A continuous fiber reinforced polyamide composite material and its preparation method

Abstract

This invention discloses a continuous fiber reinforced polyamide composite material and its preparation method. The preparation method includes: first, weaving continuous fiber reinforced polyamide unidirectional prepreg narrow strips and short fiber prepreg narrow strips oriented in the thickness direction into a two-dimensional sheet; then, hot-pressing this two-dimensional sheet into a composite board through a layup design. In this way, the interlaminar shear properties of the laminated composite board are improved by introducing oriented short fibers between the layers. The continuous fiber reinforced polyamide composite material exhibits excellent mechanical properties, especially interlaminar shear properties.

Description

Technical Field

[0001] This invention belongs to the field of composite materials, and particularly relates to polyamide composite materials, specifically to a continuous fiber reinforced polyamide composite material and its preparation method. Background Technology

[0002] Fiber-reinforced resin matrix composites can be broadly classified into thermosetting resin matrix composites and thermoplastic resin matrix composites based on the type of resin matrix. Currently, thermosetting resin matrix composites have a wider range of applications; however, their application areas are somewhat limited due to drawbacks such as poor toughness, long molding cycles, environmental unfriendliness, low damage tolerance, and difficulty in recycling. Thermoplastic resin matrix composites, on the other hand, are attracting increasing attention due to their significant advantages such as good toughness, high fatigue strength, short molding cycles, long-term storage at room temperature, easy recycling, and strong recyclability. PA is a general term for thermoplastic resins containing repeating amide groups in their molecular backbone, including aliphatic PA, aliphatic-aromatic PA, aromatic PA, and various copolymer PA forms. Carbon fiber reinforced polyamide composites have advantages such as lightweight, fatigue resistance, wear resistance, and corrosion resistance, and are used in automobiles, home appliances, and sporting goods.

[0003] Currently, continuous fiber reinforced thermoplastic composites are typically produced through the preparation of prepregs. The preparation process is relatively complex. First, continuous fiber reinforcement materials, such as unidirectional non-woven fabrics, axially warp-knitted fabrics, and plain-weave woven fabrics, are manufactured using textile processes. Then, these materials are combined with a matrix material using solution methods, melt methods, thin-film methods, or fluidized bed methods to obtain the prepreg. Each process has its own advantages and disadvantages. Finally, in practical applications, the continuous fiber reinforced thermoplastic prepregs are often laminated to form composite panels of a certain thickness.

[0004] Composite laminates exhibit good in-plane strength, and their practical application requirements can be met by modifying the reinforcing fabric type or the layup design of each layer. However, their interlaminar strength is relatively weak, and delamination is one of the main forms of damage in laminated composites. The generation and propagation of microcracks accelerate delamination. To address this, numerous anti-delamination technologies have been developed both domestically and internationally, broadly falling into two categories: utilizing textile processes to achieve interlaminar bonding of reinforcing materials. Examples include multi-directional warp and weft knitting, stitching techniques, 2.5D and three-dimensional weaving, Z-pin insertion, and three-dimensional flocking. However, these technologies also have significant drawbacks: high production costs; severe fiber damage; high degree of human intervention, resulting in poor product consistency; and unsuitability for manufacturing complex or large-sized products. The other category primarily involves adding various micro / nano reinforcements. Patent CN108908964A utilizes TiO2 nanoscale reinforcements to improve the interlaminar shear properties of laminates. Patent CN211994470U introduces hard granular sand into the interlayer. By laying a composite film with protruding particles in the interlayer, short bridges are established between the fiber layers through hot pressing, enhancing interlayer bonding and effectively inhibiting delamination and crack propagation, thus improving delamination strength. Patent CN108673968A adds nanoscale alloy powder containing rare earth elements, then uniformly coats resin onto carbon fiber cloth, and then alternately stacks the semi-finished carbon fiber cloth and PA6 film, and hot-presses them to form a laminate, significantly improving the interfacial properties and interlayer mechanical properties of carbon fiber composites. However, this technology also has some drawbacks: the manufacturing process of nanoscale reinforcements is relatively complex and costly, and the types are limited; nanoscale reinforcements have high surface energy, making them difficult to disperse when added to high-viscosity polymers, hindering the full realization of the functional properties of nanocomposites. Summary of the Invention

[0005] To overcome the problems existing in the prior art, the present invention provides a continuous fiber reinforced polyamide composite material and its preparation method. The continuous fiber reinforced polyamide composite material exhibits excellent mechanical properties, especially interlaminar shear properties. The preparation method includes: firstly, weaving continuous fiber reinforced polyamide unidirectional prepreg narrow strips and chopped short fiber prepreg narrow strips oriented in the thickness direction into a two-dimensional sheet; then, hot-pressing this two-dimensional sheet into a composite board through a layup design. Thus, the interlaminar shear properties of the laminated composite board are improved by introducing oriented short chopped fibers between the layers.

[0006] One of the objectives of this invention is to provide a continuous fiber reinforced polyamide composite material, which is a laminate material, wherein each layer is a unidirectional continuous fiber reinforced polyamide resin, and the layers are connected by oriented short fiber reinforced polyamide resin perpendicular to the unidirectional fiber reinforced polyamide resin in the layer.

[0007] In a preferred embodiment, the shear strength of the continuous fiber reinforced polyamide composite material is 92-120 MPa, preferably 95-115 MPa, for example 92 MPa, 94 MPa, 96 MPa, 98 MPa, 100 MPa, 102 MPa, 104 MPa, 106 MPa, 108 MPa, 110 MPa, 112 MPa, 114 MPa, 116 MPa, 118 MPa or 120 MPa.

[0008] A second objective of this invention is to provide a method for preparing a continuous fiber reinforced polyamide composite material, preferably used for preparing the continuous fiber reinforced polyamide composite material described in one objective of this invention. The preparation method includes:

[0009] (1) Obtaining continuous fiber-reinforced unidirectional prepreg narrow bands;

[0010] (2) Obtain multiple continuous fiber-reinforced unidirectional prepreg wide bands, hot-press them into laminates, and then cut the laminates to obtain short fiber prepreg narrow bands.

[0011] (3) The continuous fiber reinforced unidirectional prepreg narrow strip and the chopped fiber prepreg narrow strip are woven together to obtain a woven prepreg sheet;

[0012] (4) The multiple braided prepreg sheets are subjected to hot pressing to obtain the continuous fiber reinforced polyamide composite material.

[0013] In a preferred embodiment, the continuous fiber reinforced unidirectional prepreg narrow strip in step (1) can be purchased directly or obtained by melt impregnation pultrusion molding process.

[0014] In a further preferred embodiment, the continuous fiber reinforced unidirectional prepreg narrow strip is obtained by an indirect method as follows: first, a continuous fiber reinforced unidirectional wide strip is prepared by melt impregnation pultrusion molding process, and then the continuous fiber reinforced unidirectional wide strip is cut (to a specified width) along the fiber (length) direction to obtain the continuous fiber reinforced unidirectional prepreg narrow strip.

[0015] In another further preferred embodiment, the continuous fiber reinforced unidirectional prepreg narrow strip is obtained by a direct method as follows: a prepreg narrow strip of a specified width is pultruded using a melt impregnation pultrusion process combined with a die of a specific size, which is the continuous fiber reinforced unidirectional prepreg narrow strip.

[0016] The conditions for the melt impregnation pultrusion molding process can be those disclosed in the prior art, as long as the obtained continuous fiber reinforced unidirectional prepreg narrow strip meets the above parameters.

[0017] In a preferred embodiment, the continuous fiber-reinforced unidirectional prepreg narrow strip in step (1) includes polyamide resin and fiber.

[0018] In a further preferred embodiment, in the continuous fiber reinforced unidirectional prepreg narrow strip in step (1), the polyamide resin is selected from one or more of nylon 6, nylon 66, nylon 666, nylon 610, branched nylon, and hyperbranched nylon, and / or the fiber is selected from one or more of carbon fiber, aramid fiber, glass fiber, and basalt fiber.

[0019] In a further preferred embodiment, in the continuous fiber-reinforced unidirectional prepreg narrow strip in step (1), the polyamide resin has a weight content of 25% to 45%, preferably 30% to 40%, for example 25%, 30%, 35%, 40% or 45%; and / or, the fiber has a weight content of 55% to 75%, preferably 60% to 70%; and / or, the polyamide resin has a relative viscosity of 1.8 to 2.7, preferably 2.0 to 2.5, for example 1.8, 2.0, 2.2, 2.4, 2.6 or 2.7.

[0020] In a preferred embodiment, the width of the continuous fiber reinforced unidirectional prepreg narrow strip is 3-7 mm and the thickness is 0.2-0.5 mm.

[0021] For example, the width of the continuous fiber reinforced unidirectional prepreg narrow strip is 3mm, 4mm, 5mm, 6mm or 7mm, and the thickness is 0.2mm, 0.3mm, 0.4mm or 0.5mm.

[0022] In a preferred embodiment, before preparing the continuous fiber reinforced unidirectional prepreg narrow strip in step (1) and the continuous fiber reinforced unidirectional prepreg wide strip in step (2), the fibers are first subjected to surface treatment independently: under a protective atmosphere, the sizing agent on the fiber surface (preferably from the production process) is removed by heating; and then the fibers are resized.

[0023] In a further preferred embodiment:

[0024] The protective atmosphere is selected from at least one of nitrogen and inert gases; and / or,

[0025] Heating to 400–600°C, preferably 450–550°C, for 10–50 min, preferably 20–40 min; and / or,

[0026] The sizing agent used for the re-sizing is selected from one or more of the following: silane coupling agent, titanate, aluminate, water-soluble polyurethane that bonds well with thermoplastic polyamide, solvent-based polyurethane that bonds well with thermoplastic polyamide, water-soluble polyamide that bonds well with thermoplastic polyamide, and solvent-based polyamide that bonds well with thermoplastic polyamide.

[0027] Preferably, the silane coupling agent is selected from at least one of γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, and γ-methacryloyloxypropyltrimethoxysilane; preferably, the titanate is selected from at least one of isopropyltris(dioctylpyrophosphoryl)titanate, isopropyltris(dioctylpyrophosphoryl)titanate, and dicarboxyylethylenediethylene titanate; preferably, the aluminate is selected from at least one of isopropyldistearate and isopropyloxydistearate.

[0028] In a further preferred embodiment, after surface treatment, the weight content of the sizing agent in the fiber is 0.2% to 2%, preferably 0.5% to 1.5%, for example 0.2%, 0.4%, 0.6%, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8% or 2%.

[0029] In a preferred embodiment, in step (2), the continuous fiber-reinforced unidirectional prepreg broadband is stacked along 0° (upper and lower layers) and hot-pressed to form a laminate.

[0030] In a further preferred embodiment, the hot pressing in step (2) includes preheating, hot pressing, and cooling, and the process conditions include: a preheating temperature of 180℃-220℃ (e.g., 180℃, 190℃, 200℃, 210℃, or 220℃), and / or a preheating time of 5-15 min (e.g., 5 min, 6 min, 8 min, 10 min, 12 min, 14 min, or 15 min), and / or a hot pressing temperature of 220℃. The temperature is ℃-260℃ (e.g., 220℃, 230℃, 240℃, 250℃ or 260℃), and / or the hot pressing pressure is 1-10MPa (e.g., 1MPa, 2MPa, 4MPa, 6MPa, 8MPa or 10MPa), and / or the hot pressing time is 10-20min (e.g., 10min, 12min, 14min, 16min, 18min or 20min), and / or the pressure is maintained and then cooled to room temperature.

[0031] For example, the hot pressing process is as follows: preheating temperature 200℃, preheating time 10min; hot pressing temperature 240℃, hot pressing pressure 5MPa, hot pressing time 15min;

[0032] In a preferred embodiment, in step (2), the laminate is cut along a direction perpendicular to the length of the continuous fibers in the laminate (i.e., parallel to the width direction) to obtain the chopped fiber prepreg narrow strip.

[0033] Thus, the width of the chopped fiber prepreg narrow strip is equal to the thickness of the composite laminate, and the length of the chopped fiber prepreg narrow strip is equal to the width of the composite laminate or the width of the continuous fiber reinforced unidirectional prepreg wide strip.

[0034] In a preferred embodiment, the width of the chopped fiber prepreg narrow strip is 3-7 mm and the thickness is 0.1-0.5 mm, preferably 0.1-0.3 mm, for example 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm or 0.5 mm.

[0035] In a preferred embodiment, the continuous fiber-reinforced unidirectional prepreg wide band in step (2) includes polyamide resin and fiber; wherein the polyamide resin is selected from one or more of nylon 6, nylon 66, nylon 666, nylon 610, branched nylon, and hyperbranched nylon, and / or the fiber is selected from one or more of carbon fiber, aramid fiber, glass fiber, and basalt fiber.

[0036] In a further preferred embodiment, the polyamide resin in the continuous fiber reinforced unidirectional prepreg wide band in step (2) has a weight content of 30%-60%, preferably 40%-50%, for example 30%, 35%, 40%, 45%, 50%, 55% or 60%; and / or the fiber has a weight content of 40%-70%, preferably 50%-60%, for example 40%, 45%, 50%, 55%, 60%, 65% or 70%; and / or the relative viscosity of the polyamide resin in the chopped fiber prepreg narrow band is 2.7-3.2, preferably 2.8-3.0, for example 2.7, 2.8, 2.9, 3.0, 3.1 or 3.2.

[0037] In a further preferred embodiment, the relative viscosity of the polyamide resin in the continuous fiber reinforced unidirectional prepreg wide strip in step (2) is higher than the relative viscosity of the polyamide resin in the continuous fiber reinforced unidirectional prepreg narrow strip in step (1).

[0038] Among them, the relative viscosity of the polyamide resin in the short fiber prepreg narrow strip obtained by using the continuous fiber reinforced unidirectional prepreg wide strip in step (2) is higher than that of the polyamide resin in the continuous fiber reinforced unidirectional prepreg narrow strip in step (1). In this way, the high viscosity resin has poor flowability under the same temperature process, which ensures that the short fiber prepreg narrow strip flows as little as possible during the composite process, so that the short fibers in the short narrow strip can better maintain their orientation state during the hot pressing process.

[0039] In a preferred embodiment, in step (3), a prepreg sheet is obtained by weaving the chopped fiber prepreg narrow strip as warp yarn and the fiber-reinforced unidirectional prepreg narrow strip as weft yarn (preferably on a loom); preferably, the prepreg sheet is a plain weave, twill weave or satin weave prepreg sheet.

[0040] In a further preferred embodiment, the widths of the warp and weft yarns are equal.

[0041] In a preferred embodiment, in step (4), according to the required thickness of the continuous fiber reinforced polyamide composite material, (according to the requirements of laminate use) multiple woven prepreg sheets are laid up in the range of -90° to 90° layup angle (upper and lower layup), wherein the layup angle is changed by rotating based on the unidirectional prepreg narrow weft yarn in the woven prepreg sheet.

[0042] In a further preferred embodiment, multiple woven prepreg sheets are laid along the 0°C direction (i.e., laid parallel vertically) and then hot-pressed.

[0043] In a preferred embodiment, in step (4), the hot pressing process includes preheating, hot pressing, and cooling.

[0044] In a further preferred embodiment, in step (4), the conditions for the hot pressing treatment include: setting the preheating temperature to 180℃-250℃ (e.g., 180℃, 190℃, 200℃, 210℃, 220℃, 230℃, 240℃, or 250℃), and / or setting the preheating time to 30-60 min (e.g., 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, or 60 min), and / or setting the hot pressing temperature to 230℃-300℃ (e.g., 230℃, 240℃, 250℃, 26 ... 0℃, 270℃, 280℃, 290℃ or 300℃), and / or, setting the hot pressing pressure to 3-10MPa (e.g. 3MPa, 4MPa, 5MPa, 6MPa, 7MPa, 8MPa, 9MPa or 10MPa), and / or, setting the hot pressing time to 5-10min (e.g. 5min, 6min, 7min, 8min, 9min or 10min), and / or, setting the cooling rate to 30-50℃ / min (e.g. 30, 35, 40, 45 or 50℃ / min), and / or, setting the pressure holding and cooling to room temperature.

[0045] In a further preferred embodiment, in step (4), the conditions for hot pressing include: setting the preheating temperature to 200℃-230℃, and / or setting the preheating time to 40-50 min, and / or setting the hot pressing temperature to 250℃-280℃, and / or setting the hot pressing pressure to 4-8 MPa, and / or setting the hot pressing time to 5-8 min, and / or setting the cooling rate to 40-50℃ / min, and / or setting the pressure holding and cooling to room temperature.

[0046] The hot pressing process is carried out in a hydraulic press with upper and lower pressure plates. The upper and lower pressure plates have heating and cooling functions. In order to further control the thickness of the laminate, the hydraulic press is also equipped with a strip frame to assist in forming (the description of this part in the prior art is included in the present invention).

[0047] The continuous fiber reinforced polyamide composite material of the present invention is a laminate, each layer of which is reinforced with unidirectional fibers, and the layers are connected by oriented short fibers perpendicular to the unidirectional fibers in the layer.

[0048] During molding, the woven prepreg sheet can be designed with a layup angle within the range of -90° to 90° according to the requirements of the laminate. The layup angle is changed by rotating the unidirectional prepreg narrow weft yarn in the woven prepreg sheet as a reference.

[0049] The third objective of this invention is to provide a continuous fiber reinforced polyamide composite material obtained by the preparation method described in the second objective of this invention. This composite material is a laminate material, in which each layer is a unidirectional continuous fiber reinforced polyamide resin, and the layers are connected by short fiber reinforced polyamide resin perpendicular to the orientation of the unidirectional fiber reinforced polyamide resin within the layer.

[0050] In a preferred embodiment, the shear strength of the continuous fiber reinforced polyamide composite material is 92-120 MPa, preferably 95-115 MPa, for example 92 MPa, 94 MPa, 96 MPa, 98 MPa, 100 MPa, 102 MPa, 104 MPa, 106 MPa, 108 MPa, 110 MPa, 112 MPa, 114 MPa, 116 MPa, 118 MPa or 120 MPa.

[0051] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values; these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. In the following, various technical solutions can, in principle, be combined with each other to obtain new technical solutions, which should also be considered as specifically disclosed herein.

[0052] Compared with existing technologies, this invention has the following advantages: By introducing oriented short-cut fibers into the interlaminar layers of a composite laminate through simple weaving and lamination processes, this invention effectively improves the interlaminar shear resistance of continuous fiber-reinforced thermoplastic composite laminates. The resin content in the composite material is precisely controllable, expanding the material's application areas. Furthermore, this method avoids the use of technically challenging and costly methods such as three-dimensional weaving and special micro / nano powder reinforcement, making it more economical. Detailed Implementation

[0053] The present invention will now be described in detail with reference to specific embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention are still within the scope of protection of the present invention.

[0054] It should also be noted that the various specific technical features described in the following embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the various possible combinations will not be described separately in this invention.

[0055] Furthermore, various embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention. The resulting technical solutions are part of the original disclosure of this specification and also fall within the protection scope of the present invention.

[0056] Unless otherwise specified, the raw materials used in the examples and comparative examples are all disclosed in the prior art, such as those that can be directly purchased or prepared according to the preparation methods disclosed in the prior art.

[0057] In the examples and comparative examples, the tensile properties of the laminates were tested according to GB1447-2005 "Test Method for Tensile Properties of Fiber Reinforced Plastics"; the flexural strength was tested according to GB1449-2005 "Test Method for Flexural Properties of Fiber Reinforced Plastics"; and the shear strength was tested according to JC / T 773-2010 "Determination of Interlaminar Shear Strength of Fiber Reinforced Plastics by Short Beam Method".

[0058] Example 1

[0059] 1. Fiber Surface Treatment. T300 continuous carbon fibers are placed in a vacuum resistance furnace for high-temperature treatment under a nitrogen protective atmosphere. The heating temperature is set to 500℃ for 30 minutes to remove the sizing agent from the fiber surface during production. Subsequently, the fiber surface is re-sized with water-soluble polyamide at a weight content of 1%.

[0060] Preparation of fiber-reinforced unidirectional prepreg narrow strips. A relatively mature melt impregnation pultrusion molding process was used to prepare fiber-reinforced unidirectional wide strips, which were then cut along the fiber direction into 5 mm wide and 0.3 mm thick prepreg narrow strips, wherein the weight content of PA6 was 40% and the relative viscosity of PA6 was 2.5.

[0061] 2. Fiber Surface Treatment. T300 continuous carbon fibers are placed in a vacuum resistance furnace for high-temperature treatment under a nitrogen protective atmosphere. The heating temperature is set to 500℃ for 30 minutes to remove the sizing agent from the fiber surface during production. Subsequently, the fiber surface is re-sized with water-soluble polyamide at a mass content of 1%.

[0062] Preparation of chopped fiber prepreg narrow strips. A mature melt impregnation pultrusion process was used to prepare fiber-reinforced unidirectional wide strips. The unidirectional wide strips contained 50% PA6 by mass and the polyamide resin had a relative viscosity of 2.8. The prepared unidirectional wide strips were stacked along 0° (the fiber direction) and hot-pressed to form a laminate. The laminate forming process was as follows: preheating temperature 200℃, preheating time 10 min; hot pressing temperature 240℃, hot pressing pressure 5 MPa, hot pressing time 15 min; holding pressure and cooling to room temperature. Then, the laminate was cut along a direction perpendicular to the laminate, and the resulting sheet was the chopped fiber prepreg narrow strip. The width of the chopped fiber prepreg narrow strip was 5 mm, the thickness was 0.3 mm, the PA6 content in the chopped fiber prepreg narrow strip was 50% by mass, and the relative viscosity of the polyamide resin was 2.8.

[0063] 3. Preparation of woven prepreg sheets. Using chopped fiber prepreg narrow strips as warp and fiber-reinforced unidirectional prepreg narrow strips as weft, plain weave prepreg sheets are produced on a loom.

[0064] 4. Preparation of Continuous Fiber Reinforced Laminate. The woven prepreg sheets are laid at a 0° angle, meaning the weft yarns of each layer of woven prepreg sheet within the laminate are parallel, with a thickness of 3mm. It is then placed in the upper and lower plates of a hydraulic press equipped with heating and cooling functions. To control the thickness, additional trim strips are added to assist in forming. The upper and lower plates are preheated at 200℃ for 45 minutes; the hot-pressing temperature is 250℃, the hot-pressing pressure is 4MPa, and the hot-pressing time is 5 minutes; the cooling rate is 45℃ / min, and the pressure is maintained until room temperature.

[0065] Table 1 shows the average tensile strength, flexural strength, and shear strength of the laminate obtained under the conditions of Example 1. The tensile direction was along the 0° layup angle of the laminate.

[0066] Table 1 Mechanical properties of laminates in Example 1

[0067] Tensile strength / MPa Bending strength / MPa Shear strength / MPa Example 1 1100 580 110

[0068] Example 2

[0069] 1. Fiber Surface Treatment. T300 continuous carbon fibers are placed in a vacuum resistance furnace for high-temperature treatment under a nitrogen protective atmosphere. The heating temperature is set to 500℃ for 30 minutes to remove the sizing agent from the fiber surface during production. Subsequently, the fiber surface is re-sized with water-soluble polyamide at a mass content of 1%.

[0070] Preparation of fiber-reinforced unidirectional prepreg narrow strips. A relatively mature melt impregnation pultrusion molding process was used to prepare fiber-reinforced unidirectional wide strips, which were then cut along the fiber direction into 5 mm wide and 0.3 mm thick prepreg narrow strips, wherein the mass content of PA6 was 35% and the relative viscosity of PA6 was 2.5.

[0071] 2. Fiber Surface Treatment. T300 continuous carbon fibers are placed in a vacuum resistance furnace for high-temperature treatment under a nitrogen protective atmosphere. The heating temperature is set to 500℃ for 30 minutes to remove the sizing agent from the fiber surface during production. Subsequently, the fiber surface is re-sized with water-soluble polyamide at a mass content of 1%.

[0072] Preparation of chopped fiber prepreg narrow strips. A mature melt impregnation pultrusion process was used to prepare fiber-reinforced unidirectional wide strips. The unidirectional wide strips contained 50% PA6 by mass and the polyamide resin had a relative viscosity of 2.8. The prepared unidirectional wide strips were stacked along 0° (the fiber direction) and hot-pressed to form a laminate. The laminate forming process was as follows: 200℃, preheating time 10 min; hot-pressing temperature 240℃, hot-pressing pressure 5 MPa, hot-pressing time 15 min; holding pressure and cooling to room temperature. Then, the laminate was cut along a direction perpendicular to the laminate to obtain the chopped fiber prepreg narrow strips. The width of the chopped fiber prepreg narrow strips was 5 mm, the thickness was 0.3 mm, the PA6 content was 50% by mass, and the polyamide resin had a relative viscosity of 2.8.

[0073] 3. Preparation of woven prepreg sheets. Using chopped fiber prepreg narrow strips as warp and fiber-reinforced unidirectional prepreg narrow strips as weft, plain weave prepreg sheets are produced on a loom.

[0074] 4. Preparation of Continuous Fiber Reinforced Laminate. The woven prepreg sheets are laid at 0° / 90° angles, meaning the weft yarns of each layer of woven prepreg sheet in the laminate are alternately perpendicular, with a thickness of 3mm. It is then placed in the upper and lower plates of a hydraulic press equipped with heating and cooling functions. To control the thickness, additional trim strips are added to assist in forming. The upper and lower plates are preheated at 210℃ for 50 minutes; the hot-pressing temperature is 260℃, the hot-pressing pressure is 5MPa, and the hot-pressing time is 8 minutes; the cooling rate is 50℃ / min, and the pressure is maintained until room temperature.

[0075] Table 2 shows the average tensile strength, flexural strength, and shear strength of the laminate obtained under the conditions of Example 2. The tensile direction is along two perpendicular directions of the laminate.

[0076] Table 2 Mechanical properties of laminates in Example 2

[0077] Tensile strength / MPa Bending strength / MPa Shear strength / MPa Example 2 560 368 98

[0078] Example 3

[0079] 1. Fiber Surface Treatment. T300 continuous carbon fibers are placed in a vacuum resistance furnace for high-temperature treatment under a nitrogen protective atmosphere. The heating temperature is set to 500℃ for 30 minutes to remove the sizing agent from the fiber surface during production. Subsequently, the fiber surface is re-sized with water-soluble polyamide at a mass content of 1%.

[0080] Preparation of fiber-reinforced unidirectional prepreg narrow strips. A relatively mature melt impregnation pultrusion molding process was used to prepare fiber-reinforced unidirectional wide strips, which were then cut along the fiber direction into 5 mm wide and 0.3 mm thick prepreg narrow strips, wherein the mass content of PA6 was 40% and the relative viscosity of PA6 was 2.0.

[0081] 2. Fiber Surface Treatment. T300 continuous carbon fibers are placed in a vacuum resistance furnace for high-temperature treatment under a nitrogen protective atmosphere. The heating temperature is set to 500℃ for 30 minutes to remove the sizing agent from the fiber surface during production. Subsequently, the fiber surface is re-sized with water-soluble polyamide at a mass content of 1%.

[0082] Preparation of chopped fiber prepreg narrow strips. A mature melt impregnation pultrusion process was used to prepare fiber-reinforced unidirectional wide strips. The unidirectional wide strips contained 50% PA6 by mass and the polyamide resin had a relative viscosity of 3.0. The unidirectional wide strips prepared in step 1 were stacked along 0° (the fiber direction) and hot-pressed to form a laminate. The laminate forming process was as follows: 200℃, preheating time 10 min; hot pressing temperature 240℃, hot pressing pressure 5 MPa, hot pressing time 15 min; holding pressure and cooling to room temperature. Then, the strips were cut along a direction perpendicular to the laminate to obtain the chopped fiber prepreg narrow strips. The width of the chopped fiber prepreg narrow strips was 5 mm, the thickness was 0.3 mm, the PA6 content was 50% by mass, and the polyamide resin had a relative viscosity of 3.0.

[0083] 3. Preparation of woven prepreg sheets. Using chopped fiber prepreg narrow strips as warp and fiber-reinforced unidirectional prepreg narrow strips as weft, plain weave prepreg sheets are produced on a loom.

[0084] 4. Preparation of Continuous Fiber Reinforced Laminate. The woven prepreg sheets are laid at -45° / 45° angles, meaning the weft yarns of each layer of woven prepreg sheet in the laminate are laid alternately at ±45° angles, with a thickness of 3mm. It is then placed in the upper and lower plates of a hydraulic press equipped with heating and cooling functions. To control the thickness, additional trim strips are added to assist in forming. The upper and lower plates are preheated at 210℃ for 50 minutes; the hot-pressing temperature is 260℃, the hot-pressing pressure is 5MPa, and the hot-pressing time is 8 minutes; the cooling rate is 50℃ / min, and the pressure is maintained until room temperature.

[0085] Table 3 shows the average tensile strength, flexural strength, and shear strength of the laminate obtained under the conditions of Example 3. The tensile direction was along two perpendicular directions of the laminate.

[0086] Table 3 Mechanical properties of laminates in Example 3

[0087] Tensile strength / MPa Bending strength / MPa Shear strength / MPa Example 3 260 255 105

[0088] Example 4

[0089] 1. Fiber Surface Treatment. 1200D alkali-free continuous glass fibers are placed in a vacuum resistance furnace for high-temperature treatment under a nitrogen protective atmosphere. The heating temperature is set to 500℃ for 30 minutes to remove the sizing agent from the fiber surface during production. Subsequently, the fiber surface is re-sized with water-soluble polyamide at a mass content of 1%.

[0090] Preparation of fiber-reinforced unidirectional prepreg narrow strips. A relatively mature melt impregnation pultrusion molding process was used to prepare fiber-reinforced unidirectional wide strips, which were then cut along the fiber direction into 5 mm wide and 0.3 mm thick prepreg narrow strips, wherein the mass content of PA6 was 40% and the relative viscosity of PA6 was 2.5.

[0091] 2. Fiber Surface Treatment. 1200D alkali-free continuous glass fibers are placed in a vacuum resistance furnace for high-temperature treatment under a nitrogen protective atmosphere. The heating temperature is set to 500℃ for 30 minutes to remove the sizing agent from the fiber surface during production. Subsequently, the fiber surface is re-sized with water-soluble polyamide at a mass content of 1%.

[0092] Preparation of chopped fiber prepreg narrow strips. A mature melt impregnation pultrusion process was used to prepare fiber-reinforced unidirectional wide strips. The unidirectional wide strips contained 50% PA6 by mass and the polyamide resin had a relative viscosity of 2.8. The unidirectional wide strips prepared in step 1 were stacked along 0° (the fiber direction) and hot-pressed to form a laminate. The laminate forming process was as follows: 200℃, preheating time 10 min; hot pressing temperature 240℃, hot pressing pressure 5 MPa, hot pressing time 15 min; holding pressure and cooling to room temperature. Then, the strips were cut along a direction perpendicular to the laminate to obtain the chopped fiber prepreg narrow strips. The width of the chopped fiber prepreg narrow strips was 5 mm, the thickness was 0.3 mm, the PA6 content was 50% by mass, and the polyamide resin had a relative viscosity of 2.8.

[0093] 3. Preparation of woven prepreg sheets. Using chopped fiber prepreg narrow strips as warp and fiber-reinforced unidirectional prepreg narrow strips as weft, plain weave prepreg sheets are produced on a loom.

[0094] 4. Preparation of Continuous Fiber Reinforced Laminate. The woven prepreg sheets are laid at a 0° angle, meaning the weft yarns of each layer of woven prepreg sheet within the laminate are parallel, with a thickness of 3mm. It is then placed in the upper and lower plates of a hydraulic press equipped with heating and cooling functions. To control the thickness, additional trim strips are added to assist in forming. The upper and lower plates are preheated at 200℃ for 45 minutes; the hot-pressing temperature is 250℃, the hot-pressing pressure is 4MPa, and the hot-pressing time is 5 minutes; the cooling rate is 45℃ / min, and the pressure is maintained until room temperature.

[0095] Table 4 shows the average tensile strength, flexural strength, and shear strength of the laminate obtained under the conditions of Example 4. The tensile direction was along the 0° layup angle of the laminate.

[0096] Table 4 Mechanical properties of laminates in Example 4

[0097] Tensile strength / MPa Bending strength / MPa Shear strength / MPa Example 4 850 560 112

[0098] Example 5

[0099] 1. Fiber Surface Treatment. 1200D alkali-free continuous glass fibers are placed in a vacuum resistance furnace for high-temperature treatment under a nitrogen protective atmosphere. The heating temperature is set to 500℃ for 30 minutes to remove the sizing agent from the fiber surface during production. Subsequently, the fiber surface is re-sized with water-soluble polyamide at a mass content of 1%.

[0100] Preparation of fiber-reinforced unidirectional prepreg narrow strips. A relatively mature melt impregnation pultrusion molding process was used to prepare fiber-reinforced unidirectional wide strips, which were then cut along the fiber direction into 5 mm wide and 0.3 mm thick prepreg narrow strips, wherein the mass content of PA6 was 35% and the relative viscosity of PA6 was 2.5.

[0101] 2. Fiber Surface Treatment. 1200D alkali-free continuous glass fibers are placed in a vacuum resistance furnace for high-temperature treatment under a nitrogen protective atmosphere. The heating temperature is set to 500℃ for 30 minutes to remove the sizing agent from the fiber surface during production. Subsequently, the fiber surface is re-sized with water-soluble polyamide at a mass content of 1%.

[0102] Preparation of chopped fiber prepreg narrow strips. A mature melt impregnation pultrusion process was used to prepare fiber-reinforced unidirectional wide strips. The unidirectional wide strips contained 50% PA6 by mass and the polyamide resin had a relative viscosity of 2.8. The unidirectional wide strips prepared in step 1 were stacked along 0° (the fiber direction) and hot-pressed to form a laminate. The laminate forming process was as follows: 200℃, preheating time 10 min; hot pressing temperature 240℃, hot pressing pressure 5 MPa, hot pressing time 15 min; holding pressure and cooling to room temperature. Then, the strips were cut along a direction perpendicular to the laminate to obtain the chopped fiber prepreg narrow strips. The width of the chopped fiber prepreg narrow strips was 5 mm, the thickness was 0.3 mm, the PA6 content was 50% by mass, and the polyamide resin had a relative viscosity of 2.8.

[0103] 3. Preparation of woven prepreg sheets. Using chopped fiber prepreg narrow strips as warp and fiber-reinforced unidirectional prepreg narrow strips as weft, plain weave prepreg sheets are produced on a loom.

[0104] 4. Preparation of Continuous Fiber Reinforced Laminate. The woven prepreg sheets are laid at 0° / 90° angles, meaning the weft yarns of each layer of woven prepreg sheet in the laminate are alternately perpendicular, with a thickness of 3mm. It is then placed in the upper and lower plates of a hydraulic press equipped with heating and cooling functions. To control the thickness, additional trim strips are added to assist in forming. The upper and lower plates are preheated at 210℃ for 50 minutes; the hot-pressing temperature is 260℃, the hot-pressing pressure is 5MPa, and the hot-pressing time is 8 minutes; the cooling rate is 50℃ / min, and the pressure is maintained until room temperature.

[0105] Table 5 shows the average tensile strength, flexural strength, and shear strength of the laminate obtained under the conditions of Example 5. The tensile direction was along two perpendicular directions of the laminate.

[0106] Table 5 Mechanical properties of laminates in Example 5

[0107] Tensile strength / MPa Bending strength / MPa Shear strength / MPa Example 5 380 300 99

[0108] Example 6

[0109] 1. Fiber Surface Treatment. T300 continuous carbon fibers are placed in a vacuum resistance furnace for high-temperature treatment under a nitrogen protective atmosphere. The heating temperature is set to 500℃ for 30 minutes to remove the sizing agent from the fiber surface during production. Subsequently, the fiber surface is re-sized with water-soluble polyamide at a mass content of 1%.

[0110] Preparation of fiber-reinforced unidirectional prepreg narrow strips. A relatively mature melt impregnation pultrusion molding process was used to prepare fiber-reinforced unidirectional wide strips, which were then cut along the fiber direction into prepreg narrow strips with a width of 7 mm and a thickness of 0.3 mm. The mass content of PA6 was 30%, and the relative viscosity of PA6 was 2.5.

[0111] 2. Fiber Surface Treatment. T300 continuous carbon fibers are placed in a vacuum resistance furnace for high-temperature treatment under a nitrogen protective atmosphere. The heating temperature is set to 500℃ for 30 minutes to remove the sizing agent from the fiber surface during production. Subsequently, the fiber surface is re-sized with water-soluble polyamide at a mass content of 1%.

[0112] Preparation of chopped fiber prepreg narrow strips. A mature melt impregnation pultrusion process was used to prepare fiber-reinforced unidirectional wide strips. The unidirectional wide strips contained 40% PA6 by mass and the polyamide resin had a relative viscosity of 2.8. The prepared unidirectional wide strips were stacked along 0° (the fiber direction) and hot-pressed to form a laminate. The laminate forming process was as follows: preheating temperature 200℃, preheating time 10 min; hot pressing temperature 240℃, hot pressing pressure 5 MPa, hot pressing time 15 min; holding pressure and cooling to room temperature. Then, the strips were cut along a direction perpendicular to the laminate to obtain the chopped fiber prepreg narrow strips. The width of the chopped fiber prepreg narrow strips was 7 mm, the thickness was 0.3 mm, the PA6 content was 40% by mass, and the polyamide resin had a relative viscosity of 2.8.

[0113] 3. Preparation of woven prepreg sheets. Using chopped fiber prepreg narrow strips as warp and fiber-reinforced unidirectional prepreg narrow strips as weft, plain weave prepreg sheets are produced on a loom.

[0114] 4. Preparation of Continuous Fiber Reinforced Laminate. The woven prepreg sheets are laid at a 0° angle, meaning the weft yarns of each layer of woven prepreg sheet within the laminate are parallel, with a thickness of 3mm. It is then placed in the upper and lower plates of a hydraulic press equipped with heating and cooling functions. To control the thickness, additional trim strips are added to assist in forming. The upper and lower plates are preheated at 200℃ for 45 minutes; the hot-pressing temperature is 250℃, the hot-pressing pressure is 4MPa, and the hot-pressing time is 5 minutes; the cooling rate is 45℃ / min, and the pressure is maintained until room temperature.

[0115] Table 6 shows the average tensile strength, flexural strength, and shear strength of the laminate obtained under the conditions of Example 1. The tensile direction was along the 0° layup angle of the laminate.

[0116] Table 6 Mechanical properties of the laminate in Example 6

[0117] Tensile strength / MPa Bending strength / MPa Shear strength / MPa Example 6 1300 669 115

[0118] Example 7

[0119] 1. Fiber Surface Treatment. T300 continuous carbon fibers are placed in a vacuum resistance furnace for high-temperature treatment under a nitrogen protective atmosphere. The heating temperature is set to 500℃ for 30 minutes to remove the sizing agent from the fiber surface during production. Subsequently, the fiber surface is re-sized with water-soluble polyamide at a mass content of 1%.

[0120] Preparation of fiber-reinforced unidirectional prepreg narrow strips. A relatively mature melt impregnation pultrusion molding process was used to prepare fiber-reinforced unidirectional wide strips, which were then cut along the fiber direction into 5 mm wide and 0.3 mm thick prepreg narrow strips, wherein the mass content of PA6 was 40% and the relative viscosity of PA6 was 2.5.

[0121] 2. Fiber Surface Treatment. T300 continuous carbon fibers are placed in a vacuum resistance furnace for high-temperature treatment under a nitrogen protective atmosphere. The heating temperature is set to 500℃ for 30 minutes to remove the sizing agent from the fiber surface during production. Subsequently, the fiber surface is re-sized with water-soluble polyamide at a mass content of 1%.

[0122] Preparation of chopped fiber prepreg narrow strips. A mature melt impregnation pultrusion process was used to prepare fiber-reinforced unidirectional wide strips. The unidirectional wide strips contained 50% PA6 by mass and the polyamide resin had a relative viscosity of 2.8. The prepared unidirectional wide strips were stacked along 0° (the fiber direction) and hot-pressed to form a laminate. The laminate forming process was as follows: preheating temperature 200℃, preheating time 10 min; hot pressing temperature 240℃, hot pressing pressure 5 MPa, hot pressing time 15 min; holding pressure and cooling to room temperature. Then, the laminate was cut along a direction perpendicular to the laminate, and the resulting sheet was the chopped fiber prepreg narrow strip. The width of the chopped fiber prepreg narrow strip was 5 mm, the thickness was 0.3 mm, the PA6 content in the chopped fiber prepreg narrow strip was 50% by mass, and the relative viscosity of the polyamide resin was 2.8.

[0123] 3. Preparation of woven prepreg sheets. Using chopped fiber prepreg narrow strips as warp and fiber-reinforced unidirectional prepreg narrow strips as weft, plain weave prepreg sheets are produced on a loom.

[0124] 4. Preparation of Continuous Fiber Reinforced Laminate. The woven prepreg sheets are laid at a 0° angle, meaning the weft yarns of each layer of woven prepreg sheet within the laminate are parallel, with a thickness of 3mm. It is then placed in the upper and lower pressure plates of a hydraulic press equipped with heating and cooling functions. To control the thickness, additional trim strips are added to assist in forming. The upper and lower pressure plates are set with a preheating temperature of 230℃ and a preheating time of 50 minutes; a hot-pressing temperature of 280℃, a hot-pressing pressure of 8MPa, and a hot-pressing time of 8 minutes; and a cooling rate of 40℃ / min, maintaining pressure and cooling to room temperature.

[0125] Table 7 shows the average tensile strength, flexural strength, and shear strength of the laminate obtained under the conditions of Example 1. The tensile direction was along the 0° layup angle of the laminate.

[0126] Table 7 Mechanical properties of the laminate in Example 7

[0127] Tensile strength / MPa Bending strength / MPa Shear strength / MPa Example 7 1010 550 104

[0128] Example 8

[0129] 1. Fiber Surface Treatment. T300 continuous carbon fibers are placed in a vacuum resistance furnace for high-temperature treatment under a nitrogen protective atmosphere. The heating temperature is set to 500℃ for 30 minutes to remove the sizing agent from the fiber surface during production. Subsequently, the fiber surface is re-sized with water-soluble polyamide at a mass content of 1%.

[0130] Preparation of fiber-reinforced unidirectional prepreg narrow strips. A relatively mature melt impregnation pultrusion molding process was used to prepare fiber-reinforced unidirectional wide strips, which were then cut along the fiber direction into 5 mm wide and 0.3 mm thick prepreg narrow strips, wherein the mass content of PA6 was 40% and the relative viscosity of PA6 was 2.0.

[0131] 2. Fiber Surface Treatment. T300 continuous carbon fibers are placed in a vacuum resistance furnace for high-temperature treatment under a nitrogen protective atmosphere. The heating temperature is set to 500℃ for 30 minutes to remove the sizing agent from the fiber surface during production. Subsequently, the fiber surface is re-sized with water-soluble polyamide at a mass content of 1%.

[0132] Preparation of chopped fiber prepreg narrow strips. A mature melt impregnation pultrusion process was used to prepare fiber-reinforced unidirectional wide strips. The unidirectional wide strips contained 50% PA6 by mass and the polyamide resin had a relative viscosity of 3.0. The prepared unidirectional wide strips were stacked along 0° (the fiber direction) and hot-pressed to form a laminate. The laminate forming process was as follows: preheating temperature 200℃, preheating time 10 min; hot pressing temperature 240℃, hot pressing pressure 5 MPa, hot pressing time 15 min; holding pressure and cooling to room temperature. Then, the laminate was cut along a direction perpendicular to the laminate, and the resulting sheet was the chopped fiber prepreg narrow strip. The width of the chopped fiber prepreg narrow strip was 5 mm, the thickness was 0.3 mm, the PA6 by mass content was 50%, and the polyamide resin had a relative viscosity of 3.0.

[0133] 3. Preparation of woven prepreg sheets. Using chopped fiber prepreg narrow strips as warp and fiber-reinforced unidirectional prepreg narrow strips as weft, plain weave prepreg sheets are produced on a loom.

[0134] 4. Preparation of Continuous Fiber Reinforced Laminate. The woven prepreg sheets are laid at a 0° angle, meaning the weft yarns of each layer of woven prepreg sheet within the laminate are parallel, with a thickness of 3mm. It is then placed in the upper and lower plates of a hydraulic press equipped with heating and cooling functions. To control the thickness, additional trim strips are added to assist in forming. The upper and lower plates are preheated at 200℃ for 45 minutes; the hot-pressing temperature is 250℃, the hot-pressing pressure is 4MPa, and the hot-pressing time is 5 minutes; the cooling rate is 45℃ / min, and the pressure is maintained until room temperature.

[0135] Table 8 shows the average tensile strength, flexural strength, and shear strength of the laminate obtained under the conditions of Example 1. The tensile direction was along the 0° layup angle of the laminate.

[0136] Table 8 Mechanical properties of the laminate in Example 8

[0137] Tensile strength / MPa Bending strength / MPa Shear strength / MPa Example 8 1095 581 113

[0138] Example 9

[0139] 1. Fiber Surface Treatment. T300 continuous carbon fibers are placed in a vacuum resistance furnace for high-temperature treatment under a nitrogen protective atmosphere. The heating temperature is set to 500℃ for 30 minutes to remove the sizing agent from the fiber surface during production. Subsequently, the fiber surface is re-sized with water-soluble polyamide at a mass content of 1%.

[0140] Preparation of fiber-reinforced unidirectional prepreg narrow strips. A relatively mature melt impregnation pultrusion molding process was used to prepare fiber-reinforced unidirectional wide strips, which were then cut along the fiber direction into prepreg narrow strips with a width of 5 mm and a thickness of 0.2 mm. The mass content of PA6 was 40%, and the relative viscosity of PA6 was 2.5.

[0141] 2. Fiber Surface Treatment. T300 continuous carbon fibers are placed in a vacuum resistance furnace for high-temperature treatment under a nitrogen protective atmosphere. The heating temperature is set to 500℃ for 30 minutes to remove the sizing agent from the fiber surface during production. Subsequently, the fiber surface is re-sized with water-soluble polyamide at a mass content of 1%.

[0142] Preparation of chopped fiber prepreg narrow strips. A mature melt impregnation pultrusion process was used to prepare fiber-reinforced unidirectional wide strips. The unidirectional wide strips contained 50% PA6 by mass and the polyamide resin had a relative viscosity of 2.8. The prepared unidirectional wide strips were stacked along 0° (the fiber direction) and hot-pressed to form a laminate. The laminate forming process was as follows: preheating temperature 200℃, preheating time 10 min; hot pressing temperature 240℃, hot pressing pressure 5 MPa, hot pressing time 15 min; holding pressure and cooling to room temperature. Then, the strips were cut along a direction perpendicular to the laminate to obtain the chopped fiber prepreg narrow strips. The width of the chopped fiber prepreg narrow strips was 5 mm, the thickness was 0.1 mm, the PA6 content was 50% by mass, and the polyamide resin had a relative viscosity of 2.8.

[0143] 3. Preparation of woven prepreg sheets. Using chopped fiber prepreg narrow strips as warp and fiber-reinforced unidirectional prepreg narrow strips as weft, plain weave prepreg sheets are produced on a loom.

[0144] 4. Preparation of Continuous Fiber Reinforced Laminate. The woven prepreg sheets are laid at a 0° angle, meaning the weft yarns of each layer of woven prepreg sheet within the laminate are parallel, with a thickness of 3mm. It is then placed in the upper and lower plates of a hydraulic press equipped with heating and cooling functions. To control the thickness, additional trim strips are added to assist in forming. The upper and lower plates are preheated at 200℃ for 45 minutes; the hot-pressing temperature is 250℃, the hot-pressing pressure is 4MPa, and the hot-pressing time is 5 minutes; the cooling rate is 45℃ / min, and the pressure is maintained until room temperature.

[0145] Table 9 shows the average tensile strength, flexural strength, and shear strength of the laminate obtained under the conditions of Example 1. The tensile direction was along the 0° layup angle of the laminate.

[0146] Table 9 Mechanical properties of laminates in Example 9

[0147] Tensile strength / MPa Bending strength / MPa Shear strength / MPa Example 9 1160 590 114

[0148] Comparative Example 1

[0149] The process of Example 1 is repeated, except that in step 2, the prepreg narrow strips of short-cut fibers are prepared with a PA6 mass content of 100%.

[0150] Table 10 shows the average tensile strength, flexural strength, and shear strength of the laminate obtained under the conditions of Comparative Example 1. The tensile direction was along the 0° layup angle of the laminate.

[0151] Table 10 Mechanical properties of laminates in Comparative Example 1

[0152] Tensile strength / MPa Bending strength / MPa Shear strength / MPa Comparative Example 1 1080 560 85

[0153] Comparative Example 2

[0154] The process of Example 1 is repeated, except that the relative viscosity of PA6 in step 1 is 3.0, and the relative viscosity of PA6 in step 2 is 2.0. Generally, the relative viscosity of PA6 in step 2 is higher than that in step 3; otherwise, during the hot pressing process, the oriented short fibers in step 2 will become disordered as PA6 flows, weakening the shear reinforcement effect in the thickness direction.

[0155] Table 11 shows the average tensile strength, flexural strength, and shear strength of the laminate obtained under the conditions of Comparative Example 2. The tensile direction was along the 0° layup angle of the laminate.

[0156] Table 11 Mechanical properties of laminates in Comparative Example 2

[0157] Tensile strength / MPa Bending strength / MPa Shear strength / MPa Comparative Example 2 1085 557 90

[0158] Comparative Example 3

[0159] The process of Example 1 is repeated, except that in step 4, the upper and lower pressure plates are preheated to a temperature of 160°C for 25 minutes. A low preheating temperature and short preheating time prevent the sheet material from absorbing sufficient heat, resulting in insufficient adhesion between layers after subsequent hot pressing, hindering proper fusion and affecting various mechanical properties.

[0160] Table 12 shows the average tensile strength, flexural strength, and shear strength of the laminate obtained under the conditions of Comparative Example 3. The tensile direction was along the 0° layup angle of the laminate.

[0161] Table 12 Mechanical properties of the laminates in Comparative Example 3

[0162] Tensile strength / MPa Bending strength / MPa Shear strength / MPa Comparative Example 3 1001 486 77

[0163] Comparative Example 4

[0164] The process of Example 1 is repeated, except that in step 4, the upper and lower pressure plates are preheated to a temperature of 270°C for 70 minutes. Although a high preheating temperature and long preheating time can allow the sheet to absorb heat sufficiently, which is beneficial for subsequent hot-pressing and bonding, it can also cause the orientation layer to melt prematurely and excessively, reducing the orientation of the chopped fibers in the thickness direction and thus affecting various mechanical properties.

[0165] Table 13 shows the average tensile strength, flexural strength, and shear strength of the laminate obtained under the conditions of Comparative Example 4. The tensile direction was along the 0° layup angle of the laminate.

[0166] Table 13 Mechanical properties of the four laminated plates in Comparative Example 4

[0167] Tensile strength / MPa Bending strength / MPa Shear strength / MPa Comparative Example 4 1005 491 79

[0168] Comparative Example 5

[0169] The process of Example 1 is repeated, except that in step 4, the upper and lower pressure plates are set to a hot-pressing temperature of 200°C, a hot-pressing pressure of 2MPa, and a hot-pressing time of 3 minutes. If the hot-pressing temperature, pressure, and time are too low, it will hinder melting, affect the lamination of the laminate, and thus affect various mechanical properties.

[0170] Table 14 shows the average tensile strength, flexural strength, and shear strength of the laminate obtained under the conditions of Comparative Example 5. The tensile direction was along the 0° layup angle of the laminate.

[0171] Table 14 Mechanical properties of Comparative Example 5 laminates

[0172] Tensile strength / MPa Bending strength / MPa Shear strength / MPa Comparative Example 5 1006 497 76

[0173] Comparative Example 6

[0174] The process of Example 1 is repeated, except that in step 4, the upper and lower pressure plates are set to a hot-pressing temperature of 320°C, a hot-pressing pressure of 12 MPa, and a hot-pressing time of 15 min. Excessive hot-pressing temperature, pressure, and time will obviously reduce the orientation of the chopped fibers in the thickness direction, thus affecting various mechanical properties.

[0175] Table 15 shows the average tensile strength, flexural strength, and shear strength of the laminate obtained under the conditions of Comparative Example 6. The tensile direction was along the 0° layup angle of the laminate.

[0176] Table 15 Mechanical properties of 6-layer laminates (Comparative Example)

[0177] Tensile strength / MPa Bending strength / MPa Shear strength / MPa Comparative Example 6 1012 505 75

[0178] Comparative Example 7

[0179] The process of Example 1 is repeated, except that the cooling rate in step 4 is 20°C / min. A low cooling rate will cause the orientation state of the short-cut fibers in the orientation layer to continue to deteriorate, thereby affecting various mechanical properties.

[0180] Table 16 shows the average tensile strength, flexural strength, and shear strength of the laminate obtained under the conditions of Comparative Example 7. The tensile direction was along the 0° layup angle of the laminate.

[0181] Table 16 Mechanical properties of the 7-layer laminate in Comparative Example 16

[0182] Tensile strength / MPa Bending strength / MPa Shear strength / MPa Comparative Example 7 1002 495 79

[0183] Comparative Example 8

[0184] The process of Example 1 is repeated, except that the cooling rate in step 4 is 60°C / min. A high cooling rate will affect the melting of the laminate, reduce interlayer adhesion to some extent, and thus affect various mechanical properties.

[0185] Table 17 shows the average tensile strength, flexural strength, and shear strength of the laminate obtained under the conditions of Comparative Example 8. The tensile direction was along the 0° layup angle of the laminate.

[0186] Table 17 Mechanical properties of the 8-layer laminate in comparative example

[0187] Tensile strength / MPa Bending strength / MPa Shear strength / MPa Comparative Example 8 1006 499 81

[0188] The present invention has been described in detail above with reference to specific embodiments and exemplary examples; however, these descriptions should not be construed as limiting the present invention. Those skilled in the art will understand that various equivalent substitutions, modifications, or improvements can be made to the technical solutions and embodiments of the present invention without departing from the spirit and scope of the invention, and all such modifications and improvements fall within the scope of the present invention. The scope of protection of the present invention is defined by the appended claims.

Claims

1. A continuous fiber reinforced polyamide composite material, which is a laminate material, wherein each layer is a unidirectional continuous fiber reinforced polyamide resin, and the layers are connected by oriented short fiber reinforced polyamide resin perpendicular to the unidirectional fiber reinforced polyamide resin in the layer; The preparation method of the continuous fiber reinforced polyamide composite material includes: (1) obtaining continuous fiber reinforced unidirectional prepreg narrow strips; (2) obtaining multiple continuous fiber reinforced unidirectional prepreg wide strips, hot-pressing them into a laminate, and then cutting the laminate to obtain chopped fiber prepreg narrow strips; (3) weaving the continuous fiber reinforced unidirectional prepreg narrow strips and the chopped fiber prepreg narrow strips to obtain woven prepreg sheets; (4) hot-pressing multiple woven prepreg sheets to obtain the continuous fiber reinforced polyamide composite material. Step (1) The continuous fiber reinforced unidirectional prepreg narrow strip includes polyamide resin and fiber, wherein the weight content of polyamide resin is 25%~45%, the weight content of fiber is 55%~75%, and the relative viscosity of polyamide resin is 1.8-2.7; Step (2) The continuous fiber reinforced unidirectional prepreg wide strip includes polyamide resin and fiber, wherein the weight content of polyamide resin is 30%-60%, the weight content of fiber is 40%-70%, and the relative viscosity of polyamide resin in the chopped fiber prepreg narrow strip is 2.7-3.2; The relative viscosity of polyamide resin in the continuous fiber reinforced unidirectional prepreg wide strip is higher than that of polyamide resin in the continuous fiber reinforced unidirectional prepreg narrow strip in step (1); Step (2) The heat The pressing process includes preheating, hot pressing, and cooling. In step (2), the preheating temperature is 180℃-220℃, the preheating time is 5-15min, the hot pressing temperature is 220℃-260℃, the hot pressing pressure is 1-10MPa, the hot pressing time is 10-20min, and the pressure is maintained and cooled to room temperature. In step (4), the hot pressing process includes preheating, hot pressing, and cooling. In step (4), the conditions for the hot pressing process include: setting the preheating temperature to 180℃-250℃, setting the preheating time to 30-60min, setting the hot pressing temperature to 230℃-300℃, setting the hot pressing pressure to 3-10MPa, setting the hot pressing time to 5-10min, setting the cooling rate to 30-50℃ / min, and setting the pressure to maintain and cool to room temperature.

2. The continuous fiber reinforced polyamide composite material according to claim 1, characterized in that, The shear strength of the continuous fiber reinforced polyamide composite material is 92~120MPa.

3. A method for preparing the continuous fiber reinforced polyamide composite material according to claim 1 or 2, the method comprising: (1) Obtaining continuous fiber-reinforced unidirectional prepreg narrow strips; (2) Obtain multiple continuous fiber-reinforced unidirectional prepreg wide bands, hot-press them into laminates, and then cut the laminates to obtain short fiber prepreg narrow bands; (3) The continuous fiber reinforced unidirectional prepreg narrow strip and the chopped fiber prepreg narrow strip are woven to obtain a woven prepreg sheet; (4) Hot-pressing multiple braided prepreg sheets to obtain the continuous fiber reinforced polyamide composite material; Step (1) The continuous fiber reinforced unidirectional prepreg narrow strip includes polyamide resin and fiber, wherein the weight content of the polyamide resin is 25%~45%, the weight content of the fiber is 55%~75%, and the relative viscosity of the polyamide resin is 1.8-2.7; Step (2) The continuous fiber reinforced unidirectional prepreg wide strip includes polyamide resin and fiber, wherein the weight content of the polyamide resin is 30%-60%, the weight content of the fiber is 40%-70%, and the relative viscosity of the polyamide resin in the chopped fiber prepreg narrow strip is 2.7-3.2; Step ( 2) The relative viscosity of the polyamide resin in the continuous fiber reinforced unidirectional prepreg wide strip is higher than that in the continuous fiber reinforced unidirectional prepreg narrow strip in step (1); the hot pressing in step (2) includes preheating, hot pressing and cooling; in step (2), the preheating temperature is 180℃-220℃, the preheating time is 5-15min, the hot pressing temperature is 220℃-260℃, the hot pressing pressure is 1-10MPa, the hot pressing time is 10-20min, and the pressure is maintained and cooled to room temperature; in step (4), the hot pressing process includes preheating, hot pressing and cooling. In step (4), the conditions for hot pressing include: setting the preheating temperature to 180℃-250℃, setting the preheating time to 30-60min, setting the hot pressing temperature to 230℃-300℃, setting the hot pressing pressure to 3-10MPa, setting the hot pressing time to 5-10min, setting the cooling rate to 30-50℃ / min, and setting the pressure holding and cooling to room temperature.

4. The preparation method according to claim 3, characterized in that, In step (1), the continuous fiber reinforced unidirectional prepreg narrow strip is made of polyamide resin selected from one or more of nylon 6, nylon 66, nylon 610, and branched nylon, and / or the fiber is selected from one or more of carbon fiber, aramid fiber, glass fiber, and basalt fiber. And / or, In step (2), the polyamide resin in the continuous fiber reinforced unidirectional prepreg wide band is selected from one or more of nylon 6, nylon 66, nylon 610, and branched nylon, and / or the fiber is selected from one or more of carbon fiber, aramid fiber, glass fiber, and basalt fiber.

5. The preparation method according to claim 3, characterized in that, The width of the continuous fiber-reinforced unidirectional prepreg narrow strip is 3~7mm, and the thickness is 0.2~0.5mm; and / or, The width of the chopped fiber prepreg narrow strip is 3-7 mm, and the thickness is 0.1-0.5 mm.

6. The preparation method according to claim 3, characterized in that, Before preparing the continuous fiber reinforced unidirectional prepreg narrow strip in step (1) and the continuous fiber reinforced unidirectional prepreg wide strip in step (2), the fibers are first subjected to surface treatment independently: under a protective atmosphere, the sizing agent on the surface of the fibers is removed by heating; then the fibers are resized.

7. The preparation method according to claim 3, characterized in that, In step (2), the continuous fiber-reinforced unidirectional prepreg broadband is stacked along 0° and hot-pressed to form a laminate.

8. The preparation method according to claim 3, characterized in that, In step (2), the fiber is cut along a direction perpendicular to the length of the continuous fiber in the laminate to obtain the chopped fiber prepreg narrow strip.

9. The preparation method according to claim 3, characterized in that, In step (3), the chopped fiber prepreg narrow strip is used as the warp yarn and the continuous fiber reinforced unidirectional prepreg narrow strip is used as the weft yarn to weave a prepreg sheet.

10. The preparation method according to claim 3, characterized in that, In step (4), according to the required thickness of the continuous fiber reinforced polyamide composite material, multiple woven prepreg sheets are laid up in the range of -90° to 90° layup angle, wherein the layup angle is changed by rotating the continuous fiber reinforced unidirectional prepreg narrow weft yarn in the woven prepreg sheet as a reference.

11. A continuous fiber-reinforced polyamide composite material obtained by the preparation method according to any one of claims 3 to 10.