KR20110108146A - Diffuser plate and backlight unit assembly comprising the same - Google Patents

Abstract

The present invention relates to a light diffusion plate having excellent heat insulating properties used in a liquid crystal display device and a backlight unit assembly using the same, wherein the occurrence of egg phenomena is reduced due to the excellent heat insulating properties, and the light diffusing plate having improved light diffusing properties and the same It relates to a used backlight unit assembly.

Description

Diffuser Plate and Backlight Unit Assembly Comprising the Same}

The present invention relates to a light diffusion plate used in a liquid crystal display and a backlight unit assembly including the same.

A liquid crystal display used as an optical display element is an indirect light emission method of controlling the transmittance of an external light source to display an image, and a backlight unit, which is a light source device, is used as an important component for determining characteristics of a liquid crystal display.

The backlight unit sequentially passes the light emitted by using a light source such as a cold cathode fluorescent lamp (CCFL) through a light guide plate or a diffusion plate, a diffusion sheet, and a prism sheet to reach the liquid crystal panel. Here, the light guide plate is mounted in the case of an edge-type backlight unit, and the light emitted from the light source is transmitted to be distributed on the front surface of the flat liquid crystal panel, and the diffuser plate is mounted in the case of the direct view backlight unit. As a support of the film, it serves to diffuse the light so that the light emitted from the light source can be seen uniformly when viewed from the front. The diffusion sheet serves to obtain a uniform light intensity over the entire screen and to conceal a device such as a light source mounted under the diffusion member from being seen from the front. On the other hand, the prism sheet performs a light path control function for converging light rays from various directions passing through the diffusion member within a range of viewing angle θ suitable for the viewer to recognize the image to be collected. In addition, the lower portion of the light guide plate or the diffusion plate is provided with a reflective sheet for increasing the efficiency of use of the light source by being reflected back to the light that is not delivered to the liquid crystal panel and out of the path.

The diffusion plate contains an inorganic diffusion agent inside the base resin, and the film-based optical sheet, such as a prism sheet or a diffusion sheet, is placed on the top surface, focusing on simply diffusing the light of the line light source on the lower surface to be close to the surface light source. It will additionally serve as a support to prevent sagging.

If the diffuser plate is exposed to a large amount of moisture and then mounted and driven in the backlight unit, the moisture on the lower surface of the diffuser plate evaporates first by the heat from the light source, so that the diffuser plate is bent to the front side of the backlight unit and the thin liquid crystal module located at the front side. By pressing the partial difference in the thickness of the liquid crystal generated in the center of the difference in brightness (Egg Mura) is shown (Fig. 1).

This egg mura phenomenon appears on the front when watching the LCD TV for a long time in a high temperature and high humidity, causing a decrease in image quality.

In order to improve this, a liquid crystal module manufacturer or a liquid crystal TV manufacturer strongly presses and tightens the upper part when laminating the diffusion plate and the optical sheet to prevent warpage of the optical member that may occur in the future, or to prevent warpage by minimizing the water absorption of the optical member, By optimizing the resin, we are trying to minimize the egg mura by increasing the force to return to its original form given the conditions of high temperature and humidity.

An object of the present invention is to provide a light diffusion plate having excellent thermal insulation properties capable of preventing occurrence of an egg mura phenomenon occurring in a liquid crystal display device in a high temperature and high humidity environment.

In addition, the present invention is to provide a backlight unit assembly using a light diffusion plate having excellent heat insulating properties.

Accordingly, the present invention provides a light diffusing plate comprising a base resin and a light diffusing agent as a first preferred embodiment, wherein the light diffusing agent has an internal space and the material is a polymer. do.

The light diffusing agent according to the embodiment may be at least one of a hollow light diffusing agent and a porous light diffusing agent.

The internal space according to the embodiment may include air or nitrogen (N ₂ ).

The light diffusing agent according to the embodiment may be in the form of a bead (bead) or ellipsoidal shape.

The inner diameter of the hollow light diffusing agent according to the embodiment may be 60 to 98% of the outer diameter of the hollow light diffusing agent.

The internal space according to the embodiment may be 30 to 95% (v / v) of the light diffusing agent.

The content of the light diffusing agent according to the embodiment may be 0.001 to 10 parts by weight based on 100 parts by weight of the base resin.

The present invention provides a backlight unit assembly including an optical diffusion plate having an inner space and a polymer thereof as a second preferred embodiment.

1 is a photograph showing an egg mura phenomenon in a liquid crystal.
Figure 2 is a preferred embodiment of the present invention, the light diffusion plate containing a light diffusing agent in the upper and lower portions of the base resin, a schematic diagram of the cross-section (a), an enlarged photo (b) and a surface photograph ( c) is shown.
Figure 3 is a preferred embodiment of the present invention, a light diffusing plate including a light diffusing agent in the entire base resin, showing a schematic diagram (a) of the cross section and a photograph (b) to enlarge a portion of the cross section.
4 shows a schematic view of a cross section of a light diffusing plate in which a light diffusing agent is included in a central portion of the base resin.
5 is another preferred embodiment of the present invention, a light diffusing plate including a light diffusing agent in the upper portion of the base resin, a schematic diagram (a) of the cross section of the light diffusing plate containing the light diffusing agent in the upper portion of the base resin, The schematic (b) of the cross section of the light-diffusion plate containing a light-diffusion agent in the lower part, and the enlarged photograph (c) are shown.

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

As a preferred embodiment, the present invention provides a light diffusing plate comprising a base resin and a light diffusing agent, wherein the light diffusing agent has an internal space and the material is a polymer. .

The light diffusing agent is at least one or more of a hollow light diffusing agent and a porous light diffusing agent, the light diffusing plate according to the present invention is improved thermal insulation properties due to the internal space formed in the form of hollow or pores formed in the light diffusing agent Based on the principle of

The light diffusing agent may be a polymer such as PMMA, Silicon, etc. in order to enable formation of an internal space. In addition, the base resin of the light diffusion plate is polystyrene (PS), polycarbonate (PC), polymethylmethacrylate (PMMA), polypropylene (PP), and cyclic olefin copolymer (Cyclic). Olefin Copolymer, COC) may be one or more polymers.

If the light diffusing agent is made of a material such as ceramic, glass or silica, and the base resin of the light diffusing plate is a polymer as described above, the flow of the light diffusing agent is poor in the base resin of the light diffusing plate, so that the light diffusing agent is the base. There is a problem in that the optical properties, heat resistance characteristics, etc. of the light diffusion plate produced by gathering in a specific site is not well mixed in the resin.

However, when the light diffusing agent and the polymer of the base resin of the light diffusing plate are similar polymers, the flowability of the light diffusing agent is improved in the base resin of the light diffusing plate, which has the advantage of high uniformity of brightness and heat resistance characteristics.

The pores of the hollow or porous light diffusing agent of the hollow light diffusing agent according to the present invention is preferably filled with air, nitrogen (N ₂ ), etc. in consideration of improving the thermal insulation properties, in particular the hollow of the hollow light diffusing agent May be in a vacuum state.

On the other hand, when a mixture of a hollow light diffusing agent and a porous light diffusing agent is used in combination, the mixing ratio of the hollow light diffusing agent and the porous light diffusing agent is preferably 1:99 to 99: 1 in consideration of improving the thermal insulation property. More preferably, the mixing ratio may be 60:40 to 90:10.

In addition, the light diffusing agent is preferably in the form of a bead or an ellipsoid in view of securing a heat insulating property by diffusing light from a light source and in a uniform form on the front surface. It is not limited to this form. The light diffusing agent in a crushed form other than the bead shape or the elliptical form also has a problem in that the internal space is also crushed, so that it is difficult to secure proper thermal insulation properties.

In addition, the outer diameter of the light diffusing agent is also preferably 2 ~ 500㎛ in consideration of the light diffusion characteristics, more preferably 5 ~ 100㎛ in consideration of the optimization of the light diffusion characteristics. In this case, the outer diameter means the length of the longest axis of the light diffusing agent cross section, and for example, refers to the length of the longest axis of the circle or ellipse which is the cross section of the light diffusing agent in the form of beads or ellipsoids.

At this time, the inner diameter of the hollow light diffusing agent, that is, the diameter of the inner space is preferably 60 to 98% of the outer diameter of the hollow light diffusing agent in consideration of the heat insulating properties. In addition, the inner diameter also means the length of the longest axis of the light diffusing agent inner space cross-section, the cross section of the light diffusing agent inner space in the form of beads or ellipsoidal sphere refers to the length of the longest axis of the circle or ellipse.

On the other hand, the inner space of the hollow light diffusing agent or the pores of the porous light diffusing agent occupies 30 to 95% (v / v) of the light diffusing agent in consideration of the heat insulating properties, the light diffusing agent inner space The refractive index of is 1.0-1.3, which is different from the refractive index of 1.4-1.6 of the polymer constituting the base resin, and thus has excellent light diffusing characteristics due to the difference in refractive index.

The content of the light diffusing agent is preferably 0.001 to 10 parts by weight with respect to 100 parts by weight of the base resin in consideration of the improvement of the light diffusion properties, and 0.01 to 5 parts by weight in consideration of optimization of the light diffusion properties.

The light diffusing plate may be prepared by co-extrusion of a hollow light diffusing agent or a porous light diffusing agent in the base resin, the light diffusing agent of the entire base resin; Upper and lower base resins; Central portion of base resin; An upper portion of the base resin; The light diffusion plate may be manufactured by being positioned at the lower portion of the base resin.

For example, as shown in FIG. 2, when the bead-shaped light diffusing agent is positioned above and below the base resin of the light diffusing plate, the light diffusing agent exists in a layered form on each of the top and bottom of the base resin. (A) and (b) of FIG. 2, the surface of the light diffusing plate exhibits an uneven shape due to the light diffusing agent in the form of beads (FIG. 2C).

In addition, when the bead-shaped light diffusing agent is located throughout the base resin of the light diffusion plate, as shown in Figure 3, the light diffusing agent is present in the form dispersed in the base resin (Fig. 3 (a) and (b) As shown in FIG. 4, when the light diffusing agent is located at the center of the base resin of the light diffusing plate, a bead-shaped light diffusing agent is present in the form of a layer.

In addition, as shown in FIG. 5, when the bead-shaped light diffusing agent is located above or below the base resin of the light diffusion plate, the upper part of the bead-shaped light diffusing agent base resin (FIGS. 5A and 5B) may also be used. Or at the bottom, respectively, in layers (FIG. 5C).

The present invention can also provide a backlight unit assembly that minimizes the occurrence of egg mura by applying the light diffusion plate having the internal space as described above to the backlight unit assembly.

That is, in the backlight unit assembly, a light diffusing plate is positioned on a light source. When using a light diffusing plate including a hollow light diffusing agent or a porous light diffusing agent having the internal space, heat generated from the light source is blocked and Since the thermal expansion of the diffusion plate does not occur, the light diffusion plate is bent to the front to generate the egg mura or transferred to the optical sheet of the film substrate on the upper surface of the light diffusion plate to prevent the film from bending.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the scope of the present invention is not limited to the following Examples.

<Examples 1-5>

Co-extruded 100 parts by weight of the base resin to include 3 parts by weight of the light diffusing agent to prepare a light diffusing plate including the base resin layer and the light diffusing agent layer, the entire base resin (Example 1), the central portion (Example 2) Co-extrusion was carried out so that the light-diffusing agent was included in the upper and lower parts (Example 3), the upper part (Example 4) and the lower part (Example 5). In this embodiment, the base resin is polystyrene (PS), polycarbonate (PC), polymethylmethacrylate (PMMA), polypropylene (PP) and cyclic olefin copolymer ( In the case of Cyclic Olefin Copolymer, COC, a light diffusion plate was manufactured by co-extrusion to include a commercially available PMMA diffusing agent (Matsumoto Microsphere M600, Japan) as a hollow light diffusing agent. Physical properties of the PMMA diffusing agent, which is a hollow light diffusing agent, are as shown in Table 1 below.

<Example 6>

As a hollow light diffusing agent sold as a light diffusing agent in Example 1, a PMMA diffusing agent (Matsumoto Microsphere M600, Japan) and a porous diffusing agent (HPDL-040, Daejeong Gold Co., Ltd.) at a ratio of 70:30 A light diffuser plate was manufactured in the same manner except that it was included. The physical properties of the PMMA diffusing agent and the porous light diffusing agent which is a hollow light diffusing agent are as shown in Table 1 below.

material Interior space shape Light diffusing agent
Outer diameter Light diffusing agent
Bore
(Inner space
diameter) Light diffusing agent
Internal refractive index Hollow
Light diffusing agent PMMA air Bead 50 탆 35 μm 1.2 Porosity
Light diffusing agent PMMA air Bead 15 μm - 1.25

Comparative Example 1

Base resins such as polystyrene (PS), polycarbonate (PC), polymethylmethacrylate (PMMA), polypropylene (PP), cyclic olefin copolymer (Cyclic Olefin Copolymer, COC) Each extruded to 1.5mm to prepare a pure resin light diffusion plate.

Comparative Example 2

The light diffusion plate including the base resin layer and the light diffusing agent layer was prepared by co-extrusion so that 3 parts by weight of the light diffusing agent was included in 100 parts by weight of the base resin. At this time, the base resin is polystyrene (PS), polycarbonate (PC), polymethylmethacrylate (PMMA), polypropylene (PP) and cyclic olefin copolymer (Cyclic Olefin Copolymer, COC) was co-extruded to include a PMMA light diffusing agent as a light diffusing agent to prepare a light diffusing plate. The PMMA light diffusing agent is in the form of beads in which no internal space is formed.

The thicknesses of the light diffusing plate, base resin layer and light diffusing agent layer prepared in Examples and Comparative Examples are as shown in Table 2 below.

Light diffusing agent
Inclusion Form thickness Base resin layer Light diffusion layer Light diffusion plate Example 1 Base resin layer whole - 1.5mm 1.5mm Example 2 Base resin layer
center 1.0mm 0.5mm 1.5mm Example 3 Base resin layer
Top and bottom 1.1mm Upper part: 0.2mm
Bottom: 0.2mm 1.5mm Example 4 Base resin layer
Top 1.3 mm 0.2mm 1.5mm Example 5 Base resin layer
bottom 1.3 mm 0.2mm 1.5mm Example 6 Base resin layer whole - 1.5mm 1.5mm Comparative Example 1 Light diffusing agent
Not included 1.5mm - 1.5mm Comparative Example 2 Base resin layer
Top and bottom 1.1mm Upper part: 0.2mm
Bottom: 0.2mm 1.5mm

In addition, the surface temperature of the light diffusion plate obtained through the Examples and Comparative Examples was measured as follows.

(1) temperature

The light diffuser plates prepared in Examples and Comparative Examples were mounted on the LCD backlight unit, and the backlight was operated for 3 hours, and then the temperature of the upper surface of the light diffuser plate was measured using a non-contact temperature meter (FLIR Systems A20M). The results are shown in Table 3. At this time, the temperature of the upper surface is made into the average after measuring the temperature of nine places among the upper surfaces of a light-diffusion plate.

With light diffusing agent
Formation method Type of base resin polystyrene Poly
Carbonate Polymethyl meta
Acrylate Polypropylene Cyclic Olefin Copolymer Example 1 Base resin layer 41 ℃ 42 ℃ 41 ℃ 41 ℃ 43 ℃ Example 2 Base resin layer center
(1mm) 43 ℃ 43 ℃ 42 ℃ 43 ℃ 43 ℃ Example 3 Upper and lower base resin layers
(Each 200 μm) 45 ℃ 45 ℃ 46 ℃ 45 ℃ 46 ℃ Example 4 Base resin layer top
(200 μm) 47 ℃ 47 ℃ 48 ℃ 47 ℃ 48 ℃ Example 5 Lower base resin layer
(200 μm) 46 ℃ 45 ℃ 46 ℃ 46 ℃ 47 ℃ Example 6 Base resin layer 42 ℃ 43 ℃ 42 ℃ 42 ℃ 42 ℃ Comparative Example 1 Light diffusing agent
Not included 48 ℃ 51 ℃ 50 ℃ 49 ℃ 51 ℃ Comparative Example 2 Upper and lower base resin layers 48 ℃ 51 ℃ 51 ℃ 49 ℃ 50 ℃

As a result of measuring the upper surface temperature of the light diffusing plate, the light diffusing plate according to the embodiment of the present invention has a lower upper surface temperature than the comparative example and has excellent thermal insulation properties, thereby reducing the occurrence of egg mura phenomenon in the backlight unit assembly. It turned out that it is advantageous as an optical component which exists.

That is, since the LCD backlight unit, which is a light source, is located under the light diffusion plate, the upper surface temperature of the light diffusion plate is measured, and the lower the upper surface temperature is, the better the thermal insulation property is. The light diffusion agent is included in the base resin layer. The upper surface temperature of the light diffusing plates of Examples 1 to 5 is 41 ° C. to 47 ° C., and the upper part of the light diffusing plate containing the pure resin or the general PMMA light diffusing agent of Comparative Example 1 or 2 is included in the base resin layer. It appeared to be lower than surface temperature 48-51 degreeC.

In addition, in the results of Examples 1 to 5, Comparative Example 1, which does not include the light diffusing agent, regardless of which part, such as the entire, central, upper, lower, upper, lower portion of the base resin based on the base resin And a lower upper surface temperature compared to Comparative Example 2 including a light diffusing agent in which no internal space was formed.

In addition, as can be seen from the results of Example 6, even when the hollow light diffusing agent and the porous light diffusing agent are used in combination, the upper surface temperature was lower than that of Comparative Example 1 and Comparative Example 2.

Therefore, it was found that the light diffusing plate including the light diffusing agent having the internal space is superior to the heat diffusing plate including the pure resin and the light diffusing agent having no internal space.

In particular, when the light diffusing plate including the light diffusing agent according to the embodiment is applied to the backlight unit assembly, the egg diffusion phenomenon is prevented by blocking thermal expansion of the light diffusing plate by the light source due to the heat insulating property of the light diffusing plate. It can be seen that the backlight unit assembly can be manufactured to be minimized.

Claims (8)

In the light diffusion plate containing a base resin and a light diffusing agent,
The light diffusing agent is a light diffusing plate, characterized in that the inner space is formed, the material is a polymer.
The light diffusing plate of claim 1, wherein the light diffusing agent is at least one of a hollow light diffusing agent and a porous light diffusing agent.
The light diffusing plate of claim 1, wherein the internal space comprises air or nitrogen (N ₂ ).
The light diffusing plate of claim 1, wherein the light diffusing agent is in the form of a bead or an ellipsoid.
The light diffusing plate of claim 2, wherein an inner diameter of the hollow light diffusing agent is 60 to 98% of an outer diameter of the hollow light diffusing agent.
The light diffusing plate of claim 1, wherein the internal space is 30 to 95% ( v / v ) of the light diffusing agent.
The light diffusing plate of claim 1, wherein the light diffusing agent is 0.001 to 10 parts by weight based on 100 parts by weight of the base resin.
The backlight unit assembly of claim 1, wherein the internal space of any one of claims 1 to 7 is formed, and the light diffusion plate is formed of a polymer.

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