A method for preparing small-flake mica paper and the small-flake mica paper itself.

Abstract

This invention discloses a method for preparing small-flake mica paper and the mica paper thereof. The preparation method includes the following steps: Pretreatment: Mica is crushed and graded for screening to obtain mica powder with preset large, medium, and small mesh sizes; each mica powder undergoes surface modification treatment, then is pulped and subjected to ultrasonic peeling treatment; Papermaking: Composite additives are added to the pretreated pulp, and then layered processing is performed, wherein the bottom layer is made of pulp prepared with medium-mesh mica powder, the middle layer is made of pulp prepared with large and small mesh mica powder, and the top layer is made of pulp prepared with large mesh mica powder; Drying: This step adopts a three-stage temperature-controlled calendering drying process, and the paper is then slit after drying. This invention can prepare small-flake mica paper that simultaneously improves the softness, smoothness, and breaking strength of mica paper.

Description

Technical Field

[0001] This invention relates to the field of mica paper production technology, specifically to a method for preparing small-flake mica paper and the small-flake mica paper itself. Background Technology

[0002] Mica paper is a high-performance insulating material made from natural mica through processes such as crushing, pulping, and papermaking. It is widely used in high-voltage motors, high-temperature cables, electronic devices, and aerospace. As electrical equipment develops towards higher voltage, miniaturization, and flexibility, the market is placing higher demands on the performance of mica paper.

[0003] The traditional production process of mica paper mainly includes crushing, pulping and mixing, papermaking and forming, pressing, drying and calendering, and slitting. Mica paper produced using this traditional process lacks effective control over flake thickness and surface condition. Either excessively dense accumulation of fine flakes leads to paper stiffness, or too many coarse flakes result in a rough surface. Furthermore, the control of flake geometry is rudimentary, resulting in a small diameter-to-thickness ratio and large internal porosity, thus limiting the improvement of breaking strength and softness. In addition, the simplistic papermaking process and improper control of other steps easily create a contradiction between surface smoothness and internal softness, making it difficult to achieve both simultaneously. Traditional additives primarily aim to improve strength, lacking a synergistic effect on improving softness and smoothness, and have weak interfacial bonding with mica flakes, resulting in limited reinforcing effects.

[0004] Some studies have attempted to improve the preparation process of mica paper. For example, adding aramid fibers or glass fibers can increase strength, but this reduces the purity and dielectric properties of the paper. Mica paper prepared by calcination chemical methods can improve softness, but the process is complex, energy-intensive, and environmentally unfriendly. Other studies have focused on controlling the particle size distribution of mica flakes to improve paper properties, but these studies often only focus on the particle size range and neglect the control of flake thickness, surface activity, and interlayer bonding.

[0005] Therefore, developing a method for preparing small-flake mica paper that can simultaneously improve the softness, smoothness, and puncture strength of mica paper has significant industrial application value and market prospects. Summary of the Invention

[0006] The technical problem solved by this invention is to develop a method for preparing small-flake mica paper that can simultaneously improve the softness, smoothness and puncture strength of mica paper, thereby obtaining small-flake mica paper with better overall performance.

[0007] The technical problem solved by this invention is achieved by the following technical solution: A method for preparing small-scale flake mica paper includes the following steps: Pretreatment: After crushing the mica, it is graded and screened to obtain mica powder with preset large, medium and small mesh sizes; each mica powder is surface modified, then pulped and ultrasonically exfoliated. Forming: A composite additive is added to the pretreated slurry, and then it is processed in layers. The bottom layer is made of slurry prepared with medium mesh mica powder, the middle layer is made of slurry prepared with large and small mesh mica powder, and the top layer is made of slurry prepared with large mesh mica powder. Drying: This step uses a three-stage temperature-controlled calendering drying process. After drying, the product can be cut.

[0008] Furthermore, in the pretreatment step, the large-mesh mica powder is 40-45 mesh, the medium-mesh mica powder is 30-35 mesh, and the small-mesh mica powder is 20-25 mesh.

[0009] Further, in the pretreatment step, the surface modification treatment method is as follows: add 0.5-2.0% of γ-aminopropyltriethoxysilane by weight of each mica powder, adjust the pH of the system to 4-5, stir at 40-60℃ for 30-60 minutes, wash with water and dry to obtain the surface-modified mica powder.

[0010] Furthermore, in the pretreatment step, the mica powder that has undergone surface modification is slurried into an aqueous suspension with a solid content of 5-10%, and treated with ultrasonic waves at 20-40 kHz for 20-60 minutes, with an ultrasonic power density of 100-300 W / L.

[0011] Furthermore, in the papermaking step, based on the dry mica powder, the composite additive added to the 100 parts of mica powder includes the following raw materials in parts by weight: 2-8 parts of nanocellulose, 0.5-2 parts of polyethylene glycol, 0.3-1 parts of silane coupling agent, and 1-3 parts of nano silica.

[0012] Furthermore, in the copying process, the slurry concentration used for the bottom layer is 0.15-0.25%, and the amount of bottom layer slurry accounts for 30-40% of the total slurry; the slurry concentration used for the intermediate layer is 0.10-0.20%, and the amount of intermediate layer slurry accounts for 40-50% of the total slurry; the slurry concentration used for the top layer is 0.08-0.12%, and the amount of top layer slurry accounts for 10-30% of the total slurry.

[0013] Furthermore, during the papermaking process, when the moisture content of the wet paper web is 60-70%, a polyvinyl alcohol solution with a mass concentration of 0.2-0.5% is uniformly sprayed onto the front side of the paper web.

[0014] Furthermore, in the drying step, the three-stage temperature-controlled calendering drying process consists of a first stage of constant-speed drying at 80-100℃, a second stage of calendering drying at 60-80℃, and a third stage of humidity-conditioning drying at 25-30℃.

[0015] Furthermore, in the first drying stage, hot air is circulated for 5-10 minutes, reducing the paper moisture content to 30-40%; in the second stage, the calendering rollers apply a linear pressure of 30-50 kN / m for 1-3 minutes, reducing the paper moisture content to 10-15%; in the third stage, the paper is placed in an environment with a relative humidity of 65-75% for 12-24 hours, resulting in a final paper moisture content of 5-8%.

[0016] A type of small-scale mica paper is prepared using any of the methods described above.

[0017] Beneficial Effects: The method for preparing small-flake mica paper according to the present invention introduces a synergistic treatment of ultrasonic-assisted peeling and silane coupling agent surface modification in the pretreatment stage. This reduces the average thickness of the mica flakes from 1.0-1.5 μm in traditional processes to 0.22-0.26 μm, and increases the aspect ratio from less than 100 to over 200. The large aspect ratio of the small flakes allows for a tighter stacking arrangement during papermaking, significantly reducing the internal porosity of the paper. This lays the microstructural foundation for obtaining high-density, high-breakdown-strength mica paper. Furthermore, the introduction of active functional groups on the flake surface enhances the interfacial bonding between the flakes and additives, avoiding the strength loss caused by weak interfacial bonding in traditional processes.

[0018] Furthermore, based on the preliminary processing, this invention further prepares mica paper with significantly reduced softness by using layered gradient papermaking combined with a composite plasticizing system and moisture balance treatment at the drying end. The softness of the prepared product is as low as 55mN, which is far superior to the softness of existing similar products. This allows the mica paper of this invention to meet the stringent requirements of flexible electronic devices, flexible insulating substrates, and other application scenarios with demanding bending performance.

[0019] Furthermore, the present invention significantly improves the breakdown strength and prolongs the penetration time of the prepared small-scale mica paper product by stacking small flakes with a high aspect ratio, filling micropores with additives, and densifying the paper through calendering and drying. This demonstrates that the dense and tortuous pore channels inside the mica paper product effectively inhibit the development of electrical trees and liquid penetration. Detailed Implementation

[0020] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below with reference to specific embodiments.

[0021] Example 1

[0022] In this embodiment, a method for preparing small-scale mica paper includes the following steps: (1) Pretreatment: After crushing and removing impurities, the mica is graded and screened using a vibrating screen with multiple layers to obtain mica powder with preset mesh sizes of 40, 30, and 20. Each mica powder undergoes surface modification treatment, and then is pulped and subjected to ultrasonic exfoliation. The surface modification treatment method is as follows: 1.0% KH550 by mass of mica powder is added to each mica powder, wherein KH550 is dissolved in a system with a volume ratio of ethanol to water of 95:5, then the pH of the system is adjusted to 4.5, stirred at 55℃ for 45 minutes, washed with water and dried at 50℃ to obtain the surface-modified mica powder.

[0023] The ultrasonic exfoliation treatment method is as follows: each surface-modified mica powder is slurried into an aqueous suspension with an 8% solid content, and treated with 35kHz ultrasound for 45 minutes. The power density of the ultrasound is 250W / L.

[0024] (2) Copying: The modified flakes at each stage were dispersed using a hydraulic pulper and prepared into a three-layer slurry: The bottom layer slurry uses 30-mesh flake mica powder: the slurry concentration of the bottom layer is 0.25%, and the bottom layer slurry accounts for 35% of the total slurry. The middle layer slurry uses a 1:1 mass ratio of 40-mesh and 20-mesh flake mica powder: the slurry concentration of the middle layer is 0.16%, and the middle layer slurry accounts for 50% of the total slurry. The top layer slurry uses 20-mesh flake mica powder: the slurry concentration of the top layer is 0.1%, and the top layer slurry accounts for 15% of the total slurry. The composite additives added to the bottom layer, middle layer, and top layer slurries are the same, and the composite additives include the following raw materials in parts by weight: CNF 5%, PEG-400 1.0%, KH570 0.5%, and nano-SiO2 2% (all relative to the dry weight of mica powder).

[0025] A layered headbox was used, with sequential pulping: first the bottom layer, then the middle layer, and finally the top layer. The wire speed was 10 m / min. Vacuum dewatering was applied: -0.03 MPa in zone 1 and -0.05 MPa in zone 2. At a wet paper web moisture content of 65%, a 0.4% to 0.8% PVA solution was sprayed onto the top layer surface at a rate of 15 g / m². 2 .

[0026] During each layer of papermaking, when the moisture content of the wet paper web is 65%, a 0.4% polyvinyl alcohol solution is evenly sprayed onto the front side of the paper web.

[0027] (3) Drying: By using press rollers with a linear pressure of 15 kN / m, the moisture content of the wet paper web of mica paper is reduced from about 80% to 65%.

[0028] The paper is then dried using a three-stage temperature-controlled calendering process, as follows: The first stage is a constant-speed drying stage at 90℃, using hot air circulation for 7 minutes, reducing the paper moisture content to 32%; the second stage is calendering drying at 70℃, with a calendering roller linear pressure of 40kN / m for 2 minutes, reducing the paper moisture content to 12%; the third stage is humidity conditioning drying at 28℃, where the paper is placed in an environment with a relative humidity of 70% for 20 hours, resulting in a final paper moisture content of 6.5%.

[0029] Then cut to a width of 500 mm and wind up under constant tension.

[0030] Example 2

[0031] In this embodiment, a method for preparing small-scale mica paper includes the following steps: (1) Pretreatment: After crushing and removing impurities, the mica is graded and screened using a vibrating screen with multiple layers to obtain mica powder with preset mesh sizes of 40, 30, and 20. Each mica powder undergoes surface modification treatment, and then is pulped and subjected to ultrasonic exfoliation. The surface modification treatment method is as follows: 1.2% KH550 by mass of mica powder is added to each mica powder, wherein KH550 is dissolved in a system with a volume ratio of ethanol to water of 95:5, then the pH of the system is adjusted to 4.5, stirred at 50°C for 60 minutes, washed with water and dried at 50°C to obtain the surface-modified mica powder.

[0032] The ultrasonic exfoliation treatment method is as follows: each surface-modified mica powder is slurried into an aqueous suspension with an 8% solid content, and treated with 30kHz ultrasound for 45 minutes. The power density of the ultrasound is 200W / L.

[0033] (2) Copying: The modified flakes at each stage were dispersed using a hydraulic pulper and prepared into a three-layer slurry: The bottom layer slurry uses 30-mesh flake mica powder: the slurry concentration of the bottom layer is 0.25%, and the bottom layer slurry accounts for 35% of the total slurry. The middle layer slurry uses a 1:1 mass ratio of 40-mesh and 20-mesh flake mica powder: the slurry concentration of the middle layer is 0.18%, and the middle layer slurry accounts for 45% of the total slurry. The top layer slurry uses 20-mesh flake mica powder: the slurry concentration of the top layer is 0.12%, and the top layer slurry accounts for 20% of the total slurry. The composite additives added to the bottom layer, middle layer, and top layer slurries are the same, and the composite additives include the following raw materials in parts by weight: CNF 5%, PEG-400 1.0%, KH570 0.5%, and nano-SiO2 2% (all relative to the dry weight of mica powder).

[0034] A layered headbox was used, with sequential pulping: first the bottom layer, then the middle layer, and finally the top layer. The wire speed was 10 m / min. Vacuum dewatering was applied: -0.03 MPa in zone 1 and -0.05 MPa in zone 2. At a wet paper web moisture content of 65%, a 0.4% to 0.8% PVA solution was sprayed onto the top layer surface at a rate of 15 g / m². 2 .

[0035] During each layer of papermaking, when the moisture content of the wet paper web is 70%, a polyvinyl alcohol solution with a mass concentration of 0.4 is evenly sprayed onto the front side of the paper web.

[0036] (3) Drying: By using press rollers with a linear pressure of 15 kN / m, the moisture content of the wet web of mica paper is reduced to 65%.

[0037] The paper was then dried using a three-stage temperature-controlled calendering process, as follows: The first stage was a constant-speed drying stage at 85°C, using hot air circulation for 8 minutes, reducing the paper moisture content to 35%. The second stage was a calendering drying stage at 75°C, with a calendering roller linear pressure of 35°C / m for 2.5 minutes, reducing the paper moisture content to 13%. The third stage was a humidity conditioning drying stage at 26°C, where the paper was placed in an environment with a relative humidity of 75% for 18 hours, resulting in a final paper moisture content of 6.8%.

[0038] Then cut to a width of 500 mm and wind up under constant tension.

[0039] Example 3

[0040] Compared to Example 1, this embodiment focuses on improving softness. In the papermaking process, the composite additive includes the following raw materials in parts by weight: CNF 7%, PEG-400 1.5%, and KH570 0.5% (all relative to the dry weight of mica powder). The rest is the same as in Example 1.

[0041] Compare with Example 1 Compared with Example 1, this comparative example does not involve layered papermaking. Instead, 20, 30, and 40 mesh scales are mixed in a mass ratio of 1:1:1 to prepare a single slurry with a concentration of 0.15%. The composite additives are the same as in Example 1.

[0042] Then, a single-layer headbox was used for papermaking, without layered slurry distribution or surface spraying, and the rest was the same as in Example 1.

[0043] Compare with Example 2 Compared with Example 1, this comparative example uses a two-stage temperature-controlled calendering drying process. In the calendering drying stage, the roller temperature is 70°C, the linear pressure is 80 kN / m, and the time is 2 min, directly drying to a moisture content of 6%, without the moisture balancing step in the third stage of Example 1. The rest is the same as in Example 1.

[0044] Compare with Example 3 Compared with Example 1, this comparative example uses traditional processes, without any auxiliary treatment, layered papermaking, or composite additives, and uses conventional drying.

[0045] The products prepared in each embodiment and control example were subjected to performance tests, and the results are shown in Table 1.

[0046] Table 1 Performance Test Results Statistics Table 1 shows that the small-scale mica paper product prepared by this invention has better softness, smoothness, and breaking strength compared to the traditional process, resulting in a significant improvement in overall performance. Example 3 shows that adjusting the composition and ratio of the composite additives yields the product with optimal softness, while other properties are slightly weaker; adjustments can be made as needed in practical applications. Comparative Example 1 shows that without layered papermaking, the prepared product has poor smoothness and breaking strength, indicating that the layered gradient structure in this step is crucial for overall performance. Comparative Example 2 shows that when the drying stage is not properly controlled, although the flakes are very thin, excessive calendering causes the paper to become hard and brittle, deteriorating the softness to 198 mN and resulting in poor breaking strength. This is presumably due to microscopic defects caused by internal stress, indicating that appropriate calendering pressure and moisture balance are indispensable for product softness.

[0047] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing small-flake mica paper, characterized in that, Includes the following steps: Pretreatment: After crushing the mica, it is graded and screened to obtain mica powder with preset large, medium and small mesh sizes; each mica powder is surface modified, then pulped and ultrasonically exfoliated. Forming: A composite additive is added to the pretreated slurry, and then it is processed in layers. The bottom layer is made of slurry prepared with medium mesh mica powder, the middle layer is made of slurry prepared with large and small mesh mica powder, and the top layer is made of slurry prepared with large mesh mica powder. Drying: This step uses a three-stage temperature-controlled calendering drying process. After drying, the product can be cut.

2. The method for preparing small-scale flake mica paper according to claim 1, characterized in that, In the pretreatment step, the mica powder with a large mesh size is 40-45 mesh, the mica powder with a medium mesh size is 30-35 mesh, and the mica powder with a small mesh size is 20-25 mesh.

3. The method for preparing small-flake mica paper according to claim 1, characterized in that, In the pretreatment step, the surface modification treatment method is as follows: add 0.5-2.0% of γ-aminopropyltriethoxysilane by weight of each mica powder, adjust the pH of the system to 4-5, stir at 40-60℃ for 30-60 minutes, wash with water and dry to obtain the surface-modified mica powder.

4. The method for preparing small-scale flake mica paper according to claim 1, characterized in that, In the pretreatment step, the mica powder that has undergone surface modification is slurried into an aqueous suspension with a solid content of 5-10%, and treated with ultrasonic waves at 20-40kHz for 20-60 minutes, with an ultrasonic power density of 100-300W / L.

5. The method for preparing small-flake mica paper according to claim 1, characterized in that, In the copying process, based on the dry mica powder, the composite additive added to the 100 parts of mica powder includes the following raw materials in parts by weight: 2-8 parts of nanocellulose, 0.5-2 parts of polyethylene glycol, 0.3-1 parts of silane coupling agent, and 1-3 parts of nano silica.

6. The method for preparing small-flake mica paper according to claim 1, characterized in that, In the copying process, the slurry concentration used for the bottom layer is 0.15-0.25%, and the amount of bottom layer slurry accounts for 30-40% of the total slurry; the slurry concentration used for the middle layer is 0.10-0.20%, and the amount of middle layer slurry accounts for 40-50% of the total slurry; the slurry concentration used for the top layer is 0.08-0.12%, and the amount of top layer slurry accounts for 10-30% of the total slurry.

7. The method for preparing small-scale mica paper according to claim 6, characterized in that, During the papermaking process, when the moisture content of the wet paper web is 60-70%, a polyvinyl alcohol solution with a mass concentration of 0.2-0.5% is evenly sprayed onto the front side of the paper web.

8. The method for preparing small-flake mica paper according to claim 1, characterized in that, In the drying process, the three-stage temperature-controlled calendering drying consists of a first stage of constant-speed drying at 80-100℃, a second stage of calendering drying at 60-80℃, and a third stage of humidity-conditioning drying at 25-30℃.

9. The method for preparing small-scale mica paper according to claim 8, characterized in that, In the first drying stage, hot air is circulated for 5-10 minutes, reducing the paper moisture content to 30-40%. In the second stage, the calendering rollers apply a linear pressure of 30-50 kN / m for 1-3 minutes, reducing the paper moisture content to 10-15%. In the third stage, the paper is placed in an environment with a relative humidity of 65-75% for 12-24 hours, resulting in a final paper moisture content of 5-8%.

10. A type of small-scale mica paper, characterized in that, It is prepared by the method described in any one of claims 1 to 9.

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