WO2021189504A1

WO2021189504A1 - Two-layer-pe coextruded wood-plastic composite board and preparation method thereof

Info

Publication number: WO2021189504A1
Application number: PCT/CN2020/081952
Authority: WO
Inventors: 黄东辉; 唐道远; 张志勇
Original assignee: 安徽森泰木塑集团股份有限公司
Priority date: 2020-03-27
Filing date: 2020-03-29
Publication date: 2021-09-30
Also published as: CN111231469B; CN111231469A

Abstract

Disclosed is a two-layer-PE coextruded wood-plastic composite board, belonging to the field of new materials. The two-layer-PE coextruded wood-plastic composite comprises an environmentally-friendly substrate made from a first wood-plastic composite and a weather-resistant surface layer made from a second wood-plastic composite. The environmentally-friendly substrate is completely enveloped in the weather-resistant surface layer. The first wood-plastic composite is made from a first raw material comprising a wood-plastic composite board regrind and wood and bamboo flour. The second wood-plastic composite is made from a second raw material comprising virgin high-density polyethylene and wood and bamboo flour. The second raw material further comprises a weather-resistant stabilizer. A recess is formed on at least one surface of the weather-resistant surface layer by means of pressing. A greatest depth of the recess is greater than a thickness of the weather-resistant surface layer. A product of the invention is environmentally friendly, has low production costs and good surface color and texture, and has better weather-resistance than similar products in the prior art.

Description

Double-layer PE co-extruded wood-plastic board and preparation method thereof

Technical field

The invention relates to the technical field of plastic-wood material production, in particular to a double-layer PE co-extruded wood-plastic board and a preparation method thereof.

Background technique

The main materials of wood-plastic outdoor flooring are PE and wood flour or bamboo flour. After adding additives, high-speed mixing, pelletizing, and then using an extruder to extrude the pellets into a molding material. This type of flooring can be used in gardens and villas. Wait for the outdoor platform.

It is a new environmentally friendly high-tech material that combines the properties and characteristics of wood and plastic, and can replace wood and plastic. Its English abbreviation is WPC. Wood-plastic flooring has the same processing characteristics as wood. It can be sawed, drilled and nailed with ordinary tools. It is very convenient and can be used like ordinary wood. At the same time, it has the woody feel of wood and the water-proof and anti-corrosion properties of plastic, making it an outdoor waterproof and anti-corrosion building material with excellent performance and very durable. However, with the popularity of wood-plastic materials, a large amount of waste materials have become garbage, causing a great burden on the environment and resources.

CN104311948A discloses a formula of PE wood-plastic decorative panel, which includes component A and component B, wherein component A: wood powder 55-75, paraffin oil 0-1, component B is mainly recycled plastic, and also includes Some other antioxidants, kaolin, UV absorbers and other modifiers, etc. The formula of the wood-plastic decorative panel of the invention uses recycled wood powder and recycled PE plastic as the main raw materials, and the cost is low. At the same time, the invention also provides a new production process that makes the maximum addition ratio of wood flour up to 70%. The PE wood-plastic board prepared by this process and the aforementioned formula has the appearance of wood and imitation wood stripes, and has the advantages of low cost. It can be seen that the use of PE recycled materials in this invention not only solves the burden of the environment, but also turns waste into treasure and realizes effective resource utilization.

CN104890340B discloses an outdoor high-weather resistance and high-strength co-extruded plastic wood composite floor. It consists of two layers: a surface layer and an inner layer. In the composition ratio of the two layers, the surface layer contains 40-60 parts by weight of clear resin and modified resin 30～45 parts by weight, 120 mesh hardwood powder 5-20 parts by weight, calcium carbonate 1-10 parts by weight, talc 1-10 parts by weight, anti-UV agent 0.1-1 parts by weight, antioxidant 0.1-1 parts by weight, white 0.1-3 parts by weight of oil, 1.2-4.2 parts by weight of maleic anhydride grafted PP, 0.1-3 parts by weight of PE wax, 0.1-1.5 parts by weight of EBS, 0.1-3 parts by weight of zinc stearate, 2-6 parts by weight of toner The proportion of the inner layer is 30-45 parts by weight of HDPE, 35-55 parts by weight of 120 mesh hardwood powder, 2-6 parts by weight of coupling agent, 5-20 parts by weight of calcium carbonate, 15-35 parts by weight of glass fiber, 0.1 to 3 parts by weight of PE wax, 0.1 to 1.5 parts by weight of EBS, and 0.1 to 3 parts by weight of zinc stearate. The co-extruded plastic wood composite floor of the invention has the advantages of high weather resistance and high strength, but the overall idea of the invention is to change the two-layer composition to solve the mechanical properties and weather resistance, and it cannot be applied to recycled materials.

technical problem

The extensive use of waste wood and plastic has aggravated the original weakness of the board, that is, the flexural modulus and flexural strength are generally not high or unstable due to the fluctuation of the recycled plastic; at the same time, it may be because of the complex composition and other reasons that the product is more prone to microbial erosion. That is to say, the corrosion resistance of wood-plastic products has been greatly reduced. What is even more unacceptable is that even if a large number of recycled materials are pre-mixed to achieve uniform performance, it is impossible to avoid different batches due to different specifications of recycled materials. The color of the product produced a large color difference problem, which is fatal to the performance of the current wood-plastic product. This is because a large part of domestic wood-plastic products are currently exported to foreign countries, and the performance of different batches of products is likely to cause the product to be deemed unqualified, especially when the appearance and color are inconsistent, the product will be scrapped. On the other hand, since different batches of waste contain antioxidants and aging agents, after being recycled into new flooring, although there is no difference in the new product, after a period of use, different batches of The product showed different changes, which also caused this product to be unacceptable. In summary, the above technical problems hinder the secondary utilization of waste wood-plastic products.

Technical solutions

In order to solve the above technical problems, the present invention proposes a double-layer PE co-extruded wood-plastic board. The invention effectively solves the problems of poor and unstable color, weather resistance and mechanical properties of the recycled wood-plastic floor without increasing the production cost.

The technical solutions of the present invention to solve the above problems are as follows:

A double-layer PE co-extruded wood-plastic board, comprising an environmentally friendly base material composed of a first wood-plastic material and a weather-resistant surface layer composed of a second wood-plastic material, and the weather-resistant surface layer is completely wrapped on the environmentally friendly base material , The first wood-plastic material is made of a first raw material containing recycled wood-plastic board crushed material and wood bamboo powder, and the second wood-plastic material is made of a first raw material containing high-density polyethylene and wood bamboo powder. Made of two raw materials; the second raw material also contains a weathering stabilizer; at least one surface of the weathering surface layer has a pressed groove, and the maximum depth of the groove is greater than the thickness of the weathering surface layer .

Existing co-extruded sheets usually adopt a structure in which two extruded materials are connected on one side, and the present invention adopts a structure in which the weather-resistant surface layer of the outer layer completely wraps the internal environmentally friendly substrate, and the two materials are adjusted separately according to the different composition of the two materials. The different cost, appearance, weather resistance and mechanical properties of the two-layer materials are fully utilized, and the good appearance, weather resistance and mechanical properties of the overall plate are formed through the co-extrusion of the two.

The wood and bamboo flour of the present invention includes bamboo flour, wood flour and their mixtures. In some cases, some other fiber materials can be added. The addition of wood flour and bamboo flour is the key to realize the secondary processing performance of the board. , Adding wood and bamboo powder to the weather-resistant surface layer and environmentally friendly base material can realize the whole board can be sawn, planed, bonded and nailed. In fact, the recycled wood-plastic board pulverized material in the first raw material contains various wood-plastic product raw materials such as PE, wood and bamboo powder, but after a long time of use, some of the components have changed, and need to be added for secondary use. However, as the environmentally friendly substrate of the present invention, it is different from the board made of ordinary secondary recycled materials. This is because the environmentally friendly substrate of the present invention is used as the inner core, and its appearance is completely determined by the weather-resistant surface layer as the surface layer. Wrapping, therefore, can increase the amount of wood and bamboo powder used, and even allow a small amount of extrusion cracks, which can increase the wood properties of the overall board, and after the weathering surface layer completely wraps the inner core, the appearance and weather resistance of the overall board are both Mainly presented by the weather-resistant surface layer.

In the present invention, wood powder is added to both substrates to make the nail-holding force of the whole board uniform, especially in the secondary recycled material, wood and bamboo powder can also be added in large quantities, which can generally double the weight of the recycled wood-plastic board. The above, but too much may affect the extrusion performance, so it is better to control the weight of recycled wood-plastic board below twice. The quality requirements of these wood and bamboo powders are low, and they can be of various types and even waste wood and bamboo powder with some impurities. , So its cost is lower. The addition amount of wood and bamboo powder in the weather-resistant surface layer is between 10-20%, more preferably 10-15%. If there is no addition in the weather-resistant layer or the addition amount is small, it is easy to cause the processing performance between the two layers The difference makes the difference between the product and the wood too big. If the addition amount reaches the addition amount of general wood plastic, such as 30~40%, not only the fluidity and sealability of the environmentally friendly substrate will not be able to protect the inner core of the product, but also affect the overall product Waterproof and anti-corrosion performance will also affect the weather resistance performance, which may be due to the large amount of certain cellulose that has a negative impact on the performance of the weather resistance stabilizer.

The weather-resistant stabilizer comprises a light stabilizer and/or an antioxidant, usually the light stabilizer accounts for 3 to 6% of the total weight of the second raw material, and the antioxidant accounts for 0.15 to 0.4% of the total weight of the second raw material. Since the weathering layer itself does not account for a high proportion of the overall plastic wood floor, the addition of these weathering stabilizers to the weathering layer greatly reduces the amount of these additives and effectively reduces the cost, even if the amount of these additives is increased. It will have a substantial impact on the cost and the overall performance of the board. In addition, some fillers and toners should usually be added to the weather-resistant layer of the present invention, and the amount and type thereof can be adjusted according to different co-extrusion processes. Of course, those skilled in the art can add various modifiers, lubricants, flame retardants, antifungal agents, fillers, etc. commonly used in the field, such as EBS, calcium carbonate, talc, and white oil, to the second raw material as needed. , Maleic anhydride grafted PP and so on.

In order to control costs, the thickness of the weathering layer can generally be controlled below 1/5 of the environmentally friendly base material. 1.0-2.0mm is enough to meet the quality requirements. If the thickness is too thin, some lighter colors will show whiteness; if the thickness is too thick, the produced profiles will sometimes bend, so it is very important to control the thickness of the co-extrusion layer to ensure the quality of the product. Because the weathering layer is very thin, Sometimes it is difficult to co-extrusion, sometimes it even causes the warp between the two layers, and more often it is peeling during use. Although the weather-resistant layer of the present invention wraps the environmentally friendly substrate layer as a whole, this alleviates this problem to a certain extent. However, in some extreme cases, the above-mentioned defects still exist. At certain times, some new materials, namely high-density polyethylene, can be added to the first raw material, which enhances the adhesion between the two layers, but the increase is less than There will also be conflicts between production process costs. To solve this problem, the present invention can add no more than 5% of a modifier to the first raw material and the second raw material. The modifier is a terpolymer of acrylate, acrylonitrile and styrene. The addition of the meta-copolymer can make the weather-resistant surface layer and the environmentally friendly substrate core layer have better flexibility, thereby changing the originally relatively rigid contact properties between the two, thereby improving the composite of the two. At the same time, because the terpolymer dispersed between the two is not completely cured during the co-extrusion process, when the product is just co-extruded, due to the terpolymer in the weather-resistant surface layer and the environmentally friendly substrate The terpolymer is not completely cured, and has the same properties, which makes the weather-resistant surface layer and the environmentally friendly substrate based on this, have a close relationship, and the weather-resistant surface layer and environmentally friendly substrate materials have a certain degree of Homology and similarity; because when the product is just formed, the temperature and pressure can still be maintained in a more appropriate range, which further provides the possibility of fusion between the two.

At least one surface of the weather-resistant surface layer has a pressed groove. The groove can be pressed by various molds. Its shape is a wood grain concave-convex shape. Of course, this shape is determined by the shape of the mold itself. , The surface of the mold is laser-engraved into a wood grain shape, and carved on the weather-resistant layer of the present invention to form a very realistic wood grain shape. Since the weather-resistant layer of the present invention and the environmentally friendly base material are of different materials, it is easy to form wood texture only on the weather-resistant layer. In order to increase the high-end and lifelike wood grain effect of the board, the maximum depth of the groove is set to be greater than the thickness of the weather-resistant surface layer, so that part of the wood grain area will show the color and appearance of the environmentally friendly substrate itself, due to the weather-resistant layer and environmental protection The materials of the two substrate layers are different, especially the materials of the environmentally friendly substrate layers of different batches or different parts. This difference increases the effect of the deep wood grain and greatly increases the market acceptance of this product. . In addition, a high-temperature heating device can be added to the mold. This heating device is different from the general heating device. Its temperature is usually above 150 degrees Celsius, more preferably above 180 degrees Celsius, and it is best to form a temperature difference greater than 50 degrees Celsius on the mold. Of several temperature difference zones. The generally used mold is a roller. The roller is used to form wood grain grooves on the surface of the plate. The roller of the present invention uses a higher temperature to form a carbonized and semi-carbonized color transition area on the weathering layer of the plate, and its appearance color is more nature. Two sets of temperature control devices can be set in the drum. In the extreme, one set of heating devices and a set of cooling devices can be set, and the exchange pipes of the two can cross each other, so as to realize the temperature difference of the contact part between the mold and the plate.

In order to further increase the realistic effect of the wood grain of the board, the grooves on the weather-resistant surface layer are formed by pressing twice. The two pressings can form two kinds of grooves with different depths and textures. This combination is combined with each other. Can form a more natural wood texture appearance.

The present invention also provides a method for manufacturing the above-mentioned board, which includes the following steps:

a. Pretreatment of recycled materials: the recycled PE wood-plastic floor will be cleaned of various dust and impurities, rinsed with acid solution, then treated with clean water, and dried for later use;

b. Preparation of the first raw material: the reclaimed material obtained in the previous step is pulverized into powder in a pulverizer, wood and bamboo powder and other additives are added, and the first raw material is obtained after thorough mixing;

c. Preparation of the first wood-plastic material: melting the first raw material, and then extruding and granulating the first wood-plastic material by screw after melting;

d. Preparation of the second raw material: high-density polyethylene, wood and bamboo powder and other additives are mixed at high temperature, and then mixed at low temperature to obtain the second raw material;

e. Preparation of the second wood-plastic material: adding the second raw material into the screw extruder and then extruding and granulating to obtain the second wood-plastic material;

f. Co-extrusion: the particles of the first wood-plastic material and the second wood-plastic material are added to the main extruder and the auxiliary extruder respectively, and the weather-resistant surface layer and the environmentally friendly base material are obtained through the co-extrusion process, and the weather-resistant surface layer is wrapped with the environmental protection base. Wood-plastic composite wood-plastic board substrate;

g. Embossing: The formed substrate is pressed out of the groove through the roller to form the surface wood grain to obtain the product.

In the preparation process of the first raw material of the present invention, due to the large amount of wood powder added, if the extrusion performance of the product is not good, plasticizers and lubricants need to be added to improve the extrusion performance of the first wood-plastic material. In the preparation of the second raw material, the additives can be tackifiers, flame retardants, antifungal agents, and so on.

Usually after co-extrusion, the composite wood-plastic board is cooled and shaped in a shaping mold, and then rolled by a high-temperature roller to form a wood grain. The protrusion length of the protrusion of the roller is controlled to be greater than the thickness of the weather-resistant surface layer to form a deeper wood grain. At the same time, the color of the inner environmental protection layer is displayed. Therefore, in some cases, it is possible to change the color of the environmental protection layer by adding part of the color masterbatch to the first raw material to achieve a deeper wood texture effect. After the shaped composite wood-plastic board is pressed by a roller, it can be further processed after polishing and cutting. In addition, in the drying described in step 1), the temperature of the dryer is generally controlled at 90-120°C, and the moisture content is controlled within 5% after drying. The inside of the drum can be provided with multiple heating pipes and several cooling pipes. The cooling pipes can be separately distributed between the heating pipes. The temperature of the drum is controlled by the heating medium and the cooling medium respectively connected to the heating pipe and the cooling pipe to adjust and form The texture and color of the weather-resistant surface layer.

Beneficial effect

1) The two layers of the present invention are fused with modifiers, wood and bamboo powder, etc., so there will be no delamination, and the mechanical properties of the product are better than ordinary wood-plastic single-extrusion products;

2) The core material has no requirements for color, appearance, weather resistance, etc., which increases the scope of use of waste materials, and at the same time increases the amount of wood flour, improves the wood performance of the product, and greatly reduces the cost of the product, while overcoming the existing The widespread problem of product quality inconsistency in technology has greatly improved product recognition;

3) There are not many materials for the weather-resistant surface layer, so the cost is low. You can add enough various antioxidants and anti-light additives, etc., the stability of the product surface color, the weather resistance is significantly improved, and the 300h aging resistance performance is improved 25%, 1500h anti-aging performance increased by 38%;

4) The thickness of the weather-resistant surface layer is only 0.5mm ~ 2.5mm, and the core layer is almost all recycled materials, the production cost is relatively reduced, and the market competitiveness is stronger;

5) The weather-resistant surface layer not only has good weather-resistant characteristics, but because it can be processed separately, it also has a wide range of wood grain imitation performance through the embossing method. The special drum shape and temperature design can achieve a high degree of wood grain simulation effect. Further enhance the market competitiveness of this product.

The best mode of the present invention

Example 1

A double-layer PE co-extruded wood-plastic board, which includes an environmentally friendly base material composed of a first wood-plastic material and a weather-resistant surface layer composed of a second wood-plastic material. The thickness of the surface layer is one-sixth of the thickness of the environmentally friendly substrate. In any case, the weather-resistant surface layer will cover the whole. Therefore, the surface layer has a two-layer structure, and the thickness of each layer is one-sixth of the thickness of the environmentally friendly substrate, about 0.5mm The first wood-plastic material is made of the first raw material including recycled wood-plastic board crushed material and wood bamboo powder. Wood-bamboo powder is a waste material recycled in the wood processing market. Its weight is close to that of wood-plastic board crushed material. It contains a terpolymer of acrylic ester, acrylonitrile and styrene accounting for 1% of the mass fraction of the first raw material. The second wood plastic material is made of a second raw material containing high-density polyethylene HDPE5502 and bamboo powder. The second raw material also contains weathering stabilizers. The weathering stabilizers include various stabilizers such as light stabilizers and antioxidants. The light stabilizer GW-944 accounts for 6% of the total mass of the second raw material, and the antioxidant is 1010 produced by Ciba of Switzerland, accounting for 0.15% of the total mass of the second raw material; at least one surface of the weather-resistant surface layer has For the pressed groove, the maximum depth of the groove is greater than the thickness of the weather-resistant surface layer, and the second raw material further contains a terpolymer of acrylic ester, acrylonitrile and styrene accounting for 1% of the mass fraction of the second raw material. The mass ratio of wood-bamboo powder and high-density polyethylene in the second raw material is in the range of 0.5. The PE co-extruded wood-plastic board is obtained in this way. After the recycled PE wood-plastic floor is cleaned of various dust and impurities After washing with 1wt% hydrochloric acid solution, it is treated with clean water, and finally dried for later use; the reclaimed material obtained in the previous step is pulverized into powder in a pulverizer, and the same weight of wood and bamboo powder and other additives are added and mixed thoroughly Then the first raw material is obtained. The particle sizes of the two powders are controlled close to ensure that the two are evenly mixed; the first raw material is melted, and then pelletized by screw extrusion to obtain the first wood-plastic material, and the temperature in the screw machine is controlled. Ensure that the product is melted, the screw is sheared and plasticized, the granulation temperature is 140-220℃, the pressure is 20-35MPa; the high-density polyethylene and wood and bamboo powder are mixed in a ratio of 1:0.5, and the total mass content is 14% Filler, 3.85% light stabilizer and 0.15% antioxidant, mixed at high temperature 120℃ for 5 minutes, and then mixed at low temperature 20℃ for 5 minutes to obtain the second raw material; both in the first wood plastic material and the second wood plastic material It has a terpolymer of acrylate, acrylonitrile and styrene at 1% by weight. In this embodiment, the wood and bamboo powder added to the second raw material is bamboo powder, which has a size of 40 mesh and contains less than 3% ash and less than 5% moisture. Then the second raw material is added to the screw extruder and then extruded and pelletized to obtain the second wood-plastic material. The particles of the first wood-plastic material and the second wood-plastic material are added to the main extruder and the auxiliary extruder, respectively. A co-extruded wood-plastic board substrate with an environmentally friendly base material and a weather-resistant surface layer and the weather-resistant surface layer wraps the environmentally-friendly base material through a co-extrusion process, and the substrate is then cooled by a mold and a water tank. After cooling, the molded substrate is pressed out of the groove by the roller to form a surface wood grain. When embossing, a number of protruding annual ring-shaped protruding ribs are formed on the roller, and the length of the ribs gradually increases from one end of the annual ring to the other end. Increase, the maximum length is greater than the thickness of the weather-resistant surface layer. Four heating pipes and four cooling pipes are arranged inside the drum. The heating pipes and cooling pipes are arranged at intervals, respectively connected with heat transfer oil and cooling water. There are two drum convection lines arranged in sequence. The plate is pressed on-line and polished to form a product.

Embodiments of the present invention

Example 2

The difference from Example 1 is that the raw material of the weather-resistant surface layer is high-density polyethylene and wood powder in a weight ratio of 5:1. The second raw material also contains 5% terpolymer, 5% oxidized polyethylene wax, and 14%. Fillers, 3% coupling agents, 0.4% antioxidants, 3% UV-531, and 0.85% additives; the first raw material recycled wood-plastic material powder is twice the weight of wood flour, and the first raw material is also Contains 3% terpolymer, 3% plasticizer, 4% lubricant and 1% gray pigment.

The beneficial effects of the present invention: 1) The mechanical properties of the product are better than ordinary wood-plastic single-extrusion products; 2) The core layer material has no color requirements, which increases the use range of waste; 3) The surface layer material adds a large amount of anti-UV and other resistance Light and heat stabilizing additives, the stability of the product surface color, and the weather resistance are significantly improved, the 300h aging resistance performance is increased by 25%, and the 1500h aging resistance performance is increased by 38%; 4) The surface layer thickness is low, and the core layer is made of recycled waste materials. Relatively lower costs and stronger market competitiveness.

The specific embodiments of the present invention are described in detail above. It should be understood that those of ordinary skill in the art can make many modifications and changes according to the concept of the present invention without creative work. Therefore, all technical solutions that can be obtained by those skilled in the art through logical analysis, reasoning or limited experiments in the prior art with the concept of the present invention should fall within the protection scope defined by the claims.

Claims

A double-layer PE co-extruded wood-plastic board, which is characterized in that it comprises an environmentally friendly base material composed of a first wood-plastic material and a weather-resistant surface layer composed of a second wood-plastic material, and the weather-resistant surface layer is completely wrapped in the On an environmentally friendly substrate, the first wood-plastic material is made of a first raw material containing recycled wood-plastic board crushed material and wood and bamboo powder, and the second wood-plastic material is made of high-density polyethylene and wood-bamboo powder. The second raw material is made; the second raw material also contains a weathering stabilizer; at least one surface of the weathering surface layer has a pressed groove, and the maximum depth of the groove is greater than that of the weathering surface layer thickness of.
The double-layer PE co-extruded wood-plastic board according to claim 1, characterized in that: the first raw material also contains the ternary acrylate, acrylonitrile and styrene accounting for 1-5% of the mass fraction of the first raw material. Copolymer, the second raw material also contains a terpolymer of acrylate, acrylonitrile and styrene accounting for 1-5% of the mass fraction of the second raw material.
The double-layer PE co-extruded wood-plastic board according to claim 1, wherein the weathering stabilizer comprises a light stabilizer and an antioxidant, and the light stabilizer accounts for 3 to 6% of the total mass of the second raw material , Antioxidant accounts for 0.15-0.4% of the total mass of the second raw material.
The double-layer PE co-extruded wood-plastic board according to claim 1 or 2 or 3, wherein the mass ratio of wood and bamboo powder to high-density polyethylene in the second raw material ranges from 0.2 to 0.5. The thickness of the weather-resistant surface layer is less than 1/5 of the thickness of the environmentally friendly substrate, and the mass ratio of the wood and bamboo powder in the first raw material to the recycled wood-plastic board pulverized material is in the range of 0-2.
A method for preparing a double-layer PE co-extruded wood-plastic board according to claim 1, comprising the following steps:

a. Pretreatment of recycled materials: clean the recycled PE wood-plastic floor to remove all kinds of dust and impurities, rinse with acid solution, then treat with water, and dry for use;

b. Preparation of the first raw material: the reclaimed material obtained in the previous step is pulverized into powder in a pulverizer, wood and bamboo powder and other additives are added, and the first raw material is obtained after thorough mixing;

c. Preparation of the first wood-plastic material: melting the first raw material, and then extruding and granulating the first wood-plastic material by screw after melting;

d. Preparation of the second raw material: high-density polyethylene, wood and bamboo powder and other additives are mixed at high temperature, and then mixed at low temperature to obtain the second raw material;

e. Preparation of the second wood-plastic material: adding the second raw material into the screw extruder and then extruding and granulating to obtain the second wood-plastic material;

f. Co-extrusion: the particles of the first wood plastic material and the second wood plastic material are added to the main extruder and the auxiliary extruder respectively, and the environment-friendly substrate and weather-resistant surface layer are obtained through the co-extrusion process, and the weather-resistant surface layer is wrapped with the environmental protection base. Wood-plastic co-extruded wood-plastic board substrate;

g. Embossing: the formed substrate is pressed out of the groove through the roller to form the surface wood grain to obtain the product.
The method for preparing a double-layer PE co-extruded wood-plastic board according to claim 5, wherein the acid solution is dilute hydrochloric acid with a concentration of 1-2%.
The method for preparing a double-layer PE co-extruded wood-plastic board according to claim 5, wherein the roller has a protrusion, and the maximum protrusion height of the protrusion is greater than the thickness of the weather-resistant surface layer.
The method for preparing double-layer PE co-extruded wood-plastic panels according to claim 5, characterized in that: in the drying of step 1), the temperature of the dryer is set at 90-120°C, and after drying The moisture content is controlled within 5%.
The method for preparing double-layer PE co-extruded wood-plastic board according to claim 5 or 6 or 7 or 8, characterized in that: the inside of the drum is provided with a plurality of heating pipes and a plurality of cooling pipes, and the cooling pipes are at least Part of the interval is distributed between the several heating pipes, and the heating pipe and the cooling pipe are respectively connected with a heating medium and a cooling medium.
The method for preparing a double-layer PE co-extruded wood-plastic board according to claim 5 or 6 or 7 or 8, wherein the embossing step is embossing twice.