A non-homogeneous LWRT fiber composite and a method of making the same

Abstract

The application discloses a kind of heterogeneous LWRT's fiber composite material and preparation method thereof, composite material overall structure is successively from top to bottom: auxiliary material layer, thermoplastic adhesive film layer, LWRT core layer, thermoplastic adhesive film layer and auxiliary material layer, LWRT core layer includes the high density area with density 0.5-0.9g / cm 3 And the low density area with density 0.1-0.5g / cm 3 The core material of the application can be differentiated according to the demand The effective width of the fiber web of the core material felt material can be dynamically adjusted, and the specific method is to realize it by changing the position of the laying cart of the laying machine. The heterogeneous composite board material has a bulk density range of 0.1-0.9g / cm 3 , which is about 2-3kg lighter than traditional vehicle injection molding materials. Lightweight, high strength and convenient molding are its main advantages. The core layer of the fiber composite board has a large number of three-dimensional cavities, which are interconnected and connected to the outside, which makes the porous sound-absorbing board have high sound absorption, high air permeability, and also has the functions of heat preservation, mildew prevention and moisture resistance.

Description

Technical Field

[0001] This invention belongs to the category of fiber composite panels for automotive interior and exterior parts, specifically, it relates to a heterogeneous LWRT fiber composite material and its preparation method. Background Technology

[0002] LWRT is short for Lightweight Reinforced Thermoplastic, a new type of GMT (Glass-Mat Reinforced Thermoplastic) material. LWRT is a composite material made from glass fiber and PP fiber through processes such as unpacking, carding, web formation, needle punching, and hot pressing. The surface is often covered with fabric or film. Compared to traditional GMT materials, LWRT composites can significantly reduce the weight and cost of components while improving sound resistance. At the same time, LWRT materials retain the characteristics of traditional GMT materials, such as high specific strength, low thermal conductivity, small dimensional change rate, and recyclability. Currently, this material is widely used in the manufacture of automotive underbody shielding devices, load-bearing plates, roof liners, door trims, roof racks, molded roof parts, engine hoods, and trunk lids.

[0003] The low-carbon development of the automotive industry plays a crucial role in achieving dual-carbon goals, making energy conservation and emission reduction a key development direction for the industry. Lightweighting is the most direct solution for energy conservation and emission reduction. LWRT, with its inherent three-dimensional network structure, offers significant advantages in terms of lightweight and high strength, giving it a prominent lightweight advantage among automotive materials. As the dual-carbon development trend advances, LWRT will undoubtedly play an increasingly important role in energy conservation and emission reduction in the automotive industry. Therefore, against this backdrop, based on traditional LWRT materials, we have developed a special heterogeneous LWRT composite material and manufacturing process. While ensuring that the performance of the finished product does not decrease, the overall weight of the new LWRT material is reduced by 20-30% compared to conventional LWRT. This is of great significance for improving the overall material utilization rate and reducing the weight of the final product, elevating the lightweight advantages of LWRT materials to a new level. Summary of the Invention

[0004] Because LWRT fiber composites are primarily composed of multi-layered, loosely interwoven fiber webs with numerous voids, their overall density is 40%-60% lower than that of traditional GMT materials. They also exhibit advantages in specific strength and specific modulus. However, LWRT materials still face certain challenges in application. For instance, significant waste occurs during molding, and the high density and overall hardness can lead to pin punctures or die-cutting failures. Furthermore, homogeneous LWRT molding can cause material thinning and cracking in deeper areas due to strong stretching. To address these shortcomings, this invention utilizes the route and frequency variations of the web-laying equipment during LWRT production to develop a heterogeneous LWRT fiber composite material and its preparation method. This method can address these issues by differentially increasing or decreasing the material density in specific areas.

[0005] This invention is achieved through the following technical solution:

[0006] This invention discloses a heterogeneous LWRT fiber composite material. The overall structure of the composite material, from top to bottom, consists of: an auxiliary layer, a thermoplastic film layer, an LWRT core layer, another thermoplastic film layer, and the auxiliary layer. The LWRT core layer comprises materials with a density of 0.5-0.9 g / cm³. 3 High-density areas with a density of 0.1-0.5 g / cm³ 3 Low-density areas.

[0007] As a further improvement, the core fiber of the LWRT core layer of the present invention is one or more of PP fiber, glass fiber, PA fiber, PE fiber, aramid fiber, cellulose fiber, and basalt fiber. The LWRT core layer has a structure in which high-density areas on both sides and low-density areas in the middle, or a high-density area in the middle and low-density areas on both sides, or a high-density area and low-density areas are arranged alternately. When it is a structure in which high-density areas and low-density areas are arranged alternately, the number of density difference areas is an odd number greater than 3.

[0008] As a further improvement, the auxiliary material of the auxiliary layer of the present invention is one or more of PET needle-punched fabric, PP needle-punched fabric, PP / PET needle-punched fabric, PES needle-punched fabric and PA needle-punched fabric, with 30-100 layers in the high-density area and 6-30 layers in the low-density area.

[0009] As a further improvement, the hot melt adhesive film layer of the present invention is composed of one or more of PP, PE, PES, EVA, EAA and PA.

[0010] This invention also discloses a method for preparing a heterogeneous LWRT fiber composite material, comprising the following steps: the required core fiber raw material undergoes opening, mixing, carding, web laying, and needle punching processes to obtain a felt material, which serves as the core material of the LWRT composite material.

[0011] During the netting process, the width ranges from 100 to 3300 mm, the number of netting layers ranges from 6 to 100, and the netting speed ranges from 0.5 to 200 m / min.

[0012] When preparing a density of 0.5-0.9 g / cm³ 3 When using high-density core material, the number of mesh layers is 30-100, and the mesh laying speed is 50-200m / min;

[0013] When preparing a density of 0.1-0.5 g / cm³ 3 When using low-density core materials, the number of mesh layers is 6-30, and the mesh laying speed is 0.5-50m / min.

[0014] As a further improvement, when preparing the high-density areas on both sides and the low-density area in the middle, the present invention has 3 density difference areas. The density change trend from left to right is high-low-high. The net laying trolley starts from the high-density edge area on one side, passes through the low-density middle area, and then moves to the high-density edge on the other side. When passing through the high-density edge area, the net laying trolley lays back and forth to increase the density. The number of laying times is 1-5 times, which is one cycle. In a single cycle, the number of net laying layers on the left and right edges is 1-5 more than the number of net laying layers in the middle. It takes 5-50 cycles to prepare the heterogeneous core layer.

[0015] As a further improvement, when preparing the high-density zone in the middle and the low-density zones on both sides, the present invention has three density difference regions. The density changes from left to right in a low-high-low trend. The net-laying trolley starts from the low-density edge region on one side, passes through the high-density zone in the middle, and then moves to the low-density edge on the other side. When passing through the high-density zone in the middle, the net-laying trolley lays the net back and forth to increase the density. The number of lays ranges from 1 to 5 times, which is one cycle. The number of net layers in the middle of a single cycle is 1 to 5 more than the number of net layers on the left and right edges. It takes 5 to 50 cycles to prepare a heterogeneous core layer.

[0016] As a further improvement, when the high-density and low-density areas are arranged alternately, the number of density difference areas is an odd number greater than or equal to 5. The route can be divided into two categories: the first category is low density on both sides and high density in the middle, alternating between low and high density; the second category is high density on both sides and low density in the middle, alternating between high and high density. In the first category, the density change trend from left to right is low-high-n*(low-high)-low. The overall direction of the net-laying trolley is as follows: starting from a low-density edge area on one side, after a certain distance, it reaches the first high-density area. The net-laying trolley moves back and forth to increase the number of net layers, then continues to move through the second low-density area and reaches the second high-density area. The trolley moves back and forth again, then moves to the third low-density area, and so on, until it enters the low-density edge area on the other side, which is one cycle. A single cycle of high density... The number of mesh layers in the high-density region is 1-5 layers higher than that in the low-density region. Preparing a heterogeneous core layer requires 5-50 cycles. In the second case, the density trend from left to right is high-low-n*(high-low)-high. The overall movement of the mesh-laying trolley is as follows: starting from a high-density edge region on one side, it begins to lay mesh back and forth, forming the first high-density region. After that, it moves through the first low-density region to the second high-density region, laying mesh back and forth. Then it continues moving, passing through the second low-density region to reach the third high-density region, laying mesh back and forth again, and so on, until it enters the high-density edge region on the other side, completing one cycle. In a single cycle, the number of mesh layers in the high-density region is 1-5 layers higher than that in the low-density region. Preparing a heterogeneous core layer requires 5-50 cycles. The range of n is: 30 ≥ n ≥ 1.

[0017] As a further improvement, the number of density difference regions described in this invention ranges from 2 to 33, and the specific density can be adjusted within the range of 0.1-0.9 g / cm³. 3 The density difference between high and low density areas ranges from 20% to 500%, the net laying speed varies from 0.5 to 200 m / min, and the net laying line is changed accordingly according to the program settings to change the density of the corresponding area.

[0018] As a further improvement, the areal density of the heterogeneous LWRT composite material described in this invention is controllable within the range of 300-3300 g / m³. 2 The thickness is controllable within the range of 1.0-10mm.

[0019] The beneficial effects of this invention are as follows:

[0020] 1. The density of localized areas in the heterogeneous composite board material of this invention can be adjusted according to requirements to address different application scenarios. High-density areas can handle product performance and more demanding applications, leveraging the superior overall performance resulting from high density to meet higher usage requirements. Low-density areas can handle product performance and areas with lower requirements, such as those requiring perforation or punching, which helps improve material forming efficiency, reduce mold wear, and avoid problems with material not being able to be punched through. Furthermore, for needle-feeding methods, the overall density of the needle-feeding area can be reduced to prevent the material from becoming too hard and unable to be needled due to excessive density. Simultaneously, targeted low-density designs can be implemented at specific locations to achieve overall material lightweighting and reduce costs to some extent. Compared to traditional LWRT materials, the non-uniform LWRT composite material, while maintaining overall uniform density, allows for regional variations in material weight, improving the material's flexibility and adjustability.

[0021] The key feature of this invention is that the core material's web width and route can be differentiated according to requirements. Compared with the fixed width of the core layer felt in ordinary LWRT materials, the effective width of the fiber web in the core material of this invention can be dynamically adjusted. Specifically, this is achieved by changing the position of the web-laying trolley of the web-laying machine. For example, if a 1500mm width material is needed, the web-laying trolley lays the fiber web back and forth within this width range. The overall deviation in the fiber web width can be ≤10mm. As the number of fiber web layers increases, until the total weight of the laid fiber web meets the requirements, the LWRT core material is obtained.

[0022] By changing the route of the web-laying trolley, the number of times the trolley swings back and forth at the desired density adjustment point can be increased or decreased, and the web-laying speed can be adjusted accordingly (the slower the web-laying speed, the less stretch the web receives, and the higher the weight of the web). This achieves the purpose of adjusting the material density. For example, to obtain a higher density material, the number of web-laying trolley repetitions at that location can be increased, and the web-laying speed can be appropriately reduced, thereby increasing the number of web layers and the weight of a single web layer, thus giving the material at that location a higher density. Conversely, the number of web layers can be reduced and the web-laying speed can be increased to obtain a lower density material. The heterogeneous fiber composite material is obtained by adapting the number of web layers and the speed of web laying to bring about changes in local material density. It can effectively address the problems encountered by homogeneous LWRT materials in the automotive field. Furthermore, the width and range of the density difference regions can be adjusted by controlling the web laying trolley's route and speed through the system program. The web laying width is controlled by the back-and-forth swing spacing of the web laying trolley, and the material density is controlled by the number of fiber web layers. The number, width, and corresponding density of density difference regions can be adjusted by the web laying speed and route of the web laying trolley, while the web laying route and speed of the web laying trolley are controlled by system programming.

[0023] 2. The heterogeneous composite board material of the present invention has a bulk density ranging from 0.1 to 0.9 g / cm³. 3 It is about 2-3 kg lighter than traditional automotive injection molding materials, and its main advantages are its light weight, high strength and easy molding.

[0024] 3. The fiber composite board of the present invention has a large number of three-dimensional cavities in the core layer, which are interconnected and connected to the outside world. This makes the porous sound-absorbing board not only have high sound absorption and high air permeability, but also heat preservation, mildew prevention and moisture prevention functions. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the structure of the LWRT composite material described in this invention;

[0026] Figure 2 This is a schematic diagram of the web-laying machine used in this invention;

[0027] Figure 3 This is a schematic diagram of the mesh laying route of the present invention, which is high density on both sides and low density in the middle;

[0028] Figure 4 This is a schematic diagram of the mesh laying route of the present invention, which features low density on both sides and high density in the middle.

[0029] Figure 1 In the middle, 1 is the auxiliary material layer, 2 is the hot melt adhesive film layer, and 3 is the LWRT core layer;

[0030] Figure 2 In the middle, 4 is the web laying trolley, which can control the route and speed of web laying through programming; 5 is the web storage platform, which plays the role of storing the fiber web and transporting it to the next process. Detailed Implementation

[0031] This invention discloses a heterogeneous LWRT fiber composite material and its preparation method. Figure 1 This is a schematic diagram of the structure of the product of the present invention. Figure 2 This is a schematic diagram of the key equipment of this invention—the web-laying machine. The web-laying trolley 4 controls the path and speed of web laying to achieve a non-homogeneous effect in the overall material. The overall structure of the composite material, from top to bottom, consists of: auxiliary layer 1, thermoplastic film layer, LWRT core layer 3, thermoplastic film layer 1, and auxiliary layer 1. The LWRT core layer 3 contains materials with a density of 0.5-0.9 g / cm³. 3 High-density areas with a density of 0.1-0.5 g / cm³ 3The low-density area. The core fiber of LWRT core layer 3 is one or more of PP fiber, glass fiber, PA fiber, PE fiber, aramid fiber, cellulose fiber, and basalt fiber. LWRT core layer 3 has a structure in which high-density areas on both sides and low-density areas in the middle, or high-density areas in the middle and low-density areas on both sides, or high-density areas and low-density areas are arranged alternately. When it is a structure in which high-density areas and low-density areas are arranged alternately, the number of density difference areas is an odd number greater than 3.

[0032] The auxiliary material of the auxiliary layer 1 is one or more of the following: PET needle-punched fabric, PP needle-punched fabric, PP / PET needle-punched fabric, PES needle-punched fabric, and PA needle-punched fabric. The high-density area has 30-100 layers, and the low-density area has 6-30 layers. The hot melt adhesive film layer 2 is composed of one or more of the following: PP, PE, PES, EVA, EAA, and PA.

[0033] This invention also discloses a method for preparing a heterogeneous LWRT fiber composite material, comprising the following steps: the required core fiber raw material undergoes opening, mixing, carding, web laying, and needle punching processes to obtain a felt material, which serves as the core material of the LWRT composite material.

[0034] During the netting process, the width ranges from 100 to 3300 mm, the number of netting layers ranges from 6 to 100, and the netting speed ranges from 0.5 to 200 m / min.

[0035] When preparing a density of 0.5-0.9 g / cm³ 3 When using high-density core material, the number of mesh layers is 30-100, and the mesh laying speed is 50-200m / min;

[0036] When preparing a density of 0.1-0.5 g / cm³ 3 When using low-density core materials, the number of mesh layers is 6-30, and the mesh laying speed is 0.5-50m / min.

[0037] When preparing a high-density region on both sides and a low-density region in the middle. Figure 3 This is a schematic diagram of the web laying route of the present invention, which is high-density on both sides and low-density in the middle. There are 3 density difference regions. The density changes from left to right in the trend of high-low-high. The web laying trolley 4 starts from the high-density edge region on one side, passes through the low-density middle region, and then moves to the high-density edge on the other side. When passing through the high-density edge region, the web laying trolley 4 lays back and forth to increase the density. The number of lays ranges from 1 to 5 times. This is one cycle. In a single cycle, the number of web laying layers on the left and right edges is 1 to 5 more than the number of web laying layers in the middle. It takes 5 to 50 cycles to prepare the heterogeneous core layer.

[0038] When preparing the high-density zone in the middle and the low-density zones on both sides Figure 4This is a schematic diagram of the web laying route of the present invention, which is low density on both sides and high density in the middle. There are 3 density difference regions. The density changes from left to right in the trend of low-high-low. The web laying trolley 4 starts from the low density edge region on one side, passes through the middle high density region, and then moves to the low density edge on the other side. When passing through the middle high density region, the web laying trolley 4 lays back and forth to increase the density. The number of lays ranges from 1 to 5 times. This is one cycle. The number of web layers in the middle of a single cycle is 1 to 5 more than the number of web layers on the left and right edges. It takes 5 to 50 cycles to prepare a heterogeneous core layer.

[0039] When the structure is arranged with alternating high-density and low-density areas, the number of density difference areas is an odd number greater than or equal to 5. Taking 5 as an example, the route can be divided into two categories. The first category is the density change trend from left to right: low density area 1 - high density area 1 - low density area 2 - high density area 2 - low density area 3. Three low-density areas are set on both sides and in the middle, and the other two areas are high-density areas. The overall direction of the net laying trolley 4 is as follows: starting from low density area 1, after a certain distance, it reaches high density area 1. The net laying trolley 4 lays back and forth to increase the number of net layers. Then it continues to travel through low density area 2 and reaches high density area 2. The trolley lays back and forth again and then travels to low density area 3. This is one cycle. In a single cycle, the number of net layers in the high density area is 1-5 more than that in the low density area. The preparation of the heterogeneous core layer requires the above 5-50 cycles.

[0040] The second type of density variation trend from left to right is high density zone 1 - low density zone 1 - high density zone 2 - low density zone 2 - high density zone 3. Three high density zones are set on both sides and in the middle, and the other two zones are low density zones. The overall movement of the net laying trolley 4 is as follows: after starting, it begins to lay the net back and forth to form high density zone 1. After finishing, it moves through low density zone 1 to reach high density zone 2. The trolley lays the net back and forth, and then continues to move through low density zone 2 to reach high density zone 3. The trolley lays the net back and forth again. This is one cycle. The number of net layers in the high density zone is 1-5 more than that in the low density zone in a single cycle. The preparation of the heterogeneous core layer requires the above 5-50 cycles.

[0041] The present invention has 2-33 density difference regions, and the specific density can be adjusted within the range of 0.1-0.9 g / cm³. 3 The density difference between high and low density areas ranges from 20% to 500%, the web laying speed varies from 0.5 to 200 m / min, and the web laying line is adjusted according to the program settings to change the density of the corresponding area. The areal density of homogeneous LWRT composite material can be controlled within the range of 300-3300 g / m³. 2 The thickness is controllable within the range of 1.0-10mm. The storage platform 5 below serves to store the fiber web and transport it to the next process.

[0042] The technical solution of the present invention will be further described below through specific embodiments:

[0043] The specific preparation process of the heterogeneous LWRT composite board is as follows: Thermoplastic polypropylene fiber and glass fiber are mixed evenly in a certain proportion, and then carded, laid into a web, and needle-punched to obtain a blended fiber felt. The felt is placed in a high-temperature oven, and after the polypropylene is fully melted, it is removed from the oven. An adhesive film and non-woven fabric are then sequentially coated onto the surface, and the board is placed in a high-temperature laminating machine. After lamination, the high sound-absorbing fiber composite board is obtained. Oven temperature range: 200-230℃; laminating machine temperature range: 170-230℃; laminating machine gap range: 3-7mm; heating time range: 1-3min; bulk density of the porous sound-absorbing board range: 0.1-0.9g / cm³. 3 By controlling the route and speed of mesh laying, the overall material heterogeneity can be achieved.

[0044] The technical solution of the present invention will be further described below with reference to specific embodiments:

[0045] Example 1:

[0046] An LWRT composite sheet material for passenger vehicle underbody protection panel exterior trim, the overall width of which is required to be 1600mm, and the bulk density of the main body is 0.3g / cm³. 3 The density of the high-density region is 0.7 g / cm³. 3 The overall board thickness is 4.5mm. Some areas of the bottom protective plate are at risk of cracking during water immersion testing, requiring high mechanical performance. Corresponding to the aforementioned high-density areas, the mesh laying pattern described in the first category of this invention is used for production (e.g., Figure 3 This increases the material density in this region, providing higher mechanical properties to meet requirements. The specific preparation method is as follows:

[0047] The preferred areal density range for auxiliary material layer 1 is 0.06 g / cm³. 2 -0.3g / m 2 The components are PET and PES; the areal density of the melt film layer 2 is preferably in the range of 20 g / m². 2 -80g / m 2 The LWRT core material is composed of PE and PP. The thermoplastic polypropylene fiber and glass fiber are mixed evenly in a certain proportion, and then carded, laid into a web, and needle-punched to obtain the core material.

[0048] The netting method adopts the first type of mode, with a netting width of 300mm in high-density areas and a netting speed of 45m / min. The density in this area is 0.7g / cm³. 3 In low-density areas, the mesh width is 1000mm, the mesh laying speed is 60m / min, and the density in this area is 0.3g / cm³. 3.

[0049] The LWRT core material is placed in an oven and heated to 200-210℃ for 3-5 minutes. After removing it from the oven, a hot melt adhesive film layer 2 and an auxiliary material layer 1 are applied to the surface of the LWRT core material. The material is then placed in a high-temperature laminating machine at 190-210℃. After cooling and molding, the heterogeneous LWRT composite material is obtained.

[0050] According to ISO 527-4-2021 standard for determination of tensile properties of plastics and ISO 178-2019 standard for determination of flexural properties of plastics, tensile and flexural properties of high-density and low-density regions were tested using a universal testing machine. Table 1 shows the specific data.

[0051] Table 1. Comparison of mechanical properties in high and low density regions (4.5mm)

[0052]

[0053] Example 2:

[0054] A type of LWRT composite sheet material for interior parts of passenger car coat racks, the overall width of which is required to be 1400mm, and the bulk density of the main body is 0.5g / cm³. 3 The density of the low-density region is 0.2 g / cm³. 3 The overall sheet thickness is 5mm. Some areas of the coat rack component are difficult to punch and pierce, and the mechanical performance requirements in these areas are relatively low. Therefore, the aforementioned low-density areas are used, and the mesh laying method described in the second category of this invention is employed for production (e.g., Figure 4 This reduces the material density in the area, meeting the requirements for convenient punching and forming.

[0055] The specific preparation method is as follows:

[0056] The preferred areal density range for auxiliary material layer 1 is 0.06 g / cm³. 2 -0.3g / m 2 The composition is PP / PET; the preferred areal density range for the hot melt adhesive film layer 2 is 20 g / m³. 2 -80g / m 2 The component is EVA. Thermoplastic polypropylene fiber and glass fiber are mixed evenly in a certain proportion, and then carded, laid into a web, and needle-punched to obtain the LWRT core material.

[0057] The netting method adopts the second type of mode. In the low-density area, the netting width is 400mm, the netting speed is 75m / min, and the density in this area is 0.2g / cm³. 3 In high-density areas, the mesh width is 600mm, the mesh laying speed is 45m / min, and the density in this area is 0.5g / cm³. 3 .

[0058] The LWRT core material is placed in an oven and heated at 190-200℃ for 3-5 minutes. After removing it from the oven, a hot melt adhesive film layer 2 and an auxiliary material layer 1 are applied to the surface of the LWRT core material. The material is then placed in a high-temperature laminating machine at 170-185℃. After cooling and molding, the heterogeneous LWRT composite material is obtained.

[0059] Finally, it should be noted that the above examples are merely specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments and many variations are possible. All variations that can be directly derived or conceived by those skilled in the art from the disclosure of this invention should be considered within the scope of protection of this invention.

Claims

1. A method for preparing a heterogeneous LWRT fiber composite material, characterized in that, The overall structure of the heterogeneous LWRT fiber composite material, from top to bottom, consists of: an auxiliary layer, a thermoplastic film layer, an LWRT core layer, another thermoplastic film layer, and an auxiliary layer. The LWRT core layer comprises materials with a density of 0.5-0.9 g / cm³. 3 High-density areas with a density of 0.1-0.5 g / cm³ 3 The low-density area of ​​the LWRT core layer is characterized by a structure in which high-density areas on both sides and a low-density area in the middle, or a high-density area in the middle and low-density areas on both sides, or a structure in which high-density and low-density areas are arranged alternately. When the structure is an alternate arrangement of high-density and low-density areas, the number of density difference areas is an odd number greater than 3, and the density difference between high-density and low-density areas ranges from 20% to 500%. The preparation of the LWRT core layer includes the following steps: the required core layer fiber raw materials undergo opening, mixing, carding, web laying, and needle punching processes to obtain a felt material, which serves as the core material of the LWRT composite material. During the netting process, the width ranges from 100 to 3300 mm, the number of netting layers ranges from 6 to 100, and the netting speed ranges from 0.5 to 200 m / min. When preparing a density of 0.5-0.9 g / cm³ 3 When using high-density core material, the number of mesh layers is 30-100, and the mesh laying speed is 50-200m / min; When preparing a density of 0.1-0.5 g / cm³ 3 When using low-density core materials, the number of mesh layers is 6-30, and the mesh laying speed is 0.5-50m / min; When preparing the high-density areas on both sides and the low-density area in the middle, there are 3 areas with different densities. The density changes from left to right in the direction of high-low-high. The net laying trolley starts from the high-density edge area on one side, passes through the low-density middle area, and then moves to the high-density edge area on the other side. When passing through the high-density edge area, the net laying trolley lays back and forth to increase the density. The number of lays ranges from 1 to 5 times. This is one cycle. In a single cycle, the number of net layers laid on the left and right edges is 1 to 5 more than the number of net layers laid in the middle. Preparing the LWRT core layer requires 5 to 50 cycles. When preparing the high-density zone in the middle and the low-density zones on both sides, there are 3 density difference zones. The density changes from left to right in the order of low-high-low. The net laying trolley starts from the low-density edge zone on one side, passes through the high-density zone in the middle, and then moves to the low-density edge zone on the other side. When passing through the high-density zone in the middle, the net laying trolley moves back and forth to increase the density. The number of times it moves is 1-5 times. This is one cycle. The number of net layers in the middle of a single cycle is 1-5 more than the number of net layers on the left and right edges. Preparing the LWRT core layer requires 5-50 cycles. The network lines are adjusted according to the program settings to change the density of the corresponding areas.

2. The method for preparing heterogeneous LWRT fiber composite material according to claim 1, characterized in that, When the structure consists of alternating high-density and low-density areas, with more than five density difference zones, the routes are divided into two categories: the first category has low density on both sides and high density in the middle, alternating between low and high density; the second category has high density on both sides and low density in the middle, alternating between high and high density. In the first category, the density trend from left to right is low-high-n*(low-high)-low. The overall direction of the net-laying trolley is as follows: starting from a low-density edge zone on one side, after a certain distance, it reaches the first high-density zone. The net-laying trolley moves back and forth to increase the number of net layers, then continues to move through the second low-density zone and reaches the second high-density zone. The trolley moves back and forth again, then moves to the third low-density zone, and so on, until it enters the low-density edge zone on the other side, which constitutes one cycle. The number of net layers in a single cycle of high-density areas is higher than that in low-density areas. In the first type, the density region is 1-5 layers higher, and the preparation of the LWRT core layer requires 5-50 cycles. In the second type, the density change trend from left to right is high-low-n*(high-low)-high. The overall movement of the web-laying trolley is as follows: starting from the high-density edge region on one side, it begins to lay web back and forth to form the first high-density region. After that, it moves through the first low-density region to reach the second high-density region. The trolley lays web back and forth, and then continues to move. After passing through the second low-density region, it reaches the third high-density region. The trolley lays web back and forth again, and so on, until it enters the high-density edge region on the other side, which is one cycle. The number of web-laying layers in a single cycle is 1-5 layers higher in the high-density region than in the low-density region. The preparation of the LWRT core layer requires 5-50 cycles. The range of n is: 30≥n≥1.

3. The method for preparing heterogeneous LWRT fiber composite material according to claim 2, characterized in that, The areal density of the heterogeneous LWRT fiber composite material is controllable within the range of 300-3300 g / m³. 2 The thickness is controllable within the range of 1.0-10mm.

4. The method for preparing heterogeneous LWRT fiber composite material according to claim 1, characterized in that, The core fiber of the LWRT core layer is one or more of the following: PP fiber, glass fiber, PA fiber, PE fiber, aramid fiber, cellulose fiber, and basalt fiber.

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