A stretch-resistant foamed diffuser plate and a method of making the same

Abstract

The present application relates to the technical field of display screen, especially to a stretch-resistant foamed diffusion plate and a preparation method thereof.The foamed diffusion plate is a multi-layer composite diffusion plate, which comprises a lower protective layer, a foamed core layer, an upper protective layer, and a nanocellulose-based carbon dot composite film arranged on four sides of the foamed core layer close to the upper protective layer.The foamed core layer generates micro-nano bubbles through a dissolved gas release method, which has low requirements for equipment and is simple to process, and can effectively improve the uniformity of bubble distribution and the density of bubbles.The nanocellulose-based carbon dot composite film has high tensile strength, which can effectively solve the problem of tensile strength reduction caused by foaming of the diffusion plate, effectively improve the tensile resistance of the diffusion plate, effectively reduce the leakage of edge blue light, enhance the utilization rate of edge blue light, and improve the light display uniformity.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of diffusion plates, in particular to a stretch-resistant foamed diffusion plate and a preparation method thereof. BACKGROUND

[0002] Liquid crystal display is a kind of flat panel display technology widely used in electronic devices, such as computer displays, televisions, mobile phones and tablet computers, etc. It uses the optical properties of liquid crystal molecules to realize image display. The basic structure of liquid crystal display is composed of several layers, one of the key components is diffusion plate. The diffusion plate is located between the backlight and the liquid crystal panel, and the backlight is usually an LED light bar. Since the light generated by the backlight itself is often not uniform enough, the role of the diffusion plate is to evenly distribute the light to the entire liquid crystal screen through its special optical design. Using quantum dot light source conversion materials combined with blue backlight can achieve a wider color gamut, making the display can present more real and bright colors. However, as people's requirements for visual experience are increasingly improved, the problems faced by liquid crystal display are also gradually highlighted, one of which is the problem of edge blue light. Edge blue light refers to the phenomenon that when a liquid crystal display displays an image, if a quantum dot backlight scheme is used, the blue light around the screen is not fully excited, which may cause a visual blue frame. Blue light leakage is harmful to the human eye.

[0003] The conventional direct type backlight module has a limited light emitting angle and a short light path, and the light energy reaching the four corners is insufficient, which is prone to cause the problem of dark frames on the four sides. By directing the light utilization rate at the edge of the diffusion plate, the problem of dark edges of the diffusion plate is solved.

[0004] In order to save costs, the industry has been trying to disperse quantum dots into the diffusion plate. However, due to the oxidation of quantum dots, this method has limitations in the production and application of quantum dot diffusion plates. In order to solve this problem, the prior art discloses a new method for preparing quantum dot-containing optical functional plates. Specifically, this method first uses raw materials containing a chemical foaming agent to prepare resin-based granules with holes, and then loads quantum dots into the holes. Next, a high-temperature foaming agent and other components are added for mixing and extrusion molding, and finally a quantum dot optical functional plate is obtained. For example, Chinese patent application No. CN202010812282.0, entitled "Light diffusion plate and manufacturing method thereof", discloses a foamed quantum dot diffusion plate. The diffusion plate has a pore diameter of 60-400 μm. Obviously, due to the large and uneven distribution of the pore diameter formed by the chemical foaming agent, the number of reflection and refraction of light in the pores is reduced, thereby reducing the effect of uniform light. In addition, the large pore diameter also leads to a decrease in the strength of the quantum dot optical functional plate, which is prone to deformation and warping problems in high-temperature and high-humidity environments, further causing the brightness to decay. SUMMARY

[0005] The present application aims to provide a stretch-resistant foamed diffusion plate and a preparation method thereof, which utilizes a gas dissolution and release method to improve the uniformity of the distribution of the foamed core layer, and utilizes a nanocellulose-based carbon dot composite film to increase the stretch resistance of the foamed diffusion plate and reduce the leakage of blue light at the edges.

[0006] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0007] A stretch-resistant foamed diffusion plate, comprising a foamed core layer, an upper protective layer, a lower protective layer, and a nanocellulose-based carbon dot composite film; the upper protective layer is arranged on the upper surface of the foamed core layer, the lower protective layer is arranged on the lower surface of the foamed core layer, and the nanocellulose-based carbon dot composite film is arranged on the four side surfaces of the foamed core layer close to the upper surface, and the width of the nanocellulose-based carbon dot composite film is less than the thickness of the foamed core layer and does not completely cover the foamed core layer; preferably, the width of the nanocellulose-based carbon dot composite film arranged on the four side surfaces of the foamed core layer accounts for 1 / 8 of the thickness of the foamed core layer.

[0008] The thickness ratio of the foamed core layer to the upper protective layer or the lower protective layer is 7:1-9:1.

[0009] The upper protective layer and the lower protective layer are made of the same material, and the raw materials thereof include, by mass percentage, 98%-99.8% of an optical resin matrix, 0.2%-1% of a light diffusing agent, 0.2%-1% of an antioxidant, 0.02%-1% of a weathering agent, 0%-0.5% of a lubricant, and 0.2%-1% of an ultraviolet-resistant agent.

[0010] The raw materials of the foamed core layer include, by mass percentage, 98%-99.8% of an optical resin matrix, 0.1-1% of red quantum dots, and 0.1-1% of green quantum dots, and the optimal values are 99%, 0.2%, and 0.8%, respectively. The particle size of the quantum dots is 2-12 nm. A plurality of cells are formed inside the foamed core layer.

[0011] As a preferred solution, the optical resin matrix is one or several of polycarbonate (PC), polymethyl methacrylate (PMMA), polystyrene (GPPS), styrene-methyl methacrylate copolymer (MS), or polypropylene (PP).

[0012] As a preferred solution, the light diffusing agent is one or several of titanium dioxide, silicon dioxide, calcium sulfate, barium sulfate, zinc oxide, organic silicon, or PS microspheres.

[0013] As a preferred solution, the antioxidant can be one or several of hindered phenolic antioxidants, phosphite antioxidants, metal alkyl thiophosphates antioxidants, carbamic acid antioxidants, organic sulfur antioxidants.

[0014] As a preferred solution, the weathering agent includes hindered amine light stabilizers and / or ultraviolet absorbers.

[0015] As a preferred solution, the lubricant is at least one of vinyl bis stearamide, stearate, polysiloxane, PP wax, PE wax, polysiloxane, ethylene bis fatty acid amide.

[0016] As a preferred solution, the ultraviolet resistant agent is benzotriazole, hydroxybenzophenone and benzotriazole are used in combination.

[0017] As a preferred solution, the quantum dots are composed of CdS, CdSe, CdSeS, ZnS, ZnSe, ZnSeS, ZnCdSeS, InP, CuInS, GaN, GaP, GaAs, InN, InP, InGaP, GalnNP and perovskite quantum dots.

[0018] As a preferred solution, the nucleating agent is at least one of boron nitride, sodium carbonate, calcium carbonate, ultra-fine talc powder, mica, montmorillonite, silicon dioxide, titanium dioxide, apatite, magnesium aluminum hydrotalcite.

[0019] As a preferred solution, the yellow carbon dots in the nanocellulose-based carbon dot composite film are composed of CdS, CdSe, CdSeS, ZnS, ZnSe, ZnSeS, ZnCdSeS, InP, CuInS, GaN, GaP, GaAs, InN, InP, InGaP, GalnNP and perovskite yellow quantum dots.

[0020] As a preferred solution, the upper protective layer and the lower protective layer are provided with a pattern that improves the refraction and reflection performance of light away from the foamed core layer.

[0021] A method for preparing a tensile-resistant foamed diffusion plate, comprising the following steps:

[0022] S1, preparing two portions of protective layer raw materials of the same composition, one portion of foamed core layer raw materials, and one portion of nanocellulose-based carbon dot composite film;

[0023] S2, mixing and uniformly the protective layer raw materials and the foamed core layer raw materials respectively;

[0024] S3, the mixed protective layer raw materials are added to the screw extrusion equipment for heating to form a molten state; the mixed foaming core layer raw materials are heated to form a molten state, and then micro-nano bubbles are generated by a dissolved gas releasing method, and then added to the screw extrusion equipment; the nanocellulose-based carbon dot composite film is cut and then added to the screw extrusion equipment;

[0025] S4, finally, the upper protective layer, the foaming core layer and the lower protective layer are extruded in a sheet shape by the die of the screw extrusion equipment, and the nanocellulose-based carbon dot composite film is extruded in a strip shape, the upper protective layer is arranged on the upper surface of the foaming core layer, the lower protective layer is arranged on the lower surface of the foaming core layer, and the nanocellulose-based carbon dot composite film is arranged on the four side surfaces close to the upper surface of the foaming core layer, and the setting width of the nanocellulose-based carbon dot composite film is less than the thickness of the foaming core layer, and the foaming core layer is not completely covered.

[0026] As a preferred solution, the screw extrusion equipment in step S3 includes three heating zones, the first heating zone has a temperature of 140-220 DEG C, the second heating zone has a temperature of 160-240 DEG C, and the third heating zone has a temperature of 180-260 DEG C.

[0027] As a preferred solution, the gas used in the dissolved gas releasing method in step S3 is CO2 or nitrogen, or other inert gas.

[0028] As a preferred solution, the temperature of the die extrusion in step S4 is controlled in a range of 170-260 DEG C.

[0029] As a preferred solution, the screw extrusion equipment in step S4 is provided with a plurality of feeding ports, and can be used for putting a plurality of different raw materials into the screw extrusion equipment.

[0030] The foaming diffusion plate disclosed in the application has the following beneficial effects: micro-nano bubbles are generated in the foaming core layer by the dissolved gas releasing method, the bubble size is greatly reduced, the bubble size is more uniform, the stress is more uniform, the anti-deformation ability is improved, the nanocellulose-based carbon dot composite film is arranged on the four side surfaces close to the upper protective layer of the foaming core layer, the tensile strength of the foaming diffusion plate is improved, the utilization ability of the blue light at the edge of the foaming diffusion plate is improved, the phenomenon of blue light leakage at the edge of the diffusion plate and the dark phenomenon of the four side frames are reduced. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 is a preparation flow chart of the yellow carbon dots disclosed in the application.

[0032] Figure 2 is a preparation flow chart of the nanocellulose disclosed in the application.

[0033] Figure 3is a preparation flow chart of the nanocellulose-based carbon dot composite film described in the present application.

[0034] Figure 4 is a top view of the nanocellulose-based carbon dot composite film described in the present application arranged around a foamed core layer.

[0035] Figure 5 is a side view of the tensile-resistant foamed diffusion plate of the present application.

[0036] Figure 6 is a cross-sectional view of the tensile-resistant foamed diffusion plate of the present application.

[0037] Figure 7 is a TEM image of the nanocellulose-based carbon dot composite film prepared in Example 1 of the present application.

[0038] Explanation of reference numerals in the drawings:

[0039] 1, upper and lower protective layers; 2, nanocellulose-based carbon dot composite film; 30, foamed core layer; 31, red quantum dots; 32, green quantum dots; 33, cells distributed in the foamed core layer. DETAILED DESCRIPTION

[0040] The present application will be further described below in conjunction with the drawings and examples.

[0041] It should be noted that the following detailed description is exemplary in nature and is intended to provide further description of the present application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0042] It should be noted that the terms used herein are merely for the purpose of describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, the singular form is intended to include the plural form unless the context clearly indicates otherwise, and it should be further understood that the terms "comprise" and / or "include" as used herein indicate the presence of the features, steps, operations, devices, components and / or combinations thereof.

[0043] Example 1

[0044] The optical resin selected in this example is polystyrene, the light diffusing agent is methyl phenyl silicone resin (silicone), the antioxidant is 1076 antioxidant, the ultraviolet light resistant agent is benzotriazole, the red and green quantum dots are CdSe quantum dots, the weather resistant agent is HALS770, the lubricant is PETS-AP, and the nucleating agent is silicon dioxide.

[0045] See Figure 4 and Figure 5The present application discloses a kind of anti-stretching foamed diffusion plate, including foamed core layer 30, upper protective layer and lower protective layer 1, nanocellulose-based carbon dot composite film 2, the upper protective layer 1 is located in the upper surface of foamed core layer 30, the lower protective layer 1 is located in the lower surface of foamed core layer 30, the nanocellulose-based carbon dot composite film 2 is located in the four sides of foamed core layer 30 close to upper protective layer 1.The foamed core layer 30 is internally provided with red quantum dots 31, green quantum dots 32 and cell 33.

[0046] The present application provides a kind of anti-stretching foamed diffusion plate and its preparation method and the foamed quantum dot diffusion plate prepared, specific steps are as follows:

[0047] (1) preparation of yellow carbon dots (Y-CDs) aqueous solution: weigh 0.210 g of o-phenylenediamine and 0.435 g of L-tyrosine in a beaker, add 15 mL of anhydrous ethanol and 15 mL of distilled water to the beaker, ultrasonic for 20 min, and prepare a clear solution. Transfer the solution to a 50 mL hydrothermal synthesis reactor, react at 160°C for 8 h, then cool the reactor to room temperature, and place the cooled solution in a round-bottom flask for rotary evaporation. Add distilled water to dilute the solid after rotary evaporation, filter with a filter membrane (0.22 μm), and finally dialyze for 24 h with a dialysis bag with a relative molecular mass cut-off of 300. Finally, dilute the concentration to obtain a yellow carbon dot aqueous solution with a concentration of 1.0 × 10 -3 mol L -1 .

[0048] (2) Preparation of nanocellulose (CNFs): Put poplar wood powder (90 g, 60-80 mesh) into a toluene-ethanol (volume ratio 2:1) solution, and stir vigorously to disperse the poplar wood powder. Cook at 75°C for 5 h to remove lignin. After the reaction is completed, wash repeatedly with distilled water until neutral to obtain holocellulose with most of the lignin removed. Add the obtained holocellulose to a KOH aqueous solution (5 wt%), and cook at 90°C for 2 h with stirring to remove hemicellulose. The product is suction filtered and adjusted to neutral with distilled water. Place the product in a NaClO2 solution (5 wt%), and cook at 75°C for 2 h for the second lignin removal. The second hemicellulose removal is carried out by cooking in a 5 wt% NaOH aqueous solution for 2 h. The product is repeatedly washed with distilled water until neutral, and then the purified cellulose is subjected to nanotreatment using an ultrasonic instrument. The output power is 1200 W, and the reaction time is 30 min to prepare a CNFs suspension. The product suspension is washed with water by vacuum filtration. Then, the product is purified using a dialysis bag until the pH value of the dialysis solution is 7. Finally, store it at 4°C.

[0049] (3) Preparation of TEMPO-CNFs: 2 g of CNFs were added to 200 mL of an aqueous solution containing 0.032 g of 2,2,6,6-tetramethyl-l-piperidinyloxy free radical (TEMPO) (98%) and 0.2 g of NaBr (>99.0%) and kept stirring for 15 min; the TEMPO oxidation reaction was initiated by slow addition of a 13 wt% NaClO solution (12 mL) and was carried out at room temperature with slow stirring. The pH value was kept at 10.5 by addition of a 0.5 mol L -1 NaOH solution and then adjusted to 7 by addition of a 0.5 mol L -1 HCl solution; the product was completely washed with water by vacuum filtration. The isolated fraction was then put into a dialysis bag for purification until the pH value of the dialysis fluid water was 7.

[0050] (4) Preparation of nanocellulose-based carbon dot composite film: 20 mL of Y-CDs aqueous solution (1.0 mmol L -1 ), 1-ethyl-3 (dimethylaminopropyl) carbodiimide hydrochloride (EDC) (98.5%, 10.0 mg) and N-hydroxysuccinimide (NHS) (98%, 10.0 mg) were added to 20 mL of TEMPO-CNF suspension (2.0 wt%) to obtain a TEMPO-CNF / Y-CDs solution with 2 wt%. The resulting solution was dispersed by ultrasonic treatment for 1 h and magnetically stirred at 30 °C for 12 h. The TEMPO-CNF / Y-CDs suspension was put into a vacuum oven at 60 °C for 1.5 h. Different volumes of the suspension were vacuum filtered in a 500 mL filter device. Thereafter, the prepared wet film was placed in two silicon chips, and the filter film was dried at 60 °C at a pressure of 6.5-7 kPa, finally obtaining a nanocellulose-based carbon dot composite film (TEMPO-CNF / Y-CDs), the TEM image of which is shown in Figure 7 .

[0051] (5) Micro-nano bubble generation process of foaming core layer: after mixing the heated foaming core layer molten liquid and CO2 gas, the gas was dissolved in the foaming core layer molten liquid by pressing into a gas cylinder through a valve, and the pressure was obtained by a pressure gauge. After the pressure reached 0.5 MPa, the gas was released through the valve. The gas dissolution time was 10 minutes, and the release angle was 20°. The obtained micro-nano bubble diameter was 5 μm~30 μm, and the bubble cross-sectional density was 2×10 3 ~1.15×10 4 cm 2 .

[0052] (6) The process of plate extrusion: the raw materials of the upper protective layer and the lower protective layer include, by mass percentage: optical resin matrix 98.9%, light diffuser 0.2%, antioxidant 0.2%, weathering agent 0.02%, lubricant 0.48%, and ultraviolet resistant agent 0.2%. After sufficient stirring and mixing, the mixture is divided into two equal parts for standby; the raw materials of the foamed core layer include, by mass percentage: optical resin matrix 98%, red quantum dots 0.2%, green quantum dots 0.8%, and nucleating agent 1%, which are stirred and mixed for standby; the prepared nanocellulose-based carbon dot composite film is cut into a long strip with a width of about 10 mm for standby; the mixed raw materials of the upper protective layer and the lower protective layer and the foamed core layer, and the nanocellulose-based carbon dot composite strip are respectively added to four independent hoppers, and a double-screw extruder is used for blending and extrusion, with an extrusion temperature of 210°C. After traction cooling, a multi-layer co-extruded foamed quantum dot diffusion plate is obtained. The upper protective layer and the lower protective layer cover the upper and lower surfaces of the foamed core layer, and the nanocellulose-based carbon dot composite film is arranged at the four peripheral edge portions of the foamed core layer close to the upper protective layer. The thickness of the upper protective layer and the lower protective layer is 0.1 mm, the thickness of the foamed core layer is 0.8 mm, and the thickness of the nanocellulose-based carbon dot composite film is 0.1 mm.

[0053] Comparative Example 1

[0054] Comparative Example 1 differs from Example 1 only in that a nanocellulose film is used instead of a nanocellulose-based carbon dot composite film, and the rest remains the same as Example 1.

[0055] The test brightness and blue light intensity data of Example 1 are compared with those of Comparative Example 1, confirming that the edge brightness increases by 9.16% and the edge blue light intensity decreases by 9.05%.

[0056] Comparative Example 2

[0057] Comparative Example 2 differs from Example 1 only in that a nanocellulose-based carbon dot composite film is not used, and the rest remains the same as Example 1.

[0058] The test brightness and blue light intensity data of Example 1 are compared with those of Comparative Example 2, confirming that the edge brightness increases by 8.14% and the edge blue light intensity decreases by 9.07%.

[0059] Performance detection test

[0060] The optical basic properties and mechanical properties of the tensile-resistant foamed diffusion plate prepared in Example 1 and Comparative Examples 1-2 are detected, and the specific detection data are shown in Table 1.

[0061] Table 1

[0062]

[0063] Transmittance and haze are two important indicators for evaluating whether the light diffusion material is excellent, and excellent light diffusion material should have high transmittance and high haze. The transmittance refers to the ratio of the light flux through the material to the light flux on the material, which is an index for measuring the transparency of the material; the haze refers to the ratio of the scattered light flux through the material to the light flux on the material, which is an index for measuring the strength of light scattering. The tensile strength refers to the maximum stress that the material can withstand during the tensile test from the beginning of applying tension to the occurrence of fracture, which is an index for measuring the tensile strength of the material.

[0064] As can be seen from Example 1, Comparative Examples 1-2 and Table 1, adding a layer of nanocellulose-based carbon dot composite film at the edge of the foamed core layer close to the upper protective layer can effectively increase the tensile strength, and increase the absorption of edge blue light to reduce the leakage of edge blue light and improve the light display uniformity.

[0065] The technical features of the above-described embodiments can be combined arbitrarily, and to make the description concise, all possible combinations of the technical features in the above-described embodiments are not described, however, as long as the combinations of the technical features do not exist contradictions, they should be considered as the scope of the present disclosure.

[0066] The above-described embodiments only express several embodiments of the present application, and the description is more specific and detailed, but it should not be understood as a limitation on the scope of the patent. It should be pointed out that for ordinary skilled in the art, without departing from the concept of the present application, a number of variations and improvements can be made, which are all within the scope of the present application. Therefore, the scope of protection of the present application should be subject to the appended claims.

Claims

1. A stretch-resistant foam diffuser plate, characterized in that: The invention comprises a foam core layer, an upper protective layer, a lower protective layer, and a nanocellulose-based carbon dot composite film; the upper protective layer is arranged on the upper surface of the foam core layer, the lower protective layer is arranged on the lower surface of the foam core layer, and the nanocellulose-based carbon dot composite film is arranged on four sides of the foam core layer close to the upper surface, and the arrangement width of the nanocellulose-based carbon dot composite film is smaller than the thickness of the foam core layer and does not completely cover the foam core layer; The thickness ratio of the foam core layer to the upper protective layer or the lower protective layer is 7:1-9:1; The upper protective layer and the lower protective layer are made of the same material, and the raw materials thereof include, by mass percentage: 98% to 99.8% of an optical resin matrix, 0.2% to 1% of a light diffusing agent, 0.2% to 1% of an antioxidant, 0.02% to 1% of a weathering agent, 0% to 0.5% of a lubricant, and 0.2% to 1% of an anti-ultraviolet agent; The raw materials of the foaming core layer include, by mass percentage, 98% to 99.8% of an optical resin matrix, 0.1% to 1% of red quantum dots, 0.1% to 1% of green quantum dots, and 0.2% to 1% of a nucleating agent. The particle size of the quantum dots is 2-12 nm, and a plurality of micro-nano pores are formed inside the foaming core layer by a dissolved gas release method.

2. The stretch-resistant foam diffuser plate according to claim 1, characterized in that: The optical resin matrix is ​​one or more of polycarbonate, polymethyl methacrylate, polystyrene, styrene-methyl methacrylate copolymer, and polypropylene; The light diffusing agent is one or more of titanium dioxide, silicon dioxide, calcium sulfate, barium sulfate, zinc oxide, organic silicon, and PS microspheres; The antioxidant is one or more of hindered phenol antioxidants, phosphite antioxidants, metal alkylthiophosphoric acid antioxidants, carbamic acid antioxidants, and organic sulfur antioxidants; The weathering agent includes a hindered amine light stabilizer and / or a UV absorber; The lubricant is at least one of vinyl bisstearamide, stearate, polysiloxane, PP wax, PE wax, polysiloxane, and ethylene bis fatty acid amide; The anti-ultraviolet agent is benzotriazole, and hydroxybenzophenone and benzotriazole are used in combination.

3. The stretch-resistant foam diffuser plate according to claim 1, characterized in that: The quantum dots are composed of quantum dots of CdS, CdSe, CdSeS, ZnS, ZnSe, ZnSeS, ZnCdSeS, InP, CuInS, GaN, GaP, GaAs, InN, InP, InGaP, GalnNP and perovskite; The nucleating agent is at least one of boron nitride, sodium carbonate, calcium carbonate, ultrafine talc, mica, montmorillonite, silicon dioxide, titanium dioxide, apatite, and magnesium aluminum hydrotalcite.

4. The stretch-resistant foam diffuser plate according to claim 1, characterized in that: The yellow carbon dots in the nanocellulose-based carbon dot composite film are composed of yellow quantum dots of CdS, CdSe, CdSeS, ZnS, ZnSe, ZnSeS, ZnCdSeS, InP, CuInS, GaN, GaP, GaAs, InN, InP, InGaP, GalnNP and perovskite.

5. The stretch-resistant foam diffuser plate according to claim 1, characterized in that: The upper protective layer and the lower protective layer are provided with patterns on the side away from the foaming core layer to improve the refraction and reflection performance of light.

6. The stretch-resistant foam diffuser plate according to claim 1, characterized in that: The width of the nano-cellulose-based carbon dot composite film arranged on the four sides of the foaming core layer accounts for 1 / 8 of the thickness of the foaming core layer.

7. The method for preparing a stretch-resistant foam diffuser plate according to claim 1, wherein: The following steps are involved: S1. Prepare two parts of protective layer raw materials with the same composition, one part of foam core layer raw material, and one part of nanocellulose-based carbon dot composite film; S2, respectively, mixing the protective layer raw material and the foaming core layer raw material uniformly; S3, adding the mixed protective layer raw materials to a screw extruder and heating them to form a molten state; after heating the mixed foaming core layer raw materials to form a molten state, generating micro-nano bubbles by a dissolved gas release method, and then adding them to the screw extruder; cutting the nanocellulose-based carbon dot composite film and adding it to the screw extruder; S4. Finally, the upper protective layer, the foamed core layer and the lower protective layer are extruded through the die head of the screw extrusion equipment in the form of sheets, and the nano-cellulose-based carbon dot composite film is extruded in the form of strips. The upper protective layer is arranged on the upper surface of the foamed core layer, and the lower protective layer is arranged on the lower surface of the foamed core layer. The nano-cellulose-based carbon dot composite film is arranged on the four sides of the foamed core layer close to the upper surface, and the width of the nano-cellulose-based carbon dot composite film is smaller than the thickness of the foamed core layer, and does not completely cover the foamed core layer.

8. The method according to claim 7, wherein: The screw extruder in step S3 includes three heating zones, the temperature of the first heating zone is 140-220°C, the temperature of the second heating zone is 160-240°C, and the temperature of the third heating zone is 180-260°C.

9. The method according to claim 7, wherein: The gas used in the dissolved gas release method in step S3 is CO2 or nitrogen, or other inert gases.

10. The method according to claim 7, wherein: The temperature control range of the die extrusion in step S4 is 170-260° C.; the screw extrusion equipment in step S4 is provided with a plurality of feed ports, which are suitable for putting a variety of different raw materials into the screw extrusion equipment.

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