Pre-oxidation preparation method of T700-grade 192K ultra-large tow carbon fiber

Abstract

The invention discloses a pre-oxidation preparation method of T700 grade 192K ultra-large tow carbon fiber. The core of the method is as follows: the pre-oxidation process is accurately divided into four continuous temperature zones (220 + / -1 DEG C, 230 + / -1 DEG C, 240 + / -1 DEG C and 250 + / -1 DEG C), the treatment time of each temperature zone is strictly controlled to be about 17 minutes, and the wind speed (5-7-6.0-7.5 m / s) for reinforcing the 192K ultra-large tows is matched. According to the process, by precisely controlling the reaction process, the problem of uneven pre-oxidation of the 192K ultra-large tows is effectively solved, and the total treatment time is about 68 minutes. The tensile strength of the obtained 192K carbon fiber is larger than or equal to 4.80 GPa, the performance dispersion coefficient CV is smaller than or equal to 3.0%, the modulus is 228-235 GPa, the performance stably reaches the T700 level, and the 192K carbon fiber is suitable for the industrial fields of new energy automobiles, wind power and the like.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high-performance carbon fiber preparation, and particularly relates to a method for preparing T700-grade 192K super-bundle carbon fiber through a precise four-temperature-zone pre-oxidation process. BACKGROUND

[0002] Carbon fiber has become a key material for new energy and lightweight transportation due to its excellent specific strength and specific modulus. Among them, the application demand of super-bundle carbon fiber (such as 192K) has increased sharply due to its higher production efficiency and lower cost. In the preparation process of polyacrylonitrile (PAN)-based carbon fiber, pre-oxidation is a crucial link, which aims to convert linear PAN molecules into thermally stable ladder structures. For 192K super-bundle fiber, this process is prone to local overheating, fusion, and uneven oxidation due to uneven heat accumulation and oxygen diffusion inside and outside the super-bundle, resulting in a decrease in the mechanical properties of the final carbon fiber and an increase in dispersion, making it difficult to stably reach high-grade (such as T700 grade: tensile strength ≥ 4900 MPa) requirements. Traditional pre-oxidation methods use double-temperature-zone or slow programmed heating methods, which have problems such as wide process window, insufficient control precision, and long time consumption, making it difficult to balance production efficiency and product high performance and high consistency. SUMMARY

[0003] The application aims to provide a pre-oxidation method that can be industrialized, has high repeatability, and can stably prepare T700-grade 192K super-bundle carbon fiber.

[0004] The core of the application is to design a four-temperature-zone pre-oxidation process for 192K super-bundle, which is time-driven, temperature-precise, and wind speed-enhanced:

[0005] First temperature zone (initiation zone, ~222℃): wind speed of 5m / s. About 17 minutes of processing time ensures that the reaction is mild and uniform in the thicker 192K super-bundle.

[0006] Second temperature zone (acceleration zone, ~235℃): wind speed of 5m / s. About 17 minutes of processing time, the enhanced wind speed can more effectively start to take away the increased reaction heat inside the 192K super-bundle.

[0007] Third temperature zone (main reaction zone, ~245℃): wind speed significantly increased to 7m / s. About 17 minutes of precise control, the stronger wind speed is crucial for preventing heat accumulation in the 192K super-bundle during the most intense reaction stage.

[0008] Fourth temperature zone (stabilization zone, ~255℃): the wind speed is increased to the highest 6.0-7.5 m / s. The high wind speed ensures the thermal safety of the thicker 192K super large filament at the highest temperature, so that the structure stabilization process is sufficient and uniform. The four temperature zones are strictly controlled for about 17 minutes, and the total time is about 68 minutes. The matching carbonization process adopts a more moderate heating rate and slightly longer holding time to adapt to the characteristics of the 192K super large filament, and to optimize the carbon yield and structure.

[0009] Successful application to 192K super large filament: through targeted enhancement of wind speed and optimization of carbonization system, the precise four-temperature zone process is successfully applied to the more difficult-to-process 192K super large filament.

[0010] Performance stable and up to standard: the tensile strength of the prepared 192K carbon fiber is stable ≥4.80 GPa, reaching the T700 level, and the single filament strength dispersion coefficient (CV value) is ≤3.0%.

[0011] High production efficiency: the total pre-oxidation time is still controlled at about 68 minutes, which has obvious efficiency advantages compared with the traditional process.

[0012] Excellent process repeatability: very suitable for the industrialized continuous production of 192K super large filaments. DETAILED DESCRIPTION

[0013] The following scheme can be specifically used

[0014] The following embodiments are specifically described in combination with specific embodiments, and it is necessary to point out here that the following embodiments are only used to further illustrate the present application, and cannot be understood as limiting the protection scope of the present application. Some non-essential improvements and adjustments of the present application made by those skilled in the art according to the content of the present application still fall within the protection scope of the present application.

[0015] Example 1

[0016] The raw filament is a 192K raw filament spun from a PAN copolymer (containing 2.0wt% itaconic acid) with a number average molecular weight of ~180,000.

[0017] Preheat: 155°C, 5 m / s, 12 minutes. Pre-oxidation (atmosphere: 21.0% O2, dew point -55°C, furnace pressure 80 Pa): First temperature zone: 222°C, 5.0 m / s, 17.0 minutes. Second temperature zone: 235°C, 5.0 m / s, 17.0 minutes. Third temperature zone: 245°C, 7.0 m / s, 17.0 minutes. Fourth temperature zone: 255°C, 6-7.5 m / s, 17.0 minutes. (Total pre-oxidation time: 68 minutes) Slow cooling: 255°C → 175°C, 2.2 m / s, 18 minutes. Carbonization stage (high purity nitrogen): Low temperature carbonization: at 3.0°C / min → 500°C, hold for 18 minutes. High temperature carbonization: at 4.0°C / min → 1350°C, hold for 2.0 minutes.

[0018] Test results showed: Tensile strength: 4.82 GPa (average, n = 20) Strength CV: 2.8% Tensile modulus: 230 GPa Carbon yield: 49.5%

[0019] Example 2

[0020] Preform: 192K preform spun from PAN copolymer (containing 2.0 wt% itaconic acid) having a number average molecular weight of ~180,000. Preheat: 150°C, 3 m / s, 15 minutes. Pre-oxidation (atmosphere: 20.0% O2, dew point -50°C, furnace pressure 60 Pa): First temperature zone: 220°C, 3.5 m / s, 18.0 minutes. Second temperature zone: 233°C, 4.2 m / s, 18.0 minutes. Third temperature zone: 243°C, 5.8 m / s, 16.0 minutes. Fourth temperature zone: 253°C, 6.5 m / s, 16.0 minutes.

[0021] (total pre-oxidation time: 68 minutes)

[0022] Slow cooling: 253°C → 170°C, 1.8 m / s, 20 minutes. Carbonization stage (high purity nitrogen): Low temperature carbonization: at 2.8°C / min → 480°C, hold for 20 minutes. High temperature carbonization: at 3.8°C / min → 1320°C, hold for 2.2 minutes. Test results showed: Tensile strength: 4.75 GPa (average, n = 20) Strength CV: 3.2% Tensile modulus: 228 GPa Carbon yield: 48.8%

[0023] Example 3

[0024] Precursor: 192K precursor spun from PAN copolymer (containing 2.0 wt% itaconic acid) having a number average molecular weight of ~180,000. Preheat: 158°C, 6 m / s, 8 minutes. Pre-oxidation (atmosphere: 21.5% O2, dew point -58°C, furnace pressure 90 Pa): First temperature zone: 223°C, 5.5 m / s, 16.5 minutes. Second temperature zone: 236°C, 5.8 m / s, 16.5 minutes. Third temperature zone: 246°C, 7.2 m / s, 17.5 minutes. Fourth temperature zone: 256°C, 7.8 m / s, 17.5 minutes.

[0025] (total pre-oxidation time: 68 minutes)

[0026] Slow cooling: 256°C → 178°C, 2.8 m / s, 16 minutes. Carbonization stage (high purity nitrogen): Low temperature carbonization: 3.2°C / min → 510°C, hold for 16 minutes. High temperature carbonization: 4.2°C / min → 1360°C, hold for 1.8 minutes. Test results show: Tensile strength: 4.85 GPa (average, n=20) Strength CV: 2.6% Tensile modulus: 231 GPa Carbon yield: 50.0%

[0027] Example 4

[0028] Precursor: 192K precursor spun from PAN copolymer (containing 2.0 wt% itaconic acid) having a number average molecular weight of ~18000. Preheat: 152°C, 4.5 m / s, 13 minutes. Pre-oxidation (atmosphere: 21.2% O2, dew point -53°C, furnace pressure 70 Pa): First temperature zone: 221°C, 4.8 m / s, 17.5 minutes. Second temperature zone: 234°C, 5.2 m / s, 17.5 minutes. Third temperature zone: 244°C, 6.8 m / s, 16.5 minutes. Fourth temperature zone: 254°C, 7.5 m / s, 16.5 minutes.

[0029] (total pre-oxidation time: 68 minutes)

[0030] Slow cooling: 254°C → 172°C, 2.3 m / s, 19 minutes. Carbonization stage (high purity nitrogen): Low temperature carbonization: 3.1°C / min → 495°C, hold for 19 minutes. High temperature carbonization: 4.1°C / min → 1345°C, hold for 2.1 minutes. Test results show: Tensile strength: 4.79 GPa (average, n=20) Strength CV: 2.9% Tensile modulus: 229 GPa Carbon yield: 49.2%

[0031] Comparative Example: Conventional process treatment of 192K super large tow

[0032] (Using the same 192K precursor as the example, traditional two-zone process: 230℃ / 50min + 260℃ / 50min, constant wind speed 3.0m / s, total time 100min)

[0033] Performance test results: tensile strength: 4.25GPa strength CV value: 8.5% carbon yield: 46.0%

[0034] The results show that for 192K super large tow, the traditional process not only has lower performance and worse consistency, but also takes longer time, and the advantages of the present application are more significant.

[0035] Conclusion

[0036] The four-zone precise pre-oxidation process provided by the present application successfully realizes effective management of the super large tow PAN fiber cyclization / oxidation reaction kinetics by optimizing the enhanced wind speed and adjusting the supporting process for 192K super large tow. The process can stably and reliably produce 192K super large tow carbon fiber with performance reaching T700 level and high consistency, providing key technical support for its large-scale application in the industrial field.

Claims

1. A process for the production of T700 grade ultra-large tow carbon fibers, characterized by, The method comprises a pre-oxidation treatment: polyacrylonitrile (PAN) based 192K super large tow fiber is subjected to four-zone precise temperature and air flow control treatment in a pre-oxidation furnace under an oxygen-containing atmosphere, and the treatment comprises four continuous and temperature-accurately controlled temperature zones: Step 1 The first temperature zone: the temperature is 220-224℃, the air flow rate is 5m / s, and the treatment time is 16-18 minutes; The second temperature zone: the temperature is 233-237℃, the air flow rate is 5m / s, and the treatment time is 16-18 minutes; The third temperature zone: the temperature is 243-247℃, the air flow rate is 7m / s, and the treatment time is 16-18 minutes; The fourth temperature zone: the temperature is 253-257℃, the air flow rate is 6.0-7.5m / s, and the treatment time is 16-18 minutes; wherein the total time of the pre-oxidation treatment is 64-72 minutes, and the cyclization degree of the fiber is controlled to be between 60% and 65%; Step 2 Carbonization treatment: the pre-oxidized fiber is subjected to high-precision carbonization under an inert atmosphere: Low-temperature carbonization: the temperature is raised to 500±20℃ at a rate of 2.5-3.5℃ / min, and the temperature is maintained for 18±2 minutes; High-temperature carbonization: the temperature is raised to 1350±20℃ at a rate of 3.5-4.5℃ / min, and the temperature is maintained for 2.0±0.5 minutes.

2. The method of claim 1, wherein: In step 1, the oxygen-containing atmosphere has an oxygen volume fraction of 21.0±1.0% and a dew point of ≤-50℃; the number average molecular weight of the PAN-based raw yarn is 170,000-190,000, and the comonomer is itaconic acid with a content of 1.8-2.2wt%.

3. The method according to claim 1 or 2, characterized in that: In step 1, a preheating zone is provided before the first temperature zone, the temperature is 155±10℃, the air flow rate is ≤0.3m / s, and the treatment time is 12±2 minutes; and / or a slow cooling zone is provided after the fourth temperature zone, the temperature is uniformly reduced from 255℃ to below 180℃, the air flow rate is 1.8-2.8m / s, and the time is controlled to be within 18±3 minutes.

4. The method of claim 1 or 2, wherein: In step 1, the air flow direction of each temperature zone is perpendicular to the fiber running direction, and the air flow rate control accuracy is ±0.1m / s and the temperature control accuracy is ±1℃.

5. The method of claim 1 or 2, wherein: The super large tow carbon fiber has a tow number of 192K. Pre-oxidized fiber prepared by the method of any one of claims 1-5, characterized in that the cyclization degree is 62±2%, the density is 1.36-1.39 g / cm 3 , and the fiber color is uniform, the super large tow structure is complete, and there is no fusion phenomenon.

6. A T700 grade macrofilament carbon fiber produced by the method of any one of claims 1-5, characterized by: The tensile strength is ≥4800MPa (4.80GPa), the single filament strength dispersion coefficient (CV value) is ≤3.0%, the tensile modulus is 228-235GPa, and the carbon yield is ≥49%.

7. Application of the T700-grade super large tow carbon fiber according to claim 7 in the fields of new energy automobile battery box packaging, wind power blade main beam, unmanned aerial vehicle body structure, and pressure container.