A micro-extruded polymer porous foamed wire material and its preparation method and application

Abstract

The present invention discloses a micro-extruded polymer porous foamed filament, a preparation method, and an application thereof, and relates to the technical field of composite materials. The preparation method of the micro-extruded polymer porous foamed filament provided by the present invention first pre-treats continuous fibers of a specific diameter by impregnation, then co-extrudes the fibers with molten polymer particles containing a foaming agent, and performs drafting at a specific ratio at a specific temperature. The resulting filament has a continuous fiber core and a foamed skin. Not only is the diameter reduced, but the pore structure inside the foamed skin enables excellent interfacial bonding strength between the fibers and the continuous fibers. Therefore, the filament can combine the advantages of small diameter, high porosity, and high strength. The porosity is as high as 70% or more, the strength reaches 10 N or more, and the diameter is not higher than 0.45 mm.

Description

Technical Field

[0001] The present invention relates to the technical field of composite materials, and in particular to a micro-extruded polymer porous foamed filament and a preparation method and application thereof. Background Art

[0002] Due to their porous structure, polymer porous fibers have the advantages of being lightweight, thermally insulating, breathable, and highly flexible. They have broad application prospects in various fields, and their research and development and preparation processes are also receiving increasing attention. Inspired by porous fibers found in nature, such as polar bear hair and camel hair, researchers have proposed methods such as ice crystal templates and phase separation to prepare polymer porous fibers. However, existing methods for preparing polymer porous fibers produce fibers with diameters that are too large, making subsequent processing too difficult and making it difficult to meet actual application needs.

[0003] Continuous extrusion foaming technology can produce polymer foam filaments with diameters in the millimeter and micrometer ranges. For example, the prior art (Dai, C., Zhang, C., Huang, W., Chang, K. & Lee, L. Thermoplastic polyurethane microcellular fibers via supercritical carbon dioxide based extrusion foaming. Poly. Eng. Sci. 53, 2360-2369 (2013)) explored the production of polymer foam fibers using continuous extrusion foaming technology, resulting in TPU foam filaments with a well-developed foaming structure and high porosity, also with a relatively small diameter. However, the foamed structure reduces strength, making it difficult to meet practical application requirements. The question of how to prepare a polymer foam filament with both high strength and high porosity, while also exhibiting a small diameter, has become an urgent issue. Summary of the Invention

[0004] In order to address the shortcomings of the existing technology, the present invention provides a method for preparing a micro-extruded polymer porous foamed filament. First, continuous fibers of a specific diameter are pre-treated by impregnation, and then they are coaxially co-extruded with molten polymer particles containing a foaming agent, and are stretched in a specific proportion at a specific temperature. The resulting filament has a continuous fiber core and a foamed skin. Not only is the diameter reduced, but the pore structure inside the foamed skin enables it to have excellent interface bonding strength with the continuous fiber. Therefore, the filament can have a low diameter, high porosity and high strength.

[0005] Another object of the present invention is to provide a micro-extruded polymer porous foamed filament.

[0006] Another object of the present invention is to provide an application of a micro-extruded polymer porous foamed filament in the field of shoe materials.

[0007] The above-mentioned purpose of the present invention is achieved through the following technical solutions:

[0008] A method for preparing a micro-extruded polymer porous foamed filament comprises the following steps:

[0009] S1. The continuous fiber is impregnated in a pre-impregnated solution and dried to obtain a pretreated fiber; the solute of the pre-impregnated solution includes a polymer component; the diameter d1 of the continuous fiber is 0.1 to 0.5 mm;

[0010] S2. Melting polymer particles containing a foaming agent and coaxially co-extruding them with the pretreated fibers described in step S1 to obtain a foamed filament melt containing a continuous fiber core and a foamed skin. The raw materials for preparing the polymer particles containing a foaming agent include a polymer component and a foaming agent. The difference between the diameter d2 of the foamed filament melt and the diameter d1 of the continuous fiber is d2-d1=0.1-0.4 mm.

[0011] S3. The foamed filament melt obtained in step S2 is stretched to obtain a micro-extruded polymer porous foamed filament; the stretching temperature is 40-160°C, and the ratio L2 / L1 of the length L2 of the micro-extruded polymer porous foamed filament obtained after stretching to the length L1 of the foamed filament melt before stretching is 1.5-4.

[0012] In a specific embodiment of the present invention, the polymer components in steps S1 and S2 remain consistent.

[0013] In a specific embodiment of the present invention, the raw materials for preparing the polymer particles containing the foaming agent in step S2 only include polymer components and the foaming agent.

[0014] In a specific embodiment of the present invention, the diameter d2 of the foamed wire melt in step S2 is 0.2-0.9 mm, and d2>d1.

[0015] In a specific embodiment of the present invention, the coaxial coextrusion described in step S2 refers to the fact that the pretreated fibers and the melt formed by the molten polymer particles share an axis. In the extrusion process of the present invention, the pretreated fibers can be regarded as cylinders, and the melt formed by the molten polymer particles on the outer surface of the pretreated fibers is approximately a hollow cylinder. The line connecting the centers of the two ends of the cylinder or hollow cylinder is the axis of the cylinder or hollow cylinder. In the foamed filament melt prepared by the coaxial coextrusion method described in step S2, the continuous fiber inner core is coaxial with the foamed cortex, wherein the foamed cortex is prepared by foaming the molten polymer particles and can also be approximated as a hollow cylinder.

[0016] The preparation method of the micro-extruded polymer porous foamed filament provided by the present invention, first pre-impregnates the continuous fiber of a specific diameter, and then makes the fiber and the molten polymer particles containing a foaming agent be coaxially co-extruded, and draws off after extruding to obtain the foamed filament melt, it is possible to obtain a polymer filament having high porosity, high strength and low diameter, and the foam structure of the obtained filament is good. Specifically, the foamed filament obtained by the present invention contains a continuous fiber core and a foamed cortex, wherein the continuous fiber core obtained by pre-impregnation has excellent interfacial bonding strength with the foamed cortex, and its own strong strength is excellent, therefore the intensity of the obtained filament can be improved, similar to "reinforced concrete" system. After extruding the foamed filament melt, the drawing in step S3 is carried out to it, the diameter of the obtained filament can be reduced, and its fineness is improved. However, the drawing step not only reduces the diameter but also affects the pore structure of the foamed cortex in the foamed filament melt. The pore structure and the fiber core together affect the mechanical properties of the resulting filament. A suitable pore structure can absorb and relieve stress when subjected to external tension, preventing premature breakage of the continuous fiber core. The inventors of this application, through extensive experimental research, found that a polymer porous foamed filament with high strength, low diameter, and high porosity can only be obtained when the drawing temperature is 40-160°C, the drawing ratio is 1.5-4, the solute in the prepreg solution includes a polymer component, and the diameters of the continuous fiber and the foamed filament melt are 0.1-0.5 mm and 0.2-0.9 mm, respectively (the difference between the diameter d2 of the foamed filament melt and the diameter d1 of the continuous fiber is d2-d1 = 0.1-0.4 mm). The drawing process causes the pores in the foamed filament melt to deform, resulting in changes in their pore size and morphology. The abscess after drawing-off has more excellent interfacial bonding strength with the continuous fiber of specific diameter, therefore when the temperature of drawing-off or ratio are unsuitable, the degree that abscess will be caused to collapse or be deformed is unsuitable, it is impossible to form a good combination with continuous fiber, the effect of absorbing stress relief also declines, and then causes the intensity reduction of gained silk material. The diameter of continuous fiber is too large or the diameter of foaming silk material melt is too small, then the size and distribution of abscess will be affected in the foaming process of step S2, even if the drawing-off in step S3 is now carried out, good combination still cannot be achieved between fiber and foaming cortex, or foaming cortex cannot give full play to the effect of stress relief; The diameter of continuous fiber is too small or the diameter of foaming silk material melt is too large, and continuous fiber cannot give full play to effect in system, causes the insufficient strength of silk material, therefore the diameter of continuous fiber, foaming silk material melt is too large or too small and can cause the intensity reduction of gained silk material. The step of prepreg affects the combination between fiber and foaming cortex equally.The introduction of continuous fibers can act as sites for heterogeneous nucleation of bubbles in the foaming melt to reduce the energy of bubble formation. However, if the continuous fibers are not pre-impregnated, the compatibility between the fibers and the foaming melt will decrease, which in turn will affect the formation of bubbles, making the bubble structure unsuitable and thus reducing the strength of the foamed filament.

[0017] In summary, the diameter of the continuous fiber and the drawing process will affect the pore structure of the resulting filament, and the pre-impregnation step and the above variables jointly affect the strength of the resulting polymer foamed filament. At the same time, the drawing ratio and temperature parameters will also affect the diameter of the resulting filament. In order to take into account the low diameter, high strength and high porosity of the filament, the temperature and ratio of the drawing process need to be in the range of 40~160℃ and 1.5~4 respectively, the diameter of the continuous fiber is 0.1~0.5 mm, the difference between the diameter d2 of the foamed filament melt and the diameter d1 of the continuous fiber is d2-d1=0.1~0.4 mm, and the solute of the pre-impregnation solution includes the polymer component of the foamed cortex in the subsequent filament.

[0018] In a specific embodiment of the present invention, the method for preparing a micro-extruded polymer porous foam filament provided herein is performed using an apparatus comprising a screw extruder and a drafting element, wherein the extrusion die of the screw extruder has a lateral opening for introducing a continuous fiber feed port. More specifically, the diameter of the continuous fiber feed port is 0.03 to 2 mm. Preferably, the diameter of the continuous fiber feed port is 0.1 to 0.5 mm.

[0019] Preferably, the diameter of the continuous fiber in step S1 is 0.1-0.3 mm.

[0020] Preferably, the continuous fiber in step S1 comprises at least one of aramid fiber, PET (polyethylene terephthalate) fiber, ultra-high molecular weight polyethylene fiber, polyimide fiber, cellulose fiber, carbon fiber, and polytetrafluoroethylene fiber. In a specific embodiment of the present invention, the continuous fiber is commercially available continuous fiber without subsequent treatment.

[0021] Preferably, the fineness of the continuous fiber in step S1 is 120-500D.

[0022] The fineness of continuous fibers refers to the weight (in grams) of 9000 m of continuous fiber. In addition to being related to fiber thickness, it is also related to the fiber type and composition, the number of filaments in the fiber, the diameter of the filaments, and the twist of the fiber. For fibers of the same diameter, the fineness can be adjusted by adjusting the number of filaments, the diameter, and the twist. By limiting the fineness of continuous fibers to ≥120 D, both the fiber diameter and density can be controlled simultaneously. Increasing the diameter and density will result in an increase in fineness. Fibers with too low a fineness have low thickness and density, making them suitable for extrusion but lacking strength and prone to breakage during extrusion. Continuous fibers with a fineness of 120-500 D have a fineness that facilitates interfacial bonding with the outer foaming layer. Furthermore, their inherent density is suitable, so the inclusion of continuous fibers can significantly enhance the strength of the resulting foamed filament. If the fiber density is too large, it is easy to cause the pore characteristics of the cortex of the foamed filament melt to change to an inappropriate degree during the extrusion and drawing process, resulting in a decrease in interfacial bonding strength and porosity.

[0023] More preferably, the fineness of the continuous fiber in step S1 is 180-220D.

[0024] Preferably, the strength of the continuous fiber in step S1 is 4-20 cN / dtex.

[0025] More preferably, the solvent of the pre-dip solution in step S1 includes tetrahydrofuran.

[0026] More preferably, the concentration of the solute in the pre-impregnation solution in step S1 is 40-60 vol%.

[0027] More preferably, the immersion temperature in step S1 is 40-70°C.

[0028] More preferably, the immersion time in step S1 is 2 to 100 s.

[0029] More preferably, the drying temperature in step S1 is 60-100°C.

[0030] Preferably, in step S2, the difference between the diameter d2 of the foamed filament melt and the diameter d1 of the continuous fiber is d2-d1=0.2-0.3 mm.

[0031] Preferably, the polymer component in step S2 includes at least one of an amorphous polymer, a semi-crystalline polymer, a crystalline polymer, and a thermoplastic elastomer.

[0032] More preferably, the amorphous polymer in step S2 includes at least one of polystyrene, polymethyl methacrylate, polyetherimide, polyimide, and polysulfone.

[0033] More preferably, the semi-crystalline polymer in step S2 includes at least one of polyethylene terephthalate, polylactic acid, and polyetheretherketone.

[0034] More preferably, the crystalline polymer in step S2 includes at least one of polyethylene, polypropylene, and nylon.

[0035] More preferably, the thermoplastic elastomer in step S2 includes at least one of polyurethane, polyester elastomer, and nylon elastomer.

[0036] Preferably, the foaming agent in step S2 includes at least one of a fluid foaming agent and a solid foaming agent.

[0037] More preferably, the fluid foaming agent in step S2 includes a supercritical fluid.

[0038] More preferably, the supercritical fluid in step S2 includes at least one of CO2, N2, alkanes, and hydrogenated chlorofluorocarbons (HCFCs).

[0039] More preferably, the solid foaming agent in step S2 includes at least one of expandable microspheres, carbonates, N,N'-dinitrosopentamethylenetetramine, and azodicarbonamide.

[0040] More preferably, in the polymer particles containing a foaming agent in step S2, the mass ratio of the foaming agent to the polymer component is (0.1-10): (90-99.9).

[0041] In a specific embodiment of the present invention, the polymer component is in a granular form, and the polymer particles containing the foaming agent are obtained by blending the polymer component with the foaming agent.

[0042] Preferably, the melting and the coaxial co-extrusion in step S2 are carried out in a single-screw extruder, and the single-screw extruder includes a first heating section, a second heating section, and a third heating section. The temperature of the first heating section is 0~30°C, the temperature of the second heating section is 150~300°C, and the temperature of the third heating section is 200~390°C. The real-time temperature of the third heating section is higher than that of the second heating section.

[0043] In a specific embodiment of the present invention, the rotation speed of the single screw extruder in step S2 is 15-25 rpm.

[0044] In a specific embodiment of the present invention, the speed of the coaxial coextrusion in step S2 is 0.5-1.5 kg / h.

[0045] In a specific embodiment of the present invention, the extrusion die size of the single-screw extruder in step S2 is 0.3-1 mm.

[0046] Preferably, the drawing temperature in step S3 is 100-150° C., and the ratio L2 / L1 of the length L2 of the micro-extruded polymer porous foamed filament obtained after drawing to the length L1 of the foamed filament melt before drawing is 2-3.

[0047] Preferably, the stretching in step S3 is performed using a stretching unit, which includes a guide unit and a heated stretching unit. The stretching unit includes a group of guide units and at least one group of heated stretching units. The guide unit includes a pulling roller, and the stretching unit includes a heated tunnel and a stretching roller. In a specific embodiment of the present invention, the stretching temperature refers to the temperature of the heated tunnel, and the stretching ratio is the ratio of the length of the micro-extruded polymer porous foamed filament to the length of the foamed filament melt, that is, the ratio of the length of the foamed filament obtained after the melt is stretched by the last group of stretching rollers to the length of the original foamed filament melt.

[0048] Preferably, the linear speed of the pulling roller is 30-60 m / min.

[0049] Preferably, the linear speed of the drafting roller is 80-120 m / min.

[0050] The present invention also protects the micro-extruded polymer porous foamed filaments prepared by the above preparation method.

[0051] The present invention also protects the application of the micro-extruded polymer porous foamed filament in the field of shoe materials.

[0052] Compared with the prior art, the present invention has the following beneficial effects:

[0053] The micro-extruded polymer porous foamed filament provided by the present invention has excellent low diameter, high porosity and high strength. The porosity is as high as 70% or more, the strength reaches more than 10 N, the diameter is not higher than 0.45 mm, and the obtained filament has good foaming behavior, stable extrusion and uniform diameter. DETAILED DESCRIPTION

[0054] The present invention will be further described below in conjunction with specific embodiments, but the examples do not limit the present invention in any form. Unless otherwise specified, the raw materials and reagents used in the examples of the present invention are conventionally purchased raw materials and reagents. Among them, the raw material information used in each example and comparative example is as follows:

[0055] Amorphous polymer A:

[0056] A1, polystyrene PS, brand GPPS158K, produced by BASF-YPC.

[0057] A2, polyetherimide PEI, brand 1000, SABIC.

[0058] Crystalline polymer B:

[0059] B1, low-density polyethylene LDPE, brand 2426H, Maoming Petrochemical.

[0060] B2, polyetheretherketone PEEK, brand 1000, Mitsubishi Chemical.

[0061] Thermoplastic Elastomer C:

[0062] Thermoplastic polyurethane TPU, hardness Shore A60, BASF, Germany.

[0063] Continuous fiber a: aramid fiber, diameter 0.2 mm, fineness 200D, strength 20 cN / dtex, commercially available.

[0064] Continuous fiber b: aramid fiber, diameter 0.4 mm, fineness 1000D, strength 20 cN / dtex, commercially available.

[0065] Continuous fiber c: aramid fiber, diameter 0.1 mm, fineness 80D, strength 20 cN / dtex, commercially available.

[0066] Continuous fiber d: PET fiber, diameter 0.2 mm, fineness 200D, strength 4 cN / dtex, commercially available.

[0067] Continuous fiber e: polyimide fiber, diameter 0.2 mm, fineness 250D, strength 4 cN / dtex, commercially available.

[0068] Continuous fiber f: aramid fiber, diameter 0.008 mm, fineness 20D, strength 20 cN / dtex, commercially available.

[0069] Continuous fiber g: aramid fiber, diameter 0.6 mm, fineness 800D, strength 20 cN / dtex, commercially available.

[0070] Continuous fiber h: aramid fiber, diameter 0.2 mm, fineness 120D, strength 20 cN / dtex, commercially available and customized.

[0071] Continuous fiber i: Aramid fiber, diameter 0.2 mm, fineness 300D, strength 20 cN / dtex, commercially available or customized.

[0072] Examples 1 to 13

[0073] This embodiment provides a series of methods for preparing micro-extruded polymer porous foamed filaments with different raw materials, extrusion processes, and drawing processes, including the following steps:

[0074] S1. Immersing the continuous fiber in a pre-impregnation solution at 60°C for 30 seconds and then drying to obtain a pretreated fiber; the pre-impregnation solution comprises a polymer component as a solute, tetrahydrofuran as a solvent, and a solute concentration of 50 vol%; and the diameter of the continuous fiber is 0.1-0.5 mm;

[0075] S2. Prepare polymer particles containing a foaming agent, wherein the raw materials for preparing the polymer particles containing a foaming agent include 95 parts of the polymer components described in step S1 and 5 parts of the foaming agent CO2; melt the polymer particles containing a foaming agent and coaxially extrude them with the pretreated fibers described in step S1 to obtain a foamed filament melt containing a continuous fiber core and a foamed skin; the speed of the coaxial coextrusion is 1 kg / h, the screw speed is 20 rpm, and the extrusion die size is 0.4 mm; the melting and the coaxial coextrusion are carried out in a single-screw extruder, and the single-screw extruder includes a first heating section, a second heating section, and a third heating section, the temperature of the first heating section is 0-30°C, the temperature of the second heating section is 150-300°C, the temperature of the third heating section is 200-390°C, and the real-time temperature of the third heating section is higher than that of the second heating section;

[0076] S3. The foamed filament melt obtained in step S2 is stretched to obtain a micro-extruded polymer porous foamed filament; the stretching is performed using a stretching component, which includes a group of guiding units and a group of heating stretching units, the guiding unit includes a pulling roller, and the linear speed of the pulling roller is 50 m / min, the stretching unit includes a heating tunnel and a stretching roller, the temperature of the heating tunnel, i.e., the stretching temperature, is 40~160°C, the stretching ratio L2 / L1 is 1.5~4, and the linear speed of the stretching roller is 100 m / min.

[0077] The specific processing parameters in Examples 1 to 13 are shown in Table 1 below:

[0078] Table 1. Specific processing parameters in Examples 1 to 13

[0079]

[0080] Example 14

[0081] A method for preparing a micro-extruded polymer porous foamed filament, which differs from Example 5 only in that:

[0082] The continuous fiber a is replaced by the continuous fiber h, and the diameter of the foamed wire melt in step S2 is 0.5 mm.

[0083] Example 15

[0084] A method for preparing a micro-extruded polymer porous foamed filament, which differs from Example 5 only in that:

[0085] The continuous fiber a is replaced by the continuous fiber i, and the diameter of the foamed wire melt in step S2 is 0.5 mm.

[0086] Comparative Example 1

[0087] A method for preparing a micro-extruded polymer porous foamed filament, which differs from Example 5 only in that:

[0088] The continuous fiber a is replaced by the continuous fiber f, and the diameter of the foamed wire melt in step S2 is 0.12 mm.

[0089] Comparative Example 2

[0090] A method for preparing a micro-extruded polymer porous foamed filament, which differs from Example 5 only in that:

[0091] The continuous fiber a is replaced by the continuous fiber g, and the diameter of the foamed wire melt in step S2 is 0.98 mm.

[0092] Comparative Example 3

[0093] A method for preparing a micro-extruded polymer porous foamed filament, which differs from Example 5 only in that:

[0094] The ratio L2 / L1 of the length L2 of the micro-extruded polymer porous foamed filament obtained after drawing in step S3 to the length L1 of the foamed filament melt before drawing is 6.

[0095] Comparative Example 4

[0096] A method for preparing a micro-extruded polymer porous foamed filament, which differs from Example 5 only in that:

[0097] The ratio L2 / L1 of the length L2 of the micro-extruded polymer porous foamed filament obtained after drawing in step S3 to the length L1 of the foamed filament melt before drawing is 1.2.

[0098] Comparative Example 5

[0099] A method for preparing a micro-extruded polymer porous foamed filament, which differs from Example 5 only in that:

[0100] The stretching temperature in step S3 is 30°C.

[0101] Comparative Example 6

[0102] A method for preparing a micro-extruded polymer porous foamed filament, which differs from Example 5 only in that:

[0103] The stretching temperature in step S3 is 200°C.

[0104] Comparative Example 7

[0105] A method for preparing a micro-extruded polymer porous foamed filament, which differs from Example 5 only in that:

[0106] Step S1 is omitted, that is, pre-impregnation is not performed.

[0107] Comparative Example 8

[0108] A method for preparing a micro-extruded polymer porous foamed filament, which differs from Example 5 only in that:

[0109] No continuous fibers are introduced.

[0110] Performance Testing

[0111] Porosity test: Tested in accordance with GB / T21650.1-2008.

[0112] Strength test: Use universal strength meter for testing.

[0113] Diameter test: A fiber diameter tester was used to test the diameters of the micro-extruded polymer porous foamed filaments obtained in the examples and comparative examples.

[0114] Foaming behavior test: measured by visual observation.

[0115] The above performance test data is shown in Table 2 below:

[0116] Table 2. Performance test data of micro-extruded polymer porous foamed filaments obtained in Examples and Comparative Examples

[0117]

[0118]

[0119] As can be seen from Table 2 above, the micro-extruded polymer porous foamed filaments provided by the present invention have excellent low diameter, high porosity, and high strength. The porosity is as high as 70% or more, the strength is above 10 N, the diameter is not higher than 0.45 mm, and the obtained filaments have good foaming behavior, smooth extrusion, and uniform diameter.

[0120] According to the data in Examples 5-7 and Comparative Examples 1-2 in Table 2, when aramid fibers of varying diameters are used as continuous fibers for reinforcement, and the diameter of the foamed filament melt obtained in step S2 remains substantially unchanged, the continuous fiber diameter is 0.1-0.3 mm, which is preferred in the present invention, and the diameter difference d2-d1 between the continuous fiber and the foamed filament melt is 0.2-0.3 mm, which is preferred in the present invention, the resulting micro-extruded polymer porous foamed filament not only has a higher porosity but also has superior strength. This indicates that the interlocking of continuous fibers of a specific diameter with the foamed polymer cortex can achieve better reinforcement while still obtaining a good foaming structure. When the continuous fiber diameter is too large or too small (Comparative Examples 1-2), even though the thickness d2-d1 of the resulting foamed cortex is still 0.1-0.4 mm, the resulting foamed filament has an unsuitable foaming structure, a decreased porosity, and a slight decrease in strength.

[0121] According to Examples 5, 8, and 9, aramid continuous fibers with higher inherent strength are used for reinforcement (Example 5), and the resulting foamed filaments have higher strength. However, the key to achieving the reinforcement in the present invention lies not only in the introduction of continuous fibers, but also in the ability to control the structure of the foamed cortex so that the foamed cortex does not have a negative impact on the strength of the filaments, and can even further enhance the strength of the foamed filaments by forming a good bond between the foamed cortex and the fibers.

[0122] According to Examples 5, 10 to 13, when the drawing temperature in step S3 is 100 to 150° C. as preferred in the present invention and the drawing ratio is also 2 to 3 as preferred (Example 5), the foamed structure obtained by drawing is more suitable, and thus the obtained foamed filament can have both higher porosity and strength.

[0123] According to the data of Examples 5, 14, and 15, it can be seen that the denier of the same type of fiber with the same diameter will vary based on the twist, single filament diameter, and number of fibers. Under the condition that the diameter remains unchanged, the fineness of the continuous fiber is 180-220D (Example 5), which is preferred in the present invention. The resulting foamed filament can have both better strength and porosity, while having a lower diameter and a higher degree of fineness.

[0124] According to the data of Comparative Examples 3 to 6, an inappropriate stretching ratio or temperature in step S3 will affect the cell structure in the foamed skin layer, resulting in a decrease in both the porosity and strength of the obtained foamed filament.

[0125] According to the data of Comparative Example 7, if the fibers are not pre-impregnated before the continuous fibers are introduced, the compatibility between the fiber core and the foamed skin cannot be improved, resulting in a decrease in the strength of the foamed filament; at the same time, the pre-impregnation step is very critical for the nucleation of bubbles in the foaming agent at the fiber-foaming melt interface. The omission of the pre-impregnation step leads to a decrease in the porosity of the foamed filament.

[0126] According to the data of Comparative Example 8, it can be seen that not introducing continuous fibers has a great influence on the strength of the foamed filament. At the same time, since the introduction of continuous fibers can serve as sites for heterogeneous nucleation of bubbles, the energy required for bubble formation is reduced. Therefore, when continuous fibers are not introduced, the porosity of the obtained foamed filament also decreases.

[0127] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a micro-extruded polymer porous foamed wire material, characterized in that: The steps include: S1. Impregnating a continuous fiber in a pre-impregnation solution and drying the pre-impregnated fiber to obtain a pretreated fiber; the solute of the pre-impregnation solution includes a polymer component; the diameter d1 of the continuous fiber is 0.1 to 0.5 mm; the continuous fiber includes at least one of aramid fiber, PET fiber, ultra-high molecular weight polyethylene fiber, polyimide fiber, and polytetrafluoroethylene fiber; S2. Melting polymer particles containing a foaming agent and coaxially co-extruded with the pretreated fibers described in step S1 to obtain a foamed filament melt containing a continuous fiber core and a foamed skin. The raw materials for preparing the polymer particles containing a foaming agent include a polymer component and a foaming agent. The difference between the diameter d2 of the foamed filament melt and the diameter d1 of the continuous fiber is d2-d1 = 0.1-0.4 mm. The polymer components described in steps S1 and S2 are consistent. S3. The foamed filament melt obtained in step S2 is stretched to obtain a micro-extruded polymer porous foamed filament; the stretching temperature is 40-160°C, and the ratio L2 / L1 of the length L2 of the micro-extruded polymer porous foamed filament obtained after stretching to the length L1 of the foamed filament melt before stretching is 1.5-4.

2. The method for preparing a micro-extruded polymer porous foamed filament according to claim 1, wherein: The fineness of the continuous fiber in step S1 is 120~500 D.

3. The method for preparing a micro-extruded polymer porous foamed filament according to claim 1, wherein: Include at least one of the following (a) to (b): (a) The solvent of the pre-dip solution in step S1 includes tetrahydrofuran; (b) The concentration of the solute in the pre-impregnation solution in step S1 is 40-60 vol%.

4. The method for preparing a micro-extruded polymer porous foamed filament according to claim 1, wherein: Include at least one of the following (c) to (d): (c) the polymer component in step S2 comprises at least one of an amorphous polymer, a semi-crystalline polymer, a crystalline polymer, and a thermoplastic elastomer; (d) The foaming agent in step S2 includes at least one of a fluid foaming agent and a solid foaming agent.

5. The method for preparing a micro-extruded polymer porous foamed filament according to claim 1 or 4, characterized in that: In the polymer particles containing a foaming agent in step S2, the mass ratio of the foaming agent to the polymer component is (0.1-10): (90-99.9).

6. The method for preparing a micro-extruded polymer porous foamed filament according to claim 1, wherein: The melting and coaxial co-extrusion in step S2 are carried out in a single-screw extruder, and the single-screw extruder includes a first heating section, a second heating section, and a third heating section. The temperature of the first heating section is 0~30°C, the temperature of the second heating section is 150~300°C, and the temperature of the third heating section is 200~390°C. The real-time temperature of the third heating section is higher than that of the second heating section.

7. The method for preparing a micro-extruded polymer porous foamed filament according to claim 1, wherein: The drawing temperature in step S3 is 100-150° C., and the ratio L2 / L1 of the length L2 of the micro-extruded polymer porous foamed filament obtained after drawing to the length L1 of the foamed filament melt before drawing is 2-3.

8. A micro-extruded polymer porous foamed filament prepared by the preparation method according to any one of claims 1 to 7.

9. Use of the micro-extruded polymer porous foamed filament according to claim 8 in the fields of footwear, textiles, and protective gear.

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