WO2010011059A2

WO2010011059A2 - Optical sheet with reduced defect visibility, filter including the same, and image displaying device including the optical sheet or the filter

Info

Publication number: WO2010011059A2
Application number: PCT/KR2009/003989
Authority: WO
Inventors: Bu Seup Song; Jong Pil Chun; Hoi Seok Jeong; Jeong Woo Shon; Seong Joong Kim; Ki Cheol Yoon
Original assignee: Samsung Fine Chemicals Co Ltd
Current assignee: Lotte Fine Chemical Co Ltd
Priority date: 2008-07-23
Filing date: 2009-07-20
Publication date: 2010-01-28
Anticipated expiration: 2011-01-23
Also published as: KR20100010848A; TW201007226A; WO2010011059A3

Abstract

Disclosed are an optical sheet, a filter including the same, and an image display device including the optical sheet or the filter. The optical sheet includes a light transmission portion including a plurality of grooves spaced apart from each other at an end of the light transmission portion corresponding to an image light source side or an observer side; and a plurality of external light absorption portions which fill the grooves and include a light absorbable material, wherein at least one part of each of the grooves that is not filled with external light absorption portion forms a recess portion having one open side, and a difference Δd between maximum depths of two recession portions that are adjacent to each other among the recession portions satisfies the following condition: 0.01 ㎛ ≤ |Δd| ≤ 1 ㎛.

Description

OPTICAL SHEET WITH REDUCED DEFECT VISIBILITY, FILTER INCLUDING THE SAME, AND IMAGE DISPLAYING DEVICE INCLUDING THE OPTICAL SHEET OR THE FILTER

Technical Field

The present invention relates to an optical sheet, a filter including the same, and an image display device including the optical sheet or the filter. More particularly, the present invention relates to an optical sheet capable of improving image quality and production yield by reducing defect visibilities, such as white line visibility and other defect visibility, increasing a light transmission and increasing image resolution by inhibiting a decrease in a contrast ratio, a filter including the same, and an image display device including the optical sheet or the filter.

Background Art

Recently, various types of image display devices have been developed. Examples of such 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 display color images by realizing emission of the three primary lights such as red, blue, and green.

Such image display devices generally 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 has functions such as surface reflection prevention and/or color adjustment. The filter should meet the requirement for light transmittance because it is disposed on a front side of the panel assembly.

The filter, however, absorbs and/or reflects lights emitted from the panel assembly and thus decreases brightness of the image display device. In addition, in a bright environment, for example, in a bright room, external environmental light passes through the filter of the image display device and may enter the panel assembly. In this regard, the external environmental light that passes through the filter from the outside may interfere with the lights emitted from the panel assembly, thereby decreasing the contrast ratio in bright room and reducing the image display capability of the image display device.

To address these problems, an optical sheet may be used. In general, a conventional optical sheet includes wedge-shaped external light absorption portions which include a light absorbable material and are disposed at predetermined intervals in a transparent light transmission portion. Since the external light absorption portions absorb external environmental light, a contrast ratio of an image is improved.

In general, external light absorption portions are formed by filling a plurality of grooves in a light transmission portion with a light absorbable material. However, the grooves are each incompletely filled with the light absorbable material and a portion of each of the grooves forms a recess portion of an optical sheet. In addition, the amount of the light absorbable material that fills each of the grooves may vary. Thus, among a plurality of external light absorption portions, recess portions of two adjacent external light absorption portions (that is, portions that are not filled with external light absorption portions in grooves of the light transmission portion) may have very different depths. Thus, when an image display device including such an optical sheet is used, white lines may be seen on a screen and a viewer may consider the quality of an image to be poor.

Technical Problem

The present invention provides an optical sheet capable of reducing defect visibilities, such as white line visibility and other defect visibility, and improving the quality of an image and production yield.

The present invention also provides an optical sheet capable of improving a contrast ratio in a bright environment.

The present invention also provides a filter including the optical sheet.

The present invention also provides an image display device including the optical sheet or the filter, wherein the optical sheet is capable of reducing defect visibilities, such as white line visibility and other defect visibility and improving the quality of an image and production yield.

Technical Solution

According to an aspect of the present invention, there is provided an optical sheet including: a light transmission portion including a plurality of grooves spaced apart from each other at an end of the light transmission portion corresponding to an image light source side or an observer side; and a plurality of external light absorption portions which fill the grooves and include a light absorbable material, wherein at least one part of each of the grooves that is not filled with the external light absorption portion forms a recess portion having one open side, and a difference Δd between maximum depths of two recession portions that are adjacent to each other among the recession portions satisfies the following condition: 0.01 ㎛ ≤ |Δd| ≤ 1 ㎛ .

When being measured using ASTM D1003, a haze value (%H) of the optical sheet may be in the range of 5 to 25%.

Widths of the external light absorption portions may be in the range of 10 to 40 ㎛ , and maximum depths of the recess portions are in the range of 0.1 to 20 ㎛ .

Heights of the external light absorption portions may be in the range of 50 to 200 ㎛ , and maximum depths of the recess portions are in the range of 0.1 to 20 ㎛ .

Thickness-wise cross sections of the external light absorption portions may be triangular, tetragonal, or trapezoidal-shaped .

The external light absorption portions may be disposed in a stripe form, a matrix form, or a wave form .

The optical sheet may be a sheet for enhancing a contrast ratio .

According to another aspect of the present invention, there is provided a filter for an image display device, the filter including: the optical sheet described above; and a filter base.

The filter base may include a reflection prevention film, a hard coating layer, an electromagnetic wave shielding film, and a combination thereof.

The filter base may further include a color adjustment film in a side of the optical sheet corresponding to an image light source side.

According to another aspect of the present invention, there is provided an image display device including the optical sheet or the filter for an image display device described above.

Description of Drawings

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:

FIG. 1 is an exploded perspective schematic view of an image display device equipped with a filter including an optical sheet according to an embodiment of the present invention;

FIG. 2A is an exploded cross-sectional view of a filter including an optical sheet according to an embodiment of the present invention;

FIG. 2B is an exploded cross-sectional view of a filter including an optical sheet according to another embodiment of the present invention;

FIG. 3 is a partially enlarged view of the optical sheet of FIG. 2A before the optical sheet is mounted on the filter; and

FIG. 4 is an enlarged view of a portion A of the optical sheet of FIG. 3 .

Mode for Invention

Hereinafter, with reference to the accompanying drawings, an optical sheet according to an embodiment of the inventive concept, a filter including the optical sheet, and an image display device including the optical sheet or the filter will be described in detail.

FIG. 1 is an exploded perspective view 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 the filter 40 including an optical sheet 200 according to an embodiment of the present invention, and FIG. 2B is an exploded cross-sectional view of the filter 40 including the optical sheet 200 according to another embodiment of the present invention .

Referring to FIG. 1, the image display device 1 according to the present 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 .

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

Referring to FIGS. 2A and 2B, the filter 40 includes a color adjustment film 100, the optical sheet 200, and a filter base (FB) including an electromagnetic wave shielding film 300, a hard coating layer 400, and a reflection prevention film 500.

The color adjustment film 100 may include, for example, a neon light blocking colorant, and may further include a near-infrared ray absorption compound or colorant.

The optical sheet 200 includes a base film 230, a light transmission portion 210, and a plurality of external light absorption portions 220. The optical sheet 200 may be disposed under the color adjustment film 100. The optical sheet 200 described above may be, for example, a sheet for enhancing a contrast ratio, but is not limited thereto. The sheet for enhancing a contrast ratio may be interpreted in a broad sense, for example, as a sheet for increasing mainly the contrast ratio of the image display device 1.

The light transmission portion 210 transmits light emitted from the panel assembly 30 illustrated in FIG. 1. The light transmission portion 210 may include a curable resin. In particular, the light transmission portion 210 may include an acrylate resin that may be cured when exposed to ionizing radiation or heat energy.

In addition, the light transmission portion 210 may be transparent, but not necessarily completely transparent. In the latter case, the light transmission portion 210 may have a transparency level that is generally acceptable in the art as being transparent. In general, the shape of the light transmission portion 210 may be complementary to the shape of the external light absorption portions 220, which will be described later, but the shape of the light transmission portion 210 is not limited thereto. That is, the light transmission portion 210 may have a plurality of grooves g₂₁₀ disposed at predetermined intervals, and the grooves g₂₁₀ are filled with a light absorbable material to form the external light absorption portions 220 which will be described later. The grooves g₂₁₀ and the external light absorption portions 220 may be formed either at an end of the light transmission portion 210 corresponding to an image light source side (refer to FIGS. 2A, 2B, and 3), or at an end of the light transmission portion 210 corresponding to an observer side (not shown.) The refractive index of the light transmission portion 210 may be in a range of 1.3 to 1.8. It is difficult to manufacture the light transmission portion 210 to have a refractive index of less than 1.3. On the other hand, when the refractive index of the light transmission portion 210 is greater than 1.8, the transmittance of the light transmission portion 210 is significantly decreased and the contrast ratio is also decreased, resulting in a decrease in the overall resolution of the image display device 1. According to the present embodiment, each of the grooves g₂₁₀ of the light transmission portion 210 is incompletely filled with a light absorbable material so that a portion of the groove g₂₁₀ remains empty. The empty portion of the groove g₂₁₀ is referred to as a recess portion 200a. However, the structure of the grooves g₂₁₀ is not limited thereto. The recess portion 200a may be formed using various methods. For example, the recess portion 200a may be formed by compressing the light absorbable material with an elastic wiping blade when the grooves g₂₁₀ are filled with the light absorbable material. Alternatively, the recess portion 200a may be formed by completely filling the grooves g₂₁₀ with the light absorbable material and then compressing the filled light absorbable material by, for example, wiping. Alternatively, the recess portion 200a may be formed by filling the grooves g₂₁₀ with a contractible resin and then curing or drying the contractible resin. Specifically, as illustrated in FIGS. 2A and 2B, the recess portion 220a is at least one portion of the grooves g₂₁₀ which is defined by the external light absorption portions 220 and the light transmission portion 210, and has one open side. Due to formation of the recess portion 200a, the optical sheet 200 may improve a light transmission while inhibiting a decrease in an external light absorption rate, which will be described in detail later.

According to an embodiment of the present invention, a difference (Δd) between the maximum depths of two adjacent recess portions from among the plurality of recess portions 200a satisfies the following condition:

0.01 ㎛ ≤ |Δd| ≤ 1 ㎛

where Δd is d_a+1-d_a, d_a-d_a-1, or d_a-1-d_a-2.

If |Δd| is less than 0.01 ㎛ , the difference between the maximum depths of two adjacent recess portions 200a is reduced and the optical sheet 200 has a uniform appearance. However, light is less diffused, and thus defect visibility is increased. Thus, viewer may easily recognize defects of the optical sheet 200 itself or process defects caused by intermixing of impurities. On the other hand, if |Δd| is greater than 1 ㎛ , the corresponding recess portion 200a may be recognized as a white line. For example, if each of d_a-d_a-1 and d_a-1-d_a-2 is equal to or smaller than 1 ㎛ and d_a+1-d_a is greater than 1 ㎛ , the recess portion 200a having the maximum depth of d_a+1 is recognized as a white line. Herein, the 'white line' denotes a white line or spot to be viewed in a particular portion (for example, recess portion in a stripe pattern) of the optical sheet 200. By controlling |Δd| as described above, defect visibility and white line visibility may be reduced, and thus production yield may be increased while a defect rate is decreased, and image quality may be increased.

The external light absorption portions 220 are formed by filling the grooves g₂₁₀ formed in the light transmission portion 210 with a thermoplastic resin, a thermosetting resin or an ultraviolet ray curable resin, and a light absorbable material. The light absorbable material may absorb external environmental light and enhance a contrast ratio in a bright environment, thereby being possible to form high resolution images. Referring to FIG. 2A, each of the external light absorption portions 220 has a tetragonal cross section, and referring to FIG. 2B, each of the external light absorption portions 220 has a trapezoidal cross section.

When the external light absorption portions 220 include a thermosetting resin, the thermosetting resin may be the same as or similar to a thermosetting resin included in the light transmission portion 210.

Examples of the light absorbable material may include a black inorganic material, a black organic material, a black-oxidized metal, and mixtures thereof. When the external light absorption portions 220 include a black-oxidized metal, since the black-oxidized metal has low electric resistance, the electric resistance may be controlled by adjusting the amount of black-oxidized metal power or the thickness of black-oxidized metal film. Thus, the external light absorption portions 220 can shield electromagnetic waves. The external light absorption portions 220 may include a carbon-containing ultraviolet-ray curable resin. The refractive index of the external light absorption portions 220 may be similar to the refractive index of the light transmission portion 210, specifically in a range of 1.3 to 1.8.

The base film 230 is disposed on one surface of the light transmission portion 210, that is, the surface opposite to that in which the recess portions 200a 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), polyethyleneterephthalate (PET), polyphenylene sulfide (PPS), polyallylate, polyimide, polycarbonate (PC), cellulose triacetate (TAC), and cellulose acetate propionate (CAP). Preferably, the base film 230 may include polycarbonate (PC), polyethyleneterephthalate (PET), cellulose triacetate (TAC), or polyethylene naphthalate (PEN). In addition, the base film 230 may include a material having a refractive index equal or similar to the refractive index of the light transmission portion 210.

In addition, the optical sheet 200 may further include a protection film 240 (see FIGS. 3 through 4) formed on one 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 mounted on the filter 40. After the optical sheet 200 is mounted on the filter 40, the protection film 240 is separated from the optical sheet 200; however, the present invention is not limited thereto.

Meanwhile, after the optical sheet 200 is incorporated into the filter 40, the recess portions 200a may be completely filled with a part of an adhesive layer and/or the color adjustment film 100, but the present invention is not limited thereto. When the recess portions 200a are filled with a part of an adhesive layer, a material for forming the adhesive layer may have a refractive index equal or similar to the refractive index of the light transmission portion 210.

The optical sheet 200 having the structure described above may have a haze value (%H) of 5 to 25% when measured using ASTM D1003.

Referring to FIGS. 2A and 2B, the filter base (FB) is disposed on a surface of the optical sheet 200, and includes an electromagnetic wave shielding film 300, a hard coating layer 400, and a reflection prevention film 500 disposed in this order. However, the structure of the FB is not limited thereto. That is, the shielding film 300, the hard coating layer 400, and the reflection prevention film 500 may be disposed in any order in the FB. The FB may also include a layer including at least two types of materials performing different functions.

The electromagnetic wave shielding film 300 shields electromagnetic waves. The electromagnetic wave shielding film 300 may include a conductive mesh layer, a metal thin layer, a high-refractive-index transparent thin layer, or at least two of the previous layers. In FIGS. 2A and 2B, the electromagnetic wave shielding film 300 is a single layer. However, the structure of the electromagnetic wave shielding film 300 is not limited thereto. For example, the electromagnetic wave shielding film 300 may have a multi-layer structure including at least two layers.

The hard coating layer 400 has a scratch resistance and prevents the electromagnetic wave shielding film 300 or the reflection prevention film 500 from being damaged by, for example, contact with external materials. The hard coating layer 400 may include reinforced glass, or reinforced glass including polymer as a binder. In addition, the hard coating layer 400 may include an acryl-based polymer, a urethane-based polymer, an epoxy-based polymer, a siloxane-based polymer, or an ultraviolet curable resin such as oligomer. Furthermore, the hard coating layer 400 may further include a silica-based filler to increase the hardness thereof.

The reflection prevention film 500 adjusts the level of transmittance of visible light so as to minimize eye fatigue of users watching the image display device 1 for a long period of time. By using the reflection prevention film 500 to adjust the transmittance of visible light, visible light may be selectively absorbed and also, a color reproduction range such as a contrast ratio may be widened. In FIGS. 2A and 2B, the reflection prevention film 500 is a single layer. However, the structure of the reflection prevention film 500 is not limited thereto. For example, the reflection prevention film 500 may have a multi-layer structure including at least two layers.

The reflection prevention film 500 has a reflection prevention effect because visible light that enters from the outside and is reflected from the surface of the reflection prevention film 500 and visible light reflected from the interface between the reflection prevention film 500 and the hard coating layer 400 are out of phase with each other and thus destructive interference occurs.

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 include a titanium oxide or a specific fluorine resin having a low refractive index.

Hereinafter, the particular configuration and operation effects of the light transmission portion 210, the external light absorption portions 220, and the recess portion 200a will be described more fully with reference to the accompanying drawings.

FIG. 3 is a partially enlarged view of the optical sheet 200 of FIG. 2A before the optical sheet 200 is mounted on the filter 40, and FIG. 4 is an enlarged view of a portion A of FIG. 3. It should be noted that the protective film 240 is not yet removed.

In FIGS. 1 through 4, like reference numerals denote like elements.

The external light absorption portions 220 may be formed by performing a roll molding process, a thermal pressing process using a thermoplastic resin, or an injection molding process wherein the grooves g₂₁₀ of the light transmission portion 210 having a shape opposite to the pattern of the external light absorption portions 220 are filled with a thermoplastic or thermosetting resin. In addition, when the ultraviolet-ray 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, the optical sheet 200 may additionally perform these functions.

Referring to FIGS. 3 and 4, the optical sheet 200 according to the present embodiment of the present invention includes the light transmission portion 210, the external light absorption portions 220, the base film 230, and the protection film 240. The protection film 240 may be omitted. The filter 40 illustrated in FIG. 2A includes the optical sheet 200 from which the protection film 240 is removed .

The configuration of the light transmission portion 210, the external light absorption portion 220, the base film 230, and the protection film 240 is the same as described above.

The external light absorption portions 220 may be disposed in various forms, such as a stripe form, a matrix form, a wave form, etc. In addition, the external light absorption portions 220 may be disposed at predetermined intervals to allow light to pass through areas between adjacent external light absorption portions 220. In FIG. 3, the external light absorption portions 220 have tetragonal cross sections. However, the cross-sectional shape of the external light absorption portions 220 is not limited thereto. For example, the external light absorption portions 220 may have triangular, trapezoidal, or pentagonal cross sections.

As described with reference to FIGS. 2A and 2B, the external light absorption portion 220 and the recess portion 200a are sequentially formed in the groove g₂₁₀ of the light transmission portion 210. That is, the groove g₂₁₀ is partially filled with a light absorbable material to form the external light absorption portion 220 and the empty portion of the groove g₂₁₀ forms the recess portion 200a. The widthwise cross-section of the recess portion 220a is U-shaped, but the shape of the recess portion 200a is not limited thereto. When the optical sheet 200 is combined with the color adjustment film 100 to form the filter 40, the recess portion 200a may be filled with a part of an adhesive layer (not shown) having a refractive index equal or similar to the refractive index of the light transmission portion 210 .

In the optical sheet 200 according to an embodiment of the present invention , the maximum depths d_a+1,d_a, d_a-1, and d_a-2 of the recess portions 200a have a greater effect on formation of a white line than the depth of the other portion of the recess portion 220 . Specifically, if Δd, that is, the difference between the maximum depths of two adjacent recess portions, is in the range of 0.01 ㎛ to 1 ㎛ , both of defect visibility and white line visibility may be reduced.

In addition, a maximum depth d_imax of the interface between the recess portion 220a and the light transmission portion 210 also has a greater effect on a light transmission than the depth of the other portion of the recess portion 220. This will now be exemplarily described with reference to FIG. 4 showing lights L₁ and L₂ that are incident on the optical sheet 200 from the image light source side. Herein, light L₁ refers to a rightmost light that may pass through the light transmission portion 210 disposed on the left of the external light absorption portion 220 in FIG. 4 among lights emitted from an image light source when the recess portion 200a is not formed (i.e., the conventional technique), and light L₂ refers to a rightmost light that may pass through the light transmission portion 210 disposed on the left of the external light absorption portion 220 in FIG. 4 among lights emitted from the image light source when the recess portion 200a is formed (i.e., the present invention). When the recess portion 200a is formed, more lights may pass through the light transmission portion 210 between the optical paths of light L₁ and light L₂, and thus, the light transmission of the optical sheet 200 may be increased and brightness of the image display device having the optical sheet 200 may be increased.

In regard to the optical sheet 200, as described above, the grooves g₂₁₀ are formed in the light transmission portion 210 and only a portion of each of the grooves g₂₁₀ is filled with a light absorbable material to form the external light absorption portion 220, and thus, the filling process with a light absorbable material may be easily performed and the manufacturing costs may be reduced compared to conventional techniques. Furthermore, residue of the light absorbable material stuck to the light transmission portion 210 around the grooves g₂₁₀, which is a problem in the conventional art, may not be formed.

In addition, when a width W₂₂₀ of the external light absorption portion 220 is in the range of 10 to 40 ㎛ , the maximum depths d_a+1, d_a, d_a-1, and d_a-2 of the recess portions 200a may be in the range of 0.1 to 20 ㎛ .

Herein, the width W₂₂₀ of the external light absorption portion 220 refers to the width of an end of the external light absorption portion 220 corresponding to the image light source side. If the external light absorption portions 220 have a trapezoidal cross section as illustrated in FIG. 2B, the width W₂₂₀ of the external light absorption portion 220 refers to the width of an end of the external light absorption portion 220 corresponding to the image light source side, that is, the maximum width.

In addition, when a height h₂₂₀ of the external light absorption portion 220 is in the range of 50 to 200 ㎛ , the maximum depths d_a+1, d_a, d_a-1, and d_a-2 of the recess portions 200a may be in the range of 0.1 to 20 ㎛ .

The optical sheet 200 according to the present embodiment of the present invention may further include a prism portion (not shown) disposed on one surface of the base film 230, that is, the surface opposite to that on which the light transmission portion 210 is disposed. A material for forming the prism portion may be identical or similar to the material for forming the light transmission portion 210. By including the prism portion, the optical sheet 200 may have a high external light absorption rate, and then an enhanced contrast ratio and a high resolution, without a large change in transmittance .

An optical sheet or filter having the structure as described above may be included in an image display device, and thus, defect visibilities, such as white line visibility and other defect visibility of the image display device are reduced, the quality of an image is improved, a contrast ratio is increased, and high-resolution images may be obtained.

Hereinafter, the present invention will now be described in more detail with reference to the following Examples. However, these examples are given for the purpose of illustration and not of limitation.

Example 1

A molding roll having a surface on which a plurality of protrusions each having a tetragonal side cross-section were formed was manufactured. Then, by using a pattern roll apparatus equipped with an ultraviolet (UV) rays generation device, 100 g of a mixed solution (Sartomer, CN-981)(refractive index: 1.48) containing acryl-based curable resin having a low refractive index was slowly added between the molding roll and an optical PET film (manufactured by Toyobo Co., Ltd) having a thickness of 188 ㎛ and cured, thereby forming a light transmission portion having grooves with a pattern opposite to the pattern of the protrusions of the molding roll. The refractive index of the light transmission portion was 1.51. Herein, the optical PET film constituted a base film. A carbon dispersion (refractive index: 1.49) prepared by mixing 2 g of carbon black and 100 g of an acryl-based curable resin mixed solution (Sartomer, CN-985) was scattered over the grooves and then, wiping was performed thereon using a Dr. Blade formed of a soft plastic to uniformly fill the grooves, thereby forming a plurality of external light absorption portions having a refractive index of 1.52 and then a plurality of recess portions having an average maximum depth of 3 ㎛ . The wiping was performed while oscillating the Dr. Blade at a rate of 3 to 20 rpm and adjusting the difference |Δd| between the maximum depths of adjacent two recess portions to be in the range of 0.01 to 1 ㎛ . Then, the acryl-based curable resin of the carbon dispersion was cured using UV-rays, thereby obtaining an optical sheet including recess portions as illustrated in FIG. 3. Herein, the pitch of the light transmission portion was 74 ㎛ , the height and width of the external light absorption portions were 102 ㎛ and 24 ㎛ , respectively, and the thickness of the light transmission portions was 150 ㎛ . The pitch of the light transmission portion refers to a distance between corresponding sites of adjacent portions of the light transmission portion which are divided by an external light absorption portion.

Comparative Example 1

An optical sheet was manufactured in the same manner as in Example 1, except that the wiping process using Dr. Blade was performed three times while adjusting the difference |Δd| between the maximum depths of two adjacent recess portions to be less than 0.01 ㎛ .

Comparative Example 2

An optical sheet was manufactured in the same manner as in Example 1, except that the wiping process using Dr. Blade was performed at an oscillation rate of less than 3 rpm so as to adjust the difference |Δd| between the maximum depths of two adjacent recess portions to be in the range of 1 to 3 ㎛ .

Evaluation Example

The optical sheets manufactured were evaluated. The results are shown in Table 1. Table 1 includes information about whether white lines and whether other defects were viewed, and haze values (%H) measured using ASTM D1003. Herein, white lines and other defects were identified with the naked eye. '○' indicates that white lines and other defects were identified with the naked eye, and '×' indicates that white lines and other defects were not identified with the naked eye.

[Table 1]

Referring to Table 1, the optical sheet manufactured according to Example 1 did not show white lines or other defects. However, in the case of the optical sheet manufactured according to Comparative Example 1, the recess portions had a uniform depth and thus white lines were not seen but other defects were seen. In to the case if the optical sheet manufactured according to Comparative Example 2, other defects were not seen, but the recess portions had non-uniform depths and thus white lines were seen. In addition, referring to Table 1, it can be seen that there is an appropriate range of haze value (%H) in which white line visibility and other defect visibility are all reduced.

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. An optical sheet comprising:

a light transmission portion comprising a plurality of grooves spaced apart from each other at an end of the light transmission portion corresponding to an image light source side or an observer side; and

a plurality of external light absorption portions which fill the grooves and comprise a light absorbable material,

wherein at least one part of each of the grooves that is not filled with the external light absorption portion forms a recess portion having one open side, and

a difference Δd between maximum depths of two recession portions that are adjacent to each other among the recession portions satisfies the following condition:

0.01 ㎛ ≤ |Δd| ≤ 1 ㎛ .

2. The optical sheet of claim 1, wherein when measured using ASTM D1003, a haze value (%H) of the optical sheet is in the range of 5 to 25%.

3. The optical sheet of claim 1, wherein widths of the external light absorption portions are in the range of 10 to 40 ㎛ , and maximum depths of the recess portions are in the range of 0.1 to 20 ㎛ .

4. The optical sheet of claim 1, wherein heights of the external light absorption portions are in the range of 50 to 200 ㎛ , and maximum depths of the recess portions are in the range of 0.1 to 20 ㎛ .

5. The optical sheet of claim 1, wherein thickness-wise cross sections of the external light absorption portions are triangular, tetragonal, or trapezoidal-shaped .

6. The optical sheet of claim 1, wherein the external light absorption portions are disposed in a stripe form, a matrix form, or a wave form .

7. The optical sheet of claim 1, wherein the optical sheet is a sheet for enhancing a contrast ratio .

8. A filter for an image display device, the filter comprising:

the optical sheet of any one of claims 1-7; and

a filter base.

9. An image display device comprising the optical sheet of any one of claims 1-7.