KR20180066432A - Liquid crystal display - Google Patents

Abstract

The present invention relates to a liquid crystal display including an optical film. According to the present invention, provided is the liquid crystal display which can simultaneously improve the contrast ratio and brightness uniformity of exit light by selectively adjusting only light causing color mixture by applying a specific structural optical film.

Description

Liquid crystal display

This application relates to a liquid crystal display using an optical film.

BACKGROUND ART Liquid crystal displays (LCDs) are display devices using anisotropy of liquid crystal. A liquid crystal display has a structure including a liquid crystal panel including a liquid crystal layer having a liquid crystal material and polarizers disposed on both sides thereof, and changes the orientation of the liquid crystal layer to realize a monochrome state and display an image.

Since the liquid crystal panel is designed to align the polarized light with respect to the light vertically incident on the panel in general, there arises a problem that the brightness of the light changes or the color changes with respect to the light in the inclined direction.

In order to solve such a problem, for example, a method of disposing a so-called optical compensation film or the like on the visual side of the liquid crystal panel is known, as in the case of Patent Document 1, for example.

On the other hand, various modes exist in the liquid crystal display according to the orientation of the liquid crystal in the liquid crystal panel, and typically TN (Twisted Nematic), VA (Vertical Alignment) or IPS (In plane switching) modes exist.

Among the above modes, the VA mode generally has excellent contrast ratio and excellent coloring ability, but a so-called color washout phenomenon occurs in which the contrast ratio is lowered when the display is observed at the inclination angle than when the display is observed in the front direction do.

Korea Patent Publication No. 2009-0080133

It is an object of the present invention to provide a liquid crystal display which can selectively adjust only light causing color mixing by applying an optical film having a specific structure and simultaneously improve brightness uniformity and contrast ratio of emitted light.

The liquid crystal display of the present application may include a liquid crystal panel and an optical film. As shown in Fig. 1, the optical film may be disposed on a visible side surface of the liquid crystal panel. The term " visible side surface " of the liquid crystal panel in this specification means a surface closer to an observer who observes the image when the display displays the image on the upper and lower surfaces of the liquid crystal panel. The term " rear surface of the liquid crystal panel " means the surface of the upper surface and the lower surface opposite to the viewer-side surface.

The liquid crystal panel may be a VA (Vertical Alignment) type liquid crystal panel. By disposing a specific optical film to be described later on the visual side surface of a liquid crystal panel, the present inventors have succeeded in ensuring uniformity of light emitted from the front and viewing angles in various types of liquid crystal panels, washout phenomenon can be solved, and this effect is appropriately expressed in a liquid crystal display of VA mode in particular.

The specific configuration of the liquid crystal panel applied in the present application is not particularly limited, and any known general liquid crystal panel configuration can be applied.

For example, the liquid crystal panel may be a transmissive, reflective or transflective liquid crystal panel. The driving method of the liquid crystal panel in the present application is not particularly limited. For example, an active matrix method using an active electrode such as a passive matrix method, a TFT (Thin Film Transistor) electrode or a TFD (Thin Film Diode) And the like can be applied.

A liquid crystal panel typically includes a liquid crystal layer containing a liquid crystal material interposed between two transparent substrates. The transparent substrate of the liquid crystal panel may have a property of orienting the liquid crystal material constituting the liquid crystal layer in a specific alignment direction. For example, a transparent substrate on which the substrate itself has a property of aligning liquid crystals, or on which an alignment film having a property of aligning a liquid crystal material is provided, although the substrate itself has no alignment capability. As the electrode of the liquid crystal panel, a known electrode such as ITO (Indium Tin Oxide) can be applied. Such an electrode can be provided on the surface of a transparent substrate on which the liquid crystal layer is in contact with the electrode. In the case of using a transparent substrate having an alignment film, the electrode can be provided between the substrate and the alignment film.

As the liquid crystal material contained in the liquid crystal layer, a material having various negative or positive dielectric anisotropy, which is generally used in the constitution of a liquid crystal panel, can be used. Examples of such materials include, but are not limited to, various low-molecular liquid crystal materials, polymer liquid crystal materials, and mixtures thereof. In addition, the liquid crystal layer of the liquid crystal panel may contain a dye, a chiral agent, or a non-liquid crystalline substance within a range that does not impair the liquid crystallinity of the liquid crystal material.

In addition, a transflective liquid crystal panel may be constituted by replacing one substrate, for example, a substrate on the rear side of the liquid crystal panel, with a substrate having a reflective function area and a transmissive function area. A region (hereinafter, referred to as a reflection layer) having a reflection function included in the transflective electrode used in such a liquid crystal panel is not particularly limited, but a metal such as aluminum, silver, gold, chromium, An oxide such as magnesium oxide, a multilayer film of a dielectric, a liquid crystal showing selective reflection, or a combination of these. These reflective layers may be planar or curved. The reflective layer may be formed by imparting diffusive reflectivity to a surface shape such as a concavo-convex shape, or by combining electrodes on the transparent substrate on the back side of the liquid crystal panel, or a combination thereof.

The liquid crystal panel may include other constituent members in addition to the constituent members. For example, by providing a color filter, a color liquid crystal display device capable of providing multicolor or pure color display with high color purity can be manufactured.

The liquid crystal display may further include a backlight unit, a first polarizer, and a second polarizer. In the liquid crystal display, the backlight unit, the first polarizing plate, the liquid crystal panel, the second polarizing plate, and the optical film may be sequentially disposed. The absorption axes of the first polarizing plate and the second polarizing plate may be orthogonal to each other.

The first polarizing plate or the second polarizing plate polarizes the incident light and may be a polarizer conventionally known to those skilled in the art such as a polyvinyl alcohol polarizer in which a polyvinyl alcohol film is uniaxially stretched or a polyvinyl alcohol film Dehydrated polyene polarizers. The first polarizer or the second polarizer may each further include a protective film.

The first polarizing plate or the second polarizing plate may be attached to the liquid crystal panel by an adhesive layer or an adhesive layer. The adhesive layer or adhesive layer may be formed of a tacky resin, and optionally a composition comprising a crosslinking agent, a silane coupling agent, a photo-radical initiator, or a light-ion initiator. The adhesive layer or the adhesive layer may further increase the light diffusion effect by further including a light diffusing agent. The light diffusing agent may comprise conventional light diffusers known to those skilled in the art.

The backlight unit may include a light source. The backlight unit may further include a light guide plate for guiding light emitted from the light source, a reflection sheet disposed under the light guide plate, and a diffusion sheet disposed on the light guide plate. The light source generates light and may be disposed on the side of the light guide plate (edge type). The light source may be a light source lamp, a surface light source lamp, a CCFL, or an LED. A light source cover may be disposed outside the light source. The light guide plate can guide the light generated from the light source to the diffusion sheet. The light guide plate may be omitted when a direct light source is employed, and in this case, a diffusion plate may be further included. The reflective sheet may serve to reflect the light generated from the light source and supply the light toward the diffusion sheet. The diffusion sheet can diffuse and scatter light incident through the light guide plate and supply the diffusion sheet to the liquid crystal panel.

The optical film may be disposed on a visible side surface of the liquid crystal panel. The reason that the optical film is disposed on the visual side surface of the liquid crystal panel in the present application means that not only the optical film is disposed in contact with the visual side surface but also other constituent members exist between the optical film and the visual side surface Can also be included. For example, as described above, the second polarizing plate may be disposed between the optical film and the viewer-side surface of the liquid crystal panel.

The optical film may be disposed at an outermost position of the liquid crystal display. The fact that the optical film is disposed at the outermost position of the liquid crystal display in the present application may mean that any one surface of the optical film is exposed so as to be in contact with the air.

The optical film may include a first region and a second region having different refractive indices from each other. The refractive index of the first region may be higher than that of the second region. The first region may be disposed adjacent to the liquid crystal panel as compared to the second region.

The region of any one of the first region and the second region may have a patterned pattern of a convex portion formed of a plurality of inclined faces having an inclination angle of 10 degrees to 25 degrees. And the other one of the first region and the second region may have a structure filling the concave portion formed by the convex portion.

In the present application, the inclined surface (TS in Figs. 3 and 4) means a surface inclined at an angle of more than 0 to less than 90 degrees with respect to the normal direction (N in Figs. 3 and 4) .

In this application, the inclination angle (TA in Figs. 3 and 4) may mean the angle formed by the normal direction (N in Figs. 3 and 4) of the obverse side surface of the liquid crystal panel and the inclined surface. When the inclination angle of the inclined surface is within the above range, only the light causing color mixing can be selectively controlled to improve the luminance uniformity and the contrast ratio of the emitted light simultaneously.

Figs. 3 and 4 each illustrate the structure of the optical film according to the first and second embodiments of the present application.

According to the first embodiment of the present application, the first region 201 may have a structure patterned as a convex portion, and the second region 202 may have a structure to fill a concave portion formed by the convex portion. According to the first embodiment, the protruding direction of the convex portion of the first region 201 may be the viewing side direction.

According to the second embodiment of the present application, the second region 202 may have a structure patterned as convex portions, and the first region 201 may have a structure filling the concave portions formed by the convex portions. According to the second embodiment, the projecting direction of the convex portion 202 of the second region may be the liquid crystal panel side direction. The convex portion may be formed of a plurality of inclined surfaces. In this case, it is preferable that the inclination angles of all the inclined surfaces of the plurality of inclined surfaces satisfy the above range.

The inclination angles of the plurality of inclined surfaces may be equal to or different from each other. The standard deviation of the inclination angle of the plurality of inclined surfaces may be in the range of 0 degree to 5 degrees. The standard deviation may be about 5 degrees or less, about 4 or less, about 3 or less, about 2 or less or about 1 or less in other examples.

The convex portion may have a pyramid shape. The pyramid shape may have a horn shape having an n-square bottom face, and n may be 3 to 10.

The convex portions may be arranged in a multidimensional arrangement when viewed from the surface direction of the optical film. The multidimensional arrangement may mean that the convex portion is arranged along a specific axis when viewed from the surface direction, and the number of such axes is two or more.

Fig. 2 exemplarily shows a first region or a side surface of a second region in which pyramid-shaped convex portions having a quadrangular bottom surface are two-dimensionally arranged.

The height of the convex portion (H in Figs. 3 and 4) can be appropriately selected in consideration of the object of the present application. For example, the height of the convex portion may be in the range of 20 to 300 占 퐉. In this case, it may be more advantageous to improve the luminance uniformity and the contrast ratio by selectively controlling the light causing the color mixing. In another example, the height may be 20 탆 or more, 30 탆 or more, or 40 탆 or more. In another example, the height may be 300 μm or less, 200 μm or less, 100 μm or less, 90 μm or less, 80 μm or less, 70 μm or less, 60 μm or less or 50 μm or less.

The structure patterned by the convex portions may include a plurality of convex portions. The plurality of convex portions may be spaced apart from each other or disposed adjacent to each other. When the plurality of convex portions are disposed apart from each other, a region between the convex portions may be flat. The height of the flat region may be lower, higher, or equal to the height of the convex portion.

The pitch of the convex portions (P in Fig. 3 and Fig. 4) can be appropriately selected in consideration of the object of the present application. For example, the pitch of the convex portions may be 10 to 50 占 퐉. In this case, it may be more advantageous to improve the luminance uniformity and the contrast ratio by selectively controlling the light causing the color mixing. The pitch may be a shortest distance or a longest distance from a point where one convex portion starts to a point where another convex portion starts. The pitch may be about 15 탆 or more, 20 탆 or more, 25 탆 or more, 30 탆 or more, 35 탆 or 40 탆 or more in another example. Further, the pitch may be 50 mu m or less in another example.

The number of the convex portions can be appropriately selected in consideration of the object of the present application. The convex portions may be present in the surface direction 400 per unit area on the basis / mm ² to 10,000 / mm ² to the optical film. In another example, the ratio may be at least 400 / mm ^{2, at} least 450 / mm ^2, or at least 500 / mm ² . In addition, the rate of 10000 In other instances / mm ² or less, 9,000 / mm ² or less, to 8000 / mm ² or less, 7,000 / mm ² or less, 6,000 / mm ² or less, to 5000 / mm ² or less, 4000 / mm ² or less, to 3000 / mm ² or less, to 2000 / mm ² or less, to 1000 / mm ² or less, to 900 / mm ² or less, 800 / mm ² or less, 700 / mm ² or less, or 600 Mm / mm < ² >. In this case, the object of the present application can be achieved more effectively.

One surface of the region having the patterned pattern of the convex portions among the first region and the second region may be a flat surface. The one surface may refer to the opposite surface of the structure patterned with the convexities.

One surface of the region having the filling structure among the first region and the second region may be a flat surface. The one surface may refer to the opposite surface of the filling structure.

The optical film may further comprise a base layer. The base layer may be disposed on one side of a region having a structure patterned by convex portions of the first region and the second region. In one example, when the first region has a structure patterned as convex portions, the optical film may have a structure in which the base layer, the first region, and the second region are sequentially arranged in the viewing side direction on the liquid crystal panel side . In another example, in the case where the second region has a patterned pattern as a convex portion, the optical film may have a structure including a first region, a second region and a base layer sequentially in the viewing side direction on the liquid crystal panel side have.

The first region may have a higher refractive index with respect to light having a wavelength of 550 nm than the second region. The first region may be disposed adjacent to the liquid crystal panel as compared to the second region. Through this arrangement, only the light causing the color mixing can be selectively controlled, and the luminance uniformity and the contrast ratio of the emitted light can be improved at the same time.

The optical film may be disposed such that light emitted from the liquid crystal panel sequentially passes through the first region and the second region. When light is incident on a medium having a small refractive index in a medium having a large refractive index, the light has total reflection characteristics when the incident angle is greater than a critical angle. In the present application, it is possible to increase the reflectance of light of 10 to 20 degrees of the internal angle of the light source and reduce the reflectance of other light by using the total reflection principle and the inclination angle. Since the reflected light can be emitted in different directions, the brightness can be uniformly adjusted as a whole.

The difference in refractive index between the first region and the second region with respect to light having a wavelength of 550 nm may be 0.025 to 0.09. When the refractive index difference between the first and second regions is within the above range, it is more advantageous to simultaneously improve the luminance uniformity and the contrast ratio by reducing color mixing. If the refractive index difference between the first region and the second region is out of the above range, the total light amount may be reduced and the contrast ratio may be lowered.

The refractive index of the first region with respect to light having a wavelength of 550 nm may be 1.40 to 1.64. As the transparent material having the refractive index in this range, a known material can be used without any particular limitation. For example, materials used in the manufacture of so-called prism sheets in the industry can be used. As a known material, an ultraviolet (UV) or thermosetting resin such as an acrylate series may be exemplified.

The refractive index of the second region may be adjusted to satisfy a difference between the refractive index of the first region and the refractive index of the first region. A transparent material having a refractive index in a range that can satisfy the difference in refractive index with the first region is variously known. As the portion of the optical film forming the second region, for example, a known optical pressure-sensitive adhesive or an adhesive, for example, a material having a refractive index within the above range, such as an acrylic pressure-sensitive adhesive, It is not.

Wherein the optical film is formed by applying a layer of a substance in one of the first region and the second region on a flat base layer and patterning the layer so as to have a convex portion of a desired shape, And then filling and filling the structure with the other one of the first region and the second region. The patterned structure with the convex portions can be formed by roll-to-roll processing. The mold used for the roll-to-roll processing can be manufactured using a bite. In the case where the convex portions are arranged in a multi-dimensional array, a plurality of rule-rolling processing can be performed in different horizontal directions.

The method of arranging the above optical film on the visual side surface of the liquid crystal panel in the present application is not particularly limited. For example, a method of simply placing the optical film on the visual side surface in the process of assembling the liquid crystal display, or attaching the optical film to the surface of the liquid crystal panel by using a suitable double-sided adhesive or pressure sensitive adhesive is applied .

The liquid crystal display may include a member constituting another known liquid crystal display in addition to the liquid crystal panel and the optical film. Examples of such members include, but are not limited to, a polarizing plate, a backlight module, or a reflector.

The present application provides a liquid crystal display capable of selectively adjusting only light which causes color mixing, thereby improving brightness uniformity and contrast ratio of emitted light at the same time.

Fig. 1 exemplarily shows a cross section of a liquid crystal display of the present application.
Fig. 2 exemplarily shows a side surface of a first region in which a convex portion of a quadrangular pyramid shape is arranged two-dimensionally.
FIGS. 3 and 4 illustrate, by way of example, cross sections of optical films according to the first and second embodiments of the present application, respectively.
5 to 16 are graphs of grayscales of Examples 1 to 6 and Comparative Examples 1 to 6, respectively.

Hereinafter, the liquid crystal display of the present application will be described with reference to Examples and Comparative Examples according to the present application, but the scope of the present application is not limited by the following examples.

≪ Evaluation of optical property simulation &

For the evaluation of the optical property simulation, the structures in which the optical films of Examples 1 to 6 and Comparative Examples 1 to 6 were respectively disposed were set on the visual side surface of the liquid crystal panel. The optical film includes a first region having a structure patterned with a pyramid-shaped convex portion and a second region having a structure filling a concave portion formed by the convex portion, as shown in FIG. 2, The liquid crystal panel is disposed adjacent to the liquid crystal panel. As shown in Fig. 3, the optical film was disposed such that the projecting direction of the convex portion of the first region was the viewing side direction. The difference in refractive index between the first region and the second region and the refractive index with respect to light having a wavelength of 550 nm in the second region are shown in the following Table Respectively. However, in Comparative Example 1, no optical film was disposed. In Comparative Example 2, the first region and the second region of the optical film were set so as not to have a patterned structure or a filled structure as convex portions. That is, both surfaces of the first region and the second region are flat.

The simulation was performed using the ASAP program of Breault Research Organization, and the light distribution obtained by measuring the liquid crystal panel using ELDIM's EZContrast equipment was used as the light source. The liquid crystal panel is T215HVN01.1 manufactured by AUO. Light source measurements were measured in gray units, with units of 0 (black), 64, 128, 192, 255 (white). In the simulation, the light from the liquid crystal panel was used as a light source and the polarization was defined as the polarization direction of the polarizer attached to the outermost surface of the liquid crystal panel. In the structure in which the optical film adheres closely to the liquid crystal panel, the light distribution from the panel in each gray unit is measured by the luminance, and the value is corrected so that 100% is obtained for each viewing angle when white (255). Figs. 5 to 16 show grayscale graphs of Examples 1 to 6 and Comparative Examples 1 to 6. Fig. In the graph showing the normalized luminance according to the viewing angle according to the gray unit, the smaller the difference in the normalized luminance calculated for the viewing angle in the same gray unit, the smaller the color mixing. The optical characteristics of the white brightness, the black brightness, the brightness ratio, the contrast ratio, the viewing angle difference and the difference ratio were evaluated by simulation with respect to Examples 1 to 6 and Comparative Examples 1 to 6, and the results are shown in Tables 2 and 3 .

The white luminance means the vertical luminance value at gray unit 255 in gray, the black luminance means the vertical luminance value at gray unit 0, and the luminance ratio is the same as that in Examples 1 to 6 and Comparative Example Means the ratio (%) of the white luminance of Examples 1 to 6, and the ratio of light-to-darkness was obtained by dividing the white luminance of Examples 1 to 6 and Comparative Examples 1 to 6 by the luminance obtained by dividing the white luminance of Comparative Example 1 by the luminance of black, , And when the luminance value measured by the viewing angle (0 degree, 15 degree, 30 degree, 45 degree, 60 degree) is expressed by the normalized luminance, the difference according to the viewing angle is 128 in gray unit, Means a value obtained by subtracting the largest value from the smallest value, and the difference ratio means a ratio (%) of difference between viewing angles of Examples 1 to 6 and Comparative Examples 1 to 6 with respect to the viewing angle difference of Comparative Example 1.

Inclination angle The first region
Refractive index The second region
Refractive index Difference in refractive index Example 1 20 1.56 1.51 0.05 Example 2 20 1.56 1.52 0.04 Example 3 25 1.56 1.52 0.04 Example 4 15 1.56 1.51 0.05 Example 5 15 1.56 1.49 0.07 Example 6 20 1.56 1.49 0.07 Comparative Example 1 - - - - Comparative Example 2 - 1.56 1.52 0.03 Comparative Example 3 7.5 1.56 1.52 0.04 Comparative Example 4 30 1.56 1.52 -0.04 Comparative Example 5 15 1.52 1.56 -0.04 Comparative Example 6 20 1.52 1.56 -0.04

Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 White brightness
(nit) 264.17 265.93 269.64 258.29 248.50 259.46 Black brightness
(nit) 0.19 0.17 0.16 0.22 0.28 0.22 Luminance ratio 93.55 94.17 95.49 91.47 88.00 91.88 Contrast Ratio 72.42 79.32 86.46 60.75 46.75 59.97 Viewing Angle
Difference 20.26 23.17 24.79 27.35 21.97 18.35 Difference ratio 61.09 69.85 74.74 82.47 66.22 55.32

Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 White brightness
(nit) 282.38 274.83 247.47 272.65 226.42 265.42 Black brightness
(nit) 0.15 0.14 0.29 0.15 0.34 0.20 Luminance ratio 100 97.33 87.64 96.55 80.18 94.00 Contrast Ratio 100 99.44 44.62 91.04 34.74 70.28 Viewing Angle
Difference 33.17 32.77 31.87 32.41 29.95 30.55 Difference ratio 100 98.78 96.09 97.71 90.28 92.09

10: liquid crystal panel
10A: Visual side of the liquid crystal panel
10B: the back side of the liquid crystal panel
20: Optical film
201: first region
202: second region
N: Liquid crystal panel surface normal
P: pitch of convex portion
H: height of convex portion
TS: slope
TG: Incline angle

Claims (16)

A liquid crystal panel and an optical film disposed on a visual side surface of the liquid crystal panel,
Wherein the first region has a refractive index with respect to light having a wavelength of 550 nm higher than that of the second region and the first region has a refractive index higher than that of the second region with respect to the second region, A plurality of panels disposed adjacent to the panel,
Wherein one of the first region and the second region has a patterned pattern of convex portions formed of a plurality of inclined faces with an inclination angle of 10 degrees to 25 degrees and the other region has a concave portion formed by the convex portions . The method according to claim 1,
Wherein the liquid crystal panel is a VA mode liquid crystal panel. The method according to claim 1,
Wherein the liquid crystal display further comprises a backlight unit, a first polarizing plate, and a second polarizing plate, wherein the backlight unit, the first polarizing plate, the liquid crystal panel, the second polarizing plate, and the optical film are sequentially arranged. The method according to claim 1,
Wherein the optical film is disposed at an outermost position of the liquid crystal display. The method according to claim 1,
Wherein the inclination angles of the plurality of inclined surfaces are equal to or different from each other, and the standard deviation of the inclination angle is within a range of 0 to 5 degrees. The method according to claim 1,
Wherein the convex portion has a pyramid shape. The method according to claim 1,
Wherein the first region has a structure patterned as a convex portion, and the projecting direction of the convex portion is the viewing side direction. The method according to claim 1,
The protruding direction of the convex portion is the panel side direction. The method according to claim 1,
Wherein the convex portion has a height of 20 to 300 占 퐉. The method according to claim 1,
Wherein the convex portion has a pitch of 10 to 50 mu m. The method according to claim 1,
400 per unit area relative to the surface direction of the convex portions optical film pieces / mm ² to 10,000 / mm ² Existing liquid crystal displays. The method according to claim 1,
Wherein one surface of the region having the patterned pattern of the convex portions among the first region and the second region is flat. The method according to claim 1,
Wherein one surface of the region having the filling structure among the first region and the second region is flat. The method according to claim 1,
Wherein the optical film further comprises a base layer, wherein the base layer is disposed on one side of a region of the first region and the second region having a structure patterned by convex portions. The method according to claim 1,
Wherein a difference in refractive index between the first region and the second region with respect to light having a wavelength of 550 nm is 0.025 to 0.09. The method according to claim 1,
Wherein the first region has a refractive index of 1.40 to 1.64 with respect to light having a wavelength of 550 nm.

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