Composite insulation paper with adjustable dielectric constant and preparation method thereof

Abstract

The application relates to the technical field of insulating materials. Provided are a composite insulating paper with adjustable dielectric constant and a preparation method thereof. The method comprises the following steps: preparing composite insulating papers with different dielectric constants according to cyanoethyl cellulose with different degrees of substitution and fluorocarbon nanotubes with different fluorocarbon ratios. The dielectric constant of the composite insulating paper can be regulated according to the degree of substitution of the cyanoethyl cellulose and / or the fluorocarbon ratio of the fluorocarbon nanotubes, and the composite insulating paper has excellent insulating performance and thermal stability. The composite insulating paper has a good application prospect in the fields of transformers, high-performance electric machines, power capacitors and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of insulating materials, in particular to a composite insulating paper with adjustable dielectric constant and a preparation method thereof. BACKGROUND

[0002] As an important primary equipment in the power system, power transformer is an indispensable core equipment of the power grid. With the continuous development of China's economy and the continuous improvement of people's daily life, people's demand for electricity increases. The transformer can not only increase the voltage for transmission to the power consumption area, but also reduce the voltage to the normal voltage. Therefore, with the continuous improvement of voltage grade and the continuous increase of electricity consumption, the transformer also develops towards high voltage, large capacity and compactness. At the same time, as the key equipment of energy conversion and transmission in the power grid, the safety and reliability of the insulation capability of the power transformer have a decisive role in the normal operation of the power system. As an important insulating material of the power transformer, the insulating paper will be affected by electric, thermal and mechanical stress during long-term operation of the transformer, resulting in a decrease in insulation performance. Moreover, due to the non-replaceability and irreversible aging of the transformer insulating paper, the service life of the transformer is seriously reduced.

[0003] As the main insulating material inside the transformer, oil paper insulation not only has to withstand alternating current electric field, but also has to withstand direct current, alternating current and polarity reversal electric field. Therefore, under the action of electric field, the oil paper interface is easy to accumulate electric charge, resulting in distortion of electric field, which causes the internal electric field of the transformer to be too concentrated and the transformer to be damaged. However, the insulating system composed of insulating papers with different dielectric constants can optimize the internal electric field of the equipment, making the electric field distribution more smooth and uniform, preventing and treating the problem of electric field concentration. However, there is currently no method to adjust the dielectric constant of the composite insulating paper. SUMMARY

[0004] The present application provides a composite insulating paper with adjustable dielectric constant and a preparation method thereof, to realize the safe and reliable operation of high-performance transformers. The dielectric constant of the composite insulating paper can be adjusted according to the degree of substitution of cyanoethyl cellulose and the fluorocarbon ratio of fluorocarbon nanotubes. At the same time, the insulating paper can solve the problems of traditional cellulose insulating paper, such as easy moisture absorption, poor thermal stability and easy aging, and has excellent insulation performance and thermal stability, which has a good application prospect in the fields of transformers, high-performance motors, power capacitors and the like.

[0005] A preparation method of a composite insulating paper with adjustable dielectric constant, comprising:

[0006] Different dielectric constant composite insulating papers are prepared according to cyanoethyl cellulose with different degrees of substitution and fluorocarbon nanotubes with different fluorocarbon ratios.

[0007] Further, the preparation method of the composite insulating paper with adjustable dielectric constant as described above comprises the following steps:

[0008] Step one: using different degrees of substitution of cyanoethyl cellulose, different fluorocarbon ratio of carbon nanotubes, polyvinyl alcohol, corresponding to the preparation of different spinning solution; the different spinning solution is prepared by electrospinning respectively, to prepare the corresponding carbon nanotubes / cyanoethyl cellulose coaxial fiber FC@CEC;

[0009] Step two: the cellulose nanofiber dispersion liquid is mixed with different carbon nanotubes / cyanoethyl cellulose coaxial fiber FC@CEC respectively, and the different composite slurry is prepared by high speed shearing;

[0010] Step three: the different composite slurry is sprayed on the substrate by electrostatic spraying, and the different gels are prepared;

[0011] Step four: the different gels are dried in vacuum respectively, and the composite insulating paper with different dielectric constants is obtained;

[0012] Step five: the composite insulating paper with different dielectric constants is heated and pressed, and finally the composite insulating paper with different dielectric constants is obtained.

[0013] Further, in the method, the degree of substitution of cyanoethyl cellulose is 0.5-3.

[0014] Further, in the method, the fluorocarbon ratio of carbon nanotubes is 0.8-1.2, and the diameter is 20-85nm.

[0015] Further, in the method, the mass ratio of cyanoethyl cellulose to carbon nanotubes is 0.2-5:1.

[0016] Further, in the method, the preparation of the spinning solution comprises:

[0017] The cyanoethyl cellulose with different degrees of substitution, the carbon nanotubes with different fluorocarbon ratios and the polyvinyl alcohol are respectively subjected to ultrasonic, shearing and stirring treatment to prepare the spinning solution; the molecular weight of the polyvinyl alcohol is 300,000.

[0018] Further, in the method, the preparation of the cellulose nanofiber dispersion liquid comprises:

[0019] The cellulose nanofiber is diluted with water to a cellulose nanofiber dispersion liquid with a mass concentration of 0.05%-0.5%; the diameter of the cellulose nanofiber is 20-30nm.

[0020] Further, in the method, the mass ratio of the cellulose nanofiber dispersion liquid to FC@CEC is 1-5:1.

[0021] Further, the method as described above, the shearing condition is: the shearing rate is 10000-15000 rpm, and the shearing time is 15-25 min.

[0022] Further, the method as described above, the hot-pressing condition in the step five is: the pressure is 20-30 MPa, the hot-pressing temperature is 100-150 DEG C, and the hot-pressing time is 10-30 min.

[0023] The dielectric constant adjustable composite insulating paper is prepared according to the method as described above.

[0024] The application of the dielectric constant adjustable composite insulating paper as described above in the preparation of transformers.

[0025] The cellulose nanofiber provided by the application is a nanometer material derived from a natural plant, and has the characteristics of wide source, green environmental protection, high length-diameter ratio, excellent mechanical properties, and rich and adjustable physical and chemical properties.

[0026] The dielectric constant adjustable composite insulating paper provided by the application takes the cellulose nanofiber as a network skeleton, takes the cyanoethyl cellulose with different degrees of substitution and the fluorocarbon nanotube with different fluorocarbon ratios as functional units for regulating the dielectric constant of the composite insulating paper, and the dielectric constant of the composite insulating paper is regulated by changing the degree of substitution of the cyanoethyl group in the cyanoethyl cellulose and / or the fluorocarbon ratio of the fluorocarbon nanotube, so that the prepared composite insulating paper has different dielectric constants, and thus the insulation system composed of the insulating papers with different dielectric constants can optimize the electric field inside the equipment, so that the electric field distribution is more smooth and uniform, and the problem of electric field concentration is prevented. Moreover, the prepared composite insulating paper can be applied to transformers of different voltage grades, and accidents of the transformer are prevented. Moreover, compared with the traditional cellulose insulating paper, the thermal stability and the moisture resistance of the composite insulating paper are significantly improved, and the insulating performance is excellent.

[0027] The preparation method provided by the application improves the orientation of the molecular chain itself by adopting the electrostatic spinning method, greatly improves the thermal conductivity, and reduces the electrical conductivity of the material, so that the composite insulating paper has good flexibility, heat insulation and insulating performance.

[0028] The preparation method provided by the application improves the order and reliability of the microstructure of the composite insulating paper by adopting the electrostatic spraying method, and further improves the thermal stability and insulating performance of the composite insulating paper by constructing the dense and ordered topological structure of the fluorocarbon nanotube / cyanoethyl cellulose / cellulose nanofiber.

[0029] The preparation method provided by the application is simple, easy to operate, low in cost, excellent in quality, meets the social requirements of green low-carbon and degradability, and is suitable for industrialized large-scale production.

[0030] Since polyvinyl alcohol has the characteristics of good film-forming property and film strength, by controlling the molecular weight of polyvinyl alcohol at 300,000, the cyanoethyl cellulose and the cellulose nanofiber can be better combined together, and the consumables are not consumed too much. And polyvinyl alcohol has the advantages of safety and non-toxicity, so the safety of the prepared insulation paper is higher. BRIEF DESCRIPTION OF DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0032] Figure 1 The transmission electron microscope graph of cellulose nanofiber is enlarged 100,000 times;

[0033] Figure 2 The transmission electron microscope graph of cellulose nanofiber is enlarged 20,000 times;

[0034] Figure 3 The schematic diagram of electrospinning device for preparing carbon fluoride nanotube / cyanoethyl cellulose coaxial fiber;

[0035] The figure shows that 1 is carbon fluoride nanotube / cyanoethyl cellulose coaxial fiber. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical scheme and advantages of the present application more clear, the technical scheme in the present application will be described clearly and completely in the following combined with the drawings in the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0037] Since cyanoethyl cellulose has high dielectric constant and low dielectric loss, cyanoethyl cellulose can be used as dielectric material. Because the cyanoethylization degree of the molecular chain of cyanoethyl cellulose is different, that is, the degree of substitution is different, the performance will also change. Therefore, within a certain range of change, the dielectric constant of cyanoethyl cellulose will increase with the increase of the degree of substitution, and the moisture resistance, thermal stability and mechanical properties will also be strengthened. Cyanoethyl cellulose with high degree of substitution (2.6-3) has high waterproofness, high insulation and self-extinguishing property. Therefore, by combining cyanoethyl cellulose with different degrees of substitution with cellulose nanofiber, the waterproofness, thermal stability and mechanical properties of the prepared composite insulation paper are improved.

[0038] Figure 1 Transmission electron microscope image of cellulose nanofiber, magnified 100,000 times, Figure 2 Transmission electron microscope image of cellulose nanofiber, magnified 20,000 times, from Figure 1 、 Figure 2 It can be seen that the cellulose nanofiber has a large aspect ratio, and its nanoscale size and one-dimensional structure make it have a high specific surface area, high electrical conductivity, excellent mechanical strength and thermal conductivity. The excellent performance of cellulose nanofiber can make the finally prepared insulation paper have good insulation performance and excellent mechanical strength, so it can be combined with other substances to improve the insulation effect of the insulation paper. At the same time, as the fluorination degree (fluorocarbon ratio) of the fluorinated carbon nanotube increases, its electrical conductivity will decrease. That is, the higher the fluorination degree, the lower the electrical conductivity of the fluorinated carbon nanotube, and the adsorption capacity and hydrophobicity will be enhanced; at the same time, the higher the fluorine content, the better the thermal stability. Therefore, by combining fluorinated carbon nanotubes with different fluorocarbon ratios with cellulose nanofiber to prepare composite insulation paper, the thermal stability, insulation and waterproofness of the prepared composite insulation paper can also be enhanced. In addition, the insulation performance of the insulation paper can also be improved, thereby solving the problems of traditional cellulose insulation paper, such as easy moisture absorption, poor thermal stability and easy aging.

[0039] In summary, by using cyanoethyl cellulose with different degrees of substitution and / or fluorinated carbon nanotubes with different fluorocarbon ratios as functional units for regulating the dielectric constant of the insulation paper, a composite insulation paper with adjustable dielectric constant can be obtained, and the insulation system of the transformer can be constructed by using composite insulation papers with different dielectric constants, so as to realize the safe and reliable operation of the high-performance transformer.

[0040] Example 1:

[0041] The embodiment provides a preparation method of a composite insulation paper with adjustable dielectric constant, which comprises the following steps:

[0042] 1) Taking cellulose nanofiber as raw material, 10g of cellulose nanofiber gel is weighed, wherein the cellulose nanofiber content is 200mg, and it is added into 400mL of deionized water, and fully stirred and mixed uniformly to obtain a cellulose nanofiber dispersion liquid which is used as a base solution.

[0043] 2) 1g of cyanoethyl cellulose with a degree of substitution of 1.13 is weighed and added into 100g of acetone / water mixed solution Magnetic stirring for 12h to dissolve; 20g of acrylonitrile and an appropriate amount of NaOH solution (NaOH solution is obtained by dissolving 1g of NaOH in 10mL of water and cooling to room temperature) are added dropwise to the dissolved solution, and the reaction is carried out by stirring at 15℃ for 5h; then hydrochloric acid is added to the reaction solution to neutralize the reaction solution, and about twice the volume of water of the reaction solution is added dropwise to precipitate the product; the obtained product is washed with water and then vacuum dried at 80℃ for 12h to obtain white powdery cyanoethyl cellulose with a degree of substitution of 2.35.

[0044] 3) The cyanoethyl cellulose with a degree of substitution of 2.35 in step 2) is uniformly mixed with fluorocarbon nanotubes with a fluorocarbon ratio of 0.8 and polyvinyl alcohol (PVA) with a molecular weight of 300,000 at a mass ratio of 1:5 by ultrasonic, shearing and stirring treatment to obtain a spinning solution, as shown in Figure 3 The spinning solution is loaded into a syringe and fixed on the injection pump of the electrospinning machine to perform electrospinning, a suitable fiber receiving device is selected and connected to the negative electrode, placed directly below the needle, and the nanofiber is deposited on the fiber receiving device to obtain fluorocarbon nanotube / cyanoethyl cellulose coaxial fiber (FC@CEC), which is placed in a vacuum drying oven at 60℃ for 48h.

[0045] 4) The cellulose nanofiber dispersion liquid is mixed with the FC@CEC prepared in step 3) at a ratio of 1:1, and the pulp is mixed uniformly by high-speed shearing at 14000rpm for 25min, and finally the composite pulp is obtained.

[0046] 5) The composite pulp is repeatedly sprayed on the substrate by electrostatic spraying to form a gel, and the thickness of the gel is 500μm.

[0047] 6) The gel sample is dried at 60℃ in vacuum for 48h to obtain a composite insulation paper rough paper;

[0048] 7) The obtained insulation paper rough paper is hot-pressed under the conditions of 20Mpa and 150℃, and the dielectric constant of the insulation paper is detected, and finally a new type of composite insulation paper with a dielectric constant of 5.5 is obtained.

[0049] Example 2:

[0050] The difference between this example and Example 1 is that the mass ratio of cyanoethyl cellulose to fluorocarbon nanotube is 1:3, and the dielectric constant of the composite insulation paper obtained is 4.1.

[0051] Example 3:

[0052] The difference between this example and Example 1 is that the mass ratio of cyanoethyl cellulose to fluorocarbon nanotube is 1:1, and the dielectric constant of the composite insulation paper obtained is 4.6.

[0053] Example 4:

[0054] The difference between this embodiment and embodiment 1 is that the mass ratio of the cyan ethyl cellulose to the fluorocarbon nanotube is 5:1, and the dielectric constant of the composite insulation paper obtained is 3.4.

[0055] Example 5:

[0056] The difference between this embodiment and embodiment 1 is that the fluorocarbon ratio of the fluorocarbon nanotube is 1, and the dielectric constant of the composite insulation paper obtained is 5.4.

[0057] Example 6:

[0058] The difference between this embodiment and embodiment 1 is that the fluorocarbon ratio of the fluorocarbon nanotube is 1.2, and the dielectric constant of the composite insulation paper obtained is 5.7.

[0059] Example 7:

[0060] The difference between this embodiment and embodiment 1 is that the mass ratio of the cellulose nanofiber to FC@CEC is 1:5, and the dielectric constant of the composite insulation paper obtained is 5.1.

[0061] Example 8:

[0062] The difference between this embodiment and embodiment 1 is that the mass ratio of the cellulose nanofiber to FC@CEC is 5:1, and the dielectric constant of the composite insulation paper obtained is 3.6.

[0063] Comparative Example 1:

[0064] The cyan ethyl cellulose with a degree of substitution of 1.13 and the fluorocarbon nanotube with a fluorocarbon ratio of 0.8 are made into FC@CEC by electrospinning. The same coaxial fiber and cellulose nanofiber are mixed at a ratio of 1:1 by high-speed shearing to obtain a composite slurry. The composite insulation paper is obtained by electrostatic spraying, and the new composite insulation paper is obtained by high-temperature hot pressing. The dielectric constant of the composite insulation paper is 3.

[0065] Comparative Example 2:

[0066] The difference between this embodiment and embodiment 1 is that 5g of acrylonitrile is added dropwise to the dissolved solution in step 2), and the degree of substitution of the white powdery cyan ethyl cellulose prepared is 0.5. The dielectric constant of the finally prepared composite insulation paper is 3.5.

[0067] Comparative Example 3:

[0068] The difference between this embodiment and embodiment 1 is that 30g of acrylonitrile is added dropwise to the dissolved solution in step 2), and the degree of substitution of the white powdery cyan ethyl cellulose prepared is 3. The dielectric constant of the finally prepared composite insulation paper is 5.8.

[0069] Comparative Example 4:

[0070] The difference between this example and Example 1 is that the spinning solution obtained in step 3) is directly mixed with the cellulose nanofiber in step 4) at a ratio of 1:1, and the dielectric constant of the final prepared composite insulation paper is 3.7.

[0071] Comparative Example 5:

[0072] The difference between this example and Example 1 is that step 5) uses a method of vacuum filtration for 10-20 min under the condition of 0.06-0.09 MPa and hot pressing for 10-15 min under the condition of 220-240℃, and the dielectric constant of the final prepared composite insulation paper is 4.5.

[0073] As can be seen from Example 1, Example 5, and Example 6, the higher the fluorocarbon ratio of the fluorinated carbon nanotube, the higher the dielectric constant of the final prepared composite insulation paper.

[0074] As can be seen from Example 1-Example 4, when the mass ratio of cyanoethyl cellulose to fluorinated carbon nanotube is 1:5, the dielectric constant of the obtained composite insulation paper is the highest.

[0075] As can be seen from Example 1, Example 7, and Example 8, when the mass ratio of cellulose nanofiber to FC@CEC is 1:1, the dielectric constant of the obtained composite insulation paper is the highest.

[0076] As can be seen from Example 1, Comparative Example 2, and Comparative Example 3, the higher the degree of substitution of cyanoethyl cellulose, the higher the dielectric constant of the prepared insulation paper.

[0077] As can be seen from Example 1, Example 4, and Example 5, changing the ratio of cyanoethyl cellulose to fluorinated carbon nanotube has a greater effect on the dielectric constant of the composite insulation paper than changing the fluorocarbon ratio of the fluorinated carbon nanotube.

[0078] The novel composite insulation paper with adjustable dielectric constant provided by the present application can better exert its excellent strength performance when the mass ratio of cellulose nanofiber to FC@CEC is 1:1, and the cellulose nanofiber is the main part. At this time, the good insulation performance and thermal stability of the fluorinated carbon nanotube and cyanoethyl cellulose can also play a role, and the comprehensive performance of the insulation paper is improved higher.

[0079] It should be pointed out finally that the above embodiments are only used to illustrate the technical solutions of the present application, but not to limit the same; and although the present application has been described in detail with reference to the foregoing embodiments, it should be appreciated by those skilled in the art that the technical solutions recorded in the foregoing embodiments can be modified, or some technical features thereof can be replaced equivalently; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for producing a composite insulation paper with adjustable dielectric constant, characterized by, The application relates to a method for preparing composite insulating paper with adjustable dielectric constant. The application relates to a method for preparing composite insulating paper with adjustable dielectric constant. Step one: different spinning liquids are prepared by using polyvinyl alcohol, cyanoethyl cellulose with different degrees of substitution and fluorocarbon nanotubes with different fluorocarbon ratios; the different spinning liquids are respectively prepared into different fluorocarbon nanotube / cyanoethyl cellulose coaxial fibers FC@CEC by means of electrostatic spinning. Step two: different composite slurries are prepared by mixing cellulose nanofiber dispersions with the different fluorocarbon nanotube / cyanoethyl cellulose coaxial fibers FC@CEC and by high-speed shearing. Step three: different gels are prepared by respectively spraying the different composite slurries on substrates by means of electrostatic spraying. Step four: different composite insulating paper rough papers with different dielectric constants are obtained by respectively vacuum drying the different gels. Step five: finally, the composite insulating paper with different dielectric constants is obtained by respectively heat pressing the composite insulating paper rough papers with different dielectric constants. The degree of substitution of the cyanoethyl cellulose is 0.5-3. The fluorocarbon ratio of the fluorocarbon nanotube is 0.8-1.2, and the diameter is 20-85 nm.

2. The method of claim 1, wherein, The mass ratio of the cyanoethyl cellulose to the fluorocarbon nanotube is 0.2-5:

1.

3. The method of claim 1, wherein, The preparation of the spinning liquid comprises the following steps: The cyanoethyl cellulose with different degrees of substitution and the fluorocarbon nanotube with different fluorocarbon ratios are respectively subjected to ultrasonic, shearing and stirring treatment together with polyvinyl alcohol to prepare the spinning liquid; the molecular weight of the polyvinyl alcohol is 300,000.

4. The method of claim 1, wherein, The preparation of the cellulose nanofiber dispersion liquid comprises the following steps: The cellulose nanofiber is diluted with water to a cellulose nanofiber dispersion liquid with a mass concentration of 0.05%-0.5%; the diameter of the cellulose nanofiber is 20-30 nm; and the mass ratio of the cellulose nanofiber to the fluorocarbon nanotube / cyanoethyl cellulose coaxial fiber FC@CEC in the cellulose nanofiber dispersion liquid is 1-5:

1.

5. The method of claim 1, wherein, The shearing condition is that the shearing speed is 10,000-15,000 rpm, and the shearing time is 15-25 min; and the heat pressing condition in step five is that the pressure is 20-30 MPa, the heat pressing temperature is 100-150 DEG C, and the heat pressing time is 10-30 min.

6. The composite insulating paper with adjustable dielectric constant is prepared by the method in any one of claims 1-5.

7. The application of the composite insulating paper with adjustable dielectric constant in preparing transformers.

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