A high-performance thermoplastic prepreg impregnation mold and its application method

Abstract

This invention relates to the field of B29B11 / 10, and more particularly to a high-performance thermoplastic prepreg impregnation mold and its method of use. The mold includes an upper mold, a front part of a lower mold, and a rear part of a lower mold. The upper mold is provided with a mold head, and the mold head and the front part of the lower mold form a resin molten pool. A resin inlet is provided below the resin molten pool. The resin pressure of the impregnation mold of this invention comes directly from the pressure of the melt pump. This pressure acts directly on the fibers without indirectly increasing the resin pressure by increasing the fiber tension. Therefore, the impregnation pressure can be increased while maintaining a relatively low fiber tension, thus ensuring minimal fiber damage. Furthermore, the fibers can be impregnated on both sides within the molten pool, shortening the resin impregnation path and improving impregnation efficiency, thereby reducing the porosity content of the prepreg.

Description

Technical Field

[0001] This invention relates to the field of B29B11 / 10, and more particularly to a high-performance thermoplastic prepreg impregnation mold and its method of use. Background Technology

[0002] Compared to metallic materials, resin-based composites have advantages such as high specific strength and high specific modulus. Currently, thermosetting composites are more commonly used. Compared to thermosetting composites, high-performance thermoplastic composites have advantages such as good impact toughness, fatigue resistance, and repairability. Furthermore, they can be manufactured in a low-cost, automated manner through in-situ molding processes. Thermoplastic prepregs are intermediate materials in the preparation of thermoplastic composites. High-performance thermoplastic prepregs refer to continuous sheets with a certain thickness (0.1mm-1mm) and resin content (30%-50%), using high-performance thermoplastic resins (such as polyaryletherketone (PAEK) resins) as the matrix and continuous fibers (such as carbon fibers) as reinforcement. In-situ molding processes require thermoplastic prepregs to have extremely low porosity and minimal fiber damage. However, high-performance thermoplastic resins typically have high melting temperatures (e.g., polyetheretherketone (PEEK, a type of PAEK) has a melting temperature of 343 °C) and high melt viscosity (generally above 300 Pa·s). Preparing high-performance thermoplastic prepregs using the hot-melt method usually requires high-temperature conditions, applying pressure for a certain period to allow the resin to fully impregnate the fibers. However, due to the high resin viscosity, it is difficult for the resin to fully impregnate the fibers within a limited impregnation time. This results in numerous porosity defects within the prepared prepreg. Furthermore, increasing the pressure leads to severe fiber damage and prepreg cracking.

[0003] Existing technologies for pre-impregnation of continuous fiber-reinforced high-performance thermoplastic composites typically include melt impregnation, slurry impregnation, and powder impregnation. Melt impregnation is currently the most commonly used method. Its principle involves heating and melting the resin, then impregnating the fiber bundle with the resin in a mold to achieve full resin impregnation of the fibers. The key to melt impregnation lies in the design of the impregnation mold. Its advantages include simple operation and easy control of resin content. However, its disadvantages include difficulty in fully impregnating the fibers, especially with high-viscosity resins. This leads to high porosity, severe fiber damage, and low material mechanical properties. For prepregs with wide widths and continuous production, cracking is also a common problem. In the slurry impregnation process, since high-performance thermoplastic resins (such as PEEK) are difficult to dissolve in common organic solvents, resin powder can be dispersed in the impregnation system. Continuous carbon fibers are oriented by rollers, and under the action of the traction system, the resin powder adheres to the fiber surface through the impregnation system. The pressure of the rollers allows the resin to penetrate into the fiber bundle, and finally, heating and shaping complete the winding process. In addition, before entering the heating system, the upper and lower surfaces of the carbon fibers are covered with a release film to prevent resin powder from falling off. The release film is peeled off after heating. The advantages of powder suspension technology are short resin residence time in the molten state, minimal weight loss, high wetting efficiency, and low cost, making it suitable for mass production. However, if the dispersant is not completely removed, the performance of the product will be affected to some extent, and this technology has high requirements for resin powder particle size. The powder method first requires the resin to be made into tiny resin powders, the fibers to be dispersed, and then the resin powder to be adsorbed onto the carbon fiber surface through electrostatic action. The resin is then melted in a high-temperature chamber to obtain the prepreg. Relying on electrostatic adsorption, the high viscosity of the resin does not affect the adsorption, thus not affecting the wetting effect. The powder method can also accurately control the resin content and has a good wetting effect with minimal fiber damage, but it requires small resin powder particle size, resulting in higher manufacturing costs.

[0004] The above analysis shows that different methods for preparing thermoplastic prepregs have both advantages and disadvantages. Currently, melt impregnation is generally considered to be the simplest and most commonly used method for preparing thermoplastic prepregs. However, the problems with melt impregnation are also the main factors limiting the promotion and application of thermoplastic composite materials.

[0005] Patent US11118292 describes an impregnation mold that supplies resin from above and employs a dendritic resin channel to ensure uniform resin distribution in the width direction of the prepreg. However, the patent does not explain how to ensure sufficient resin impregnation of the fibers or how to reduce prepreg cracking.

[0006] Patent CN105904611B describes an ultra-thin continuous fiber reinforced thermoplastic resin prepreg and its preparation method. The method uses a two-stage impregnation process to achieve full impregnation of the resin and fiber. The two-stage impregnation module includes a front high-temperature heating roller, a rear high-temperature heating roller, and a small arc-shaped hot plate between the two. The two-stage impregnation method not only makes the equipment more complex, but also makes it difficult to achieve complete impregnation of the resin and fiber, and it is difficult to control the resin content and prepreg cracks. Similarly, fiber damage cannot be avoided.

[0007] Patent CN110142892A discloses a long fiber reinforced thermoplastic composite impregnation mold and impregnation process. It employs a liftable upper pressure roller combined with a stationary lower pressure roller, and provides resin overflow holes on the contact surfaces between the upper and lower pressure rollers and the fibers. Continuous and uniform resin addition through these overflow holes improves the impregnation efficiency and effect. This invention is primarily used for preparing long fiber reinforced thermoplastic composites, not continuous fiber reinforced plastic prepregs. Its main function is to quickly remove residual resin from the mold. While it improves the impregnation degree, it cannot be used to produce continuous fiber reinforced thermoplastic prepregs requiring extremely low porosity.

[0008] Patent CN111267374A discloses a novel fiber tension adjustable thermoplastic composite impregnation device. The upper shell of the mold in this device can be mechanically moved up and down to adjust the tension on the fiber bundle, thereby changing the fiber impregnation effect. However, for polyetheretherketone thermoplastic resins, it is difficult to achieve sufficient impregnation of the fiber by adjusting the fiber tension alone. It is necessary to comprehensively adjust the fiber tension, resin pressure, impregnation time, etc. to achieve the purpose of preparing prepreg with low porosity content.

[0009] Patent CN113043568B discloses a prepreg hot melt impregnation mold, which includes a preheating mold on the inlet side and a transition lip on the outlet side for heat preservation of the prepreg. This mold utilizes a combination of conical and wave-shaped designs to gradually increase the extrusion pressure on the fiber crests, facilitating the melt impregnation of the fiber and plastic resin and reducing wear damage between the fiber and the mold. However, this mold does not solve the problem of cracks appearing during continuous prepreg production.

[0010] Patent CN206551304U discloses a continuous fiber reinforced plastic impregnation mold. The mold contains four cylindrical pins, each with a curved portion within the mold cavity. The first two cylindrical pins bend in the same direction, as do the latter two, and the two bend directions are symmetrically arranged. Fiber bundles contact the four curved structures sequentially from left to right, with the contact surface being an arc surface. This increases the spread width of the fiber bundle and allows adjacent fibers to open up. Furthermore, the curvature of the contact surface between the continuous fiber bundle and the cylindrical pins is adjustable, improving fiber dispersion. A drawback of this invention is that the fiber bundles may bunch together on the curved cylindrical pins (the fiber bundles slide to both sides), leading to more severe cracking of the prepreg.

[0011] The above analysis shows that existing technologies focus on improving the wettability of resin to fibers, while neglecting to ensure low fiber damage and no cracking of prepreg while improving the wettability of resin to fibers. In fact, this is also a common problem in high-performance thermoplastic prepregs, namely (1) the resin cannot fully wet the fibers; (2) the fibers are severely damaged and the prepreg is severely cracked, making it impossible to continuously and stably produce high-quality prepregs; and (3) the fiber distribution in the prepreg is uneven. Summary of the Invention

[0012] The hot-melt method for preparing high-performance thermoplastic prepregs faces challenges due to the high viscosity of the resin, making it difficult to completely impregnate the fibers. Furthermore, the prepreg preparation process can lead to fiber damage and cracking. To improve the resin's wetting effect on the fibers, the following methods are necessary:

[0013] (1) Extend the impregnation time. Extending the impregnation time is beneficial to increasing the impregnation depth, but this will reduce production efficiency or lead to an excessively long impregnation mold;

[0014] (2) Increase impregnation pressure. Increasing pressure is beneficial to obtaining greater impregnation driving force, but it is difficult to obtain a large impregnation pressure for an open impregnation mold. The usual practice is to use a wavy impregnation mold, but the wavy impregnation mold has limited effect on increasing impregnation pressure. If only increasing impregnation pressure is pursued, new problems will be brought about, such as severe fiber damage and cracking of prepreg.

[0015] (3) Double-sided impregnation can shorten the resin travel in the prepreg by half, which is beneficial to improve the impregnation effect under the same conditions and time.

[0016] To increase resin impregnation pressure and ensure that fibers can improve impregnation and fiber distribution uniformity while minimizing damage and preventing cracking of the prepreg, the first aspect of the present invention provides a high-performance thermoplastic prepreg impregnation mold, the mold comprising an upper mold 1, a lower mold front part 2, and a lower mold rear part 3, the upper mold 1 being provided with a mold pressure head 10, the mold pressure head 10 and the lower mold front part 2 forming a resin molten pool 5, and a resin inlet 7 being provided below the resin molten pool 5.

[0017] The inventors incorporated a die pressure head in the upper mold. This head compresses the resin molten pool into a U-shaped structure and presses the fibers downwards. As the molten resin enters the resin molten pool from the resin inlet, this pressure acts directly on the fibers. The higher impregnation pressure allows the molten resin to impregnate the fibers more quickly, improving wettability. The molten resin impregnates the fibers under pressure, while the fibers remain tightly attached to the die pressure head above the resin molten pool. This ensures that the fibers are neither scattered nor damaged due to excessive tension under high pressure, a crucial guarantee for preventing cracking of the prepreg and ensuring uniform fiber distribution. The die pressure head above the resin molten pool presses the fibers downwards, completely immersing them in the molten resin. This indirectly achieves double-sided impregnation, shortening the impregnation path and improving wettability. Furthermore, the complete immersion of the fibers in the molten resin reduces the impact of minor fluctuations in resin supply on the resin content of the prepreg.

[0018] In a preferred embodiment, the mold further includes a mold inlet 8 and a mold outlet 9, wherein the height of the mold inlet 8 is higher than or equal to the height of the mold outlet 9.

[0019] In a preferred embodiment, the upper mold 1 and the rear part 3 of the lower mold form a wavy resin impregnation zone 11.

[0020] The height of the resin molten pool and the corrugated resin impregnation zone is lower than that of the mold inlet and mold outlet, which helps the molten resin to fill the mold cavity and improves the impregnation effect.

[0021] The number of wavy resin impregnation zones is adjusted according to the resin viscosity. Preferably, there are 2-20 wavy resin impregnation zones, and more preferably 5-15.

[0022] In a preferred embodiment, each vertex of the wavy resin impregnation area 11 is an arc shape.

[0023] In a preferred embodiment, the height of the upper apex of the wavy resin impregnation zone 11 is lower than the height of the mold inlet 8 and the height of the mold outlet 9.

[0024] In a preferred embodiment, the resin molten pool 5 is a U-shaped resin molten pool.

[0025] In a preferred embodiment, all corners of the resin melt pool 5 are rounded, with a radius of R5-R10.

[0026] Preferably, the radius of the rounded corner is R5.

[0027] In a preferred embodiment, the resin is fed upwards into the resin molten pool 5 from the lower part of the resin inlet 7.

[0028] In a preferred embodiment, the mold is equipped with a heating unit and a temperature sensor inside, and with heat insulation components on the outside.

[0029] A second aspect of the present invention provides a method for using a high-performance thermoplastic prepreg impregnation mold, the method comprising the following steps:

[0030] S1. Heat the mold to the prepreg processing temperature and maintain the temperature;

[0031] S2. Open the upper mold 1, and let the fibers that have been spread through the yarn pass through the mold inlet 8 and out of the mold outlet 9;

[0032] S3. Cover the upper mold 1, start the extruder, and squeeze the molten resin from the resin inlet 7 into the resin melt pool 5 to impregnate the fiber;

[0033] S4. Start the traction motor to move the fiber along the fiber running direction under the action of the traction motor. During the movement, the fiber is fully impregnated by the molten resin. As the temperature outside the mold decreases, the resin solidifies to form a thermoplastic prepreg.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] (1) Improve the wetting effect and reduce fiber damage

[0036] As analyzed above, improving the impregnation effect requires increasing impregnation pressure, extending impregnation time, or using double-sided impregnation. Existing mold designs typically require increasing fiber tension to increase impregnation pressure, and extending impregnation time usually means extending mold length or reducing the impregnation rate. Both increasing fiber tension and extending mold length can severely damage fibers and reduce material mechanical properties, while reducing the impregnation rate lowers production efficiency, hindering mass production of prepregs. The impregnation mold described in this invention uses resin pressure directly from the melt pump, which acts directly on the fibers without indirectly increasing resin pressure by increasing fiber tension. Therefore, it can increase impregnation pressure while maintaining relatively low fiber tension, thus ensuring minimal fiber damage.

[0037] (2) Prevent the prepreg from cracking and ensure uniform fiber distribution.

[0038] In existing mold designs, resin is extruded into the mold from the die head. When the resin passes through the fibers, it may disperse the already unrolled fibers, creating gaps. These gaps can lead to prepreg cracking and uneven fiber distribution across the width of the prepreg. However, the mold described in this invention ensures that the fibers adhere tightly to the die head where resin pressure is applied. This guarantees that the fibers have a certain degree of constraint in the width direction and are not dispersed by the resin, thus preventing prepreg cracking and ensuring uniform fiber distribution across the width of the prepreg. Attached Figure Description

[0039] Figure 1 This is a structural diagram of the high-performance thermoplastic prepreg impregnation mold of the present invention, wherein 1 is the upper mold, 2 is the front part of the lower mold, 3 is the rear part of the lower mold, 4 is the fiber, 5 is the resin molten pool, 6 is the molten resin, 7 is the resin inlet, 8 is the mold inlet, 9 is the mold outlet, 10 is the mold pressure head, 11 is the wavy resin impregnation zone, and 12 is the fiber running direction.

[0040] Figure 2 This is a cross-sectional view of the carbon fiber reinforced polyether ether ketone prepreg prepared in Example 1. Detailed Implementation

[0041] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0042] Example 1

[0043] See Figure 1 This embodiment provides the preparation of carbon fiber reinforced polyether ether ketone (PEEK) prepreg, specifically including the following steps:

[0044] S1. The resin supply module is connected to the front of the lower mold of the impregnation mold;

[0045] S2. Heat the mold to the prepreg molding temperature and hold for 30 minutes;

[0046] S3. Open the upper mold 1, and let the unfurled fibers pass through the mold inlet 8 and out of the mold outlet 9;

[0047] S4. Cover the upper mold 1, start the extruder, and squeeze the molten PEEK resin from the resin inlet 7 into the resin melt pool 5 to impregnate the fiber;

[0048] S5. Start the traction motor to move the fiber along the fiber running direction under the action of the traction motor. During the movement, the fiber is fully impregnated by the molten PEEK resin. As the temperature outside the mold decreases, the PEEK resin solidifies to form a thermoplastic prepreg.

[0049] Performance testing

[0050] The thermoplastic prepreg prepared using the impregnation mold and the above method of this invention has a resin content of 35%, a porosity of less than 0.5%, and good appearance and internal quality. A cross-sectional view of the prepared prepreg is shown below. Figure 2 The image shows a cross-sectional view of the prepreg between the two dashed lines. The circular area represents the fiber cross-section, and the remaining gray area represents the resin matrix. As can be seen from the image, the prepreg has a low porosity (less than 0.5%), the resin and fiber are evenly distributed, and the prepreg thickness is relatively uniform, ranging from 0.14 to 0.15 mm.

[0051] The mechanical properties of the composite material prepared using the prepreg in an autoclave process are shown in Table 1. As can be seen from Table 1, the composite material has good mechanical properties.

[0052] For resin content testing methods, refer to: HB 7736.5

[0053] For testing methods of porosity content, refer to: GB / T 3365

[0054] 0° Tensile Strength Test Method Reference: ASTM D3039

[0055] 0° bending strength test method reference: Q / 6S 2708

[0056] Interlaminar shear strength test method reference: ASTM D2344

[0057] Table 1

[0058] Test Project Test Results 0° Tensile strength 2712 MPa 0° bending strength 1463 MPa Interlaminar shear strength 106 MPa

[0059] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A high-performance thermoplastic prepreg impregnation mold, the mold comprising an upper mold (1), a lower mold front portion (2), and a lower mold rear portion (3), characterized in that, The upper mold (1) is provided with a mold pressure head (10), the mold pressure head (10) and the front part (2) of the lower mold form a resin molten pool (5), and a resin inlet (7) is provided below the resin molten pool (5). The mold also includes a mold inlet (8) and a mold outlet (9), wherein the height of the mold inlet (8) is higher than or equal to the height of the mold outlet (9); The upper mold (1) and the rear part (3) of the lower mold form a wavy resin impregnation area (11). Each vertex of the wavy resin impregnation area (11) is an arc shape; The height of the upper apex of the wavy resin impregnation zone (11) is lower than the height of the mold inlet (8) and the height of the mold outlet (9); The resin molten pool (5) is a U-shaped resin molten pool; All corners of the resin melt pool (5) are rounded, and the radius of the rounded corners is R5-R10; The resin is fed upwards into the resin molten pool (5) from the lower part of the resin inlet (7); The mold needs to be equipped with a heating unit and a temperature sensor inside, and with heat insulation components on the outside; The resin is polyetheretherketone.

2. A method of using a high-performance thermoplastic prepreg impregnation mold according to claim 1, characterized in that, The method of use includes the following steps: S1. Heat the mold to the prepreg processing temperature and maintain the temperature; S2. Open the upper mold (1), and insert the fibers that have been spread through the mold inlet (8) and out of the mold outlet (9); S3. Cover the upper mold (1), start the extruder, and squeeze the molten resin from the resin inlet (7) into the resin melt pool (5) to impregnate the fiber; S4. Start the traction motor to move the fiber along the fiber running direction under the action of the traction motor. During the movement, the fiber is fully impregnated by the molten resin. The temperature outside the mold decreases and the resin solidifies to form a thermoplastic prepreg. The fiber is carbon fiber.

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