Method for preparing high-strength polyethylene fiber

Abstract

The invention discloses a method for preparing high-strength polyethylene fibers and belongs to the technical field of fiber processing. The preparation method comprises the following steps: feeding controllable molecular weight distribution polyethylene resin into a screw extruder, melting, mixing and extruding into a spinning box, and extruding by a spinneret plate which limits the aperture of spinneret orifices, the length-diameter ratio of the spinneret orifices and the flow of each spinneret orifice in a structural system of a spinning assembly of the spinning box; melt trickles extruded by the spinneret plate pass through the heat preservation section, then enter the air cooling channel and are cooled by cold air, the cold air temperature of the air cooling channel and the air speed of the cold air are controlled, the melt trickles out of the air cooling channel are subjected to double-roller hot drafting, the hot drafting temperature and the hot drafting total multiple are controlled, winding is conducted, and the high-strength polyethylene fibers are obtained. The method has the advantages of simple process, easy control of the fiber forming stage, convenient operation and low cost; the environment friendliness is embodied; the orientation degree of the fibers can be improved through the shearing rate of the spinneret orifices, strengthening is achieved, and the fabric made of the obtained fibers can meet the requirements for softness and skin-fitting softness.

Description

Technical Field

[0001] The invention belongs to the technical field of fiber processing, and in particular relates to a method for preparing high-strength polyethylene fiber. Background Art

[0002] The aforementioned high-strength polyethylene fiber is one of the three major high-performance fibers (the other two are carbon fiber and aramid fiber). Its physical indicators include high tensile strength, high tensile modulus, low elongation at break, low density, excellent specific strength and specific modulus. It also has good chemical resistance.

[0003] Due to the maturity of the process and the adaptability of industrialized production, the preparation of high-strength polyethylene by gel (also known as "jelly") spinning has always been favored by the industry to a large extent, but the shortcomings of gel spinning are also increasingly concerned by the industry. The so-called shortcomings are mainly but not limited to the following factors: the process is long and relatively complex and the energy consumption is high; solid waste such as undissolved polyethylene, residual solvents, fiber waste, waste liquid and waste residues of cleaning equipment, and residual additives are difficult to properly deal with. If the solid waste is not properly handled, it is difficult to avoid damage to the environment. At present, the general use is to deal with it by incineration or landfill, which will cause undesirable but unavoidable secondary pollution.

[0004] The advantages of preparing high-strength polyethylene fibers by melt spinning compared to gel spinning are at least: the process is simple, because the polyethylene can be directly heated to a molten state and then spun; the preparation efficiency is high, because there is no need for solvent treatment and no gelation process, so the preparation speed is fast and the efficiency is high; the preparation cost is low, because there is no need to use solvents, there is no factor of solvent recovery, and the equipment investment and operating costs are low; it is environmentally friendly, because it does not involve the use of solvents, and thus can avoid the problem of organic solvents damaging the environment; the fiber performance is stable, because the fiber structure is uniform and the performance is stable, it is more suitable for industrial scale-up production, etc.

[0005] It is precisely because the melt spinning method has many advantages that are not limited to the aforementioned ones that it has been increasingly valued by people in recent years and has been seen in both Chinese and foreign patent literature. For example, CN111733465A recommends "a method and device for melt spinning high-strength polyethylene fibers". Although this patent has the two major technical effects recorded in the technical effect column in the specification, it still has shortcomings, because the embodiments of the patent clearly point out multiple continuous hot roller stretching. This method will cause the fiber to have an unavoidable stretching point slip problem due to the large stretching tension, and the stretching point slip will at least cause the following adverse factors: uneven fiber structure, fiber diameter fluctuation (uneven yarn dryness); decreased mechanical properties, reduced production efficiency, increased wear of equipment such as stretching rollers, increased energy consumption, unstable product quality, etc. For example, the TW1318251B application filed by Toyobo Co., Ltd. in Taiwan, China, provides "a high-strength polyethylene fiber and its preparation method", which is to roll up the polyethylene raw material after high-speed spinning, and then perform secondary hot stretching at a specific temperature. In short, it is oriented and shaped through large extrusion volume and large stretching tension, and finally obtains polyethylene fiber with an average strength of more than 15cN / dtex. Another example is U.S. Patent US4228118A, which introduces "high-strength polyethylene fiber and its manufacturing method". The patent emphasizes that the hot stretching step is separated from the extrusion and curing, and finally obtains a high-strength polyethylene fiber greater than 12g / d. This is equivalent to completing the preparation of the fiber in two steps, which is extremely unfavorable for the control of production costs.

[0006] In short, it is of positive significance to explore a one-step process for preparing high-strength polyethylene that is easier to control, has a lower cost, is environmentally friendly, and has less demanding requirements on equipment. The technical solution to be introduced below was produced in this context. Summary of the invention

[0007] The task of the present invention is to provide a method for preparing high-strength polyethylene fiber, which has simple process, easy control of the fiber forming stage, convenient operation, low cost, environmental friendliness, low equipment requirements and can make the obtained fiber meet the requirements of producing soft and skin-friendly fabrics.

[0008] The task of the present invention is accomplished in this way. A method for preparing high-strength polyethylene fiber comprises the following steps: feeding a polyethylene resin with a controllable molecular weight distribution into a screw extruder for melt mixing and extrusion to a spinning box, and extruding the resin through a spinneret that limits the diameter of the spinneret holes, the aspect ratio of the spinneret holes, and the flow rate of each spinneret hole in the structural system of the spinning assembly of the spinning box. The melt stream extruded from the spinneret passes through a heat preservation section and then enters an air cooling channel, where it is cooled by cold air, and the cold air temperature and wind speed of the air cooling channel are controlled. The fiber exiting the air cooling channel is subjected to hot stretching by a pair of rollers, and the hot stretching temperature and the total hot stretching multiple are controlled, and the fiber is wound to obtain high-strength polyethylene fiber.

[0009] In a specific embodiment of the present invention, the controlled molecular weight distribution polyethylene tree refers to the weight average molecular weight (M W ) is 100,000-300,000 and the weight average molecular weight (M W ) and number average molecular weight (M n ) ratio (M W / M n ) is less than 3.5 polyethylene resin.

[0010] In another specific embodiment of the present invention, the spinneret that limits the pore size of the spinneret holes, the aspect ratio of the spinneret holes and the flow rate of each spinneret hole limits the pore size of each spinneret hole to 0.3-0.8 mm, the aspect ratio of the spinneret holes to 5-10, and the flow rate of the spinneret holes to 0.1-0.5 g / min.

[0011] In another specific embodiment of the present invention, the insulation section is located between the spinneret and the air-cooling tunnel and the insulation area length of the insulation section is 10-25 cm.

[0012] In yet another specific embodiment of the present invention, the temperature of the insulation section is 60-90°C.

[0013] In another specific embodiment of the present invention, the cold air temperature of the air cooling channel is controlled to be 7-15°C, and the cold air speed is controlled to be 0.3-1.2 m / s.

[0014] In a further specific embodiment of the present invention, the air-cooling tunnel is an air-cooling tunnel for cooling by circulating air.

[0015] In a further specific embodiment of the present invention, the number of groups of the rollers is four, five or six.

[0016] In yet another specific embodiment of the present invention, the controlling of the hot stretching temperature is to control the hot stretching temperature to 115-140° C.; the controlling of the total hot stretching multiple is to control the total hot stretching multiple to 6-12 times.

[0017] In yet another specific embodiment of the present invention, the average strength of the high-strength polyethylene fiber is greater than 13 cN / dtex.

[0018] The technical effect of the technical scheme provided by the present invention is that: since the melt stream extruded from the spinneret is sequentially cooled and solidified through the heat preservation section, the air-cooling channel and the roller drawing, the whole process is a continuous production line, and no intermediate steps or additional equipment are required, which reflects a one-step preparation method. Not only is the process simple, the fiber forming stage is easy to control, the operation is convenient, but also the cost is low; since there is no need to use organic solvents, the damage to the environment by organic solvents can be avoided, thereby reflecting environmental friendliness; since the screw extruder and the spinning box used have no harsh and picky requirements, the equipment requirements are low; since a polyethylene resin with a controllable molecular weight distribution is used, it has the advantages of narrow and uniform molecular weight distribution, and since the aperture of the spinneret hole, the aspect ratio of the spinneret hole and the flow rate of each spinneret hole are limited, the orientation degree of the fiber can be increased by the shear rate of the spinneret hole to achieve strength enhancement, and the fabric made of the obtained fiber can meet the softness and skin-fitting properties, reflecting an ideal wearing comfort effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 A schematic diagram of an apparatus used in the method for preparing high-strength polyethylene fiber of the present invention.

[0020] In the figure: 1. screw extruder; 2. spinning box; 21. spinneret; 3. insulation section; 4. air cooling tunnel; 5. pair of rollers; 6. winding roller. DETAILED DESCRIPTION Example 1

[0021] With Figure 1 The method for preparing high-strength polyethylene fibers by the apparatus shown in the figure is as follows: preferably, a weight average molecular weight (M) is detected and confirmed by a detection device such as gel permeation chromatography (GPC). W ) is 100,000-300,000 and the weight average molecular weight (M W ) and number average molecular weight (M n ) ratio (M W / M n ) is less than 3.5. The polyethylene resin is fed into the screw extruder from the feeding hopper of the screw extruder 1, melt-mixed and extruded from the screw extruder 1 to the spinning box 2, and extruded from the spinneret 21 of the structural system of the spinning assembly of the spinning box 2. The number of spinneret holes of the spinneret 21 is 300F, the diameter of the spinneret holes is 0.45mm, the aspect ratio of the spinneret holes is 6, and the extrusion flow rate of each spinneret hole is limited to 0.1g / min. The melt extruded from the spinneret 21 passes through the insulation section 3 with an insulation temperature of 70°C and a length of 15cm between the spinneret 21 and the air-cooling channel 4, and then enters the air-cooling tunnel 4. The cold air temperature of the air-cooling tunnel 4 is controlled to be 8°C, and the speed of the cold air is controlled to be 0.6m / s. Figure 1The hollow arrow at the lower right of the air cooling channel 4 in the figure indicates the cold air inlet, and the hollow arrow at the upper left of the air cooling channel 4 indicates the air outlet. The air cooling channel 4 is an air cooling channel for annular air cooling. The filament bundle obtained after exiting the air cooling channel 4 is stretched by four groups (also called four pairs) of rollers 5. The hot stretching temperature, i.e., the temperature of the rollers 5, is controlled to be 120°C, and the total stretching multiple is 8 times. After exiting the four groups of rollers 5 (i.e., exiting the hot stretching area), the fiber is wound by the winding roller 6 (i.e., the winding roller) to obtain a high-strength polyethylene fiber with an average strength of 13 cN / dtex. Determine the weight average molecular weight (M) W ) and number average molecular weight (M n ), that is, M W / M n Less than 3.5 is determined by gel permeation chromatography (GPC), which involves dissolving the sample and separating it through a chromatographic column to detect the concentration of components with different molecular weights, and obtaining a molecular weight distribution curve. W / M n Calculate the molecular weight distribution index. The present invention uses the technical means of small aperture and large aspect ratio to select the aperture of the spinneret 21 to be 0.45mm, and the aspect ratio of the spinneret is selected to be 6, so as to improve the orientation degree, and the smaller aperture is conducive to the generation of finer fibers, which is suitable for the production of ultrafine fibers and even nanofibers, and is conducive to reducing the fluctuation of fiber diameter and improving the uniformity of fibers (good yarn consistency), which is suitable for the production of high-end textiles. The reason why the fiber stream extruded from the spinneret 21 passes through the insulation section 3 and enters the air cooling channel 4 (also called "quick cooling channel") is to prevent the fiber from cooling prematurely and maintain its plasticity to facilitate subsequent drafting. The present invention determines the drafting temperature, that is, the roller 5, to be 120°C after a non-limited number of tests, and selects the total drafting multiple to be 8 times. This is based on the rearrangement of the fiber molecular chain, the improvement of mechanical properties, and the improvement of the tensile strength, modulus and wear resistance of the fiber. Example 2

[0022] With Figure 1 The method for preparing high-strength polyethylene fibers by the apparatus shown in the figure is as follows: preferably, a weight average molecular weight (M) is detected and confirmed by a detection device such as gel permeation chromatography (GPC). W ) is 100,000-300,000 and the weight average molecular weight (M W ) and number average molecular weight (M n ) ratio (M W / M n) is less than 3.5. The polyethylene resin is fed into the screw extruder from the feeding hopper of the screw extruder 1, melt-mixed and extruded from the screw extruder 1 to the spinning box 2, and extruded from the spinneret 21 of the structural system of the spinning assembly of the spinning box 2. The number of spinneret holes of the spinneret 21 is 300F, the diameter of the spinneret holes is 0.3mm, the aspect ratio of the spinneret holes is 5, and the extrusion flow rate of each spinneret hole is limited to 0.3g / min. The melt extruded from the spinneret 21 passes through the insulation section 3 with an insulation temperature of 60°C and a length of 10cm between the spinneret 21 and the air-cooling channel 4, and then enters the air-cooling tunnel 4. The cold air temperature of the air-cooling tunnel 4 is controlled to be 7°C, and the speed of the cold air is controlled to be 1.2m / s. Figure 1 The hollow arrow at the lower right of the air cooling channel 4 in the figure indicates the cold air inlet, and the hollow arrow at the upper left of the air cooling channel 4 indicates the air outlet. The air cooling channel 4 is an air cooling channel for annular air cooling. The filament bundles obtained after exiting the air cooling channel 4 are stretched by four groups (also called four pairs) of rollers 5. The hot stretching temperature, i.e., the temperature of the rollers 5, is controlled to be 115°C, and the total stretching multiple is 6 times. After exiting the four groups of rollers 5 (i.e., exiting the hot stretching area), the fibers are wound by the winding roller 6 (i.e., the winding roller) to obtain high-strength polyethylene fibers with an average strength of 14.5 cN / dtex. Determine the weight average molecular weight (M) W ) and number average molecular weight (M n ), that is, M W / M n Less than 3.5 is determined by gel permeation chromatography (GPC), which involves dissolving the sample and separating it through a chromatographic column to detect the concentration of components with different molecular weights, and obtaining a molecular weight distribution curve. W / M n Calculate the molecular weight distribution index. The present invention uses a small aperture and a large aspect ratio to select the aperture of the spinneret 21 to be 0.3 mm, and the aspect ratio of the spinneret is selected to be 5, so as to improve the orientation degree, and the smaller aperture is conducive to the generation of finer fibers, which is suitable for the production of ultrafine fibers and even nanofibers, and is conducive to reducing the fluctuation of fiber diameter and improving the uniformity of the fibers (good yarn consistency), which is suitable for the production of high-end textiles. The reason why the present invention allows the fiber stream extruded from the spinneret 21 to enter the air cooling tunnel 4 (also known as the "quick cooling tunnel") after passing through the insulation section 3 is to prevent the fiber from cooling prematurely and maintain its plasticity to facilitate subsequent drafting. The present invention determines the drafting temperature, that is, the roller 5, to be 115°C after a non-limited number of tests, and selects the total drafting multiple to be 6 times. This is based on the rearrangement of the fiber molecular chain, the improvement of mechanical properties, and the improvement of the tensile strength, modulus and wear resistance of the fiber. Example 3

[0023] With Figure 1The method for preparing high-strength polyethylene fibers by the apparatus shown in the figure is as follows: preferably, a weight average molecular weight (M) is detected and confirmed by a detection device such as gel permeation chromatography (GPC). W ) is 100,000-300,000 and the weight average molecular weight (M W ) and number average molecular weight (M n ) ratio (M W / M n ) is less than 3.5. The polyethylene resin is fed into the screw extruder from the feeding hopper of the screw extruder 1, melt-mixed and extruded from the screw extruder 1 to the spinning box 2, and extruded from the spinneret 21 of the structural system of the spinning assembly of the spinning box 2. The number of spinneret holes of the spinneret 21 is 300F, the diameter of the spinneret holes is 0.8mm, the aspect ratio of the spinneret holes is 10, and the extrusion flow rate of each spinneret hole is limited to 0.5g / min. The melt extruded from the spinneret 21 passes through the insulation section 3 with an insulation temperature of 90°C and a length of 25cm between the spinneret 21 and the air-cooling channel 4, and then enters the air-cooling tunnel 4. The cold air temperature of the air-cooling tunnel 4 is controlled to be 15°C, and the speed of the cold air is controlled to be 0.3m / s. Figure 1 The hollow arrow at the lower right of the air cooling channel 4 in the figure indicates the cold air inlet, and the hollow arrow at the upper left of the air cooling channel 4 indicates the air outlet. The air cooling channel 4 is an air cooling channel for annular air cooling. The filament bundle obtained after exiting the air cooling channel 4 is stretched by six groups (also called six pairs) of rollers 5. The hot stretching temperature, i.e., the temperature of the rollers 5, is controlled to be 140°C, and the total stretching multiple is 12 times. After exiting the six groups of rollers 5 (i.e., exiting the hot stretching area), the fiber bundle is wound by the winding roller 6 (i.e., the winding roller) to obtain a high-strength polyethylene fiber with an average strength of 16 cN / dtex. Determine the weight average molecular weight (M) W ) and number average molecular weight (M n ), that is, M W / M n Less than 3.5 is determined by gel permeation chromatography (GPC), which involves dissolving the sample and separating it through a chromatographic column to detect the concentration of components with different molecular weights, and obtaining a molecular weight distribution curve. W / M nCalculate the molecular weight distribution index. The present invention uses a small aperture and a large aspect ratio to select the aperture of the spinneret 21 to be 0.8 mm, and the aspect ratio of the spinneret is selected to be 10, so as to improve the degree of orientation, and the smaller aperture is conducive to the generation of finer fibers, which is suitable for the production of ultrafine fibers and even nanofibers, and is conducive to reducing the fluctuation of the fiber diameter and improving the uniformity of the fiber (good consistency of the strands), which is suitable for the production of high-end textiles. The reason why the fiber stream extruded from the spinneret 21 passes through the insulation section 3 and enters the air cooling tunnel 4 (also called "quick cooling tunnel") is to prevent the fiber from cooling prematurely and maintain its plasticity to facilitate subsequent drafting. The present invention determines the drafting temperature, that is, the roller 5, to be 140°C after a non-limited number of tests, and selects the total drafting multiple to be 12 times. This is based on the rearrangement of the fiber molecular chain, the improvement of mechanical properties, and the improvement of the tensile strength, modulus and wear resistance of the fiber. Example 4

[0024] With Figure 1 The method for preparing high-strength polyethylene fibers by the apparatus shown in the figure is as follows: preferably, a weight average molecular weight (M) is detected and confirmed by a detection device such as gel permeation chromatography (GPC). W ) is 100,000-300,000 and the weight average molecular weight (M W ) and number average molecular weight (M n ) ratio (M W / M n ) is less than 3.5. The polyethylene resin is fed into the screw extruder from the feeding hopper of the screw extruder 1, melt-mixed and extruded from the screw extruder 1 to the spinning box 2, and extruded from the spinneret 21 of the structural system of the spinning assembly of the spinning box 2. The number of spinneret holes of the spinneret 21 is 300F, the diameter of the spinneret holes is 0.65mm, the aspect ratio of the spinneret holes is 8, and the extrusion flow rate of each spinneret hole is limited to 0.4g / min. The melt extruded from the spinneret 21 passes through the insulation section 3 with an insulation temperature of 80°C and a length of 20cm between the spinneret 21 and the air-cooling channel 4, and then enters the air-cooling tunnel 4. The cold air temperature of the air-cooling tunnel 4 is controlled to be 10°C, and the speed of the cold air is controlled to be 0.8m / s. Figure 1 The hollow arrow at the lower right of the air cooling channel 4 in the figure indicates the cold air inlet, and the hollow arrow at the upper left of the air cooling channel 4 indicates the air outlet. The air cooling channel 4 is an air cooling channel for annular air cooling. The filament bundle obtained after exiting the air cooling channel 4 is stretched by five groups (also called five pairs) of rollers 5. The hot stretching temperature, i.e., the temperature of the rollers 5, is controlled to be 130°C, and the total stretching multiple is 10 times. After exiting the five groups of rollers 5 (i.e., exiting the hot stretching area), the fiber is wound by the winding roller 6 (i.e., the winding roller) to obtain a high-strength polyethylene fiber with an average strength of 15 cN / dtex. Determine the weight average molecular weight (M) W ) and number average molecular weight (Mn ), that is, M W / M n Less than 3.5 is determined by gel permeation chromatography (GPC), which involves dissolving the sample and separating it through a chromatographic column to detect the concentration of components with different molecular weights, and obtaining a molecular weight distribution curve. W / M n Calculate the molecular weight distribution index. The present invention uses a small aperture and a large aspect ratio to select the aperture of the spinneret 21 to be 0.6 mm, and the aspect ratio of the spinneret is selected to be 8, so as to improve the orientation degree, and the smaller aperture is conducive to the generation of finer fibers, which is suitable for the production of ultrafine fibers and even nanofibers, and is conducive to reducing the fluctuation of the fiber diameter and improving the uniformity of the fiber (good consistency of the strands), and is suitable for the production of high-end textiles. The reason why the fiber stream extruded from the spinneret 21 passes through the insulation section 3 and enters the air cooling tunnel 4 (also called "quick cooling tunnel") is to prevent the fiber from cooling prematurely and maintain its plasticity to facilitate subsequent drafting. The present invention determines the drafting temperature, that is, the roller 5, to be 130°C after a non-limited number of tests, and selects the total drafting multiple to be 10 times. This is based on the rearrangement of the fiber molecular chain, the improvement of mechanical properties, and the improvement of the tensile strength, modulus and wear resistance of the fiber.

Claims

1. A method for preparing high-strength polyethylene fiber, characterized in that: The method comprises the following steps: feeding a polyethylene resin with a controllable molecular weight distribution into a screw extruder for melt mixing and extruding the resin to a spinning box, and then extruding the resin from a spinneret which limits the diameter of the spinneret holes, the aspect ratio of the spinneret holes and the flow rate of each spinneret hole in the structural system of the spinning assembly of the spinning box. The melt stream extruded from the spinneret passes through a heat preservation section and then enters an air cooling tunnel, where it is cooled by cold air and the temperature and wind speed of the cold air in the air cooling tunnel are controlled. The melt exiting the air cooling tunnel is subjected to hot stretching by a pair of rollers and the hot stretching temperature and the total hot stretching multiple are controlled, and then the melt is wound to obtain high-strength polyethylene fibers.

2. The method for preparing high-strength polyethylene fiber according to claim 1, characterized in that: The controlled molecular weight distribution polyethylene resin refers to a polyethylene resin with a weight average molecular weight of 100,000 to 300,000 and a ratio of the weight average molecular weight to the number average molecular weight of less than 3.

5.

3. The method for preparing high-strength polyethylene fiber according to claim 1, characterized in that: The spinneret that limits the diameter of the spinneret holes, the aspect ratio of the spinneret holes and the flow rate of each spinneret hole limits the diameter of each spinneret hole to 0.3-0.8mm, the aspect ratio of the spinneret holes to 5-10, and the flow rate of the spinneret holes to 0.1-0.5g / min.

4. The method for preparing high-strength polyethylene fiber according to claim 1, characterized in that: The insulation section is located between the spinneret and the air-cooling tunnel, and the insulation area length of the insulation section is 10-25 cm.

5. The method for preparing high-strength polyethylene fiber according to claim 1 or 4, characterized in that: The temperature of the insulation section is 60-90°C.

6. The method for preparing high-strength polyethylene fiber according to claim 1, characterized in that: The method for controlling the cold air temperature of the air cooling corridor is to control the cold air temperature to 7-15°C, and the method for controlling the cold air speed is to control the cold air speed to 0.3-1.2 m / s.

7. The method for preparing high-strength polyethylene fiber according to claim 1 or 6, characterized in that: The air-cooling tunnel is a wind-cooling tunnel for cooling by circulating air.

8. The method for preparing high-strength polyethylene fiber according to claim 1, characterized in that: The number of groups of the roller pairs is four, five or six.

9. The method for preparing high-strength polyethylene fiber according to claim 1, characterized in that: The controlling of the heat stretching temperature is to control the heat stretching temperature to 115-140° C.; the controlling of the total heat stretching multiple is to control the total heat stretching multiple to 6-12 times.

10. The method for preparing high-strength polyethylene fiber according to claim 1, characterized in that: The average strength of the high-strength polyethylene fiber is greater than 13 cN / dtex.

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