TW202140253A - Optical film - Google Patents

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

Optical film

The present invention relates to an optical film, in particular to an optical film that can be used in a backlight module to increase the brightness.

Liquid crystal displays have become the mainstream of current display technology due to their advantages such as high image quality, low radiation, low power consumption, and better space utilization. The main structure of a liquid crystal display includes two parts: a liquid crystal panel and a backlight module. Since the liquid crystal panel itself does not emit light, a backlight module must be used to provide the surface light source required by the liquid crystal panel so that the liquid crystal panel can display images.

Various optical films are used in the backlight module to cloud the light source and increase the brightness. This approach does not need to change any component design or consume additional energy, and is a more economical and simple solution. Optical films commonly used in backlight modules include: reflective film, diffuser, diffuser, light-concentrating film, and dual brightness enhancement film (Dual Brightness Enhancement Film), etc. Brightness Enhancement Film (BEF), also known as Brightness Enhancement Film (BEF), is mainly used to concentrate scattered light to a positive viewing angle (On-axis) of about ±35 degrees through the microstructure to enhance the liquid crystal panel. The brightness. Different from the light-concentrating film, the reflective brightness enhancement film is made of multiple layers of materials with different refractive indexes as the core layer, which can pass the polarized light in the penetrating direction and reflect the polarized light in the non-penetrating direction back to the backlight mode. Group, through the action of other films (such as reflective film) in the backlight module, make it return to the reflective brightness enhancement film and partially convert it into polarized light in the penetrating direction. The light that should be absorbed by the polarizer in the liquid crystal panel is converted into usable effective light to achieve a brightening effect. Therefore, the reflective brightness enhancement film can not only replace the light-concentrating film, but also be matched with the light-concentrating film, which can be applied to high-end display products.

Fig. 1 is a schematic diagram of the structure of a general reflective brightness enhancement film. As shown in FIG. 1, a general reflective brightness enhancement film 100 has a core layer 11 with a 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 reflective brightness enhancement film is relatively expensive. Therefore, in the technical field, an optical film with high light utilization and price advantage is expected.

In addition, the light source in the backlight module can be, for example, a point light source or a line light source. However, whether it is a point light source or a line light source, if the light emitted by the backlight module cannot be homogenized, an obvious light source profile can be observed on the panel, which affects the image quality. Therefore, this technical field also expects an optical film that can homogenize light to shield the contour of the light source.

The present invention provides an optical film that can improve brightness, has a shielding effect, and has a cost advantage. The optical film of the present invention includes: a reflective polarizing element having a first surface and a second surface opposite to the first surface; and a concavo-convex structure layer on the first surface of the polarizing element, wherein the concavo-convex structure The layer contains a plurality of acrylic resin particles.

The present invention provides a backlight module containing the above-mentioned optical film.

Hereinafter, the optical film of the present invention will be described in detail with examples in conjunction with the accompanying drawings. It should be noted that the drawings described below are only part of the embodiments of the present invention, and various structures thereof may not be drawn to scale, and the sizes of various structures may be increased or decreased for clarity of discussion. Any modifications and changes that can be easily achieved by a person with ordinary knowledge in the relevant technical field are included in the disclosure of this specification.

In this specification and the scope of the patent application, unless the context clearly dictates otherwise, the singular form "a" and "the" include the singular or plural. Unless otherwise claimed, the use of any and all examples or illustrative language (such as "such as") provided herein is only to better illustrate the content of the present invention, and should not limit the scope of the present invention. The language in this specification should not be interpreted as indicating that any unclaimed element is necessary for implementing the present invention.

As used herein, the terms "approximately", "substantially", "substantially" and "about" are used to describe and illustrate small changes. When used in conjunction with an event or situation, the term may refer to an example in which the event or situation occurs precisely and an example in which the event or situation occurs very closely. For example, when used in conjunction with a value, the term can refer to a range of variation less than or equal to ±10% of the stated 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 values is less than or equal to ±10% of the average value of the value (for example, 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 values can be considered "substantially" the same.

In addition, sometimes amounts, ratios, and other numerical values are presented in range format herein. It should be understood that this type of range format is for convenience and brevity, and should be understood flexibly. It not only includes values explicitly designated as range limits, but also encompasses all individual values or sub-ranges within the range, as if clearly Specify each value and sub-range in general.

Fig. 2 is a schematic structural diagram of an optical film provided according to some embodiments of the present invention. As shown in FIG. 2, the optical film 200 provided by the embodiment of the present invention includes a reflective polarizing element 21 and a concavo-convex structure layer 22 on the first surface of the reflective polarizing element 21. The concavo-convex structure layer contains a plurality of acrylic resin particles 23.

The reflective polarizing element 21 used in the present invention may be a suitable reflective polarizing element known to those with ordinary knowledge in the art, such as a multilayer reflective polarizing element. The multilayer reflective polarizing element includes at least a first birefringent layer and a second birefringent layer. The first birefringent layer and the second birefringent layer are respectively composed of different birefringent polymers, so that the interface between the two layers forms a light Reflection plane. The first birefringent layer and the second birefringent layer are alternately stacked into multiple layers, and the number of layers and the thickness of each layer can be adjusted according to the desired reflection polarization effect. The number of layers generally ranges from 2 to 5000, such as 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, and is generally less than 1 micrometer ( μm ).

The thickness of the reflective polarizing element 21 depends on the layers included and the thickness of each layer. In some embodiments of the present invention, the reflective polarizing element 21 used has a thickness ranging from 2 micrometers ( μm ) to 10 micrometers ( μm ), for example, 2 μm , 3 μm , 4 μm , 5 μm. μ m, 6 μ m, 8 μ m or 10 μ m; preferably 3 μ m to 6 μ m.

In some embodiments of the present invention, the materials of the one birefringent layer and the second birefringent layer may be: polyester, such as polyethylene terephthalate (PET), polyethylene terephthalate Polybutylene terephthalate (PBT), polyethylene naphthalate (PEN) or polybutylene naphthalate (PBN); polymethacrylate (polymethacrylate) ); Polyimide resin (polyimide resin); Polystyrene (polystyrene); Polyolefin resin (polyolefin); Cyclic olefin copolymer (COC); Polycarbonate (polycarbonate); Polyurethane Ester resin (polyurethane); triacetate cellulose (TAC); polylactic acid (Polylactide, PLA); or a material obtained by mixing or polymerizing the above materials, preferably polyester or polycarbonate. The one birefringent layer and the second birefringent layer are uniaxially or biaxially stretched to form a polarization effect.

In some embodiments of the present invention, the concavo-convex structure layer 22 is formed by coating a resin coating containing a plurality of acrylic resin particles and a bonding agent on the first surface of the reflective polarizing element 21. Knowing that the reflective brightness enhancement film does not need to use an expensive polycarbonate film, at the same time, the optical film of the present invention can exhibit excellent brightness gain value and has a cost advantage. In addition, in some preferred embodiments of the present invention, the optical film of the present invention can further provide a good shielding effect.

In some embodiments of the present invention, the bonding agent of the present invention can be selected from the group consisting of ultraviolet curable resin, thermal setting resin, thermal plastic resin and mixtures thereof, and can be cured by heating as necessary. , Ultraviolet curing, or heating and ultraviolet dual curing (dual curing) to form the resin coating of the present invention.

The ultraviolet curable resin that can be used in the present invention is composed of at least one acrylic monomer or acrylate monomer having one or more functional groups, preferably an acrylate monomer. Acrylic monomers that can be used in the present invention include, but are not limited to: (meth)acrylate, such as 2-hydroxy-3-phenoxypropyl acrylate; urethane acrylate ((meth)acrylate) urethane acrylate, such as aliphatic urethane acrylate, aliphatic urethane hexaacrylate, or aromatic urethane hexaacrylate ); polyester acrylate, such as polyester diacrylate; epoxy acrylate, such as bisphenol-A epoxy diacrylate, phenolic ring Novolac epoxy acrylate; or a mixture thereof.

The average molecular weight of the thermosetting resin that can be used in the present invention is generally between about 10 ⁴ and about 2×10 ⁶ , preferably between about 2×10 ⁴ and about 3×10 ⁵ , and more preferably between about 4×10 between about ⁴ to ^105. The thermosetting resin of the present invention can be selected from polyester resins, epoxy resins, polymethacrylate resins, polyamide resins, fluorine resins, and polyamides containing carboxyl groups (-COOH) and/or hydroxyl groups (-OH). A group consisting of amine resin, polyurethane resin, alkyd resin and mixtures thereof, preferably polymethacrylate containing carboxyl group (-COOH) and/or hydroxyl group (-OH) Resin or polyacrylate resin, such as polymethacrylic polyol resin.

The thermoplastic resins that can be used in the present invention can be selected from the group consisting of polyester resins; polymethacrylate resins, such as polymethyl methacrylate (PMMA); and their mixtures.

In some embodiments of the present invention, the concavo-convex structure layer 22 has a plurality of acrylic resin particles 23. The inventor of the present invention found that compared with other types of particles (such as silica particles, polystyrene particles, nylon particles), The use of acrylic resin particles can increase the brightness and have a good masking effect. In some embodiments of the present invention, the acrylic resin particles may be homopolymers or copolymers made from the following acrylate monomers: methyl methacrylate, butyl methacrylate, 2-phenoxy 2-phenoxy ethyl acrylate, ethoxylated 2-phenoxy ethyl acrylate, 2-(2-ethoxyethoxy) ethyl acrylate ( 2-(2-ethoxyethoxy)ethyl acrylate), cyclic trimethylolpropane formal acrylate, β-carboxyethyl acrylate, lauric acid methacrylate ( lauryl methacrylate, isooctyl acrylate, stearyl methacrylate, isodecyl acrylate, isoborny methacrylate, benzyl Acrylate (benzyl acrylate), 2-hydroxyethyl metharcrylate phosphate (2-hydroxyethyl metharcrylate phosphate), hydroxyethyl acrylate (HEA), 2-hydroxyethyl methacrylate (2-hydroxyethyl acrylate) methacrylate (HEMA) and their mixtures are preferably methyl methacrylate, butyl methacrylate or a combination thereof.

In some embodiments of the present invention, the shape of the acrylic resin particles is not particularly limited. For example, they may be spherical, elliptical, or irregular, and preferably spherical. The average particle size of the acrylic resin particles ranges from 3 microns ( μ m) to 10 microns ( μ m), for example, 3 μ m, 4 μ m, 5 μ m, 6 μ m, 7 μ m, 8 μm , 9 μm, or 10 μm , preferably 5 μm to 8 μm , so that the optical film can have an excellent brightness gain value and a good shielding effect. In some embodiments of the present invention, if the average particle size of the acrylic resin particles is less than 3 μm or exceeds 10 μm , the shielding effect cannot be exerted.

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

In some embodiments of the present invention, the acrylic resin particles may protrude completely or partly from the resin coating to provide a concave-convex surface. In some embodiments of the present invention, as shown in FIG. 1, the acrylic resin particles can be all embedded in the resin coating and still provide a concave-convex surface.

In some embodiments of the present invention, the uneven structure layer has an arithmetic average 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 average roughness (Ra) can be measured using the JIS B-0601 standard method. If the arithmetic average roughness of the concavo-convex structure layer is too small (for example, less than 700 nm), the shielding property will be insufficient. If the arithmetic average roughness of the concavo-convex structure layer is too high (for example, greater than 1800 nm), the light will diverge too much and affect the brightness.

In some embodiments of the present invention, the thickness of the concave-convex structure layer is between about 5 micrometers ( μm ) to about 10 micrometers ( μm ), for example, 5 μm , 6 μm , 7 μm , 8 μm. μ m, 9 μ m or 10 μ m.

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

In some embodiments of the present invention, the second surface of the reflective polarizing element may include one or more functional coatings or films, so that the optical film has enhanced or additional functions. The aforementioned functional coatings or films are, for example, but not limited to, polycarbonate film, polyester film, adhesion prevention layer, antistatic layer, anti-scratch layer, or sheet, or a combination 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 sheet, or a combination thereof.

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 FIGS. 3 to 5, the scallop sheet or polyester film is directly attached to the second surface, it is only for illustrative purposes. Under the scope of the present invention, a functional coating or film There may be one or more other coatings or membranes between the sheet and the second surface as needed, and the above-mentioned other coatings or membranes may be another functional coating or membrane.

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

As shown in FIG. 4, in some embodiments of the present invention, the second surface of the reflective polarizing element 21 includes a polyester film 25, and the polyester film 25 is attached to the second surface through an adhesive 24a. Adding a polyester film can increase 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, for example, 100 micrometers ( μm ) to 300. The range of micrometers ( μm ), for example, 100 μm , 120 μm , 150 μm , 180 μm , 200 μm , 250 μm , 280 μm, or 300 μm . The adhesive may be an appropriate adhesive known to those with ordinary knowledge in the art.

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 material of the bonding agent and particles 27 contained in the coating layer 26 may be the same as or different from the bonding agent and acrylic resin particles of the concave-convex structure layer 23. The particles 27 may be acrylic resin particles of the present invention or other particles commonly used in optical films. In some embodiments of the present invention, the coating 26 is the same or similar to the concave-convex structure layer 23, which can be used with the concave-convex 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 layer 26 can be made to have a smaller thickness and the particle content can be reduced. The coating 26 containing the particles 27 has the effect of preventing adhesion. In the embodiment of FIG. 5, the second surface of the reflective polarizing element 21 sequentially includes a polyester film 25 and a coating layer 26 containing particles 27 (wherein the polyester film 25 is affixed to it through an adhesive 24a) On the second surface); however, in some embodiments, the particle 27-containing coating 26 can also be directly prepared on the second surface of the reflective polarizing element 21.

The optical film of the present invention has good brightness gain and shielding effects, so it can be applied to a backlight module to be used 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. Compared with conventional backlight modules, the optical film of the present invention has better brightness gain and shielding effect.

Hereinafter, the optical film of the present invention is described in detail with specific embodiments in conjunction with the accompanying drawings, but it is not intended to limit the scope of the present invention. Any modifications and changes that can be easily achieved by a person with ordinary knowledge in the relevant technical field are included in the disclosure of the specification of this case. [ Test method ]

Surface roughness test : Use a hand-held roughness meter (model: SJ-201P) to measure the surface roughness (Ra) of the optical film under test according to the standard method JIS B 0601.

Evaluation of shielding effect: Set the optical film to be tested at a distance of 30 cm in front of the lamp tube, so that the uncoated surface faces the light source and the coated surface faces away from the light source. Observed by naked eyes, if the outline of the lamp tube can be clearly observed through the diaphragm, the shielding effect is poor; if the outline of the lamp tube cannot be observed through the diaphragm, and the light is uniform, the shielding effect is good. Figures 6(a) to 6(d) are schematic diagrams of the evaluation of the degree of shielding of the diaphragm: (a) the test tube; (b) the shielding effect of the uncoated diaphragm (comparative example 1); (c), ( d) and (e) respectively show that the shielding effect is poor, the shielding effect is fair, and the shielding effect is good.

Luminance gain test: Assemble the optical film to be tested to the 22-side backlight module provided by BenQ, and use a luminance meter (Topcon, model: SC-777) directly above the backlight module (0° angle) 50 At a distance of cm, the central brightness (Brightness; unit: cd/m ² ) is measured at a measuring angle of 2°. Take the center luminance value of the module assembled with the uncoated membrane (ie, sample 1-1) as the base value, divide the center luminance value of the module assembled with another membrane to be tested by the base value and multiply by 100% , You can know the brightness gain value of the sample to be tested. More than 100%, it means that the coating provides brightness gain effect; less than 100%, it means that the coating causes brightness loss. [ Description of abbreviation ] PMMA (2 μ m): Polymethyl methacrylate particles (SSX-102 model, Taiwan Sekisui Chemical Products Co., Ltd.) PMMA (3 μ m): Polymethyl methacrylate particles (SSX- Model 103, Taiwan Sekisui Chemical Products Co., Ltd.) PMMA (5 μm ): Polymethylmethacrylate particles (Model MBX-05, Taiwan Sekisui Chemicals Co., Ltd.) PMMA (8 μm ): Polymethacrylic acid Methyl ester particles (MBX-08 model, Taiwan Sekisui Chemical Products Co., Ltd.) PBMA (5 μm ): Polybutyl methacrylate particles (BM30X-5 model, Taiwan Sekisui Chemical Products Co., Ltd.) PBMA (12 μ m ): Polybutyl methacrylate particles (Model BM30X-12, Taiwan Sekisui Chemical Co., Ltd.) PS (5 μm ): Polystyrene particles (Model SBX-4, Taiwan Sekisui Chemical Co., Ltd.) Nylon ( 5 μ m): Nylon particles (in- house synthesis) Silica (5 μ m): Silicon dioxide particles (sunsil 50 model, Sunjin Chemical Company) [ Example 1]

Mix the particles with acrylic resin (ETERMER 2386 and ETERCURE 6145-100, Evergreen Materials Co., Ltd.; solid content is about NV40%) at the particle/resin solid content ratio (hereinafter referred to as "BB value") listed in Table 1. Prepared into paint.

Use RDS smear stick #12 to coat the coating on the surface of a multilayer polymeric optical film substrate (AF model, Hongteng Optoelectronics Co., Ltd.) with a thickness of 38 μm . After drying, a coating with a thickness of about 6 μm is obtained. Various tests are carried out on the optical film. Table 1 sample Particle material Particle size BB value Roughness (nm) Brightness gain value (%) Masking 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

As can be seen from Table 1, compared to other types of particles (such as silica particles, polystyrene particles, nylon particles), the use of acrylic resin particles (such as PMMA particles, PBMA particles) coating film can provide excellent Brightness gain effect and good shading effect. [ Example 2]

With the same method as in Example 1, the particles and BB values in Table 2 were changed to prepare coatings and optical films, and various tests were performed. Table 2 sample Particle material Particle size BB value Roughness (nm) Brightness gain value (%) Masking 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 ╳

It can be seen from Table 2 that the acrylic resin particles have a brightness gain effect; however, if the particle size is too small or too large, the brightness gain value will be reduced and the shielding effect will not be good. [ Example 3]

With the same method as in Example 1, the particles and BB values in Table 3 were changed to prepare coatings and optical films, and various tests were performed. table 3 sample Particle material Particle size BB value Roughness (nm) Brightness gain value (%) Masking 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

It can be seen from Table 3 that an increase in the content of acrylic resin particles can improve the shielding effect; however, too much particle content will result in a decrease in the brightness gain value.

The above-mentioned embodiments are only illustrative of the implementation of the present invention, and illustrate the technical features of the present invention, and are not used to limit the protection scope of the present invention. Any changes or arrangements that can be easily made by a person familiar with the present invention without departing from the technical principles and spirit of the present invention fall within the scope of the present invention. Therefore, the scope of protection of the rights of the present invention is as listed in the appended patent scope.

11: core layer 12, 13: Polycarbonate film 14a, 14b: Adhesive 21: Reflective polarizing element 22: Concave-convex structure layer 23: Acrylic resin particles 24: 稜鏡片 24a: Adhesive 25: Polyester film 26: Coating 27: particles 100: reflective brightness enhancement film 200: Optical film

Figure 1 is a schematic diagram of the structure of a general reflective brightness enhancement film.

2 to 5 are schematic diagrams of the structure of optical films provided according to some embodiments of the present invention.

Figures 6(a) to 6(e) are schematic diagrams of the evaluation of the shielding effect of the diaphragm: (a) the test tube; (b) the shielding effect of the uncoated diaphragm; (c) the poor shielding effect; (d) The covering effect is acceptable; (e) The covering effect is good.

21: Reflective polarizing element

22: Concave-convex structure layer

23: Acrylic resin particles

200: Optical film

Claims (9)

An optical film comprising: A reflective polarizing element, the reflective polarizing element has a first surface and a second surface opposite to the first surface; and a concavo-convex structure layer on the first surface of the polarizing element, wherein the concavo-convex structure layer includes a plurality of acrylic resin particles . The average particle size of the acrylic resin particles ranges from 3 microns to 10 microns. The optical film of claim 1, wherein the concave-convex structure layer has an arithmetic average roughness (Ra) ranging from 700 nm to 1800 nm. The optical film of claim 1, wherein the concavo-convex structure layer comprises a plurality of acrylic resin particles and a bonding agent, wherein the bonding agent is selected from ultraviolet curable resin or thermosetting resin, and the ultraviolet curable resin is composed of at least one having one or more functionalities. The thermosetting resin can be selected from polyester resin, epoxy resin, polymethacrylate resin containing carboxyl group (-COOH) and/or hydroxyl group (-OH) , Polyamide resin, fluorine resin, polyimide resin, polyurethane resin, alkyd resin and mixtures thereof. The optical film of claim 3, wherein the weight ratio of the acrylic resin particles to the bonding agent is 0.8 to 1.8. The optical film of claim 1, wherein the second surface of the reflective polarizing element includes one or more functional coatings or films. Such as the optical film of claim 5, wherein the one or more functional coatings or films are polycarbonate film, polyester film, adhesion prevention layer, antistatic layer, anti-scratch layer or sheet or combination thereof. The optical film of claim 1, wherein the optical film can produce a luminance gain of more than 1% for the light-emitting device compared with the same optical film without acrylic resin particles. The optical film of claim 1, wherein the acrylic resin particles may be a homopolymer or copolymer selected from the following acrylic acid ester monomers: methyl methacrylate, butyl methacrylate, 2-phenoxy Ethyl acrylate, ethoxylated 2-phenoxyethyl acrylate, 2-(2-ethoxyethoxy) ethyl acrylate, cyclotrimethylolpropane methylal acrylate, β-carboxyethyl Base acrylate, lauric acid methacrylate, isooctyl acrylate, stearic acid methacrylate, isodecyl acrylate, isobornyl methacrylate, benzyl acrylate, 2-hydroxyethylmethacrylate It is a group consisting of acrylate phosphate, hydroxyethyl acrylate, 2-hydroxyethyl methacrylate and their mixtures. A backlight module comprising the optical film as claimed in any one of claims 1 to 8.

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