阅读说明：本技术 一种多层发泡再生塑料及其制备方法 (Multilayer foamed recycled plastic and preparation method thereof ) 是由 沈佳斌 何露 郭少云 于 2020-06-24 设计创作，主要内容包括：本发明公开了一种多层发泡再生塑料及其制备方法,包括由废旧塑料与发泡剂熔融共混造粒制得的发泡层树脂原料,和以废旧塑料、或塑料新料、或以废旧塑料与塑料新料的熔融共混物为树脂基体,与功能组分熔融共混造粒制得的支撑层树脂原料,经共挤出制备得到发泡层与支撑层交替排布的多层状结构,其中,发泡孔仅选择性的分布在所述发泡层中提供减重、隔音、隔热作用,所述支撑层提供力学支撑,并根据填加的功能组分种类提供一种或多种性能特性。所述多层发泡再生塑料的层数、层厚比以及泡孔结构可调可控。本发明将组分配方设计与层状仿生结构设计相结合,最大限度发挥各组分性能优势,实现废旧塑料的轻量化和高性能化再生利用。(The invention discloses a multilayer foaming recycled plastic and a preparation method thereof, and the multilayer foaming recycled plastic comprises a foaming layer resin raw material prepared by melting, blending and granulating waste plastics and foaming agents, and a supporting layer resin raw material prepared by melting, blending and granulating functional components by taking the waste plastics, or new plastic materials, or a molten blend of the waste plastics and the new plastic materials as a resin matrix, and is prepared by coextrusion to obtain a multilayer structure with the foaming layers and the supporting layers alternately arranged, wherein foaming holes are only selectively distributed in the foaming layers to provide the functions of weight reduction, sound insulation and heat insulation, the supporting layers provide mechanical support, and one or more performance characteristics are provided according to the types of the added functional components. The number of layers, the layer thickness ratio and the cell structure of the multilayer foamed regenerated plastic are adjustable and controllable. The invention combines the component formula design and the layered bionic structure design, gives full play to the performance advantages of each component to the maximum extent, and realizes the light weight and high performance recycling of the waste plastics.)

1. The preparation method of the multilayer foamed recycled plastic is characterized by comprising the following steps of:

A. Adding a foaming agent into the waste plastic, and then performing melt blending granulation above the viscous flow temperature of the waste plastic and below the decomposition temperature of the foaming agent to obtain a foaming layer resin raw material;

B. taking waste plastics, or new plastic materials, or a melt blend of the waste plastics and the new plastic materials as a resin matrix, fully mixing the resin matrix with functional components, and then carrying out melt blending granulation to obtain a resin raw material of the supporting layer;

C. and respectively putting the foaming layer resin raw material and the supporting layer resin raw material into two extruders of a co-extrusion device for melt extrusion, filtering large-particle-size particles from the extruded melts by a filter screen of a filtering device, superposing the large-particle-size particles in a confluence device, regulating the layer number through the cutting and superposing action of a layer multiplier connected with the confluence device, finally extruding the mixture from an outlet die, and obtaining the layered composite material with the foaming layer and the supporting layer alternately arranged through the shaping action of a shaping die and the traction action of a traction machine.

2. The method for preparing a multi-layer foamed recycled plastic as claimed in claim 1, wherein the virgin plastic material is a plastic raw material which has not been subjected to a thermoplastic forming process; the waste plastic is a plastic raw material obtained by recycling, cleaning and crushing after being subjected to one-time thermoplastic forming and processing; the foaming layer resin raw material is waste plastic with a solid content of less than 5% by mass, the supporting layer resin raw material is waste plastic with a solid content of less than 20% by mass, and the solid content refers to metal, inorganic matters or high-melting-point organic matters which can not be melted in the thermoplastic processing of the waste plastic.

3. The method for preparing the multilayer foaming recycled plastic as claimed in claim 1, wherein the melt viscosity and the melt strength of the foaming layer waste plastic are regulated and controlled by adding one of a cross-linking agent, a chain extender, rubber particles or a thermoplastic elastomer so as to meet the requirements of stable flow and controllable foaming in the co-extrusion process.

4. The method for preparing a multi-layer foamed recycled plastic according to claim 1, wherein the resin raw material of the support layer can be added with one or more of the following functional components according to the requirements of thermoplastic processing or performance:

A. adding one of a cross-linking agent, a chain extender, rubber particles or a thermoplastic elastomer into the supporting layer resin to regulate and control the melt viscosity or melt strength of the supporting layer resin;

B. adding 5-40% by mass of rubber or thermoplastic elastomer into the support layer resin to regulate and control the mechanical toughness of the layered composite material;

C. adding 5-30% of inorganic powder into the support layer resin to regulate and control the mechanical strength and rigidity of the layered composite material, wherein the inorganic particles can be one or more of talcum powder, silicon dioxide, barium sulfate, glass fiber and montmorillonite;

D. Adding 10-30% of flame retardant by mass into the support layer resin to regulate and control the flame retardant property of the layered composite material;

E. adding 15-40% of phase change material in mass percent into the support layer resin to regulate and control the heat preservation and heat insulation performance of the layered composite material;

F. conductive particles with the mass fraction of 5% -30% are added into the supporting layer resin, so that the conductive, dielectric, electromagnetic shielding and antistatic properties of the layered composite material are regulated and controlled.

5. The method for preparing a multi-layer foamed recycled plastic according to claim 1, wherein the foamed layer is foamed by one of the following three foaming methods:

A. extrusion foaming method: controlling the co-extrusion temperature, setting the temperature of each section of an extruder of a multilayer co-extrusion system to be lower than the decomposition temperature of a foaming agent, and setting the temperatures of a confluence device, a layer multiplier and an outlet die to be higher than the decomposition temperature of the foaming agent, so that a foaming layer of the layered composite material has a foam cell structure after leaving the outlet die, then cooling and shaping the foaming layer by a shaping die, and finally drawing the foaming layer by a traction machine to obtain the multilayer foaming material;

B. a die release foaming method: controlling the co-extrusion temperature, setting the temperature of each section of the whole multilayer co-extrusion system to be lower than the decomposition temperature of a foaming agent, so that a foaming layer of the layered composite material does not generate a foam structure when leaving an outlet die, then entering a shaping die, and leading the foaming layer to be fully foamed when the temperature of the die is higher than the decomposition temperature of the foaming agent, and finally leading the foamed material out by a traction machine to obtain the multilayer foamed material;

C. A batch foaming method: controlling the co-extrusion temperature, and setting the temperature of each section of the whole multilayer co-extrusion system to be lower than the decomposition temperature of the foaming agent, so that the foaming layer of the layered composite material still does not generate a cellular structure after being shaped and cooled by a shaping mold and pulled by a traction machine; and cutting the co-extruded product according to the required size and shape, putting the co-extruded product into a shaping mold, setting the temperature of the mold to be higher than the decomposition temperature of the foaming agent so as to fully foam the foaming layer, shaping and cooling to obtain the multilayer foaming material.

6. The method for preparing the multilayer foaming recycled plastic as claimed in claim 1, wherein a filtering device is arranged between the extruder and the junction station, a filter screen is arranged in the filtering device to filter out large-size particles in the melt to promote particle dispersion, and the maximum mesh number of the filter screen is 400 meshes.

7. The method for preparing a multi-layer foamed recycled plastic according to claim 1,the method is characterized in that the number of the layer multipliers is n (0, 1, 2, 3, …), and the corresponding number of the composite material layers is 2^（n+1）And the maximum value of n can be selected to be 10.

8. The method for preparing a multi-layer foamed recycled plastic as claimed in claim 1, wherein the degree of foaming and cell structure of the foamed layer are controlled by:

A. The regulation and control formula comprises: the types and the addition amounts of the nucleating agent, the foaming agent and the auxiliary foaming agent in the foaming layer and the melt strength of the resin raw material;

B. the structure of the regulation layer: namely the total number of layers and the total thickness of the multilayer foaming material, and the co-extrusion rate ratio of the foaming layer resin raw material and the supporting layer resin raw material;

C. and (3) regulating and controlling a foaming process: namely, the foaming method, the foaming temperature and the foaming time.

9. A multilayer foamed recycled plastic is characterized in that: the multilayer foamed regenerated plastic is of an at least two-layer or multilayer overlapping structure, wherein foaming holes are only selectively distributed in the foaming layer to provide the functions of weight reduction, sound insulation and heat insulation; the support layer provides mechanical support and provides one or more performance characteristics to the multilayer foamed recycled plastic according to the added functional component types.

Technical Field

The invention relates to the technical field of plastic recycling, in particular to a multilayer foamed recycled plastic and a preparation method thereof.

Background

With the popularization of the material mode of replacing steel with plastics and replacing wood with plastics, the high polymer material is widely applied in various industries, so that a large amount of waste plastics are generated. In 2050 years, 120 hundred million tons of waste plastics are expected to flow into the nature, which causes great environmental problems, and thus the demand for recycling the waste plastics is urgent.

Lightweight materials are the key field of new material development in China, and foaming is the most direct means for realizing lightweight of polymers. In addition, with the rapid development of the industries such as aerospace, national defense, energy, transportation, packaging, electrical appliances, sports equipment and the like, the polymer foam material with excellent mechanical properties and the characteristics of heat insulation, sound insulation, buffering, flame retardance, electromagnetic shielding and the like is increasingly demanded.

To achieve weight reduction and functionalization of the material, it is conceivable to combine addition of functional particles and foaming. Take the addition of functional nanoparticles as an example. 201610943930.X discloses a preparation method of a graphene nanoribbon/PMMA micro-foamed nanocomposite. According to the method, a multi-walled carbon nanotube is longitudinally expanded by an oxidation method to obtain a graphene oxide nanobelt, the graphene oxide nanobelt is dispersed in DMF and subjected to high-temperature reflux for reduction to obtain a graphene nanobelt dispersion liquid, the graphene nanobelt dispersion liquid and PMMA are blended, then the graphene nanobelt/PMMA nanocomposite material is obtained through ultrasonic dispersion, anti-solvent precipitation, freeze drying and hot press molding, and finally the graphene nanobelt/PMMA micro-foaming nanocomposite material is obtained by utilizing a supercritical carbon dioxide foaming technology. The obtained material has better electrical properties. 201710504151.4 discloses a method for preparing electromagnetic shielding foaming composite material. The method comprises the steps of pretreating graphite and carbon fibers, carrying out solution blending and ultrasonic-assisted dispersion to obtain a homogeneous nano carbon conductive fiber material, carrying out solution blending with PVC, carrying out electrostatic spinning to prepare the nano conductive fiber material, finally mechanically blending with EVA, PVC, a foaming agent and a processing aid, carrying out open milling in an open mill, and foaming in a flat vulcanizing machine to obtain the electromagnetic shielding foaming material. Both of the above-mentioned methods achieve the lightening and functionalization of plastics, however they all suffer from some similar drawbacks: in order to realize good dispersion of the nano particles in the matrix, the added nano particles are subjected to complicated pretreatment, a large amount of organic solvent is used in the process, and secondary pollution is caused; and the preparation process of the material is too complicated, the energy consumption is high, the cost is high, and continuous and batch production is difficult to realize. In addition, the traditional foaming system is difficult to add various functional components and the performance is difficult to regulate and control due to the foaming requirement. The electrical properties of the PU/CNT foam material were also studied by related researchers (Small, 2007, 3: 408-411). They found that: with the reduction of density, the cell walls become thin, so that the three-dimensional permeation of electrons is converted to two-dimensional, the percolation threshold value is improved, and the conductivity of the cell walls is reduced; the lower the density of the foam, the more cells there are, which increases the difficulty of the CNTs forming conductive channels in the cell walls; since the CNTs do not detach from the cell walls due to the change in the density of the foam, the content of CNTs in the cell walls does not change, so that when the density of the foam decreases, the cell walls are subjected to a greater tensile force, the number of contact points of the CNT conductive paths in the cell walls decreases, and the conductivity decreases. Therefore, the addition of functional particles to the conventional foaming system has the disadvantage that the performance is not easy to control.

At present, most foamed plastics are chemically or physically foamed by uniformly dispersing a foaming agent in a polymer matrix. The cell structure can be controlled by the type and content of the foaming agent and the foaming process. And for the waste plastics, the melt strength is lower and the foaming difficulty is higher due to one-time or even multiple times of thermoplastic processing. If other functional components are added into the foaming system, the cell structure and the foaming quality are further obviously influenced, which brings many problems to the design, processing and the like of the material. Therefore, the problems of high-quality foaming and high performance of the waste plastics are difficult to simultaneously solve through the traditional blending process, and a plurality of limitations are brought to the recycling of the waste plastics. Coextrusion techniques enable the construction of layered, overlapping structures. Compared with the traditional polymer blending system, the continuous layer space of the multilayer alternating composite material can provide mechanical support and resist deformation to the maximum extent; the rich layer interface can effectively inhibit the silver crack from diffusing, absorb energy and reflect sound waves; and the layered distribution of the functional particles can also endow the material with excellent electrical, flame retardant, sound insulation and other properties under low filling amount, which provides possibility for solving the problem of high-performance modification of the waste plastics. It is expected that the material has excellent comprehensive performance by organically combining the foaming structure and the layered overlapping structure, thereby realizing high-performance recycling of the waste plastics.

Disclosure of Invention

The invention aims to prepare a multilayer foaming material taking waste plastics as a matrix by combining formula design, structure design and process design aiming at the current situations of recycling and noise pollution of the waste plastics, so as to realize high-performance reutilization of the waste plastics in the fields of sound insulation, noise reduction and heat preservation.

In order to achieve the purpose, the invention adopts the following technical scheme:

the invention comprises the following steps:

A. adding a foaming agent into the waste plastic, and then performing melt blending granulation above the viscous flow temperature of the waste plastic and below the decomposition temperature of the foaming agent to obtain a foaming layer resin raw material;

B. waste plastics, or new plastic materials, or a melt blend of the waste plastics and the new plastic materials are used as a resin raw material of the supporting layer;

C. respectively putting foaming layer resin raw materials and supporting layer resin raw materials into two extruders of a co-extrusion device, after melting and plasticizing, superposing two strands of melts in a confluence device, then regulating and controlling the layer number through the cutting and superposing action of a layer multiplier connected with the confluence device, finally extruding from an outlet die, and obtaining the layered composite material with the foaming layer and the supporting layer alternately arranged through the shaping action of a shaping die and the traction action of a traction machine.

The layered composite material is formed by compounding foaming layers and supporting layers in an alternating layered structure, and at least one continuous layered interface exists in the material, namely at least 2 continuous layered structures exist.

The number of layer multipliers is n (0, 1, 2, 3, …), and the corresponding number of composite layers is 2^（n+1）And the maximum value of n can be selected to be 10.

The new plastic material is a plastic raw material which is not subjected to thermoplastic forming processing; the waste plastic is a plastic raw material obtained by recycling, cleaning and crushing after being subjected to one-time thermoplastic forming and processing.

The mass fraction of the solid content in the waste plastic selected as the foaming layer resin raw material is less than 5%; the support layer resin raw material is waste plastic with solid content of less than 30% by mass, wherein the solid content refers to metal, inorganic matters or high-melting-point organic matters which can not be melted in the thermoplastic processing of the waste plastic.

The melt viscosity and the melt strength of the waste plastic of the foaming layer are regulated and controlled by adding one of a cross-linking agent, a chain extender, rubber particles or a thermoplastic elastomer so as to meet the requirements of stable flow and controllable foaming in the co-extrusion process.

The cross-linking agent or the chain extender is one of dicumyl peroxide, benzoyl peroxide, azobisisobutyronitrile and azobisisoheptonitrile, and the addition amount is 0.5-2 parts; the rubber particles or the thermoplastic elastomer are one or more of natural rubber, nitrile rubber, ethylene-octene copolymer (POE), ethylene-vinyl acetate copolymer (EVA), styrene-butadiene-styrene block copolymer (SBS) and styrene-ethylene/butylene-styrene block copolymer (SEBS), and the addition amount is 5-40 parts.

Besides the waste plastics and the foaming agent, the foaming layer resin raw material components also need to be added with a proper amount of necessary processing aids, such as a cross-linking agent, an auxiliary foaming agent, a foam cell nucleating agent and a surfactant.

The foaming agent is one of Azodicarbonamide (AC), Azodiisobutyronitrile (AIBN), diisopropyl azodicarboxylate (DIAD), diethyl azodicarboxylate (DEAD), Diazoaminobenzene (DAB), barium azodicarboxylate, dinitrosopentamethylenetetramine and p-toluenesulfonyl hydrazide (OBSH), the addition amount is 1-10 parts, and the decomposition temperature of the foaming agent is adjusted by an auxiliary foaming agent; the auxiliary foaming agent is one of zinc oxide, zinc stearate and chromium oxide, and the addition amount is 1-5 parts; the auxiliary crosslinking agent is one of triallyl isocyanurate, triallyl isocyanurate and divinylbenzene, and the addition amount is 0.1-2 parts; the foam cell nucleating agent is SiO₂Talc powder and CaCO₃0.5-2 parts of one of the components; the surfactant is one of silicone oil, white oil and liquid paraffin, and the addition amount is 1-5 parts.

The resin raw material of the supporting layer can be added with one or more of the following components according to the requirements of thermoplastic processing or performance:

A. Adding one of a cross-linking agent, a chain extender, rubber particles or a thermoplastic elastomer into the supporting layer resin to regulate the melt viscosity or the melt strength of the supporting layer resin;

B. adding 5-40% by mass of rubber or thermoplastic elastomer into the support layer resin to improve the mechanical toughness of the layered composite material;

C. inorganic powder with the mass fraction of 5% -30% is added into the supporting layer resin, so that the mechanical strength and rigidity of the layered composite material are improved;

D. adding 5-30% of flame retardant by mass into the support layer resin to improve the flame retardant property of the layered composite material;

E. phase change materials with the mass fraction of 5% -40% are added into the supporting layer resin, so that the heat preservation and heat insulation performance of the layered composite material is improved; .

The inorganic powder is SiO₂、CaCO₃And talc powder; the flame retardant is an Intumescent Flame Retardant (IFR); the phase change material is selected from solid-liquid organic phase change materials, and paraffin is selected here.

The foaming layer is foamed by one of the following three foaming modes:

A. extrusion foaming method: controlling the co-extrusion temperature, setting the temperature of each section of an extruder of a multilayer co-extrusion system to be lower than the decomposition temperature of a foaming agent, and setting the temperatures of a confluence device, a layer multiplier and an outlet die to be higher than the decomposition temperature of the foaming agent, so that a foaming layer of the layered composite material has a foam cell structure after leaving the outlet die, then cooling and shaping the foaming layer by a shaping die, and finally drawing the foaming layer by a traction machine to obtain the multilayer foaming material;

B. A die release foaming method: controlling the co-extrusion temperature, setting the temperature of each section of the whole multilayer co-extrusion system to be lower than the decomposition temperature of a foaming agent, so that a foaming layer of the layered composite material does not generate a foam structure when leaving an outlet die, then entering a shaping die, and leading the foaming layer to be fully foamed when the temperature of the die is higher than the decomposition temperature of the foaming agent, and finally leading the foamed material out by a traction machine to obtain the multilayer foamed material;

C. a batch foaming method: controlling the co-extrusion temperature, and setting the temperature of each section of the whole multilayer co-extrusion system to be lower than the decomposition temperature of the foaming agent, so that the foaming layer of the layered composite material still does not generate a cellular structure after being shaped and cooled by a shaping mold and pulled by a traction machine; and cutting the co-extruded product according to the required size and shape, putting the co-extruded product into a shaping mold, setting the temperature of the mold to be higher than the decomposition temperature of the foaming agent so as to fully foam the foaming layer, shaping and cooling to obtain the multilayer foaming material.

The foaming degree and the cell structure of the foaming layer are regulated and controlled in the following modes:

A. the regulation and control formula comprises: the types and the addition amounts of the nucleating agent, the foaming agent and the auxiliary foaming agent in the foaming layer and the melt strength of the resin raw material;

B. the structure of the regulation layer: namely the total number of layers and the total thickness of the multilayer foaming material, and the co-extrusion rate ratio of the foaming layer resin raw material and the supporting layer resin raw material;

C. And (3) regulating and controlling a foaming process: namely, the foaming method, the foaming temperature and the foaming time.

The invention has the following advantages:

1. the component formula design, the layered structure design and the processing technology design are combined, the performance advantages of each component are exerted to the maximum extent, and the high-performance recycling of the waste plastics is realized.

2. The foaming layer and the supporting layer are arranged alternately to form a special layered structure with a large number of layered interfaces and porous structures. Therefore, when the sound wave is transmitted to the layered interface, the sound wave is reflected, and in addition, the sound energy is further attenuated by the porous structure of the foaming layer, so that the material prepared by the invention has better sound insulation performance.

3. The high polymer material has low heat conductivity coefficient, and a large number of holes (the air heat conductivity coefficient is only 0.023W/(mK)) in the foaming layer, so the material prepared by the invention has better heat insulation performance.

4. The foaming degree and the cell structure of the foaming layer can be regulated and controlled by regulating and controlling the formula composition, the layer structure and the foaming process of the foaming layer, so that the final performance of the material can be regulated and controlled.

5. The materials can have different properties by regulating and controlling the formula composition of the resin raw materials of the supporting layer.

6. The method has the advantages of simple operation, low cost, high efficiency and easy continuous production.

The invention also has some advantages in other respects.

Drawings

FIG. 1 is a schematic structural diagram of a multi-layer foamed recycled plastic according to the present invention;

in the figure: 1-supporting layer and 2-foaming layer.

Detailed Description

The present invention will be described in further detail with reference to the following examples, but it should be understood that the described examples are only a part of the present invention, and not all of the present invention. In the following examples, the amounts of the components are by weight. It should be noted that the following examples are given solely for the purpose of illustration and are not to be construed as limitations on the scope of the invention, as those skilled in the art will be able to make insubstantial modifications and variations of the invention in light of the above teachings, while still remaining within the scope of the invention. The invention comprises the following steps:

A. adding a foaming agent into the waste plastic, and then performing melt blending granulation above the viscous flow temperature of the waste plastic and below the decomposition temperature of the foaming agent to obtain a foaming layer resin raw material;

B. taking waste plastics, or new plastic materials, or a melt blend of the waste plastics and the new plastic materials as a resin matrix, fully mixing the resin matrix with functional components, and then carrying out melt blending granulation to obtain a resin raw material of the supporting layer;

C. And respectively putting the foaming layer resin raw material and the supporting layer resin raw material into two extruders of a co-extrusion device for melt extrusion, filtering large-particle-size particles from the extruded melts by a filter screen of a filtering device, superposing the large-particle-size particles in a confluence device, regulating the layer number through the cutting and superposing action of a layer multiplier connected with the confluence device, finally extruding the mixture from an outlet die, and obtaining the layered composite material with the foaming layer and the supporting layer alternately arranged through the shaping action of a shaping die and the traction action of a traction machine.

The new plastic material is a plastic raw material which is not subjected to thermoplastic forming processing; the waste plastic is a plastic raw material obtained by recycling, cleaning and crushing after being subjected to one-time thermoplastic forming and processing; the foaming layer resin raw material is waste plastic with a solid content of less than 5% by mass, the supporting layer resin raw material is waste plastic with a solid content of less than 20% by mass, and the solid content refers to metal, inorganic matters or high-melting-point organic matters which can not be melted in the thermoplastic processing of the waste plastic.

The melt viscosity and the melt strength of the waste plastic of the foaming layer are regulated and controlled by adding one of a cross-linking agent, a chain extender, rubber particles or a thermoplastic elastomer so as to meet the requirements of stable flow and controllable foaming in the co-extrusion process.

The resin raw material of the supporting layer can be added with one or more of the following functional components according to the requirements of thermoplastic processing or performance:

A. adding one of a cross-linking agent, a chain extender, rubber particles or a thermoplastic elastomer into the supporting layer resin to regulate and control the melt viscosity or melt strength of the supporting layer resin;

B. adding 5-40% by mass of rubber or thermoplastic elastomer into the support layer resin to regulate and control the mechanical toughness of the layered composite material;

C. adding 5-30% of inorganic powder into the support layer resin to regulate and control the mechanical strength and rigidity of the layered composite material, wherein the inorganic particles can be one or more of talcum powder, silicon dioxide, barium sulfate, glass fiber and montmorillonite;

D. adding 10-30% of flame retardant by mass into the support layer resin to regulate and control the flame retardant property of the layered composite material;

E. adding 15-40% of phase change material in mass percent into the support layer resin to regulate and control the heat preservation and heat insulation performance of the layered composite material;

F. conductive particles with the mass fraction of 5% -30% are added into the supporting layer resin, so that the conductive, dielectric, electromagnetic shielding and antistatic properties of the layered composite material are regulated and controlled.

The foaming layer is foamed by one of the following three foaming modes:

A. extrusion foaming method: controlling the co-extrusion temperature, setting the temperature of each section of an extruder of a multilayer co-extrusion system to be lower than the decomposition temperature of a foaming agent, and setting the temperatures of a confluence device, a layer multiplier and an outlet die to be higher than the decomposition temperature of the foaming agent, so that a foaming layer of the layered composite material has a foam cell structure after leaving the outlet die, then cooling and shaping the foaming layer by a shaping die, and finally drawing the foaming layer by a traction machine to obtain the multilayer foaming material;

B. a die release foaming method: controlling the co-extrusion temperature, setting the temperature of each section of the whole multilayer co-extrusion system to be lower than the decomposition temperature of a foaming agent, so that a foaming layer of the layered composite material does not generate a foam structure when leaving an outlet die, then entering a shaping die, and leading the foaming layer to be fully foamed when the temperature of the die is higher than the decomposition temperature of the foaming agent, and finally leading the foamed material out by a traction machine to obtain the multilayer foamed material;

C. a batch foaming method: controlling the co-extrusion temperature, and setting the temperature of each section of the whole multilayer co-extrusion system to be lower than the decomposition temperature of the foaming agent, so that the foaming layer of the layered composite material still does not generate a cellular structure after being shaped and cooled by a shaping mold and pulled by a traction machine; and cutting the co-extruded product according to the required size and shape, putting the co-extruded product into a shaping mold, setting the temperature of the mold to be higher than the decomposition temperature of the foaming agent so as to fully foam the foaming layer, shaping and cooling to obtain the multilayer foaming material.

And a filter device is arranged between the extruder and the junction station, a filter screen is arranged in the filter device to filter out large-particle-size particles in the melt so as to promote particle dispersion, and the maximum mesh number of the filter screen is 400 meshes.

The preparation method of the multilayer foamed recycled plastic is characterized in that the number of the layer multipliers is n (0, 1, 2, 3, …), and the number of the corresponding layers of the composite material is 2^（n+1）And the maximum value of n can be selected to be 10.

The preparation method of the multilayer foaming recycled plastic is characterized in that the foaming degree and the cell structure of the foaming layer are regulated and controlled in the following way:

A. the regulation and control formula comprises: the types and the addition amounts of the nucleating agent, the foaming agent and the auxiliary foaming agent in the foaming layer and the melt strength of the resin raw material;

B. the structure of the regulation layer: namely the total number of layers and the total thickness of the multilayer foaming material, and the co-extrusion rate ratio of the foaming layer resin raw material and the supporting layer resin raw material;

C. and (3) regulating and controlling a foaming process: namely, the foaming method, the foaming temperature and the foaming time.

The multilayer foamed recycled plastic is of an at least two-layer or multilayer overlapped structure, wherein foaming pores are only selectively distributed in the foaming layer to provide the functions of weight reduction, sound insulation and heat insulation; the support layer provides mechanical support and provides one or more performance characteristics to the multilayer foamed recycled plastic according to the added functional component types.