Aramid precipitation nanofiber reinforced aramid insulation paper and preparation method thereof

Abstract

The invention provides aramid precipitation nanofiber reinforced aramid insulation paper and a preparation method thereof, and belongs to the technical field of preparation of aramid insulation paper. The aramid precipitation nanofibers are added when the insulating paper is prepared, pores between the aramid chopped fibers and the aramid precipitation fibers can be filled, so that the aramid chopped fibers and the aramid precipitation fibers are fully adhered and interwoven, the tensile strength of the aramid insulating paper is improved, and the insulativity of the insulating paper is improved; the cationic polyelectrolyte and the anionic polyelectrolyte are added in the wet-process paper forming process and can form a binary retention and drainage aid, loss of aramid precipitation nanofibers in the paper preparation process can be reduced in the wet-process paper forming process, and then the mechanical property and insulativity of the aramid insulation paper are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of aramid paper insulation paper, and particularly relates to aramid paper reinforced by aramid deposition nanofiber and a preparation method thereof. BACKGROUND

[0002] Insulation paper belongs to solid insulation material and is widely applied in electrical equipment such as transformers and capacitors. Aramid paper is a kind of paper prepared from aramid fiber. The aramid fiber has excellent properties such as high strength, high modulus, insulation, high temperature resistance and acid and alkali resistance, and has a wide application prospect in the field of insulation paper. However, although the aramid fiber has the above excellent properties, due to the defects such as smooth surface, few active groups and strong chemical inertness of the aramid fiber, the aramid fiber lacks effective combination between components, the interface bonding force is poor, and the uniformity is poor during paper making, which further leads to the problems such as low strength of the insulation paper prepared from the aramid fiber, and the excellent performance of the aramid fiber itself cannot be fully utilized.

[0003] In view of the above problems, the common solution at present is to add reinforcing fibers to enhance the aramid paper. For example, thermoplastic bonding fibers with obvious melting temperature are added during paper preparation, and the bonding fibers are melted by hot pressing to improve the bonding force between fibers. However, this method can enhance the aramid paper to a certain extent, but the melted thermoplastic fibers will cause larger pores or holes in the paper, which is not conducive to the improvement of the insulation performance of the aramid paper. For another example, aramid nanofiber is added during paper preparation, and the prepared aramid paper is dried and hot pressed, so that the nanofiber is fully bonded and interwoven with the surface of the chopped fiber, and the tensile strength and tear strength of the aramid paper are further improved, thereby improving the mechanical properties of the aramid paper. However, this method improves the mechanical properties of the aramid paper through the bonding and interweaving between the aramid nanofiber and the chopped fiber, and the physical overlap and interweaving will cause a large number of pores in the aramid paper. These pores can provide a breakdown path for the current during electrical breakdown, and the relatively loose structure greatly limits the insulation performance of the aramid paper, resulting in the decrease of the insulation of the aramid paper.

[0004] It can be seen that the existing aramid insulation paper has the problem that the mechanical properties and insulation are difficult to be considered. Therefore, it is urgent to provide an aramid insulation paper with high mechanical properties, high breakdown strength and low dielectric constant. SUMMARY

[0005] The present application aims to provide an aramid paper reinforced by aramid deposition nanofiber and a preparation method thereof. The aramid paper reinforced by aramid deposition nanofiber provided by the present application has high mechanical properties, high breakdown strength and low dielectric constant.

[0006] In order to achieve the above application purpose, the present application provides the following technical solutions:

[0007] The application provides an aramid fiber precipitation nanofiber reinforced aramid insulation paper, comprising a fiber network and cationic polyelectrolyte and anionic polyelectrolyte dispersed in the fiber network; the fiber network is formed by interweaving of aramid short fibers, aramid precipitation fibers and aramid precipitation nanofibers.

[0008] Preferably, the length of the aramid precipitation nanofiber is 10-100 μm, and the diameter of the aramid precipitation nanofiber is 80-120 nm.

[0009] Preferably, the length of the aramid short fiber is 3-5 mm, and the diameter of the aramid short fiber is 10-30 μm.

[0010] Preferably, the mass ratio of the aramid short fiber, the aramid precipitation fiber and the aramid precipitation nanofiber is (40-70):(30-70):(5-25).

[0011] The application provides a preparation method of the aramid fiber precipitation nanofiber reinforced aramid insulation paper.

[0012] (1) mixing aramid precipitation fibers with lye to perform alkali treatment, to obtain fine precipitation fibers;

[0013] (2) mixing the fine precipitation fibers obtained in the step (1) with water to perform homogenization treatment, to obtain aramid precipitation nanofibers;

[0014] (3) mixing aramid short fibers, aramid precipitation fibers, the aramid precipitation nanofibers obtained in the step (2), water, cationic polyelectrolyte and anionic polyelectrolyte, to obtain mixed slurry;

[0015] (4) performing wet paper making on the mixed slurry obtained in the step (3), to obtain aramid fiber precipitation nanofiber reinforced aramid base paper;

[0016] (5) performing hot pressing treatment on the aramid fiber precipitation nanofiber reinforced aramid base paper obtained in the step (4), to obtain aramid fiber precipitation nanofiber reinforced aramid insulation paper.

[0017] Preferably, the temperature of the alkali treatment in the step (1) is 60-120 ℃, and the time of the alkali treatment is 1-5 h.

[0018] Preferably, the pressure of the homogenization treatment in the step (2) is 50-100 MPa, and the time of the homogenization treatment is 1-3 h.

[0019] Preferably, the cationic polyelectrolyte in the step (3) is cationic polyacrylamide, and the mass of the cationic polyelectrolyte accounts for 0.03%-0.07% of the mass of the mixed slurry.

[0020] Preferably, the anionic polyelectrolyte in step (3) is an anionic polyacrylamide, and the mass of the anionic polyelectrolyte accounts for 0.08% to 0.12% of the mass of the mixed slurry.

[0021] Preferably, the temperature of the hot-pressing treatment in step (5) is 220 to 280℃, and the pressure of the hot-pressing treatment is 8 to 18 MPa.

[0022] The present application provides an aramid fiber precipitation nanofiber reinforced aramid insulation paper, comprising a fiber network and cationic polyelectrolyte and anionic polyelectrolyte dispersed in the fiber network; the fiber network is formed by interweaving fibers comprising aramid short fibers, aramid precipitation fibers and aramid precipitation nanofibers. The present application adds aramid precipitation fibers when preparing the insulation paper, which can interweave with aramid short fibers into a fiber layer; the present application adds aramid precipitation nanofibers when preparing the insulation paper, which can fill the pores between aramid short fibers and aramid precipitation fibers, so that the aramid short fibers and aramid precipitation fibers are fully adhered and interwoven, thereby improving the tensile strength of the aramid insulation paper; at the same time, the addition of aramid precipitation nanofibers can reduce the possible breakdown path of the current and increase the electron trap density of the aramid insulation paper; the excellent insulation performance of aramid precipitation nanofibers itself provides insulation performance for the aramid insulation paper; the present application adds cationic polyelectrolyte and anionic polyelectrolyte in the wet papermaking process, which can form a dual retention aid and reduce the loss of aramid precipitation nanofibers in the papermaking process, thereby making the aramid precipitation nanofibers fully fill the pores between the short fibers and the aramid precipitation fibers. The results of the examples show that the aramid fiber precipitation nanofiber reinforced aramid insulation paper provided by the present application has a tensile strength of 31.2 to 35.7 N / cm, a tear strength of 2065 to 2503 mN, a breakdown voltage of 1184 to 1564 V, a breakdown strength of 16.4 to 21.14 KV / mm, and a dielectric constant of 2.035 to 2.076, which has high mechanical properties, high breakdown strength and low dielectric constant. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 SEM image of the aramid fiber precipitation nanofiber reinforced aramid insulation paper prepared in Example 1 of the present application. DETAILED DESCRIPTION

[0024] The present application provides an aramid fiber precipitation nanofiber reinforced aramid insulation paper, comprising a fiber network and cationic polyelectrolyte and anionic polyelectrolyte dispersed in the fiber network; the fiber network is formed by interweaving fibers comprising aramid short fibers, aramid precipitation fibers and aramid precipitation nanofibers.

[0025] The aramid fiber precipitation nanofiber reinforced aramid insulation paper provided by the application comprises a fiber network.

[0026] In the application, the fiber network is formed by interweaving aramid short fibers, aramid precipitation fibers and aramid precipitation nanofibers.

[0027] In the application, the length of the aramid short fibers is preferably 3-5 mm, and more preferably 4-5 mm; and the diameter of the aramid short fibers is preferably 10-30 μm, and more preferably 15-30 μm. In the preparation of the insulation paper, the aramid short fibers are added, and the content is controlled in the above range, so that the aramid short fibers and the aramid precipitation fibers are interwoven and overlapped, thereby enhancing the tensile strength and tear strength of the aramid insulation paper.

[0028] In the application, the length of the aramid precipitation fibers is preferably 1-3 mm, and more preferably 2-3 mm; and the diameter of the aramid precipitation fibers is preferably 20-50 μm, and more preferably 30-40 μm. The aramid precipitation fibers used in the application have a large specific surface area, and are more conducive to interweaving and overlapping with the aramid short fibers, thereby enhancing the tensile strength and tear strength of the aramid insulation paper.

[0029] In the application, the length of the aramid precipitation nanofibers is preferably 10-100 μm, and more preferably 10-50 μm; and the diameter of the aramid precipitation nanofibers is preferably 80-120 nm, and more preferably 100-120 nm. The aramid precipitation nanofibers used in the application have the above size, and can be fully filled in the gaps formed by the interweaving and overlapping of the aramid short fibers and the aramid precipitation fibers.

[0030] In the application, the mass ratio of the aramid short fibers, the aramid precipitation fibers and the aramid precipitation nanofibers is preferably (40-70):(30-70):(5-25), and more preferably (50-65):(35-60):(5-15). The use amount of the three is controlled in the above range, so that the aramid precipitation nanofibers can be fully filled in the fiber pores formed by the aramid short fibers and the aramid precipitation fibers, thereby improving the adhesion between the fibers.

[0031] The application fills the pores between the aramid short fibers and the aramid precipitation fibers with the aramid precipitation nanofibers, thereby improving the insulation performance of the aramid insulation paper, and making the aramid insulation paper have high mechanical properties, high breakdown strength and low dielectric constant.

[0032] The application provides a preparation method of the aramid fiber precipitation nanofiber reinforced aramid insulation paper.

[0033] (1) mixing aramid precipitation fibers with lye, and performing alkali treatment to obtain fine precipitation fibers;

[0034] (2) mixing the fine precipitated fiber obtained in the step (1) with water, and performing homogenization treatment to obtain aramid precipitated nanofiber;

[0035] (3) mixing aramid short-cut fiber, aramid precipitated fiber, aramid precipitated nanofiber obtained in the step (2), water, cationic polyelectrolyte and anionic polyelectrolyte to obtain mixed slurry;

[0036] (4) performing wet papermaking on the mixed slurry obtained in the step (3) to obtain aramid precipitated nanofiber reinforced aramid base paper;

[0037] (5) performing hot-pressing treatment on the aramid precipitated nanofiber reinforced aramid base paper obtained in the step (4) to obtain aramid precipitated nanofiber reinforced aramid insulating paper.

[0038] In the present application, the fine precipitated fiber is obtained by mixing aramid precipitated fiber with alkali solution and performing alkali treatment.

[0039] In the present application, the method for preparing aramid precipitated fiber preferably comprises:

[0040] The aramid stock solution is obtained by mixing phenylenediamine, phthaloyl chloride, cosolvent and organic solvent, and then performing polymerization reaction.

[0041] The aramid precipitated fiber is obtained by performing mechanical treatment on the sheet-like membrane-shaped precipitated fiber.

[0042] The aramid precipitated fiber is obtained by performing mechanical treatment on the sheet-like membrane-shaped precipitated fiber.

[0043] In the present application, the aramid stock solution is obtained by mixing phenylenediamine, phthaloyl chloride, cosolvent and organic solvent, and then performing polymerization reaction.

[0044] In the present application, the phenylenediamine is preferably m-phenylenediamine or p-phenylenediamine, and the phthaloyl chloride is preferably m-phthaloyl chloride or p-phthaloyl chloride. In the present application, the phenylenediamine and phthaloyl chloride are used as raw materials for preparing aramid precipitate, and they can perform polymerization reaction to obtain aramid. When the phenylenediamine is m-phenylenediamine and the phthaloyl chloride is m-phthaloyl chloride, m-aramid is obtained; when the phenylenediamine is p-phenylenediamine and the phthaloyl chloride is p-phthaloyl chloride, p-aramid is obtained.

[0045] In the present application, the molar ratio of phthaloyl chloride to phenylenediamine is preferably 0.8-1.4:1, and more preferably 0.9-1.2:1. In the present application, the molar ratio of the two is controlled in the above range, which is more conducive to the full reaction of the two to obtain aramid.

[0046] In the present application, the co-solvent preferably includes lithium chloride, lithium bromide, calcium chloride or calcium bromide. The present application is more advantageous for dissolving phenylenediamine and terephthaloyl chloride in the organic solvent by adding the co-solvent.

[0047] In the present application, the mass of the co-solvent preferably accounts for 5% to 10% of the mass of the organic solvent, and more preferably 7% to 9%. The present application can promote the rapid dissolution of phenylenediamine and terephthaloyl chloride in the organic solvent by controlling the amount of the co-solvent in the above range.

[0048] In the present application, the organic solvent preferably includes N,N-dimethylacetamide, N,N-dimethylformamide or N-methylpyrrolidone. The present application has good solubility for phenylenediamine and terephthaloyl chloride by using the above-mentioned organic solvent.

[0049] In the present application, the mass of the phenylenediamine preferably accounts for 3% to 10% of the mass of the organic solvent, and more preferably 4% to 7%. The present application can make phenylenediamine and terephthaloyl chloride completely dissolved by controlling the amount of phenylenediamine in the above range.

[0050] The present application does not have special limitations on the method of mixing the phenylenediamine, terephthaloyl chloride, co-solvent and organic solvent, and can completely dissolve the phenylenediamine, terephthaloyl chloride and co-solvent in the organic solvent.

[0051] In the present application, the temperature of the polymerization reaction is preferably 60 to 100℃, and more preferably 60 to 80℃; the time of the polymerization reaction is preferably 5 to 10h, and more preferably 6 to 8h. The present application can promote the sufficient reaction of phenylenediamine and terephthaloyl chloride to obtain aramid fiber by controlling the temperature and time of the polymerization reaction in the above range.

[0052] The present application preferably adds a base after the polymerization reaction. In the present application, the base is preferably a mixed base composed of sodium hydroxide and potassium hydroxide, and the mass ratio of the sodium hydroxide and potassium hydroxide is preferably (5 to 8):(2 to 5), and more preferably 1:1. The present application can neutralize the acidic product generated in the polymerization reaction by adding a base in the polymerization reaction, so that the reaction environment is kept in a neutral or nearly neutral state, thereby being advantageous for the continuous progress of the polymerization reaction and the quality control of the product. The present application does not have special limitations on the amount of the base, and the amount of the base can be added according to the reaction condition, and the reaction system can be adjusted to maintain a neutral or nearly neutral state.

[0053] The present application preferably adds an organic solvent to the polymerization reaction system after the polymerization reaction, so that the mass concentration of aramid fiber in the aramid fiber stock solution is 3% to 15%, and preferably 5%. The present application adjusts the mass concentration of the aramid fiber stock solution in the above range, which is more advantageous for obtaining the precipitated fiber in the form of a sheet membrane in the subsequent high-speed shearing coagulation bath.

[0054] After obtaining the aramid stock solution, the aramid stock solution is preferably injected into a high-speed shearing coagulation bath to obtain the sheet-like membrane-shaped precipitated fiber in the coagulation bath.

[0055] In the present application, the shearing rate of the high-speed shearing coagulation bath is preferably 600-2000 rpm, and more preferably 1000-2000 rpm. The coagulation bath of the high-speed shearing coagulation bath is preferably a mixture of dimethylacetamide and deionized water, and the mass ratio of the dimethylacetamide and deionized water is preferably (10-50):(20-90), and more preferably 10:90. By high-speed shearing precipitation of the aramid stock solution in the high-speed shearing coagulation bath, the present application can obtain aramid precipitated fiber with a thin film structure, which has a large specific surface area, and is beneficial to improving the fiber interweaving and hydrogen bond connection effect in the aramid paper, and further improving the interface bonding effect of the fiber.

[0056] The present application preferably filters and dries the solid obtained in the coagulation bath in sequence to obtain the sheet-like membrane-shaped precipitated fiber. The present application does not have special limitations on the method of filtering and drying, and the obtained solid can be dried by using conventional filtering and drying.

[0057] After obtaining the sheet-like membrane-shaped precipitated fiber, the present application preferably mechanically processes the sheet-like membrane-shaped precipitated fiber to obtain aramid precipitated fiber.

[0058] In the present application, the method of mechanical processing is preferably beating, and the method of beating is preferably mixing the sheet-like membrane-shaped precipitated fiber with water and beating. The present application does not have special limitations on the device for beating, and conventional beating devices can be used. In the embodiments of the present application, the device for beating can be a PFI beater.

[0059] In the present application, the mass ratio of the sheet-like membrane-shaped precipitated fiber to water is preferably (10-50):(100-300), and more preferably 20:300. By controlling the mass ratio of the two within the above range, the present application is more beneficial to fully defibrating the sheet-like membrane-shaped precipitated fiber into aramid precipitated fiber.

[0060] In the present application, the number of revolutions of beating is preferably 10000-40000 rpm, and more preferably 20000-30000 rpm; and the beating degree is preferably 38-46 °S rpm, and more preferably 42 °S rpm. By controlling the parameters of beating within the above range, the present application can make the aramid precipitated fiber have a large specific surface area.

[0061] In the present application, the alkali liquor is preferably an alkali metal hydroxide solution, more preferably a sodium hydroxide solution and / or a potassium hydroxide solution. In the present application, when the alkali liquor is a sodium hydroxide solution and a potassium hydroxide solution, the volume ratio of the sodium hydroxide to the potassium hydroxide is preferably (20-50):(50-80), more preferably 1:1. The present application is more conducive to transverse cutting of aramid precipitation fibers by using the above alkali liquor for alkali treatment, and reduces the size of aramid precipitation fibers.

[0062] In the present application, the concentration of the alkali liquor is preferably 10%-50%, more preferably 25%-35%. The present application is more conducive to transverse cutting of aramid precipitation fibers by controlling the concentration of the alkali liquor within the above range.

[0063] The present application does not have specific limitations on the amount of the alkali liquor, which can be adjusted according to the amount of aramid precipitation fibers, so that the aramid precipitation fibers can be fully immersed in the alkali liquor.

[0064] In the present application, the temperature of the alkali treatment is preferably 60-120°C, more preferably 80-100°C; and the time of the alkali treatment is preferably 1-5h, more preferably 3-5h. The present application can promote transverse cutting of aramid precipitation fibers to form fine precipitation fibers by performing alkali treatment at the above temperature and time.

[0065] The present application preferably sequentially performs washing and drying on the system obtained after the alkali treatment to obtain fine precipitation fibers. In the present application, the length of the fine precipitation fibers is preferably 100-300μm. The present application does not have special limitations on the operation method of the washing and drying, which can be performed by using conventional operation methods of washing and drying, so that the fine precipitation fibers can be fully dried.

[0066] After obtaining the fine precipitation fibers, the present application mixes the fine precipitation fibers with water, performs homogenization treatment, and obtains aramid precipitation nanofibers.

[0067] In the present application, the water is used as a dispersant for the fine precipitation fibers during homogenization treatment, and needs to be removed after obtaining aramid precipitation nanofibers. Therefore, the present application does not have special limitations on the mass ratio of the fine precipitation fibers to the water, which can be adjusted according to needs, so that the homogenization treatment can be fully performed.

[0068] In the present application, the pressure of the homogenization treatment is preferably 50-80 MPa, more preferably 50-80 MPa; the time of the homogenization treatment is preferably 1-3 h, more preferably 2-3 h. By homogenization treatment under the above parameter range, the present application can destroy the dense entanglement between the microfibers in the fine as-spun fiber core layer, realize effective separation of the microfibers and fine fibers in the fine as-spun fiber core layer, and thus obtain aramid as-spun nanofibers with a diameter of 80-120 nm. The device for the homogenization treatment is not particularly limited in the present application, and a conventional homogenizer can be used.

[0069] The present application preferably dries the solid obtained by the homogenization treatment to obtain aramid as-spun nanofibers. The method for the drying is not particularly limited in the present application, and the homogenized fibers can be fully dried.

[0070] The present application can obtain aramid as-spun fibers with a length of 1-3 mm and a diameter of 20-50 μm by using the above preparation method.

[0071] After obtaining the aramid as-spun nanofibers, the present application mixes aramid chopped fibers, aramid as-spun fibers, the aramid as-spun nanofibers, water, a cationic polyelectrolyte and an anionic polyelectrolyte to obtain a mixed slurry.

[0072] In the present application, the cationic polyelectrolyte is preferably cationic polyacrylamide, abbreviated as CPAM. In the present application, the molecular weight of the CPAM is preferably 2×10 4 -5×10 5 , more preferably 3×10 4 -4×10 5 . In the present application, the mass of the cationic polyelectrolyte preferably accounts for 0.03%-0.07% of the mass of the mixed slurry, more preferably 0.05%-0.06%.

[0073] In the present application, the anionic polyelectrolyte is preferably anionic polyacrylamide, abbreviated as APAM. In the present application, the molecular weight of the APAM is preferably 5×10 6 -10×10 6 , more preferably 6×10 6 -8×10 6 . In the present application, the mass of the anionic polyelectrolyte preferably accounts for 0.08%-0.12% of the mass of the mixed slurry, more preferably 0.10%-0.12%.

[0074] By adding the cationic polyelectrolyte and the anionic polyelectrolyte, the present application can form a dual retention and drainage system, reduce the loss of aramid as-spun nanofibers during wet papermaking, and thus make the added aramid as-spun nanofibers fully fill the pores of the aramid chopped fibers and the aramid as-spun fibers.

[0075] In the present application, the water is preferably deionized water, and the water is preferably added in an amount such that the total mass concentration of aramid short fibers, aramid fibrids and aramid fibrid nanofibers in the mixed slurry is 0.02-0.05%, more preferably 0.05%.

[0076] The method for mixing the aramid short fibers, aramid fibrids, aramid fibrid nanofibers, water, cationic polyelectrolyte and anionic polyelectrolyte is not particularly limited in the present application, and the above components can be mixed uniformly. In the embodiments of the present application, the method for mixing the aramid short fibers, aramid fibrids, aramid fibrid nanofibers, water, cationic polyelectrolyte and anionic polyelectrolyte can be specifically as follows: after mixing the aramid short fibers, aramid fibrids, aramid fibrid nanofibers and water, the mixture is transferred to a high-speed shearing device, cationic polyelectrolyte CPAM is added, and after shearing and stirring at a speed of 1500 rpm for 3 min, anionic polyelectrolyte APAM is added to obtain a mixed slurry.

[0077] After obtaining the mixed slurry, the mixed slurry is subjected to wet papermaking in the present application to obtain aramid fibrid nanofiber-reinforced aramid base paper.

[0078] Preferably, in the present application, the mixed slurry is mixed with a dispersant and a defoaming agent before wet papermaking. By adding a dispersant and a defoaming agent, the dispersing uniformity of fibers in the mixed slurry is more improved.

[0079] The method for mixing the mixed slurry with a dispersant and a defoaming agent is not particularly limited in the present application, and the above components can be mixed uniformly.

[0080] In the present application, the dispersant is preferably a water-soluble polymer PEO, and the molecular weight of the water-soluble polymer PEO is preferably 7x10 4 ~5x10 5 ; and the mass of the dispersant is preferably 0.1-0.5% of the mass of the mixed slurry, more preferably 0.2-0.4%. By adding a dispersant, the dispersing stability of fibers in the mixed slurry is more improved.

[0081] In the present application, the defoaming agent is preferably a polyether defoaming agent, more preferably polyethylene glycol, polyethylene oxide alcohol or polyether siloxane; and the mass of the defoaming agent is preferably 0.01-0.05% of the mass of the mixed slurry, more preferably 0.02-0.04%. By adding a defoaming agent, air bubbles in the mixed slurry can be eliminated, and the distribution uniformity of aramid insulating paper fibers is more improved.

[0082] In the present application, the wet paper forming method is preferably inclined wire wet paper forming, and the mode of the inclined wire wet paper forming is preferably a white water circulation mode. In an embodiment of the present application, the inclined wire wet paper forming method can specifically be as follows: mixing the mixed slurry, the dispersing agent and the defoaming agent to obtain a mixed dispersion liquid, pouring the mixed dispersion liquid into an inclined wire wet paper former, and then sequentially performing pressing and drying to obtain aramid sink nano-fiber reinforced aramid base paper. The present application does not specially limit the amount of the mixed dispersion liquid poured into the inclined wire wet paper former, which can be adjusted according to the thickness of the paper to be prepared.

[0083] In the present application, the pressure of the pressing is preferably 0.3-0.7 MPa, and more preferably 0.6 MPa; the temperature of the drying is preferably 100-110℃, and more preferably 105℃; and the time of the drying is preferably 5-15 min, and more preferably 10 min. By controlling the parameters of the pressing and the drying within the above ranges, the present application can obtain dried aramid sink nano-fiber reinforced aramid base paper.

[0084] After obtaining the aramid sink nano-fiber reinforced aramid base paper, the present application performs hot pressing treatment on the aramid sink nano-fiber reinforced aramid base paper to obtain aramid sink nano-fiber reinforced aramid insulation paper.

[0085] In the present application, the method of the hot pressing treatment is preferably roll hot pressing. In the present application, the temperature of the roll hot pressing is preferably 220-280℃, and more preferably 240-250℃; the pressure of the roll hot pressing is preferably 8-18 MPa, and more preferably 9-15 MPa; and the roller speed of the roll hot pressing is preferably 2-5 m / min, and more preferably 3-5 m / min. The present application can make the combination between aramid short fibers and sink fibers more close through hot pressing treatment.

[0086] The method provided by the present application can prepare aramid sink fibers with a thin film structure and a large specific surface area through high-speed shearing sink method, which is beneficial to improving the fiber interweaving and hydrogen bond connection effect in the aramid paper, and further improving the interface combination effect of the fibers; the present application adds cationic polyelectrolyte and anionic polyelectrolyte in the wet paper forming process to form a dual retention and drainage aid, which can reduce the loss of aramid sink nano-fibers in the paper preparation process; the present application combines the wet paper forming technology with the hot pressing technology, and the synergistic effect of high temperature and high pressure can make the combination between short fibers and sink fibers more close through physical means, and further improve the mechanical properties and insulation of the aramid insulation paper.

[0087] The technical solutions in the present application will be clearly and completely described below in combination with the embodiments in the present application. Apparently, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative effort belong to the scope of the present application.

[0088] Embodiment 1

[0089] A preparation method of aramid deposition nanofiber reinforced aramid insulation paper, the steps are:

[0090] (1) The preparation method of aramid deposition fiber is that 24 g of m-phenylenediamine and 35 lithium chloride auxiliary solvent are dissolved in 350 mL of N, N-dimethylacetamide, then 24 g of isophthaloyl chloride is added, after 8 h of polymerization reaction at 60 DEG C, a mixed alkali (mass ratio of 1:1) of sodium hydroxide and potassium hydroxide is added to make the reaction system neutral, and aramid stock solution with a mass concentration of 5% of aramid is obtained;

[0091] The aramid stock solution is injected into a high-speed shearing coagulation bath with a rotation speed of 1000 rpm / min, a mixture of dimethylacetamide and water (mass ratio of DMAc to H2O is 10:90), and a sheet film-shaped deposition fiber is obtained in the coagulation bath, and after filtration and drying, a dry sheet film-shaped deposition fiber is obtained;

[0092] The dry sheet film-shaped deposition fiber 20 g is placed in a PFI beater with 300 g of deionized water, and beating treatment is performed, the beating rotation speed is 20000 rpm, and the beating degree is 42 °S rpm, and aramid deposition fiber is obtained;

[0093] A 50% concentration sodium hydroxide solution and a 50% concentration potassium hydroxide solution are mixed according to a volume ratio of 1:1 to obtain an alkali solution, the aramid deposition fiber is immersed in the alkali solution, alkali treatment is performed at 80 DEG C for 3 h, then the obtained fiber is washed with deionized water, and dried at 105 DEG C to obtain fine deposition fiber;

[0094] (2) The fine deposition fiber obtained in the step (1) is mixed with 1000 mL of water, injected into a homogenizer, and homogenized at 100 MPa for 2 h, and after drying, aramid deposition nanofiber is obtained;

[0095] (3) mixing aramid short-cut fiber with length of 3-5 mm and diameter of 10-30 pm, aramid fibrid with length of 1-3 mm and diameter of 20-50 pm, aramid fibrid nanofiber with length of 10-100 pm and diameter of 80-120 nm obtained in step (2) according to mass ratio of 58.2:38.8:3, and 2000 mL deionized water, and then transferring into a high-speed shearing device, adding cationic polyelectrolyte CPAM (molecular weight of 2 x 10 4 ~ 5 x 10 5 ), and then adding anionic polyelectrolyte APAM (molecular weight of 5 x 10 6 ~ 10 x 10 6 ) after shearing and stirring at 1500 rpm for 3 min to obtain a mixed slurry; wherein the amount of deionized water is added to make the total mass concentration of aramid short-cut fiber, aramid fibrid and aramid fibrid nanofiber in the mixed slurry 0.05%; the mass of the cationic polyelectrolyte accounts for 0.04% of the mass of the mixed slurry, and the mass of the anionic polyelectrolyte accounts for 0.1% of the mass of the mixed slurry;

[0096] (4) mixing the mixed slurry obtained in step (3) with dispersant (0.1% PEO) and 1 mL of polyethylene glycol defoaming agent with a concentration of 0.02%, and then pouring into a inclined net wet paper page former, and then paper preparation is carried out in a white water circulation mode, and then pressing is carried out at 0.6 MPa, and then drying is carried out at 105 °C for 10 min to obtain aramid fibrid nanofiber reinforced aramid base paper;

[0097] (5) aramid fibrid nanofiber reinforced aramid insulation paper is obtained by roll hot pressing the aramid fibrid nanofiber reinforced aramid base paper obtained in step (4) under the conditions of temperature of 240 °C, pressure of 12 MPa, and roller speed of 3 m / min;

[0098] The SEM image of the aramid fibrid nanofiber reinforced aramid insulation paper prepared in this example is shown in Figure 1 .

[0099] Example 2

[0100] A method for preparing aramid fibrid nanofiber reinforced aramid insulation paper is as follows:

[0101] (1) mixing sodium hydroxide solution with a concentration of 50% and potassium hydroxide solution with a concentration of 50% according to volume ratio of 1:1 to obtain lye, and then immersing aramid fibrid prepared according to the method of example 1 in the lye, and then alkali treatment is carried out at 80 °C for 3 h, and then the obtained fiber is washed with deionized water, and then drying is carried out at 105 °C to obtain fine fibrid;

[0102] (2) The fine precipitated fiber obtained in step (1) is mixed with 1000 mL of water, injected into a homogenizer, and homogenized at 80 MPa for 2 h, and after drying, aramid precipitated nanofibers are obtained;

[0103] (3) Aramid short fibers with a length of 3-5 mm and a diameter of 10-30 μm, aramid precipitated fibers with a length of 1-3 mm and a diameter of 20-50 μm, and aramid precipitated nanofibers with a length of 10-100 μm and a diameter of 80-120 nm obtained in step (2) are mixed in a mass ratio of 58.2:38.8:3 with 2000 mL of deionized water, and then transferred to a high-speed shearing device, and a cationic polyelectrolyte CPAM (molecular weight 2 x 10 4 ~ 5 x 10 5 ) is added, and after shearing stirring at a speed of 1500 rpm for 3 min, an anionic polyelectrolyte APAM (molecular weight 5 x 10 6 ~ 10 x 10 6 ) is added to obtain a mixed slurry; wherein the amount of deionized water is such that the total mass concentration of aramid short fibers, aramid precipitated fibers and aramid precipitated nanofibers in the mixed slurry is 0.05%; the mass of the cationic polyelectrolyte accounts for 0.03%-0.07% of the mass of the mixed slurry, and the mass of the anionic polyelectrolyte accounts for 0.08%-0.12% of the mass of the mixed slurry;

[0104] (4) The mixed slurry obtained in step (3) is mixed with a dispersant (0.1% PEO) and 1 mL of a polyethylene glycol antifoam agent with a concentration of 0.02%, and then poured into a inclined net wet paper sheet former, and paper is prepared using a white water circulation mode, and then pressed at 0.6 MPa and dried at 105°C for 10 min to obtain aramid precipitated nanofiber-reinforced aramid base paper;

[0105] (5) The aramid precipitated nanofiber-reinforced aramid base paper obtained in step (4) is subjected to roll hot pressing under the conditions of a temperature of 240°C, a pressure of 12 MPa, and a roll speed of 3 m / min to obtain aramid precipitated nanofiber-reinforced aramid insulating paper.

[0106] Example 3

[0107] A method for preparing aramid precipitated nanofiber-reinforced aramid insulating paper is as follows:

[0108] (1) A lye is obtained by mixing a 50% sodium hydroxide solution and a 50% potassium hydroxide solution in a volume ratio of 1:1, aramid precipitated fibers prepared according to the method of Example 1 are immersed in the lye, alkali-treated at 80°C for 3 h, and then washed with deionized water, and dried at 105°C to obtain fine precipitated fibers;

[0109] (2) The fine precipitated fiber obtained in step (1) is mixed with 1000 mL of water, injected into a homogenizer, and homogenized at 100 MPa for 2 h, and after drying, aramid precipitated nanofibers are obtained;

[0110] (3) Aramid short fibers with a length of 3-5 mm and a diameter of 10-30 μm, aramid precipitated fibers with a length of 1-3 mm and a diameter of 20-50 μm, and aramid precipitated nanofibers with a length of 10-100 μm and a diameter of 80-120 nm obtained in step (2) are mixed in a mass ratio of 56.4:37.6:6 with 2000 mL of deionized water, and then transferred to a high-speed shearing device, and a cationic polyelectrolyte CPAM (molecular weight of 2 x 10 4 - 5 x 10 5 ) is added, and after shearing stirring at a speed of 1500 rpm for 3 min, an anionic polyelectrolyte APAM (molecular weight of 5 x 10 6 - 10 x 10 6 ) is added to obtain a mixed slurry; wherein the amount of deionized water is such that the total mass concentration of aramid short fibers, aramid precipitated fibers and aramid precipitated nanofibers in the mixed slurry is 0.05%; the mass of the cationic polyelectrolyte accounts for 0.03%-0.07% of the mass of the mixed slurry, and the mass of the anionic polyelectrolyte accounts for 0.08%-0.12% of the mass of the mixed slurry;

[0111] (4) The mixed slurry obtained in step (3) is mixed with a dispersant (0.1% PEO) and 1 mL of a polyethylene glycol antifoam agent with a concentration of 0.02%, and then poured into a inclined net wet paper sheet former, and paper is prepared using a white water circulation mode, and then pressed at 0.6 MPa and dried at 105°C for 10 min to obtain aramid precipitated nanofiber-reinforced aramid base paper;

[0112] (5) The aramid precipitated nanofiber-reinforced aramid base paper obtained in step (4) is subjected to roll hot pressing under the conditions of a temperature of 240°C, a pressure of 12 MPa, and a roll speed of 3 m / min to obtain aramid precipitated nanofiber-reinforced aramid insulating paper.

[0113] Example 4

[0114] A method for preparing aramid precipitated nanofiber-reinforced aramid insulating paper is as follows:

[0115] (1) A lye is obtained by mixing a 50% sodium hydroxide solution and a 50% potassium hydroxide solution in a volume ratio of 1:1, aramid precipitated fibers prepared according to the method of Example 1 are immersed in the lye, alkali-treated at 80°C for 3 h, and then washed with deionized water, and dried at 105°C to obtain fine precipitated fibers;

[0116] (2) The fine precipitated fibers obtained in step (1) are mixed with 1000 mL of water, injected into a homogenizer, and homogenized at 100 MPa for 2 h, and after drying, aramid precipitated nanofibers are obtained;

[0117] (3) Aramid short fibers with a length of 3-5 mm and a diameter of 10-30 μm, aramid precipitated fibers with a length of 1-3 mm and a diameter of 20-50 μm, and aramid precipitated nanofibers with a length of 10-100 μm and a diameter of 80-120 nm obtained in step (2) are mixed in a mass ratio of 54.6:36.4:9 with 2000 mL of deionized water, and then transferred to a high-speed shearing device, and a cationic polyelectrolyte CPAM (molecular weight of 2 x 10 4 -5 x 10 5 ) is added, and after shearing and stirring at a speed of 1500 rpm for 3 min, an anionic polyelectrolyte APAM (molecular weight of 5 x 10 6 -10 x 10 6 ) is added to obtain a mixed slurry; wherein the amount of deionized water is such that the total mass concentration of aramid short fibers, aramid precipitated fibers and aramid precipitated nanofibers in the mixed slurry is 0.05%; the mass of the cationic polyelectrolyte accounts for 0.03%-0.07% of the mass of the mixed slurry, and the mass of the anionic polyelectrolyte accounts for 0.08%-0.12% of the mass of the mixed slurry;

[0118] (4) The mixed slurry obtained in step (3) is mixed with a dispersant (0.1% PEO) and 1 mL of a polyethylene glycol antifoam agent with a concentration of 0.02%, and then poured into a inclined net wet paper sheet former, and paper is prepared using a white water circulation mode, and then pressed at 0.6 MPa and dried at 105°C for 10 min to obtain aramid precipitated nanofiber-reinforced aramid base paper;

[0119] (5) The aramid precipitated nanofiber-reinforced aramid base paper obtained in step (4) is subjected to roll hot pressing under the conditions of a temperature of 240°C, a pressure of 12 MPa, and a roll speed of 3 m / min to obtain aramid precipitated nanofiber-reinforced aramid insulating paper.

[0120] Example 5

[0121] A method for preparing aramid precipitated nanofiber-reinforced aramid insulating paper is as follows:

[0122] (1) 50% concentration of sodium hydroxide solution and 50% concentration of potassium hydroxide solution were mixed in a volume ratio of 1:1 to obtain an alkali solution, and the aramid ripening fiber prepared according to the method of Example 1 was immersed in the alkali solution, treated with alkali at 80°C for 3h, and then the obtained fiber was washed with deionized water and dried at 105°C to obtain fine ripening fiber;

[0123] (2) The fine ripening fiber obtained in step (1) was mixed with 1000 mL of water, injected into a homogenizer, and homogenized at 100 MPa for 2h, and then dried to obtain aramid ripening nanofiber;

[0124] (3) Aramid short fiber with a length of 3-5mm and a diameter of 10-30μm, aramid ripening fiber with a length of 1-3mm and a diameter of 20-50μm, and aramid ripening nanofiber with a length of 10-100μm and a diameter of 80-120nm obtained in step (2) were mixed in a mass ratio of 54.6:36.4:9, and 2000mL of deionized water was added and transferred to a high-speed shearing device, and cationic polyelectrolyte CPAM (molecular weight of 2×10 4 ~5×10 5 ) was added, and after shearing stirring at a speed of 1500rpm for 3min, anionic polyelectrolyte APAM (molecular weight of 5×10 6 ~10×10 6 ) was added to obtain a mixed slurry; wherein the amount of deionized water added is such that the total mass concentration of aramid short fiber, aramid ripening fiber and aramid ripening nanofiber in the mixed slurry is 0.05%; the mass of the cationic polyelectrolyte accounts for 0.03%-0.07% of the mass of the mixed slurry, and the mass of the anionic polyelectrolyte accounts for 0.08%-0.12% of the mass of the mixed slurry;

[0125] (4) The mixed slurry obtained in step (3) was mixed with a dispersing agent (0.1% PEO) and 1mL of 0.02% concentration of polyethylene glycol defoaming agent, and then poured into a inclined net wet paper sheet former, and paper was prepared in a white water circulation mode, and then pressed at 0.6MPa and dried at 105°C for 10min to obtain aramid ripening nanofiber reinforced aramid base paper;

[0126] (5) The aramid ripening nanofiber reinforced aramid base paper obtained in step (4) was subjected to roll hot pressing under the conditions of a temperature of 240°C, a pressure of 9MPa, and a roll speed of 3m / min to obtain aramid ripening nanofiber reinforced aramid insulating paper.

[0127] Comparative Example 1

[0128] An aramid insulation paper, which is different from Example 1 in that the homogenization pressure in step (2) is 50 MPa, and the remaining steps are the same as Example 1.

[0129] Comparative Example 2

[0130] An aramid insulation paper, which is different from Example 1 in that no aramid precipitation nanofiber is added in step (3), and the remaining steps are the same as Example 1.

[0131] Comparative Example 3

[0132] An aramid insulation paper, which is different from Example 1 in that no cationic polyelectrolyte CPAM and anionic polyelectrolyte APAM are added in step (3), and the remaining steps are the same as Example 1.

[0133] Comparative Example 4

[0134] An aramid insulation paper, which is different from Example 1 in that the hot-pressing temperature of the roll hot-pressing in step (5) is 180°C, and the remaining steps are the same as Example 1.

[0135] Comparative Example 5

[0136] An aramid insulation paper, which is different from Example 1 in that the pressure of the roll hot-pressing in step (5) is 3 MPa, and the remaining steps are the same as Example 1.

[0137] Test Example

[0138] The test results of the aramid precipitation nanofiber reinforced aramid insulation paper prepared in Examples 1-5 and the aramid paper prepared in Comparative Examples 1-5 are shown in Table 1:

[0139] Table 1 Test results of aramid insulation paper prepared in Examples 1-5 and Comparative Examples 1-5

[0140]

[0141]

[0142] From Table 1, from Examples 1-5, it can be seen that when the fibers in the aramid deposition nanofiber reinforced aramid insulation paper are controlled to be aramid chopped fibers, aramid deposition fibers and aramid deposition nanofibers, the aramid deposition nanofiber reinforced aramid insulation paper can have excellent mechanical properties and insulation; this is because the present application uses aramid deposition nanofibers to fill the pores between aramid chopped fibers and aramid deposition fibers, improves the insulation performance of aramid insulation paper, and makes the aramid insulation paper have high tensile strength, high breakdown strength and low dielectric constant. From the results of Comparative Example 1, it can be seen that when the homogenization pressure is small, the aramid deposition nanofibers prepared are not conducive to fully filling the pores in the aramid chopped fibers and aramid deposition fibers, and thus the mechanical properties of the aramid insulation paper prepared are lower than those of the aramid deposition nanofiber reinforced aramid insulation paper prepared in Example 1. From the results of Comparative Example 2, it can be seen that without adding aramid deposition nanofibers, the mechanical properties and insulation of the aramid insulation paper are lower than those of the aramid deposition nanofiber reinforced aramid insulation paper prepared in Example 1, because the pores in the aramid chopped fibers and aramid deposition fibers are large, and these pores provide a breakdown path for the current during electrical breakdown, becoming a weak point of the paper. From the results of Comparative Example 3, it can be seen that because no cationic polyelectrolyte CPAM and anionic polyelectrolyte APAM are added, a dual retention and drainage system cannot be formed, resulting in a large amount of aramid deposition nanofibers being lost during the preparation of aramid insulation paper, so that the filling amount of aramid deposition nanofibers in the aramid insulation paper is lower than that of Example 1, and the effect of filling the pores in the aramid chopped fibers and aramid deposition fibers is not sufficient, and thus the mechanical properties of the aramid insulation paper prepared are lower than those of the aramid deposition nanofiber reinforced aramid insulation paper prepared in Example 1. From the results of Comparative Examples 4 and 5, it can be seen that when the pressure and temperature of the roll hot pressing are low, the aramid deposition fibers and aramid deposition nanofibers cannot perform a melting and bonding effect on the aramid chopped fibers, which reduces the mechanical properties of the paper itself, and because there is no effective connection between the fibers, most of them are physically connected, resulting in more pores in the aramid paper, which greatly reduces the performance indicators of the aramid paper.

[0143] The above only describes the preferred embodiments of the present application, and it should be noted that those skilled in the art can make several improvements and refinements without departing from the principles of the present application, and these improvements and refinements should also be considered within the scope of protection of the present application.

Claims

1. An aramid insulating paper reinforced with aramid precipitated nanofibers, comprising a fiber network and cationic polyelectrolytes and anionic polyelectrolytes dispersed in the fiber network; the fiber network is formed by interlacing fibers including aramid chopped fibers, aramid precipitated fibers and aramid precipitated nanofibers.

2. The aramid insulating paper reinforced with aramid precipitated nanofibers according to claim 1, characterized in that, The aramid precipitated nanofibers have a length of 10–100 μm and a diameter of 80–120 nm.

3. The aramid insulating paper reinforced with aramid precipitated nanofibers according to claim 1, characterized in that, The length of the aramid chopped fibers is 3-5 mm, and the diameter of the aramid chopped fibers is 10-30 μm.

4. The aramid insulating paper reinforced with aramid precipitated nanofibers according to claim 1, characterized in that, The mass ratio of the aramid chopped fibers, aramid precipitated fibers and aramid precipitated nanofibers is (40-70):(30-70):(5-25).

5. A method for preparing aramid insulating paper reinforced with aramid precipitated nanofibers as described in any one of claims 1 to 4, comprising the following steps: (1) Mix aramid precipitated fibers with alkaline solution and perform alkaline treatment to obtain fine precipitated fibers; (2) The fine precipitated fibers obtained in step (1) are mixed with water and homogenized to obtain aramid precipitated nanofibers. (3) Mix aramid short-cut fibers, aramid precipitated fibers, aramid precipitated nanofibers obtained in step (2), water, cationic polyelectrolyte and anionic polyelectrolyte to obtain a mixed slurry; (4) The mixed pulp obtained in step (3) is wet-processed into paper to obtain aramid base paper reinforced with aramid precipitated nanofibers; (5) The aramid base paper reinforced with aramid precipitated nanofibers obtained in step (4) is subjected to hot pressing treatment to obtain aramid insulating paper reinforced with aramid precipitated nanofibers.

6. The preparation method according to claim 5, characterized in that, In step (1), the temperature of the alkali treatment is 60-120℃, and the time of the alkali treatment is 1-5h.

7. The preparation method according to claim 5, characterized in that, The homogenization pressure in step (2) is 50-100 MPa, and the homogenization time is 1-3 h.

8. The preparation method according to claim 5, characterized in that, In step (3), the cationic polyelectrolyte is cationic polyacrylamide, and the mass of the cationic polyelectrolyte accounts for 0.03% to 0.07% of the mass of the mixed slurry.

9. The preparation method according to claim 5 or 8, characterized in that, In step (3), the anionic polyelectrolyte is anionic polyacrylamide, and the mass of the anionic polyelectrolyte accounts for 0.08% to 0.12% of the mass of the mixed slurry.

10. The preparation method according to claim 5, characterized in that, The temperature of the hot pressing treatment in step (5) is 220-280℃, and the pressure of the hot pressing treatment is 8-18MPa.

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