In-situ doped ZnO paper-based insulating material and preparation method thereof

Abstract

The invention discloses an in-situ doped ZnO paper-based insulating material and a preparation method thereof, and belongs to the technical field of paper-based special materials in paper industry. The method disclosed by the invention comprises the following steps: mixing and stirring zinc chloride and water to obtain a zinc chloride hydrated eutectic solvent; then soaking the porous base paper in a zinc chloride hydrated deep-eutectic solvent for swelling treatment to obtain gelatinized base paper; immersing the gelatinized raw paper into an ethanol / water anti-solvent system for regeneration treatment to obtain regenerated raw paper; then dipping the regenerated raw paper in alkali liquor for in-situ deposition treatment to obtain raw paper with ZnO micro-nano particles loaded and doped on the surface; and performing post-treatment on the body paper with the surface loaded and doped with the ZnO micro-nano particles to obtain the in-situ doped ZnO paper-based insulating material. According to the method disclosed by the invention, in-situ doping of the ZnO micro-nano particles is successfully realized in the densified base paper, and the dielectric property is further remarkably improved by cooperating with the densification effect.

Description

Technical Field

[0001] This invention belongs to the technical field of paper-based special materials in the paper industry, specifically relating to an in-situ doped ZnO paper-based insulating material and its preparation method. Background Technology

[0002] The rapid development of modern electrical and electronic technologies has led to an increasing demand for high-performance insulating dielectric materials, requiring these materials to possess excellent insulation properties, mechanical strength, hydrophobicity, and environmental stability. Cellulose, as a natural and renewable polymer, is rich in hydroxyl groups along its main chain. These hydroxyl groups endow cellulose with inherent polarity, making it an ideal candidate material for insulation applications in the electrical industry. However, the inherently low dielectric constant of cellulose (typically 1.3–4.0) and the porous structure of traditional cellulose paper severely limit its direct application in high-precision electronic equipment. Therefore, developing cellulose-based insulating materials that combine enhanced dielectric properties, maintained mechanical integrity, and scalability for industrial applications remains a key requirement.

[0003] Nanoparticle doping technology has been successfully applied to the modification of insulating materials. The incorporation of metal oxides with excellent insulating properties (such as BaTiO3, Al2O3, SiO2, TiO2, and ZnO) can serve as functional fillers for next-generation nanodielectrics. Chinese patent applications CN107190565A and CN113584948A, respectively, directly blend Al2O3 and MgO nanoparticles, which have wide bandgap and excellent insulating properties, into regenerated cellulose, improving the dielectric properties and reducing dielectric loss. However, these processes primarily employ single-addition methods for nanoparticle doping, resulting in uneven distribution of nanoparticles in the regenerated fiber and a tendency for particle agglomeration. Simultaneously, the porosity of the regenerated cellulose paper is not significantly improved, leading to the continued susceptibility of charge carriers in the electric field environment to breakdown of the nanoparticle-modified insulating material. In short, paper-based insulating materials still face the problems of high porosity in cellulose paper and uneven distribution and agglomeration of blended nanoparticles. Therefore, finding an integrated technology that can both control the porosity of paper sheets and achieve metal oxide loading and doping is of great practical significance. Summary of the Invention

[0004] The purpose of this invention is to provide an in-situ doped ZnO paper-based insulating material and its preparation method, in order to solve the technical problem that existing methods are unable to simultaneously achieve paper porosity control and paper porosity regulation.

[0005] To achieve the above objectives, the present invention employs the following technical solution: This invention discloses a method for preparing in-situ doped ZnO paper-based insulating material, comprising the following steps: After mixing and stirring zinc chloride and water, a zinc chloride hydrated eutectic solvent is obtained. The porous base paper was then impregnated in a zinc chloride hydrate eutectic solvent for swelling treatment to obtain gelled base paper; the gelled base paper was then impregnated in an ethanol / water antisolvent system for regeneration treatment to obtain regenerated base paper; The recycled paper was then impregnated in an alkaline solution for in-situ deposition treatment to obtain paper with ZnO micro- and nano-particles loaded on its surface. By post-processing the base paper with ZnO micro- and nano-particles loaded on its surface, an in-situ ZnO-doped paper-based insulating material is obtained.

[0006] Furthermore, the mixing and stirring method is magnetic stirring; the temperature during magnetic stirring is 40~90℃, and the time is 15~120min.

[0007] Furthermore, the molar ratio of zinc chloride to water is 1:(2~9). The chemical formula of the zinc chloride hydrate DES is ZnCl2·nH2O, ZnCl2 / AlCl3·nH2O / ZnCl2 / FeCl3·nH2O or ZnCl2 / CuCl2·nH2O; Where n is the number of water molecules, specifically ranging from 2 to 9.

[0008] Furthermore, the temperature during the swelling treatment is 35~90℃, and the time is 30s~30min.

[0009] Furthermore, the porous base paper is made of cotton fiber, softwood, hardwood or non-wood fiber. The porous base paper has a cellulose mass percentage of 80% to 95%, a fiber porosity range of 50% to 70%, and a pore size of 5 to 30 μm.

[0010] Furthermore, by mass percentage, the ethanol / water antisolvent system comprises 60% to 100% anhydrous ethanol and 0% to 40% deionized water; The regeneration process is carried out at room temperature for 10 to 60 minutes.

[0011] Furthermore, the alkaline solution is a KOH solution, a NaOH solution, or ammonia water; The concentration of the alkaline solution is 0.1~3.0 mol / L.

[0012] Furthermore, the temperature of the in-situ deposition treatment is 20~55℃; The post-processing includes sequential washing, hot pressing, and drying. The hot pressing pressure is 2~4MPa, the temperature is 50~100℃, and the time is 30~120min.

[0013] The present invention also discloses an in-situ doped ZnO paper-based insulating material prepared by the above preparation method, wherein the particle size of the ZnO micro-nano particles in the in-situ doped ZnO paper-based insulating material is 200~5000nm, and the doping mass fraction of the ZnO micro-nano particles is 0.1~7.0wt%.

[0014] Furthermore, the ZnO micro / nano particles in the in-situ doped ZnO paper-based insulating material have a particle size of 500~750nm and a doping mass fraction of 0.5~2wt%.

[0015] Compared with the prior art, the present invention has the following beneficial effects: This invention discloses a method for preparing in-situ doped ZnO paper-based insulating material. By using zinc chloride and water to synthesize a zinc chloride hydrate eutectic solvent and controlling it to form a swelling system, the surface fibers of the paper base are swollen and undergo gelation transformation while maintaining the paper base fiber skeleton. Subsequently, the regeneration effect of the alcohol / water antisolvent system promotes the densification of the paper base fibers, forming a dense structure without obvious pores. In this process, the densification of the paper base by the zinc chloride hydrate eutectic solvent significantly improves the breakdown strength and enhances the insulation performance of the paper base material. The zinc chloride hydrate remaining in the fibers can serve as a zinc source for ZnO semiconductors. By impregnating the paper base with an alkaline solution, in-situ doping of ZnO micro / nano particles is successfully achieved in the densified paper, further synergistically enhancing the dielectric properties through densification.

[0016] Furthermore, through a creative experimental process, this method demonstrates that when the molar ratio of water and zinc chloride in the zinc chloride hydrate eutectic solvent increases, the DES system exhibits a dissolving effect on the base paper fibers. The filter paper fibers gradually dissolve, failing to achieve swelling and densification. Under these conditions, the dielectric properties of the modified paper-based material doped under these conditions are not significantly improved. However, when regenerating and doping ZnO in a high-concentration alkaline solution, the ZnO particle size increases by 2-3 times, and the loading also increases by 6-8 times. However, when the ZnO particle size is too large and the loading is too high, the charge carriers at the breakdown voltage more easily conduct the modified and densified paper-based insulating material. Therefore, this invention sets a suitable molar ratio of zinc chloride and water, and designs a synthesized zinc chloride hydrate eutectic solvent with dual functions—it can both induce swelling and gelation of the base paper fibers and provide a zinc source for the formation of ZnO semiconductor metal oxides, offering integrated preparation advantages and significantly simplifying the process.

[0017] Furthermore, this invention innovatively proposes utilizing the dual function of zinc chloride hydrated DES—it can both achieve the swelling and gelation of the base paper fibers and provide a zinc source for the formation of ZnO semiconductor metal oxides, significantly simplifying the process flow. The synergistic effect of the densified structure on the paper surface and the ZnO micro / nano particles effectively improves the insulation performance of the paper-based insulating material (such as breakdown strength and reduced dielectric loss). This invention also possesses the process characteristics of continuous and rapid swelling and densification on roll to roll and in-situ ZnO doping, demonstrating excellent potential for large-scale production and application. Attached Figure Description

[0018] Figure 1 The image shows scanning electron microscope (SEM) images of the fibers of the filter paper base paper after treatment with DES hydrated with ZnCl2 at different molar ratios in Example 1 of the present invention. Figure 2 The images shown are scanning electron microscope (SEM) images of the filter paper base paper in Example 2 of the present invention before and after densification and in-situ ZnO doping in a ZnCl2 hydrated DES system. Wherein: a- Planar morphology of filter paper base (×400x and ×1000x); b- Cross-sectional morphology of filter paper base (×400x); c- Planar morphology of filter paper base after densification (×400x and ×1000x); d- Cross-sectional morphology of filter paper base after densification (×400x); e- Planar morphology of filter paper base after densification and in-situ deposition of ZnO doping (×400x and ×1000x); f- Cross-sectional morphology of filter paper base after densification and in-situ deposition of ZnO doping (×400x). Figure 3 The breakdown strength, dielectric constant, and dielectric loss properties of the filter paper base paper and paper-based insulating material before and after modification in Example 2 of the present invention; Where: a-the breakdown strength of the filter paper base material, the densified paper, and the ZnO in-situ doped paper base material; b-the dielectric constant of the filter paper base material, the densified paper, and the ZnO in-situ doped paper base material; c-the dielectric constant of the filter paper base material, the densified paper, and the ZnO in-situ doped paper base material; Figure 4 These are scanning electron microscope (SEM) images of in-situ ZnO-doped paper-based insulating materials after densification of filter paper base paper in Examples 3-5 of the present invention under different NaOH alkali concentrations. Wherein: a- Planar morphology images of ZnO-0.1 samples prepared in Example 3 (×400x and ×1000x); b- Planar morphology images of ZnO-0.25 samples prepared in Example 2 (×400x and ×1000x); c- Planar morphology images of ZnO-0.5 samples (×400x and ×1000x); d- Planar morphology images of ZnO-0.25 samples (×400x and ×1000x); e- Planar morphology images of ZnO-0.25 samples (×400x and ×1000x). Detailed Implementation

[0019] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0020] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0021] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0022] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0023] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0024] This invention provides a method for preparing densified in-situ doped ZnO insulating materials. The designed and synthesized zinc chloride hydrate DES has a dual function—it can both induce swelling and gelation of the base paper fibers and provide a zinc source for the formation of ZnO semiconductor metal oxides, offering integrated preparation advantages and significantly simplifying the process flow. This invention also possesses the process characteristics of continuous, rapid swelling and densification on roll-to-roll and in-situ ZnO doping, demonstrating excellent potential for large-scale production and application. The method specifically includes the following steps: First, a zinc chloride hydrated eutectic solvent (DES) was designed and synthesized, and used to impregnate porous base paper to induce swelling and gelation of the paper fibers. Second, the gelled base paper was regenerated using an ethanol / water antisolvent system to achieve material densification. Subsequently, ZnO micro / nano particles were loaded onto the surface of the regenerated base paper through an in-situ deposition process in NaOH alkaline solution. Finally, after calendering, a densified in-situ doped ZnO paper-based insulating material was obtained.

[0025] Preferably, the characteristics of the zinc chloride hydrate eutectic solvent include ZnCl2·nH2O, but are not limited to mono-ZnCl2 or binary or even ternary ZnCl2 hydrated DES, such as ZnCl2 / AlCl3·nH2O, ZnCl2 / FeCl3·nH2O, where n is the number of water molecules, specifically ranging from 2 to 5; when the base paper is impregnated in ZnCl2 hydrated DES for swelling treatment, the solvent system temperature is 35℃-90℃, and the treatment time ranges from 30s to 30min; the ratio of base paper to solvent content is required to ensure that the base paper can be impregnated in the designed ZnCl2 hydrated DES.

[0026] Preferably, the paper base paper used includes paper made from cotton fiber, softwood, hardwood, and non-wood fibers, such as filter paper. The cellulose content of the base paper is 80% to 95%, the fiber porosity is 50% to 70%, and the pore size is 5 to 30 μm.

[0027] Preferably, the regenerated antisolvent ethanol / water solution has the following characteristics: the ratio of ethanol to water is 60%~100% anhydrous ethanol and 0%~40% deionized water. The temperature of the ethanol / water solution regeneration bath can be room temperature, 23~30℃ in summer and 15~30℃ in winter.

[0028] Preferably, micro-nano ZnO is in-situ doped onto a densified paper substrate in an alkaline solution solvent system. The alkaline substance in the alkaline solution includes solutions prepared from potassium hydroxide (KOH), sodium hydroxide (NaOH), ammonia (NH3H2O), etc.; the concentration of the alkaline solution ranges from 0.1 to 3.0 mol / L; and the in-situ deposition temperature ranges from room temperature to low-temperature heating, such as 20 to 55°C.

[0029] Preferably, the particle size range of the in-situ doped ZnO micro / nanoparticles is 200 nm to 5000 nm, with the optimal range being 500 nm to 750 nm; meanwhile, the mass fraction of ZnO doping in the densified paper-based material is 0.1 to 7.0 wt%, with the optimal ZnO doping mass fraction being less than 0.5 to 2 wt%.

[0030] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0031] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" refers to weight percentage, "parts" refers to parts by weight, and "ratio" refers to weight proportion.

[0032] Example 1 Zinc chloride and deionized water were added and mixed in molar ratios of 1:2, 1:3, 1:5, 1:7, and 1:9. The mixture was then magnetically stirred at 75°C. After about 15 minutes, a transparent and clear liquid was formed, and zinc chloride hydrate eutectic solvents with different molar ratios were obtained and named S1, S2, S3, S4, and S5, respectively. A circular filter paper (FP) with a basis weight of 0.5 g and a diameter of 9 cm was immersed in the above S1, S2, S3, S4 and S5 at a set temperature of 75°C and constant temperature for 30 minutes, and subjected to swelling treatment for 1 minute to obtain different gelled base paper, named S1-F, S2-F, S3-F, S4-F and S5-F. The morphology of the treated filter paper fibers was observed using a scanning electron microscope. Figure 1 The microstructure of filter paper fibers after treatment with ZnCl2 hydrated DES at different molar ratios is shown. After treatment with the swelling system, the surfaces of samples S1-F and S2-F showed no obvious pores, achieving densification. However, the fibers on the surfaces of samples S3-F, S4-F, and S5-F showed a gradual dissolution. Based on the above experimental phenomena and results, the optimal solvent molar ratio for densification with zinc chloride hydrated DES is 1:3.

[0033] Example 2 A method for preparing an in-situ doped ZnO paper-based insulating material includes the following steps: Zinc chloride and deionized water were added and mixed in a 1:3 molar ratio. The mixture was stirred magnetically at 75°C for about 15 minutes to form a transparent and clear liquid, which yielded a zinc chloride hydrate eutectic solvent. Take a circular filter paper with a weight of 0.5g and a diameter of 9cm, immerse it in ZnCl2·3H2O (zinc chloride hydrate eutectic solvent) at a set temperature of 75℃ for 30 minutes, and the immersion swelling time is 1min. During this time, the filter paper swells and gels. Then, it is immersed in anhydrous ethanol antisolvent for 10min for regeneration treatment to obtain the regenerated filter paper. The recycled paper was then impregnated in a NaOH alkaline solution for in-situ deposition. The NaOH alkaline solution concentration was 0.25 mol / L, and the impregnation time was 2 h. After swelling and densification, the surface of the paper fibers still contained zinc source. Under alkaline conditions, the hydrated zinc ions self-assembled and in-situ doped through hydrogen bonding with the hydroxyl groups of the fibers, which could be deposited and transformed into ZnO micro-nano particles. Subsequently, the densified in-situ doped ZnO paper-based insulating material was washed with deionized water until neutral, pre-dried by hot pressing, and then placed in a 60°C oven for drying. The hot press pressure was 4 MPa, the hot pressing temperature was 50°C, and the hot pressing time was 30 min, to obtain the in-situ doped ZnO paper-based insulating material.

[0034] The morphology and structure of cellulose paper have a significant impact on the performance of insulating materials prepared from cellulose fibers. For example... Figure 2 As shown in ab, the initial filter paper (FP) exhibits a highly porous structure due to the disordered entanglement of cellulose fibers. Figure 2 The CD shows swollen gelled-regenerated cellulose paper (SP) and Figure 2 Morphological changes in in-situ doped ZnO paper-based materials (ZnO-n) after swelling and densification. Compared with the highly porous fiber network in the FP sample, the surface morphology of the SP sample became more dense and smooth after partial dissolution-reorganization treatment with a ZnCl2-based hydrate swelling system. Figure 2 c).

[0035] The dielectric properties of the paper-based insulating material with densified synergistic in-situ doping of ZnO are as follows: Figure 3 As shown, after densification and in-situ ZnO doping modification, the breakdown strength of the filter paper increased from 8.4 kV / mm to 48.6 kV / mm and 108.8 kV / mm; the dielectric loss also decreased from 0.9 to 0.02.

[0036] Example 3 A method for preparing an in-situ doped ZnO paper-based insulating material includes the following steps: Zinc chloride and deionized water were added and mixed in a 1:3 molar ratio. The mixture was stirred magnetically at 75°C for about 15 minutes to form a transparent and clear liquid, which yielded a zinc chloride hydrate eutectic solvent. Take a circular filter paper with a weight of 0.5 g and a diameter of 9 cm, immerse it in ZnCl2·3H2O at a set temperature of 75℃ for 30 minutes, and the immersion swelling time is 1 minute. During this time, the filter paper swells and gels. Then, it is immersed in anhydrous ethanol antisolvent for 10 minutes to regenerate the filter paper and obtain the regenerated filter paper. The regenerated paper was then immersed in a 0.1 mol / L NaOH alkaline solution for in-situ deposition for 2 hours. The surface of the paper fibers after swelling and densification still contained zinc. Under alkaline conditions, hydrated zinc ions self-assembled and in-situ doped through hydrogen bonding with the hydroxyl groups of the fibers, depositing and transforming into ZnO micro / nano particles. The densified in-situ doped ZnO paper-based insulating material was then washed with deionized water until neutral, pre-dried by hot pressing, and then dried in a 60°C oven. The hot press pressure was 4 MPa, the hot pressing temperature was 50°C, and the hot pressing time was 30 minutes, yielding a ZnO-n sample after partial dissolution and in-situ regeneration.

[0037] Example 4 A method for preparing an in-situ doped ZnO paper-based insulating material includes the following steps: Zinc chloride and deionized water were added and mixed in a 1:3 molar ratio. The mixture was stirred magnetically at 75°C for about 15 minutes to form a transparent and clear liquid, which yielded a zinc chloride hydrate eutectic solvent. Take a circular filter paper with a weight of 0.5 g and a diameter of 9 cm, immerse it in ZnCl2·3H2O at a set temperature of 75℃ for 30 minutes, and the immersion swelling time is 1 minute. During this time, the filter paper swells and gels. Then, it is immersed in anhydrous ethanol antisolvent for 10 minutes to regenerate the filter paper and obtain the regenerated filter paper. The regenerated paper was then impregnated in a 0.5 mol / L NaOH alkaline solution for in-situ deposition for 2 hours. The surface of the paper fibers after swelling and densification still contained zinc sources. Under alkaline conditions, hydrated zinc ions self-assembled and in-situ doped through hydrogen bonding with the hydroxyl groups of the fibers, depositing and transforming into ZnO micro / nano particles. The densified in-situ doped ZnO paper-based insulating material was then washed with deionized water until neutral, pre-dried by hot pressing, and then dried in a 60°C oven. The hot press pressure was 4 MPa, the hot pressing temperature was 50°C, and the hot pressing time was 30 minutes, yielding a ZnO-0.5 sample after partial dissolution and in-situ regeneration.

[0038] Example 5 A method for preparing an in-situ doped ZnO paper-based insulating material includes the following steps: Zinc chloride and deionized water were added and mixed in a 1:3 molar ratio. The mixture was stirred magnetically at 75°C for about 15 minutes to form a transparent and clear liquid, which yielded a zinc chloride hydrate eutectic solvent. Take a circular filter paper with a weight of 0.5 g and a diameter of 9 cm, immerse it in ZnCl2·3H2O at a set temperature of 75℃ for 30 minutes, and the immersion swelling time is 1 minute. During this time, the filter paper swells and gels. Then, it is immersed in anhydrous ethanol antisolvent for 10 minutes to regenerate the filter paper and obtain the regenerated filter paper. Subsequently, the regenerated base paper was impregnated in 1.0 mol / L and 2.0 mol / L NaOH alkaline solutions for in-situ deposition treatment for 2 hours. After swelling and densification treatment, zinc source remained on the surface of the base paper fibers. Under alkaline conditions, zinc hydrates self-assembled and in-situ doped through hydrogen bonding with the hydroxyl groups of the fibers, which could be deposited and transformed into ZnO micro and nano particles. The densified in-situ doped ZnO paper-based insulating material was then washed with deionized water until neutral, pre-dried by hot pressing, and then placed in a 60°C oven for drying. The hot press pressure was 4 MPa, the hot pressing temperature was 50°C, and the hot pressing time was 30 min, resulting in ZnO-1.0 and ZnO-2.0 samples after partial dissolution and in-situ regeneration treatment.

[0039] Figure 4 The morphology of ZnO nanoparticles in the ZnO-n samples after partial dissolution and in-situ regeneration is shown. ImageJ software analysis revealed that, under low-concentration NaOH solution conditions, the ZnO doping sizes of the ZnO-0.1 (Example 3) and ZnO-0.25 (Example 2) samples were approximately 350–1080 nm and 730–960 nm, respectively. Furthermore, during the low-alkali concentration regeneration treatment, the doping content of both cellulose composite insulating papers did not exceed 1.0 wt% (0.1 wt% and 0.55 wt%, respectively). Figure 4 With increasing alkali concentration, both the size and content of ZnO doping significantly increased: the size of ZnO-0.5 (Example 4) samples increased to 1360~1770 nm, ZnO-1.0 (Example 5) reached 2400~2780 nm, and ZnO-2.0 (Example 5) reached 1830~4020 nm, achieving a clear transition from the nanoscale to the microscale. Ultimately, in-situ doping of ZnO semiconductor particles improved the performance of paper-based insulating materials.

[0040] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A method for preparing an in-situ doped ZnO paper-based insulating material, characterized in that, Includes the following steps: After mixing and stirring zinc chloride and water, a zinc chloride hydrated eutectic solvent is obtained. The porous base paper was then impregnated in a zinc chloride hydrate eutectic solvent for swelling treatment to obtain gelled base paper; the gelled base paper was then impregnated in an ethanol / water antisolvent system for regeneration treatment to obtain regenerated base paper; The recycled paper was then impregnated in an alkaline solution for in-situ deposition treatment to obtain paper with ZnO micro- and nano-particles loaded on its surface. By post-processing the base paper with ZnO micro- and nano-particles loaded on its surface, an in-situ ZnO-doped paper-based insulating material is obtained.

2. The method for preparing an in-situ doped ZnO paper-based insulating material according to claim 1, characterized in that, The mixing method is magnetic stirring; the temperature during magnetic stirring is 40~90℃, and the time is 15~120min.

3. The method for preparing an in-situ doped ZnO paper-based insulating material according to claim 1, characterized in that, The molar ratio of zinc chloride to water is 1:(2~9); The chemical formula of the zinc chloride hydrate DES is ZnCl2·nH2O, ZnCl2 / AlCl3·nH2O / ZnCl2 / FeCl3·nH2O or ZnCl2 / CuCl2·nH2O; Where n is the number of water molecules, specifically ranging from 2 to 9.

4. The method for preparing an in-situ doped ZnO paper-based insulating material according to claim 1, characterized in that, The swelling treatment is performed at a temperature of 35~90℃ for a time of 30s~30min.

5. The method for preparing an in-situ doped ZnO paper-based insulating material according to claim 1, characterized in that, The porous base paper is made of cotton fiber, softwood, hardwood or non-wood fiber. The porous base paper has a cellulose mass percentage of 80% to 95%, a fiber porosity range of 50% to 70%, and a pore size of 5 to 30 μm.

6. The method for preparing an in-situ doped ZnO paper-based insulating material according to claim 1, characterized in that, By mass percentage, the ethanol / water antisolvent system comprises 60% to 100% anhydrous ethanol and 0% to 40% deionized water; The regeneration process is carried out at room temperature for 10 to 60 minutes.

7. The method for preparing an in-situ doped ZnO paper-based insulating material according to claim 1, characterized in that, The alkaline solution is a KOH solution, a NaOH solution, or ammonia water; The concentration of the alkaline solution is 0.1~3.0 mol / L.

8. The method for preparing an in-situ doped ZnO paper-based insulating material according to claim 1, characterized in that, The temperature for the in-situ deposition treatment is 20~55℃; The post-processing includes sequential washing, hot pressing, and drying. The hot pressing pressure is 2~4MPa, the temperature is 50~100℃, and the time is 30~120min.

9. An in-situ ZnO-doped paper-based insulating material, characterized in that, It was prepared by the preparation method according to any one of claims 1 to 8; The ZnO micro / nano particles in the in-situ doped ZnO paper-based insulating material have a particle size of 200~5000nm and a doping mass fraction of 0.1~7.0wt%.

10. The in-situ doped ZnO paper-based insulating material according to claim 9, characterized in that, The ZnO micro / nano particles in the in-situ doped ZnO paper-based insulating material have a particle size of 500~750nm and a doping mass fraction of 0.5~2wt%.

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