Patent Publication Number: US-2019195468-A1

Title: Reflection film

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of China application serial no. 201711428377.7, filed on Dec. 26, 2017. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to a reflection film, and particularly relates to a reflection film including a wavelength conversion material. 
     Description of Related Art 
     In today&#39;s technology, by coating a reflection film behind a backlight source of a display, a light-emitting efficiency of the light source may be improved, to enhance a light-emitting brightness of the display. Therefore, the reflection film is an important component in the display, and reflectivity thereof may influence a brightness effect of the display. 
     In the existing technology, a method for forming the reflection film is to add scattering inorganic particles to a polymer film or forming hollow pores in the polymer film. The reflection film has a light reflecting effect due to a difference between refractive indexes of the polymer film and the inorganic particles and the hollow pores. However, the reflection film obtained based on the above method has a problem of yellow-stain due to absorption of an ultraviolet light and heat emitted by a light-emitting diode (LED) bar, which results in a fact that reflectivity of the reflection film is decreased. Presently, a commonly used solution is to add an ultraviolet absorbent in the polymer film, however, although the ultraviolet absorbent has a protection effect, it also has many disadvantages, and the biggest disadvantage is that a spectral absorption band thereof generally extends to a blue light part of a visible light, so that the film presents a yellow tone. Therefore, in order to avoid the color changing problem of the film, only a small amount of the ultraviolet absorbent may be added, however, the small amount of the ultraviolet absorbent cannot achieve a complete protection effect, and after the film is irradiated by the light source for a period of time, the problem of yellow-stain is still occurred. 
     Therefore, to produce a reflection film capable of mitigating the problem of film yellow-stain, improving a backlight brightness and improving a color saturation is a target to be achieved in this field at present. 
     SUMMARY OF THE INVENTION 
     The invention is directed to a reflection film, which does not have a problem of yellow-stain and is adapted to provide higher backlight brightness and color saturation. 
     Other objects and advantages of the invention can be further illustrated by the technical features broadly embodied and described as follows. 
     The invention provides a reflection film including a reflection film substrate and a wavelength conversion layer. The wavelength conversion layer is disposed on the reflection film substrate. The wavelength conversion layer includes a wavelength conversion material, a plurality of nanoparticles and a base material. 
     In an embodiment of the invention, the wavelength conversion material comprises a quantum dot material, a rod-like material, or a combination thereof. 
     In an embodiment of the invention, a particle diameter of the quantum dot material is 0.5 nm-200 nm. 
     In an embodiment of the invention, a length of the rod-like material is 5 nm-500 nm, and a diameter of the rod-like material is 5 nm-200 nm. 
     In an embodiment of the invention, the wavelength conversion material includes a III-V group semiconductor material, a II-VI group semiconductor material, a IV-VI group semiconductor material, or a combination thereof. 
     In an embodiment of the invention, the wavelength conversion material is doped with a dopant, and the dopant comprises manganese, boron, nitrogen, a rare earth element or a combination thereof. 
     In an embodiment of the invention, a particle diameter of the nanoparticles is 0.5 nm-100 nm. 
     In an embodiment of the invention, a material of the nanoparticles includes a metal material or a semiconductor material. 
     In an embodiment of the invention, the base material includes a thermosetting resin or a light cured resin. 
     In an embodiment of the invention, the reflection film substrate includes a pore structure. 
     Since the reflection film of the invention includes the wavelength conversion material, the wavelength conversion material may absorb the ultraviolet light capable causing the problem of yellow-stain and convert the same into a visible light, so that the backlight brightness and the color saturation of the reflection film are improved. Moreover, the reflection film of the invention further includes a plurality of nanoparticles, by which the visible light converted by the adjacent wavelength conversion material further improves the backlight brightness and the color saturation of the reflection film. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of a reflection film according to an embodiment of the invention. 
         FIG. 2  is a spectral energy distribution diagram of the reflection film of the invention only includes a wavelength conversion material and the reflection film includes both of the wavelength conversion material and a plurality of nanoparticles. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Referring to  FIG. 1 , the reflection film  10  of the invention includes a reflection film substrate  100  and a wavelength conversion layer  200 . The reflection film  10  may be applied for a backlight or lighting of a liquid crystal display, though the invention is not limited thereto. 
     The reflection film substrate  100  includes a pore structure  110 . In an embodiment, the pore structure  110  is composed of inorganic particles and/or bubbles. A material of the inorganic particles includes TiO 2 , BaSO 4  or a combination thereof. A particle diameter of the inorganic particles is preferably 0.01 μm-2 μm. The content of the inorganic particles relative a total weight of the reflection film substrate  100  is 5-50%, and is preferably 10-20%. A material of the reflection film substrate  100  includes polyethylene terephthalate (PET), polypropylene (PP) or a combination thereof. In the present embodiment, the material of the reflection film substrate  100  is PET. It should be noted that the material of the reflection film substrate  100  is not particularly specified as long as it is properly selected according to a usage purpose or a required characteristic. 
     The wavelength conversion layer  200  is disposed on the reflection film substrate  100 . A process of disposing the wavelength conversion layer  200  on the reflection film substrate  100  may be a film coating method, though the invention is not limited thereto. The wavelength conversion layer  200  includes a wavelength conversion material  210 , a plurality of nanoparticles  220  and a base material  230 . 
     In an embodiment, the wavelength conversion material  210  comprises a quantum dot material, a rod-like material, or a combination thereof. A particle diameter of the quantum dot material is preferably 0.5 nm-200 nm. A length of the rod-like material is preferably 5 nm-500 nm, and a diameter of the rod-like material is preferably 5 nm-200 nm. A material of the wavelength conversion material  210  includes a III-V group semiconductor material, a II-VI group semiconductor material, a IV-VI group semiconductor material, or a combination thereof. For example, the material of the wavelength conversion material  210  may be InP, InAs, CdSe, InGaAs, InAsP, InSb, ZnO, InS, InGaN, Si, GaN, graphene nanosheets(GNS), ZnS or a combination thereof. When the wavelength conversion material  210  is made of the above materials, the wavelength conversion material  210  may convert an ultraviolet light absorbed by thereof into a visible light, to avoid a problem of yellow-stain and improve a backlight brightness and a color saturation of the reflection film  10 . 
     The wavelength conversion material  210  may be a single layer structure, a double layer structure or a multi-layer structure. In an embodiment, the wavelength conversion material  210  is a core-shell type double layer structure. When the wavelength conversion material  210  is the core-shell type double layer structure, a range of wavelengths changed by the wavelength conversion material  210  is enlarged (i.e. the ultraviolet light is more easy to be converted into the visible light), so that a wavelength conversion rate is enhanced. Moreover, when the wavelength conversion material  210  is the core-shell type double layer structure, it may protect a core structure to avoid oxidation. The wavelength conversion material  210  is doped with a dopant, and the dopant comprises manganese, boron, nitrogen, a rare earth element or a combination thereof. When the wavelength conversion material  210  is doped with the aforementioned elements, not only the wavelength conversion material  210  may maintain spectral characteristics of the undoped wavelength conversion material  210 , but it may avoid reduction of a light-emitting intensity caused by a self-quenching problem due to Stokes shift. 
     A particle diameter of the nanoparticles  220  is preferably 0.5 nm-100 nm. A material of the nanoparticles  220  includes a metal material or a semiconductor material. For example, the material of the nanoparticles  220  may be a metal material of gold, silver, platinum, copper, aluminium or alloys thereof, etc., or a semiconductor material, and the above materials have characteristics of negative real part dielectric constant and small imaginary part dielectric constant. In an embodiment, the material of the nanoparticles  220  is gold nanoparticles. 
     Referring to  FIG. 2 , according to  FIG. 2 , it is known that a stronger light-emitting intensity is achieved when the reflection film  10  includes both of the wavelength conversion material  210  and the nanoparticles  220 , and a reason thereof is that after the nanoparticles  220  are excited by the ultraviolet light, free electrons on the nanoparticles  220  have periodic relative displacement relative to ions on lattice. The charges are accumulated on an opposite surface due to the above relative displacement to cause increase of a local electric field intensity, which is referred to as a localized surface plasmon resonance (LSPR) effect. Through the LSPR effect of the nanoparticles  220  excited by the ultraviolet, the light-emitting intensity of the wavelength conversion material  210  may be further increased, to further improve the backlight brightness and the color saturation of the reflection film  10 . Moreover, since the nanoparticles  220  have the effect of enhancing the light-emitting intensity, the desired light-emitting intensity may be obtained by adjusting an adding ratio of the wavelength conversion material  210  and the nanoparticles  220  according to an actual requirement. For example, a plurality of nanoparticles  220  may be added to decrease a usage amount of the wavelength conversion material  210 , to decrease the process cost of the reflection film  10 . 
     A material of the base material  230  may be a thermosetting resin or a light cured resin. For example, the material of the base material  230  is acrylic resin, epoxy resin or a combination thereof. In the wavelength conversion layer  200 , the amount of the wavelength conversion material  210  is preferably 0.1 wt %-10 wt %, the amount of the nanoparticles  220  is preferably 0.05 wt %-10 wt %, and the amount of the base material  230  is preferably 80 wt %-99.85 wt %. 
     Since the reflection film of the invention includes the wavelength conversion material, the wavelength conversion material may absorb the ultraviolet light capable causing the problem of yellow-stain and convert the same into a visible light, so that the backlight brightness and the color saturation of the reflection film are improved. Moreover, by using the wavelength conversion material with the core-shell type double layer structure, a range of wavelengths changed by the wavelength conversion material is enlarged, to increase a wavelength conversion rate. Moreover, the reflection film of the invention further includes a plurality of nanoparticles, and based on the LSPR effect of the nanoparticles excited by the ultraviolet light, the visible light converted by the adjacent wavelength conversion material further improves the backlight brightness and the color saturation of the reflection film.