Aramid insulation paper and a method for producing the same

Abstract

The present application relates to the technical field of special insulating material, and particularly discloses aramid insulation paper and a preparation method thereof.The aramid insulation paper is composed of modified meta-aramid short-cut fiber, modified meta-aramid fibrid, functionalized composite nano-filler, synergistic additive and deionized water.The mass fractions of the raw materials are as follows: modified meta-aramid short-cut fiber 45-60 parts, modified meta-aramid fibrid 25-35 parts, functionalized composite nano-filler 5-12 parts, synergistic additive 1-3 parts, and deionized water 180-250 parts.The present application has the following advantages: synergistic performance improvement: through multi-stage modification of the fiber and optimization of the composite nano-filler, the internal interface bonding state of the material is significantly improved, and air gap defects are reduced.The prepared aramid insulation paper has a breakdown field strength of greater than or equal to 38 kV / mm (an increase of more than 35% compared with traditional products), a tensile strength of greater than or equal to 280 N / 10 mm (an increase of more than 40%), and a thermal conductivity of greater than or equal to 0.52 W·m⁻¹·K⁻¹ (an increase of more than 100%), thereby achieving a synergistic breakthrough in insulation, mechanics and thermal conductivity.

Description

Technical Field

[0001] This invention relates to the field of special insulating materials technology, specifically to an aramid insulating paper and its preparation method. Background Technology

[0002] Aramid (aromatic polyamide) insulating paper has become an indispensable key material in high-voltage electrical equipment, aerospace, new energy and other fields due to its excellent high-temperature resistance, electrical insulation, mechanical strength and chemical stability. Among them, meta-aramid insulating paper, with its good flexibility and processing performance, is widely used in slot insulation, phase insulation and turn insulation of equipment such as transformers, motors, and capacitors.

[0003] However, existing aramid insulating paper still faces several technical bottlenecks in practical applications: First, the strong inertness and low polarity of aramid fibers result in weak interfacial bonding between chopped fibers and precipitated fibers, easily leading to air gap defects. This not only reduces the breakdown field strength of the insulating paper but also induces partial discharge under the influence of an electric field, accelerating material aging. Second, the low thermal conductivity of single aramid materials (typically ≤0.25 W·m⁻¹·K⁻¹) makes it difficult to meet the heat dissipation requirements of high-end electrical equipment, and heat accumulation easily leads to insulation performance degradation. Third, traditional modification methods such as single coupling agent grafting or plasma treatment can improve fiber interfacial bonding, but often result in asynchronous improvement of insulation and mechanical properties. Some modification processes can also damage the fiber body, affecting the long-term stability of the material. Fourth, compared with imported Nomex paper, domestically produced aramid insulating paper still lags behind in breakdown field strength and partial discharge resistance under a multilayer oil-impregnated structure, mainly due to insufficient control of interfacial defects and optimization of production processes.

[0004] To address these issues, various improvement schemes have been proposed in related research. For example, plasma-assisted coupling agent treatment can improve hydrogen bonding at the fiber interface, or BN nanofillers can be added to enhance thermal conductivity. However, the former offers limited improvement in mechanical properties, while the latter is prone to insulation degradation due to uneven filler dispersion. Another patent uses high heat-shrinkable fibers and a dual-stage hot-pressing process to improve internal bonding strength, but this does not solve the problem of insufficient thermal conductivity.

[0005] Therefore, developing an aramid insulating paper with high insulation strength, excellent mechanical properties and good thermal conductivity, and optimizing its preparation process, has become the current research focus in this field. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing technologies and provide an aramid insulating paper and its preparation method. This aramid insulating paper achieves a synergistic improvement in insulation performance, mechanical properties, and thermal conductivity through multi-level fiber modification, optimization of composite nanofillers, and process innovation. Simultaneously, the preparation process is stable and controllable, making it suitable for industrial production.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] An aramid insulating paper is composed of modified meta-aramid chopped fibers, modified meta-aramid precipitated fibers, functionalized composite nanofillers, synergistic additives, and deionized water. The mass proportions of each raw material are as follows: 45-60 parts modified meta-aramid chopped fibers, 25-35 parts modified meta-aramid precipitated fibers, 5-12 parts functionalized composite nanofillers, 1-3 parts synergistic additives, and 180-250 parts deionized water.

[0009] Modified meta-aramid chopped fibers: These fibers, with a length of 3-6 mm and a diameter of 12-18 μm, are selected as the substrate and modified by plasma activation and grafting with polycationic PDDA. Plasma activation introduces active groups such as hydroxyl and carbonyl groups onto the fiber surface, improving surface roughness and reactivity. The grafting of polycationic PDDA onto the fiber surface via electrostatic adsorption and chemical bonding enhances the interfacial interaction between the chopped fibers and the precipitated fibers and nanofillers, reducing air gap defects.

[0010] Modified meta-aramid precipitated fiber: This material is prepared by modifying meta-aramid precipitated fiber with a specific surface area ≥85 m² / g with an amino-terminated coupling agent (AP). The amino groups of the amino-terminated coupling agent can form hydrogen bonds with the carbonyl groups of the aramid fiber, and simultaneously react with the hydroxyl groups on the surface of the nanofiller, acting as a bridge to further improve the interfacial compatibility between the fiber and the filler.

[0011] Functionalized composite nanofiller: Prepared by blending hydroxylated BN and γ-Al2O3 at a mass ratio of 2:1, and then modifying with silane coupling agent KH-550. BN has excellent thermal conductivity and insulation properties, while γ-Al2O3 can improve the bonding force between the filler and the matrix. The blending of the two can achieve a synergistic improvement in thermal conductivity and mechanical properties. The silane coupling agent modification can reduce the surface energy of the filler, prevent agglomeration, and ensure its uniform dispersion in pulp.

[0012] Synergistic additives: These are composed of dispersant PEO and antistatic agent polyethylene glycol fatty acid ester mixed at a mass ratio of 3:1. PEO (molecular weight 200,000-300,000) has good dispersion stability and can effectively prevent fiber and filler agglomeration; polyethylene glycol fatty acid ester (HLB value 12-14) can reduce the surface resistivity of insulating paper and avoid performance damage caused by static electricity accumulation.

[0013] This invention also provides a method for preparing the above-mentioned aramid insulating paper, specifically including five steps: raw material pretreatment, pulp preparation, wet papermaking, gradient hot pressing, and post-treatment testing.

[0014] 1. Raw material pretreatment:

[0015] Modification of meta-aramid chopped fibers: First, plasma activation is performed (discharge power 80-120W, treatment time 3-8min, argon / oxygen volume ratio 4:1, vacuum degree 0.03-0.08MPa). Then, the activated fibers are immersed in 1.5-3.0% PDDA solution at a bath ratio of 1:50 and reacted at 55-65℃ for 60-90min. After washing, the fibers are vacuum dried (80-90℃, 4-6h) to obtain modified meta-aramid chopped fibers.

[0016] Modification of meta-aramid precipitated fibers: The precipitated fibers are dispersed in deionized water, and 0.8-1.5% AP solution is added. The mixture is stirred and reacted at 40-50℃ for 45-70 min. After filtration, the mixture is dried by blowing air (70-80℃, 3-5 h) to obtain modified meta-aramid precipitated fibers.

[0017] Functional modification of composite nanofillers: Hydroxylated BN and γ-Al2O3 were mixed at a mass ratio of 2:1, and deionized water was added for ultrasonic dispersion for 30-45 min. Then, 3-6% of KH-550 by the mass of the filler was added, and the mixture was refluxed at 75-85℃ for 120-150 min. After centrifugation, the mixture was dried (100-110℃, 8-10 h) and ground through a 500-mesh sieve to obtain the functionalized composite nanofiller.

[0018] 2. Pulp preparation: Weigh the modified short-cut fibers, modified precipitated fibers and deionized water according to the formula ratio, add them to the beater, and beat in stages (beat at 800-900 r / min for 10-15 min first, then raise the temperature to 40-50℃ and beat at 1000-1200 r / min for 10-25 min), controlling the freeness to 35-45°SR; then add the functionalized composite nanofiller and synergistic additives, and continue to stir and disperse for 60-90 min to obtain a uniform pulp suspension with a concentration of 0.8-1.5wt%.

[0019] 3. Wet papermaking: The pulp suspension is fed to a wire paper machine (wire vibration frequency 200-300 times / min, amplitude 2-5mm) and formed into a wet paper web under a vacuum of 0.02-0.05MPa; then it is sent to a pre-press (temperature 80-100℃, pressure 3-6MPa, time 3-5min) for pre-pressing and dewatering to obtain the base paper.

[0020] 4. Gradient hot pressing: The base paper is placed in a multi-layer hot press and hot-pressed according to the following gradient process: first stage (180-200℃, 8-12MPa, 10-15min), second stage (240-260℃, 14-18MPa, 20-30min), third stage (220-230℃, 10-12MPa, 15-20min), with a heating rate of 5-8℃ / min and a cooling rate of 3-5℃ / min; after hot pressing, it is naturally cooled to room temperature to obtain aramid insulating paper.

[0021] 5. Post-processing and testing: Trim the edges and clean the surface of the product. Test the breakdown field strength, tensile strength, thermal conductivity and other properties according to relevant standards. Qualified products are finished products.

[0022] The beneficial effects of this invention are as follows:

[0023] Excellent high-temperature stability: When used for a long time in a high-temperature environment of 220℃, the performance retention rate is ≥90%, which is far superior to traditional aramid insulating paper (usually ≤75%), and can meet the long-term operation requirements of high-end electrical equipment under high-temperature conditions.

[0024] Innovative modification process: Short-cut fibers are treated with plasma activation-polycationic grafting composite modification process, combined with terminal amino coupling agent modification of precipitated fibers, which not only enhances the interfacial bonding force between fibers, but also avoids the damage to the fiber body caused by single modification; After the composite nanofiller is modified with silane coupling agent, the dispersibility and compatibility are significantly improved, and the thermal conductivity is effectively enhanced.

[0025] Controllable production process: Optimized process parameters such as segmented pulping and gradient hot pressing ensure the stability of product quality; the entire preparation process requires no special equipment, the production cost is moderate, and it is suitable for large-scale industrial production.

[0026] Obviously, based on the above description of the present invention, and according to common technical knowledge and conventional methods in the field, various other modifications, substitutions or alterations can be made without departing from the basic technical concept of the present invention.

[0027] The following detailed embodiments further illustrate the above-described content of the present invention. However, this should not be construed as limiting the scope of the present invention to the following examples. All technologies implemented based on the above-described content of the present invention fall within the scope of the present invention. Detailed Implementation

[0028] The present invention is illustrated below with specific embodiments, which are not intended to limit the scope of the invention.

[0029] Example 1,

[0030] An aramid insulating paper, comprising the following raw materials in parts by weight: 50 parts modified meta-aramid short-cut fibers, 30 parts modified meta-aramid precipitated fibers, 8 parts functionalized composite nanofillers, 2 parts synergistic additives, and 220 parts deionized water.

[0031] The preparation method is as follows:

[0032] Raw material pretreatment:

[0033] Short fiber modification: Plasma activation parameters were: discharge power 100W, treatment time 5min, argon / oxygen volume ratio 4:1, vacuum degree 0.05MPa; PDDA solution concentration 2.0%, bath ratio 1:50, reaction at 60℃ for 75min, and vacuum drying at 85℃ for 5h.

[0034] Precipitation fiber modification: AP solution concentration 1.2%, reaction at 45℃ for 60 min, and drying at 75℃ for 4 h.

[0035] Filler modification: Hydroxylated BN to γ-Al2O3 mass ratio 2:1, KH-550 added at 4% of filler mass, refluxed at 80℃ for 130 min, dried at 105℃ for 9 h, and ground through a 500 mesh sieve.

[0036] Pulp preparation: Add modified fiber and deionized water to a beater, beat at 850 r / min for 12 min, then heat to 45℃ and beat at 1100 r / min for 20 min, with a freeness of 40°SR; add filler and synergistic additives, stir and disperse for 75 min, and the pulp concentration is 1.2 wt%.

[0037] Wet papermaking: Inclined wire paper machine speed 2.0m / min, vibration frequency 250 times / min, amplitude 3mm, vacuum degree 0.03MPa; pre-pressing temperature 90℃, pressure 4MPa, time 4min.

[0038] Gradient hot pressing: First stage 190℃, 10MPa, 12min; Second stage 250℃, 16MPa, 25min; Third stage 225℃, 11MPa, 18min; Heating rate 6℃ / min, cooling rate 4℃ / min.

[0039] Post-processing: Trim and clean the edges, then test the performance.

[0040] The aramid insulating paper was tested and found to have a breakdown field strength of 40.2 kV / mm, a tensile strength of 295 N / 10 mm, a thermal conductivity of 0.55 W·m⁻¹·K⁻¹, and a performance retention rate of 92% after 1000 hours at 220℃.

[0041] Example 2,

[0042] An aramid insulating paper, comprising the following raw materials in parts by weight: 45 parts modified meta-aramid short-cut fibers, 25 parts modified meta-aramid precipitated fibers, 5 parts functionalized composite nanofiller, 1 part synergistic agent, and 180 parts deionized water.

[0043] The preparation method is the same as in Example 1, with some parameters adjusted: plasma treatment time 3 min, PDDA solution concentration 1.5%, AP solution concentration 0.8%, KH-550 addition amount 3%; freeness 35°SR, pulp concentration 0.8wt%; gradient hot pressing: first stage 180℃, 8MPa, 10 min, second stage 240℃, 14MPa, 20 min, third stage 220℃, 10MPa, 15 min.

[0044] The aramid insulating paper was tested and found to have a breakdown field strength of 38.1 kV / mm, a tensile strength of 282 N / 10 mm, a thermal conductivity of 0.52 W·m⁻¹·K⁻¹, and a performance retention rate of 90% after 1000 hours at 220℃.

[0045] Example 3,

[0046] An aramid insulating paper, comprising the following raw materials in parts by weight: 60 parts modified meta-aramid short-cut fibers, 35 parts modified meta-aramid precipitated fibers, 12 parts functionalized composite nanofillers, 3 parts synergistic additives, and 250 parts deionized water.

[0047] The preparation method is the same as in Example 1, with some parameters adjusted as follows: plasma treatment time 8 min, PDDA solution concentration 3.0%, AP solution concentration 1.5%, KH-550 addition amount 6%; freeness 45°SR, pulp concentration 1.5wt%; gradient hot pressing: first stage 200℃, 12MPa, 15 min, second stage 260℃, 18MPa, 30 min, third stage 230℃, 12MPa, 20 min.

[0048] The aramid insulating paper was tested and found to have a breakdown field strength of 42.3 kV / mm, a tensile strength of 310 N / 10 mm, a thermal conductivity of 0.58 W·m⁻¹·K⁻¹, and a performance retention rate of 93% after 1000 hours at 220℃.

[0049] Comparative Example 1,

[0050] Aramid insulating paper was prepared using unmodified meta-aramid chopped fibers and precipitated fibers, without the addition of composite nanofillers, and with the other raw materials being the same as in Example 1, following a traditional process (single hot pressing temperature 250℃, pressure 15MPa, time 30min).

[0051] Testing revealed that the insulation paper had a breakdown field strength of 28.5 kV / mm, a tensile strength of 205 N / 10 mm, a thermal conductivity of 0.22 W·m⁻¹·K⁻¹, and a performance retention rate of 72% after 1000 hours at 220°C. All of these properties were significantly lower than those of the product in Example 1 of this invention.

[0052] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0053] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

[0054] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. An aramid insulating paper, characterized in that, The product is composed of the following raw materials in parts by weight: 45-60 parts of modified meta-aramid chopped fiber, 25-35 parts of modified meta-aramid precipitated fiber, 5-12 parts of functionalized composite nanofiller, 1-3 parts of synergistic agent, and 180-250 parts of deionized water; the modified meta-aramid chopped fiber is a meta-aramid chopped fiber modified by plasma activation and grafting with polycationic PDDA, with a fiber length of 3-6 mm and a diameter of 12-18 μm; the modified meta-aramid precipitated fiber is a meta-aramid precipitated fiber modified by terminal amino coupling agent AP, with a specific surface area ≥85 m² / g; the functionalized composite nanofiller is prepared by compounding hydroxylated BN and γ-Al2O3 in a mass ratio of 2:1 and then modifying it with silane coupling agent KH-550, with a particle size distribution of 500 nm-2 μm; the synergistic agent is a mixture of dispersant PEO and antistatic agent polyethylene glycol fatty acid ester in a mass ratio of 3:

1.

2. The aramid insulating paper according to claim 1, characterized in that, The plasma activation process parameters are: discharge power 80-120W, processing time 3-8min, working gas is a mixture of argon and oxygen with a volume ratio of 4:1, and vacuum degree 0.03-0.08MPa; the process conditions for the polycationic PDDA graft modification are: PDDA solution mass concentration 1.5-3.0%, bath ratio 1:50, constant temperature reaction at 55-65℃ for 60-90min, and after the reaction, the modified meta-aramid short fibers are obtained by washing and vacuum drying.

3. The aramid insulating paper according to claim 1, characterized in that, The process parameters for modifying meta-aramid precipitated fibers with the terminal amino coupling agent AP are as follows: AP solution mass concentration 0.8-1.5%, stirring reaction at 40-50℃ for 45-70 min, and amino content on the surface of the modified fiber ≥0.32mmol / g; the process conditions for modifying composite nanofillers with the silane coupling agent KH-550 are as follows: KH-550 addition amount is 3-6% of the mass of composite nanofiller, reflux reaction at 75-85℃ for 120-150 min, and contact angle of the modified filler surface ≤35°.

4. The aramid insulating paper according to claim 1, characterized in that, The dispersant PEO has a molecular weight of 200,000-300,000 and is added at a rate of 0.4-0.8% of the total mass of the raw materials; the antistatic agent polyethylene glycol fatty acid ester has an HLB value of 12-14 and is added at a rate of 0.1-0.3% of the total mass of the raw materials.

5. A method for preparing aramid insulating paper as described in any one of claims 1-4, characterized in that, Includes the following steps: Step 1: Raw material pretreatment (1) Modification of meta-aramid chopped fibers: The meta-aramid chopped fibers were subjected to plasma activation treatment and polycationic PDDA grafting modification in sequence. After washing, they were vacuum dried at 80-90℃ for 4-6h to obtain modified meta-aramid chopped fibers. (2) Modification of meta-aramid precipitated fiber: The meta-aramid precipitated fiber was dispersed in deionized water, and the terminal amino coupling agent AP solution was added. After stirring and reacting at a constant temperature, the mixture was filtered and dried in a forced air at 70-80℃ for 3-5 hours to obtain the modified meta-aramid precipitated fiber. (3) Functional modification of composite nanofillers: Hydroxylated BN and γ-Al2O3 were mixed at a mass ratio of 2:1, deionized water was added and ultrasonically dispersed for 30-45 min, then silane coupling agent KH-550 was added, the mixture was heated and refluxed, centrifuged and separated, dried at 100-110℃ for 8-10 h, and ground through a 500-mesh sieve to obtain functionalized composite nanofillers; Step 2: Pulp preparation, Weigh the modified meta-aramid chopped fibers, modified meta-aramid precipitated fibers, and deionized water according to the formula ratio, add them to a pulper, and pulp for 20-40 minutes at a speed of 800-1200 r / min, controlling the freeness to be 35-45°SR; then add the functionalized composite nanofiller and synergistic additives, and continue stirring and dispersing for 60-90 minutes to obtain a uniform pulp suspension; Step 3: Wet papermaking, The pulp suspension is fed to an inclined wire paper machine for papermaking, with the papermaking speed controlled at 1.5-3.0 m / min and the vacuum degree at 0.02-0.05 MPa, to form a wet paper web; The wet paper web is then sent to a pre-press machine for pre-pressing. The pre-pressing temperature is 80-100℃, the pressure is 3-6MPa, and the pre-pressing time is 3-5min to remove some moisture and obtain the base paper. Step 4: Gradient hot pressing molding, The base paper is placed in a multi-layer hot press for gradient hot pressing. The hot pressing process consists of three stages: the first stage is at a temperature of 180-200℃ and a pressure of 8-12MPa, held for 10-15 minutes; the second stage is at a temperature of 240-260℃ and a pressure of 14-18MPa, held for 20-30 minutes; the third stage is at a temperature of 220-230℃ and a pressure of 10-12MPa, held for 15-20 minutes. After hot pressing, the paper is allowed to cool naturally to room temperature to obtain aramid insulating paper. Step 5: Post-processing and inspection. After cooling, the aramid insulating paper is trimmed and its surface is cleaned. Then, its performance, such as breakdown field strength, tensile strength, and thermal conductivity, is tested according to relevant standards. Qualified products are considered finished products.

6. The preparation method according to claim 5, characterized in that, In step 2, the pulping process adopts a segmented pulping method: first, pulping is carried out at a speed of 800-900 r / min for 10-15 min, then the temperature is raised to 40-50℃, and pulping is continued at a speed of 1000-1200 r / min for 10-25 min; the concentration of the pulp suspension is controlled at 0.8-1.5 wt%.

7. The preparation method according to claim 5, characterized in that, In step 3, the vibration frequency of the wire section of the inclined wire paper machine is 200-300 times / min, and the amplitude is 2-5mm; the temperature uniformity error of the pressure roller of the pre-press machine is ≤±3℃.

8. The preparation method according to claim 5, characterized in that, In step 4, the heating rate of the gradient hot pressing process is 5-8℃ / min, and the cooling rate is 3-5℃ / min; the parallelism error of the hot press plate is ≤0.02mm.