Patent Publication Number: US-2023140137-A1

Title: Optical film, method for manufacturing the same, and backlight module

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION 
     This application claims the benefit of priority to Taiwan Patent Application No. 110141054, filed on Nov. 4, 2021. The entire content of the above identified application is incorporated herein by reference. 
     Some references, which may include patents, patent applications and various publications, may be cited and discussed in the description of this disclosure. The citation and/or discussion of such references is provided merely to clarify the description of the present disclosure and is not an admission that any such reference is “prior art” to the disclosure described herein. All references cited and discussed in this specification are incorporated herein by reference in their entireties and to the same extent as if each reference was individually incorporated by reference. 
     FIELD OF THE DISCLOSURE 
     The present disclosure relates to a backlight module, a cadmium-free optical film, and a method for manufacturing the cadmium-free optical film, and more particularly to a backlight module, and a cadmium-free quantum dot optical film and a method for manufacturing the same capable of being applied to the backlight module and an LED package. 
     BACKGROUND OF THE DISCLOSURE 
     In recent years, with the progression of display technologies, people have higher expectations for the quality of display devices. Quantum dot technology has attracted recent attention from researchers due to their unique quantum confinement effects. Compared with conventional organic light-emitting materials, the luminous efficacy of the quantum dots has advantages of having a narrow full width at half maximum (FWHF), small particles, no scattering loss, a spectrum that is scalable with size, and stable photochemical performance. In addition, optical, electrical, and transmission properties of the quantum dots can be adjusted through a synthesis process. These advantages have contributed to the importance of the quantum dots. Recently, polymer composite materials that contain the quantum dots have been used in fields such as those relating to backlights and display devices. 
     The representative quantum dots are cadmium-based quantum dots that include cadmium selenide (CdSe), cadmium telluride (CdTe), and cadmium sulfide (CdS). An advantage of the cadmium-based quantum dots is having a wider energy band. However, heavy metals of cadmium have high toxicity and a high environmental load, and can cause risks of heavy metal pollution in the environment (not only at a production end but also during disposal of the display devices or waste treatment). Further, lifetime of the quantum dots may also be affected by acid hydrolysis occurred during a conventional manufacturing process. 
     The quantum dots that do not include cadmium (i.e., cadmium-free quantum dots) can be, for example, chalcopyrite quantum dots that include copper indium sulfide (CuInS 2 ) or silver indium sulfide (AgInS 2 ), indium phosphide (InP) quantum dots, or perovskite quantum dots, which have disadvantages of being not resistant to moisture and oxygen. Further, when a quantum dot film is being prepared by use of such quantum dots, a double-layered water-oxygen barrier film layer and a polyester film are still required for being attached to one another in a sandwich structure, so as to improve barrier properties of an optical film against moisture and oxygen and prolong the lifetime of the quantum dots. 
     Therefore, how to enhance water-oxygen barrier effects of a cadmium-free quantum dot film through an improvement in preparation of a quantum dot film layer, so as to omit the water-oxygen barrier film layer and overcome the above-mentioned deficiencies, has become one of the important issues to be solved in the industry. 
     SUMMARY OF THE DISCLOSURE 
     In response to the above-referenced technical inadequacies, the present disclosure provides a backlight module, and a cadmium-free quantum dot optical film and a method for manufacturing the same capable of being applied to the backlight module and an LED package. 
     In one aspect, the present disclosure provides an optical film. The optical film includes a cadmium-free quantum dot gel layer and a polyester layer disposed on the cadmium-free quantum dot gel layer. The cadmium-free quantum dot gel layer includes a first polymer and a plurality of cadmium-free quantum dots dispersed in the first polymer. To be specific, based on a total weight of the cadmium-free quantum dot gel layer being 100 wt %, a content of the cadmium-free quantum dots ranges from 0.1 wt % to 5 wt %. The first polymer includes: 1 wt % to 5 wt % of a photoinitiator; 3 wt % to 30 wt % of scattering particles; 10 wt % to 40 wt % of a thiol compound; 5 wt % to 30 wt % of a monofunctional acrylic monomer; 5 wt % to 20 wt % of a bifunctional acrylic monomer; 10 wt % to 40 wt % of a multifunctional acrylic monomer; 5 wt % to 20 wt % of an organosilicon grafted oligomer; and 100 ppm to 2,000 ppm of an inhibitor. 
     In certain embodiments, the polyester layer further has a chemically-treated surface, and the polyester layer is disposed on the cadmium-free quantum dot gel layer via the chemically-treated surface. 
     In certain embodiments, the thiol compound is selected from the group consisting of: 2, 2′-(ethylenedioxy)diethyl mercaptan, 2, 2′-thiodiethyl mercaptan, trimethylolpropane tris(3-mercaptopropionate), polyethylene glycol dithiol, pentaerythritol tetrakis(3-mercaptopropionate), ethylene glycol dimercaptoacetate, ethyl 2-mercaptopropionate, pentaerythritol tetrakis(3-mercaptobutyrate), 1, 3, 5-tris(3-mercapto butyloxyethyl)-1, 3, 5-triazine-2, 4, 6(1H, 3H, 5H)-trione, and 1,4-butanediol bis(3-mercaptobutyric acid) ester. 
     In certain embodiments, the monofunctional acrylic monomer is selected from the group consisting of: dicyclopentadiene methacrylate, triethylene glycol ethyl ether methacrylate, alkoxylated lauryl acrylate, isobornyl methacrylate, lauryl methacrylate, stearyl methacrylate, lauryl acrylate, isobornyl acrylate, tridecyl acrylate, caprolactone acrylate, octylphenol acrylate, and alkoxylated acrylate. 
     In certain embodiments, the bifunctional acrylic monomer is selected from the group consisting of: bisphenol A ethoxylate dimethacrylate, 1,3-butanediol diacrylate, 1,4-butanediol dimethacrylate, 1,6-hexanediol diacrylate, tetra(ethylene glycol) diacrylate, and polyethylene glycol (400) diacrylate. 
     In certain embodiments, the multifunctional acrylic monomer is selected from the group consisting of: trimethylolpropane triacrylate, ethoxylated (20) trimethylolpropane triacrylate, ditrimethylolpropane tetraacrylate, pentaerythritol tetraacrylate, dipentaerythritol pentaacrylate, and ethoxylated (4) pentaerythritol tetraacrylate. 
     In certain embodiments, the organosilicon grafted oligomer is a polyoctahedral silsesquioxane. 
     In certain embodiments, the cadmium-free quantum dots are quantum dots that have a core-shell structure. A core of the core-shell structure is at least one selected from the group consisting of: silicon (Si), germanium (Ge), selenium (Se), zinc (Zn), tellurium (Te), boron (B), nitrogen (N), phosphorus (P), arsenic (As), zinc sulfide (ZnS), zinc selenide (ZnSe), zinc telluride (ZnTe), mercury sulfide (HgS), mercury selenide (HgSe), mercury telluride (HgTe), aluminum nitride (AlN), aluminum phosphide (AlP), aluminum arsenide (AlAs), aluminum antimonide (AlSb), gallium nitride (GaN), gallium phosphide (GaP), gallium arsenide (GaAs), gallium antimonide (GaSb), gallium selenide (GaSe), indium nitride (InN), indium phosphide (InP), indium arsenide (InAs), indium antimonide (InSb), thallium nitride (TlN), thallium phosphide (TlP), thallium arsenide (TlAs), thallium antimonide (TlSb), lead sulfide (PbS), lead selenide (PbSe), and lead telluride (PbTe). 
     In certain embodiments, a shell of the core-shell structure is at least one selected from the group consisting of: zinc oxide (ZnO), zinc sulfide (ZnS), zinc selenide (ZnSe), zinc telluride (ZnTe), magnesium oxide (MgO), magnesium sulfide (Mg S), magnesium selenide (MgSe), magnesium telluride (MgTe), mercury oxide (HgO), mercury sulfide (HgS), mercury selenide (HgSe), mercury telluride (HgTe), aluminum nitride (AlN), aluminum phosphide (AlP), aluminum arsenide (AlAs), aluminum antimonide (AlSb), gallium nitride (GaN), gallium phosphide (GaP), gallium arsenide (GaAs), gallium antimonide (GaSb), indium nitride (InN), indium phosphide (InP), indium arsenide (InAs), indium antimonide (InSb), thallium nitride (TlN), thallium phosphide (TlP), thallium arsenide (TlAs), thallium antimonide (TlSb), lead sulfide (PbS), lead selenide (PbSe), lead telluride (PbTe), indium gallium phosphide (In x Ga 1-x P), copper indium sulfide (CuInS 2 ), copper indium selenide (CuInSe 2 ), copper indium sulfide selenide (CuInS x Se 2-x ), copper indium gallium sulfide (CuIn x Ga 1-x S 2 ), copper indium gallium selenide (CuIn x Ga 1-x Se 2 ), copper gallium sulfide (CuGaS 2 ), copper indium aluminum selenide (CuIn x Al 1-x Se 2 ), copper gallium aluminum selenide (CuGa x Al 1-x Se 2 ), copper indium sulfide zinc sulfide (CuInS 2-x ZnS 1-x ), and copper indium selenide zinc selenide (CuInSe 2x ZnSe 1-x ). 
     In another aspect, the present disclosure provides a method for manufacturing an optical film, which includes: (a) dispersing a plurality of cadmium-free quantum dots in a first polymer to obtain a quantum dot composite material; (b) placing the quantum dot composite material onto a polyester layer, and attaching a release substrate onto the quantum dot composite material, so that the quantum dot composite material is interposed between the polyester layer and the release substrate; (c) curing the quantum dot composite material with an ultraviolet light; and (d) removing the release substrate, so as to obtain the optical film. To be specific, based on a total weight of the quantum dot composite material being 100 wt %, a content of the cadmium-free quantum dots ranges from 0.1 wt % to 5 wt %. The first polymer includes: 1 wt % to 5 wt % of a photoinitiator; 3 wt % to 30 wt % of scattering particles; 10 wt % to 40 wt % of a thiol compound; 5 wt % to 30 wt % of a monofunctional acrylic monomer; 5 wt % to 20 wt % of a bifunctional acrylic monomer; 10 wt % to 40 wt % of a multifunctional acrylic monomer; 5 wt % to 20 wt % of an organosilicon grafted oligomer; and 100 ppm to 2,000 ppm of an inhibitor. 
     In yet another aspect, the present disclosure provides a backlight module, which includes: a light guide unit, at least one light emitting unit, and an optical film. The light guide unit has a light input side, and the at least one light emitting unit corresponds in position to the light input side. The optical film corresponds in position to the light input side, and is disposed between the light guide unit and the at least one light emitting unit. The optical film includes a cadmium-free quantum dot gel layer and a polyester layer disposed on the cadmium-free quantum dot gel layer. The cadmium-free quantum dot gel layer includes a first polymer and a plurality of cadmium-free quantum dots dispersed in the first polymer. Based on a total weight of the cadmium-free quantum dot gel layer being 100 wt %, a content of the cadmium-free quantum dots ranges from 0.1 wt % to 5 wt %. The first polymer includes: 1 wt % to 5 wt % of a photoinitiator; 3 wt % to 30 wt % of scattering particles; 10 wt % to 40 wt % of a thiol compound; 5 wt % to 30 wt % of a monofunctional acrylic monomer; 5 wt % to 20 wt % of a bifunctional acrylic monomer; 10 wt % to 40 wt % of a multifunctional acrylic monomer; 5 wt % to 20 wt % of an organosilicon grafted oligomer; and 100 ppm to 2,000 ppm of an inhibitor. 
     Therefore, in the optical film, the method for manufacturing the same, and the backlight module provided by the present disclosure, by virtue of 10 wt % to 40 wt % of the thiol compound, 5 wt % to 30 wt % of the monofunctional acrylic monomer, 5 wt % to 20 wt % of the bifunctional acrylic monomer, 10 wt % to 40 wt % of the multifunctional acrylic monomer, and 5 wt % to 20 wt % of the organosilicon grafted oligomer, water-oxygen resistant properties of the cadmium-free quantum dot gel layer can be enhanced, and a sandwich structure of a water-oxygen barrier layer can be omitted. Further, instead of having the polyester layer disposed on both sides, the polyester layer is only required to be disposed on one side. In this way, a thickness of the optical film can be effectively reduced, while an excellent water-oxygen resistant effect (as if having the sandwich structure of the water-oxygen barrier layer) can still be achieved. 
     These and other aspects of the present disclosure will become apparent from the following description of the embodiment taken in conjunction with the following drawings and their captions, although variations and modifications therein may be affected without departing from the spirit and scope of the novel concepts of the disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The described embodiments may be better understood by reference to the following description and the accompanying drawings, in which: 
         FIG.  1    is a schematic cross-sectional view of an optical film according to one embodiment of the present disclosure; 
         FIG.  2    is a schematic cross-sectional view of the optical film according to another embodiment of the present disclosure; 
         FIG.  3    is a flowchart of a method for manufacturing the optical film according to one embodiment of the present disclosure; and 
         FIG.  4    is a schematic cross-sectional view of a backlight module according to one embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS 
     The present disclosure is more particularly described in the following examples that are intended as illustrative only since numerous modifications and variations therein will be apparent to those skilled in the art. Like numbers in the drawings indicate like components throughout the views. As used in the description herein and throughout the claims that follow, unless the context clearly dictates otherwise, the meaning of “a”, “an”, and “the” includes plural reference, and the meaning of “in” includes “in” and “on”. Titles or subtitles can be used herein for the convenience of a reader, which shall have no influence on the scope of the present disclosure. 
     The terms used herein generally have their ordinary meanings in the art. In the case of conflict, the present document, including any definitions given herein, will prevail. The same thing can be expressed in more than one way. Alternative language and synonyms can be used for any term(s) discussed herein, and no special significance is to be placed upon whether a term is elaborated or discussed herein. A recital of one or more synonyms does not exclude the use of other synonyms. The use of examples anywhere in this specification including examples of any terms is illustrative only, and in no way limits the scope and meaning of the present disclosure or of any exemplified term. Likewise, the present disclosure is not limited to various embodiments given herein. Numbering terms such as “first”, “second” or “third” can be used to describe various components, signals or the like, which are for distinguishing one component/signal from another one only, and are not intended to, nor should be construed to impose any substantive limitations on the components, signals or the like. 
     Referring to  FIG.  1   , a first embodiment of the present disclosure provides an optical film M, which includes a cadmium-free quantum dot gel layer  10  and a polyester layer  20 . In detail, the cadmium-free quantum dot gel layer  10  includes a first polymer  101  and a plurality of cadmium-free quantum dots  102  dispersed in the first polymer  101 . Moreover, the cadmium-free quantum dot gel layer  10  has a first surface  10 A and a second surface  10 B. The polyester layer  20  is disposed on the first surface  10 A, and the second surface  10 B is exposed and not covered. Preferably, a thickness of the optical film M ranges approximately from 25 μm to 125 μm. It should be noted that the optical film M of the present disclosure has good water-oxygen barrier effects mainly due to materials of the cadmium-free quantum dot gel layer  10  and the polyester layer  20 . The thickness of the optical film M has a lesser influence in this regard. 
     Referring to  FIG.  2   , the optical film M of the present disclosure further has a chemically-treated surface  201  that is disposed on the polyester layer  20 . In addition, the chemically-treated surface  201  is positioned between the polyester layer  20  and the cadmium-free quantum dot gel layer  10 . The chemically-treated surface  201  can enhance an adhesion between the cadmium-free quantum dot gel layer  10  and the polyester layer  20 . As for formation of the chemically-treated surface  201 , descriptions thereof will be provided below. 
     A more detailed description is provided for a composition ratio of a cadmium-free quantum dot gel layer. The cadmium-free quantum dot gel layer includes a first polymer and a plurality of cadmium-free quantum dots dispersed in the first polymer. To be specific, based on a total weight of the cadmium-free quantum dot gel layer being 100 wt %, a content of the cadmium-free quantum dots ranges from 0.1 wt % to 5 wt %. Further, the first polymer includes: 1 wt % to 5 wt % of a photoinitiator; 3 wt % to 30 wt % of scattering particles; 10 wt % to 40 wt % of a thiol compound; 5 wt % to 30 wt % of a monofunctional acrylic monomer; 5 wt % to 20 wt % of a bifunctional acrylic monomer; 10 wt % to 40 wt % of a multifunctional acrylic monomer; 5 wt % to 20 wt % of an organo silicon grafted oligomer; and 100 ppm to 2,000 ppm of an inhibitor. 
     The photoinitiator can be selected from the group consisting of: 1-hydroxycyclohexyl phenyl ketone, benzoyl isopropanol, tribromomethyl phenyl sulfone, and diphenyl(2, 4, 6-trimethylbenzoyl)phosphine oxide. However, curing cannot be easily achieved if a content of the photoinitiator is less than 1 wt %, and volatility of the overall properties of a gel material will be affected if the content of the photoinitiator is more than 5 wt %. 
     The scattering particles have a particle size ranging from 0.5 μm to 20 μm, and are surface-treated microbeads. The material of the microbeads can be acrylic, silicon dioxide, germanium dioxide, titanium dioxide, zirconium dioxide, aluminum oxide or polystyrene. Preferably, the scattering particles are acrylic, silicon dioxide or polystyrene microbeads that are surface-treated, and the particle size thereof ranges from 0.5 μm to 10 μm. A refractive index of the scattering particles ranges approximately from 1.39 to 1.45. Due to the scattering particles, light scattering of the quantum dots is improved, so that light generated through the cadmium-free quantum dot gel layer is more uniform. If a content of the scattering particles is less than 3 wt %, the haze is insufficient. If the content of the scattering particles is more than 30 wt %, the haze will be too much, which can result in insufficiency of a resin content in the overall material, affect dispersity, and increase processing difficulty. In some embodiments, the content of the scattering particles can also be 5 wt %, 10 wt %, 15 wt %, 20 wt %, 25 wt %, or 30 wt %. 
     Specifically, the thiol compound is selected from the group consisting of: 2, 2′-(ethylenedioxy)diethyl mercaptan, 2, 2′-thiodiethyl mercaptan, trimethylolpropane tris(3-mercaptopropionate), polyethylene glycol dithiol, pentaerythritol tetrakis(3-mercaptopropionate), ethylene glycol dimercaptoacetate, ethyl 2-mercaptopropionate, pentaerythritol tetrakis(3-mercaptobutyrate), 1, 3, 5-tris(3-mercapto butyloxyethyl)-1, 3, 5-triazine-2, 4, 6(1H, 3H, 5H)-trione, and 1,4-butanediol bis(3-mercaptobutyric acid) ester. 
     The thiol compound is a non-aromatic compound that contains a sulfhydryl (—SH) functional group, which provides a functional group that can form a better bond with the quantum dots. Thus, the dispersity of the quantum dots can be improved, thereby enhancing water-oxygen barrier properties of the optical film M. A content of the thiol compound is higher in comparison to that of the related art, which results in a higher degree of polymerization. If the content of the thiol compound is less than 10 wt %, no effect can be achieved. However, if said content is more than 40 wt %, the gel material becomes too soft and is easily bent. Further, the water-oxygen barrier properties may be decreased. In some embodiments, the content of the thiol compound can also be 10 wt %, 15 wt %, 20 wt %, 25 wt %, 30 wt %, 35 wt %, or 40 wt %. 
     Furthermore, the monofunctional acrylic monomer is selected from the group consisting of: dicyclopentadiene methacrylate, triethylene glycol ethyl ether methacrylate, alkoxylated lauryl acrylate, isobornyl methacrylate, lauryl methacrylate, stearyl methacrylate, lauryl acrylate, isobornyl acrylate, tridecyl acrylate, caprolactone acrylate, octylphenol acrylate, and alkoxylated acrylate. Too low a content of the monofunctional acrylic monomer can result in poor dispersity of the quantum dots. However, if the content of the monofunctional acrylic monomer is too high, a polymerization efficiency will decrease and the weather resistance will become poor. In some embodiments, the content of the monofunctional acrylic monomer can also be 5 wt %, 10 wt %, 15 wt %, 20 wt %, 25 wt %, or 30 wt %. 
     The bifunctional acrylic monomer is selected from the group consisting of: bisphenol A ethoxylate dimethacrylate, 1,3-butanediol diacrylate, 1,4-butanediol dimethacrylate, 1,6-hexanediol diacrylate, tetra(ethylene glycol) diacrylate, and polyethylene glycol (400) diacrylate. Specifically, the bifunctional acrylic monomer has good compatibility with surface ligands of the quantum dots, and its property is more balanced by being in-between a monofunctional group and a multi-functional group. In some embodiments, a content of the bifunctional acrylic monomer can also be 5 wt %, 10 wt %, 15 wt %, or 20 wt %. 
     The multifunctional acrylic monomer is selected from the group consisting of: trimethylolpropane triacrylate, ethoxylated (20) trimethylolpropane triacrylate, ditrimethylolpropane tetraacrylate, pentaerythritol tetraacrylate, dipentaerythritol pentaacrylate, and ethoxylated (4) pentaerythritol tetraacrylate. If the multifunctional acrylic monomer is added in an excessive amount, the gel material may easily become too brittle and be prone to breakage. Moreover, the multifunctional acrylic monomer does not include the above-mentioned bifunctional acrylic monomer. In some embodiments, a content of the multifunctional acrylic monomer can also be 10 wt %, 15 wt %, 20 wt %, 25 wt %, 30 wt %, 35 wt %, or 40 wt %. 
     The organosilicon grafted oligomer is a polyoctahedral silsesquioxane. The organosilicon grafted oligomer not only can increase the weather resistance of a polymer, but can also enhance the mechanical strength of the polymer. Preferably, macromolecules of the polyoctahedral silsesquioxane in a web structure have a molecular weight (Mw) that is greater than 3,000, so that the cadmium-free quantum dot gel layer can be better protected. In detail, a weight-average molecular weight of the polyoctahedral silsesquioxane is between 3,000 g/mol and 10,000 g/mol. Preferably, the weight-average molecular weight of the polyoctahedral silsesquioxane can be 4,000 g/mol, 5,000 g/mol, 6,000 g/mol, 7,000 g/mol, 8,000 g/mol, or 9,000 g/mol. When a polyester layer is omitted from a conventional optical film, not only will said optical film have decreased water and oxygen tolerance, but its mechanical strength will also be insufficient. In the present disclosure, 5 wt % to 20 wt % of the organosilicon grafted oligomer is added to enhance the mechanical strength of the cadmium-free quantum dot gel layer. If a content of the organosilicon grafted oligomer exceeds the above-mentioned range, the dispersity and the processability of the cadmium-free quantum dot gel layer can be affected, and the costs can be increased. 
     The inhibitor is selected from the group consisting of: pyrogallol (PYR), hydroquinone, catechol, potassium iodide-iodine mixtures, hindered phenol antioxidants, aluminum/ammonium cupferronate salt (N-nitrosophenyl hydroxylamine ammonium salt), N-nitroso-N-phenylhydroxylamine aluminum salt, 3-propenylphenol, triaryl phosphines, triaryl phosphites, phosphonic acid, and a combination of alkenyl-phenol and cupferronate salt. 
     The inhibitor can effectively slow down a reaction rate, and prevent component formulas from affecting one another. For example, the thiol compound and the multifunctional acrylic monomer are prone to self-react at a room temperature. An addition of the inhibitor during preparation allows for an improved processability and a more stable preservation. However, an inhibition effect cannot be achieved if an added amount of the inhibitor is less than 100 ppm, and a photocuring efficiency can be affected if the added amount is more than 2,000 ppm. It should be noted that, although the added amount of the inhibitor is not high, an effective amount of the inhibitor must be added in a macromolecule system where the thiol compound and the multifunctional acrylic monomer are both present. 
     The cadmium-free quantum dots are quantum dots that do not contain a cadmium element, and can be selected from quantum dots that have a homogeneous single structure or a core-shell structure, multi-shell quantum dots (i.e., having a plurality of shell layers), or gradient-structured quantum dots. More specifically, in the core-shell structure of the gradient-structured quantum dots, an element content of a core layer gradually decreases from the core to the shell, and an element content of a shell layer gradually increases from the core to the shell. 
     The cadmium-free quantum dots are preferably the quantum dots that have the core-shell structure. The core of the core-shell structure is at least one or a combination selected from the group consisting of: silicon (Si), germanium (Ge), selenium (Se), zinc (Zn), tellurium (Te), boron (B), nitrogen (N), phosphorus (P), arsenic (As), zinc sulfide (ZnS), zinc selenide (ZnSe), zinc telluride (ZnTe), mercury sulfide (HgS), mercury selenide (HgSe), mercury telluride (HgTe), aluminum nitride (AlN), aluminum phosphide (AlP), aluminum arsenide (AlAs), aluminum antimonide (AlSb), gallium nitride (GaN), gallium phosphide (GaP), gallium arsenide (GaAs), gallium antimonide (GaSb), gallium selenide (GaSe), indium nitride (InN), indium phosphide (InP), indium arsenide (InAs), indium antimonide (InSb), thallium nitride (TlN), thallium phosphide (TlP), thallium arsenide (TlAs), thallium antimonide (TlSb), lead sulfide (PbS), lead selenide (PbSe), and lead telluride (PbTe). Preferably, the core of the core-shell structure is indium phosphide (InP). 
     The shell of the core-shell structure can be single-layered or multi-layered, and its material is at least one or a combination selected from the group consisting of: zinc oxide (ZnO), zinc sulfide (ZnS), zinc selenide (ZnSe), zinc telluride (ZnTe), magnesium oxide (MgO), magnesium sulfide (Mg S), magnesium selenide (MgSe), magnesium telluride (MgTe), mercury oxide (HgO), mercury sulfide (HgS), mercury selenide (HgSe), mercury telluride (HgTe), aluminum nitride (AlN), aluminum phosphide (AlP), aluminum arsenide (AlAs), aluminum antimonide (AlSb), gallium nitride (GaN), gallium phosphide (GaP), gallium arsenide (GaAs), gallium antimonide (GaSb), indium nitride (InN), indium phosphide (InP), indium arsenide (InAs), indium antimonide (InSb), thallium nitride (TlN), thallium phosphide (TlP), thallium arsenide (TlAs), thallium antimonide (TlSb), lead sulfide (PbS), lead selenide (PbSe), lead telluride (PbTe), indium gallium phosphide (In x Ga 1-x P), copper indium sulfide (CuInS 2 ), copper indium selenide (CuInSe 2 ), copper indium sulfide selenide (CuInS x Se 2-x ), copper indium gallium sulfide (CuIn x Ga 1-x S 2 ), copper indium gallium selenide (CuIn x Ga 1-x Se 2 ), copper gallium sulfide (CuGaS 2 ), copper indium aluminum selenide (CuIn x Al 1-x Se 2 ), copper gallium aluminum selenide (CuGa x Al 1-x Se 2 ), copper indium sulfide zinc sulfide (CuInS 2x ZnS 1-x ), and copper indium selenide zinc selenide (CuInSe 2x ZnSe 1-x ). 
     The polyester layer of the present disclosure is formed by a polyester film. The polyester layer has good light permeability, and its light transmittance is over 90%. A rate of elongation of the polyester layer ranges from 70 kg/cm 2  to 130 kg/cm 2 , so that an optical film can have improved physical properties. Further, a surface tension of a chemically-treated surface of the polyester layer is greater than or equal to 45 dyn. Preferably, the material of the polyester layer is thermoplastic resins, such as polyethylene terephthalate (PET). A thickness of the polyester layer ranges from 25 μm to 125 μm. Preferably, the polyester layer has dielectric properties, and can also provide an insulation effect. 
     The chemically-treated surface allows the cadmium-free quantum dot gel layer and the polyester layer to have an improved adhesion, and can be a water-based coating on a surface of the polyester layer. The water-based coating can include: 30 wt % to 70 wt % of a solvent, 5 wt % to 15 wt % of isopropyl alcohol (IPA), 5 wt % to 15 wt % of sodium bicarbonate, 5 wt % to 20 wt % of organic acid, and 10 wt % to 30 wt % of an acrylic monomer. Preferably, the pH value of the chemically-treated surface is weak acidic (i.e., between pH 5.0 and pH 6.7), and a thickness of the chemically-treated surface ranges approximately from 0.01 μm to 0.1 μm. 
     The acrylic monomer of the chemically-treated surface can be, for example, tetrahydrofurfuryl methacrylate, stearyl acrylate, lauryl methacrylate, lauryl acrylate, isobornyl methacrylate, tridecyl acrylate, alkoxylated nonylphenol acrylate, tetraethylene glycol dimethacrylate, polyethylene glycol (600) dimethacrylate, tripropylene glycol diacrylate, ethoxylated (10) bisphenol A dimethacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, ethoxylated (20) trimethylolpropane triacrylate, and pentaerythritol triacrylate. 
     Referring to  FIG.  3   , the present disclosure also provides a method for manufacturing the optical film. The method includes: dispersing the plurality of cadmium-free quantum dots in the first polymer to obtain a quantum dot composite material (step S 100 ); placing the quantum dot composite material onto the polyester layer, and attaching a release substrate onto the quantum dot composite material, so that the quantum dot composite material is interposed between the polyester layer and the release substrate (step S 200 ); curing the quantum dot composite material with an ultraviolet light (step S 300 ); and removing the release substrate, so as to obtain the optical film (step S 400 ). 
     The composition of the first polymer and the cadmium-free quantum dots are as illustrated above. Preferably, in the step S 100 , the plurality of quantum dots are dispersed in the monofunctional acrylic monomer. Then, the inhibitor is added, which is followed by addition of the thiol compound. The bifunctional acrylic monomer and the multifunctional acrylic monomer are also added and mixed. Finally, the photoinitiator, the scattering particles, and the organosilicon grafted oligomer are added. 
     That is to say, in the step of dispersing the plurality of cadmium-free quantum dots in the first polymer, the cadmium-free quantum dots are not dispersed in a completely mixed first polymer. Instead, these cadmium-free quantum dots are pre-dispersed in a specific composition, and then other components are further added for a complete mixing. 
     Through a biaxially stretching treatment, the polyester layer in the step S 200  can have good flexibility and ductility. The chemically-treated surface is pre-formed on the polyester layer, and then the polyester layer that has the chemically-treated surface can be formed by undergoing the curing step (e.g., thermal curing or light curing). The quantum dot composite material is further placed onto the chemically-treated surface. That is to say, the polyester layer has an outer surface and an inner surface, and the chemically-treated surface is disposed on the inner surface. 
     In the step S 200  of placing the quantum dot composite material onto the polyester layer, the release substrate is further attached to the quantum dot composite material, so that the quantum dot composite material is molded and interposed between the polyester layer and the release substrate. 
     Apart from the foregoing steps, the method for manufacturing the optical film of the present disclosure further includes: performing a cutting process to cut the optical film into at least one required size; and performing a winding process to wind the rest of the optical film into a roll for use or storage. However, the aforementioned example describes only one of the embodiments of the present disclosure, and the present disclosure is not intended to be limited thereto. 
     Referring to  FIG.  4   , the present disclosure further provides a backlight module S, which includes: a light guide unit  30 , at least one light emitting unit  40 , and the optical film M. The light guide unit  30  has a light input side  30 A. The at least one light emitting unit  40  is positioned relative to the light input side  30 A, and includes a plurality of light emitting elements  401 . The optical film M is positioned relative to the light input side  30 A, and is disposed between the light guide unit  30  and the at least one light emitting unit  40 . Specifically, the light guide unit  30  has the light input side  30 A and a light output side  30 B that are opposite to each other, and the optical film M is disposed on the light input side  30 A. More specifically, the optical film M is the above-mentioned optical film of the present disclosure. However, the aforementioned example describes only one of the embodiments of the present disclosure, and the present disclosure is not intended to be limited thereto. 
     Examples 
     Cadmium-free quantum dot gel layers of Examples 1 to 3 and Comparative Examples 1 to 3 are prepared according to formulas and ratios as shown in Table 1, and further undergo product quality tests. Specifically, the following ratios are based on the total weight of the cadmium-free quantum dot gel layer being 100 wt %. 
     After the above-mentioned quantum dot composite material is placed onto the polyester layer (that has the chemically-treated surface) and is further attached with the release substrate, the curing treatment is conducted with UV radiation. Finally, the release substrate is removed, so as to obtain the cadmium-free quantum dot gel layer of the present disclosure. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
             
            
               
                   
                   
               
               
                   
                 Examples 
                 Comparative Examples 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Ratio (wt %) 
                 1 
                 2 
                 3 
                 1 
                 2 
                 3 
               
               
                   
               
               
                 Cadmium-free 
                  1% 
                  1% 
                  1% 
                  1% 
                  1% 
                  1% 
               
               
                 quantum dots 
               
               
                 Photoinitiator 
                  3% 
                  3% 
                  3% 
                  3% 
                  3% 
                  3% 
               
               
                 Scattering particles 
                 15% 
                 15% 
                 15% 
                 15% 
                 15% 
                 15% 
               
               
                 Thiol compound 
                  20.9%  
                  15.9%  
                  15.9%  
                  0% 
                 45% 
                  20.9%  
               
               
                 Monofunctional 
                 15% 
                 10% 
                 10% 
                  10.9%  
                 9.9%  
                 19% 
               
               
                 acrylic monomer 
               
               
                 Bifunctional 
                 10% 
                  5% 
                 10% 
                 10% 
                  8% 
                 18% 
               
               
                 acrylic monomer 
               
               
                 Multifunctional 
                 25% 
                 40% 
                 20% 
                 30% 
                  8% 
                 23% 
               
               
                 acrylic monomer 
               
               
                 Organosilicon 
                 10% 
                 10% 
                 20% 
                 10% 
                 10% 
                  0% 
               
               
                 grafted oligomer 
               
               
                 Inhibitor 
                 0.1%  
                 0.1%  
                 0.1%  
                 0.1%  
                 0.1%  
                 0.1%  
               
               
                 Thickness (μm) 
                 200 
                 200 
                 200 
                 200 
                 200 
                 200 
               
               
                 Water-oxygen resistant 
                 500 
                 400 
                 450 
                 350 
                 300 
                 350 
               
               
                 reliability (hour) 
               
               
                 Transmittance 
                 75% 
                 75% 
                 75% 
                 75% 
                 75% 
                 75% 
               
               
                 Refractive index 
                    1.57 
                    1.55 
                    1.54 
                    1.49 
                    1.47 
                    1.57 
               
               
                 Adhesion 
                 not separate 
                 not separate 
                 not separate 
                 not separate 
                 separate 
                 not separate 
               
               
                 Shrinkage 
                 no warpage 
                 no warpage 
                 no warpage 
                 warpage 
                 no warpage 
                 no warpage 
               
               
                 Luminance (Cd/m 2 ) 
                 4500  
                 4350  
                 4300  
                 3550  
                 4500  
                 4300  
               
               
                   
               
            
           
         
       
     
     In Table 1, the test of water-oxygen resistant reliability is conducted by placing a backlight module in an environment where a temperature is 65° C. and a relative humidity is 95%. The backlight module is continuously irradiated by a blue backlight, and the time taken for a chromaticity coordinate deviation to reach 0.01 is recorded. 
     Adhesion: using a tensile testing machine to test an adhesion degree of the optical film. 
     Shrinkage: placing the optical film in an oven at 85° C. for half an hour, so as to observe its state of shrinkage. The optical film is indicated to have “warpage” when its degree of warpage is greater than or equal to 0.2 cm, and is indicated to have “no warpage” when its degree of warpage is less than 0.2 cm. 
     Luminance: using a spectrophotometer (model: SR-3AR) to measure a luminance of a mixed light beam generated by the backlight module with use of a blue light source (power: 12 W; chromaticity coordinate: x=0.155, y=0.026; wavelength: 450 nm; FWHM: 20 nm). 
     According to the results of Comparative Example 1, the thiol compound is added in the present disclosure to increase a degree of polymerization of the first polymer, which allows the cadmium-free quantum dot gel layer to have good water-oxygen barrier effects. In the test of water-oxygen resistant reliability, the duration for each of Examples 1 to 3 is greater than 400 hours. 
     According to the results of Comparative Example 2, adding an excessive amount of the thiol compound not only keeps the cadmium-free quantum dot gel layer from having good water-oxygen barrier effects but also gives rise to an issue of poor adhesion. 
     According to the results of Comparative Example 3, adding the organosilicon grafted oligomer in the present disclosure can further assist the cadmium-free quantum dot gel layer in having good water-oxygen barrier effects. In the test of water-oxygen resistant reliability, the duration for each of Examples 1 to 3 is greater than 400 hours. 
     Beneficial Effects of the Embodiments 
     In conclusion, in the optical film, the method for manufacturing the same, and the backlight module provided by the present disclosure, by virtue of 10 wt % to 40 wt % of the thiol compound, 5 wt % to 30 wt % of the monofunctional acrylic monomer, 5 wt % to 20 wt % of the bifunctional acrylic monomer, 10 wt % to 40 wt % of the multifunctional acrylic monomer, and 5 wt % to 20 wt % of the organosilicon grafted oligomer, water-oxygen resistant properties of the cadmium-free quantum dot gel layer can be enhanced, and a sandwich structure of a water-oxygen barrier layer can be omitted. Further, instead of having the polyester layer disposed on both sides, the polyester layer is only required to be disposed on one side. In this way, a thickness of the optical film can be effectively reduced, while an excellent water-oxygen resistant effect (as if having the sandwich structure of the water-oxygen barrier layer) can still be achieved. 
     More specifically, the thiol compound provides the non-aromatic compound containing the sulfhydryl (—SH) functional group, which can form a better bond with the quantum dots. Accordingly, the dispersity of the quantum dots can be improved. The content of the thiol compound is higher in comparison to that of the related art, which results in a higher degree of polymerization. 
     During preparation and mixing of the formulas of the present disclosure, an issue of mutual influence is also taken into particular consideration. As such, after numerous experiments, a specific inhibitor is further selected in the present disclosure, so as to effectively slow down the reaction rate and prevent the thiol compound and the multifunctional acrylic monomer from self-reacting at the room temperature. In this way, an improved processability can be provided, and a more stable preservation can be obtained. 
     The foregoing description of the exemplary embodiments of the disclosure has been presented only for the purposes of illustration and description and is not intended to be exhaustive or to limit the disclosure to the precise forms disclosed. Many modifications and variations are possible in light of the above teaching. 
     The embodiments were chosen and described in order to explain the principles of the disclosure and their practical application so as to enable others skilled in the art to utilize the disclosure and various embodiments and with various modifications as are suited to the particular use contemplated. Alternative embodiments will become apparent to those skilled in the art to which the present disclosure pertains without departing from its spirit and scope.