Pre-oxidation system and preparation system of polyacrylonitrile-based large tow carbon fiber

Abstract

The utility model relates to the field of big tow carbon fiber preparation discloses preoxidation system and polyacrylonitrile based big tow carbon fiber's preparation system. The preoxidation system includes primary oxidation unit and secondary oxidation unit, the primary oxidation unit includes first oxidizing furnace and second traction device, and the export end of second traction device is connected with the secondary oxidation unit. The system can slow lifting the bulk density and the cyclization rate of preoxidized yarn, effectively reduces carbon fiber strength uneven rate, modulus uneven rate and elongation uneven rate.

Description

Technical Field

[0001] This utility model relates to the field of large-tow carbon fiber preparation, specifically to a pre-oxidation system and a preparation system for polyacrylonitrile-based large-tow carbon fiber. Background Technology

[0002] During the pre-oxidation process of polyacrylonitrile-based precursor fibers, highly oriented polyacrylonitrile-based precursor fibers undergo physical shrinkage. In the initial stage of oxidation, as the heat treatment temperature increases, the internal macromolecular chains of the fiber are heated and coiled, causing physical shrinkage and leading to a continuous increase in fiber thermal stress. When the heat treatment temperature exceeds the glass transition temperature of the polyacrylonitrile-based fiber, the mobility of the internal macromolecular chains of the fiber increases, and relative slippage occurs between chain segments. The fiber thermal stress shows a downward trend, resulting in the appearance of physical stress peaks.

[0003] As the heat treatment temperature continues to rise, polyacrylonitrile (PA) fibers begin to undergo chemical reactions such as oxidation and cyclization. These reactions cause cyclization and cross-linking between macromolecular chain segments, leading to further chemical shrinkage. As the chemical reactions intensify, when the thermal shrinkage caused by the chemical reactions exceeds the thermal relaxation caused by chain slippage, the fiber stress begins to increase. When the heat treatment temperature is sufficiently high, chain segment cleavage causes the fiber stress to decrease until the ultimate heat resistance temperature of the PA fiber is reached, resulting in fiber breakage and a sharp drop in stress, thus creating a chemical stress peak. Applying tension stretching can control the degree of shrinkage caused by the chemical reactions. Therefore, applying tension stretching during the pre-oxidation process is an effective measure to suppress physical shrinkage and control chemical shrinkage.

[0004] Currently, in the industrial production of carbon fiber, the draw ratio of each oxidation zone is controlled by a single process during the pre-oxidation process.

[0005] CN111101241B discloses a manufacturing method for improving the strength of carbon fibers. This method involves dividing the pre-oxidation process into four sequential zones during carbon fiber production, and increasing the oxygen concentration in the reaction atmosphere of the first, second, and third oxidation zones. During oxidation, more oxygen diffuses from the fiber sheath into the fiber core to participate in the oxidation reaction, rapidly increasing the speed of the oxidation and cyclization reactions, effectively shortening the total oxidation time to 20-32 minutes. This significantly reduces the electricity consumption of the oxidation furnace during oxidation operation, substantially lowering production and operating costs. Simultaneously, this method also improves the uniformity of oxygen distribution in the fiber's radial direction, reduces the sheath-core structure of the pre-oxidized fiber, reduces radial defects in the carbon fiber during carbonization, and improves the carbon fiber's strength. However, this technology requires control of the atmosphere concentration within the oxidation chamber during the pre-oxidation process, increasing the design and operational requirements of the oxidation furnace.

[0006] CN114481367A discloses a method for preparing 35K large-tow carbon fiber. The method involves placing 35K large-tow polyacrylonitrile fibers in an oxidation furnace for pre-oxidation in air to obtain 35K large-tow carbon fiber pre-oxidized fibers. The pre-oxidized fibers are then subjected to low-temperature carbonization, followed by high-temperature carbonization, and finally surface treatment, sizing, and drying to produce 35K large-tow polyacrylonitrile carbon fiber. This method effectively solves the core-sheath structure problem in large-tow pre-oxidation. However, this technology uses a gradient heating method with six oxidation furnaces, requiring six furnaces to produce the pre-oxidized fibers. The large number of furnaces increases the need for circulating fans and exhaust fans, resulting in high equipment investment and production costs. Utility Model Content

[0007] The purpose of this invention is to overcome the problems of uneven oxidation and cyclization reactions during the pre-oxidation of polyacrylonitrile-based carbon fiber precursors, resulting in uneven strength, modulus, and elongation of the produced large-tow carbon fibers. This invention provides a pre-oxidation system and a preparation system for polyacrylonitrile-based large-tow carbon fibers. This system can alleviate the disorientation of polyacrylonitrile macromolecular chain segments, promote cyano cyclization, increase the bulk density and cyclization rate of the pre-oxidized fibers, and effectively reduce the unevenness of carbon fiber strength, modulus, and elongation.

[0008] To achieve the above objectives, such as Figures 1 to 4 As shown, this utility model provides a pre-oxidation system, which includes a primary oxidation unit and a secondary oxidation unit. The primary oxidation unit includes a first oxidation furnace 3 and a second traction device 4, and the outlet end of the second traction device 4 is connected to the secondary oxidation unit.

[0009] The first oxidation furnace 3 is equipped with n metal rollers on its exterior. The second traction device 4, which is connected to the first oxidation furnace 3, is provided with (n+1) / m traction zones, where m is an even number from 4 to 10 and n+1 is a multiple of m and n+1≤20. The n metal rollers are used to guide the filament bundle to pass through the furnace chamber of the first oxidation furnace 3 in an “S” shaped path to form n layers of filament feeding. The furnace wall of the first oxidation furnace 3 is provided with filament bundle inlet and filament bundle outlet corresponding to each filament feeding layer. Each traction zone of the second traction device 4 is provided with a traction inlet and a traction outlet, so that the filament bundle enters the second traction device 4 for n+1 / m tractions during the n-layer filament feeding process.

[0010] The second aspect of this invention provides a system for preparing polyacrylonitrile-based large-tow carbon fibers, which includes the pre-oxidation system and post-treatment device described in this invention.

[0011] Compared with the prior art, this utility model has at least the following beneficial effects:

[0012] The pre-oxidation system of this invention controls the roller speed of the first oxidation furnace by setting up (n+1) / m level traction zones to oxidize and stretch the carbon fiber precursor in stages. By controlling the oxidation tension in stages, physical shrinkage and chemical shrinkage can be carried out more efficiently and orderly, thereby improving the density of the pre-oxidized filament and the cyclization rate of the pre-oxidized filament.

[0013] The preparation system for polyacrylonitrile-based large-tow carbon fibers of this invention not only alleviates the disorientation of polyacrylonitrile macromolecular chains and promotes cyano cyclization, but also effectively controls the oxidation and cyclization reactions to proceed smoothly during the oxidation process, improving the stability of the oxidation reaction. This not only improves the tensile strength, modulus, and elongation of polyacrylonitrile-based large-tow carbon fibers, but also reduces the strength unevenness, modulus unevenness, and elongation unevenness of polyacrylonitrile-based large-tow carbon fibers, thereby reducing production costs. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the structure of the preparation system of polyacrylonitrile-based large-tow carbon fiber in a preferred embodiment of this utility model;

[0015] Figure 2 This is a side view of the first oxidation furnace 3 in a preferred embodiment of this utility model;

[0016] Figure 3 This is a front view of the second traction device 4 in a preferred embodiment of this utility model;

[0017] Figure 4 This is a side view of the second traction device 4 in a preferred embodiment of the present invention;

[0018] Figure 5 This is a top view of the second traction device 4 in a preferred embodiment of this utility model.

[0019] Explanation of reference numerals in the attached figures

[0020] 1. Yarn frame; 2. First traction device; 3. First oxidation furnace; 4. Second traction device; 5. Second oxidation furnace; 6. Third traction device; 7. Third oxidation furnace; 8. Fourth traction device; 9. Fourth oxidation furnace; 10. Fifth traction device; 11. Low-temperature carbonization furnace; 12. Sixth traction device; 13. High-temperature carbonization furnace; 14. Seventh traction device; 15. Electrolytic cell; 16. Washing tank; 17. First dryer; 18. Sizing tank; 19. Second dryer; 20. Eighth traction device; 21. Winding and take-up machine;

[0021] 31. First metal roller at the inlet end; 33. Second metal roller at the inlet end; 35. Third metal roller at the inlet end; 37. Fourth metal roller at the inlet end; 39. Fifth metal roller at the inlet end; 311. Sixth metal roller at the inlet end; 32. First metal roller at the outlet end; 34. Second metal roller at the outlet end; 36. Third metal roller at the outlet end; 38. Fourth metal roller at the outlet end; 310. Fifth metal roller at the outlet end;

[0022] 41. Traction Roller 1; 42. Traction Roller 2; 43. Traction Roller 3; 44. Traction Roller 4; 45. Traction Roller 5; 46. Traction Roller 6; 47. Traction Roller 7; 48. Traction Roller 8; 49. Traction Roller 9; 410. Guide Roller; 411. Pressure Roller; 412. First-level Traction Zone; 413. Second-level Traction Zone; 414. Third-level Traction Zone Detailed Implementation

[0023] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0024] In this utility model, unless otherwise stated, directional terms such as "upper," "lower," "left," and "right" generally refer to the upper, lower, left, and right positions shown in the accompanying drawings; "inner" and "outer" refer to the inner and outer positions relative to the outline of each component; and "upper," "lower," "top," and "bottom" are generally descriptive terms describing the relative positions of the components in relation to the directions shown in the accompanying drawings or in relation to vertical, perpendicular, or gravitational directions.

[0025] In this utility model, "device" refers to a unit composed of various components that have the same function and / or perform related functions.

[0026] In this utility model, "traction unit" refers to a unit composed of traction rollers and various components with power and / or driving functions.

[0027] In this utility model, the "oxidation furnace" is made of steel plate and consists of a heating chamber, a process chamber and a porch. The heating chamber has a circulating fan and an electric heating system.

[0028] like Figures 1 to 4 As shown, this utility model provides a pre-oxidation system, which includes a primary oxidation unit and a secondary oxidation unit. The primary oxidation unit includes a first oxidation furnace 3 and a second traction device 4, and the outlet end of the second traction device 4 is connected to the secondary oxidation unit.

[0029] The first oxidation furnace 3 is equipped with n metal rollers on its exterior. The second traction device 4, which is connected to the first oxidation furnace 3, is provided with (n+1) / m traction zones, where m is an even number from 4 to 10 and n+1 is a multiple of m and n+1≤20. The n metal rollers are used to guide the filament bundle to pass through the furnace chamber of the first oxidation furnace 3 in an “S” shaped path to form n layers of filament feeding. The furnace wall of the first oxidation furnace 3 is provided with filament bundle inlet and filament bundle outlet corresponding to each filament feeding layer. Each traction zone of the second traction device 4 is provided with a traction inlet and a traction outlet, so that the filament bundle enters the second traction device 4 for n+1 / m tractions during the n-layer filament feeding process.

[0030] In this invention, the pre-oxidation system controls the roller speed of the first oxidation furnace by setting up (n+1) / m level traction zones to oxidize and stretch the carbon fiber precursor in stages. By controlling the oxidation tension in stages, physical shrinkage and chemical shrinkage can be carried out more efficiently and orderly, thereby improving the density and cyclization rate of the pre-oxidized fiber.

[0031] In one embodiment of this utility model, (n+1) / 2 metal rollers are arranged sequentially from bottom to top on the outside of the inlet side of the first oxidation furnace 3, and (n-1) / 2 metal rollers are arranged sequentially from bottom to top on the outside of the outlet side of the first oxidation furnace 3.

[0032] The first oxidation furnace 3 has a wire feeding zone consisting of m layers from bottom to top, which corresponds one-to-one with the traction zone from bottom to top in the second traction device 4. The wire bundle outlet of the (m-1)th wire feeding zone in each wire feeding zone is set to correspond to the traction inlet of the corresponding traction zone, and the wire bundle inlet of the mth wire feeding zone is set to correspond to the traction outlet of the corresponding traction zone. The traction outlet of the (n+1) / mth traction zone in the second traction device 4 is set to correspond to the inlet of the secondary oxidation unit.

[0033] For example, when m takes the value 4 and n takes the value 11, such as Figures 1-4As shown, in one embodiment of this utility model, the first oxidation furnace 3 is provided with 11 metal rollers forming 11 layers of wire-feeding layers, and the second traction device 4 is provided with 3 traction zones. Six metal rollers are arranged sequentially from bottom to top at the inlet end of the first oxidation furnace 3, and five metal rollers are arranged sequentially from bottom to top at the outlet end. The carbon fiber precursor is drawn by the first metal roller 31 at the inlet end and enters the first oxidation furnace 3 through the inlet of the first wire-feeding layer. The wire-feeding layer is drawn sequentially by the first metal roller 32 at the outlet end and the second metal roller 33 at the inlet end, then enters the second traction device 4 through the outlet of the third wire-feeding layer. After being drawn for the first time by the first traction zone 412, it is drawn by the second metal roller 34 at the outlet end and returns to the first traction zone 4 through the inlet of the fourth wire-feeding layer. Oxidation furnace 3; the wire bundle of the wire feeding layer is sequentially drawn by the third metal roller 35 at the inlet end, the third metal roller 36 at the outlet end, and the fourth metal roller 37 at the inlet end, and then re-enters the second traction device 4 through the outlet of the seventh wire feeding layer, and after being drawn for the second time through the second-stage traction area 413, it is drawn by the fourth metal roller 38 at the outlet end and returns to the first oxidation furnace 3 through the inlet of the eighth wire feeding layer; the wire bundle of the wire feeding layer is sequentially drawn by the fifth metal roller 39 at the inlet end, the fifth metal roller 310 at the outlet end, and the sixth metal roller 311 at the inlet end, and then re-enters the second traction device 4 through the outlet of the eleventh wire feeding layer, and after being drawn for the third time through the third-stage traction area 414, the wire bundle is driven to the second oxidation furnace 5 through the traction outlet of the third-stage traction area 414.

[0034] According to one embodiment of the present invention, each traction area is provided with a traction unit, and the draw ratio of the traction unit in the second traction device 4 formed on the filament bundle gradually decreases from bottom to top.

[0035] Each traction unit includes at least three traction rollers. In each wire feeding region, the wire of the (m-1)th wire feeding layer passes through the wire bundle outlet and the traction inlet of the corresponding traction region, and then passes through the traction rollers in the traction unit from bottom to top to complete the corresponding drafting.

[0036] For example, when the traction unit includes three traction rollers, such as Figure 5 As shown, three traction rollers and components with power and / or drive functions constitute a traction unit. In this invention, the components with power and / or drive functions are conventional components in the art, as long as they can achieve the purpose of this invention, they will not be described in detail here.

[0037] For example, when m is 4, n is 11, and each traction unit is equipped with three traction rollers, such as... Figure 4As shown, in one embodiment of this utility model, the second traction device 4 is a vertical nine-roller traction device, with nine traction rollers arranged sequentially from bottom to top. Traction roller 1 41 draws the filament bundle from the outlet of the third layer of the first oxidation furnace 3 into the second traction device 4, and the first drawing is completed by traction roller 2 42 and traction roller 3 43; traction roller 44 draws the filament bundle from the outlet of the seventh layer of the first oxidation furnace 3 into the second traction device 4, and the second drawing is completed by traction roller 5 45 and traction roller 6 46; traction roller 7 47 draws the filament bundle from the outlet of the eleventh layer of the first oxidation furnace 3 into the second traction device 4, and the third drawing is completed by traction roller 8 48 and traction roller 9 49.

[0038] According to one embodiment of this utility model, such as Figure 4 As shown, a pressure roller 411 is provided on the side wall of the (n+1) / m stage traction area of ​​the second traction device 4, which is used to clamp the yarn bundle and stop the operation of the yarn bundle when it is necessary to stop the yarn feeding.

[0039] According to one embodiment of this utility model, such as Figure 4 As shown, guide rollers 410 are provided for guiding the filament bundle to the secondary oxidation unit.

[0040] In one embodiment of this utility model, such as Figure 1 As shown, the secondary oxidation unit includes a first oxidation furnace 3, a second traction device 4, a second oxidation furnace 5, a third traction device 6, a third oxidation furnace 7, a fourth traction device 8, a fourth oxidation furnace 9, and a fifth traction device 10 connected in series.

[0041] The second oxidation furnace 5, the third oxidation furnace 7, and the fourth oxidation furnace 9 are equipped with 11 metal rollers to form 11 wire feeding layers.

[0042] The third traction device 6, the fourth traction device 8, and the fifth traction device 10, which are respectively connected to the second oxidation furnace 5, the third oxidation furnace 7, and the fourth oxidation furnace 9, are vertical six-roller traction devices.

[0043] The second aspect of this invention provides a system for preparing polyacrylonitrile-based large-tow carbon fibers, which includes the pre-oxidation system and post-treatment device described in this invention.

[0044] The preparation system for polyacrylonitrile-based large-tow carbon fibers of this invention not only alleviates the disorientation of polyacrylonitrile macromolecular chains and promotes cyano cyclization, but also effectively controls the oxidation and cyclization reactions to proceed smoothly during the oxidation process, improving the stability of the oxidation reaction. This not only improves the tensile strength, modulus, and elongation of polyacrylonitrile-based large-tow carbon fibers, but also reduces the strength unevenness, modulus unevenness, and elongation unevenness of polyacrylonitrile-based large-tow carbon fibers, thereby reducing production costs.

[0045] According to one embodiment of this utility model, such as Figure 1 As shown, the post-processing device includes a low-temperature carbonization furnace 11, a sixth traction device 12, a high-temperature carbonization furnace 13, a seventh traction device 14, an electrolytic cell 15, a washing tank 16, a first dryer 17, a sizing tank 18, a second dryer 19, an eighth traction device 20, and a winding and take-up machine 21, which are connected in series.

[0046] In this invention, the low-temperature carbonization furnace 11 is used for low-temperature carbonization of carbon fibers, the high-temperature carbonization furnace 13 is used for high-temperature carbonization of carbon fibers, the electrolytic cell 15 is used for carbon fiber surface treatment, the washing tank is used for washing carbon fibers after surface treatment, the first dryer 17 is used for drying carbon fibers after washing, the sizing tank 18 is used for sizing carbon fibers, the second dryer 19 is used for drying carbon fibers after sizing, the winding and take-up machine 21 is used for winding and take-up of carbon fibers, and the sixth traction device 12, the seventh traction device 14, and the eighth traction device 20 are used for drawing carbon fibers. These devices are all conventional in the art and can be replaced by various functional units with the same function. This invention is only illustrative and does not limit the scope of this invention.

[0047] According to one embodiment of the present invention, the sixth traction device 12 is a vertical six-roller traction device.

[0048] According to one embodiment of the present invention, the seventh traction device 14 is a vertical six-roller traction device.

[0049] According to one embodiment of the present invention, the eighth traction device 20 is a horizontal five-roller traction device.

[0050] According to one embodiment of the present invention, the low-temperature carbonization furnace 11 is provided with 6 heating zones.

[0051] According to one embodiment of the present invention, the high-temperature carbonization furnace 13 is provided with 6 heating zones.

[0052] According to one embodiment of this utility model, such as Figure 1 As shown, the preparation system for polyacrylonitrile-based large-tow carbon fiber also includes: a yarn frame 1 and a first traction device 2;

[0053] The yarn frame 1 is used to unwind the polyacrylonitrile-based carbon fiber precursor and guide it to the primary oxidation unit via the first traction device 2.

[0054] According to one embodiment of the present invention, the first traction device 2 is a vertical four-roller traction device.

[0055] The preparation system of this invention can be used, for example, to prepare polyacrylonitrile-based large-tow carbon fibers according to the following steps:

[0056] Includes the following steps:

[0057] Step 1 Pre-oxidation

[0058] In this invention, the pre-oxidation production process is carried out in four oxidation furnaces divided into four heating zones, namely, the first oxidation furnace 3, the second oxidation furnace 5, the third oxidation furnace 7, and the fourth oxidation furnace 9. The number of metal rollers installed at the inlet and outlet ends of each oxidation furnace is the same, and the filament bundles run along the same path in each oxidation furnace. After the pre-oxidation is completed, pre-oxidized filaments are obtained.

[0059] In one embodiment of this utility model, 6 metal rollers are installed at the inlet end of each oxidation furnace and 5 metal rollers are installed at the outlet end. The number of layers of the filament bundle in each oxidation furnace is 11.

[0060] In one embodiment of this utility model, the pre-oxidation time is the same for each oxidation furnace, and the total pre-oxidation time is 30 to 80 minutes.

[0061] In one embodiment of this utility model, the temperature of the first oxidation furnace 3 is 150-250°C, preferably 222-230°C.

[0062] In one embodiment of this utility model, the temperature of the second oxidation furnace 5 is 150-280°C, preferably 234-243°C.

[0063] In one embodiment of this utility model, the temperature of the third oxidation furnace 7 is 150-280°C, preferably 245-257°C.

[0064] In one embodiment of this utility model, the temperature of the fourth oxidation furnace 9 is 150-300°C, preferably 255-270°C.

[0065] In one embodiment of this utility model, the second traction device 4 is a vertical nine-roller traction device, which is installed at the outlet of the first oxidation furnace 3 and can be divided into three areas to control the roller speed.

[0066] In one embodiment of this utility model, the first-stage traction region 412 of the second traction device 4 controls the draw ratio to be 1.000 to 1.200, preferably 1.050 to 1.086.

[0067] In one embodiment of this utility model, the second-stage traction region 413 of the second traction device 4 controls the draw ratio to be 1.000 to 1.100, preferably 1.020 to 1.055.

[0068] In one embodiment of this utility model, the third-stage traction region 414 of the second traction device 4 controls the draw ratio to be 1.000 to 1.100, preferably 1.010 to 1.025.

[0069] In one embodiment of this utility model, the third traction device 6 installed at the outlet of the second oxidation furnace 5 is a vertical six-roller device, which controls the draw ratio of the filament bundle in the second oxidation temperature zone to be 0.950 to 0.998, preferably 0.980 to 0.990.

[0070] In one embodiment of this utility model, the fourth traction device 8 installed at the outlet of the third oxidation furnace 7 is a vertical six-roller device, which controls the draw ratio of the filament bundle in the third oxidation temperature zone to be 0.950 to 0.998, preferably 0.969 to 0.980.

[0071] In one embodiment of this utility model, the fifth traction device 10 installed at the outlet of the fourth oxidation furnace 9 is a vertical six-roller device, which controls the draw ratio of the filament bundle in the fourth oxidation temperature zone to be 0.950 to 0.998, preferably 0.980 to 0.990.

[0072] Step 2 Low-temperature carbonization

[0073] In one embodiment of this utility model, the low-temperature carbonization production process is carried out in a low-temperature carbonization furnace 11, which is divided into 6 heating zones with temperatures of 0-600℃, 0-600℃, 0-700℃, 0-700℃, 0-900℃, and 0-900℃, respectively.

[0074] In one embodiment of this utility model, the draw ratio is controlled to be 1.000 to 1.300 during operation in the low-temperature carbonization furnace 11, and the total residence time in the low-temperature carbonization furnace is 0 to 10 minutes.

[0075] Step 3 High-temperature carbonization

[0076] In one embodiment of this utility model, the high-temperature carbonization production process is carried out in a high-temperature carbonization furnace 13, which is divided into 6 heating zones with temperatures of 0-1300℃, 0-1500℃, 0-1700℃, 0-1950℃, 0-1950℃, and 0-1950℃, respectively.

[0077] In one embodiment of this utility model, the draw ratio is controlled to be 0.600 to 0.990 during operation in the high-temperature carbonization furnace 13, and the total residence time in the high-temperature carbonization furnace is 0 to 10 minutes.

[0078] Step 4: Surface treatment and water washing

[0079] In one embodiment of this utility model, the filament bundle from the outlet of the high-temperature carbonization furnace 13 enters the electrolytic cell 15 and the water washing tank 16 sequentially via the seventh traction device 14. The present utility model uses ammonium sulfate aqueous solution as electrolyte, voltage of 20V, electrolyte concentration of 13%, residence time of filament bundle in electrolyte of 2.5min, water washing flow rate of 4550L / hour, and water washing temperature of 48℃ as exemplary conditions, and does not limit the scope of this utility model.

[0080] Step 5: Sizing and Drying

[0081] In one embodiment of this utility model, the filament bundles from the outlet of the washing tank 16 sequentially enter the first dryer 17, the sizing tank 18, and the second dryer 19.

[0082] The following conditions are used as examples in this utility model and are not intended to limit the scope of this utility model. For example, the drying temperature of the first dryer 17 is 110°C, and the modified epoxy resin emulsion carbon fiber sizing agent of model SP-2 produced by the Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences is used. The sizing agent concentration in the sizing tank 18 is 2.8%, the immersion time is 50s, and the sizing carbon fiber enters the second dryer 19 for drying at a temperature of 165°C.

[0083] Step 6: Winding and winding

[0084] In one embodiment of this utility model, the sized and dried carbon fiber enters the carbon fiber winding and winding machine 21, and is wound and wound under a tension of 2500~3200cN (tension decreases linearly with the roll diameter) to obtain polyacrylonitrile-based large tow carbon fiber.

[0085] The present invention will be described in detail below through embodiments.

[0086] In the following embodiments,

[0087] Total draw ratio in the first oxidation temperature zone = first draw ratio × second draw ratio × ... nth draw ratio;

[0088] Total draw ratio of oxidation = Total draw ratio of first temperature zone × Draw ratio of second temperature zone × Draw ratio of third temperature zone × Draw ratio of fourth temperature zone;

[0089] The bulk density parameter was measured using the national standard GB / T 30019-2013 "Method for Determination of Carbon Fiber Density";

[0090] The cyclization rate parameter was measured using infrared spectroscopy, and the formula for calculating the cyclization rate is as follows:

[0091]

[0092] In the formula,

[0093] I C≡N —The intensity of the characteristic absorption peak of the stretching vibration of the —C≡N triple bond at wavenumber 2240 cm⁻¹;

[0094] I C＝N —Intensity of the characteristic absorption peak of the stretching vibration at wavenumber 1630 cm⁻¹ —C=N—.

[0095] The tensile strength and tensile strength dispersion coefficient, modulus and modulus dispersion coefficient, elongation and elongation dispersion coefficient parameters were measured using the national standard GB / T 3362-2017 "Test Method for Tensile Properties of Carbon Fiber Multifilament".

[0096] The raw materials for 48k carbon fiber, 55k carbon fiber, 60k carbon fiber, 96k carbon fiber, 130k carbon fiber, and 200k carbon fiber are SF-3-48k precursor yarn, SF-3-55k precursor yarn, SF-3-60k precursor yarn, SF-3-96k precursor yarn, SF-3-130k precursor yarn, and SF-3-200k precursor yarn, respectively, from Sinopec Shanghai Petrochemical Co., Ltd.

[0097] Comparative Example 1:

[0098] 100 strands of 60K precursor fiber are used for industrial production of carbon fiber, such as Figure 1 As shown, 60K raw yarn bundles are sequentially unwound from yarn rack 1, first traction device 2, first oxidation furnace 3, second traction device 4, second oxidation furnace 5, third traction device 6, third oxidation furnace 7, fourth traction device 8, fourth oxidation furnace 9, fifth traction device 10, low-temperature carbonization furnace 11, sixth traction device 12, high-temperature carbonization furnace 13, seventh traction device 14, electrolytic cell 15, washing tank 16, first dryer 17, sizing tank 18, second dryer 19, eighth traction device 20, and winding and winding machine 21 to produce 60K carbon fiber.

[0099] The first oxidation furnace 3 is equipped with 11 metal rollers on its exterior, and the second traction device 4 is a vertical six-roller device with a first-level traction area.

[0100] Step 1: Pre-oxidation

[0101] The temperatures of the four oxidation furnace zones are 227℃, 240℃, 253℃, and 266℃, respectively.

[0102] The draw ratios of the second, fourth, sixth, and eighth traction devices are 1.117, 0.984, 0.977, and 0.984, respectively.

[0103] The total pre-oxidation time is 50 min.

[0104] Step 2: Low-temperature carbonization

[0105] The low-temperature carbonization furnace 11 is divided into 6 zones with temperatures of 370℃, 450℃, 520℃, 560℃, 690℃, and 630℃. The draw ratio is controlled at 1.068, and the total residence time in the low-temperature carbonization furnace 11 is 1.5 min.

[0106] Step 3: High-temperature carbonization

[0107] The high-temperature carbonization furnace 13 is divided into 6 zones with temperatures of 1080℃, 1340℃, 1485℃, 1485℃, 1485℃, and 1340℃ respectively. The draw ratio is controlled at 0.948, and the total residence time in the high-temperature carbonization furnace 13 is 1.5 min.

[0108] Step 4: Surface treatment and washing

[0109] The fiber bundles exiting the high-temperature carbonization furnace 13 are sequentially drawn into the electrolytic cell 15 and the water washing tank 16 via the seventh traction device 14. Ammonium sulfate aqueous solution is used as the electrolyte, the voltage is 20V, the electrolyte concentration is 13%, and the residence time of the fiber bundles in the electrolyte is 2.5min. The water washing flow rate is 4550L / hour, and the water washing temperature is 48℃.

[0110] Step 5: Sizing and Drying

[0111] The filament bundles from the outlet of the washing tank 16 sequentially enter the first dryer 17, the sizing tank 18, and the second dryer 19.

[0112] The drying temperature of the first dryer 17 is 110℃. A modified epoxy resin emulsion-type carbon fiber sizing agent, model SP-2, produced by the Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, is used. Impregnation sizing is employed, with the sizing agent concentration in the sizing tank 18 at 2.8% and an impregnation time of 50 seconds. The sized carbon fiber then enters the second dryer 19 for drying at 165℃.

[0113] Step 6: Winding and winding the yarn

[0114] After sizing and drying, the carbon fiber enters the carbon fiber winding and take-up machine 21 and is wound and taken up under a tension of 2500~3200cN (tension decreases linearly with the roll diameter) to obtain 60K carbon fiber.

[0115] Example 1

[0116] In Example 1, the second traction device 4 uses the vertical nine-roller traction device proposed in this utility model. The device employing this utility model, such as... Figures 1-5 As shown, with n=11 and m=4, carbon fiber is industrially produced by employing graded oxidation drawing and graded control of oxidation tension. The specific process includes pre-oxidation, low-temperature carbonization, high-temperature carbonization, surface treatment, washing, sizing, drying, and winding / winding.

[0117] In this Example 1, the specific processes of low-temperature carbonization, high-temperature carbonization, surface treatment, water washing, sizing, drying, and winding are the same as those in Comparative Example 1, and the process parameters are the same.

[0118] The specific process of the pre-oxidation production step in Example 1 is different from that in Comparative Example 1. The oxidation production steps are as follows:

[0119] The temperatures of the four oxidation furnace zones are 227℃, 240℃, 253℃, and 266℃, respectively.

[0120] The second traction device performs three traction operations with traction ratios of 1.063, 1.032, and 1.018 respectively, for a total traction ratio of 1.117. The traction ratios of the fourth, sixth, and eighth traction devices are 1.117, 0.984, 0.977, and 0.984 respectively.

[0121] The second traction device 4 is different from Comparative Example 1. The second traction device is a vertical nine-roller traction device, which adopts a graded oxidation stretching and graded control of oxidation tension.

[0122] During the implementation process, samples were taken at the outlet of each oxidation furnace to determine the oxidation performance indicators, which are shown in Table 1; the carbon fiber performance indicators are shown in Table 2.

[0123] Table 1 Performance Indicators of Pre-oxidized Fiber

[0124]

[0125] Table 2 Performance Indicators of Carbon Fiber

[0126]

[0127] As can be seen from the results in Tables 1 and 2, the polyacrylonitrile-based large-tow carbon fiber prepared by the polyacrylonitrile-based large-tow carbon fiber preparation system of this invention has higher tensile strength, modulus and elongation, and significantly lower strength unevenness, modulus unevenness and elongation unevenness. The volume density and cyclization rate of the pre-oxidized fiber are also higher.

[0128] The preferred embodiments of this utility model have been described in detail above; however, this utility model is not limited thereto. Within the scope of the technical concept of this utility model, various simple modifications can be made to the technical solution of this utility model, including combining the various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed by this utility model and are all within the protection scope of this utility model.

Claims

1. A pre-oxidation system, characterized in that, The pre-oxidation system includes a primary oxidation unit and a secondary oxidation unit. The primary oxidation unit includes a first oxidation furnace (3) and a second traction device (4). The outlet end of the second traction device (4) is connected to the secondary oxidation unit. The first oxidation furnace (3) is equipped with n metal rollers on its exterior. The second traction device (4) connected to the first oxidation furnace (3) is equipped with (n+1) / m traction zones, where m is an even number from 4 to 10 and n+1 is a multiple of m and n+1≤20. The n metal rollers are used to guide the filament bundle to pass through the furnace chamber of the first oxidation furnace (3) in an "S" shaped path to form n layers of filament. The furnace wall of the first oxidation furnace (3) is provided with filament bundle inlet and filament bundle outlet corresponding to each layer of filament. Each traction zone of the second traction device (4) is provided with traction inlet and traction outlet, so that the filament bundle enters the second traction device (4) for (n+1) / m tractions during the n-layer filament process.

2. The pre-oxidation system according to claim 1, characterized in that, The inlet side of the first oxidation furnace (3) is provided with (n+1) / 2 metal rollers from bottom to top, and the outlet side of the first oxidation furnace (3) is provided with (n-1) / 2 metal rollers from bottom to top. The first oxidation furnace (3) has a wire feeding area with each m wire feeding layer from bottom to top as a wire feeding area, which corresponds one-to-one with the traction area from bottom to top in the second traction device (4). The wire bundle outlet of the (m-1)th wire feeding layer in each wire feeding area is set to correspond to the traction inlet of the corresponding traction area, and the wire bundle inlet of the mth wire feeding layer is set to correspond to the traction outlet of the corresponding traction area. The traction outlet of the (n+1) / m stage traction zone in the second traction device (4) is set to correspond to the inlet of the secondary oxidation unit.

3. The pre-oxidation system according to claim 2, characterized in that, Each traction area is equipped with a traction unit, and the draw ratio of the traction unit in the second traction device (4) gradually decreases from bottom to top; Each traction unit includes at least three traction rollers. In each wire feeding region, the wire of the (m-1)th wire feeding layer passes through the wire bundle outlet and the traction inlet of the corresponding traction region, and then passes through the traction rollers in the traction unit from bottom to top to complete the corresponding drafting.

4. The pre-oxidation system according to claim 3, characterized in that, The second traction device (4) has pressure rollers (411) installed on the side wall of the (n+1) / m stage traction zone, used to clamp the yarn bundle and stop its operation when it is necessary to stop the yarn feeding; and / or A guide roller (410) is provided for guiding the filament bundle to the secondary oxidation unit.

5. The pre-oxidation system according to claim 1, characterized in that, The secondary oxidation unit includes a second oxidation furnace (5), a third traction device (6), a third oxidation furnace (7), a fourth traction device (8), a fourth oxidation furnace (9), and a fifth traction device (10) connected in series. The second oxidation furnace (5), the third oxidation furnace (7), and the fourth oxidation furnace (9) are equipped with n metal rollers to form n layers of wire feeding layers; The third traction device (6), the fourth traction device (8), and the fifth traction device (10) are vertical six-roller traction devices.

6. A system for preparing polyacrylonitrile-based large-tow carbon fibers, characterized in that, The preparation system for polyacrylonitrile-based large-tow carbon fibers includes the pre-oxidation system and post-treatment device as described in any one of claims 1-5.

7. The preparation system for polyacrylonitrile-based large-tow carbon fibers according to claim 6, characterized in that, The post-processing device includes a low-temperature carbonization furnace (11), a sixth traction device (12), a high-temperature carbonization furnace (13), a seventh traction device (14), an electrolytic cell (15), a water washing tank (16), a first dryer (17), a sizing tank (18), a second dryer (19), an eighth traction device (20), and a winding and take-up machine (21), which are connected in series.

8. The preparation system for polyacrylonitrile-based large-tow carbon fibers according to claim 7, characterized in that, The sixth traction device (12) is a vertical six-roller traction device; and / or The seventh traction device (14) is a vertical six-roller traction device; and / or The eighth traction device (20) is a horizontal five-roller traction device.

9. The preparation system for polyacrylonitrile-based large-tow carbon fibers according to claim 7, characterized in that, The low-temperature carbonization furnace (11) is provided with 6 heating zones; and / or The high-temperature carbonization furnace (13) is equipped with 6 heating zones.

10. The preparation system for polyacrylonitrile-based large-tow carbon fibers according to claim 6, characterized in that, The preparation system for polyacrylonitrile-based large-tow carbon fibers also includes: a yarn frame (1) and a first traction device (2); The yarn frame (1) is used to guide the unwound polyacrylonitrile filaments through the first traction device (2) to the primary oxidation unit; and / or The first traction device (2) is a vertical four-roller traction device.

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