Nylon 66 fiber for filter fabric as well as preparation method and application of nylon 66 fiber

Abstract

The invention relates to the technical field of synthetic fibers, and particularly discloses a nylon 66 fiber for filter fabric as well as a preparation method and application of the nylon 66 fiber. Nylon 66A and nylon 66B melts with different relative viscosities are distributed in a parallel composite spinning mode and then extruded through a special-shaped spinneret plate, forming is conducted through a TCS one-step spinning process, and the nylon 66 fiber with micro grooves in the fiber surface and with a twisted spiral structure in the length direction is prepared. Even if warp and weft crossed meshes of the fabric are blocked by solid particles, under the action of filtering pressure, fluid can still be transferred to the lower portion from the position above the fibers (the direction of incoming flow of filtered fluid) along the micro-grooves, and it can be guaranteed that the fluid penetrates through the filter cloth to flow smoothly by stacking the micro-grooves layer by layer. The prepared composite parallel fiber has the advantages of being small in filtering resistance, high in filtering precision, long in service life and the like, can be widely applied to the field of filter fabrics, and has high application and popularization value.

Description

Technical Field

[0001] The invention relates to the technical field of synthetic fibers, and in particular to a nylon 66 fiber for filter fabrics, and a preparation method and application thereof. Background Art

[0002] In the process of spinning and forming synthetic fibers, fibers or hollow fibers with non-circular cross-sections spun by using special-shaped spinnerets are called special-shaped interface fibers, or special-shaped fibers for short. Special-shaped cross-section fibers have a larger specific surface area than circular cross-section fibers, and have a higher bending modulus, so they have strong deformation resistance and good wrinkle resistance. In addition, there are two or more unmixed polymers on the cross section of the fiber. This kind of chemical fiber is called composite fiber or bicomponent fiber. Composite fibers can be divided into two categories according to their morphology: double-layer type and multi-layer type. Double-layer type includes parallel type and skin-core type. Among them, the main characteristic of parallel type composite fibers is high curling.

[0003] Filter fabric refers to textiles used to filter impurities in gas or liquid. Separating solid particles from liquid is called wet filtration, while purifying air and separating dust and smoke from gas is called dry filtration. There are many types of filter fabrics, such as organic fabrics, non-woven fabrics, felt sheets, and screens. Among them, woven fabrics have a smooth surface, which is easy to remove filter residues and conducive to the recovery of solid matter, and are often used for wet filtration. Woven fabrics use the mesh formed by the intersection of warp and weft threads (the size is generally tens to 2000 μm) and / or the gaps between the fibers of the warp and weft threads themselves to provide filtering effects.

[0004] Nylon filter cloth is made of polyamide fiber, which has the advantages of high temperature resistance, chemical corrosion resistance, high tensile strength, etc. It is often used in a variety of industrial applications such as liquid filtration, gas filtration, powder filtration, etc. Its fine fiber structure can capture tiny particles and impurities, thereby achieving efficient filtration effects. However, in situations where the filtration load is large or the filtration accuracy is high, the particle capture efficiency is very high, and the filter holes and gaps of the woven fabric will quickly be blocked and occupied by particles, resulting in increased flow resistance, reduced service life of the filter element, flow path blockage and other adverse consequences. Therefore, it is of great significance to develop a high-quality filter woven fabric with a small mesh size, high particle capture efficiency, long service life and low flow resistance. Summary of the invention

[0005] In view of the problems of short service life and large flow resistance in the use of nylon filter cloth in the prior art, the present invention provides a nylon 66 fiber for filter fabric and a preparation method thereof. The present invention adopts a parallel composite spinning method to control the process parameters of the spinning process, and prepares a woven filter cloth with micro grooves on the fiber surface and a twisted spiral structure along the length direction of the fiber itself. The woven filter cloth has small filtration resistance, high filtration accuracy, long service life, and can realize continuous production, and has broad market prospects.

[0006] In order to solve the above technical problems, the technical solution provided by the present invention is:

[0007] In a first aspect, the present invention further provides a nylon 66 fiber for filter fabric, which is a parallel composite fiber, comprising 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 micro grooves and the fiber itself has a twisted spiral structure along the length direction, and the cross-sectional profile is 20% to 55%, and the twist degree is 30 to 90;

[0008] The relative viscosities of nylon 66A and nylon 66B are both 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 common woven filter cloths, such as polyolefin, polyester, polyamide and other fibers, are formed by melt spinning, and their monofilaments have a circular cross-section. According to the characteristics of the weaving process, the intersection of the warp and weft yarns of the woven fabric will form a mesh structure (such as Figure 1 As shown in the figure, it can intercept solid particles in the filtered fluid; if the warp and weft yarns are multifilaments, when the filtered fluid flows through the gaps between the yarns, the fine particles in the fluid can also be intercepted by adsorption. Therefore, the filtering effect of the woven filter cloth is related to its weaving structure. If the size of the elementary particles to be filtered is small, it is necessary to reduce the size of the mesh of the warp and weft and the gaps between the yarns.

[0010] One method to achieve the above purpose is to reduce the thickness of the yarn (reduce the fineness or increase the count). The larger the yarn count, the easier it is to obtain a dense woven structure. This can be achieved by reducing the number of single filaments in the multifilament yarn and / or reducing the fineness of the single filament. In addition, special-shaped fibers can also be used. Non-circular cross-sectional fibers with the same cross-sectional area have a larger circumference than circular cross-sectional fibers, and therefore have a larger specific surface area, thereby providing a stronger adsorption effect.

[0011] However, when the filtration load is large (i.e., there are a large number of particles in the fluid) or the filtration accuracy is high (i.e., there are a large number of fine particles in the fluid), the mesh interception and microstructure adsorption of the woven fabric will easily reach saturation, and the smaller the mesh size and the stronger the adsorption effect, the faster it reaches saturation, thereby blocking the flow path and causing the filtration flow resistance to increase.

[0012] In order to solve the above problems, the present invention provides a special-shaped fiber, the surface of which has a micro-groove structure and the fiber itself has a twisted spiral structure along the length direction (such as Figure 2-3As shown in the figure, the fiber itself is straight, but the cross section of the fiber along the fiber axis is twisted. The straight fiber can fit more closely to avoid deformation under the filtering pressure and ensure the filtering effect. At the same time, the twisted cross section can make the micro groove structure on the fiber surface transfer from one side to the other side, so that even if the warp and weft cross mesh of the fabric itself is blocked by solid particles, under the action of filtering pressure, the fluid can still be transferred from the top of the fiber (the filtering fluid flow direction) to the bottom along the micro groove. When stacked layer by layer, it can ensure that the fluid penetrates the filter cloth and flows smoothly.

[0013] However, due to the large molecular weight, the mixing entropy change of polymers is much smaller than that of small molecules, so the compatibility is generally poor. In order to ensure that the special-shaped cross-section of the parallel composite yarn is not destroyed, the present invention uses nylon 66 with different relative viscosities to prepare the special-shaped composite yarn. The physical properties of nylons with different relative viscosities are different, so the curling effect of the parallel composite yarn can be produced; at the same time, because there is hydrogen bond interaction between nylon molecules, the compatibility between components is relatively good. In addition, compared with nylon 6, nylon 66 has better heat resistance and mechanical properties, which is conducive to improving the service life of the filter fabric.

[0014] It should be noted that the relative viscosity of nylon 66A and nylon 66B described in the present invention refers to the relative viscosity measured by the formic acid method, and the test method refers to GB / T 12006.1-2009 "Plastic polyamide Part 1: Determination of viscosity number".

[0015] It should be noted that the degree of twist is the number of cycles of helical 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 single-filament fineness of the nylon 66 fiber used for the filter fabric is 0.9 dtex to 1.5 dtex.

[0017] Furthermore, the breaking strength of the nylon 66 fiber for the filter fabric is 5.5 cN / dtex to 7.5 cN / dtex, the breaking strength CV value is 1.5±0.5%, the breaking elongation is 13.0% to 23.5%, the breaking elongation CV value is 5.0±0.5%, and the network degree is 10 to 20 pieces / m.

[0018] In a second aspect, the present invention provides a method for preparing nylon 66 fiber for filter fabric, comprising the following steps:

[0019] Nylon 66A melt and nylon 66B melt with different relative viscosities are distributed in a parallel composite spinning mode and then extruded through a special-shaped spinneret, and then formed through a hot pipe spinning process after cooling to obtain nylon 66 fiber for filter fabric;

[0020] Among them, the aspect ratio of the spinneret holes of the special-shaped spinneret is 2:1-5:1; the nozzle stretching ratio is 80-100; the cooling air temperature is 16°C-18°C, the cooling air speed is 0.3m / s-0.5m / s; and the heat pipe temperature is 195°C-215°C.

[0021] The main technical points of the method for preparing nylon 66 fiber for filter fabric provided by the present invention are: first, to make nylon 66 fiber produce and maintain high profile, so that a micro-groove structure is formed on the fiber surface; second, to straighten the spring-like curled structure (i.e., the twisted structure of the axis itself in the fiber length direction) that is usually produced by the parallel composite fiber and convert it into a spiral twist of the fiber cross section along the fiber axis. The spring-like curled yarn structure is fluffy and is easily deformed under the action of filtering pressure, so that the gap between fibers becomes larger and loses the filtering effect. In order to achieve the above purpose, the present invention adopts the following means:

[0022] (1) Nylon 66A and nylon 66B with different viscosities are used as composite parallel spinning raw materials. The physical properties of nylons with different relative viscosities (i.e., different molecular weights) are different, which can produce the curling effect of parallel composite yarns. At the same time, due to the hydrogen bond interaction between nylon molecules, the compatibility between the components is relatively good, which can ensure that the special-shaped cross-section of the parallel composite yarn is not destroyed.

[0023] (2) Using a special-shaped spinneret with a higher spinneret hole aspect ratio and setting a higher nozzle stretch ratio, the melts with different molecular weights have different fluidity, and different internal structures (such as orientation force and internal stress) will be formed under the action of the flow field force when the melt enters the spinneret hole. The large spinneret hole aspect ratio is conducive to the relaxation of some internal stress of the spinning melt in the hole; at the same time, using a higher nozzle stretch ratio, on the one hand, will make the orifice expansion of the spinning melt smaller, which is conducive to the maintenance of the special-shaped cross-section, and at the same time will play a certain role in weakening the structural differences of the parallel components, which is conducive to straightening the curled structure that is usually easy to form during subsequent stretching.

[0024] (3) The conditions of enhanced cooling are adopted to accelerate the cooling of the spinning melt stream by controlling the air cooling temperature and cooling wind speed, and at the same time, the special shapes of the solidified filaments and the structural differences of the parallel components are improved.

[0025] (4) Heat pipe stretching is used and a relatively high stretching temperature is set. In the stretching section (front end) of the heat pipe, the parallel components with different structures will produce different stress responses under the action of the tensile force and produce a curling tendency. Under the action of the tensile stress, the fiber is straightened while the torsional structure remains on the fiber itself, just like the effect of a spring being straightened. In the shaping section (rear end) of the heat pipe, this structure with a special-shaped cross-section that is helically twisted around the length direction of the fiber is fixed by the tensile stress and hot air through a tensile heat shaping mechanism.

[0026] Specifically, the preparation method of nylon 66 fiber for filter fabric comprises the following steps:

[0027] Step a, introducing nylon 66A melt and nylon 66B melt into a composite spinning assembly through respective melt pipes according to a preset ratio, and extruding through parallel composite special-shaped spinnerets to obtain primary yarn;

[0028] Step b, after cooling the spun silk, entering into a hot pipe for stretching and winding to obtain nylon 66 fiber for filter fabric.

[0029] Furthermore, 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] Furthermore, 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] If the parallel composite ratio of nylon 66A melt and nylon 66B melt is too far from 1, the curling effect will be poor, and if it is too close to 1, the curling will be too strong and difficult to straighten.

[0032] Furthermore, nylon 66A and nylon 66B of the present invention are melt-extruded by a screw extruder. Specifically, the temperature of each temperature of the screw extruder can be set according to the properties of the nylon 66 raw material, and the present invention does not make any special restrictions.

[0033] As a specific embodiment of the present invention, nylon 66A melt and nylon 66B melt are passed through a metering pump and then enter a composite spinning assembly.

[0034] Specifically, in step a, the spinneret holes of the parallel composite special-shaped spinneret are in a Y-shape, an H-shape, a C-shape, an 8-shape or a cross-shape.

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

[0036] By controlling the above conditions, nylon 66 fibers with a special-shaped cross section and a spiral structure along the length direction can be prepared, providing a fiber raw material with excellent performance for filter machine fabrics.

[0037] In a third aspect, the present invention further provides a single-layer woven plain fabric, which is prepared from the nylon 66 fiber for filter fabric described in any one of the above items.

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

[0039] The present invention distributes nylon 66A and nylon 66B melts with different relative viscosities in a parallel composite spinning mode, extrude them through a special-shaped spinneret, and form them using a TCS one-step spinning process to obtain nylon 66 fibers with a special-shaped cross-section and a spiral twisted structure along the length of the fiber. The process of the present invention has good continuity and high controllability, and can realize industrial continuous production. The prepared composite parallel fibers have the advantages of small filtration resistance, high filtration accuracy, long service life, etc., and can be widely used in the field of filter fabrics, and have high promotion and application value. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0041] Figure 2 A schematic diagram of the micro-groove structure on the surface of nylon 66 fiber prepared in an embodiment of the present invention;

[0042] Figure 3 This is a SEM image of nylon 66 fiber monofilament for filter fabric prepared in an embodiment of the present invention. DETAILED DESCRIPTION

[0043] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0044] In order to better illustrate the present invention, further examples are given below.

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

[0046] The test method for fiber profile refers to FZ / T 50002-2013 "Test method for chemical fiber profile".

[0047] Fiber twist test method: Under room temperature of 25°C and humidity of 65%, take a single fiber with an effective length of 30 cm, apply a tension of 0.1 cN / dtex, observe the number of cycles of spiral twisting of the fiber cross section along the fiber length direction, and take the average value of the results of 20 groups of parallel tests, which is defined as the twist.

[0048] The fiber interlacing degree is tested according to FZT 50001-Test method for interlacing degree of synthetic fiber.

[0049] The fiber breaking strength and breaking elongation are determined in accordance with GB / T 14344-2022 "Test method for tensile properties of chemical fiber filaments".

[0050] The fiber is used to prepare a single-layer plain woven fabric, and the test method for the air permeability of the obtained fabric refers to GB / T 5453-1997 "Determination of Air Permeability of Textile Fabrics"; the test of filtration resistance and filtration efficiency of NaCl aerosol refers to GB / T38413-2019 "Test Method for Filtration Performance of Fine Particles in Textiles"; the test method of the most penetrating particle size refers to GB / T38398-2019 "Determination of the Most Penetrating Particle Size of Filtration Performance of Textiles".

[0051] Example 1

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

[0053] Step 1, slice dry nylon 66 with a relative viscosity of 2.4, and melt extrude it using a screw extruder with zone temperatures of 265°C, 275°C, 285°C, 295°C, and 295°C; at the same time, slice dry nylon 66 with a relative viscosity of 2.8, and melt extrude it using a screw extruder with zone temperatures of 270°C, 280°C, 290°C, 295°C, and 295°C; the two nylon 66 melts are respectively measured by metering pumps, and are merged into a composite spinning box at a volume ratio of 1:1.4, the box temperature is 295°C, and then extruded through a Y-shaped hole spinneret with a spinneret length-to-diameter ratio of 4:1 to obtain primary yarn;

[0054] Step 2: The spun yarn is subjected to a one-step TCS spinning-hot pipe stretching process, with the nozzle stretching ratio set to 100, the cooling air temperature to 16°C, the cooling air speed to 0.5 m / s, the cooling air humidity to 80%, the first guide roller speed to 800 m / min, the hot pipe temperature to 210°C, the second guide roller speed to 3000 m / min, and the winding speed to 2750 m / min to obtain nylon 66 fiber for filter fabric.

[0055] The obtained fiber has a single-filament fineness of 0.9 dtex, a profile of 55%, a torsion 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] The above fibers were used to prepare a single-layer plain woven fabric, the resulting fabric had a thickness of 0.5 mm and a weight of 100 g / m 2 , air permeability is 0.0032m 3 / m 2 ·s, the filtration resistance to NaCl aerosol is 150Pa, the filtration efficiency is 99.6%, and the most penetrating particle size is 0.12μm.

[0057] Example 2

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

[0059] Step 1, slice dry nylon 66 with a relative viscosity of 2.2, and melt extrude it using a screw extruder with zone temperatures of 265°C, 270°C, 275°C, 285°C, and 290°C; at the same time, slice dry nylon 66 with a relative viscosity of 2.5, and melt extrude it using a screw extruder with zone temperatures of 270°C, 275°C, 285°C, 290°C, and 290°C; the two nylon 66 melts are respectively measured by metering pumps, and are merged into a composite spinning box at a volume ratio of 1:1.5, the box temperature is 290°C, and then extruded through an H-shaped hole spinneret with a spinneret aspect ratio of 3:1 to obtain primary yarn;

[0060] Step 2: The spun yarn is subjected to a one-step TCS spinning-hot pipe stretching process, with the nozzle stretching ratio set to 80, the cooling air temperature to 17°C, the cooling air speed to 0.3 m / s, the cooling air humidity to 75%, the first guide roller speed to 600 m / min, the hot pipe temperature to 210°C, the second guide roller speed to 3000 m / min, and the winding speed to 2750 m / min to obtain nylon 66 fiber for filter fabric.

[0061] The obtained fiber has a single-filament fineness of 1.5 dtex, a profile of 30%, a torsion 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] The above fibers were used to prepare a single-layer plain woven fabric, the resulting fabric had a thickness of 2.0 mm and a weight of 500 g / m 2 , air permeability is 0.0013m 3 / m 2 ·s, the filtration resistance to NaCl aerosol is 230Pa, the filtration efficiency is 97.3%, and the most penetrating particle size is 0.63μm.

[0063] Example 3

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

[0065] Step 1, slice dry nylon 66 with a relative viscosity of 2.5, and melt extrude it using a screw extruder with zone temperatures of 275°C, 285°C, 295°C, 300°C, and 300°C; at the same time, slice dry nylon 66 with a relative viscosity of 3.0, and melt extrude it using a screw extruder with zone temperatures of 280°C, 295°C, 300°C, 300°C, and 300°C; the two nylon 66 melts are respectively measured by metering pumps, and are merged into a composite spinning box at a volume ratio of 1:1.3, the box temperature is 290°C, and then extruded through an 8-shaped hole spinneret with a spinneret length-to-diameter ratio of 4:1 to obtain primary yarn;

[0066] Step 2: The spun yarn is subjected to a one-step TCS spinning-hot pipe stretching process, and the nozzle stretching ratio is set to 90, the cooling air temperature is 17°C, the cooling air speed is 0.4 m / s, the cooling air humidity is 75%, the first guide roller speed is 700 m / min, the hot pipe temperature is 205°C, the second guide roller speed is 3500 m / min, and the winding speed is 3350 m / min to obtain nylon 66 fiber for filter fabric.

[0067] The obtained fiber has a single-filament fineness of 1.3 dtex, a profile of 20%, a torsion 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] The above fibers were used to prepare a single-layer plain woven fabric, the resulting fabric had a thickness of 1.0 mm and a weight of 354 g / m 2 , air permeability is 0.0018m 3 / m 2 ·s, the filtration resistance to NaCl aerosol is 192Pa, the filtration efficiency is 98.9%, and the most penetrable particle size is 0.51μm.

[0069] Example 4

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

[0071] Step 1, slice dry nylon 66 with a relative viscosity of 2.6, and melt extrude it using a screw extruder with zone temperatures of 275°C, 285°C, 295°C, 300°C, and 305°C; at the same time, slice dry nylon 66 with a relative viscosity of 3.2, and melt extrude it using a screw extruder with zone temperatures of 280°C, 295°C, 300°C, 305°C, and 305°C; the two nylon 66 melts are respectively measured by metering pumps, and are merged into a composite spinning box at a volume ratio of 1:0.67, the box temperature is 305°C, and then extruded through a C-shaped hole spinneret with a spinneret aspect ratio of 3:1 to obtain primary yarn;

[0072] Step 2: The spun yarn is subjected to a one-step TCS spinning-hot pipe stretching process, with the nozzle stretching ratio set to 90, the cooling air temperature to 18°C, the cooling air speed to 0.4 m / s, the cooling air humidity to 77%, the first guide roller speed to 750 m / min, the hot pipe temperature to 200°C, the second guide roller speed to 4000 m / min, and the winding speed to 3700 m / min to obtain nylon 66 fiber for filter fabric.

[0073] The obtained fiber has a single-filament fineness of 1.1 dtex, a profile of 40%, a torsion 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] The above fibers were used to prepare a single-layer plain woven fabric, the resulting fabric had a thickness of 0.86 mm and a weight of 210 g / m 2 , air permeability is 0.0024m 3 / m 2 ·s, the filtration resistance to NaCl aerosol is 175Pa, the filtration efficiency is 99.1%, and the most penetrable particle size is 0.33μm.

[0075] Example 5

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

[0077] Step 1, slice dry nylon 66 with a relative viscosity of 2.6, and melt extrude it using a screw extruder with zone temperatures of 275°C, 285°C, 295°C, 300°C, and 305°C; at the same time, slice dry nylon 66 with a relative viscosity of 3.2, and melt extrude it using a screw extruder with zone temperatures of 280°C, 295°C, 300°C, 305°C, and 305°C; the two nylon 66 melts are respectively measured by metering pumps, and are merged into a composite spinning box at a volume ratio of 1:0.77, the box temperature is 305°C, and then extruded through a cross-shaped hole spinneret with a spinneret aspect ratio of 5:1 to obtain primary yarn;

[0078] Step 2: The spun yarn is subjected to a one-step TCS spinning-hot pipe stretching process, with the nozzle stretching ratio set to 90, the cooling air temperature to 16°C, the cooling air speed to 0.3 m / s, the cooling air humidity to 77%, the first guide roller speed to 650 m / min, the hot pipe temperature to 195°C, the second guide roller speed to 3000 m / min, and the winding speed to 2800 m / min to obtain nylon 66 fiber for filter fabric.

[0079] The obtained fiber has a single-filament fineness of 1.0 dtex, a profile of 50%, a torsion 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] The above fibers were used to prepare a single-layer plain woven fabric, the resulting fabric had a thickness of 1.5 mm and a weight of 450 g / m 2 , air permeability is 0.0015m 3 / m 2 ·s, the filtration resistance to NaCl aerosol is 210Pa, the filtration efficiency is 99.2%, and the most penetrable particle size is 0.24μm.

[0081] Example 6

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

[0083] Step 1, slice dry nylon 66 with a relative viscosity of 2.6, and melt extrude it using a screw extruder with zone temperatures of 275°C, 285°C, 295°C, 300°C, and 305°C; at the same time, slice dry nylon 66 with a relative viscosity of 2.9, and melt extrude it using a screw extruder with zone temperatures of 280°C, 295°C, 300°C, 305°C, and 305°C; the two nylon 66 melts are respectively metered by metering pumps, and are merged into a composite spinning box at a volume ratio of 1:0.72, the box temperature is 305°C, and then extruded through a cross-shaped hole spinneret with a spinneret aspect ratio of 4:1 to obtain primary yarn;

[0084] Step 2: The spun yarn is subjected to a one-step TCS spinning-hot pipe stretching process, with the nozzle stretching ratio set to 100, the cooling air temperature to 16°C, the cooling air speed to 0.4 m / s, the cooling air humidity to 80%, the first guide roller speed to 700 m / min, the hot pipe temperature to 215°C, the second guide roller speed to 3700 m / min, and the winding speed to 3350 m / min to obtain nylon 66 fiber for filter fabric.

[0085] The obtained fiber has a single-filament fineness of 1.0 dtex, a profile of 45%, a torsion 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] The above fibers were used to prepare a single-layer plain woven fabric, the resulting fabric had a thickness of 0.8 mm and a weight of 178 g / m 2 , air permeability is 0.0028m 3 / m 2 ·s, the filtration resistance to NaCl aerosol is 162Pa, the filtration efficiency is 99.4%, and the most penetrable particle size is 0.19μm.

[0087] Comparative Example 1

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

[0089] The obtained fiber had a single-filament fineness of 0.79 dtex, a profile of 50%, a torsion 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] The above fibers were used to prepare a single-layer plain woven fabric, the resulting fabric had a thickness of 0.43 mm and a weight of 89 g / m 2 , air permeability is 0.0008m 3 / m 2 ·s, the filtration resistance to NaCl aerosol is 271Pa, the filtration efficiency is 99.7%, and the most penetrating particle size is 0.1μm.

[0091] By comparison, it can be found that although the comparative example obtained shaped fibers and the uneven cooling caused by the non-circular cross-section produced a certain degree of twisting, the twisting effect was significantly lower than that of Example 1. In addition, the fibers were more densely packed due to the shaped cross-section, resulting in a significant decrease in the air permeability of the prepared filter cloth and a sharp increase in the filtration resistance.

[0092] Comparative Example 2

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

[0094] The obtained fiber had a single-filament fineness of 0.91 dtex, a twist degree 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] The above fibers were used to prepare a single-layer plain woven fabric, the resulting fabric had a thickness of 0.51 mm and a weight of 105 g / m 2 , air permeability is 0.0011m 3 / m 2 ·s, the filtration resistance to NaCl aerosol is 251Pa, the filtration efficiency is 96.1%, and the most penetrating particle size is 0.45μm.

[0096] By comparison, it can be found that the circular cross-section self-twisted fiber obtained by parallel composite spinning has low air permeability and large filtration resistance because there is no groove structure on the fiber surface as an auxiliary channel for filtering fluid.

[0097] Comparative Example 3

[0098] This comparative example provides a method for preparing nylon 66 fiber for filter fabric, which is different from Example 6 only in that the aspect ratio of the spinneret used is 1.5:1, and the rest is exactly the same.

[0099] The obtained fiber has a single-filament fineness of 1.0 dtex, a profile of 15%, a torsion 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] The above fibers were used to prepare a single-layer plain woven fabric, the resulting fabric had a thickness of 0.75 mm and a weight of 160 g / m 2 , air permeability is 0.0012m 3 / m 2 ·s, the filtration resistance to NaCl aerosol is 250Pa, the filtration efficiency is 99.3%, and the most penetrable particle size is 0.31μm.

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

[0102] Comparative Example 4

[0103] This comparative example provides a method for preparing nylon 66 fiber for filter fabric, which is different from Example 6 only in that the heat pipe temperature is 185°C, and the other conditions are exactly the same.

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

[0105] The above fibers were used to prepare a single-layer plain woven fabric, and the resulting fabric had a thickness of 1.24 mm and a weight of 251 g / m 2 , air permeability is 0.0051m 3 / m 2 ·s, the filtration resistance to NaCl aerosol is 113Pa, the filtration efficiency is 31.3%, and the most penetrable particle size is 0.8μm.

[0106] Compared with Example 6, the heat pipe temperature of this comparative example is relatively low, resulting in a large drafting tension, which amplifies the stress difference between the two parallel phases, aggravates the fiber curling, and at this relatively low temperature, most of the spring-like curling of the fiber is not straightened but converted into the twisting of the fiber itself along the fiber axis, and the resulting multifilament is fluffy; and the resulting fabric structure is loose, the filtration efficiency is sharply reduced, and the filtration effect is almost lost.

[0107] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modification, equivalent substitution or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A nylon 66 fiber for filter fabric, 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 micro grooves and the fiber itself has a twisted spiral structure along the length direction, the cross-sectional profile is 20% to 55%, and the twist degree is 30 to 90; The relative viscosities of nylon 66A and nylon 66B are both 2.2 to 3.2, and the relative viscosity of nylon 66B is 0.3 to 0.6 greater than that of nylon 66A.

2. The nylon 66 fiber for filter fabric according to claim 1, characterized in that: The single-filament fineness of the nylon 66 fiber used for the filter fabric is 0.9 dtex to 1.5 dtex.

3. The nylon 66 fiber for filter fabric according to claim 1, characterized in that: The nylon 66 fiber for 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 pieces / m.

4. The method for preparing nylon 66 fiber for filter fabric according to any one of claims 1 to 3, characterized in that: The steps include: The nylon 66A melt and the nylon 66B melt are distributed in a parallel composite spinning mode, extruded through a special-shaped spinneret, cooled, and formed through a hot pipe spinning process to obtain nylon 66 fiber for filter fabric; Among them, the aspect ratio of the spinneret holes of the special-shaped spinneret is 2:1-5:1; the nozzle stretching ratio is 80-100; the cooling air temperature is 16°C-18°C, the cooling air speed is 0.3m / s-0.5m / s; and the heat pipe temperature is 195°C-215°C.

5. The method for preparing nylon 66 fiber for filter fabric according to claim 4, characterized in that: The specific steps include: Step a, introducing nylon 66A melt and nylon 66B melt into a composite spinning assembly through respective melt pipes according to a preset ratio, and extruding through parallel composite special-shaped spinnerets to obtain primary yarn; Step b, after cooling the spun silk, entering into a hot pipe for stretching and winding to obtain nylon 66 fiber for filter fabric.

6. The method for preparing nylon 66 fiber for filter fabric according to 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 fabric according to claim 5, characterized in that: In step a, the spinneret holes of the parallel composite special-shaped spinneret are in a Y-shape, an H-shape, a C-shape, an 8-shape or a cross-shape.

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

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

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

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