A polyacrylonitrile fiber and a method for producing the same

Abstract

This invention provides a polyacrylonitrile fiber and its preparation method, relating to the field of polyacrylonitrile-based carbon fiber production technology. The method includes the following steps: sequentially subjecting nascent fibers to a water washing process, a hot water drawing process, an oiling process, a drying and densification process, and a steam drawing process to obtain polyacrylonitrile fibers. In any of the water washing, hot water drawing, oiling, and drying and densification processes, the following condition must be met: D×E×N / A = constant; where D is the diameter of the polyacrylonitrile fiber monofilament; A is the fiber width in the first step; E is the cumulative draw ratio applied to the fiber in each step of the second step; and N is the K number of the polyacrylonitrile fiber. This invention proposes matching production processes and drawing speeds for different fiber specifications to ensure thorough coagulation, washing, oiling, drying, and drawing of the fibers, avoiding unevenness of monofilaments in multifilaments, and preparing homogeneous polyacrylonitrile fibers.

Description

Technical Field

[0001] This invention belongs to the field of polyacrylonitrile-based carbon fiber production technology, specifically relating to a polyacrylonitrile fiber and its preparation method. Background Technology

[0002] Carbon fiber is a high-strength, high-modulus emerging fiber material. Due to its many excellent properties, including high strength, high modulus, low density, low electrical resistance, fatigue resistance, and high-temperature resistance, it is widely used in military and civilian materials. Among them, polyacrylonitrile-based carbon fiber has good production stability and occupies a leading position among various carbon fibers, possessing broad market prospects.

[0003] The main problems with domestically produced carbon fiber are unstable performance, large coefficient of variation, and issues such as fuzzy fibers and broken fibers, resulting in significant deviations in morphology and appearance. Instability in the quality of precursor fiber production is a key factor. In the precursor fiber production process, both wet spinning and dry-jet wet spinning generally involve processes such as coagulation in a medium, washing, oiling, and drying. During these processes, uneven fiber width, including scattering and stacking, is inevitable. Specifically, in the coagulation bath, uneven fiber width means inconsistent diffusion, leading to inconsistent morphology of the nascent fibers. In washing, uneven width results in poor washing of individual fibers, leaving solvent residue and numerous surface defects, even causing heat melting during subsequent carbonization and oxidation. In oiling, uneven width affects the oiling effect. Ultimately, this leads to low yield and poor performance of both precursor fiber and carbon fiber.

[0004] Therefore, effectively controlling the width of each fiber bundle segment is a prerequisite for preparing homogeneous polyacrylonitrile fibers and polyacrylonitrile-based carbon fibers. Current technologies control the fiber bundle width using width-control devices, but specific research on the parameters for width control is lacking. This makes it impossible to ensure the preparation of homogeneous polyacrylonitrile fibers for different fiber specifications. Summary of the Invention

[0005] Therefore, the present invention provides a polyacrylonitrile fiber and a method for preparing the same, the main purpose of which is to control the fiber width in each process step for fibers of different specifications, thereby preparing homogenized polyacrylonitrile fibers.

[0006] To address the above problems, this invention provides a method for preparing polyacrylonitrile fibers, comprising the following steps: sequentially performing a water washing treatment, a hot water stretching treatment, an oiling treatment, a drying and densification treatment, and a steam stretching treatment on nascent fibers to obtain polyacrylonitrile fibers.

[0007] In any of the following steps—washing, hot water stretching, oiling, and drying densification—the following conditions must be met:

[0008] D×E×N / A = constant;

[0009] Where D is the diameter of a single filament of polyacrylonitrile fiber;

[0010] A represents the fiber width in the first step;

[0011] E represents the cumulative number of draw ratios applied to the fiber in each step of the second step.

[0012] N is the K number of polyacrylonitrile fiber;

[0013] The first step is any one of the following steps: water washing, hot water stretching, oiling, and drying and densification; the second step is the step following the first step.

[0014] If the first step is a water washing process, then the constant is 20±5;

[0015] If the first step is a hot water stretching treatment or an oiling treatment, then the constant is 15±5;

[0016] If the first step is a drying and densification process, then the constant is 12±5.

[0017] Furthermore, prior to the water washing step, the procedure also includes:

[0018] The steps for preparing nascent fibers are as follows: The polyacrylonitrile spinning solution is spun and solidified to obtain the nascent fibers; wherein the polyacrylonitrile spinning solution is spun from a spinneret with an orifice diameter of 0.10-0.15 mm; and / or

[0019] The spinning speed is 7-11 m / min.

[0020] Furthermore, in the solidification and forming process, the drawing speed is 15-35 m / min.

[0021] Furthermore, in the water washing process: the fiber running speed is 15-35 m / min; and / or

[0022] The fiber width during the washing process is 20-60 mm;

[0023] Preferably, if the fiber is 3K fiber, the fiber width in the washing process is 20-30 mm;

[0024] If the fiber is 6K fiber, the fiber width in the washing process is 30-40mm;

[0025] If the fiber is 12K fiber, the fiber width in the washing process is 50-60mm.

[0026] Furthermore, in the hot water stretching treatment step and the oiling treatment step: the fiber running speed is 35-90 m / min; and / or

[0027] The fiber width is 10-50mm in both the hot water stretching treatment and the oiling treatment steps;

[0028] Preferably, if the fiber is 3K fiber, the fiber width in the hot water stretching treatment step and the oiling treatment step is 10-20mm;

[0029] If the fiber is 6K fiber, the fiber width in the hot water stretching process and the oiling process is 20-30mm.

[0030] If the fiber is 12K fiber, the fiber width after the hot water stretching treatment and the oiling treatment is 40-50mm.

[0031] Furthermore, in the drying and densification process: the fiber running speed is 35-90 m / min; and / or

[0032] The fiber width during the drying and densification process is 15-55 mm.

[0033] Preferably, if the fiber is 3K fiber, the fiber width in the drying and densification process is 15-25 mm;

[0034] If the fiber is 6K fiber, the fiber width in the drying and densification process is 25-35mm;

[0035] If the fiber is 12K fiber, the fiber width in the drying and densification process is 45-55 mm.

[0036] Furthermore, in the steam drawing process, the fiber running speed is 200-400 m / min.

[0037] On the other hand, the present invention provides a polyacrylonitrile fiber, wherein the monofilament diameter of the polyacrylonitrile fiber is 8-12 μm.

[0038] Furthermore, the batch-to-batch and batch-to-batch coefficients of variation of the linear density of the polyacrylonitrile fiber are both ≤0.5%; and / or

[0039] The batch-to-batch and batch-to-batch coefficients of variation for the oiling rate of the polyacrylonitrile fibers are both ≤1.0%; and / or

[0040] The batch-to-batch and batch-to-batch coefficients of variation for the tensile strength, elastic modulus, and elongation of the polyacrylonitrile fiber are all ≤1.5%.

[0041] Furthermore, the polyacrylonitrile fiber is prepared using any of the methods described above.

[0042] The polyacrylonitrile fiber and its preparation method provided by this invention have the following beneficial effects:

[0043] 1. This invention targets fibers of different specifications and controls the fiber width in the washing, hot water drawing, oiling, and drying / densification steps to ensure synergistic matching between the fiber width and other processes and parameters (e.g., monofilament diameter, fiber draw ratio, etc.). This allows the fibers to undergo sufficient solidification, washing, oiling, drying, and drawing, avoiding unevenness of monofilaments in multifilaments, thereby producing homogeneous polyacrylonitrile fibers. Specifically, the washing, hot water drawing, oiling, and drying / densification steps meet the condition: D×E×N / A=constant; where D is the monofilament diameter of the polyacrylonitrile fiber; A is the fiber width in the first step; E is the cumulative draw ratio applied to the fiber in each step of the second step; N is the K number of the polyacrylonitrile fiber; the constant in the washing step is 20±5; the constants in the hot water drawing and oiling steps are 15±5; and the fiber constant in the drying / densification step is 12±5.

[0044] 2. Furthermore, the present invention obtains the fiber stretching ratio for each step in the second step by controlling the fiber running speed in the water washing treatment step, hot water stretching treatment step, oiling treatment step, drying and densification treatment step and steam stretching treatment step.

[0045] 3. The present invention prepares homogenized polyacrylonitrile fibers by the above method, with a single filament diameter of 8-12 μm, and the batch-to-batch and batch-to-batch dispersion coefficients of linear density are both ≤0.5%, the batch-to-batch and batch-to-batch dispersion coefficients of oiling rate are both ≤1.0%, and the batch-to-batch and batch-to-batch dispersion coefficients of tensile strength, elastic modulus and elongation are both ≤1.5%. Detailed Implementation

[0046] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, a brief introduction will be given below regarding the methods used in describing the embodiments or the prior art. The descriptions below are merely exemplary, and those skilled in the art can obtain other embodiments based on the provided extensions without any creative effort.

[0047] The purpose of this invention is to provide a method for preparing polyacrylonitrile fibers, which proposes matching the width and draw ratio of each segment for fibers of different specifications, so that the fibers can be fully solidified, washed, oiled, dried, and drawn, avoiding unevenness of monofilaments in multifilaments, and preparing homogeneous polyacrylonitrile fibers. The specific scheme is as follows:

[0048] On the one hand, the present invention provides a method for preparing polyacrylonitrile fibers, comprising the following steps: sequentially performing a water washing treatment step, a hot water stretching treatment step, an oiling treatment step, a drying and densification treatment step, and a steam stretching treatment step on nascent fibers to obtain polyacrylonitrile fibers;

[0049] In any of the following steps—washing, hot water stretching, oiling, and drying densification—the following conditions must be met:

[0050] D×E×N / A = constant;

[0051] Where D is the diameter of a single filament of polyacrylonitrile fiber;

[0052] A represents the fiber width in the first step;

[0053] E represents the cumulative stretching ratio applied to the fiber in each step of the second step;

[0054] N is the K number of polyacrylonitrile fiber;

[0055] The first step is any one of the following steps: water washing, hot water stretching, oiling, and drying and densification. The second step is any step following the first step. Specifically, if the first step is water washing, then the second step includes all steps of the following processes: hot water stretching, oiling, drying and densification, and steam stretching; if the first step is hot water stretching, then the second step includes all steps of the following processes: oiling, drying and densification, and steam stretching; if the first step is oiling, then the second step includes both drying and densification and steam stretching; if the first step is drying and densification, then the second step is steam stretching.

[0056] If the first step is a water washing process, then the constant is in the range of 20±5.

[0057] If the first step is a hot water stretching treatment or an oiling treatment, the constant is in the range of 15±5.

[0058] If the first step is a drying and densification process, the constant is in the range of 12±5.

[0059] The K number of polyacrylonitrile fiber refers to the number of monofilaments contained in a bundle of fiber filaments. For example, 3K means there are 3000 monofilaments.

[0060] E (i.e., the cumulative number of draw ratios applied to the fiber in each step of the second step) is obtained by multiplying the draw ratios applied to the fiber in each step of the second step. For example, if the fiber width in the washing step is calculated, the value of E is the product of the draw ratios in the hot water drawing step, the oiling step, the drying and densification step, and the steam drawing step. The draw ratio in each step is the ratio of the end-of-process drive speed to the beginning-of-process drive speed in that step.

[0061] In some embodiments, the process further includes the following steps prior to the water washing step:

[0062] The steps for preparing nascent fibers are as follows: The polyacrylonitrile spinning solution is spun and solidified to obtain nascent fibers; wherein the polyacrylonitrile spinning solution is spun from a spinneret with an orifice diameter of 0.10-0.15 mm; and / or

[0063] The spinning speed is 7-11 m / min. The spinning speed affects the solidification and molding effect. Too fast a speed will lead to filament breakage, discontinuous spinning, and incomplete solidification; too slow a speed will easily cause uneven diffusion between the surface and the core. In addition, the spinning speed must be matched and coordinated with the process such as the spinning speed of the solidification bath.

[0064] In some embodiments, the drawing speed is 15-35 m / min during the solidification forming process.

[0065] In some embodiments, during the washing process: the fiber running speed is 15-35 m / min; and / or

[0066] The fiber width during the washing process is 20-60 mm;

[0067] Preferably, if the fiber is 3K fiber, the fiber width in the washing process is 20-30 mm;

[0068] If the fiber is 6K fiber, the fiber width in the washing process is 30-40mm;

[0069] If the fiber is 12K fiber, the fiber width in the washing process is 50-60mm.

[0070] In some embodiments, during the hot water stretching treatment step and the oiling treatment step: the fiber running speed is 35-90 m / min; and / or

[0071] The fiber width is 10-50mm in both the hot water stretching treatment and the oiling treatment steps;

[0072] Preferably, if the fiber is 3K fiber, the fiber width in the hot water stretching treatment step and the oiling treatment step is 10-20mm;

[0073] If the fiber is 6K fiber, the fiber width in the hot water stretching process and the oiling process is 20-30mm.

[0074] If the fiber is 12K fiber, the fiber width in the hot water stretching process and the oiling process is 40-50mm.

[0075] In some embodiments, during the drying and densification step: the fiber running speed is 35-90 m / min; and / or

[0076] The fiber width during the drying and densification process is 15-55 mm.

[0077] Preferably, if the fiber is 3K fiber, the fiber width in the drying and densification process is 15-25 mm;

[0078] If the fiber is 6K fiber, the fiber width in the drying and densification process is 25-35mm;

[0079] If the fiber is 12K fiber, the fiber width in the drying and densification process is 45-55 mm.

[0080] In some embodiments, the fiber running speed is 200-400 m / min during the steam drawing process.

[0081] On the other hand, the present invention provides a polyacrylonitrile fiber, wherein the monofilament diameter of the polyacrylonitrile fiber is 8-12 μm.

[0082] In some embodiments, the batch-to-batch and batch-to-batch coefficients of variation of the linear density of the polyacrylonitrile fibers are both ≤0.5%; and / or

[0083] The batch-to-batch and batch-to-batch coefficients of variation for the oiling rate of polyacrylonitrile fibers are both ≤1.0%; and / or

[0084] The batch-to-batch and batch-to-batch coefficients of variation for tensile strength, elastic modulus, and elongation of polyacrylonitrile fibers are all ≤1.5%.

[0085] In some embodiments, the polyacrylonitrile fibers are prepared using any of the methods described above.

[0086] The present invention will be further described below with reference to specific embodiments and comparative examples.

[0087] Example 1

[0088] This embodiment provides a method for preparing T800S-12K polyacrylonitrile fiber, specifically including the following steps:

[0089] Preparation of nascent fibers: The polyacrylonitrile spinning solution is spun out from a spinneret with an orifice diameter of 0.12 mm at a spinneret speed of 8 m / min, and then enters a coagulation bath for coagulation and shaping. The solution is then drawn out of the coagulation bath at a drawing speed of 22 m / min to obtain nascent fibers.

[0090] Washing process: The nascent fibers enter the washing tank under the traction of the drive rollers. The fiber width is controlled to 60mm by the beat rollers and the spreading frame. The fiber running speed is 22m / min during the washing process.

[0091] Hot water drawing process: The washed fibers are drawn into the hot drawing tank by the drive rollers for hot water drawing.

[0092] Oiling process: The fibers after hot water stretching are oiled.

[0093] In the hot water stretching process and the oiling process, the fiber width is 50 mm, and the fiber running speed during the hot water stretching process is 57 m / min.

[0094] Drying and densification process: After oiling, the fibers pass through the oiling roller and enter the drying and densification section; the fiber width is 55mm and the fiber running speed is 57m / min.

[0095] Steam drawing process: After drying and densification, the fibers are processed by a steam drawing section to obtain polyacrylonitrile fibers; the fiber running speed is 272 m / min.

[0096] The polyacrylonitrile fiber prepared in this embodiment has a single filament diameter of 9 μm. The batch-to-batch and intra-batch CV values ​​of the linear density of the polyacrylonitrile fiber are 0.5% and 0.3%, respectively. The batch-to-batch and intra-batch CV values ​​of the oiling rate are 1.0% and 0.8%, respectively. The batch-to-batch and intra-batch CV values ​​of tensile strength, elastic modulus, and elongation are all ≤1.0%.

[0097] In this embodiment, the fiber width in the water washing step is approximately 60 mm, calculated using A = D × E × N / constant = (9 μm × 12000 / 1000) mm × 4.77 × 2.59 / 22.2; the fiber width in the hot water stretching and oiling steps is approximately 50 mm (A = (9 μm × 12000 / 1000) mm × 4.77 / 10.3); and the fiber width in the drying and densification step is approximately 55 mm (A = (9 μm × 12000 / 1000) mm × 4.77 / 9.4).

[0098] Among them, 4.77 is the stretching ratio applied to the fiber in the steam stretching treatment step, and 2.59 is the stretching ratio applied to the fiber in the hot water stretching treatment step. The stretching ratio in the oiling treatment step and the drying and densification treatment step is approximately 1. The stretching ratio applied to the fiber in the raw yarn production process is concentrated in the coagulation bath, hot water stretching, and steam stretching, while the stretching ratio in the other processes is approximately 1.

[0099] Example 2

[0100] This embodiment provides a method for preparing T700S-12K polyacrylonitrile fiber, specifically including the following steps:

[0101] The steps for preparing nascent fibers are as follows: the polyacrylonitrile spinning solution is spun out from a spinneret with an aperture of 0.12 mm at a spinneret speed of 11 m / min, and then enters a coagulation bath for coagulation and shaping. The solution is then drawn out of the coagulation bath at a drawing speed of 30 m / min to obtain nascent fibers.

[0102] Washing process: The nascent fibers enter the washing tank under the traction of the drive rollers. The fiber width is controlled to 60mm by the beat rollers and the spreading frame. The fiber running speed is 30m / min during the washing process.

[0103] Hot water drawing process: The washed fibers are drawn into the hot drawing tank by the drive rollers for hot water drawing.

[0104] Oiling process: The fibers after hot water stretching are oiled; the fiber width in the hot water stretching and oiling processes is 50 mm, and the fiber running speed during the hot water stretching process is 70 m / min.

[0105] Drying and densification process: After oiling, the fibers pass through an oiling roller and enter the drying and densification process; the fiber width is 55mm and the fiber running speed is 70m / min.

[0106] Steam drawing process: After drying and densification, the fibers are processed by a steam drawing section to obtain polyacrylonitrile fibers; the fiber running speed is 260 m / min.

[0107] The polyacrylonitrile fiber prepared in this embodiment has a single filament diameter of 12 μm. The batch-to-batch and intra-batch CV values ​​of the linear density of the polyacrylonitrile fiber are 0.5% and 0.5%, respectively. The batch-to-batch and intra-batch CV values ​​of the oiling rate are 1.0% and 1.0%, respectively. The batch-to-batch and intra-batch CV values ​​of tensile strength, elastic modulus, and elongation are all ≤1.5%.

[0108] In this embodiment, the fiber width in the water washing step is approximately 60 mm, calculated using A = D × E × N / constant = (12 μm × 12000 / 1000) mm × 3.71 × 2.33 / 21; the fiber width in the hot water stretching and oiling steps is approximately 50 mm (A = (12 μm × 12000 / 1000) mm × 3.71 / 10.6); and the fiber width in the drying and densification step is approximately 55 mm (A = (12 μm × 12000 / 1000) mm × 3.71 / 9.7).

[0109] Among them, 3.71 is the stretching ratio applied to the fiber in the steam stretching treatment step, and 2.33 is the stretching ratio applied to the fiber in the hot water stretching treatment step; the stretching ratio in the oiling treatment step and the drying and densification treatment step is approximately 1. The stretching ratio applied to the fiber in the raw yarn production process is concentrated in the coagulation bath, hot water stretching, and steam stretching, while the stretching ratio in the other processes is approximately 1.

[0110] Example 3

[0111] This embodiment provides a method for preparing T700S-3K polyacrylonitrile fiber, specifically including the following steps:

[0112] The steps for preparing nascent fibers are as follows: the polyacrylonitrile spinning solution is spun out from a spinneret with an aperture of 0.12 mm at a spinneret speed of 11 m / min, and then enters a coagulation bath for coagulation and shaping. The solution is then drawn out of the coagulation bath at a drawing speed of 30 m / min to obtain nascent fibers.

[0113] Washing process: The nascent fibers enter the washing tank under the traction of the drive rollers. The fiber width is controlled to 20mm by the beat rollers and the spreading frame. The fiber running speed is 30m / min during the washing process.

[0114] Hot water drawing process: The washed fibers are drawn into the hot drawing tank by the drive rollers for hot water drawing.

[0115] Oiling process: The fibers after hot water stretching are oiled; the fiber width in the hot water stretching and oiling processes is 12 mm, and the fiber running speed during the hot water stretching process is 70 m / min.

[0116] Drying and densification process: After oiling, the fibers pass through an oiling roller and enter the drying and densification process; the fiber width is 18mm and the fiber running speed is 70m / min.

[0117] Steam drawing process: After drying and densification, the fibers are processed by a steam drawing section to obtain polyacrylonitrile fibers; the fiber running speed is 260 m / min.

[0118] The polyacrylonitrile fiber prepared in this embodiment has a single filament diameter of 12 μm. The batch-to-batch and intra-batch CV values ​​of the linear density of the polyacrylonitrile fiber are 0.5% and 0.4%, respectively. The batch-to-batch and intra-batch CV values ​​of the oiling rate are 1.0% and 1.0%, respectively. The batch-to-batch and intra-batch CV values ​​of tensile strength, elastic modulus, and elongation are all ≤1.3%.

[0119] In this embodiment, the fiber width in the water washing step is approximately 20 mm, calculated using A = D × E × N / constant = (12 μm × 3000 / 1000) mm × 3.71 × 2.33 / 15.5; the fiber width in the hot water stretching and oiling steps is approximately 12 mm (A = (12 μm × 3000 / 1000) mm × 3.71 / 11); and the fiber width in the drying and densification step is approximately 18 mm (A = (12 μm × 3000 / 1000) mm × 3.71 / 7.4).

[0120] Among them, 3.71 is the stretching ratio applied to the fiber in the steam stretching treatment step, and 2.33 is the stretching ratio applied to the fiber in the hot water stretching treatment step; the stretching ratio in the oiling treatment step and the drying and densification treatment step is approximately 1. The stretching ratio applied to the fiber in the raw yarn production process is concentrated in the coagulation bath, hot water stretching, and steam stretching, while the stretching ratio in the other processes is approximately 1.

[0121] Example 4

[0122] This embodiment provides a method for preparing T800S-12K polyacrylonitrile fiber, specifically including the following steps:

[0123] The steps for preparing nascent fibers are as follows: the polyacrylonitrile spinning solution is spun out from a spinneret with an aperture of 0.12 mm at a spinneret speed of 7 m / min, then enters a coagulation bath for coagulation and shaping, and is drawn out of the coagulation bath at a drawing speed of 21 m / min to obtain nascent fibers.

[0124] Washing process: The nascent fibers enter the washing tank under the traction of the drive rollers. The fiber width is controlled to 50mm by the beat rollers and the spreading frame. The fiber running speed is 21m / min during the washing process.

[0125] Hot water drawing process: The washed fibers are drawn into the hot drawing tank by the drive rollers for hot water drawing.

[0126] Oiling process: The fibers after hot water stretching are oiled.

[0127] In the hot water stretching and oiling processes, the fiber width is 40 mm, and the fiber running speed during the hot water stretching process is 52 m / min.

[0128] Drying and densification process: After oiling, the fibers pass through the oiling roller and enter the drying and densification section; the fiber width is 45mm and the fiber running speed is 52m / min.

[0129] Steam drawing process: After drying and densification, the fibers are processed by a steam drawing section to obtain polyacrylonitrile fibers; the fiber running speed is 238 m / min.

[0130] The polyacrylonitrile fiber prepared in this embodiment has a single filament diameter of 9 μm. The batch-to-batch and intra-batch CV values ​​of the linear density of the polyacrylonitrile fiber are 0.5% and 0.3%, respectively. The batch-to-batch and intra-batch CV values ​​of the oiling rate are 1.0% and 0.8%, respectively. The batch-to-batch and intra-batch CV values ​​of tensile strength, elastic modulus, and elongation are all ≤1.0%.

[0131] In this embodiment, the fiber width in the water washing step is approximately 50 mm, calculated using A = D × E × N / constant = (9 μm × 12000 / 1000) mm × 4.58 × 2.48 / 24.5; the fiber width in the hot water stretching and oiling steps is approximately 40 mm (A = (9 μm × 12000 / 1000) mm × 4.58 / 12.4); and the fiber width in the drying and densification step is approximately 45 mm (A = (9 μm × 12000 / 1000) mm × 4.58 / 11).

[0132] Among them, 4.58 is the stretching ratio applied to the fiber in the steam stretching treatment step, and 2.48 is the stretching ratio applied to the fiber in the hot water stretching treatment step. The stretching ratio in the oiling treatment step and the drying and densification treatment step is approximately 1. The stretching ratio applied to the fiber in the raw yarn production process is concentrated in the coagulation bath, hot water stretching, and steam stretching, while the stretching ratio in the other processes is approximately 1.

[0133] Comparative Example 1

[0134] This comparative example provides a method for preparing T800S-12K polyacrylonitrile fiber, specifically including the following steps:

[0135] Preparation of nascent fibers: The polyacrylonitrile spinning solution is spun out from a spinneret with an orifice diameter of 0.12 mm at a spinneret speed of 8 m / min, and then enters a coagulation bath for coagulation and shaping. The solution is then drawn out of the coagulation bath at a drawing speed of 22 m / min to obtain nascent fibers.

[0136] Washing process: The nascent fibers enter the washing tank under the traction of the drive rollers. The fiber width is controlled to 30mm by the beat rollers and the spreading frame. The fiber running speed is 22m / min during the washing process.

[0137] Hot water drawing treatment: The washed fibers are drawn into the hot drawing tank by the drive rollers for hot water drawing treatment;

[0138] Oiling process: The fibers after hot water stretching are oiled; the fiber width in the hot water stretching and oiling processes is 35 mm, and the fiber running speed during the hot water stretching process is 57 m / min.

[0139] Drying and densification process: After oiling, the fibers pass through an oiling roller and enter the drying and densification process; the fiber width is 55mm and the fiber running speed is 57m / min.

[0140] Steam drawing process: After drying and densification, the fibers are processed by a steam drawing section to obtain polyacrylonitrile fibers; the fiber running speed is 272 m / min.

[0141] The batch-to-batch and intra-batch CV values ​​of the linear density of the polyacrylonitrile fibers prepared in this comparative example were 3.0% and 2.5%, respectively, and the batch-to-batch and intra-batch CV values ​​of oiling rate, tensile strength, elastic modulus, and elongation were all >3.0%.

[0142] Due to the narrow fiber width, incomplete washing, high sulfoxide residue, and uneven oiling during the preparation process of Comparative Example 1, the fiber was prone to thermal melting during carbonization, resulting in poor uniformity of drying and densification, poor fiber density, and easy fiber breakage during the steam drawing process. Consequently, the tensile strength, elastic modulus, and other indicators of the prepared fiber decreased compared to Example 1, and the fiber orientation was low.

[0143] Comparative Example 2

[0144] This comparative example provides a method for preparing T700S-3K polyacrylonitrile fiber, specifically including the following steps:

[0145] The steps for preparing nascent fibers are as follows: the polyacrylonitrile spinning solution is spun out from a spinneret with an aperture of 0.12 mm at a spinneret speed of 11 m / min, and then enters a coagulation bath for coagulation and shaping. The solution is then drawn out of the coagulation bath at a drawing speed of 30 m / min to obtain nascent fibers.

[0146] Washing process: The nascent fibers enter the washing tank under the traction of the drive rollers. The fiber width is controlled to 60mm by the beat rollers and the spreading frame. The fiber running speed is 30m / min during the washing process.

[0147] Hot water drawing process: The washed fibers are drawn into the hot drawing tank by the drive rollers for hot water drawing.

[0148] Oiling process: The fibers after hot water stretching are oiled; the fiber width in the hot water stretching and oiling processes is 50 mm, and the fiber running speed during the hot water stretching process is 70 m / min.

[0149] Drying and densification process: After oiling, the fibers pass through an oiling roller and enter the drying and densification process; the fiber width is 55mm and the fiber running speed is 70m / min.

[0150] Steam drawing process: After drying and densification, the fibers are processed by a steam drawing section to obtain polyacrylonitrile fibers; the fiber running speed is 260 m / min.

[0151] In this comparative example, the fiber width control during the washing, hot water stretching, oiling, and drying densification steps did not consider the matching with the fiber K number, meaning that the condition D×E×N / A=constant was not met in these steps; where D is the monofilament diameter of the polyacrylonitrile fiber; A is the fiber width in the first step; E is the cumulative stretching ratio applied to the fiber in each step of the second step; and N is the K number of the polyacrylonitrile fiber. This resulted in monofilament drifting out during the preparation process, easy entanglement with rollers and fiber crosstalk during operation, and unstable operation. The batch-to-batch and intra-batch CV values ​​of the linear density of the prepared polyacrylonitrile fiber were 4.0% and 3.5%, respectively, and the batch-to-batch and intra-batch CV values ​​of oiling rate, tensile strength, elastic modulus, and elongation were all >5.0%.

[0152] It will be readily understood by those skilled in the art that, without conflict, the advantageous technical features of the above-mentioned methods can be freely combined and superimposed.

[0153] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention. The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the protection scope of the present invention.

Claims

1. A process for the production of polyacrylonitrile fibers, characterized in that, The process includes the following steps: sequentially performing water washing, hot water stretching, oiling, drying and densification, and steam stretching on the nascent fibers to obtain polyacrylonitrile fibers. In any of the following steps—washing, hot water stretching, oiling, and drying densification—the following conditions must be met: D×E×N / A = constant; Where D is the diameter of a single filament of polyacrylonitrile fiber; A represents the fiber width in the first step; E represents the cumulative number of draw ratios applied to the fiber in each step of the second step. N is the K number of the polyacrylonitrile fiber; The first step is any one of the following steps: water washing, hot water stretching, oiling, and drying and densification; the second step is the step following the first step. If the first step is a water washing process, then the constant is 20±5; If the first step is a hot water stretching treatment or an oiling treatment, then the constant is 15±5; If the first step is a drying and densification process, then the constant is 12±5.

2. The polyacrylonitrile fiber production method according to claim 1, characterized by, Prior to the water washing step, the following is also included: The steps for preparing nascent fibers are as follows: the polyacrylonitrile spinning solution is spun and coagulated to obtain the nascent fibers. In this process, the polyacrylonitrile spinning solution is ejected from a spinneret with an orifice diameter of 0.10-0.15 mm; and / or The spinning speed is 7-11 m / min.

3. The method for preparing polyacrylonitrile fibers according to claim 2, characterized in that, During the solidification and forming process, the wire drawing speed is 15-35 m / min.

4. The method for preparing polyacrylonitrile fibers according to claim 1, characterized in that, In the water washing process: the fiber running speed is 15-35 m / min; and / or The fiber width during the washing process is 20-60 mm; If the fiber is 3K fiber, the fiber width in the washing process is 20-30mm; If the fiber is 6K fiber, the fiber width in the washing process is 30-40mm; If the fiber is 12K fiber, the fiber width in the washing process is 50-60mm.

5. The polyacrylonitrile fiber production method according to claim 1, wherein In the hot water stretching treatment step and the oiling treatment step: the fiber running speed is 35-90 m / min; and / or The fiber width is 10-50mm in both the hot water stretching treatment and the oiling treatment steps; If the fiber is 3K fiber, the fiber width in the hot water stretching process and the oiling process is 10-20mm. If the fiber is 6K fiber, the fiber width in the hot water stretching process and the oiling process is 20-30mm. If the fiber is 12K fiber, the fiber width in the hot water stretching process and the oiling process is 40-50mm.

6. The polyacrylonitrile fiber production method according to claim 1, wherein In the drying and densification process: the fiber running speed is 35-90 m / min; and / or The fiber width during the drying and densification process is 15-55 mm. If the fiber is 3K fiber, the fiber width in the drying and densification process is 15-25 mm. If the fiber is 6K fiber, the fiber width in the drying and densification process is 25-35mm; If the fiber is 12K fiber, the fiber width in the drying and densification process is 45-55 mm.

7. The polyacrylonitrile fiber production method according to claim 1, wherein In the steam drawing process, the fiber running speed is 200-400 m / min.

8. A polyacrylonitrile fiber prepared by the method for preparing polyacrylonitrile fiber according to any one of claims 1-7, characterized in that, The diameter of the single filament of the polyacrylonitrile fiber is 8-12 μm.

9. The polyacrylonitrile fiber according to claim 8, characterized by The linear density of the polyacrylonitrile fiber has a batch-to-batch coefficient of variation and a batch-to-batch coefficient of variation of ≤0.5%; and / or The batch-to-batch and batch-to-batch coefficients of variation for the oiling rate of the polyacrylonitrile fibers are both ≤1.0%; and / or The batch-to-batch and batch-to-batch coefficients of variation for the tensile strength, elastic modulus, and elongation of the polyacrylonitrile fiber are all ≤1.5%.