KR101269720B1 - Diffuser Sheet and Brightness Enhancement Film - Google Patents

Abstract

The present invention relates to a diffusion sheet applied to a luminance-enhanced film used in a liquid crystal display, the light diffusion layer is formed on at least one surface of the substrate layer using a uniaxial stretched film as a substrate layer will be.

Description

Diffusion Sheet and Brightness Enhancement Film Comprising the Same {Diffuser Sheet and Brightness Enhancement Film}

The present invention relates to a diffusion sheet used in the liquid crystal display.

In general, a BLU, a reflective film, a diffusion film, a prism film, or the like is used for high brightness and uniformity of light. In addition, a brightness enhancement film having brightness enhancement and light diffusion functions is also used. In the case of the brightness enhancement film, it is necessary to introduce a diffusion layer having a diffusion function on the multilayer film so that the polarized light is emitted at a wider angle. It is common. As a method of forming a diffusion layer on the brightness enhancement film, a coating is performed on a polyethylene terephthalate or polycarbonate film using a diffusion agent, then laminated with an alternating multilayer film and an adhesive, or a coating of a diffusion agent directly on an alternating multilayer film. And, it can be prepared through the surface matte treatment in the production of polyethylene terephthalate film or polycarbonate film.

In addition, a diffusion sheet may be introduced into the brightness enhancement film. In general, the diffusion sheet is formed by coating a light diffusion layer on a biaxially stretched polyethylene terephthalate film used as a base layer. However, the diffusing film having such a configuration is a factor to deteriorate the overall optical characteristics by depolarizing the polarized light or causing back scattering.

An object of the present invention is to provide a diffusion sheet capable of minimizing depolarization or backscattering of polarized light.

Accordingly, the present invention provides a preferred embodiment, the base layer consisting of a uniaxial stretched film; And it provides a diffusion sheet comprising a light diffusion layer formed on at least one surface of the base layer.

The uniaxially oriented film according to the embodiment may be selected from the group consisting of polyethylene terephthalate film, polycarbonate film, polyethylene film, polystyrene film, polyepoxy film.

The in-plane refractive index difference (Δn = | n _x -n _y |) of the uniaxial stretched film according to the embodiment may be 0.03 or more, wherein n _x is a refractive index in the stretching direction in the uniaxial stretched film, and n _y is It is the refractive index in the direction perpendicular to the stretching direction.

The refractive index of the uniaxial stretched film according to the embodiment may be 1.0 or more and 1.65 or less.

The stretching direction of the uniaxial stretched film according to the embodiment may be that of the MD direction.

The stretching direction of the uniaxial stretched film according to the embodiment may be a TD direction.

The light diffusion layer according to the embodiment is a binder resin; And 20 to 200 parts by weight of light diffusing particles based on 100 parts by weight of the binder resin.

The light diffusing particles according to the embodiment may include at least one of first light diffusing particles having an average particle diameter of 1 to 10 μm and second light diffusing particles having an average particle diameter of 10 to 30 μm.

The light diffusing particles according to the embodiment have a first particle having an average particle diameter of 1 to 10 μm and a refractive index of n1; And second light-diffusing particles having an average particle diameter of 10 to 30 µm and a refractive index of n2, wherein | n1-n2 | > 0.02.

The light diffusion particles according to the embodiment may include the first light diffusion particles and the second light diffusion particles in a content of 10:90 to 90:10.

The diffusion sheet according to the embodiment may be for the brightness enhancement film.

The diffusion sheet of the present invention can minimize the non-polarization and the backscattered polarized light by using a uniaxially stretched film as the substrate, and exhibits a brightness enhancement effect, and therefore, is particularly suitable for a brightness enhancement film.

1 is a longitudinal cross-sectional view of a diffusion sheet according to the present invention.
<Detailed Description of Drawings>
(1) base material layer, (2) light diffusing layer

Hereinafter, the present invention will be described in detail.

The present invention is a substrate layer consisting of a uniaxial stretched film; And a light diffusion layer formed on at least one surface of the substrate layer.

The uniaxially stretched film may block or reduce depolarization or reverse scattering of polarized light. The uniaxially oriented film may be a film selected from the group consisting of polyethylene terephthalate film, polycarbonate film, polyethylene film, polystyrene film, polyepoxy film.

The uniaxial stretched film has an in-plane refractive index difference (Δn = | nx -ny |) of the uniaxial stretched film of 0.03 or more, preferably 0.05 or more, more preferably 0.5 or more, more preferably 1.0 or more, more preferably May be 1.5 or more. If the refractive index difference Δn = | nx−ny | is less than 0.03, there may be a problem of depolarization or backscattering of the light, thereby reducing the luminance. Here, nx is the refractive index of the extending direction in a uniaxial stretched film, and ny is the refractive index of the direction perpendicular | vertical to a extending direction. The refractive index of the uniaxial stretched film may be 1.0 or more and 1.65 or less.

The stretching direction of the uniaxial stretched film may be a MD (Machine Direction) direction or a TD (Tentor Direction) direction.

The light diffusion layer may include a binder resin and light diffusion particles.

Although it does not specifically limit as said binder resin, For example, polyvinyl resin, acrylic resin, polyester resin, styrene resin, alkyd resin, amino resin, polyurethane resin, epoxy resin, etc. Thermosetting resin or ultraviolet curable resin, etc. may be included alone or in combination of two or more.

Examples of the light diffusion particles included in the light diffusion layer include organic or inorganic particles. Examples of the inorganic particles include silica, zirconia, calcium carbonate, barium sulfate, titanium oxide, and the like, and examples of the organic particles include styrene, melamine formaldehyde, benzoguanamine formaldehyde, benzoguanamine berylamine, Homopolymers or copolymers obtained from monomers such as propylene, ethylene, silicone, urethane, methyl (meth) acrylate, and the like, and mono- or polydisperse forms thereof, and the like, but are not limited thereto. no.

The content of the light diffusion particles may be 20 to 200 parts by weight based on 100 parts by weight of the binder resin. If the content of the light diffusing particles is less than 20 parts by weight, the diffusion function is reduced, the luminance is lowered at the vertical viewing angle of 50 ~ 60 degrees when the front is 0 degrees. If the content is more than 200 parts by weight, the turbidity of the film is increased and the detachment of particles due to external impact occurs, thereby reducing the overall luminance.

On the other hand, when the light diffusing layer includes light diffusing particles having different particle diameters, since the light diffusing layer has suitable concealability and brightness enhancement properties, the light diffusing layer has a first light diffusing particle having an average particle diameter of 1 to 10 μm and an average particle diameter of 10 to It may include at least one of the second light diffusion particles having a 30㎛.

When the light diffusing particles having different refractive indices in addition to the particle diameter are included, concealability and luminance improvement may be further improved. As an example, the light diffusing particles include first light diffusing particles having an average particle diameter of 1 to 10 μm and a refractive index of n1; And the case where the second light-diffusing particles having an average particle diameter of 10 to 30 µm and a refractive index of n2 are introduced. When n1 and n2 are different, | n1-n2 | > 0.02 can be satisfied, if the range of the refractive index difference is not satisfied, the diffusion function is slightly reduced, the concealability is reduced, and the moiré is not concealed in the multi-layer extrusion, causing relatively poor.

Preferably, the light diffusing layer may include the first light diffusing particles and the second light diffusing particles in a content ratio of 10:90 to 90:10. If the light diffusing layer is out of this range, the small particles fill the pores between the large particles. The effect is to increase the turbidity of the overall film to reduce the brightness.

The haze of the light diffusion layer may be 30 to 100%, preferably 35 to 100%, more preferably 40 to 100%. If the haze is less than 30%, the light diffusion effect may be insignificant.

The diffusion sheet as described above is particularly suitable for brightness enhancing films used in liquid crystal displays.

In general, a brightness enhancing film means a film that emits specific light by applying polarization technology and continuously reflects specific light to increase light efficiency. Therefore, when applying the diffusion sheet of the present invention using a uniaxial stretched film as a substrate to the luminance-enhanced film, it is possible to minimize the depolarization or reverse scattering of the polarized light to improve the efficiency of the luminance-enhanced film.

Specifically, the diffusion sheet of the present invention is formed on the brightness enhancement film including the multilayer thin film, by adjusting the angle between the reflection axis of the brightness enhancement film multilayer thin film and the optical axis of the diffusion sheet uniaxial stretched film, Depolarization or backscatter can be reduced. Preferably, when the angle between the reflection axis of the multilayer thin film and the optical axis of the diffusion film is 40 degrees or less, more preferably 20 degrees or less, and more preferably 0 degrees, the luminance is increased by minimizing depolarization or reverse scattering of light. Can increase the effect.

When applying the diffusion sheet including the uniaxial stretched film to the luminance-enhanced film, it is easy to implement the roll to roll process to control the angle between the reflection axis of the multilayer film and the optical axis of the diffusion sheet mono-axial stretched film. However, the diffusion sheet including the biaxially stretched film may have a U-shape so that the polarized light may be offset when applied to the Roll to Roll process.

Hereinafter, the present invention will be described in detail with reference to the following Examples, the present invention is not limited by the Examples.

&Lt; Example 1 >

100 parts by weight of methyl ethyl ketone and 100 parts by weight of toluene were diluted with respect to 100 parts by weight of acrylic resin A814 (manufactured by Aekyung Chemical Co., Ltd.), and then spherical polymethyl methacrylate particles MX1500 having an average particle diameter of 15 µm as second light diffusing particles (Japan Socan company) (n = 1.49) and the weight ratio of the polyester particles (n = 1.54) having an average particle diameter of 8㎛ as the first light-diffusion particles was added at 90:10, the spherical particles were mixed by 170 parts by weight of the binder mill After dispersing into a 188㎛ thick uniaxially stretched PET (Kolon H11F) substrate layer was coated with a coating solution using a gravure and dried to apply a thickness of 30um to form a light diffusion layer, to prepare a diffusion sheet .

<Examples 2-5>

A diffusion sheet was manufactured in the same manner as in Example 1 except that the weight ratio of the first light diffusing particles to the second light diffusing particles was included as shown in Table 1.

&Lt; Comparative Example 1 &

A diffusion sheet was prepared in the same manner as in Example 1 except that a biaxially stretched PET film was used as the substrate layer.

Haze and luminance were measured for the diffusion sheets prepared in Examples and Comparative Examples, and the results are shown in Table 1.

(1) Hayes

The measurement is performed according to JIS K 7136 standard by using Nippon Denshoku's NDH2000 equipment so that the light source incidence part is located on the back side to obtain the measured value.

(2) luminance

The luminance was measured using a Topcon BM-7A device by mounting a diffusion sheet to be measured on a BLU preheated for 60 minutes or longer.

(3) relative brightness

The luminance measured above is calculated by applying the following equation.

Relative luminance = (luminance without diffusion sheet-luminance without diffusion sheet) / (luminance without diffusion sheet)

Particle ratio
(First Light Diffusion Particle: Second Light Diffusion Particle) Hayes Relative luminance (%) Example 1 90:10 96 94 Example 2 100: 0 97 83 Example 3 50:50 96 92 Example 4 10:90 97 92 Example 5 0: 100 97 81 Comparative Example 1 90:10 96 75

As a result of the physical property evaluation, as shown in Table 1, when the characteristics of the diffusion sheet were confirmed as described above, when only one particle was added (Example 5), when the ratio of particles having different refractive indices was 90:10 to 10:90 (Example 1 to 4) It can be seen that the relative luminance represents a value of 90% or more. In particular, when the ratio of the particle | grains 1 and 2 was 90:10, it had the best relative luminance (Example 1).

However, even if the ratio of particles 1 and 2 is 90:10, when the base layer of the diffusion sheet is a biaxially oriented film (Comparative Example 1), the haze value is not significantly different from that of other films, but it is confirmed that the relative luminance is greatly decreased. Could.

Therefore, a diffusion sheet coated with a diffusion bath liquid containing a particle ratio of 90:10 having different refractive indices in a uniaxially stretched polyethylene terephthalate film as in the diffusion sheet of Example 1 is applied to a brightness enhancement film used in an LCD panel. It can be seen that it will exhibit excellent physical properties in application.

While the present invention has been described in connection with certain exemplary embodiments, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined by the appended claims.

Therefore, since the embodiments described above are provided to completely inform the scope of the invention to those skilled in the art, it should be understood that they are exemplary in all respects and not limited. The invention is only defined by the scope of the claims.

Claims (12)

Substrate layer consisting of a uniaxial stretched film; And
It includes a light diffusion layer formed on at least one surface of the base layer,
The light diffusion layer is a binder resin; And 20 to 200 parts by weight of light diffusing particles based on 100 parts by weight of the binder resin,
The light diffusing particles include at least one of first light diffusing particles having an average particle diameter of 1 to 10 μm and second light diffusing particles having an average particle diameter of 10 to 30 μm,
The light diffusion particles are diffusion sheet, characterized in that it comprises a first light diffusion particles and the second light diffusion particles in the content of 10:90 ~ 90:10.
The method of claim 1,
The uniaxially oriented film is a diffusion sheet, characterized in that selected from the group consisting of polyethylene terephthalate film, polycarbonate film, polyethylene film, polystyrene film, polyepoxy film.
The method of claim 1,
The in-plane refractive index difference (Δn = | n _x -n _y |) of the uniaxial stretched film is 0.03 or more, wherein n _x is a refractive index in the stretching direction in the uniaxial stretched film, and n _y is a stretching direction It is the refractive index in the direction perpendicular to.
The method of claim 1,
The refractive index of the said uniaxial stretched film is 1.0 or more and 1.65 or less.
The method of claim 1,
A diffusion sheet in which the stretching direction of said uniaxial stretched film is MD direction.
The method of claim 1,
A diffusion sheet in which the stretching direction of the uniaxial stretched film is a TD direction.
delete delete The method of claim 1,
The light diffusing particles are first light diffusing particles having an average particle diameter of 1 to 10 μm and a refractive index of n1; And second light-diffusing particles having an average particle diameter of 10 to 30 µm and a refractive index of n2, wherein | n1-n2 | Diffusion sheet, characterized in that> 0.02.
delete The method of claim 1,
Diffusion sheet for the brightness enhancement film.
A brightness enhancement film comprising the diffusion sheet of claim 1.

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