Aramid precipitation nanofiber reinforced aramid paper as well as preparation method and application thereof

Abstract

The invention provides aramid precipitation nanofiber reinforced aramid paper as well as a preparation method and application thereof, and belongs to the technical field of aramid insulation paper. The meta-aramid precipitation nanofibers are adopted to prepare the fiber coating, a compact protection layer is formed on the surface of the aramid paper after coating, pores in the surface of the aramid paper are filled, the overall structure of the aramid paper is densified, the concentration of electron traps is increased, electron breakdown paths are reduced, and compared with para-aramid precipitation nanofibers, the surface of the aramid paper is more compact. In the preparation process, water is used as a solvent, no organic solvent is contained, the aramid paper is safe, environmentally friendly, green and non-toxic, the aramid fibers cannot be damaged, and various properties of the aramid paper are further improved.

Description

Technical Field

[0001] The invention belongs to the technical field of aramid insulation paper, and specifically relates to aramid precipitated nanofiber reinforced aramid paper and a preparation method and application thereof. Background Art

[0002] Aramid insulation paper is a high-performance special paper-based material with specific properties and uses, which is made by wet-forming aramid short fibers and aramid precipitated fibers and then coated with a coating liquid. Aramid fiber itself has excellent high temperature resistance, good chemical stability, excellent electrical insulation, flame retardancy and corrosion resistance, and plays an important role in the fields of electrical insulation, rail transportation, aerospace, and national defense and military industries.

[0003] The aramid fibers in the existing coating liquid are generally para-aramid fibers. For example, the patent with publication number CN111235944A provides a method for preparing aramid paper coated with aramid nanofibers, in which para-aramid nanofibers are used for coating, and the coating liquid contains dimethyl sulfoxide organic solvent. The performance of the aramid paper prepared in the prior art is still relatively general, and the organic solvent in the coating liquid will cause harm to the environment and human body. Therefore, how to avoid using organic solvents in the preparation process and further improve the performance of aramid paper has become a difficult problem in the prior art. Summary of the invention

[0004] The object of the present invention is to provide an aramid precipitated nanofiber reinforced aramid paper and a preparation method and application thereof. No organic solvent is used in the preparation process of the aramid paper provided by the present invention and the prepared aramid paper has better mechanical properties and insulation properties.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a method for preparing aramid precipitated nanofiber reinforced aramid paper, comprising the following steps:

[0007] (1) mixing meta-aramid precipitated nanofiber slurry with water and a binder to obtain a fiber coating;

[0008] (2) mixing the meta-aramid fiber, the meta-aramid fibrid and water, and performing delamination to obtain a mixed slurry;

[0009] (3) mixing the mixed slurry obtained in step (2) with a dispersant and a defoamer, and forming the mixed slurry to obtain aramid base paper;

[0010] (4) applying the fiber coating obtained in step (1) to the surface of the aramid base paper obtained in step (3), and then hot pressing to obtain aramid precipitated nanofiber reinforced aramid paper;

[0011] There is no chronological order for steps (1) and (2).

[0012] Preferably, in the meta-aramid precipitated nanofiber slurry of step (1), the diameter of the meta-aramid precipitated nanofiber is 80-120 nm, and the length of the meta-aramid precipitated nanofiber is 10-100 μm.

[0013] Preferably, the adhesive in step (1) comprises at least one of ethylene-vinyl acetate copolymer adhesive, epoxy resin adhesive and polyurethane adhesive.

[0014] Preferably, based on absolute dry mass, the mass ratio of the solid matter in the meta-aramid precipitated nanofibers and the solid matter in the adhesive in the meta-aramid precipitated nanofiber slurry of step (1) is (6-9.5): (0.5-4).

[0015] Preferably, the mass concentration of the fiber in the fiber coating in step (1) is 0.5-3%.

[0016] Preferably, based on absolute dry mass, the mass ratio of the meso-aramid fiber to the meta-aramid fibrid in step (2) is (40-70):(30-60).

[0017] Preferably, the total mass concentration of the fibers in the mixed slurry in step (2) is 0.02-0.5%.

[0018] Preferably, the coating amount of the fiber coating in step (4) is 2 to 6 g / m 2 .

[0019] The present invention also provides aramid precipitated nanofiber reinforced aramid paper prepared by the preparation method described in the above technical solution.

[0020] The present invention also provides the application of the aramid precipitated nanofiber reinforced aramid paper described in the above technical solution in the fields of electrical insulation, rail transportation, aerospace and national defense military industry.

[0021] The invention provides a method for preparing aramid precipitated nanofiber reinforced aramid paper, comprising the following steps: (1) mixing meta-aramid precipitated nanofiber pulp with water and a binder to obtain a fiber coating; (2) mixing meta-aramid fibers, meta-aramid precipitated fibrils and water to decompose the mixture to obtain a mixed slurry; (3) mixing the mixed slurry obtained in the step (2) with a dispersant and a defoaming agent to form the mixture to obtain aramid base paper; (4) coating the fiber coating obtained in the step (1) onto the surface of the aramid base paper obtained in the step (3), and then hot pressing the mixture to obtain aramid precipitated nanofiber reinforced aramid paper; there is no time sequence for steps (1) and (2). The present invention adopts meta-aramid precipitated nanofibers to prepare fiber coatings. After coating, a dense protective layer is formed on the surface of aramid paper, filling the pores on the surface of aramid paper, making the overall structure of aramid paper dense, increasing the concentration of electron traps, reducing the electron breakdown path, and further improving the insulation and mechanical properties of aramid paper compared to para-aramid precipitated nanofibers. In addition, water is used as solvent in the preparation process, and organic solvent is not contained. It is safe, environmentally friendly, green and non-toxic, and will not cause damage to aramid fibers, further improving the various properties of aramid paper. The results of the embodiment show that the tensile strength of the aramid paper prepared by the present invention can reach 58.3N / cm, the tear strength can reach 2658mN, the breakdown voltage can reach 1474V, and the breakdown strength can reach 18.73kV / mm. DETAILED DESCRIPTION

[0022] The present invention provides a method for preparing aramid precipitated nanofiber reinforced aramid paper, comprising the following steps:

[0023] (1) mixing meta-aramid precipitated nanofiber slurry with water and a binder to obtain a fiber coating;

[0024] (2) mixing the meta-aramid fiber, the meta-aramid fibrid and water, and performing delamination to obtain a mixed slurry;

[0025] (3) mixing the mixed slurry obtained in step (2) with a dispersant and a defoamer, and forming the mixed slurry to obtain aramid base paper;

[0026] (4) applying the fiber coating obtained in step (1) to the surface of the aramid base paper obtained in step (3), and then hot pressing to obtain aramid precipitated nanofiber reinforced aramid paper;

[0027] There is no chronological order for steps (1) and (2).

[0028] Unless otherwise specified, the present invention has no particular limitation on the sources of the raw materials, and commercially available products known to those skilled in the art may be used.

[0029] The invention mixes meta-aramid precipitated nanofiber pulp with water and a binder to obtain a fiber coating.

[0030] In the present invention, the diameter of the meta-aramid nanofibers in the meta-aramid nanofiber slurry is preferably 80-120 nm. As an embodiment, the diameter of the meta-aramid nanofibers in the meta-aramid nanofiber slurry can be 90-110 nm, or 100 nm.

[0031] In the present invention, the length of the meta-aramid precipitated nanofibers in the meta-aramid precipitated nanofiber slurry is preferably 10 to 100 μm. As an embodiment, the length of the meta-aramid precipitated nanofibers can be 15 to 80 μm, or 50 μm. The present invention controls the diameter and length of the meta-aramid precipitated nanofibers in the meta-aramid precipitated nanofiber slurry within the above range, which can further improve the mechanical properties and insulation properties of aramid paper.

[0032] In the present invention, the mass concentration of the meta-aramid precipitated nanofibers in the meta-aramid precipitated nanofiber slurry is preferably 0.5-1.5%. As an embodiment, the mass concentration of the meta-aramid precipitated nanofibers in the meta-aramid precipitated nanofiber slurry can be 0.8-1.2%, or 1%. The present invention limits the mass concentration of the meta-aramid precipitated nanofibers in the meta-aramid precipitated nanofiber slurry to the above range, so that the meta-aramid precipitated nanofibers can be more fully and evenly dispersed.

[0033] In the present invention, the method for preparing the meta-aramid precipitated nanofiber pulp is preferably:

[0034] 1) mixing meta-aramid fibrid with water and beating the mixture to obtain meta-aramid fibrid slurry;

[0035] 2) mixing the meta-aramid fibrid slurry obtained in step 1) with a mixed alkali, and cutting the mixture to obtain fibrid;

[0036] 3) Mixing the precipitated fibers obtained in step 2) with water and performing homogenization treatment to obtain meta-aramid precipitated nanofiber slurry.

[0037] In the present invention, the meta-aramid fibrid is preferably mixed with water and beaten to obtain the meta-aramid fibrid pulp.

[0038] In the present invention, the length of the meta-aramid fibrid is preferably 1 to 3 mm. As an embodiment, the length of the meta-aramid fibrid can be 1.5 to 2.5 mm, or can be 2 mm.

[0039] In the present invention, the mass ratio of the meta-aramid fibrid to water is preferably 1: (13-15), more preferably 1: 14. The present invention limits the mass ratio of the meta-aramid fibrid to water to the above range, which is more conducive to pulping.

[0040] The present invention has no special limitation on the operation of mixing the meta-aramid fibrid and water, and a technical solution for mixing materials well known to those skilled in the art may be adopted.

[0041] In the present invention, the beating rotation number is preferably 20000-30000r, more preferably 20000-25000r.

[0042] In the present invention, the beating degree of the meta-aramid fibrid pulp is preferably 75-80°SR, more preferably 78°SR. The present invention limits the beating degree of the meta-aramid fibrid pulp to the above range, which can further improve various properties of aramid paper.

[0043] The present invention has no special limitation on the pulping equipment, and any pulping equipment known to those skilled in the art can be used. In an embodiment of the present invention, the pulping is preferably performed in a PFI machine.

[0044] After obtaining the meta-aramid fibrid slurry, the present invention preferably mixes the meta-aramid fibrid slurry with a mixed alkali and performs a cutting treatment to obtain the fibrid.

[0045] In the present invention, the mixed alkali is preferably a mixed alkali of sodium hydroxide and potassium hydroxide; the volume ratio of sodium hydroxide to potassium hydroxide in the mixed alkali is preferably 1:(0.5-1.5), more preferably 1:1.

[0046] In the present invention, the mass ratio of the meta-aramid fibrid pulp to the mixed alkali is preferably 1:(0.1-0.5), and more preferably 1:(0.3-0.5).

[0047] The present invention has no special limitation on the operation of mixing the meta-aramid fibrid pulp and the mixed alkali, and the technical scheme of material mixing well known to those skilled in the art can be adopted.

[0048] In the present invention, the cutting treatment is preferably a transverse cutting treatment; the cutting treatment temperature is preferably 80-100°C, more preferably 80-90°C; the cutting treatment time is preferably 1-3h, more preferably 2-3h; the cutting treatment is preferably carried out under water bath heating conditions.

[0049] In the present invention, the length of the fibrils is preferably 10 to 100 μm. The present invention limits the length of the fibrils to the above range, which can further improve various properties of the aramid paper.

[0050] After the cutting process is completed, the present invention preferably sequentially washes and dries the product of the cutting process to obtain fibrids.

[0051] The present invention has no special limitation on the washing operation, and the mixed alkali and the like can be removed by using a washing technical solution well known to those skilled in the art.

[0052] In the present invention, the drying temperature is preferably 100-110° C., more preferably 105° C. The present invention has no particular limitation on the drying time, as long as the moisture in the fiber can be sufficiently removed.

[0053] After obtaining the precipitated fibrids, the present invention preferably mixes the precipitated fibrids with water and performs homogenization treatment to obtain meta-aramid precipitated nanofiber slurry.

[0054] The present invention has no special limitation on the amount of water used, as long as the mass concentration of the meta-aramid precipitated nanofibers in the meta-aramid precipitated nanofiber slurry is ensured to be 0.5-1.5%.

[0055] The present invention has no special limitation on the operation of mixing the fibrid and water, and the technical scheme of material mixing well known to those skilled in the art can be adopted.

[0056] In the present invention, the pressure of the homogenization treatment is preferably 90-110 MPa, more preferably 100 MPa; the time of the homogenization treatment is preferably 1-3 hours, more preferably 2 hours. The present invention limits the pressure and time of the homogenization treatment to the above ranges, which can make the fiber dispersion more uniform.

[0057] The present invention has no particular limitation on the equipment for the homogenization process, and any equipment for the homogenization process well known to those skilled in the art can be used. In an embodiment of the present invention, the homogenization process is preferably performed in a homogenizer.

[0058] In the present invention, the binder preferably includes at least one of ethylene-vinyl acetate copolymer adhesive, epoxy resin adhesive and polyurethane adhesive, more preferably ethylene-vinyl acetate copolymer adhesive, and further preferably ethylene-vinyl acetate copolymer water-based adhesive. In the present invention, the average molecular weight of ethylene-vinyl acetate copolymer in the ethylene-vinyl acetate copolymer water-based adhesive is preferably 100-300, more preferably 200. In the present invention, the mass concentration of the ethylene-vinyl acetate copolymer water-based adhesive is preferably 1-10%. As an embodiment, the mass concentration of the ethylene-vinyl acetate copolymer water-based adhesive can be 2-8%, or 4-6%. The present invention limits the parameters of the adhesive within the above range, which is more conducive to its mixing with the meta-aramid precipitated nanofiber pulp.

[0059] In the present invention, based on absolute dry mass, the mass ratio of the solid matter in the meta-aramid precipitated nanofibers and the adhesive in the meta-aramid precipitated nanofiber slurry is preferably (6-9.5): (0.5-4). In an embodiment of the present invention, the mass ratio of the solid matter in the meta-aramid precipitated nanofibers and the adhesive in the meta-aramid precipitated nanofiber slurry can specifically be 9.5:0.5, 9:1, 8:2, 7:3 or 6:4. The present invention limits the mass ratio of the solid matter in the meta-aramid precipitated nanofiber slurry and the adhesive in the meta-aramid precipitated nanofiber slurry to the above range, which is more conducive to the subsequent coating and further improves the various properties of aramid paper.

[0060] In the present invention, the mass concentration of the fiber in the fiber coating is preferably 0.5-3%. In an embodiment of the present invention, the mass concentration of the fiber in the fiber coating can be specifically 0.5%, 1%, 1.5%, 2%, 2.5% or 3%. The present invention limits the mass concentration of the fiber in the fiber coating to the above range, which can facilitate subsequent coating and further improve the various properties of aramid paper.

[0061] The present invention has no particular limitation on the amount of water used, as long as the mass concentration of the fiber in the fiber coating is within the above range.

[0062] In the present invention, the mixing is preferably carried out under ultrasonic conditions; the power of the ultrasound is preferably 700 to 900 Hz, more preferably 800 Hz; the time of the ultrasound is preferably 10 to 20 min, more preferably 15 min.

[0063] The invention mixes meta-aramid fiber, meta-aramid fibrid and water, and performs delamination to obtain mixed slurry.

[0064] In the present invention, the length of the meta-aramid fiber is preferably 3 to 5 mm; the diameter of the meta-aramid fiber is preferably 10 to 30 μm.

[0065] In the present invention, the length of the meta-aramid fibrid is preferably 1 to 3 mm; the diameter of the meta-aramid fibrid is preferably 20 to 50 μm.

[0066] In the present invention, the mass ratio of the meta-aramid fiber to the meta-aramid fibrid is preferably (40-70): (30-60), more preferably (50-70): (30-50), and further preferably 60: 40, based on absolute dry mass. The present invention limits the mass ratio of the meta-aramid fiber to the meta-aramid fibrid to the above range, which can further improve the mechanical properties and insulation properties of the aramid paper.

[0067] In the present invention, the total mass concentration of the fibers in the mixed slurry is preferably 0.02-0.5%, more preferably 0.05-0.3%. The present invention limits the total mass concentration of the fibers in the mixed slurry to the above range, which can make the fibers dispersed more evenly.

[0068] The present invention has no special limitation on the amount of water used, as long as the total mass concentration of the fibers in the mixed slurry is within the above range.

[0069] In the present invention, the deflaking temperature is preferably 18-25°C; the deflaking time is preferably 3-5 minutes. The present invention limits the deflaking temperature and time to the above ranges, which can make the fibers disperse more fully.

[0070] After obtaining the mixed slurry, the present invention mixes the mixed slurry with a dispersant and a defoamer, and performs molding to obtain aramid base paper.

[0071] In the present invention, the dispersant is preferably water-soluble polyethylene oxide (PEO); the relative molecular weight of the water-soluble polyethylene oxide is preferably 70,000 to 500,000.

[0072] In the present invention, the mass of the dispersant is preferably 0.1-0.5% of the mass of the mixed slurry, and more preferably 0.1-0.3%. The present invention limits the type and amount of the dispersant to the above range, which can further improve the dispersibility of the fiber.

[0073] In the present invention, the defoamer is preferably a polyether defoamer. In the present invention, the mass of the defoamer is preferably 0.01-0.05% of the mass of the mixed slurry, and more preferably 0.02-0.04%. The present invention limits the amount of the defoamer to the above range, which can fully eliminate the bubbles in the mixed system and further improve the mechanical properties and insulation properties of the aramid paper.

[0074] The present invention has no special limitation on the operation of mixing the mixed slurry with the dispersant and the defoamer, and a technical solution for mixing materials well known to those skilled in the art may be adopted.

[0075] In the present invention, the forming is preferably an inclined screen wet forming method. The present invention has no special limitation on the specific operation of the forming, and the paper forming operation well known to those skilled in the art can be used.

[0076] After the forming is completed, the present invention preferably sequentially presses and dries the formed product to obtain aramid base paper.

[0077] The present invention has no special limitation on the pressing operation, and any pressing technical solution well known to those skilled in the art may be used.

[0078] In the present invention, the drying temperature is preferably 100-110° C., more preferably 105° C. The present invention has no particular limitation on the drying time, as long as the moisture is sufficiently removed.

[0079] After obtaining the fiber coating and the aramid base paper, the present invention applies the fiber coating to the surface of the aramid base paper, and then performs hot pressing to obtain the aramid precipitated nanofiber reinforced aramid paper.

[0080] In the present invention, the coating is preferably double-sided coating.

[0081] In the present invention, the coating amount is preferably 2 to 6 g / m 2 .

[0082] In the present invention, the coating preferably includes roller coating or spray coating.

[0083] In the present invention, the speed of the roller coating is preferably 0.5 to 5 m / min. In an embodiment of the present invention, the speed of the roller coating can be specifically 0.5 m / min, 1 m / min, 2 m / min, 3 m / min, 4 m / min or 5 m / min.

[0084] In the present invention, it is preferred to first roll-coat one side, then air-dry it for the first time, then roll-coat the other side, and then air-dry it for the second time.

[0085] In the present invention, the time for the first air-drying and the second air-drying are preferably independently 3 to 10 minutes.

[0086] In the present invention, the spraying speed is preferably 0.5 to 1.5 m / s. 2 / min.

[0087] In the present invention, it is preferred to spray one side first, then air dry it for a first time, then spray the other side, and then air dry it for a second time.

[0088] In the present invention, the time for the first air-drying and the second air-drying are preferably independently 3 to 10 minutes.

[0089] The present invention limits the speed and spraying amount of roller coating or spraying within the above range, so that the fiber coating can be more fully and evenly coated on the surface of the aramid base paper to form a dense coating, further improving the mechanical properties and insulation properties of the aramid paper.

[0090] In the present invention, the hot pressing is preferably roller hot pressing; the temperature of the hot pressing is preferably 220-280°C, more preferably 240-260°C; the pressure of the hot pressing is preferably 8-18MPa, more preferably 12-15MPa; the roller speed of the hot pressing is preferably 2-5m / min, more preferably 3-4m / min. During the hot pressing process, the synergistic effect of high temperature and high pressure makes the coating on the surface of the aramid base paper in a molten state, and the combination with the aramid base paper is tighter, thereby improving the mechanical properties and insulation properties of the aramid paper. The present invention limits the parameters of the hot pressing within the above range, which can further improve the mechanical properties and insulation properties of the aramid paper.

[0091] The present invention adopts meta-aramid precipitated nanofibers to prepare fiber coatings. After coating, a dense protective layer is formed on the surface of aramid paper, which fills the pores on the surface of the aramid paper, densifies the overall structure of the aramid paper, increases the concentration of electron traps, and reduces the electron breakdown path. Compared with para-aramid precipitated nanofibers, the insulation performance and mechanical properties of the aramid paper are further improved. In addition, water is used as a solvent in the preparation process, and no organic solvent is contained. The process is safe, environmentally friendly, green and non-toxic, and will not cause damage to the aramid fiber, thereby further improving various properties of the aramid paper.

[0092] The present invention also provides aramid precipitated nanofiber reinforced aramid paper prepared by the preparation method described in the above technical solution.

[0093] The thickness of the aramid precipitated nanofiber reinforced aramid paper prepared by the present invention is preferably 70-80 μm; the aramid precipitated nanofiber reinforced aramid paper has a tensile strength of up to 58.3 N / cm, a tear strength of up to 2658 mN, a breakdown voltage of up to 1474 V, and a breakdown strength of up to 18.73 kV / mm, and has excellent mechanical properties and insulation properties.

[0094] The present invention also provides the application of the aramid precipitated nanofiber reinforced aramid paper described in the above technical solution in the fields of electrical insulation, rail transportation, aerospace and national defense military industry.

[0095] The present invention has no special limitation on the operation of the application, and the technical solutions of the application well known to those skilled in the art may be adopted.

[0096] The technical solutions in the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0097] Example 1

[0098] The preparation method of aramid precipitated nanofiber reinforced aramid paper is as follows:

[0099] (1) adding 20 g of absolute dry meta-aramid fibrid to 300 g of deionized water (the length of the meta-aramid fibrid is 1 to 3 mm, and the mass ratio of the meta-aramid fibrid to water is 1:14), placing the mixture in a PFI machine for beating at a beating speed of 20,000 r and a beating degree of 78° SR to obtain a meta-aramid fibrid pulp;

[0100] (2) mixing the meta-aramid fibrid pulp obtained in step (1) with a mixed alkali (sodium hydroxide and potassium hydroxide in a volume ratio of 1:1) (the mass ratio of the meta-aramid fibrid pulp to the mixed alkali is 7:3), performing a transverse cutting treatment at 80° C. for 3 h, washing, and drying at 105° C. to obtain fibrids (with a length of 10 to 100 μm);

[0101] (3) adding deionized water to 1000 mL of the precipitated fibers obtained in step (2), and pouring the mixture into a homogenizer for homogenization at 100 MPa for 2 h to obtain meta-aramid precipitated nanofiber slurry (the mass concentration of the meta-aramid precipitated nanofibers in the meta-aramid precipitated nanofiber slurry is 0.5%, the length is 10 to 100 μm, and the diameter is 80 to 120 nm);

[0102] (4) mixing the meta-aramid precipitated nanofiber slurry obtained in step (3) with water and an aqueous ethylene-vinyl acetate copolymer adhesive (the average molecular weight of the ethylene-vinyl acetate copolymer is 200), wherein the mass ratio of the solid matter in the meta-aramid precipitated nanofiber slurry to the meta-aramid precipitated nanofiber and the adhesive is 9:1 based on the absolute dry mass, and performing ultrasound at 800 Hz for 15 minutes to obtain a fiber coating (the mass concentration of the fiber coating is 0.5%);

[0103] (5) mixing meta-aramid fibers (having a length of 3 to 5 mm and a diameter of 10 to 30 μm), meta-aramid fibrids (having a length of 1 to 3 mm and a diameter of 20 to 50 μm) and water, wherein the mass ratio of the meta-aramid fibers to the meta-aramid fibrids is 6:4 based on the absolute dry mass, and dispersing the mixture at 20° C. for 4 min to obtain a mixed slurry, wherein the total mass concentration of the fibers in the mixed slurry is 0.05%;

[0104] (6) adding 20 mL of aqueous polyethylene oxide dispersant and 1 mL of polyether defoamer to the mixed slurry obtained in step (5), wherein the mass of the dispersant is 0.1% of the mass of the mixed slurry, and the mass of the defoamer is 0.02% of the mass of the mixed slurry, and pouring the mixed slurry into an inclined wire wet paper former for paper forming, and then pressing and drying at 105° C. in sequence to obtain aramid base paper;

[0105] (7) 5 mL of the fiber coating obtained in step (4) is roller-coated onto one side of the aramid base paper obtained in step (6), and the roller coating amount of the fiber coating is 2 g / m 2 , the roller coating speed is 4m / min, and the paper is air-dried for 5min in a well-ventilated place. Then the above operation is repeated to coat the other side of the aramid base paper with a roller, air-dried for 5min, and then hot-pressed with a roller hot press at 240℃ and 12MPa, with a roller speed of 3m / min, to obtain aramid precipitated nanofiber reinforced aramid paper.

[0106] Example 2

[0107] The mass ratio of the solid matter in the intermediate aramid precipitated nanofibers and the adhesive in the intermediate aramid precipitated nanofiber slurry in step (4) of Example 1 is replaced with 8:2, and the other parameters are the same as those in Example 1.

[0108] Example 3

[0109] The mass concentration of the fiber coating in step (4) of Example 1 was replaced by 1%, and the other parameters were the same as those of Example 1.

[0110] Example 4

[0111] The mass concentration of the fiber coating in step (4) of Example 1 was replaced with 1.5%, and the other parameters were the same as those of Example 1.

[0112] Comparative Example 1

[0113] The mass ratio of the solid matter in the meso-aramid precipitated nanofiber slurry and the adhesive in step (4) of Example 1 is replaced with 5:5, and the other parameters are the same as those in Example 1.

[0114] Comparative Example 2

[0115] The meta-aramid precipitated nanofibers in the fiber coating in step (4) of Example 1 were replaced with para-aramid nanofibers, and the other parameters were the same as those in Example 1.

[0116] The thickness, tensile strength, tear strength, breakdown voltage and breakdown strength of the aramid papers prepared in Examples 1 to 4 and Comparative Examples 1 to 2 were tested using a paper thickness tester, an L&W paper tensile strength tester, an L&W paper tear strength tester and a ZJH-90T paper dielectric properties tester. The results are shown in Table 1.

[0117] Table 1 Thickness, tensile strength, tear strength, breakdown voltage and breakdown strength of aramid paper prepared in Examples 1 to 4 and Comparative Examples 1 to 2

[0118]

[0119] As can be seen from Table 1, the present invention uses meta-aramid precipitated nanofibers to prepare fiber coatings, which improves the mechanical properties and insulation properties of aramid paper.

[0120] Example 5

[0121] The preparation method of aramid precipitated nanofiber reinforced aramid paper is as follows:

[0122] (1) adding 20 g of absolute dry meta-aramid fibrid to 300 g of deionized water (the length of the meta-aramid fibrid is 1 to 3 mm, and the mass ratio of the meta-aramid fibrid to water is 1:14), placing the mixture in a PFI machine for beating at a beating speed of 20,000 r and a beating degree of 78° SR to obtain a meta-aramid fibrid pulp;

[0123] (2) mixing the meta-aramid fibrid pulp obtained in step (1) with a mixed alkali (sodium hydroxide and potassium hydroxide in a volume ratio of 1:1) (the mass ratio of the meta-aramid fibrid pulp to the mixed alkali is 7:3), performing a transverse cutting treatment at 80° C. for 3 h, washing, and drying at 105° C. to obtain fibrids (with a length of 10 to 100 μm);

[0124] (3) adding deionized water to 1000 mL of the precipitated fibers obtained in step (2), and pouring the mixture into a homogenizer for homogenization at 100 MPa for 2 h to obtain meta-aramid precipitated nanofiber slurry (the mass concentration of the meta-aramid precipitated nanofibers in the meta-aramid precipitated nanofiber slurry is 0.5%, the length is 10 to 100 μm, and the diameter is 80 to 120 nm);

[0125] (4) mixing the meta-aramid precipitated nanofiber slurry obtained in step (3) with water and an aqueous ethylene-vinyl acetate copolymer adhesive (the average molecular weight of the ethylene-vinyl acetate copolymer is 200), wherein the mass ratio of the solid matter in the meta-aramid precipitated nanofiber slurry to the solid matter in the adhesive is 9.5:0.5 based on the absolute dry mass, and performing ultrasound at 800 Hz for 15 minutes to obtain a fiber coating (the mass concentration of the fiber coating is 0.5%);

[0126] (5) mixing meta-aramid fibers (having a length of 3 to 5 mm and a diameter of 10 to 30 μm), meta-aramid fibrids (having a length of 1 to 3 mm and a diameter of 20 to 50 μm) and water, wherein the mass ratio of the meta-aramid fibers to the meta-aramid fibrids is 6:4 based on the absolute dry mass, and dispersing the mixture at 20° C. for 4 min to obtain a mixed slurry, wherein the total mass concentration of the fibers in the mixed slurry is 0.05%;

[0127] (6) adding 20 mL of aqueous polyethylene oxide dispersant and 1 mL of polyether defoamer to the mixed slurry obtained in step (5), wherein the mass of the dispersant is 0.1% of the mass of the mixed slurry, and the mass of the defoamer is 0.02% of the mass of the mixed slurry, and pouring the mixed slurry into an inclined wire wet paper former for paper forming, and then pressing and drying at 105° C. in sequence to obtain aramid base paper;

[0128] (7) Transfer 10 mL of the fiber coating obtained in step (4) to a spray gun and quickly and evenly spray it onto one side of the aramid base paper obtained in step (6). The spraying amount of the fiber coating is 2 g / m 2 , spraying speed is 1m 2 / min, air-dry for 5 minutes in a well-ventilated place, and then repeat the above operation to spray on the other side of the aramid base paper, air-dry for 5 minutes, and then use a roller hot press to perform hot pressing at 240°C and 12MPa with a roller speed of 3m / min to obtain aramid precipitated nanofiber reinforced aramid paper.

[0129] Example 6

[0130] The mass ratio of the solid matter in the intermediate aramid precipitated nanofibers and the adhesive in the intermediate aramid precipitated nanofiber slurry in step (4) of Example 5 is replaced with 9:1, and the other parameters are the same as those in Example 5.

[0131] Example 7

[0132] The amount of single-sided fiber coating in step (7) of Example 5 was replaced with 13 mL, and the spraying amount of fiber coating was 4 g / m 2 , other parameters are the same as those in Example 5.

[0133] Example 8

[0134] The amount of single-sided fiber coating in step (7) of Example 5 was replaced with 20 mL, and the spraying amount of fiber coating was 6 g / m 2 , other parameters are the same as those in Example 5.

[0135] Comparative Example 3

[0136] The water-based ethylene-vinyl acetate copolymer adhesive in step (4) of Example 5 was omitted, and other parameters were the same as those in Example 5.

[0137] Comparative Example 4

[0138] The meta-aramid precipitated nanofibers in the fiber coating in step (4) of Example 6 were replaced with para-aramid nanofibers, and the other parameters were the same as those in Example 6.

[0139] The thickness, tensile strength, tear strength, breakdown voltage and breakdown strength of the aramid paper in Examples 5 to 8 and Comparative Examples 3 to 4 were tested using a paper thickness tester, an L&W paper tensile strength tester, an L&W paper tear strength tester and a ZJH-90T paper dielectric properties tester. The results are shown in Table 2.

[0140] Table 2 Thickness, tensile strength, tear strength, breakdown voltage and breakdown strength of aramid paper prepared in Examples 5 to 8 and Comparative Examples 3 to 4

[0141]

[0142] As can be seen from Table 2, the present invention uses meta-aramid precipitated nanofibers to prepare fiber coatings, which improves the mechanical properties and insulation properties of aramid paper.

[0143] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing aramid precipitated nanofiber reinforced aramid paper, comprising the following steps: (1) mixing meta-aramid precipitated nanofiber slurry with water and a binder to obtain a fiber coating; (2) mixing the meta-aramid fiber, the meta-aramid fibrid and water, and performing delamination to obtain a mixed slurry; (3) mixing the mixed slurry obtained in step (2) with a dispersant and a defoamer, and forming the mixed slurry to obtain aramid base paper; (4) applying the fiber coating obtained in step (1) to the surface of the aramid base paper obtained in step (3), and then hot pressing to obtain aramid precipitated nanofiber reinforced aramid paper; There is no chronological order for steps (1) and (2).

2. The preparation method according to claim 1, characterized in that: The diameter of the meta-aramid precipitated nanofibers in the meta-aramid precipitated nanofiber slurry of step (1) is 80-120 nm, and the length of the meta-aramid precipitated nanofibers is 10-100 μm.

3. The preparation method according to claim 1, characterized in that: The adhesive in step (1) includes at least one of ethylene-vinyl acetate copolymer adhesive, epoxy resin adhesive and polyurethane adhesive.

4. The preparation method according to claim 1, characterized in that: Calculated on an absolute dry basis, the mass ratio of the solid matter in the meta-aramid precipitated nanofibers and the solid matter in the adhesive in the meta-aramid precipitated nanofiber slurry of step (1) is (6-9.5):(0.5-4).

5. The preparation method according to claim 1, characterized in that: The mass concentration of the fiber in the fiber coating in step (1) is 0.5-3%.

6. The preparation method according to claim 1, characterized in that: Calculated on an absolute dry basis, the mass ratio of the meso-aramid fiber to the meta-aramid fibrid in the step (2) is (40-70):(30-60).

7. The preparation method according to claim 1, characterized in that: The total mass concentration of the fibers in the mixed slurry in step (2) is 0.02-0.5%.

8. The preparation method according to claim 1, characterized in that: The coating amount of the fiber coating in step (4) is 2 to 6 g / m 2 .

9. Aramid precipitated nanofiber reinforced aramid paper prepared by the preparation method according to any one of claims 1 to 8.

10. Application of the aramid precipitated nanofiber reinforced aramid paper according to claim 9 in the fields of electrical insulation, rail transportation, aerospace, and national defense.

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