Nylon 66 fiber for filter woven fabric and its preparation method and application

Abstract

The present application relates to the technical field of synthetic fibers, and discloses a nylon 66 fiber for filter woven fabric, a preparation method and application thereof. The nylon 66A and nylon 66B melt with different relative viscosities are distributed in parallel composite spinning mode, extruded through a special-shaped spinneret, and formed by TCS one-step spinning process to obtain the nylon 66 fiber with micro-grooves on the fiber surface and a twisted spiral structure along the length direction of the fiber. Even if the warp-weft intersection mesh of the fabric itself is blocked by solid particles, under the action of the filtering pressure, the fluid can still transfer from above the fiber (filter fluid inflow side) to below along the micro-grooves, and the fluid can flow smoothly through the filter cloth by layer-by-layer stacking. The composite parallel fiber prepared by the present application has the advantages of small filtering resistance, high filtering precision, long service life and the like, and can be widely applied to the field of filter woven fabric, and has high popularization and application value.

Description

Technical Field

[0001] This invention relates to the field of synthetic fiber technology, and in particular to a nylon 66 fiber for filter fabrics, its preparation method, and its application. Background Technology

[0002] In the spinning and forming process of synthetic fibers, fibers with non-circular cross-sections or hollow fibers spun using irregularly shaped spinnerets are called irregularly shaped interface fibers, or simply irregularly shaped fibers. Irregularly shaped cross-section fibers have a larger specific surface area and a higher flexural modulus than circularly shaped cross-section fibers, thus exhibiting stronger resistance to deformation and better wrinkle resistance. Furthermore, chemical fibers containing two or more immiscible polymers in their cross-section are called composite fibers or bicomponent fibers. Composite fibers can be classified into two main categories according to their morphology: bilayer and multilayer. Bilayer fibers include side-by-side and core-sheath types. The main characteristic of side-by-side composite fibers is their high crimp.

[0003] Filter fabrics are textiles used to filter impurities from gases or liquids. Separating solid particles from liquids is called wet filtration, while purifying air and separating dust and smoke from gases is called dry filtration. Filter fabrics come in various types, including organic fabrics, non-woven fabrics, felt sheets, and mesh. Among these, woven fabrics have a smooth surface, making it easy to remove filter residue and facilitating the recovery of solid matter, and are commonly used in wet filtration. Woven fabrics utilize the mesh (typically ranging from tens to 2000 μm in size) formed by the intersection of warp and weft threads and / or the gaps between the warp and weft fibers themselves to provide filtration.

[0004] Nylon filter cloth, made of polyamide fibers, boasts advantages such as high temperature resistance, chemical corrosion resistance, and high tensile strength. It is commonly used in various industrial applications including liquid filtration, gas filtration, and powder filtration. Its fine fiber structure effectively captures tiny particles and impurities, resulting in highly efficient filtration. However, in applications with high filtration loads or high filtration precision requirements, the high particle capture efficiency quickly clogs and occupies the pores and gaps of the woven fabric, leading to increased flow resistance, reduced filter cartridge lifespan, and flow path blockage. Therefore, developing a high-quality filter woven fabric with smaller mesh size, high particle capture efficiency, long service life, and low flow resistance is of great significance. Summary of the Invention

[0005] To address the problems of short service life and high flow resistance in existing nylon filter cloths, this invention provides a nylon 66 fiber for filter fabrics and its preparation method. This invention employs a parallel composite spinning method, controlling the process parameters during spinning to prepare a woven filter cloth with microgrooves on the fiber surface and a twisted helical structure along its length. This woven filter cloth exhibits low filtration resistance, high filtration accuracy, long service life, and can be produced continuously, showing broad market prospects.

[0006] To solve the above-mentioned technical problems, the technical solution provided by the present invention is as follows:

[0007] In a first aspect, the present invention also provides a nylon 66 fiber for filter fabrics, which is a parallel composite fiber, including a first parallel structure and a second parallel structure, wherein the first parallel structure is nylon 66A and the second parallel structure is nylon 66B; the surface of the parallel composite fiber has microgrooves and the fiber itself has a twisted helical structure along the length direction, and its cross-sectional irregularity is 20% to 55%, and its twist is 30 to 90.

[0008] The relative viscosities of both Nylon 66A and Nylon 66B are 2.2 to 3.2, and the relative viscosity of Nylon 66B is 0.3 to 0.6 greater than that of Nylon 66A.

[0009] The yarns used in the weaving of typical woven filter cloths, such as polyolefin, polyester, and polyamide fibers, are melt-spun, and their monofilaments have a circular cross-section. Due to the characteristics of the weaving process, a mesh structure is formed at the intersections of the warp and weft yarns in the woven fabric (e.g., ...). Figure 1 As shown, woven filter cloth can intercept solid particles in the filtered fluid. If the warp and weft yarns are multifilaments, the fine particles in the fluid can also be trapped by adsorption when the filtered fluid flows through the gaps between the individual filaments. Therefore, the filtration effect of woven filter cloth is related to its weaving structure. If the size of the basic particles to be filtered is small, the mesh size of the warp and weft yarns and the size of the gaps between the individual filaments need to be reduced.

[0010] One method to achieve the above objectives is to reduce the yarn thickness (reduce fineness or increase yarn count). A higher yarn count makes it easier to obtain a dense woven structure, which can be achieved by reducing the number of monofilaments in multifilament yarns and / or reducing the fineness of the monofilaments. Alternatively, shaped fibers can be used. Non-circular cross-section fibers have a larger perimeter than circular cross-section fibers of the same cross-sectional area, thus having a larger specific surface area and providing a stronger adsorption effect.

[0011] However, when the filtration load is large (i.e., the number of particles in the fluid is large) or the filtration precision is high (i.e., the number of fine particles in the fluid is high), the mesh interception and microstructure adsorption of the woven fabric will easily reach saturation. Moreover, the smaller the mesh size, the stronger the adsorption effect and the faster the saturation will be reached, thus blocking the flow path and causing the flow resistance of the filter to increase.

[0012] To address the aforementioned problems, this invention provides a profiled fiber with a microgroove structure on its surface and a twisted helical structure along its length (e.g., Figures 2-3As shown, the fiber itself is straight, but the cross-section of the fiber along the fiber axis is twisted. Straight fibers can fit together more tightly, avoiding deformation under filtration pressure and ensuring filtration effect. At the same time, the twisted cross-section allows the microgroove structure on the fiber surface to be transferred from one side to the other. This means that even if the warp and weft mesh of the fabric itself is blocked by solid particles, under the action of filtration pressure, the fluid can still be transferred from the top of the fiber (the direction from which the filtration fluid flows) to the bottom along the microgrooves. As these layers are stacked, the fluid can be guaranteed to flow smoothly through the filter cloth.

[0013] However, due to their large molecular weight, polymers have a much smaller entropy change in mixing compared to smaller molecules, resulting in generally poor compatibility. To ensure that the irregular cross-section of the parallel composite yarns is not damaged, this invention uses nylon 66 with different relative viscosities to prepare the irregular composite yarns. The different physical properties of nylons with different relative viscosities allow for the production of the crimped effect of the parallel composite yarns. Simultaneously, because of the hydrogen bonding interactions between nylon molecules, the compatibility between components is relatively good. Furthermore, compared to nylon 6, nylon 66 has better heat resistance and mechanical properties, which is beneficial for improving the service life of the filter fabric.

[0014] It should be noted that the relative viscosity of Nylon 66A and Nylon 66B mentioned in this invention refers to the relative viscosity measured by the formic acid method, and the test method refers to GB / T 12006.1-2009 "Plastics Polyamide Part 1: Determination of Viscosity".

[0015] It should be noted that the torsion degree is the number of cycles of spiral twisting of the fiber cross section along the fiber length direction when a tension of 0.1 cN / dtex is applied to a fiber monofilament with an effective length of 30 cm.

[0016] Furthermore, the nylon 66 fiber used in the filter fabric has a single filament fineness of 0.9 dtex to 1.5 dtex.

[0017] Furthermore, the nylon 66 fiber used in the filter fabric has a breaking strength of 5.5 cN / dtex to 7.5 cN / dtex, a breaking strength CV value of 1.5 ± 0.5%, a breaking elongation of 13.0% to 23.5%, a breaking elongation CV value of 5.0 ± 0.5%, and a network density of 10 to 20 fibers / m.

[0018] Secondly, the present invention provides a method for preparing nylon 66 fibers for filter fabrics, comprising the following steps:

[0019] Nylon 66A melt and Nylon 66B melt with different relative viscosities are distributed in a parallel composite spinning method, extruded through a shaped spinneret, cooled, and then shaped by a heat pipe spinning process to obtain nylon 66 fiber for filter fabrics.

[0020] The spinneret has a spinneret orifice length-to-diameter ratio of 2:1 to 5:1; a nozzle stretch ratio of 80 to 100; a cooling air temperature of 16℃ to 18℃; a cooling air velocity of 0.3m / s to 0.5m / s; and a heat pipe temperature of 195℃ to 215℃.

[0021] The key points of the preparation method for nylon 66 fibers for filter fabrics provided by this invention are: first, to generate and maintain high anisotropy in the nylon 66 fibers, resulting in a microgroove structure on the fiber surface; and second, to straighten and transform the spring-like crimped structure (i.e., the twisted structure of the fiber axis itself along its length) that typically occurs in parallel composite fibers into a helical twist along the fiber axis in the fiber cross-section. The spring-like crimped yarn structure is loose and easily deforms under filtration pressure, increasing the gaps between fibers and thus losing its filtration function. To achieve the above objectives, this invention employs the following means:

[0022] (1) Using Nylon 66A and Nylon 66B with different viscosities as composite parallel spinning raw materials, the physical properties of nylons with different viscosities (i.e. different molecular weights) are different, which can produce the crimping effect of parallel composite yarns; at the same time, because there are hydrogen bond interactions between nylon molecules, the compatibility between components is relatively good, which can ensure that the irregular cross section of the parallel composite yarn is not destroyed.

[0023] (2) Using a shaped spinneret with a high spinneret length-to-diameter ratio and setting a high nozzle draw ratio, the different molecular weights of the melt have different fluidity. Under the action of the flow field force when the melt enters the spinneret, different internal structures (such as orientation force and internal stress) will be formed. A large spinneret length-to-diameter ratio is beneficial for the spinning melt to relax some of the internal stress in the hole. At the same time, using a high nozzle draw ratio will, on the one hand, make the orifice of the spinning melt expand smaller, which is beneficial for maintaining the shaped cross section. On the other hand, it will weaken the structural differences of parallel components to a certain extent, which is beneficial for straightening the curled structure that is usually easy to form during subsequent stretching.

[0024] (3) By adopting enhanced cooling conditions, the cooling of the spinning melt stream is accelerated by controlling the temperature and cooling wind speed of the air cooling, while solidifying the irregular shape of the filament and the structural differences of the parallel components.

[0025] (4) By using heat pipe stretching and setting a high stretching temperature, in the stretching section (front end) of the heat pipe, parallel components with structural differences will produce different stress responses under the action of stretching force and produce a curling tendency. Under the action of stretching stress, the fiber is straightened and the twisted structure is kept on the fiber itself, just like the effect of a spring being straightened. In the shaping section (rear end) of the heat pipe, this irregular cross section spirally twisted around the fiber length direction is fixed by the mechanism of tensile heat shaping under the action of stretching stress and hot air.

[0026] Specifically, the method for preparing the nylon 66 fiber for the filter fabric includes the following steps:

[0027] Step a: Nylon 66A melt and Nylon 66B melt are fed into the composite spinning assembly through their respective melt pipes according to a preset ratio, and extruded through parallel composite shaped spinnerets to obtain nascent filament;

[0028] Step b: After cooling the nascent filaments, they are stretched and wound into a heat pipe to obtain nylon 66 fibers for filter fabrics.

[0029] Further, in step a, the volume ratio of the nylon 66A melt to the nylon 66B melt is 1:0.67 to 1:0.77.

[0030] Further, in step a, the volume ratio of the nylon 66A melt to the nylon 66B melt is 1:1.3 to 1:1.5.

[0031] When nylon 66A melt and nylon 66B melt are combined side-by-side, if the distance between them is too far (1), the curling effect will be poor; if they are too close (1), the curling will be too strong and it will be difficult to straighten.

[0032] Furthermore, the nylon 66A and nylon 66B of this invention are melt-extruded using a screw extruder. Specifically, the temperatures of each part of the screw extruder can be set according to the properties of the nylon 66 raw material, and this invention does not impose any special limitations.

[0033] In one specific embodiment of the present invention, nylon 66A melt and nylon 66B melt are fed into the composite spinning assembly via a metering pump.

[0034] Specifically, in step a, the spinneret holes of the parallel composite irregular spinneret are Y-shaped, H-shaped, C-shaped, figure-eight-shaped, or cross-shaped.

[0035] Furthermore, the temperature of the composite spinning assembly is 290℃~305℃, the humidity of the cooling air is 75%~80%, the rotation speed of the first guide roller is 600m / min~800m / min, the rotation speed of the second guide roller is 3000m / min~4000m / min, and the winding speed is 2750m / min~3700m / min.

[0036] By controlling the above conditions, nylon 66 fibers with irregular cross-sections and helical structures along the length direction can be prepared, providing a high-performance fiber raw material for filter fabrics.

[0037] Thirdly, the present invention also provides a single-layer woven plain weave fabric prepared from nylon 66 fiber of the filter fabric described in any of the above claims.

[0038] Furthermore, the thickness of the single-layer woven plain weave fabric is 0.5mm to 2.0mm, and the weight per unit area is 100g / m². 2 ~500g / m 2 The air permeability is 0.0013m. 3 / m 2 ·s~0.0032m 3 / m 2 The filtration resistance of NaCl aerosol is 150 Pa to 230 Pa, the filtration efficiency is 97.3% to 99.6%, and the most easily penetrating particle size is 0.12 μm to 0.63 μm.

[0039] This invention involves distributing nylon 66A and nylon 66B melts with different relative viscosities in a parallel composite spinning manner, extruding them through a shaped spinneret, and forming them using a one-step TCS spinning process to obtain nylon 66 fibers with a shaped cross-section and a helical twist structure along the fiber length. The process of this invention offers good continuity and high controllability, enabling continuous industrial production. The resulting composite parallel fibers exhibit advantages such as low filtration resistance, high filtration accuracy, and long service life, making them widely applicable in the field of filter fabrics and possessing significant potential for widespread application. Attached Figure Description

[0040] Figure 1 A schematic diagram of the mesh structure of existing woven filter cloth;

[0041] Figure 2 A schematic diagram of the microgroove structure on the surface of nylon 66 fibers prepared according to an embodiment of the present invention;

[0042] Figure 3 SEM image of nylon 66 fiber monofilament for filter fabric prepared according to an embodiment of the present invention. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0044] To better illustrate the present invention, further examples are provided below.

[0045] The test method for the relative viscosity of nylon 66 in the following examples refers to GB / T 12006.1-2009 "Plastics Polyamide Part 1: Determination of Viscosity".

[0046] The test method for fiber irregularity refers to FZ / T 50002-2013 "Test Method for Irregularity of Chemical Fibers".

[0047] Fiber torsion test method: Under the conditions of room temperature 25℃ and humidity 65%, take a single filament from a fiber with an effective length of 30cm, apply a tension of 0.1cN / dtex, observe the number of cycles of spiral torsion of the fiber cross section along the fiber length direction, and take the average value of 20 sets of parallel test results as the torsion degree.

[0048] The fiber network density was tested according to FZT 50001 - Test Method for Network Degree of Synthetic Fiber Networks.

[0049] The tensile strength and elongation at break of the fiber were determined in accordance with the method specified in GB / T 14344-2022 "Test Method for Tensile Properties of Chemical Fiber Filaments".

[0050] The air permeability of the fabric prepared by fiber was tested according to GB / T 5453-1997 "Determination of Air Permeability of Textile Fabrics"; the filtration resistance and filtration efficiency of NaCl aerosol were tested according to GB / T38413-2019 "Test Method for Filtration Performance of Fine Particulate Matter in Textiles"; and the test method for the most easily penetrating particle size was tested according to GB / T38398-2019 "Determination of Most Easily Penetrating Particle Size for Filtration Performance of Textiles".

[0051] Example 1

[0052] This embodiment provides a method for preparing nylon 66 fiber for filter fabrics, including the following steps:

[0053] Step 1: Dry nylon 66 chips with a relative viscosity of 2.4 are melt-extruded using a screw extruder with zone temperatures of 265℃, 275℃, 285℃, 295℃, and 295℃. Simultaneously, dry nylon 66 chips with a relative viscosity of 2.8 are melt-extruded using a screw extruder with zone temperatures of 270℃, 280℃, 290℃, 295℃, and 295℃. The two streams of nylon 66 melt are metered separately using a metering pump and fed into a composite spinning box at a volume ratio of 1:1.4. The box temperature is 295℃. The nylon 66 melt is then extruded through a Y-shaped spinneret with a spinneret length-to-diameter ratio of 4:1 to obtain nascent filament.

[0054] Step 2: The nascent yarn is spun using a one-step TCS spinning-heat pipe drawing process. The nozzle stretch ratio is set to 100, the cooling air temperature to 16℃, the cooling air velocity to 0.5m / s, the cooling air humidity to 80%, the first guide roller speed to 800m / min, the heat pipe temperature to 210℃, the second guide roller speed to 3000m / min, and the winding speed to 2750m / min, to obtain nylon 66 fiber for filter fabrics.

[0055] The resulting fiber has a single filament fineness of 0.9 dtex, an anisotropy of 55%, and a twist of 90°; a breaking strength of 5.5 cN / dtex, a breaking strength CV value of 2.0%, a breaking elongation of 23.5%, and a breaking elongation CV value of 5.5%.

[0056] A single-layer plain weave woven fabric was prepared using the above-mentioned fibers, resulting in a fabric thickness of 0.5 mm and a weight of 100 g / m². 2 The air permeability is 0.0032m. 3 / m 2 The filtration resistance for NaCl aerosol is 150 Pa, the filtration efficiency is 99.6%, and the most easily penetrating particle size is 0.12 μm.

[0057] Example 2

[0058] This embodiment provides a method for preparing nylon 66 fiber for filter fabrics, including the following steps:

[0059] Step 1: Dry nylon 66 chips with a relative viscosity of 2.2 are melt-extruded using a screw extruder with zone temperatures of 265℃, 270℃, 275℃, 285℃, and 290℃. Simultaneously, dry nylon 66 chips with a relative viscosity of 2.5 are melt-extruded using a screw extruder with zone temperatures of 270℃, 275℃, 285℃, 290℃, and 290℃. The two streams of nylon 66 melt are metered separately using a metering pump and fed into a composite spinning box at a volume ratio of 1:1.5. The box temperature is 290℃. The nylon 66 melt is then extruded through an H-shaped spinneret with a spinneret length-to-diameter ratio of 3:1 to obtain nascent filament.

[0060] Step 2: The nascent yarn is spun using a one-step TCS spinning-heat pipe drawing process. The nozzle stretch ratio is set to 80, the cooling air temperature to 17℃, the cooling air velocity to 0.3m / s, the cooling air humidity to 75%, the first guide roller speed to 600m / min, the heat pipe temperature to 210℃, the second guide roller speed to 3000m / min, and the winding speed to 2750m / min, to obtain nylon 66 fiber for filter fabrics.

[0061] The resulting fiber has a single filament fineness of 1.5 dtex, an anisotropy of 30%, and a twist of 30; a breaking strength of 6.5 cN / dtex, a breaking strength CV value of 1.0%, a breaking elongation of 20.3%, and a breaking elongation CV value of 5.0%.

[0062] A single-layer plain weave woven fabric was prepared using the above-mentioned fibers, resulting in a fabric thickness of 2.0 mm and a weight of 500 g / m². 2 The air permeability is 0.0013m. 3 / m 2 The filtration resistance for NaCl aerosol is 230 Pa, the filtration efficiency is 97.3%, and the most easily penetrating particle size is 0.63 μm.

[0063] Example 3

[0064] This embodiment provides a method for preparing nylon 66 fiber for filter fabrics, including the following steps:

[0065] Step 1: Dry nylon 66 chips with a relative viscosity of 2.5 are melt-extruded using a screw extruder with zone temperatures of 275℃, 285℃, 295℃, 300℃, and 300℃. Simultaneously, dry nylon 66 chips with a relative viscosity of 3.0 are melt-extruded using a screw extruder with zone temperatures of 280℃, 295℃, 300℃, 300℃, and 300℃. The two streams of nylon 66 melt are metered separately using a metering pump and fed into a composite spinning box at a volume ratio of 1:1.3. The box temperature is 290℃. The nylon 66 melt is then extruded through a figure-eight spinneret with a spinneret orifice length-to-diameter ratio of 4:1 to obtain nascent filament.

[0066] Step 2: The nascent yarn is spun using a one-step TCS spinning-heat pipe drawing process. The nozzle stretch ratio is set to 90, the cooling air temperature to 17℃, the cooling air velocity to 0.4m / s, the cooling air humidity to 75%, the first guide roller speed to 700m / min, the heat pipe temperature to 205℃, the second guide roller speed to 3500m / min, and the winding speed to 3350m / min, to obtain nylon 66 fiber for filter fabrics.

[0067] The resulting fiber has a single filament fineness of 1.3 dtex, an anisotropy of 20%, and a twist of 70°; a breaking strength of 6.8 cN / dtex, a breaking strength CV value of 1.3%, a breaking elongation of 15.2%, and a breaking elongation CV value of 4.9%.

[0068] A single-layer plain weave woven fabric was prepared using the above-mentioned fibers, resulting in a fabric thickness of 1.0 mm and a weight of 354 g / m². 2 The air permeability is 0.0018m. 3 / m 2 The filtration resistance for NaCl aerosol is 192 Pa, the filtration efficiency is 98.9%, and the most easily penetrating particle size is 0.51 μm.

[0069] Example 4

[0070] This embodiment provides a method for preparing nylon 66 fiber for filter fabrics, including the following steps:

[0071] Step 1: Dry nylon 66 chips with a relative viscosity of 2.6 are melt-extruded using a screw extruder with zone temperatures of 275℃, 285℃, 295℃, 300℃, and 305℃. Simultaneously, dry nylon 66 chips with a relative viscosity of 3.2 are melt-extruded using a screw extruder with zone temperatures of 280℃, 295℃, 300℃, 305℃, and 305℃. The two streams of nylon 66 melt are metered separately using a metering pump and fed into a composite spinning box at a volume ratio of 1:0.67. The box temperature is 305℃. The nylon 66 melt is then extruded through a C-shaped spinneret with a spinneret length-to-diameter ratio of 3:1 to obtain nascent filament.

[0072] Step 2: The nascent yarn is spun using a one-step TCS spinning-heat pipe drawing process. The nozzle stretch ratio is set to 90, the cooling air temperature to 18℃, the cooling air velocity to 0.4m / s, the cooling air humidity to 77%, the first guide roller speed to 750m / min, the heat pipe temperature to 200℃, the second guide roller speed to 4000m / min, and the winding speed to 3700m / min, to obtain nylon 66 fiber for filter fabrics.

[0073] The resulting fiber has a single filament fineness of 1.1 dtex, an anisotropy of 40%, and a twist of 55; a breaking strength of 7.5 cN / dtex, a breaking strength CV value of 1.6%, a breaking elongation of 13.0%, and a breaking elongation CV value of 4.5%.

[0074] A single-layer plain weave woven fabric was prepared using the above-mentioned fibers, resulting in a fabric thickness of 0.86 mm and a weight of 210 g / m². 2 The air permeability is 0.0024m. 3 / m 2 The filtration resistance for NaCl aerosol is 175 Pa, the filtration efficiency is 99.1%, and the most easily penetrating particle size is 0.33 μm.

[0075] Example 5

[0076] This embodiment provides a method for preparing nylon 66 fiber for filter fabrics, including the following steps:

[0077] Step 1: Dry nylon 66 chips with a relative viscosity of 2.6 are melt-extruded using a screw extruder with zone temperatures of 275℃, 285℃, 295℃, 300℃, and 305℃. Simultaneously, dry nylon 66 chips with a relative viscosity of 3.2 are melt-extruded using a screw extruder with zone temperatures of 280℃, 295℃, 300℃, 305℃, and 305℃. The two streams of nylon 66 melt are metered separately using a metering pump and fed into a composite spinning box at a volume ratio of 1:0.77. The box temperature is 305℃. The nylon 66 melt is then extruded through a cross-shaped spinneret with a spinneret length-to-diameter ratio of 5:1 to obtain nascent filament.

[0078] Step 2: The nascent yarn is spun using a one-step TCS spinning-heat pipe drawing process. The nozzle stretch ratio is set to 90, the cooling air temperature to 16℃, the cooling air velocity to 0.3m / s, the cooling air humidity to 77%, the first guide roller speed to 650m / min, the heat pipe temperature to 195℃, the second guide roller speed to 3000m / min, and the winding speed to 2800m / min, to obtain nylon 66 fiber for filter fabrics.

[0079] The obtained fiber has a single filament fineness of 1.0 dtex, an anisotropy of 50%, and a twist of 79; a breaking strength of 7.1 cN / dtex, a breaking strength CV value of 1.8%, a breaking elongation of 15.5%, and a breaking elongation CV value of 5.5%.

[0080] A single-layer plain weave woven fabric was prepared using the above-mentioned fibers, resulting in a fabric thickness of 1.5 mm and a weight of 450 g / m². 2 The air permeability is 0.0015m. 3 / m 2 The filtration resistance for NaCl aerosol is 210 Pa, the filtration efficiency is 99.2%, and the most easily penetrating particle size is 0.24 μm.

[0081] Example 6

[0082] This embodiment provides a method for preparing nylon 66 fiber for filter fabrics, including the following steps:

[0083] Step 1: Dry nylon 66 chips with a relative viscosity of 2.6 are melt-extruded using a screw extruder with zone temperatures of 275℃, 285℃, 295℃, 300℃, and 305℃. Simultaneously, dry nylon 66 chips with a relative viscosity of 2.9 are melt-extruded using a screw extruder with zone temperatures of 280℃, 295℃, 300℃, 305℃, and 305℃. The two streams of nylon 66 melt are metered separately using a metering pump and fed into a composite spinning box at a volume ratio of 1:0.72. The box temperature is 305℃. The nylon 66 melt is then extruded through a cross-shaped spinneret with a spinneret length-to-diameter ratio of 4:1 to obtain nascent filament.

[0084] Step 2: The nascent yarn is spun using a one-step TCS spinning-heat pipe drawing process. The nozzle stretch ratio is set to 100, the cooling air temperature to 16℃, the cooling air velocity to 0.4m / s, the cooling air humidity to 80%, the first guide roller speed to 700m / min, the heat pipe temperature to 215℃, the second guide roller speed to 3700m / min, and the winding speed to 3350m / min, to obtain nylon 66 fiber for filter fabrics.

[0085] The obtained fiber has a single filament fineness of 1.0 dtex, an anisotropy of 45%, and a twist of 66; a breaking strength of 6.8 cN / dtex, a breaking strength CV value of 1.9%, a breaking elongation of 19.3%, and a breaking elongation CV value of 5.11%.

[0086] A single-layer plain weave woven fabric was prepared using the above-mentioned fibers, resulting in a fabric thickness of 0.8 mm and a weight of 178 g / m². 2 The air permeability is 0.0028m. 3 / m 2 The filtration resistance for NaCl aerosol is 162 Pa, the filtration efficiency is 99.4%, and the most easily penetrating particle size is 0.19 μm.

[0087] Comparative Example 1

[0088] This comparative example provides a method for preparing nylon 66 fiber for filter fabrics. The only difference from Example 1 is that parallel composite spinning is not used. Instead, a single dry nylon 66 chip with a relative viscosity of 2.4 is used for melt extrusion using a screw extruder with zone temperatures of 265°C, 275°C, 285°C, 295°C, and 295°C. The melt is delivered to the housing at a flow rate equal to the sum of the pump feed rates of the two screws in Example 1. All other conditions are exactly the same as in Example 1.

[0089] The obtained fiber has a single filament fineness of 0.79 dtex, an anisotropy of 50%, a twist of 3, a breaking strength of 6.0 cN / dtex, a breaking strength CV value of 1.8%, a breaking elongation of 20.6%, and a breaking elongation CV value of 5.2%.

[0090] A single-layer plain weave woven fabric was prepared using the above-mentioned fibers, resulting in a fabric thickness of 0.43 mm and a weight of 89 g / m². 2 The air permeability is 0.0008m. 3 / m 2 The filtration resistance for NaCl aerosol is 271 Pa, the filtration efficiency is 99.7%, and the most easily penetrating particle size is 0.1 μm.

[0091] The comparison revealed that although the comparative example obtained irregularly shaped fibers and caused some torsion due to uneven cooling caused by the non-circular cross-section, the torsion effect was significantly lower than that of Example 1. Moreover, the irregular cross-section resulted in a more compact fiber packing, which led to a significant decrease in the air permeability of the prepared filter cloth and a sharp increase in filtration resistance.

[0092] Comparative Example 2

[0093] This comparative example provides a method for preparing nylon 66 fiber for filter fabrics. The only difference from Example 1 is that a round-hole spinneret is used instead of a Y-shaped spinneret; otherwise, they are exactly the same.

[0094] The resulting fiber has a single filament fineness of 0.91 dtex, a twist rate of 76, a breaking strength of 6.2 cN / dtex, a breaking strength CV value of 2.2%, a breaking elongation of 19.2%, and a breaking elongation CV value of 7.3%.

[0095] A single-layer plain weave woven fabric was prepared using the above-mentioned fibers, resulting in a fabric thickness of 0.51 mm and a weight of 105 g / m². 2 The air permeability is 0.0011m. 3 / m 2 The filtration resistance for NaCl aerosol is 251 Pa, the filtration efficiency is 96.1%, and the most easily penetrating particle size is 0.45 μm.

[0096] Comparison reveals that circular cross-section self-twisting fibers obtained through parallel composite spinning have low air permeability and high filtration resistance because the fiber surface lacks groove structures to serve as auxiliary channels for fluid filtration.

[0097] Comparative Example 3

[0098] This comparative example provides a method for preparing nylon 66 fiber for filter fabrics. The only difference from Example 6 is that the spinneret used has an aspect ratio of 1.5:1, while the rest are exactly the same.

[0099] The obtained fiber has a single filament fineness of 1.0 dtex, an anisotropy of 15%, and a twist of 51; a breaking strength of 6.9 cN / dtex, a breaking strength CV value of 1.8%, a breaking elongation of 18.2%, and a breaking elongation CV value of 5.3%.

[0100] A single-layer plain weave woven fabric was prepared using the above-mentioned fibers, resulting in a fabric thickness of 0.75 mm and a weight of 160 g / m². 2 The air permeability is 0.0012m. 3 / m 2 The filtration resistance for NaCl aerosol is 250 Pa, the filtration efficiency is 99.3%, and the most easily penetrating particle size is 0.31 μm.

[0101] Compared with Example 6, the spinneret used in this comparative example has a smaller aspect ratio and significant orifice expansion. The shape retention of the melt ejected from the spinneret is significantly reduced, resulting in a significant decrease in the shape of the final fiber. The depth of the grooves on the fiber surface is reduced, and the additional passage of the filtration fluid provided is reduced, thus reducing air permeability and increasing filtration resistance.

[0102] Comparative Example 4

[0103] This comparative example provides a method for preparing nylon 66 fiber for filter fabrics. The only difference from Example 6 is that the heat pipe temperature is 185°C, while the other conditions are exactly the same.

[0104] The obtained fiber has a single filament fineness of 1.0 dtex, an anisotropy of 40%, a twist of 15, and is spring-like; its breaking strength is 6.1 cN / dtex, its breaking strength CV value is 2.1%, its breaking elongation is 21%, and its breaking elongation CV value is 5.4%.

[0105] A single-layer plain weave woven fabric was prepared using the above-mentioned fibers, resulting in a fabric thickness of 1.24 mm and a weight of 251 g / m². 2 The air permeability is 0.0051m. 3 / m 2 The filtration resistance for NaCl aerosol is 113 Pa, the filtration efficiency is 31.3%, and the most easily penetrating particle size is 0.8 μm.

[0106] Compared with Example 6, the heat pipe temperature in this comparative example is lower, which leads to a large stretching tension and amplifies the stress difference between the two parallel phases, resulting in increased fiber crimping. At this lower temperature, most of the spring-like crimp of the fibers is not straightened but is transformed into the twisting of the fibers themselves along the fiber axis, resulting in fluffy multifilaments. As a result, the fabric structure is loose, the filtration efficiency drops sharply, and it almost loses its filtration effect.

[0107] 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 or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A type of nylon 66 fiber for filter fabrics, characterized in that, It is a parallel composite fiber, including a first parallel structure and a second parallel structure. The first parallel structure is nylon 66A and the second parallel structure is nylon 66B. The surface of the parallel composite fiber has microgrooves and the fiber itself has a twisted helical structure along the length direction. Its cross-sectional irregularity is 20%~55% and its twist is 30~90. The relative viscosities of both nylon 66A and nylon 66B are 2.2 to 3.2, and the relative viscosity of nylon 66B is 0.3 to 0.6 greater than that of nylon 66A. The nylon 66 fiber used in the filter fabric is prepared by the following method: Nylon 66A melt and Nylon 66B melt are distributed in a parallel composite spinning method and extruded through a shaped spinneret. After cooling, they are shaped by a heat pipe spinning process to obtain Nylon 66 fiber for filter fabrics. The spinneret has a spinneret orifice length-to-diameter ratio of 2:1 to 5:1; a nozzle draw ratio of 80 to 100; a cooling air temperature of 16℃ to 18℃; a cooling air velocity of 0.3m / s to 0.5m / s; and a heat pipe temperature of 195℃ to 215℃. By using heat pipe drawing and setting a high drawing temperature, in the drawing section of the heat pipe, parallel components with structural differences will produce different stress responses under the action of tensile force, resulting in a curling tendency. Under the action of tensile stress, the fiber is straightened and the torsional structure is maintained on the fiber itself, just like the effect of a spring being straightened. In the shaping section of the heat pipe, this irregular cross-section helically twisted structure around the fiber length direction is fixed under the action of tensile stress and hot air through the mechanism of tension heat shaping.

2. The nylon 66 fiber for filter fabrics as described in claim 1, characterized in that, The nylon 66 fiber used in the filter fabric has a single filament fineness of 0.9 dtex to 1.5 dtex.

3. The nylon 66 fiber for filter fabrics as described in claim 1, characterized in that, The nylon 66 fiber used in the filter fabric has a breaking strength of 5.5 cN / dtex to 7.5 cN / dtex, a breaking strength CV value of 1.5 ± 0.5%, a breaking elongation of 13.0% to 23.5%, a breaking elongation CV value of 5.0 ± 0.5%, and a network density of 10 to 20 fibers / m.

4. The method for preparing nylon 66 fiber for filter fabrics according to any one of claims 1 to 3, characterized in that, Includes the following steps: Nylon 66A melt and Nylon 66B melt are distributed in a parallel composite spinning method and extruded through a shaped spinneret. After cooling, they are shaped by a heat pipe spinning process to obtain Nylon 66 fiber for filter fabrics. The spinneret has a spinneret orifice length-to-diameter ratio of 2:1 to 5:1; a nozzle stretch ratio of 80 to 100; a cooling air temperature of 16℃ to 18℃; a cooling air velocity of 0.3m / s to 0.5m / s; and a heat pipe temperature of 195℃ to 215℃.

5. The method for preparing nylon 66 fiber for filter fabrics as described in claim 4, characterized in that, Specifically, the steps include the following: Step a: Nylon 66A melt and Nylon 66B melt are fed into the composite spinning assembly through their respective melt pipes according to a preset ratio, and extruded through parallel composite shaped spinnerets to obtain nascent filament; Step b: After cooling the nascent filaments, they are stretched and wound into a heat pipe to obtain nylon 66 fibers for filter fabrics.

6. The method for preparing nylon 66 fiber for filter fabrics as described in claim 5, characterized in that, In step a, the volume ratio of the nylon 66A melt to the nylon 66B melt is 1:0.67 to 1:0.77; or In step a, the volume ratio of the nylon 66A melt to the nylon 66B melt is 1:1.3 to 1:1.

5.

7. The method for preparing nylon 66 fiber for filter fabrics as described in claim 5, characterized in that, In step a, the spinneret holes of the parallel composite irregular spinneret are Y-shaped, H-shaped, C-shaped, figure-eight-shaped, or cross-shaped.

8. The method for preparing nylon 66 fiber for filter fabrics as described in claim 5, characterized in that, The temperature of the composite spinning assembly is 290℃~305℃, the humidity of the cooling air is 75%~80%, the rotation speed of the first guide roller is 600m / min~800m / min, the rotation speed of the second guide roller is 3000m / min~4000m / min, and the winding speed is 2750m / min~3700m / min.

9. A single-layer woven plain weave fabric, characterized in that, It is prepared from nylon 66 fiber of filter fabric as described in any one of claims 1 to 3.

10. The single-layer woven plain weave fabric as described in claim 9, characterized in that, The thickness of the single-layer woven plain weave fabric is 0.5mm~2.0mm, and the weight per unit area is 100g / m². 2 ~500g / m 2 The air permeability is 0.0013m. 3 / m 2 ․ s~0.0032m 3 / m 2 The filtration resistance for NaCl aerosol is 150 Pa to 230 Pa, the filtration efficiency is 97.3% to 99.6%, and the most easily penetrating particle size is 0.12 μm to 0.63 μm.

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