Method and apparatus for semi-continuous uniform heat treatment of liquid crystalline polyarylate fibers

Abstract

This invention discloses a semi-continuous uniform heat treatment control method and equipment for liquid crystal polyarylate fibers. After being unwound from a yarn rack, the liquid crystal polyarylate precursor fibers sequentially pass through a first drive roller group, a first heat treatment tunnel, a second drive roller group, a second heat treatment tunnel, a third drive roller group, a third heat treatment tunnel, and a fourth drive roller group, finally being wound up by a take-up machine. By controlling the fiber path length between heat treatment tunnels, the length of each heat treatment tunnel, the heat treatment temperature, the heat treatment tension, and the equipment operation program, the static residence and intermittent transmission of the fibers in each heat treatment tunnel are achieved. This invention achieves static residence heat treatment and transmission of liquid crystal polyarylate fibers using the above control method, ensuring uniformity of fiber heating and tension. It can handle a wide range of precursor fibers, with linear densities of 5–110 tex and breaking strengths of 6–12 cN / dtex. Furthermore, the operation is simple and easy to control, and it can simultaneously process multiple fiber bundles with high efficiency.

Description

Technical Field

[0001] This invention relates to a semi-continuous uniform heat treatment control method and equipment for liquid crystal polyarylate fibers, specifically a tunnel-type semi-continuous uniform heat treatment control method and equipment suitable for liquid crystal polyarylate fibers, belonging to the field of synthetic fiber preparation. Background Technology

[0002] Liquid crystal polyarylate fiber is a high-performance organic fiber. It is produced by melt spinning of polyarylate polymers exhibiting liquid crystal phenomena above their melting point, followed by prolonged high-temperature heat treatment. During heat treatment, polymerization continues, requiring continuous nitrogen purging or vacuuming to remove small molecule compounds generated during polymerization. The heat treatment of polyarylate thermotropic liquid crystal fiber precursor fibers requires stepped heating and prolonged heat treatment, typically exceeding 10 hours. Therefore, existing heat treatment technologies usually employ intermittent winding heat treatment, where the fiber precursor is first wound onto a metal can, and then the can is placed in a hot furnace (purged with nitrogen or under vacuum) for heat treatment. Temperature and time control are used to achieve varying fiber temperatures and prolonged heat treatment. Commercial products also require unwinding the heat-treated fiber from the metal can onto paper tubes for sale. In methods for preparing polyarylate thermotropic liquid crystal fibers disclosed in patents such as JP5791284B2, JP6121866B2, and JP06166909A, the heat treatment of the raw yarn all employs a wound-type intermittent heat treatment method. This involves winding the raw yarn onto a stainless steel cylinder with side openings and then placing it in a high-temperature furnace purged with nitrogen for heat treatment. While intermittent wound heat treatment offers the advantage of high processing efficiency, it also presents problems such as difficulty in volatile small molecules due to the thickness of the wound and uneven heating and stress distribution.

[0003] Tunnel-type heat treatment technology offers advantages such as uniform fiber heating and stress distribution, and it also enables continuous online heat treatment. Therefore, it is widely used in the field of organic fibers, such as heterocyclic aramids and PBO fibers, which employ tunnel-type heat treatment for high-temperature processing, as illustrated by patents ZL201010108522.5, ZL201010108545.6, and ZL201510369621.1. However, these fibers have a short residence time in the tunnel, typically within a few minutes, and the heat treatment temperature is relatively constant. Therefore, continuous, uniform, and stable passage through the tunnel is relatively easy to achieve in this case. In contrast, liquid crystal polyaramid fibers require much longer heat treatment times, usually several hours or more, and require variable-temperature heat treatment. Even achieving uniform, continuous transmission at a low speed (0.1 m / min) necessitates tunnels tens to hundreds of meters long, making implementation difficult.

[0004] In the heat treatment process of thermotropic liquid crystal polyarylate fibers, existing technologies, such as patent ZL201510135152.7, use a heated vacuum sealed chamber as the heat treatment device. Inside the chamber are sequentially arranged unwinding rollers, heated tension rollers, and winding rollers. Outside the chamber are heating devices and vacuum suction devices. During use, the thermotropic liquid crystal polyarylate monofilament is fed into the heated vacuum heat treatment device and heat-treated under oxygen-free, high-temperature conditions. This causes molecular chain rearrangement, resulting in more complete crystallization and significantly improving its strength, modulus, and heat resistance. During the heat treatment process, the speed of the unwinding roller is controlled at 0.01–0.5 m / min, and the speed of the winding roller is 0.02–1 m / min. Treatment lasts 6–32 hours, increasing the strength of the thermotropic liquid crystal polyarylate fiber to 20.6 cN / dtex. However, this patent heat-treats a single bundle of fibers, and the unwinding and winding equipment are both in a high-temperature vacuum environment, placing high demands on the equipment, making operation cumbersome, and posing significant challenges to process control.

[0005] Patent ZL201610728879.0 employs a heat treatment device consisting of two or more heating chambers. These chambers, under an inert gas protective atmosphere, are sequentially configured with low-temperature and high-temperature zones. Heating rollers and filament-separating guide rollers are also installed within each chamber. A constant tension regulator and filament-separating guide rollers are positioned between the chambers. During use, thermotropic liquid crystal polyarylate fibers are drawn between the two or more chambers for multi-temperature zone thermo-solid-phase polycondensation treatment. This method can improve the efficiency and effectiveness of solid-phase polycondensation heat treatment. The winding speed is controlled at 0.1–300 m / min, and the maximum heat treatment time is 150 hours. The fiber properties can achieve a strength of over 20 cN / dtex. While this patent relates to a continuous heat treatment process for liquid crystal polyarylate fibers using a chamber gradient heating method, the contact heating between the fibers and the heating rollers within the heating chambers presents uniformity issues. Furthermore, fiber breakage or rewinding during heat treatment requires reopening the chambers and redrawing the fibers, making operation inconvenient. Additionally, the heat treatment time is long, energy-intensive, and inefficient.

[0006] Patent ZL202010065986.6 employs a heat treatment reaction apparatus connected to a heating and cooling system, a vacuum system, and an inert gas system. During use, a whole roll of fiber is placed in the heat treatment reaction apparatus for heating. The vacuum system evacuates the apparatus, and a temperature control system regulates the temperature within the apparatus. Inert gas is simultaneously introduced during the heat treatment process to create a nitrogen-filled atmosphere, preventing fiber oxidation, removing small molecules precipitated on the fiber surface, and improving the uniformity of the temperature in the heat treatment atmosphere. The heat treatment reaction apparatus is configured with an inert gas flow rate of 1–100 L / min per 1 kg of fiber, and a temperature set at 240–300℃. The resulting polyarylate fiber bundles have a strength ≥23 CN / dtex and a strength uniformity CV value ≤5%, significantly improving both fiber strength and strength uniformity. This patent uses a batch heat treatment method to heat the whole roll of fiber, resulting in high heat treatment efficiency, but it still suffers from operational inconvenience and issues with uniformity. Summary of the Invention

[0007] The purpose of this invention is to provide a semi-continuous uniform heat treatment control method for liquid crystal polyarylate fibers. Specifically, it employs a three-section tunnel-type high-temperature heat treatment equipment and four sets of drive rollers, in conjunction with a yarn unwinding frame and a yarn take-up machine. Through program control, the method achieves static residence and intermittent transmission of the fibers within the high-temperature heat treatment tunnel, enabling continuous step-by-step temperature changes and long-term high-temperature uniform heat treatment of the fibers. Simultaneously, the heat treatment tunnel does not need to be too long, making it easy to implement. To this end, this invention also provides equipment for implementing this control method, namely, a semi-continuous uniform heat treatment equipment for liquid crystal polyarylate fibers.

[0008] This invention is achieved through the following technical solution: a semi-continuous uniform heat treatment control method for liquid crystal polyarylate fibers. After the liquid crystal polyarylate precursor fibers are unwound by a yarn rack, they sequentially pass through a first transmission roller group, a first heat treatment tunnel, a second transmission roller group, a second heat treatment tunnel, a third transmission roller group, a third heat treatment tunnel, and a fourth transmission roller group, and are finally wound up by a winding machine. By controlling the fiber path length between heat treatment tunnels, the length of each heat treatment tunnel, the heat treatment temperature, the heat treatment tension, and the equipment operation program, the static dwell and intermittent transmission of the fibers in each heat treatment tunnel can be achieved.

[0009] The liquid crystal polyarylate precursor fiber is obtained by melt spinning of liquid crystal polyarylate with a melting point of 270-300℃.

[0010] The linear density of the liquid crystal polyarylate precursor fiber is 5–110 tex, and the tensile strength is 6–12 cN / dtex.

[0011] The length of the wire path between the heat treatment tunnels is 0.6 to 1.2 meters. The length of the first heat treatment tunnel is 1 to 3 times the length of the wire path; the length of the second heat treatment tunnel is 2 to 4 times the length of the wire path; and the length of the third heat treatment tunnel is 8 to 20 times the length of the wire path.

[0012] The heat treatment temperature of the first heat treatment tunnel is 190-230℃, the heat treatment tension is 0.005-0.03cN / dtex, and the residence time is 1.5-3h.

[0013] The heat treatment temperature of the second heat treatment tunnel is 220-260℃, the heat treatment tension is 0.008-0.06cN / dtex, and the residence time is 2-5h.

[0014] The heat treatment temperature of the third heat treatment tunnel is 250-300℃, the heat treatment tension is 0.01-0.08cN / dtex, and the residence time is 8-20h.

[0015] The transmission speed is 5-10 m / min, and the transmission interval is 30-60 min.

[0016] All heat treatment tunnels are purged with nitrogen.

[0017] A semi-continuous uniform heat treatment device for liquid crystal polyarylate fibers includes a yarn rack, a first drive roller group, a first heat treatment tunnel, a second drive roller group, a second heat treatment tunnel, a third drive roller group, a third heat treatment tunnel, a fourth drive roller group, and a take-up machine arranged sequentially.

[0018] It also includes a storage device, a processor, and a computer program stored on the processor that runs on the processor, wherein the processor executes the computer program to implement the control method described above.

[0019] In this invention, it should be noted that: the fiber path length between heat treatment channels refers to the path length traversed by the fibers between the heat treatment channels; the heat treatment tension refers to the tension of the fibers in the heat treatment channels after being stretched by two sets of transmission rollers; the residence time refers to the time during which the fibers remain stationary in the heat treatment channels; the transmission speed refers to the speed at which the fibers are transmitted through the transmission rollers and / or the winding machine; and the transmission interval time refers to the interval time during the interval transmission process.

[0020] This invention employs a non-contact heat transfer tunnel-type heat treatment device to heat treat liquid crystal polyarylate fibers, which has the following advantages and beneficial effects compared with the prior art:

[0021] (1) By using a multi-stage transmission roller group and a multi-stage heat treatment channel with intervals, the liquid crystal polyarylate fiber can be subjected to step-by-step temperature change heat treatment, and multiple bundles of fibers can be heat treated at the same time, which can significantly improve the heat treatment efficiency of liquid crystal polyarylate fiber.

[0022] (2) A semi-continuous control method is adopted, that is, program control is used to realize the static residence and intermittent transmission of the fiber in the heat treatment channel, thereby realizing long-term heat treatment of the fiber at different heat treatment temperature stages.

[0023] (3) The non-contact heat transfer heat treatment using a tunnel and the tension fine control using multiple transmission roller groups, with its specific layout, can ensure the uniformity of heating and stress on the liquid crystal polyarylate fiber at each stage. Moreover, the transmission rollers and heat treatment tunnel are conventional devices with simple structure and convenient operation.

[0024] In summary, this invention provides a non-contact, semi-continuous, uniform heat treatment control method for liquid crystal polyarylate fibers. It can be achieved using only a multi-stage tunnel-type high-temperature heat treatment device and drive rollers. The static residence heat treatment and conveying of the liquid crystal polyarylate fibers are completed through program settings, ensuring uniformity of fiber heating and tension. It can handle a wide range of raw fibers with linear densities of 5–110 tex and breaking strengths of 6–12 cN / dtex. Furthermore, it is simple to operate and easy to control, and can simultaneously process multiple fiber bundles with high efficiency. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the structure of the present invention.

[0026] Among them, 1—yarn frame, 2—first drive roller group, 3—first heat treatment tunnel, 4—second drive roller group, 5—second heat treatment tunnel, 6—third drive roller group, 7—third heat treatment tunnel, 8—fourth drive roller group, and 9—wind take-up machine. Detailed Implementation

[0027] The present invention will be further described in detail below with reference to embodiments, but the implementation of the present invention is not limited thereto.

[0028] Example 1: Semi-continuous homogeneous heat treatment equipment for liquid crystal polyarylate fibers

[0029] like Figure 1 As shown, Figure 1As shown, the heat treatment equipment consists of a yarn frame 1, a first drive roller group 2, a first heat treatment tunnel 3, a second drive roller group 4, a second heat treatment tunnel 5, a third drive roller group 6, a third heat treatment tunnel 7, a fourth drive roller group 8, and a take-up machine 9, arranged sequentially. During operation, the liquid crystal polyarylate precursor yarn is unwound from the yarn frame 1 and then sequentially passed through the first drive roller group 2, the first heat treatment tunnel 3, the second drive roller group 4, the second heat treatment tunnel 5, the third drive roller group 6, the third heat treatment tunnel 7, and the fourth drive roller group 8 before being taken up by the take-up machine 9. The program control keeps the fibers stationary and allows for intermittent transmission; the transmission speed can be controlled between 5 and 10 m / min, and the intermittent transmission time is set to 30 to 60 min.

[0030] According to the above operating procedure, the liquid crystal polyarylate precursor fibers are subjected to static residence and intermittent transmission in multi-stage heat treatment tunnels at different temperatures. Simultaneously, by setting the fiber path length between tunnels and the length of each heat treatment tunnel, the residence time of the fiber bundle in each heat treatment tunnel is varied, thereby achieving stepped temperature changes and long-term heat treatment of different durations in the multi-stage heat treatment process. Furthermore, to rationally control the fiber bundle tension and its residence time and heating temperature at different heating stages, a storage device, a processor, and a computer program running on the processor can be used. The above-mentioned operation control method can be implemented by the processor executing the computer program, which can improve equipment operating efficiency and simplify process control.

[0031] Example 2:

[0032] The equipment described in Example 1 was used to heat treat liquid crystal polyarylate precursor fibers with a linear density of 5 tex and a breaking strength of 9.5 cN / dte (obtained by melt spinning of liquid crystal polyarylate with a melting point of 285℃). The fiber path length between the channels was 1 meter. The specific control parameters are shown in Table 1 below.

[0033] Table 1. Process control parameters for Example 2

[0034]

[0035] Example 3:

[0036] The equipment described in Example 1 was used to heat treat liquid crystal polyarylate precursor fibers with a linear density of 30 tex and a breaking strength of 9.2 cN / dte (obtained by melt spinning of liquid crystal polyarylate with a melting point of 285℃). The fiber path length between the channels was 1 meter. The specific control parameters are shown in Table 2 below.

[0037] Table 2 Process control parameters for Example 3

[0038]

[0039] Example 4:

[0040] The equipment described in Example 1 was used to heat treat liquid crystal polyarylate precursor fibers with a linear density of 110 tex and a breaking strength of 6.3 cN / dte (obtained by melt spinning of liquid crystal polyarylate with a melting point of 290℃). The fiber path length between the channels was 0.8 meters. The specific control parameters are shown in Table 3 below.

[0041] Table 3 Process control parameters for Example 4

[0042]

[0043] Example 5:

[0044] The equipment described in Example 1 was used to heat treat liquid crystal polyarylate precursor fibers with a linear density of 55 tex and a breaking strength of 7.8 cN / dte (obtained by melt spinning of liquid crystal polyarylate with a melting point of 285℃). The fiber path length between the channels was 1 meter. The specific control parameters are shown in Table 4 below.

[0045] Table 4 Process control parameters for Example 5

[0046]

[0047] Example 6:

[0048] The equipment described in Example 1 was used to heat treat liquid crystal polyarylate precursor fibers with a linear density of 23 tex and a breaking strength of 11.3 cN / dte (obtained by melt spinning of liquid crystal polyarylate with a melting point of 285℃). The fiber path length between the channels was 1 meter. The specific control parameters are shown in Table 5 below.

[0049] Table 5 Process control parameters for Example 6

[0050]

[0051] Comparative Example 1: Liquid crystal polyarylate precursor fibers were subjected to intermittent heat treatment on a whole roll.

[0052] In this comparative example, the same liquid crystal polyarylate precursor yarn roll (a perforated metal tube, with nitrogen blown into the tube so that the nitrogen blown out through the fiber roll layer from the inside of the tube to the outside, and the fiber roll thickness is 1 cm) from Example 3 was placed in an oven-type heat treatment device and subjected to step heat treatment at 210℃ (2h), 240℃ (2h), and 270℃ (10h) to obtain liquid crystal polyarylate fiber.

[0053] Comparative Example 2: Liquid crystal polyarylate precursor fibers were statically heated using a heat treatment tunnel.

[0054] This comparative example uses a tunnel-type heat treatment device to perform static stepped heat treatment on liquid crystal polyarylate fibers. Compared with the present invention, only one high-temperature heat treatment tunnel is used. The same liquid crystal polyarylate precursor fiber as in Example 3 is used for heat treatment. One end of the precursor fiber is fixed outside the tunnel inlet, and the other end is suspended by a rotating wheel outside the tunnel outlet. The tunnel length is 10 meters. The heat treatment tension is controlled to be 0.03 cN / dtex by the suspended weight. Stepped heating heat treatment is performed at 210℃ (2h), 240℃ (2h), and 270℃ (10h) to obtain liquid crystal polyarylate fibers.

[0055] The liquid crystal polyarylate fibers of Examples 2 to 6, Comparative Example 1 and Comparative Example 2 were tested for performance according to the method of GB / T19975-2005, as shown in Table 6 below.

[0056] Table 6 Performance Comparison of Liquid Crystal Polyarylate Fibers

[0057]

[0058] As can be seen from the above, the semi-continuous tunnel heating method adopted in this invention can handle a wide range of raw fibers (fiber linear density of 5-110 tex and breaking strength of 6-12 cN / dtex are all acceptable), with fiber strength reaching above 18 cN / dtex and high uniformity, with strength CV values ​​all below 4%. Comparative Example 1 uses intermittent whole-roll autoclave heating, which improves fiber strength to some extent, but fiber uniformity is still above 4%, especially for fibers with high raw fiber linear density, where uniformity is not ideal. Comparative Example 2 uses tunnel-type static stepped heat treatment, which is also an intermittent heating method. Although the fiber strength and uniformity of the heat-treated fibers are comparable to the method of this invention, the cycle time of this method is long. Because a single channel is used to achieve stepped heating heat treatment, after each heating, cooling is required before the next stage of heat treatment can be carried out, resulting in low efficiency and being unfavorable for industrial production.

[0059] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications or equivalent changes made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for controlling the semi-continuous uniform heat treatment of liquid crystal polyarylate fibers, characterized in that: After the liquid crystal polyarylate precursor yarn is unwound by the yarn rack (1), it passes sequentially through the first drive roller group (2), the first heat treatment tunnel (3), the second drive roller group (4), the second heat treatment tunnel (5), the third drive roller group (6), the third heat treatment tunnel (7), and the fourth drive roller group (8), and is finally wound up by the winding machine (9). The following controls are performed during this process: (I) The length of the wire path between each heat treatment tunnel is set to be 0.6 to 1.2 meters, and the length of the first heat treatment tunnel (3) is 1 to 3 times the length of the wire path; the length of the second heat treatment tunnel (5) is 2 to 4 times the length of the wire path, and the length of the third heat treatment tunnel (7) is 8 to 20 times the length of the wire path; (II) The heat treatment temperature of the first heat treatment tunnel (3) is set at 190-215℃, the heat treatment temperature of the second heat treatment tunnel (5) is set at 220-250℃, and the heat treatment temperature of the third heat treatment tunnel (7) is set at 250-280℃. (III) The heat treatment tension of the first heat treatment channel (3) is set to 0.005~0.03cN / dtex, the heat treatment tension of the second heat treatment channel (5) is set to 0.008~0.06cN / dtex, and the heat treatment tension of the third heat treatment channel (7) is set to 0.01~0.08cN / dtex; (Ⅳ) Set the residence time of the filament bundle in the first heat treatment tunnel (3) to 1.5-3h, the residence time of the filament bundle in the second heat treatment tunnel (5) to 2-5h, and the residence time of the filament bundle in the third heat treatment tunnel (7) to 8-20h; (V) Set the transmission speed of the wire bundles in each heat treatment tunnel to 5-10 m / min and the transmission interval time to 30-60 min.

2. The control method according to claim 1, characterized in that: The liquid crystal polyarylate precursor fiber is obtained by melt spinning of liquid crystal polyarylate with a melting point of 270-300℃.

3. The control method according to claim 1, characterized in that: The linear density of the liquid crystal polyarylate precursor fiber is 5–110 tex, and the tensile strength is 6–12 cN / dtex.

4. The control method according to claim 1, characterized in that: All heat treatment tunnels are purged with nitrogen.

5. A semi-continuous uniform heat treatment device for liquid crystal polyarylate fibers, characterized in that: It includes a yarn frame (1), a first drive roller group (2), a first heat treatment tunnel (3), a second drive roller group (4), a second heat treatment tunnel (5), a third drive roller group (6), a third heat treatment tunnel (7), a fourth drive roller group (8), and a take-up machine (9), arranged in sequence. It also includes a storage device, a processor, and a computer program stored on the processor and running thereon, wherein the processor executes the computer program to implement the control method as described in any one of claims 1 to 4.

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