High-strength medium-modulus carbon fiber densification regulation and control method

Abstract

The invention relates to a high-strength medium-modulus carbon fiber densification regulation and control method, belongs to the technical field of polyacrylonitrile carbon fiber spinning, and solves at least one of the problems of insufficient densification, many hole type defects, large performance fluctuation and the like of high-strength medium-modulus carbon fibers (especially precursors) in the prior art. The invention discloses a high-strength medium-modulus carbon fiber densification regulation and control method, which comprises the following steps of: solidifying and stretching an acrylonitrile-based polymer spinning solution to obtain nascent fibers, adopting a step-by-step heating multi-section water washing process, and applying 1.01-1.10 times of drafting to each section of water washing; and the washed fibers are subjected to hot water drafting (multi-section), and the draft multiple and the hot water temperature of each sub-section are gradually increased. According to the regulation and control method, through technological process design and parameter optimization, sulfoxide residues in precursor fibers are lower, the orientation degree is higher, and densification is better; the orientation degree of the precursor prepared by the regulation and control method is greater than or equal to 91.5%, the strength of the precursor is greater than or equal to 6.8 cN / dtex, the elasticity modulus of the prepared carbon fiber is 320-340 GPa, and the drafting strength is greater than 6000 MPa.

Description

Technical Field

[0001] The present invention relates to the technical field of polyacrylonitrile carbon fiber spinning, and particularly to a method for controlling the densification of high-strength and medium-modulus carbon fibers. Background Art

[0002] Polyacrylonitrile carbon fiber is an inorganic material with a carbon content of more than 90%. The strength largely depends on the densification degree of the precursor fiber. The precursor fiber is formed by polymerizing acrylonitrile monomers to form a spinning solution. The spinning solution passes through a spinneret to become a single-filament stream, and the single-filament stream is prepared into the precursor fiber under the action of coagulation double diffusion and the synergistic action of hot water drawing during water washing.

[0003] Since spinning solutions with different compositions are highly sensitive to the parameters of the coagulation bath and the drawing process (temperature, medium, draw ratio, etc.), defects such as poor orientation consistency of the precursor fiber, many hole-type defects, and insufficient densification are likely to occur during the preparation process, which in turn affects the densification degree and strength of the subsequent prepared carbon fiber.

[0004] Therefore, it is necessary to develop a method for controlling the densification of high-strength and medium-modulus carbon fibers, and then obtain a carbon fiber with a high densification degree, high draw strength, high draw modulus, and excellent comprehensive performance. Summary of the Invention

[0005] In view of the above analysis, the embodiments of the present invention aim to provide a method for controlling the densification of high-strength and medium-modulus carbon fibers to solve at least one of the problems such as poor orientation consistency of the existing precursor fiber, many hole-type defects, and insufficient densification, and then improve the densification degree and comprehensive performance of the subsequent prepared carbon fiber.

[0006] The present invention provides a method for controlling the densification of high-strength and medium-modulus carbon fibers, and the control method includes the following steps:

[0007] S1: Prepare an acrylonitrile-based polymer spinning solution. After the spinning solution is extruded through a spinneret, it enters a coagulating liquid for a coagulation bath and is simultaneously drawn to obtain a coagulated filament, that is, a nascent fiber.

[0008] S2: Wash the nascent fiber. In the washing stage, a multi-stage washing process with gradually increasing temperature is adopted, and a draw ratio of 1.01 to 1.10 times is applied in each stage of washing.

[0009] S3: Perform hot water drawing on the washed fiber. In the hot water drawing stage, a multi-stage drawing process is adopted, and the draw ratio and hot water temperature of each sub-stage gradually increase. After the drawing is completed and the fiber is cooled, it is oiled, dried, and steam drawn to obtain a densified precursor fiber, and the precursor fiber is used to prepare high-strength and medium-modulus carbon fibers.

[0010] Specifically, the acrylonitrile-based polymer spinning solution described in step S1 is prepared by a polymerization reaction of a copolymer solution, and the copolymer solution includes a copolymer main monomer acrylonitrile, a comonomer itaconic acid, an initiator, and a solvent;

[0011] Among them, the mass ratio of acrylonitrile to itaconic acid is 50-80:20-50, the sum of the masses of acrylonitrile and itaconic acid accounts for 15-25% of the mass of the copolymer solution, the mass of the initiator accounts for 1-1.5% of the mass of the copolymer solution, and the rest is the solvent.

[0012] Specifically, the specific operation of step S1 is as follows:

[0013] The wet spinning process is adopted. The spinning solution is ejected through a spinneret plate and enters the coagulating liquid. The coagulating liquid is a mixed solution of dimethyl sulfoxide and water, and the mass fraction of dimethyl sulfoxide is 70-78%, and the coagulation temperature is 20-60°C.

[0014] Specifically, during the coagulation bath process in step S1, the coagulated filament is drawn, and the draw ratio is 1.01-1.20 times.

[0015] Furthermore, the spinneret plate is an annular spinneret plate, and liquid is introduced into its inner ring. The flow rate of the liquid in the inner ring is controlled to be 100-1000 L / h. The inner ring liquid is a mixed solution of dimethyl sulfoxide and water, and the mass fraction of dimethyl sulfoxide is 65-75%;

[0016] Among them, the mass fraction of dimethyl sulfoxide in the coagulating liquid is greater than the mass fraction of dimethyl sulfoxide in the inner ring liquid, and the temperatures of the coagulating liquid and the inner ring liquid are the same.

[0017] Specifically, step S2 adopts a flower roller type water washing, the water flow direction is countercurrent to the fiber direction, the water washing temperature is gradually increased section by section, and the water washing temperature range is controlled to be 30-80°C;

[0018] During the water washing process, draw distribution is carried out. When the water washing temperature ≤ 45°C, a draw of 1.01-1.03 times is applied; when the water washing temperature > 45°C, a draw of 1.02-1.05 times is applied;

[0019] Among them, the temperature and draw ratio of the next section of water washing are not less than the temperature and draw ratio of the previous section of water washing.

[0020] Preferably, the total number of water washing sections in step S2 is 16 sections. The first section is set at 30-40 degrees, and each section of water washing is increased by 2-4 degrees step by step. The 16th section of water washing is 60-70 degrees.

[0021] Specifically, in step S3, the hot water temperature ≥ 70°C, and the total hot water draw ratio is 2-4 times; the hot water draw is divided into 2-6 sections, and the hot water temperature and draw ratio of each section gradually increase.

[0022] More preferably, the hot water drawing is in four stages;

[0023] Among them, the first stage is at 70-80°C with a drawing ratio of 1.1-1.2 times; the second stage is at 75-85°C with a draw of 1.2-1.3 times; the third stage is at 80-90°C with a draw of 1.3-1.4 times; the fourth stage is at 85-95°C with a draw of 1.4-1.5 times.

[0024] The present invention also discloses a high-strength medium-modulus carbon fiber, which is prepared from the precursor obtained by the regulation method;

[0025] The orientation degree of the precursor is ≥91.5%, and the strength of the precursor is >6.5 cN / dtex; the elastic modulus of the carbon fiber is 320-340 GPa, and the draw strength is >6000 MPa.

[0026] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0027] 1. The present invention provides a precursor with a high degree of orientation consistency, the orientation degree of the precursor is ≥91.5%, and the strength of the precursor is >6.5 cN / dtex; the residual dimethyl sulfoxide in the precursor is significantly reduced, and the residual amount of dimethyl sulfoxide in the precursor is <1000 ppm, thereby significantly reducing the pore-type defects in the precursor and improving the densification degree and strength of the precursor; furthermore, the comprehensive performance of the subsequently prepared carbon fiber is improved.

[0028] Since the precursor is composed of multiple single filaments, each single filament has a certain diameter, and the solidification and diffusion of the single filament ejected from the spinneret hole proceed gradually from the outer surface to the core of the single filament. During the double-diffusion solidification process, the skin of the single filament solidifies first and gradually densifies, hindering the double diffusion of the core of the single filament. Therefore, the dimethyl sulfoxide in the core cannot be released, forming defects. The present invention first realizes the fining of solidification by adjusting parameters such as the concentration of the coagulation solution, the coagulation temperature, and the drawing ratio. The fiber becomes thinner in the coagulation bath, which is more conducive to the precipitation of dimethyl sulfoxide in the core of the single filament, and the densification of the as-spun fiber after solidification is better (that is, the content of dimethyl sulfoxide in the as-spun fiber is reduced).

[0029] More preferably, when using an annular spinneret plate, by controlling the concentration and flow rate of the inner ring liquid, the contact between the spinning solution and the coagulation liquid (strictly speaking, the inner ring liquid is also part of the coagulation liquid) can be made more sufficient, the solidification process is more uniform, and it is beneficial to improve the orientation and uniformity of the as-spun fiber.

[0030] Furthermore, the present invention significantly increases the number of water washing stages in the water washing stage, particularly preferably 16-stage water washing. During the water washing process, the temperature is gradually increased, and the draw ratio is strictly controlled (slightly increased according to the temperature change). In this process, the purpose of washing out the coagulant dimethyl sulfoxide and further improving the fiber densification is achieved, and the residual amount of dimethyl sulfoxide in the raw silk is <1000 ppm. Too few water washing stages or too low temperature will result in too high sulfoxide content in the fiber bundle. With fewer water washing stages, the washing time is insufficient, and the sulfoxide residue will be high. When the water washing temperature is too low, the plasticity of the fiber is poor, which becomes a defect during drawing and affects the densification. Too many water washing stages will cause waste of resources and a long process; the water washing temperature should not be too high either. On the one hand, high temperature will cause the residual dimethyl sulfoxide to diffuse rapidly. Although the residual coagulant is removed, it will cause pore-type defects inside or on the surface of the raw silk. On the other hand, when the water washing temperature > 90 °C, the crystallinity in the raw silk will decrease, resulting in changes in the internal structure, and then the strength of the raw silk will decrease. In addition, it will also cause waste of energy.

[0031] Furthermore, the present invention strictly controls the temperature of hot water drawing and divides it into multiple stages / sub-stages, and different draw ratios are set for each stage to achieve the gradual optimization of the internal structure of the raw silk. If the number of stages is too small and the draw distribution for each stage is too large, it will cause wire breakage and form defects. The temperature of each stage increases step by step, and the draw ratio increases with the temperature. The draw ratio also gradually increases. As the temperature increases step by step, the plasticity of the fiber becomes better, the draw ratio gradually increases, the fiber becomes finer and finer, and the densification becomes better.

[0032] Particularly preferably, the hot water drawing is 4 stages; among them, the first stage is 70 - 80 °C, and the draw ratio is 1.1 - 1.2 times; the second stage is 75 - 85 °C, and the draw is 1.2 - 1.3 times; the third stage is 80 - 90 °C, and the draw is 1.3 - 1.4 times; the fourth stage is 85 - 95 °C, and the draw is 1.4 - 1.5 times. The preferred scheme has a gentle temperature gradient and a gentle draw ratio, which causes little damage to the fiber drawing, and the densification of the fiber is higher.

[0033] Through the linkage of the above steps (corresponding to S1, S2, S3), aiming at the characteristics of the acrylonitrile-based polymer spinning solution and the coagulating solution (dimethyl sulfoxide), the technical objectives and parameter designs of each process section are closely related and work synergistically, and finally the densification control of the raw silk is achieved (low residue, reduced pore-type defects, high orientation consistency), thereby improving the performance of the raw silk and downstream carbon fiber products.

[0034] 2. The equipment involved in the regulation method provided by the present invention is easy to obtain, the process conditions are mild, the energy consumption is small, and it is suitable for large-scale production and wide promotion.

[0035] In the present invention, the above technical solutions can also be combined with each other to achieve more preferred combination solutions. Other features and advantages of the present invention will be described in the following specification. Moreover, some advantages will become apparent from the specification or can be understood by implementing the present invention. The objectives and other advantages of the present invention can be achieved and obtained from the content specifically pointed out in the specification and the drawings. Description of the Drawings

[0036] The drawings are only for the purpose of showing specific embodiments and are not considered as a limitation to the present invention. Throughout the drawings, the same reference signs denote the same components.

[0037] Figure 1 It is a physical photo of carbon fiber in Example 1. Detailed Embodiments

[0038] The following will specifically describe the preferred embodiments of the present invention with reference to the drawings. The drawings form a part of this application and are used together with the embodiments of the present invention to explain the principles of the present invention, rather than to limit the scope of the present invention.

[0039] The present invention provides a method for regulating the densification of high-strength medium-modulus carbon fiber. The regulation method includes the following steps:

[0040] S1: Prepare an acrylonitrile-based polymer spinning solution. After the spinning solution is extruded through a spinneret, it enters a coagulation bath in a coagulating liquid and is simultaneously stretched to obtain a coagulated filament, that is, a nascent fiber.

[0041] S2: Wash the nascent fiber. In the washing stage, a multi-stage washing process with gradually increasing temperature is adopted, and a stretching of 1.01 - 1.10 times is applied in each stage of washing.

[0042] S3: Perform hot stretching on the washed fiber. In the hot stretching stage, a multi-stage stretching process is adopted, and the stretching ratio and hot water temperature in each sub-stage gradually increase. After completion of stretching and cooling, it is oiled, dried, and steam-stretched to obtain a densified precursor fiber, and the precursor fiber is used for preparing high-strength medium-modulus carbon fiber.

[0043] It should be noted that this regulation method is applicable to the wet spinning process using an acrylonitrile-based polymer spinning solution, especially applicable to a coagulating liquid system using dimethyl sulfoxide as a coagulant. When the acrylonitrile-based polymer spinning solution meets certain specific conditions, the effect of this regulation method is more significant, and the properties of the obtained precursor fiber and carbon fiber are more excellent.

[0044] Specifically, the acrylonitrile-based polymer spinning solution in step S1 is prepared by a polymerization reaction of a copolymer solution. The copolymer solution includes a copolymer main monomer acrylonitrile, a copolymer monomer itaconic acid, an initiator, and a solvent.

[0045] Among them, the mass ratio of acrylonitrile to itaconic acid is 50-80:20-50, the sum of the masses of acrylonitrile and itaconic acid accounts for 15-25% of the mass of the copolymer solution, the mass of the initiator accounts for 1-1.5% of the mass of the copolymer solution, and the rest is the solvent. Increasing the mass fraction of the main copolymerization monomer as much as possible within a reasonable range helps to obtain a spinning solution with high viscosity and high solid content. The higher the main copolymerization monomer acrylonitrile, the higher the solid content of the polymer, but it cannot be increased indefinitely; in a high-concentration polymerization and high-solid-content system, gels will appear if the polymerization conditions are slightly inappropriate. The gels are PAN particles, which are likely to block the spinneret holes during spinning, causing filament breakage and affecting the quality of the raw silk and the stability of the spinning process.

[0046] Preferably, the initiator accounts for 1-1.2% of the mass of the copolymer solution, and the initiator is azobisisobutyronitrile. If the content of the initiator is too low, the reaction is incomplete, and there will be more remaining main copolymerization monomers and comonomers. If the content is too high, first, the reaction is violent and it is not easy to control the process. Second, although the unreacted monomers will decrease, most of the polymers produced have relatively short molecular chains and low viscosity.

[0047] Among them, the solvent is dimethyl sulfoxide. Particularly preferably, both the solvent and the coagulant of the spinning solution are dimethyl sulfoxide. On the one hand, it is conducive to effectively removing it in subsequent steps (if different solvents and coagulants are selected, due to the different properties of different substances, it is difficult to remove them completely at the same time or the number of process steps increases). On the other hand, it is conducive to the recycling of dimethyl sulfoxide.

[0048] Specifically, after the polymerization reaction is completed, after degassing and defoaming, a spinning solution with appropriate viscosity and solid content is obtained in the storage tank of the thermostatic circulating water.

[0049] Specifically, the viscosity of the spinning solution is 500-800P, and the solid content is 19.00-21.00%.

[0050] Specifically, the specific operation of step S1 is:

[0051] Using the wet spinning process, the spinning solution is output by a spinning metering pump, flows through a buffer, enters a spinneret and is ejected into a coagulation bath. The coagulation bath is a mixed solution of dimethyl sulfoxide and water, where the mass fraction of dimethyl sulfoxide is 60 - 80%, preferably 70 - 78%, and the coagulation temperature is 20 - 60°C. The spinning solution is a mixed solution of dimethyl sulfoxide and polyacrylonitrile. The solid content of 19 - 21% represents the content of polyacrylonitrile, and the content of dimethyl sulfoxide is 79 - 81%. The coagulation process is a double-diffusion process, where diffusion occurs from high concentration to low concentration. That is, dimethyl sulfoxide in the spun filament after passing through the spinneret diffuses into the coagulation bath, and water in the coagulation bath diffuses into the spun filament after passing through the spinneret. Therefore, the concentration of dimethyl sulfoxide in the coagulation bath is lower than that of the corresponding component in the spinning solution. The coagulation temperature is generally equivalent to the temperature of the spinning solution, and the temperature of the spinning solution is generally controlled below 60°C. If the temperature is too high, the viscosity of the spinning solution is low, and the fiber properties deteriorate. If the temperature is too low, the viscosity of the spinning solution is too high, and it is difficult to form a spun filament through the spinneret holes, resulting in poor spinnability. Therefore, the range of the coagulation temperature is 20 - 60°C.

[0052] Specifically, during the coagulation bath process in step S1, the coagulated filament is drawn, and the draw ratio is 1.01 - 1.20 times. When forming fibers through double-diffusion coagulation, the nascent filament is extremely "delicate" with very weak intermolecular forces, easily deformed, and it is not easy to apply a large uniaxial drawing force. Otherwise, the filament will be damaged, resulting in hairy filaments and broken filaments, causing irregular deformation. The drawing tension is controlled below 200 mg / monofilament, and the monofilament tension corresponding to a draw ratio of 1.20 times is approximately 200 mg / monofilament.

[0053] Furthermore, the spinneret is an annular spinneret, and liquid is introduced into its inner ring. The flow rate of the liquid in the inner ring is controlled to be 100 - 1000 L / h. The liquid in the inner ring is a mixed solution of dimethyl sulfoxide and water, where the mass fraction of dimethyl sulfoxide is 60 - 80%, preferably 65 - 75%.

[0054] When using an annular spinneret, by controlling the concentration and flow rate of the liquid in the inner ring, the contact between the spinning solution and the coagulation bath (strictly speaking, the liquid in the inner ring is also part of the coagulation bath) can be made more sufficient, and the coagulation process can be more uniform, which is beneficial to improving the orientation and uniformity of the nascent fibers.

[0055] Among them, the mass fraction of dimethyl sulfoxide in the coagulation bath is greater than that in the inner ring liquid, and the temperatures of the coagulation bath and the inner ring liquid are the same. Driven by the pressure of the metering pump, the spinning solution is extruded from the spinneret and forms a filament that enters the coagulation bath. The filament is in a columnar state, and the solvent concentration in the filament is greater than that in the coagulation bath. Under the action of the concentration difference, the solvent in the filament diffuses into the coagulation bath. The solvent concentration in the inner ring of the columnar filament is relatively high. To make the concentration of the coagulation liquid in the inner ring (the liquid in the inner ring) the same as that of the coagulation liquid outside the columnar filament, the concentration of the coagulation liquid (the liquid in the inner ring) in the inner ring should be lower than that of the coagulation bath.

[0056] Since the raw silk is composed of multiple filaments, each filament has a certain diameter, and the solidification and diffusion of the filaments ejected from the spinneret holes proceed gradually from the outer surface to the core of the filaments. During the double-diffusion solidification process, the surface of the filaments solidifies first and gradually densifies, hindering the double diffusion of the core of the filaments. Therefore, the dimethyl sulfoxide in the core cannot be released, forming defects. First, by adjusting parameters such as the concentration of the coagulation solution, the coagulation temperature, and the drawing ratio, the present invention realizes coagulation fineness. The fibers become finer in the coagulation bath, which is more conducive to the precipitation of dimethyl sulfoxide in the core of the filaments, and the densification of the as-spun fibers after coagulation is better (that is, the content of dimethyl sulfoxide in the as-spun fibers is reduced); when the temperature of the coagulation bath increases, the denseness of the as-spun fibers first increases and then decreases. When the temperature is relatively low, the coagulation double diffusion is relatively gentle, forming dense as-spun fibers. As the temperature increases, the double diffusion becomes intense, and the dense surface layer hinders the progress of the double diffusion. Therefore, the sulfoxide inside the filaments cannot be released, forming hole defects. When the concentration of the coagulation liquid increases, the concentration difference between the coagulation bath and the main body of the spinning solution decreases, and the double diffusion is slow, making the fiber structure regular and the densification strong. When the concentration of the coagulation liquid decreases, the concentration difference between the two becomes larger, the double diffusion becomes faster, and the filament will become obviously opaque and white because the coagulation is too fast, forming fine-hole defects. The purpose of drawing is to make the fibers finer. The finer fibers are conducive to the complete release of the sulfoxide in the core of the filaments, conducive to the progress of double diffusion, and improve densification.

[0057] Specifically, in step S2, a flower roller type water washing is adopted, the water flow direction is countercurrent to the fiber direction, and the water washing temperature is gradually increased, and the water washing temperature range is controlled at 30-80 °C;

[0058] During the water washing process, drawing distribution is carried out. When the water washing temperature ≤ 45 °C, a draw ratio of 1.01-1.03 times is applied; when the water washing temperature > 45 °C, a draw ratio of 1.02-1.05 times is applied;

[0059] Among them, the temperature and draw ratio of the next-stage water washing are not less than those of the previous-stage water washing.

[0060] The present invention significantly increases the number of washing stages in the water washing stage, particularly preferably 16 stages of water washing, and gradually raises the temperature during the water washing process, and strictly controls the draw ratio (slightly increasing according to the temperature change). In this process, the purpose of washing out the coagulant dimethyl sulfoxide and further improving the densification of the fiber is achieved, and the residual amount of dimethyl sulfoxide in the raw silk is <1000 ppm. Too few washing stages or too low a temperature will result in too high a sulfoxide content in the fiber bundle. If the number of washing stages is small, the washing time is insufficient, and the sulfoxide residue will be high. If the water washing temperature is too low, the plasticity of the fiber is poor, which becomes a defect during drawing and affects the densification. Too many washing stages will cause waste of resources and a lengthy process; the temperature during water washing should not be too high either. On the one hand, high temperature will cause the remaining dimethyl sulfoxide to diffuse rapidly. Although the remaining coagulant is removed, it will cause hole-type defects inside or on the surface of the raw silk. On the other hand, when the water washing temperature > 90 °C, the crystallinity in the raw silk will decrease, resulting in a change in the internal structure, and then the strength of the raw silk will decrease. In addition, it will also cause waste of energy.

[0061] Preferably, the total number of water washing stages in step S2 is 16 stages. The temperature of the first stage is set at 30 - 40 °C, and the temperature of each stage of water washing increases by 2 - 4 °C step by step. The temperature of the 16th stage of water washing is 60 - 70 °C.

[0062] Specifically, in the hot water drawing step in step S3, the hot water temperature ≥ 70 °C, and the total hot water drawing ratio is 2 - 4 times; the hot water drawing is divided into 2 - 6 stages, and the hot water temperature and drawing ratio of each stage gradually increase.

[0063] The present invention strictly controls the temperature of hot water drawing and divides it into multiple stages / sub-stages, and sets different drawing ratios for each stage to achieve the gradual optimization of the internal structure of the raw silk. If the number of stages is too small and the drawing distribution of each stage is too large, it will cause broken filaments and form defects. The temperature of each stage increases step by step, and the drawing ratio increases with the temperature. As the temperature increases step by step, the plasticity of the fiber becomes better, the drawing ratio gradually increases, the fiber becomes finer and finer, and the densification becomes better.

[0064] More preferably, the hot water drawing is 4 stages;

[0065] Among them, the temperature of the first stage is 70 - 80 °C, and the drawing ratio is 1.1 - 1.2 times; the temperature of the second stage is 75 - 85 °C, and the drawing is 1.2 - 1.3 times; the temperature of the third stage is 80 - 90 °C, and the drawing is 1.3 - 1.4 times; the temperature of the fourth stage is 85 - 95 °C, and the drawing is 1.4 - 1.5 times. The preferred scheme has a gentle temperature gradient and a gentle drawing ratio, which causes less damage to the fiber drawing, and the densification of the fiber is higher.

[0066] The present invention also discloses a high-strength medium-modulus carbon fiber, which is made from the raw silk prepared by the above-mentioned regulation method;

[0067] The degree of orientation of the raw silk is ≥91.5%, and the strength of the raw silk is ≥6.8 cN / dtex; the elastic modulus of the carbon fiber is 320-340 GPa, and the drawing strength is >6000 MPa.

[0068] Exemplarily, the raw silk is made into carbon fiber through processes such as constant-tension wire drawing, pre-oxidation, low-temperature carbonization, high-temperature carbonization, electrolysis, sizing, drying, and wire winding.

[0069] Dimethyl sulfoxide is used as the solvent and coagulant in all examples and comparative examples.

[0070] Example 1

[0071] The mass fraction of the copolymer main monomer acrylonitrile in the copolymer is 52%, the mass fraction of the comonomer itaconic acid in the copolymer is 48%, and the initiator azobisisobutyronitrile accounts for 1.2% of the total mass of the copolymer solution. After the polymerization reaction, degassing and de-bubbling, a spinning solution with a viscosity of 700 P and a solid content of 20.00% is obtained in a storage tank with circulating water maintained at 80°C.

[0072] The flow rate of the liquid introduced into the inner ring of the spinneret is 200 L / h, and the mass fraction of dimethyl sulfoxide in the inner ring liquid is 70%; the concentration of dimethyl sulfoxide in the coagulating liquid is controlled at 75%, and the temperature of the coagulating liquid is controlled at 35°C;

[0073] The draw ratio in the coagulating liquid is 1.10 times. The water washing method uses a flower roll type water washing, and the water flow direction is countercurrent to the fiber direction. When the water washing temperature is ≤45°C, a draw ratio of 1.02 times is applied, and when the water washing temperature >45°C, a draw ratio of 1.04 times is applied.

[0074] The number of water washing sections is 16. The first section is set at 30 degrees, and each section of water washing increases by 2 degrees step by step. The 16th section of water washing is 60 degrees.

[0075] The hot drawing uses 4 sections. The first section is at 70 degrees with a draw ratio of 1.1 times; the second section is at 80 degrees with a draw ratio of 1.3 times; the third section is at 90 degrees with a draw ratio of 1.4 times; the fourth section is at 95 degrees with a draw ratio of 1.5 times.

[0076] Then, the finished raw silk 1 is obtained through oiling, drying, and steam drawing.

[0077] Example 2

[0078] The mass fraction of the main monomer acrylonitrile in the copolymer is 55%, the mass fraction of the comonomer itaconic acid in the copolymer is 45%, and the initiator azobisisobutyronitrile accounts for 1.5% of the total mass of the copolymer solution. After the polymerization reaction, degassing and de-bubbling, a spinning solution with a viscosity of 750 P and a solid content of 21.00% is obtained in a storage tank with circulating water maintained at 80°C.

[0079] The flow rate of the liquid introduced into the inner ring of the spinneret plate is 500 L / h, and the mass fraction of dimethyl sulfoxide in the inner ring liquid is 75%; the concentration of dimethyl sulfoxide in the coagulating liquid is controlled at 78%, and the temperature of the coagulating liquid is controlled at 40 °C;

[0080] The draw ratio in the coagulating liquid is 1.15 times. The water washing method is the flower roller type water washing, and the water flow direction is countercurrent to the fiber direction. When the water washing temperature ≤ 45 °C, a draw ratio of 1.02 times is applied; when the water washing temperature > 45 °C, a draw ratio of 1.04 times is applied.

[0081] The number of water washing stages is 16. The first stage is set at 40 °C, and the water washing temperature increases by 2 °C for each stage. The water washing temperature of the 16th stage is 70 °C.

[0082] The hot drawing is carried out in 4 stages. The first stage is at 75 °C with a draw ratio of 1.1 times; the second stage is at 80 °C with a draw ratio of 1.3 times; the third stage is at 90 °C with a draw ratio of 1.4 times; the fourth stage is at 95 °C with a draw ratio of 1.5 times.

[0083] Then, the finished raw silk 2 is obtained through oiling, drying, and steam drawing.

[0084] Example 3

[0085] The mass fraction of the main monomer acrylonitrile in the copolymer is 60%, the mass fraction of the comonomer itaconic acid in the copolymer is 40%, and the initiator azobisisobutyronitrile accounts for 1.0% of the total mass of the copolymer solution. After the polymerization reaction, monomer removal and degassing, a spinning solution with a viscosity of 750 P and a solid content of 21.00% is obtained in a storage tank with circulating water at 80 °C.

[0086] The flow rate of the liquid introduced into the inner ring of the spinneret plate is 500 L / h, and the mass fraction of dimethyl sulfoxide in the inner ring liquid is 75%; the concentration of dimethyl sulfoxide in the coagulating liquid is controlled at 78%, and the temperature of the coagulating liquid is controlled at 40 °C;

[0087] The draw ratio in the coagulating liquid is 1.20 times. The water washing method is the flower roller type water washing, and the water flow direction is countercurrent to the fiber direction. When the water washing temperature ≤ 45 °C, a draw ratio of 1.03 times is applied; when the water washing temperature > 45 °C, a draw ratio of 1.05 times is applied.

[0088] The number of water washing stages is 16. The first stage is set at 45 °C, and the water washing temperature increases by 2 °C for each stage. The water washing temperature of the 16th stage is 75 °C.

[0089] The hot drawing is carried out in 4 stages. The first stage is at 75 °C with a draw ratio of 1.1 times; the second stage is at 80 °C with a draw ratio of 1.3 times; the third stage is at 85 °C with a draw ratio of 1.4 times; the fourth stage is at 90 °C with a draw ratio of 1.5 times.

[0090] Then, the finished raw silk 3 is obtained through oiling, drying, and steam drawing.

[0091] Example 4

[0092] The mass fraction of the main monomer acrylonitrile accounts for 75% of the mass of the copolymer, the mass fraction of the comonomer itaconic acid accounts for 25% of the mass of the copolymer, and the mass fraction of the initiator azobisisobutyronitrile accounts for 1.2% of the total mass of the copolymer solution. After the polymerization reaction, single monomer removal and degassing, a spinning solution with a viscosity of 750 P and a solid content of 21.00 is obtained in a storage tank with circulating water maintained at 80 °C.

[0093] The flow rate of the liquid introduced into the inner ring of the spinneret plate is 500 L / h, and the mass fraction of the liquid dimethyl sulfoxide in the inner ring is 75%; the concentration of dimethyl sulfoxide in the coagulating liquid is controlled at 78%, and the temperature of the coagulating liquid is controlled at 40 °C;

[0094] The draw ratio in the coagulating liquid is 1.10 times. The water washing method uses a flower roll type water washing, and the water flow direction is countercurrent to the fiber direction. When the water washing temperature ≤ 45 °C, a draw ratio of 1.03 times is applied, and when the water washing temperature > 45 °C, a draw ratio of 1.05 times is applied.

[0095] The number of water washing stages is 16. The first stage is set at 45 degrees, and each stage of water washing increases by 2 degrees step by step. The 16th stage of water washing is 75 degrees.

[0096] The hot drawing is carried out in 4 stages. The first stage is at 75 degrees with a draw ratio of 1.15 times; the second stage is at 85 degrees with a draw ratio of 1.2 times; the third stage is at 90 degrees with a draw ratio of 1.3 times; the fourth stage is at 95 degrees with a draw ratio of 1.4 times.

[0097] Then, the finished raw silk 4 is obtained through oiling, drying, and steam drawing.

[0098] Example 5

[0099] The mass fraction of the main monomer acrylonitrile accounts for 60% of the mass of the copolymer, the mass fraction of the comonomer itaconic acid accounts for 40% of the mass of the copolymer, and the mass fraction of the initiator azobisisobutyronitrile accounts for 1.2% of the total mass of the copolymer solution. After the polymerization reaction, single monomer removal and degassing, a spinning solution with a viscosity of 750 P and a solid content of 21.00% is obtained in a storage tank with circulating water maintained at 80 °C.

[0100] The flow rate of the liquid introduced into the inner ring of the spinneret plate is 500 L / h, and the mass fraction of the liquid dimethyl sulfoxide in the inner ring is 75%; the concentration of dimethyl sulfoxide in the coagulating liquid is controlled at 78%, and the temperature of the coagulating liquid is controlled at 40 °C;

[0101] The draw ratio in the coagulating liquid is 1.10 times. The water washing method uses a flower roll type water washing, and the water flow direction is countercurrent to the fiber direction. When the water washing temperature ≤ 45 °C, a draw ratio of 1.03 times is applied, and when the water washing temperature > 45 °C, a draw ratio of 1.05 times is applied.

[0102] The number of water washing stages is 16. The first stage is set at 40 degrees, and each stage of water washing increases by 2 degrees step by step. The 16th stage of water washing is 70 degrees.

[0103] The hot drawing is carried out in 4 stages. The temperature of the first stage is 80 °C and the drawing ratio is 1.20 times; the temperature of the second stage is 85 °C and the drawing ratio is 1.3 times; the temperature of the third stage is 90 °C and the drawing ratio is 1.35 times; the temperature of the fourth stage is 95 °C and the drawing ratio is 1.4 times.

[0104] Then, the finished raw silk 5 is obtained through oiling, drying, and steam drawing.

[0105] Example 6

[0106] The acrylonitrile spinning solution disclosed in Patent CN 103145915 A (the spinning solution in Example 1 of Patent CN103145915A) is used.

[0107] The flow rate of the liquid introduced into the inner ring of the spinneret plate is 500 L / h, and the mass fraction of dimethyl sulfoxide in the inner ring liquid is 75%; the concentration of dimethyl sulfoxide in the coagulating liquid is controlled at 78%, and the temperature of the coagulating liquid is controlled at 40 °C;

[0108] The drawing ratio in the coagulating liquid is 1.15 times. The flower roll type water washing is adopted for the water washing method, and the water flow direction is countercurrent to the fiber direction. When the water washing temperature ≤ 45 °C, a drawing ratio of 1.02 times is applied; when the water washing temperature > 45 °C, a drawing ratio of 1.04 times is applied.

[0109] The number of water washing stages is 16. The temperature of the first stage is set at 40 °C, and the temperature of each stage of water washing increases by 2 °C step by step. The temperature of the 16th stage of water washing is 70 °C.

[0110] The hot drawing is carried out in 4 stages. The temperature of the first stage is 75 °C and the drawing ratio is 1.1 times; the temperature of the second stage is 80 °C and the drawing ratio is 1.3 times; the temperature of the third stage is 90 °C and the drawing ratio is 1.4 times; the temperature of the fourth stage is 95 °C and the drawing ratio is 1.5 times.

[0111] Then, the finished raw silk 6 is obtained through oiling, drying, and steam drawing.

[0112] Example 7

[0113] The acrylonitrile spinning solution disclosed in Patent CN 103145915 A (the spinning solution in Example 2 of Patent CN 103145915A) is used.

[0114] The drawing ratio in the coagulating liquid is 1.20 times. The flower roll type water washing is adopted for the water washing method, and the water flow direction is countercurrent to the fiber direction. When the water washing temperature ≤ 45 °C, a drawing ratio of 1.03 times is applied; when the water washing temperature > 45 °C, a drawing ratio of 1.05 times is applied.

[0115] The number of water washing stages is 16. The temperature of the first stage is set at 45 °C, and the temperature of each stage of water washing increases by 2 °C step by step. The temperature of the 16th stage of water washing is 75 °C.

[0116] The hot drawing is carried out in 4 stages. The temperature of the first stage is 75 °C and the drawing ratio is 1.1 times; the temperature of the second stage is 80 °C and the drawing ratio is 1.3 times; the temperature of the third stage is 85 °C and the drawing ratio is 1.4 times; the temperature of the fourth stage is 90 °C and the drawing ratio is 1.5 times.

[0117] The finished raw silk 7 is obtained through oiling, drying, and steam drawing.

[0118] Example 8

[0119] The mass fraction of the main monomer acrylonitrile in the copolymer is 52%, the mass fraction of the comonomer itaconic acid in the copolymer is 48%, and the initiator azobisisobutyronitrile accounts for 1.2% of the total mass of the copolymer. After the polymerization reaction, monomer removal and degassing, a spinning solution with a viscosity of 700P and a solid content of 20.00% is obtained in a storage tank with circulating water maintained at 80°C.

[0120] The flow rate of the liquid introduced into the inner ring of the spinneret plate is 200 L / h, and the mass fraction of the inner ring liquid dimethyl sulfoxide is 70%; the concentration of the coagulating liquid dimethyl sulfoxide is controlled at 75%, and the temperature of the coagulating liquid is controlled at 35°C;

[0121] The draw ratio in the coagulating liquid is 1.00 times. The water washing method uses a flower roll type water washing, and the water flow direction is countercurrent to the fiber direction. When the water washing temperature is ≤45°C, a draw ratio of 1.02 times is applied, and when the water washing temperature > 45°C, a draw ratio of 1.04 times is applied.

[0122] The number of water washing stages is 16. The first stage is set at 35 degrees, and each stage of water washing increases by 2 degrees step by step. The 16th stage of water washing is 75 degrees.

[0123] The hot drawing is carried out in 2 stages. The first stage is at 90 degrees with a draw ratio of 1.5 times; the second stage is at 95 degrees with a draw ratio of 1.8 times. The finished raw silk 8 is obtained through oiling, drying, and steam drawing.

[0124] Example 9

[0125] The mass fraction of the main monomer acrylonitrile in the copolymer is 52%, the mass fraction of the comonomer itaconic acid in the copolymer is 48%, and the initiator azobisisobutyronitrile accounts for 1.2% of the total mass of the copolymer. After the polymerization reaction, monomer removal and degassing, a spinning solution with a viscosity of 700P and a solid content of 20.00 is obtained in a storage tank with circulating water maintained at 80°C.

[0126] The flow rate of the liquid introduced into the inner ring of the spinneret plate is 200 L / h, and the mass fraction of the inner ring liquid dimethyl sulfoxide is 70%; the concentration of the coagulating liquid dimethyl sulfoxide is controlled at 75%, and the temperature of the coagulating liquid is controlled at 35°C;

[0127] The draw ratio in the coagulating liquid is 1.10 times. The water washing method uses a flower roll type water washing, and the water flow direction is countercurrent to the fiber direction. When the water washing temperature is ≤45°C, a draw ratio of 1.02 times is applied, and when the water washing temperature > 45°C, a draw ratio of 1.04 times is applied.

[0128] The number of water washing stages is 16. The first stage is set at 35 degrees, and each stage of water washing increases by 2 degrees step by step. The 16th stage of water washing is 75 degrees.

[0129] The hot drawing is carried out in 6 stages. The first stage is at 75°C with a draw ratio of 1.1 times; the second stage is at 80°C with a draw ratio of 1.15 times, the third stage is at 85°C with a draw ratio of 1.15 times, the fourth stage is at 90°C with a draw ratio of 1.25 times, the fifth stage is at 95°C with a draw ratio of 1.25 times, and the sixth stage is at 98°C with a draw ratio of 1.3 times. Then, through oiling, drying, and steam drawing, the finished raw silk 9 is obtained.

[0130] Comparative Example 1

[0131] The same spinning solution as in Example 6 is used.

[0132] The flow rate of the liquid introduced into the inner ring of the spinneret plate is 500 L / h, and the mass fraction of dimethyl sulfoxide in the inner ring liquid is 75%; the concentration of dimethyl sulfoxide in the coagulation liquid is controlled at 78%, and the temperature of the coagulation liquid is controlled at 40°C;

[0133] The draw ratio in the coagulation liquid is 1.10 times. The water washing method uses a flower roll type water washing, and the water flow direction is countercurrent to the fiber direction. When the water washing temperature is ≤45°C, a draw ratio of 1.03 times is applied, and when the water washing temperature > 45°C, a draw ratio of 1.05 times is applied.

[0134] The number of water washing stages is 10, each stage of water washing is at 65°C, and the draw ratio for each stage of water washing is 1.03 times.

[0135] The hot drawing is carried out in 4 stages. The first stage is at 75°C with a draw ratio of 1.15 times; the second stage is at 85°C with a draw ratio of 1.4 times; the third stage is at 90°C with a draw ratio of 1.3 times; the fourth stage is at 95°C with a draw ratio of 1.4 times.

[0136] Then, through oiling, drying, and steam drawing, the finished raw silk 10 is obtained.

[0137] Comparative Example 2

[0138] The mass fraction of the main monomer acrylonitrile in the copolymer is 60%, the mass fraction of the comonomer itaconic acid in the copolymer is 40%, and the initiator azobisisobutyronitrile accounts for 1.2% of the total mass of the copolymer solution. After polymerization reaction, monomer removal and degassing, a spinning solution with a viscosity of 750 P and a solid content of 21.00 is obtained in a storage tank with circulating water at 80°C.

[0139] The flow rate of the liquid introduced into the inner ring of the spinneret plate is 500 L / h, and the mass fraction of dimethyl sulfoxide in the inner ring liquid is 75%; the concentration of dimethyl sulfoxide in the coagulation liquid is controlled at 78%, and the temperature of the coagulation liquid is controlled at 40°C;

[0140] The draw ratio in the coagulation liquid is 1.10 times. The water washing method uses a flower roll type water washing, and the water flow direction is countercurrent to the fiber direction. When the water washing temperature is ≤45°C, a draw ratio of 1.03 times is applied, and when the water washing temperature > 45°C, a draw ratio of 1.05 times is applied.

[0141] The number of water washing stages is 10, and the temperature of each water washing stage is 65 degrees. The draft ratio of each water washing stage is 1.03 times.

[0142] Four stages of hot drawing are adopted. The temperature of the first stage is 75 degrees and the draft ratio is 1.4 times; the temperature of the second stage is 85 degrees and the draft ratio is 1.4 times; the temperature of the third stage is 90 degrees and the draft ratio is 1.2 times; the temperature of the fourth stage is 95 degrees and the draft ratio is 1.1 times. In the hot water drawing stage, the operation is not carried out in accordance with gradually increasing temperature and draft ratio segment by segment. Fibrils are generated after the first two stages of drawing, and there is a phenomenon of roller winding.

[0143] Then, the finished raw silk 11 is obtained through oiling, drying, and steam drawing.

[0144] The above-mentioned raw silk (1 - 11) is made into carbon fiber through processes such as constant-tension wire drawing, pre-oxidation, low-temperature carbonization, high-temperature carbonization, electrolysis, sizing, drying, and wire winding.

[0145] Table 1 Performance table of examples and comparative examples

[0146]

[0147]

[0148] *The evaluation of hole-type defects is based on the observation results of an electron microscope at a magnification of 2000.

[0149] In Comparative Example 1 (raw silk 10), due to the relatively low water washing temperature and the absence of gradient temperature increase and draft ratio increase, the residual amount of dimethyl sulfoxide is relatively high, resulting in a small amount of hole defects in the elements, and further leading to a decrease in the strength of the raw silk and carbon fiber.

[0150] In Comparative Example 2 (raw silk 11), on the one hand, the water washing parameters are poor, and on the other hand, due to the operation of the hot water drawing step not in accordance with gradually increasing temperature and draft ratio segment by segment, fibrils are generated after the first two stages of drawing, and there is a phenomenon of roller winding. All properties of the raw silk and carbon fiber have decreased.

[0151] In summary, the raw silk / carbon fiber prepared in Examples 1 - 9 all have good comprehensive properties. The orientation degree of the raw silk provided by the present invention is ≥91.5%, and the strength of the raw silk is ≥6.8 cN / dtex; the elastic modulus of the carbon fiber is 320 - 340 GPa, and the draw strength > 6000 MPa.

[0152] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for controlling the densification of high-strength medium-modulus carbon fibers, characterized in that: The control method comprises the following steps: S1: preparing acrylonitrile-based polymer spinning solution, the spinning solution is spun into a coagulation solution for coagulation bath and simultaneously drawn to obtain coagulated filaments, i.e., primary fibers; S2: washing the spun fiber with water, using a multi-stage washing process with gradually increasing temperature, and applying a draft of 1.01 to 1.10 times in each washing stage; S3: The washed fibers are subjected to hot water drawing. A multi-stage drawing process is adopted in the hot water drawing stage. The drawing multiple and hot water temperature of each sub-segment are gradually increased. After the drawing is completed and cooled, the fibers are oiled, dried, and steam drawn to obtain densified raw fibers, which are used to prepare high-strength medium-modulus carbon fibers.

2. The control method according to claim 1, characterized in that: The acrylonitrile-based polymer spinning solution in step S1 is prepared by polymerization of a copolymer solution, wherein the copolymer solution comprises acrylonitrile as a main copolymer monomer, itaconic acid as a copolymer monomer, an initiator and a solvent; The mass ratio of acrylonitrile to itaconic acid is 50-80:20-50, the sum of the mass of acrylonitrile and itaconic acid accounts for 15-25% of the mass of the copolymer solution, the mass of the initiator accounts for 1-1.5% of the mass of the copolymer solution, and the rest is solvent.

3. The control method according to claim 1, characterized in that: The specific operations of step S1 are: The wet spinning process is adopted, the spinning solution is sprayed out through the spinneret and enters the coagulation solution, the coagulation solution is a mixed solution of dimethyl sulfoxide and water, the mass fraction of dimethyl sulfoxide is 70-78%, and the coagulation temperature is 20-60°C.

4. The control method according to claim 1, characterized in that: In step S1, the coagulated filaments are drawn during the coagulation bath process, and the drawing ratio is 1.01 to 1.20 times.

5. The control method according to claim 3, characterized in that: The spinneret is an annular spinneret, and liquid is introduced into the inner ring thereof, and the flow rate of the liquid in the inner ring is controlled to be 100-1000 L / h. The liquid in the inner ring is a mixed solution of dimethyl sulfoxide and water, and the mass fraction of dimethyl sulfoxide is 65-75%; The mass fraction of dimethyl sulfoxide in the coagulation liquid is greater than the mass fraction of dimethyl sulfoxide in the inner ring liquid, and the temperatures of the coagulation liquid and the inner ring liquid are the same.

6. The control method according to claim 1, characterized in that: Step S2 adopts flower roller type water washing, the water flow direction is countercurrent to the fiber direction, the water washing temperature is increased step by step, and the water washing temperature range is controlled to be 30-80°C; During the washing process, draft distribution is performed. When the washing temperature is ≤45°C, 1.01 to 1.03 times of draft is applied; when the washing temperature is greater than 45°C, 1.02 to 1.05 times of draft is applied. The temperature and the draft ratio of the next water washing section are not less than the temperature and the draft ratio of the previous water washing section.

7. The control method according to claim 1, characterized in that: In step S2, the total number of water washing stages is 16 stages, the first stage is set at 30-40 degrees, each stage of water washing increases by 2-4 degrees, and the 16th stage of water washing is 60-70 degrees.

8. The control method according to claim 1, characterized in that: In step S3, the hot water temperature is ≥70°C, and the total hot water drawing ratio is 2 to 4 times; the hot water drawing is divided into 2 to 6 sections, and the hot water temperature and the drawing ratio of each section gradually increase.

9. The control method according to claim 8, characterized in that: The hot water drawing is divided into 4 sections; Among them, the first section is 70-80℃, the stretching ratio is 1.1-1.2 times; the second section is 75-85℃, the stretching ratio is 1.2-1.3 times; the third section is 80-90℃, the stretching ratio is 1.3-1.4 times; the fourth section is 85-95℃, 1.4-1.5 times.

10. A high-strength medium modulus carbon fiber, characterized in that: The carbon fiber is made from the precursor prepared by the control method according to any one of claims 1 to 9; The orientation degree of the precursor is ≥91.5%, and the strength of the precursor is ≥6.8 cN / dtex; the elastic modulus of the carbon fiber is 320-340 GPa, and the tensile strength is >6000 MPa.

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