JPH0452620A - Liquid crystal display device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Field of Application) The present invention relates to a liquid crystal display device that can display images with high contrast in both transmission type and reflection type.

(Prior Art) In recent years, as the demand for increased display capacity and larger display area for word processors, personal computers, etc. has increased, TN-type liquid crystal display elements have encountered problems such as insufficient contrast and narrow viewing angle range. Because of this, the so-called ST(
super twist) type liquid crystal display element (SID, 8B
DIGET, p. 122) has been used. As shown in FIG. 9(a), two substrates 1.
1' and a liquid crystal composition sandwiched therebetween, polarizing plates 3.4 are arranged before and after the liquid crystal cell 2.The display principle of the liquid crystal cell 2 is explained with reference to FIG. 9(b). The linearly polarized light 100 that has passed through the liquid crystal cell 2 generally becomes elliptically polarized light 101 by passing through the liquid crystal cell 2 . The elliptically polarized light that has passed through the liquid crystal cell 2 passes through a polarizing plate 4 placed at a predetermined angle (10
2) and can be detected by the human eye. The shape of the ellipse at this time is determined by the twist angle W, which is the twist angle of the liquid crystal molecules in the liquid crystal cell 2, the retardation R-Δndcosθ, and the wavelength λ. Here, Δn is the birefringence index of the liquid crystal composition in the liquid crystal cell, d is the cell thickness (substrate spacing), and θ is the tilt angle. Generally, the transmittance changes depending on the wavelength, and the transmitted light is colored. By applying an electric field to the liquid crystal cell and changing the orientation of the liquid crystal molecules, the birefringence Δn effectively changes, which changes the retardation R and changes the transmittance, which is used to display images. .

Since the ST type liquid crystal display element performs display using birefringence in this way, the display is colored.

Specifically, yellow mode [dark blue (o
Blue mode (white (on) / blue (o!'f)).Yellow mode is commercialized as a reflective display format, and blue mode is commercialized as a transmissive display format. However, the reflective yellow mode is difficult to use in dark places, and the transmissive blue mode requires backlighting such as EL or FL, resulting in a problem of high current consumption.

OMI type liquid crystal display elements are known as a method to eliminate this coloration (Appl, Phys, Lett,
50(5) 191i7 p, 236). That is, the twist angle of the liquid crystal is 180°, and the retardation R-Δ
The value of n d cos θ is 0.5 to 0.6, the angle of the absorption axis of the polarizing plate is 90°, and it is used as a reflective liquid crystal display device. OMI type liquid crystal display elements display achromatic colors or display in a reflective manner, making it difficult to use them in dark places.

In addition, as a black-and-white display and transmissive system, Japanese Patent Application Laid-Open No. 57
-48227 publication, JP-A-57-96315 publication,
JP-A-57-125919 discloses a method in which two liquid crystal cells are stacked, polarizing plates are placed on both sides, and the display color is achromatic.
A so-called two-layer cell type liquid crystal display element was proposed. The basic structure of this is to use two of the above-mentioned ST type liquid crystal cells which have mutually optically complementary properties. The two-layer cell type ST type liquid crystal display element has a black and white display and back lighting, and has the advantage of being usable in dark places. However, considering the yield rate of two liquid crystal cells, using two liquid crystal cells becomes very expensive, so in recent years, stretched thermoplastic resin has been used instead of one liquid crystal cell in the two-layer cell system. An optical retardation plate type liquid crystal display device in which at least one optical retardation plate made of a film-like material is installed between a liquid crystal cell and a polarizing plate has been developed. However, 2
Although both the layer cell type and the optical delay plate type can display black and white, they have the disadvantage of high current consumption because they have backlighting.

(Problem to be solved by the invention) As mentioned above, colored ST type and O type with achromatic display color
The MI method, the two-layer cell method, and the optical retardation plate method are limited to either a reflective type or a transmissive type, and it is not possible to select a suitable usage type depending on the place of use.

The present invention has been made in view of these points, and an object of the present invention is to provide a liquid crystal display device that can provide a high contrast display in both reflective and transmissive display formats.

[Configuration of the Invention (Means for Solving the Problems) In other words, the liquid crystal display device of the present invention has first electrodes arranged facing each other and having electrodes formed in the X direction and the Y direction on each facing surface.
and a first liquid crystal cell consisting of a second substrate and a liquid crystal composition twisted and oriented between these substrates, and third and fourth liquid crystal cells placed facing each other and having electrodes formed on the entire surface of each facing surface. a second liquid crystal cell consisting of a substrate and a liquid crystal composition aligned in parallel between these substrates; and one cell disposed between or outside of either the first liquid crystal cell and the second liquid crystal cell. and first and second polarizing plates disposed on both sides of a liquid crystal display element comprising first and second liquid crystal cells and the optical delay plate. .

(Function) In the liquid crystal display device having the above configuration, an X electrode and a Y electrode are formed on the first and second substrates, respectively, and a first liquid crystal composition filled with a twistedly oriented liquid crystal composition is provided between the first and second substrates. The liquid crystal cell displays characters, etc. by applying a signal. On the other hand, the second liquid crystal cell, in which solid electrodes are formed on each of the third and fourth substrates, and a parallelly aligned liquid crystal composition is filled between these substrates, is homogeneously aligned when no voltage is applied. Since birefringence of the liquid crystal composition occurs, it acts similar to an optical retardation plate, and when a voltage is applied, the liquid crystal composition is homogeneously aligned or aligned in the normal direction of the liquid crystal cell, so the birefringence effect due to the liquid crystal composition It does not produce light and does not play any optical role.

When the liquid crystal display device of the present invention is used as a transmissive type with backlighting, as shown in FIGS.
A voltage is applied to the liquid crystal cell 10.

FIG. 3 shows that no voltage is applied to the first liquid crystal cell 11, o
ff state, the incident light becomes linearly polarized light 103 by passing through the polarizing plate 12, and this linearly polarized light 10
3 passes through the first liquid crystal cell 11 and becomes elliptically polarized light 104. This elliptically polarized light 104 becomes polarized light 105 close to linear polarization in the optical retardation plate 13, and then passes through the second liquid crystal cell 1.
0, the polarization state does not change, and the polarization state is 105, which is close to linear polarization. Polarizing plate 1 is perpendicular to this polarized light 105.
By setting the transmission axis of 4, it is observed by the observer 15 as a dark state. That is, non-pixel areas to which no voltage is applied are in a dark state, and a high-contrast display can be obtained in a transmissive liquid crystal display device with bright backlighting.

On the other hand, as shown in FIG. 4, a voltage was applied to the first liquid crystal cell 11. In the n state, the linearly polarized light 103 passes through the first liquid crystal cell 11 and becomes elliptically polarized light 106 different from the elliptically polarized light 104, and further passes through the optical delay plate 13 to become perpendicular to the polarized light 105. The polarized light 107 is close to linearly polarized light. The polarized light 107 is observed by the observer 15 as a bright state due to the same effect as described above. Therefore, this liquid crystal display device can perform high contrast display as a transmissive type with backlighting.

Next, when the liquid crystal display device of the present invention is used as a reflective type, no voltage is applied to the second liquid crystal cell 10 as shown in FIGS. 5 and 6. FIG. 5 shows the first liquid crystal cell 11.
This indicates an of'r state in which no voltage is applied to
As explained for the transmission type, the incident light passes through the polarizing plate 12 to become linearly polarized light 103, then passes through the first liquid crystal cell 11 to become elliptically polarized light 104, and then passes through the optical delay plate 13 to become linearly polarized light. It becomes polarized light 105, which is close to polarized light. However, in the next step, this polarized light 105 passes through the second liquid crystal cell 10 and becomes polarized light 108 that is perpendicular to the polarized light 105 and is close to linearly polarized light.

That is, the polarization state is almost the same as the polarization state 107 in FIG. 4. Therefore, it is observed by the observer 15 as a bright state. That is, non-pixel areas to which no voltage is applied are in a bright state, which is desirable in order to obtain a bright display with high contrast as a reflective type without backlighting.

On the other hand, as shown in FIG. 6, in the so-called on state where a voltage is applied to the first liquid crystal cell 11, the linearly polarized light 103 that has passed through the polarizing plate 12 is in the first passes through the liquid crystal cell 11 and becomes elliptically polarized light 106,
Then, it passes through an optical retardation plate 13 and becomes polarized light 1 close to linear polarization.
It will be 07. By passing the next second liquid crystal cell, the polarized light 107 becomes polarized light 10 unlike in the case of the transmission type shown in FIG.
The polarized light 109 is close to linearly polarized light that is perpendicular to the polarized light 7. This polarized light 109 has almost the same polarization state as the polarized light 105 in FIG. 3, and is observed by the observer 15 as a dark state.

Therefore, this liquid crystal display device can perform high contrast display as a reflective type.

That is, the liquid crystal display device of the present invention can be used as either a transmissive type or a reflective type, and high contrast display is possible in both cases.

Further, the optical delay plate 13 is connected to the first liquid crystal cell 11 and the polarizing plate 1.
Similar effects can be obtained even if the liquid crystal cell 10 is placed between the liquid crystal cell 10 and the polarizing plate 14 or between the second liquid crystal cell 10 and the polarizing plate 14.

The liquid crystal composition used in the liquid crystal display device of the present invention preferably has a large twist angle so that the orientation angle of the liquid crystal molecules changes rapidly with respect to voltage.
A value between 0' is desirable. A stretched organic film is used as the optical retardation plate, and this optical retardation plate can also serve as a substrate for a liquid crystal cell.

(Example) Hereinafter, an example of the present invention will be described based on the drawings, particularly a case where black and white display is possible.

In addition, in all the drawings, the same reference numerals are added to the common parts.

FIG. 1 is a sectional view of a liquid crystal display device according to an embodiment of the present invention, and shows the lamination relationship of each component of this liquid crystal display device, the orientation direction, absorption axis or optical axis direction, etc. of each component corresponding thereto. The relationship is shown in Figure 2. In this liquid crystal display device, as the first liquid crystal cell 11, substrates 17 and 18 on which transparent electrodes 15 and 16 in the X and Y directions are formed are installed substantially in parallel, and a liquid crystal composition 19 is sealed between them. Its periphery is sealed and fixed with a sealant 20 made of epoxy adhesive. Its cell thickness (substrate spacing) d is 8.3
The liquid crystal molecules have a twist angle II' counterclockwise depending on the alignment direction r1 of the substrate 18 and the alignment direction r' of the substrate 17.
The orientation is twisted at -240'.

The liquid crystal composition 19 of this first liquid crystal cell 11 contains ZL1.
2293 (manufactured by Merck & Co., Ltd.) as a counterclockwise chiral agent, S-811 (E, manufactured by Merck & Co., Ltd.) was added d/pt (pt:
Pisochi) was added to approximately 0.6.

As the second liquid crystal cell 10, a transparent liquid crystal electrode 21.2 is used.
2 substrates 23 and 24 are installed substantially parallel to each other,
A liquid crystal composition 25 is sealed between them, and the periphery thereof is sealed and fixed with a sealant 20 made of epoxy adhesive. In this second liquid crystal cell 10, the liquid crystal molecules are aligned in parallel with the alignment direction r+ of the substrate 24 and the alignment direction r1 of the substrate 23, and the cell thickness (substrate spacing) d is 4.8μ.
It is l. Note that rl and "1' were set at an angle of A-60 degrees with respect to the alignment direction r' of the substrate 17 of the first liquid crystal cell 11, as shown in FIG.

The liquid crystal composition 25 of the second liquid crystal cell 10 contains ZL141.
19 (manufactured by Merck & Co.) was used. Since the birefringence Δn of this liquid crystal composition 25 was 0.08, the retardation R
-Δndcosθ was approximately 0.290μ.

On the other hand, the optical retardation plate 13 laminated between the first and second liquid crystal cells 11.10 is made of stretched polyvinyl alcohol with a thickness of about 0.5W, and its stretching direction is the same as that of the substrate of the first liquid crystal cell 11. It was arranged at an angle of A-60 degrees with respect to the orientation direction r' of No. 17. At this time, the retardation R of the optical delay plate 13 was 0°290 μm.

In addition, LLC-8, 1-18 (manufactured by Sanritsu Electric Co., Ltd.) was used as the polarizing plates 12 and 14 placed before and after such a liquid crystal display element, and as shown in FIG.
The absorption axes p1 and p2 of 2.14 are the orientation direction r' of the substrate 17.
IJ-158P2~117'.

Furthermore, in this embodiment, a semi-transparent plate 27 was installed between the polarizing plate 12 and the illumination (backlight) 26.

In the liquid crystal display device configured as described above, when a voltage is applied to the first liquid crystal cell 11 while the backlight 26 is turned on and a voltage is applied to the second liquid crystal cell 10 (lighting), FIG. 7 shows the wavelength dependence of the transmittance of B when no voltage is applied (non-lighting). As is clear from this graph, both the transmittance when lit and unlit can be displayed in a flat, achromatic color almost regardless of the waveform, and the display is white when lit and black when not lit, which is the so-called normally black mode. Become. Also, when this liquid crystal cell is multiplex driven at 17400 duty, the contrast is approximately 10:1.
It was expensive.

Meanwhile, the backlight 26 is turned off and the second liquid crystal cell 10
When a voltage is applied to the first liquid crystal cell 11 (lit) with no voltage applied to C, and when no voltage is applied (not lit)
The wavelength dependence of the transmittance of D is shown in FIG. As is clear from this graph, both the transmittance when lit and unlit can be displayed in a flat, achromatic color almost regardless of the waveform, and the display is black when lit and white when not lit, which is the so-called normally white mode. Become. Also, this liquid crystal cell is I/400
The contrast when multiplexed at duty was approximately 5:1.

In this example, we have described the case in which a black and white display is obtained, but by appropriately selecting the arrangement of the optical retardation plate, its retardation value, or the polarizing plate, it is possible to obtain a high contrast display even in a colored display. is clear.

[Effects of the Invention] As explained above, the liquid crystal display device of the present invention is capable of high-contrast display in both reflective and transmissive types, and a suitable mode of use can be freely selected at that time. .

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing a liquid crystal display device according to an embodiment of the present invention, and FIG. 2 is a diagram schematically explaining the structure of the liquid crystal display device of FIG. 1 and the relationship between the optical directions of each component. 3 to 6 are diagrams explaining the operation of the liquid crystal display device of the present invention, FIGS. 7 and 8 are graphs showing the wavelength dependence of the transmittance of the liquid crystal display device of FIG. 1, and FIG. (a) and (b) are diagrams each explaining the configuration of an ST-type liquid crystal display device and its display principle. DESCRIPTION OF SYMBOLS 10... Second liquid crystal cell, 11... First liquid crystal cell, 12.14... Polarizing plate, 13... Optical retardation plate, 1
5.16.21.22...electrode, 17.18.23.
24...Substrate, 19.25...Liquid crystal composition, 20.
...Sealant, 27...Semi-transparent plate

Claims (1)

[Claims] A first liquid crystal cell comprising first and second substrates placed opposite each other and having electrodes formed in the X direction and the Y direction on their opposing surfaces, and a liquid crystal composition twisted and oriented between these substrates; , a second liquid crystal cell comprising third and fourth substrates arranged opposite to each other and having electrodes formed on the entire surface of each of the opposite surfaces, and a liquid crystal composition parallelly aligned between these substrates; one optical retardation plate disposed between the liquid crystal cell and the second liquid crystal cell or outside either side of the liquid crystal cell, and both sides of a liquid crystal display element consisting of the first and second liquid crystal cells and the optical retardation plate. 1. A liquid crystal display device comprising: first and second polarizing plates arranged in the same direction.