Optical film

Abstract

An optical film is provided. The optical film includes a reflective polarizing element having a first surface and a second surface opposing the first surface and a concave-convex layer disposed on the first surface. The concave-convex layer include a plurality of acrylic resin particles. The optical film has excellent brightness enhancement effect and is cost-effective.

Description

[Technical Field]

[0001] This invention relates to an optical film, and more particularly to an optical film that can be used in a backlight module to increase the brightness of the output light. [Previous Technology]

[0002] Liquid crystal displays (LCDs) are currently the mainstream display technology due to their advantages such as high image quality, low radiation, low power consumption, and better space utilization. The main structure of an LCD consists of two parts: the liquid crystal panel and the backlight module. Since the liquid crystal panel itself does not emit light, a backlight module is needed to provide the surface light source required by the liquid crystal panel so that the liquid crystal panel can display images.

[0003] Various optical films are used in backlight modules to cloud the light source and improve brightness. This approach does not require any changes to component design or consumes additional energy, making it a more economical and simple solution. Commonly used optical films in backlight modules include: reflective films, diffuser plates, light-concentrating films, and dual brightness enhancement films. The light-concentrating film, also known as a brightness enhancement film (BEF), mainly uses prism microstructures to concentrate scattered light into an on-axis direction of approximately ±35 degrees, thereby improving the brightness of the LCD panel. Unlike light-concentrating films, reflective brightness enhancement films utilize multiple layers of materials with different refractive indices as the core layer. This allows polarized light in the transmission direction to pass through, while reflecting polarized light in the non-transmission direction back to the backlight module. Then, through the action of other films in the backlight module (such as reflective films), the light returns to the reflective brightness enhancement film and is partially converted back into polarized light in the transmission direction. This process is repeated multiple times, ultimately converting most of the light that would otherwise be absorbed by the polarizer in the LCD panel into usable, effective light, achieving a brightness enhancement effect. Therefore, reflective brightness enhancement films can not only replace light-concentrating films but also be used in conjunction with them in high-end display products.

[0004] Figure 1 is a schematic diagram of a typical reflective brightness enhancement film. As shown in Figure 1, a typical reflective brightness enhancement film 100 has a core layer 11 with reflective polarization effect, and polycarbonate films 12 and 13 are attached to the upper and lower surfaces of the core layer using adhesives 14a and 14b. Although the surface of the polycarbonate film is embossed to provide scattering and diffusion effects, the effect is limited. In addition, this type of reflective brightness enhancement film is relatively expensive. Therefore, there is a need in the technical field for an optical film with high light utilization and a price advantage.

[0005] Furthermore, the light source in the backlight module can be, for example, a point light source or a line light source. However, regardless of whether it is a point light source or a line light source, if the light emitted by the backlight module cannot be homogenized, a noticeable light source outline can be observed on the panel, affecting the image quality. Therefore, this technical field also desires an optical film that can homogenize light to shield the light source outline. [Summary of the Invention]

[0006] The present invention provides an optical film that can improve brightness, has a shielding effect, and is cost-effective. The optical film of the present invention comprises: a reflective polarizing element having a first surface and a second surface opposite to the first surface; and an uneven structure layer located on the first surface of the polarizing element, wherein the uneven structure layer comprises a plurality of acrylic resin particles.

[0007] The present invention provides a backlight module comprising the above-mentioned optical film.

Implementation Method

[0008] The optical film of the present invention will now be described in detail with reference to the accompanying drawings and embodiments. It should be noted that the drawings described below represent only some embodiments of the present invention, and the various structures may not be drawn to scale, and the dimensions of the various structures may be increased or decreased for clarity of explanation. Any modifications and alterations that can be easily made by those skilled in the art are included in the disclosure herein.

[0009] In this specification and the claims, unless the context clearly requires otherwise, the singular forms "a" and "the" include both singular and plural. Unless otherwise asserted, the use of any and all examples or illustrative language (such as "like") provided herein is merely for the purpose of better setting out the invention and should not be construed as limiting the scope of the invention. The language in this specification should not be construed as indicating that any unclaimed element is necessary for carrying out the invention.

[0010] As used herein, the terms “approximately,” “generally,” “substantially,” and “about” are used to describe and indicate small variations. When used in conjunction with an event or situation, the terms may refer to examples in which the event or situation occurred precisely and examples in which the event or situation occurred very approximately. For example, when used in conjunction with numerical values, the term may refer to a range of variation less than or equal to ±10% of the numerical value, such as less than or equal to ±5%, less than or equal to ±4%, less than or equal to ±3%, less than or equal to ±2%, less than or equal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%. For example, if the difference between two numerical values ​​is less than or equal to ±10% of the average of the values ​​(e.g., less than or equal to ±5%, less than or equal to ±4%, less than or equal to ±3%, less than or equal to ±2%, less than or equal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%), then the two numerical values ​​may be considered “generally” the same.

[0011] In addition, quantities, ratios and other values ​​are sometimes presented in range format in this document. It should be understood that such range format is for convenience and brevity and should be interpreted flexibly to include not only the values ​​explicitly specified as range limits, but also all individual values ​​or subranges covered within that range, as if each value and subrange were explicitly specified.

[0012] FIG2 is a schematic diagram of the structure of an optical film provided according to some embodiments of the present invention. As shown in FIG2, the optical film 200 provided in the embodiments of the present invention includes a reflective polarization element 21 and an uneven structure layer 22 located on a first surface of the reflective polarization element 21, the uneven structure layer containing a plurality of acrylic resin particles 23.

[0013] The reflective polarization element 21 used in this invention can be any suitable reflective polarization element known to those skilled in the art, such as a multilayer reflective polarization element. The multilayer reflective polarization element comprises at least a first birefringent layer and a second birefringent layer, which are respectively composed of different birefringent polymers, such that the interface between the two layers forms a light-reflecting plane. The first and second birefringent layers are alternately stacked in multiple layers, and the number of layers and the thickness of each layer can be adjusted according to the desired reflective polarization effect. The number of layers is generally between 2 and 5000, for example, 2, 25, 50, 75, 100, 200, 500, 1000, 2000, 3000, 4000, 5000, or any number in between. The thickness of each layer can be the same or different, generally less than 1 micrometer (μm).

[0014] The thickness of the reflective polarization element 21 depends on the layers contained therein and the thickness of each layer. In some embodiments of the present invention, the reflective polarization element 21 used has a thickness between 2 micrometers (μm) and 10 micrometers (μm), for example, 2μm, 3μm, 4μm, 5μm, 6μm, 8μm or 10μm; preferably 3μm to 6μm.

[0015] In some embodiments of the present invention, the materials of the first birefringent layer and the second birefringent layer may be: polyester, such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), or polybutylene naphthalate (PBN); polymethacrylate; polyimide resin; polystyrene; polyolefin resin; cyclic olefin copolymer (COC); polycarbonate; polyurethane; triacetate cellulose (TAC); polylactic acid (PLA). PLA; or a material obtained by mixing or polymerizing the above materials, preferably polyester or polycarbonate. The first and second birefringent layers are formed by uniaxial or biaxial stretching to give them a polarizing effect.

[0016] In some embodiments of the present invention, the uneven structure layer 22 is formed by coating a resin coating containing a plurality of acrylic resin particles and a binder onto the first surface of the reflective polarizing element 21. Therefore, compared with conventional reflective brightening films, it is not necessary to use expensive polycarbonate films. At the same time, the optical film of the present invention can exhibit excellent brightness gain and has a cost advantage. Furthermore, in some preferred embodiments of the present invention, the optical film of the present invention can further provide good shielding effect.

[0017] In some embodiments of the present invention, the adhesive of the present invention may be selected from the group consisting of ultraviolet curable resin, thermosetting resin, thermoplastic resin and mixtures thereof, and may be treated by heat curing, ultraviolet curing or dual curing as needed to form the resin coating of the present invention.

[0018] The UV-curing resin used in this invention is composed of at least one acrylic monomer or acrylate monomer having one or more functional groups, preferably an acrylate monomer. Acrylate monomers used in this invention include, but are not limited to: (meth)acrylates, such as 2-hydroxy-3-phenoxypropyl acrylate; urethane acrylates, such as aliphatic urethane acrylate, aliphatic urethane hexaacrylate, or aromatic urethane hexaacrylate; polyester acrylates, such as polyester diacrylate; epoxy acrylates, such as bisphenol-A epoxy diacrylate, novolac epoxy acrylate; or mixtures thereof.

[0019] The thermosetting resins used in this invention generally have an average molecular weight between about 10⁴ and about 2 × 10⁶, preferably between about 2 × 10⁴ and about 3 × 10⁵, and more preferably between about 4 × 10⁴ and about 10⁵. The thermosetting resins of this invention may be selected from the group consisting of polyester resins, epoxy resins, polymethyl methacrylate resins, polyamide resins, fluoropolymer resins, polyimide resins, polyurethane resins, alkyd resins, and mixtures thereof containing carboxyl groups (-COOH) and / or hydroxyl groups (-OH). Preferably, they are polymethyl methacrylate resins or polyacrylate resins containing carboxyl groups (-COOH) and / or hydroxyl groups (-OH), such as polymethyl methacrylate polyol resins.

[0020] The thermoplastic resin that can be used in this invention may be selected from the group consisting of polyester resins; polymethyl methacrylate resins, such as polymethyl methacrylate (PMMA); and mixtures thereof.

[0021] In some embodiments of the present invention, the uneven structure layer 22 has a plurality of acrylic resin particles 23. The inventors of this case have found that, compared with other types of particles (such as silicon dioxide particles, polystyrene particles, nylon particles), the use of acrylic resin particles can improve brightness and has a good shielding effect. In some embodiments of the present invention, the acrylic resin particles may be homopolymers or copolymers made from a selection of the following acrylate monomers: methyl methacrylate, butyl methacrylate, 2-phenoxyethyl acrylate, ethoxylated 2-phenoxyethyl acrylate, 2-(2-ethoxyethoxy)ethyl acrylate, cyclic trimethylolpropane formal acrylate, β-carboxyethyl acrylate, lauryl methacrylate, isooctyl acrylate, stearyl methacrylate, isodecyl acrylate, isodecyl acrylate, isoborny methacrylate, benzyl acrylate, and 2-hydroxyethyl methacrylate phosphate. The group consisting of phosphate, hydroxyethyl acrylate (HEA), 2-hydroxyethyl methacrylate (HEMA) and mixtures thereof, preferably methyl methacrylate, butyl methacrylate or combinations thereof.

[0022] In some embodiments of the present invention, the shape of the acrylic resin particles is not particularly limited, and may be spherical, ellipsoidal, or irregular, with spherical shape being preferred. The average particle size of the acrylic resin particles ranges from 3 micrometers (μm) to 10 micrometers (μm), for example, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, or 10μm, with 5μm to 8μm being preferred, thereby enabling the optical film to possess excellent brightness gain and good shielding effect. In some embodiments of the present invention, if the average particle size of the acrylic resin particles is less than 3μm or more than 10μm, the shielding effect cannot be achieved.

[0023] In some embodiments of the present invention, the weight ratio of the acrylic resin particles to the binder is between 0.8 and 1.8, for example, 0.8, 0.9, 1, 1.2, 1.5, 1.6 or 1.8.

[0024] In some embodiments of the present invention, the acrylic resin particles may protrude wholly or partially beyond the resin coating to provide an uneven surface. In some embodiments of the present invention, as shown in FIG1, the acrylic resin particles may be completely embedded in the resin coating, yet still provide an uneven surface.

[0025] In some embodiments of the present invention, the uneven structure layer has an arithmetic mean roughness (Ra) of 700 nanometers (nm) to 1800 nanometers (nm), such as 700nm, 800nm, 900nm, 1000nm, 1100nm, 1200nm, 1300nm, 1400nm, 1500nm, 1600nm, 1700nm, or 1800nm; preferably 900nm to 1800nm. The aforementioned arithmetic mean roughness (Ra) can be measured using the JIS B-0601 standard method. If the arithmetic mean roughness of the uneven structure layer is too small (e.g., less than 700nm), the shielding effect is insufficient; if the arithmetic mean roughness of the uneven structure layer is too high (e.g., greater than 1800nm), the light is too diffused, affecting the brightness.

[0026] In some embodiments of the present invention, the thickness of the uneven structure layer is between about 5 micrometers (μm) and about 10 micrometers (μm), for example, it can be 5μm, 6μm, 7μm, 8μm, 9μm or 10μm.

[0027] In some embodiments of the present invention, the optical film can provide a luminance gain of more than 1% (i.e., a luminance gain value of 101% or higher) to the light-emitting device compared to the same optical film without acrylic resin particles, for example, more than 1%, more than 2%, more than 5%, more than 10%, more than 20%, more than 30%, or more than 40%. The light-emitting device is, for example, but not limited to, a backlight module.

[0028] In some embodiments of the present invention, the second surface of the reflective polarizing element may include one or more functional coatings or films to give the optical film enhanced or additional effects. The aforementioned functional coatings or films are, for example, but not limited to, polycarbonate films, polyester films, anti-adhesion layers, antistatic layers, scratch-resistant layers, or prisms, or combinations thereof. The polyester film is preferably a polyethylene terephthalate film or a polyethylene naphthalate film. In some embodiments of the present invention, the second surface of the reflective polarizing element includes a polycarbonate film, a polyester film, or a prism, or combinations thereof.

[0029] Figures 3 to 5 illustrate embodiments in which the second surface of the reflective polarizing element in the optical film of the present invention includes one or more functional coatings or films. Although in the embodiments illustrated in Figures 3 to 5, the prism or polyester film is directly attached to the second surface, this is only for illustrative purposes. Within the scope of the present invention, one or more other coatings or films may be present between a functional coating or film and the second surface as needed, and the aforementioned other coatings or films may be another functional coating or film.

[0030] As shown in FIG. 3, in some embodiments of the present invention, the second surface of the reflective polarizing element 21 includes a prism 24. The prism 24 may be any known commercially available prism or may be made of suitable materials known to those skilled in the art. In some embodiments of the present invention, the prism may be made of any resin with a refractive index greater than that of air; generally, the higher the refractive index, the better the effect. The resin used to form the prism is well known to those skilled in the art, for example, a thermosetting resin or an ultraviolet-curing resin, preferably an ultraviolet-curing resin. The types of thermosetting or ultraviolet-curing resins are as described above. The height of the prism may be, for example, in the range of 5 micrometers (μm) to 100 micrometers (μm); the apex angle of the prism structure may be, for example, in the range of 40° to 120°, preferably in the range of 85° to 95°.

[0031] As shown in FIG. 4, in some embodiments of the present invention, a polyester film 25 is included on the second surface of the reflective polarizing element 21, the polyester film 25 being attached to the second surface through an adhesive 24a. Adding the polyester film increases the support of the polarizing element. In some embodiments of the present invention, the polyester film is a polyethylene terephthalate film or a polyethylene naphthalate film, and the thickness of the polyester film can be in the range of, for example, 100 micrometers (μm) to 300 micrometers (μm), for example, 100 μm, 120 μm, 150 μm, 180 μm, 200 μm, 250 μm, 280 μm, or 300 μm. The adhesive can be a suitable adhesive known to those skilled in the art.

[0032] As shown in FIG. 5, in some embodiments of the present invention, the second surface of the reflective polarizing element 21 includes a coating 26 containing particles 27. The materials of the binder and particles 27 contained in the coating 26 may be the same as or different from the binder and acrylic resin particles of the uneven structure layer 23. The particles 27 may be the acrylic resin particles of the present invention or other particles commonly found in optical films. In some embodiments of the present invention, the coating 26 is the same as or similar to the uneven structure layer 23, which can be used in conjunction with the uneven structure layer 23 to further adjust the brightness gain and shielding effect of the optical film to the best. In other embodiments of the present invention, the coating 26 may have a smaller thickness and a lower particle content. The coating 26 containing particles 27 has an anti-adhesion effect. In the embodiment shown in FIG5, the second surface of the reflective polarizing element 21 sequentially includes a polyester film 25 and a coating 26 containing particles 27 (wherein the polyester film 25 is attached to the second surface through an adhesive 24a); however, in some embodiments, the coating 26 containing particles 27 can also be directly prepared on the second surface of the reflective polarizing element 21.

[0033] The optical film of the present invention has good brightness gain and shielding effect, and therefore can be applied to backlight modules for use in conjunction with other optical films, or can replace one or more other optical films. Therefore, the present invention further provides a backlight module including the optical film of the present invention, which has better brightness gain and shielding effect compared with conventional backlight modules.

[0034] The optical film of the present invention will now be described in detail with reference to specific embodiments and accompanying drawings, but this is not intended to limit the scope of the invention. Any modifications and alterations that can be easily made by those skilled in the art are included in the disclosure of this specification. [Test Method]

[0035] Surface roughness test: The surface roughness (Ra) of the optical film under test was measured using a handheld roughness meter (model: SJ-201P) according to the standard method JIS B 0601.

[0036] Evaluation of shading effect: The optical film to be tested is placed 30 cm in front of the lamp tube, with the uncoated side facing the light source and the coated side facing away from the light source. By visual observation, if the outline of the lamp tube can still be clearly observed through the film, the shading effect is poor; if the outline of the lamp tube cannot be observed through the film and the light output is uniform, the shading effect is good. Figures 6(a) to 6(d) are schematic diagrams for evaluating the shading degree of the film: (a) the lamp tube used for testing; (b) the shading effect of the uncoated film (Comparative Example 1); (c), (d) and (e) show the shading effect as poor, fair, and good, respectively.

[0037] Brightness Gain Test: The optical film under test was assembled into a 22-sided backlight module provided by BenQ. A luminance meter (Topcon, model: SC-777) was used at a distance of 50 cm directly above the backlight module (0° angle) to measure the center luminance (unit: cd / m2) at a 2° measurement angle. The center luminance value obtained by assembling the module with the uncoated film (i.e., sample 1-1) was used as the base value. The center luminance value obtained by assembling the module with another film under test was divided by the base value and then multiplied by 100% to obtain the luminance gain value of the sample under test. A value greater than 100% indicates that the coating provides a luminance gain effect; a value less than 100% indicates that the coating causes a luminance reduction. [Abbreviations] PMMA (2μm): Polymethyl methacrylate particles (SSX-102 model, Sekisui Chemicals Co., Ltd., Taiwan) PMMA (3μm): Polymethyl methacrylate particles (SSX-103 model, Sekisui Chemicals Co., Ltd., Taiwan) PMMA (5μm): Polymethyl methacrylate particles (MBX-05 model, Sekisui Chemicals Co., Ltd., Taiwan) PMMA (8μm): Polymethyl methacrylate particles (MBX-08 model, Sekisui Chemicals Co., Ltd., Taiwan) PBMA (5μm): Polybutyl methacrylate particles (BM30X-5 model, Sekisui Chemicals Co., Ltd., Taiwan) PBMA (12μm): Polybutyl methacrylate particles (BM30X-12 model, Sekisui Chemicals Co., Ltd., Taiwan) PS (5μm): Polystyrene particles (SBX-4 model, Sekisui Chemicals Co., Ltd., Taiwan) Nylon (5μm): Nylon particles (self-synthesized) Silica (5μm): Silicon dioxide particles (Sunsil 50, Sunjin Chemical Company) [Example 1]

[0038] The particles and acrylic resin (ETERMER 2386 and ETERCURE 6145-100, Chang Hsing Materials Co., Ltd.; solids content approximately NV40%) are uniformly mixed at the particle / resin solids ratio (hereinafter referred to as "BB value") listed in Table 1 to prepare a coating.

[0039] The coating was applied to the surface of a multilayer polymer optical film substrate (AF model, Hung Teng Optoelectronics Co., Ltd.) with a thickness of 38 μm using an RDS applicator #12. After drying, an optical film with a coating thickness of approximately 6 μm was obtained and various tests were performed. Table 1 sample Particle Material Particle size BB value Roughness (nm) Brightness gain value (%) occlusion effect 1-1 Uncoated - - - 100 ╳ 1-2 PS 5μm 1.0 800 8.4 〇 1-3 Nylon 5μm 1.0 1300 12.8 ╳ 1-4 Silica 5μm 1.0 1800 21.7 ╳ 1-5 PMMA 5μm 1.0 960 118.3 〇 1-6 PBMA 5μm 1.0 1570 111.3 〇

[0040] As shown in Table 1, compared to other types of particles (e.g., silicon dioxide particles, polystyrene particles, nylon particles), films using coatings containing acrylic resin particles (e.g., PMMA particles, PBMA particles) provide excellent brightness gain and good shielding effect. [Example 2]

[0041] Using the same method as in Example 1, but with the particle size and BB value listed in Table 2, coatings and optical films were prepared, and various tests were performed. Table 2 sample Particle Material Particle size BB value Roughness (nm) Brightness gain value (%) occlusion effect 2-1 PMMA 2μm 1.0 650 108.6 ╳ 2-2 PMMA 3μm 1.0 740 115.5 △ 2-3 PMMA 5μm 1.0 960 118.3 〇 2-4 PMMA 8μm 1.0 1800 116.9 〇 2-5 PMMA 15μm 1.0 4100 111.7 ╳ 2-6 PBMA 5μm 1.0 1570 111.3 〇 2-7 PBMA 8μm 1.0 1700 111.2 〇 2-8 PBMA 12μm 1.0 2600 110.7 ╳

[0042] As shown in Table 2, acrylic resin particles have a brightness-enhancing effect; however, if the particle size is too small or too large, the brightness gain value decreases and the masking effect is poor. [Example 3]

[0043] Using the same method as in Example 1, but with the particle size and BB value listed in Table 3, coatings and optical films were prepared, and various tests were performed. Table 3 sample Particle Material Particle size BB value Roughness (nm) Brightness gain value (%) occlusion effect 3-1 PMMA 5μm 0.5 840 96.2 ╳ 3-2 PMMA 5μm 0.7 950 101.4 ╳ 3-3 PMMA 5μm 1.0 960 118.3 〇 3-4 PMMA 5μm 1.5 1110 105.2 〇 3-5 PMMA 5μm 2.0 850 95.8 〇 3-6 PBMA 5μm 0.5 1130 101.8 ╳ 3-7 PBMA 5μm 0.7 1450 102.1 ╳ 3-8 PBMA 5μm 1.0 1570 111.3 〇 3-9 PBMA 5μm 1.5 1620 107.5 〇 3-10 PBMA 5μm 2.0 1580 97.5 〇

[0044] As shown in Table 3, increasing the content of acrylic resin particles can improve the masking effect; however, excessive particle content will lead to a decrease in the brightness gain value.

[0045] The above embodiments are merely illustrative of the embodiments of the present invention and to illustrate the technical features of the present invention, and are not intended to limit the scope of protection of the present invention. Any modifications or arrangements that can be easily made by those skilled in the art without departing from the technical principles and spirit of the present invention are within the scope claimed by the present invention. Therefore, the scope of protection of the present invention is as listed in the attached patent application. [Simplified Explanation of the Diagram]

[0047] Figure 1 is a schematic diagram of the structure of a typical reflective brightening film.

[0048] Figures 2 to 5 are schematic diagrams of the structure of the optical film provided according to some embodiments of the present invention.

[0049] Figures 6(a) to 6(e) are schematic diagrams for evaluating the shading effect of the diaphragm: (a) test lamp; (b) shading effect of uncoated diaphragm; (c) poor shading effect; (d) acceptable shading effect; (e) good shading effect.

Claims

1. An optical film comprising: a reflective polarizing element having a first surface and a second surface opposite to the first surface; and an uneven structure layer located on the first surface of the polarizing element, wherein the uneven structure layer comprises a plurality of acrylic resin particles. The average particle size of the acrylic resin particles ranges from 3 micrometers to 10 micrometers.

2. The optical film of claim 1, wherein the uneven structure layer has an arithmetic mean roughness (Ra) between 700 nanometers and 1800 nanometers.

3. The optical film of claim 1, wherein the uneven structure layer comprises a plurality of acrylic resin particles and a binder, wherein the binder is selected from ultraviolet-curing resin or thermosetting resin, the ultraviolet-curing resin being composed of at least one acrylic monomer or acrylate monomer having one or more functional groups, and the thermosetting resin being selected from polyester resin, epoxy resin, polymethyl methacrylate resin, polyamide resin, fluoropolymer resin, polyimide resin, polyurethane resin, alkyd resin and mixtures thereof containing carboxyl (-COOH) and / or hydroxyl (-OH) groups.

4. The optical film of claim 3, wherein the weight ratio of the acrylic resin particles to the binder is between 0.8 and 1.

8.

5. The optical film of claim 1, wherein the second surface of the reflective polarizing element includes one or more functional coatings or films.

6. The optical film of claim 5, wherein the one or more functional coatings or films are polycarbonate films, polyester films, anti-adhesion layers, antistatic layers, anti-scratch layers, or prisms or combinations thereof.

7. The optical film of claim 1, wherein the optical film can produce a brightness gain of more than 1% for the light-emitting device compared to the same optical film without acrylic resin particles.

8. The optical film of claim 1, wherein the acrylic resin particles may be a homopolymer or copolymer made from a selection of the following acrylate monomers: methyl methacrylate, butyl methacrylate, 2-phenoxyethyl acrylate, ethoxylated 2-phenoxyethyl acrylate, 2-(2-ethoxyethoxy)ethyl acrylate, cyclotrimethylolpropane methyl acetal acrylate, β-carboxyethyl acrylate, methyl laurate, isooctyl acrylate, methyl stearate, isodecanyl acrylate, isoborneol methacrylate, benzyl acrylate, 2-hydroxyethyl methacrylate phosphate, hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, and mixtures thereof.

9. A backlight module comprising an optical film as claimed in any one of claims 1 to 8.

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