A method for efficiently preparing fiber-reinforced thermoplastic composite materials and structures

Abstract

This invention relates to the field of materials preparation technology, specifically disclosing a method for efficiently preparing fiber-reinforced thermoplastic composite materials and structures. The method includes: mixing reinforcing fibers with thermoplastic resin fibers and / or resin powder to pre-prepare a fiber-mixed felt and laying it in a mold cavity; closing the mold and introducing saturated steam or superheated steam at a pressure of 0.3–20 MPa and a temperature of 120–400°C into the mold cavity for 3–120 seconds to rapidly heat the material by volume, causing the resin to melt and impregnate the reinforcing fibers; subsequently, pressure molding is performed in the same mold, with vacuum treatment if necessary, to complete the preparation of the composite material product. This invention achieves an integrated process of heating, impregnation, and molding, and has advantages such as high heating efficiency, short molding cycle, low energy consumption, and excellent product density and mechanical properties.

Description

Technical Field

[0001] This invention belongs to the field of materials manufacturing technology, specifically relating to a method for efficiently preparing fiber-reinforced thermoplastic composite materials and structures. Background Technology

[0002] Fiber-reinforced composite materials, due to their high specific strength and high specific stiffness, have been widely used in wind power equipment, automobiles, and aerospace. Currently, thermosetting composite materials with epoxy resins and unsaturated polyesters as matrices are mainly used in engineering applications. These materials form a three-dimensional network structure through chemical cross-linking reactions, thus possessing high mechanical properties and good molding stability. However, thermosetting composite materials cannot be remelted after curing, making recycling difficult and easily leading to resource waste and environmental burden. Furthermore, their molding process relies on chemical curing reactions, typically requiring long curing times, resulting in long production cycles, low production efficiency, and high manufacturing costs, making it difficult to meet the demands of modern industry for high-efficiency and large-scale manufacturing.

[0003] Compared to thermosetting composites, thermoplastic composites, using thermoplastic resins as a matrix, possess the characteristics of being heat-melted and reprocessable multiple times, thus exhibiting excellent recyclability. Their molding process does not require chemical curing reactions, significantly shortening the molding cycle and making them suitable for automated and high-efficiency production. Furthermore, the thermoplastic resin matrix typically possesses high toughness, resulting in superior impact resistance and damage tolerance in the composites. Therefore, against the backdrop of increasingly stringent requirements for energy conservation, emission reduction, and sustainable development, the development and application of thermoplastic composites to replace traditional thermosetting composites has become an important development direction in the field of composite materials.

[0004] Currently, the traditional manufacturing process for fiber-reinforced thermoplastic composite structures typically employs a "intermediate material preparation + secondary heating and molding" approach. Specifically, this involves first preparing intermediate materials such as continuous fiber-reinforced thermoplastic prepreg or randomly oriented fiber sheets (GMT), then heating these intermediate materials to a molten state (the thermoplastic resin), and finally transferring them to a mold for compression molding. However, this process has several drawbacks: First, because thermoplastic resin has a high viscosity in its molten state, the wetting process within the fiber bundles and between fibers is inefficient, resulting in a time-consuming and inefficient intermediate material preparation process, leading to higher manufacturing costs. Second, the compression molding process requires reheating the intermediate materials to a molten state, which is not only time-consuming but also energy-intensive, further reducing overall production efficiency and increasing manufacturing costs. Furthermore, when the intermediate material used is a continuous fiber unidirectional prepreg, multi-layer layup is required before compression molding, a complex process that relies heavily on manual labor, further extending the production cycle. In summary, although thermoplastic composites have advantages over thermosetting composites, such as recyclability and higher molding efficiency, the existing manufacturing processes for thermoplastic composites and their structural components still generally suffer from problems such as long production cycles and high energy consumption, resulting in high overall manufacturing costs. This, to some extent, restricts the wider application and further development of thermoplastic composites in various fields.

[0005] In recent years, various improved processes have been proposed, among which the long fiber reinforced thermoplastic composite direct molding process (LFT-D) is an online mixing-compression molding technology for industrial application. This process melts thermoplastic resin in an extruder, mixes it with long fibers in the mixing zone of the extruder, and then directly feeds it into a mold for molding, thus eliminating intermediate material preparation steps and improving production efficiency to some extent. However, the LFT-D process still has significant limitations: on the one hand, the high-shear mixing process easily leads to fiber breakage, significantly reducing fiber length and weakening the reinforcement effect; on the other hand, the uniformity of fiber distribution in the molten resin is poor, easily resulting in local agglomeration or resin-depleted areas; furthermore, due to the short impregnation time and lack of effective pressure, the resin cannot fully impregnate the fiber bundles, resulting in high porosity in the product, thus affecting its strength and fatigue performance. Therefore, although the existing LFT-D process can improve production efficiency, it still cannot meet the application requirements of high-performance structural components in terms of fiber length retention, impregnation quality, and product performance stability.

[0006] In summary, existing thermoplastic composite molding technologies generally suffer from inherent problems such as long process flows and high energy consumption. Furthermore, when employing simplified direct molding processes, significant shortcomings often exist in areas such as fiber length retention, distribution uniformity, impregnation quality, and process adaptability, making it difficult to simultaneously meet the demands for high-performance and high-efficiency manufacturing. Therefore, there is an urgent need to develop an efficient method for preparing fiber-reinforced thermoplastic composites that features a wide range of fiber applicability, relatively simple equipment structure, low energy consumption, short molding cycle, and guarantees excellent mechanical properties in the finished product. This method aims to overcome the deficiencies of existing technologies and meet the practical needs of engineering applications and large-scale production. Summary of the Invention

[0007] This invention provides a method for efficiently preparing fiber-reinforced thermoplastic composite materials and structures, aiming to solve the technical problems existing in the prior art, such as long production cycle, high energy consumption, insufficient fiber impregnation, and unstable product performance.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A method for efficiently preparing fiber-reinforced thermoplastic composite materials and structures includes the following steps:

[0010] (a) Pre-preparing a fiber-blended felt by mixing reinforcing fibers with thermoplastic resin fibers and / or resin powder;

[0011] (b) The fiber-mixed felt is cut to a size and shape that matches the target product and placed in a mold. The fiber-mixed felt is then partially stacked and laid in the mold according to the local shape and thickness requirements of the product.

[0012] (c) The upper and lower molds of the mold are preheated to a temperature above 100°C; and at least one of the upper and lower molds is provided with a steam passage and a steam hole communicating with the mold cavity for introducing steam into the mold cavity;

[0013] (d) Close the mold so that the fiber-mixed felt is located inside the mold cavity and remains sealed;

[0014] (e) Introduce saturated steam or superheated steam at a pressure of 0.3 to 20 MPa and a temperature of 120 to 400°C into the mold cavity for 3 to 120 seconds to melt the thermoplastic resin and impregnate the reinforcing fibers;

[0015] (f) After steam heating is completed, the molten resin and reinforcing fibers are press-molded in the same mold, wherein the press-molding is performed in any of the following ways:

[0016] (1) The molten resin and reinforcing fiber are subjected to one-step or step-by-step pressure molding using the same upper mold;

[0017] (2) After changing the upper mold, pressurize the composite system, which is still in a molten state, to form a new composite system.

[0018] Furthermore, the mold cavity is vacuumed before and / or during the pressurization process before pressurization is performed;

[0019] (g) Open the mold and remove the molded product.

[0020] Furthermore, the reinforcing fiber is a pre-impregnated fiber with a thin layer of thermoplastic resin on its surface, and the thickness of the resin layer is 5% to 20% of the diameter of the reinforcing fiber.

[0021] Furthermore, in the fiber-mixed felt, the reinforcing fibers and thermoplastic resin are uniformly interwoven in a two-dimensional plane or three-dimensional space.

[0022] Furthermore, the reinforcing fiber is selected from at least one of the following: carbon fiber, glass fiber, basalt fiber, aramid fiber, ultra-high molecular weight polyethylene fiber, PET fiber, plant fiber, ceramic fiber, and metal fiber, and the volume content of the reinforcing fiber is 3% to 80%.

[0023] Furthermore, the thermoplastic resin in the fiber-blended felt is present in the form of fibers and / or powder, and the thermoplastic resin is selected from at least one of the following: polyvinyl chloride, polyvinylidene chloride, vinyl acetate resin, polyvinyl alcohol, polystyrene, AS resin, ABS resin, acrylic resin, methacrylic resin, polyethylene, polypropylene, polyamide, polyacetal, polycarbonate, PET, PEN, PBT, polyarylate, polyphenylene ether, polyphenylene sulfide, polysulfone, polyether ether ketone, polylactic acid, or copolymers, blends, and combinations thereof, and may contain additives.

[0024] Furthermore, the reinforcing fibers and / or thermoplastic resin fibers include continuous fibers and / or discontinuous fibers with a fiber length of 2 mm to a continuous length.

[0025] Furthermore, the reinforcing fibers are distributed in the fiber-mixed felt in an in-plane, isotropically distributed or oriented along a predetermined direction.

[0026] Furthermore, the fiber-mixed felt contains reinforcing fibers distributed along the thickness direction, and the reinforcing fibers are stitched together to form a three-dimensional reinforcing structure.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] First, this invention integrates the heating, impregnation, and molding processes by introducing saturated or superheated steam into a sealed mold cavity to rapidly heat the fiber-mixed felt by volume, and then immediately applying pressure molding within the same mold. The steam heat energy can quickly penetrate into the material, causing the thermoplastic resin to melt uniformly in a short time. Simultaneously, because the reinforcing fibers and resin fibers and / or resin powder are already uniformly mixed in the initial state, the molten resin can fully impregnate the reinforcing fibers within a short transport distance, thus achieving a highly efficient impregnation process, significantly shortening the molding cycle and reducing energy consumption.

[0029] Secondly, in this invention, the resin melting and impregnation process and the pressure molding process are completed continuously in the same mold, so that the molten resin can maintain a relatively stable temperature during the pressure stage, thereby having good fluidity and being able to mold complex structural parts.

[0030] Third, the present invention preferably employs a step-by-step pressure molding method within the same mold. First, a lower pressure is applied and maintained for a certain time to facilitate the expulsion of air and other gases from within the material. Then, a higher pressure is applied to densify the material and improve molding quality. Furthermore, by simultaneously applying a vacuum to the mold cavity during the pressurization process, gases within the system can be effectively eliminated, suppressing the generation of porosity defects and thus improving the density and uniformity of the composite material.

[0031] Fourth, the present invention uses a mixed fiber felt composed of reinforcing fibers and thermoplastic resin as the initial structure. Its fiber type, distribution form and resin morphology have high adjustability. It can be flexibly designed and combined according to the performance requirements of different structural parts. It has good process adaptability and scalability and is suitable for the efficient preparation of various fiber-reinforced thermoplastic composite structural parts. Attached Figure Description

[0032] Figure 1 This is a flowchart of the present invention. Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.

[0034] In the description of this invention, the reinforcing fiber may be selected from at least one of carbon fiber, glass fiber, basalt fiber, aramid fiber, ultra-high molecular weight polyethylene fiber, PET polymer fiber, various plant fibers, ceramic fibers, and metal fibers, and its volume content in the composite material is 3% to 80%. The average fiber diameter of the reinforcing fiber is preferably 3 to 40 μm, more preferably 5 to 20 μm. When the reinforcing fiber is a fiber such as carbon fiber that requires sizing treatment, it is preferable to attach a sizing agent to its surface; the amount of sizing agent attached is preferably 0.01 to 10 parts by weight based on 100 parts by weight of the reinforcing fiber.

[0035] The fiber mat, which is composed of reinforcing fibers and resin fibers and / or resin powder, is prepared by a method that is not particularly limited, but preferably by processes such as air-flow web forming, mechanical carding, papermaking, or cross-laying (applicable to continuous fibers).

[0036] Both the reinforcing fiber and the resin fiber can be at least one of continuous or discontinuous fibers, with a fiber length ranging from 2 mm to continuous fibers; when discontinuous fibers are used, a fiber length of 5 mm to 50 mm is preferred. In the same mixed fiber felt, the lengths of the reinforcing fiber and the resin fiber can be the same or different. The reinforcing fiber can be in the form of monofilaments, fiber bundles, or a combination of both.

[0037] In this invention, the reinforcing fiber can also be a pre-impregnated fiber with a thin layer of thermoplastic resin coating on its surface. Pre-impregnated fiber refers to a continuous and uniform thin layer of thermoplastic resin pre-formed on the surface of the reinforcing fiber through processes such as melt impregnation, solution impregnation, or powder coating. The thickness of the resin layer is controlled within the range of 5% to 20% of the diameter of the reinforcing fiber. During steam heating, the resin layer melts first, significantly shortening the impregnation path between the resin and the reinforcing fiber and improving impregnation efficiency. Simultaneously, the pre-impregnated fiber reduces the relative displacement between the reinforcing fiber and the resin fiber or powder during the preparation of the mixed felt, helping to maintain the uniformity of fiber distribution and the stability of the structure. The pre-impregnated fiber can be in the form of continuous fiber or chopped fiber, and its preparation methods include, but are not limited to, melt extrusion coating, suspension impregnation, or electrostatic powder coating.

[0038] In this invention, vacuuming refers to evacuating the mold cavity before and / or during pressurization by connecting a vacuum passage within the mold to the cavity, reducing the cavity pressure to -0.06 MPa to -0.1 MPa (gauge pressure). This removes air, moisture, and low-molecular-weight volatiles that may be generated during resin melting from the fiber-reinforced felt and the molten resin. Vacuuming can be performed separately before pressurization or simultaneously during the initial pressurization and low-pressure holding phases to further promote gas removal, reduce porosity defects in the molded product, and improve the density and interfacial bonding quality of the composite material. When vacuuming and pressurization are performed simultaneously, it is essential to ensure good mold cavity sealing to prevent external air from entering.

[0039] The diameter of the resin fiber is not particularly limited, but is preferably 5 μm to 100 μm, more preferably 10 μm to 30 μm, in order to improve the melting performance of the resin during the heating process and its wetting effect on the reinforcing fiber.

[0040] The reinforcing fibers in a fiber felt can be distributed uniformly in the plane or oriented in a specific direction, and can also include reinforcing structures in the thickness direction, such as three-dimensional fiber felts formed by sewing or needle punching.

[0041] In fiber mats, reinforcing fibers and resin fibers and / or resin powder can be uniformly interwoven in a two-dimensional plane or three-dimensional space.

[0042] The resin is in fiber or powder form, and the resin types include at least one of polyvinyl chloride, polyvinylidene chloride, vinyl acetate, polyvinyl alcohol, polystyrene, AS resin, ABS resin, acrylic resin, methacrylic resin, polyethylene, polypropylene, polyamide 6, polyamide 11, polyamide 12, polyamide 46, polyamide 66, polyamide 610, polyacetal, polycarbonate, PET, PEN, PBT, polyarylate, polyphenylene ether, polyphenylene sulfide, polysulfone, polyether ether ketone, and polylactic acid, or copolymers or alloys thereof, and may add flame retardants, stabilizers, UV resistant agents, antistatic agents, pigments, release agents, softeners, plasticizers, and surfactants as needed.

[0043] At least one of the upper and lower molds of the mold is provided with a steam pipe and steam holes for introducing steam into the mold cavity. The steam holes can be evenly distributed or directionally distributed according to the structural characteristics of the product to be molded.

[0044] When surface precision of the molded product is required, it is preferable to arrange the outer surface of the molded product on the upper mold side, and replace it with an upper mold with a smooth inner surface before compression molding to obtain high-precision outer surface molding quality. Furthermore, when the outer surface of the molded product is formed by the lower mold and its surface precision is required, it is preferable not to provide steam passages and steam holes in the lower mold, but only to provide steam passages and steam holes in the upper mold to ensure that the outer surface formed by the lower mold has high molding precision.

[0045] During the molding process, both the upper and lower molds need to be preheated to a certain temperature, preferably above 100°C, and more preferably 110°C to 190°C.

[0046] In the preparation process of the composite material of the present invention, without compromising the purpose of the present invention, in addition to the above-mentioned main raw materials, various fibrous or non-fibrous fillers, as well as additives such as flame retardants, stabilizers, UV resistant agents, antistatic agents, pigments, release agents, softeners, plasticizers and surfactants may be added as needed.

[0047] In this invention, stepwise pressurization refers to a process in which different pressures are applied in stages within the same mold, based on the physical state changes of the material during the molding process. Specifically, after steam heating is completed, a lower pressure (e.g., 0.5–5 MPa) is first applied and held for 5–30 seconds to facilitate the expulsion of internal gas and uniform resin flow; subsequently, a higher pressure (e.g., 10–25 MPa) is applied and held for 20–60 seconds to achieve material densification. Stepwise pressurization effectively avoids defects such as excessive resin flow, uneven fiber distribution, or gas retention caused by sudden pressure increases. One-step pressurization, on the other hand, refers to a pressurization method in which the required molding pressure is directly applied after steam heating and held until the product solidifies or sets, suitable for molding products with simple structures and uniform thickness.

[0048] Example 1:

[0049] This embodiment provides a method for efficiently preparing fiber-reinforced thermoplastic composite materials and structures, specifically including the following steps:

[0050] (a) Material preparation:

[0051] Carbon fibers (T700 grade) with a length of 20 mm and PA6 resin fibers with a length of 25 mm and a diameter of 15 μm are mixed at a volume ratio of 35:65 and prepared into a fiber-mixed felt with an areal density of 2720 g / m² by air-flow web forming process. Square fiber felt preforms with a size of 500 mm × 500 mm are then cut out for later use.

[0052] (b) Laying out and closing the mold:

[0053] Place a 500 mm × 500 mm square fiber felt preform into a mold cavity of the same size, close the mold and keep it sealed.

[0054] (c) Steam heating and immersion:

[0055] Superheated steam at a pressure of 0.8 MPa and a temperature of 260 ℃ is introduced into the mold cavity for 15 seconds to melt the PA6 resin fiber and impregnate the carbon fiber.

[0056] (d) Pressure molding:

[0057] After steam heating is completed, keep the mold closed and gradually apply pressure to the molten material in the molten state by moving the upper mold until the thickness of the molded product is 2.0 mm. Stop pressurizing and hold the pressure for 50 seconds to achieve compaction molding of the product.

[0058] (e) Demolding and part removal:

[0059] After releasing the pressure and opening the mold, remove the molded product and let it cool to room temperature.

[0060] Observation revealed that the molded plate with dimensions of 500 mm × 500 mm × 2 mm had a uniform surface gloss and no obvious flow marks, bubbles, or exposed fibers. The tensile modulus of elasticity of the molded plate in the 0° and 90° directions was tested, and the results showed that its elastic modulus ratio was 1.05, indicating that the fibers were basically isotropically distributed in the plane.

[0061] Example 2:

[0062] This embodiment provides a method for efficiently preparing fiber-reinforced thermoplastic composite materials and structures, specifically including the following steps:

[0063] (a) Material preparation:

[0064] Glass fibers with a length of 20 mm and polypropylene resin fibers with a length of 20 mm and a diameter of 20 μm were uniformly mixed at a volume ratio of 35:65. The mixture was then mechanically combed to obtain a mixed fiber mat with an areal density of 3750 g / m². The mixed fiber mat was then cut into square fiber mat preforms with a size of 500 mm × 500 mm.

[0065] (b) Laying out and closing the mold:

[0066] Place the fiber-mixed felt preform into the mold, close the mold, and keep it sealed.

[0067] (c) Steam heating and immersion:

[0068] Saturated steam at a pressure of 2.3 MPa and a temperature of 220 °C is introduced into the mold cavity for 15 seconds to melt the polypropylene resin fiber and impregnate the glass fiber.

[0069] (d) Pressure molding:

[0070] After steam heating is completed, the mold cavity is evacuated to -0.08 MPa, and then stepwise pressurization is carried out in the same mold: first apply 1.5 MPa pressure and hold for 15 seconds, then apply 10 MPa pressure and hold for 45 seconds.

[0071] (e) Demolding and part removal:

[0072] After depressurizing and opening the mold, remove the molded product and cool it to room temperature.

[0073] Observation revealed that the resulting molded plate had a uniform gloss and no obvious flow marks, bubbles, or exposed fiber defects. Tensile modulus tests were conducted on the molded plate at 0° and 90°, showing a modulus ratio of 1.05, indicating that the fibers were essentially isotropically distributed within the plane. Ultrasonic testing of the resulting composite material molded product revealed no unwetted areas or porosity defects.

[0074] Example 3:

[0075] This embodiment provides a method for efficiently preparing fiber-reinforced thermoplastic composite materials and structures, specifically including the following steps:

[0076] (a) Material preparation:

[0077] Basalt fibers with a length of 25 mm and polyamide 6 resin fibers with a length of 25 mm are mixed at a volume ratio of 40:60 and wet-molded to produce a mixed fiber felt with a surface density of 3660 g / m². Two square fiber felt preforms with a size of 350 mm × 350 mm are then cut from the mixed fiber felt.

[0078] (b) Laying out and closing the mold:

[0079] Two fiber-mixed felt preforms are stacked one on top of the other and laid inside a mold cavity with a cavity size of 500 mm × 500 mm. The mold is then closed and sealed.

[0080] (c) Steam heating and immersion:

[0081] Superheated steam at a pressure of 0.6 MPa and a temperature of 290 ℃ is introduced into the mold cavity for 20 seconds to melt the polyamide 6 resin fiber and impregnate the basalt fiber.

[0082] (d) Pressure molding:

[0083] After steam heating, the mold cavity is opened and the original upper mold is removed. A new upper mold with a smooth inner surface and preheated to 120°C is then quickly closed to keep the mold cavity sealed. The mold cavity is then evacuated to -0.08 MPa. When the resin is in a molten state, a pressure of 15 MPa is applied to the fiber and resin system for molding, and this pressure is maintained for 40 seconds.

[0084] (e) Demolding and part removal:

[0085] After releasing the pressure and opening the mold, remove the molded product and let it cool to room temperature.

[0086] Observation revealed that the material completely filled the mold cavity, resulting in a regular square of 500 mm × 500 mm with intact edges and no obvious material shortages or other molding defects. The upper surface of the molded plate was smooth and evenly glossy, with no obvious flow marks, bubbles, or exposed fibers. Tensile modulus tests were conducted on the molded plate at 0° and 90°, showing a modulus ratio of 1.05, indicating that the fibers were essentially isotropically distributed within the plane. Ultrasonic testing of the resulting composite material molded product revealed no unwetted areas or porosity defects.

[0087] Example 4:

[0088] This embodiment provides a method for efficiently preparing fiber-reinforced thermoplastic composite materials and structures, specifically including the following steps:

[0089] (a) Material preparation:

[0090] Continuous glass fibers and continuous polypropylene resin fibers with a diameter of 20 μm were uniformly mixed at a volume ratio of 40:60. The mixed fibers were reinforced in the thickness direction by needle punching to prepare a mixed fiber mat with an areal density of 3160 g / m². The mixed fiber mat was then cut into square fiber mat preforms with a size of 500 mm × 500 mm.

[0091] (b) Laying out and closing the mold:

[0092] Place the fiber felt preform into a mold of the same area, close the mold and seal it.

[0093] (c) Steam heating and immersion:

[0094] Superheated steam at a pressure of 0.6 MPa and a temperature of 260 ℃ is introduced into the mold cavity for 15 seconds to melt the polypropylene resin fiber and impregnate the glass fiber.

[0095] (d) Pressure molding:

[0096] After steam heating, the mold cavity is opened and the original upper mold is removed. A new upper mold with a smooth inner surface and preheated to 110°C is then quickly closed to keep the mold cavity sealed. The mold cavity is then evacuated to -0.08 MPa. When the resin is in a molten state, a pressure of 8 MPa is applied to the fiber and resin system for molding, and this pressure is maintained for 40 seconds.

[0097] (e) Demolding and part removal:

[0098] After releasing the pressure and opening the mold, remove the molded product and let it cool to room temperature.

[0099] Observation revealed that the upper surface of the molded plate was smooth and evenly glossy, with no obvious flow marks, bubbles, or exposed fiber defects. Tensile modulus of elasticity of the molded plate was tested at 0° and 90°, showing a modulus ratio of 1.05, indicating that the fibers are essentially isotropically distributed within the plane. Ultrasonic testing of the resulting composite material molded product revealed no unwetted areas or porosity defects. Comparative Example 1:

[0100] This comparative example provides a method for preparing fiber-reinforced thermoplastic composites using a conventional thermoplastic composite compression molding process, specifically including the following steps:

[0101] (a) Material preparation: Purchased thermoplastic glass fiber mat reinforced thermoplastic composite intermediate sheet was selected, in which the glass fiber volume fraction was 35%, the matrix resin was polypropylene, and the sheet thickness was 2.5 mm. The sheet was cut into square specimens with a size of 500 mm × 500 mm.

[0102] (b) Heat treatment: The square sample was placed in an infrared heating furnace at 240 °C and heated for 6 minutes.

[0103] (c) Transfer and molding: Take the heated sheet out of the infrared heating furnace and quickly transfer it into the mold cavity with an initial temperature of 80°C and a cavity plane size of 500 mm × 500 mm. Quickly close the mold and apply a pressure of 15 MPa for molding, and hold the pressure for 80 seconds.

[0104] (d) Demolding and removing parts: After molding is completed, open the mold, remove the product, and cool it to room temperature.

[0105] Example of effect:

[0106] The molded products obtained in Example 2 and Comparative Example 1 were subjected to performance tests and comparative analysis.

[0107] I. Testing Methods

[0108] (1) Molding cycle: The time from the start of mold closing to the end of product demolding.

[0109] (2) Tensile strength: Tested in accordance with ISO 527 standard.

[0110] (3) Porosity: determined according to ASTM D2734 standard.

[0111] (4) Unit energy consumption: measured in accordance with ISO 50001 standard.

[0112] The test results are shown in the table below;

[0113] Performance indicators Test Standards Example 2 Comparative Example 1 Molding cycle (s) — 75 420 Tensile strength (MPa) ISO 527 213±5 141±16 Porosity (%) ASTM D2734 0.9 2.3 Energy consumption per unit (kWh / kg) ISO 50001 0.082 0.56

[0114] II. Results Analysis

[0115] As shown in Table 1, compared with Comparative Example 1, the molding cycle of Example 2 was shortened from 420 s to 75 s, significantly improving production efficiency; the tensile strength increased from 141 MPa to 213 MPa, an increase of approximately 50%; the porosity decreased from 2.3% to 0.9%, significantly improving internal quality; and the unit energy consumption decreased from 0.56 kWh / kg to 0.082 kWh / kg, a reduction of over 80%.

[0116] The above results demonstrate that the technical solution of this invention achieves uniform heating by using steam volume heating, which allows heat to rapidly penetrate into the material's interior. Simultaneously, the initial uniform distribution of resin and reinforcing fibers shortens the impregnation path and improves impregnation efficiency. Furthermore, the step-by-step pressurization combined with vacuum treatment effectively removes internal gases and inhibits pore formation. In addition, continuous in-mold molding avoids temperature loss and improves resin flowability and interfacial bonding quality. Therefore, this invention can achieve high density and high performance in composite materials while ensuring the integrity of the fiber structure, significantly shortening the molding cycle while greatly reducing energy consumption, and effectively improving the mechanical properties and internal density of the composite material.

[0117] In summary, the method of the present invention can significantly shorten the molding cycle, greatly reduce energy consumption, and effectively improve the mechanical properties and internal density of composite materials, thus possessing significant technical advantages and industrial application value.

Claims

1. A method for efficiently preparing fiber-reinforced thermoplastic composite materials and structures, characterized in that, Includes the following steps: (a) Pre-preparing a fiber-blended felt by mixing reinforcing fibers with thermoplastic resin fibers and / or resin powder; (b) The fiber-mixed felt is cut to a size and shape that matches the target product and placed in a mold. The fiber-mixed felt is then partially stacked and laid in the mold according to the local shape and thickness requirements of the product. (c) Both the upper and lower molds of the mold are preheated to a temperature above 100°C; and at least one of the upper and lower molds is provided with a steam passage and a steam hole communicating with the mold cavity for introducing steam into the mold cavity; (d) Close the mold so that the fiber-mixed felt is located inside the mold cavity and remains sealed; (e) Introduce saturated steam or superheated steam at a pressure of 0.3 to 20 MPa and a temperature of 120 to 400°C into the mold cavity for 3 to 120 seconds to melt the thermoplastic resin and impregnate the reinforcing fibers; (f) After steam heating is completed, the molten resin and reinforcing fibers are press-molded in the same mold, wherein the press-molding is performed in any of the following ways: (1) The molten resin and reinforcing fiber are subjected to one-step or step-by-step pressure molding using the same upper mold; (2) After changing the upper mold, pressurize the composite system, which is still in a molten state, to form a new composite system. Furthermore, the mold cavity is vacuumed before and / or during the pressurization process before pressurization is performed; (g) Open the mold and remove the molded product.

2. The method for efficiently preparing fiber-reinforced thermoplastic composite materials and structures according to claim 1, characterized in that: The reinforcing fiber is a pre-impregnated fiber with a thin layer of thermoplastic resin on its surface, and the thickness of the resin layer is 5% to 20% of the fiber diameter.

3. The method for efficiently preparing fiber-reinforced thermoplastic composite materials and structures according to claim 1, characterized in that: In the fiber-blended felt, reinforcing fibers and thermoplastic resin are uniformly interwoven in a two-dimensional plane or three-dimensional space.

4. The method for efficiently preparing fiber-reinforced thermoplastic composite materials and structures according to claim 1, characterized in that: The reinforcing fiber includes at least one of carbon fiber, glass fiber, basalt fiber, aramid fiber, ultra-high molecular weight polyethylene fiber, PET fiber, plant fiber, ceramic fiber, and metal fiber, with a fiber volume content of 3% to 80%.

5. The method for efficiently preparing fiber-reinforced thermoplastic composite materials and structures according to claim 1, characterized in that: The thermoplastic resin in the fiber-blended felt is present in the form of fibers and / or powder. The thermoplastic resin includes at least one of polyvinyl chloride, polyvinylidene chloride, vinyl acetate resin, polyvinyl alcohol, polystyrene, AS resin, ABS resin, acrylic resin, methacrylic resin, polyethylene, polypropylene, polyamide 6, polyamide 11, polyamide 12, polyamide 46, polyamide 66, polyamide 610, polyacetal, polycarbonate, PET, PEN, PBT, polyarylate, polyphenylene ether, polyphenylene sulfide, polysulfone, polyetheretherketone, and polylactic acid, or copolymers or alloys thereof, and additives may be added.

6. The method for efficiently preparing fiber-reinforced thermoplastic composite materials and structures according to claim 1, characterized in that: The reinforcing fibers and thermoplastic resin fibers include continuous fibers and discontinuous fibers, with fiber lengths ranging from 2 mm to continuous fibers.

7. The method for efficiently preparing fiber-reinforced thermoplastic composite materials and structures according to claim 1, characterized in that: The reinforcing fibers in the fiber-mixed felt are distributed either uniformly in-plane or oriented along a predetermined direction.

8. The method for efficiently preparing fiber-reinforced thermoplastic composite materials and structures according to claim 1, characterized in that: The fiber-mixed felt comprises reinforcing fibers distributed along the thickness direction, which are stitched together to form a three-dimensional reinforcing structure.

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