A method for the production of physically regenerated nylon 6

Abstract

The present invention relates to a preparation method of physically regenerated nylon 6, which is characterized by comprising the following steps: (1) classifying and recycling waste silk and waste blocks in the production process according to glossiness and whether they contain spinning oil, and then cutting the waste silk into short fibers of 5-10 cm, and crushing the waste blocks into short fibers of 5-8 mm. 2 (2) extracting the cut or crushed waste silk and waste blocks with 100°C desalted boiling water for 8-10 hours to fully remove the monomers, oligomers and oils in the waste silk or waste blocks; (3) drying the waste silk and waste particles after extraction, and drying the moisture in the material to below 400ppm; the present invention omits the intermediate re-granulation step through the above process steps, making the entire production cost lower and the operation simpler, and performing two monomer removal steps, so that the spinning stability is high and the product quality is comparable to that of conventional chip spinning.

Description

Technical field:

[0002] The present invention relates to a preparation method of regenerated nylon 6, in particular to a preparation method of physically regenerated melt-spun nylon 6. Technical background:

[0004] Green environmental protection is a persistent global theme, and China has been continuously striving in this direction in recent years. Nylon 6, originally made from petroleum byproducts, is a non-renewable resource. Given that China is a country facing a shortage of petroleum, recycling discarded nylon 6 is crucial for environmental protection and resource conservation. Currently, there are two common methods for regenerating nylon 6: chemical regeneration, which involves depolymerizing nylon 6 into monomers and then repolymerizing them. This method offers the advantage of comparable performance between the regenerated nylon 6 chips and conventional nylon 6 chips, resulting in stable spinning and high product quality. However, its disadvantages are the complexity, high energy consumption, and high cost of the entire process. Physical regeneration, on the other hand, involves re-pelletizing nylon 6 waste yarn and pellets, which are then spun to produce nylon 6 fiber. This method offers the advantages of a simpler, more convenient, and relatively lower cost process. However, due to the high monomer content of the chips after two or more extrusions, degradation and breakage are common during the spinning process, impacting spinning stability and product quality.

[0005] Currently retrieved Chinese patents:

[0006] CN 114775096 A A method for producing regenerated nylon 6 fiber using solid phase polycondensation direct spinning technology: This solid phase polycondensation melt direct spinning method can increase the molecular weight of the polymer, but cannot effectively remove monomers and oligomers in the slices, which will seriously affect the spinning stability and product quality.

[0007] CN 115302654 A discloses a granulation and spinning process for recycled polyamide 6. This technology first pelletizes waste yarn through a screw extruder before spinning. This process becomes cumbersome and increases costs. The slices pass through the twin-screw extruder an additional time. Each additional pass through the twin-screw extruder increases the degradation of the slices, affecting spinning stability and product quality. Patent CN 114248364 (A method for implementing a recycled nylon 6 slice production system) also uses a twin-screw extruder to pelletize the waste yarn into recycled slices. Summary of the invention:

[0009] In view of the above-mentioned deficiencies in the prior art, the object of the present invention is to provide a method for preparing physically recycled nylon 6, which omits the intermediate re-granulation step, thereby lowering the overall production cost and simplifying the operation; a monomer extraction system is added to the process to remove monomers and oligomers from the nylon 6 melt, so that the monomer and oligomer content in the recycled nylon 6 melt is maintained at a low level, thereby improving production stability and product quality.

[0010] The preparation method of physically regenerated nylon 6 of the present invention is characterized by comprising the following steps:

[0011] (1) Cut the waste silk in the production process into short fibers of 5-10 cm, and crush the waste blocks into 5-8 mm 2 Small pieces of material on the left and right;

[0012] (2) Extract the cut or crushed waste silk and waste blocks with 100°C desalted boiling water for 8-10 hours to fully remove the monomers, oligomers and oils in the waste silk or waste blocks;

[0013] (3) After the extraction, the waste silk and waste particles are dried to a moisture content of less than 400 ppm;

[0014] (4) The dried material enters the twin-screw equipment for melting, compression and mixing. The mixed melt enters the filter to remove large particles of impurities contained in the melt;

[0015] (5) The filtered melt is transported to a vacuum impurity removal device, where high-temperature vacuum is applied to further remove monomers and oligomers from the melt to ensure spinning stability;

[0016] (6) The melt treated by the vacuum impurity removal device is transported to the spinning manifold through the melt pump. The metering pump in the spinning manifold quantitatively transports the melt to the components in the spinning manifold. The melt is filtered by the metal sand and non-woven fabric inside the component and then ejected from the spinneret to form fibers. After the fibers come out of the spinneret, the monomer suction hood removes the high-temperature volatile monomer and oligomer smoke to prevent it from adhering to the spinneret of the spinneret or around the component and affecting production stability.

[0017] (7) The fiber is blown by the side blowing net and quickly cooled and solidified by the cooling air. The solidified fiber has sufficient strength to be stretched;

[0018] (8) After the fibers are cooled by side-blown air, they are oiled through an oil nozzle to bundle, anti-static, lubricate, and further cool the fibers.

[0019] Furthermore, after step (8), the fibers pass through the first guide hook and the spinning tunnel in turn to reach the pre-network device, where the oil on the fibers is blown evenly and the fibers are placed on the network to increase the adhesion between the fibers. The air pressure at the pre-network device is 0.05-0.2MPa.

[0020] Furthermore, the fibers processed by the pre-network device enter the drafting rollers, which include a cold roller group and a hot roller group in sequence. The function of the drafting rollers is to stretch and shape the fibers to improve the strength and stability of the fibers.

[0021] Furthermore, the fibers after the drafting roller pass through the godet, the second godet hook, and arrive at the winding head for package formation. The godet is mainly used to adjust the direction and tension of the fibers.

[0022] Furthermore, in the extraction step of step (2), the extraction is carried out through several extraction kettles connected in series, the extraction kettle contains a partition filled with heat transfer oil as a heat medium, and the extraction kettle is equipped with a stirring paddle, and stirring helps to quickly extract the material; and the kettle is also equipped with a temperature sensor and a level meter, which are respectively used to detect the temperature and level of the extraction system in the kettle, and a material conveying pump is installed between each extraction kettle to convey the material from the previous extraction kettle to the next extraction kettle.

[0023] Furthermore, in the drying step of step (3), the material extracted in the previous step is first separated from the water by a centrifuge and then sent to two drying towers in series for drying. A pump is provided at the bottom of the first tower to transport the dried material in the first tower to the top of the second drying tower for further drying. The two drying towers in series can greatly save the time of drying the material. The drying medium is nitrogen with a purity of 99.999% and a temperature of 120°C. The nitrogen flows from the drying tower from bottom to top and the material flows from top to bottom, and the two flow in opposite directions to fully dry the material. There are a total of 8 nitrogen outlets in the entire tower, 4 at the bottom and 4 in the middle. The residence time of the material in the first and second drying towers is 30-60 minutes, respectively.

[0024] Furthermore, in step (4), the temperature setting range of the twin-screw equipment is 250-270°C, and one or two masterbatch or functional powder adding devices and a mixing and stirring device are also provided at the feed port of the twin-screw equipment. The material, masterbatch and functional powder are fully mixed and then fed into the twin-screw to prepare differentiated and functionalized nylon 6 fiber, wherein the filter element of the melt filter is 10μ.

[0025] Furthermore, in step (5), the vacuum degree of the vacuum impurity removal device is controlled at -0.08~-0.1MPa, the melt flows into the vacuum impurity removal device from top to bottom, a hole for vacuuming is provided at the top of the device, the vacuuming system is entirely insulated with biphenyl, and a pressure gauge, a thermometer, and a liquid level gauge are provided to monitor the pressure, temperature, and liquid level in the device respectively. The vacuum impurity removal device uses a biphenyl interlayer for heating and insulation, a port is provided at the bottom of the vacuum impurity removal device for sampling and testing, and a melt pump is provided at the bottom outlet to transport the melt after vacuuming.

[0026] Furthermore, in step (6), the spinning box is insulated with biphenyl at the same temperature as the melt temperature, wherein the metal sand is 40-60 mesh, the non-woven fabric is 25μ, and the assembly pressure is controlled between 130-160 bar; in step (7), the side blowing wind speed and wind temperature are 0.3-0.55 m / s and 17-21°C, respectively.

[0027] Furthermore, the speeds of the cold roller group and the hot roller group are 2000-4500 m / min and 3000-5500 m / min, respectively, and the temperatures are 25° C. and 130-195° C., respectively; and the winding speed of the winding head is 2900-5500 m / min.

[0028] Advantages of the present invention:

[0029] The present invention omits the intermediate re-granulation step through the above-mentioned process steps, thereby lowering the overall production cost and simplifying the operation. In addition, the monomer removal steps are performed twice, resulting in high melt quality and high spinning stability. High-strength nylon 6 fiber can be prepared, or functional powder can be added to prepare functional regenerated nylon 6 fiber, and the product quality is comparable to that of conventional chip spinning. Description of the drawings:

[0031] Figure 1 It is a process flow chart of the present invention;

[0032] Figure 2 It is a schematic diagram of the structure of the vacuum impurity removal device;

[0033] Figure 3-4 yes Figure 2 A partial view of

[0034] Figure 5 It is a schematic diagram of the structure of the extraction equipment. Specific implementation method:

[0036] 1. The waste silk and waste blocks in the production process are classified and recycled according to glossiness and different viscosities. The waste silk is cut into 5-10cm short fibers, and the waste blocks are crushed into 5-8mm 2 Small pieces of material on the left and right.

[0037] 2. The cut or crushed waste silk and waste blocks are then extracted with 100°C boiling water (desalted water) under pressure for 2-5 hours, with the pressure controlled at 0.05-0.10MPa, to fully remove the monomers, oligomers, and oil agents in the waste silk or waste blocks. The extraction equipment is several extraction kettles connected in series, and the number of extraction kettles can be 2-4. The extraction kettle contains a partition filled with heat medium (thermal oil). The extraction medium is 100°C hot water, and the kettle is equipped with a stirring paddle. Stirring helps to quickly extract the material; and the kettle is also equipped with a temperature sensor, a level meter, and a pressure gauge, which are respectively used to detect the temperature, material level, and pressure of the extraction system in the kettle. A material-water separator is provided at the lower discharge port of each kettle to prevent the extraction water in the previous kettle from being transported to the next kettle. A material conveying pump is installed between each kettle to transport the material from the previous extraction kettle to the next extraction kettle.

[0038] 3. After extraction, the waste silk and waste particles are first separated from the material and water by a centrifuge and then sent to two drying towers connected in series for drying. The moisture in the material is dried to below 400ppm. A suction pump is installed at the bottom of the first tower to transport the dried material in the first tower to the top of the second drying tower for further drying. The two drying towers in series can greatly save the drying time of the material. The drying medium is nitrogen with a purity of 99.999% and a temperature of 120°C. The nitrogen flows from the bottom of the drying tower to the top, and the material flows from the top to the bottom, in opposite directions to fully dry the material. There are 8 nitrogen outlets in the entire tower, 4 at the bottom and 4 in the middle. The material stays in the first and second drying towers for 30-60 minutes, respectively. A temporary silo is installed after the second drying tower to store the dried material.

[0039] 4. The material in the drying tower is then sucked into a twin-screw device for melting, compression, mixing, and then transported to a melt filter to remove large particles of impurities in the melt. Two melt filters are provided here, one of which is a spare device. The filter element of the melt filter is 10μ mesh. The filtered melt is transported to a vacuum impurity removal device, which is vacuumed at high temperature to further remove monomers and oligomers in the melt to ensure the stability of spinning.

[0040] The temperature setting range of the twin-screw equipment is 250-270°C. It is also equipped with one or two masterbatch or functional powder adding devices and a mixing and stirring device. The materials, masterbatch and functional powder are fully mixed and then fed into the twin-screw to prepare differentiated and functionalized nylon 6 fibers.

[0041] The vacuum degree at the vacuum impurity removal device is controlled at -0.08~-0.1MPa. The melt flows into the vacuum impurity removal device from top to bottom. There is a hole for vacuuming at the top of the vacuum impurity removal device. The vacuuming system is entirely insulated with biphenyl and is equipped with a pressure gauge, thermometer, and liquid level gauge to monitor the pressure, temperature and liquid level in the device respectively. The vacuum impurity removal device uses biphenyl interlayer for heating and insulation. There is a port at the bottom of the device for sampling and testing, and a melt pump is provided at the bottom outlet to transport the melt after vacuuming.

[0042] 5. The melt is transported to the spinning manifold through the melt pump. The spinning manifold is insulated with biphenyl (temperature is the same as the melt temperature). The metering pump in the spinning manifold transports the melt to the component in a quantitative manner. The melt is filtered by the metal sand and non-woven fabric inside the component and then ejected from the spinneret to form fibers. The metal sand is 40-60 mesh and the non-woven fabric is 25μ. The component pressure is controlled between 130-160 bar.

[0043] 6. After the fiber comes out of the spinneret, the monomer and oligomer smoke volatile at high temperature is extracted through the monomer suction hood to prevent it from adhering to the spinneret of the spinneret or around the components and affecting production stability. The water pressure of the monomer suction hood is 0.1-0.35MPa (the monomer suction hood is an existing conventional device, and its specific structure is not described here).

[0044] 7. The fiber then passes through the side-blown air net and is quickly cooled and solidified by the cooling air. The solidified fiber has sufficient strength to be stretched. The side-blown wind speed and wind temperature are 0.3-0.55m / s and 17-21℃ respectively.

[0045] 8. After being cooled by side-blown air, the fiber is oiled through the oil nozzle. The purpose of oiling is to make the fiber bundle, anti-static, lubricated and further cooled. Then the fiber passes through the wire guide hook and the spinning tunnel in turn to the pre-network device. The main function of the pre-network device is to blow the oil on the fiber evenly and provide a landing point for the fiber to be netted, thereby increasing the cohesion between the fibers. The air pressure at the pre-network device is 0.05-0.2MPa.

[0046] 9. The fiber then enters the drafting rollers, which include a cold roller group and a hot roller group. The function of the drafting rollers is to stretch and shape the fiber to improve its strength and stability. The speeds of the cold roller group and the hot roller group are 2000-4500m / min and 3000-5500m / min respectively, and the temperatures are 25℃ and 130-195℃ respectively.

[0047] 10. The fiber then passes through the godet, guide hook, and reaches the winding head for package formation. The godet is mainly used to adjust the fiber direction and tension. The winding speed of the winding head is 2900-5500m / min.

[0048] Comparison table of test results of products obtained by the technical solution of this application and products obtained by prior art:

[0049] FDY round glossy 40D12F Density / D Breaking strength / (cN / dtex) Elongation at break / % Unevenness of strips / % Gray Scale Dyeing Grade Conventional silk 40.3 4.52 46.2 0.98 Level 4.5-5 This application regenerated silk 40.2 4.50 45.7 1.02 Level 4.5-5

[0050] The specific structure of the vacuum impurity removal device is as follows ( Figure 2-4 ): It includes a first tank body A1 and a second tank body A2 connected by a pipeline. The first tank body A1 and the second tank body A2 can both be cylindrical tank bodies made of stainless steel material, and the bottom of the tank body is conical to facilitate discharge.

[0051] A first melt input pipe A3 (for inputting melt), a first nitrogen input pipe A4 (for inputting nitrogen) and a vacuum suction pipe A5 (for vacuuming) are provided on the upper part of the first tank body A1. The vacuum suction pipe A5 is connected to the first vacuum pump A6. A pressure gauge A20, a first thermometer and a first liquid level gauge A14 are provided on the first tank body.

[0052] A second melt input pipe A7 (for inputting melt) and a second nitrogen input pipe A8 (for inputting nitrogen) are provided on the upper part of the second tank body A2. The lower part of the first tank body A1 is connected to the second tank body A2 through the second melt input pipe A7. A melt pump A9 and a first valve A10 are provided on the second melt input pipe A7. The melt pump A9 is used to pump the melt in the first tank body A1 into the second tank body A2. The first valve A10 is used to open and close the second melt input pipe A7 to achieve communication between the first tank body A1 and the second tank body A2.

[0053] An output pipeline A11 is provided at the lower part of the second tank body, on which a second valve A12 and a second vacuum pump A13 are provided. The second vacuum pump A13 is used to suck the air in the second tank body to achieve the vacuum degree of the second tank body; a second thermometer and a second liquid level gauge A15 are provided on the second tank body.

[0054] Specifically, the first tank body and the second tank body are provided with a thermal insulation and heating layer A16, which can be biphenyl insulation and heating; in order to facilitate degassing and observation of the situation inside the tank, the first tank body and the second tank body are provided with a vent A17 and a visual window A18, the vent A17 is convenient for degassing, and the visual window A18 is convenient for observing the situation inside the tank.

[0055] For reasonable design, a shower nozzle A19 is provided at the discharge end of the first melt input pipe. The shower nozzle A19 is used to spray the melt, thereby increasing the specific surface area of ​​the melt when it flows in, which is beneficial to the removal of small molecular substances in the melt.

[0056] The method of using the vacuum impurity removal device is as follows: first, nitrogen is introduced into the first tank body and the second tank body respectively and discharged to remove the air in the tank, and then the melt is transported from the melt pipe to the first tank body, and then the first vacuum pump is connected. The vacuum degree can be controlled at -0.08~-0.1MPa. When the melt in the first tank body accumulates to one-fourth of the tank body volume, the valve connecting the first and second tank bodies is opened to transport the melt in the first tank body to the second tank body. By controlling the nitrogen valve or the second vacuum pump, the pressure of the second tank body is controlled to be 0.001MPa to 0.1MPa. The melt is vacuumed by high temperature to remove monomers and oligomers in the melt, thereby ensuring the stability of subsequent spinning production.

[0057] The vacuum impurity removal device can remove monomers and oligomers from the nylon 6 melt, keeping the monomer and oligomer content in the recycled nylon 6 melt at a low level, thereby improving the production stability and product quality of recycled nylon 6.

[0058] The specific extraction equipment includes a first extraction kettle B1 and a second extraction kettle B2. The first extraction kettle is provided with a first feed port B3, a first agitator B4, a thermometer and a liquid level gauge B5, as well as a first discharge port B6 and a third feed port B14. The second extraction kettle B2 is provided with a second feed port B7, a second agitator B8, a thermometer and a liquid level gauge B9, and a second discharge port B10. The first discharge port B6 and the second feed port B7 are connected by a connecting pipe B11, and the connecting pipe is provided with a pump B12 and a material-water separator B13; both the first extraction kettle B1 and the second extraction kettle B2 are provided with a visual window B15 and a thermal insulation heating layer B16.

[0059] The specific embodiments described above further illustrate the purpose of the present invention, technical solutions, and beneficial effects. It should be understood that the above description is merely a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. In particular, it should be noted that for those skilled in the art, any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing physically regenerated nylon 6, characterized by: The following steps are included: (1) Cut the waste silk in the production process into short fibers of 5-10 cm, and crush the waste blocks into 5-8 mm 2 Small pieces of material on the left and right; (2) Extract the cut or crushed waste silk and waste blocks with 100°C desalted boiling water for 2-5 hours to fully remove the monomers, oligomers and oils in the waste silk or waste blocks; (3) After the extraction, the waste silk and waste particles are dried to a moisture content of less than 400 ppm; (4) The dried material enters the twin-screw equipment for melting, compression and mixing. The mixed melt enters the filter to remove large particles of impurities contained in the melt; (5) The filtered melt is transported to a vacuum impurity removal device, where high-temperature vacuum is applied to further remove monomers and oligomers from the melt to ensure spinning stability; (6) The melt treated by the vacuum impurity removal device is transported to the spinning manifold through the melt pump. The metering pump in the spinning manifold quantitatively transports the melt to the components in the spinning manifold. The melt is filtered by the metal sand and non-woven fabric inside the component and then ejected from the spinneret to form fibers. After the fibers come out of the spinneret, the monomer suction hood removes the high-temperature volatile monomer and oligomer smoke to prevent it from adhering to the spinneret of the spinneret or around the component and affecting production stability. (7) The fiber is blown by the side blowing net and quickly cooled and solidified by the cooling air. The solidified fiber has sufficient strength to be stretched; (8) The fibers are cooled by side-blown air and then oiled through an oil nozzle to bundle, anti-static, lubricate, and further cool the fibers; After step (8), the fiber passes through the first wire guide hook and the spinning tunnel in turn to the pre-network device, where the oil on the fiber is blown evenly and the fiber is placed on the network to increase the bonding between the fibers. The air pressure at the pre-network device is 0.05-0.2MPa; the fiber treated by the pre-network device enters the drawing roller, which includes a cold roller group and a hot roller group in turn. The function of the drawing roller is to draw and shape the fiber to improve the strength and stability of the fiber; the fiber after the drawing roller passes through the wire guide disk, the second wire guide hook, and reaches the winding head for winding and forming. The wire guide disk is mainly used to adjust the direction and tension of the fiber; in the extraction step of step (2), extraction is carried out through several extraction kettles connected in series, the extraction kettle contains an interlayer filled with heat transfer oil heat medium, and the extraction kettle is equipped with a stirring paddle, and stirring helps to quickly extract the material; and the kettle is also equipped with a temperature sensor and a material level sensor. The meter is used to detect the temperature and material level of the extraction system in the kettle respectively. A material conveying pump is installed between each extraction kettle to convey the material from the previous extraction kettle to the next extraction kettle; in the drying step of step (3), the material extracted in the previous step is first separated from the water by a centrifuge and then sent to two drying towers in series for drying. A suction pump is provided at the bottom of the first tower to convey the dried material in the first tower to the top of the second drying tower for further drying. The two drying towers in series can save the time of material drying; the drying medium is nitrogen with a purity of 99.999% and a temperature of 120°C. The nitrogen flows from the drying tower from bottom to top and the material flows from top to bottom, and the two flow in opposite directions to fully dry the material; there are 8 nitrogen outlets in the entire tower, 4 at the bottom and 4 in the middle; the residence time of the material in the first and second drying towers is 30-60 minutes respectively.

2. The method for preparing physically regenerated nylon 6 according to claim 1, characterized in that: The temperature setting range of the twin-screw equipment in step (4) is 250-270°C. One or two masterbatch or functional powder adding devices and a mixing and stirring device are also provided at the feed port of the twin-screw equipment. The material, masterbatch and functional powder are fully mixed and then fed into the twin-screw to prepare differentiated and functionalized nylon 6 fiber, wherein the filter element of the melt filter is 10μ.

3. The method for preparing physically regenerated nylon 6 according to claim 2, wherein: In step (5), the vacuum degree of the vacuum impurity removal device is controlled at -0.08~-0.1MPa. The melt flows into the vacuum impurity removal device from top to bottom. There is a hole for vacuuming at the top of the device. The vacuuming system is entirely insulated with biphenyl and is equipped with a pressure gauge, a thermometer, and a liquid level gauge to monitor the pressure, temperature and liquid level in the device respectively. The vacuum impurity removal device uses a biphenyl interlayer for heating and insulation. A port is provided at the bottom of the vacuum impurity removal device for sampling and testing, and a melt pump is provided at the bottom outlet to transport the melt after vacuuming.

4. The method for preparing physically regenerated nylon 6 according to claim 3, characterized in that: In step (6), the spinning box is insulated with biphenyl at the same temperature as the melt temperature, wherein the metal sand is 40-60 mesh, the non-woven fabric is 25μ, and the assembly pressure is controlled between 130-160 bar; in step (7), the side blowing wind speed and wind temperature are 0.3-0.55 m / s and 17-21 ° C, respectively.

5. The method for preparing physically regenerated nylon 6 according to claim 4, characterized in that: The speeds of the cold roller group and the hot roller group are 2000-4500 m / min and 3000-5500 m / min respectively, and the temperatures are 25° C. and 130-195° C. respectively; the winding speed of the winding head is 2900-5500 m / min.

Images