KR20050082478A - Difussion film for backlight unit - Google Patents

Abstract

The present invention relates to a diffusion film for a backlight unit having excellent electromagnetic shielding ability and having a high brightness. The diffusion film for a backlight unit in which a diffusion layer, a transparent base film layer, an electromagnetic wave shielding conductive thin film layer, and a low refractive layer are sequentially stacked has a surface resistance of 1,000 ohms. The electromagnetic wave shielding ability is excellent and the brightness is improved by 3% or more, which is applicable to the backlight unit.

Description

Diffusion film for backlight unit {Difussion film for backlight unit}

The present invention relates to a diffuser film for a backlight unit, and more particularly, a diffusion layer, a transparent base film layer, an electromagnetic wave shielding conductive thin film layer, and a low refractive layer are sequentially stacked to provide excellent electromagnetic shielding ability and to provide a high brightness backlight unit. It is about.

As the development of liquid crystal display devices has progressed, their applications have been extended to laptops, monitors, and televisions. Accordingly, the development of products with large screen, high brightness, high quality, and low power is required.

In general, the backlight unit requires a light diffusion film that serves to diffuse the light of the lateral light source lamp from one side or the rear of the LCD display into the entire screen and to deflect the light into a uniform light in the front direction due to the structure of the LCD display. Do.

In addition, reflective films, light guide plates, and prism films are used to perform their respective roles, and the intensity of light emitted from the initial light source is gradually offset by the other mediums above. Only one hundredth (1/100) of the light source.

Recently, there have been many attempts to eliminate the backlight unit itself, but due to the basic characteristics of the LCD, it is currently impossible to form a screen without a separate light source, such as a self-luminous LED element.

Previously, liquid crystal display devices were mainly used in notebooks or small displays, but are now becoming larger as they are applied to monitors and televisions. Therefore, the core technology of the display device applied to the liquid crystal television can realize a large screen and high brightness.

On the other hand, as the liquid crystal display device becomes larger and higher in quality, more pixels are generated and electromagnetic waves are generated accordingly. At this time, the generated electromagnetic waves may cause malfunctions of the device or defects in the appearance of the panel, and thus it is necessary to block them.

As a conventional technology for the electromagnetic shielding, the electromagnetic wave shielding ability is provided by using a diffusion film and an electromagnetic wave shielding film, respectively, or by adding an ITO thin film that can block electromagnetic waves to the diffusion film as in Korean Patent Laid-Open No. 2002-64244. Excellent diffusion film is presented.

In addition, as in Japanese Patent Publication 2003-107210, Japanese Patent Publication 2003-107211, Japanese Patent Publication 2003-107212, Japanese Patent Publication 2003-107213, a method of manufacturing a diffusion film to which electromagnetic wave shielding capability is provided by adding a conductive filler to a binder. There is this.

In addition, a method of manufacturing a hybrid anti-reflection film having an anti-reflection capability on a coating film having electromagnetic shielding capability, as in Korean Patent Laid-Open Publication No. 2000-0008286, has also been developed. In order to develop a high-brightness liquid crystal display, research on a high-brightness light source (cold cathode fluorescent lamp) and a backlight component is performed as in Korean Patent Laid-Open Publication No. 2000-0008458.

However, in the case of using the diffusion film and the electromagnetic wave blocking film as described above, since the constituents of the backlight unit film are increased, the process is increased, the thinning is disadvantageous, the cost increases, and the electromagnetic wave blocking diffusion film is used. In this case, there is a disadvantage in that transmittance is lowered and luminance is lowered than when using a general diffusion film.

Accordingly, the present inventors are trying to develop a diffusion film that can improve the brightness while giving electromagnetic wave shielding ability to the diffusion film, the diffusion layer, the transparent base film layer, the electromagnetic wave shielding conductive thin film layer and the low refractive layer is sequentially stacked As a result of manufacturing the diffuser film for the backlight unit, it was found that the electromagnetic wave shielding ability is excellent and that the diffuser film of high brightness can be produced.

Accordingly, an object of the present invention is to provide a diffusion film for a backlight unit having excellent electromagnetic shielding ability and high brightness.

In order to achieve the object of the present invention, the backlight unit diffusion film is characterized in that the diffusion layer, the transparent base film layer, the electromagnetic wave shielding conductive thin film layer and the low refractive layer is sequentially stacked.

Hereinafter, the present invention will be described in more detail.

As shown in FIG. 1, the laminated structure of the diffusion film 10 according to the present invention includes a diffusion layer 2, a transparent base film 3, an electromagnetic wave shielding conductive thin film layer 4, and a low refractive index layer 5. .

The diffusion layer 2 applicable to the present invention is for enhancing light transmission and diffusion efficiency, and is formed by dispersing transparent spherical organic particles in a transparent binder resin on a base film.

As the transparent binder resin, an acryl-based, urethane-based, epoxy-based, melamine-based polymer or copolymer or ternary copolymer can be used.

The particles to be applied include olefinic particles such as acrylic, polyethylene, polystyrene, and polypropylene, and polymers or copolymers of acrylic and olefins or terpolymers or homopolymers. Multilayered multicomponent particles made by covering with monomer can be used.

At this time, the average particle diameter of the particles used is preferably 1 µm to 50 µm for dispersion with the binder resin.

In the present invention, a transparent binder resin and a solution in which the particles are dispersed in an organic solvent are used as the diffusion layer composition.

The diffusion layer 2 plays a role of showing diffusion efficiency due to the difference in refractive index between the particles and the resin. The diffusion layer coats the prepared diffusion layer composition with a thickness of 1 to 50 μm, and when the diffusion layer is less than 1 μm, the diffusion efficiency decreases. Particles of the coating film may be detached, and when it exceeds 50 μm, it is difficult to mount on a thin product and there is a disadvantage in that the transmission efficiency is reduced by lamination of particles.

In addition, the base film of the present invention can be used for any transparent base film, for example, polycarbonate, polypropylene, polyethylene terephthalate, polyethylene, epoxy and the like, polyethylene terephthalate is particularly preferred.

The base film should have adhesion to the resin used and should not affect the light diffusing layer due to its high light transmittance within it, and the surface smoothness should be uniform so that there is no variation in luminance.

The thickness of the base film of the present invention is preferably 25 to 400㎛, preferably 50 to 300㎛. When the thickness is less than 25 μm, the mechanical properties and the heat resistance of the film may be insufficient, and when it exceeds 400 μm, it may be a problem that the product is thick and mounted on the thinned product.

In addition, the electromagnetic wave shielding conductive thin film layer of the present invention may be applied by applying an indium tin oxide (ITO), antimony tin oxide (ATO), SnO ₂ , and a metal thin film to a thickness of 5 nm to 1 μm. When the thickness of the electromagnetic wave shielding conductive thin film layer is less than 5 nm, electromagnetic shielding efficiency and electrical stability may be lowered. The transparent conductive thin film is formed by dry coating such as sputtering, electron beam deposition, ion-plating, spray pylolysis, chemical vapor deposition, and the like. It is preferable to form, because there is a problem that the electromagnetic shielding ability is lowered when the coating film is formed by a wet coating method.

The low refractive index layer of the present invention is to improve the brightness of the product, SiO ₂ , Al ₂ O ₃ , MgF ₂ particles or silica magnesium fluoride hydrate composite colloidal particles having a low refractive index or wet coating of a low refractive index fluorine-based resin To form a coating film.

In this case, the refractive index of the low refractive layer used is preferably 1.20 to 1.60, more preferably 1.30 to 1.50. When the refractive index exceeds 1.60, the antireflection effect is lowered, and the brightness enhancement effect is lowered. When the refractive index is lower than 1.20, it is difficult to form a coating film of a suitable low refractive index layer.

The fluorine resin used in the low refractive layer of the present invention is a polymer polymerized by substituting fluorine for a part of a monomer applied to a general polymer polymerization reaction. For example, polyfluoroacrylate, polyfluoromethacrylate, polyalkoxyfluoride Silane, polytetrafluoroethylene, polyfluoroethylene propylene, polytrifluorochloroethylene, vinylidene fluoride, fluorine rubber and the like.

The solution which melt | dissolved the said fluorine resin in the organic solvent is used as a low refractive layer composition.

The theoretical optimum thin film thickness for the antireflection performance is 1% to 100% of the optical thickness with respect to the design wavelength (450 to 650 nm) of the visible light region. The optical thickness is the product of the actual thickness and the refractive index of the coating layer. In the actual wet coating method, since it is difficult to control the thickness of the thin film, a low refractive index layer is formed to a thickness of 10 nm to 1 μm. When the thickness of the low refractive layer coating film is less than 10 nm, the thickness uniformity may be lowered, and thus the antireflection performance may be reduced due to the thickness nonuniformity.

On the other hand, the structure of the direct type backlight using the diffusion film having the laminated structure as described above is as shown in FIG. A diffusion layer is applied to one side of the transparent base film and an electromagnetic wave shielding conductive thin film layer is applied to the other side. By applying a low refractive index layer on the applied electromagnetic wave shielding conductive thin film layer to finally produce a diffusion film having an electromagnetic shielding ability.

Thus prepared diffusion film of the present invention has a surface resistance value of less than 1,000 Ω, if the surface resistance of the prepared diffusion film exceeds 1,000 Ω has a problem that the electromagnetic shielding ability is difficult to perform its role.

Therefore, as in the present invention When the diffuser film for the backlight unit in which the diffusion layer, the transparent base film layer, the electromagnetic wave shielding conductive thin film layer, and the low refractive index layer are sequentially laminated is used for the backlight, electromagnetic waves are shielded to prevent distortion of the screen by the electromagnetic waves and have stable driving while achieving stable driving. .

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

Example 1

200 parts by weight of acrylic particles GM2001 (manufactured by Ganz) having an average particle diameter of 20 µm were added to the weight of acrylic resin Surcol836 (manufactured by Allied Colloids), and 150 parts by weight of methyl ethyl ketone solvent were dispersed in a mill (manufactured by Ika) to prepare a diffusion layer composition. It was. The prepared diffusion layer composition was applied to one surface of a PET substrate film FCTT (manufactured by Kolon) having a thickness of 125 μm by a gravure coating method. Next, indium tin oxide (ITO) was dry-coated to an optical thickness of 120 nm by DC magnetron sputtering as a conductive thin film layer having electromagnetic shielding ability on the other side of the PET base film.

The low-refractive layer (refractive index 1.483) having an optical thickness of 360 nm was formed by coating a solution in which polyfluorinated acrylate was added at 2 parts by weight based on the weight of methyl ethyl ketone on the conductive thin film, and having an optical thickness of 360 nm. An electromagnetic wave shielding diffusion film was prepared.

Example 2

200 parts by weight of acrylic particles MR20G (manufactured by Soken) having an average particle diameter of 20 µm were added to the weight of acrylic resin Surcol836 (manufactured by Allied Colloids), and 150 parts by weight of methyl ethyl ketone solvent was dispersed in a mill (manufactured by Ika) to prepare a diffusion layer composition. It was. The prepared diffusion layer composition was applied to one surface of a PET substrate film FCTT (manufactured by Kolon) having a thickness of 125 μm by a gravure coating method. Indium tin oxide (ITO) was dry-coated to an optical thickness of 720 nm by DC magnetron sputtering as a conductive thin film layer having electromagnetic shielding ability on the other side of the PET base film.

The low-refractive layer (refractive index 1.475) having an optical thickness of 840 nm was formed by coating a solution in which polyfluorinated acrylate was added at 2 parts by weight based on the weight of methyl ethyl ketone on the electromagnetic shielding conductive thin film layer and having an optical thickness of 840 nm. The electromagnetic wave shielding diffusion film was prepared.

Example 3

200 parts by weight of acrylic particles MPB20H (manufactured by Kolon) with an average particle diameter of 20 µm was added to the weight of acrylic resin Surcol836 (manufactured by Allied Colloids), and 150 parts by weight of methyl ethyl ketone solvent was dispersed in a mill (manufactured by Ika) to prepare a diffusion layer composition. It was. The prepared diffusion layer composition was applied to one surface of a PET substrate film FCTT (manufactured by Kolon) having a thickness of 125 μm by a gravure coating method. Antimony tin oxide (ATO) was dry-coated with an optical thickness of 370 nm by DC magnetron sputtering as a conductive thin film layer having electromagnetic shielding ability on the other side of the PET base film.

The low-refractive layer (refractive index of 1.450) having an optical thickness of 410 nm was formed by coating a solution in which polyfluorinated acrylate was added in an amount of 2 parts by weight based on the weight of methyl ethyl ketone on the electromagnetic shielding conductive thin film layer and having an optical thickness of 410 nm. The electromagnetic wave shielding diffusion film was prepared.

Example 4

MPB20H (Kolon Co., Ltd.), acrylic particles having an average particle diameter of 20 µm, was dispersed in a milling machine (manufactured by Ika) by adding 200 parts by weight to 150 parts by weight of methyl ethyl ketone solvent and 200 parts by weight of acrylic resin Surcol836 (Allied Colloids). Prepared. The prepared diffusion layer composition was applied to one surface of a PET substrate film FCTT (manufactured by Kolon) having a thickness of 125 μm by a gravure coating method. Antimony tin oxide (ATO) was dry-coated with an optical thickness of 380 nm by DC magnetron sputtering as a conductive thin film layer having electromagnetic shielding ability on the other side of the PET substrate film.

A low refractive index layer (refractive index 1.461) having an optical thickness of 280 nm was formed by coating a solution containing 2 parts by weight of polyfluorinated acrylate relative to the weight of methyl ethyl ketone on the electromagnetic shielding conductive thin film layer to form an optical layer of 280 nm. An electromagnetic wave shielding diffusion film having a structure was prepared.

Example 5

200 parts by weight of GM2001 (manufactured by Ganz), acrylic particles having an average particle diameter of 20 µm, and 150 parts by weight of methyl ethyl ketone solvent were added to an acrylic resin Surcol836 (manufactured by Allied Colloids), and dispersed in a milling machine (manufactured by Ika). Prepared. The prepared diffusion layer composition was applied to one surface of a PET substrate film FCTT (manufactured by Kolon) having a thickness of 125 μm by a gravure coating method. Antimony tin oxide (ATO) was dry-coated with an optical thickness of 380 nm by DC magnetron sputtering as a conductive thin film layer having electromagnetic shielding ability on the other side of the PET substrate film.

On the electromagnetic shielding conductive thin film layer, a solution in which 10 parts by weight of MgF ₂ was added to the weight of methyl ethyl ketone and dispersed was coated by a gravure coating method to form a low refractive layer (refractive index of 1.421) having an optical thickness of 300 nm. An electromagnetic wave shielding diffusion film having a structure was prepared.

Comparative Example 1

200 parts by weight of acrylic particles GM2001 (manufactured by Ganz) having an average particle diameter of 20 µm were added to the weight of acrylic resin Surcol836 (manufactured by Allied Colloids), 150 parts by weight of methyl ethyl ketone solvent, and dispersed in a mill (Ika). Prepared. The prepared diffusion layer was applied to one side of a PET substrate film FCTT (manufactured by Kolon) having a thickness of 125 μm by a gravure coating method.

2 parts by weight of polyfluorinated acrylate relative to the weight of methyl ethyl ketone was added to the other side of the PET base film to form a low refractive layer (refractive index 1.483) having an optical thickness of 250 nm by a gravure coating method.

Comparative Example 2

200 parts by weight of acrylic particles GM2001 (manufactured by Ganz) having an average particle diameter of 20 µm were added to the weight of acrylic resin Surcol836 (manufactured by Allied Colloids), 150 parts by weight of methyl ethyl ketone solvent, and dispersed in a mill (Ika). Prepared. The prepared diffusion layer composition was applied to one surface of a PET substrate film FCTT (manufactured by Kolon) having a thickness of 125 μm by a gravure coating method.

Indium tin oxide (ITO) was dry-coated to an optical thickness of 400 nm by DC magnetron sputtering as a conductive thin film layer having electromagnetic shielding ability on the other side of the PET base film.

The physical properties of the diffusion films prepared in Examples and Comparative Examples were measured as follows, and the results are shown in Table 1 below.

(1) brightness

After cutting the diffuser film to be mounted on the backlight unit, the brightness of the diffuser film on the backlight unit LGP and the final dual brightness enhancement film (Dual Brightness Enhancement Film, Vikuiti ™ DBEF-D440, manufactured by 3M) ) Were measured and compared with 9 different luminance by TOPCON BM7 luminance meter.

(2) Electromagnetic shielding ability (surface resistance)

The electromagnetic shielding ability can be converted from the surface resistance of the final manufactured diffusion film, and the surface resistance of 1000 ohm or less is required to show the electromagnetic shielding ability. Thus, Keithley's 238 model was used to measure the surface resistance of the backside of the diffusion layer.

Coating thickness (nm) Luminance (Cd / ㎡) Surface resistance (ohm) Electromagnetic shielding conductive thin film layer Low refractive layer Example 1 120 360 3050 620 Example 2 720 840 3015 280 Example 3 370 410 3035 420 Example 4 380 280 3030 450 Example 5 380 300 3025 560 Comparative Example 1 - 250 3040 More than 10 ⁷ Comparative Example 2 400 - 2910 360

From the results of Table 1, according to the present invention, the diffusion film having a structure in which the diffusion layer, the transparent base film layer, the electromagnetic wave shielding conductive thin film layer, and the low refractive index layer were sequentially laminated not only has excellent total light transmittance and brightness, but also has surface resistance. All are less than 1,000 ohms, excellent in electromagnetic shielding ability.

As described above in detail, when the diffusion film according to the present invention is applied to the backlight, the luminance is improved by 3% or more while the electromagnetic wave shielding ability is reduced to 1,000 ohm or less.

1 is a cross-sectional view showing a laminated structure of a diffusion film for a backlight unit having a high brightness, electromagnetic shielding ability according to the present invention,

2 shows a structure of a direct backlight including a diffusion film according to the present invention.

<Short description of the symbols in the drawings>

10: diffusion film 2: diffusion layer

3: PET base film 4: electromagnetic wave shielding conductive thin film layer

5: low refractive layer 6: prism

7: cold cathode fluorescent lamp 8: reflective film

9: mold frame

Claims (10)

A diffusion film for a backlight unit in which a diffusion layer, a transparent base film layer, an electromagnetic wave shielding conductive thin film layer, and a low refractive index layer are sequentially stacked. The diffusion film for a backlight unit according to claim 1, wherein the low refractive layer is coated with a fluorine resin containing fluorine. The backlight unit of claim 1, wherein the low refractive layer is coated with one or two or more particles selected from SiO ₂ , Al ₂ O ₃ , MgF ₂ particles or silica magnesium fluoride hydrate composite colloidal particles. Diffusion film. The diffusion film for a backlight unit according to claim 1, wherein the low refractive layer has a thickness of 10 nm to 1 m. The diffusion film of claim 1, wherein the low refractive index layer has a refractive index of 1.20 to 1.60. The diffusion film for a backlight unit according to claim 1, wherein the electromagnetic wave blocking conductive thin film layer is selected from indium tin oxide (ITO), antimony tin oxide (ATO), SnO ₂ , and a metal thin film. The diffusion film for a backlight unit according to claim 1, wherein the electromagnetic wave blocking conductive thin film layer has a thickness of 5 nm to 1 m. The diffusion film for a backlight unit according to claim 1, wherein the surface resistance of the diffusion film is 1,000 ohm or less. The diffusion film of claim 1, wherein the transparent base film is a polyethylene terephthalate film having a thickness of 25 μm to 400 μm. A backlight unit comprising the diffusion film of any one of claims 1 to 9.