KR100615638B1 - Photo diffusion film - Google Patents

Abstract

The present invention relates to a light diffusing film used in a backlight unit of an LCD, and more particularly, to a light diffusing film used in a thin film transistor liquid crystal display (TFT-LCD) or a super twisted nematic liquid crystal display (STN-LCD). The present invention relates to a light diffusing film that can obtain a clear light image by inducing uniform surface light while passing light from linear light emitted from a cold cathode fluorescent lamp located at a side or a back side to obtain a clear image of a display. The light diffusing film according to the invention is a light diffusing film formed of a resin film and a diffusion layer coated with a binder resin and a resin particle on the resin film, wherein the resin particles are the largest particles, the particle size distribution is ± 20 of the average particle diameter Mono-disperse particles present in at least 80% within% and at least two particles smaller than the largest particle And that is characterized.

Light Diffusion, Monodisperse Particles, Half Monodisperse Particles, Lake Surface, Backlight, Luminance, Shielding

Description

Light Diffusion Film {PHOTO DIFFUSION FILM}

1 is an enlarged plan view of a light diffusing film.

2 is a conceptual diagram showing light passing through the lake surface of the light diffusion film.

3 is a conceptual diagram showing light passing through the light diffusing film according to the present invention.

<Explanation of symbols for the main parts of the drawings>

1: Resin film 2,2a, 2b: resin particle

3: binder resin 4: lake surface

5: light going straight 6: light scattering

7: diffusion layer

The present invention relates to a light diffusing film used in a backlight unit of an LCD, and more particularly, to a light diffusing film used in a thin film transistor liquid crystal display (TFT-LCD) or a super twisted nematic liquid crystal display (STN-LCD). The present invention relates to a light diffusing film capable of obtaining a clear light image by inducing uniform surface light while passing light from linear light emitted from a cold cathode fluorescent lamp located on a side or a back side to obtain a clear image of a display.

Generally, the light diffusion film for LCD backlight is installed with a linear lamp on one side of the light guide plate which is used in small size such as car navigation system, mobile phone, PDA, digital camera, portable TV, camcorder, etc. In the SIDE type backlight unit in which the EDGE type backlight unit and one or more lamps are installed and used, the shape of the diffused DOT and V type cross sections installed at the bottom to obtain an angle to send light to the upper part of the light guide plate may be erased. Its function is to convert uneven light sources from the light guide plate into the uniform light centered on the front of the backlight unit. Even when a lamp or a flat lamp is installed, it is possible to spread the light visually And performs the function of a surface light source screen of the forward distribution center, it comes to have the effect of increasing the luminance in the front direction from the function for switching the distribution center of the light towards the front.

In order to perform the function of concealment and diffusion in the function of the light diffusion film for LCD backlight and improve the brightness, a method of applying transparent organic resin particles or inorganic particles with a transparent resin binder has been developed (Japan Korean Patent Laid-Open No. Hei 7-174909, Korean Laid-Open Publication No. 2000-0027862, Korean Laid-open Publication No. 1998-0020430).

However, the conventional techniques as described above have a problem that the area of the surface of the diffusion layer is large, so that the diffusion and shielding functions are lowered, the luminance is lowered, and the surface and thickness of the diffusion layer are nonuniform.

The present invention has been made to solve the above problems, the object of the present invention is to minimize the light surface area of the light diffusion layer by minimizing the light passing through the refraction, scattering of light to improve the diffusion function to improve the hiding power and brightness It is intended to provide a light diffusing film.

In another aspect, the present invention is to provide a light diffusion film that can increase the efficiency of the backlight.

In the light diffusing film according to the present invention for achieving the above object is a light diffusion film formed of a resin film and a diffusion layer coated with a binder resin and a resin particle on the resin film, the resin particles are the largest particles, It is characterized in that the distribution comprises monodisperse particles in which 80% or more is present within ± 20% of the average particle diameter, and two or more particles having an average particle diameter smaller than the largest particle.

In a preferred embodiment, the largest average particle diameter of the largest mono-dispersion particles is 10㎛ to 50㎛, the maximum average particle diameter of the two or more particles smaller than the largest monodispersion particles is 3㎛ 7㎛ and 1㎛, respectively To 3 μm.

In the light diffusing film according to another embodiment of the present invention is a light diffusing film formed of a resin film and a diffusion layer coated with a binder resin and a resin particle on the resin film, the resin particles have a particle size distribution of ± 30 of the average particle diameter It is characterized in that it comprises semi-dispersed particles present in more than 70%.

In a preferred embodiment, the maximum average particle diameter of the semi-stage dispersed particles is 10 μm to 50 μm.

More preferably, the thickness of the diffusion layer is 150% or less of the resin particles having the largest average particle diameter among the resin particles, and the area of the lake surface on which the resin particles are not applied is 15% or less of the total area.

Hereinafter, the present invention will be described in detail with reference to embodiments and drawings of the present invention. These examples are only for illustrating the present invention in more detail, it will be apparent to those skilled in the art that the scope of the present invention is not limited by these examples in accordance with the gist of the present invention. .

In forming the light diffusion layer by the light diffusing agent, the optical function is determined by the lens shape or the curved shape of the surface formed by the light diffusing agent. The more the lens shape or the curved shape of the surface is, the more shielding and diffusing function of the light diffusing film is obtained. It becomes bigger. In order to increase the area of the lens shape, it is preferable to use large particles having an average particle diameter of 7 microns or more, and more preferably, having a particle size distribution having an average particle diameter of 10 microns or more and 50 microns or less, having 80% within ± 20% of the average particle diameter. It is preferable to use particles (hereinafter referred to as "monodispersed particles"). The particle size distribution may be a method of measuring particle size by using scattering of light with a particle size distribution measuring device LS PARTICLE SIZE ANALYZER of Coulter. However, when such relatively large particles are used alone, in the wet coating method, since the particles are not applied to the diffusion layer, portions (4, lake surface) remaining in the planar shape in the diffusion layer are formed, and the lake surface 4 diffuses the function. When deterioration is caused and polydisperse particles having a large particle size distribution are used, there is an effect of covering the lake surface 4, but it is difficult to obtain a diffusion surface 7 having a uniform surface structure and a uniform thickness. In particular, in the backlight unit of the direct type LAMP system which uses a large number of lamps on the rear to increase the amount of light emission, it is used on the lake surface (4) in order to improve the luminance by maximizing the diffusion function and to erase the lamp line. The light (5) passed directly without refraction or scattering causes a bright line to deteriorate the light.

Therefore, the maximum average particle diameter of the transparent spherical organic particles 2a is larger and more advantageous than 7 microns, in order to increase the diffusion function and hiding power by minimizing the surface area of the surface to increase the lens shape, and at the same time to increase the brightness. More preferably, they are monodisperse particles of 10 microns or more and 50 microns or less. When the average particle diameter particle size of 50 microns or more is used, wet coating is difficult and it is difficult to disperse the coating liquid. In addition, in order to minimize the lake surface, it is preferable to mix two or more kinds of particles (2b, 2c) smaller than the maximum average particle diameter particles. In a preferred embodiment, the maximum average particle diameter of the two small particles is preferably 3 µm to 7 µm and 1 µm to 3 µm, respectively.

In the case of particles that are present at 70% or more within ± 30% of the average particle diameter by filtering the polydisperse particles (hereinafter referred to as "half monodisperse particles" or "half monodisperse particles"), those having an average particle diameter of 10 microns or more alone or smaller are smaller than the average particle diameter. The same effect can be obtained also when mixed with polydisperse, monodisperse, and semi-monodisperse particles of. Here, the polydispersed particles mean particles having a larger particle size distribution than monodisperse particles and semi-disperse particles.

In addition, in order to maximize the luminance by minimizing the optical loss (LOSS), the light transmittance of the transparent plastic film (1) used as the substrate of the light diffusion film is preferably between 85% and 95%, more preferably 90% to 94% Good relationship In order to improve adhesion and coating property of the transparent resin layer and the light diffusing layer, it is preferable to use a substrate coated with a primer, a corona, or a plasma-treated plastic substrate.

As the light diffusing agent (2), spherical transparent particles are suitable. As the transparent particles, organic particles such as acrylic particles, styrene particles, and silicon particles, and inorganic particles such as synthetic silica, glass beads, and diamond may be used. May be used alone or in combination of two or more thereof.

The binder resin (3) used in the light diffusing layer of the light diffusing film should be transparent and acrylic, urethane, epoxy, vinyl, polyester, polyamide, etc., such as polymethyl methacrylate or methacrylic acid ester copolymer. It can be used individually or in mixture of 2 or more types in resin. The refractive index of this transparent resin should be a value smaller than the refractive index of the plastic base material while the difference from the refractive index of the plastic base material is 0.22 or less. When the refractive index of the binder resin is larger than the refractive index of the plastic substrate, the light is more reflected at the interface between the light diffusion layer and the plastic substrate in the direction of the light from the transparent resin layer to the light diffusing layer, thereby lowering the light transmittance. In addition, when the difference in refractive index is 0.22 or more, it is difficult to manufacture a light diffusing film that can obtain high luminance due to a lot of refraction and scattering of light at the interface of the light diffusing layer / plastic substrate.

As a method of diluting and applying the light diffusing agent and the organic resin binder to a transparent base film in a solvent, conventional wet coating methods such as a knife coating method, a gravure transfer coating method, and a reverse roll coating method may be used.

At this time, even after application, if it does not exceed 150% of the particle | grains which have the largest average particle diameter, the preferable effect of a uniform application surface will be obtained. If the coating degree exceeds 150% of the average particle diameter of the particle having the maximum average particle diameter, it may cause a decrease in luminance due to the excessive amount of particles per unit area.

The smaller the area of the lake surface, the better the diffusion and concealment functions. This lake area is preferably less than 15% of the total area when photographing magnified images at 15 times magnification of the optical microscope. If the area of the lake surface exceeds 15%, the diffusion function due to refracted and scattered straight light is degraded. This is because excellent concealment cannot be expected.

An application having an antistatic function for the purpose of imparting slip properties to the back surface of the transparent resin film and the light diffusion layer formed on one side, increasing the hardness for suppressing scratches generated during the cutting and assembling operations, and preventing the incorporation of foreign substances. It may also form a layer.

<Example 1>

A coating liquid having the following composition was applied to one side of the transparent polyester film (Toray Saehan XG-6DF2-P, 100 μm) using a bar coater, and then dried at 100 ° C. for 2 minutes to provide light. A diffusion film was prepared.

Composition of Coating Liquid

 Binder Resin (Sensho Chemical DAI-3A): 26.0 wt%

 Curing agent (Sensho Chemical DAI-3B): 6.0 wt%

 -Synthetic resin particles (Soken Chemical: MX-1000 monodispersed average particle diameter: 10 mu m): 19.5 wt%

 -Synthetic resin particles (Soken Chemical: MX-500 monodispersed average particle size 5㎛): 7.0% by weight

 -Synthetic resin particles (Soken Chemical: MX-300 monodispersed average particle diameter: 3㎛): 2.5% by weight

 Methyl ethyl ketone: 39.0 wt%

<Example 2>

The light diffusion layer was applied to the plastic substrate as in Example 1 using a coating liquid having the following composition, followed by drying at 100 ° C. for 2 minutes to prepare a light diffusion film.

Composition of Coating Liquid

 Binder Resin (Sensho Chemical DAI-3A): 23.0 wt%

 Curing agent (Sensho Chemical DAI-3B): 5.0 wt%

 -Synthetic resin particles (Sokken Chemical: MX-1500 monodispersed average particle diameter 10㎛): 22.5% by weight

 -Synthetic resin particles (Sokken Chemical: MX-500 monodispersed average particle size 5㎛): 7.5% by weight

 -Synthetic resin particles (Soken Chemical: MX-300 monodispersed average particle diameter 3㎛): 3.0% by weight

 Methyl ethyl ketone: 39.0 wt%

<Example 3>

The light diffusion layer was applied to the plastic substrate as in Example 1 using a coating liquid having the following composition, and dried at 100 ° C. for 2 minutes to prepare a light diffusion film.

Composition of Coating Liquid

 Binder Resin (Sensho Chemical DAI-3A): 23.0 wt%

 Curing agent (Sensho Chemical DAI-3B): 5.0 wt%

 -Synthetic resin particles (Sokken Chemical: MX-1500 monodispersed average particle diameter 10㎛): 22.5% by weight

 -Synthetic resin particles (Sokken Chemical: MX-500 monodispersed average particle size 5㎛): 7.5% by weight

 -Synthetic resin particles (Soken Chemical: MX-300 Monodispersed Average Particle Size: 3㎛): 2.2 wt%

 -Synthetic resin particles (Sokken Chemical: MX-150 monodispersed average particle diameter 3㎛): 0.8% by weight

 Methyl ethyl ketone: 39.0 wt%

<Example 4>

A coating liquid having the following composition was applied to one side of the transparent polyester film (Toray Saehan XG-6DF2-P, 100 μm) using a bar coater, and then dried at 100 ° C. for 2 minutes to provide light. A diffusion film was prepared.

Composition of Coating Liquid

 Binder Resin (Sensho Chemical DAI-3A): 23.0 wt%

 Curing agent (Sensho Chemical DAI-3B): 5.0 wt%

 -Synthetic resin particles (Sekis Industrial Co., Ltd .: MBXS-15 half-stage dispersion average particle diameter 15㎛): 33.0% by weight

 Methyl ethyl ketone: 39.0 wt%

Comparative Example 1

The light diffusion layer was applied to the plastic substrate as in Example 1 using a coating liquid having the following composition, followed by drying at 100 ° C. for 2 minutes to prepare a light diffusion film.

Composition of Coating Liquid

 Binder Resin (Sensho Chemical DAI-3A): 23.0 wt%

 Curing agent (Sensho Chemical DAI-3B): 5.0 wt%

 -Synthetic resin particles (Soken Chemical: MX-1000 Monodispersion Average particle size: 10㎛): 33.0 wt%

 Methyl ethyl ketone: 39.0 wt%

Comparative Example 2

The light diffusion layer was applied to the plastic substrate as in Example 1 using a coating liquid having the following composition, followed by drying at 100 ° C. for 2 minutes to prepare a light diffusion film.

Composition of Coating Liquid

 Binder Resin (Sensho Chemical DAI-3A): 23.0 wt%

 Curing agent (Sensho Chemical DAI-3B): 5.0 wt%

 -Synthetic resin particles (Soken Chemical: MX-1000 Monodispersion Average particle size: 10㎛): 24.5 wt%

 -Synthetic resin particles (Soken Chemical: MX-500 Monodispersion Average particle size: 5㎛): 8.5 parts by weight

 Methyl ethyl ketone: 39.0 wt%

Comparative Example 3

The light diffusion layer was applied to the plastic substrate as in Example 1 using a coating liquid having the following composition, followed by drying at 100 ° C. for 2 minutes to prepare a light diffusion film.

Composition of Coating Liquid

 Binder Resin (Sensho Chemical DAI-3A): 22.0 wt%

 Curing agent (Sensho Chemical DAI-3B): 5.0 wt%

 -Synthetic resin particles (Sokken Chemical: MX-1500 monodispersion average particle diameter 10㎛): 34.0 wt%

 Methyl ethyl ketone: 38.0 wt%

<Comparative Example 4>

The light diffusion layer was applied to the plastic substrate as in Example 1 using a coating liquid having the following composition, followed by drying at 100 ° C. for 2 minutes to prepare a light diffusion film.

Composition of Coating Liquid

 Binder Resin (Sensho Chemical DAI-3A): 22.0 wt%

 Curing agent (Sensho Chemical DAI-3B): 5.0 wt%

 -Synthetic resin particles (Sokken Chemical: MX-1500 monodispersion average particle diameter 10㎛): 25.5 wt%

 -Synthetic resin particles (Soken Chemical: MX-500 Monodispersion Average particle size: 5㎛): 8.5% by weight

 Methyl ethyl ketone: 39.0 wt%

The coating amount of the Examples and Comparative Examples was adjusted to the number of Mayer bar and the coating speed as shown in Table 1 so that the coating layer thickness is 150% or less of the maximum particle size.

<Evaluation method>

-The thickness of the diffusion layer 7 was measured by a micrometer using a pressure gauge. The total thickness including the plastic substrate is shown by subtracting the thickness of the plastic substrate.

-HAZE was measured according to ASTM D-1003, and the measuring instrument was NIPPON DENSHOKU KOGYO Co. Ltd. Ltd. Model 1000 was used.

-The hiding power was evaluated in the order of ○, △, X from the low visibility of the lamp line with the light diffusion film assembled in the direct backlight.

The surface area of the lake surface was expressed as a percentage of the area where no particles exist in the optical microscope 150 times magnification of the diffusing film surface and was expressed as an average value measured for three photographs of unspecified positions.

-The brightness of the backlight assembly was measured by using Topcon's BM-7 equipment.

TABLE 1

Process conditions Properties Overall evaluation Meyer Bar Application speed Even after application Haze Hiding power Lake area Luminance unit No. cm / sec Μm % ○, △, X % cd / ㎡ Example 1 14 10 11.2 88.5 ○ 5 1892 Good Example 2 16 5 16.3 89.2 ○ 10 1890 Good Example 3 16 5 16.1 89.1 ○ 6 1899 Good Example 4 16 5 18.3 89.0 ○ 8 1889 Good Comparative Example 1 14 10 11.0 86.1 X 22 1790 Bad Comparative Example 2 14 10 11.2 87.4 △ 18 1815 Bad Comparative Example 3 16 5 16.0 85.8 X 23 1785 Bad Comparative Example 4 16 5 16.1 86.9 △ 19 1807 Bad

As can be seen in Table 1, as in Examples 1, 2, and 3, the light produced by mixing three or more particles having a maximum particle size monodispersed particle having a diameter of 10 microns or more and a particle size smaller than the maximum particle size monodispersed particle was mixed into three particles It is understood that the diffusion film has a smaller lake area than the light diffusion film composed of two or less kinds of particles as in Comparative Examples 1, 2, 3, and 4, and has excellent hiding power and high backlight brightness, thereby improving the efficiency of the backlight. Can be. In addition, even when half-dispersion particles are used as in Example 4, it can be seen that the lake area can be effectively reduced and excellent hiding power and high luminance can be realized.

The above embodiments are intended to specifically illustrate the present invention, and do not limit the scope of the present invention. In addition, it can be seen that all simple modifications and variations of the present invention are included in the scope of the present invention.

As described above, according to the light diffusing film according to the present invention, it can be seen that the lake area can be reduced, thereby improving the diffusion function and providing a light diffusing film having excellent brightness as well as hiding power. Can be.

Claims (6)

delete In the light-diffusion film formed of the resin film 1 and the diffusion layer 7 apply | coated with the binder resin 3 and the resin particle 2, 2a, 2b on the said resin film 1, The resin particles are the largest particles, monodisperse particles having a particle size distribution of 80% or more within ± 20% of the average particle diameter, Including two or more kinds of particles having an average particle diameter smaller than the largest particle, The largest average particle diameter of the largest monodispersion particles is 10㎛ to 50㎛, The light-diffusion film, characterized in that the maximum average particle diameter of the two kinds of particles smaller than the largest mono-dispersed particles are 3㎛ 7㎛ and 1㎛ 3㎛, respectively delete In the light-diffusion film formed of the resin film 1 and the diffusion layer 7 apply | coated with the binder resin 3 and the resin particle 2, 2a, 2b on the said resin film 1, The resin particles include half-dispersion particles having a particle size distribution of 70% or more within ± 30% of the average particle diameter, wherein the maximum average particle diameter of the half-dispersion particles is 10㎛ to 50㎛, light diffusion film. The method of claim 2, The diffusion layer 7 has a thickness of 150% or less of the resin particles having the largest average particle diameter among the resin particles, and an area of the lake surface 4 on which the resin particles are not applied is 15% or less of the total area. , Light diffusion film. The method of claim 4, wherein The diffusion layer 7 has a thickness of 150% or less of the resin particles having the largest average particle diameter among the resin particles, and an area of the lake surface 4 on which the resin particles are not applied is 15% or less of the total area. , Light diffusion film.

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