Preparation method of thermoplastic in-situ polymerization polyamide composite material plate spring and plate spring

Abstract

The invention provides a preparation method of a thermoplastic in-situ polymerization polyamide composite material plate spring and the plate spring. The preparation method comprises the following steps that fiber fabric is pre-formed and then laid in a mold, a low-viscosity thermoplastic resin monomer mixture is injected into the mold at high pressure, a fiber pre-formed body is fully soaked, and the plate spring is obtained; and heating, pressurizing and performing in-situ polymerization to form the composite material plate spring. The low-viscosity resin monomer is used for one-time high-pressure injection and infiltration of the fiber fabric for forming, the prepreg manufacturing procedures are reduced, the material cost is reduced, the paving time is shortened, meanwhile, the forming time is shortened to be within 30 min, the production efficiency is greatly improved, the requirements of large-batch products can be met, and the problems that thermoplastic resin is large in viscosity, and the cost is low are solved. The fiber fabric cannot be quickly and effectively infiltrated.

Description

Technical Field

[0001] This application relates to the technical field of automotive leaf springs, and particularly relates to a preparation method and a leaf spring of a thermoplastic in-situ polymerization polyamide composite material leaf spring. Background Art

[0002] As an important part of the automotive suspension, the main function of the leaf spring is to bear and transmit the vertical force and various forces other than the vertical force between the frame and the axle and the torque formed by them, and to ensure that the wheels move relative to the frame (or body) according to a certain relationship, to relieve and suppress the impact caused by uneven road surfaces, and to ensure the ride comfort and handling stability of the vehicle. The working conditions are harsh. At present, automotive leaf springs are mainly made of multiple alloy steel leaf springs, accounting for 10-20% of the chassis weight, and have problems such as large weight and complex forming processes.

[0003] In recent years, fiber-reinforced composite material leaf springs substituting steel with plastic have gradually become a development trend. Compared with steel leaf springs, fiber-reinforced composite material leaf springs have the characteristics of light weight, large elastic strain, high specific strain, long fatigue life, and good "safe fracture property".

[0004] Fiber-reinforced composite materials can be divided into thermosetting composite materials and thermoplastic composite materials. Among them, thermosetting composite materials are widely used due to their good designability, light weight and high strength, corrosion resistance, etc. At present, composite material leaf springs are basically made of thermosetting composite materials, and have problems such as long molding cycle, poor toughness, and non-recyclability. In contrast, thermoplastic composite materials have the advantages of high specific strength, high specific modulus, good impact resistance, recyclability, etc., and are the best choice for realizing the lightweight of structural parts in the fields of automobiles, rail transit, new energy, etc., and substituting steel with plastic.

[0005] There are usually two preparation methods for existing composite material leaf springs. One is prepreg compression molding, and the other is HP-RTM molding. The forming process of thermosetting composite material leaf springs is relatively mature. For example, the patent with the publication number CN102785372A discloses a manufacturing method of a fiber-reinforced plastic plate spring. It uses prepreg layup and is compression molded under high temperature and high pressure. The layup and curing time are more than 2 hours, and the efficiency is relatively low. The patent with the publication number CN115782238A discloses a rapid forming process for a composite material leaf spring body. It uses a glass fiber fabric for layup, preforms it and then puts it into a mold, injects epoxy resin under high pressure, and is compression molded under high temperature and high pressure. The forming cycle is 5 minutes, and its performance is better than that of prepreg compression molded leaf springs, which can meet the needs of mass production of automobiles. However, there are still problems such as difficult recycling and poor toughness. Because of the high melt viscosity of thermoplastic resin, it is impossible to quickly and effectively infiltrate fibers, and it is difficult to directly use the HP-RTM process. At present, there is only an application of thermoplastic composite prepreg compression molded leaf springs in China. For example, the patent with the publication number CN111497281A discloses a thermoplastic composite leaf spring and its manufacturing method. After the prepreg is heated and melted layer by layer by point heating, pressure is applied through a pressure roller for bonding, and forming is carried out while laying up, to produce a continuous fiber-reinforced thermoplastic composite leaf spring. However, this method has low efficiency and cannot meet the needs of mass production of products.

[0006] It can be seen that the existing technologies have the following problems:

[0007] (1) The prepreg compression molding process has a long layup time. After being put into the mold, it needs to be heated for 30 minutes without pressure first to soften and make the epoxy resin flowable, and the curing time after pressurization is also about 2 hours. Moreover, the thicker the leaf spring product, the longer the required time, and the production efficiency is relatively low, unable to meet the mass demand. In addition, the process from fabric to prepreg semi-finished product increases the production process, resulting in a relatively high cost of prepreg.

[0008] (2) Although the HP-RTM process improves the production efficiency, it is currently only applicable to thermosetting composite materials and cannot solve the problems of non-recyclability and poor toughness of thermosetting composite materials. Summary of the Invention

[0009] This application is made in view of the above problems, and its purpose is to provide a preparation method and a leaf spring of a thermoplastic in-situ polymerization polyamide composite material, which have high preparation efficiency and excellent mechanical properties and recyclability.

[0010] Specifically, the first aspect of this application provides a preparation method of a thermoplastic in-situ polymerization polyamide composite material leaf spring, including the following steps:

[0011] Lay the fiber fabric in a preform mold, heat and apply pressure to obtain a preform;

[0012] Inject a low-viscosity thermoplastic resin monomer mixture into the mold under high pressure, fully infiltrate the fiber preform, and heat and press for in-situ polymerization to form a composite leaf spring.

[0013] Further, the thermoplastic resin monomer mixture includes material A and material B, wherein material A is a mixture of lactam and a catalyst in a mass ratio of 100:0.01 to 4.

[0014] Further, material B is a mixture of lactam, activator, mold release agent, and antioxidant in a mass ratio of 100:0.1 to 4:0.01 to 1:0.01 to 1.

[0015] Further, the mass ratio of material A to material B is 1:0.8 to 1.2.

[0016] Further, the lactam is caprolactam and / or laurolactam, preferably caprolactam.

[0017] Further, the catalyst is one or more of isocyanate, isocyanurate, biuret, urethane, uretdione, carbodiimide, or a compound of caprolactam.

[0018] Further, the activator is one or more of alkali metal lactam halides, alkaline earth metal lactam halides, alkali metal lactam salts, alkaline earth metal lactam salts, alkali metal hydroxides, and alkaline earth metal hydroxides.

[0019] Among them, lactam halide, preferably magnesium lactam bromide; alkali metal lactam salt, preferably disodium lactam, sodium lactam, potassium lactam; alkaline earth metal lactam salt, preferably magnesium lactam; alkali metal hydroxide, preferably sodium hydroxide; alkaline earth metal hydroxide, preferably magnesium hydroxide.

[0020] Further, the mold release agent is a silicone grease mold release agent and can be added to material A or material B.

[0021] Further, the antioxidant is a nylon-based antioxidant and can be added to material A or material B.

[0022] Further, the fiber fabric is woven from any one or more of glass fiber, carbon fiber, basalt fiber, aramid fiber, and organic fiber.

[0023] Further, the weaving form of the fiber fabric is any one or a mixture of 2D, 2.5D, and 3D.

[0024] Further, the temperature of the thermoplastic resin monomer mixture is 80 to 140 °C.

[0025] Further, before the thermoplastic resin monomer mixture is injected into the mold, the mold clamping pressure is lower than 0.5 MPa, the vacuum is pumped to a vacuum degree of -0.09 MPa to -0.1 MPa, the injection pressure is 0.1 to 20 MPa, and after the injection is completed, the curing pressure is increased to 10 to 20 MPa.

[0026] Further, the temperature of the pressure curing is 140 to 180 °C, and the time is 5 to 30 min.

[0027] The second aspect of the present application provides a leaf spring for an automobile, and the leaf spring for an automobile is prepared by the preparation method of the thermoplastic in-situ polymerization polyamide composite material leaf spring.

[0028] The present invention has the following beneficial effects:

[0029] (1) By using a one-time high-pressure injection of resin monomers to infiltrate the fiber fabric for molding, the present invention reduces the prepreg manufacturing process, reduces the material cost, shortens the laying time compared with the preparation of the existing thermoplastic composite leaf spring (CN111497281A), and at the same time shortens the molding time to within 30 min, greatly improving the production efficiency, meeting the demand for mass-produced products, and solving the problem that the viscosity of thermoplastic resin is large and it cannot quickly and effectively infiltrate the fiber fabric.

[0030] (2) The thermoplastic in-situ polymerization polyamide composite material leaf spring prepared by the method of the present invention has performance equivalent to that of the thermosetting composite material leaf spring, better toughness, and at the same time has the advantage of being recyclable, meeting the requirements of green environmental protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the present drawings or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present drawings. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on the structures shown in these drawings.

[0032] Figure 1 It is a schematic structural diagram of the leaf spring of the present invention.

[0033] The realization, functional characteristics and advantages of the present drawings will be further described in conjunction with the embodiments with reference to the drawings. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0034] In order to make the objectives, technical solutions and advantages of the present application more clear and understandable, the following describes and explains the present application in combination with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application. Based on the embodiments provided in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present application.

[0035] Obviously, the following description is only some examples or embodiments of the present application. For those of ordinary skill in the art, without creative efforts, the present application can also be applied to other similar scenarios. In addition, it can also be understood that although the efforts made in this development process may be complex and lengthy, for those of ordinary skill in the art related to the content disclosed in the present application, some design, manufacturing or production changes based on the technical content disclosed in the present application are only conventional technical means and should not be understood as the content disclosed in the present application being insufficient.

[0036] If there is no special explanation, the "including" and "comprising" mentioned in the present application mean open-ended, and can also be closed-ended. For example, the "including" and "comprising" can mean that other components not listed can also be included or comprised, or only the components listed can be included or comprised.

[0037] An embodiment of the first aspect of the present invention provides a method for preparing a thermoplastic in-situ polymerization polyamide composite leaf spring, including the following steps:

[0038] Lay the fiber fabric into the preforming mold in a specific order, heat and press to obtain a preform;

[0039] Inject the low-viscosity thermoplastic resin monomer mixture into the mold under high pressure, infiltrate the preform, and pressurize and heat to cure to form a composite leaf spring.

[0040] The present invention prepares a preform by laying fiber fabrics into a preforming mold in a specific order, ensuring that the fibers are arranged in a predetermined direction and density within the mold, thereby optimizing the mechanical properties and structural stability of the composite material. Through this step, a preform with a predetermined shape and structure is obtained for subsequent infiltration and curing molding of thermoplastic resin. Then, the preform is placed into the cavity of the mold, the mold is closed, the closing pressure is lower than 0.5 MPa, and then the mold is evacuated, and the vacuum degree is -0.098 MPa to remove the air in the mold and avoid the generation of bubbles, thereby further improving the quality of the leaf spring. The present invention infiltrates a thermoplastic resin monomer mixture into the preform, and by precisely controlling the temperature and injection pressure of the resin, it is ensured that the resin can uniformly and quickly infiltrate into every part of the fiber preform. The key to this step lies in the temperature control of the thermoplastic resin monomer mixture, and its range is precisely set at 80 - 140 °C to ensure that the fluidity and wettability of the resin reach the best state. After infiltration, the molding pressure is increased to 10 - 20 MPa to ensure the tight combination of the resin and the fiber preform. Finally, through the pressurized curing process, the composite leaf spring is cured at a temperature of 140 - 180 °C for 5 - 30 min to completely cure the resin and form a leaf spring with excellent mechanical properties.

[0041] In an embodiment of the present invention, the thermoplastic resin monomer mixture includes material A and material B. Among them, material A is a mixture of lactam and a catalyst in a ratio of 100:0.01 - 4, and material B is a mixture of lactam, activator, mold release agent, and antioxidant in a ratio of 100:0.1 - 4:0.01 - 1:0.01 - 1. When in use, material A and material B are mixed. The role of the activator is to promote the ring-opening polymerization of lactam, and the catalyst plays a role in accelerating the polymerization reaction. The mixing ratio of material A and material B and the respective component ratios are carefully designed to ensure that the resin mixture has appropriate fluidity and curing speed during the infiltration and curing processes, thereby meeting the preparation requirements of the thermoplastic in-situ polymerization polyamide composite leaf spring. By adjusting the mixing ratio of material A and material B, the performance of the resin can be further optimized to adapt to different fiber types, weaving forms, and molding conditions.

[0042] In an embodiment of the present invention, the mass ratio of material A to material B is 1:0.8 - 1.2. Preferably, the mass ratio of material A to material B is 1:1.

[0043] Furthermore, the lactam is caprolactam and / or laurolactam, preferably caprolactam.

[0044] The catalyst is one or a combination of isocyanate, isocyanurate, biuret, urethane, uretdione, carbodiimide, or a compound of caprolactam, and the compound of caprolactam can be bisacylated caprolactam-1,6-hexanediamine, etc.

[0045] The catalyst is preferably toluene-2,4-diisocyanate.

[0046] The activator is one or more of alkali metal lactam halides, alkaline earth metal lactam halides, alkali metal lactam salts, alkaline earth metal lactam salts, alkali metal hydroxides, and alkaline earth metal hydroxides.

[0047] Among them, the lactam halide is preferably magnesium lactam bromide; the alkali metal lactam salt is preferably disodium lactam, sodium lactam, potassium lactam; the alkaline earth metal lactam salt is preferably magnesium lactam; the alkali metal hydroxide is preferably sodium hydroxide; the alkaline earth metal hydroxide is preferably magnesium hydroxide.

[0048] Preferably, the activator is sodium hydroxide.

[0049] The demolding agent is a silicone grease demolding agent, such as Release B (Brugmann).

[0050] The antioxidant is a nylon-based antioxidant, preferably antioxidant 168.

[0051] Specifically, the preparation method of the thermoplastic resin monomer mixture is as follows: Using a high-pressure injection molding machine, the A and B materials of the polyamide monomer are mixed at a ratio of 1:1. The A and B materials are separately melted by heating to 120-135 °C before mixing, and the moisture is removed by vacuum pumping respectively. The vacuum degree is -0.098 MPa, and the vacuum pumping time is not less than 30 min. The A and B materials are mixed in the injection gun head, and the temperature of the injection gun head is 80-140 °C. After the A and B materials are mixed, they are immediately injected into the mold.

[0052] In the embodiments of the present invention, the fiber fabric is woven from any one or more of glass fiber, carbon fiber, basalt fiber, aramid fiber, and organic fiber, and the weaving form is any one or more mixtures of 2D, 2.5D, and 3D.

[0053] The specific preparation process of the preform is as follows: Using a cutting machine, the warp knitted fabrics of ±45° glass fiber, carbon fiber, basalt fiber, etc. with a weight of 600 g / m 2 are cut into specific shapes and quantities, and are sequentially laid in a preform mold according to the laying sequence. Each layer of fabric is shaped using a sizing agent; the preform mold is closed, heated to 105-115 °C, pressurized to 1.8-2.2 MPa, and the forming time is 15-30 min to bond multiple layers of fabric into a whole to obtain a preform.

[0054] In an embodiment of the present invention, the temperature of the thermoplastic resin monomer mixture before injection is 80 to 140 °C. Specifically, the temperature of the resin mixture before injection is any one of 80 °C, 85 °C, 90 °C, 100 °C, 110 °C, 120 °C, 130 °C, and 140 °C. If the temperature is too low, the resin has poor fluidity and it is difficult to fully penetrate the fiber layer; if the temperature is too high, the resin may cure prematurely, affecting the overall performance of the composite material. During the injection process, the temperature and pressure need to be strictly controlled to ensure uniform distribution of the resin and form a dense structure.

[0055] In an embodiment of the present invention, before the thermoplastic resin monomer mixture is injected into the mold, the mold closing pressure is less than 0.5 MPa, evacuated to a vacuum degree of -0.098 MPa, the injection pressure is 0.1 to 20 MPa, and after injection, the forming pressure is increased to 10 to 20 MPa. The evacuation process effectively removes air bubbles to ensure no defects inside the material. Pressurization after injection allows the resin to fully penetrate, further improving the density and strength of the composite material, and finally obtaining a high-performance leaf spring.

[0056] In an embodiment of the present invention, the temperature for curing the preform is 140 to 180 °C, and the time is 5 to 30 min. The curing temperature is preferably 160 °C and the time is 10 min. Under these conditions, the resin is completely cured and the fiber structure is stable, ensuring that the leaf spring has excellent mechanical properties and long-term stability. After curing, it is cooled to room temperature and the finished product is removed from the mold.

[0057] An embodiment of the second aspect of the present application provides an automotive leaf spring, which is prepared by the method for preparing a thermoplastic in-situ polymerization polyamide composite leaf spring. This leaf spring not only has significant weight reduction, but also has excellent mechanical properties, toughness and recyclability. It is suitable for various automotive suspension systems, effectively improving vehicle driving stability and comfort, extending service life, reducing maintenance costs, and being environmentally friendly.

[0058] Example 1

[0059] A method for preparing a thermoplastic in-situ polymerization polyamide composite leaf spring includes the following steps:

[0060] S1: Use a cutting machine to cut glass fibers (diameter 15 μm, tensile strength 1500 MPa) into specific shapes and quantities, and lay them in a preform mold in a specific laying order. Between each layer of fabric, E-100 glass fiber sizing emulsion adhesive is used for sizing. The dosage ratio of glass fiber to E-100 glass fiber sizing emulsion adhesive is 100:2;

[0061] S2: Close the preform mold, heat it to 110 °C, pressurize it to 2.2 MPa, and the forming time is 20 min to bond multiple layers of fabric into a whole to obtain a preform;

[0062] S3: Heat the mold to 165°C and spray a mold release agent inside the mold.

[0063] S4: Mix caprolactam and tolylene diisocyanate in a ratio of 100:1 to form Material A, and mix caprolactam, sodium hydroxide, silicone grease mold release agent, and antioxidant 168 in a ratio of 100:0.5:0.3:0.6 to form Material B. Use a high-pressure injection molding machine to mix Material A and Material B of the polyamide monomer in a ratio of 1:1. Heat Material A and Material B to 125°C for melting before mixing, then evacuate to remove moisture, with a vacuum degree of -0.098 MPa and a vacuum evacuation time of 30 min; then mix Material A and Material B, and control the temperature of the injection gun head at 100°C.

[0064] S5: Place the preform into the cavity of the mold, close the mold, control the closing pressure at 0.5 MPa, then evacuate the mold cavity with a vacuum degree of -0.098 MPa, and then inject the resin mixture into the mold containing the preform, with an injection pressure of 5 MPa. After injection, increase the molding pressure to 15 MPa to cure the preform.

[0065] S6: The molding temperature is 165°C, the molding time is 10 min, demold and take out to obtain the molded thermoplastic in-situ polymerization polyamide composite leaf spring.

[0066] Example 2

[0067] A preparation method of a thermoplastic in-situ polymerization polyamide composite leaf spring, comprising the following steps:

[0068] S1: Use a cutting machine to cut glass fibers (diameter 15 μm, tensile strength 1500 MPa) into specific shapes and quantities, and sequentially lay them in a preform mold according to the laying sequence. Use E-100 glass fiber sizing emulsion adhesive to bond between each layer of fabric, and the dosage ratio of fiber to E-100 glass fiber sizing emulsion adhesive is 100:2.

[0069] S2: Close the preform mold, heat it to 110°C, apply pressure to 2.2 MPa, and the molding time is 20 min to bond multiple layers of fabric into a whole to obtain a preform.

[0070] S3: Heat the mold to 150°C and spray a mold release agent inside the mold.

[0071] S4: Mix caprolactam and toluene diisocyanate in a ratio of 100:2 to form Material A, and mix caprolactam, sodium hydroxide, silicone grease release agent, and antioxidant 168 in a ratio of 100:0.5:0.3:0.6 to form Material B. Use a high-pressure injection molding machine to mix Material A and Material B of polyamide monomers in a ratio of 1:1. Heat Material A and Material B to 125°C for melting before mixing, and then evacuate to remove moisture. The vacuum degree is -0.098 MPa, and the evacuation time is 30 min. Then mix Material A and Material B, and control the temperature of the injection gun head at 120°C;

[0072] S5: Place the preform into the cavity of the mold, close the mold, control the closing pressure at 0.5 MPa, then evacuate the mold cavity. The vacuum degree of evacuation is -0.098 MPa. Then inject the resin mixture into the mold with the preform placed inside. The injection pressure is 0.5 MPa. After injection, increase the forming pressure to 15 MPa to cure the preform;

[0073] S6: The forming temperature is 150°C, the forming time is 25 min. Demold and take out to obtain the formed thermoplastic in-situ polymerization polyamide composite leaf spring.

[0074] Example 3

[0075] A preparation method of a thermoplastic in-situ polymerization polyamide composite leaf spring, comprising the following steps:

[0076] S1: Use a cutting machine to cut glass fibers (diameter 15 μm, tensile strength 1500 MPa) into specific shapes and quantities, and sequentially lay them in a preform mold according to the laying order. Use E-100 glass fiber sizing emulsion adhesive to size between each layer of fabric. The dosage ratio of the fiber to the E-100 glass fiber sizing emulsion adhesive is 100:2;

[0077] S2: Close the preform mold, heat it to 110°C, apply pressure to 2.2 MPa, and the forming time is 20 min to bond multiple layers of fabric into a whole to obtain a preform;

[0078] S3: Heat the mold to 170°C and spray a release agent inside the mold;

[0079] S4: Mix caprolactam and a compound of caprolactam (bisacylated lactam - 1,6 - hexanediamine) at a ratio of 100:3 to form Material A, and mix caprolactam, magnesium lactamide bromide, silicone grease release agent, and antioxidant 168 at a ratio of 100:2:0.3:0.6 to form Material B. Use a high - pressure injection machine to mix Material A and Material B of polyamide monomers at a ratio of 1:1. Heat Material A and Material B to 125°C for melting before mixing, then evacuate to remove moisture, with a vacuum degree of - 0.098 MPa and a vacuum time of 30 min. Then mix Material A and Material B, and control the temperature of the injection gun head at 80°C;

[0080] S5: Place the preform into the cavity of the mold, close the mold, control the closing pressure at 0.5 MPa, then evacuate the mold cavity with a vacuum degree of - 0.098 MPa, and then inject the resin mixture into the mold with the preform placed inside. The injection pressure is 10 MPa, and after injection, increase the molding pressure to 14 MPa to cure the preform;

[0081] S6: The molding temperature is 170°C, the molding time is 5 min, demold and take out to obtain the molded thermoplastic in - situ polymerization polyamide composite leaf spring.

[0082] Example 4

[0083] A preparation method of a thermoplastic in - situ polymerization polyamide composite leaf spring, comprising the following steps:

[0084] S1: Use a cutting machine to cut basalt fibers and aramid fibers (the dosage ratio of basalt fibers to aramid fibers is 1:1, where the elastic modulus of basalt fibers is 105 GPa and the tensile strength is 4500 MPa; the diameter of aramid fibers is 14 μm and the tensile strength is 2800 MPa) into specific shapes and quantities, and sequentially lay them in a pre - forming mold according to the laying order. Use nano - glue for shaping between each layer of fabric, and the dosage ratio of fibers to nano - glue is 100:1.5;

[0085] S2: Close the pre - forming mold, heat to 115°C, pressurize to 1.8 MPa, and the molding time is 30 min to bond multiple layers of fabric into a whole to obtain a preform;

[0086] S3: Heat the mold to 165°C and spray a release agent inside the mold;

[0087] S4: Mix caprolactam and carbodiimide at a ratio of 100:3.5 to form Material A, and mix caprolactam, sodium dilactam, silicone grease release agent, and antioxidant 168 at a ratio of 100:2.5:0.3:0.6 to form Material B. Use a high-pressure injection molding machine to mix Material A and Material B of the polyamide monomer at a ratio of 1:1. Heat Material A and Material B to 125 °C for melting before mixing, and then evacuate to remove moisture. The vacuum degree is -0.098 MPa, and the evacuation time is 30 min. Then mix Material A and Material B, and control the temperature of the injection gun head at 90 °C;

[0088] S5: Place the preform into the cavity of the mold, close the mold, control the closing pressure at 0.4 MPa, then evacuate the mold cavity. The vacuum degree of evacuation is -0.098 MPa. Then inject the resin mixture into the mold with the preform placed inside. The injection pressure is 17 MPa. After injection, increase the molding pressure to 20 MPa to cure the preform;

[0089] S6: The molding temperature is 165 °C, the molding time is 10 min. Demold and take out to obtain the molded thermoplastic in-situ polymerization polyamide composite leaf spring.

[0090] Example 5

[0091] A preparation method of a thermoplastic in-situ polymerization polyamide composite leaf spring, comprising the following steps:

[0092] S1: Use a cutting machine to cut carbon fiber (with a diameter of 11 μm and a tensile strength of 5000 MPa) into specific shapes and quantities, and sequentially lay and cover them in a preform mold. Use nano glue for sizing between each layer of fabric. The dosage ratio of fiber to nano glue is 100:1.8;

[0093] S2: Close the preform mold, heat to 110 °C, apply pressure to 2 MPa, and the molding time is 25 min. Bond multiple layers of fabric into a whole to obtain a preform;

[0094] S3: Heat the mold to 165 °C and spray a release agent inside the mold;

[0095] S4: Mix caprolactam and uretdione at a ratio of 100:1 to form Material A, and mix caprolactam, sodium lactam, silicone grease release agent, and antioxidant 168 at a ratio of 100:0.5:0.3:0.6 to form Material B. Use a high-pressure injection molding machine to mix Material A and Material B of the polyamide monomer at a ratio of 1:1. Heat Material A and Material B to 125 °C for melting before mixing, and then evacuate to remove moisture. The vacuum degree is -0.098 MPa, and the evacuation time is 30 min. Then mix Material A and Material B, and control the temperature of the injection gun head at 110 °C;

[0096] S5: Place the preform into the cavity of the mold, close the mold, control the mold closing pressure to be lower than 0.5 MPa, then evacuate the mold cavity, with the vacuum degree being -0.098 MPa, and then inject the resin mixture into the mold with the preform placed therein, with the injection pressure being 8 MPa. After the injection is completed, increase the molding pressure to 15 MPa to cure the preform;

[0097] S6: The molding temperature is 165 °C, the molding time is 10 min, demold and take out to obtain the formed thermoplastic in-situ polymerization polyamide composite leaf spring.

[0098] Comparative Example 1

[0099] Adopt the HP-RTM process, lay the glass fiber into the preform mold, lay a 10-μm thermoplastic phenolphthalein-based polyether ketone resin film between each layer of reinforcing fiber fabric, put the laid preform into the mold for heating and compaction, melt the thermoplastic phenolphthalein-based polyether ketone resin film to bond the reinforcing fiber fabrics into one body to form a preform; put the preform into the cavity of the injection mold, evacuate the mold, then inject the resin of the RA-8930A / B system under high pressure, and add an internal mold release agent to the resin. The resin injection temperature is 65 °C, and cure at a pressure of 5 MPa and a temperature of 120 °C for 10 min, and obtain the composite leaf spring body after cooling.

[0100] Comparative Example 2

[0101] This comparative example is basically the same as Example 1, the difference being that the fiber content in the leaf spring is 55%.

[0102] Prepare the leaf springs according to the methods of Examples 1-5 and Comparative Examples 1-2, and conduct corresponding performance tests, and the results are shown in Table 1.

[0103] Table 1 Performance of the leaf springs of Examples 1-5

[0104]

[0105] As can be seen from Table 1, when the fiber weight content in the composite leaf springs in Examples 1-5 of the present invention is 65%, the tensile strength is between 801 MPa and 950 MPa, the flexural strength is between 801 MPa and 900 MPa, and the impact strength is between 198 KJ / m 2 to 213 KJ / m 2Among them, excellent mechanical properties are demonstrated. The interlaminar shear strength also remains at a relatively high level, ensuring the stability and durability of the leaf spring in practical applications. In Example 4, basalt fiber and aramid fiber, and in Example 5, carbon fiber are used, which significantly improve the mechanical properties of the leaf spring compared to the leaf springs prepared from glass fiber in Examples 1-3. These performance data fully verify the feasibility and effectiveness of the preparation method described in the present invention, providing a solid experimental basis for the wide application of thermoplastic in-situ polymerization polyamide composite leaf springs. At the same time, the thermoplastic resin material used in the present invention is recyclable, which conforms to the current environmental protection concept and is conducive to achieving sustainable development.

[0106] From Examples 1-5 and Comparative Example 1, it can be seen that the present invention uses thermoplastic resin as the main raw material, resulting in higher impact strength of the leaf spring. The reason may be that the molecular chains of thermoplastic resin are linear or branched structures, and when subjected to impact, they can absorb energy through the slip and orientation of molecular chains, showing a higher elongation at break. In Comparative Example 1, the thermosetting resin forms a three-dimensional cross-linked network after curing, and the molecular chain movement is restricted, showing brittle fracture characteristics. This structural difference enables thermoplastic materials to dissipate energy through plastic deformation under impact loads rather than directly cracking.

[0107] From Examples 1-5 and Comparative Example 2, it can be seen that when the fiber content in the leaf spring is 55%, the performance of the leaf spring deteriorates. The reason is that the mechanical properties of the fiber are much higher than those of the resin matrix. When the fiber content decreases, the overall load-bearing capacity of the material decreases. At the same time, when the fiber content decreases, the stress transfer paths become fewer, local stress concentration intensifies, which is prone to early failure. Moreover, a low fiber content may lead to insufficient resin wrapping and a decrease in interfacial bonding strength, further weakening the performance.

[0108] Recyclability

[0109] Recyclability is a significant advantage of thermoplastic composites. In Example 1, thermoplastic resin is used as the main raw material. When heated to a certain temperature, the resin will soften and melt, and can be molded again after cooling, and this process can be repeated.

[0110] The recycling methods are as follows: The discarded thermoplastic composite leaf spring is crushed into small particles, and then ground to a finer state. Then, screening and grading are carried out. Through screening and grading, particles of different sizes are separated for subsequent processing. In this way, longer carbon fibers can be screened out to improve the quality of the recycled material. The graded carbon fibers can be used to manufacture new automotive parts according to their length and performance.

[0111] Alternatively, the discarded thermoplastic composite leaf spring powder or production waste can be simply shredded into smaller pieces, melt granulated, and remolded into new products with lower performance requirements through injection molding or compression molding.

[0112] However, the thermosetting epoxy resin used in Comparative Example 1, or other thermosetting resins such as polyurethane resin, etc., form a stable structure after curing and are difficult to recycle and reuse. Compared with the thermoplastic resin material of the present invention, there are obvious disadvantages in terms of environmental protection and sustainability.

[0113] In summary, the thermoplastic in-situ polymerization polyamide composite leaf spring and its preparation method provided by the present invention not only solve the problems of large weight and insufficient mechanical properties of the leaf spring in the prior art, but also achieve the goals of recyclable environmental protection and efficient production, which is of great significance for promoting the lightweight process and energy conservation and emission reduction in the automotive industry.

[0114] It should be noted that this application is not limited to the above embodiments. The above embodiments are only examples, and embodiments with the same structure and the same effect as the technical idea within the technical scope of this application are included in the technical scope of this application. In addition, within the scope not departing from the gist of this application, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways constructed by combining some constituent elements of the embodiments are also included in the scope of this application.

Claims

1. A preparation method of a thermoplastic in-situ polymerization polyamide composite leaf spring, characterized in that, It includes the following steps: Lay the fiber fabric in a preforming mold, heat and apply pressure to obtain a preform; Inject the thermoplastic resin monomer mixture into the mold, fully infiltrate the preform, and heat and apply pressure to in-situ polymerize to form a composite leaf spring; The thermoplastic resin monomer mixture includes material A and material B. Material A is a mixture of lactam and a catalyst in a mass ratio of 100:0.01-4, and material B is a mixture of lactam, activator, mold release agent, and antioxidant in a mass ratio of 100:0.1-4:0.01-1:0.01-1; The fiber content in the composite leaf spring is 60-65%; 2. The preparation method of the thermoplastic in-situ polymerization polyamide composite leaf spring according to claim 2, characterized in that, The mass ratio of material A to material B is 1:0.8-1.2; 3. The preparation method of the thermoplastic in-situ polymerization polyamide composite leaf spring according to claim 2, characterized in that, The lactam is caprolactam and / or laurolactam; 4. The preparation method of the thermoplastic in-situ polymerization polyamide composite leaf spring according to claim 2, characterized in that, The catalyst is one or more combinations of isocyanate, isocyanurate, biuret, urethane, uredione, carbodiimide, or a compound of caprolactam; 5. The preparation method of the thermoplastic in-situ polymerization polyamide composite leaf spring according to claim 2, characterized in that, The activator is one or more of alkali metal lactam halides, alkaline earth metal lactam halides, alkali metal lactam salts, alkaline earth metal lactam salts, alkali metal hydroxides, and alkaline earth metal hydroxides; 6. The preparation method of a thermoplastic in-situ polymerization polyamide composite leaf spring according to claim 2, characterized in that, The mold release agent is a silicone grease-based mold release agent; 7. The preparation method of the thermoplastic in-situ polymerization polyamide composite leaf spring according to claim 1, characterized in that, The fiber fabric is woven from any one or more of glass fiber, carbon fiber, basalt fiber, aramid fiber, and organic fiber, and the weaving form is any one or more mixtures of 2D, 2.5D, and 3D; 8. The preparation method of the thermoplastic in-situ polymerization polyamide composite leaf spring according to claim 1, characterized in that, Before injecting the thermoplastic resin monomer mixture into the mold, the clamping pressure is less than 0.5 MPa, evacuate to a vacuum degree of -0.09 MPa to -0.1 MPa, the injection pressure is 0.1-20 MPa, and after injection, increase the curing pressure to 10-20 MPa; 9. The preparation method of the thermoplastic in-situ polymerization polyamide composite leaf spring according to claim 1, wherein, The heating temperature after injecting the thermoplastic resin monomer mixture into the mold is 140-180 °C, and the time is 5-30 min; 10. A leaf spring, characterized in that, Prepared by the method according to any one of claims 1-9.

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