KR101205768B1 - Tansflective type liquid crystal display device - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflection type liquid crystal display device, and more particularly, to a reflection type liquid crystal display device having the same polarization characteristics in reflection mode and transmission mode and having improved reagent angle characteristics.

The reflective liquid crystal display device according to the present invention includes a polarizer, a first positive A plate, a first negative A plate, a reflective liquid crystal panel, and a second liquid crystal panel from the bottom. And a negative A plate, a second positive A plate, and an analyzer.

As described above, when the positive A plate and the negative A plate are superimposed and each optical axis is configured in parallel, there is an advantage that the viewing angle can be widened as compared with the general wide band λ / 4 plate (W_QWP).

Description

Reflective type liquid crystal display device {Tansflective type liquid crystal display device}

1 is a cross-sectional view schematically showing the configuration of a conventional transflective liquid crystal display device;

FIG. 2 is a view illustrating polarization characteristics of light passing through a transmission part when a lower phase difference film is not formed in the reflective transmissive liquid crystal display when the voltage is in an on state.

FIG. 3 is a view illustrating polarization characteristics of light passing through the transmission part D when the lower phase difference film 30 is configured in the reflective transmissive liquid crystal display when the voltage is in an on state.

4 is a cross-sectional view of a transflective liquid crystal panel according to a second example of the prior art;

5 is a perspective view showing a compensation film according to the present invention;

6 is a graph showing phase values of wavelengths of each of the negative A plate and the positive A plate,

7 is a graph showing phase values for each wavelength when a negative A plate and a positive A plate are used at the same time.

FIG. 8 is an exploded perspective view schematically illustrating a reflective transmissive liquid crystal display device;

9 is an exploded perspective view schematically illustrating a configuration of a reflective transmissive liquid crystal display device including a compensation film according to the present invention.

<Explanation of symbols for main parts of drawing>

300: reflection-transmissive liquid crystal display device. 310: reflection type liquid crystal panel

320: liquid crystal layer 410: polarizing plate

412: First Positive A Plate 414: First Negative A Plate

416: second negative A plate 418: second positive A plate

220: detector plate

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly, to a reflective liquid crystal display device for realizing high image quality and wide viewing angle.

In general, a liquid crystal display device may be classified into a transmission type and a reflection type according to a light source to be used, and the transmission type liquid crystal display device is a backlight that is a back light source attached to a rear surface of a liquid crystal panel. The artificial light emitted from) is incident on the liquid crystal to adjust the amount of light according to the arrangement of the liquid crystal to display color.

By the above-described configuration, the transmissive liquid crystal display device uses an artificial back light source, so that power consumption is large. On the other hand, the reflective liquid crystal display device depends on external natural light or artificial light source for most of the light. As a result, the power consumption is lower than that of the transmissive liquid crystal display. However, the reflective liquid crystal display device has a limitation that external light cannot be used in a dark place or when the weather is cloudy.

Accordingly, there has been proposed a reflective and transmissive liquid crystal display device, that is, a reflective transmissive liquid crystal display device, in which the two modes can be appropriately selected and used according to a necessary situation.

However, since the reflection-transmissive liquid crystal display device configures the reflection part and the transmission part on one substrate, the configuration of the optical film to be configured in the reflection part is not necessary for the transmission part, which causes the optical efficiency of the transmission part to be lowered.

Therefore, a means for compensating for this is further configured to correspond to the transmission portion.

FIG. 1 is a cross-sectional view schematically showing a configuration of a reflective transmissive liquid crystal display device according to the related art. FIG.

As shown in the drawing, in the conventional reflective liquid crystal display device 10, the first substrate 20 and the second substrate 40 defined by the reflective part B and the transparent part D may be formed of the liquid crystal layer 50. The first electrode 20 is spaced apart from each other, and on one surface of the first substrate 20 facing each other, the reflective electrode (reflector) 28 corresponds to the reflective portion B, and the transparent electrode 22 corresponds to the transmissive portion D. It is composed.

The transparent electrode 22 and the reflective electrode 28 may be formed with the insulating layer 26 interposed therebetween, and may be formed in a direct contact with each case.

On the other surface not facing the first substrate 20, the lower retardation film 30 and the lower polarizing film 32 are sequentially formed, and the upper portion of the second substrate 40 not facing the first substrate 20. The upper retardation film 42 and the upper polarizing film 44 is sequentially configured.

The backlight 40 is formed under the second substrate 40.

In the above-described configuration, the liquid crystal panel 10 can be used simultaneously in the transmissive mode and the reflective mode. In the transmissive mode, the light of the lower backlight is used, and external natural light is used in the reflective mode.

In the above configuration, the presence of the lower retardation film 42 is configured because of the presence of the upper retardation film 42.

Only when the upper retardation film 22 is present is able to have a clear white and black characteristics in the reflecting portion (B). On the other hand, from the perspective of the transmissive part D, the presence of the upper retardation film is not actually necessary.

Therefore, in the structure in which the transmissive portion D and the reflecting portion B are configured in one pixel, the lower retardation film 30 is disposed in correspondence to the transmissive portion to compensate for the phase difference generated by the upper retardation film 22. It is more organized.

2 and 3, the polarization characteristics of the reflective transmissive liquid crystal display device with or without the lower retardation film will be described.

FIG. 2 is a diagram illustrating polarization characteristics of light passing through a transmission part when a lower phase difference film is not configured in the reflective transmissive liquid crystal display when the voltage is in an on state.

As shown, first, light linearly polarized at 45 degrees parallel to the polarization axis of the lower polarizing film 32 of the natural light emitted from the backlight 55 of FIG. 1 passes through the lower polarizing film 32, and the linear polarized light. The silver passes through the liquid crystal layer 50 as it is.

The linearly polarized light passing through the liquid crystal layer 50 is changed to left circularly polarized light while passing through the upper retardation film 42, and the left circularly polarized light meets the upper polarizing film 44 and is parallel to the polarization axis of the upper polarizing film 44. One component of light is transmitted.

Thus, gray is observed from the liquid crystal panel.

On the other hand, when the lower retardation film 30 is configured in the liquid crystal display, different results may be obtained. A description with reference to FIG. 3 is as follows.

FIG. 3 is a view illustrating polarization characteristics of light passing through the transmission part D when the lower phase difference film 30 is configured in the reflective transmissive liquid crystal display when the voltage is in an on state.

As shown, first, the scattered light emitted from the backlight (60 of FIG. 1) is passed through the lower polarizing film 32, the light linearly 45 degrees parallel to the polarization axis of the lower polarizing film 32, the linearly polarized light Passing through the retardation film 30 is changed to the right circularly polarized light.

The right circularly polarized light simply passes through the liquid crystal layer 50. The circularly polarized light passing through the liquid crystal layer 50 is changed to 45 degrees linearly polarized light while passing through the upper retardation film 42.

The linearly polarized light is in a direction perpendicular to the polarization axis of the upper polarizing film 44 and is completely absorbed by the upper polarizing film 44.

Therefore, the liquid crystal panel is observed to be completely black.

In the configuration of FIG. 1, if the upper retardation film 42 does not exist, it would be possible to realize a completely black state in the transmission portion.

However, since the upper retardation film 42 exists for the reflecting portion, the lower retardation film 30 corresponding to the transmissive portion must be configured in order to compensate for the optical degradation such as that the complete black state can be exhibited.

However, in the above-described configuration, from the viewpoint of reflectance according to the wavelengths of red, green, and blue, the light of the blue wavelength (around 430 nm) and the blue wavelength (around 630 nm) has high reflectivity, but the wavelength of the green wavelength (near 530 nm) is The reflectance is very low.

Due to this characteristic, the reflectance according to each wavelength shows a narrow band shape graph. This phenomenon not only lowers the overall brightness but also results in poor contrast.

Therefore, in order to solve this problem, a structure for constituting a wide band QWP in which red, green, and blue wavelengths have similar reflectances is proposed by combining QWP and HWP instead of the QWP.

4 is a perspective view schematically illustrating a configuration of a reflective transmissive liquid crystal display device according to a second example.

As illustrated, the reflective liquid crystal display device 60 according to the second example of the present invention includes a QWP 74 and a semi-transmissive substrate 62 in which the reflective portion B and the transparent portion D are defined. A first wide band QWP 80a composed of an HWP 72 and a polarizing plate 70 formed below the first wide band QWP 80a, and a QWP 76 and an HWP 78 formed above the transflective substrate 62. The two wide band QWP 80b and the analyzer plate 80 are comprised.

The first wide band QWP 80a configured in the lower portion is configured such that the optical axes of the QWP 74 and the HWP 72 constituting the same are 75 degrees and 15 degrees, respectively, and the second wide band QWP 80b constitutes the same. The QWP 76 and the HWP 78 are configured to have optical axes of 165 degrees and 105 degrees, respectively.

The liquid crystal layer 64 is positioned on the reflective transparent substrate 62, and a compensation film (not shown) may be further configured between the liquid crystal layer 64 and the second wide band QWP 80b.

As described above, unlike the first example, light of the red, green, and blue wavelength bands may have a similar reflectance value in the reflector.

Therefore, the contrast can also be greatly improved since a low reflectance can be secured in a black condition.

At this time, the polarization characteristics of the light, when viewed from the front, the ideal shape in the reflecting portion (B) and the transmission portion (D) can be obtained a characteristic of a clear black or clear white.

However, when the optical film of the above-described type is viewed from the side, it exhibits different polarization characteristics from those observed from the front.

That is, the light passing through the polarizing plate 70 and the first wide band QWP 80b is observed in the form of circularly polarized light when viewed from the front, but the optical axis and the phase value of the compensation film are different for the light incident from the side. It is not converted into polarized light and is observed as elliptical polarization.

Due to this phenomenon, the color of light observed from the front and the side is changed, resulting in a problem that the reagent angle becomes very narrow.

The present invention has been proposed to solve the above-described problem, and an object of the present invention is to propose a reflection-transmissive liquid crystal display device capable of realizing a wide viewing angle while having similar reflectance of red, green, and blue wavelength bands.

According to an aspect of the present invention, there is provided a reflective transmissive liquid crystal display device; A polarizing plate formed under the liquid crystal panel; A first negative A plate and a first positive A plate configured to be disposed between the polarizing plate and the liquid crystal panel; An analyzer configured on the upper portion of the liquid crystal panel; And a second positive A plate and a second negative A plate, which are configured to be different from each other between the detector plate and the liquid crystal panel.

The reflective liquid crystal panel includes: a first substrate including a thin film transistor array unit, a reflective electrode, and a transmission electrode; A second substrate spaced apart from the first substrate and configured with a color filter and a common electrode; And a liquid crystal layer formed on the first and second substrates.

The first positive A plate and the first negative A plate are configured to have the same optical axis of 45 degrees, and the second positive A plate and the second negative A plate are configured to have the same optical axis of 135 degrees.

The analyzer and the polarizing plate are configured such that the optical axes are perpendicular to each other at 0 degrees and 90 degrees, respectively, and when the first positive A plate is configured on the first negative A plate, the second positive A plate is The lower portion of the second negative A plate is characterized in that.

Example

5 is a perspective view showing a compensation film according to the present invention.

As shown, the form of the compensation film proposed in the present invention is characterized in that the positive A plate (positive A plate, 202) and negative A plate (negative A plate, 204) is laminated.

The linearly polarized light passing through the lower polarizing plate 200 passes through the positive A plate 202 and the negative A plate 204 to correspond to the blue area B, the green area G, and the red area R. Due to the phase value that the light senses, the polarization characteristic of the light can be displayed in a similar form at the front and the periphery, and thus, the same color can be obtained at a wide viewing angle range.

In general, the positive A plate 202 is manufactured in a stretching manner (produced by stretching uniaxially), and the negative A plate 204 has a structure in which discotic liquid crystals (distoic liquid crystals) are disposed on the film surface.

In this case, the refractive index Δn of the positive A plate 202 has a value of Δn> 0. In contrast, the refractive index Δn of the negative A plate 204 has a value of Δn <0.

The present invention is characterized in that the positive A plate 202 and the negative A plate 204 having such refractive index characteristics are configured such that the optical axes are parallel to each other, in which case the light passing through the two films 202 and 204 Since the phase difference felt can be represented by the difference between the absolute values of the phase values of the two films, the change in the phase value according to the wavelength shows a different characteristic from that in the case of using the films, respectively.

Hereinafter, FIG. 6 is a graph showing a relationship between wavelength retardation values for each of the positive A plate and the negative A plate.

As shown, each of the positive A plate and the negative A plate tends to have a smaller phase value perceived by light as the wavelength increases.

In particular, in the case of the negative A plate, since the change in refractive index is larger than that of the positive A plate, the decrease in the retardation value according to the wavelength tends to increase.

As such, when the wavelength increases, the phase value decreases, for example, light of the blue wavelength and the red wavelength is changed to be closer to the elliptical polarized light rather than the circularly polarized light.

In such a case, the contrast is reduced.

Therefore, when the negative A plate and the positive A plate are used at the same time, as described above, the phase value for each wavelength is different from that of FIG. 7 because the phase value for each wavelength appears as a difference between the absolute values of the phase values of each film. Will be shown.

7 is a graph illustrating retardation values according to wavelengths when a double film of a negative A plate and a positive A plate according to the present invention is used.

As shown, when the positive A plate and the negative A plate are used together, the overall phase value dΔn can be obtained as follows.

Total phase value (dΔn) = [ _dΔn ] _posi + [ _dΔn ] _nega

That is, as shown, the larger the wavelength value, the larger the phase value can be obtained.

For example, when applied to the λ / 4 plate (QWP), it has to have a phase value of 112nm, 137nm, 163nm in the red, green, blue region (R, G, B) to convert the circular polarization.

Therefore, by configuring the negative A plate and the positive A plate, the above tendency can be obtained, so that the viewing angle compensation is performed at the outside of the panel, thereby obtaining the characteristic of widening the viewing angle.

An optical compensation film having such characteristics can be applied to a reflective liquid crystal display device and a reflective transmissive liquid crystal display device, and in particular, when applied to a reflective transmissive liquid crystal display device having both the reflective characteristic and the transmissive characteristic, the luminance is improved and the viewing angle is improved. There is an advantage that can be obtained at the same time.

8 is a perspective view schematically showing a transflective liquid crystal display, and FIG. 9 is a perspective view schematically showing a transflective liquid crystal display including the optical film according to the present invention.

8 is a cross-sectional view schematically showing the configuration of a reflective liquid crystal display device according to the present invention. (Structure without Optical Film)

As illustrated, the reflective liquid crystal panel 99 is spaced apart from the first substrate 100 including the thin film transistor array unit and the second substrate 118 including the color filter 114 with the liquid crystal layer 108 therebetween. Configure.

The first substrate 100 includes a gate line 102 extending in one direction and a data line 120 crossing the vertical line and defining a pixel area P with the gate line 102. Configure.

The thin film transistor T including the gate electrode 124, the active layer 126, the source electrode 128, and the drain electrode 130 is formed at the intersection point of the gate line 102 and the data line 120.

The pixel area P is defined as a transmissive portion D and a reflective portion B, and forms a transparent electrode 106 corresponding to the transmissive portion D and a reflective electrode corresponding to the reflective portion B. Configure 104.

Accordingly, the reflecting unit B operates in the reflective mode, and the transmitting unit D operates in the transmissive mode.

With reference to the above-described configuration, the configuration of the reflective liquid crystal display device including the optical film proposed in the present invention will be described.

FIG. 9 is an exploded perspective view schematically illustrating a configuration of a reflective liquid crystal display device including an optical film having the above characteristics. (The liquid crystal panel shows only the reflective and transmissive portions and the liquid crystal layer according to one pixel.)

As shown, the reflective liquid crystal display device 300 according to the present invention has a polarizing plate 410 and a first positive A plate from the bottom with respect to the substrate 310 defined by the reflective and transmissive portions B and D. 412 and the first negative A plate 412, and the second negative A plate 414, the second positive A plate 416, and the detector plate 418 are stacked on the substrate 310. It is characterized by one configuration.

In this case, the first positive and the first negative A plates 412 and 414 configured below have an optical axis of 45 degrees, and the second negative and the second positive A plates 416 and 418 are configured to have an optical axis of 135 degrees. .

In addition, the polarizing plate 410 and the detector plate 220 are configured to have an optical axis of 0 degrees and 90 degrees, respectively, so that the optical axes are perpendicular to each other.

When the optical film is designed in the reflective transmissive liquid crystal display device, the design is performed based on the reflecting part. Accordingly, the separate optical film is designed as a compensation concept in order to minimize the influence on the transmissive part.

That is, since the second negative and the second positive A plates 416 and 418 are for polarization characteristics of light passing through the reflecting portion B, the first positive and lower portions of the second positive and second positive A plates 416 and 418 are compensated for corresponding to the transmitting portion D. The first negative A plates 412 and 414 are further configured.

Therefore, the optical axes of the first positive and first negative A plates 412 and 414 and the second negative and positive A plates 416 and 418 are perpendicular to each other so that the light passing through the transmission part D and the reflecting part The polarization characteristics of the reflected light can be equally obtained.

In this case, the stacking order of the first positive and the first negative A plates 412 and 414 may be changed, and the second negative and the second positive A may be changed according to the stacking order of the first positive and the first negative A plates 412 and 414. The plates 416 and 418 may be configured.

That is, when the first negative A plate 414 is directly formed under the liquid crystal panels 310 and 320, the second negative A plate 416 configured as the optical axis perpendicular to the upper part of the liquid crystal panels 310 and 320 may be configured. .

As described above, when the optical film according to the present invention is applied to the reflective transmissive liquid crystal display device, the contrast can be improved and the view angle can be further widened.

The reflective liquid crystal display device according to the present invention as described above uses a negative A plate and a positive A plate as a compensation film, and thus has an effect of improving contrast and viewing angle.

Claims (5)

A reflective transmissive liquid crystal panel; A polarizing plate formed under the liquid crystal panel; A first negative A plate and a first positive A plate configured to be disposed between the polarizing plate and the liquid crystal panel; An analyzer configured on the upper portion of the liquid crystal panel; A second positive A plate and a second negative A plate configured to be different from each other between the detector plate and the liquid crystal panel; / RTI &gt; And a phase value of each of the first negative and positive A plates formed up and down and the second positive and negative A plates formed up and down increases as the wavelength increases. The method of claim 1, The reflective transparent liquid crystal panel A first substrate including a thin film transistor array unit, a reflective electrode, and a transparent electrode; A second substrate spaced apart from the first substrate and configured with a color filter and a common electrode; And a liquid crystal layer formed on the first and second substrates. The method of claim 1, The first positive A plate and the first negative A plate are configured to have the same optical axis of 45 degrees, and the second positive A plate and the second negative A plate are configured to have the same optical axis of 135 degrees. Device. The method of claim 1, And the detector plate and the polarizer plate are configured such that optical axes are perpendicular to each other at 0 degrees and 90 degrees, respectively. The method of claim 1, And when the first positive A plate is formed on the first negative A plate, the second positive A plate is formed on the lower part of the second negative A plate.

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