Para-aramid paper and preparation method thereof

Abstract

The invention provides para-aramid paper and a preparation method thereof, and the preparation method comprises the following steps: (1) mixing para-aramid chopped fibers with a surfactant solution, and then carrying out plasma surface treatment to obtain hydrophilic para-aramid chopped fibers; (2) pulping the para-aramid chopped fibers to obtain para-aramid fiber pulp; (3) carrying out ultrasonic treatment on the para-aramid fiber pulp to obtain a suspension, and then shearing to obtain nanofibers; and (4) mixing the hydrophilic para-aramid chopped fibers with the para-aramid fiber pulp to obtain an aramid fiber pulp, then carrying out papermaking molding, spraying nanofibers to obtain para-aramid base paper, and carrying out hot pressing to obtain the para-aramid paper. By adopting a method of combining the para-aramid fiber pulp, the para-aramid chopped fibers and the specific nanofibers, the obtained para-aramid paper has excellent tensile strength, tearing strength, compressive strength and electrical performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of papermaking, and particularly relates to a para-aramid paper and a preparation method thereof. Background Art

[0002] Para-aramid is formed by polycondensation of terephthaloyl chloride and p-phenylenediamine, and is also called "aramid 1414" according to the position of substituents on the benzene ring. Para-aramid fiber (poly-p-phenylene terephthalamide) has excellent properties such as high specific strength, high specific modulus, high temperature resistance and corrosion resistance, and has advantages such as fatigue resistance, shear resistance, low relative density and good dimensional stability. It is a typical representative of high-performance synthetic fibers. Current products are mainly para-aramid short cut fibers, para-aramid pulp fibers and para-aramid precipitated fibers. With the development of the modern papermaking industry, para-aramid fibers have become an important papermaking raw material. Para-aramid paper is prepared by wet papermaking process with para-aramid short cut fibers and precipitated fibers (or pulp fibers) in a certain proportion. In the structure of para-aramid fiber paper, short cut fibers are used as the skeleton material, evenly dispersed in the paper, determining the physical strength and mechanical properties of the paper; precipitated fibers (or pulp fibers) are used as filling materials and bonding materials, softening during the hot pressing process, and forming an overall mechanical structure through bonding short cut fibers and self-bonding, endowing the paper with overall strength and insulation properties. Para-aramid paper has strong mechanical properties, excellent dielectric properties and flexible processing properties, and can be widely used as insulation materials, structural materials, electronic materials in important high-tech industries such as electric power, transportation, electronics, aerospace, etc. Currently, most para-aramid papers are made by mixing and papermaking para-aramid short cut fibers and para-aramid pulp fibers.

[0003] Para-aramid paper has the characteristics of light specific gravity, high specific strength, high specific stiffness, impact resistance, high temperature resistance, outstanding corrosion resistance and electromagnetic wave transmission performance. However, compared with meta-aramid paper, due to the rigid structure of the fiber molecular chain and the chemical inertness of the fiber surface in the para-aramid paper base material, there is a lack of effective bonding between fibers, resulting in poor mechanical properties and unable to fully reflect the high strength and high modulus characteristics of the fibers themselves. Therefore, special strengthening treatment is required.

[0004] CN105568750A discloses a para-aramid fiber mica composite paper and its production method, including 10 - 20% of para-aramid short-cut fibers, 20 - 40% of para-aramid precipitated fibers and 40 - 70% of mica flakes. By preparing mica flake slurry with a mass concentration of 1 - 6%, para-aramid short-cut fiber slurry with a mass concentration of 0.01 - 0.05% and para-aramid precipitated fiber slurry with a mass concentration of 0.05 - 0.5%, mixing and dispersing them evenly, forming by wet papermaking, drying and then hot pressing to obtain the para-aramid fiber mica composite paper. The obtained composite paper has a low basis weight, a small porosity, excellent mechanical strength, and while ensuring the mechanical strength and dielectric strength of the mica composite paper, significantly improves its high-temperature stability, and the preparation steps are simple.

[0005] CN103174053A discloses a production method of aramid 1414 paper-based material. Mix the aramid 1414 short-cut fiber slurry, modified thermoplastic fiber slurry and aramid 1414 pulp fiber slurry evenly and then defibrate, then add maleic anhydride-acrylic acid copolymer for slurry mixing and dispersing, then adjust the pulp concentration, and form and hot press the obtained slurry suspension to obtain the aramid 1414 paper-based base paper; immerse the aramid 1414 paper-based base paper in polyimide resin sizing solution, and then dry to remove volatile solvents to obtain the aramid 1414 paper-based material. The production method of this invention is environmentally friendly, can prevent the recontamination of metal ions to fibers, and avoids the bubble problem of conventional dispersants during papermaking, makes up for the shortcomings of adding a third fiber and organic resin alone, and the physical properties, high-temperature resistance and insulation properties of the obtained finished paper are significantly increased, fully meeting the functional indexes of high-performance aramid 1414 paper-based materials.

[0006] CN110055807A discloses a preparation method of para-aramid and graphene oxide / graphene composite paper. This method first prepares a para-aramid nanofiber aqueous dispersion by a surfactant-free one-step polymerization method. Utilizing the characteristics that both para-aramid nanofibers and graphene oxide have good dispersibility in water, uniformly mix the two dispersions in proportion, and then use the traditional papermaking method to prepare para-aramid / graphene oxide composite paper; then reduce graphene oxide by wet or dry method to obtain para-aramid / graphene composite paper. In addition to continuously and large-scale producing para-aramid and graphene / graphene oxide composite paper, the obtained composite paper has excellent properties, and the corresponding production environment is friendly, the cost is low, and the process is simple.

[0007] Due to a series of defects in the mechanical properties and dielectric properties of para-aramid paper. Therefore, how to provide a para-aramid paper with excellent mechanical properties and dielectric properties has become an urgent problem to be solved. Summary of the Invention

[0008] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a para-aramid paper and a preparation method thereof. By adopting a method of combining para-aramid fiber pulp, para-aramid short-cut fibers and specific nanofibers, the obtained para-aramid paper has excellent tensile, tear, compressive strength and electrical properties.

[0009] To achieve the purpose of this invention, the following technical solutions are adopted:

[0010] On the one hand, the present invention provides a preparation method of para-aramid paper, and the preparation method includes the following steps:

[0011] (1) Mix the para-aramid short-cut fibers with a surfactant solution, and then perform plasma surface treatment to obtain hydrophilic para-aramid short-cut fibers;

[0012] (2) Beat the para-aramid short-cut fibers to obtain para-aramid fiber pulp;

[0013] (3) Ultrasonically treat the para-aramid fiber pulp to obtain a suspension, and then shear it to obtain nanofibers;

[0014] (4) Mix the hydrophilic para-aramid short-cut fibers with the para-aramid fiber pulp to obtain aramid fiber slurry, then form it by papermaking and spray nanofibers to obtain the para-aramid base paper, and obtain the para-aramid paper after hot pressing.

[0015] Steps (1) and steps (2)-(3) do not distinguish the order.

[0016] In the above method, the para-aramid short-cut fibers are ground to obtain a suitable fibrillated pulp, and then the pulp is further cut into nanofibers. The para-aramid fiber pulp and the para-aramid short-cut fibers are combined for papermaking. After forming, nanofibers are sprayed, thereby improving the interlayer bonding force between pulp fibers, significantly enhancing the mechanical properties of the paper, effectively filling the gaps between pulp fibers at the same time, improving the retention rate, barrier properties, reducing paper linting and powdering, optimizing the papermaking process, reducing raw material losses, and improving the uniformity, mechanical properties and electrical properties of the paper.

[0017] Preferably, the surfactant in step (1) includes any one or a combination of at least two of Remol A, sodium dodecylbenzenesulfonate or lauryl alcohol phosphate.

[0018] Preferably, the mass fraction of the solute in the surfactant solution in step (1) is 25-30%, such as 25%, 26%, 27%, 28%, 29% or 30%, etc., but not limited to the values listed above. Other unlisted values within the above numerical range are equally applicable.

[0019] Preferably, the power of the ultrasonic treatment in step (3) is 300 - 800 W, and the frequency is 40 - 100 kHz. The power can be 300 W, 400 W, 500 W, 600 W, 700 W, 800 W, etc., and the frequency can be 40 kHz, 50 kHz, 60 kHz, 70 kHz, 80 kHz, 90 kHz, 100 kHz, etc., but is not limited to the values listed above. Other unlisted values within the above numerical range are equally applicable.

[0020] Preferably, the ultrasonic treatment in step (3) is performed at least 3 times. The treatment time for each time is 4 - 6 min, and the interval is 8 - 12 min. The treatment time for each time can be 4 min, 4.5 min, 5 min, 5.5 min, 6 min, etc., and the interval can be 8 min, 9 min, 10 min, 11 min, 12 min, etc., but is not limited to the values listed above. Other unlisted values within the above numerical range are equally applicable.

[0021] Preferably, the pressure of the shearing in step (3) is 100 - 300 MPa, the temperature is 20 - 50 °C, the rotation speed is 1000 - 3000 r / min, the shearing cycle is 2 - 5 times, each time is 2 - 3 min, and the mass fraction of the suspension is 1 - 3%.

[0022] Among them, the pressure can be 100 MPa, 150 MPa, 200 MPa, 250 MPa, 300 MPa, etc., the mass fraction of the suspension can be 1%, 1.5%, 2%, 2.5%, 3%, etc., the temperature can be 20 °C, 25 °C, 30 °C, 35 °C, 40 °C, 45 °C, 50 °C, etc., and the rotation speed can be 1000 r / min, 1500 r / min, 2000 r / min, 2500 r / min, 3000 r / min, etc., but is not limited to the values listed above. Other unlisted values within the above numerical range are equally applicable.

[0023] Preferably, the mass ratio of the hydrophilic para - aramid short - cut fibers to the para - aramid fiber pulp in step (4) is (3 - 6):(4 - 7). The number of parts of the hydrophilic para - aramid short - cut fibers can be 3, 4, 5, 6, etc., and the number of parts of the para - aramid fiber pulp can be 4, 5, 6, 7, etc., but is not limited to the values listed above. Other unlisted values within the above numerical range are equally applicable.

[0024] Preferably, in the sprayed nanofibers in step (4), the mass fraction of the nanofiber suspension is 1 - 6%, such as 1%, 2%, 3%, 4%, 5%, 6%, etc., but is not limited to the values listed above. Other unlisted values within the above numerical range are equally applicable.

[0025] Preferably, in the sprayed nanofibers in step (4), the spraying amount is 1-5% of the mass of the para-aramid base paper, such as 1%, 2%, 3%, 4% or 5%, etc., but not limited to the values listed above. Other unlisted values within the above numerical range are equally applicable.

[0026] The above specific parameters can enable the prepared nanofibers to more effectively fill the voids of the paper, increase the paper density, and thus improve the product performance.

[0027] Preferably, before the hot pressing in step (4), pre-hot pressing is also carried out;

[0028] Preferably, the temperature of the pre-hot pressing is 150-200°C, and the time is 5-10 s. Among them, the temperature can be 150°C, 160°C, 170°C, 180°C, 190°C or 200°C, etc., and the time can be 5 s, 6 s, 7 s, 8 s, 9 s or 10 s, etc., but not limited to the values listed above. Other unlisted values within the above numerical range are equally applicable.

[0029] The above pre-hot pressing process can effectively evaporate the moisture in the base paper before hot pressing, increase the bonding force between para-aramid fibers, reduce the air permeability of the para-aramid formed paper, and thus improve the mechanical properties and electrical properties of the para-aramid paper.

[0030] Preferably, the temperature of the hot pressing is 250-320°C, the linear pressure is 250-450 kN / m, and the vehicle speed is 1.0-10.0 m / min.

[0031] The above hot pressing process can cause the aramid pulp to soften and melt, coat and bond the short-cut fibers, and make the two into a whole, thus endowing the final product with strength and insulation performance. High-temperature hot pressing not only enhances the mechanical strength and electrical properties of the aramid paper, but also makes it have excellent flame retardancy and chemical stability.

[0032] Preferably, after the hot pressing in step (4), cooling treatment is also carried out;

[0033] Preferably, the temperature of the cooling treatment is 15-25°C. Among them, the temperature can be 15°C, 16°C, 17°C, 18°C, 19°C, 20°C, 23°C or 25°C, etc., but not limited to the values listed above. Other unlisted values within the above numerical range are equally applicable.

[0034] The above cooling treatment helps to stabilize the structure and performance of the paper, ensuring that it can still maintain good electrical performance and mechanical strength at high temperatures. During the cooling process, the fibers and pulp of the aramid paper will further solidify, forming a more solid structure, thus improving its high-temperature resistance, corrosion resistance and insulation performance.

[0035] On the other hand, the present invention also provides a para-aramid paper prepared by the preparation method as described above.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] (1) The present invention uses para-aramid fiber pulp as the bonding material for para-aramid paper. The para-aramid fiber pulp has good bonding ability, and its relatively high specific surface area can increase the bonding force and bonding area between fibers, reduce the pores in the paper, thereby improving the mechanical strength and stability of the aramid insulating paper;

[0038] (2) The nanofibers prepared by a specific method can effectively fill the voids in the paper, increase the paper density, and thus can significantly enhance the tensile, tear, compressive strength and electrical properties of the paper;

[0039] (3) The pre-heat pressing process can effectively evaporate the moisture in the base paper before hot pressing, increase the bonding force between para-aramid fibers, reduce the air permeability of the para-aramid formed paper, and thus improve the mechanical properties and electrical properties of the para-aramid paper. Specific Embodiments

[0040] To further elaborate on the technical means and effects adopted by the present invention, the following further illustrates the technical solution of the present invention in combination with the preferred embodiments of the present invention, but the present invention is not limited to the scope of the embodiments.

[0041] Example 1

[0042] This example provides a para-aramid paper, and the preparation method is as follows:

[0043] Step 1: Pretreat the para-aramid short fibers with an aqueous solution of Remazol A (concentration 28%, 40 °C), wash them with clean water, and then perform surface treatment with plasma (the ionized gas is carbon tetrafluoride, the radio frequency is 40 kHz, the vacuum degree of the treatment chamber is controlled at 20 kPa, the temperature is 10 °C, and the treatment time is 3 s) to obtain hydrophilic para-aramid short fibers;

[0044] Step 2: Add deionized water to the para-aramid short fibers treated in Step 1 to prepare a short fiber suspension with a mass fraction of 2%, and perform beating treatment with a trough beater (the working current is 100 A, after normal operation for 40 minutes, it is intermittent for 5 minutes, the total time is 90 minutes, and the beating degree is controlled between 30 - 48 °SR) to obtain para-aramid fiber pulp;

[0045] Step 3: Pretreat the para-aramid fiber pulp obtained in Step 2 with an ultrasonic processor (power: 500 W, frequency: 70 kHz, single ultrasonic treatment time: 5 minutes, ultrasonic interval time: 10 minutes, total ultrasonic treatment time: 35 minutes), and then perform shearing treatment with a high-pressure homogenizer (pressure: 200 MPa, power: 30 kW, mass fraction: 2%, temperature: 40 °C, rotation speed: 2000 r / min, circulate 3 times) to obtain nanofibers with a fiber diameter between 10 - 50 nm, a length between 500 - 2000 nm, and a specific surface area between 150 - 300 m 2 / g;

[0046] Step 4: Mix the short para-aramid fibers and the para-aramid fiber pulp obtained in Step 1 and Step 2 respectively to prepare a para-aramid fiber slurry with a mixing mass ratio of 4:6;

[0047] Step 5: Form the para-aramid fiber slurry obtained in Step 4 on an inclined wire paper machine, then spray with nanofibers, control the mass fraction of the nanofiber suspension to be 4%, control the spraying amount to be 2% of the mass of the original paper, and then obtain the para-aramid base paper after pressing and drying;

[0048] Step 6: Pre-press the para-aramid base paper obtained in Step 5 with a high-temperature hot press, the pre-pressing time is 8 s, the temperature is 170 °C, then perform high-temperature hot pressing, the high-temperature hot pressing temperature is 270 °C, the linear pressure is 350 kN / m, the vehicle speed is 2.0 m / min, and finally obtain the para-aramid paper after cooling (15 °C).

[0049] Example 2

[0050] This example provides a para-aramid paper, and the preparation method is as follows:

[0051] Step 1: Pretreat the short para-aramid fibers with an aqueous solution of Remol A (concentration: 25%, 40 °C), wash with clean water, and then perform surface treatment with plasma (ionized gas: carbon tetrafluoride, radio frequency: 40 kHz, the vacuum degree of the treatment chamber is controlled at 20 kPa, the temperature is 10 °C, and the treatment time is 3 s) to obtain hydrophilic short para-aramid fibers;

[0052] Step 2: Add deionized water to the short para-aramid fibers treated in Step 1 to prepare a short fiber suspension with a mass fraction of 2%, and perform beating treatment with a trough beater (working current: 100 A, intermittent for 5 minutes after normal operation for 40 minutes, total time: 90 minutes, beating degree controlled between 30 - 48 °SR) to obtain para-aramid fiber pulp;

[0053] Step 3: Pretreat the para-aramid fiber pulp obtained in Step 2 with an ultrasonic processor (power: 800 W, frequency: 100 kHz, ultrasonic time for one time: 5 minutes, ultrasonic interval time: 10 minutes, total ultrasonic treatment time: 35 minutes), and then perform shear treatment with a high-pressure homogenizer (pressure: 100 MPa, power: 30 kW, mass fraction: 1%, temperature: 20 °C, rotation speed: 1000 r / min, circulate 3 times) to obtain nanofibers with a fiber diameter between 10 - 50 nm, a length between 500 - 2000 nm, and a specific surface area between 150 - 300 m 2 / g;

[0054] Step 4: Mix the short-cut para-aramid fibers and the para-aramid fiber pulp obtained in Step 1 and Step 2 respectively to prepare a para-aramid fiber slurry with a mixing mass ratio of 5:5;

[0055] Step 5: Form the para-aramid fiber slurry obtained in Step 4 on an inclined screen paper machine, and then spray with nanofibers. Control the mass fraction of the nanofiber suspension to be 1%, control the spraying amount to be 5% of the mass of the original paper. After pressing and drying, obtain the para-aramid base paper;

[0056] Step 6: Pre-press the para-aramid base paper obtained in Step 5 with a high-temperature hot press. The pre-pressing time is 10 s, the temperature is 150 °C, and then perform high-temperature hot pressing. The high-temperature hot pressing temperature is 280 °C, the linear pressure is 380 kN / m, the vehicle speed is 2.0 m / min, and finally cool (15 °C) to obtain the para-aramid paper.

[0057] Example 3

[0058] This example provides a para-aramid paper, and the preparation method is as follows:

[0059] Step 1: Pretreat the short-cut para-aramid fibers with an aqueous solution of Remol A (concentration: 30%, 40 °C), wash with clean water, and then perform surface treatment with plasma (ionized gas: carbon tetrafluoride, radio frequency: 40 kHz, the vacuum degree of the treatment chamber is controlled at 20 kPa, temperature: 10 °C, treatment time: 3 s) to obtain hydrophilic short-cut para-aramid fibers;

[0060] Step 2: Add deionized water to the short-cut para-aramid fibers treated in Step 1 to prepare a short-cut fiber suspension with a mass fraction of 2%, and perform beating treatment with a trough beater (working current: 100 A, intermittent for 5 minutes after normal operation for 40 minutes, total time: 90 minutes, beating degree is controlled between 30 - 48 °SR) to obtain para-aramid fiber pulp;

[0061] Step 3: Pretreat the para-aramid fiber pulp in Step 2 with an ultrasonic processor (power: 300 W, frequency: 40 kHz, single ultrasonic time: 5 minutes, ultrasonic interval time: 10 minutes, total ultrasonic treatment time: 35 minutes), and then perform shear treatment with a high-pressure homogenizer (pressure: 300 MPa, power: 30 kW, mass fraction: 3%, temperature: 50 °C, rotation speed: 3000 r / min, circulate 3 times) to obtain nanofibers with a fiber diameter between 10 - 50 nm, a length between 500 - 2000 nm, and a specific surface area between 150 - 300 m 2 / g.

[0062] Step 4: Mix the short-cut para-aramid fibers and para-aramid fiber pulp obtained in Step 1 and Step 2 respectively to prepare a para-aramid fiber slurry with a mixing mass ratio of 6:4.

[0063] Step 5: Form the para-aramid fiber slurry obtained in Step 4 on an inclined wire paper machine, then spray with nanofibers, control the mass fraction of the nanofiber suspension to be 6%, control the spraying amount to be 1% of the mass of the original paper, and then obtain the para-aramid base paper after pressing and drying.

[0064] Step 6: Pre-press the para-aramid base paper obtained in Step 5 with a high-temperature hot press, the pre-pressing time is 5 s, the temperature is 200 °C, then perform high-temperature hot pressing, the high-temperature hot pressing temperature is 270 °C, the linear pressure is 300 kN / m, the vehicle speed is 3.0 m / min, and finally obtain the para-aramid paper after cooling (15 °C).

[0065] Example 4

[0066] This example provides a para-aramid paper. The preparation method is the same as that of Example 1 except for the following Step 3:

[0067] Step 3: Pretreat the para-aramid fiber pulp in Step 2 with an ultrasonic processor (power: 200 W, frequency: 30 kHz, single ultrasonic time: 5 minutes, ultrasonic interval time: 10 minutes, total ultrasonic treatment time: 35 minutes), and then perform shear treatment with a high-pressure homogenizer (pressure: 200 MPa, power: 30 kW, mass fraction: 2%, temperature: 40 °C, rotation speed: 2000 r / min, circulate 3 times) to obtain nanofibers with a fiber diameter between 10 - 50 nm, a length between 500 - 2000 nm, and a specific surface area between 150 - 300 m 2 / g.

[0068] Example 5

[0069] This example provides a para-aramid paper. The preparation method is the same as that of Example 1 except for the following Step 3:

[0070] Step 3: Pretreat the para-aramid fiber pulp in Step 2 with an ultrasonic processor (power: 900 W, frequency: 110 kHz, one-time ultrasonic time: 5 minutes, ultrasonic interval time: 10 minutes, total ultrasonic treatment time: 35 minutes), and then perform shear treatment with a high-pressure homogenizer (pressure: 200 MPa, power: 30 kW, mass fraction: 2%, temperature: 40 °C, rotation speed: 2000 r / min, circulate 3 times) to obtain nanofibers with a fiber diameter between 10 - 50 nm, a length between 500 - 2000 nm, and a specific surface area between 150 - 300 m 2 ² / g.

[0071] Example 6

[0072] This example provides a para-aramid paper. Except for the following Step 3, the preparation method is the same as that in Example 1:

[0073] Step 3: Pretreat the para-aramid fiber pulp in Step 2 with an ultrasonic processor (power: 500 W, frequency: 70 kHz, one-time ultrasonic time: 5 minutes, ultrasonic interval time: 10 minutes, total ultrasonic treatment time: 35 minutes), and then perform shear treatment with a high-pressure homogenizer (pressure: 80 MPa, power: 30 kW, mass fraction: 2%, temperature: 10 °C, rotation speed: 500 r / min, circulate 3 times) to obtain nanofibers with a fiber diameter between 10 - 50 nm, a length between 500 - 2000 nm, and a specific surface area between 150 - 300 m 2 ² / g.

[0074] Example 7

[0075] This example provides a para-aramid paper. Except for the following Step 3, the preparation method is the same as that in Example 1:

[0076] Step 3: Pretreat the para-aramid fiber pulp in Step 2 with an ultrasonic processor (power: 500 W, frequency: 70 kHz, one-time ultrasonic time: 5 minutes, ultrasonic interval time: 10 minutes, total ultrasonic treatment time: 35 minutes), and then perform shear treatment with a high-pressure homogenizer (pressure: 350 MPa, power: 30 kW, mass fraction: 2%, temperature: 60 °C, rotation speed: 3500 r / min, circulate 3 times) to obtain nanofibers with a fiber diameter between 10 - 50 nm, a length between 500 - 2000 nm, and a specific surface area between 150 - 300 m 2 ² / g.

[0077] Example 8

[0078] This example provides a para-aramid paper. Except for the following Step 5, the preparation method is the same as that in Example 1:

[0079] Step 5: The para-aramid fiber slurry obtained in Step 4 is formed by papermaking on an inclined wire paper machine, and then sprayed with nanofibers. Control the mass fraction of the nanofiber suspension to be 4%, control the spraying amount to be 0.5% of the mass of the original paper, and then obtain the para-aramid base paper after pressing and drying.

[0080] Example 9

[0081] This example provides a para-aramid paper. The preparation method is the same as that of Example 1 except that Step 5 is as follows:

[0082] Step 5: The para-aramid fiber slurry obtained in Step 4 is formed by papermaking on an inclined wire paper machine, and then sprayed with nanofibers. Control the mass fraction of the nanofiber suspension to be 4%, control the spraying amount to be 8% of the mass of the original paper, and then obtain the para-aramid base paper after pressing and drying.

[0083] Comparative Example 1

[0084] This comparative example provides a para-aramid paper. The preparation method is as follows:

[0085] Step 1: The para-aramid short fibers are pretreated with an aqueous solution of Remol A (concentration 28%, 40 °C), washed with clean water, and then surface-treated with plasma (the ionized gas is carbon tetrafluoride, the radio frequency is 40 kHz, the vacuum degree of the treatment chamber is controlled at 20 kPa, the temperature is 10 °C, and the treatment time is 3 s) to obtain hydrophilic para-aramid short fibers;

[0086] Step 2: The para-aramid short fibers treated in Step 1 are added with deionized water to prepare a short fiber suspension with a mass fraction of 2%, and beaten with a trough beater (the working current is 100 A, intermittent for 5 minutes after normal operation for 40 minutes, the total time is 90 minutes, and the beating degree is controlled between 30 - 48 °SR) to obtain para-aramid fiber pulp;

[0087] Step 3: The para-aramid short fibers and para-aramid fiber pulp obtained in Step 1 and Step 2 are mixed to prepare a para-aramid fiber slurry with a mixing mass ratio of 4:6;

[0088] Step 4: The para-aramid fiber slurry obtained in Step 3 is formed by papermaking on an inclined wire paper machine, and then obtained the para-aramid base paper after pressing and drying;

[0089] Step 5: The para-aramid base paper obtained in Step 4 is pre-pressed by a high-temperature hot press, the pre-pressing time is 8 s, the temperature is 170 °C, then high-temperature hot pressing is carried out, the high-temperature hot pressing temperature is 270 °C, the linear pressure is 350 kN / m, the vehicle speed is 2.0 m / min, and finally cooled (15 °C) to obtain the para-aramid paper.

[0090] Effect test:

[0091] The mechanical properties and electrical properties of the para-aramid papers provided in Examples 1-9 and Comparative Example 1 were tested, and the test methods are as follows:

[0092] 1. Thickness

[0093] Reference national standard: GB / T 451.3-2002 Determination of the thickness of paper and paperboard;

[0094] 2. Grammage

[0095] Reference national standard: GB / T 451.2-2002 Determination of the basis weight of paper and paperboard;

[0096] 3. Tensile strength

[0097] Reference national standard: GB / T12914-2018 Determination of the tensile strength of paper and paperboard;

[0098] 4. Tear strength

[0099] Reference national standard: GB / T455-2002 Determination of the tear strength of paper and paperboard;

[0100] 5. Dielectric strength

[0101] Reference national standard: GB / T 1408.1-2006 Test method for the electrical strength of insulating materials.

[0102] The results are as follows:

[0103]

[0104] It can be found from the above data that the products prepared by the method provided by the present invention have excellent mechanical properties and electrical properties; by comparing Examples 1-9, it can be found that by controlling the preparation and spraying parameters of nanofibers, the nanofibers prepared by the present invention can more effectively fill the voids of the paper, improve the paper density, and thus improve the product performance; by comparing Example 1 and Comparative Example 1, it can be found that by preparing specific nanofibers and spraying them, the mechanical properties and electrical properties of the product can be significantly improved, showing significant progress compared with the prior art.

[0105] The applicant declares that the present invention uses the above examples to illustrate the para-aramid paper and its preparation method of the present invention, but the present invention is not limited to the above examples, that is, it does not mean that the present invention must rely on the above examples to be implemented. Those skilled in the art should understand that any improvement of the present invention, the equivalent replacement of each raw material of the product of the present invention, the addition of auxiliary components, and the selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

[0106] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0107] In addition, it should be noted that, in the various specific technical features described in the above specific embodiments, they can be combined in any suitable manner without conflict. To avoid unnecessary repetition, the present invention will not separately describe various possible combination methods.

Claims

1. A preparation method of para-aramid paper, characterized in that The preparation method comprises the following steps: (1) Mix and process the para-aramid short-cut fibers with a surfactant solution, and then perform plasma surface treatment to obtain hydrophilic para-aramid short-cut fibers; (2) Pulp the para-aramid short-cut fibers to obtain para-aramid fiber pulp; (3) Ultrasonically treat the para-aramid fiber pulp to obtain a suspension, and then shear it to obtain nanofibers; (4) Mix the hydrophilic para-aramid short-cut fibers with the para-aramid fiber pulp to obtain an aramid fiber slurry, then form it by papermaking, spray the nanofibers, obtain a para-aramid base paper, and obtain the para-aramid paper after hot pressing; Steps (1) and steps (2)-(3) do not distinguish the sequence.

2. The preparation method according to claim 1, wherein The surfactant described in step (1) includes any one or a combination of at least two of Remol A, sodium dodecylbenzenesulfonate, or lauryl alcohol phosphate.

3. The preparation method according to claim 1 or 2, characterized in that, The mass fraction of the solute in the surfactant solution described in step (1) is 25-30%.

4. The preparation method according to any one of claims 1 to 3, characterized in that, The power of the ultrasonic treatment described in step (3) is 300-800 W, and the frequency is 40-100 kHz.

5. The preparation method according to any one of claims 1-4, characterized in that, The ultrasonic treatment described in step (3) is performed at least 3 times, with each treatment time being 4-6 min and the interval being 8-12 min.

6. The preparation method according to any one of claims 1-5, characterized in that, The pressure of the shear described in step (3) is 100-300 MPa, the temperature is 20-50 °C, the rotation speed is 1000-3000 r / min, the shear cycle is 2-5 times, each time being 2-3 min, and the mass fraction of the suspension is 1-3%.

7. The preparation method according to any one of claims 1-6, characterized in that, The mass ratio of the hydrophilic para-aramid short-cut fibers to the para-aramid fiber pulp described in step (4) is (3-6):(4-7).

8. The preparation method according to any one of claims 1-7, characterized in that, In the spraying of nanofibers described in step (4), the mass fraction of the nanofiber suspension is 1-6%.

9. The preparation method according to any one of claims 1-8, characterized in that, In the spraying of nanofibers described in step (4), the spraying amount is 1-5% of the mass of the para-aramid base paper; Preferably, pre-hot pressing is also performed before the hot pressing described in step (4); Preferably, the temperature of the pre-hot pressing is 150-200 °C and the time is 5-10 s.

10. A para-aramid paper prepared by the preparation method according to any one of claims 1-9.

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