KR20090117641A - In-plane switching liquid crystal display comprising biaxial retardation film with negative refractive property and biaxial retardation film with positive refractive property - Google Patents

Abstract

PURPOSE: An in-plane switching liquid crystal display device with biaxial retardation film of a negative refractive index characteristic and a positive refractive index characteristic is provided to control retardation between a retardation film and a polarizer protection film, thereby realizing a wide view angle and high durability under a rapid temperature change. CONSTITUTION: A refractive index ratio(NZ) of the biaxial first retardation film(40) is -2.0<NZ<-0.7. A ground axis of the biaxial first retardation film is orthogonal to an absorbing axis(21) of the second polarizing plate(20). A refractive index ratio of the biaxial second retardation film is 1.3<NZ<4. The ground axis of the biaxial second retardation film(50) is orthogonal to the absorbing axis of the second polarizing plate. In a protection film of a liquid crystal cell(30) of the first polarizing plate(10), a retardation value in thickness direction is in the range of 0 to 10 nm at 589 nm wavelength. A visibility omni-directional maximum transmittance satisfies compensation relation less than 0.2%.

Description

IN-PLANE SWITCHING LIQUID CRYSTAL DISPLAY COMPRISING BIAXIAL RETARDATION FILM WITH NEGATIVE REFRACTIVE PROPERTY AND BIAXIAL RETARDATION FILM WITH POSITIVE REFRACTIVE PROPERTY}

The present invention relates to a technique for controlling the optical characteristics of the retardation film and the polarizer protective film of the planar switching mode (IPS mode) used in the liquid crystal display device to facilitate the viewing angle compensation, physical properties and mass production process.

Liquid crystal displays (LCDs) have a disadvantage of having a narrow viewing angle despite various excellent characteristics. The wide viewing angle technology applied with the liquid crystal driving mode and the optical film made it possible to improve the viewing angle. In particular, the IPS mode, the liquid crystal driving mode capable of realizing the wide viewing angle, is used to improve the viewing angle characteristics of the liquid crystal display device. It's known in the most outstanding way.

IPS mode is a mode that drives the liquid crystal using a lateral electric field. TN (Twisted Nematic) or VA (Vertical Alignment) mode is a liquid crystal and the electric field is formed between the upper and lower plates (vertical) Orientation), IPS mode is characterized in that the direction of the electric field is formed in parallel to the liquid crystal array direction using a horizontal alignment liquid crystal.

In addition, in the plane switching mode, a polarizing plate for polarizing light is required on the outside of the liquid crystal cell containing the liquid crystal, and in general, a protective film made of a triacetyl cellulose (TAC) film on one or both surfaces of the polarizer is a polarizer (PVA). It is provided to protect the.

In recent years, large size TVs have been manufactured in such a plane switching mode, and accordingly, wider viewing angle characteristics are required. Nevertheless, the TAC film used in the conventional low-cost planar switching liquid crystal display device has a negative C-plate birefringence characteristic of Nx = Ny> Nz, but because of the birefringence and retardation value (Rth) of the film itself, There was a problem of making the viewing angle of the device significantly narrower. Here, the retardation value (Rth) is defined as Rth = ((Nx + Ny) / 2-Nz) × d when the thickness of the film is d (where Nx, Ny is the planar refractive index, Nz is the thickness of the protective layer Directional refractive index, d represents the thickness of the protective layer).

In addition, the Rth of TAC films commonly used in low-cost IPS-LCDs exceeds 0 nm and these optical properties adversely affect the narrowing of the viewing angle in IPS mode. Accordingly, a compensation film having a better wide viewing angle is urgently needed in an IPS mode display product, and various compensation configurations have been developed.

The viewing angle compensation in the in-plane switching mode (IPS mode) is a compensation configuration using a retardation film having a negative birefringence, which is optically advantageous, but most of them are weak in durability and roll to roll production is difficult in producing a polarizing plate. There were disadvantages that were not. Therefore, there is an urgent need to develop a planar switching liquid crystal display device capable of mass-producing roll-to-roll production in a mass production process while providing excellent viewing angle compensation in an efficient manner.

The present invention is a display device using an on-plane switching mode (IPS mode), a narrow viewing angle problem, durability against temperature and roll-to-roll application in the production process of the conventional low-cost IPS-LCD It is an object of the present invention to provide a planar switching liquid crystal display device which is easily mass-produced.

The present invention relates to a planar switching liquid crystal display (IPS-LCD) formed by stacking a first polarizing plate, a liquid crystal cell, a biaxial first phase difference film, a biaxial second phase difference film, and a second polarizing plate from a backlight unit. The biaxial first phase difference film has a refractive index ratio of -2.0 <NZ <-0.7, its slow axis is orthogonal to the absorption axis of the second polarizing plate, and the biaxial second phase difference film has a refractive index ratio of 1.3 <NZ <4, The slow axis is orthogonal to the absorption axis of the second polarizing plate, and the protective film on the liquid crystal cell side of the first polarizing plate has a thickness retardation value (Rth) in a range of 0 to 10 nm at a wavelength of 589 nm, and the maximum permeability of all directions The characteristics of the planar switching liquid crystal display device satisfying a compensation relationship of 0.2% or less.

The planar switching liquid crystal display device of the present invention exhibits a more preferable effect in terms of wide viewing angle, especially when the combination of the biaxial first phase difference film and the biaxial second phase difference film satisfies the viewing angle compensation relationship, and thus, the actual production of the product. It is possible.

The planar switching liquid crystal display of the present invention includes a first polarizing plate and a second polarizing plate having protective films on both sides of the polarizer, a biaxial first phase difference film having negative refractive indices in which the slow axis direction and the phase difference value are adjusted; A biaxial second phase difference film having a positive refractive index is used, and the protective film on the liquid crystal cell side of the first polarizing plate has a low phase difference protective film having a thickness retardation value Rth of 0 to 10 nm (589 nm wavelength). Is used to implement viewing angle compensation.

In addition, the first retardation film of the present invention can implement roll-to-roll production during manufacturing of high durability and composite polarizing plates (polarizing plates and retardation plates) through biaxial stretching.

Other specific embodiments of the present invention will be described in detail in the following detailed description.

The present invention relates to a display device using an in-plane switching mode (IPS mode) method that can control the phase difference between the polarizer protective film and the retardation film to realize high durability at a wide wide viewing angle and a sudden temperature change. That is, according to the present invention includes a biaxial first retardation film having a negative refractive index through biaxial stretching between the liquid crystal cell and the second polarizing plate and a biaxial second retardation film having a positive refractive index, each of the retardation film The on-axis switching liquid crystal display device which can control the slow axis direction and the retardation value of the polarizing plate and the retardation value of the polarizer protective film provided on the liquid crystal cell side in the second polarizing plate, can improve the narrow viewing angle and weak durability problem of the conventional liquid crystal display device. IPS-LCD).

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a perspective view showing the basic structure of an area switching liquid crystal display (IPS-LCD) according to the present invention.

In the IPS-LCD according to the present invention, the first polarizing plate 10, the liquid crystal cell 30, the biaxial first phase difference film 40, the biaxial second phase difference film 50, and the second side from the backlight unit 60 side The polarizing plate 20 is stacked in a series order, and the absorption axis 11 of the first polarizing plate 10 and the absorption axis 21 of the second polarizing plate 20 are arranged perpendicular to each other, and the first polarizing plate ( The absorption axis 11 of 10 and the alignment direction 31 of the liquid crystal contained in the liquid crystal cell 30 are arranged in parallel with each other.

FIG. 2 shows the alignment direction 31 which shows the direction in which the liquid crystals are arranged when viewed from the viewer side (opposite to the backlight unit), and the absorption axes 11 and 21 of the first polarizing plate and the second polarizing plate. .

In the first polarizing plate 10 and the second polarizing plate 20, polyvinyl alcohol (PVA) layers 12 and 22, which are polarizers having polarization functions through stretching and dyeing, are positioned, respectively, and poly Protective films 23 are formed on both sides of the vinyl alcohol (PVA) layer 12 on the viewing side of the polyvinyl alcohol (PVA) layer 22 of the second polarizing plate. The thickness retardation value Rth of the protective film is defined by Equation 1 below.

Rth = [(Nx + Ny) / 2-Nz] × d

Where Nx and Ny are planar refractive indices, Nz is the thickness direction refractive index of the film, and d represents the thickness of the protective layer.

In the present invention, the slow axes 41, 51 directions of the biaxial first phase difference film 40 and the biaxial second phase difference film 50 stacked between the liquid crystal cell 30 and the second polarizing plate 20, By controlling the phase difference value R0 defined by Equation 2 below and the refractive index ratio NZ defined by Equation 3 to a certain range, the conventional LCD solves the problem of narrow viewing angle in the IPS mode. .

R0 = (Nx-Ny) × d

(Where Nx and Ny are the plane refractive indices of the retardation film, and d represents the thickness of the film, where Nx ≧ Ny)

NZ = (Nx-Nz) / (Nx-Ny)

(Where Nx and Ny are in-plane refractive indices of the retardation film, and Nz represents a refractive index in the thickness direction, where Nx ≥ Ny)

Specifically, the liquid crystal display device using the compensation film according to the present invention is a horizontally oriented liquid crystal cell filled with a liquid crystal having a positive dielectric anisotropy (Δε> 0) between the first polarizing plate 10 and two glass substrates ( 30) and a second polarizing plate 20, wherein one of the glass substrates of the liquid crystal cell 30 includes an active matrix drive electrode including an electrode pair on an adjacent surface of the liquid crystal cell 30. The absorption axis 11 of the first polarizing plate 10 and the absorption axis 21 of the second polarizing plate 20 are arranged perpendicular to each other, and the absorption axis 11 of the first polarizing plate 10 and The alignment directions 31 of the liquid crystals contained in the liquid crystal cell 30 are arranged in parallel with each other.

In the IPS-LCD of the present invention having such a structure, the liquid crystal cell 30 preferably maintains a panel retardation value (Δn × d) value defined by Equation 4 below at a range of 200 to 400 nm at a wavelength of 589 nm. . When the voltage is applied to the IPS-LCD panel, the light that is linearly polarized in the horizontal direction through the first polarizing plate 10 passes through the liquid crystal cell 30 and is linearly polarized in the vertical direction after being passed through the liquid crystal cell 30 so as to have a bright state. This is because the phase difference value of the liquid crystal cell 30 of the LCD panel should be half wavelength of 589 nm (the brightest monochromatic light felt by a person), and may be adjusted to be slightly longer or shorter than the half wavelength in order to achieve a white color. Therefore, it is more preferable that the phase difference value has a range around 295 nm, which is a half wavelength of 589 nm monochromatic light.

Δn × d = (n _e -n _o ) × d

Where n _e represents the extraordinary refractive index of the liquid crystal, n _o represents the normal ray refractive index, and d represents the cell gap; Note Δn and d are not vectors.

The LCD of the present invention includes aligning liquid crystals into multi-domains or dividing them into multiple regions by applied voltage. LCDs are classified into In-Plane-Switching (IPS), Super-In-Plane-Switching (IPS), and Ring-Field-Switching (FFS), depending on the mode of the active matrix drive electrode including the electrode pair. At this time, the IPS-LCD in the present invention includes the super-IPS and FFS.

Referring to FIG. 3, the refractive indexes of the first retardation film 40 and the second retardation film 50 used for the viewing angle compensation of the IPS-LCD according to the present invention will be described. Direction), the refractive index of Nx (1), the refractive index of the axis (y-axis direction) with a small refractive index is Ny (2) and the refractive index of the thickness direction (z-axis direction) can be referred to as Nz (3). This determines the characteristics of the retardation film. When the refractive indices in the three axial directions are different from each other, there are two optical axes, which are optical paths in the film, in which no phase difference occurs. This is called a biaxial retardation film, and the first phase difference film according to the present invention ( 40) has a refractive index ratio of the following equation (5) by the stretching in the manufacturing process and the second phase difference film 50 has a refractive index ratio of the following equation (6). At this time, the stretching method is not particularly limited as long as it is generally performed in the art, and may be used as long as it satisfies the refractive index ratio of the following Equation 5 regardless of factors such as stress gradient and absolute value of the stretching. .

-2.0 <NZ = (Nx-Nz) / (Nx-Ny) <-0.7

 (Where Nx and Ny are plane refractive indices Nx > Ny, Nz represents the thickness direction refractive index of the film, and d represents the thickness of the film)

1.3 <NZ = (Nx-Nz) / (Nx-Ny) <4

(Where Nx and Ny are plane refractive indices Nx > Ny, Nz represents the thickness direction refractive index of the film, and d represents the thickness of the film)

The structure of the viewing angle compensation by the biaxial first retardation film 40 and the biaxial second retardation film according to the present invention is shown in FIG. 1.

The liquid crystal cell 30 or the liquid crystal molecules of the liquid crystal cell disposed between the first polarizing plate 10 and the second polarizing plate 20 having the absorption axes orthogonal to each other are arranged in parallel with the liquid crystal substrate, and rubbing (liquid crystal Is aligned in the direction of the substrate surface treatment method for aligning in one direction. In order for the liquid crystal display of the present invention to have a viewing angle compensation function, the biaxial first phase difference film 40 and the biaxial second phase difference film 50 are sequentially disposed between the liquid crystal cell 30 and the second polarizing plate 20. Should be placed. When viewed from the viewer side (opposite to the backlight unit), the absorption axis 11 of the first polarizing plate 10 is located in the vertical direction, and the absorption axis 11 is the liquid crystal alignment direction 31 in the liquid crystal panel 30, That is, parallel to the rubbing direction, the absorption axis 21 of the second polarizing plate 20 is perpendicular to the liquid crystal alignment direction 31 of the liquid crystal panel 30.

The reason why the absorption axis 11 of the first polarizing plate 10 should be located in the vertical direction when viewed from the viewer side is as follows. When the absorption axis 11 of the first polarizing plate 10 near the backlight unit 60 is in the vertical direction, light passing through the first polarizing plate 10 is polarized in the horizontal direction, which causes the liquid crystal 30 of the panel to be polarized. When passing through, the light is in a vertical direction and passes through the second polarizing plate 20 on the side of the viewer whose absorption axis is in the horizontal direction. In this case, a person wearing a polarized sunglasses whose absorption axis is in the horizontal direction (the absorption axis of the polarization sunglasses is in the horizontal direction) must be able to recognize the light emitted from the liquid crystal display. If the absorption axis 11 of the first polarizing plate 10 near the backlight unit 50 is in the horizontal direction, there is a problem that the image is not visible to the person wearing the polarized sunglasses.

In addition, in the case of a large liquid crystal display, a general liquid crystal display except for a special purpose liquid crystal display such as an advertisement is widely used in consideration of the fact that a human's field of view is wider than a vertical direction so that an image can be easily seen from the viewer. The height ratio is produced in the form of 4: 3 or 16: 9.

The slow axis (41) (51) of the retardation film of the present invention is the electric field of polarized light through which the light passes most slowly by the retardation film when the light passing through the retardation film (40) (50) is vertically incident Meaning the direction of vibration means the direction of the largest refractive index, which is distinguished from the optical axis (phase difference) does not occur when passing through the retardation film. In the present invention, the slow axes 41 and 51 are parallel to the alignment direction 31 of the liquid crystal in the liquid crystal cell 30. Since the alignment direction 31 of the liquid crystal is parallel to the absorption axis 11 of the first polarizing plate 10 and is perpendicular to the absorption axis 21 of the second polarizing plate 20, the retardation films 40 and 50 of the present application. The slow axes 41 and 51 of the first polarizing plate 10 are parallel to the absorption axis 11 of the first polarizing plate 10 and perpendicular to the absorption axis 21 of the second polarizing plate 20.

In the present invention, the biaxial first phase difference film 40 is in the range of -2.0 <NZ <-0.7, preferably -1.5 <NZ <-0.8, which is the refractive index ratio of Equation 5, and the slow axis 41 has a second axis. Orthogonal to the absorption axis 21 of the polarizing plate 20, the retardation value R0 of the first phase difference film 40 is in the range of 30 nm to 90 nm, preferably in the range of 40 nm to 80 nm, biaxial at 589 nm wavelength. While the second phase difference film 50 is in the range of 1.3 <NZ <4, preferably 1.4 <NZ <2, which is the refractive index ratio of Equation 6, the slow axis 51 is the absorption axis of the second polarizing plate 20 ( 21 and the phase difference value R0 of the second phase difference film 50 is in the range of 30 to 110 nm, preferably in the range of 50 nm to 100 nm at a wavelength of 589 nm, and the liquid crystal cell 30 of the first polarizing plate 10. If the retardation value (Rth) of the polarizer protective film 14 of the side is maintained in the range of 0 nm to 10 nm at a wavelength of 589 nm may have a viewing angle compensation relationship for the purpose of the present invention. The refractive index ratio and the retardation value of the first retardation film and the second retardation film are easy to achieve effects such as ensuring a wide viewing angle without leakage of light for the purpose of the present invention in each preferred range.

When the liquid crystal displays black, the absorption axes 11 and 21 of the orthogonal polarizing plates 10 and 20 cannot maintain orthogonality on the four sides of the surface due to their geometrical characteristics. Leaking and narrowing the viewing angle due to the light, in the conditions of the present invention, the liquid crystal cell 30 and the retardation film 40 (50) between the polarizers 12 and 22 of the two polarizing plates 10 and 20. Since the optical system including) can keep the absorption axes 11 and 21 of the polarizing plates 10 and 20 in the orthogonal state on the slope, light does not leak and the viewing angle is not narrowed. The light does not leak in the phase difference value condition of the present invention can be confirmed through Tech Wiz LCD 1D (man system, Korea) which is a simulation program in an embodiment of the present invention.

The protective film 13 of the first polarizing plate 10 and the protective film 23 of the second polarizing plate 20, which are other polarizer protective films, do not affect the viewing angle according to the phase difference value Rth. The phase difference value Rth is not particularly limited.

The range of the retardation value R0 and the refractive index ratio NZ of the biaxial first retardation film and the biaxial second retardation film may be explained by Poincare Sphere. 4 is a diagram illustrating changes in polarization states of light exiting in a θ = 60 ° and Φ = 45 ° directions when a black is displayed in a plane switching liquid crystal display device using the first phase difference film and the second phase difference film of FIG. 1. Is expressed in the Poincare Sphere. Specifically, when viewed from the front, the direction of the polarization state of the light emitted in the front direction when the surface of the Φ direction is rotated by θ to the viewer side is shown on the Puan Cureg, and the S3 axis on the Puan Cureg When the coordinates are positive (+), the right circularly polarized light represents the right circularly polarized light. When the polarized horizontal component is Ex and the vertical component is Ey, the light of Ex component is slower in phase than the light of Ey component. A light that is larger and smaller than half-wavelength.

 Light passing through the polyvinyl alcohol (PVA) layer, which is the polarizer of the first polarizing plate 10, is polarized to P1 on the Poincare Sphere in FIG. 4, and the polarization state is protected by the first polarizing plate 10. There is no change after passing through the layer 14 and the liquid crystal panel 30.

P2 in FIG. 4 is a polarization state of the light passing through the first retardation film 40 and the second retardation film 50 in a polarization state coinciding with the absorption axis of the polyvinyl alcohol (PVA) layer of the second polarizing plate 20. Is expressed as P2 on the Poincare Sphere, it has less leaking light when viewed in the θ = 60 ° and Φ = 45 ° directions. In the case of the first retardation film, the refractive index ratio (NZ) in the manufacturing process is -2 <NZ <-0.7. In the case of the second retardation film, the refractive index ratio (NZ) applicable to the optical process including the manufacturing process and color and luminance is considered. ) Ranges from 1.3 <NZ <4.

At this time, when the NZ of the first retardation film is -0.7, the change of polarization state on the Poincare Sphere is path 1; When NZ of the first retardation film is -2, the change in polarization state is path 2; When the NZ of the second retardation film is 1.3, the change in polarization state is path 3; And when the NZ of the second retardation film is 4, the change in polarization state is represented by path 4. The range of polarization states changeable by the first phase difference film 40 at P1 is a range between path 1 and path 2 in FIG. 4, and the polarization state that can change the polarization state to P2 with the second phase difference film 50. Is the range between path 3 and path 4. The portion where the range between the path 1 and the path 2 and the range between the path 3 and the path 4 overlap is a phase difference range for implementing a wide viewing angle in the present invention.

In the present invention, since the combination of the first retardation film and the second retardation film is mathematically infinite, it is impossible to describe all the cases. Therefore, the portion where path 1 and path 3 meet in FIG. 4 is defined as R1, the portion where path 1 and path 4 meet as R2, and the portion where path 2 and path 3 meet as R3, and the portion where path 2 and path 4 meet as R4. When the front phase difference R0 is found for each of R1, R2, R3, and R4, the phase difference value R0 of the first phase difference film and the second phase difference film may be defined in the present invention.

The phase difference (R0) search was performed in R1, R2, R3, and R4 of FIG. 4 in TECH WIZ 1D (many system, Korea), and the details of the experiment are as described in the following examples. In the calculation of the phase difference value R0 search result, the range that satisfies the compensation relationship of the maximum visibility transmittance of 0.2% or less (0 to 0.2%) in the black display when the color filter is excluded is summarized in Table 1 below. It was. In Table 1, it can be seen that the retardation value (R0) range of the first retardation film is 30 to 90 nm, the retardation value (R0) range of the second retardation film 50 is 30 to 110 nm.

The first retardation film 40 preferably has a three-layer structure in which polymethyl methacrylate (PMMA), polystyrene (PS) and polymethyl methacrylate (PMMA) are sequentially stacked, which has optical isotropy. It is a structure provided with the PS layer which has the negative refractive index characteristic in which a refractive index becomes small in a extending direction between two PMMA layers which are acrylic resins. The first phase difference film 40 is manufactured by, for example, a triple extrusion method, and imparts retardation through stretching after the extrusion. In this case, the change of the refractive index through the stretching occurs mainly in the polystyrene (PS) layer. Accordingly, in the structure, the polystyrene (PS) layer serves as a center layer for determining the optical properties of the first retardation film 40, and polymethyl methacrylate (PMMA) provided on both sides of the polystyrene (PS) layer. ) Layer serves as an acrylic resin to protect the polystyrene (PS) layer. When the polystyrene (PS) is used as a single layer film, the polystyrene (PS) is easily broken or torn by an external force, thereby reducing the efficiency of the process in manufacturing the composite polarizing plate (polarizing plate + phase difference plate) and forming a liquid crystal display device. Since it causes a decrease in durability when the protective film is arranged on the outside of polystyrene (PS), by applying a triple extrusion method to the protective film arrangement can be more easily manufactured. In addition, in the case of using the triple extrusion method, there is no need for a separate pressure-sensitive adhesive or adhesive layer, there is an advantage that no additional process occurs. In addition, the retardation film 40 may be applied as long as it has an optically negative refractive index and the same retardation film R0 and refractive index ratio NZ as the retardation film, and a preferred example is modified polycarbonate (PC). . When the modified polycarbonate (PC) is used, it may be a retardation film 40 having at least one modified polycarbonate (PC).

As described above, the second retardation film 50 is not limited to being made of a specific material when the refractive index ratio NZ and the retardation value R0 of Equation 3 are expressed in the range of 30 to 110 nm, and thus are applied to the present invention. Specifically, for example, triacetyl cellulose (TAC), cycloolefin polymer (COP), cycloolefin copolymer (COC), polyethylene terephthalate (PET), polypropylene (PP), polycarbonate (PC) A single compound or a mixture of two or more selected from polysulfone (PSF) and polymethyl methacrylate (PMMA) may be used.

The first polarizing plate is provided with a protective film on both sides of the polarizer, the protective film 14 of the liquid crystal cell side is made of an isotropic film so that the phase difference value (Rth) can be in the range of 0 to 10 nm. The protective film 14 is not limited to being made of a specific material, specifically triacetyl cellulose (TAC), cycloolefin polymer (COP), cycloolefin copolymer (COC), polyethylene terephthalate (PET), polypropylene One single compound or a mixture of two or more selected from (PP), polycarbonate (PC) , polysulfone (PSF) and polymethyl methacrylate (PMMA) can be used.

In addition, the protective film 13 on the backlight side of the first polarizing plate and the protective film 23 of the second polarizing plate may also be the same as the material used in the protective film 14.

The second polarizing plate 20 and the retardation film 40, 50 according to the present invention is preferably bonded to have the same machine direction (Machine Direction). As shown in FIG. 5, the direction in which the film is wound on the roll in the roll bundle of films is called a machine direction, that is, an MD direction. That is, in manufacturing the optical film provided in the liquid crystal display according to the present invention, the absorption axis 21 of the second polarizing plate 20 coincides with the MD direction of the second polarizing plate 20 and the first phase difference film 40 The slow axis 41 and the slow axis 51 of the second retardation film 50 are formed perpendicular to the MD direction. According to the present invention, the absorption axis 21 and the retardation film 40 of the second polarizing plate 20 are provided. In order to make the slow axis (41) of orthogonal to each other perpendicularly, the roll to roll method is used to integrate the second polarizing plate 20, the first retardation film 40, and the second retardation film 50. Most preferred. Accordingly, the second polarizing plate 20 and the retardation film 40 may be bonded to have the same MD direction.

That is, since the first phase difference film 40 or the polystyrene (PS) layer used as the center layer thereof has negative refractive index characteristics, the slow axis 41 of the first phase difference film 40 is It is formed perpendicular to the stretching direction when imparting a phase difference through stretching in the manufacturing process. In the present invention, the slow axis of the viewing angle compensation film must be oriented perpendicular to the absorption axis 21 of the second polarizing plate 20, that is, the MD direction. When the film having the negative refractive index characteristic is stretched in the MD direction shown in Fig. 5, Nx (ground axis 41) is formed in the direction perpendicular to the MD and has the refractive index characteristic of NZ being zero. In this case, the retardation film has a structure in which molecules are arranged uniaxially and easily torn by external force, and thus durability of the retardation film is significantly decreased. In order to compensate for this, by stretching in a direction perpendicular to the MD, the molecules of the first retardation film 40 may be prevented from being excessively biased in one direction to prevent tearing by external force, thereby improving durability. The stretched retardation film has a refractive index characteristic of NZ <0 and as a result of the manufacturing process has a refractive index ratio range of the equation (5).

The second phase difference film 50 according to the present invention has a positive refractive index characteristic and is formed perpendicular to the stretching direction when imparting a phase difference through stretching in the manufacturing process. In the present invention, the slow axis of the viewing angle compensation film must be oriented perpendicular to the absorption axis 21 of the second polarizing plate 20, that is, the MD direction. When a film having a positive refractive index characteristic is stretched perpendicularly to the MD direction shown in Fig. 5, Nx (ground axis 51) is formed in a direction perpendicular to the MD and has a refractive index characteristic of NZ> 1. At this time, the value of NZ does not increase indefinitely, and there is an NZ limit value depending on the material of the retardation film. When a NZ value higher than this limit is realized, the initial retardation film is stretched in the MD direction and then stretched perpendicularly to the MD direction. This results in an NZ value that is higher than the NZ limit, and in some cases it can be made infinite.

Thus, the second polarizing plate 20, the first phase difference film 40 and the second phase difference film bonded to have the same MD direction can be bonded in a roll-to-roll manner during the manufacturing process. There is also an effect that can be lowered.

Next, the viewing angle improvement effect by the said structure was put together in the following Example and a comparative example. The invention can be better understood by the following examples, which are intended to illustrate the invention and are not intended to limit the scope of protection as defined by the appended claims.

Example

In Example 1 and Comparative Example 1, a simulation was performed using the LCD simulation program TECH WIZ LCD 1D (man system, KOREA) to compare the wide viewing angle effect, and in Example 2 and Comparative Example 2, durability was evaluated through thermal shock experiments. .

Example 1 Liquid Crystal Display According to Embodiment of the Present Invention

Measurement data of each optical film, a liquid crystal cell, and a backlight according to the present invention were laminated on a TECH WIZ LCD 1D (man system, KOREA) with a structure as shown in FIG. 1. Referring to the structure of Figure 1 in detail.

The backlight unit 60 , the first polarizing plate 10, the liquid crystal cell 30, the biaxial first phase difference film 40, the biaxial second phase difference film 50, and the second polarizing plate 20 are sequentially stacked. More specifically, the first polarizing plate 10 is composed of the protective film 13, PVA polarizer 12, the protective film 14 in order from the backlight unit 60 side, the second polarizing plate from the liquid crystal cell side It consists of the PVA polarizer 22 and the protective film 23 in order.

The polarizers 10, 20, which are TACs 13, 14, and 23 as polarizer protective films and which give the PVAs 12 and 22 through stretching and dyeing, are applied to the IPS mode liquid crystal panel ( Absorption shafts 11 and 21 were arranged orthogonally to each other on both sides of 30). The IPS mode liquid crystal cell 30 is in the vertical direction when the alignment direction 31 of the liquid crystal is viewed from the viewing side when displaying the dark BLACK on the viewing side (the opposite side of the backlight unit). However, the liquid crystal cell 30 does not include a color filter for the convenience of simulation.

When the polarizing plate on the backlight unit 60 side is referred to as the first polarizing plate 10 and the viewer side is called the second polarizing plate 20, the liquid crystal alignment direction 31 and the first polarizing plate 10 of the IPS mode liquid crystal panel 30 are used. Absorption shaft 11 of) is parallel and orthogonal to the absorption axis 21 of the second polarizing plate 20. Also, between the second polarizing plate 20 on the side of the viewer and the IPS mode liquid crystal panel 30, a first phase difference film in which a PS having negative refractive index characteristics is laminated between two PMMAs having optical isotropy from the liquid crystal panel 30 ( 40) (I-Film, Optes, Japan) and the second phase difference film (Zeonor, Optes, Japan) were sequentially arranged. The slow axes 41 and 51 of the first retardation film 40 and the second retardation film 50 are arranged to be orthogonal to the absorption axis 21 of the second polarizing plate 20.

Detailed optical properties of each optical film and backlight used in the above examples were used as defined below.

라고 할 때 하기 수학식 7 내지 11에 의해 정의된다. 여기서 S(λ)는 광원스펙트럼이며 보통 C광원을 사용한다.First, the polarizers of the first polarizing plate 10 and the second polarizing plate 20 impart a polarizer function by dyeing iodine on the stretched PVA. More than%, visibility was over 41%. The visibility polarization and the visibility single transmittance are the TD (λ) transmittance of the transmission axis according to the wavelength, and the transmittance correction of the absorption axis according to the wavelength of MD (λ).

Is defined by the following equations (7) to (11). Where S (λ) is the light source spectrum and usually uses a C light source.

The optical characteristics of TAC, which is a protective layer of the polarizing plates 10 and 20, are Nx, Ny, and Nz for the rectangular coordinate system whose thickness direction is the z-axis, and when the thickness is d, Nx = Ny. Has a negative C-plate refractive index characteristic of> Nz, and the phase difference value Rth defined by Equation 1 for incident light 589.3 nm is 3 nm in the case of TAC 14, and in the case of TAC 13, 23 50 nm was used.

The biaxial first phase difference film 40 biaxially stretches an I-film (Optes, Japan) to realize a phase difference, and its optical characteristic is expressed by the above equation for a rectangular coordinate system having the z axis in the thickness direction when the incident light is 589.3 nm. NZ, defined as 2, was -2.0 to -0.7.

The second retardation film 50 is biaxially stretched Zeonor film (Optes, Japan) to realize the phase difference, the optical characteristic is defined by the equation (3) for the Cartesian coordinate system with the z-axis in the thickness direction when the incident light is 589.3 nm NZ is 1.3 to 8, and the front minimum retardation value R0 is 30 nm.

As the backlight unit 50, actual measurement data mounted on a 32-inch TV LC320WX4 model (LG PHILIPS LCD) was used.

As a result of the simulation on the planar switching liquid crystal display having the above-described configuration, the theoretical number of solutions is theoretically infinite, and in consideration of the minimum retardation value R0 of the retardation film, the compensable NZ range is I-. -2 <NZ <-0.7 for the first retardation film 40 to which Film (Optes, Japan) is applied, and 1.3 <NZ <to the second retardation film 50 to which Zeonor (Optes, Japan) is applied. 4, the phase difference range having a compensation relationship at the NZ critical point of the first retardation film 40 and the second retardation film 50 was searched.

In this case, when NZ of the first retardation film is -0.7 and NZ of the second retardation film is 1.3, R1; R2 when NZ of the first retardation film is -0.7 and NZ of the second retardation film is 4; R3 when NZ of the first retardation film is -2 and NZ of the second retardation film is 1.3; When NZ of the first retardation film is -2 and NZ of the second retardation film is 4; The R1, R2, R3, and R4 are NZ critical points for the first retardation film 40 and the second retardation film 50 in the wide viewing angle compensation technique of the present application, and at each NZ critical point. The optimum retardation value R0 of the first retardation film 40 and the second retardation film 50 is searched for, and the result of retrieving the retardation value R0 at R1 is shown in FIG. 7, the result of retrieving phase difference R0 in R3 is shown in FIG. 8, and the result of retrieving phase difference R0 in R4 is shown in FIG. As a result of the search, when the color filter is excluded from each NZ critical point, a phase difference range having a compensating relationship of maximum transmittance of 0.2% or less is summarized in Table 1 above.

6 to 9 show the distribution of the omnidirectional transmittance when displaying the black according to the phase difference value (BLACK) on the screen, the scale range is 0% to 0.2% transmittance, 0.2% transmittance when displaying the arm Areas exceeding are marked with red, and areas with low permeability are marked with blue. In this case, the wider the range of blue in the center, the wider the viewing angle.

In addition, when the configuration of FIG. 1 is viewed from the viewer, the horizontal direction is the x-axis, the vertical direction is the y-axis, and the thickness direction is the z-axis. If the straight line is projected on the xy plane and the angle formed by the x-axis is Φ, these can be represented by the spherical coordinate system of FIG. 10. When the direction of the eye is Φ = 45 ° and θ = 60 °, the polarization state in each optical system is As shown in FIG. 4, it can be expressed on a Poincare Sphere which is often used to explain the viewing angle compensation principle of a liquid crystal display in a paper.

Comparative Example 1 : Liquid crystal display device containing isotropic protective film

A liquid crystal display including an isotropic protective film as Comparative Example 1 corresponding to Example 1 is illustrated in FIG. 11. In FIG. 1, the first phase retardation film 40 and the second phase retardation film 50 are removed and replaced with an isotropic film having a retardation value Rth of 0 nm, which is currently a low-cost planar switching liquid crystal display (IPS). -LCD) is a configuration generally applied. The other components and their optical properties are the same as in Example 1 above.

As in Example 1 with the above-described configuration, the results of the simulation in the Tech Wiz LCD 1D (man system, Korea) are shown in FIG. 12.

Experimental results according to Example 1 and Comparative Example 1 are when the liquid crystal display device displays black, and FIGS. 6 to 9 and 12 show the transmittance results in each optical simulation, and the center blue That is, the wider the portion of the lower transmittance means that the viewing angle is wider, the central blue portion in Figures 6 to 9 is wider than that of Figure 12, confirming that Embodiment 1 according to the present invention is implemented a wider viewing angle Can be. In addition, the omnidirectional maximum transmittance excluding the color filter effect is calculated to be 0.1% for the example and 1.4% for the comparative example, indicating that the maximum transmittance of all directions is about 14 times larger than that of Example 1. have.

Example 2  : Liquid crystal display device durability test according to an embodiment of the present invention

Each optical film according to the present invention was laminated on both sides of the liquid crystal cell as shown in FIG. At this time, both sides of the polarizer are bonded to each other with an adhesive, between the film and the film, and between the liquid crystal cell and the film with a pressure-sensitive adhesive (PSA), and NZ defined by (Nx-Nz) / (Nx-Ny) exhibits a refractive index characteristic of -1.0. A biaxially stretched I-film (Optes, Japan) having was used as the retardation film 40. The liquid crystal cell is LG. PHILIPS LCD's 32-inch TV LC320WX4 model was used.

The liquid crystal cell was placed in a thermal shock absorber TSC-2160 (Neurotfit, Korea), set at -40 ° C. and 70 ° C. for 30 minutes, and then put out for 500 hours, assembled with a backlight, and the screen state was observed while only the backlight was turned on.

Comparative Example 2  : Liquid Crystal Display Durability Test Including Uniaxially Stretched First Phase Difference Film

As Comparative Example 2 corresponding to Example 2, other components and test methods except for the phase difference film 40 of Example 2 were the same. The retardation film applied in Comparative Example 2 is a uniaxially stretched film having negative refractive index characteristics, and a uniaxially stretched I-film (Optes, Japan) having NZ of 0 defined as (Nx-Nz) / (Nx-Ny) is used. It was.

In Example 2 and Comparative Example 2, the results show that the dark state was uniformly distributed over the entire area in Example 2, but in Comparative Example 2, seven lines of light leaking in the horizontal direction were observed. It is shown in Figure 13 that the uniaxially stretched retardation film is torn by the thermal shock. This confirmed that Example 2 including biaxial stretching had higher durability compared with Comparative Example 1 including uniaxial stretching.

As described above, the planar switching liquid crystal display device according to the present invention can provide a compensation film capable of realizing a wide viewing angle through a roll-to-roll method and a high durability display device of the planar switching mode (IPS mode) using the same. have.

1 is a perspective view showing the structure of a planar switching liquid crystal display device (IPS-LCD) including a biaxial first and second phase difference film according to the present invention;

2 is a schematic view for explaining the arrangement of the absorption axis and the alignment direction of the liquid crystal of the polarizing plate according to the present invention;

3 is a schematic view for explaining the refractive index of the retardation film according to the present invention;

FIG. 4 illustrates phase difference compensation on a Poincare Sphere at a slope (θ = 60 ° and Φ = 45 °) for a planar switching liquid crystal display according to the present invention. The biaxial first phase difference film 40 ) And the range of solutions that can be compensated according to the NZ of the biaxial second phase difference film 50;

5 is a schematic view showing the MD direction in the manufacturing process for explaining the stretching direction of the retardation film and the second polarizing plate according to the present invention;

6 is a result showing the visibility omnidirectional transmittance according to the retardation value R0 of each retardation film when NZ of the biaxial first retardation film is -0.7 and NZ of the biaxial second retardation film is 1.3. ;

7 is a result showing the visibility omnidirectional transmittance according to the retardation value (R0) of each retardation film when NZ of the biaxial first retardation film is -0.7, NZ of the biaxial second retardation film is 4 ;

8 is a result showing the visibility omnidirectional transmittance according to the retardation value (R0) of each retardation film when NZ of the biaxial first retardation film is -2, NZ of the biaxial second retardation film is 1.3 ego;

9 is a result showing the visibility omnidirectional transmittance according to the phase difference value R0 of each retardation film when NZ of the biaxial first retardation film is -2 and NZ of the biaxial second retardation film is 4; ;

FIG. 10 is a schematic diagram for explaining representation of simulation data of an on-plane switching liquid crystal display (IPS-LCD) according to an embodiment of the present invention in a circular coordinate system in θ and Φ;

11 is a perspective view showing the structure of a planar switching liquid crystal display device (IPS-LCD) including the isotropic protective film of Comparative Example 1;

12 is a result of simulating the visibility omnidirectional transmittance for the planar switching liquid crystal display device (IPS-LCD) including the isotropic protective film of Comparative Example 1;

It is a schematic diagram which shows the durability test result of the comparative example 2.

Claims (13)

An area switching liquid crystal display device (IPS-LCD) formed by stacking a first polarizing plate, a liquid crystal cell, a biaxial first phase difference film, a biaxial second phase difference film, and a second polarizing plate from a backlight unit side, The biaxial first phase difference film has a refractive index ratio of -2.0 <NZ <-0.7, and its slow axis is orthogonal to the absorption axis of the second polarizing plate, The biaxial second phase difference film has a refractive index ratio of 1.3 <NZ <4, and its slow axis is orthogonal to the absorption axis of the second polarizing plate, The liquid crystal cell side protective film of the first polarizing plate has a thickness retardation value (Rth) in a range of 0 to 10 nm at a wavelength of 589 nm, A field switching liquid crystal display device characterized by satisfying a compensating relationship of a maximum visibility of transmittance of 0.2% or less. The planar switching liquid crystal display of claim 1, wherein an absorption axis of the first polarizing plate and an absorption axis of the second polarizing plate are perpendicular to each other, and a liquid crystal alignment direction of the liquid crystal cell is parallel to the absorption axis of the first polarizing plate. According to claim 1, wherein the first polarizing plate is provided with a protective film on both sides of the polarizer, the protective film on the liquid crystal cell side is triacetyl cellulose (TAC), cycloolefin polymer (COP), cycloolefin copolymer (COC), polyethylene Terephthalate (PET), polypropylene (PP), polycarbonate (PC) , polysulfone (PSF) and polymethyl methacrylate (PMMA) is a single compound or a mixture of two or more selected from Switching liquid crystal display. 2. The planar switching liquid crystal display of claim 1, wherein the liquid crystal cell has a positive dielectric anisotropy (Δε> 0). The planar switching liquid crystal display according to claim 1 or 4, wherein the liquid crystal cell has a retardation value in a range of 200 to 400 nm at a wavelength of 589 nm. The planar switching liquid crystal of claim 1, wherein the biaxial first phase difference film has a structure in which polymethyl methacrylate (PMMA), polystyrene (PS), and polymethyl methacrylate (PMMA) are sequentially stacked. Display device. The planar switching liquid crystal display device according to claim 1 or 6, wherein the biaxial first phase difference film has a structure having at least one or more modified polycarbonates (PCs). 2. The planar switching liquid crystal display of claim 1, wherein the biaxial first phase difference film has a planar retardation value (R0) in a range of 30 to 90 nm at a wavelength of 589 nm. The planar switching liquid crystal display of claim 1, wherein the biaxial first phase difference film has a planar retardation value (R 0) ranging from 40 nm to 80 nm at a wavelength of 589 nm. The method of claim 1, wherein the biaxial second phase difference film is triacetyl cellulose (TAC), cycloolefin polymer (COP), cycloolefin copolymer (COC), polyethylene terephthalate (PET), polypropylene (PP), poly And a single compound or a mixture of two or more selected from carbonate (PC) , polysulfone (PSF), and polymethyl methacrylate (PMMA). 2. The planar switching liquid crystal display of claim 1, wherein the biaxial second phase difference film has a planar retardation value (R0) in a range of 30 to 110 nm at a wavelength of 589 nm. 12. The planar switching liquid crystal display of claim 1 or 11, wherein the biaxial second phase difference film has a planar retardation value (R0) of 50 nm to 100 nm at a wavelength of 589 nm. The planar switching liquid crystal display device according to claim 1, wherein the second polarizing plate is provided with a protective film only on the viewing side of the polarizer (opposite to the backlight unit).

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