Light diffusion polystyrene composite material with low thermal expansion coefficient as well as preparation and application thereof

Abstract

The invention discloses a light diffusion polystyrene composite material with a low thermal expansion coefficient, a preparation method thereof and an application of the light diffusion polystyrene composite material in extrusion molding of a frameless television display screen backlight plate. The composite material is prepared from the following raw materials in parts by mass: 35 to 45 parts of GPPS (General Purpose Polystyrene) resin, 20 to 30 parts of HIPS (High Impact Polystyrene) resin, 8 to 15 parts of PPO (Polyphenylene Oxide) resin, 3 to 5 parts of compatilizer, 5 to 10 parts of light diffusant, 5 to 15 parts of filling mineral and 3 to 5 parts of liquid crystal polymer fiber, the filling minerals comprise one or more than two of high-whiteness nano synthetic mica, nano boehmite and magnesium sulfate whiskers; the whiteness L value of the high-whiteness nano synthetic mica is gt; 92; the average length of the magnesium sulfate whisker is 10-60 [mu] m, and the length-diameter ratio is gt; 30.

Description

Technical Field

[0001] This invention relates to the field of light-diffusing polystyrene composite materials, specifically to a polystyrene composite material with a low coefficient of thermal expansion (CTE) and high light diffusion performance, suitable for applications such as LED lighting devices and optical display panels where dimensional stability and optical uniformity are critical. Background Technology

[0002] As a core optical component of modern display and lighting systems, light diffuser plates play a crucial role in transforming point or line light sources into uniform surface light sources.

[0003] Polystyrene (PS)-based light diffuser plates dominate the display industry due to their excellent optical transparency, ease of processing and molding, and cost-effectiveness. Compared to alternative materials such as polycarbonate (PC) and polymethyl methacrylate (PMMA), polystyrene possesses an ideal refractive index range of 1.59-1.60, high light transmittance of over 90%, and controllable haze adjustment capabilities, allowing for precise matching of the optical design requirements of LCD backlight modules. In terms of market size, global demand for PS light diffuser plates is showing a steady growth trend, with television applications accounting for 65%. In particular, the accelerated commercialization of Mini-LED direct-view display technology has placed even more stringent demands on the overall performance of PS light diffuser plates in the application of display backlights.

[0004] Traditional polystyrene diffusion plates have revealed a series of technical bottlenecks in practical applications, mainly manifested in three key performance defects: excessively high coefficient of thermal expansion (CTE), insufficient dimensional stability, and mechanical property degradation under high temperature conditions.

[0005] Patent specification CN103073805A discloses a high-impact-strength light-diffusing polystyrene material and its preparation method. The material is composed of 90-96% polystyrene resin, 3-8% K-resin, 0.4-1% light-diffusing agent, 0.2-0.4% lubricant, and 0.1-0.2% antioxidant. This patented technology aims to address the problem that introducing a light-diffusing agent into PS material further reduces its toughness, leading to cracking and reduced product quality in LED lighting products. It improves the material's toughness while maintaining high haze and high light transmittance, without addressing the issue of reducing the coefficient of thermal expansion of PS material.

[0006] Patent specification CN114410023A discloses a polystyrene material, its preparation method, and its applications. The purpose of this patent is to provide a polystyrene material capable of foaming to generate a cell structure with specific parameters, resulting in products with high light transmittance and effective diffusion capabilities, as well as good rigidity and resistance to deformation. While the specification describes increasing rigidity to address material deformation, the core issue of reducing the material's coefficient of thermal expansion is not considered. When the backlight is on for extended periods, the internal temperature of the entire display device rises rapidly, and the deformation problem of the light-diffusing sheet cannot be completely resolved.

[0007] Patent specification CN114031864A discloses a light-diffusing polystyrene composite material and its preparation method. This patented technology uses sodium sulfate micropowder mixed with boron oxide micropowder, and incorporates a light-diffusing agent and stearate to replace traditional inorganic light-diffusing agents. Compared to traditional inorganic light-diffusing agents, this significantly reduces the amount of light-diffusing agent added. Its effect on the light transmittance and haze modification of PS materials is essentially the same as that of organic light-diffusing agents. The main advantage is a substantial reduction in material production costs. However, the low coefficient of thermal expansion and dimensional stability of the light-diffusing PS material are not investigated.

[0008] Therefore, based on the shortcomings of existing light-diffusing PS materials, this invention develops a low thermal expansion coefficient light-diffusing polystyrene composite material suitable for direct-lit backlight modules to solve the dimensional stability problem of backlight panels under high and low temperature operating conditions. Summary of the Invention

[0009] As mentioned in the background section, existing light-diffusing PS materials suffer from key performance defects, with traditional light-diffusing PS exhibiting a CTE as high as (60~80)×10⁻⁶. -6 / K, is prone to warping and deformation under temperature fluctuations, leading to problems with the dimensional stability of the parts; carbon fiber / glass fiber reinforcement can reduce CTE, but it results in decreased light transmittance (<50%) and uneven haze; single nanofillers (such as nano-clay) can suppress expansion, but they are prone to agglomeration and the generation of light spots. This invention provides a low thermal expansion coefficient light-diffusing polystyrene composite material, its preparation method, and its application. The physical properties of the low thermal expansion coefficient light-diffusing polystyrene composite material of this invention can achieve CTE≤52×10 -6 With a density of 6K, haze >93%, and light transmittance >70%, it is used for extrusion sheet processing to meet the stringent requirements of optical display panels for the dimensional stability and optical uniformity of PS diffusion materials.

[0010] The specific technical solution is as follows: In a first aspect, the present invention provides a light-diffusing polystyrene composite material with a low coefficient of thermal expansion, comprising, by mass parts: 35-45 parts (e.g., 40 parts) of GPPS resin, 20-30 parts (e.g., 25 parts) of HIPS resin, 8-15 parts (e.g., 10 parts) of PPO resin, 3-5 parts of compatibilizer, 5-10 parts of light-diffusing agent, 5-15 parts (e.g., 9 parts, 10 parts) of filler mineral, and 3-5 parts of liquid crystal polymer (LCP) fiber. The filling minerals include one or more of high-whiteness nano-synthetic mica, nano-boehmite, and magnesium sulfate whiskers; the whiteness L value of the high-whiteness nano-synthetic mica is >92; the average length of the magnesium sulfate whiskers is 10~60μm and the aspect ratio is >30.

[0011] Low thermal expansion coefficient light-diffusing polystyrene composites require a certain level of light transmittance and haze while also possessing a low thermal expansion coefficient to meet the dimensional stability requirements for use in backlight panels. The rigidity of the polystyrene molecular chain in the base resin makes it prone to orientation along the molding flow direction, leading to cracking of the extruded sheet when cut along this orientation direction and resulting in defective parts. Therefore, in addition to selecting high-transmittance GPPS resin, HIPS needs to be compounded to improve the overall toughness of the material and address the balance between optical performance and material brittleness. Adding 8%~15% (based on the total mass of GPPS resin, HIPS resin, PPO resin, compatibilizer, light diffusing agent, filler minerals, and liquid crystal polymer fibers as 100%) of PPO resin is beneficial because PS and PPO have good compatibility at the molecular level. The resulting PPO / PS alloy effectively combines the advantages of both, significantly reducing the CTE of the material system, improving heat resistance and dimensional stability, while maintaining relatively good processing fluidity and lower cost.

[0012] The uniform and soft diffusion of light in PS materials is mainly due to light diffusing agents. Nano-filled minerals (high-whiteness nano-synthetic mica, nano-boehmite) also have a certain light-diffusing effect and can increase the material's heat distortion temperature. They also serve as filler systems for PS with low thermal expansion coefficients. However, it is difficult for PS materials with only added filler minerals to achieve a thermal expansion coefficient of ≤52×10 in both the longitudinal and transverse directions. -6 / K, adding 3%~5% (based on the total mass of GPPS resin, HIPS resin, PPO resin, compatibilizer, light diffusing agent, filler minerals and liquid crystal polymer fibers as 100%) of liquid crystal polymer fibers can suppress anisotropic expansion and further reduce the coefficient of thermal expansion.

[0013] This invention provides a light-diffusing polystyrene composite material with a low coefficient of thermal expansion. While maintaining high light diffusion efficiency (high haze), good light transmittance / brightness, and excellent processing fluidity, this material has a significantly reduced coefficient of thermal expansion and a higher heat distortion temperature, overcoming the shortcomings of the prior art and meeting the requirements for dimensional stability and optical uniformity of backlight panels under high and low temperature conditions.

[0014] Preferably, the total mass fraction of GPPS resin, HIPS resin, PPO resin, compatibilizer, light diffusing agent, filler minerals, and liquid crystal polymer fibers is 100 parts.

[0015] Preferably, the GPPS resin is transparent white.

[0016] Preferably, the GPPS resin has a light transmittance of >90% at 1mm and a melt index of 5~8g / 10min at 200℃ and 5kg.

[0017] Preferably, the HIPS resin is milky white in color.

[0018] Preferably, the HIPS resin has a light transmittance of >65% over 1mm and a notched impact strength of >11KJ / m. 2 The melt index at 200℃ and 5kg is 5~10g / 10min, for example 5.5g / 10min.

[0019] Preferably, the PPO resin is milky white in color.

[0020] Preferably, the PPO resin has a light transmittance of >50% over 1mm and a notched impact strength of >15KJ / m. 2 The melt index at 280℃ and 5kg is 8~20g / 10min.

[0021] Preferably, the compatibilizer comprises SEBS-grafted maleic anhydride (SEBS-MAH).

[0022] Preferably, the SEBS-grafted maleic anhydride particles are transparent.

[0023] Preferably, the maleic anhydride grafting rate of the SEBS grafted maleic anhydride is 1.4% to 2%.

[0024] Preferably, the light diffusing agent comprises core-shell organosilicon microspheres.

[0025] Preferably, the core layer of the core-shell organosilicon microspheres is cross-linked silicone resin, and the shell layer is methylphenylsiloxane. Preferably, the hardness of the cross-linked silicone resin is 75-80D. Preferably, the refractive index of the methylphenylsiloxane is 1.52.

[0026] Preferably, the particle size of the nanoboehmite is 10~15 nm.

[0027] The nano-boehmite and / or the high-whiteness nano-synthetic mica are pre-treated with a silane coupling agent (preferably including KH-570, etc.) and a dispersing solvent (preferably including ethanol, etc.) to perform surface activation modification treatment, thereby increasing compatibility with PS substrate.

[0028] Preferably, the filler minerals include high-whiteness nano-synthetic mica, nano-boehmite, and magnesium sulfate whiskers. Further, the mass ratio of the high-whiteness nano-synthetic mica, nano-boehmite, and magnesium sulfate whiskers is preferably 1~3:1~3:1~3, more preferably 2.5~3:1.5~2:1, and even more preferably 2.9~3:1.9~2:1. The high-whiteness nano-synthetic mica, with its layered structure, is the main component responsible for reducing lateral expansion (CTE). The nano-boehmite, containing hydroxyl groups, also has a layered structure that helps enhance interfacial bonding. The magnesium sulfate whiskers, with their specific length and aspect ratio, provide excellent longitudinal support through a fibrous framework structure. This optimized mass ratio of high-whiteness nano-synthetic mica:nano-boehmite:magnesium sulfate whiskers, combined with a network of sheet-like structures and fibers, can effectively limit the thermal motion of polymer chains in multiple dimensions, thereby more effectively reducing the CTE value of the material.

[0029] Preferably, the melting range of the liquid crystal polymer fiber is 280-320°C.

[0030] Preferably, the linear density of the liquid crystal polymer fiber is 105~115 dtex and the aspect ratio is ≥30.

[0031] Preferably, the raw material composition further includes 0.5 to 1 part of processing aids.

[0032] Preferably, the processing aid includes one or more of a primary antioxidant, a secondary antioxidant, and a lubricant. The primary antioxidant preferably includes antioxidant 1010. The secondary antioxidant preferably includes antioxidant 168. The lubricant preferably includes pentaerythritol stearate (PETS).

[0033] Preferably, in the processing aid, the mass ratio of the primary antioxidant to the secondary antioxidant is 1:2.

[0034] In a second aspect, the present invention provides a method for preparing the low thermal expansion coefficient light-diffusing polystyrene composite material described in the first aspect, comprising: mixing raw materials other than the liquid crystal polymer fiber and the magnesium sulfate whiskers to obtain a premix; feeding the premix into the main feed port of a twin-screw extruder; adding the liquid crystal polymer fiber or the liquid crystal polymer fiber and the magnesium sulfate whiskers from the middle side feed port of the melt section of the twin-screw extruder; controlling the temperature of the twin-screw extruder at 180~230℃ (preferably 180~220℃); and after the molten material is mixed and plasticized, extruded and granulated, cooled, and dried to obtain low thermal expansion coefficient light-diffusing polystyrene composite plastic granules.

[0035] Preferably, the main motor speed of the twin-screw extruder is 280~320 rpm.

[0036] Thirdly, the present invention provides the application of the low thermal expansion coefficient light-diffusing polystyrene composite material described in the first aspect or the low thermal expansion coefficient light-diffusing polystyrene composite material plastic granules prepared by the preparation method described in the second aspect for extrusion molding of frameless TV display screen backlight panels, which is suitable for direct-lit backlight modules to solve the problems of dimensional stability and optical uniformity of backlight panels under high and low temperature working conditions.

[0037] Existing technical pain points: The CTE of pure PS or ordinary light-diffusing PS is as high as (60~80)×10. -6 While adding conventional fillers (such as glass fiber and mineral powder) can reduce CTE, it often sacrifices light transmittance (down to <50%) or leads to uncontrolled haze. Organic light diffusing agents have limited effect on improving CTE.

[0038] Compared with the prior art, the beneficial effects of this invention are as follows: This invention uses a compound PPO, selects specific filling minerals, and combines it with LCP fibers to maintain high light transmittance (T>70%) while synergistically reducing the CTE effect of the material. The CTE is reduced by more than 40% compared with pure PS-based materials. It achieves a breakthrough ultra-low coefficient of thermal expansion (CTE) and dimensional stability, as well as an excellent balance between light diffusion performance and light transmittance.

[0039] Conventional PS has a heat distortion temperature (HDT) of only 70-80°C, making it prone to deformation and failure at high temperatures. The PS material of this invention has an HDT > 90°C, which greatly improves its heat resistance and reliability, solving the problems of heat deformation, warping, and yellowing failure of traditional PS light diffusion plates, and significantly improving its lifespan and reliability. Attached Figure Description

[0040] Figure 1 Photographs of light-diffusing PS backlight panels cut from the low thermal expansion coefficient light-diffusing polystyrene composite material of Example 4 after extrusion molding. Detailed Implementation

[0041] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Operating methods not specifically specified in the following embodiments are generally performed under conventional conditions or as recommended by the manufacturer.

[0042] Unless otherwise specified, all embodiments and comparative examples were injection molded into corresponding standard specimens or parts according to standard requirements and tested. Tensile strength conformed to GB / T 1040 standard. Flexural strength and flexural modulus conformed to GB / T 9341 standard. Cantilever beam notched impact strength conformed to GB / T 1843 standard. Heat distortion temperature (HDT) conformed to GB / T 1634 standard, 0.45MPa. Light transmittance and haze conformed to GB / T2410 standard. Coefficient of thermal expansion (CTE) conformed to GJB 332A standard. Cyclic thermal stability test: 100mm×100mm×1.5mm square plates were subjected to 100 cycles of hot and cold (the sample was kept at -40℃ for 30 minutes in a low-temperature chamber, and then rapidly transferred to a high-temperature chamber at 90℃ for 30 minutes as one cycle), and then cooled to room temperature for 24 hours before the dimensional change rate was tested (the absolute values ​​of the change rates of the four side lengths were averaged).

[0043] The raw materials used in the various embodiments and comparative examples of this invention are as follows: GPPS resin: GPPS1050 (200℃, 5kg melt index 5g / 10min), INEOS styrene resin; transparent white base color; 1mm light transmittance >90%.

[0044] HIPS resin: HIPS8250 (200℃, 5kg melt index 5.5g / 10min), Ningbo Taihua; color: milky white; light transmittance >65% at 1mm; notched impact strength >11KJ / m². 2 .

[0045] PPO resin: NORYL™ 7310 resin, SABIC Basic Chemicals; color: milky white; light transmittance >50% at 1mm; cantilever beam notched impact strength >15KJ / m 2 The melt index at 280℃ and 5kg is 8~20g / 10min.

[0046] Compatibilizer SEBS-MAH: FG 1901, Kraton, USA; transparent particles; maleic anhydride grafting rate 1.4%~2%.

[0047] Core-shell organosilicon microspheres: Core layer cross-linked silicone resin (hardness 75~80D), shell layer methylphenylsiloxane (refractive index 1.52) specifications customized, Maisong Chemical Materials Co., Ltd.

[0048] Nano-boehmite: crystal grain size (120-reflex) 10~15nm, Xuancheng Jingrui New Materials Co., Ltd.

[0049] High-whiteness nano-synthetic mica: GHM-3, Anhui Gree New Material Technology Co., Ltd.; whiteness L value > 92.

[0050] Nano talc: HTP Ultra 5L, from Imfabi, Italy.

[0051] High-whiteness nano-barium sulfate: LZ-998, Guangxi Lianzhuang Technology Co., Ltd.; whiteness L value ≥98, average particle size 1.0~1.2μm.

[0052] Magnesium sulfate whiskers: NP-YW2, Fengzhu Technology; average length 10~60μm, aspect ratio L / D>30.

[0053] Liquid crystal polymer (LCP) fiber: copolymen® short fiber, Ningbo Juji New Material Technology Co., Ltd.; melting range 280-320℃, linear density 105~115dtex, aspect ratio ≥30.

[0054] Short-cut glass fiber for thermoplastics: ECS306-3-K, Chongqing International Composite Materials Co., Ltd.

[0055] Processing aids: Primary antioxidant Irganox 1010 (hindered phenol), BASF, Germany; Secondary antioxidant Irganox 168 (organophosphite), BASF, Germany; Lubricant PETS-AHS, FAG, Italy.

[0056] The following embodiment describes a method for preparing a light-diffusing polystyrene composite material with a low coefficient of thermal expansion, comprising the following steps: (1) Take nano-filled mineral nano-boehmite and / or high white nano-synthetic mica, add 0.6% KH-570 and 0.2% ethanol by mass fraction (based on the total mass of nano-boehmite and / or high white nano-synthetic mica as 100%) and mix at high speed (1000 rpm) for 5 min to activate surface modification treatment for later use.

[0057] (2) Weigh the raw materials according to Table 1 (unit is parts by weight) the parts by weight of GPPS resin, HIPS resin, PPO resin, compatibilizer SEBS-MAH, core-shell organosilicon microspheres, and nano-filled minerals that have undergone surface treatment in step (1) and each processing aid.

[0058] (3) Add the weighed raw materials of each component in step (2) into the high-speed mixer and mix evenly (mixing speed: 800 rpm, mixing time 1.5 min) to make a premix.

[0059] (4) The premixed material is added to the main feed port of the twin-screw extruder by loss-in-weight weighing. The liquid crystal polymer fiber or liquid crystal polymer fiber and magnesium sulfate whiskers are added from the middle side feed port of the extruder by loss-in-weight weighing. The material is melt-extruded through the extruder at a temperature of 180~220℃ and a main machine speed of 280~320rpm. Then, the material is cooled in a water tank, dried, granulated, mixed, and packaged to obtain the product PS composite plastic granules.

[0060] Preparation of test standard specimens and other components: The obtained PS composite plastic granules were placed in a forced-air drying oven and dried at 85°C for 2 hours. Then, they were injection molded to prepare test specimens and 1mm test plates for light transmittance and haze, as well as 100mm×100mm×1.5mm square plates, etc., for performance index testing. The performance test results of the example are shown in Table 2.

[0061] Table 1 Table 2 The following comparative example illustrates a method for preparing a light-diffusing polystyrene composite material, comprising the following steps: (1) The nano-filled minerals involved in Table 3 are prepared according to step (1) of the preparation method in the example and are activated by surface modification treatment for later use.

[0062] (2) Weigh the raw materials according to Table 3 (unit: parts by weight) the GPPS resin, HIPS resin, PPO resin, compatibilizer SEBS-MAH, core-shell organosilicon microspheres, and nano-filled minerals that have undergone surface treatment in step (1) and each processing aid; then, according to the method of steps (3) and (4) in the preparation method of the example, add thermoplastic plastics with chopped glass fibers or LCP fibers in proportion by loss weighing from the middle side feed port of the extruder to prepare light-diffusing polystyrene composite material.

[0063] The preparation of test standard specimens and other components was the same as in the example. The performance test results of the comparative example are shown in Table 4.

[0064] Table 3 Table 4 The following conclusions can be drawn from the experimental data in each table: The experimental data from Examples 1 to 3 show that as the content of GPPS decreases, the content of HIPS increases accordingly. The rigidity of the PS composite material increases, the toughness decreases, the HDT, light transmittance, and cyclic thermal stability increase, and the coefficient of thermal expansion decreases slightly. Therefore, the ratio of GPPS to HIPS should be balanced according to the application requirements.

[0065] Comparing Example 1 with Examples 4 and 5, it can be seen that, under the same formulation ratio, the single-filler mineral synthesized mica GHM-3 has a lower coefficient of thermal expansion than nano-boehmite and magnesium sulfate whiskers in contributing to the PS composite material. At the same time, the material has a smaller dimensional change rate in cyclic thermal stability, and the micro-layered structure of fluorophlogopite has a smaller coefficient of thermal expansion.

[0066] Comparing Examples 4 with Examples 6 and 7, it can be seen that, under the same mineral addition conditions, the mass ratio of high-whiteness nano-synthetic mica, nano-boehmite, and magnesium sulfate whiskers of approximately 3:2:1 achieves a network of sheet-like + sheet-like + fiber structures. This can restrict the thermal movement of polymer chains in multiple dimensions, thereby more effectively reducing the CTE value of the material. This is superior to using a single filler mineral or a mass ratio of three filler minerals of approximately 1:1:1 to reduce the coefficient of thermal expansion of PS materials.

[0067] Comparing Example 6 with Example 8, it can be seen that increasing the PPO content in the material system can comprehensively improve the overall mechanical properties, toughness, heat distortion temperature, longitudinal and transverse thermal expansion coefficients, and dimensional stability of the PS composite material, but the light transmittance will decrease. The ratio should be adjusted appropriately according to the material cost requirements.

[0068] Compared with Examples 1 and 4, and Comparative Examples 1 and 2, it can be found that, under the same formulation ratio, the effect of filling mineral nano-talc powder and high-whiteness nano-barium sulfate on reducing the thermal expansion coefficient of PS material is much lower than that of synthetic mica GHM-3 and nano-boehmite. Synthetic mica has a complete layered crystal structure, and nano-boehmite constrains the movement of molecular chains through hydrogen bond networks, exhibiting a superior low expansion coefficient.

[0069] The comparison between Example 4 and Comparative Example 3 further verifies that the removal of PPO from the PS composite material system results in a significant and drastic decrease in the material's mechanical properties and dimensional stability, while the coefficient of thermal expansion increases substantially.

[0070] The comparison between Example 4 and Comparative Examples 4 and 6 verifies the differences between LCP fiber and conventional glass fiber. LCP fiber has better compatibility with the substrate as a skeleton in PS composite material, relatively more outstanding mechanical strength, and smaller difference in CTE values ​​in the longitudinal and transverse directions. Although glass fiber can reduce the CTE value of PS material, the material orientation is serious, and the large difference in CTE values ​​in the longitudinal and transverse directions has an adverse effect on dimensional stability.

[0071] A comparison of Example 8 and Comparative Example 5 reveals that the compatibilizer SEBS grafted with maleic anhydride can effectively improve the compatibility of the PPO / PS alloy matrix, significantly enhance the interfacial bonding ability between the resin matrix and the filled minerals and LCP fibers, result in a lower CTE value for the material, and improve the overall mechanical properties and dimensional stability.

[0072] Figure 1 The image shows a photograph of a light-diffusing PS backlight panel cut from a low thermal expansion coefficient light-diffusing polystyrene composite material extruded according to Example 6.

[0073] Furthermore, it should be understood that after reading the above description of the present invention, those skilled in the art can make various alterations or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims.

Claims

1. A light-diffusing polystyrene composite material with a low coefficient of thermal expansion, characterized in that, By mass, the raw material composition includes: 35-45 parts GPPS resin, 20-30 parts HIPS resin, 8-15 parts PPO resin, 3-5 parts compatibilizer, 5-10 parts light diffusing agent, 5-15 parts filler mineral, and 3-5 parts liquid crystal polymer fiber. The filling minerals include one or more of high-whiteness nano-synthetic mica, nano-boehmite, and magnesium sulfate whiskers; the whiteness L value of the high-whiteness nano-synthetic mica is >92; the average length of the magnesium sulfate whiskers is 10~60μm and the aspect ratio is >30.

2. The low thermal expansion coefficient light-diffusing polystyrene composite material according to claim 1, characterized in that, The total mass fraction of GPPS resin, HIPS resin, PPO resin, compatibilizer, light diffusing agent, filler minerals, and liquid crystal polymer fibers is 100 parts. The GPPS resin is transparent white; the GPPS resin has a light transmittance of >90% at 1mm and a melt index of 5~8g / 10min at 200℃ and 5kg. The HIPS resin is milky white in color; the HIPS resin has a light transmittance of >65% over 1mm and a notched impact strength of >11KJ / m². 2 The melt index at 200℃ and 5kg is 5~10g / 10min; The PPO resin is milky white in color; the PPO resin has a light transmittance of >50% over 1mm and a notched impact strength of >15KJ / m². 2 The melt index at 280℃ and 5kg is 8~20g / 10min.

3. The low thermal expansion coefficient light-diffusing polystyrene composite material according to claim 1, characterized in that, The compatibilizer includes SEBS grafted maleic anhydride; The SEBS-grafted maleic anhydride particles are transparent; The maleic anhydride grafting rate of the SEBS grafted maleic anhydride was 1.4% to 2%.

4. The low thermal expansion coefficient light-diffusing polystyrene composite material according to claim 1, characterized in that, The light diffusing agent comprises core-shell organosilicon microspheres; The core layer of the core-shell organosilicon microspheres is cross-linked silicone resin, and the shell layer is methylphenylsiloxane. The hardness of the cross-linked silicone resin is 75~80D; The refractive index of the methylphenylsiloxane is 1.

52.

5. The low thermal expansion coefficient light-diffusing polystyrene composite material according to claim 1, characterized in that, The particle size of the nanoboehmite is 10~15 nm; The nano-boehmite and / or the high-whiteness nano-synthetic mica are pre-treated by mixing and stirring with a silane coupling agent preferably including KH-570 and a dispersion solvent preferably including ethanol for surface activation modification. The filling minerals include high-whiteness nano-synthetic mica, nano-boehmite, and magnesium sulfate whiskers; In the filling mineral, the mass ratio of the high-whiteness nano-synthetic mica, nano-boehmite and magnesium sulfate whiskers is 1~3:1~3:1~3, more preferably 2.5~3:1.5~2:1, and even more preferably 2.9~3:1.9~2:

1.

6. The low thermal expansion coefficient light-diffusing polystyrene composite material according to claim 1, characterized in that, The melting range of the liquid crystal polymer fiber is 280-320℃; The linear density of the liquid crystal polymer fiber is 105~115 dtex, and the aspect ratio is ≥30.

7. The low thermal expansion coefficient light-diffusing polystyrene composite material according to any one of claims 1 to 6, characterized in that, The raw material composition also includes 0.5 to 1 part of processing aids; The processing aids include one or more of a primary antioxidant, a secondary antioxidant, and a lubricant; the primary antioxidant includes antioxidant 1010; the secondary antioxidant includes antioxidant 168; and the lubricant includes pentaerythritol stearate.

8. The low thermal expansion coefficient light-diffusing polystyrene composite material according to claim 7, characterized in that, In the processing aid, the mass ratio of the primary antioxidant to the secondary antioxidant is 1:

2.

9. The method for preparing the low thermal expansion coefficient light-diffusing polystyrene composite material according to any one of claims 1 to 8, characterized in that, include: The raw materials, excluding the liquid crystal polymer fiber and the magnesium sulfate whiskers, are mixed to obtain a premix. The premix is ​​fed into the main feed port of a twin-screw extruder. The liquid crystal polymer fiber or the liquid crystal polymer fiber and the magnesium sulfate whiskers are added from the side feed port in the middle of the melting section of the twin-screw extruder. The temperature of the twin-screw extruder is controlled at 180~230℃. After the molten material is mixed and plasticized, it is extruded, granulated, cooled, and dried to obtain low thermal expansion coefficient light-diffusing polystyrene composite plastic granules.

10. The low thermal expansion coefficient light-diffusing polystyrene composite material according to any one of claims 1 to 8, or the low thermal expansion coefficient light-diffusing polystyrene composite material plastic granules prepared by the preparation method according to claim 9, are used for extrusion molding of frameless TV display screen backlight panels.

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