KR101424273B1 - Backlight unit - Google Patents

Abstract

A backlight unit having an optical film with improved brightness is provided. A backlight unit according to an embodiment of the present invention includes a light source and an optical film that transmits light generated in the light source, wherein the optical film includes a base material and a protrusion located on the base material, At least one of the diffusion members is dispersed in the inside of a polyhedron having the same shape. The diffusion agent is made of magnesium oxide powder having a hexahedral shape, and the magnesium oxide powder is transparent and made of a single crystal and has a diameter of 0.5 to 2 탆.

LCD, backlight, diffuser, magnesium oxide, MgO, powder, cube, prism sheet

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to an optical film,

The present invention relates to an optical film and a backlight unit having the same, and more particularly, to an optical film capable of improving brightness and a backlight unit having the same.

A liquid crystal display device (LCD) displays an image corresponding to a video signal by adjusting a light transmittance of liquid crystal cells arranged in a matrix form as a video signal supplied thereto.

To this end, the liquid crystal display device includes a liquid crystal display panel in which liquid crystal cells for controlling the amount of light transmitted from the bottom are arranged in an active matrix form, and a backlight unit for projecting light from the bottom of the liquid crystal panel.

The backlight unit serves to uniformly project white light from the rear surface of the liquid crystal panel. The backlight unit has a direct type and an edge type according to the position of the light source.

The edge type backlight unit is provided with a light source at one edge of the liquid crystal display device and irradiates the light incident from the light source to the liquid crystal display panel through the light guide plate and the optical film.

In addition, a direct-type backlight unit places a plurality of light sources directly below a liquid crystal display device, and irradiates the light incident from the light sources to a liquid crystal display panel through a diffusion plate and an optical film.

In the backlight unit having such a constitution, generally, the optical film includes a diffusion sheet, a prism sheet, a protective sheet, and a reflective polarizing film.

The diffusion sheet diffuses light from the light source to uniform the brightness and to increase the viewing angle, and the diffusion agent is dispersed in the inside or at least one side.

The diffusing agent is an inorganic filler for diffusing light and containing silica, aluminum hydroxide, aluminum oxide, titanium oxide, zinc oxide, barium sulfate, magnesium silicate or a mixture thereof, an acrylic resin, acrylonitrile, polyurethane An organic filler such as polyvinyl chloride, polystyrene resin, polyacrylonitrile, polyamide, polysiloxane resin, melamine resin and benzoguanamine resin is used, and its shape is in the form of spherical beads .

The prism sheet condenses light diffused by the diffusion sheet to improve brightness.

The protective sheet is disposed on the prism sheet to protect the prism sheet from dust and the like, and widen the viewing angle of the liquid crystal display panel that is narrowed by the prism sheet.

On the other hand, the liquid crystal display panel disposed on the optical film transmits only a part of light provided from the backlight unit. For example, the panel transmits the longitudinal wave (P wave) and the transverse wave (S wave) among the light proceeding from the backlight unit. Thus, a reflective polarizing film is used in the backlight unit to utilize the transverse waves absorbed by the panel.

On the other hand, in order to further improve the diffusion effect, a diffusion agent in the form of a bead is dispersed in the prism sheet.

However, the bead type diffusing agent has a problem in that the light that is refracted into the beads is more absorbed or scattered than the bead penetrating effect, thereby lowering the luminance of light passing through the prism sheet.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an optical film capable of effectively improving brightness and a backlight unit having the optical film.

According to an aspect of the present invention, there is provided a backlight unit including a light source and an optical film that transmits light generated in the light source, the optical film including a substrate, And a diffusion agent made of a polyhedron having the same shape is dispersed in at least one of the substrate and the projecting portion.

The diffusion agent is made of magnesium oxide powder having a hexahedral shape, and the magnesium oxide powder is transparent and made of a single crystal and has a diameter of 0.5 to 2 탆.

The light source and the optical film may be arranged in a direct-type or edge-type manner.

According to an aspect of the present invention, there is provided an optical film comprising a base material and a projection positioned on the base material, .

The cross-sectional shape of the protruding portion may be any one of isosceles triangle, equilateral triangle, and equilateral triangle.

In the magnesium oxide powder used as a diffusing agent in the present invention, the effect of permeation is greater than the effect of absorption. Therefore, an optical film using magnesium oxide powder as a diffusing agent emits more light than a conventional optical film using spherical beads as a diffusing agent. Therefore, the backlight unit of the present invention has an advantage that the brightness is improved.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings, which will be readily apparent to those skilled in the art to which the present invention pertains. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

In the drawings, the thickness is enlarged to clearly represent the layers and regions. Like parts are designated with like reference numerals throughout the specification. When a portion of a layer, a film, a region, a plate, or the like is on another portion, it includes not only the portion directly above another portion but also the case where another portion exists in the middle. Conversely, when a part is directly above another part, it means that there is no other part in the middle.

≪ Example 1 >

Hereinafter, a first embodiment of the present invention will be described in detail with reference to Figs. 1 to 4. Fig.

FIG. 1 is a schematic view showing an assembled state of a liquid crystal display device having a direct-type backlight unit according to Embodiment 1 of the present invention, and FIG. 2 is a perspective view of an optical film, particularly, a prism sheet shown in FIG.

3A to 3C illustrate various embodiments according to a cross-sectional shape of a prism pattern formed on the prism sheet of FIG. 2, and FIG. 4 is an enlarged perspective view of a diffuser used in the optical film of FIG.

In the liquid crystal display panel, a plurality of data lines and a plurality of scan lines are arranged in an intersecting manner, and liquid crystal cells are arranged in an active matrix form between upper and lower substrates. In the liquid crystal display panel, pixel electrodes and a common electrode for applying an electric field to each of the liquid crystal cells are formed.

Thin film transistors (TFTs) for switching data voltages to be applied to the pixel electrodes in response to a scan signal are formed at intersections of a plurality of data lines and a plurality of scan lines. In such a liquid crystal display panel, gate drive integrated circuits and data drive integrated circuits are electrically connected through a tape carrier package (TCP: Tape Carrier Package).

1, the direct-type backlight unit disposed at the lower portion of the liquid crystal display panel includes a linear light source 110, a diffusion plate 120 for scattering light, and a condenser 120 for condensing light scattered by the diffusion plate 120 And an optical film 130 for polarizing light and effectively outputting light are combined in order. In order to improve the utilization efficiency of light at a position opposite to the back surface of the linear light source 110, that is, the diffusion plate 120 A lower cover 140 having a reflection plate or a reflective film is disposed.

The linear light source 110 is a light source whose shape is linear, such as a fluorescent lamp, and a cold cathode tube is usually used in a backlight unit for a liquid crystal television. In the direct-type backlight unit, a plurality of linear light sources 110 are arranged. In order to reduce the number of parts, a linear light source is often bent into a U-shape.

The diffusion sheet 131, the prism sheet 133, the protective sheet 135, the reflective polarizing film (not shown), the viewing angle adjusting film (Not shown), etc. These are usually used in combination. In addition, an ITO film (not shown) is often used for electromagnetic shielding.

The diffusion plate 120 is a resin plate containing a light-transmitting thermoplastic resin such as an acrylic resin, a styrene resin, a methyl methacrylate / styrene copolymer resin (MS resin), a polycarbonate resin or an olefin resin, (Not shown) is dispersed in the diffuser plate to adjust the transmittance.

The diffusion plate 120 may be a single plate including a light-transmitting resin, that is, a single plate, or may have a multi-layer structure of two or more layers for high functionality.

The diffusion plate 120 can be manufactured by using a conventional method for producing a thermoplastic resin such as a casting method or an extrusion method.

The casting method is a method in which a thermoplastic resin is polymerized and solidified in a pair of molds, usually between a glass plate and a stainless steel plate to form a plate.

The extrusion method is a method in which a thermoplastic resin is heated and melted in an extruder, extruded from a die having a sheet-like sleeve, a so-called die, and sandwiched between the abrasive rolls to form a plate.

The optical film 130 disposed on the diffusion plate 120 includes a diffusion sheet 131, a prism sheet 133, and a protective sheet 135.

The prism sheet 133 serves to diffuse and condense the light emitted from the diffusion sheet 131. The prism sheet 133 has a function of diffusing and condensing light emitted from the diffusion sheet 131. [

To this end, the prism sheet 133 includes a substrate 133a and a projection 133b located on the substrate.

The projecting portion 133b forms a prism pattern. The projecting portion 133b has a cross-sectional shape of any one of isosceles triangle, equilateral triangle, and equilateral triangle as shown in Figs. 3A to 3C.

At this time, the prism pattern may have a horizontal portion therebetween, but it is preferable that the prism pattern is continuously formed so as to effectively suppress luminance unevenness.

A transparent and monocrystalline magnesium oxide (MgO) powder 133c shown in FIG. 4 is diffused into the protrusions 133b of the prism sheet 133 to prevent the luminance from being lowered due to the diffusion agent while obtaining a diffusion effect. Zero dispersion.

The magnesium oxide powder 133c is formed in a hexahedron shape and has a diameter of 0.5 to 2 mu m.

In general, a prism sheet including spherical beads has a lower luminance than a general prism sheet because, when the light is refracted into the beads, the light is more absorbed or scattered than the beads are transmitted.

On the other hand, the magnesium oxide powder 133c formed in a hexahedron shape is larger in transparency than the absorption effect, and the prism sheet containing magnesium oxide has a higher luminance than the prism sheet including spherical beads do.

In addition, since the magnesium oxide powder 133c has many times of reflection within the magnesium oxide powder 133c, the amount of light emitted to the outside increases compared with the spherical beads conventionally used as a diffusing agent.

Although the prism sheet 133 has been described above in which the magnesium oxide powder 133c is dispersed in the protrusions 133b as described above, the magnesium oxide powder 133c may be dispersed in the prism sheet 133a And may be coated on the surface of the prism sheet 133 corresponding to the opposite side of the projection 133b.

In addition, the magnesium oxide powder 133c can be used for a diffusion film which is one of the optical films.

≪ Example 2 >

Hereinafter, a second embodiment of the present invention will be described with reference to FIG. The backlight unit disposed below the liquid crystal display panel includes a linear light source 210, a light source housing 220, a light guide plate 230, a reflection plate 231, and an optical film 240 ).

The light guide plate 230 has an incident surface (not shown) on which light is incident and an exit surface (not shown) on which light is emitted, and is disposed below the liquid crystal display panel.

A linear light source 210, for example, a cold cathode fluorescent lamp, is installed on the incident surface side of the light guide plate 230 by a lamp housing 220. Here, other types of light sources may be used in place of cold cathode fluorescent lamps.

A reflection plate 231 is disposed below the light guide plate 230 to prevent light from leaking through the rear surface and an optical film 240 is disposed between the light guide plate 230 and the liquid crystal display panel.

The optical film 240 may further include at least one diffusion sheet 241 and at least one prism sheet 243 and may further include a protective sheet 245 disposed on the prism sheet 243 . Of course, the protective sheet 245 may be replaced with a diffusion sheet. Thus, the structure of the optical film 240 is not limited to the embodiment, and various kinds of sheets can be combined in various forms.

In the liquid crystal display device having such a configuration, the optical film 240, particularly the prism sheet 243, may have the same configuration as that of Embodiment 1 described above. Although not specifically shown, the prism sheet 243 has magnesium oxide powder dispersed in the inside of the base material or in the protrusions forming the prism pattern.

Although the magnesium oxide powder is described as being dispersed in the prism sheet, the magnesium oxide powder can also be used as a diffusion agent in a diffusion sheet or an expansion plate for diffusing light.

As described above, the scope of rights of the present invention is not limited to the above embodiments, and various modifications and improvements of the person skilled in the art using the basic concept of the present invention defined in the following claims are also within the scope of the present invention.

1 is a view schematically showing an assembly state of a liquid crystal display device having a direct-type backlight unit according to Embodiment 1 of the present invention,

Fig. 2 is a perspective view of the optical film shown in Fig. 1, in particular, a prism sheet,

FIGS. 3A to 3C illustrate various embodiments according to a cross-sectional shape of a prism pattern formed on the prism sheet of FIG. 2,

Fig. 4 is an enlarged perspective view of a diffusing agent used in the optical film of Fig. 2,

5 is a view schematically showing an assembly state of a liquid crystal display device having an edge type backlight unit according to Embodiment 1 of the present invention.

Description of the Related Art

110: linear light source 120: diffusion plate

130: optical film 133: prism sheet

133c: Magnesium oxide powder 140: Lower cover

Claims (8)

Light source, and A diffusion plate for diffusing light generated from the light source; And a prism sheet for condensing or polarizing the light diffused by the diffusion plate, The prism sheet includes: Substrate, and A protrusion located on the substrate, Wherein a diffuser made of magnesium oxide powder having a hexahedral shape is dispersed in at least one of the substrate or the projecting portion. delete The method of claim 1, The magnesium oxide powder is transparent and made of a single crystal. 4. The method of claim 3, Wherein the magnesium oxide powder has a diameter of 0.5 to 2 占 퐉. 5. The method according to any one of claims 1 and 3, Wherein the light source and the prism sheet are arranged in a direct-type manner. 5. The method according to any one of claims 1 and 3, Wherein the light source and the prism sheet are arranged in an edge-type manner. delete delete

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