KR100886865B1 - Reflective type liquid crystal display - Google Patents

Abstract

The present invention discloses a reflective liquid crystal display device, and in the disclosed reflective liquid crystal display device, a lower substrate having a reflective electrode and a lower alignment layer, and an upper substrate having a color filter and an upper alignment layer are disposed under the liquid crystal layer. On the opposite side of the upper substrate, a phase film for converting linearly polarized light into circularly polarized light is attached, and a reflective liquid crystal display device having a polarizing plate for converting natural light incident from the outside into linearly polarized light on the phase film. The phase delay value (dΔn) of the liquid crystal layer is 0.24 to 0.27 μm, the phase film has a λ / 4 phase compensation function and has an optical axis of 140 to 146 °, and the alignment angle of the upper alignment layer is in a horizontal line. 40 to 55 degrees, and the alignment angle of the lower alignment layer is -10 to 20 degrees with respect to the horizontal line, and the transmission axis of the polarizing plate is 102 to 122.5 degrees, wherein the liquid crystal layer is It consists of twisted nematic liquid crystals with a twist angle of 60 °. According to the present invention, the process margin of the cell gap can be improved by appropriately changing the parameters of the components while increasing the cell gap, and the contrast and the color characteristics can be improved.

Description

Reflective Liquid Crystal Display {REFLECTIVE TYPE LIQUID CRYSTAL DISPLAY}

1 is a cross-sectional view schematically showing a conventional reflective liquid crystal display device.

2 is a graph illustrating a twist angle and a phase delay value of a reflective liquid crystal display device according to the present invention;

3 is a view showing an axial arrangement of each component in the reflective liquid crystal display device according to the present invention.

4 to 6 are graphs for explaining reflectance characteristics according to voltage of a reflective liquid crystal display device according to the present invention;

Explanation of symbols on the main parts of the drawings

1: lower substrate 2: reflective electrode

3: lower alignment layer 4: upper substrate

5: color filter 6: upper alignment layer

7: phase film 8: polarizing plate

10: liquid crystal layer

The present invention relates to a reflective liquid crystal display device, and more particularly, to a reflective liquid crystal display device in which a cell gap margin is increased while improving a reflectance and contrast ratio by optimizing a characteristic parameter.

Reflective liquid crystal display devices that do not require a backlight are useful for portable display devices because they can achieve low power consumption, thinness, and light weight, and their demands are gradually increasing as the market of mobile phones and portable devices expands.

Such a reflective liquid crystal display device includes a lower substrate, a reflective electrode, a lower alignment layer, a liquid crystal layer, an upper alignment layer, an upper transparent electrode, an upper substrate, a phase film, and a polarizing plate. Have

In addition, the phase of the liquid crystal used in the reflective liquid crystal display device is nematic (nematic) and the like, in the liquid crystal molecule array, all the liquid crystal molecules are arranged almost parallel to both substrate surfaces, the arrangement orientation Is continuously twisted at a predetermined angle.

The display implementation according to the optical properties of the reflective liquid crystal display device is as follows.

When no voltage is applied, the linearly polarized light passing through the polarizing plate passes through the phase film and becomes circularly polarized light, for example, left circularly polarized light, which is converted into linearly polarized light while passing through the liquid crystal layer and reflected by the reflective electrode. The reflected linearly polarized light changes to left circularly polarized light while passing through the liquid crystal layer, and then passes through the phase film, and the polarization direction is transformed into linearly polarized light parallel to the polarization axis of the polarizing plate and passes through the polarizing plate, whereby the state of white Is implemented.                         

When voltage is applied, the light converted to the left circularly polarized light through the polarizing plate and the phase film passes through the liquid crystal layer as it is without any change and is reflected by the reflective electrode to the right circularly polarized light. It is deformed into linearly polarized light perpendicular to the polarization axis of, and thus cannot pass through the polarizing plate, thereby implementing a dark state.

On the other hand, in such a reflective liquid crystal display device, a good display screen depends on how to optimize the characteristic values of each component. That is, in order to effectively increase the reflectance in the reflective liquid crystal display device, the transmission axis angle of the polarizing plate, the optical characteristics of the phase film, the thickness of the liquid crystal layer (d), the phase delay value (dΔn) of the liquid crystal layer, the twist angle of the liquid crystal, and the alignment film The orientation angle of, the characteristics of the reflector and the like should be optimized.

Hereinafter, a cell configuration of a conventional reflective liquid crystal display device for implementing a good display screen will be described.

1 is a cross-sectional view schematically showing a conventional reflective liquid crystal display device. As shown in the drawing, a reflective liquid crystal display device includes a lower substrate 1 and a color having a reflective electrode 2 and a lower alignment layer 3. The upper substrate 4 having the filter 5 and the upper alignment layer 6 is disposed opposite to the liquid crystal layer 10, and on the outer surface of the upper substrate 4, a phase film, i. The λ / 4 film 7, which is a uniaxial film for optical compensation having a phase difference of / 4, and the polarizing plate 8 are sequentially attached.

Here, the reflective electrode 2 has surface irregularities through a lithography method or a holography method.                         

In such a reflective liquid crystal display device, in order to obtain a good display screen, one or two λ / 4 films 7 may be applied to a 90 ° TN cell, and the alignment angle of the upper alignment layer 6 is lower than the lower alignment layer ( 3) to form an orientation angle of 90 °, and the transmission axis of the polarizing plate 8 forms an angle of orientation of the upper alignment layer 6 to 20 ° and an angle of 45 ° to the optical axis angle of the λ / 4 film 7.

The twist angle of the liquid crystal may be 63 °, and in this case, the phase delay value of the liquid crystal layer 10 has a thickness of about 0.20 μm when the thickness thereof is 2.94 μm.

In addition, the twist angle of the liquid crystal can be made to be 65 to 75 °, in this case, the phase delay value of the liquid crystal layer 10 is about 0.20 ~ 0.28㎛.

In addition, the twist angle of the liquid crystal is 60 ° while the phase delay value of the liquid crystal layer 10 is about 0.193 μm when the thickness thereof is 0.344 μm, and the alignment angle of the upper alignment layer 5 is the polarizing plate 8. ), And make 30 ° with the transmission axis.

In addition, the twist angles of the liquid crystals are 63.6 °, 70 °, 80 °, and 53 °, respectively, and the phase delay values of the liquid crystal layer 10 are about 0.192 μm, 0.278 μm, 0.272 μm, and 0.525 μm, respectively, and The orientation angles of the upper alignment layer 5 are 0 °, 20 °, 20 ° and 0 ° with the transmission axis of the polarizing plate 8, respectively.

As a result, the conventional reflective liquid crystal display device adjusts the phase delay value of the liquid crystal layer to 0.45 to 0.53 mu m and the twist angle of the liquid crystal to about 53 to 60 degrees without using a phase film, or uses a phase film. A good display screen is obtained by adjusting the phase delay value of the liquid crystal layer to 0.20 to 0.27 mu m and the twist angle of the liquid crystal to about 63 to 80 degrees.

However, in the conventional reflective liquid crystal display device, the use of two λ / 4 films to reduce the reflectance is caused to optimize the cell design, while when using one λ / 4 film, the λ over a wide range of visible light wavelengths Since the function of giving a phase difference of / 4 cannot be properly performed, there is a problem in that display characteristics are not good.

In addition, the conventional reflective liquid crystal display device has a low cell gap, and thus has a problem in that yield is lowered in the actual process.

Accordingly, an object of the present invention is to provide a reflective liquid crystal display device having a high contrast ratio, good color characteristics, and improved process margin of a cell gap.

In order to achieve the above object, in the present invention, a lower substrate having a reflective electrode and a lower alignment layer, and an upper substrate having a color filter and an upper alignment layer are disposed to face each other under the liquid crystal layer, and an outer surface of the upper substrate. In a reflective liquid crystal display device having a phase film for converting linearly polarized light into circularly polarized light and a polarizing plate for converting natural light incident from the outside into linearly polarized light on the phase film, the phase delay value of the liquid crystal layer is 0.24 to 0.27㎛, the phase film has a lambda / 4 phase compensation function, the optical axis is 140 ~ 146 °, the alignment angle of the upper alignment layer is 40 to 55 degrees with respect to the horizontal line, the alignment angle of the lower alignment layer Is -10 to 20 degrees with respect to the horizontal line, and the transmission axis of the polarizing plate is 102 to 122.5 degrees, it provides a reflective liquid crystal display device.                     

Here, preferably, the liquid crystal layer is composed of twisted nematic liquid crystals having a twist angle of 60 °.

In addition, in the present invention, a lower substrate having a reflective electrode and a lower alignment layer and an upper substrate having a color filter and an upper alignment layer are disposed to face each other under a liquid crystal layer, and linearly polarize the linearly polarized light on the outer surface of the upper substrate. A reflective liquid crystal display device having a phase film for converting and a polarizing plate for converting natural light incident from the outside into linearly polarized light on the phase film, wherein the phase delay value of the liquid crystal layer is 0.23 to 0.27 μm. The retardation film has a λ / 4 phase compensation function and has an optical axis of 160 to 168 °, the alignment angle of the upper alignment layer is 55 to 65 degrees with respect to the horizontal line, and the alignment angle of the lower alignment layer is 0 to with respect to the horizontal line. 10 degrees, and the transmission axis of the said polarizing plate is 117.5-127.5 degrees, The reflection type liquid crystal display device is provided.

Here, the liquid crystal layer is composed of twisted nematic liquid crystals having a twist angle of 76 °.

Furthermore, in the present invention, a lower substrate having a reflective electrode and a lower alignment layer and an upper substrate having a color filter and an upper alignment layer are disposed to face each other under the liquid crystal layer, and linearly polarize the linearly polarized light on the outer surface of the upper substrate. A reflective liquid crystal display device having a phase film for converting and a polarizing plate for converting natural light incident from the outside into linearly polarized light on the phase film, wherein the phase delay value of the liquid crystal layer is 0.17 to 0.21 μm. The retardation film has a lambda / 4 phase compensation function and has an optical axis of 135 to 145 °, the alignment angle of the upper alignment layer is 50 to 56 degrees with respect to the horizontal line, and the alignment angle of the lower alignment layer is 0 to with respect to the horizontal line. 10 degrees, and the transmission axis of the said polarizing plate is 62-66 degrees, The reflection type liquid crystal display device is provided.

Here, preferably, the liquid crystal layer is composed of twisted nematic liquid crystals having a twist angle of 53 °.

According to the present invention, the process margin of the cell gap can be improved by appropriately changing the parameters of the components while increasing the cell gap, and the contrast and the color characteristics can be improved.

(Example)

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

In the reflective LCD according to the present invention, the lower substrate having the reflective electrode having the surface irregularities and the lower alignment layer and the upper substrate having the color filter and the upper alignment layer are disposed to face each other under the liquid crystal layer. A phase film for converting linearly polarized light into circularly polarized light is attached on the outer surface of the upper substrate, and a polarizing plate for converting natural light incident from the outside into linearly polarized light is attached to the phase film.

In addition, the reflective liquid crystal display device of the present invention achieves an optimal cell configuration that can realize a good display screen by combining the changed parameter values of each component while changing the parameters of the components different from the conventional ones.

Here, the upper and lower substrates have the same thickness and refractive index of 0.4 to 0.7t and 1.5, respectively, the counter electrode thickness and the refractive index of the upper substrate are 1500Å and 1.7, and the thickness and refractive index of the upper alignment layer are 750Å and 1.6, respectively. The thickness of the reflecting electrode made of AlNd material is about 1500 mW.

In addition, the upper and lower alignment layer is made of a polyamic acid series considering the affinity with the liquid crystal and the adhesion of the substrate in order to align the liquid crystal molecules more effectively.

In addition, one sheet of the phase film is used, and uniaxially stretches a polymer film such as polycarbonate, polyvinylachole, and polystyrene to have a specific phase difference.

Parameters for constituting the optimal cell include the transmission axis angle of the polarizing plate, the optical axis angle of the two birefringent films constituting the λ / 4 film, the phase delay value of the liquid crystal layer and the orientation angle of the alignment film, and the like. The optical experiments were carried out with the conditions, the transmission axis angle of the polarizer, the phase delay value of the liquid crystal layer, and the alignment angle of the alignment layer. The characteristic values of the components that can form an optimal cell are as follows.

[Experiment 1]

When the twisted nematic liquid crystal, the twist angle of the liquid crystal is 60 degrees, and the phase delay value of the liquid crystal is 0.24 to 0.27 µm, a reflective liquid crystal display device having a high cell gap margin and excellent contrast ratio and color characteristics is obtained. Lose.

At this time, the optical axis of the λ / 4 film is 140 ~ 146 °, the alignment angle of the upper alignment layer is 40 to 55 ° with respect to the horizontal line, the alignment angle of the lower alignment layer is -10 to 20 ° with respect to the horizontal line, and the transmission of the polarizing plate The axis is 102-122.5 degrees.                     

[Experiment 2]

When the twisted nematic liquid crystal, the twist angle of the liquid crystal is 76 degrees, and the phase delay value of the liquid crystal is 0.23 to 0.27 占 퐉, a reflective liquid crystal display device having a high cell gap margin and excellent contrast ratio and color characteristics is obtained. Lose.

At this time, the optical axis of the λ / 4 film is 160 ~ 168 °, the alignment angle of the upper alignment layer is 55 to 65 ° with respect to the horizontal line, the alignment angle of the lower alignment layer is 0 to 10 ° with respect to the horizontal line, and the transmission axis of the polarizing plate is 117-127.5 degrees.

[Experiment 3]

When the twisted nematic liquid crystal, the twist angle of the liquid crystal is 53 degrees, and the phase delay value of the liquid crystal is 0.17 to 0.21 µm, a reflective liquid crystal display device having a high cell gap margin and excellent contrast ratio and color characteristics is obtained. Lose.

At this time, the optical axis of the λ / 4 film is 135 ~ 145 °, the alignment angle of the upper alignment layer is 50 to 56 ° with respect to the horizontal line, the alignment angle of the lower alignment layer is 0 to 10 ° with respect to the horizontal line, and the transmission axis of the polarizing plate is 62-66 degrees.

As a result, the reflective liquid crystal display of the present invention, as shown in Figure 2, the phase delay value of the liquid crystal layer and the twist angle of the liquid crystal is in the middle of the range of values (A, B) designed to realize a conventional good display screen By designing to have a range (C) of values corresponding to the degree, it is possible to have a better contrast ratio and color characteristics, and in particular, to improve the process margin with respect to the cell gap can be increased than before.

On the other hand, in the above experiments 1 to 3, the angle between the orientation angle of the upper alignment film and the transmission axis of the polarizing plate is 28 to 32 ° when the twist angle of the liquid crystal is 60 °, and the twist angle of the liquid crystal is 76 ° Are designed at 31.5 to 37.5 °.

3 is a diagram showing the arrangement of the axes of the components of the reflective LCD according to the present invention, wherein a is a rubbing axis of a lower substrate, b is a rubbing axis of an upper substrate, and c is a λ / 4 film. D represents the transmission axis of the polarizing plate, respectively.

4 to 6 are graphs for describing reflectance characteristics according to voltage in a reflective liquid crystal display device according to the present invention, wherein FIG. 4 is a graph showing reflectance according to voltage of a Japanese Matsushita reflective liquid crystal display device. 5 and 6 are graphs showing reflectance with respect to voltage in the reflective liquid crystal display according to the present invention, wherein the twist angles of the liquid crystals are 60 ° and 70 °.

As shown in FIG. 4, while the reflective liquid crystal display of Matsushita Corporation does not form a complete dark when voltage is applied, as shown in FIGS. 5 and 6, the reflective liquid crystal display according to the present invention is shown. Is in a dark state when voltage is applied, and therefore, it can be seen that the reflection type liquid crystal display device of the present invention has better reflectance characteristics according to voltage than that of Matsushita Corporation.

In addition, the liquid crystal display according to the present invention can lower the driving voltage at the same level of contrast ratio.

In conclusion, the conventional reflective liquid crystal display device has a liquid crystal twist angle of 70 °, a phase delay value of 0.24 μm, a cell gap of about 3.53 μm, or a liquid crystal twist angle of 63 °, and a phase delay value of 0.20. While the cell gap is designed to be about 2.94 μm while the reflective liquid crystal display device according to the present invention is designed by displaying the cell gap at 3.6 μm while the twist angle of the liquid crystal is 76 ° and the phase delay value of the liquid crystal layer is 0.25 μm. The properties can be improved as well as facilitate their application in actual processes.

As described above, the present invention can increase the contrast ratio and color characteristics by optimizing the design of the liquid crystal cell, thereby increasing the reflectance according to the voltage, and therefore, it is possible to provide a reflective liquid crystal display device having an excellent display screen.

In addition, the present invention can increase the process margin by increasing the cell gap than that of the conventional, thereby improving the productivity.

In addition, this invention can be implemented in various changes within the range which does not deviate from the summary.

Claims (6)

A lower substrate having a reflective electrode and a lower alignment layer, and an upper substrate having a color filter and an upper alignment layer are disposed to face each other under the liquid crystal layer, and a phase film for converting linearly polarized light into circular polarization is attached on the outer surface of the upper substrate. In the reflective liquid crystal display device with a polarizing plate for converting the natural light incident from the outside on the phase film to linearly polarized light, The phase delay value dΔn of the liquid crystal layer is 0.24 to 0.27 μm, The retardation film has a lambda / 4 phase compensation function and the optical axis is 140 ~ 146 °, The alignment angle of the upper alignment layer is 40 to 55 degrees with respect to the horizontal line, The alignment angle of the lower alignment layer is -10 to 20 ° with respect to the horizontal line, The transmission axis of said polarizing plate is 102-122.5 degrees, The reflection type liquid crystal display device characterized by the above-mentioned. The reflective liquid crystal display of claim 1, wherein the liquid crystal layer is made of twisted nematic liquid crystals having a twist angle of 60 degrees. delete delete A lower substrate having a reflective electrode and a lower alignment layer, and an upper substrate having a color filter and an upper alignment layer are disposed to face each other under the liquid crystal layer, and a phase film for converting linearly polarized light into circular polarization is attached on the outer surface of the upper substrate. In the reflective liquid crystal display device with a polarizing plate for converting the natural light incident from the outside on the phase film to linearly polarized light, The phase delay value dΔn of the liquid crystal layer is 0.17 to 0.21 μm, The retardation film has a lambda / 4 phase compensation function and the optical axis is 135 ~ 145 °, The alignment angle of the upper alignment layer is 50 to 56 degrees with respect to the horizontal line, The alignment angle of the lower alignment layer is 0 to 10 ° with respect to the horizontal line, A reflection type liquid crystal display device, wherein the transmission axis of the polarizing plate is 62 to 66 degrees. The liquid crystal display of claim 5, wherein the liquid crystal layer is made of twisted nematic liquid crystals having a twist angle of 53 degrees.

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