Polyacrylonitrile-based carbon fiber and preparation method thereof

Abstract

The invention relates to polyacrylonitrile-based carbon fibers and a preparation method thereof.The preparation method of the polyacrylonitrile-based carbon fibers comprises the steps that polyacrylonitrile fibers are sequentially subjected to unwinding treatment, pre-oxidation treatment, low-temperature carbonization treatment, high-temperature carbonization treatment and surface treatment, and the polyacrylonitrile-based carbon fibers are obtained; before the pre-oxidation treatment, the fiber tows subjected to unwinding treatment are subjected to first steering treatment through a first steering roller and subjected to second steering treatment through a second steering roller in sequence; wherein the parameters of the first steering treatment are as follows: the steering angle is 10-40 degrees, the fiber tows run for 5-20 m along the first direction, and the tension applied to the fiber tows is 500-1500 cN; wherein the parameters of the second steering treatment are as follows: the steering angle is 10-40 degrees, the fiber tows run for 5-20 m along the second direction, and the tension applied to the fiber tows is 1000-1500 cN; wherein the first direction and the second direction are two opposite directions. The device is mainly used for avoiding fiber bundle abrasion and improving the tension control precision.

Description

Technical Field

[0001] The invention relates to the technical field of carbon fibers, and in particular to a polyacrylonitrile-based carbon fiber and a preparation method thereof. Background Art

[0002] In the process of carbon fiber production, steering generally occurs in processes such as pre-oxidation furnaces and carbonization furnaces. Through steering, carbon fiber tows can be transported along a reasonable path between different production equipment, making the layout of each equipment more compact, reducing production space occupation, and improving site utilization. In addition, reasonable steering can avoid sudden or uneven tow tension and ensure stable force on carbon fiber during production, which is crucial to ensuring the quality and performance of carbon fiber, and can make its strength, modulus and other performance indicators more stable and consistent; at the same time, smooth steering can reduce production abnormalities such as doubling, crossing, twisting, roller entanglement, and broken wires, avoid production interruptions, achieve stable and continuous production, improve production efficiency, and reduce production costs.

[0003] Existing steering technologies mainly include: (1) guide roller steering technology: guide rollers are set in pre-oxidation furnaces, carbonization furnaces and other equipment, and the position and angle of the guide rollers are changed to make the carbon fiber bundles turn along a predetermined path; (2) pulley steering technology: the direction of the bundle is changed by the rotation of the pulley, which is similar to the guide roller, but the rotation of the pulley is more flexible, which can reduce the friction between the bundle and the steering device. It is often used in production links with high requirements for bundle tension and surface quality; (3) airflow steering technology: the carbon fiber bundle is steered with the help of airflow, and the direction, speed and pressure of the airflow are controlled to make the bundle turn as required. It has the advantages of flexible steering and little damage to the bundle, but the equipment is complex, the cost is high, and the process control requirements are strict.

[0004] However, the inventors of the present invention have found that the above-mentioned steering technology has at least the following technical problems:

[0005] (1) There is friction between the steering devices such as guide rollers and pulleys and the tow. If the steering control is unreasonable, it is very easy to cause wear and fluffing on the surface of the tow, thus affecting the performance and appearance quality of the carbon fiber.

[0006] (2) It is difficult to accurately control the tension of the tow using existing steering technology. Tension fluctuations are prone to occur during the steering process, affecting the quality and production stability of the carbon fiber. For high-performance carbon fiber production, insufficient tension control accuracy will reduce product performance indicators.

[0007] (3) Some steering technologies have poor adaptability to carbon fiber tows of different specifications and materials. For example, a steering device works well when processing small tows of carbon fiber, but may cause problems such as poor steering and uneven tension when processing large tows.

[0008] (4) For more complex technologies such as airflow steering, the equipment maintenance cost is high and requires professional personnel to perform maintenance, which increases the company's production cost and technical difficulty. Summary of the invention

[0009] In view of this, the present invention provides a polyacrylonitrile-based carbon fiber and a preparation method thereof, the main purpose of which is to avoid wear of the fiber bundle and improve the control accuracy of the tension.

[0010] In order to achieve the above object, the present invention mainly provides the following technical solutions:

[0011] On the one hand, an embodiment of the present invention provides a method for preparing polyacrylonitrile-based carbon fiber, wherein the method for preparing polyacrylonitrile-based carbon fiber comprises the following steps:

[0012] The polyacrylonitrile fiber is subjected to unwinding treatment, preoxidation treatment, low-temperature carbonization treatment, high-temperature carbonization treatment, and surface treatment in sequence to obtain polyacrylonitrile-based carbon fiber; wherein,

[0013] Before the pre-oxidation treatment, the unwinding fiber tow is sequentially passed through a first turning roller for a first turning treatment and a second turning roller for a second turning treatment; wherein the first turning treatment and the second turning treatment are used to narrow the fiber tow;

[0014] The parameters of the first steering process are as follows: the steering angle is 10-40°, the fiber tow runs 5-20m along the first direction, and the tension applied to the fiber tow is 500-1500cN;

[0015] The parameters of the second steering process are as follows: the steering angle is 10-40°, the fiber tow runs 5-20m along the second direction, and the tension applied to the fiber tow is 1000-1500cN;

[0016] Wherein, the first direction and the second direction are two opposite directions;

[0017] Preferably, the first direction is the direction in which the fiber bundles run upward, and the second direction is the direction in which the fiber bundles run downward.

[0018] Preferably, the fiber bundles after the unwinding process are arranged in groups on the grooved roller; wherein the spacing between two adjacent groups of fiber bundles is 20 to 40 mm; and the spacing between the fiber bundles in each group is 8 to 8.5 mm.

[0019] Preferably, after the fiber bundles after the unwinding treatment undergo the first turning treatment and the second turning treatment, the spacing between two adjacent groups of fiber bundles is reduced from 20 to 40 mm to 0 to 5 mm; the fiber spacing between the fiber bundles in each group is reduced from 8 to 8.5 mm to 7 to 7.5 mm.

[0020] Preferably, after the low-temperature carbonization treatment and before the high-temperature carbonization treatment: the fiber tow after the low-temperature carbonization treatment is sequentially passed through a third turning roller for a third turning treatment and a fourth turning roller for a fourth turning treatment; wherein the fiber tow is narrowed by the third turning treatment and the fourth turning treatment;

[0021] The parameters of the third steering treatment are as follows: the steering angle is 5 to 20°, and the tension applied to the fiber bundle is 500 to 1000 cN;

[0022] The parameters of the fourth steering process are as follows: the steering angle is 5 to 20 degrees, and the tension applied to the fiber bundle is 1500 to 3000 cN.

[0023] Preferably, after the fiber bundles after the low-temperature carbonization treatment are subjected to the third turning treatment and the fourth turning treatment, the spacing between two adjacent groups of fiber bundles remains unchanged; and the fiber spacing of the fiber bundles in each group is reduced from 7 to 7.5 mm to 5 to 5.5 mm.

[0024] Preferably, after the high-temperature carbonization treatment and before the surface treatment: the fiber bundle after the high-temperature carbonization treatment is sequentially passed through a fifth turning roller for a fifth turning treatment and a sixth turning roller for a sixth turning treatment; wherein the fifth turning treatment is used to expand the width of the fiber bundle; and the sixth turning treatment is used to shrink the width of the fiber bundle;

[0025] The parameters of the fifth steering process are as follows: the steering angle is 20-50°, and the tension applied to the fiber bundle is 2000-3000 cN;

[0026] The parameters of the sixth steering process are as follows: the steering angle is 2 to 10°, and the tension applied to the fiber bundle is 2000 to 3000 cN.

[0027] Preferably, after the fibers after high-temperature carbonization treatment undergo the fifth and sixth turning treatments, the spacing between two adjacent groups of fiber bundles increases from 0 to 5 mm to 15 to 20 mm, and the spacing between fiber bundles in each group increases from 5 to 5.5 mm to 6.5 to 7 mm.

[0028] Preferably, the first steering roller and the second steering roller are grooved rollers;

[0029] Preferably, the third steering roller and the fourth steering roller are grooved rollers;

[0030] Preferably, the fifth steering roller and the sixth steering roller are grooved rollers;

[0031] Preferably, the wire path depth on the grooved roller is 1 to 5 mm;

[0032] Preferably, the groove roller includes a first end, a second end and a wire-feeding portion located between the first end and the second end; wherein the wire path is arranged on the wire-feeding portion; wherein the first end and the second end of the groove roller are 10 to 50 mm higher than the wire-feeding portion.

[0033] Preferably, after the fiber bundle after unwinding treatment enters the pre-oxidation furnace after turning treatment, the distance between the two sides of the fiber bundle and the inner wall of the pre-oxidation furnace is 30 to 100 mm; and / or

[0034] After the fiber bundles after low-temperature carbonization treatment enter the high-temperature carbonization furnace after turning treatment, the distance between the two sides of the fiber bundles and the inner wall of the high-temperature carbonization furnace is 30 to 100 mm; and / or

[0035] After the fiber bundles after high-temperature carbonization treatment enter the surface treatment device after deflection treatment, the distance between the fiber bundles and the inner wall of the surface treatment device is 30 to 100 mm; and / or

[0036] The pre-oxidation temperature is 220-270°C; and / or

[0037] The temperature of the low temperature carbonization treatment is 350-800°C; and / or

[0038] The temperature of the high temperature carbonization treatment is 1000-1500°C; and / or

[0039] The mass concentration of the electrolyte used in the surface treatment is 2-8%.

[0040] Preferably, after the surface treatment, it also includes water washing, sizing and drying treatment; preferably, the conductivity of the water used in the water washing treatment is ≤200μs / cm; the concentration of the sizing liquid used in the sizing treatment is 1-2.5wt%; the temperature of the drying treatment is 200-240°C.

[0041] On the other hand, an embodiment of the present invention provides a polyacrylonitrile-based carbon fiber, wherein the polyacrylonitrile-based carbon fiber is prepared by any of the above-mentioned methods for preparing the polyacrylonitrile-based carbon fiber;

[0042] The hairiness of the polyacrylonitrile-based carbon fiber is ≤0.4 g / km; the CV value of the batch tensile strength of the polyacrylonitrile-based carbon fiber is ≤2%, the CV value of the linear density is ≤0.8%, and the CV value of the sizing amount is ≤3%.

[0043] Compared with the prior art, the polyacrylonitrile-based carbon fiber and the preparation method thereof of the present invention have at least the following beneficial effects:

[0044] On the one hand, a method for preparing polyacrylonitrile-based carbon fiber provided by an embodiment of the present invention designs two-stage steering (i.e., the first steering treatment and the second steering treatment) after the unwinding treatment and before the pre-oxidation treatment, and controls the steering angle, running distance, and tension range applied to the fiber bundles of the steering treatment. What needs to be explained about the above scheme is that this embodiment matches the steering angle and tension of the first steering treatment and the second steering treatment, and controls the running distance to achieve steering and width reduction, so as to avoid the filament bundles being fuzzed due to excessive tension or excessive steering. This embodiment reserves an adjustment range for tension control, so as to avoid the fiber index difference and the adaptability problem of fibers of different specifications caused by the tension control accuracy not meeting the standards; in addition, the steering roller and path steering used in this embodiment avoid the high maintenance cost caused by the airflow steering.

[0045] Furthermore, in a method for preparing polyacrylonitrile-based carbon fiber provided in an embodiment of the present invention, two-stage steering (third steering treatment and fourth steering treatment) is designed after low-temperature carbonization treatment and before high-temperature carbonization treatment. Here, this embodiment achieves width reduction by matching the steering angle and tension of the steering treatment. This can avoid the yarn bundle being fuzzed due to excessive tension or excessive steering, and at the same time reserve an adjustment range for tension control, thereby avoiding the fiber index differences and adaptability problems of fibers of different specifications caused by unsatisfactory tension control accuracy.

[0046] Furthermore, a method for preparing polyacrylonitrile-based carbon fiber provided in an embodiment of the present invention further designs two-stage turning (fifth turning treatment, sixth turning treatment) after high-temperature carbonization treatment and before surface treatment. Here, this embodiment achieves expansion by matching the turning angle and tension of the turning treatment, which can avoid the grinding of the yarn bundle due to excessive tension or excessive turning. At the same time, an adjustment range is reserved for tension control, avoiding the differences in fiber indicators and adaptability of fibers of different specifications caused by unsatisfactory tension control accuracy.

[0047] On the other hand, an embodiment of the present invention provides a polyacrylonitrile-based carbon fiber, wherein the polyacrylonitrile-based carbon fiber is prepared by the above-mentioned method for preparing the polyacrylonitrile-based carbon fiber, and therefore, the comprehensive qualified rate of the appearance of the polyacrylonitrile-based carbon fiber is high.

[0048] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention and implement it according to the contents of the specification, the preferred embodiments of the present invention are described in detail as follows. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 Schematic diagram of two groups of fiber bundles in the embodiment undergoing a third turning process through a third turning roller. Figure 1 Middle: 1: steering angle; 2: fiber tow; 3: third steering roller; 4: fiber running direction. DETAILED DESCRIPTION

[0050] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the specific implementation methods, structures, features and effects of the present invention application are described in detail below in combination with the preferred embodiments. In the following description, different "one embodiment" or "embodiment" does not necessarily refer to the same embodiment. In addition, specific features, structures, or characteristics in one or more embodiments may be combined in any suitable form.

[0051] Example 1

[0052] The present embodiment provides a method for preparing polyacrylonitrile-based carbon fiber, wherein the method for preparing polyacrylonitrile-based carbon fiber comprises the following steps: sequentially performing unwinding treatment, pre-oxidation treatment, low-temperature carbonization treatment, high-temperature carbonization treatment, and surface treatment on polyacrylonitrile fiber (precursor) to obtain polyacrylonitrile-based carbon fiber; wherein, before the pre-oxidation treatment, the unwinding fiber bundle is sequentially passed through a first turning roller for a first turning treatment and passed through a second turning roller for a second turning treatment; wherein the parameters of the first turning treatment are as follows: the turning angle is 10 to 40°, the fiber bundle runs 5 to 20 m in the first direction, and the tension applied to the fiber bundle is 500 to 1500 cN; wherein, the parameters of the second turning treatment are as follows: the turning angle is 10 to 40°, the fiber bundle runs 5 to 20 m in the second direction, and the tension applied to the fiber bundle is 1000 to 1500 cN; wherein, the first direction and the second direction are two opposite directions.

[0053] Preferably, the first direction is the upward running direction (ascending) of the fiber tow, and the second direction is the downward running direction (descending) of the fiber tow.

[0054] Preferably, the fiber bundles after unwinding are arranged in groups horizontally on the grooved roller; wherein the spacing between two adjacent groups of fiber filaments is 20 to 40 mm; and the spacing between the fiber filaments in each group is 8 to 8.5 mm.

[0055] Preferably, after the fiber bundles after unwinding treatment undergo the first turning treatment and the second turning treatment, the spacing between two adjacent groups of fiber bundles is reduced from 20 to 40 mm to 0 to 5 mm; the fiber spacing within each group is reduced from 8 to 8.5 mm to 7 to 7.5 mm, thereby reducing the effective space of the equipment design and reducing costs.

[0056] The present embodiment provides a method for preparing polyacrylonitrile-based carbon fiber, which designs two-stage steering (i.e., the first steering treatment and the second steering treatment) after the unwinding treatment and before the pre-oxidation treatment, and controls the steering angle, running distance, and the tension range applied to the fiber bundles. What needs to be explained about the above scheme is that the present embodiment achieves the reduction by matching the steering angle and tension of the first steering treatment and the second steering treatment, and controlling the running distance, so as to avoid the grinding of the bundles due to excessive tension or excessive steering. The present embodiment reserves an adjustment range for the tension control, so as to avoid the difference in fiber indicators and the adaptability of fibers of different specifications caused by the substandard tension control accuracy; in addition, the steering roller and path steering used in the present embodiment avoid the high maintenance cost caused by the airflow steering.

[0057] Here, taking the first steering process as an example, the “steering angle” needs to be explained as follows: the steering angles of all groups of fiber bundles are controlled within the range of 10 to 40 degrees, but the steering angles of different groups of fiber bundles can be different, depending on the required spacing. The same applies to the second steering process, the third steering process, the fourth steering process, the fifth steering process, and the sixth steering process.

[0058] Example 2

[0059] Preferably, the present embodiment provides a method for preparing polyacrylonitrile-based carbon fiber. Compared with Example 1, the present embodiment further comprises the following steps: after the low-temperature carbonization treatment and before the high-temperature carbonization treatment: the fiber bundle after the low-temperature carbonization treatment is sequentially passed through a third turning roller for a third turning treatment and a fourth turning roller for a fourth turning treatment; wherein the parameters of the third turning treatment are as follows: the turning angle is 5 to 20°, and the tension applied to the fiber bundle is 500 to 1000 cN; wherein the parameters of the fourth turning treatment are as follows: the turning angle is 5 to 20°, and the tension applied to the fiber bundle is 1500 to 3000 cN.

[0060] The steering angle of this embodiment is described as follows: Figure 1 As shown, two groups of fiber tows 2 start running along the first fiber running direction 4, and then turn after passing through the third turning roller 3, wherein: Figure 1 The turning angle of the fiber bundle on the left is 5 to 10 degrees. Figure 1 The turning angle 1 of the right group of fiber bundles is 10-15°, and the turning angles of the two groups of fiber bundles are both in the range of 5-20°. After the turning, the distance between the two groups of fiber bundles becomes smaller.

[0061] It should be noted here that: if the low-temperature carbonization furnace is a vertical furnace, it is necessary to run upward during the third turning process and run downward during the fourth turning process; if the low-temperature carbonization furnace is a horizontal furnace, it is not necessary.

[0062] Preferably, after the fiber bundles after low-temperature carbonization treatment are subjected to the third turning treatment and the fourth turning treatment, the spacing between two adjacent groups of fiber bundles remains unchanged; the fiber spacing within each group is reduced from 7 to 7.5 mm to 5 to 5.5 mm, so as to reduce the effective space of the equipment design, reduce costs, and adapt to the double-layer high-temperature carbonization furnace.

[0063] Here, this embodiment further designs two-stage steering (third steering treatment, fourth steering treatment) after the low-temperature carbonization treatment and before the high-temperature carbonization treatment. Here, this embodiment achieves width reduction by matching the steering angle and tension of the steering treatment. This can avoid the yarn bundle being fuzzed due to excessive tension or excessive steering, and at the same time reserve an adjustment range for tension control to avoid differences in fiber indicators and adaptability problems of fibers of different specifications caused by unsatisfactory tension control accuracy.

[0064] Example 3

[0065] Preferably, this embodiment provides a method for preparing polyacrylonitrile-based carbon fiber. Compared with the above embodiment, this embodiment, after the high-temperature carbonization treatment and before the surface treatment: the fiber tow after the high-temperature carbonization treatment is sequentially passed through the fifth turning roller for the fifth turning treatment and the sixth turning roller for the sixth turning treatment; wherein, the fiber tow is expanded by the fifth turning treatment; and the fiber filaments are narrowed by the sixth turning treatment. However, these two turns are combined to achieve the expansion of the fiber. Among them, the parameters of the fifth turning treatment are as follows: the turning angle is 20 to 50°, and the tension applied to the fiber tow is 2000 to 3000 cN; wherein, the parameters of the sixth turning treatment are as follows: the turning angle is 2 to 10°, and the tension applied to the fiber tow is 2000 to 3000 cN.

[0066] Preferably, after the fiber bundles after high-temperature carbonization treatment undergo the fifth turning treatment and the sixth turning treatment, the spacing between two adjacent groups of fiber bundles increases from 0-5mm to 15-20mm, and the spacing between fiber bundles in each group increases from 5-5.5mm to 6.5-7mm.

[0067] It should be noted here that: if the high-temperature carbonization furnace is a vertical furnace, it is necessary to run upward during the fifth turning process and run downward during the sixth turning process; if the high-temperature carbonization furnace is a horizontal furnace, it is not necessary.

[0068] Here, this embodiment further designs two-stage steering (fifth steering treatment, sixth steering treatment) after high-temperature carbonization treatment and before surface treatment. Here, this embodiment achieves width expansion by matching the steering angle and tension of the steering treatment, which can avoid the yarn bundle being fuzzed due to excessive tension or excessive steering. At the same time, an adjustment range is reserved for tension control to avoid differences in fiber indicators and adaptability problems of fibers of different specifications caused by unsatisfactory tension control accuracy.

[0069] In summary, the steering treatment of Example 3 is described as follows: the first steering treatment and the second steering treatment before the pre-oxidation treatment are to achieve width reduction and tightly arrange the fiber bundles. After entering the pre-oxidation treatment, the efficiency can be improved, and the space can be reduced and the cost can be reduced when designing the pre-oxidation furnace. The third and fourth steering treatments after low-temperature carbonization are to cooperate with the double-layer high-temperature carbonization furnace. The advantage of the double-layer high-temperature carbonization furnace is that it can run more fiber bundles with higher efficiency. The steering treatment after the high-temperature carbonization treatment is to expand the width, which is beneficial to the uniformity of the surface treatment and the processability of the carbon fiber.

[0070] Example 4

[0071] Preferably, this embodiment provides a method for preparing polyacrylonitrile-based carbon fiber. Compared with the above embodiment, this embodiment is further designed as follows:

[0072] The steering rollers are grooved rollers; specifically, the first steering roller and the second steering roller are grooved rollers; the third steering roller and the fourth steering roller are grooved rollers; the fifth steering roller and the sixth steering roller are grooved rollers.

[0073] Here, the present embodiment provides a method for preparing polyacrylonitrile-based carbon fiber, which only requires the use of grooved rollers for steering. On the one hand, it avoids the high maintenance cost caused by the airflow steering. On the other hand, the grooved rollers are used to match the steering angle and tension of the steering treatment to achieve expansion / contraction, so as to avoid the yarn bundle being fuzzed due to excessive tension or excessive steering. At the same time, an adjustment range is reserved for the tension control, so as to avoid the fiber index differences and adaptability problems of fibers of different specifications caused by the tension control accuracy not meeting the standards.

[0074] Preferably, the wire path depth on the grooved roller is 1-5 mm; preferably, the grooved roller comprises a first end, a second end and a wire-traveling portion between the first end and the second end; wherein the wire path is arranged on the wire-traveling portion; wherein the first end and the second end of the grooved roller are 10-50 mm higher than the wire-traveling portion. The above design can prevent the fiber bundle from slipping out of the grooved roller during the turning process (the two ends of the existing grooved roller are at the same height as the wire-traveling portion).

[0075] Example 5

[0076] Preferably, this embodiment provides a method for preparing polyacrylonitrile-based carbon fiber. Compared with the above embodiment, this embodiment is further designed as follows:

[0077] After the fiber bundle after unwinding treatment enters the pre-oxidation furnace after turning treatment, the distance between the two sides of the fiber bundle and the inner wall of the pre-oxidation furnace is 30 to 100 mm. After the fiber bundle after low-temperature carbonization treatment enters the high-temperature carbonization furnace after turning treatment, the distance between the two sides of the fiber bundle and the inner wall of the high-temperature carbonization furnace is 30 to 100 mm. After the fiber bundle after high-temperature carbonization treatment enters the surface treatment device after turning treatment, the distance between the fiber bundle and the inner wall of the surface treatment device is 30 to 100 mm. Here, through the above design, the difference in fiber performance indicators can be avoided and the CV value of performance indicators between different spinning positions within a batch can be reduced.

[0078] Preferably, the temperature of the pre-oxidation treatment is 220-270°C; the temperature of the low-temperature carbonization treatment is 350-800°C; the temperature of the high-temperature carbonization treatment is 1000-1500°C; the concentration of the electrolyte used for the surface treatment is 2-8%. It should be noted here that after matching the steering treatment technology of the above embodiment, the process range values ​​of each section are reduced, saving energy and reducing costs. For example, before matching the above-mentioned steering technology, under the same conditions, the pre-oxidation temperature needs to be set to 250-300°C to prepare fibers with equivalent performance indicators. After matching the steering technology of the present invention, the pre-oxidation temperature of 220-270°C can meet the standards.

[0079] After the surface treatment, it also includes water washing, sizing, and drying treatment; preferably, the conductivity of the water used for the water washing treatment is ≤200μs / cm; the concentration of the sizing solution used for the sizing treatment is 1-2.5wt%; the temperature of the drying treatment is 200-240°C. It should be noted here that after the above-mentioned steering treatment, for example, the same sizing concentration and drying temperature can achieve better sizing and drying effects. Because the steering treatment directly affects the spacing, arrangement and single filament width between spinning positions, it directly affects the treatment effect and uniformity of each process.

[0080] Example 6

[0081] Preferably, the present embodiment provides a polyacrylonitrile-based carbon fiber, wherein the polyacrylonitrile-based carbon fiber of the present embodiment is prepared by the preparation method of the polyacrylonitrile-based carbon fiber described in any one of the above items, so that the appearance of the polyacrylonitrile-based carbon fiber of the present embodiment is qualified, the fluff is controlled at a better level (fluff ≤ 0.4g / km), and the indicators are stable (the CV value of the batch tensile strength of the polyacrylonitrile-based carbon fiber is ≤ 2%, the CV value of the linear density is ≤ 0.8%, and the CV value of the sizing amount is ≤ 3%).

[0082] The present invention is further described below by specific experimental examples:

[0083] Experimental Example 1

[0084] This experimental example provides a method for preparing polyacrylonitrile-based carbon fibers, which is to turn the fibers before pre-oxidation treatment, high-temperature carbonization treatment, and surface treatment, so that the fiber bundles are turned along a predetermined path to avoid fiber grinding and uneven tension. The main steps are as follows:

[0085] Unwinding treatment: The polyacrylonitrile fiber (raw yarn) is unwound. After unwinding, the fiber bundles are arranged in groups on the groove roller.

[0086] The first turning treatment and the second turning treatment: the fiber bundle after the unwinding treatment is sequentially passed through the first turning roller for the first turning treatment and the second turning roller for the second turning treatment; wherein the parameters of the first turning treatment are as follows: the turning angle of the first group of fiber bundles is 20° (closed width), and the turning angle of the second group of fiber bundles is 10° (closed width); the fiber bundles rise by 10m, and the tensions applied to the first and second groups of fiber bundles are 1000cN and 800cN respectively; wherein the parameters of the second turning treatment are as follows: the turning angle of the first group of fiber bundles is 20° (closed width), the turning angle of the second group of fiber bundles is 10° (closed width), the fiber bundles fall by 10m, and the tensions applied to the first and second groups of fiber bundles are 1000cN and 800cN respectively. Here, through the first turning treatment and the second turning treatment, the spacing between the two adjacent groups of fiber bundles is reduced from 20 to 40mm to 0 to 5mm; the spacing between the fiber bundles in each group is reduced from 8 to 8.5mm to 7 to 7.5mm.

[0087] Pre-oxidation treatment: After the unwinding treatment, the fiber bundle enters the pre-oxidation furnace for pre-oxidation treatment after the turning treatment (the temperature of the pre-oxidation treatment is 220-270°C); wherein, the distance between the two sides of the fiber bundle and the inner wall of the pre-oxidation furnace is about 50mm.

[0088] Low temperature carbonization treatment: The fiber bundle after low temperature carbonization treatment is subjected to low temperature carbonization treatment at 350-800°C.

[0089] The third turning treatment and the fourth turning treatment: the fiber bundles after low-temperature carbonization treatment are sequentially passed through the third turning roller for the third turning treatment and the fourth turning roller for the fourth turning treatment; wherein the parameters of the third turning treatment are as follows: the turning angle of the first group of fiber bundles is 5° (closed width), the turning angle of the second group of fiber bundles is 10° (closed width), and the tensions applied to the first and second groups of fiber bundles are 800cN and 900cN respectively; wherein the parameters of the fourth turning treatment are as follows: the turning angle of the first group of fiber bundles is 5° (closed width), the turning angle of the second group of fiber bundles is 10° (closed width), and the tensions applied to the first and second groups of fiber bundles are 1500cN and 2000cN respectively. After the third and fourth turning treatments of the fiber bundles after low-temperature carbonization treatment, the spacing between the two adjacent groups of fiber bundles remains unchanged; the spacing between the fiber bundles in each group is reduced from 7 to 7.5 mm to 5 to 5.5 mm

[0090] High-temperature carbonization treatment: After the low-temperature carbonization treatment, the fiber bundle enters the high-temperature carbonization furnace after the turning treatment for high-temperature carbonization treatment (the temperature of the high-temperature carbonization treatment is 1000-1500°C), and the distance between the two sides of the fiber bundle and the inner wall of the high-temperature carbonization furnace is about 50mm.

[0091] The fifth turning treatment and the sixth turning treatment: the fiber bundles after high temperature carbonization treatment are sequentially passed through the fifth turning roller for the fifth turning treatment and the sixth turning roller for the sixth turning treatment; wherein the parameters of the fifth turning treatment are as follows: the turning angle of the first group of fiber bundles is 20° (widening), the turning angle of the second group of fiber bundles is 50° (widening), and the tensions applied to the first and second groups of fiber bundles are 2000cN and 3000cN respectively; wherein the parameters of the sixth turning treatment are as follows: the turning angle of the first group of fiber bundles is 2° (shrinking), the turning angle of the second group of fiber bundles is 10° (shrinking), and the tensions applied to the first and second groups of fiber bundles are 2000cN and 3000cN respectively. After the fifth and sixth turning treatments of the fiber after high temperature carbonization treatment, the spacing between the two adjacent groups of fiber bundles increases from 0 to 5mm to 15 to 20mm, and the spacing between the fiber bundles in each group increases from 5 to 5.5mm to 6.5 to 7mm.

[0092] Surface treatment: After high-temperature carbonization treatment, the fiber bundle enters the surface treatment device for surface treatment after deflection treatment (the mass concentration of the electrolyte is 3%); wherein, the distance between the fiber bundle and the inner wall of the surface treatment device is about 50 mm.

[0093] Finally, after water washing (the electrical conductivity of the water is 200 μs / cm), sizing (the concentration of the sizing solution is 1.5 wt%), drying (temperature is 200° C.), and winding, polyacrylonitrile-based carbon fibers are obtained.

[0094] In addition, it should be noted that: the steering roller of this embodiment adopts a grooved roller, and the wire path depth on the grooved roller is 2 mm; preferably, the grooved roller includes a first end, a second end and a wire-feeding portion located between the first end and the second end; wherein the wire path is arranged on the wire-feeding portion; wherein the first end and the second end of the grooved roller are 50 mm higher than the wire-feeding portion.

[0095] The polyacrylonitrile-based carbon fiber prepared in this embodiment has a smooth surface, and the measured hairiness is 0.37 g / km; the CV value of the batch tensile strength is ≤2%, the CV value of the linear density is ≤0.8%, and the CV value of the sizing amount is ≤3%. The comprehensive qualified rate of batch indicators, fixed length, and appearance is 92%.

[0096] Experimental Example 2

[0097] This experimental example provides a method for preparing polyacrylonitrile-based carbon fibers, which is to turn the fibers before pre-oxidation treatment, high-temperature carbonization treatment, and surface treatment, so that the fiber bundles are turned along a predetermined path to avoid fiber grinding and uneven tension. The main steps are as follows:

[0098] Unwinding treatment: The polyacrylonitrile fiber (raw yarn) is unwound. After unwinding, the fiber bundles are arranged in groups on the groove roller.

[0099] The first turning treatment and the second turning treatment: the fiber bundles after the unwinding treatment are sequentially passed through the first turning roller for the first turning treatment and the second turning roller for the second turning treatment; wherein the parameters of the first turning treatment are as follows: the turning angle of the first group of fiber bundles is 20° (closed width), the turning angle of the second group of fiber bundles is 10° (closed width), the fiber bundles rise 15m, and the tensions applied to the first and second groups of fiber bundles are 1500cN and 800cN respectively; wherein the parameters of the second turning treatment are as follows: the turning angle of the first group of fiber bundles is 30° (closed width), the turning angle of the second group of fiber bundles is 40° (closed width), the fiber bundles fall 15m, and the tensions applied to the first and second groups of fiber bundles are 1200cN and 1500cN respectively. Here, through the first turning treatment and the second turning treatment, the spacing between the two adjacent groups of fiber bundles is reduced from 20 to 40mm to 0 to 5mm; the spacing between the fiber bundles in each group is reduced from 8 to 8.5mm to 7 to 7.5mm.

[0100] Pre-oxidation treatment: After the unwinding treatment, the fiber bundle enters the pre-oxidation furnace for pre-oxidation treatment after the turning treatment (the temperature of the pre-oxidation treatment is 220-270°C); wherein, the distance between the two sides of the fiber bundle and the inner wall of the pre-oxidation furnace is about 50mm.

[0101] Low temperature carbonization treatment: The fiber bundle after low temperature carbonization treatment is subjected to low temperature carbonization treatment at 400-700°C.

[0102] The third turning treatment and the fourth turning treatment: the fiber bundles after low-temperature carbonization treatment are sequentially passed through the third turning roller for the third turning treatment and the fourth turning roller for the fourth turning treatment; wherein the parameters of the third turning treatment are as follows: the turning angle of the first group of fiber bundles is 5° (closed width), the turning angle of the second group of fiber bundles is 10° (closed width), and the tensions applied to the first and second groups of fiber bundles are 500cN and 800cN respectively; wherein the parameters of the fourth turning treatment are as follows: the turning angle of the first group of fiber bundles is 15° (closed width), the turning angle of the second group of fiber bundles is 20° (closed width), and the tensions applied to the first and second groups of fiber bundles are 2000cN and 3000cN respectively. After the third and fourth turning treatments of the fiber bundles after low-temperature carbonization treatment, the spacing between two adjacent groups of fiber bundles remains unchanged; the spacing between the fiber bundles in each group is reduced from 7 to 7.5 mm to 5 to 5.5 mm

[0103] High-temperature carbonization treatment: After the low-temperature carbonization treatment, the fiber bundle enters the high-temperature carbonization furnace after the turning treatment for high-temperature carbonization treatment (the temperature of the high-temperature carbonization treatment is 1000-1500°C), and the distance between the two sides of the fiber bundle and the inner wall of the high-temperature carbonization furnace is about 50mm.

[0104] The fifth turning treatment and the sixth turning treatment: the fiber bundles after high temperature carbonization treatment are sequentially passed through the fifth turning roller for the fifth turning treatment and the sixth turning roller for the sixth turning treatment; wherein the parameters of the fifth turning treatment are as follows: the turning angle of the first group of fiber bundles is 20° (widening), the turning angle of the second group of fiber bundles is 40° (widening), and the tensions applied to the first and second groups of fiber bundles are 2000cN and 2500cN respectively; wherein the parameters of the sixth turning treatment are as follows: the turning angle of the first group of fiber bundles is 2° (shrinking), the turning angle of the second group of fiber bundles is 10° (shrinking), and the tensions applied to the first and second groups of fiber bundles are 2000cN and 3000cN respectively. After the fifth and sixth turning treatments of the fiber after high temperature carbonization treatment, the spacing between the two adjacent groups of fiber bundles increases from 0 to 5mm to 15 to 20mm, and the spacing between the fiber bundles in each group increases from 5 to 5.5mm to 6.5 to 7mm.

[0105] Surface treatment: After high-temperature carbonization treatment, the fiber bundle enters the surface treatment device for surface treatment after deflection treatment (the mass concentration of the electrolyte is 4%); wherein, the distance between the fiber bundle and the inner wall of the surface treatment device is about 50 mm.

[0106] Finally, after water washing (the electrical conductivity of the water is 200 μs / cm), sizing (the concentration of the sizing solution is 1.5 wt%), drying (temperature is 200° C.), and winding, polyacrylonitrile-based carbon fibers are obtained.

[0107] In addition, it should be noted that: the steering roller of this embodiment adopts a grooved roller, and the wire path depth on the grooved roller is 5 mm; preferably, the grooved roller includes a first end, a second end and a wire-feeding portion located between the first end and the second end; wherein the wire path is arranged on the wire-feeding portion; wherein the first end and the second end of the grooved roller are 50 mm higher than the wire-feeding portion.

[0108] The polyacrylonitrile-based carbon fiber prepared in this embodiment has a smooth appearance, a measured hairiness of 0.34 g / km, a CV value of batch tensile strength of 1.5%, a CV value of linear density of 0.5%, a CV value of sizing amount of 3%, and a comprehensive qualified rate of batch indicators / appearance / fixed length of 94%.

[0109] Comparative Example 1

[0110] Comparative Example 1 provides a method for preparing polyacrylonitrile-based carbon fiber. Compared with Experimental Example 1, the difference is that the parameters of the first steering treatment and the second steering treatment are different, and the others are the same.

[0111] The parameters of the first steering treatment of Comparative Example 1 are as follows: the steering angle of the first group of fiber bundles is 50° (closed width), the steering angle of the second group of fiber bundles is 60° (closed width), the fiber bundles rise 22m, and the tensions applied to the first and second groups of fiber bundles are 3000cN and 4000cN respectively; the parameters of the second steering treatment are as follows: the steering angle of the first group of fiber bundles is 50° (closed width), the steering angle of the second group of fiber bundles is 60° (closed width), the fiber bundles fall 22m, and the tensions applied to the first and second groups of fiber bundles are 3000cN and 4000cN respectively. After the first steering treatment and the second steering treatment of the fiber bundles after the unwinding treatment, the spacing between the two adjacent groups of fiber bundles is reduced from 20 to 40mm to 0 to 3mm; the spacing between the fiber bundles in each group is reduced from 8 to 8.5mm to 5 to 5.5mm.

[0112] Here, due to the excessive fiber turning angle and excessive tension during the first and second turning treatments of Comparative Example 1, the unwound fibers are easily abraded and entangled with the rollers, and the measured hairiness is 0.87 g / km. The CV value of the tensile strength of the carbon fiber batch prepared in Comparative Example 1 is 6%, the CV value of the linear density is 7%, the CV value of the sizing amount is 6%, and the comprehensive qualified rate of indicators, fixed length, and appearance is 75%.

[0113] Comparative Example 2

[0114] Comparative Example 2 provides a method for preparing polyacrylonitrile-based carbon fiber. Compared with Experimental Example 1, the difference is that Comparative Example 2 only performs one-stage turning treatment (width reduction) after high-temperature carbonization treatment and before surface treatment, and the parameters are as follows: the turning angle of the first group of fiber bundles is 10° (width reduction), and the turning angle of the second group of fiber bundles is 20° (width reduction), and the tensions applied to the first and second groups of fiber bundles are 1000cN and 2000cN, respectively.

[0115] Here, during the surface treatment of Comparative Example 2, due to insufficient fiber gaps at each workstation, the fibers are easily connected to form large pieces of entangled fibers, and ultimately the comprehensive qualified rate of the prepared carbon fiber batch indicators, fixed length, and appearance is 65%, and the measured hairiness is 1.54 g / km.

[0116] Comparative Example 3

[0117] Comparative Example 3 provides a method for preparing polyacrylonitrile-based carbon fiber. Compared with Experimental Example 1, the difference is that the parameters of the six turning treatments in Comparative Example 3 and Experimental Example 1 are different.

[0118] Among them, the steering processing parameters of comparative example 3 are designed as follows:

[0119] The parameters of the first steering treatment are as follows: the steering angle of the first group of fiber bundles is 50° (closed width), the steering angle of the second group of fiber bundles is 60° (closed width), the fiber bundles rise 10m, and the tensions applied to the first and second groups of fiber bundles are 2000cN and 3000cN respectively; the parameters of the second steering treatment are as follows: the steering angle of the first group of fiber bundles is 50° (closed width), the steering angle of the second group of fiber bundles is 60° (closed width), the fiber bundles fall 10m, and the tensions applied to the first and second groups of fiber bundles are 2000cN and 3000cN respectively. Through the first steering treatment and the second steering treatment, the spacing between two adjacent groups of fiber bundles is reduced from 20 to 40mm to 0 to 4mm; the spacing between the fiber bundles in each group is reduced from 8 to 8.5mm to 6 to 6.5mm.

[0120] The parameters of the third steering treatment are as follows: the steering angle of the first group of fiber bundles is 25° (closed width), the steering angle of the second group of fiber bundles is 30° (closed width), and the tensions applied to the first and second groups of fiber bundles are 1500cN and 2000cN respectively; the parameters of the fourth steering treatment are as follows: the steering angle is 25° (closed width), and the tension applied to the fiber bundles is 3500cN. The fiber spacing of each group of fiber bundles is reduced from 6 to 6.5 mm to 4 to 4.5 mm

[0121] The parameters of the fifth steering treatment are as follows: the steering angle of the first group of fiber bundles is 50° (expansion), the steering angle of the second group of fiber bundles is 60° (expansion), and the tensions applied to the first and second groups of fiber bundles are 3500cN and 4000cN respectively; the parameters of the sixth steering treatment are as follows: the steering angle of the first group of fiber bundles is 10° (expansion), the steering angle of the second group of fiber bundles is 20° (expansion), and the tensions applied to the first and second groups of fiber bundles are 3500cN and 4000cN respectively. After the fifth and sixth steering treatments, the spacing between the two adjacent groups of fiber bundles increased from 0 to 4 mm to 15 to 20 mm, and the spacing between the fiber bundles in each group increased from 4 to 4.5 mm to 6.5 to 7 mm.

[0122] In Comparative Example 2, due to the large steering angle, the fibers are prone to hair and broken strands during operation, and the prepared polyacrylonitrile-based carbon fiber has hair and hair balls on the surface, and the measured hairiness is 2.89g / km. The CV value of the batch tensile strength is 8%, the CV value of the linear density is 7%, and the CV value of the sizing amount is 10%. The comprehensive qualified rate of batch indicators, fixed length, and appearance is 50%.

[0123] In summary, an embodiment of the present invention provides a polyacrylonitrile-based carbon fiber and a preparation method thereof, which performs bipolar steering treatment on the fiber bundle before pre-oxidation treatment, high-temperature carbonization treatment, and surface treatment, and matches corresponding steering treatment parameters to make the carbon fiber bundle turn along a predetermined path, thereby avoiding fiber grinding and uneven tension.

[0124] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention still falls within the scope of the technical solution of the present invention.

Claims

1. A method for preparing polyacrylonitrile-based carbon fiber, characterized in that: The method for preparing the polyacrylonitrile-based carbon fiber comprises the following steps: The polyacrylonitrile fiber is subjected to unwinding treatment, preoxidation treatment, low-temperature carbonization treatment, high-temperature carbonization treatment, and surface treatment in sequence to obtain polyacrylonitrile-based carbon fiber; wherein, Before the pre-oxidation treatment, the unwinding fiber tow is sequentially passed through a first turning roller for a first turning treatment and a second turning roller for a second turning treatment; wherein the first turning treatment and the second turning treatment are used to narrow the fiber tow; The parameters of the first steering process are as follows: the steering angle is 10-40°, the fiber tow runs 5-20m along the first direction, and the tension applied to the fiber tow is 500-1500cN; The parameters of the second steering process are as follows: the steering angle is 10-40°, the fiber tow runs 5-20m along the second direction, and the tension applied to the fiber tow is 1000-1500cN; Wherein, the first direction and the second direction are two opposite directions; Preferably, the first direction is the direction in which the fiber bundles run upward, and the second direction is the direction in which the fiber bundles run downward.

2. The method for preparing polyacrylonitrile-based carbon fiber according to claim 1, characterized in that: The fiber bundles after unwinding are arranged in groups on the grooved roller; wherein, The distance between two adjacent groups of fiber bundles is 20 to 40 mm; the distance between the fiber bundles in each group is 8 to 8.5 mm.

3. The method for preparing polyacrylonitrile-based carbon fiber according to claim 1 or 2, characterized in that: After the unwinding fiber bundles undergo the first turning process and the second turning process, the spacing between two adjacent groups of fiber bundles is reduced from 20 to 40 mm to 0 to 5 mm; the spacing between the fiber bundles in each group is reduced from 8 to 8.5 mm to 7 to 7.5 mm.

4. The method for preparing polyacrylonitrile-based carbon fiber according to any one of claims 1 to 3, characterized in that: After the low-temperature carbonization treatment and before the high-temperature carbonization treatment: the fiber tow after the low-temperature carbonization treatment is sequentially passed through a third turning roller for a third turning treatment and a fourth turning roller for a fourth turning treatment; wherein the fiber tow is narrowed by the third turning treatment and the fourth turning treatment; The parameters of the third steering treatment are as follows: the steering angle is 5 to 20°, and the tension applied to the fiber bundle is 500 to 1000 cN; The parameters of the fourth steering process are as follows: the steering angle is 5 to 20 degrees, and the tension applied to the fiber bundle is 1500 to 3000 cN.

5. The method for preparing polyacrylonitrile-based carbon fiber according to claim 4, characterized in that: After the fiber bundles treated with low temperature carbonization are subjected to the third turning treatment and the fourth turning treatment, the spacing between two adjacent groups of fiber bundles remains unchanged; and the spacing between the fiber bundles in each group is reduced from 7 to 7.5 mm to 5 to 5.5 mm.

6. The method for preparing polyacrylonitrile-based carbon fiber according to any one of claims 1 to 5, characterized in that: After the high-temperature carbonization treatment and before the surface treatment: the fiber bundle after the high-temperature carbonization treatment is sequentially passed through a fifth turning roller for a fifth turning treatment and a sixth turning roller for a sixth turning treatment; wherein the fifth turning treatment is used to expand the width of the fiber bundle; and the sixth turning treatment is used to shrink the width of the fiber bundle; The parameters of the fifth steering process are as follows: the steering angle is 20-50°, and the tension applied to the fiber bundle is 2000-3000 cN; The parameters of the sixth steering process are as follows: the steering angle is 2 to 10°, and the tension applied to the fiber bundle is 2000 to 3000 cN.

7. The method for preparing polyacrylonitrile-based carbon fiber according to any one of claim 6, characterized in that: After the fifth and sixth turning treatments of the fibers after high-temperature carbonization, the spacing between two adjacent groups of fiber bundles increases from 0 to 5 mm to 15 to 20 mm, and the spacing between fiber bundles in each group increases from 5 to 5.5 mm to 6.5 to 7 mm.

8. The method for preparing polyacrylonitrile-based carbon fiber according to any one of claims 1 to 7, characterized in that: The first steering roller and the second steering roller are grooved rollers; Preferably, the third steering roller and the fourth steering roller are grooved rollers; Preferably, the fifth steering roller and the sixth steering roller are grooved rollers; Preferably, the wire path depth on the grooved roller is 1 to 5 mm; Preferably, the groove roller includes a first end, a second end and a wire-feeding portion located between the first end and the second end; wherein the wire path is arranged on the wire-feeding portion; wherein the first end and the second end of the groove roller are 10 to 50 mm higher than the wire-feeding portion.

9. The method for preparing polyacrylonitrile-based carbon fiber according to any one of claims 1 to 8, characterized in that: After the fiber tow after unwinding is turned and enters the pre-oxidation furnace, the distance between the two sides of the fiber tow and the inner wall of the pre-oxidation furnace is 30 to 100 mm; and / or After the fiber bundles after low-temperature carbonization treatment enter the high-temperature carbonization furnace after turning treatment, the distance between the two sides of the fiber bundles and the inner wall of the high-temperature carbonization furnace is 30 to 100 mm; and / or After the fiber bundles after high-temperature carbonization treatment enter the surface treatment device after deflection treatment, the distance between the fiber bundles and the inner wall of the surface treatment device is 30 to 100 mm; and / or The pre-oxidation temperature is 220-270°C; and / or The temperature of the low temperature carbonization treatment is 350-800°C; and / or The temperature of the high temperature carbonization treatment is 1000-1500°C; and / or The mass concentration of the electrolyte used in the surface treatment is 2-8%; Preferably, after the surface treatment, it also includes water washing, sizing and drying treatment; preferably, the conductivity of the water used in the water washing treatment is ≤200μs / cm; the concentration of the sizing liquid used in the sizing treatment is 1-2.5wt%; the temperature of the drying treatment is 200-240°C.

10. A polyacrylonitrile-based carbon fiber, characterized in that: The polyacrylonitrile-based carbon fiber is prepared by the preparation method of the polyacrylonitrile-based carbon fiber according to any one of claims 1 to 9; Wherein, the hairiness of the polyacrylonitrile-based carbon fiber is ≤0.4 g / km; Among them, the CV value of the batch tensile strength of the polyacrylonitrile-based carbon fiber is ≤2%, the CV value of the linear density is ≤0.8%, and the CV value of the sizing amount is ≤3%.

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