Preparation method and device of aramid corrugated paper and application thereof

Abstract

The present application relates to the technical field of crepe paper preparation, and particularly relates to a preparation method, a preparation device and application of aramid crepe paper; the aramid base paper is sent into a treatment unit group; the treatment unit group is sequentially provided with a first temperature zone, a second temperature zone and a speed difference shearing unit along the continuous advancing direction of the paper; the aramid base paper is first subjected to heat pressing and pre-densification treatment in the first temperature zone to obtain pre-densified aramid paper; the pre-densified aramid paper is simultaneously subjected to final heat pressing and densification and microstructure imprinting in the second temperature zone, and a vibration auxiliary treatment is arranged in the second temperature zone to form microstructure crepe on the surface of the aramid paper; the aramid paper subjected to the microstructure imprinting is sent into the speed difference shearing unit to be subjected to speed difference shearing treatment; and finally, the aramid crepe paper is obtained through cooling and setting treatment. The aramid crepe paper has excellent comprehensive performance, the preparation process is simple and efficient, and is more suitable for application in oil-immersed transformers, electric reactors, electric machines or high-temperature electrical insulation components.

Description

Technical Field

[0001] This invention relates to a method for preparing aramid crepe paper, a preparation apparatus for preparing the same, and its application, belonging to the field of crepe paper preparation technology. Background Technology

[0002] Aramid paper is widely used in the insulation systems of high-end electrical equipment such as transformers, motors, and reactors due to its excellent heat resistance, mechanical strength, and electrical insulation properties. Especially in oil-immersed equipment, processing aramid paper into a wrinkled form can create continuous oil flow channels on the paper surface, achieving efficient heat dissipation through insulating oil convection, thereby reducing the operating temperature of the equipment and extending its service life.

[0003] Currently, the preparation of aramid crepe paper generally employs a two-step method: hot pressing followed by creping. For example, CN115897292A discloses this two-step method, which involves first hot-pressing and densifying the aramid base paper under high temperature and pressure to obtain densified aramid paper; then cooling and winding the hot-pressed paper, followed by a separate process of secondary heating and mechanical creping. While existing technologies can balance the mechanical and electrical properties of paper to some extent, they still suffer from several insurmountable technical defects, as detailed below.

[0004] First, the process is lengthy and energy-intensive. After hot pressing, cooling and winding are required, and then reheating is needed when wrinkling again. Repeated heating and cooling result in a large amount of energy loss. The production process is long and inefficient, which does not meet the requirements of green and low-carbon manufacturing.

[0005] Second, hot pressing and wrinkling have mutually exclusive mechanisms. Hot pressing aims to achieve dense fiber bonding and avoid random wrinkles, while wrinkling requires controlled deformation. The process conditions and stress control directions of the two are contradictory and difficult to reconcile in the same process.

[0006] Third, wrinkling can damage the fiber interface. The fiber bond formed by hot pressing tends to be stable after cooling. When it is heated and wrinkled again, the mechanical force can easily break the interface bond, resulting in a decrease in paper strength.

[0007] Fourth, the wrinkle formation quality is poor, and the depth-to-width ratio is low. In the traditional wrinkling process, fibers tend to form bridges at the entrance of the microstructure grooves, which cannot fully fill the inside of the grooves, resulting in shallow wrinkles, poor uniformity, and insufficient structural fullness, making it difficult to form a regular microstructure with a high depth-to-width ratio.

[0008] Fifth, the lack of multi-level structure limits overall performance. Existing processes can only achieve macroscopic wrinkles, making it difficult to simultaneously obtain high-precision microscopic wrinkles. The regularity of oil flow channels is insufficient, limiting heat dissipation performance. At the same time, the disordered arrangement of fibers leads to a shorter insulation breakdown path, making it difficult to further improve insulation reliability.

[0009] In summary, traditional two-step processes cannot simultaneously achieve high efficiency, synergistic hot pressing and wrinkling, interface protection, precise wrinkle formation, and multi-level structure construction, making it difficult to meet the high-performance requirements of aramid crepe paper for high-end electrical insulation. There is an urgent need in this field for an integrated preparation method that, while ensuring strength and insulation performance, achieves continuous production, controllable wrinkle formation, and efficient construction of multi-level structures. Summary of the Invention

[0010] This invention addresses the shortcomings of existing technologies by providing a method, apparatus, and application for preparing aramid crepe paper. It solves a series of technical problems caused by the incompatible mechanisms of hot-pressing densification and creping in traditional two-step processes, including lengthy processes, high energy consumption, easy damage to fiber interfaces, poor crepe quality, and lack of multi-level structure in the product. This invention integrates features such as zoned temperature control, dual-frequency vibration assistance, microstructure imprinting, and speed differential shearing creping in a continuous, integrated process. By constructing a continuous process architecture of "pre-densification - simultaneous final densification and microstructure imprinting - macroscopic creping," the vibration field promotes dynamic healing and full filling of the fiber interface, thereby simultaneously achieving densification and controllable creping in the same process. This directly produces multi-level aramid crepe paper with regular micro-folds, high macroscopic elasticity, and excellent insulation and heat dissipation properties, simultaneously improving the paper's strength, elongation, and insulation reliability.

[0011] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: a method for preparing aramid crepe paper, wherein the preparation method is as follows: The aramid base paper is fed into the processing unit group, which is provided with a first temperature zone, a second temperature zone and a speed difference shearing unit in sequence along the continuous travel direction of the paper. The aramid base paper is first subjected to hot pressing pre-densification treatment in the first temperature zone to obtain pre-densified aramid paper; The pre-densified aramid paper undergoes final hot-press densification and microstructure imprinting simultaneously in the second temperature zone, and vibration-assisted treatment is provided in the second temperature zone to form microstructure wrinkles on the surface of the aramid paper. The aramid paper after microstructure imprinting is fed into the speed difference shearing unit for speed difference shearing, so that the aramid paper as a whole forms macroscopic wrinkles. Finally, after cooling and shaping, the aramid crepe paper is obtained.

[0012] Furthermore, the surface of the hot press roller in the first temperature zone is smooth, the temperature is 200-260℃, and the linear pressure is 30-80kN / m; The temperature in the second temperature zone is 260-300℃, and the linear pressure is 100-150 kN / m.

[0013] Furthermore, the aramid paper is heated between the first and second temperature zones so that the surface temperature of the aramid paper when it enters the second temperature zone is no more than 30°C different from the surface temperature of the hot press roller in the second temperature zone.

[0014] Furthermore, the second temperature zone is provided with at least one pair of hot press rollers, and the surface of the at least one pair of hot press rollers in the second temperature zone is provided with a micron-level concave-convex structure; the depth of the micron-level concave-convex structure is 20-150 microns, and the concave-convex density is 30-250 per 10cm.

[0015] Furthermore, a vibration-assisted system is provided in the second temperature zone to apply high-frequency micro-amplitude vibration to the aramid paper passing through the second temperature zone; the vibration frequency is 10-50kHz and the amplitude is 1-10μm. The vibration-assisted system adopts a dual-frequency composite vibration mode, including: a first vibration frequency f1 of 10-20kHz and a second vibration frequency f2 of 30-50kHz; f1 and f2 are applied simultaneously.

[0016] Furthermore, at least one pair of hot press rollers used in the speed difference shearing process have a speed difference, and the linear velocities of the two rollers with the speed difference hot press rollers are v1 and v2, respectively, with a speed difference Δv =|v1 - v2|, where Δv is 5-10 m / min; the running tension of the aramid paper in the speed difference shearing unit is controlled at 5-20 N / cm.

[0017] The present invention also discloses an apparatus for preparing aramid crepe paper, the apparatus comprising: The first temperature zone hot press roller group, the second temperature zone hot press roller group, the speed difference shearing unit, and the cooling and shaping roller are arranged sequentially along the paper's travel direction. The first temperature zone hot press roller group has a smooth roller surface and is used to perform hot pressing pre-densification treatment on aramid base paper. The second temperature zone hot press roller group includes at least one pair of hot press rollers with micron-level uneven structures on their surfaces, used to simultaneously perform final hot pressing densification and microstructure imprinting on the pre-densified aramid paper; the hot press rollers in the second temperature zone hot press roller group have the same linear velocity. The second temperature zone hot press roller group is integrated with a vibration assist system. The vibration applied by the vibration assist system is transmitted to the aramid paper in the printing area through the roller surface. The speed difference shearing unit includes at least one pair of smooth hot press rollers with a speed difference, used to apply speed difference shearing to the microstructure imprinted aramid paper to form macroscopic wrinkles; The cooling and shaping roller is used to cool and shape the aramid paper processed by the speed difference shearing unit.

[0018] Furthermore, the vibration assistance system applies high-frequency micro-amplitude vibration to the hot press roller in the second temperature zone through a piezoelectric vibrator, and the piezoelectric vibrator is equipped with a water-cooled jacket or a heat insulation layer.

[0019] Furthermore, the smooth hot press roller with speed difference in the speed difference shearing unit is electrically connected to the speed difference control system, which is used to control the linear speed difference between the two rollers in the pair of hot press rollers.

[0020] The present invention also discloses an application of aramid crepe paper, which is used in oil-immersed transformers, reactors, motors or electrical insulation components.

[0021] The beneficial effects of this invention are: This invention constructs a spatiotemporally continuous integrated process architecture of "pre-densification - simultaneous final densification and microstructure imprinting - macroscopic creping," integrating features such as zoned temperature control, dual-frequency vibration assistance, microstructure imprinting, and speed difference shearing creping into a complete multi-physics collaborative manufacturing system. This fundamentally eliminates the inherent defects of traditional two-step methods, such as lengthy processes, high energy consumption, and frequent thermal stress microcracks caused by intermediate cooling, winding, and secondary heating. Simultaneously, it achieves a significant and synergistic improvement in the three core performance indicators of aramid crepe paper: tensile strength, elongation at break, and breakdown voltage. Pre-densification, simultaneous densification, microstructure imprinting, and macroscopic creping are completed in a single step, eliminating the need for intermediate cooling, winding, and secondary heating, thus shortening the process flow and reducing energy consumption.

[0022] The zoned temperature control and independent speed differential shearing design fundamentally resolve the contradiction between hot pressing and wrinkling. The first temperature zone completes pre-densification at low temperature and low pressure, while the second temperature zone simultaneously performs final densification and microstructure imprinting at high temperature and high pressure. An independent subsequent speed differential shearing unit completes macroscopic wrinkling. The three functions are separated and work together.

[0023] Vibration assists in solving the deformation resistance of fiber networks and promotes interface healing. This invention applies high-frequency micro-amplitude vibrations with a frequency of 10-50 kHz (where f1 = 10-20 kHz, f2 = 30-50 kHz) and an amplitude of 1-10 μm in the second temperature zone. This causes micron-level relative slippage in the softened fiber network, endowing the fibers with the necessary microscopic fluidity, thereby allowing them to precisely flow into the depths of the microstructure grooves. Simultaneously, the vibration promotes the diffusion and entanglement of molecular chains at the fiber interface, improving the retention rate of tensile strength.

[0024] Dual-frequency composite vibration offers significant advantages over single-frequency vibration. This invention employs a dual-frequency composite vibration mode where f1 and f2 are applied simultaneously. Compared to single-frequency vibration, dual-frequency composite vibration can excite the fiber network over a wider frequency range, more effectively balancing overall fiber flow and localized fine filling, thereby improving wrinkle formation quality and overall paper performance.

[0025] The separation of microstructure imprinting and speed differential shearing achieves a dual breakthrough in microscopic precision and macroscopic performance. The second temperature zone's concave and convex rollers have no speed difference, ensuring accurate replication of the microstructure; the independent smooth differential rollers provide controllable shearing, significantly improving paper elongation without damaging the microstructure.

[0026] More specifically, the well-ordered microstructure formed in the second temperature zone, strengthened by interface healing, provides an ideal mechanical matrix for the safe creping of the subsequent speed-difference shearing unit. Since the microstructure imprinting is completed under the same speed conditions and the fiber bonding strength is significantly enhanced due to vibration, the paper possesses the mechanical toughness to withstand shear deformation without significant interface tearing. The independently configured smooth roller speed-difference shearing unit applies controllable macroscopic deformation to this strong matrix, imparting high elongation at break to the paper without damaging the well-ordered microstructure established in the second temperature zone. This allows for a better balance between "microscopic regularity" and "macroscopic elasticity."

[0027] In the preparation method and apparatus described in this invention, a multi-level structure works synergistically to simultaneously improve heat dissipation and insulation performance. The micro-wrinkles formed in the second temperature zone not only construct continuous, regular micron-level oil flow channels for efficient convective heat dissipation, but also, under the synergistic effect of vibration-assisted fiber orientation, further extend the breakdown path in the thickness direction and homogenize the electric field distribution, thereby significantly improving insulation strength and breakdown voltage. The macro-folds formed by the velocity difference shearing unit provide the paper with high flexibility and high elongation, enabling the paper to adhere to irregular components and buffer mechanical stress. The combination of these two elements forms a multi-level structure of "micro-folds + macro-folds." Under stress, the micro-folds preferentially unfold to absorb small strains, while the macro-folds subsequently provide large deformation reserves, resulting in a breaking elongation of the paper far exceeding that of traditional products. In the electro-thermal combined field, the continuous oil flow channels constructed by the micro-folds are responsible for efficient heat dissipation and electric field homogenization, while the high flexibility provided by the macro-folds allows the paper to fully contact the insulating oil and adhere to irregularly shaped components. These two elements complement each other, jointly achieving a simultaneous improvement in heat dissipation efficiency and insulation reliability.

[0028] The modular design of the device enhances production adaptability. The microstructure roller surface can be flexibly replaced, and vibration frequency and speed difference parameters can be adjusted according to product requirements, adapting to the production of various product specifications.

[0029] This invention, through an integrated design of "pre-densification in the first temperature zone, vibration-assisted microstructure imprinting in the second temperature zone, and macro-creeping by velocity difference shearing in the third unit," avoids thermal stress damage while enabling micro-creases to construct continuous oil flow channels and extend the breakdown path to improve heat dissipation and insulation. The macro-creases endow the paper with high flexibility and high elongation, ultimately achieving a comprehensive breakthrough in the strength, elasticity, insulation, and heat dissipation performance of aramid crepe paper. Attached Figure Description

[0030] Figure 1 This is a flowchart illustrating the preparation process of the aramid crepe paper described in this invention. Figure 2 This is a schematic diagram of the apparatus for preparing aramid crepe paper according to the present invention; Figure 3 A schematic diagram of the sawtooth wave hot press roller structure in the second temperature zone; In the figure, 1 is the first temperature zone hot press roller group; 2 is the second temperature zone hot press roller group; 3 is the speed difference shearing unit; 4 is the cooling and shaping roller; 5 is the infrared radiation heater; 6 is the temperature sensor; and 7 is the piezoelectric vibrator. Detailed Implementation

[0031] The specific embodiments of the present invention will be described in detail below. The present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein.

[0032] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used is for describing particular embodiments only and is not intended to limit the invention.

[0033] like Figure 1 As shown, a method for preparing aramid crepe paper is described, wherein the preparation method is as follows: The aramid base paper is fed into the processing unit group, which is provided with a first temperature zone, a second temperature zone and a speed difference shearing unit 3 in sequence along the continuous travel direction of the paper. The aramid base paper is first subjected to hot pressing pre-densification treatment in the first temperature zone to obtain pre-densified aramid paper; The pre-densified aramid paper undergoes final hot-press densification and microstructure imprinting simultaneously in the second temperature zone, and vibration-assisted treatment is provided in the second temperature zone to form microstructure wrinkles on the surface of the aramid paper. The aramid paper after microstructure imprinting is fed into the speed difference shearing unit 3 for speed difference shearing, so that the aramid paper as a whole forms macroscopic wrinkles. Finally, after cooling and shaping, the aramid crepe paper is obtained.

[0034] Specifically, the surface of the hot press roller in the first temperature zone is smooth, the temperature is 200-260℃, and the linear pressure is 30-80 kN / m; The temperature in the second temperature zone is 260-300℃, and the linear pressure is 100-150 kN / m.

[0035] Specifically, the paper is heated between the first and second temperature zones by an infrared radiation heater 5, and a closed-loop temperature control is used to ensure that the surface temperature of the paper when it enters the second temperature zone is no more than 30°C compared with the surface temperature of the hot press roller in the second temperature zone. That is, the surface temperature of the paper is detected by a temperature sensor 6, which is electrically connected to the infrared radiation heater 5, and a closed-loop temperature control is formed between the temperature sensor 6 and the infrared radiation heater 5.

[0036] Preferably, the surface temperature difference between the aramid paper and the surface temperature of the hot press roller in the second temperature zone is no more than 15°C.

[0037] Specifically, the second temperature zone is provided with at least one pair of hot press rollers, and the surface of the at least one pair of hot press rollers in the second temperature zone is provided with a micron-level concave-convex structure; the depth of the micron-level concave-convex structure is 20-150 microns, and the concave-convex density is 30-250 per 10cm.

[0038] More specifically, the micron-level uneven structure on the surface of the hot press roller is selected from sine waves, sawtooth waves (such as... Figure 3 (as shown) one or more combinations thereof, wherein the linear velocities of the two rollers in the same hot press roller group in the second temperature zone are the same.

[0039] Specifically, a vibration-assisted system is provided in the second temperature zone to apply high-frequency micro-amplitude vibration to the aramid paper passing through the second temperature zone; the vibration frequency is 10-50kHz and the amplitude is 1-10μm. The vibration-assisted system adopts a dual-frequency composite vibration mode, including: a first vibration frequency f1 of 10-20kHz and a second vibration frequency f2 of 30-50kHz; f1 and f2 are applied simultaneously.

[0040] Specifically, at least one pair of hot press rollers used in the speed difference shearing process has a speed difference, with the linear velocities of the two rollers being v1 and v2, respectively, and the speed difference Δv = |v1 - v2|, where Δv is 5-10 m / min; the running tension of the aramid paper in the speed difference shearing unit 3 is controlled at 5-20 N / cm. The linear speed difference between the pair of hot press rollers is controlled by a speed difference control system. Under these conditions, the speed difference shearing process causes macroscopic wrinkles to form on the aramid paper as a whole.

[0041] More specifically, the aramid base paper used in the above general steps is produced by papermaking using aramid precipitated fibers and aramid chopped fibers, comprising, by weight: 40-80 parts aramid precipitated fibers and 20-60 parts aramid chopped fibers; the freeness of the aramid precipitated fibers is 50-60°SR, and the length of the aramid chopped fibers is 3.0-7.0 mm. Specific proportions can be selected within this range in each embodiment.

[0042] like Figure 2As shown, an apparatus for preparing aramid crepe paper includes: The first temperature zone hot press roller group 1, the second temperature zone hot press roller group 2, the speed difference shearing unit 3, and the cooling and shaping roller 4 are arranged sequentially along the paper's travel direction. The roller surface of the first temperature zone hot press roller group 1 is smooth and is used to perform hot pressing pre-densification treatment on aramid base paper. The second temperature zone hot press roller group 2 includes at least one pair of hot press rollers with micron-level uneven structures on their surfaces, used to simultaneously perform final hot pressing densification and microstructure imprinting on the pre-densified aramid paper; the hot press rollers in the second temperature zone hot press roller group 2 have the same linear velocity. The second temperature zone hot press roller group 2 is integrated with a vibration auxiliary system. The vibration applied by the vibration auxiliary system is transmitted to the aramid paper in the printing area through the roller surface. The speed difference shearing unit 3 includes at least one pair of smooth hot press rollers with a speed difference, used to apply speed difference shearing to the microstructure imprinted aramid paper to form macroscopic wrinkles; The cooling and shaping roller 4 is used to cool and shape the aramid paper processed by the speed difference shearing unit 3.

[0043] Specifically, the first temperature zone hot press roller group 1 and the second temperature zone hot press roller group 2 are equipped with an infrared radiation heater 5 and a temperature sensor 6. The infrared radiation heater 5 heats the paper, and the temperature sensor 6 detects the surface temperature of the paper. The temperature sensor 6 is electrically connected to the infrared radiation heater 5, and a temperature closed-loop control is formed between the temperature sensor 6 and the infrared radiation heater 5 to achieve control of the paper surface temperature.

[0044] Specifically, the vibration assistance system applies high-frequency micro-amplitude vibration to the hot press roller in the second temperature zone through a piezoelectric vibrator 7, and the piezoelectric vibrator 7 is provided with a water-cooled jacket or a heat insulation layer.

[0045] Specifically, the smooth hot press roller with speed difference in the speed difference shearing unit 3 is electrically connected to the speed difference control system, which is used to control the linear speed difference between the two rollers in the pair of hot press rollers.

[0046] An application of aramid crepe paper, wherein the aramid crepe paper is used in oil-immersed transformers, reactors, motors or high-temperature electrical insulation components.

[0047] Example 1: Preparation of aramid crepe paper.

[0048] A method for preparing aramid crepe paper is as follows: Along the continuous travel direction of the paper, aramid base paper sequentially passes through a first temperature zone, a second temperature zone, a speed difference shearing unit, and a cooling and shaping roller to obtain aramid crepe paper. The paper is heated between the first and second temperature zones using an infrared radiation heater. A vibration-assisted system is installed in the second temperature zone to apply high-frequency micro-amplitude vibration to the aramid paper passing through it. The specific process conditions involved in the preparation are as follows.

[0049] Aramid base paper: By weight, the raw material composition is 60 parts precipitated fiber (freezing degree 52°) and 40 parts chopped fiber (2D 5mm).

[0050] First temperature zone: temperature 220℃, linear pressure 50 kN / m, linear speed 10 m / min (same for both rollers).

[0051] Temperature transition: Infrared heating closed-loop control ensures that the temperature difference between the paper surface before entering the second temperature zone and the roller surface temperature in the second temperature zone is ≤15℃.

[0052] Second temperature zone: temperature 280℃, linear pressure 120 kN / m; concave-convex structure depth 80 micrometers, density 100 pieces / 10cm, shape is sine wave; hot press roller linear speed 10 m / min (same for both rollers); dual frequency composite: f1=15kHz, f2=35kHz, applied simultaneously.

[0053] Speed ​​difference shearing unit: smooth hot press roller, v1=10m / min, v2=18m / min, Δv=8m / min, tension 10 N / cm.

[0054] Cooling and shaping: Aramid crepe paper is obtained by cooling through conventional cooling and shaping rollers.

[0055] Example 2: Preparation of aramid crepe paper.

[0056] A method for preparing aramid crepe paper is as follows: Along the continuous travel direction of the paper, aramid base paper sequentially passes through a first temperature zone, a second temperature zone, a speed difference shearing unit, and a cooling and shaping roller to obtain aramid crepe paper. The paper is heated between the first and second temperature zones using an infrared radiation heater. A vibration-assisted system is installed in the second temperature zone to apply high-frequency micro-amplitude vibration to the aramid paper passing through it. The specific process conditions involved in the preparation are as follows.

[0057] Aramid base paper: 50 parts precipitated fiber (beating degree 50°), 50 parts chopped fiber (2D 5mm).

[0058] First temperature zone: temperature 240℃, linear pressure 60 kN / m, hot press roller linear speed 12 m / min (same for both rollers).

[0059] Temperature transition: Infrared heating closed-loop control ensures that the temperature difference between the paper surface before entering the second temperature zone and the roller surface temperature in the second temperature zone is ≤15℃.

[0060] Second temperature zone: temperature 290℃, linear pressure 140 kN / m; concave-convex structure depth 120 micrometers, density 200 pieces / 10cm, shape is sawtooth wave; hot press roller linear speed 12 m / min (same for both rollers); dual frequency composite: f1=18kHz, f2=45kHz, applied simultaneously.

[0061] Speed ​​difference shearing unit: smooth hot press roller, v1=12m / min, v2=20m / min, Δv=8m / min, tension 12 N / cm.

[0062] Cooling and shaping: Aramid crepe paper is obtained by cooling through conventional cooling and shaping rollers.

[0063] Example 3: Preparation of aramid crepe paper.

[0064] A method for preparing aramid crepe paper is as follows: Along the continuous travel direction of the paper, aramid base paper sequentially passes through a first temperature zone, a second temperature zone, a speed difference shearing unit, and a cooling and shaping roller to obtain aramid crepe paper. The paper is heated between the first and second temperature zones using an infrared radiation heater. A vibration-assisted system is installed in the second temperature zone to apply high-frequency micro-amplitude vibration to the aramid paper passing through it. The specific process conditions involved in the preparation are as follows.

[0065] Aramid base paper: 40 parts precipitated fiber (freezing degree 51°), 60 parts chopped fiber (1.8D 6mm).

[0066] First temperature zone: temperature 200℃, linear pressure 30 kN / m; hot press roller linear speed 15 m / min (same for both rollers).

[0067] Temperature transition: Infrared heating closed-loop control ensures that the temperature difference between the paper surface before entering the second temperature zone and the roller surface temperature in the second temperature zone is ≤30℃.

[0068] Second temperature zone: temperature 260℃, linear pressure 100 kN / m; concave-convex structure depth 20 micrometers, density 250 pieces / 10cm, shape is sawtooth wave; hot press roller linear speed 15 m / min (both rollers are the same); dual frequency composite: f1=10kHz, f2=30kHz, applied simultaneously.

[0069] Speed ​​difference shearing unit: smooth hot press roller, v1=15m / min, v2=20m / min, Δv=5m / min, tension 8 N / cm.

[0070] Cooling and shaping: Aramid crepe paper is obtained by cooling through conventional cooling and shaping rollers.

[0071] Example 4: Preparation of aramid crepe paper.

[0072] A method for preparing aramid crepe paper is as follows: Along the continuous travel direction of the paper, aramid base paper sequentially passes through a first temperature zone, a second temperature zone, a speed difference shearing unit, and a cooling and shaping roller to obtain aramid crepe paper. The paper is heated between the first and second temperature zones using an infrared radiation heater. A vibration-assisted system is installed in the second temperature zone to apply high-frequency micro-amplitude vibration to the aramid paper passing through it. The specific process conditions involved in the preparation are as follows.

[0073] Aramid base paper: 80 parts precipitated fiber (freezing degree 60°SR), 20 parts chopped fiber (length 3.0mm).

[0074] First temperature zone: temperature 260℃, linear pressure 80 kN / m; hot press roller linear speed 5 m / min (same for both rollers).

[0075] Temperature transition: Infrared heating closed-loop control ensures that the temperature difference between the paper surface before entering the second temperature zone and the roller surface temperature in the second temperature zone is ≤15℃.

[0076] Second temperature zone: temperature 300℃, linear pressure 150 kN / m; concave-convex structure depth 150 micrometers, density 30 pieces / 10cm, shape is sine wave; hot press roller linear speed 5 m / min (both rollers are the same); dual frequency composite: f1=20kHz, f2=50kHz, applied simultaneously.

[0077] Speed ​​difference shearing unit: smooth hot press roller, v1=5m / min, v2=15m / min, Δv=10m / min, tension 15 N / cm.

[0078] Cooling and shaping: Aramid crepe paper is obtained by cooling through conventional cooling and shaping rollers.

[0079] Comparative Example 1: Preparation of aramid crepe paper using the traditional two-step method.

[0080] Aramid crepe paper is prepared using a traditional two-step process of "hot pressing followed by creping". The specific preparation method is as follows: Step 1: Hot pressing densification: Using a smooth hot press roller assembly at a temperature of 280℃, a linear pressure of 120 kN / m, and a linear speed of 10 m / min, aramid base paper of the same composition (60 parts precipitated fiber, freeness 52°; 40 parts chopped fiber, 2D 5mm) was subjected to hot pressing densification treatment to obtain densified aramid paper. The hot-pressed paper was then allowed to cool naturally to room temperature (ambient temperature 25℃) in air and wound into rolls.

[0081] Step 2, Independent Wrinkling: After unwinding the densified aramid paper roll obtained in the first step, it is continuously passed through a preheating oven at a linear speed of 10 m / min, so that the surface temperature of the paper is uniformly raised to 220°C before entering the creping roller group. It is then fed into a separate creping device, which includes a pair of smooth hot press rollers, with the temperature controlled at 220°C. The upper roller has a linear speed of 10 m / min, the lower roller has a linear speed of 18 m / min, and the speed difference Δv = 8 m / min. No vibration assistance is applied during the creping process. It is particularly important to emphasize that: ① the surface of the hot press rollers in this separate creping device is smooth (without micron-level unevenness); ② no form of vibration assistance is applied during the creping process; ③ the entire unwinding, preheating, and creping process uses industrially standard constant tension control (the tension value is set to the same as the set tension of the speed difference shearing unit in Example 1). Immediately after creping, it is cooled and shaped using the same cooling and shaping rollers as in Example 1 to obtain aramid crepe paper.

[0082] Comparative Example 2: Preparation of aramid crepe paper.

[0083] The same equipment process as in Example 1 was used (i.e., sequentially passing through the first temperature zone, the second temperature zone, the speed difference shearing unit, and the cooling and shaping roller), but the vibration auxiliary system of the second temperature zone was turned off, and the remaining process parameters were the same as in Example 1.

[0084] Composition and basis weight of aramid base paper: same as in Example 1.

[0085] The prepared aramid crepe paper was tested using the same method, and the results are shown in Table 1 below.

[0086] Comparative Example 3: Preparation of aramid crepe paper.

[0087] Comparative Example 3 (microstructure imprinting and speed differential shearing integrated into the same pair of rollers, without functional separation) uses the same equipment flow and process parameters as Example 1, but modifies the operation method of the second temperature zone hot press roller group, specifically: A speed difference is set between a pair of hot press rollers with micron-level concave and convex structures in the second temperature zone: the linear speed of the upper roller v1 = 10 m / min, the linear speed of the lower roller v2 = 18 m / min, and the speed difference Δv = 8 m / min (the same as Δv of the speed difference shearing unit in Example 1).

[0088] At the same time, the subsequent independent speed difference shearing unit is shut down (making it inactive, and the paper passes directly through), meaning that macroscopic wrinkling is entirely completed by the differential speed convex and concave rollers in the second temperature zone.

[0089] All other parameters (temperature, pressure, vibration frequency, dual-frequency composite mode, cooling and shaping, etc.) are exactly the same as in Example 1.

[0090] The prepared aramid crepe paper was tested using the same method, and the results are shown in Table 1 below.

[0091] Comparative Example 4: Preparation of aramid crepe paper.

[0092] The process, equipment, and parameters were exactly the same as in Example 1, but the frequency mode of the vibration-assisted system was modified: the dual-frequency composite (f1=15kHz, f2=35kHz applied simultaneously) was changed to single-frequency vibration, with the frequency set to 35kHz and the amplitude remaining at 5μm. All other parameters were exactly the same as in Example 1.

[0093] The prepared aramid crepe paper was tested using the same method, and the results are shown in Table 1 below.

[0094] Comparative Example 4A: Preparation of aramid crepe paper.

[0095] The process flow, equipment, and parameters are exactly the same as in Example 1, but the frequency mode of the vibration-assisted system is modified: f1=15kHz and f2=35kHz in the dual-frequency composite are changed to f1=5kHz and f2=8kHz. All other parameters are exactly the same as in Example 1.

[0096] Comparative Example 4B: Preparation of aramid crepe paper.

[0097] The process flow, equipment, and parameters are exactly the same as in Example 1, but the frequency mode of the vibration-assisted system is modified: in the dual-frequency composite, f1=15kHz and f2=35kHz are changed to f1=15kHz and f2=10kHz. All other parameters are exactly the same as in Example 1.

[0098] Comparative Example 4C: Preparation of aramid crepe paper.

[0099] The process, equipment, and parameters are exactly the same as in Example 1, but the first vibration frequency f1 of the dual-frequency composite vibration is increased from 15kHz to 25kHz, and the second vibration frequency f2 is increased from 35kHz to 60kHz (both higher than the upper limits of 20kHz and 50kHz specified in this invention). All other parameters are exactly the same as in Example 1.

[0100] Comparative Example 5: Preparation of aramid crepe paper.

[0101] The process and equipment are exactly the same as in Example 1, but the infrared radiation heater and temperature closed-loop control system between the first and second temperature zones are turned off, and no active heating compensation is applied to the paper. All other parameters are exactly the same as in Example 1.

[0102] Because the paper loses heat during its natural transmission in the air after being output from the first temperature zone, the measured surface temperature when it enters the second temperature zone is 200℃, while the surface temperature of the hot press roller in the second temperature zone remains at 280℃, resulting in a temperature difference of 80℃, which is more than 30℃.

[0103] Comparative Example 6: Preparation of aramid crepe paper.

[0104] The process flow, equipment, and parameters are exactly the same as in Example 1, but the speed difference of the speed difference shearing unit is modified: Δv=8 m / min is changed to Δv=3 m / min. All other parameters are exactly the same as in Example 1.

[0105] The prepared aramid crepe paper was tested using the same method, and the results are shown in Table 1 below.

[0106] Comparative Example 7: Preparation of aramid crepe paper.

[0107] The process flow, equipment, and parameters are exactly the same as in Example 1, but the speed difference of the speed difference shearing unit is modified: Δv=8 m / min is changed to Δv=15 m / min. All other parameters are exactly the same as in Example 1.

[0108] The prepared aramid crepe paper was tested using the same method, and the results are shown in Table 1 below.

[0109] Comparative Example 8: Preparation of aramid crepe paper.

[0110] The process flow, equipment, and parameters were exactly the same as in Example 1, but the temperature of the first temperature zone was changed from 220°C to 180°C. All other parameters were exactly the same as in Example 1.

[0111] The prepared aramid crepe paper was tested using the same method, and the results are shown in Table 1 below.

[0112] Comparative Example 9: Preparation of aramid crepe paper.

[0113] The process flow, equipment, and parameters were exactly the same as in Example 1, but the temperature of the first temperature zone was changed from 220°C to 280°C. All other parameters were exactly the same as in Example 1.

[0114] The prepared aramid crepe paper was tested using the same method, and the results are shown in Table 1 below.

[0115] Comparative Example 10: Preparation of aramid crepe paper.

[0116] The process flow, equipment, and parameters were exactly the same as in Example 1, but the temperature of the second temperature zone was changed from 280°C to 240°C. All other parameters were exactly the same as in Example 1.

[0117] The prepared aramid crepe paper was tested using the same method, and the results are shown in Table 1 below.

[0118] Comparative Example 11: Preparation of aramid crepe paper.

[0119] The process flow, equipment, and parameters were exactly the same as in Example 1, but the temperature of the second temperature zone was changed from 280°C to 320°C. All other parameters were exactly the same as in Example 1.

[0120] The prepared aramid crepe paper was tested using the same method, and the results are shown in Table 1 below.

[0121] Comparative Example 12: Preparation of aramid crepe paper.

[0122] The process, equipment, and parameters were exactly the same as in Example 1, but the amplitude of the vibration-assisted system was increased from 5 μm to 15 μm (higher than the upper limit of 10 μm specified in this invention). All other parameters were exactly the same as in Example 1.

[0123] The prepared aramid crepe paper was tested using the same method, and the results are shown in Table 1 below.

[0124] Test methods: basis weight, thickness, tensile strength, elongation at break, and breakdown voltage were all tested according to JB / T10441.2-2004 Test method for corrugated insulating paper for electrical use.

[0125] Table 1. Performance Test Results of Aramid Crepe Paper

[0126] As shown in the table above, under the same quantitative conditions, the longitudinal tensile strength of Example 1 is 21.6% higher than that of Comparative Example 1, the longitudinal elongation at break is 23.5% higher than that of Comparative Example 1, and the breakdown voltage is 25.5% higher than that of Comparative Example 1. The mechanism is as follows.

[0127] (1) Strength improvement: In Comparative Example 1, after hot pressing, the paper is cooled to room temperature and then heated again to wrinkle. The cooling process generates thermal stress microcracks, and the cracks expand during wrinkling, resulting in a decrease in strength. Example 1 adopts an integrated process, and the paper is always in a high temperature state, which completely avoids thermal stress microcracks; at the same time, the high-frequency vibration of the second temperature zone promotes the mutual diffusion and entanglement of the molecular chains at the fiber interface, realizing "dynamic healing during wrinkling", so that the interface bonding strength surpasses that of traditional processes.

[0128] (2) Improved elongation: Comparative Example 1 only forms random macroscopic wrinkles, with limited deformation capacity. Example 1 first uses a non-speed-difference embossing roller to imprint regular microscopic wrinkles, and then uses subsequent speed-difference shearing to form macroscopic wrinkles, forming a multi-level structure of "microscopic wrinkles + macroscopic wrinkles". During stretching, the microscopic wrinkles unfold first to absorb strain, and the macroscopic wrinkles then provide a large deformation reserve, thus significantly improving the elongation.

[0129] (3) Improved breakdown voltage: In Comparative Example 1, the fibers are randomly arranged, resulting in a short breakdown path in the thickness direction. In Example 1, the high-frequency vibration induces the fibers to align along the paper plane, which is equivalent to extending the breakdown path in the thickness direction; at the same time, the regular micro-folds homogenize the electric field distribution under oil immersion conditions, thereby obtaining a higher breakdown voltage.

[0130] The above results show that the aramid crepe paper prepared by the preparation method of the present invention in Examples 1-4 has excellent comprehensive performance. During the preparation process, the synergistic effect of integrated continuous process, vibration-assisted interface healing, and separation of microstructure and macro wrinkling function has overcome the technical problem of mutual restriction between "strength-elongation-insulation" in traditional process.

[0131] As shown in Table 1, the longitudinal tensile strength, longitudinal elongation at break, and breakdown voltage of Comparative Example 2 are significantly lower than those of Example 1. Although Comparative Example 2 adopts an integrated continuous process, avoiding the thermal stress microcracks caused by cooling-reheating in the traditional two-step method, it does not apply vibration assistance in the second temperature zone. Due to the lack of vibration, the fibers in the second temperature zone cannot effectively overcome the "bridging effect" at the entrance of the microstructure groove, resulting in shallow micro-imprinting depth and poor uniformity. The rough surface formed becomes a point of electric field distortion during subsequent use. At the same time, the fiber-fiber interface fails to form sufficient molecular chain diffusion entanglement under hot pressing, resulting in insufficient interfacial bonding strength. When the paper enters the speed difference shearing unit of the third unit, it directly bears shear force in a high-temperature softened state. The stress preferentially peels off along the weak interface rather than causing uniform deformation of the fiber network as a whole, resulting in severe interface damage. The comparison between Comparative Example 2 and Example 1 shows that simply making hot pressing and wrinkling continuous without the aid of vibration interface healing not only fails to improve performance but also causes more severe performance degradation than the traditional two-step method.

[0132] The longitudinal tensile strength, longitudinal elongation at break, and breakdown voltage of Comparative Example 3 were significantly lower than those of Example 1. In Comparative Example 3, the microstructure imprinting and speed differential shearing were performed simultaneously on the same pair of convex and concave rollers. The horizontal shearing force interfered with the filling of the fibers into the depth of the microstructure grooves, resulting in shallow and uneven microstructure formation and performance that was significantly lower than that of Example 1, which separated functions.

[0133] Comparative Example 4 showed significantly lower longitudinal tensile strength, longitudinal elongation at break, and breakdown voltage compared to Example 1. This indicates that single-frequency vibration cannot replace the synergistic advantages of dual-frequency composite vibration in promoting fiber filling and interface healing.

[0134] Comparative Examples 4A-4C further verified the criticality of the vibration frequency range. In Comparative Example 4A, both frequencies were below 10kHz, and the tensile strength, elongation at break, and breakdown voltage of the paper were significantly worse than those of Example 1. In Comparative Example 4B, f2 was below 30kHz, and the performance also decreased significantly. In Comparative Example 4C, both frequencies were above the upper frequency limit (25kHz / 60kHz) specified in this invention, and the three performance indicators of the aramid crepe paper were all far lower than those of Example 1. The above comparisons show that, under the process conditions of this invention, the vibration frequency needs to be controlled within the range of f1=10-20kHz and f2=30-50kHz, which is more conducive to obtaining aramid crepe paper with excellent overall performance.

[0135] The longitudinal tensile strength, longitudinal elongation at break, and breakdown voltage of Comparative Example 5 were significantly lower than those of Example 1. In Comparative Example 5, the temperature difference between the surface of the paper and the roll surface when the paper entered the second temperature zone exceeded 30°C. This temperature difference led to: firstly, the paper surface was instantaneously heated, which may have induced microcracks; at the same time, insufficient temperature weakened the vibration-assisted interface healing effect, resulting in a decrease in interfacial bonding strength, both of which together led to a significant reduction in tensile strength; secondly, the low core temperature resulted in insufficient fiber plasticity, making it difficult for the fibers to fully flow into the depths of the microstructure grooves, resulting in a shallow and uneven microstructure and a decrease in elongation at break; in addition, poor interfacial bonding and uneven microstructure together led to uneven electric field distribution, and the breakdown voltage also decreased accordingly.

[0136] Compared to Example 1, Comparative Example 6 exhibits significantly lower longitudinal tensile strength, longitudinal elongation at break, and breakdown voltage. The small speed difference in Comparative Example 6 results in insufficient tensile deformation of the paper, preventing the effective formation of macroscopic wrinkles. The paper remains largely flat overall, and the elongation is significantly reduced. Furthermore, the lack of sufficient wrinkles and fiber rearrangement also leads to a decrease in breakdown voltage.

[0137] Compared to Example 1, Comparative Example 7 exhibits significantly lower longitudinal tensile strength, longitudinal elongation at break, and breakdown voltage. In Comparative Example 7, the speed difference Δv = 15 m / min. This excessive speed difference leads to excessive shearing and stretching of the paper in the speed difference shearing unit, causing micro-tears or even fractures at the fiber interface due to excessive stress, resulting in a significant decrease in tensile strength. Simultaneously, excessive stretching disrupts the regular micro-fold structure already formed in the second temperature zone, and fiber fracture prevents effective stress transfer during stretching, leading to a decrease in elongation. Furthermore, mechanical damage and structural defects in the fibers become electric field concentration points, causing a decrease in breakdown voltage.

[0138] Comparative Example 8 reduced the temperature of the first temperature zone to 180°C, which is lower than the lower limit of 200°C for the first temperature zone of this invention. At this time, the aramid fibers were not sufficiently softened, the hot-pressing pre-densification effect was insufficient, and the inter-fiber bonding strength was poor, resulting in tensile strength, elongation at break, and breakdown voltage being lower than those of Example 1.

[0139] Comparative Example 9 raised the temperature of the first temperature zone to 280°C (higher than the upper limit of 260°C), resulting in excessive paper densification, increased fiber network rigidity, and decreased plasticity. Upon entering the second temperature zone, the fibers struggled to fully fill the microstructural grooves, making them prone to microcracks during subsequent differential shearing. Tensile strength, elongation at break, and breakdown voltage were all lower than in Example 1. This demonstrates that the temperature of the first temperature zone needs to be controlled between 200-260°C to avoid excessive densification.

[0140] Comparative Example 10 reduced the temperature of the second temperature zone to 240°C, which is lower than the lower limit of 260°C for the second temperature zone of this invention. The fiber plasticity is insufficient, failing to fully fill the microstructure grooves of the convex and concave rollers, resulting in shallow and irregular microstructure wrinkles; simultaneously, the vibration-assisted effect is weakened, and the elongation at break decreases significantly.

[0141] Comparative Example 11 raised the temperature of the second temperature zone to 320°C, which is higher than the upper limit of 300°C for the second temperature zone of this invention. This resulted in excessive fiber softening, adhesion or collapse during microstructure imprinting, and easy interface damage during subsequent differential shearing. All three properties showed a significant decrease. This demonstrates that the temperature of the second temperature zone must be strictly limited to 260-300°C.

[0142] Comparative Example 12 increased the amplitude to 15 μm, exceeding the upper limit of 10 μm of this invention. Excessive amplitude caused excessive misalignment of the fiber network, disrupting the existing inter-fiber bonds. It also led to inaccurate fiber positioning during microstructure imprinting, decreased wrinkle regularity, and lower tensile strength, elongation at break, and breakdown voltage compared to Example 1. This demonstrates that the amplitude needs to be controlled within the range of 1-10 μm.

[0143] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are exhaustively listed. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0144] For those skilled in the art, various modifications and improvements can be made without departing from the concept of the present invention, and these modifications and improvements are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the appended claims.

Claims

1. A method for preparing aramid crepe paper, characterized in that, The preparation method is as follows: The aramid base paper is fed into the processing unit group, which is provided with a first temperature zone, a second temperature zone and a speed difference shearing unit in sequence along the continuous travel direction of the paper. The aramid base paper is first subjected to hot pressing pre-densification treatment in the first temperature zone to obtain pre-densified aramid paper; The pre-densified aramid paper undergoes final hot-press densification and microstructure imprinting simultaneously in the second temperature zone, and vibration-assisted treatment is provided in the second temperature zone to form microstructure wrinkles on the surface of the aramid paper. The aramid paper after microstructure imprinting is fed into the speed difference shearing unit for speed difference shearing, so that the aramid paper as a whole forms macroscopic wrinkles. Finally, after cooling and shaping, the aramid crepe paper is obtained.

2. The method for preparing aramid crepe paper according to claim 1, characterized in that, The surface of the hot press roller in the first temperature zone is smooth, the temperature is 200-260℃, and the linear pressure is 30-80 kN / m. The temperature in the second temperature zone is 260-300℃, and the linear pressure is 100-150 kN / m.

3. The method for preparing aramid crepe paper according to claim 1, characterized in that, The aramid paper is heated between the first and second temperature zones so that the surface temperature of the aramid paper when it enters the second temperature zone is no more than 30°C different from the surface temperature of the hot press roller in the second temperature zone.

4. The method for preparing aramid crepe paper according to claim 1, characterized in that, The second temperature zone is provided with at least one pair of hot press rollers, and the surface of the at least one pair of hot press rollers in the second temperature zone is provided with a micron-level concave-convex structure; the depth of the micron-level concave-convex structure is 20-150 microns, and the concave-convex density is 30-250 per 10cm.

5. The method for preparing aramid crepe paper according to claim 1, characterized in that, The second temperature zone is equipped with a vibration-assisted system to apply high-frequency micro-amplitude vibration to the aramid paper passing through the second temperature zone; the vibration frequency is 10-50kHz and the amplitude is 1-10μm. The vibration-assisted system adopts a dual-frequency composite vibration mode, including: a first vibration frequency f1 of 10-20kHz and a second vibration frequency f2 of 30-50kHz; f1 and f2 are applied simultaneously.

6. The method for preparing aramid crepe paper according to claim 1, characterized in that, At least one pair of hot press rollers used in the speed difference shearing process have a speed difference, and the linear velocities of the two rollers with the speed difference are v1 and v2, respectively. The speed difference Δv =|v1 - v2|, and Δv is 5-10 m / min. The running tension of the aramid paper in the speed difference shearing unit is controlled at 5-20 N / cm.

7. An apparatus for preparing aramid crepe paper, characterized in that, The preparation apparatus includes: The first temperature zone hot press roller group, the second temperature zone hot press roller group, the speed difference shearing unit, and the cooling and shaping roller are arranged sequentially along the paper's travel direction. The first temperature zone hot press roller group has a smooth roller surface and is used to perform hot pressing pre-densification treatment on aramid base paper. The second temperature zone hot press roller group includes at least one pair of hot press rollers with micron-level uneven surfaces, used to simultaneously perform final hot pressing densification and microstructure imprinting on pre-densified aramid paper; the hot press rollers in the second temperature zone hot press roller group have the same linear velocity; The second temperature zone hot press roller group is integrated with a vibration assist system. The vibration applied by the vibration assist system is transmitted to the aramid paper in the printing area through the roller surface. The speed difference shearing unit includes at least one pair of smooth hot press rollers with a speed difference, used to apply speed difference shearing to the microstructure imprinted aramid paper to form macroscopic wrinkles; The cooling and shaping roller is used to cool and shape the aramid paper processed by the speed difference shearing unit.

8. The apparatus for preparing aramid crepe paper according to claim 7, characterized in that, The vibration-assisted system applies high-frequency micro-amplitude vibration to the hot press roller in the second temperature zone through a piezoelectric vibrator, which is equipped with a water-cooled jacket or a heat insulation layer.

9. The apparatus for preparing aramid crepe paper according to claim 7, characterized in that, The smooth hot press roller with speed difference in the speed difference shearing unit is electrically connected to the speed difference control system. The speed difference control system is used to control the linear speed difference between the two rollers in the pair of hot press rollers.

10. An application of the aramid crepe paper prepared by the method according to any one of claims 1-6, characterized in that, The aramid crepe paper is used in oil-immersed transformers, reactors, motors, or electrical insulation components.

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