Preparation method of high-thermal-conductivity cellulose insulating paper

Abstract

The application discloses a kind of preparation methods of high-thermal-conductivity cellulose insulating paper, belong to insulating paper technical field.The method includes: to unbleached needle leaf pulp is pretreated and controls beating degree, it is mixed with the boron nitride high-thermal-conductivity filler that TEMPO cellulose nanofiber dispersion processing is handled, and uniform composite slurry is formed;Subsequently, it is formed by sheet forming, in the forming process, add binary retention system by specific component composition, again, dehydration, drying and polishing treatment, and the high-thermal-conductivity cellulose insulating paper is prepared.The method effectively improves the dispersibility and retention rate of filler in paper sheet, significantly enhances the thermal conductivity of paper, while maintaining good electrical insulation strength, can satisfy the comprehensive requirements of ultra-high voltage transformer to insulating material thermal conductivity and insulation performance.

Description

Technical Field

[0001] This invention belongs to the field of insulating paper technology, specifically relating to a method for preparing high thermal conductivity cellulose insulating paper. Background Technology

[0002] Cellulose insulating paper, primarily made from natural cellulose fibers such as wood pulp or hemp pulp, has become an indispensable key solid insulating material in high-voltage electrical equipment such as oil-immersed power transformers, reactors, and capacitors due to its excellent electrical insulation properties, mechanical strength, impregnation properties, environmental friendliness, and relatively low cost. In these devices, insulating paper not only performs the core function of electrical insulation but also plays a crucial role in supporting and isolating conductive components.

[0003] With the rapid development of power transmission technology in my country, power equipment such as oil-immersed transformers are moving towards larger scale and higher integration. During continuous high-load operation, a large amount of heat accumulates within the limited space of the insulation windings, which not only severely restricts the operating efficiency of the equipment but also directly threatens its long-term reliability and shortens its service life. Against this backdrop, the performance bottleneck of cellulose insulating paper, the core of the oil-paper insulation structure, is becoming increasingly prominent. Especially with the trend of continuously increasing voltage levels, existing materials are finding it difficult to simultaneously meet the stringent requirements for insulation strength and thermal conductivity.

[0004] Cellulose-based composites have been widely used in electrical insulation due to their advantages such as low density, good processability, and high mechanical strength. However, cellulose materials have poor thermal conductivity, with a thermal conductivity significantly lower than that of traditional ceramics and metals, which greatly limits their application in the field of thermal insulation. This is mainly because cellulose, as a polymer, lacks free electrons in its saturated system, and heat transfer relies primarily on phonon conduction rather than lattice waves, resulting in low thermal conductivity.

[0005] To improve the thermal conductivity of cellulose insulating paper, existing technologies have explored various approaches, primarily focusing on inorganic filler composite methods. This involves adding highly thermally conductive inorganic nano- or micro-particles (such as boron nitride, alumina, and aluminum nitride) to cellulose slurry to create interconnected heat conduction pathways. Boron nitride nanosheets (BNNS), with their graphene-like hexagonal lattice structure and wide bandgap properties, are ideal fillers combining high thermal conductivity with good electrical insulation. They effectively improve the polymer's thermal conductivity while maintaining the matrix's dielectric and insulating properties, making them particularly suitable for applications like power equipment where both heat dissipation and insulation are critical. However, these methods generally suffer from the following insurmountable drawbacks in practical applications and industrialization:

[0006] (1) Poor interfacial compatibility and agglomeration problem: The poor interfacial compatibility between hydrophilic cellulose fibers and hydrophobic inorganic fillers makes it difficult for the fillers to be evenly dispersed in the pulp and they are prone to agglomeration. This not only fails to form a continuous heat conduction network, but also introduces defects at the agglomeration points, resulting in a decrease in the mechanical strength of the insulating paper, deterioration of electrical properties (such as breakdown field strength), and may cause partial discharge.

[0007] (2) Process complexity and cost issues: In order to improve the dispersibility of fillers, complex surface modification treatments (such as silane coupling agent modification) are usually required for fillers, which increases the number of process steps and production costs. At the same time, the addition of a large amount of fillers will seriously affect the water permeability of pulp and paper performance, posing a huge challenge to the existing papermaking process.

[0008] (3) The challenge of balancing performance: While simply increasing the amount of filler may improve thermal conductivity to some extent, it often comes at the cost of sacrificing the mechanical and electrical insulation properties of the insulating paper. How to achieve the best balance between high thermal conductivity, high insulation, and high mechanical strength is a problem that has not yet been effectively solved by existing technologies. Therefore, how to improve the thermal conductivity of cellulose insulating paper has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0009] During long-term operation, cellulose insulating paper in ultra-high voltage transformers is susceptible to internal heat accumulation due to the combined effects of temperature, electric field, and winding mechanical stress, which is difficult to dissipate in time, ultimately leading to insulation system failure. To improve these problems, this invention provides a method for preparing high thermal conductivity cellulose insulating paper. This method enhances the thermal conductivity of the matrix by introducing high thermal conductivity fillers into the slurry and adding an appropriate amount of retention aid to significantly improve the retention rate of the fillers during the wet forming process. Furthermore, by combining hot pressing, the paper sheet density and structural compactness are effectively improved, thereby producing insulating paper with excellent thermal conductivity, meeting the safety and stability requirements of transformers during long-term operation.

[0010] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is as follows:

[0011] A method for preparing a high thermal conductivity cellulose insulating paper, comprising the following steps:

[0012] (1) Pretreatment of wood pulp board: Soak the wood pulp board in deionized water for 4-6 hours to allow it to fully swell, and then mechanically decompose it to obtain decomposed pulp; based on the oven-dry weight of the decomposed pulp, add water to the decomposed pulp to prepare a pulp suspension with a concentration of 10-15 wt%, and mechanically beat it, controlling the beatness within the range of 30-60 °SR;

[0013] (2) Pretreatment of thermally conductive filler: The thermally conductive filler is mixed with TEMPO cellulose nanofiber dispersion for pretreatment to obtain a high thermal conductivity filler dispersion; the thermally conductive filler includes boron nitride nanosheets (BNNS) and boron nitride (BN);

[0014] (3) Take the wood pulp prepared in step (1) according to the proportion and mix it with the high thermal conductivity filler dispersion. Place it in a standard delamination machine and delamination at a speed of 10000 r for 1-10 minutes to obtain the mixed pulp.

[0015] (4) Add a retention aid to the mixed pulp and obtain a wet paper sheet using wet forming technology;

[0016] (5) Press, dry and hot press the obtained wet paper to obtain high thermal conductivity cellulose insulating paper.

[0017] Preferably, the mass ratio of boron nitride nanosheets (BNNS) to boron nitride (BN) in the thermally conductive filler is 1:(0.25-4); the diameter of the boron nitride nanosheets (BNNS) is 0.1-0.4 μm, and the diameter of the boron nitride (BN) sheets is 5-10 μm.

[0018] Preferably, the beating degree range in step (1) is 30. o SR-60 o SR.

[0019] Preferably, the basis weight of the high thermal conductivity cellulose insulating paper is 60-80 g / m³. 2 .

[0020] Preferably, the amount of thermally conductive filler added is 10-50% of the basis weight of the high thermally conductive cellulose insulating paper.

[0021] Preferably, the concentration of the TEMPO cellulose nanofiber dispersion is 1-2 wt%; the oven-dry mass ratio of the TEMPO cellulose nanofiber to the thermally conductive filler is (1-2):1.

[0022] Preferably, in step (3), the dry mass of the wood pulp prepared in step (1) is 1:(10-100) to the mass ratio of the high thermal conductivity filler dispersion.

[0023] Preferably, the retention aid in step (4) includes cationic polyacrylamide, anionic polyacrylamide and chitosan quaternary ammonium salt as a synergist, and the mass ratio of cationic polyacrylamide to anionic polyacrylamide is (1-2):1.

[0024] Preferably, based on the oven-dry pulp quality, the amount of cationic polyacrylamide added is 0.04%-0.2%, the amount of anionic polyacrylamide added is 0.04%-0.1%, and the amount of chitosan quaternary ammonium salt added is 0.01-0.05%.

[0025] Preferably, the pressing treatment is performed at a pressure of 0.2-0.7 MPa and a pressing time of 2-4 min; the drying temperature is 95℃ and the time is 10-15 min; the calendering treatment is performed at a temperature of 60-70℃ and a pressure of 2-3 MPa.

[0026] The beneficial effects of this invention are:

[0027] (1) Introduction of TEMPO cellulose nanofibers as a high-efficiency dispersant: The surface of TEMPO cellulose nanofibers is rich in carboxyl groups, which effectively prevent the agglomeration of boron nitride nanosheets (BNNS) and boron nitride (BN) through electrostatic repulsion and steric hindrance effects, ensuring the uniform dispersion of thermally conductive fillers in the slurry. This not only avoids the decrease in mechanical strength and the deterioration of electrical properties caused by filler agglomeration, but also promotes the formation of a continuous thermally conductive network, significantly improving the thermal conductivity of the insulating paper.

[0028] (2) A retention aid system composed of cationic / anionic polyacrylamide / chitosan quaternary ammonium salt: In this system, the single CPAM / APAM system may form large but loose flocs, which are easily broken up during the papermaking process, resulting in uneven filler distribution; while the molecular chain of chitosan quaternary ammonium salt is relatively short, which can work synergistically with CPAM and APAM, and promote the formation of more small, dense and strong flocs through a composite flocculation mechanism. Through bridging and charge neutralization, it greatly improves the retention rate of thermally conductive fillers in the wet forming process, reduces filler loss, and improves the uniformity of paper forming and the density of the structure. At the same time, the chitosan quaternary ammonium salt in the retention aid contains both cationic groups and hydroxyl and amino groups that can form hydrogen bonds with cellulose. It can act as a "molecular bridge" between the filler and the fiber, strengthen the interfacial bonding between the filler and the fiber, and ensure that good water permeability and paper forming performance are maintained even with high filler addition, thus solving the problem of low filler retention rate in traditional processes.

[0029] (3) By adjusting the mass ratio of BNNS to BN, and utilizing the small size and high specific surface area of ​​BNNS and the large size filling effect of BN, a multi-scale heat conduction path was constructed. BNNS enhanced the phonon transmission efficiency, while BN played a bridging and supporting role. The two worked together to improve the thermal conductivity, while avoiding the performance bottleneck caused by the size of a single filler.

[0030] (4) The high thermal conductivity cellulose insulating paper obtained by this invention ensures the uniform distribution of fillers in the paper sheet through the effective dispersion of TEMPO cellulose nanofibers, avoiding local defects caused by filler agglomeration. This not only improves thermal conductivity but also helps to ensure and improve the paper's breakdown strength. The application of the binary polymer retention system significantly improves the retention rate of fillers and fine fibers, and greatly enhances the tensile index, folding endurance, and other mechanical properties of the paper. The final hot-pressing process further optimizes the internal structure of the paper sheet, minimizing interfacial thermal resistance. This significantly improves the thermal conductivity of the paper while maintaining excellent electrical insulation performance and mechanical strength, expanding its application prospects in the field of high-efficiency thermally conductive insulating materials. This multi-component synergistic effect enables the insulating paper prepared by this invention to achieve the best balance between thermal conductivity, electrical insulation strength, and mechanical properties, meeting the stringent requirements of ultra-high voltage transformers for heat dissipation and reliability. Detailed Implementation

[0031] The technical solution of the present invention will be further described below with reference to specific embodiments, but is not limited thereto. The TEMPO cellulose nanofibers used in the present invention were purchased from Tianjin Wood Elf Biotechnology Co., Ltd.; anionic polyacrylamide: molecular weight 15-18 million, degree of hydrolysis 25-30%; cationic polyacrylamide: molecular weight 8-10 million, degree of ionization 30-35%.

[0032] Example 1

[0033] A method for preparing a high thermal conductivity cellulose insulating paper, comprising the following steps:

[0034] (1) Pretreatment of wood pulp board: Soak the pulp board in deionized water for 4 hours to fully swell, then decompose it, take the decomposed pulp, weigh 30 g of oven dry weight, add water to prepare a pulp suspension with a total weight of 300 g, use a PFI refiner to pulp, and control the pulping degree to 40°SR.

[0035] (2) The total amount of thermally conductive filler added is 10% of the paper basis weight. Weigh 0.1178 g of BNNS and 0.1178 g of BN. Add TEMPO cellulose nanofiber in the form of an aqueous dispersion with a concentration of 1 wt%. The ratio of its oven-dry mass to the oven-dry mass of the thermally conductive filler is 1.27:1. The mixture is first ultrasonically treated for 30 minutes and then mechanically stirred for 2 hours to finally obtain a uniform and stable high thermal conductivity filler dispersion.

[0036] (3) Based on the paper basis weight of 75 g / m 2Weigh 2.12 g of pretreated softwood pulp and mix it with 30.2356 g of high thermal conductivity filler dispersion; then, place the mixture in a standard delamination machine and delamination at 10000 r for 1-10 minutes to obtain mixed pulp.

[0037] (4) Add a retention aid with a total mass of 0.00192 g to the mixed slurry. The retention aid consists of 0.85 mg cationic polyacrylamide, 0.85 mg anionic polyacrylamide, and 0.22 mg chitosan quaternary ammonium salt. The resulting suspension is poured into a sheet-making machine for dehydration and molding to prepare a quantitative 75 g / m³ sheet. 2 The wet paper pages;

[0038] (5) The wet paper sheet is processed in a standard press at a pressure of 0.6 MPa and a pressing time of 3 min; then the wet paper sheet is dried in a paper dryer at 95°C for 10 min to obtain the base paper. The base paper is calendered at a temperature of 65°C and a pressure of 3 MPa to obtain high thermal conductivity cellulose insulating paper.

[0039] Example 2

[0040] A method for preparing a high thermal conductivity cellulose insulating paper, comprising the following steps:

[0041] (1) Pretreatment of wood pulp board: Soak the pulp board in deionized water for 4 hours to fully swell, then decompose it, take the decomposed pulp, weigh 30 g of oven dry weight, add water to prepare a pulp suspension with a total weight of 300 g, use a PFI refiner to pulp, and control the pulping degree to 50°SR.

[0042] (2) The total amount of thermally conductive filler added is 10% of the paper basis weight. Weigh 0.078 g of BNNS and 0.157 g of BN, and add them to the TEMPO cellulose nanofiber in the form of an aqueous dispersion with a concentration of 1 wt%. The ratio of the dry weight of the thermally conductive filler to the dry weight of the thermally conductive filler is 2:1. The mixture is first ultrasonically treated for 30 minutes, and then mechanically stirred for 2 hours to finally obtain a uniform and stable high thermal conductivity filler dispersion.

[0043] (3) Based on the paper basis weight of 75 g / m 2 Weigh 2.12 g of pretreated softwood pulp and mix it with 47.3556 g of high thermal conductivity filler dispersion; then, place the mixture in a standard delamination machine and delamination at 10000 r for 1-10 minutes to obtain mixed pulp.

[0044] (4) Add a retention aid with a total mass of 0.00334 g to the mixed slurry. The retention aid consists of 1.8 mg cationic polyacrylamide, 0.9 mg anionic polyacrylamide, and 0.64 mg chitosan quaternary ammonium salt. Pour the resulting suspension into a sheet-making machine for dehydration and molding to prepare a quantitative 75 g / m³ sheet. 2 The wet paper pages;

[0045] (5) The wet paper sheet is processed in a standard press at a pressure of 0.6 MPa and a pressing time of 3 min; then the wet paper sheet is dried in a paper dryer at 95°C for 10 min to obtain the base paper. The base paper is calendered at a temperature of 65°C and a pressure of 3 MPa to obtain high thermal conductivity cellulose insulating paper.

[0046] Example 3

[0047] A method for preparing a high thermal conductivity cellulose insulating paper, comprising the following steps:

[0048] (1) Pretreatment of wood pulp board: Soak the pulp board in deionized water for 4 hours to fully swell, then decompose it, take the decomposed pulp, weigh 30 g of oven dry weight, add water to prepare a pulp suspension with a total weight of 300 g, use a PFI refiner to pulp, and control the pulping degree to 60°SR.

[0049] (2) The total amount of thermally conductive filler added is 20% of the paper basis weight. Weigh 0.2356 g of BNNS and 0.2356 g of BN. Add TEMPO cellulose nanofiber in the form of an aqueous dispersion with a concentration of 1 wt%. The ratio of its oven-dry mass to the oven-dry mass of the thermally conductive filler is 1.06:1. The mixed system is first ultrasonically treated for 30 minutes and then mechanically stirred for 2 hours to finally obtain a uniform and stable high thermal conductivity filler dispersion.

[0050] (3) Based on the paper basis weight of 75 g / m 2 Weigh 1.8848 g of pretreated softwood pulp and mix it with 50.4712 g of high thermal conductivity filler dispersion; then, place the mixture in a standard delamination machine and delamination at 10000 r for 1-10 minutes to obtain mixed pulp.

[0051] (4) Add a retention aid of 5.3 mg by total mass to the mixed slurry. The retention aid consists of 2.12 mg cationic polyacrylamide, 2.12 mg anionic polyacrylamide, and 1.06 mg chitosan quaternary ammonium salt. Pour the resulting suspension into a sheet-making machine for dehydration and molding to prepare a quantitative 75 g / m³ sheet. 2 The wet paper pages;

[0052] (5) The wet paper sheet is processed in a standard press at a pressure of 0.6 MPa and a pressing time of 3 min; then the wet paper sheet is dried in a paper dryer at 95°C for 10 min to obtain the base paper. The base paper is calendered at a temperature of 65°C and a pressure of 3 MPa to obtain high thermal conductivity cellulose insulating paper.

[0053] Example 4

[0054] A method for preparing a high thermal conductivity cellulose insulating paper, comprising the following steps:

[0055] (1) Pretreatment of wood pulp board: Soak the pulp board in deionized water for 4 hours to fully swell, then decompose it, take the decomposed pulp, weigh 30 g of oven dry weight, add water to prepare a pulp suspension with a total weight of 300 g, use a PFI refiner to pulp, and control the pulping degree to 30°SR.

[0056] (2) The total amount of thermally conductive filler added is 20% of the paper basis weight. Weigh 0.157 g of BNNS and 0.314 g of BN. Add TEMPO cellulose nanofibers in the form of an aqueous dispersion with a concentration of 1 wt%. The ratio of the oven-dry mass of the nanofibers to the oven-dry mass of the thermally conductive filler is 1.5:1. The mixture is first ultrasonically treated for 30 minutes, and then mechanically stirred for 2 hours to finally obtain a uniform and stable dispersion of high thermal conductivity filler.

[0057] (3) Based on the paper basis weight of 75 g / m 2 Weigh 1.8848 g of pretreated softwood pulp and mix it with 71.1512 g of high thermal conductivity filler dispersion; then, place the mixture in a standard delamination machine and delamination at 10000 r for 1-10 minutes to obtain mixed pulp.

[0058] (4) Add a retention aid with a total mass of 0.0036 g to the mixed slurry. The retention aid consists of 1.5 mg cationic polyacrylamide, 1.5 mg anionic polyacrylamide, and 0.6 mg chitosan quaternary ammonium salt. Pour the resulting suspension into a sheet-making machine for dehydration and molding to prepare a quantitative 75 g / m³ sheet. 2 The wet paper pages;

[0059] (5) The wet paper sheet is processed in a standard press at a pressure of 0.6 MPa and a pressing time of 3 min; then the wet paper sheet is dried in a paper dryer at 95°C for 10 min to obtain the base paper. The base paper is calendered at a temperature of 65°C and a pressure of 3 MPa to obtain high thermal conductivity cellulose insulating paper.

[0060] Comparative Example 1

[0061] A method for preparing high thermal conductivity cellulose insulating paper, without adding TEMPO cellulose nanofibers, directly mixes BNNS / BN thermally conductive filler with pulp, and the other steps are exactly the same as in Example 1.

[0062] Comparative Example 2

[0063] A method for preparing high thermal conductivity cellulose insulating paper, except that TEMPO cellulose nanofibers are replaced with aramid nanofibers by the same mass, the other steps and parameters are the same as in Example 1.

[0064] Comparative Example 3

[0065] A method for preparing high thermal conductivity cellulose insulating paper, without adding retention aids, with other steps being the same as in Example 1.

[0066] Comparative Example 4

[0067] A method for preparing high thermal conductivity cellulose insulating paper, wherein the retention aid is only cationic polyacrylamide, and the other steps are the same as in Example 1.

[0068] Comparative Example 5

[0069] A method for preparing high thermal conductivity cellulose insulating paper, wherein the retention aid is only anionic polyacrylamide, and the other steps are the same as in Example 1.

[0070] Comparative Example 6

[0071] A method for preparing high thermal conductivity cellulose insulating paper, wherein the retention aid does not contain chitosan quaternary ammonium salt, and the total mass of the retention aid is 0.00192 g, consisting of 0.96 mg cationic polyacrylamide and 0.96 mg anionic polyacrylamide, and the other steps are the same as in Example 1.

[0072] Comparative Example 7

[0073] A method for preparing high thermal conductivity cellulose insulating paper is identical to that in Example 1, except that the mass ratio of cationic polyacrylamide to anionic polyacrylamide in the retention aid is 3:1.

[0074] Comparative Example 8

[0075] A method for preparing high thermal conductivity cellulose insulating paper is identical to that in Example 1, except that the mass ratio of cationic polyacrylamide to anionic polyacrylamide in the retention aid is 0.5:1.

[0076] Comparative Example 9

[0077] A method for preparing high thermal conductivity cellulose insulating paper, except that the mass ratio of BNNS to BN is 1:0.1, all other steps and parameters are the same as in Example 1.

[0078] Comparative Example 10

[0079] A method for preparing high thermal conductivity cellulose insulating paper, except that the mass ratio of BNNS to BN is 1:5, all other steps and parameters are the same as in Example 1.

[0080] Performance testing

[0081] The performance of the high thermal conductivity cellulose insulating paper obtained in Examples 1-4 and Comparative Examples 1-10 was tested, and the specific test results are shown in Table 1 below.

[0082] Table 1 Performance Test Results

[0083]

[0084] As can be seen from the above results, Examples 1-4 of this invention, by introducing TEMPO cellulose nanofibers as a highly efficient dispersant in the preparation of high thermal conductivity cellulose insulating paper, combined with a cationic / anionic polyacrylamide retention aid system and hot pressing process, achieved synergistic enhancement of each process step: TEMPO cellulose nanofibers effectively improved the dispersion uniformity and retention rate (reaching 82.1%-85.5%) of BNNS / BN thermally conductive fillers, avoiding performance defects caused by filler agglomeration; the retention aid system of this invention further enhanced the bonding between fillers and fibers, keeping the tensile strength at a relatively high level of 3.87-4.01 kN / m; while the hot pressing process significantly improved the paper density and structural compactness, greatly reduced the interfacial thermal resistance, and made the planar thermal conductivity reach 3.437-4.106 W / (m·K), and the overall thermal conductivity increased to 0.3306-0.4011 W / (m·K), while maintaining excellent electrical insulation performance. In Comparative Example 1, the planar and overall thermal conductivity were 3.106 and 0.2315 W / (m·K), respectively, with a filler retention rate of only 75.1%, and significantly lower tensile and breakdown strengths. Comparative Example 2 also showed further declines in various properties, indicating that the unique surface carboxyl groups of TEMPO cellulose nanofibers are irreplaceable in dispersing BNNS / BN. TEMPO cellulose nanofibers effectively prevent BNNS / BN aggregation and promote the formation of a thermally conductive network through electrostatic repulsion and steric hindrance, which is key to improving thermal conductivity and filler retention. In Comparative Example 3, the filler retention rate plummeted to 55.4%, and thermal conductivity, mechanical, and electrical properties all declined, demonstrating that the retention aid system used in this invention is crucial for filler fixation and paper sheet formation. Furthermore, Comparative Examples 4-8 altered the composition of the retention aid raw materials and the mass ratio of cationic to anionic polyacrylamide in this invention. When the raw material composition or dosage ratio exceeded the scope of this invention, the retention rate, thermal conductivity, mechanical properties, and other aspects of the obtained cellulose insulating paper all decreased. This indicates that only when a specific ratio of CPAM / APAM works synergistically with the synergistic component chitosan quaternary ammonium salt, through bridging and charge neutralization, can the retention rate of fillers and fine fibers be significantly improved, thereby enhancing paper uniformity and structural density. In Comparative Examples 9 and 10, the BNNS:BN ratio was imbalanced, resulting in significantly lower performance compared to the original example. This demonstrates that an imbalanced filler ratio cannot effectively construct a continuous thermal conductivity pathway. Therefore, this invention optimizes multi-scale phonon transport paths and synergistically improves thermal conductivity by controlling the mass ratio of BNNS (small size, high specific surface area) to BN (large size, bridging support).

[0085] It is evident that the dispersion, retention, and hot pressing processes employed in this invention have a significant synergistic enhancement effect. While significantly improving the thermal conductivity of the insulating paper, they also take into account its electrical strength and mechanical properties, providing a high-performance and highly reliable paper insulating material for ultra-high voltage transformer insulation systems.

[0086] It should be noted that the above embodiments are merely some preferred embodiments of the present invention, and not all embodiments. Obviously, based on the above embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

Claims

1. A method for preparing a high thermal conductivity cellulose insulating paper, characterized in that, It includes the following steps: (1) Pretreatment of wood pulp board: Soak the wood pulp board in deionized water for 4-6 hours to allow it to fully swell, and then mechanically decompose it to obtain decomposed pulp; based on the oven-dry weight of the decomposed pulp, add water to the decomposed pulp to prepare a pulp suspension with a concentration of 10-15 wt%, and mechanically beat it, controlling the beatness within the range of 30-60 °SR; (2) Pretreatment of thermally conductive filler: The thermally conductive filler is mixed with TEMPO cellulose nanofiber dispersion for pretreatment to obtain a high thermal conductivity filler dispersion; the thermally conductive filler includes boron nitride nanosheets (BNNS) and boron nitride (BN); (3) Take the wood pulp prepared in step (1) in proportion and mix it with the high thermal conductivity filler dispersion. Place it in a standard delamination machine and delamination at a speed of 10000 r for 1-10 minutes to obtain the mixed pulp. (4) Add a retention aid to the mixed pulp and obtain a wet paper sheet using wet forming technology; (5) Press, dry and hot press the obtained wet paper sheets to obtain high thermal conductivity cellulose insulating paper; The mass ratio of boron nitride nanosheets (BNNS) to boron nitride (BN) in the thermally conductive filler is 1:(0.25-4); the diameter of the boron nitride nanosheets (BNNS) is 0.1-0.4 μm, and the diameter of the boron nitride (BN) nanosheets is 5-10 μm. The retention aid in step (4) includes cationic polyacrylamide, anionic polyacrylamide and chitosan quaternary ammonium salt as the synergist, and the mass ratio of cationic polyacrylamide to anionic polyacrylamide is (1-2):

1.

2. The method for preparing high thermal conductivity cellulose insulating paper according to claim 1, characterized in that, The basis weight of the high thermal conductivity cellulose insulating paper is 60-80 g / m³. 2 .

3. The method for preparing high thermal conductivity cellulose insulating paper according to claim 1, characterized in that, The amount of thermally conductive filler added is 10-50% of the basis weight of the high thermally conductive cellulose insulating paper.

4. The method for preparing high thermal conductivity cellulose insulating paper according to claim 1, characterized in that, The concentration of the TEMPO cellulose nanofiber dispersion is 1-2 wt%; the oven-dry mass ratio of the TEMPO cellulose nanofiber to the thermally conductive filler is (1-2):

1.

5. The method for preparing high thermal conductivity cellulose insulating paper according to claim 1, characterized in that, In step (3), the ratio of the oven-dry mass of the wood pulp prepared in step (1) to the mass of the high thermal conductivity filler dispersion is 1:(10-100).

6. The method for preparing high thermal conductivity cellulose insulating paper according to claim 1, characterized in that, Based on the oven-dry pulp quality, the amount of cationic polyacrylamide added is 0.04%-0.2%, the amount of anionic polyacrylamide added is 0.04%-0.1%, and the amount of chitosan quaternary ammonium salt added is 0.01-0.05%.

7. The method for preparing high thermal conductivity cellulose insulating paper according to claim 1, characterized in that, The pressing process is carried out at a pressure of 0.2-0.7 MPa and a pressing time of 2-4 min; the drying temperature is 95℃ and the time is 10-15 min; the calendering process is carried out at a temperature of 60-70℃ and a pressure of 2-3 MPa.

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