KR20050116575A - Diffuser film for high luminance lcd backlight - Google Patents

Abstract

In the present invention, the lenticular organic particles having an average particle diameter of 1 to 50 μm and the ratio of the long and short diameters are 1: 1 to 5: 1 and the spherical organic particles having a ratio of the long and short diameters of less than 1.1: 1 are from 1:10 to 50. A light diffusing layer comprising organic particles mixed in a 10: 1 weight ratio, wherein the ratio of the total organic particles is 50 to 350 parts by weight based on 100 parts by weight of the binder, and the thickness thereof is 1 to 50 µm is laminated on at least one surface of the base film. It provides a diffusion film for a backlight unit of the liquid crystal display obtained by, which can ensure a high brightness by increasing the brightness in the vertical direction due to the light condensing effect of the lenticular particles.

Description

Diffuser film for high luminance LCD backlight

The present invention relates to a diffuser film for a backlight unit of a liquid crystal display, and more particularly, to a diffuser film for a backlight unit of a liquid crystal display having improved brightness by providing a light diffusion layer using a mixture of lenticular organic particles and spherical particles as organic particles. It is about.

In recent years, the development of display technology has revolutionized the development of large-screen, low-power and high-brightness LCD displays.

In order to cope with such demands, various studies are being conducted on liquid crystal modules and backlight components which are components of TFT-LCDs. In the backlight unit, large screen, low power, and high brightness are in progress. Recently, many attempts have been made to eliminate the backlight unit.However, due to the basic characteristics of LCDs, it is not possible to form a screen without a separate light source like an LED device that emits light. This is impossible.

In the backlight unit, the light diffusion film plays a role of diffusing the light of the lateral light source lamp on one side or the back of the LCD display to the entire screen and refracting the light into a uniform light in the front direction. In addition, reflective films, light guide plates, and pre-pain films are used to perform their respective roles, and the intensity of light from the initial light source is gradually offset by the other mediums above, so that the brightness on the screen as we see It is only one hundredth of the original light source. Many attempts have been made to solve this problem. For example, there are methods of increasing the brightness of the light source, reducing the thickness of each of the light guide plate, the reflecting film, the prism, and the diffuser plate. There is a limit to reducing Recently, attempts have been made to change the patterning of the light guide plate in various ways.

Among them, the light diffusion film plays a role of spreading light evenly using particles having good diffusion efficiency, and many attempts have been made for high brightness such as particle selection and coating thickness or antireflection treatment of back layer coating.

The light diffusion film is formed by applying a light diffusion layer on at least one surface of a base film, and the particles used in the light diffusion layer use organic mechanical polymer particles having good diffusion efficiency. However, since most of these organic polymers are polymers obtained by emulsion polymerization, the types of particles are limited, and when inorganic particles are used, there are no particles having good compatibility with binder resins and good diffusion effects.

The recent trend is that high brightness of all components is progressing as a high brightness display device is required. In the case of a lamp unit, the luminance emitted from the backlight through the backlight is reduced to a certain amount of ten minutes, and when the liquid crystal panel is mounted again, the luminance is reduced to one hundredth or one hundredth of the initial luminance. As such, the greatest concern for realizing the image of the liquid crystal display device is to increase the luminance. Therefore, liquid crystal display companies need to make efforts to secure high aperture ratios, but it is not exaggeration to say that such efforts are already at the limit, so the rest of them are trying to reduce the thickness. .

Conventional technologies related to backlight units include Korean Patent Publication Nos. 2003-0077472, 2003-0077469, 2003-0077468, 2002-0069110, 2002-0066386, 2002-0052999, and 20002. -0048116, 2002-0038233, 2001-0110179, 2001-0066830, 2001-0053886, 2001-0053886, 2001-0054274, 2001-0054284, 2001-0005208 and 2001-0048774 An arc etc. are mentioned, Here, it is disclosed with respect to the light-diffusion film which hardened by disperse | distributing the binder and particle | grains on the transparent base sheet with the film attached to the backlight structure for surface light sources. In particular, Korean Patent Publication No. 2001-0054274 discloses a light diffusing film having a particle size of the light diffusing layer having an aggregated particle size of 50 μm or less and a lamination ratio of 10% or less.

Accordingly, the inventors of the present invention, while seeking to improve the brightness in the diffusion film for the liquid crystal backlight unit, as a result of mixing and dispersing lenticular organic particles and spherical organic particles as organic particles in the diffusion layer crude liquid at a predetermined ratio, It has been found that the present invention can be improved to complete the present invention.

Accordingly, an object of the present invention is to provide a diffuser film for a backlight unit of a liquid crystal display of high brightness.

Diffusion film for liquid crystal backlight of the present invention for achieving the above object is a light diffusing layer comprising a binder and organic particles on at least one surface of the base film, wherein the light diffusing layer has an average particle diameter of 1 to 50㎛ In addition, the lenticular organic particles having a ratio of long diameter to short diameter of 1.1: 1 to 5: 1 and spherical organic particles having a ratio of long diameter to short diameter of less than 1.1: 1 include organic particles mixed in a weight ratio of 1:10 to 10: 1. And the ratio of the total organic particles is 50 to 350 parts by weight with respect to 100 parts by weight of the binder, the thickness is characterized in that 1 to 50㎛.

The present invention will be described in more detail as follows.

In the structure of the diffusion film for a liquid crystal backlight of the present invention, as shown in FIG. 1, the light diffusion layer 1 is applied to at least one surface of the base film 2, and a separate blocking prevention layer 4 may be applied.

In the diffusing film, the light diffusion layer 1 scatters and reflects and refracts the incident light to diffuse the light, and at the same time, transmits the light through the light guide plate to spread the light evenly throughout the LCD screen.

Therefore, the light diffusion layer uses a resin having good adhesion with the base film and having good compatibility with particles (diffusion particles) that play a role of light diffusion as a binder. For example, a polyester resin or At least one transparent binder resin of acrylic resin for surface hardness or cellulose acetate resin for heat and ultraviolet stability may be used. More specifically, unsaturated polyester, methyl methacrylate, ethyl methacrylate, isobutyl methacrylate, normal butyl methacrylate, normal butyl methyl methacrylate, acrylic acid, methacrylic acid, hydroxyethyl methacrylate, Hydroxypropyl methacrylate, hydroxy ethyl acrylate, acrylamide, metyrol acrylamide, glycidyl methacrylate, ethyl acrylate, isobutyl acrylate, normal butyl acrylate, 2-ethylhexyl acrylate polymer or Acrylic type, urethane type, epoxy type, melamine type etc., such as a copolymer or a terpolymer, etc. are mentioned, In order to improve heat resistance, abrasion resistance, and adhesiveness, it uses a hardening film of a resin using a hardening | curing agent. At this time, the resin used is preferably a high light transmittance, and in particular, the adhesive force with the base film is important because it constitutes a light diffusion layer.

In the present invention, organic particles are used as the diffusion particles dispersed in such a binder resin, because the organic particles are excellent in light diffusivity compared to the inorganic particles.

The organic particles are used in an amount of 50 to 350 parts by weight based on 100 parts by weight of the binder, and have an average particle diameter of 1 to 50 μm, wherein the ratio of the long diameter to the short diameter is 1.1: 1 to 5: 1. Spherical organic particles having a ratio of less than 1.1: 1 are mixed and used in a 1:10 to 10: 1 weight ratio. Since lenticular particles have a larger light condensing effect than spherical particles, the lenticular particles increase the luminance in the vertical direction.

If the ratio between the long and short diameters of the lenticular organic particles in the organic particles is less than 1.1: 1, the shape becomes close to the spherical shape, and there is no luminance improvement effect due to the lenticular particles. When mixed with the spherical particles it is difficult to obtain a uniform appearance.

When the mixing ratio of such lenticular organic particles and spherical organic particles is less than 1:10, the luminance improvement effect due to the mixing of the lenticular organic particles is minute.

The size of the spherical organic particles and the lenticular organic particles, that is, the average diameter of the spherical organic particles, the average long diameter and the average short diameter of the lenticular organic particles is preferably 1 to 50㎛, if the average particle diameter of 1 If the thickness is less than μm, the diffusion efficiency may be lowered and the particles of the coating film may be detached. If the thickness is larger than 50 μm, the diffusion efficiency may be difficult due to the difficulty in mounting to a thin product and lamination of particles.

Organic particles can be used in various ways to increase the light transmittance and diffusivity while having a difference in refractive index from ordinary resins. Typically, methyl methacrylate, ethyl methacrylate, isobutyl methacrylate, and normal butyl methacrylate. Normal butyl methyl methacrylate, acrylic acid, methacrylic acid, hydroxyethyl methacrylate, hydroxypropyl methacrylate, hydroxyethyl acrylate, acrylamide, metyrolacrylamide, glycidyl methacrylate, ethyl Olefinic particles such as acrylates, isobutyl acrylates, normal butyl acrylates, 2-ethylhexyl acrylate polymers or copolymers or terpolymers, olefinic particles such as polyethylene, polystyrene, polypropylene, copolymers of acrylics and olefins , After forming the particles of homopolymer, Ssuiwoseo covered with and organic particles such as made of a multi-layer multi-component particles.

Such organic particles are used to 50 to 350 parts by weight with respect to 100 parts by weight of the binder, if the content is less than 50 parts by weight of light diffusion efficiency is lower than 350 parts by weight is difficult to use due to the turbidity due to the particle lamination. .

As the base film 3 to which the light diffusion layer 1 thus formed is applied, any of the transparent supports can be used, and examples thereof include polycarbonate, polypropylene, polyethylene terephthalate, polyethylene, and epoxy. Among them, polyethylene terephthalate is mainly used. Recently, polyethylene naphthalate having ultraviolet blocking effect is used without adding a UV stabilizer to the light diffusion layer, but it is not commercialized due to its high price.

Such a base film should have adhesion to the resin used in the light diffusing layer, and should not affect the light diffusing layer due to its high light transmittance, and the surface smoothness should be uniform so that there is no variation in luminance.

As for the thickness of a base film, 50-250 micrometers is suitable normally, More preferably, 75-200 micrometers is suitable. If the thickness is less than 50 μm, the mechanical properties and heat resistance of the film may be insufficient, and if the thickness is greater than 250 μm, the product becomes thick and becomes a problem in mounting a thin product.

Coating of the light diffusion layer crude liquid on the base film is made by a comma knife or gravure, the thickness of the light diffusion layer is suitable 5 to 50㎛. If the thickness of the light diffusing layer is less than 5 μm, it is difficult to distribute the particles to have light diffusing properties.

An example of the structure of the direct backlight unit to which the diffusion film thus obtained is applied is schematically illustrated in FIG. 2, wherein the mold frame 11, the reflective film 12, the cold cathode fluorescent lamp 13, the diffusion film 100, and the prism are shown. 14 has a laminated structure.

Hereinafter, the present invention will be described in detail with reference to Examples, which are used to facilitate understanding of the present invention, but the present invention is not limited to the following Examples.

In the present invention, as a tool for analyzing the long and short diameters of the lenticular particles, the particle size distribution was analyzed by expanding the analysis at 300 magnification using a Field emission scanning electronic microscope (FE-SEM) S-4300 model of Hitachi. Select N particles (N = 100 or more) observed by the FE-SEM and measure the diameter of the N particles using a length measuring method using a scale bar of the FE-SEM apparatus. At this time, the particle diameter of the long and short diameters less than 1.1: 1 was defined as spherical particles, and the ratio of the spherical particles and the lenticular particles was measured by dividing the particles having the long and short diameters of 1.1: 1 or more into lenticular particles. According to this classification criteria, the spherical particles were measured the average diameter, the lenticular particles were measured the long and short diameters.

Example 1

100 parts by weight of methyl ethyl ketone and 100 parts by weight of toluene were added to 100 parts by weight of acrylic resin 52-666 (manufactured by Aekyung Chemical Co., Ltd.), and diluted.Spherical polymethylmethacryl having an average long diameter of 12.83 µm, an average short diameter of 12.57 µm, and an average particle diameter of 12.7 µm. The particle size PBX010 (KOLON Corporation) and the lenticular particle PBA030 (KOLON Corporation) having an average long diameter of 15.2 μm and an average short diameter of 10.6 μm were mixed in a 1: 0.2 weight ratio so that 120 parts by weight of the binder was mixed and dispersed by a milling machine. After using a gravure on one side or both sides of a 125 μm ultra-transparent polyethylene terephthalate film (T600, manufactured by Mitsubishi Corporation) was applied to a coating thickness of 10 to 30 μm after drying.

Example 2

100 parts by weight of methyl ethyl ketone and 100 parts by weight of toluene were added to 100 parts by weight of acrylic resin 52-666 (manufactured by Aekyung Chemical Co., Ltd.), and diluted.Spherical polymethylmethacryl having an average long diameter of 12.83 µm, an average short diameter of 12.57 µm, and an average particle diameter of 12.7 µm. The particle size PBX010 (manufactured by Kolon Corporation) and the lenticular particle PBA030 (manufactured by Kolon Corporation) having an average long diameter of 15.2 μm and an average short diameter of 10.6 μm were mixed at a ratio of 0.2: 1 by weight so as to be 120 parts by weight of the binder, and dispersed in a milling machine. After using a gravure on one side or both sides of a 100 μm ultra-transparent polyethylene terephthalate film (T600, manufactured by Mitsubishi), the coating was applied so as to have a coating thickness of 10 to 30 μm.

Comparative Example 1

100 parts by weight of methyl ethyl ketone and 100 parts by weight of toluene were added to 100 parts by weight of acrylic resin 52-666 (manufactured by Aekyung Chemical Co., Ltd.), and diluted with spherical polymethyl methacrylate particles PBX010 (manufactured by Kolon Corporation) having an average particle diameter of 12.7 µm. 125 µm ultra-transparent polyethylene terephthalate film (15.2 µm long and 10.6 µm average particle diameter PBA030 (KOLON Co., Ltd.) was mixed at a weight of 120 parts by weight so as to disperse with a milling machine. Gravure was used on one side or both sides of T600, manufactured by Mitsubishi Corporation, and then applied to dry the coating thickness of 10 to 30 μm.

Comparative Example 2

100 parts by weight of methyl ethyl ketone and 100 parts by weight of toluene were added to 100 parts by weight of acrylic resin 52-666 (manufactured by Aekyung Chemical Co., Ltd.), and diluted with spherical polymethyl methacrylate particles PBX010 (manufactured by Kolon Corporation) having an average particle diameter of 12.7 µm. 125 μm ultra-transparent polyethylene terephthalate film (10.5 μm in diameter and 10.9 μm in average diameter) was mixed with a particle size of PBA030 (KOLON Corporation) at a ratio of 1: 0.5 to 120 parts by weight of the binder and dispersed in a mill. Gravure was used on one side or both sides of T600, manufactured by Mitsubishi Corporation, and then applied to dry the coating thickness of 10 to 30 μm.

Comparative Example 3

100 parts by weight of methyl ethyl ketone and 100 parts by weight of toluene were added to 100 parts by weight of acrylic resin 52-666 (manufactured by Aekyung Chemical Co., Ltd.), followed by dilution, and the spherical polymethyl methacrylate particles PBX010 (manufactured by Kolon Corporation) having an average particle diameter of 12.7 μm was diluted. 120 parts by weight of the mixture was dispersed and dispersed in a mill, and then coated using a gravure on one or both sides of a 125 μm ultra-transparent polyethylene terephthalate film (T600, manufactured by Mitsubishi Co., Ltd.) to a coating thickness of 10 to 30 μm.

The brightness of the diffusion films obtained in Examples 1 to 2 and Comparative Examples 1 to 3 was evaluated, and the results are shown in Table 1 below.

The brightness was measured by cutting the diffuser film into the backlight unit, and then the brightness of the light diffuser film on the backlight unit light guide plate and finally the dual brightness enhancement film (Vikuiti ^TM DBEF-D440, 3M). 9) luminance was measured with TOPCON's BM7 luminance meter and averaged.

Spherical Particles: Lenticular Particle Mixing Ratio (weight ratio) Long diameter of lenticular particle: Short diameter (μm) Luminance (Cd / ㎡) Example One 1: 0.2 15.2: 10.6 3120 2 0.2: 1 15.2: 10.6 3191 Comparative example One 0.05: 1 15.2: 10.6 3015 2 1: 0.5 11.4: 10.9 3007 3 1: 0 - 3004

As described above in detail, according to the present invention, a diffusion film including a light diffusion layer using a mixture of lenticular organic particles and spherical organic particles as organic particles may increase luminance in a vertical direction due to the light condensing effect of the lenticular particles, thereby increasing the luminance. Can be guaranteed.

1 is a cross-sectional view of the laminated structure of the diffusion film according to the present invention,

Figure 2 is an exploded perspective view of a direct backlight unit including a diffusion film according to the present invention.

* Description of the symbols for the main parts of the drawings *

1-light diffusing layer, 2-diffused particles

3-base film, 4-blocking layer

11-mold frame, 12-reflective film

13-cold cathode fluorescent lamp, 14-prism

100-Diffusion Film

Claims (3)

In the diffusion film for a liquid crystal backlight having a light diffusing layer comprising a binder and organic particles on at least one surface of the base film, The light diffusing layer has an average particle diameter of 1 to 50 μm and has a long diameter and a short diameter of 1.1: 1 to 5: 1 lenticular organic particles and a long diameter and a short diameter of less than 1.1: 1 of the spherical organic particles of 1:10. To 10: 1 by weight, including organic particles mixed, the ratio of the total organic particles is 50 to 350 parts by weight with respect to 100 parts by weight of the binder, the thickness of the backlight unit of the liquid crystal display, characterized in that Diffusion film. According to claim 1, the field emission scanning electronic microscope (FE-SEM) to analyze the particle size distribution by expanding analysis, FE-SEM observed N particles (N = 100 or more) to select N particles When the ratio of spherical particles to lenticular particles was measured by dividing into spherical particles and lenticular particles, and the average particle diameter, long diameter, and short diameter were measured, the ratio between the long diameter and the short diameter was 1.1: 1 to A liquid crystal display comprising a light diffusion layer comprising 5: 1 lenticular organic particles and spherical organic particles having a ratio of long diameter to short diameter less than 1.1: 1, and organic particles mixed in a weight ratio of 1:10 to 10: 1. Diffusion film for backlight units. A liquid crystal backlight unit comprising the diffusion film of claim 1.