Aramid insulation paper and preparation method and application thereof

Abstract

The application discloses aramid insulation paper and a preparation method and application thereof, and relates to the technical field of aramid paper.The application provides a preparation method of aramid insulation paper, and the application starts from the surface polarity of aramid fiber raw materials, and through the means of polarity reversal, the surface of one of the precipitated fibers and the short-cut fibers is subjected to polarity reversal, so that the electrostatic repulsion between the interfaces of the precipitated fibers and the short-cut fibers is weakened, the stability of the paper interface is enhanced, the hollow phenomenon is reduced, and the mechanical and insulating properties of the paper are improved.

Description

Technical Field

[0001] This invention relates to the field of aramid paper technology, and in particular to an aramid insulating paper, its preparation method, and its application. Background Technology

[0002] Aramid paper is widely used in aerospace, rail transportation, and power equipment due to its excellent mechanical, insulation, heat resistance, corrosion resistance, and flame retardant properties. However, high-end aramid paper has long been monopolized by companies such as DuPont (USA) and Teijin (Japan), resulting in persistently high prices. Although some domestic manufacturers have achieved mass production of aramid paper, weak technological accumulation has led to gaps in some product performance compared to foreign products. For aramid paper, since precipitated fibers and chopped fibers are essentially two forms of the same substance with identical surface polarities, they exhibit electrostatic repulsion. During papermaking, this mutual repulsion hinders interfacial stability, leading to voids in the paper after forming, which in turn affects the mechanical and insulation properties of the finished paper.

[0003] Therefore, an aramid insulating paper with excellent mechanical and insulating properties has broad application prospects. Summary of the Invention

[0004] Based on this, the purpose of the present invention is to overcome the shortcomings of the prior art and provide an aramid insulating paper with excellent mechanical and insulating properties, its preparation method and application.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a method for preparing aramid insulating paper, comprising the following steps:

[0006] (1) Add aramid short-cut fibers or aramid precipitated fibers to a mixed solution of dimethyl sulfoxide and water to obtain a mixed slurry. After ultrasonic stirring, add potassium hydroxide and continue ultrasonic stirring to obtain a aramid short-cut fiber dispersion or a aramid precipitated fiber dispersion.

[0007] (2) Add a cationic polymer surfactant to the aramid short-cut fiber dispersion or the aramid precipitated fiber dispersion, stir evenly, filter, wash, and dry to obtain reverse polarity aramid short-cut fibers or reverse polarity aramid precipitated fibers; the zeta potential of the reverse polarity aramid short-cut fibers or the reverse polarity aramid precipitated fibers is 10mV-45mV; the cationic polymer surfactant is at least one of cationic polyacrylamide, polyquaternary ammonium salt polymer, and polyethyleneamine; the polyquaternary ammonium salt polymer is at least one of polyquaternary ammonium salt-5, polyquaternary ammonium salt-6, polyquaternary ammonium salt-7, and polyquaternary ammonium salt-39;

[0008] (3) The reverse polarity aramid short-cut fibers and untreated aramid precipitated fibers are decomposed into a slurry suspension. The slurry suspension is dehydrated, formed, and hot-pressed to obtain the aramid insulating paper.

[0009] Alternatively, the reverse polarity aramid precipitated fibers and untreated aramid chopped fibers are decomposed into a slurry suspension, and the slurry suspension is dehydrated, shaped, and hot-pressed to obtain the aramid insulating paper.

[0010] During actual experiments, the inventors discovered that the outer molecular chains of aramid fibers are mainly composed of carbonyl groups. Due to their electronegativity, free electrons and hydroxyl groups in the environment are adsorbed, exhibiting negative polarity. When treated with cationic polymer surfactants, the cationic components are attracted to the negatively charged fibers, forming a discrete layer on the fiber surface. At this point, the fiber's polarity changes to positive, thus generating electrostatic attraction between the polarity-reversed fibers and untreated fibers. Simultaneously, the repulsive forces between the polarity-reversed fibers remain, thereby inhibiting fiber aggregation. This change in the fiber surface polarity facilitates the uniform distribution of fibers in the pulp and alters the paper's structure.

[0011] During actual experiments, the inventors discovered that using a potassium hydroxide (KOH) / dimethyl sulfoxide (DMSO) system to chemically swell and partially dissolve aramid fibers enhanced the movement and diffusion of fiber molecular chains. The swollen or regenerated fibers shortened the distance between aramid fibers, increasing their interaction. Furthermore, the inventors found that aramid fibers treated with the potassium hydroxide (KOH) / dimethyl sulfoxide (DMSO) system were more prone to potential reversal during subsequent mixing with cationic polymer surfactants. Moreover, in the subsequent delamination and papermaking process of reverse-polarity aramid fibers and untreated aramid fibers, the resulting aramid insulating paper was more dense, significantly improving its mechanical and insulating properties.

[0012] This invention addresses the issue of surface polarity of aramid fiber raw materials by reversing the polarity of one of the surfaces of precipitated fibers and chopped fibers. This reduces the electrostatic repulsion between the interfaces of precipitated fibers and chopped fibers, enhances the stability of the paper interface, reduces voids, and ultimately improves the mechanical and insulating properties of the paper.

[0013] Preferably, the aramid fiber raw material used in this invention is para-aramid fiber or meta-aramid fiber. In the process of preparing aramid insulating paper, it can be para-aramid insulating paper or meta-aramid insulating paper.

[0014] Preferably, the aramid fiber raw material used in this invention is meta-aramid fiber, which is used to prepare meta-aramid insulating paper.

[0015] Preferably, in steps (1) and (2), the aramid short-cut fibers are processed to obtain reverse polarity aramid short-cut fibers.

[0016] During actual experiments, the inventors discovered that the original chopped fibers exhibited agglomeration, leading to direct contact between different chopped fibers. Furthermore, the rigidity of the chopped fibers themselves made interface mitigation difficult. Reversing the polarity of the chopped fibers could reduce direct contact between them. With less direct contact, the gaps between the chopped fibers were more easily surrounded by precipitated fibers, further reducing perforation and thus improving the mechanical and insulating properties of the paper.

[0017] Preferably, in step (1), the beating degree of the aramid chopped fiber slurry is 40-60°SR, and the beating degree of the aramid precipitated fiber is 40-60°SR.

[0018] Preferably, the zeta potential of the reverse polar aramid chopped fiber or the reverse polar aramid precipitated fiber is 29.5mV-31.55mV.

[0019] Preferably, in step (2), the cationic polymer surfactant is a mixture of cationic polyacrylamide, polyquaternary ammonium salt polymer, and polyethyleneamine.

[0020] Preferably, the weight ratio of the cationic polyacrylamide, the polyquaternary ammonium salt polymer, and the polyethyleneamine is cationic polyacrylamide: polyquaternary ammonium salt polymer: polyethyleneamine = 1:(2-3):(1-2).

[0021] During actual experiments, the inventors discovered that the type of cationic polymer surfactant further affects the zeta potential, thereby further affecting the mechanical strength and insulation performance of the aramid insulating paper. When the cationic polymer surfactant is selected as described above, the prepared aramid insulating paper exhibits better mechanical strength and insulation performance.

[0022] Preferably, in step (3), the oven-dry weight percentage of the reverse polarity aramid fiber and the untreated aramid fiber in the slurry suspension is 0.1-0.5 wt%; the weight ratio of the reverse polarity aramid chopped fiber to the untreated aramid precipitated fiber is reverse polarity aramid chopped fiber: untreated aramid precipitated fiber = (1.5-2):1; the weight ratio of the reverse polarity aramid precipitated fiber to the untreated aramid chopped fiber is reverse polarity aramid precipitated fiber: untreated aramid chopped fiber = (1.5-2):1.

[0023] During actual experiments, the inventors discovered that the weight ratio of the reverse polarity aramid fiber to the untreated aramid fiber affects the mechanical strength and insulation performance of the final aramid insulating paper. When the weight ratio of the reverse polarity aramid fiber to the untreated aramid fiber is within the above range, the mechanical strength and insulation performance of the prepared aramid insulating paper are better.

[0024] Preferably, in step (1), the mass-to-volume ratio of the aramid chopped fiber or aramid precipitated fiber, dimethyl sulfoxide, and water is aramid chopped fiber or aramid precipitated fiber: dimethyl sulfoxide: water = (5-10): (500-1000): (10-30); the first ultrasonic stirring time is 10-30 min, and the rotation speed is 1000-3000 r / min; the second ultrasonic stirring time is 12-24 h, and the rotation speed is 1000-3000 r / min; the mass percentage of potassium hydroxide in the dispersion is 0.1-1.5%.

[0025] Preferably, in step (2), the cationic polymer surfactant has a mass percentage content of 0.2-1% in the reverse polar aramid chopped fibers or reverse polar aramid precipitated fibers.

[0026] Preferably, in step (3), the rotation speed of the dissolution is 3000-5000 r / min, and the hot pressing conditions are: hot pressing temperature is 200-260℃, hot pressing pressure is 8.0-10.0 MPa, and hot pressing time is 10-30 min.

[0027] Furthermore, the present invention provides aramid insulating paper prepared by the aforementioned method.

[0028] Furthermore, the present invention provides the application of the aramid insulating paper in the field of transformers.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention starts from the perspective of the surface polarity of aramid fiber raw materials. By means of polarity reversal, the polarity of one of the surfaces of precipitated fibers and chopped fibers is reversed, thereby reducing the electrostatic repulsion between the interface of precipitated fibers and chopped fibers, enhancing the stability of the paper interface, reducing the perforation phenomenon, and thus improving the mechanical and insulating properties of the paper. Attached Figure Description

[0030] Figure 1 This is a cross-sectional view of the aramid insulating paper prepared in Example 1;

[0031] Figure 2 This is a cross-sectional view of the aramid insulating paper prepared in Comparative Example 1. Detailed Implementation

[0032] To better illustrate the purpose, technical solution, and advantages of this invention, the invention will be further described below in conjunction with the accompanying drawings and specific embodiments. The purpose is to provide a detailed understanding of the invention, not to limit it. All other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention. Unless otherwise specified, the experimental reagents and instruments designed in the embodiments and comparative examples of this invention are commonly used reagents and instruments, all of which are commercially available. Unless otherwise specified, the experimental methods used in the embodiments and comparative examples are conventional methods; and unless otherwise specified, the raw materials used in parallel experiments are from the same batch.

[0033] Examples and Comparative Examples

[0034] A method for preparing aramid insulating paper includes the following steps:

[0035] (1) Add aramid chopped fibers or aramid precipitated fibers to a mixed solution of dimethyl sulfoxide and water to obtain a mixed slurry. After ultrasonic stirring, add potassium hydroxide and continue ultrasonic stirring to obtain an aramid chopped fiber dispersion or an aramid precipitated fiber dispersion. The freeness of the aramid chopped fiber slurry is 40-60°SR, and the freeness of the aramid precipitated fibers is 40-60°SR. The mass-volume ratio of the aramid chopped fibers or aramid precipitated fibers, dimethyl sulfoxide, and water is aramid chopped fibers or aramid precipitated fibers: dimethyl sulfoxide: water = (5-10): (500-1000): (10-30). The first ultrasonic stirring time is 10-30 min, and the rotation speed is 1000-3000 r / min. The second ultrasonic stirring time is 12-24 h, and the rotation speed is 1000-3000 r / min. The mass percentage of potassium hydroxide in the dispersion is 0.1-1.5%.

[0036] (2) Add a cationic polymer surfactant to the aramid short-cut fiber dispersion or the aramid precipitated fiber dispersion, stir evenly, filter, wash, and dry to obtain reverse polarity aramid short-cut fibers or reverse polarity aramid precipitated fibers; the zeta potential of the reverse polarity aramid short-cut fibers or the reverse polarity aramid precipitated fibers is 10mV-45mV; the cationic polymer surfactant is at least one of cationic polyacrylamide, polyquaternary ammonium salt polymer, and polyethyleneamine; the polyquaternary ammonium salt polymer is at least one of polyquaternary ammonium salt-5, polyquaternary ammonium salt-6, polyquaternary ammonium salt-7, and polyquaternary ammonium salt-39; the mass percentage of the cationic polymer surfactant in the reverse polarity aramid short-cut fibers or the reverse polarity aramid precipitated fibers is 0.2-1%;

[0037] (3) The reverse polarity aramid short-cut fibers and untreated aramid precipitated fibers are decomposed into a slurry suspension. The slurry suspension is dehydrated, formed, and hot-pressed to obtain the aramid insulating paper.

[0038] Alternatively, the reverse polarity aramid precipitated fibers and untreated aramid chopped fibers are disintegrated into a slurry suspension, and the slurry suspension is dehydrated, shaped, and hot-pressed to obtain the aramid insulating paper.

[0039] The oven-dry weight percentage of reverse polarity aramid fibers and untreated aramid fibers in the slurry suspension is 0.1-0.5 wt%; the weight ratio of reverse polarity aramid chopped fibers to untreated aramid precipitated fibers is reverse polarity aramid chopped fibers: untreated aramid precipitated fibers = (1.5-2):1; the weight ratio of reverse polarity aramid precipitated fibers to untreated aramid chopped fibers is reverse polarity aramid precipitated fibers: untreated aramid chopped fibers = (1.5-2):1;

[0040] The rotation speed for dissolving is 3000-5000 r / min, and the hot pressing conditions are: hot pressing temperature of 200-260℃, hot pressing pressure of 8.0-10.0 MPa, and hot pressing time of 10-30 min.

[0041] Preferably, the cationic polymer surfactant is a mixture of cationic polyacrylamide, polyquaternary ammonium salt polymer, and polyethyleneamine, and the weight ratio of cationic polyacrylamide, polyquaternary ammonium salt polymer, and polyethyleneamine is cationic polyacrylamide: polyquaternary ammonium salt polymer: polyethyleneamine = 1:(2-3):(1-2).

[0042] In the embodiments and comparative examples of this invention, the aramid short-cut fibers and aramid precipitation fibers used are all meta-aramid fibers.

[0043] Example 1

[0044] A method for preparing aramid insulating paper includes the following steps:

[0045] (1) Aramid chopped fibers were added to a mixed solution of dimethyl sulfoxide and water to obtain a mixed slurry. After ultrasonic stirring, potassium hydroxide was added and ultrasonic stirring was continued to obtain an aramid chopped fiber dispersion. The freeness of the aramid chopped fiber slurry was 50°SR. The mass-volume ratio of the aramid chopped fibers, dimethyl sulfoxide, and water was aramid chopped fibers: dimethyl sulfoxide: water = 8:800:20. The first ultrasonic stirring time was 10 min and the rotation speed was 3000 r / min. The second ultrasonic stirring time was 12 h and the rotation speed was 3000 r / min. The mass percentage of potassium hydroxide in the dispersion was 0.6%.

[0046] (2) Add a cationic polymer surfactant to the aramid chopped fiber dispersion, stir evenly, filter, wash, and dry to obtain reverse polarity aramid chopped fibers; the cationic polymer surfactant is a mixture of cationic polyacrylamide, polyquaternary ammonium salt polymer, and polyethyleneamine; the polyquaternary ammonium salt polymer is polyquaternary ammonium salt-5; the weight ratio is cationic polyacrylamide: polyquaternary ammonium salt polymer: polyethyleneamine = 1:2:2; the mass percentage of the cationic polymer surfactant in the reverse polarity aramid chopped fibers is 0.4%;

[0047] (3) The reverse polarity aramid short-cut fibers and untreated aramid precipitated fibers are decomposed into a slurry suspension. The slurry suspension is dehydrated, formed, and hot-pressed to obtain the aramid insulating paper.

[0048] The oven-dry weight percentage of reverse polarity aramid fibers and untreated aramid fibers in the slurry suspension is 0.3 wt%; the weight ratio of reverse polarity aramid chopped fibers to untreated aramid precipitated fibers is 1.5:1; the delamination speed is 5000 r / min; and the hot-pressing conditions are: hot-pressing temperature of 260℃, hot-pressing pressure of 10.0 MPa, and hot-pressing time of 10 min.

[0049] Example 2

[0050] A method for preparing aramid insulating paper includes the following steps:

[0051] (1) Aramid chopped fibers were added to a mixed solution of dimethyl sulfoxide and water to obtain a mixed slurry. After ultrasonic stirring, potassium hydroxide was added and ultrasonic stirring was continued to obtain an aramid chopped fiber dispersion. The freeness of the aramid chopped fiber slurry was 40°SR. The mass-volume ratio of the aramid chopped fibers, dimethyl sulfoxide, and water was aramid chopped fibers: dimethyl sulfoxide: water = 8:800:20. The first ultrasonic stirring time was 30 min at a speed of 1000 r / min, and the second ultrasonic stirring time was 24 h at a speed of 1000 r / min. The mass percentage of potassium hydroxide in the dispersion was 0.6%.

[0052] (2) Add a cationic polymer surfactant to the aramid chopped fiber dispersion, stir evenly, filter, wash, and dry to obtain reverse polarity aramid chopped fibers; the cationic polymer surfactant is a mixture of cationic polyacrylamide, polyquaternary ammonium salt polymer, and polyethyleneamine; the polyquaternary ammonium salt polymer is polyquaternary ammonium salt-5; the weight ratio is cationic polyacrylamide: polyquaternary ammonium salt polymer: polyethyleneamine = 1:2:2;

[0053] The cationic polymer surfactant has a mass percentage content of 0.4% in the reverse polar aramid chopped fibers;

[0054] (3) The reverse polarity aramid short-cut fibers and untreated aramid precipitated fibers are decomposed into a slurry suspension. The slurry suspension is dehydrated, formed, and hot-pressed to obtain the aramid insulating paper.

[0055] The oven-dry weight percentage of reverse polarity aramid fibers and untreated aramid fibers in the slurry suspension is 0.3 wt%; the weight ratio of reverse polarity aramid chopped fibers to untreated aramid precipitated fibers is 1.5:1; the delamination speed is 3000 r / min; and the hot-pressing conditions are: hot-pressing temperature of 200℃, hot-pressing pressure of 8.0 MPa, and hot-pressing time of 30 min.

[0056] Example 3

[0057] A method for preparing aramid insulating paper includes the following steps:

[0058] (1) Aramid chopped fibers are added to a mixed solution of dimethyl sulfoxide and water to obtain a mixed slurry. After ultrasonic stirring, potassium hydroxide is added and ultrasonic stirring is continued to obtain an aramid chopped fiber dispersion. The freeness of the aramid chopped fiber slurry is 60°SR. The mass-volume ratio of aramid chopped fibers, dimethyl sulfoxide, and water is aramid chopped fibers: dimethyl sulfoxide: water = 8:800:20. The first ultrasonic stirring time is 10-30 min at a speed of 2000 r / min, and the second ultrasonic stirring time is 18 h at a speed of 2000 r / min. The mass percentage of potassium hydroxide in the dispersion is 0.6%.

[0059] (2) Add a cationic polymer surfactant to the aramid chopped fiber dispersion, stir evenly, filter, wash, and dry to obtain reverse polarity aramid chopped fibers; the cationic polymer surfactant is a mixture of cationic polyacrylamide, polyquaternary ammonium salt polymer, and polyethyleneamine; the polyquaternary ammonium salt polymer is polyquaternary ammonium salt-5; the weight ratio is cationic polyacrylamide: polyquaternary ammonium salt polymer: polyethyleneamine = 1:2:2;

[0060] The cationic polymer surfactant has a mass percentage content of 0.4% in the reverse polar aramid chopped fibers;

[0061] (3) The reverse polarity aramid short-cut fibers and untreated aramid precipitated fibers are decomposed into a slurry suspension. The slurry suspension is dehydrated, formed, and hot-pressed to obtain the aramid insulating paper.

[0062] The oven-dry weight percentage of reverse polarity aramid fibers and untreated aramid fibers in the slurry suspension is 0.3 wt%; the weight ratio of reverse polarity aramid chopped fibers to untreated aramid precipitated fibers is 1.5:1; the delamination speed is 4000 r / min; and the hot-pressing conditions are: hot-pressing temperature of 230℃, hot-pressing pressure of 9.0 MPa, and hot-pressing time of 20 min.

[0063] Example 4

[0064] Compared with Example 1, only the choice of cationic polymer surfactant in step (2) is different. Specifically, the cationic polymer surfactant is a mixture of cationic polyacrylamide, polyquaternium-5, and polyethyleneamine; the polyquaternium-5 polymer is polyquaternium-5; the weight ratio is cationic polyacrylamide: polyquaternium-5 polymer: polyethyleneamine = 1:3:1, and the remaining components, weight parts and preparation process are exactly the same as in Example 1.

[0065] Example 5

[0066] Compared with Example 1, only the choice of cationic polymer surfactant in step (2) is different. Specifically, the cationic polymer surfactant is a mixture of cationic polyacrylamide, polyquaternium-5, and polyethyleneamine; the polyquaternium-5 polymer is polyquaternium-5; the weight ratio is cationic polyacrylamide: polyquaternium-5 polymer: polyethyleneamine = 1:5:0.5, and the remaining components, weight parts and preparation process are exactly the same as in Example 1.

[0067] Example 6

[0068] Compared with Example 1, only the choice of cationic polymer surfactant in step (2) is different. Specifically, the cationic polymer surfactant is a mixture of cationic polyacrylamide, polyquaternium-5, and polyethyleneamine; the polyquaternium-5 polymer is polyquaternium-5; the weight ratio is cationic polyacrylamide: polyquaternium-5 polymer: polyethyleneamine = 3:1:1, and the remaining components, weight parts and preparation process are exactly the same as in Example 1.

[0069] Example 7

[0070] Compared with Example 1, only the choice of cationic polymer surfactant in step (2) is different. Specifically, the cationic polymer surfactant is cationic polyacrylamide, and the other components, weight parts and preparation process are exactly the same as in Example 1.

[0071] Example 8

[0072] Compared with Example 1, only the choice of cationic polymer surfactant in step (2) is different. Specifically, the cationic polymer surfactant is polyquaternary ammonium salt-7, and the other components, weight parts and preparation process are exactly the same as in Example 1.

[0073] Example 9

[0074] Compared with Example 1, only the amount of cationic polymer surfactant used in step (2) is different. Specifically, the mass percentage of the cationic polymer surfactant in the reverse polar aramid chopped fiber is 0.3%, and the other components, weight parts and preparation process are exactly the same as in Example 1.

[0075] Example 10

[0076] Compared with Example 1, only the amount of cationic polymer surfactant used in step (2) is different. Specifically, the mass percentage of the cationic polymer surfactant in the reverse polar aramid chopped fiber is 1.3%, and the other components, weight parts and preparation process are exactly the same as in Example 1.

[0077] Example 11

[0078] Compared with Example 1, only the amount of cationic polymer surfactant used in step (2) is different. Specifically, the mass percentage of the cationic polymer surfactant in the reverse polar aramid chopped fiber is 2%, and the other components, weight parts and preparation process are exactly the same as in Example 1.

[0079] Example 12

[0080] Compared with Example 1, only the amount of cationic polymer surfactant used in step (2) is different. Specifically, the mass percentage of the cationic polymer surfactant in the reverse polar aramid chopped fiber is 0.05%, and the other components, weight parts and preparation process are exactly the same as in Example 1.

[0081] Example 13

[0082] Compared with Example 1, only the weight ratio of reverse polar aramid chopped fiber and untreated aramid precipitated fiber in step (3) is different. The ratio of reverse polar aramid chopped fiber to untreated aramid precipitated fiber is 2:1. The other components, weight parts and preparation process are exactly the same as in Example 1.

[0083] Example 14

[0084] Compared with Example 1, only the weight ratio of reverse polar aramid chopped fiber and untreated aramid precipitated fiber in step (3) is different. The ratio of reverse polar aramid chopped fiber to untreated aramid precipitated fiber is 3:1. The other components, weight parts and preparation process are exactly the same as in Example 1.

[0085] Example 15

[0086] Compared with Example 1, only the weight ratio of reverse polar aramid chopped fiber and untreated aramid precipitated fiber in step (3) is different. The ratio of reverse polar aramid chopped fiber to untreated aramid precipitated fiber is 1:1. The other components, weight parts and preparation process are exactly the same as in Example 1.

[0087] Example 16

[0088] Compared with Example 1, only the reverse polar aramid short-cut fibers were modified to reverse polar aramid precipitated fibers, while the other components, weight parts and preparation processes were exactly the same as in Example 1.

[0089] Comparative Example 1

[0090] Compared to Example 1, no polarity reversal operation is performed. Specifically, the preparation method of the aramid insulating paper is as follows:

[0091] (1) Aramid chopped fibers were added to a mixed solution of dimethyl sulfoxide and water to obtain a mixed slurry. After ultrasonic stirring, potassium hydroxide was added and ultrasonic stirring was continued to obtain an aramid chopped fiber dispersion. The freeness of the aramid chopped fiber slurry was 50°SR. The mass-volume ratio of the aramid chopped fibers, dimethyl sulfoxide, and water was aramid chopped fibers: dimethyl sulfoxide: water = 8:800:20. The first ultrasonic stirring time was 10 min and the rotation speed was 3000 r / min. The second ultrasonic stirring time was 12 h and the rotation speed was 3000 r / min. The mass percentage of potassium hydroxide in the dispersion was 0.6%.

[0092] (2) The aramid short-cut fibers and aramid precipitated fibers described in step (1) are disintegrated into a slurry suspension. The slurry suspension is dehydrated, formed, and hot-pressed to obtain the aramid insulating paper.

[0093] The aramid fiber content in the slurry suspension is 0.3 wt% by oven-dry weight; the weight ratio of aramid chopped fiber to aramid precipitated fiber is 1.5:1; the delamination speed is 5000 r / min; and the hot-pressing conditions are: hot-pressing temperature of 260℃, hot-pressing pressure of 10.0 MPa, and hot-pressing time of 10 min.

[0094] Performance testing

[0095] The zeta potential was tested according to GB / T 24993-2010 "Determination of Zeta Potential in Wet End of Papermaking".

[0096] The zeta potential of the untreated meta-aramid chopped fibers used in this invention is -11.3 mV, and the zeta potential of the untreated meta-aramid precipitated fibers used in this invention is -14.8 mV.

[0097] The Zeta potentials of the reverse polarity aramid chopped fibers or reverse polarity aramid precipitated fibers prepared by steps (1)-(2) in the embodiments of the present invention are shown in Table 1. The Zeta potentials of the aramid chopped fibers in Comparative Example 1 of the present invention are also shown in Table 1.

[0098] The tensile strength, elongation at break, and electrical strength were tested according to GB / T 29627.2-2013 "Electrical grade polyaramid fiber paperboard - Part 2: Test methods" and GB / T20629.3-2019 "Electrical grade non-cellulose paper - Part 3: Unfilled polyaramid fiber paper". The test results are shown in Table 2 below.

[0099] Table 1

[0100]

[0101] Table 2

[0102]

[0103]

[0104] As shown in the table above, reversing the polarity of either the precipitated fiber or the chopped fiber can improve the mechanical (tensile strength, elongation at break) and insulating (electrical strength) properties of aramid paper to a certain extent.

[0105] Depend on Figure 1-2 The comparison shows that the aramid paper in Example 1 has a more compact cross-section with fewer perforations, while the aramid paper in Comparative Example 1 has more perforations. This indicates that when the preparation process and conditions are the same, reversing the polarity of either the precipitated fibers or the chopped fibers results in a more compact structure of the aramid paper.

[0106] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing aramid insulating paper, characterized in that, Includes the following steps: (1) Add aramid short-cut fibers or aramid precipitated fibers to a mixed solution of dimethyl sulfoxide and water to obtain a mixed slurry. After ultrasonic stirring, add potassium hydroxide and continue ultrasonic stirring to obtain a aramid short-cut fiber dispersion or a aramid precipitated fiber dispersion. (2) Add a cationic polymer surfactant to the aramid short-cut fiber dispersion or the aramid precipitated fiber dispersion, stir evenly, filter, wash, and dry to obtain reverse polarity aramid short-cut fibers or reverse polarity aramid precipitated fibers; the zeta potential of the reverse polarity aramid short-cut fibers or the reverse polarity aramid precipitated fibers is 10mV-45mV; the cationic polymer surfactant is at least one of cationic polyacrylamide, polyquaternary ammonium salt polymer, and polyethyleneamine; the polyquaternary ammonium salt polymer is at least one of polyquaternary ammonium salt-5, polyquaternary ammonium salt-6, polyquaternary ammonium salt-7, and polyquaternary ammonium salt-39; (3) The reverse polarity aramid short-cut fibers and untreated aramid precipitated fibers are decomposed into a slurry suspension. The slurry suspension is dehydrated, formed, and hot-pressed to obtain the aramid insulating paper. Alternatively, the reverse polarity aramid precipitated fibers and untreated aramid chopped fibers are decomposed into a slurry suspension, and the slurry suspension is dehydrated, shaped, and hot-pressed to obtain the aramid insulating paper.

2. The method for preparing aramid insulating paper as described in claim 1, characterized in that, In step (1), the beating degree of the aramid chopped fiber slurry is 40-60°SR, and the beating degree of the aramid precipitated fiber is 40-60°SR.

3. The method for preparing aramid insulating paper as described in claim 1, characterized in that, In step (2), the cationic polymer surfactant is a mixture of cationic polyacrylamide, polyquaternary ammonium salt polymer and polyethyleneamine.

4. The method for preparing aramid insulating paper as described in claim 3, characterized in that, In step (2), the weight ratio of cationic polyacrylamide, polyquaternary ammonium salt polymer, and polyethyleneamine is cationic polyacrylamide: polyquaternary ammonium salt polymer: polyethyleneamine = 1:(2-3):(1-2).

5. The method for preparing aramid insulating paper as described in claim 1, characterized in that, In step (3), the oven-dry weight percentage of the reverse polarity aramid fibers and untreated aramid fibers in the slurry suspension is 0.1-0.5 wt%. The weight ratio of the reverse polarity aramid chopped fiber to the untreated aramid precipitated fiber is (1.5-2):

1.

6. The method for preparing aramid insulating paper as described in claim 1, characterized in that, In step (1), the mass-to-volume ratio of the aramid short-cut fiber or aramid precipitated fiber, dimethyl sulfoxide, and water is aramid short-cut fiber or aramid precipitated fiber: dimethyl sulfoxide: water = (5-10): (500-1000): (10-30); the first ultrasonic stirring time is 10-30 min, and the rotation speed is 1000-3000 r / min; the second ultrasonic stirring time is 12-24 h, and the rotation speed is 1000-3000 r / min; the mass percentage of potassium hydroxide in the dispersion is 0.1-1.5%. And / or, in step (2), the cationic polymer surfactant has a mass percentage content of 0.2-1% in the reverse polar aramid chopped fiber or the reverse polar aramid precipitated fiber; The volume-to-weight ratio of aramid short-cut fiber dispersion or aramid precipitated fiber dispersion to cationic polymer surfactant is aramid short-cut fiber dispersion or aramid precipitated fiber dispersion: cationic polymer surfactant = (500-1000) mL: (2-5) g; And / or, in step (3), the rotation speed of the dissolution is 3000-5000 r / min, and the hot pressing conditions are: hot pressing temperature is 200-260℃, hot pressing pressure is 8.0-10.0 MPa, and hot pressing time is 10-30 min.

7. An aramid insulating paper prepared by the method of any one of claims 1-6.

8. The application of the aramid insulating paper as described in claim 7 in the field of transformers.

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