Prepreg preparation method for continuous production and prepreg

Abstract

The invention belongs to the technical field of prepreg preparation, and discloses a prepreg preparation method for continuous production and a prepreg, the preparation method comprises the following steps: sequentially carrying out low-viscosity resin solution ultrasonic impregnation, first drying, high-viscosity resin solution impregnation, second drying and hot pressing treatment on continuous fibers, the continuous fibers advance in the length direction of the continuous fibers, and the advancing direction is perpendicular to the horizontal direction. By adopting a two-step liquid phase impregnation process of ultrasonic impregnation of a low-viscosity resin solution and re-impregnation of a high-viscosity resin solution, a uniform resin thin layer is firstly formed on the surface of the fiber in the first step, and the resin content is additionally supplemented in the subsequent second step, so that the preparation efficiency is improved; therefore, the problem that the prepreg with high surface density and / or high resin mass fraction and / or low porosity and / or low solvent residue is difficult to prepare is solved. And a functional filler can be additionally added into the high-viscosity resin, so that the functional problem is solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of prepreg preparation, and in particular relates to a prepreg preparation method and prepreg for continuous production. Background Art

[0002] Continuous fiber reinforced thermoplastic composites have gradually become a research hotspot in the fields of aerospace, automotive, electronics, etc. in recent years due to their excellent mechanical properties, lightweight and recyclability. However, during the material preparation process, the impregnation process of fibers and resins directly affects the performance of the final product. Currently, prepreg (a prepreg is a composite made by impregnating continuous fibers and their fabrics with resin under strictly controlled conditions, which is a structural unit with certain mechanical properties and also an intermediate product of continuous fiber reinforced thermoplastic composites) preparation technologies mainly include hot melt method, slurry method and solution method. Among them, the hot melt method directly impregnates fibers with molten resin, avoiding the problem of solvent residue. However, the high viscosity of the resin melt makes it difficult for it to fully penetrate into the interior of the fiber bundle, and the prepreg is prone to porosity or dry yarn phenomenon. The slurry method suspends resin particles in a liquid medium, and after impregnating the fibers, it is then formed by high-temperature melting. It has the advantage of uniform impregnation. However, the dispersion medium used in the slurry method has a low viscosity, and functional fillers are extremely easy to settle, making it difficult to prepare functionalized prepregs with stable performance. The solution method dissolves the resin in a solvent to form a sizing solution to impregnate the fibers. The equipment is simple and can effectively improve the wettability of the fibers, and it is suitable for preparing prepregs with a low areal density. When preparing high-areal density thick prepregs, due to the tight stacking between fiber layers, it is difficult for the resin to fully penetrate, resulting in low production efficiency and easy occurrence of unimpregnated areas. In addition, the warp and weft of the fabric overlap, and it is difficult to unfold the fabric, which limits the resin solution penetration effect and also makes it difficult for the solvent to completely volatilize, affecting the material performance stability.

[0003] Therefore, in the prior art, the hot melt method is limited by the high viscosity of the molten resin, resulting in the resin being difficult to deeply penetrate into the interior of the fiber bundle for impregnation, and it is impossible to effectively prepare prepregs with a high areal density and a high resin mass fraction, and the prepreg is prone to porosity; the dispersion medium used in the slurry method has a low viscosity, and functional fillers are extremely easy to settle, making it difficult to prepare functionalized prepregs with stable performance. When the solution method is used to prepare high-areal density prepregs, there are problems such as insufficient resin penetration, long production cycle and difficult complete removal of the solvent. Therefore, the prior art has significant deficiencies in terms of resin impregnation efficiency and solvent residue control, and there is an urgent need to develop a new prepreg preparation technology with high areal density, high resin mass fraction, high manufacturing efficiency, low porosity and low solvent residue. Summary of the Invention

[0004] To solve the deficiencies and drawbacks of the prior art, the present invention provides a method for preparing prepreg for continuous production and the prepreg. By adopting a two-step liquid-phase impregnation process of "ultrasonic impregnation with low-viscosity resin solution + re-impregnation with high-viscosity resin solution", a uniform resin thin layer is first formed on the fiber surface in the first step, and then in the subsequent second step, the high-viscosity resin additionally supplements the resin content and improves the preparation efficiency, thereby solving the problem that it is difficult to prepare prepregs with high areal density and / or high resin mass fraction and / or low porosity and / or low solvent residue. And further, functional fillers can be carried by the high-viscosity resin for impregnation, thereby effectively solving the problem of easy sedimentation and slip of the functional fillers.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] In the first aspect, a method for preparing prepreg for continuous production includes: successively subjecting continuous fibers to ultrasonic impregnation with low-viscosity resin solution, first drying, impregnation with high-viscosity resin solution, second drying and hot pressing to obtain prepreg; wherein,

[0007] The viscosity of the low-viscosity resin solution used in the ultrasonic impregnation process of the low-viscosity resin solution is lower than the viscosity of the high-viscosity resin solution used in the impregnation process of the high-viscosity resin solution;

[0008] During the first drying and the second drying, the continuous fibers all travel along their length direction, and the traveling directions are both perpendicular to the horizontal direction.

[0009] Further, the viscosity of the low-viscosity resin solution is 30 - 3000 mPa·s;

[0010] and / or, the temperature of the ultrasonic impregnation of the low-viscosity resin solution is 20 - 80 °C;

[0011] and / or, the ultrasonic frequency of the ultrasonic impregnation of the low-viscosity resin solution is 20 - 100 kHz;

[0012] and / or, the ultrasonic energy density of the ultrasonic impregnation of the low-viscosity resin solution is 0.3 - 3.0 W / cm 2 .

[0013] Further, the viscosity of the high-viscosity resin solution is 3000 - 8000 mPa·s;

[0014] and / or, the temperature of the impregnation with the high-viscosity resin solution is 30 - 80 °C.

[0015] Further, a functional filler is added to the high-viscosity resin solution, and the mass ratio of the functional filler to the high-viscosity resin in the high-viscosity resin solution is 0.01 to 0.3:1.0; further, the functional filler includes at least one of a conductive filler, a heat-conductive filler, or a wave-absorbing filler; furthermore, the conductive filler includes a metal-based conductive filler, a carbon-based conductive filler, a metal-oxide conductive filler, a conductive polymer filler, or a combination thereof; the heat-conductive filler includes a metal-based heat-conductive filler, a carbon-based heat-conductive filler, a ceramic-based heat-conductive filler, a polymer-based heat-conductive filler, or a combination thereof; the wave-absorbing filler includes a ferrite, a metal magnetic powder, a carbon-based material, a conductive polymer, or a combination thereof.

[0016] Further, the impregnation with the high-viscosity resin solution and the second drying are performed one or more times; further, when the impregnation with the high-viscosity resin solution and the second drying are performed multiple times, the viscosity of the high-viscosity resin solution for the subsequent impregnation is the same as that of the previous one, or increases by 1500 to 4000 mPa·s compared with the previous one.

[0017] Further, the temperature of the first drying is 80 to 160 °C;

[0018] and / or, the temperature of the second drying is 80 to 240 °C.

[0019] Further, the temperature of the hot pressing treatment is 200 to 400 °C;

[0020] and / or, the pressure of the hot pressing treatment is 0.5 to 10 MPa.

[0021] Further, the resin content of the prepreg is 20 to 45%;

[0022] and / or, in the prepreg, the mass ratio of the low-viscosity resin to the high-viscosity resin is 0.05 to 0.55:1.

[0023] Further, the resin solution satisfies at least one of the following conditions:

[0024] (1) The resin in the resin solution includes one or more of the following:

[0025] A polyarylether containing a phthalazinone biphenyl structure, a polycarbonate, a polysulfone, a polyether sulfone, a polyarylate, a thermoplastic polyimide, a polyamideimide, a polyphenylene ether, a polyetherimide; wherein,

[0026] The polyarylether resin containing a phthalazinone biphenyl structure has the following structural formula:

[0027]

[0028] Among them, m is a positive integer, and n is 0 or a positive integer; Ar1 is a dihalogen monomer structural unit, including one or more than two of the following structural connection combinations:

[0029]

[0030] Ar2 is a bisphenol or bisphenol-like structural unit, including one or more than two of the following structural connection combinations:

[0031]

[0032] Among them, the structure of Y1 is as follows:

[0033]

[0034] The structure of Y2 is as follows:

[0035]

[0036] R1, R2, R3, and R4 are hydrogen, halogen substituents, phenyl, phenoxy, straight-chain alkyls containing at least 1 carbon atom, branched-chain alkyls containing at least 1 carbon atom, or branched-chain alkoxys containing at least 1 carbon atom, and the structures of R1, R2, R3, and R4 are the same or different;

[0037] (2) The solvent used in the resin solution includes one or more of the following:

[0038] N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, chloroform;

[0039] And / or, the continuous fiber includes unidirectional continuous fiber bundles or fiber fabrics;

[0040] And / or, the continuous fiber includes at least one of the following categories:

[0041] (1) Inorganic fibers: carbon fibers, glass fibers, quartz fibers, basalt fibers, silicon carbide fibers, alumina fibers, boron fibers;

[0042] (2) Organic high-performance fibers: aramid fibers, ultra-high molecular weight polyethylene fibers, polybenzoxazole fibers, polyimide fibers, polyether ether ketone fibers, poly(p-phenylene benzobisoxazole) fibers;

[0043] (3) Metal fibers: stainless steel fibers, titanium fibers, copper fibers, aluminum fibers;

[0044] (4) Natural fibers: flax fibers, sisal fibers, ramie fibers;

[0045] (5) Composite fibers: metal-coated fibers, multi-component hybrid fiber bundles.

[0046] In a second aspect, a prepreg is obtained by the preparation method described in the first aspect.

[0047] Compared with the prior art, the present invention has at least the following beneficial effects:

[0048] (1) In the preparation method of the present invention, a two-step liquid-phase impregnation process of "ultrasonic impregnation with a low-viscosity resin solution + re-impregnation with a high-viscosity resin solution" is adopted. By reintroducing the high-viscosity resin solution in the second step, it can additionally supplement the resin content, improve the preparation efficiency, and at the same time avoid the problem that it is difficult for the high-viscosity resin to fully penetrate into the fiber bundle after directly contacting the fiber. It is particularly worth emphasizing that in the present invention, a uniform resin thin layer is formed on the fiber surface in the low-viscosity prepreg stage of the first step, which not only improves the initial wetting effect but also creates conditions for the subsequent high-viscosity resin to carry functional fillers to penetrate the fiber, thus further effectively solving the problem of easy sedimentation and slippage of functional fillers during use while solving the problem of preparing prepregs with high areal density and high resin mass fraction.

[0049] Compared with the existing solution method prepreg process, in the case of omitting the yarn spreading process in the present invention, there is no dry yarn phenomenon formed inside the fiber bundle due to insufficient resin fluidity. Moreover, it breaks the tradition of impregnation with a single-viscosity resin solution. Through the two-step impregnation of high and low viscosities by the pure solution method, prepregs with high areal density, high resin content, and low solvent residue are prepared, which not only avoids the problem that it is difficult to impregnate due to high resin viscosity in the hot melt method and / or solution method but also avoids the problems of low resin content and / or uneven distribution of prepregs.

[0050] Specifically, the present invention takes advantage of the fact that a low-viscosity resin solution can easily penetrate into the fiber bundle, enabling a small amount of resin to quickly fill the gaps between individual fiber filaments along with the solution. Combining with ultrasonic vibration, the cavitation effect is utilized to break the gas adsorption layer on the fiber surface, enhancing the wetting speed of the resin on the fiber. Therefore, after impregnation and drying with the low-viscosity resin solution, the surface of each fiber filament is evenly coated with resin, increasing the surface tension and expelling the gas between the overlapping fiber filaments. When impregnating with a high-viscosity resin solution later, it is very easy to fully wet the fiber bundle, significantly increasing the resin mass fraction of the prepreg and greatly reducing the porosity inside the prepreg. Therefore, by using the first impregnation with the low-viscosity sizing solution + ultrasonic to fully wet the fiber, a foundation can be laid for the penetration of the second high-viscosity sizing solution, and sufficient wetting of the yarn bundles inside the thick prepreg can be ensured without an additional melt extrusion process. This not only reduces equipment investment, simplifies the process route, but also avoids the problem of fiber overheating that may occur during the melt extrusion process. It is worth mentioning that the method of the present invention is applicable to the production of prepregs with a higher areal density (such as fabrics), and can also achieve uniform impregnation for materials with a large content of fiber bundles and a wide width, obtaining prepregs with a high areal density, a high resin mass fraction, and a uniform resin distribution. At the same time, a higher areal density can significantly improve the manufacturing efficiency of the prepreg, and increasing the resin mass fraction and its distribution uniformity can enhance the mechanical properties of the composite material.

[0051] In addition, the low-viscosity resin solution of the present invention has a high surface energy, which plays a role in secondary sizing of the fiber, changes the surface state of the fiber, and improves the wetting effect of the fiber in the high-viscosity resin solution. At the same time, the low-viscosity resin solution can effectively elute part of the original fiber sizing agent and attach a uniform high-surface-energy resin layer on the fiber surface, enabling the subsequent high-viscosity resin solution to fully impregnate the fiber bundle, significantly enhancing the resin content and the uniformity of the resin distribution of the prepreg. The first impregnation with the low-viscosity resin solution of the present invention avoids the situation in the existing solution method for prepreg process that due to the lack of special modification of the fiber surface, the high-viscosity resin solution has insufficient wettability on the fiber, making it difficult to improve the resin content and uniformity of the prepreg.

[0052] The present invention can prepare a prepreg with a high resin content and high quality by continuously pulling the continuous fiber through two resin impregnation tanks and a drying device in sequence. It has a high production efficiency and can adapt to continuous production with winding and reeling; it avoids the long-cycle and low-efficiency non-pipeline continuous production of separately applying glue, static leveling, and flipping treatment to each piece of fabric; it also avoids the situation where when impregnating once after mixing high- and low-viscosity resins, the improvement of penetrability is limited and the resin content is limited.

[0053] (2) In the preparation method of the present invention, functionalization can also be achieved by directly adding fillers, and it is avoided that the granular functionalized fillers have relatively sharp edges, which may cause fiber damage. The present invention uses a low-viscosity resin solution to impregnate the fiber bundle, so as to form a uniform and continuous resin protection layer on the surface of the fiber filaments. Then, it is impregnated with a high-viscosity resin solution containing functionalized fillers. The high-viscosity resin solution can suspend the filler particles and inhibit their sedimentation, thereby endowing excellent functionalization characteristics without weakening the mechanical properties of the prepreg.

[0054] (3) In the preparation method of the present invention, by controlling the viscosity parameter, it is beneficial to monitor and adjust in a timely manner by using an on-line viscosity detection means, so as to accurately control the resin content and the stability and controllability of its impregnation process, and effectively ensure the high stability of the prepreg quality and the process reliability. It avoids that in the existing solution method prepreg process, the resin content control is mainly achieved by adjusting the concentration of the resin solution. In the actual impregnation process, the heating condition will cause the solvent to volatilize and the resin solution concentration to rise, making it difficult to control the resin mass fraction of the prepreg.

[0055] (4) In the preparation method of the present invention, by adopting a vertical drying process, the influence of the gravity on the uneven resin distribution on the upper and lower sides of the prepreg is eliminated, effectively improving the consistency and stability of the prepreg product quality. It avoids the horizontal drying process usually adopted in the existing solution method prepreg production, which causes the uneven resin distribution on the upper and lower surfaces of the prepreg due to the influence of gravity during the drying process of the prepreg.

[0056] (5) For the prepreg of the present invention, the resin mass fraction can reach 42.6%, and the areal density can reach 352 g / m 2 , while the volatile content (mainly residual solvent) is not higher than 0.15%, and the porosity does not exceed 0.2%. Detailed Embodiments

[0057] To make the purpose, technical solution and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of protection of the present invention. The process parameters without specific conditions noted in the following embodiments are usually in accordance with conventional conditions.

[0058] In the ranges disclosed in the present invention, the endpoints and any values of the ranges are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed in the present invention.

[0059] According to the first aspect of the present invention, there is provided a method for preparing a prepreg for continuous production, comprising: sequentially subjecting continuous fibers to ultrasonic impregnation with a low-viscosity resin solution, first drying, impregnation with a high-viscosity resin solution, second drying, and hot pressing to obtain a prepreg; wherein,

[0060] The viscosity of the low-viscosity resin solution used in the ultrasonic impregnation process of the low-viscosity resin solution is lower than the viscosity of the high-viscosity resin solution used in the impregnation process of the high-viscosity resin solution;

[0061] During the first drying and the second drying processes, the continuous fibers all travel along their length directions, and the traveling directions are both perpendicular to the horizontal direction.

[0062] The present invention adopts a two-step liquid-phase impregnation process of "ultrasonic impregnation with a low-viscosity resin solution + re-impregnation with a high-viscosity resin solution". By re-introducing the high-viscosity resin solution in the second step, it can additionally supplement the resin content, improve the preparation efficiency, and at the same time avoid the problem that it is difficult for the high-viscosity resin to fully penetrate into the fiber bundle after directly contacting the fiber. It is particularly worth emphasizing that through the low-viscosity prepreg stage in the first step, a uniform resin thin layer is formed on the fiber surface, which not only improves the initial wetting effect but also creates conditions for the subsequent high-viscosity resin to carry functional fillers to penetrate the fiber, thus further effectively solving the problem of easy sedimentation and slip of functional fillers during the use process while solving the problem of preparing prepregs with high areal density and high resin mass fraction.

[0063] Compared with the existing solution method prepreg process, in the case of omitting the yarn spreading process, there is no dry yarn phenomenon formed inside the fiber bundle due to insufficient resin fluidity. Moreover, it breaks the tradition of impregnation with a single-viscosity resin solution. Through the two-step impregnation of high and low viscosities by the pure solution method, prepregs with high areal density, high resin content, and low solvent residue are prepared, which not only avoids the problem that it is difficult to wet due to high resin viscosity in the hot melt method and / or solution method, but also avoids the problems of low resin content and / or uneven distribution of the prepreg.

[0064] Specifically, the present invention takes advantage of the fact that a low-viscosity resin solution can easily penetrate into the fiber bundle, enabling a small amount of resin to quickly fill the gaps between individual fiber filaments along with the solution. Combining with ultrasonic vibration, the cavitation effect is utilized to break the gas adsorption layer on the fiber surface, enhancing the impregnation rate of the resin onto the fiber. Therefore, after impregnation and drying with the low-viscosity resin solution, the surface of the individual fiber filaments is evenly coated with resin, increasing the surface tension and expelling the gas between the overlapping individual fiber filaments. When impregnating with a high-viscosity resin solution subsequently, it is very easy to fully impregnate the fiber bundle, significantly increasing the resin mass fraction of the prepreg and greatly reducing the porosity inside the prepreg. Thus, by using the first impregnation with the low-viscosity adhesive solution + ultrasonic treatment to fully wet the fiber, a foundation can be laid for the penetration of the second high-viscosity adhesive solution, ensuring the full impregnation of the yarn bundles inside the thick prepreg without the need for an additional melt extrusion process. This not only reduces equipment investment, simplifies the process route, but also avoids the problem of fiber overheating that may occur during the melt extrusion process. It is worth mentioning that the method of the present invention is applicable to the production of prepregs with a higher areal density (such as fabrics), and can also achieve uniform impregnation for materials with a large content of fiber bundles and a wide width, obtaining prepregs with a high areal density, a high resin mass fraction, and a uniform resin distribution. In addition, a higher areal density can significantly improve the manufacturing efficiency of the prepreg, and increasing the resin mass fraction and the uniformity of distribution can enhance the mechanical properties of the composite material.

[0065] The present invention can prepare a prepreg with a high resin content and high quality by continuously drawing the continuous fiber through two resin impregnation tanks and a drying device in sequence, with high production efficiency and being adaptable to continuous production of winding and rewinding; it avoids the long-cycle and low-efficiency non-pipeline continuous production of individually applying glue, static leveling, and flipping treatment to each piece of fabric; it also avoids the situation where a single impregnation with a mixture of high- and low-viscosity resins has limited improvement in impregnation and limited resin content.

[0066] As an optional implementation manner of the prepreg preparation method of the present invention, the viscosity of the low-viscosity resin solution is 30 - 3000 mPa·s;

[0067] and / or, the temperature of ultrasonic impregnation of the low-viscosity resin solution is 20 - 80 °C;

[0068] and / or, the ultrasonic frequency of ultrasonic impregnation of the low-viscosity resin solution is 20 - 100 kHz;

[0069] and / or, the ultrasonic energy density of ultrasonic impregnation of the low-viscosity resin solution is 0.3 - 3.0 W / cm 2 .

[0070] In the above technical solution, the present invention controls the viscosity of the low-viscosity resin solution to be 30 to 3000 mPa·s, and typically but not limitedly, it can be selected as 50 mPa·s, 100 mPa·s, 500 mPa·s, 1000 mPa·s, 1300 mPa·s, 1500 mPa·s, 1700 mPa·s, 2000 mPa·s, 2300 mPa·s, 2500 mPa·s, 2700 mPa·s, 2900 mPa·s, etc.; this can not only avoid too low content of the resin in the solvent, resulting in too thin adhesive solution, making it difficult to deposit enough resin on the fibers and reducing the impregnation efficiency, but also avoid difficulties in wetting the fiber bundle and losing the penetration advantage that the "low-viscosity" impregnation should have.

[0071] The present invention controls the temperature of ultrasonic impregnation of the low-viscosity resin solution to be 20 to 80 °C, and typically but not limitedly, it can be selected as 30 °C, 40 °C, 50 °C, 60 °C, 70 °C, etc.; this can not only avoid too low temperature, which increases the resin viscosity and affects the impregnation effect and efficiency, but also avoid too high temperature, which causes the solvent to volatilize too fast and is likely to cause premature volatilization of the solvent before the fibers are fully wetted.

[0072] The present invention controls the ultrasonic frequency of ultrasonic impregnation of the low-viscosity resin solution to be 20 to 100 kHz, and typically but not limitedly, it can be selected as 30 kHz, 40 kHz, 50 kHz, 60 kHz, 70 kHz, 80 kHz, 90 kHz, etc.; this can not only avoid too low ultrasonic frequency, where the cavitation effect is not obvious, but also avoid too high ultrasonic frequency, where the ultrasonic penetration ability is insufficient and it is difficult to achieve the equipment, making it difficult to effectively break the bubbles in the fiber bundle and the improvement of the impregnation effect is limited.

[0073] The present invention controls the ultrasonic energy density of ultrasonic impregnation of the low-viscosity resin solution to be 0.3 to 3 W / cm 2 , and typically but not limitedly, it can be selected as 0.4 W / cm 2 , 0.6 W / cm 2 , 0.8 W / cm 2 , 1 W / cm 2 , 1.2 W / cm 2 , 1.4 W / cm 2 , 1.6 W / cm 2 , 1.8 W / cm 2 , 2 W / cm 2 , 2.2 W / cm 2 , 2.4 W / cm 2 , 2.6 W / cm 2 , 2.8 W / cm 2etc.; it can not only avoid too low ultrasonic power, which is difficult to form sufficient cavitation effect and cannot significantly improve impregnation, but also avoid too high ultrasonic energy, which may cause local overheating of the resin or damage to the fibers, and is instead not conducive to the stability of the impregnation quality.

[0074] As an optional implementation mode of the prepreg preparation method of the present invention, the viscosity of the high-viscosity resin solution is 3000-8000 mPa·s;

[0075] and / or, the temperature of impregnation with the high-viscosity resin solution is 30-80°C.

[0076] In the above technical solution, the present invention controls the viscosity of the high-viscosity resin solution to be 3000-8000 mPa·s, typically but not limitedly optionally 3050 mPa·s, 3500 mPa·s, 4000 mPa·s, 4500 mPa·s, 5000 mPa·s, 5500 mPa·s, 6000 mPa·s, 6500 mPa·s, 7000 mPa·s, 7500 mPa·s, etc.; it can not only avoid the small difference in viscosity between the high-viscosity impregnating adhesive and the low-viscosity impregnation, which is difficult to significantly increase the total resin content of the prepreg and the insufficient suspension effect on the functional filler, but also avoid the extremely viscous adhesive, which makes it difficult for the fiber bundle to be impregnated and may instead coat the surface of the fiber while there is still dry yarn inside, and increases the operation difficulty such as pumping.

[0077] The present invention controls the temperature of ultrasonic impregnation with the high-viscosity resin solution to be 30-80°C, typically but not limitedly optionally 35°C, 40°C, 50°C, 60°C, 70°C, etc.; it can not only avoid too low temperature, poor fluidity of the high-viscosity resin solution, and a significant reduction in the impregnation rate, but also avoid too high temperature, where the solvent volatilizes too quickly, causing the resin adhesive that has not yet penetrated into the fiber gaps to concentrate prematurely, also resulting in uneven impregnation. In addition, generally, a large amount of organic solvents volatilize above 80°C, increasing the safety and environmental protection pressure, so the upper temperature limit is set at 80°C.

[0078] As an optional implementation mode of the prepreg preparation method of the present invention, functional fillers are added to the high-viscosity resin solution, and the mass ratio of the functional fillers to the high-viscosity resin in the high-viscosity resin solution is 0.01-0.3:1.0.

[0079] The high-viscosity resin solution of the present invention can be additionally added with functional fillers as needed. The mass ratio of the filler to the resin is 0.01-0.3:1.0. It should be noted that the viscosity of the aforementioned high-viscosity resin solution is the viscosity of the resin-solvent mixture system before adding the filler. When the high-viscosity resin solution is added with functional fillers, the mass ratio of the functional filler to the high-viscosity resin in the high-viscosity resin solution is controlled to be 0.01-0.3:1.0, typically but not limited to 0.01:1, 0.05:1, 0.1:1, 0.15:1, 0.2:1, 0.25:1, 0.27:1, etc.; it can not only avoid the situation where the proportion of the functional filler is too low and the functional modification effect is not obvious, but also avoid the situation where the proportion of the functional filler is too high, resulting in a sharp increase in the viscosity of the new mixture system after the composition of the adhesive liquid changes, making impregnation difficult, and the fillers are prone to agglomeration, resulting in the deterioration of the mechanical properties of the prepreg. Through experiments, the addition amount of the filler is preferably 1%-30% of the mass of the high-viscosity resin. Within this range, the prepreg can obtain the desired functional characteristics and maintain good processability.

[0080] In the present invention, there is no special limitation on the functional filler. Existing functional filler materials can be selected according to functional requirements, such as conductive fillers, heat-conductive fillers or wave-absorbing fillers, etc. For another example, metal-based conductive fillers (silver powder, copper powder, nickel powder), carbon-based conductive fillers (carbon black, carbon fiber, graphene, carbon nanotube), metal oxide conductive fillers (indium tin oxide, zinc oxide, graphene oxide), conductive polymer fillers (polyaniline, polypyrrole, polythiophene, doped polyacetylene) or their combinations, etc. in the conductive fillers; metal-based heat-conductive fillers (silver, copper, aluminum), carbon-based heat-conductive fillers (graphene, carbon nanotube, graphite), ceramic-based heat-conductive fillers (aluminum nitride, aluminum oxide, boron nitride, silicon carbide), polymer-based heat-conductive fillers (heat-conductive silica gel) or their combinations, etc. in the heat-conductive fillers; ferrites (manganese-zinc ferrite, nickel-zinc ferrite, hexagonal ferrite), metal magnetic powders (carbonyl iron powder, iron-cobalt alloy), carbon-based materials (silicon carbide, carbon nanotube, graphene, carbon black), conductive polymers (polyaniline, polypyrrole) or their combinations, etc. in the wave-absorbing fillers.

[0081] In the present invention, the impregnation of the high-viscosity resin solution and the second drying can be carried out one or more times as needed; when impregnating and drying multiple times, the viscosity of the high-viscosity resin solution for the latter impregnation increases by 1500-4000 mPa·s compared with the previous time, or the same concentration can also be adopted.

[0082] As an optional implementation manner of the prepreg preparation method of the present invention, the temperature of the first drying is 80-160 °C (such as 90 °C, 100 °C, 110 °C, 120 °C, 130 °C, 140 °C, 150 °C, etc.);

[0083] And / or, the temperature of the second drying is 80 to 240 °C (such as 90 °C, 110 °C, 130 °C, 150 °C, 170 °C, 190 °C, 210 °C, 240 °C, etc.).

[0084] In the above technical solution, if the drying temperature is too low, it is not sufficient to completely remove the solvent on the fibers (especially inside thick fiber bundles or fabrics, and low temperature is likely to leave residual solvent); however, too high a temperature will also bring adverse effects. When exceeding the above upper limit, the resin in the low-viscosity stage may undergo excessive thermal melting or decomposition, and the resin and / or functional fillers in the high-viscosity stage may also deteriorate. In addition, the mechanical properties of the fibers (such as organic fibers) may be damaged at too high a temperature. Through experiments, it is determined that the two-stage drying temperatures should not exceed the above ranges respectively, in order to balance the full removal of the solvent and avoid the decline of material properties.

[0085] As an alternative embodiment of the prepreg preparation method of the present invention, the temperature of the hot pressing treatment is 200 to 400 °C (such as 210 °C, 230 °C, 250 °C, 270 °C, 290 °C, 310 °C, 340 °C, 360 °C, 380 °C, etc.);

[0086] And / or, the pressure of the hot pressing treatment is 0.5 to 10 MPa (such as 1 MPa, 2 MPa, 3 MPa, 4 MPa, 5 MPa, 6 MPa, 7 MPa, 8 MPa, 9 MPa, etc.).

[0087] In the above technical solution, when the hot pressing temperature is lower than 200 °C, the melt flow of most high-performance thermoplastic resins (such as heteroarylene biphenyl polyethersulfone ketone, thermoplastic polyimide, etc.) is not sufficient, and it is impossible to wet and fuse the prepreg layer interface well; when the temperature is higher than 400 °C, it may cause the resin and fibers to decompose or their properties to decay. The present invention selects a hot pressing temperature above 200 °C and below 400 °C to ensure that the resin is completely melted and flowed without thermal damage to the material. When the hot pressing pressure is lower than 0.5 MPa, the compaction during the prepreg lamination process is insufficient, and microvoids are likely to remain; when the pressure is higher than 10 MPa, it may break the fibers or extrude too much resin, instead reducing the mechanical properties of the composite material, and the energy consumption cost of ultra-high pressure equipment is too large and uneconomical. Therefore, the preferred pressure range is 0.5 to 10 MPa.

[0088] As an alternative embodiment of the prepreg preparation method of the present invention, the resin content of the prepreg is 20 to 45%; and / or, in the prepreg, the mass ratio of the low-viscosity resin to the high-viscosity resin is 0.05 to 0.55:1.

[0089] The final prepreg with a resin content of 20-45% can be obtained by using the preparation method of the present invention. In the obtained final prepreg, if the resin content is lower than 20%, the fibers will not be sufficiently infiltrated, dry spots may appear in the product, and the interlayer bonding force will decrease; while if the resin content is higher than 45%, the excessive resin in the prepreg will not only increase the material density and reduce the mechanical properties of the composite material (the fiber volume fraction is too low), but also may generate resin enrichment areas and excessive flow waste during subsequent molding. The range of 20-45% not only covers the resin dosage required for general prepregs, but also can ensure excellent performance of the composite material products through experimental verification. Further, in the finally obtained prepreg, the mass ratio of the low-viscosity resin to the high-viscosity resin should be controlled to be 0.05-0.55:1. Typically but not limitedly, it can be selected as 0.06:1, 0.08:1, 0.1:1, 0.12:1, 0.14:1, 0.16:1, 0.18:1, 0.20:1, 0.22:1, 0.24:1, 0.26:1, 0.28:1, 0.30:1, 0.33:1, 0.35:1, 0.37:1, 0.4:1, 0.43:1, 0.45:1, 0.47:1, 0.49:1, etc.; this ratio represents the mass proportion of the two viscosity resins contained in the final prepreg. If it is lower than 0.05:1 (the low-viscosity resin is less than 5% of the high-viscosity resin), it means that the resin introduced in the first stage is extremely small and cannot play a role in improving the initial infiltration of the fibers, which is equivalent to an ineffective step; if it is higher than 0.55:1 (the low-viscosity resin exceeds 55% of the high-viscosity resin), the proportion of the low-viscosity resin is too large, which may instead lead to a smaller gain of the high-viscosity resin in the second stage and cannot significantly increase the final resin content. Moreover, too much low-viscosity resin may re-trigger problems such as too strong resin fluidity in the fiber bundle and filler sinking. Therefore, it is reasonable and necessary to control the amount of the low-viscosity resin in the high-viscosity resin within the range of 5%-55%.

[0090] As an optional implementation manner of the prepreg preparation method of the present invention, the preparation method includes the following steps:

[0091] (1) Impregnation and drying of the low-viscosity resin solution:

[0092] Immerse continuous fibers into a low-viscosity resin solution with a viscosity of 30-3000 mPa·s and an impregnation temperature of 20-80 °C, and then dry at 80-160 °C. During the drying process, the prepreg travels along the length direction of the continuous fibers, and the traveling direction is perpendicular to the horizontal direction; apply ultrasonic vibration of 20-100 kHz during the impregnation process, and the ultrasonic energy density is adjusted in the range of 0.3-3.0 W / cm 2 。

[0093] (2) Impregnation and drying of the high-viscosity resin solution:

[0094] The prepreg after being impregnated and dried with a low-viscosity resin solution is immersed in a high-viscosity resin solution with a viscosity of 3000 - 8000 mPa·s and an impregnation temperature of 30 - 80°C, and then dried at 80 - 240°C. During the drying process, the prepreg travels along the length direction of the continuous fiber, and the traveling direction is perpendicular to the horizontal direction. This step can be carried out once or repeated multiple times.

[0095] (3) Hot pressing treatment: The dried prepreg is treated by a hot pressing process with a temperature of 250 - 400°C and a pressure of 0.5 - 10 MPa to prepare a prepreg with a resin content of 20% - 45%, where the mass ratio of the low-viscosity resin to the high-viscosity resin is 0.05 - 0.55:1.

[0096] In the present invention, there are no particular limitations on the resin, solvent, and fiber, and existing materials can be selected according to functional requirements. Specifically, they can be as follows:

[0097] (a) The resin in the resin solution includes one or more of the following:

[0098] Polyarylether containing a phthalazinone biphenyl structure, polycarbonate, polysulfone ether, polysulfone, polyarylate, thermoplastic polyimide, polyamideimide, polyphenylene ether, polyetherimide. Among them,

[0099] The polyarylether resin containing a phthalazinone biphenyl structure has the following structural formula:

[0100]

[0101] Among them, Ar1 is a bis-halogen monomer structural unit, including one or more of the following connection combinations:

[0102]

[0103] Among them, Ar2 is a bisphenol or bisphenol-like structural unit, including one or more of the following connection combinations:

[0104]

[0105] Among them, the structure of Y1 is as follows:

[0106]

[0107] The structure of Y2 is as follows:

[0108]

[0109] Among them, R1, R2, R3, and R4 are hydrogen, halogen substituents, phenyl, phenoxy, straight-chain alkyl groups containing at least 1 carbon atom, branched alkyl groups containing at least 1 carbon atom, or branched alkoxy groups containing at least 1 carbon atom, and the structures of R1, R2, R3, and R4 are the same or different;

[0110] m is a positive integer;

[0111] n is 0 or a positive integer.

[0112] Specifically, for example, heterocyclic naphthalene biphenyl polyarylether resins with a number average molecular weight range of 1000 to 60000: heterocyclic naphthalene biphenyl polyether ketone, heterocyclic naphthalene biphenyl polyether sulfone, heterocyclic naphthalene biphenyl polyether nitrile, heterocyclic naphthalene biphenyl polyether ketone ketone, heterocyclic naphthalene biphenyl polyether sulfone ketone, heterocyclic naphthalene biphenyl polyether nitrile sulfone, heterocyclic naphthalene biphenyl polyether nitrile ketone ketone, heterocyclic naphthalene biphenyl polyether sulfone ketone ketone, heterocyclic naphthalene biphenyl polyether nitrile sulfone ketone, heterocyclic naphthalene biphenyl polyether nitrile sulfone ketone ketone, bisdiazanaphthone polyarylether sulfone, bisdiazanaphthone polyether nitrile, bisdiazanaphthone polyether ketone ketone, bisdiazanaphthone polyether sulfone ketone, bisdiazanaphthone polyether nitrile sulfone, bisdiazanaphthone polyether nitrile ketone ketone, bisdiazanaphthone polyether sulfone ketone ketone, bisdiazanaphthone polyether nitrile sulfone ketone, bisdiazanaphthone polyether nitrile sulfone ketone ketone;

[0113] Again, for example, amorphous high-performance thermoplastic resins with a number average molecular weight range of 1000 to 60000: polycarbonate, polyethersulfone, polysulfone, polyarylate, polyimide, polyamideimide, polyphenylene ether.

[0114] (b) The solvent used in the resin solution includes one or more of the following:

[0115] N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, chloroform.

[0116] (c) The continuous fiber includes a unidirectional continuous fiber bundle or a fiber fabric, and the continuous fiber types include at least one of the following categories:

[0117] (1) Inorganic fibers: carbon fiber, glass fiber, quartz fiber, basalt fiber, silicon carbide fiber, alumina fiber, boron fiber;

[0118] (2) High-performance organic fibers: aramid fiber, ultra-high molecular weight polyethylene fiber, polybenzoxazole fiber, polyimide fiber, polyetheretherketone fiber, poly(p-phenylene benzobisoxazole) fiber;

[0119] (3) Metal fibers: stainless steel fiber, titanium fiber, copper fiber, aluminum fiber;

[0120] (4) Natural fibers: flax fiber, sisal fiber, ramie fiber;

[0121] (5) Composite fibers: metal-coated fibers, multi-component hybrid fiber bundles.

[0122] According to the second aspect of the present invention, there is provided a prepreg prepared by the preparation method described in the first aspect, with a resin mass fraction up to 45%, a surface density up to 360 g / m 2 , a volatile content not higher than 0.15%, and a porosity not exceeding 0.2%.

[0123] The present invention will be further described in detail below with reference to specific examples and comparative examples.

[0124] Example 1

[0125] This example provides a prepreg preparation method for continuous production, and the specific steps are as follows:

[0126] (1) Impregnation and drying of low-viscosity resin solution:

[0127] Immerse the carbon fiber fabric into a solution of heterocyclic naphthalene polyether sulfone ketone with a viscosity of 3000 mPa·s and a number average molecular weight of 1000. The solvent is N-methylpyrrolidone, and the impregnation temperature is 80°C. During the impregnation process, ultrasonic vibration with a frequency of 100 kHz and an energy density of 3.0 W / cm2 is applied. Subsequently, it is dried at 100°C. During the drying process, the prepreg travels along the length direction of the continuous fiber, and the traveling direction is perpendicular to the horizontal direction. The resin mass fraction in the prepreg obtained after impregnation with the low-viscosity resin solution is 12.55%.

[0128] (2) Impregnation and drying of high-viscosity resin solution:

[0129] First impregnation: Immerse the prepreg after impregnation and drying treatment with the low-viscosity resin solution into a solution of heterocyclic naphthalene polyether sulfone ketone with a viscosity of 5000 mPa·s, a number average molecular weight of 1000, and an impregnation temperature of 30°C. The solvent is N-methylpyrrolidone. Subsequently, it is dried at 240°C. During the drying process, the prepreg travels along the length direction of the continuous fiber, and the traveling direction is perpendicular to the horizontal direction. The resin mass fraction in the prepreg obtained after the first impregnation with the high-viscosity resin solution is 31.9%.

[0130] Second impregnation: Immerse the prepreg after the first impregnation treatment into a solution of heterocyclic naphthalene polyether sulfone ketone with a viscosity of 8000 mPa·s, a number average molecular weight of 1000, and an impregnation temperature of 30°C. The solvent is N-methylpyrrolidone. Subsequently, it is dried at 240°C. During the drying process, the prepreg travels along the length direction of the continuous fiber, and the traveling direction is perpendicular to the horizontal direction. The resin mass fraction in the prepreg obtained after the second impregnation with the high-viscosity resin solution is 41.7%.

[0131] (3) Hot pressing treatment:

[0132] The dried prepreg is treated by a hot pressing process at a temperature of 350 °C and a pressure of 5 MPa to obtain the final prepreg.

[0133] Example 2

[0134] This example provides a method for preparing a prepreg for continuous production, and the specific steps are as follows:

[0135] (1) Impregnation and drying of low-viscosity resin solution:

[0136] The unidirectional carbon fiber is immersed in a solution of heterocyclic naphthalene biphenyl polyether sulfone ketone with a viscosity of 1000 mPa·s and a number-average molecular weight of 20,000. The solvent is N,N-dimethylacetamide, and the impregnation temperature is 50 °C. During the impregnation process, ultrasonic vibration with a frequency of 40 kHz and an energy density of 1.3 W / cm 2 is applied, and then it is dried at 100 °C. During the drying process, the prepreg travels along the length direction of the continuous fiber, and the traveling direction is perpendicular to the horizontal direction. The resin mass fraction in the prepreg obtained after impregnation with the low-viscosity resin solution is 8.55%.

[0137] (2) Impregnation and drying of high-viscosity resin solution:

[0138] First impregnation: The prepreg after impregnation and drying with the low-viscosity resin solution is immersed in a solution of heterocyclic naphthalene biphenyl polyether sulfone ketone with a viscosity of 3000 mPa·s, a number-average molecular weight of 20,000, and an impregnation temperature of 60 °C. The solvent is N,N-dimethylacetamide, and 15% of boron nitride based on the mass of the high-viscosity resin in the high-viscosity resin solution is additionally added. Then it is dried at 220 °C. During the drying process, the prepreg travels along the length direction of the continuous fiber, and the traveling direction is perpendicular to the horizontal direction. The resin mass fraction in the prepreg obtained after the first impregnation with the high-viscosity resin solution is 21.36%.

[0139] Second impregnation: The prepreg after the first impregnation treatment is immersed again in a solution of heterocyclic naphthalene biphenyl polyether sulfone ketone with a viscosity of 6000 mPa·s, a number-average molecular weight of 20,000, and an impregnation temperature of 60 °C. The solvent is N,N-dimethylacetamide, and 15% of boron nitride based on the mass of the high-viscosity resin in the high-viscosity resin solution is additionally added. Then it is dried at 220 °C. During the drying process, the prepreg travels along the length direction of the continuous fiber, and the traveling direction is perpendicular to the horizontal direction. The resin mass fraction in the prepreg obtained after the second impregnation with the high-viscosity resin solution is 39.9%.

[0140] (3) Hot pressing treatment:

[0141] The dried prepreg is treated by a hot pressing process at a temperature of 320 °C and a pressure of 10 MPa to obtain the final prepreg.

[0142] Example 3

[0143] This embodiment provides a method for preparing prepreg for continuous production, and the specific steps are as follows:

[0144] (1) Impregnation and drying of low-viscosity resin solution:

[0145] Immerse the glass fiber fabric into a solution of heteroarylene biphenyl polyether nitrile ketone with a viscosity of 600 mPa·s and a number-average molecular weight of 60,000. The solvent is N-methylpyrrolidone, and the impregnation temperature is 40°C. During the impregnation process, apply ultrasonic vibration with a frequency of 60 kHz and an energy density of 2.3 W / cm 2 and then dry at 100°C. During the drying process, the prepreg travels along the length direction of the continuous fiber, and the traveling direction is perpendicular to the horizontal direction. The resin mass fraction in the prepreg obtained after impregnation with the low-viscosity resin solution is 6.59%.

[0146] (2) Impregnation and drying of high-viscosity resin solution:

[0147] First impregnation: Immerse the prepreg after impregnation and drying with the low-viscosity resin solution into a solution of heteroarylene biphenyl polyether nitrile ketone with a viscosity of 8000 mPa·s, a number-average molecular weight of 60,000, and an impregnation temperature of 80°C. The solvent is N-methylpyrrolidone, and additionally add 10% silver powder and 8% graphene based on the mass of the high-viscosity resin in the high-viscosity resin solution. Then dry at 240°C. During the drying process, the prepreg travels along the length direction of the continuous fiber, and the traveling direction is perpendicular to the horizontal direction. The resin mass fraction in the prepreg obtained after the first impregnation with the high-viscosity resin solution is 33.1%.

[0148] (3) Hot pressing treatment:

[0149] Use a hot pressing process with a temperature of 370°C and a pressure of 3 MPa to treat the dried prepreg to prepare the final prepreg.

[0150] Example 4

[0151] This embodiment provides a method for preparing prepreg for continuous production, and the specific steps are as follows:

[0152] (1) Impregnation and drying of low-viscosity resin solution:

[0153] Immerse the unidirectional carbon fiber into a solution of heteroarylene biphenyl polyether sulfone ketone with a viscosity of 30 mPa·s and a number-average molecular weight of 30,000. The solvent is N-methylpyrrolidone, and the impregnation temperature is 20°C. During the impregnation process, apply ultrasonic vibration with a frequency of 20 kHz and an energy density of 0.3 W / cm 2Ultrasonic vibration is carried out, and then it is dried at 100 °C. During the drying process, the prepreg travels along the length direction of the continuous fiber, and the traveling direction is perpendicular to the horizontal direction. The resin mass fraction in the prepreg obtained after impregnation with the low-viscosity resin solution is 2.23%.

[0154] (2) Impregnation and drying with high-viscosity resin solution:

[0155] First impregnation: The prepreg after impregnation and drying with the low-viscosity resin solution is immersed in a solution of poly(phthalazinone ether sulfone ketone) with a viscosity of 3000 mPa·s, a number-average molecular weight of 30000, and an impregnation temperature of 80 °C. The solvent is N-methylpyrrolidone, and an additional 20% of the mass of the high-viscosity resin in the high-viscosity resin solution is added with carbon nanotubes. Subsequently, it is dried at 240 °C. During the drying process, the prepreg travels along the length direction of the continuous fiber, and the traveling direction is perpendicular to the horizontal direction. The resin mass fraction in the prepreg obtained after the first impregnation with the high-viscosity resin solution is 15.43%.

[0156] Second impregnation: The prepreg after the first impregnation and drying is immersed in a solution of poly(phthalazinone ether sulfone ketone) with a viscosity of 4500 mPa·s, a number-average molecular weight of 30000, and an impregnation temperature of 80 °C. The solvent is N-methylpyrrolidone, and an additional 20% of the mass of the high-viscosity resin in the high-viscosity resin solution is added with carbon nanotubes. Subsequently, it is dried at 240 °C. During the drying process, the prepreg travels along the length direction of the continuous fiber, and the traveling direction is perpendicular to the horizontal direction. The resin mass fraction in the prepreg obtained after the second impregnation with the high-viscosity resin solution is 33.40%.

[0157] Third impregnation: The prepreg after the second impregnation and drying is immersed in a solution of poly(phthalazinone ether sulfone ketone) with a viscosity of 8000 mPa·s, a number-average molecular weight of 30000, and an impregnation temperature of 80 °C. The solvent is N-methylpyrrolidone, and an additional 20% of the mass of the high-viscosity resin in the high-viscosity resin solution is added with carbon nanotubes. Subsequently, it is dried at 240 °C. During the drying process, the prepreg travels along the length direction of the continuous fiber, and the traveling direction is perpendicular to the horizontal direction. The resin mass fraction in the prepreg obtained after the third impregnation with the high-viscosity resin solution is 42.6%.

[0158] (3) Hot pressing treatment:

[0159] The dried prepreg is treated by a hot pressing process at a temperature of 350 °C and a pressure of 8 MPa to prepare the final prepreg.

[0160] Example 5

[0161] This example provides a method for preparing a prepreg for continuous production, and the specific steps are as follows:

[0162] (1) Impregnation and drying with low-viscosity resin solution:

[0163] The unidirectional carbon fiber is immersed in a polycarbonate solution with a viscosity of 1500 mPa·s and a number-average molecular weight of 50000. The solvent is chloroform, and the impregnation temperature is 60 °C. During the impregnation process, ultrasonic vibration with a frequency of 80 kHz and an energy density of 2.7 W / cm 2 is applied. Subsequently, it is dried at 100 °C. During the drying process, the prepreg travels along the length direction of the continuous fiber, and the traveling direction is perpendicular to the horizontal direction. The resin mass fraction in the prepreg obtained after impregnation with the low-viscosity resin solution is 9.32%.

[0164] (2) Impregnation and drying with high-viscosity resin solution:

[0165] First impregnation: The prepreg after impregnation and drying with the low-viscosity resin solution is immersed in a polycarbonate solution with a viscosity of 6000 mPa·s, a number-average molecular weight of 50000, and an impregnation temperature of 60 °C. The solvent is chloroform. Subsequently, it is dried at 80 °C. During the drying process, the prepreg travels along the length direction of the continuous fiber, and the traveling direction is perpendicular to the horizontal direction. The resin mass fraction in the prepreg obtained after the first impregnation with the high-viscosity resin solution is 30.2%.

[0166] (3) Hot pressing treatment:

[0167] The dried prepreg is treated by a hot pressing process at a temperature of 200 °C and a pressure of 0.5 MPa to prepare the final prepreg.

[0168] Example 6

[0169] This example provides a method for preparing a prepreg for continuous production, and the specific steps are as follows:

[0170] (1) Impregnation and drying with low-viscosity resin solution:

[0171] The unidirectional carbon fiber is immersed in a polyimide solution with a viscosity of 2000 mPa·s and a number-average molecular weight of 40000. The solvent is dimethyl sulfoxide, and the impregnation temperature is 70 °C. During the impregnation process, ultrasonic vibration with a frequency of 90 kHz and an energy density of 2.8 W / cm2 is applied. Subsequently, it is dried at 100 °C. During the drying process, the prepreg travels along the length direction of the continuous fiber, and the traveling direction is perpendicular to the horizontal direction. The resin mass fraction in the prepreg obtained after impregnation with the low-viscosity resin solution is 10.56%.

[0172] (2) Impregnation and drying with high-viscosity resin solution:

[0173] First impregnation: The prepreg after drying treatment by dipping in a low-viscosity resin solution is immersed in a polyimide solution with a viscosity of 7000 mPa·s, a number-average molecular weight of 40000, and an impregnation temperature of 70 °C. The solvent is dimethyl sulfoxide, and additionally 30% of the mass of the high-viscosity resin in the high-viscosity resin solution of carbon nanotubes is added. Subsequently, it is dried at 200 °C. During the drying process, the prepreg travels along the length direction of the continuous fiber, and the traveling direction is perpendicular to the horizontal direction. The resin mass fraction in the prepreg obtained after the first impregnation with the high-viscosity resin solution is 31.5%.

[0174] (3) Hot pressing treatment:

[0175] The dried prepreg is treated by a hot pressing process at a temperature of 400 °C and a pressure of 5 MPa to prepare the final prepreg.

[0176] Comparative example 1

[0177] The same process route as in Example 3 is adopted, but the first-step low-viscosity resin solution impregnation is not carried out (i.e., directly carry out high-viscosity resin solution impregnation and subsequent processes), and the other conditions are the same. This comparative example is used to verify the influence of the low-viscosity pre-impregnation step on the performance of the final prepreg.

[0178] Comparative example 2

[0179] The same process as in Example 4 is adopted, but the viscosity of the first-step low-viscosity resin solution is set to 20 mPa·s, and the other conditions are the same, which is used to investigate the effect when the viscosity of the low-viscosity adhesive is lower.

[0180] Comparative example 3

[0181] The same process as in Example 3 is adopted, but the viscosity of the first-step low-viscosity resin solution is set to 3500 mPa·s, and the others are the same, which is used to investigate the influence when the viscosity of the low-viscosity adhesive is higher.

[0182] Comparative example 4

[0183] The same process as in Example 1 is adopted, but ultrasonic vibration is not applied during the first-step impregnation, and the other steps are the same, which is used to verify the contribution of the ultrasonic field to the impregnation effect.

[0184] Comparative example 5

[0185] The same process as in Example 1 is adopted, but the first-step ultrasonic parameter, i.e., the ultrasonic frequency, is increased to 110 kHz, and the others are the same, which is used to evaluate the influence of a higher ultrasonic frequency on the prepreg.

[0186] Comparative example 6

[0187] The same process as in Example 3 was adopted, but a low-viscosity resin solution with a viscosity of about 1000 mPa·s was used for both the high- and low-viscosity impregnations (i.e., in the second step, instead of using a high-viscosity resin, a low-viscosity resin was used for impregnation again), and the other conditions remained unchanged. This comparative example simulated the situation where the viscosities of the two impregnations were the same and relatively low.

[0188] Comparative Example 7

[0189] The same process as in Example 3 was adopted, but a high-viscosity resin solution with a viscosity of about 8000 mPa·s was used for both the high- and low-viscosity impregnations (equivalent to omitting the low-viscosity impregnation in the first step and performing two impregnations with a high-viscosity adhesive solution), and the others were the same. This comparative example was used to simulate the situation where the viscosities of the two impregnations were the same and relatively high.

[0190] Comparative Example 8

[0191] The same process as in Example 1 was adopted, but during the first and second drying processes, the prepreg traveled along the length direction of the continuous fiber, and the traveling direction was horizontal, and the other steps were the same, which was used to evaluate the contribution of the drying process to the prepreg effect.

[0192] Tests and Results

[0193] The following tests were conducted on the final prepregs obtained from the examples and comparative examples:

[0194] (1) The mass fraction of the resin in the prepreg obtained in each step of the example was determined by the loss-on-ignition method, that is, the prepreg obtained in this step was weighed and then burned at a high temperature until the mass did not change, indicating that the resin was completely burned, and then the mass ratio of the low-viscosity resin to the high-viscosity resin in the final prepreg was calculated through Formulas 1 and 2, where

[0195] Formula 1: (1 - mass of residue after burning resin / mass of prepreg before burning) * 100% = total resin mass fraction in the prepreg obtained in this step,

[0196] Formula 2: total resin mass fraction after low-viscosity resin impregnation / (total resin mass fraction after high-viscosity resin final impregnation - total resin mass fraction after low-viscosity resin impregnation) = mass ratio of low-viscosity resin to high-viscosity resin in the final prepreg.

[0197] The results are shown in Table 1:

[0198] Table 1 Data Characterization of Examples / Comparative Examples

[0199]

[0200] (2) Referring to the GB / T 32788.3-2016 standard, the volatile content of the prepreg was tested, and the results of the examples / comparative examples are shown in Table 1;

[0201] (3) The porosity of the prepreg was tested with reference to the ASTM D2734-16 (2021) standard. The results of the examples / comparative examples are shown in Table 1;

[0202] (4) The areal density of the prepreg was tested with reference to the GB / T 32791-2016 standard. The results of the examples / are shown in Table 1;

[0203] Results and Analysis

[0204] The prepregs prepared in the examples of the present invention showed excellent performance in various properties. Among them, the resin mass fraction of the prepregs of the present invention could reach 42.6%, and the areal density could reach 352 g / m 2 , while the volatile content (mainly residual solvent) in the prepreg was not higher than 0.15%, and the porosity did not exceed 0.2%. It can be seen that through the stepwise impregnation and drying strategy of low-viscosity ultrasonic impregnation + drying + high-viscosity impregnation + drying, the present invention effectively reduced the volatile residue and internal defects while ensuring high resin content and high areal density, and greatly improved the quality consistency of the prepreg.

[0205] By comparing the examples with the comparative examples, the contributions of the core process elements of the present invention to the properties of the prepreg can be clearly clarified: in the present invention, low-viscosity impregnation and ultrasonic action ensure the full wetting and degassing of the fiber bundles, high-viscosity impregnation ensures sufficient and uniform resin loading, and reasonable drying and hot pressing steps enable thorough solvent volatilization and dense and pore-free prepregs. In contrast, the lack of low-viscosity impregnation in Comparative Example 1 will lead to poor resin impregnation; when the viscosity of the low-viscosity resin solution in Comparative Example 2 is relatively low, the adhesive solution is too thin to deposit enough resin on the fibers, resulting in a decrease in the areal density of the prepreg and a low impregnation efficiency; when the viscosity of the low-viscosity resin solution in Comparative Example 3 is relatively high, the resin viscosity is too high, making it difficult for the fibers to be infiltrated and losing the advantages of "low-viscosity" impregnation, resulting in a decrease in the resin content and areal density of the prepreg, while the volatile content and porosity increase; the lack of ultrasonic vibration in Comparative Example 4 will lead to residual bubbles and pores in the prepreg; the ultrasonic frequency in Comparative Example 5 is too high, with insufficient penetration, making it difficult to effectively break the bubbles in the fiber bundles, and the improvement of the impregnation effect is limited; single-viscosity impregnation in Comparative Examples 6 and 7, regardless of the viscosity level, it is difficult to balance wettability and high resin content even after multiple impregnations; in Comparative Example 8, the continuous fiber travels horizontally during the drying process, and the resin distribution on the upper and lower surfaces is uneven due to the influence of gravity; these comparison results highlight the superiority of the present invention's solution both quantitatively and qualitatively.

[0206] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing prepreg for continuous production, characterized in that: Including: Successively subjecting continuous fibers to ultrasonic impregnation with a low-viscosity resin solution, first drying, impregnation with a high-viscosity resin solution, second drying, and hot pressing to obtain a prepreg; wherein, The viscosity of the low-viscosity resin solution used in the ultrasonic impregnation process of the low-viscosity resin solution is lower than the viscosity of the high-viscosity resin solution used in the impregnation process of the high-viscosity resin solution; During the first drying and the second drying, the continuous fibers both travel along their length directions, and the traveling directions are both perpendicular to the horizontal direction.

2. The prepreg preparation method according to claim 1, wherein: The viscosity of the low-viscosity resin solution is 30 to 3000 mPa·s; And / or, the temperature of the ultrasonic impregnation of the low-viscosity resin solution is 20 to 80 °C; And / or, the ultrasonic frequency of the ultrasonic impregnation of the low-viscosity resin solution is 20 to 100 kHz; And / or, the ultrasonic energy density for ultrasonic impregnation of the low-viscosity resin solution is 0.3 to 3.0 W / cm 2 .

3. The prepreg preparation method according to claim 1, characterized in that: The viscosity of the high-viscosity resin solution is 3000 to 8000 mPa·s; And / or, the temperature of the impregnation with the high-viscosity resin solution is 30 to 80 °C.

4. The prepreg preparation method according to claim 1, wherein: Adding a functional filler to the high-viscosity resin solution, and the mass ratio of the functional filler to the high-viscosity resin in the high-viscosity resin solution is 0.01 to 0.3:1.0; further, the functional filler includes at least one of a conductive filler, a heat-conductive filler, or a wave-absorbing filler; furthermore, the conductive filler includes a metal-based conductive filler, a carbon-based conductive filler, a metal-oxide conductive filler, a conductive polymer filler, or a combination thereof; the heat-conductive filler includes a metal-based heat-conductive filler, a carbon-based heat-conductive filler, a ceramic-based heat-conductive filler, a polymer-based heat-conductive filler, or a combination thereof; the wave-absorbing filler includes a ferrite, a metal magnetic powder, a carbon-based material, a conductive polymer, or a combination thereof.

5. The prepreg preparation method according to claim 1, characterized in that: The impregnation with the high-viscosity resin solution and the second drying are carried out one or more times; further, when the impregnation with the high-viscosity resin solution and the second drying are carried out multiple times, the viscosity of the high-viscosity resin solution for the subsequent impregnation is the same as that of the previous time, or, increases by 1500 to 4000 mPa·s compared with the previous time.

6. The prepreg preparation method according to claim 1, characterized in that: The temperature of the first drying is 80 to 160 °C; And / or, the temperature of the second drying is 80 to 240 °C.

7. The prepreg preparation method according to claim 1, characterized in that: The temperature of the hot pressing is 200 to 400 °C; And / or, the pressure of the hot pressing is 0.5 to 10 MPa.

8. The prepreg preparation method according to claim 1, characterized in that: The resin content of the prepreg is 20 to 45%; And / or, in the prepreg, the mass ratio of the low-viscosity resin to the high-viscosity resin is 0.05 to 0.55:

1.

9. The prepreg preparation method according to claim 1, characterized in that: The resin solution satisfies at least one of the following conditions: (1) The resin in the resin solution includes one or more of the following: Polyarylether containing a phthalazinone biphenyl structure, polycarbonate, polyethersulfone, polysulfone, polyarylate, thermoplastic polyimide, polyamideimide, polyphenylene ether, polyetherimide; wherein, The polyarylether resin containing a phthalazinone biphenyl structure has the following structural formula: Wherein, m is a positive integer, n is 0 or a positive integer; Ar1 is a bis-halogen monomer structural unit, including one or more than two connection combinations of the following structures: Ar2 is a bisphenol or bisphenol-like structural unit, including one or more than two connection combinations of the following structures: Wherein, the structure of Y1 is as follows: The structure of Y2 is as follows: R1, R2, R3, and R4 are hydrogen, a halogen substituent, phenyl, phenoxy, a straight-chain alkyl group containing at least 1 carbon atom, a branched alkyl group containing at least 1 carbon atom, or a branched alkoxy group containing at least 1 carbon atom, and the structures of R1, R2, R3, and R4 are the same or different; (2) The solvent used in the resin solution includes one or more of the following: N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, chloroform; and / or, the continuous fiber includes a unidirectional continuous fiber bundle or a fiber fabric; and / or, the continuous fiber includes at least one of the following categories: (1) Inorganic fibers: carbon fiber, glass fiber, quartz fiber, basalt fiber, silicon carbide fiber, alumina fiber, boron fiber; (2) Organic high-performance fibers: aramid fiber, ultra-high molecular weight polyethylene fiber, polybenzoxazole fiber, polyimide fiber, polyetheretherketone fiber, poly(p-phenylene benzobisoxazole) fiber; (3) Metal fibers: stainless steel fiber, titanium fiber, copper fiber, aluminum fiber; (4) Natural fibers: flax fiber, sisal fiber, ramie fiber; (5) Composite fibers: metal-coated fibers, multi-component hybrid fiber bundles.

10. A prepreg, characterized in that, Obtained by the preparation method according to any one of claims 1 to 9.

Images