A method for high temperature saturated steam synergistic pretreatment of carbon fiber precursor

Abstract

The present application relates to carbon fiber precursor preparation technical field, disclose a kind of high-temperature saturated steam cooperates the method for pretreating carbon fiber precursor, to solve the problem that existing steam treatment cannot simultaneously realize cleaning, uniform humidification and densification synergy effect.The technical scheme main point is: after the polyacrylonitrile-based carbon fiber precursor of solidification, washing and oiling is introduced into saturated steam pretreatment unit, by the penetration and stripping effect of high-temperature saturated steam, remove surface residual spinning solvent and impurities, and adjust moisture content to 8%~15%;Again, after drying densification treatment, moisture content is reduced to 0.8%~1.5%, while applying draft, realize the promotion of macromolecular chain orientation degree and regularity.The present application is mainly used for preparing high-performance polyacrylonitrile-based carbon fiber precursor, to provide uniform structure high-quality precursor for subsequent pre-oxidation and carbonization process.After treatment, the density CV value of precursor is ≤3%, and the strength of carbon fiber can reach more than 5.8 GPa.

Description

Technical Field

[0001] This invention relates to the technical field of carbon fiber precursor preparation, and in particular to a method for high-temperature saturated steam co-treatment of carbon fiber precursor. Background Technology

[0002] The modulus and strength of carbon fibers are closely related to the preferred orientation of their internal graphite-like structures along the fiber axis and the pore structure within the fiber. The formation and evolution of these structural features permeate the entire process of spinning solution preparation, precursor fiber formation, and subsequent pre-oxidation and carbonization. Among these, the structural uniformity and defect level of the precursor fiber are inherited into the carbon fibers through subsequent heat treatment processes, having an irreversible impact on the final properties of the carbon fibers.

[0003] During the high-pressure steam drawing stage, any fluctuation in process conditions will lead to unstable drawing tension, resulting in more structural defects inside the carbon fiber precursor. At the same time, the friction between the fiber bundles will also cause a large number of fuzzy fibers to be generated in the pre-oxidized fiber, ultimately leading to the deterioration of the carbon fiber strength, modulus and elongation.

[0004] High-temperature saturated steam possesses both excellent thermal conductivity and plasticizing properties, enabling it to penetrate deep into PAN precursor fibers while effectively removing surface impurities. However, existing steam treatment technologies primarily focus on achieving high-ratio uniform drawing and reducing drawing stress to improve production efficiency. They cannot achieve the synergistic effects of cleaning, uniform humidification, and densification in the same process, making it difficult to meet the requirements for preparing high-performance carbon fiber precursor fibers. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art, such as uneven densification of carbon fiber precursor and high pre-oxidation filament rate, and to provide a method for high-temperature saturated steam co-processing of carbon fiber precursor. Through the multiple effects of saturated steam, the precursor is efficiently cleaned, densified and drawn simultaneously, the overall performance of the precursor is improved, and the foundation is laid for subsequent pre-oxidation, carbonization and other processes.

[0006] The technical solution adopted by this invention to solve its technical problem is: a method for high-temperature saturated steam co-treatment of carbon fiber precursor, comprising the following steps: S1, introducing polyacrylonitrile-based carbon fiber precursor, after coagulation, washing and oiling, into a saturated steam pretreatment unit at a running speed of 5~20 m / min, and treating it in a high-temperature saturated steam environment at a temperature of 120~180℃ and a pressure of 0.2~0.8 MPa for 30~120 s, removing residual spinning solvent and impurities on the surface of the precursor through the permeation and stripping of saturated steam, and adjusting the moisture content of the precursor to 8%~15%; S2, sending the steam-treated precursor into a drying unit for drying and densification treatment at 80~180℃ to obtain pretreated carbon fiber precursor.

[0007] Further specified, the tow specifications of the polyacrylonitrile-based carbon fiber precursor in S1 are 3K~12K, and the moisture content before entering the saturated steam pretreatment unit is 10%~50%.

[0008] Further specified, the flow rate of the high-temperature saturated steam in S1 is 0.6~1.0 m / s, the steam purity is ≥99.9%, and the Ca content in the steam is... 2+ Content <0.02 mg / L, Na + Content < 0.02 mg / L.

[0009] Further, the processing time of the raw filaments in the saturated steam pretreatment unit in S1 is determined according to the filament specifications: 3K filaments are 30~60 s, 6K filaments are 60~70 s, and 12K filaments are 80~120 s.

[0010] Further specified, during the saturated steam pretreatment process in S1, stretching is applied with a total stretching ratio of 1.10 to 1.16 times; of which the front section of the steam chamber bears 60% of the stretching, the middle section of the chamber bears 30% of the stretching, and the rear section of the chamber outlet bears 10% of the stretching.

[0011] Further specifying, in S2, the drying and densification process adopts a composite drying method with hot roller drying as the main method and hot air auxiliary heating on both sides. The drying medium is clean air at normal pressure. During the drying process, stretching is applied with a stretching ratio of 1.03 to 1.08 times.

[0012] Further specifying, in S2, the drying and densification process adopts a three-stage gradient temperature increase: the first stage preheating zone is 75~85℃; the second stage main drying zone is 95~105℃; and the third stage conditioning zone is 115~125℃.

[0013] Further specified, in S2, the moisture content of the raw filament after drying and densification treatment is controlled at 0.8%~1.5%; the residence time of the raw filament in the drying unit is determined according to the filament bundle specifications: 120~160 s for 3K~6K filament bundles and 180~240 s for 12K filament bundles.

[0014] Further specifying, after S2, it also includes: S3, cooling the dried and densified raw yarn to room temperature by horizontal blowing with clean air at room temperature; S4, winding the cooled raw yarn in parallel with rollers, with the winding tension controlled at 12~28 cN / tex, wherein the winding tension of 3K~6K yarn bundles is 12~20 cN / tex, the winding tension of 7K~11K yarn bundles is 18~26 cN / tex, and the winding tension of 12K yarn bundles is 20~28 cN / tex.

[0015] Further specified, the precursor fiber in S1 travels back and forth in the steam chamber 3 to 5 times, with each time having an effective length of 8 to 12 m, and a total effective steam treatment length of 24 to 60 m.

[0016] The beneficial effects of this invention are as follows: After high-temperature saturated steam co-treatment, the densification uniformity of the precursor fiber is significantly improved, and the bulk density CV value can be controlled within 3%. Simultaneously, the orientation degree and crystal regularity of the macromolecular chains are significantly enhanced, providing high-quality precursor fibers with uniform structure and stable quality for subsequent carbonization processes. Furthermore, this method is adaptable to different specifications of filament bundles from 3K to 12K and is compatible with various spinning processes such as dry-jet wet spinning and wet spinning, showing promising prospects for industrial application. Attached Figure Description

[0017] Figure 1 This is a flowchart illustrating the method of the present invention. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] like Figure 1 As shown, the method of the present invention includes a steam treatment step, a drying and densification step, and a cooling and winding step. In the steam treatment step, the polyacrylonitrile-based carbon fiber precursor, after coagulation, washing, and oiling, is introduced into a saturated steam pretreatment unit. In a high-temperature saturated steam environment, it undergoes infiltration, steam lifting, and stretching treatments to remove residual spinning solvents and impurities from the precursor surface and adjust the moisture content to the target range. In the drying and densification step, the steam-treated precursor is sent to a drying unit for drying and densification treatment, further reducing the moisture content of the precursor to the target range. The process parameters for each step can be adaptively adjusted according to the precursor fiber bundle specifications. The method of this application is particularly applicable to polyacrylonitrile-based carbon fiber precursors of 3K to 12K specifications and is compatible with various spinning processes such as dry-jet wet spinning and wet spinning.

[0020] In the steam treatment process, the polyacrylonitrile-based carbon fiber precursor has undergone solidification, washing, and oiling processes before entering the saturated steam pretreatment unit. Its moisture content is 10% to 50%, and the fiber bundle specifications are 3K to 12K. The precursor is introduced into the saturated steam pretreatment unit at a speed of 5 to 20 m / min. The saturated steam pretreatment unit is a closed cavity structure. The precursor travels back and forth within the cavity 3 to 5 times, with each pass having an effective length of 8 to 12 m, for a total effective steam treatment length of 24 to 60 m. The steam treatment environmental parameters are controlled as follows: temperature 120 to 180℃, pressure 0.2 to 0.8 MPa. Under saturated conditions, pressure and temperature correspond one-to-one: 0.2 MPa corresponds to a saturated temperature of 120℃, and 0.8 MPa corresponds to a saturated temperature of 175 to 180℃. Intermediate pressures are matched to the corresponding temperatures according to the physical properties of saturated steam, relying on pressure to ensure a saturated steam environment inside the cavity and preventing overheated steam. The steam flow rate is controlled between 0.6 and 1.0 m / s. A flow rate below 0.6 m / s results in poor steam permeability and uneven temperature distribution within the cavity; a flow rate above 1.0 m / s causes the high-speed airflow to scour the fiber bundles, leading to friction between the bundles and the generation of numerous fuzzy fibers. The steam purity is no less than 99.9%, with calcium ion content less than 0.02 mg / L and sodium ion content less than 0.02 mg / L. Metal ions remaining inside the precursor fiber will form defects after carbonization, affecting the strength of the carbon fiber. A steam purity of 99.92% to 99.95% is preferred. The residence time of the precursor fiber in the saturated steam pretreatment unit is 30 to 120 s, specifically determined according to the fiber bundle specifications: 30 to 60 s for 3K fiber bundles, 60 to 70 s for 6K fiber bundles, and 80 to 120 s for 12K fiber bundles. Too short a residence time prevents sufficient solvent removal from the micropores, while too long a time reduces production efficiency and may even cause molecular chain relaxation. During steam treatment, stretching is applied with a total stretching ratio of 1.10 to 1.16, which is the ratio of the fiber speed at the steam chamber outlet to the fiber speed at the inlet. The stretching load distribution is as follows: 60% stretching is carried out in the front section of the steam chamber, 30% in the middle section, and 10% at the outlet. The high-temperature steam's plasticizing effect is fully utilized in the early stages to complete most of the stretching, while a small proportion of stretching is used for shaping in the later stages to alleviate macromolecular shrinkage. The steam temperature is selected based on the following: the glass transition temperature of polyacrylonitrile precursor fiber is approximately 105℃. Above 105℃, the molecular chain segments are capable of movement; below 120℃, the plasticizing effect is insufficient; and above 180℃, the polyacrylonitrile macromolecules undergo thermal degradation, causing the precursor fiber to yellow and its strength to decrease. Therefore, 120 to 180℃ is selected as the appropriate steam treatment temperature range.The mechanism of steam penetration and stripping is as follows: At high temperatures, water molecules are small and can penetrate into the micropores of polyacrylonitrile precursor fibers. Water molecules are miscible with polar solvents such as dimethyl sulfoxide, dimethylacetamide, and dimethylformamide. The high-speed flowing steam carries the dissolved solvent molecules out of the fiber interior, simultaneously sweeping away small molecule impurities attached to the fiber surface, achieving deep impurity removal. Compared to ordinary hot water cleaning or organic solvent cleaning, the molecules of high-temperature saturated steam can penetrate deep into the microporous structure, simultaneously completing molecular orientation during solvent removal. Furthermore, the steam condensate can be recycled, resulting in lower processing costs. The mechanism for achieving consistent outlet performance across a wide inlet moisture content range of 10% to 50% is as follows: This application employs a two-stage structure combining drying and conditioning with steam treatment. The first step, gradient drying, uniformly adjusts precursor fibers with different initial moisture contents to 0.8% to 1.5%, then introduces them into the steam chamber to replenish moisture. This drying step offsets fluctuations in inlet moisture content, thus ensuring stable products within an inlet moisture content range of 10% to 50%.

[0021] In the drying and densification process, a composite drying method is adopted, primarily using hot roller drying with auxiliary heating from both sides. Infrared drying is not used throughout the process. The hot rollers ensure heat conduction, and the hot air evenly distributes the temperature on both sides of the filament bundle, preventing uneven heating in certain areas. The drying medium is clean air at normal pressure, and the drying chamber is circulated with flowing air to promptly remove volatile solvent vapors and prevent solvent from re-adhering to the surface of the raw filament. During the drying process, a stretching ratio of 1.03 to 1.08 is applied. This low stretching ratio constrains the filament bundle relaxation, preventing wrinkles and defects inside the fiber. The drying and densification treatment employs a three-stage gradient temperature increase: the first stage, the preheating zone, is 75 to 85°C to remove surface free water; the second stage, the main drying zone, is 95 to 105°C to remove bound water from the micropores; and the third stage, the conditioning zone, is 115 to 125°C to balance the moisture content of the surface and core layers of the monofilament. This three-stage gradient temperature increase avoids the problem of rapid evaporation of surface moisture while internal moisture is difficult to remove, effectively suppressing the formation of a core-sheath structure. After drying and densification, the moisture content of the raw yarn is controlled between 0.8% and 1.5%. If the moisture content exceeds 1.5%, the fibers are prone to bubbling during subsequent steam treatment. If the moisture content is below 0.8%, the raw yarn is too rigid, and breakage and fuzzing are likely to occur during steam treatment. The residence time of the raw yarn in the drying unit is determined according to the yarn bundle specifications: 120 to 160 s for 3K to 6K yarn bundles, and 180 to 240 s for 12K yarn bundles. For other specifications between 3K and 12K, the residence time can be adjusted accordingly within the above ranges based on the yarn bundle specifications.

[0022] In the cooling and take-up process, the raw yarn, after drying and densification, is first cooled to room temperature by transverse blowing with clean air. This cooling process fixes the orientation structure of the macromolecules and inhibits the relaxation and shrinkage of polyacrylonitrile molecules at high temperatures. The cooled raw yarn is then wound into a parallel roller, with guide rollers ensuring a flat yarn bundle arrangement and avoiding yarn overlap and compression. The take-up speed is higher than the spinning inlet speed, and the speed difference matches the total draw ratio of the drying and steam sections. The overall draw ratio is the product of the drying draw ratio and the steam draw ratio, and the overall draw is achieved by the speed difference between the front and back sections. The take-up tension is controlled at 12 to 28 cN / tex, determined according to the yarn bundle specifications: 12 to 20 cN / tex for 3K to 6K yarn bundles, 18 to 26 cN / tex for 7K to 11K yarn bundles, and 20 to 28 cN / tex for 12K yarn bundles. Too little tension results in loose winding, while too much tension introduces residual stress into the raw yarn.

[0023] Example 1: 3K dry-jet wet-spun polyacrylonitrile precursor was selected. The precursor was coagulated, washed, and oiled, with a moisture content of 10% and a running speed of 12 m / min. A three-stage gradient heating method was used, with temperatures of 76℃, 100℃, and 116℃, a drying residence time of 130 s, and a drying draw ratio of 1.03. The steam pressure was 0.2 MPa, corresponding to a saturation temperature of 120℃, a steam flow rate of 0.6 m / s, and a steam purity of 99.92%. The process involved three reciprocating passes with a steam residence time of 30 s. Draw was applied during the steam treatment process, with a total draw ratio of 1.10, distributed as follows: 60% in the front section, 30% in the middle section, and 10% in the rear section. The take-up tension was 15 cN / tex. Testing showed a 99.1% residual solvent removal rate, a moisture content CV of 3.1%, a bulk density CV of 2.0%, an orientation degree of 0.91, and a crystallinity of 71%. After oxidation and carbonization treatment, the carbon fiber strength was 6.4 GPa.

[0024] Example 2: 6K dry-jet wet-spun polyacrylonitrile precursor was selected. The precursor was coagulated, washed, and oiled, with a moisture content of 30% and a running speed of 9 m / min. A three-stage gradient heating method was used, with temperatures of 80℃, 103℃, and 120℃, a drying residence time of 180 s, and a drying draw ratio of 1.05. The steam pressure was 0.5 MPa, corresponding to a saturation temperature of 150℃, a steam flow rate of 0.8 m / s, and a steam purity of 99.93%. The process involved four reciprocating passes with a steam residence time of 60 s. Draw was applied during the steam treatment, with a total draw ratio of 1.13, distributed as follows: 60% in the initial stage, 30% in the middle stage, and 10% in the final stage. The take-up tension was 20 cN / tex. Testing showed a 99.3% residual solvent removal rate, a moisture content CV of 3.3%, a bulk density CV of 2.2%, an orientation degree of 0.94, and a crystallinity of 76%. After oxidation and carbonization treatment, the carbon fiber strength was 6.1 GPa.

[0025] Example 3: 12K dry-jet wet-spun polyacrylonitrile precursor yarn was selected. This yarn was coagulated, washed, and oiled, with a moisture content of 50% and a running speed of 6 m / min. A three-stage gradient heating method was used, with temperatures of 78℃, 105℃, and 122℃, a drying residence time of 230 s, and a drying draw ratio of 1.08. The steam pressure was 0.8 MPa, corresponding to a saturation temperature of 180℃, a steam flow rate of 1.0 m / s, and a steam purity of 99.95%. The yarn was passed through 5 times, with a steam residence time of 120 s. Draw was applied during the steam treatment process, with a total draw ratio of 1.16, distributed as follows: 60% in the initial stage, 30% in the middle stage, and 10% in the final stage. The take-up tension was 26 cN / tex. Testing showed a 99.6% residual solvent removal rate, a moisture content CV of 4.5%, a bulk density CV of 2.8%, an orientation degree of 0.96, and a crystallinity of 79%. After oxidation and carbonization treatment, the carbon fiber strength is 5.9 GPa.

[0026] Example 4: 6K dry-jet wet-spun polyacrylonitrile precursor was selected. The precursor was coagulated, washed, and oiled, with a moisture content of 30% and a running speed of 10 m / min. A three-stage gradient heating method was used, with temperatures of 78℃, 102℃, and 118℃, a drying residence time of 150 s, and a drying draw ratio of 1.04. The steam pressure was 0.32 MPa, corresponding to a saturation temperature of 135℃, a steam flow rate of 0.7 m / s, and a steam purity of 99.92%. The process involved four reciprocating passes with a steam residence time of 65 s. Draw was applied during the steam treatment process, with a total draw ratio of 1.12, distributed as follows: 60% in the initial stage, 30% in the middle stage, and 10% in the final stage. The take-up tension was 18 cN / tex. Testing showed a 99.2% removal rate of residual solvent on the surface and a bulk density (CV) of 2.1%. After oxidation and carbonization treatment, the carbon fiber strength was 6.2 GPa.

[0027] Example 5: 12K dry-jet wet-spun polyacrylonitrile precursor yarn was selected. This precursor yarn was coagulated, washed, and oiled, with a moisture content of 40% and a running speed of 8 m / min. A three-stage gradient heating method was used, with temperatures of 80℃, 104℃, and 120℃, a drying residence time of 200 s, and a drying draw ratio of 1.06. The steam pressure was 0.6 MPa, corresponding to a saturation temperature of 160℃, a steam flow rate of 0.9 m / s, and a steam purity of 99.94%. The yarn was passed through 5 times, with a steam residence time of 90 s. Draw was applied during the steam treatment process, with a total draw ratio of 1.14, distributed as follows: 60% in the front section, 30% in the middle section, and 10% in the rear section. The take-up tension was 24 cN / tex. Testing showed a 99.4% removal rate of residual solvent on the surface and a bulk density (CV) of 2.4%. After oxidation and carbonization treatment, the carbon fiber strength was 6.0 GPa.

[0028] Example 6: 3K dry-jet wet-spun polyacrylonitrile precursor was selected. The precursor was coagulated, washed, and oiled, with a moisture content of 15% and a running speed of 14 m / min. A three-stage gradient heating method was used, with temperatures of 82℃, 98℃, and 116℃, a drying residence time of 125 s, and a drying draw ratio of 1.03. The steam pressure was 0.7 MPa, corresponding to a saturation temperature of 170℃, a steam flow rate of 0.75 m / s, and a steam purity of 99.93%. The process involved three reciprocating passes with a steam residence time of 45 s. Draw was applied during the steam treatment process, with a total draw ratio of 1.11, distributed as follows: 60% in the front section, 30% in the middle section, and 10% in the rear section. The take-up tension was 14 cN / tex. Testing showed a 99.5% removal rate of residual solvent on the surface and a bulk density (CV) of 1.9%. After oxidation and carbonization treatment, the carbon fiber strength was 6.3 GPa.

[0029] Comparative Example 1: 12K precursor fibers from the same batch as those in Example 3 were treated using conventional processes, without undergoing the saturated steam synergistic pretreatment step described in this application. Testing revealed that the densified precursor fibers had a moisture content (CV) of 12%, a bulk density (CV) of 8%, a crystallinity of 65%, and an orientation degree of 0.85. The filament count during the pre-oxidation stage was 1.5 fibers / 100,000 m. The final carbon fiber strength was 5.0 GPa, and the modulus was 370 GPa.

[0030] Comparative Example 2: Immersion in 95℃ hot water for 60 seconds was used instead of saturated steam treatment. This precursor fiber was from the same batch as in Example 3, and the remaining drying, drawing, and winding parameters were consistent with Example 3. Testing showed that the surface residual solvent removal rate was 86.7%, the moisture content CV was 7.9%, and the bulk density CV was 6.6%. The filament rate during the pre-oxidation stage was 1.2 strands / 100,000 m. The final carbon fiber strength was 5.0 GPa.

[0031] Comparative Example 3: The steam parameters were the same as in Example 3, but the drying process was not segmented with temperature increases; the overall temperature was kept constant at 120°C. Testing showed that the moisture content CV was 8.3%, the bulk density CV was 5.1%, and the filament count in the pre-oxidation stage was 0.96 strands / 100,000 m. This demonstrates that segmented drying is necessary for controlling the uniformity of moisture content and densification.

[0032] Comparative Example 4: The 12K precursor fiber skipped the gradient drying process and entered the steam chamber directly, with steam parameters consistent with Example 3. The initial moisture content of the precursor fiber was too high, the fibers became sticky, the fiber bundles clumped together, and the solvent residue exceeded the standard, making normal production impossible. This verified the necessity of synergistic drying and steam treatment.

[0033] Comparative Example 5: 12K precursor fibers underwent only three-stage gradient drying without passing through a steam chamber, and the drying parameters were consistent with those of Example 3. Testing revealed an orientation degree of 0.85, a crystallinity of 65%, and a significant decrease in carbon fiber modulus, proving that the steam plasticizing and stretching process is indispensable.

[0034] Comparative Example 6: The steam temperature was set to 110°C, and the steam pressure was adjusted accordingly. All other parameters remained the same as in Example 3. The steam temperature did not reach the glass transition temperature of polyacrylonitrile, resulting in insufficient plasticization. The surface residual solvent removal rate was only 90.2%, and the improvement in fiber orientation was not significant.

[0035] Comparative Example 7: The steam temperature was set to 190℃, and the steam pressure was adjusted accordingly. All other parameters remained the same as in Example 3. Polyacrylonitrile molecules underwent thermal degradation, the precursor fibers turned yellow, and the number of broken fibers increased dramatically, making normal production impossible.

[0036] As can be seen from the above embodiments and comparative examples, this application achieves a synergistic effect of efficient cleaning of the precursor fiber, uniform control of moisture content, and densification stretching through high-temperature saturated steam synergistic pretreatment, significantly improving the structural uniformity and orientation of the precursor fiber. Compared with conventional processes, the moisture content CV value of the precursor fiber treated by this application is reduced to below 4.5%, the bulk density CV value is controlled within 2.8%, and both orientation and crystallinity are significantly improved, ultimately resulting in a significant improvement in the mechanical properties of the carbon fiber. The main performance data of each embodiment and comparative example are summarized in Table 1.

[0037] Table 1 Summary of key performance data for each embodiment and comparative example

[0038] Example 1 99.1% 3.1% 2.0% 0.91 71% 6.4 GPa Example 2 99.3% 3.3% 2.2% 0.94 76% 6.1 GPa Example 3 99.6% 4.5% 2.8% 0.96 79% 5.9 GPa Example 4 99.2% — 2.1% — — 6.2 GPa Example 5 99.4% — 2.4% — — 6.0 GPa Example 6 99.5% — 1.9% — — 6.3 GPa Comparative Example 1 — 12.0% 8.0% 0.85 65% 5.0 GPa Comparative Example 2 86.7% 7.9% 6.6% — — 5.0 GPa Comparative Example 3 — 8.3% 5.1% — — — Comparative Example 5 — — — 0.85 65% — Comparative Example 6 90.2% — — — — —

[0039] The testing methods for each performance index in this application are as follows: Moisture content is tested according to GB / T 6505-2017, Chemical Fiber Moisture Regain Test Method, using an oven drying method at 105±2℃ to constant weight, and the mass loss rate before and after drying is calculated; Moisture content fluctuation coefficient (CV) is calculated as follows: Random samples are taken every 10 m along the fiber bundle length, with no fewer than 20 samples. The moisture content of each sample is measured, and the CV is calculated as the standard deviation divided by the average value and then multiplied by 100%; Densification uniformity, i.e., bulk density (CV), is calculated as follows: One sample is taken every 10 m along the fiber bundle length, with no fewer than 10 samples, according to GB / T... 14343-2008 The linear density was determined, and the bulk density was calculated by multiplying the CV by the standard deviation by the average value and then by 100%. Crystallinity was determined by X-ray diffraction, and the crystallinity was calculated by the ratio of the crystallization diffraction peak area to the total scattering area. Orientation was determined by X-ray diffraction or the sound velocity method to determine the degree of orientation of the molecular chains in the fiber along the fiber axis. The surface residual solvent removal rate was determined by gas chromatography, using dimethyl sulfoxide, dimethylacetamide or dimethylformamide standards to establish a standard curve, and the amount of solvent residue in the raw yarn before and after treatment was determined to calculate the removal rate. The pre-oxidized fuzz rate was counted by an online fuzz detector, and the number of fuzz breaks per 100,000 meters of length was counted.

[0040] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for pretreating carbon fiber precursor fibers with high-temperature saturated steam, characterized in that, Includes the following steps: S1. The polyacrylonitrile-based carbon fiber precursor, after coagulation, washing, and oiling, is introduced into the saturated steam pretreatment unit at a running speed of 5~20 m / min. It is treated in a high-temperature saturated steam environment with a temperature of 120~180℃ and a pressure of 0.2~0.8 MPa for 30~120 s. Through the permeation and stripping of saturated steam, the residual spinning solvent and impurities on the surface of the precursor are removed, and the moisture content of the precursor is adjusted to 8%~15%. S2. The steam-treated precursor fiber is sent to the drying unit and dried and densified at 80~180℃ to obtain the pretreated carbon fiber precursor fiber.

2. The method for high-temperature saturated steam co-pretreatment of carbon fiber precursor as described in claim 1, characterized in that, The polyacrylonitrile-based carbon fiber precursor described in S1 has a bundle specification of 3K~12K and a moisture content of 10%~50% before entering the saturated steam pretreatment unit.

3. The method for high-temperature saturated steam co-pretreatment of carbon fiber precursor as described in claim 1, characterized in that, The high-temperature saturated steam described in S1 has a flow rate of 0.6~1.0 m / s, a steam purity ≥99.9%, and a Ca content in the steam. 2+ Content <0.02 mg / L, Na + Content < 0.02 mg / L.

4. The method for high-temperature saturated steam co-pretreatment of carbon fiber precursor as described in claim 1, characterized in that, The processing time of the raw filament in the saturated steam pretreatment unit described in S1 is determined according to the filament specifications: 3K filament for 30~60 s, 6K filament for 60~70 s, and 12K filament for 80~120 s.

5. The method for high-temperature saturated steam co-pretreatment of carbon fiber precursor as described in claim 1, characterized in that, During the saturated steam pretreatment process described in S1, stretching is applied with a total stretching ratio of 1.10 to 1.16 times; wherein the front section of the steam chamber bears 60% of the stretching, the middle section of the chamber bears 30% of the stretching, and the rear section of the chamber outlet bears 10% of the stretching.

6. The method for high-temperature saturated steam co-treatment of carbon fiber precursor as described in claim 1, characterized in that, in S2, the drying and densification treatment adopts a composite drying method with hot roller drying as the main method and hot air auxiliary heating on both sides, the drying medium is clean air at normal pressure, and stretching is applied during the drying process, with a stretching ratio of 1.03 to 1.08 times.

7. The method for high-temperature saturated steam co-pretreatment of carbon fiber precursor as described in claim 1, characterized in that, in S2, the drying and densification treatment adopts a three-stage gradient heating: the first stage preheating zone 75~85℃; the second stage main drying zone 95~105℃; and the third stage tempering zone 115~125℃.

8. The method for high-temperature saturated steam co-pretreatment of carbon fiber precursor as described in claim 1, characterized in that, in S2, the moisture content of the precursor after the drying and densification treatment is controlled to be 0.8%~1.5%; the residence time of the precursor in the drying unit is determined according to the fiber bundle specifications: 120~160 s for 3K~6K fiber bundles, and 180~240 s for 12K fiber bundles.

9. The method for high-temperature saturated steam co-pretreatment of carbon fiber precursor as described in claim 1, characterized in that, Following S2, the following also includes: S3. Cool the dried and densified raw yarn to room temperature by horizontal blowing with clean air at room temperature. S4. The cooled raw yarn is wound in parallel on a roller, and the winding tension is controlled at 12~28 cN / tex. The winding tension of the 3K~6K yarn bundle is 12~20 cN / tex, the winding tension of the 7K~11K yarn bundle is 18~26 cN / tex, and the winding tension of the 12K yarn bundle is 20~28 cN / tex.

10. The method for high-temperature saturated steam co-pretreatment of carbon fiber precursor as described in claim 1, characterized in that, The precursor fiber described in S1 travels back and forth in the steam chamber for 3 to 5 single passes, with each single pass having an effective length of 8 to 12 m, and a total effective steam treatment length of 24 to 60 m.

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