive insulating paint.

Application Example 5

It is basically the same as Application Example 1, except that the modified carbon nanotubes are prepared in Example 2.

Application Example 6

It is basically the same as Application Example 1, except that the modified carbon nanotubes are prepared in Example 3.

Application Comparative Example 1

It is basically the same as Application Example 1, except that the modified carbon nanotubes are prepared by using Comparative Example 1.

Application Comparative Example 2

It is basically the same as Application Example 1, except that the modified carbon nanotubes are prepared by using Comparative Example 2.

Performance Testing

The following performance tests were performed on the thermally conductive insulating varnishes prepared in the application examples 1-6 and the application comparative examples 1-2 as follows, and the specific results are shown in Table 1.

The viscosity is tested directly with insulating paint according to the standard. The electrical strength, volume resistivity, and dielectric loss tangent value are prepared according to the standard of 1mm thickness paint. The curing process: 140℃, 2h; 160℃, 6h. Thermal conductivity: According to the standard, the length and width are 10mm×10mm, and the thickness is 1mm. The curing process: 140℃, 2h; 160℃, 6h. The bonding strength is prepared according to the standard of the spiral coil. The preparation process is to put the spiral coil into the paint for 10 minutes, take it out and put it in a 140℃ oven for 2h; then put the spiral coil into the paint in the reverse direction and put it into the oven at 140℃, 2h; 160℃ , 6h. Heat resistance index is prepared according to the standard with a thickness of 5mm, and the curing process: 140℃, 2h; 160℃, 6h.

Table 1

It can be seen from the above table that even if only 2 parts are added to the thermally conductive insulating varnish of the present invention, for example, application example 2, it can still obtain a more ideal thermal conductivity. However, although 4 parts are added in application comparative example 1, the effect is not as good as the present invention. ; Among them, although the application of Comparative Example 2 has obtained a better thermal conductivity, but its electrical properties are poor, which is not conducive to application in insulating materials.

The above-mentioned embodiments are only to illustrate the technical concept and features of the present invention, and their purpose is to enable those skilled in the art to understand the content of the present invention and implement them accordingly, and should not limit the scope of protection of the present invention. The equivalent changes or modifications made by the spirit essence should all be covered within the protection scope of the present invention.

Claims (10)

1. A preparation method of modified carbon nanotubes, characterized in that, the preparation method includes the following steps:

   (1) Preparation of carbon nanotubes with surface carboxylation;

   (2) The surface carboxylated carbon nanotubes prepared in step (1) are dissolved in a mixed solution of water and ethanol, and then ethyl orthosilicate, vinyl triethoxysilane and ammonia are added to react to prepare The modified carbon nanotube is formed, and the surface of the modified carbon nanotube has a vinyl group.
2. The method for preparing modified carbon nanotubes according to claim 1, wherein the modified carbon nanotubes produced by the preparation method comprise a carbon nanotube core layer and a carbon nanotube core layer formed on the carbon nanotube core layer. On the surface of the silica shell layer, the carbon nanotube core layer and the silica shell layer are partially or completely connected by chemical bonds.
3. The method for preparing modified carbon nanotubes according to claim 1 or 2, characterized in that, in step (2), the reaction is carried out at 30-50°C.
4. The method for preparing modified carbon nanotubes according to claim 1 or 2, wherein in step (2), the ethyl orthosilicate, the vinyl triethoxy silane and the ammonia water are respectively Add to the mixed solution in the form of dropwise addition.
5. The method for preparing modified carbon nanotubes according to claim 4, wherein in step (2), the ethyl orthosilicate, the vinyl triethoxy silane and the ammonia are added to the mixed solution The specific steps are as follows: firstly, the part of the mixture of the ethyl orthosilicate and the vinyl triethoxy silane is added dropwise to the mixed solution, while a part of the ammonia water is added dropwise to react; then the remaining parts are added separately Part of the mixture and the ammonia water.
6. The method for preparing modified carbon nanotubes according to claim 1 or 2, wherein in step (2), the surface carboxylated carbon nanotubes, the ethyl orthosilicate and the vinyl group The feed mass ratio of the mixture of triethoxysilane and the ammonia water is 1:0.9-1.2:1-1.2; and/or, in step (2), the feed mass ratio of the water to the ethanol is 1: 0.95-1.1.
7. The method for preparing modified carbon nanotubes according to claim 1 or 2, wherein in step (2), one of the ethyl orthosilicate and the vinyl triethoxysilane is controlled to be relatively The feed mass ratio to the other is within 3 times.
8. The method for preparing modified carbon nanotubes according to claim 1 or 2, wherein in step (1), the surface carboxylated carbon nanotubes are heated by mixing the carbon nanotubes with a mixed acid at 105-115°C. The mixed acid is made by the lower mixing reaction, and the mixed acid is composed of sulfuric acid and nitric acid.
9. The method for preparing modified carbon nanotubes according to claim 8, wherein the feed mass ratio of the sulfuric acid to the nitric acid is 2-4:1; and/or, the carbon nanotubes are multi-walled Carbon nanotubes and/or single-walled carbon nanotubes.
10. An application of modified carbon nanotubes made by the method for preparing modified carbon nanotubes according to any one of claims 1-9 in a thermally conductive insulating material.