KR102089405B1 - Liquid crystal display - Google Patents

Abstract

This application relates to a liquid crystal display comprising an optical film. In the present application, it is possible to provide a liquid crystal display capable of simultaneously improving the luminance uniformity and contrast ratio of emitted light by selectively adjusting only the light that causes color mixing by applying an optical film having a specific structure.

Description

Liquid crystal display

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

A liquid crystal display (LCD) is a display device using anisotropy of liquid crystal. A liquid crystal display generally has a structure having a liquid crystal panel including a liquid crystal layer having a liquid crystal material and a polarizing plate disposed on both sides thereof, and changing the orientation of the liquid crystal layer to implement a black and white state and display an image.

Since the liquid crystal panel generally adjusts polarization with respect to light incident perpendicularly to the panel, a problem arises in that the brightness of the light changes or the color changes with respect to light in the inclined direction.

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

On the other hand, the liquid crystal display has a variety of modes depending on the orientation of the liquid crystal in the liquid crystal panel, and typically there are TN (Twisted Nematic), VA (Vertical Alignment) or IPS (In plane switching) mode.

Among the above modes, in the case of the VA mode, in general, it has a good contrast ratio and excellent color reproduction, but a color washout phenomenon occurs in which the contrast ratio falls when observing the display at an angle of inclination compared to observing the display in the front direction. do.

Korean Patent Publication No. 2009-0080133

An object of the present application is to provide a liquid crystal display capable of simultaneously improving the luminance uniformity and contrast ratio of the emitted light by selectively adjusting only light that causes color mixing by applying an optical film having a specific structure.

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 the viewing side surface of the liquid crystal panel. As used herein, the term “viewing-side surface” of a liquid crystal panel means a surface closer to an observer observing the image when the display displays the image among the upper and lower surfaces of the liquid crystal panel. In addition, the term “back-side surface” of the liquid crystal panel means a surface opposite to the viewing-side surface among the upper and lower surfaces.

The liquid crystal panel may be a VA (Vertical Alignment) type liquid crystal panel. The present inventors arrange a unique optical film, which will be described later, on the viewing-side surface of the liquid crystal panel, thereby ensuring uniformity of emitted light at front and viewing angles in various types of liquid crystal panels, and so-called color mixing that may occur in a white state. washout) can be solved, and it was confirmed that such an effect is particularly well expressed in a VA mode liquid crystal display.

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

For example, the liquid crystal panel may be a transmissive, reflective or semi-transmissive liquid crystal panel. The driving method of the liquid crystal panel is not particularly limited in the present application, for example, an active matrix method using a passive matrix method, an active electrode such as a thin film transistor (TFD) electrode or a thin film diode (TFD) electrode, and a plasma address method. Known driving methods, such as, can be applied.

The liquid crystal panel usually 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 aligning the liquid crystal material constituting the liquid crystal layer in a specific alignment direction. For example, the substrate itself has a property of aligning liquid crystals, or the substrate itself has no alignment ability, but a transparent substrate or the like having an alignment film having properties of aligning liquid crystal materials may be used. As the electrode of the liquid crystal panel, a known electrode such as ITO (Indium Tin Oxide) may be applied. Such an electrode can be usually provided on the surface of a transparent substrate in contact with the liquid crystal layer, or when a transparent substrate having an alignment film is used, it can also be provided between the substrate and the alignment film.

As the liquid crystal material included in the liquid crystal layer, a material having various negative or positive dielectric anisotropy generally used in the construction of the liquid crystal panel may be used. As such a material, various low molecular liquid crystal materials, high molecular liquid crystal materials, and mixtures thereof may be exemplified, but are not limited thereto. In addition, the liquid crystal layer of the liquid crystal panel may include a dye or a chiral agent or a non-liquid crystal material in a range that does not impair the liquid crystal properties of the liquid crystal material.

In addition, a semi-transflective liquid crystal panel may be configured by replacing one substrate on the liquid crystal panel, for example, a substrate on the rear side, with a substrate having a reflective function region and a transparent function region. The region having a reflective function (hereinafter, referred to as a reflective layer) included in the semi-transmissive electrode used in the liquid crystal panel is not particularly limited, but is one of metals such as aluminum, silver, gold, chromium, platinum, or one of them. Examples include alloys containing the above, oxides such as magnesium oxide, multilayer films of dielectrics, liquid crystals showing selective reflection, or combinations thereof. These reflective layers may be flat or curved. In addition, the reflective layer may be formed by processing a surface shape such as an uneven shape to have a diffuse reflection property, a combination of electrodes on the transparent substrate on the back side of the liquid crystal panel, or a combination of these.

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 a multicolor or pure color display with high color purity can be manufactured.

The liquid crystal display may further include a backlight unit, a first polarizing plate, and a second polarizing plate. 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 axis 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 is to polarize the incident light, a polarizer commonly known to those skilled in the art, for example, a polyvinyl alcohol-based polarizer in which a polyvinyl alcohol-based film is uniaxially stretched, or a polyvinyl alcohol-based film And a dehydrated polyene polarizer. The first polarizer or the second polarizer may 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 an adhesive resin, and optionally a composition comprising a crosslinking agent, a silane coupling agent, a photoradical initiator, or a photocationic initiator. The adhesive layer or the adhesive layer may further enhance the light diffusion effect by further including a light diffusion agent. The light diffusing agent may include conventional light diffusing agents 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 guiding light emitted from the light source, a reflective sheet positioned under the light guide plate, and a diffusion sheet positioned above the light guide plate. The light source generates light, and may be disposed on the side surface of the light guide plate (edge type). As the light source, various light sources such as a line light source lamp or a surface light source lamp, CCFL or LED may be used. 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 light generated from the light source and supply it in the direction of the diffusion sheet. The diffusion sheet may diffuse and scatter light incident through the light guide plate and supply it to the liquid crystal panel.

The optical film may be disposed on the viewing side surface of the liquid crystal panel. The fact that the optical film is disposed on the viewing-side surface of the liquid crystal panel in the present application means that other constituent members exist between the optical film and the viewing-side surface, as well as when the optical film is disposed in contact with the viewing-side surface. Cases may also be included. For example, as described above, a second polarizing plate may be disposed between the optical film and the viewing side surface of the liquid crystal panel.

The optical film may be disposed on the outermost side of the liquid crystal display. In the present application, that the optical film is disposed on the outermost side of the liquid crystal display may mean that any one surface of the optical film is exposed to the outside and is disposed to contact the air.

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

Any one of the first region and the second region may have a structure patterned by a convex portion formed of a plurality of inclined surfaces having an inclination angle of 10 to 25 degrees. Another region of the first region and the second region may have a structure filling a concave portion formed by the convex portion.

In this application, the inclined surface (TS in FIGS. 3 and 4) means a surface inclined at an angle of greater than 0 degrees to less than 90 degrees with respect to the normal direction (N in FIGS. 3 and 4) on the viewing side surface of the liquid crystal panel. You can.

In this application, the inclination angle (TA in FIGS. 3 and 4) may mean an angle formed by the normal direction (N in FIGS. 3 and 4) of the viewing side surface of the liquid crystal panel and the inclined surface. When the inclination angle of the inclined surface is within the above range, the brightness uniformity and the contrast ratio of the emitted light can be simultaneously improved by selectively adjusting only the light that causes color mixing.

3 and 4 illustrate structures of optical films according to first and second embodiments of the present application, respectively.

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 filling 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 a visual direction.

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

The inclination angles of the plurality of inclined surfaces may be the same or different from each other. The standard deviation of the inclination angles of the plurality of inclined surfaces may be in a range of 0 degrees to 5 degrees. In other examples, 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.

The convex portion may have a pyramid shape. The pyramid shape may mean an horn shape having an n-sided base, and n may be 3 to 10.

The convex portions may be arranged multidimensionally when observed in the surface direction of the optical film. The multidimensional arrangement may mean a case where the convex portions are arranged along a specific axis when observed in the surface direction, and there are two or more such axes.

FIG. 2 exemplarily shows a side surface of a first region or a second region in which a convex portion of a pyramid shape having a quadrilateral shape is arranged in two dimensions.

The height of the convex portion (H in FIGS. 3 and 4) may be appropriately selected in consideration of the purpose of the present application. For example, the height of the convex portion may be in the range of 20 to 300 μm. In this case, it may be more advantageous to improve luminance uniformity and contrast ratio by selectively adjusting light that causes color mixing. In another example, the height may be 20 μm or more, 30 μm or more, or 40 μm or more. In addition, 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 in other examples.

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

The pitch of the convex portion (P in FIGS. 3 and 4) may be appropriately selected in consideration of the purpose of the present application. For example, the pitch of the convex portion may be 10 to 50 μm. In this case, it may be more advantageous to improve luminance uniformity and contrast ratio by selectively adjusting light that causes color mixing. In the above, the pitch may be a shortest distance or a longest distance from a point where one convex part starts to a point where another convex part starts. In another example, the pitch may be about 15 μm or more, 20 μm or more, 25 μm or more, 30 μm or more, 35 μm or more, or 40 μm or more. In addition, the pitch may be 50 μm or less in another example.

The number of convex portions may be appropriately selected in consideration of the purpose of the present application. The convex portion may be 400 pieces / mm ² to 10000 pieces / mm ² per unit area based on the surface direction of the optical film. In another example, the ratio may be 400 / mm ² or more, 450 / mm ² or more, or 500 / mm ² or more. 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, 3000 / mm ² or less, 2000 / mm ² or less, 1000 / mm ² or less, 900 / mm ² or less, 800 / mm ² or less, 700 / mm ² or less, or 600 It may be less than / mm ² . In this case, the purpose of the present application can be achieved more effectively.

One surface of the first region and the second region having a structure patterned by the convex portion may be a flat surface. The one surface may mean an opposite surface of the structure patterned with the convex portion.

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

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

The first region may have a higher refractive index for 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, it is possible to selectively adjust only the light that causes color mixing to simultaneously improve the luminance uniformity and contrast ratio of the emitted light.

The optical film may be arranged such that the light emitted from the liquid crystal panel passes through the first region and the second region sequentially and is discharged. When light enters from a medium having a large refractive index to a medium having a small refractive index, when the angle of incidence is greater than or equal to a critical angle, there is a characteristic of total reflection. The present application can increase the reflectance of light that is 10 to 20 degrees of the inner angle of the light source by using the total reflection principle and the inclination angle, and lower the reflectance of other light. Since the reflected light can be emitted in different directions, the luminance can be uniformly adjusted as a whole.

The difference in refractive index for light of 550 nm wavelength in the first region and the second region may be 0.025 to 0.09. When the difference in refractive index between the first region and the second region is within the above range, color mixing may be reduced to improve luminance uniformity and contrast ratio simultaneously. When the difference between the refractive indices of the first region and the second region is outside the above range, the total amount of light decreases and the contrast ratio may drop.

The first region may have a refractive index of 1.40 to 1.64 for light having a wavelength of 550 nm. As a transparent material having a refractive index in this range, a known material can be used without particular limitation. For example, materials used in the production of so-called prism sheets in the industry can be used. In addition, ultraviolet (UV) or thermosetting resins such as acrylate-based materials may be exemplified as known materials.

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

The optical film is coated with a layer of a material of any one of the first region and the second region on a flat substrate layer, patterned so that the layer has a convex portion of a desired shape, and then patterned with the convex portion It can be produced by applying and filling another material of the first region and the second region to the structure. The structure patterned with the convex portion may be formed by roll-to-roll processing. The mold used for the roll-to-roll processing can be manufactured using bite. When the convex portions are to be arranged in a multi-dimensional manner, a plurality of rule-to-roll processing may be performed in different horizontal directions.

In the present application, the method for disposing the optical film as described above on the viewing side surface of the liquid crystal panel is not particularly limited. For example, in the process of assembling the liquid crystal display, the optical film may be simply placed on the viewing side surface, or a method of attaching the optical film to the surface of the liquid crystal panel using an appropriate double-sided adhesive or adhesive may be applied. You can.

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. As such a member, for example, a polarizing plate, a backlight module or a reflecting plate may be exemplified, but is not limited thereto.

In the present application, a liquid crystal display capable of simultaneously improving luminance uniformity and contrast ratio of emitted light by selectively adjusting only light that causes color mixing is provided.

1 exemplarily shows a cross section of a liquid crystal display of the present application.
2 exemplarily shows a side surface of the first region in which the convex portions of the quadrangular pyramid shape are arranged in two dimensions.
3 and 4 illustrate cross sections of optical films according to the first and second embodiments of the present application, respectively.
5 to 16 are grayscale graphs of Examples 1 to 6 and Comparative Examples 1 to 6, respectively.

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

<Optical characteristics simulation evaluation>

In order to evaluate the optical properties simulation, structures in which the optical films of Examples 1 to 6 and Comparative Examples 1 to 6 below were disposed on the surface of the viewer side of the liquid crystal panel were set, respectively. The optical film includes a first region having a structure patterned as 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, wherein the first region is the second region Compared to the liquid crystal panel, it was arranged to be adjacent. The optical film was arranged such that the protruding direction of the convex portion of the first region was the viewing side direction as shown in FIG. The table below shows the difference between the inclination angle of the inclined surface constituting the convex portion of the optical film, the refractive index for light at a wavelength of 550 nm in the first region, the refractive index for light at a wavelength of 550 nm in the second region, and the refractive index between the first region and the second region Summarized in 1. However, in Comparative Example 1, an optical film was not disposed, and in Comparative Example 2, the first region and the second region of the optical film were set so as not to have a structure patterned or filled with convex portions. That is, both surfaces of the first region and the second region are flat.

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

In the above, white luminance means a vertical luminance value in gray unit 255, black luminance means a vertical luminance value in gray unit 0, and the luminance ratio is Examples 1 to 6 and comparison with respect to white luminance in Comparative Example 1 The ratio (%) of white luminance of Examples 1 to 6 refers to the contrast ratio, and the white luminance of Examples 1 to 6 and Comparative Examples 1 to 6 for the value obtained by dividing the white luminance of Comparative Example 1 by the black luminance is black luminance. It means the ratio (%) of the value divided by, and the difference by viewing angle is set to 128 in gray units, and when the measured luminance value for each viewing angle (0 degrees, 15 degrees, 30 degrees, 45 degrees, 60 degrees) is expressed as normalized luminance, It means the value obtained by subtracting the largest value from the smallest value, and the difference ratio means the ratio (%) of the difference between viewing angles of Examples 1 to 6 and Comparative Examples 1 to 6 with respect to the difference according to viewing angles of Comparative Example 1.

Tilt angle Area 1
Refractive index Area 2
Refractive index Refractive index difference 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 By 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 By 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: viewer side of the liquid crystal panel
10B: rear side of the liquid crystal panel
20: optical film
201: first area
202: second area
N: Liquid crystal panel surface normal
P: Pitch of convex part
H: Height of the convex part
TS: Slope
TG: Tilt angle

Claims (16)

It includes a liquid crystal panel in the vertical alignment (VA) mode and an optical film disposed on the viewing side surface of the liquid crystal panel,
The optical film includes a first region and a second region having different refractive indices, and the first region has a higher refractive index for light at a wavelength of 550 nm than the second region, and the first region has a liquid crystal compared to the second region. Placed adjacent to the panel,
Any one of the first region and the second region has a patterned structure with a convex portion having a pyramid shape composed of a plurality of inclined surfaces having an inclination angle of 10 to 25 degrees, and the other region is a concave formed by the convex portion A liquid crystal display having a structure for filling wealth. delete According to claim 1,
The liquid crystal display further includes a backlight unit, a first polarizing plate, and a second polarizing plate, and the backlight unit, the first polarizing plate, the liquid crystal panel, the second polarizing plate, and the optical film are sequentially arranged. According to claim 1,
The optical film is a liquid crystal display disposed on the outermost side of the liquid crystal display. According to claim 1,
The inclination angles of the plurality of inclined surfaces are the same or different from each other, and the standard deviation of the inclination angles is within a range of 0 degrees to 5 degrees. delete According to claim 1,
The liquid crystal display having a structure in which the first region is patterned as a convex portion, and a protruding direction of the convex portion is a visual side. According to claim 1,
The liquid crystal display having a structure in which the second region is patterned as a convex portion, and a projecting direction of the convex portion is a panel side direction. According to claim 1,
The convex portion has a height of 20 to 300 ㎛ liquid crystal display. According to claim 1,
The convex portion has a pitch of 10 to 50 ㎛ liquid crystal display. According to claim 1,
The convex portion is 400 pieces / mm ² to 10000 pieces / mm ² per unit area based on the surface direction of the optical film Liquid Crystal Display. According to claim 1,
One surface of a region having a structure patterned by the convex portion among the first region and the second region is a flat liquid crystal display. According to claim 1,
One surface of the first region and the second region having the filling structure is a flat liquid crystal display. According to claim 1,
The optical film further includes a base layer, and the base layer is a liquid crystal display disposed on one surface of a region having a structure patterned as a convex portion of the first region and the second region. According to claim 1,
The difference between the refractive indices for light having a wavelength of 550 nm between the first region and the second region is 0.025 to 0.09. According to claim 1,
A liquid crystal display having a refractive index of 1.40 to 1.64 for light having a wavelength of 550 nm in the first region.

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