Composite insulation paper with adjustable dielectric constant and preparation method thereof

Abstract

The invention relates to the technical field of insulating materials. The invention provides composite insulation paper with an adjustable dielectric constant and a preparation method thereof. The method comprises the step of preparing composite insulation paper with different dielectric constants according to cyanoethyl cellulose with different substitution degrees and carbon fluoride nanotubes with different fluorocarbon ratios. The dielectric constant of the composite insulation paper can be regulated and controlled according to the substitution degree of the cyanoethyl cellulose and / or the fluorocarbon ratio of the fluorinated carbon nanotubes, and the composite insulation paper has excellent insulation performance and thermal stability. Good application prospects are realized in the fields of transformers, high-performance motors, power capacitors and the like.

Description

Technical Field

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

[0002] As an important primary equipment in the power system, the power transformer is an indispensable core equipment of the power grid. With the continuous development of my country's economy and the continuous improvement of residents' daily living standards, people's demand for electricity consumption has increased. Transformers can both increase the voltage and transmit it to the power consumption area and reduce the voltage to the commonly used voltage. Therefore, with the continuous increase in voltage levels and the continuous increase in electricity consumption, transformers are also developing in the direction of high voltage, large capacity and compactness. At the same time, as a key equipment for energy conversion and transmission in the power grid, the safety and reliability of the insulation capacity of the power transformer play a decisive role in the normal operation of the power system. As an important insulating material for power transformers, the insulation paper will be affected by electrical, thermal and mechanical stresses during the long-term operation of the transformer, resulting in a decrease in insulation performance. In addition, due to the irreplaceability of the transformer insulation paper and the irreversibility of aging, the life of the transformer is seriously reduced.

[0003] As the main insulating material inside the transformer, oil-paper insulation must withstand both AC electric fields and DC, AC / DC composite and polarity reversal electric fields. Therefore, the oil-paper interface is prone to accumulate charges under the action of the electric field, causing the electric field to be distorted, which causes the electric field inside the transformer to be too concentrated and damage the transformer. The insulation system composed of insulating papers with different dielectric constants can optimize the electric field inside the equipment, making the electric field distribution smoother and more uniform, and preventing the problem of electric field concentration. However, there is currently no method to adjust the dielectric constant of composite insulating paper. Summary of the invention

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

[0005] A method for preparing composite insulating paper with adjustable dielectric constant, comprising:

[0006] Composite insulating papers with different dielectric constants are prepared based on cyanoethyl cellulose with different substitution degrees and fluorinated carbon nanotubes with different fluorine-carbon ratios.

[0007] Furthermore, the method for preparing the composite insulating paper with adjustable dielectric constant as described above comprises the following steps:

[0008] Step 1: using cyanoethyl cellulose with different degrees of substitution, fluorinated carbon nanotubes with different fluorine-carbon ratios, and polyvinyl alcohol, different spinning solutions are prepared accordingly; the different spinning solutions are respectively subjected to electrospinning to prepare corresponding fluorinated carbon nanotube / cyanoethyl cellulose coaxial fibers FC@CEC;

[0009] Step 2: mixing the cellulose nanofiber dispersion with different fluorinated carbon nanotube / cyanoethyl cellulose coaxial fibers FC@CEC respectively, and preparing different composite slurries by high-speed shearing;

[0010] Step 3: spraying the different composite slurries onto the substrates respectively by electrostatic spraying to produce different gels accordingly;

[0011] Step 4: vacuum drying the different gels respectively to obtain composite insulating paper rough papers with different dielectric constants;

[0012] Step 5: hot-pressing the composite insulating paper and rough paper with different dielectric constants respectively, and finally obtaining composite insulating paper with different dielectric constants.

[0013] Furthermore, in the method as described above, the degree of substitution of the cyanoethyl cellulose is 0.5-3.

[0014] Furthermore, in the method as described above, the fluorine-carbon ratio of the fluorinated carbon nanotubes is 0.8 to 1.2, and the diameter is 20 to 85 nm.

[0015] Furthermore, in the method as described above, the mass ratio of the cyanoethyl cellulose to the fluorinated carbon nanotubes is 0.2 to 5:1.

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

[0017] The spinning solution is prepared by subjecting cyanoethyl cellulose with different substitution degrees, fluorinated carbon nanotubes with different fluorine-carbon ratios and polyvinyl alcohol to ultrasonic, shearing and stirring treatments respectively; the molecular weight of the polyvinyl alcohol is 300,000.

[0018] Furthermore, in the method as described above, the preparation of the cellulose nanofiber dispersion comprises:

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

[0020] Furthermore, in the method as described above, the mass ratio of the cellulose nanofiber dispersion to FC@CEC is 1 to 5:1.

[0021] Furthermore, in the method as described above, the shearing conditions are: a shearing rate of 10000 to 15000 rpm, and a shearing time of 15 to 25 min.

[0022] Furthermore, in the method as described above, the hot pressing conditions in step five are: pressure of 20-30 MPa, hot pressing temperature of 100-150° C., and hot pressing time of 10-30 min.

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

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

[0025] The cellulose nanofiber provided by the present invention is a nanomaterial derived from natural plants and has the characteristics of wide source, green and environmental protection, high aspect ratio, excellent mechanical properties, rich and adjustable physical and chemical properties, etc.

[0026] The composite insulating paper with adjustable dielectric constant provided by the present invention uses cellulose nanofibers as a network skeleton, uses cyanoethyl cellulose with different substitution degrees and fluorinated carbon nanotubes with different fluorine-carbon ratios as functional elements for regulating the dielectric constant of the composite insulating paper, and regulates the dielectric constant of the composite insulating paper by changing the substitution degree of cyanoethyl in the molecular chain of cyanoethyl cellulose and / or the fluorine-carbon ratio of fluorinated carbon nanotubes, so that the prepared composite insulating paper has different dielectric constants, so that the insulating system composed of insulating papers with different dielectric constants can optimize the internal electric field of the equipment, make the electric field distribution smoother and more uniform, and prevent the problem of electric field concentration. Moreover, the prepared composite insulating paper can also be suitable for transformers of different voltage levels to prevent accidental damage to the transformer. Moreover, compared with traditional cellulose insulating paper, the thermal stability and moisture resistance of the insulating paper are significantly improved, and the insulating performance is excellent.

[0027] The preparation method provided by the present invention improves the orientation of the molecular chain itself by adopting the electrostatic spinning method, so that the thermal conductivity is greatly improved and the conductivity of the material is reduced, so that the composite insulating paper has good flexibility, thermal insulation and insulating properties.

[0028] The preparation method provided by the present invention improves the orderliness and reliability of the microstructure of the composite insulating paper by adopting an electrostatic spraying method, and further improves the thermal stability and insulating performance of the composite insulating paper by constructing a dense and orderly topological structure of fluorinated carbon nanotubes / cyanoethyl cellulose / cellulose nanofibers.

[0029] The preparation method provided by the present invention is simple, easy to operate, low-cost, and of high quality, and meets the social requirements of being green, low-carbon, and degradable, and is suitable for industrial large-scale production.

[0030] Since polyvinyl alcohol has the characteristics of good film-forming property and film strength, the present invention can better combine cyanoethyl cellulose and cellulose nanofibers by controlling the molecular weight of polyvinyl alcohol to 300,000 without excessive material consumption. In addition, polyvinyl alcohol has the advantages of safety and non-toxicity, so the prepared insulating paper can be made safer. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0032] Figure 1 This is a transmission electron microscope image of cellulose nanofibers magnified 100,000 times;

[0033] Figure 2 This is a transmission electron microscope image of cellulose nanofibers magnified 20,000 times;

[0034] Figure 3 Schematic diagram of the electrospinning device for preparing fluorinated carbon nanotube / cyanoethyl cellulose coaxial fibers;

[0035] Reference numerals: 1 - fluorinated carbon nanotube / cyanoethyl cellulose coaxial fiber. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings of the present invention. Obviously, the described embodiments are 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.

[0037] Since cyanoethyl cellulose has a high dielectric constant and low dielectric loss, cyanoethyl cellulose can be used as a dielectric material. However, due to the different degrees of cyanoethylation of the molecular chain of cyanoethyl cellulose, that is, the different degrees of substitution, its performance will also change accordingly. Therefore, within a certain range of variation, the dielectric constant of cyanoethyl cellulose will increase with the increase of the degree of substitution, and its moisture resistance, thermal stability and mechanical properties will also be strengthened. And cyanoethyl cellulose with a high degree of substitution (2.6-3) has high water resistance, high insulation and self-extinguishing properties. Therefore, the present invention can improve the water resistance, thermal stability and mechanical properties of the prepared composite insulating paper by combining cyanoethyl cellulose with different degrees of substitution with cellulose nanofibers.

[0038] Figure 1 This is a transmission electron microscope image of cellulose nanofibers magnified 100,000 times. Figure 2 This is a transmission electron microscope image of cellulose nanofibers magnified 20,000 times. Figure 1 , Figure 2 It can be seen that cellulose nanofibers have a large aspect ratio, and their nanoscale size and one-dimensional structure make them have a high specific surface area, high electrical conductivity, excellent mechanical strength and thermal conductivity. The excellent performance of cellulose nanofibers can be used to prepare insulating paper, which can make the final prepared insulating paper have good insulating properties and excellent mechanical strength, so it can be combined with other substances to improve the insulating effect of insulating paper. At the same time, due to the increase in the degree of fluorination (fluorine-carbon ratio) of fluorinated carbon nanotubes, its conductivity will be reduced. That is: the higher the degree of fluorination, the lower the conductivity of the fluorinated carbon nanotubes, and the adsorption capacity and hydrophobicity will be enhanced accordingly; at the same time, the higher the fluorine content, the better its thermal stability. Therefore, the present invention prepares composite insulating paper by combining fluorinated carbon nanotubes with different fluorine-carbon ratios with cellulose nanofibers, which can also enhance the thermal stability, insulation and waterproofness of the prepared composite insulating paper. In addition, the insulating performance of insulating paper can also be improved, thereby solving the problems of easy moisture absorption, poor thermal stability and easy aging of traditional cellulose insulating paper.

[0039] In summary, the present invention uses cyanoethyl cellulose with different degrees of substitution and / or fluorinated carbon nanotubes with different fluorine-carbon ratios as functional elements for regulating the dielectric constant of insulating paper, so as to obtain composite insulating paper with adjustable dielectric constant, and utilizes composite insulating paper with different dielectric constants to construct the insulation system of the transformer, so as to achieve safe and reliable operation of high-performance transformers.

[0040] Embodiment 1:

[0041] This embodiment provides a method for preparing a composite insulating paper with adjustable dielectric constant, comprising the following steps:

[0042] 1) Using cellulose nanofibers as raw materials, weigh 10 g of cellulose nanofiber gel, wherein the cellulose nanofiber content is 200 mg, add it into 400 mL of deionized water, stir and mix thoroughly to obtain a cellulose nanofiber dispersion liquid, which is used as a matrix solution.

[0043] 2) Weigh 1g of 1.13 degree of substitution cyanoethyl cellulose and add 100g of acetone / water mixed solution The mixture was stirred magnetically for 12 hours until dissolved; 20 g of acrylonitrile and an appropriate amount of NaOH solution (the NaOH solution was obtained by dissolving 1 g of NaOH in 10 mL of water and cooling to room temperature) were added dropwise to the dissolved solution, and the mixture was stirred at 15°C for 5 hours to react; hydrochloric acid was then added to the reaction solution to neutralize the reaction solution, and water approximately twice the volume of the reaction solution was added dropwise to precipitate the product; the obtained product was washed with water and vacuum dried at 80°C for 12 hours 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 and the fluorinated carbon nanotubes with a fluorine-carbon ratio of 0.8 in step 2) are uniformly mixed with polyvinyl alcohol (PVA) with a molecular weight of 300,000 in a mass ratio of 1:5 by ultrasonic, shearing and stirring to obtain a spinning solution, such as Figure 3 As shown, the spinning solution is loaded into a syringe and fixed on the syringe pump of the electrospinning machine for electrospinning, a suitable fiber receiving device is selected, connected to the negative electrode and placed directly below the needle, and the nanofibers are deposited on the fiber receiving device to obtain fluorinated carbon nanotube / cyanoethyl cellulose coaxial fibers (FC@CEC), which are placed in a vacuum drying oven at 60°C and dried for 48 hours.

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

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

[0047] 6) drying the gel sample at 60° C. in vacuum for 48 h to obtain composite insulating paper rough paper;

[0048] 7) The obtained insulating paper rough paper was hot-pressed under the conditions of 20 MPa and 150° C., and the dielectric constant of the insulating paper was tested, and finally a new composite insulating paper with a dielectric constant of 5.5 was obtained.

[0049] Embodiment 2:

[0050] The difference between this embodiment and embodiment 1 is that the mass ratio of the cyanoethyl cellulose to the fluorinated carbon nanotubes is 1:3, and the dielectric constant of the obtained composite insulating paper is 4.1.

[0051] Embodiment 3:

[0052] The difference between this embodiment and embodiment 1 is that the mass ratio of the cyanoethyl cellulose to the fluorinated carbon nanotubes is 1:1, and the dielectric constant of the obtained composite insulating paper is 4.6.

[0053] Embodiment 4:

[0054] The difference between this embodiment and embodiment 1 is that the mass ratio of cyanoethyl cellulose to fluorinated carbon nanotubes is 5:1, and the dielectric constant of the composite insulating paper obtained is 3.4.

[0055] Embodiment 5:

[0056] The difference between this embodiment and embodiment 1 is that the fluorine-carbon ratio of the fluorinated carbon nanotubes is 1, and the dielectric constant of the obtained composite insulating paper is 5.4.

[0057] Embodiment 6:

[0058] The difference between this embodiment and embodiment 1 is that the fluorine-carbon ratio of the fluorinated carbon nanotubes is 1.2, and the dielectric constant of the obtained composite insulating paper is 5.7.

[0059] Embodiment 7:

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

[0061] Embodiment 8:

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

[0063] Comparative Example 1:

[0064] FC@CEC was made by electrospinning cyanoethyl cellulose with a degree of substitution of 1.13 and fluorinated carbon nanotubes with a fluorine-carbon ratio of 0.8. The coaxial fiber and cellulose nanofibers were mixed in a ratio of 1:1 by high-speed shearing to obtain a composite slurry. Composite insulating paper rough paper was obtained by electrostatic spraying. The new composite insulating paper was obtained by high-temperature hot pressing, and the dielectric constant of the composite insulating paper was detected to be 3.

[0065] Comparative Example 2:

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

[0067] Comparative Example 3:

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

[0069] Comparative Example 4:

[0070] The difference between this embodiment and embodiment 1 is that in this embodiment, the spinning solution obtained in step 3) is directly mixed with the cellulose nanofibers in step 4) in a ratio of 1:1, and the dielectric constant of the composite insulating paper finally prepared is 3.7.

[0071] Comparative Example 5:

[0072] The difference between this embodiment and embodiment 1 is that in step 5) of this embodiment, vacuum filtration is performed at 0.06-0.09 MPa for 10-20 min and hot pressing is performed at 220-240° C. for 10-15 min, and the dielectric constant of the composite insulating paper finally prepared is 4.5.

[0073] It can be seen from Example 1, Example 5 and Example 6 that the higher the fluorine-carbon ratio of the fluorinated carbon nanotubes is, the higher the dielectric constant of the composite insulating paper finally prepared is.

[0074] It can be seen from Examples 1 to 4 that when the mass ratio of cyanoethyl cellulose to fluorinated carbon nanotubes is 1:5, the dielectric constant of the obtained composite insulating paper is the highest.

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

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

[0077] It can be seen from Example 1, Example 4 and Example 5 that changing the ratio of cyanoethyl cellulose to fluorinated carbon nanotubes has a greater influence on the dielectric constant of the composite insulating paper than changing the fluorine-carbon ratio of the fluorinated carbon nanotubes.

[0078] The novel composite insulating paper with adjustable dielectric constant provided by the present invention has a main component of cellulose nanofibers and FC@CEC in a mass ratio of 1:1, and can better exert its excellent strength performance. At this time, the good insulating performance and thermal stability of fluorinated carbon nanotubes and cyanoethyl cellulose can also play a role, thereby further improving the comprehensive performance of the insulating paper.

[0079] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing composite insulating paper with adjustable dielectric constant, characterized in that: include: Composite insulating papers with different dielectric constants are prepared based on cyanoethyl cellulose with different substitution degrees and fluorinated carbon nanotubes with different fluorine-carbon ratios.

2. The method for preparing composite insulating paper with adjustable dielectric constant according to claim 1, characterized in that: include: Step 1: using polyvinyl alcohol, cyanoethyl cellulose with different degrees of substitution, and fluorinated carbon nanotubes with different fluorine-carbon ratios to prepare different spinning solutions; The different spinning solutions are respectively electrospun to prepare different fluorinated carbon nanotube / cyanoethyl cellulose coaxial fibers FC@CEC; Step 2: mixing the cellulose nanofiber dispersion with different fluorinated carbon nanotube / cyanoethyl cellulose coaxial fibers FC@CEC respectively, and preparing different composite slurries by high-speed shearing; Step 3: spraying the different composite slurries onto the substrates respectively by electrostatic spraying to produce different gels accordingly; Step 4: vacuum drying the different gels respectively to obtain composite insulating paper rough papers with different dielectric constants; Step 5: hot-pressing the composite insulating paper and rough paper with different dielectric constants respectively, and finally obtaining composite insulating paper with different dielectric constants.

3. The method according to claim 2, characterized in that The substitution degree of the cyanoethyl cellulose is 0.5-3.

4. The method according to claim 2, characterized in that: The fluorine-carbon ratio of the fluorinated carbon nanotube is 0.8-1.2, and the diameter is 20-85nm.

5. The method according to claim 2, characterized in that: The mass ratio of the cyanoethyl cellulose to the fluorinated carbon nanotubes is 0.2-5:

1.

6. The method according to claim 2, characterized in that The preparation of the spinning solution comprises: The spinning solution is prepared by subjecting cyanoethyl cellulose with different substitution degrees, fluorinated carbon nanotubes with different fluorine-carbon ratios and polyvinyl alcohol to ultrasonic, shearing and stirring treatments respectively; the molecular weight of the polyvinyl alcohol is 300,000.

7. The method according to claim 2, characterized in that The preparation of the cellulose nanofiber dispersion comprises: The cellulose nanofibers are diluted with water to a cellulose nanofiber dispersion with a mass concentration of 0.05% to 0.5%; the diameter of the cellulose nanofibers is 20 to 30 nm; the mass ratio of the cellulose nanofibers to the fluorinated carbon nanotube / cyanoethyl cellulose coaxial fibers FC@CEC in the cellulose nanofiber dispersion is 1 to 5:

1.

8. The method according to claim 2, characterized in that: The shearing conditions are: a shear rate of 10000-15000 rpm, and a shearing time of 15-25 min; the hot pressing conditions in step 5 are: a pressure of 20-30 MPa, a hot pressing temperature of 100-150° C., and a hot pressing time of 10-30 min.

9. Composite insulating paper with adjustable dielectric constant prepared according to any one of the methods of claims 1-8.

10. Use of the composite insulating paper with adjustable dielectric constant according to claim 9 in the preparation of transformers.

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