KR20120078508A - Optical sheet - Google Patents

Abstract

PURPOSE: An optical sheet is provided to maintain high brightness while securing excellent obliterating power. CONSTITUTION: A first light diffusing layer is formed on one side of a base material layer. A second light diffusing layer is formed on the other side of the base material layer. The first light diffusing layer comprises a binder and an optical diffusion particle. The second light diffusing layer comprises a binder and an optical diffusion particle which has different refractive index and diameter with the optical diffusion particle of the first light diffusing layer. A rear side layer is formed on the other side of the base material layer.

Description

Optical Sheet {Optical Sheet}

The present invention relates to an optical sheet.

Optical film, which occupies a key field in BLU (Back Light Unit), is a very important component in improving LCD performance. In general, the film used in the BLU is a reflective film, a diffuser film, a prism film, a reflective polarizing film, and the like, and aims at high brightness and uniformity of light emitted to the entire surface of the BLU by using various optical properties thereof. Recently, as the demand for LCD using an LED light source increases, research into an optical film having high brightness and high hiding power is particularly active.

One embodiment of the present invention is to provide an optical sheet with excellent concealability while maintaining high brightness.

Accordingly, the present invention is a first preferred embodiment, the base layer; A first light diffusion layer formed on one surface of the base layer; And a second light diffusing layer formed on a rear surface of the base layer, wherein the first light diffusing layer includes a binder and light diffusing particles, and the second light diffusing layer has a binder and light having different refractive indices and particle diameters. It characterized in that it comprises diffused particles, the haze of 60 to 100%, the brightness reduction rate compared to the optical sheet including a base layer, a light diffusion layer formed on one side of the base layer and a back layer formed on the back side of the base layer 10% It provides less than an optical sheet.

The first light diffusing layer and the second light diffusing layer according to the embodiment may each include 20 to 200 parts by weight of light diffusing particles based on 100 parts by weight of the binder.

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

The light diffusion layer according to the embodiment may include the first light diffusion particles and the second light diffusion particles from 10:90 to 90:10.

The light diffusing particles according to the above embodiment are inorganic particles selected from the group consisting of silica, zirconia, calcium carbonate, barium sulfate and titanium oxide or styrene, melamine formaldehyde, benzoguanamine formaldehyde, and benzoguanamine bellamine formaldehyde. , Organic particles which are homopolymers or copolymers obtained from monomers selected from the group consisting of propylene, ethylene, silicone, urethane, nylon and methyl (meth) acrylate.

The binder according to the embodiment may be selected from the group consisting of polyvinyl resin, acrylic resin, polyester resin, styrene resin, alkyd resin, amino resin and polyurethane resin.

1 is a cross-sectional view of a conventional optical sheet.
2 is a cross-sectional view of an optical sheet according to the present invention.

Hereinafter, the present invention will be described in more detail.

The present invention is a preferred embodiment, the base layer; A first light diffusion layer formed on one surface of the base layer; And a second light diffusing layer formed on a rear surface of the base layer, wherein the first light diffusing layer includes a binder and light diffusing particles, and the second light diffusing layer has a binder and light having different refractive indices and particle diameters. It characterized in that it comprises diffused particles, the haze of 60 to 100%, the brightness reduction rate compared to the optical sheet including a base layer, a light diffusion layer formed on one side of the base layer and a back layer formed on the back side of the base layer 10% It relates to an optical sheet which is less than.

The optical sheet has a luminance reduction rate of less than 10% compared to an optical sheet having a conventional back layer, where the luminance reduction ratio means a difference in relative luminance with respect to conventional optical sheet luminances. The conventional optical sheet having a rear layer is an optical sheet having a light diffusion layer formed on one surface of the substrate layer and a rear layer formed on the rear surface of the substrate layer, and may be, for example, a blocking prevention layer.

In the conventional optical sheet method, in order to increase the hiding power, the thickness of the coating layer including the binder and the light diffusing particles is increased or the amount of the light diffusing particles is used. However, in this case, a satisfactory level of hiding power may not be obtained. However, in comparison with this, there is a problem in using the optical sheet due to the severe decrease in luminance.

That is, in the present invention, by adjusting the type and size of particles used in the light diffusing layer to achieve a haze of 60 to 100% and a decrease in luminance of less than 10% by securing the hiding power and anti-brightness prevention characteristics, The optical sheet including the light diffusing layer can also be applied to a monitor and a TV.

The thickness of a base material layer may be about 50 micrometers-about 400 micrometers, and any base material can be used as long as it is a sheet made of a transparent resin used for an optical sheet. Examples thereof include polyethylene terephthalate film, polycarbonate film, polypropylene film, polyethylene film, polystyrene film or polyepoxy film.

The light diffusing layer is formed of a composition containing light diffusing particles and a binder.

The first light diffusing layer of the light diffusing layer includes a binder and light diffusing particles, and the second light diffusing layer includes a binder and light diffusing particles having different refractive indices and particle diameters.

The second light diffusing layer may include light diffusing particles having different average particle diameters in order to secure concealability and brightness suitable for a small and medium-sized display device, for example, a monitor. Preferably, the second light diffusing layer has a first light diffusing particle having an average particle diameter of 1 to 10, a refractive index of n1 and a second light diffusing particle having an average particle diameter of 10 to 30, and a refractive index of n2. It may be included in an amount of 10 to 90. Where | n1-n2 | > 0.02.

The light diffusing particles are composed of organic particles and / or inorganic particles, and the inorganic particles are selected from the group consisting of silica, zirconia, calcium carbonate, barium sulfate and titanium oxide, and the organic particles are styrene, melamine formaldehyde, benzoguanamine. Homopolymers or copolymers obtained from monomers, such as formaldehyde, benzoguanamine and velamine formaldehyde, propylene, ethylene, silicone, urethane, nylon, methyl (meth) acrylate, and the like, and monodispersion or polydispersion thereof. It may be of the form.

Particularly, it is preferable to use silicon beads as light diffusing particles. When silicon beads are used, they can not only improve the concealability of the optical sheet due to the excellent diffusibility compared to the same amount of methyl methacryl beads, Thin film sheet can be realized by reducing coating thickness

In addition, the light-diffusing particles are preferably contained 20 to 200 parts by weight with respect to 100 parts by weight of the binder, if the content of the light-diffusing particles is less than 20 parts by weight can not obtain the proper diffusivity diffuses the light source incident from the light guide plate If the brightness is lowered, the light guide plate is transmitted through the light, and the concealment is also lowered. If it is more than 200 parts by weight, the concealment is secured, but there is a problem in that the brightness is lowered due to an excessive diffusion effect.

The binder may be selected from the group consisting of polyvinyl resin, acrylic resin, polyester resin, styrene resin, alkyd resin, amino resin and polyurethane resin.

The optical sheet according to the present invention may be prepared by applying and drying the crude liquid obtained from the light diffusing particles and the binder on both sides of the substrate layer.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the scope of the present invention is not limited to the following Examples.

Comparative example  One

100 parts by weight of methyl ethyl ketone and 100 parts by weight of toluene were diluted with 100 parts by weight of acrylic resin A814 (manufactured by Aekyung Chemical Co., Ltd.), and the spherical polymethyl methacrylate particles MX1500 (manufactured by Socan Co., Ltd.) having an average particle diameter of 15 µm was prepared. 150 parts by weight of the mixture was dispersed in a mill and then coated on one surface of a PET (Kolon H11F) substrate layer having a thickness of 188 using gravure and dried to apply a thickness of 20 μm to form a light emitting surface light diffusion layer. .

After diluting 200 parts by weight of methyl ethyl ketone and 150 parts by weight of toluene in 100 parts by weight of acrylic resin on the other side of the base layer, 10 parts by weight of spherical polymethyl methacrylate particles MX300 (manufactured by Socan, Japan) with an average particle diameter of 3 After mixing and dispersing the parts, the light incident surface blocking prevention layer is coated to have a thickness of 1 μm to 2 μm after drying using gravure to prepare an optical sheet coated on both sides.

Comparative example  2

100 parts by weight of methyl ethyl ketone and 100 parts by weight of toluene were diluted with 100 parts by weight of acrylic resin A814 (manufactured by Aekyung Chemical Co., Ltd.), and the spherical polymethyl methacrylate particles MX1500 (manufactured by Socan Co., Ltd.) having an average particle diameter of 15 µm was prepared. 150 parts by weight of the mixture was dispersed in a mill and then coated on one surface of a PET (Kolon H11F) substrate layer having a thickness of 188 using gravure and dried to apply a thickness of 40 μm to form a light emitting surface light diffusion layer. .

After diluting 200 parts by weight of methyl ethyl ketone and 150 parts by weight of toluene in 100 parts by weight of an acrylic resin on the other side of the base layer, spherical polymethyl methacrylate particles MX300 (manufactured by Socan Co., Ltd.) having an average particle diameter of 3 µm was used. After mixing and dispersing the parts by weight, a light incident surface blocking prevention layer is coated to have a thickness of 1 to 2 after drying using gravure to prepare an optical sheet coated on both sides.

Comparative example  3

After diluting 100 parts by weight of methyl ethyl ketone and 100 parts by weight of toluene with respect to 100 parts by weight of acrylic resin A814 (manufactured by Aekyung Chemical Co., Ltd.), spherical polymethyl methacrylate particles MX1500 (manufactured by Socan Co., Ltd.) having an average particle diameter of 15 was 150. After mixing by weight and dispersed in a mill, a coating solution was applied to one surface of PET (Kolon H11F) substrate layer having a thickness of 188 using gravure, and dried to apply a thickness of 60 to form a light emitting surface light diffusion layer.

After diluting 200 parts by weight of methyl ethyl ketone and 150 parts by weight of toluene in 100 parts by weight of acrylic resin on the other side of the base layer, 10 parts by weight of spherical polymethyl methacrylate particles MX300 (manufactured by Socan, Japan) with an average particle diameter of 3 After mixing and dispersing the parts, the light incident surface blocking prevention layer is coated to have a thickness of 1 to 2 after drying using gravure to prepare an optical sheet coated on both sides.

Comparative example  4

After diluting 100 parts by weight of methyl ethyl ketone and 100 parts by weight of toluene with respect to 100 parts by weight of acrylic resin A814 (manufactured by Aekyung Chemical Co., Ltd.), the spherical polymethyl methacrylate particles MX1500 (manufactured by Socan Co., Ltd.) having an average particle diameter of 200 was 200 compared to the binder. After mixing by weight and dispersed in a mill, a coating solution was applied to one surface of PET (Kolon H11F) substrate layer having a thickness of 188 using gravure, and dried to apply a thickness of 30 to form a light emitting surface light diffusion layer.

On the other side of the base layer, 200 parts by weight of methyl ethyl ketone and 150 parts by weight of toluene were diluted in 100 parts by weight of acrylic resin, and then spherical polymethyl methacrylate particles MX300 (manufactured by Socan Co., Ltd.) having an average particle diameter of 10 µm was 10% by weight. After mixing and dispersing the parts, the light incident surface blocking prevention layer is coated to have a thickness of 1 to 2 after drying using gravure to prepare an optical sheet coated on both sides.

Comparative example  5

After diluting 100 parts by weight of methyl ethyl ketone and 100 parts by weight of toluene with respect to 100 parts by weight of acrylic resin A814 (manufactured by Aekyung Chemical Co., Ltd.), the spherical polymethyl methacrylate particles MX1500 (manufactured by Socan Co., Ltd.) having an average particle size of 250 was 250 compared to the binder. After mixing by weight and dispersed in a mill, a coating solution was applied to one surface of PET (Kolon H11F) substrate layer having a thickness of 188 using gravure, and dried to apply a thickness of 30 to form a light emitting surface light diffusion layer.

After diluting 200 parts by weight of methyl ethyl ketone and 150 parts by weight of toluene in 100 parts by weight of acrylic resin on the other side of the base layer, 10 parts by weight of spherical polymethyl methacrylate particles MX300 (manufactured by Socan, Japan) with an average particle diameter of 3 After mixing and dispersing the parts, the light incident surface blocking prevention layer is coated to have a thickness of 1 to 2 after drying using gravure to prepare an optical sheet coated on both sides.

Example  1 to Example  24

After diluting 100 parts by weight of methyl ethyl ketone and 100 parts by weight of toluene with respect to 100 parts by weight of acrylic resin A814 (manufactured by Aekyung Chemical Co., Ltd.), the spherical polymethyl methacrylate particles MX1500 (manufactured by Socan Co., Ltd.) having an average particle size of 250 was 250 compared to the binder. After mixing by weight and dispersing with a milling machine, a coating solution was applied to one surface of PET (Kolon H11F) substrate layer having a thickness of 188 using gravure, and dried to apply a thickness of 30 to form a light emitting surface light diffusion layer. It is called a 1st light-diffusion layer.

After diluting 200 parts by weight of methyl ethyl ketone and 150 parts by weight of toluene in 100 parts by weight of an acrylic resin on the other side of the base layer, the particles were mixed and dispersed as shown in Table 1 below, and then dried using gravure to dry the coated optical sheet. To make. At this time, the light diffusing layer formed on the other surface of the substrate layer was called a second light diffusing layer.

Unit: parts by weight Example Particle refractive index Particle Ratio (Particle 1: Particle 2) Amount of Particles Compared to Binder
(By weight) n1 n2 One 1.49 1.54 9: 1 70 2 1.49 1.54 9: 1 170 3 1.49 1.54 5: 5 70 4 1.49 1.54 5: 5 170 5 1.49 1.54 1: 9 70 6 1.49 1.54 1: 9 170 7 1.54 1.49 9: 1 70 8 1.54 1.49 9: 1 170 9 1.54 1.49 5: 5 70 10 1.54 1.49 5: 5 170 11 1.54 1.49 1: 9 70 12 1.54 1.49 1: 9 170 13 1.42 1.49 9: 1 70 14 1.42 1.49 9: 1 170 15 1.42 1.49 5: 5 70 16 1.42 1.49 5: 5 170 17 1.42 1.49 1: 9 70 18 1.42 1.49 1: 9 170 19 1.49 1.42 9: 1 70 20 1.49 1.42 9: 1 170 21 1.49 1.42 5: 5 70 22 1.49 1.42 5: 5 170 23 1.49 1.42 1: 9 70 24 1.49 1.42 1: 9 170

The refractive index 1.49 used polymethyl methacrylate particle, the refractive index 1.54 used polystyrene particle, and the refractive index 1.42 used silicon particle.

Haze, brightness, and hiding power were measured for the optical sheets prepared in Examples 1 to 24 and Comparative Examples 1 to 5.

(1) haze measurement

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 measurement

Mount the sheet to be measured on the BLU preheated for more than 30 minutes and measure the luminance by Dell 13 point position using Topcon BM-7A. Each luminance was evaluated by the relative value when the luminance of the light converging optical sheet manufactured in Comparative Example 4 was 100.

(3) hiding power measurement

The 22-inch BLU is turned on, and the optical sheet to be measured is placed and then evaluated by comparing the degree of light guide plate pattern reflected.

5 4 3 2 1

High hiding power (pattern poet) Low hiding power (pattern poet)

Haze (%) Relative brightness (%) Hiding power Comparative Example 1 95 100 One Comparative Example 2 96 85 3 Comparative Example 3 98 72 4 Comparative Example 4 96 87 3 Comparative Example 5 97 83 4 Example 1 96 97 4 Example 2 96 94 5 Example 3 97 95 4 Example 4 97 92 5 Example 5 97 93 5 Example 6 98 92 5 Example 7 97 93 4 Example 8 97 91 5 Example 9 96 94 4 Example 10 96 93 5 Example 11 95 95 4 Example 12 96 94 4 Example 13 98 97 4 Example 14 98 92 5 Example 15 97 95 4 Example 16 97 92 5 Example 17 96 94 4 Example 18 96 91 4 Example 19 96 93 4 Example 20 96 91 4 Example 21 96 95 4 Example 22 96 92 4 Example 23 96 96 5 Example 24 96 93 5

As a result of evaluating the physical properties of the optical sheets prepared in Examples and Comparative Examples, Examples 1 to 24 are less than 10% of the brightness reduction rate and excellent hiding power compared to Comparative Example 1, but Comparative Examples 2 to 5 have a high brightness reduction rate or The hiding power was shown to be low.

As a result, an optical sheet having excellent haze and hiding power without forming a light diffusion layer including light diffusing particles containing particles having different refractive indices on the back surface of the substrate layer having a light diffusing layer formed on one surface of the optical sheet. It was confirmed that the production of. This overcomes the problem that the conventional optical sheet does not secure proper concealability and is not used for small and medium display devices, and the optical sheet of the present invention will be optimal for small and medium display devices, for example, a monitor or a TV. Able to know.

Claims (6)

A base layer;
A first light diffusion layer formed on one surface of the base layer; And
An optical sheet including a second light diffusion layer formed on the back surface of the base layer,
The first light diffusing layer includes a binder and light diffusing particles,
The second light diffusing layer includes a binder and light diffusing particles having different refractive indices and particle diameters,
Haze is 60-100%,
An optical sheet having a luminance reduction ratio of less than 10% compared to an optical sheet including a substrate layer, a light diffusion layer formed on one surface of the substrate layer, and a back layer formed on the back surface of the substrate layer.
The optical sheet of claim 1, wherein each of the first and second light diffusing layers comprises 20 to 200 parts by weight of light diffusing particles based on 100 parts by weight of the binder.
The method of claim 1, wherein the second light diffusion layer
First light diffusing particles having a refractive index of n1 and an average particle diameter of 1 to 10; And
The optical sheet containing the 2nd light-diffusion particle whose refractive index is n2 and whose average particle diameter is 10-30.
The optical sheet of claim 3, wherein the second light diffusing layer comprises first light diffusing particles and second light diffusing particles in a content ratio of 90:10 to 10:90.
The method of claim 1, wherein the light diffusing particles are inorganic particles selected from the group consisting of silica, zirconia, calcium carbonate, barium sulfate and titanium oxide or styrene, melamine formaldehyde, benzoguanamine formaldehyde, benzoguanamine berylamine An optical sheet which is an organic particle which is a homopolymer or copolymer obtained from a monomer selected from the group consisting of formaldehyde, propylene, ethylene, silicone, urethane, nylon and polymethyl methacrylate.
The optical sheet of claim 1, wherein the binder is selected from the group consisting of polyvinyl resin, acrylic resin, polyester resin, styrene resin, alkyd resin, amino resin, and polyurethane resin.

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