KR101114412B1 - Optical sheet in which nano quantum dots are dispersed and backlight unit including the same - Google Patents

Abstract

The present invention includes a reflective layer, and a wavelength conversion layer formed on the reflective layer, wherein the wavelength conversion layer discloses an optical sheet formed by dispersing quantum dots in a polymer resin and a backlight unit including the same.

Description

Optical sheet including nano quantum dot and backlight unit using the same}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical sheet, and to an optical sheet capable of preventing oxidation of a metal reflective layer and increasing the amount of light in a blue wavelength band to maintain an overall RGB value uniformly, and a backlight unit including the same.

Recently, due to the rapid growth of the display market, the development of next-generation displays such as organic EL, PDP, TFT-LCD, and the like is being actively conducted to improve the performance of components and the improvement of the manufacturing process.

Of these, the TFT-LCD requires a separate light source because there is no self-generating light source, and the backlight unit serves as a back light source of the TFT-LCD panel.

In the lateral method of such a backlight unit, a point light source emitted from a light source arranged on the side of the light guide plate is converted into a surface light source in the light guide plate and is emitted to the upper part of the light guide plate. In addition, the light emitted to the lower portion of the light guide plate is incident to the light guide plate again by the reflective sheet.

In general, a reflective sheet of silver (Ag) is mainly used, and a protective coating layer is formed to prevent oxidation of silver (Ag). However, Surface Plasmon Resonance (SPR) occurs at the interface between the protective coating layer and the silver (Ag) reflector, causing the reflectance of the reflecting sheet to rapidly decrease at a wavelength of 450 nm or less.

As a result, much of the light in the blue wavelength band is lost in the backlight unit, so that the luminance is reduced.

The present invention has been made to solve the above problems, and provides an optical sheet and a backlight unit including the same, which can prevent oxidation of the reflection layer and increase the amount of blue wavelengths to maintain the overall RGB value uniformly.

In order to achieve the above object, the optical sheet according to the present invention includes a reflection layer, and a wavelength conversion layer formed on the reflection layer, wherein the wavelength conversion layer is formed by quantum dots dispersed in a polymer resin.

In addition, the reflective layer may be formed of a metal thin film or a metal layer may be formed on the base substrate to have a predetermined thickness.

In addition, the quantum dots may be configured to have a light emission wavelength of 380nm to 480nm.

And the weight ratio of the polymer resin and the quantum dot may be composed of 99: 1 to 97: 3.

In addition, the thickness of the wavelength conversion layer may be controlled to 100nm to 10㎛.

In order to achieve the above object, the backlight unit according to the present invention includes a light guide plate having a light incident surface, a light emitting element arranged on the light incident surface of the light guide plate, and an optical sheet formed under the light guide plate, wherein the optical sheet Includes a reflective layer and a wavelength conversion layer formed on the reflective layer, wherein the wavelength conversion layer is formed by dispersing quantum dots in a polymer resin.

According to the present invention, white light can be realized by preventing oxidation of the reflective layer and increasing the amount of light in the blue wavelength range to maintain a uniform RGB value as a whole.

In addition, it is possible to utilize the light of the short wavelength band lost in the backlight unit has the advantage that the brightness is increased. And it is possible to solve the problem that light is absorbed in the light guide plate.

1 is a schematic diagram of a backlight unit according to an embodiment of the present invention,
2 is a cross-sectional view of an optical sheet according to an embodiment of the present invention,
3 is a modification of the optical sheet according to the embodiment of the present invention,
4 is a schematic view of a backlight unit according to another embodiment of the present invention.

As the invention allows for various changes and numerous embodiments, particular embodiments will be illustrated in the drawings and described in detail in the written description.

However, this is not intended to limit the present invention to specific embodiments, it should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention.

The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting of the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise.

In the present application, the terms "comprises", "having", and the like are used to specify that a feature, a number, a step, an operation, an element, a component, But do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof.

In addition, it is to be understood that the accompanying drawings in this application are shown enlarged or reduced for convenience of description.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to the drawings. Like reference numerals designate like elements throughout, and duplicate descriptions thereof will be omitted.

1 is a schematic view of a backlight unit according to an embodiment of the present invention, Figure 2 is a cross-sectional view of an optical sheet according to an embodiment of the present invention, Figure 3 is a modification of the optical sheet according to an embodiment of the present invention.

The backlight unit according to the embodiment of the present invention is formed on the light guide plate 200 having a light incident surface 201, the light emitting device 100 arranged on the light incident surface of the light guide plate 200, and a lower portion of the light guide plate 200. It includes an optical sheet 300.

The light guide plate 200 is an optical sheet for converting a point light source incident from the light emitting device 100 into a surface light source, and may be variously changed according to the embodiment as well as the general shape of the light guide plate 200. For example, any suitable surface shape may be applied to the corner portion, such as straight surfaces, curved surfaces, and the like.

In addition, although not shown in the drawings, the prism-shaped unevenness may be formed on the upper surface of the light guide plate 200, and the prism-shaped unevenness may be formed in any surface form such as a straight surface, a refractive surface, a curved surface, or the like.

The light emitting device 100 may be formed in plural along the light incident surface of the light guide plate 200, and may be formed of an LED device. In this case, the light emitting device 100 may be configured as a white LED or a UV LED which may emit light having a short wavelength.

The optical sheet 300 reflects the light emitted to the lower portion of the light guide plate 200 and serves to reenter the light guide plate 200 again. Thus, a variety of materials and configurations that are most suitable for reflecting light can be selected.

The optical sheet 300 according to the present invention is largely composed of a reflective layer 310 and a wavelength conversion layer 320. First, the reflective layer 310 may be applied to all configurations of a general display reflector.

For example, a metal thin film such as silver (Ag) or aluminum (Al) may be used, and a metal paste 312 such as silver (Ag) is applied to a predetermined thickness on a base substrate 311 such as a film. It can be prepared by post curing. Alternatively, the metal layer may be formed by sputtering or screen coating metal particles on the base substrate 311.

The wavelength conversion layer 320 is formed by dispersing a quantum dot 322 in the polymer resin 321. Quantum Dots (QDs) are nanoparticles of a certain size with quantum confinement effects. They absorb light (excited light) with a wavelength smaller than the emission wavelength of quantum dots and generate strong fluorescence in a narrow wavelength band. .

Such quantum dots 322 include group II-VI compound semiconductors such as ZnS, ZnSe, ZnTe, and CdS CdSe, group III-V compound semiconductors such as PbS, PbSe, PbTe, AlN, AlP, and AlAs, and group IV-VI compound semiconductors. Or a mixture thereof.

The manufacturing method of the quantum dot can be applied to all the manufacturing methods commonly used. For example, in the case of CdSe quantum dots, after dissolving the Cd precursor and Se precursor, respectively, the Se precursor solution may be slowly injected into the solution in which the Cd precursor is dissolved and stirred for about 20 hours to prepare a CdSe quantum dot core. Subsequently, a ZnS precursor may be grown around the core in the same manner to prepare a quantum dot of a core-shell structure.

In this case, the size of the quantum dot may be controlled to have a desired emission wavelength. A method for controlling the size of a quantum dot may also be applied to various known methods. For example, the cores may be grown according to temperature conditions and time by a colloidal method to produce different core sizes of quantum dots.

The polymer resin 321, which is a dispersion medium of the quantum dots 322, is preferably a light resistant or moisture resistant material that is not discolored or altered by excitation light such as epoxy resin or silicon. The wavelength conversion layer 320 may be molded into a sheet by a known method such as rolling after mixing the polymer resin 321 and the quantum dots 322 in a liquid state and before curing.

The polymer resin 321 mixed with the quantum dots 322 may be molded and cured to form a wavelength conversion layer 320 including a large area and a uniform concentration of quantum dots 322 on the reflective layer 310. have.

In the present invention, the excitation light (including the ultraviolet region) incident on the optical sheet 300 from the light guide plate 200 is controlled to be converted into light having a blue wavelength band (380 nm to 480 nm) while passing through the wavelength conversion layer 320. That is, as shown in FIG. 2, the quantum dot 322 absorbs excitation light P1 having a wavelength band of 380 nm or less and then emits light P2 having a wavelength band of 380 nm to 480 nm.

Since the light emission wavelength is smaller as the size of the quantum dot is smaller, it is preferable that the core of the quantum dot 322 has a size of about 5 nm or less in order to have a light emission wavelength of 480 nm or less.

As a result, even if the reflectance of light having a wavelength band of 450 nm or less is reduced by Surface Plasmon Resonance (SPR) occurring at the interface between the reflective layer 310 and the wavelength conversion layer 320, the wavelength band of 380 nm to 480 nm. Since the light quantity of the light having increases, it is possible to compensate for the decrease in reflectance in the blue region wavelength band. In addition, since the light of short wavelength that is not reflected by the conventional reflector is utilized, the overall amount of light is increased, thereby increasing the luminance.

In this case, when the weight ratio of the quantum dot 322 is less than 1 wt% of the polymer resin, there is a problem in that the amount of light in the blue wavelength band cannot be increased enough to compensate for surface plasmon resonance (SPR), and 3 wt% of the polymer resin. In case of exceeding, the phenomenon of re-absorption of quantum dots close to the emitted light due to self quenching occurs, which causes a problem in that the luminous efficiency is greatly decreased. Therefore, the weight ratio (wt%) of the polymer resin and the quantum dots is preferably 99: 1 to 97: 3.

In addition, when the thickness of the wavelength conversion layer 320 is less than 100nm, the loss of light reflected from the optical sheet is small but the SPR effect is relatively large, there is a problem that the light loss of the blue wavelength band is larger, the thickness is more than 10㎛ In this case, the reduction effect by the SPR is small, but the amount of light re-injected into the light guide plate is relatively small due to the thick thickness, there is a problem that the film peeling phenomenon of the wavelength conversion layer occurs. Accordingly, the thickness of the wavelength conversion layer 320 is preferably 100 nm or more and 10 μm or less.

According to the present invention, the metal of the reflective layer 310 is prevented from being oxidized by the wavelength conversion layer 320, and the amount of light having a wavelength band of 380 nm to 480 nm is increased by the quantum dot 322 to be re-entered into the light guide plate 200. The RGB value of the entire light can be controlled to be uniform.

However, the configuration of the optical sheet 300 is not necessarily limited thereto, and various modifications are possible. For example, a separate protective layer 330 may be formed on the reflective layer 310 and the wavelength conversion layer 320 may be formed thereon as shown in FIG. 3.

Hereinafter, after mixing the quantum dots having a central emission wavelength band of 410nm, 450nm to the polymer resin, and then coated on the reflective layer (Example 1, Example 2) and the protective coating silver (Ag) reflector (Comparative Example 1) The luminance and color coordinates were measured for each, and are shown in Table 1 below.

Luminance (%) Color coordinates X Y Example 1 (Ag + 410 nm QD) 4876 0.3086 0.3206 Example 2 (Ag + 450 nm QD) 4856 0.3097 0.3222 Comparative Example 1 (Ag Sheet + coating) 4616 0.3141 0.3325

Referring to Table 1, it can be seen that in the case of Examples 1 and 2, the brightness is increased in comparison with Comparative Example 1, the color coordinate value of the X-axis and Y-axis is close to the coordinates of the white light region in Comparative Example 1 It can be seen that closer to white light.

4 is a schematic diagram of a backlight unit according to another exemplary embodiment of the present invention. Referring to this, in the backlight unit according to the present invention, the wavelength conversion layer 320 may be formed under the light guide plate 200.

In this case, the wavelength conversion layer 320 may be integrally formed under the light guide plate 200 by a coating method, or may be formed on the reflective layer 310 of the optical sheet 300 and attached to the light guide plate 200. have. When the wavelength conversion layer 320 is formed under the light guide plate 200, the optical sheet 300 may have a configuration of a general reflecting plate.

By this configuration, some of the light incident through the incident surface of the first LGP 200 is incident toward the wavelength conversion layer 320.

In this case, when the wavelength conversion layer 320 has a higher refractive index than the light guide plate 200, the light refracted at an angle greater than the total reflection critical angle is reflected on the interface with the light guide plate 200, thereby continuously performing the wavelength conversion layer 320. When reflected and refracted / scattered at an angle smaller than the total reflection critical angle, the light is incident on the light guide plate 200.

In addition, when the wavelength conversion layer 320 is formed relatively thinner than the light guide plate 200, the number of times the light is repeatedly refracted / scattered / reflected between the boundary surface of the light guide plate 200 and the boundary surface of the reflective layer 310. Since is increased, the probability of being emitted at an angle smaller than the total reflection angle is increased before being absorbed in the wavelength conversion layer 320, thereby solving the problem of light being absorbed in the light guide plate 200.

The present invention includes a liquid crystal display device including a backlight unit, but the configuration of the liquid crystal display device may be applied to all known configurations, and thus a detailed description thereof will be omitted.

As described above, the present invention has been described in detail through the preferred embodiments, but the present invention is not limited to the contents of these embodiments. Those skilled in the art to which the present invention pertains, although not disclosed in the embodiments, various modifications, changes or additions are possible within the scope of the appended claims, all of which fall within the technical scope of the present invention. You will have to look.

100: light emitting device 200: light guide plate
300: optical sheet 310: reflective layer
320: wavelength conversion layer 321: polymer resin
322: quantum dots

Claims (13)

Reflective layer; And
Including; a wavelength conversion layer formed on the reflective layer,
The wavelength conversion layer is an optical sheet formed by dispersing quantum dots in a polymer resin. The optical sheet of claim 1, wherein the reflective layer is a metal thin film or a metal layer is formed on a base substrate. The optical sheet of claim 1, wherein the quantum dots have a light emission wavelength of 380 nm to 480 nm. The optical sheet of claim 1, wherein a weight ratio of the polymer resin and the quantum dots is 99: 1 to 97: 3. The optical sheet of claim 1, wherein the wavelength conversion layer has a thickness of 100 nm to 10 μm. A light guide plate having a light incident surface;
A light emitting element arranged on a light incident surface of the light guide plate; And
Including an optical sheet formed under the light guide plate,
The optical sheet includes a reflective layer and a wavelength conversion layer formed on the reflective layer, wherein the wavelength conversion layer is formed by dispersing quantum dots in a polymer resin. A light guide plate having a light incident surface;
A light emitting element arranged on a light incident surface of the light guide plate; And
Including an optical sheet formed under the light guide plate,
A wavelength conversion layer is formed below the light guide plate, and the wavelength conversion layer is formed by dispersing quantum dots in a polymer resin. The backlight unit of claim 6, wherein a refractive index of the polymer resin is higher than that of the light guide plate. The backlight unit of claim 6, wherein a thickness of the wavelength conversion layer is smaller than a thickness of the light guide plate. The backlight unit of claim 6, wherein the quantum dot has a light emission wavelength of 380 nm to 480 nm. The backlight unit according to claim 6 or 7, wherein a weight ratio of the polymer resin and the quantum dots is 99: 1 to 97: 3. 8. The backlight unit of claim 6 or 7, wherein the wavelength conversion layer has a thickness of 100 nm to 10 µm. A liquid crystal display device comprising the backlight unit of claim 6.

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