Supercritical carbon dioxide optical foaming diffusion plate and preparation process

Abstract

The invention discloses a supercritical carbon dioxide optical foaming diffusion plate and a preparation process, and relates to the technical field of foaming diffusion plates, and the optical foaming diffusion plate comprises a first protection layer, a foaming layer and a second protection layer which are sequentially stacked. According to the supercritical carbon dioxide optical foaming diffusion plate and the preparation technology, a physical foaming technology and a three-layer co-extrusion technology are adopted, low-price and non-toxic carbon dioxide is used as a foaming agent, and supercritical carbon dioxide fluid and a nucleating agent are packaged in carrier resin; the optical diffusion plate forms a uniform honeycomb structure and cell size, so that the properties of dispersion, refraction, transmission and the like of a light source are effectively improved, the light source can be homogenized after passing through the optical foaming diffusion plate, the weight of the optical foaming diffusion plate is reduced, the overall mechanical property is good, and the production cost is reduced while the product quality is improved. The production cost can be greatly reduced, and the method can be better applied to production of electronic display devices.

Description

Technical Field

[0001] The present invention relates to the technical field of foaming diffusion plates, and particularly to a supercritical carbon dioxide optical foaming diffusion plate and a preparation process thereof. Background Art

[0002] A light diffusion plate is an optical plate with a certain haze and light transmittance, which is widely used in the fields of LCD, TV and LED lighting. The light diffusion plate utilizes light to pass through a diffusion layer made of materials such as polycarbonate (PC) / polymethyl methacrylate (PMMA) / polystyrene (PS) / methyl methacrylate-styrene copolymer (MS resin) as the substrate, and when it encounters a medium (diffusion particles or bubble holes) with a refractive index different from that of the substrate, refraction, reflection or scattering occurs, thereby changing the propagation route of the light and achieving sufficient divergence of the incident light, so as to produce an optical diffusion effect.

[0003] The foaming diffusion plate is a type of light diffusion plate, which uses bubble holes as the medium for light diffusion to achieve the light diffusion function. Because of its advantages such as low density, high haze, high light transmittance, and low cost, it is widely used. The most core process of the foaming diffusion plate is the foaming process. Currently, the main foaming processes include chemical foaming method (i.e., adding a chemical foaming agent for foaming) and physical foaming method (such as supercritical fluid foaming method).

[0004] Among them, the preparation method of the chemical foaming method is relatively convenient, and the requirements for equipment are relatively low, and it can be widely used in industrial production. However, the optical foaming diffusion plates produced by the existing chemical foaming method, as Figure 4 shown, have poor cell morphology, few nucleation numbers, uneven cell distribution, relatively high product density, and high production cost. For the existing physical foaming method, there are high requirements for equipment integration, great difficulty, great difficulty in process control, and it is still in the stage of industrial promotion. Some processes rely on experience accumulation and have not yet formed a standardized production process. Summary of the Invention

[0005] The main purpose of the present invention is to provide a supercritical carbon dioxide optical foaming diffusion plate and a preparation process thereof, which can effectively solve the problems in the background art.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows: A supercritical carbon dioxide optical foaming diffusion plate includes a first protective layer, a foaming layer and a second protective layer which are sequentially stacked; The material of the foaming layer includes a first resin raw material, a nucleating agent, a first auxiliary agent and a foaming agent; The materials of the first protective layer and the second protective layer include a second resin raw material and a second auxiliary agent.

[0007] Preferably, the material of the first resin raw material is at least one of GPPS, PET, PC, MS, and PMMA; The material of the second resin raw material is at least one of GPPS, MS, PMMA, PE, PP, HIPS, K resin, and PET.

[0008] Preferably, the first additive and the second additive are at least one of a dispersant, an antioxidant, and a lubricant.

[0009] Preferably, the material of the foaming agent is at least one of carbon dioxide and nitrogen.

[0010] Preferably, the nucleating agent is at least one of calcium carbonate, talcum powder, montmorillonite, silica, and titanium dioxide.

[0011] Preferably, the thickness of the foaming layer is 0.5 - 5 mm, and the thicknesses of the first protective layer and the second protective layer are 0.05 - 1 mm.

[0012] Preferably, the material of the foaming layer is composed of the following components by weight: 100 parts of GPPS, 0.5 - 5 parts of talcum powder, and 0.05% - 1% of carbon dioxide.

[0013] A preparation process of an optical foaming diffuser plate includes the following operating steps: S1: The foaming agent is stored in a cylinder in a liquid / gaseous form, metered and pressurized by a high-pressure metering pump, and back-pressure valves are used for back-pressure to ensure that the foaming agent is accurately and stably injected into the twin-screw extruder through an injection valve according to the flow rate and pressure set values of the process conditions; S2: The temperature in zones 1 to 7 of the twin-screw extruder is controlled at 180 - 220 °C, and the temperature of the foaming layer melt gradually decreases from zone 1 to the three-layer coextrusion die. The pressure in the barrel of the twin-screw extruder is controlled within the range of 5 - 14 Mpa, and the screw speed is 150 - 300 r / min. After the first resin raw material, the nucleating agent, and the first additive are melt-blended in the twin-screw extruder, they are precisely metered by a melt metering pump, further homogenized and mixed through a static mixer, and enter the middle layer of the three-layer coextrusion die through a distributor. At the moment when the foaming layer melt is extruded from the die lip, due to the sudden drop in pressure, the foaming agent rapidly expands around the bubble nuclei, forming a dense honeycomb-like pore structure to form the foaming layer; S3: The temperature in zones 1 to 5 of the single-screw extruder is controlled between 180 - 230 °C, and the pressure in the barrel of the single-screw extruder is controlled at 5 - 10 MPa. After the second resin raw material and the second additive are melt-blended in the single-screw extruder, they are precisely metered by a melt metering pump, divided into two paths by a distributor, and respectively enter the upper and lower layers of the three-layer coextrusion die, wrapping the foaming layer in the middle to form the first protective layer and the second protective layer on the upper and lower sides of the foaming layer; S4: The temperatures of the three melts of the first protective layer, the foaming layer, and the second protective layer in the three-layer co-extrusion die are controlled in zones. Among them, the temperatures of the first protective layer and the second protective layer are maintained between 180°C and 230°C, and the temperature of the foaming layer is maintained at 150°C - 180°C. After the foaming layer, the first protective layer, and the second protective layer are extruded through the three-layer co-extrusion die, they quickly enter the calender for shaping and cooling, and a diffusion plate product with certain texture is extruded.

[0014] Preferably, both the first resin raw material and the second resin raw material are GPPS. The melt index of the first resin raw material GPPS is 2 - 3 g / 10min, and the melt index of the second resin raw material GPPS is 5 - 8 g / 10min.

[0015] Preferably, the twin-screw extruder is divided into zone 1, zone 2, zone 3, zone 4, zone 5, zone 6, zone 7, the connecting section, and the die head along the extrusion direction. The temperatures of zone 1 to zone 6 are 190°C, the temperature of zone 7 is 185°C. The connecting section includes the screen-changing temperature, the connecting temperature 1, the melt pump temperature, and the connecting temperature 2. The screen-changing temperature is 185°C, and the connecting temperature 1, the melt pump temperature, and the connecting temperature 2 are 180°C. The temperature of the die head is 175°C. The single-screw extruder is divided into zone 1, zone 2, zone 3, zone 4, zone 5, and the connecting section along the extrusion direction. The temperatures of zone 1 to zone 5 are 190°C. The connecting section includes the screen-changing temperature, the connecting temperature 1, the melt pump temperature, the connecting temperature 2, and the distributor temperature. The screen-changing temperature is 185°C, and the connecting temperature 1, the melt pump temperature, and the connecting temperature 2 are 180°C. The temperature of the die head is 175°C.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The supercritical carbon dioxide optical diffusion plate technology adopts a physical foaming process and a three-layer co-extrusion technology. Using inexpensive and non-toxic carbon dioxide as the foaming agent, by encapsulating supercritical carbon dioxide fluid and nucleating agent in the carrier resin to form nucleated pores, the optical diffusion plate forms a uniform honeycomb structure and pore size. The pore size can be controlled in the range of 50 - 200 μm, and the error of the pore diameter is less than 10%. Thus, it effectively improves the performance of light source dispersion, refraction, and transmission, enables the light source to be homogenized after passing through the optical foamed diffusion plate, reduces the weight of the optical foamed diffusion plate, and has good overall mechanical properties. While improving the product quality, the production cost can be significantly reduced, and it also has a positive significance for the comprehensive utilization of carbon. The product can be better applied to the production of electronic display devices. Description of the Drawings

[0017] Figure 1 is a schematic structural diagram of the optical foamed diffusion plate of the present invention; Figure 2 is a process diagram for preparing the optical foamed diffusion plate of the present invention; Figure 3 It is a schematic diagram of the internal structure of the foaming layer in the prior art; Figure 4 It is a schematic diagram of the internal structure of the foaming layer of the present invention.

[0018] In the figure: 1, gas cylinder; 2, high-pressure metering pump; 3, back pressure valve; 4, injection valve; 5, twin-screw extruder; 6, loss-in-weight scale; 7, single-screw extruder; 8, melt metering pump; 9, static mixer; 10, distributor; 11, three-layer coextrusion die; 12, calender; 13, foaming diffusion plate product; 100, first protective layer; 200, foaming layer; 300, second protective layer. Specific embodiments

[0019] In order to make the technical means, creative features, achieved purposes and effects of the present invention easy to understand, the present invention will be further described below in conjunction with specific embodiments.

[0020] Example 1, as Figure 2 shown, a processing equipment mechanism for a supercritical carbon dioxide optical foaming diffusion plate of the present invention includes a gas cylinder 1, a twin-screw extruder 5, a single-screw extruder 7 and a static mixer 9. One end of the gas cylinder 1 is connected to a high-pressure metering pump 2. One end of the high-pressure metering pump 2 is connected to a back pressure valve 3. An injection valve 4 is fixedly installed on the top of the twin-screw extruder 5. One end of the back pressure valve 3 is fixedly connected to the injection valve 4 through a connecting pipe. Loss-in-weight scales 6 are fixedly installed on the tops of the twin-screw extruder 5 and the single-screw extruder 7. One end of the twin-screw extruder 5 and the single-screw extruder 7 are fixedly connected to melt metering pumps 8. The twin-screw extruder 5 is connected to the static mixer 9 through the melt metering pump 8. One end of the static mixer 9 is fixedly connected to a distributor 10. The single-screw extruder 7 is fixedly connected to the distributor 10 through the melt metering pump 8. One end of the distributor 10 is fixedly connected to a three-layer coextrusion die 11. A calender 12 is placed on one side of the three-layer coextrusion die 11.

[0021] The main function of the calender 12 is the cooling and shaping of the foaming diffusion plate and the conveying of the plate. By adjusting the traction speed of the calender rollers, the gap and temperature of the rollers, the thickness and surface shape of the diffusion plate can be adjusted.

[0022] The present invention combines a twin-screw extruder with a single-screw extruder. The foaming agent metering injection system adopts a closed-loop design for intelligent control. According to the total feeding amount of the first resin raw material, a mass flowmeter is used to accurately calculate the ratio and inject. The designed twin-screw extruder can fully dissolve the foaming agent and the first resin raw material, and the bubble nucleation distribution is uniform. The foaming agents used are all inert gases, so there will be no carbonization and other residue phenomena on the surface of the end product. The principle of chemical foaming is to incorporate chemical substances that can generate gas when heated, such as citric acid, etc., into the main material. However, the defect of this process is that the gas generation amount will also change with the processing environment such as temperature and pressure, which will easily cause fluctuations in the foaming agent formula ratio. Because chemical foaming generally uses a single-screw extruder with a relatively low rotational speed and a conveying thread design structure, the mixing ability is poor, resulting in poor solubility between the foaming agent and the main material melt, and a relatively low bubble nucleation rate, resulting in a relatively low qualified rate of the end product.

[0023] Example two, as Figure 1 shown, a supercritical carbon dioxide optical foaming diffusion plate, comprising a first protective layer 100, a foaming layer 200 and a second protective layer 300 which are sequentially stacked; The material of the foaming layer 200 includes a first resin raw material, a nucleating agent, a first auxiliary agent and a foaming agent; The materials of the first protective layer 100 and the second protective layer 300 include a second resin raw material and a second auxiliary agent.

[0024] Among them, the material of the first resin raw material is at least one of GPPS, PET, PC, MS and PMMA; The material of the second resin raw material is at least one of GPPS, MS, PMMA, PE, PP, HIPS, K resin and PET.

[0025] Among them, the first auxiliary agent and the second auxiliary agent are at least one of a dispersant, an antioxidant and a lubricant.

[0026] Among them, the material of the foaming agent is at least one of carbon dioxide and nitrogen.

[0027] Among them, the nucleating agent is at least one of calcium carbonate, talcum powder, montmorillonite, silicon dioxide and titanium dioxide.

[0028] Among them, the thickness of the foaming layer is 0.5 - 5 mm, and the thicknesses of the first protective layer and the second protective layer are 0.05 - 1 mm.

[0029] Among them, the material of the foaming layer is composed of the following components by weight: 100 parts of GPPS, 0.5 - 5 parts of talcum powder, and 0.05% - 1% parts of carbon dioxide.

[0030] Example 3. A preparation process of an optical foaming diffuser plate includes the following operating steps: S1: The blowing agent is stored in cylinder 1 in liquid / gaseous form, metered and pressurized by high-pressure metering pump 2, and backpressure valve 3 provides backpressure to ensure that the blowing agent is accurately and stably injected into twin-screw extruder 5 through injection valve 4 according to the flow rate and pressure set values of the process conditions; S2: The temperature in zones 1 to 7 of twin-screw extruder 5 is controlled at 180 - 220 °C, and the temperature of the foaming layer melt gradually decreases from zone 1 to the three-layer coextrusion die 11, ensuring that the temperature of the foaming layer melt in the three-layer coextrusion die 11 is within the appropriate foaming temperature range. The pressure in the barrel of twin-screw extruder 5 is controlled within the range of 5 - 14 Mpa, and the screw speed is 150 - 300 r / min, ensuring that the blowing agent has good solubility and is evenly dispersed in the foaming layer melt. The first resin raw material, nucleating agent, and first additive are continuously fed at the feed port after being metered by loss-in-weight scale 6. The blowing agent (CO2 or N2) is injected into twin-screw extruder 5 through injection valve 4 in the fifth zone of twin-screw extruder 5. The above materials are melted at high temperature in twin-screw extruder 5 and mixed evenly during the shearing and conveying by the twin-screw thread assembly. From the inlet to the outlet, the residence time of the materials in twin-screw extruder 5 is about 5 - 10 minutes. After being melt-blended by twin-screw extruder 5, it is precisely metered by melt metering pump 8 and further homogenized and mixed by static mixer 9, and then enters the middle layer of three-layer coextrusion die 11 through distributor 10. At the moment when the foaming layer melt is extruded from the die lip, due to the sudden pressure drop, the blowing agent rapidly expands around the bubble nuclei, forming a dense honeycomb-like pore structure to form the foaming layer 200; S3: The temperature in zones 1 to 5 of single-screw extruder 7 is controlled between 180 - 230 °C, and the pressure in the barrel of single-screw extruder 7 is controlled at 5 - 10 MPa, ensuring that the first protective layer melt and the second protective layer melt have good fluidity. After the second resin raw material and the second additive are melt-blended by single-screw extruder 7, they are precisely metered by melt metering pump 8 and divided into two paths by distributor 10, respectively entering the upper and lower layers of three-layer coextrusion die 11, wrapping the foaming layer 200 in the middle, forming the first protective layer 100 and the second protective layer 300 on the upper and lower sides of the foaming layer 200, avoiding the rupture of the pores on the surface of the foaming layer 200. At the same time, the first protective layer 100 and the second protective layer 300 can maintain good mechanical strength of the plate; S4: In the three-layer coextrusion die 11, the temperatures of the three melts of the first protective layer 100, the foaming layer 200, and the second protective layer 300 are controlled in zones. Among them, the temperatures of the first protective layer 100 and the second protective layer 300 are maintained between 180 - 230 °C, and the temperature of the foaming layer 200 is maintained at 150 - 180 °C. After the foaming layer 200, the first protective layer 100, and the second protective layer 300 are extruded through the three-layer coextrusion die 11, they quickly enter the calender 12 for shaping and cooling, and a foamed diffusion plate product 13 with certain textures is extruded, avoiding the continuous expansion of the foaming agent in the high-temperature melt, resulting in overly large cell pores.

[0031] The material of the foaming layer is controlled and extruded by the twin-screw extruder 5, and the materials of the first protective layer and the second protective layer are controlled and extruded by the single-screw extruder 7. The two materials converge in the three-layer coextrusion die 11 under the precise control of the extrusion flow rate and pressure by a melt pump 8 respectively, and are extruded into the foamed diffusion plate product 13 after three-layer superimposed distribution.

[0032] Among them, both the first resin raw material and the second resin raw material are GPPS. The melt index of the first resin raw material GPPS is 2 - 3 g / 10 min, and the melt index of the second resin raw material GPPS is 5 - 8 g / 10 min.

[0033] Among them, the twin-screw extruder is divided into Zone 1, Zone 2, Zone 3, Zone 4, Zone 5, Zone 6, Zone 7, the connection section, and the die head along the extrusion direction. The temperatures of Zone 1 to Zone 6 are 190 °C, the temperature of Zone 7 is 185 °C. The connection section includes the screen-changing temperature, the first connection temperature, the melt pump temperature, and the second connection temperature. The screen-changing temperature is 185 °C, the first connection temperature, the melt pump temperature, and the second connection temperature are 180 °C, and the temperature of the die head is 175 °C. The single-screw extruder is divided into Zone 1, Zone 2, Zone 3, Zone 4, Zone 5, and the connection section along the extrusion direction. The temperatures of Zone 1 to Zone 5 are 190 °C. The connection section includes the screen-changing temperature, the first connection temperature, the melt pump temperature, the second connection temperature, and the distributor temperature. The screen-changing temperature is 185 °C, the first connection temperature, the melt pump temperature, and the second connection temperature are 180 °C, and the temperature of the die head is 175 °C. The specific parameters are shown in Table 1 and Table 2 as follows.

[0034] Table 1. Temperature Parameters of Twin-Screw Extruder

[0035] Table 2. Temperature Parameters of Single-Screw Extruder

[0036] The melt metering pump 8 is mainly used to accurately and stably control the ratio (or thickness ratio) of the foaming layer to the first protective layer and the second protective layer materials, and to ensure the stability of the board thickness dimension. The melt metering pump 8 works in conjunction with the loss-in-weight scale 6 to adjust the processing load of the production line, the body pressure of the screw blending system, etc. The specific adjustment parameters are shown in Table 3 below.

[0037] Table 3. Data table of the influence of the mixing ratio differences of GPPS, nucleating agent, and foaming agent on the finished product

[0038] The data in the above table.

[0039] 1. Feeding data: It mainly reflects the mixing ratio differences of the key raw materials GPPS, nucleating agent, and foaming agent. Among them, the addition amounts of CO2 and N2 are in units of volume flow. Because it is not easy to determine their densities under different pressure and temperature conditions, it is not easy to convert their mass flow rates. Therefore, in the experiment, they are mainly recorded in units of volume flow. For example, in No. 1, when the GPPS feed is 18 kg / h, the injection amount of CO2 is 1.2 ml / min, and its mass flow rate is 55.44 g / h (density is about 0.771 g / cm³ at 20°C), then the mass percentage of the foaming agent in the total material is 0.31%.

[0040] 2. Data of the twin-screw extruder: (1) The three data of the barrel pressure, the pressure before the melt pump, and the die head pressure mainly affect the solubility and dispersion of the foaming agent (CO2, N2). A higher pressure is beneficial to the solubility of the foaming agent and forms more uniform pores.

[0041] (2) The twin-screw rotation speed mainly affects the mixing of the GPPS melt and the foaming agent. Appropriately increasing the rotation speed and shearing and mixing through the threads of the twin-screw is beneficial to improving the solubility and dispersion of the foaming agent and forming more uniform pores.

[0042] (3) The melt pump rotation speed mainly controls the discharge speed at the die head and the thickness of the middle foaming layer, ensuring the consistency of the thickness of the foamed board and maintaining an appropriate pressure at the die head.

[0043] 3. Single-screw extruder (55 machine refers to the equipment model) (1) Melt pump rotation speed of the 55 machine: It mainly ensures the stable output of the materials of the upper and lower layers (the first protective layer and the second protective layer) of the foamed diffusion board according to the controlled thickness.

[0044] (2) GPPS feeding amount: The amount of feed mainly affects the thickness ratio of the first protective layer and the second protective layer.

[0045] (3) The rotational speed of the 55 machine is not a key factor. As long as the stable output of the upper and lower layer materials and the thickness requirements of the first and second protective layers are ensured.

[0046] It can be seen from the above results that: The optical foamed diffusion plate prepared by the present invention, such as Figure 4 shown, has round pores, uniform distribution, a large number of pores, a low product density, and good optical properties. The pore size can be controlled in the range of 50 - 200 μm, and the pore diameter error is less than 10%. Thus, the performance in aspects such as the dispersion, refraction, and transmission of the light source is effectively improved. Moreover, the density of the optical foamed diffusion plate is below 1.0 g / cm³, and can be as low as 0.637 g / cm³, with a haze > 94%, and can be as high as 100%.

[0047] The above shows and describes the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. What is described in the above embodiments and the specification only illustrates the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of the present invention claimed is defined by the appended claims and their equivalents.

Claims

1. A supercritical carbon dioxide optical foaming diffusion plate, characterized in that: The optical foaming diffusion plate includes a first protective layer, a foaming layer, and a second protective layer that are sequentially stacked; The material of the foaming layer includes a first resin raw material, a nucleating agent, a first additive, and a foaming agent; The materials of the first protective layer and the second protective layer include a second resin raw material and a second additive.

2. The supercritical carbon dioxide optical foaming diffusion plate according to claim 1, wherein: The material of the first resin raw material is at least one of GPPS, MS, PC, PET, and PMMA; The material of the second resin raw material is at least one of GPPS, MS, PMMA, PE, PP, HIPS, K resin, and PET.

3. The supercritical carbon dioxide optical foaming diffusion plate according to claim 1, characterized in that: The first additive and the second additive are at least one of a diffusing agent, an antioxidant, and a lubricant.

4. A supercritical carbon dioxide optical foaming diffusion plate according to claim 1, wherein: The material of the foaming agent is at least one of carbon dioxide and nitrogen.

5. The supercritical carbon dioxide optical foaming diffusion plate according to claim 1, wherein: The nucleating agent is at least one of calcium carbonate, talcum powder, montmorillonite, silica, and titanium dioxide.

6. The supercritical carbon dioxide optical foaming diffusion plate according to claim 1, wherein: The thickness of the foaming layer is 0.5 - 5 mm, and the thicknesses of the first protective layer and the second protective layer are 0.05 - 1 mm.

7. An optical foaming diffusion plate of supercritical carbon dioxide according to claim 1, characterized in that: The material of the foaming layer consists of the following components by weight fraction Composition: 100 parts of GPPS, 0.5 - 5 parts of talcum powder, 0.05% - 1% parts of carbon dioxide.

8. A preparation process of an optical foaming diffusion plate, applicable to a supercritical carbon dioxide optical foaming diffusion plate according to any one of claims 1-7, characterized in that: It includes the following operation steps: S1: The foaming agent is stored in a cylinder in a liquid / gaseous form, metered and pressurized by a high-pressure metering pump, and back-pressure valve is used for standby pressure to ensure that the foaming agent is accurately and stably injected into the twin-screw extruder through the injection valve according to the flow rate and pressure set values of the process conditions; S2: The temperature in zones 1 to 7 of the twin-screw extruder is controlled at 180 - 220 °C, and the temperature of the foaming layer melt gradually decreases from zone 1 to the three-layer coextrusion die. The pressure in the barrel of the twin-screw extruder is controlled within the range of 5 - 14 Mpa, and the screw speed is 150 - 300 r / min. After the first resin raw material, nucleating agent, and first additive are melt-blended in the twin-screw extruder, they are precisely metered by a melt metering pump, further homogenized and mixed through a static mixer, and enter the middle layer of the three-layer coextrusion die through a distributor. At the moment when the foaming layer melt is extruded from the die lip, due to the sudden decrease in pressure, the foaming agent rapidly expands around the bubble nuclei, forming a dense honeycomb-like pore structure to form the foaming layer; S3: The temperature in zones 1 to 5 of the single-screw extruder is controlled between 180 - 230 °C, the pressure in the barrel of the single-screw extruder is controlled at 5 - 10 MPa. After the second resin raw material and the second additive are melt-blended in the single-screw extruder, they are precisely metered by a melt metering pump, and are divided into two paths by a distributor, respectively entering the upper and lower layers of the three-layer coextrusion die, wrapping the foaming layer in the middle, and forming the first protective layer and the second protective layer on both sides of the foaming layer; S4: The temperatures of the three melts of the first protective layer, the foaming layer, and the second protective layer in the three-layer coextrusion die are controlled in zones respectively. Among them, the first protective layer and the second protective layer maintain a temperature between 180 - 230 °C, and the foaming layer maintains a temperature of 150 - 180 °C. After the foaming layer, the first protective layer, and the second protective layer are extruded from the three-layer coextrusion die, they quickly enter the calender rolls for shaping and cooling, and extrude a diffusion plate product with a certain texture.

9. The preparation process of an optical foamed diffusion plate according to claim 8, characterized in that: The first resin raw material and the second resin raw material are both GPPS. The melt index of the first resin raw material GPPS is 2-3 g / 10 min, and the melt index of the second resin raw material GPPS is 5-8 g / 10 min.

10. The preparation process of an optical foamed diffusion plate according to claim 9, characterized in that: The twin-screw extruder is divided into Zone 1, Zone 2, Zone 3, Zone 4, Zone 5, Zone 6, Zone 7, the connecting section and the die head along the extrusion direction. The temperatures of Zone 1 to Zone 6 are 190 °C, the temperature of Zone 7 is 185 °C. The connecting section includes the screen-changing temperature, the connecting temperature 1, the melt pump temperature and the connecting temperature 2. The screen-changing temperature is 185 °C, and the connecting temperature 1, the melt pump temperature and the connecting temperature 2 are 180 °C. The temperature of the die head is 175 °C. The single-screw extruder is divided into Zone 1, Zone 2, Zone 3, Zone 4, Zone 5 and the connecting section along the extrusion direction. The temperatures of Zone 1 to Zone 5 are 190 °C. The connecting section includes the screen-changing temperature, the connecting temperature 1, the melt pump temperature, the connecting temperature 2 and the distributor temperature. The screen-changing temperature is 185 °C, and the connecting temperature 1, the melt pump temperature and the connecting temperature 2 are 180 °C. The temperature of the die head is 175 °C.

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