A light diffusion plate with low thermal expansion coefficient and a method for manufacturing and using the same

Abstract

The present application relates to a kind of low thermal expansion coefficient light diffusion plate preparation method, comprising the following steps: the composition comprising PPO resin, ethylene-alpha-olefin copolymer, polyacrylic acid resin microspheres, foaming agent is stirred uniformly after heating to obtain the mixture of molten state process;With the process of multilayer co-extrusion casting process, the molten state mixture is co-extruded to obtain light diffusion plate process.The light diffusion plate prepared by the preparation method provided by the present application has low thermal expansion coefficient, can meet the strict requirements of dimensional stability and optical uniformity under high and low temperature working conditions.

Description

Technical Field

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

[0002] This section provides background information relevant to this application, which does not necessarily constitute prior art.

[0003] As a core optical component of modern display and lighting systems, light diffusers play a crucial role in transforming point or line light sources into uniform surface light sources. When light generated by a light source passes through a light diffuser and encounters a medium (diffusing particles) with a different refractive index, the light undergoes refraction, reflection, and scattering at multiple angles and in multiple directions, thereby achieving a more uniform and comfortable light output effect.

[0004] Existing materials for preparing light diffusion plates include polycarbonate (PC), polystyrene (GPPS), and polypropylene (PP). Among them, PC has insufficient hardness, is easily scratched, is not corrosion-resistant, is not UV-resistant, and is prone to aging; GPPS has excellent electrical insulation and its light transmittance is second only to plexiglass, but it is highly brittle, has poor solvent resistance, a large coefficient of thermal expansion, and is prone to internal stress. Under long-term use and the heat from the light source, the diffusion plate is prone to deformation due to heat; PP has low temperature resistance, high shrinkage, low rigidity, and high warpage. It will vitrify at low temperatures, and its impact resistance will decrease significantly.

[0005] Polyphenylene oxide (PPO) is a thermoplastic material characterized by a high glass transition temperature, good mechanical properties, dimensional stability, and flame retardancy. Furthermore, it exhibits excellent long-term chemical resistance, is free from stress cracking, does not readily decompose in water, and has good heat aging resistance, making it a potential substrate for light diffusion plates. However, research has found that simply replacing GPPS resin with PPO resin results in light diffusion plates with very poor light diffusion performance. Possible reasons include: firstly, the refractive index mismatch between PPO resin and existing light diffusing agents leads to poor light diffusion; secondly, poor compatibility between existing light diffusing agents and PPO resin causes aggregation and uneven distribution of the existing agents, further resulting in poor light diffusion. Summary of the Invention

[0006] The present invention aims to provide a light diffusion plate with a low coefficient of thermal expansion, wherein the CTE of the light diffusion plate is not greater than 52 × 10⁻⁶. - 6cm / cm℃ (CTE of existing GPPS resin-based light diffusion plates is as high as approximately 60 × 10⁻⁶ cm / cm℃) -6 cm / cm℃ Approximately 80×10 -6 The light diffuser plate also meets the following requirements: haze not less than 95% and light transmittance not less than 45%. The light diffuser plate can meet the stringent requirements of dimensional stability and optical uniformity under high and low temperature working conditions.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: a method for preparing a light diffusion plate with a low coefficient of thermal expansion, comprising the following steps: The process involves stirring a composition containing PPO resin, ethylene-α-olefin copolymer, polyacrylic acid resin microspheres, and a foaming agent until homogeneous, and then heating it to obtain a molten mixture. The process of co-extruding a molten mixture to obtain a light diffusion plate using a multi-layer co-extrusion casting film process.

[0008] The composition comprises, by weight parts: 90-110 parts of PPO resin; 3-8 parts of polyacrylic acid resin microspheres; 5-10 parts of ethylene-α-olefin copolymer 0.2-1 parts of foaming agent.

[0009] The PPO resin meets the following requirements: it is milky white in appearance, has a light transmittance of not less than 60% per 1mm, and a notched impact strength of not less than 17KJ / m². 2 The melt index at 280℃ and 5kg is 15-20g / 10min, and the intrinsic viscosity is 39.5-41.5mL / g (tested according to GB / T1632.1-2008 standard, with chloroform as the solvent).

[0010] The polyacrylic acid resin microspheres have good compatibility with PPO resin, and the dispersibility of the polyacrylic acid resin microspheres in PPO resin can be improved by adding ethylene-α-olefin copolymer. The polyacrylic acid resin microspheres can act as a light diffusing agent to significantly improve the haze and light transmittance of the light diffusing plate.

[0011] Preferably, the polyacrylic resin microspheres are low-expansion polyacrylic resin microspheres. Based on micromechanical property testing, the polyacrylic resin microspheres meet the following requirements: compressibility ≤20% and expansion ≤20%. The polyacrylic acid resin microspheres can be prepared using existing technologies (including homogenization emulsification, suspension polymerization, microfluidics, etc.). For example, the preparation method of the polyacrylic acid resin microspheres is as follows: acrylic acid, ethylene / acrylic acid / VA copolymer, initiator (at least one of ammonium persulfate, potassium persulfate, and water-soluble azo initiator), and crosslinking agent (1,3-butanediol dimethacrylate and / or 1,4-butanediol dimethacrylate) are mixed in water to obtain a dispersed phase solution; a surfactant (at least one of Span 85, Tween 80, and Tween 85) is dissolved in an oil phase (vegetable oil or mineral oil) to obtain a continuous phase solution; the dispersed phase solution and the continuous phase solution are mixed into droplets using a microfluidic device; the mixed droplets are introduced into a high-temperature oil phase (vegetable oil or mineral oil) for crosslinking; after crosslinking, the upper oil phase solution is removed to obtain the microsphere precursor; the microsphere precursor is washed and dried to obtain the polyacrylic acid resin microspheres.

[0012] From the viewpoint of improving the rigidity, impact resistance and dimensional stability of the light diffusion plate, the average particle size D50 of the polyacrylic resin microspheres (determined based on particle size distribution measurement data on a volume basis determined by laser diffraction) is preferably from about 1 μm to about 20 μm, more preferably from about 2 μm to about 5 μm.

[0013] The ethylene-α-olefin copolymer is obtained by polymerizing ethylene and an α-olefin with a C4 or higher carbon structure using a polymerization catalyst. Examples of α-olefins with a C4 or higher carbon structure include C4 to C12 α-olefins. Examples of C4 to C12 α-olefins include 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, and 1-decene. Preferably, 1-butene, 1-hexene, and 1-octene are also considered. The α-olefins may also be cyclic α-olefins such as vinylcyclopropane and vinylcyclobutane. In one or more embodiments, the ethylene-α-olefin copolymer is at least one of ethylene-1-butene copolymer, ethylene-1-hexene copolymer, ethylene-1-octene copolymer, ethylene-1-decene copolymer, ethylene-(3-methyl-1-butene) copolymer, and copolymers of ethylene and cyclic α-olefins.

[0014] One key aspect is whether the foaming agent can impart pores to the light diffuser plate. These pores can act as a medium for light diffusion. With a fixed thickness, smaller and denser pores result in more reflections and refractions of light passing through the diffuser, facilitating light diffusion and increasing its haze. However, this increased reflection and refraction leads to energy loss due to interfacial effects, reducing transmittance. Conversely, with a fixed thickness, larger and denser pores result in fewer reflections and refractions, reducing interfacial energy loss and achieving higher transmittance but lower haze. Unexpectedly, it was discovered that by using a foaming agent to create pores in the light diffuser plate, regardless of pore size or number, the amount of polyacrylic acid resin microspheres can be adjusted to achieve a synergistic effect between the pores and the microspheres, resulting in both high transmittance and good light uniformity. Preferably, the pore size of the bubble is in the range of 200-600μm.

[0015] In one or more embodiments, the foaming agent is at least one selected from n-pentane, isopentane, cyclohexane, neopentane, isohexane, and n-hexane.

[0016] In one or more embodiments, the foaming agent is at least one selected from sodium bicarbonate, citric acid, sodium monohydrogen citrate, sodium dihydrogen citrate, potassium dihydrogen citrate, citrate choline salt, sodium dihydrogen phosphate, calcium dihydrogen phosphate, zinc dihydrogen phosphate, potassium dihydrogen phosphate, manganese dihydrogen phosphate, and sodium percarbonate.

[0017] In one or more embodiments, the multilayer co-extrusion cast film process is a conventional three-layer co-extrusion cast film process in the art, specifically: the upper layer, middle layer and lower layer are extruded through their respective screws through the die lip, the three layers are co-extruded by screws, flow through the same die lip, are drawn (corona-electrode), wound to cooling, shaping and slitting to obtain the light diffusion plate, and there are no specific requirements for the preparation process.

[0018] In one or more embodiments, the method for preparing the light diffusion plate with a low coefficient of thermal expansion includes the following steps: Step 1: After the composition containing PPO resin, ethylene-α-olefin copolymer, polyacrylic acid resin microspheres and foaming agent is stirred evenly, it is added to a single screw extruder; Step 2: The composition is heated by a single-screw extruder to obtain a molten mixture; Step 3: The molten mixture is co-extruded in three layers using a single-screw extruder to obtain a light diffusion plate. The process parameters include: zone 1 temperature 250-260℃, zone 2 temperature 260-270℃, zone 3 temperature 270-280℃, zone 4 temperature 270-280℃, zone 5 temperature 275-285℃, zone 6 temperature 270-280℃, zone 7 temperature 260-270℃, die temperature 255-265℃, and production rate 315-325 kg / h.

[0019] Without affecting the technical effect of the present invention, the composition may contain additives other than those described above. Examples of such additives include: neutralizing agents, antioxidants, ultraviolet absorbers, nucleating agents, lubricants, antistatic agents, anti-blocking agents, processing aids, organic peroxides, colorants (inorganic pigments, organic pigments, pigment dispersants), plasticizers, flame retardants, crosslinking agents, crosslinking aids, brightening agents, antibacterial agents, compatibilizers, and light diffusing agents. These additives are commonly used in the art, and those skilled in the art can select and determine their dosage as needed.

[0020] Without affecting the technical effect of the present invention, the composition may further contain filler materials, including inorganic and organic filler materials. Examples of inorganic filler materials include: glass microspheres, silicate minerals, boehmite, bauxite, silica, silicon dioxide, titanium dioxide, iron oxide, tin oxide, aluminum oxide, magnesium oxide, antimony oxide, barium ferrite, strontium ferrite, beryllium oxide, magnesium hydroxide, aluminum hydroxide, basic magnesium carbonate, calcium carbonate, magnesium carbonate, carbonate minerals, calcium sulfate, magnesium sulfate, basic copper phosphate, basic magnesium sulfate, calcium sulfite, carbon black, and cadmium sulfide. Examples of organic filler materials include: organosilicon microspheres, polyester, aromatic polyamide, liquid crystal polymer fibers, cellulose, and vinylon. The filler material can be plate-shaped, needle-shaped, or fibrous.

[0021] The light diffusion plate prepared by the method provided in this invention can maintain high light diffusion efficiency (high haze) and good light transmittance / brightness while significantly reducing the coefficient of thermal expansion and increasing the heat distortion temperature, overcoming the shortcomings of the prior art and meeting the requirements for dimensional stability and optical uniformity of light diffusion plates under high and low temperature conditions. Preferably, the thickness of the light diffusion plate is 0.5-5 mm. Within this thickness range, the light diffusion plate can significantly suppress thermal deformation and warping under high temperature conditions.

[0022] The present invention also provides the application of the light diffusion plate in the fields of display and lighting.

[0023] Compared with the prior art, the beneficial effects of this invention include at least the following: (1) The present invention uses PPO resin to prepare light diffusion plates. By compounding polyacrylic acid resin microspheres and ethylene-α-olefin copolymer, the CTE of the light diffusion plate can be reduced in a synergistic manner while maintaining high light transmittance, thereby achieving low coefficient of thermal expansion (CTE) and dimensional stability. (2) The present invention uses PPO resin to prepare a light diffusion plate. By compounding a foaming agent and polyacrylic acid resin microspheres, the light diffusion plate achieves uniform and soft light diffusion. Furthermore, it forms uniformly distributed pores inside the light diffusion plate. There is an air medium inside the pores. When light enters the light diffusion plate, it is further refracted and reflected through the pores, resulting in a higher total internal reflection effect, better light transmission and uniformity. In addition, due to the presence of pores inside the light diffusion plate, the density is reduced, and the overall weight is also reduced. (3) The present invention uses PPO resin to prepare a light diffusion plate. By compounding polyacrylic acid resin microspheres and ethylene-α-olefin copolymer, the light diffusion effect and the heat distortion temperature (HDT) of the light diffusion plate are simultaneously improved. The HDT of the light diffusion plate is not lower than 105℃ (the HDT of the existing GPPS resin light diffusion plate is 70-80℃, which is prone to deformation and failure at high temperature), greatly improving the heat resistance and reliability, and significantly improving the life and reliability. (4) The present invention uses PPO resin to prepare light diffusion plates. By compounding polyacrylic acid resin microspheres, ethylene-α-olefin copolymer and foaming agent, the light diffusion plates prepared can still meet the impact test of IEC60598 and GB7000.1 at a low temperature of -20℃, and have better anti-aging performance. Under high intensity ultraviolet irradiation, yellowing can still be inhibited, which solves the problems of heat deformation, warping and yellowing failure of existing light diffusion plates prepared by GPPS resin.

[0024] The following description is based on specific embodiments. Detailed Implementation

[0025] It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0026] In the embodiments of the present invention, unless otherwise specified, all equipment and raw materials can be purchased from the market or are commonly used in the industry. Unless otherwise specified, the methods in the following embodiments are conventional methods in the art.

[0027] In this embodiment of the invention, the PPO resin used has a melt flow rate of 12 g / 10 min at 280℃ / 5.0 kg, a milky white appearance, a light transmittance of >50% at 1 mm, and a notched cantilever beam impact strength >15 KJ / m. 2 It is selected from NORYL™ PX9406P-7001 from Basic Innovative Plastics (Shanghai).

[0028] [Example 1] This embodiment provides a light diffusion plate, all of which have a thickness of 1.5 mm. The preparation method of the light diffusion plate includes the following steps: Step 1: The composition comprising 90 parts of PPO resin, 5 parts of ethylene-1-butene copolymer, 8 parts of polyacrylic acid resin microspheres (the average particle size D50 of the polyacrylic acid resin microspheres is 5 μm), and 0.2 parts of n-pentane is stirred evenly and then added to a single screw extruder. Step 2: The composition is heated by a single-screw extruder to obtain a molten mixture; Step 3: The molten mixture is co-extruded in three layers using a single-screw extruder to obtain a light diffusion plate. The process parameters include: zone 1 temperature 250℃, zone 2 temperature 260℃, zone 3 temperature 270℃, zone 4 temperature 270℃, zone 5 temperature 275℃, zone 6 temperature 270℃, zone 7 temperature 260℃, die temperature 255℃, and production rate 315kg / h.

[0029] [Example 2] This embodiment provides a light diffusion plate, all of which have a thickness of 1.5 mm. The preparation method of the light diffusion plate includes the following steps: Step 1: The composition comprising 110 parts of PPO resin, 10 parts of ethylene-1-hexene copolymer, 3 parts of polyacrylic acid resin microspheres (the average particle size D50 of the polyacrylic acid resin microspheres is 2 μm) is stirred evenly and then added to a single screw extruder. Step 2: The composition is heated by a single-screw extruder to obtain a molten mixture; Step 3: The molten mixture is co-extruded in three layers using a single-screw extruder to obtain a light diffusion plate. The process parameters include: zone 1 temperature 260℃, zone 2 temperature 270℃, zone 3 temperature 280℃, zone 4 temperature 280℃, zone 5 temperature 285℃, zone 6 temperature 280℃, zone 7 temperature 270℃, die temperature 265℃, and production rate 325kg / h.

[0030] [Example 3] This embodiment provides a light diffusion plate, all of which have a thickness of 1.5 mm. The preparation method of the light diffusion plate includes the following steps: Step 1: The composition comprising 100 parts of PPO resin, 8 parts of ethylene-1-octene copolymer, 5 parts of polyacrylic acid resin microspheres (the average particle size D50 of the polyacrylic acid resin microspheres is 4 μm), and 0.6 parts of n-hexane is stirred evenly and then added to a single screw extruder. Step 2: The composition is heated by a single-screw extruder to obtain a molten mixture; Step 3: The molten mixture is co-extruded in three layers using a single-screw extruder to obtain a light diffusion plate. The process parameters include: zone 1 temperature 255℃, zone 2 temperature 265℃, zone 3 temperature 275℃, zone 4 temperature 275℃, zone 5 temperature 280℃, zone 6 temperature 275℃, zone 7 temperature 265℃, die head temperature 260℃, and production rate 320Kg / h.

[0031] [Comparative Examples 1-6] Comparative Example 1 provides a light diffusion plate, which differs from the light diffusion plate provided in Example 3 only in that GPPS resin (Total GPPS1050, 200°C, 5kg melt index 5g / 10min) is used instead of PPO resin when preparing the light diffusion plate provided in this comparative example.

[0032] Comparative Example 2 provides a light diffusion plate, which differs from the light diffusion plate provided in Example 3 only in that HIPS resin (Ningbo Formosa Plastics HIPS8250, 200℃, 5kg melt index 5.5g / 10min) is used instead of PPO resin when preparing the light diffusion plate provided in this comparative example.

[0033] Comparative Example 3 provides a light diffusion plate, which differs from the light diffusion plate provided in Example 3 only in that: when preparing the light diffusion plate provided in this comparative example, acrylic maleic acid copolymer (CAS No.: 26677-99-6) is used instead of ethylene-1-octene copolymer.

[0034] Comparative Example 4 provides a light diffusion plate, which differs from the light diffusion plate provided in Example 3 only in that methyl silicone resin microspheres (average particle size D50 of 4 μm) are used instead of polyacrylic acid resin microspheres when preparing the light diffusion plate provided in this comparative example.

[0035] Comparative Example 5 provides a light diffusion plate, which differs from the light diffusion plate provided in Example 3 only in that: when preparing the light diffusion plate provided in this comparative example, polyacrylic acid resin microspheres are not used, and the amount of foaming agent (n-hexane) is increased to 5.6 parts.

[0036] Comparative Example 6 provides a light diffusion plate, which differs from the light diffusion plate provided in Example 3 only in that: when preparing the light diffusion plate provided in this comparative example, no foaming agent (n-hexane) is used, and the amount of polyacrylic acid resin microspheres added is increased to 5.6 parts.

[0037] [Comparison Test] The light diffusion plates provided in Examples 1-3 and Comparative Examples 1-6 were subjected to the following tests: The coefficient of thermal expansion was tested according to ASTM D696 standard; The heat distortion temperature was tested according to ASTM D648 standard; Impact strength was tested according to ASTM D256 standard; Flame retardancy was tested according to UL94 standard; Light transmittance and haze were tested according to ASTM D1003 standard; Center luminance and average luminance were tested according to GY / T 326-2019 standard.

[0038] The test results are shown in Table 1.

[0039] Table 1

[0040] The following conclusions can be drawn from the test data shown in Table 1: As can be seen from the comparison between Examples 1-3 and Comparative Examples 1-2, the light diffusion plate based on PPO resin provided by the present invention has significantly improved heat distortion temperature, impact strength and flame retardancy compared with the diffusion plate based on GPPS resin, and the coefficient of thermal expansion is significantly reduced.

[0041] As can be seen from the comparison between Example 3 and Comparative Example 3, the ethylene-α-olefin copolymer can effectively improve the overall mechanical properties of the light diffusion plate prepared based on PPO resin, and make the CTE value lower and the dimensional stability higher.

[0042] A comparison of Example 3 and Comparative Example 4 shows that polyacrylic acid resin microspheres contribute a lower coefficient of thermal expansion than methyl silicone resin microspheres, while achieving both high light transmittance and good light uniformity.

[0043] The comparison between Example 3 and Comparative Examples 5-6 shows that the foaming agent and polyacrylic acid resin microspheres have a synergistic effect, which enables the light-emitting diffuser plate to have both high light transmittance and good light uniformity.

[0044] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0045] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for preparing a light diffusion plate with a low coefficient of thermal expansion, characterized in that, The process includes the following steps: The process involves stirring a composition containing PPO resin, ethylene-α-olefin copolymer, polyacrylic acid resin microspheres, and a foaming agent until homogeneous, and then heating it to obtain a molten mixture. The process of obtaining a light diffusion plate by co-extruding a molten mixture using a multi-layer co-extrusion casting process; The composition comprises: 90-110 parts of PPO resin, 3-8 parts of polyacrylic acid resin microspheres, 5-10 parts of ethylene-α-olefin copolymer, and 0.2-1 parts of foaming agent. The average particle size D50 of the polyacrylic acid resin microspheres is 2-5 μm; The ethylene-α-olefin copolymer is at least one of ethylene-1-butene copolymer, ethylene-1-hexene copolymer, ethylene-1-octene copolymer, ethylene-1-decene copolymer, ethylene-(3-methyl-1-butene) copolymer, and copolymer of ethylene with α-olefin having a cyclic structure.

2. The preparation method according to claim 1, characterized in that, The PPO resin meets the following requirements: milky white appearance, light transmittance of not less than 60% at 1mm, and notched impact strength of not less than 17KJ / m². 2 The melt index at 280℃ and 5kg is 15-20g / 10min, and the intrinsic viscosity is 39.5-41.5mL / g.

3. The preparation method according to claim 1, characterized in that, The foaming agent is at least one of the following: n-pentane, isopentane, cyclohexane, neopentane, isohexane, n-hexane, baking soda, citric acid, sodium monohydrogen citrate, sodium dihydrogen citrate, potassium dihydrogen citrate, citrate choline salt, sodium dihydrogen phosphate, calcium dihydrogen phosphate, zinc dihydrogen phosphate, potassium dihydrogen phosphate, manganese dihydrogen phosphate, and sodium percarbonate.

4. The preparation method according to claim 1, characterized in that, The multi-layer co-extrusion casting process is a three-layer co-extrusion casting process.

5. A light diffusion plate with a low coefficient of thermal expansion, characterized in that, The light diffusion plate is prepared by the preparation method described in any one of claims 1-4.

6. The application of the light diffusion plate according to claim 5 in the fields of display and lighting.

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