High-transmittance high-temperature-resistant polystyrene-based composite light guide plate and preparation method thereof

Abstract

The application discloses a high-transmittance high-temperature-resistant polystyrene-based composite light guide plate and a preparation method thereof. The light guide plate is prepared through a unique material design and process, and has the functions of high transmittance, high heat resistance, light guiding and light homogenization. The preparation method is simple and easy to implement. The high-transmittance high-temperature-resistant polystyrene-based composite light guide plate is prepared from the following raw materials in parts by weight: crystalline polystyrene 20-50 parts, traditional amorphous polystyrene 50-80 parts, nucleating agent 0.1-1 part, toughening agent 2-8 parts, antioxidant 0.1-0.5 part and ultraviolet absorber 0.1-0.5 part. The nucleating agent induces the crystalline polystyrene to form microcrystals with an average particle size of 0.5-10 microns in the traditional amorphous polystyrene matrix, and the microcrystals serve as light scattering points, so that the light guide plate has the functions of light transmission and light diffusion.

Description

Technical Field

[0001] This invention relates to a light guide plate for use in liquid crystal display backlight modules or LED lighting fixtures and its preparation method, specifically to a high-transmittance, high-temperature resistant polystyrene-based composite light guide plate and its preparation method, belonging to the field of optical device technology. Background Technology

[0002] The light guide plate in LCD backlight modules or LED lighting fixtures is a core optical component of edge-lit LED backlight modules and panel lights. Its main function is to convert line or point light sources into uniform surface light sources. Currently, commonly used light guide plate substrates mainly include polymethyl methacrylate, polycarbonate, and polystyrene.

[0003] General purpose polystyrene (GPPS, amorphous) is widely used due to its high light transmittance, low cost, and excellent processing properties. However, a fatal flaw of GPPS is its poor heat resistance, with a heat distortion temperature typically below 80°C. In LED lighting fixtures, especially high-power or enclosed fixtures, the high operating temperature easily leads to thermal deformation and warping of the GPPS light guide plate, severely affecting light uniformity and the lifespan of the fixture.

[0004] To improve the heat resistance of GPPS or to give it light diffusion function, the following methods are usually used in the prior art: (1) Use PMMA or PC materials with better heat resistance; however, PMMA is brittle, has poor impact resistance and is expensive; although PC has good toughness and heat resistance, it is expensive and has high processing temperature and high energy consumption. (2) Add inorganic or organic light diffusing agents (such as silica, acrylate microspheres) to GPPS to achieve uniform light by scattering light through the two-phase interface; however, this method will introduce an additional light scattering interface, resulting in a significant decrease in transmittance (usually below 85%), and there are problems such as uneven dispersion of diffusing agents, poor compatibility with the matrix and easy migration. Long-term use may affect optical stability. In addition, the blending process increases production steps and costs. (3) Use a multi-layer composite structure, that is, an independent light guide plate plus a diffuser plate; this increases material costs and assembly steps, and also reduces light efficiency.

[0005] Therefore, developing a light guide plate material that combines high light transmittance, high heat resistance, good light diffusion function, low cost, and simple structure has become an urgent technical problem to be solved in this field. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a high-transmittance, high-temperature resistant polystyrene-based composite light guide plate and its preparation method. Through unique material design and process, this light guide plate significantly improves heat resistance while maintaining high light transmittance and realizes the integrated function of light guiding and light uniformity; at the same time, the preparation method is simple and easy to implement.

[0007] The technical solution of the present invention is as follows: The high-transmittance, high-temperature resistant polystyrene-based composite light guide plate of the present invention is made from the following raw materials in parts by weight: 20-50 parts of crystalline polystyrene, 50-80 parts of traditional amorphous polystyrene, 0.1-1 parts of nucleating agent, 2-8 parts of toughening agent, 0.1-0.5 parts of antioxidant, and 0.1-0.5 parts of ultraviolet absorber; wherein, the nucleating agent induces the crystalline polystyrene to form microcrystals with an average particle size of 0.5-10 μm in the traditional amorphous polystyrene matrix. These microcrystals serve as light scattering points, enabling the light guide plate to simultaneously possess light transmission and light diffusion functions.

[0008] A further technical solution of the high light transmittance and high temperature resistant polystyrene-based composite light guide plate of the present invention is that the crystalline polystyrene is syndiotactic polystyrene, abbreviated as SPS.

[0009] The high-transmittance, high-temperature resistant polystyrene-based composite light guide plate of the present invention may be further described in a way that the nucleating agent is one or a combination of organic phosphates, sorbitol derivatives, aromatic carboxylates, or inorganic nanoparticles.

[0010] A further technical solution to the high-transmittance, high-temperature resistant polystyrene-based composite light guide plate of the present invention may be that the toughening agent is a styrene-based thermoplastic elastomer. A further technical solution is that the styrene-based thermoplastic elastomer is preferably hydrogenated styrene-butadiene-styrene block copolymer (SEBS), styrene-butadiene-styrene block copolymer (SBS), or styrene-isoprene-styrene block copolymer (SIS).

[0011] A further technical solution of the high-transmittance, high-temperature resistant polystyrene-based composite light guide plate of the present invention may be that the heat distortion temperature of the light guide plate under a load of 0.45MPa is not lower than 90°C, the total light transmittance is not lower than 85%, and the haze is 20% to 80%.

[0012] The preparation method of the high light transmittance and high temperature resistant polystyrene-based composite light guide plate of the present invention includes the following steps: S1: Weigh each raw material according to the formula and dry it at 80-100℃ for 3-6 hours; S2: Mix the dried raw materials evenly to obtain a premix; S3: The premixed material is melt-blended at 200-260°C, then extruded, cooled and granulated to obtain composite resin granules; S4: After drying the composite resin granules, injection molding is performed at an injection temperature of 220-250℃ and a mold temperature of 70-90℃. After cooling, a high-transmittance, high-temperature resistant polystyrene-based composite light guide plate is obtained.

[0013] The core concept of this invention lies in precisely controlling the crystallization behavior of crystalline polystyrene by introducing a specific nucleating agent. During the cooling process after melt processing, the nucleating agent provides numerous heterogeneous nucleation sites, inducing the crystalline polystyrene to form a large number of uniformly dispersed microcrystals with an average particle size of 0.5~10μm in situ within the continuous amorphous polystyrene phase. These in-situ formed microcrystals have a slight refractive index difference with the surrounding amorphous matrix due to differences in density and molecular chain arrangement. Thus, the microcrystals constitute an intrinsic, three-dimensional light scattering network within the light guide plate. When light propagates within the plate via total internal reflection, it is continuously scattered by these microcrystals, thereby disrupting the total internal reflection condition and causing the light to exit uniformly from the light-emitting surface. This mechanism allows a single plate to simultaneously achieve efficient light guidance (light guiding) and excellent light homogenization (diffusion) functions without any external diffusion layer or second-phase scattering particles, achieving structural simplification and improved light efficiency.

[0014] Meanwhile, the introduction of high-melting-point, highly regular crystalline phases (especially syndiotactic polystyrene) and the resulting microcrystalline structure significantly improve the heat resistance of the composite material as a reinforcing phase. Its heat distortion temperature can be more than 20°C higher than that of pure amorphous polystyrene (GPPS) matrix, fundamentally overcoming the key defects of traditional PS light guide plates, such as easy deformation and warping, in high-temperature lighting applications. Toughening agents (such as SEBS) are used to improve the toughness of the composite material and prevent brittle fracture; the antioxidants and UV absorbers are used to ensure the stability of the material under long-term heat and light irradiation, preventing yellowing and performance degradation. Through the synergistic effect of the above components and their proportions, the light guide plate obtained by this invention possesses the following excellent properties: its heat distortion temperature (0.45MPa load) can reach 90℃ or higher; its total light transmittance can be maintained at a high level of over 85%; and its haze can be flexibly controlled within a wide range of 20% to 80% by adjusting the formulation (such as the content of crystalline phase, the type and amount of nucleating agent) and processing technology (such as mold temperature and cooling rate) to meet the needs of different application scenarios, from display backlights with high brightness requirements (usually requiring medium to low haze) to general lighting panels with higher uniformity requirements (usually requiring medium to high haze). In summary, the light guide plate of this invention possesses the following core characteristics: a heat distortion temperature (0.45MPa load) not lower than 90℃, a total light transmittance not lower than 85%, and an adjustable haze range of 20% to 80%. These characteristics enable it to simultaneously meet the requirements of high heat resistance, high luminous efficiency, and uniform light.

[0015] The present invention has the following beneficial effects: 1) Excellent optical performance, achieving integrated high light transmittance and uniform light distribution. This invention utilizes micron-sized, controllable crystallites of polystyrene induced by nucleating agents to form intrinsic scattering centers within a matrix. Compared to externally added inorganic / organic diffusing particles, these crystallites exhibit excellent compatibility with the matrix (also polystyrene), resulting in minimal interfacial light loss. This allows for superior light diffusion (adjustable haze from 20% to 80%) while maintaining a total light transmittance of over 85%, even approaching 90%. This overcomes the inherent problem of traditional diffusion schemes where the addition of external particles leads to a significant decrease in transmittance (typically below 85%). Furthermore, the light homogenization function is integrated with the light guide plate, simplifying the optical structure and improving luminous efficiency.

[0016] 2) Significantly improved heat resistance, breaking through the application temperature bottleneck of traditional polystyrene light guide plates. The introduction of crystalline polystyrene (especially syndiotactic polystyrene) and the resulting regular microcrystalline structure significantly improve the heat resistance of the material as a reinforcing phase. The light guide plate produced by this invention has a heat distortion temperature (0.45 MPa) exceeding 90°C, even surpassing 100°C, which is 20°C or more higher than that of traditional general-purpose polystyrene (GPPS) light guide plates (typically around 75-80°C). This enables its stable application in high-power, enclosed, and other high-temperature operating environments of LED lighting fixtures, fundamentally solving the industry problem of traditional GPPS light guide plates being prone to heat deformation and warping leading to failure.

[0017] 3) Low overall cost and outstanding cost-performance ratio The main substrate of this invention is inexpensive general-purpose polystyrene (GPPS). Although some crystalline polystyrene and a small amount of functional additives are used, the overall raw material cost is still far lower than that of heat-resistant engineering plastic polycarbonate (PC) and optical-grade polymethyl methacrylate (PMMA). At the same time, the integrated structure eliminates the need for additional diffusion layers, diffusion particles, or complex blending / coating processes in traditional solutions, further reducing material and manufacturing costs and providing the market with a highly competitive high-performance, low-cost light guide plate solution.

[0018] 4) Good synergy between materials and processes, simple processing and controllable performance. Crystalline polystyrene and amorphous polystyrene have similar chemical structures and good compatibility. Through the synergistic effect of nucleating agents, toughening agents, and matrix materials, not only is precise control over the size and distribution of crystallites achieved, thereby controlling optical properties, but the toughness of the material is also improved. The preparation process of this invention is fully compatible with existing general-purpose processing equipment for polystyrene plastics (such as extrusion and injection molding), requiring no special or expensive equipment. By adjusting key parameters such as the type / dosage of nucleating agents, mold temperature, and cooling rate, the core properties of the final product, such as haze and heat resistance, can be flexibly controlled within a wide range. The process window is wide, repeatability is good, and it is easy to achieve stable large-scale production.

[0019] 5) High product reliability and long service life By adding appropriate amounts of antioxidants and UV absorbers, the aging process of the material under long-term heat and light irradiation is effectively inhibited, preventing yellowing and embrittlement, ensuring the stability of the optical performance of the light guide plate throughout the entire life cycle of the lamp, and extending the product's service life. Attached Figure Description

[0020] Figure 1 This is a schematic diagram illustrating the optical working principle of the high-transmittance, high-temperature resistant polystyrene-based composite light guide plate in an embodiment of the present invention.

[0021] Figure 2 This is a SEM image of the high-transmittance, high-temperature resistant polystyrene-based composite light guide plate in an embodiment of the present invention. Detailed Implementation

[0022] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments, but the present invention is not limited to the embodiments.

[0023] Raw materials used in the examples and comparative examples: 1) Traditional amorphous polystyrene: general-purpose polystyrene, grade PG-33 (Chi Mei Industrial Co., Ltd.).

[0024] 2) Crystalline polystyrene: Syndiotactic polystyrene, grade XAREC 90ZC (produced by Idemitsu Kogyo, Japan).

[0025] 3) Nucleating agent A: Organophosphate nucleating agent, brand name NA-11 (Japan Adico).

[0026] 4) Nucleating agent B: Sorbitol derivative nucleating agent, brand name Millad NX8000 (Milliken, USA).

[0027] 5) Nucleating agent C: Sodium benzoate 6) Toughening agent: SEBS, grade YH-533 (Sinopec Baling) 7) Antioxidant: Pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], brand name 1010.

[0028] 8) Ultraviolet absorber: 2-(2′-hydroxy-3′-tert-butyl-5′-methylphenyl)-5-chlorobenzotriazole, brand name UV-326.

[0029] The main testing standards and methods in this invention are as follows: Heat distortion temperature: determined according to ISO 75-2 standard, under a bending load of 0.45 MPa.

[0030] Total light transmittance and haze: according to ASTM D1003 standard.

[0031] Light uniformity: An LED strip (3000K, 60mA) was installed on one side of the 200mm×200mm×3mm light guide plate sample. After it was stably lit in a dark room, the brightness values ​​of 9 evenly distributed points on the light surface were measured using a color luminance meter. The uniformity was calculated as (minimum brightness value / maximum brightness value) × 100%.

[0032] Notched impact strength of simply supported beams: determined according to ASTM D256 standard.

[0033] The general preparation process described in the examples is as follows: 1) Drying: Dry all raw materials in a 90℃ forced-air drying oven for 4 hours.

[0034] 2) Premix: Add each raw material to a high-speed mixer and mix for 5 minutes according to the weight ratio shown in Table 1 to obtain the premix.

[0035] 3) Melt blending and granulation: The premixed material is added to a co-rotating twin-screw extruder (length-to-diameter ratio 40:1). The temperatures of each section of the extruder are set as follows: Zone 1 200℃, Zone 2 230℃, Zone 3 240℃, and die head 235℃. After melt extrusion, the material is water-cooled and pelletized to obtain composite resin granules.

[0036] 4) Injection Molding: After drying the composite granules again at 90℃ for 4 hours, injection molding is performed using an injection molding machine. The injection molding process parameters are: barrel temperature 230℃, injection pressure 80MPa, holding time 15 seconds, and mold temperature 85℃. The molded sample is an optical test template with dimensions of 200mm×200mm×3mm.

[0037] Examples 1-3 and Comparative Examples 1-4 Different light guide plate samples were prepared according to the formula (unit: parts by weight) shown in Table 1 and the general process described above, and their performance was tested. The results are listed in Table 1.

[0038] Table 1: Formulations and Performance Test Results of Examples and Comparative Examples Group Raw materials (parts by weight) Heat distortion temperature (°C) Total light transmittance (%) Haze (%) Light uniformity (%) Notched impact strength (kJ / m²) Example 1 GPPS: 75, sPS: 25, NA-11: 0.2 96 89 48 93 2.1 Example 2 GPPS:70,sPS: 30,NA-11: 0.2,SEBS: 5 99 87 62 95 4.8 Example 3 GPPS:65,sPS:35,NX8000: 0.5,SEBS: 8 101 85 75 94 5.5 Example 4 GPPS: 72, SPS: 28, Sodium Benzoate: 0.4%, SEBS: 3 92 88 52 91 4.6 Comparative Example 1 GPPS: 100 76 92 2 65 2.0 Comparative Example 2 <![CDATA[GPPS:94,SiO2: 6]]> 78 84 88 92 1.8 Comparative Example 3 sPS: 100, NA-11: 0.2 102 88 50 89 1.5

[0039] The above examples and comparative data fully demonstrate that the present invention, through a specific ratio and synergistic design of crystalline polystyrene / amorphous polystyrene / nucleating agent / toughening agent, coupled with an optimized processing technology, has successfully prepared an integrated light guide plate that combines high light transmittance (≥85%), high heat resistance (HDT≥90℃), good toughness, and flexible controllable optical performance.

Claims

1. A high-transmittance, high-temperature resistant polystyrene-based composite light guide plate, characterized in that, It is made from raw materials in parts by weight: 20-50 parts crystalline polystyrene, 50-80 parts traditional amorphous polystyrene, 0.1-1 parts nucleating agent, 2-8 parts toughening agent, 0.1-0.5 parts antioxidant, and 0.1-0.5 parts ultraviolet absorber; wherein, the nucleating agent induces the crystalline polystyrene to form microcrystals with an average particle size of 0.5-10 μm in the traditional amorphous polystyrene matrix. These microcrystals serve as light scattering points, enabling the light guide plate to simultaneously possess light transmission and light diffusion functions.

2. The high-transmittance, high-temperature resistant polystyrene-based composite light guide plate according to claim 1, characterized in that, The crystalline polystyrene mentioned is syndiotactic polystyrene, abbreviated as SPS.

3. The high-transmittance, high-temperature resistant polystyrene-based composite light guide plate according to claim 1, characterized in that, The nucleating agent is one or a combination of organophosphates, sorbitol derivatives, aromatic carboxylates, or inorganic nanoparticles.

4. The high-transmittance, high-temperature resistant polystyrene-based composite light guide plate according to claim 1, characterized in that, The toughening agent is a styrene-based thermoplastic elastomer.

5. The high-transmittance, high-temperature resistant polystyrene-based composite light guide plate according to claim 4, characterized in that, The styrene-based thermoplastic elastomer is a hydrogenated styrene-butadiene-styrene block copolymer, a styrene-butadiene-styrene block copolymer, or a styrene-isoprene-styrene block copolymer.

6. The high-transmittance, high-temperature resistant polystyrene-based composite light guide plate according to claim 1, characterized in that, The light guide plate has a heat distortion temperature of not less than 90°C under a load of 0.45MPa, a total light transmittance of not less than 85%, and a haze of 20% to 80%.

7. A method for preparing a high-transmittance, high-temperature resistant polystyrene-based composite light guide plate as described in any one of claims 1-6, characterized in that, Includes the following steps: S1: Weigh each raw material according to the formula and dry it at 80-100℃ for 3-6 hours; S2: Mix the dried raw materials evenly to obtain a premix; S3: The premixed material is melt-blended at 200-260°C, then extruded, cooled and granulated to obtain composite resin granules; S4: After drying the composite resin granules, injection molding is performed at an injection temperature of 220-250℃ and a mold temperature of 70-90℃. After cooling, a high-transmittance, high-temperature resistant polystyrene-based composite light guide plate is obtained.

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