CN102483537B - In-plane switching mode liquid crystal display - Google Patents

Abstract

The invention relates to an in-plane switching mode liquid crystal display. More precisely, the present invention relates to an in-plane switching mode liquid crystal display including a first polarizing plate, a second polarizing plate, and a liquid crystal cell, because the optical properties of the compensation film are determined according to the change in the polarization state of the liquid crystal orientation on the Poincaré sphere And because the slow axis of the compensation film of the first polarizing plate is parallel to the liquid crystal orientation and the absorption axis of the polarizing plate, the contrast in the oblique viewing direction is improved, and its design has a wide viewing angle and is economical. The present invention achieves mass production of thin liquid crystal displays with high yield (reduced defective rate due to foreign substances or impurities), and since larger coupled polarizing plates can be produced, ultra-large liquid crystal displays can be provided because the coupled polarized A wide viewing angle can be secured by using only one sheet of compensation film for the upper polarizing plate and the lower polarizing plate.

Description

In-plane switching mode LCD

technical field

The present invention relates to an in-plane switching mode liquid crystal display capable of securing a wide viewing angle by improving contrast in oblique viewing directions.

Background technique

Liquid crystal displays (LCDs) are widely used as general image displays. Although it has various excellent characteristics, a narrow viewing angle is pointed out as a drawback.

The modes of liquid crystal displays can be classified according to the initial arrangement of liquid crystal cells, the structure of electrodes, and the properties of liquid crystals, and the most commonly used modes of liquid crystal displays are twisted nematic (TN) mode, vertical alignment (VA) mode, and in-plane switching ( IPS) mode.

In addition, according to whether it transmits light when no voltage is received, it is divided into normally black mode and normally white mode. According to the area and initial arrangement of the liquid crystal, the VA mode is divided into PVA (Picture Vertical Alignment) mode and SPVA (Super Image Vertical Alignment) mode. and MVA (Multiple Area Vertical Alignment) mode, and, IPS mode is classified into S-IPS mode (Super In-Plane Switching) mode or FFS (Fringe Field Switching) mode.

When the liquid crystal molecules are not activated, the in-plane switching mode has a uniform and substantially parallel alignment to the substrate surface. When the light transmission axis of the lower polarizing plate is in the same direction as the fast axis of the liquid crystal molecules, due to the optical properties of the liquid crystal, even on an inclined plane, the light transmission axis of the liquid crystal is in the same direction as the fast axis, so even if the light passes through the lower polarizing plate After passing through the liquid crystal, there is no change in the polarization state, so it can pass through the liquid crystal layer without change. Therefore, a certain degree of black state can be displayed in an inactive state by the arrangement of the polarizing plates on the upper surface and the lower surface of the substrate.

Such an in-plane switching mode liquid crystal display can generally achieve a wide viewing angle without using an optical film, so that it has the advantage of providing uniform image quality and viewing angle across the entire screen while ensuring natural light transmittance. Therefore, the in-plane switching mode liquid crystal display is mainly used for high-end displays larger than 18 inches.

A liquid crystal display using an in-plane switching mode of the related art requires a polarizing plate outside a liquid crystal cell including a liquid crystal to polarize light, and a protective film formed of a TAC (triacetyl cellulose) film is provided on the polarizing plate one or both sides to protect the polarizer. In this configuration, when the liquid crystal displays a black state, the light polarized by the polarizer on the lower polarizing plate is elliptically polarized by the TAC film not in the front but in oblique viewing directions. Elliptical polarized light creates a problem: because it changes polarization in the liquid crystal cell, this causes the color of the display to change.

Furthermore, in recent years, a wide viewing angle is required to manufacture a large image display device, for example, a large-sized TV using an in-plane switching mode. Therefore, in an in-plane switching mode liquid crystal display (IPS-LCD), a display has been prepared by a polarizing plate (polyvinyl alcohol) between a liquid crystal cell and one of two polarizing plates for the liquid crystal cell Between the TAC film, an isotropic protective layer is arranged, and between the liquid crystal cell and the polarizer (polyvinyl alcohol) of the other polarizer among the two polarizers, two or more Compensation layers with different optical properties or Z-axis orientation (orientation in the thickness direction) film in order to ensure a wide viewing angle.

In-plane switching mode liquid crystal displays use three compensation film-type coupled polarizing plates formed by laminating two layers with different optical properties on one side of the liquid crystal layer (one isotropic film below and two above compensation layer), or it is difficult to have a large-area Z-axis oriented film due to the lower economic efficiency and the necessary shrinking process caused by using the shrink film in the manufacturing process.

Therefore, it is difficult to manufacture thinner products due to the use of coupled polarizing plates laminated by three compensation films; bending due to changes in temperature or humidity due to the difference in thickness on both sides of the liquid crystal cell; and Less price-competitive, its use is limited to high-cost in-plane switching mode LCDs. In addition, since it is not easy to manufacture a wide polarizing plate including a polarizing plate and a compensation film, it is difficult to develop a large-sized liquid crystal display.

Contents of the invention

technical problem

The present invention provides an in-plane switching mode liquid crystal display comprising a first polarizing plate, a second polarizing plate and a liquid crystal cell, because the change of the polarization state according to the orientation of the liquid crystal on the Poincaré sphere determines the optical properties of the compensation film. Performance, and because the slow axis of the compensation film of the first polarizing plate is parallel to the liquid crystal alignment and the absorption axis of the polarizing plate, the contrast in the oblique viewing direction is improved, and the in-plane switching mode liquid crystal display has a wide viewing angle, and since it can pass By width-stretching to fabricate compensation films with specific optical properties, the fabrication of large coupled polarizer plates can be simplified, allowing for large, economical, and thin in-plane switching-mode liquid crystal displays.

Technical solutions

The present invention provides an in-plane switching mode liquid crystal display comprising: a first polarizing plate having a protective film, a polarizing plate, and a first compensation film formed in this order from top to bottom; a liquid crystal cell; and, a second polarizing plate, which has a second compensation film, a polarizing plate, and a protective film, and is formed in this order from top to bottom, wherein the absorption axis of the polarizing plate in the first polarizing plate is perpendicular to the absorption axis of the polarizing plate in the second polarizing plate axis, the first compensation film has an in-plane retardation (R0) of 40nm to 80nm, a retardation in the thickness direction (Rth) of -150nm to -60nm, and a refractive index ratio (NZ) of -2 to -1, and its slow axis is parallel The absorption axis of the polarizer in the orientation of the liquid crystal and the first polarizing plate, and the second compensation film have an in-plane retardation (R0) of 150nm to 270nm and a refractive index ratio (NZ) of -1 to 0, and its slow axis is parallel The absorption axis of the polarizer in the second polarizer.

Beneficial effect

According to the in-plane switching mode liquid crystal display of the present invention, a wide viewing angle comparable to that achieved by using three-layer compensation films in the related art can be ensured. In addition, since a wide viewing angle can be ensured with only one layer of compensation film for the first polarizing plate and the second polarizing plate, the present invention can realize the large size of a thin liquid crystal display with high yield (reduced defective rate due to foreign substances or impurities). Scale production, and since larger coupled polarizing plates can be produced, can provide very large LCD displays.

Description of drawings

In the attached picture:

1 and 2 are perspective views showing the structure of an in-plane switching mode liquid crystal display (S-IPS and FFS) according to the present invention;

3 is a schematic diagram showing the refractive index of a compensation film according to the present invention;

4 is a schematic view showing a machine direction (MD) in a manufacturing method for clarifying a stretching direction of a compensation film and a polarizing plate;

Figure 5 is a schematic diagram showing the representation of Φ and θ in the coordinate system of the present invention;

6 is a graph showing changes in polarization states on a Poincaré sphere in visual directions of Φ=45° and θ=60° according to Example 1 of the present invention;

7 is a graph showing simulation results of light transmittance in all viewing directions of Example 1 of the present invention;

8 is a graph showing simulation results of light transmittance in all viewing directions of Example 2 of the present invention;

9 is a graph showing changes in polarization states on a Poincaré sphere in visual directions of Φ=45° and θ=60° according to Example 3 of the present invention;

10 is a graph showing simulation results of light transmittance in all viewing directions of Example 3 of the present invention;

11 is a graph showing simulation results of light transmittance in all viewing directions of Example 4 of the present invention.

Detailed ways

The present invention relates to an in-plane switching mode liquid crystal display comprising a first polarizing plate, a second polarizing plate and a liquid crystal cell, which is designed to have a wide viewing angle and economy because according to the orientation of the liquid crystal on the Poincare sphere (PoincareSphere) The change of the polarization state determines the optical properties of the compensation film, and, since the slow axis of the compensation film of the first polarizing plate is parallel to the liquid crystal orientation and the absorption axis of the polarizing plate, the contrast ratio in the oblique viewing direction is improved.

Hereinafter, embodiments of an in-plane switching mode liquid crystal display according to the present invention will be described.

The in-plane switching mode liquid crystal display includes a first polarizing plate, a liquid crystal cell and a second polarizing plate.

The first polarizing plate includes a first compensation film, a polarizing plate and a protective film, and is arranged in this order from the side of the liquid crystal cell; Start in that order. The absorption axis of the polarizers in the first polarizing plate is perpendicular to the absorption axis of the polarizing plates in the second polarizing plate.

The alignment of the first polarizing plate and the second polarizing plate depends on the liquid crystal orientation of the liquid crystal cell.

When the liquid crystal orientation is measured counterclockwise from the right horizontal direction of the display side, if the liquid crystal cell has a liquid crystal orientation of 90° (S-IPS), configure the first polarizing plate as the lower polarizing plate and the second polarizing plate as shown in Figure 1 The plate is an upper polarizing plate. In this case, at a wavelength of 589 nm, the panel retardation of the liquid crystal cell determined by Equation 1 below is 300 nm to 330 nm.

【Formula 1】

(Δn×d)=(ne-no)×d

Among them, ne is the extraordinary ray refractive index of the liquid crystal, no is the ordinary ray refractive index, d is the liquid crystal cell gap, and Δn and d are scalars rather than vectors.

In addition, when the liquid crystal orientation is measured counterclockwise from the horizontal direction on the right side of the display, if the liquid crystal cell has a liquid crystal orientation (FFS) of 0°, configure the first polarizing plate as the upper polarizing plate and the second polarizing plate as shown in FIG. 2 The plate is a lower polarizing plate. In this case, at a wavelength of 589 nm, the panel retardation of the liquid crystal cell is 370 nm to 400 nm.

The first compensation film in the first polarizing plate has an in-plane retardation (R0) of 40 nm to 80 nm, a thickness direction retardation (Rth) of -150 nm to -60 nm, and a refractive index ratio (NZ) of -2 to -1.

It is necessary to find an appropriate lower limit value of the in-plane retardation (R0) of the compensation film, because a small in-plane retardation (R0) results in contrast from the direction of the viewer due to non-uniformity in the direction of the slow axis when the film is manufactured. worse. In the present invention, the in-plane retardation (R0) is preferably 40 nm. In addition, the in-plane retardation (R0) of the compensation film exceeding 120 nm may cause color distortion according to viewing directions due to dispersion characteristics of wavelengths. The range of the refractive index ratio (NZ) is a range in which the structure of the liquid crystal display according to the present invention can be constituted, and, when the refractive index ratio (NZ) is within the above range, the compensation film can be stably manufactured by stretching.

The slow axis of the first compensation film is configured to be parallel to the liquid crystal alignment and the absorption axis of the polarizers in the first polarizing plate.

The second compensation film in the second polarizing plate has an in-plane retardation (R0) of 150 nm to 270 nm and a refractive index ratio (NZ) of -1 to 0, preferably using a refractive index ratio (NZ) of -1 to -0.3.

In the range of the in-plane retardation (R0), 150 nm is the minimum value for compensating the in-plane retardation of the liquid crystal, and 270 nm is the maximum value for manufacturing the compensation film by stretching. In addition, the refractive index ratio (NZ) is determined according to the optical properties of the liquid crystal and the first compensation film.

The slow axis of the second compensation film is configured to be parallel to the absorption axis of the polarizing plate in the second polarizing plate.

As shown in Figure 1, when the liquid crystal orientation is measured counterclockwise from the horizontal direction on the right side of the display side, if the liquid crystal cell has a liquid crystal orientation of 90°, the first polarizing plate is configured as the lower polarizing plate, and the inside of the first polarizing plate Align the first compensation film and polarizer parallel to the liquid crystal at 90°.

In addition, as shown in Figure 2, when the liquid crystal orientation is measured in the counterclockwise direction from the horizontal direction on the right side of the display side, if the liquid crystal cell has a liquid crystal orientation of 0°, configure the first polarizing plate as the upper polarizing plate, and the first polarizing plate The first compensation film and the polarizer inside the plate are aligned parallel to the liquid crystal at 0°.

In the present invention, the optical properties of the first compensation film and the second compensation film are determined for all wavelengths in the visible light region by Equation 2 to Equation 4 below.

If there is no special statement about the wavelength of the light source, the optical performance at 589nm is described, where Nx is the refractive index of the axis with the maximum refractive index in the in-plane direction, and Ny is the direction perpendicular to Nx in the in-plane direction The refractive index of and Nz is the refractive index of the thickness direction, which is expressed by formula 2 as follows:

【Formula 2】

Rth＝[(Nx+Ny)/2-Nz]×d

where Nx and Ny are in-plane refractive indices, and Nx≥Ny, Nz is the refractive index of light vibrating in the thickness direction of the film, and d is the thickness of the film;

【Formula 3】

R0=(Nx-Ny)×d

where Nx and Ny are the in-plane refractive indices of the compensation film, and d is the thickness of the film, and Nx≥Ny; and

【Formula 4】

NZ=(Nx-Nz)/(Nx-Ny)=Rth/R0+0.5

Here, Nx and Ny are in-plane refractive indices, and Nx≧Ny, and Nz is the refractive index of light vibrating in the thickness direction of the film.

Here, Rth in Equation 2 is the retardation in the thickness direction, which represents the phase difference relative to the average refractive index in the thickness direction, and R0 in Equation 3 is the in-plane retardation, which is when the light The phase difference when passing through a film in the normal direction (perpendicular direction).

In addition, NZ in Equation 4 is a refractive index ratio, whereby the plate type of the compensation film can be distinguished.

The types of plates of the compensation film can be divided into: 1) A-plates, which have an optical axis in the in-plane direction of the film, 2) C-plates, which have an optical axis perpendicular to the plane direction, and, 3) when Biaxial plates when there are two optical axes. Specifically, 1) when NZ=1, the refractive index satisfies Nx>Ny=Nz, and is called A-plate, and 2) when 1<NZ, the refractive index satisfies Nx>Ny>Nz, and is called negative biaxial A - plate, 3) when 0<NZ<1, the refractive index meets Nx>Nz>Ny, and is called Z-axis alignment film, 4) when NZ=0, the refractive index has the relationship Nx=Nz>Ny, and is called As a negative A-plate, 5) when NZ<0, the refractive index has a relationship Nz>Nx>Ny, and it is called a positive biaxial A-plate, 6) when NZ=∞, the refractive index has a relationship Nx=Ny> Nz, and is called a negative C-plate, 7) When NZ=-∞, the refractive index has the relationship Nz>Nx=Ny, and is called a positive C-plate.

However, according to the theoretical definition, A-plates and C-plates that fully meet the theoretical definition cannot be fabricated in real-world methods. Therefore, in a general process, the A-plate and the C-plate are distinguished by setting a predetermined value within the approximate range of the refractive index ratio of the A-plate and the range of the in-plane retardation of the C-plate. However, setting predetermined values cannot be applied to all other materials having different refractive indices according to stretching. Therefore, the compensation films included in the upper and lower polarizing plates of the present invention are expressed numerically by NZ, R0, Rth, etc., which are optical properties of the plates, not in terms of isotropy of refractive index.

The compensation films of the first polarizing plate and the second polarizing plate in the present invention can be manufactured by stretching.

These compensating films provide retardation by stretching, where a film with an increased refractive index in the stretching direction has positive (+) refractive index properties and a film with a decreased refractive index in the stretching direction has negative (-) refractive index properties . The compensation film with positive (+) refractive index properties can be selected from TAC (triacetyl cellulose), COP (cycloolefin polymer), COC (cycloolefin copolymer), PET (polyethylene terephthalate ), PP (polypropylene), PC (polycarbonate), PSF (polysulfone) and PMMA (polymethyl methacrylate), and the compensation film with negative (-) refractive index can be specifically Made of modified PS (polystyrene) or modified PC (polycarbonate).

The stretching method for providing optical properties to the compensation film is divided into fixed-end stretching and free-end stretching. The fixed-end stretching is to fix the length in directions other than the stretching direction during stretching of the film, and the free-end stretching is to provide freedom in directions other than the stretching direction during stretching of the film. Spend. In general, during stretching, the film shrinks in directions other than the stretching direction, but Z-axis oriented films require a special shrinking process rather than a stretching process.

The unwinding direction of the rolled film is called MD (machine direction), and the direction perpendicular to the MD is called TD (transverse direction). In addition, in this process, free-end stretching stretches the film in MD, and fixed-end stretching stretches the film in TD.

NZ and plate type are determined according to the drawing method (when only the first process is applied). In particular, 1) positive A-plates can be fabricated by stretching films with positive (+) refractive index properties at free ends; 2) negative biaxial A-plates can be fabricated by stretching films with positive (+) refractive index properties at fixed ends - plate; 3) films with positive (+) or negative (-) refractive properties by free-end stretching and subsequent fixed-end shrinkage can produce Z-axis oriented films; 4) by free-end stretching with negative ( -) Films with refractive properties can produce negative A-plates; and 5) Positive biaxial A-plates can be produced by fixed-end stretching films with negative (-) refractive properties.

In addition to the above-mentioned first stretching method, the direction of the slow axis, phase difference, and NZ value can be controlled by applying an increased process such as second stretching or adding additives. Such an added process is one of many processes commonly employed in the field including the present invention and is not particularly limited thereto. .

The first compensation film and the second compensation film are preferably produced by subjecting a film having a negative (-) refractive index to one or more fixed-end stretches. At this time, more stretching should be performed in TD than in MD so that the slow axis is in MD. This is for ease of application in a roll-to-roll process when manufacturing coupled polarizing plates according to the present invention.

Any material conforming to the optical properties of the present invention can be used as the first compensation film and the second compensation film. Specifically, one material selected from PC (polycarbonate), modified PS (polystyrene), and PMMA (polymethyl methacrylate) can be used.

PVA (polyvinyl alcohol) layers, which are polarizers that provide a polarizing function by stretching and dyeing, are provided on the polarizers of the first polarizing plate and the second polarizing plate, respectively. The absorption axis of the first polarizing plate is perpendicular to the absorption axis of the second polarizing plate.

The protective films are respectively provided on the PVA layer of the first polarizing plate and the PVA layer of the second polarizing plate on opposite sides to the liquid crystal cell.

In the protective film of the first polarizing plate and the protective film of the second polarizing plate, the optical performance according to the difference in refractive index does not affect the viewing angle, and thus the refractive index is not particularly limited in the present invention. Materials commonly used in this field can be used for the protective films of the first polarizing plate and the second polarizing plate, specifically, materials selected from TAC (triacetyl cellulose), COP (cycloolefin polymer), COC ( Cycloolefin copolymer), PET (polyethylene terephthalate), PP (polypropylene), PC (polycarbonate), PSF (polysulfone) and PMMA (polymethyl methacrylate) kind.

The first polarizing plate and the second polarizing plate may be prepared by methods commonly used in the art, specifically, a roll-to-roll method and a sheet-to-sheet method may be used. In view of productivity and efficiency in the production process, it is preferable to use a roll-to-roll method.

In the present invention, since the absorption axis of the PVA polarizer is fixed on the MD and the slow axis of the compensation film is perpendicular to the absorption axis of the polarizing plate, the first polarizing plate can be prepared by applying a roll-to-roll method. When a polarizing plate is combined with a compensation film such that the slow axis of the compensation film is perpendicular to the absorption axis of the polarizing plate, it is preferable to use a roll-to-roll method to reduce manufacturing costs.

FIG. 1 shows the structure of an in-plane switching mode liquid crystal display according to the present invention.

The in-plane switching mode liquid crystal display shown in FIG. 1 includes a first polarizing plate 10 , a liquid crystal cell 30 and a second polarizing plate 20 arranged in order from the backlight module 40 side. In FIG. 2 , the in-plane switching mode liquid crystal display has a second polarizing plate 20 , a liquid crystal cell 30 and a first polarizing plate 10 arranged sequentially from the side of the backlight module 40 . The liquid crystal cell shown in FIG. 1 is an S-IPS liquid crystal cell, and the liquid crystal cell shown in FIG. 2 is an FFS liquid crystal cell.

The first polarizing plate 10 includes a first polarizing film 14 , a polarizing plate 11 and a protective film 13 arranged sequentially from the side of the liquid crystal cell. The second polarizing plate 20 includes a second polarizing film 24 , a polarizing plate 21 and a protective film 23 arranged in order from the side of the liquid crystal cell.

The absorption axis 12 of the polarizer 11 is perpendicular to the absorption axis 22 of the polarizer 21 , and the slow axis 15 of the first compensation film 14 is parallel to the absorption axis 12 of the polarizer 11 and the liquid crystal alignment 31 .

The first compensation film 14 has an in-plane retardation (R0) of 40 nm to 80 nm, a thickness direction retardation (Rth) of -130 nm to -60 nm, and a refractive index ratio of -2 to -1, and the second compensation film 24 It has an in-plane retardation (R0) of 150nm to 270nm and a refractive index ratio (NZ) of -1 to 0.

In the present invention, the absorption axis of the polarizer of the lower polarizing plate should be vertically placed when viewed from the front. Specifically, when the absorption axis of the lower polarizing plate close to the backlight module is in the vertical direction, the light passing through the lower polarizing plate is polarized in the horizontal direction. When the white state is achieved by passing a panel voltage across the liquid crystal cell, the light travels vertically and passes through the upper polarizing plate on the display side with an absorption axis in the horizontal direction. Even a person wearing polarized sunglasses with the absorption axis in the horizontal direction on the display side (the absorption axis of polarized sunglasses is generally in the horizontal direction) can see the light from the liquid crystal display. If the absorption axis of the lower polarizing plate close to the backlight module is horizontal, people wearing polarized sunglasses cannot see the image.

The effect of the viewing angle compensation of the present invention can be explained by the change in the polarization state of light as it passes through each optical layer within the Poincaré sphere.

The Poincaré sphere is useful for showing the change in polarization state at a particular viewing angle, so when light traveling at a particular viewing angle in a liquid crystal display (which uses polarization to display images) passes through the various optical elements inside the liquid crystal display , it can show a change in polarization state.

The specific viewing angle in the present invention is the direction of Φ=45° and θ=60° in the hemispherical coordinate system shown in FIG. The change of the polarization state on the ray sphere can show the characteristics of the wavelength distribution.

FIG. 6 shows the polarization states of the liquid crystal display according to the present invention at viewing angles of Φ=45° and θ=60°. Specifically, when the Φ-directed surface is rotated to the display side at an angle of θ around the axis of Φ+90° in the front face, it shows the polarization state of the light coming out from the front on the Poincaré sphere Variety. When the coordinate of the S3 axis is positive (+) on the Poincaré sphere, right-handed circular polarization appears, wherein, when a certain polarization horizontal component is Ex and the polarization vertical component is Ey, right-handed circular polarization means: Ex The phase retardation of the light of the component relative to the light of the Ey component is greater than 0 and less than half the wavelength.

The optical parameter of the liquid crystal display of the present invention is: the maximum light transmittance from all light directions is less than or equal to 0.2%.

Hereinafter, the effect of improving the wide viewing angle according to the above configuration is compared by way of examples and comparative examples. Although the present invention can be understood more easily through the following embodiments, the embodiments provided below are only examples of the present invention, rather than limiting the protection scope of the present invention claimed by the above claims.

example

The wide viewing angle effect was compared by simulation using TECH WIZ LCD 1D (Sanayi System Co., Ltd., Korea), which is the LCD simulation system in the example below.

Example 1

The actual measured data of each optical film, liquid crystal cell and backlight module according to the present invention were applied to TECH WIZ LCD 1D (Sanayi System Co., Ltd., Korea) with the laminated structure shown in Figure 1. The structure of Fig. 1 is described in detail below.

Starting from the backlight module 40 side, the first polarizing plate 10, the in-plane switching mode liquid crystal cell 30 (when the liquid crystal orientation is measured in the counterclockwise direction from the right horizontal direction of the display side under the state where no voltage is applied), the liquid crystal cell has 90° liquid crystal orientation) and a second polarizing plate 20, wherein the first polarizing plate 10 is formed by laminating the first compensation film 14, the polarizer 11, and the protective film 13 from the liquid crystal cell 30 side, and the first polarizing plate 10 is formed from the liquid crystal cell 30 side The second polarizing plate 20 is formed by laminating the second compensation film 24 , the polarizing plate 21 and the protective film 23 .

As for the liquid crystal cell, a 42-inch panel of LC420WU5 produced by LG Display Co., Ltd. was used without considering the absorption of the color filter. The actual measurement data assembled by a 32-inch model TV LC320WX4 was used for the backlight module 40 .

Meanwhile, each optical film and backlight module used in this example has the following optical properties.

First, the polarizing plate 11 and the polarizing plate 21 of the first polarizing plate 10 and the second polarizing plate 20 have a polarizing function by dyeing stretched PVA with iodine, and the polarizing performance of the polarizing plate is in the visible light range of 370nm to 780nm It has a brightness degree of polarization of 99.9% or greater than 99.9% and a brightness group light transmittance of 41% or greater. When the transmittance of the light transmission axis according to the wavelength is TD(λ), the light transmittance of the absorption axis according to the wavelength is MD(λ), and the brightness compensation value defined in JIS Z 8701:1999 is When , the degree of polarization of the brightness and the light transmittance of the brightness group are defined by the following formulas 5 to 9, wherein, S(λ) is the spectrum of the light source, and the light source is a C-light source.

【Formula 5】

${\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; TD</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; K</span>}{<span\; class="notranslate">\; \&Integral;</span>}_{\mathrm{<span\; class="notranslate">\; 380</span>}}^{\mathrm{<span\; class="notranslate">\; 780</span>}}\mathrm{<span\; class="notranslate">\; S</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&lambda;</span>}<span\; class="notranslate">\; )</span>\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; the\; y</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&lambda;</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; TD</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&lambda;</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; d\&lambda;</span>}$

【Formula 6】

${\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; MD</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; K</span>}{<span\; class="notranslate">\; \&Integral;</span>}_{\mathrm{<span\; class="notranslate">\; 380</span>}}^{\mathrm{<span\; class="notranslate">\; 780</span>}}\mathrm{<span\; class="notranslate">\; S</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&lambda;</span>}<span\; class="notranslate">\; )</span>\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; the\; y</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&lambda;</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; MD</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&lambda;</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; d\&lambda;</span>}$

【Formula 7】

$\mathrm{<span\; class="notranslate">\; K</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 100</span>}}{{<span\; class="notranslate">\; \&Integral;</span>}_{\mathrm{<span\; class="notranslate">\; 380</span>}}^{\mathrm{<span\; class="notranslate">\; 780</span>}}\mathrm{<span\; class="notranslate">\; S</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&lambda;</span>}<span\; class="notranslate">\; )</span>\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; the\; y</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&lambda;</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; d\&lambda;</span>}}$

[Formula 8]

【Formula 9】

According to the optical performance resulting from the difference in the internal refractive index in the direction of each film, a second compensation with an in-plane retardation (R0) of 180 nm and a refractive index ratio (NZ) of -0.5 for a 589.3 nm source was used The film 24, and the first compensation film 14 having an in-plane retardation (R0) of 52 nm, a thickness direction retardation (Rth) of -130 nm, and a refractive index ratio of -2. By applying one or more fixed-end stretches, a first compensation film and a second compensation film are fabricated. The first compensation film can be manufactured by applying both fixed-end stretching and free-end stretching (the fixed-end stretching rate is greater than that of the free end) or by applying only the fixed-end stretching, and by applying only the fixed-end stretching, manufacturing the second compensation film.

In this case, the absorption axis 12 of the polarizing plate 11 is parallel to the slow axis 15 of the first polarizing film 14 and the liquid crystal alignment 31 .

In addition, TAC (triacetyl cellulose) having an optical performance of Rth of 50 nm for incident light of 598.3 nm was used for the outer protective films 13 and 23 as protective layers of the first polarizing plate 10 and the second polarizing plate 20 .

Fig. 6 shows the variation of the polarization state in an in-plane switching mode liquid crystal display on a Poincaré sphere at viewing angles of Φ = 45° and θ = 60°. Specifically, when the light passes through the polarizing plate 11 of the first polarizing plate 10 with a wavelength of 550 nm on the Poincaré sphere, the polarization state is the polarization state at the starting point, and when the light passes through the first compensation film 14, After the liquid crystal cell 30 and the second compensation film 24, the polarization state reaches the end point.

Figure 7 shows the light transmittance for all light directions of an in-plane switching mode liquid crystal display, where the light transmittance is 0% to 1% in the scale range, and when the black state is shown, the light transmittance exceeds 1 The % portion is shown in red, and the low transmittance portion is shown in blue. In this case, it can be seen that the wider the blue part at the center, the easier it is to secure a wider viewing angle, and it can be confirmed from Figure 7 that since the blue part at the center is wider, it is possible to ensure a wider perspective.

Example 2

Although the same configuration as in Example 1, the second compensation film 24 has an in-plane retardation (R0) of 200 nm and a refractive index ratio (NZ) of −0.5, and the first compensation film 14 has an in-plane retardation ( R0) and a refractive index ratio (NZ) of -1.1, the second compensation film 24 and the first compensation film 14 are used to manufacture an in-plane switching mode liquid crystal display.

The variation of the polarization state in the ISMLCD above the Poincaré sphere according to the wavelength is similar to that in Fig. 6, and the transmittance results for all light directions are the same as in Fig. 8. It can be confirmed from FIG. 8 that since the blue portion at the center is wider, a wider viewing angle can be ensured.

Example 3

Although configured the same as in Example 1, in the laminated structure shown in FIG. 2, the second compensation film 24 has an in-plane retardation (R0) of 270 nm and a refractive index ratio (NZ) of -0.5, and the first compensation film 14 has In-plane retardation (R0) of 60nm, thickness direction retardation (Rth) of -150nm and refractive index ratio (NZ) of -2, and the in-plane switching mode was fabricated using the second compensation film 24 and the first compensation film 14 LCD Monitor. In this case, an in-plane switching mode liquid crystal cell 30 (FFS) whose liquid crystal orientation was 0° when measured counterclockwise from the right horizontal direction of the display in a state where no voltage was received was used.

Figure 9 shows the variation of the polarization state of an in-plane switching mode liquid crystal display on the Poincaré sphere at viewing angles of Φ=45° and θ=60° according to wavelength, and Figure 10 shows the light transmittance for all light directions simulation results.

As shown in Figure 9, the polarization state when the light passes through the polarizing plate 21 of the second polarizing plate 20 with a wavelength of 550nm on the Poincaré sphere is the polarization state of the starting point, and when the light passes through the second compensation After film 24, liquid crystal cell 30 and first compensation film 14, the polarization state reaches an end point.

It can be confirmed from FIG. 10 that since the blue portion at the center is wider, a wider viewing angle can be ensured.

Example 4

Although the same configuration as in Example 3, the second compensation film 24 has an in-plane retardation (R0) of 270 nm and a refractive index ratio (NZ) of −0.3, and the first compensation film 14 has an in-plane retardation ( R0), thickness direction retardation (Rth) of -112.5nm and refractive index ratio (NZ) of -2, and using the second compensation film 24 and the first compensation film 14 to manufacture an in-plane switching mode liquid crystal display.

According to the wavelength, the variation of the polarization state of the ISMLCD above the Poincaré sphere is similar to that in FIG. 9, and the transmittance results for all light directions are the same as in FIG. 11. It can be confirmed from FIG. 11 that since the blue portion at the center is wider, a wider viewing angle can be ensured.

Industrial Applicability

As described above, the in-plane switching mode liquid crystal display according to the present invention can be applied to a large liquid crystal display requiring high viewing angle performance because it can provide excellent image quality for all viewing directions.

Claims (8)

1. An in-plane switching mode liquid crystal display comprising: a first polarizing plate, the first polarizing plate has a first compensation film, a polarizer and a protective film, and is arranged in this order from the side of the liquid crystal cell; the liquid crystal cell; and a second polarizing plate, the second polarizing plate has a second compensation film, a polarizer and a protective film, and is arranged in this order from the side of the liquid crystal cell, Wherein, the absorption axis of the polarizer in the first polarizer is perpendicular to the absorption axis of the polarizer in the second polarizer, The first compensation film has an in-plane retardation R0 of 40 nm to 80 nm, a thickness direction retardation Rth of -150 nm to -60 nm, and a refractive index ratio NZ of -2 to -1, and the slow axis of the first compensation film is parallel to in the liquid crystal orientation and the absorption axis of the polarizer in the first polarizer, and The second compensation film has an in-plane retardation R0 of 150 nm to 270 nm and a refractive index ratio NZ of -1 to 0, and the slow axis of the second compensation film is parallel to the absorption of the polarizer in the second polarizer axis, And where, NZ=(Nx-Nz)/(Nx-Ny), Nx is the refractive index of the axis with the maximum refractive index in the in-plane direction, Ny is the refractive index in the direction perpendicular to Nx in the in-plane direction and Nz is the refractive index in the thickness direction. 2. The in-plane switching mode liquid crystal display of claim 1, wherein the second compensation film has a refractive index ratio (NZ) of -1 to -0.3. 3. The in-plane switching mode liquid crystal display as claimed in claim 1, wherein the first polarizing plate is a lower polarizing plate, the second polarizing plate is an upper polarizing plate, and when viewed from the right horizontal direction of the display side The liquid crystal cell has a liquid crystal orientation of 90° when measured in a counterclockwise direction. 4. The in-plane switching mode liquid crystal display of claim 3, wherein the liquid crystal cell has a panel retardation of 300 nm to 330 nm at a wavelength of 589 nm. 5. The in-plane switching mode liquid crystal display as claimed in claim 1, wherein the first polarizing plate is an upper polarizing plate, the second polarizing plate is a lower polarizing plate, and when viewed from the right horizontal direction of the display side The liquid crystal cell has a liquid crystal orientation of 0° when the liquid crystal orientation is measured in the counterclockwise direction. 6. The in-plane switching mode liquid crystal display of claim 5, wherein the liquid crystal cell has a panel retardation of 370 nm to 400 nm at a wavelength of 589 nm. 7. The in-plane switching mode liquid crystal display of claim 1, wherein the first compensation film and the second compensation film are manufactured by applying one or more fixed-end stretches, respectively. 8. The in-plane switching mode liquid crystal display of claim 1, wherein the first compensation film is manufactured by applying free-end stretching one or more times.