A high-stability quantum dot reflective film for display and its preparation method

Abstract

The present invention relates to the field of quantum dot reflective film technology, disclosing a high-stability quantum dot reflective film for display and its preparation method. The film comprises a three-layer structure, A / B / A. The raw materials for layer A include a matrix resin and an antistatic agent; the raw materials for layer B include a matrix resin and fluorescent quantum dot composite microspheres. The fluorescent quantum dot composite microspheres comprise fluorescent quantum dots whose surfaces have been passivated with tert-dodecyl mercaptan and a cycloolefin polymer coating the surfaces. The method first passivates surface defects of the fluorescent quantum dot material with alkyl mercaptan, then uses a cycloolefin polymer as a secondary shell material. The composite particles are mixed with the matrix resin. The resulting quantum dot reflective film exhibits high fluorescence efficiency and wide color gamut display capabilities, while also exhibiting superhydrophobicity and anti-oxidative chemical stability.

Description

Technical Field

[0001] The present invention relates to the technical field of quantum dot reflective films, and in particular to a high-stability quantum dot reflective film for display and a preparation method thereof. Background Art

[0002] Liquid crystal displays (LCDs) are currently the world's most mainstream display technology. However, the broad spectrum of phosphors used in common LCD backlights limits further improvements in color display capabilities and overall lumen efficiency. Quantum dots, with their narrow emission spectrum and high fluorescence efficiency, offer a new technological path to improving LCD color quality and perceived brightness.

[0003] Perovskite quantum dots, as semiconductor nanocrystals, possess unique optical and electrical properties and hold broad application prospects in display, lighting, biomedicine, and other fields. Due to their strong ionicity, high surface energy, and metastable structure, they are highly sensitive to their environment and are easily dissolved by polar solvents to form large nanocrystals, resulting in structural collapse, shape deformation, and a rapid decrease in quantum yield (QYs). Even exposure to air can cause phase transitions, aggregation, and even degradation under the synergistic effects of water and oxygen, leading to fluorescence quenching and a decrease in the device's photoelectric conversion efficiency. Therefore, maintaining the high efficiency and stability of quantum dots in display devices is crucial for promoting their application in the display field.

[0004] CN117930545A discloses a quantum dot reflective film, its preparation method, and a backlight module. Its primary function is to improve the stability and optical performance of the quantum dot reflective film by adding quantum dots and bubbles to a resin layer and applying a functional coating. However, this method suffers from insufficient adhesion of the functional coating, and during use, the coating may delaminate or peel from the resin layer or quantum dots, affecting the film's optical performance and stability.

[0005] CN103852817B discloses a quantum dot film for backlight modules. The microporous structure on the surface of silica gel particles allows quantum dots to be adsorbed in the micropores, improving the atomized light source of the quantum dots, thereby achieving the effect of improving the color gamut and brightness. Compared to the diffusion film in the traditional backlight module, the quantum dot film can save costs and therefore can be widely used in various display devices. However, this method uses the microporous structure of silica gel particles to adsorb quantum dots, which has problems with compatibility with the resin interface, making it difficult to ensure a completely uniform distribution of quantum dots within the film.

[0006] CN114214066B discloses a perovskite quantum dot coating, a preparation method, a fluorescent film and its application, which provides a perovskite quantum dot coating to alleviate the technical problem that the luminescent layer in the prior art cannot have both green and red light functions. The perovskite quantum dot CsPb used in this perovskite quantum dot coating is a kind of perovskite quantum dot coating.x Mn 1-x Cl3 has dual luminescence peaks at 430nm and 600nm, exhibiting excellent dual-wavelength fluorescence emission characteristics, manifesting as bright orange light. Its application in backlight modules greatly simplifies the structure of white LED backlights. However, this method is complex in its preparation process, involving quantum dot synthesis, mixing with polymers and other materials, and coating. This leads to high costs, and coating uniformity is difficult to ensure, affecting the uniformity of the display effect. Summary of the Invention

[0007] The present invention aims to overcome the above-mentioned problems existing in the application of quantum dots in display devices in the prior art and provides a high-stability quantum dot reflective film for display and a preparation method thereof. The surface defects of the fluorescent quantum dot material are first passivated by alkyl mercaptan, and then a cycloolefin polymer is used as the secondary shell material. The composite particles are mixed with a matrix resin. The prepared quantum dot reflective film has high fluorescence efficiency and high color gamut display capability, while also having super-hydrophobicity and anti-oxidation chemical stability.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions:

[0009] A high-stability quantum dot reflective film for display has an A / B / A three-layer structure; the raw materials of layer A include a matrix resin and an antistatic agent; the raw materials of layer B include a matrix resin and fluorescent quantum dot composite microspheres; the fluorescent quantum dot composite microspheres include fluorescent quantum dots whose surfaces are passivated with tert-dodecyl mercaptan and a cycloolefin polymer coated on the surface; the fluorescent quantum dots are selected from at least one of CuInS quantum dots, CuInS / ZnS quantum dots, InP / ZnS quantum dots, CdSe / ZnS quantum dots, and CdTe / CdSe / ZnS quantum dots.

[0010] The present invention first uses tert-dodecyl mercaptan (TMA) to react with unsaturated lead ions on the surface of fluorescent quantum dots to form a stable coordination structure, thereby passivating surface defects of the fluorescent quantum dot material. The passivated fluorescent quantum dots are then coated with a cycloolefin polymer. The cycloolefin polymer has excellent optical properties, high transparency, and a high refractive index, and improves the reflectivity of the reflective film. At the same time, the cycloolefin polymer has a high molecular structure rigidity, low water absorption, good thermal stability, and excellent water and oxygen barrier properties. Using it as a second shell layer can enhance the ability of the fluorescent quantum dot material to resist moisture and oxygen corrosion. The formed protective layer can reduce environmental damage to the internal structure of the material and improve the photoelectric conversion efficiency. In addition, the cycloolefin polymer can serve as a carrier for the quantum dot material. During the stretching process when preparing the reflective film, ellipsoidal microparticle cavities of uniform size and distribution are formed, which gives the reflective film excellent reflectivity and significantly improves the luminescence performance. Due to its good thermal stability and high glass transition temperature, the ellipsoidal bubbles formed in the matrix are not easy to collapse, and the reflective film has good stability.

[0011] Therefore, the present invention achieves a functional gradient design by layering TMA and cycloolefin polymer coatings on the surface of fluorescent quantum dots: TMA enhances the stability of the quantum dot material, while the cycloolefin polymer further isolates water and oxygen. Furthermore, the long TMA alkyl chains form a coating on the surface of the fluorescent quantum dot particles, generating steric hindrance. This steric hindrance prevents the quantum dots from approaching and aggregating, improving the dispersion compatibility of the fluorescent quantum dots within the cycloolefin polymer, enhancing the uniformity of the cycloolefin polymer coating on the quantum dots, improving the interface quality between the layers, reducing defects, and enhancing the stability and durability of the overall structure.

[0012] Preferably, the green light emission band of the fluorescent quantum dots is 500-580 nm. The green light emission band is consistent with the visual characteristics of the human eye, has high perceptual intensity, high luminous efficiency and color gamut coverage, and contributes significantly to improving the overall brightness of liquid crystal displays.

[0013] Preferably, in the fluorescent quantum dot composite microspheres, the mass ratio of the fluorescent quantum dots whose surfaces are passivated and modified by tert-dodecyl mercaptan to the cycloolefin polymer is 10:90~2:98; in the fluorescent quantum dots whose surfaces are passivated and modified by tert-dodecyl mercaptan, the mass ratio of the fluorescent quantum dots to tert-dodecyl mercaptan is 1:1~1:10.

[0014] Preferably, the cycloolefin polymer is at least one selected from polycyclopentene, polycyclohexene, polycyclooctene, polynorbornene, and ethylene-cycloolefin copolymer.

[0015] Preferably, the mass ratio of the matrix resin to the antistatic agent in layer A is 95:5-98:2; the mass ratio of the matrix resin to the fluorescent quantum dot composite microspheres in layer B is 60:40-90:10.

[0016] Preferably, the total thickness of the high-stability quantum dot reflective film for display is 75-188 μm, and the thickness ratio of layer A to layer B is 1:15-1:5.

[0017] Preferably, the matrix resin is selected from at least one of polypropylene (PP), ethylene-propylene copolymer (EPM), low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), high-density polyethylene (HDPE), ultra-low-density polyethylene (VLDPE), polyethylene terephthalate (PET), polytrimethylene terephthalate (PTT), terephthalate-ethylene glycol-1,4-cyclohexanedimethanol terpolymer (PETG), terephthalate-isophthalate-ethylene glycol terpolymer (APET), and polyethylene naphthalate (PEN).

[0018] Preferably, the intrinsic viscosity of the base resin is 0.64-0.91 dL / g.

[0019] The present invention also discloses a method for preparing the above-mentioned high-stability quantum dot reflective film for display, comprising the following steps:

[0020] (1) Coating tert-dodecyl mercaptan on the surface of fluorescent quantum dots to obtain fluorescent quantum dots with surface passivation modified by tert-dodecyl mercaptan;

[0021] (2) coating the surface of fluorescent quantum dots passivated with tert-dodecyl mercaptan with a cycloolefin polymer to obtain fluorescent quantum dot composite microspheres;

[0022] (3) The raw materials of layer A and layer B are mixed separately, and then subjected to three-layer co-extrusion, cast film, biaxial stretching, and heat setting to obtain the high-stability quantum dot reflective film for display.

[0023] Preferably, the modification method in step (1) is as follows: the fluorescent quantum dots are dispersed in anhydrous ethanol, tert-dodecyl mercaptan is added, and the reaction is stirred in a constant temperature water bath at 70-80°C for 6-8 hours. After evaporation of the solvent, deionized water is added, and the mixture is allowed to stand after shaking. The upper layer of liquid is taken and the unreacted tert-dodecyl mercaptan is removed. The obtained liquid is freeze-dried to obtain fluorescent quantum dots whose surface is passivated and modified by tert-dodecyl mercaptan.

[0024] Preferably, the coating method in step (2) is: mixing the cycloolefin polymer and the fluorescent quantum dots whose surfaces are passivated and modified by tert-dodecyl mercaptan, melt-extruding, cooling, drying, and pelletizing to obtain the fluorescent quantum dot composite microspheres; the melt extrusion temperature is 220~270℃.

[0025] Preferably, the temperature of the three-layer co-extrusion in step (3) is 240-285°C;

[0026] During biaxial stretching, first perform longitudinal stretching of 2 to 5 times, then perform transverse stretching of 1 to 3 times, and the temperature during stretching is 120 to 140°C;

[0027] The heat setting temperature is 180~220℃, and the heat setting time is 5~60s.

[0028] Therefore, the present invention has the following beneficial effects:

[0029] (1) TMA is used to passivate the surface defects of the fluorescent quantum dot material to enhance the stability of the quantum dot material, and then the passivated fluorescent quantum dots are coated with cycloolefin polymers to further isolate water and oxygen, so that the reflective film has high fluorescence efficiency and high color gamut display capabilities while also having super hydrophobicity and anti-oxidation chemical stability;

[0030] (2) The long TMA alkyl chain can form a coating layer on the surface of the fluorescent quantum dot particles, thereby generating a steric hindrance effect, improving the dispersion compatibility of the fluorescent quantum dots within the cycloolefin polymer, improving the uniformity of the cycloolefin polymer coating on the quantum dots, improving the interface quality between the layers, reducing defects, and enhancing the stability and durability of the overall structure. DETAILED DESCRIPTION

[0031] The present invention will be further described below in conjunction with specific embodiments.

[0032] In the present invention, unless otherwise specified, all equipment and raw materials can be purchased from the market or are commonly used in the industry. The methods in the following embodiments, unless otherwise specified, are all conventional methods in the art.

[0033] Overall embodiment:

[0034] A high-stability quantum dot reflective film for display has an A / B / A three-layer structure; the raw materials of layer A include a matrix resin and an antistatic agent; the raw materials of layer B include a matrix resin and fluorescent quantum dot composite microspheres; the fluorescent quantum dot composite microspheres include fluorescent quantum dots whose surfaces are passivated with tert-dodecyl mercaptan and a cycloolefin polymer coated on the surface; the fluorescent quantum dots are selected from at least one of CuInS quantum dots, CuInS / ZnS quantum dots, InP / ZnS quantum dots, CdSe / ZnS quantum dots, and CdTe / CdSe / ZnS quantum dots.

[0035] As a specific embodiment, the green light emission band of the fluorescent quantum dots is 500~580nm.

[0036] As a specific embodiment, in the fluorescent quantum dot composite microspheres, the mass ratio of the fluorescent quantum dots whose surfaces are passivated and modified by tert-dodecyl mercaptan to the cycloolefin polymer is 10:90~2:98; in the fluorescent quantum dots whose surfaces are passivated and modified by tert-dodecyl mercaptan, the mass ratio of the fluorescent quantum dots to tert-dodecyl mercaptan is 1:1~1:10.

[0037] As a specific embodiment, the cycloolefin polymer is selected from at least one of polycyclopentene, polycyclohexene, polycyclooctene, polynorbornene, and ethylene-cyclic olefin copolymer; preferably, it is an addition copolymer of ethylene and norbornene with a glass transition temperature of 80~160°C.

[0038] As a specific implementation manner, the mass ratio of the matrix resin to the antistatic agent in layer A is 95:5-98:2; the mass ratio of the matrix resin to the fluorescent quantum dot composite microspheres in layer B is 60:40-90:10.

[0039] As a specific embodiment, the total thickness of the high-stability quantum dot reflective film for display is 75-188 μm, and the thickness ratio of layer A to layer B is 1:15-1:5.

[0040] As a specific embodiment, the matrix resin is selected from at least one of PP, EPM, LDPE, LLDPE, HDPE, VLDPE, PET, PTT, PETG, APET, and PEN; preferably, it is PP or PET.

[0041] As a specific embodiment, the intrinsic viscosity of the base resin is 0.64-0.91 dL / g.

[0042] The method for preparing the above-mentioned high-stability quantum dot reflective film for display comprises the following steps:

[0043] (1) Coating tert-dodecyl mercaptan on the surface of fluorescent quantum dots to obtain fluorescent quantum dots with surface passivation modified by tert-dodecyl mercaptan;

[0044] (2) coating the surface of fluorescent quantum dots passivated with tert-dodecyl mercaptan with a cycloolefin polymer to obtain fluorescent quantum dot composite microspheres;

[0045] (3) The raw materials of layer A and layer B are mixed separately, and then subjected to three-layer co-extrusion, cast film, biaxial stretching, and heat setting to obtain the high-stability quantum dot reflective film for display.

[0046] As a specific embodiment, the modification method in step (1) is as follows: the fluorescent quantum dots are dispersed in anhydrous ethanol, tert-dodecyl mercaptan is added, and the reaction is stirred in a constant temperature water bath at 70-80° C. for 6-8 hours. After evaporation of the solvent, deionized water is added, and the mixture is allowed to stand after shaking. The upper layer of liquid is taken and the unreacted tert-dodecyl mercaptan is removed. The obtained liquid is freeze-dried to obtain fluorescent quantum dots whose surface is passivated and modified by tert-dodecyl mercaptan.

[0047] As a specific embodiment, the coating method in step (2) is: mixing a cycloolefin polymer and fluorescent quantum dots whose surfaces are passivated and modified by tert-dodecyl mercaptan, melt-extruding, cooling, drying, and pelletizing to obtain the fluorescent quantum dot composite microspheres; the melt extrusion temperature is 220~270℃.

[0048] As a specific embodiment, the temperature of the three-layer co-extrusion in step (3) is 240~285℃;

[0049] During biaxial stretching, first perform longitudinal stretching of 2 to 5 times, then perform transverse stretching of 1 to 3 times, and the temperature during stretching is 120 to 140°C;

[0050] The heat setting temperature is 180~220℃, and the heat setting time is 5~60s.

[0051] Example 1:

[0052] A high-stability quantum dot reflective film for display use has a thickness of 188 μm and a three-layer A / B / A structure (the thickness ratio of the A to B layers is 1:15). The raw materials for the A layer include a base resin of polyethylene terephthalate (Sinopec, PET film-grade chips, intrinsic viscosity GB / T 14190-2017: 0.8 dL / g) and an antistatic agent (Shanghai Toyo Ink, PET antistatic masterbatch) in a mass ratio of 98:2. The raw materials for the B layer include a base resin of polyethylene terephthalate (Sinopec, PET film-grade chips, intrinsic viscosity GB / T 14190-2017: 0.8 dL / g) and fluorescent quantum dot composite microspheres in a mass ratio of 84:16.

[0053] The method for preparing the above-mentioned high-stability quantum dot reflective film for display comprises the following steps:

[0054] (1) InP / ZnS quantum dots (Shanghai Aladdin Biochemical Technology Co., Ltd., fluorescence emission wavelength: 540 nm) were dispersed in anhydrous ethanol, with the mass volume ratio of fluorescent quantum dots to anhydrous ethanol being 1:5; then tert-dodecyl mercaptan (TMA, Shanghai Aladdin Biochemical Technology Co., Ltd., 98%) was added at a mass ratio of 5:1 to the fluorescent quantum dots, and the mixture was stirred in a constant temperature water bath at 80°C for 6 h. After evaporation of the solvent, 200 mL of deionized water was added and the mixture was transferred to a 250 mL separatory funnel; after shaking and allowing to stand, the upper layer of liquid was taken and the unreacted tert-dodecyl mercaptan was removed. The obtained liquid was freeze-dried to obtain passivated modified fluorescent quantum dots;

[0055] (2) The addition copolymer of ethylene and norbornene (Mitsui Chemicals, Japan, APL6013T, Tg: 135℃, MFR-260℃, 2.16kg: 15g / 10min) and passivated modified fluorescent quantum dots were added into a twin-screw extruder at a mass ratio of 98:2 through a weight loss scale, mixed and extruded at 235℃, cooled in a water tank, dried to remove water, and pelletized to obtain fluorescent quantum dot composite microspheres;

[0056] (3) The raw materials of layer A and layer B are mixed in proportion, and then subjected to three-layer co-extrusion, cast film, biaxial stretching, and heat setting to obtain the high-stability quantum dot reflective film for display; the temperature of the three-layer co-extrusion is 285°C; during biaxial stretching, the longitudinal stretching is performed 3 times, and then the transverse stretching is performed 4 times, and the temperature during stretching is 130°C; the heat setting temperature is 220°C, and the heat setting time is 5s.

[0057] Example 2:

[0058] A high-stability quantum dot reflective film for display use has a thickness of 188 μm and a three-layer A / B / A structure (the thickness ratio of the A layer to the B layer is 1:15); the raw materials of the A layer include a base resin polyethylene terephthalate (same as in Example 1) and an antistatic agent (same as in Example 1) in a mass ratio of 98:2; the raw materials of the B layer include a base resin polyethylene terephthalate (same as in Example 1) and fluorescent quantum dot composite microspheres in a mass ratio of 84:16.

[0059] The method for preparing the above-mentioned high-stability quantum dot reflective film for display comprises the following steps:

[0060] (1) InP / ZnS quantum dots (same as in Example 1) were dispersed in anhydrous ethanol, with the mass volume ratio of fluorescent quantum dots to anhydrous ethanol being 1:5; then tert-dodecyl mercaptan (same as in Example 1) was added at a mass ratio of 8:1 to fluorescent quantum dots, and stirred in a constant temperature water bath at 80°C for 6 h. After evaporation of the solvent, 200 mL of deionized water was added, and the mixture was transferred to a 250 mL separatory funnel; after shaking, the mixture was allowed to stand, the upper layer of liquid was taken, and the unreacted tert-dodecyl mercaptan was removed. The obtained liquid was freeze-dried to obtain passivated modified fluorescent quantum dots;

[0061] (2) The addition copolymer of ethylene and norbornene (same as in Example 1) and the passivated modified fluorescent quantum dots were added to a twin-screw extruder at a mass ratio of 95:5 through a weight loss scale, mixed and extruded at 220°C, cooled in a water tank, dried to remove water, and pelletized to obtain fluorescent quantum dot composite microspheres;

[0062] (3) The raw materials of layer A and layer B are mixed in proportion, and then subjected to three-layer co-extrusion, cast film, biaxial stretching, and heat setting to obtain the high-stability quantum dot reflective film for display; the temperature of the three-layer co-extrusion is 265°C; during biaxial stretching, the longitudinal stretching is performed 3 times, and then the transverse stretching is performed 4 times, and the temperature during stretching is 130°C; the heat setting temperature is 220°C, and the heat setting time is 5s.

[0063] Example 3:

[0064] A high-stability quantum dot reflective film for display, having a thickness of 188 μm and an A / B / A three-layer structure (the thickness ratio of the A layer to the B layer is 1:15); the raw materials of the A layer include a base resin polyethylene terephthalate (same as in Example 1) and an antistatic agent (same as in Example 1) in a mass ratio of 98:2; the raw materials of the B layer include a base resin polyethylene terephthalate (same as in Example 1) and fluorescent quantum dot composite microspheres in a mass ratio of 90:10.

[0065] The method for preparing the above-mentioned high-stability quantum dot reflective film for display comprises the following steps:

[0066] (1) InP / ZnS quantum dots (same as in Example 1) were dispersed in anhydrous ethanol, with the mass volume ratio of fluorescent quantum dots to anhydrous ethanol being 1:5; then tert-dodecyl mercaptan (same as in Example 1) was added at a mass ratio of 10:1 to the fluorescent quantum dots, and the mixture was stirred in a constant temperature water bath at 80°C for 6 h. After evaporation of the solvent, 200 mL of deionized water was added, and the mixture was transferred to a 250 mL separatory funnel; after shaking and allowing to stand, the upper layer of liquid was collected, and the unreacted tert-dodecyl mercaptan was removed. The obtained liquid was freeze-dried to obtain passivated modified fluorescent quantum dots;

[0067] (2) The addition copolymer of ethylene and norbornene (same as in Example 1) and the passivated modified fluorescent quantum dots were added into a twin-screw extruder at a mass ratio of 90:10 through a weight loss scale, mixed and extruded at 235°C, cooled in a water tank, dried to remove water, and pelletized to obtain fluorescent quantum dot composite microspheres;

[0068] (3) The raw materials of layer A and layer B are mixed in proportion, and then subjected to three-layer co-extrusion, cast film, biaxial stretching, and heat setting to obtain the high-stability quantum dot reflective film for display; the temperature of the three-layer co-extrusion is 285°C; during biaxial stretching, the longitudinal stretching is performed 3 times, and then the transverse stretching is performed 4 times, and the temperature during stretching is 130°C; the heat setting temperature is 220°C, and the heat setting time is 5s.

[0069] Example 4:

[0070] A high-stability quantum dot reflective film for display use has a thickness of 188 μm and a three-layer A / B / A structure (the thickness ratio of the A layer to the B layer is 1:15); the raw materials of the A layer include a base resin polyethylene terephthalate (same as in Example 1) and an antistatic agent (same as in Example 1) in a mass ratio of 98:2; the raw materials of the B layer include a base resin polyethylene terephthalate (same as in Example 1) and fluorescent quantum dot composite microspheres in a mass ratio of 73:27.

[0071] The method for preparing the above-mentioned high-stability quantum dot reflective film for display comprises the following steps:

[0072] (1) InP / ZnS quantum dots (same as in Example 1) were dispersed in anhydrous ethanol, with the mass volume ratio of fluorescent quantum dots to anhydrous ethanol being 1:5; then tert-dodecyl mercaptan (same as in Example 1) was added at a mass ratio of 10:1 to the fluorescent quantum dots, and the mixture was stirred in a constant temperature water bath at 80°C for 6 h. After evaporation of the solvent, 200 mL of deionized water was added, and the mixture was transferred to a 250 mL separatory funnel; after shaking and allowing to stand, the upper layer of liquid was collected, and the unreacted tert-dodecyl mercaptan was removed. The obtained liquid was freeze-dried to obtain passivated modified fluorescent quantum dots;

[0073] (2) The addition copolymer of ethylene and norbornene (same as in Example 1) and the passivated modified fluorescent quantum dots were added into a twin-screw extruder at a mass ratio of 90:10 through a weight loss scale, mixed and extruded at 235°C, cooled in a water tank, dried to remove water, and pelletized to obtain fluorescent quantum dot composite microspheres;

[0074] (3) The raw materials of layer A and layer B are mixed in proportion, and then subjected to three-layer co-extrusion, cast film, biaxial stretching, and heat setting to obtain the high-stability quantum dot reflective film for display; the temperature of the three-layer co-extrusion is 285°C; during biaxial stretching, the longitudinal stretching is performed 3 times, and then the transverse stretching is performed 4 times, and the temperature during stretching is 130°C; the heat setting temperature is 220°C, and the heat setting time is 5s.

[0075] Example 5:

[0076] A high-stability quantum dot reflective film for display, having a thickness of 188 μm and an A / B / A three-layer structure (the thickness ratio of the A layer to the B layer is 1:5.6); the raw materials of the A layer include a base resin polyethylene terephthalate (same as in Example 1) and an antistatic agent (same as in Example 1) in a mass ratio of 98:2; the raw materials of the B layer include a base resin polyethylene terephthalate (same as in Example 1) and fluorescent quantum dot composite microspheres in a mass ratio of 84:16.

[0077] The method for preparing the above-mentioned high-stability quantum dot reflective film for display comprises the following steps:

[0078] (1) InP / ZnS quantum dots (same as in Example 1) were dispersed in anhydrous ethanol, with the mass volume ratio of fluorescent quantum dots to anhydrous ethanol being 1:5; then tert-dodecyl mercaptan (same as in Example 1) was added at a mass ratio of 10:1 to the fluorescent quantum dots, and the mixture was stirred in a constant temperature water bath at 80°C for 6 h. After evaporation of the solvent, 200 mL of deionized water was added, and the mixture was transferred to a 250 mL separatory funnel; after shaking and allowing to stand, the upper layer of liquid was collected, and the unreacted tert-dodecyl mercaptan was removed. The obtained liquid was freeze-dried to obtain passivated modified fluorescent quantum dots;

[0079] (2) The addition copolymer of ethylene and norbornene (same as in Example 1) and the passivated modified fluorescent quantum dots were added into a twin-screw extruder at a mass ratio of 90:10 through a weight loss scale, mixed and extruded at 235°C, cooled in a water tank, dried to remove water, and pelletized to obtain fluorescent quantum dot composite microspheres;

[0080] (3) The raw materials of layer A and layer B are mixed in proportion, and then subjected to three-layer co-extrusion, cast film, biaxial stretching, and heat setting to obtain the high-stability quantum dot reflective film for display; the temperature of the three-layer co-extrusion is 285°C; during biaxial stretching, the longitudinal stretching is performed 3 times, and then the transverse stretching is performed 4 times, and the temperature during stretching is 130°C; the heat setting temperature is 220°C, and the heat setting time is 5s.

[0081] Comparative Example 1 (passivation without TMA):

[0082] A high-stability quantum dot reflective film for display use has a thickness of 188 μm and a three-layer A / B / A structure (the thickness ratio of the A layer to the B layer is 1:15); the raw materials of the A layer include a base resin polyethylene terephthalate (same as in Example 1) and an antistatic agent (same as in Example 1) in a mass ratio of 98:2; the raw materials of the B layer include a base resin polyethylene terephthalate (same as in Example 1) and fluorescent quantum dot composite microspheres in a mass ratio of 84:16.

[0083] The method for preparing the above-mentioned high-stability quantum dot reflective film for display comprises the following steps:

[0084] (1) The addition copolymer of ethylene and norbornene (same as in Example 1) and InP / ZnS quantum dots (same as in Example 1) were added to a twin-screw extruder at a mass ratio of 98:2 through a loss-in-weight scale, mixed and extruded at 235°C, cooled in a water tank, dried to remove water, and pelletized to obtain fluorescent quantum dot composite microspheres;

[0085] (2) The raw materials of layer A and layer B are mixed in proportion, and then subjected to three-layer co-extrusion, cast film, biaxial stretching, and heat setting to obtain the high-stability quantum dot reflective film for display; the temperature of the three-layer co-extrusion is 285°C; during biaxial stretching, the longitudinal stretching is performed 3 times, and then the transverse stretching is performed 4 times, and the temperature during stretching is 130°C; the heat setting temperature is 220°C, and the heat setting time is 5s.

[0086] Comparative Example 2 (without coating of cycloolefin polymer):

[0087] A high-stability quantum dot reflective film for display, having a thickness of 188 μm and an A / B / A three-layer structure (the thickness ratio of the A layer to the B layer is 1:15); the raw materials of the A layer include a base resin polyethylene terephthalate (same as in Example 1) and an antistatic agent (same as in Example 1) in a mass ratio of 98:2; the raw materials of the B layer include a base resin polyethylene terephthalate (same as in Example 1) and passivated modified fluorescent quantum dots in a mass ratio of 84:16.

[0088] The method for preparing the above-mentioned high-stability quantum dot reflective film for display comprises the following steps:

[0089] (1) InP / ZnS quantum dots (same as in Example 1) were dispersed in anhydrous ethanol, with the mass volume ratio of fluorescent quantum dots to anhydrous ethanol being 1:5; then tert-dodecyl mercaptan (same as in Example 1) was added at a mass ratio of 5:1 to the fluorescent quantum dots, and the mixture was stirred in a constant temperature water bath at 80°C for 6 h. After evaporation of the solvent, 200 mL of deionized water was added, and the mixture was transferred to a 250 mL separatory funnel; after shaking and allowing to stand, the upper layer of liquid was taken, and the unreacted tert-dodecyl mercaptan was removed. The obtained liquid was freeze-dried to obtain passivated modified fluorescent quantum dots;

[0090] (2) The raw materials of layer A and layer B are mixed in proportion, and then subjected to three-layer co-extrusion, cast film, biaxial stretching, and heat setting to obtain the high-stability quantum dot reflective film for display; the temperature of the three-layer co-extrusion is 285°C; during biaxial stretching, the longitudinal stretching is performed 3 times, and then the transverse stretching is performed 4 times, and the temperature during stretching is 130°C; the heat setting temperature is 220°C, and the heat setting time is 5s.

[0091] Comparative Example 3 (TMA and cycloolefin polymer mixed coating):

[0092] The difference between Comparative Example 3 and Example 1 is that the preparation method of fluorescent quantum dot composite microspheres is as follows: an addition copolymer of ethylene and norbornene (same as in Example 1), tert-dodecyl mercaptan (same as in Example 1), and InP / ZnS fluorescent quantum dots (same as in Example 1) are added to a twin-screw extruder at a mass ratio of 98:10:2 via a loss-in-weight scale, mixed and extruded at 235° C., cooled in a water tank, dried to remove water, and pelletized to obtain fluorescent quantum dot composite microspheres;

[0093] The rest are the same as in Example 1.

[0094] Comparative Example 4 (using poly-4-methyl-1-pentene instead of cycloolefin polymer):

[0095] The difference between Comparative Example 4 and Example 1 is that, when preparing fluorescent quantum dot composite microspheres, poly-4-methyl-1-pentene (Mitsui Chemicals RT18, glass transition temperature: 35°C, melt index 22 g / 10 min) is used instead of the addition copolymer of ethylene and norbornene, and the rest is the same as in Example 1.

[0096] The properties of the reflective films prepared in the above embodiments and comparative examples were tested, and the results are shown in Table 1.

[0097] The reflectance at 550nm was measured using a ColorQuest XE spectrophotometer.

[0098] The tensile properties were measured using a universal tensile testing machine with a sample size of 150 mm × 15 mm, a tensile rate of 100 mm / min, and a sample spacing of 100 mm.

[0099] Porosity = (unstretched sample density - stretched sample density) / unstretched sample density × 100%;

[0100] High-temperature and high-humidity reliability testing: After being placed in a 60°C / 90% RH environment for 240 hours, the 550nm reflectivity was re-measured to evaluate the reliability of the quantum dot reflective film.

[0101] Table 1: Reflective film performance test results

[0102]

[0103] As can be seen from Table 1, the reflective films prepared using the method of the present invention in Examples 1 to 5 all have a reflectivity of over 97.9% at a wavelength of 550 nm, effectively reducing light absorption and transmission losses, exhibiting excellent reflective properties, and enhancing the brightness and contrast of the display screen. Furthermore, the films have good mechanical properties and resistance to humidity and oxygen corrosion, and the reflectivity shows little change before and after the reliability test.

[0104] In Comparative Example 1, the quantum dots were directly coated with cycloolefin polymer without TMA passivation. Due to the large number of defect states on the quantum dot surface, the fluorescence intensity was weakened, resulting in a decrease in luminescence performance and a significant decrease in reflectivity compared with Example 1. In Comparative Example 2, the quantum dots were passivated only with TMA without coating with cycloolefin polymer. The quantum dots had poor dispersion uniformity and lacked the cycloolefin polymer as a carrier to form ellipsoidal cells inside the incompatible resin. The porosity of the reflective film decreased, and the number of interface reflection layers decreased, resulting in a significant decrease in the reflective performance of the reflective film compared with Example 1. In Comparative Example 3, TMA and cycloolefin polymer were directly mixed to coat the quantum dots. Due to the weakening of the surface passivation effect of the quantum dots by direct mixing with TMA, the overall structure and stability of the microspheres decreased, resulting in a decrease in film reliability. The reflectivity before and after the reliability test decreased significantly (in this field, a difference of 0.3% in reflectivity will result in a significant difference in brightness). In Comparative Example 4, poly (4-methyl-1-pentene) was used instead of cycloolefin polymer for coating. Since poly (4-methyl-1-pentene) has a lower refractive index and glass transition temperature, the internal cells of the resin easily collapse at high temperatures, resulting in a decrease in the reflective performance of the reflective film compared with that in Example 1.

Claims

1. A high-stability quantum dot reflective film for display, characterized in that: It is a three-layer structure of A / B / A; The raw materials of layer A include base resin and antistatic agent; The raw materials of layer B include base resin and fluorescent quantum dot composite microspheres; The fluorescent quantum dot composite microspheres include fluorescent quantum dots whose surfaces are passivated and modified by tert-dodecyl mercaptan and cycloolefin polymers coated on the surfaces; The fluorescent quantum dots are selected from at least one of CuInS quantum dots, CuInS / ZnS quantum dots, InP / ZnS quantum dots, CdSe / ZnS quantum dots, and CdTe / CdSe / ZnS quantum dots; The cycloolefin polymer is selected from at least one of polycyclopentene, polycyclohexene, polycyclooctene, polynorbornene, and ethylene-cycloolefin copolymer; In the fluorescent quantum dot composite microspheres, the mass ratio of the fluorescent quantum dots whose surfaces are passivated and modified by tert-dodecyl mercaptan to the cycloolefin polymer is 10:90-2:98; in the fluorescent quantum dots whose surfaces are passivated and modified by tert-dodecyl mercaptan, the mass ratio of the fluorescent quantum dots to tert-dodecyl mercaptan is 1:1-1:

10.

2. The high-stability quantum dot reflective film for display according to claim 1, wherein: The mass ratio of the matrix resin to the antistatic agent in layer A is 95:5~98:2; the mass ratio of the matrix resin to the fluorescent quantum dot composite microspheres in layer B is 60:40~90:

10.

3. The high-stability quantum dot reflective film for display according to claim 1 or 2, characterized in that: The total thickness of the high-stability quantum dot reflective film for display is 75~188μm, and the thickness ratio of layer A to layer B is 1:15~1:

5.

4. The high-stability quantum dot reflective film for display according to claim 1 or 2, characterized in that: The matrix resin is selected from at least one of PP, EPM, LDPE, LLDPE, HDPE, VLDPE, PET, PTT, PETG, and PEN.

5. A method for preparing a high-stability quantum dot reflective film for display according to any one of claims 1 to 4, characterized in that: The steps include: (1) Coating tert-dodecyl mercaptan on the surface of fluorescent quantum dots to obtain fluorescent quantum dots with surface passivation modified by tert-dodecyl mercaptan; (2) coating the surface of fluorescent quantum dots passivated with tert-dodecyl mercaptan with a cycloolefin polymer to obtain fluorescent quantum dot composite microspheres; (3) The raw materials of layer A and layer B are mixed separately, and then subjected to three-layer co-extrusion, cast film, biaxial stretching, and heat setting to obtain the high-stability quantum dot reflective film for display.

6. The method for preparing a high-stability quantum dot reflective film for display according to claim 5, wherein: The modification method in step (1) is as follows: the fluorescent quantum dots are dispersed in anhydrous ethanol, tert-dodecyl mercaptan is added, and the reaction is stirred in a constant temperature water bath at 70-80°C for 6-8 hours. After evaporation of the solvent, deionized water is added, and the mixture is allowed to stand after shaking. The upper layer of liquid is taken and the unreacted tert-dodecyl mercaptan is removed. The obtained liquid is freeze-dried to obtain fluorescent quantum dots whose surface is passivated and modified by tert-dodecyl mercaptan.

7. The method for preparing a high-stability quantum dot reflective film for display according to claim 5, wherein: The coating method in step (2) is: mixing the cycloolefin polymer and the fluorescent quantum dots whose surfaces are passivated and modified by tert-dodecyl mercaptan, melt-extruding, cooling, drying, and pelletizing to obtain the fluorescent quantum dot composite microspheres.

8. The method for preparing a high-stability quantum dot reflective film for display according to claim 5, wherein: The temperature of the three-layer co-extrusion in step (3) is 240~285℃; During biaxial stretching, first perform longitudinal stretching of 2 to 5 times, then perform transverse stretching of 1 to 3 times, and the temperature during stretching is 120 to 140°C; The heat setting temperature is 180~220℃, and the heat setting time is 5~60s.

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