KR100573372B1 - Light diffusion film with transparent plastic base film for liquid crystal display - Google Patents

Abstract

The present invention relates to a light diffusing film for a liquid crystal display device based on a transparent plastic film, and an object thereof is to provide a light diffusing film that can satisfy high total light transmittance and light diffusivity.

The light diffusing film according to the present invention comprises a transparent plastic base material (1) made of any one resin selected from the group consisting of polyester, polycarbonate, polymethyl methacrylate or polystyrene; A transparent resin layer (2) laminated on one surface of the transparent plastic substrate and having a refractive index greater than that of the transparent plastic substrate; And a light diffusing layer 3 laminated on the opposite side of the transparent plastic substrate and made of a mixed layer of a binder resin, light diffusing particles, and an antistatic agent. It is preferable that the refractive index of the transparent resin layer 2 is larger than the refractive index of the transparent plastic base material 2 in 0.2 or less range. Moreover, it is preferable that the binder resin which forms the light-diffusion layer 3 is small in the range whose refractive index is 0.22 or less with respect to the refractive index of the transparent plastic base material 1.

LCD, Light Diffusion Film, Light Diffusion Layer, Light Diffusion Plate, Backlight

Description

LIGHT DIFFUSION FILM WITH TRANSPARENT PLASTIC BASE FILM FOR LIQUID CRYSTAL DISPLAY}

1 is a laminated view showing a light diffusing film according to the present invention.

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

1: transparent plastic substrate, 2: transparent resin layer,

3: light diffusion layer

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light diffusing film for liquid crystal display devices based on transparent plastic films, and in particular, to thin film transistor liquid crystal display devices (hereinafter referred to as "TFT-LCD") or super-twisted nematic liquid crystal displays. It is used in a device (hereinafter referred to as "STN-LCD"), and is made of a transparent plastic film as a base to induce uniform light diffusion while passing light emitted from a light source lamp located on the side or the back of the liquid crystal display. The present invention relates to a light diffusing film for liquid crystal display devices based on a transparent plastic film capable of obtaining a clear optical image.

In the conventional display method of the liquid crystal display device, a light guide plate using an acrylic resin having a relatively high light transparency also serves as a light diffusion role, which is advantageous in terms of cost. However, in a TFT-LCD which requires a clearer image, a conventional light guide plate is required. The method of imparting light diffusion to light (see Japanese Patent Application Laid-Open No. 4-270302 and US Pat. No. 5,289,351) has limitations. It is used for the backlight unit of TFT-LCDs, such as a television.

The light diffusing film used separately on the light guide plate is generally made by mixing light diffusing particles in a transparent plastic sheet or coating light diffusing particles on a plastic sheet (Japanese Patent Laid-Open No. 7-174909).

High light transmittance and high haze are the most important characteristics of a light diffusing film having a function of uniformly diffusing while passing through the light guide plate irradiated from the light source lamp without loss.

Accordingly, an object of the present invention is to provide a light diffusing film that can satisfy high total light transmittance and light diffusivity.

In order to achieve the above object, in the light diffusion film according to the present invention, a transparent resin layer is applied to one side of the transparent plastic substrate and the light diffusion layer is laminated on the opposite side of the transparent plastic substrate. As a transparent plastic base material, things, such as a polyester film, a polycarbonate film, a polymethyl methacrylate film, polystyrene, etc. are employ | adopted. The light diffusing layer is composed of a mixed layer of a binder resin, light diffusing particles, and an antistatic agent.

In the case of the conventional light diffusion film, the light diffusion layer is generally applied directly to the transparent substrate layer, so that light reflection and scattering may occur between the transparent substrate layer and the light diffusion layer, thereby reducing the total light transmittance of the light diffusion film.

However, when the light diffusion layer is laminated on one side of the transparent plastic substrate and the transparent resin layer having a larger refractive index in the range of 0.2 or less than the refractive index of the transparent plastic substrate is laminated on the opposite side as in the present invention, the transparent resin layer and the transparent plastic substrate Light reflection and scattering at the interface between the transparent plastic substrate and the interface between the transparent plastic substrate and the light diffusing layer can be reduced, thereby improving the total light transmittance of the entire light diffusing film. Since the total light transmittance at this time is a path through which light travels from the transparent resin layer to the light diffusion layer, optical characteristics such as light transmittance, haze, and glossiness in this direction are the largest for the luminance and uniformity of the entire backlight unit. It can be said to affect.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

The light transmittance of the transparent plastic substrate 1 used as the substrate of the light diffusion film is preferably in the range of 85 to 95%, more preferably 90 to 94%. In addition, in order to improve the adhesion between the transparent resin layer 2 and the light diffusing layer 3 and to improve the coating property, it is also possible to use a substrate coated with a primer or a transparent plastic substrate 1 subjected to corona or plasma treatment. .

On the other hand, the binder resin used in the light diffusion layer 3 should be transparent, and acrylic, urethane, epoxy, vinyl, polyester, polaramide, etc., such as polymethyl methacrylate or methacrylic acid ester copolymer. It can use individually or in mixture of 2 or more types in resin. Especially, when the polyester film is used as the transparent plastic base material 1 of a light-diffusion film, the polyester type which is excellent in adhesive force with a polyester film, and a urethane-polyester copolymer are especially preferable.

In addition, the refractive index of the transparent binder resin should be smaller than the refractive index of the transparent plastic substrate 1 while the difference from the refractive index of the transparent plastic substrate 1 is in the range of 0.22 or less. When the refractive index of the binder resin is larger than the refractive index of the transparent plastic substrate 1, the light diffuses from the transparent resin layer 2 toward the light diffusing layer 3 and the light diffusing layer 3 and the transparent plastic substrate 1. At the interface between and, more reflection occurs than transmission, which lowers light transmittance. In addition, when the difference in the refractive index is 0.22 or more, a lot of light refraction and scattering occurs at the interface between the light diffusing layer 3 and the transparent plastic substrate 1, making it difficult to obtain a light diffusing film having high luminance.

And the thickness of the light-diffusion layer 3 has the preferable range of 0.1-80 micrometers. When the thickness of the light diffusing layer 3 is 0.1 μm or less, the haze is not high, so that high uniformity of light is hardly obtained in the backlight unit. It is difficult to obtain high luminance in the backlight unit of the display device.

As the light diffusing agent used in the light diffusing layer 3, transparent particles or white particles are preferably used. 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. As the white particles, titanium oxide, zinc oxide, barium sulfate, calcium carbonate, magnesium carbonate, aluminum hydroxide, clay, and the like may be used, and a light diffusing agent of these transparent particles or white particles may be used alone or in combination of two or more kinds thereof. Can be.

The antistatic agent added to the coating liquid of the light diffusing layer 3 is required to lower the surface resistance of the light diffusing film to prevent foreign matter from being mixed due to static electricity in the assembly process of the backlight unit using the light diffusing film. The antistatic agent is preferably a colorless cationic polymer antistatic agent or a nonionic polymer antistatic agent which does not affect the light transmittance of the light diffusion film, and is used in an amount of 0.1 wt% to 5 wt% based on the content of the binder resin. good. When the antistatic agent is used in an amount of 0.1 wt% or less with respect to the binder resin, it is difficult to have a surface resistance value (10 ¹² kPa or less) that is effective in preventing foreign matters. The hardness of 3) deteriorates and the scratch resistance of the light diffusing film is lowered.

In addition, in order to manufacture a light diffusing film for use in a liquid crystal display device having a predetermined range of optical characteristics, it is important to properly adjust the ratio of the binder resin and the light diffusing agent. In particular, in order to produce a light diffusing film having a total light transmittance of 85 to 94%, the ratio of the light diffusing agent to the binder resin is preferably in the range of 20 to 300% by weight. If the ratio of the light diffusing agent to the binder resin is 20% by weight or less, it is difficult to obtain excellent light diffusivity due to the low haze. If the ratio of the light diffusing agent to the binder resin is 300% by weight or more, the total light transmittance is lowered to have a high light transmittance. Light diffusion film cannot be obtained.

In addition, in order to adjust the light transmittance, the thickness of the light-diffusion layer 3 is 3-50 micrometers, More preferably, it is the range of 10-30 micrometers. If the thickness of the light diffusion layer 3 is 3 μm or less, the light transmittance and haze are reduced. If the thickness of the light diffusion layer 3 is 50 μm or more, the total light transmittance is 85% or less, resulting in cracks in the light diffusion layer 3 during the reliability test. This may occur and the desired light diffusion film may not be manufactured.

On the other hand, as an additive used in the light diffusing layer 3, a coupling agent may be used to increase the mixing property of the binder resin and the light diffusing agent, but the amount of the additive is preferably 2 to 10% by weight based on the light diffusing agent, more preferably. It is the range of 4-8 weight%. When 2 wt% or less of the coupling agent is used with respect to the light diffusing agent, there is no significant effect in improving the mixing properties of the binder resin and the light diffusing agent. The light transmittance of the light diffusing film can be reduced. As the coupling agent mainly used, a silane coupling agent is used.

On the other hand, the transparent resin layer applied to the opposite side of the transparent plastic substrate 1 is made of a transparent resin having a refractive index having a larger value in the range of 0.2 or less than the refractive index of the transparent plastic substrate 1 as described above. The refractive index of the transparent plastic substrate 1 should be greater than that of the transparent plastic substrate 1 so that light is more easily transmitted to the transparent plastic substrate 1 than to reflection at the interface between the transparent plastic substrate 1 and the transparent resin layer 2. However, when the refractive index of the transparent resin is greater than 0.2 than the transparent plastic substrate 1, scattering and refraction occur a lot at the interface, and thus lower the overall light transmittance of the light diffusing film. Resin is not recommended.

For example, when the transparent plastic substrate 1 is PET (polyethylene terephthalate, refractive index 1.64), the transparent resin for the transparent resin layer 2 may be polydiphenylmethane bis (4-phenyl) carbonate (refractive index 1.66), Polyvinyl naphthalene (refractive index 1.68), polypentabromophenyl methacrylate (refractive index 1.71), etc. are mentioned. The thickness of the transparent resin layer 2 is preferably in the range of 1 to 30 µm. When the thickness of the transparent resin layer 2 is 1 μm or less, there is almost no improvement in light transmittance. When the thickness of the transparent resin layer 2 is 30 μm or more, the light transmittance may be due to light absorption of the transparent resin layer 2 itself. Because of this decrease, the transparent resin layer 2 should not be applied to a thickness greater than this.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples.

<Example 1>

As a transparent plastic substrate 1, polyvinyl naphthalene resin (refractive index 1.68) was added to one side of a transparent polyester film (Saehan, XG-500, 100 µm, refractive index 1.64) using a bar coater. After applying to a thickness of μm to make a transparent resin layer (2), the coating liquid having the following composition on the opposite side of the transparent polyester film using a bar coater, and then dried at 100 ℃ for 2 minutes to give a light diffusion layer (3 A light diffusing film having a thickness of 20 m) was prepared.

Composition of Coating Liquid

-Polyester resin (TOYOBO, VYLON 200, refractive index 1.50): 25.0g

-Synthetic acrylic beads (SOKEN CHEMICAL, MX-150): 6.0g

-Synthetic silica particles (FUSI-SILYSIA, SILYSIA 250): 3.0g

-Silane coupling agent (OSI SPECIALTIES, A-189): 0.5g

-Antistatic Agent (ACL, STATICIDE 2002): 0.25g

Methyl ethyl ketone: 66.0 g

<Example 2>

As the transparent plastic substrate 1, a polyvinyl naphthalene resin (refractive index 1.68) was used on one side of a transparent polyester film (Saehan Co., Ltd., XG-500, 100 µm, refractive index 1.64) using a bar coater. After applying to a thickness of μm to make a transparent resin layer (2), the coating liquid having the following composition on the opposite side of the transparent polyester film using a bar coater, and then dried at 100 ℃ for 2 minutes to give a light diffusion layer (3 A light diffusing film having a thickness of 20 m) was prepared.

Composition of Coating Liquid

Urethane-polyester resin (TOYOBO, UR-1400): 25.0 g

-Synthetic acrylic beads (SOKEN CHEMICAL, MX-150): 5.0g

-Synthetic silica particles (FUSI-SILYSIA, SILYSIA 250): 4.0g

-Silane coupling agent (OSI SPECIALTIES, A-189): 0.5g

-Antistatic Agent (ACL, STATICIDE 2002): 0.25g

Methyl ethyl ketone: 66.0 g

<Example 3>

As a transparent plastic substrate (1), a bar coater was coated with a polypentabromophenyl methacrylate resin (refractive index 1.71) on one side of a transparent polyester film (Saehan, XG-500, 100 µm, refractive index 1.64). After applying to a thickness of 10㎛ using a) to make the transparent resin layer (2), the light diffusing layer (3) has the same composition as in Example 1 to produce a light diffusing film having a thickness of 20㎛. It was.

Comparative Example 1

10 μm of the transparent resin layer 2 was applied as in Example 1, and then the light diffusing layer 3 was coated with the following composition to prepare a light diffusing film.

Composition of Coating Liquid

-Polyester resin (TOYOBO, VYLON 200): 25.0g

-Synthetic acrylic beads (SOKEN CHEMICAL, MX-150): 2.0g

-Synthetic silica particles (FUSI-SILYSIA, SILYSIA 250): 2.0g

-Silane coupling agent (OSI SPECIALTIES, A-189): 0.5g

-Antistatic Agent (ACL, STATICIDE 2002): 0.25g

Methyl ethyl ketone: 66.0 g

Comparative Example 2

10 μm of the transparent resin layer 2 was applied as in Example 1, and then the light diffusing layer 3 was coated with the following composition to prepare a light diffusing film.

Composition of Coating Liquid

-Polyester resin (TOYOBO, VYLON 200): 25.0g

-Synthetic acrylic beads (SOKEN CHEMICAL, MX-150): 80.0g

-Synthetic silica particles (FUSI-SILYSIA, SILYSIA 250): 15.0g

-Silane coupling agent (OSI SPECIALTIES, A-189): 0.5g

-Antistatic Agent (ACL, STATICIDE 2002): 0.25g

Methyl ethyl ketone: 66.0 g

Comparative Example 3

10 μm of the transparent resin layer 2 was applied as in Example 1, and then the light diffusing layer 3 was coated with the following composition to prepare a light diffusing film.

Composition of Coating Liquid

-Polyester resin (TOYOBO, VYLON 200): 25.0g

-Synthetic acrylic beads (SOKEN CHEMICAL, MX-150): 6.0g

-Synthetic silica particles (FUSI-SILYSIA, SILYSIA 250): 3.0g

-Silane coupling agent (OSI SPECIALTIES, A-189): 0.5g

-Antistatic Agent (ACL, STATICIDE 2002): 0.015g

Methyl ethyl ketone: 66.0 g

<Comparative Example 4>

10 μm of the transparent resin layer 2 was applied as in Example 1, and then the light diffusing layer 3 was coated with the following composition to prepare a light diffusing film.

Composition of Coating Liquid

-Polyester resin (TOYOBO, VYLON 200): 25.0g

-Synthetic acrylic beads (SOKEN CHEMICAL, MX-150): 6.0g

-Synthetic silica particles (FUSI-SILYSIA, SILYSIA 250): 3.0g

-Silane coupling agent (OSI SPECIALTIES, A-189): 0.5g

-Antistatic Agent (ACL, STATICIDE 2002): 2.0g

Methyl ethyl ketone: 66.0 g

Comparative Example 5

Instead of applying the transparent resin layer 2 to the transparent plastic substrate 1, a light diffusion layer 3 is applied to the transparent plastic substrate 1 using a coating liquid having the same composition as in Example 1 to prepare a light diffusion film. It was.

Comparative Example 6

The transparent resin layer 2 was applied to the transparent plastic substrate 1 using polytetrachlorofluoroethylene (PTCFE, refractive index 1.38) instead of polyester or urethane-polyester, and the opposite side of the transparent plastic substrate 1 The light diffusing layer 3 was applied using a coating liquid having the same composition as in Example 1 to prepare a light diffusing film.

Table 1 below shows the light diffusing films according to Examples 1 to 3 and the light diffusing films according to Comparative Examples 1 to 6 to compare total light transmittance, haze, surface resistance, and scratch resistance, respectively. will be.

The total light transmittance and the haze were measured according to ASTM D-1003, and the measuring device used a model 1000 of NIPPON DENSHOKU CO., LTD. In addition, the surface resistance was measured according to ASTM D 257, and the measuring apparatus was measured using the model P-618 of KAWAGUCHI ELECTRIC WORKS. In addition, scratch resistance was good as pencil hardness was 2H or more, and it was judged as bad when it was less.

Total light transmittance (%) Haze Surface resistance Scratch resistance Example 1 92.5 88.5 10 ¹⁰ Good Example 2 91.6 89.2 10 ¹⁰ Good Example 3 93.4 89.1 10 ¹⁰ Good Comparative Example 1 92.1 45.5 10 ¹⁰ Good Comparative Example 2 62.3 97.6 10 ¹⁰ Good Comparative Example 3 92.4 88.6 10 ¹⁴ Good Comparative Example 4 91.2 88.9 10 ⁸ Bad Comparative Example 5 75.2 88.6 10 ¹⁰ Good Comparative Example 6 72.2 89.1 10 ¹⁰ Good

As can be seen from Table 1, on the one side of the transparent plastic substrate 1 as in Examples 1 to 3 by applying a resin having a refractive index larger than the substrate 1 in the range of 0.2 or less, the transparent resin layer (2) In the case of lamination, a high light transmittance can be obtained. However, even if there is no transparent resin layer 2 as in Comparative Example 5, if the refractive index is smaller than that of the transparent plastic substrate 1 as in Comparative Example 6, the desired light transmittance cannot be obtained. It can be seen that. When the amount of the light diffusing agent is excessive, as in Comparative Example 1, the haze is very high but the light transmittance is low, so that the desired light diffusing film cannot be obtained. In addition, when the addition amount of the antistatic agent is insufficient, as in Comparative Example 3, the surface resistance is high, the effect of preventing foreign matters is not seen. In addition, when the amount of the antistatic agent added is excessive as in Comparative Example 4, it can be seen that the surface resistance is very low but the scratch resistance is poor.

In the light-diffusion film for liquid crystal display devices based on the transparent plastic film which concerns on this invention comprised as mentioned above, the refractive index of one side of the transparent plastic base material 1 is 0.2 or less than the transparent plastic base material 1 in the range. The transparent resin layer 2 is laminated, and the light diffusing layer 3 is laminated on the opposite side of the transparent plastic substrate 1 so that excellent light diffusion, haze and scratch resistance are excellent, and the surface resistance is low. Since a plate can be obtained, the quality of a liquid crystal display device can be improved.

Claims (3)

Transparent plastic base material which consists of any resin chosen from the group containing polyester, polycarbonate, polymethyl methacrylate, or polystyrene; A transparent resin layer laminated on one surface of the transparent plastic substrate and having a refractive index greater than that of the transparent plastic substrate; And, A transparent plastic film laminated on the opposite side of the transparent plastic substrate, comprising a light diffusion layer comprising a binder resin, a light diffusion particle, and a mixed layer of an antistatic agent having a refractive index smaller than that of the transparent plastic substrate. Light diffusing film for liquid crystal display device as a base material. The light diffusing film for a liquid crystal display device according to claim 1, wherein the refractive index of the transparent resin layer is larger than the refractive index of the transparent plastic substrate in a range of 0.2 or less. The method of claim 1, wherein the binder resin forming the light diffusion layer is used by mixing any one or two or more selected from the group consisting of acrylic resin, urethane, epoxy, vinyl, polyester or polaramide resin and In addition, the refractive index is small in the range of 0.22 or less with respect to the refractive index of the transparent plastic substrate, The light diffusing particles are any one selected from the group consisting of acrylic particles, styrene particles, silicon particles, synthetic silica, glass beads, diamond, titanium oxide, zinc oxide, barium sulfate, calcium carbonate, magnesium carbonate, aluminum hydroxide or clay Or a mixture of two or more kinds, The antistatic agent is a liquid crystal display device based on a transparent plastic film, characterized in that a colorless cationic polymer antistatic agent or a nonionic polymer antistatic agent is used and its content is 0.1 to 5% by weight relative to the binder resin. Light diffusion film.

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