Sizing agent suitable for high-modulus mesophase pitch-based carbon fiber, preparation method and application

Abstract

The invention discloses a sizing agent suitable for high-modulus mesophase pitch-based carbon fibers, a preparation method and application, and belongs to the field of carbon fiber sizing agent preparation.The sizing agent is prepared from 100 parts of compound modified epoxy resin, 0.02-0.05 part of an emulsifier, 0.05-0.1 part of a diluent, 0.005-0.01 part of a softener, 0.001-0.002 part of a preservative and 150-300 parts of deionized water, the compound modified epoxy resin is formed by compounding two kinds of modified epoxy resin with large viscosity difference, and the viscosity is 3000-15000 cp, so that the stiffness of the fibers is controlled, the fibers are softer, the matching property of the sizing agent and the high-modulus mesophase pitch-based carbon fibers is improved, the sizing effect is good, and the sizing effect is good. And a series of production problems in preparation of the prepreg from the high-modulus asphalt-based carbon fiber are solved.

Description

Technical Field

[0001] This invention belongs to the field of carbon fiber sizing agent preparation, and specifically relates to a sizing agent, preparation method and application suitable for high modulus mesophase pitch-based carbon fibers. Background Technology

[0002] High-modulus mesophase pitch-based carbon fibers are typically prepared from coal tar pitch, petroleum pitch, etc., through the following process: preparation of high-purity spinnable mesophase pitch, melt spinning, oxidation, low-temperature carbonization, high-temperature carbonization, graphitization, surface treatment, sizing, and drying. High-modulus mesophase pitch-based carbon fibers prepared in this way possess advantages such as lightweight, low coefficient of thermal expansion, and high thermal conductivity. Currently, high-modulus mesophase pitch-based carbon fibers are mainly used as intermediate products in the preparation of prepregs, which can be further processed into carbon fiber composite products. Due to their high modulus and brittleness, high-modulus mesophase pitch-based carbon fibers result in a low yield rate in prepreg preparation. Furthermore, the fiber spreading properties of high-modulus mesophase pitch-based carbon fibers affect the stability of the prepreg preparation process by influencing resin impregnation uniformity. The amount of fuzz also affects the stability of the prepreg preparation process by causing fiber breakage, clump formation, and uneven resin distribution. In addition, resin system compatibility, process parameter control, fiber surface treatment, storage stability, and environmental conditions also affect the stability of the prepreg preparation process.

[0003] After high-temperature carbonization and graphitization, high-modulus mesophase pitch-based carbon fibers exhibit chemical inertness on their surface, resulting in numerous grooves and defects. Subsequent sizing and drying processes form a protective film on the fiber surface, which compensates for these defects, improves fiber wettability, introduces surface-active groups, enhances fiber bundle cohesion and abrasion resistance, and improves fiber flexibility. Currently, there is no dedicated sizing agent for mesophase pitch-based carbon fibers, especially for high-modulus mesophase pitch-based carbon fibers. Patent CN 115710824 A, entitled "A Water-Soluble Epoxy Resin Emulsion for Carbon Fiber Surface Treatment and Its Preparation Method and Uses," discloses a water-soluble epoxy resin emulsion prepared from polyethylene glycol, epoxy resin, and a catalyst. This emulsion is used to modify carbon fibers and to prepare composite materials. However, this method primarily focuses on the interfacial properties between the carbon fibers and the matrix, aiming to improve the bonding between the carbon fibers and the resin matrix.

[0004] The invention patent with publication number CN 116716737 A, entitled "A Pitch-Based Carbon Fiber Sizing Agent and Its Preparation Method," describes a method that improves the uniformity of the sizing agent coating on the fiber surface. This method addresses the issues of easy oxidation, poor wear resistance, and fuzzing of the fiber bundle surface after sizing pitch-based carbon fibers, while also effectively strengthening the bond strength between the fiber and resin. However, this method is unsuitable for high-modulus mesophase pitch-based carbon fibers. Currently, using commercially available sizing agents results in poor fiber processability, characterized by strong bundle aggregation, high stiffness, and a large amount of fiber fuzz. This leads to fiber breakage and filament breakage during the prepreg unfolding process, causing severe fiber damage in subsequent production and failing to fully realize the superior performance of high-modulus mesophase pitch-based carbon fibers. Summary of the Invention

[0005] To address the processability issues in the preparation of high-modulus mesophase pitch-based carbon fibers in existing technologies, this invention provides a sizing agent, preparation method, and application suitable for high-modulus mesophase pitch-based carbon fibers. This improves the compatibility between the sizing agent and high-modulus mesophase pitch-based carbon fibers and can be used in the production of high-modulus mesophase pitch-based carbon fibers and their prepregs.

[0006] This invention is achieved through the following technical solution: A sizing agent suitable for high-modulus mesophase pitch-based carbon fibers, comprising, by mass percentage: 100 parts modified epoxy resin, 2-6 parts emulsifier, 1-10 parts reactive diluent, 0.5-1 part softener, 0.1-0.2 parts preservative, and 150-500 parts deionized water. The modified epoxy resin includes a first modified epoxy resin and a second modified epoxy resin. The viscosity of the first modified epoxy resin is 2000 cp to 8000 cp, and the viscosity of the second modified epoxy resin is 10000 cp to 30000 cp. The first modified epoxy resin, the second modified epoxy resin, and the reactive diluent form a compound modified epoxy resin with a viscosity of 3000 cp to 15000 cp.

[0007] Preferably, the emulsifier is a mixture of anionic and nonionic surfactants in a mass ratio of 1:(5-20), wherein the anionic surfactant is an alkyl carboxylate, alkyl sulfonate, or alkyl sulfate, and the nonionic surfactant is a polyoxyethylene type nonionic surfactant.

[0008] Preferably, the diluent is a monofunctional glycidyl ether or a difunctional glycidyl ether.

[0009] Preferably, the fabric softener is a fatty acid ester compound.

[0010] Preferably, the preservative is an isothiazolinone compound.

[0011] A method for preparing a sizing agent suitable for high-modulus mesophase pitch-based carbon fibers involves mixing a first modified epoxy resin, a second modified epoxy resin, and an active diluent evenly. Then, a mixture obtained by mixing an emulsifier with a portion of deionized water is added to the mixture. After mixing evenly, a softener and a preservative are added while stirring, and finally the remaining deionized water is added to obtain the sizing agent.

[0012] Preferably, the mass ratio of the emulsifier to the corresponding deionized water is (6-8):1. First, the deionized water is added dropwise at a rate of 1-2 mL / min in a uniform manner. When the conductivity of the resulting mixture increases sharply, the stirring speed is increased. When the conductivity remains constant, the remaining deionized water is added and stirring is continued to obtain the sizing agent.

[0013] A method for preparing high-modulus mesophase pitch-based carbon fibers includes the following steps: Step 1: Dilute the sizing agent with deionized water to a mass percentage of 1.5-3.0%, then stir evenly to obtain the slurry; Step 2: Immerse the surface-treated and dried mesophase pitch-based carbon fiber in slurry for 20-30 seconds, and then dry it at 120℃-160℃ to obtain high-modulus mesophase pitch-based carbon fiber.

[0014] A method for preparing a high-modulus mesophase pitch-based carbon fiber prepreg involves hot-melting the high-modulus mesophase pitch-based carbon fiber on a winding beam using a hot-melt method, controlling the fiber spreading width using a spreading roller, and achieving an areal density of 80–150 g / m² for the resulting prepreg. 2 .

[0015] Compared with the prior art, the present invention has the following beneficial technical effects: This invention discloses a sizing agent suitable for high-modulus mesophase pitch-based carbon fibers. It employs two modified epoxy resins with significantly different viscosities as the main agent, allowing adjustment of the ratio of the two modified epoxy resins. Simultaneously, an appropriate amount of reactive diluent is added to ensure the viscosity of the compounded resin remains within a suitable range, thereby controlling fiber stiffness, making the fibers more flexible, and improving the compatibility between the sizing agent and the high-modulus mesophase pitch-based carbon fibers. Reactive diluent, emulsifier, softener, and preservative are used as auxiliary agents. The reactive diluent reduces the viscosity of the resin system, improves resin flowability, and enhances resin wettability and permeability. The emulsifier enables the epoxy resin to form a relatively stable emulsion in water. The softener reduces fiber abrasion, and the preservative maintains the stability of the emulsion's physicochemical properties.

[0016] This invention discloses a method for preparing a sizing agent suitable for high-modulus mesophase pitch-based carbon fibers. The method employs a phase inversion method, in which first and second modified epoxy resins and an active diluent are mixed evenly, and then a mixture obtained by mixing an emulsifier with a portion of deionized water is added to the mixture. After mixing evenly, a softener and a preservative are added while stirring, and finally the remaining deionized water is added to obtain the sizing agent.

[0017] Furthermore, the emulsion inversion point was monitored in real time during the preparation process. Then, the stirring speed was increased, and when the conductivity remained constant, all the remaining deionized water was added, which improved the emulsion preparation efficiency.

[0018] This invention discloses a method for preparing high-modulus mesophase pitch-based carbon fiber. The method involves diluting a sizing agent and then impregnating surface-treated and dried mesophase pitch-based carbon fiber. The resulting fiber is soft and smooth with low stiffness and good sizing effect, thus solving the problem of stiff and non-soft fiber bundles.

[0019] This invention discloses a method for preparing high-modulus mesophase pitch-based carbon fiber prepreg. The method employs a hot-melt process on a winding beam, exhibiting excellent fiber opening and applicability in prepreg production. During the prepreg preparation process, the fibers exhibit good splitting properties, smooth unwinding without breakage, no fiber sticking to the roller, no stubble breakage, and minimal fuzz. By controlling the fiber spreading width using the spreading roller, the resulting prepreg can achieve an areal density of 80 g / m³. 2 ~150g / m 2 The prepreg has a good appearance and can be used to produce high-modulus pitch-based carbon fiber prepregs with excellent performance, solving a series of production problems in the preparation of high-modulus pitch-based carbon fiber prepregs. Attached Figure Description

[0020] Figure 1 This is a graph showing the change in conductivity during the preparation of the sizing agent described in this invention. Figure 2 This is a photograph of the sizing agent described in Embodiment 1 of the present invention; Figure 3 This is a state diagram of the sizing agent after centrifugal stability test according to Example 1 of the present invention; Figure 4 This is a schematic diagram of the preparation process of the mesophase pitch-based carbon fiber described in this invention; Figure 5 This is a surface state diagram of the pitch-based carbon fiber after sizing as described in Embodiment 1 of the present invention under an optical microscope. Figure 6 This is a surface morphology (SEM) image of the pitch-based carbon fiber after sizing as described in Embodiment 1 of the present invention. Figure 7 This is a diagram illustrating the effect of using the sizing fibers described in this invention to prepare prepreg. Figure 8 This is a viscosity-modulus correspondence diagram of epoxy resin in the sizing agent used for the high-modulus pitch-based carbon fiber described in this invention. Figure 9 This is a viscosity-temperature diagram showing the blending of high-viscosity and low-viscosity resins in different proportions according to the present invention. Detailed Implementation

[0021] The present invention will be further described in detail below with reference to specific embodiments. These descriptions are for explanation purposes only and are not intended to limit the scope of the invention. This invention discloses a high-modulus mesophase pitch-based carbon fiber sizing agent, wherein the carbon fiber has a modulus range of 650 GPa to 1000 GPa. The agent comprises a modified epoxy resin as the main component, an active diluent, an emulsifier, a softener, and a preservative. The active diluent reduces the viscosity of the resin system, improves resin flowability, and enhances resin wettability and permeability. The emulsifier enables the epoxy resin to form a relatively stable emulsion in water. The softener reduces fiber abrasion. The preservative maintains the stability of the emulsion's physicochemical properties. Deionized water is used as the solvent, and two types of modified epoxy resins (low viscosity and high viscosity) and the active diluent are compounded to obtain a compound modified epoxy resin. By mass percentage, when the compounded modified epoxy resin is 100 parts, it includes 40-90 parts of low viscosity modified epoxy resin, 10-60 parts of high viscosity modified epoxy resin, 1-10 parts of reactive diluent, 2-6 parts of emulsifier, 0.5-1 part of softener, 0.1-0.2 parts of preservative, and 150-500 parts of deionized water.

[0022] The viscosity range of low-viscosity modified epoxy resin is 2000cp to 8000cp, the viscosity range of high-viscosity modified epoxy resin is 10000cp to 30000cp, and the viscosity range of compound modified epoxy resin is 3000cp to 15000cp.

[0023] This invention, through experiments, demonstrates that for high-modulus pitch-based carbon fibers to achieve better processability, the fibers need to be more flexible and have a lower stiffness level; consequently, the epoxy resin in the fiber sizing agent needs to be within a low viscosity range. As an explanation, Figure 8 The viscosity range of epoxy resin in the sizing agent is given when the modulus of the asphalt-based fiber is 500 GPa to 900 GPa. The resin viscosity is obtained by rotational viscometer. Then, according to the modulus characteristics of the produced fiber, the epoxy resin with the corresponding viscosity range is selected to prepare the sizing agent.

[0024] Figure 9In the diagram, B represents a high-viscosity resin, and A represents a low-viscosity resin. The mixing ratio of both is A:B. As shown in the graph, the viscosity of the blended epoxy resin increases as the proportion of low-viscosity resin A decreases. Therefore, by changing the ratio of epoxy resins A and B, the viscosity of the blended epoxy resin can be adjusted to a value between the viscosity of resin A and the viscosity of resin B. Figure 9 Based on the blending ratio of resins with different viscosities, reactive diluents can be added to adjust the viscosity of the blended modified epoxy resin to achieve the desired level. Figure 8 The viscosity range of epoxy resin, the main component of the sizing agent, for medium- and high-modulus pitch-based carbon fibers.

[0025] Emulsifiers include both anionic and nonionic surfactants. Anionic surfactants are one of the following: alkyl carboxylates, alkyl sulfonates, and alkyl sulfates. Nonionic surfactants are polyoxyethylene type, such as fatty alcohol polyoxyethylene ethers. Anionic and nonionic surfactants are compounded in deionized water according to the HLB (hydrophilic-lipophilic balance) matching principle, with a mass ratio of 1:(5-20).

[0026] The reactive diluent can be a monofunctional glycidyl ether or a difunctional glycidyl ether, such as ethylene glycol diglycidyl ether.

[0027] Fabric softeners are fatty acid ester compounds, such as isooctyl palmitate.

[0028] The preservative is an isothiazolinone compound, such as 1,2-benzisothiazol-3-one.

[0029] This invention provides a method for preparing a high-modulus mesophase pitch-based carbon fiber sizing agent, the specific steps of which are as follows: (1) Compound emulsifier: The total amount of anionic surfactant and nonionic surfactant and the mass ratio of deionized water are (6-8):1. Add deionized water to the anionic surfactant and stir until it is completely dissolved. Then add the nonionic surfactant and place it in a 50°C water bath. After it becomes liquid, stir it evenly to prepare the compound emulsifier.

[0030] (2) Preparation of main materials: Two modified epoxy resins with different viscosities are added together in a beaker, and then an active diluent is added. The mixture is stirred evenly under a 50°C water bath to obtain a compound modified epoxy resin mixture.

[0031] (3) Mixing and mixing: Place the conductivity meter in the beaker and start monitoring the change in conductivity of the liquid in real time. Add the prepared emulsifier to the mixture and stir at high speed with a high shear disperser in a 50°C water bath for 5 to 10 minutes at a speed of 500 to 1000 r / min to make it evenly mixed. Add the softener and preservative while stirring.

[0032] (4) Preparation of sizing agent: While maintaining a 50°C water bath, add deionized water slowly and uniformly at a rate of 1-2 mL / min to the mixture. When the conductivity increases rapidly, increase the rotation speed. When the conductivity remains constant, add all the remaining deionized water and continue to shear and stir to obtain an emulsion-like sizing agent.

[0033] Figure 1 Initially, the system consists only of a mixture of epoxy resin, reactive diluent, emulsifier, softener, and preservative. At this stage, the conductivity is extremely low, close to 0. During the period from 0 to A1, water is slowly added under shear stress. The water is dispersed in the oil phase, forming a water-in-oil (W / O) emulsion. Since a continuous conductive path cannot be formed, the conductivity remains near 0. During the period from A1 to B1, as the amount of water increases, the system reaches a critical point. The continuous phase transforms from oil to water, and the emulsion changes from W / O to O / W, forming a conductive network, and the conductivity increases instantaneously. During the period from B1 to D1, the O / W emulsion is gradually diluted to the target solids content. The resin is sheared and dispersed into finer droplets. During the period from C1 to D1, water addition ends, but high-speed shearing continues for a period to ensure a uniform particle size distribution in the emulsion. At this point, the conductivity stabilizes at a high value. After shearing was stopped, a sizing agent with a certain solid content was obtained. As the standing storage time was extended, the conductivity of the emulsion remained stable without significant change, indicating that the emulsion has good storage stability.

[0034] The centrifugal stability of the sizing agent was tested by centrifuging at 3000 r / min for 10 min.

[0035] The sizing agent obtained by the above preparation method can be applied to the production of high-modulus mesophase pitch-based carbon fibers and prepregs. Specifically, the hot-melt method is used to prepare high-modulus mesophase pitch-based carbon fiber prepregs, and the specific steps are as follows: (1) Slurry preparation: Dilute the slurry agent with deionized water so that the mass percentage of the slurry agent in the resulting mixture is 1.5 to 3.0%. Stir clockwise for 5 minutes until the mixture is homogeneous and the slurry is obtained.

[0036] (2) Preparation of mesophase pitch-based carbon fibers: such as Figure 4 As shown, the sizing process was prepared by immersion sizing. Sizing solution was placed in a sizing agent tank, and the fibers were first spun, oxidized, carbonized at low temperature, carbonized at high temperature, graphitized, surface treated and dried according to conventional processes. Then, the fibers were immersed in the sizing agent tank for 20-30 seconds. The sized fibers were dried at a temperature of 120℃-160℃. The obtained high modulus mesophase pitch-based carbon fibers were wound on a fiber spool, and the sizing quality of the fiber surface was observed by optical microscope and scanning electron microscope.

[0037] (3) Unwinding and preparation: The pitch-based carbon fiber is drawn out from the unwinding frame and enters the winding shaft in the prepreg production equipment in the form of fiber bundles through the guide hole, guide roller, and spreading roller (to control the surface density of the prepreg).

[0038] (4) Fiber spreading and prepreg preparation: Adjust the vibration frequency of the spreading roller to control the fiber spreading width, so that the prepreg surface density (80g / m²) is achieved. 2 ~150g / m 2 The state of the fibers after spreading is shown in the figure. Figure 7 There were no branching, breakage, or filament breakage during the preparation process.

[0039] Example 1: (1) Compound emulsifier: According to the HLB value theory, the HLB of the compound emulsifier of two surfactants, sodium dodecyl sulfate (SDS) and fatty alcohol polyoxyethylene ether-7 (AEO-7), is 16. The amount of the two surfactants is determined by calculation and compounded. 5g of emulsifier SDS is weighed with an electronic balance and added to 5g of deionized water and stirred until completely dissolved. Then, 25g of emulsifier AEO-7 is added and placed in a 50°C water bath. After it becomes liquid, it is stirred evenly to prepare the compound emulsifier. (2) Main material preparation: It has been confirmed that high modulus pitch-based carbon fibers with a strength of 650 GPa need to be prepared. Figure 8 The viscosity range of the epoxy resin used in the sizing agent was determined to be 5000cp~13000cp. Two types of polyether-modified epoxy resin with viscosities of 4500cp and 25000cp were taken, with 40g of the low-viscosity polyether-modified epoxy resin and 20g of the high-viscosity polyether-modified epoxy resin respectively. They were added together to a beaker, and then 4g of ethylene glycol diglycidyl ether was added. The resin was stirred in a 50°C water bath to mix evenly. The viscosity of the compounded resin was 5000cp, and the mixture was obtained.

[0040] (3) Mixing ingredients: Place the conductivity meter in the beaker and start monitoring the change in conductivity of the liquid in real time. Add 2.5g of the prepared compound emulsifier to the mixture, place it in a 50°C water bath, and stir at high speed with a high shear disperser for 5 minutes at 1000r / min to make it evenly mixed. While stirring, add 0.6g of isooctyl palmitate and 0.06g of 1,2-benzisothiazol-3-one.

[0041] (4) Preparation of sizing agent: While maintaining a 50°C water bath, slowly and uniformly add 200g of deionized water to the mixture at a rate of 1mL / min while continuously stirring. When the conductivity increases rapidly, increase the rotation speed to 6000r / min. When the conductivity remains constant, add all the remaining deionized water and continue shearing and stirring for 30min to obtain a sizing agent with a solid content of 25%.

[0042] like Figure 2 It can be seen that the prepared emulsion is milky white, without sedimentation, stratification, or flocculation, and the system is uniform and stable.

[0043] Centrifugation at 3000 rpm for 10 minutes was used to test the centrifugal stability of the sizing agent. Centrifugal stability is used to evaluate the storage stability and anti-agglomeration ability of the emulsion. By applying a centrifugal force much greater than gravity, the stratification, sedimentation, or demulsification phenomena that may occur in the emulsion during long-term standing are simulated in a short time. The actual physical state is as follows: Figure 3 As shown in the image, tube 1 is the sample before centrifugation, and tube 2 is the sample after centrifugation. It can be seen that no stratification, sedimentation, or demulsification occurred, indicating centrifugal stability.

[0044] The sizing agent obtained by the above preparation method is applied in the production of high-modulus mesophase pitch-based carbon fibers and prepregs, specifically as follows: (1) Slurry preparation: Dilute the slurry agent to a concentration of 2.5% with deionized water and stir clockwise for 5 minutes. At this time, the slurry is evenly mixed and the slurry is obtained.

[0045] (2) Fiber preparation: The slurry is continuously transported to the sizing agent tank to ensure that the slurry is always at the designed height. After spinning, oxidation, low-temperature carbonization, high-temperature carbonization, graphitization, surface treatment and drying, 12K pitch-based carbon fiber is immersed in the sizing agent tank for sizing, ensuring that the immersion time is 30 seconds. After sizing, the fiber is dried at a drying temperature of 150℃. The dried fiber is wound on a fiber shaft. The modulus of the fiber is about 650 GPa and the average stiffness is 94.6 mm.

[0046] The sizing quality of the fiber surface was observed using optical microscopy and scanning electron microscopy, and the results are as follows: Figure 5 and Figure 6 As shown, from Figure 5 It can be seen that the fiber surface exhibits a uniform, continuous single color or a softly transitioning color. Based on the constructive interference conditions and color wavelength, this indicates uniform sizing and a good sizing process. Figure 6 As can be seen, the fiber surface is flat and smooth, without any impurities or particles from the sizing agent, indicating that the sizing agent is evenly attached to the fiber surface and the sizing effect is good.

[0047] (3) Unwinding and preparation: Pitch-based carbon fiber prepreg is prepared by hot melt method. The pitch-based carbon fiber is drawn out from the unwinding frame and enters the winding shaft in the prepreg production equipment in the form of fiber bundles through the guide hole, guide roller, and spreading roller (to control the surface density of the prepreg).

[0048] (4) Fiber spreading and prepreg preparation: Adjust the vibration frequency of the spreading roller to control the fiber spreading width and prepare the areal density to 80 g / m². 2 The prepreg material was prepared without any branching, breakage, or filament breakage.

[0049] Example 2: (1) Compound emulsifier: According to the HLB value theory, the HLB of the compound emulsifier of sodium dodecyl sulfate (SDS) and fatty alcohol polyoxyethylene ether-7 (AEO-7) is 12. The amount of the two surfactants was determined by calculation and compounded. 2g of emulsifier SDS was weighed using an electronic balance and added to 5g of deionized water and stirred until completely dissolved. Then, 40g of emulsifier AEO-7 was added and placed in a 50°C water bath. After it became liquid, it was stirred evenly to prepare the compound emulsifier. (2) Preparation of main materials: It has been confirmed that high modulus pitch-based carbon fibers with a strength of 800 GPa need to be prepared. Figure 8 The viscosity range of the epoxy resin used in the sizing agent was determined to be 3500cp~8500cp. Two types of modified bisphenol A epoxy resin with viscosities of 3000cp and 27000cp were taken, with 45g of the low-viscosity modified bisphenol A epoxy resin and 15g of the high-viscosity modified bisphenol A epoxy resin respectively. They were added together to a beaker, and then 5g of ethylene glycol diglycidyl ether was added. The resin was stirred in a 50°C water bath to mix evenly. The viscosity of the compounded resin was 4200cp, and the mixture was obtained.

[0050] (3) Mixing ingredients: Place the conductivity meter in the beaker and start monitoring the change in conductivity of the liquid in real time. Add 3.5g of the prepared compound emulsifier to the mixture, place it in a 50°C water bath, and stir at high speed with a high shear disperser at 500r / min for 10min to make it evenly mixed. While stirring, add 0.3g of isooctyl palmitate and 0.09g of 1,2-benzisothiazol-3-one.

[0051] (4) Preparation of sizing agent: While maintaining a 50°C water bath, slowly and uniformly add 250g of deionized water to the mixture at a rate of 1mL / min while stirring continuously. When the conductivity increases rapidly, increase the rotation speed to 7000r / min. When the conductivity remains constant, add all the remaining deionized water and continue stirring for 45min to obtain a sizing agent with a solid content of 22%.

[0052] The sizing agent obtained by the above preparation method is applied in the production of high-modulus mesophase pitch-based carbon fibers and prepregs, specifically as follows: (1) Slurry preparation: Dilute the slurry agent to a concentration of 3.0% with deionized water and stir clockwise for 5 minutes. At this time, the slurry is evenly mixed and the slurry is obtained.

[0053] (2) Fiber preparation: The slurry is continuously transported to the sizing agent tank to ensure that the slurry is always at the designed height. After spinning, oxidation, low-temperature carbonization, high-temperature carbonization, graphitization, surface treatment and drying, 6K pitch-based carbon fiber is immersed in the sizing agent tank for sizing, ensuring that the immersion time is 25 seconds. After sizing, the fiber is dried at a drying temperature of 140℃. The dried fiber is wound on a fiber shaft. The modulus of the sized fiber is about 800 GPa and the average stiffness is 105.2 mm.

[0054] (3) Unwinding and preparation: Pitch-based carbon fiber prepreg is prepared by hot melt method. The pitch-based carbon fiber is drawn out from the unwinding frame and enters the winding shaft in the prepreg production equipment in the form of fiber bundles through the guide hole, guide roller, and spreading roller (to control the surface density of the prepreg).

[0055] (4) Fiber spreading and prepreg preparation: Adjust the vibration frequency of the spreading roller to control the fiber spreading width and prepare the areal density to 120 g / m². 2 The prepreg has a good appearance and there are no branching, breakage, or filament breakage during the preparation process. According to the testing standard GB / T 41567-2022, under the same conditions, the stiffness of the pitch-based carbon fibers obtained in Example 1 and Example 2 was tested five times, and the results are shown in Table 1 below.

[0056] Table 1. Stiffness test results of high-modulus pitch-based carbon fiber (mm)

[0057] As shown in Table 1, the average stiffness of high-modulus mesophase pitch-based carbon fibers produced using the formulated sizing agent is approximately 95 mm for 650 GPa fibers and approximately 105 mm for 800 GPa fibers. Lower stiffness improves the processability of high-modulus mesophase pitch-based carbon fibers during use. Furthermore, stiffness gradually increases with increasing modulus.

Claims

1. A sizing agent suitable for high modulus mesophase pitch based carbon fibers, characterized in that, According to the mass percentage, the modified epoxy resin 100 parts, emulsifier 2-6 parts, active diluent 1-10 parts, softener 0.5-1 parts, preservative 0.1-0.2 parts, deionized water 150-500 parts; The modified epoxy resin comprises a first modified epoxy resin and a second modified epoxy resin, the viscosity of the first modified epoxy resin is 2000-8000 cp, and the viscosity of the second modified epoxy resin is 10000-30000 cp; The first modified epoxy resin, the second modified epoxy resin and the active diluent form a complex modified epoxy resin, and the viscosity is 3000-15000 cp.

2. The sizing agent suitable for high modulus mesophase pitch-based carbon fiber according to claim 1, characterized by, The emulsifier is mixed by anionic surfactant and nonionic surfactant with a mass ratio of 1: (5-20) ; The anionic surfactant is alkyl carboxylate, alkyl sulfonate or alkyl sulfate, and the nonionic surfactant is polyoxyethylene nonionic surfactant.

3. The sizing agent suitable for high modulus mesophase pitch based carbon fiber according to claim 1, characterized by, The active diluent is monofunctional glycidyl ether or difunctional glycidyl ether.

4. The sizing agent suitable for high modulus mesophase pitch-based carbon fiber according to claim 1, characterized by, The softener is a fatty acid ester compound.

5. The sizing agent suitable for high modulus mesophase pitch based carbon fiber according to claim 1, characterized by, The preservative is an isothiazolinone compound.

6. The method for preparing a sizing agent suitable for high-modulus mesophase pitch-based carbon fibers as described in any one of claims 1 to 5, characterized in that, The method comprises the following steps: The first modified epoxy resin, the second modified epoxy resin and the active diluent are mixed uniformly, then the mixed solution of the emulsifier and a part of deionized water is added, and after mixing uniformly, the softener and the preservative are added while stirring, and finally the remaining deionized water is added to obtain the sizing agent.

7. The process for preparing a sizing agent suitable for high modulus mesophase pitch based carbon fibers according to claim 6, characterized in that, The mass ratio of the emulsifier to the corresponding deionized water is (6-8) : 1; First, add deionized water at a constant speed of 1-2 mL / min, when the conductivity of the obtained mixed system increases sharply, increase the stirring speed, when the conductivity remains unchanged, add the remaining deionized water, continue to stir to obtain the sizing agent.

8. A process for the production of high modulus mesophase pitch-based carbon fibers, characterized by, The method comprises the following steps: S1, dilute the sizing agent of any one of claims 6-7 to 1.5-3.0% by mass percentage with deionized water, and stir uniformly to obtain a slurry; S2, immerse the surface-treated and dried mesophase pitch-based carbon fiber in the slurry, and then dry to obtain a high modulus mesophase pitch-based carbon fiber.

9. The process for the production of high modulus mesophase pitch-based carbon fibers according to claim 8, characterized in that, S2 immerse the mesophase pitch-based carbon fiber in the slurry for 20-30 seconds, and then dry at 120-160℃ to obtain a high modulus mesophase pitch-based carbon fiber.

10. A process for the preparation of a high modulus mesophase pitch based carbon fiber prepreg, characterized in that, The high modulus mesophase pitch-based carbon fiber according to any one of claims 8 to 9 is wound on a winding shaft using a hot melt method, and the fiber is controlled in width by a spreader roller, so that the surface density of the resulting prepreg is 80 g / m 2 ~ 150 g / m 2 .

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