Aramid long fiber-reinforced thermoplastic resin matrix composite and method of manufacture

Abstract

The present application relates to the technical field of composite materials, and in particular to an aramid long fiber reinforced thermoplastic resin-based composite material and a preparation method thereof, the preparation method being: mixing aramid long fibers and thermoplastic resin long fibers to obtain a uniform mixed yarn; the mixed yarn is subjected to airflow dispersion and pre-heating treatment to obtain a fiber mat; the fiber mat is sequentially fed into a first-stage pre-plasticizing mechanism and a second-stage injection mechanism to realize conveying and melting, and then is fed into a mold assembly to realize injection molding; a screw is arranged in each of the first-stage pre-plasticizing mechanism and the second-stage injection mechanism; the fiber mat is first fed into a rear conveying section through a front conveying section in the first-stage pre-plasticizing mechanism, is pre-heated and melted in the rear conveying section, and then is fed into a compression section in the second-stage injection mechanism, is subjected to mixing, compression and pressurized venting in the compression section, and is then fed into a metering section to be uniformly mixed and then is subjected to injection molding. The composite material has high strength and high modulus performance, and the preparation method can realize efficient mass production.

Description

Technical Field

[0001] This invention relates to an aramid long fiber reinforced thermoplastic resin-based composite material and its preparation method, belonging to the field of composite material technology. Background Technology

[0002] In the field of composite materials, fiber-reinforced structures are classified according to the morphology of the reinforcing phase, including continuous fiber-reinforced composites, long fiber-reinforced composites, and short fiber-reinforced composites. Continuous fiber-reinforced composites are those where the two ends of the fiber are located at the boundaries of the composite material, exhibiting anisotropy. Short fiber-reinforced composites are those where short fibers (generally <6mm in length) are randomly arranged in the matrix, exhibiting isotropy. Currently, continuous fiber-reinforced composites, with their excellent properties of lightweight, high specific strength, and high specific modulus, firmly occupy the "performance-first" fields such as aerospace and high-end sporting goods, such as the fuselage skin of the Airbus A350 and high-end golf club shafts. Short fiber-reinforced composites, on the other hand, are widely used in the "mass-production-first" markets such as automotive parts and electronic appliance housings, thanks to their efficient injection molding and extrusion processes and moderate cost, such as car hoods and laptop casings. Both types of composites, in their balance between performance and cost-effectiveness, meet specific needs and form clear application boundaries.

[0003] Long fiber reinforced composites (fiber length 30 mm-80 mm) break this inherent boundary, exhibiting unique advantages. Their fiber length can, to some extent, form a load transfer path similar to continuous fibers, providing mechanical properties far exceeding those of short fibers, making them suitable for industrial components with high strength requirements. Furthermore, because they do not require complex layup processes, production costs are significantly lower than those of continuous fiber composites. In addition, the length of the long fibers reduces the agglomeration problems that are prone to occur with short fibers in finished products, and also improves the low interlaminar shear strength defect of continuous fibers, achieving a balanced optimization of properties in all directions. This provides new solutions for lightweight automotive structural components, mass production of high-end sports equipment, and other fields.

[0004] Patent application CN106916447A discloses a method for preparing aramid fiber-modified long glass fiber reinforced thermoplastic: based on the long fiber reinforced thermoplastic pelleting process, utilizing the high strength, high toughness, and high flexibility of aramid fibers, the aramid fibers are uniformly dispersed and interwoven in the three-dimensional rigid skeleton of the long glass fiber reinforced thermoplastic, thereby increasing the toughness and impact resistance of the composite material. The materials in the formulation, except for the long glass fiber and aramid fiber, are mixed evenly and then fed into an extruder for high-temperature melting. The melt is then fed into a special mold for impregnating long glass fibers, allowing the melt to impregnate and coat the long glass fibers. The mixture is then drawn, cooled, and pelletized to obtain the long glass fiber reinforced thermoplastic. The key feature of this thermoplastic masterbatch is that the glass fibers in the product particles are arranged in parallel radial directions, and the axial length of the product particles is equal to the length of the glass fibers in the particles, with a particle length of 5-25mm. A certain proportion of thermoplastic resin raw materials and additives are mixed evenly and fed into the main feed hopper of an extruder. Short-cut aramid fibers are mixed into the melt from the main feed or side feed hopper, or continuous long-filament aramid fibers are mixed into the melt from the exhaust hole (glass fiber hole) of the plasticizing section of the extruder. After extrusion, cooling and granulation, aramid modified thermoplastic masterbatch is obtained. Then, long glass fiber reinforced thermoplastic masterbatch and aramid modified thermoplastic masterbatch are mixed evenly in a certain proportion to obtain aramid fiber modified long glass fiber reinforced thermoplastic product. Patent application CN118756431A discloses a high-fiber-content, highly oriented recycled fiber reinforced composite material and its preparation method: Step 1, waste composite laminate is recycled and cut into composite fragments, wherein the internal reinforcing fiber size of the composite fragments is 10-200mm; Step 2, the waste composite fragments are recycled to obtain recycled reinforcing fibers through chemical degradation; Step 3, after cleaning the residual resin on the surface of the recycled reinforcing fibers, they are mixed with thermoplastic resin fibers in a certain proportion and opened, the opened fiber mixture is combed, and the fiber mixture is... The composite materials are interlocked in the form of a mesh, then gathered into strips, twisted, and made into continuous long yarns to obtain blended yarn mesh and blended yarn strips; wherein the mass ratio of recycled reinforcing fibers in the fiber mixture is 1%-100% pure spinning; the ratio can be adjusted arbitrarily; Step 4: Use the blended yarn strips or blended yarn mesh as raw materials for thermoplastic composite preforms, heat and mold them, so that the thermoplastic resin fibers as the matrix melt between the recycled reinforcing fibers, thereby directly bonding with the surrounding recycled reinforcing fibers at the interface, cooling, and molding to obtain a high fiber content, highly oriented recycled fiber reinforced composite material.

[0005] However, the currently available methods for preparing composite materials with long fiber reinforcements are only applicable to long glass fibers, not aramid fibers. This is because conventional methods tend to cause aramid fibers to agglomerate, resulting in uneven dispersion of the aramid fibers in the composite material and significantly reducing their strength-enhancing effect. Aramid fibers, on the other hand, possess advantages such as better strength, lightweight properties, and high-temperature resistance. Therefore, developing a thermoplastic resin-based composite material reinforced with aramid long fibers and its preparation method is of significant value. Summary of the Invention

[0006] This invention addresses the shortcomings of existing technologies by providing an aramid long fiber reinforced thermoplastic resin matrix composite material and its preparation method. The composite material has high strength and high modulus properties, and the preparation method enables efficient mass production. It uses aramid long fibers with a length of 30 mm to 80 mm as reinforcement, breaking through the performance and cost bottlenecks of traditional fiber-reinforced materials.

[0007] The technical solution of this invention to solve the above-mentioned technical problems is as follows: A method for preparing an aramid long fiber reinforced thermoplastic resin-based composite material, wherein the preparation method is as follows:

[0008] S1. Preparation of blended yarn strips:

[0009] Aramid long fibers and thermoplastic resin long fibers are blended to obtain uniform blended yarns.

[0010] S2. Preparation of fiber felt:

[0011] Blended yarns are dispersed by airflow and preheated to obtain fiber mats;

[0012] S3, Melt Mixing and Injection Molding:

[0013] The fiber felt is sequentially fed into the first-stage pre-plasticizing mechanism and the second-stage injection mechanism for conveying and melting, and then enters the mold assembly for injection molding;

[0014] The first-stage pre-plasticizing mechanism and the second-stage injection mechanism are each equipped with a screw. The fiber felt first enters the rear conveying section through the front conveying section of the first-stage pre-plasticizing mechanism, where it is preheated and melted. Then it enters the compression section of the second-stage injection mechanism, where it is mixed, compressed, and pressurized to exhaust air. Finally, it enters the metering section, where it is mixed evenly and then injection molded.

[0015] Furthermore, the aramid long fiber is a crimped aramid long fiber with a length of 30 mm-80 mm; the thermoplastic resin long fiber is a crimped long fiber with a length of 30 mm-80 mm.

[0016] The total weight of the aramid long fiber and the thermoplastic resin long fiber is calculated as 100, and the weight ratio of the aramid long fiber and the thermoplastic resin long fiber is (10-40):(60-90).

[0017] Furthermore, the thermoplastic resin long fiber is at least one of polyamide 66 (PA66) long fiber, polyamide 6 (PA6) long fiber, polypropylene (PP) long fiber, polyphenylene sulfide (PPS) long fiber, and polyethylene (PE) long fiber.

[0018] Furthermore, in step S1, a combined cleaning and carding machine is used for blending, sequentially passing through the cleaning, carding, and drawing processes. In the cleaning machine, the fiber raw material is opened; the carding machine uses the carding cloth of the cylinder and the cardboard to fully mix the aramid long fibers and thermoplastic resin long fibers, with the cylinder speed at 300-450 r / min, the secondary roller speed at 700-800 r / min, and the doffer speed at 5-20 r / min; the drawing frame combines 6-8 slivers and drafts them, with a total draft ratio of 6-10 times and a back zone draft ratio of 1-1.5 times, forming a uniform blended yarn sliver;

[0019] The linear density of the blended yarn is 2800-3200 tex, and the breaking strength is ≥15 cN / tex.

[0020] Furthermore, in step S2, the blended yarn is dispersed by airflow in the airflow dispersion chamber, and the gas pressure introduced into the airflow dispersion chamber is 0.1-0.3 MPa;

[0021] The temperature conditions for the preheating treatment are 80-160℃.

[0022] Furthermore, the first-stage pre-plasticizing mechanism includes a first-stage barrel, a first-stage screw located within the first-stage barrel, and a drive component for driving the first-stage screw to rotate; the first-stage barrel includes a front conveying section and a rear conveying section, with a heater provided on the outer side of the rear conveying section; the second-stage injection mechanism includes a second-stage barrel communicating with the rear conveying section, a second-stage screw located within the second-stage barrel, a drive component for driving the second-stage screw to rotate, and a drive component for driving the second-stage screw to perform reciprocating injection molding motion; a heater is provided on the outer side of the second-stage barrel, and the second-stage barrel includes a compression section and a metering section; the bottom surface of the screw groove of the second-stage screw located in the compression section adopts a wave-shaped structure.

[0023] Furthermore, the length of the first-order screw in the front conveying section accounts for 20-40%, and the length of the first-order screw in the rear conveying section accounts for 60-80%.

[0024] The ratio of the total length of the first-order screw in the front conveying section and the rear conveying section, the length of the second-order screw in the compression section, and the length of the second-order screw in the metering section is (20-50%): (25-60%): (10-30%).

[0025] Furthermore, the pitch of the first-stage screw located in the front conveying section is less than the width of the fiber felt, and the gap between the tooth crest of the first-stage screw and the first-stage barrel located in the front conveying section is less than the thickness of the fiber felt.

[0026] The pitch of the first-stage screw located in the rear conveying section is not less than the width of the fiber felt, and the gap between the tooth crest of the first-stage screw located in the rear conveying section and the first-stage barrel is less than the gap between the tooth crest of the first-stage screw located in the front conveying section and the first-stage barrel.

[0027] Furthermore, the radius of the fillet of the wave structure on the bottom surface of the spiral groove is not less than 0.5 mm, the amplitude of the wave structure is 1 / 6 to 1 / 3 of the spiral groove depth, and the wavelength of the wave structure is 0.5 to 2.5 times the lead.

[0028] From the inlet to the outlet direction of the second-stage barrel, the screw groove volume of the second-stage screw in the compression section gradually decreases;

[0029] The groove depth of the second-order screw located in the metering section is (0.03-0.1)*D, where D is the diameter of the second-order screw.

[0030] The present invention also discloses an aramid long fiber reinforced thermoplastic resin-based composite material, which is prepared according to the preparation method described in the present invention.

[0031] The beneficial effects of this invention are:

[0032] In the preparation method of the aramid long fiber reinforced thermoplastic resin matrix composite material of the present invention, long fibers of 30 mm-80 mm are innovatively selected as reinforcement to construct a load transfer network between continuous fibers and short fibers. The mutual cooperation of the preparation of blended yarn, the preparation of fiber mat, melt mixing and injection molding processes ensures that the long fibers maintain stable length and uniform dispersion during processing, and enables continuous mass production.

[0033] In the aramid long fiber reinforced thermoplastic resin matrix composite material of this invention, the length of the aramid long fibers allows them to form a near-continuous stress transmission path in the composite product. Compared with short fibers, the tensile strength and flexural modulus are improved, which can meet the high strength requirements of automotive chassis, engineering machinery structural components, etc. Moreover, through improvements in process conditions and equipment structure, mass production of aramid long fiber reinforced thermoplastic resin matrix composite materials through injection molding can be achieved, improving production efficiency and reducing costs compared to continuous fiber composite materials. In terms of performance balance, the appropriate length of the long fibers avoids the problems of short fiber agglomeration and interlaminar defects in continuous fibers, thereby improving the interlaminar shear strength of the composite material and effectively expanding the application boundaries of the composite material.

[0034] The injection molding equipment used in the preparation method of this invention features a first-stage pre-plasticizing mechanism and a second-stage injection mechanism. The fiber felt is pre-plasticized in the first-stage barrel, compressed and degassed in the second-stage barrel, and the injection action is completed by the movement of the second-stage screw. The first-stage screw does not participate in the reciprocating injection action, preventing the fiber felt from being cut by the screw injection action, thus improving automation and ensuring the continuity of injection molding. The appropriate ratio of the lengths of the front conveying section, rear conveying section, compression section, and metering section ensures uniform mixing while avoiding damage to the material within the fiber felt, ensuring high-quality long-fiber reinforced composite materials and enabling smoother continuous injection molding production. The bottom surface of the screw groove in the screw compression section adopts a wave-shaped design, periodically changing the groove volume. This causes the fiber felt to repeatedly experience a "compression-expansion" state during its forward movement, making it easier to release the gas trapped inside. The change in groove depth results in high flow velocity and strong shear at the crests of the wave, and slow flow velocity and greater filling at the troughs, forming a strong turbulent mixing effect, reducing the risk of fiber agglomeration and improving the quality of the injection-molded products.

[0035] In the melt mixing and injection molding process of the preparation method described in this invention, segmented temperature control and variable pitch screw design ensure that the retention rate of long fibers is ≥85% and that they are uniformly dispersed during processing. Compared with traditional short fiber reinforced materials, the composite material prepared by this invention has a 2-3 times higher tensile strength, a 1.5-2 times higher flexural modulus, and an interlaminar shear strength increase of more than 40%. Furthermore, its production efficiency is more than 10 times higher than that of continuous fiber composite materials, and its cost is reduced by more than 50%. It combines the advantages of high performance and mass production, making it suitable for automotive structural parts, engineering machinery, and other fields. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the injection molding equipment for long fiber reinforced composite materials described in the embodiment;

[0037] Figure 2 This is an internal cross-sectional view of the injection molding equipment for long fiber reinforced composite materials described in the embodiment;

[0038] Figure 3 This is a schematic diagram of the felt-laying assembly described in the embodiment;

[0039] Figure 4 This is a schematic diagram of the internal structure of the felt feeding assembly described in the embodiment;

[0040] Figure 5 This is a schematic diagram of the first-order pre-plasticizing mechanism described in the embodiment;

[0041] Figure 6 This is a schematic diagram of the second-order injection mechanism described in the embodiment;

[0042] Figure 7 This is an unfolded and sectional view of the wave-shaped spiral groove.

[0043] In the diagram, 1. Felt feeding assembly; 2. Felt infeed assembly; 3. Injection assembly; 4. Mold assembly;

[0044] 11. Felt cylinder; 12. Braking component; 13. Connecting shaft; 14. Brake;

[0045] 21. Driven roller; 22. Driven roller; 23. Roller gear; 24. Screw gear; 25. Drive shaft; 26. Driven shaft; 27. Gearbox;

[0046] 31. First-order pre-plasticizing mechanism; 32. Second-order injection mechanism;

[0047] 311. First-stage barrel; 312. First-stage screw; 313. First-stage drive unit; 314. Front conveyor section; 315. Rear conveyor section;

[0048] 321. Second-stage barrel; 322. Second-stage screw; 323. Second-stage drive unit; 324. Injection driving unit; 325. Compression section; 326. Metering section; 327. Nozzle;

[0049] 5. Heater; 6. Mounting bracket. Detailed Implementation

[0050] The specific embodiments of the present invention will be described in detail below. The present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed.

[0051] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used is for describing particular embodiments only and is not intended to limit the invention.

[0052] A method for preparing an aramid long fiber reinforced thermoplastic resin-based composite material, wherein the preparation method comprises:

[0053] S1. Preparation of blended yarn strips:

[0054] Aramid long fibers and thermoplastic resin long fibers are blended to obtain uniform blended yarns.

[0055] S2. Preparation of fiber felt:

[0056] Blended yarns are dispersed by airflow and preheated to obtain fiber mats;

[0057] S3, Melt Mixing and Injection Molding:

[0058] use Figures 1-7 The injection molding equipment shown performs melting and mixing and injection molding. The fiber felt enters the first-stage pre-plasticizing mechanism 31 and the second-stage injection mechanism 32 in sequence to achieve conveying and melting, and then enters the mold assembly 4 to achieve injection molding.

[0059] Both the first-stage pre-plasticizing mechanism 31 and the second-stage injection mechanism 32 are equipped with screws. The fiber felt first enters the rear conveying section 315 through the front conveying section 314 of the first-stage pre-plasticizing mechanism 31, where it is preheated and melted. Then, it enters the compression section 325 of the second-stage injection mechanism 32, where it is mixed, compressed, and pressurized for degassing. Finally, it enters the metering section 326 for uniform mixing before injection molding. The entire injection molding equipment is fixedly installed by the fixing frame 6. In actual production, the structure of the mold assembly 4 is selected according to the requirements of the injection molding shape and size.

[0060] Specifically, the aramid long fiber is a crimped aramid long fiber with a length of 30 mm to 80 mm; the thermoplastic resin long fiber is a crimped long fiber with a length of 30 mm to 80 mm.

[0061] The total weight of the aramid long fiber and the thermoplastic resin long fiber is calculated as 100, and the weight ratio of the aramid long fiber and the thermoplastic resin long fiber is (10-40):(60-90).

[0062] Specifically, the thermoplastic resin long fiber is at least one of polyamide 66 (PA66) long fiber, polyamide 6 (PA6) long fiber, polypropylene (PP) long fiber, polyphenylene sulfide (PPS) long fiber, and polyethylene (PE) long fiber.

[0063] More specifically, the denier of the crimped para-aramid long fibers used in this embodiment of the invention is 1.5D. The crimping process involves oiling and humidifying followed by a preheating process, then mechanical crimping for shaping. The degree of crimping is controlled by the pressure of the crimping roller, and the crimping degree is controlled between 10% and 15%.

[0064] Specifically, in step S1, a combined cleaning and carding machine is used for blending, sequentially passing through the cleaning, carding, and drawing processes. In the cleaning machine, the fiber raw material is opened; the carding machine uses the carding cloth of the cylinder and the cardboard to fully mix the aramid long fibers and thermoplastic resin long fibers, with the cylinder speed at 300-450 r / min, the secondary roller speed at 700-800 r / min, and the doffer speed at 5-20 r / min; the drawing frame combines 6-8 slivers and drafts them together, with a total draft ratio of 6-10 times and a back zone draft ratio of 11.5 times, forming a uniform blended yarn sliver.

[0065] The blended yarn has a linear density of 2800-3200 tex and a breaking strength of ≥15 cN / tex, providing a good foundation for subsequent processing.

[0066] Preferably, the speed ratio between the cylinder speed and the doffer speed is 45-66.

[0067] Specifically, in step S2, the blended yarn is dispersed by airflow in the airflow dispersion chamber. The gas pressure introduced into the airflow dispersion chamber is 0.1-0.3MPa, so that the yarn is disintegrated into a single fiber state under the impact of airflow.

[0068] The preheating treatment is performed at a temperature of 80-160℃ to reduce the energy consumption of subsequent melting and mixing, and to ensure that the thermoplastic resin long fibers are elastic, which facilitates the subsequent conveying process. This stage can ensure that the long fibers are evenly dispersed and avoid tangling.

[0069] Specifically, the injection molding equipment includes: a felt unwinding assembly 1, a felt feeding assembly 2, an injection assembly 3, and a mold assembly 4; the felt unwinding assembly 1 performs the function of unwinding the fiber felt, the felt feeding assembly 2 performs the function of automatically and continuously introducing the fiber felt, the injection assembly 3 performs the functions of conveying, plasticizing, storing and injecting, and the mold assembly 4 performs the function of injection molding into the part.

[0070] like Figure 3 As shown, the felt-releasing assembly 1 includes a felt cylinder 11 and a braking component 12 that provides tension to the fiber felt. Fiber felt is wound on the felt cylinder 11, and the felt cylinder 11 is connected to the braking component 12 via a connecting shaft 13. The felt-releasing assembly 1 is mounted on a bracket 14.

[0071] like Figure 4As shown, the felt feeding assembly 2 includes an active roller 21, a passive roller 22, a roller gear 23, and a screw gear 24. The screw gear 24 is fixedly installed with the first-order screw 312. The first-order drive component 313 drives the first-order screw 312 and the screw gear 24 to rotate synchronously. The screw gear 24 is meshed with the roller gear 23, and the screw gear 24 drives the roller gear 23 to rotate. The roller gear 23 is fixedly installed with the active roller 21 on the active shaft 25. The active roller 21, the active shaft 25, and the roller gear 23 together form an active shaft 25 system. The rotation of the active shaft 25 system is achieved by the rotation of the roller gear 23. The passive roller 22 is installed on the passive shaft 26. The active roller 21 and the passive roller 22 together clamp the fiber felt. The rotation of the active roller 21 drives the passive roller 22 to rotate, causing the fiber felt to be fed into the front conveying section 314 of the injection assembly 3, thereby achieving continuous feeding of the fiber felt. Both roller gear 23 and screw gear 24 are installed inside gearbox 27.

[0072] like Figures 5-6 As shown, the first-stage pre-plasticizing mechanism 31 includes a first-stage barrel 311, a first-stage screw 312 located inside the first-stage barrel 311, and a first-stage driving component 313 that drives the first-stage screw 312 to rotate; the first-stage barrel 311 includes a front conveying section 314 and a rear conveying section 315, and a heater 5 is provided on the outer side of the rear conveying section 315; the second-stage injection mechanism 32 includes a second-stage barrel 321 communicating with the rear conveying section 315, a second-stage screw 322 located inside the second-stage barrel 321, a second-stage driving component 323 that drives the second-stage screw 322 to rotate, and an injection driving component 324 that drives the second-stage screw 322 to perform reciprocating injection molding motion; a heater 5 is provided on the outer side of the second-stage barrel 321, and the second-stage barrel 321 includes a compression section 325 and a metering section 326; the bottom surface of the screw groove of the second-stage screw 322 located in the compression section 325 adopts a wave-shaped structure;

[0073] The first-stage barrel 311 is located above the second-stage barrel 321. The screw head of the first-stage screw 312 faces the outlet of the first-stage barrel 311. The outlet of the first-stage barrel 311 is connected to the inlet of the second-stage barrel 321. A nozzle 327 is fixedly connected to the outlet of the second-stage barrel 321 through a flange. The screw head of the second-stage screw 322 faces the nozzle 327. The metering section 326 is connected to the mold assembly 4 through the nozzle 327.

[0074] The pitch of the first-stage screw 312 located in the front conveying section 314 is less than the width of the fiber felt, and the gap between the tooth crest of the first-stage screw 312 and the first-stage material cylinder 311 located in the front conveying section 314 is less than the thickness of the fiber felt; through the connection between the first-stage driving component 313 and the first-stage screw 312, rotational power is transmitted to the first-stage screw 312, and the first-stage screw 312 can wind the fiber felt introduced by the felt feeding assembly 2 around the outer circumference of the first-stage screw 312 to realize the conveying of the fiber felt.

[0075] The pitch of the first-stage screw 312 located in the rear conveying section 315 is not less than the width of the fiber felt. The gap between the tooth crest of the first-stage screw 312 and the first-stage barrel 311 located in the rear conveying section 315 is smaller than the gap between the tooth crest of the first-stage screw 312 and the first-stage barrel 311 located in the front conveying section 314. Upon entering the rear conveying section 315, the fiber felt falls into the screw groove, and the heater 5 pre-plasticizes the fiber felt during conveying.

[0076] The first-stage screw 312 accounts for 20-40% of the length in the front conveying section 314, and 60-80% of the length in the rear conveying section 315. The front conveying section 314 and the rear conveying section 315 realize the conveying, pushing and preheating of the fiber felt. In the rear conveying section 315, it is necessary to ensure that the thermoplastic resin long fibers in the fiber felt can be heated to the melting point.

[0077] Specifically, the first-stage screw 312 accounts for 20-40% of the length of the front conveying section 314, and 60-80% of the length of the rear conveying section 315. The front conveying section 314 and the rear conveying section 315 realize the conveying, pushing and preheating of the fiber felt. In the rear conveying section 315, it is necessary to ensure that the thermoplastic resin long fibers in the fiber felt can be heated to the melting point. For crystalline thermoplastic resin long fibers, the rear conveying section 315 can be longer, followed by non-crystalline thermoplastic resin long fibers. When the thermoplastic resin long fibers are heat-sensitive materials, the length of the rear conveying section 315 is set to the shortest.

[0078] The ratio of the total length of the first-order screw 312 in the front conveying section 314 and the rear conveying section 315, the length of the second-order screw 322 in the compression section 325, and the length of the second-order screw 322 in the metering section 326 is (20-50%): (25-60%): (10-30%).

[0079] Compression section 325 mixes, compresses, and pressurizes the thermoplastic resin material to remove fumes. The raw materials passing through this section are almost completely melted.

[0080] Specifically, when the thermoplastic resin long fibers are made of polycarbonate or rigid polyvinyl chloride, the length of the second-stage screw 322 in the compression section 325 accounts for 25-40% of the total working length of the second-stage screw 322; when the thermoplastic resin long fibers are made of polyetheretherketone or polyphenylene sulfide (high viscosity, low conductivity, high additives, etc., thermoplastic materials), the length of the second-stage screw 322 in the compression section 325 accounts for 40-60% of the total working length of the second-stage screw 322.

[0081] When the thermoplastic resin long fiber is a heat-sensitive material, the length of the second-stage screw 322 in the metering section 326 accounts for 10-20% of the total working length of the second-stage screw 322; when the thermoplastic resin long fiber is not a heat-sensitive material, the length of the second-stage screw 322 in the metering section 326 accounts for 20-25% of the total working length of the second-stage screw 322.

[0082] Specifically, such as Figure 7 As shown, the radius of the rounded corners of the wave structure in the spiral groove is not less than 0.5mm, and the amplitude of the wave structure is 1 / 6 to 1 / 3 of the maximum depth of the spiral groove (the amplitude of each wave structure is calculated based on the maximum depth of the spiral groove in the next wavelength); the wavelength of the wave structure is 0.5 to 2.5 times the lead; if there are sharp corners in the recessed area of ​​the wave structure, it will form a dead corner for the material, and the fibers will accumulate in the dead corner, which will lead to more serious local agglomeration. Therefore, a high-quality wave design needs to make a "rounded corner transition" (the radius of the rounded corner between the bottom of the recess and the edge of the protrusion is ≥0.5mm) to avoid dead corners.

[0083] Preferably, when the length of the aramid long fibers in the fiber felt is 30mm-40mm, the amplitude of the wave structure is 1 / 6 to 1 / 4 of the maximum depth of the spiral groove; the wavelength of the wave structure is 1.5 to 2.5 times the lead. When the length of the aramid long fibers in the fiber felt is 40mm or more, the amplitude of the wave structure is 1 / 4 to 1 / 3 of the maximum depth of the spiral groove; the wavelength of the wave structure is 0.5 to 1.5 times the lead.

[0084] From the inlet to the outlet direction of the second-stage barrel 321, the screw channel volume of the second-stage screw 322 in the compression section 325 gradually decreases. In the compression section 325, the thermoplastic resin gradually melts, and the screw channel volume decreases accordingly (achieved by gradually shallowing the screw channel depth) to correspond to the decrease in the geometric volume of the thermoplastic resin; otherwise, the material would not be compacted, heat transfer would be slow, and venting would be poor.

[0085] Preferably, the screw channel volume of the second-stage screw 322 in the compression section 325 gradually decreases according to the following principle: the melting difficulty, thermal stability, and viscosity characteristics of the resin directly determine whether a "slow gradual change" or a "rapid gradual change" is needed. This is the primary consideration in designing the speed of screw channel volume change. For refractory resins (high melting temperature / slow melting rate): the screw channel volume needs to change slowly. For heat-sensitive resins (easily thermally decomposed): the screw channel volume needs to change slowly. For high-viscosity resins (poor melt flowability): the screw channel volume needs to change slowly. Furthermore, for high compression ratios and large aspect ratios, the screw channel volume tends to change slowly; for low compression ratios and small aspect ratios, the screw channel volume tends to change rapidly.

[0086] The present invention also discloses an aramid long fiber reinforced thermoplastic resin-based composite material, which is prepared according to the preparation method described in the present invention.

[0087] Example 1

[0088] A method for preparing an aramid long fiber reinforced thermoplastic resin-based composite material:

[0089] S1. Preparation of blended yarn strips:

[0090] Using a textile industry cleaning and combing equipment, 51mm long aramid fibers (para-aramid fibers, denier 1.5D) and 51mm long PPS fibers (denier 2D, purchased from Guangzhou Longta Chemical Fiber) are blended at a mass ratio of 40:60.

[0091] The carding and combing equipment sequentially performs the following processes: In the carding machine, the fiber raw material is opened by a beater; the carding machine uses the carding cloth of the cylinder and the flats to fully mix the aramid long fibers and thermoplastic resin long fibers, with the cylinder speed at 330 r / min, the secondary roller speed at 700 r / min, and the doffer speed at 5 r / min; the drawing frame combines and drafts eight slivers, with a total draft ratio of 8.5 times and a back zone draft ratio of 1.2 times, forming a uniform blended yarn. The linear density of this yarn is controlled at 3000 tex, and the breaking strength is ≥15 cN / tex.

[0092] S2. Preparation of fiber felt:

[0093] The blended yarn is fed into the airflow dispersion chamber and the preheating chamber in sequence through the conveying guide roller and the spiral pushing mechanism. The spiral pushing mechanism conveys the blended yarn to the airflow dispersion chamber at a uniform speed of 20 r / min. In the airflow dispersion chamber, compressed air of 0.3 MPa is used to break the yarn into single fibers under the impact of the airflow to obtain fiber mat (the width of the fiber mat is 50 mm). The preheating chamber raises the fiber temperature to 160℃.

[0094] S3, Melt Mixing and Injection Molding:

[0095] The fiber felt is sequentially fed into the first-stage pre-plasticizing mechanism and the second-stage injection mechanism for conveying and melting, and then enters the mold assembly for injection molding;

[0096] The first-stage pre-plasticizing mechanism and the second-stage injection mechanism are respectively equipped with a first-stage screw and a second-stage screw; the fiber felt first enters the rear conveying section through the front conveying section of the first-stage pre-plasticizing mechanism, where it is preheated and melted, and then enters the compression section of the second-stage injection mechanism, where it is mixed, compressed and pressurized to exhaust air, and then enters the metering section to be mixed evenly before injection molding.

[0097] The length-to-diameter ratio of the first-order screw and the second-order screw is 24:1, and the compression ratio of the fiber felt raw material in the injection molding equipment is 2.5:1.

[0098] The first-order screw accounts for 25% of the length in the front conveying section and 75% of the length in the rear conveying section.

[0099] The ratio of the total length of the first-order screw in the front conveying section and the rear conveying section, the length of the second-order screw in the compression section, and the length of the second-order screw in the metering section is 30%:50%:20%.

[0100] Front conveyor section: transports the fiber felt to the rear conveyor section;

[0101] Rear conveying section: The temperature rises to 310℃, and the thermoplastic resin melts and impregnates the aramid filament fiber through shearing and conduction; from the beginning of the front conveying section to the end of the rear conveying section, the pitch of the first-order screw changes from 25mm to 50mm.

[0102] Compression section: Temperature maintained at 320℃, mixing residence time approximately 45s; screw diameter 50mm, groove depth gradually decreasing from 7.5mm to 3.0mm; the amplitude of the groove wave structure is 1 / 3 of the maximum groove depth (the amplitude of each wave structure is calculated based on the maximum groove depth within the next wavelength); the wavelength of the wave structure is 1.0 times the lead.

[0103] Metering section: The temperature is maintained at the same level as the compression section, the pitch is 50mm, the conveying is stable, and the melt pressure is established.

[0104] During injection molding, the uniformly mixed material is injected into the mold assembly, and the molding parameters are set as follows:

[0105] Injection pressure: 160MPa;

[0106] Pressure holding pressure: 80MPa, pressure holding time: 20s;

[0107] Mold temperature: 80℃;

[0108] Cooldown time: 30 seconds.

[0109] Example 2

[0110] A method for preparing an aramid long fiber reinforced thermoplastic resin-based composite material:

[0111] S1. Preparation of blended yarn strips:

[0112] Using a textile industry cleaning and combing equipment, 51mm long aramid fibers (para-aramid fibers, denier 1.5D) and 51mm long PA6 fibers (denier 2D, purchased from Guangzhou Longta Chemical Fiber) are blended at a mass ratio of 40:60.

[0113] The carding and combing equipment sequentially performs the following processes: In the carding machine, the fiber raw material is opened by a beater; the carding machine uses the carding cloth of the cylinder and the flats to fully mix the aramid long fibers and thermoplastic resin long fibers, with the cylinder speed at 350 r / min, the secondary roller speed at 750 r / min, and the doffer speed at 7 r / min; the drawing frame combines and drafts up to 6 slivers, with a total draft ratio of 8 times and a back zone draft ratio of 1.1 times, forming a uniform blended yarn. The linear density of this yarn is controlled at 3000 tex, and the breaking strength is ≥15 cN / tex.

[0114] S2. Preparation of fiber felt:

[0115] The blended yarn is fed into the airflow dispersion chamber and the preheating chamber in sequence through the conveying guide roller and the spiral pushing mechanism. The spiral pushing mechanism conveys the blended yarn to the airflow dispersion chamber at a uniform speed of 20 r / min. In the airflow dispersion chamber, compressed air of 0.2 MPa is used to break the yarn into single fibers under the impact of the airflow to obtain fiber mat (the width of the fiber mat is 50 mm). The preheating chamber raises the fiber temperature to 110℃.

[0116] S3, Melt Mixing and Injection Molding:

[0117] The fiber felt is sequentially fed into the first-stage pre-plasticizing mechanism and the second-stage injection mechanism for conveying and melting, and then enters the mold assembly for injection molding;

[0118] The first-stage pre-plasticizing mechanism and the second-stage injection mechanism are respectively equipped with a first-stage screw and a second-stage screw; the fiber felt first enters the rear conveying section through the front conveying section of the first-stage pre-plasticizing mechanism, where it is preheated and melted, and then enters the compression section of the second-stage injection mechanism, where it is mixed, compressed and pressurized to exhaust air, and then enters the metering section to be mixed evenly before injection molding.

[0119] The length-to-diameter ratio of the first-order screw and the second-order screw is 24:1, and the compression ratio of the fiber felt raw material in the injection molding equipment is 2.5:1.

[0120] The first-order screw accounts for 30% of the length in the front conveying section and 70% of the length in the rear conveying section.

[0121] The ratio of the total length of the first-order screw in the front conveying section and the rear conveying section, the length of the second-order screw in the compression section, and the length of the second-order screw in the metering section is 50%:30%:20%.

[0122] Front conveyor section: transports the fiber felt to the rear conveyor section;

[0123] Rear conveying section: The temperature rises to 240℃, and the thermoplastic resin melts and impregnates the aramid filament fiber through shearing and conduction; from the beginning of the front conveying section to the end of the rear conveying section, the pitch of the first-stage screw changes from 25mm to 50mm.

[0124] Compression section: Temperature maintained at 250℃, mixing residence time approximately 45s; screw diameter 50mm, groove depth gradually decreasing from 7.5mm to 3.0mm; the amplitude of the groove wave structure is 1 / 3 of the maximum groove depth (the amplitude of each wave structure is calculated based on the maximum groove depth within the next wavelength); the wavelength of the wave structure is 1.0 times the lead.

[0125] Metering section: The temperature is kept consistent with that of the compression section, the pitch is 50mm, the feed is stable, and the melt pressure is established.

[0126] During injection molding, the uniformly mixed material is injected into the mold assembly, and the molding parameters are set as follows:

[0127] Injection pressure: 140 MPa;

[0128] Pressure holding pressure: 80MPa, pressure holding time: 20s;

[0129] Mold temperature: 80℃;

[0130] Cooldown time: 30 seconds.

[0131] Example 3

[0132] A method for preparing an aramid long fiber reinforced thermoplastic resin-based composite material:

[0133] S1. Preparation of blended yarn strips:

[0134] Using a textile industry cleaning and combing equipment, 51mm long aramid fibers (para-aramid fibers, denier 1.5D) and 51mm long PP fibers (denier 2D, purchased from Guangzhou Longta Chemical Fiber) are blended at a mass ratio of 40:60.

[0135] The carding and combing equipment sequentially performs the following processes: In the carding machine, the fiber raw material is opened by a beater; the carding machine uses the carding cloth of the cylinder and the flats to fully mix the aramid long fibers and thermoplastic resin long fibers, with the cylinder speed at 450 r / min, the secondary roller speed at 800 r / min, and the doffer speed at 10 r / min; the drawing frame combines and drafts eight slivers, with a total draft ratio of 9 times and a back zone draft ratio of 1.5 times, forming a uniform blended yarn. The linear density of this yarn is controlled at 3000 tex, and the breaking strength is ≥15 cN / tex.

[0136] S2. Preparation of fiber felt:

[0137] The blended yarn is fed into the airflow dispersion chamber and the preheating chamber in sequence through the conveying guide roller and the spiral pushing mechanism. The spiral pushing mechanism conveys the blended yarn to the airflow dispersion chamber at a uniform speed of 20 r / min. In the airflow dispersion chamber, compressed air of 0.1 MPa is used to break the yarn into single fibers under the impact of the airflow to obtain fiber mat (the width of the fiber mat is 50 mm). The preheating chamber raises the fiber temperature to 80℃.

[0138] S3, Melt Mixing and Injection Molding:

[0139] The fiber felt is sequentially fed into the first-stage pre-plasticizing mechanism and the second-stage injection mechanism for conveying and melting, and then enters the mold assembly for injection molding;

[0140] The first-stage pre-plasticizing mechanism and the second-stage injection mechanism are respectively equipped with a first-stage screw and a second-stage screw; the fiber felt first enters the rear conveying section through the front conveying section of the first-stage pre-plasticizing mechanism, where it is preheated and melted, and then enters the compression section of the second-stage injection mechanism, where it is mixed, compressed and pressurized to exhaust air, and then enters the metering section to be mixed evenly before injection molding.

[0141] The length-to-diameter ratio of the first-order screw and the second-order screw is 24:1, and the compression ratio of the fiber felt raw material in the injection molding equipment is 2.5:1.

[0142] The first-order screw accounts for 30% of the length in the front conveying section and 70% of the length in the rear conveying section.

[0143] The ratio of the total length of the first-order screw in the front conveying section and the rear conveying section, the length of the second-order screw in the compression section, and the length of the second-order screw in the metering section is 40%:40%:20%.

[0144] Front conveyor section: transports the fiber felt to the rear conveyor section;

[0145] Rear conveying section: The temperature rises to 210℃, and the thermoplastic resin melts and impregnates the aramid filament fibers through shearing and conduction; from the beginning of the front conveying section to the end of the rear conveying section, the pitch of the first-order screw changes from 25mm to 50mm.

[0146] Compression section: Temperature maintained at 230℃, mixing residence time approximately 45s; screw diameter 50mm, groove depth gradually decreasing from 7.5mm to 3.0mm; the amplitude of the groove wave structure is 1 / 3 of the maximum groove depth (the amplitude of each wave structure is calculated based on the maximum groove depth within the next wavelength); the wavelength of the wave structure is 1.0 times the lead.

[0147] Metering section: The temperature is maintained at the same level as the compression section, the pitch is 50mm, the conveying is stable, and the melt pressure is established.

[0148] During injection molding, the uniformly mixed material is injected into the mold assembly, and the molding parameters are set as follows:

[0149] Injection pressure: 120MPa;

[0150] Pressure holding pressure: 80MPa, pressure holding time: 20s;

[0151] Mold temperature: 80℃;

[0152] Cooldown time: 30 seconds.

[0153] Example 4

[0154] A method for preparing an aramid long fiber reinforced thermoplastic resin-based composite material:

[0155] S1. Preparation of blended yarn strips:

[0156] Using a textile industry cleaning and combing equipment, 80mm long aramid fibers (para-aramid fibers, denier 1.5D) and 80mm long polyamide 66 fibers (denier 2D, purchased from Guangzhou Longta Chemical Fiber) are blended at a mass ratio of 10:90.

[0157] The carding and combing equipment sequentially performs the following processes: In the carding machine, the fiber raw material is opened by a beater; the carding machine uses the carding cloth of the cylinder and the flats to fully mix the aramid long fibers and thermoplastic resin long fibers, with the cylinder speed at 300 r / min, the secondary roller speed at 700 r / min, and the doffer speed at 5 r / min; the drawing frame combines up to 7 slivers and drafts them, with a total draft ratio of 10 and a back zone draft ratio of 1.5, forming a uniform blended yarn. The linear density of this yarn is controlled at 3000 tex, and the breaking strength is ≥15 cN / tex.

[0158] S2. Preparation of fiber felt:

[0159] The blended yarn is fed into the airflow dispersion chamber and the preheating chamber in sequence through the conveying guide roller and the spiral pushing mechanism. The spiral pushing mechanism conveys the blended yarn to the airflow dispersion chamber at a uniform speed of 20 r / min. In the airflow dispersion chamber, compressed air of 0.3 MPa is used to break the yarn into single fibers under the impact of the airflow to obtain fiber mat (the width of the fiber mat is 50 mm). The preheating chamber raises the fiber temperature to 90℃.

[0160] S3, Melt Mixing and Injection Molding:

[0161] The fiber felt is sequentially fed into the first-stage pre-plasticizing mechanism and the second-stage injection mechanism for conveying and melting, and then enters the mold assembly for injection molding;

[0162] The first-stage pre-plasticizing mechanism and the second-stage injection mechanism are respectively equipped with a first-stage screw and a second-stage screw; the fiber felt first enters the rear conveying section through the front conveying section of the first-stage pre-plasticizing mechanism, where it is preheated and melted, and then enters the compression section of the second-stage injection mechanism, where it is mixed, compressed and pressurized to exhaust air, and then enters the metering section to be mixed evenly before injection molding.

[0163] The length-to-diameter ratio of the first-order screw and the second-order screw is 24:1, and the compression ratio of the fiber felt raw material in the injection molding equipment is 2.5:1.

[0164] The first-order screw accounts for 40% of the length in the front conveying section and 60% of the length in the rear conveying section.

[0165] The ratio of the total length of the first-order screw in the front conveying section and the rear conveying section, the length of the second-order screw in the compression section, and the length of the second-order screw in the metering section is 50%:30%:20%.

[0166] Front conveyor section: transports the fiber felt to the rear conveyor section;

[0167] Rear conveying section: The temperature rises to 250℃, and the thermoplastic resin melts and impregnates the aramid filament fiber through shearing and conduction; from the beginning of the front conveying section to the end of the rear conveying section, the pitch of the first-stage screw changes from 25mm to 50mm.

[0168] Compression section: Temperature maintained at 260℃, mixing residence time approximately 45s; screw diameter 50mm, groove depth gradually decreasing from 7.5mm to 3.0mm; the amplitude of the groove wave structure is 1 / 3 of the maximum groove depth (the amplitude of each wave structure is calculated based on the maximum groove depth within the next wavelength); the wavelength of the wave structure is 0.5 times the lead.

[0169] Metering section: The temperature is kept consistent with that of the compression section, the pitch is 50mm, the feed is stable, and the melt pressure is established.

[0170] During injection molding, the uniformly mixed material is injected into the mold assembly, and the molding parameters are set as follows:

[0171] Injection pressure: 140 MPa;

[0172] Pressure holding pressure: 80MPa, pressure holding time: 20s;

[0173] Mold temperature: 80℃;

[0174] Cooldown time: 30 seconds.

[0175] Example 5

[0176] A method for preparing an aramid long fiber reinforced thermoplastic resin-based composite material:

[0177] S1. Preparation of blended yarn strips:

[0178] Using a textile industry cleaning and combing equipment, 38mm long aramid fibers (para-aramid fibers, denier 1.5D) and 38mm long PPS fibers (denier 2D, purchased from Guangzhou Longta Chemical Fiber) are blended at a mass ratio of 30:70.

[0179] The carding and combing equipment sequentially performs the following processes: In the carding machine, the fiber raw material is opened by a beater; the carding machine uses the carding cloth of the cylinder and the flats to fully mix the aramid long fibers and thermoplastic resin long fibers, with the cylinder speed at 330 r / min, the secondary roller speed at 700 r / min, and the doffer speed at 5 r / min; the drawing frame combines and drafts eight slivers, with a total draft ratio of 8.5 times and a back zone draft ratio of 1.2 times, forming a uniform blended yarn. The linear density of this yarn is controlled at 3000 tex, and the breaking strength is ≥15 cN / tex.

[0180] S2. Preparation of fiber felt:

[0181] The blended yarn is fed into the airflow dispersion chamber and the preheating chamber in sequence through the conveying guide roller and the spiral pushing mechanism. The spiral pushing mechanism conveys the blended yarn to the airflow dispersion chamber at a uniform speed of 20 r / min. In the airflow dispersion chamber, compressed air of 0.3 MPa is used to break the yarn into single fibers under the impact of the airflow to obtain fiber mat (the width of the fiber mat is 50 mm). The preheating chamber raises the fiber temperature to 160℃.

[0182] S3, Melt Mixing and Injection Molding:

[0183] The fiber felt is sequentially fed into the first-stage pre-plasticizing mechanism and the second-stage injection mechanism for conveying and melting, and then enters the mold assembly for injection molding;

[0184] The first-stage pre-plasticizing mechanism and the second-stage injection mechanism are respectively equipped with a first-stage screw and a second-stage screw; the fiber felt first enters the rear conveying section through the front conveying section of the first-stage pre-plasticizing mechanism, where it is preheated and melted, and then enters the compression section of the second-stage injection mechanism, where it is mixed, compressed and pressurized to exhaust air, and then enters the metering section to be mixed evenly before injection molding.

[0185] The length-to-diameter ratio of the first-order screw and the second-order screw is 24:1, and the compression ratio of the fiber felt raw material in the injection molding equipment is 2.5:1.

[0186] The first-order screw accounts for 30% of the length in the front conveying section and 70% of the length in the rear conveying section.

[0187] The ratio of the total length of the first-order screw in the front conveying section and the rear conveying section, the length of the second-order screw in the compression section, and the length of the second-order screw in the metering section is 35%:45%:20%.

[0188] Front conveyor section: transports the fiber felt to the rear conveyor section;

[0189] Rear conveying section: The temperature rises to 310℃, and the thermoplastic resin melts and impregnates the aramid filament fiber through shearing and conduction; from the beginning of the front conveying section to the end of the rear conveying section, the pitch of the first-order screw changes from 25mm to 50mm.

[0190] Compression section: Temperature maintained at 320℃, mixing residence time approximately 45s; screw diameter 50mm, groove depth gradually decreasing from 7.5mm to 3.0mm; the amplitude of the groove wave structure is 1 / 6 of the maximum groove depth (the amplitude of each wave structure is calculated based on the maximum groove depth within the next wavelength); the wavelength of the wave structure is 2.5 times the lead.

[0191] Metering section: The temperature is maintained at the same level as the compression section, the pitch is 50mm, the conveying is stable, and the melt pressure is established.

[0192] During injection molding, the uniformly mixed material is injected into the mold assembly, and the molding parameters are set as follows:

[0193] Injection pressure: 160MPa;

[0194] Pressure holding pressure: 80MPa, pressure holding time: 20s;

[0195] Mold temperature: 80℃;

[0196] Cooldown time: 30 seconds.

[0197] Comparative Example 1

[0198] The composite material was prepared using the same method as in Example 1, except that the length of the aramid fiber in Comparative Example 1 was 20 mm and the length of the PPS fiber was 20 mm (i.e., the fiber length was lower than the fiber length defined in this invention). Other process conditions were the same as in Example 1.

[0199] Comparative Example 2

[0200] The composite material was prepared using the same method as in Example 1, except that the cylinder speed and doffer speed were reduced in Comparative Example 2. The cylinder speed was 264 r / min and the doffer speed was 4 r / min (i.e., the cylinder-doffer speed ratio was kept the same as in Example 1, but the cylinder speed and doffer speed were reduced). Other process conditions were the same as in Example 1.

[0201] Comparative Example 3

[0202] The composite material was prepared using the same method as in Example 1, except that the cylinder speed and doffer speed were increased in Comparative Example 3. The cylinder speed was 528 r / min and the doffer speed was 8 r / min (i.e., the cylinder-doffer speed ratio was kept the same as in Example 1, only the cylinder speed and doffer speed were increased). Other process conditions were the same as in Example 1.

[0203] Comparative Example 4

[0204] The composite material was prepared using the same method as in Example 1, except that no preheating treatment was performed in step S2 of Comparative Example 4, and the other process conditions were the same as in Example 1.

[0205] Comparative Example 5

[0206] The composite material was prepared using the same method as in Example 1, except that the preheating temperature was increased in step S2 of Comparative Example 5, and the preheating temperature of Comparative Example 4 was 180°C (higher than the temperature range defined in this invention). Other process conditions were the same as in Example 1.

[0207] Comparative Example 6

[0208] The composite material was prepared using the same method as in Example 1, except that the bottom surface of the screw groove of the second-order screw in the compression section of Comparative Example 6 was a smooth screw groove (not a wavy structure), and the other process conditions were the same as in Example 1.

[0209] Comparative Example 7

[0210] The composite material was prepared using the same method as in Example 1, except that: in this Comparative Example 7, the lengths of the first-stage screw and the first-stage barrel were increased, and a compression section with the same proportional length as in Example 1 was placed in the first-stage barrel; only the metering section was retained in the second-stage barrel, and other process conditions were the same as in Example 1.

[0211] Comparative Example 8

[0212] The composite material was prepared using the same method as in Example 1, except that the length ratio of the compression section was shortened in Comparative Example 8, and the ratio of the total length of the first-order screw in the front conveying section and the rear conveying section, the length of the second-order screw in the compression section, and the length of the second-order screw in the metering section in Comparative Example 8 was 50%:20%:30%. Other process conditions were the same as in Example 1.

[0213] Comparative Example 9

[0214] The composite material was prepared using the same method as in Example 1, except that: the length ratio of the extended compression section in Comparative Example 9, the ratio of the total length of the first-order screw in the front conveying section and the rear conveying section, the length of the second-order screw in the compression section, and the length of the second-order screw in the metering section in Comparative Example 9 were 20%:70%:10%, and other process conditions were the same as in Example 1.

[0215] Comparative Example 10

[0216] The composite material was prepared using traditional short fiber reinforced PA6. The specific preparation process is as follows:

[0217] Aramid short fibers (6 mm long, denier 1.5 D) and PA66 granules were blended and extruded using a twin-screw extruder at a temperature of 260℃. The blended granules were then injection molded in an injection molding machine to obtain the corresponding samples.

[0218] All composite materials used in the above embodiments and comparative examples were injection molded into samples with the same structural dimensions. The tensile sample dimensions were based on GB / T 1040.3-2022, and the bending sample dimensions were based on GB / T 9341-2008. Performance tests were performed on these injection-molded samples, and the specific test results are shown in Table 1 below. The test methods involved were in accordance with ISO 527 standard.

[0219] Table 1 Performance Test Results

[0220]

[0221] The experimental data above show that the aramid long fiber reinforced thermoplastic resin matrix composites prepared by the preparation method described in Examples 1-5 have superior tensile strength and flexural modulus properties. Moreover, through improvements in process conditions and equipment structure, mass production of aramid long fiber reinforced thermoplastic resin matrix composites by injection molding can be achieved, with improved production efficiency and reduced costs compared to continuous fiber composites. In terms of performance balance, the appropriate length of the long fibers avoids the problems of short fiber agglomeration and interlaminar defects in continuous fibers, thereby improving the interlaminar shear strength of the composite material and effectively expanding the application boundaries of the composite material.

[0222] A comparison of the data from Comparative Example 1 and Example 1 shows that if the fiber length is lower than the fiber length specified in this invention, the mechanical properties of the prepared long fiber plastic will be reduced because the reinforcing fiber length is reduced, thus weakening the reinforcing effect on the material.

[0223] A comparison of the data from Comparative Example 2 and Example 1 shows that reducing the cylinder speed and doffer speed reduces the mechanical properties of the prepared long fiber plastic because the fiber dispersion is affected, resulting in uneven dispersion.

[0224] A comparison of the data from Comparative Example 3 and Example 1 shows that if the cylinder rotation speed is increased, the mechanical properties of the prepared long fiber plastic are affected, resulting in uneven dispersion.

[0225] The data comparison between Comparative Example 4 and Example 1 shows that if the preheating treatment is not performed in step S2, the impact on the mechanical properties of long fiber plastics is relatively low, because the fiber dispersion may be uneven during the blending stage.

[0226] The data comparison between Comparative Example 5 and Example 1 shows that if the preheating temperature in step S2 is too high, the impact on the mechanical properties of long fiber plastics will be low, because it may cause uneven fiber dispersion during the blending stage.

[0227] The data comparison between Comparative Example 6 and Example 1 shows that if the bottom surface of the screw groove of the second-order screw in the compression section is a smooth screw groove (not a wavy structure), the mechanical properties of the prepared long fiber plastic will be reduced because the smooth screw groove leads to uneven fiber dispersion and easy agglomeration.

[0228] The data comparison between Comparative Example 7 and Example 1 shows that if the compression section is set in the first-stage barrel and only the metering section is retained in the second-stage barrel, the mechanical properties of the prepared long-fiber plastic will be reduced because it will cause uneven fiber dispersion and easy agglomeration. At the same time, it will reduce the retention length of the fiber in the final part and affect the reinforcement effect of the composite material.

[0229] A comparison of the data from Comparative Example 8 and Example 1 shows that shortening the length ratio of the compression section reduces the mechanical properties of the prepared long-fiber plastic because it leads to uneven fiber dispersion and easy agglomeration.

[0230] A comparison of the data from Comparative Example 9 and Example 1 shows that if the length ratio of the compression section is extended, the mechanical properties of the prepared long-fiber plastic are reduced because the retention length of the fiber in the final part is reduced, which affects the reinforcement effect of the composite material.

[0231] The data comparison between Comparative Example 10 and Example 2 shows that the composite material prepared by the preparation method of the present invention has significantly improved performance compared with traditional short fiber reinforced PA6. In actual production, it was found that the production efficiency of the preparation method of the present invention is 12 times higher than that of continuous fiber composite material, and the unit cost is reduced by 48%.

[0232] The features can be combined in any way. For the sake of brevity, not all possible combinations of the various technical features in the above embodiments are exhaustively listed. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0233] For those skilled in the art, various modifications and improvements can be made without departing from the concept of the present invention, and these modifications and improvements are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the appended claims.

Claims

1. A method for preparing an aramid long fiber reinforced thermoplastic resin-based composite material, characterized in that, The preparation method is as follows: S1. Preparation of blended yarn strips: Aramid long fibers and thermoplastic resin long fibers are blended to obtain uniform blended yarns. S2. Preparation of fiber felt: Blended yarns are dispersed by airflow and preheated to obtain fiber mats; S3, Melt Mixing and Injection Molding: The fiber felt is sequentially fed into the first-stage pre-plasticizing mechanism and the second-stage injection mechanism for conveying and melting, and then enters the mold assembly for injection molding; The first-stage pre-plasticizing mechanism and the second-stage injection mechanism are each equipped with a screw; the fiber felt first enters the rear conveying section through the front conveying section of the first-stage pre-plasticizing mechanism, where it is preheated and melted, and then enters the compression section of the second-stage injection mechanism, where it is mixed, compressed and pressurized to exhaust air, and then enters the metering section to be mixed evenly before being injection molded. The first-stage pre-plasticizing mechanism includes a first-stage barrel, a first-stage screw located inside the first-stage barrel, and a drive component for driving the first-stage screw to rotate; the first-stage barrel includes a front conveying section and a rear conveying section, and a heater is provided on the outer side of the rear conveying section; the second-stage injection mechanism includes a second-stage barrel communicating with the rear conveying section, a second-stage screw located inside the second-stage barrel, a drive component for driving the second-stage screw to rotate, and a drive component for driving the second-stage screw to perform reciprocating injection molding motion; a heater is provided on the outer side of the second-stage barrel, and the second-stage barrel includes a compression section and a metering section; the bottom surface of the screw groove of the second-stage screw located in the compression section adopts a wave-shaped structure; The pitch of the first-stage screw located in the front conveying section is less than the width of the fiber felt, and the gap between the tooth crest of the first-stage screw and the first-stage barrel located in the front conveying section is less than the thickness of the fiber felt. The pitch of the first-stage screw located in the rear conveying section is not less than the width of the fiber felt, and the gap between the tooth crest of the first-stage screw located in the rear conveying section and the first-stage barrel is less than the gap between the tooth crest of the first-stage screw located in the front conveying section and the first-stage barrel.

2. The method for preparing an aramid long fiber reinforced thermoplastic resin matrix composite material according to claim 1, characterized in that, The aramid long fiber is a crimped aramid long fiber with a length of 30 mm to 80 mm; the thermoplastic resin long fiber is a crimped long fiber with a length of 30 mm to 80 mm. The total weight of the aramid long fiber and the thermoplastic resin long fiber is calculated as 100, and the weight ratio of the aramid long fiber and the thermoplastic resin long fiber is (10-40):(60-90).

3. The method for preparing an aramid long fiber reinforced thermoplastic resin matrix composite material according to claim 1, characterized in that, The thermoplastic resin long fiber is at least one of polyamide 66 long fiber, polyamide 6 long fiber, polypropylene long fiber, polyphenylene sulfide long fiber, and polyethylene long fiber.

4. The method for preparing an aramid long fiber reinforced thermoplastic resin-based composite material according to claim 1, characterized in that, In step S1, a combined cleaning and carding machine is used for blending, sequentially passing through the cleaning, carding, and drawing processes. In the cleaning machine, the fiber raw material is opened; the carding machine uses the carding cloth of the cylinder and the cardboard to fully mix the aramid long fibers and thermoplastic resin long fibers. The cylinder speed is 300-450 r / min, the secondary roller speed is 700-800 r / min, and the doffer speed is 5-20 r / min; the drawing frame combines 6-8 slivers and drafts them together, with a total draft ratio of 6-10 times and a back zone draft ratio of 11.5 times, forming a uniform blended yarn sliver. The linear density of the blended yarn is 2800-3200 tex, and the breaking strength is ≥15 cN / tex.

5. The method for preparing an aramid long fiber reinforced thermoplastic resin-based composite material according to claim 1, characterized in that, In step S2, the blended yarn is dispersed by airflow in an airflow dispersion chamber, and the gas pressure introduced into the airflow dispersion chamber is 0.1-0.3 MPa. The temperature conditions for the preheating treatment are 80-160℃.

6. The method for preparing an aramid long fiber reinforced thermoplastic resin matrix composite material according to claim 1, characterized in that, The length of the first-order screw in the front conveying section accounts for 20-40%, and the length of the first-order screw in the rear conveying section accounts for 60-80%. The ratio of the total length of the first-order screw in the front conveying section and the rear conveying section, the length of the second-order screw in the compression section, and the length of the second-order screw in the metering section is (20-50%): (25-60%): (10-30%).

7. The method for preparing an aramid long fiber reinforced thermoplastic resin matrix composite material according to claim 1, characterized in that, The radius of the fillet of the wave structure at the bottom of the spiral groove is not less than 0.5 mm, the amplitude of the wave structure is 1 / 6 to 1 / 3 of the spiral groove depth, and the wavelength of the wave structure is 0.5 to 2.5 times the lead. From the inlet to the outlet direction of the second-stage barrel, the screw groove volume of the second-stage screw in the compression section gradually decreases; The groove depth of the second-order screw located in the metering section is (0.03-0.1)*D, where D is the diameter of the second-order screw.

8. An aramid long fiber reinforced thermoplastic resin-based composite material, characterized in that, The composite material is prepared according to the preparation method described in any one of claims 1-7.

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