KR100940789B1 - Reflective plate, backlight unit and liquid crystal display including the same - Google Patents

Abstract

PURPOSE: A reflective plate for backlight unit, a backlight unit including the same, and a liquid crystal display including the same are provided to improve the overall brightness of a liquid crystal display by improving the reflective efficiency of the light emitted in the light guide plate. CONSTITUTION: A light source emits the light. A light guide plate distributes the light emitted from a light source to overall area. A cholesteric liquid crystal layer(130) reflects the first polarized light and the second polarized light emitted in the light guide plate. A reflector(RP) comprises a reflective layer(140).

Description

Reflector for backlight unit, backlight unit and liquid crystal display having the same {REFLECTIVE PLATE, BACKLIGHT UNIT AND LIQUID CRYSTAL DISPLAY INCLUDING THE SAME}

The present invention relates to a reflector for a backlight unit, and more particularly, to a reflector for a backlight unit capable of improving the reflection efficiency of light lost in the light guide plate and thus improving the brightness of the liquid crystal display, a backlight unit having the same, and a liquid crystal display. It is about.

As is well known, liquid crystal displays (LCDs) are widely used as information displays for notebooks, personal computers or TVs.

The liquid crystal display displays an image by using a difference in refractive index of light according to the anisotropy of the liquid crystal injected between the array substrate and the color filter substrate, and has a structure in which polarizers are disposed on the front and rear surfaces of the two substrates. In addition, since the liquid crystal display cannot emit light by itself, it is dimmed by a backlight unit composed of various optical systems.

1 is an exemplary view illustrating a configuration of a conventional liquid crystal display mentioned above, and is roughly divided into a backlight unit 10 and a liquid crystal panel unit 20.

The backlight unit 10 includes a light source 11 for irradiating light, a light guide plate 12 for distributing light incident from the light source, an reflector 13 for reflecting light emitted from the light guide plate, and a light guide plate 12. A diffuser sheet 14 for diffusing the emitted light, a prism sheet 15 for condensing light incident from the diffusion sheet 14, and a polarizer 16 for transmitting light in one direction among the light emitted from the prism sheet 15. And a phase delay plate 17 for converting circularly polarized light emitted from the polarizer 16 into linearly polarized light.

Here, the reflective plate 13 reflects a part of the light emitted from the light guide plate 12 and re-injects the light into the light guide plate 12. The conventional reflective plate is made of silver, aluminum, and AL having excellent reflectance. It is made of a structure that is made or a plurality of polymer layers are stacked in multiple stages.

However, such a conventional reflector does not induce total reflection of light due to the property of the material, leading to loss of light, and thus there is a problem in that the brightness of the liquid crystal display cannot be expected.

In more detail, as shown in FIG. 1, some light L1 emitted from the light guide plate 12 is reflected by the reflector 13 and re-entered into the light guide plate 12, and the remaining light L2 is diffused. It exits in the sheet 14 direction. At this time, the light L2 emitted in the direction of the diffusion sheet 14 does not transmit 100% of the optical elements-the diffusion sheet 14, the prism sheet 15, the polarizer 16, etc. of the backlight unit 10 and the reflecting plate. Reflected by (13), the reflected light (L2) is reflected by the reflecting plate 13 is subjected to the process of being re-introduced back to the light guide plate 12, a portion of the light is recycled inside the backlight unit 10 It will exist. Therefore, when the reflection efficiency through the reflection plate 13 is lowered, the luminance of the liquid crystal display is also lowered as light is lost or absorbed as much as the decrease.

In other words, the increase in the reflection efficiency through the reflecting plate 13 improves the brightness of the backlight unit 10 and further the entire liquid crystal display. That is, even if the reflectance of the reflector 13 is increased by only about 1 to 2%, the luminance improvement of about 5 to 10% can be expected in the liquid crystal display.

The present invention has been made to solve the above-mentioned conventional problems, an object of the present invention is to improve the reflection efficiency of the light lost in the light guide plate, thereby improving the luminance of the entire liquid crystal display cholester for the backlight unit The present invention provides a rig reflector and a backlight unit and a liquid crystal display with improved brightness.

The reflection plate for the backlight unit of the present invention for achieving the above object is a reflection plate provided in the backlight unit to reflect the incident light, the cholesteric liquid crystal layer for reflecting the incident first polarized light and the second polarized light, It includes a reflective layer disposed to reflect unreflected light through the cholesteric liquid crystal layer.

The cholesteric liquid crystal layer reflects a first cholesteric liquid crystal layer that transmits a second polarized light while reflecting an incident first polarized light, and reflects a second polarized light transmitted through the first cholesteric liquid crystal layer. It is preferable that the second cholesteric liquid crystal layer is formed, and the reflection band to be reflected by the cholesteric liquid crystal layer preferably includes a visible light region.

In this case, the first cholesteric liquid crystal layer is a single cholester having a continuous pitch change while going from the top to the bottom so as to stack several cholesteric liquid crystals having different center wavelengths or to reflect the first polarized light. Rick liquid crystals may be used.

The second cholesteric liquid crystal layer is a single cholesteric liquid crystal having a continuous pitch change while going from the bottom to the top so as to stack several cholesteric liquid crystals having different center wavelengths or reflecting the second polarized light. Can be made.

The reflective layer may include a base substrate and a reflective material applied to at least one surface of the base substrate, or may be formed of a reflective material coated on one surface of the cholesteric liquid crystal layer.

In this case, the reflective material may be made of at least one selected from gold, silver, copper, nickel, aluminum, and TiO 2.

On the other hand, the backlight unit having a reflecting plate of the present invention for achieving the above object includes a light source for irradiating light, a light guide plate for distributing the light incident from the light source, the first polarized light emitted from the light guide plate and It includes a reflecting plate made of a cholesteric liquid crystal layer and a reflective layer to reflect the second polarized light.

As a result, a liquid crystal display having the backlight unit as described above is implemented.

According to the present invention implemented by the above means, the light emitted from the light guide plate is reflected through the cholesteric liquid crystal layer and the reflection layer to improve the reflection efficiency, which is very useful to expect the brightness improvement of the entire liquid crystal display It works.

Hereinafter, with reference to the accompanying drawings, preferred embodiments of the present invention will be described in detail.

The backlight unit 100 provided with the cholesteric reflector 130 according to the present invention includes a light source 110 for irradiating light, a light guide plate 120 for distributing the light incident from the light source 110, and a total area; The technical concept of the present invention is to include a reflective plate RP composed of the cholesteric liquid crystal layer 130 and the reflective layer 140 to reflect the first polarized light and the second polarized light emitted from the light guide plate 120.

The light source 110 irradiates light to the light guide plate 120. In FIG. 2, the light source 110 is implemented as a so-called edge illumination type in which the light source 110 is disposed at at least one end of the light guide plate 120. Accordingly, the light source 110 may be implemented as a top-down method type disposed between the reflecting plate and the diffusion sheet of the backlight unit, and the light guide plate may be omitted. And the light source 110 is CCFL (Cold Cathode Fluorescent), EEFL (External Electrode Flourscent Lamp), EL (Electrluminescent), FFL (Flat Fluorescent Lamp), LED ( Light Emitting Diodes;

As the light guide plate 120 diffuses and scatters the light emitted from the light source 110, the light guide plate 120 is uniformly distributed over the entire area and is emitted to the liquid crystal panel unit 200 (shown in FIG. 7). It is preferably made of an acrylic resin having transparency, and at least one surface of the light guide plate 120 is preferably provided with a scattering pattern (not shown) to diffuse and scatter incident light.

The scattering pattern may be implemented by printing a screen with a dot on one surface of the light guide plate 120 or by providing an uneven pattern on one surface of the light guide plate 120. Alternatively, the scattering pattern may be implemented by forming a prism pattern on one surface of the light guide plate 120 to be integrally formed on the light guide plate 120.

Optionally, the light guide plate 120 may contain fine particles, which may be made of any one of transparent materials including acryl, styrene, silicon, synthetic silica, diamond, or the like, or may include titanium oxide, zinc oxide, and sulfuric acid. It is made of any one of white materials including barium, calcium carbonate, magnesium carbonate, aluminum hydroxide, clay and the like to diffuse and scatter incident light incident on the light guide plate 120. If necessary, the microparticles may incorporate several selected materials from the above materials into the light guide plate 120.

The reflecting plate RP reflects incident light, and more preferably, is disposed under the light guide plate 120 to re-inject the first and second polarized light emitted from the light guide plate 120 to the light guide plate 120. . The reflective plate RP includes the first polarized light L1 and the second polarized light L2 that are incident, that is, the first polarized light L1 and the second polarized light L2 emitted from the light guide plate 120 as shown in FIG. 3. The cholesteric liquid crystal layer 130 for reflecting the () and the reflection layer 140 for reflecting the unreflected light (L3) through the cholesteric liquid crystal layer 130 is implemented.

Here, the cholesteric liquid crystal layer 130 is implemented as a cholesteric liquid crystal in which each very thin molecular layer forms a helical structure as a whole. The cholesteric liquid crystal has a spiral rotational direction and a circular polarization direction of the liquid crystal and has a wavelength. There is a characteristic of reflecting only circularly polarized light such as the spiral pitch, and the specific wavelength band can be adjusted according to the coating thickness of the liquid crystal and the length of the spiral pitch. The reflection band to be reflected by the cholesteric liquid crystal layer 130 preferably includes a visible light region consisting of 380 ~ 780nm.

3 is a cross-sectional view showing an embodiment of the cholesteric liquid crystal layer 130, the cholesteric liquid crystal layer 130 according to an embodiment reflects the first polarized light emitted from the light guide plate 120 While laminating the first cholesteric liquid crystal layer 131 which transmits the second polarized light as it is and the second cholesteric liquid crystal layer 132 which reflects the second polarized light transmitted through the first cholesteric liquid crystal layer. Is implemented. At this time, the stacking order of the first cholesteric liquid crystal layer 131 and the second cholesteric liquid crystal layer 132 is not limited.

Referring to FIG. 3, the operation of the cholesteric liquid crystal layer 130 will be described in more detail. The first cholesteric liquid crystal layer 131 reflects the first polarized light L1 emitted from the light guide plate 120 and the second piece. The light L2 is transmitted as it is. The second polarization L2 transmitted through the first cholesteric liquid crystal layer 131 is reflected by the second cholesteric liquid crystal layer 132. Accordingly, the first polarization L1 and the second polarization L2 in the vertical and random directions emitted from the light guide plate 120 are formed by the first cholesteric liquid crystal layer 131 and the second cholesteric liquid crystal layer 132. Total reflection is induced.

Here, each of the cholesteric liquid crystal layers 131 and 132 may be implemented as a single cholesteric liquid crystal. That is, it is implemented as a cholesteric liquid crystal having a change in pitch continuously from top to bottom to selectively reflect different polarizations.

Alternatively, each of the cholesteric liquid crystal layers 131 and 132 may be implemented by stacking several cholesteric liquid crystals having different center wavelengths in multiple stages. 4 is a cross-sectional view showing another embodiment of the cholesteric liquid crystal layer 130, in which several cholesteric liquid crystals having different center wavelengths are stacked to selectively reflect light of different wavelength bands.

In addition, the reflective layer 140 is formed of a material having an appropriate reflectance, and is preferably stacked below the second cholesteric liquid crystal layer 132 as shown in FIG. 3, wherein the material of the reflective layer 140 has excellent reflectance. Gold, silver, cupper, nickel, aluminum, aluminum, titanium dioxide (TiO 2) or a plurality of polymer layers may be implemented in a multi-layered form. .

Optionally, the reflective layer 140 may be integrated by depositing a reflective material of any one selected from gold, silver, copper, nickel, aluminum, and TiO 2 having excellent reflectance on at least one surface of a thin base substrate.

Optionally, the reflective layer 140 coats the reflective material on one surface of the second cholesteric liquid crystal layer 132 to reflect unreflected light through each of the cholesteric liquid crystal layers 131 and 132. It can be implemented as.

Here, it is clear that the reflective material includes all the materials having excellent reflectivity to reflect unreflected light through each of the cholesteric liquid crystal layers 131 and 132, in addition to the above-mentioned materials.

Referring to the operation of the reflection plate RP configured as described above with reference to FIG. 3, the first and second polarizations incident on the cholesteric reflection plate 130 are the first cholesteric liquid crystal layer 131 and the second cholesteric liquid crystal. Reflected through the layer 132, as shown in FIG. 3, the unreflected light L3 through each of the cholesteric liquid crystal layers 131 and 132 is reflected by the reflective layer 140 to enhance the reflection efficiency. do. In this case, the unreflected light L3 is the second unreflected light by the first polarized light L1 and the second cholesteric liquid crystal layer 132 that are not reflected by the first cholesteric liquid crystal layer 131. It includes both polarization L2. Such non-reflected light, ideally, the first and second polarized light is present at the same ratio to achieve a state without polarization, that is, a non-polarized state.

Based on the above description, the difference in reflectance between the reflecting plate according to the present invention and the conventional reflecting plate will be described in detail through an experimental example.

<Example 1>

A cholesteric liquid crystal layer including a first cholesteric liquid crystal layer reflecting the first polarization and a second cholesteric liquid crystal layer reflecting the second polarization is laminated on the reflective layer made of aluminum, and set as a reflecting plate. After that, the backlight unit in which the reflector is disposed under the light guide plate provided with the light source is modeled.

<Example 2>

A cholesteric liquid crystal layer including a first cholesteric liquid crystal layer reflecting the first polarization and a second cholesteric liquid crystal layer reflecting the second polarization is laminated on the reflective layer made of silver material and set as a reflecting plate. After that, the backlight unit in which the reflector is disposed under the light guide plate provided with the light source is modeled.

Comparative Example 1

The backlight unit was modeled by placing a reflector plate made of only aluminum under the light guide plate provided with a light source.

Comparative Example 2

The backlight unit was modeled by arranging a reflector made of silver material under the light guide plate provided with a light source.

Experimental Example

Reflectances measured through the simulation of the backlight unit modeled under the conditions of Examples 1 and 2 and Comparative Examples 1 and 2 are graphically shown in FIGS. 5 and 6.

From the graph of FIG. 5, it can be seen that the visible light region (400 to 650 nm) reflectance (shown in dotted lines) of the reflector made under the conditions of Comparative Example 1 is maintained at about 90 to 92%, and from the graph of FIG. 6, Comparative Example 2 It can be seen that the visible light region reflectance (shown by dotted lines) of the reflector made of the condition of about 82-94% is maintained.

On the other hand, the visible light region reflectance (shown in solid line) of the reflector made under the conditions of Example 1 was approximately 95 to 99%, much higher than 90%, and the visible light region of the reflector made of the conditions of Example 2 Reflectance (shown by solid line) ranged from 90 to 99%.

Therefore, the reflecting plates of Examples 1 and 2 exhibited much improved reflectances as compared with Comparative Examples 1 and 2, and as a result, the luminance of the liquid crystal display is improved.

Meanwhile, FIG. 7 is a view illustrating a liquid crystal display having a backlight unit configured as described above, and the liquid crystal display includes a backlight unit 100 and a liquid crystal panel unit 200.

Here, the backlight unit 100 includes a diffusion sheet 140 that transforms the light incident from the light guide plate 120 into a surface light source having uniform brightness, in addition to the light source 110, the light guide plate 120, and the reflective plate 130. At least one prism sheet 150 may be further included to condense the light emitted from the diffusion sheet 140 and output the light to the reflective polarization film 160.

The liquid crystal panel unit 200 may include a liquid crystal, a front polarizer and a rear polarizer provided on the front and rear surfaces of the liquid crystal, and an absorption type polarizer may be interposed between the rear polarizer and the reflective polarizer.

The present invention is not limited only to the above-described embodiments, and various modifications, changes, substitutions, and additions can be made in various forms without departing from the spirit of the present invention. I can understand. If such improvement, change, replacement, or addition is carried out within the scope of the following claims, it is obvious that the technical idea also belongs to the present invention.

1 is an exemplary view showing a conventional liquid crystal display.

2 is a side view showing a backlight unit according to the present invention;

3 is a side view of the reflector according to the present invention;

Figure 4 is a side view showing another embodiment of the reflecting plate according to the present invention.

5 is a graph showing the results of Example 1 and Comparative Example 1 according to the present invention.

6 is a graph showing the results of Example 2 and Comparative Example 2 according to the present invention.

7 is a side view showing a liquid crystal display according to the present invention.

Claims (12)

In the reflector provided in the backlight unit to reflect the incident light, And a cholesteric liquid crystal layer reflecting incident first and second polarized light, and a reflecting layer arranged to reflect unreflected light through the cholesteric liquid crystal layer. The method according to claim 1, The cholesteric liquid crystal layer, A first cholesteric liquid crystal layer reflecting incident first polarized light and transmitting a second polarized light, and a second cholesteric liquid crystal layer reflecting second polarized light transmitted through the first cholesteric liquid crystal layer A reflector for the backlight unit, characterized in that. The method according to claim 2, The first cholesteric liquid crystal layer is a reflection plate for a backlight unit, characterized in that several cholesteric liquid crystals having different center wavelengths are stacked. The method according to claim 2 or 3, The second cholesteric liquid crystal layer is a reflection plate for a backlight unit, characterized in that several cholesteric liquid crystals having different center wavelengths are stacked. The method according to claim 2, The first cholesteric liquid crystal layer is a reflective plate for a backlight unit, characterized in that made of a single cholesteric liquid crystal having a pitch change continuously from top to bottom to reflect the first polarized light. The method according to claim 2 or 5, The second cholesteric liquid crystal layer is a reflection plate for a backlight unit, characterized in that made of a single cholesteric liquid crystal having a pitch change continuously from top to bottom to reflect the second polarized light. The method according to claim 1, The reflective layer is a reflective plate for a backlight unit, characterized in that the base substrate and a reflective material applied to at least one surface of the base substrate. The method according to claim 1, The reflecting layer is a reflector for a backlight unit, characterized in that made of a reflective material coated on at least one side of the cholesteric liquid crystal layer. The method according to claim 7 or 8, The reflective material is a reflector for a backlight unit, characterized in that made of at least one selected from gold, silver, copper, nickel, aluminum, TiO2. The method according to claim 1, Reflecting band to be reflected in the cholesteric liquid crystal layer reflector for the backlight unit, characterized in that it comprises a visible light region. A backlight unit having a reflector of any one of claims 1, 2, 3, 5, 7, 7, 8 and 10. A liquid crystal display having the backlight unit of claim 11.

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