WO2021128102A1 - Flame-retardant wood-plastic surface layer composite, and method for preparing wood-plastic composite material having flame-retardant wood-plastic surface composite - Google Patents

Abstract

Disclosed are a flame-retardant wood-plastic surface layer composite, and a method for preparing a wood-plastic composite material having the flame-retardant wood-plastic surface layer composite, relating to the technical field of wood-plastic materials. Raw materials of the flame-retardant wood-plastic surface layer composite specifically comprise, in parts by mass, the following components: 10 to 50 parts of a high-density polyethylene, 10 to 50 parts of polypropylene, 10 to 50 parts of an ethylene-acrylic acid copolymer, 10 to 50 parts of a filler, 10 to 30 parts of a flame retardant, 0.1 to 0.5 part of an anti-ultraviolet agent, 0.1 to 0.5 part of an antioxidant, 0.5 to 8 parts of a color powder, 0.1 to 1 part of an anti-mildew agent, 0.1 to 3 parts of a lubricant, and 0.5 to 6 parts of a layered silicate. The present invention has fireproof and flame retardant effects, and the bonding strength between a wood-plastic flame-retardant surface layer and a core layer is high.

Description

Flame-retardant wood-plastic surface layer composite and preparation method of wood-plastic composite material with the flame-retardant wood-plastic surface layer composite Technical field

The invention relates to the technical field of wood-plastic materials, in particular to a flame-retardant wood-plastic surface layer composite and a preparation method of the wood-plastic composite material with the flame-retardant wood-plastic surface layer composite.

Background technique

Wood plastic, that is, wood plastic composite material, is a new type of composite material that has flourished at home and abroad in recent years. It refers to the use of polyolefin resins such as polyethylene, polypropylene and polyvinyl chloride instead of common resin adhesives. Rice husk, straw and other waste plant fibers are mixed into new wood materials, and then subjected to plastic processing techniques such as extrusion, molding, and injection molding to produce plates or profiles. At present, my country's natural forest resources are declining, and the market demand for wood products is increasing day by day. As a new environmentally friendly and replaceable wood material with excellent performance, polyolefin-based wood plastic has room for rapid development.

Co-extrusion and coating a layer of special weather-resistant modified plastic on the surface of ordinary wood-plastic, achieve wood-like effects through techniques such as pattern, color mixing, and polishing in different ways. Polyolefin-based wood-plastic flooring is mainly used in outdoor landscapes such as gardens and courtyards. Because the two main raw materials in polyolefin-based wood-plastic are flammable materials, in order to meet the fire protection requirements of wood-plastic flooring against forest fires, co-extruded wood The surface layer of plastic weather-resistant modified plastic is flame-retardant modified to meet the increasing market demand.

The Chinese Patent Authorized Announcement No. CN102218883B discloses a wood-plastic board coated with a silicon flame-retardant coating. The surface of the wood-plastic board is coated with a silicon flame-retardant coating with a thickness of 0.3mm. The preparation of the silicon flame-retardant coating Method: Take the weight components of the raw materials: 20-35 parts of resin, 25-45 parts of silicon flame retardant, 8-12 parts of flame retardant synergist and 6-10 parts of pigments and fillers; each component is ground and passed through a 325-mesh sieve. Stir evenly with a thermostatic magnetic stirrer, and apply evenly along the vertical and horizontal directions of the wood-plastic board with a brush, so that the thickness of the coating reaches 0.3mm, and dry for 24 hours to make the fire resistance time reach 35min.

The above technical solution has the following defects: Although the flame retardant coating on the surface of the wood-plastic board has a certain flame-retardant effect, through the coating method, the adhesion between the flame-retardant coating and the wood-plastic board is poor, which affects the wood-plastic board. The flame retardant effect of the board.

Summary of the invention

The first object of the present invention is to provide a flame-retardant wood-plastic surface layer composite, which has the effect of fire and flame retardancy and has high bonding strength between the flame-retardant wood-plastic surface layer and the core layer; the second object of the present invention is to provide a The preparation method of the wood-plastic composite material of the flame-retardant wood-plastic surface layer composite has a simple preparation process and good adhesion between the flame-retardant wood-plastic surface layer and the core layer.

The first technical purpose of the present invention is achieved through the following technical solutions: a flame-retardant wood-plastic surface layer composite, in terms of parts by mass, the raw material of the flame-retardant wood-plastic surface layer specifically includes the following components: high-density polyethylene 10 ～50 parts, polypropylene 10-50 parts, ethylene acrylic acid copolymer 10-50 parts, filler 10-50 parts, flame retardant 10-30 parts, anti-ultraviolet agent 0.1-0.5 part, antioxidant 0.1-0.5 part , 0.5 to 8 parts of toner, 0.1 to 1 part of anti-mold agent, 0.1 to 3 parts of lubricant, and 0.5 to 6 parts of layered silicate.

By adopting the above technical scheme, polypropylene has low density, good mechanical properties and higher strength than polyethylene. Adding polypropylene can improve the tensile properties, bending properties and impact resistance of wood-plastic materials.

Ethylene acrylic acid copolymer is a polymer with thermoplasticity and extremely high adhesion. Due to the presence of carboxyl groups and the effect of hydrogen bonds, the crystallization of the polymer is inhibited and the linearity of the main chain is destroyed, which improves the ethylene acrylic acid. The viscosity of the copolymer can increase the adhesion between the core layer and the surface layer and ensure the fireproof effect of the wood-plastic floor.

The addition of flame retardant can improve the flame retardant effect of wood-plastic floor and reduce the possibility of burning the core layer of wood-plastic floor.

The present invention is further provided that: the flame retardant includes at least ammonium polyphosphate, melamine cyanurate, red phosphorus flame retardant, pentaerythritol, aluminum hypophosphite, decabromodiphenylethane, antimony trioxide, and hydroxide One of magnesium and aluminum hydroxide.

By adopting the above technical solution, the ammonium polyphosphate will expand when heated to cover the surface of the substrate and isolate the air, thereby achieving a flame retardant effect, and is non-toxic and tasteless, and does not generate corrosive gas. When melamine cyanurate burns, the carbon foam layer formed protects the polymer and insulates the polymer from heat and oxygen. Pentaerythritol is an intumescent flame retardant, which expands when burned, covers the surface of the substrate, insulates air, prevents combustion, and achieves the effect of flame retardancy. At a certain temperature, aluminum hypophosphite produces a new insulating material, forming a glass-like or stable foam covering layer, which insulates oxygen and prevents combustible gas from overflowing, so as to achieve the purpose of flame retardancy. Decabromodiphenyl ethane has high bromine content, good thermal stability and good UV resistance. Its flame retardant mechanism is that when the polymer is decomposed, decabromodiphenyl ethane also begins to decompose, producing hydrogen bromide and bromination Hydrogen consumption polymer explains the free radicals produced, delay or interrupt the chain reaction of combustion, and hydrogen bromide is a kind of flame-retardant gas, the density is greater than air, it can form a barrier on the surface of polymer materials, reduce the density of flammable gas , So as to play a flame retardant effect. In the initial stage of combustion, the antimony trioxide melts and forms a protective film on the surface of the material to isolate the air; under high temperature conditions, the antimony trioxide is vaporized, diluting the oxygen concentration in the air, and thus plays a flame retardant effect. The flame-retardant mechanism of magnesium hydroxide is to release combined water during combustion, which has the effect of cooling and slowing down the burning rate. Magnesium hydroxide is environmentally friendly, does not emit smoke, does not produce harmful gases, and has low cost. The proportion of chemically bound water contained in the aluminum hydroxide molecule is as high as 34%. This bound water remains stable during the processing of the flame-retardant wood-plastic surface composite. It begins to decompose when it exceeds 200°C and release water vapor for cooling. , The effect of slowing down the burning rate.

The present invention is further provided that: the lubricant includes at least one of silicone powder, oxidized polyethylene wax, stearamide, stearate, and polyethylene wax.

By adopting the above technical solution, in order to improve the problem of poor fluidity and slow production rate caused by the addition of flame retardant, the lubricant can speed up the production rate and reduce the impact on the performance of wood-plastic flooring. Silicone powder can be uniformly dispersed in the system, and the friction coefficient between silicone and silicone is small, which can improve the fluidity of processing and improve the lubricating performance. Oxidized polyethylene wax has low viscosity, high softening point, high hardness, good thermal stability, and low high temperature volatility. It has excellent external lubricity and strong internal lubrication. Oxidized polyethylene wax contains hydroxyl and carboxyl groups, and has good compatibility with polyethylene and polypropylene. Stearamide and stearate have good lubricity and can be evenly dispersed to improve the lubrication effect of the extrusion process. As a lubricant, polyethylene wax has stable chemical properties. It has good compatibility with polyethylene and polypropylene and can improve the fluidity of the extrusion process.

A further arrangement of the present invention is that the layered silicate includes at least one of modified kaolin or modified montmorillonite.

By adopting the above technical scheme, the function of modified kaolin and modified montmorillonite is to have a synergistic effect on flame retardant performance with the added flame retardant. The modified kaolin and modified montmorillonite are nanostructures, wood-plastic composite materials When burning, modified kaolin and modified montmorillonite can accumulate on the surface of the flame-retardant wood-plastic surface composite, forming a dense protective layer on the surface of the flame-retardant wood-plastic surface composite to prevent further combustion and effectively protect the core Floor.

The present invention is further configured as follows: the preparation method of the modified kaolin is: 1) the raw material kaolin is mixed with 60-80wt% urea aqueous solution in a mass ratio of 1:2, and then mechanically stirred, while ultrasonic treatment is performed at 20-100KHz 6 ~12h, after the end of ultrasound, wash several times until the urea on the surface of the kaolin is cleaned and dried to obtain intercalated modified kaolin; 2) Grind the intercalated modified kaolin prepared in 1) and place it in an oven, Treated at 140～220℃ for 0.5～1h to obtain exfoliated kaolin; 3) According to mass percentage, 96～99% of exfoliated kaolin, 0.2～0.8% of stearic acid, 0.5～3% of sodium dodecylbenzene sulfonate Place it in a ball mill and grind for 2 to 4 hours to obtain modified kaolin.

The present invention is further provided as follows: the preparation method of the modified montmorillonite is as follows: 1) The raw material montmorillonite and water are mixed in a mass ratio of 1:4-8, and stirred until the montmorillonite is evenly dispersed in the water, and then Heat to 100°C; 2) Add quaternary ammonium salt to step 1, the amount of quaternary ammonium salt added is 5-12% of the mass of montmorillonite, continue to stir for 2 to 4 hours; 3) filter the mixture in step 2), Wash and wash until the surface of montmorillonite is free of chloride ions. After drying, organic montmorillonite is obtained, and after drying, it is ground through a 300-mesh sieve; 4) 15-20 parts of organic montmorillonite is added to 40-50 parts of epoxy resin Add 5-8 parts of curing agent and stir and mix uniformly; 5) Vacuum to remove bubbles, pour the mixture into a preheated mold, heat and cure in an oven, and cure at a temperature of 100～120℃, and a curing time of 2～ After 5h, the curing is completed, and the modified montmorillonite is obtained by grinding through a 300-mesh sieve.

A further arrangement of the present invention is that the antifungal agent includes at least one of thiazolyl benzimidazoles or isothiazolinones.

By adopting the above technical scheme, the thiazolyl benzimidazole antifungal agent has the characteristics of strong inhibition and good bactericidal effect, and can effectively sterilize by inhibiting the formation of bacterial biofilm. Isothiazolinones have a sterilization effect by breaking the bonds between bacteria and algae proteins. After the isothiazolinones are in contact with microorganisms, they can quickly and irreversibly inhibit their growth, leading to the death of microbial cells. Isothiazolinones can have a strong inhibitory and killing effect on common bacteria, fungi, algae, etc., with high killing efficiency, good degradability, and no residue.

The second technical objective of the present invention is achieved through the following technical solutions: a method for preparing a wood-plastic composite material with a flame-retardant wood-plastic surface layer composite: specifically including the following steps:

Step 1. Mixing of the flame-retardant wood-plastic surface layer compound: Weigh the components according to the formula of the flame-retardant wood-plastic surface layer compound, and then mix the components evenly before use. The mixing temperature is 60～150℃. The time is 10～15min;

Step 2. Pelletizing the flame-retardant wood-plastic surface layer compound: After step 1, the uniformly mixed raw materials are pelletized by a screw extruder, and the pelletizing temperature is 170 to 190°C. After the materials are melted, they are stretched, cooled, and then passed through the pelletizer. The granulator melts and granulates to obtain flame-retardant wood-plastic surface composite particles with a diameter of 2-5mm;

Step 3. Extrusion: The wood powder and flame-retardant wood-plastic surface layer composite particles are respectively added to the core cavity and surface cavity of the co-extrusion die through an extruder to extrude the core and wrap it in The surface layer of the outer core layer and the core layer extrusion temperature are respectively: 160～230℃ in the first zone, 160～230℃ in the second zone, 130～180℃ in the third zone, 130～180℃ in the fourth zone, 130～170℃ in the mould; The extrusion temperature of the wood plastic surface layer is: 120～160℃ in the first zone, 150～220℃ in the second zone, 150～220℃ in the third zone, 150～220℃ in the fourth zone, 160～200℃ in the mold;

Step 4. Shaping: After the shaping mold is set, the cooling water is used for cooling and shaping, and the cooling temperature is 30-50 ℃; Step 5. Cutting: The cooled semi-finished product enters the cutting machine, and is cut into finished products that meet the size requirements according to the requirements. .

By adopting the above technical scheme, after mixing the raw materials of the flame-retardant wood-plastic surface layer compound evenly, the pelletizer is used to granulate, and then the core material wood powder and the flame-retardant wood-plastic surface layer compound particles are co-extruded to form the flame-retardant wood-plastic surface layer Wrapped on the outside of the core layer, the bonding strength between the core layer and the flame-retardant wood-plastic surface layer is high, and it is not easy to separate. The preparation process is simple and convenient to operate.

The present invention is further configured as follows: in the step 3, the extrusion thickness of the flame-retardant wood-plastic surface layer is 0.4-1.5 mm.

By adopting the above technical scheme, the extrusion thickness is 0.4-1.5mm, which can not only ensure the flame retardant effect, but also will not make the flame retardant wood plastic surface layer too thick and cause waste.

In summary, the beneficial technical effects of the present invention are:

1. Polypropylene has low density, good mechanical properties and higher strength than polyethylene. Adding polypropylene can improve the tensile properties, bending properties and impact resistance of wood-plastic materials. Ethylene acrylic acid copolymer is a polymer with thermoplasticity and extremely high adhesion. Due to the presence of carboxyl groups and the effect of hydrogen bonds, the crystallization of the polymer is inhibited and the linearity of the main chain is destroyed, which improves the ethylene acrylic acid. The viscosity of the copolymer can increase the adhesion between the core layer and the surface layer and ensure the fireproof effect of the wood-plastic floor. Adding flame retardant can improve the flame retardant effect of wood plastic floor and reduce the possibility of burning the core layer of wood plastic floor;

2. Lubricant In order to improve the problem of poor fluidity and slow production rate caused by the addition of flame retardants, the addition of lubricant can speed up the production rate and reduce the impact on the performance of wood-plastic flooring. Silicone powder can be uniformly dispersed in the system, and the friction coefficient between the silicone and the silicone is small, which can improve the fluidity of processing and improve the lubricating performance. As a lubricant, polyethylene wax has stable chemical properties, and has good compatibility with polyethylene and polypropylene, which can improve the fluidity of the extrusion process;

3. The role of modified kaolin and modified montmorillonite is to have a synergistic effect on the flame retardant properties of the added flame retardant. Modified kaolin and modified montmorillonite are nanostructures. When wood-plastic composite materials are burned, they will change Reactive kaolin and modified montmorillonite can accumulate on the surface of the flame-retardant wood-plastic surface composite to form a dense protective layer on the surface of the flame-retardant wood-plastic surface composite to prevent further combustion and effectively protect the core layer.

Detailed ways

In the following, the present invention will be further described in detail in conjunction with the embodiments.

Example 1

Table 1 shows the raw materials and quality of a flame-retardant wood-plastic surface composite of Example 1

Component	Mass (kg)	Component	Mass (kg)
High-density polyethylene	50	Anti-ultraviolet agent	0.5
Polypropylene	10	Toner	1
Ethylene acrylic acid copolymer	50	Thiazolylbenzimidazoles	1.0
Stuffing	10	Polyethylene wax	0.8
Decabromodiphenylethane	10	Silicone powder	1.6
Modified Kaolin	6	To	To

The preparation method of modified kaolin is as follows: 1) 10kg of raw material kaolin is mixed with 20kg of urea aqueous solution with a mass fraction of 60wt%, then mechanically stirred, and at the same time ultrasonic treatment is performed at 100KHz for 6h, after the ultrasonic is finished, washed 5 times, and then dried to obtain Intercalation modified kaolin; 2) Grind the intercalation modified kaolin prepared in 1), place it in an oven, and treat it at 140°C for 1 hour to obtain exfoliated kaolin; 3) 5kg exfoliated kaolin, 0.01kg stearic acid, 0.04 kg of sodium dodecylbenzene sulfonate was placed in a ball mill and ground for 4 hours to obtain modified kaolin.

A preparation method of a wood-plastic composite material with the flame-retardant wood-plastic surface layer composite specifically includes the following steps:

Step 1. Mixing of the flame-retardant wood-plastic surface layer compound: Weigh the components according to the formula of the flame-retardant wood-plastic surface layer compound in Example 1, and then mix the components evenly and pour them into the storage tank for later use. The mixing temperature is 150℃, and the mixing time is 10min;

Step 2. Pelletizing the flame-retardant wood-plastic surface layer composite: After step 1, the uniformly mixed raw materials are pelletized by a screw extruder at a pelletizing temperature of 170°C. After the materials are melted, they are stretched, cooled and then melted by the pelletizer Pelletizing to obtain flame-retardant wood-plastic surface composite particles with a diameter of 2mm;

Step 3. Extrusion: The wood powder and flame-retardant wood-plastic surface layer composite particles are respectively added to the core cavity and surface cavity of the co-extrusion die through an extruder to extrude the core and wrap it in The surface layer of the core outer layer and the core layer extrusion temperature are respectively: 160℃ in the first zone, 160℃ in the second zone, 130℃ in the third zone, 130℃ in the fourth zone, and 130℃ in the mold; the extrusion temperature of the flame-retardant wood-plastic surface layer is respectively ：120℃ in zone one, 150℃ in zone two, 150℃ in zone three, 150℃ in zone four, mould 160℃, extrusion thickness of flame-retardant wood-plastic surface layer is 0.4mm;

Step 4. Shaping: After the shaping mold is set, the shape is cooled by cooling water, and the cooling temperature is 30°C;

Step 5. Cutting: The cooled semi-finished product enters the cutting machine, and is cut into finished products that meet the size requirements according to the requirements.

Example 2

Table 2 shows the raw materials and quality of a flame-retardant wood-plastic surface composite of Example 2

Component	Mass (kg)	Component	Mass (kg)
High-density polyethylene	10	Modified Kaolin	0.5
Polypropylene	50	Anti-ultraviolet agent	0.3
Ethylene acrylic acid copolymer	10	Toner	5.5
Stuffing	50	Isothiazolinones	0.8
Aluminum hydroxide	15	Polyethylene wax	0.5
Modified montmorillonite	0.5	Silicone powder	2.5

The preparation method of modified montmorillonite is: 1) 10kg raw material montmorillonite is mixed with 40kg water and continuously stirred, stirred until the montmorillonite is evenly dispersed in the water, and then heated to 100°C; 2) 0.5 is added to step 1. kg cetyltrimethylammonium bromide, continue to stir for 2h; 3) filter the mixture of step 2), wash 3 times, dry to obtain organic montmorillonite, dry and grind through a 300 mesh sieve; 4 ) Add 5kg of organic montmorillonite to 10k epoxy resin, add 1.25kg of isophorone diamine and stir and mix uniformly; 5) Vacuum to remove bubbles, pour the mixture into a preheated mold, and heat it in an oven After curing, the curing temperature is 100° C., the curing time is 2 hours, and the curing is completed, and the modified montmorillonite is obtained by grinding through a 300-mesh sieve.

The preparation method of modified kaolin is as follows: 1) 10kg of raw kaolin is mixed with 20kg of urea aqueous solution with a mass fraction of 80wt%, and then mechanically stirred, while ultrasonic treatment is performed at 20KHz for 12h. After the ultrasonic is finished, wash 6 times until the urea on the surface of the kaolin is removed. Wash and dry to obtain intercalated modified kaolin; 2) Grind the intercalated modified kaolin prepared in 1), place it in an oven, and treat it at 220°C for 0.5h to obtain exfoliated kaolin; 3) add 4.81 kg The peeled kaolin, 0.04 kg stearic acid, and 0.15 kg sodium dodecylbenzene sulfonate were placed in a ball mill and ground for 2 hours to obtain modified kaolin.

A preparation method of a wood-plastic composite material with the flame-retardant wood-plastic surface layer composite specifically includes the following steps:

Step 1. Mixing of the flame-retardant wood-plastic surface layer compound: Weigh the components according to the formula of the flame-retardant wood-plastic surface layer compound in Example 2, and then mix the components evenly and pour them into the storage tank for later use. The mixing temperature is 60℃, and the mixing time is 15min;

Step 2. Granulation of flame-retardant wood-plastic surface compound: After step 1, the uniformly mixed raw materials are granulated by a screw extruder at a granulation temperature of 190°C. After the materials are melted, they are stretched, cooled and then melted by the granulator Pelletizing to obtain flame-retardant wood-plastic surface composite particles with a diameter of 3mm;

Step 3. The wood powder and flame-retardant wood-plastic surface layer composite particles are respectively added to the core cavity and surface cavity of the co-extrusion die through an extruder to extrude the core body and wrap it in the outer core layer. The extrusion temperature of the surface layer and the core layer are respectively: 230°C in the first zone, 230°C in the second zone, 180°C in the third zone, 180°C in the fourth zone, and 170°C in the mold; the extrusion temperature of the flame-retardant wood-plastic surface layer is: 160°C, 220°C in the second zone, 220°C in the third zone, 220°C in the fourth zone, 200°C in the die, and the extrusion thickness of the flame-retardant wood-plastic surface layer is 0.8mm;

Step 4. Shaping: After the shaping mold is set, the shape is cooled by cooling water, and the cooling temperature is 50°C;

Step 5. Cutting: The cooled semi-finished product enters the cutting machine, and is cut into finished products that meet the size requirements according to the requirements.

Example 3

Table 3 shows the raw materials and quality of a flame-retardant wood-plastic surface composite of Example 3

Component	Mass (kg)	Component	Mass (kg)
High-density polyethylene	25	Modified Kaolin	0.7
Polypropylene	20	Anti-ultraviolet agent	0.4
Ethylene acrylic acid copolymer	20	Toner	6
Stuffing	20	Thiazolylbenzimidazoles	0.9
Decabromodiphenylethane	11	Stearate	0.3
Melamine Cyanurate	4	Silicone powder	2.1
Modified montmorillonite	0.5	To	To

The preparation method of modified montmorillonite is as follows: 1) Mix 10kg of raw material montmorillonite with 60kg of water and continuously stir until the montmorillonite is evenly dispersed in the water, and then heat to 100°C; 2) Add to step 1 0.8kg of octadecyltrimethylammonium chloride, continue to stir for 3h; 3) suction filter and wash the mixture of step 2) 4 times, dry to obtain organic montmorillonite, dry and grind through a 300-mesh sieve; 4) Add 5kg of organic montmorillonite to 12.5kg of epoxy resin, add 1.75kg of vinyltriamine and stir and mix evenly; 5) Vacuum to remove bubbles, pour the mixture into a preheated mold, and heat in an oven After curing, the curing temperature is 110° C., the curing time is 3 hours, and the curing is completed. The modified montmorillonite is obtained by grinding through a 300-mesh sieve.

The preparation method of modified kaolin is as follows: 1) Mix 10kg of raw kaolin with 20kg of urea aqueous solution with a mass fraction of 70wt%, then mechanically stir, and at the same time ultrasonic treatment at 60KHz for 10h, after the end of the ultrasonic, wash 5 times to remove the urea on the surface of the kaolin. Wash, dry, and obtain intercalated modified kaolin; 2) Grind the intercalated modified kaolin prepared in 1), place it in an oven, and treat it at 180°C for 0.5-1h to obtain exfoliated kaolin; 3) 4.85 kg of peeled kaolin, 0.03 kg of stearic acid, and 0.12 kg of sodium dodecylbenzene sulfonate were ground in a ball mill for 3 hours to obtain modified kaolin.

A preparation method of a wood-plastic composite material with the flame-retardant wood-plastic surface layer composite specifically includes the following steps:

Step 1. Mixing of the flame-retardant wood-plastic surface layer compound: Weigh the components according to the formula of the flame-retardant wood-plastic surface layer compound in Example 3, then mix the components evenly and pour them into the storage tank for later use. The mixing temperature is 90℃, and the mixing time is 10min;

Step 2. Pelletizing the flame-retardant wood-plastic surface layer compound: After step 1, the uniformly mixed raw materials are pelletized by a screw extruder at a pelletizing temperature of 180°C. After the materials are melted, they are stretched and cooled and then melted by the pelletizer Pelletizing to obtain flame-retardant wood-plastic surface composite particles with a diameter of 5mm;

Step 3. The wood powder and flame-retardant wood-plastic surface layer composite particles are respectively added to the core cavity and surface cavity of the co-extrusion die through an extruder to extrude the core body and wrap it in the outer core layer. The extrusion temperature of the surface layer and the core layer are respectively: 200°C in the first zone, 200°C in the second zone, 150°C in the third zone, 150°C in the fourth zone, and 150°C in the die; the extrusion temperature of the flame-retardant wood-plastic surface layer is: 140°C, 150°C in the second zone, 220°C in the third zone, 150°C in the fourth zone, 180°C in the mold, and the extrusion thickness of the flame-retardant wood-plastic surface layer is 1.2mm;

Step 4. Shaping: After the shaping by the shaping mold, the shaping is cooled and shaped with cooling water, and the cooling temperature is 40°C;

Step 5. Cutting: The cooled semi-finished product enters the cutting machine, and is cut into finished products that meet the size requirements according to the requirements.

Example 4

Table 4 shows the raw materials and quality of a flame-retardant wood-plastic surface composite of Example 4

Component	Mass (kg)	Component	Mass (kg)
High-density polyethylene	25	Modified Kaolin	0.5
Polypropylene	20	Anti-ultraviolet agent	0.4
Ethylene acrylic acid copolymer	20	Toner	7
Stuffing	17.5	Thiazolylbenzimidazoles	0.1
Ammonium Polyphosphate	12.5	Isothiazolinones	0.1
Pentaerythritol	5	Oxidized polyethylene wax	0.7
Modified montmorillonite	0.7	Silicone powder	1.5

The preparation method of the modified montmorillonite is the same as in Example 3.

The preparation method of modified kaolin is the same as in Example 3.

A preparation method of a wood-plastic composite material with the flame-retardant wood-plastic surface layer composite specifically includes the following steps:

Step 1. Flame-retardant wood-plastic surface layer compound mixing: Weigh the components according to the formula in Example 4, then mix the components evenly and pour them into the storage tank for later use. The mixing temperature is 120°C. The time is 15min;

Step 2. Pelletizing the flame-retardant wood-plastic surface layer compound: After step 1, the uniformly mixed raw materials are pelletized by a screw extruder at a pelletizing temperature of 180°C. After the materials are melted, they are stretched and cooled and then melted by the pelletizer Pelletizing to obtain flame-retardant wood-plastic surface composite particles with a diameter of 4mm;

Step 3. The wood-plastic core material and flame-retardant wood-plastic surface layer composite particles are respectively added to the core cavity and surface cavity of the co-extrusion die through an extruder to extrude the core and the surface layer wrapped in the outer layer of the core. , The core layer extrusion temperature is: zone one 190℃, zone two 200℃, zone three 160℃, zone four 160℃, die 150℃; the extrusion temperature of the flame retardant wood plastic surface layer is: zone one 140℃ , The second zone is 180℃, the third zone is 200℃, the fourth zone is 190℃, the mold is 180℃, and the extrusion thickness of the flame-retardant wood-plastic surface layer is 1.5mm;

Step 4. Shaping: After the shaping by the shaping mold, the shaping is cooled and shaped with cooling water, and the cooling temperature is 40°C;

Step 5. Cutting: The cooled semi-finished product enters the cutting machine, and is cut into finished products that meet the size requirements according to the requirements.

Example 5

Table 5 shows the raw materials and quality of a flame-retardant wood-plastic surface composite of Example 5

Component	Mass (kg)	Component	Mass (kg)
High-density polyethylene	25	Modified Kaolin	1.1
Polypropylene	20	Anti-ultraviolet agent	0.5
Ethylene acrylic acid copolymer	20	Toner	8
Stuffing	15	Thiazolylbenzimidazoles	0.3
Decabromodiphenylethane	14	Isothiazolinones	0.2
Red phosphorus flame retardant	6	Polyethylene wax	0.6
Modified montmorillonite	0.8	Silicone powder	1.1

The preparation method of modified montmorillonite is the same as in Example 3.

The preparation method of modified kaolin is the same as in Example 3.

A preparation method of a wood-plastic composite material with the flame-retardant wood-plastic surface layer composite is different from Example 3 in that each component is weighed according to the formula in Example 5, and the rest is the same as Example 3.

Example 6

Table 6 shows the raw materials and quality of a flame-retardant wood-plastic surface composite of Example 6

Component	Mass (kg)	Component	Mass (kg)
High-density polyethylene	22.5	Modified Kaolin	1.3
Polypropylene	17.5	Anti-ultraviolet agent	0.5
Ethylene acrylic acid copolymer	20	Toner	6
Stuffing	17.5	Thiazolylbenzimidazoles	0.3
Decabromodiphenylethane	2.5	Isothiazolinones	0.4
Antimony Trioxide	7.5	Polyethylene wax	0.6
magnesium hydroxide	4	Silicone powder	0.6
Aluminum hypophosphite	8.5	Stearamide	0.4
Modified montmorillonite	0.5	To	To

The preparation method of modified montmorillonite is the same as in Example 3.

The preparation method of modified kaolin is the same as in Example 3.

A preparation method of a wood-plastic composite material with the flame-retardant wood-plastic surface layer composite is different from Example 3 in that each component is weighed according to the formula in Example 6, and the rest is the same as Example 3.

Example 7

Table 7 shows the raw materials and quality of a flame-retardant wood-plastic surface composite of Example 7

Component	Mass (kg)	Component	Mass (kg)
High-density polyethylene	22.5	Anti-ultraviolet agent	0.3
Polypropylene	17.5	Toner	6.5
Ethylene acrylic acid copolymer	20	Thiazolylbenzimidazoles	0.3
Stuffing	15	Isothiazolinones	0.3
Pentaerythritol	15	Polyethylene wax	0.8
Aluminum hydroxide	10	Silicone powder	0.7
Modified montmorillonite	1.5	To	To

The preparation method of modified montmorillonite is the same as in Example 3.

A method for preparing a wood-plastic composite material with the flame-retardant wood-plastic surface layer composite is different from Example 3 in that each component is weighed according to the formula in Example 7, and the rest is the same as Example 3.

Example 8

Table 8 shows the raw materials and quality of a flame-retardant wood-plastic surface composite of Example 8

Component	Mass (kg)	Component	Mass (kg)
High-density polyethylene	20	Modified Kaolin	0.8
Polypropylene	20	Anti-ultraviolet agent	0.4
Ethylene acrylic acid copolymer	20	Toner	7
Stuffing	17.5	Thiazolylbenzimidazoles	0.3
magnesium hydroxide	12.5	Isothiazolinones	0.7
Aluminum hydroxide	15	Polyethylene wax	0.8
Modified montmorillonite	0.8	Silicone powder	0.5

The preparation method of modified montmorillonite is the same as in Example 3.

The preparation method of modified kaolin is the same as in Example 3.

A method for preparing a wood-plastic composite material with the flame-retardant wood-plastic surface layer composite is different from Example 3 in that each component is weighed according to the formula in Example 8, and the rest is the same as Example 3.

Example 9

Table 9 shows the raw materials and quality of a flame-retardant wood-plastic surface composite of Example 9

Component	Mass (kg)	Component	Mass (kg)
High-density polyethylene	25	Modified Kaolin	1.2
Polypropylene	20	Anti-ultraviolet agent	0.5
Ethylene acrylic acid copolymer	20	Toner	7.5
Stuffing	15	Thiazolylbenzimidazoles	0.1
magnesium hydroxide	10	Isothiazolinones	0.2
Aluminum hydroxide	20	Polyethylene wax	1
Modified montmorillonite	0.6	Silicone powder	0.2

The preparation method of modified montmorillonite is the same as in Example 3.

The preparation method of modified kaolin is the same as in Example 3.

A preparation method of a wood-plastic composite material with the flame-retardant wood-plastic surface layer composite is different from Example 3 in that each component is weighed according to the formula in Example 9, and the rest is the same as Example 3.

Comparative example 1

A flame-retardant wood-plastic surface layer composite, which is different from Example 6 in that it does not include modified kaolin and modified montmorillonite, and the others are the same as in Example 6.

Comparative example 2

A flame-retardant wood-plastic surface layer composite, which is different from Example 6 in that the modified montmorillonite is replaced by montmorillonite, and the others are the same as in Example 6.

Comparative example 3

A flame-retardant wood-plastic surface layer composite, which is different from Example 6 in that the modified kaolin is replaced with kaolin, and the others are the same as in Example 6.

Comparative example 4

A flame-retardant wood-plastic surface layer composite, which is different from Example 6 in that the modified montmorillonite is replaced by montmorillonite, and the modified kaolin is replaced by kaolin, and the others are the same as in Example 6.

Comparative example 5

A flame-retardant wood-plastic surface layer composite, which is different from Example 6 in that the antifungal agent is a thiazolyl benzimidazole with a mass of 0.7 kg, and the others are the same as in Example 6.

Comparative example 6

A flame-retardant wood-plastic surface layer composite. The difference from Example 6 is that the antifungal agent is isothiazolinone with a mass of 0.7 kg, and the others are the same as in Example 6.

Comparative example 7

A flame-retardant wood-plastic surface layer composite, which is different from Example 6 in that no anti-mold agent is added, and the others are the same as Example 6.

The performance tests are as follows.

1. Fireproof performance test: The flame retardant wood-plastic surface layer and core layer prepared in Example 1 to Example 9 and Comparative Example 1 to Comparative Example 4 are co-extruded to form a wood-plastic floor with a length of 1800mm, a width of 137mm, and a thickness of 23mm , And then use flat-head bolts to vertically fix 6 wood-plastic floors on 6 aluminum alloy joists. The distance between each joist is 450mm, and the distance between each wood-plastic floor is 3mm. The Australian standard AS1530.8.1-2018 "Fire test of building materials, components and components-Test of building components exposed to fire in the simulation zone-Radiant heat and small flames" was used for testing. According to the results of heat flow test, the fire performance of the Australian standard ranges from high to low into BAL: A40, BAL: A29, BAL: A19, BAL: A12.5, BAL: low, wherein A40 represents BAL is, when exposed class a bed and radiative heat flux peak 40kW / m ^2, and The sample meets the performance standard of the trial, and the other fire protection grades are deduced by analogy. According to the test results, the fireproof performance of the examples all reached BAL: A29; the fireproof performance of the comparative example reached BAL: A19.

Table 10 shows the heat flow data for 60 minutes of testing

2. Flame-retardant performance test: Refer to European Standards Association EN13501-1: 2007+A1: 2009 "Classification of building products and components, classification based on test data of combustion test reaction" for testing, and specific test standards refer to EN ISO 13823 Single burning test of building materials or products, EN ISO 11925-2 building material flammability test, the specific standard of C grade is: Figra (combustion growth rate index) ≤ 250W/S, the larger the Figra index, the higher the combustion growth The faster; LFS≤the edge of the sample; THR _600s ≤15MJ; F _s ≤150mm within 60 seconds; Smogra (smoke generation rate index) ≤30m ² /s ² ; TSP _600s ≤50m ² .

Table 11 shows the flame retardant performance test results of the flame retardant wood-plastic surface layer of the examples and comparative examples

3. Bending performance test: refer to the international standard BS EN 15534-1:2014+A1:2017 Annex A EN 15534-4:2014 Section 4.5.2, the test requirements must reach the maximum load average value ≥ 3300N, the minimum value ≥ 3000N; The average value of 500N deflection is ≤2.0mm, and the maximum value is ≤2.5mm.

Table 12 shows the test results of the bending performance of the examples and comparative examples

4. Test of tensile strength (peel force) of flame-retardant wood-plastic surface layer: Refer to European Standards Association EN319-1993 for testing, sample size 50mm×50mm (length×width), adhesive: hot melt adhesive, test speed: 5mm/min, Test environment: (23±2)℃, relative humidity (50±5)%.

Table 13 shows the tensile strength test results of the flame-retardant wood-plastic surface layer of the examples and comparative examples

To	Tensile strength (N/mm 2 )
Example 1	6.7
Example 2	7.0
Example 3	7.2
Example 4	7.1
Example 5	7.5
Example 6	8.5
Example 7	7.3

Example 8	7.4
Example 9	7.6
Comparative example 1	4.5
Comparative example 2	5.1
Comparative example 3	5.2
Comparative example 4	4.8
Comparative example 5	6.6
Comparative example 6	6.3
Comparative example 7	6.5

The flame-retardant wood-plastic surface layer and the core layer prepared in the examples have high bonding strength, are not easy to peel off, and have more stable performance during use.

5. REACH detection: For substances that meet the requirements of Article 57 of REACH, it is generally considered to be a substance of very high concern (SVHC). The detection method adopts inductively coupled argon plasma spectroscopy, gas chromatography-mass spectrometry, liquid chromatography-mass spectrometry Combination, ultraviolet-visible spectrophotometer, gas chromatography-electron capture detector, headspace gas chromatography-mass spectrometry, and high performance liquid chromatography are used to detect SVHC substances. The test results of Examples 1 to 9 are as follows:

The first batch of SVHC list includes 15 substances, and the 15 substances in the list are not detected in Examples 1 to 9;

The second batch of SVHC list includes 13 substances, and the 13 substances in the list are not detected in Examples 1 to 9;

The third batch of SVHC list includes 8 substances, and the 8 substances in the list are not detected in Examples 1 to 9;

The fourth batch of SVHC list includes 8 substances, and the 8 substances in the list are not detected in Examples 1 to 9;

The fifth batch of SVHC list includes 7 substances, and the 7 substances in the list are not detected in Examples 1 to 9;

The sixth batch of SVHC list includes 20 substances, and the 20 substances in the list are not detected in Examples 1 to 9;

The seventh batch of SVHC list includes 13 substances, and the 13 substances in the list are not detected in Examples 1 to 9;

The eighth batch of SVHC list includes 54 substances, and 54 substances in the list are not detected in Examples 1 to 9;

The ninth batch of SVHC list includes 6 substances, and the 6 substances in the list are not detected in Examples 1 to 9;

The tenth batch of SVHC list includes 7 substances, and the 7 substances in the list are not detected in Examples 1 to 9;

The eleventh batch of SVHC list includes 4 substances, and the 4 substances in the list are not detected in Examples 1 to 9;

The twelfth batch of SVHC list includes 6 substances, and the 6 substances in the list are not detected in Examples 1 to 9;

The thirteenth batch of SVHC list includes 2 substances, and the 2 substances in the list are not detected in Examples 1 to 9;

The fourteenth batch of SVHC list includes 5 substances, and the 5 substances in the list are not detected in Examples 1 to 9;

The fifteenth batch of SVHC list includes 1 substance, and 1 substance in the list is not detected in Examples 1 to 9;

The sixteenth batch of SVHC list includes 4 substances, and the 4 substances in the list are not detected in Examples 1 to 9;

The seventeenth batch of SVHC list includes 1 substance, and 1 substance in the list is not detected in Examples 1 to 9;

The eighteenth batch of SVHC list includes 7 substances, and the 7 substances in the list are not detected in Examples 1 to 9;

The nineteenth batch of SVHC list includes 10 substances, and the 10 substances in the list are not detected in Examples 1 to 9;

The twentieth batch of SVHC list includes 6 substances, and the 6 substances in the list are not detected in Examples 1-9.

6. VOC test: Refer to ASTM D5116&ISO 16000-9:2006/COR1-2007&ISO 16000-6:2011&ISO 16000-3:2011 for testing. The test is conducted in an indoor ^{space of 1m 3} , using Tenax-TA and DNPH tubes for sampling. TDS-GC/MS and HPLC-DAD for analysis.

Table 14 shows the VOC test results of Examples and Comparative Examples

To	TVOC(ug/m 3 )
Example 1	37.4
Example 2	38.2
Example 3	37.8
Example 4	37.5
Example 5	35.9
Example 6	32.6

Example 7	33.4
Example 8	34.8
Example 9	34.6
Comparative example 1	39.5
Comparative example 2	40.2
Comparative example 3	39.6
Comparative example 4	40.3
Comparative example 5	38.6
Comparative example 6	39.1
Comparative example 7	39.6

The wood-plastic flame-retardant surface layer prepared by the invention has a low content of volatile organic compounds, is safer to use, and is environmentally friendly.

7. Anti-slip performance test: Refer to DIN 51130: 2014 Slope Wet Oil Anti-Slip Test. The anti-slip grades are divided into R9(6°﹤X≤10°), R10(10°﹤X≤19°), R11(19°﹤) X≤27°), R12(27°﹤X≤35°), R13(X﹥35°), where X represents the angle.

Table 15 shows the anti-slip performance test results of Examples and Comparative Examples

To	Angle (°)	grade
Example 1	13.6	R10
Example 2	14.1	R10
Example 3	12.9	R10
Example 4	15.2	R10
Example 5	14.8	R10
Example 6	17.6	R10
Example 7	15.5	R10
Example 8	15.3	R10
Example 9	14.2	R10
Comparative example 1	7.2	R9
Comparative example 2	8.0	R9
Comparative example 3	8.3	R9
Comparative example 4	7.7	R9
Comparative example 5	12.3	R10
Comparative example 6	11.9	R10
Comparative example 7	13.5	R10

The anti-slip performance of the examples all reach R10, which is better than the comparative examples 1-4.

8. Aging performance test: Refer to EN15534-1:2014+A1-2017Section 8.1 and ISO 4892-2:2013, test on cycle1, test environment: (23±2)℃, relative humidity (50±5)%, test conditions : Irradiate at (65±3)℃ black standard temperature for 102min, chamber temperature (38±3)℃, relative humidity (50±10)%; light and water spray for 18min; irradiance: 0.51±0.02 at 340nm narrow band W/(m ² ·nm). △L* represents the brightness factor, when △L* is a positive value, it means white; when △L* is a negative value, it means black. △a* represents the red/green factor. When △a* is positive, it means reddish; when △a* is negative, it means greenish. △b* represents the yellow/blue factor. When △b* is positive, it means yellowish; when △b* is negative, it means blueish. Calculate △E* according to the above three factors, △E* represents the size of the total color difference.

Table 16 shows the aging performance test results

To	Exposure time (h)	△L*	△a*	△b*	△E*
Example 1	2000	-0.46	-0.49	0.85	1.24
Example 2	2000	-0.49	-0.52	0.88	1.32
Example 3	2000	-0.46	-0.51	0.86	1.29
Example 4	2000	-0.45	-0.48	0.87	1.26
Example 5	2000	-0.52	-0.55	0.90	1.35
Example 6	2000	-0.32	-0.43	0.81	1.05
Example 7	2000	-0.42	-0.46	0.82	1.16
Example 8	2000	-0.43	-0.44	0.80	1.12
Example 9	2000	-0.45	-0.47	0.84	1.22
Comparative example 1	2000	-0.56	-0.61	0.95	1.63
Comparative example 2	2000	-0.52	-0.58	0.92	1.58
Comparative example 3	2000	-0.50	-0.56	0.89	1.55
Comparative example 4	2000	-0.53	-0.56	0.93	1.60
Comparative example 5	2000	-0.51	-0.49	0.86	1.45
Comparative example 6	2000	-0.48	-0.51	0.87	1.48
Comparative example 7	2000	-0.50	-0.48	0.88	1.51

According to the over-aging performance test result, the flame-retardant wood-plastic surface layer prepared in the example has a small total color difference and is suitable for outdoor use.

9. Anti-mold performance test: Refer to ISO 16869:2008 for testing. Test organisms: Aspergillus niger ATCC 6275, Chaetomium globosum ATCC 6205, Paecilomyces CBS 628.66, Penicillium ATCC 9644, Trichoderma longum ATCC 13631; Test conditions: The time is 21 days, the humidity is >85%RH, and the temperature is 24°C. The test results are divided into three levels: "0" means that there is no fungus growth, indicating that the material is resistant to fungal attack; "1" means that the fungus has begun to grow, indicating that the material has been partially protected from fungal attack and is not vulnerable to fungal attack; "2" "Represents the obvious growth of fungi and sporulation, indicating that the material is vulnerable to fungi.

Table 17 shows the test results of the anti-mold performance of the examples and comparative examples

According to the anti-mold performance test results, it is shown that the flame-retardant wood-plastic surface layer prepared in Examples 1-9 has no fungus growth, indicating that the material is resistant to fungal attack. Comparing Example 6 with Comparative Examples 5-6, Comparative Examples 5-6 only added one kind of antifungal agent, and the fungus began to grow, indicating that the material has been partially protected from fungus attack and is not susceptible to fungus attack. Two antifungal agents The effect of the compound use is better than the effect of the antifungal agent alone; Comparative Example 7 does not add the antifungal agent, and the fungus grows obviously, indicating that the material is vulnerable to fungus.

This specific embodiment is only an explanation of the present invention, not a limitation of the present invention. After reading this specification, those skilled in the art can make modifications without creative contribution to this embodiment as needed, provided that they are within the scope of the claims of the present invention. Both are protected by patent law.

Claims (9)

1. A flame-retardant wood-plastic surface layer composite, which is characterized in that, in terms of parts by mass, the raw materials of the flame-retardant wood-plastic surface layer specifically include the following components: 10-50 parts of high-density polyethylene, 10-50 parts of polypropylene, and ethylene 10-50 parts of acrylic copolymer, 10-50 parts of filler, 10-30 parts of flame retardant, 0.1-0.5 parts of anti-ultraviolet agent, 0.1-0.5 parts of antioxidant, 0.5-8 parts of toner, 0.1 part of anti-mold agent ～1 part, 0.1～3 parts of lubricant and 0.5～6 parts of layered silicate.
2. The flame-retardant wood-plastic surface composite according to claim 1, wherein the flame retardant at least comprises ammonium polyphosphate, melamine cyanurate, red phosphorus flame retardant, pentaerythritol, aluminum hypophosphite, One of decabromodiphenylethane, antimony trioxide, magnesium hydroxide, and aluminum hydroxide.
3. The flame-retardant wood-plastic surface composite according to claim 1, wherein the lubricant includes at least silicone powder, oxidized polyethylene wax, stearamide, stearate, and polyethylene wax. One kind.
4. The flame-retardant wood-plastic surface layer composite according to claim 1, wherein the layered silicate comprises at least one of modified kaolin or modified montmorillonite.
5. A flame-retardant wood-plastic surface composite according to claim 4, characterized in that: the preparation method of the modified kaolin is: 1) the raw material kaolin and 60-80wt% urea aqueous solution are in a mass ratio of 1:2 Mix, then mechanically stir, and ultrasonic treatment at 20-100KHz for 6-12h at the same time. After the ultrasonic is finished, wash several times until the urea on the surface of the kaolin is cleaned and dried to obtain the intercalated modified kaolin; 2) 1) The prepared intercalation modified kaolin was ground, placed in an oven, and treated at 140-220°C for 0.5-1h to obtain peeled kaolin; 3) In terms of mass percentage, 96-99% of peeled kaolin and 0.2-0.8 of stearic acid %, 0.5-3% of sodium dodecylbenzene sulfonate is placed in a ball mill and ground for 2 to 4 hours to obtain modified kaolin.
6. A flame-retardant wood-plastic surface composite according to claim 4, characterized in that the preparation method of the modified montmorillonite is: 1) The mass ratio of raw material montmorillonite and water is 1:4-8 Mix and stir until the montmorillonite is evenly dispersed in the water, and then heat to 100°C; 2) Add the quaternary ammonium salt to step 1, the amount of quaternary ammonium salt added is 5-12% of the mass of the montmorillonite, continue stirring 2 ~4h; 3) Suction filter and wash the mixture of step 2) until the surface of the montmorillonite is free of chloride ions. After drying, the organic montmorillonite is obtained, and after drying, it is ground through a 300-mesh sieve; 4) 15-20 Add 1 part of organic montmorillonite to 40-50 parts of epoxy resin, add 5-8 parts of curing agent and stir and mix evenly; 5) Vacuum to remove bubbles, pour the mixture into a preheated mold, and heat and cure in an oven , The curing temperature is 100-120 DEG C, the curing time is 2-5h, the curing is over, the modified montmorillonite is obtained by grinding through a 300-mesh sieve.
7. The flame-retardant wood-plastic surface layer composite according to claim 1, wherein the anti-mold agent includes at least one of thiazolyl benzimidazoles or isothiazolinones.
8. A method for preparing a wood-plastic composite material with a flame-retardant wood-plastic surface layer composite, which is characterized in that it specifically includes the following steps:

   Step 1. Mixing of the flame-retardant wood-plastic surface layer compound: Weigh the components according to the formula of the flame-retardant wood-plastic surface layer compound, and then mix the components evenly before use. The mixing temperature is 60～150℃. The time is 10～15min;

   Step 2. Pelletizing the flame-retardant wood-plastic surface layer compound: After step 1, the uniformly mixed raw materials are pelletized by a screw extruder, and the pelletizing temperature is 170 to 190°C. After the materials are melted, they are stretched, cooled, and then passed through the pelletizer. The granulator melts and granulates to obtain flame-retardant wood-plastic surface composite particles with a diameter of 2-5mm;

   Step 3. Extrusion: The wood powder and flame-retardant wood-plastic surface layer composite particles are respectively added to the core cavity and surface cavity of the co-extrusion die through an extruder to extrude the core and wrap it in The surface layer of the outer core layer and the core layer extrusion temperature are respectively: 160～230℃ in the first zone, 160～230℃ in the second zone, 130～180℃ in the third zone, 130～180℃ in the fourth zone, 130～170℃ in the mould; The extrusion temperature of the wood plastic surface layer is: 120～160℃ in the first zone, 150～220℃ in the second zone, 150～220℃ in the third zone, 150～220℃ in the fourth zone, 160～200℃ in the mold;

   Step 4. Shaping: the shaping is done by the shaping mold first, and then cooling and shaping with cooling water, the cooling temperature is 30-50℃;

   Step 5. Cutting: The cooled semi-finished product enters the cutting machine, and is cut into finished products that meet the size requirements according to the requirements.
9. The method for preparing a wood-plastic composite material with a flame-retardant wood-plastic surface layer composite according to claim 8, wherein the extrusion thickness of the flame-retardant wood-plastic surface layer in the step 3 is 0.4-1.5 mm.