An ultra-thin meta-aramid precipitated fiber, its preparation method and application

Abstract

The present invention provides an ultra-thin meta-aramid precipitated fiber, a preparation method thereof and an application thereof. The preparation method comprises the following steps: (1) Preparation of a meta-aramid resin solution: adding isophthaloyl chloride and m-phenylenediamine into a solvent for polymerization reaction, and obtaining a meta-aramid resin solution after neutralization, filtration and dilution; (2) Preparation of the meta-aramid precipitated fiber: coating the prepared meta-aramid resin solution on a substrate to obtain an ultra-thin resin coating, allowing the ultra-thin resin coating to enter a coagulation bath with the substrate for coagulation and precipitation to obtain an ultra-thin fiber layer, subjecting the ultra-thin fiber layer to high-pressure hydraulic impact and fragmentation after leaving the coagulation bath, and then washing to obtain the ultra-thin meta-aramid precipitated fiber. By using the preparation method provided by the present invention, an ultra-thin meta-aramid precipitated fiber can be prepared, the thickness thereof is as low as 0.3-2 μm, and the thickness and morphology of the precipitated fiber are regular and uniform, and the film structure is rich, and the thickness dimension thereof can be precisely controlled.

Description

Technical Field

[0001] The present invention belongs to the technical field of synthetic fibers, specifically to the technical field of aramid fiber preparation, and relates to an ultra-thin meta-aramid precipitated fiber and its preparation method and application, and particularly to an ultra-thin uniform film-like meta-aramid precipitated fiber and its preparation method and application. Background Art

[0002] High-performance aramid paper has excellent mechanical strength, electrical insulation, high temperature resistance, flame retardancy, chemical corrosion resistance and other properties, and has become an important basic material in high-end fields such as rail transit, aerospace, national defense and military industry, and new energy. As one of the key raw materials of aramid paper, meta-aramid precipitated fiber has excellent flexibility, chemical stability, flame retardancy, and outstanding high temperature resistance and insulation performance. It plays a role in filling and bonding in the aramid paper structure, and usually accounts for more than 50% in aramid paper. Its structure and properties are crucial for paper sheet forming and product characteristics, and have a great impact on the mechanical strength, especially the electrical insulation performance of aramid paper.

[0003] At present, the research on meta-aramid precipitated fiber at home and abroad mainly focuses on the improvement of precipitation equipment and precipitation process, but there is a lack of research on the control of the thickness, morphology, and uniformity of precipitated fiber and its impact on the properties of the formed paper. The meta-aramid precipitated fiber prepared by the traditional process route is obtained by injecting a meta-aramid resin solution in the form of a thin stream into a coagulation bath or a precipitant, and precipitating under the action of high-speed shear to obtain fibers with a film-like or fibril-like appearance on the outside. This process is completed in a precipitator.

[0004] CN1952226A discloses a meta-aramid precipitated fiber and its preparation method. At a stable lower temperature, a meta-aramid amide stock solution and a certain proportion of precipitation solvent are transported to a precipitation device for mixing. The precipitation device operates at a specified speed. The stock solution solidifies to form ultra-short fibers while being sheared, and the precipitation solvent is washed out and recycled using ordinary pulp washing equipment. It changes the existing manufacturing method of first spinning and then cutting into ultra-short fibers. No other polymerization monomers need to be added during the stock solution preparation process. Using a key precipitation device, it directly forms under the action of high-speed shear, without the need for beating and refining processes and equipment. The process is simple and effective, the solvent corrosion is not high, and the recycling is simple and convenient.

[0005] CN106245141A discloses a production method of high-purity meta-aramid precipitated fiber, including steps such as resin heating, precipitation liquid cooling, resin precipitation, and water washing and separation; by the resin heating step, the apparent viscosity of the system is reduced, the fluidity is increased, the production efficiency is improved, and the production cost is reduced; the calcium ion content in the obtained meta-aramid precipitated fiber is below 20 ppm.

[0006] CN115110171A discloses a preparation method of aramid precipitated fiber, which includes the following steps: (1) Preparation of a neutral aramid polymer solution; (2) Preparation of a precipitation stock solution: adding a solvent and a modifier to the neutral aramid polymer solution, and fully mixing and dispersing to obtain a spinning stock solution; the modifier is at least one of polyethylene glycol and polyvinylpyrrolidone; (3) Preparation of aramid precipitated fiber: conveying the precipitation stock solution to a precipitation device, and after non-solvent cross-intersection diffusion pre-solidification treatment, forming sheet-like precipitated fiber under the action of primary high-speed shearing. The precipitation fiber preparation method provided by the invention is simple to operate, convenient for industrial production, can prepare precipitated fiber with a unique fibrillated filamentous morphology, and has a larger specific surface area.

[0007] CN115787123A discloses a preparation method of meta-aramid precipitated fiber with a concentrated length distribution and high water retention value, which includes the following steps: (1) Preparing a meta-aramid resin solution, wherein the polymer content in the aramid resin solution is 6% - 14%, the logarithmic viscosity ratio is 1.5 - 1.8 dL / g, and the temperature is 40°C - 70°C; (2) Injecting the meta-aramid resin solution and a precipitant into a precipitator, precipitating and cooling to form, obtaining a crude product of precipitated fiber, and the crude product of precipitated fiber is subjected to beating, defibrating, and sieving treatments to obtain a precipitated fiber slurry; (3) Washing the precipitated fiber slurry to obtain meta-aramid precipitated fiber with a concentrated length distribution and high water retention value. The prepared precipitated fiber has a high water retention value, good dispersibility, a uniform membrane structure, and a concentrated length distribution.

[0008] The above-mentioned prior arts are all prepared based on traditional process routes, that is, precipitated fiber is prepared through the high-speed shearing action of a precipitator. This route cannot produce ultra-thin precipitated fiber, and the fiber morphology is irregular, with uneven and uncontrollable thickness.

[0009] In addition, there are also some prior arts that innovate in the process route.

[0010] For example, CN115627556A discloses a preparation method of a high electrical conductivity meta-aramid precipitated fiber resin. Dissolve m-phenylenediamine in DMAc, and sequentially add isophthaloyl chloride, a modified conductive graphite / DMAc suspension, and isophthaloyl chloride for reaction, then add a LiOH powder / DMAc suspension, and adjust the pH to neutral or weakly acidic to obtain it. This method also discloses a preparation method of high electrical conductivity meta-aramid precipitated fiber. The precipitated fiber resin is formed by spray coagulation, and the fiber appearance is sheet-like and fiber fibrillation-like.

[0011] CN114717678A discloses a method for preparing spiral ribbon-shaped aramid fibrids for papermaking, belonging to the technical field of synthetic fiber manufacturing, and comprising the following steps: preparing aramid polymer; emulsifying the aramid polymer; preparing a precipitation solution; mixing the emulsified aramid polymer and the precipitation solution in a ball mill at a high speed according to a proportion; and washing the aramid fibrids to form aramid fibrids with rich hairiness and a wide spiral ribbon shape.

[0012] Although the above-mentioned prior art has made innovations in the process route, the prepared precipitated fibers still have problems such as uneven fiber thickness, different shapes, and few membrane structures. It is still impossible to produce ultra-thin membrane-like meta-aramid precipitated fibers with uniform thickness and regular shape.

[0013] In view of the fact that the meta-aramid fibrils prepared by the prior art have less membrane-like structures, large differences in fiber morphology, and an average fiber thickness of 3 to 8 μm, and their thickness and morphology are irregular and non-uniform, it is impossible to prepare ultra-thin fibrils, resulting in the fiber arrangement in the forming process being not regular and orderly, the fiber bonding degree of the finished paper being poor, and the uniformity of the paper being poor, the filling and bonding effect of the microscopic pores being insufficient, and the ability to hinder the passage of current when subjected to the electric field being weak, resulting in unsatisfactory product performance that is difficult to meet the application requirements of high-end fields. Therefore, how to provide an ultra-thin uniform membrane-like meta-aramid fibrils has become a technical problem that needs to be urgently solved in the preparation of high-performance aramid paper. Summary of the invention

[0014] In view of the deficiencies in the prior art, the purpose of the present invention is to provide an ultra-thin meta-aramid fibrils and a preparation method and application thereof, and in particular to provide an ultra-thin uniform film-like meta-aramid fibrils and a preparation method and application thereof. The ultra-thin fibrils prepared by the preparation method provided by the present invention have controllable and uniform fiber thickness, regular morphology, and are rich in a large number of film-like structures. When the fibrils of the present invention are used to paper meta-aramid paper, the fiber arrangement during the forming process is regular and orderly, the fiber bonding degree and uniformity of the finished paper are good, the microscopic pores are fully filled and bonded, and the ability to hinder the passage of current when subjected to an electric field is strong. The obtained product has excellent comprehensive performance, and indicators such as electrical strength exceed imported products, which can meet the application requirements of high-end fields and realize domestic substitution.

[0015] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0016] In a first aspect, the present invention provides a method for preparing ultra-thin meta-aramid fibrids, the preparation method comprising the following steps:

[0017] (1) Preparation of meta-aramid resin solution: adding isophthaloyl chloride and meta-phenylenediamine into a solvent for polymerization reaction, and then neutralizing, filtering and diluting to obtain a meta-aramid resin solution;

[0018] (2) Preparation of meta-aramid precipitated fibers: The prepared meta-aramid resin solution is coated on a flat substrate to obtain an ultra-thin resin coating. The ultra-thin resin coating enters the coagulation bath with the substrate and is coagulated and precipitated to obtain an ultra-thin fiber layer. After the ultra-thin fiber layer exits the coagulation bath, it is broken by high-pressure hydraulic impact, and after collection and thorough washing, the ultra-thin meta-aramid precipitated fibers are obtained.

[0019] In the present invention, the meta-aramid resin solution prepared by polymerization is precisely coated on a flat substrate. The obtained ultra-thin resin coating enters the coagulation bath with the substrate and is coagulated and precipitated by the phase inversion method to obtain an ultra-thin fiber layer. Then, the precipitated ultra-thin fiber layer is uniformly broken by high-pressure hydraulic impact. After collection and thorough washing, the ultra-thin meta-aramid precipitated fibers are obtained. The precipitated fibers have a uniform film-like structure. The aramid paper made by using the precipitated fibers of the present invention has more excellent comprehensive properties.

[0020] Preferably, the molar ratio of isophthaloyl chloride to m-phenylenediamine in step (1) is (0.95 - 1.05):1, such as 0.95:1, 0.96:1, 0.97:1, 0.98:1, 0.99:1, 1:1, 1.01:1, 1.02:1, 1.03:1, 1.04:1, 1.05:1, etc.

[0021] Preferably, the solvent in step (1) includes N,N-dimethylformamide (DMF) and / or N,N-dimethylacetamide (DMAC).

[0022] Preferably, the solvent used for dilution in step (1) includes N,N-dimethylformamide and / or N,N-dimethylacetamide.

[0023] Preferably, the solvent used for dilution in step (1) is the same solvent as that used in the polymerization reaction.

[0024] Preferably, the concentration of the meta-aramid resin solution in step (1) is 5 - 15 wt.%, such as 5 wt.%, 6 wt.%, 7 wt.%, 8 wt.%, 9 wt.%, 10 wt.%, 11 wt.%, 12 wt.%, 13 wt.%, 14 wt.%, 15 wt.%, etc.

[0025] Preferably, the coating in step (2) is precision coating, including any one of microgravure coating, slot die extrusion coating, and multi-roll transfer coating.

[0026] Preferably, the substrate in step (2) is a metal coil or a plastic film coil.

[0027] Preferably, the metal coil includes copper foil or aluminum foil.

[0028] Preferably, the plastic film roll includes any one of polyethylene film roll, polypropylene film roll, polyester film roll, polyimide film roll, and polytetrafluoroethylene film roll.

[0029] Preferably, the thickness of the substrate is 0.05 - 0.35 mm, such as 0.05 mm, 0.08 mm, 0.1 mm, 0.13 mm, 0.15 mm, 0.18 mm, 0.2 mm, 0.23 mm, 0.25 mm, 0.28 mm, 0.3 mm, 0.32 mm, 0.34 mm, 0.35 mm, etc., and the substrate can be recycled.

[0030] Preferably, the thickness of the ultra-thin resin coating is 0.5 - 3 μm, such as 0.5 μm, 0.8 μm, 1 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2 μm, 2.2 μm, 2.4 μm, 2.6 μm, 2.8 μm, 3 μm, etc.

[0031] Preferably, the coagulation bath includes an aqueous solution of N,N-dimethylformamide (DMF) and / or N,N-dimethylacetamide (DMAC) with a concentration of 20 - 50 wt.%, such as 20 wt.%, 25 wt.%, 30 wt.%, 35 wt.%, 40 wt.%, 45 wt.%, 50 wt.%, etc.

[0032] Preferably, the high-pressure hydraulic impact crushing includes two-stage high-pressure spraying. Among them, the pressure of the first-stage high-pressure spraying is 300 - 3000 kPa (such as 300 kPa, 500 kPa, 800 kPa, 1000 kPa, 1200 kPa, 1400 kPa, 1600 kPa, 1800 kPa, 2000 kPa, 2200 kPa, 2400 kPa, 2600 kPa, 2800 kPa, 3000 kPa, etc.), and the pressure of the second-stage high-pressure spraying is 500 - 4000 kPa (such as 500 kPa, 800 kPa, 1000 kPa, 1200 kPa, 1400 kPa, 1600 kPa, 1800 kPa, 2000 kPa, 2200 kPa, 2400 kPa, 2600 kPa, 2800 kPa, 3000 kPa, 3200 kPa, 3400 kPa, 3600 kPa, 3800 kPa, 4000 kPa, etc.), and the two-stage sprayings are staggered.

[0033] Preferably, the high-pressure spraying includes needle-shaped spraying.

[0034] That is, the high-pressure hydraulic impact crushing described in the present invention includes two-stage high-pressure needle-shaped spraying, and the needles of the two-stage sprayings are staggered.

[0035] Preferably, the thickness of the ultra-thin meta-aramid precipitated fiber is 0.3 - 2 μm, such as 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2 μm, etc.; the dryness is 5 - 20 wt.%, such as 5 wt.%, 6 wt.%, 7 wt.%, 8 wt.%, 9 wt.%, 10 wt.%, 11 wt.%, 12 wt.%, 13 wt.%, 14 wt.%, 15 wt.%, 16 wt.%, 17 wt.%, 18 wt.%, 19 wt.%, 20 wt.%, etc.; the initial beating degree is 40 - 60 °SR, such as 40 °SR, 42 °SR, 44 °SR, 46 °SR, 48 °SR, 50 °SR, 52 °SR, 54 °SR, 56 °SR, 58 °SR, 60 °SR, etc.; and the beating degree after defibrating 120,000 revolutions by a standard defibrator is 65 - 90 °SR, such as 65 °SR, 68 °SR, 70 °SR, 72 °SR, 74 °SR, 76 °SR, 78 °SR, 80 °SR, 82 °SR, 84 °SR, 86 °SR, 88 °SR, 90 °SR, etc.

[0036] As a preferred technical solution of the present invention, the preparation method includes the following steps:

[0037] (1) Preparation of meta-aramid resin solution: Add isophthaloyl chloride and m-phenylenediamine into a solvent for polymerization reaction, and obtain a meta-aramid resin solution with a concentration of 5 - 15 wt.% after neutralization, filtration, and dilution;

[0038] (2) Preparation of meta-aramid precipitated fiber: Coating the prepared meta-aramid resin solution on a substrate by microgravure coating, slot die extrusion coating or multi-roll transfer coating to obtain an ultra-thin resin coating with a thickness of 0.5 - 3 μm. The ultra-thin resin coating enters an aqueous solution of N,N-dimethylformamide and / or N,N-dimethylacetamide with a concentration of 20 - 50 wt.% along with the substrate to solidify and precipitate, obtaining an ultra-thin fiber layer. After the ultra-thin fiber layer exits the coagulation bath, it is subjected to two-stage high-pressure spraying, and then washed to obtain the ultra-thin meta-aramid precipitated fiber;

[0039] Among them, the pressure of the first-stage high-pressure spraying is 300 - 3000 kPa, the pressure of the second-stage high-pressure spraying is 500 - 4000 kPa, and the two-stage high-pressure sprayings are staggered.

[0040] In the second aspect, the present invention provides an ultra-thin meta-aramid precipitated fiber, which is prepared by the preparation method as described in the first aspect.

[0041] Thirdly, the present invention provides an application of the ultra-thin meta-aramid precipitated fiber as described in the second aspect in aramid paper.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] (1) The ultra-thin meta-aramid precipitated fiber can be prepared by using the preparation method provided by the present invention, with a thickness as low as 0.3 - 2 μm, and the thickness and morphology of the precipitated fiber are regular and uniform, with rich film-like structures, and its thickness size can be precisely controlled.

[0044] (2) The present invention prepares the meta-aramid precipitated fiber by the phase inversion method, without using traditional equipment such as precipitators. The equipment investment is small, the operation is convenient, the production efficiency is high, the auxiliary substrate can be reused, continuous large-scale production can be achieved, and it has a great cost advantage.

[0045] (3) Using the precipitated fiber prepared by the present invention to prepare aramid paper can effectively improve the regularity of fiber arrangement during the forming process, the fiber bonding degree of the formed paper, and the paper evenness. The microscopic pores are fully filled and bonded, the paper sheet has high density, and the properties such as the tensile strength, electrical strength, and air permeability of the prepared aramid paper are significantly improved, exceeding the level of imported products. Among them, indicators such as electrical strength exceed those of imported products by more than 20%.

[0046] (4) The preparation idea of the ultra-thin uniform film-like meta-aramid precipitated fiber provided by the present invention can also be extended to products such as para-aramid (PPTA), arylsulfone aramid (PSA), and polyaryloxadiazole (POD). BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 It is a process flow chart of the preparation of the ultra-thin meta-aramid precipitated fiber provided by the embodiment of the present invention.

[0048] Figure 2 It is a schematic structural diagram of the equipment used to prepare the ultra-thin meta-aramid precipitated fiber in the embodiment of the present invention;

[0049] Among them, 1 - substrate unwinding part, 2 - coating device, 3 - coagulation bath pool, 4 - coagulation bath, 5 - coating support back roll, 6 - primary high-pressure spray, 7 - secondary high-pressure spray, 8 - fiber collection pool, 9 - substrate winding part.

[0050] Figure 3 It is an SEM image of the ultra-thin meta-aramid precipitated fiber prepared in Example 1.

[0051] Figure 4 It is an SEM image of the ultra-thin meta-aramid precipitated fiber prepared in Example 2.

[0052] Figure 5SEM image of the meta-aramid precipitated fiber prepared in Comparative Example 1.

[0053] Figure 6 SEM image of the surface of the aramid paper before hot pressing, which is made of the ultra-thin meta-aramid precipitated fiber prepared in Example 1.

[0054] Figure 7 SEM image of the cross-section of the aramid paper before hot pressing, which is made of the ultra-thin meta-aramid precipitated fiber prepared in Example 1.

[0055] Figure 8 SEM image of the surface of the aramid paper before hot pressing, which is made of the meta-aramid precipitated fiber prepared in Comparative Example 1.

[0056] Figure 9 SEM image of the cross-section of the aramid paper before hot pressing, which is made of the meta-aramid precipitated fiber prepared in Comparative Example 1.

[0057] Figure 10 SEM image of the surface of the aramid paper after hot pressing, which is made of the ultra-thin meta-aramid precipitated fiber prepared in Example 1.

[0058] Figure 11 SEM image of the cross-section of the aramid paper after hot pressing, which is made of the ultra-thin meta-aramid precipitated fiber prepared in Example 1.

[0059] Figure 12 SEM image of the surface of the aramid paper after hot pressing, which is made of the meta-aramid precipitated fiber prepared in Comparative Example 1.

[0060] Figure 13 SEM image of the cross-section of the aramid paper after hot pressing, which is made of the meta-aramid precipitated fiber prepared in Comparative Example 1. Detailed implementation manners

[0061] The technical solution of the present invention will be further described below through specific implementation manners. Those skilled in the art should understand that the described embodiments are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention.

[0062] Example 1

[0063] In this example, an ultra-thin meta-aramid precipitated fiber is provided, and its preparation method includes the following steps:

[0064] (1) Preparation of the meta-aramid resin solution: Isophthaloyl chloride and m-phenylenediamine (the molar ratio of the two is 0.95:1) are added to N,N-dimethylformamide (DMF) for polymerization reaction. After neutralization, filtration, and dilution (the diluting solvent is DMF), an 8 wt.% meta-aramid resin solution with an inherent viscosity of 1.6 dL / g is obtained.

[0065] (2) Preparation of meta-aramid precipitated fibers: The prepared meta-aramid resin solution was coated on a flat copper foil by micro-gravure coating. The thickness of the copper foil was 0.05 mm, and the thickness of the resin coating was 0.5 μm. The resin coating entered a 30 wt.% aqueous solution of N,N-dimethylformamide (DMF) with the copper foil and solidified and precipitated to obtain a fiber layer. After the fiber layer exited the coagulation bath with the copper foil substrate, it was uniformly broken by two-stage high-pressure spray impact. The pressure of the first needle-shaped spray was 1000 kPa, and the pressure of the second needle-shaped spray was 1500 kPa. The two-stage sprays were staggered. After collecting the fibers in the fiber collection tank and then thoroughly washing, ultra-thin and uniform film-like meta-aramid precipitated fibers were obtained. Their thickness was 0.3 μm, dryness was 8 wt.%, the initial beating degree was 58°SR, and the beating degree was 86°SR after being refined by a standard refiner for 120,000 revolutions.

[0066] Example 2

[0067] In this example, an ultra-thin meta-aramid precipitated fiber is provided, and its preparation method includes the following steps:

[0068] (1) Preparation of meta-aramid resin solution: Isophthaloyl chloride and m-phenylenediamine (the molar ratio of the two is 1.05:1) were added to N,N-dimethylacetamide (DMAC) for polymerization reaction. After neutralization, filtration, and dilution (the diluting solvent was DMAC), a 15 wt.% meta-aramid resin solution was obtained, and its inherent viscosity was 1.8 dL / g.

[0069] (2) Preparation of meta-aramid precipitated fibers: The prepared meta-aramid resin solution was coated on a flat polyester film by slot die extrusion coating. The thickness of the polyester film was 0.35 mm, and the thickness of the resin coating was 3 μm. The resin coating entered a 20 wt.% aqueous solution of N,N-dimethylacetamide (DMAC) with the polyester film and solidified and precipitated to obtain a fiber layer. After the fiber layer exited the coagulation bath with the polyester film substrate, it was uniformly broken by two-stage high-pressure spray impact. The pressure of the first needle-shaped spray was 3000 kPa, and the pressure of the second needle-shaped spray was 3500 kPa. The two-stage sprays were staggered. After collecting the fibers in the fiber collection tank and then thoroughly washing, ultra-thin and uniform film-like meta-aramid precipitated fibers were obtained. Their thickness was 2 μm, dryness was 15 wt.%, the initial beating degree was 45°SR, and the beating degree was 72°SR after being refined by a standard refiner for 120,000 revolutions.

[0070] Example 3

[0071] In this example, an ultra-thin meta-aramid precipitated fiber is provided, and its preparation method includes the following steps:

[0072] (1) Preparation of meta-aramid resin solution: Isophthaloyl chloride and m-phenylenediamine (with a molar ratio of 1:1) were added to N,N-dimethylacetamide (DMAC) for polymerization reaction. After neutralization, filtration, and dilution (the diluting solvent was DMAC), a 10 wt.% meta-aramid resin solution was obtained, with an inherent viscosity of 1.7 dL / g;

[0073] (2) Preparation of meta-aramid precipitated fibers: The prepared meta-aramid resin solution was coated on a flat polypropylene film by multi-roll transfer coating. The thickness of the polypropylene film was 0.15 mm, and the thickness of the resin coating was 2 μm. The resin coating entered a 40 wt.% aqueous solution of N,N-dimethylacetamide (DMAC) with the polypropylene film and solidified and precipitated to obtain a fiber layer. After the fiber layer left the coagulation bath with the polypropylene film substrate, it was uniformly broken by two-stage high-pressure spray impact. The pressure of the first-stage needle-shaped spray was 2000 kPa, and the pressure of the second-stage needle-shaped spray was 3000 kPa. The two-stage sprays were staggered. After collecting the fibers in the fiber collection tank and washing them thoroughly, ultra-thin and uniform film-like meta-aramid precipitated fibers were obtained. Their thickness was 1.4 μm, dryness was 12 wt.%, initial beating degree was 51°SR, and the beating degree was 79°SR after being refined by a standard refiner for 120,000 revolutions.

[0074] Example 4

[0075] In this example, an ultra-thin meta-aramid precipitated fiber is provided, and its preparation method includes the following steps:

[0076] (1) Preparation of meta-aramid resin solution: Isophthaloyl chloride and m-phenylenediamine (with a molar ratio of 1:1) were added to N,N-dimethylformamide (DMF) for polymerization reaction. After neutralization, filtration, and dilution (the diluting solvent was DMF), a 5 wt.% meta-aramid resin solution was obtained, with an inherent viscosity of 1.7 dL / g;

[0077] (2) Preparation of meta-aramid precipitated fibers: The prepared meta-aramid resin solution was coated on a flat copper foil by microgravure coating. The thickness of the copper foil was 0.05 mm, and the thickness of the resin coating was 0.8 μm. The resin coating entered a 50 wt.% aqueous solution of N,N-dimethylformamide (DMF) with the copper foil and solidified and precipitated to obtain a fiber layer. After the fiber layer left the coagulation bath with the copper foil substrate, it was uniformly broken by two-stage high-pressure spray impact. The pressure of the first-stage needle-shaped spray was 300 kPa, and the pressure of the second-stage needle-shaped spray was 500 kPa. The two-stage sprays were staggered. After collecting the fibers in the fiber collection tank and washing them thoroughly, ultra-thin and uniform film-like meta-aramid precipitated fibers were obtained. Their thickness was 0.4 μm, dryness was 10 wt.%, initial beating degree was 55°SR, and the beating degree was 84°SR after being refined by a standard refiner for 120,000 revolutions.

[0078] Comparative Example 1

[0079] In this comparative example, a meta-aramid precipitated fiber is provided, and its preparation method includes the following steps:

[0080] (1) Preparation of meta-aramid resin solution: Isophthaloyl chloride and m-phenylenediamine (the molar ratio of the two is 0.95:1) are added to N,N-dimethylformamide (DMF) for polymerization reaction. After neutralization, filtration, and dilution (the diluting solvent is DMF), an 8 wt.% meta-aramid resin solution with an inherent viscosity of 1.6 dL / g is obtained;

[0081] (2) Preparation of meta-aramid precipitated fiber: The prepared meta-aramid resin solution and a 30 wt.% aqueous solution of N,N-dimethylformamide (DMF) (i.e., the precipitant) are injected into a high-speed rotating disk-type precipitator at a volume ratio of 1:16. By continuously collecting the flocculated fibers and thoroughly washing them, meta-aramid precipitated fibers are obtained. Their average thickness is 6 μm, the dryness is 20 wt.%, the initial beating degree is 35°SR, and the beating degree is 58°SR after being refined by a standard refiner for 120,000 revolutions.

[0082] Comparative Example 2

[0083] The difference between this comparative example and Example 1 is only that in step (2), after the fiber layer exits the coagulation bath with the copper foil substrate, it only undergoes primary high-pressure spray impact fragmentation, and the needle-shaped spray pressure is 1000 kPa.

[0084] The process flow chart of the preparation process of the ultra-thin meta-aramid precipitated fiber provided by the embodiment of the present invention is as Figure 1 shown, and among them, the schematic diagram of the equipment structure used is as Figure 2 shown.

[0085] The SEM image of the ultra-thin meta-aramid precipitated fiber prepared in Example 1 of the present invention is as Figure 3 shown, and the SEM image of the ultra-thin meta-aramid precipitated fiber prepared in Example 2 is as Figure 4 shown. It can be seen that the meta-aramid precipitated fiber provided by the embodiment of the present invention has a uniform film-like structure.

[0086] The SEM image of the meta-aramid precipitated fiber prepared in Comparative Example 1 is as Figure 5 shown. It can be seen that the morphology of the meta-aramid precipitated fiber provided in Comparative Example 1 is irregular and the thickness is non-uniform. This is because Comparative Example 1 adopts a traditional preparation route, that is, precipitated fibers are prepared by the high-speed shearing action of a precipitator, and ultra-thin precipitated fibers cannot be prepared.

[0087] Preparation of meta-aramid paper

[0088] The precipitated fibers prepared in the examples and comparative examples were respectively mixed with chopped fibers (2D, 6 mm) on a paper machine at a mass ratio of 55:45 to make meta-aramid paper with a basis weight of 40 g / m 2 . After hot pressing, samples were taken for performance testing. The testing methods are as follows:

[0089] (1) Thickness: Tested in accordance with GB / T 451.3-2002 "Determination of the Thickness of Paper and Board".

[0090] (2) Basis weight: Tested in accordance with GB / T 451.2-2023 "Paper and Board - Part 2: Determination of Basis Weight".

[0091] (3) Tensile strength and elongation at break: Tested in accordance with GB / T 20629.2-2013 "Non-Cellulosic Papers for Electrical Use - Part 2: Test Methods".

[0092] (4) Electrical strength: Tested in accordance with GB / T 1408.1-2016 "Test Methods for Electrical Strength of Insulating Materials - Part 1: Tests at Power Frequency".

[0093] (5) Air permeability: Tested by the Schopper method in accordance with GB / T 458-2008 "Determination of the Air Permeability of Paper and Board".

[0094] The performance test results are shown in Table 1.

[0095] Table 1

[0096]

[0097] As can be seen from the data in the above table, the aramid paper made from the precipitated fibers prepared by the present invention has excellent tensile strength (MD: 4.04 - 4.15 kN / m; CD: 2.05 - 2.25 kN / m), elongation at break (MD: 6.9% - 7.6%; CD: 6.3% - 6.8%), electrical strength (21.9 - 22.7 kV / mm) and air permeability barrier properties. In particular, the properties such as electrical strength exceed those of the imported sample by more than 20%.

[0098] The surface SEM images and cross-section SEM images of the aramid paper made from the ultra-thin meta-aramid precipitated fibers prepared in Example 1 of the present invention before hot pressing are shown in Figure 6 and Figure 7 respectively; the surface SEM images and cross-section SEM images of the aramid paper made from the meta-aramid precipitated fibers prepared in Comparative Example 1 before hot pressing are shown in Figure 8 and Figure 9 respectively.

[0099] The surface SEM images and cross-section SEM images of the aramid paper made from the ultra-thin meta-aramid precipitated fibers prepared in Example 1 of the present invention after hot pressing are shown inFigure 10 and Figure 11 shown; the surface SEM image and cross-section SEM image of the aramid paper after hot pressing made from the meta-aramid precipitated fibers prepared in Comparative Example 1 are respectively as shown in Figure 12 and Figure 13 shown.

[0100] From Figures 6 - 13 it can be seen that, compared with Comparative Example 1, when using the precipitated fibers prepared in Example 1 to make the meta-aramid paper, the fibers are arranged regularly and orderly during the forming process, the fiber binding degree and paper uniformity of the formed paper are good, and the paper page is denser.

[0101] In summary, the ultra-thin precipitated fibers prepared by the preparation method provided by the present invention have controllable and uniform fiber thickness, regular morphology, and are rich in a large number of film-like structures. When using the precipitated fibers of the present invention to make the meta-aramid paper, the fibers are arranged regularly and orderly during the forming process, the fiber binding degree and paper uniformity of the formed paper are good, the ability to hinder the passage of current when subjected to an electric field is strong, the comprehensive performance of the obtained product is excellent, and indicators such as electrical strength exceed imported products, which can meet the application requirements of high-end fields such as aerospace, national defense, rail transit, and new energy, and realize domestic substitution.

[0102] The applicant declares that the present invention uses the above embodiments to illustrate the ultra-thin meta-aramid precipitated fibers and their preparation methods and applications of the present invention, but the present invention is not limited to the above embodiments, that is, it does not mean that the present invention must rely on the above embodiments to be implemented. Those skilled in the art should understand that any improvement to the present invention, the equivalent substitution of the raw materials selected for 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.

Claims

1. A method for preparing ultra-thin meta-aramid fiber, characterized in that: The preparation method comprises the following steps: (1) Preparation of meta-aramid resin solution: adding isophthaloyl chloride and meta-phenylenediamine into a solvent for polymerization reaction, and then neutralizing, filtering and diluting to obtain a meta-aramid resin solution; (2) Preparation of meta-aramid fibrids: the prepared meta-aramid resin solution is coated on a substrate to obtain an ultra-thin resin coating, the ultra-thin resin coating enters a coagulation bath along with the substrate to coagulate and precipitate to obtain an ultra-thin fiber layer, the ultra-thin fiber layer is crushed by high-pressure hydraulic impact after exiting the coagulation bath, and then washed to obtain the ultra-thin meta-aramid fibrids; The high-pressure hydraulic impact crushing includes two-stage high-pressure spraying, wherein the pressure of the first-stage high-pressure spraying is 300-3000 kPa, the pressure of the second-stage high-pressure spraying is 500-4000 kPa, and the two-stage spraying is staggered.

2. The preparation method according to claim 1, characterized in that: The molar ratio of isophthaloyl chloride to m-phenylenediamine in step (1) is (0.95-1.05):

1.

3. The preparation method according to claim 1, characterized in that: The solvent in step (1) includes N,N-dimethylformamide and / or N,N-dimethylacetamide.

4. The preparation method according to claim 1, characterized in that: The solvent used for the dilution in step (1) includes N,N-dimethylformamide and / or N,N-dimethylacetamide.

5. The preparation method according to claim 1, characterized in that: The concentration of the meta-aramid resin solution in step (1) is 5-15 wt.%.

6. The preparation method according to claim 1, characterized in that: The coating in step (2) includes any one of micro-concave coating, slit extrusion coating, and multi-roller transfer coating.

7. The preparation method according to claim 1, characterized in that: The substrate in step (2) is a metal coil or a plastic film coil.

8. The preparation method according to claim 7, characterized in that: The metal coil comprises copper foil or aluminum foil.

9. The preparation method according to claim 7, characterized in that: The plastic film roll includes any one of a polyethylene film roll, a polypropylene film roll, a polyester film roll, a polyimide film roll, and a polytetrafluoroethylene film roll.

10. The preparation method according to claim 1, characterized in that: The thickness of the substrate is 0.05-0.35 mm.

11. The preparation method according to claim 1, characterized in that: The thickness of the ultra-thin resin coating is 0.5-3 μm.

12. The preparation method according to claim 1, characterized in that: The coagulation bath comprises an aqueous solution of N,N-dimethylformamide and / or N,N-dimethylacetamide with a concentration of 20-50 wt.%.

13. The preparation method according to claim 1, characterized in that: The high pressure spraying includes a needle spraying.

14. The preparation method according to claim 1, characterized in that: The ultra-thin meta-aramid fiber has a thickness of 0.3-2 μm, a dryness of 5-20 wt.%, an initial beating degree of 40-60°SR, and a beating degree of 65-90°SR after being deflated by a standard deflagrator for 120,000 revolutions.

15. The preparation method according to claim 1, characterized in that: The preparation method comprises the following steps: (1) Preparation of meta-aramid resin solution: adding isophthaloyl chloride and meta-phenylenediamine into a solvent for polymerization reaction, and obtaining a meta-aramid resin solution with a concentration of 5-15 wt.% after neutralization, filtration and dilution; (2) Preparation of meta-aramid fibrids: The prepared meta-aramid resin solution is coated on a substrate by micro-concave coating, slit extrusion coating or multi-roll transfer coating to obtain an ultra-thin resin coating with a thickness of 0.5-3 μm, and the ultra-thin resin coating enters an aqueous solution of N,N-dimethylformamide and / or N,N-dimethylacetamide with a concentration of 20-50wt.% along with the substrate to coagulate and precipitate to obtain an ultra-thin fiber layer, and the ultra-thin fiber layer is subjected to two-stage high-pressure spraying after exiting the coagulation bath, and then washed to obtain the ultra-thin meta-aramid fibrids; Among them, the pressure of the first-level high-pressure spray is 300~3000 kPa, the pressure of the second-level high-pressure spray is 500~4000 kPa, and the two-level high-pressure spray is staggered.

16. An ultra-thin meta-aramid fiber, characterized in that: The ultra-thin meta-aramid fibrid is prepared by the preparation method according to any one of claims 1 to 15.

17. Use of the ultra-thin meta-aramid fibrid according to claim 16 in aramid paper.

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