Preparation method of meta-aramid coated high-performance aramid paper

Abstract

The invention relates to a preparation method of meta-aramid coated high-performance aramid paper. The preparation method comprises the steps of stock solution preparation, coagulating bath preparation, raw paper pretreatment, stock solution coating, coagulating treatment, final hot pressing and the like. By adding the pretreatment step, the porosity of the aramid paper is effectively reduced, the mechanical strength and the dielectric property are improved, and the anisotropy problem is solved. The tensile strength of the prepared aramid paper is improved by 30% or above, the porosity is reduced by 20%-30%, and the surface smoothness and the electric breakdown resistance are remarkably enhanced. The product is suitable for the fields of electronic equipment insulating materials, aerospace and the like, and has a wide application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of aramid paper, and in particular to a method for preparing meta-aramid-coated high-performance aramid paper. Background Art

[0002] In recent years, the rapid growth in demand for high-performance materials has led to higher performance requirements for insulation and protective materials in sectors such as aerospace, rail transit, new energy, and national defense. Aramid fibers, particularly meta-aramid fibers (such as poly(m-phenylene isophthalamide) or PMIA), are an ideal choice for these applications due to their exceptional mechanical properties, high-temperature resistance, flame retardancy, electrical insulation, and chemical stability. For example, aramid fibers have shown broad application prospects in aircraft fireproofing and thermal insulation, high-speed train insulation components, and battery insulation for new energy vehicles.

[0003] However, existing aramid paper production technologies still face challenges in practical application. Aramid fibers have a high degree of crystallinity, a smooth surface, and strong chemical inertness. This results in fibers relying primarily on a small amount of hydrogen bonding, making it difficult to achieve sufficient chemical bonding. During the traditional wet papermaking process, the bonds between aramid chopped fibers and fibrids are relatively loose, making it difficult to form a dense interwoven structure. Furthermore, during the papermaking process, the fibers are often subjected to strong pulling forces in the machine direction (MD), resulting in high fiber orientation in the MD and relatively sparse fiber arrangement in the cross direction (CD). This anisotropic property results in high porosity, numerous surface defects, and insufficient mechanical properties in the CD direction in the resulting aramid paper. These issues have limited the further application of aramid paper in high-performance insulation materials. For example, in electronic device insulation, high porosity can increase the risk of electrical breakdown, while in mechanical components, insufficient CD strength can lead to performance fluctuations during use.

[0004] Chinese patent CN116926982A discloses a composite meta-aramid paper comprising a meta-aramid base paper and an aramid microfiber network layer attached to one or both surfaces. The name of the aramid microfiber network layer suggests that its material is porous at a certain scale. It is manufactured by air-spinning, electrospinning, or a combination of both, but neither method achieves high density. Therefore, the aramid microfiber network layer does not enhance the strength of the composite meta-aramid paper.

[0005] Chinese patent CN113005820A discloses a method for preparing multi-layer composite aramid paper. Aramid fiber dispersion serves as the adhesive for the aramid paper. The fluidity of the aramid fiber solution allows the aramid fibers to penetrate the pores of the paper sheets, resulting in a high-strength, low-porosity multi-layer composite aramid paper. However, the degree of exposure of the pores in the paper sheets is uncertain. If the pores are exposed, some of the aramid fiber solution must be filled into them to generate adhesion, while the unfilled portion forms a thin layer between the two aramid papers. However, even with the same amount of aramid fiber solution, the thickness of the thin layer formed is unstable. The greater the number of layers, the more difficult it is to control the total thickness.

[0006] Therefore, it is necessary to improve the preparation method to solve the above problems. Summary of the Invention

[0007] The main purpose of the present invention is to provide a method for preparing meta-aramid-coated high-performance aramid paper, which can obtain composite aramid paper with high strength, low porosity and stable thickness.

[0008] The present invention achieves the above-mentioned object through the following technical solution: a method for preparing meta-aramid-coated high-performance aramid paper, comprising the following steps: S1. Preparation of stock solution: Mix PMIA and DMAc to form a PMIA / DMAc solution; S2. Coagulation bath preparation: DMAc and deionized water were mixed and stirred thoroughly to prepare a DMAc system coagulation bath; S3. Base paper pretreatment: placing the aramid base paper in a hot pressing device and performing hot pressing pretreatment at 120-140°C to obtain pretreated aramid base paper; S4, stock solution coating: uniformly coating the surface of the pretreated aramid base paper with the stock solution to form a continuous and uniform coating layer; S5, coagulation treatment: immersing the coated aramid paper in a DMAc system coagulation bath, then washing the DMAc remaining on the surface with deionized water, and then drying to obtain dried aramid paper; S6. Final hot pressing: The dried aramid paper is finally hot pressed to obtain meta-aramid coated high-performance aramid paper.

[0009] Specifically, the aramid base paper has a basis weight of 60-80 g / m², and its fiber composition includes meta-aramid short fibers and precipitated fibers, wherein the length of the meta-aramid short fibers is 3-6 mm, the linear density is 2-5 dtex, and the addition amount of the precipitated fibers is 40%-50%.

[0010] Specifically, in step S1, the mass ratio of PMIA to DMAc is 1:9.

[0011] Specifically, in step S1, the mixing temperature is 40° C. and the stirring time is 4 hours.

[0012] Specifically, in step S2, the mass ratio of DMAc to deionized water is 3:7, the stirring time is 10-15 minutes, and the coagulation bath temperature is set at 20-25°C.

[0013] Specifically, in step S4, the molecular weight of the PMIA is in the range of 50,000 to 80,000.

[0014] Specifically, the coating amount of the aramid stock solution is preferably 10% to 15%.

[0015] Specifically, in step S5, the coated aramid paper is immersed in the DMAc system coagulation bath for 5 minutes, and then the residual DMAc on the surface is rinsed with deionized water.

[0016] Specifically, the drying method in step S5 is vacuum drying at 100° C. for 2 hours.

[0017] Specifically, in step S6, the final hot pressing temperature is 250° C., the hot pressing pressure is 5 MPa, and the hot pressing time is 3 to 5 minutes.

[0018] The beneficial effects of the technical solution of the present invention are: 1. The porosity and surface quality of aramid paper are significantly improved by combining solution coating with coagulation treatment. The solution coating process can fill the microscopic defects on the surface of the aramid base paper, while the coagulation treatment promotes the PMIA molecular chains to form a highly dense coating structure on the surface, effectively reducing the porosity of the aramid paper. 2. The introduction of hot pressing pretreatment and final hot pressing steps optimizes the bonding strength between aramid fibers. Hot pressing pretreatment initially compacts the aramid base paper at a lower temperature, reducing the gaps between fibers; final hot pressing further strengthens the hydrogen bonding between fibers under higher temperature and pressure conditions, improving the overall mechanical properties of the aramid paper. 3. This method can effectively solve the anisotropy problem of aramid paper. Through the introduction of the coating layer and the synergistic effect of the hot pressing process, the mechanical properties of the aramid paper in the horizontal and vertical directions are balanced, thus meeting the strict requirements of the field of high-performance insulation materials for material isotropy. 4. This method offers high process controllability and production efficiency. The process parameters for the stock solution coating and solidification treatment can be flexibly adjusted according to actual needs to ensure the thickness and uniformity of the coating layer. The hot pressing process can quickly complete the final shaping of the aramid paper, making it suitable for large-scale industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a diagram showing the changes in the aramid paper produced by the method of the present invention; Figure 2These are microscope images of the aramid paper before and after coating with the original solution of the present invention.

[0020] The numbers in the figure represent: 1a-aramid base paper, 1b-pretreated base paper, 2a-aramid stock solution, 2b-coating. DETAILED DESCRIPTION

[0021] The present invention is further described in detail below with reference to specific embodiments.

[0022] Example 1: The preparation of high-performance aramid paper with meta-aramid coating is carried out according to the following steps: S1. Preparation of stock solution: Mix meta-aramid (PMIA) and dimethylacetamide (DMAc) in a mass ratio of 1:9. Use a stirring device to continuously stir the mixture at 40°C for 4 hours to obtain a stable PMIA / DMAc solution. During this process, the molecular weight of PMIA must be strictly controlled between 50,000 and 80,000. This concentration range ensures good fluidity of the solution and a uniform and dense film thickness after subsequent coating. The stirring speed of the stirring device should be set to 300-500 rpm to avoid bubbles or unevenness in the solution due to excessive stirring speed.

[0023] S2. Prepare the coagulation bath by mixing DMAc and deionized water in a mass ratio of 3:7. Stir thoroughly to ensure even distribution of the solvent and water to form a DMAc coagulation bath. The specific stirring time is 10-15 minutes. When using a stirrer, ensure that the distance between the stirring blade and the bottom of the container is within 5-10 mm to ensure that there is no stratification within the solution. Set the coagulation bath temperature to 20-25°C. This temperature range facilitates the rapid precipitation and solidification of PMIA on the aramid paper surface, avoiding uneven film formation caused by excessively high or low temperatures.

[0024] S3. Pretreatment of base paper: Aramid base paper with a basis weight of 60-80 g / m² is selected. Its fiber composition includes meta-aramid short-cut fibers and precipitated fibers. The length of the meta-aramid short-cut fibers is 3-6 mm, the linear density is 2-5 dtex, and the amount of precipitated fibers added is 40%-50%. This ratio can ensure the strength of the base paper while providing sufficient pores for subsequent coating liquid penetration. Base paper 1 is placed in a hot pressing device and hot-pressed at 120°C with a pressure set to 1.5 MPa for 3-5 minutes. Hot pressing under these conditions can effectively improve the bonding state between fibers, reduce the porosity inside the base paper, and improve the flatness and surface finish of the paper. The upper and lower pressing plates of the hot pressing device must be kept parallel, and the error range must be controlled within ±0.1 mm to ensure that the base paper is evenly stressed during the hot pressing process.

[0025] S4. Stock Solution Coating: Secure the heat-pressed aramid base paper to the coating equipment. Use a scraper or sprayer to evenly apply the PMIA / DMAc solution to the base paper surface, controlling the coating weight to 5% (solution weight relative to the mass of the aramid base paper). During the coating process, the distance between the scraper and the base paper surface should be adjusted according to the specific parameters of the coating equipment, typically set at 0.5-1 mm to ensure a uniform coating thickness. After coating, the base paper surface should exhibit a uniform gloss, without noticeable bubbles or sunken areas.

[0026] S5. Coagulation treatment: Immerse the coated aramid paper in a DMAc coagulation bath for 5-10 minutes at a temperature of 20-25°C. Under these conditions, PMIA can be fully precipitated and form a dense film on the surface of the aramid paper. The depth of the coagulation bath must be greater than the width of the aramid paper to ensure that the paper is completely immersed and to avoid incomplete film layers due to local non-infiltration. Subsequently, the residual DMAc on the surface is rinsed with deionized water for 5 minutes at a water flow rate of 0.5-1 m / s to avoid environmental pollution caused by organic solvents.

[0027] After rinsing, vacuum drying is performed. The aramid paper is placed in a vacuum drying oven with a set temperature of 100°C and a vacuum pressure of -0.08 MPa for 10-15 minutes. Drying under these conditions effectively removes moisture from the surface and interior of the aramid paper while preventing cracking or deformation of the film caused by high temperatures. The shelves in the drying oven must be kept level within a tolerance of ±0.2 mm to prevent curling or deformation of the paper during the drying process.

[0028] S5. Final Hot Pressing: The solidified aramid paper is placed back into the hot press and hot pressed at 250°C with a pressure of 5 MPa for 3-5 minutes. This hot pressing process further enhances the density of the aramid paper, strengthens the bond between the coating and the base paper, and significantly improves the overall mechanical properties of the aramid paper. The hot press's heating plate must have excellent thermal conductivity, and the surface temperature uniformity must be controlled within ±2°C to ensure even heat distribution during the hot pressing process.

[0029] Because aramid fibers have high molecular crystallinity, smooth surface and strong chemical inertness, it is difficult for fibers to form effective chemical bonds. In the traditional wet papermaking process, there is only a small amount of hydrogen bonding between aramid short fibers and precipitated fibers, making it difficult to form a dense interwoven structure; after the stock solution is coated, the surface of the aramid stock paper will become dense, but the internal holes will make the surface of the aramid stock solution uneven (such as Figure 2 As shown in the figure, the darker part is the concave position, and the concave area is significantly reduced after coating). Figure 1As shown, the design concept of the present invention is to press the aramid base paper 1a into a pretreated base paper 1b and preliminarily shape it below the glass transition temperature of the meta-aramid (between 200°C and 250°C), so that the air inside is expelled, the structure becomes compact, the mechanical strength is improved, and the surface pore space is also reduced. In this way, only a small amount of aramid stock solution 2a needs to be filled in the pores, and the vast majority of the aramid stock solution can form a coating 2b with a stable and controllable thickness on the surface of the aramid base paper.

[0030] Example 2: S1. Preparation of stock solution: PMIA and DMAc were mixed in a mass ratio of 1:9, heated to 40°C, and stirred for 4 h to obtain a stable PMIA / DMAc solution; S2. Coagulation bath preparation: DMAc and deionized water were mixed in a mass ratio of DMAc to water of 3:7 and stirred thoroughly to ensure uniform mixing of the solvent and water to prepare a DMAc system coagulation bath; S3. Base paper pretreatment: hot pressing the base paper at 140°C; S4, stock solution coating: the stock solution is applied to the surface of the pretreated aramid base paper, and the coating amount is controlled to be 5%; S5, coagulation treatment: the coated aramid paper is immersed in a DMAc coagulation bath, PMIA is precipitated and solidified on the surface of the aramid paper to form a uniform film, and then the residual DMAc on the surface is washed away and vacuum dried at 100°C; S6. Final hot pressing: The coated aramid paper is finally hot pressed at 250° C. to obtain low-porosity, high-dielectric aramid paper.

[0031] The main difference between Example 2 and Example 1 is that the pretreatment temperature is slightly increased.

[0032] Example 3: S1. Preparation of stock solution: PMIA and DMAc were mixed in a mass ratio of 1:9, heated to 40°C, and stirred for 4 h to obtain a stable PMIA / DMAc solution; S2. Coagulation bath preparation: DMAc and deionized water were mixed in a mass ratio of DMAc to water of 3:7, and stirred thoroughly to ensure uniform mixing of the solvent and water to prepare a DMAc system coagulation bath; S3. Base paper pretreatment: hot pressing the base paper at 140°C; S4, stock solution coating: the stock solution is applied to the surface of the pretreated aramid base paper, and the coating amount is controlled to 10%; S5, coagulation treatment: the coated aramid paper is immersed in a DMAc coagulation bath, PMIA is precipitated and solidified on the surface of the aramid paper to form a uniform film, and then the residual DMAc on the surface is washed away and vacuum dried at 100°C; S6. Final hot pressing: The coated aramid paper is finally hot pressed at 250° C. to obtain aramid paper with low porosity and high dielectric properties.

[0033] The main difference between Example 3 and Example 2 is that the coating amount is increased.

[0034] Example 4 S1. Preparation of stock solution: PMIA and DMAc were mixed in a mass ratio of 1:9, heated to 40°C, and stirred for 4 h to obtain a stable PMIA / DMAc solution; S2. Coagulation bath preparation: DMAc and deionized water were mixed in a mass ratio of DMAc to water of 3:7, and stirred thoroughly to ensure uniform mixing of the solvent and water to prepare a DMAc system coagulation bath; S3. Base paper pretreatment: hot pressing the base paper at 140°C; S4, stock solution coating: the stock solution is applied to the surface of the pretreated aramid base paper, and the coating amount is controlled to 15%; S5, coagulation treatment: the coated aramid paper is immersed in a DMAc coagulation bath, PMIA is precipitated and solidified on the surface of the aramid paper to form a uniform film, and then the residual DMAc on the surface is washed away and vacuum dried at 100°C; S6. Final hot pressing: The coated aramid paper is finally hot pressed at 250° C. to obtain aramid paper with low porosity and high dielectric properties.

[0035] The main difference between Example 4 and Example 2 is that the coating amount is further increased.

[0036] Comparative Example 1: The aramid base paper is finally hot-pressed at 250°C to obtain aramid paper with conventional properties.

[0037] Comparative Example 2: The surface of the untreated aramid base paper was coated with 5% aramid stock solution, and then hot-pressed at 250°C to obtain aramid paper with conventional properties.

[0038] Comparative Example 3: The surface of the untreated aramid base paper was coated with 10% aramid stock solution, and then hot-pressed at 250°C to obtain aramid paper with conventional properties.

[0039] Then, Examples 1-4 and Comparative Examples 1-3 were tested: Tensile strength test: tested according to GB / T 12914-2008; Electric strength test: Tested according to GB / T1408.1-2006;

[0040] The results are shown in Table 1.

[0041] Table 1:

[0042] The design of different pretreatment temperatures and coating amounts is intended to study the effects of pretreatment conditions and film thickness on the properties of aramid paper. The experimental results show that a high pretreatment temperature slightly improves product performance, and the overall performance is better when the coating amount is 10% and 15%.

[0043] The meta-aramid-coated high-performance aramid paper produced through the above process significantly reduces the porosity of the aramid paper by adding a pretreatment step, thereby improving its mechanical strength and dielectric properties. This product has demonstrated excellent performance in practical applications, such as a tensile strength increase of more than 30% compared to conventional aramid paper, a porosity reduction of 20%-30%, and a dielectric constant and dielectric loss tangent that are superior to existing products. These performance characteristics make the aramid paper of the present invention promising for broad application in fields such as electronic equipment insulation materials and aerospace.

[0044] The above are only some embodiments of the present invention. For those skilled in the art, several modifications and improvements can be made without departing from the inventive concept of the present invention, which all fall within the scope of protection of the present invention.

Claims

1. A method for preparing meta-aramid-coated high-performance aramid paper, characterized in that the steps include: S1. Preparation of stock solution: Mix PMIA and DMAc to form a PMIA / DMAc solution; S2. Coagulation bath preparation: DMAc and deionized water were mixed and stirred thoroughly to prepare a DMAc system coagulation bath; S3. Base paper pretreatment: placing the aramid base paper in a hot pressing device and performing hot pressing pretreatment at 120-140°C to obtain pretreated aramid base paper; S4, stock solution coating: uniformly coating the surface of the pretreated aramid base paper with the stock solution to form a continuous and uniform coating layer; S5, coagulation treatment: immersing the coated aramid paper in a DMAc system coagulation bath, then washing the DMAc remaining on the surface with deionized water, and then drying to obtain dried aramid paper; S6. Final hot pressing: The dried aramid paper is finally hot pressed to obtain meta-aramid coated high-performance aramid paper.

2. The method for preparing meta-aramid-coated high-performance aramid paper according to claim 1, characterized in that: The aramid base paper has a basis weight of 60-80 g / m², and its fiber composition includes meta-aramid short fibers and fibrids. The meta-aramid short fibers have a length of 3-6 mm and a linear density of 2-5 dtex, and the addition amount of fibrids is 40%-50%.

3. The method for preparing meta-aramid-coated high-performance aramid paper according to claim 1, characterized in that: In step S1, the mass ratio of PMIA to DMAc is 1:

9.

4. The method for preparing meta-aramid-coated high-performance aramid paper according to claim 1, characterized in that: In step S1, the mixing temperature is 40° C. and the stirring time is 4 hours.

5. The method for preparing meta-aramid-coated high-performance aramid paper according to claim 1, characterized in that: In step S2, the mass ratio of DMAc to deionized water is 3:7, the stirring time is 10-15 minutes, and the coagulation bath temperature is set at 20-25°C.

6. The method for preparing meta-aramid-coated high-performance aramid paper according to claim 1, characterized in that: In step S4, the molecular weight of the PMIA is in the range of 50,000 to 80,000.

7. The method for preparing meta-aramid-coated high-performance aramid paper according to claim 1, characterized in that: The coating amount of the aramid stock solution is preferably 10% to 15%.

8. The method for preparing meta-aramid-coated high-performance aramid paper according to claim 1, characterized in that: In step S5, the coated aramid paper is immersed in the DMAc system coagulation bath for 5 minutes, and then the residual DMAc on the surface is rinsed with deionized water.

9. The method for preparing meta-aramid-coated high-performance aramid paper according to claim 1, characterized in that: The drying method in step S5 is vacuum drying at 100° C. for 2 hours.

10. The method for preparing meta-aramid-coated high-performance aramid paper according to claim 1, characterized in that: In step S6, the final hot pressing temperature is 250° C., the hot pressing pressure is 5 MPa, and the hot pressing time is 3 to 5 minutes.

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