Long glass fiber reinforced polyamide foam material and preparation method thereof

Abstract

The invention provides a long glass fiber reinforced polyamide foam material and a preparation method thereof, the long glass fiber reinforced polyamide foam material comprises the following components by mass: 42-72 parts of nylon mixed resin including 28%-31% of amorphous nylon and 69%-72% of crystalline nylon; 20 to 40 parts of long glass fiber; 2-4 parts of a toughening agent; 1-3 parts of a chain extender; 2-5 parts of a processing aid; the foaming agent master batch comprises 24%-26% of a foaming agent, 73%-75% of LLDPE (Linear Low Density Polyethylene) and 1%-2% of a foaming aid; the nylon mixed resin, the long glass fiber, the flexibilizer, the chain extender and the processing aid are blended to prepare premix particles, the standard deviation of the particle size distribution of the premix particles and the foaming agent master batch is less than 3mm, and the average particle size difference of the premix particles and the foaming agent master batch is controlled within 2mm. By controlling the particle size of the foaming agent master batch, the foaming agent master batch is more uniform when being mixed with premix particles in batches, meanwhile, amorphous nylon resin is added into the formula, and the strength of a resin melt is increased through chain extension to meet the technical requirements of a chemical foaming mode, so that a long glass fiber reinforced polyamide foaming product meeting market requirements is prepared.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer materials, and particularly relates to a long glass fiber reinforced polyamide foaming material and a preparation method thereof. Background Art

[0002] Polyamide (also known as nylon, PA) is one of the five general engineering plastics. Due to its excellent comprehensive properties, such as high mechanical strength, heat resistance, chemical resistance (resistance to acids, alkalis and general solvents), and good electrical insulation, it is widely used in technical fields such as automobiles, electronics, and aerospace. In recent years, the market demand for long glass fiber reinforced composites has shown an explosive growth. At present, most of the materials in the market are long glass fiber reinforced polypropylene materials. However, in some applications with higher requirements for high temperature resistance, such as the new energy vehicle field, etc., they cannot meet the application requirements. Therefore, there is an urgent need for high-performance alternative materials, such as long glass fiber reinforced polyamide materials. However, due to the relatively large production difficulty of long glass fiber reinforced polyamide materials, their output is low and the market supply is small, unable to meet the rapidly growing market demand. In addition, in the context of the national "dual carbon" strategy promoting lightweight development, the composite material foaming technology has become an important direction for the innovation of composite material lightweighting, which is of great significance for fields such as the lightweighting of new energy vehicles (such as battery pack casings). Therefore, with the increasing market demand for excellent comprehensive performance and lightweight materials, developing a long glass fiber reinforced polyamide material suitable for microcellular foaming has become the key point for industry breakthrough.

[0003] Currently, the foaming process is generally used at home and abroad to achieve the purpose of product lightweighting. Among them, the foaming process is divided into two types: physical foaming and chemical foaming. Physical foaming mainly involves directly injecting inert gases such as CO 2 , N 2Etc. This method is simple to operate. However, due to the high cost of the equipment and the fact that the stability of the equipment is currently difficult to meet the requirements for market products, its use is limited both at home and abroad. Chemical foaming is a process in which chemical foaming agents are batch-mixed in the formulation, gases are generated by the decomposition of the material when heated in an injection molding machine, and the melt and gases are mixed by the rotation of the screw and then foamed. The biggest problem with this foaming process is the uneven mixing of the foaming agent and the modified material. For ordinary modified plastic particles, since the size of the foaming agent masterbatch is similar to that of ordinary modified plastic particles, it is relatively easy to mix evenly. However, for long glass fiber reinforced nylon material particles, due to the reinforcing effect of the long glass fibers, a relatively large retention length of the glass fibers is required (generally reaching 10 mm or more), while the particle size of ordinary foaming agent masterbatches is generally very small, mostly less than 2 mm, and the addition ratio is relatively low, generally only about 2%. According to Stokes' law, the particle sedimentation velocity is proportional to the square of the particle size. If the particle size of the premix particles (including long glass fibers) is 10 mm and the particle size of the foaming agent masterbatch is 2 mm, the sedimentation velocity difference can reach 25 times, resulting in the rapid sinking of the foaming agent masterbatch during the batch mixing process, leading to uneven dispersion and ultimately a large difference in the foaming effect of the product. This is an important problem currently existing. In addition, there are relatively few nylon resin foaming materials on the market at present, and most are polypropylene resin foaming materials, mainly because the processing temperature of nylon resin is high while the melt strength is low, resulting in poor foaming effect.

[0004] The existing patent "Low Dielectric Constant Microcellular Foamed Glass Fiber Reinforced Polypropylene Composite and Its Preparation Method" CN111073148 improves the foamability of polypropylene long glass fiber reinforced materials through the form of blending low melt index homopolymer and copolymer polypropylene, and prepares a low dielectric constant microcellular foamed glass fiber reinforced polypropylene composite through physical foaming. The equipment involved in this process is expensive, and the air intake stability of the equipment is poor, resulting in limited market application. Summary of the Invention

[0005] Based on the above defects, in order to meet the existing market demand for microcellular long glass fiber reinforced polyamide materials, the present invention provides a long glass fiber reinforced polyamide foaming material and its preparation method. By controlling the particle size of the foaming agent masterbatch so that the difference from the particle size of the premix particles containing long glass fibers is controlled within 2 mm, the batch mixing of the two is made more uniform. At the same time, amorphous nylon resin is added to the formulation, and a chain extender is used to increase the melt strength of the resin to meet the technical requirements of the chemical foaming method, and a long glass fiber reinforced polyamide foaming product that meets the market demand is prepared.

[0006] To achieve the above object, the present invention proposes the following technical solutions:

[0007] A long glass fiber reinforced polyamide foam material, comprising the following components by mass:

[0008] 42-72 parts of nylon mixed resin, including 28%-31% amorphous nylon and 69%-72% crystalline nylon;

[0009] 20-40 parts of long glass fiber;

[0010] 2-4 parts of toughening agent;

[0011] 1-3 parts of chain extender;

[0012] 2-5 parts of processing aid;

[0013] 3-6 parts of foaming agent masterbatch, including 24%-26% foaming agent, 73%-75% LLDPE, and 1%-2% foaming aid;

[0014] The nylon mixed resin, the long glass fiber, the toughening agent, the chain extender and the processing aid are blended to prepare premix particles. The standard deviation of the particle size distribution of the premix particles and the foaming agent masterbatch is less than 3 mm, and the difference in average particle size between the two is controlled within 2 mm.

[0015] As a preferred technical solution of the present invention, the crystalline nylon includes at least one of nylon 6, nylon 66, nylon 6T, and nylon 56; and the amorphous nylon is semi-aromatic nylon.

[0016] As a preferred technical solution of the present invention, the particle size of the premix particles is 10-12 mm, and the particle size of the foaming agent masterbatch is 10-12 mm.

[0017] As a preferred technical solution of the present invention, the toughening agent is at least one of a "shell-core" copolymer, a copolymerization monomer or a polyolefin elastomer graft.

[0018] As a preferred technical solution of the present invention, the chain extender is at least one of isocyanates, esterified dilactams, imidazolines, epoxies, and oxazolines.

[0019] As a preferred technical solution of the present invention, the processing aid includes two or more of an antioxidant, a lubricant, a nucleating agent, a masterbatch, and an anti-ultraviolet agent.

[0020] As a preferred technical solution of the present invention, the foaming agent is at least one of sodium bicarbonate, sodium citrate, barium azodicarboxylate, azodicarbonamide, and p-toluenesulfonylamide urea.

[0021] As a preferred technical solution of the present invention, the foaming aid includes at least two of an antioxidant, a lubricant, and a nucleating agent.

[0022] The present invention also provides a method for preparing a long glass fiber reinforced polyamide foaming material, comprising the following steps:

[0023] (1) Weigh the nylon mixed resin, the toughening agent, the chain extender, and the processing aid according to parts by mass, mix them evenly, then melt and extrude to obtain a nylon resin melt. Immerse the long glass fibers fully in the nylon resin melt, extrude, cool, draw, and pelletize to obtain the premixed material particles;

[0024] (2) Mix the foaming agent, the nylon carrier resin, and the foaming aid evenly, and through melting and plasticizing, kneading and mixing, extruding, cooling, pelletizing, and drying, obtain the foaming agent masterbatch;

[0025] (3) Mix the premixed material particles and the foaming agent masterbatch evenly, and then obtain a long glass fiber reinforced polyamide foaming product through a microcellular injection molding process.

[0026] As a preferred technical solution of the present invention, the injection molding temperature of the microcellular injection molding process is 240°C - 270°C, the injection speed is 100 - 120 m / s, the injection pressure is 60 - 90 MPa, the back pressure is 10 - 20 MPa, and no holding pressure is applied.

[0027] As can be seen from the above technical solutions, the present invention provides a long glass fiber reinforced polyamide foaming material and a method for preparing the same. As is well known, the melt strength of ordinary crystalline nylon such as nylon 6 is relatively low, and it cannot effectively restrain gas expansion during the foaming process, easily leading to cell collapse or the formation of an open-cell structure. Moreover, long glass fibers (10 mm) will form a physical barrier, hindering the uniform nucleation of bubbles, and the interfacial shear strength between the glass fibers and the nylon matrix (about 20 MPa) is lower than the bubble expansion stress during the foaming process (about 30 MPa), resulting in the pulling out of glass fibers and destroying the integrity of the pore structure. The orientation of glass fibers leads to anisotropy in melt fluidity, further exacerbating the uneven distribution of cells.

[0028] (1) In the embodiments of the present invention, by adding the dual effects of semi-aromatic nylon and a chain extender to the formulation, the foamability of the material is improved, and the drawback of difficult foaming of long glass fiber reinforced nylon products is solved. Among them, the amorphous region of semi-aromatic nylon can provide more foaming active sites, and the rigidity of its molecular chain can delay crystallization and extend the melt foaming window; while the chain extender reacts with the terminal amino group of nylon through the groups it carries (such as -NCO groups), increasing the molecular weight of nylon from 15,000 to over 30,000, and increasing the melt strength by 2 - 3 times, thereby inhibiting the escape of gas during the foaming process and promoting the uniform nucleation of cells at the same time.

[0029] (2) In the embodiments of the present invention, the difference between the particle sizes of the premixed particles containing long glass fibers and the masterbatch particles of the foaming agent is controlled within 2 mm, and the difference in sedimentation rates between the two is controlled within 5 times, ensuring that the lateral diffusion distance of the masterbatch particles of the foaming agent matches the axial movement distance of the premixed particles within a mixing time of 10 minutes, ultimately achieving uniform dispersion at the microscale, thereby avoiding excessive or insufficient local concentration of the masterbatch particles of the foaming agent, ensuring the uniformity of the cell structure, and obtaining a long glass fiber-reinforced polyamide foamed product with good foaming effect and high stability.

[0030] (3) The embodiments of the present invention solve the blank of long glass fiber-reinforced polyamide foaming materials in the current market.

[0031] (4) The long glass fiber-reinforced polyamide foaming material prepared in the embodiments of the present invention has excellent product performance.

[0032] It should be understood that all combinations of the foregoing concepts and additional concepts described in more detail below can be regarded as part of the inventive subject matter of the present disclosure as long as such concepts do not contradict each other.

[0033] The foregoing and other aspects, embodiments, and features of the teachings of the present invention can be more fully understood from the following description in conjunction with the accompanying drawings. Other additional aspects of the present invention, such as the features and / or beneficial effects of the exemplary embodiments, will be apparent from the following description or will be learned through the practice of the specific embodiments according to the teachings of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The drawings are not drawn to scale in accordance with real reference objects. In the drawings, each identical or approximately identical component shown in each figure may be denoted by the same reference numeral. For the sake of clarity, not every component is labeled in each figure. Now, embodiments of various aspects of the present invention will be described by way of example and with reference to the drawings, wherein:

[0035] Figure 1 is the internal structure diagram of the product of Embodiment 1 of the present invention;

[0036] Figure 2 is the internal structure diagram of the product of Embodiment 2 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0037] In order to make the purpose, technical solution and advantages of the embodiment of the present invention clearer, the technical solution of the embodiment of the present invention will be clearly and completely described below in conjunction with the drawings of the embodiment of the present invention. Obviously, the described embodiment is a part of the embodiment of the present invention, not all of the embodiments. Based on the described embodiment of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. Unless otherwise defined, the technical terms or scientific terms used herein should be the common meanings understood by people with ordinary skills in the field to which the present invention belongs.

[0038] The words "first", "second" and similar words used in the patent application specification and claims of the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. Similarly, unless the context clearly indicates otherwise, the singular form of "a", "an" or "the" and similar words do not indicate a quantity limitation, but indicate the existence of at least one. "Include" or "comprises" and similar words mean that the elements or objects appearing before "include" or "comprises" include the features, wholes, steps, operations, elements and / or components listed after "include" or "comprises", and do not exclude the existence or addition of one or more other features, wholes, steps, operations, elements, components and / or their collections.

[0039] In order to solve the technical problem that the existing long glass fiber reinforced polyamide materials have poor foaming effect due to the high processing temperature of nylon resin and low melt strength, the present invention provides a long glass fiber reinforced polyamide foam material and a preparation method thereof. By improving the foaming agent masterbatch so that it is evenly mixed with the long glass fiber reinforced polyamide material, and by using a chain extender to increase the melt strength of the nylon resin to improve the foamability of the composite material, a long glass fiber reinforced polyamide foam material that meets market demand is prepared.

[0040] The embodiment of the present invention provides a long glass fiber reinforced polyamide foam material, which comprises the following components by weight:

[0041] 42-72 parts of nylon mixed resin, wherein the nylon mixed resin includes 28%-31% amorphous nylon and 69%-72% crystalline nylon, so as to balance the material strength and foaming performance, ensure the controllable foaming area, and avoid foaming failure caused by an imbalance in the ratio of the two.

[0042] 20-40 parts of long glass fiber;

[0043] 2-4 parts of toughening agent;

[0044] 1-3 parts of chain extender;

[0045] 2-5 parts of processing aid;

[0046] 3-6 parts of foaming agent masterbatch, including 24%-26% foaming agent, 73%-75% LLDPE, and 1%-2% foaming aid;

[0047] The nylon mixed resin, long glass fiber, toughening agent, chain extender, and processing aid are blended to obtain premix particles, and the standard deviation of the particle size distribution of the premix particles and the foaming agent masterbatch is less than 3 mm. In the embodiment of the present invention, it is necessary to ensure that the size difference between the particle size of the premix particles and the particle size of the foaming agent masterbatch is less than 2 mm. Because the difference in particle size between the two is too large, stratification will occur during the mixing process due to density and particle size differences, resulting in uneven distribution of the foaming agent masterbatch. The particle size of the foaming agent masterbatch is close to that of the premix particles, and the fluidity and mixing dynamics of the two are matched, so that uniform blending can be achieved, ensuring that the foaming agent masterbatch is evenly distributed in the melt. In addition, during the injection molding process, particles with similar particle sizes have the same melting rate in the screw, avoiding local overheating or unmelted particles causing premature decomposition of the foaming agent masterbatch. If the foaming agent masterbatch is too small, it may be decomposed prematurely in the high temperature zone, and the premix particles have not yet been completely melted, resulting in gas escape or pore merging. Evenly dispersed foaming agent masterbatch can provide uniform nucleation sites to form a small and evenly distributed closed-cell structure. If the mixing is uneven, excessive local foaming agent concentration will lead to large bubbles or interconnected pores, reducing the mechanical properties of the material.

[0048] Taking into account the processing equipment, processing difficulty, and uniformity of premix particles and foaming agent masterbatch during batch mixing, in the embodiment of the present invention, the particle size of the premix particles is 10-12 mm, and the particle size of the foaming agent masterbatch is 10-12 mm, wherein both are preferably 10 mm.

[0049] In the embodiments of the present invention, hydrolytic-resistant continuous glass fibers with a diameter of 12 μm are preferably used as the fiber material for reinforcing polyamide. The 12-μm glass fiber diameter provides a larger specific surface area, enhancing the interfacial bonding force between the fiber and the polyamide matrix. Although finer glass fibers (such as less than 10 μm) have a larger specific surface area, they are prone to breakage during the processing, resulting in a shortened fiber length and affecting the polyamide reinforcement effect. While coarser fibers (greater than 15 μm) have a weaker interfacial bonding, which may lead to a decrease in the stress transfer efficiency. In addition, the glass fibers of this size have moderate flexibility and can resist the damage of shear force during twin-screw extrusion and injection molding, retaining the original length (10 μm), thereby giving full play to the "bridging" reinforcement effect of long glass fibers and significantly improving the tensile strength and impact performance of the material. The 12-μm long glass fibers are compatible with the melt viscosity of polyamide (240°C - 270°C), avoiding a decrease in melt fluidity or local fiber agglomeration caused by overly thick long glass fibers, thereby reducing injection molding defects (such as surface ripples and sink marks). Finally, 12-μm glass fibers are a widely used standard specification in the industry, with a mature supply chain and controllable costs. Compared with finer fibers (such as 9 μm), the production process of 12 μm is more stable and the fracture risk is lower; compared with coarser fibers (such as 15 μm), its reinforcement efficiency is higher and the cost performance is better.

[0050] Therefore, the embodiments of the present invention select 12 μm, which is the result of comprehensively optimizing the interfacial bonding strength, processing stability, environmental resistance, and economy. It avoids the vulnerability of overly fine fibers and overcomes the weak interfacial bonding problem of overly coarse fibers, while ensuring long-term reliability in a humid environment through the surface.

[0051] In the embodiments of the present invention, the crystalline nylon includes at least one of nylon 6, nylon 66, nylon 6T, and nylon 56; the amorphous nylon is semi-aromatic nylon. Since semi-aromatic nylon is a polymer with an amorphous molecular structure, and crystalline nylon is a semi-crystalline polymer with both random chain segments and ordered chain segments in its molecular structure, and polymer foaming often occurs in the amorphous region of the polymer, adding semi-aromatic nylon can increase the amorphous region of the nylon blend resin, thereby increasing the foaming region of the composite material and improving the foaming performance of the composite material. In addition, semi-aromatic nylon has low water absorption and more stable product dimensions. Therefore, it can improve the stability of the composite material.

[0052] In the embodiments of the present invention, the toughening agent is at least one of a "core-shell" copolymer, a copolymerization reaction monomer, or a polyolefin elastomer graft. Specifically, one or several of functional polymers such as EPDM-g-MAH, PP-g-MAH, PP-g-GMA, PE-g-MAH, POE-g-MAH, POE-g-GMA, SEBS-g-MAH, and styrene-maleic anhydride copolymer can be selected. From the perspective of market application, the toughening effect of POE-g-MAH as a polyamide toughening agent is more obvious. Therefore, POE-g-MAH is preferably used as the toughening agent in the embodiments of the present invention.

[0053] To improve the melt strength of the nylon resin, in the embodiments of the present invention, a chain extender is used to extend the chain of the nylon resin, increase its molecular weight, so that the gas can be better coated inside the polymer during the foaming process of the composite material and the escape is reduced. Preferably, the chain extender is at least one of isocyanates, esterified bislactams, imidazolines, epoxies, oxazolines.

[0054] In the embodiments of the present invention, to improve the performance of the composite material, processing aids can also be added to the formulation. Preferably, the processing aids can be selected from two or more of antioxidants, lubricants, nucleating agents, color masterbatches, and ultraviolet absorbers. For example, antioxidants can inhibit oxidative degradation (such as molecular chain breakage, color change, etc.) during high-temperature processing or long-term use, and extend the service life of the material; nucleating agents can lower the crystallization temperature, accelerate the crystallization rate, reduce the residence time of the material during high-temperature processing, indirectly reduce the oxidation risk, and can induce the PA matrix to form a more uniform and finer crystal structure, increase the crystallinity, enhance the rigidity and strength of the material, so that the thermal stability of the material during high-temperature injection molding or long-term high-temperature environment is significantly enhanced; lubricants can reduce the melt viscosity, improve the fluidity, reduce the shear heat generation during the injection molding process, and avoid degradation caused by local overheating; at the same time, improve the demolding property and reduce surface defects. Adding lubricants together with nucleating agents and antioxidants can produce a significant synergistic effect, improve the processing efficiency, enhance the surface finish of the product, and reduce the rejection rate. Ultraviolet absorbers can absorb or shield ultraviolet rays to prevent the PA molecular chain from breaking due to photooxidation (such as surface powdering, embrittlement, etc.). Color masterbatches can endow the material with color, make the color of the material more stable during long-term use, and meet the scenarios with strict appearance requirements; at the same time, some color masterbatch carriers may contain dispersants, which can improve the interfacial bonding between glass fibers and the matrix.

[0055] In the embodiments of the present invention, the blowing agent masterbatch, by weight, comprises 24%-26% blowing agent, 73%-75% LLDPE (linear low density polyethylene), and 1%-2% blowing aid. Among them, the blowing agent is at least one of sodium bicarbonate, sodium citrate, barium azodicarboxylate, azodicarbonamide, and p-toluenesulfonyl semicarbazide. However, when using a single blowing agent, the decomposition temperature is single. The compounding of blowing agents can cover a wider processing temperature range. Considering the gas generation amount of the blowing agent, the solubility of the released gas in polyamide, and environmental protection, sodium bicarbonate and azodicarbonamide are preferably compounded. Because the compounding of sodium bicarbonate (decomposition temperature 100°C - 120°C) and azodicarbonamide (decomposition temperature 180°C - 200°C), such as in a ratio of 7:3, can make the gas be released in stages during the foaming process of the material, optimize the gas release kinetics, thereby improving the foaming uniformity of the material and making the cell density reach 10 7 -10 9 cells / cm 3 , and the cell diameter is controlled within 50μm - 200μm.

[0056] 1%-2% of blowing aid is also added to the blowing agent masterbatch, and the blowing aid is at least two of antioxidant, lubricant, and nucleating agent. Adding antioxidant to the blowing agent masterbatch can inhibit the oxidative decomposition of the blowing agent masterbatch during storage and processing, and ensure the stability of the blowing agent. The lubricant can reduce the interfacial tension between the blowing agent and the resin, promote the uniform dispersion of the blowing agent in the LLDPE matrix, and avoid uneven foaming caused by too high local concentration. The nucleating agent can regulate the nucleation behavior during the foaming process, optimize the cell structure. For example, it provides a large number of nucleation sites, promotes the uniform distribution of bubbles, reduces the formation of large bubbles or connected bubbles, and increases the cell density.

[0057] The embodiments of the present invention also provide a preparation method of a long glass fiber reinforced polyamide foaming material, comprising the following steps:

[0058] (1) Weigh the nylon resin, the toughening agent, the chain extender, and the processing aid according to mass parts. Blend the above raw material components in a low-speed mixer for 15 - 25 minutes, then add them into a twin-screw extruder to be melted to obtain a nylon resin melt. Squeeze the nylon resin melt into an impregnation mold connected to the head of the twin-screw extruder. Then pass the long glass fiber through the impregnation mold so that the long glass fiber is fully impregnated by the nylon resin melt. Finally, cool, draw, and pelletize to obtain pre-mixed particles, that is, long glass fiber reinforced polyamide. In the embodiments of the present invention, the particle size of the pre-mixed particles is preferably 10mm.

[0059] (2) Mix the foaming agent, the carrier resin, and the foaming aid in a low-speed mixer at a weight ratio of 25:75:2 for 15 - 25 minutes, then add them to a twin-screw extruder and mix evenly at a temperature of 100°C - 135°C. The obtained mixed material is melt-plasticized, kneaded and mixed, extruded, cooled, pelletized, and dried to obtain the foaming agent masterbatch. In the embodiment of the present invention, the particle size of the foaming agent masterbatch is preferably 10 mm, and the difference in particle size between the foaming agent masterbatch and the above-mentioned premixed material particles is controlled within 2 mm to ensure that the particle sizes of the two are similar, making it easier to mix them evenly during batch mixing.

[0060] (3) Mix the premixed material particles and the foaming agent masterbatch evenly in a high-speed mixer for 30 minutes, then add the mixed material to a microcellular injection molding machine and prepare a long glass fiber-reinforced polyamide foamed product through the microcellular injection molding process.

[0061] Among them, in the embodiment of the present invention, the injection temperature of the microcellular injection molding process is 240°C - 270°C, the injection speed is 100 - 120 m / s, the injection pressure is 60 - 90 MPa, the back pressure is 10 - 20 MPa, and no holding pressure is applied.

[0062] Prepare several foaming agent masterbatches with different formulation ratios according to the above preparation method of the foaming agent masterbatch. The main differences are the component ratios and particle sizes, as shown in Table 1 specifically.

[0063] Table 1 Preparation of Foaming Agent Masterbatch

[0064] Blowing Agent Masterbatch A Blowing Agent Masterbatch B Blowing Agent Masterbatch C Blowing Agent Masterbatch D Blowing Agent Masterbatch E LLDPE 70 70 70 50 30 Sodium Bicarbonate 30 21 21 50 70 Azodicarbonamide - 9 9 - - Blowing Agent Auxiliary 2 2 2 2 2 Particle Length 2mm 2mm 10mm 10mm 10mm

[0065] Prepare six examples and comparative examples according to the method for preparing long glass fiber-reinforced polyamide foamed materials described in the embodiment of the present invention. The specific formulations are shown in Table 2.

[0066] Table 2 Preparation of Long Glass Fiber-Reinforced Polyamide Foamed Materials

[0067] Comparative Example 1 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Crystalline Nylon 65 40 40 40 40 42 43 Semi-aromatic Nylon - 15 15 15 15 15 15 Long Glass Fiber 30 30 30 30 30 30 30 Chain Extender - - 2 2 2 2 2 Blowing Agent Masterbatch A - - - 4 - - - Blowing Agent Masterbatch B - - - - 4 - - Blowing Agent Masterbatch C 4 4 4 - - - - Blowing Agent Masterbatch D - - - - - 2 - Blowing Agent Masterbatch E - - - - - - 1 Toughening Agent 3 3 3 3 3 3 3 Processing Aid 2 2 2 2 2 2 2

[0068] The corresponding performance results of the above examples and comparative examples are shown in Table 3 below.

[0069] Table 3 Performance Results of Example and Comparative Example Products

[0070]

[0071] The performance test specimens of all examples and comparative examples in Table 3 were sampled from the foamed products.

[0072] From the comprehensive comparison of Table 1, Table 2 and Table 3, it can be found that compared with Comparative Example 1, in Example 1, amorphous nylon such as semi-aromatic nylon was added to the formulation, and the weight loss ratio of the obtained material product was greatly improved, and its appearance was also improved, both of which were better than those of Comparative Example 1 without adding semi-aromatic nylon. This is because the molecular structure of semi-aromatic nylon is an amorphous structure, while nylon 6 and nylon 66 are semi-crystalline polymers. As is well known, polymer foaming often occurs in its amorphous region. Therefore, adding semi-aromatic nylon can increase the foaming region of the nylon mixed resin, thereby improving its foaming performance of the material. In addition, the water absorption of semi-aromatic nylon is relatively low, which can make the size of the material product more stable.

[0073] Comparing Example 1 with Example 2, as can be seen from Table 3, the tensile strength, flexural modulus, weight loss ratio, appearance and other indicators of Example 2 with a chain extender added are better than those of Example 1. This is because the nylon mixed resin was chain-extended by the chain extender, increasing its molecular chain and improving the melt strength of the nylon resin, so that the gas can be better coated inside the polymer during the foaming process and rarely escapes, resulting in no white appearance on the surface of the product.

[0074] The comparison between Comparative Example 1 and Example 3 shows that the latter has uneven cell structure due to mismatched particle sizes. Comparing Example 3 with Example 2, Example 2 has a large and uniform cell density and no white appearance on the surface, verifying the necessity of particle size matching. Therefore, through the comprehensive comparison of Examples 1-6, it can be seen that the difference between the particle size of the premix particles and the particle size of the blowing agent masterbatch has a certain impact on the performance of the product. When the particle size of the blowing agent masterbatch is close to that of the material particles, the obtained product is more stable and the cells of the material are uniform.

[0075] Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Those with ordinary knowledge in the technical field to which the present invention pertains can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be subject to that defined by the claims.

Claims

1. A long glass fiber reinforced polyamide foam material, characterized in that: The components are as follows by mass: 42-72 parts of nylon mixed resin, including 28%-31% amorphous nylon and 69%-72% crystalline nylon; 20-40 parts of long glass fiber; 2-4 parts of toughening agent; 1-3 parts of chain extender; 2-5 parts of processing aid; 3-6 parts of foaming agent masterbatch, including 24%-26% foaming agent, 73%-75% LLDPE, and 1%-2% foaming aid; The nylon mixed resin, the long glass fiber, the toughening agent, the chain extender and the processing aid are blended to prepare premix particles. The standard deviation of the particle size distribution of the premix particles and the foaming agent masterbatch is less than 3 mm, and the difference in average particle size between the two is controlled within 2 mm.

2. The long glass fiber reinforced polyamide foam material according to claim 1, characterized in that: The crystalline nylon includes at least one of nylon 6, nylon 66, nylon 6T and nylon 56; the amorphous nylon is semi-aromatic nylon.

3. The long glass fiber reinforced polyamide foam material according to claim 1, characterized in that: The particle size of the premix particles is 10-12 mm, and the particle size of the foaming agent masterbatch is 10-12 mm.

4. The long glass fiber reinforced polyamide foam material according to claim 1, characterized in that: The toughening agent is at least one of a "shell-core" copolymer, a copolymerization monomer or a polyolefin elastomer graft.

5. The long glass fiber reinforced polyamide foam material according to claim 1, characterized in that: The chain extender is at least one of isocyanates, esterified dilactams, imidazolines, epoxies, and oxazolines.

6. The long glass fiber reinforced polyamide foam material according to claim 1, characterized in that: The processing aids include two or more of antioxidants, lubricants, nucleating agents, masterbatches, and anti-ultraviolet agents.

7. The long glass fiber reinforced polyamide foam material according to claim 1, characterized in that: The foaming agent is at least one of sodium bicarbonate, sodium citrate, barium azodicarboxylate, azodicarbonamide, and p-phenylsulfonylamide urea.

8. The long glass fiber reinforced polyamide foam material according to claim 1, characterized in that: The foaming aid includes at least two of an antioxidant, a lubricant, and a nucleating agent.

9. The method for preparing the long glass fiber reinforced polyamide foam material according to claim 1, characterized in that: The following steps are involved: (1) weighing the nylon mixed resin, the toughening agent, the chain extender, and the processing aid according to their mass fractions and mixing them uniformly, then melting and extruding to obtain a nylon resin melt, fully impregnating the long glass fiber in the nylon resin melt, extruding, cooling, pulling, and pelletizing to obtain the premix particles; (2) uniformly mixing the foaming agent, the nylon carrier resin and the foaming aid, and subjecting the mixture to melt plasticization, kneading and mixing, extrusion, cooling, pelletizing and drying to obtain the foaming agent masterbatch; (3) The premix particles are uniformly mixed with the foaming agent masterbatch, and then a long glass fiber reinforced polyamide foam product is prepared by a micro-foaming injection molding process.

10. The method for preparing the long glass fiber reinforced polyamide foam material according to claim 9, characterized in that: The micro-foam injection molding process has an injection temperature of 240° C.-270° C., an injection speed of 100-120 m / s, an injection pressure of 60-90 MPa, a back pressure of 10-20 MPa, and no holding pressure.

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