KR100820976B1 - Reflecting sheet, backlight unit and display apparatus including the same, and manufacturing method of reflecting sheet - Google Patents

Abstract

A reflecting sheet, a backlight unit and a display apparatus having the reflecting sheet, and a reflecting sheet manufacturing method are provided to discharge heat generated from a light source and to increase luminance of the backlight unit by using the reflecting sheet having a reflecting layer of high reflectivity and a heat diffusion layer preventing deformation of the reflecting layer. A reflecting sheet(226) is composed of a reflecting layer(310) containing polypropylene and a heat diffusion layer(320) formed on one surface of the reflecting layer to contain heat diffusible matter. The heat diffusible matter is a composition containing graphite powder, a binder, a filler, a dispersing agent, a solvent, and inorganic powder. The inorganic powder is at least one selected from a group comprising aluminum powder, TiO2(Titanium Dioxide), SiO2(Silicon Dioxide), zinc oxide, and silicone carbide.

Description

REFLECTING SHEET, BACKLIGHT UNIT AND DISPLAY APPARATUS INCLUDING THE SAME, AND MANUFACTURING METHOD OF REFLECTING SHEET}

1 is a perspective view illustrating a liquid crystal display device using an edge-light backlight unit according to an exemplary embodiment of the present invention.

FIG. 2 is a cross-sectional view of the liquid crystal display panel of FIG. 1.

3 is a cross-sectional view illustrating a backlight unit of a direct type according to another embodiment of the present invention.

4 is a perspective view illustrating a reflective sheet on which a reflective layer and a thermal diffusion layer are formed according to an exemplary embodiment of the present invention.

5A to 5C are cross-sectional views illustrating a manufacturing process of a reflective sheet according to an exemplary embodiment of the present invention.

The present invention relates to a reflective sheet, a backlight unit including the same, and a display device, and more particularly, to a method of manufacturing a reflective sheet including a reflective layer having a high reflectance.

In general, a liquid crystal display device (hereinafter, referred to as an LCD device) is an electronic device that changes and transmits electrical information generated by various devices to visual information by using a change in liquid crystal transmittance according to an applied voltage. to be.

Such an LCD element is such a display element of various information and does not have its own light source. Therefore, there is a need for a separate device that illuminates the entire screen of the LCD device by installing a light source at the rear thereof. As a device that satisfies such a condition, a back light unit that provides light to the screen of the LCD element is used.

The backlight unit is classified into a direct-lighting method in which the light source is located under the liquid crystal panel and an edge-light method in which the light source is located at the side of the light guide plate according to the location where the light source is installed.

The edge-light backlight unit includes a light source unit, a light guide plate, a reflective sheet, and an optical film.

The light source unit includes one or more light sources and a light source reflector for generating light of a predetermined wavelength. Light generated by the light source is reflected by the light source reflector and the reflective sheet constituted by the reflector. The reflected light is then spread evenly across the light guide plate.

The optical film includes a diffusion sheet, a prism sheet, and a protective sheet.

The function of each component constituting the optical film is briefly described as follows.

Light uniformly diffused in the light guide plate passes through the diffusion sheet. The diffusion sheet diffuses or condenses the light passing through the light guide plate to make the luminance uniform and to widen the viewing angle.

Light passing through the diffusion sheet is significantly reduced in brightness. To prevent this, a prism sheet is used. The prism sheet refracts the light emitted from the diffusion sheet and concentrates the light incident at a low angle toward the front to increase the luminance in the effective viewing angle range.

The protective sheet is located above the prism sheet. Therefore, the function of preventing the scratch of the prism sheet and widening the viewing angle narrowed by the prism sheet.

In order to increase the brightness of the light provided by the LCD element in the backlight unit, a reflective sheet is disposed on the bottom surface of the backlight unit. This is because the light that has not entered the diffusion sheet direction among the light incident on the light guide plate may be reflected by the reflection sheet and may again enter the diffusion sheet direction.

The reflective sheet is generally manufactured using PET (polyethylen terephthalate). However, the reflecting sheet made of PET has a relatively low reflectance, which lowers the efficiency of the backlight unit and lowers the brightness of the LCD element.

An object of the present invention includes a backlight unit capable of effectively dissipating heat generated from a light source and improving luminance by using a reflective sheet including a reflective layer having a high reflectance and a thermal diffusion layer capable of preventing deformation of the reflective layer, and a luminance thereof. It is to provide a display device.

It is also an object of the present invention to provide a method for producing a reflective sheet which can improve the brightness by forming a reflective layer with a high reflectance of polypropylene.

In order to achieve the above object, a display device according to an embodiment of the present invention includes a backlight unit and a liquid crystal display panel for implementing a predetermined image using the light provided by the backlight unit.

The backlight unit may include a light source emitting light of a predetermined wavelength; And a reflective layer reflecting light emitted from the light source and comprising polypropylene; And a reflective sheet including a thermal diffusion layer including a thermal diffusion material on one surface of the reflective layer.

The reflective layer is formed by stretching the polypropylene by adding a blowing agent and barium sulfate (BaSO ₄ ).

The backlight unit and the display device including the same may effectively emit heat generated from a light source and improve luminance by using a reflective sheet including a reflective layer having a high reflectance and a thermal diffusion layer capable of preventing deformation of the reflective layer. .

Hereinafter, with reference to the accompanying drawings will be described in detail preferred embodiments of a reflective sheet, a backlight unit and a display device including the same, and a manufacturing method of the reflective sheet according to the present invention.

1 is a perspective view illustrating a liquid crystal display device using an edge-light backlight unit according to an exemplary embodiment of the present invention, and FIG. 2 is a cross-sectional view of the liquid crystal display panel of FIG. 1.

Referring to FIGS. 1 and 2, a liquid crystal display device (hereinafter referred to as an “LCD device”) 200 may include a liquid crystal panel 210 displaying an image according to a driving signal and a data signal applied from the outside; The backlight unit 220 is disposed on the rear surface of the liquid crystal panel 210 to illuminate the liquid crystal panel 210.

In understanding and practicing the invention, the precise structural characteristics of the liquid crystal panel 210 are not important, and the idea of the present invention can be applied to a wide range of liquid crystal panels commonly used in LCD devices. Therefore, the structure of the liquid crystal panel 210 described below is merely provided as an example for understanding the present invention.

The liquid crystal panel 210 includes an upper substrate 211b and a lower substrate 211a, a color filter 212, a black matrix 217, a pixel electrode 214, a common electrode 215, a liquid crystal layer 216, and a TFT array. 213, and a pair of polarizing films 218a and 218b are disposed on both surfaces of the liquid crystal panel 210.

The color filter 212 includes color filters corresponding to red (R), green (G), and blue (B). When light is applied, the color filter 212 generates an image corresponding to the color of red, green, or blue.

The TFT array 213 switches the pixel electrode 214 as a switching element.

The common electrode 215 and the pixel electrode 214 convert an array of molecules of the liquid crystal layer 216 according to a predetermined voltage applied from the outside.

The liquid crystal layer 216 is composed of a plurality of liquid crystal molecules, and the liquid crystal molecules change an arrangement in accordance with a voltage difference generated between the pixel electrode 214 and the common electrode 215, whereby the backlight unit ( Light provided from 220 is incident on the color filter 212 in response to a change in the molecular arrangement of the liquid crystal layer 216.

The backlight unit 220 is positioned at the rear of the liquid crystal panel 210 and provides light, for example, white light, to the liquid crystal panel 210.

The backlight unit 220 is a direct light source and a lamp positioned below the liquid crystal panel according to a method of installing a light source, for example, a cold cathode fluorescent lamp (hereinafter referred to as “CCFL”). There is an edge-light method located on the side.

Referring back to FIG. 1, the backlight unit 220 is driven by an edge-light method, and includes a light source unit 222, a light guide plate 224, a reflective sheet 226, and an optical film 228. ).

The light source unit 222 is positioned at the side of the backlight unit 220 and includes a light source 222a and a light source reflector 222b.

The light source 222a is formed of a plurality of cold cathode fluorescent lamps (CCFLs) as an aggregate. The CCFL is a lamp that provides very bright white light.

In addition to the CCFL, the light source 222a may be a light emitting diode (LED) or an external electrode fluorescent lamp (EEFL).

The LED can be composed of red, green and blue or a single color of white light. In the case of the backlight unit 220 using the LED as a light source, it is possible to maintain the uniformity of the light while miniaturizing the backlight unit 220 and improving the light efficiency.

The EEFL has a higher luminance than the CCFL and is advantageous in that the electrode is external to operate in parallel. In particular, the EEFL can reduce the number of inverters required by the conventional light source, thereby reducing the cost of components and the weight of the LCD module.

The light source reflector 222b mounts the light source 222a and is intended to improve light efficiency by allowing light from the light source 222a to enter the side of the light guide plate 224. To this end, the light source reflector 222b is made of a highly reflective material, and may coat silver (Ag) on its surface.

The reflective sheet 226 includes a reflective layer 310 and a thermal diffusion layer 320. The reflective layer 310 is disposed under the light guide plate 224 to reflect light from the light source 222a to the front surface of the light guide plate 224.

On the other hand, heat generated in the light source 302 during the light generation process is transferred to the reflective sheet 226 located below. Accordingly, the reflective sheet 226 forms a thermal diffusion layer 320 on the lower surface of the reflective layer to allow the heat transferred to the reflective sheet 226 to be discharged.

The reflective sheet 226 will be described later.

The light guide plate 224 is designed such that continuous total reflection occurs below a critical angle after light is incident on the side surface. Since the light source 222a is located at the side of the backlight unit 220, the light generated from the light source 222a is concentrated at the edge of the backlight unit 220 without being uniformly transmitted. Accordingly, the light guide plate 224 is required to uniformly transmit light to the front surface. The light guide plate 224 is generally made of a transparent acrylic resin such as polymethyl methacrylate (hereinafter referred to as "PMMA"). The PMMA is characterized by high strength, low cracking, low deformation, and high visible light transmittance.

In addition, the light guide plate 224 propagates light toward the liquid crystal panel 210.

The optical film 228 includes a diffusion sheet 228a, a prism sheet 228b, and a protective sheet 228c.

Light emitted from the light guide plate 224 toward the liquid crystal panel 210 passes through the diffusion sheet 228a. The diffusion sheet 228a disperses the light incident from the light guide plate 224 to prevent the light from being partially concentrated. To make the luminance uniform, and to widen the viewing angle.

The light passing through the diffusion sheet 228a is sharply lowered in brightness, and the prism sheet 228b is used to prevent this. The prism sheet 228b collects some of the light diffused or collected by the diffusion sheet 228a in the direction of the protective sheet 228c and reflects the remaining light in the direction of the diffusion sheet 228a.

The protective sheet 228c is located on the prism sheet 228b to prevent scratches of the prism sheet 228b, and also to widen the viewing angle narrowed by the prism sheet 228b.

Meanwhile, the light may be provided to the liquid crystal panel 210 using the backlight unit of the direct type in addition to the above-described edge-light backlight unit 220.

3 is a cross-sectional view illustrating a backlight unit of a direct type according to another embodiment of the present invention.

Referring to FIG. 3, the backlight unit 420 is driven in a direct light method and includes a light source 422, a transparent plate 424, a reflective sheet 226, and an optical film 428. do.

The light source 422 is formed by a plurality of cold cathode fluorescent lamps (CCFL). The CCFL is a lamp that provides very bright white light.

In addition to the CCFL, the light source 422 may include a light emitting diode (LED) or an external electrode fluorescent lamp (EEFL).

The LED can be composed of red, green and blue or a single color of white light. In the case of the backlight unit 420 using the LED as a light source, it is possible to maintain the uniformity of the light while miniaturizing the backlight unit 420 and improving the light efficiency.

The EEFL has a higher luminance than the CCFL and is advantageous in that the electrode is external to operate in parallel. In particular, the EEFL can reduce the number of inverters required by the conventional light source, thereby reducing the cost of components and the weight of the LCD module.

The reflective sheet 226 includes a reflective layer 310 and a thermal diffusion layer 320. The reflective layer 310 is positioned below the transparent plate 424 to reflect light from the light source 222a to the front surface of the transparent plate 424.

On the other hand, heat generated in the light source 302 during the light generation process is transferred to the reflective sheet 226 located below. Accordingly, the reflective sheet 226 forms the thermal diffusion layer 320 on the lower surface of the reflective layer 310 to allow the heat transferred to the reflective sheet 226 to be emitted.

The reflective sheet 226 will be described later.

On the other hand, the light source 422 is mounted by placing a light source reflector (not shown) under the light source 422 instead of the reflective sheet 226, and the light emitted from the light source 422 is incident on the diffusion sheet 428a to provide light efficiency. It can also be configured to improve. The light source reflector is made of a highly reflective material, and may be coated with silver (Ag) on the surface.

The transparent plate 424 passes light incident from the light source 422. The transparent plate 424 preferably uses polymethyl methacrylate (PMMA).

Unlike the edge-lighting method of the backlight unit 420 of the direct method, since the plurality of light sources 422 are positioned under the liquid crystal panel 210, the bright lines generated from the light source 422 are disposed on the upper part of the liquid crystal panel 210. Will appear in a pattern. The transparent plate 424 has a pattern, and serves to pass light while removing bright lines generated from the light source 422. However, of course, the backlight unit 420 according to the present invention may use a transparent plate on which a pattern is not formed.

The optical film 428 includes a diffusion sheet 428a, a prism sheet 428b, and a protective sheet 428c.

Light emitted from the transparent plate 424 toward the liquid crystal panel 210 passes through the diffusion sheet 428a. The diffusion sheet 428a diffuses the light incident from the transparent plate 424 to partially condense the light. To prevent and make the luminance uniform.

The light passing through the diffusion sheet 428a is sharply lowered in brightness, and the prism sheet 428b is used to prevent this. The prism sheet 428b collects some of the light diffused or collected by the diffusion sheet 428a in the direction of the protective sheet 428c and reflects the remaining light in the direction of the diffusion sheet 428a.

The protective sheet 428c is positioned on the prism sheet 428b to prevent scratches of the prism sheet 428b and also to widen the viewing angle narrowed by the prism sheet 428b.

Hereinafter, the light emission operation of the LCD element 200 will be described in detail.

Referring back to FIG. 2, the backlight units 220 and 420 provide planar light, which is white light, to the liquid crystal panel 210.

Subsequently, the TFT array 213 switches the pixel electrode 214.

Subsequently, a predetermined voltage difference is applied between the pixel electrode 214 and the common electrode 215, and as a result, the liquid crystal layer 216 is arranged corresponding to the red color filter, the green color filter, and the blue color filter, respectively.

In this case, the light provided from the backlight units 220 and 420 passes through the liquid crystal layer 216, and the light amount is adjusted, and the light with the adjusted light amount is provided to the color filter 212.

As a result, the color filter 212 implements an image with a predetermined gray scale.

In detail, the red color filter, the green color filter, and the blue color filter form one pixel, and the pixels implement a predetermined image by a combination of light passing through the red color filter, the green color filter, and the blue color filter. do.

Hereinafter, the configuration of the reflective sheet 226 and the manufacturing method thereof according to the present invention will be described in detail.

4 is a perspective view illustrating a reflective sheet on which a reflective layer and a thermal diffusion layer are formed according to an exemplary embodiment of the present invention. 5A to 5C are cross-sectional views illustrating a manufacturing process of a reflective sheet according to an exemplary embodiment of the present invention.

Referring to FIG. 4, the reflective sheet 226 includes a reflective layer 310 and a thermal diffusion layer 320.

The reflective layer 310 is produced by dispersing bubbles for scattering light in a sheet made of synthetic resin such as polypropylene (PP).

More specifically, as shown in FIG. 5A, after the foaming agent and the inorganic material are added to the polypropylene sheet 300, the polypropylene sheet 300 is stretched in the uniaxial direction to form the reflective layer 310. .

The blowing agent is an additive for blending with the polymer to produce a porous foam such as sponge or styrofoam. Types of blowing agents are classified into solvent types (butane, propane and freon gas) used for physical foaming and reaction types used for chemical foaming. In addition, in the case of pure blowing agents, the decomposition temperature is too high to lower the foaming temperature and activate the foaming agent. The kicker responsible for this is used. The kind of kicker is a polyol, urea, amine, salts and metal compounds such as lead, zinc, cadmium, and the like, pigments or fillers generally play a role. Although the raw materials and composition ratio of the blowing agent vary depending on the type of the product, in general, hydrazine hydride (Hydrazine Hydrate) occupies 63%, and other caustic soda, urea, liquid chlorine, hexamine (Hexamine) and the like are used.

As the type of blowing agent, ADCA (Azodicarbonamide), modified ADCA, OBSH, DPT, TSH or PTSS may be used.

The inorganic material is a material added to increase the reflectance of the reflective layer 310, for example, barium sulfate (BaSO ₄ ) or the like.

As described above, when the foaming agent and the inorganic material are added to the polypropylene sheet 300 and then stretched in the uniaxial direction, as shown in FIG. 5B, the reflective layer 310 having the bubbles 312 dispersed therein is formed. do.

On the other hand, when the polypropylene sheet 300 is stretched in one axial direction, the polypropylene sheet 300 may be twisted in a direction perpendicular to the stretched direction. This is because there is a high possibility of shrinkage due to heat due to the nature of the polypropylene.

Accordingly, the thermal diffusion layer 320 is formed under the reflective layer 310 to prevent deformation of the reflective layer 310.

In addition, the thermal diffusion layer 320 is formed to dissipate heat transferred to the reflective sheet 226.

More specifically, as shown in FIG. 5C, a composition for forming the thermal diffusion layer 320 is applied or adhered to the bottom of the reflective layer 310, and then dried to form the thermal diffusion layer 320.

The thermal diffusion layer 320 may have excellent thermal conductivity to effectively absorb heat transferred to the reflective sheet 226.

As such, the thermal diffusion layer 320 formed on the surface of the reflective layer 310 may effectively diffuse heat generated from the light sources 222a and 422 to prevent the temperature of the light sources 222a and 422 from being excessively increased.

Accordingly, even when the LCD element is driven for a long time, the light sources 222a and 422 maintain a temperature at which the best efficiency can be achieved.

In addition, the thermal diffusion layer 320 may prevent deformation of the reflective layer 310.

The composition forming the thermal diffusion layer 320 is a liquid mixture comprising graphite powder, inorganic powder, binder, hardener, and filler. In addition, the liquid mixture may further include a dispersant and a solvent. Preferably, the liquid mixture further comprises a leveling agent, a wetting agent, a polyvalent basic acid and an acid anhydride.

The inorganic powder is composed of at least one material selected from the group consisting of aluminum (Al) powder, TiO ₂ , SiO ₂ , zinc oxide, and silicon carbide.

The binder is preferably a material having excellent thermal conductivity and heat resistance, such as polyester resin, urethane resin, epoxy resin, acrylic resin and the like.

More specifically, the binder includes a polyester resin having a carboxyl end group, a polyester resin having a hydroxyl end group, an epoxy resin having an oxirane functional group, an acrylic resin having a carboxyl end group, and a hydroxyl end group. It is made of at least one material selected from the group consisting of an acrylic resin having, an acrylic resin having a GMA end group and a urethane resin.

The binder integrates the graphite powder particles. Therefore, even though an external impact is applied to the thermal diffusion layer 320, the binding of the graphite powder particles is not released by the binder, and thus the thermal diffusion layer 320 is not easily broken.

The curing agent allows the composition applied or adhered to the reflective layer 310 to be easily dried and cured. The curing agent includes an epoxy resin curing agent having an oxirane group, a TGIC (triglycidyl isocyanurate) curing agent having an oxirane group, a curing agent having an isocyanate group, a curing agent having a blocked isocyanate group, a curing agent having an carboxyl end group, and an epoxide. At least one curing agent selected from the group consisting of aliphatic and aromatic curing agents comprising an anhydride reactor.

As a material to help the filler heat diffusion, it is made of one or more materials selected from the group consisting of Al ₂ O ₃ , Al, BN and Ag coated Cu.

Cu is likely to be oxidized when making the composition. Thus, when Cu is oxidized, the performance of the composition may be lowered. Therefore, Cu is preferably coated with Ag. Of these filler materials, preferably BN is used.

The dispersant comprises at least one material selected from the group consisting of polyamineamides, phosphoric acid esters, polyisobutylene, oleic acid, stearic acid, fish oil, ammonium salts of polycarboxylic acids and sodium carboxymethyl.

The solvent may be an alcohol-based material having a low freezing point.

The leveling agent may use a polyacrylate-based leveling agent.

The thermal diffusion layer 320 formed of such a composition is excellent in thermal stability, mechanical properties (ductility and tensile strength) as well as thermal conductivity. Therefore, the heat of the reflective sheet 226 can be diffused effectively and released.

On the other hand, the reflective sheet 226 as described above is not limited to the LCD element, it can be used in the plasma display panel (PDP), the organic electroluminescent element (OLED) is a matter of course.

Preferred embodiments of the invention described above have been disclosed for purposes of illustration. Therefore, those skilled in the art having ordinary knowledge of the present invention will be capable of various modifications, changes, and additions within the spirit and scope of the present invention, and such modifications, changes and additions should be regarded as belonging to the following claims.

As described above, the backlight unit and the display device including the same according to the present invention effectively utilize heat generated from a light source by using a reflective sheet including a reflective layer having a high reflectance and a thermal diffusion layer capable of preventing deformation of the reflective layer. There is an advantage that can emit, and improve the brightness.

In addition, the manufacturing method of the reflective sheet according to the present invention has the advantage of improving the luminance by forming a reflective layer with a high reflectance of polypropylene.

Claims (14)

A reflective layer comprising polypropylene; And Reflective sheet, characterized in that it comprises a thermal diffusion layer containing a thermal diffusion material on one surface of the reflective layer. The method of claim 1, The thermal diffusion material is a composition comprising a graphite powder, a binder, a filler, a binder, a dispersant and a solvent. The method of claim 2, The thermal diffusion material further comprises an inorganic powder. The method of claim 3, wherein The inorganic powder is at least one material selected from the group consisting of aluminum (Al) powder, TiO ₂ , SiO ₂ , zinc oxide (Zinc Oxide) and silicon carbide. The method of claim 1, The reflective layer is formed by adding a blowing agent and an inorganic substance to the polypropylene and stretching the same. The method of claim 5, wherein The inorganic material is a reflective sheet, characterized in that the barium sulfate (BaSO ₄ ). A light source emitting light of a predetermined wavelength; A reflective layer reflecting light emitted from the light source and comprising polypropylene; And a reflective sheet including a thermal diffusion layer including a thermal diffusion material on one surface of the reflective layer. The method of claim 7, wherein The thermal diffusion material is a backlight unit, characterized in that the composition comprising a graphite powder, an inorganic powder, a binder, a filler, a binder, a dispersant and a solvent. The method of claim 8, The inorganic powder is at least one material selected from the group consisting of aluminum (Al) powder, TiO ₂ , SiO ₂ , zinc oxide (Zinc Oxide) and silicon carbide. The method of claim 7, wherein The reflective layer is formed by stretching by adding a blowing agent and barium sulfate (BaSO ₄ ) to the polypropylene. A light source emitting light of a predetermined wavelength; A reflective layer reflecting light emitted from the light source and comprising polypropylene; And a reflection sheet including a heat diffusion layer including a heat diffusion material on one surface of the reflection layer. And It includes a liquid crystal display panel for implementing a predetermined image using the light provided by the backlight unit, And the reflective layer is formed by adding a blowing agent and barium sulfate (BaSO ₄ ) to the polypropylene. Adding a blowing agent and an inorganic substance to the polypropylene substrate and stretching the same to form a reflective layer; And And forming a thermal diffusion layer by applying a thermal diffusion material to one surface of the reflective layer. The method of claim 12, The inorganic material is a method of manufacturing a reflective sheet, characterized in that the barium sulfate (BaSO ₄ ). The method of claim 13, In the forming of the reflective layer, the polypropylene substrate is stretched in one axial direction.

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