A method of flash spinning above the cloud point pressure

Abstract

The application designs a method for flash spinning above the cloud point pressure, comprising the following steps: step S1, polymer melt and organic solvent are respectively extruded into polymer melt flow channel and solvent flow channel; step S2, the polymer melt and organic solvent are in contact and diffuse with each other in a laminar flow mode in a diffusion function area; step S3, the polymer melt and organic solvent flowing out of the diffusion function area are further dispersed and mixed in a non-shearing and gentle mode in a mixing function area, forming a two-phase dispersion with polymer-rich phase and solvent-rich phase inside; step S4, the two-phase dispersion is extruded through a spinneret above the cloud point pressure of the homogeneous solution before the two-phase dispersion reaches diffusion equilibrium, and flash spinning is completed. The heterogeneous solution system prepared in the application avoids strong mechanical shearing and stirring process, and the flash spinning is completed by extruding the solution from the spinneret at high pressure, forming a uniform, small-diameter, high-strength and easily controlled production speed flash non-woven fabric web.

Description

Technical Field

[0001] This invention belongs to the field of nonwoven fabric preparation, specifically relating to a method for flash spinning at a pressure above the cloud point. Background Technology

[0002] Flash spinning, also known as instantaneous solvent evaporation web formation or instantaneous pressure-relief spinning, is characterized by the rapid formation of fibers from polymers during solvent flash evaporation. Chinese patent CN217628742U discloses a functional spinneret for flash spinning, comprising a solution supply block, a combined pressure-reducing chamber, and a spinneret assembly arranged sequentially. The solution supply block has an inlet port. The combined pressure-reducing chamber includes at least two sections, each containing a solution channel. The spinneret assembly includes a spinneret block with an outlet port. The inlet port communicates with the solution channel via a pressure-reducing port, and the solution channel communicates with the outlet port via a spinneret orifice. The inner diameters of the pressure-reducing port and the spinneret orifice are smaller than the inner diameters of the inlet port and the outlet port, respectively. For example, Chinese patent CN113005543A discloses a method for preparing polymer-based filament films-fiber tapes, which specifically includes the following steps: Step 1, generating a spinning solution, wherein the spinning solution contains 5 wt.% to 30 wt.% of one or more polymer types of spinning solution, a main spinning agent selected from the group consisting of dichloromethane, cis-1,2-dichloroethylene and trans-1,2-dichloroethylene, and a co-spinning agent containing 1H,6H-perfluorohexane, 1H-perfluoroheptane or 1H-perfluorohexane; Step 2, flashing the spinning solution under a pressure greater than the autogenous pressure of the spinning solution. The polymer is spun into a lower pressure region to form a filament film-fiber tape; however, the design method needs to meet the following conditions: first, the solvent is non-solvent for the polymer below the temperature and pressure corresponding to its boiling point; second, a homogeneous solution is formed with the polymer under high temperature and high pressure; third, when the solution pressure is appropriately reduced to a certain pressure in the depressurization chamber, a certain degree of phase separation occurs, forming a two-phase dispersion with one phase being rich in polymer and the other phase being rich in solvent, this pressure is called the cloud point pressure; fourth, when the two-phase dispersion is released into a lower pressure region through the spinneret, the solvent is rapidly flash vaporized.

[0003] The basic process of flash spinning involves heating and pressurizing the polymer and solvent together in an autoclave for several hours with stirring to ensure complete dissolution and form a homogeneous spinning solution. Under pressure, the solution enters a depressurization chamber, where phase separation occurs due to the pressure dropping below the cloud point. The solution is then extruded through spinnerets and solidified into highly oriented, mesh-like ultrafine fibers. The solution undergoes a process from a heterogeneous mixture to a homogeneous solution, and then back to a heterogeneous dispersion. When the solution is extruded from the spinnerets, the sudden release of pressure causes the solvent to rapidly vaporize, creating a supersonic gas flow that stretches the polymer at high speed. Simultaneously, the solvent vaporization absorbs a large amount of heat, causing the polymer to rapidly cool and crystallize, solidifying into fibers. The fiber bundle passes through a high-speed rotating deflector and is then charged by corona discharge to open the fibers, forming a uniform, sheet-like fiber web. The fiber web is then adsorbed onto a screen and pressed into shape by rollers to obtain a high-strength flash-spun nonwoven fabric. The key to preparing high-performance flash-spun nonwoven fabrics is utilizing a depressurization chamber to reduce the solution pressure below the cloud point, causing phase separation. If a polymer solution in a homogeneous state above the cloud point pressure is extruded from the nozzle, the fiber diameter will be coarse and the fibers will easily stick together, making it difficult to form uniform, fine, and high-strength flash fibers.

[0004] Existing flash spinning processes have the following drawbacks: 1. Preparing a homogeneous solution using a high-pressure stirred tank is inefficient and time-consuming, typically requiring several hours to obtain a uniform polymer solution that meets the requirements of flash spinning. The larger the polymer molecular weight and the lower the melt index, the more difficult it is to obtain a homogeneous solution, and the longer the stirring and mixing time. 2. Using a depressurization chamber to reduce the spinning solution pressure below the cloud point pressure for flash spinning is beneficial for producing finer flash fibers; however, the phase structure of a two-phase dispersion is unstable, and the interfacial tension between the two phases causes a rapid increase in phase size (coarsening), leading to increased fiber diameter and decreased strength. Since the rate of phase coarsening is sensitive to pressure and temperature fluctuations, nozzle temperature and pressure must be strictly controlled, thus increasing the complexity of the equipment and its control system. 3. The depressurization chamber results in lower solution pressure during flash spinning, leading to a lower jetting speed, which is detrimental to improving fiber mechanical properties and reducing diameter. 4. Intensifying mechanical stirring and shearing is a common method to improve polymer solution preparation efficiency; however, under strong shear and stirring conditions, polymers are prone to degradation, and a decrease in molecular weight leads to a decline in mechanical properties. Summary of the Invention

[0005] Based on the traditional method of first preparing a homogeneous polymer solution by mechanical stirring under high temperature and high pressure, and then reducing the solution pressure below the cloud point pressure to cause a certain degree of phase separation before flash spinning, this application designs a method for flash spinning above the cloud point pressure. This aims to eliminate the strong mechanical shearing and stirring steps, maintain the heterogeneous state of the polymer solution, and ultimately achieve the technical effect of forming a uniform, small-diameter, high-strength flash nonwoven fiber web with easily controllable production speed.

[0006] A method for flash spinning at a pressure above the cloud point includes the following steps:

[0007] Step S1: The polymer melt and organic solvent are extruded into the polymer melt channel and solvent channel, respectively;

[0008] Step S2: The polymer melt and the organic solvent come into contact with and diffuse into each other in a laminar flow manner in the diffusion functional region;

[0009] Step S3: The polymer melt and organic solvent flowing out from the diffusion functional zone are further dispersed and mixed in the mixing functional zone in a non-shear, gentle manner to form a two-phase dispersion with a polymer-rich phase and a solvent-rich phase inside.

[0010] Step S4: Before the two-phase dispersion reaches diffusion equilibrium, the filaments are extruded through the spinneret above the turbidity point pressure of the homogeneous solution to complete flash spinning.

[0011] Preferably, the polymer melt is one or more of the following polyesters: polyethylene, polypropylene, polybutene, polymethylpentene, polyvinylidene fluoride, ethylene-tetrafluoroethylene copolymer, PET, or polylactic acid.

[0012] Preferably, the organic solvent may be one or more of toluene, benzene, n-hexane, butane, pentene, heptane, octane, cyclohexane, dichloromethane, carbon tetrachloride, chloroform, chloromethane, chloroethane, dichloroethylene, trichlorofluoromethane, dichlorotrifluoroethane, other Freons, pentafluoropropane, heptafluoropropane, 1H-perfluorohexane, 6H-perfluorohexane, 1H-perfluoroheptane, 1H-perfluorohexane, octafluorocyclopentane, and alcohol solvents; nitrogen or carbon dioxide gas may be mixed in the organic solvent.

[0013] Preferably, the device used in the method is a spinneret structure, which includes a polymer melt flow channel, a solvent flow channel, a diffusion functional zone, a mixing functional zone, and a spinneret orifice;

[0014] The outlet of the polymer melt flow channel and the outlet of the solvent flow channel are respectively connected to the inlet of the diffusion functional zone;

[0015] The outlet of the diffusion functional area is connected to the inlet of the mixing functional area;

[0016] The outlet of the mixed functional area is connected to the spinneret hole.

[0017] Preferably, the cross-sectional dimensions of the polymer melt channel, solvent channel, diffusion functional zone, mixing functional zone, and spinneret orifice are 0.5–30 mm.

[0018] Preferably, the cross-sectional dimension of the mixed functional area is less than 5 mm;

[0019] The mixed functional area adopts a curved flow channel design, including groove-shaped, serpentine, broken line, curved, arc-shaped, spiral and Tesla flow channels, and no obstacles are placed in the flow channel.

[0020] Preferably, the cross-sectional dimension of the mixed functional area is greater than 5 mm;

[0021] The mixing functional area is a straight flow channel; obstacles or grooves are provided in the straight flow channel of the mixing functional area to promote mixing.

[0022] Preferably, the diffusion functional area is a straight flow channel;

[0023] The ratio of the length of the diffusion functional zone to its cross-sectional dimension is 10 to 5000:1.

[0024] Preferably, the ratio of the length to the cross-sectional dimension of the mixed functional area is 100-5000:1.

[0025] Preferably, the cross-sectional dimensions of the polymer melt channel, solvent channel, diffusion functional zone, mixing functional zone, and spinneret orifice are 1-10 mm.

[0026] The advantages and effects of this application are as follows:

[0027] 1. The spinneret structure designed in this application includes a polymer melt flow channel, a solvent flow channel, a diffusion functional zone, a mixing functional zone, and a spinneret orifice; wherein the polymer melt and organic solvent are continuously and gently mixed and dispersed through the spinneret structure at cloud point pressure, so that the polymer melt and organic solvent mixture solution is always kept as a heterogeneous solution system containing both polymer-rich and solvent-rich phases, avoiding strong mechanical shearing and stirring processes, and then extruded under high pressure from the spinneret orifice to complete flash spinning, forming a uniform, small-diameter, high-strength flash nonwoven fiber web with easily controllable production speed.

[0028] 2. The flow channel of the mixing functional area designed in this application adopts a straight flow channel when the cross-sectional size of the flow channel is greater than 5mm. At the same time, several obstacles and grooves are set in the flow channel to cause repeated flow splitting, displacement and merging of the fluid, and generate additional fluid disturbance or vortex to improve mixing efficiency. The obstacles or grooves have a cross-sectional shape of square, rectangle, rhombus or circle. When the cross-sectional size of the flow channel of the mixing functional area is less than 5mm, a curved flow channel is adopted, including groove-shaped, serpentine, broken line, curved, arc, spiral and Tesla flow channels, etc. Obstacles may not be set in the flow channel. The vortex formed by the velocity difference on both sides when the fluid passes through the curved flow channel promotes dispersion and mixing.

[0029] 3. The spinneret structure designed in this application does not require the use of a decompression chamber to regulate the pressure of the solution, thus reducing the complexity of the equipment and its pressure control system; it also significantly increases the pressure at the spinneret orifice during flash spinning, which is beneficial to the stretching orientation and performance improvement of the fiber; it significantly simplifies the mixing process of polymer melt and solvent in flash spinning, solves the problem of low efficiency and long time required for intermittent preparation of homogeneous solution using a high-pressure stirred tank, makes it easy to achieve continuous flash spinning process, and is suitable for flash spinning of polymers with high molecular weight;

[0030] 4. The present application proposes a method for flash spinning above the cloud point pressure, in which polymer melt and solvent are extruded into the spinneret structure in the form of a thin stream at high temperature and above the cloud point pressure. The two come into contact with each other and diffuse into each other in a laminar flow manner to form a mixed solution with a concentration gradient. Then, they are further dispersed and mixed in a non-shear and gentle manner to form a heterogeneous mixed solution with a polymer-rich phase and a solvent-rich phase inside, thus avoiding the degradation effect of mechanical stirring and shearing on the polymer.

[0031] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the preferred embodiments of this application are described in detail below with reference to the accompanying drawings.

[0032] The above and other objects, advantages and features of this application will become more apparent to those skilled in the art from the following detailed description of specific embodiments in conjunction with the accompanying drawings. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. In all drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn to scale.

[0034] Figure 1 A flowchart of a method for flash spinning above cloud point pressure provided in this application;

[0035] Figure 2 A schematic diagram of the internal flow channel of the first type of spinneret provided in this application;

[0036] Figure 3 A diagram of the mixed solution in the internal flow channel of the first type of spinneret provided in this application;

[0037] Figure 4 A schematic diagram of the internal flow channel of the second type of spinneret provided in this application;

[0038] Figure 5 A schematic diagram of the internal flow channel of the third type of spinneret provided in this application;

[0039] Figure 6 A schematic diagram of the internal flow channel of the fourth type of spinneret provided in this application;

[0040] Figure 7 A schematic diagram of the internal flow channel of the spinneret without a mixing zone provided in this application;

[0041] Figure 8 A schematic diagram of the internal flow channel of the apparatus for homogeneous solution flash spinning provided in Comparative Example 2 of this application;

[0042] Figure 9 A schematic diagram of the internal flow channel of the spinneret with a decompression chamber provided for this application;

[0043] Reference numerals: 1. Polymer melt flow channel; 2. Solvent flow channel; 3. Diffusion functional zone; 4. Mixing functional zone; 5. Spinneret orifice; 6. Polymer melt; 7. Organic solvent; 8. Pressure relief chamber; 9. Pressure measuring orifice. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. In the following description, specific details such as specific configurations and components are provided merely to help fully understand the embodiments of this application. Therefore, those skilled in the art should understand that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of this application. In addition, for clarity and brevity, descriptions of known functions and structures are omitted in the embodiments.

[0045] It should be understood that the phrase "an embodiment" or "this embodiment" throughout the specification means that a specific feature, structure, or characteristic related to the embodiment is included in at least one embodiment of this application. Therefore, "an embodiment" or "this embodiment" appearing throughout the specification does not necessarily refer to the same embodiment. Furthermore, these specific features, structures, or characteristics can be combined in any suitable manner in one or more embodiments.

[0046] Furthermore, reference numerals and / or letters may be repeated in different examples within this application. Such repetition is for the purpose of simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or settings discussed.

[0047] In this article, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can mean: A exists alone, B exists alone, and A and B exist simultaneously. The term " / and" in this article describes another type of relationship between related objects, indicating that two relationships can exist. For example, A / and B can mean: A exists alone, and A and B exist alone. In addition, the character " / " in this article generally indicates that the related objects before and after it are in an "or" relationship.

[0048] In this article, the term "at least one" is merely a description of the relationship between related objects, indicating that there can be three relationships. For example, "at least one of A and B" can mean: A exists alone, A and B exist simultaneously, or B exists alone.

[0049] It should also be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion.

[0050] Example 1

[0051] This embodiment mainly introduces a first design of a flash spinning method above the cloud point pressure, including the following steps:

[0052] Step S1: High-density polyethylene melt and solvent n-hexane are extruded into polymer melt channel 1 and solvent channel 2 at 160 degrees Celsius and 20 MPa, respectively.

[0053] Step S2: Next, the polyethylene melt and solvent n-hexane are pushed into a diffusion functional zone with a width and depth of 5 mm and a length of 360 mm.

[0054] Furthermore, since polyethylene and solvent are miscible at this temperature and pressure, molecular diffusion occurs at the interface of the two fluids, forming a liquid flow with a high polyethylene concentration in the core layer and a high solvent concentration around the perimeter.

[0055] Step S3: The liquid flow that has passed through the diffusion functional zone is passed through the mixing functional zone with a length of 180mm. Due to the repeated diversion, movement and merging of the square columnar obstacle, the solution is further dispersed and mixed. Finally, it is ejected from the flow channel outlet, i.e. the spinneret hole, to form flash fiber bundles. After the fibers are opened, they are deposited on the mesh belt to obtain a fiber web, which is then hot-rolled with rollers to form a nonwoven fabric.

[0056] Please refer to the following for specific effects. Figure 3 ,from Figure 3 It can be clearly seen that the polymer melt and organic solvent are continuously and gently mixed and dispersed through the spinneret structure at the cloud point pressure, so that the polymer melt and organic solvent mixture solution always remains a heterogeneous solution system containing both polymer-rich and solvent-rich phases.

[0057] For the specific design of the spinneret used in the first method, please refer to [reference needed]. Figure 2 , Figure 2 This application provides a schematic diagram of the internal flow channel structure of a first type of spinneret; specifically including a polymer melt flow channel 1, a solvent flow channel 2, a diffusion functional zone 3, a mixing functional zone 4, and a spinneret orifice 5; characterized in that,

[0058] The outlet of the polymer melt channel 1 and the outlet of the solvent channel 2 are respectively connected to the inlet of the diffusion functional region 3.

[0059] The outlet of the diffusion functional zone 3 is connected to the inlet of the mixing functional zone 4;

[0060] The outlet of the mixed functional area 4 is connected to the spinneret 5.

[0061] Furthermore, the cross-sectional dimensions of the polymer melt channel 1, solvent channel 2, diffusion functional zone 3, mixing functional zone 4, and spinneret orifice 5 are 0.5–30 mm.

[0062] Furthermore, the cross-sectional dimension of the hybrid functional area 4 is greater than 5 mm;

[0063] The mixed functional area 4 is a straight flow channel.

[0064] Furthermore, obstacles or grooves are provided in the flow channels of the mixing functional area 4 to promote mixing.

[0065] Furthermore, the cross-sectional dimensions of the polymer melt channel 1, solvent channel 2, diffusion functional zone 3, mixing functional zone 4, and spinneret orifice 5 are 1-10 mm.

[0066] Furthermore, the diffusion functional region 3 is a straight flow channel;

[0067] The ratio of the length to the cross-sectional dimension of the diffusion functional region 3 is 100-2000:1.

[0068] Furthermore, the ratio of the length to the cross-sectional dimension of the mixed functional area 4 is 100-2000:1.

[0069] The flow channel of the mixed functional area designed in this application adopts a straight flow channel when the cross-sectional size of the flow channel is greater than 5mm. At the same time, several obstacles and grooves are set in the flow channel to make the fluid repeatedly split, displace and merge, and generate additional fluid disturbance or eddies to improve the mixing efficiency. The obstacles or grooves are square, rectangular, rhomboid or circular in shape.

[0070] Example 2

[0071] Based on the above embodiment 1, this embodiment mainly introduces a second design of a flash spinning method above the cloud point pressure, including the following steps:

[0072] Step S1: Heat the solvent trichlorofluoromethane and the high-density polyethylene melt to 220 degrees Celsius;

[0073] Step S2: The polymer melt flow channel 1 and solvent flow channel 2 are respectively injected into the polymer melt flow channel 1 and solvent flow channel 2 at a pressure of 16MPa using a constant flow pump;

[0074] In step S3, the polyethylene melt and solvent then enter a diffusion functional zone with a width of 20 mm, a depth of 0.5 mm, and a length of 120 mm.

[0075] Step S4: Then, through a mixed functional area with a length of 240mm;

[0076] Furthermore, due to the turbulent effect of the 0.5mm deep groove on the fluid, the solution is further dispersed and mixed, and finally ejected from the spinneret to form flash fiber bundles. After the fibers are opened, they are deposited on the mesh belt to obtain a fiber web, which is then hot-rolled into nonwoven fabric.

[0077] For the specific design of the spinneret used in the second method, please refer to [reference needed]. Figure 4 , Figure 4 This application provides a schematic diagram of the internal flow channel structure of a second type of spinneret; specifically, it includes a polymer melt flow channel 1, a solvent flow channel 2, a diffusion functional zone 3, a mixing functional zone 4, and a spinneret orifice 5; characterized in that,

[0078] The outlet of the polymer melt channel 1 and the outlet of the solvent channel 2 are respectively connected to the inlet of the diffusion functional region 3.

[0079] The outlet of the diffusion functional zone 3 is connected to the inlet of the mixing functional zone 4;

[0080] The outlet of the mixed functional area 4 is connected to the spinneret 5.

[0081] Furthermore, the cross-sectional dimensions of the polymer melt channel 1, solvent channel 2, diffusion functional zone 3, mixing functional zone 4, and spinneret orifice 5 are 0.5–30 mm.

[0082] Furthermore, the cross-sectional dimension of the hybrid functional area 4 is less than 5 mm;

[0083] The mixed functional area 4 adopts a curved groove-shaped flow channel design, and no obstacles are placed in the flow channel.

[0084] Furthermore, the cross-sectional dimensions of the polymer melt channel 1, solvent channel 2, diffusion functional zone 3, mixing functional zone 4, and spinneret orifice 5 are 1-10 mm.

[0085] Furthermore, the diffusion functional region 3 is a straight flow channel;

[0086] The ratio of the length to the cross-sectional dimension of the diffusion functional region 3 is 100-2000:1.

[0087] Furthermore, the ratio of the length to the cross-sectional dimension of the mixed functional area 4 is 100-2000:1.

[0088] When the cross-sectional dimension of the flow channel in the mixed functional area of ​​this application is less than 5mm, a curved groove-shaped flow channel design is adopted. No obstacles are placed in the flow channel. The vortex formed by the velocity difference on both sides when the fluid passes through the curved flow channel promotes dispersion and mixing.

[0089] Example 3

[0090] Based on the above embodiment 1, this embodiment mainly introduces a third design of a flash spinning method above the cloud point pressure, including the following steps:

[0091] Step S1: Heat the high-density polyethylene melt and solvent dichloromethane to 180 degrees Celsius;

[0092] Step S2: Extrude the polymer melt into channel 1 and solvent channel 2 at a pressure of 18 MPa respectively;

[0093] Step S3: Then enter the diffusion functional area with a width of 1mm, a depth of 20mm, and a length of 120mm;

[0094] Step S4: Then, the fibers pass through a serpentine mixing functional zone with a length of 360mm and are finally ejected from the spinneret to form flash fiber bundles. After fiber opening, the fibers are deposited on the mesh belt to obtain a fiber web, which is then hot-rolled into nonwoven fabric.

[0095] For the specific design of the spinneret used in the third method, please refer to [reference needed]. Figure 5 , Figure 5 This application provides a schematic diagram of the internal flow channel structure of a third type of spinneret; specifically, it includes a polymer melt flow channel 1, a solvent flow channel 2, a diffusion functional zone 3, a mixing functional zone 4, and a spinneret orifice 5; the outlet of the polymer melt flow channel 1 and the outlet of the solvent flow channel 2 are respectively connected to the inlet of the diffusion functional zone 3;

[0096] The outlet of the diffusion functional zone 3 is connected to the inlet of the mixing functional zone 4;

[0097] The outlet of the mixed functional area 4 is connected to the spinneret 5.

[0098] Furthermore, the cross-sectional dimensions of the polymer melt channel 1, solvent channel 2, diffusion functional zone 3, mixing functional zone 4, and spinneret orifice 5 are 0.5–30 mm.

[0099] Furthermore, the cross-sectional dimension of the hybrid functional area 4 is less than 5 mm;

[0100] The hybrid functional area 4 adopts a curved serpentine flow channel design; no obstacles are placed in the flow channel.

[0101] Furthermore, the cross-sectional dimensions of the polymer melt channel 1, solvent channel 2, diffusion functional zone 3, mixing functional zone 4, and spinneret orifice 5 are 1-10 mm.

[0102] Furthermore, the diffusion functional region 3 is a straight flow channel;

[0103] The ratio of the length to the cross-sectional dimension of the diffusion functional region 3 is 100-2000:1.

[0104] Furthermore, the ratio of the length to the cross-sectional dimension of the mixed functional area 4 is 100-2000:1.

[0105] When the cross-sectional dimension of the flow channel in the mixed functional area of ​​this application is less than 5mm, a curved serpentine flow channel design is adopted. No obstacles are placed in the flow channel. The vortex formed by the velocity difference on both sides when the fluid passes through the curved flow channel promotes dispersion and mixing.

[0106] Example 4

[0107] Based on the above embodiment 1, this embodiment mainly introduces 1. A fourth design of a flash spinning method above the cloud point pressure, including the following steps:

[0108] Step S1: Heat the high-density polypropylene melt and the solvent dichloromethane to 200 degrees Celsius;

[0109] Step S2: Extrude the polymer melt into the polymer melt channel 1 and the solvent channel 2 at a pressure of 12 MPa, respectively;

[0110] Step S3: Then enter the diffusion functional area with a width of 2mm, a depth of 1mm, and a length of 60mm;

[0111] Step S4: Then, the fibers are mixed through a curved flow channel with a length of 240 mm and finally ejected from the spinneret to form flash fiber bundles. After opening, the fibers are deposited on the mesh belt to obtain a fiber web, which is then hot-rolled into a nonwoven fabric.

[0112] For the specific design of the spinneret used in the fourth method, please refer to [reference needed]. Figure 6 , Figure 6 This application provides a schematic diagram of the internal flow channel structure of a fourth type of spinneret; specifically including a polymer melt flow channel 1, a solvent flow channel 2, a diffusion functional zone 3, a mixing functional zone 4, and a spinneret orifice 5; characterized in that,

[0113] The outlet of the polymer melt channel 1 and the outlet of the solvent channel 2 are respectively connected to the inlet of the diffusion functional region 3.

[0114] The outlet of the diffusion functional zone 3 is connected to the inlet of the mixing functional zone 4;

[0115] The outlet of the mixed functional area 4 is connected to the spinneret 5.

[0116] Furthermore, the cross-sectional dimensions of the polymer melt channel 1, solvent channel 2, diffusion functional zone 3, mixing functional zone 4, and spinneret orifice 5 are 0.5–30 mm.

[0117] Furthermore, the cross-sectional dimension of the hybrid functional area 4 is less than 5 mm;

[0118] The mixed functional area 4 adopts a curved flow channel design, and no obstacles are placed in the flow channel.

[0119] Furthermore, the cross-sectional dimensions of the polymer melt channel 1, solvent channel 2, diffusion functional zone 3, mixing functional zone 4, and spinneret orifice 5 are 1-10 mm.

[0120] Furthermore, the diffusion functional region 3 is a straight flow channel;

[0121] The ratio of the length to the cross-sectional dimension of the diffusion functional region 3 is 100-2000:1.

[0122] Furthermore, the ratio of the length to the cross-sectional dimension of the mixed functional area 4 is 100-2000:1.

[0123] When the cross-sectional dimension of the flow channel in the mixed functional area of ​​this application is less than 5mm, a curved flow channel design is adopted. No obstacles are placed in the flow channel. The vortex formed by the velocity difference on both sides when the fluid passes through the curved flow channel promotes dispersion and mixing.

[0124] Example 5

[0125] Based on the above embodiments 1-4, this embodiment mainly introduces a method for flash spinning at a pressure above the cloud point. Please refer to the following for details. Figure 1 This includes the following steps:

[0126] Step S1: The polymer melt 6 and organic solvent 7 are extruded into the polymer melt channel 1 and solvent channel 2, respectively;

[0127] Step S2: The polymer melt 6 and the organic solvent 7 contact and diffuse with each other in a laminar flow manner in the diffusion functional region 3;

[0128] Step S3: The polymer melt 6 and organic solvent 7 flowing out from the diffusion functional zone 3 are further dispersed and mixed in the mixing functional zone 4 in a non-shear, gentle manner to form a two-phase dispersion with a polymer-rich phase and a solvent-rich phase inside.

[0129] Step S4: Before the two-phase dispersion reaches diffusion equilibrium, the spinneret is extruded above the turbidity point pressure to complete flash spinning.

[0130] Furthermore, the pressure inside the flow channel is maintained above the cloud point pressure of the polymer solution. The filaments are driven by the high-pressure airflow and pass through a high-speed rotating steering wheel. After being corona charged, they are opened and deposited on the mesh belt to form a uniform fiber web. Finally, they are hot rolled by a pair of rollers to form a uniform nonwoven fabric.

[0131] Furthermore, the flow channel system of the spinneret assembly is formed on the surface of a flat metal material such as carbon steel, stainless steel, or titanium alloy by engraving or CNC milling, or by cutting a thin metal plate of a certain thickness, and then encapsulating it with a metal plate of the same material and sealing it with high-strength bolts.

[0132] Furthermore, the polymer melt 6 is one or more of the following polyesters: polyethylene, polypropylene, polybutene, polymethylpentene, polyvinylidene fluoride, ethylene-tetrafluoroethylene copolymer, PET, or polylactic acid.

[0133] Furthermore, the organic solvent 7 can be one or more of toluene, benzene, n-hexane, butane, pentene, heptane, octane, cyclohexane, dichloromethane, carbon tetrachloride, chloroform, chloromethane, chloroethane, dichloroethylene, trichlorofluoromethane, dichlorotrifluoroethane, other Freons, pentafluoropropane, heptafluoropropane, 1H-perfluorohexane, 6H-perfluorohexane, 1H-perfluoroheptane, 1H-perfluorohexane, octafluorocyclopentane, and alcohol solvents; nitrogen or carbon dioxide gas can be mixed in the organic solvent.

[0134] Furthermore, the device used in the method is a spinneret structure, which includes a polymer melt flow channel 1, a solvent flow channel 2, a diffusion functional zone 3, a mixing functional zone 4, and a spinneret orifice 5.

[0135] The outlet of the polymer melt channel 1 and the outlet of the solvent channel 2 are respectively connected to the inlet of the diffusion functional region 3.

[0136] The outlet of the diffusion functional zone 3 is connected to the inlet of the mixing functional zone 4;

[0137] The outlet of the mixed functional area 4 is connected to the spinneret 5.

[0138] Furthermore, the cross-sectional dimensions of the polymer melt channel 1, solvent channel 2, diffusion functional region 3, mixing functional region 4, and spinneret 5 are 0.5–30 mm. If the tens of micrometers of channels commonly used in microfluidic chip mixing technology are large, it will lead to extremely large flow resistance and pressure drop, which is not suitable for mixing polymer melt and solvent. On the other hand, excessively large channels will result in excessively large polymer melt and solvent fine stream sizes, which is not conducive to mutual diffusion.

[0139] Furthermore, the cross-sectional dimension of the hybrid functional area 4 is less than 5 mm;

[0140] The mixed functional area 4 adopts a curved flow channel design, including groove-shaped, serpentine, broken line, curved, arc-shaped, spiral and Tesla flow channels, and no obstacles are set in the flow channel.

[0141] Furthermore, the cross-sectional dimension of the mixing functional zone 4 is greater than 5 mm; the function of the diffusion functional zone is to enable the polymer melt and solvent to achieve preliminary mixing through molecular diffusion in a laminar flow state. Since the viscosity difference between the polymer melt and the solvent is more than four orders of magnitude, it is difficult to obtain an ideal dispersion effect if the polymer melt and solvent are directly squeezed into the mixing functional zone for mixing without passing through the diffusion functional zone.

[0142] The mixing functional area 4 is a straight flow channel; obstacles or grooves are provided in the straight flow channel of the mixing functional area 4 to promote mixing.

[0143] Furthermore, the diffusion functional region 3 is a straight flow channel;

[0144] The length-to-section ratio of the diffusion functional region 3 is 10-5000:1; too small an aspect ratio is not conducive to diffusion between the polymer and the solvent, resulting in an excessively large solution concentration gradient; while too large an aspect ratio results in an excessively small solution concentration gradient, which is not conducive to the formation of a heterogeneous solution.

[0145] Furthermore, the ratio of the length to the cross-sectional dimension of the mixing functional zone 4 is 100-5000:1; if the aspect ratio of the mixing functional zone is too small, it will not be conducive to mixing and the solution concentration difference will be too large; while if the aspect ratio is too large, the solution concentration difference will be too small, or even a homogeneous solution will be formed, which will not be conducive to the formation of flash evaporation fibers.

[0146] Furthermore, the cross-sectional dimensions of the polymer melt channel 1, solvent channel 2, diffusion functional zone 3, mixing functional zone 4, and spinneret orifice 5 are 1-10 mm.

[0147] This application first involves extruding a polymer melt and solvent into the flow channel system of a spinneret assembly in a thin stream form at high temperature and above the cloud point pressure. The two react and diffuse with each other in a laminar flow manner to form a mixed solution with a concentration gradient. Then, the mixture is further dispersed and mixed in a non-shear, gentle manner to form a heterogeneous mixed solution containing both polymer-rich and solvent-rich phases. Before the above mixed solution reaches diffusion equilibrium, it is extruded through the spinneret orifice above the cloud point pressure to complete flash spinning. This application provides a method and spinneret structure for mixing a polymer and solvent to form a heterogeneous dispersion and performing flash spinning above the cloud point pressure of the homogeneous solution, replacing the traditional method of first preparing a homogeneous polymer solution under high temperature and high pressure by mechanical stirring, then reducing the solution pressure below the cloud point pressure to allow for a certain degree of phase separation before flash spinning.

[0148] In this application, the polymer melt and organic solvent are gently mixed and dispersed through a continuous flow channel system above the cloud point pressure, ensuring that the solution remains a heterogeneous solution system containing both polymer-rich and solvent-rich phases. This solution is then extruded under high pressure from a spinneret to complete flash spinning, forming a uniform, small-diameter, high-strength flash-spun nonwoven fiber web with easily controllable production speed. The phase structure changes of the solution during the flash spinning process are as follows: Figure 3 As shown. Unlike the phase change process of traditional flash spinning, the polymer solution in this application does not undergo strong mechanical shearing and stirring, and remains in a heterogeneous state; it does not undergo the process of first dissolving into a homogeneous solution under high temperature and high pressure and then obtaining a heterogeneous solution by decompression.

[0149] The spinneret structure designed in this application includes a polymer melt flow channel, a solvent flow channel, a diffusion functional zone, a mixing functional zone, and a spinneret orifice. The polymer melt and organic solvent are continuously and gently mixed and dispersed through the spinneret structure at cloud point pressure, so that the polymer melt and organic solvent mixture is always kept as a heterogeneous solution system containing both polymer-rich and solvent-rich phases, avoiding strong mechanical shearing and stirring processes. Then, it is extruded from the spinneret orifice under high pressure to complete flash spinning, forming a uniform, small-diameter, high-strength flash nonwoven fiber web with easily controllable production speed.

[0150] The flow channel of the mixing functional area designed in this application adopts a straight flow channel when the cross-sectional size of the flow channel is greater than 5mm. At the same time, several obstacles and grooves are set in the flow channel to cause repeated splitting, displacement and merging of the fluid, and generate additional fluid disturbance or vortex to improve the mixing efficiency. The obstacles or grooves have cross-sectional shapes such as square, rectangle, rhombus or circle. When the cross-sectional size of the flow channel of the mixing functional area is less than 5mm, a curved flow channel is adopted, including groove-shaped, serpentine, broken line, curved, arc, spiral and Tesla flow channels, etc. Obstacles may not be set in the flow channel. The vortex formed by the velocity difference on both sides when the fluid passes through the curved flow channel promotes dispersion and mixing.

[0151] The spinneret structure designed in this application eliminates the need for pressure chamber control of the solution, reducing the complexity of the equipment and its pressure control system. It also significantly increases the pressure at the spinneret orifice during flash spinning, which is beneficial for fiber stretching, orientation, and performance improvement. Furthermore, it significantly simplifies the mixing process of polymer melt and solvent in flash spinning, solving the problems of low efficiency and long time required for intermittent preparation of homogeneous solutions using high-pressure stirred tanks. This facilitates the continuous operation of the flash spinning process and is suitable for flash spinning of polymers with high molecular weight.

[0152] This application presents a method for flash spinning above the cloud point pressure. The method involves extruding polymer melt and solvent into the spinneret structure in the form of a thin stream at high temperature and above the cloud point pressure. The two react and diffuse with each other in a laminar flow to form a mixed solution with a concentration gradient. Then, the solution is further dispersed and mixed in a non-shear-resistant and gentle manner to form a heterogeneous mixed solution with a polymer-rich phase and a solvent-rich phase, thus avoiding the degradation of the polymer caused by mechanical stirring and shearing.

[0153] Example 6

[0154] Based on the above embodiments 1-5, this embodiment mainly introduces the effect verification of this application.

[0155] First, in Comparative Example 1, high-density polyethylene melt and trichlorofluoromethane solvent were heated to 200 degrees Celsius and then extruded separately through a constant pressure pump at a pressure of 12 MPa into... Figure 7 The polymer melt channel 1 and solvent channel 2 are shown. The channel width is 2 mm and the depth is 1 mm. The polyethylene melt and solvent advance along the channel into the 60 mm long diffusion zone 3, then through a 240 mm long straight channel, and finally exit from the spinneret to form flash fiber bundles. After fiber opening, these bundles are deposited on a mesh belt to obtain a fiber web, which is then hot-rolled into a nonwoven fabric. The difference between Comparative Example 1 and Examples 1-5 is that a mixing zone is not provided within the channel.

[0156] Secondly, please refer to Comparative Example 2. Comparative Example 2 involves heating high-density polyethylene melt and the solvent trichlorofluoromethane in an autoclave to 200 degrees Celsius and stirring for 4 hours under a pressure of approximately 20 MPa to prepare a homogeneous solution with a concentration of 15 wt%. This solution was then processed as follows: Figure 8 The flow channel shown enters the spinneret. The flow channel dimensions are the same as in Example 2, but the flow channel is a simple straight flow channel without any obstructions or grooves inside, and it does not have a mixing function. Finally, it is ejected from the spinneret orifice to form flash fiber bundles. After fiber opening, it is deposited on a mesh belt to obtain a fiber web, which is then hot-rolled into a nonwoven fabric. The significant difference between Comparative Example 2 and Examples 1-5 and Comparative Example 1 is that the spinneret solution is first prepared into a homogeneous solution using conventional methods, and then spinned above the cloud point pressure.

[0157] Finally, please refer to Comparative Example 3. In Comparative Example 3, high-density polyethylene melt and solvent trichlorofluoromethane were heated to 200 degrees Celsius in an autoclave and stirred for 4 hours under a pressure of approximately 14 MPa to prepare a homogeneous solution with a concentration of 18 wt%. Figure 9 The diffusion zone shown enters the spinneret. The flow channel dimensions are the same as in Comparative Example 2, but a pressure-reducing chamber 8 and a pressure measuring hole 9 are provided before the spinneret to reduce the pressure inside the chamber to 7 MPa. Finally, the fibers are ejected from the spinneret to form flash fiber bundles. After fiber opening, they are deposited on a mesh belt to obtain a fiber web, which is then hot-rolled into a nonwoven fabric. The difference between Comparative Example 3 and Examples 1-5 and Comparative Examples 1-2 is that a pressure-reducing chamber is used to reduce the pressure of the solution to below the cloud point pressure for spinning.

[0158] The fiber fineness and fiber strength of the tows prepared in the examples and comparative examples were tested, and the results are shown in Table 1.

[0159] Table 1 Test results of flash fiber tow properties

[0160]

[0161] The test results show that the flash-evaporated fiber bundles prepared by the method of this invention have a small fiber diameter ratio, a large specific surface area, and high strength. Comparative Example 1 demonstrates that diffusion mixing alone cannot achieve the ideal flash-evaporation effect; mixing functional zones help reduce fiber diameter, increase specific surface area, and increase bundle strength. Comparative Example 2 demonstrates that high-density polyethylene flash-evaporated fiber bundles prepared by spinning a homogeneous polymer solution above the cloud point pressure have poor performance and large fiber diameter. Comparative Example 3 demonstrates that high-density polyethylene flash-evaporated fiber bundles prepared by spinning a polymer solution using a decompression chamber to reduce the pressure to below the cloud point pressure have higher performance than Comparative Examples 1 and 2, but compared to Examples 1-4 of this invention, their mechanical properties are still lower and their fiber diameter is larger.

[0162] The above description is merely a preferred embodiment of the present invention and does not limit the scope of protection of the present invention. For those skilled in the art, the present invention can have various modifications and variations. Any changes, modifications, substitutions, integrations, and parameter alterations to these embodiments within the spirit and principles of the present invention, achieved through conventional substitutions or by achieving the same function without departing from the principles and spirit of the present invention, fall within the scope of protection of the present invention.

Claims

1. A method for flash spinning at a pressure above the cloud point, characterized in that, Includes the following steps: Step S1: The polymer melt (6) and organic solvent (7) are extruded into the polymer melt channel (1) and solvent channel (2) respectively; Step S2: The polymer melt (6) and the organic solvent (7) come into contact with each other and diffuse into each other in a laminar flow manner in the diffusion functional region (3); Step S3: The polymer melt (6) and organic solvent (7) flowing out from the diffusion functional zone (3) are further dispersed and mixed in the mixing functional zone (4) in a non-shear, gentle manner to form a two-phase dispersion with a polymer-rich phase and a solvent-rich phase inside. Step S4: Before the two-phase dispersion reaches diffusion equilibrium, the filaments are extruded through the spinneret above the turbidity point pressure of the homogeneous solution to complete flash spinning.

2. The method for flash spinning at a pressure above the cloud point according to claim 1, characterized in that, The polymer melt (6) is polyethylene, polypropylene, polybutene, polymethylpentene, polyvinylidene fluoride, or ethylene. One or more of the following: tetrafluoroethylene copolymer, PET, or polylactic acid polyester.

3. A method for flash spinning at a pressure above the cloud point according to any one of claims 1 or 2, characterized in that, The organic solvent (7) is toluene, benzene, n-hexane, butane, pentene, heptane, octane, cyclohexane, dichloromethane, carbon tetrachloride, chloroform, chloromethane, chloroethane, dichloroethylene, trichlorofluoromethane, dichlorotrifluoroethane, other Freons, pentafluoropropane, heptafluoropropane, 1H Perfluorohexane, 6H Perfluorohexane, 1H Perfluoroheptane, 1H One or more of perfluorohexane, octafluorocyclopentane, and alcohol solvents; an organic solvent mixed with nitrogen or carbon dioxide gas.

4. The method for flash spinning above the cloud point pressure according to claim 1, characterized in that, The device used in the method is a spinneret structure, which includes a polymer melt flow channel (1), a solvent flow channel (2), a diffusion functional zone (3), a mixing functional zone (4), and a spinneret orifice (5). The outlet of the polymer melt flow channel (1) and the outlet of the solvent flow channel (2) are respectively connected to the inlet of the diffusion functional zone (3); The outlet of the diffusion functional zone (3) is connected to the inlet of the mixing functional zone (4); The outlet of the mixed functional area (4) is connected to the spinneret hole (5).

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