A novel multi-channel polyimide optical fiber coating drawing process

Abstract

The application relates to a novel multi-channel polyimide optical fiber coating drawing process, and belongs to the technical field of optical fiber manufacturing, which comprises the following steps: heating and drawing an optical fiber preform to form an optical fiber filament; making the optical fiber filament pass through a coater to perform first polyimide coating; making the optical fiber filament after the polyimide coating into a corresponding solidification furnace group for heat curing, wherein the solidification furnace group comprises at least two solidification furnaces arranged in sequence along the running direction of the optical fiber filament; after the optical fiber filament passes through the solidification furnace group, the optical fiber filament is guided and redirected by a guide wheel group, so that the optical fiber filament forms a U-turn running path, thereby the solidification furnace group forms a multi-row U-turn arrangement, and the polyimide coating, heat curing and guide redirection are repeatedly performed to form a multi-channel polyimide optical fiber coating on the surface of the optical fiber filament. The application has the effects of effectively reducing the transverse space occupation of the equipment and improving the compactness of the production line arrangement under the premise of meeting the requirements of the multi-channel polyimide optical fiber coating drawing process, and the process has high flexibility.

Description

Technical Field

[0001] This application relates to the field of optical fiber manufacturing technology, and in particular to a novel multi-channel polyimide optical fiber coating drawing process. Background Technology

[0002] Polyimide optical fibers, due to their good high-temperature resistance, are often used in applications with high requirements for operating temperature. In the fabrication process of polyimide optical fibers, the drawn fiber typically undergoes sequential coating and thermosetting treatments to form a polyimide coating on the fiber surface. For processes requiring multiple polyimide coatings, the fiber often needs to be coated and thermoset multiple times to meet the requirements for the number of coating layers and related performance.

[0003] In existing technologies, to achieve the aforementioned multi-stage polyimide optical fiber coating process, multiple sets of coaters and curing ovens are typically installed sequentially along the optical fiber's running path, allowing the fiber to continuously undergo multiple coating and thermal curing processes after drawing. As the number of coating and curing cycles increases, the related process units are arranged sequentially in the horizontal direction, easily resulting in a large lateral dimension of the entire production line, occupying a significant amount of space, hindering compact equipment layout, and causing inconvenience for production line installation and deployment. Summary of the Invention

[0004] To address the aforementioned issues, this application provides a novel multi-pass polyimide optical fiber coating and drawing process.

[0005] This application provides a novel multi-channel polyimide optical fiber coating and drawing process using the following technical solution: A novel multi-pass polyimide optical fiber coating and drawing process includes the following steps: The optical fiber preform is heated and drawn to form an optical fiber filament; the optical fiber filament is then subjected to a first polyimide coating using a coating machine. The polyimide-coated optical fiber is placed into a corresponding curing oven group for thermal curing. The curing oven group includes at least two curing ovens arranged sequentially along the running direction of the optical fiber. After the optical fiber passes through the curing furnace, the optical fiber is guided and redirected by the guide wheel assembly to form a folding running path, thereby forming a multi-row folding arrangement in the curing furnace. This process of polyimide coating, thermal curing, and guidance redirection is repeated to form a multi-layer polyimide optical fiber coating on the surface of the optical fiber.

[0006] By adopting the above technical solution, when multiple polyimide coatings need to be constructed, the guide wheel assembly causes the optical fiber to form a zigzag running path between multiple curing oven groups, thereby transforming the original sequentially unfolded multiple curing oven groups in a single direction into a multi-row zigzag arrangement. Compared to arranging multiple coaters and curing oven groups linearly in the same direction, this application, while ensuring that the optical fiber can sequentially complete multiple polyimide coatings and multiple thermal curings, can effectively reduce the space occupied by the equipment in the lateral direction, improve the compactness of the entire production line layout, and is more conducive to implementing the multi-stage polyimide optical fiber coating and drawing process in a limited space.

[0007] Optionally, each group of curing furnaces includes a first curing furnace and a second curing furnace arranged sequentially along the direction of optical fiber movement. The curing temperature of the second curing furnace is higher than that of the first curing furnace, so that the coated optical fiber is pre-cured and further cured sequentially.

[0008] By adopting the above technical solution, each curing oven group is configured as a first curing oven and a second curing oven with sequentially increasing temperatures. This allows the polyimide coating to undergo pre-curing in the first curing oven before further curing at high temperatures. This enables the gradual removal of volatile components from the coating and allows the coating to gradually transition from a preliminary settling state to a further cured state. This approach not only reduces the adverse effects of sudden temperature increases on coating formation but also improves the adequacy of the polyimide coating's thermal curing, reducing the likelihood of incomplete curing and localized defects.

[0009] Optionally, the diameter of the guide wheel assembly and the spacing between adjacent guide wheels are set to ensure that the optical fiber filament forms a reversal path with a radius greater than a preset minimum bending radius during the guidance and reversal process.

[0010] By adopting the above technical solution and coordinating the wheel diameter of the guide wheel assembly and the spacing between adjacent guide wheels, the optical fiber filament maintains an operating state greater than the preset minimum bending radius during the folding and guiding process, thereby preventing excessive bending of the optical fiber filament during multiple folding and guiding operations. This helps reduce coating damage, fiber breakage risk, and operational instability caused by excessively abrupt guidance changes, thus improving the reliability of the multi-stage polyimide optical fiber coating drawing process under folding and arrangement conditions.

[0011] Optionally, a recoating device is provided between the first curing oven and the second curing oven in at least one set of the curing oven groups. After the optical fiber is pre-cured in the first curing oven, it is coated with polyimide again by the recoating device and then enters the second curing oven for further curing.

[0012] By adopting the above technical solution, a recoating device is set between the first curing oven and the second curing oven, allowing the optical fiber filaments pre-cured in the first curing oven to be coated with polyimide again, and then further cured in the subsequent second curing oven. Therefore, without significantly increasing the thickness of a single coating pass, the construction efficiency of multi-pass polyimide coatings can be improved, and it is beneficial to achieve layer-by-layer stacking and curing of polyimide coatings, thus balancing the quality of single-layer coatings with the overall efficiency of multi-pass coating formation.

[0013] Optionally, the polyimide coating, thermosetting, and orientation reversal are repeated 3-5 times to form a multi-layer polyimide fiber coating on the surface of the fiber filament.

[0014] By adopting the above technical solution, the polyimide coating, thermosetting, and orientation reversal are controlled to be repeated 3-5 times. This ensures the layer-by-layer formation of multi-layer polyimide fiber coatings while balancing the complexity of the process and the length of the equipment path. If the number of repetitions is too few, it will be difficult to form a multi-layer polyimide coating that meets the requirements; if the number of repetitions is too many, it will easily lead to an excessively long process flow and increased equipment control complexity. Therefore, setting the number of repetitions to 3-5 times is beneficial to achieving a better balance between the coating construction requirements and the difficulty of process implementation.

[0015] Optionally, during the thermal curing of the polyimide coating in at least one of the curing oven groups, gas circulation or exhaust treatment is performed within the curing oven groups to reduce the partial pressure of volatile solvents within the curing oven groups.

[0016] By adopting the above technical solution and implementing gas circulation or exhaust treatment within the curing oven, volatile components generated during the thermosetting of the polyimide coating can be discharged in a timely manner, thereby reducing the partial pressure of volatile solvents within the curing oven. This facilitates the removal of volatile components from the polyimide coating, reduces solvent residue, and improves the thermosetting effect of the polyimide coating, thus contributing to improved forming quality and interlayer stability of multi-layer polyimide coatings.

[0017] Optionally, between two adjacent polyimide coatings, the optical fiber filament after the previous thermosetting is cooled so that the temperature of the optical fiber filament before entering the next coating is within the preset coating temperature range.

[0018] By employing the above technical solution, cooling the optical fiber after the previous thermosetting between adjacent polyimide coatings ensures that the fiber temperature before entering the next coater is within the preset coating temperature range. This avoids the adverse effects of excessively high fiber temperature after the previous thermosetting on the subsequent polyimide coating process. This improves the stability of the subsequent polyimide coating process and helps control the forming state and thickness uniformity of the polyimide coating.

[0019] Optionally, the tension of the optical fiber at the guide wheel before entering the curing furnace group and the guide wheel after leaving the curing furnace group is detected, and the traction speed is adjusted according to the detection results so that the tension of the optical fiber during the folding operation is kept within a preset range.

[0020] By adopting the above technical solution, and by detecting the tension of the optical fiber filament and adjusting the traction speed based on the detection results, the optical fiber filament can maintain a relatively stable tension state throughout multiple folding operations. This improves the operational stability of the optical fiber filament under multi-row folding arrangements, reduces the adverse effects of tension fluctuations on optical fiber forming and subsequent polyimide coating quality, and helps ensure the consistency of multi-layer polyimide coating formation.

[0021] Optionally, after each layer of polyimide coating is completed, the outer diameter of the optical fiber is detected online, and the coating amount, traction speed and curing parameters of the coater are adjusted according to the detection results.

[0022] By adopting the above technical solution, the forming dimensions during the multi-stage polyimide fiber coating drawing process can be controlled in real time. This helps improve the dimensional consistency of each polyimide coating layer during construction, reduces the impact of process fluctuations on the final outer diameter, and further enhances the stability and controllability of the entire multi-stage polyimide fiber coating drawing process.

[0023] In summary, this application includes at least one of the following beneficial technical effects: 1. This application sets up a guide wheel group to make the optical fiber wire form a zigzag running path between multiple curing furnace groups, and to make the multiple curing furnace groups form a multi-row zigzag compact arrangement, thereby effectively reducing the lateral space occupied by the equipment and improving the compactness of the production line layout while meeting the requirements of the multi-stage polyimide optical fiber coating and drawing process. 2. Based on the optical fiber filament folding operation achieved by the guide wheel assembly, this application combines staged curing, multiple thin-layer coatings, bending radius control, inter-furnace recoating, in-furnace gas circulation or exhaust, cooling between adjacent coatings, tension detection and adjustment, and online detection feedback to ensure stable operation of the optical fiber filament and stable formation of multi-layer polyimide coating under compact folding arrangement conditions, thereby improving the stability and controllability of the multi-layer polyimide optical fiber coating drawing process. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the overall structure of an embodiment of this application.

[0025] Figure 2 This is a flowchart illustrating an embodiment of this application.

[0026] Explanation of reference numerals in the attached drawings: 1. Optical fiber preform; 2. Optical fiber filament; 3. Coating device; 4. Heating and drawing furnace; 5. Curing furnace group; 51. First curing furnace; 52. Second curing furnace; 53. Third curing furnace; 6. Guide wheel group; 9. Online detection device. Detailed Implementation

[0027] The following is in conjunction with the appendix Figure 1-2 This application will be described in further detail.

[0028] This application discloses a novel multi-channel polyimide optical fiber coating and drawing process.

[0029] like Figure 1 and Figure 2 The novel multi-pass polyimide optical fiber coating and drawing process includes the following steps: S1. The optical fiber preform 1 is heated and drawn to form an optical fiber filament 2, and the optical fiber filament 2 is coated with polyimide for the first time by the coating machine 3. First, the optical fiber preform 1 is fed into the heating and drawing furnace 4 for heating and softening, and then drawn downwards under traction to form an optical fiber filament 2. After the optical fiber filament 2 is formed, it enters the first coating unit 3 along a predetermined running path (usually a vertical downward path) to form the first polyimide coating on the outer periphery of the optical fiber filament 2.

[0030] S2. The polyimide-coated optical fiber 2 is placed into the corresponding curing oven group 5 for thermal curing. The curing oven group 5 includes at least two curing ovens arranged sequentially along the running direction of the optical fiber 2. After coating, the optical fiber filament 2 continues to enter the corresponding curing oven group 5 for heat curing. The curing oven group 5 includes at least two curing ovens arranged sequentially along the running direction of the optical fiber filament 2, so that the newly coated polyimide coating is cured under continuous heat treatment. In the embodiment of this application, the first curing oven group 5 is also arranged along the vertical traction direction of the optical fiber filament 2, so that the optical fiber filament 2 has a certain initial strength before being bent and entering the next coating.

[0031] S3. After the optical fiber 2 passes through the curing furnace group 5, the guide wheel group 6 guides and redirects the optical fiber 2 so that the optical fiber 2 forms a folding running path, thereby forming a multi-row folding arrangement in the curing furnace group 5. After the first curing oven group 5 completes heat curing, the optical fiber filament 2 is output from the curing oven group 5 and changes its running direction under the guidance of the guide wheel group 6 to form a reversible running path. Through the guidance and reversal of the guide wheel group 6, the optical fiber filament 2 no longer extends in a straight line in a single direction, but enters the next group of coaters 3 and the next group of curing oven groups 5 to continue subsequent processes. In this way, multiple curing oven groups 5 can be arranged in a multi-row manner, with adjacent rows connected by the reversible path, thus transforming the original arrangement of multiple curing oven groups 5, which needed to be sequentially deployed in the same direction, into a compact reversible arrangement.

[0032] Specifically, after completing the first polyimide coating and initial heat curing, the optical fiber filament 2 is redirected by the guide wheel assembly 6 to enter the next polyimide coating station, where a new polyimide coating is formed on the outside of the previously formed polyimide coating. Subsequently, the optical fiber filament 2 continues into the next set of curing ovens 5 for heat curing. After completing heat curing in this set of curing ovens 5, the optical fiber filament 2 is again redirected by the guide wheel assembly 6 and enters subsequent coating stations and subsequent curing ovens 5. Following this process, polyimide coating, heat curing, and redirection are repeatedly performed, allowing the optical fiber filament 2 to gradually form multiple polyimide fiber coatings during repeated back-and-forth movements.

[0033] In this embodiment, multiple curing oven groups 5 can be arranged in a multi-row zigzag pattern according to site conditions and process requirements. For example, each curing oven in curing oven group 5 is arranged longitudinally, while each group of curing ovens is arranged laterally. According to process requirements, all curing ovens can be arranged in N rows and N columns, such as 2 rows and 2 columns - 2 rows and 5 columns, 3 rows and 2 columns - 3 rows and 5 columns, etc.

[0034] During the repeated processes of polyimide coating, thermosetting, and reorientation, after each polyimide coating, the fiber enters a corresponding curing oven group 5 for thermosetting, and then is reoriented by guide wheel group 6 before entering the next polyimide coating process. By repeating the above process multiple times, a multi-layer polyimide fiber coating can be gradually built on the surface of the fiber filament 2. The number of repetitions can be adjusted according to the actual product requirements to meet the needs of preparing multi-layer polyimide fiber coatings with different thicknesses, number of layers, or performance requirements. This ensures that the fiber filament 2 can complete multiple polyimide coatings and thermosetting processes sequentially, while reducing the lateral space occupied by the equipment, which is beneficial for implementing the multi-layer polyimide fiber coating drawing process under limited space conditions.

[0035] Each curing furnace group 5 includes a first curing furnace 51 and a second curing furnace 52 arranged sequentially along the running direction of the optical fiber filament 2. The curing temperature of the second curing furnace 52 is higher than that of the first curing furnace 51. After each polyimide coating is completed, the optical fiber filament 2 first enters the first curing furnace 51 for pre-curing, and then enters the second curing furnace 52 for further curing, so that the polyimide coating is gradually cured during continuous heat treatment.

[0036] In this application, a total of three curing oven groups 5 are provided. The first curing oven group 5 and the third curing oven group 5 also include a third curing oven 53. The temperature of the third curing oven 53 is higher than that of the second curing oven 52, so that the polyimide coating undergoes preliminary devolatilization, transition curing, and further curing in sequence. The third curing oven 53 may also not be operated depending on the actual curing process. By providing three curing ovens, the process flexibility is improved.

[0037] Specifically, after the fiber filament 2 is coated with polyimide by the coater 3, the newly formed polyimide coating is still in a relatively wet or unstable state. At this time, the fiber filament 2 first enters the first curing oven 51 with a relatively low temperature. Under the relatively gentle heat treatment conditions, the volatile components in the polyimide coating are gradually removed, and the polyimide coating achieves a preliminary shaping effect. After treatment in the first curing oven 51, the polyimide coating has a certain degree of stability. Subsequently, the fiber filament 2 continues to enter the second curing oven 52 with a higher temperature for further curing of the polyimide coating under higher temperature conditions, so that the polyimide coating achieves a more complete heat treatment effect. The third curing oven 53 plays a role in strengthening the curing. Thus, the polyimide coating can be cured gradually according to the heat treatment rhythm from gentle to strong, which is beneficial to improving the stability of the polyimide coating formation.

[0038] In practical applications, the specific curing temperatures of the first curing oven 51 and the second curing oven 52 can be adjusted according to the characteristics of the polyimide coating material, the thickness of a single coating, the running speed of the optical fiber filament 2, and the target performance requirements of the multi-pass polyimide coating. This ensures that the polyimide coating undergoes a relatively mild pre-curing treatment in the first stage, followed by further curing in the second stage. This not only improves the controllability of the polyimide coating heat treatment process but also provides a more stable coating foundation for subsequent repeated coatings and rework operations.

[0039] For example, the first curing oven 51 is mainly used for pre-curing the optical fiber filament 2 that has just been coated with polyimide. Preferably, the curing temperature of the first curing oven 51 can be set to 100°C-200°C to gradually remove the volatile components in the polyimide coating and to give the polyimide coating a preliminary shaping effect.

[0040] The second curing oven 52 is mainly used to further cure the pre-cured polyimide coating. Preferably, the curing temperature of the second curing oven 52 can be set to 200°C-320°C to further heat-treat the polyimide coating. The third curing oven 53 is mainly used to strengthen the curing of the pre-cured polyimide coating. Preferably, the curing temperature of the second curing oven 52 can be set to 320°C-380°C to improve the curing sufficiency and forming stability of the polyimide coating.

[0041] In this embodiment, the guide wheel assembly 6 is used not only to guide and redirect the optical fiber filament 2, but also to control the bending state of the optical fiber filament 2 during the folding-back operation. Specifically, the wheel diameter of the guide wheel assembly 6 and the spacing between adjacent guide wheels are set in accordance with the outer diameter of the optical fiber filament 2, the thickness of the polyimide coating, the number of coating layers, and the operating state of the optical fiber filament 2 after thermosetting, so that the optical fiber filament 2 forms a folding-back operation path with a bending radius greater than the preset minimum bending radius during each guidance and redirection process.

[0042] In practice, after the optical fiber filament 2 completes the thermal curing of a set of curing ovens 5, it leaves the output end of the curing ovens 5 and changes its running direction under the action of the guide wheel set 6 before entering the next station. The guide wheels in the guide wheel set 6 are not arbitrarily set, but rather, through the combined action of the guide wheel diameter and the spacing between the guide wheels, the optical fiber filament 2 forms a smooth, arc-shaped return path when passing through the guide wheel set 6, rather than forming an overly abrupt turn in a localized location. In other words, the optical fiber filament 2 maintains a running state greater than the preset minimum bending radius throughout the return guidance process, thereby avoiding localized stress concentration caused by overly abrupt changes in direction.

[0043] In this embodiment, the preset minimum bending radius can be determined based on the strength of the optical fiber filament 2, the number of polyimide coating layers, the thickness of a single coating layer, and the surface state of the optical fiber filament 2 after thermosetting. For the multi-pass polyimide coating drawing process, as the polyimide coating is formed layer by layer on the surface of the optical fiber filament 2, the stress state and surface state of the optical fiber filament 2 will change during the folding operation. Therefore, the wheel diameter of the guide wheel group 6 and the spacing between adjacent guide wheels are preferably matched and set according to the actual process conditions during the formation of the multi-pass polyimide coating to ensure that the optical fiber filament 2 at different folding stations can be smoothly redirected.

[0044] For example, in this embodiment, the outer diameter of the fiber filament 2 formed after the fiber preform 1 is heated and drawn can be 80μm-125μm, preferably 125μm. During the multi-pass polyimide coating process, the thickness of the single-layer polyimide coating formed by each polyimide coating can be 2μm-8μm, preferably 3μm-5μm; after repeating the polyimide coating and heat curing 3-5 times, the total outer diameter of the multi-pass polyimide fiber coating formed on the outer surface of the fiber filament 2 can be 145μm-200μm, preferably 145μm-180μm. In this embodiment, the wheel diameter of the guide wheel group 6 and the spacing between adjacent guide wheels are matched according to the outer diameter of the fiber filament 2, the total thickness of the multi-pass polyimide coating, the number of folds, and the surface state of the fiber filament 2 after heat curing. Specifically, the guide wheel diameter can be set to 50 mm-200 mm, preferably 80 mm-150 mm; the spacing between adjacent guide wheels can be set to 300 mm-500 mm; and the preset minimum bending radius can be set to 25 mm-100 mm, preferably 40 mm-75 mm. By ensuring that the guide wheel diameter and the spacing between adjacent guide wheels satisfy the above relationship, the optical fiber filament 2 forms a reversing running path with a bending radius greater than the preset minimum bending radius during the guiding and reversing process, thereby avoiding excessive bending of the optical fiber filament 2 during the reversing running process.

[0045] In practice, after the optical fiber filament 2 completes the thermal curing of a set of curing ovens 5, it leaves the output end of the curing ovens 5 and changes its running direction under the action of the guide wheel set 6 before entering the next station. During this process, the optical fiber filament 2 forms an arc-shaped transition path when passing the guide wheels, rather than forming a sharp angle turn in a local area. For example, when the outer diameter of the optical fiber filament 2 is 125μm and the total outer diameter after the multi-layer polyimide coating is formed is 155μm-180μm, the diameter of the guide wheel can be preferably set to 80 mm-120mm, and the distance between adjacent guide wheels can be preferably set to 350mm-400mm, so that the actual bending radius of the optical fiber filament 2 at each turning station is greater than 40mm, thereby meeting the stable operation requirements during multiple turning guidance processes.

[0046] Furthermore, a recoating device can be provided between the first curing oven 51 and the second curing oven 52 (not provided in this embodiment), or between the second curing oven and the third curing oven 53 (not provided in this embodiment). The arrangement of the recoating device between the first curing oven 51 and the second curing oven 52 can be adjusted according to the running speed of the optical fiber filament 2 and the state of the polyimide coating. Preferably, the recoating device is positioned close to the output end of the first curing oven 51, so that the optical fiber filament 2 enters the recoating station promptly after the initial polyimide coating has completed pre-curing, and uses its residual heat from the first curing oven 51 to set the recoated material.

[0047] In a preferred embodiment, the outer diameter of the optical fiber 2 can be 125 μm. The thickness of the first polyimide coating layer formed after the initial coating can be 3 μm-5 μm. After pre-curing in the first curing oven 51 at 120°C-180°C, a second polyimide coating layer with a thickness of 2 μm-4 μm is formed by a recoating device. Subsequently, it enters the second curing oven 52 at a temperature of 260°C-340°C for further curing. In this way, two polyimide coating layers can be constructed in one round of curing oven group 5 without using a one-time thick coating process, thus balancing the quality of single-layer coating and the overall efficiency of multi-layer construction.

[0048] In this embodiment, during the heat curing of the polyimide coating in at least one curing oven group 5, gas circulation or exhaust treatment is performed within the curing oven group 5 to reduce the partial pressure of volatile solvents within the curing oven group 5. Specifically, the curing oven group 5 can be equipped with a circulating air duct and an exhaust channel. During the heat curing of the polyimide coating, the circulating airflow carries the volatile components inside the oven towards the exhaust end and discharges them outside the oven through the exhaust channel, thereby ensuring that the polyimide coating remains in a low volatile solvent partial pressure environment throughout the heat treatment process.

[0049] In this embodiment, gas circulation or exhaust treatment can be applied to the first curing oven 51, the second curing oven 52, or both simultaneously. For the first curing oven 51, gas circulation or exhaust treatment is mainly used to promote the timely removal of volatile components generated immediately after polyimide coating, thus preventing their accumulation within the oven. For the second curing oven 52, gas circulation or exhaust treatment is mainly used to further reduce the partial pressure of volatile solvents within the oven at higher temperatures, thereby improving the heat treatment effect of the subsequent curing stage.

[0050] In practice, the circulating gas within the curing oven 5 can be air, dry air, or an inert gas. Preferably, dry air or an inert gas is used for circulation and exhaust to reduce the influence of the external environment on the polyimide thermosetting process. In one embodiment, the circulating airflow can flow along the direction of the optical fiber filament 2; in another embodiment, the circulating airflow can flow in the opposite direction to the direction of the optical fiber filament 2, or a circulating flow field can be formed within the oven cavity. Regardless of the airflow organization method used, the aim is to promptly remove the volatile components released during the thermosetting of the polyimide coating.

[0051] Furthermore, in this embodiment, the exhaust treatment can be either continuous or intermittent. Preferably, when the optical fiber filament 2 is continuously heat-cured through the curing furnace group 5, a continuous exhaust method is adopted to ensure that the volatile solvents in the furnace are continuously discharged during the heat treatment of the polyimide coating, thereby avoiding an increase in the concentration of volatile components in the furnace. By combining continuous gas circulation with continuous exhaust, a low partial pressure environment of volatile solvents can be maintained inside the curing furnace group 5, which is beneficial to the continuous removal of volatile components from the polyimide coating.

[0052] To achieve the aforementioned airflow treatment, the first curing oven 51 and the second curing oven 52 can be equipped with a circulating fan, a guide duct, and an exhaust port. The circulating fan drives the airflow within the oven, the guide duct guides the airflow to form a circulating flow field within the oven cavity, and the exhaust port discharges the gas carrying volatile components outside the oven. When an inert gas is used, a gas supply interface, a flow control valve, and a gas delivery pipeline can also be provided to maintain a circulating atmosphere within the oven.

[0053] In this embodiment, between two adjacent polyimide coatings, the optical fiber filament 2, after the previous thermosetting, is cooled to ensure its temperature is within a preset coating temperature range before entering the next coating unit 3. This is because the optical fiber filament 2 is typically still at a relatively high temperature after the previous thermosetting. If it were to directly enter the next coating unit 3 for polyimide coating, it would easily affect the spreading and forming state of the polyimide coating solution on the surface of the optical fiber filament 2, which would be detrimental to the stable control of the subsequent polyimide coating thickness. Publicly available information also mentions that the optical fiber temperature affects the coating geometry and thickness variations.

[0054] In this embodiment, the temperature of the optical fiber filament 2 after the previous heat curing when it leaves the curing oven group 5 can be 120°C-340°C. Specifically, when the optical fiber filament 2 only undergoes the pre-curing stage, the output temperature can be 120°C-200°C; when the optical fiber filament 2 undergoes a further curing stage, the output temperature can be 220°C-340°C. To ensure the stability of the next polyimide coating, the optical fiber filament 2 is cooled before entering the next coating unit 3, reducing its temperature to a preset coating temperature range. Preferably, the preset coating temperature range can be 40°C-90°C.

[0055] In specific implementation, the cooling method can be natural cooling, airflow cooling, or cooling channel cooling. Preferably, airflow cooling is used, so that the optical fiber filament 2 is cooled by a cooling air duct or cooling chamber before entering the next coating station from the previous curing station. The cooling gas can be air, dry air, or inert gas. More preferably, dry air is used to cool the optical fiber filament 2 to reduce the influence of the external environment on the polyimide coating process. To achieve this cooling process, a cooling section can be set between the previous curing oven group 5 and the next coating unit 3. The length of the cooling section can be 0.5m-5m, preferably 1m-3m, so as to reduce the temperature of the optical fiber filament 2 to the preset coating temperature range without significantly increasing the overall path complexity.

[0056] By adopting the above-described embodiments, the optical fiber 2 after the previous heat curing is cooled between two adjacent polyimide coatings, so that the temperature of the optical fiber 2 before entering the next coating machine 3 is within the preset coating temperature range. This reduces the adverse effects of the residual heat from the previous heat curing on the subsequent polyimide coating process, improves the stability of the subsequent polyimide coating, and helps to control the thickness uniformity and process controllability of the multi-layer polyimide coating.

[0057] In this embodiment, the running tension of the optical fiber filament 2 is detected at the guide wheel before entering the curing furnace group 5 and / or at the guide wheel after leaving the curing furnace group 5. The traction speed is adjusted according to the detection results to keep the tension of the optical fiber filament 2 within a preset range during the folding operation. The reason for this setting is that when the optical fiber filament 2 folds back and forth between multiple curing furnace groups 5, it will pass through the guide wheel multiple times to change direction. If the running tension fluctuates too much, it will easily affect the running stability of the optical fiber filament 2 and the consistency of the subsequent polyimide coating construction.

[0058] In this embodiment, tension detection can be achieved using a guide wheel with built-in tension detection. Specifically, the guide wheel with built-in tension detection can be a force-measuring guide wheel, a tension detection guide wheel, a tension measuring roller, a tension sensing guide wheel assembly, or a three-roller tension sensor.

[0059] In specific implementation, the preset tension range can be set according to the outer diameter of the optical fiber filament 2, the number of polyimide coating layers, the total coating thickness, and the running speed of the optical fiber filament 2. Preferably, the preset tension range of the optical fiber filament 2 during the folding operation can be 0.05 N-0.50 N. When the tension detection value is higher than the upper limit of the preset range, the traction speed is reduced; when the tension detection value is lower than the lower limit of the preset range, the traction speed is increased so that the running tension of the optical fiber filament 2 returns to the preset range. The traction speed adjustment can be achieved through a servo drive mechanism connected to the traction device, thereby forming a real-time feedback adjustment process based on the tension detection results. This can reduce the adverse effects of tension fluctuations on the forming of the optical fiber filament 2 and the construction process of the multi-stage polyimide coating, and improve the operational stability and process controllability of the multi-stage polyimide optical fiber coating drawing process.

[0060] In this embodiment, after each layer of polyimide coating is completed, the outer diameter of the optical fiber filament 2 is detected online, and the coating amount, traction speed, and curing parameters are adjusted based on the detection results, thereby achieving closed-loop control in the multi-layer polyimide optical fiber coating construction process. This is because the multi-layer polyimide coating fiber drawing process requires repeated polyimide coating, thermal curing, and folding operations. If the outer diameter of each polyimide coating layer cannot be detected and adjusted in a timely manner, it can easily lead to the accumulation of process errors over multiple rounds, thus affecting the final outer diameter consistency and coating construction quality.

[0061] In this embodiment, the online detection device 9 can be a laser diameter gauge, optical diameter gauge, or other online detection device 9 suitable for continuous measurement of the optical fiber filament 2. Preferably, an online detection point is set after each polyimide coating is completed and before entering the corresponding curing station, so as to obtain the outer diameter detection value in a timely manner after the polyimide coating is formed; in some embodiments, a detection point can also be set again after the corresponding curing station to verify the change in outer diameter after heat curing. In the above manner, the outer diameter data after coating and the outer diameter data after curing can be obtained respectively, thereby providing a basis for subsequent parameter adjustment.

[0062] In specific implementation, when the online detection result is higher than the upper limit of the target outer diameter of the corresponding layer, the coating amount can be reduced, the traction speed increased, and / or the curing parameters reduced; when the online detection result is lower than the lower limit of the target outer diameter of the corresponding layer, the coating amount can be increased, the traction speed decreased, and / or the curing parameters increased. Preferably, the coating amount can be adjusted by adjusting the liquid supply of the coater 3, the flow rate of the metering pump, or the operating parameters of the coater 3; the traction speed can be adjusted by adjusting the running speed of the traction device; and the curing parameters can be adjusted by adjusting the temperature of the first curing oven 51 and the second curing oven 52, the heat treatment time, or the airflow conditions inside the oven.

[0063] In a preferred embodiment, the outer diameter deviation control range can be set to ±5μm, preferably ±2μm. When the online detection result exceeds the target outer diameter range, the coating amount can be adjusted by 2%-10%; the traction speed can be adjusted by 1%-8%; and the curing temperature can be adjusted by 5°C-30°C, preferably 10°C-20°C. For example, when the target outer diameter after the first layer of polyimide coating is 133μm and the allowable deviation is ±2μm, if the online detection result is greater than 135μm, the coating amount can be appropriately reduced and the traction speed increased; if the online detection result is less than 131μm, the coating amount can be appropriately increased and the traction speed decreased.

[0064] Furthermore, in the multi-layer polyimide fiber coating drawing process, since the fiber filament 2 needs to undergo multiple polyimide coatings and multiple thermal curings, if the outer diameter deviation after the formation of the previous polyimide coating layer is not corrected in time, this deviation is likely to continue to accumulate in subsequent polyimide coating layers. By performing online detection after each polyimide coating layer is completed, and adjusting the coating amount, traction speed, and curing parameters in real time based on the detection results, the diffusion of outer diameter deviation can be suppressed in a timely manner, thereby improving the dimensional consistency during the layer-by-layer construction process of the multi-layer polyimide fiber coating.

[0065] The implementation principle of this application embodiment is as follows: First, the optical fiber preform 1 is heated and drawn to form an optical fiber filament 2, and the optical fiber filament 2 undergoes multiple polyimide coatings and multiple thermosetting processes. Between each thermosetting process, the optical fiber filament 2 is guided and redirected by the guide wheel group 6, so that the optical fiber filament 2 forms a folding running path, thereby enabling multiple curing furnace groups 5 to form a multi-row folding compact arrangement to reduce the lateral space occupied by the equipment. At the same time, by controlling the curing process in stages, building multiple thin-layer coatings layer by layer, controlling the bending radius and running tension during the folding process, circulating and discharging volatile components in the curing furnace, cooling the optical fiber filament 2 between adjacent coatings, and online detection and feedback adjustment of the outer diameter after each polyimide coating layer, the optical fiber filament 2 can still operate stably under the folding compact arrangement conditions, and the stable formation of multiple polyimide coatings can be achieved.

[0066] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A novel multi-pass polyimide optical fiber coating and drawing process, characterized in that: Includes the following steps: The optical fiber preform (1) is heated and drawn to form an optical fiber filament (2); The optical fiber filament (2) is first coated with polyimide by the coater (3); The polyimide-coated optical fiber (2) is placed into the corresponding curing oven group (5) for thermal curing. The curing oven group (5) includes at least two curing ovens arranged sequentially along the running direction of the optical fiber (2). After the optical fiber (2) passes through the curing furnace group (5), the optical fiber (2) is guided and redirected by the guide wheel group (6) so that the optical fiber (2) forms a folding running path, thereby forming a multi-row folding arrangement in the curing furnace group (5). In this way, polyimide coating, heat curing and guidance redirection are repeated to form a multi-layer polyimide optical fiber coating on the surface of the optical fiber (2).

2. The novel multi-pass polyimide optical fiber coating and drawing process according to claim 1, characterized in that: Each curing furnace group (5) includes a first curing furnace (51) and a second curing furnace (52) arranged sequentially along the running direction of the optical fiber (2). The curing temperature of the second curing furnace (52) is higher than that of the first curing furnace (51), so that the coated optical fiber (2) can be pre-cured and further cured sequentially.

3. The novel multi-pass polyimide optical fiber coating and drawing process according to claim 1, characterized in that: The diameter of the guide wheel group (6) and the spacing between adjacent guide wheels are set to make the optical fiber (2) form a return running path with a radius greater than the preset minimum bending radius during the guidance and reversal process.

4. The novel multi-pass polyimide optical fiber coating and drawing process according to claim 1, characterized in that: A recoating device is provided between the first curing oven (51) and the second curing oven (52) of at least one set of curing oven groups (5). After the optical fiber (2) is pre-cured in the first curing oven (51), it is coated with polyimide again by the recoating device and then enters the second curing oven (52) for further curing.

5. The novel multi-pass polyimide optical fiber coating and drawing process according to claim 1, characterized in that: The polyimide coating, thermosetting, and orientation reversal are repeated 3-5 times to form a multi-layer polyimide fiber coating on the surface of the fiber filament (2).

6. The novel multi-pass polyimide optical fiber coating and drawing process according to claim 1, characterized in that: During the process of heat curing the polyimide coating in at least one of the curing oven groups (5), gas circulation or exhaust treatment is performed in the curing oven group (5) to reduce the partial pressure of volatile solvents in the curing oven group (5).

7. The novel multi-pass polyimide optical fiber coating and drawing process according to claim 1, characterized in that: Between two adjacent polyimide coatings, the optical fiber filament (2) after the previous heat curing is cooled so that the temperature of the optical fiber filament (2) before entering the next coating machine (3) is within the preset coating temperature range.

8. The novel multi-pass polyimide optical fiber coating and drawing process according to claim 1, characterized in that: The tension of the optical fiber filament (2) at the guide wheel before entering the curing oven group (5) and the guide wheel after leaving the curing oven group (5) is detected, and the traction speed is adjusted according to the detection results so that the tension of the optical fiber filament (2) is kept within a preset range during the folding operation.

9. The novel multi-pass polyimide optical fiber coating and drawing process according to claim 1, characterized in that: After each layer of polyimide coating is completed, the outer diameter of the optical fiber (2) is detected online, and the coating amount, traction speed and curing parameters of the coating device (3) are adjusted according to the detection results.

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