KR100611460B1 - Light diffusing film having excellent anti-refraction ability and Backlight unit using the Same - Google Patents

Abstract

The present invention relates to a light diffusing film excellent in antireflection performance, and more particularly, a light diffusing layer formed of a transparent resin and a diffusion bead is formed on one side of a transparent substrate and a low refractive index layer having a refractive index of 1.2 to 1.45 on the other side. The present invention relates to a light diffusing film that is laminated alone or sequentially with a high refractive index layer having a refractive index of 1.6 to 2.9. When the backlight unit is configured using the light diffusing film, a high brightness liquid crystal display device may be provided without increasing illuminance of a light source.

Anti-reflection, light diffusion film, high brightness, backlight unit, transparent substrate, high refractive layer, low refractive layer, liquid crystal display device

Description

Light diffusing film having excellent anti-refraction ability and Backlight unit using the Same}             

1 is a cross-sectional view illustrating a structure of a backlight unit constituting a liquid crystal display device.

2 is an explanatory diagram showing the progress of incident light and reflected light in a structure in which a single layer thin film is formed on a glass substrate.

3 is a cross-sectional view showing a layer structure of a light diffusing film having excellent antireflection performance composed of a high refractive index layer and a low refractive layer layer on a back surface thereof.

4 is a cross-sectional view showing the layer structure of the light diffusing film excellent in the antireflection performance of which the white surface is composed of a hard coating layer, a high refractive layer, and a low refractive layer.

5 is a cross-sectional view showing the layer structure of the light diffusing film excellent in the antireflection performance of which the white surface is composed of an antiblocking layer, a high refractive layer, and a low refractive layer.

Fig. 6 is a cross-sectional view showing the layer structure of the light diffusion film having excellent antireflection performance in which the white surface is composed of only the low refractive layer.

FIG. 7 is a cross-sectional view showing a layer structure of a light diffusing film having excellent antireflection performance, in which a back surface is composed of a hard coating layer and a low refractive layer.

8 is a cross-sectional view showing the layer structure of the light diffusing film excellent in the antireflection performance of which the back surface is composed of an antiblocking layer and a low refractive layer.

The present invention relates to a light diffusing film having excellent antireflection and a backlight unit using the same. More specifically, a light diffusing layer is formed on one surface of a transparent substrate and a low refractive index layer having a refractive index of 1.2 to 1.45 on the other surface alone, or The present invention relates to a light diffusing film sequentially stacked with a high refractive index layer having a refractive index of 1.6 to 2.9. When the backlight unit of the liquid crystal display device is used using the light diffusing film, the light diffusing film having excellent antireflection performance can be provided.

Conventionally, in order to improve the brightness of a liquid crystal display, brightness improvement in the backlight unit can be obtained through various methods such as applying a brightness enhancement film (BEF), changing a light guide plate design, changing a particle design of a light diffusing film, and using a highly transparent transparent substrate. However, the present invention has reached the limit of the brightness enhancement technology. In the present invention, in the light diffusing film for the backlight unit, a light diffusing film having an antireflection layer formed on the opposite side of the light diffusing layer (front surface) is provided to provide a liquid crystal display device. I want to get high brightness.

In general, an antireflection film (AR film) has been used to improve the clarity and visibility of an image by reducing reflection of external light by being applied to an optical filter of a polarizing plate or a plasma display panel (PDP) of a liquid crystal display device. Publication 2003-149413, Republic of Korea Patent Publication No. 2003-0066178). There has long been known in the optics theories of antireflective coatings that extinguish the reflected light reflected from the surface by forming thin films of different refractive indices on the surface of the object. However, this theory has been difficult to realize due to the absence of thin film formation technology. Since the 1940s, the development of dry thin film formation technology by vacuum deposition method and sputtering method has been applied to the real life. With the development and advancement, the demand for anti-reflective coating is greatly increased.

Reflected light reflected from the surface of the optical product causes the following major problems. First, the ratio of the reflected light reflected from the surface of the substrate to the incident light is the lowest with respect to the vertical incident light (incident angle 0 ° in the normal) and increases as the angle of observation and the incident light increases. In the case of flat panel displays such as liquid crystal displays and plasma display panel (PDP) TVs, the resolution ratio of the image is remarkably reduced due to the difference in the reflection ratio, and the image is completely blurred according to the viewing angle. Secondly, the increase in the reflected light reduces the transmittance of the substrate, causing problems in products requiring high transmittance such as glasses and optical lenses. As in the case of a compound eye lens or the like, in the case of an optical base such that the reflected light is amplified, the problem of such a decrease in transmittance is very serious. Third, unnecessary glossiness appears on the surface of the optical substrate due to the reflected light. In order to solve these problems, antireflective coatings have recently been widely applied to optical substrates and display products.

Korean Patent Laid-Open Publication No. 2003-0057335 discloses an antireflection layer composed of concave and convex portions on an exit surface of a light guide plate to achieve high transmittance through an excellent antireflection effect in order to improve the brightness of a liquid crystal display device. Techniques for improving are disclosed. Such an antireflection layer reduces the reflectance on the surface by forming fine irregularities such as micro-patterns on the surface of the optical substrate without using the high and low refractive layers of the thin film. The concave and convex portions formed by the concave portion and the convex portion are formed by a molding method by injection or extrusion. If the micro-pattern cannot be precisely processed due to the limitation of the process, the concave and convex portions are emitted to the upper part of the scattering of visible light or the upper part of the light guide plate, which may lower the luminance of the liquid crystal display device. It has a problem that may be an obstacle to the progress of light.

Japanese Laid-Open Patent Publication No. 2003-149413 provides a liquid crystal display device having a wide viewing angle and an anti-reflection function that does not cause contrast deterioration, grayscale or black reversal, and color change according to visual changes. In order to realize this, a light diffusing layer formed of a light-transmitting resin containing a high refractive monomer or an inorganic particle and a light-transmitting fine particle (scatter) on a cellulose acetate film is formed, and a low refractive index layer is formed on the light diffusing layer. Is applied to the viewing side (liquid crystal cell basis) of the liquid crystal display device. In order to impart the antireflection function of external light to the polarizing plate on the viewing side, a low refractive index layer having a refractive index of 1.35 to 1.45 and a high refractive monomer or inorganic particle, which is a cross-linked cured product by thermal or ionizing radiation, of a composition containing a fluorine-containing compound and inorganic fine particles An anti-glare film composed of a light diffusing layer composed of a light transmitting resin having a refractive index of 1.64 to 1.8 and light transmitting fine particles (scattering body) is proposed. However, this anti-glare film is an anti-glare film for polarizing plates that cannot be used for a backlight unit of a liquid crystal display device.

In general, the backlight unit includes a cold cathode fluorescent lamp (CCFL), a reflective film, a light guide plate, a light diffusion film, and a prism sheet as shown in FIG. 1. When the antiglare film is applied to the backlight unit, since the low refractive layer formed on the light diffusion layer containing a large amount of scattering material is located on the opposite side to the direction in which light is emitted from the backlight, the effect of reducing the reflectance may be exerted. And therefore does not contribute to the brightness improvement of the liquid crystal display device. In addition, when the low refractive layer formed on the light diffusing layer is positioned in the light emitting direction (positioned to be in contact with the upper part of the light guide plate), the light diffusing layer is located in the light emitting direction although there is an effect of reducing the reflectance. As a result, the luminance of the liquid crystal display is rather reduced.

The present invention has been studied to improve the transmittance and brightness by reducing the reflectance at low power, and as a result, a new light composite film and an external antireflective film in which a high refractive index layer and / or a low refractive layer are laminated on one surface of the light diffusing film An optical design is provided and a backlight unit is used to improve the brightness of a liquid crystal display device.

That is, in one aspect of the present invention, a light diffusion layer is formed on one side of the transparent substrate, the refractive index is different from the transparent substrate on the other side, and a high refractive layer having a refractive index of 1.6 to 2.9 and a low refractive layer having a refractive index of 1.2 to 1.45 are sequentially The present invention relates to a light diffusion film having excellent laminated antireflection capability.

Another aspect of the present invention relates to a light diffusing film having excellent antireflection capability in which a light diffusing layer is formed on one side of a transparent substrate and a low refractive layer having a refractive index of 1.2 to 1.45 is formed on the other side.

Another aspect of the present invention relates to a backlight unit of a liquid crystal display device having a light diffusion film having excellent antireflection capability such that the light diffusion layer (front surface) is on the viewing side (liquid crystal module direction).

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

The light diffusing film having excellent anti-reflection capability of the present invention forms a light diffusing layer on one side of the transparent substrate, and on the other side, a low refractive index layer having a refractive index of 1.2 to 1.45 alone or a high refractive layer having a refractive index of 1.6 to 2.9 sequentially. The present invention relates to a film laminated with a high refractive index layer, a hard coating layer, or an anti-blocking layer between the transparent substrate and the low refractive index layer.

In the present invention, the method of reducing the reflectance at the surface of the substrate is a method of thin film coating the low refractive index material alone or the low refractive index material and the high refractive index material sequentially on the substrate, wherein the low refractive index layer is always applied to the high refractive index layer with respect to the substrate surface. It must be located at the top. In addition, by applying the anti-reflective optical theory, optimal low and high refractive index materials should be used, and it is necessary to optimize the thickness of the thin film of each layer.

As shown in FIG. 2, the anti-reflective coating through thin film formation is a principle that the light reflected from the upper part of the thin film and the light reflected from the lower part have a phase difference of 180 ° to be offset. For the design and fabrication of optical thin films, the concept of optical thickness, phase thickness, and physical thickness is used.

Physical thickness: d

Optical thickness: nd

Optical phase thickness: δ = 2πnd / λ

1/4 wavelength optical thickness: nd = (2m + 1) λ / 4 (m = 0, 1, 2, 3)

Antireflection conditions (refractive index) at 1/4 wavelength optical thickness: n12 = no × n2

As shown in Fig. 2, when the optical thickness nd of the thin film is λ / 4 (m = 0), the phase thickness δ at this time is π / 2, and the total phase difference is π. Therefore, the reflected light is completely canceled interference is the principle to be used in the present invention.

Hereinafter, each element constituting the film of the present invention will be described in more detail.

[Transparent mention]

The transparent substrate used in the high brightness light diffusing film of the present invention is not limited as long as it is a high transparent film having excellent transmittance, low haze and excellent mechanical properties. Examples of preferred transparent substrates that can be used for the production of high brightness light diffusing films include polyethylene terephthalate (PET) films, polyethylene naphthalate (PEN) films, polycarbonate (PC) films, polystyrene films, polyvinyl chloride films, and polyethylene films. And polypropylene films, and the like, but are not limited thereto. It is preferable that the thickness of these transparent base materials is 50-200 micrometers. If a transparent substrate having a thickness of 50 μm or less is used, wrinkles may occur due to heat shrinkage and tension applied to the film in the coating and drying process. In addition, when the thickness of the transparent substrate is thin, there is a disadvantage in that bending phenomenon (Curl) may occur when the film is cut to the size of the backlight unit due to the difference in shrinkage between the light diffusion layer and the antireflection layer. In the case of using a transparent substrate having a thickness of 200 μm or more, the overall thickness of the film is increased more than necessary, which causes a reduction in weight and thickness of the backlight unit.

[Light Diffusion Layer]

The light-diffusion layer constituting the high brightness light-diffusion film of the present invention is composed of a light-transmitting organic polymer particle or inorganic particle serving as a light scattering body and a light-transmitting resin serving as a binder as in the case of a normal light-diffusion film.

As light-transmitting organic polymer particle | grains, the particle | grains made from polymers, such as a crosslinking type acrylic resin, methacryl resin, and polystyrene, are preferable, and polymethyl methacrylate (PMMA) is more preferable as said crosslinking type acrylic resin. As the inorganic particles, silica or titanium dioxide is preferable. The particle diameter of the organic polymer particles or the inorganic particles is preferably 1 μm or more and 30 μm or less. The monodisperse particles having the same particle diameters and the polydisperse particles in which particles having different particle diameters are mixed may be used alone or in combination of two. When only monodisperse particles are used, haze of a light-diffusion layer is low, and when polydisperse particles are used, haze increases by many light scattering.

As translucent resin which comprises a light-diffusion layer, resin hardened | cured by an ultraviolet-ray or a heat can be used. In order to remove fine dust or foreign matter adhering to the surface during the work process of cutting the light diffusing film or mounting the backlight unit, it is frequently performed to wash the surface of the light diffusion layer with an alcohol solvent such as IPA (isopropyl alcohol). Therefore, the light-transmitting resin should have solvent resistance to these solvents, otherwise it will cause whitening phenomenon and the transmittance will decrease or the light uniformity will not be able to serve as a light diffusion film. Examples of the translucent resin include acrylic resins or methacrylic resins, urethane resins, polyester resins, styrene-acrylonitrile copolymer resins such as homopolymers or copolymers containing acrylic esters or methacrylic esters as a component of a monomer. , Styrene resin, vinyl acetate resin, vinyl chloride resin, butyral resin, silicone resin and the like. More preferred is a highly transparent acrylic resin or methacryl resin having excellent transmittance.

The thermosetting light diffusing layer is composed of a gravure roll coating method, a reverse roll coating method, a die coating method, a blade coating method, and a comma coating by blending a transparent organic polymer particle or an inorganic particle, a thermosetting resin, a curing agent, and other additives. It can coat on a base material by the method etc., and it is obtained by drying under the temperature of 50-150 degreeC.

Monomers used in thermosetting resins are acrylic acid, methacrylic acid, acrylate, methacrylate, ethyl acrylate, butyl acrylate, methyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate and hydride. Hydroxymethyl acrylate, hydroxy ethyl acrylate, hydroxy butyl acrylate, hydroxy methyl methacrylate, hydroxy ethyl methacrylate, hydroxy butyl methacrylate and the like. The monomer can be readily prepared by radical polymerization using a suitable initiator in a suitable organic solvent such as methyl ethyl ketone. Such a thermosetting acrylic resin has a polar functional group such as a hydroxyl group or a carboxyl group present in the polymer side chain to form a hydrogen bond with a substrate such as polyester or cellulose acetate, thereby improving the adhesion of the coating film to the substrate.

The curing agent of the thermosetting resin is one selected from the group consisting of isocyanate, melamine formaldehyde, urea formaldehyde, polyaziridine, titanate, zirconium complex and epoxy which can easily react with hydroxyl group or carboxyl group which is a reactor of thermosetting acrylic resin. It may be abnormal.

It is preferable that the addition ratio of the hardening | curing agent with respect to a thermosetting resin shall be 1: 10-10: 1 on a solid content basis. If the amount of the curing agent added to the thermosetting resin is less than 1/10, the curing reaction is insufficient, so that the heat and scratch resistance of the coating layer is lowered. If the curing time is 10 times or more, the pot life of the coating solution is shortened due to the excessive use of the curing agent. have.

In consideration of manufacturing efficiency, cost, or scratch resistance, the ultraviolet curable resin is more suitable, but the ultraviolet curable light diffusion layer can be formed as follows. The coating liquid is prepared by adding UV-curable resin, light-transmitting organic polymer particles or inorganic particles, and other additives in a suitable solvent and dissolving or dispersing them in a predetermined ratio, respectively. As said other additive, a photoinitiator, a ultraviolet absorber, a light stabilizer, antioxidant, a leveling agent, an antifoamer, etc. are mentioned.

As the ultraviolet curable resin, a composition in which monomers, oligomers, and prepolymers having a polymerizable unsaturated bond, such as acryloyl group, methacryloyl group, acryloyloxy group, and methacryloyloxy group, can be appropriately mixed according to the intended use are used. do. Examples of the monomer include methyl acrylate, methyl methacrylate, methoxy polyethylene methacrylate, cyclohexyl methacrylate, phenoxyethyl methacrylate, ethylene glycol dimethacrylate, dipentaerythritol hexane acrylate, styrene and the like. Can be. Examples of the oligomers or prepolymers include acrylates such as polyester acrylates, polyurethane acrylates, epoxy acrylates, polyethyl acrylates, alkyd acrylates, melamine acrylates and silicone acrylates, unsaturated polyesters, and epoxy compounds. have. When durability is required in a harsh environment such as heat resistance, abrasion resistance, and solvent resistance of the cured film, it is preferable to increase the amount of monomer and to use a trifunctional or higher acrylate monomer.

In order to harden said ultraviolet curable resin, it is necessary to add a photoinitiator. Examples of the photopolymerization initiator include acetphenones such as diethoxyacetphenone, benzyl dimethyl ketal, and 1-hydroxycyclohexyl phenyl ketone, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin isobutyl ether, and the like. Benzoin ethers, benzophenone, 4-phenylbenzophenone, 4-benzoyl-N, N-dimethyl-N- [2- (1-oxo-2-propenyloxy) ethyl] benzenmetanium bromide , Benzophenones such as (4-benzoylbenzyl) trimethylammonium chloride, thioxanthones such as 2,4-diethyl thioxanthone and 1-chloro-4-dichlorothioxanthone, and 2,4,6-trimethylbenzoyl Diphenyl benzoyl oxide etc. are mentioned. These can be used individually or in mixture of many. Moreover, as an accelerator (sensitizer), amine compounds, such as N and N- dimethyl paratoluidine, can also be used. As content of a photoinitiator, the range of 0.1-10 weight% is preferable with respect to an ultraviolet curable resin on a solid content basis.

When the coating film is formed by UV curing, the above materials must be properly blended or a device is provided to satisfy the following characteristics; ① UV curing should be less interference (N2 Purging device), ② curing shrinkage should be small, ③ adhesion to substrate should be good.

[High refractive layer]

The high refractive index layer contains at least one of a translucent resin cured by ultraviolet rays or heat, a monomer having high refractive index, and inorganic fine particles. The refractive index of the high refractive layer is in the range of 1.6 to 2.9, and the thickness is preferably 30 to 300 nm. In addition, when giving a high refractive index function to the hard coating layer can form a high refractive layer in the range of 30nm ~ 5um. If the refractive index is less than 1.6, it is difficult to obtain an optical film excellent in antireflection performance, and it is difficult to form a layer having a refractive index of greater than 2.9 with the present technology and materials.

If the anti-reflection capability required is not high (i.e., a low reflection antireflection layer), a low refraction layer may be formed directly on the transparent substrate of the light diffusing film or on the anti-blocking layer on the back surface. In this case, the refractive index of the transparent base material or the antiblocking layer under the low refractive layer is about 1.4 to 1.6.

As said high refractive inorganic fine particle, what is necessary is just to be able to obtain the layer in the range of refractive index 1.6-2.9, and it will not specifically limit. For example, TiO ₂ (refractive index 2.3-2.9), ITO (indium tin oxide, refractive index 1.95), ATO (antimony in oxide) 1, SnO ₂ (refractive index 2.0-2.1), ZnOx (refractive index 1.9-2.1), ZrO ₂ ( Refractive index 2.05), Sb ₂ O ₃ (refractive index 1.7), Y ₂ O ₂ (refractive index 1.87), La ₂ O ₃ (refractive index 1.95), and the like. These inorganic fine particles can be used individually by 1 type, and can also be used in combination of 2 or more type. Although content of a high refractive inorganic fine particle does not have a restriction | limiting in particular, Usually, it is 200-2000 weight part with respect to 100 weight part of translucent resin. If the high refractive index layer contains inorganic fine particles of 200 parts by weight or less, the required high refractive index cannot be obtained. If the high refractive index layer is added in excess of 2000 parts by weight, the dispersibility of the inorganic fine particles in the resin may occur, causing agglomeration between particles. aggregation may appear.

The ultraviolet curable high refractive layer can be formed as follows. Ultraviolet curable resins, high refractive monomers, inorganic fine particles, and other various additives are added to a suitable solvent at predetermined ratios to dissolve or disperse to prepare a coating solution. As said other additive, a photoinitiator, a ultraviolet absorber, a light stabilizer, antioxidant, a leveling agent, an antifoamer, etc. are mentioned. Ultraviolet curable resin, a photoinitiator, etc. which were demonstrated by the said light-diffusion layer part can be applied.

[Low refractive layer]

The low refractive layer is composed of a thermosetting or ultraviolet curable resin, fine particles having a low refractive index, and other additives. If the refractive index of the low refractive index layer is less than or equal to the refractive index of the high refractive layer, it can serve as an antireflection layer, but preferably has a refractive index of 1.2 to 1.45. It is preferable that the thickness of a low refractive layer is 30-300 nm.

As low refractive index resin (refractive index 1.5 or less), thermosetting polysiloxane resin (for example, KP-854 and KP-85 by Shin-Etsu Chemical Co., Ltd.), thermosetting fluorine-containing polysiloxane resin, and ultraviolet curable resin are mentioned. As ultraviolet curable resin with a low refractive index, it is preferable to use the low refractive index acrylate like trifluoroacrylate (refractive index 1.32), for example. Moreover, X-12-2400 (brand name, Shin-Etsu Chemical Co., Ltd.) can also be used as an example of ultraviolet curable silicone resin.

In general, UV curable resins used in combination with low refractive index resins have a higher refractive index than low refractive index resins, and are mainly used to increase the strength of the coating because they are related to scratch resistance, solvent resistance, and surface hardness. Polyfunctional acrylates having two or more unsaturated groups are preferred. From the viewpoint of the refractive index, the addition amount of this polyfunctional acrylate is better to be small, but in order to improve the scratch resistance, it is usually added 5 parts by weight or more, more preferably 10 parts by weight or more based on 100 parts by weight of the UV curable resin having a low refractive index. It is preferred, and generally exceeding 60 parts by weight deviates from the object of the present invention.

In order to lower the refractive index of a low refractive index layer, it is generally more preferable to use together a fluorine-containing monomer, an oligomer, or the microparticles | fine-particles of a low refractive index. When using these microparticles | fine-particles together, the microparticles | fine-particles content of a low refractive layer is about 100-1000 weight part with respect to 100 weight part of resin of a low refractive layer. Moreover, when using general ultraviolet curable resin together for the purpose of hardness improvement, it is preferable to also use together the microparticles | fine-particles of this low refractive index normally. It is preferable that these microparticles | fine-particles usually have a particle diameter of 5 nm-500 nm, and refractive index 1.45 or less. Specific examples of low refractive index fine particles include CaF ₂ (refractive index 1.23), NaF (refractive index 1.29), Na ₃ AlF ₆ (refractive index 1.33), SiO _x (silica sol, refractive index 1.35 to 1.48), AlF ₃ (refractive index 1.38), LiF (refractive index 1.4), MgF ₂ (refractive index 1.4), 3NaF-AlF ₃ (refractive index 1.4), etc. are mentioned. In particular, when the fluorine-based fine particles are used in combination, it is possible to provide an excellent antifouling property by improving the surface contact angle.

In addition, in order to prevent surface contamination, the low refractive index layer may contain an antifouling surfactant. Examples of the antifouling surfactants include fluorine-based surfactants and silicone-based surfactants, and the addition amount is 10% by weight or less, preferably 0.5 to 5% by weight based on the total amount of the resin.

[Hard Coating Layer]

The hard coat layer may be formed using a thermosetting resin and a curing agent or a UV curing resin, a photopolymerization initiator, and the like, which are presented in the light diffusion layer. In view of weather resistance, heat resistance, scratch resistance, surface hardness, storage stability and productivity, it is preferable to use an ultraviolet curable resin. In order to improve adhesiveness with a base material and to reduce shrinkage | contraction at the time of hardening of a hard coat layer, you may contain inorganic particles, such as a silica particle, in the said resin layer. The inorganic particles preferably have a particle diameter of 5 nm to 5 μm and a content of 5 wt% or less, that is, 1 to 4 wt%, based on the total composition solids. When the particle size of the inorganic particles is 5 nm or less, there is no effect of improving the adhesion to the substrate and the shrinkage rate, and when added in an amount exceeding 5 μm or more than 5 wt%, the haze of the light diffusion film increases. .

[Antiblocking Floor]

The anti-blocking layer may be formed by mixing the anti-blocking agent and the like with the thermosetting resin, the ultraviolet curable resin, and the like described in the light diffusion layer. Examples of the antiblocking agent include organic particles and inorganic particles having a particle diameter of 1 μm to 30 μm. Examples of the organic particles include PMMA, polystyrene, and the like, and examples of the inorganic particles include silica and TiO ₂ . This is to prevent blocking between the film surfaces generated when the light-diffusion film is wound in a roll state. The amount of particles added is preferably 30% by weight or less, more preferably 5 to 10% by weight based on the total composition.

In the present invention;

(1) A light diffusing film having excellent anti-reflection capability, in which a light diffusing layer is formed on one side of a transparent substrate, and a high refractive layer having a different refractive index and a low refractive layer having a refractive index of 1.2 to 1.45 are sequentially stacked on the other side (FIG. 3). Reference),

(2) the light diffusing film excellent in the antireflection performance described in (1) in which a hard coat layer was formed between the transparent substrate and the high refractive layer (see FIG. 4),

(3) the light diffusing film excellent in the antireflection performance according to (1), wherein an antiblocking layer is formed between the transparent substrate and the high refractive layer (see FIG. 5);

(4) a light diffusing film having excellent antireflection capability having a structure in which a light diffusing layer is formed on one side of the transparent substrate and a low refractive layer having a refractive index of 1.2 to 1.45 on the other side (see FIG. 6);

(5) a light diffusing film excellent in antireflection performance as described in (4), wherein a hard coat layer is formed between the transparent substrate and the low refractive layer (see FIG. 7), and

(6) providing a light diffusing film having excellent antireflection capability (see FIG. 8) according to (4), wherein an antiblocking layer is formed between the transparent substrate and the low refractive layer, and employing a light diffusing film having excellent antireflection capability. A backlight unit of a liquid crystal display device is provided. In the manufacture of the backlight unit, the forward direction of the film is made in the order of the light guide plate → light diffusion film [back plane / transparent substrate / light diffusion layer] → prism sheet, and the reverse direction is the light guide plate → light diffusion film [light diffusion layer / transparency]. Substrate / Back surface] → prism sheet.

In the light diffusing film of (1), the high refractive layer is first formed on the basis of the transparent substrate of the light diffusing film to prevent reflection of light incident on the back surface of the light diffusing film, and the low refractive layer is laminated thereon to pass the light guide plate. The antireflection layer is designed to pass through the low refractive layer first (see FIG. 3).

Since the light diffusing film of (2) is stacked on the upper surface of the light guide plate, when the backlight unit or the liquid crystal display device is moved, scratches may occur on the antireflection layer due to the fine movement of the light diffusion film or the light guide plate. This is to prevent a problem appearing as a defect in the image of the liquid crystal display device. Therefore, in order to improve the surface hardness of the antireflection layer, it is necessary to form a thermosetting or ultraviolet curing hard coating layer on the transparent substrate, and then coat and stack the high refractive index layer and the low refractive layer in order (see FIG. 4).

In the light diffusing film of (3), the light diffusion layer is formed on one side of the transparent substrate and the anti-reflection layer is formed on the other side, so that the film is wound in a roll state in the winding machine of the coating line. At this time, it is to solve the problem that blocking occurs between the surfaces of the wound film. In order to solve this problem, an anti-blocking layer formed of a light-transmissive resin, an inorganic particle or an organic particle is formed on a transparent substrate, and then an antireflection layer is laminated (see FIG. 5).

In addition, the light diffusing film of (4) to (6) is different from the above (1) to (3) in that only the low refractive layer is formed on the opposite surface of the light diffusing layer, the high refractive layer and the low refractive layer The reflectance is slightly higher than that of the light diffusing film having the same structure, but has a lower reflectance than the light diffusing film (see FIGS. 6 to 8).

Each of the layers constituting the light diffusing film may be formed by a wet coating or a dry coating, and is not particularly limited thereto.

As described above, the backlight unit of the liquid crystal display device is generally stacked in the order of a reflecting film, a light guide plate, a light diffusion film, and a prism sheet, and a cold cathode fluorescent lamp, which is a backlight, is mounted on the side or the back of the light guide plate. Optionally, a prism protective film for protecting the prism sheet may be laminated on the prism sheet.

Light is emitted from the cold cathode fluorescent lamp and passes through the light guide plate to pass through the light diffusion film, and light scattering occurs. The light is aligned in the normal direction of the prism sheet while passing through the prism sheet. In the present invention, a light diffusing film is provided so that the light diffusing layer (front face) is on the viewing side (liquid crystal module direction), and when light passes through the light diffusing film after passing through the light guide plate, it is generated on the light diffusing film back face. The luminance of the liquid crystal display device is improved by reducing the amount of reflected light.

Example

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. The scope of the invention is not limited by the following examples.

In the following Examples and Comparative Examples, the physical property evaluation of the produced light diffusing film excellent in antireflection performance was carried out by the following method.

(1) total light transmittance and haze

It was measured according to ASTM D1003 using a Transmittance and Haze Meter (Nippon Denshoku Kogyo Co.). The film was mounted so that the measurement light transmitted from the back surface (antireflection layer surface) of the light diffusion film in the light diffusion layer direction.

Total light transmittance = (transmission / incident light) × 100 (%)

Haze = (scattered light / transmitted light) × 100 (%)

(2) reflectance

Using a spectrophotometer (UV3101PC, Shimazu Co., Ltd.), the 5 degree reflectance was measured in the wavelength range of 380 ~ 780nm. It was measured without marking black on the back side.

(3) pencil hardness

It measured based on JIS-K5400 using the pencil hardness tester (Yoshimitsu company).

(4) Scratch resistance (scratch resistance)

 The surface was scratched visually by rubbing 20 times using steel wool.

(5) Contact angle of surface water

Water droplets were dropped on the low refractive layer surface (Examples 1 to 3) and the antiblocking layer (comparative example) of the light diffusion film, and the contact angle was measured using a contact angle meter (Elma G-I type contact system).

Example 1

As the transparent base material, a 100 μm polyethylene terephthalate (hereinafter, abbreviated as PET) film primer-treated with a urethane-based coating agent was used. The light-diffusion layer was agitated by mixing 100 parts by weight of thermosetting acrylic resin A811 (Aekyung Chemical) with 150 parts by weight of ethyl acetate (EA) and 150 parts by weight of toluene, followed by crosslinking with polymethyl methacrylate (PMMA). MBX-12 (Sekisui) and MBX-20 (Sekisui), which are particles, were added to the diluting solvent at 30 parts by weight and 90 parts by weight, respectively, and sufficiently stirred and dispersed in the resin. One hour before coating, 10 parts by weight of an isocyanate curing agent was added to the dispersion to finally prepare a coating solution. This was coated and dried by Bar coating method to obtain a light diffusion layer of 20um.

100 parts by weight of thermosetting acrylic resin was diluted with 100 parts by weight of ethyl acetate and 50 parts by weight of toluene, and then 10 parts by weight of isocyanate curing agent and 3 parts by weight of melamine curing agent for coating of the high refractive layer formed on the opposite side of the light diffusing layer based on the transparent substrate. Added. Sol, in which 50 parts by weight of methanol and 50 parts by weight of isopropyl alcohol, and 300 parts by weight of SnO 2 and ATO (Antimony Tin Oxide) were added to the diluent of the resin and the curing agent, Through sufficient dispersion process, a high refractive coating solution was prepared. The coating solution was coated and dried by a bar coating method to obtain a high refractive index layer having a refractive index of 1.7 with a thickness of 100 nm.

In order to form a low refractive layer on the high refractive layer, a fluorine-containing siloxane-based coating liquid (Shin-Etsu Chemical, X-12-2138) having a solid content of 3% by weight was coated and dried by a bar coating method to obtain a thickness of 100 nm and a refractive index of 1.4. A low refractive index layer was obtained. The structure of the film thus produced is shown in FIG. 3.

Example 2

After forming the light diffusion layer as in Example 1, the hard coating layer was formed as follows before coating the high refractive index layer on a transparent substrate on the opposite side. As a solid content of the hard coating solution, 100 parts by weight of EB5129 (SK-UCB), which is a 6-functional aliphatic urethane acrylate (Aliphatic Urethane Acrylate) based oligomer, 30 parts by weight of PETIA (SK-UCB) as a monomer, and Igacure as a photo initiator 184 10 parts by weight, other less than 1 part by weight of the labeling agent and the ultraviolet absorber were added to 30 parts by weight of toluene and 30 parts by weight of MEK to prepare a coating solution. The crude liquid was wet coated by a bar coating method to form a 5 μm hard coating layer between the transparent substrate and the high refractive layer. The high and low refractive layers were formed in the same manner as in Example 1. The film prepared as above is shown in FIG. 4.

Example 3

After forming the light diffusion layer as in Example 1, the anti-blocking layer was formed as follows before coating the high refractive index layer on a transparent substrate on the opposite side. The antiblocking layer was agitated by stirring 100 parts by weight of a thermosetting acrylic resin A811 (Aekyung Chemical) 200 parts by weight of a mixture of ethyl acetate (EA) and 200 parts by weight of toluene, followed by polymethyl methacrylate (PMMA). MBX-12 (Sekisui) and silica particles, which are crosslinked particles, were added to the diluting solvent at 2 parts by weight and 1 part by weight, respectively, and the mixture was sufficiently stirred and dispersed in the resin. One hour before coating, 10 parts by weight of an isocyanate curing agent was added to the dispersion to finally prepare a coating solution. This was coated and dried by Bar coating method to obtain an anti-blocking layer of 10um. The high and low refractive layers were formed in the same manner as in Example 1. The structure of the film thus produced is shown in FIG. 5.

Example 4

A light diffusing layer was formed on the transparent substrate in the same manner as in Example 1, and only a low refractive layer was formed on the transparent substrate in the same manner as in Example 1 on the opposite side to obtain a film having the structure shown in FIG.

Example 5

A light diffusion layer was formed on the transparent substrate in the same manner as in Example 1, and the hard coating layer and the low refractive layer were laminated on the transparent substrate in the same manner as in Example 2 on the opposite side to form a film having a structure as shown in FIG. Got it.

Example 6

The light diffusion layer was formed on the transparent substrate in the same manner as in Example 1, and the anti-blocking layer and the low refractive layer were laminated on the transparent substrate in the same manner as in Example 3 on the opposite side to form a film having a structure as shown in FIG. Got.

Comparative example

After forming the light diffusion layer on the transparent substrate in the same manner as in Example 1, the anti-blocking layer was formed on the opposite side in the same manner as in Example 3.

Experimental results of Examples 1 to 6 and Comparative Examples are shown in Table 1 below.

As described above, the light diffusing films obtained in Examples 1 to 6 exhibit excellent optical properties with lower reflectance and improved transmittance than the conventional light diffusing films obtained in Comparative Examples. In addition, Examples 1 to 6 also have excellent antifouling properties since they have a contact angle larger than the back surface (antiblocking layer) of the conventional light diffusing film of the comparative example, as a result of forming the low refractive layer in order to impart an antireflection effect.

The present invention can provide a high-brightness light diffusion film having low reflectance and improved transmittance by forming an antireflection layer by laminating the low refractive layer alone or the high refractive layer on the opposite side of the light diffusing layer, and in particular, the low refractive layer has fluorine-based fine particles By including it, surface contact angle can be improved and excellent antifouling property can be provided.

Claims (10)

The light diffusing layer is formed on one side of the transparent substrate, the high refractive index layer having a refractive index of 1.6 to 2.9, and the low refractive layer having a refractive index of 1.2 to 1.45 are sequentially stacked on the other side of the transparent substrate, Excellent light diffusion film. The light diffusing film of claim 1, wherein a hard coating layer is further laminated between the transparent substrate and the high refractive layer. The light diffusing film of claim 1, further comprising an antiblocking layer further laminated between the transparent substrate and the high refractive layer. The light diffusing film according to any one of claims 1 to 3, wherein the high refractive index layer and the low refractive layer have a thickness of 30 to 300 nm and a transparent substrate having a thickness of 50 to 200 µm. A light diffusing film excellent in antireflection, in which a light diffusing layer is formed on one side of a transparent substrate and a low refractive index layer having a refractive index of 1.2 to 1.45 is laminated on the other side. The light diffusing film of claim 5, wherein the hard coating layer is further laminated between the transparent substrate and the low refractive layer. The light diffusing film of claim 5, wherein an anti-blocking layer is further laminated between the transparent substrate and the low refractive layer. The light diffusing film according to any one of claims 5 to 7, wherein the low refractive index layer has a thickness of 30 to 300 nm and a transparent substrate having a thickness of 50 to 200 μm. The method according to any one of claims 1 to 3 and 5 to 7, wherein the low refractive index layer is a curable resin and CaF ₂ , NaF, Na ₃ AlF ₆ , AlF ₃ , LiF, MgF ₂ , and 3NaF in combination a low-refractive index fine particles selected at least one from the group consisting of AlF ₃ and formed all around the room intelligence is superior light-diffusing film. Liquid crystal provided with the light-diffusion film excellent in the antireflection property of any one of Claims 1-3 and 5-7 so that a light-diffusion layer (front surface) may be in the visual recognition side (liquid crystal module direction). Backlight unit of the display device.

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