KR101129595B1 - Light diffusing film and back light unit for lcd having the same - Google Patents

Abstract

In the present invention, the base film; A first diffusion layer laminated on one surface of the base film and having first light diffusion particles fixed to the binder resin; And a second light diffusion film stacked on top of the first light diffusion layer, the second light diffusion particles having a different refractive index and an average particle diameter different from the first light diffusion particles, and fixed to a binder resin. Provided is a backlight unit for an LCD.
In the light diffusing film of the present invention, by stacking light diffusing layers having different refractive indices of light diffusing particles and binder resin, the uniformity and condensing efficiency of the surface of the diffusing layer can be increased to improve the brightness of the light diffusing film for LCD.

Description

LIGHT DIFFUSING FILM AND BACK LIGHT UNIT FOR LCD HAVING THE SAME}

The present invention relates to a light diffusing film and a backlight unit having the same. More specifically, a plurality of light diffusing layers are laminated on a base film, and the refractive index and particle size of the light diffusing particles and the binder resin constituting each light diffusing layer are controlled. The present invention relates to a multilayer light diffusing film having improved luminance and a backlight unit having the same.

BACKGROUND ART Liquid crystal displays (LCDs) are being used as information display devices such as mobile phones, portable information terminals (PDAs), computers, televisions, and the like, by utilizing characteristics such as thinning, light weight, and low power consumption.

Since the liquid crystal display itself uses a liquid crystal layer of a non-light-emitting material, a separate light source is installed, and a back light unit serves as a back light unit. The composition includes a lamp, a reflective film, a light guide plate, a light diffusion film, a prism film, It consists of a protective film.

The reflective film serves to improve light efficiency by reflecting the light emitted from the rear surface of the light guide plate back to the light guide plate, and the light guide plate equalizes light incident through the light incident surface disposed on the side, and is substantially perpendicular to the light incident surface. Light is emitted in the direction of the liquid crystal panel disposed on the upper side through the light emitting surface disposed. The light diffusing film is composed of a transparent base film, a diffusing layer formed on the upper surface of the base film, and an anti-blocking layer formed on the lower surface of the base, and light diffusing particles inside each layer. ) Are distributed so that the light of the light source from one side or the back is diffused to the whole screen, and the light is refracted to convert the light into a uniform light in the front direction. The prism film is composed of an array of a plurality of fine prisms disposed on one surface of the base film. The prism film having the structure refracts the light emitted from the diffusion film in a direction perpendicular to the visible surface of the liquid crystal panel, thereby concentrating light incident at a low angle toward the front, thereby increasing luminance in the effective viewing angle range.

Recently, various methods for developing a high brightness light diffusing film have been proposed. For example, Patent Literature 1 discloses a content of a light diffusing film for a liquid crystal display backlight unit including light diffusing particles formed by mixing two or more kinds of organic particles having different refractive indices and a light diffusing film having a binder fixed to a support. have.

Patent Literature 2 discloses a light diffusing film, wherein the difference in refractive index between the resin and the particles is 0.1 or more.

Patent document 3 discloses an optical film which improves luminance by fixing a plurality of spherical particles to a binder resin to form a light diffusion layer, and laminating a plurality of light diffusion layers with an intermediate layer interposed therebetween.

However, the above-described conventional techniques do not secure uniformity and condensing efficiency of the diffusion layer, and thus the problem of falling luminance continues, and thus the necessity to improve them continues. Thus, the present inventors, while stacking a plurality of light diffusion layers on the base film, and confirmed that the brightness of the light diffusion film can be significantly improved by adjusting the refractive index and particle size of the light diffusion particles and binder resin of each light diffusion layer. It came to invention.

Republic of Korea Patent No. 10-834406 Republic of Korea Patent No. 10-587905 Republic of Korea Patent No. 10-801024

An object of the present invention is to provide a light diffusion film with improved brightness by sequentially stacking a multi-layer light diffusion layer on one surface of the base film.

Another object of the present invention is to provide a light diffusion film further provided with an anti-blocking layer on the other side of the base film.

Still another object of the present invention is to provide a backlight unit for an LCD using the light diffusing film as a member.

Light diffusing film according to an embodiment of the present invention, the base film; A first diffusion layer laminated on one surface of the base film and having first light diffusion particles fixed to the binder resin; And a second diffusion layer stacked on the first diffusion layer, wherein second light diffusion particles having different refractive indices and average particle diameters from the first light diffusion particles are fixed to the binder resin.

It is preferable that the average particle diameter of the said 1st light-diffusion particle is 1-8 micrometers, and the average particle diameter of the said 2nd light-diffusion particle is 10-30 micrometers.

The refractive indexes of the first and second light diffusing particles are 1.30 to 1.70; The refractive index of the first light diffusing particles of the first diffusion layer is smaller than the refractive index of the binder resin; It is preferable that the refractive index of the second light diffusing particles of the second diffusion layer is larger than that of the binder resin.

The difference in refractive index between the first light diffusing particles and the binder resin of the first diffusion layer is 0.05 or more; It is preferable that the refractive index difference of the 2nd light-diffusion particle of the said 2nd diffused layer and binder resin is 0.05 or less.

On the other hand, the light diffusing film according to another embodiment of the present invention, the base film; A first diffusion layer laminated on one surface of the base film and having first light diffusion particles fixed to the binder resin; A second diffusion layer stacked on the first diffusion layer and having second light diffusion particles having a different refractive index and an average particle diameter from the first light diffusion particles are fixed to the binder resin; And an antiblocking layer formed on one surface of the base film and formed on an opposite surface of the first diffusion layer.

In the light diffusion film of the present invention, one or more components selected from the group consisting of a light source unit, a light guide plate, and a reflective sheet may be used as the backlight unit for LCD.

In the light diffusing film of the present invention, by stacking a light diffusing layer having different refractive indices of light diffusing particles and a binder resin, it is possible to improve the uniformity and condensing efficiency of the surface of the diffusing layer to improve the brightness of the light diffusing film for LCD.

The present invention provides a light diffusion film that can improve the front brightness by minimizing the loss of light by performing different optical functions on the entrance and exit surfaces of the film by forming the first diffusion layer and the second diffusion layer of the light diffusion film It has the effect of increasing the utilization of light emitted from the light source by controlling the surface structure of the entrance surface and the exit surface.

In addition, the present invention provides an improved luminance value even by using the same light source by increasing the utilization of light emitted from the light source, thereby reducing the energy consumption, thereby reducing power consumption.

1 is a cross-sectional view of a preferred embodiment of a light diffusing film 100 according to the present invention.
2 is a cross-sectional view of another embodiment of a light diffusing film 200 according to the present invention.

The light diffusion film of the present invention is a base film; A first diffusion layer laminated on one surface of the base film and having first light diffusion particles fixed to the binder resin; And a second diffusion layer stacked on the first diffusion layer, wherein second light diffusion particles having different refractive indices and average particle diameters from the first light diffusion particles are fixed to the binder resin.

Hereinafter, a light diffusing film of the present invention will be described with reference to the accompanying drawings. 1 is a cross-sectional view of a preferred embodiment of a light diffusing film 100 according to the present invention. Light diffusing film 100 according to an embodiment of the present invention is a base film 130; A first diffusion layer 110 laminated on one surface of the base film 130 and having first light diffusing particles 111 fixed to the first binder resin 112; And second light diffusing particles 121 stacked on the first diffusion layer 110 and having different refractive indices and average particle diameters from the first light diffusing particles 111 and fixed to the second binder resin 122. 2 includes a diffusion layer (120).

In this case, a transparent plastic film is generally used as the base film 130. If the material can withstand heat generated from a light source (not shown), which is an essential component of the LCD panel, the material is not particularly limited. In addition, the base film should have excellent adhesion with the binder resin, and the transmittance of light incident from the rear surface should be 90% or more. Suitable materials for such uses and functions include polyacrylates, polyimides, polycarbonates, polyesters, polypropylenes, polyethylenes, epoxy resins, and the like. Preferably, polyesters are used. It is preferable that the thickness of a base film is 50-250 micrometers. If the thickness is 50㎛ or less, the mechanical properties and heat resistance of the film is insufficient, and if the thickness is 250㎛ or more, the product is thick and the price rises to have a structure contrary to the recent trend of thinning the LCD module.

In the light diffusion film 100 of the present invention, a first diffusion layer 110 in which the first light diffusion particles 111 are fixed to the first binder resin 112 is stacked on one surface of the base film 130.

The first diffusion layer 110 is a layer for maximally scattering light at various angles to the second diffusion layer 120. In the first diffusion layer 110, in order to minimize the recycling and loss of light, the average particle diameter of the particles is limited to a certain range, and the refractive index difference between the particles and the resin is configured to be 0.05 or more, and the refractive index of the particles is smaller than the refractive index of the binder resin. Thereby maximizing diffusivity and serves to send light to the second diffusion layer 120.

As the first light diffusing particles 111, organic or inorganic particles having a refractive index of 1.3 to 1.7 may be used as spherical transparent particles. Examples of the particles include organic polymer particles such as acrylic resin particles (refractive index = 1.49), styrene resin particles (refractive index = 1.59), and silicone resin particles (refractive index = 1.43); Inorganic particles such as synthetic silica (refractive index = 1.47) and glass beads (refractive index = 1.51) may be used, and these light diffusing particles may be used alone or in combination of two or more thereof.

It is preferable that the average particle diameter of the said 1st light-diffusion particle 111 is 1-8 micrometers.

When the average particle diameter of the first diffusion layer is less than 1 μm, the light diffusion effect of the particles may be reduced, and when the average particle diameter is larger than 8 μm, the distribution of small particles may be uneven and the surface uniformity may be reduced.

As the first binder resin 112 for fixing the first light diffusing particles 111 in a single layer, at least one resin selected from acrylic resin, melamine resin, ester resin, and urethane resin is used. The refractive index of the first light diffusing particles 111 of the first diffusion layer 110 should be smaller than the refractive index of the first binder resin 112, and preferably, the difference in refractive index should be 0.05 or more.

The light diffusivity due to the refractive index difference between the particles and the resin is increased from the refractive index difference between the particles and the resin at least 0.05, and the light diffusivity is increased as the refractive index of the resin is larger than the refractive index of the particles. On the contrary, when the refractive index of the particles is larger than that of the binder resin, the light collecting effect due to the lens effect of the particles is increased rather than diffusion.

On the other hand, the refractive index difference between the first binder resin 112 and the base film 110 is within the range of 0.2 or less, it is preferable that the refractive index of the base film 110 is larger than the refractive index of the first binder resin 112. In the case where the refractive index of the first binder resin 112 is large, in the traveling direction of the light from the base film 130 to the first diffusion layer 110, the light is more reflected at the interface than the transmission, thereby lowering the light transmittance. . In addition, when the difference in refractive index is greater than or equal to 0.2, it is difficult to obtain a light diffusing film having high luminance due to the increase in the refraction and scattering of light at the interface between the first diffusion layer 110 and the base film 130.

In the manufacture of the light diffusion film 110 according to the preferred embodiment of the present invention, there is no particular limitation on the method of laminating the first diffusion layer on the base film 130, but, in general, the first binder resin is added to an appropriate solvent. After dissolving and kneading the first light diffusing particles 111, the coating liquid is laminated on the base film 130 by coating. The coating method may also be used without particular limitation, but preferably, methods such as knife coating, gravure coating, reverse roll coating and the like may be used. In addition, the shape of the coating layer may be compressed by using a mold having a shape in order to obtain a surface shape.

In the optical diffuser film 100 of the present invention, on the first diffusion layer 110, again, the second light diffusion particle 121 having a different refractive index and an average particle diameter from the first light diffusion particle 111 is the second binder. The second diffusion layer 120 fixed to the resin 122 is stacked.

As the second light diffusing particles 121, organic or inorganic particles having a refractive index of 1.3 to 1.7 may be used as spherical transparent particles. Examples of the particles include organic polymer particles such as acrylic resin particles (refractive index = 1.49), styrene resin particles (refractive index = 1.59), and silicone resin particles (refractive index = 1.43); Inorganic particles such as synthetic silica (refractive index = 1.47) and glass beads (refractive index = 1.51) may be used, and these light diffusing particles may be used alone or in combination of two or more thereof.

It is preferable that the average particle diameter of the said 2nd light-diffusion particle 112 is 10-30 micrometers.

If the average diameter of the second light-diffusing particles is less than 10 μm, it is difficult to expect the light condensing effect by the particles. If the average diameter of the second light-diffusing particles exceeds 30 μm, there is a concern that the light-diffusing particles may escape and the product becomes thick. There is a backing problem.

In addition, when particles having particle sizes of different sizes are mixed, the uniformity and regularity of the particle surface smoothness are lowered, which causes a problem of lowering the luminance.

As the second binder resin 122 which fixes the second light diffusing particles 121 in a single layer, at least one resin selected from acrylic resin, melamine resin, ester resin, and urethane resin is used. The refractive index of the second light diffusion particles 121 of the second diffusion layer 120 is greater than the refractive index of the second binder resin 122, but the difference should be within 0.05.

When the difference between the refractive index of the particles and the resin is 0.05 or more, the diffusivity of the light is improved. When the difference in the refractive index is less than 0.05, the light condensing effect is enhanced. In addition to the geometric focusing by the lens effect, the light condensing function due to the difference in refractive index inside the coating layer is added to further improve the luminance characteristics.

Meanwhile, the coating method of the second diffusion layer 120 is the same as that of the first diffusion layer 110.

2 is a cross-sectional view of another embodiment of a light diffusing film 200 according to the present invention. In FIG. 2, in another embodiment of the present invention, in the light diffusing film 100 according to the first embodiment, one side of the base film 130 may be formed on an opposite side to which the first and second diffusion layers are stacked. Blocking layer 140 may be further stacked.

In addition, the light diffusing film 200 according to another embodiment of the present invention having the anti-blocking layer further includes one or more components selected from the group consisting of a light source unit, a light guide plate, and a reflective sheet to be used as a backlight unit for LCD. Can be.

Hereinafter, the configuration and effects of the present invention will be described in more detail with reference to Examples and Comparative Examples. However, this embodiment is only illustrative of the present invention in more detail, and the scope of the present invention is not limited to these examples.

Example 1

A coating liquid having the following composition was applied to one surface of the transparent polyester film (XG-6DF2P, 100 µm Toray Advanced Materials Co., Ltd.) using a bar coater, and dried at 120 ° C. for 2 minutes to form a first diffusion layer. In the second diffusion layer, 15 wt% of the same binder resin on the first diffusion layer, 17.5 wt% of glass beads particles having a refractive index of 1.51 and an average particle diameter of 10 μm were mixed and applied using a bar coater, and dried at 120 ° C. for 2 minutes to coat the coating layer. It formed in a single layer and produced the light-diffusion film.

First diffusion layer  Composition of Coating Liquid

-Binder Resin (Refractive Index 1.49 Acrylic Type): 15.0wt%

Curing agent (isocyanate): 1.5wt%

-Synthetic resin particle (refractive index 1.44, silicon particle average particle diameter: 5㎛): 20wt%

Methyl ethyl ketone: 63.5 wt%

2nd diffusion layer  Composition of Coating Liquid

-Binder Resin (Refractive Index 1.49 Acrylic Type): 15.0wt%

Curing agent (isocyanate): 1.5wt%

-Synthetic resin particles (refractive index 1.51, glass beads 10㎛): 17.5wt%

Methyl ethyl ketone: 63.5 wt%

[Example 2]

A light diffusion film was manufactured in the same manner as in Example 1, except that the average particle diameter of the glass beads was 20 μm for the second diffusion layer.

 Example 3

A light diffusion film was manufactured in the same manner as in Example 1, except that the average particle diameter of the glass beads was 30 μm in the second diffusion layer.

Example 4

A light diffusing film was manufactured in the same manner as in Example 1, except that particles having a refractive index of the second diffusion layer larger than those of glass beads (refractive index 1.53, alumina average particle diameter of 10 μm) were used.

Comparative Example 1

Same as Example 1 except that the light diffusion layer was formed on one surface of the same transparent polyester film as that of Example 1 (XG-6DF2P, Toray Advanced Materials, Inc., 100 μm) using the following composition. To prepare a film.

Composition of Coating Liquid

-Binder Resin (Refractive Index 1.49 Acrylic Type): 15.0wt%

Curing agent (isocyanate): 1.5wt%

-Synthetic resin particles (acrylic particles (PMMA) particles 10㎛, refractive index 1.49): 25wt%

Methyl ethyl ketone: 63.5 wt%

Comparative Example 2

A light diffusion film was manufactured in the same manner as in Example 1, except that light diffusing particles of the first diffusion layer and the same refractive index of the binder resin were used.

Comparative Example 3

A light diffusing film was manufactured in the same manner as in Example 1, except that particles having an average particle diameter of 10 μm were used for the first diffusion layer.

[Comparative Example 4]

A light diffusion film was manufactured in the same manner as in Example 1, except that particles having an average particle diameter of 5 μm were used for the second diffusion layer.

[Comparative Example 5]

A light diffusion film was manufactured in the same manner as in Example 1, except that the particles of the second diffusion layer were increased to 27.5 wt% and the particles were laminated.

Comparative Example 6

A light diffusion film was manufactured in the same manner as in Example 1, except that the particles of the second diffusion layer had a refractive index of 1.47 and an average particle diameter of 10 μm and an acrylic resin having a refractive index of 1.49.

Comparative Example 7

A light diffusion film was manufactured in the same manner as in Example 1, except that grease bead particles having an average particle diameter of 40 μm were used for the second diffusion layer.

[evaluation]

1. Luminance

The light diffusing films prepared in Examples 1 to 4 and Comparative Examples 1 to 7 were measured using an average value of 9 points of vertical luminance on the backlight unit assembly using TOPCON BM-7A equipment, based on Comparative Example 1. Table 1 shows the relative luminance (%).

2. Haze

The haze of the light diffusing films prepared in Examples 1 to 4 and Comparative Examples 1 to 7 was based on ASTM D-1003, using a haze meter (NIPPON DENSHOKU KOGYO Co. Ltd. Model 2000) manufactured by Nippon Densoku Co., Ltd. The measurement is shown in Table 1.

3. Appearance Evaluation

The light diffusing films prepared in Examples 1 to 4 and Comparative Examples 1 to 7 were mounted on a backlight unit (BLU), and visually observed after lighting to check coating defects and other foreign matters. Judgment is shown in Table 1.

Good: Not discernible from front and side

Normal: Not discernible from the front but discernible from the side

Poor: can be identified from the front

4. Lamination (second diffusion layer)

The light diffusing films prepared in Examples 1 to 4 and Comparative Examples 1 to 7 were observed with a scanning electron microscope (SEM S-4800, Hitachi, Japan) to show the laminated structure in Table 1.

5. Adhesion (second diffusion layer)

With respect to the light diffusing films prepared in Examples 1 to 4 and Comparative Examples 1 to 7, using a cross hatch cutter (Cross Hatch cutter) to make 100 scales of 10x10 horizontal x vertical, when the adhesive tape attached and peeled off Judging by the degree, if one of the 100 falls, it was judged as 'NG', and if not falling, it is judged as 'good' and is shown in Table 1.

The relative luminance, haze, total light transmittance, appearance and lamination of the second diffusion layer of the light diffusing films prepared in Examples 1 to 4 and Comparative Examples 1 to 7 were evaluated.

Relative luminance (%) Haze (%) Light rays
Transmittance Appearance Evaluation Lamination Adhesion Example 1 104 94 74 Good fault Good Example 2 106 93 73 Good fault Good Example 3 106 92 74 usually fault Good Example 4 107 92 76 usually fault Good Comparative Example 1 100 85 83 Good fault Good Comparative Example 2 101 93 68 Good fault Good Comparative Example 3 102 91 73 Good fault Good Comparative Example 4 97 96 67 Good fault Good Comparative Example 5 98 95 79 Good Second floor Good Comparative Example 6 99 96 8 Good fault Good Comparative Example 7 92 88 81 Bad fault NG

As shown in Table 1, it can be seen that the luminance is relatively higher than the light diffusing film prepared in other comparative examples based on the light diffusing film prepared in Examples 1 to 4.

In the light-diffusion film of Comparative Example 1, the luminance was lower than that of Example 1 considering the refractive index, the resin refractive index, and the particle size of the single layer without difference in refractive index between the particles and the binder. If the refractive indices of the particles in the diffusion layer and the binder are the same, the relative luminance is lower than that in Example 1, because the larger the difference in refractive index between the particles and the binder, the better the diffusion and condensing the light to the second diffusion layer. Compared to the diffusion efficiency is low, the brightness is low.

In the case of the light diffusing film of Comparative Example 3, the particles of the first diffusion layer were adjusted to compare with Example 1, and the experiment was performed by changing the particle average particle diameter of the first diffusion layer from 5 μm to 10 μm. The case is better in terms of luminance.

In the light diffusing film of Comparative Example 4, it can be seen that the luminance is lowered when the particles of the second diffusion layer are changed to smaller particles as an example compared to Example 1 by adjusting the particle size of the second diffusion layer.

In the case of Comparative Example 5, the second diffusion layer particles are increased to cause lamination, and the diffusion is increased rather than condensation on the surface, thereby increasing the total light transmittance, and thus, the luminance is lower than that of the light diffusion film of Example 1. .

In the light diffusing film of Comparative Example 6, when the refractive index of the particles of the second diffusion layer is smaller than the binder refractive index, compared to Example 1, the surface particles of the second diffusion layer increase the diffusion of light rather than condensing and fall below the luminance of Example 1 It can be seen that.

Finally, in the case of the light diffusing film of Comparative Example 7, when the particle average particle diameter of the second diffusion layer uses 40㎛, it can be seen that the adhesion strength with the binder during coating decreases and the NG determination and the luminance fall.

Although the above has been described with respect to the preferred embodiment of the present invention, the present invention is not limited to this and can be modified and modified in various forms within the scope of the spirit of the present invention can be known to those skilled in the art, Such modifications and variations are obviously belonging to the appended claims.

100 .. Light Diffusion Film
110. First diffusion layer 111. First light diffusion particle
120. The second diffusion layer 121. The second light diffusion particle
130. Base film
140 .. Anti-blocking layer

Claims (6)

Base film; A first diffusion layer laminated on one surface of the base film and having first light diffusing particles fixed to the first binder resin; And a second diffusion layer stacked on top of the first diffusion layer, wherein second light diffusion particles having different refractive indices and average particle diameters from the first light diffusion particles are fixed to a second binder resin.
The refractive indexes of the first and second light diffusing particles are 1.30 to 1.70; The refractive index of the first light diffusing particles of the first diffusion layer is less than the refractive index of the first binder resin; The refractive index of the second light diffusion particles of the second diffusion layer is larger than the refractive index of the second binder resin, the light diffusion film. The light diffusing film of claim 1, wherein an average particle diameter of the first light diffusing particles is 1 to 8 μm, and an average particle diameter of the second light diffusing particles is 10 to 30 μm. delete The method of claim 1, wherein the difference in refractive index between the first light diffusing particles and the first binder resin of the first diffusion layer is 0.05 or more; The difference between the refractive indices of the second light diffusing particles and the second binder resin of the second diffusion layer is 0.05 or less. Base film; A first diffusion layer laminated on one surface of the base film and having first light diffusing particles fixed to the first binder resin; A second diffusion layer laminated on the first diffusion layer and having second light diffusion particles having different refractive indices and average particle diameters from the first light diffusion particles and fixed to the second binder resin; And an anti-blocking layer formed on one surface of the base film and formed on an opposite side of the first diffusion layer.
The refractive indexes of the first and second light diffusing particles are 1.30 to 1.70; The refractive index of the first light diffusing particles of the first diffusion layer is less than the refractive index of the first binder resin; The refractive index of the second light diffusion particles of the second diffusion layer is larger than the refractive index of the second binder resin, the light diffusion film. The backlight unit for LCD which is provided with the light-diffusion film of Claim 5 further equipped with one or more structure chosen from the group which consists of a light source part, a light guide plate, and a reflection sheet.

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