KR20100053801A - Reflection-type liquid crystal display device - Google Patents

Abstract

PURPOSE: A reflective liquid crystal display device is provided to implement an optimized reflection rate and improve a front-view angle by optimally designing a cell layout. CONSTITUTION: To make a twist angle of an LCD layer be 68-72 degree, an orientation axis of a lower alignment film is angled at 247-253 degree from a horizontal line and the orientation axis of an upper alignment film is angled at -5 to 5 degree from the horizontal line. A penetration axis of a polarized plate maintains 165-175 degrees. A phase delay value of the LCD is 0.21-0.24 micrometers.

Description

Reflective Liquid Crystal Display Device

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflective liquid crystal display device, and more particularly, to a reflective liquid crystal display device which can prevent a phenomenon in which a reflectance decrease is delayed when voltage is applied by optimizing a cell configuration.

In general, the reflection type liquid crystal display device is a liquid crystal display device of a type that does not require a separate light source is provided to reflect the light introduced to the reflector provided in the liquid crystal display device using the incident light introduced from the outside as a display light source. Accordingly, low power consumption can be driven and a thin film can be realized.

Such a reflective liquid crystal display device includes a lower substrate, a reflective plate, a lower alignment layer, a liquid crystal layer, an upper alignment layer, an upper substrate, a retardation plate, a polarizing plate, and the like.

The lower substrate and the upper substrate are spaced apart at regular intervals to face each other, and the liquid crystal is interposed between the upper substrate and the lower substrate.

In addition, the liquid crystal included in the liquid crystal layer is a twisted nematic liquid crystal, and the phase of the liquid crystal is nematic among the types of nematic and cholesteric, and the molecular arrangement of the liquid crystal in the nematic is Homogeneous, homeotropic, hybrid, twisted, and the like.

In the twisted liquid crystal molecular array, all liquid crystal molecules are arranged almost parallel to both substrate surfaces, but the orientation of the liquid crystal molecules is twisted at a constant angle. Therefore, the alignment orientation of the twisted liquid crystal molecules is a form in which the twisted liquid crystal molecules are continuously twisted and arranged between the two substrates.

The display implementation by the optical property of such a twisted nematic liquid crystal (hereinafter referred to as "TN mode") is as follows.

When no voltage is applied, the linearly polarized light passing through the polarizer passes through the retardation plate and changes into circularly polarized light (assuming left circularly polarized light). This light passes through the liquid crystal layer and changes into linearly polarized light and is reflected by the reflective layer. The light reflected from the reflective layer passes through the liquid crystal layer to be converted into left circularly polarized light, passes through the birefringent layer, and the polarization direction is transformed into linearly polarized light parallel to the polarization axis of the polarizer.

On the other hand, when voltage is applied, linearly polarized light passing through the polarizing plate passes through the retardation plate to change into circularly polarized light (left circularly polarized light). This light passes through the liquid crystal layer without any change, is reflected by the reflective layer, and converted into right circularly polarized light. This light passes again through the liquid crystal layer and the retardation plate to be blocked by being linearly polarized with the polarization direction perpendicular to the polarization axis of the polarizer.

The image implementation of such a reflective liquid crystal display device depends largely on how to optimize parameter values. The parameter may be a twist angle and a phase delay value of the liquid crystal, a transmission axis angle of the polarizing plate, an optical structure and a phase delay value of the retardation plate, an alignment angle of the upper and lower alignment layers, and the like.

1 is a liquid crystal display device of a conventional 90 ° TN mode disclosed in Republic of Korea Patent No. 0417918. Referring to FIG. 1, in the conventional 90 ° TN mode reflective liquid crystal display device 100, the liquid crystal layer 130 is interposed between the lower substrate 110 and the upper substrate 120 that are disposed to face each other. The reflective plate 111 and the lower alignment layer 112 are sequentially formed on the upper portion 110. In addition, an upper alignment layer 121 is formed below the upper substrate 120, and a retardation plate 122 and a polarizer 123 are sequentially formed on the upper substrate 120.

At this time, although not shown, a TFT may be formed between the lower substrate 110 and the reflective plate 111, and a color filter is formed between the upper substrate 120 and the upper alignment layer 121, and the lower alignment layer 112 and the lower alignment layer 112 are formed. The upper alignment layer 121 is rubbed to align the liquid crystal of the liquid crystal layer 130 at a predetermined angle.

Here, the retardation plate 122 is composed of two uniaxial films, the upper film 122a and the lower film 122b.

That is, the cell configuration of the reflection type liquid crystal display device 100 in the 90 ° TN mode uses a liquid crystal mode twisted at 90 °, and the light transmission axis of the polarizing plate is 90 ° in the phase difference plate 122 composed of two sheets. The upper film 122a has a birefringence value of 270nm optical axis angle of 107.5 °, the lower film 122b has a birefringence 140nm optical axis angle of 170 °, and the alignment angle of the upper alignment layer 121 is configured to be 90 ° with the alignment angle of the lower alignment layer 112. It was.

However, the above-described reflective liquid crystal display device of 90 ° TN mode converts the incident light by configuring the phase difference plate 122 in two pieces, but scattering or diffraction of the light occurs, and thus the incident light is not converted. Since the retardation plate is configured, there are many problems in manufacturing cost and number of processes.

Accordingly, the present applicant has proposed a reflective liquid crystal display of 60 ° TN mode in which the retardation plate is composed of one sheet in Korean Patent Laid-Open Publication No. 2004-0012199.

2 is a reflection type liquid crystal display device of 60 ° TN mode. 2, the lower substrate 210, the reflecting plate 211, the lower alignment layer 212, the liquid crystal layer 230, the upper alignment layer 221, the upper substrate 220, the retardation plate 222, and the polarizing plate 223. )

Here, the reflective liquid crystal display device 200 in the 60 ° TN mode is composed of one phase difference plate as compared with the above-described reflective liquid crystal display device in the 90 ° TN mode, and constitutes a cell structure. The parameters are as follows:

The phase delay value of the liquid crystal layer 230 is 0.24 μm to 0.27 μm, the optical axis angle of the retardation plate is 140 ° to 146 °, the alignment angle of the upper alignment layer is 40 ° to 55 °, and the alignment angle of the lower alignment layer is −. The transmission axis of 10 degrees-20 degrees and a polarizing plate consisted of 102 degrees-122.5 degrees.

In this way, even when one retardation plate was used, the viewing angle could be further secured as compared with the conventional 90 ° TN mode reflective liquid crystal display device.

On the other hand, the reflective liquid crystal display device 200 of the 60 ° TN mode described above is reduced in the reflectance of the light reflected by the reflecting plate when voltage is applied to gradually convert from white (white) to gray to dark (dark) do.

However, the above-described cell configuration of the reflective liquid crystal display 200 in the 60 ° TN mode has a problem in that a reflectance delay phenomenon occurs in which the reflectance does not decrease immediately after the voltage is applied. There was a narrowing problem.

For this reason, there is a problem in that the gray scale range is reduced according to the application of voltage and the quality of the screen is reduced.

Accordingly, an object of the present invention is to solve such a conventional problem, and to provide a reflective liquid crystal display device that can realize an optimal reflectance according to an improvement in frontal viewing angle and voltage application by optimizing the design of a cell configuration. Is in.

In addition, it is possible to improve the quality of the screen by implementing the optimal reflectance, and to provide a reflective liquid crystal display device that can reduce the power consumption.

The object is that, according to the present invention, a lower substrate having a reflecting plate and a lower alignment layer and an upper substrate having a color filter and an upper alignment layer are arranged under the interposition of the liquid crystal layer, and the linear polarization is applied on the outer surface of the upper substrate. A reflection type liquid crystal display device having a polarizing plate attached to convert a circularly polarized light into linearly polarized light by polarized light and converting natural light incident from the outside into linearly polarized light on the phase difference plate, wherein the twist angle of the liquid crystal of the liquid crystal layer The angle of the orientation axis of the lower alignment layer is any one of 247 ° to 253 ° with respect to the horizontal line so that the angle of the orientation of the upper alignment layer is -5 ° with respect to the horizontal line so that it may be any one of 68 ° to 72 °. It is any one of 5 °, the transmission axis angle of the polarizing plate is any one of 165 ° to 175 °, the optical axis angle of the retardation plate and the transmission axis angle of the polarizing plate Any one of 118 ° to 132 ° to form 43 ° to 47 °, the phase delay value dΔn is any one of 137 nm to 159 nm, and the phase delay value dΔn of the liquid crystal is any one of 0.21 μm to 0.24 μm. It is achieved by a reflective liquid crystal display device which is one twisted nematic liquid crystal.

Here, the retardation plate preferably has a refractive index of nx, ny, nz satisfying nx = ny> nz.

In addition, the reflector is preferably formed in an embossing shape so as to reflect the incident light.

According to the present invention, there is provided a reflective liquid crystal display device capable of optimizing the design of a cell configuration to realize an improvement in frontal viewing angle and optimal reflectance according to voltage application.

In addition, the reflection type liquid crystal display device capable of improving the quality of the screen and reducing power consumption by implementing the optimal reflectance is provided.

Prior to the description, in the various embodiments, components having the same configuration will be representatively described in the first embodiment using the same reference numerals, and in other embodiments, different configurations from the first embodiment will be described. do.

Hereinafter, a reflective liquid crystal display device according to a first embodiment of the present invention will be described in detail with reference to the accompanying drawings.

3 is a schematic diagram of a reflective liquid crystal display device according to a first embodiment of the present invention. Referring to FIG. 3, the reflective liquid crystal display device A according to the first embodiment of the present invention may include a lower substrate 10, an upper substrate 20, and a liquid crystal layer 30. Here, the lower substrate 10 and the upper substrate 20 may be a glass substrate.

In addition, the reflective plate 11 and the lower alignment layer 12 may be sequentially stacked on the lower substrate 10. At this time, although not shown, a gate line, a data line, and a plurality of electrodes may be formed between the lower substrate 10 and the reflector 11 to define a thin film transistor and a pixel region for driving the liquid crystal.

The reflector 11 may be made of metal such as aluminum to increase reflectance, and may be embossed to reflect light incident from the liquid crystal layer 30 to be described later. .

The lower alignment layer 12 may be a polyimide-based or polyvinyl acetate resin in consideration of heat resistance, affinity with liquid crystals, adhesion to a substrate, and the like, as a means for effectively aligning liquid crystal molecules. have. In addition, the lower alignment layer 12 may be rubbed to align the liquid crystal molecules in a predetermined direction by a predetermined means or method.

Next, an upper alignment layer 21 may be formed below the upper substrate 20, and a retardation plate 22 and a polarizer 23 may be sequentially stacked on the upper substrate 20. At this time, although not shown, a color filter of any one of red, green, and blue may be formed between the upper substrate 20 and the upper alignment layer 21 to combine the colors of the respective pixels. .

The upper alignment layer 21 may be formed of a material corresponding to the lower alignment layer 12 described above, and may be rubbed to align the liquid crystal in a predetermined direction like the lower alignment layer 12.

The retardation plate 22 is a λ / 4 phase difference plate for converting linearly polarized light into circularly polarized light. The retardation plate 22 may be a polymer film such as polycarbonate, poly vinyl alcohol, and poly styrene. It is formed to have a specific phase difference by uniaxial stretching.

Here, it is preferable that the refractive index of the retardation plate 22 satisfy the refractive index nx, ny, nz as nx = ny> nz, as shown in FIG. That is, it is preferable that the refractive indices nx and ny of the two horizontal axes are the same, and the refractive index nz of the vertical axis has a value smaller than the refractive indices nx and ny of the horizontal axis. Meanwhile, the retardation plate 22 and the polarizing plate 23 may be integrally formed.

In addition, the polarizer 23 is a means for converting natural light incident from the outside into linearly polarized light, the liquid crystal of the liquid crystal layer 30 may be a twisted nematic liquid crystal.

The display implementation by the optical properties of the reflective liquid crystal display device A according to the first embodiment of the present invention configured as described above is as follows. 4 and 5 are light transmission diagrams of a reflective liquid crystal display device according to a first embodiment of the present invention.

Referring to FIG. 4, when no voltage is applied, light passing through the polarizing plate 23 is linearly polarized, and the linearly polarized light passes through the phase difference plate 22 and is converted into circularly polarized left circularly polarized light.

The left circularly polarized light is converted into linearly polarized light while passing through the liquid crystal layer 30 and then reflected by the reflecting plate 11 and then passed through the liquid crystal layer 30 to be converted into left circularly polarized light.

Subsequently, the left circularly polarized light is converted into linearly polarized light while passing through the retardation plate 22, and is converted to be parallel to the polarization direction of the polarizing plate 23, and then emitted to the outside through the polarizing plate 23. This implements the state of white.

Referring to FIG. 5, when voltage is applied, light passing through the polarizing plate 23 is linearly polarized, and the linearly polarized light passes through the phase difference plate 22 to be converted into circularly polarized left circularly polarized light.

The left circularly polarized light passes through the liquid crystal layer 30 in a left circularly polarized state because a voltage is applied thereto, and is converted into right circularly polarized light while being reflected by the reflector 11.

Subsequently, the right circularly polarized light is converted into linearly polarized light while passing through the retardation plate 22, but is converted to cross perpendicularly to the polarization direction of the polarizing plate 123 so as not to pass through the polarizing plate 23. This achieves a dark state.

In order to implement such a reflection type liquid crystal display device, the first embodiment of the present invention has set the optimum design conditions for each cell configuration as described above.

The alignment angle of the upper alignment layer 21 may be set to any one of −5 ° to 5 ° with respect to the horizontal line so that the twist angle of the liquid crystal of the liquid crystal layer 30 may be formed at any one of 68 ° to 72 °. The alignment angle of the alignment film 12 is set to either 247 ° to 253 ° with respect to the horizontal line. Here, it is most preferable to form so that the twist angle of liquid crystal may make 70 degrees.

The phase delay value dΔn of the retardation plate 22 may be any one of 137 nm to 159 nm, and the optical axis angle may be set to any one of 118 ° to 132 °.

The transmission axis of the polarizing plate 23 may be any one of the transmission axis angle of 165 ° to 175 ° such that the optical axis angle of the retardation plate 22 is 43 ° to 47 °.

The phase delay value dΔn of the liquid crystal layer 30 may be 0.21 μm to 0.24 μm.

Here, as an example of the above-mentioned conditions, the twist angle of the liquid crystal which is the most preferable case is demonstrated to 70 degree as an example. 7 is an axial arrangement diagram of each component according to the first embodiment of the present invention.

Referring to FIG. 7, the angle of the alignment axis a of the upper alignment layer 21 is 0 ° and the alignment axis b of the lower alignment layer 10 is formed such that the twist angle θ ₁ of the liquid crystal is 70 °. Set the angle to 250 °. Further, the angle of optical axis c of the phase difference plate 22 is 118 ° to 132 ° and the polarizing plate so that the angle θ ₂ formed between the phase difference plate 22 and the polarizing plate 23 forms 43 ° to 47 °. The transmission axis (d) angle of (23) can be set to 165 degrees-175 degrees.

However, in designing such a cell, when the phase difference plate 22 and the polarizing plate 23 are bonded to the upper portion of the upper substrate 20, the upper alignment layer 21 and the liquid crystal layer, which are lower regions of the upper substrate 20, are formed. 30, the maximum reflectance for implementing a white state and the lowest reflectance for implementing a dark state are different depending on the cell region including the lower alignment layer 12 and the reflector plate 11, and the forming angle. Accordingly, the contrast ratio is very different depending on the viewing angle.

Accordingly, the viewing angles of the conventional 60 ° TN mode reflective liquid crystal display device and the 70 ° TN mode reflective liquid crystal display device according to the first embodiment of the present invention are simulated by reflecting the above-described conditions of each component. Looking at the contrast ratio (CR) according to the following.

8A is a reflection type liquid crystal display device of 60 ° TN mode, and FIG. 8B is a contrast ratio simulation diagram according to a viewing angle of the reflection type liquid crystal display device of 70 ° TN mode according to the present invention.

As shown in FIGS. 8A and 8B, it can be seen that the contrast ratio of the reflective liquid crystal display of the 70 ° TN mode according to the present invention is remarkably improved compared to the reflective liquid crystal display of the 60 ° TN mode. It can be seen that the front viewing angle is also improved.

That is, it is possible to implement a wide viewing angle liquid crystal display device through the design conditions of this embodiment.

9 shows a graph comparing the reflectances of the reflective liquid crystal display of 60 ° TN mode and the reflective liquid crystal display of 70 ° TN mode according to the present embodiment.

Referring to FIG. 9, the graph C of the reflection type liquid crystal display device of 60 ° TN mode continues to show a white state even in the "B" region exceeding the threshold voltage when voltage is applied, and gradually becomes gray. It is changing to a state. In other words, the design is not optimized in the liquid crystal drive, the reflectance is reduced from the time of applying a higher voltage voltage rather than the actual threshold voltage, the quality of the screen is reduced and the power consumption is increased.

On the other hand, in the graph D of the reflective LCD according to the present embodiment, the threshold voltage is applied when the voltage is applied and the transition from the white state to the gray state is widened, thereby widening the gray scale range. The screen quality and power consumption can be reduced.

The scope of the present invention is not limited to the above-described embodiment, but may be embodied in various forms of embodiments within the scope of the appended claims. Without departing from the gist of the invention claimed in the claims, it is intended that any person skilled in the art to which the present invention pertains falls within the scope of the claims described in the present invention to various extents which can be modified.

1 is a schematic view of a reflective liquid crystal display device of a conventional 90 ° TN mode;

2 is a schematic diagram of a reflective liquid crystal display device of a conventional 60 ° TN mode;

3 is a schematic view of a reflective liquid crystal display device according to a first embodiment of the present invention;

4 and 5 are light transmission diagrams of a reflective liquid crystal display device according to a first embodiment of the present invention;

6 is a refractive index relation diagram of the retardation plate according to the first embodiment of the present invention;

7 is a axial arrangement diagram of each component according to the first embodiment of the present invention;

8A and 8B illustrate contrast ratio simulation diagrams of a reflective liquid crystal display device in a conventional 60 ° TN mode and contrast ratio simulation diagrams of a reflective liquid crystal display device according to a first embodiment of the present invention;

FIG. 9 is a graph comparing reflectance between a reflective liquid crystal display device having a twist angle of 60 ° and a reflective liquid crystal display device according to a first embodiment of the present invention.

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

10: lower substrate 11: reflector 12: lower alignment film

20: upper substrate 21: upper alignment layer 22: phase difference plate

23: polarizing plate 30: liquid crystal layer

Claims (3)

A lower substrate having a reflecting plate 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 an intervening liquid crystal layer. In the reflective liquid crystal display device having a polarizing plate attached to the retardation plate, and converts the natural light incident from the outside into linearly polarized light on the retardation plate, The angle of the alignment axis of the lower alignment layer is any one of 247 ° to 253 ° with respect to the horizontal line so that the twist angle of the liquid crystal of the liquid crystal layer may be any one of 68 ° to 72 °, and the angle of the alignment axis of the upper alignment layer is Any one of -5 ° to 5 ° for the horizontal line, The transmission axis angle of the polarizing plate is any one of 165 ° to 175 °, The optical axis angle of the retardation plate is any one of 118 ° to 132 ° to form a transmission axis angle of the polarizing plate and 43 ° to 47 °, and the phase delay value dΔn is any one of 137 nm to 159 nm. A reflection type liquid crystal display device, wherein the phase delay value (dΔn) of the liquid crystal is a twisted nematic liquid crystal having any one of 0.21 µm to 0.24 µm. The method of claim 1, And the retardation plate has a refractive index of nx, ny, nz satisfying nx = ny> nz. The method according to claim 1 or 2, And the reflecting plate is embossed to reflect the incident light.

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