KR20150078300A

KR20150078300A - Diffuser Plate and Back Light Unit Comprising the Same

Info

Publication number: KR20150078300A
Application number: KR1020130167551A
Authority: KR
Inventors: 심상화; 두준길; 정갑하; 김용수
Original assignee: 코오롱인더스트리 주식회사
Priority date: 2013-12-30
Filing date: 2013-12-30
Publication date: 2015-07-08

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diffusion plate and a backlight unit including the same, and more particularly, A core layer and a second skin layer are sequentially laminated to form a multi-layered structure, wherein diffusion, in which the shape, content, and refractive index of the light diffusion particles contained in each layer are different, Plate and a backlight unit including the same.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a diffusion plate and a backlight unit including the diffusion plate.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diffusion plate used in a liquid crystal display (hereinafter referred to as LCD) and a backlight unit including the diffusion plate.

In the case of a liquid crystal display device, a back light unit (BLU: Back Light Unit) is provided on the rear surface thereof because it is not a self light emitting device. Such a backlight unit can be divided into a direct type which is mainly applied to a large size such as a television and a digital information display (DID), an edge type which is mainly applied to a small size such as a monitor and a notebook, and the like .

In particular, recent liquid crystal displays have become slimmer and the number of LEDs as a light source has gradually decreased, so that a backlight unit of a direct-type backlight unit has been required to have a diffusion plate with improved performance compared to a diffusion plate used in the past.

On the other hand, in order to develop a diffusion plate with improved performance compared with the diffusion plate used in the past, a scheme of applying a scattering mechanism to a diffusion plate is considered.

Scattering Mechanism can be divided into two types, one is Rayleigh scattering and the other is Mie Scattering. The two types of scattering mechanisms vary depending on the particle size. When the particle size is similar to the wavelength of light, Rayleigh scattering occurs. When the particle size is equal to the wavelength of light, mie scattering occurs. In general, since the diffusion plate contains particles in the order of μm, Mie scattering occurs.

Assuming that the light of the cross sectional area A is incident on the scattering body (V = A -? X) of the volume V having the thickness DELTA x, if there are N particles per unit volume, There is a particle. In this case, assuming that the radius of a particle is r, the cross-sectional area of each particle is r ² , and assuming that one particle does not enter into the shadow of another particle,

Equation 1

NA = Σ △ xπr ²

However, the scattering cross-sectional area of the light actually affected by the particles and the cross-sectional area of the particles are not exactly the same because light diffuses due to the difference in refractive index between the particles and the medium. The ratio of the two cross-sectional areas for correcting this value is called the extinction factor K. Usually the value of K is greater than 1 because the particle extinction is greater than the expected extinction from the actual size. Therefore, the ratio of the intensity (i) of light that extinguishes after scattering to the intensity (I _o ) of light incident on the scattering body in Mie Scattering is expressed by Equation 2 below.

Equation 2

In Equation (2)

(

: Turbidity) is substituted, and A and DELTA x are eliminated,

Is replaced with Mie extinction coefficient mu, the following equation 3 is obtained.

Equation 3

Equation (3) implies that the turbidity of the diffuser plate is related to the density of the particles (N), the refractive index difference (K) with the base layer and the size of the particles (r).

In this way, the correlation between the diffusing plate and the density, refractive index and size of the particles is more specifically identified, and a study is made on a technique capable of developing a diffusing plate having improved performance compared to the diffusing plate used in the past There is a need.

Disclosure of the Invention The present invention provides a diffusion plate having improved hiding power and diffusibility compared to the conventional diffusion plate.

The present invention also provides a backlight unit including the diffusion plate.

Accordingly, the present invention provides, as a first preferred embodiment, a light emitting device comprising: a first skin layer containing gas-containing light-diffusing particles; A core layer formed on the first skin layer and including light diffusing particles comprising at least one selected from organic particles and inorganic particles; And a second skin layer formed on the core layer and including light diffusing particles comprising at least one selected from organic particles and inorganic particles.

The gas according to this embodiment may be at least one selected from the group consisting of oxygen, nitrogen and air.

The gas-containing light-diffusing particles according to the above embodiments may have a gas content of 30 to 95% by volume.

The gas-containing light-diffusing particles according to the above embodiments may have a size of 5 to 20 μm.

The content of the gas-containing light-diffusing particles in the first skin layer according to the embodiment may be more than 0 wt% and not more than 50 wt%.

The light diffusion particles included in the core layer and the second skin layer according to the embodiment may have a size of 10 mu m or less.

The light diffusion particles according to the embodiment may have a content of more than 0 wt% and less than 50 wt% in the core layer.

The light diffusion particles according to the embodiment may have a content of more than 0 wt% and less than 10 wt% in the second skin layer.

The diffusion plate according to the embodiment may have a thickness of 0.5 to 3 mm.

The thickness of the core layer according to the embodiment may be 80 to 95% of the total thickness of the diffusion plate and the thickness of the first and second skin layers may be 2 to 10% .

The present invention also provides, as a second preferred embodiment, a backlight unit including the diffusion plate.

According to the present invention, it is possible to provide a diffusing plate having improved hiding and diffusibility without lowering brightness compared to the conventional diffusing plate.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 schematically shows a longitudinal section of a diffusion plate according to the present invention. FIG.
2 is a graph showing a distribution curve obtained by measurement using a Gonio photometer (trade name: GC-5000L), which is a standard for evaluating the hiding power and diffusivity of the diffusing plate according to Examples and Comparative Examples of the present invention .

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

The present invention provides a light emitting device comprising: a first skin layer containing gas-containing light-diffusing particles; A core layer formed on the first skin layer and including light diffusing particles comprising at least one selected from organic particles and inorganic particles; And a second skin layer formed on the core layer, the second skin layer including light diffusion particles comprising at least one selected from organic particles and inorganic particles (Fig. 1).

[First Skin Layer]

In the present invention, the first skin layer may include a base resin and a gas-containing light-diffusing particle, wherein the base resin is selected from the group consisting of polystyrene (PS), polycarbonate (PC), polymethyl methacrylate May be at least one selected from the group consisting of polymethylmethacrylate (PMMA), polypropylene (PP), and cyclic olefin copolymer (COC). However, It is not.

The content of the particles in the first skin layer may be greater than 0% by weight and less than 50% by weight. When the content of the particles is 0% by weight, the light hiding ability may be lowered and the light source may be visible on the back surface. Light transmittance and luminance may be lowered.

The gas-containing light-diffusing particles may be in the form of hollow or porous. In consideration of heat insulation and mechanical properties, the gas-containing light-diffusing particles may be filled with one or more gases selected from the group consisting of oxygen, nitrogen and air, Type, the hollow may be in a vacuum state.

When the gas-containing light-diffusing particle is a hollow light-diffusing particle, the inner diameter of the hollow light diffusing particle may be 60 to 98% of the outer diameter of the hollow light diffusing particle in consideration of the heat insulating property of the inner space. In this case, the inner diameter of the hollow light diffusing particle means the length of the longest axis of the cross section of the inner space of the particle.

On the other hand, the inner space of the hollow light diffusing particles or the pores of the porous light diffusing agent may account for 30 to 95% by volume of the light diffusing particles in consideration of the heat insulating property and the mechanical strength.

The gas-containing light-diffusing particles may have a size of 5 to 20 μm. If the size is less than 5 μm, the effect of increasing the hiding power of the LED light is insignificant. At this time, the gas-containing light-diffusing particles are spherical, and the size means the diameter of the particles.

The thickness of the first skin layer may be 2 to 10% of the total thickness of the diffusion plate. If the thickness of the first skin layer is less than 2% of the total thickness of the diffusion plate, the light shielding property is insufficient and the light source of the back surface may be exposed. If the thickness of the first skin layer is more than 10%, the mechanical properties of the light diffusion plate may be weakened.

[Core layer]

In the present invention, the core layer may include light diffusing particles formed on the first skin layer, formed on the first skin layer, and containing at least one selected from organic particles and inorganic particles.

The base resin of the core layer may be selected from the group consisting of polystyrene (PS), polycarbonate (PC), polymethylmethacrylate (PMMA), polypropylene (PP), and cyclic olefin copolymer COC). However, it is not limited to the resin that can be used as the base resin of the diffusion plate.

The organic particles may be at least one selected from the group consisting of polymethylmethacrylate (PMMA), methyl methacrylate-co-styrene, polystyrene, and silicone resin, The inorganic particles may be selected from the group consisting of calcium carbonate (CaCO ₃ ), barium sulfate (BaSO ₄ ), titanium oxide (TiO ₂ ), aluminum hydroxide (Al (OH) ₃ ), silica, glass beads, talc, white carbon, magnesium oxide (MgO), and zinc oxide (ZnO ₂ ).

The light diffusion particles may be contained in the core layer in an amount of more than 0% by weight and 50% by weight or less. If the content of the light diffusion particles is 0% by weight, the light shielding property is insufficient, The light transmittance and the luminance may be lowered.

The size of the light-diffusing particles may be 10 μm or less. If the size is more than 10 μm, the decrease in luminance may be suppressed due to the improvement of the light hiding property, and preferably, the size may be 0.01 to 10 μm. At this time, the light-diffusing particles are spherical, and the size means the diameter of the particles.

The light-diffusing particles may be in the form of a circle or an ellipsoidal shape, but the shape of the light-diffusing particles is not limited thereto, so long as the shape of the particles is not deformed during resin processing and the particle shape can be maintained.

The light diffusing particles included in the core layer may have a refractive index difference of 0.5 or less with respect to the core layer base resin and a difference in refractive index from the first skin layer is more than 0.5.

The light diffusing particles included in the core layer may have a refractive index difference of 0.05 or more with respect to the core layer base resin. If the difference in refractive index from the first skin layer is less than 0.05, light diffusibility due to refraction may be reduced.

The thickness of the core layer may be 80 to 95% of the total thickness of the diffusion plate. If the thickness of the core layer is less than 80% of the total thickness of the diffusion plate, the light diffusibility is insufficient and the luminance uniformity may be lowered. If the thickness is more than 95%, the light shielding property may be insufficient.

[Second Skin Layer]

In the present invention, the second skin layer may include light diffusing particles formed on the core layer and containing at least one selected from organic particles and inorganic particles.

The base resin of the second skin layer may be selected from the group consisting of polystyrene (PS), polycarbonate (PC), polymethylmethacrylate (PMMA), polypropylene (PP), and cyclic olefin copolymer Copolymer (COC)), but it is not limited to a resin that can be used as a base resin of a diffusion plate.

The amount of the light diffusing particles contained in the second skin layer may be greater than 0 wt% and less than 10 wt%. If the content of the light diffusing particles is 0 wt%, the backlight hiding ability may be insufficient, If it is more than 1 wt%, the light transmittance and the luminance may be lowered.

The size of the light-diffusing particles may be 10 μm or less. If the size is more than 10 μm, the size of the light-diffusing particles may be 10 μm or less. If the size is more than 10 μm, May be reduced, and preferably the size may be 0.01 to 10 mu m. At this time, the light-diffusing particles are spherical, and the size means the diameter of the particles.

The thickness of the second skin layer may be 2 to 10% of the total thickness of the diffusion plate. If the thickness of the core layer is less than 2% of the total thickness of the diffusion plate, the light diffusibility is insufficient and the luminance uniformity may be lowered. If the thickness is more than 10%, the light-

As described above, the diffusion plate according to the present invention can be manufactured by coextrusion, in the form of a multi-layer structure in which a first skin layer, a core layer and a second skin layer are sequentially formed.

If the thickness of the diffusion plate is less than 0.5 mm, the mechanical properties may deteriorate. If the thickness of the diffusion plate is more than 3.0 mm, the diffusion plate becomes heavy, .

The diffusion plate as described above has a multi-layer structure. The first skin layer, which is the lowermost layer, includes at least one gas selected from oxygen and nitrogen, and includes light diffusing particles having a size of 5 to 20 탆 to enhance hiding power The core layer and the second skin layer formed on the upper surface of the first skin layer may have a size of 0.01 to 10 times larger than that of the light diffusion particles of the first skin layer so as to diffuse the light coming from the first skin layer without extinction, It is possible to enhance the hiding power and diffusibility compared to the conventional diffusing plate without lowering the luminance by enhancing the diffusibility by including the light diffusing particles as small as about 탆.

Hereinafter, the present invention will be described in more detail with reference to Examples. It is to be understood by those skilled in the art that these embodiments are only for describing the present invention in more detail and that the scope of the present invention is not limited by these embodiments.

&Lt; Example 1 >

1st Skin layer

As a base resin, 80 wt% of a polystyrene resin was mixed with 20 wt% of air-containing light-diffusing particles as gas-containing light-diffusing particles to prepare a first skin layer-forming material.

The air-containing light-diffusing particles have an air content of 60% by volume and a size of 10 탆. The refractive index difference between the air-containing light-diffusing particles and the base resin is 0.2 to 0.3.

At this time, the volume percentage of the gas contained in the gas-containing light-diffusing particles was measured by cutting the gas-containing light-diffusing particles through microtoming using a diamond knife, and measuring the cross-sectional area of the beads through the TEM Next, the gas area was measured with respect to the total area to measure the capacity%.

Core layer

As a base resin, 94 wt% of polystyrene resin and 6 wt% of light diffusion particles were mixed to prepare a material for forming a core layer.

The light-diffusing particles are silicon inorganic particles having a size of 1 to 2 탆, and a refractive index difference between the light-diffusing particles and the base resin is 0.13 to 0.15.

Second Skin layer

As a base resin, 99 wt% of polystyrene resin was mixed with 1 wt% of light diffusing particles to prepare a material for forming a second skin layer.

The light diffusion particles are silicon inorganic particles having a size of 1 to 2 占 퐉, and a refractive index difference between the light diffusion particles and the base resin is 0.13 to 0.15.

The first skin layer forming material, the core layer forming material and the second skin layer forming material were co-extruded to prepare a diffusion plate. The thickness of the diffusion plate was 1.5 mm, and the thickness of the first skin layer The thickness of the core layer is 0.9 mm, and the thickness of the second skin layer is 0.3.

< Example 2 to Example 5>

A diffuser plate was prepared in the same manner as in Example 1, except that the air content of the air-containing light diffusing particles in the first skin layer was changed as shown in Table 1.

< Example 6 and Example 9>

A diffusion plate was prepared in the same manner as in Example 1, except that the size of the air-containing light-diffusing particles in the first skin layer was changed as shown in Table 1.

< Example 10 and Example 13>

A diffusion plate was prepared in the same manner as in Example 1, except that the content of air-containing light-diffusing particles in the first skin layer was changed as shown in Table 1.

< Example 14 and Example 17>

A diffusion plate was prepared in the same manner as in Example 1, except that the size of the light diffusion particles in the core layer was changed as shown in Table 1.

< Example 18 and Example 21>

A diffusion plate was prepared in the same manner as in Example 1, except that the content of the light diffusion particles in the core layer was changed as shown in Table 1.

< Comparative Example 1>

A diffusion plate was prepared in the same manner as in Example 1, except that PMMA light diffusion particles were used instead of air-containing light diffusion particles in the first skin layer.

< Comparative Example 2>

A diffusion plate was prepared in the same manner as in Example 1, except that the light diffusion particles were not used in the second skin layer.

The first skin layer Core layer The second skin layer Air-containing particles Light diffusion particle Light diffusion particle content
(%) size
(탆) Air content
(Volume%) content
(%) size
(탆) content
(%) size
(탆) Example 1 20 10 60 6 5 One One Example 2 20 10 30 6 5 One One Example 3 20 10 90 6 5 One One Example 4 20 10 25 6 5 One One Example 5 20 10 98 6 5 One One Example 6 20 5 60 6 5 One One Example 7 20 20 60 6 5 One One Example 8 20 3 60 6 5 One One Example 9 20 25 60 6 5 One One Example 10 10 10 60 6 5 One One Example 11 40 10 60 6 5 One One Example 12 0 10 60 6 5 One One Example 13 55 10 60 6 5 One One Example 14 20 10 60 6 2 One One Example 15 20 10 60 6 10 One One Example 16 20 10 60 6 One One One Example 17 20 10 60 6 13 One One Example 18 20 10 60 3 5 One One Example 19 20 10 60 50 5 One One Example 20 20 10 60 0 5 One One Example 21 20 10 60 52 5 One One Comparative Example 1 20 10 0 6 5 One One Comparative Example 2 20 10 60 6 5 0 0

Brightness, luminance uniformity, hiding power and diffusibility were measured for the diffuser plate prepared in Examples and Comparative Examples in the following manner, and the results are shown in Table 2.

(1) Brightness

A 32-inch direct-type backlight unit was cut into a size of 720 mm in length and 420 mm in length, and the luminance of 17 points was measured with a BM- " manufactured by TOPCON Co., Ltd. and the average value thereof was measured by luminance.

(2) Brightness uniformity

From the luminance measurement results of (1) above, the luminance uniformity was evaluated from the maximum luminance and the minimum luminance by using the following room. Has the best value when the value is 1.00 according to the following formula, and the luminance uniformity becomes worse as the value becomes larger.

Luminance uniformity = maximum luminance / minimum luminance

(3) Hiding power and diffusing power

The normal distribution curve obtained by measurement using a Gonio photometer (trade name: GC-5000L) is expressed by the transmittance (%) by measuring the light emitted from the light source by angle. The x-axis represents the angle at which light is spread, and the y-axis is the transmittance at each angle.

In the normal distribution curve graph, the half angle represents diffusivity, which means that the higher the value, the higher the diffusivity is when the light source is emitted at 45 ^° and the light is diffused through the diffusion plate.

In the case of occlusion, the maximum tansmittance value is calculated by the transmittance of the light at the half angle.

. This value is expressed in units of%. The smaller the value, the higher the concealment. However, if it is too high, the luminance decreases. (Fig. 2).

Brightness (cd / m ² ) Luminance uniformity Concealment (%) Half angle (°) Example 1 5430 1.36 66.52 52 Example 2 5424 1.35 65.43 49 Example 3 5432 1.36 66.08 56 Example 4 5429 1.33 66.08 47 Example 5 5437 1.33 65.42 53 Example 6 5441 1.24 65.22 47 Example 7 5328 1.38 72.58 54 Example 8 5446 1.22 65.87 45 Example 9 5333 1.35 71.85 51 Example 10 5521 1.29 73.88 45 Example 11 5228 1.40 60.02 56 Example 12 5527 1.24 74.62 43 Example 13 5240 1.37 59.42 53 Example 14 5444 1.35 67.60 46 Example 15 5391 1.41 63.05 57 Example 16 5450 1.32 68.28 43 Example 17 5401 1.37 62.42 54 Example 18 5421 1.36 67.60 49 Example 19 5347 1.38 64.57 54 Example 20 5428 1.33 68.28 44 Example 21 5355 1.35 63.92 51 Comparative Example 1 5435 1.13 59.24 31 Comparative Example 2 5441 1.17 60.02 36

As a result of measurement of physical properties, as shown in Table 2,

When light diffusing particles of PMMA organic material other than air-containing light diffusing particles were used for the first skin layer as in Comparative Example 1, or when light diffusing particles were not used for the second skin layer as in Comparative Example 2, And concealability and diffusibility were decreased.

While the present invention has been particularly shown and described with reference to specific embodiments thereof, those skilled in the art will appreciate that such specific embodiments are merely preferred embodiments and that the scope of the present invention is not limited thereto will be. Accordingly, the actual scope of the present invention will be defined by the appended claims and their equivalents.

10: First skin layer
20: core layer
30: Second skin layer

Claims

A first skin layer containing gas-containing light-diffusing particles;
A core layer formed on the first skin layer and including light diffusing particles comprising at least one selected from organic particles and inorganic particles; And
And a second skin layer formed on the core layer and including light diffusing particles comprising at least one selected from organic particles and inorganic particles.

The method according to claim 1,
Wherein the gas is at least one selected from the group consisting of oxygen, nitrogen and air.

The method according to claim 1,
Wherein the gas-containing light-diffusing particles have a gas content of 30 to 95% by volume.

The method according to claim 1,
Wherein the gas-containing light-diffusing particles have a size of 5 to 20 占 퐉.

The method according to claim 1,
Wherein the content of the gas-containing light-diffusing particles in the first skin layer is more than 0 wt% and not more than 50 wt%.

The method according to claim 1,
Wherein the light diffusion particles contained in the core layer and the second skin layer have a size of 0.01 to 10 mu m.

The method according to claim 1,
Wherein the content of the light diffusion particles in the core layer is more than 0 wt% and not more than 50 wt%.

The method according to claim 1,
Wherein the content of the light diffusion particles in the second skin layer is more than 0 wt% and not more than 10 wt%.

The method according to claim 1,
Wherein the diffusion plate has a thickness of 0.5 to 3 mm.

The method according to claim 1,
The core layer has a thickness of 80 to 95% of the total thickness of the diffusion plate,
Wherein the first skin layer and the second skin layer each have a thickness of 2 to 10% of the total thickness of the diffuser plate.

The method according to claim 1,
Wherein the light diffusion particles are hollow light diffusion particles or porous light diffusion particles.

12. A backlight unit comprising the diffuser plate of any one of claims 1 to 11.