A method for preparing a polyamide ultra-fine fiber two-dimensional membrane by a reactive melt-blowing technique, the two-dimensional membrane and application

Abstract

This invention proposes a method for preparing polyamide ultrafine fiber two-dimensional membranes using reactive meltblown technology, along with the two-dimensional membranes and their applications. The invention includes the following steps: a mixture of caprolactam monomer and catalyst is fed into a reactive screw extruder. The feed conveying section is at 90-200°C, the reaction section at 200-280°C, and the compression extrusion section at 200-280°C. The process involves extrusion, spinning, stretching, curing, fiber formation, and random web formation to obtain the two-dimensional membrane. This invention continuously completes the mixing, polymerization, and melt extrusion of the raw material formulation, as well as the spinning, stretching, and web formation of the fibers. Polyamide ultrafine fiber two-dimensional membranes are obtained from monomers in a one-step process, effectively reducing the spinning process temperature of the polyamide melt. This enables the continuous and uninterrupted processing of polyamide ultrafine fiber two-dimensional membranes, meeting the requirements of large-scale production with high yield. It has wide applications in industrial filtration, medical dressings, hygiene protection, and precision instrument packaging.

Description

Technical Field

[0001] This invention relates to the technical field of porous membranes, and in particular to a method for preparing polyamide microfiber two-dimensional membranes using reactive meltblown technology, as well as the two-dimensional membranes and their applications. Background Technology

[0002] Polyamide 6 is a class of engineering thermoplastics with significant commercial value. Due to its excellent properties such as high toughness, wear resistance, self-lubrication, solvent resistance, and a wide operating temperature range, it is widely used in textiles, apparel, and other industrial fields. Commercially, polyamide 6 fibers are mainly produced using melt spinning. Synthesized high-molecular-weight polyamide 6 chips are extracted, and under high melt pressure and high temperature (typically 265-285℃), the molten fluid is extruded through micropores in a spinneret to form continuous fiber filaments. These filaments are then quenched and further drawn and solidified to reduce their diameter to the desired level (generally above 10μm). Finally, they are wound into continuous spindles or spun into a fiber web structure. Because of the high melt viscosity of polyamide 6, this method cannot produce submicron or nanoscale polyamide 6 fibers. Furthermore, the process involves high temperatures, poor coordination between upstream synthesis and downstream spinning, and is complex with extremely high energy consumption.

[0003] To obtain polyamide 6 fibers with smaller dimensions, electrospinning technology is commonly used in the prior art. Electrospinning technology includes solution electrospinning and melt electrospinning.

[0004] Chinese patent CN115364678A discloses a high-strength nanofiber composite polyamide microfiltration membrane and its preparation method. It uses high molecular weight polyamide 6 and polyamide 66 chips to prepare an electrospinning solution, using formic acid and acetic acid as solvents. The mass fraction of the fine fiber spinning solution is between 10-15%, and the voltage reaches 50-70KV. Chinese patent CN107271513A discloses a silica / nanofiber functional composite modified electrode, its preparation method, and its application. The composite nanofiber PA6-GR modified electrode is formed by mixing polyamide 6 and graphene in a mixed solvent of m-cresol / formic acid / N,N-dimethylformamide to form a precursor spinning solution, which is collected on the surface of a bare electrode through electrospinning. These polyamide electrospinning technologies are solution electrospinning technologies. The raw material is a pre-polymerized high molecular weight polymer. The melt spinning process has a high temperature, and solvents are required in the electrospinning process. The mass fraction of the solvent is 85-90%. This part of the solvent needs to be evaporated during fiber forming, which greatly reduces the fiber yield. Moreover, the evaporated solvent needs to be recycled, which increases the production cost. In addition, these solvents also pose potential threats to human health and the environment.

[0005] The Journal of the Japanese Society of Fiber Science, 2008, published an article on the preparation of ultra-fine fibers by laser electrospinning (Takasaki M, Fu H, Nakata K, et al. Ultra-fine fibers produced by laser-electrospinning[J]. Sen'i Gakkaishi, 2008, 64(1):29-31). The Journal of Applied Polymer Science, 2010, published an article on the preparation of polyvinyl alcohol and nylon 6 / 12 nanofibers by melt electrospinning system equipped with a line-like laser beam melting device (Shimada N, Tsutsumi H, Nakane K, et al. Poly(ethylene-co-vinyl alcohol) and nylon 6 / 12 nanofibers produced by melt electrospinning system equipped with a line-like laser beam melting device[J]. The paper "Science, 2010, 116(5):2998-3004" discloses that laser-heated melt electrospinning (LES) can be used to prepare polyamide 6 / 12 fibers with an average diameter of about 1 μm. The method involves using a laser beam to irradiate the tip of a rod-shaped polymer and applying a high-voltage electric field to the molten part to stretch it into fibers. This local instantaneous melting method results in a low fiber production efficiency. At the same time, the high laser output power leads to high energy consumption and is very likely to cause polymer decomposition. In 2009, Fiber Chemistry disclosed a method for producing nonwovens by electrospinning from polymer melts (Malakhov SN, Khomenko AY, Belousov SI, et al. Method of manufacturing nonwovens by electrospinning from polymer melts[J]. Fibre Chemistry, 2009, 41(6):355-359) which involved adding sodium stearate and sodium oleic acid-high fatty acid salts at a ratio of 2-10% to polyamide 6 as plasticizers to reduce the melt viscosity of polyamide 6. However, the addition of large amounts of plasticizers can affect the properties of the fibers. Moreover, this method uses extreme process conditions (temperatures up to 345°C and voltages up to a dangerous 130kV). These extreme process conditions can easily cause polymer decomposition, leading to a decrease in polymer molecular weight and thus affecting the properties of the fibers, especially their mechanical properties. In addition, these extreme process conditions are difficult to implement and pose a significant risk to operators.

[0006] Furthermore, Chinese patent CN113279149A discloses a method for preparing thermoplastic polyamide microfiber nonwoven two-dimensional membranes. Using low-viscosity caprolactam monomer as the starting material, and utilizing the intermediate state of polyamide 6 polymerization reaction (i.e., low degree of polymerization and low viscosity) under laboratory conditions, micro / nanofiber and two-dimensional nonwoven materials are obtained through single-hole extrusion with a pusher and electrostatic stretching. This process does not use any solvents. However, the fiber production efficiency (yield) of this technology is still at a level comparable to single-hole electrospinning technology. In addition, this pusher-type pipeline reactor inevitably experiences wall adhesion, causing the pipeline to become clogged due to long residence time of the reaction melt and excessive polymerization, ultimately leading to spinning interruption. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing polyamide microfiber two-dimensional membranes using reactive meltblown technology, as well as the two-dimensional membranes and their applications, aiming to solve the problems of discontinuous production process and low yield in the existing polyamide microfiber two-dimensional membrane preparation methods.

[0008] To solve the above-mentioned technical problems, the technical solution of the present invention is implemented as follows:

[0009] The present invention discloses a method for preparing polyamide microfiber two-dimensional films using reactive meltblown technology, comprising the following steps:

[0010] 1) Take caprolactam monomer, add catalyst, the amount of catalyst is 0.1-10% of the molar amount of caprolactam monomer, melt, stir, and obtain reaction mixture;

[0011] 2) The reaction mixture obtained in step 1) is fed to the feed port of a reactive screw extruder. The screw speed of the reactive screw extruder is 10-500 r / min and the screw temperature is 90-280℃. The feed conveying section is 90-200℃, the reaction section is 200-280℃, and the compression extrusion section is 200-280℃, so that the reaction mixture continues to polymerize to obtain a melt, and the obtained melt is continuously extruded.

[0012] 3) The molten material extruded in step 2) is conveyed to the die head of the meltblown device for spinning. The die head temperature is 150-300℃. Under the action of the hot air flow from the meltblown device, the material is stretched, cured, and formed into fibers. The hot air flow temperature is 150-300℃, and the hot air flow rate is 10-50 m³ / h. 3 The flow rate is 500-5000 Pa, and the polyamide ultrafine fiber two-dimensional membrane is obtained by randomly laying and aggregating the fibers into a web under the suction of the receiving device.

[0013] This invention uses low-viscosity caprolactam monomer as the starting material and utilizes a reactive screw extruder and a melt-blowing device to complete the mixing of raw material formulations, polymerization reaction, melt extrusion of the reaction system, high-speed hot airflow stretching into fibers, and web laying. Polyamide ultrafine fiber two-dimensional membranes are continuously obtained from monomers in a one-step process. This effectively reduces the spinning process temperature of the polyamide melt and achieves the integrated processing of polyamide ultrafine fiber two-dimensional membranes. The process flow is short, highly automated, and the reaction proceeds smoothly. The reactive screw extruder does not exhibit wall-sticking effects, avoiding long-term retention of the reaction melt. The viscosity of the melt is controlled by the conversion rate of the caprolactam anionic ring-opening polymerization reaction system, ensuring that the viscosity of the extruded melt always meets the spinning requirements of the melt-blowing device. This achieves continuous preparation of polyamide ultrafine fiber two-dimensional membranes, avoiding the phenomenon of spinning interruption due to over-polymerization and clogging. The output is high, meeting the requirements of large-scale production.

[0014] In a preferred embodiment, in step 1), an initiator is added, with the amount of initiator being 0.1-10% of the molar amount of caprolactam monomer; in step 2), the screw temperature is 90-200℃, wherein the feeding conveying section is 90-140℃, the reaction section is 140-200℃, and the compression extrusion section is 140-200℃. In this invention, an initiator may or may not be added when the caprolactam monomer is polymerized. When no initiator is added to the raw material formulation, i.e., when the raw material formulation consists of caprolactam monomer and catalyst, the caprolactam monomer and catalyst generate caprolactam anions in the liquid state. Chain initiation begins with the reaction of the caprolactam anion with other caprolactams to generate aminoacetylcaprolactam. Aminoacetylcaprolactam has an imide structure and strong electrophilic properties, making it easily attacked by caprolactam anions, resulting in a ring-opening reaction that continuously cycles, thereby achieving chain growth. This chain initiation reaction requires a relatively high temperature (above 200℃) to occur. When an initiator (various isocyanates) is added to the raw material formulation, i.e., when the raw material formulation consists of caprolactam monomer, catalyst, and initiator, the caprolactam monomer reacts with the initiator to form caprolactam-terminated isocyanates with an imide structure. This eliminates the need for the reaction of the caprolactam anion with other caprolactams to form aminoacetylcaprolactam, allowing direct chain growth. This significantly reduces the activation energy, multiplies the reaction rate, and greatly lowers the polymerization temperature. As the degree of polymerization increases, the melt viscosity continuously increases. When the polymerization reaction reaches a viscosity range suitable for spinning, the melt stream ejected from the spinneret is stretched under a high-speed hot airflow to form ultrafine fibers, which are then randomly laid on a receiving device (e.g., a web forming machine) to obtain a polyamide ultrafine fiber two-dimensional film.

[0015] In a preferred embodiment, in step 1), the amount of catalyst used is 0.1-2% of the molar amount of caprolactam monomer. The amount of catalyst used in this invention is added according to actual process requirements. Sometimes a larger amount of catalyst is needed, reaching 10%, while sometimes a smaller amount is needed, such as 0.1%. Typically, the amount of catalyst used is 0.1-2%, and it can also be 0.8-2%, thus meeting the requirements of large-scale industrial production.

[0016] In a preferred embodiment, in step 1), the amount of initiator is 0.1-2% of the molar amount of caprolactam monomer. In this invention, the initiator may or may not be added; adding an initiator can lower the reaction temperature. The amount of initiator is added according to actual process requirements; the amount of initiator can reach 10%, or it can be 0.1%. Typically, the amount of catalyst is 0.1-2% to improve the reaction rate, reduce energy consumption, and meet the requirements of large-scale industrial production.

[0017] In a preferred embodiment, in step 2), the relative viscosity of the melt is 1.4-3.0, the intrinsic viscosity is 35-135 mL / g, and the viscosity-average molecular weight is 9800-46200 g / mol. This invention controls the degree of polymerization of caprolactam monomer and its conversion rate by controlling the viscosity of the extruded melt in a reactive screw extruder, thereby obtaining a melt that meets the requirements of the meltblown process. In this invention, the monomer conversion rate of the continuously extruded melt in the reactive screw extruder is typically 40-95%, preferably 50-95%.

[0018] In a preferred embodiment, in step 2), the reaction mixture is conveyed to the feed port of the reactive screw extruder via a liquid metering device, and the flow rate of the reaction mixture in the liquid metering device is 10-500 L / h. This invention uses a liquid metering device (e.g., an industrial peristaltic pump) to meter the reaction mixture conveyed to the reactive screw extruder (e.g., a reactive screw extruder), controlling the feed rate, thereby controlling the amount of raw material formulation in the reactive screw extruder, ensuring close coordination with the screw speed, and thus obtaining a melt that meets the requirements. Typically, the flow rate of the reaction mixture in the liquid metering device is 10-500 L / h. Preferably, the flow rate of the reaction mixture in the liquid metering device is 10-300 L / h, at which point the screw speed of the reactive screw extruder is 10-300 r / min. More preferably, the flow rate of the reaction mixture in the liquid metering device is 10-150 L / h, at which point the screw speed of the reactive screw extruder is 10-150 r / min. More preferably, the flow rate of the reaction mixture in the liquid metering device is 10-100 L / h, at which point the screw speed of the reactive screw extruder is 20-100 r / min.

[0019] In a preferred embodiment, in step 3), the melt is first filtered and then transported to the die head of the meltblown device by a metering pump. The metering pump operates at a speed of 10-500 r / min and a temperature of 150-300°C. In this invention, the melt continuously extruded from the reactive screw extruder is first filtered by a melt filter, and then transported to the meltblown device by a metering pump. The meltblown device is typically a meltblown machine. The speed of the metering pump controls the formation rate of the polyamide microfiber two-dimensional membrane, thereby controlling the yield of the polyamide microfiber two-dimensional membrane. Typically, the metering pump operates at a speed of 10-500 r / min; preferably, it operates at 10-300 r / min; and more preferably, it operates at 12-150 r / min.

[0020] In a preferred embodiment, in step 3), the diameter of the spinneret orifice in the meltblown device is 0.1-0.5 mm during spinning. The spinneret orifice is the last capillary through which the melt passes before being stretched into fibers. The finer the spinneret orifice, the finer the diameter of the initial fluid, and the finer the fiber at the same stretching ratio. However, the finer the spinneret orifice, the greater the force it bears at the same extrusion pressure. Typically, the diameter of the spinneret orifice is 0.1-0.5 mm, and the diameter of the spinneret orifice is also called the aperture.

[0021] In this invention, caprolactam monomers are typically dried in a vacuum drying oven at 55-65°C for 20-30 hours before use to remove moisture. Vacuum drying of the caprolactam monomers before use ensures that no moisture is introduced during the anionic ring-opening polymerization reaction of caprolactam. The suction air pressure is 500-5000 Pa, preferably 500-3000 Pa, and more preferably 800-2500 Pa.

[0022] In this invention, the flow rate of the reaction mixture in the liquid metering device, the screw speed, the metering pump speed, the number of dies, the number and distribution of the spinneret holes are closely coordinated to adjust the yield of the newly formed fibers. Under normal circumstances, the yield of polyamide microfiber two-dimensional membrane is 5-500 kg / h. In small-scale experiments, the yield is low, in pilot-scale experiments, the yield gradually increases, and in large-scale production, the yield can reach 500 kg / h.

[0023] In a preferred embodiment, the catalyst is any one of sodium hydride, potassium hydride, lithium hydride, sodium hydroxide, potassium hydroxide, and lithium hydroxide. The catalyst is suspended in mineral oil, and the catalyst content in the mineral oil is 20-80%. Because the hydride catalyst of this invention is highly reactive, for safety reasons and to control the polymerization reaction rate, the catalyst is pre-suspended in mineral oil. This catalyst is convenient to use, easy to store, and has good performance.

[0024] As a preferred embodiment, the initiator is any one of TDI, MDI, NDI, PPDI, IPDI, HMDI, XDI, HDI, LDI, TODI, TTI, TPTI, EI, and tBI. The initiator of this invention is an isocyanate capable of forming an open-ring imide structure with caprolactam monomers, including toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), 1,5-naphthalene diisocyanate (NDI), terephthalic diisocyanate (PPDI), isophorone diisocyanate (IPDI), dicyclohexylmethane diisocyanate (HMDI), phenyl dimethylene diisocyanate (XDI), hexamethylene diisocyanate (HDI), lysine diisocyanate (LDI), 3,3'-dimethyl-4,4'-biphenyl diisocyanate (TODI), triphenylmethane triisocyanate (TTI), 4,4',4”-triphenyl triisocyanate thiophosphate (TPTI), ethyl isocyanate (EI), tert-butyl isocyanate (tBI), etc.

[0025] In another aspect, the present invention provides a polyamide microfiber two-dimensional membrane, wherein the polyamide microfiber two-dimensional membrane is prepared by a method for preparing a polyamide microfiber two-dimensional membrane according to any one of the above-described reactive meltblown technology.

[0026] The polyamide microfiber two-dimensional membrane of this invention is prepared by reactive meltblowing technology. In a reactive screw extruder, the raw materials are mixed, polymerized, and melt extruded. The extruded melt is then spun, stretched, and web-laid through a meltblowing device, resulting in a continuous one-step production of the polyamide microfiber two-dimensional membrane. Based on the dynamic change in viscosity of the reaction system with the reaction conversion rate, the viscosity of the melt is controlled by controlling the conversion rate of the caprolactam anionic ring-opening polymerization reaction system. This ensures that the melt viscosity always meets the spun requirements of the meltblowing device, thereby achieving continuous preparation of the polyamide microfiber two-dimensional membrane. This polyamide microfiber two-dimensional membrane is a polycaprolactam microfiber two-dimensional membrane, chemically composed of polycaprolactam (nylon 6). It consists of smooth, solid columnar fibers with a diameter ranging from 800 nm to 25 μm, laid out in a random distribution. It possesses the excellent mechanical and engineering properties of nylon 6, with controllable fiber diameter and micropore size, and has significant application value in industrial filtration, medical dressings, hygiene protection, and precision instrument packaging.

[0027] In a preferred embodiment, the polyamide microfiber two-dimensional membrane further includes any one or more of the following: filler, inert filler, and non-reactive functional components that do not participate in the anionic polymerization reaction in step 2). The total amount of the filler, inert filler, and non-reactive functional components that do not participate in the anionic polymerization reaction in step 2) added does not exceed 10% of the total weight of the polyamide microfiber two-dimensional membrane. During the preparation of the polyamide microfiber two-dimensional membrane of the present invention, fillers, inert fillers, or non-reactive functional components that do not participate in the above polymerization reaction can also be added to the raw material formulation to improve the overall performance of the polyamide microfiber two-dimensional membrane.

[0028] In a preferred embodiment, the filler is any one or more of plasticizers, antioxidants, anti-aging agents, and toughening agents, and the inert filler is any one or two of talc and quartz sand. The use of these fillers in this invention can improve the plasticity, aging resistance, and toughness of the polyamide microfiber two-dimensional membrane; the addition of inert fillers such as talc and quartz sand can improve the strength and hardness of the polyamide microfiber two-dimensional membrane; and the addition of non-reactive functional components that do not participate in the above polymerization reaction can improve other functionalities of the polyamide microfiber two-dimensional membrane, thereby further improving the overall performance of the polyamide microfiber two-dimensional membrane.

[0029] In another aspect, the present invention relates to the application of a polyamide microfiber two-dimensional membrane in the preparation of nonwoven fabrics.

[0030] The polyamide microfiber two-dimensional membrane of the present invention can be used to make nonwoven fabrics. These nonwoven fabrics are composed of disordered microfibers, have a large specific surface area, small pores and high porosity, a loose structure, good isotropy, a soft hand feel, and excellent filtration, air permeability and heat insulation properties. They are widely used in industrial filtration, medical dressings, hygiene protection and precision instrument packaging and other fields.

[0031] In a preferred embodiment, the polyamide microfiber two-dimensional membrane is fed to a hot rolling mill. The hot rolling mill temperature is 100-200℃, and the hot rolling mill pressure is 50-100 N / mm. Under the high temperature and high pressure of the rolling mill, the polyamide microfiber two-dimensional membrane is solidified and shaped, and then collected into rolls by a winding machine at a winding speed of 10-100 m / min to obtain a nonwoven fabric. The polyamide microfiber two-dimensional membrane of this invention, after being solidified and shaped by a hot rolling mill and collected into rolls by a winding machine, yields a nonwoven fabric. This nonwoven fabric has a certain strength, is easy to apply directly, and is convenient to use.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention uses low-viscosity caprolactam monomer as the starting material, and realizes the mixing, polymerization and melt extrusion of the raw material formulation in a reactive screw extrusion device. The extruded melt is used to realize the spinning, stretching and web laying of fibers through a melt-blowing device. Polyamide ultrafine fiber two-dimensional membranes are obtained continuously in one step from the monomer, which effectively reduces the spinning process temperature of polyamide melt, realizes the linkage processing of polyamide ultrafine fiber two-dimensional membranes, has a short process flow, high degree of automation, smooth reaction, no wall sticking effect, avoids long-term retention of reaction melt, and controls the viscosity of melt by controlling the conversion rate of caprolactam anionic ring-opening polymerization reaction system, so that the viscosity of extruded melt always meets the spinning requirements of melt-blowing device, thereby realizing the continuous preparation of polyamide ultrafine fiber two-dimensional membranes, avoiding the phenomenon of spinning interruption due to clogging caused by over-polymerization, and has high output, meeting the requirements of large-scale production. The chemical composition of this polyamide microfiber two-dimensional membrane is polycaprolactam (nylon 6), which is composed of smooth solid columnar fibers with a fiber diameter ranging from 800 nm to 25 μm. The fibers are laid out in a random distribution and have the excellent mechanical and engineering properties of nylon 6. The fiber diameter and micropore size are controllable. It is used to prepare nonwoven fabrics and is widely used in industrial filtration, medical dressings, hygiene protection and precision instrument packaging. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the planar structure of the spinning equipment used in the method for preparing polyamide ultrafine fiber two-dimensional membranes using reactive meltblowing technology provided by the present invention.

[0034] Figure 2The molecular weight and integral distribution curves of the polyamide microfiber two-dimensional membrane obtained in Example 1 of this invention are shown.

[0035] Figure 3 The molecular weight and integral distribution curves of the polyamide microfiber two-dimensional membrane obtained in Example 3 of this invention are shown.

[0036] Figure 4 This is a scanning electron microscope image of the polyamide microfiber two-dimensional membrane obtained in Example 1 of the present invention;

[0037] Figure 5 This is a scanning electron microscope image of the polyamide microfiber two-dimensional membrane obtained in Example 2 of the present invention;

[0038] Figure 6 This is a scanning electron microscope image of the polyamide microfiber two-dimensional membrane obtained in Example 3 of the present invention;

[0039] Figure 7 This is a scanning electron microscope image of the polyamide microfiber two-dimensional membrane obtained in Example 4 of the present invention;

[0040] Figure 8 This is a scanning electron microscope image of the polyamide microfiber two-dimensional membrane obtained in Example 5 of the present invention;

[0041] Figure 9 The differential scanning calorimetry (DSC) thermal analysis curve of the polyamide microfiber two-dimensional membrane obtained in Example 1 of this invention;

[0042] Figure 10 The differential scanning calorimetry (DSC) thermal analysis curve of the polyamide microfiber two-dimensional membrane obtained in Example 2 of this invention is shown below.

[0043] Figure 11 The differential scanning calorimetry (DSC) thermal analysis curve of the polyamide microfiber two-dimensional membrane obtained in Example 3 of this invention is shown below.

[0044] Figure 12 The differential scanning calorimetry (DSC) thermal analysis curve of the polyamide microfiber two-dimensional membrane obtained in Example 4 of this invention is shown below.

[0045] Figure 13 The differential scanning calorimetry (DSC) thermal analysis curve of the polyamide microfiber two-dimensional membrane obtained in Example 5 of this invention;

[0046] Figure 14 Differential scanning calorimetry thermal analysis curve of the control sample selected for this invention;

[0047] In the diagram: 1-mixing tank; 2-conveying pipeline; 3-industrial peristaltic pump; 4-reactive screw extruder; 5-melt filter; 6-metering pump; 7-meltblown machine; 8-high-speed hot air flow; 9-web forming machine; 10-exhaust fan; 11-hot rolling mill; 12-hot rolling roll; 13-winding machine. Detailed Implementation

[0048] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0049] The present invention discloses a method for preparing polyamide microfiber two-dimensional films using reactive meltblown technology, comprising the following steps:

[0050] 1) Take caprolactam monomer, add catalyst, the amount of catalyst is 0.1-10% of the molar amount of caprolactam monomer, melt, stir, and obtain reaction mixture;

[0051] 2) The reaction mixture obtained in step 1) is fed to the feed port of a reactive screw extruder. The screw speed of the reactive screw extruder is 10-500 r / min and the screw temperature is 90-280℃. The feed conveying section is 90-200℃, the reaction section is 200-280℃, and the compression extrusion section is 200-280℃, so that the reaction mixture continues to polymerize to obtain a melt, and the obtained melt is continuously extruded.

[0052] 3) The molten material extruded in step 2) is conveyed to the die head of the meltblown device for spinning. The die head temperature is 150-300℃. Under the action of the hot air flow from the meltblown device, the material is stretched, cured, and formed into fibers. The hot air flow temperature is 150-300℃, and the hot air flow rate is 10-50 m³ / h. 3 The flow rate is 500-5000 Pa, and the polyamide ultrafine fiber two-dimensional membrane is obtained by randomly laying and aggregating the fibers into a web under the suction of the receiving device.

[0053] Preferably, in step 1), an initiator is added, and the amount of initiator is 0.1-10% of the molar amount of caprolactam monomer; in step 2), the screw temperature is 90-200℃, wherein the feeding and conveying section is 90-140℃, the reaction section is 140-200℃, and the compression and extrusion section is 140-200℃.

[0054] Furthermore, in step 2), the relative viscosity of the melt is 1.4-3.0, the intrinsic viscosity is 35-135 mL / g, and the viscosity-average molecular weight is 9800-46200 g / mol.

[0055] Preferably, in step 2), the reaction mixture is conveyed to the feed port of the reactive screw extruder via a liquid metering device, and the flow rate of the reaction mixture in the liquid metering device is 10-500 L / h.

[0056] Preferably, in step 3), the melt is first filtered and then transported to the die head of the meltblown device by a metering pump. The metering pump rotates at a speed of 10-500 r / min and has a temperature of 150-300℃.

[0057] Preferably, in step 3), the diameter of the spinneret orifice of the meltblown device is 0.1-0.5 mm when the meltblown device is spinning the wire.

[0058] Preferably, the catalyst is any one of sodium hydride, potassium hydride, lithium hydride, sodium hydroxide, potassium hydroxide, and lithium hydroxide.

[0059] Preferably, the initiator is any one of TDI, MDI, NDI, PPDI, IPDI, HMDI, XDI, HDI, LDI, TODI, TTI, TPTI, EI, and tBI.

[0060] The present invention discloses a polyamide microfiber two-dimensional membrane, wherein the polyamide microfiber two-dimensional membrane is prepared by the method for preparing polyamide microfiber two-dimensional membrane according to any one of the above-described reactive meltblown technology.

[0061] Preferably, the polyamide microfiber two-dimensional membrane further includes any one or more of fillers, inert fillers, and non-reactive functional components that do not participate in the anionic polymerization reaction in step 2), wherein the total amount of fillers, inert fillers, and non-reactive functional components that do not participate in the anionic polymerization reaction in step 2) added does not exceed 10% of the total weight of the polyamide microfiber two-dimensional membrane.

[0062] Preferably, the filler is any one or more of plasticizers, antioxidants, anti-aging agents, and toughening agents, and the inert filler is any one or two of talc powder and quartz sand.

[0063] The present invention relates to the application of a polyamide microfiber two-dimensional membrane in the preparation of nonwoven fabrics.

[0064] Preferably, the polyamide microfiber two-dimensional film is conveyed to a hot rolling mill, the temperature of the hot rolling roll is 100-200℃, and the pressure of the hot rolling roll is 50-100N / mm, so that the polyamide microfiber two-dimensional film is solidified and shaped under the high temperature and high pressure between the rolls, and then collected into rolls by a winding machine at a winding speed of 10-100m / min to obtain a nonwoven fabric.

[0065] See appendix Figure 1The present invention discloses a method for preparing polyamide microfiber two-dimensional membranes using reactive meltblown technology. The spinning equipment used in the preparation of the polyamide microfiber two-dimensional membrane includes a mixing tank 1, a reactive screw extruder, a meltblown device, and a receiving device. This spinning equipment is also connected to a hot rolling mill 11 and a winding machine 13. Specifically, the reactive screw extruder is a reactive screw extruder 4, the meltblown device is a meltblown machine 7, and the receiving device is a web forming machine 9. The mixing tank 1 is a closed mixing tank. The raw material formulation is mixed in the mixing tank 1. The mixing tank 1 can be set with a temperature and has a stirring function. The raw material formulation is melted, stirred, and mixed evenly in the mixing tank 1. The mixing tank 1 also has vacuum and gas replacement functions to ensure that the raw material formulation is isolated from air during mixing and melting, thereby preventing moisture in the air from affecting the polymerization reaction. Mixing tank 1 is connected to a liquid metering device via conveying pipe 2. The liquid metering device, which can be an industrial peristaltic pump 3, measures the quantity of raw materials. The conveying pipe 2 and the industrial peristaltic pump 3 can be heated to regulate their temperature, ensuring the raw materials remain in a low-viscosity fluid state. A flow meter 3 is connected to a reactive screw extruder 4. The reactive screw extruder 4 allows for temperature and screw speed settings to ensure continuous polymerization of the reaction system and continuous quantitative extrusion of the melt. A melt filter 5 is connected to the outlet of the reactive screw extruder 4. The melt filter 5 allows for temperature and filtration accuracy settings, filtering out impurities and unmelted materials. The melt filter 5 is connected to a metering pump 6, which allows for temperature and speed settings. Metering pump 6 is connected to meltblown machine 7. The die head of meltblown machine 7 can be set with temperature, and a high-speed hot air stream 8 is installed on the die head of meltblown machine 7. The high-speed hot air stream 8 can be set with airflow temperature and flow rate. The filtered melt is metered by metering pump 6 and quantitatively delivered to the die head of meltblown machine 7. It is then evenly distributed to each spinneret hole of spinneret plate by the distribution plate inside meltblown machine 7. The fine melt stream ejected from the spinneret hole is rapidly stretched into fibers by high-ratio through high-speed hot air stream 8. Meltblown machine 7 is also connected to web forming machine 9, which is equipped with suction fan 10. With the assistance of suction fan 10, the fibers are randomly laid and gathered into a fiber web on web forming machine 9. The random laying of the fiber web is achieved by the matching action of the air pressure of suction fan 10, the screen of web forming machine 9, and the transmission speed, ensuring the uniformity of the fiber web. The fiber web is then fed into the hot rolling mill 11, where it is solidified and shaped under the combined action of the high temperature of the hot rolling rolls 12 and the high pressure generated between the hot rolling rolls 12, thereby obtaining a nonwoven fabric; finally, it is collected into a roll by the winding machine 13.

[0066] Example 1

[0067] See appendix Figure 1 On the spinning equipment shown, a method for preparing polyamide microfiber two-dimensional membranes using reactive meltblown technology according to the present invention includes the following steps:

[0068] 1) Take caprolactam monomer, catalyst - sodium hydride and initiator - toluene-2,4-diisocyanate (TDI), with a molar ratio of caprolactam monomer, catalyst and initiator of 100:0.8:2, place them in mixing tank 1 of the spinning equipment, evacuate the vacuum to remove the air in mixing tank 1, heat to 95°C to melt caprolactam monomer, catalyst and initiator, stir evenly to obtain reaction mixture;

[0069] 2) The reaction mixture obtained in step 1) is injected into the feed port of the reactive twin-screw extruder by an industrial peristaltic pump 3 at a flow rate of 10 L / h. The screw speed of the reactive twin-screw extruder is 65 r / min. The temperatures of each zone from the feed port to the extrusion port of the twin-screw extruder are 130℃-138℃-145℃-150℃-154℃-157℃-160℃-155℃-150℃ respectively (the first two zones are the feeding and conveying section, the middle five zones are the reaction section, and the last two zones are the compression and extrusion section). At this time, the polymerization reaction continues to occur in the reaction system, and the polymerization conversion rate is controlled to be about 50%, so that the melt is continuously extruded.

[0070] 3) The melt extruded in step 2) is filtered through melt filter 5, which is at a temperature of 150°C. Metering pump 6, also at 150°C, is used to meter the melt, causing it to be conveyed at a speed of 50 r / min to the die head of the meltblown machine 7. The spinneret used in the die head is 600 mm long, with a spinneret orifice density of 1333 orifices / m and an orifice diameter of 0.3 mm. The die head temperature is 150°C. Under the action of the high-speed hot airflow 8 from the meltblown machine 7, the high-speed hot airflow 8, at a temperature of 150°C, has a flow rate of 25 m³ / min. 3 The molten fine stream ejected from the spinneret is rapidly stretched and solidified into fibers at a high ratio of / min, and randomly laid and aggregated into a fiber web with the assistance of the suction air 10 of the web forming machine 9. The pressure of the suction air 10 is 1000Pa, and a polyamide ultrafine fiber two-dimensional membrane is obtained.

[0071] Example 2

[0072] See appendix Figure 1 On the spinning equipment shown, a method for preparing polyamide microfiber two-dimensional membranes using reactive meltblown technology according to the present invention includes the following steps:

[0073] 1) Take caprolactam monomer and catalyst - sodium hydride, with a molar ratio of caprolactam to catalyst of 100:2, place them in mixing tank 1 of the spinning equipment, replace the air in mixing tank 1 with nitrogen, heat to 95°C to melt caprolactam monomer and catalyst, stir evenly to obtain reaction mixture;

[0074] 2) The reaction mixture obtained in step 1) is injected into the feed port of the reactive twin-screw extruder 4 by an industrial peristaltic pump 3 at a flow rate of 10 L / h. The screw speed of the reactive twin-screw extruder 4 is 32 r / min. The temperatures of each zone from the feed port to the extrusion port of the twin-screw extruder 4 are 130℃-150℃-190℃-230℃-240℃-245℃-250℃-255℃-255℃ (the first three zones are the feeding and conveying section, the middle four zones are the reaction section, and the last two zones are the compression and extrusion section). At this time, the polymerization reaction continues to occur in the reaction system, and the polymerization conversion rate is controlled to be about 90%, so that the melt is continuously extruded.

[0075] 3) The melt extruded in step 2) is filtered through melt filter 7 (temperature 260℃). Metering pump 6 (temperature 260℃) is used to meter the melt, causing it to be delivered to the die head of meltblown machine 7 at a speed of 22 r / min. The spinneret used in the die head is 500 mm long, with a spinneret orifice density of 1428 orifices / m and an orifice diameter of 0.35 mm. The die head temperature is 260℃. Under the action of the high-speed hot airflow 8 of meltblown machine 7 (temperature 260℃, flow rate 25 m³ / min), the melt is further processed. 3 The molten fine stream ejected from the spinneret is rapidly stretched and solidified into fibers at a high ratio of / min, and randomly laid and aggregated into a fiber web with the assistance of the suction air 10 of the web forming machine 9. The pressure of the suction air 10 is 800Pa, and a polyamide ultrafine fiber two-dimensional membrane is obtained.

[0076] Example 3

[0077] See appendix Figure 1 On the spinning equipment shown, the method for preparing polyamide microfiber two-dimensional membranes using reactive meltblown technology in this embodiment includes the following steps:

[0078] 1) Take caprolactam monomer and catalyst - sodium hydride, with a molar ratio of caprolactam to catalyst of 100:2, place them in mixing tank 1 of the spinning equipment, replace the air in mixing tank 1 with helium, heat to 95°C to melt caprolactam monomer and catalyst, stir evenly to obtain reaction mixture;

[0079] 2) The reaction mixture obtained in step 1) is injected into the feed port of the reactive twin-screw extruder 4 by an industrial peristaltic pump 3 at a flow rate of 10 L / h. The screw speed of the reactive twin-screw extruder 4 is 20 r / min. The temperatures of each zone from the feed port to the extrusion port of the twin-screw extruder 4 are 130℃-150℃-190℃-230℃-240℃-245℃-250℃-255℃-255℃ (the first three zones are the feeding and conveying section, the middle four zones are the reaction section, and the last two zones are the compression and extrusion section). At this time, the polymerization reaction continues to occur in the reaction system, and the polymerization conversion rate is controlled to be about 90%, so that the melt is continuously extruded.

[0080] 3) The molten material extruded in step 2) is filtered through a melt filter 5 at a temperature of 260°C. Metering is performed using a metering pump 6 at 260°C, causing the melt to be delivered to the die head of the meltblown machine 7 at a speed of 12 r / min. The spinneret used in the die head is 500 mm long, with a spinneret orifice density of 1428 orifices / m and an orifice diameter of 0.3 mm. Under the action of the high-speed hot airflow 8 from the meltblown machine 7 (temperature 260°C and flow rate 25 m³ / min), the melt is further processed. 3 The molten fine stream ejected from the spinneret is rapidly stretched and solidified into fibers at a high ratio of / min, and randomly laid and aggregated into a fiber web with the assistance of the suction air 10 of the web forming machine 9. The pressure of the suction air 10 is 2000Pa, and a polyamide ultrafine fiber two-dimensional membrane is obtained.

[0081] Example 4

[0082] See appendix Figure 1 On the spinning equipment shown, a method for preparing polyamide microfiber two-dimensional membranes using reactive meltblown technology according to the present invention includes the following steps:

[0083] 1) Take caprolactam monomer and catalyst - sodium hydride, with a molar ratio of caprolactam to catalyst of 100:2, place them in mixing tank 1 of the spinning equipment, evacuate the vacuum tank 1 to remove the air, heat to 95°C to melt the caprolactam monomer and catalyst, stir evenly to obtain the reaction mixture.

[0084] 2) The reaction mixture obtained in step 1) is injected into the feed port of the reactive twin-screw extruder 4 by an industrial peristaltic pump 3 at a flow rate of 10 L / h. The screw speed of the reactive twin-screw extruder 4 is 32 r / min. The temperatures of each zone from the feed port to the extrusion port of the twin-screw extruder 4 are 130℃-150℃-190℃-230℃-240℃-245℃-250℃-255℃-255℃ (the first three zones are the feeding and conveying section, the middle four zones are the reaction section, and the last two zones are the compression and extrusion section). At this time, the polymerization reaction continues to occur in the reaction system, and the polymerization conversion rate is controlled to be about 90%, so that the melt is continuously extruded.

[0085] 3) The melt extruded in step 2) is filtered through melt filter 5 at a temperature of 260°C. Metering pump 6, also at 260°C, is used to meter the melt, which is then conveyed to the die head of the meltblown machine 7 at a speed of 22 r / min. The spinneret used in the die head is 500 mm long, with a spinneret orifice density of 1428 orifices / m and an orifice diameter of 0.35 mm. The die head temperature is 260°C. Under the action of the high-speed hot airflow 8 from the meltblown machine 7 (temperature 260°C, flow rate 30 m³ / min), the melt is further processed. 3The molten fine stream ejected from the spinneret is rapidly stretched and solidified into fibers at a high ratio of / min, and randomly laid and aggregated into a fiber web with the assistance of the suction air 10 of the web forming machine 9. The pressure of the suction air 10 is 1000Pa, and a polyamide ultrafine fiber two-dimensional membrane is obtained.

[0086] Example 5

[0087] See appendix Figure 1 On the spinning equipment shown, a method for preparing polyamide microfiber two-dimensional membranes using reactive meltblown technology according to the present invention includes the following steps:

[0088] 1) Take caprolactam monomer and catalyst - sodium hydride, with a molar ratio of caprolactam to catalyst of 100:1, place them in mixing tank 1 of the spinning equipment, evacuate the vacuum tank 1 to remove the air, heat to 95°C to melt the caprolactam monomer and catalyst, stir evenly to obtain the reaction mixture;

[0089] 2) The reaction mixture obtained in step 1) is injected into the feed port of the reactive twin-screw extruder 4 by an industrial peristaltic pump 3 at a flow rate of 100 L / h. The screw speed of the reactive twin-screw extruder 4 is 100 r / min. The temperatures of each zone from the feed port to the extrusion port of the twin-screw extruder 4 are 130℃-150℃-190℃-230℃-240℃-245℃-250℃-255℃-255℃ (the first three zones are the feeding and conveying section, the middle four zones are the reaction section, and the last two zones are the compression and extrusion section). At this time, the polymerization reaction continues to occur in the reaction system, and the polymerization conversion rate is controlled to be about 90%, so that the melt is continuously extruded.

[0090] 3) The melt extruded in step 2) is filtered through melt filter 5 at a temperature of 270°C. Metering pump 6, also at 270°C, is used to meter the melt, which is then conveyed to the die head of the meltblown machine 7 at a speed of 150 r / min. The spinneret used in the die head is 1600 mm long, with a spinneret orifice density of 1968 orifices / m and an orifice diameter of 0.35 mm. The die head temperature is 270°C. Under the action of the high-speed hot airflow 8 from the meltblown machine 7, the high-speed hot airflow 8, at a temperature of 270°C and a flow rate of 40 m³ / min, is also present. 3 The molten fine stream ejected from the spinneret is rapidly stretched and solidified into fibers at a high ratio at a speed of / min. With the assistance of the suction air 10 of the web forming machine 9, the fibers are randomly laid and aggregated into a web. The pressure of the suction air 10 is 2500Pa, resulting in a polyamide ultrafine fiber two-dimensional membrane.

[0091] Experiment 1

[0092] During the continuous extrusion of melt using a reactive screw extruder in Examples 1 to 5 of this invention, samples were taken, quenched, and collected. The monomer conversion rate was tested using thermogravimetric analysis and solvent extraction, respectively. Then, the extruded melt was diluted with 96% concentrated sulfuric acid to a very dilute solution with a concentration of 0.01 g / mL. Its relative viscosity was measured at room temperature using an Ubbelohde viscometer. Based on the dependence of solution viscosity on concentration, the intrinsic viscosity of the extruded melt was calculated. Finally, the viscosity-average molecular weight of the extruded melt was calculated using the Mark-Houwink nonlinear equation. The results are listed in Table 1.

[0093] As shown in Table 1, in the method for preparing polyamide ultrafine fiber two-dimensional membranes using reactive meltblown technology of the present invention, the monomer conversion rate calculated by thermogravimetric analysis is 53.9-92.8%, and the monomer conversion rate calculated by solvent extraction is 51.6-90.5%. The relative viscosity of the melt continuously extruded by the reactive screw extruder of the present invention is 1.42-2.73, the intrinsic viscosity is 37.24-120.47 mL / g, and the viscosity-average molecular weight is 10347-40715 g / mol. Therefore, the present invention achieves the control of melt viscosity by controlling the conversion rate of the caprolactam anionic ring-opening polymerization reaction system. The control process is convenient and the results are accurate. The melt viscosity is the key to whether fiber and film formation can be achieved in reactive meltblown technology, and plays a vital role in the continuous, large-scale, and high-efficiency production of polyamide ultrafine fiber two-dimensional membranes using reactive meltblown technology.

[0094] Table 1. Viscosity test results of different melts

[0095]

[0096] Experiment 2

[0097] The polyamide microfiber two-dimensional membranes obtained in Examples 1 to 5 of this invention were placed on an Agilent 1260 Infinity II system manufactured by Agilent Technologies for gel permeation chromatography. The testing system was equipped with a refractive index detector, and two PL HFIP-gel columns (300×7.5mm) were used in series. Hexafluoroisopropanol containing sodium trifluoroacetate at a concentration of 10 mmol / L was used as the mobile phase.

[0098] Taking Examples 1 and 3 as examples, the following analysis is performed. (From the appendix...) Figure 2It can be seen that the polyamide microfiber two-dimensional membrane obtained in Example 1 of this invention has a number-average molecular weight of 3141, a weight-average molecular weight of 7669, and a dispersion index of 2.44. If theoretical calculations are used, the number-average molecular weight of the fiber sample in this example, when the monomer conversion rate is around 50%, is approximately 3000. Therefore, the experimental results are consistent with the theoretical calculation results. (See attached...) Figure 3 It can be seen that the polyamide ultrafine fiber two-dimensional membrane obtained in Example 3 of this invention has a number-average molecular weight of 10976, a weight-average molecular weight of 18715, and a dispersion index of 1.71. According to theoretical calculations, the number-average molecular weight of the fiber sample in this example, using the raw material formulation—caprolactam monomer-catalyst—is approximately 10000 when the monomer conversion rate is around 90%. Therefore, the experimental results are consistent with the theoretical calculation results. This indicates that in the reactive meltblown technology method for preparing polyamide ultrafine fiber two-dimensional membranes of this invention, the caprolactam monomer achieves continuous and efficient polymerization, ultimately yielding a high molecular weight polyamide ultrafine fiber two-dimensional membrane in a one-step process.

[0099] Experiment 3

[0100] The polyamide microfiber two-dimensional membranes obtained in Examples 1 to 5 of this invention were observed under a scanning electron microscope (MVE0352891782) manufactured by Phineas GmbH, Germany. (See attached image.) Figure 4 As can be seen, the polyamide ultrafine fiber two-dimensional membrane obtained in Example 1 of this invention is composed of smooth, solid columnar fibers, existing in the form of a randomly arranged fiber membrane. The fiber diameter in the field of view is distributed in the range of 11.1-21.0 μm, and the measured average fiber diameter is 15.3 μm. (See attached...) Figure 5 As can be seen, the polyamide ultrafine fiber two-dimensional membrane obtained in Example 2 of this invention is composed of smooth, solid columnar fibers, existing in the form of a randomly arranged fiber membrane. The fiber diameter in the field of view is distributed in the range of 4.8-9.7 μm, and the measured average fiber diameter is 8.6 μm. (See attached...) Figure 6 As can be seen, the polyamide ultrafine fiber two-dimensional membrane obtained in Example 3 of this invention is composed of smooth, solid columnar fibers, existing in the form of a randomly arranged fiber membrane. The fiber diameter distribution in the field of view ranges from 800 nm to 7.5 μm, and the measured average fiber diameter is 2.8 μm. (See attached...) Figure 7 As can be seen, the polyamide ultrafine fiber two-dimensional membrane obtained in Example 4 of this invention is composed of smooth, solid columnar fibers, existing in the form of a randomly arranged fiber membrane. The fiber diameter in the field of view is distributed in the range of 3.9-9.1 μm, and the measured average fiber diameter is 6.5 μm. (See attached...) Figure 8As can be seen, the polyamide microfiber two-dimensional membrane obtained in Example 5 of this invention is composed of smooth, solid columnar fibers, existing in the form of a randomly arranged fiber membrane. The fiber diameter is distributed in the range of 2.0-5.9 μm in the field of view, and the measured average fiber diameter is 4.2 μm. Therefore, the polyamide microfiber two-dimensional membrane obtained by the reactive melt-blown technology of this invention is composed of smooth, solid columnar fibers. The diameter range and distribution of the microfibers can be controlled by changing the preparation parameters (such as raw material formulation, screw and metering pump speed, screw temperature, high-speed hot airflow stretching speed, etc.). The reactive melt-blown technology method of this invention realizes the industrial-scale production of ultrafine melt-spun fibers, and the fiber diameter can reach the nanometer level.

[0101] Experiment 4

[0102] The polyamide microfiber two-dimensional membranes obtained in Examples 1 to 5 of the present invention, as well as a thermoplastic polyamide microfiber nonwoven two-dimensional membrane (control sample) obtained by Chinese Patent CN113279149A described in the background art, were respectively tested in a STARe Default DB V16.00 differential scanning calorimeter (DSC) manufactured by Mettler Toledo.

[0103] From the appendix Figure 9 It can be seen that the polyamide microfiber two-dimensional membrane obtained in Example 1 of this invention has a fiber melting temperature of 214.8℃, a crystallinity of 40.6%, and a product melt crystallization temperature of 172.1℃. (See attached...) Figure 10 It can be seen that the polyamide microfiber two-dimensional membrane obtained in Example 2 of this invention has a fiber melting temperature of 216.8℃, a crystallinity of 34.0%, and a product melt crystallization temperature of 174℃. (See attached...) Figure 11 It can be seen that the polyamide microfiber two-dimensional membrane obtained in Example 3 of this invention has a fiber melting temperature of 212.4℃, a crystallinity of 40.0%, and a product melt crystallization temperature of 172.2℃. (See attached...) Figure 12 It can be seen that the polyamide microfiber two-dimensional membrane obtained in Example 4 of this invention has a fiber melting temperature of 214.8℃, a crystallinity of 36.8%, and a product melt crystallization temperature of 172.8℃. (See attached...) Figure 13 It can be seen that the polyamide microfiber two-dimensional membrane obtained in Example 5 of this invention has a fiber melting temperature of 212.9℃, a crystallinity of 33.3%, and a product melt crystallization temperature of 172.3℃. (See attached...) Figure 14 It can be seen that the melting temperature of the fiber in the control sample was 203.1℃ and the crystallinity was 17.7%, while the melting and crystallization temperature of the product was 156.7℃.

[0104] Therefore, compared with the control sample, the polyamide microfiber two-dimensional membrane obtained by the reactive melt-blowing technology of the present invention has higher fiber melting temperature and product melting crystallization temperature, as well as higher crystallinity. This indicates that the polyamide microfiber two-dimensional membrane obtained by the reactive melt-blowing technology has superior thermal properties and a higher level of crystallinity when it is mass-produced.

[0105] Experiment 5

[0106] In the process of preparing polyamide microfiber two-dimensional membranes using reactive meltblown technology in Examples 1 to 5 of this invention, the continuous spinning time was statistically analyzed and the yield was calculated. The continuous spinning time of a thermoplastic polyamide microfiber nonwoven two-dimensional membrane (control sample) obtained by Chinese Patent CN113279149A described in the background art was statistically analyzed and the yield was calculated. The results are listed in Table 2.

[0107] As shown in Table 2, the method for preparing polyamide microfiber two-dimensional membranes using reactive meltblown technology of the present invention, under the conditions of the above embodiments, achieves a yield of 5-15 kg / h, realizing continuous spinning without interruption during the spinning process. This method allows for continuous operation without interruption when raw materials are continuously supplied; for example, it can run continuously for a whole day without interruption. Of course, in large-scale production, a single start-up can allow for longer continuous operation until the equipment requires maintenance or repair. The yield of polyamide microfiber two-dimensional membranes obtained by this method is 5-500 kg / h. At low yields, one die head is sufficient; at high yields, a large reactive screw extruder with multiple dies is required. However, the continuous spinning time of the control sample was only 30 minutes, which could not achieve large-scale production, and the yield was only 0.004-0.008 kg / h, which limited its application.

[0108] Table 2 Statistical Table of Different Spinning Processes

[0109] spinning process Continuous spinning time Yield (Kg / h) Example 1 Continuous 15 Example 2 Continuous 7 Example 3 Continuous 5 Example 4 Continuous 7 Example 5 Continuous 5 control sample 30min 0.004-0.008

[0110] Therefore, compared with the prior art, the beneficial effects of the present invention are as follows: The present invention uses low-viscosity caprolactam monomer as the starting material, and realizes the mixing, polymerization and melt extrusion of the raw material formulation in a reactive screw extrusion device. The extruded melt is spun, stretched and web-laid by a melt-blowing device, and polyamide ultrafine fiber two-dimensional membranes are continuously obtained from monomers in one step. This effectively reduces the spinning process temperature of polyamide melt, realizes the linkage processing of polyamide ultrafine fiber two-dimensional membranes, has a short process flow, high degree of automation, smooth reaction, no wall sticking effect, and avoids long-term retention of the reaction melt. By controlling the conversion rate of the caprolactam anionic ring-opening polymerization reaction system, the viscosity of the melt is controlled, so that the viscosity of the extruded melt always meets the spinning requirements of the melt-blowing device, thereby realizing the continuous preparation of polyamide ultrafine fiber two-dimensional membranes, avoiding the phenomenon of spinning interruption due to clogging caused by excessive polymerization, and achieving high output, meeting the requirements of large-scale production. The chemical composition of this polyamide microfiber two-dimensional membrane is polycaprolactam (nylon 6), which is composed of smooth solid columnar fibers with a fiber diameter ranging from 800 nm to 25 μm. The fibers are laid out in a random distribution and have the excellent mechanical and engineering properties of nylon 6. The fiber diameter and micropore size are controllable. It is used to prepare nonwoven fabrics and is widely used in industrial filtration, medical dressings, hygiene protection and precision instrument packaging.

[0111] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing polyamide microfiber two-dimensional films using reactive meltblown technology, characterized in that, Includes the following steps: 1) Take caprolactam monomer, add catalyst, the amount of catalyst is 0.1-10% of the molar amount of caprolactam monomer, melt, stir, and obtain reaction mixture; 2) The reaction mixture obtained in step 1) is fed to the feed port of the reactive screw extruder through a liquid metering device. The flow rate of the reaction mixture in the liquid metering device is 10-500 L / h, the screw speed of the reactive screw extruder is 10-500 r / min, and the screw temperature is 90-280 ℃. The feed conveying section is 90-200 ℃, the reaction section is 200-280 ℃, and the compression extrusion section is 200-280 ℃, so that the reaction mixture continues to polymerize to obtain a melt. The obtained melt is continuously extruded. The viscosity of the melt is controlled by controlling the conversion rate of the caprolactam anionic ring-opening polymerization reaction system. The relative viscosity of the melt is 1.4-3.0, the intrinsic viscosity is 35-135 mL / g, and the viscosity-average molecular weight is 9800-46200 g / mol. 3) The melt extruded in step 2) is first filtered and then transported to the die head of the meltblown device by a metering pump. The metering pump speed is 10-500 r / min, and the metering pump temperature is 150-300 ℃. Under the action of the hot air flow of the meltblown device, the filaments are spun, with a filament orifice diameter of 0.1-0.5 mm, stretched, cured, and fiberized. The die head temperature is 150-300 ℃, the hot air flow temperature is 150-300 ℃, and the hot air flow rate is 10-50 m³ / min. 3 The flow rate is 500-5000 Pa, and the fiber web is randomly laid and aggregated under the suction of the receiving device. The pressure of the suction is 500-5000 Pa, resulting in a polyamide ultrafine fiber two-dimensional membrane.

2. The method for preparing polyamide ultrafine fiber two-dimensional membranes using reactive meltblown technology according to claim 1, characterized in that: In step 1), an initiator is also added, and the amount of the initiator is 0.1-10% of the molar amount of caprolactam monomer.

3. The method for preparing polyamide ultrafine fiber two-dimensional membranes using reactive meltblown technology according to claim 2, characterized in that: The initiator is any one of TDI, MDI, NDI, PPDI, IPDI, HMDI, XDI, HDI, LDI, TODI, TTI, TPTI, EI, and tBI.

4. The method for preparing polyamide ultrafine fiber two-dimensional membranes using reactive meltblown technology according to claim 1, characterized in that: In step 2), the screw temperature is 90-200 ℃, of which the feeding and conveying section is 90-140 ℃, the reaction section is 140-200 ℃, and the compression and extrusion section is 140-200 ℃.

5. The method for preparing polyamide ultrafine fiber two-dimensional membranes using reactive meltblowing technology according to any one of claims 1-4, characterized in that: The catalyst is any one of sodium hydride, potassium hydride, lithium hydride, sodium hydroxide, potassium hydroxide, and lithium hydroxide.

6. A polyamide microfiber two-dimensional membrane, characterized in that: The polyamide microfiber two-dimensional membrane is prepared by the method for preparing polyamide microfiber two-dimensional membrane using reactive meltblown technology according to any one of claims 1-5.

7. The polyamide microfiber two-dimensional membrane according to claim 6, characterized in that: The polyamide microfiber two-dimensional membrane further includes any one or more of the following: filler, inert filler, and non-reactive functional components that do not participate in the anionic polymerization reaction in step 2). The total amount of the filler, inert filler, and non-reactive functional components that do not participate in the anionic polymerization reaction in step 2) shall not exceed 10% of the total weight of the polyamide microfiber two-dimensional membrane.

8. The polyamide microfiber two-dimensional membrane according to claim 7, characterized in that: The filler is any one or more of plasticizers, antioxidants, anti-aging agents, and toughening agents, and the inert filler is any one or two of talc powder and quartz sand.

9. The application of a polyamide microfiber two-dimensional membrane according to any one of claims 6-8 in the preparation of nonwoven fabrics.

10. The application of the polyamide microfiber two-dimensional membrane according to claim 9 in the preparation of nonwoven fabrics, characterized in that: The polyamide microfiber two-dimensional film is fed to a hot rolling mill. The temperature of the hot rolling rolls is 100-200 ℃ and the pressure of the hot rolling rolls is 50-100 N / mm. The polyamide microfiber two-dimensional film is solidified and shaped under the high temperature and high pressure of the rolls. It is then collected into rolls by a winding machine at a winding speed of 10-100 m / min to obtain a nonwoven fabric.

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