WO2009002049A1

WO2009002049A1 - Optical sheet with excellent adhesive force, filter comprising the same, and display device including the sheet or the filter

Info

Publication number: WO2009002049A1
Application number: PCT/KR2008/003507
Authority: WO
Inventors: Bu-Seup Song; Jong-Pil Chun; Woo-Ju Jeong; Ki-Chul Yoon
Original assignee: Samsung Fine Chemicals Co., Ltd.
Priority date: 2007-06-22
Filing date: 2008-06-20
Publication date: 2008-12-31
Also published as: CN101784920A; JP2010531465A; TW200912397A

Abstract

Provided are an optical sheet, a filter including the same, and an image display device including the sheet or the filter. The optical sheet includes a light transmission portion in which a plurality of grooves spaced apart from each other at predetermined intervals are formed; and a plurality of external light absorption portions, respectively formed in the grooves, comprising a light absorbing material, wherein a surface of each of the external light absorption portions and a corresponding surface of the light transmission portion respectively have a surface roughness SR220 and a surface roughness SR210, wherein the surface roughness SR220 of the external light absorption portions is greater than the surface roughness SR210 of the corresponding surface of the light transmission portion. Therefore, the optical sheet, the filter including the same, and the image display device including the sheet or the filter can reduce ghost images and prevent the occurrence of the Moiré phenomenon by having excellent adhesive force, and can maintain high resolution and have an improved electromagnetic wave shielding effect by having a relatively high contrast ratio.

Description

OPTICAL SHEET WITH EXCELLENT ADHESIVE FORCE, FILTER COMPRISING THE SAME, AND DISPLAY DEVICE

INCLUDING THE SHEET OR THE FILTER

Technical Field

[1] The present invention relates to an optical sheet with excellent adhesive force, a filter comprising the same, and an image display device including the optical sheet or the filter, and more particularly, to an optical sheet in which image deterioration, such as formation of ghost images due to layer separation and a reduction of contrast ratio does not occur due to excellent adhesive force of the optical sheet, a filter comprising the same, and an image display device including the optical sheet or the filter. Background Art

[2] Recently, various types of image display devices have been developed and used practically. Examples of image display devices include liquid crystal displays (LCDs), plasma display panels (PDPs), field emission displays (FEDs), cathode ray tubes (CRTs), vacuum fluorescence displays, and field emission display panels. These image display devices realize emission of light of the three primary colors of red, blue, and green, thereby displaying color images.

[3] Such image display devices include a panel assembly that forms images and a filter that shields electromagnetic waves, near-infrared rays, and/or orange light emitted from the panel assembly and have functions such as surface reflection prevention, color adjustment, and/or resolution improvement. The filter is disposed on a front side of the panel assembly, and thus the filter should be able to transmit light.

[4] In addition, in a bright environment, for example, in a bright room, external surrounding light is transmitted through the filter and is incident to the panel assembly. In this case, the external surrounding light transmitted through the filter interferes with the image light emitted from the panel assembly. Due to this, the contrast ratio in the bright environment is decreased, and thus image display capability of the image display device deteriorates. To address these problems, Japanese Patent Laid-open Publication No. 2005-338270 discloses a viewing angle control sheet. The viewing angle control sheet has a structure in which external light absorption portions that have a wedge shape and include a black light absorbing material are disposed at predetermined intervals in contact with a transparent light transmission portion. In addition, by forming the external light absorption portions with a material having a smaller refractive index than that of the light transmission portion and a light absorbing material, an image light source incident on the external light absorption portions in an inclined direction can more effectively reach observers by total reflection, resulting in improved transmittance. However, when an optical sheet having such configuration is attached to other elements in a filter by an adhesive layer, layer separation caused by deterioration of adhesive force may easily occur. In addition, impurities such as air permeate between separated layers, thereby causing contrast ratio reduction and formation of ghost images, resulting in a reduction in image quality.

[5] In addition, image display devices generate strong electromagnetic waves during operation. Electromagnetic waves are harmful to humans and can also cause malfunction of ambient electronic devices. Thus, the electromagnetic wave radiation should be controlled to meet a legal standard. Therefore, image display devices include a film shielding electromagnetic waves. The film shielding electromagnetic waves is generally used in an image display device in a film filter form, together with a reflection prevention film, an orange light blocking film, and/or a near-infrared ray blocking film, rather than used alone in an image display device.

[6] However, in a conventional electromagnetic wave shielding film used in an image display device having large-size screen greater than 30 inch- or greater-sized screen or a filter including the same, an expensive conducting shielding film requiring a complicated manufacturing process is required, or at least one additional film is further used, thereby compensating for shielding effects that a single electromagnetic wave shielding film is unable to realize. Disclosure of Invention Technical Problem

[7] The present invention provides an optical sheet with excellent adhesive force.

[8] The present invention also provides an optical sheet having a function of shielding electromagnetic waves.

[9] The present invention also provides an optical sheet that increases contrast ratio and decreases ghost images.

[10] The present invention also provides an optical sheet that can prevent the Moire phenomenon.

[11] The present invention also provides a filter comprising the optical sheet.

[12] The present invention also provides an image display device with excellent image quality, excellent electromagnetic wave shielding effect and resolution, and reduced Moire phenomenon, by including the optical sheet or the filter. Technical Solution

[13] According to an aspect of the present invention, there is provided a n optical sheet comprising: a light transmission portion in which a plurality of grooves spaced apart from each other at predetermined intervals are formed; and a plurality of external light absorption portions, respectively formed in the grooves, comprising a light absorbing material, wherein a surface of each of the external light absorption portions and a corresponding surface of the light transmission portion respectively have a surface roughness SR₂₂₀ and a surface roughness SR₂io, wherein the surface roughness SR₂₂₀ of the external light absorption portion is greater than the surface roughness SR₂io of the light transmission portion.

[14] According to another aspect of the present invention, there is provided an optical sheet comprising: a light transmission portion in which a plurality of grooves spaced apart from each other at predetermined intervals are formed; a plurality of external light absorption portions, respectively formed in the grooves, comprising a light absorbing material; and an electromagnetic wave shielding layer formed by filling at least one part of the groove on the top of the external light absorption portion with a conducting material wherein a surface of the electromagnetic wave shielding layer and a corresponding surface of the light transmission portion respectively have a surface roughness SR225 and a surface roughness SR21₀, wherein the surface roughness SR225 of the electromagnetic wave shielding layer is greater than the surface roughness SR₂₁₀ of the corresponding surface of the light transmission portion.

[15] The electromagnetic wave shielding layer may account for 2 to 50 volume% based on 100 volume% of the external light absorption portion.

[16] The electromagnetic wave shielding layer may comprise at least one selected from the group consisting of a metal, a metal oxide, and a conducting polymer.

[17] The surface roughness SR₂₂₀ of the external light absorption portions or the surface roughness SR₂₂₅ of the electromagnetic wave shielding layer may be in a range of 0.15 to 5.0 μm, and the surface roughness SR₂io of the light transmission portion may be in a range of 0.05 to 0.5 μm.

[18] The surface roughness SR₂₂₀ of the external light absorption portion or the surface roughness SR₂₂₅ of the electromagnetic wave shielding layer , and the surface roughness SR₂io of the light transmission portion may satisfy the following conditions:

[19] 0.1 < SR₂₂₀ (or SR₂₂₅) ^~ SR₂₁₀ < 4.95 μm.

[20] A refractive index of the light transmission portion may be less than a refractive index of the external light absorption portion.

[21] Each of the external light absorption portions may have a triangular, tetragonal or trapezoidal cross section.

[22] Each of the external light absorption portions may be disposed in a stripe form, matrix form or wave form.

[23] A longitudinal direction of the external light absorption portions may not be parallel to a side of the optical sheet.

[24] The optical sheet may be a high-resolution sheet. [25] According to another aspect of the present invention, there is a filter for an image display device, comprising the optical sheet according to one of the embodiments described above and a filter base. [26] According to another aspect of the present invention, there is an image display device comprising the optical sheet according to one of the embodiments described above.

Description of Drawings [27] The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: [28] FIG. 1 is an exploded perspective view schematically illustrating a structure of an image display device equipped with a filter including an optical sheet according to an embodiment of the present invention; [29] FIG. 2A is an exploded cross-sectional view of a filter including an optical sheet according to an embodiment of the present invention; [30] FIG. 2B is an exploded cross-sectional view of a filter including an optical sheet according to another embodiment of the present invention; [31] FIG. 3 is a cross-sectional view of an optical sheet according to an embodiment of the present invention;

[32] FIG. 4 is an enlarged view of a portion A of the optical sheet of FIG. 3;

[33] FIG. 5 is a partial exploded perspective view of a modified example of the optical sheet of FIG. 3, which is designed for preventing the Moire phenomenon, according to an en embodiment of the present invention; [34] FIG. 6A is an exploded cross-sectional view of a filter including an optical sheet having a function of shielding electromagnetic waves, according to an embodiment of the present invention; [35] FIG. 6B is an exploded cross-sectional view of a filter including an optical sheet having a function of shielding electromagnetic waves, according to another embodiment of the present invention; [36] FIG. 7 is a cross-sectional view of an optical sheet having a function of shielding electromagnetic waves, according to an embodiment of the present invention; [37] FIG. 8 is an enlarged view of a portion A' of the optical sheet of FIG. 7; and

[38] FIG. 9 is a partial exploded perspective view of a modified example of the optical sheet having the function of shielding electromagnetic waves of FIG. 7, which is designed for preventing the Moire phenomenon, according to an embodiment of the present invention.

Best Mode [39] The present invention will now be described more specifically with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown.

[40] FIG. 1 is an exploded perspective view schematically illustrating a structure of an image display device 1 equipped with a filter 40 including an optical sheet according to an embodiment of the present invention. FIG. 2A is an exploded cross-sectional view of a filter 40 including an optical sheet according to an embodiment of the present invention. FIG. 2B is an exploded cross-sectional view of a filter 40 including an optical sheet according to another embodiment of the present invention. Hereinafter, like reference numerals in the drawings denote like elements or portions thereof.

[41] Referring to FIG. 1, the image display device 1 equipped with the filter 40 including the optical sheet according to an embodiment of the present invention includes a case 10, a cover 50 covering a top portion of the case 10, a driving circuit substrate 20 accommodated in the case 10, a panel assembly 30 that forms images, and the filter 40.

[42] Visible images formed in the panel assembly 30 by an electrical signal applied from the driving circuit substrate 20 are displayed to the outside via the filter 40.

[43] Referring to FIGS. 2A and 2B, the filter 40 includes a color adjustment film 100, an optical sheet 200, and a filter base (FB) including a reflection prevention film 500.

[44] The color adjustment film 100 primarily includes, for example, a neon light blocking colorant, and may also include a near- infrared ray absorption compound or a colorant.

[45] The neon light blocking colorant included in the color adjustment film 100 may be a compound such as cyanines, squaryliums, azomethines, xanthenes, oxonols, or azos. Here, neon light refers to unnecessary light at around a wavelength of about 585 nm, generated as a neon gas is excited.

[46] When the near- infrared ray absorption compound is included in the color adjustment film 100, the compound may be a copper atom-containing resin, a copper or phosphorous compound-containing resin, a copper compound or thiourea derivative- containing resin, or a tungsten-based compound-containing resin. Here, near-infrared rays cause malfunction of ambient electronic devices, and thus near-infrared rays need to be blocked.

[47] The optical sheet 200 includes a light transmission portion 210 and a plurality of external light absorption portions 220 formed on a base film 230, and is disposed below the color adjustment film 100. The optical sheet 200 having such a structure may be, for example, a high-resolution sheet; however, the present invention is not limited thereto. Here, the high-resolution sheet is interpreted in a broad sense, as a sheet used for increasing resolution of an image display device.

[48] The light transmission portion 210 transmits light emitted from the panel assembly

30 illustrated in FIG. 1. The light transmission portion 210 may be formed of a curable resin. In particular, the light transmission portion 210 may be formed of an acrylate resin cured by ionizing radiation or heat energy. [49] In addition, the light transmission portion 210 may be transparent, but not necessarily completely transparent, and may have a level of transparency generally acceptable in the art as being transparent. The light transmission portion 210 generally may have a shape complementary to the shape of the external light absorption portions 220, which will be described later, but the present invention is not limited thereto. That is, grooves g₂io are formed in the light transmission portion 210, separated from each other at predetermined intervals, and the grooves g₂i₀ are filled with an external light absorption portion-forming composition including a light absorbing material and a thermoplastic resin, thermosetting resin or ultra violet curable resin to form the external light absorption portions 220, which will be described later. In the present embodiments, the grooves g₂i₀ are formed in a side of the light transmission portion 210 corresponding to an image light source side. However, the present invention is not limited thereto, and the grooves g₂i₀ may be formed in a side of the light transmission portion 210 corresponding to an observer side. The light transmission portion 210 may have a refractive index n₂io of 1.33 to 1.6. It is difficult to manufacture the light transmission portion 210 to have a refractive index of less than 1.33. If the refractive index n₂i₀ of the light transmission portion 210 is greater than 1.6, the transmittance of the light transmission portion 210 is significantly decreased and the contrast ratio is also decreased, resulting in a decrease in overall resolution.

[50] In addition, a surface of the light transmission portion 210, i.e., a surface thereof on an image light source side may not be completely smooth, but has a predetermined roughness, i.e., a surface roughness SR_2I0 of 0.05 to 0.5 μm. It is difficult to manufacture the light transmission portion 210 to have a surface roughness SR_2I0 of less than 0.05 μm . If the surface roughness SR_2I0 of the light transmission portion 210 is greater than 0.5 μm, light transmitted through the light transmission portion 210 from the image light source may be diffusely reflected, thereby forming ghost images.

[51] The external light absorption portions 220 are respectively formed by filling the grooves g₂₁₀ formed in the light transmission portion 210, which are spaced apart from each other at predetermined intervals, with a composition including a thermoplastic resin, thermosetting resin or ultra violet curable resin and a light absorbing material. The external light absorption portions 220 absorb external surrounding light, and thus improve a contrast ratio in a bright environment, and ultimately maintain high resolution. In FIG. 2A, each of the external light absorption portions 220 has a tetragonal cross-section, and in FIG. 2B, each of the external light absorption portions 220 has a trapezoidal cross-section. However, the present invention is not limited to the embodiments illustrated in FIGS. 2A and 2B or embodiments illustrated in FIGS. 3 through 5, which will be described later. Alternatively, the light transmission portion 210 may be in a flat-plate form without including grooves therein, and the external light absorption portions 220 may be disposed on a surface of the light transmission portion 210, that is, the surface facing the color adjustment film 100.

[52] When the curable resin is included in the external light absorption portions 220, the resin may be the same or similar material as that of the light transmission portion 210.

[53] Examples of the light absorbing material may include a black inorganic material, a black organic material, a black-oxidized metal, and a mixture of at least two of these materials. When the external light absorption portions 220 includes the black-oxidized metal having a low electrical resistance, the external light absorption portions 220 can also shield electromagnetic waves. The external light absorption portions 220 may be primarily formed of an ultra violet ray curable resin containing carbon. The refractive index n₂₂o of the external light absorption portions 220 may be in a range of 1.33 to 1.6, similar to that of the light transmission portion 210.

[54] In addition, a surface of each of the external light absorption portions 220, i.e., the surfaces thereof on the image light source side may have a predetermined roughness, i.e., a surface roughness SR22₀ of 0.15 to 5.0 μm. If the surface roughness SR22₀ of the external light absorption portions 220 is less than 0.15 μm, the adhesive force may be weak. If the surface roughness SR22₀ of the external light absorption portions 220 is greater than 5.0 μm, the light transmittance of the image light source may be decreased. More preferably, the surface roughness SR22₀ of the external light absorption portions 220 may be greater than the surface roughness SR₂₁₀ of the light transmission portion 210. Most preferably, the surface roughness SR₂₂₀ of the external light absorption portions 220 and the surface roughness SR₂io of the light transmission portion 210 may satisfy the following conditions:

[55] 0.1 < SR₂₂₀ - SR210 < 4.95 μm .

[56] As described above, by adjusting the surface roughness SR₂io of the light transmission portion 210 on the image light source side and the surface roughness SR 220 of the external light absorption portions 220 on the image light source side, the optical sheet 200 does not affect the light transmittance of the image light source and the external light absorption rate and has excellent adhesive force. That is, the diffused reflection rate of the light transmission portion 210 can be decreased by reducing the surface roughness SR₂io of the light transmission portion 210 on the image light source side, and the surface adhesive force of the external light absorption portions 220 can be increased by increasing the surface roughness SR₂₂₀ of the external light absorption portions 220 on the image light source side. Here, there is no change in the external light absorption rate of the external light absorption portions 220. In general, the greater the surface roughness of a material, the better the surface adhesive force of the material. Here, the adhesive force of the optical sheet 200 indicates an adhesive force between the external light absorption portions 220 and the color adjustment film 100 or a film with another function in the filter 40. By increasing the adhesive force of the optical sheet 200, problems such as layer separation caused by deterioration of adhesive force and resulting filter contamination, image quality reduction, and the like can be overcome.

[57] The base film 230 is disposed on a surface of the light transmission portion 210, that is, the surface opposite to that in which the external light absorption portions 220 are formed. The base film 230 supports the light transmission portion 210 in which the external light absorption portions 220 are formed. The base film 230 may include at least one material selected from the group consisting of polyethersulphone (PES), polyacrylate (PAR), polyetherimide (PEI), polyethylene naphthalate (PEN), polyethyl- eneterephthalate (PET,), polyphenylene sulfide (PPS), polyallylate, polyimide, polycarbonate (PC), cellulose triacetate (TAC), and cellulose acetate propionate (CAP). Preferably, the base film 230 may be formed of polycarbonate (PC), polyethyl- eneterephthalate (PET), cellulose triacetate (TAC), or polyethylene naphthalate (PEN). In addition, the base film 230 may be formed of a material having the same or similar refractive index as that of the light transmission portion 210.

[58] In addition, the optical sheet 200 according to the current embodiments of the present invention may further include a protection film 240, as illustrated in FIGS. 3 and 4 that will be described later, formed on a surface of the light transmission portion 210, that is, the surface opposite to that on which the base film 230 is formed. The protection film 240 protects the optical sheet 200 until the optical sheet 200 is installed in the filter 40. In general, when the optical sheet 200 is installed in the filter 40, the protection film 240 is separated from the optical sheet 200; however, the present invention is not limited thereto.

[59] In FIGS. 2A and 2B, the filter base (FB) is disposed on a side of the optical sheet

200, and includes an electromagnetic wave shielding film 300, a hard coating layer 400, and a reflection prevention film 500 in this order. However, the present invention is not limited thereto. That is, the electromagnetic wave shielding film 300, the hard coating layer 400, and the reflection prevention film 500 may be disposed in the FB in any order, and the FB can also be a single layer formed of at least two types of materials having different functions.

[60] The electromagnetic wave shielding film 300 shields electromagnetic waves. The electromagnetic wave shielding film 300 may have various structures, such as a conductive mesh layer, a metal thin film, a high-refractive-index transparent thin film, or a laminated structure of at least two layers thereof. In FIGS. 2A and 2B, the electromagnetic wave shielding film 300 is in a single-layer form; however, the present invention is not limited thereto, and the electromagnetic wave shielding film 300 may have a multi-layer structure including at least two layers. [61] The hard coating layer 400 has resistance to scratching, thus preventing the electromagnetic wave shielding film 300 or the reflection prevention film 500 that will be described later from being damaged by contact with outside materials. The hard coating layer 400 may be formed of a reinforced glass alone, or may be formed of a reinforced glass including polymer as a binder. In addition, the hard coating layer 400 may include an acryl-based, urethane-based, epoxy-based, or siloxane-based polymer, and may include an ultraviolet curable resin such as oligomer. Further, the hard coating layer 400 may further include a silica-based filler to increase the hardness thereof.

[62] The reflection prevention film 500 minimizes eye tiredness of users viewing the image display device 1 for a long period of time by adjusting the transmittance of visible light. By adjusting the transmittance of visible light by installing the reflection prevention film 500, not only selective absorption effects of visible light but also widening effects of color reproduction ranges such as a contrast ratio can be obtained. In FIGS. 2A and 2B, the reflection prevention film 500 is in a single-layer form. However, the present invention is not limited thereto, and the reflection prevention film 500 may have a multi-layer structure including at least two layers.

[63] The reflection prevention film 500 has reflection prevention effects by a principle in which visible light that is incident from the outside and reflected from the surface of the reflection prevention film 500 and visible light reflected later from an interface between the reflection prevention film 500 and the hard coating layer 400 are out of phase from each other, and thus destructive interference occurs.

[64] The reflection prevention film 500 may be formed by curing and fixing a mixture of indium tin oxide (ITO) and silicon oxide (SiO₃), a mixture of nickel chromate (NiCr) and silicon oxide (SiO₂), or the like. In addition, the reflection prevention film 500 may be formed of titanium oxide or a specific fluorine resin having a low refractive index.

[65] Hereinafter, particular configuration and operation effects of the light transmission portion 210 and the external light absorption portion 220 will be described more fully with reference to the accompanying drawings.

[66] FIG. 3 is a cross-sectional view of an optical sheet 200 according to an embodiment of the present invention. FIG. 4 is an enlarged view of a portion A of the optical sheet 200 of FIG. 3. Referring to FIGS. 3 and 4, the optical sheet 200 according to the current embodiment of the present invention includes a light transmission portion 210, a plurality of external light absorption portions 220, a base film 230, and a protection film 240. In FIGS. 3 and 4, each of the external light absorption portions 220 has a tetragonal cross-section; however, the present invention is not limited thereto.

[67] The external light absorption portions 220 may be formed by roll forming, thermal pressing using a thermoplastic resin, or injection molding performed by filling the grooves g₂io of the light transmission portion 210, having a shape opposite to the pattern of the external light absorption portions 220, with a thermoplastic or thermosetting resin.

[68] In addition, when the ultra violet curable resin included in the light transmission portion 210 has a reflection prevention function, an electromagnetic wave shielding function, a color adjustment function, or a combined function thereof, the optical sheet 200 can additionally perform these functions.

[69] In the optical sheet 200 according to the current embodiment of the present invention, the protection film 240 may be optionally omitted. A surface of the light transmission portion 210 on an image light source side has a surface roughness SR₂io, and a surface of each of the external light absorption portions 220 on the image light source side has a surface roughness SR₂₂o- Referring to FIG. 4, the surface roughness SR₂₂₀ of the external light absorption portions 220 on the image light source side is greater than the surface roughness SR₂io of the light transmission portion 210 on the image light source. By adjusting the surface roughnesses SR21₀ and SR22₀, the optical sheet 200 can maintain high light transmittance and the external light absorption rate and also have excellent adhesive force.

[70] The relative disposition of the light transmission portion 210, the external light absorption portions 220, the base film 230, and the protection film 240 in the optical sheet 200 is the same as described above. The external light absorption portions 220 may have various structures, such as stripes, matrices, waves, or the like. In addition, the external light absorption portions 220 are disposed to be spaced apart from each other at predetermined intervals in order to transmit light therebetween. In FIG. 3, the external light absorption portions 220 have a tetragonal cross-section. However, the present invention is not limited thereto, and the external light absorption portions 220 may have triangular, a trapezoidal, pentagonal cross- sections, or the like.

[71] Although not illustrated in FIGS. 3 and 4, the optical sheet 200 according to the current embodiment of the present invention may further include a prism film disposed on a surface of the base film 230, that is, the surface opposite to the light transmission portion 210. The prism film may be formed of the same or similar material as that of the light transmission portion 210. By including the prism film, the optical sheet 200 can have an improved external light absorption rate, increased contrast ratio, and improved resolution without a large variation in light transmittance.

[72] In the current embodiment, the refractive index n₂₂o of the external light absorption portions 220 is adjusted to be higher than the refractive index n₂io of the light transmission portion 210 (that is, n₂io < n₂2o). The refractive index difference ( Δ n= n 2io-n₂2o) between the light transmission portion 210 and the external light absorption portions 220 may be in a range of -0.05 <Δ n < 0 . Thus, the external light absorption rate of the optical sheet 200 is increased, resulting in a reduction in formation of ghost images. This operation will be described later. Here, the ghost images are generated in such a manner that the light emitted from the panel assembly 30 as described above is interfered with by external surrounding light that is not fully absorbed by the external light absorption portions 220 and is reflected back to the outside. Therefore, users viewing an image display device including the optical sheet 200 realize an image as two overlapped images.

[73] A principle of reducing or eliminating ghost images by adjusting the refractive index difference between the external light absorption portions 220 and the light transmission portion 210 will now be described more fully with reference to FIG. 4. Referring to FIG. 4, when external surrounding lights Ll, L2 and L3 incident from the outside are incident on the external light absorption portion 220, the lights Ll, L2 and L3 are completely absorbed by the external light absorption portion 220 without being reflected from the interface between the light transmission portion 210 and the external light absorption portions 220, due to the refractive index difference

[74] adjusted as described above, regardless of an incidence angle, that is, angles (0 ° , θ

1, θ 2) between the lights Ll, L2, L3 and the normal of the interface between the light transmission portion 210 and the external light absorption portion 220. Thus, the external light absorption rate is increased, and accordingly, the generation of ghost images is reduced.

[75] In the optical sheet 200 according to the current embodiment of the present invention, the refractive index difference ( Δ n= n₂io-n₂₂o) between the light transmission portion 210 and the external light absorption portion 220 may have a positive value. In this case, an image light which is incident on the interface between the light transmission portion 210 and the external light absorption portion 220 at an angle less than a critical angle is totally reflected, thereby being displayed on an observer side. As a result, separate images different from the images generated by the panel assembly 30, that is, ghost images are formed.

[76] FIG. 5 is a partial exploded perspective view of a modified example 200 of the optical sheet 200 of FIG. 3, according to an embodiment of the present invention. The modified example 200 illustrated in FIG. 5 is designed for preventing the Moire phenomenon. The Moire phenomenon refers to a phenomenon by which an interference fringe is formed when at least two periodic patterns overlap each other.

[77] Referring to FIG. 5, a longitudinal direction of the external light absorption portions

220 is not parallel to a side of the optical sheet 200, and a bias angle α greater than 0 ° exists therebetween. Although not illustrated in FIG. 5, the panel assembly 30 includes a plurality of cells that emit visible light forming images. The cells may be disposed in a stripe form, matrix form, or wave form, and thus are disposed similarly to the external light absorption portions 220 of the optical sheet 200. In this case, when the disposition direction of the external light absorption portions 220 coincides with the disposition direction of the cells, both patterns overlap each other, and thus the Moire phenomenon occurs. By adjusting the bias angle α between the longitudinal direction of the external light absorption portions 220 and a longitudinal side of the light transmission portion 210 to be greater than 0 ° , both patterns do not coincide with each other when observed by users, thereby preventing the Moire phenomenon. Preferably, the bias angle α may be in a range of 5 to 80 ° .

[78] The optical sheet 200 having the configurations described above or the filter including the same may be included in an image display device, whereby the adhesive force of the optical sheet 200 is excellent, ghost images of the image display device can be reduced and the contrast ratio thereof can be relatively high, resulting in high resolution, and the Moire phenomenon can be prevented.

[79] FIG. 6A is an exploded cross-sectional view of a filter 40 including an optical sheet

200 having a function of shielding electromagnetic waves, according to an embodiment of the present invention. FIG. 6B is an exploded cross-sectional view of a filter 40 including an optical sheet 200 having a function of shielding electromagnetic waves, according to another embodiment of the present invention.

[80] Differences between the optical sheets 200 of FIGS. 6A and 6B and the optical sheets

200 of FIGS. 2A and 2B are as follows. That is, each of the optical sheets 200 of FIGS. 6A and 6B has a further electromagnetic wave shielding layer 225 formed on at least one part of the groove on each of the external light absorption portions 220 and including a conductive material, and the surface of each electromagnetic wave shielding layer 225 has a surface roughness SR₂₂₅. In this case, the surface roughness SR₂₂₅ of the electromagnetic wave shielding layer 225 is greater than the surface roughness SR₂io of the light transmission portion 210.

[81] Particular configurations, operations and effects of the base film 230, the light transmission portion 210 and the external light absorption portions 220 included in the optical sheets 200 of FIGS. 6 A and 6B are the same as described with reference to the optical sheets 200 of FIGS. 2A and 2B, and therefore, detailed descriptions thereof are not provided here.

[82] In the optical sheets 200 of FIGS. 6A and 6B, the electromagnetic wave shielding layers 225 are formed in a portion of the grooves g₂i₀ in which the external light absorption portions 220 are not formed, that is, on the external light absorption portions 220. The electromagnetic wave shielding layers 225 may comprise metal, metal oxide, conducting polymer, or a mixture thereof. The metal may be copper, platinum, aluminum, iron, cobalt, nickel, zinc, ruthenium, tin, tungsten, lead (Pb), silver (Ag), or mixtures thereof. The metal oxide may be tin oxide, indium oxide, antimony oxide, zinc oxide, zirconium oxide, titanium oxide, magnesium oxide, silicon oxide, aluminum oxide, metal alkoxide, indium tin oxide (ITO), antimony tin oxide (ATO), or mixtures thereof. In particular, when a metal oxide is included in the electromagnetic wave shielding layer 225, oxidation or deterioration of other metals can be prevented in comparison with when the electromagnetic wave shielding layer 225 does not include a metal oxide. The electromagnetic wave shielding layer 225 is generally formed in a paste form, and then cured and/or dried, thereby completing the preparation thereof; however, the present invention is not limited thereto. In addition, the electromagnetic wave shielding layer 225 may account for 2 to 50 volume% based on 100 volume% of the external light absorption portion 220. If the electromagnetic wave shielding layer 225 accounts for less than 2 volume% based on 100 volume% of the external light absorption portion 220, effects of shielding electromagnetic wave may be insignificant. If the electromagnetic wave shielding layer 225 accounts for greater than 50 volume% based on 100 volume% of the external light absorption portion 220, the external light absorption rate may be excessively decreased.

[83] By disposing the electromagnetic wave shielding layer 225 comprising a highly- conductive material on the external light absorption portion 220 in the groove g₂io, the total volume of the filter 40 is not increased, the light transmittance of the optical sheet 200 and the external light absorption rate are not decreased, and the optical sheet 200 has an excellent electromagnetic wave shielding effect. In particular, the electromagnetic wave shielding layer 225 assists the electromagnetic wave shielding film 300 described above, thereby improving the effect of shielding electromagnetic waves, or can be used alone without the electromagnetic wave shielding film 300.

[84] In addition, the surface roughness SR₂₂₅ of the surface of the electromagnetic wave shielding layer 225 on the image light source side may be 0.15 to 5.0 μm. If the surface roughness SR_{225 π}of the electromagnetic wave shielding layer 225 is less than 0.15 μm, the adhesive force thereof may be weak. If the surface roughness SR_{225 α}θf the electromagnetic wave shielding layer 225 is greater than 5.0 μm, the light transmittance of the image light source may be decreased. More preferably, the surface roughness SR_{225 α}θf the electromagnetic wave shielding layer 225 and the surface roughness SR₂io _αθf the light transmission portion 210 may satisfy the following conditions:

[85] 0.1 < SR₂₂₅ - SR₂₁₀ < 4.95 μm

[86] As described above, by adjusting the surface roughness SR_2I0 of the light transmission portion 210 on the image light source side and the surface roughness SR 225 of the electromagnetic wave shielding layer 225 on the image light source side, the optical sheet 200 does not reduce the light transmittance of the image light source and the external light absorption rate and has excellent adhesive force. That is, the diffused reflection rate of the light transmission portion 210 can be decreased by reducing the surface roughness SR_2I0 of the light transmission portion 210 on the image light source side, and the surface adhesive force of the electromagnetic wave shielding layer 225 can be increased by increasing the surface roughness SR₂₂₅ of the electromagnetic wave shielding layer 225 on the image light source side. Here, there is no change in the electromagnetic wave shielding effect of the electromagnetic wave shielding layer 225.

[87] The optical sheets 200 of FIGS. 6A and 6B are illustrated in FIGS. 7 through 9, which respectively correspond to FIGS. 3 through 5. That is, FIG. 7 is a cross-sectional view of an optical sheet 200 having a function of shielding electromagnetic waves, according to an embodiment of the present invention, FIG. 8 is an enlarged view of a portion A' of the optical sheet 200 of FIG. 7, and FIG. 9 is a partially exploded perspective view of a modified example of the optical sheet 200 having the function of shielding electromagnetic waves of FIG. 7, which is designed for preventing the Moire phenomenon, according to an embodiment of the present invention. Detailed descriptions of the optical sheets 200 of FIGS. 7 through 9 are almost the same as those of FIGS. 3 through 5, except that the optical sheets 200 of FIGS. 7 through 9 further include the electromagnetic wave shielding layer 225, wherein a surface of the electromagnetic wave shielding layer 225 has a surface roughness SR₂₂₅, and thus detailed descriptions of the optical sheets 200 of FIGS. 7 through 9 are not provided here. Mode for Invention

[88] Hereinafter, t he present invention will be described in further detail with reference to the following examples. These examples are for illustrative purposes only and are not intended to limit the scope of the present invention.

[89] Example 1

[90] A molding roll with protrusions formed thereon, which were in a form opposite to a tetragonal- shaped optical sheet, was manufactured. Then, by using pattern roll equipment equipped with an ultra violet device(Hirano company), with 100 g of an acryl-based curable resin having a low refractive index (1.48) (Sartomer company, CN981) being added slowly between the molding roll and a base film, that is, an optical PET film having a thickness of 188 μ m (Toyobo company), the mixed solution was cured. As a result, a light transmission portion with grooves having a shape transferred from the shape of the protrusions formed on the molding roll and a refractive index of 1.48 was obtained. A carbon dispersion solution (refractive index: 1.49) prepared by mixing 2 g of carbon black with 100 g of the acryl-based curable resin( Sartomer company, CN985 ) was distributed in the transferred grooves. Then, the resulting structure was wiped several times using a doctor blade formed of soft plastic, thereby uniformly filling the grooves with the carbon dispersion solution to complete the manufacture of external light absorption portions having a refractive index of 1.49. When wiping, the doctor blade was oscillated to provide each external light absorption portion with a surface roughness. Then, the resultant was cured by ultra-violet rays to manufacture an optical sheet as illustrated in FIG. 3. Here, the pitch of the light transmission portion was 107.5 μ m, the height of the external light absorption portions was 160 μ m, and the thickness of the light transmission portion was 200 μ m. Here, the pitch of the light transmission portion refers to a distance between corresponding points of adjacent external light absorption portions . The surface roughness of the manufactured optical sheet was measured using a surface roughness analyzer. As a result, the surface roughness of the light transmission portion was 0.13 μ m, and the surface roughness of the external light absorption portions was 1.10 μ m.

[91] Here, the surface roughness was measured using an analyzer, Confocal Laser

Scanning Microscope (CLSM, Model: Leica TCS SP2 RS), and the surface roughnesses of 15 portions of each of the external light absorption portions and the light transmission portion were measured and an average value thereof was obtained.

[92] Example 2-1

[93] A molding roll with protrusions formed thereon, which were in a form opposite to a tetragonal- shaped optical sheet, was manufactured. Then, by using pattern roll equipment equipped with an ultra violet device(Hirano company), with 100 g of an acryl-based curable resin having a low refractive index (1.48)( Sartomer company, CN981 ) being added slowly between the molding roll and a base film, that is, an optical PET film having a thickness of 188 μ m (Toyobo company), the mixed solution was cured. As a result, a light transmission portion with grooves having a shape transferred from the shape of the protrusions formed on the molding roll and a refractive index of 1.48 was obtained. A carbon dispersion solution (refractive index: 1.49) prepared by mixing 2 g of carbon black with 100 g of the acryl-based curable resin( Sartomer company, CN985 ) was distributed in the transferred grooves. Then, the resulting structure was wiped using a doctor blade formed of soft plastic, thereby uniformly filling the grooves with the carbon dispersion solution to complete the manufacture of external light absorption portions having a refractive index of 1.49, wherein a recessed portion having an approximate volume of 6% of the groove was formed in each groove. Then, an appropriate amount of UV-curing silver (Ag) paste was deposited on each of the external light absorption portions. The resulting structure was then slowly wiped using a doctor blade formed of soft plastic, thereby filling the conducting material in the recessed portions to complete the manufacture of electromagnetic wave shielding layer, and the resultant was cured using ultra violet rays. When this wiping, the doctor blade was oscillated to provide each electromagnetic wave shielding layer with a surface roughness. As a result, an optical sheet having an electromagnetic wave shielding function as illustrated in FIG. 3 was manufactured.

[94] Here, the pitch of the light transmission portion was 74 μ m, the height of the external light absorption portions was 100 μ m, and the thickness of the light transmission portion was 150 μ m. The surface roughness of the manufactured optical sheet was measured using the surface roughness analyzer of Example 1. As a result, the surface roughness of the light transmission portion was 0.13 μ m, and the surface roughness of the electromagnetic wave shielding layer was 1.50 μ m.

[95] In addition, as a result of measurement of the manufactured optical sheet, the electromagnetic wave shielding effect, and black luminance values showing external light absorption rate are shown in Table 1 below. Here, the electromagnetic wave shielding effect was measured using an ASTM D-4935-89, and the black luminance values were measured using a CSlOOO (Minolta Co., Ltd.) by installing the optical sheet in a panel (SDI V4 module standard) under external light of 150 Lux.

[96] Example 2-2

[97] An optical sheet was manufactured in the same manner as in Example 2-1, except that in the process of forming the recessed portions, recessed portions having about 20 volume% of the grooves were formed and the recessed portions were coated with a conducting material. The surface roughness of the manufactured optical sheet was measured using the surface roughness analyzer of Example 1. As a result, the surface roughness of the light transmission portion was 0.13 μ m, and the surface roughness of the electromagnetic wave shielding layer was 1.60 μ m .

[98] In addition, as a result of measurement of the manufactured optical sheet, the electromagnetic wave shielding effect, and black luminance values showing external light absorption rate are shown in Table 1 below.

[99] Comparative Example 2- 1

[100] An optical sheet was manufactured in the same manner as in Example 2-1, except that the recessed portions were not formed, the external light absorption portions were not coated with a conducting material, and when wiping, the doctor blade was not oscillated.

[101] In addition, as a result of measurement of the manufactured optical sheets, the electromagnetic wave shielding effect, and black luminance values showing external light absorption rate are shown in Table 1 below.

[102] <Table 1>

[103] [Table 1] [Table ]

[104] Referring to Table 1, the larger the volume ratio of electromagnetic wave shielding layer to external light absorption portion (6.25% → 18.75%), the better the electromagnetic wave shielding effect (28 → 32) and the higher the black luminance (0.97 → 1.15) (Example 2-1 and Example 2-2). On the other hand, when the optical sheet did not include the electromagnetic wave shielding layer, the optical sheet did not have the electromagnetic wave shielding effect, and slightly lower black luminance compared with when the optical sheet included the electromagnetic wave shielding layer (Comparative Example 2-1). From this result, it can be confirmed that an optical sheet including an electromagnetic wave shielding layer can have a significantly improved electromagnetic wave shielding effect without a large change in the external light absorption rate.

[105] While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.

Claims

[1] 1. An optical sheet comprising: a light transmission portion in which a plurality of grooves spaced apart from each other at predetermined intervals are formed; and a plurality of external light absorption portions, respectively formed in the grooves, comprising a light absorbing material, wherein a surface of each of the external light absorption portions and a corresponding surface of the light transmission portion respectively have a surface roughness SR22₀ and a surface roughness SR21₀, wherein the surface roughness SR22₀ of the external light absorption portion is greater than the surface roughness SR₂io of the light transmission portion.

[2] 2. An optical sheet comprising: a light transmission portion in which a plurality of grooves spaced apart from each other at predetermined intervals are formed; a plurality of external light absorption portions, respectively formed in the grooves, comprising a light absorbing material; and an electromagnetic wave shielding layer formed by filling at least one part of the groove on the external light absorption portion with a conducting material, wherein a surface of the electromagnetic wave shielding layer and a corresponding surface of the light transmission portion respectively have a surface roughness SR₂₂₅ and a surface roughness SR₂io, wherein the surface roughness SR₂₂₅ of the electromagnetic wave shielding layer is greater than the surface roughness SR₂io of the corresponding surface of the light transmission portion.

[3] 3. The optical sheet of claim 2, wherein the electromagnetic wave shielding layer accounts for 2 to 50 volume% based on 100 volume% of the external light absorption portion.

[4] 4. The optical sheet of claim 2, wherein the electromagnetic wave shielding layer comprises at least one selected from the group consisting of a metal, a metal oxide, and a conducting polymer.

[5] 5. The optical sheet of claim 1 or 2, wherein the surface roughness SR22₀ of the external light absorption portions or the surface roughness SR₂₂₅ of the electromagnetic wave shielding layer is in a range of 0.15 to 5.0 μm, and the surface roughness SR₂io of the light transmission portion is in a range of 0.05 to 0.5 μm.

[6] 6. The optical sheet of claim 5, wherein the surface roughness SR₂₂₀ of the external light absorption portion or the surface roughness SR₂₂₅ of the electromagnetic wave shielding layer , and the surface roughness SR₂io of the light transmission portion satisfy the following conditions: 0.1 < SR₂₂₀ (or SR₂₂₅) - SR₂₁₀ < 4.95 μm.

[7] 7. The optical sheet of claim 1 or 2, wherein a refractive index of the light transmission portion is less than a refractive index of the external light absorption portion.

[8] 8. The optical sheet of claim 1 or 2, wherein each of the external light absorption portions has a triangular, tetragonal or trapezoidal cross section.

[9] 9. The optical sheet of claim 1 or 2, wherein each of the external light absorption portions is disposed in a stripe form, matrix form or wave form.

[10] 10. The optical sheet of claim 1 or 2, wherein a longitudinal direction of the external light absorption portions is not parallel to a side of the optical sheet.

[11] 11. The optical sheet of claim 1 or 2, wherein the optical sheet is a high- resolution sheet.

[12] 12. A filter for an image display device, comprising the optical sheet according to claim 1 or 2 and a filter base.

[13] 13. An image display device comprising the optical sheet according to claim 1 or