KR20080059832A - Display apparatus - Google Patents

Abstract

A display device is provided to vary wavelength dispersion characteristics of an in-plane retardation value and a thickness direction retardation value of a compensation film, thereby compensating wavelength dispersion characteristics of LC and effectively preventing light leakage in a black state. An LC(Liquid Crystal) panel(100) comprises a first substrate(110), a second substrate(120) facing the first substrate, and an LC layer(130) interposed between the first and second substrates. A first polarizing plate(210) is disposed in a lower side of the LC panel. A second polarizing plate(220) is disposed in an upper side of the LC panel. A retardation compensation film(300) is disposed between the LC panel and one of the first and second polarizing plates. The retardation compensation film has an in-plane retardation value and a thickness direction retardation value. The in-plane retardation value having reverse wavelength dispersion is increased according as a wavelength is increased. The thickness directional retardation value is reduced according as a wavelength is increased.

Description

Display device {DISPLAY APPARATUS}

1A is an exploded perspective view illustrating a display device according to an exemplary embodiment of the present invention.

FIG. 1B is an enlarged view of a portion A of FIG. 1A.

FIG. 2 is an exploded perspective view illustrating the retardation film of FIG. 1A. FIG.

3 is a graph illustrating a phase difference value of the phase difference compensation film of FIG. 1A.

Figure 4 is a graph showing the relative phase difference value for each wavelength of the retardation compensation film of Figure 1a.

FIG. 5 is a conceptual diagram schematically illustrating phase difference compensation in a diagonal direction of the display device of FIG. 1A.

<Description of the symbols for the main parts of the drawings>

100: display panel 210: first polarizing plate

220: second polarizing plate 300: phase difference compensation film

310: a plate film 320: c plate film

The present invention relates to a display device, and more particularly, to a display device for improving viewing angle characteristics.

In general, a liquid crystal display device is a flat panel display that displays an image by using the light transmittance of the liquid crystal. The liquid crystal display includes a display panel that displays an image using light and a backlight assembly that provides light to the display panel.

The display panel includes a pair of transparent substrates, a liquid crystal layer interposed between the transparent substrates, and a pair of polarizing films disposed outside the transparent substrates. When light emitted from the backlight assembly passes through the liquid crystal layer having refractive index anisotropy, retardation occurs according to the angle at which the light is incident.

For example, in the VA (Vertical Alignment) mode in which a vertical electric field is applied to the display panel to drive the liquid crystal layer, the liquid crystals are aligned in the vertical direction. In the VA mode as described above, the light incident perpendicularly to the liquid crystal layer passes through the optical axis of the liquid crystal, and thus no phase difference occurs, but the light incident at an oblique angle is generated. That is, according to the position of viewing the image, the transmission refractive index of the light and the phase difference of the light is generated, and when viewing the image from the side, the light leakage phenomenon that the amount of light and wavelength characteristics are different from the front occurs. Accordingly, in the display device, a phenomenon such as contrast ratio and color shift according to the viewing angle occurs.

In order to solve this problem, the display device uses a compensation film disposed between the display panel and the polarizing film to compensate the phase difference of the liquid crystal layer in reverse. However, the compensation film has various refractive indexes depending on the wavelength due to the molecular structure of the raw material and the characteristics of the additive. As such, wavelength dependence of light transmittance occurs due to the wavelength dispersion of the phase difference of the compensation film.

On the other hand, since the backlight assembly emits visible light having a plurality of wavelengths instead of a single wavelength, if the wavelength dispersion of the liquid crystal layer and the wavelength dispersion of the compensation film are different from each other, complete compensation cannot be made for light in all wavelength bands. In particular, when the wavelength dispersion of the compensation film and the wavelength dispersion of the liquid crystal are different in the black state of the display device, the phase difference compensation may not be completely performed. As a result, light leakage occurs at the side surface, and a problem occurs that the viewing angle of the display device is reduced.

Therefore, the technical problem of the present invention is to solve such a conventional problem, and an object of the present invention is to provide a display device that can improve the viewing angle characteristics by adjusting the wavelength dispersion characteristics of the compensation film.

In accordance with an aspect of the present invention, a display device includes a first substrate, a second substrate facing the first substrate, and a liquid crystal layer interposed between the first substrate and the second substrate. A liquid crystal panel, a first polarizing plate disposed below the liquid crystal panel, a second polarizing plate disposed above the liquid crystal panel, and a phase difference compensation film disposed between any one of the first and second polarizing plates. It includes. The retardation compensation film has an in-plane retardation value of inverse wavelength dispersion (Ro) with respect to the refractive index nx in the direction of the high refractive index, the refractive index ny in the direction of the small refractive index, and the refractive index nz in the thickness direction of the retardation compensation film. ((nx-ny) × d)) and the thickness direction retardation value Rth ({nx− (ny + nz) / 2} × d) of the wavelength dispersion in which the phase difference value decreases as the wavelength increases. .

At this time, the retardation compensation film includes a positive a plate film of reverse wavelength dispersion and a negative c plate film of positive wavelength dispersion.

According to such a display device, by adjusting a wavelength dispersion by applying a phase difference compensation film having a different phase retardation value and a thickness direction retardation value, it is possible to prevent light leakage from the side to improve viewing angle characteristics.

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

1A is an exploded perspective view illustrating a display device according to an exemplary embodiment of the present invention. FIG. 1B is an enlarged view of a portion A of FIG. 1A.

1A and 1B, the display device 400 according to an exemplary embodiment of the present invention includes a liquid crystal panel 100, a first polarizing plate 210, a second polarizing plate 220, and a phase difference compensation film 300. Include.

The liquid crystal panel 100 includes a first substrate 110, a second substrate 120 facing the first substrate 110, and a liquid crystal layer 130 interposed between the first substrate 110 and the second substrate 120. ).

The first substrate 110 is a transparent substrate through which light is transmitted. A plurality of gate lines and data lines that cross each other are formed on the first substrate 110, and a plurality of unit pixels are defined by the gate lines and the data lines. Specifically, each unit pixel is formed with a thin film transistor for switching the driving of each unit pixel and a pixel electrode receiving a pixel voltage from the thin film transistor.

The second substrate 120 faces the first substrate 110 and is a transparent substrate through which light is transmitted. On the opposite surface of the second substrate 120 facing the first substrate 110, R, G, and B color filters and a common electrode for implementing colors are formed.

The liquid crystal layer 130 is interposed between the first substrate 110 and the second substrate 120 and is arranged in a vertical direction by an electric field formed between the pixel electrode and the common electrode. For example, the liquid crystal layer 130 of the present exemplary embodiment may be formed in a vertically aligned VA mode, a PVA mode, and an ECB mode. That is, the optical axes of the liquid crystal molecules of the liquid crystal layer 130 may be disposed in directions perpendicular to the first and second substrates 110 and 120. For example, the vertically aligned liquid crystal molecules may have a refractive index of nx <ny <nz. . As the liquid crystal array of the liquid crystal layer 130 changes, the light transmittance of the light applied from the outside may be adjusted to display an image having a desired gray scale.

The first polarizing plate 210 is disposed below the liquid crystal panel 100 to linearly polarize light in the first direction. For example, the transmission axis P of the first direction and the absorption axis of the second direction perpendicular to the first direction may be formed in the first polarizing plate 210. Accordingly, the first polarizing plate 210 transmits the light vibrating in the first direction and absorbs the light vibrating in the second direction.

The second polarizer 220 is disposed above the liquid crystal panel 100 to linearly polarize light in the second direction. For example, a transmission axis A in the second direction and an absorption axis in the first direction perpendicular to the second direction are formed in the second polarizing plate 220. Accordingly, the second polarizing plate 220 transmits the light vibrating in the second direction and absorbs the light vibrating in the first direction.

For example, the transmission axis P of the first polarizing plate 210 and the transmission axis A of the second polarizing plate 220 may be perpendicular to each other. Accordingly, in order for the linearly polarized light passing through the first polarizing plate 210 to pass through the second polarizing plate 220, the phase difference of the liquid crystal layer 130 is about half wavelength (λ / 2) of the optical wavelength λ. The range can be adjusted.

Specifically, the phase difference Δnd of the liquid crystal layer 130 is about 200 to 350 nm at a wavelength of about 590 nm. For example, the phase difference Δnd of the liquid crystal layer 130 may be about 310 nm. Here, the cell gap d of the liquid crystal layer 130 represents a gap between the first substrate 110 and the second substrate 120, and may be about 3.5 μm to 4.0 μm. Meanwhile, the director of the liquid crystal molecules of the liquid crystal layer 130, that is, the long axis direction of the liquid crystal molecules may form about 45 degrees with the absorption axis of the first polarizing plate 210.

The retardation compensation film 300 may be disposed between any one of the first and second polarizing plates 210 and 220 and the liquid crystal panel 100. For example, the retardation compensation film 300 may be disposed between the first polarizing plate 210 and the first substrate 110 or may be disposed between the second polarizing plate 220 and the second substrate 120. Alternatively, the phase difference compensation film 300 is disposed between the first polarizing plate 210 and the first substrate 110 and between the second polarizing plate 220 and the second substrate 120, that is, above and below the liquid crystal panel 100. Can be. On the other hand, the phase difference compensation film 300 of the present embodiment may be formed integrally with the first and second polarizing plates (210, 220).

As in one embodiment of the present invention, the retardation compensation film 300 may be disposed between the vertically aligned liquid crystal panel 100 and the second polarizing plate 220. The retardation compensation film 300 may be a biaxial film having a refractive index of nx> ny> nz to compensate for the phase delay of the liquid crystal layer 130. Here, nx represents a refractive index in a direction where the refractive index is large, nx represents a refractive index in a direction where the refractive index is small, and a refractive index in the thickness direction is nz.

In addition, the in-plane retardation value Ro of the retardation compensation film 300 is (nx-ny) × d, and the thickness direction retardation value Rth is {nx− (ny + nz) / 2} × d. As in an embodiment of the present invention, the phase difference compensation film 300 has an in-plane retardation value Ro of reverse wavelength dispersion in which the retardation value increases as the wavelength increases, and a positive wavelength dispersion in which the retardation value decreases as the wavelength increases. It may have a thickness direction retardation value Rth.

Meanwhile, when a vertical electric field is applied to the liquid crystal panel 100, the long axes of the liquid crystal molecules of the liquid crystal layer 130 are vertically arranged with the first and second substrates 110 and 120. At this time, the phase delay is not generated in the light L1 incident to the front along the optical axis direction of the liquid crystal molecules.

On the contrary, in the light L2 incident to the side surface obliquely off the optical axis of the liquid crystal molecules, phase delay may occur due to refractive index anisotropy of the liquid crystal molecules, and the polarization state may be changed. In addition, since the polarization axis P of the first polarizing plate 210 and the polarization axis A of the second polarizing plate 220 which are disposed perpendicular to each other deviate from each other at the side surfaces, light leakage may occur.

Accordingly, in the present invention, the phase difference compensation film 300 is disposed on the upper side or the lower side of the liquid crystal panel 100 to compensate for the phase delay caused by the liquid crystal molecules of the liquid crystal layer 130, and the first and second polarizing plates ( The wide viewing angle of the display device 400 may be realized by compensating for light leakage generated when the polarization axes P and A of the 210 and 220 are perpendicular to each other.

FIG. 2 is an exploded perspective view illustrating the retardation film of FIG. 1A. FIG.

1A and 2, as in the embodiment of the present invention, the retardation compensation film 300 may include a positive a plate film 310 and a negative c plate film 320. For reference, the refractive index in the x-axis direction parallel to the plane of the retardation compensation film 300 is nx, the refractive index in the y-axis direction parallel to the plane of the film is ny, and the refractive index in the thickness direction perpendicular to the plane of the film is represented by nz. .

Specifically, the a plate film 310 has an optical axis in the plane of the film, and may have a value of nx> ny = nz. For example, a plate film 310 may be a uniaxially stretched film formed by stretching the polymer resin film in one direction. Accordingly, the a plate film 310 may be formed of a positive stretched film having a refractive index nx in the optical axis direction greater than that of the other directions ny, nz, that is, a large refractive index in the orientation direction.

The c plate film 320 may have an optical axis in a normal line of the film, that is, in a thickness direction, and have a value of nx = ny> nz. For example, the c plate film 320 may be formed by stretching the polymer resin film in a direction perpendicular to the one direction in a plane. Accordingly, the c plate film 320 may be formed of a negative stretched film having a refractive index nz in the optical axis direction smaller than that in the other directions (nx, ny), that is, a small refractive index in the orientation direction. As in an embodiment of the present invention, the c plate film 320 may be a film coated with a refractive index anisotropic material, such as a discotic discotic liquid crystal.

In the present embodiment, the retardation compensation film 300 combines the c plate film 320 coated with the refractive anisotropic material using the a plate film 310 as a base substrate, thereby forming a single film having negative biaxiality. Can be. Meanwhile, the vertical position relationship of the a plate film 310 and the c plate film 320 in the display device 400 may be changed.

As such, by combining the two films to form the retardation compensation film 300, mutual wavelength dispersion can be compensated for each other. Accordingly, the amount of light leaked from the display device 400 over the visible light region can be reduced.

3 is a graph illustrating a phase difference value of the phase difference compensation film of FIG. 1A. Figure 4 is a graph showing the relative phase difference value for each wavelength of the retardation compensation film of Figure 1a. FIG. 5 is a conceptual diagram schematically illustrating phase difference compensation in a diagonal direction of the display device of FIG. 1A.

Referring to FIG. 3, as in the exemplary embodiment of the present invention, the retardation compensation film 300 may have wavelength dispersion in which the in-plane retardation value Ro and the thickness direction retardation value Rth are different from each other.

Specifically, the a plate film 310 may have a reverse wavelength dispersion in which the retardation value increases as the wavelength increases. That is, the in-plane retardation value Ro of the a plate film 310 having the optical axis in the plane of the film increases as the wavelength increases.

On the other hand, the c plate film 320 may have a positive wavelength dispersion in which the retardation value decreases as the wavelength increases. That is, the phase difference value Rth of the c plate film 320 whose optical axis is in the thickness direction of the film decreases as the wavelength increases.

The retardation compensation film 300 according to the present exemplary embodiment may be composed of the a plate film 310 and the c plate film 320 as described above. Accordingly, the in-plane retardation value Ro and the forward wavelength dispersion of reverse wavelength dispersion It may have a thickness direction retardation value Rth.

For example, the in-plane retardation value Ro of the retardation compensation film 300 may satisfy Ro450 <Ro590 <Ro650, and the thickness direction retardation value Rth may satisfy Rth450> Rth590> Rth650. Here, 650 represents a red (R) wavelength band (650 nm), 590 represents a green (G) wavelength band (590 nm), and 450 represents a blue (B) wavelength band (450 nm).

1A and 4, in detail, in order to compensate for wavelength dispersion of the liquid crystal layer 130, the relative phase difference value R of each wavelength W1 between the retardation compensation film 300 and the liquid crystal layer 130 (R ( λ) / R 590). For reference, wavelength dispersion shows the difference in refractive index according to the wavelength of light.

First, referring to the polarization state variation in the display device 400, the light passing through the first polarizing plate 210 is linearly polarized in the direction of the polarization axis P of the first polarizing plate 210, and the linearly polarized light is the liquid crystal layer ( While passing through 130), the polarization state is changed by 2πΔnd / λ. Subsequently, the light passing through the liquid crystal layer 130 passes through the c plate film 320, which is the lower plate of the retardation compensation film 300, and is again polarized by 2πΔnd / λ by the retardation value of the retardation compensation film 300. The state may change.

As such, light incident on the display device 400 passes through the liquid crystal layer 130 and the retardation compensation film 300, and the polarization state may be dispersed according to the difference in the retardation value for each RGB wavelength. That is, the polarization state of the light passing through the display device 400 may vary depending on the RGB wavelength and the wavelength dispersion of the phase difference compensation film 300.

Specifically, the polarization state of the light passing through the liquid crystal layer 130 is changed by 2πΔnd / λ by the c plate film 320. Accordingly, the relationship between the retardation value LC_Rth of the liquid crystal layer 130 and the thickness retardation value Rth of the retardation compensation film 300 will be described. Here, each of the thickness direction retardation values Rth of the retardation compensation film 300 at the wavelengths of 450 nm, 590 nm, and 650 nm is represented by Rth450, Rth590, and Rth650, and the respective thickness direction retardation values of the liquid crystal layer 130 ( LC_Rth) is represented by LC_Rth450, LC_Rth590, LC_Rth650.

In order for the RGB polarization state dispersed by the liquid crystal layer 130 to be collected again by the phase difference compensation film 300, the value of (Rth450 / Rth590) / (LC_Rth450 / LC_Rth590) is preferably 1 or more. In addition, considering that Δnd of the liquid crystal layer 130 is about 310 nm at a wavelength of 590 nm, and the thickness retardation value Rth of the phase difference compensation film 300 is optimized to about 120 nm at a wavelength of 590 nm, (Rth450 / Rth590) / (LC_Rth450 / LC_Rth590) The value is preferably 3 or less.

As in an embodiment of the present invention, the wavelength dispersion characteristics of the retardation compensation film 300 and the thickness direction retardation value Rth of the liquid crystal layer 130 will be described. The value of (Rth450 / Rth590) / (LC_Rth450 / LC_Rth590)] is about 1.0 to 3.0, and the relative phase difference ratio [(Rth650 / Rth590) / (LC_Rth650 / LC_Rth590)] at two wavelengths of 650 nm and 590 nm is about 0.33 to May be 1.0.

On the other hand, the light passing through the c plate film 320 is changed by the a plate film 310 by 2πΔnd / λ polarization state. The a plate film 310 in the present invention serves to collect the light passing through the c plate film 320 in a direction perpendicular to the polarization axis A of the second polarizing plate 220. In this case, the phase difference value of the a plate film 310 may be adjusted to satisfy 2πΔnd / 450nm = 2πΔnd / 590nm = 2πΔnd / 650nm for each wavelength. As such, by adjusting the wavelength dispersion of the phase difference compensation film 300 such that the phase difference values of the light passing through the display device 400 are the same, the wavelength dispersion characteristic may be minimized.

As in one embodiment of the present invention, looking at the wavelength dispersion characteristics of the retardation compensation film 300, the relative retardation ratio (Ro450 / Ro590) of the two wavelengths 450nm, 590nm is about 0.7 ~ 1.0, two wavelengths The relative phase difference ratio (Ro650 / Ro590) values at 650 nm and 590 nm may be about 1.0 to 1.3. In this case, the in-plane retardation value Ro of the retardation compensation film 300 may be, for example, about 30 nm to 100 nm at a wavelength of 590 nm, and the thickness retardation value Rth may be about 80 nm to 200 nm at a wavelength of 590 nm.

As described above, the wavelength dispersion and the phase difference compensation film 300 of the liquid crystal layer 130 are applied by applying the phase difference compensation film 300 having the wavelength dispersion characteristic in which the in-plane phase difference value Ro and the thickness direction phase difference value Rth are different from each other. By mutually adjusting the wavelength dispersion of the light, the RGB dispersion of the light passing through the display device 400 may be minimized. In addition, as described above, the relative phase difference ratio of each wavelength is adjusted to block light leakage from the side surface, thereby increasing the viewing angle of the display device 400.

4 and 5, in order to achieve perfect black on the side of the display device 400, the first polarizing plate 210, the liquid crystal panel 100, and the phase difference compensation film 300 are incident obliquely in a diagonal direction. The polarization state of the light L3 that has passed should be in the extinction point EP, which is a position perpendicular to the polarization axis A of the second substrate 220. However, the light passing through the liquid crystal panel 100 has a phase difference value according to the viewing angle, and has a characteristic in which the phase difference value varies for each RGB wavelength within the range of visible light. As such, when the light passing through the liquid crystal panel 100 changes in polarization state for each of the RGB wavelengths, light may leak, particularly in the black mode implemented by blocking the light.

Referring to FIGS. 1A and 5, the phase difference compensation film 300 rotates linearly polarized light incident to the display device 400 at an angle and passed through the first polarizing plate 210 to elliptical polarization, thereby transmitting the second polarizing plate 220. By converting the light into the polarization state orthogonal to the axis A, light leakage of the display device 400 can be effectively blocked.

As such, when the retardation compensation film 300 as in the exemplary embodiment of the present invention is applied to the display device 400, the wavelength dependence may be minimized by adjusting the change in transmittance according to the RGB wavelength in the same manner. That is, the in-plane retardation value Ro and the thickness direction retardation value Rth of the retardation compensation film 300 according to the wavelength so that the retardation values of the red, green, and blue wavelengths of the light passing through the retardation compensation film 300 are the same. By adjusting the relative phase difference ratio of, the viewing angle characteristic of the display device 400 may be further improved.

As described above, by controlling the wavelength dispersion characteristics of the in-plane retardation value and the thickness direction retardation value of the retardation compensation film differently, it is possible to effectively block the light leakage in the black state of the display device by compensating the wavelength dispersion characteristics of the liquid crystal. . Accordingly, color characteristics on the side of the display device can be improved, and viewing angle characteristics can be improved.

Although described above with reference to the embodiments, those skilled in the art can be variously modified and changed within the scope of the invention without departing from the spirit and scope of the invention described in the claims below. I can understand.

Claims (8)

A liquid crystal panel including a first substrate, a second substrate facing the first substrate, and a liquid crystal layer interposed between the first substrate and the second substrate; A first polarizer disposed under the liquid crystal panel; A second polarizer disposed on an upper side of the liquid crystal panel; And A phase difference compensation film disposed between any one of the first and second polarizing plates and the liquid crystal panel; The retardation compensation film has an in-plane retardation value of inverse wavelength dispersion (Ro) with respect to the refractive index nx in the direction of the high refractive index, the refractive index ny in the direction of the small refractive index, and the refractive index nz in the thickness direction of the retardation compensation film. ((nx-ny) × d)) and the thickness direction retardation value (Rth ({nx− (ny + nz) / 2} × d)) of positive wavelength dispersion in which the phase difference value decreases as the wavelength increases. Display device characterized in that. The in-plane retardation values Ro450, Ro590, and Ro650 of claim 1, respectively, at wavelengths of 450 nm, 590 nm, and 650 nm. The wavelength dispersion (Ro450 / Ro590) at 450 nm and 590 nm of the phase difference compensation film is 0.7 to 1.0, and the wavelength dispersion (Ro650 / Ro590) at 650 nm and 590 nm is 1.0 to 1.3. Display. The thickness difference retardation values Rth450, Rth590, and Rth650 of the retardation compensation film at wavelengths of 450 nm, 590 nm, and 650 nm, and thickness retardation values LC_Rth450, LC_Rth590, and LC_Rth650 of the liquid crystal layer, respectively. about, The wavelength dispersion ((Rth450 / Rth590) / (LC_Rth450 / LC_Rth590)) at 450 nm and 590 nm is 1.0 to 3.0, and the wavelength dispersion ((Rth650 / Rth590) / (LC_Rth650 / LC_Rth590) at 650 nm and 590 nm. )) Is 0.33 to 1.0. The display device of claim 1, wherein an in-plane retardation value Ro of the retardation compensation film is 30 nm to 100 nm at a wavelength of 590 nm. The display device of claim 1, wherein a thickness direction retardation value Rth of the retardation compensation film is 80 nm to 200 nm at a wavelength of 590 nm. The display device of claim 1, wherein the retardation compensation film comprises a positive a plate film having a reverse wavelength dispersion and a negative c plate film having a positive wavelength dispersion. The display device of claim 6, wherein the positive a-plate film is a uniaxially oriented film. The display device of claim 6, wherein a refractive index anisotropic material is coated on the negative c plate film.

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