KR20130095235A - Brightness enhancement film and backlight unit comprising the same - Google Patents

Abstract

PURPOSE: A brightness enhancement film and a backlight unit including the same are provided to implement a low driving voltage, by increasing brightness of an output light and the viewing angle of the output light. CONSTITUTION: An adhesive layer (24) is formed on both sides of a multi-layered thin film (3). Light diffusion films (1,5) are formed on the adhesive layer. A first thin film comprises optical isotropy. A second thin film comprises anisotropy. A light diffusion layer is formed at least one surface of the multi-layered thin film.

Description

[0001] The present invention relates to a brightness enhancement film and a backlight unit including the brightness enhancement film.

The present invention relates to a brightness enhancement film used in a display.

In general, a liquid crystal display is one of flat panel display devices for displaying images using liquid crystal, and is thinner and lighter than other flat panel display devices, has advantages of low driving voltage and low power consumption, .

The liquid crystal display includes a thin film transistor (TFT) substrate, a color filter substrate facing the TFT substrate, and a liquid crystal panel interposed between the both substrates and having a liquid crystal layer for changing the transmittance of light. In addition, since the liquid crystal display for displaying an image is a non-luminescent element that can not emit light by itself, a liquid crystal display requires a backlight unit for supplying light to the liquid crystal panel.

The backlight unit includes at least one optical film laminated on a light guide plate or a diffusion plate in order to secure advantages such as improvement of brightness of output light and improvement of viewing angle of output light.

The optical films may be classified into a film capable of enhancing brightness and a film capable of diffusing light. In recent years, it is necessary to combine these characteristics in response to the trend of thinning of a liquid crystal display.

As a part of such a complexation, a film capable of enhancing brightness, for example, a reflective polarizing film and a film capable of diffusing light, for example, a light diffusion film, is laminated (refer to Japanese Patent Application Laid-open No. 10-2006-055341).

However, it has been difficult to prevent deterioration in brightness due to long-term use simply by laminating composite films having different functions.

The present invention is to provide a brightness enhancement film and a backlight unit including the same, which can ensure reliability against changes in external environment.

As a first embodiment, there is provided a brightness enhancement film comprising a multilayer thin film having improved hydrophilicity and a light diffusion layer on at least one side of the multilayer thin film. The brightness enhancement film has a high reliability against changes in the external environment such as temperature and / or humidity while improving brightness. In addition, the brightness enhancement film has high reliability for the external environment of the liquid crystal display, Recall rate, life characteristics, and the like can be improved.

The first embodiment includes a multilayer thin film including a plurality of optically isotropic first thin films and optically anisotropic second thin films and having a surface contact angle of 50 to 85 DEG; And a light diffusion layer formed on one surface of the multilayer thin film.

According to an aspect of the present invention, the brightness enhancement film includes a first axis and a second axis orthogonal to each other in the film plane, and reflects light polarized along the first axis among lights incident on the brightness enhancement film, It is possible to transmit the light polarized along the second axis among the lights incident on the brightness enhancement film.

As a second embodiment, there is provided a backlight unit including the brightness enhancement film.

1 is a schematic view showing a cross section of a brightness enhancement film according to an embodiment of the present invention.

Hereinafter, the present invention will be described in detail.

One embodiment of the present invention provides a brightness enhancement film comprising a multilayer thin film including a plurality of first thin films and second thin films. The brightness enhancement film includes a light diffusion layer on at least one side of the multilayered thin film, wherein the light diffusion layer may be in the form of a coating layer formed from a conventional light diffusion liquid and may include a form including a light diffusion film on a base film And the case of the form of a light diffusion film. Specifically, the light diffusion film can be understood as a polycarbonate (PC) film having a diffusion function or a film having a diffusion layer.

For example, the light-diffusing layer includes a binder resin and light-diffusing particles. Here, the binder may be a thermosetting or ultraviolet-curable resin such as a polyvinyl resin, an acrylic resin, a polyester resin, a styrene resin, an alkyd resin, an amino resin, a polyurethane resin or an epoxy resin. Examples of the inorganic particles include silica, zirconia, calcium carbonate, barium sulfate, and titanium oxide. Examples of the organic particles include styrene, melamine formaldehyde, Homopolymers or copolymers obtained from monomers such as benzoguanamine formaldehyde, benzoguanamine bellamine formaldehyde, propylene, ethylene, silicone, urethane, methyl (meth) acrylate and the like. And the like, but the present invention is not limited thereto.

If the light-diffusing layer is in the form of a light-diffusing film, an adhesive layer may be applied on the multilayer film for laminating the multilayer film and the light-diffusing film, and the light-diffusing film may be laminated. Here, the adhesive layer may be a UV curable adhesive.

1 shows a brightness enhancement film including adhesive layers 2 and 4 on both sides of the multilayer thin film 3 and light diffusion films 1 and 5 on the adhesive layer. However, the structure of the brightness enhancement film of the present invention is limited thereto Of course not.

The brightness enhancement film obtained by laminating the light diffusion film with the multilayer thin film often has a lowered brightness depending on the temperature condition and the use time. This is because the layer separation of the surface of the multilayer thin film and the light diffusion film is one cause Respectively. Of course, this phenomenon can also occur in a case where the light diffusion layer is formed by applying the light diffusion layer coating liquid on the multilayer thin film.

Accordingly, it has been found that, in one embodiment of the present invention, when the surface roughness of the multilayer thin film is improved, it is possible to directly coat the light diffusion layer coating liquid or to secure sufficient interlaminar adhesion even with a laminate of a light diffusion film using an adhesive.

In this respect, the surface contact angle of the multilayered film is 50 to 85 deg., Preferably 70 to 85 deg..

The brightness enhancement film can be used to improve the brightness of a backlight unit installed as an external light source of a liquid crystal display having no self-emission source. The characteristics of the brightness enhancement film required for a liquid crystal display need to be further improved due to various forms, uses, etc. of the liquid crystal display. For example, in order to secure reliability against changes in the external environment of a liquid crystal display, It is necessary to minimize the luminance reduction rate so that the luminance characteristic can be maintained even when the external environment change occurs. The brightness enhancement film of the present invention can satisfy this demand.

As a method for improving the surface hydrophilicity of the multilayer thin film, it may be possible to physically and chemically change the surface properties, but in the case of the physical treatment, it is possible to impart the hydrophilic property simultaneously with the extrusion, There are cases where it is difficult to obtain change and satisfactory prosperity. In the case of chemical modification, there is a method of coating the primer after the extrusion process, but it is disadvantageous in that it is difficult to match the refractive index with the refractive index of the resins formed in the multilayer thin film, thereby lowering the luminance. In the present invention, And / or a resin which does not undergo solid-state polymerization as the resin constituting the second thin film. In the case of forming a multilayer thin film with a polymer resin not proceeding with solid phase polymerization, the hydrophilicity of the surface of the multilayer thin film can be increased, which can be interpreted as the hydroxyl group remaining at the end of the polymer resin. By increasing the hydrophilicity of the multilayer thin film as described above, the adhesion between the multilayer thin film and the adhesive layer, the adhesion between the adhesive layer and the light diffusion film, or the adhesion between the multilayer thin film and the light diffusion layer can be improved.

The first thin film and / or the second thin film constituting the brightness enhancement film may include organic and / or inorganic materials, but it is preferable that the first thin film and / or the second thin film include an organic material in consideration of film formability, flexibility,

For example, the first thin film may be an optically anisotropic thin film, and the second thin film may be optically isotropic thin film. Optical isotropy in the description above and below means that the refractive index associated with all the axes in the plane of the thin film is substantially the same and the optical anisotropy means that the refractive index associated with the axis in the plane of the thin film is substantially different .

Examples of the polymer capable of forming the optically anisotropic first thin film include a resin having an ethylene naphthalate repeating unit content of 80 mol% or more, a resin having 85 mol% or more, a resin having 90 mol% or more, Resin, or a resin having 98 mol% or more. Alternatively, the first thin film may include a resin having an ethylene naphthalate repeating unit content of 100 mol%, and may include at least two kinds of the resins.

The first thin film may include a resin in which the content of ethylene naphthalate repeating units is 80 mol% or more and 100 mol% and the content of ethylene terephthalate repeating units is 20 mol% or less and 0 mol%. Preferably, the first thin film may include a resin having ethylene naphthalate repeating units of 90 mol% or more and 100 mol% or less, and ethylene terephthalate repeating units of 10 mol% or less and 0 mol% or more.

The resin of the first thin film may be selected from the group consisting of dimethylcarboxylic naphthalate (NDC) and ethylene glycol (EG); Or condensation polymerization of dimethylcarboxylic naphthalate (NDC), ethylene glycol (EG) and terephthalic acid (TPA).

The second thin film may contain a resin having a content of ethylene naphthalate repeating units of 10 mol% or more and 60 mol% or less. Preferably, the content of ethylene naphthalate repeating units is 10 mol% or more and 60 mol% or less, And a resin having a content of ethylene terephthalate repeating units of 40 mol% or more and 90 mol% or less. More preferably, it may contain a resin in which the content of the ethylene naphthalate repeating unit is 40 mol% or more and 60 mol% or less and the content of the ethylene terephthalate repeating unit is 40 mol% or more and 60 mol% or less.

The resin of the second thin film may be prepared by condensation polymerization of dimethylcarboxylic naphthalate (NDC), ethylene glycol (EG), and terephthalic acid (TPA).

The multilayered thin film may be in the form of a laminated structure of the repeating units, that is, alternating multilayered films, in which the first thin film and the second thin film constitute one repeating unit, but the present invention is not limited thereto. For example, at least one thin film different from the first thin film and the second thin film may be interposed between the first thin film and the second thin film at any position in the repeating unit to constitute the repeating unit. As another example, the repeating unit composed of the first thin film and the second thin film, and the at least one repeating unit having a different lamination form from the repeating unit may be regularly or irregularly stacked.

The brightness enhancement film may be produced by any method such as extrusion drawing, vapor deposition, or coating. Preferably, the first and second thin films may be multilayer extruded and stretched. The extrusion drawing manufacturing process will be schematically described as follows, for example. First, dimethyl carbonate naphthalate (NDC), ethylene glycol (EG) and terephthalic acid (TPA) were added to a polymer polymerization reactor at a constant ratio, and the first polymer resin and the second polymer resin To prepare a polymer resin. Preferably, the first polymer resin and / or the second polymer resin does not proceed solid-state polymerization and does not complete polymerization. The polymer resin thus prepared is dried to remove moisture, and then a multilayer extruded film in which a first polymer resin and a second polymer resin are alternately laminated is produced through coextrusion in an extruder equipped with a multilayer feed block. The produced multilayer extruded film is continuously stretched and wound up as a uniaxial stretching machine at a constant temperature, stretching ratio and stretching speed to produce a brightness enhanced film. As described above, the multilayer thin film obtained from the polymer resin which has not undergone the solid state polymerization has a high surface property and a high hydrophilicity. Thereafter, a UV curable adhesive may be applied to both sides of the oriented multilayered film, and then a polycarbonate (PC) film having a diffusion function or a polyester film having a diffusion layer may be laminated and passed through a UV curing machine. By such a laminating method, it is possible to secure the stability of the brightness according to the temperature change and the long-time use. Further, a film having a diffusion layer may be attached to one surface of the drawn multilayer film, and a film having an anti-blocking layer having a relatively low turbidity may be laminated on the other surface. This is for imparting slipperiness to the optical member positioned at the bottom, and the turbidity of the anti-blocking layer is preferably 1 to 30%. When the turbidity is more than 30%, when the light passing through the lower optical member is incident on the brightness enhancement film, scattering of light on the surface occurs more than light transmission, It is preferable to form an anti-blocking layer.

If the light diffusing layer is directly applied on the stretched multilayer film, the light diffusing layer coarse solution can be formed by applying and drying according to a usual method. At this time, a light diffusion layer may be formed on one side of the drawn multilayer film, and on the other side, an anti-blocking layer having a turbidity of 1 to 30% may be formed in order to impart slipperiness to the optical member positioned below.

Wherein the brightness enhancement film includes a first axis and a second axis orthogonal to each other in the film plane and reflects light polarized along the first axis among the lights incident on the brightness enhancement film, It is possible to transmit the polarized light along the second axis. The light may be ultraviolet light, visible light, infrared light, or the like. For example, when the brightness enhancement film is employed in a display, the light may be a visible light ray.

The first thin film and the second thin film may each have an optical thickness defined by a product of a refractive index and a thickness so that the brightness enhancement film has selective transmittance and reflectivity for light of a specific wavelength band, And may be varied to have a thickness gradient from top to bottom. For example, the first and second thin films may each have an optical thickness of 0.05 to 0.60 탆, preferably 0.09 to 0.45 탆, more preferably 0.1 to 0.40 탆.

The refractive index difference between the first thin film and the second thin film along the first axis may be at least 0.05. The refractive index difference between the first thin film and the second thin film along the second axis may be 0.03 or less. The brightness enhancement film may include an axis in the normal direction perpendicular to the film surface, that is, a third axis, and the refractive index difference between the first thin film and the second thin film along the third axis may be 0.03 or less. If the refractive index difference between the first thin film and the second thin film along the first axis is less than at least 0.05, the light reflected at the interface between the first thin film and the second thin film is less, and the brightness increasing effect may be insignificant. When the refractive index difference between the first thin film and the second thin film along the second axis is more than 0.03 or the refractive index difference between the first thin film and the second thin film along the third axis exceeds 0.03, The amount of light reflected on the surface increases, and the increase in luminance can be suppressed. The refractive index difference along the first to third axes can be achieved through a material that induces birefringence by stretching and a material that does not cause birefringence or which is insignificant. Here, the stretching axis may be the first axis.

When the first thin film and the second thin film each include a polymer resin, the difference between the glass transition temperature of the first polymer resin and the glass transition temperature of the second polymer resin may be 30 ° C or less. When the glass transition temperature difference exceeds 30 캜, it is difficult to control the thickness of each layer uniformly and it becomes difficult to form a layer because the difference in melting point of the resin is large when pneumatically shipped.

As described above, in the brightness enhancement film including the first thin film and the second thin film disposed adjacent to the first thin film, the components of the first and second thin films, the difference in refractive index between the first thin film and the second thin film, By adjusting the temperature difference and the like in detail, it is possible to ensure reliability with respect to a desired external environment.

Hereinafter, the present invention will be described in more detail with reference to the following examples. However, the present invention is not limited to the following examples.

≪ Example 1 >

Dimethylcarboxylic naphthalate (NDC) and ethylene glycol (EG) were added to the polymeric polymerization reactor and condensation polymerization was conducted to prepare a first polymer resin having 100 mole% of ethylene naphthalate repeating units. Dimethylcarboxylic naphthalate (Ethylene glycol), ethylene glycol (EG), and terephthalic acid (TPA) were introduced into the reactor, respectively, and condensation polymerization was carried out as described above to obtain ethylene naphthalate repeating units of 40 mol% and ethylene terephthalate repeating units Was 60 mol%. The first polymer resin and the second polymer resin were completely polymerized in a state in which solid phase polymerization did not proceed. The prepared first polymer resin was dried at 100 ° C for 24 hours to remove moisture, and the second polymer resin was dried at 70 ° C for 48 hours to remove moisture. The first polymer resin and the second polymer resin were finally formed into a 1,024-layer multilayer extruded film through a 256-fold multilayered feed block at a rate of 30 kg / hr, respectively. The prepared multi-layer extruded film was uniaxially stretched at a temperature of 130 ° C at a five-fold stretch ratio, coated with an acrylic UV curable adhesive on both sides of the stretched multilayer film, laminated with a diffusion film of Kolon Co. (LD102) To prepare a brightness enhancement film.

≪ Examples 2 to 3 >

In order to form the first and second polymer resin layers in Example 1, the amounts of dimethylcarboxylic naphthalate (NDC), ethylene glycol (EG) and terephthalic acid (TPA) , A brightness enhancement film was prepared in the same manner as in Table 1, except that the first and second polymer resins having different ethylene naphthalate repeating units and ethylene terephthalate repeating units were used. As in Example 1, the first and second polymer resins were completely polymerized in a state in which solid phase polymerization did not proceed.

≪ Examples 4 to 6 >

The multilayer extruded films prepared using the first and second polymers used in Examples 1 to 3 were stretched in the same manner as in Example 1, and then polymethylmethacrylate of 10 m in thickness was laminated on the film in an amount of 100 parts by weight of a urethane acrylate binder And 135 parts by weight in terms of parts by weight. In order to prevent blocking with the lower optical member, 5 μm of polymethyl methacrylate particles were added to 15 parts by weight of a urethane acrylate binder An anti-blocking layer was formed, and finally a brightness enhancement film was produced.

≪ Comparative Example 1 &

Dimethylcarboxylic naphthalate (NDC) and ethylene glycol (EG) were added to the polymeric polymerization reactor and condensation polymerization was conducted to prepare a first polymer resin having 100 mole% of ethylene naphthalate repeating units. Dimethylcarboxylic naphthalate (Ethylene glycol), ethylene glycol (EG), and terephthalic acid (TPA) were introduced into the reactor, respectively, and condensation polymerization was carried out as described above to obtain ethylene naphthalate repeating units of 40 mol% and ethylene terephthalate repeating units Was 60 mol%. The first polymer resin and the second polymer resin proceeded to solid state polymerization and completed the polymerization. The prepared first polymer resin was dried at 100 ° C for 24 hours to remove moisture, and the second polymer resin was dried at 70 ° C for 48 hours to remove moisture. The first polymer resin and the second polymer resin were finally formed into a 1,024-layer multilayer extruded film through a 256-fold multilayered feed block at a rate of 30 kg / hr, respectively. The prepared multi-layer extruded film was uniaxially stretched at a temperature of 130 ° C at a five-fold stretch ratio, coated with an acrylic UV curable adhesive on both sides of the stretched multilayer film, laminated with a diffusion film of Kolon Co. (LD102) To prepare a brightness enhancement film.

≪ Comparative Examples 2 and 3 >

In Comparative Example 1, the amounts of dimethylcarboxylic naphthalate (NDC), ethylene glycol (EG), and terephthalic acid (TPA) were varied to form the first and second polymer resin layers , A brightness enhancement film was prepared in the same manner as in Table 1, except that the first and second polymer resins having different ethylene naphthalate repeating units and ethylene terephthalate repeating units were used. Similar to Comparative Example 1, the first and second polymer resins proceeded to solid state polymerization and completed polymerization.

≪ Comparative Examples 4 to 6 >

The multilayer extruded films were formed using the first and second polymers used in Comparative Examples 1 to 3, respectively, and stretched in the same manner as in Comparative Example 1. Thereafter, the same diffusion layers as in Examples 4 to 6 were formed directly on the stretched film To prepare a brightness enhancement film.

The brightness enhancement films prepared in the above Examples and Comparative Examples were measured for the luminance reduction rate according to the respective environmental changes as described below.

 (1) Reduction rate of luminance

A brightness enhancement film conforming to each condition is laminated on a 22-inch backlight unit, a diffusion film (XC210, Kolon Corporation) and a prism film (LC217, Kolon) are combined as an optical film, or a conventional brightness enhancement film is laminated , A 22-inch LCD panel was placed on the panel, and a power of 12 V was applied thereto. Then, the brightness was measured by a luminance meter (BM-7, TOPCON, Japan) to measure the luminance reduction rate according to each condition.

(2) Glass transition temperature

The first and second polymer resin chips in the form of a pellet were each weighed to a weight of 4 mg to prepare a sample. The temperature was raised to 30 to 300 ° C by a differential scanning calorimeter (DSC, Perkin Elmer) The glass transition temperature of the polymer resin was measured, and the glass transition temperature difference between the first and second polymer resins was calculated from this value.

(3) Refractive index

The first polymer resin and the second polymer resin were separately prepared into sheets, uniaxially stretched at a temperature of 130 ° C in a stretching machine of a laboratory scale, and then cut into a size of 50 mm × 50 mm. Then, a prism coupler (SPA-3DR, manufactured by Sairon Technology) The refractive indices of the first and second polymer resin sheets were calculated from the measured values.

(4) Evaluation of adhesion

In the case of the brightness enhancement film obtained by laminating the stretched multilayer film and the diffusion film with a UV curable resin (adhesive layer), the brightness enhancement film was cut into 25 mm × 150 mm, and then boiled in water boiled at 100 ° C. for 1 hour. Attach the multilayer film to each Zig, and check the Load value when peeling at 180 ° and 300mm / min.

In the case of a brightness enhancement film on which a diffusion layer is directly applied on a stretched multilayer film, it is measured as a cross cut test. The film is scratched so that there are about 100 lattices on the surface of the film, followed by bonding as an adhesive tape (3M) Check the number of gratings attached to the tape that remain on the film surface without being removed.

 (5) Multilayer thin film surface contact angle

A 50 mm x 50 mm sample was fixed on the plate, and a drop of DI Water was dropped. The contact angle was measured using a Drop Shape Analyzer (DSA100). A drop of DI water was dropped and the average was determined by measuring the instrument more than 10 times, and the average was obtained by measuring 9 points per sample.

The first thin film The second thin film Ethylene
Naphthalate content Ethylene
Terephthalate content Ethylene
Naphthalate content Ethylene
Terephthalate content Example 1 100 mol% 0 mol% 40 mol% 60 mol% Example 2 90 mol% 10 mol% 60 mol% 40 mol% Example 3 80 mol% 20 mol% 50 mol% 50 mol% Example 4 100 mol% 0 mol% 40 mol% 60 mol% Example 5 90 mol% 10 mol% 60 mol% 40 mol% Example 6 80 mol% 20 mol% 50 mol% 50 mol% Comparative Example 1 100 mol% 0 mol% 40 mol% 60 mol% Comparative Example 2 90 mol% 10 mol% 60 mol% 40 mol% Comparative Example 3 80 mol% 20 mol% 50 mol% 50 mol% Comparative Example 4 100 mol% 0 mol% 40 mol% 60 mol% Comparative Example 5 90 mol% 10 mol% 60 mol% 40 mol% Comparative Example 6 80 mol% 20 mol% 50 mol% 50 mol%

Luminance reduction rate The first and second polymeric resins
Glass transition temperature difference Refractive index
Difference 50 캜, 1000 hours 60 ° C, 95% RH, 1000 hours -20 ° C, 1000 hours 70 ° C / 60 minutes -20 ° C / 60 minutes 100 cycles Example 1 5% 7% 5% 5% 20 0.01 Example 2 8% 10% 7% 10% 25 0.03 Example 3 9% 10% 7% 10% 10 0.03 Example 4 6% 8% 5% 6% 20 0.01 Example 5 8% 10% 6% 9% 25 0.03 Example 6 7% 10% 7% 10% 10 0.03 Comparative Example 1 15% 13% 15% 15% 20 0.01 Comparative Example 2 15% 15% 15% 15% 25 0.03 Comparative Example 3 15% 18% 15% 17% 10 0.03 Comparative Example 4 16% 15% 18% 19% 20 0.01 Comparative Example 5 16% 18% 18% 18% 25 0.03 Comparative Example 6 15% 16% 19% 19% 10 0.03

Adhesiveness Multilayer thin film
Surface contact angle (°) Example 1 1.5kg / 25mm 70 Example 2 1.3kg / 25mm 71 Example 3 1.4kg / 25mm 72 Example 4 100kg / 100mm 70 Example 5 100kg / 100mm 72 Example 6 100kg / 100mm 73 Comparative Example 1 0.5kg / 25mm 90 Comparative Example 2 0.45kg / 25mm 93 Comparative Example 3 0.45kg / 25mm 93 Comparative Example 4 50kg / 100mm 90 Comparative Example 5 45kg / 100mm 93 Comparative Example 6 45kg / 100mm 93

As a result of evaluation of the physical properties, as shown in Tables 2 to 3, it was found that the luminance reduction rate characteristics of the examples were better than those of the comparative examples, and that the luminance reduction rate characteristics were associated with the surface contact angle and interlayer adhesion of the multilayer thin film there was. In other words, the improvement of the hydrophilicity of the multilayer thin film showed excellent results in the adhesion evaluation even when the light diffusion layer coating liquid was directly applied or the light diffusion film was laminated. As a result, the luminance reduction rate can be lowered.

While the present invention has been described in connection with certain exemplary embodiments, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined by the appended claims.

Therefore, it should be understood that the above-described embodiments are provided so that those skilled in the art can fully understand the scope of the present invention, and are therefore to be considered in all respects as illustrative and not restrictive, The invention is only defined by the scope of the claims.

(1): Light diffusion film
(2): Adhesive layer
(3): The multilayer thin film
(4): Adhesive layer
(5): Light diffusion film

Claims (6)

A multilayer thin film comprising a plurality of optically isotropic first thin films and a plurality of optically anisotropic second thin films, and having a surface contact angle of 50 to 85 °; And a light diffusion layer formed on at least one surface of the multilayer thin film,
Wherein the brightness enhancement film includes a first axis and a second axis orthogonal to each other in the film plane and a third axis perpendicular to the brightness enhancement film plane,
Enhancing film and reflects the light polarized along the first axis among the light incident on the brightness enhancement film and transmits the polarized light along the second axis among the light incident on the brightness enhancement film,
Wherein the refractive index difference between the first thin film and the second thin film along the third axis is 0.03 or less. The method of claim 1,
Wherein the light diffusion layer is in the form of a light diffusion film including a light diffusion layer on a base film. The method of claim 2,
And an adhesive layer formed between the multilayer thin film and the light diffusion film. The method of claim 1,
The multilayer thin film is a luminance-enhanced film comprising a polymer resin that is not subjected to the solid-state polymerization of the resin of the first thin film or the second thin film. The method of claim 1,
The multilayer thin film;
A light diffusion layer formed on one surface of the multilayer thin film; And
And an anti-blocking layer formed on the other surface of said multilayered film. A backlight unit comprising the brightness enhancement film of claim 1.

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