KR20180006121A

KR20180006121A - Optical sheet, backlight unit and display device including the same

Info

Publication number: KR20180006121A
Application number: KR1020160086825A
Authority: KR
Inventors: 이기욱; 이병훈; 임채리; 이민수
Original assignee: 주식회사 엘엠에스
Priority date: 2016-07-08
Filing date: 2016-07-08
Publication date: 2018-01-17
Also published as: WO2018008938A1; KR101933141B1

Abstract

The embodiment includes a base layer, a first diffusion layer disposed on one side of the base layer, and a second diffusion layer disposed on the other side of the base layer, wherein the first diffusion layer or the second diffusion layer absorbs light of a predetermined wavelength band An optical sheet including a light absorber and a display device including the same are disclosed.

Description

TECHNICAL FIELD [0001] The present invention relates to an optical sheet, a backlight unit, and a display device including the optical sheet. BACKGROUND OF THE INVENTION [0001]

An embodiment relates to an optical sheet for converting the color coordinates of incident light.

2. Description of the Related Art [0002] A liquid crystal display device is a display device used in a notebook computer, a personal computer, a mobile terminal, a TV, or the like.

A liquid crystal display device which is a non-light emitting device has a back light unit as a light source. The backlight includes a light source and a plurality of optical sheets. Such an optical sheet concentrates or diffuses incident light to supply uniform light to the liquid crystal panel.

In general, the light provided by the backlight unit provides relatively yellowish white light. However, since the white light has a low color temperature, the light efficiency is lowered. Therefore, there is a problem that an LED having a high color temperature must be used in order to compensate.

The embodiment provides an optical sheet capable of increasing the color temperature by converting the color coordinates of incident light.

The problems to be solved by the present invention are not limited to the above description, and can be more easily understood in the course of describing a specific embodiment of the present invention.

An optical sheet according to an embodiment of the present invention includes: a base layer; A first diffusion layer disposed on one surface of the base layer; And a second diffusion layer disposed on the other surface of the base layer, wherein the first diffusion layer or the second diffusion layer includes a light absorbent that absorbs light of a predetermined wavelength band.

The optical sheet can convert the color coordinates of the incident light.

The y coordinate change amount? Y of the converted color coordinate may be -0.010 to -0.0030.

The brightness of light emitted from the optical sheet may satisfy 96% to 100% based on 100% brightness of light incident on the optical sheet.

The light absorbing agent may have an absorption peak at a wavelength band of 580 nm to 650 nm.

The light absorbent may be contained in an amount of 0.0005 wt% to 0.006 wt%.

The light absorbent may be contained in an amount of 0.0005 wt% to 0.0015 wt%.

A display device according to an embodiment of the present invention includes: a backlight unit having any one of the above-described optical sheets; And a display panel for generating an image using the light whose color coordinates are converted by the optical sheet.

According to the embodiment, the color coordinates of the light provided by the backlight unit can be changed to increase the color temperature. Therefore, the manufacturing cost can be reduced because an LED class having a low luminance can be used.

The various and advantageous advantages and effects of the present invention are not limited to the above description, and can be more easily understood in the course of describing a specific embodiment of the present invention.

1 is a conceptual view of a diffusion sheet according to an embodiment of the present invention,
2 is a view for explaining a state in which a color coordinate is changed by a diffusion sheet according to an embodiment of the present invention,
3 is a graph showing a change in transmittance according to the content of the light absorbent,
4 is a graph showing changes in luminance and chromaticity coordinates according to the content of the light absorbent,
5 is a conceptual view of a diffusion sheet according to another embodiment,
FIG. 6 is a graph showing luminance measured by varying the surface roughness of the upper diffusion layer and the lower diffusion layer of the diffusion sheet,
7 is a graph showing luminance measured by controlling the die densities of the upper diffusion layer and the lower diffusion layer of the diffusion sheet differently,
8 is a graph in which the brightness is measured by controlling the thicknesses of the upper diffusion layer and the lower diffusion layer of the diffusion sheet differently,
9 is a conceptual diagram of a display device according to an embodiment of the present invention.

The present invention is capable of various modifications and various embodiments, and specific embodiments are illustrated and described in the drawings. It should be understood, however, that the invention is not intended to be limited to the particular embodiments, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

The terms including ordinal, such as second, first, etc., may be used to describe various elements, but the elements are not limited to these terms. The terms are used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the second component may be referred to as a first component, and similarly, the first component may also be referred to as a second component. And / or < / RTI > includes any combination of a plurality of related listed items or any of a plurality of related listed items.

The terminology used in this application is used only to describe a specific embodiment and is not intended to limit the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise. In the present application, the terms "comprises" or "having" and the like are used to specify that there is a feature, a number, a step, an operation, an element, a component or a combination thereof described in the specification, But do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms such as those defined in commonly used dictionaries are to be interpreted as having a meaning consistent with the contextual meaning of the related art and are to be interpreted as either ideal or overly formal in the sense of the present application Do not.

Hereinafter, embodiments will be described in detail with reference to the accompanying drawings, wherein like or corresponding elements are denoted by the same reference numerals, and redundant description thereof will be omitted.

FIG. 1 is a conceptual diagram of a diffusion sheet according to an embodiment of the present invention, and FIG. 2 is a view for explaining a state in which a color coordinate is changed by a diffusion sheet according to an embodiment of the present invention.

1, an optical sheet 12 according to an embodiment of the present invention includes a base layer 121, a first diffusion layer 122 disposed on one side of the base layer 121, and a base layer 121, And a second diffusion layer 123 disposed on the other surface of the second diffusion layer 123. The optical sheet 12 described in this embodiment may be a diffusion sheet.

The base layer 121 may be a variety of polymer films. As an example, the base layer 121 may be a light-transmitting polyethylene terephthalate film, a polycarbonate film, a polypropylene film. Or a polyethylene film. The thickness of the base layer 121 may be 10 탆 to 100 탆, but is not limited thereto.

The first diffusion layer 122 may be disposed on one side of the base layer 121. The first diffusion layer 122 includes a first resin layer 122a and a light absorbent P dispersed in the first resin layer 122a. And may further include particles (bead particles or the like) that induce diffusion as required. The thickness of the first diffusion layer 122 may be about 5 탆 to 10 탆, but is not limited thereto.

The first resin layer 122a may be formed by applying a polymer resin to the base layer 121 and then curing the same. The polymer resin may be any one selected from the group consisting of acrylic resin, urethane resin, polyethylene resin, polypropylene resin, polystyrene resin and polyamide resin. Or more, but not necessarily limited thereto.

The first diffusion layer 122 may have a diffusion pattern of a shape for diffusing incident light such as a lens pattern and a semicircular column pattern. Such a diffusion pattern can be formed regularly or irregularly. There is no limitation on the shape of the diffusion pattern. Alternatively, diffusion function may be imparted by using bead particles or the like without such a diffusion pattern.

The second diffusion layer 123 is disposed on the other surface of the base layer 121. The second diffusion layer 122 may include a second resin layer 123a and a light absorber (P). The structure of the second diffusion layer 123 may be the same as that of the first diffusion layer 122.

The first diffusion layer (122) or the second diffusion layer (123) includes a light absorbent (P). The light absorbent (P) absorbs light of a predetermined wavelength range. The light absorbent (P) may have an absorption peak at a wavelength band of 580 to 650 nm. The light absorber (P) may be dispersed in at least one of the first diffusion layer (122) and the second diffusion layer (123).

When the light absorber P is dispersed in the first diffusion layer 122 and the second diffusion layer 123, the light absorptivity can be increased as compared with the case where the light absorber P is dispersed only in one of the layers. The light absorber (P) may be a die (Dye) or a particle (Pigment) which absorbs light of a predetermined wavelength band.

2, the color coordinates of the light emitted from the optical sheet 12 according to the present invention (hereinafter referred to as outgoing light L2) may be different from the color coordinates of the light incident on the optical sheet 12 (hereinafter referred to as incident light L1) have. The color temperature of the emitted light L2 can be made higher than the incident light L1 by the conversion of the color coordinates.

When the incident light L1 is a yellowish white light, the color temperature may be relatively low. However, light passing through the optical sheet 12 according to an embodiment of the present invention may be absorbed in a wavelength range of 580 nm to 650 nm so that the color coordinates may change and the color temperature may be increased. That is, the outgoing light L2 can be converted into blueish white light with a relatively high color temperature.

FIG. 3 is a graph showing the change in transmittance according to the content of the light absorbing agent, and FIG. 4 is a graph showing changes in luminance and color coordinates according to the content of the light absorbing agent.

Referring to FIG. 3, it can be seen that when the optical sheet does not have a light absorber (Base polymer), the transmittance exceeds 90% in the entire region of the visible light wavelength range. However, the transmittance in the wavelength range of 580 nm to 650 nm is relatively high, so that the emitted light becomes relatively yellow. However, when light having a wavelength range of 580 to 650 nm is absorbed by the light absorbing agent and the transmittance is decreased, the emitted light becomes relatively blue and the light efficiency can be increased. Therefore, a low-rank LED can be used as a light source.

When the light transmittance in the wavelength range of about 580 nm to 600 nm is suppressed, the y coordinate on the CIE chromaticity coordinates can be effectively shifted, so that the desired color temperature can be adjusted. The y-coordinate change amount? y is preferably -0.010 to -0.003 with respect to the y-coordinate of the incident light. In this case, the white light having a yellow color can be converted into the white light having a blue color.

Referring to FIG. 3, it can be seen that as the content (wt%) of the light absorbent increases, the transmittance of the wavelength band of about 580 nm decreases. Also, as shown in FIG. 4, when the content (wt%) of the light absorbent is 0.0007 wt% or less, the absorption ratio of the wavelength band of about 580 nm is small. 003 to -0.010 is not satisfied.

The half width (FWHM) of the absorption peak is preferably 60 nm or less. When the half width is more than 60 nm, there is a problem that the transmittance of the adjacent wavelength band is decreased at the same time, thereby increasing the loss of the overall color coordinates and luminance. That is, in order to effectively remove the wavelength band corresponding to yellow, the absorption curve half width of the light absorbent (P) can be adjusted to 60 nm or less.

Referring to FIG. 4, it can be seen that as the content of the light absorber increases, the luminance of emitted light decreases. The luminance of emitted light is preferably controlled to 95% to 100% based on 100% luminance of the incident light. Therefore, it is preferable that the light absorbent (P) is 0.0007 wt% to 0.002 wt%. The content of the light absorbent (P) is preferably 0.0007 wt% to 0.002 wt% with respect to the weight of the polymer resin constituting the absorbent layer.

FIG. 5 is a conceptual diagram of a diffusion sheet according to another embodiment. FIG. 6 is a graph showing luminance measured by varying surface roughness of an upper diffusion layer and a lower diffusion layer of a diffusion sheet, FIG. 8 is a graph showing the brightness measured by controlling the thicknesses of the upper diffusion layer and the lower diffusion layer of the diffusion sheet differently. FIG.

Referring to FIG. 5, in the diffusion sheet according to the embodiment, the surface roughness of the first diffusion layer 122 and the second diffusion layer 123 may be different from each other. The surface roughness can be defined as an average value of an acid and a valley formed on the surfaces of the first diffusion layer 122 and the second diffusion layer 123.

The concentration of the light absorbing agent dispersed in the first diffusion layer 122 and the second diffusion layer 123 may be different from each other and the thickness of the first diffusion layer 122 and the thickness of the second diffusion layer 123 may be different from each other . Hereinafter, the second diffusion layer 123, into which the light L1 emitted from the light source is incident, is defined as a lower layer and the first diffusion layer 122 is defined as an upper layer.

Referring to FIG. 6, in Experimental Example 1, the surface roughness of the diffusion layers on both sides was controlled to 1.2 μm and the luminance was measured. In Experimental Example 2, the surface roughness was controlled to be the same as in Experimental Example 1, and a light absorbent was added. It can be seen that the luminance of Experimental Example 2 is reduced by about 5% as compared with Experimental Example 1. [ That is, it can be seen that the brightness decreases when the light absorbing agent is added under the same conditions.

However, in Experimental Example 3, in which the surface roughness of the upper layer was 2.1 탆 and the surface roughness of the lower layer was controlled to 0.9 탆, the luminance was measured as 99.2%. That is, although the light absorber was added, the brightness was higher than that of Experimental Example 2.

On the other hand, in Experiment 4 in which the surface roughness of the lower layer was set to 2.1 탆 and the surface roughness of the upper layer was controlled to 0.9 탆, no increase in luminance was observed.

It can also be seen that in Experiment 5, in which the surface roughness of the upper layer is 1.2 탆 and the surface roughness of the lower layer is 0.9 탆, the luminance is higher than that of Experiment 2. On the other hand, in Experimental Example 6, in which the surface roughness of the upper layer is controlled to 0.9 탆 and the surface roughness of the lower layer is controlled to 1.2 탆, the increase in luminance is relatively small.

As a result, it can be seen that when the surface roughness of the upper layer is rougher than the lower surface roughness, that is, when the surface of the lower layer is smoother than the surface of the upper layer, the brightness is relatively higher. As a result of the experiment, the surface roughness (Ra) of the first diffusion layer was 2.1 to 2.7, and the surface roughness (Ra) of the second diffusion layer was 1.8 to 2.3.

Referring to FIG. 7, in Experiment 8 in which 0.002 pt of the light absorber was dispersed in the upper and lower layers based on 100% luminance of Experimental Example 7 in which the light absorber was not added, the luminance was measured to be 96.8%. Further, in Experimental Example 10 in which the light absorber of 0.004 pts was dispersed only in the upper layer, the luminance was measured to be 96.6%.

It can be seen that the experimental examples 8 and 10 have similar luminance. On the other hand, in Experimental Example 9 in which the light absorbent was dispersed only in the lower layer, the luminance was higher than Experimental Example 8 and Experimental Example 10.

In addition, in the case of Experimental Example 9, the color coordinate variation is small compared to Experimental Examples 8 and 10. That is, it can be deduced that the effect of improving the color coordinate is small when the light absorbent is added to the lower layer.

Referring to FIG. 8, in the case of Experimental Example 12 having a thickness of 56 탆, the luminance was decreased by 1.1% as compared with Experimental Example 11, and the luminance was decreased by 1.8% as compared with Experimental Example 11 in Experimental Example 13, The luminance was reduced by 3.3% as compared with Experimental Example 11. Therefore, it can be seen that as the thickness of the diffusion layer becomes larger, the luminance gradually decreases.

9 is a conceptual diagram of a display device according to an embodiment of the present invention.

Referring to FIG. 9, a display device according to an embodiment of the present invention includes a backlight unit 10 and a display panel 20. The display panel 20 implements an image by adjusting the amount of light transmitted through the backlight unit 10. The display panel 20 may be a liquid crystal panel. Specifically, the display panel 20 includes a TFT substrate 22, a color filter 14, and a liquid crystal 23 filled between the TFT substrate 22 and the color filter 24.

Although not shown, a polarizing plate may be disposed on the upper and lower surfaces of the display panel 20. Therefore, the amount of light can be controlled by adjusting the voltage applied to the liquid crystal 23 to deform the arrangement direction of the liquid crystal.

The backlight unit 10 includes a plurality of light sources 16 and a light guide plate 11 that converts the light emitted from the light source 16 into a surface light source; a light guide plate 11 that reflects light emitted from the light guide plate 11 toward the display panel 20 A reflective sheet 15, and a plurality of optical sheets 12, 13, and 14. The plurality of optical sheets may be a diffusion sheet 12 and a pair of prism sheets 13 and 14. [

At this time, the diffusion sheet 12 and the reflection sheet 15 can be applied as they are. Therefore, the light emitted from the light source 16 can be converted into color coordinates by the diffusion sheet 12 and the reflection sheet 15 and provided to the liquid crystal panel. Thus, the light source 16 can be replaced with a relatively low LED grade.

10: Backlight unit
12: diffusion sheet
121: base layer
122: first diffusion layer
123: second diffusion layer
15: reflective sheet
151: base layer
152: reflective layer
153: Coating layer
P: light absorber

Claims

A base layer;
A first diffusion layer disposed on one surface of the base layer; And
And a second diffusion layer disposed on the other surface of the base layer,
Wherein at least one of the first diffusion layer and the second diffusion layer includes a light absorbing agent that absorbs light of a predetermined wavelength range.

The method according to claim 1,
Wherein the optical sheet converts a color coordinate of incident light.

3. The method of claim 2,
And the y coordinate change amount (? Y) of the converted color coordinate is -0.010 to -0.003.

The method according to claim 1,
Wherein the brightness of light emitted from said optical sheet is 96% to 100% based on 100% luminance of incident light.

The method according to claim 1,
Wherein the light absorber has an absorption peak at a wavelength band of 580 to 650 nm.

The method according to claim 1,
Wherein the optical absorbent is 0.0007 wt% to 0.002 wt%.

The method according to claim 1,
Wherein the surface roughness (Ra) of the first diffusion layer is different from the surface roughness (Ra) of the second diffusion layer.

8. The method of claim 7,
Wherein the surface roughness (Ra) of the first diffusion layer is from 2.1 to 2.7, and the surface roughness (Ra) of the second diffusion layer is from 1.8 to 2.3.

The method according to claim 1,
Wherein the content of the light absorbing agent contained in the first diffusion layer is higher than the content of the light absorbing agent contained in the second diffusion layer.

The method according to claim 1,
Wherein the first diffusion layer and the second diffusion layer have a thickness of 4 to 10 占 퐉.

Light source; And
And an optical sheet for diffusing the first light emitted from the light source,
In the optical sheet,
A base layer;
A first diffusion layer disposed on one side of the base layer and having the first light incident thereon; And
And a second diffusion layer disposed on the other surface of the base layer and emitting the first light,
Wherein at least one of the first diffusion layer and the second diffusion layer includes a light absorbent that absorbs light of a predetermined wavelength band.

12. The method of claim 11,
Wherein a surface roughness (Ra) of the first diffusion layer is different from a surface roughness (Ra) of the second diffusion layer.

13. The method of claim 12,
Wherein a surface roughness (Ra) of the first diffusion layer is 2.1 to 2.7, and a surface roughness (Ra) of the second diffusion layer is 1.8 to 2.3.

12. The method of claim 11,
Wherein the content of the light absorbing agent contained in the first diffusion layer is higher than the content of the light absorbing agent contained in the second diffusion layer.

12. The method of claim 11,
Wherein the first diffusion layer and the second diffusion layer have a thickness of 4 to 10 mu m.

A backlight unit according to any one of claims 11 to 15; And
And a display panel for generating an image using light whose color coordinates are converted by the optical sheet.