Method for producing optical diffusion plate and optical diffusion plate

Abstract

The application provides a preparation method of an optical diffusion plate and the optical diffusion plate, and particularly relates to the technical field of optical plate materials. The preparation method of the optical diffusion plate comprises the following steps: A, polystyrene (PS), polypropylene (PP), a toughening agent, an antioxidant, a light stabilizer and a compatilizer are mixed, then melt blending, granulation and drying are performed to obtain a PS-based composite material; B, the PS-based composite material is added into an injection molding machine, a supercritical fluid system is used to inject a supercritical fluid as a physical foaming agent in a melt plasticizing process, so that the supercritical fluid is dissolved in a polymer melt and a uniform polymer / gas single-phase melt is formed; C, the polymer / gas single-phase melt is injected into a mold cavity, pressure is maintained, then primary mold opening is performed to release pressure for inducing foaming, then cooling and shaping are performed, secondary mold opening and demolding are performed, and the optical diffusion plate with a microporous structure is obtained.

Description

Technical Field

[0001] This invention relates to the field of optical sheet technology, and in particular to a method for preparing an optical diffusion plate and the optical diffusion plate itself. Background Technology

[0002] As a core optical component in backlight modules such as liquid crystal displays (LCDs), LED lighting, and advertising light boxes, the main function of optical diffusers is to efficiently convert point or line light sources into surface light sources with uniform brightness and no bright spots, thereby improving display quality and visual comfort.

[0003] Currently, the mainstream manufacturing processes for optical diffusers mainly include traditional injection molding and compression molding. In these processes, to achieve the desired light diffusion effect, a certain amount of light diffusing agent is usually added to a transparent matrix resin such as polystyrene (PS) or polycarbonate (PC). However, the interfacial compatibility between the added diffusing agent and the matrix is ​​difficult to match perfectly, easily leading to light absorption and ineffective reflection, resulting in the loss of some incident light and significantly reducing the light transmittance of the material. The uniformity of the additive dispersion in the polymer melt is greatly affected by processing conditions, and agglomeration is prone to occur, forming appearance defects such as crystal points and fisheyes, which seriously affect the imaging quality and display consistency of optical devices. In addition, the introduction of a high proportion of filler may also exacerbate the brittleness of the material, reduce its impact strength and durability, and limit its application in high-reliability scenarios.

[0004] On the other hand, traditional chemical foaming technology has also been attempted to manufacture lightweight diffuser plates. However, this method suffers from problems such as uncontrollable foaming processes and difficulty in matching gas release rates with injection molding cycles, often resulting in defects such as large cell size, uneven distribution, high open-cell ratio, and even collapse. This coarse cell structure not only weakens the mechanical properties of the material but also fails to form a stable and efficient light scattering interface, making it difficult to meet the precision requirements of microstructures for high-end optical applications.

[0005] In recent years, supercritical fluid (ScF) microporous foaming technology has attracted widespread attention as a green and controllable physical foaming method. However, existing research has mostly focused on the preparation of general-purpose foamed materials, and there are still challenges in its application to optical-grade transparent products: pure PS material itself is brittle, and after the introduction of microporous structures, it is prone to crack propagation due to stress concentration, which leads to a further decrease in toughness.

[0006] In view of this, the present invention is hereby proposed. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing an optical diffusion plate and an optical diffusion plate, which aims to solve at least one of the above-mentioned technical problems in the prior art.

[0008] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: A first aspect of the present invention provides a method for preparing an optical diffuser plate, comprising the following steps: A. After mixing polystyrene (PS), polypropylene (PP), toughening agent, antioxidant, light stabilizer and compatibilizer, the mixture is melt-blended, pelletized and dried to obtain PS-based composite material; B. The PS-based composite material is added to the injection molding machine. During the melting and plasticizing process, supercritical fluid is injected through a supercritical fluid system as a physical foaming agent, so that it dissolves in the polymer melt and forms a uniform polymer / gas single-phase melt. C. The polymer / gas single-phase melt is injected into the mold cavity, and after holding the pressure, the mold is opened once to release the pressure and induce foaming. Then, it is cooled and shaped, and then the mold is opened a second time to demold, so as to obtain an optical diffusion plate with a microporous structure.

[0009] Further, in step A, by weight parts, the polystyrene is 70-90 parts, the polypropylene is 10-30 parts, the toughening agent is 0.1-3 parts, the antioxidant is 0.1-3 parts, the light stabilizer is 0.1-3 parts, and the compatibilizer is 0.1-3 parts.

[0010] Furthermore, the toughening agent is selected from at least one of methyl methacrylate-butadiene-styrene copolymer (MBS), styrene-butadiene-styrene triblock copolymer (SBS), and styrene-isoprene-styrene block copolymer (SIS).

[0011] Preferably, the antioxidant is selected from at least one of β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate and tris(2,4-di-tert-butylphenyl)phosphite.

[0012] Preferably, the light stabilizer is selected from at least one of 2-(3-tert-butyl-2-hydroxy-5-methylphenyl)-5-chlorobenzotriazole, bis(2,2,6,6-tetramethyl-4-piperidinyl) sebacate and 2-hydroxy-4-n-octyloxybenzophenone.

[0013] Preferably, the compatibilizer is maleic anhydride-grafted SEBS.

[0014] Further, in step B, the supercritical fluid is supercritical carbon dioxide and / or supercritical nitrogen.

[0015] Preferably, the supercritical fluid accounts for 0.2 to 5 wt% of the polymer / gas single-phase melt.

[0016] Furthermore, in step B, the temperature of the melt plasticization is 190~230℃.

[0017] Preferably, the injection pressure of the supercritical fluid is 5~15MPa, and the mixing time of the supercritical fluid is 15~20s.

[0018] Furthermore, in step C, the injection speed of the polymer / gas single-phase melt is 100~120 mm / s.

[0019] Preferably, the temperature of the mold is 50~75℃.

[0020] Preferably, the pressure held is 10~30MPa and the time is 20~50s.

[0021] Preferably, the cooling and shaping time is 60~120s.

[0022] Preferably, during the induced foaming process, the weight loss ratio is set to 5-10%.

[0023] A second aspect of the present invention provides an optical diffusion plate, which is prepared using the preparation method described in the first aspect.

[0024] Furthermore, the density of the optical diffuser plate is 0.78~0.94 g / cm³. 3 .

[0025] Furthermore, in the optical diffusion plate, the average pore size is <100μm and the pore density is >10. 6 cell / cm 3 .

[0026] Furthermore, the optical diffuser plate has a tensile strength ≥30MPa and a notched impact strength ≥3.0kJ / m. 2 Light transmittance ≥35%.

[0027] Compared with the prior art, the present invention has at least the following beneficial effects: The preparation method provided by this invention modifies polystyrene and polypropylene by blending, and adds toughening agents, antioxidants and light stabilizers to improve the comprehensive performance of the composite material. Then, combined with supercritical fluid physical foaming process, a uniform microporous structure is induced by pressure release during injection molding. The resulting optical diffusion plate not only has the high light transmittance of polystyrene and the excellent mechanical properties of polypropylene, but also achieves excellent optical diffusion effect due to the light scattering effect of micropores. At the same time, the addition of antioxidants and light stabilizers effectively enhances the weather resistance and anti-aging ability of the plate. The supercritical fluid foaming process is more environmentally friendly than traditional chemical foaming and can precisely control the size and distribution of micropores, further ensuring the uniformity of light transmission and the stability of use of the optical diffusion plate.

[0028] The optical diffuser plate of this invention features a closed-cell microstructure with small (average <100μm) pore size, highly uniform distribution, and high pore density, significantly improving the material's overall optical and mechanical properties. It not only achieves a light transmittance of over 35%, meeting the high-efficiency light diffusion requirements of backlight modules, but also endows the material with excellent mechanical strength and toughness, with a tensile strength ≥30MPa and a notched impact strength ≥3.0 kJ / m². 2 Simultaneously, the porous structure can improve the internal stress and warpage deformation of the diffuser plate. Furthermore, the microporous structure itself acts as an endogenous light scattering center, replacing external light diffusing agents and improving optical uniformity and product yield. Combining the advantages of supercritical fluids—being green and controllable—this method also achieves material lightweighting (density as low as 0.78~0.94 g / cm³). 3 This reduces raw material consumption and production costs, and has good prospects for industrial application. Attached Figure Description

[0029] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0030] Figure 1 This is a SEM image of the cross-section of the PS optical diffuser obtained in Example 1; Figure 2 This is a SEM image of the cross-section of the PS optical diffuser obtained in Example 2; Figure 3 This is a SEM image of the cross-section of the PS optical diffuser obtained in Example 3; Figure 4 The image shows a cross-sectional SEM image of the PS optical diffuser plate obtained in Example 4. Figure 5 This is a 3D microscope image of the cross-section of the PS optical diffuser obtained in Comparative Example 1; Figure 6 This is a 3D microscope image of the cross-section of the PS optical diffuser obtained in Comparative Example 2; Figure 7 This is a 3D microscope image of the cross-section of the PS optical diffuser obtained in Comparative Example 3. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0032] In the following, the terms “comprising,” “having,” and their cognates, which may be used in various embodiments of the invention, are intended only to indicate a particular feature, number, step, operation, element, component, or combination thereof, and should not be construed as excluding, firstly, the presence of one or more other features, numbers, steps, operations, elements, components, or combinations thereof, or adding the possibility of one or more features, numbers, steps, operations, elements, components, or combinations thereof.

[0033] A first aspect of the present invention provides a method for preparing an optical diffuser plate, comprising the following steps: A. After mixing polystyrene (PS), polypropylene (PP), toughening agent, antioxidant, light stabilizer and compatibilizer, the mixture is melt-blended, pelletized and dried to obtain PS-based composite material; B. The PS-based composite material is added to the injection molding machine. During the melting and plasticizing process, supercritical fluid is injected through a supercritical fluid system as a physical foaming agent, so that it dissolves in the polymer melt and forms a uniform polymer / gas single-phase melt. C. The polymer / gas single-phase melt is injected into the mold cavity, and after holding the pressure, the mold is opened once to release the pressure and induce foaming. Then, it is cooled and shaped, and then the mold is opened a second time to demold, so as to obtain an optical diffusion plate with a microporous structure.

[0034] The preparation method provided by this invention modifies polystyrene and polypropylene by blending, and adds toughening agents, antioxidants and light stabilizers to improve the comprehensive performance of the composite material. Then, combined with supercritical fluid physical foaming process, a uniform microporous structure is induced by pressure release during injection molding. The resulting optical diffusion plate not only has the high light transmittance of polystyrene and the excellent mechanical properties of polypropylene, but also achieves excellent optical diffusion effect due to the light scattering effect of micropores. At the same time, the addition of antioxidants and light stabilizers effectively enhances the weather resistance and anti-aging ability of the plate. The supercritical fluid foaming process is more environmentally friendly than traditional chemical foaming and can precisely control the size and distribution of micropores, further ensuring the uniformity of light transmission and the stability of use of the optical diffusion plate.

[0035] This invention introduces appropriate amounts of PP and toughening agents (such as MBS and SBS) into the material system, effectively improving the inherent brittleness of PS and significantly enhancing the impact toughness and processing stability of the composite material. Simultaneously, the addition of PP helps reduce raw material costs and enhances process economy. Furthermore, the antioxidants added to the formulation can inhibit the thermo-oxidative degradation of PS during high-temperature processing and long-term use, preventing molecular chain breakage, maintaining melt strength, and ensuring structural integrity during foaming. The light stabilizer, by efficiently absorbing ultraviolet light and dissipating energy, effectively prevents yellowing, chalking, and mechanical property degradation caused by photoaging of PS. The synergistic effect of antioxidants and light stabilizers not only ensures the color stability and molding quality of the material during processing but also significantly improves the weather resistance and long-term service reliability of optical diffusers in practical applications, providing solid technical support for achieving high-performance, high-durability, lightweight optical products.

[0036] The introduction of polypropylene (PP) and toughening agents (such as MBS, SBS, or SIS) achieves synergistic toughening of brittle polystyrene (PS) matrices. PP, as a dispersed second phase, works in conjunction with the toughening agent to effectively induce numerous crazing and shear bands when the material is subjected to impact loads. The branching and termination of crazing, along with the extensive plastic deformation of the shear bands, absorbs and dissipates impact energy, significantly improving the notched impact strength of PS-based composites while maintaining high tensile strength. This synergistic toughening mechanism not only overcomes the problem of brittle fracture during processing or use caused by the high rigidity and poor toughness of pure PS, but also enhances the structural stability of the material during microcellular foaming, preventing cell collapse or cracking caused by stress concentration. This ensures that the optical diffuser plate, while lightweight and with high light transmittance, still maintains excellent mechanical integrity and long-term reliability.

[0037] This invention utilizes supercritical fluid to generate a large number of uniform, closed micropores with sizes much smaller than the wavelength of visible light in situ during the injection molding process. These micropores and the polymer matrix form countless refractive index interfaces, enabling efficient Rayleigh scattering of light. Thus, without relying on traditional light diffusing agents, it simultaneously imparts excellent optical properties to the product, fundamentally solving the technical problem of reduced light transmittance caused by the addition of external diffusing agents.

[0038] This invention integrates material preparation and microporous foaming molding into a one-step injection molding process, which greatly simplifies the production process and improves production efficiency. The resulting uniform microporous structure not only constitutes an optical functional layer but also significantly reduces the weight of the product, saves raw materials, and effectively improves the internal stress and dimensional stability of the product, reducing warpage.

[0039] Further, in step A, by weight parts, the polystyrene is 70-90 parts, the polypropylene is 10-30 parts, the toughening agent is 0.1-3 parts, the antioxidant is 0.1-3 parts, the light stabilizer is 0.1-3 parts, and the compatibilizer is 0.1-3 parts.

[0040] Typically, but not limitingly, the amount of polystyrene used can be, for example, 70 parts, 72 parts, 75 parts, 78 parts, 80 parts, 82 parts, 85 parts, 88 parts, or 90 parts, or any value within the range of 70 to 90 parts; the amount of polypropylene used can be, for example, 10 parts, 12 parts, 15 parts, 18 parts, 20 parts, 22 parts, 25 parts, 28 parts, or 30 parts, or any value within the range of 10 to 30 parts; the amount of toughening agent used can be, for example, 0.1 parts, 0.5 parts, 1 part, 1.5 parts, 2 parts, 2.5 parts, or 3 parts, or 0 parts. The amount of antioxidant can be any value within the range of 1 to 3 parts; the amount of antioxidant can be, for example, 0.1 parts, 0.5 parts, 1 part, 1.5 parts, 2 parts, 2.5 parts, or 3 parts, or any value within the range of 0.1 to 3 parts; the amount of light stabilizer can be, for example, 0.1 parts, 0.5 parts, 1 part, 1.5 parts, 2 parts, 2.5 parts, or 3 parts, or any value within the range of 0.1 to 3 parts; the amount of compatibilizer can be, for example, 0.1 parts, 0.5 parts, 1 part, 1.5 parts, 2 parts, 2.5 parts, or 3 parts, or any value within the range of 0.1 to 3 parts.

[0041] It should be noted that in the formulation of the PS-based composite material, polystyrene (PS) and polypropylene (PP) are the main polymer components, and the sum of the two is constant at 100 parts, that is, the formulation ratio is based on 100 parts of PS and PP.

[0042] Furthermore, the toughening agent is selected from at least one of methyl methacrylate-butadiene-styrene copolymer (MBS), styrene-butadiene-styrene triblock copolymer (SBS), and styrene-isoprene-styrene block copolymer (SIS).

[0043] Preferably, the antioxidant is selected from at least one of β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate and tris(2,4-di-tert-butylphenyl)phosphite.

[0044] Preferably, the light stabilizer is selected from at least one of 2-(3-tert-butyl-2-hydroxy-5-methylphenyl)-5-chlorobenzotriazole, bis(2,2,6,6-tetramethyl-4-piperidinyl) sebacate and 2-hydroxy-4-n-octyloxybenzophenone.

[0045] Preferably, the compatibilizer is maleic anhydride-grafted SEBS.

[0046] Further, in step B, the supercritical fluid is supercritical carbon dioxide and / or supercritical nitrogen.

[0047] Preferably, the supercritical fluid accounts for 0.2~5 wt% of the polymer / gas single-phase melt. This ensures sufficient foaming gas for effective weight reduction and the formation of a uniform microporous structure, avoiding insufficient cell density or incomplete foaming due to insufficient gas. It also prevents excessive gas from causing cell merging, collapse, or increased open-cell ratio, thus maintaining the integrity of the cell morphology and the stability of the closed-cell structure. This range facilitates precise control of the foaming kinetics process, ensuring the acquisition of small (<100 μm), uniformly distributed, and high-density closed-cell microstructures. This synergistically improves the light scattering efficiency, transmittance, mechanical strength, and dimensional stability of the optical diffuser plate, while ensuring the repeatability of the processing and the controllability of the process window.

[0048] Typically, but not limitingly, the supercritical fluid may constitute a mass fraction of the polymer / gas single-phase melt of, for example, 0.2 wt%, 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, or 5 wt%, or any value in the range of 0.2 to 5 wt%.

[0049] Furthermore, in step B, the temperature of the melt plasticization is 190~230℃.

[0050] Typically, but not limitingly, in step B, the temperature of the melt plasticization can be, for example, 190°C, 195°C, 200°C, 205°C, 210°C, 215°C, 220°C, 225°C, or 230°C, or any value within the range of 190°C to 230°C.

[0051] Preferably, the injection pressure of the supercritical fluid is 5~15MPa, and the mixing time of the supercritical fluid is 15~20s.

[0052] Typically, but not limitingly, the injection pressure of the supercritical fluid can be, for example, 5 MPa, 6 MPa, 7 MPa, 8 MPa, 9 MPa, 10 MPa, 11 MPa, 12 MPa, 13 MPa, 14 MPa or 15 MPa, or any value in the range of 5 to 15 MPa; the time for maintaining the supercritical fluid mixing can be, for example, 15 s, 16 s, 17 s, 18 s, 19 s or 20 s, or any value in the range of 15 to 20 s.

[0053] Furthermore, in step C, the injection speed of the polymer / gas single-phase melt is 100~120 mm / s.

[0054] Typically, but not limitingly, the injection rate of the polymer / gas single-phase melt can be, for example, 100 mm / s, 102 mm / s, 105 mm / s, 108 mm / s, 110 mm / s, 112 mm / s, 115 mm / s, 118 mm / s, or 120 mm / s, or any value in the range of 100 to 120 mm / s.

[0055] Preferably, the temperature of the mold is 50~75℃.

[0056] Typically, but not limitingly, the temperature of the mold can be, for example, 50°C, 55°C, 60°C, 65°C, 70°C, or 75°C, or any value within the range of 50°C to 75°C.

[0057] Preferably, the pressure held is 10~30MPa and the time is 20~50s.

[0058] Typically, but not limitingly, the holding pressure can be, for example, 10 MPa, 12 MPa, 15 MPa, 18 MPa, 20 MPa, 22 MPa, 25 MPa, 28 MPa or 30 MPa, or any value within the range of 10 to 30 MPa; the holding time can be, for example, 20 s, 25 s, 30 s, 35 s, 40 s, 45 s or 50 s, or any value within the range of 20 to 50 s.

[0059] Preferably, the cooling and shaping time is 60~120s.

[0060] Typically, but not limitingly, the cooling and setting time can be, for example, 60s, 70s, 80s, 90s, 100s, 110s, or 120s, or any value within the range of 60 to 120s.

[0061] Preferably, during the induced foaming process, the weight loss ratio is set to 5-10%.

[0062] Typically, but not limitingly, during the induced foaming process, the weight loss ratio can be set to, for example, 5%, 6%, 7%, 8%, 9% or 10%, or any value within the range of 5% to 10%.

[0063] A second aspect of the present invention provides an optical diffusion plate, which is prepared using the preparation method described in the first aspect.

[0064] The optical diffuser plate of this invention features a closed-cell microstructure with small (average <100μm) pore size, highly uniform distribution, and high pore density, significantly improving the material's overall optical and mechanical properties. It not only achieves a light transmittance of over 35%, meeting the high-efficiency light diffusion requirements of backlight modules, but also endows the material with excellent mechanical strength and toughness, with a tensile strength ≥30MPa and a notched impact strength ≥3.0 kJ / m². 2 Furthermore, the microporous structure itself acts as an intrinsic light scattering center, which can replace external light diffusing agents, improving optical uniformity and product yield. Combining the advantages of supercritical fluids—being green and controllable—this method also achieves material lightweighting (density as low as 0.78~0.94 g / cm³). 3 This reduces raw material consumption and production costs, and has good prospects for industrial application.

[0065] Furthermore, the density of the optical diffuser plate is 0.78~0.94 g / cm³. 3 .

[0066] Furthermore, in the optical diffusion plate, the average pore size is <100μm and the pore density is >10. 6 cell / cm 3 .

[0067] Furthermore, the optical diffuser plate has a tensile strength ≥30MPa and a notched impact strength ≥3.0kJ / m. 2 Light transmittance ≥35%.

[0068] The present invention is further illustrated below with specific embodiments and comparative examples. However, it should be understood that these embodiments are merely for illustrative purposes and should not be construed as limiting the invention in any way. Unless otherwise specified, the raw materials used in the embodiments and comparative examples of the present invention were carried out under conventional conditions or conditions recommended by the manufacturer. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0069] Example 1 This embodiment provides an optical diffusion plate, and the specific fabrication process is as follows: 1. Place polystyrene (PS) and polypropylene (PP) in a constant temperature oven and dry at 80℃ for 12 hours to remove moisture from the materials. Weigh out 80 parts PS, 20 parts PP, 0.5 parts methyl methacrylate-butadiene-styrene copolymer (MBS) as a toughening agent, 0.25 parts β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate and 0.25 parts tris(2,4-di-tert-butylphenyl) phosphite as antioxidants, 0.5 parts 2-(3-tert-butyl-2-hydroxy-5-methylphenyl)-5-chlorobenzotriazole as a light stabilizer, and 2 parts maleic anhydride-grafted SEBS (SEBS-g-MAH) as a compatibilizer. Add the above materials sequentially to a high-speed mixer and mix for 6 minutes to ensure uniform dispersion of the components, thus obtaining a premix.

[0070] 2. Add the premixed material to a twin-screw extruder for melt blending. Set the screw speed to 45 rpm. After the extruded strip material is water-cooled and shaped, it is cut into granules by a pelletizer. The resulting granules are then placed in an 80℃ oven to dry for 12 hours to obtain a dry PS-based composite material.

[0071] 3. The dried PS-based composite material is added to a microporous injection molding foaming equipment, heated and plasticized at 210°C, and supercritical carbon dioxide is injected through a supercritical fluid system. The injection pressure is controlled at 10 MPa so that the mass fraction of CO2 in the polymer melt reaches 0.5 wt%, and it is fully dissolved under the shearing action of the screw to form a uniform and stable polymer / gas single-phase melt.

[0072] 4. The above single-phase melt is injected into the mold cavity through the nozzle at an injection speed of 100 mm / s. The mold temperature is controlled at 80℃, the holding pressure is 20 MPa, and the holding time is 30 s. After the holding time is completed, the moving mold side is opened rapidly at a speed of 10 mm / s to a certain distance (i.e., one mold opening) to achieve a sudden drop in pressure in the cavity, inducing uniform bubble nucleation and growth in the polymer / gas system, and the weight reduction ratio is controlled at 5%. Then the mold is closed and the product is cooled and solidified for 80 s. Finally, the product is ejected by a second mold opening to obtain the PS-based optical diffusion plate.

[0073] Example 2 This embodiment provides an optical diffusion plate. Unlike embodiment 1, in step 3, the mass fraction of CO2 in the polymer melt reaches 0.8 wt%. The rest of the preparation method is the same as in embodiment 1, and will not be described again here.

[0074] Example 3 This embodiment provides an optical diffusion plate. Unlike embodiment 1, in step 4, the weight reduction ratio is controlled at 10%. The rest of the preparation methods are the same as in embodiment 1, and will not be described again here.

[0075] Example 4 This embodiment provides an optical diffusion plate. Unlike embodiment 1, in step 3, supercritical nitrogen gas is injected through a supercritical fluid system. The rest of the preparation method is the same as in embodiment 1, and will not be described again here.

[0076] Example 5 This embodiment provides an optical diffusion plate. Unlike embodiment 1, in step 1, the amount of PS is 90 parts and the amount of PP is 10 parts. The rest of the preparation method is the same as in embodiment 1, and will not be described again here.

[0077] Example 6 This embodiment provides an optical diffusion plate. Unlike embodiment 1, in step 1, the amount of PS is 70 parts and the amount of PP is 30 parts. The rest of the preparation method is the same as in embodiment 1, and will not be described again here.

[0078] Example 7 This embodiment provides an optical diffusion plate. Unlike embodiment 1, in step 3, supercritical carbon dioxide is injected through a supercritical fluid system, and the injection pressure is controlled at 5 MPa so that the mass fraction of CO2 in the polymer melt reaches 0.1 wt%. The rest of the preparation method is the same as in embodiment 1, and will not be described again here.

[0079] Example 8 This embodiment provides an optical diffusion plate. Unlike embodiment 1, in step 3, supercritical carbon dioxide is injected through a supercritical fluid system, and the injection pressure is controlled at 5 MPa so that the mass fraction of CO2 in the polymer melt reaches 0.2 wt%. The rest of the preparation method is the same as in embodiment 1, and will not be described again here.

[0080] Example 9 This embodiment provides an optical diffusion plate. Unlike embodiment 1, in step 3, supercritical carbon dioxide is injected through a supercritical fluid system, and the injection pressure is controlled at 15 MPa so that the mass fraction of CO2 in the polymer melt reaches 5 wt%. The rest of the preparation method is the same as in embodiment 1, and will not be described again here.

[0081] Example 10 This embodiment provides an optical diffusion plate. Unlike embodiment 1, in step 3, supercritical carbon dioxide is injected through a supercritical fluid system, and the injection pressure is controlled at 15 MPa so that the mass fraction of CO2 in the polymer melt reaches 5.5 wt%. The rest of the preparation method is the same as in embodiment 1, and will not be described again here.

[0082] Comparative Example 1 This comparative example provides an optical diffusion plate, the specific fabrication process of which is as follows: 1. Same as the steps in Example 1.

[0083] 2. Same as the steps in Example 1.

[0084] 3. The dried PS-based composite material and 0.5 parts of sodium bicarbonate are added to the injection molding equipment for plasticization and melting. The mixture is heated and plasticized at 210°C. The melt is injected into the mold cavity through the nozzle at an injection speed of 100 mm / s using the injection molding machine screw. The mold temperature is controlled at 80°C, the holding pressure is 20 MPa, and the holding time is 30 s. After the holding time is completed, the moving mold side is opened rapidly at a speed of 10 mm / s, and the weight reduction ratio is controlled at 5%. The mold is then closed and cooled and solidified for another 80 s. Finally, the mold is opened a second time to eject the product, resulting in a PS-based optical diffusion plate.

[0085] Comparative Example 2 This comparative example provides an optical diffusion plate. Unlike Comparative Example 1, the amount of PS is 90 parts and PP is 10 parts. The other raw materials and preparation methods are the same as those in Comparative Example 1, and will not be described again here.

[0086] Comparative Example 3 This comparative example provides an optical diffusion plate. Unlike Comparative Example 2, the amount of sodium bicarbonate used is 1.0 part, and the weight loss ratio in step 3 is controlled at 10%. The other raw materials and preparation methods are the same as those in Comparative Example 2, and will not be described again here.

[0087] Comparative Example 4 This embodiment provides an optical diffusion plate. Unlike embodiment 1, it does not use PP. The rest of the preparation method is the same as that of embodiment 1, and will not be described again here.

[0088] Characterization Example 1 A scanning electron microscope was used to examine the cross-section of the optical diffusion plate obtained in the example, and a 3D micrograph was taken of the cross-section of the optical diffusion plate obtained in the comparative example.

[0089] Figure 1 The image shown is a cross-sectional SEM image of the PS optical diffuser obtained in Example 1. Figure 1 It can be seen that the pore size is small and the distribution is highly uniform, with the pore diameter generally much smaller than 100μm. The pore density is high, the pore walls are intact and dense, and there is no obvious collapse or merging phenomenon.

[0090] Figure 2 The image shown is a cross-sectional SEM image of the PS optical diffuser plate obtained in Example 2. Figure 2As can be seen, despite the increased gas concentration, Example 2 still maintained a relatively uniform cell distribution. The cell size increased slightly but remained within the micron-level fine range, without significant cell aggregation or structural instability. This figure reflects that even at a higher degree of foaming, the method of the present invention still possesses good structural controllability, and can maintain a relatively stable cell morphology while achieving more significant weight reduction.

[0091] Figure 3 The image shown is a cross-sectional SEM image of the PS optical diffuser plate obtained in Example 3. Figure 3 It can be seen that the cells maintain good monodispersity and regular arrangement. Although the cells in some areas show a slight elongation trend, the overall structural integrity is good, and no large-area openings or cracks appear. This indicates that the foaming kinetics can be effectively controlled by releasing pressure through mold opening in one step, and stable molding can still be achieved under conditions of large volume expansion, demonstrating the process's good adaptability to high weight reduction requirements.

[0092] Figure 4 The image shown is a cross-sectional SEM image of the PS optical diffuser plate obtained in Example 4. Figure 4 It can be seen that the pore structure is uniform and dense, and the size and distribution characteristics are similar to those of the CO2 foamed sample, indicating that nitrogen can also achieve good dissolution and nucleation effects in this system.

[0093] Figure 5 The image shows a 3D micrograph of the cross-section of the PS optical diffuser obtained in Comparative Example 1. Figure 5 It can be seen that the pore size is large and unevenly distributed, with obvious coexistence of large and small pores. In some areas, pore merging and membrane rupture occur, resulting in a loose and discontinuous structure. This reflects the difficulty in precisely controlling the gas release rate during chemical foaming, leading to uneven nucleation and uncontrolled growth, which seriously affects the mechanical strength and optical uniformity of the material.

[0094] Figure 6 The image shows a 3D micrograph of the cross-section of the PS optical diffuser obtained in Comparative Example 2. Figure 6 As can be seen, the foam exhibits significant non-uniformity, with large cavities coexisting with densely packed small pores, indicating a high risk of localized stress concentration. This figure illustrates that adjusting the formulation alone cannot fundamentally solve the inherent problems of strong nucleation randomness and poor diffusion control in chemical foaming; its structural defects are systemic.

[0095] Figure 7 The image shows a 3D micrograph of the cross-section of the PS optical diffuser plate obtained in Comparative Example 3. Figure 7As can be seen, the structure contains numerous irregular large pores and interconnected pores, with extremely thin or even broken pore walls, forming a degraded structure resembling a "honeycomb collapse." This crude foam structure not only severely weakens the material's strength but also causes non-directional light scattering, reducing light transmittance and diffusion uniformity, highlighting the fundamental limitations of traditional chemical foaming technology in the application of high-performance optical products.

[0096] Test Example 1 The optical diffusers obtained in the examples and comparative examples were tested, specifically including density, tensile strength, notched impact strength, and light transmittance.

[0097] Tensile strength was tested according to ISO 527; notched impact strength was tested according to ASTM D256; and light transmittance was tested according to ISO 13468-1.

[0098] The obtained data is shown in Table 1 below.

[0099] Table 1

[0100] As shown in Table 1, Examples 1-10 all employed supercritical CO2 or N2 foaming, achieving high gas solubility and uniform dispersion within the polymer melt. This induced a closed-cell microstructure with small cell size, uniform distribution, and high cell density during a single mold opening and pressure reduction process. This fine structure not only enabled effective weight reduction in the material, but also resulted in densities as low as 0.76~0.94 g / cm³ in the examples. 3 This significantly enhances its mechanical integrity: the tensile strength of the embodiments is generally higher than 30 MPa, and the notched impact strength reaches 2.5~4.2 kJ / m. 2 It is significantly better than the comparison ratio.

[0101] Although comparative examples 1-3 also achieved a weight reduction of approximately 5-10%, the use of chemical foaming agents such as sodium bicarbonate made it difficult to control the gas release rate. This resulted in large, low-density, uneven structure, and fragile pore walls, making them prone to stress concentration points. Consequently, their notched impact strength was generally below 3.0 kJ / m². 2 Its mechanical properties have deteriorated significantly.

[0102] Comparative Example 4 further demonstrates that even using the same supercritical foaming process, without the synergistic modification of PP and toughening agent, the notched impact strength still drops significantly to 1.5 kJ / m. 2 This indicates that PP not only helps with cost control, but also plays a key role in improving resilience.

[0103] In terms of optical performance, although the light transmittance values ​​of some comparative examples seem to be relatively high at 43-50%, their coarse and irregular bubble structure leads to non-uniform scattering of light, resulting in bright spots and imaging defects. In contrast, the embodiment uses in-situ generated micron-sized uniform micropores as intrinsic light scattering centers, achieving a more efficient and uniform light diffusion effect while ensuring that the light transmittance is not less than 30%, fundamentally avoiding the interface loss problem caused by the addition of external diffusing agents.

[0104] In summary, this invention successfully integrates previously mutually restrictive goals such as lightweight design, superior optical performance, outstanding mechanical strength, and significant cost advantages through supercritical fluid microporous foaming technology. It is not merely a process replacement, but represents an advanced manufacturing concept that achieves breakthroughs in material performance limits through precise microstructural control. This lays a solid technical foundation for its large-scale application in high-end LED lighting, precision display backlighting, and lightweight vehicle light guide components, possessing extremely high industrialization value and market competitiveness.

[0105] Finally, it should be noted that the above-described embodiments are merely specific implementations of the present invention, used to illustrate the technical solutions of the present invention, and not to limit it. The scope of protection of the present invention is not limited thereto. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any person skilled in the art can still modify or easily conceive of changes to the technical solutions described in the foregoing embodiments within the technical scope disclosed in the present invention, or make equivalent substitutions for some of the technical features; and these modifications, changes, or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing an optical diffusion plate, characterized in that, Includes the following steps: A. Mix 80 parts of polystyrene, 20 parts of polypropylene, toughening agent, antioxidant, light stabilizer and compatibilizer, and then melt blend, pelletize and dry to obtain PS-based composite material; B. The PS-based composite material is added to the injection molding machine. During the melting and plasticizing process, supercritical fluid is injected through a supercritical fluid system as a physical foaming agent, so that it dissolves in the polymer melt and forms a uniform polymer / gas single-phase melt. C. The polymer / gas single-phase melt is injected into the mold cavity, and after holding the pressure, the mold is opened once to release the pressure and induce foaming. Then, it is cooled and shaped, and then the mold is opened a second time to demold, so as to obtain an optical diffusion plate with a microporous structure.

2. The preparation method according to claim 1, characterized in that, In step A, the toughening agent is 0.1 to 3 parts by weight, the antioxidant is 0.1 to 3 parts, the light stabilizer is 0.1 to 3 parts, and the compatibilizer is 0.1 to 3 parts.

3. The preparation method according to claim 1 or 2, characterized in that, The toughening agent is selected from at least one of methyl methacrylate-butadiene-styrene copolymer, styrene-butadiene-styrene triblock copolymer, and styrene-isoprene-styrene block copolymer.

4. The preparation method according to claim 1 or 2, characterized in that, The antioxidant is selected from at least one of β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate and tris(2,4-di-tert-butylphenyl)phosphite.

5. The preparation method according to claim 1 or 2, characterized in that, The light stabilizer is selected from at least one of 2-(3-tert-butyl-2-hydroxy-5-methylphenyl)-5-chlorobenzotriazole, bis(2,2,6,6-tetramethyl-4-piperidinyl) sebacate and 2-hydroxy-4-n-octyloxybenzophenone.

6. The preparation method according to claim 1 or 2, characterized in that, The compatibilizer is maleic anhydride-grafted SEBS.

7. The preparation method according to claim 1 or 2, characterized in that, In step B, the supercritical fluid is supercritical carbon dioxide and / or supercritical nitrogen.

8. The preparation method according to claim 1 or 2, characterized in that, The supercritical fluid accounts for 0.2 to 5 wt% of the mass fraction of the polymer / gas single-phase melt.

9. The preparation method according to claim 1 or 2, characterized in that, In step B, the temperature for melting and plasticizing is 190~230℃.

10. The preparation method according to claim 1 or 2, characterized in that, The injection pressure of the supercritical fluid is 5~15MPa, and the mixing time of the supercritical fluid is 15~20s.

11. The preparation method according to claim 1 or 2, characterized in that, In step C, the injection speed of the polymer / gas single-phase melt is 100~120mm / s.

12. The preparation method according to claim 1 or 2, characterized in that, The temperature of the mold is 50~75℃.

13. The preparation method according to claim 1 or 2, characterized in that, The pressure held is 10~30MPa, and the time is 20~50s.

14. The preparation method according to claim 1 or 2, characterized in that, The cooling and shaping time is 60~120s.

15. The preparation method according to claim 1 or 2, characterized in that, During the induced foaming process, the weight loss ratio is set to 5-10%.

16. An optical diffusion plate, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 15.

17. The optical diffuser plate according to claim 16, characterized in that, Its density is 0.78~0.94 g / cm³. 3 .

18. The optical diffuser plate according to claim 16, characterized in that, Average cell size <100μm, cell density >10 6 cell / cm 3 .

19. The optical diffusion plate according to any one of claims 16 to 18, characterized in that, Tensile strength ≥30MPa, notched impact strength ≥3.0kJ / m 2 Light transmittance ≥35%.

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