A kind of polyamide foam material and preparation method thereof

Abstract

The present invention discloses a polyamide foam material and a preparation method thereof, and relates to the technical field of buffer protection, in order to solve the problem of poor resilience and compressive strength of polyamide foam materials. A polyamide composite material is subjected to a cross-linking reaction to obtain a polyamide material to be foamed, wherein the polyamide composite material includes a composite material formed by a polyethylene resin and polyamide; the polyamide material to be foamed is subjected to two-stage foaming by a supercritical foaming method to obtain a polyamide foam material. The polyamide foam material and the preparation method thereof are used to improve the resilience and compressive strength of the polyamide foam material.

Description

Technical Field

[0001] The invention relates to the technical field of buffer protection, and in particular to a polyamide foam material and a preparation method thereof. Background Art

[0002] Polyamide is widely used in various parts due to its high strength, high heat resistance, high fatigue resistance, chemical resistance and good oil resistance. Closed-cell nylon foam material has excellent heat insulation and noise reduction properties. Compared with traditional foam materials such as polypropylene, polyethylene, and ethylene-vinyl acetate, it has outstanding high temperature resistance, organic hydrocarbon solvent resistance, and compression resistance. However, due to the segment structure of nylon materials, the compression resilience of nylon foam after foaming is poor, especially the compression permanent deformation rate is usually as high as 30% or more, and some systems even reach 50%, which limits its application in the field of buffer protection.

[0003] At present, in order to improve the resilience of polyamide materials after foaming, copolymerization is usually used to introduce polyether soft segments into the polyamide chain segments. However, this method will significantly reduce the compressive strength of the foamed material and greatly increase the cost. Summary of the invention

[0004] The object of the present invention is to provide a method for preparing a polyamide foam material, so as to improve the resilience and compression strength of the polyamide foam material.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] Carrying out a cross-linking reaction on the polyamide composite material to obtain a polyamide material to be foamed, wherein the polyamide composite material comprises a composite material formed by a polyethylene resin and polyamide;

[0007] The polyamide material to be foamed is foamed in two stages by using a supercritical foaming method to obtain a polyamide foamed material.

[0008] Compared with the prior art, in the preparation method of the polyamide material to be foamed provided by the present invention, the polyamide composite material is first subjected to a cross-linking reaction to obtain the polyamide material to be foamed. Wherein, the polyamide composite material includes a composite material formed by polyethylene resin and polyamide. After the polyamide segment is introduced into the flexible structure polyethylene, the melt strength of the polyamide can be improved, the toughness of the polyamide and the compression resilience can be improved, and it is beneficial to obtain a polyamide material to be foamed with higher resilience. In order to avoid the reduction of the anti-compression strength of the material after the polyamide segment is introduced into the flexible structure polyethylene, the polyamide composite material can be subjected to a cross-linking reaction, and in this process, the polyethylene resin and the polyamide resin in the composite material form an interpenetrating network structure, so that the melt strength and expandability of the polyamide material to be foamed are greatly improved. Finally, when the polyamide material to be foamed with good expandability is subjected to two-stage foaming by a supercritical foaming method, its foaming ratio increases, and a polyamide foam material with higher resilience and anti-compression strength can be obtained. In addition, since the polyethylene resin in the polyamide foam material has the characteristic of rapid crystallization, during the cooling process after foaming, the polyethylene resin quickly crystallizes to produce physical crosslinking points, thereby improving the foaming dimensional stability and flatness of the polyamide foam material.

[0009] In a second aspect, the present invention further provides a polyamide foam material prepared by the above-mentioned method for preparing the polyamide foam material.

[0010] Compared with the prior art, the beneficial effects of the polyamide foam material provided by the present invention are the same as the beneficial effects of the method for preparing a polyamide foam material in the first aspect, which will not be described in detail here. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0012] Figure 1 The preparation flow chart of the polyamide foam material provided in this embodiment is shown. DETAILED DESCRIPTION

[0013] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0014] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "multiple" is two or more, unless otherwise clearly and specifically defined. The meaning of "several" is one or more, unless otherwise clearly and specifically defined.

[0015] At present, polyamide foam materials have poor compression resilience, especially the compression permanent deformation rate is usually as high as 30% or more, and some systems even reach 50%, which limits its application in the field of cushioning and protection. In order to improve the resilience of polyamide materials after foaming, it is usually chosen to introduce polyether soft segments into the polyamide chain segments by copolymerization, but this method will significantly reduce the compression strength of the foamed material and greatly increase the cost.

[0016] In view of the above problems, an embodiment of the present invention provides a method for preparing a polyamide foam material to improve the resilience and compression strength of the polyamide foam material. Figure 1 The preparation flow chart of the polyamide foam material provided in this embodiment is shown. Figure 1 As shown, the preparation method of the polyamide foam material comprises:

[0017] Step 101: subjecting the polyamide composite material to a cross-linking reaction to obtain a polyamide material to be foamed.

[0018] Exemplarily, the polyamide composite material includes a composite material formed by polyethylene resin and polyamide resin. After the polyamide segment is introduced into the flexible structure polyethylene, the melt strength of the polyamide can be improved, the toughness of the polyamide and the compression resilience can be improved, which is conducive to obtaining a polyamide foaming material with high resilience. In order to avoid the reduction of the compressive strength of the material after the polyamide segment is introduced into the flexible structure polyethylene, the polyamide composite material can be subjected to a cross-linking reaction. The cross-linking reaction is a radiation cross-linking reaction, and the radiation source of the reaction is a gamma ray. Under the radiation of gamma rays, the polyethylene molecular chain and the polyamide segment are cross-linked, so that the two resins form an interpenetrating network structure, which greatly improves the polymer melt strength and can prepare a high foaming ratio foam. Among them, the polyamide foaming material generally used for foaming is in the form of a plate with a thickness of 4-16mm, and the corresponding gamma ray irradiation dose is 5kGy~50kGy, preferably 15kGy~30kGy. At this dosage, cross-linking of polyethylene molecular chains and polyamide chain segments can be ensured. It should be understood that the dosage of gamma ray irradiation can be adjusted according to actual conditions. For composite materials with a thickness exceeding 16 mm, higher irradiation energy is required.

[0019] Step 102: The polyamide material to be foamed is foamed in two stages by using a supercritical foaming method to obtain a polyamide foamed material.

[0020] Exemplarily, the supercritical foaming agent used in the supercritical foaming method includes supercritical CO2 or supercritical N2. The supercritical foaming agent can reduce the interfacial tension of the polymer system and has a good plasticizing effect on the polymer melt.

[0021] Exemplarily, the two-stage foaming process includes a first-stage foaming process and a second-stage foaming process.

[0022] The process parameters of the first stage foaming process include: the injection temperature of the supercritical foaming agent is 150℃~210℃, the reaction pressure is 5Mpa~15Mpa, preferably 10Mpa~15Mpa, and the heat preservation time is 10min~30min. When the temperature is 150℃~210℃, the polyethylene molecular chain segments have melted, the supercritical CO2 can penetrate into the melt, and the polyamide molecular chain segments still maintain a crystalline state. This crystalline state plays a role similar to a physical cross-linking point, which keeps the polyethylene part of the pore structure from collapsing during the temperature rise foaming process.

[0023] Among them, the process parameters of the second stage foaming process include: the reaction temperature of injecting the supercritical foaming agent again is 220℃~270℃, the reaction pressure is 10Mpa~20Mpa, preferably 15Mpa~20Mpa, and the insulation time is 20min-40min. When the system temperature reaches 220℃~270℃, the polyamide segment is semi-molten to completely melted, CO2 can be dissolved into the melt, and the immersion process is completed. At the same time, an interpenetrating network structure is generated between the cross-linked polyethylene and the cross-linked polyamide segment. This structure greatly improves the overall melt strength, and the foaming process is completed with the rapid pressure relief process. In the prior art, if only polyamide material is used as the material to be foamed, during the foaming and cooling process after pressure relief, due to the slow crystallization speed of the polyamide material and the insufficient melt strength, collapse often occurs and causes warping deformation. When polyamide and polyethylene are compounded, during the foaming and cooling process after pressure relief, due to the characteristics of rapid crystallization of polyethylene, physical cross-linking points can be quickly crystallized to improve the foaming dimensional stability and flatness of the overall material.

[0024] In an optional manner, before the polyamide composite material is subjected to a cross-linking reaction to obtain a polyamide foaming material, the method for preparing the polyamide foaming material further comprises:

[0025] Mixing the dried polyamide resin, the dried polyethylene resin and the additive to obtain a premix;

[0026] The premix is ​​extruded and modified by using an extruder to obtain a polyamide composite material.

[0027] Exemplarily, polyethylene resin is a polymer with a long-chain branched structure, with high toughness and excellent low-temperature resistance. After the polyamide segment is introduced into polyethylene, the melt strength of polyamide can be improved, the toughness of polyamide and the compression resilience can be improved, which is conducive to obtaining a polyamide foaming material with high resilience. The polyamide resin used in the embodiment of the present invention is nylon 6, and the relative viscosity of the polyamide resin is 2.8 to 3.4. The polyethylene resin used in the embodiment of the present invention is an extrusion-grade polyethylene resin or a film-grade low-density polyethylene resin. The melt index of the polyethylene resin is 0.5g / 10min to 5g / 10min under the test conditions of 190°C and 2.14kg. According to the mass fraction, the mass fraction of the dried polyamide resin is 50 to 90 parts, and the mass fraction of the dried polyethylene resin is 10 to 50 parts. Preferably, the mass fraction of the dried polyamide resin is 60 to 80 parts, and the mass fraction of the dried polyethylene resin is 20 to 40 parts.

[0028] For example, the water content of the polyamide resin after drying is less than 200 ppm, and the water content of the polyethylene resin after drying is less than 200 ppm.

[0029] Exemplarily, the above-mentioned additives include a compatibilizer, a nucleating agent, a chain extender and an antioxidant. In terms of weight, the weight of the compatibilizer is 5 to 20 parts, the weight of the nucleating agent is 0.1 to 1 part, the weight of the chain extender is 1 to 5 parts, and the weight of the antioxidant is 0.5 to 2 parts.

[0030] Wherein, compatibilizer is used to improve the compatibility between reaction systems. Specifically, polyethylene resin is a polymer with a long-chain branched structure, has high toughness and excellent low-temperature resistance, has a certain toughening effect on polyamide materials, and introduces a compatibilizer into the reaction system. The intermolecular bonding force can be used to combine the above-mentioned two incompatible polymers together, and the polyethylene / polyamide / compatibility agent ternary system formed has a good microscopic compatibility structure, and after the foaming process, the compression resilience of the polyamide foam material can be significantly improved at low cost. The compatibilizer used in the embodiment of the present invention is at least one of low-density polyethylene grafted maleic anhydride (LDPE-g-MAH), polyolefin elastomer grafted maleic anhydride (POE-g-MAH), ethylene-vinyl acetate copolymer (EVA), and ethylene-methyl acrylate copolymer (EMA).

[0031] The nucleating agent is used to disperse the gas phase uniformly during the polymer foaming process and then nucleate the cells. The nucleating agent used in the embodiment of the present invention can be one or a combination of magnesium oxide (MgO), silicon dioxide (SiO2), talc (Talc), montmorillonite (MMT), and nano whiskers.

[0032] Chain extenders are used to couple or branch with polyamide resin to achieve polyamide chain extension. Specifically, polyamide material is a semi-crystalline polymer with a linear molecular chain structure, which usually exhibits a low melt strength during molten state processing and is difficult to resist the severe tensile stress borne during cell growth. The introduction of chain extenders can form comb-like or resin-like segments of polyamide, effectively increasing the probability of molecular chain entanglement in polymers, thereby improving its melt strength. Under irradiation, the polyamide segments and polyethylene segments after chain extension undergo cross-linking reactions to produce an interpenetrating network structure, thereby greatly improving the expandability of the material and increasing the expansion ratio. The chain extender used in the embodiment of the present invention is at least one of maleic anhydride, isocyanate, bisoxazoline chain extender or multifunctional epoxy compound.

[0033] Antioxidants are one of the additives frequently used in plastic materials. When only a small amount exists in plastic, it can delay or inhibit the degradation process of the plastic during polymerization, storage, transportation, processing, and use due to the effects of atmospheric oxygen, ozone, etc., thereby preventing material aging and significantly extending the service life. The types of antioxidants used in the embodiments of the present invention are not limited, and can be conventional antioxidants on the market, such as antioxidant 1010, antioxidant 1076, antioxidant 168, antioxidant CA, antioxidant 330, antioxidant 264, etc.

[0034] The embodiment of the present invention further provides a polyamide foam material, which is prepared by using the above-mentioned method for preparing the polyamide foam material, and has low cost and high compression strength and resilience.

[0035] In order to verify the effect of the method for preparing the polyamide foam material provided by the embodiment of the present invention, the embodiment of the present invention is demonstrated by comparing the embodiment with the comparative example.

[0036] The sources of the raw materials used in the embodiments of the present invention are as follows:

[0037] Nylon 6 resin YH800 was purchased from Baling Petrochemical Co., Ltd.

[0038] Polyethylene resin LD080 was purchased from ExxonMobil.

[0039] Polyolefin elastomer grafted with maleic anhydride FB521A was purchased from Jiayirong Polymer Co., Ltd.

[0040] 20 μm SiO2 was purchased from Hangzhou Zhitai Purification Technology Co., Ltd.

[0041] Multifunctional epoxy chain extender ADR4368 was purchased from BASF, Germany.

[0042] Embodiment 1

[0043] The method for preparing a polyamide foam material provided by an embodiment of the present invention comprises the following steps:

[0044] The first step is to prepare a polyamide composite material. Take 50 parts by mass of nylon 6 resin YH800, 50 parts by mass of polyethylene resin LD080, and 10 parts by mass of polyolefin elastomer grafted maleic anhydride FB521A (compatibilizer), dry them in advance, and the moisture content is required to be less than 200ppm. The dried nylon 6 resin, the dried polyethylene resin, the compatibilizer FB521A, 0.5 parts by mass of 20μm nucleating agent SiO2, 3.2 parts by mass of multifunctional epoxy chain extender ADR4368, and 0.2 parts by mass of antioxidant 168 are mixed evenly by a high mixer to obtain a premix. After the premix is ​​extruded through a twin-screw extruder with a T-type extrusion die head and an aspect ratio of 52 and a diameter of 25mm, a polyamide composite material with a thickness of 8mm is obtained.

[0045] The second step is to prepare a polyamide material to be foamed. The polyamide composite material is irradiated with 20 kGy of gamma rays to obtain a polyamide material to be foamed.

[0046] The third step is to prepare the polyamide foam material. The polyamide material to be foamed is placed in an autoclave or a molded foaming device, and supercritical CO2 is used as a foaming agent to perform two-stage foaming, namely: first, supercritical CO2 is injected at 200°C until the reaction pressure reaches 10Mpa, and the temperature is kept for 10 minutes to complete the first stage of foaming; then the reaction temperature is increased to 230°C, and supercritical CO2 is injected again to make the reaction pressure reach 20Mpa, and the temperature is kept for 30 minutes to complete the second stage of foaming, and then the reaction system is quickly depressurized to 0Mpa to complete the foaming process and obtain the polyamide foam material. The performance parameters of the polyamide foam material prepared in Example 1 of the present invention are shown in Table 1.

[0047] Embodiment 2

[0048] The method for preparing a polyamide foam material provided by an embodiment of the present invention comprises the following steps:

[0049] The first step is to prepare a polyamide composite material. Take 90 parts by mass of nylon 6 resin YH800, 10 parts by mass of polyethylene resin LD080, and 10 parts by mass of polyolefin elastomer grafted maleic anhydride FB521A (compatibilizer), dry them in advance, and the moisture content is required to be less than 200ppm. The dried nylon 6 resin, the dried polyethylene resin, the compatibilizer FB521A, 0.5 parts by mass of 20μm nucleating agent SiO2, 2.4 parts by mass of multifunctional epoxy chain extender ADR4368, and 0.2 parts by mass of antioxidant 168 are mixed evenly by a high mixer to obtain a premix. After the premix is ​​extruded through a twin-screw extruder with a T-type extrusion die head and an aspect ratio of 52 and a diameter of 25mm, a polyamide composite material with a thickness of 8mm is obtained.

[0050] The second step is to prepare a polyamide material to be foamed. The polyamide composite material is irradiated with 30 kGy of gamma rays to obtain a polyamide material to be foamed.

[0051] The third step is to prepare the polyamide foam material. The polyamide material to be foamed is placed in an autoclave or a molded foaming device, and supercritical CO2 is used as a foaming agent to perform two-stage foaming, namely: first, supercritical CO2 is injected at 200°C until the reaction pressure reaches 10Mpa, and the temperature is kept for 10 minutes to complete the first stage of foaming; then the reaction temperature is increased to 230°C, and supercritical CO2 is injected again to make the reaction pressure reach 20Mpa, and the temperature is kept for 30 minutes to complete the second stage of foaming, and then the reaction system is quickly depressurized to 0Mpa to complete the foaming process and obtain the polyamide foam material. The performance parameters of the polyamide foam material prepared in Example 2 of the present invention are shown in Table 1.

[0052] Embodiment 3

[0053] The method for preparing a polyamide foam material provided by an embodiment of the present invention comprises the following steps:

[0054] The first step is to prepare a polyamide composite material. Take 75 parts by mass of nylon 6 resin YH800, 25 parts by mass of polyethylene resin LD080, and 10 parts by mass of polyolefin elastomer grafted maleic anhydride FB521A (compatibilizer), dry them in advance, and the moisture content is required to be less than 200ppm. The dried nylon 6 resin, the dried polyethylene resin, the compatibilizer FB521A, 0.5 parts by mass of 20μm nucleating agent SiO2, 3 parts by mass of multifunctional epoxy chain extender ADR4368, and 0.2 parts by mass of antioxidant 168 are mixed evenly by a high mixer to obtain a premix. After the premix is ​​extruded through a twin-screw extruder with a T-type extrusion die head and an aspect ratio of 52 and a diameter of 25mm, a polyamide composite material with a thickness of 8mm is obtained.

[0055] The second step is to prepare the polyamide material to be foamed. The polyamide composite material is irradiated with 25 kGy of gamma rays to obtain the polyamide material to be foamed.

[0056] The third step is to prepare the polyamide foam material. The polyamide material to be foamed is placed in an autoclave or a molded foaming device, and supercritical N2 is used as a foaming agent to perform two-stage foaming, namely: first, supercritical N2 is injected at 200°C until the reaction pressure reaches 10Mpa, and the temperature is kept for 10 minutes to complete the first stage of foaming; then the reaction temperature is increased to 230°C, and supercritical N2 is injected again to make the reaction pressure reach 20Mpa, and the temperature is kept for 30 minutes to complete the second stage of foaming, and then the reaction system is quickly depressurized to 0Mpa to complete the foaming process and obtain the polyamide foam material. The performance parameters of the polyamide foam material prepared in Example 3 of the present invention are shown in Table 1.

[0057] Comparative Example 1

[0058] The method for preparing the polyamide foam material provided in Comparative Example 1 of the present invention comprises the following steps:

[0059] The first step is to prepare a polyamide foaming material. Take 75 parts by mass of nylon 6 resin YH800, 25 parts by mass of polyethylene resin LD080, and 10 parts by mass of polyolefin elastomer grafted maleic anhydride FB521A (compatibilizer), dry them in advance, and the moisture content is required to be less than 200ppm. The dried nylon 6 resin, the dried polyethylene resin, the compatibilizer FB521A, 0.5 parts by mass of 20μm nucleating agent SiO2, 3 parts by mass of multifunctional epoxy chain extender ADR4368, and 0.2 parts by mass of antioxidant 168 are mixed evenly by a high mixer to obtain a premix. After the premix is ​​extruded through a twin-screw extruder with a T-type extrusion die head and an aspect ratio of 52 and a diameter of 25mm, a polyamide foaming material with a thickness of 8mm is obtained.

[0060] The second step is to prepare a polyamide foam material. The polyamide material to be foamed is placed in an autoclave or a molded foaming device, and supercritical N2 is used as a foaming agent to perform two-stage foaming, namely: first, supercritical N2 is injected at 200°C until the reaction pressure reaches 10Mpa, and the temperature is kept for 10 minutes to complete the first stage of foaming; then the reaction temperature is increased to 230°C, and supercritical N2 is injected again to make the reaction pressure reach 20Mpa, and the temperature is kept for 30 minutes to complete the second stage of foaming, and then the reaction system is quickly depressurized to 0Mpa to complete the foaming process, and the polyamide foam material is obtained. The performance parameters of the polyamide foam material prepared in Comparative Example 1 of the present invention are shown in Table 1.

[0061] Comparative Example 2

[0062] The preparation method of the polyamide foam material provided in Comparative Example 2 of the present invention comprises the following steps:

[0063] The first step is to prepare a polyamide foaming material. Take 100 parts by mass of nylon 6 resin YH800 and dry it in advance. The moisture content is required to be less than 200ppm. The dried nylon 6 resin, 0.5 parts by mass of 20μm nucleating agent SiO2, 4 parts by mass of multifunctional epoxy chain extender ADR4368, and 0.2 parts by mass of antioxidant 1076 are mixed evenly by a high mixer to obtain a premix. After the premix is ​​extruded through a twin-screw extruder with a T-type extrusion die head and an aspect ratio of 52 and a diameter of 25mm, a polyamide foaming material with a thickness of 8mm is obtained.

[0064] The second step is to prepare a polyamide material to be foamed. The polyamide composite material is irradiated with 20 kGy of gamma rays to obtain a polyamide material to be foamed.

[0065] The third step is to prepare a polyamide foam material. The polyamide material to be foamed is placed in an autoclave or a compression foaming device, supercritical CO2 is used as a foaming agent, supercritical CO2 is first injected at 230°C, the polyamide material to be foamed is placed in a reactor, the reaction pressure reaches 20Mpa, and the temperature is kept for 30 minutes, and then the reaction system is quickly depressurized to 0Mpa to complete the foaming process, and the polyamide foam material is obtained. The performance parameters of the polyamide foam material prepared in Comparative Example 2 of the present invention are shown in Table 1.

[0066] Comparative Example 3

[0067] The preparation method of the polyamide foam material provided in Comparative Example 3 of the present invention comprises the following steps:

[0068] The first step is to prepare a polyamide foaming material. Take 75 parts by mass of nylon 6 resin YH800, 25 parts by mass of polyethylene resin LD080, and 10 parts by mass of polyolefin elastomer grafted maleic anhydride FB521A (compatibilizer), dry them in advance, and the moisture content is required to be less than 200ppm. The dried nylon 6 resin, the dried polyethylene resin, the compatibilizer FB521A, 0.5 parts by mass of 20μm nucleating agent SiO2, 3 parts by mass of multifunctional epoxy chain extender ADR4368, and 0.2 parts by mass of antioxidant 168 are mixed evenly by a high mixer to obtain a premix. After the premix is ​​extruded through a twin-screw extruder with a T-type extrusion die head and an aspect ratio of 52 and a diameter of 25mm, a polyamide foaming material with a thickness of 8mm is obtained.

[0069] The second step is to prepare a polyamide foam material. The polyamide material to be foamed is placed in an autoclave or a molded foaming device, and supercritical N2 is used as a foaming agent. The polyamide material to be foamed is placed in an autoclave or a molded foaming device. That is, supercritical N2 is first injected at 230°C, and the polyamide material to be foamed is placed in a reactor, so that the reaction pressure reaches 20Mpa, and the temperature is kept for 30 minutes, and then the reaction system is quickly depressurized to 0Mpa to complete the foaming process, and the polyamide foam material is obtained. The performance parameters of the polyamide foam material prepared in Comparative Example 3 of the present invention are shown in Table 1.

[0070] Table 1 shows the performance parameters of the polyamide foam materials prepared in Examples 1 to 3 of the present invention and Comparative Examples 1 to 3

[0071] Table 1

[0072]

[0073] From the data in Table 1, it can be seen that the foaming performance of the entire composite material system can be improved by introducing polyethylene resin into the polyamide resin and producing an interpenetrating network structure of the two resins through a radiation cross-linking process. The above-mentioned polyamide material to be foamed is foamed in two stages using a supercritical foaming agent, and the compression permanent deformation of the polyamide foamed material finally foamed is reduced to a minimum of 10%. By adjusting the proportion of polyethylene, a product with a compression strength of 400 kPa and a compression permanent deformation of 18% can be obtained, and the overall performance is balanced and has a high level. The polyamide and polyolefin blending system, gamma-ray irradiation and two-stage foaming process in the preparation method of the polyamide foam material of the present invention are key steps. Comparative Example 1 does not use gamma-ray irradiation, does not cross-link LDPE in advance, and the compression strength of the obtained foam material is seriously reduced; the foam material obtained by not using the polyamide and polyolefin blending system in Comparative Example 2 has a serious collapse phenomenon, which is because the lack of LDPE causes the polyamide to have defects of poor foam toughness and poor compression resilience; Comparative Example 3 only performs one-stage foaming, the foaming ratio is low, and the foaming is not sufficient, resulting in high compression strength and low permanent deformation of the obtained foam material.

[0074] The above is only a specific embodiment of the present invention. Obviously, various modifications and combinations can be made without departing from the spirit and scope of the present invention. Accordingly, this specification and the drawings are only exemplary illustrations of the present invention as defined by the attached claims, and are deemed to have covered any and all modifications, changes, combinations or equivalents within the scope of the present invention. Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is intended to include these changes and variations. Any technician familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be based on the scope of protection of the claims.

Claims

1. A method for preparing a polyamide foam material, characterized in that: include: The dried polyamide resin, the dried polyethylene resin and the additives are mixed to obtain a premix; the additives include a compatibilizer, a nucleating agent, a chain extender and an antioxidant; the polyamide resin is nylon 6, the relative viscosity of the polyamide resin is 2.8 to 3.4, the polyethylene resin is an extrusion-grade polyethylene resin or a film-grade low-density polyethylene resin, and the melt index of the polyethylene resin is 0.5 g / 10 min to 5 g / 10 min under the test conditions of 190° C. and 2.14 kg; Using an extruder to perform extrusion modification on the premix to obtain a polyamide composite material; The polyamide composite material is subjected to a cross-linking reaction to obtain a polyamide foaming material, wherein the polyamide composite material includes a composite material formed by a polyethylene resin and a polyamide; the cross-linking reaction is a radiation cross-linking reaction, the radiation source of the radiation cross-linking reaction is a gamma ray, and the irradiation dose of the gamma ray is 5 kGy to 50 kGy; The polyamide material to be foamed is subjected to two-stage foaming by a supercritical foaming method to obtain a polyamide foamed material; the supercritical foaming agent used in the supercritical foaming method is supercritical CO2 or supercritical N2.

2. The method for preparing a polyamide foam material according to claim 1, characterized in that: In terms of weight percentage, the weight percentage of the dried polyamide resin is 50 to 90 parts, the weight percentage of the dried polyethylene resin is 10 to 50 parts, the weight percentage of the compatibilizer is 5 to 20 parts, the weight percentage of the nucleating agent is 0.1 to 1 part, the weight percentage of the chain extender is 1 to 5 parts, and the weight percentage of the antioxidant is 0.5 to 2 parts.

3. The method for preparing a polyamide foam material according to claim 1, characterized in that: The two-stage foaming process includes a first stage foaming process and a second stage foaming process, wherein the process parameters of the first stage foaming process include: the injection temperature of the supercritical foaming agent is 150° C. to 210° C., the reaction pressure is 5 MPa to 15 MPa, and the insulation time is 10 min to 30 min; The process parameters of the second stage foaming process include: the reaction temperature of the supercritical foaming agent injected again is 220° C. to 270° C., the reaction pressure is 10 MPa to 20 MPa, and the insulation time is 20 min to 40 min.

4. The method for preparing a polyamide foam material according to claim 1, characterized in that: The water content of the dried polyamide resin is less than 200 ppm, and the water content of the dried polyethylene resin is less than 200 ppm.

5. The method for preparing a polyamide foam material according to claim 2, characterized in that: The compatibilizer includes at least one of low-density polyethylene grafted with maleic anhydride LDPE-g-MAH, polyolefin elastomer grafted with maleic anhydride POE-g-MAH, ethylene-vinyl acetate copolymer EVA, and ethylene-methyl acrylate copolymer EMA; The chain extender is at least one of isocyanate, maleic anhydride chain extender and multifunctional epoxy compound.

6. A polyamide foam material prepared by the method for preparing a polyamide foam material according to any one of claims 1 to 5.

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