Tear-resistant aramid nanometer insulation paper, and preparation method and application thereof

Abstract

The application provides a tear-resistant aramid nanometer insulation paper and a preparation method and application thereof. The tear-resistant aramid nanometer insulation paper is obtained by secondary forming and hot pressing of multi-scale compounded meta-aramid short fibers with high elongation and good rigidity and para-aramid nanofibers with unique nanometer scale structure, rich functional groups and excellent mechanical properties. The excellent film-forming performance of the para-aramid nanofibers and the advantage that the rich functional groups on the surface of the para-aramid nanofibers are easy to produce a strong network crosslinking structure with the meta-aramid short fibers are fully utilized. A new aramid paper-based insulation material with high tear resistance and high dielectric strength is developed. The defects of stress concentration damage and poor dielectric strength caused by easy tearing of the current aramid nanometer insulation paper are improved. Meanwhile, the aramid nanometer insulation paper can be applied to the next generation of special electrical equipment with high light weight and integration as an ultrathin insulation layer, so that the equipment miniaturization, integration and structure weight reduction are realized.

Description

Technical Field

[0001] The present invention relates to the field of aramid paper-based insulating materials, and in particular to tear-resistant aramid nano insulating paper, a preparation method thereof, and applications thereof. Background Art

[0002] Currently, aramid paper-based insulation materials are rapidly developing, primarily used as primary insulation materials for turns, phases, windings, and wire ends in large electrical equipment such as high-power dry-type transformers, oil-immersed transformers, special mining motors, high-speed train traction motors, wind turbines, and ultra-high voltage transformers. However, traditional aramid paper-based insulation materials are still primarily made from macroscopic aramid chopped, precipitated, or pulp fibers. Due to the monotonous morphology, smooth, hydrophobic surface, and high inertness of the macroscopic aramid fibers, these traditional aramid paper-based insulation materials suffer from a loose structure, weak interfacial bonding, and low mechanical and dielectric strength, making them difficult to meet the application requirements of high-end applications.

[0003] Aramid nanofibers (ANFs) retain most of the properties of macroscopic aramid fibers, including thermal stability and high crystallinity. At the same time, the abundant active groups on the surface of aramid nanofibers, their large aspect ratio, and specific surface area give them the excellent characteristics of nanomaterials, bringing them mechanical and optical properties that conventional macroscopic aramid fibers cannot achieve. In addition, aramid nanofibers can form a cross-linked network structure through strong hydrogen bonds, which has excellent paper-forming properties. The paper has the advantages of high strength, high temperature resistance, transparency, and good flexibility, and has great application prospects in the field of electrical insulation materials. Aramid nano insulation paper is made from aramid nanofibers through wet forming or sol-gel phase transformation. It has excellent dielectric strength and tensile strength, extremely thin thickness, and excellent high temperature resistance, and has broad application prospects in the field of advanced electrical insulation. However, since the diameter of aramid nanofibers is about 10-15nm and the length is relatively short, only 3 to 5μm, the physical interlacing and mechanical bonding between the fibers are weak, and they are easily torn under the action of external forces, especially when there are gaps. This poses a huge safety hazard to its future application in the field of high-end electrical insulation.

[0004] The existing aramid nanometer insulation paper manufacturing process is mainly to mix different types of meta-aramid in different proportions, and to disperse the mixed fiber dispersion liquid for papermaking and drying; the invention patent CN109468882A proposes to modify the pretreated aramid short fiber and the p-aramid pulp fiber with a coupling agent or a coupling agent solution, to make paper, to use nano p-aramid fiber to enhance the gradient structure of the paper, and to obtain a gradient structure nano aramid paper, but the distribution of nano aramid fiber in the paper structure is uneven, resulting in low dielectric strength; the invention patent CN112609493A proposes to prepare a traditional short fiber and pulp or precipitated fiber to make a meta-aramid or p-aramid nanofiber composite wet paper sheet, to spray or size the p-aramid nanofiber dispersion liquid on the surface of the wet paper sheet, and then to composite and dry to form a nano-enhanced aramid paper, which although enhances the strength of the aramid paper, the papermaking process is complex, and the dielectric strength of the paper is still low. SUMMARY

[0005] The present application aims to provide a tear-resistant aramid nanometer insulation paper and its preparation method and application, to overcome the problems in the prior art, and to provide a tear-resistant aramid nanometer insulation paper with simple raw materials, excellent product performance and high dielectric strength, and a preparation method thereof, which improves the defects of current insulation paper base material, such as stress concentration and low dielectric strength; at the same time, it can also be applied to the next generation of highly lightweight and integrated special electrical equipment as an ultra-thin insulation layer, realizing the miniaturization, integration and weight reduction of the equipment, and promoting the development of modern compact and lightweight electrical insulation equipment towards more efficient and reliable direction.

[0006] To achieve the above-mentioned purpose, the technical scheme of the present application is as follows:

[0007] A preparation method of a tear-resistant aramid nanometer insulation paper, comprising the following specific steps:

[0008] (1) Preparing a p-aramid nanofiber water dispersion liquid: under stirring, injecting deionized water into the p-aramid nanofiber (PPTA) dispersion liquid in a dimethyl sulfoxide (DMSO), potassium hydroxide (KOH) and deionized water (H2O) system, and then washing with deionized water under vacuum filtration until a gel is obtained, to obtain a p-aramid nanofiber water dispersion liquid A dispersed in deionized water; diluting the p-aramid nanofiber water dispersion liquid A, and then dispersing by beating and stirring to obtain a p-aramid nanofiber water dispersion liquid B;

[0009] (2) Preparing a meta-aramid short fiber water dispersion liquid: dispersing meta-aramid short fibers of different lengths in water, adding a dispersant, and then dispersing by beating and stirring to obtain a meta-aramid short fiber water dispersion liquid C;

[0010] (3) Papermaking the meta-aramid chopped fiber aqueous dispersion C obtained in (2) to obtain a loose, porous insulating paper matrix; the basis weight of the insulating paper matrix is ​​3 to 30 g / m 2 ;

[0011] (4) The para-aramid nanofiber aqueous dispersion B obtained in (1) is subjected to secondary forming and papermaking on the insulating paper substrate obtained in (3) to obtain aramid nano insulating paper; the aramid nano insulating paper has a basis weight of 30 to 60 g / m 2 , wherein the mass ratio of para-aramid nanofiber: meta-aramid short fiber is 50-90:10-50;

[0012] (5) further squeezing, drying, and hot pressing the aramid nano-insulation paper obtained in (4) to obtain tear-resistant aramid nano-insulation paper;

[0013] Furthermore, the preparation method of the para-aramid nanofiber dispersion (ANFs) in the dimethyl sulfoxide, potassium hydroxide and deionized water system in (1) is as follows: para-aramid short fibers, potassium hydroxide, dimethyl sulfoxide and deionized water are mixed in proportion and sealed, and then stirred at a speed of 1200 to 1500 r / min for 2 to 4 hours to obtain a para-aramid nanofiber dispersion with a concentration of 5 to 15 mg / mL; the diameter of the para-aramid nanofibers in the para-aramid nanofiber dispersion is 8 to 15 nm and the length is 3 to 8 μm;

[0014] Furthermore, in said (1), the speed of stirring the para-aramid nanofiber dispersion in the dimethyl sulfoxide, potassium hydroxide and deionized water system is 1000-1500 r / min;

[0015] Furthermore, in said (1), the para-aramid nanofiber aqueous dispersion A is dispersed and stirred for 20,000 to 30,000 hours; the mass concentration of said para-aramid nanofiber aqueous dispersion B is 0.05 to 0.12%;

[0016] Furthermore, the ratio of the meta-aramid short fibers of different lengths in (2) is 10-30:30-50:30-50 by weight of meta-aramid short fibers: meta-aramid short fibers; the length of the meta-aramid short fibers is 4-6 mm, the length of the meta-aramid short fibers is 7-9 mm, and the length of the meta-aramid short fibers is 10-12 mm.

[0017] Furthermore, the stirring and dispersion in (2) is performed for 20,000 to 30,000 rpm; the mass concentration of the meta-aramid chopped fiber aqueous dispersion C is 0.05 to 0.12%;

[0018] Furthermore, the (3) is specifically as follows: the meta-aramid short fiber aqueous dispersion C obtained in (2) is papered on a 200-400 mesh forming net to obtain a loose and porous insulating paper matrix;

[0019] Furthermore, the pressing and drying in (5) are carried out using conventional papermaking processes, with a hot pressing temperature of 230-245° C., a hot pressing pressure of 10-15 MPa, and a hot pressing time of 5-10 min;

[0020] A tear-resistant aramid nano-insulating paper is obtained based on any of the above-mentioned methods for preparing the tear-resistant aramid nano-insulating paper.

[0021] An application of the tear-resistant aramid nano-insulation paper as an ultra-thin insulation layer in the field of next-generation highly lightweight and integrated special electrical equipment.

[0022] The above technical solution has the following advantages or beneficial effects:

[0023] The present invention provides a method for preparing tear-resistant aramid nano-insulating paper, which uses meta-aramid short fibers as a skeleton matrix structure, and para-aramid nano-fibers with unique nanoscale structure, high strength and high modulus, high specific surface area, high aspect ratio, and excellent temperature resistance as coating and filling materials for the meta-aramid short fiber skeleton structure. A micro / nano-rough combination is constructed on the smooth surface of the aramid short fibers to overcome the problems of the smooth surface, strong inertness, and few active groups of the short fibers, thereby improving the defects of the current insulating paper-based materials such as easy stress concentration and breakage and low dielectric strength, and enhancing the bonding force between fibers. The entire manufacturing process of the present invention has the characteristics of simple raw materials and excellent product performance. The aramid nano-insulating paper obtained by multiple forming of meta-aramid short fibers and para-aramid nano-fibers of different dimensions has the characteristics of tear resistance, high temperature resistance, flame retardancy, and high dielectric strength.

[0024] Furthermore, a secondary forming method is used for papermaking. Meta-aramid chopped fibers of varying lengths are compounded to form the insulating paper's skeleton matrix. The interweaving of fibers of varying lengths enhances the fibers' mechanical strength. Para-aramid nanofibers are then vacuum-filtered onto the meta-aramid chopped fiber skeleton matrix. The aramid nanofibers then fill the porous matrix, uniformly coating the meta-aramid chopped fibers with a dense membrane, creating a structure similar to reinforced concrete. This secondary forming method not only improves the insulation paper's tear resistance but also prevents nanofiber loss.

[0025] Furthermore, high temperature and high pressure hot pressing is used to soften the meta-aramid chopped fibers, achieve deformation and migration between the fibers, fill the pores between the fibers, and make the insulating paper have a dense aramid nano-layered structure, in which composite meta-aramid chopped fibers of different lengths exist; this process significantly improves the tightness and tear resistance of the aramid nano-insulating paper and makes the paper surface smoother.

[0026] The present invention provides a tear-resistant aramid nano-insulation paper. The tear strength of the aramid nano-insulation paper is 13 to 29 times higher than that of pure aramid nano-film. The aramid nano-insulation paper can also achieve thinning of the insulation layer and high tear performance while ensuring excellent insulation performance.

[0027] The present invention provides a tear-resistant aramid nano-insulating paper for use as an ultra-thin insulating layer in the field of next-generation highly lightweight and integrated special electrical equipment, such as in the fields of electrical equipment for 5G communication power systems, rail transit, new energy vehicles, etc. It can effectively solve the problems of poor active heat dissipation and short service life of electrical equipment due to the low thermal conductivity of insulating paper, realize the miniaturization, integration and structural weight reduction of equipment, and promote the development of modern compact lightweight electrical insulation equipment towards a more efficient and reliable direction. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a process flow chart of a method for preparing tear-resistant aramid nano-insulating paper according to the present invention;

[0029] FIG2(a) is a scanning electron microscope image of the surface of the aramid nano-insulating paper obtained in Example 4 of the present invention, and FIG2(b) is a partially enlarged scanning electron microscope image of the surface of the aramid nano-insulating paper obtained in Example 4 of the present invention;

[0030] Figure 3 This is a scanning electron microscope image of the cross section of the aramid nano-insulation paper obtained in Example 4 of the present invention;

[0031] FIG4( a ) is a scanning electron microscope image of the breakdown point of the aramid nano-insulating paper obtained in Example 4 of the present invention, and FIG4( b ) is a locally enlarged scanning electron microscope image of the breakdown point of the aramid nano-insulating paper obtained in Example 4 of the present invention. DETAILED DESCRIPTION

[0032] The present invention will be further described in detail below with reference to specific embodiments, which are intended to explain the present invention rather than to limit it.

[0033] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0034] It should be noted that the terms "first", "second", etc. in the description and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that the numbers used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0035] A method for preparing tear-resistant aramid nano-insulation paper, see Figure 1 , including the following specific steps:

[0036] (1) preparing a para-aramid nanofiber aqueous dispersion: injecting deionized water into a para-aramid nanofiber dispersion in a system of dimethyl sulfoxide, potassium hydroxide, and deionized water under high pressure while stirring, and then washing with deionized water under vacuum filtration until it becomes colloidal, thereby obtaining a para-aramid nanofiber aqueous dispersion A dispersed in deionized water; diluting the para-aramid nanofiber aqueous dispersion A, and then dispersing it by dispersing and stirring to obtain a para-aramid nanofiber aqueous dispersion B;

[0037] (2) Preparing a meta-aramid short fiber aqueous dispersion: dispersing meta-aramid short fibers of different lengths in water, adding a dispersant to prevent fiber flocculation, and then dispersing by stirring and delamination to obtain a meta-aramid short fiber aqueous dispersion C;

[0038] (3) The meta-aramid short fiber aqueous dispersion C obtained in (2) is paper-made to obtain a loose and porous insulating paper matrix, and the paper basis weight of the insulating paper matrix is ​​3 to 30 g / m 2 Aramid nanofibers are filled into a loose and porous skeleton matrix structure, forming a structure similar to reinforced concrete. This secondary forming method not only improves the tear resistance of the insulating paper, but also prevents the loss of nanofibers.

[0039] (4) The para-aramid nanofiber aqueous dispersion B obtained in (1) is subjected to secondary forming and papermaking on the insulating paper substrate obtained in (3) to obtain aramid nano insulating paper; the aramid nano insulating paper obtained has a paper basis weight of 30 to 60 g / m 2 , wherein the mass ratio of para-aramid nanofiber: meta-aramid short fiber is 50-90:10-50;

[0040] (5) The aramid nano-insulating paper obtained in (4) is further squeezed, dried, and hot-pressed to obtain tear-resistant aramid nano-insulating paper; high temperature and high pressure hot pressing is used to soften the meta-aramid short fibers, thereby achieving deformation and migration between the fibers, filling the pores between the fibers, and making the insulating paper have a dense aramid nano-layered structure, and compound meta-aramid short fibers of different lengths exist therein; this process significantly improves the tightness and tear resistance of the aramid nano-insulating paper and makes the paper surface smoother;

[0041] Preferably, the preparation method of the para-aramid nanofiber dispersion in the dimethyl sulfoxide, potassium hydroxide and deionized water system in (1) is as follows: para-aramid short fibers, potassium hydroxide, dimethyl sulfoxide and deionized water are mixed in proportion and sealed, and then stirred at a speed of 1200 to 1500 r / min for 2 to 4 hours to obtain a para-aramid nanofiber dispersion with a concentration of 5 to 15 mg / mL; the diameter of the para-aramid nanofibers in the para-aramid nanofiber dispersion is 8 to 15 nm and the length is 3 to 8 μm;

[0042] Preferably, in said (1), the speed of stirring the para-aramid nanofiber dispersion in the dimethyl sulfoxide, potassium hydroxide and deionized water system is 1000-1500 r / min;

[0043] Preferably, in said (1), the para-aramid nanofiber aqueous dispersion A is dispersed and stirred for 20,000 to 30,000 hrs; the mass concentration of said para-aramid nanofiber aqueous dispersion B is 0.05 to 0.12%;

[0044] Preferably, the ratio of the meta-aramid short fibers of different lengths in (2) is 10-30:30-50:30-50 by weight of meta-aramid short fibers: meta-aramid short fibers; the length of the meta-aramid short fibers is 4-6 mm, the length of the meta-aramid short fibers is 7-9 mm, and the length of the meta-aramid short fibers is 10-12 mm; the fibers of different lengths are interwoven with each other, thereby enhancing the mechanical strength of the paper;

[0045] Preferably, the stirring and dispersion in (2) is 20000-30000r; the mass concentration of the meta-aramid chopped fiber aqueous dispersion C is 0.05-0.12%;

[0046] Preferably, the step (3) is as follows: papermaking the meta-aramid chopped fiber aqueous dispersion C obtained in step (2) on a 200-400 mesh forming net to obtain a loose and porous insulating paper matrix;

[0047] Preferably, the drying in (5) is carried out using a conventional papermaking process, with a hot pressing temperature of 230-245° C., a hot pressing pressure of 10-15 MPa, and a hot pressing time of 5-10 min.

[0048] A tear-resistant aramid nano-insulating paper is obtained based on any of the above-mentioned methods for preparing the tear-resistant aramid nano-insulating paper.

[0049] An application of the above-mentioned tear-resistant aramid nano-insulating paper as an ultra-thin insulating layer in the field of next-generation highly lightweight and integrated special electrical equipment, such as in the fields of electrical equipment for 5G communication power systems, rail transit, new energy vehicles, etc., can effectively solve the problems of poor active heat dissipation and short service life of electrical equipment due to low thermal conductivity of insulating paper, realize equipment miniaturization, integration and structural weight reduction, and promote the development of modern compact lightweight electrical insulation equipment towards a more efficient and reliable direction.

[0050] The present invention will be further described in detail below with reference to specific embodiments, which are intended to explain the present invention rather than to limit it.

[0051] Example 1:

[0052] The method for preparing tear-resistant aramid nano-insulating paper in this embodiment specifically includes the following steps:

[0053] (1) Para-aramid short fibers, potassium hydroxide, dimethyl sulfoxide and deionized water are mixed in proportion and sealed, and rapidly stirred at 1200 r / min for 2 h to obtain a para-aramid nanofiber dispersion with a concentration of 8 mg / mL; the diameter of the para-aramid nanofibers in the para-aramid nanofiber dispersion is 8 to 15 nm and the length is 3 to 8 μm; then, deionized water is injected into the para-aramid nanofiber dispersion under high pressure while stirring at a speed of 1000 r / min, and then washed with deionized water under vacuum filtration until it becomes a gel, to obtain a para-aramid nanofiber aqueous dispersion A dispersed in deionized water; the para-aramid nanofiber aqueous dispersion A is diluted, and then dispersed by dispersing and stirring for 20000 r to obtain a para-aramid nanofiber aqueous dispersion B with a mass concentration of 0.05%;

[0054] (2) Dispersing meta-aramid short staple fibers, meta-aramid short medium-long fibers, and meta-aramid short long fibers in water at a ratio of 10:30:60, adding a dispersant for dispersion, and then dispersing by stirring for 20,000 seconds to obtain a meta-aramid short staple fiber aqueous dispersion C with a mass concentration of 0.1%;

[0055] (3) The meta-aramid short-cut fiber aqueous dispersion C obtained in (2) is papered on a 200-mesh forming net to obtain a loose, porous insulating paper substrate; the paper basis weight of the obtained insulating paper substrate is 4.1 g / m 2 ;

[0056] (4) forming the para-aramid nanofiber aqueous dispersion B obtained in (1) on the insulating paper substrate obtained in (3) to obtain aramid nano-insulating paper;

[0057] (5) The aramid nano-insulating paper obtained in (4) is further pressed, dried, and hot-pressed to obtain tear-resistant aramid nano-insulating paper; the drying is carried out using a conventional papermaking process; the hot-pressing temperature is 235° C., the hot-pressing pressure is 10 MPa, and the hot-pressing time is 8 min; the mass ratio of para-aramid nanofiber to meta-aramid short-cut fiber in the tear-resistant aramid nano-insulating paper obtained is 90:10; the prepared paper has a basis weight of 41 g / m 2 .

[0058] Example 2:

[0059] The method for preparing tear-resistant aramid nano-insulating paper in this embodiment specifically includes the following steps:

[0060] (1) Para-aramid short fibers, potassium hydroxide, dimethyl sulfoxide and deionized water are mixed in proportion and sealed, and rapidly stirred at 1300 r / min for 2.5 h to obtain a para-aramid nanofiber dispersion with a concentration of 10 mg / mL; the diameter of the para-aramid nanofibers in the para-aramid nanofiber dispersion is 8 to 15 nm and the length is 3 to 8 μm; then, deionized water is injected into the para-aramid nanofiber dispersion under high pressure while stirring at a speed of 1200 r / min, and then washed with deionized water under vacuum filtration until it becomes a gel, to obtain a para-aramid nanofiber aqueous dispersion A dispersed in deionized water; the para-aramid nanofiber aqueous dispersion A is diluted, and then dispersed by dispersing and stirring for 25000 r to obtain a para-aramid nanofiber aqueous dispersion B with a mass concentration of 0.1%;

[0061] (2) dispersing meta-aramid short staple fibers, meta-aramid short medium-long fibers, and meta-aramid short long fibers in water at a ratio of 20:30:50, adding a dispersant for dispersion, and then dispersing by stirring for 25000r to obtain a meta-aramid short staple fiber aqueous dispersion C with a mass concentration of 0.05%;

[0062] (3) The meta-aramid short fiber aqueous dispersion C obtained in (2) is papered on a 200-mesh forming net to obtain a loose, porous insulating paper substrate; the paper basis weight of the obtained insulating paper substrate is 8.2 g / m 2 ;

[0063] (4) forming the para-aramid nanofiber aqueous dispersion B obtained in (1) on the insulating paper substrate obtained in (3) to obtain aramid nano-insulating paper;

[0064] (5) The aramid nano-insulating paper obtained in (4) is further pressed, dried, and hot-pressed to obtain tear-resistant aramid nano-insulating paper; the drying is carried out using a conventional papermaking process; the hot-pressing temperature is 230° C., the hot-pressing pressure is 11 MPa, and the hot-pressing time is 5 min; the mass ratio of para-aramid nanofiber to meta-aramid short-cut fiber in the tear-resistant aramid nano-insulating paper obtained is 80:20; the prepared paper has a basis weight of 41 g / m 2 .

[0065] Example 3:

[0066] The method for preparing tear-resistant aramid nano-insulating paper in this embodiment specifically includes the following steps:

[0067] (1) Para-aramid short fibers, potassium hydroxide, dimethyl sulfoxide and deionized water are mixed in proportion and sealed, and rapidly stirred at 1400 r / min for 3 h to obtain a para-aramid nanofiber dispersion with a concentration of 15 mg / mL; the diameter of the para-aramid nanofibers in the para-aramid nanofiber dispersion is 8 to 15 nm and the length is 3 to 8 μm; then, deionized water is injected into the para-aramid nanofiber dispersion under high pressure while stirring at a speed of 1300 r / min, and then washed with deionized water under vacuum filtration until it becomes a gel, to obtain a para-aramid nanofiber aqueous dispersion A dispersed in deionized water; the para-aramid nanofiber aqueous dispersion A is diluted, and then dispersed by dispersing and stirring for 30,000 r to obtain a para-aramid nanofiber aqueous dispersion B with a mass concentration of 0.08%;

[0068] (2) Dispersing meta-aramid short staple fibers, meta-aramid short medium-long fibers, and meta-aramid short long fibers in water at a ratio of 30:40:30, adding a dispersant for dispersion, and then dispersing by stirring for 30,000 seconds to obtain a meta-aramid short staple fiber aqueous dispersion C with a mass concentration of 0.08%;

[0069] (3) The meta-aramid short fiber aqueous dispersion C obtained in (2) is papered on a 200-mesh forming net to obtain a loose, porous insulating paper substrate; the paper basis weight of the obtained insulating paper substrate is 12.3 g / m2 ;

[0070] (4) forming the para-aramid nanofiber aqueous dispersion B obtained in (1) on the insulating paper substrate obtained in (3) to obtain aramid nano-insulating paper;

[0071] (5) The aramid nano-insulation paper obtained in (4) is further pressed, dried, and hot-pressed to obtain tear-resistant aramid nano-insulation paper; the drying is carried out using a conventional papermaking process; the hot-pressing temperature is 240°C, the hot-pressing pressure is 10 MPa, and the hot-pressing time is 8 minutes; the mass ratio of para-aramid nanofiber to meta-aramid short fiber in the tear-resistant aramid nano-insulation paper is 70:30; the prepared paper has a basis weight of 41 g / m 2 .

[0072] Example 4:

[0073] The method for preparing tear-resistant aramid nano-insulating paper in this embodiment specifically includes the following steps:

[0074] (1) Para-aramid short fibers, potassium hydroxide, dimethyl sulfoxide and deionized water were mixed in proportion and sealed, and rapidly stirred at 1500 r / min for 3.5 h to obtain a para-aramid nanofiber dispersion with a concentration of 10 mg / mL; the diameter of the para-aramid nanofibers in the para-aramid nanofiber dispersion was 8 to 15 nm and the length was 3 to 8 μm; then, deionized water was injected into the para-aramid nanofiber dispersion under high pressure under the stirring action of 1100 r / min, and then washed with deionized water under vacuum filtration until it was in a gel state, to obtain a para-aramid nanofiber aqueous dispersion A dispersed in deionized water; the para-aramid nanofiber aqueous dispersion A was diluted, and then dispersed by dispersing and stirring for 20000 r to obtain a para-aramid nanofiber aqueous dispersion B with a mass concentration of 0.11%;

[0075] (2) Dispersing meta-aramid short staple fibers, meta-aramid short medium-long fibers, and meta-aramid short long fibers in water at a ratio of 20:30:50, adding a dispersant for dispersion, and then dispersing by stirring for 20,000 seconds to obtain a meta-aramid short staple fiber aqueous dispersion C with a mass concentration of 0.09%;

[0076] (3) The meta-aramid short fiber aqueous dispersion C obtained in (2) is papered on a 200-mesh forming net to obtain a loose, porous insulating paper substrate; the paper basis weight of the obtained insulating paper substrate is 16.4 g / m 2 ;

[0077] (4) forming the para-aramid nanofiber aqueous dispersion B obtained in (1) on the insulating paper substrate obtained in (3) to obtain aramid nano-insulating paper;

[0078] (5) The aramid nano-insulating paper obtained in (4) is further pressed, dried, and hot-pressed to obtain tear-resistant aramid nano-insulating paper; the drying is carried out using a conventional papermaking process; the hot-pressing temperature is 245° C., the hot-pressing pressure is 12 MPa, and the hot-pressing time is 8 min; the mass ratio of para-aramid nanofiber to meta-aramid short-cut fiber in the tear-resistant aramid nano-insulating paper obtained is 60:40; the prepared paper has a basis weight of 41 g / m 2 .

[0079] Taking Example 4 as an example, the surface of the tear-resistant aramid nano-insulating paper prepared by the present invention was first observed. Figure 2(a) is a scanning electron microscope image of the surface of the aramid nano-insulating paper obtained in Example 4 of the present invention, and Figure 2(b) is a partially enlarged scanning electron microscope image of the surface of the aramid nano-insulating paper obtained in Example 4 of the present invention. From the figure, we can clearly see that the aramid nanofibers are tightly combined with the meta-aramid short fibers, and the aramid nanofibers completely wrap the meta-aramid short fibers to form a dense aramid nano-network, which makes the paper surface smooth, increases the bonding force between the fibers, and improves the tear resistance of the paper. Secondly, the cross-section of the aramid nano-insulating paper is observed, as shown in FIG. Figure 3 As shown in the figure, there is an obvious layered structure inside the paper. After hot pressing, the meta-aramid chopped fibers reach their glass transition temperature, the fibers soften and undergo slight deformation and migration, filling the pores between the fibers and making the structure between the fibers dense. Finally, in order to verify its excellent dielectric properties, the aramid nano-insulating paper was subjected to an electrical breakdown test and its SEM image was observed. Figure 4(a) is a scanning electron microscope image of the breakdown point of the aramid nano-insulating paper obtained in Example 4 of the present invention, and Figure 4(b) is a locally enlarged scanning electron microscope image of the breakdown point of the aramid nano-insulating paper obtained in Example 4 of the present invention. It can be observed that dense carbon particles are generated around the breakdown site, and the structure is tight. Even after the breakdown, other parts of the insulating paper will not become loose.

[0080] Taking Example 4 as an example, the tear-resistant aramid nano-insulation paper prepared by the present invention was tested and the quantitative value was 41g / m 2 The average thickness is 0.05mm, the tear strength is 392mN, and the dielectric strength is 36kV / mm, showing excellent tear strength and dielectric strength. This tear-resistant aramid nano-insulation paper has excellent mechanical and electrical properties and has potential applications in large-scale electrical equipment such as high-power dry-type transformers, oil-immersed transformers, special motors for mining, high-speed train traction motors, wind turbines, and ultra-high voltage transformers.

[0081] Example 5:

[0082] The method for preparing tear-resistant aramid nano-insulating paper in this embodiment specifically includes the following steps:

[0083] (1) Para-aramid short fibers, potassium hydroxide, dimethyl sulfoxide and deionized water are mixed in proportion and sealed, and rapidly stirred at 1300 r / min for 4 h to obtain a para-aramid nanofiber dispersion with a concentration of 10 mg / mL; the para-aramid nanofibers in the para-aramid nanofiber dispersion have a diameter of 8 to 15 nm and a length of 3 to 8 μm; then, deionized water is injected into the para-aramid nanofiber dispersion under high pressure while stirring at a speed of 1300 r / min, and then the para-aramid nanofiber dispersion is washed with deionized water under vacuum filtration until it becomes a gel, thereby obtaining a para-aramid nanofiber aqueous dispersion A dispersed in deionized water; the para-aramid nanofiber aqueous dispersion A is diluted, and then dispersed by dispersing and stirring for 30,000 r to obtain a para-aramid nanofiber aqueous dispersion B with a mass concentration of 0.12%;

[0084] (2) Dispersing meta-aramid short staple fibers, meta-aramid short medium-long fibers, and meta-aramid short long fibers in water at a ratio of 10:40:50, adding a dispersant for dispersion, and then dispersing by stirring for 30,000 seconds to obtain a meta-aramid short staple fiber aqueous dispersion C with a mass concentration of 0.1%;

[0085] (3) The meta-aramid short fiber aqueous dispersion C obtained in (2) is papered on a 200-mesh forming net to obtain a loose, porous insulating paper substrate; the paper basis weight of the obtained insulating paper substrate is 20.5 g / m 2 ;

[0086] (4) forming the para-aramid nanofiber aqueous dispersion B obtained in (1) on the insulating paper substrate obtained in (3) to obtain aramid nano-insulating paper;

[0087] (5) The aramid nano-insulating paper obtained in (4) is further pressed, dried, and hot-pressed to obtain tear-resistant aramid nano-insulating paper; the drying is carried out using a conventional papermaking process; the hot-pressing temperature is 235° C., the hot-pressing pressure is 15 MPa, and the hot-pressing time is 10 min; the mass ratio of para-aramid nanofiber to meta-aramid short-cut fiber in the tear-resistant aramid nano-insulating paper obtained is 50:50; the prepared paper has a basis weight of 41 g / m 2 .

[0088] Example 6:

[0089] The method for preparing tear-resistant aramid nano-insulating paper in this embodiment specifically includes the following steps:

[0090] (1) Para-aramid short fibers, potassium hydroxide, dimethyl sulfoxide and deionized water are mixed in proportion and sealed, and rapidly stirred at 1200 r / min for 4 h to obtain a para-aramid nanofiber dispersion with a concentration of 11 mg / mL; the diameter of the para-aramid nanofibers in the para-aramid nanofiber dispersion is 8 to 15 nm and the length is 3 to 8 μm; then, deionized water is injected into the para-aramid nanofiber dispersion under high pressure while stirring at a speed of 1500 r / min, and then washed with deionized water under vacuum filtration until it becomes a gel, to obtain a para-aramid nanofiber aqueous dispersion A dispersed in deionized water; the para-aramid nanofiber aqueous dispersion A is diluted, and then dispersed by dispersing and stirring for 25000 r to obtain a para-aramid nanofiber aqueous dispersion B with a mass concentration of 0.06%;

[0091] (2) Dispersing meta-aramid short staple fibers, meta-aramid short medium-long fibers, and meta-aramid short long fibers in water at a ratio of 10:50:40, adding a dispersant for dispersion, and then dispersing by stirring for 25,000 seconds to obtain a meta-aramid short staple fiber aqueous dispersion C with a mass concentration of 0.11%;

[0092] (3) The meta-aramid short fiber aqueous dispersion C obtained in (2) is papered on a 200-mesh forming net to obtain a loose, porous insulating paper substrate; the paper basis weight of the obtained insulating paper substrate is 9 g / m 2 ;

[0093] (4) forming the para-aramid nanofiber aqueous dispersion B obtained in (1) on the insulating paper substrate obtained in (3) to obtain aramid nano-insulating paper;

[0094] (5) The aramid nano-insulation paper obtained in (4) is further pressed, dried, and hot-pressed to obtain tear-resistant aramid nano-insulation paper; the drying is carried out using a conventional papermaking process; the hot-pressing temperature is 245° C., the hot-pressing pressure is 14 MPa, and the hot-pressing time is 5 min; the mass ratio of para-aramid nanofiber to meta-aramid short-cut fiber in the tear-resistant aramid nano-insulation paper obtained is 70:30; the prepared paper has a basis weight of 30 g / m 2 .

[0095] Example 7:

[0096] The method for preparing tear-resistant aramid nano-insulating paper in this embodiment specifically includes the following steps:

[0097] (1) Para-aramid short fibers, potassium hydroxide, dimethyl sulfoxide and deionized water are mixed in proportion and sealed, and rapidly stirred at 1400 r / min for 3.5 h to obtain a para-aramid nanofiber dispersion with a concentration of 5 mg / mL; the diameter of the para-aramid nanofibers in the para-aramid nanofiber dispersion is 8 to 15 nm and the length is 3 to 8 μm; then, deionized water is injected into the para-aramid nanofiber dispersion under high pressure while stirring at a speed of 1400 r / min, and then washed with deionized water under vacuum filtration until it becomes a gel, to obtain a para-aramid nanofiber aqueous dispersion A dispersed in deionized water; the para-aramid nanofiber aqueous dispersion A is diluted, and then dispersed by dispersing and stirring for 30,000 r to obtain a para-aramid nanofiber aqueous dispersion B with a mass concentration of 0.1%;

[0098] (2) Dispersing meta-aramid short staple fibers, meta-aramid short medium-long fibers, and meta-aramid short long fibers in water at a ratio of 20:50:30, adding a dispersant for dispersion, and then dispersing by stirring for 30,000 seconds to obtain a meta-aramid short staple fiber aqueous dispersion C with a mass concentration of 0.12%;

[0099] (3) The meta-aramid short fiber aqueous dispersion C obtained in (2) is papered on a 400-mesh forming net to obtain a loose, porous insulating paper substrate; the paper basis weight of the obtained insulating paper substrate is 24 g / m 2 ;

[0100] (4) forming the para-aramid nanofiber aqueous dispersion B obtained in (1) on the insulating paper substrate obtained in (3) to obtain aramid nano-insulating paper;

[0101] (5) The aramid nano-insulating paper obtained in (4) is further pressed, dried, and hot-pressed to obtain tear-resistant aramid nano-insulating paper; the drying is carried out using a conventional papermaking process; the hot-pressing temperature is 240° C., the hot-pressing pressure is 13 MPa, and the hot-pressing time is 9 minutes; the mass ratio of para-aramid nanofiber to meta-aramid short fiber in the tear-resistant aramid nano-insulating paper obtained is 60:40; the prepared paper has a basis weight of 60 g / m 2 .

[0102] Example 8:

[0103] The method for preparing tear-resistant aramid nano-insulating paper in this embodiment specifically includes the following steps:

[0104] (1) mixing para-aramid short fibers, potassium hydroxide, dimethyl sulfoxide and deionized water in proportion and sealing, stirring at 1500 r / min for 4h to obtain a para-aramid nanofiber dispersion liquid with a concentration of 10 mg / mL; the diameter of the para-aramid nanofiber in the para-aramid nanofiber dispersion liquid is 8-15 nm, and the length of the para-aramid nanofiber in the para-aramid nanofiber dispersion liquid is 3-8 μm; then under the stirring of the para-aramid nanofiber dispersion liquid at a speed of 1500 r / min, deionized water is injected into the para-aramid nanofiber dispersion liquid under high pressure, and then the para-aramid nanofiber dispersion liquid is washed to a gel state under vacuum filtration with deionized water to obtain a para-aramid nanofiber water dispersion liquid A dispersed in deionized water; the para-aramid nanofiber water dispersion liquid A is diluted, and then dispersed by beating and stirring for 20000 r to obtain a para-aramid nanofiber water dispersion liquid B with a mass concentration of 0.08%;

[0105] (2) dispersing meta-aramid short fibers, meta-aramid short medium fibers and meta-aramid short long fibers in water in a proportion of 30:40:30, and adding the obtained PEO water dispersion liquid, and then dispersing by beating and stirring for 20000 r to obtain a meta-aramid short fiber water dispersion liquid C with a mass concentration of 0.12%;

[0106] (3) forming the meta-aramid short fiber water dispersion liquid C obtained in (2) on a 300-mesh forming net to obtain a loose and porous insulation paper matrix; the paper basis weight of the obtained insulation paper matrix is 10 g / m 2 ;

[0107] (4) performing secondary forming on the para-aramid nanofiber water dispersion liquid B obtained in (1) on the insulation paper matrix obtained in (3) to obtain an aramid nanometer insulation paper;

[0108] (5) further pressing, drying and hot pressing the aramid nanometer insulation paper obtained in (4) to obtain a tear-resistant aramid nanometer insulation paper; the drying is performed by using a conventional papermaking process; the hot pressing temperature is 230°C, the hot pressing pressure is 10 MPa, and the hot pressing time is 10 min; the mass ratio of para-aramid nanofiber to meta-aramid short fiber in the obtained tear-resistant aramid nanometer insulation paper is 80:20, and the paper basis weight is 50 g / m 2 .

[0109] Comparative Example 1

[0110] The preparation method of the tear-resistant aramid nanometer insulation paper in the embodiment specifically comprises the following steps:

[0111] (1) Para-aramid short fibers, potassium hydroxide, dimethyl sulfoxide, and deionized water are mixed in proportion and sealed, and the mixture is rapidly stirred for reaction for 4 hours to obtain a para-aramid nanofiber dispersion with a concentration of 10 mg / mL; the diameter of the para-aramid nanofibers in the para-aramid nanofiber dispersion is 8 to 15 nm, and the length is 3 to 8 μm; deionized water is then injected into the para-aramid nanofiber dispersion under high pressure while stirring, and the mixture is subsequently washed with deionized water under vacuum filtration until it becomes colloidal, thereby obtaining a para-aramid nanofiber aqueous dispersion A dispersed in deionized water; the para-aramid nanofiber aqueous dispersion A is diluted, and then dispersed in a deflaking machine by deflaking and stirring for 20,000 seconds to obtain a para-aramid nanofiber aqueous dispersion B;

[0112] (2) The para-aramid nanofiber dispersion B obtained in (1) was diluted to a mass concentration of 0.1%, and then papered on a 500-mesh forming net, pressed, and dried to obtain aramid nanopaper; the pressing and drying were both carried out using conventional papermaking processes.

[0113] (3) The aramid nanopaper obtained in (2) is subjected to hot pressing treatment to obtain aramid nano-insulating paper; the hot pressing temperature is 240° C., the hot pressing pressure is 12 MPa, and the hot pressing time is 5 min.

[0114] The performance analysis and testing standards for the aramid nano-insulating paper samples of Examples 2-7 of the present invention and Comparative Example 1 are as follows:

[0115] The tearing strength of paper samples was determined according to GB / T 455-2002 “Paper and board—Determination of tearing strength”.

[0116] The tear strength of the aramid nano insulating paper prepared in comparative example 1 is only 20 mN. The tear strength of the aramid nano insulating paper prepared by embodiments 2-7 of the technical solution of the present invention is 251-577 mN, which is 13-29 times higher than that of comparative example 1.

[0117] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing tear-resistant aramid nano-insulation paper, characterized in that: The steps include: S1, preparing a para-aramid nanofiber aqueous dispersion: injecting deionized water into a para-aramid nanofiber dispersion in a system of dimethyl sulfoxide, potassium hydroxide, and deionized water under high pressure while stirring, and then washing with deionized water under vacuum filtration until it becomes a gel, thereby obtaining a para-aramid nanofiber aqueous dispersion A dispersed in deionized water; diluting the para-aramid nanofiber aqueous dispersion A, and then dispersing the para-aramid nanofiber aqueous dispersion B by dispersing and stirring; S2, preparing an aqueous dispersion of meta-aramid chopped fibers: dispersing meta-aramid chopped fibers of different lengths in water, adding a dispersant, and then dispersing by dispersing and stirring to obtain an aqueous dispersion C of meta-aramid chopped fibers; the ratio of the meta-aramid chopped fibers of different lengths in S2, in parts by weight, is 10-30:30-50:30-50 for meta-aramid chopped short fibers:30-50 for meta-aramid chopped long fibers; the length of the meta-aramid chopped short fibers is 4-6 mm, the length of the meta-aramid chopped medium-long fibers is 7-9 mm, and the length of the meta-aramid chopped long fibers is 10-12 mm; S3, papermaking the meta-aramid chopped fiber aqueous dispersion C obtained in S2 to obtain a loose and porous insulating paper matrix; the basis weight of the insulating paper matrix is ​​3 to 30 g / m 2 ; S4, the para-aramid nanofiber aqueous dispersion B obtained in S1 is subjected to secondary forming and papermaking on the insulating paper substrate obtained in S3 to obtain aramid nano-insulating paper; the aramid nano-insulating paper has a basis weight of 30 to 60 g / m 2 , wherein the mass ratio of para-aramid nanofiber: meta-aramid short fiber is 50-90:10-50; S5, further squeezing, drying, and hot-pressing the aramid nano-insulation paper obtained in S4 to obtain tear-resistant aramid nano-insulation paper.

2. The method for preparing tear-resistant aramid nano-insulation paper according to claim 1, characterized in that: The preparation method of the para-aramid nanofiber dispersion in the dimethyl sulfoxide, potassium hydroxide and deionized water system in S1 is: para-aramid chopped fibers, potassium hydroxide, dimethyl sulfoxide and deionized water are mixed in proportion and sealed, and then stirred and reacted at a speed of 1200 to 1500 r / min for 2 to 4 hours to obtain a para-aramid nanofiber dispersion with a concentration of 5 to 15 mg / mL; the diameter of the para-aramid nanofibers in the para-aramid nanofiber dispersion is 8 to 15 nm, and the length is 3 to 8 μm.

3. The method for preparing tear-resistant aramid nano-insulation paper according to claim 1, characterized in that: In the above S1, the para-aramid nanofiber dispersion in the dimethyl sulfoxide, potassium hydroxide and deionized water system is stirred at a rotation speed of 1000 to 1500 r / min.

4. The method for preparing tear-resistant aramid nano-insulation paper according to claim 1, characterized in that: In the S1, the para-aramid nanofiber aqueous dispersion A is dispersed and stirred for 20,000 to 30,000 seconds; the mass concentration of the para-aramid nanofiber aqueous dispersion B is 0.05 to 0.12%.

5. The method for preparing tear-resistant aramid nano-insulation paper according to claim 1, characterized in that: The S2 is dispersed by stirring for 20,000 to 30,000 seconds; and the mass concentration of the meta-aramid chopped fiber aqueous dispersion C is 0.05 to 0.12%.

6. The method for preparing tear-resistant aramid nano-insulation paper according to claim 1, characterized in that: The S3 specifically comprises: papermaking the meta-aramid chopped fiber aqueous dispersion C obtained in S2 on a 200-400 mesh forming net to obtain a loose and porous insulating paper matrix.

7. The method for preparing tear-resistant aramid nano-insulation paper according to claim 1, characterized in that: The pressing and drying in S5 are both carried out using conventional papermaking processes, with a hot pressing temperature of 230-245° C., a hot pressing pressure of 10-15 MPa, and a hot pressing time of 5-10 minutes.

8. A tear-resistant aramid nano-insulation paper, characterized in that: The invention is obtained based on the preparation method of the tear-resistant aramid nano insulating paper according to any one of claims 1 to 7.

9. An application of the tear-resistant aramid nano-insulation paper according to claim 8 in the field of next-generation highly lightweight and integrated special electrical equipment.

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