Preparation method of high-strength polyethylene fiber

Abstract

The invention discloses a preparation method of high-strength polyethylene fibers, and belongs to the technical field of polyethylene fiber preparation. The method comprises the following steps: firstly, introducing high-molecular-weight polyethylene resin into a pretreatment system, introducing a solvent into the pretreatment system for swelling, controlling the swelling temperature and swelling time of the pretreatment system, controlling the mass ratio of the solvent to the high-molecular-weight polyethylene resin, and then separating to obtain swelled high-molecular-weight polyethylene resin; mixing the swelled high-molecular-weight polyethylene resin and the non-swelled low-molecular-weight polyethylene resin according to a mass ratio to obtain a mixed raw material; the preparation method comprises the following steps: mixing and plasticizing the obtained mixed raw material by using double screws, extruding and spinning by using a single-screw extruder to obtain a polyethylene fiber to be drafted, and carrying out hot roller drafting to obtain the high-strength polyethylene fiber. The method has the advantages that solution viscosity is improved, and melt fluidity is increased; the hot roller is fast in heat transfer and high in efficiency, and fiber heating is more uniform; the drafting consistency is good, the prepared fibers are more uniform, and the comprehensive mechanical property is better.

Description

Technical Field

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

[0002] High-strength polyethylene fiber usually refers to a fiber with a breaking strength greater than 15cn / dtex. It has extremely high specific strength and specific modulus, that is, the strength and stiffness are very high relative to its weight. This fiber has a low density and can float on the water, so it has excellent impact resistance and cut resistance, as well as good resistance to ultraviolet radiation and neutrons and gamma rays. In addition, it also has a low dielectric constant, high electromagnetic wave transmittance, and excellent wear resistance, low temperature resistance, ultraviolet resistance, and shielding resistance, as well as good flexibility and impact energy absorption. These characteristics make high-strength polyethylene fiber products quite popular in areas such as defense, aviation, and civil use.

[0003] The melt spinning method for preparing high-strength polyethylene fiber was first developed by Professor IM Ward of Leeds University in the UK in the early 1970s, and then transferred to Snia in Italy and Hoechst Celanese in the United States. The two companies launched polyethylene fibers under the trade names of Tenfor and Certran respectively, with multiple varieties and specifications, but the strength was only 14g / d and the modulus was 540g / d. Due to poor performance, production was stopped later.

[0004] Although the melt spinning method for producing polyethylene fibers has the advantages of simple process, high production efficiency and low cost, it generally uses raw materials with low molecular weight due to melt fluidity, and there are many defects caused by the large number of terminal groups. If high molecular weight raw materials are used, not only will spinning be difficult, but also it will be difficult to disentangle polyethylene macromolecules without solvents. Entanglement makes it more difficult to orient the molecular chains, and subsequent high-multiple stretching is impossible, so it is difficult to obtain high-strength products.

[0005] Due to the above limitations, the art still needs a more effective method to prepare high-strength polyethylene fibers. The present invention provides a solution to this problem. Summary of the invention

[0006] The task of the present invention is to provide a method for preparing high-strength polyethylene fiber, which eliminates the shortcomings of the prior art by pretreating the raw materials and then using a melt spinning method to obtain the high-strength polyethylene fiber.

[0007] The task of the present invention is accomplished by a method for preparing a high-strength polyethylene fiber, comprising the following steps:

[0008] A) preparing a swollen high molecular weight polyethylene resin, firstly introducing the high molecular weight polyethylene resin into a pretreatment system, and introducing a solvent into the pretreatment system for swelling, and controlling the swelling temperature and swelling time of the pretreatment system, and controlling the mass ratio of the solvent to the high molecular weight polyethylene resin, and then separating to obtain the swollen high molecular weight polyethylene resin;

[0009] B) preparing a mixed raw material by mixing the swollen high molecular weight polyethylene resin obtained in step A) with the unswollen low molecular weight polyethylene resin according to a mass ratio to obtain a mixed raw material;

[0010] C) preparing polyethylene fibers, first subjecting the mixed raw materials obtained in step B) to twin-screw mixing and plasticization, then subjecting the mixed raw materials to single-screw extruder extrusion spinning to obtain polyethylene fibers to be drawn, and then subjecting the mixed raw materials to hot roller drawing to obtain high-strength polyethylene fibers.

[0011] In a specific embodiment of the present invention, the swelling temperature and swelling time of the pretreatment system in step A) are controlled to be 105-115° C. and 10-30 min.

[0012] In another specific embodiment of the present invention, the pretreatment system includes a swelling kettle, a separation kettle and a storage tank, the swelling kettle and the separation kettle are connected by a first pipeline and a first delivery pump is arranged on the pipeline of the first pipeline, the separation kettle and the storage tank are connected by a second pipeline and a second delivery pump is arranged on the pipeline of the second pipeline, the storage tank and the swelling kettle are connected by a third pipeline and a third delivery pump is arranged on the pipeline of the third pipeline, wherein the swelling kettle is provided with an insulation jacket, and the insulation medium circulating in the insulation jacket is connected to the pipeline of the external heating system, the swelling kettle is also provided with a stirring device for high-speed shear dispersion of the high molecular weight polyethylene resin to increase the swelling rate, and the rotation speed of the stirring device is 1000-3500rpm; the separation kettle includes a pressurizing device and a filtering device for filtering the mixed liquid and achieving rapid separation.

[0013] In another specific embodiment of the present invention, the intrinsic viscosity [η] of the swollen high molecular weight polyethylene resin in steps A) and B) is 5.0-9.0 dl / g, and the number of branches per 1000 carbon atoms in the main chain is less than 0.5.

[0014] In another specific embodiment of the present invention, the mass ratio of the solvent to the high molecular weight polyethylene resin in step A) is controlled to be 2-10:1, and after swelling, the mass percentage of the solvent in the swollen high molecular weight polyethylene resin is <5%.

[0015] In another specific embodiment of the present invention, the solvent is a combination of one or more of mineral oil, halogenated hydrocarbons, decahydronaphthalene, tetrahydronaphthalene, naphthalene, xylene, toluene, dodecane, undecane, decane, nonane, octene, chlorobenzene, petroleum ether and low molecular weight polyethylene wax.

[0016] In a more specific embodiment of the present invention, the mass ratio in step B) refers to mixing the swollen high molecular weight polyethylene resin obtained in step A) with the unswollen high molecular weight polyethylene resin in a mass ratio of 5-20:80-95, the mixing device used for mixing is a high-speed mixer, and the mixing time of the high-speed mixer is 10-30 minutes, and the shear rate of the material is 50-500S -1 .

[0017] In a further specific embodiment of the present invention, the unswollen low molecular weight polyethylene resin is prepared by copolymerization of ethylene and straight chain α-olefin, wherein the straight chain α-olefin accounts for less than 0.5 mol% in ethylene, and the branched chain is a C1-C20 hydrocarbon group, and the C1-C20 hydrocarbon group is selected from methyl, ethyl, propyl, butyl, pentyl, hexyl, octyl and cyclohexyl, their isomers and mixtures thereof; the unswollen low molecular weight polyethylene resin has a characteristic viscosity [η] of 2.0-5.0 dl / g, and contains 0.5-2.3 branches for every 1000 carbon atoms in the main chain.

[0018] In yet another specific embodiment of the present invention, the twin screws in step C) are co-rotating parallel twin screws, and the extrusion pressure of the single screw extrusion spinning is 5.0-7.0 MPa.

[0019] In yet another specific embodiment of the present invention, the stretching in step C) is hot roller stretching, the diameter of the hot roller is 400-500 mm, the stretching temperature is 143-155°C, the stretching is divided into 3-5 groups, the stretching multiple is gradually reduced, and the hot stretching is completed once or multiple times; the breaking strength of the high-strength polyethylene fiber is 18-23 g / d, and the fiber is measured for melting heat by DSC, and the first heating curve has more than one endothermic peak.

[0020] The technical effect of the technical solution provided by the present invention is that: compared with conventional melt spinning in the prior art, the present invention pre-treats the raw materials, and uses a mixture of swollen high molecular weight polyethylene and unswollen low molecular weight polyethylene as the raw material. The high molecular weight part acts as a skeleton, and the entangled network structure greatly improves the mechanical properties of the fiber. The low molecular weight part can help the molecular chain end to diffuse quickly and enter the crystallization area to act as a lubricant. Moreover, the small solvent molecules that swell into the high molecular weight polyethylene can significantly improve the solution viscosity and increase the melt fluidity. In addition, a large hot roller is used as the main body of the drafting. Compared with the hot box drafting, the hot roller has fast heat transfer and high efficiency, and the fiber is heated more evenly, and the phenomenon of the traditional small roller being easy to entangle with the roller is effectively reduced. Moreover, the drafting distance between adjacent hot rollers is short, the drafting consistency is good, the prepared fiber is more uniform, and the comprehensive mechanical properties are better. In addition, the hot roller occupies a small area, the equipment operation is simple, and the process adjustment is more convenient. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a schematic diagram of a pretreatment system involved in step A) of the present invention;

[0022] Figure 2 Schematic diagram of hot roller drawing of polyethylene fibers involved in step C) of the present invention;

[0023] Figure 3 This is the DSC spectrum of the copolymer of ethylene and 4-methyl-1-pentene involved in the present invention. DETAILED DESCRIPTION

[0024] Embodiment 1:

[0025] A) Preparation of swollen high molecular weight polyethylene resin, see Figure 1 First, a high molecular weight polyethylene resin having 0.1 branched chains per 1000 carbon atoms in the main chain and having an intrinsic viscosity [η] of 5.0 dl / g is selected and introduced into the swelling kettle 1 through the feed port 11 of the swelling kettle 1 of the structural system of the pretreatment system, and then a mineral oil (commercially available 50# white petroleum oil, with a kinematic viscosity of 5±2 mm at 40° C.) in an amount twice the mass of the high molecular weight polyethylene resin and serving as a solvent is injected into the swelling kettle 1 through the third pipeline 6 from the storage tank 3 of the structural system of the pretreatment system. 2 / s, average molecular weight is 415), that is, the mass ratio of mineral oil to high molecular weight polyethylene resin is 2:1, and the high molecular weight polyethylene resin is swollen in the swelling kettle 1. The mass percentage of the solvent in the high molecular weight polyethylene resin after the swelling is 5% (i.e., the solvent residue). The swelling temperature in this embodiment is controlled to be 112°C, and the swelling time is controlled to be 20min to obtain a swollen high molecular weight polyethylene resin. The above-mentioned pretreatment system in this step can be seen in detail. Figure 1, including the swelling kettle 1, separation kettle 2 and storage tank 3 mentioned above, the swelling kettle 1 and the separation kettle 2 are connected by a first pipeline 4 and a first delivery pump 41 is arranged on the pipeline of the first pipeline 4, the separation kettle 2 and the storage tank 3 are connected by a second pipeline 5 and a second delivery pump 51 is arranged on the pipeline of the second pipeline 5, the storage tank 3 and the swelling kettle 1 are connected by a third pipeline 6 and a third delivery pump 61 is arranged on the pipeline of the third pipeline 6, wherein the swelling kettle 1 is provided with a heat preservation jacket, and the heat preservation medium circulating in the heat preservation jacket is connected to the pipeline of the external heating system, the swelling kettle 1 is also provided with a stirring device for high-speed shearing and dispersing the high molecular weight polyethylene resin to increase the swelling speed, in this embodiment, the stirring speed of the stirring device is 2500rpm; the separation kettle 2 includes a pressurizing device and a filtering device for filtering the mixed liquid and achieving rapid separation, after the swelling of the swelling kettle 1 is completed, the bottom valve of the swelling kettle 1 is opened to allow the mixed liquid to enter the separation kettle 2. Start the press, use the intermittent circulation mode, when the oil agent seeps out in large quantities, the pressing plate will stop moving forward, and when the oil agent seeps out less, the pressing plate will be started again, and the extrusion will be repeated multiple times. Finally, the mineral oil filtered out in the separation kettle 2 is transported to the storage tank 3 through the second delivery pump 51, and the high molecular weight polyethylene resin that has been left and completed swelling is collected by the separation kettle discharge port 21 of the separation kettle 2 for standby use. In summary, the specific operation of this step can be summarized as follows: add the high molecular weight polyethylene resin to the swelling kettle 1 through the feeding port 11 of the swelling kettle 1, and then inject the prepared solvent from the storage tank 3 into the swelling kettle 1, stir and heat, wait until the temperature rises to the set value, keep warm and continue stirring. Then open the bottom valve of the kettle to let the mixed liquid enter the separation kettle 2. Start the press, and as the pressing plate gradually moves downward, the solvent seeps out from the bottom filtration system. The press can be used continuously, preferably intermittently, and the pressing plate will be started again for multiple extrusions when the solvent seeps out less. Finally, the solvent filtered out of the separation kettle 2 is transported to the storage tank 3 through the second delivery pump 51 for continued recycling, and the swollen high molecular weight polyethylene is collected by the separation kettle discharge port 21 for standby use. The solvent in the storage tank 3 will be gradually consumed, and can be replenished through the oil filling port 31 of the storage tank 3. During operation, the solvent is preferably mineral oil, because it is neither volatile, nor flammable and explosive, has stable performance, and is widely available. The composition of mineral oil is a mixture of hydrocarbon saturated alkanes, and the kinematic viscosity at 40°C is 5-50mm 2 / s, average molecular weight ≤ 500, solvent content can be controlled by the swelling process, the higher the swelling temperature and the longer the swelling time, the more sufficient the swelling and the higher the solvent content. On the contrary, the solvent content is low. In the above operation, vacuum filtration is preferred when the separation kettle 2 is used for pressure filtration. Vacuum filtration is suitable for treating more complex suspensions, fine particles and other occasions. It can be filtered under conditions below atmospheric pressure. By generating a vacuum under the filter, the flow rate of the liquid is enhanced, thereby accelerating the filtration process;

[0026] B) preparing a mixed raw material, mixing the swollen high molecular weight polyethylene resin obtained in step A) with the unswollen low molecular weight polyethylene resin according to a mass ratio to obtain a mixed raw material, wherein the mass ratio of the swollen high molecular weight polyethylene resin to the unswollen low molecular weight polyethylene resin in this embodiment is 20:80, and the mixing device used for the above mixing is a high-speed mixer, the mixing time of the high-speed mixer (i.e., the high-speed stirring mixing time) is 20 minutes, and the shear rate of the material is 500S -1 A tree-fork type dispersion roller is fixed on the side of the high-speed mixer, so that the material can hit the dispersion roller when rotating at high speed. Under the impact, it is easier to disperse in multiple directions to improve the mixing effect. Among them, the unswollen low molecular weight polyethylene resin is obtained by copolymerization of ethylene and straight-chain α-olefins, the proportion of the straight-chain α-olefins is less than 0.5 mol%, and the branched chain is a C1-C20 hydrocarbon group, and the C1-C20 hydrocarbon group is selected from methyl, ethyl, propyl, butyl, pentyl, hexyl, octyl and cyclohexyl, their isomers and mixtures thereof. Compared with homopolymers, copolymers can change the crystallinity, melting point and flexibility of the polymer by adjusting the proportion and type of copolymer monomers, so as to have better toughness, transparency and low temperature performance. Moreover, copolymers usually have better fluidity and processing properties, which can reduce energy consumption and the difficulty of melt spinning processing. The intrinsic viscosity of the unswollen low molecular weight polyethylene resin is 2.0 dl / g, and the main chain contains 0.5-3 branches per 1000 carbon atoms. If the branching degree is too low, the polyethylene crystallinity will not be significantly reduced, the fluidity will not be improved much, and it will not be conducive to post-stretching. Otherwise, it will cause severe entanglement of polyethylene and seriously affect the spinning performance. In this embodiment, 0.5 is selected. The above-mentioned unswollen low molecular weight polyethylene resin is prepared by copolymerization of ethylene and 0.1 mol% 4-methyl 1-pentene, wherein the DSC spectrum of the copolymer of ethylene and 4-methyl 1-pentene is shown in Figure 3 ;

[0027] C) preparing polyethylene fibers, firstly subjecting the mixed raw materials obtained in step B) to a parallel twin-screw extruder for mixing and plasticizing, then subjecting the mixed raw materials to a single-screw extruder for extrusion spinning to obtain polyethylene fibers 7 to be drawn, and ... Figure 2The hot rollers shown in the figure are stretched to obtain high-strength polyethylene fibers. The pressure of the single-screw extruder spinning in this step is 5.5 MPa. The roller stretching is a hot roller stretching using a roller, i.e., a stretching roller (i.e., a hot roller 8), with a diameter of 400 mm. This embodiment uses three groups of hot rollers for stretching, but it can also be four or five groups. Each group of hot rollers 8 consists of three rollers, wherein each group of rollers, i.e., the first one in each group of hot rollers 8, is provided with a rubber pressure roller 9 to prevent the fiber from slipping during stretching. The stretching multiples of the three groups of hot rollers 8 for stretching are respectively It is 4.3 times, 2 times and 1.4 times, and is actually 12.04 times (4.3 times × 2 times × 1.4 times, the same in the following embodiments), and the integer is 12 times (this embodiment is a single stretching). The stretching temperatures of the three groups of stretching rollers are 145°C, 150°C and 155°C respectively. Compared with the hot box stretching, the hot roller has fast heat transfer and high efficiency, and the fiber is heated more evenly, the stretching consistency is good, the performance fluctuation is small, and the hot roller occupies a small area, the equipment operation is relatively simple, and the process adjustment is more convenient. The breaking strength of the high-strength polyethylene fiber obtained in this embodiment is 19g / d.

[0028] Embodiment 2:

[0029] A) Preparation of swollen high molecular weight polyethylene resin, see Figure 1 First, a high molecular weight polyethylene resin having 0.2 branches per 1000 carbon atoms in the main chain and an intrinsic viscosity [η] of 9 dl / g is selected and introduced into the swelling kettle 1 through the feed port 11 of the swelling kettle 1 as the structural system of the pretreatment system, and then a mixture of xylene and toluene as a solvent in an amount of 8 times the mass of the high molecular weight polyethylene resin is injected into the swelling kettle 1 through the third pipeline 6 from the storage tank 3 of the structural system of the pretreatment system, that is, the mass ratio of the mixture of xylene and toluene to the high molecular weight polyethylene resin is 8:1, so that the high molecular weight polyethylene resin is swollen in the swelling kettle 1. After the swelling, the mass percentage of the solvent in the high molecular weight polyethylene resin is 4% (i.e., the solvent residue). The swelling temperature in this embodiment is controlled to be 115° C., and the swelling time is controlled to be 30 min to obtain a swollen high molecular weight polyethylene resin. The aforementioned pretreatment system in this step can be seen in detail. Figure 1, including the swelling kettle 1, separation kettle 2 and storage tank 3 mentioned above, the swelling kettle 1 and the separation kettle 2 are connected by a first pipeline 4 and a first delivery pump 41 is arranged on the pipeline of the first pipeline 4, the separation kettle 2 and the storage tank 3 are connected by a second pipeline 5 and a second delivery pump 51 is arranged on the pipeline of the second pipeline 5, the storage tank 3 and the swelling kettle 1 are connected by a third pipeline 6 and a third delivery pump 61 is arranged on the pipeline of the third pipeline 6, wherein the swelling kettle 1 is provided with a heat preservation jacket, and the heat preservation medium circulating in the heat preservation jacket is connected to the pipeline of the external heating system, the swelling kettle 1 is also provided with a stirring device for high-speed shearing and dispersing the high molecular weight polyethylene resin to increase the swelling speed, in this embodiment, the stirring speed of the stirring device is 3500rpm; the separation kettle 2 includes a pressurizing device and a filtering device for filtering the mixed liquid and achieving rapid separation, after the swelling of the swelling kettle 1 is completed, the bottom valve of the swelling kettle 1 is opened to allow the mixed liquid to enter the separation kettle 2. Start the press, use the intermittent circulation mode, when the oil agent seeps out in large quantities, the pressing plate will stop moving forward, and when the oil agent seeps out less, the pressing plate will be started again, and the extrusion will be repeated multiple times. Finally, the mineral oil filtered out in the separation kettle 2 is transported to the storage tank 3 through the second delivery pump 51, and the high molecular weight polyethylene resin that has been left and completed swelling is collected by the separation kettle discharge port 21 of the separation kettle 2 for standby use. In summary, the specific operation of this step can be summarized as follows: add the high molecular weight polyethylene resin to the swelling kettle 1 through the feeding port 11 of the swelling kettle 1, and then inject the prepared solvent from the storage tank 3 into the swelling kettle 1, stir and heat, wait until the temperature rises to the set value, keep warm and continue stirring. Then open the bottom valve of the kettle to let the mixed liquid enter the separation kettle 2. Start the press, and as the pressing plate gradually moves downward, the solvent seeps out from the bottom filtration system. The press can be used continuously, preferably intermittently, and the pressing plate will be started again for multiple extrusions when the solvent seeps out less. Finally, the solvent filtered out of the separation kettle 2 is transported to the storage tank 3 by the second delivery pump 51 for continued recycling, while the high molecular weight polyethylene that has completed swelling is collected by the separation kettle discharge port 21 for standby use. The solvent in the storage tank 3 will be gradually consumed, and the material can be replenished through the oil filling port 31 of the storage tank 3. The solvent content can be controlled by the swelling process. The higher the swelling temperature and the longer the time, the more sufficient the swelling is and the higher the solvent content is. On the contrary, the solvent content is low. In the aforementioned operation, vacuum filtration is preferred for pressure filtration in the separation kettle 2. Vacuum filtration is suitable for processing more complex suspensions, fine particles and the like. It can be filtered under conditions below atmospheric pressure. By generating a vacuum under the filter, the flow rate of the liquid is enhanced, thereby accelerating the filtration process;

[0030] B) preparing a mixed raw material, mixing the swollen high molecular weight polyethylene resin obtained in step A) with the unswollen low molecular weight polyethylene resin according to a mass ratio to obtain a mixed raw material, wherein the mass ratio of the swollen high molecular weight polyethylene resin to the unswollen low molecular weight polyethylene resin in this embodiment is 5:95, and the mixing device used for the above mixing is a high-speed mixer, the mixing time of the high-speed mixer (i.e., the high-speed stirring mixing time) is 20 minutes, and the shear rate of the material is 500S -1 A tree-fork type dispersion roller is fixed on the side of the high-speed mixer, so that the material can hit the dispersion roller when rotating at high speed. Under the impact, it is easier to disperse in multiple directions to improve the mixing effect. Among them, the unswollen low molecular weight polyethylene resin is obtained by copolymerization of ethylene and linear α-olefins, the linear α-olefin accounts for less than 0.5 mol%, and the branched chain is a C1-C20 hydrocarbon group, and the C1-C20 hydrocarbon group is selected from methyl, ethyl, propyl, butyl, pentyl, hexyl, octyl and cyclohexyl, their isomers and mixtures thereof. Compared with homopolymers, copolymers can change the crystallinity, melting point and flexibility of the polymer by adjusting the proportion and type of copolymer monomers, so as to have better toughness, transparency and low temperature performance. Moreover, copolymers usually have better fluidity and processing properties, which can reduce energy consumption and the difficulty of melt spinning processing. The intrinsic viscosity of the unswollen low molecular weight polyethylene resin is 5.0 dl / g, and the main chain contains 0.5-3 branches per 1000 carbon atoms. If the branching degree is too low, the polyethylene crystallinity will not be significantly reduced, the fluidity will not be improved much, and it will not be conducive to post-stretching. Otherwise, it will cause severe entanglement of polyethylene and seriously affect the spinning performance. In this embodiment, 0.9 is selected. The above-mentioned unswollen low molecular weight polyethylene resin is prepared by copolymerization of ethylene and 0.3 mol% 4-methyl 1-pentene, wherein the DSC spectrum of the copolymer of ethylene and 4-methyl 1-pentene is shown in Figure 3 ;

[0031] C) preparing polyethylene fibers, firstly subjecting the mixed raw materials obtained in step B) to a parallel twin-screw extruder for mixing and plasticizing, then subjecting the mixed raw materials to a single-screw extruder for extrusion spinning to obtain polyethylene fibers 7 to be drawn, and ... Figure 2The hot rollers shown in the figure are stretched to obtain high-strength polyethylene fibers. The pressure of the single screw extruder for extrusion spinning in this step is 6.8 MPa. The roller stretching is a hot roller stretching with a roller, i.e., a stretching roller (i.e., a hot roller 8), having a diameter of 420 mm. This embodiment uses three groups of hot rollers for stretching, but it can also be four or five groups. Each group of hot rollers 8 consists of three rollers, wherein each group of rollers, i.e., the first one in each group of hot rollers 8, is provided with a rubber pressure roller 9 to prevent the fiber from slipping during stretching. The three groups of hot rollers 8 are stretched to obtain high-strength polyethylene fibers. The secondary drawing, the drawing multiples are 4.3 times, 2 times, 1.4 times, 1.15 times and 1.1 times respectively, totaling 15.23 times, rounded to an integer of 15 times, the drawing temperatures of the three sets of drawing rollers are 143°C, 150°C and 155°C respectively. Compared with the hot box drawing, the hot roller has fast heat transfer and high efficiency, the fiber is heated more evenly, the drawing consistency is good, the performance fluctuation is small, the hot roller occupies a small area, the equipment operation is relatively simple, and the process adjustment is more convenient. The breaking strength of the high-strength polyethylene fiber obtained in this embodiment is 23g / d.

[0032] Embodiment 3:

[0033] A) Preparation of swollen high molecular weight polyethylene resin, see Figure 1 First, a high molecular weight polyethylene resin having 0.3 branches per 1000 carbon atoms in the main chain and an intrinsic viscosity [η] of 8.0 dl / g is selected and introduced into the swelling kettle 1 through the feed port 11 of the swelling kettle 1 as the structural system of the pretreatment system, and then a low molecular weight polyethylene wax as a solvent in an amount 10 times that of the high molecular weight polyethylene resin is injected into the swelling kettle 1 through the third pipeline 6 from the storage tank 3 of the structural system of the pretreatment system, that is, the mass ratio of the low molecular weight polyethylene wax to the high molecular weight polyethylene resin is 10:1, so that the high molecular weight polyethylene resin is swollen in the swelling kettle 1. After the dissolution, the mass percentage of the solvent in the high molecular weight polyethylene resin is 3% (i.e., the solvent residue). In this embodiment, the swelling temperature is controlled to be 105° C., and the swelling time is controlled to be 10 min to obtain a swollen high molecular weight polyethylene resin. The aforementioned pretreatment system in this step can be seen in detail. Figure 1, including the swelling kettle 1, separation kettle 2 and storage tank 3 mentioned above, the swelling kettle 1 and the separation kettle 2 are connected by a first pipeline 4 and a first delivery pump 41 is arranged on the pipeline of the first pipeline 4, the separation kettle 2 and the storage tank 3 are connected by a second pipeline 5 and a second delivery pump 51 is arranged on the pipeline of the second pipeline 5, the storage tank 3 and the swelling kettle 1 are connected by a third pipeline 6 and a third delivery pump 61 is arranged on the pipeline of the third pipeline 6, wherein the swelling kettle 1 is provided with a heat preservation jacket, and the heat preservation medium circulating in the heat preservation jacket is connected to the pipeline of the external heating system, the swelling kettle 1 is also provided with a stirring device for high-speed shearing and dispersing the high molecular weight polyethylene resin to increase the swelling speed, in this embodiment, the stirring speed of the stirring device is 2500rpm; the separation kettle 2 includes a pressurizing device and a filtering device for filtering the mixed liquid and achieving rapid separation, after the swelling of the swelling kettle 1 is completed, the bottom valve of the swelling kettle 1 is opened to allow the mixed liquid to enter the separation kettle 2. Start the press, use the intermittent circulation mode, when the oil agent seeps out in large quantities, the pressing plate will stop moving forward, and when the oil agent seeps out less, the pressing plate will be started again, and the extrusion will be repeated multiple times. Finally, the mineral oil filtered out in the separation kettle 2 is transported to the storage tank 3 through the second delivery pump 51, and the high molecular weight polyethylene resin that has been left and completed swelling is collected by the separation kettle discharge port 21 of the separation kettle 2 for standby use. In summary, the specific operation of this step can be summarized as follows: add the high molecular weight polyethylene resin to the swelling kettle 1 through the feeding port 11 of the swelling kettle 1, and then inject the prepared solvent from the storage tank 3 into the swelling kettle 1, stir and heat, wait until the temperature rises to the set value, keep warm and continue stirring. Then open the bottom valve of the kettle to let the mixed liquid enter the separation kettle 2. Start the press, and as the pressing plate gradually moves downward, the solvent seeps out from the bottom filtration system. The press can be used continuously, preferably intermittently, and the pressing plate will be started again for multiple extrusions when the solvent seeps out less. Finally, the solvent filtered out of the separation kettle 2 is transported to the storage tank 3 by the second delivery pump 51 for continued recycling, while the high molecular weight polyethylene that has completed swelling is collected by the separation kettle discharge port 21 for standby use. The solvent in the storage tank 3 will be gradually consumed, and the material can be replenished through the oil filling port 31 of the storage tank 3. The solvent content can be controlled by the swelling process. The higher the swelling temperature and the longer the time, the more sufficient the swelling is and the higher the solvent content is. On the contrary, the solvent content is low. In the aforementioned operation, vacuum filtration is preferred for pressure filtration in the separation kettle 2. Vacuum filtration is suitable for processing more complex suspensions, fine particles and the like. It can be filtered under conditions below atmospheric pressure. By generating a vacuum under the filter, the flow rate of the liquid is enhanced, thereby accelerating the filtration process;

[0034] B) preparing a mixed raw material, mixing the swollen high molecular weight polyethylene resin obtained in step A) with the unswollen low molecular weight polyethylene resin according to a mass ratio to obtain a mixed raw material, wherein the mass ratio of the swollen high molecular weight polyethylene resin to the unswollen low molecular weight polyethylene resin in this embodiment is 20:80, and the mixing device used for the above mixing is a high-speed mixer, the mixing time of the high-speed mixer (i.e., the high-speed stirring mixing time) is 30 minutes, and the shear rate of the material is 400S -1 A tree-fork type dispersion roller is fixed on the side of the high-speed mixer, so that the material can hit the dispersion roller when rotating at high speed. Under the impact, it is easier to disperse in multiple directions to improve the mixing effect. Among them, the unswollen low molecular weight polyethylene resin is obtained by copolymerization of ethylene and linear α-olefins, the linear α-olefin accounts for less than 0.5 mol%, and the branched chain is a C1-C20 hydrocarbon group, and the C1-C20 hydrocarbon group is selected from methyl, ethyl, propyl, butyl, pentyl, hexyl, octyl and cyclohexyl, their isomers and mixtures thereof. Compared with homopolymers, copolymers can change the crystallinity, melting point and flexibility of the polymer by adjusting the proportion and type of copolymer monomers, so as to have better toughness, transparency and low temperature performance. Moreover, copolymers usually have better fluidity and processing properties, which can reduce energy consumption and the difficulty of melt spinning processing. The intrinsic viscosity of the unswollen low molecular weight polyethylene resin is 2.0 dl / g, and the main chain contains 0.5-3 branches per 1000 carbon atoms. If the branching degree is too low, the polyethylene crystallinity will not be significantly reduced, the fluidity will not be improved much, and it will not be conducive to post-stretching. Otherwise, it will cause severe entanglement of polyethylene and seriously affect the spinning performance. In this embodiment, 2.3 is selected. The above-mentioned unswollen low molecular weight polyethylene resin is prepared by copolymerization of ethylene and 0.5 mol% 4-methyl 1-pentene, wherein the DSC spectrum of the copolymer of ethylene and 4-methyl 1-pentene is shown in Figure 3 ;

[0035] C) preparing polyethylene fibers, firstly subjecting the mixed raw materials obtained in step B) to a parallel twin-screw extruder for mixing and plasticizing, then subjecting the mixed raw materials to a single-screw extruder for extrusion spinning to obtain polyethylene fibers 7 to be drawn, and ... Figure 2The hot rollers shown in the figure are stretched to obtain high-strength polyethylene fibers. The pressure of the single screw extruder for extrusion spinning in this step is 5 MPa. The roller stretching is a hot roller stretching with a roller diameter of 450 mm, that is, a stretching roller (also known as a hot roller 8). This embodiment uses three groups of hot rollers for stretching, but it can also be four or five groups. Each group of hot rollers 8 consists of three rollers, wherein each group of rollers, that is, the first one in each group of hot rollers 8, is equipped with a rubber pressure roller 9 to prevent the fiber from slipping during stretching. The three groups of hot rollers 8 are stretched to form a rubber pressure roller 9. The stretching multiples of the line stretching are 4.3 times, 2 times and 1.3 times, respectively, totaling 11.18 times, and the integer is 11 times (this embodiment is a single stretching). The stretching temperatures of the three groups of stretching rollers are 145°C, 150°C and 155°C, respectively. Compared with the hot box stretching, the hot rollers have fast heat transfer and high efficiency, and the fibers are heated more evenly, with good stretching consistency and small performance fluctuations. The hot rollers occupy a small area, the equipment operation is relatively simple, and the process adjustment is more convenient. The breaking strength of the high-strength polyethylene fiber obtained in this embodiment is 18g / d.

[0036] Embodiment 4:

[0037] A) Preparation of swollen high molecular weight polyethylene resin, see Figure 1 First, a high molecular weight polyethylene resin having 0.2 branches per 1000 carbon atoms in the main chain and an intrinsic viscosity [η] of 7.0 dl / g is selected and introduced into the swelling kettle 1 through the feed port 11 of the swelling kettle 1 of the structural system of the pretreatment system, that is, added to the swelling kettle 1. Then, a mixture of decane, nonane and octene as a solvent in an amount of 4 times the mass of the high molecular weight polyethylene resin is injected into the swelling kettle 1 through the third pipeline 6 from the storage tank 3 of the structural system of the pretreatment system. That is, the mass ratio of the mixture of decane, nonane and octene to the high molecular weight polyethylene resin is 4:1, so that the high molecular weight polyethylene resin is swollen in the swelling kettle 1. After the swelling, the mass percentage of the solvent in the high molecular weight polyethylene resin is 1% (i.e., the solvent residue). In this embodiment, the swelling temperature is controlled to be 110° C., and the swelling time is controlled to be 15 min to obtain a swollen high molecular weight polyethylene resin. The aforementioned pretreatment system in this step can be seen in detail. Figure 1, including the swelling kettle 1, separation kettle 2 and storage tank 3 mentioned above, the swelling kettle 1 and the separation kettle 2 are connected by a first pipeline 4 and a first delivery pump 41 is arranged on the pipeline of the first pipeline 4, the separation kettle 2 and the storage tank 3 are connected by a second pipeline 5 and a second delivery pump 51 is arranged on the pipeline of the second pipeline 5, the storage tank 3 and the swelling kettle 1 are connected by a third pipeline 6 and a third delivery pump 61 is arranged on the pipeline of the third pipeline 6, wherein the swelling kettle 1 is provided with a heat preservation jacket, and the heat preservation medium circulating in the heat preservation jacket is connected to the pipeline of the external heating system, the swelling kettle 1 is also provided with a stirring device for high-speed shearing and dispersing the high molecular weight polyethylene resin to increase the swelling speed, in this embodiment, the stirring speed of the stirring device is 1000rpm; the separation kettle 2 includes a pressurizing device and a filtering device for filtering the mixed liquid and achieving rapid separation, after the swelling of the swelling kettle 1 is completed, the bottom valve of the swelling kettle 1 is opened to allow the mixed liquid to enter the separation kettle 2. Start the press, use the intermittent circulation mode, when the oil agent seeps out in large quantities, the pressing plate will stop moving forward, and when the oil agent seeps out less, the pressing plate will be started again, and the extrusion will be repeated multiple times. Finally, the mineral oil filtered out in the separation kettle 2 is transported to the storage tank 3 through the second delivery pump 51, and the high molecular weight polyethylene resin that has been left and completed swelling is collected by the separation kettle discharge port 21 of the separation kettle 2 for standby use. In summary, the specific operation of this step can be summarized as follows: add the high molecular weight polyethylene resin to the swelling kettle 1 through the feeding port 11 of the swelling kettle 1, and then inject the prepared solvent from the storage tank 3 into the swelling kettle 1, stir and heat, wait until the temperature rises to the set value, keep warm and continue stirring. Then open the bottom valve of the kettle to let the mixed liquid enter the separation kettle 2. Start the press, and as the pressing plate gradually moves downward, the solvent seeps out from the bottom filtration system. The press can be used continuously, preferably intermittently, and the pressing plate will be started again for multiple extrusions when the solvent seeps out less. Finally, the solvent filtered out of the separation kettle 2 is transported to the storage tank 3 by the second delivery pump 51 for continued recycling, while the high molecular weight polyethylene that has completed swelling is collected by the separation kettle discharge port 21 for standby use. The solvent in the storage tank 3 will be gradually consumed, and the material can be replenished through the oil filling port 31 of the storage tank 3. The solvent content can be controlled by the swelling process. The higher the swelling temperature and the longer the time, the more sufficient the swelling is and the higher the solvent content is. On the contrary, the solvent content is low. In the aforementioned operation, vacuum filtration is preferred for pressure filtration in the separation kettle 2. Vacuum filtration is suitable for processing more complex suspensions, fine particles and the like. It can be filtered under conditions below atmospheric pressure. By generating a vacuum under the filter, the flow rate of the liquid is enhanced, thereby accelerating the filtration process;

[0038] B) preparing a mixed raw material, mixing the swollen high molecular weight polyethylene resin obtained in step A) with the unswollen low molecular weight polyethylene resin according to a mass ratio to obtain a mixed raw material, wherein the mass ratio of the swollen high molecular weight polyethylene resin to the unswollen low molecular weight polyethylene resin in this embodiment is 10:90, and the mixing device used for the above mixing is a high-speed mixer, the mixing time of the high-speed mixer (i.e., the high-speed stirring mixing time) is 25 minutes, and the shear rate of the material is 100S -1 A tree-fork type dispersion roller is fixed on the side of the high-speed mixer, so that the material can hit the dispersion roller when rotating at high speed. Under the impact, it is easier to disperse in multiple directions to improve the mixing effect. Among them, the unswollen low molecular weight polyethylene resin is obtained by copolymerization of ethylene and linear α-olefins, the linear α-olefin accounts for less than 0.5 mol%, and the branched chain is a C1-C20 hydrocarbon group, and the C1-C20 hydrocarbon group is selected from methyl, ethyl, propyl, butyl, pentyl, hexyl, octyl and cyclohexyl, their isomers and mixtures thereof. Compared with homopolymers, copolymers can change the crystallinity, melting point and flexibility of the polymer by adjusting the proportion and type of copolymer monomers, so as to have better toughness, transparency and low temperature performance. Moreover, copolymers usually have better fluidity and processing properties, which can reduce energy consumption and the difficulty of melt spinning processing. The intrinsic viscosity of the unswollen low molecular weight polyethylene resin is 3.0 dl / g, and the main chain contains 0.5-3 branches per 1000 carbon atoms. If the branching degree is too low, the polyethylene crystallinity will not be significantly reduced, the fluidity will not be improved much, and it will not be conducive to post-stretching. Otherwise, it will cause severe entanglement of polyethylene and seriously affect the spinning performance. In this embodiment, 0.8 is selected. The above-mentioned unswollen low molecular weight polyethylene resin is obtained by copolymerization of ethylene and 0.4 mol% 1-butene, wherein the DSC spectrum of ethylene and 4-methyl 1-pentene copolymer can be found in Figure 3 ;

[0039] C) preparing polyethylene fibers, firstly subjecting the mixed raw materials obtained in step B) to a parallel twin-screw extruder for mixing and plasticizing, then subjecting the mixed raw materials to a single-screw extruder for extrusion spinning to obtain polyethylene fibers 7 to be drawn, and ... Figure 2The hot roller 8 shown in the figure is used for hot roller drawing to obtain high-strength polyethylene fiber. The pressure of the single screw extruder extrusion spinning in this step is 5.7MPa. The roller drawing is a hot roller drawing with a roller, i.e., a drawing roller (i.e., hot roller 8), having a diameter of 430mm. This embodiment uses three groups of hot rollers for drawing, but it can also be four or five groups. Each group of hot rollers 8 consists of three rollers, wherein each group of rollers, i.e., the first one in each group of hot rollers 8, is provided with a rubber pressure roller 9 to prevent the fiber from slipping during drawing. The three groups of hot rollers are The stretching multiples for 8 stretching are 4.7 times, 2 times and 1.4 times, respectively, totaling 13.16 times, and the integer is 13 times (this embodiment is a single stretching). The stretching temperatures of the three groups of stretching rollers are 145°C, 150°C and 155°C, respectively. Compared with hot box stretching, the hot rollers have fast heat transfer and high efficiency, and the fibers are heated more evenly, with good stretching consistency and small performance fluctuations. The hot rollers occupy a small area, the equipment operation is relatively simple, and the process adjustment is more convenient. The breaking strength of the high-strength polyethylene fiber obtained in this embodiment is 20g / d.

[0040] Embodiment 5:

[0041] A) Preparation of swollen high molecular weight polyethylene resin, see Figure 1 First, a high molecular weight polyethylene resin having 0.4 branches per 1000 carbon atoms in the main chain and an intrinsic viscosity [η] of 6.0 dl / g is selected and introduced into the swelling kettle 1 through the feed port 11 of the swelling kettle 1 of the structural system of the pretreatment system, and then a mineral oil (commercially available 50# white petroleum oil, with a kinematic viscosity of 5±2 mm at 40° C.) in an amount of 6 times the mass of the high molecular weight polyethylene resin and serving as a solvent is injected into the swelling kettle 1 from the storage tank 3 of the structural system of the pretreatment system through the third pipeline 6. 2 / s, average molecular weight is 415), that is, the mass ratio of mineral oil to high molecular weight polyethylene resin is 6:1, so that the high molecular weight polyethylene resin is swollen in the swelling kettle 1, and the mass percentage of the solvent in the high molecular weight polyethylene resin after the swelling is 2% (i.e., the solvent remains). The swelling temperature in this embodiment is controlled to be 110°C, and the swelling time is controlled to be 10min, to obtain a swollen high molecular weight polyethylene resin. The above-mentioned pretreatment system in this step can be seen in detail. Figure 1, including the swelling kettle 1, separation kettle 2 and storage tank 3 mentioned above, the swelling kettle 1 and the separation kettle 2 are connected by a first pipeline 4 and a first delivery pump 41 is arranged on the pipeline of the first pipeline 4, the separation kettle 2 and the storage tank 3 are connected by a second pipeline 5 and a second delivery pump 51 is arranged on the pipeline of the second pipeline 5, the storage tank 3 and the swelling kettle 1 are connected by a third pipeline 6 and a third delivery pump 61 is arranged on the pipeline of the third pipeline 6, wherein the swelling kettle 1 is provided with a heat preservation jacket, and the heat preservation medium circulating in the heat preservation jacket is connected to the pipeline of the external heating system, the swelling kettle 1 is also provided with a stirring device for high-speed shearing and dispersing the high molecular weight polyethylene resin to increase the swelling speed, in this embodiment, the stirring speed of the stirring device is 3000rpm; the separation kettle 2 includes a pressurizing device and a filtering device for filtering the mixed liquid and achieving rapid separation, after the swelling kettle 1 is swollen, the bottom valve of the swelling kettle 1 is opened to allow the mixed liquid to enter the separation kettle 2. Start the press, use the intermittent circulation mode, when the oil agent seeps out in large quantities, the pressing plate will stop moving forward, and when the oil agent seeps out less, the pressing plate will be started again, and the extrusion will be repeated multiple times. Finally, the mineral oil filtered out in the separation kettle 2 is transported to the storage tank 3 through the second delivery pump 51, and the high molecular weight polyethylene resin that has been left and completed swelling is collected by the separation kettle discharge port 21 of the separation kettle 2 for standby use. In summary, the specific operation of this step can be summarized as follows: add the high molecular weight polyethylene resin to the swelling kettle 1 through the feeding port 11 of the swelling kettle 1, and then inject the prepared solvent from the storage tank 3 into the swelling kettle 1, stir and heat, wait until the temperature rises to the set value, keep warm and continue stirring. Then open the bottom valve of the kettle to let the mixed liquid enter the separation kettle 2. Start the press, and as the pressing plate gradually moves downward, the solvent seeps out from the bottom filtration system. The press can be used continuously, preferably intermittently, and the pressing plate will be started again for multiple extrusions when the solvent seeps out less. Finally, the solvent filtered out of the separation kettle 2 is transported to the storage tank 3 through the second delivery pump 51 for continued recycling, and the swollen high molecular weight polyethylene is collected by the separation kettle discharge port 21 for standby use. The solvent in the storage tank 3 will be gradually consumed, and can be replenished through the oil filling port 31 of the storage tank 3. During operation, the solvent is preferably mineral oil, because it is neither volatile, nor flammable and explosive, has stable performance, and is widely available. The composition of mineral oil is a mixture of hydrocarbon saturated alkanes, and the kinematic viscosity at 40°C is 5-50mm 2 / s, average molecular weight ≤ 500, solvent content can be controlled by the swelling process, the higher the swelling temperature and the longer the swelling time, the more sufficient the swelling and the higher the solvent content. On the contrary, the solvent content is low. In the above operation, vacuum filtration is preferred when the separation kettle 2 is used for pressure filtration. Vacuum filtration is suitable for treating more complex suspensions, fine particles and other occasions. It can be filtered under conditions below atmospheric pressure. By generating a vacuum under the filter, the flow rate of the liquid is enhanced, thereby accelerating the filtration process;

[0042] B) preparing a mixed raw material, mixing the swollen high molecular weight polyethylene resin obtained in step A) with the unswollen low molecular weight polyethylene resin according to a mass ratio to obtain a mixed raw material, wherein the mass ratio of the swollen high molecular weight polyethylene resin to the unswollen low molecular weight polyethylene resin in this embodiment is 10:90, and the mixing device used for the above mixing is a high-speed mixer, the mixing time of the high-speed mixer (i.e., the high-speed stirring mixing time) is 10 minutes, and the shear rate of the material is 500S -1 A tree-fork type dispersion roller is fixed on the side of the high-speed mixer, so that the material can hit the dispersion roller when rotating at high speed. Under the impact, it is easier to disperse in multiple directions to improve the mixing effect. Among them, the unswollen low molecular weight polyethylene resin is obtained by copolymerization of ethylene and linear α-olefins, the linear α-olefin accounts for less than 0.5 mol%, and the branched chain is a C1-C20 hydrocarbon group, and the C1-C20 hydrocarbon group is selected from methyl, ethyl, propyl, butyl, pentyl, hexyl, octyl and cyclohexyl, their isomers and mixtures thereof. Compared with homopolymers, copolymers can change the crystallinity, melting point and flexibility of the polymer by adjusting the proportion and type of copolymer monomers, so as to have better toughness, transparency and low temperature performance. Moreover, copolymers usually have better fluidity and processing properties, which can reduce energy consumption and the difficulty of melt spinning processing. The intrinsic viscosity of the unswollen low molecular weight polyethylene resin is 3.0 dl / g, and the main chain contains 0.5-3 branches per 1000 carbon atoms. If the branching degree is too low, the polyethylene crystallinity will not be significantly reduced, the fluidity will not be improved much, and it will not be conducive to post-stretching. Otherwise, it will cause severe entanglement of polyethylene and seriously affect the spinning performance. In this embodiment, two are selected. The above-mentioned unswollen low molecular weight polyethylene resin is obtained by copolymerization of ethylene and 0.4 mol% 1-butene, wherein the DSC spectrum of ethylene and 4-methyl 1-pentene copolymer can be found in Figure 3 ;

[0043] C) preparing polyethylene fibers, firstly subjecting the mixed raw materials obtained in step B) to a parallel twin-screw extruder for mixing and plasticizing, then subjecting the mixed raw materials to a single-screw extruder for extrusion spinning to obtain polyethylene fibers 7 to be drawn, and ... Figure 2The hot rollers shown in the figure are stretched to obtain high-strength polyethylene fibers. The pressure of the single screw extruder for extrusion spinning in this step is 6 MPa. The roller stretching is a hot roller stretching with a roller diameter of 440 mm, that is, a stretching roller (also known as a hot roller 8). This embodiment uses three groups of hot rollers for stretching, but it can also be four or five groups. Each group of hot rollers 8 consists of three rollers, wherein each group of rollers, that is, the first one in each group of hot rollers 8, is equipped with a rubber pressure roller 9 to prevent the fiber from slipping during stretching. The three groups of hot rollers 8 are stretched to form a rubber pressure roller 9. The stretching multiples of the line stretching are 4.7 times, 2 times and 1.14 times, respectively, totaling 13.16 times, and the integer 13 times is taken as one-time stretching in this embodiment). The stretching temperatures of the three groups of stretching rollers are 145°C, 150°C and 155°C, respectively. Compared with the hot box stretching, the hot roller has fast heat transfer and high efficiency, the fiber is heated more evenly, the stretching consistency is good, the performance fluctuation is small, and the hot roller occupies a small area, the equipment operation is relatively simple, and the process adjustment is more convenient. The breaking strength of the high-strength polyethylene fiber obtained in this embodiment is 20g / d.

[0044] Embodiment 6:

[0045] A) Preparation of swollen high molecular weight polyethylene resin, see Figure 1 First, a high molecular weight polyethylene resin having 0.25 branches per 1000 carbon atoms in the main chain and an intrinsic viscosity [η] of 6.5 dl / g is selected and introduced into the swelling kettle 1 through the feed port 11 of the swelling kettle 1 of the structural system of the pretreatment system, and then a mineral oil (commercially available 50# white petroleum oil, with a kinematic viscosity of 5±2 mm at 40° C.) in an amount of 9 times the mass of the high molecular weight polyethylene resin and serving as a solvent is injected into the swelling kettle 1 from the storage tank 3 of the structural system of the pretreatment system through the third pipeline 6. 2 / s, average molecular weight is 415), that is, the mass ratio of mineral oil to high molecular weight polyethylene resin is 9:1, so that the high molecular weight polyethylene resin is swollen in the swelling kettle 1, and the mass percentage of the solvent in the high molecular weight polyethylene resin after the swelling is 3.5% (i.e., the solvent residue). The swelling temperature in this embodiment is controlled to be 105°C, and the swelling time is controlled to be 25min, to obtain a swollen high molecular weight polyethylene resin. The above-mentioned pretreatment system in this step can be seen in detail. Figure 1, including the swelling kettle 1, separation kettle 2 and storage tank 3 mentioned above, the swelling kettle 1 and the separation kettle 2 are connected by a first pipeline 4 and a first delivery pump 41 is arranged on the pipeline of the first pipeline 4, the separation kettle 2 and the storage tank 3 are connected by a second pipeline 5 and a second delivery pump 51 is arranged on the pipeline of the second pipeline 5, the storage tank 3 and the swelling kettle 1 are connected by a third pipeline 6 and a third delivery pump 61 is arranged on the pipeline of the third pipeline 6, wherein the swelling kettle 1 is provided with a heat preservation jacket, and the heat preservation medium circulating in the heat preservation jacket is connected to the pipeline of the external heating system, the swelling kettle 1 is also provided with a stirring device for high-speed shearing and dispersing the high molecular weight polyethylene resin to increase the swelling speed, in this embodiment, the stirring speed of the stirring device is 1500rpm; the separation kettle 2 includes a pressurizing device and a filtering device for filtering the mixed liquid and achieving rapid separation, after the swelling of the swelling kettle 1 is completed, the bottom valve of the swelling kettle 1 is opened to allow the mixed liquid to enter the separation kettle 2. Start the press, use the intermittent circulation mode, when the oil agent seeps out in large quantities, the pressing plate will stop moving forward, and when the oil agent seeps out less, the pressing plate will be started again, and the extrusion will be repeated multiple times. Finally, the mineral oil filtered out in the separation kettle 2 is transported to the storage tank 3 through the second delivery pump 51, and the high molecular weight polyethylene resin that has been left and completed swelling is collected by the separation kettle discharge port 21 of the separation kettle 2 for standby use. In summary, the specific operation of this step can be summarized as follows: add the high molecular weight polyethylene resin to the swelling kettle 1 through the feeding port 11 of the swelling kettle 1, and then inject the prepared solvent from the storage tank 3 into the swelling kettle 1, stir and heat, wait until the temperature rises to the set value, keep warm and continue stirring. Then open the bottom valve of the kettle to let the mixed liquid enter the separation kettle 2. Start the press, and as the pressing plate gradually moves downward, the solvent seeps out from the bottom filtration system. The press can be used continuously, preferably intermittently, and the pressing plate will be started again for multiple extrusions when the solvent seeps out less. Finally, the solvent filtered out of the separation kettle 2 is transported to the storage tank 3 through the second delivery pump 51 for continued recycling, and the swollen high molecular weight polyethylene is collected by the separation kettle discharge port 21 for standby use. The solvent in the storage tank 3 will be gradually consumed, and can be replenished through the oil filling port 31 of the storage tank 3. During operation, the solvent is preferably mineral oil, because it is neither volatile, nor flammable and explosive, has stable performance, and is widely available. The composition of mineral oil is a mixture of hydrocarbon saturated alkanes, and the kinematic viscosity at 40°C is 5-50mm 2 / s, average molecular weight ≤ 500, solvent content can be controlled by the swelling process, the higher the swelling temperature and the longer the swelling time, the more sufficient the swelling and the higher the solvent content. On the contrary, the solvent content is low. In the above operation, vacuum filtration is preferred when the separation kettle 2 is used for pressure filtration. Vacuum filtration is suitable for treating more complex suspensions, fine particles and other occasions. It can be filtered under conditions below atmospheric pressure. By generating a vacuum under the filter, the flow rate of the liquid is enhanced, thereby accelerating the filtration process;

[0046] B) preparing a mixed raw material, mixing the swollen high molecular weight polyethylene resin obtained in step A) with the unswollen low molecular weight polyethylene resin according to a mass ratio to obtain a mixed raw material, wherein the mass ratio of the swollen high molecular weight polyethylene resin to the unswollen low molecular weight polyethylene resin in this embodiment is 10:90, and the mixing device used for the above mixing is a high-speed mixer, the mixing time of the high-speed mixer (i.e., the high-speed stirring mixing time) is 30 minutes, and the shear rate of the material is 50 seconds. -1 A tree-fork type dispersion roller is fixed on the side of the high-speed mixer, so that the material can hit the dispersion roller when rotating at high speed. Under the impact, it is easier to disperse in multiple directions to improve the mixing effect. Among them, the unswollen low molecular weight polyethylene resin is obtained by copolymerization of ethylene and linear α-olefins, the linear α-olefin accounts for less than 0.5 mol%, and the branched chain is a C1-C20 hydrocarbon group, and the C1-C20 hydrocarbon group is selected from methyl, ethyl, propyl, butyl, pentyl, hexyl, octyl and cyclohexyl, their isomers and mixtures thereof. Compared with homopolymers, copolymers can change the crystallinity, melting point and flexibility of the polymer by adjusting the proportion and type of copolymer monomers, so as to have better toughness, transparency and low temperature performance. Moreover, copolymers usually have better fluidity and processing properties, which can reduce energy consumption and the difficulty of melt spinning processing. The intrinsic viscosity of the unswollen low molecular weight polyethylene resin is 3.0 dl / g, and the main chain contains 0.5-3 branches per 1000 carbon atoms. If the branching degree is too low, the polyethylene crystallinity will not be significantly reduced, the fluidity will not be improved much, and it will not be conducive to post-stretching. Otherwise, it will cause severe entanglement of polyethylene and seriously affect the spinning performance. In this embodiment, 1.5 is selected. The above-mentioned unswollen low molecular weight polyethylene resin is prepared by copolymerization of ethylene and 0.3 mol% 1-butene, wherein the DSC spectrum of ethylene and 4-methyl 1-pentene copolymer can be found in Figure 3 ;

[0047] C) preparing polyethylene fibers, firstly subjecting the mixed raw materials obtained in step B) to a parallel twin-screw extruder for mixing and plasticizing, then subjecting the mixed raw materials to a single-screw extruder for extrusion spinning to obtain polyethylene fibers 7 to be drawn, and ... Figure 2The hot roller 8 shown in the figure is used for hot roller drawing to obtain high-strength polyethylene fiber. The pressure of the single screw extruder extrusion spinning in this step is 5.9 MPa. The roller drawing is a hot roller drawing with a roller, i.e., a drawing roller (i.e., hot roller 8), having a diameter of 500 mm. This embodiment uses three groups of hot rollers for drawing, but it can also be four or five groups. Each group of hot rollers 8 consists of three rollers, wherein each group of rollers, i.e., the first one in each group of hot rollers 8, is equipped with a rubber pressure roller 9 to prevent the fiber from slipping during stretching. The three groups of hot rollers are The stretching multiples for 8 stretching are 4.3 times, 2 times and 1.4 times, respectively, totaling 12.04 times, and the integer is 12 times (this embodiment is one-time stretching). The stretching temperatures of the three groups of stretching rollers are 145°C, 150°C and 155°C, respectively. Compared with hot box stretching, the hot rollers have fast heat transfer and high efficiency, and the fibers are heated more evenly, with good stretching consistency and small performance fluctuations. The hot rollers occupy a small area, the equipment operation is relatively simple, and the process adjustment is more convenient. The breaking strength of the high-strength polyethylene fiber obtained in this embodiment is 19g / d.

[0048] Comparative Example 1:

[0049] The difference of Comparative Example 1 is that no swelling high molecular weight polyethylene resin raw material is used, and no blending is performed. Instead, a copolymerized polyethylene with an intrinsic viscosity [η] of 5.0 dl / g is directly selected, and plasticized by co-rotating parallel twin screws, and then extruded and spun by a single screw extruder to obtain a polyethylene fiber semi-finished product. Then, the semi-finished product is drawn by a hot roller to obtain a finished high-strength polyethylene fiber, and the fiber breaking strength is 16 g / d.

[0050] Comparative Example 2:

[0051] The difference of Comparative Example 2 is that not only the raw materials are not swollen and blended, but also hot box drawing is adopted. A copolymerized polyethylene with an intrinsic viscosity [η] of 3.0 dl / g is selected, mixed and plasticized by a co-rotating parallel twin screw extruder, and then extruded and spun by a single screw extruder to obtain a polyethylene fiber semi-finished product. Then, through three-stage hot box drawing, a finished high-strength polyethylene fiber is obtained, and the fiber breaking strength is 14g / d, but the CV value of the strength is 32% higher than that of Comparative Example 1.

[0052] The test results of the performance of the cut-resistant high-performance polyethylene fibers obtained in Examples 1 to 6 and Comparative Examples 1 to 2 are summarized in the following table:

[0053]

[0054] According to the above test results, the fiber product prepared by the method of this patent has significantly better performance than the fiber prepared by the comparative example without the swelling method.

[0055] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A method for preparing high-strength polyethylene fiber, Features: The following steps are involved: A) preparing a swollen high molecular weight polyethylene resin, firstly introducing the high molecular weight polyethylene resin into a pretreatment system, and introducing a solvent into the pretreatment system for swelling, and controlling the swelling temperature and swelling time of the pretreatment system, and controlling the mass ratio of the solvent to the high molecular weight polyethylene resin, and then separating to obtain the swollen high molecular weight polyethylene resin; B) preparing a mixed raw material by mixing the swollen high molecular weight polyethylene resin obtained in step A) with the unswollen low molecular weight polyethylene resin according to a mass ratio to obtain a mixed raw material; C) preparing polyethylene fibers, first subjecting the mixed raw materials obtained in step B) to twin-screw mixing and plasticization, then subjecting the mixed raw materials to single-screw extruder extrusion spinning to obtain polyethylene fibers to be drawn, and then subjecting the mixed raw materials to hot roller drawing to obtain high-strength polyethylene fibers.

2. The method for preparing a high-strength polyethylene fiber according to claim 1, Features: The swelling temperature and swelling time of the pretreatment system in step A) are controlled to be 105-115° C. and 10-30 min.

3. A method for preparing a high-strength polyethylene fiber according to claim 1 or 2, Features: The pretreatment system comprises a swelling kettle (1), a separation kettle (2) and a storage tank (3); the swelling kettle (1) and the separation kettle (2) are connected by a first pipeline (4), and a first delivery pump (41) is arranged on the pipeline of the first pipeline (4); the separation kettle (2) and the storage tank (3) are connected by a second pipeline (5), and a second delivery pump (51) is arranged on the pipeline of the second pipeline (5); the storage tank (3) and the swelling kettle (1) are connected by a third pipeline (6), and a second delivery pump (51) is arranged on the pipeline of the third pipeline (6); A third delivery pump (61) is arranged on the pipeline of the road (6), wherein the swelling kettle (1) is provided with a heat preservation jacket, and the heat preservation medium circulating in the heat preservation jacket is connected to the external heating system pipeline, and the swelling kettle (1) is also provided with a stirring device for high-speed shear dispersion of the high molecular weight polyethylene resin to increase the swelling rate, and the rotation speed of the stirring device is 1000-3500rpm; the separation kettle (2) includes a pressurizing device and a filtering device for filtering the mixed liquid and achieving rapid separation.

4. The method for preparing a high-strength polyethylene fiber according to claim 1, Features: The swollen high molecular weight polyethylene resin in steps A) and B) has an intrinsic viscosity [η] of 5.0-9.0 dl / g and contains less than 0.5 branches per 1000 carbon atoms in the main chain.

5. The method for preparing a high-strength polyethylene fiber according to claim 1, Features: The mass ratio of the solvent to the high molecular weight polyethylene resin in step A) is controlled to be 2-10:1, and after swelling, the mass percentage of the solvent in the swollen high molecular weight polyethylene resin is less than 5%.

6. A method for preparing a high-strength polyethylene fiber according to claim 1 or 2, Features: The solvent is a combination of one or more of mineral oil, halogenated hydrocarbons, decahydronaphthalene, tetrahydronaphthalene, naphthalene, xylene, toluene, dodecane, undecane, decane, nonane, octene, chlorobenzene, petroleum ether and low molecular weight polyethylene wax.

7. The method for preparing a high-strength polyethylene fiber according to claim 1, Features: The mass ratio in step B) refers to mixing the swollen high molecular weight polyethylene resin obtained in step A) with the unswollen high molecular weight polyethylene resin in a mass ratio of 5-20:80-95, the mixing device used for mixing is a high-speed mixer, and the mixing time of the high-speed mixer is 10-30 minutes, and the shear rate of the material is 50-500S -1 .

8. A method for preparing a high-strength polyethylene fiber according to claim 1 or 7, Features: The unswollen low molecular weight polyethylene resin is prepared by copolymerization of ethylene and straight chain α-olefin, wherein the straight chain α-olefin accounts for less than 0.5 mol% in ethylene, and the branch chain is a C1-C20 hydrocarbon group, and the C1-C20 hydrocarbon group is selected from methyl, ethyl, propyl, butyl, pentyl, hexyl, octyl and cyclohexyl, their isomers and mixtures thereof; the unswollen low molecular weight polyethylene resin has a characteristic viscosity [η] of 2.0-5.0 dl / g, and contains 0.5-2.3 branches per 1000 carbon atoms in the main chain.

9. The method for preparing a high-strength polyethylene fiber according to claim 1, Features: The twin screws in step C) are co-rotating parallel twin screws, and the extrusion pressure of the single screw extrusion spinning is 5.0-7.0 MPa.

10. The method for preparing a high-strength polyethylene fiber according to claim 1, Features: The stretching in step C) is hot roller stretching, the diameter of the hot roller is 400-500 mm, the stretching temperature is 143-155° C., the stretching is divided into 3-5 groups, the stretching multiple is gradually reduced, and the hot stretching is completed once or multiple times; the breaking strength of the high-strength polyethylene fiber is 18-23 g / d, and the fiber is measured for melting heat by DSC, and the first heating curve has more than one endothermic peak.

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