Large-diameter high-strength medium-modulus carbon fiber and preparation method thereof

Abstract

The invention relates to a large-diameter high-strength medium-modulus carbon fiber and a preparation method thereof, and belongs to the technical field of carbon fiber production. The preparation method comprises the following steps: copolymerizing acrylonitrile and a comonomer to prepare a spinning solution; in the spinning solution, the mass percent of the copolymer is 15wt%-35wt%, and the viscosity average molecular weight is 250,000-550,000; the optical density difference value delta OD of the skin part and the core part of the precursor is smaller than or equal to 0.3, the orientation degree is larger than or equal to 87%, and the average defect size is smaller than or equal to 120 nm; and sequentially carrying out pre-oxidation, low-temperature carbonization, high-temperature carbonization and the like on the precursor to obtain the large-diameter high-strength medium-modulus carbon fiber. The large-diameter, high-strength and medium-modulus carbon fiber is prepared by matching the precursor with the radial homogeneous structure with an oxygen carbonization process, and the application requirements in the fields of pressure vessels, low-altitude economy, commercial spaceflight and the like can be greatly met.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of carbon fiber production, and particularly relates to a large-diameter high-strength medium-modulus carbon fiber and a preparation method thereof. BACKGROUND

[0002] The tensile strength of the high-strength medium-modulus carbon fiber is 4.5 GPa to 7.5 GPa, and the tensile modulus is 260 GPa to 350 GPa, which has the dual advantages of 'high strength and anti-fracture' and'medium modulus and rigidity preservation', and thus can simultaneously realize lightweight and structural stability, and has a wide application prospect in the fields of pressure vessels, low-altitude economy and commercial aerospace. For high-strength carbon fibers, the diameter of the fiber often presents a negative correlation with the tensile strength, and the radial unevenness of the carbon fiber with a larger diameter is serious, which is not conducive to the improvement of the mechanical properties. According to the Weibull weakest link theory and the Griffith fracture theory, the fiber tensile fracture usually occurs at the largest defect, and the larger the fiber size, the higher the probability of occurrence of a larger defect, so the thinner the diameter of the fiber, the higher the tensile strength of the carbon fiber. For example, the diameter of T800-grade carbon fiber is about 5 μm, and the tensile strength thereof can reach more than 5500 MPa, while the diameter of T700-grade carbon fiber is about 7 μm, and the tensile strength thereof is relatively low, about 4500 MPa to 4900 MPa.

[0003] In the prior art, in order to improve the mechanical properties of carbon fibers, the commonly used strategy is fine denier, that is, reducing the diameter of the carbon fiber to prepare a carbon fiber with higher crystallinity, higher orientation, and fewer defects. However, in actual application, the reduction of the diameter is not conducive to the improvement of the compression performance, strength conversion rate and the like of the carbon fiber. The larger the diameter of the carbon fiber, the easier the tows are impregnated when the tows are compounded with resin to prepare a composite material, the higher the molding efficiency, and the higher the compression strength of the composite material. However, at present, due to the limitation of the control technology of the radial structure difference, it is difficult to prepare a large-diameter high-strength medium-modulus carbon fiber with good radial uniformity, high mechanical strength and a large diameter. SUMMARY

[0004] To solve the above problems, the purpose of the embodiments of the present application includes providing a large-diameter high-strength medium-modulus carbon fiber and a preparation method thereof, so as to improve the problem that the existing high-strength carbon fiber preparation technology is difficult to simultaneously improve the diameter and the mechanical strength.

[0005] In a first aspect, the present application provides a preparation method of a large-diameter high-strength medium-modulus carbon fiber, comprising the following steps: S10: copolymerizing acrylonitrile and a comonomer to obtain a spinning dope; in the spinning dope, the mass percentage of the copolymer is 15wt% to 35wt%, and the viscosity-average molecular weight is 250,000 to 550,000; S20: using a dry-jet wet spinning process, the spinning dope is sequentially subjected to coagulation forming, washing, oiling, drying densification, steam drawing to obtain a precursor filament; the light density difference ΔOD between the skin and core of the precursor filament is ≤0.3, the orientation degree is ≥87%, and the average defect size is ≤120 nm; S30: sequentially performing pre-oxidation, low-temperature carbonization, high-temperature carbonization, surface treatment, sizing, drying and winding on the precursor filament to obtain a large-diameter high-strength mesophase carbon fiber.

[0006] In the above technical solution, first, the present application optimizes the copolymer molecular structure by introducing a comonomer to ensure the high drawability of the large-diameter precursor filament and efficient mass and heat transfer under long radial pre-oxidation: (1) introducing a comonomer into the polymer molecular chain structure is conducive to reducing intramolecular hydrogen bonding, facilitating the stretching of the molecular chain in the large-diameter precursor filament, and greatly improving the spinnability of the precursor filament; (2) the concentration of the copolymer is relatively high, and the molecular weight is relatively high, which is conducive to the stable supply of the large-diameter primary fiber dope during subsequent spinning, helps the spinning solution to form a relatively uniform, stable and dense structure during the coagulation forming process, reduces the original defects caused by the process, and effectively reduces the end group defects caused by the length of the long molecular chain. During the subsequent pre-oxidation and carbonization process, a larger planar structure is formed, which is conducive to the preparation of high-performance carbon fibers.

[0007] Secondly, the present application uses the above-mentioned spinning dope combined with a dry-jet wet spinning process to control the large-diameter precursor filament from a microstructure, and a precursor filament with high radial homogeneous structure, high orientation degree and low defects is prepared. (1) By characterizing the light density difference between the skin and core of the precursor filament, ΔOD≤0.3 is controlled, which corresponds to the precursor filament having a relatively optimal radial homogeneous structure. (2) Since the radial structure of the carbon fiber has heredity and inheritance, optimizing the structure of the precursor filament helps to optimize the structure of the carbon fiber. By controlling the orientation degree of the precursor filament to be ≥88% and the average defect size to be ≤120 nm, the prepared carbon fiber has relatively high mechanical strength.

[0008] The precursor filament prepared by the present application has high radial homogeneous structure, high orientation degree and low defects. Through matching the oxygen-carbonization process, the general production of large-diameter high-strength mesophase carbon fiber is realized. The tensile strength of the large-diameter high-strength mesophase carbon fiber prepared is 4.5GPa~7.0GPa, the tensile modulus is 260GPa~350GPa, the diameter is 5.0μm~15μm, and it has good compression performance and strength conversion rate, that is, it can simultaneously realize a large diameter and good mechanical properties, which can greatly meet the application requirements of the fields of pressure vessels, low-altitude economy, commercial aerospace, etc.

[0009] In some embodiments, step S10 comprises: solution polymerizing the acrylonitrile, the first comonomer, the second comonomer, and the initiator in a first solvent to obtain a polymerization stock solution; and subjecting the polymerization stock solution to single-removing, defoaming, and ammoniation to form a spinning stock solution; wherein the first comonomer comprises at least one of itaconic acid amide or vinyl acetate, and the second comonomer comprises at least one of methyl methacrylate or isobutyl acrylate.

[0010] In the above technical solution, by preferably using specific first and second comonomers, the intramolecular hydrogen bonding is further reduced, the molecular chain in the large-diameter filament is stretched, and the spinnability of the filament is greatly improved. Moreover, compared with small-diameter filaments, the large-diameter filaments have a significantly increased radial length, and the mass and heat transfer in the fiber is difficult. By introducing the comonomer having a large side group, a loose channel is formed between the molecular chains, the mass and heat transfer in the fiber is strengthened, and the more side groups also help the molecular chain to form a planar structure by easily resolving the helix during the pre-oxidation stage, and more annular ladder structures are formed, thereby further improving the radial structure homogeneity of the large-diameter carbon fiber, reducing defects, and improving the mechanical properties.

[0011] Further, the ammoniation degree of the spinning stock solution is 1.5-4.0, and the intrinsic viscosity is 2.0-4.0.

[0012] Further, the initiator comprises azobisdimethyl isobutyronitrile; and the first solvent comprises at least one of dimethyl sulfoxide, dimethyl formamide, dimethyl acetamide, nitric acid, a zinc chloride solution, or a sodium thiocyanate solution.

[0013] In some embodiments, in step S20, the coagulation forming section comprises: spraying the spinning stock solution from a spinneret, passing through an air layer, and then entering a coagulation bath to form a nascent fiber; wherein the spinning speed is 15 m / min-30 m / min, and the height of the air layer is 2 mm-15 mm; the coagulation bath comprises a second solvent and water, the mass percentage of the second solvent is 25wt%-55wt%, the number of stages of the coagulation bath is 1-6, the temperature is 3℃-20℃, the pH is 5.0-12.0, and the draw ratio is 1.5-3.0.

[0014] In the technical solution, the high-draft multi-stage coagulation bath is used to effectively prolong the coagulation forming time, and to prepare the high-homogeneity and high-orientation primary fibers. (1) The 1-6 stage coagulation bath is used, and the coagulation forming condition is relatively mild, which is beneficial to the full diffusion, and the roundness and homogeneity of the large-diameter primary fibers are better; (2) According to the temperature-induced coagulation forming mechanism of the dry-jet wet spinning, the coagulation bath temperature of 3-20 ℃ is used to fully ensure the phase separation, and to further promote the homogeneity of the primary fibers; (3) On the basis, the draft ratio is set to 1.5-3.0, and the large draft ratio promotes the polymer macromolecular chains in the primary fibers to arrange along the axial direction from the source, so as to further improve the orientation and reduce the defects. Further, the second solvent includes at least one of dimethyl sulfoxide, dimethyl formamide, dimethyl acetamide, nitric acid, zinc chloride solution, or sodium thiocyanate solution.

[0015] In some embodiments, in step S20, the water washing section includes: the primary fibers obtained through the coagulation forming treatment are washed and stretched at a draft ratio of 0.9-2.0 in a multi-stage water bath at 20-60 ℃, and then stretched at a draft ratio of 2.0-3.0 in a hot water bath at 50-100 ℃. In the technical solution, the primary fibers obtained through the coagulation forming treatment are washed and stretched at a draft ratio of 0.9-2.0 in a multi-stage water bath at 20-60 ℃, and then stretched at a draft ratio of 2.0-3.0 in a hot water bath at 50-100 ℃, which can more effectively remove the residual solvent, so as to reduce the defects of the primary fibers, and is beneficial to promoting the structural units in the fibers to arrange along the axial direction, and further improving the orientation of the primary fibers.

[0016] In some embodiments, in step S20, the oiling section uses the oil agent including the following components in weight percentage: modified silicone oil 30-40 parts, surfactant 5-10 parts, water 50-65 parts, and additive 1-3 parts; in the modified silicone oil, the mass ratio of amino-modified silicone oil, polyether-modified silicone oil, and phenyl-modified silicone oil is (60-75):(20-25):(15-20). In the technical solution, the oil agent with high permeability and high heat resistance is used for the oiling according to the characteristics of the large-diameter primary fiber bundle width and thickness, which has the following advantages: (1) compared with the small-diameter primary fiber, the large-diameter primary fiber has increased running flux, and the bundle width and thickness are increased, which puts higher requirements on the oil agent permeability, and the modified silicone oil is obtained by using the amino-modified silicone oil, the polyether-modified silicone oil, and the phenyl-modified silicone oil and controlling the ratio, so as to improve the permeability and heat resistance of the oil agent, which is beneficial to forming a continuous and heat-stable functional oil film on the fiber surface, and improving the oil agent protection effect; (2) under the same K number, the increased friction between the large-diameter primary fibers causes the increased hairiness, and the high-permeability oil agent helps to improve the hairiness of the primary fibers, enhances the bundling of the primary fibers, and reduces the friction coefficient of the primary fibers. In some embodiments, the residual mass accounts for no less than 75% of the initial mass after the oiling agent is heated at 450℃ for 5 minutes. In the above technical solution, further requirements are proposed for the oiling agent body performance, the oiling agent is stable and does not separate, and has high heat resistance, which is beneficial to greatly improve the protection of the fiber surface in the subsequent pre-oxidation and carbonization processes, so that the ash content is ≤0.03%, which is much smaller than the standard requirement of ≤0.50%. In some embodiments, the temperature of the oiling section is 20℃-35℃, and the oiling rate is 0.5wt%-1.0wt%.

[0017] In the above technical solution, the temperature in the appropriate range is beneficial to realize uniform coating of the oiling agent and protect the fiber structure; and the oiling rate in the appropriate range is beneficial to form a uniform and continuous oil film on the fiber surface. In some embodiments, in step S20, the drying and densification section has a drying temperature of 150℃-220℃; the steam stretching section has a draw ratio of 3.5-5.5 times, a steam pressure of 0.4MPa-0.8MPa, and a spinning speed of 300m / min-450m / min. In the above technical solution, the high-temperature drying method is used for drying and densification treatment, which is beneficial to form a uniform and dense protective film for the oil film after oiling, and at the same time, activates the thermal motion of the copolymer molecular chain, fills the small pores in the fiber bundle, improves the density, and makes the fiber structure more dense, and further eliminates the residual internal stress of the fiber through heat setting. Under a certain steam pressure and spinning speed, high draw ratio is adopted, the matching of steam draw pressure and draw ratio is optimized, and the copolymer macromolecular chains in the original yarn are arranged along the axial direction, which is helpful to further improve the orientation degree of the original yarn. In some embodiments, in step S30, the pre-oxidation section has 3-6 temperature zones, a temperature of 200℃-280℃, and a draw ratio of 0.9-1.0 times; the low-temperature carbonization section has 5-8 temperature zones, a temperature of 300℃-780℃, a heating rate of 40℃ / min-100℃ / min, and a draw ratio of 0.98-1.05 times; the high-temperature carbonization section has 5-8 temperature zones, a temperature of 1300℃-2000℃, a heating rate of 100℃ / min-150℃ / min, and a draw ratio of 0.95-1.0 times; and the draw ratio of the low-temperature carbonization section is higher than that of the high-temperature carbonization section.

[0018] In the above technical solution, in the pre-oxidation section, the temperature zone, temperature and draft ratio are controlled in a suitable range to realize precise control of the ring degree of the pre-oxidized fiber. Further, by controlling the low-temperature high-draft and high-temperature low-draft, in combination with the temperature and temperature zone settings of pre-oxidation, low-temperature carbonization and high-temperature carbonization, the overgrowth of microcrystals can be effectively inhibited, and the stress concentration at the grain boundary is reduced, thereby facilitating further improvement of the mechanical properties of the carbon fiber. In some embodiments, the high-temperature carbonization section further comprises: air sealing the high-temperature carbonization furnace, the air sealing angle is 15°-45°, and the oxygen content in the furnace is 0-5 ppm.

[0019] In the above technical solution, compared with small-diameter carbon fibers, the carbonization volume is increased, the small molecule gas generated by the carbonization reaction of the fiber is increased, and the control difficulty of the atmosphere stability is increased. By adopting air sealing and controlling the air sealing angle, the oxygen, moisture and dust adsorbed on the surface of the fiber are blown away in time, oxidation substances are prevented from affecting the atmosphere of the furnace body and reacting with the fiber to cause defects; the oxygen content in the furnace is controlled to be 0-5 ppm, dust deposition and pollution of the fiber surface are effectively reduced, long-time stable control of the atmosphere in the furnace is realized, which is beneficial to reducing the dispersion coefficient of the fiber strength and further improving the radial structure uniformity and mechanical properties of the large-diameter carbon fiber.

[0020] In some embodiments, the surface treatment comprises sequentially performing first surface treatment and second surface treatment on the carbonized fiber obtained after high-temperature carbonization, the electric quantity of the first surface treatment and the second surface treatment is independently 15C / g-90C / g, and the electrolyte is independently acid, alkali or salt; wherein the carboxyl content on the surface of the large-diameter high-strength medium-modulus carbon fiber is 4.0%-6.0%, and the mass ratio O / C of O element and C element is 0.15-0.25.

[0021] In the above technical solution, by controlling the number of surface treatment stages and the electric quantity, the fiber surface is fully oxidized, the content of the active group on the fiber surface is increased, and the interfacial properties of the carbon fiber are further improved.

[0022] In some embodiments, in the sizing and drying section, a modified epoxy sizing agent is used, the temperature of the drying roller is 120°C-200°C, and the temperature of the drying furnace is 180°C-230°C; wherein the content of the modified epoxy sizing agent in the large-diameter high-strength medium-modulus carbon fiber is 0.4wt%-1.2wt%.

[0023] In the above technical solution, the increase of the diameter of the carbon fiber leads to the increase of the gap between the filaments, the increase of the sizing amount of the fiber, and the increase of the drying difficulty. The application utilizes the drying roll viscosity and drying furnace temperature synergistic sensing technology to realize the independent regulation and control of the drying furnace temperature, prevents the fiber from sticking to the roll and the filaments from being combined, and greatly reduces the product problems caused by the mismatch of the drying temperature process. Further, a modified epoxy sizing agent is selected, different modified groups are selected for different resin systems such as epoxy, bismaleimide, and hydrocyanic acid, the interfacial properties of the large-diameter carbon fiber can be enhanced, and the requirements of fiber winding, garbage, prepreg, fabric, and the like can be met.

[0024] In a second aspect, the application provides a large-diameter high-strength medium-modulus carbon fiber prepared by the preparation method of the first aspect of the application. The tensile strength of the large-diameter high-strength medium-modulus carbon fiber is 4.5 GPa to 7.0 GPa, the tensile modulus is 260 GPa to 350 GPa, and the diameter is 5.0 μm to 15 μm.

[0025] In the above technical solution, the large-diameter high-strength medium-modulus carbon fiber provided in the application has high strength and modulus, large diameter, and good compression performance and strength conversion rate, that is, it can simultaneously realize large diameter and good mechanical properties, and can greatly meet the application requirements in the fields of pressure vessels, low-altitude economy, commercial spaceflight, and the like.

[0026] In some embodiments, the large-diameter high-strength medium-modulus carbon fiber includes a T700-grade carbon fiber, a T800-grade carbon fiber, or a T1000-grade carbon fiber. The tensile strength of the T700-grade carbon fiber is 4.5 GPa to 5.6 GPa, the tensile modulus is 260 GPa to 290 GPa, and the diameter is 7.0 μm to 15 μm. The tensile strength of the T800-grade carbon fiber is 5.5 GPa to 6.3 GPa, the tensile modulus is 290 GPa to 350 GPa, and the diameter is 5.0 μm to 10 μm. The tensile strength of the T1000-grade carbon fiber is 6.3 GPa to 7.0 GPa, the tensile modulus is 290 GPa to 350 GPa, and the diameter is 5.0 μm to 10 μm. BRIEF DESCRIPTION OF DRAWINGS In order to more clearly illustrate the technical solutions of the embodiments of the application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some embodiments of the application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.

[0027] Figure 1 A process flow chart of a preparation method of a large-diameter high-strength medium-modulus carbon fiber provided in an embodiment of the application.

[0028] Figure 2SEM images of the large-diameter high-strength intermediate modulus carbon fibers prepared in Examples 1 to 6 of the present application.

[0029] Figure 3 SEM images of the large-diameter high-strength intermediate modulus carbon fibers prepared in Examples 7 to 10 of the present application.

[0030] Figure 4 SEM images of the large-diameter high-strength intermediate modulus carbon fibers prepared in Examples 11 to 13 of the present application. DETAILED DESCRIPTION

[0031] Hereinafter, the embodiments of the large-diameter high-strength intermediate modulus carbon fibers and the method for producing the same according to the present application will be described in detail with appropriate reference to the accompanying drawings, but there will be cases where unnecessary detailed description is omitted. For example, there will be cases where detailed description of matters well known, repeated description of substantially the same structure, and the like are omitted.

[0032] The ranges disclosed herein are defined by the lower and upper limits of the range in the form of a range, and the given range is defined by selecting one lower limit and one upper limit, and the selected lower limit and upper limit define the boundaries of the particular range. The ranges defined in this way can be inclusive or exclusive of the end values, and can be arbitrarily combined, i.e., any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, it is understood that ranges of 60-110 and 80-120 are also contemplated. Further, if a minimum range value of 1 and 2 is listed, and if a maximum range value of 3, 4, and 5 is listed, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In the present application, unless otherwise stated, a numerical range "a-b" indicates a shorthand way of describing all of the real combinations of a to b, where a and b are both real numbers. For example, the numerical range "0-5" indicates that all of the real numbers between "0-5" have been listed herein, and "0-5" is just a shorthand way of describing these numerical combinations. In addition, when it is stated that a parameter is an integer ≥ 2, it is equivalent to disclose that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, and the like.

[0033] If there is no special indication, all the embodiments and optional embodiments of the present application can be combined to form new technical solutions. If there is no special indication, all the technical features and optional technical features of the present application can be combined to form new technical solutions. If there is no special indication, all the processes of the present application can be carried out in sequence, or randomly, preferably in sequence. For example, the method comprises steps (a) and (b), which means that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, the method also comprises step (c), which means that step (c) can be added to the method in any order, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0034] As described above, since the diameter of the fiber is often negatively correlated with the tensile strength, the radial non-uniformity of the carbon fiber with large diameter is serious, which is not conducive to the improvement of the mechanical properties. In the prior art, in order to prepare high-strength carbon fiber, the common strategy is fine denier, that is, to reduce the diameter of the carbon fiber to prepare carbon fiber with higher crystallinity, higher orientation, and fewer defects. However, the reduction of the diameter is not conducive to the improvement of the compression performance and strength conversion rate of the carbon fiber. Therefore, it is crucial to solve the problem of radial structure difference of large-diameter carbon fiber and prepare carbon fiber with high orientation, tensile modulus and tensile strength, and large diameter.

[0035] In the existing research, when preparing large-diameter high-strength medium-modulus carbon fiber, the pre-oxidation process is usually improved, for example, patent applications CN201810903315.5 and CN202010174019.3. However, by adjusting the pre-oxidation process, the mechanical properties of the fiber are improved, and the diameter is significantly reduced. There is still a contradiction between the diameter and the mechanical properties. In the case of improving the diameter, the radial uniformity of the fiber becomes worse, and it is difficult to maintain the mechanical properties. Based on this, the present application provides a preparation method of large-diameter high-strength medium-modulus carbon fiber, Figure 1 The process flow chart of the preparation method of large-diameter high-strength medium-modulus carbon fiber provided in the present application is shown in Figure 1 The preparation method of large-diameter high-strength medium-modulus carbon fiber provided by the present application comprises the following steps: S10: copolymerizing acrylonitrile and a comonomer to obtain a spinning dope; in the spinning dope, the mass percentage of the copolymer is 15wt%-35wt%, and the viscosity average molecular weight is 250,000-550,000.

[0036] For example, the mass percentage of the copolymer in the spinning dope is any one of 15 wt%, 18 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, or a range value between any two of them; the viscosity-average molecular weight is any one of 250,000, 300,000, 350,000, 400,000, 450,000, 500,000, 550,000, or a range value between any two of them.

[0037] In some embodiments, step S10 comprises: performing solution polymerization on the acrylonitrile, the first comonomer, the second comonomer, and the initiator in a first solvent to obtain a polymerization dope; and performing single removal, defoaming, and ammoniation on the polymerization dope to form the spinning dope; wherein the first comonomer comprises at least one of itaconic acid amide or vinyl acetate, and the second comonomer comprises at least one of methyl methacrylate or isobutyl acrylate.

[0038] Further, the initiator comprises at least one of azobisdimethylvaleronitrile, azobisdimethylhexanonitrile, or azobisdimethylamidinum hydrochloride; and the first solvent comprises at least one of dimethyl sulfoxide, dimethylformamide, dimethylacetamide, nitric acid, zinc chloride solution, or sodium thiocyanate solution. Preferably, the initiator comprises azobisdimethylvaleronitrile, and the first solvent comprises dimethyl sulfoxide.

[0039] Further, the ammoniation degree of the spinning dope is 1.5-4.0, and the intrinsic viscosity is 2.0-4.0. For example, but not limited to, the ammoniation degree is any one of 1.5, 2.0, 2.5, 3.0, 3.5, or 4.0, or a range value between any two of them; and the intrinsic viscosity is 2.0-4.0, for example, but not limited to, the intrinsic viscosity is any one of 2.0, 2.5, 3.0, 3.5, or 4.0, or a range value between any two of them.

[0040] In the present application, the concentration of the copolymer in the spinning dope, the molecular weight, the ammoniation degree, and the intrinsic viscosity are limited within the above ranges, so that the spinning dope has relatively suitable flowability and viscoelasticity, thereby making the spinning dope fine stream have a relatively stable morphology at the outlet of the spinneret, which helps to improve the problem of easy yarn breakage or yarn doubling in the spinning stage; at the same time, the suitable concentration and molecular weight also help the spinning dope to form a relatively uniform structure in the coagulation and molding process, which helps to further enhance the mechanical properties and drawability of the fiber.

[0041] S20: adopting a dry-jet wet spinning process, the spinning dope is sequentially subjected to coagulation and molding, washing, oiling, drying and densification, and steam drawing to obtain a raw yarn; the light density difference ΔOD between the skin part and the core part of the raw yarn is ≤0.3, the orientation degree is ≥87%, and the average defect size is ≤120 nm. For example, the difference in optical density ΔOD between the skin and the core of the original wire is any one of the point values of 0.01, 0.03, 0.05, 0.10, 0.12, 0.17, 0.30 or a range value between any two of them; the orientation degree is any one of the point values of 87%, 88%, 90%, 91%, 92% or a range value between any two of them; the average defect size is any one of the point values of 50 nm, 60 nm, 80 nm, 100 nm, 120 nm or a range value between any two of them.

[0042] Further, the difference in optical density ΔOD between the skin and the core of the original wire is ≤0.15.

[0043] In some embodiments, the coagulation forming section comprises: the spinning dope is sprayed out of the spinneret, passes through an air layer and enters the coagulation bath to form a nascent fiber; wherein the spinning speed is 15 m / min to 30 m / min, and the height of the air layer is 2 mm to 15 mm.

[0044] For example, the spinning speed can be any one of the point values of 15 m / min, 18 m / min, 20 m / min, 25 m / min, 30 m / min or a range value between any two of them; the height of the air layer can be any one of the point values of 2 mm, 5 mm, 10 mm or 15 mm or a range value between any two of them.

[0045] In the embodiments of the present application, the coagulation bath air layer and the spinning speed are limited within the above ranges, which is beneficial to stabilize the extrusion, to facilitate the molecular chain orientation and structure densification of the nascent fiber, and at the same time, the high shear rate inhibits the extrusion expansion, thereby improving the molecular chain orientation.

[0046] Further, the coagulation bath comprises a second solvent and water, the mass percentage of the second solvent is 25wt% to 55wt%, the number of stages of the coagulation bath is 1 to 6, the temperature is 3°C to 20°C, the pH is 5.0 to 12.0, and the draw ratio is 1.5 to 3.0.

[0047] For example, the mass percentage of the second solvent in the coagulation bath can be any one of the point values of 25wt%, 30wt%, 35wt%, 40wt%, 45wt%, 50wt%, 55wt% or a range value between any two of them; the number of stages of the coagulation bath can be any one of 1 stage, 2 stages, 3 stages, 4 stages, 5 stages or 6 stages; the temperature can be any one of the point values of 3°C, 5°C, 10°C, 15°C, 20°C or a range value between any two of them; the pH can be any one of the point values of 5.0, 8.0, 10.0, 12.0 or a range value between any two of them; and the draw ratio can be any one of the point values of 1.5, 1.8, 2.0, 2.5, 3.0 or a range value between any two of them.

[0048] In some embodiments, the pH value of the coagulation bath can be adjusted by ammonia, aqueous sodium hydroxide solution or other inorganic alkaline solution; the second solvent includes at least one of dimethyl sulfoxide, dimethyl formamide, dimethyl acetamide, nitric acid, zinc chloride solution or sodium thiocyanate solution. Understandably, the first solvent and the second solvent are the same solvent. Preferably, the second solvent is dimethyl sulfoxide.

[0049] In the embodiments of the present application, the coagulation bath stage, the coagulation bath temperature, the coagulation bath concentration, the coagulation bath pH value and the drawing ratio are limited in the above ranges, which is beneficial to realize the controllable double diffusion of solvent-non-solvent, reduce the holes and skin-core structure caused by violent phase separation, and realize plastic deformation by grading application to reduce the structure gradient, and finally further improve the structure compactness, orientation degree and reduce defects of the original wire.

[0050] In some embodiments, the water washing section includes: the nascent fiber obtained by the coagulation molding treatment is washed and drawn at a drawing ratio of 0.9-2.0 in a multi-stage water bath at 20-60°C, and then drawn at a drawing ratio of 2.0-3.0 in a hot water bath at 50-100°C.

[0051] As an example, the water washing section first adopts 5, 8, 10, 12 or 15 multi-stage water washing; the temperature of each stage of water washing is independently any one of 20°C, 30°C, 35°C, 40°C, 45°C, 50°C or 60°C or a range value between any two of them; the drawing ratio is any one of 0.9, 1.0, 1.5 or 2 or a range value between any two of them. Then hot water bath drawing is carried out, and the temperature of the hot water bath can be any one of 50°C, 70°C, 80°C, 90°C or 100°C or a range value between any two of them; the drawing ratio can be any one of 2.0, 2.5 or 3.0 or a range value between any two of them.

[0052] Further, the original wire K bundle is controlled at 1K-36K, and the residual amount of solvent in the washed wire obtained after the water washing section is 0-60ppm. The recovery efficiency of the solvent can reach 99.0%-100%.

[0053] In the embodiments of the present application, the hot water bath drawing ratio and temperature are limited in the above ranges, which is beneficial to activate the macromolecular chain movement ability, promote the amorphous zone molecular chain segment movement ability, and at the same time, the molecular chain rearrangement is beneficial to release the internal stress accumulated by the coagulation bath drawing.

[0054] In some embodiments, the oil agent used in the oiling section comprises the following components in parts by weight: modified silicone oil 30-40 parts, surfactant 5-10 parts, water 50-65 parts, and auxiliary agent 1-3 parts; in the modified silicone oil, the mass ratio of amino-modified silicone oil, polyether-modified silicone oil, and phenyl-modified silicone oil is (60-75):(20-25):(15-20).

[0055] For example, the mass ratio of the amino-modified silicone oil, the polyether-modified silicone oil, and the phenyl-modified silicone oil can be 60:25:15, 65:25:10, 70:20:10, 75:15:10, etc. In the oil agent, the weight fraction of the modified silicone oil can be 30 parts, 32 parts, 35 parts, 38 parts, 40 parts, etc.; the weight fraction of the surfactant can be 5 parts, 6 parts, 8 parts, 10 parts, etc.; the weight fraction of the water can be 50 parts, 55 parts, 60 parts, 65 parts, etc.; and the weight fraction of the auxiliary agent can be 1 part, 2 parts, 3 parts, etc. Further, after the oil agent is heated at 450℃ for 5 minutes, the remaining mass accounts for no less than 75% of the initial mass.

[0056] Further, the temperature of the oiling section is 20℃-35℃, and the oiling rate is 0.5wt%-1.0wt%.

[0057] For example, the temperature of the oiling section is 20℃, 25℃, 30℃, 35℃, etc.; and the oiling rate is 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1.0wt%, etc.

[0058] In the embodiments of the present application, the oil agent type, the oiling temperature, and the oiling rate are limited within the above ranges, which is conducive to forming a continuous and thermally stable functional oil film on the fiber surface, improving the protection of the oil agent on the original yarn, enhancing the bundling property of the original yarn, and reducing the friction coefficient of the original yarn.

[0059] In some embodiments, in the drying and densifying section, the drying temperature is 150℃-220℃. For example, in the drying and densifying section, the drying temperature is 150℃, 180℃, 200℃, 220℃, etc.

[0060] In the embodiments of the present application, the drying temperature is limited within the above range, which is conducive to achieving deep removal of the solvent under the lowest thermal damage to the original yarn, and providing a structurally stable original yarn for subsequent pre-oxidation and carbonization.

[0061] In some embodiments, in the steam drawing section, the draw ratio is 3.5-5.5, the steam pressure is 0.4MPa-0.8MPa, and the spinning speed is 300m / min-450m / min. For example, in the steam drawing section, the draw ratio is 3.5, 4.0, 4.5, 5.0, 5.5, etc.; the steam pressure is 0.4 MPa, 0.5 MPa, 0.6 MPa, 0.7 MPa, 0.8 MPa, etc.; and the spinning speed is 300 m / min, 350 m / min, 400 m / min, 450 m / min, etc.

[0062] In the embodiments of the present application, the steam drawing ratio and the steam pressure are limited within the above ranges, which is beneficial to realizing super-high plastic deformation of the precursor in a high-temperature saturated steam environment. The high-temperature steam makes the amorphous region of the copolymer reach a melt-like state, eliminates the entanglement barrier of the molecular chains, and accelerates the rearrangement of the molecular chains in the core layer, thereby eliminating the difference in the skin-core structure formed by the coagulation bath, and facilitating the realization of maximum orientation.

[0063] Further, the present application adopts a high-temperature drying process for drying and densification, and the steam and condensed water discharged in the drying and steam drawing process can be used as a heat source for the water washing and water drawing processes after secondary flash evaporation. The ozone coupling micro-nano bubble process is used to treat the recovered waste water, and the treated waste water has no odor and is neutral in pH, which can be introduced into the water washing section of the spinning process to replace the desalted water, thereby maintaining the water washing effect and realizing the recycling of the waste water.

[0064] S30: sequentially performing pre-oxidation, low-temperature carbonization, high-temperature carbonization, surface treatment, sizing, drying, and winding on the precursor to obtain a large-diameter high-strength medium modulus carbon fiber.

[0065] In some embodiments, the pre-oxidation section adopts 3-6 temperature zones, the temperature is 200-280℃, and the draw ratio is 0.9-1.0.

[0066] For example, the pre-oxidation section adopts 3, 4, 5, or 6 temperature zones, and the temperature is gradiently increased within the range of 200-280℃; the draw ratio is 0.9, 0.92, 0.95, 0.98, 1.0, etc.

[0067] Further, the pre-oxidation furnace can be a layer furnace, a box furnace, etc., and the heating mode in the pre-oxidation furnace is circulating hot air heating; the air supply mode can be the axial direction of the tow, the longitudinal direction of the tow, the horizontal and vertical direction of the tow, etc.

[0068] In the embodiments of the present application, the pre-oxidation temperature zone, the pre-oxidation temperature, and the pre-oxidation draw ratio are limited within the above ranges, which is beneficial to realizing controllable cyclization / oxidation of the copolymer molecules and preparing pre-oxidized yarns with excellent structures, thereby providing a low-defect precursor for carbonization.

[0069] In some embodiments, the low-temperature carbonization section adopts 5-8 temperature zones, the temperature is 300-780℃, the heating rate is 40-100℃ / min, and the draw ratio is 0.98-1.05.

[0070] For example, the low-temperature carbonization section adopts 5, 6, 7 or 8 temperature zones, and the temperature is gradually increased in the range of 300-780℃; the temperature increasing rate can be any one of 40℃ / min, 60℃ / min, 80℃ / min, 100℃ / min or a range value between any two of them; the draft ratio can be any one of 0.98, 0.99, 1.0, 1.02, 1.05 or a range value between any two of them.

[0071] Further, the protective gas in the low-temperature carbonization furnace can be nitrogen, helium, neon, argon, etc.

[0072] In the embodiments of the present application, the low-temperature carbonization temperature zone, the low-temperature carbonization temperature, the low-temperature carbonization temperature increasing rate and the low-temperature carbonization draft ratio are limited in the above ranges, which is beneficial to remove non-carbon elements (N, H, O) and build an initial carbon skeleton, and a specific draft ratio helps to remove nitrogen and cross-link ring structure in the low-temperature zone (300-600℃), and form an initial carbon plane in the medium-temperature zone (600-780℃).

[0073] In some embodiments, the high-temperature carbonization section adopts 5-8 temperature zones, the temperature is 1300-2000℃, the temperature increasing rate is 100-150℃ / min, and the draft ratio is 0.95-1.0; wherein the draft ratio of the low-temperature carbonization section is higher than that of the high-temperature carbonization section.

[0074] For example, the high-temperature carbonization section adopts 5, 6, 7 or 8 temperature zones, and the temperature is gradually increased in the range of 1300-2000℃; the temperature increasing rate can be any one of 100℃ / min, 110℃ / min, 120℃ / min, 130℃ / min, 140℃ / min, 150℃ / min or a range value between any two of them; the draft ratio can be any one of 0.95, 0.96, 0.97, 0.98, 1.0 or a range value between any two of them.

[0075] In the embodiments of the present application, the high-temperature carbonization temperature zone, the high-temperature carbonization temperature, the high-temperature carbonization temperature increasing rate and the high-temperature carbonization draft ratio are limited in the above ranges, which is beneficial to develop carbon net plane orientation and eliminate residual defects, and appropriate draft ratio is used to optimize the arrangement of microcrystals to obtain high-performance carbon fibers.

[0076] Further, the high-temperature carbonization section further includes: air sealing of the high-temperature carbonization furnace, the air sealing angle is 15-45°, and the oxygen content in the furnace is 0-5ppm.

[0077] As an example, the gas sealing angle can be any one of 15°, 20°, 30°, 45° or a range value between any two of them; the oxygen content in the furnace can be any one of 0 ppm, 1 ppm, 2 ppm, 3 ppm, 5 ppm or a range value between any two of them.

[0078] In the embodiments of the present application, the high-temperature carbonization gas sealing angle is limited in the above range, which is beneficial to control the nitrogen injection direction, form a "gas barrier" at the furnace opening, prevent air backflow, improve the purity of the furnace atmosphere, reduce the direct impact force, ensure the smooth running of the fiber bundle, and reduce the hairiness rate.

[0079] Further, the protective gas in the high-temperature carbonization furnace can be nitrogen, helium, neon, argon, etc.

[0080] Further, the rollers of the pre-oxidation furnace, the low-temperature carbonization furnace, and the high-temperature carbonization furnace are all coated with high-temperature resistant coating, and defect monitoring devices are arranged at the furnace tail to avoid mechanical damage to the fiber during the production of large-diameter carbon fibers, further realize precise process control, and ensure the uniformity of the fiber bundle. As an example, the high-temperature resistant coating used can use silicon carbide and ceramic coating.

[0081] It should be noted that the carbon fiber runs at a constant speed during the pre-oxidation and carbonization processes, so the time spent in each temperature zone is the same.

[0082] In some embodiments, the surface treatment includes sequentially performing first surface treatment and second surface treatment on the carbonized fiber obtained after high-temperature carbonization, the electric quantity of the first surface treatment and the second surface treatment is independently 15C / g~90C / g, and the electrolyte is independently acid, alkali or salt; wherein the carboxyl content on the surface of the large-diameter high-strength medium modulus carbon fiber is 4.0%~6.0%, and the mass ratio of O element and C element O / C is 0.15~0.25.

[0083] As an example, the electric quantity of the first surface treatment and the second surface treatment can be any one of 15C / g, 20C / g, 30C / g, 50C / g, 80C / g, 90C / g or a range value between any two of them.

[0084] Further, the acid electrolyte can include sulfuric acid or nitric acid; the alkali electrolyte can include sodium hydroxide or strong potassium oxide; and the salt electrolyte can include ammonium salt.

[0085] As an example, the carboxyl content of the surface of the large-diameter high-strength intermediate-modulus carbon fiber can be any one of 4.0%, 4.5%, 5.0%, 5.5%, 6.0% or a range value between any two of them; the mass ratio of O element and C element O / C can be any one of 0.15, 0.18, 0.20, 0.22, 0.25 or a range value between any two of them. In some embodiments, in the sizing and drying section, a modified epoxy sizing agent is used, the temperature of the drying roller is 120-200 DEG C, and the temperature of the drying furnace is 180-230 DEG C; wherein in the large-diameter high-strength intermediate-modulus carbon fiber, the content of the modified epoxy sizing agent is 0.4-1.2 wt%.

[0086] As an example, the temperature of the drying roller can be any one of 120 DEG C, 150 DEG C, 180 DEG C, 200 DEG C or a range value between any two of them; the temperature of the drying furnace can be any one of 180 DEG C, 200 DEG C, 210 DEG C, 230 DEG C or a range value between any two of them; the content of the modified epoxy sizing agent can be any one of 0.4 wt%, 0.5 wt%, 0.8 wt%, 1.0 wt%, 1.2 wt% or a range value between any two of them.

[0087] In the embodiments of the present application, the drying furnace can realize real-time temperature adjustment, and utilizes the drying roller viscosity drying furnace temperature cooperative sensing technology to realize self-regulation and control of the drying furnace temperature, greatly reducing the product problems caused by the mismatch of the drying temperature process, and is especially suitable for large-diameter fiber drying process.

[0088] It should be noted that the processes or steps not specifically mentioned or limited in the preparation process of the carbon fiber can be selected according to the conventional selection in the art, and are not specifically limited in the embodiments of the present application.

[0089] In addition, the present application also provides a large-diameter high-strength intermediate-modulus carbon fiber prepared by the above preparation method. The tensile strength of the large-diameter high-strength intermediate-modulus carbon fiber is 4.5-7.0 GPa, the tensile modulus is 260-350 GPa, and the diameter is 5.0-15 μm.

[0090] In some embodiments, the large-diameter high-strength intermediate modulus carbon fiber comprises a T700-grade carbon fiber, a T800-grade carbon fiber, or a T1000-grade carbon fiber; wherein the T700-grade carbon fiber has a tensile strength of 4.5 GPa to 5.6 GPa, a tensile modulus of 260 GPa to 290 GPa, and a diameter of 7.0 μm to 15 μm; the T800-grade carbon fiber has a tensile strength of 5.5 GPa to 6.3 GPa, a tensile modulus of 290 GPa to 350 GPa, and a diameter of 5.0 μm to 10 μm; and the T1000-grade carbon fiber has a tensile strength of 6.3 GPa to 7.0 GPa, a tensile modulus of 290 GPa to 350 GPa, and a diameter of 5.0 μm to 10 μm.

[0091] The features and benefits of the application are further illustrated by reference to the following examples. Unless otherwise indicated, conventional procedures or those modifications of the procedures described in the manufacturer's literature were used. Unless otherwise indicated, all reagents or materials were obtained from commercial suppliers and used without further purification.

[0092] Example 1 The embodiments of the present application provide a large-diameter high-strength intermediate modulus carbon fiber, and a preparation method thereof, which comprises the following steps: (1) A polymerization stock solution is obtained by mixing acrylonitrile, itaconic acid amide, and isobutyl acrylate in a mass ratio of 95:3:2, using azobisisobutyronitrile as an initiator and dimethyl sulfoxide as a solvent, and then performing ternary homogeneous solution polymerization; the polymerization stock solution is subjected to single removal, defoaming, and ammoniation to obtain a spinning stock solution. In the spinning stock solution, the mass percentage of the copolymer is 22 wt%, the viscosity-average molecular weight is 450,000, the degree of ammoniation of the spinning stock solution is 3.7, and the intrinsic viscosity is 3.5.

[0093] (2) The spinning stock solution is spun out of a spinneret through a dry-jet wet spinning process, enters a coagulation bath after passing through an air layer, and is coagulated and formed, and then is subjected to washing, oiling, drying and densification, and steam drawing to obtain a precursor fiber.

[0094] In the coagulation and forming section, the spinning speed is 20 m / min, the air layer height is 10 mm, the coagulation bath has 6 stages, the solvent is dimethyl sulfoxide, the concentration is 40 wt%, the temperature is 3°C, the draw ratio is 2.5, and the pH is 11.0.

[0095] The washing section includes: the nascent fiber obtained after the coagulation and forming treatment is washed and stretched at a draw ratio of 1.5 in a multi-stage water bath at 35°C, and then is stretched at a draw ratio of 2.5 in a hot water bath at 70°C, and the residual amount of dimethyl sulfoxide solvent is 25 ppm.

[0096] The oiling section includes oiling at 22℃. The oiling agent used has the following composition: modified silicone oil 35%, surfactant sodium dodecyl sulfate 8%, pure water 55%, and other additives 2%. The internal component ratio of the modified silicone oil is amino-modified silicone oil: polyether-modified silicone oil: phenyl-modified silicone oil = 65:20:15. The oiling rate is 0.70wt%.

[0097] The drying densification section includes drying the oil-coated tow at 190℃.

[0098] In the steam drawing section, the draw ratio is 5 times, the steam pressure is 0.6 MPa, and the spinning speed is 400 m / min.

[0099] The prepared K-tow has a diameter of 12K, and the optical density difference ΔOD between the skin and the core of the prepared fiber is 0.17, the orientation degree is 91.8%, and the average defect size is 59 nm.

[0100] (3) The prepared fiber is sequentially subjected to pre-oxidation, low-temperature carbonization, high-temperature carbonization, surface treatment, sizing, drying, and winding to obtain a large-diameter high-strength medium-modulus carbon fiber.

[0101] The pre-oxidation is performed in a box furnace with three temperature zones in the range of 200℃-280℃ for temperature gradient heating, and the draw ratio is 0.92 times. The low-temperature carbonization is performed in a 7-zone controlled low-temperature carbonization furnace with a temperature gradient heating in the range of 300℃-780℃ at a heating rate of 60℃ / min, and the draw ratio in the low-temperature furnace is 1.05 times. The high-temperature carbonization is performed in an 8-zone controlled high-temperature carbonization furnace with a temperature gradient heating in the range of 800℃-1800℃ at a heating rate of 150℃ / min, and the draw ratio in the high-temperature furnace is 0.95 times. The gas sealing angle of the high-temperature carbonization furnace is 18°. The protective gas in the low-temperature carbonization furnace and the high-temperature carbonization furnace is nitrogen.

[0102] The surface treatment includes two-stage surface treatment, the first-stage surface treatment has an electric quantity of 25 C / g, the second-stage surface treatment has an electric quantity of 45 C / g, the electrolyte is sodium hydroxide, and the carboxyl content on the surface of the fiber after the surface treatment is 4.84%, and the O / C element ratio is 0.206.

[0103] The sizing and drying section includes using a double-modified epoxy sizing agent for sizing, the sizing agent drying roller temperature is 140℃, and the drying furnace temperature is 210℃.

[0104] The large-diameter high-strength medium-modulus carbon fiber prepared in Example 1 has a tensile strength of 6.8 GPa, a tensile modulus of 306 GPa, and a diameter of 5.51 μm.

[0105] Example 2 The large-diameter high-strength medium-modulus carbon fiber provided by the embodiment of the present application is different from that of Example 1 in that In step (1), the mass percentage of the copolymer is 21wt%, the viscosity average molecular weight is 420,000, the ammonia degree of the spinning dope is 3.6, and the intrinsic viscosity is 3.3.

[0106] In step (2), the temperature of the solidification forming section is 5℃; the residual amount of the solvent after the water washing section is 40ppm; in the oiling section, the component ratio of the modified silicon oil is amino-modified silicon oil: polyether-modified silicon oil: phenyl-modified silicon oil = 64:19:17.

[0107] The prepared K-tow of the raw yarn is 12K, the tested light density difference ΔOD between the skin and the core of the raw yarn is 0.14, the orientation degree is 91.3%, and the average defect size is 63nm.

[0108] In step (3), the high-temperature carbonization gas sealing angle is 20°; in the surface treatment section, the 2nd-stage surface treatment electric quantity is 35C / g, the carboxyl content on the surface of the fiber after the surface treatment is 4.96%, and the O / C element ratio is 0.211.

[0109] Example 3 The example of the present application provides a large-diameter high-strength medium-mold carbon fiber, and the difference between the preparation method and example 1 is that: In step (1), the mass percentage of the copolymer is 30wt%, the viscosity average molecular weight is 300,000, the ammonia degree of the spinning dope is 3.7, and the intrinsic viscosity is 3.5.

[0110] The prepared K-tow of the raw yarn is 12K, the tested light density difference ΔOD between the skin and the core of the raw yarn is 0.22, the orientation degree is 88.3%, and the average defect size is 73nm.

[0111] Example 4 The example of the present application provides a large-diameter high-strength medium-mold carbon fiber, and the difference between the preparation method and example 1 is that: In step (2), in the solidification forming section, the air layer height is 7mm, 4-stage solidification baths are used, the temperature of the solidification bath is 15℃, and the draft ratio is 2.0.

[0112] The prepared K-tow of the raw yarn is 12K, the tested light density difference ΔOD between the skin and the core of the raw yarn is 0.20, the orientation degree is 89.1%, and the average defect size is 64nm.

[0113] Example 5 The example of the present application provides a large-diameter high-strength medium-mold carbon fiber, and the difference between the preparation method and example 1 is that: In step (2), in the oiling section, the component ratio of the modified silicon oil is amino-modified silicon oil: polyether-modified silicon oil: phenyl-modified silicon oil = 60%:25%:15%.

[0114] The prepared K-tow of the raw silk is 12K, the tested optical density difference ΔOD between the skin and the core of the raw silk is 0.23, the orientation degree is 89.6%, and the average defect size is 77nm.

[0115] Example 6 The embodiment of the application provides a large-diameter high-strength medium-mold carbon fiber, and the preparation method is different from that of the embodiment 1. In step (2), the oiling section comprises: oiling at 22 DEG C. The oiling agent composition used in the oiling comprises: modified silicone oil 35%, surfactant sodium dodecyl sulfate 8%, pure water 55%, and other additives 2%. The component ratio of the modified silicone oil is: amino-modified silicone oil: epoxy-modified silicone oil = 80%:20%.

[0116] The prepared K-tow of the raw silk is 12K, the tested optical density difference ΔOD between the skin and the core of the raw silk is 0.29, the orientation degree is 89.5%, and the average defect size is 89nm.

[0117] Example 7 The embodiment of the application provides a large-diameter high-strength medium-mold carbon fiber, and the preparation method is different from that of the embodiment 1. In step (1), the mass percentage of the copolymer is 19wt%, the viscosity average molecular weight is 400,000, the ammoniation degree of the spinning dope is 3.6, and the intrinsic viscosity is 3.4.

[0118] In step (2), the temperature of the coagulation forming section is 8 DEG C; the residual amount of the solvent after the washing section is 30ppm; in the oiling section, the component ratio of the modified silicone oil is: amino-modified silicone oil: polyether-modified silicone oil: phenyl-modified silicone oil = 64:20:12; and the steam drawing multiple is 4.5 times.

[0119] The prepared K-tow of the raw silk is 12K, the tested optical density difference ΔOD between the skin and the core of the raw silk is 0.12, the orientation degree is 91.0%, and the average defect size is 69nm.

[0120] In step (3), the pre-oxidation drawing multiple is 0.94 times; the high-temperature carbonization gas sealing angle is 22 DEG ; in the surface treatment section, the 2-stage surface treatment electric quantity is 25C / g, the carboxyl content of the fiber surface after the surface treatment is 5.01%, and O / C is 0.215.

[0121] Example 8 The embodiment of the application provides a large-diameter high-strength medium-mold carbon fiber, and the preparation method is different from that of the embodiment 1. In step (1), the mass percentage of the copolymer is 19wt%, the viscosity average molecular weight is 400,000, the ammoniation degree of the spinning dope is 3.6, and the intrinsic viscosity is 3.4.

[0122] In step (2), the temperature of the solidification forming section is 8℃; the residual amount of solvent after the water washing section is 30ppm; in the oiling section, the component ratio of the modified silicon oil is amino-modified silicon oil: polyether-modified silicon oil: phenyl-modified silicon oil = 65:18:17; the steam draft ratio is 4.5 times.

[0123] The prepared K-tow of the raw yarn is 12K, the tested light density difference ΔOD between the skin and the core of the raw yarn is 0.11, the orientation degree is 90.7%, and the average defect size is 71nm.

[0124] In step (3), the pre-oxidation draft ratio is 0.94 times; the high-temperature carbonization gas sealing angle is 22°; in the surface treatment section, the 2nd-stage surface treatment electric quantity is 25C / g, the carboxyl content on the surface of the fiber after the surface treatment is 5.17%, and the O / C element ratio is 0.218; the sizing agent is a medium-temperature sizing agent, and the sizing agent drying roller temperature is 130℃.

[0125] Example 9 The embodiment of the present application provides a large-diameter high-strength medium-mold carbon fiber, and the difference between the preparation method and the embodiment 1 is that: In step (1), the mass percentage of the copolymer is 19wt%, the viscosity average molecular weight is 380,000, the ammoniation degree of the spinning dope is 3.1, and the intrinsic viscosity is 3.0.

[0126] In step (2), in the solidification forming section, the air layer height is 15mm, the temperature of the coagulation bath is 10℃, and the draft ratio is 2.2; the residual amount of solvent after the water washing section is 46ppm; in the oiling section, the component ratio of the modified silicon oil is amino-modified silicon oil: polyether-modified silicon oil: phenyl-modified silicon oil = 66:17:17; the steam draft ratio is 4.0 times.

[0127] The prepared K-tow of the raw yarn is 12K, the tested light density difference ΔOD between the skin and the core of the raw yarn is 0.10, the orientation degree is 90.3%, and the average defect size is 83nm.

[0128] In step (3), the pre-oxidation draft ratio is 0.94 times; the high-temperature carbonization gas sealing angle is 25°; in the surface treatment section, the 2nd-stage surface treatment electric quantity is 25C / g, the carboxyl content on the surface of the fiber after the surface treatment is 5.25%, and the O / C element ratio is 0.222; the sizing agent drying roller temperature is 130℃, and the drying furnace temperature is 200℃.

[0129] Example 10 The embodiment of the present application provides a large-diameter high-strength medium-mold carbon fiber, and the difference between the preparation method and the embodiment 1 is that: In step (1), the mass percentage of the copolymer is 19wt%, the viscosity average molecular weight is 380,000, the ammoniation degree of the spinning dope is 3.1, and the intrinsic viscosity is 3.0.

[0130] In step (2), the temperature of the coagulation bath in the coagulation forming section is 8℃, the draw ratio is 2.0; the residual amount of solvent after the water washing section is 30ppm; in the oiling section, the component ratio of the modified silicon oil is amino-modified silicon oil: polyether-modified silicon oil: phenyl-modified silicon oil = 65:18:17; the steam draw ratio is 4.5 times.

[0131] The prepared K-tow of the raw yarn is 3K, the tested light density difference ΔOD between the skin and the core of the raw yarn is 0.11, the orientation degree is 91.5%, and the average defect size is 62nm.

[0132] In step (3), the pre-oxidation draw ratio is 0.93 times; the high-temperature carbonization gas sealing angle is 30°; in the surface treatment section, the 2nd-stage surface treatment electric quantity is 25C / g, the carboxyl content on the surface of the fiber after the surface treatment is 5.05%, and the O / C is 0.216; the drying roll temperature of the sizing agent is 130℃, and the drying furnace temperature is 200℃.

[0133] Example 11 The example of the present application provides a large-diameter high-strength intermediate modulus carbon fiber, and the difference between the preparation method and example 1 is that: In step (1), the mass percentage of the copolymer is 18wt%, the viscosity-average molecular weight is 350,000, the ammoniation degree of the spinning dope is 3.0, and the intrinsic viscosity is 2.8.

[0134] In step (2), in the coagulation forming section, the air layer height is 15mm, the temperature of the coagulation bath is 15℃, and the draw ratio is 2.2; the residual amount of solvent after the water washing section is 46ppm; in the oiling section, the component ratio of the modified silicon oil is amino-modified silicon oil: polyether-modified silicon oil: phenyl-modified silicon oil = 64:20:16; the steam draw ratio is 4.0 times.

[0135] The prepared K-tow of the raw yarn is 12K, the tested light density difference ΔOD between the skin and the core of the raw yarn is 0.09, the orientation degree is 89.8%, and the average defect size is 87nm.

[0136] In step (3), the pre-oxidation draw ratio is 0.94 times; the low-temperature furnace draw ratio is 1.04 times; the high-temperature carbonization temperature is 1700℃, and the high-temperature carbonization gas sealing angle is 26°; in the surface treatment section, the 2nd-stage surface treatment electric quantity is 25C / g, the carboxyl content on the surface of the fiber after the surface treatment is 5.32%, and the O / C element ratio is 0.229; the drying roll temperature of the sizing agent is 130℃, and the drying furnace temperature is 200℃.

[0137] Example 12 The example of the present application provides a large-diameter high-strength intermediate modulus carbon fiber, and the difference between the preparation method and example 1 is that: In step (1), the mass percentage of the copolymer is 16wt%, the viscosity average molecular weight is 320,000, the ammonia degree of the spinning dope is 3.0, and the intrinsic viscosity is 2.8.

[0138] In step (2), in the solidification forming section, the air layer height is 7mm, the temperature of the coagulation bath is 20℃, and the draw ratio is 2.0; the residual amount of the solvent after the washing section is 35ppm; in the oiling section, the component ratio of the modified silicone oil is: amino-modified silicone oil: polyether-modified silicone oil: phenyl-modified silicone oil = 64:18:18; and the steam draw ratio is 4.0 times.

[0139] The prepared K-tow of the raw yarn is 12K, the tested light density difference ΔOD between the skin and the core of the raw yarn is 0.03, the orientation degree is 87.6%, and the average defect size is 101nm.

[0140] In step (3), the pre-oxidation draw ratio is 0.94 times; the high-temperature carbonization temperature is 1700℃, the temperature rising rate is 140℃ / min, and the gas sealing angle is 28°; in the surface treatment section, the 2nd-stage surface treatment electric quantity is 25C / g, the carboxyl content on the surface of the fiber after the surface treatment is 5.35%, and the O / C element ratio is 0.233; the drying roll temperature of the sizing agent is 130℃, and the drying furnace temperature is 200℃.

[0141] Example 13 The example of the present application provides a large-diameter high-strength intermediate modulus carbon fiber, and the difference between the preparation method and example 1 is that: In step (1), the mass percentage of the copolymer is 16wt%, the viscosity average molecular weight is 320,000, the ammonia degree of the spinning dope is 2.7, and the intrinsic viscosity is 2.7.

[0142] In step (2), in the solidification forming section, the air layer height is 7mm, the temperature of the coagulation bath is 20℃, and the draw ratio is 2.0; the residual amount of the solvent after the washing section is 40ppm; in the oiling section, the component ratio of the modified silicone oil is: amino-modified silicone oil: polyether-modified silicone oil: phenyl-modified silicone oil = 65:19:16; and the steam draw ratio is 4.0 times.

[0143] The prepared K-tow of the raw yarn is 24K, the tested light density difference ΔOD between the skin and the core of the raw yarn is 0.05, the orientation degree is 87.4%, and the average defect size is 115nm.

[0144] In step (3), the pre-oxidation draw ratio is 0.94 times; the high-temperature carbonization temperature is 1700℃, and the gas sealing angle is 35°; in the surface treatment section, the 2nd-stage surface treatment electric quantity is 25C / g, the carboxyl content on the surface of the fiber after the surface treatment is 5.31%, and the O / C element ratio is 0.230; the drying roll temperature of the sizing agent is 130℃, and the drying furnace temperature is 200℃.

[0145] Performance test and result analysis The performance of the precursor filaments and carbon fibers prepared in the above examples and comparative examples was tested, and the test results are shown in Table 1. The specific test methods are as follows: 1. Precursor filament (1) Optical density difference ΔOD: The radial structure homogeneity of the precursor filament was calculated by optical density method. The fiber was filled into a mold with epoxy resin and curing agent mixed according to a mass ratio of 15:2, and placed at room temperature for 72 h for curing. A certain thickness of section was made by an ultrathin sectioning machine, and was observed and photographed under a high-power optical microscope at 500 times magnification. The optical density value of the fiber cross-section photo obtained by microscope observation was analyzed using Image Pro software. The optical density (OD) of the transmitted light intensity gray of each fiber section was calculated according to formula (1).

[0146] Formula (1) Wherein, G0 is the background gray of the transmitted light of the optical microscope in the picture (the brightest point of the image); G i is the gray of the transmitted light after reflection, scattering and absorption of the fiber section sample.

[0147] The optical density difference ΔOD of the core and the skin was calculated according to formula (2), which represented the radial structure homogeneity of the precursor filament.

[0148] Formula (2) Wherein, OD core is the optical density of the core of the precursor filament, and OD skin is the optical density of the skin of the precursor filament.

[0149] (2) Orientation degree: calculated according to the determination of crystal region orientation function of polyacrylonitrile-based carbon fiber precursor filament in GB 23442-2009.

[0150] (3) Average defect size: calculated according to the determination of micropore defects in polyacrylonitrile-based carbon fiber and precursor filament in GB 23442-2009.

[0151] 2. Carbon fiber (1) Surface carboxyl content and O / C element ratio: X-ray photoelectron spectrometer (XPS) was used to test the surface carboxyl content and O / C element ratio of the carbon fiber.

[0152] (2) Tensile strength and tensile modulus: the tensile strength and tensile modulus of the carbon fiber were determined according to the test standard of GB 26752-2020.

[0153] (3) Diameter: the diameter of the carbon fiber was determined according to the test standard of GB 26752-2020.

[0154] Table 1. Performance test results of the raw filaments and carbon fibers

[0155] As can be seen from Table 1, the difference in optical density ΔOD between the skin and the core of the raw filaments prepared in Examples 1-13 of the present application is ≤0.3, the degree of orientation is ≥87%, and the average defect size is ≤120 nm; the tensile strength of the corresponding carbon fibers prepared is 4.5-7.0 GPa, the tensile modulus is 260-350 GPa, and the diameter is 5.0-15 μm.

[0156] In combination with Figure 2 As can be seen from Table 1, since the tensile strength of the T1000-grade carbon fibers is 6.3-7.0 GPa, the tensile modulus is 290-350 GPa, and the diameter is usually 5.0 μm, the diameter of the T1000-grade carbon fibers prepared in Examples 1-6 of the present application can reach 7.08 μm.

[0157] In combination with Figure 3 As can be seen from Table 1, since the tensile strength of the T800-grade carbon fibers is 5.5-6.3 GPa, the tensile modulus is 290-350 GPa, and the diameter is usually 5.0 μm, the diameter of the T800-grade carbon fibers prepared in Examples 7-10 of the present application can reach 7.96 μm.

[0158] In combination with Figure 4 As can be seen from Table 1, since the tensile strength of the T700-grade carbon fibers is 4.5-5.6 GPa, the tensile modulus is 260-290 GPa, and the diameter is usually 7.0 μm, the diameter of the T700-grade carbon fibers prepared in Examples 11-13 of the present application can reach 10.11 μm. The above-described embodiments are part of, but not all of the embodiments of the present application. The detailed description of the embodiments of the present application is not intended to limit the scope of the claimed present application, but only represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work, fall within the scope of protection of the present application.

Claims

1. A method for preparing large-diameter, high-strength, intermediate-modulus carbon fibers, characterized in that, Includes the following steps: S10: Acrylonitrile and comonomer are copolymerized to obtain a spinning solution; the copolymer accounts for 15wt%~35wt% of the mass percentage in the spinning solution and has a viscosity-average molecular weight of 250,000~550,000. S20: The spinning solution is subjected to solidification, washing, oiling, drying and densification, and steam drawing in sequence to obtain the raw yarn; the optical density difference between the sheath and the core of the raw yarn is ΔOD≤0.3, the orientation degree is ≥87%, and the average defect size is ≤120nm. S30: The precursor fiber is subjected to pre-oxidation, low-temperature carbonization, high-temperature carbonization, surface treatment, sizing, drying and winding in sequence to obtain large-diameter high-strength medium-modulus carbon fiber.

2. The preparation method according to claim 1, characterized in that, Step S10 includes: performing solution polymerization of the acrylonitrile, the first comonomer, the second comonomer, and the initiator in a first solvent to obtain a polymerization solution; and performing demonomer removal, degassing, and amination on the polymerization solution to form the spinning solution; wherein the first comonomer includes at least one of itaconic acid amide or vinyl acetate, and the second comonomer includes at least one of methyl methacrylate or isobutyl acrylate.

3. The preparation method according to claim 1, characterized in that, In step S20, the coagulation and forming section includes: spraying the spinning solution from the spinneret, passing through an air layer and entering the coagulation bath to coagulate and form nascent fibers. The spinning speed is 15m / min to 30m / min, and the height of the air layer is 2mm to 15mm. The coagulation bath includes a second solvent and water, the mass percentage of the second solvent is 25wt% to 55wt%, the number of stages of the coagulation bath is 1 to 6, the temperature is 3℃ to 20℃, the pH is 5.0 to 12.0, and the draw ratio is 1.5 to 3.

0.

4. The preparation method according to claim 1, characterized in that, In step S20, the washing section includes: washing the nascent fibers obtained after the coagulation and molding process in a multi-stage water bath at 20°C to 60°C while stretching them at a stretching ratio of 0.9 to 2.0, and then stretching them in a hot water bath at 50°C to 100°C at a stretching ratio of 2.0 to 3.

0.

5. The preparation method according to claim 1, characterized in that, In step S20, the oiling agent used in the oiling section includes the following components in parts by weight: 30-40 parts modified silicone oil, 5-10 parts surfactant, 50-65 parts water, and 1-3 parts additives; in the modified silicone oil, the mass ratio of amino-modified silicone oil, polyether-modified silicone oil, and phenyl-modified silicone oil is (60-75):(20-25):(15-20). And / or, in step S20, the temperature of the oiling section is 20℃~35℃, and the oiling rate is 0.5wt%~1.0wt%.

6. The preparation method according to claim 1, characterized in that, In step S20, the temperature of the drying and densifying chemical section is 150℃~220℃; And / or, in the steam drawing section, the drawing ratio is 3.5 to 5.5 times, the steam pressure is 0.4 MPa to 0.8 MPa, and the spinning speed is 300 m / min to 450 m / min.

7. The preparation method according to claim 1, characterized in that, In step S30, the pre-oxidation section uses 3 to 6 temperature zones with a temperature of 200℃ to 280℃ and a draw ratio of 0.9 to 1.

0. The low-temperature carbonization section employs 5-8 temperature zones, with temperatures ranging from 300℃ to 780℃, a heating rate of 40℃ / min to 100℃ / min, and a draw ratio of 0.98 to 1.

05. The high-temperature carbonization section employs 5-8 temperature zones, with temperatures ranging from 1300℃ to 2000℃, a heating rate of 100℃ / min to 150℃ / min, and a draw ratio of 0.95 to 1.

0. The draw ratio of the low-temperature carbonization section is higher than that of the high-temperature carbonization section.

8. The preparation method according to claim 7, characterized in that, The high-temperature carbonization section also includes: gas sealing the high-temperature carbonization furnace, with a gas sealing angle of 15°~45° and an oxygen content of 0~5ppm inside the furnace.

9. The preparation method according to claim 1, characterized in that, In step S30, the surface treatment section includes: sequentially performing a primary surface treatment and a secondary surface treatment on the carbonized fibers obtained after high-temperature carbonization, wherein the charge of the primary surface treatment and the secondary surface treatment are each independently 15C / g~90C / g, and the electrolytes are each independently acidic, alkaline, or salty; wherein the carboxyl content on the surface of the large-diameter high-strength intermediate-modulus carbon fiber is 4.0%~6.0%, and the mass ratio of O to C is 0.15~0.25; And / or, the sizing and drying section uses a modified epoxy sizing agent, the temperature of the drying roller is 120℃~200℃, and the temperature of the drying oven is 180℃~230℃; wherein, in the large-diameter high-strength intermediate modulus carbon fiber, the content of the modified epoxy sizing agent is 0.4wt%~1.2wt%.

10. A large-diameter, high-strength, intermediate-modulus carbon fiber, characterized in that, Prepared by the preparation method according to any one of claims 1 to 9; The large-diameter, high-strength, intermediate-modulus carbon fiber has a tensile strength of 4.5 GPa to 7.0 GPa, a tensile modulus of 260 GPa to 350 GPa, and a diameter of 5.0 μm to 15 μm.

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