Carbon fiber reinforced bismaleimide resin composite material and preparation method thereof

Abstract

The invention discloses a carbon fiber reinforced bismaleimide resin composite material and a preparation method thereof, belongs to the technical field of carbon fiber sizing agents, and solves the problems of relatively low interlayer shear strength and bending strength of a carbon fiber composite material in the prior art. According to the carbon fiber reinforced bismaleimide resin composite material, sizing carbon fibers are prepared through a specific sizing agent, the mechanical property of the sizing carbon fibers can be remarkably improved, and then the sizing carbon fibers are used for preparing the carbon fiber reinforced bismaleimide resin composite material through a specific method. The prepared carbon fiber reinforced bismaleimide resin composite material has high interlaminar shear strength and bending strength.

Description

Technical Field

[0001] This invention relates to the field of carbon fiber sizing agent technology, and in particular to a carbon fiber reinforced bismaleimide resin composite material and its preparation method. Background Technology

[0002] Carbon fiber reinforced bismaleimide resin matrix composites are widely used in high-end fields such as aerospace, weaponry, and electronics due to their lightweight, high strength, excellent high-temperature resistance, and chemical stability. However, unsized carbon fibers have high surface inertia and low surface energy, resulting in poor interfacial bonding with the bismaleimide resin matrix, which severely affects the interfacial and overall mechanical properties of the composite material.

[0003] CN119931247A discloses a continuous fiber reinforced thermoplastic resin-based composite material and its preparation method. The composite material comprises a thermoplastic resin and a continuous fiber material. The thermoplastic resin has a weight-average molecular weight (Mw) ≥ 500 kg / mol. The preparation method involves adding a photoinitiator or thermal initiator to monomer D (methacrylate, acrylate, styrene, acrylonitrile, or vinyl acetate), mixing thoroughly to obtain a polymerization system, and then impregnating the continuous fiber material into the polymerization system to obtain a prepreg system. The thermoplastic resin monomer D is a general-purpose plastic with relatively low mechanical properties, resulting in low overall mechanical properties of the final composite material.

[0004] Current carbon fiber composite materials still have many shortcomings, such as the inability to simultaneously achieve excellent temperature resistance and interlaminar shear strength, poor stability of sizing agents, and complex composite material preparation processes. These issues make it difficult to meet the stringent performance requirements of high-end applications. Therefore, developing a high-performance carbon fiber reinforced bismaleimide resin composite material is of great significance. Summary of the Invention

[0005] In view of the above, the present invention aims to provide a carbon fiber reinforced bismaleimide resin composite material and its preparation method, to solve at least one of the following problems: (1) the carbon fiber composite material in the prior art cannot have both high interlaminar shear strength and flexural strength; (2) due to the poor stability of the sizing agent in the prior art, it is easy to fail and has poor temperature resistance, and cannot withstand the molding temperature of the bismaleimide resin composite material, resulting in poor mechanical properties of the bismaleimide resin composite material.

[0006] The objective of this invention is mainly achieved through the following technical solutions:

[0007] The first aspect of this invention provides a method for preparing carbon fiber reinforced bismaleimide resin composite material, comprising the following steps:

[0008] S1. The carbon fiber bundle is sized using a modified bismaleimide resin sizing agent to obtain sized carbon fiber.

[0009] S2. After preheating the bismaleimide resin, coat it on the release paper to obtain a bismaleimide resin film.

[0010] S3. The bismaleimide resin film is bonded to both sides of the sized carbon fiber, and then passed through hot rollers and cold rollers respectively to obtain bismaleimide resin prepreg.

[0011] S4: The prepreg from step S3 is laid up layer by layer and then molded to obtain carbon fiber reinforced bismaleimide resin composite material.

[0012] Furthermore, the method also includes weaving sized carbon fibers to obtain carbon fiber fabric.

[0013] Further, in step S1, the sizing conditions include: at 30-50°C, passing the carbon fiber bundle through the sizing agent at a traction speed of 5-12 m / min for 30-100 s.

[0014] Furthermore, in step S2, the preheating conditions include: a temperature of 70-90°C and a time of 30-50 minutes.

[0015] Furthermore, the coating speed is 10-15 m / min.

[0016] Furthermore, the thickness of the adhesive film is 0.05-0.3 mm.

[0017] Furthermore, the bonding conditions include setting the spinning speed of both the bismaleimide resin film and the sized carbon fiber or carbon fiber fabric to 4-6 m / min.

[0018] Furthermore, the temperature of the hot roller is 70-90℃, and the roller pressure is 2-5MPa.

[0019] Furthermore, the temperature of the cold roller is 10-20℃, and the roller pressure is 2-5MPa.

[0020] Furthermore, the tension of the sized carbon fiber or carbon fiber fabric is 30-50N.

[0021] Furthermore, the number of layers in the layup is 15-30.

[0022] Furthermore, the molding process is carried out in an autoclave for curing.

[0023] Furthermore, the molding conditions include: vacuum degree ≥ -0.095MPa, molding temperature 170-200℃, and holding time 3-8h.

[0024] Furthermore, the modified bismaleimide resin sizing agent comprises: 20-40 parts by weight of modified bismaleimide resin, 3-6 parts by weight of emulsifier and 60-80 parts by weight of deionized water.

[0025] Furthermore, the modified bismaleimide resin has the structure shown in Formula A;

[0026]

[0027] Wherein, R1 is selected from H or an alkyl group having 1-4 carbon atoms, and R2 is... One of them.

[0028] Furthermore, n represents the average degree of polymerization, where n > 0.

[0029] Furthermore, the preparation method of the modified bismaleimide resin includes:

[0030] (1) Dissolve the organic solvent and bismaleimide resin monomer by stirring at 60-110℃ to obtain a bismaleimide resin solution with a mass concentration of 15-35%.

[0031] (2) The initiator is slowly added dropwise to the bismaleimide resin solution to obtain a mixed solution, wherein the amount of initiator is 0.5-2% of the mass of the bismaleimide resin monomer;

[0032] (3) Add the modifier dropwise to the mixed solution obtained in step 2 and carry out free radical polymerization reaction for 3-6 hours at a reaction temperature of 60-110℃. After the reaction is completed, cool and filter to remove the solvent and obtain modified bismaleimide resin.

[0033] Furthermore, the emulsifier is a mixture of nonionic and anionic emulsifiers.

[0034] Furthermore, the mass ratio of the nonionic emulsifier to the anionic emulsifier is 1:0.5-1.

[0035] The second aspect of the present invention provides a carbon fiber reinforced bismaleimide resin composite material prepared by the preparation method described in the first aspect.

[0036] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0037] (1) The modified bismaleimide resin sizing agent of the present invention has good wettability in carbon fiber tow, and the sizing effect is uniform. It can synergistically enhance the coating speed during subsequent film preparation, improve the uniformity of the film, and also cooperate with the subsequent hot roller operation. After the film softens after passing through the hot roller, it is fully impregnated into the sized carbon fiber. It works synergistically with the sizing agent in the sized carbon fiber to improve the thickness uniformity of the obtained bismaleimide resin prepreg, thereby making the composite material made from the prepreg...

[0038] (2) The present invention prepares carbon fiber reinforced bismaleimide resin composite material by layup method. The process is simple and can improve production efficiency. By controlling the coating speed to obtain film of different thicknesses and by controlling the feeding speed of film and sized carbon fiber or carbon fiber fabric, it is possible to ensure uniform film thickness, sufficient fiber impregnation and neat fiber arrangement while ensuring production efficiency. At the same time, it reduces the generation of defects and improves the internal quality and performance stability of carbon fiber reinforced bismaleimide resin composite material.

[0039] (3) The modified bismaleimide resin sizing agent provided by the present invention contains a specific structure and a specific content of modified bismaleimide resin, which can have good wettability and film-forming properties on the carbon fiber surface. At the same time, the sizing agent contains a specific content and a specific type of emulsifier, which makes the carbon fiber sizing agent containing the modified bismaleimide resin sizing agent have excellent heat resistance and can withstand high temperatures above 250°C, ensuring that the sizing agent does not fail in the composite material molding process.

[0040] (4) The modified bismaleimide resin in the modified bismaleimide resin sizing agent provided by the present invention is prepared by introducing hydrophilic modified groups into the bismaleimide resin molecule, which effectively improves the water solubility of the modified bismaleimide resin, enabling it to be uniformly dispersed in water to form a stable emulsion. At the same time, it synergistically enhances with the specific emulsifier in the sizing agent, thereby improving the stability of the modified bismaleimide resin sizing agent prepared by the sizing agent, and can be stored for more than 3 months without failure.

[0041] (5) The sized carbon fiber provided by the present invention is prepared by sizing carbon fiber bundles with modified bismaleimide resin sizing agent. Since the modified bismaleimide resin sizing agent contains modified bismaleimide resin and emulsifier with specific structure and content, it can significantly improve the mechanical properties of the sized carbon fiber. Its tensile strength is not less than 5600MPa. The interlaminar shear strength of the carbon fiber composite material prepared by the sized carbon fiber is significantly improved and is not less than 105MPa. At the same time, the mechanical properties of the carbon fiber composite material prepared by the sized carbon fiber are significantly improved and the bending strength is not less than 1600MPa.

[0042] (6) The present invention utilizes sized carbon fiber or carbon fiber fabric containing modified bismaleimide resin sizing agent, and the above-mentioned specific modified bismaleimide resin sizing agent has excellent high temperature resistance and can withstand the molding temperature of carbon fiber reinforced bismaleimide resin composite material, so as to obtain a composite material with high bending performance and interlaminar shear strength.

[0043] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of what is particularly pointed out in the written description and the accompanying drawings. Attached Figure Description

[0044] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0045] Figure 1 The infrared spectrum of the modified bismaleimide resin synthesized in Example 1 of this invention;

[0046] Figure 2 The DSC spectrum of the modified bismuth substituent prepared in Example 1 of this invention;

[0047] Figure 3 This is an appearance diagram of the modified bismuth subsalicylate prepared in Example 1 of the present invention after standing for 90 days. Detailed Implementation

[0048] The preferred preparation examples of the present invention will be described in detail below with reference to the accompanying drawings, which constitute a part of the present invention and, together with the preparation examples of the present invention, serve to illustrate the principles of the present invention.

[0049] The first aspect of this invention provides a method for preparing carbon fiber reinforced bismaleimide resin composite material, comprising the following steps:

[0050] S1. The carbon fiber bundle is sized using a modified bismaleimide resin sizing agent to obtain sized carbon fiber.

[0051] S2. After preheating the bismaleimide resin, coat it on the release paper to obtain a bismaleimide resin film.

[0052] S3. The bismaleimide resin film is bonded to both sides of the sized carbon fiber, and then passed through hot rollers and cold rollers respectively to obtain bismaleimide resin prepreg.

[0053] S4: The prepreg from step S3 is laid up layer by layer and then molded to obtain carbon fiber reinforced bismaleimide resin composite material.

[0054] This invention prepares carbon fiber reinforced bismaleimide resin composites via a layup method. The process is simple and improves production efficiency. By controlling the coating speed to obtain films of varying thicknesses and by controlling the feed speed between the film and the sized carbon fibers or carbon fiber fabric, it is possible to ensure uniform film thickness, sufficient fiber impregnation, and neat fiber arrangement while maintaining production efficiency. This also reduces defects and improves the internal quality and performance stability of the carbon fiber reinforced bismaleimide resin composites.

[0055] According to the present invention, the method further includes weaving sized carbon fibers to obtain carbon fiber fabric.

[0056] In this invention, the carbon fiber fabric can be a carbon fiber fabric produced by processes such as weaving, knitting, and braiding.

[0057] In this invention, during weaving, the tension of a single warp yarn bundle is controlled at 5-6N, and a radial unwinding method is used to achieve uniform warp feeding; the tension of the weft yarn is controlled at 5-7.5N.

[0058] According to the present invention, in step S1, the sizing conditions include: at 30-50°C, passing the carbon fiber bundle through the sizing agent at a traction speed of 5-12 m / min for 30-100 s.

[0059] In this invention, the traction speed of the carbon fiber bundle can be 5m / min, 6m / min, 7m / min, 8m / min, 9m / min, 10m / min, 11m / min, 12m / min, or any two of the above values.

[0060] In this invention, the inventors discovered that when carbon fiber bundles pass through the diluted sizing agent at a speed of 5-12 m / min at 30-50°C, the viscosity of the diluted sizing agent decreases within the above temperature range, ensuring that the diluted sizing agent penetrates into the interior of the carbon fiber bundle in a shorter time. At the same time, in conjunction with the above traction speed, the tension and shear force generated by the bundle can promote the spreading of the sizing agent on the carbon fiber surface, enabling the diluted sizing agent to form a film layer of uniform thickness on the carbon fiber surface, ensuring the stability of the properties of the carbon fiber and the subsequently prepared composite materials.

[0061] In this invention, the carbon fiber bundle is immersed in the diluted sizing agent for 30-100 seconds, which enables the carbon fiber and the sizing agent to achieve sufficient physical adsorption and chemical coupling of active groups, thereby improving the coating effect of the sizing agent.

[0062] In this invention, it is understood that in step S1, when sizing carbon fiber bundles with modified bismaleimide resin sizing agent, the modified bismaleimide resin sizing agent is diluted beforehand to obtain a diluted sizing agent. The modified bismaleimide resin accounts for 0.45%-2% of the mass fraction of the diluted sizing agent, which can uniformly coat the carbon fiber surface, thereby improving the interfacial bonding strength of the carbon fiber. The above concentration range can ensure that the sizing agent forms a dense protective film on the carbon fiber surface, while taking into account both the coating efficiency and the economy of raw materials. If the mass fraction of modified bismaleimide resin is less than 0.45%, the sizing agent film on the carbon fiber surface will be too thin, resulting in uneven wetting and a decrease in the interlaminar shear force of the carbon fiber composite material. Fiber debonding is likely to occur at high temperatures. If the mass fraction of modified bismaleimide resin is greater than 2%, the viscosity of the sizing agent will increase sharply, the coating fluidity will deteriorate, air bubbles will remain in the carbon fiber bundle, and the sizing agent film will have uneven thickness or cracks. Excessively high concentrations will also increase production costs and may lead to an excessive increase in the hardness of the cured film, a decrease in flexibility, and affect the fatigue resistance of the composite material.

[0063] In this invention, in order to make the components more uniformly mixed, the dilution operation is carried out under stirring conditions. Specifically, the stirring conditions include: stirring temperature of 50-70℃, stirring speed of 600-1100r / min, and stirring time of 20-60min.

[0064] In this invention, the inventors discovered that when the stirring temperature and rate meet the above-mentioned range, the shear stress of the modified bismaleimide resin oil phase and water phase can be kept within a suitable range, ensuring that the emulsifier molecules are rapidly oriented at the phase interface to form a stable amphiphilic layer structure, thus avoiding phenomena such as layering and demulsification of the sizing agent.

[0065] In this invention, step S1 further includes drying and winding the sized carbon fibers to obtain sized carbon fibers.

[0066] In this invention, the drying conditions include a drying temperature of 100-180℃ and a drying time of 10-30 minutes. When the drying conditions meet the above range, the residual stress of the sizing agent film can be reduced, and cracking of the sizing agent film can be prevented.

[0067] In this invention, the carbon fiber can be a high-strength medium-modulus carbon fiber commonly used in the art, such as at least one of TZ800H, TZ800S, TZ800G, GT800G, and GT1000 carbon fibers.

[0068] In this invention, the sized carbon fiber has excellent mechanical properties, with a tensile strength of not less than 5600 MPa.

[0069] According to the present invention, considering the issue of reducing viscosity to facilitate coating, the preheating conditions in step S2 include: a temperature of 70-90°C and a time of 30-50 min.

[0070] According to the present invention, considering the issue of uniform film thickness, the coating speed is 10-15 m / min.

[0071] In this invention, the coating speed can be 10 m / min, 11 m / min, 12 m / min, 13 m / min, 14 m / min, 15 m / min, or any two of the above values, preferably 12-14 m / min.

[0072] According to the present invention, the thickness of the adhesive film is 0.05-0.3 mm. When the thickness of the adhesive film meets the above range, the prepreg made from the adhesive film can have a uniform thickness and a small areal density deviation, thereby producing a carbon fiber reinforced bismaleimide resin composite material with excellent interlaminar shear strength.

[0073] According to the present invention, the bonding conditions include setting the spinning speed of both the bismaleimide resin film and the sized carbon fiber or carbon fiber fabric to 4-6 m / min.

[0074] In this invention, it is understood that the spinning speed of the bismaleimide resin film and the sized carbon fiber or carbon fiber fabric is equal. The spinning speed can be 4 m / min, 4.5 m / min, 5 m / min, 5.5 m / min, 6 m / min, or any combination of two of these values. Preferably, it is 4-5 m / min.

[0075] The inventors discovered that the wire feed speed affects the performance of the final product. A feed speed less than 4 m / min results in a thicker coating, increasing the weight and cost of the composite material. A speed greater than 6 m / min leads to uneven coating, inconsistent thickness, and defects such as pores and voids, resulting in weak bonding between the carbon fiber and bismaleimide resin. A wire feed speed of 4-6 m / min ensures uniform coating thickness, thereby improving the interfacial properties and overall quality of the composite material.

[0076] According to the present invention, considering the control of bismaleimide resin flowability and rapid resin characterization, the temperature of the hot roller is 70-90°C and the roller pressure is 2-5 MPa, and the temperature of the cold roller is 10-20°C and the roller pressure is 2-5 MPa.

[0077] In this invention, the rolling pressure of both the hot and cold rollers is 2-5 MPa. This is to ensure the uniform thickness of the adhesive film and to fully impregnate the bismaleimide resin into the sized carbon fiber or carbon fiber fabric, thereby improving the interlaminar shear strength of the composite material. Preferably, it is 3-4 MPa.

[0078] According to the present invention, the tension of the sized carbon fiber or carbon fiber fabric is 30-50N.

[0079] In this invention, the tension is a range of 30N, 32N, 35N, 38N, 40N, 45N, 48N, 50N, or any two of the above values, preferably 35-45N.

[0080] In this invention, a tension of less than 30N results in fiber relaxation, irregular arrangement, and uneven fiber accumulation or dispersion, affecting the mechanical properties and appearance quality of the composite material. A tension greater than 50N leads to excessive fiber stretching or even breakage, affecting the integrity and continuity of the sized carbon fiber or carbon fiber fabric, thereby reducing the bending performance and interlaminar shear strength of the composite material.

[0081] According to the present invention, the number of layers is 15-30, which can produce composite materials with uniform thickness, and the thickness of the composite material can be adjusted according to different needs, making the method more flexible.

[0082] According to the present invention, the molding is performed by curing in an autoclave.

[0083] The curing and molding process includes: encapsulating the prepreg after layup in a vacuum bag, then curing it in an autoclave while maintaining a vacuum level of ≥-0.095 MPa, a molding temperature of 170-200℃, and a holding time of 3-8 hours. After molding, once the autoclave temperature drops below 60℃, the product is removed to obtain a carbon fiber reinforced bismaleimide resin composite material.

[0084] According to the present invention, the modified bismaleimide resin sizing agent comprises: 20-40 parts by weight of modified bismaleimide resin, 3-6 parts by weight of emulsifier and 60-80 parts by weight of deionized water.

[0085] In this invention, the modified bismaleimide resin sizing agent contains a specific structure and a specific amount of modified bismaleimide resin. Due to the introduction of hydrophilic modifying groups into the bismaleimide resin, the sizing agent has good water solubility and can exhibit good wettability and film-forming properties on the carbon fiber surface during the sizing process. At the same time, the specific amount of emulsifier component contained in the modified bismaleimide resin sizing agent can synergistically enhance the effect with the aforementioned specific amount of modified bismaleimide resin, resulting in excellent heat resistance of the modified bismaleimide resin sizing agent, which can withstand high temperatures above 250°C. Furthermore, the sized carbon fibers prepared by this sizing agent exhibit excellent mechanical properties.

[0086] It is understandable that the sum of the weight percentages of all components in the above modified bismaleimide resin sizing agent is 100%.

[0087] It is understood that the bismaleimide resin is a bismaleimide resin.

[0088] In this invention, the inventors discovered through extensive research that when the modified bismaleimide resin content in the sizing agent is only 20-40 parts by weight, the emulsifier content is 3-6 parts by weight, and the deionized water content is 60-80 parts by weight, the components can work synergistically to achieve their optimal performance. If the modified bismaleimide resin content is less than 20 parts by weight or the emulsifier content is less than 3 parts by weight, it will affect the subsequent production efficiency and result in poor emulsification. It will be unable to effectively reduce the interfacial tension between the oil phase and the water phase, leading to unstable dispersion of oil droplets. After standing, the emulsion is prone to obvious stratification or even demulsification, and the shelf life will be significantly shortened. If the modified bismaleimide resin content is greater than 80 parts by weight or the emulsifier content is greater than 6 parts by weight, it will cause the viscosity of the sizing agent emulsion to increase sharply, or even become gel-like, making it difficult to coat the carbon fiber surface evenly. Furthermore, the presence of a large amount of emulsifier will significantly reduce the interlayer properties of the subsequent carbon fiber composite material.

[0089] Specifically, the content of the modified bismaleimide resin is 20 parts by weight, 20.5 parts by weight, 20.8 parts by weight, 21 parts by weight, 21.5 parts by weight, 22 parts by weight, 22.5 parts by weight, 23 parts by weight, 24 parts by weight, 24.5 parts by weight, 25 parts by weight, 28 parts by weight, 28.5 parts by weight, 30 parts by weight, 32 parts by weight, 35 parts by weight, 37 parts by weight, 40 parts by weight, or any two of the above values, preferably 28-37 parts by weight.

[0090] Specifically, the content of the emulsifier is 3 parts by weight, 3.4 parts by weight, 3.5 parts by weight, 3.6 parts by weight, 4 parts by weight, 4.5 parts by weight, 4.8 parts by weight, 4.9 parts by weight, 5 parts by weight, 5.2 parts by weight, 5.5 parts by weight, 5.8 parts by weight, 6 parts by weight, and any two of the above values, preferably 3.5-4.5 parts by weight.

[0091] Specifically, the content of the deionized water is 60 parts by weight, 61 parts by weight, 62 parts by weight, 63 parts by weight, 65 parts by weight, 68 parts by weight, 70 parts by weight, 72 parts by weight, 73 parts by weight, 75 parts by weight, 77 parts by weight, 78 parts by weight, 80 parts by weight, or any two of the above values, preferably 62-68 parts by weight.

[0092] According to the present invention, the modified bismaleimide resin has the structure shown in Formula A;

[0093]

[0094] Furthermore, in formula A, R1 is selected from H or an alkyl group having 1-4 carbon atoms, and R2 is... One of them, where n is the average degree of polymerization, and n > 0.

[0095] In this invention, the modified bismaleimide resin satisfies the above structure, possessing a large number of hydroxyl groups and ether bonds. The hydroxyl groups have strong polarity, giving the modified bismaleimide resin a certain degree of hydrophilicity. The ether bonds have a high degree of rotational freedom, which can reduce the rotational steric hindrance within the molecular chain, making the molecular chain of the modified bismaleimide resin more flexible and improving its chemical stability. This, in turn, enhances the reactivity of the modified bismaleimide resin and strengthens the hydrogen bonding effect. The hydrogen bonds provide strength, and the ether bonds provide flexibility. The combination of the two can achieve the effect of "combining rigidity and flexibility" in the modified bismaleimide resin, that is, it enables the sizing agent containing the modified bismaleimide resin to spread well on the carbon fiber surface while improving the tensile properties of the resulting sized carbon fiber.

[0096] According to a preferred embodiment of the present invention, in formula A, R1 is selected from H, methyl or ethyl, and R2 is selected from...

[0097] In this invention, n>0, but considering that the modified bismaleimide resin with low degree of polymerization has lower viscosity and significantly improved fluidity; and that it can form a more uniform network structure after crosslinking, reducing stress and improving toughness; and that the reaction is easier to control with low degree of polymerization, thus reducing costs, n is taken as 10-100.

[0098] In this invention, the modified bismaleimide resin sizing agent has excellent temperature resistance and film-forming properties, and can be well applied to sizing carbon fibers or carbon fiber composites. Specifically, the modified bismaleimide resin sizing agent has a temperature resistance of ≥250℃, a viscosity of 150-280cp at 25℃, and excellent film-forming properties.

[0099] In this invention, the viscosity of the modified bismaleimide resin sizing agent at 25°C is 150 cp, 155 cp, 160 cp, 170 cp, 175 cp, 180 cp, 185 cp, 190 cp, 195 cp, 200 cp, 205 cp, 210 cp, 220 cp, 225 cp, 230 cp, 235 cp, 240 cp, 250 cp, 260 cp, 265 cp, 270 cp, 280 cp, or any two of the above values.

[0100] In this invention, the preparation method of the bismaleimide resin sizing agent is as follows: modified bismaleimide resin is crushed into 80-120 mesh particles and added to deionized water. Under the conditions of stirring temperature of 50-70℃ and stirring speed of 600-1500r / min, the above-mentioned emulsifier is added and stirred for 1-3 hours to obtain the modified bismaleimide resin sizing agent.

[0101] The inventors discovered that pulverizing modified bismaleimide resin into 80-120 mesh particles can significantly increase the interfacial contact area. Furthermore, by adding an emulsifier at the above stirring temperature and speed, rapid hydration and dispersion can be achieved, improving emulsification efficiency. The preparation method is simple, and the resulting modified bismaleimide resin sizing agent has a suitable particle size, stable properties, and does not become ineffective after long-term storage (more than 3 months).

[0102] According to the present invention, the method for preparing the modified bismaleimide resin includes:

[0103] (1) Dissolve the organic solvent and bismaleimide resin monomer by stirring at 60-110℃ to obtain a bismaleimide resin solution with a mass concentration of 15-35%.

[0104] (2) The initiator is slowly added dropwise to the bismaleimide resin solution to obtain a mixed solution, wherein the amount of initiator is 0.5-2% of the mass of the bismaleimide resin monomer;

[0105] (3) Add the modifier dropwise to the mixed solution obtained in step 2, and carry out a free radical polymerization reaction for 3-6 hours at a reaction temperature of 60-110℃. After the reaction is completed, cool and filter to remove the solvent to obtain the modified bismaleimide resin. In this invention, the organic solvent can be at least one of DMF (N,N-dimethylformamide), toluene, and xylene.

[0106] In this invention, the initiator is selected from azo initiators and / or peroxide initiators. Preferably, the initiator is selected from at least one of diisobutyronitrile (AIBN), azobisisoheptanenitrile (ABVN), or benzoyl peroxide (BPO).

[0107] In this invention, it is understood that the initiator is added in the form of an initiator solution, which includes an initiator and a solvent, wherein the solvent may be at least one of N,N-dimethylformamide (DMF), toluene, and xylene.

[0108] In this invention, the concentration of the initiator solution can be a conventional concentration in the art, such as 0.0001-0.001 mol / L.

[0109] In this invention, the amount of initiator used is 0.5-2% of the mass of the bismaleimide resin monomer, which can achieve the beneficial effect of promoting double bond crosslinking and improving the degree of resin curing.

[0110] It is understandable that the amount of initiator relative to the bismaleimide resin monomer is calculated based on the initiator itself.

[0111] In this invention, the amount of initiator is 0.5%, 0.6%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2% of the mass of bismaleimide resin monomer, or any two of the above values.

[0112] In this invention, the inventors discovered that when the initiator is added at a rate of 0.2-0.45 g / s, the initiator can be uniformly distributed in the system, allowing the reaction to proceed smoothly, thereby obtaining a modified bismaleimide resin with high crosslinking density and stable performance.

[0113] In this invention, the dropping rate of the initiator can be 0.2 g / s, 0.25 g / s, 0.3 g / s, 0.35 g / s, 0.4 g / s, 0.45 g / s, or any two of the above values.

[0114] In this invention, the modifier is at least one selected from 2-hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxyethyl ethyl acrylate, and acrylic acid.

[0115] The inventors made an unexpected discovery that when the modifier is selected from at least one of the above compounds, the modified bismaleimide resin can be made to have good flexibility, thereby enabling the sizing agent containing the modified bismaleimide resin to spread well on the carbon fiber surface, thus improving the interfacial compatibility between the sizing agent and the carbon fiber and resulting in better film formation.

[0116] In this invention, the amount of the modifier is 10-30% of the amount of bismaleimide resin. This significantly improves the cross-linking network toughness of the modified bismaleimide resin molecules, achieving a balance between the heat resistance of the sizing agent and the wettability and film-forming properties between the sizing agent and the carbon fiber.

[0117] In this invention, it is important to note that the modifier needs to be slowly added dropwise to the mixed solution in step 2. The inventors have discovered that when the dropwise addition rate of the modifier is 2-6 g / s, it can avoid excessively vigorous reactions or excessively high local concentrations of monomers that could lead to side reactions, thereby further optimizing the crosslinking network structure, promoting the orderly arrangement of molecular chains, improving the uniformity of the crosslinking structure, and thus enhancing the interlaminar shear strength of the carbon fiber composite material.

[0118] According to the present invention, considering the synergistic effect with the above-mentioned modified bismaleimide resin, the emulsifier is a compound of nonionic emulsifier and anionic emulsifier.

[0119] In this invention, the emulsifier is a mixture of nonionic and anionic emulsifiers. This is because the nonionic emulsifier can form hydrogen bonds with the hydroxyl groups in the modifier, enhancing the coating stability of the modified bismaleimide resin particles, reducing the emulsion particle size, and improving the shelf life. The anionic emulsifier can prevent particle aggregation through electrostatic repulsion, and its hydrophobic segments form π-π stacks with the benzene rings in the bismaleimide resin molecules, improving the interfacial bonding force. Through the combination of emulsifiers, both steric hindrance stability and electrostatic stability mechanisms are taken into account, resulting in excellent comprehensive performance of the modified bismaleimide resin sizing agent. In particular, the carbon fiber composite material containing this modified bismaleimide resin sizing agent has excellent mechanical properties.

[0120] The inventors unexpectedly discovered that when the mass ratio of nonionic emulsifier to anionic emulsifier is 1:0.5-1, the performance of modified bismaleimide resin can be significantly improved, further enhancing the temperature resistance of the sizing agent and simultaneously increasing the bonding force between the sizing agent and carbon fiber, thus resulting in sizing carbon fiber with superior mechanical properties. Furthermore, when the mass ratio of nonionic emulsifier to anionic emulsifier is 1:0.5-0.7, all of the above properties are further improved.

[0121] Specifically, the nonionic emulsifier is selected from at least one of Tween 80, Span 20, or polyoxyethylene ether, and the anionic emulsifier is selected from at least one of sodium dodecyl sulfate, sodium dodecyl sulfonate, and sodium dodecylbenzene sulfonate.

[0122] The second aspect of the present invention provides a carbon fiber reinforced bismaleimide resin composite material prepared by the preparation method described in the first aspect.

[0123] In this invention, the flexural strength of the carbon fiber reinforced bismaleimide resin composite material is not less than 1597 MPa, and the interlaminar shear strength is not less than 91 MPa.

[0124] The advantages of precise control of process parameters in this invention will be demonstrated below through specific preparation examples and comparative preparation examples.

[0125] In the following examples, the temperature resistance of the modified bismaleimide resin sizing agent was determined by a TGA thermogravimetric analyzer under N2 atmosphere, with the 5wt% weight loss temperature as the temperature resistance index.

[0126] The viscosity of the modified bismaleimide resin sizing agent was determined by a rotational viscometer.

[0127] Wettability was characterized by the dynamic contact angle between the sizing agent and the carbon fiber monofilament using a DCAT21 surface / interfacial tensiometer; the specific steps are as follows:

[0128] (1) Place the bare carbon fiber filaments after removing the sizing agent into an oven at 120°C and dry them. Then cut them into 20mm long segments. Randomly select 5 monofilaments and fix them with the clamps of the DCAT21 surface / interfacial tension meter. Maintain a 5mm gap between adjacent carbon fiber monofilaments and cut off the excess part so that the lengths exposed to the clamps are as equal as possible.

[0129] (2) Place the container containing the sizing agent liquid on the lifting platform of the DCAT21 surface / interfacial tension meter, install the clamps that fix the 5 carbon fiber monofilaments in the corresponding positions of the instrument, ensure that the carbon fiber monofilaments are vertical, set the depth of the carbon fiber monofilaments inserted into the sizing agent liquid to be 5mm, and the forward and backward wetting speeds are both 0.03mm / s.

[0130] (3) Start the measurement program. The DCAT21 surface / interface tension meter automatically controls the lifting platform to rise, so that the liquid surface gradually approaches the carbon fiber monofilament. When the carbon fiber monofilament comes into contact with the sizing agent liquid surface, the instrument's force sensor measures the wetting force based on the immersion depth and combines it with the carbon fiber monofilament diameter data. During the upward movement of the sample stage, the dynamic contact angle between the sizing agent and the carbon fiber monofilament in the wetting stage can be measured.

[0131] The interlaminar shear strength of carbon fiber composites was determined using a universal testing machine with a three-point bending method according to ASTM D2344.

[0132] The flexural strength of carbon fiber composites was determined according to ASTM D790 standard.

[0133] Unless otherwise stated, all reagents used below are commercially available.

[0134] The following preparation examples illustrate the preparation of modified bismaleimide resin.

[0135] Preparation Example 1

[0136] 1. Dissolve 4 kg of DMF and 1 kg of bismaleimide resin monomer by stirring at 90°C to obtain a bismaleimide resin solution with a mass concentration of 20%.

[0137] 2. Add 10g of initiator AIBN to the above bismaleimide resin solution at a rate of 0.3g / s to obtain a mixed solution, wherein the amount of initiator is 1% of the mass of the bismaleimide resin monomer;

[0138] 3. At 70°C, 150g of hydroxyethyl ethyl acrylate is added dropwise to the mixed solution obtained in step 2 at a rate of 3g / s, and a free radical polymerization reaction is carried out at 70°C for 4.5 hours. After the reaction is completed, the solvent is removed by cooling and filtration to obtain modified bismaleimide resin G1, wherein the amount of the modifier is 15% of the amount of bismaleimide resin.

[0139] Where R1 is C2H5, R2 is n is 80. Figure 1 The infrared spectrum of the modified bismaleimide resin prepared in this preparation example is shown below. Figure 1 The characteristic peaks indicate that the modified bismaleimide resin meeting the requirements has been successfully synthesized.

[0140] Preparation Example 2

[0141] Modified bismaleimide resin G2 was synthesized according to the method of Preparation Example 1, except that 2-hydroxyethyl acrylate was replaced with 200g of acrylic acid, and the amount of modifier was 20% of the amount of bismaleimide resin.

[0142] Where R1 is H, R2 is n is 80.

[0143] Preparation Example 3

[0144] Modified bismaleimide resin G3 was synthesized according to the method of Preparation Example 1, except that in step 1, 2.33 kg of xylene and 1 kg of bismaleimide resin monomer were stirred and dissolved at 90 °C to obtain a bismaleimide resin solution with a mass concentration of 30%.

[0145] Where R1 is C2H5, R2 is n is 80.

[0146] Preparation Example 4

[0147] Modified bismaleimide resin G4 was synthesized according to the method of Preparation Example 1, except that the modifier was 2-hydroxyethyl acrylate. In the obtained modified bismaleimide resin G4, R2 was...

[0148] Comparative Preparation Example 1

[0149] The method is the same as in Preparation Example 1, except that step 3 is omitted, i.e., the bismaleimide resin is not modified, i.e., the bismaleimide resin polymer D1 is prepared.

[0150] Where R1 is H, R2 is H, and n is 78.

[0151] Comparative Preparation Example 2

[0152] Modified bismaleimide resin D2 was prepared according to the method of Preparation Example 1, except that in step 3, 2-hydroxyethyl acrylate was replaced with an equal amount of ethyl acrylate.

[0153] Where R1 is H, R2 is n is 80.

[0154] The following examples illustrate the preparation of modified bismaleimide resin sizing agents.

[0155] Examples 1-9, Comparative Examples 1-4

[0156] According to the composition formulation in Table 1, the modified bismaleimide resin in the composition was pulverized into 100-mesh particles and mixed with deionized water. Then, under the conditions of stirring temperature of 50°C and stirring speed of 1000 r / min, emulsifiers polyoxyethylene sorbitan fatty acid ester (referred to as emulsifier A in Table 1) and sodium dodecylbenzenesulfonate (referred to as emulsifier B in Table 1) were added and mixed evenly. In Example 9, emulsifier A was hexadecyltrimethylammonium chloride.

[0157] Table 1

[0158] serial number Modified bismaleimide resin Emulsifier A Emulsifier B Deionized water Example 1 28 G1 2.5 portions 1.5 copies 68 copies Example 2 28 G2 2.5 portions 1.5 copies 68 copies Example 3 28 G3 2.5 portions 1.5 copies 68 copies Example 4 28 G4 2.5 portions 1.5 copies 68 copies Example 5 36 G1 2.5 portions 1.5 copies 60 copies Example 6 28 G1 1 copy 3 copies 69 copies Example 7 25 G1 2 copies 2 copies 71 copies Example 8 28 G1 - 4 copies 68 copies Example 9 28 G1 2.5 portions 1.5 copies 68 copies Comparative Example 1 28 copies of D1 2.5 portions 1.5 copies 68 copies Comparative Example 2 28 servings of D2 2.5 portions 1.5 copies 68 copies Comparative Example 3 18 G1 2.5 portions 1.5 copies 78 copies Comparative Example 4 28 G1 4 copies 4 copies 64 copies

[0159] Example 10

[0160] The method is the same as in Example 1, except that the stirring temperature is 45°C and the stirring speed is 900 r / min.

[0161] The temperature resistance, film-forming properties, and viscosity of the modified bismaleimide resin sizing agents prepared in the above examples and comparative examples were tested, and the results are shown in Table 2.

[0162] Table 2

[0163]

[0164]

[0165] Figure 2 The image shows the DSC chart of the modified bismaleimide resin sizing agent prepared in Example 1. Figure 2 As can be seen from the results, the modified bismaleimide resin sizing agent prepared in Example 1 did not have any endothermic or exothermic peaks before 250°C, indicating that the sizing agent did not undergo significant chemical reactions before 250°C and has excellent high-temperature resistance.

[0166] Figure 3 The image shows the appearance of the modified double-mask sizing agent emulsion after standing for more than 3 months. It can be seen that the sizing agent did not show any stratification or demulsification, and has good storage stability.

[0167] The following application examples illustrate the preparation of carbon fiber reinforced bismaleimide resin composites.

[0168] Application Example 1

[0169] S1. The modified bismaleimide resin sizing agent prepared in Example 1 is diluted with deionized water to obtain a diluted sizing agent. The amount of deionized water added is such that the mass fraction of modified bismaleimide resin in the diluted sizing agent is 1%. The diluted sizing agent is introduced into the sizing tank and the temperature is set to 35°C. TZ800H carbon fiber bundles are passed through the sizing agent tank at a traction speed of 8 m / min. The immersion time of TZ800H carbon fiber bundles in the modified bismaleimide resin sizing agent is 35 s. Then, they are dried at 110°C for 15 min to obtain sizing carbon fiber.

[0170] S2. Preheat the bismaleimide resin at 80°C for 30 minutes, set the coating speed to 12 m / min, and coat it onto the release paper to form a bismaleimide resin film with a thickness of 0.1 mm.

[0171] S3. Set the wire speed of the bismaleimide resin film and the sized carbon fiber to 5m / min, the hot roller pressure and the cold roller pressure to be the same, both 3MPa, the hot roller temperature to 80℃, the cold roller temperature to 10℃, and the tension of the sized carbon fiber to 40N to obtain carbon fiber prepreg.

[0172] S4. Cut the prepreg obtained in step S3 neatly, ensuring the carbon fiber direction is consistent and the edges are neat. Lay 20 layers in a layer-by-layer manner, with the total thickness controlled at 3±0.2mm. After sealing in a vacuum bag, cure and form in an autoclave, maintaining a vacuum degree of ≥-0.095MPa, a forming temperature of 180℃, and a holding time of 4 hours. After forming, wait for the autoclave temperature to drop below 60℃, then remove the product to obtain carbon fiber reinforced bismaleimide resin composite material T1.

[0173] Application Example 2-10

[0174] Following the method of Application Example 1, except that the modified bismaleimide resin sizing agent prepared in Example 1 was replaced with the modified bismaleimide resin sizing agent prepared in Examples 2-10. Carbon fiber reinforced bismaleimide resin composites T2-T10 were obtained.

[0175] Application Example 11

[0176] Following the method of Application Example 1, except that in step S1, the amount of deionized water added is such that the mass fraction of modified bismaleimide resin in the sizing agent is 1%, the temperature is set at 38°C, and the TZ800H carbon fiber tow is passed through the sizing agent tank at a traction speed of 9 m / min, with a drying temperature of 115°C. This yields carbon fiber reinforced bismaleimide resin composite material T11.

[0177] Application Example 12

[0178] S1, same as application example 1;

[0179] S2. Preheat the bismaleimide resin at 70°C for 30 minutes, set the cold roller temperature to 20°C, and set the coating speed to 10 m / min. Coat the resin onto the release paper to form a bismaleimide resin film with a thickness of 0.2 mm.

[0180] S3. Set the feeding speed of the bismaleimide resin film and the sized carbon fiber to 6m / min, the rolling pressure of the hot roller and the cold roller to be the same, both to 2MPa, and control the tension of the sized carbon fiber at 30N to obtain carbon fiber prepreg.

[0181] S4, molding conditions are the same as in application example 1.

[0182] T12, a carbon fiber reinforced bismaleimide resin composite material, was obtained.

[0183] Application Example 13

[0184] S1, same as application example 1;

[0185] S2. The sized carbon fiber is woven into a plain weave carbon fiber woven fabric. During weaving, the tension of a single bundle of warp yarns is controlled at 5N, and the radial unwinding method is used to achieve uniform warp feeding; the tension of the weft yarns is controlled at 6.5N. The warp yarn density of the woven fabric is 5.2 yarns / cm, the weft yarn density is 5.2 yarns / cm, and the unit area mass is 220g / m2.

[0186] The other steps are the same as in Example 1.

[0187] T13, a carbon fiber reinforced bismaleimide resin composite material, was obtained.

[0188] Compare and contrast examples 1-4

[0189] Following the method of Application Example 1, except that the modified bismaleimide resin sizing agent prepared in Example 1 was replaced with the sizing agent prepared in Comparative Examples 1-4. Carbon fiber reinforced bismaleimide resin composites DT1-DT4 were obtained.

[0190] Comparative Application Example 5

[0191] An emulsion-type epoxy resin sizing agent (domestic No. 10 sizing agent) was used to sizing the carbon fibers according to the same method as in Example 1. This yielded carbon fiber reinforced bismaleimide resin composite material DT5.

[0192] Comparative Application Example 6

[0193] Commercially available T800H grade carbon fiber was used, and the sizing agent was an epoxy resin sizing agent (brand name 40B). This yielded DT6, a carbon fiber reinforced bismaleimide resin composite material.

[0194] Comparative Application Example 7

[0195] S1, same as application example 1;

[0196] S2. Preheat the bismaleimide resin at 60℃ for 30 minutes, set the cold roller temperature to 10℃, set the coating speed to 8m / min, and coat it onto the release paper to form a bismaleimide resin film with uneven thickness.

[0197] S3. Set the feeding speed of the bismaleimide resin film and the sized carbon fiber to 7m / min, the rolling pressure of the hot roller and the cold roller to be the same, both to 6MPa, and control the tension of the sized carbon fiber at 50N to obtain carbon fiber prepreg.

[0198] S4, molding conditions are the same as in application example 1.

[0199] DT7, a carbon fiber reinforced bismaleimide resin composite material, was obtained.

[0200] The carbon fiber reinforced bismaleimide resin composites T1-T13 and DT1-DT7 prepared above were cut into 20mm×10mm sample strips, and the interlaminar shear strength was tested according to ASTM D2344 standard.

[0201] The carbon fiber reinforced bismaleimide resin composites T1-T13 and DT1-DT7 prepared above were cut into 50mm×10mm specimen strips, and the bending strength was tested according to ASTM D790 standard.

[0202] Table 3

[0203] Composite materials Interlaminar shear strength / MPa Bending strength / MPa T1 106 1701 T2 104 1693 T3 108 1751 T4 106 1743 T5 103 1689 T6 105 1721 T7 103 1693 T8 101 1680 T9 99 1679 T10 105 1719 T11 98 1688 T12 75 1510 T13 82 813 DT1 86 1453 DT2 82 1439 DT3 80 1451 DT4 67 1369 DT5 73 1410 DT6 63 1475 DT7 58 1382

[0204] The results above show that the carbon fiber using the modified bismaleimide sizing agent of this invention has a higher tensile strength than carbon fibers treated with other types of sizing agents because the bismaleimide sizing agent has good film-forming properties on the carbon fiber surface, which can effectively protect the carbon fiber and prevent it from producing fuzz or broken fibers. Furthermore, the modified bismaleimide sizing agent has better compatibility with the bismaleimide resin matrix used in the preparation of composite materials, thus resulting in higher interlaminar shear strength and flexural strength.

[0205] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a carbon fiber reinforced bismaleimide resin composite material, characterized in that, Includes the following steps: S1. The carbon fiber bundle is sized using a modified bismaleimide resin sizing agent to obtain sized carbon fiber. S2. After preheating the bismaleimide resin, coat it on the release paper to obtain a bismaleimide resin film. S3. The bismaleimide resin film is bonded to both sides of the sized carbon fiber, and then passed through hot rollers and cold rollers respectively to obtain bismaleimide resin prepreg. S4. The prepreg from step S3 is laid up layer by layer and then molded to obtain carbon fiber reinforced bismaleimide resin composite material.

2. The preparation method according to claim 1, characterized in that, The method also includes weaving sized carbon fibers to obtain carbon fiber fabric.

3. The preparation method according to claim 1, characterized in that, In step S1, the sizing conditions include: at 30-50°C, passing the carbon fiber bundle through the sizing agent at a traction speed of 5-12 m / min for 30-100 s. And / or, in step S2, the preheating conditions include: a temperature of 70-90°C and a time of 30-50 minutes; And / or, the coating speed is 10-15 m / min; And / or, the thickness of the adhesive film is 0.05-0.3 mm.

4. The preparation method according to claim 2, characterized in that, In step S3, the bonding conditions include setting the yarn feed speed of both the bismaleimide resin film and the sized carbon fiber or carbon fiber fabric to 4-6 m / min. And / or, the temperature of the hot roller is 70-90°C, and the roller pressure is 2-5 MPa; And / or, the temperature of the cold roller is 10-20℃, and the roller pressure is 2-5MPa; And / or, the tension of the sized carbon fiber or carbon fiber fabric is 30-50N.

5. The preparation method according to claim 1, characterized in that, In step S4, the number of layers is 15-30; And / or, the molding is performed by curing in an autoclave; And / or, the molding conditions include: vacuum degree ≥ -0.095MPa, molding temperature 170-200℃, and holding time 3-8h.

6. The preparation method according to any one of claims 1-5, characterized in that, The modified bismaleimide resin sizing agent comprises: 20-40 parts by weight of modified bismaleimide resin, 3-6 parts by weight of emulsifier and 60-80 parts by weight of deionized water.

7. The preparation method according to claim 1, characterized in that, The modified bismaleimide resin has the structure shown in Formula A; Wherein, R1 is selected from H or an alkyl group having 1-4 carbon atoms, and R2 is... One of them; n is the average degree of polymerization, n > 0.

8. The preparation method according to claim 1, characterized in that, The preparation method of the modified bismaleimide resin includes: (1) Dissolve the organic solvent and bismaleimide resin monomer by stirring at 60-110℃ to obtain a bismaleimide resin solution with a mass concentration of 15-35%. (2) The initiator is slowly added dropwise to the bismaleimide resin solution to obtain a mixed solution, wherein the amount of initiator is 0.5-2% of the mass of the bismaleimide resin monomer; (3) Add the modifier dropwise to the mixed solution obtained in step 2 and carry out free radical polymerization reaction for 3-6 hours at a reaction temperature of 60-110℃. After the reaction is completed, cool and filter to remove the solvent and obtain modified bismaleimide resin.

9. The preparation method according to claim 1, characterized in that, The emulsifier is a mixture of nonionic and anionic emulsifiers; And / or, the mass ratio of the nonionic emulsifier to the anionic emulsifier is 1:0.5-1.

10. The carbon fiber reinforced bismaleimide resin composite material prepared by the preparation method according to any one of claims 1-9.

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