A method for preparing recycled hollow nylon 6

Abstract

This invention relates to the field of spinning technology, and more particularly to a method for preparing recycled hollow nylon 6. The method includes (1) drying; (2) raw material extrusion; (3) spinning; and (4) drawing and winding. This invention adds a nitrogen-filled hole in the middle of the spinneret, which firstly accelerates melt cooling, reduces the fiber melt expansion effect, and simultaneously ensures that the fiber melt expansion mainly occurs outwards, increasing the hollowness; secondly, it protects the freshly produced recycled yarn from oxidation at high temperatures, ensuring spinning stability. Furthermore, by optimizing the spinning process, recycled hollow nylon 6 fibers with good spinning stability and high hollowness are obtained.

Description

Technical Field

[0001] This invention relates to the field of spinning technology, and in particular to a method for preparing recycled hollow nylon 6. Background Technology

[0002] Environmental protection and recycling are key topics of concern in today's society. Nylon 6 generates some waste yarn and waste products during the production process. These waste yarns and waste products can be melted and granulated again to be spun into recycled nylon 6, thus achieving the purpose of waste recycling and reuse.

[0003] Hollow fiber, due to its hollow structure along the fiber's longitudinal direction, stores a large amount of air inside the fiber, so the fabric woven from it can achieve excellent weight reduction and warmth retention, making it highly favored by the market. However, since physically recycled chips need to undergo at least three twin-screw processing steps to be spun into fibers, and each time they pass through a twin-screw, the chips will undergo a certain degree of degradation. Therefore, physically recycled chips have poor thermal stability. Especially during the spinning process, if the melt is still at a high temperature and comes into direct contact with air, it is very easy to undergo oxidative degradation or yellowing, causing production breakage and affecting production stability and product quality.

[0004] As is well known, viscoelastic polymer melts undergo melt expansion after being extruded from capillaries, and the melt expansion effect of nylon 6 is quite severe. Therefore, to date, it has not been possible to significantly improve the hollowness of hollow nylon 6 through melt spinning. If physical recycling is combined with conventional hollow spinnerets (such as a nylon C-shaped spinneret in patent CN203295673U, a spinneret with three C-shaped filament holes in patent CN 202809029U, and a double C-shaped spinneret assembly in patent CN217499522U) and their spinning methods, the resulting recycled hollow nylon 6 fibers not only have low hollowness but also poor spinning stability. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for preparing recycled hollow nylon 6, thereby obtaining recycled hollow nylon 6 fibers with good production stability and high hollowness.

[0006] This invention is implemented as follows:

[0007] A method for preparing recycled hollow nylon 6 specifically includes the following steps:

[0008] (1) Drying

[0009] The regenerated slices were dried until the moisture content was below 300 ppm;

[0010] (2) Raw material extrusion

[0011] The dried slices are transported through pipelines to a screw extruder for melting, mixing, and conveying;

[0012] (3) Spinning

[0013] The polymer melt is transported to the spinning box through the melt pipeline. After being quantitatively delivered by the metering pump, it reaches the spinning assembly. The melt is then expelled from the spinneret holes of the hollow spinneret after being subjected to high pressure by the metal sand and nonwoven fabric inside the assembly. After being cooled by the side blowing air, it forms hollow fiber nascent filaments.

[0014] The spinneret has an additional nitrogen channel in the center of the conventional hollow spinneret hole, allowing nitrogen to enter the fiber; the conventional hollow spinneret hole structure is double C.

[0015] (4) Stretching and winding

[0016] Hollow fiber nascent yarn is oiled through an oil nozzle, and then sequentially passes through a pre-networker, cold roller, hot roller, main networker, and winding to obtain recycled hollow nylon 6.

[0017] Furthermore:

[0018] The screw extruder described in step (2) is divided into 5 zones, with temperatures of 145℃, 156℃, 157℃, 156℃ and 155℃ respectively. Nitrogen gas is connected to the screw feed inlet for protection.

[0019] The pressure of the nitrogen gas in step (3) is 0.008 MPa.

[0020] The nonwoven fabric in step (3) has a pore size of 15 μm.

[0021] In step (3), the pressure of the high pressure is controlled between 170-180 bar.

[0022] In step (4), the rotation speed of the cold roller is 4550 m / min and the temperature is room temperature; the rotation speed of the hot roller is 5050 m / min and the temperature is 145℃.

[0023] The oiling process described in step (4) results in an oil content of 2.0% in the hollow fibers.

[0024] The winding speed in step (4) is 5000 m / min.

[0025] Furthermore, the spinneret has several evenly distributed spinneret holes, and the port cross-section of the spinneret holes is double C-shaped; a nitrogen outlet channel is provided at the center of the port of the spinneret hole; a nitrogen inlet is provided on the side of the spinneret, and the nitrogen inlet extends into the interior to provide a nitrogen inlet channel; the nitrogen outlet channel is vertically upward and passes through the C-shaped notch, merging with the nitrogen inlet channel.

[0026] Furthermore, the nitrogen outlet channels of all the spinnerets form a series channel through the nitrogen inlet channels.

[0027] Furthermore, the nitrogen inlet is connected to an external nitrogen generator via a nitrogen input pipe.

[0028] Specifically, a nitrogen pressure control valve and a pressure gauge are installed on the nitrogen input pipeline.

[0029] Furthermore, adjacent spinnerets are connected by nitrogen delivery pipes, extending to the last spinneret, which is sealed at the other end, allowing nitrogen to flow between all the spinnerets.

[0030] This invention has the following advantages: By improving the existing hollow spinneret structure and optimizing the spinning process, this invention produces recycled hollow nylon 6 fibers with higher hollowness. Specifically:

[0031] (1) Add a nitrogen gas passage in the middle of the spinneret orifice. When the melt comes out of the C-shaped spinneret orifice, the nitrogen gas ejected from the orifice, which is under a certain pressure, can play the following role:

[0032] a. To protect the newly produced recycled yarn from oxidation at high temperatures and ensure the stability of spinning;

[0033] b. Accelerate melt cooling to reduce the fiber melt expansion effect and improve hollowness;

[0034] c. Due to the presence of nitrogen inside the fiber, the internal pressure of the fiber is greater than that outside, causing the fiber melt to expand mainly outward, thus increasing the hollowness.

[0035] (2) The cold roller speed is higher than that of general FDY products (the conventional FDY cold roller speed is 2000-3000m / min) in order to reduce the melt expansion effect under the stretching of the high-speed nozzle, improve the hollowness of the hollow fiber, and make the hollowness of the obtained recycled hollow nylon 6 reach the maximum value. Attached Figure Description

[0036] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0037] Figure 1 This is a schematic diagram of a single spinneret.

[0038] Figure 2 This is a schematic diagram of the internal structure of the spinneret (only some of the spinneret holes are shown).

[0039] Figure 3 This is a schematic diagram of the structure of multiple spinnerets.

[0040] Figure 4 This is a cross-sectional view of the spinneret orifice.

[0041] Figure 5 This is a schematic diagram of the port cross-section of the spinneret orifice.

[0042] Figure 6 This is a cross-sectional view of the hollow fiber in sample 1.

[0043] Figure 7 This is a cross-sectional view of the hollow fiber in sample 2.

[0044] Figure 8 This is a cross-sectional view of the hollow fiber in sample 3.

[0045] Figure 9 This is a cross-sectional view of the hollow fiber in sample 4.

[0046] Figure 10 This is a cross-sectional view of the hollow fiber in sample 5. Detailed Implementation

[0047] Example 1

[0048] A method for preparing recycled hollow nylon 6 (FDY full dull 70D20F) is as follows: (1) The recycled chips (relative viscosity: 2.3-2.5; oxidation degree: 3-4% (normal oxidation degree of new chips)) are prepared.

[0049] <1%)) Dry the slices to a moisture content of less than 300 ppm using a dryer. Low moisture content can prevent melt from breaking off when the melt comes out of the spinneret orifice, thus avoiding breakage and affecting production.

[0050] (2) The dried slices are then transported through a pipeline to a screw extruder for melting, mixing and conveying. The temperatures of zones 1-5 of the screw extruder are 145℃, 156℃, 157℃, 156℃ and 155℃, respectively, and nitrogen gas is connected to the screw feed inlet for protection.

[0051] (3) The polymer melt is transported to the spinning box through the melt pipeline. After being quantitatively transported by the metering pump, it reaches the component. The melt is sprayed out from the spinneret hole of the hollow spinneret under high pressure to form hollow fibers.

[0052] The metal nonwoven fabric used in the components is 15μm, which can effectively filter impurities in the recycled chips. In addition, in order to obtain higher component pressure, so that the melt can be ejected from the spinneret with stronger injection pressure, thereby preventing filament breakage under subsequent high-speed cold roll nozzle stretching, the component pressure is controlled between 170-180 bar.

[0053] The spinneret is a double-C hollow spinneret with a nitrogen gas inlet added in the middle of its spinneret orifices. When the molten metal comes out of the C-shaped spinneret orifice, the nitrogen gas ejected from the orifice, which is pressurized, can achieve the following effects:

[0054] 1. Protect the recycled yarn that has just been ejected from the spinneret from oxidation at high temperatures, thus ensuring the stability of spinning;

[0055] 2. Accelerate melt cooling to reduce the fiber melt expansion effect and improve hollowness;

[0056] 3. Due to the presence of nitrogen inside the fiber, the internal pressure of the fiber is greater than that on the outside, causing the fiber melt to expand mainly outward, thus increasing the hollowness.

[0057] The nitrogen vent on the spinneret is connected to an external nitrogen pipeline, and a nitrogen pressure control valve is installed on the pipeline to regulate the nitrogen flow rate. The nitrogen pressure is 0.008 MPa.

[0058] (4) The hollow fibers ejected from the spinneret are then first subjected to a monomer suction device to remove monomers and oligomers, preventing crystallization around the spinneret from affecting production stability. The monomer suction pressure is...

[0059] The pressure is 0.15 MPa, and then the hollow fiber is cooled by side blowing air to make the fiber solid so that it can be stretched and shaped. The side blowing air temperature is 19.5℃ and the air speed is 0.5 m / s.

[0060] (5) The hollow fiber is oiled through the oil nozzle. The purpose is to humidify the fiber, prevent static electricity, lubricate it, and increase the cohesion of the fiber bundle. The oil content of the hollow fiber is 2.0%.

[0061] (6) Then the hollow fibers pass through the guide hook and spinning channel to the pre-networker, where the air pressure is 0.08 MPa. Its main functions are as follows: 1. To blow the oil agent on the fiber evenly; 2. To give the fiber network points to increase fiber cohesion.

[0062] (7) The fibers then pass through the guide rod and guide hook in sequence to reach the cold roller and the hot roller. The main function of the two pairs of rollers is to stretch and shape the fibers to increase their strength.

[0063] The cold roller speed is 4550 m / min, and the temperature is 25℃; the hot roller speed is 5050 m / min, and the temperature is 145℃. The cold roller speed here is higher than that of general FDY products (the conventional FDY cold roller speed is 2000-3000 m / min), in order to reduce the melt expansion effect under the stretching of the high-speed nozzle and improve the hollowness of the hollow fiber.

[0064] (8) Then the fiber is fed into the main network device to improve the cohesion of the fiber. The pressure of the main network device is 0.45MPa.

[0065] (9) The fiber then passes through the guide disc and guide hook and reaches the winding head for winding. The speed of the guide disc is 5030m / min, and its main function is to guide the fiber and adjust the tension; the speed of the winding head winding roller is 5000m / min.

[0066] For further technical solutions, please refer to Figures 1-5 As shown (taking a double C-type spinneret as an example), a perforation (nitrogen inlet 2) is made on the side of the spinneret, extending into the interior to form a nitrogen inlet channel 3. The nitrogen inlet 2 is connected to an external nitrogen generator via a nitrogen input pipe 10, and adjacent spinnerets are connected by a high-temperature resistant nitrogen delivery pipe 11, extending to the last spinneret, whose other end is closed, allowing nitrogen to flow between all spinnerets. To maintain a stable nitrogen output pressure, a nitrogen pressure control valve (such as a nitrogen pressure reducing valve) and a pressure gauge are installed on the nitrogen input pipe, which can automatically adjust the output pressure to ensure the stability, uniformity, and accuracy of the nitrogen supply during use.

[0067] Specifically, the spinneret has several evenly distributed spinneret holes 1, and the cross-sectional shape of the ends of the spinneret holes is a double C-shaped ring. The notch between two adjacent C-shapes faces the center of the spinneret. A nitrogen outlet hole 4 (nitrogen outlet, diameter 0.03 mm, hole depth 0.8 mm) is provided at the center of the ring. The nitrogen outlet hole 4 is vertically upward and passes through the C-shaped notch, merging with the nitrogen inlet channel 3, so that the nitrogen holes of each spinneret hole 1 are connected in series.

[0068] For ease of processing, the nitrogen inlet channel 3 extends to the side of the spinneret. When in use, all channels are closed, leaving only the nitrogen inlet 2 and its symmetrical outlets located on the other side of the spinneret (except for the last spinneret) for connecting adjacent spinnerets.

[0069] To verify the influence of various process parameters on fiber performance, the present invention divided the above-mentioned recycled chips into 5 parts, prepared hollow fibers using the above method, and compared the fiber performance under different process parameters.

[0070] Table 1 Fiber Performance Indicators

[0071]

[0072] As shown in Table 1, both the high-speed cooling roller and the nitrogen gas inlet in the spinneret significantly improve fiber hollowness. While increasing the cooling roller speed increases the number of fiber breaks, this remains within a controllable production range. Additionally, although increasing nitrogen pressure also improves hollowness, it leads to production instability and an increased number of fiber breaks; therefore, this invention uses a nitrogen pressure of 0.008 MPa. Furthermore, the area of ​​the hollow portion within the fiber cross-section also reflects changes in hollowness, such as... Figure 6-10 As shown.

[0073] While specific embodiments of the present invention have been described above, those skilled in the art should understand that the specific embodiments described are merely illustrative and not intended to limit the scope of the present invention. Equivalent modifications and variations made by those skilled in the art in accordance with the spirit of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for the preparation of regenerated hollow polyamide 6, characterized by: Specifically comprising the following steps: (1) drying The regenerated chips are dried to a moisture content of less than 300 ppm; (2) raw material extrusion The dried chips are transported through a pipeline to a screw extruder for melting, mixing and conveying; (3) spinning The polymer melt is conveyed to the spinning box through the melt pipeline, quantitatively conveyed by the metering pump to the spinning assembly, and then sprayed from the spinneret hole of the hollow spinneret plate after the melt forms high pressure in the metal sand and non-woven fabric inside the assembly. After being cooled by side blowing, the hollow fiber primary filament is formed; The spinneret plate is provided with a nitrogen gas passage in the center of the conventional hollow spinneret hole, so that nitrogen gas enters the fiber interior; (4) drawing and winding The hollow fiber primary filament is oiled through the oil nozzle, and then passes through the pre-networker, cold roller, hot roller, main networker and winding in sequence to obtain regenerated hollow nylon 6; The pressure of the nitrogen gas in step (3) is 0.008 MPa; The rotating speed of the cold roller in step (4) is 4550 m / min, and the temperature is normal temperature; the rotating speed of the hot roller is 5050 m / min, and the temperature is 145℃; The screw extruder in step (2) is divided into five zones, and the temperatures of zones 1-5 are 145℃, 156℃, 157℃, 156℃ and 155℃ respectively. Nitrogen gas is connected at the screw feeding port for protection; The pore size of the non-woven fabric in step (3) is 15μ; The pressure of the high pressure in step (3) is controlled between 170-180bar; The spinneret plate is provided with a plurality of uniformly distributed spinneret holes, the port cross-sectional shape of the spinneret hole is double C type, the center of the spinneret hole is provided with a nitrogen gas outlet channel, the side of the spinneret plate is provided with a nitrogen gas inlet, the nitrogen gas inlet extends to the inside to set a nitrogen gas inlet channel, and the nitrogen gas outlet channel vertically upward and from the C type gap, and the nitrogen gas inlet channel converges.

2. The method of producing regenerated hollow polynosic 6 according to claim 1, characterized in that: In step (4), the oiling is performed to make the oil content of the hollow fiber be 2.0%.

3. The method of producing regenerated hollow polynosic 6 according to claim 1, characterized in that: The winding speed in step (4) is 5000 m / min.

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