Method for preparing meta-aramid ultrafine fibers, method for preparing meta-aramid composite paper, and application thereof

Abstract

The present invention relates to the technical field of fiber composite materials, and particularly relates to a preparation method of meta-aramid ultrafine fibers, a preparation method of meta-aramid composite paper, and an application thereof. The preparation method of the meta-aramid ultrafine fibers is as follows: meta-aramid and a solvent are mixed uniformly under heating and pressurization conditions to obtain a spinning solution, and the spinning solution is ejected through a spinneret of a flash spinning device, and the solvent in the spinning solution evaporates rapidly to obtain meta-aramid ultrafine fibers. The preparation method of the meta-aramid composite paper is as follows: the meta-aramid ultrafine fibers are evenly laid, cold-pressed and hot-pressed to obtain a meta-aramid ultrafine fiber sheet, and the meta-aramid ultrafine fiber sheet is used as the surface layer and the bottom layer, and meta-aramid film and meta-aramid paper are used as the core layer, and after being laminated and compounded in the order of the surface layer, the core layer and the bottom layer, hot pressing treatment is carried out to obtain the meta-aramid composite paper. The meta-aramid composite paper has excellent bonding strength, electrical insulation performance and mechanical properties.

Description

Technical Field

[0001] The present invention relates to a method for preparing meta-aramid ultrafine fibers, a method for preparing meta-aramid composite paper, and applications thereof, belonging to the technical field of fiber composite materials. Background Art

[0002] Meta-aramid is a high-temperature resistant fiber variety that has been developed early, widely used, produced in large quantities, and developed rapidly. The flame retardant grade of meta-aramid is VTM-0, and it can be used at 180°C for a long time, belonging to Class C insulating materials.

[0003] At present, aramid fibers are prepared by dry spinning, wet spinning, dry-jet wet spinning or electrospinning technology of aramid solutions. The fiber diameters are uniform, and the cross-sections of the fibers are regular shapes such as circular, oval, cashew-shaped, and broad bean-shaped according to the size of the spinneret. The bite force between the regular-shaped fibers is poor, and the fiber diameter > 5um, so it is impossible to directly prepare a structurally dense meta-aramid paper using long fibers.

[0004] Aramid paper uses aramid pulp fibers and aramid short cut fibers as raw materials, and is formed by wet papermaking and hot pressing. It has excellent mechanical properties and insulating properties, and can be used as insulating materials, honeycomb core materials, and composite materials. However, the short fibers inside the aramid paper will have surface fuzzing and hair loss phenomena when subjected to friction during use. When the thick paper is subjected to alternating loads, it is easy to have delamination or blistering phenomena. The low surface strength and interlayer bonding strength limit the application of aramid paper in high-end fields such as aerospace, rail transit, and national defense and military industries.

[0005] In order to improve the bonding strength of aramid fibers, a one-time high-temperature hot pressing composite molding method is adopted in Chinese Patent Application No. CN110886145A to improve the bonding force between fibers. However, the aramid fibers are severely plasticized at high temperatures, resulting in a decrease in the tearing performance of aramid paper, a low thermal conductivity of aramid, poor bonding of thick paper, and easy delamination. In Chinese Patent Application CN111235944A, aramid nanofibers are used to improve the bonding force of aramid paper. However, the aramid nanofibers prepared by the phase conversion method are small in size, poor in evenness, complex in method, and difficult to industrialize. In Chinese Patent Application CN112746522A, the bonding force of aramid fibers is improved by adding glue, but the adhesive causes a decrease in the insulation performance and heat resistance of aramid paper. In Chinese Patent Application CN207765231U, an H-class insulation composite material is prepared by laminating aramid paper and polyester film, etc., which can improve the voltage resistance and corona resistance of the composite material and is applied to new energy vehicles. In Chinese Patent Application CN106531374A, a flame-retardant insulation composite material is prepared by laminating aramid paper and polyimide film, etc., which can improve the high-temperature resistance and flame-retardant performance of the composite material and is applied to transformers of various frequencies. However, these methods introduce powders or film materials of different materials into aramid paper, and the interfacial effects of different materials result in weak interfacial bonding forces between the two materials, which are prone to delamination and blistering during long-term use. Therefore, it is of great value to develop a meta-aramid composite paper with high bonding force and its preparation method.

[0006] The present invention first prepares meta-aramid ultrafine fibers by the flash spinning method, combines the meta-aramid ultrafine fibers, meta-aramid film and meta-aramid paper to prepare a meta-aramid composite paper with 100% aramid composition. The method provided by the present invention has the characteristics of simple operation, no use of adhesives, strong material bonding force, etc., and solves the problems of fluffing, delamination and blistering on the surface of aramid paper. The aramid composite paper produced by the present invention has the characteristics of high surface strength, high dielectric strength, high tearing degree, high modulus, corona resistance, inherent flame retardancy, high temperature resistance, simple operation and low cost, and can be used in insulation packaging, honeycomb core materials, composite material reinforcement, building fire protection fields, new energy vehicle drive motors, offshore wind power, large oil-immersed transformers, oil-cooled motor fields. Summary of the Invention

[0007] Aiming at the deficiencies of the existing technology, the present invention provides a method for preparing meta-aramid ultrafine fibers, a method for preparing meta-aramid composite paper and its application. The meta-aramid ultrafine fibers are prepared by the flash spinning technology, and the meta-aramid ultrafine fiber sheet, meta-aramid film and meta-aramid paper are combined to prepare the meta-aramid composite paper. The meta-aramid composite paper has the characteristics of high surface strength, high dielectric strength, high tearing degree, high modulus, corona resistance, inherent flame retardancy, high temperature resistance, simple operation and low cost, and solves the problems of fluffing, delamination and blistering on the surface of conventional aramid paper.

[0008] The technical solution of the present invention to solve the above technical problems is as follows: A preparation method of meta-aramid ultrafine fibers, wherein the preparation method of the meta-aramid ultrafine fibers is: mixing meta-aramid and a solvent uniformly under heating and pressurization conditions to obtain a spinning solution, and the spinning solution is ejected through a spinneret of a flash spinning device, and hot nitrogen is continuously introduced around the spinneret, and the solvent in the spinning solution evaporates rapidly to obtain meta-aramid ultrafine fibers.

[0009] Further, the heating condition is 100 - 300 °C, the pressurization condition is 1 - 30 Mpa, the stirring condition is 20 - 500 r / min, and the stirring time is 1 - 2.5 hours.

[0010] Further, the solvent is one or several of n-butane, n-pentane, cyclopentane, n-hexane, n-heptane, n-octane, benzene, toluene, trichlorofluoromethane, dichloromethane, carbon tetrachloride, dichloroethylene, chloroform, chloroethane, dichloroethane, chloromethane, hexafluoroisopropanol, dichloroacetic acid, 1,2,3-trichlorobenzene, nitromethane, carbon dioxide, sulfur dioxide, carbon disulfide, ammonia, water, nitrogen, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, concentrated sulfuric acid, acetone, ethylene carbonate, pyridine, acetonitrile, tetrahydrofuran, 2,2,2-trifluoro-N,N-dimethylacetamide, caprolactam, 2,6-difluorobenzamide, 2,5-difluorobenzamide, 2-methyltetrahydrofuran, dimethyl carbonate.

[0011] Further, the mass concentration of meta-aramid in the spinning solution is 1 - 30 wt%, the viscosity of the spinning solution is 10 - 4000 poise, the aperture of the spinneret is 1 - 5.0 mm, the diameter of the fiber is 0.01 - 20 μm, the spinning speed is 5 - 20 km / min, and the temperature of the hot nitrogen is 50 - 500 °C.

[0012] The present invention also discloses a preparation method of meta-aramid composite paper: uniformly arranging, separating, laying, cold pressing, and hot pressing the meta-aramid ultrafine fibers to obtain a meta-aramid ultrafine fiber sheet, using the meta-aramid ultrafine fiber sheet as the surface layer and the bottom layer, using the meta-aramid film and the meta-aramid paper as the core layer, laminating and compounding in the order of the surface layer, the core layer, and the bottom layer, and then performing hot pressing treatment to obtain the meta-aramid composite paper.

[0013] Further, the preparation method of the meta-aramid film is: under room temperature and nitrogen drying environment, under stirring conditions, isophthaloyl chloride and m-phenylenediamine are subjected to a polymerization reaction in DMAc. After the reaction ends, the polymerization solution is obtained through neutralization and filtration, and the polymerization solution forms a film, and is dried in multiple stages and corona treated to obtain the meta-aramid film.

[0014] Further, the preparation method of the meta-aramid paper is as follows: Pulp the meta-aramid short cut fibers and the meta-aramid precipitated fibers respectively. After mixing the two slurries, obtain the meta-aramid base paper through papermaking, pressing, and drying. The meta-aramid base paper is obtained through hot pressing treatment and corona treatment to obtain the meta-aramid paper;

[0015] The crystallinity of the meta-aramid short cut fibers is 10-40%, the profiled degree of the meta-aramid short cut fibers > 10%, and the cross-section of the meta-aramid short cut fibers is one or more of circular, spindle-shaped, cashew-shaped, cross-shaped, and triangular; The meta-aramid precipitated fibers adopt a low-temperature precipitation process at -5°C to 10°C, and the crystallinity of the meta-aramid precipitated fibers is 5-15%.

[0016] Further, when preparing the meta-aramid ultrafine fiber sheet, the fiber splitting includes disk fiber laying, electrostatic fiber splitting, and slit air flow fiber splitting; The line pressure of the cold pressing is 0-100 N / mm, the lower roll of the pressing roller is a metal roll, and the upper roll is a soft roll doped with conductive fibers or a metal roll; The hot pressing temperature is 150°C to 300°C, the line pressure is 10-100 N / mm, the roll speed is 1-40 m / min, the number of hot pressing times is 1-3 times, the hot pressing roller is a metal roll and a soft roll or a metal roll and a metal roll, and the Shore hardness of the soft roll is D70-100.

[0017] The lamination and compounding is to unwind the meta-aramid ultrafine fiber sheet, the meta-aramid paper, and the meta-aramid film simultaneously according to multi-station unwinding, and then enter the nip of the hot rolling roll of the roller type hot press after guiding the paper at the same time; The temperature of the hot pressing treatment is 250°C to 330°C, the line pressure is 100-200 kN / m, the roll speed is 1-20 m / min, and the number of hot pressing times is 1-3 times.

[0018] Further, the fiber diameter of the meta-aramid ultrafine fiber is 0.01-3 μm, and the fiber strength is 5-30 g / d;

[0019] The crystallinity of the meta-aramid film is 10-40%, corona treat both surfaces, and the surface energy after corona treatment is 50-100 mN / m, and the basis weight is 5-100 g / m 2 ;

[0020] The basis weight of the meta-aramid ultrafine fiber sheet is 5-100 g / m 2 , the thickness of the meta-aramid composite paper is 0.025-0.76 mm, and the meta-aramid composite paper is composed of 100% meta-aramid.

[0021] In the present invention, the fiber laying is multi-faceted conical frustum fiber laying, and the fiber splitting is electrostatic fiber splitting, slit air flow fiber splitting, and air flow shaking fiber splitting.

[0022] The present invention also discloses the application of the meta-aramid composite paper, characterized in that the meta-aramid composite paper is applied to the fields of insulation packaging, honeycomb core materials, composite material reinforcement, building fire prevention, new energy vehicle drive motors, offshore wind power, large oil-immersed transformers, and oil-cooled motor fields.

[0023] The beneficial effects of the present invention are as follows:

[0024] (1) The present invention prepares meta-aramid ultrafine fibers by the flash spinning method. The meta-aramid ultrafine fibers are composed of a continuous long fiber bundle of porous spider-web-like fibers, and the fiber cross-section is irregular. The diameter of the prepared meta-aramid ultrafine fibers is 0.01 - 20 μm, and the fiber strength is 5 - 30 g / d. The meta-aramid ultrafine fibers have the characteristics of large specific surface area, inherent flame retardancy, high temperature resistance, high strength and high modulus, and resistance to acids, alkalis, salts, and organic solvents, and can be applied to the fields of insulation packaging, honeycomb core materials, composite material reinforcement, building fire prevention, new energy vehicle drive motors, offshore wind power, large oil-immersed transformers, and oil-cooled motor fields.

[0025] The conventional preparation methods of meta-aramid fibers are dry spinning, wet spinning, dry-jet wet spinning, or electrospinning. The meta-aramid fibers prepared by these methods have a uniform diameter, and the fiber cross-section is in regular shapes such as circular, oval, cashew-shaped, and broad-bean-shaped according to the spinneret size. The fiber diameter > 5 μm, the fibers are smooth, and the bite force between the fibers is poor. The long fibers prepared by the conventional spinning method cannot directly prepare an aramid paper with a dense structure. However, the flash spinning method prepares a bundle of ultrafine fiber reticulated filaments with a diameter of 0.01 - 20 μm and a fiber strength of 5 - 30 g / d. Under the action of rapid solvent volatilization and high-speed air flow stretching, the fiber thickness is uneven, and the cross-section of the fiber is irregular. The irregular diameter results in a very high bite force between the fibers. When using the flash-spun meta-aramid ultrafine fiber filaments to prepare sheet materials or paper-based materials, the long fibers do not need to be cut. The continuous long fibers are formed into a sheet with a uniform and dense structure after fiber laying, fiber opening, web laying, cold pressing, and hot pressing. The fibers inside the sheet composed entirely of long fibers bite each other, and there are no hair filaments or broken filaments on the sheet surface, effectively solving the problem of fluffing and fuzzing caused by short-cut fibers on the surface of conventional aramid paper. The surface strength of the meta-aramid composite paper can reach 23A.

[0026] (2) The present invention controls the temperature of the precipitating agent during the formation of the precipitated fibers of the meta-aramid paper, reduces the crystallinity of the precipitated fibers, and the meta-aramid molecular chains in the precipitated fibers remain in an amorphous state. When hot pressing and compounding above the glass transition temperature of the meta-aramid, the molecular chain segments of the low-crystallinity precipitated fibers move when heated, and the precipitated fibers undergo micro-melting to produce an adhesive effect, retaining the porous characteristics of the meta-aramid paper while having a high interlayer bonding strength.

[0027] (3) The meta-aramid ultrafine fiber sheet of the present invention uses 100% meta-aramid as raw material and is prepared by flash spinning technology. Compared with the high-density polyethylene fiber and non-woven fabric prepared by traditional flash spinning, the meta-aramid ultrafine fiber sheet has the characteristics of inherent flame retardancy (limiting oxygen index 28%), high temperature resistance (long-term use temperature 180 °C), good insulation performance (insulation class VTM-0 or V-0), and solvent resistance.

[0028] (4) There is a meta-aramid film inside the meta-aramid composite paper of the present invention. The meta-aramid film effectively improves the compactness of the paper-based material and effectively improves the compressive strength of the meta-aramid composite paper.

[0029] (5) The meta-aramid composite paper of the present invention is composed of 100% pure aramid. The meta-aramid film and meta-aramid paper are subjected to surface corona treatment, resulting in increased surface roughness and surface energy, and being in an activated state. The same-component fibers are hot-pressed and compounded, and the molecular chain segments at the two-phase interface of the fibers have strong binding force, effectively improving the interlayer bonding strength, tensile strength, and tearing degree of the meta-aramid composite paper. It combines the excellent characteristics of three materials: meta-aramid ultrafine fibers, meta-aramid films, and meta-aramid papers. The meta-aramid composite paper has excellent bonding force, electrical insulation performance, and mechanical properties. The meta-aramid composite paper has the characteristics of good insulation performance, inherent flame retardancy, light weight and high strength, high temperature resistance, and resistance to acids, alkalis, salts, and organic solvents, and can be widely used in the fields of insulation, honeycomb core materials, and composite material reinforcement. Specifically, it can be used in the fields of new energy vehicle drive motors, offshore wind power, large oil-immersed transformers, oil-cooled motors, honeycomb core materials, etc. Description of the Drawings

[0030] Figure 1 Schematic structural diagram of the meta-aramid composite paper of Example 1, Example 2, and Example 7;

[0031] Figure 2 Schematic structural diagram of the meta-aramid composite paper of Example 3.

[0032] Figure 3 Optical microscope photograph of the meta-aramid ultrafine fiber prepared in Example 1. Detailed Description of the Invention

[0033] The following makes a detailed description of the specific embodiments of the present invention. The present invention can be implemented in many other ways different from those described herein. Those skilled in the art can make similar improvements without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The terms used are only for describing specific embodiments and do not limit the present invention.

[0035] A preparation method of meta-aramid ultrafine fibers, the preparation method of the meta-aramid ultrafine fibers is as follows: adding meta-aramid and a solvent into an autoclave, mixing evenly under heating, pressurization and stirring conditions to obtain a spinning solution, spraying the spinning solution through a spinneret of a flash spinning device, continuously introducing hot nitrogen gas around the spinneret, and rapidly evaporating the solvent in the spinning solution to obtain meta-aramid ultrafine fibers.

[0036] Specifically, the heating condition is 100 - 300 °C, the pressurization condition is 1 - 30 Mpa, the stirring condition is 20 - 500 r / min, and the stirring time is 1 - 2.5 hours.

[0037] Specifically, the solvent is one or several of n-butane, n-pentane, cyclopentane, n-hexane, n-heptane, n-octane, benzene, toluene, trichlorofluoromethane, dichloromethane, carbon tetrachloride, dichloroethylene, chloroform, chloroethane, dichloroethane, chloromethane, hexafluoroisopropanol, dichloroacetic acid, 1,2,3-trichlorobenzene, nitromethane, carbon dioxide, sulfur dioxide, carbon disulfide, ammonia, water, nitrogen, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, concentrated sulfuric acid, acetone, ethylene carbonate, pyridine, acetonitrile, tetrahydrofuran, 2,2,2-trifluoro-N,N-dimethylacetamide, caprolactam, 2,6-difluorobenzamide, 2,5-difluorobenzamide, 2-methyltetrahydrofuran, dimethyl carbonate.

[0038] Specifically, the mass concentration of meta-aramid in the spinning solution is 1 - 30 wt%, the viscosity of the spinning solution is 10 - 4000 poise, the aperture of the spinneret is 1 - 5.0 mm, the diameter of the fiber is 0.01 - 20 μm, the spinning speed is 5 - 20 km / min, and the temperature of the hot nitrogen gas is 50 - 500 °C.

[0039] A preparation method of meta-aramid composite paper, the preparation method of the meta-aramid composite paper is as follows: uniformly arranging, separating, laying, cold pressing and hot pressing the meta-aramid ultrafine fibers to obtain a meta-aramid ultrafine fiber sheet, using the meta-aramid ultrafine fiber sheet as the surface layer and the bottom layer, using meta-aramid film and meta-aramid paper as the core layer, laminating and compounding in the order of the surface layer, the core layer and the bottom layer, and then performing hot pressing treatment to obtain the meta-aramid composite paper.

[0040] Specifically, the preparation method of the meta-aramid film is as follows: under room temperature and nitrogen drying environment, under stirring conditions, isophthaloyl chloride and m-phenylenediamine are subjected to a polymerization reaction in DMAc. After the reaction is completed, the polymerization solution is obtained through neutralization and filtration, the polymerization solution is formed into a film, and after multi-stage drying and corona treatment, the meta-aramid film is obtained.

[0041] Specifically, the preparation method of the meta-aramid paper is as follows: The meta-aramid short-cut fibers and the meta-aramid precipitated fibers are respectively pulped. After the two slurries are mixed, they are formed into a sheet, pressed, and dried to obtain the meta-aramid base paper. The meta-aramid base paper is subjected to hot pressing treatment and corona treatment to obtain the meta-aramid paper;

[0042] The crystallinity of the meta-aramid short-cut fibers is 10-40%, the profiled degree of the meta-aramid short-cut fibers > 10%, and the cross-section of the meta-aramid short-cut fibers is one or more of circular, spindle-shaped, cashew-shaped, cruciform, and triangular; The meta-aramid precipitated fibers adopt a low-temperature precipitation process at -5°C - 10°C, and the crystallinity of the meta-aramid precipitated fibers is 5-15%.

[0043] Specifically, when preparing the meta-aramid ultrafine fiber sheet, the fiber splitting includes placing the filaments on a tray, electrostatic fiber splitting, and slit air flow fiber splitting; The line pressure of the cold pressing is 0-100 N / mm, the lower roller of the press roller is a metal roller, and the upper roller is a soft roller doped with conductive fibers or a metal roller; The hot pressing temperature is 150°C - 300°C, the line pressure is 10 - 100 N / mm, the roller speed is 10-40 m / min, the number of hot pressing times is 1-3 times, the hot pressing roller is a metal roller and a soft roller or a metal roller and a metal roller, and the Shore hardness of the soft roller is D70-100;

[0044] The lamination and composite is to unwind the meta-aramid ultrafine fiber sheet, the meta-aramid paper, and the meta-aramid film simultaneously according to multi-station unwinding, and after simultaneously guiding the paper, enter the nip of the hot rolling roller of the roller-type hot press; The temperature of the hot pressing treatment is 250°C - 330°C, the line pressure is 100 - 200 kN / m, the roller speed is 1 - 20 m / min, and the number of hot pressing times is 1-3 times.

[0045] Specifically, the fiber diameter of the meta-aramid ultrafine fibers is 0.01-20 μm, and the fiber strength is 5-30 g / d;

[0046] The crystallinity of the meta-aramid film is 10-40%, both surfaces are subjected to corona treatment, the surface energy after corona treatment is 50-100 mN / m, and the basis weight is 5-100 g / m 2 ;

[0047] The basis weight of the meta-aramid ultrafine fiber sheet is 5-100 g / m 2 The thickness of the meta-aramid composite paper is 0.025-0.76 mm, and the meta-aramid composite paper is composed of 100% meta-aramid.

[0048] The application of the meta-aramid composite paper prepared by a preparation method of a meta-aramid composite paper, wherein the meta-aramid composite paper is applied to the fields of insulation packaging, honeycomb core materials, composite material reinforcement, building fire prevention, new energy vehicle drive motors, offshore wind power, large oil-immersed transformers, and oil-cooled motors.

[0049] Example 1

[0050] (1) Preparation of meta-aramid ultrafine fiber sheet: 5 wt% of meta-aramid, 30 wt% of N,N-dimethylformamide, and 65 wt% of carbon tetrachloride were added to a reaction kettle. At a temperature of 300 °C, under the condition of stirring at 150 r / min by controlling nitrogen to reach a pressure of 15 MPa, stirring was carried out for 1.5 hours to obtain a uniform spinning solution. The viscosity of the meta-aramid spinning solution was 150 poises. The meta-aramid spinning solution was ejected through a spinneret with a pore diameter of 5.0 mm of a flash spinning device at a spinning speed of 6 km / min. Hot nitrogen at 200 °C was continuously introduced around the spinneret, and the solvent in the spinning solution evaporated rapidly to obtain meta-aramid ultrafine fibers. As shown in Figure 3 , the diameter range of the obtained meta-aramid ultrafine fibers was 0.1 - 20 μm, the average diameter was 17.7 μm, and the fiber strength was 12 g / d. After three-sided conical frustum fiber laying, electrostatic fiber splitting at a voltage of 10 kV, web laying, and cold pressing, the silicone rubber roller used for cold pressing was doped with 4 wt% of copper fibers, with a Shore hardness D75 and a linear pressure of 30 N / mm. After hot pressing, a meta-aramid ultrafine fiber sheet with a basis weight of 5 g / m 2 was obtained. The hot pressing was carried out using a metal roller and an ethylene propylene diene monomer (EPDM) rubber roller, at a temperature of 200 °C, a linear pressure of 100 N / mm, a roller speed of 10 m / min, and the number of hot pressing times was 1 time.

[0051] (2) Preparation of meta-aramid film: At room temperature, under a nitrogen drying environment with a pressure of 0.03 MPa, under stirring conditions, isophthaloyl chloride and m-phenylenediamine were added to DMAc for polymerization reaction. After neutralization and filtration, a polymerization solution was obtained. The polymerization solution was formed into a film on the surface of tempered glass, and after multi-stage drying and double-sided corona treatment, a meta-aramid film was obtained. The basis weight of the meta-aramid film was 16 g / m 2 , the thickness was 15 μm, the crystallinity was 20%, and the surface energy was 60 mN / m;

[0052] (3) Preparation of meta-aramid paper: Meta-aramid short cut fibers with a crystallinity of 40%, a profiled degree of 20%, and a spindle-shaped cross-section were used to prepare meta-aramid precipitated fibers with a relative crystallinity of 5% by a -5 °C low-temperature precipitation process; the two fiber slurries were pulped separately, and the two slurries were mixed in the headbox of an inclined wire paper machine. Among them, calculated according to the absolute dry weight of the fiber raw materials, the meta-aramid short cut fibers accounted for 50 wt%, and the meta-aramid precipitated fibers accounted for 50 wt%. After papermaking, pressing, and drying, a meta-aramid base paper was obtained. The meta-aramid base paper was subjected to high-temperature and high-pressure treatment and double-sided corona treatment by a hot press to obtain meta-aramid paper. The basis weight of the obtained meta-aramid paper was 41 g / m 2 , the thickness was 50 μm, and the surface energy was 80 mN / m.

[0053] (4) Preparation of aramid composite paper: The meta-aramid ultrafine fiber sheet prepared in step (1) is used as the surface layer and the bottom layer, and the meta-aramid film and the meta-aramid paper prepared in steps (2) and (3) are used as the core layer. As shown in Figure 1 , after laminating and compounding in the order of meta-aramid ultrafine fiber sheet, meta-aramid film, meta-aramid paper, meta-aramid film, and meta-aramid ultrafine fiber sheet, hot pressing treatment is carried out using a hot press. The laminating and compounding is to unwind several rolls of meta-aramid ultrafine fiber, meta-aramid paper, and meta-aramid film simultaneously by multi-station unwinding, and then enter the nip of the hot rolling roller after guiding the paper at the same time. The first hot pressing temperature is 250 °C, the linear pressure is 100 kN / m, the roller speed is 5 m / min, the second hot pressing temperature is 280 °C, the linear pressure is 150 kN / m, the roller speed is 10 m / min, and the third hot pressing temperature is 320 °C, the linear pressure is 200 kN / m, the roller speed is 20 m / min, to obtain meta-aramid composite paper. The thickness of the obtained meta-aramid composite paper is 0.08 mm, the basis weight is 95 g / m², the withstand voltage strength is 45.4 kV / mm, the surface strength is 23 A, and the interlayer bonding strength is 230 J / m². Figure 1 As shown, after laminating and compounding in the order of meta-aramid ultrafine fiber sheet, meta-aramid film, meta-aramid paper, meta-aramid film, and meta-aramid ultrafine fiber sheet, hot pressing treatment is carried out using a hot press. The laminating and compounding is to unwind several rolls of meta-aramid ultrafine fiber, meta-aramid paper, and meta-aramid film simultaneously by multi-station unwinding, and then enter the nip of the hot rolling roller after guiding the paper at the same time. The first hot pressing temperature is 250 °C, the linear pressure is 100 kN / m, the roller speed is 5 m / min, the second hot pressing temperature is 280 °C, the linear pressure is 150 kN / m, the roller speed is 10 m / min, and the third hot pressing temperature is 320 °C, the linear pressure is 200 kN / m, the roller speed is 20 m / min, to obtain meta-aramid composite paper. 2 The thickness of the obtained meta-aramid composite paper is 0.08 mm, the basis weight is 95 g / m², the withstand voltage strength is 45.4 kV / mm, the surface strength is 23 A, and the interlayer bonding strength is 230 J / m². 2 .

[0054] Example 2

[0055] (1) Preparation of meta-aramid ultrafine fiber sheet: 30 wt% of meta-aramid, 30 wt% of N-methylpyrrolidone, 30 wt% of dichloromethane, and 10 wt% of carbon tetrachloride are added to the reaction kettle. At a temperature of 200 °C, under the condition of stirring at 200 r / min by controlling nitrogen to reach a pressure of 20 MPa, stirring is carried out for 1 hour to obtain a uniform spinning solution. The viscosity of the meta-aramid spinning solution is 4000 poises. The meta-aramid spinning solution is ejected through a spinneret with a pore diameter of 1.0 mm of the flash spinning equipment at a spinning speed of 14 km / min. Hot nitrogen at 150 °C is continuously introduced around the spinneret, and the solvent in the spinning solution quickly evaporates to obtain meta-aramid ultrafine fibers. The diameter range of the obtained meta-aramid ultrafine fibers is 0.5 - 5 μm, the average diameter is 1.5 μm, the fiber strength is 18 g / d. After three-sided conical frustum silk laying, web laying, and cold pressing, the aramid roller used for cold pressing is doped with 10 wt% of carbon fiber, the Shore hardness is D85, the linear pressure is 50 N / mm, and hot pressing is carried out to obtain a meta-aramid ultrafine fiber sheet with a basis weight of 5 g / m². The hot pressing uses a metal roller and a metal roller, the temperature is 300 °C, the linear pressure is 50 N / mm, the roller speed is 40 m / min, and the number of hot pressing times is 1 time. 2 The thickness of the obtained meta-aramid ultrafine fiber sheet is 5 g / m². The hot pressing uses a metal roller and a metal roller, the temperature is 300 °C, the linear pressure is 50 N / mm, the roller speed is 40 m / min, and the number of hot pressing times is 1 time.

[0056] (2) Preparation of meta-aramid film: At room temperature, under a nitrogen drying environment with a pressure of 0.03 MPa, while stirring, isophthaloyl chloride and m-phenylenediamine are added to DMAc for polymerization reaction. After neutralization and filtration, a polymerization solution is obtained. The polymerization solution is formed into a film on the surface of tempered glass, and after multi-stage drying and double-sided corona treatment, a meta-aramid film is obtained. The basis weight of the meta-aramid film is 9 g / m 2 , the thickness is 8 μm, the crystallinity is 10%, and the surface energy is 60 mN / m;

[0057] (3) Preparation of meta-aramid paper: Using meta-aramid short-cut fibers with a crystallinity of 35%, a profiled degree of 20%, and a cross-section in the shape of a broad bean, meta-aramid precipitated fibers with a relative crystallinity of 8% are obtained by a low-temperature precipitation process at -3°C; the two fiber slurries are pulped separately, and the two slurries are mixed in the headbox of an inclined wire paper machine. Among them, calculated by the absolute dry weight of the fiber raw material, the meta-aramid short-cut fibers account for 50 wt%, and the meta-aramid precipitated fibers account for 50 wt%. After papermaking, pressing, and drying, a meta-aramid base paper is obtained. The meta-aramid base paper is subjected to high-temperature and high-pressure treatment and double-sided corona treatment by a hot press to obtain meta-aramid paper. The basis weight of the obtained meta-aramid paper is 21 g / m 2 , the thickness is 25 μm, and the surface energy is 90 mN / m.

[0058] (4) Preparation of aramid composite paper: The meta-aramid ultrafine fiber sheet prepared in step 1) is used as the surface layer and the bottom layer, and the meta-aramid film and meta-aramid paper prepared in steps 2) and 3) are used as the core layer. After laminating and compounding in the order of meta-aramid ultrafine fiber sheet, meta-aramid film, meta-aramid paper, meta-aramid film, and meta-aramid ultrafine fiber sheet, hot pressing treatment is carried out using a hot press. The laminating and compounding is to unwind several rolls of meta-aramid ultrafine fibers, meta-aramid paper, and meta-aramid film simultaneously according to multi-station unwinding, and then enter the nip of the hot rolling rolls after guiding the paper at the same time. The first hot pressing temperature is 255°C, the linear pressure is 150 kN / m, and the roll speed is 5 m / min. The second hot pressing temperature is 290°C, the linear pressure is 100 kN / m, and the roll speed is 10 m / min. The third hot pressing temperature is 330°C, the linear pressure is 200 kN / m, and the roll speed is 10 m / min, to obtain a meta-aramid composite paper. The thickness of the obtained meta-aramid composite paper is 0.05 mm, the withstand voltage strength is 30.3 kV / mm, the surface strength is 23 A, and the interlayer bonding strength is 240 J / m 2 .

[0059] Example 3

[0060] (1) Preparation of meta-aramid ultrafine fiber sheet: 20 wt% of meta-aramid, 25 wt% of trichlorofluoromethane, 35 wt% of butane, and 20 wt% of n-hexane were added to a reaction kettle. At a temperature of 170 °C, by controlling carbon dioxide to reach a pressure of 8 Mpa, and under the stirring condition of 500 r / min for 1 hour, a uniform spinning solution was obtained. The viscosity of the meta-aramid spinning solution was 1700 poise. The meta-aramid spinning solution was ejected through a spinneret with a pore diameter of 1.5 mm of a flash spinning device at a spinning speed of 5 km / min. Hot nitrogen at 50 °C was continuously introduced around the spinneret, and the solvent in the spinning solution evaporated rapidly to obtain meta-aramid ultrafine fibers. The diameter range of the obtained meta-aramid ultrafine fibers was 0.5 - 20 μm, the average diameter was 15 μm, and the fiber strength was 5 g / d. After three-sided conical frustum silk laying, web forming, and cold pressing, the cotton felt roller used for cold pressing was doped with 8 wt% silver wire, with a Shore hardness of D70 and a linear pressure of 100 N / mm, and hot pressing was carried out to obtain a meta-aramid ultrafine fiber sheet with a basis weight of 8 g / m 2 The meta-aramid ultrafine fiber sheet was hot-pressed using a metal roller and a metal roller at a temperature of 150 °C, a linear pressure of 100 N / mm, a roller speed of 30 m / min, and the number of hot pressing times was 1 time..

[0061] (2) Preparation of meta-aramid film: Under a nitrogen drying environment at room temperature and a pressure of 0.03 MPa, under stirring conditions, isophthaloyl chloride and m-phenylenediamine were added to DMAc for polymerization reaction. After neutralization and filtration, a polymerization solution was obtained. The polymerization solution was formed into a film on the surface of tempered glass, and after multi-stage drying and double-sided corona treatment, a meta-aramid film was obtained. The basis weight of the meta-aramid film was 11 g / m 2 , with a thickness of 10 μm, a crystallinity of 30%, and a surface energy of 100 mN / m;

[0062] (3) Preparation of meta-aramid paper: Using meta-aramid short cut fibers with a crystallinity of 10%, an irregularity of 40%, and a cross-shaped cross-section, meta-aramid precipitated fibers with a relative crystallinity of 10% were prepared by a 3 °C low-temperature precipitation process; the two fiber slurries were pulped separately, and the two slurries were mixed in the headbox of an inclined wire paper machine. Among them, calculated according to the absolute dry weight of the fiber raw materials, the meta-aramid short cut fibers accounted for 50 wt%, and the meta-aramid precipitated fibers accounted for 50 wt%. After papermaking, pressing, and drying, a meta-aramid base paper was obtained. The meta-aramid base paper was subjected to high-temperature and high-pressure treatment and double-sided corona treatment by a hot press to obtain meta-aramid paper. The basis weight of the obtained meta-aramid paper was 41 g / m 2 , with a thickness of 50 μm and a surface energy of 90 mN / m.

[0063] (4) Preparation of aramid composite paper: Use the meta-aramid ultrafine fiber sheet prepared in step (1) as the surface layer and the bottom layer, and use the meta-aramid film and meta-aramid paper prepared in steps (2) and (3) as the core layer. Stack and laminate them in the order of meta-aramid ultrafine fiber sheet, meta-aramid film, meta-aramid paper, meta-aramid film, meta-aramid paper, meta-aramid film, and meta-aramid ultrafine fiber sheet, and then perform hot pressing treatment with a hot press. The laminating and compounding is to unwind several rolls of meta-aramid ultrafine fiber, meta-aramid paper, and meta-aramid film simultaneously by multi-station unwinding, and then enter the nip of the hot rolling rolls after guiding the paper. The first hot pressing temperature is 255 °C, the linear pressure is 150 kN / m, and the roll speed is 5 m / min. The second hot pressing temperature is 290 °C, the linear pressure is 100 kN / m, and the roll speed is 10 m / min. The third hot pressing temperature is 330 °C, the linear pressure is 200 kN / m, and the roll speed is 10 m / min, obtaining the meta-aramid composite paper. The thickness of the obtained meta-aramid composite paper is 0.13 mm, the withstand voltage strength is 56.9 kV / mm, the surface strength is 23 A, and the interlayer bonding strength is 235 J / m 2 .

[0064] Example 4

[0065] (1) Preparation of meta-aramid ultrafine fiber sheet: Add 20 wt% of meta-aramid, 30 wt% of tetrahydrofuran, and 50 wt% of N,N-dimethylformamide with a mass fraction into a reaction kettle. At a temperature of 230 °C, control the carbon dioxide to reach a pressure of 15 MPa, and stir for 2 hours under the stirring condition of 150 r / min to obtain a uniform spinning solution. The viscosity of the meta-aramid spinning solution is 2800 poises. The meta-aramid spinning solution is ejected through a spinneret with a pore diameter of 1.0 mm of a flash spinning device at a spinning speed of 18 km / min. Hot nitrogen at 200 °C is continuously introduced around the spinneret, and the solvent in the spinning solution quickly evaporates to obtain meta-aramid ultrafine fibers. The diameter range of the obtained meta-aramid ultrafine fibers is 0.5 - 20 μm, the average diameter is 10.6 μm, and the fiber strength is 10 g / d. After six-sided conical frustum filament laying, 100 hz frequency air flow swinging filament splitting, web laying, and cold pressing, the wool roll used for cold pressing is doped with 15 wt% of carbon fiber, the Shore hardness D is 70, the linear pressure is 10 N / mm, and hot pressing is performed to obtain a meta-aramid ultrafine fiber sheet with a basis weight of 15 g / m 2 . The hot pressing uses metal rolls, the temperature is 150 °C, the linear pressure is 10 N / mm, the roll speed is 1 m / min, and the number of hot pressing times is 1 time.

[0066] (2) Preparation of meta-aramid film: At room temperature, under a nitrogen drying environment with a pressure of 0.03 MPa, phthaloyl chloride and m-phenylenediamine were added to DMAc for polymerization reaction under stirring conditions. After neutralization and filtration, a polymerization solution was obtained. The polymerization solution was formed into a film on the surface of tempered glass, and after multi-stage drying and double-sided corona treatment, a meta-aramid film was obtained. The basis weight of the meta-aramid film was 5.5 g / m 2 , with a thickness of 5 μm, a crystallinity of 40%, and a surface energy of 80 mN / m;

[0067] (3) Preparation of meta-aramid paper: Using meta-aramid short cut fibers with a crystallinity of 20%, an irregularity of 60%, and a triangular cross-section, meta-aramid precipitated fibers with a relative crystallinity of 15% were obtained by a low-temperature precipitation process at 5°C; the two fiber slurries were pulped separately, and the two slurries were mixed in the headbox of an inclined wire paper machine. Among them, according to the absolute dry weight of the fiber raw materials, the meta-aramid short cut fibers accounted for 50 wt%, and the meta-aramid precipitated fibers accounted for 50 wt%. After papermaking, pressing, and drying, a meta-aramid base paper was obtained. The meta-aramid base paper was subjected to high-temperature and high-pressure treatment and double-sided corona treatment by a hot press to obtain meta-aramid paper. The basis weight of the obtained meta-aramid paper was 68.8 g / m2, the thickness was 80 μm, and the surface energy was 70 mN / m.

[0068] (4) Preparation of aramid composite paper: The meta-aramid ultrafine fiber sheet prepared in step (1) was used as the surface layer and the bottom layer, and the meta-aramid film and meta-aramid paper prepared in steps (2) and (3) were used as the core layer. After laminating and compounding in the order of meta-aramid ultrafine fiber sheet, meta-aramid paper, meta-aramid film, meta-aramid paper, meta-aramid film, meta-aramid paper, and meta-aramid ultrafine fiber sheet, hot pressing treatment was carried out using a hot press. The laminating and compounding was carried out by multi-station unwinding to unwind several rolls of meta-aramid ultrafine fibers, meta-aramid paper, and meta-aramid film at the same time, and after guiding the paper at the same time, it entered the nip of the hot rolling rolls. The first hot pressing temperature was 255°C, the linear pressure was 150 kN / m, and the roll speed was 5 m / min. The second hot pressing temperature was 290°C, the linear pressure was 100 kN / m, and the roll speed was 10 m / min. The third hot pressing temperature was 330°C, the linear pressure was 200 kN / m, and the roll speed was 10 m / min, to obtain meta-aramid composite paper. The thickness of the obtained meta-aramid composite paper was 0.25 mm, the withstand voltage strength was 79.5 kV / mm, the surface strength was 23 A, and the interlayer bonding strength was 230 J / m 2 .

[0069] Example 5

[0070] (1) Preparation of meta-aramid ultrafine fiber sheet: 10 wt% of meta-aramid, 25 wt% of hexafluoroisopropanol, 35 wt% of N,N-dimethylformamide, and 30 wt% of carbon tetrachloride were added to a reaction kettle. At a temperature of 100 °C, by controlling nitrogen to reach a pressure of 13 MPa, under the stirring condition of 400 r / min, stirring was carried out for 2.5 hours to obtain a uniform spinning solution. The viscosity of the meta-aramid spinning solution was 2400 poises. The meta-aramid spinning solution was ejected through a spinneret with a pore diameter of 1.0 mm of a flash spinning device at a spinning speed of 14 km / min. Hot nitrogen at 100 °C was continuously introduced around the spinneret, and the solvent in the spinning solution evaporated rapidly to obtain meta-aramid ultrafine fibers. The diameter range of the obtained meta-aramid ultrafine fibers was 0.5 - 15 μm, the average diameter was 12.5 μm, the fiber strength was 22 g / d. After six-sided conical frustum fiber laying, slit air draft drawing, web laying, and cold pressing, the aramid roller used for cold pressing was doped with 10 wt% of carbon fiber, with a Shore hardness D85 and a linear pressure of 100 N / mm. Through hot pressing, a meta-aramid ultrafine fiber sheet with a basis weight of 41 g / m² was obtained. The hot pressing was carried out using a metal roller and a metal roller, at a temperature of 200 °C, a linear pressure of 50 N / mm, a roller speed of 30 m / min, and the number of hot pressing times was 3 times.

[0071] (2) Preparation of meta-aramid film: At room temperature, under a nitrogen drying environment with a pressure of 0.03 MPa, under the stirring condition, isophthaloyl chloride and m-phenylenediamine were added to DMAc for polymerization reaction. After neutralization and filtration, a polymerization solution was obtained. The polymerization solution was formed into a film on the surface of tempered glass, and after multi-stage drying and double-sided corona treatment, a meta-aramid film was obtained. The basis weight of the meta-aramid film was 33 g / m 2 , with a thickness of 30 μm, a crystallinity of 20%, and a surface energy of 100 mN / m;

[0072] (3) Preparation of meta-aramid paper: Using meta-aramid short cut fibers with a crystallinity of 40%, a profiled degree of 40%, and a cross-section in the shape of a cashew nut, meta-aramid precipitated fibers with a relative crystallinity of 8% were prepared by a -5 °C low-temperature precipitation process; the two fiber slurries were respectively pulped, and the two slurries were mixed in the headbox of an inclined wire paper machine. Among them, according to the absolute dry weight of the fiber raw materials, the meta-aramid short cut fibers accounted for 50 wt%, and the meta-aramid precipitated fibers accounted for 50 wt%. After papermaking, pressing, and drying, a meta-aramid base paper was obtained. The meta-aramid base paper was subjected to high-temperature and high-pressure treatment and double-sided corona treatment by a hot press to obtain meta-aramid paper. The basis weight of the obtained meta-aramid paper was 115 g / m 2 , with a thickness of 130 μm and a surface energy of 80 mN / m.

[0073] (4) Preparation of aramid composite paper: Use the meta-aramid ultrafine fiber sheet prepared in step (1) as the surface layer and the bottom layer, and use the meta-aramid film and meta-aramid paper prepared in steps (2) and (3) as the core layer. Stack and laminate them in the order of meta-aramid ultrafine fiber sheet, meta-aramid paper, meta-aramid film, meta-aramid paper, meta-aramid film, meta-aramid paper, and meta-aramid ultrafine fiber sheet, and then perform hot pressing treatment using a hot press. The lamination is carried out by unwinding several rolls of meta-aramid ultrafine fibers, meta-aramid papers, and meta-aramid films simultaneously at multiple stations, and after guiding the paper, it enters the nip of the hot rolling rolls. The first hot pressing temperature is 255 °C, the linear pressure is 150 kN / m, and the roll speed is 5 m / min. The second hot pressing temperature is 290 °C, the linear pressure is 100 kN / m, and the roll speed is 10 m / min. The third hot pressing temperature is 330 °C, the linear pressure is 200 kN / m, and the roll speed is 10 m / min, obtaining the meta-aramid composite paper. The thickness of the obtained meta-aramid composite paper is 0.51 mm, the withstand voltage strength is 92.7 kV / mm, the surface strength is 23 A, and the interlayer bonding strength is 240 J / m 2 .

[0074] Example 6

[0075] (1) Preparation of meta-aramid ultrafine fiber sheet: Add 15 wt% meta-aramid, 35% N,N-dimethylformamide, and 50% acetonitrile by mass fraction into a reaction kettle. At a temperature of 245 °C, control the nitrogen to reach a pressure of 12 MPa, and stir for 1.5 hours under the stirring condition of 250 r / min to obtain a uniform spinning solution. The viscosity of the meta-aramid spinning solution is 650 poise. The meta-aramid spinning solution is ejected through a spinneret with a pore diameter of 5.0 mm of a flash spinning device at a spinning speed of 8 km / min, and hot nitrogen at 400 °C is continuously introduced around the spinneret. The solvent in the spinning solution evaporates rapidly, obtaining meta-aramid ultrafine fibers. The diameter range of the obtained meta-aramid ultrafine fibers is 0.1 - 13 μm, the average diameter is 8 μm, the fiber strength is 30 g / d. After five-sided conical frustum fiber laying, 20 kV static voltage fiber splitting, web laying, and cold pressing, the upper roll used for cold pressing is a metal roll with a Shore hardness D85 and a linear pressure of 50 N / mm, and hot pressing is carried out to obtain a meta-aramid ultrafine fiber sheet with a basis weight of 70 g / m 2 . The hot pressing uses a metal roll and a roll made of poly(p-phenylene benzobisoxazole), the temperature is 300 °C, the linear pressure is 100 N / mm, the roll speed is 40 m / min, and the number of hot pressing times is 2 times.

[0076] (2) Preparation of meta-aramid film: Under a nitrogen drying environment at room temperature and a pressure of 0.03 MPa, add isophthaloyl chloride and m-phenylenediamine to DMAc for polymerization reaction under stirring conditions. After neutralization and filtration, a polymerization solution is obtained. The polymerization solution forms a film on the surface of tempered glass, and after multi-stage drying and double-sided corona treatment, a meta-aramid film is obtained. The basis weight of the meta-aramid film is 68 g / m2 , with a thickness of 60 μm, a crystallinity of 15%, and a surface energy of 90 mN / m;

[0077] (3) Preparation of meta-aramid paper: Use meta-aramid short-cut fibers with a crystallinity of 30%, a profiled degree of 30%, and a spindle-shaped cross-section to prepare meta-aramid precipitated fibers with a relative crystallinity of 10% by a low-temperature precipitation process at -5°C; pulp the two fiber slurries separately, and mix the two slurries in the headbox of an inclined wire paper machine. Among them, calculated by the absolute dry weight of the fiber raw material, the meta-aramid short-cut fibers account for 50 wt%, and the meta-aramid precipitated fibers account for 50 wt%. After forming, pressing, and drying, the meta-aramid base paper is obtained. The meta-aramid base paper is subjected to high-temperature and high-pressure treatment by a hot press and double-sided corona treatment to obtain meta-aramid paper. The basis weight of the obtained meta-aramid paper is 161 g / m 2 , with a thickness of 180 μm and a surface energy of 90 mN / m.

[0078] (4) Preparation of aramid composite paper: Use the meta-aramid ultrafine fiber sheet prepared in step (1) as the surface layer and the bottom layer, and use the meta-aramid film and meta-aramid paper prepared in steps (2) and (3) as the core layer. Stack and laminate them in the order of meta-aramid ultrafine fiber sheet, meta-aramid paper, meta-aramid film, meta-aramid paper, meta-aramid film, meta-aramid paper, and meta-aramid ultrafine fiber sheet, and then perform hot pressing treatment with a hot press. The stack lamination is to unwind several rolls of meta-aramid ultrafine fibers, meta-aramid papers, and meta-aramid films simultaneously by multi-station unwinding, and then enter the nip of the hot rolling rolls after guiding the paper at the same time. The first hot pressing temperature is 255°C, the linear pressure is 150 kN / m, and the roll speed is 5 m / min. The second hot pressing temperature is 290°C, the linear pressure is 100 kN / m, and the roll speed is 10 m / min. The third hot pressing temperature is 330°C, the linear pressure is 200 kN / m, and the roll speed is 10 m / min to obtain the meta-aramid composite paper. The thickness of the obtained meta-aramid composite paper is 0.76 mm, the withstand voltage strength is 122 kV / mm, the surface strength is 23 A, and the interlayer bonding strength is 237 J / m 2 .

[0079] Example 7

[0080] (1) Preparation of meta-aramid ultrafine fiber sheet: Add 1% by mass of meta-aramid, 60% of N,N-dimethylacetamide, and 39% of hexafluoroisopropanol into a reaction kettle. At a temperature of 300 °C, control nitrogen to reach a pressure of 10 MPa, and stir for 1.5 hours under the stirring condition of 350 r / min to obtain a uniform spinning solution. The viscosity of the meta-aramid spinning solution is 10 poises. The meta-aramid spinning solution is ejected through a spinneret with a pore diameter of 1.0 mm of a flash spinning device at a spinning speed of 20 km / min, and hot nitrogen at 100 °C is continuously introduced around the spinneret. The solvent in the spinning solution evaporates rapidly to obtain meta-aramid ultrafine fibers. The diameter range of the obtained meta-aramid ultrafine fibers is 0.01 - 10 μm, the average diameter is 2.35 μm, the fiber strength is 5 g / d. After six-sided conical frustum fiber laying, 25 kV static voltage fiber splitting, web laying, and cold pressing, the aramid roller used for cold pressing is doped with 10 wt% carbon fiber, the Shore hardness is D85, and the linear pressure is 50 N / mm. After hot pressing, a meta-aramid ultrafine fiber sheet with a basis weight of 10 g / m 2 is obtained. For hot pressing, metal rollers are used. The temperature is 300 °C, the linear pressure is 100 N / mm, the roller speed is 20 m / min, and the number of hot pressing times is 2 times.

[0081] (2) Preparation of meta-aramid film: Under a nitrogen drying environment at room temperature and a pressure of 0.03 MPa, under stirring conditions, add isophthaloyl chloride and m-phenylenediamine into DMAc for polymerization reaction. After neutralization and filtration, a polymerization solution is obtained. The polymerization solution forms a film on the surface of tempered glass, and after multi-stage drying and double-sided corona treatment, a meta-aramid film is obtained. The basis weight of the meta-aramid film is 23 g / m 2 , the thickness is 20 μm, the crystallinity is 10%, and the surface energy is 50 mN / m;

[0082] (3) Preparation of meta-aramid paper: Use meta-aramid short cut fibers with a crystallinity of 10%, a profiled degree of 60%, and a triangular cross-section. Through a -5 °C low-temperature precipitation process, meta-aramid precipitated fibers with a relative crystallinity of 12% are obtained; the two fiber slurries are pulped respectively, and the two slurries are mixed in the headbox of an inclined wire paper machine. Among them, calculated according to the absolute dry weight of the fiber raw material, the meta-aramid short cut fibers account for 50 wt%, and the meta-aramid precipitated fibers account for 50 wt%. After papermaking, pressing, and drying, a meta-aramid base paper is obtained. The meta-aramid base paper is subjected to high-temperature and high-pressure treatment and double-sided corona treatment by a hot press to obtain meta-aramid paper. The basis weight of the obtained meta-aramid paper is 178 g / m 2 , the thickness is 200 μm, and the surface energy is 90 mN / m.

[0083] (4) Preparation of aramid composite paper: Use the meta-aramid ultrafine fiber sheet prepared in step 1) as the surface layer and the bottom layer, and use the meta-aramid film and meta-aramid paper prepared in step 2) and step 3) as the core layer, as Figure 1As shown in the figure, after laminating and compounding in the order of meta-aramid ultrafine fiber sheet, meta-aramid film, meta-aramid paper, meta-aramid film and meta-aramid ultrafine fiber sheet, hot pressing treatment is carried out using a hot press. The laminating and compounding is to unwind several rolls of meta-aramid ultrafine fibers, meta-aramid paper and meta-aramid films simultaneously according to multi-station unwinding, and then enter the nip of the hot rolling rolls after guiding the paper. The first hot pressing temperature is 255 °C, the linear pressure is 150 kN / m, the roll speed is 5 m / min, the second hot pressing temperature is 290 °C, the linear pressure is 100 kN / m, the roll speed is 10 m / min, and the third hot pressing temperature is 330 °C, the linear pressure is 200 kN / m, the roll speed is 10 m / min, to obtain meta-aramid composite paper. The obtained meta-aramid composite paper has a thickness of 0.25 mm, a withstand voltage strength of 80.2 kV / mm, a surface strength of 23 A, and an interfacial bonding strength of 207 J / m 2 .

[0084] Example 8

[0085] (1) Preparation of meta-aramid ultrafine fiber sheet: Add 5% by mass of meta-aramid, 60% of N,N-dimethylformamide, and 35% of dichloromethane into the reaction kettle. At a temperature of 200 °C, control the nitrogen to reach a pressure of 5 MPa, and stir for 1.5 hours under the stirring condition of 200 r / min to obtain a uniform spinning solution. The viscosity of the meta-aramid spinning solution is 500 poise. The meta-aramid spinning solution is ejected through a spinneret with a pore diameter of 1.0 mm of the flash spinning equipment at a spinning speed of 5 km / min, and hot nitrogen at 300 °C is continuously introduced around the spinneret. The solvent in the spinning solution evaporates rapidly to obtain meta-aramid ultrafine fibers. The diameter range of the obtained meta-aramid ultrafine fibers is 5 - 20 μm, the average diameter is 16 μm, the fiber strength is 28 g / d. After six-sided conical frustum silk laying, 15 kV static voltage wire splitting, web laying, and cold pressing, the aramid roll used for cold pressing is doped with 10 wt% carbon fiber, the Shore hardness is D85, the linear pressure is 50 N / mm, and hot pressing is carried out to obtain a meta-aramid ultrafine fiber sheet with a basis weight of 100 g / m 2 . The hot pressing uses metal rolls and metal rolls, the temperature is 300 °C, the linear pressure is 100 N / mm, the roll speed is 20 m / min, and the number of hot pressing times is 2 times.

[0086] (2) Preparation of meta-aramid film: Under the nitrogen drying environment at room temperature and a pressure of 0.03 MPa, under the stirring condition, add isophthaloyl chloride and m-phenylenediamine into DMAc for polymerization reaction. After neutralization and filtration, a polymerization solution is obtained. The polymerization solution forms a film on the surface of tempered glass, and after multi-stage drying and double-sided corona treatment, a meta-aramid film is obtained. The basis weight of the meta-aramid film is 18 g / m 2 , the thickness is 15 μm, the crystallinity is 20%, and the surface energy is 90 mN / m;

[0087] (3) Preparation of meta-aramid paper: Use meta-aramid short-cut fibers with a crystallinity of 40%, profiled degree of 40%, and a cross-section in the shape of a broad bean, and prepare meta-aramid precipitated fibers with a relative crystallinity of 12% by a low-temperature precipitation process at 3°C; pulp the two fiber slurries separately, and mix the two slurries in the headbox of an inclined wire paper machine. Among them, calculated according to the absolute dry weight of the fiber raw materials, the meta-aramid short-cut fibers account for 50 wt%, and the meta-aramid precipitated fibers account for 50 wt%. After forming, pressing, and drying, obtain the meta-aramid base paper. The meta-aramid base paper is subjected to high-temperature and high-pressure treatment by a hot press and double-sided corona treatment to obtain meta-aramid paper. The basis weight of the obtained meta-aramid paper is 159 g / m 2 , with a thickness of 180 μm and a surface energy of 100 mN / m.

[0088] (4) Preparation of aramid composite paper: Use the meta-aramid ultrafine fiber sheet prepared in step (1) as the surface layer and the bottom layer, and use the meta-aramid film and meta-aramid paper prepared in steps (2) and (3) as the core layer. As Figure 2 shown, stack and laminate them in the order of meta-aramid ultrafine fiber sheet, meta-aramid paper, meta-aramid film, meta-aramid paper, meta-aramid film, meta-aramid paper, meta-aramid film, and meta-aramid ultrafine fiber sheet, and then perform hot pressing treatment using a hot press. The stacking and lamination are carried out by multi-station unwinding to unwind several rolls of meta-aramid ultrafine fibers, meta-aramid paper, and meta-aramid film simultaneously, and then enter the nip of the hot rolling rolls after guiding the paper at the same time. The first hot pressing temperature is 255°C, the linear pressure is 150 kN / m, the roll speed is 3 m / min, the second hot pressing temperature is 290°C, the linear pressure is 100 kN / m, the roll speed is 3 m / min, and the third hot pressing temperature is 330°C, the linear pressure is 200 kN / m, the roll speed is 1 m / min, to obtain the meta-aramid composite paper. The thickness of the obtained meta-aramid composite paper is 0.76 mm, the withstand voltage strength is 82.0 kV / mm, the surface strength is 23 A, and the interlayer bonding strength is 234 J / m 2 .

[0089] Comparative Example 1

[0090] (1) Preparation of meta-aramid ultrafine fiber sheet: The 2-denier aramid long fibers prepared by wet spinning are used to prepare a meta-aramid fiber sheet through a needling process to obtain a felt-like meta-aramid non-woven fabric. The lowest basis weight of this non-woven fabric is 190 g / m 2 , with a thickness of 250 μm and a loose structure. After hot pressing, the meta-aramid needled non-woven fabric cannot be effectively bonded with the meta-aramid paper and meta-aramid film, and the meta-aramid composite paper cannot be prepared.

[0091] Comparative Example 2

[0092] The same method as in Example 1 was used to prepare the meta-aramid ultrafine fiber sheet, except that the temperature condition for preparing the meta-aramid ultrafine fiber was 80 °C (lower than the temperature of the present invention). At a temperature lower than that of the present invention, the meta-aramid cannot be completely dissolved in the solution to obtain a uniform solution, and the nozzle is prone to blockage, making it impossible to prepare meta-aramid ultrafine fibers.

[0093] Comparative Example 3

[0094] The same method as in Example 1 was used to prepare the meta-aramid ultrafine fiber sheet, except that the temperature condition for preparing the meta-aramid ultrafine fiber was 450 °C (higher than the temperature of the present invention). At a temperature higher than that of the present invention, the molecular chains of the meta-aramid undergo aging and cracking at high temperature, the solvent undergoes thermal decomposition, the meta-aramid cannot be completely dissolved in the solution to obtain a uniform solution, and the nozzle is prone to blockage, making it impossible to prepare meta-aramid ultrafine fibers.

[0095] Comparative Example 4

[0096] The same method as in Example 1 was used to prepare the meta-aramid ultrafine fiber sheet, except that the pressure condition for preparing the meta-aramid ultrafine fiber was normal pressure (lower than the pressure of the present invention). At a pressure lower than that of the present invention, the meta-aramid cannot be completely dissolved in the solution to obtain a uniform solution, and slag-like debris is ejected from the nozzle, making it impossible to prepare continuous long fibers and impossible to prepare meta-aramid ultrafine fibers.

[0097] Comparative Example 5

[0098] The same method as in Example 1 was used to prepare the meta-aramid ultrafine fiber sheet, except that hot nitrogen was not introduced into the nozzle for preparing the meta-aramid ultrafine fiber. After the meta-aramid spinning solution is ejected from the nozzle, the solvent volatilizes insufficiently, forming viscous small droplets, making it impossible to prepare continuous long fibers and impossible to prepare meta-aramid ultrafine fibers.

[0099] In Examples 1-8 and Comparative Examples 1-5, the prepared meta-aramid ultrafine fiber sheets were subjected to performance tests. The relevant test methods were as follows: basis weight, GB / T 451.2-2002; thickness, GB / T 451.3-2002; tensile strength and elongation at break, GB / T12914-2008; internal tearing strength, GB / T 455-2002; edge tearing strength, GB / T20629.2-2013; surface strength, GB / T22837-2008; interlayer bonding strength, GB / T26203; compressive strength, GB / T 1408.1. The specific data are shown in Table 1 below:

[0100] Table 1 Performance test data of meta-aramid ultrafine fiber sheets

[0101]

[0102] It can be seen from the data comparison in Table 1 above that: the meta-aramid ultrafine fibers prepared by the preparation method described in the present invention in Examples 1-8 have the characteristics of fine fiber diameter, continuous long fiber state, and high strength. The meta-aramid ultrafine fiber sheet prepared therefrom is paper-like, having the characteristics of high bulk density, high tensile strength, high tearing strength, and non-fuzzing. The ultrafine fiber sheet prepared by the flash spinning process has a finer fiber diameter. The irregular cross-section results in a greater bonding force between the fibers after cold pressing and hot pressing, and the structure of the sheet is more dense. While the meta-aramid ultrafine fiber sheet prepared by the conventional needle-punched non-woven method in Comparative Example 1 has a loose structure, low bulk density, cannot prepare a low basis weight sheet, has fuzzing on the surface, is in a felt state, has low strength, and large deformation, and cannot be tested using the same test standards as in Examples 1-8. It can be seen from the experimental data comparison between Example 1 and Comparative Example 1 that the performance of Comparative Example 1 is significantly lower than that of Examples 1-8 because the flash spinning technology prepares a continuous ultrafine fiber network bundle. One long fiber lays one sheet, without fiber breakage, and there will be no fuzzing on the surface due to the presence of short fibers. In the flash spinning process, the solvent rapidly volatilizes under high temperature and high pressure, leaving behind polymer fibers with an irregular diameter cross-section. The diameter of the prepared meta-aramid ultrafine fibers is 0.01-20 μm, and the fiber strength is 5-20 g / d. It has the characteristics of a very large specific surface area, inherent flame retardancy, high temperature resistance, high strength and high modulus, acid, alkali, salt, and organic solvent resistance. The fibers with an irregular cross-section have a strong bite force, and the meta-aramid ultrafine fiber sheet has high breaking strength and tearing strength; the surface of the meta-aramid composite paper is bonded by meta-aramid ultrafine fiber filaments, with a large fiber bonding force and non-fuzzing. After hot pressing above the glass transition temperature, it retains its porous characteristics and has a high surface strength. While the meta-aramid fiber sheet in Comparative Example 1 has a thick fiber diameter, a single fiber cross-section shape, a poor bite force between the fibers, cannot prepare a low basis weight sheet, and the sheet structure is loose.

[0103] In addition, it can be seen from the experimental data comparison between Comparative Examples 2-5 and Example 1 that flash spinning under the temperature and pressure conditions described in the present invention in Example 1 is more conducive to obtaining high-quality meta-aramid ultrafine fibers.

[0104] Comparative Example 6

[0105] The meta-aramid film and meta-aramid paper were prepared by the same method as in Example 8, and the meta-aramid composite paper was prepared under the same conditions as in Example 8, except that: the meta-aramid ultrafine fiber sheet was not added, and only the meta-aramid paper, meta-aramid film, meta-aramid paper, meta-aramid film, meta-aramid paper, and meta-aramid film were laminated in sequence and hot-pressed. The surface strength of the obtained meta-aramid composite paper was 16A. When the corresponding surface of the meta-aramid paper was adhered with tape, fluffed phenomenon occurred, and cracked fine lines appeared on the corresponding surface of the meta-aramid film. While in Examples 1-8, the surface strength of the prepared meta-aramid composite paper was greater than 23A, and no fluffed phenomenon occurred when the surface was adhered with tape.

[0106] Comparative Example 7

[0107] The meta-aramid ultrafine fiber sheet and meta-aramid paper were prepared by the same method as in Example 8, and the meta-aramid composite paper was prepared under the same conditions as in Example 8, except that: during the preparation of the meta-aramid film, corona treatment was not carried out.

[0108] The meta-aramid composite papers prepared in Examples 1-8 were subjected to performance testing. In addition, the relevant performance data of the aramid / polyimide / aramid composite paper, namely NHN, on the market were also measured for comparison. The specific measurement results are shown in Table 2 below.

[0109] Table 2 Performance data of meta-aramid composite paper

[0110]

[0111] It can be seen from the data comparison in Table 2 that the meta-aramid composite paper prepared by the preparation method described in the present invention in Examples 1-8 has excellent performance, with a breakdown voltage strength (dielectric strength) ≥ 20 kV / mm, a surface strength of the meta-aramid composite film of 23A, and an interfacial bonding strength > 200 J / m 2 . Its relevant performance is significantly better than that of the commercially available conventional NHN. Examples 4 and 7 with the same thickness were compared with the commercially available NHN. Specifically, the meta-aramid ultrafine fiber sheet improves the surface strength, the meta-aramid film improves the dielectric properties, corona treatment effectively improves the bonding strength between the meta-aramid film and the meta-aramid paper and the meta-aramid ultrafine fiber sheet, and the use of low-crystallinity meta-aramid precipitated fibers effectively improves the interfacial bonding strength during the hot pressing process.

[0112] From the comparison of the experimental data in Example 8 and Comparative Example 6, it can be seen that the meta-aramid ultrafine fiber sheet prepared by the method of the present invention can effectively improve the surface strength of the meta-aramid composite paper. The surface strength of the meta-aramid composite film is 23A. If the meta-aramid ultrafine fiber sheet described in the present invention is not added, the surface strength of the meta-aramid composite paper will decrease significantly. From the comparison of the experimental data in Example 8 and Comparative Example 7, it can be seen that in the preparation method of the present invention, corona treatment of the meta-aramid film and the meta-aramid paper can improve the bonding strength between the meta-aramid film, the meta-aramid paper and the meta-aramid ultrafine fiber sheet, thereby improving the interlayer bonding strength of the meta-aramid composite paper.

[0113] The application cases of the meta-aramid composite paper are as follows:

[0114] The honeycomb core with hexagonal cell lattice, side length of 1.82 mm and density of 47.74 kg / m was prepared by using the meta-aramid composite paper prepared in Example 1 through the processes of sticking core strip glue, laminating, hot pressing, stretching, dipping, drying and curing. 3 , the instability compression strength of the honeycomb core is 4.5 MPa, the compression strength is 5.6 MPa, the shear modulus in the L direction is 107.3 MPa, the shear modulus in the W direction is 62.4 MPa, the shear strength in the L direction is 4.0 MPa, and the shear strength in the W direction is 2.9 MPa.

[0115] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, all possible combinations of the technical features in the above embodiments are not exhausted. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0116] For those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. The protection scope of the present invention shall be subject to the appended claims.

Claims

1. A preparation method of meta-aramid composite paper, characterized in that, The preparation method of the meta-aramid composite paper is as follows: The meta-aramid ultrafine fibers are evenly laid, separated, spread, cold-pressed and hot-pressed to obtain a meta-aramid ultrafine fiber sheet. The meta-aramid ultrafine fiber sheet is used as the surface layer and the bottom layer, and the meta-aramid film and the meta-aramid paper are used as the core layer. After laminating and compounding in the order of the surface layer, the core layer and the bottom layer, hot pressing treatment is carried out to obtain the meta-aramid composite paper; The preparation method of the meta-aramid ultrafine fibers is as follows: The meta-aramid and the solvent are added to an autoclave, and are uniformly mixed under the conditions of heating, pressurization and stirring to obtain a spinning solution. The spinning solution is ejected through the spinneret of a flash spinning device, and hot nitrogen is continuously introduced around the spinneret. The solvent in the spinning solution quickly evaporates to obtain the meta-aramid ultrafine fibers.

2. The preparation method of a meta-aramid composite paper according to claim 1, characterized in that, When preparing the meta-aramid ultrafine fibers, the heating condition is 100 - 300 °C, the pressurization condition is 1 - 30 Mpa, the stirring condition is 20 - 500 r / min, and the stirring time is 1 - 2.5 hours.

3. The preparation method of a meta-aramid composite paper according to claim 1, characterized in that, The solvent is one or more of n-butane, n-pentane, cyclopentane, n-hexane, n-heptane, n-octane, benzene, toluene, trichlorofluoromethane, dichloromethane, carbon tetrachloride, dichloroethylene, chloroform, chloroethane, dichloroethane, chloromethane, hexafluoroisopropanol, dichloroacetic acid, 1,2,3-trichlorobenzene, nitromethane, carbon dioxide, sulfur dioxide, carbon disulfide, ammonia, water, nitrogen, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, concentrated sulfuric acid, acetone, ethylene carbonate, pyridine, acetonitrile, tetrahydrofuran, 2,2,2-trifluoro-N,N-dimethylacetamide, caprolactam, 2,6-difluorobenzamide, 2,5-difluorobenzamide, 2-methyltetrahydrofuran, dimethyl carbonate.

4. The preparation method of a meta-aramid composite paper according to claim 1, characterized in that, The mass concentration of meta-aramid in the spinning solution is 1 - 30 wt%, the viscosity of the spinning solution is 10 - 4000 poise, the aperture of the spinneret is 1 - 5.0 mm, the diameter of the fiber is 0.01 - 20 μm, the spinning speed is 5 - 20 km / min, and the temperature of the hot nitrogen is 50 - 500 °C.

5. The preparation method of a meta-aramid composite paper according to claim 1, characterized in that The preparation method of the meta-aramid film is as follows: At room temperature, under a nitrogen drying environment and stirring conditions, isophthaloyl chloride and m-phenylenediamine carry out a polymerization reaction in DMAc. After the reaction ends, the polymerization solution is obtained after neutralization and filtration. The polymerization solution forms a film, and after multi-stage drying and corona treatment, the meta-aramid film is obtained.

6. The preparation method of a meta-aramid composite paper according to claim 1, wherein, The preparation method of the meta-aramid paper is as follows: The meta-aramid short-cut fibers and the meta-aramid precipitated fibers are respectively pulped. After the two slurries are mixed, they are subjected to papermaking, pressing and drying to obtain the meta-aramid base paper. The meta-aramid base paper is subjected to hot pressing treatment and corona treatment to obtain the meta-aramid paper; The crystallinity of the meta-aramid short-cut fibers is 10 - 40%, the profile degree of the meta-aramid short-cut fibers > 10%, and the cross-section of the meta-aramid short-cut fibers is one or more of spindle-shaped, cashew-shaped, cruciform, triangular; The meta-aramid precipitated fibers adopt a low-temperature precipitation process at -5 °C - 10 °C, and the crystallinity of the meta-aramid precipitated fibers is 5 - 15%.

7. The preparation method of a meta-aramid composite paper according to claim 1, characterized in that, When preparing the meta-aramid ultrafine fiber sheet, the fiber splitting includes arranging the filaments on a tray, electrostatic fiber splitting, and slit air flow fiber splitting; the line pressure of the cold pressing is 0 - 100 N / mm, the lower roller of the pressing roller is a metal roller, and the upper roller is a soft roller doped with conductive fibers or a metal roller; the hot pressing temperature is 150°C to 300°C, the line pressure is 10 - 100 N / mm, the roller speed is 1 - 40 m / min, the number of hot pressing times is 1 - 3 times, the hot pressing rollers are metal roller and soft roller or metal roller and metal roller, and the Shore hardness of the soft roller is D70 - 100; The lamination and composite is to unwind the meta-aramid ultrafine fiber sheet, meta-aramid paper, and meta-aramid film simultaneously according to multi-station unwinding, and then enter the nip of the hot rolling roller of the roller type hot press after guiding the paper at the same time; the temperature of the hot pressing treatment is 250°C to 330°C, the line pressure is 100 - 200 kN / m, the roller speed is 1 - 20 m / min, and the number of hot pressing times is 1 - 3 times.

8. The preparation method of a meta-aramid composite paper according to claim 1, characterized in that, The fiber diameter of the meta-aramid ultrafine fiber is 0.01 - 20 μm, and the fiber strength is 5 - 30 g / d; The crystallinity of the meta-aramid film is 10-40%, both surfaces are corona-treated, the surface energy after corona treatment is 50-100 mN / m, and the basis weight is 5-100 g / m 2 ; The basis weight of the meta-aramid ultrafine fiber sheet is 5-100 g / m 2 , the thickness of the meta-aramid composite paper is 0.025-0.76 mm, and the meta-aramid composite paper is composed of 100% meta-aramid components.

9. Use of a meta-aramid composite paper prepared by the preparation method of a meta-aramid composite paper according to any one of claims 1-8, characterized in that, The meta-aramid composite paper is applied to the fields of insulation packaging, honeycomb core materials, composite material reinforcement, building fire prevention, new energy vehicle drive motors, offshore wind power, large oil-immersed transformers, and oil-cooled motors.

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