A method for preparing aramid fiber mica paper

Abstract

The invention discloses a method for preparing aramid fiber mica paper, comprising the following steps: after aramid chopped fibers and aramid precipitated fibers are washed with Si-WPU emulsion and H-SiO2 emulsion, vacuum filtration is performed under stirring, and deionized water and anhydrous ethanol are used to wash repeatedly and alternately during the filtration process; the obtained aramid fiber slurry is mechanically stirred and dispersed in deionized water to prepare an aramid fiber dispersion liquid; mica flaky powder is ultrasonically dispersed in a sodium hexametaphosphate solution, stirred evenly, a cationic styrene-acrylic emulsion is added, stirred evenly, and a flaky mica slurry is obtained; the aramid fiber dispersion liquid and the flaky mica slurry are mixed and stirred evenly, subjected to instantaneous high-pressure homogenization, formed on the net, and aramid fiber mica paper is obtained after squeezing and drying. The present invention can improve the retention rate of aramid fiber and mica and the uniformity of distribution, and improve the bonding strength, thereby significantly enhancing the dielectric strength and mechanical strength of the aramid fiber mica paper.

Description

Technical Field

[0001] The invention relates to the technical field of mica paper manufacturing, and in particular to a method for preparing aramid fiber mica paper. Background Art

[0002] Mica paper has a series of advantages such as low dielectric constant, high volume resistivity, corona resistance, small expansion coefficient, and high thermal stability. It is the most ideal high-temperature resistant insulating material in the world. However, its mechanical strength is low and it must be reinforced with aramid fiber or resin. For example, Chinese patent CN102760513A discloses a fiber mica paper and its production method, which uses 6-15% aramid fiber 1313 and 85-94% mica as raw materials, and prepares mica paper with higher dielectric strength through a round-net paper machine; Chinese invention patent CN105568750A discloses a para-aramid fiber mica paper and its preparation method, which mixes para-aramid fiber slurry and mica slurry, wet-forms, dries, and hot-presses to obtain aramid fiber mica paper, which has the characteristics of small porosity, high mechanical strength and high dielectric strength.

[0003] At present, aramid mica paper is basically made by wet papermaking technology, which is to mix aramid fiber slurry and mica, and then form, dry and hot press them. Its biggest disadvantages are: poor dispersion of aramid fiber, fiber agglomeration, many chemical residues in fiber, uneven distribution of mica and fiber, poor bonding strength, low retention rate, etc., which limits the improvement of mechanical strength and dielectric strength of the obtained aramid fiber mica paper. Summary of the invention

[0004] To solve the above problems, the present invention provides a method for preparing aramid fiber mica paper, which can improve the retention rate and distribution uniformity of mica and aramid fiber, and improve the bonding strength, thereby significantly enhancing the dielectric strength and mechanical strength of the aramid mica paper and significantly improving the insulation performance.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] A method for preparing aramid fiber mica paper comprises the following steps:

[0007] S1. After washing the aramid short fibers and aramid precipitated fibers with Si-WPU emulsion and H-SiO2 emulsion, vacuum filtration is performed under continuous mechanical stirring. During the filtration process, deionized water and anhydrous ethanol are used to wash alternately for several times to obtain aramid fiber slurry.

[0008] S2, dispersing the obtained aramid fiber slurry in deionized water under the action of high-speed mechanical hydraulic pulping to prepare an aramid fiber dispersion;

[0009] S3, ultrasonically dispersing the flaky mica powder in the sodium hexametaphosphate solution, stirring evenly, adding the cationic styrene acrylic emulsion, stirring evenly again, and obtaining a uniformly suspended flaky mica slurry;

[0010] S4, mixing the obtained aramid fiber dispersion and the flaky mica slurry evenly, and subjecting them to instantaneous high-pressure homogenization treatment,

[0011] The aramid fiber mica paper is formed on the net, pressed and dried.

[0012] Furthermore, in the step S1, after the Si-WPU emulsion and the H-SiO2 emulsion are respectively configured into solutions with a concentration of 90 g / L, the aramid chopped fibers and the aramid fibrils are first placed in the solution configured with the Si-WPU emulsion, stirred at 200 r / min for 30 minutes, and then the solution configured with the H-SiO2 emulsion is added, wherein the mass ratio of the total mass of the aramid chopped fibers and the aramid fibrils to the mass ratio of the Si-WPU emulsion and the H-SiO2 emulsion is 100:5-15.

[0013] Furthermore, in the step S1, the absolute dry mass ratio of the aramid chopped fibers to the aramid fibrids is 1:(2-3).

[0014] 4. The method for preparing aramid fiber mica paper according to claim 1, characterized in that: in the step S1, the mass ratio of Si-WPU emulsion to H-SiO2 emulsion is 3:1.

[0015] Furthermore, in step S3, the mass concentration of the flaky mica slurry is 30% to 50%, wherein, by mass, the mica powder is 20 parts, the sodium hexametaphosphate is 0.03 parts, and the cationic styrene acrylic emulsion is 0.3 parts.

[0016] Furthermore, in the step S4, during mixing, the mass ratio of the aramid fiber to the mica powder is 1:4-10.

[0017] Furthermore, in the step S4, during the instantaneous high pressure treatment, the pressure is adjusted to 200-220 MPa, the treatment flow rate is 5-10 L / h, and the temperature is 30-50°C.

[0018] In the above scheme, H-SiO2 emulsion and Si-WPU emulsion are innovatively used to wash the aramid fiber. While strengthening the mechanical strength of the aramid fiber, micro-nano-sized protrusions are formed on the surface of the aramid fiber. When these protrusions are combined with the cationic styrene-acrylic emulsion, a multi-level rough structure is generated, thereby improving the bonding strength. At the same time, with the instantaneous high-pressure homogenization treatment technology, the mica powder can be more evenly adsorbed in these multi-level rough structures, improving the retention rate and distribution uniformity of mica and aramid fiber, thereby significantly enhancing the dielectric strength and mechanical strength of the aramid mica paper. DETAILED DESCRIPTION

[0019] The present invention is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several variations and improvements may be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0020] In the following embodiments:

[0021] Si-WPU emulsion: Add polyethylene glycol (PEG), PDMS, isophorone diisocyanate (IPDI), and 2,2-dihydroxymethylpropionic acid (DMPA) into a three-necked flask in sequence, heat to 85°C, add a catalyst and react for 6 hours, cool to room temperature, add triethylamine (TEA) to neutralize, continue stirring for 10 minutes, add deionized water and stir at a high speed of 1500rpm / min for emulsification to obtain Si-WPU emulsion.

[0022] H-SiO2 emulsion: It is prepared by emulsion polymerization using sodium dodecylbenzenesulfonate (SDBS), tetraethoxysilane (TEOS), ammonia water, and hexadecyltrimethoxysilane (HDTMS) using the sol-gel method. During the preparation, first obtain a pre-emulsion of sodium dodecylbenzenesulfonate (SDBS) and tetraethoxysilane (TEOS), then slowly add ammonia water to initiate the hydrolysis and condensation reaction of silane for 4 hours; then, add hexadecyltrimethoxysilane (HDTMS) and continue the reaction for 2 hours to obtain H-SiO2 emulsion.

[0023] Mica powder: The raw material is calcined mica flakes. Natural mica flakes are calcined at 700℃, 800℃, 900℃ and 950℃ to obtain four types of calcined mica flakes. The calcined mica flakes are mixed in the proportion of 20%, 20%, 50% and 10% respectively and put into the jaw crusher for preliminary crushing. The preliminary crushed mica is screened with a vibrating screen to remove impurities and defective products to obtain qualified mica powder.

[0024] Example 1

[0025] A method for preparing aramid fiber mica paper comprises the following steps:

[0026] S1. After the Si-WPU emulsion and the H-SiO2 emulsion are respectively prepared into solutions with a concentration of 90 g / L, the aramid short fibers and the aramid fibrils are first placed in the solution prepared by the Si-WPU emulsion, stirred at 200 r / min for 30 min, and then the solution prepared by the H-SiO2 emulsion is added, and the stirring is continued at 200 r / min for 30 min. Under continuous mechanical stirring, vacuum filtration is performed, and deionized water and anhydrous ethanol are used to wash alternately 5 times during the filtration process to obtain an aramid fiber slurry; wherein, the total mass ratio of the aramid short fibers and the aramid fibrils to the mass ratio of the Si-WPU emulsion and the H-SiO2 emulsion is 100:5; the absolute dry mass ratio of the aramid short fibers and the aramid fibrils is 1:2; the mass ratio of the Si-WPU emulsion to the H-SiO2 emulsion is 3:1;

[0027] S2, dispersing the obtained aramid fiber slurry in deionized water under mechanical stirring to prepare an aramid fiber dispersion;

[0028] S3, ultrasonically dispersing mica powder in sodium hexametaphosphate solution, stirring evenly, adding cationic styrene acrylic emulsion, stirring evenly again, to obtain flaky mica slurry; wherein the mass concentration of the flaky mica slurry is 30%, wherein, by mass, 20 parts of mica powder, 0.03 parts of sodium hexametaphosphate, and 0.3 parts of cationic styrene acrylic emulsion;

[0029] S4. Mix the obtained aramid fiber dispersion and mica liquid and stir them evenly, perform instantaneous high-pressure homogenization treatment, and form them on a screen with a screen concentration of 0.005%. After pressing, dry them at 105°C and 0.6Mpa to obtain aramid fiber mica paper; wherein, during mixing, the mass ratio of aramid fiber to mica powder is 1:4, and during instantaneous high-pressure treatment, the pressure is adjusted to 200MPa, the treatment flow rate is 5L / h, and the temperature is 30°C.

[0030] Example 2

[0031] A method for preparing aramid fiber mica paper comprises the following steps:

[0032] S1. After the Si-WPU emulsion and the H-SiO2 emulsion are respectively prepared into solutions with a concentration of 90 g / L, the aramid short fibers and the aramid fibrils are first placed in the solution prepared by the Si-WPU emulsion, stirred at 200 r / min for 30 min, and then the solution prepared by the H-SiO2 emulsion is added, and the stirring is continued at 200 r / min for 30 min. Under continuous mechanical stirring, vacuum filtration is performed, and deionized water and anhydrous ethanol are used to alternately wash 5 times during the filtration process to obtain an aramid fiber slurry; wherein, the total mass ratio of the aramid short fibers and the aramid fibrils to the mass ratio of the Si-WPU emulsion and the H-SiO2 emulsion is 100:10; the absolute dry mass ratio of the aramid short fibers and the aramid fibrils is 1:2.5; the mass ratio of the Si-WPU emulsion to the H-SiO2 emulsion is 3:1;

[0033] S2, dispersing the obtained aramid fiber slurry in deionized water under mechanical stirring to prepare an aramid fiber dispersion;

[0034] S3, ultrasonically dispersing mica powder in sodium hexametaphosphate solution, stirring evenly, adding cationic styrene acrylic emulsion, stirring evenly again, to obtain flaky mica slurry; wherein the mass concentration of the flaky mica slurry is 40%, wherein, by mass, 20 parts of mica powder, 0.03 parts of sodium hexametaphosphate, and 0.3 parts of cationic styrene acrylic emulsion;

[0035] S4. Mix the obtained aramid fiber dispersion and mica liquid and stir them evenly, perform instantaneous high-pressure homogenization treatment, and form them on a screen with a screen concentration of 0.005%. After pressing, dry them at 105°C and 0.6Mpa to obtain aramid fiber mica paper; wherein, during mixing, the mass ratio of aramid fiber to mica powder is 1:7, and during instantaneous high-pressure treatment, the pressure is adjusted to 210MPa, the treatment flow rate is 7.5L / h, and the temperature is 40°C.

[0036] Example 3

[0037] A method for preparing aramid fiber mica paper comprises the following steps:

[0038] S1. After the Si-WPU emulsion and the H-SiO2 emulsion are respectively prepared into solutions with a concentration of 90 g / L, the aramid short fibers and the aramid fibrils are first placed in the solution prepared by the Si-WPU emulsion, stirred at 200 r / min for 30 min, and then the solution prepared by the H-SiO2 emulsion is added, and the stirring is continued at 200 r / min for 30 min. Under continuous mechanical stirring, vacuum filtration is performed, and deionized water and anhydrous ethanol are used to wash alternately for 5 times during the filtration process to obtain an aramid fiber slurry; wherein, the total mass ratio of the aramid short fibers and the aramid fibrils to the mass ratio of the Si-WPU emulsion and the H-SiO2 emulsion is 100:15; the absolute dry mass ratio of the aramid short fibers and the aramid fibrils is 1:3; the mass ratio of the Si-WPU emulsion to the H-SiO2 emulsion is 3:1;

[0039] S2, dispersing the obtained aramid fiber slurry in deionized water under mechanical stirring to prepare an aramid fiber dispersion;

[0040] S3, ultrasonically dispersing mica powder in sodium hexametaphosphate solution, stirring evenly, adding cationic styrene acrylic emulsion, stirring evenly again, to obtain flaky mica slurry; wherein the mass concentration of the flaky mica slurry is 50%, wherein, by mass, 20 parts of mica powder, 0.03 parts of sodium hexametaphosphate, and 0.3 parts of cationic styrene acrylic emulsion;

[0041] S4. Mix and stir the obtained aramid fiber dispersion and mica liquid evenly, perform instantaneous high-pressure homogenization treatment, and form on a screen with a screen concentration of 0.005%. After pressing, dry at 105°C and 0.6Mpa to obtain aramid fiber mica paper; wherein, during mixing, the mass ratio of aramid fiber to mica powder is 1:10, and during instantaneous high-pressure treatment, the pressure is adjusted to 220MPa, the treatment flow rate is 10L / h, and the temperature is 50°C.

[0042] The study found that compared with the traditional wet papermaking technology, the preparation method of the present invention can significantly improve the retention rate and distribution uniformity of mica and aramid fibers. The aramid fiber mica paper prepared in this embodiment was tested using a tensile strength tester and a pressure tester. The test results are shown in Table 1.

[0043] Example 1 Example 2 Example 3 Tensile strength(N / cm) 32.1 36.7 36.3 Dielectric strength (Kv / mm) 24.8 26.1 28.9

[0044] It can be seen from Table 1 that the aramid fiber mica paper prepared in the embodiment of the present invention has excellent tensile strength and dielectric strength.

[0045] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art may make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A method for preparing aramid fiber mica paper, characterized in that: The steps include: S1. After respectively preparing Si-WPU emulsion and H-SiO2 emulsion into solutions with a concentration of 90 g / L, firstly placing aramid short fibers and aramid precipitated fibers in the solution prepared by Si-WPU emulsion, stirring at 200 r / min for 30 min, then adding the solution prepared by H-SiO2 emulsion, stirring at 200 r / min for 30 min, vacuum filtering under continuous mechanical stirring, repeatedly washing with deionized water and anhydrous ethanol for several times during the filtration process, to obtain aramid fiber slurry; The mass ratio of the total mass of aramid chopped fibers and aramid fibrids to the mass ratio of Si-WPU emulsion and H-SiO2 emulsion is 100:5-15; The absolute dry mass ratio of aramid short fibers to aramid fibrids is 1:2-3; The mass ratio of Si-WPU emulsion to H-SiO2 emulsion is 3:1; S2, dispersing the obtained aramid fiber slurry in deionized water under mechanical stirring to prepare an aramid fiber dispersion; S3, ultrasonically dispersing the flaky mica powder in the sodium hexametaphosphate solution, stirring evenly, adding the cationic styrene acrylic emulsion, stirring evenly again, and obtaining a uniformly suspended flaky mica slurry; S4, mixing and stirring the obtained aramid fiber dispersion and flaky mica slurry, subjecting them to instantaneous high-pressure homogenization, forming them on a screen, and obtaining aramid fiber mica paper after pressing and drying; during mixing, the mass ratio of aramid fiber to mica powder is 1:4-10; The preparation method of the Si-WPU emulsion is as follows: polyethylene glycol, PDMS, isophorone diisocyanate, and 2,2-dimethylol propionic acid are sequentially added into a three-necked flask, heated to 85° C., and then a catalyst is added to react for 6 hours, cooled to room temperature, and then triethylamine is added to neutralize and stirred for 10 minutes, and deionized water is added to stir and emulsify at a high speed of 1500 rpm / min to obtain the emulsion; The preparation method of the H-SiO2 emulsion is: it is prepared from sodium dodecylbenzenesulfonate, tetraethoxysilane, ammonia water, and hexadecyltrimethoxysilane. During the preparation, first obtain a pre-emulsion of sodium dodecylbenzenesulfonate and tetraethoxysilane, then slowly add ammonia water to initiate the hydrolysis condensation reaction of silane for 4 hours; then, add hexadecyltrimethoxysilane and continue the reaction for 2 hours to obtain the H-SiO2 emulsion.

2. The method for preparing aramid fiber mica paper according to claim 1, characterized in that: In step S3, the mass concentration of the flaky mica slurry is 30% to 50%, wherein, by mass, the mica powder is 20 parts, the sodium hexametaphosphate is 0.03 parts, and the cationic styrene acrylic emulsion is 0.3 parts.

3. The method for preparing aramid fiber mica paper according to claim 1, characterized in that: In the step S4, during the instantaneous high pressure treatment, the pressure is adjusted to 200-220 MPa, the treatment flow rate is 5-10 L / h, and the temperature is 30-50°C.