Polyimide foaming diffusion plate and preparation method thereof

Abstract

The invention discloses a polyimide foaming diffusion plate and a preparation method thereof, and the polyimide foaming diffusion plate comprises the following components: modified PI resin, benzyl methacrylate-titanium dioxide composite microspheres, a silane coupling agent, an antioxidant, an ultraviolet light absorber, a hindered amine light stabilizer, liquid paraffin, a whitening agent, a foaming agent and the like. The method is characterized in that the modified PI resin is used as a diffusion plate base material, it is guaranteed that the diffusion plate has high heat resistance, meanwhile, benzyl methacrylate-titanium dioxide composite microspheres which are good in compatibility with the modified PI resin and matched with the modified PI resin in refractive index are prepared to serve as a light diffusion agent, the optical performance of the diffusion plate is effectively improved, and through formula and process innovation, the diffusion plate can be widely applied to the field of light diffusion. The polyimide foaming diffusion plate which is excellent in optical effect and mechanical property is successfully prepared.

Description

Technical Field

[0001] The present invention relates to the technical field of diffusion plates, and particularly to a polyimide foamed diffusion plate and a preparation method thereof. Background Art

[0002] Diffusion plates are widely used in liquid crystal displays, LED lighting, imaging and other systems. Their main function is to fully scatter incident light to achieve a softer and more uniform illumination effect. With the continuous progress of display technology, the requirements for optical materials are becoming increasingly stringent. Especially in the fields of liquid crystal displays (LCDs) and organic light-emitting diodes (OLEDs), the performance requirements for optical diffusion plates have reached a new height. Traditional optical diffusion plates mainly rely on materials such as GPPS and acrylic resins. However, these materials are prone to problems such as yellowing and deformation in high-temperature and high-humidity environments, which greatly limit their application scope. In contrast, polyimide (PI) resin has the potential to be used as the substrate of a diffusion plate due to the unique imide ring structure in its main chain, which endows it with excellent thermal stability, mechanical properties, chemical inertness and electrical insulation properties. Currently, there are no relevant reports on the application of modified PI resin in the technical field of light diffusion plates. Our research found that if PI resin is directly used to replace traditional acrylic resin to prepare a diffusion plate, its light diffusion effect and mechanical properties are very poor, probably mainly because: firstly, the refractive index of PI resin does not match that of existing light diffusing agents (such as glass microspheres, etc.) and their compatibility is poor, resulting in ineffective scattering of light during propagation and reducing the light diffusion efficiency; secondly, pure PI resin is brittle and easy to break, affecting the balance of the mechanical properties and optical properties of the material, making it difficult for the diffusion plate to meet the requirements of high-performance display devices. Summary of the Invention

[0003] To solve the above problems, one of the purposes of this application is achieved by adopting the following technical solutions: A polyimide foamed diffusion plate comprises the following components in parts by weight: 55 - 68 parts of modified PI resin, 12 - 18 parts of benzyl methacrylate - titanium dioxide composite microspheres, 6 - 10 parts of silane coupling agent, 2.4 - 3 parts of antioxidant, 2.7 - 3.1 parts of ultraviolet absorber, 2.3 - 2.7 parts of hindered amine light stabilizer, 0.85 - 1.15 parts of liquid paraffin, 1.35 - 1.45 parts of whitening agent, and 4.4 - 5.6 parts of foaming agent.

[0004] Preferably, the silane coupling agent is KH570.

[0005] Preferably, the antioxidant is any one of antioxidant 1024, antioxidant 1010 or antioxidant 1076.

[0006] Preferably, the ultraviolet absorber is selected from any one of ultraviolet absorber UV - 327, UV - 329, UV - 531.

[0007] Preferably, the hindered amine light stabilizer is selected from any one of hindered amine light stabilizer 770, hindered amine light stabilizer 944 or hindered amine light stabilizer 622.

[0008] Preferably, the foaming agent is sodium bicarbonate.

[0009] The second object of this application is achieved by the following technical solution: A method for preparing a polyimide foamed diffusion plate includes the following steps: Prepare a modified PI resin; Prepare benzyl methacrylate-titanium dioxide composite microspheres; Add 55-68 parts of the modified PI resin, 6-10 parts of the silane coupling agent to a container, stir at 40-60 °C for 20-40 min to obtain a mixture a, and then add 12-18 parts of benzyl methacrylate-titanium dioxide composite microspheres, 2.4-3 parts of antioxidant, 2.7-3.1 parts of ultraviolet absorber, 2.3-2.7 parts of hindered amine light stabilizer, 0.85-1.15 parts of liquid paraffin, 1.35-1.45 parts of whitening agent and 4.4-5.6 parts of foaming agent to the above mixture a, stir evenly at a speed of 400-600 r / min, and finally put it into a single-screw extruder to be heated and melted and extruded to obtain a polyimide foamed diffusion plate; Among them, the temperatures of each zone of the single-screw extruder are: the temperature of the first zone is 220-230 °C, the temperature of the second zone is 240-250 °C, the temperature of the third zone is 250-260 °C, the temperature of the fourth zone is 260-270 °C, the temperature of the fifth zone is 290-310 °C, the temperature of the sixth zone is 270-290 °C, the temperature of the seventh zone is 260-280 °C, the die head temperature is 230-240 °C, and the production speed is 200-250 Kg / h.

[0010] Preferably, the preparation of the above-mentioned modified PI resin includes the following steps: Add 35-49 parts of thermoplastic polyimide resin, 16-20 parts of polyethyleneimine resin, 13-15 parts of polycarbonate, 6-8 parts of diallyl bisphenol A resin, 8-12 parts of 3-5 mm glass fiber and 8-10 parts of polyimide grafted maleic anhydride to a container, stir evenly, and then put it into a single-screw extruder to be heated and melted and extruded to obtain the modified PI resin; among them, the temperatures of each zone of the twin-screw extruder are: the temperature of the first zone is 230-240 °C, the temperature of the second zone is 240-250 °C, the temperature of the third zone is 250-260 °C, the temperature of the fourth zone is 260-270 °C, the temperature of the fifth zone is 270-280 °C, the die head temperature is 250-260 °C, and the production speed is 200-250 Kg / h.

[0011] Preferably, the preparation of the above-mentioned benzyl methacrylate-titanium dioxide composite microspheres includes the following steps: Mix 75 - 85 parts of benzyl methacrylate with 10 - 15 parts of acrylic acid, add 2 - 4 parts of azobisisobutyronitrile, and stir and react at 60 - 70 °C for 3 - 5 h to obtain surface carboxylated benzyl methacrylate; Dropwise add 60 - 70 wt% HNO to 100 parts of 80 - 90 wt% ethanol aqueous solution 3 Adjust to a pH between 4 and 5, then add 30 - 40 parts of 7 - 9 wt% tetrabutyl titanate ethanol solution, heat up to 45 - 55 °C, stir and react for 1 - 3 h, add 10 - 15 parts of 15 - 17 wt% PEG2000 ethanol solution, then add 1 - 3 parts of 2 - 4 wt% polyvinylpyrrolidone ethanol solution, continue to stir for 0.5 - 1.5 h, dry at 50 - 60 °C for 2 - 4 h, and then calcine at 350 - 400 °C for 3 - 5 h to obtain nano - mesoporous titanium dioxide. Disperse 30 - 40 parts of nano - mesoporous titanium dioxide in 100 parts of 80 - 90 wt% ethanol aqueous solution, and successively add 5 - 7 parts of 10 - 14 wt% sodium hydroxide and 1 - 2 parts of silane coupling agent KH570, and stir at 60 - 70 °C for 2 - 3 h to obtain modified nano - mesoporous titanium dioxide; Mix 10.5 - 23.5 parts of modified nano - mesoporous titanium dioxide, 70.5 - 80.5 parts of surface carboxylated benzyl methacrylate, 0.8 - 1.2 parts of azobisisobutyronitrile, 3 - 5 parts of ethylene glycol dimethacrylate, 3 - 6 parts of sodium dodecyl sulfate, and 5 - 9 parts of silane coupling agent KH570, and stir at 60 - 70 °C at 500 - 1000 rpm for 3 - 5 h, filter and collect the filter residue. Wash the above filter residue 3 - 5 times with 70 - 80 wt% ethanol aqueous solution, and then dry at 40 - 60 °C for 4 - 6 h to obtain benzyl methacrylate - titanium dioxide composite microspheres.

[0012] The beneficial effects are as follows: In the preparation of the diffusion plate, the modified PI resin is used as the matrix. To solve the problem that pure PI resin is brittle and easy to break, the thermoplastic polyimide is used as the matrix framework, and polyethyleneimine resin is added to improve the toughness and processing fluidity of the modified PI resin. Polycarbonate is added to enhance the transparency and impact strength of the modified PI resin. The diallyl bisphenol A resin forms a three-dimensional network through double bond polymerization, and the glass fiber significantly improves the tensile strength and modulus of the modified PI resin through the synergistic effect of mechanical interlocking. The MAH groups of polyimide grafted maleic anhydride react with the polar groups of polyethyleneimine resin and polycarbonate to reduce phase separation. Moreover, polyimide grafted maleic anhydride can also react with the hydroxyl groups on the surface of glass fiber to improve the interfacial bonding force between the fiber and the resin. Thus, it provides a basis for obtaining an optical diffusion plate with excellent mechanical properties. At the same time, the melting point of PI resin is reduced by the modified PI resin, making the melting point of PI resin as close as possible to the decomposition temperature of the light diffusing agent benzyl methacrylate-titanium dioxide composite microspheres and sodium bicarbonate, avoiding the decomposition or failure of the composite microspheres and sodium bicarbonate before PI is completely melted during the processing; To improve the optical effect of the optical diffusion plate, benzyl methacrylate-titanium dioxide composite microspheres with good compatibility and refractive index matching with the modified PI resin are prepared as the light diffusing agent in this application, effectively improving the optical performance of the diffusion plate. The refractive index of the light diffusing agent benzyl methacrylate-titanium dioxide composite microspheres is 1.6988, which is relatively close to the refractive index of the modified PI resin of 1.8021, and can effectively scatter light and reduce light reflection, improving the diffusion uniformity. Specifically, benzyl methacrylate is coated on titanium dioxide through in-situ polymerization to form an organic-inorganic core-shell structure. After the surface of titanium dioxide is modified by KH570, it reacts with the benzyl methacrylate monomer to form a chemical bond, thus avoiding the agglomeration of titanium dioxide and stabilizing the structure of the composite microspheres. The mesoporous titanium dioxide structure in the composite microspheres provides a high specific surface area and light scattering ability. The light is refracted or reflected by the mesoporous titanium dioxide and then the light path is changed multiple times by the core-shell structure, improving the diffusion uniformity of light. During the preparation of the composite microspheres and the final material mixing process, the silane coupling agent KH570 is added. Multiple operations significantly improve the compatibility between the composite microspheres and the modified PI resin. In addition, to further improve the optical effect of the diffusion plate, sodium bicarbonate is added as a foaming agent to form a porous structure, which can also increase the light scattering path and form a multi-level scattering with the composite microspheres, improving the haze and light diffusion effect of the diffusion plate; To inhibit the oxidative yellowing of the diffusion plate during high-temperature processing and long-term use, this application adopts a triple protection system of antioxidant + ultraviolet absorber + hindered amine light stabilizer, and prolongs the service life of the diffusion plate and maintains optical stability through the synergistic effect of multiple mechanisms such as inhibiting thermal oxygen aging, absorbing ultraviolet rays, and capturing free radicals; In summary, through formula and process innovation, the present application has successfully prepared a polyimide foamed diffusion plate that exhibits excellent performance in both optical effects and mechanical properties. Detailed implementation manners

[0013] The following further elaborates on the present invention in conjunction with specific embodiments, so that those skilled in the art can understand the present invention more clearly.

[0014] The following embodiments are only used to illustrate the present invention, but not to limit the scope of the present invention. Based on the specific embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the protection scope of the present invention.

[0015] In the embodiments of the present invention, unless otherwise specified, all raw material components are commercially available products well-known to those skilled in the art; in the embodiments of the present invention, unless specifically specified, the technical means used are conventional means well-known to those skilled in the art.

[0016] Source of raw materials: Silane coupling agent 570, purchased from Shandong Yuanjin New Materials Co., Ltd.; Antioxidant, purchased from Shandong Xuxiang Chemical Co., Ltd.; Ultraviolet absorber, purchased from Jinan Xiangfeng Weiye Chemical Co., Ltd.; Hindered amine light stabilizer, purchased from Shanghai Tiandui New Materials Co., Ltd.; Liquid paraffin, purchased from Jinan Xuchuang Chemical Technology Co., Ltd.; Whitening agent, purchased from Guangzhou Yuanda New Materials Co., Ltd.; Sodium bicarbonate, purchased from Shandong Haihua New Materials Co., Ltd.; Thermoplastic polyimide resin, purchased from Changzhou Deyi New Materials Technology Co., Ltd.; Polyethyleneimine resin, Ultem 1000, purchased from Sabic; Polycarbonate, model PC-110, purchased from Chi Mei Industries Co., Ltd., Taiwan, China; Diallyl bisphenol A resin, purchased from Honghu Shuangma New Materials Technology Co., Ltd.; 3 - 5 mm glass fiber, purchased from Guangzhou Jingchen Plastics Co., Ltd.; Polyimide grafted maleic anhydride PI-g-MAH, purchased from Shanghai Kelaman Reagent Co., Ltd.; Benzyl methacrylate, purchased from Shanghai Yuanye Bio-Technology Co., Ltd.; Acrylic acid, purchased from Wuhan Jiyesheng Chemical Co., Ltd.; Azobisisobutyronitrile, purchased from Zibo Tongyizhai Chemical Co., Ltd.; Absolute ethanol, purchased from Guangdong Wengjiang Chemical Reagent Co., Ltd.; Tetrabutyl titanate, purchased from Shandong Dongfang Riqi New Materials Co., Ltd.; PEG2000, purchased from Nantong Renda Chemical Co., Ltd.; Polyvinylpyrrolidone, purchased from Jinan Zhengkang Chemical Co., Ltd.; Sodium hydroxide, purchased from Jinan Jumeihui Chemical Co., Ltd.; Ethylene glycol dimethacrylate, purchased from Shandong Wanduofu New Materials Co., Ltd.; Sodium dodecyl sulfate, purchased from Shaanxi Changji Auxiliary Biotechnology Co., Ltd.; The remaining reagents are all commercially available.

[0017] Example 1 This example provides a polyimide foamed diffusion plate, which includes the following components by weight: 68 parts of modified PI resin, 12 parts of benzyl methacrylate - titanium dioxide composite microspheres, 6 parts of silane coupling agent, 2.4 parts of antioxidant, 2.7 parts of ultraviolet absorber, 2.3 parts of hindered amine light stabilizer, 0.85 part of liquid paraffin, 1.35 parts of whitening agent, and 4.4 parts of foaming agent; Among them, the silane coupling agent is KH570; the antioxidant is antioxidant 1024; the ultraviolet absorber is selected from ultraviolet absorber UV - 327; the hindered amine light stabilizer is selected from hindered amine light stabilizer 770; the foaming agent is sodium bicarbonate.

[0018] The preparation method of the above polyimide foamed diffusion plate includes the following steps: Prepare modified PI resin: Add 49 parts of thermoplastic polyimide resin, 16 parts of polyethyleneimine resin, 13 parts of polycarbonate, 6 parts of diallyl bisphenol A resin, 8 parts of 3mm glass fiber, and 8 parts of polyimide grafted maleic anhydride to a container, stir evenly, and then put it into a single - screw extruder to heat and melt and extrude to obtain modified PI resin; among them, the temperatures of each zone of the twin - screw extruder are: the temperature of the first zone is 230 °C, the temperature of the second zone is 240 °C, the temperature of the third zone is 250 °C, the temperature of the fourth zone is 260 °C, the temperature of the fifth zone is 270 °C, the die head temperature is 250 °C, and the production speed is 200 Kg / h; Prepare benzyl methacrylate - titanium dioxide composite microspheres: Mix 85 parts of benzyl methacrylate with 10 parts of acrylic acid, add 2 parts of azobisisobutyronitrile, and stir and react at 60 °C for 3 h to obtain surface - carboxylated benzyl methacrylate; Drop 60wt% HNO into 100 parts of 80 wt% ethanol aqueous solution 3Adjust to between pH 4, then add 30 parts of 7wt% tetrabutyl titanate ethanol solution, heat up to 45 °C, stir and react for 1 h, add 10 parts of 15wt% PEG2000 ethanol solution, then add 1 part of 2wt% polyvinylpyrrolidone ethanol solution, continue to stir for 0.5 h, dry at 50 °C for 2 h, and then calcine at 350 °C for 3 h to obtain nano-porous titanium dioxide. Disperse 30 parts of nano-porous titanium dioxide in 100 parts of 80wt% ethanol aqueous solution and sequentially add 5 parts of 10wt% sodium hydroxide and 1 part of silane coupling agent KH570, stir at 60 °C for 2 h to obtain modified nano-porous titanium dioxide; Mix 10.5 parts of modified nano-porous titanium dioxide, 80.5 parts of surface-carboxylated benzyl methacrylate, 0.8 part of azobisisobutyronitrile, 3 parts of ethylene glycol dimethacrylate, 3 parts of sodium dodecyl sulfate, and 5 parts of silane coupling agent KH570, and stir at 60 °C at 500 rpm for 3 h, filter and collect the filter residue, wash the above filter residue 3 times with 70wt% ethanol aqueous solution, and dry at 40 °C for 4 h to obtain benzyl methacrylate-titanium dioxide composite microspheres; Add 68 parts of modified PI resin and 6 parts of silane coupling agent to a container, stir at 40 °C for 20 min to obtain mixture a, then add 12 parts of benzyl methacrylate-titanium dioxide composite microspheres, 2.4 parts of antioxidant, 2.7 parts of ultraviolet absorber, 2.3 parts of hindered amine light stabilizer, 0.85 part of liquid paraffin, 1.35 parts of whitening agent, and 4.4 parts of foaming agent to the above mixture a, stir evenly at a speed of 400 r / min, and finally put it into a single-screw extruder to heat and melt and extrude to obtain a polyimide foamed diffusion plate; among them, the temperatures of each zone of the single-screw extruder are: the temperature of the first zone is 220 °C, the temperature of the second zone is 240 °C, the temperature of the third zone is 250 °C, the temperature of the fourth zone is 260 °C, the temperature of the fifth zone is 290 °C, the temperature of the sixth zone is 270 °C, the temperature of the seventh zone is 260 °C, the die head temperature is 230 °C, and the production speed is 200 Kg / h.

[0019] Example 2 This example provides a polyimide foamed diffusion plate, which includes the following components by weight: 61.5 parts of modified PI resin, 15 parts of benzyl methacrylate-titanium dioxide composite microspheres, 8 parts of silane coupling agent, 2.7 parts of antioxidant, 2.9 parts of ultraviolet absorber, 2.5 parts of hindered amine light stabilizer, 1 part of liquid paraffin, 1.4 parts of whitening agent, and 5 parts of foaming agent; Among them, the silane coupling agent is KH570; the antioxidant is antioxidant 1010; the ultraviolet absorber is selected from ultraviolet absorber UV-329; the hindered amine light stabilizer is hindered amine light stabilizer 944; the foaming agent is sodium bicarbonate.

[0020] The preparation method of the above polyimide foamed diffusion plate includes the following steps: Preparation of modified PI resin: Add 42 parts of thermoplastic polyimide resin, 18 parts of polyethyleneimine resin, 14 parts of polycarbonate, 7 parts of diallyl bisphenol A resin, 10 parts of 4 mm glass fiber and 9 parts of polyimide grafted maleic anhydride into a container, stir evenly, and then put it into a single-screw extruder for heating, melting and extrusion to obtain the modified PI resin. Among them, the temperatures of each zone of the twin-screw extruder are as follows: the temperature of the first zone is 235 °C, the temperature of the second zone is 245 °C, the temperature of the third zone is 255 °C, the temperature of the fourth zone is 265 °C, the temperature of the fifth zone is 275 °C, the temperature of the die head is 255 °C, and the production speed is 225 Kg / h; Preparation of benzyl methacrylate-titanium dioxide composite microspheres: Mix 80 parts of benzyl methacrylate with 12.5 parts of acrylic acid, add 3 parts of azobisisobutyronitrile, and stir and react at 65 °C for 4 h to obtain surface carboxylated benzyl methacrylate; Drop 65 wt% HNO into 100 parts of 85 wt% ethanol aqueous solution 3 Adjust to between pH 5, then add 35 parts of 8 wt% tetrabutyl titanate ethanol solution, raise the temperature to 50 °C, stir and react for 2 h, add 12.5 parts of 16 wt% PEG2000 ethanol solution, then add 2 parts of 3 wt% polyvinylpyrrolidone ethanol solution, continue to stir for 1 h, dry at 55 °C for 3 h, and then calcine at 375 °C for 4 h to obtain nano-porous titanium dioxide. Disperse 35 parts of nano-porous titanium dioxide in 100 parts of 85 wt% ethanol aqueous solution, and sequentially add 6 parts of 12 wt% sodium hydroxide and 1.5 parts of silane coupling agent KH570, and stir at 65 °C for 2.5 h to obtain modified nano-porous titanium dioxide; Mix 17 parts of modified nano-porous titanium dioxide, 75.5 parts of surface carboxylated benzyl methacrylate, 1 part of azobisisobutyronitrile, 4 parts of ethylene glycol dimethacrylate, 4.5 parts of sodium dodecyl sulfate, and 7 parts of silane coupling agent KH570, and stir at 65 °C at 750 rpm for 4 h. Filter and collect the filter residue. Wash the above filter residue 4 times with 75 wt% ethanol aqueous solution, and then dry at 50 °C for 5 h to obtain benzyl methacrylate-titanium dioxide composite microspheres; Add 61.5 parts of modified PI resin and 8 parts of silane coupling agent into a container, stir for 30 min at 50 °C to obtain mixture a. Then add 15 parts of benzyl methacrylate-titanium dioxide composite microspheres, 2.7 parts of antioxidant, 2.9 parts of ultraviolet absorber, 2.5 parts of hindered amine light stabilizer, 1 part of liquid paraffin, 1.4 parts of whitening agent and 5 parts of foaming agent into the above mixture a, stir evenly at a speed of 500 r / min, and finally put it into a single-screw extruder to heat, melt and extrude to obtain a polyimide foamed diffusion plate; among them, the temperatures of each zone of the single-screw extruder are: the temperature of the first zone is 225 °C, the temperature of the second zone is 245 °C, the temperature of the third zone is 255 °C, the temperature of the fourth zone is 265 °C, the temperature of the fifth zone is 300 °C, the temperature of the sixth zone is 280 °C, the temperature of the seventh zone is 270 °C, the die head temperature is 235 °C, and the production speed is 225 Kg / h.

[0021] Example 3 This example provides a polyimide foamed diffusion plate, which includes the following components by weight: 55 parts of modified PI resin, 18 parts of benzyl methacrylate-titanium dioxide composite microspheres, 10 parts of silane coupling agent, 3 parts of antioxidant, 3.1 parts of ultraviolet absorber, 2.7 parts of hindered amine light stabilizer, 1.15 parts of liquid paraffin, 1.45 parts of whitening agent, 5.6 parts of foaming agent; Among them, the silane coupling agent is KH570; the antioxidant is antioxidant 1076; the ultraviolet absorber is selected from ultraviolet absorber UV-531; the hindered amine light stabilizer is hindered amine light stabilizer 622; the foaming agent is sodium bicarbonate.

[0022] The preparation method of the above polyimide foamed diffusion plate includes the following steps: Prepare modified PI resin: Add 35 parts of thermoplastic polyimide resin, 20 parts of polyethyleneimine resin, 15 parts of polycarbonate, 8 parts of diallyl bisphenol A resin, 12 parts of 5 mm glass fiber and 10 parts of polyimide grafted maleic anhydride into a container, stir evenly, and then put it into a single-screw extruder to heat, melt and extrude to obtain modified PI resin; among them, the temperatures of each zone of the twin-screw extruder are: the temperature of the first zone is 240 °C, the temperature of the second zone is 250 °C, the temperature of the third zone is 260 °C, the temperature of the fourth zone is 270 °C, the temperature of the fifth zone is 280 °C, the die head temperature is 260 °C, and the production speed is 250 Kg / h; Prepare benzyl methacrylate-titanium dioxide composite microspheres: Mix 75 parts of benzyl methacrylate and 15 parts of acrylic acid, add 4 parts of azobisisobutyronitrile, and stir and react at 70 °C for 5 h to obtain surface carboxylated benzyl methacrylate; Drop 70wt% HNO into 100 parts of 90 wt% ethanol aqueous solution 3Adjust to between pH 4, then add 40 parts of 9 wt% tetrabutyl titanate ethanol solution, heat up to 55 °C, stir and react for 3 h, add 15 parts of 17 wt% PEG2000 ethanol solution, then add 3 parts of 4 wt% polyvinylpyrrolidone ethanol solution, continue to stir for 1.5 h, dry at 60 °C for 4 h, and then calcine at 400 °C for 5 h to obtain nano-porous titanium dioxide. Disperse 40 parts of nano-porous titanium dioxide in 100 parts of 90 wt% ethanol aqueous solution and sequentially add 7 parts of 14 wt% sodium hydroxide and 2 parts of silane coupling agent KH570, stir at 70 °C for 3 h to obtain modified nano-porous titanium dioxide; Mix 23.5 parts of modified nano-porous titanium dioxide, 70.5 parts of surface-carboxylated benzyl methacrylate, 1.2 parts of azobisisobutyronitrile, 5 parts of ethylene glycol dimethacrylate, 6 parts of sodium dodecyl sulfate, and 9 parts of silane coupling agent KH570, and stir at 70 °C at 1000 rpm for 5 h, filter and collect the filter residue. Wash the above filter residue 5 times with 80 wt% ethanol aqueous solution, and then dry at 60 °C for 6 h to obtain benzyl methacrylate-titanium dioxide composite microspheres; Add 55 parts of modified PI resin and 10 parts of silane coupling agent to a container, stir at 60 °C for 40 min to obtain mixture a. Then add 18 parts of benzyl methacrylate-titanium dioxide composite microspheres, 3 parts of antioxidant, 3.1 parts of ultraviolet absorber, 2.7 parts of hindered amine light stabilizer, 1.15 parts of liquid paraffin, 1.45 parts of whitening agent, and 5.6 parts of foaming agent to the above mixture a, stir evenly at a speed of 600 r / min, and finally put it into a single-screw extruder to heat and melt and extrude to obtain a polyimide foamed diffusion plate; among them, the temperatures of each zone of the single-screw extruder are: the temperature of the first zone is 230 °C, the temperature of the second zone is 250 °C, the temperature of the third zone is 260 °C, the temperature of the fourth zone is 270 °C, the temperature of the fifth zone is 310 °C, the temperature of the sixth zone is 290 °C, the temperature of the seventh zone is 280 °C, the die head temperature is 240 °C, and the production speed is 250 Kg / h.

[0023] Comparative Example 1 The difference between this comparative example and Example 2 is that 61.5 parts of PI resin are used to replace 61.5 parts of modified PI resin in Example 2, and the experimental steps for preparing modified PI resin are removed, and other components and experimental steps are the same as those in Example 2.

[0024] Comparative Example 2 The difference between this comparative example and Example 2 is that 15 parts of glass microspheres are used to replace 15 parts of benzyl methacrylate-titanium dioxide composite microspheres in Example 2, and other components and experimental steps are the same as those in Example 2.

[0025] Comparative Example 3 This comparative example is different from Example 2 in that the amount of modified PI resin is increased from 61.5 parts to 66.5 parts, and sodium bicarbonate as a foaming agent is not added. Other components and experimental procedures are the same as those in Example 2.

[0026] Comparative Example 4 This comparative example is different from Example 2 in that when preparing the modified PI resin, the amount of thermoplastic polyimide resin is increased from 42 parts to 55 parts, and glass fiber and polyimide grafted maleic anhydride are not added. Other components and experimental procedures are the same as those in Example 2.

[0027] The diffusion plates prepared in Examples 1 to 3 and Comparative Examples 1 to 4 were tested.

[0028] Test method: The heat distortion temperature was tested in accordance with ASTM D648 standard; The impact strength was tested in accordance with ASTM D256 standard; The flexural modulus was tested in accordance with ASTM D790 standard; The light transmittance and haze were tested in accordance with ASTM D1003 standard; The center brightness and average brightness were tested in accordance with GY / T 326-2019 standard, The density was tested in accordance with ASTM D792 standard; The test results are shown in Table 1.

[0029] Table 1 Performance test results of diffusion plates

[0030] From the above experimental data, all performance indicators in Examples 1 to 3 are better than those in the comparative examples. Moreover, the heat distortion temperature, impact strength, flexural modulus, light transmittance and haze indicators in Example 2 are better than those in Examples 1 and 3. This may be related to the ratio of the modified PI resin and benzyl methacrylate-titanium dioxide composite microspheres in Example 2 and the optimization of the processing technology. By comparing and analyzing the data of Example 2 with those of the four groups of comparative examples, it is found that for the diffusion plate prepared by using the modified PI resin in Example 2 compared with the diffusion plate prepared by simply using PI resin in Comparative Example 1, its heat distortion temperature, impact strength data and flexural modulus have been greatly improved. This shows that using the modified PI resin to prepare the diffusion plate in this application helps to improve the heat resistance and impact resistance of the diffusion plate, and enables the diffusion plate to maintain a good shape when subjected to external forces. After using glass microspheres to replace benzyl methacrylate-titanium dioxide composite microspheres as the light diffusing agent in Comparative Example 2, the light transmittance of the prepared diffusion plate increased and the haze decreased. This indicates that using glass microspheres allows more light to directly pass through the diffusion plate, weakening the light diffusion effect on the light entering the diffusion plate. This may be because the refractive index difference between the glass microspheres used as the light diffusing agent and the modified PI resin substrate is too large or the compatibility is poor, resulting in ineffective light scattering during light propagation and reducing the light diffusion efficiency of the diffusion plate. After not adding the foaming agent sodium bicarbonate in Comparative Example 3, the light transmittance, central brightness, and average brightness of the diffusion plate all increased, and the haze decreased. This may be because the diffusion plate cannot form pores and the light diffusion effect relying only on the composite microspheres is limited. However, after using the foaming agent sodium bicarbonate in Example 2, the diffusion plate forms a porous structure that can increase the light scattering path and form multi-level scattering with the composite microspheres. Therefore, the haze and light diffusion effect of the diffusion plate can be significantly improved. After not adding glass fiber and polyimide grafted maleic anhydride in Comparative Example 4, the heat distortion temperature, impact strength, and flexural modulus of the diffusion plate also deteriorated. This shows that adding glass fiber and polyimide grafted maleic anhydride in Example 2 may help improve the mechanical properties and heat resistance of the diffusion plate. The MAH groups of polyimide grafted maleic anhydride react with the polar groups of polyethyleneimine resin and polycarbonate, which can reduce phase separation. Moreover, polyimide grafted maleic anhydride can also react with the hydroxyl groups on the surface of glass fiber to improve the interfacial bonding force between the fiber and the resin, and can improve the optical properties of the diffusion plate. In summary, in this application, a modified PI resin is used as the substrate of the diffusion plate to ensure that the diffusion plate has high heat resistance. At the same time, benzyl methacrylate-titanium dioxide composite microspheres with good compatibility and refractive index matching with the modified PI resin are prepared as the light diffusing agent, effectively improving the optical properties of the diffusion plate. In addition, through formula and process innovation, a polyimide foaming diffusion plate with excellent performance in both optical effects and mechanical properties is successfully prepared.

[0031] The above are only the embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the scope of the claims of the present invention.

Claims

1. A polyimide foam diffuser plate, characterized in that: The invention comprises the following components in parts by weight: 55-68 parts of modified PI resin, 12-18 parts of benzyl methacrylate-titanium dioxide composite microspheres, 6-10 parts of silane coupling agent, 2.4-3 parts of antioxidant, 2.7-3.1 parts of ultraviolet absorber, 2.3-2.7 parts of hindered amine light stabilizer, 0.85-1.15 parts of liquid paraffin, 1.35-1.45 parts of brightener and 4.4-5.6 parts of foaming agent.

2. The polyimide foam diffuser plate according to claim 1, characterized in that: The silane coupling agent is KH570.

3. The polyimide foam diffuser plate according to claim 1, characterized in that: The antioxidant is any one of antioxidant 1024, antioxidant 1010 or antioxidant 1076.

4. The polyimide foam diffuser plate according to claim 1, characterized in that: The ultraviolet absorber is selected from any one of ultraviolet absorbers UV-327, UV-329, and UV-531.

5. The polyimide foam diffuser plate according to claim 1, characterized in that: The hindered amine light stabilizer is selected from any one of hindered amine light stabilizer 770, hindered amine light stabilizer 944 or hindered amine light stabilizer 622.

6. The polyimide foam diffuser plate according to claim 1, characterized in that: The foaming agent is sodium bicarbonate.

7. The method for preparing a polyimide foamed diffuser plate according to any one of claims 1 to 6, characterized in that: The following steps are involved: preparing modified PI resin; Preparation of benzyl methacrylate-titanium dioxide composite microspheres; Add the modified PI resin and silane coupling agent in the above-mentioned weight proportions into a container, stir for 20-40 minutes at 40-60° C. to obtain a mixture a, then add the above-mentioned weight proportions of benzyl methacrylate-titanium dioxide composite microspheres, antioxidant, ultraviolet absorber, hindered amine light stabilizer, liquid paraffin, brightener and foaming agent into the mixture a, stir evenly at a speed of 400-600 r / min, and finally put into a single-screw extruder to heat, melt and extrude to obtain a polyimide foam diffuser plate; Among them, the temperatures of each zone of the single-screw extruder are: zone one temperature is 220~230℃, zone two temperature is 240~250℃, zone three temperature is 250~260℃, zone four temperature is 260~270℃, zone five temperature is 290~310℃, zone six temperature is 270~290℃, zone seven temperature is 260~280℃, die head temperature is 230~240℃, and the production speed is 200~250Kg / h.

8. The method for preparing a polyimide foamed diffuser plate according to claim 7, characterized in that: The preparation of the modified PI resin comprises the following steps: 35-49 parts of thermoplastic polyimide resin, 16-20 parts of polyethyleneimine resin, 13-15 parts of polycarbonate, 6-8 parts of diallyl bisphenol A resin, 8-12 parts of 3-5 mm glass fiber and 8-10 parts of polyimide grafted maleic anhydride are added into a container and stirred evenly, and then put into a single-screw extruder for heating, melting and extrusion to obtain a modified PI resin; wherein, the temperature of each zone of the twin-screw extruder is as follows: the temperature of zone 1 is 230-240°C, the temperature of zone 2 is 240-250°C, the temperature of zone 3 is 250-260°C, the temperature of zone 4 is 260-270°C, the temperature of zone 5 is 270-280°C, the temperature of the die head is 250-260°C, and the production rate is 200-250Kg / h.

9. The method for preparing a polyimide foamed diffuser plate according to claim 7, characterized in that: The preparation of the benzyl methacrylate-titanium dioxide composite microspheres comprises the following steps: 75-85 parts of benzyl methacrylate and 10-15 parts of acrylic acid are mixed, 2-4 parts of azobisisobutyronitrile are added, and the mixture is stirred and reacted at 60-70°C for 3-5 hours to obtain surface carboxylated benzyl methacrylate; To 100 parts of 80-90 wt% ethanol aqueous solution, add 60-70 wt% HNO3 dropwise to adjust the pH to 4-5, then add 30-40 parts of 7-9 wt% tetrabutyl titanate ethanol solution, heat to 45-55 ° C, stir and react for 1-3 h, add 10-15 parts of 15-17 wt% PEG2000 ethanol solution, then add 1-3 parts of 2-4 wt% polyvinyl pyrrolidone ethanol solution, continue stirring for 0.5-1.5 h, dry at 50-60 ° C for 2-4 h, and heat at 350- Calcinate at 400°C for 3-5h to obtain nano-mesoporous titanium dioxide, disperse 30-40 parts of the nano-mesoporous titanium dioxide in 100 parts of 80-90wt% ethanol aqueous solution, add 5-7 parts of 10-14wt% sodium hydroxide and 1-2 parts of silane coupling agent KH570 in sequence, and stir at 60-70°C for 2-3h to obtain modified nano-mesoporous titanium dioxide; 10.5-23.5 parts of the modified nano-mesoporous titanium dioxide, 70.5-80.5 parts of the surface carboxylated benzyl methacrylate, 0.8-1.2 parts of azobisisobutyronitrile, 3-5 parts of ethylene glycol dimethacrylate, 3-6 parts of sodium dodecyl sulfate, and 5-9 parts of silane coupling agent KH570 are mixed and stirred at 60-70° C. and 500-1000 rpm for 3-5 hours, and the residue is collected by filtration. The residue is washed 3-5 times with 70-80wt% ethanol aqueous solution, and then dried at 40-60° C. for 4-6 hours to obtain the benzyl methacrylate-titanium dioxide composite microspheres.

Images