Fiber spinning process, spun fibers and uses thereof

Abstract

The present invention relates to a spun fiber, its use, and a fiber spinning method, which comprises the steps of extruding a spinning solution and spinning it, and then cooling and forming the resulting fibrils, drying and stretching them in sequence, the cooling and forming method comprising contacting the fibrils with a fluid at a temperature of −10° C. or less. The polyethylene spun fiber obtained by this fiber spinning method has a breaking strength of 40 CN / dtex or more and a modulus of elasticity of 1400 CN / dtex or more.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of Chinese patent application No. 202011148949.8, filed on October 23, 2020, the contents of which are incorporated herein by reference.

[0002] The present invention relates to fiber spinning, a spinning process for producing said spun fibers and uses thereof. [Background technology]

[0003] Ultra-high molecular weight polyethylene fiber, along with aramid and carbon fiber, is known as one of the three major high-tech materials of the 21st century, and is widely used in the fields of national defense, defense industry protection and civil industry due to its excellent properties such as high strength, high elastic modulus, high orientation, wear resistance and aging resistance. In recent years, with the improvement of high-performance polyethylene fiber technology and the widespread domestic production of raw materials, it has vigorously promoted the rapid development of the high-performance polyethylene fiber industry in China.

[0004] CN101148783B discloses a method for producing ultra-high molecular weight polyethylene fibers by using a coagulation bath method and controlling the air temperature to 30-110°C.

[0005] CN110791821A adopts water bath cooling at 0~80℃, and then sends it to a heated drawing tank for solvent recovery and hot drawing, producing a new ultra-high strength and high modulus polyethylene fiber by a one-step method.

[0006] On the whole, the above methods have been effective in improving the properties of polyethylene fiber products to a certain extent, but there is still room for improvement. In addition, these methods have the problem of poor stability, and the properties vary greatly depending on the lot. Summary of the Invention [Problem to be solved by the invention]

[0007] In order to further improve the properties of polyethylene fiber products, the inventors of the present invention conducted extensive research and discovered that low-temperature dry air quenching molding can produce high-performance polyethylene fiber products with significantly improved breaking strength and elastic modulus, thereby completing the present invention. [Means for solving the problem]

[0008] A first aspect of the present invention provides a spun fiber which is a crystalline polymer, characterized in that the unevenness is 2% or less, preferably 0.5 to 1%, the crystallinity measured by differential scanning calorimetry is 60 to 95%, preferably 85 to 90%, the crystal grain size in the normal direction to the (020) crystal plane is 7.4 to 9.6 nm, preferably 7.8 to 9 nm, the crystal grain size in the normal direction to the (110) crystal plane is 8.8 to 11.5 nm, preferably 8.9 to 10 nm, and the crystal grain size in the normal direction to the (200) crystal plane is 7.3 nm to 11 nm, preferably 7.8 to 10.5 nm, measured by X-ray diffraction (XRD).

[0009] A second aspect of the present invention provides a fiber spinning method comprising extruding a spinning solution and spinning the fibrils thus obtained, followed by cooling shaping, drying and stretching, characterized in that the fibrils obtained by the cooling shaping have an unevenness of 3% or less, preferably 1.5 to 2%.

[0010] The fiber spinning method of the present invention improves the crystal orientation of gel yarn by a new cold air quenching accelerated molding, thereby reducing the crystal grain size and greatly improving the breaking strength and elastic modulus of polyethylene fiber products, and the reproducibility of the method is excellent, and the characteristics of each lot of products are close, so the difference in product characteristics from lot to lot is small. Furthermore, the method does not introduce any impurities by introducing cold air quenching, and can be applied to both dry production process and wet production process, especially to dry spinning technology.

[0011] In the present invention, by combining the low-temperature air quenching accelerated forming with a drying oven having a specific structure of air knife, the drying efficiency of the material can be effectively improved, and the effect of the fiber yarn product can be enhanced. In addition, the blowing amount and blowing direction of the air knife outlet can be adjusted, so that the use of the air knife is more flexible, and the air knife can meet various usage needs.

[0012] According to the method of the present invention, it is possible to produce spun fibers with extremely fine fineness, and even with a fine fineness, high breaking strength and elastic modulus can be obtained. Preferably, the polyethylene spun fibers of the present invention have a breaking strength of 40 CN / dtex or more and an elastic modulus of 1800 CN / dtex or more, which is obviously superior in properties and has a significantly smaller product variation rate than the breaking strength of 35 CN / dtex or less in the same type of product and can be expected to be used in applications requiring high elastic modulus and high breaking strength, such as aerospace parachutes, anchor ropes, fixed ropes for drilling platforms, bulletproof products, civilian sports equipment, puncture prevention products, medical materials, and fish nets for aquaculture fish boxes. [Brief description of the drawings]

[0013] [Figure 1] 1 is a process flow diagram of one particular embodiment of a fiber spinning method according to the present invention. [Diagram 2] FIG. 2 is a structural schematic diagram of an embodiment of an air knife. [Diagram 3] 3 is a cross-sectional view of the inner cylinder and the outer cylinder in FIG. 2. [Figure 4] FIG. 3 is a schematic diagram showing the structure of the movable flange in FIG. 2. [Diagram 5] FIG. 3 is a schematic diagram showing the structure of a fixing flange in FIG. 2. [Figure 6] FIG. 2 is a structural schematic diagram of one embodiment of the spinning tube in the present invention. [Figure 7] 1 shows DSC curves of the spun fibers obtained in Examples 1 to 3 and Comparative Example 1 of the present invention. [Figure 8]FIG. 2 is an XRD diagram of the spun fibers obtained in Examples 1 to 3 and Comparative Example 1 of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The endpoints of the ranges and any values ​​disclosed herein should be understood to be not limited to the exact ranges or values, but to include values ​​close to these ranges or values. In the case of numerical ranges, the values ​​between the endpoints of each range, between the endpoints of each range and the individual point values, and between the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be considered to be specifically disclosed herein.

[0015] In the present invention, directional terms such as "up, down, left, right" generally refer to the orientations shown with reference to the drawings, unless otherwise stated to the contrary. "Inside, outside" refers to inside and outside with respect to the contour of each part itself.

[0016] In the fiber spinning method according to the present invention, the cooling and forming method and conditions may be controlled so that the unevenness of the undrawn gel yarn obtained by cooling and forming is 3% or less, preferably 1.5-2%, and as a result, the unevenness of the semi-finished fiber yarn obtained by drying is 1.5% or less, preferably 0.5-1%, so that the fiber yarn product obtained after drawing has small unevenness and high breaking strength and elastic modulus, and further, the method has excellent reproducibility, the characteristics of the products of each lot are similar, and the difference in the product characteristics between lots is small.

[0017] Preferably, the cooling and shaping method includes blowing the fibrils with a fluid having a temperature of −10° C. or less, preferably a gas having a temperature of −10° C. or less (low-temperature quench air). The introduction of low-temperature quench air does not introduce any impurities and can be applied to both dry and wet production process methods, especially to dry spinning technology.

[0018] In the present invention, the low-temperature quenching method refers to quenching the fibrils ejected from the spinning holes using a fluid with a temperature of -10°C or less. In the current conventional technology, regardless of whether it is a dry or wet method, cooling is performed using a gas with a temperature of 0°C or more. The inventor of the present invention has found through research that although a gas with a temperature of 0°C or more is extremely low compared to the temperature of the spinning (fibril) ejected from the nozzle and the temperature difference is large, the mechanical properties and stability of the fiber product are further improved when a fluid with a temperature of -10°C or less is used. The reason for this is believed to be that the molten material before entering the spinneret and being extruded is in a uniform state and the internal folded chain structure is stable, and after being extruded, the surface is cooled and rapidly hardened and molded, so that the stable folded chain structure inside the raw yarn does not change, and when it is further heated and stretched, the internal folded chains are gradually stretched to form a stable crystal lattice structure. This is believed to shorten the quenching time of the raw yarn, maximally protect the stable internal structure of the fiber, and improve the spinnability of the fiber.

[0019] Theoretically, any fluid with a temperature of -10°C or less can be used in the present invention, but taking into consideration the total energy consumption and the characteristics of the textile product, the temperature of the fluid for cooling and molding is preferably -50 to -10°C, preferably -40 to -10°C, and more preferably -30 to -20°C.

[0020] Low temperature air is used to promote the hardening of the gel filaments, and the lower the temperature, the shorter the hardening molding time, which prevents the gel filaments from being interfered with by the wind speed, ensures a stable internal structure of the gel filaments, and effectively avoids the gel filaments from sticking.

[0021] The fluid may be a gas or a liquid, and may be any inert fluid that does not react with the fiber yarn product to have a negative effect on the fiber yarn product, such as one or more of liquid ammonia, liquid nitrogen, air, an ethylene glycol aqueous solution, an ethanol aqueous solution, etc.

[0022] The present invention preferably uses a cooled forming fluid, preferably a gas. For dry spinning processes, an inert gas such as nitrogen gas is used instead of air.

[0023] The contact method is preferably blowing, and the blowing method is preferably circumferential blowing with the ejected fibrils as the center. The so-called circumferential blowing means that a quenching fluid for cooling and forming is blown around the fibrils with the fibrils as the center to sufficiently cool the fibrils.

[0024] According to one preferred embodiment of the present invention, the blowing time is 0.1 to 1 second, preferably 0.5 to 0.7 seconds, and the blowing pressure is 0 to 100 kPa, preferably 3 to 10 kPa. The blowing time is the time period from when the fiber yarn comes into contact with the quenching fluid to when it is separated from the quenching fluid. The pressure here is the pressure (gauge pressure) at which the quenching fluid flows out.

[0025] In the present invention, the blowing is a continuous and stable process, and the purging effect is related to the drawing speed of the spinning head, the faster the speed, the shorter the blowing time per unit amount of yarn. When the drawing ratio of the spinning head is 6-50 times, the extrusion speed of the spinning head is preferably 2-5 m / min, more preferably 3-3.5 m / min.

[0026] The above-mentioned low-temperature, dry-air quenching circumferential blowing molding method according to the present invention can be applied to both conventional wet processes and dry processes. It is preferably applied to the dry process. The combination of the above-mentioned quenching molding method and the dry process will be further described below.

[0027] In the present invention, the cooled fibrils are contacted with a drying gas having a speed of 20 meters / second or more, and the surface of the fiber is heated by a hot roll to promote softening of the fiber surface and precipitation of decalin inside the fiber, facilitating subsequent drawing. The decalin precipitated on the surface of the fiber is quickly air-dried by adjusting the wind speed and flow rate of the air knife in the drying oven. In the prior art, the drying step after cooling is usually performed by purging and baking with hot air or by placing the fiber in an extraction liquid to perform extraction and separation to remove the solvent, and the purge and bake wind speed is usually 10 meters / second or less.

[0028] Preferably, the flow rate of the drying gas is 30 to 40 meters / second.

[0029] According to one preferred embodiment of the present invention, the above flow rate can be achieved by performing drying in a drying oven shown in Figure 2. The structure of the drying oven will be described later.

[0030] The dry gas may be nitrogen gas or other inert gas, and the pressure is preferably controlled to 0 to 1 MPa, more preferably 0.4 to 0.6 MPa.

[0031] In the present invention, the temperature of the drying gas may be 0 to 140° C., but is preferably 40 to 80° C., which further promotes the removal of the solvent in the fibrils.

[0032] In the present invention, for convenience of explanation, the fiber yarn after spinning and before drawing is called fibril or gel filament, and the product after drawing is called fiber yarn product.

[0033] In the present invention, the fibers may be one or more of various plastic yarn products, such as polyethylene, acrylic fibers, etc.

[0034] As mentioned above, the spinning process has high requirements for the cooling forming fluid and drying gas, and in order to increase the utilization rate of the above fluids and solvents and reduce environmental pollution, preferably, the spinning method according to the present invention further includes recovering the solvent in the fluid after cooling forming and the solvent in the drying gas after drying.

[0035] Since the spinning method of the present invention uses a low-temperature quenching method, the volatility of the solvent is low in the low-temperature stage (i.e., the cooling and forming stage), the solvent is substantially absent in the gas phase, and the mixed gas exists in the form of an aerosol. For this gas, a simple separation method such as cyclone separation can be used to separate the coolant (particularly the cooling gas) and the solvent, and the coolant and the solvent can be recovered and recycled. Meanwhile, in the drying stage, the temperature of the gas is high and a large amount of the solvent volatilizes, so a deep separation method is required to separate the drying gas and the solvent. For this reason, in the present invention, the energy consumed within the system is reasonably distributed by processing in stages using return air of various temperatures, and the solvent recovery rate reaches 95% or more. Preferably, the deep separation method is a method that integrates cooling separation-cryogenic separation-compression-cooling separation-adsorption and desorption, in which the cooling separation temperature is controlled to be less than 40°C and the cryogenic separation temperature is controlled to be less than -5°C, and thus the solvent recovery rate exceeds 95%, the gas is recycled and used, and the solvent is recovered and recycled. Therefore, according to one preferred embodiment of the present invention, the method for recovering the solvent in the fluid after cooling and molding is a cyclone separation method, and the method for recovering the solvent in the dry gas is a combination of cryogenic separation and adsorption / desorption.

[0036] Preferably, the adsorbent for adsorption may be one or more of activated carbon, coconut shell activated carbon, carbon molecular sieve, etc. The specific operation and conditions of adsorption and desorption may be carried out with reference to the prior art.

[0037] According to one particular embodiment of the present invention, the high-performance polyethylene dry spinning method according to the present invention is based on low-temperature dry air quenching molding, and comprises the steps of: pre-swelling the ultra-high molecular weight polyethylene raw material with a solvent and a spinning aid, dissolving the spinning solution in a twin-screw extruder, sending it to a static mixer under shear to be uniformly mixed, sending it to a spinning tube, extruding it through a spinning assembly by a metering pump, and quenching it by circumferentially blowing dry air at a low temperature to form it; preheating the formed undrawn gel filaments with a heating 5-roller and sending it to a drying oven, and using an air knife to quickly volatilize the solvent on the fiber surface; feeding the treated gel filaments into a pre-drawing system to obtain a semi-finished yarn; sending the semi-finished yarn to a drawing system to be drawn multiple times to form a finished fiber; and recovering the solvent during the process by a solvent recovery device.

[0038] According to one preferred embodiment of the present invention, the spinning solution contains polyethylene, a solvent and a spinning aid, and the weight ratio of polyethylene to the solvent is 1 to 30:100, preferably 4 to 20:100, and the weight ratio of the spinning aid to polyethylene is 0.3 to 3:100, preferably 0.5 to 2:100.

[0039] The polyethylene may be any of various ethylene polymer products available for spinning, and preferably, the polyethylene has a number average molecular weight of 4 to 5 million and may be polyethylene produced by any of various processes such as a Ziegler-Natta catalytic process or a metallocene catalytic process.

[0040] The solvent may be any organic solvent capable of sufficiently swelling polyethylene, but is preferably one or more of aromatic solvents containing one or more benzene rings, such as decalin, tetralin, toluene, xylene, and the like.

[0041] The spinning aid may be one or more of various substances that contribute to spinning, such as antioxidants, plasticizers, modifiers, and lubricants.

[0042] In the present invention, the draw ratio (draft ratio) of the drawing may be as high as 1000 times or more, for example, 160 to 1200, and in order to obtain a fiber yarn having a fineness, it is preferably 600 to 900. The drawing may be performed once or in a plurality of steps, and is preferably performed in a plurality of steps. When the drawing is performed in a plurality of steps, the above draw ratio is a total draw ratio.

[0043] Because the fiber yarn of the present invention has high strength, it is possible to draw (draft) it at a high draw ratio to obtain fine fibers with a diameter of 30 μm or less, which is a level that cannot be achieved with similar products currently available.

[0044] The stretch ratio is the length of the fiber product after stretching divided by the length of the fibrils after cooling and forming.

[0045] Preferably, the drawing by the spinning head is 6 to 30 times, the pre-drawing ratio in the first spinning is 1 to 3.5 times, and the draw ratio in the second spinning is 6 to 20 times.

[0046] Preferably, to facilitate storage of the product, the method of the present invention may further comprise winding the drawn fiber yarn product.

[0047] In the present invention, the specific operations and conditions of melt extrusion, spinning, drawing, and winding can be carried out with reference to the prior art.

[0048] The spun fiber obtained by the method of the present invention is a crystalline polymer, has an unevenness of 1.5% or less, preferably 0.9-1%, a crystallinity measured by differential scanning calorimetry (DSC) of 60-95%, preferably 85-90%, and a melting point measured by XRD of 148-151° C., preferably 149-150° C. The crystallinity measured by X-ray diffraction (XRD) is 60-95%, preferably 80-90%, the crystal grain size in the normal direction to the (020) crystal plane is 7.4-9.6 nm, preferably 7.8-9 nm, the crystal grain size in the normal direction to the (110) crystal plane is 8.8-11.5 nm, preferably 8.9-10 nm, and the crystal grain size in the normal direction to the (200) crystal plane is 7.3-11 nm, preferably 7.8-10.5 nm.

[0049] The polyethylene spun fiber produced by the method of the present invention has a breaking strength of not less than 40 CN / dtex and an elastic modulus of not less than 1400 CN / dtex, preferably not less than 1800 CN / dtex, which are far superior to the properties of the same products obtained by the prior art methods.

[0050] The polyethylene spun fiber obtained in a preferred embodiment of the present invention has a CV of elongation and a CV of strength both less than 5%, preferably less than 2% and less than 1.5%, respectively, which are within the ranges of 1.5 to 1.9% and 1.15 to 1.45%, respectively, both of which meet the quality requirements of excellent products.

[0051] Preferably, the fiber yarn has a fineness of 40 to 80 dtex, preferably 40 to 55 dtex.

[0052] The fiber spinning method of the present invention can produce the above-mentioned high performance spun fibers, which are expected to be used in applications requiring high elastic modulus and high breaking strength, such as aerospace parachutes, anchor ropes, fixing ropes for drilling platforms, bulletproof products, civilian sporting goods, puncture-resistant products, medical materials, and fish nets for aquaculture fish boxes.

[0053] In the present invention, the breaking strength, elastic modulus, elongation variation CV, and strength variation CV can be measured according to the methods of GB / T29554-2013 and GB / T19975-2005, respectively.

[0054] According to one preferred embodiment of the present invention, the fiber spinning process of the present invention is carried out in a fiber spinning system as shown in FIG. 1, the fiber spinning system including a melt extrusion unit, a spinning unit, a drying unit, a drawing unit, and a winding unit, the melt extrusion unit supplies molten spinning raw material to the spinning unit, the drying unit dries the fibrils spun by the spinning unit to remove the solvent, the drawing unit draws the fibrils dried by the drying unit, the spinning unit includes a spinning tube, a cooling fluid supplying device, and a spinning hole provided in the spinning tube, the cooling fluid supplying device supplies a cooling fluid to the spinning tube, and the fibrils ejected from the spinning holes in the spinning tube are rapidly cooled and molded.

[0055] Preferably, as shown in FIG. 2, the drying unit includes a drying oven 6 including a box and an air knife 60, a drying chamber for drying a material is provided in the box, the air knife 60 is provided in the drying chamber, and a second outlet 621 of the air knife 60 is aligned with the material, the box is provided with a supply port, an exhaust port, a drying gas inlet and a drying gas outlet communicating with the drying chamber, and an inlet 611 of the air knife 60 is connected to the drying gas inlet, and the second outlet 621 of the air knife 60 is connected to the drying gas outlet.

[0056] The air knife is positioned primarily to forcefully blow off the solvent deposited on the surface of the fibers and keep the surfaces of the gel filaments dry.

[0057] In use, the blowing amount and blowing direction of the air knife 60 can be adjusted as required. The drying gas entering the drying chamber from the drying gas inlet enters the air knife 60 through the blowing port 611, and is collected from the air knife 60 at a predetermined blowing amount and blowing direction and blown onto the material, thereby quickly air-drying the material.

[0058] Here, as shown in Fig. 2, the supply port and the discharge port are located on opposite sides of the box (on the left and right sides of the drying oven 6 shown in Fig. 2), and the drying gas inlet and the drying gas outlet are located on opposite sides of the box (on the top and bottom sides of the drying oven 6 shown in Fig. 2). A plurality of air knives 60 may be provided in the drying chamber, and the plurality of air knives 60 extend perpendicularly to the direction in which the material is carried in and out, and are arranged at intervals in the direction in which the material is carried in and out (see the left and right direction shown in Fig. 1). In this way, the drying efficiency and effect are further improved.

[0059] When a plurality of air knives 60 are provided in the drying chamber, the box may be provided with a plurality of the drying gas inlets and drying gas outlets, as shown in Fig. 1. The positions corresponding to the black arrows of the drying oven 6 shown in Fig. 1 are the drying gas inlets and drying gas outlets.

[0060] The internal structure of the air knife is shown in Figure 2. By adjusting the position of the bearing rod to control the blowing speed and direction, the solvent precipitated on the surface of the gel filaments can be quickly dried.

[0061] As shown in FIG. 2, the air knife 60 includes an inner tube 61 and an outer tube 62 nested coaxially. One end of the inner tube 61 is open and serves as an inlet 611 of the air knife 60. A first outlet 612 communicating with the inlet 611 is formed in the cylindrical wall of the inner tube 61. A second outlet 621 is formed in the cylindrical wall of the outer tube 62 (the second outlet 621 is an outlet of the air knife 60). A radial space is provided between the inner tube 61 and the outer tube 62 to form a communication passage 63 connecting the first outlet 612 and the second outlet 621. At least one of the inner tube 61 and the outer tube 62 is configured to move along the radial direction of the air knife 60 to adjust the amount and direction of air flow from the second outlet 621.

[0062] In the above, it should be understood that, during use, wind enters the inner cylinder 61 from the air inlet 611, then enters the communication passage 63 from the first air outlet 612, and is finally discharged from the second air outlet 621. When the inner cylinder 61 is moved so as to approach the second air outlet 621, the air outlet amount of the second air outlet 621 gradually decreases, and when the inner cylinder 61 is moved so as to move away from the second air outlet 621, the air outlet amount of the second air outlet 621 gradually increases. When the wall of the inner cylinder 61 partially blocks the second air outlet 621, the air outlet direction of the second air outlet 621 can be changed.

[0063] In addition, in the above, at least one of the inner tube 61 and the outer tube 62 is arranged to be movable along the radial direction of the air knife 60, and there are three forms: a first form in which the outer tube 62 is fixed and the inner tube 61 is configured to be movable along the radial direction of the air knife 60 relative to the outer tube 62; a second form in which the inner tube 61 is fixed and the outer tube 62 is configured to be movable along the radial direction of the air knife 60 relative to the inner tube 61; and a third form in which the inner tube 61 and the outer tube 62 are configured to be movable relative to each other along the radial direction of the air knife 60.

[0064] By adopting the above technical solution, the blowing amount and blowing direction of the air knife outlet can be adjusted, making the use of the air knife 60 more flexible and able to meet various usage needs; when the air knife 60 is used in a drying oven, it can effectively improve the drying efficiency and effect of materials.

[0065] In the present invention, the first outlet 612 and the second outlet 621 may have any appropriate shape and arrangement as long as they can achieve the above-mentioned functions. For example, the cross sections of the first outlet 612 and the second outlet 621 may be elliptical, rectangular, etc., and the first outlet 612 and the second outlet 621 may be arranged at intervals along the axial direction and / or circumferential direction of the air knife 60. Of course, there may be a plurality of first outlets 612 and second outlets 621.

[0066] 2 and 3, there is one each of the first outlet 612 and the second outlet 621, the first outlet 612 is elongated and extends along the axial direction of the inner cylinder 61, and the second outlet 621 is elongated and extends along the axial direction of the outer cylinder 62. In such a case, the first outlet 612 and the second outlet 621 are arranged offset from each other in the circumferential direction of the air knife 60, that is, the first outlet 612 and the second outlet 621 are preferably not aligned so that the air that has entered the inner cylinder 61 is not directly discharged from the second outlet 621 after being discharged from the first outlet 612.

[0067] Here, preferably, the first air outlet 612 and the second air outlet 621 are provided opposite to each other in the circumferential direction of the air knife 60 as shown in FIG.

[0068] The cross section of first outlet 612 and second outlet 621 is preferably rectangular, and the opening angle of first outlet 612 and second outlet 621 in the circumferential direction of air knife 60 is 0 to 90°, preferably 25 to 40°.

[0069] In the present invention, the side of inner cylinder 61 away from air inlet 611 is closed, and both ends of communicating passage 63 are closed, so that air that has entered air knife 60 is not discharged from other ports of inner cylinder 61 and / or communicating passage 63. Inner cylinder 61 may be closed by an end wall that is integrated with the cylinder wall, or may be closed by a mounting assembly (described below) or other structure to which the air knife is attached (for example, a drying oven described below), and communicating passage 63 may be closed by a mounting assembly or other structure to which the air knife is attached.

[0070] In the present invention, in order to integrate the inner cylinder 61 and the outer cylinder 62 and facilitate easy installation and removal of the air knife 60 as a whole, the air knife 60 may further include a mounting assembly for mounting the inner cylinder 61 and the outer cylinder 62. The mounting assembly may be any member that can allow movement of the inner cylinder 61 and / or the outer cylinder 62 while integrating the inner cylinder 61 and the outer cylinder 62 together.

[0071] In order to simplify the structure of the air knife 60 and reduce the manufacturing cost of the air knife 60, according to one preferred embodiment of the present invention, taking the case where the outer cylinder 62 is fixed and the inner cylinder 61 moves along the radial direction of the air knife 60 relative to the outer cylinder 62 as an example, as shown in FIG. 2, the mounting assembly may include two movable flanges 64 respectively attached to both ends of the inner cylinder 61 and two fixed flanges 65 respectively attached to both ends of the outer cylinder 62, and the two movable flanges 64 are respectively connected to the two fixed flanges 65 (i.e., the movable flanges 64 and the fixed flanges 65 located on the same side of the air knife 60 are connected to each other), and the two movable flanges 64 are configured to be lockably movable along the radial direction of the air knife 60 relative to the corresponding fixed flanges 65.

[0072] The movable flange 64 is attached in a sealed manner to the inner cylinder 61, and the fixed flange 65 is attached in a sealed manner to the outer cylinder 62. As shown in Figures 4 and 5, the movable flange 64 has a mounting hole for mounting the inner cylinder 61, and the fixed flange 65 has a mounting hole for mounting the outer cylinder 62. Since the diameter of the inner cylinder 61 is smaller than the diameter of the outer cylinder 62, the diameter of the mounting hole of the movable flange 64 is set smaller than the diameter of the mounting hole of the fixed flange 65.

[0073] 4, the movable flange 64 is located outside the fixed flange 65, and both ends of the inner cylinder 61 are inserted through the mounting holes of the fixed flange 65 and the movable flange 64, respectively, and both ends of the outer cylinder 62 are inserted through the mounting holes of the fixed flange 65. In this case, both ends of the communication passage 63 can be closed by two movable flanges 64, respectively.

[0074] In the above, it should be noted that, as shown in Fig. 2, the left end surface of the inner tube 61 may extend outside the left movable flange 64, may be located inside the movable flange 64, or may be flush with the left end surface of the movable flange 64. The right end surface of the inner tube 61 may extend outside the right movable flange 64, or may be flush with the right end surface of the movable flange 64. In these two cases, the right end port of the inner tube 61 may be closed by an end wall integrated with the cylindrical wall, or may be closed by another structure to which the air knife 60 is attached, and the right end surface of the inner tube 61 may also be located inside the right movable flange 64. In such a case, the right end port of the inner tube 61 may be closed by an end wall integrated with the cylindrical wall, or may be closed by the movable flange 64. That is, in the movable flange 64, the mounting hole to which the inner tube 61 is attached is not a through hole, but a semi-closed hole with a right side wall.

[0075] Furthermore, as shown in Figures 4 and 5, the movable flange 64 and the fixed flange 65 may be connected by a fastener, and each of the movable flange 64 and the fixed flange 65 has a through hole for inserting the fastener, the through hole of the movable flange 64 being a circular hole 641, and the through hole of the fixed flange 65 being an oval hole 651.

[0076] In the above, it should be noted that the diameter of the circular hole 641 is adapted to the diameter of the fastener, and the oval hole 651 has a small hole diameter and a large hole diameter, the small hole diameter is adapted to the diameter of the fastener, and the large hole diameter is larger than the diameter of the fastener. The fastener locks the extension direction of the circular hole 641 along the oval hole 651 at a specific position of the oval hole 651, thereby locking and connecting the movable flange 64 to the fixed flange 65. The extension direction of the oval hole 651 is the movement direction of the inner tube 61. For example, as shown in FIG. 4, the oval hole 651 extends vertically, and in this case, the inner tube 61 and the movable flange 64 can move up and down along the vertical direction relative to the outer tube 62 and the fixed flange 65, and the first blowing port 612 and the second blowing port 621 are located in the vertical direction.

[0077] To strengthen the connection, as shown in Figures 4 and 5, the movable flange 64 may be provided with a plurality of circular holes 641, and therefore the fixed flange 65 may be provided with a plurality of oval holes 651, with the extension directions of the plurality of oval holes 651 coinciding.

[0078] In use, the fasteners can be loosened, the inner tube 61 and the movable flange 64 can be moved to a desired position, and then the fasteners can be tightened to lock the movable flange 64 to the fixed flange 65.

[0079] It should be noted that in the present invention, the fastener may be any part that can connect the movable flange 64 to the fixed flange 65. For example, the fastener may be a bolt, in which case the circular hole 641 and the oblong hole 651 may be threaded holes.

[0080] In the above, the air knife 60 installed in the drying oven 6 can strongly blow off the solvent precipitated on the surface of the fibrils, and ensure the dry state of the surface of the fibrils. The drying gas used in the air knife 60 may be nitrogen gas or other inert gas, and the pressure may be controlled to preferably 0 to 1 MPa, more preferably 0.4 to 0.6 MPa. The temperature of the drying gas may be 0 to 140°C, preferably 40 to 80°C. The drying gas discharged from the air knife 60 contacts the fibrils at a speed of preferably 20 meters / second (or more preferably 30 to 40 meters / second). This further promotes the removal of the solvent in the fibrils.

[0081] 1, the drying unit further includes a heated roll-type stretching device 5 and a non-heated roll-type stretching device 7, which are respectively provided before and after the drying oven 6. Both the heated roll-type stretching device 5 and the non-heated roll-type stretching device 7 are preferably five-roll stretching devices. It should be noted that the roll-type stretching device of the drying unit mainly performs a drying function and does not apply a large stretching force to perform stretching, so the stretching action thereof may be ignored.

[0082] In the present invention, as shown in FIG. 6 , the melt extrusion unit may include a twin-screw extruder 1, a booster pump 2 and a static mixer 3, the spinning unit may include a cooling fluid supply device and a spinning tube 4, the drawing unit may include a drawing oven 8 and a drawing device 9, and the winding unit may include a winder 11.

[0083] The twin-screw extruder 1 is used to melt and extrude the spinning solution to form a stable melt, the booster pump 2 is used to apply a stable pressure to the melt so as to stably discharge the melt, the static mixer 3 is used to form a stable and uniform melt, the cooling fluid supply device is used to supply a cooling fluid to the spinning tube 4 to quench and mold the fibrils ejected from the spinning holes (described below) in the spinning tube 4, the spinning tube 4 is used to convert the melt into a gel elastic fluid and quench it with dry air to form solid gel threads (i.e., fibrils), the stretching oven 8 and the stretching device 9 are used to stretch the dried fibrils, where the stretching oven 8 is used to perform hot stretching and volatilize the solvent during hot stretching, and the winder 11 is used to wind the stretched fibrils.

[0084] The fiber spinning system may also include an oiling device 10 disposed before the winder 11 for oiling the surfaces of the fibrils.

[0085] It should be noted that in the embodiment of the fiber spinning system shown in FIG. 1, the black arrows represent the direction of gas flow.

[0086] In one preferred embodiment of the spinner tube 4 according to the present invention, as shown in FIG. 6, the spinner tube 4 includes a motor 41, a metering pump 42, a spinner tube housing 43, a spinning assembly 44, a heat-insulating oil jacket 45, a circumferential blowing element 46, and a godet roller 47. The motor 41 and the metering pump 42 are mounted in the spinner tube housing 43, and the spinning assembly 44, the heat-insulating oil jacket 45, the circumferential blowing element 46, and the godet roller 47 are all mounted in the spinner tube housing 43.

[0087] Here, the spinning assembly 44 includes a spinning hole, and the spinning solution is sprayed from the spinning hole to form fibrils. The circumferential blowing part 46 includes an annular pipe extending in the circumferential direction of the spinning tube housing 43, and the annular pipe has an opening toward the center. The cooling fluid supply device supplies a fluid having a temperature of -10°C or less to the annular pipe, and performs circumferential blowing of the cooling fluid to the spinning hole.

[0088] Here, the metering pump 42 is a device for metering the material, and the motor 41 is used to drive the metering pump 42 to meter and extrude. The spinning tube housing 43 is a box that can supply a thermostatic bath. The spinning assembly 44 includes a press plate, a filter mat, and a spinneret, which are arranged from top to bottom in order, and the press plate and the spinneret are fixed by bolts, the spinneret is provided with a spinning hole, and the spinning liquid is ejected from the spinning hole to form fibrils. The heat-retaining oil jacket 45 supplies the heat required for the volatilization of the solvent, maintains the spinneret surface at a predetermined temperature, and keeps the melt in a stable flow state, thereby preventing the spinneret surface from being affected by the quenching wind and causing clogging or thread breakage in the melt on the surface. The circumferential blowing part 46 provides a stable circumferential blowing wind and balances the amount of wind around the tow. The circumferential blowing element 46 includes an annular pipe extending in the circumferential direction of the spinning tube housing 43, the annular pipe having an opening toward the center, and the cooling fluid supply device supplies a fluid having a temperature of -10°C or less to the annular pipe to perform circumferential blowing of the cooling fluid to the spinning holes. The godet roller 47 changes the moving direction of the fibrils.

[0089] Preferably, the annular pipe has an opening ratio of 30-35%, and the ratio of the opening size to the inner diameter of the spinning tube housing 43 is 1:4-10. If the ratio of the opening size to the spinning tube housing 43 is too small, the solvent cannot be effectively discharged by the circumferential wind inside the housing, the solvent accumulates in the spinning tube housing, the recovery efficiency is greatly reduced, and a large amount of solvent droplets adhere to the surface of the fiber, which is disadvantageous for the subsequent stretching and drying. If the ratio of the opening size to the spinning tube housing is too large, the wind speed increases significantly, which causes vibration when the fiber falls, and adversely affects the quality of the fibrils.

[0090] The annular piping is provided between the heat-retaining oil jacket 45 and the godet roller 47, and the diameter of the annular piping is 80 cm or more. Preferably, the ratio of the diameter of the annular piping to the inner diameter of the spinning tube housing 43 is 1:5-10.

[0091] According to one preferred embodiment of the present invention, the fiber spinning system of the present invention further comprises a solvent recovery unit to recover the solvent throughout the spinning process, recycle the cooling and drying gases and the spinning solvent, and reduce environmental pollution.

[0092] As described above, it has been found that in the low-temperature stage, the solvent content in the gas is low and the solvent can be removed by simple cyclone separation, while in the high-temperature stage, a deep separation method is adopted. Therefore, preferably, the solvent recovery unit includes a cyclone separator for recovering the solvent from the spinning unit and a composite separator for recovering the solvent from the drying unit, and the composite separator is in the form of a combination of cryogenic separation and adsorption / desorption.

[0093] The composite separation device includes a cooling device, a cryocooler, a gas-liquid separator and an adsorption / desorption device connected in series, which performs the integrated operation of cooling separation-cryogenic separation-compression-cooling separation-adsorption / desorption to achieve the purpose of deep separation, where the temperature of cooling separation is controlled to be less than 40°C, and the temperature of cryogenic separation is controlled to be less than -5°C, thus achieving a solvent recovery rate of more than 95%, and recycling the gas and recovering and recycling the solvent.

[0094] Preferably, the adsorbent for adsorption is one or more of activated carbon, coconut shell activated carbon, and carbon molecular sieve. Specific adsorption and desorption operations and conditions can be referred to the prior art.

[0095] The dry spinning production process of high-performance polyethylene spinning based on low-temperature dry air quenching using the above fiber spinning system includes the steps of: preparing a spinning solution from polyethylene raw material, solvent and auxiliary agents in a predetermined ratio, mixing and pre-swelling the solution after pre-swelling in a cooling kettle and stirring it, sending it to a twin-screw extruder to dissolve it, applying shear, and sending it to a metering pump through a static mixer by a booster pump, and after metering, extruding the gel filaments from the spinning tube, ensuring the solvent volatilization of the yarn and the temperature of the spinneret surface by a heat-insulating jacket, and quenching and molding by circumferential blowing of low-temperature air during falling, preheating the formed gel filaments by a heating five-roller and sending them to a drying oven, and quickly volatilizing the solvent on the fiber surface by an air knife, feeding the treated gel filaments into a pre-drawing system and drawing them multiple times in the drawing system to form a finished fiber product, and recovering the solvent generated during cooling and drying by a solvent recovery system.

[0096] The thermal insulation jacket mainly serves to provide sufficient heat to volatilize the solvent on the surface of the gel filaments, to protect the temperature of the spinneret surface from the influence of the low-temperature circumferential wind below it, and to ensure the extrusion stability of the gel filaments.

[0097] The extrusion speed of the spinneret is preferably 1 to 10 m / min.

[0098] The present invention has the following salient features: Compared with the conventional high-performance polyethylene fiber spinning process, the gel filaments thus produced are pre-drawn and drawn, resulting in no fluff or yarn breakage, obviously improved fiber property indexes, fiber breaking strength exceeding 45 CN / dtex, elastic modulus exceeding 1800 CN / dtex, yarn unevenness less than 1%, fiber retention reaching 98% or more, and solvent recovery rate exceeding 95%.

[0099] The present invention is further illustrated by the following examples, in which all raw materials are commercially available unless otherwise stated.

[0100] The DSC crystallinity is calculated according to the following Equation 1.

[0101]

number

[0102] In formula 1, X c is the crystallinity, ΔH is the enthalpy of fusion of the fiber sample, and ΔH f is the melting enthalpy of fully crystallized polyethylene, which is 293 J / g.

[0103] The XRD crystallinity is calculated according to the following Equation 2, and the crystal grain size L is calculated according to the Scherrer equation (Equation 3).

[0104]

number

[0105] In formula 2, X c is the degree of crystallinity, I a is the relative intensity of the amorphous peak, I c is the relative intensity of the crystalline region, and in Eq. 3, L hkl is the crystal grain size (unit: nm), λ is the wavelength of the X-ray, k is the Scherrer constant, H is the half-width of the hkl diffraction peak, and θ is the Bragg angle of the hkl diffraction.

[0106] The breaking strength, breaking elongation, elastic modulus, elongation variation CV%, and strength variation CV% are measured according to the GB / T19975-2005 method, respectively.

[0107] The fineness is measured using a commercially available fineness measuring machine, and in the specific measurement method, the fineness value of the product is determined by measuring the weight of the fiber after rotating the fineness measuring machine 100 times. Five consecutive measurements are taken, and the average value is the fineness value of the product of that lot. The ratio of the absolute value of the difference between the fineness value with the largest difference from the average value and the average value to the average value is determined as the unevenness. This method is suitable for testing the fineness value and unevenness of fiber yarns at each stage (cooling and forming, drying, and drawing).

[0108] The fiber spinning system shown in FIG. 1 used in the following examples includes a twin screw extruder, a spinner, a hot five-roll stretcher, a drying oven, a five-roll stretcher 1, a stretching oven, a five-roll stretcher 2, and a winder, which are connected in series. In the spinning tube housing, an annular pipe with an opening rate of 35% and an opening size of 5 mm is provided for circumferential blowing of air, and the inner diameter of the spinning tube housing is 1000 x 1200 mm. The drying oven includes a box and a plurality of air knives evenly arranged along the axial direction of the box (the direction in which the material is carried in and out), and there is a predetermined distance between two adjacent air knives. A drying chamber for drying the material is provided in the box, the air knife is provided in the drying chamber, and the second blowing port of the air knife is aligned with the material. The box is provided with a supply port, a discharge port, a drying gas inlet, and a drying gas outlet that are connected to the drying chamber, the blowing port is connected to the drying gas inlet, and the second blowing port is connected to the drying gas outlet. the supply port and the discharge port are located on opposite sides of the box, the air knife includes an inner tube and an outer tube nested coaxially, one end of the inner tube is open and serves as an inlet of the air knife, a first outlet communicating with the inlet is formed in a cylindrical wall of the inner tube, the first outlet is elongated and extends along the axial direction of the inner tube, a second outlet is elongated and extends along the axial direction of the outer tube is formed in a cylindrical wall of the outer tube, a radial space is provided between the inner tube and the outer tube to form a communication passage connecting the first outlet and the second outlet, and the first outlet and the second outlet are shifted from each other in the circumferential direction of the air knife. The first and second outlets have an opening angle of 40° in the circumferential direction of the air knife, and both the inner tube and the outer tube are configured to be movable radially of the air knife to adjust the amount and direction of air being blown from the second outlet.

[0109] First, the solvent, polyethylene powder, and spinning aid are mixed, and the ultra-high molecular weight polyethylene powder is pre-swollen. The mixture is then put into a twin-screw extruder and thoroughly dissolved. After shearing, the mixture is sent to a static mixer by a booster pump. The stabilized solution is then sent to a metering pump and extruded at an extrusion speed of 1 to 10 m / min using a spinning tube. The extruded gel strand is passed through a heat-insulating oil jacket (200°C) to ensure the evaporation temperature of the solvent and the stable temperature of the spinneret. The gel strand that has passed through the heat-retaining oil jacket is circumferentially blown with dry air to be quenched and molded at high speed, the pressure of the circumferentially blown air is 0-50 kPa, the temperature is -50°C to -10°C, and the quenched yarn is quickly cured and molded to obtain an undrawn gel yarn, which is passed through a godet roller and placed in a hot five-roller, which heats it at a temperature of 30-100°C to volatilize the solvent on the fiber surface, and the yarn is sent to a drying oven, where the solvent on the fiber surface is quickly volatilized by an air knife inside the drying oven, and the drying hot air from the air knife is hot nitrogen gas. The temperature inside the drawing oven is controlled to 40-150°C, and then pre-drawing is performed to obtain a semi-finished yarn, which is then drawn and wound up, with a total draw ratio of 160-1200 times (including drawing by the spinning head). Solvent recovery is carried out in stages at different temperatures. A cyclone separator is used in the low temperature region, and an integrated form of cooling separation-cryogenic separation-cooling separation-adsorption / desorption is used in the high temperature region. The temperatures of cyclone separation and cooling separation are below 40°C, and the temperature of cryogenic separation is below -5°C.

[0110] Example 1 The mass / volume ratio of the raw material (polyethylene with a number average molecular weight of 4.87 million) and the solvent (decalin) is 8%, the auxiliary agent includes an antioxidant and calcium stearate, and the amount used is 0.7% and 0.3% in terms of the mass of the raw material, respectively, the swelling temperature is 98 ° C, the extrusion speed is 3 m / min, and the heat-retaining oil jacket is 200 ° C. Circumferential blowing of air with a quenching temperature of -25 ° C was performed at a wind pressure of 0.4 MPa for 0.5 s. The temperature of the hot roll is 40 ° C, the temperature of the drying oven is 40 ° C (air knife is wind temperature 40 ° C, wind speed 30 meters / sec, wind pressure 0.4 MPa), the temperature of the stretching oven is 125 ° C, the pre-stretching ratio is 3 times, the temperature of the multi-stage stretching oven is 140 to 145 ° C, and the total stretching ratio is 220 times. The solvent recovery is carried out in stages at different temperatures, with a cyclone separator in the low temperature region and an integrated cooling separation-cryogenic separation-cooling separation-adsorption / desorption in the high temperature region, where the temperatures of the cyclone separation and cooling separation are below 40°C, and the temperature of the cryogenic separation is below -5°C, and the adsorbent is activated carbon. The DSC curve and XRD diagram of the spun fiber are shown in Sample 2 in Figures 7 and 8, respectively, and the characteristic detection indexes are shown in Table 1 below. The solvent recovery rate was 97.35%.

[0111] [Table 1]

[0112] Example 2 The mass / volume ratio of the raw material (polyethylene with a number average molecular weight of 4.87 million) and the solvent (decalin) is 8%, the auxiliary agent includes an antioxidant and calcium stearate, the amount of which is 0.7% and 0.3% in terms of the mass of the raw material, respectively, the swelling temperature is 98 ° C, the extrusion speed is 3.25 m / min, and the heat-retaining oil jacket is 200 ° C. Circumferential blowing of air with a quenching temperature of -20 ° C was performed at a wind pressure of 10 kPa for 0.7 s. The hot roll temperature is 50 ° C, the drying oven temperature is 50 ° C (air knife has a wind temperature of 50 ° C, a wind speed of 30 meters / sec, and a wind pressure of 0.4 MPa), the stretching oven temperature is 125 ° C, the pre-stretching ratio is 3 times, the temperature of the multi-stage stretching oven is 140 to 145 ° C, and the total stretching ratio is 220 times. The solvent recovery is carried out in stages at different temperatures, with a cyclone separator in the low temperature region and an integrated cooling separation-cryogenic separation-cooling separation-adsorption and desorption in the high temperature region, where the temperatures of the cyclone separation and cooling separation are less than 40°C, and the temperature of the cryogenic separation is less than -5°C, and the adsorbent is activated carbon. The DSC curve and XRD diagram of the spun fiber are shown in Figures 7 and 8 for sample 2, respectively, and the characteristic detection indexes are shown in Table 2 below. The solvent recovery rate is 97.19%.

[0113] [Table 2]

[0114] Example 3 The mass / volume ratio of the raw material (polyethylene with a number average molecular weight of 4.25 million) and the solvent (decalin) is 8%, the auxiliary agent includes an antioxidant and calcium stearate, the amount of which is 0.7% and 0.3% in terms of the mass of the raw material, respectively, the swelling temperature is 98 ° C, the extrusion speed is 3.25 m / min, and the heat-retaining oil jacket is 200 ° C. Circumferential blowing of air with a quenching temperature of -15 ° C was performed at a wind pressure of 4 kPa for 0.54 s. The temperature of the hot roll is 40 ° C, the temperature of the drying oven is 40 ° C (air knife has a wind temperature of 40 ° C, a wind speed of 30 meters / sec, and a wind pressure of 0.4 MPa), the temperature of the stretching oven is 125 ° C, the pre-stretching ratio is 3 times, the temperature of the multi-stage stretching oven is 140 to 145 ° C, and the total stretching ratio is 240 times. The solvent recovery is carried out in stages at different temperatures, with a cyclone separator in the low temperature region and an integrated cooling separation-cryogenic separation-cooling separation-adsorption and desorption in the high temperature region, where the temperatures of the cyclone separation and cooling separation are less than 40°C, and the temperature of the cryogenic separation is less than -5°C, and the adsorbent is activated carbon. The DSC curve and XRD diagram of the spun fiber are shown in Figures 7 and 8 for sample 3, respectively, and the characteristic detection indexes are shown in Table 3 below. The solvent recovery rate is 97.22%.

[0115] [Table 3]

[0116] Example 4 The mass / volume ratio of the raw material (polyethylene with a number average molecular weight of 4.25 million) and the solvent (decalin) is 8%, the ratio of the auxiliary (weight ratio of antioxidant and calcium stearate 7:3) to the raw material is 0.8 mass%, the swelling temperature is 98 ° C, the extrusion speed is 3 m / min, and the heat-retaining oil jacket is 200 ° C. Circumferential blowing of air with a quenching temperature of -10 ° C was performed at a wind pressure of 5 kPa for 0.64 s. The temperature of the hot roll is 40 ° C, the temperature of the drying oven is 40 ° C (air knife has a wind temperature of 40 ° C, a wind speed of 30 meters / sec, and a wind pressure of 0.4 MPa), the temperature of the stretching oven is 125 ° C, the pre-stretching ratio is 3 times, the temperature of the multi-stage stretching oven is 140 to 145 ° C, and the total stretching ratio is 200 times. Solvent recovery is performed in stages at different temperatures, with a cyclone separator in the low temperature region and an integrated cooling separation-cryogenic separation-cooling separation-adsorption and desorption in the high temperature region, where the temperatures of cyclone separation and cooling separation are below 40°C, and the temperature of cryogenic separation is below -5°C, and the adsorbent is activated carbon. Four tubes of fiber were randomly taken from the same batch for testing, and the DSC curves and XRD patterns of the spun fiber products were similar to those in Figures 7 and 8, respectively, and the characteristic detection indexes are shown in Table 4 below. The solvent recovery rate is 97.17%.

[0117] [Table 4]

[0118] Example 5 The mass / volume ratio of the raw material (polyethylene with a number average molecular weight of 4.87 million) and the solvent (tetralin) is 6.5%, the auxiliary agent includes an antioxidant and calcium stearate, the amount of which is 0.7% and 0.3% in terms of the mass of the raw material, respectively, the swelling temperature is 98 ° C, the extrusion speed is 3.25 m / min, and the heat-retaining oil jacket is 200 ° C. The circumferential blowing of nitrogen gas with a quenching temperature of -20 ° C was performed at a wind pressure of 5 kPa for 0.6 s. The temperature of the hot roll is 40 ° C, the temperature of the drying oven is 80 ° C (air knife has a wind temperature of 80 ° C, a wind speed of 40 meters / sec, and a wind pressure of 0.4 MPa), the temperature of the stretching oven is 125 ° C, the pre-stretching ratio is 3 times, the temperature of the multi-stage stretching oven is 140 to 145 ° C, and the total stretching ratio is 220 times. The solvent recovery is carried out in stages at different temperatures, with a cyclone separator in the low temperature region and an integrated cooling separation-cryogenic separation-cooling separation-adsorption and desorption in the high temperature region, where the temperatures of the cyclone separation and cooling separation are less than 40°C, and the temperature of the cryogenic separation is less than -5°C, and the adsorbent is coconut shell activated carbon. The DSC curve and XRD diagram of the spun fiber are similar to those in Figures 7 and 8 respectively, and the characteristic detection indexes are shown in Table 5 below. The solvent recovery rate is 98.0%.

[0119] [Table 5]

[0120] Example 6 The mass / volume ratio of the raw material (polyethylene with a number average molecular weight of 4.87 million) and the solvent (toluene) was 6.5%, the auxiliary agent included an antioxidant and calcium stearate, and the amounts used were 0.7% and 0.3% in terms of the mass of the raw material, respectively, the swelling temperature was 98 ° C, the extrusion speed was 3.25 m / min, and the heat-retaining oil jacket was 200 ° C. Circumferential blowing of air with a quenching temperature of -10 ° C was performed at a wind pressure of 5 kPa for 0.6 s. The temperature of the hot roll was 40 ° C, the temperature of the drying oven was 60 ° C (air knife has a wind temperature of 60 ° C, a wind speed of 50 meters / sec, and a wind pressure of 0.4 MPa), the temperature of the stretching oven was 125 ° C, the pre-stretching ratio was 3 times, the temperature of the multi-stage stretching oven was 140 to 145 ° C, and the total stretching ratio was 300 times. The solvent recovery is carried out in stages at different temperatures, with a cyclone separator in the low temperature region and an integrated cooling separation-cryogenic separation-cooling separation-adsorption and desorption in the high temperature region, where the temperatures of the cyclone separation and cooling separation are below 40°C, the temperature of the cryogenic separation is below -5°C, and the adsorbent is molecular sieve. The solvent recovery rate is 98.5%. The DSC curve and XRD diagram of the spun fiber are similar to those in Figures 7 and 8, respectively, and the characteristic detection indexes of the fiber are shown in Table 6 below.

[0121] [Table 6]

[0122] Example 7 Except for using a normal drying oven, that is, the drying oven without an air knife structure, spinning is performed according to the method of Example 4, and the DSC curve and XRD pattern of the spun fiber are similar to those in Figures 7 and 8 respectively, and the characteristic detection indexes are shown in Table 7 below. The solvent recovery rate is 84%.

[0123] [Table 7]

[0124] Example 8 Except that the air knife in the drying oven was of a straight-through structure, the spinning was carried out according to the method of Example 4. The DSC curves and XRD patterns of the spun fibers of each batch are similar to those in Figures 7 and 8, respectively, and the characteristic detection indexes are shown in Table 8 below. The solvent recovery rate is 95%.

[0125] [Table 8]

[0126] Comparative Example 1 Fiber yarn was produced according to the method of Example 4, except that the circumferential blowing method was changed to the side blowing method described in CN106544741B, the air at a temperature of 10°C was blown sideways, and the drying oven was not provided with an air knife structure. The DSC curve and XRD diagram of the spun fiber are shown in Sample 1 of Figures 7 and 8, respectively, and the property indexes of the fiber obtained in each lot are shown in Table 9 below.

[0127] [Table 9]

[0128] Comparative Example 2 Fiber yarn was produced according to the method of Example 4, except that the circumferential air was air at a temperature of 10° C. The property index of the resulting fiber is shown in Table 10 below.

[0129] [Table 10]

[0130] Unevenness detection Except for adjusting the draw ratio and pre-draw ratio by the spinning head as shown in the following table, spinning was performed according to the methods of Comparative Example 1 and Example 1. The fineness and unevenness of the undrawn gel yarn obtained by cooling and forming, and the semi-finished yarn product obtained by removing the solvent by drying are shown in the following Tables 11 and 12, respectively.

[0131] [Table 11]

[0132] [Table 12]

[0133] Comparing Tables 11 and 12, the undrawn gel yarn has a large fluctuation width of fineness when measuring the fineness because the solvent has not been removed, whereas the semi-finished yarn has a relatively uniform fineness and a small fluctuation width of fineness when measuring the fineness because the solvent has been removed. However, regardless of whether it is undrawn gel yarn or semi-finished yarn, the unevenness is significantly reduced when the method of the present invention is adopted.

[0134] All of the fiber yarn products obtained by drawing the above semi-finished yarn products had unevenness between 0.9 and 1%, while all of the fiber yarn products obtained by the side blowing process in Comparative Example 1 had unevenness exceeding 3%.

[0135] It is clear from the data in the above table that the fibers produced using the method according to the present invention have higher breaking strength and modulus, and less unevenness.

[0136] Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications of the technical solution of the present invention can be made, including combining each technical feature in any suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed in the present invention, and all belong to the patent scope of the present invention.

Claims

1. a spun fiber that is a crystalline polymer, the crystalline polymer comprising ultra-high molecular weight polyethylene; A spun fiber characterized in that the unevenness in fineness is 1.5% or less, the crystallinity measured by differential scanning calorimetry is 60 to 95%, preferably 85 to 90%, the crystal grain size in the normal direction of the (020) crystal plane is 7.4 to 9.6 nm, preferably 7.8 to 9 nm, the crystal grain size in the normal direction of the (110) crystal plane is 8.8 to 11.5 nm, preferably 8.9 to 10 nm, and the crystal grain size in the normal direction of the (200) crystal plane is 7.3 to 11 nm, preferably 7.8 to 10.5 nm, as measured by X-ray diffraction (XRD).

2. The spun fiber of claim 1, having a fineness variation of 0.9-1% and a crystallinity measured by X-ray diffraction (XRD) of 60-95%, preferably 80-90%.

3. 3. Spun fibre according to claim 1 or 2, having a melting point of 148-151°C, preferably 149-151°C, as measured by differential scanning calorimetry.

4. 4. The spun fiber according to claim 1, 2 or 3, which is a polyethylene spun fiber having a fineness of 6 to 100 dtex, a breaking strength of 40 to 55 CN / dtex and an elastic modulus of 1800 CN / dtex or more, preferably 1850 to 2000 CN / dtex.

5. A fiber spinning method comprising the steps of extruding and spinning a spinning solution containing ultra-high molecular weight polyethylene, and cooling and shaping, drying and stretching the fibrils thus obtained, The cooling molding method includes spraying the fibrils with a fluid having a temperature of −10° C. or less; The fiber spinning method is characterized in that the unevenness in fineness of the undrawn gel yarn obtained by the cooling and forming is 3% or less, preferably 1.5 to 2%.

6. The method according to claim 5, wherein the fiber yarn semi-finished product obtained by cooling and drying has a fineness variation of 1.5% or less, preferably 0.5 to 0.95%.

7. The method according to claim 5 or 6, wherein the temperature of the cold moulding fluid is from -50 to -10°C, preferably from -40 to -10°C, more preferably from -30 to -20°C.

8. The method according to any one of claims 5 to 7, wherein the fluid is a gas, and preferably the blowing method is circumferential blowing around the fibril.

9. The method according to any one of claims 5 to 8, wherein the spraying time is 0.5 to 0.7 seconds and the pressure is 0 to 100 kPa, preferably 3 to 10 kPa.

10. The method according to any one of claims 5 to 9, wherein the cooling forming fluid is one or more of liquid nitrogen, air, an inert gas.

11. 11. The method according to any one of claims 5 to 10, wherein the drying regime comprises contacting the chill-formed fibrils with a drying gas having a velocity of at least 20 meters / second, preferably 30-40 meters / second, and preferably the temperature of the drying gas is between 0 and 140°C, preferably 40-80°C.

12. The drying is performed in a drying oven (6), the drying oven (6) including a box and an air knife (60), a drying chamber for drying the material is provided in the box, the air knife (60) is provided in the drying chamber, the air knife (60) includes an inner cylinder (61) and an outer cylinder (62) nested coaxially, one end of the inner cylinder (61) is open and serves as an inlet (611) of the air knife (60), a first outlet (612) communicating with the inlet (611) is provided in a cylindrical wall of the inner cylinder (61), a second outlet (621) is provided in a cylindrical wall of the outer cylinder (62), and the first outlet (612) and the the air knife (60) is configured to move along a radial direction of the air knife (60) to adjust the blowing amount and blowing direction of the second blowing outlet (621), the second blowing outlet (621) of the air knife (60) is aligned with the material, the box is provided with a supply port, a discharge port, a dry gas inlet and a dry gas outlet which are all connected to the drying chamber, the blowing port (611) is connected to the dry gas inlet and the second blowing outlet (621) is connected to the dry gas outlet.

13. the first outlet (612) is elongated and extends in the axial direction of the inner cylinder (61), the second outlet (621) is elongated and extends in the axial direction of the outer cylinder (62), the first outlet (612) and the second outlet (621) are offset from each other in the circumferential direction of the air knife (60), and / or one end of the inner cylinder (61) away from the blowing port (611) is closed, and both ends of the communication passage (63) are closed, the first outlet (612) and the second outlet (621) are provided opposite to each other in the circumferential direction of the air knife (60); and / or The method according to claim 12, wherein the first outlet (612) and the second outlet (621) have an opening angle in a circumferential direction of the air knife (60) of 0 to 90°, preferably 25 to 40°.

14. the air knife (60) includes a mounting assembly for mounting the inner cylinder (61) and the outer cylinder (62); and / or The method according to claim 12 or 13, wherein the inner cylinder (61) is configured to be movable along a radial direction of the air knife (60) relative to the outer cylinder (62).

15. 15. The method according to claim 14, wherein the mounting assembly includes two movable flanges (64) attached to opposite ends of the inner cylinder (61) and two fixed flanges (65) attached to opposite ends of the outer cylinder (62), each of the two movable flanges (64) being connected to the two fixed flanges (65) and configured to be lockably movable along a radial direction of the air knife (60) relative to a corresponding one of the fixed flanges (65).

16. The movable flange (64) and the fixed flange (65) are connected by a fastener, and the movable flange (64) and the fixed flange (65) each have a through hole through which the fastener is inserted and installed, the through hole of the movable flange (64) being a circular hole (641) and the through hole of the fixed flange (65) being an oval hole (651); and / or The method according to claim 15, wherein one end of the inner cylinder (61) where the blowing port (611) is provided extends outside the movable flange (64).

17. The method according to any one of claims 13 to 16, wherein the inlet and the outlet are located on opposite sides of the box, respectively, and a plurality of the air knives (60) are provided in the drying chamber, the plurality of the air knives (60) extending perpendicular to the material feeding direction and arranged at intervals along the material feeding direction.

18. The method according to any one of claims 5 to 17, wherein the total draw ratio of said draw is from 100 to 1000, preferably from 200 to 940.

19. The method according to any one of claims 5 to 18, further comprising recovering the solvent in the cooling and molding step and the drying step, wherein the method for recovering the solvent in the cooling and molding step is a cyclone separation method, and the method for recovering the solvent in the drying step is a method combining cryogenic separation and adsorption and desorption.

20. The method according to claim 19, wherein the temperature of the cyclone separation is below 40°C, preferably between 10 and 30°C.

21. The method according to claim 19 or 20, wherein the combined cryogenic separation and adsorption / desorption method is to first perform cryogenic separation and then perform adsorption / desorption.

22. 22. The method according to any one of claims 19 to 21, wherein the temperature of the cryogenic separation is below -5°C, preferably between -20 and -10°C.

23. The method according to any one of claims 19 to 22, wherein the adsorption mode is to contact the gas from the drying step with an adsorbent.

24. 24. The method of claim 23, wherein the adsorbent is one or more of activated carbon, coconut shell charcoal, and molecular sieve, preferably cylindrical activated carbon with a diameter of 3-6 mm.

25. 25. The method of any one of claims 19 to 24, wherein the desorption conditions include a desorption temperature of 5 to 25°C and a pressure of 0.1 to 5 MPa.

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