SiO2 / carbon nanotube composite high temperature flexible flame retardant electric heating film and preparation method thereof

Abstract

The patent of the present invention proposes a method for preparing a SiO2 / carbon nanotube composite high-temperature flexible flame-retardant electric heating film, which combines the flexibility, high electric-to-heat conversion efficiency, and intelligent temperature control of the carbon nanotube film with the high-temperature stability of SiO2; ammonia water is used to catalyze the hydrolysis reaction of tetraethyl orthosilicate, and the film is allowed to stand at room temperature for 7 hours to coat SiO2 on the surface of the carbon nanotubes. The maximum electric heating temperature is as high as 370°C, which is 124°C higher than that of pure carbon nanotube film. The present invention provides a new idea for the preparation of high-temperature electric heating materials.

Description

Technical Field

[0001] The present application relates to the technical field of high-temperature flexible electric heating film preparation, and in particular to a SiO2 / carbon nanotube composite high-temperature flexible flame-retardant electric heating film and a preparation method thereof. Background Art

[0002] With the progress of social production, the field of materials is flourishing, and electric heating materials are unique among them. They have not only attracted much attention in the fields of industry, aerospace, heavy metals, etc., but also played an extremely important role in daily life. The future society's demand for wearable smart devices and research potential are destined to start a new competition in the field of materials for the choice of material flexibility. Flexible materials not only need to have good flexibility and bendability, but also pay attention to whether the material fits closely with the heated object and the heat conduction loss. Carbon nanotube film has become a popular candidate for electric heating film materials due to its good conductivity, heat transfer and flexibility. Carbon nanotubes have the potential to become the leader of the next generation of new flexible electric heating film materials due to their excellent electric heating properties. As an electric heating film material, one of the most critical requirements is to improve its electric heating temperature window and service life.

[0003] Studies have shown that when the temperature of the current generated by the carbon nanotubes reaches 100°C, the efficiency of converting electrical energy into thermal energy is the highest, close to 100%, and the heating performance of the carbon nanotubes is stable at this time. The electrothermal conversion efficiency is close to linear in the range of 0°C to 100°C, which is the ideal electrothermal working temperature range for carbon nanotubes. However, as the temperature rises, the electrothermal conversion efficiency of the carbon nanotube film begins to decrease, and the conductivity gradually decreases. When the temperature reaches the range of 300°C to 400°C, the electrothermal film appears a faint red light, and then breaks from the red light, and the carbon nanotube film can no longer be used. In addition, experiments have also confirmed that when the temperature exceeds 200°C, the isotropy of the carbon nanotubes changes, causing its electrothermal performance at low temperatures to change.

[0004] Under the demand for high temperature in industrial production and intelligent equipment, bare carbon nanotubes are no longer suitable for flexible high-temperature membrane materials. The research on composite materials has opened a new channel for flexible electric heating film materials. It has been proven to be a feasible method to coat inorganic materials on the surface of carbon nanotubes to significantly improve their high-temperature conductive window and utilize the excellent properties of organic / inorganic composite materials. Ceramic materials, as a major functional material among inorganic materials, have the advantages of high melting point, high hardness, high wear resistance, and oxidation resistance. Among them, SiO2, as a widely used ceramic material, has excellent stability and physical and chemical properties. It can be used as a coating material for carbon nanotube films for research, in an effort to improve the high-temperature service temperature window of carbon nanotube electric heating films.

[0005] The present invention proposes that a new type of high-temperature flexible electric heating film material is obtained by coating the surface of each carbon nanotube of a carbon nanotube film with a layer of SiO2 by using ammonia water to catalyze the hydrolysis reaction of tetraethyl orthosilicate. Summary of the invention

[0006] The purpose of the present invention is to obtain a new type of high-temperature flexible electric heating film material by coating the surface of each carbon nanotube of the carbon nanotube film with a layer of SiO2 by using ammonia water to catalyze the hydrolysis reaction of tetraethyl orthosilicate, thereby fundamentally solving the problem that pure carbon nanotube films are easily oxidized and fail at high temperatures, and improving the high-temperature service life of electric heating films.

[0007] The present application discloses a method for preparing a SiO2 / carbon nanotube composite high-temperature flexible flame-retardant electric heating film, comprising the following steps:

[0008] S1 Acidification: Soak a certain area of ​​carbon nanotube film in 5 wt.% hydrochloric acid for 2 h, then soak it in concentrated nitric acid for 2 h, wash it repeatedly with water until it is neutral, and freeze-dry it;

[0009] S2 coating: soak the treated carbon nanotube film in tetraethyl orthosilicate at a certain temperature for 10 minutes, take it out and immerse it in a mixed solution of ethanol-ammonia-deionized water, and let it stand for a certain period of time;

[0010] S3 Drying: After repeated washing, the film was dried in an oven for 24 h to obtain the final product, SiO2-coated carbon nanotube film.

[0011] Preferably, the area of ​​the carbon nanotube film in step S1 is 3 to 20 cm 2 .

[0012] Preferably, in step S2, the volume ratio of the ethanol-ammonia-deionized water mixed solution is about 10:1.5:1, the total volume is 40-60 mL, and the ammonia concentration is 25-28 wt.%.

[0013] Preferably, the temperature of the static reaction in step S2 is 0 to 80° C., and the reaction time is 3 to 10 h.

[0014] Preferably, the drying temperature in step S3 is 80-150°C.

[0015] The advantages of the present invention are that the flexibility, high electrothermal conversion efficiency, and intelligent temperature control characteristics of the carbon nanotube film are combined with the high temperature stability and easy nano-coating of inorganic SiO2. After the carbon nanotubes are acidified, the surface film is stretched open and it is easy for inorganic substances to coat them. Under alkaline conditions, tetraethyl orthosilicate can be catalyzed by ammonia water to react and catalyze the generation of spherical silicon dioxide particles coated on the surface of the carbon nanotube film at room temperature. The role of ethanol is to protect the polarity of the solution. The heating temperature of the SiO2-coated carbon nanotube composite film prepared by the present invention can reach 370°C, which is 124°C higher than the service temperature of the pure carbon nanotube film (uncoated) at the same power. This preparation method provides a new idea for the field of high-temperature electric heating materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0017] Figure 1 Shown is a SEM image of the SiO2-coated carbon nanotube high-temperature flexible electric heating film prepared in Example 1 of the present invention;

[0018] Figure 2 Shown are temperature-voltage curves of composite films and uncoated films prepared in different ways in Examples 1 and 2;

[0019] Figure 3 Shown is a temperature-voltage curve of the composite films prepared at different static reaction temperatures in Examples 1, 4 and 5. DETAILED DESCRIPTION

[0020] The following will describe the technical solutions in the embodiments of the present invention in detail in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0021] Example 1

[0022] A carbon nanotube film with an area of ​​3 cm×3 cm was soaked in 5 wt.% hydrochloric acid for 2 h, then soaked in concentrated nitric acid for 2 h, repeatedly washed with water until neutral, and freeze-dried; then, the treated carbon nanotube film was soaked in tetraethyl orthosilicate at room temperature for 10 minutes, taken out and immersed in a mixed solution of ethanol-ammonia-deionized water, and allowed to react at room temperature (26°C) for 7 h; finally, after repeated washing, the film was dried in an oven for 24 h to obtain the final product, SiO2-coated carbon nanotube film.

[0023] Figure 1 This is a SEM image of the SiO2 coated carbon nanotube high temperature flexible electric heating film prepared in Example 1. It can be seen that the entire film presents a network structure, and the surface of a single carbon nanotube is evenly coated with a dense particle layer. The SiO2 coating layer and the carbon nanotube are very tightly bonded.

[0024] Example 2

[0025] The ethanol-ammonia-deionized water mixed solution was allowed to stand for mechanical stirring, and other conditions were the same as those in Example 1.

[0026] Figure 2 The temperature-voltage curves of the composite films and uncoated films prepared in different ways in Examples 1 and 2 are shown. It can be seen that under the same voltage, the surface temperature of the pure carbon nanotube film is the lowest (only 94°C), the temperature of the electrothermal film prepared by mechanical stirring reaches 103°C, and the highest electrothermal temperature of the composite film prepared by static reaction can reach 139°C. This result shows that the static reaction method can make SiO2 uniformly coated on the surface of the carbon nanotubes, which effectively increases the service temperature.

[0027] Example 3

[0028] The reaction temperature was changed to 0°C (ice-water mixture water bath), and other conditions were the same as in Example 1.

[0029] Example 4

[0030] The static reaction temperature was changed to 60°C, and the other conditions were the same as in Example 1.

[0031] Figure 3 The temperature-voltage curves of the composite films prepared at different static reaction temperatures in Examples 1, 3 and 4 are shown. By comparison, it is found that when different reaction temperatures are used for static reaction, the composite film prepared at room temperature (Example 1) has the highest service temperature and the most obvious improvement in the electric thermal window, which is due to the best SiO2 coating effect.

[0032] If the temperature of the static reaction is too high or too low, the SiO2 coating effect will be affected. For the sample prepared by the reaction at 60°C (Example 4), the electric heating window of the composite film only reaches 250°C, while the temperature of the sample prepared by the reaction at 0°C (Example 3) is only 180°C; when the voltage rises to about 6 V at 0°C and 250°C, the carbon nanotubes are partially broken. At low temperatures, the hydrolysis reaction of tetraethyl orthosilicate slows down, and the low temperature reduces the growth rate and amount of SiO2 on the carbon nanotubes, so there is not much SiO2 coated on the carbon nanotubes at 0°C. When the reaction is at 60°C, the decomposition reaction of tetraethyl orthosilicate is too violent, and SiO2 is mainly generated in the solution, so the amount of SiO2 grown and coated on the surface of the carbon nanotubes is relatively small.

[0033] This implementation mode is only an exemplary description of this patent and does not limit its protection scope. Personnel in this field may also make partial changes to it. As long as it does not exceed the spirit of this patent, it shall be regarded as an equivalent replacement of this patent and shall be within the protection scope of this patent.

Claims

1. A method for preparing SiO2 / carbon nanotube composite high temperature flexible flame retardant electric heating film, characterized in that: The steps include: S1 Acidification: Soak a certain area of ​​carbon nanotube film in 5 wt .% hydrochloric acid for 2 h, then soak it in concentrated nitric acid for 2 h, wash it repeatedly with water until it is neutral, and freeze-dry it; S2 coating: soak the treated carbon nanotube film in tetraethyl orthosilicate at a certain temperature for 10 minutes, take it out and immerse it in a mixed solution of ethanol-ammonia-deionized water, and let it stand for a certain period of time; S3 Drying: After repeated washing, the film was dried in an oven for 24 h to obtain the final product, SiO2-coated carbon nanotube film.

2. The method for preparing the electric heating film according to claim 1, characterized in that: The area of ​​the carbon nanotube film in step S1 is 3 to 20 cm 2 .

3. The method for preparing the electric heating film according to claim 1, characterized in that: In step S2, the volume ratio of the ethanol-ammonia-deionized water mixed solution is 10:1.5:1, the total volume is 40-60 mL, and the concentration of ammonia is 25-28 wt.%.

4. The method for preparing the electric heating film according to claim 1, characterized in that: The temperature of the static reaction in step S2 is 0 to 80° C. and the reaction time is 3 to 10 h.

5. The method for preparing the electric heating film according to claim 1, characterized in that: The drying temperature in step S3 is 80-150°C.

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