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CN-122008667-A - Optical-grade high-brightness polyester film and preparation method thereof

CN122008667ACN 122008667 ACN122008667 ACN 122008667ACN-122008667-A

Abstract

The invention discloses an optical-grade high-brightness polyester film and a preparation method thereof, wherein the optical-grade high-brightness polyester film comprises a nanoscale multilayer structure formed by alternately laminating PET layers and PEN layers, the total number of layers is 350-700, the total thickness is 30-60 mu m, the refractive index of the PET layers is 1.58-1.62, the refractive index of the PEN layers is 1.64-1.68, the average reflectivity of the film at the wavelength of 550nm is more than or equal to 98.5%, the light transmittance is more than or equal to 91.5%, the haze is less than or equal to 0.5%, and the interlayer peeling strength is more than or equal to 3.0N/cm. According to the invention, through the design of the nanoscale multilayer structure with alternately laminated PET and PEN, the cooperative optimization of optical performance, mechanical strength and thermal stability is realized. The optical fiber has excellent optical performance through hundreds of layers of nanoscale alternating structures, obviously improves interlayer binding force through molecular modification of laminated layers, and realizes breakthrough in reflection efficiency, interface stability and processing yield by adopting a unidirectional stretching process while ensuring layer thickness uniformity.

Inventors

  • WU PEIFU
  • PAN JIANZHONG
  • WU DI
  • CHI WEI
  • ZHANG YAN
  • GU YANG

Assignees

  • 江苏双星彩塑新材料股份有限公司

Dates

Publication Date
20260512
Application Date
20250414

Claims (10)

  1. 1. The optical-grade high-brightness polyester film is characterized by comprising a nanoscale multilayer structure formed by alternately laminating PET layers and PEN layers, wherein the total number of layers is 350-700, the total thickness is 30-60 mu m, the refractive index of the PET layers is 1.58-1.62, the refractive index of the PEN layers is 1.64-1.68, the average reflectivity of the film at 550nm wavelength is more than or equal to 98.5%, the light transmittance is more than or equal to 91.5%, the haze is less than or equal to 0.5%, and the interlayer peeling strength is more than or equal to 3.0N/cm.
  2. 2. The polyester film of claim 1, wherein the PET layer has a refractive index of 1.58 and the PEN layer has a refractive index of 1.64.
  3. 3. The polyester film according to claim 1, wherein the PET layer is prepared from 50 to 55 parts by weight of terephthalic acid, 25 to 28 parts by weight of ethylene glycol, 8 to 12 parts by weight of cyclohexanedimethanol, 0.4 to 0.6 parts by weight of tetrafluoroterephthalic acid, 0.1 to 0.3 parts by weight of an antioxidant, and 0.05 to 0.1 parts by weight of a catalyst.
  4. 4. The polyester film according to claim 1, wherein the PEN layer is prepared from 48 to 52 parts by weight of naphthalene dicarboxylic acid, 30 to 32 parts by weight of ethylene glycol, 5 to 8 parts by weight of terephthalic acid, 1.0 to 1.5 parts by weight of a polyester elastomer, and 0.05 to 0.1 parts by weight of a catalyst.
  5. 5. A process for preparing the optical-grade high-brightness polyester film as claimed in any one of claims 1 to 4, which is characterized by comprising the steps of preparing modified PET slices and modified PEN slices respectively, feeding the prepared modified PET slices into a PET twin-screw extruder, feeding the prepared modified PEN slices into the PEN twin-screw extruder, feeding the melt extruded by the PET twin-screw extruder and the PEN twin-screw extruder into a multi-layer coextrusion die, distributing the extruded PET melt and PEN melt through the multi-layer coextrusion die, laminating and doubling to form a thick sheet with 350 to 700 layers of nano-grade multi-layer structure, feeding the thick sheet extruded by the multi-layer coextrusion die into a unidirectional stretcher for longitudinal stretching, wherein the stretching ratio is 3.5 to 4.0 times, then carrying out heat setting treatment on the film after longitudinal stretching, wherein the heat setting temperature is 210 to 220 ℃, the heat setting time is 5 to 8 seconds, controlling the heat shrinkage rate to be less than 1.0%, and finally drying, slitting and rolling the film.
  6. 6. The process according to claim 5, wherein the process for preparing the modified PET chips comprises the steps of adding terephthalic acid, ethylene glycol and cyclohexanedimethanol in a certain proportion into a reaction kettle, heating to 240-250 ℃, introducing nitrogen for protection, stirring at 200-300rpm, carrying out esterification dehydration until the esterification rate is more than 95%, adding tetrafluoroterephthalic acid after the later stage of the esterification process, namely after 1.5 hours of the esterification reaction, continuing the reaction for 0.5 hours to ensure that fluorine-containing monomers are embedded into the main chain, heating to 270-280 ℃ after the esterification rate reaches 95%, reducing the pressure to 5-10kPa, adding a catalyst, pre-polycondensing for 1 hour, increasing the intrinsic viscosity to 0.4-0.5dL/g, reducing the pressure to 50-100Pa, increasing the temperature to 285-295 ℃ and polycondensing for 2-3 hours until the intrinsic viscosity reaches 0.8-0.9dL/g, vacuum drying the melt generated in the reaction kettle into modified PET chips with particle size of 3-5mm by a particle cutting machine for 4-6 hours, and keeping the content of <50ppm for standby.
  7. 7. The method of claim 5, wherein the step of preparing the modified PEN resin comprises vacuum drying naphthalene dicarboxylic acid at 80 ℃ for 4 hours to enable the moisture content to be less than 100ppm, drying terephthalic acid at 100 ℃ for 6 hours to prevent caking, crushing the polyester elastomer to a particle size of less than 500 μm, pre-dispersing the polyester elastomer with ethylene glycol according to a mass ratio of 1:5 (ultrasonic treatment for 30 minutes) to form an elastomer slurry, adding raw materials except the elastomer slurry into a stainless steel reaction tank according to a proportion, heating to 240-250 ℃ under the protection of nitrogen, reducing the pressure to 0.2-0.3MPa, stirring at 200rpm, carrying out esterification dehydration reaction for 2.5-3 hours until the water yield reaches more than 95% of a theoretical value, cooling to 220 ℃ after the esterification is completed, adding the pre-dispersed elastomer slurry, stirring at 500rpm for 30 minutes, heating to 250 ℃ to 50kPa, removing residual EG, continuing to heat up to 270-280 ℃, reducing the pressure to 1-5kPa, granulating to a melt with the viscosity of 1-5 Pa-3 mm, granulating the melt after the esterification reaction is completed, cooling to a viscosity of 1-5 ℃ to2 ppm, granulating to a water content of the melt, and finishing the reaction in a vacuum condition of 1-3 mm, granulating to be more than 0.3mm, and finishing the reaction, and granulating to obtain the modified PEN resin by granulating by a vacuum.
  8. 8. The method of claim 5, wherein the temperature of the multilayer coextrusion die is controlled at 265 ℃ to 300 ℃.
  9. 9. The method of claim 5, wherein the unidirectional stretching has a preheating temperature of 85-100 ℃, a stretching temperature of 100-120 ℃, and a stretching direction of longitudinal direction.
  10. 10. The method of claim 5, wherein the film is dried at 120-150 ℃ for 4-8 hours after heat setting to a moisture content of less than or equal to 50ppm.

Description

Optical-grade high-brightness polyester film and preparation method thereof Technical Field The invention relates to a high-brightness polyester film used in the fields of liquid crystal display, illumination and the like, in particular to an optical-grade high-brightness polyester film and a preparation method thereof. Background Optical-grade high-brightness polyester films are widely used in various high-tech and industrial fields due to their excellent optical properties (such as high light transmittance, low haze, high reflectivity) and physicochemical stability. For example, in the display and electronic industries, the high-brightness polyester film can be used as a backlight module of liquid crystal display and other devices, and can be used as a brightness enhancement film or a reflection film to improve the brightness and uniformity of a screen. In the illumination field, the LED light source can be used as a reflecting layer of an LED lamp, so that the light efficiency and the heat dissipation performance are improved, and the light loss is reduced. In the field of solar cells, the back plate can be used for a photovoltaic module, and has high reflectivity so as to improve photoelectric conversion efficiency. In the packaging and printing fields, the high-transparency label can be used as a high-transparency label, and the appearance texture of the product is improved. In chinese patent CN 112946794B filed earlier by the applicant, a high-luminance DOP composite membrane is disclosed, and a greater luminance is obtained by changing the surface physical structure of the membrane. However, the composite membrane is only suitable for the special liquid crystal display field, has a complex structure and excessive thickness, and is difficult to be widely applied to other fields. CN 106526726B discloses a polyester film which is obtained by coating a coating layer containing inorganic particles on the surface of a substrate to obtain high brightness, high light transmittance and low haze. These inorganic particles may be alumina, aluminum hydroxide, silica, titania, zirconia, calcium carbonate, magnesium carbonate, and barium sulfate. However, the inorganic particles themselves have a fixed light refractive index, and have problems of compatibility and dispersibility with the coating paste, and it is difficult to change the brightness value of the polyester film with an excessively low addition amount, while an excessively high addition amount decreases the light transmittance and deteriorates the mechanical properties of the coating. The prior art has many examples of changing the surface brightness value of polyester film by means of optical coating. For example, CN 114196052A, CN 102108173B and CN 106707373B, these prior arts have problems of compatibility and dispersibility of optical particles of the coating, and the coating is only attached to the surface of the film, and cannot change the brightness value of the film itself, and once the coating is dropped or uneven, the overall performance of the film is greatly affected. Disclosure of Invention The technical problem to be solved by the invention is to provide an optical grade high brightness polyester film and a preparation method thereof, so as to reduce or avoid the problems. In order to solve the technical problems, the invention provides an optical-grade high-brightness polyester film which comprises a nanoscale multilayer structure formed by alternately laminating PET layers and PEN layers, wherein the total number of layers is 350-700, the total thickness is 30-60 mu m, the refractive index of the PET layers is 1.58-1.62, the refractive index of the PEN layers is 1.64-1.68, the average reflectivity of the film at 550nm wavelength is more than or equal to 98.5%, the light transmittance is more than or equal to 91.5%, the haze is less than or equal to 0.5%, and the interlayer peeling strength is more than or equal to 3.0N/cm. Preferably, the refractive index of the PET layer is 1.58 and the refractive index of the PEN layer is 1.64. Preferably, the PET layer is prepared from 50 to 55 parts by weight of terephthalic acid, 25 to 28 parts by weight of ethylene glycol, 8 to 12 parts by weight of cyclohexanedimethanol, 0.4 to 0.6 part by weight of tetrafluoroterephthalic acid, 0.1 to 0.3 part by weight of an antioxidant, and 0.05 to 0.1 part by weight of a catalyst. Preferably, the PEN layer is prepared from 48 to 52 parts by weight of naphthalene dicarboxylic acid, 30 to 32 parts by weight of ethylene glycol, 5 to 8 parts by weight of terephthalic acid, 1.0 to 1.5 parts by weight of a polyester elastomer, and 0.05 to 0.1 parts by weight of a catalyst. The invention also provides a method for preparing the optical-grade high-brightness polyester film, which comprises the following steps of respectively preparing modified PET slices and modified PEN slices, putting the prepared modified PET slices into a PET twin-screw extruder, putting the prep