JP2003330024A - Liquid crystal display and electronic equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transflective liquid crystal display having excellent display characteristics of both transmission and reflection modes. <P>SOLUTION: The transflective liquid crystal display 10 has a liquid crystal layer 16 held between an upper substrate 14 and a lower substrate 13 and a transmission display region T and a reflection display region R in one dot region. An upper polarizing plate 36 and a lower polarizing plate 28 are provided on the outer surface sides of the upper substrate 14 and the lower substrate 13, respectively, the liquid crystal layer 16 contains a liquid crystal composition mixed with a dichroic dye and having positive dielectric anisotropy, liquid crystal molecules L are twisted by nearly 90° between the upper substrate 14 and the lower substrate 13 when non-selective voltage is applied, the transmission axis direction of the upper polarizing plate 36 and the alignment direction of the liquid crystal molecules coming in contact with the inner surface of the upper substrate are nearly parallel to each other and the transmission axis direction of the lower polarizing plate 28 and the alignment direction of the liquid crystal molecules coming in contact with the inner surface of the lower substrate are nearly vertical to each other. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device and electronic equipment, and more particularly to a transflective liquid crystal display device capable of sufficiently bright display not only in reflection mode but also in transmission mode. The present invention relates to a configuration of a liquid crystal display device having excellent visibility.

[0002]

2. Description of the Related Art Conventionally, there has been proposed a liquid crystal display device that utilizes external light in a bright place like a normal reflection type liquid crystal display device and makes a display visually recognizable by an internal light source in a dark place. There is. This liquid crystal display device employs a display method that has both a reflective mode and a transmissive mode, and by switching to one of the display methods depending on the ambient brightness, power consumption is reduced and even when the surroundings are dark. A clear display can be performed. Hereinafter, in this specification, this type of liquid crystal display device is referred to as a “semi-transmissive reflective liquid crystal display device”. As one form of a semi-transmissive reflection type liquid crystal display device, there is one in which a reflective film in which an opening for light transmission is formed in a metal film such as aluminum is provided on the inner surface of the lower substrate and the reflective film functions as a semi-transmissive reflective film. Proposed. In addition,
In this specification, the surface of each substrate constituting the liquid crystal display device on the liquid crystal side is referred to as “inner surface”, and the surface on the opposite side is referred to as “outer surface”.

FIG. 8 shows an example of a transflective liquid crystal display device using this type of transflective film. In this liquid crystal display device 100, a pair of glass substrates 101, 102
A liquid crystal layer 103 is sandwiched between them, and a semi-transmissive reflective layer 104 having an opening 104a, a transparent electrode 108, and an alignment film 107 are formed on the inner surface of the lower substrate 101. on the other hand,
The transparent electrode 112 and the alignment film 11 are formed on the inner surface of the upper substrate 102.
3 is formed. Further, on the outer surface side of the upper substrate 102, two retardation plates 118 and 119 (these retardation plates function as a quarter-wave plate 120) and an upper polarization plate 114.
Are arranged, and a quarter wavelength plate 115 and a lower polarizing plate 116 are provided on the outer surface side of the lower substrate 101. A backlight 117 including a light source 122, a light guide plate 123, a reflection plate 124, etc. is arranged below the lower polarizing plate 116. The quarter-wave plates 115 and 120 can convert linearly polarized light into substantially circularly polarized light in a certain wavelength band.

A transflective liquid crystal display device 10 shown in FIG.
The display principle of 0 will be described below with reference to FIG. It should be noted that FIG. 9 shows only the constituent elements of the liquid crystal display device of FIG. 8 that are necessary for explaining the display principle. First, when dark display is performed, a voltage is applied to the liquid crystal layer 103 (on state) so that there is no phase difference in the liquid crystal layer 103. In reflective display, light incident from above the upper polarizing plate 114 is linearly polarized light perpendicular to the paper surface after passing through the upper polarizing plate 114, assuming that the transmission axis of the upper polarizing plate 114 is perpendicular to the paper surface. After passing through the quarter-wave plate 120, it becomes a left-handed circularly polarized light and passes through the liquid crystal layer 103.
Then, when the light is reflected on the surface of the semi-transmissive reflection layer 104, the rotation direction is reversed to become clockwise circularly polarized light, which passes through the liquid crystal layer 103 and the quarter wavelength plate 120, and then becomes linearly polarized light parallel to the paper surface. Become. Here, since the upper polarizing plate 114 has a transmission axis perpendicular to the paper surface, the reflected light is absorbed by the upper polarizing plate 114 and does not return to the outside (observer side), resulting in a dark display.

On the other hand, in the transmissive display, the light emitted from the backlight 117 is transmitted through the lower polarizing plate 116 after the transmission axis of the lower polarizing plate 116 is parallel to the paper surface.
Linearly polarized light parallel to the plane of the paper, and a quarter wave plate 11
After passing through 5, the liquid crystal layer 103 becomes clockwise circularly polarized light, and the liquid crystal layer 103
Through. Then, the clockwise circularly polarized light is a quarter wavelength plate 1.
After passing through 20, the light becomes a linearly polarized light parallel to the paper surface, and is absorbed by the upper polarizing plate 114 as in the reflection mode to provide a dark display.

Next, when performing bright display, the liquid crystal layer 10
No voltage is applied to 3 (OFF state), and the phase difference due to the birefringence effect in the liquid crystal layer 103 at this time is set to be ¼ wavelength. In the reflective display, the light is incident from above the upper polarizing plate 114, and the upper polarizing plate 114, 1 /
The counterclockwise circularly polarized light that has passed through the four-wave plate 120 becomes linearly polarized light that is parallel to the paper surface when it reaches the surface of the semi-transmissive reflective layer 104 after passing through the liquid crystal layer 103. Then, when the light is reflected on the surface of the semi-transmissive reflective layer 104 and transmitted through the liquid crystal layer 103, it becomes a counterclockwise circularly polarized light again, and after passing through the quarter wavelength plate 120, becomes a linearly polarized light perpendicular to the paper surface. Here, since the upper polarizing plate 114 has a transmission axis perpendicular to the paper surface,
The reflected light passes through the upper polarizing plate 114 and returns to the outside (observer side), resulting in a bright display.

On the other hand, in the transmissive display, the light is incident from the backlight 117, and the lower polarizing plate 116 and the quarter wave plate 11 are used.
The clockwise circularly polarized light after passing through 5 becomes linearly polarized light perpendicular to the paper surface at the stage of passing through the liquid crystal layer 103. When the linearly polarized light perpendicular to the paper surface passes through the quarter-wave plate 120, it becomes left-handed circularly polarized light. Since the upper polarizing plate 114 has a transmission axis perpendicular to the paper surface, among the left-handed circularly polarized light. Only linearly polarized light that is perpendicular to the paper surface passes through the upper polarizing plate 114 to provide a bright display.

[0008]

As described above, according to the liquid crystal display device 100 shown in FIGS. 8 and 9, although the display can be visually recognized regardless of the presence or absence of external light, the display is transparent as compared with the reflective display. There was a problem that the brightness of the display was insufficient.
One of the causes is, as described in the description of the display principle with FIG. 9, when the bright display is performed by the transmissive display, the liquid crystal layer 103,
Since the light transmitted through the quarter-wave plate 120 and incident on the upper polarization plate 114 is circularly polarized light, about half of the circularly polarized light is absorbed by the upper polarization plate 114, which contributes to the display. Because not.

One of the other causes is the backlight 1.
Of the light emitted from 17, the light that does not pass through the opening 104a of the semi-transmissive reflective layer 104 and is reflected on the back surface of the semi-transmissive reflective layer 104 has its rotation direction inverted and becomes counterclockwise circularly polarized light. When it passes through the / 4 wavelength plate 115, it becomes linearly polarized light perpendicular to the paper surface. Then, this linearly polarized light is absorbed by the lower polarizing plate 116 having a transmission axis parallel to the paper surface. That is, of the light emitted from the backlight 117, the light that did not pass through the opening 104a is transmitted through the lower polarizing plate 116 and returned to the backlight 117 without being absorbed by the lower polarizing plate 116. For example, this return light is emitted toward the liquid crystal cell again, but in reality, after being reflected by the back surface of the semi-transmissive reflective layer 104, almost all is absorbed by the lower polarizing plate 116 and cannot be reused. is there.

By the way, a liquid crystal containing a dichroic dye, that is, a so-called guest-host liquid crystal is well known.
When this guest-host liquid crystal is used in a transflective liquid crystal display device, light passes through the liquid crystal layer twice in the reflective display portion, whereas light passes through the liquid crystal layer in the transmissive display portion. Since it is only the number of times, the amount of light absorbed by the dichroic dye is different between the reflective display section and the transmissive display section. Therefore, if the dye concentration is adjusted so that sufficient contrast can be obtained in transmissive display, only reflective display with a very low reflectance can be obtained. On the contrary, if the dye concentration is adjusted so that sufficient brightness and proper contrast can be obtained in reflective display, there is a problem that the contrast becomes extremely low in transmissive display. As described above, when the guest-host liquid crystal is applied to the transflective liquid crystal display device, it is difficult to obtain good optical characteristics in both reflective display and transmissive display.
A method for solving this problem is disclosed in JP-A-11-242226.
As disclosed in the publication, in this method, it is indispensable that the reflective display section and the transmissive display section have different alignment states of liquid crystal at the same time, which makes the device configuration complicated and difficult to manufacture. It has drawbacks.

The present invention has been made to solve the above problems, and in a transflective liquid crystal display device capable of both reflective display and transmissive display, the display characteristics in both display modes are An object of the present invention is to provide a liquid crystal display device having improved visibility and a method for manufacturing the same.
Another object of the present invention is to provide an electronic device including a liquid crystal display section having excellent visibility.

[0012]

In order to achieve the above-mentioned object, a liquid crystal display device of the present invention has a liquid crystal layer sandwiched between an upper substrate and a lower substrate facing each other, and within a single dot area. A transflective liquid crystal display device having a transmissive display region and a reflective display region, wherein an upper polarizing plate is provided on the outer surface side of the upper substrate and a lower polarizing plate is provided on the outer surface side of the lower substrate, The liquid crystal layer includes a liquid crystal composition having a positive dielectric anisotropy mixed with a dichroic dye, and liquid crystal molecules of the liquid crystal layer are formed between the upper substrate and the lower substrate when a non-selective voltage is applied. It is twisted by approximately 90 ° in a plane parallel to the substrate surface, the transmission axis direction of the upper polarizing plate and the alignment direction of liquid crystal molecules in contact with the inner surface of the upper substrate are substantially parallel, and the transmission axis of the lower polarizing plate is Direction and the alignment direction of the liquid crystal molecules in contact with the inner surface of the lower substrate are roughly Characterized in that it is vertical.

That is, the liquid crystal display device of the present invention comprises an upper substrate and a lower substrate sandwiching a liquid crystal layer having a liquid crystal composition having a positive dielectric anisotropy mixed with a dichroic dye and having a substantially 90 ° twist orientation. A polarizing plate is arranged on the outer surface of each substrate at a predetermined angle. In this configuration, in the reflective display, the optical rotatory power of the liquid crystal and the absorption of the light by the dichroic dye are used, and in the transmissive display, only the optical rotatory power of the liquid crystal is used, which allows both the reflective display and the transmissive display. The display characteristics can be improved at the same time.

Speaking from the transmissive display side, the transmissive display uses the TN (twisted nematic) mode which utilizes the optical rotatory power of the liquid crystal due to the twist of the liquid crystal alignment, regardless of the dichroism of the dye. A high contrast can be easily obtained independently of the contrast. In addition, since circularly polarized light is not used for transmissive display, there is no component that is absorbed by the upper polarizing plate during bright display, and there is also a component that light reflected on the back surface side of the reflective layer in the reflective display region is absorbed by the lower polarizing plate. Since there is no light, the light can be reused and the transmissive display can be brightened. The detailed operation and display principle of the present invention will be described in the [Embodiment of the Invention] section. Further, in the liquid crystal display device of the present invention, the alignment states of the liquid crystal of the transmissive display portion and the reflective display portion at the same time may be basically the same, and a complicated configuration is not required.

A color filter may be provided between the upper substrate and the lower substrate. With this configuration, it is possible to realize a liquid crystal display device capable of clear color display in both reflective display and transmissive display.

An electronic apparatus of the present invention is characterized by including the liquid crystal display device of the present invention. According to this configuration,
It is possible to provide an electronic device including a liquid crystal display unit that is bright in both reflective display and transmissive display and has excellent visibility.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a cross-sectional view showing a schematic configuration of the liquid crystal display device of the present embodiment, and FIG. 2 is a diagram for explaining the display principle thereof, showing only the components necessary for explaining the display principle. Is. The present embodiment is an example of an active matrix type transflective color liquid crystal display device. In all of the following drawings, in order to make the drawings easy to see, the film thicknesses, the dimensional ratios, and the like of the respective constituent elements are appropriately changed.

The liquid crystal display device 10 of this embodiment is shown in FIG.
As shown in, the liquid crystal cell 11 and the backlight 12 (illumination device) are provided. In the liquid crystal cell 11, a lower substrate 13 and an upper substrate 14 are arranged so as to face each other.
A liquid crystal layer 16 is formed by enclosing a TN liquid crystal having a positive dielectric anisotropy, to which a dichroic dye is added, in a space sandwiched between the lower substrate 13 and the substrate. The backlight 12 is arranged on the rear surface side of the liquid crystal cell 11 (the outer surface side of the lower substrate 13). The dichroic dye in the present embodiment is one in which the dichroic dye molecule S is aligned in the same direction as the liquid crystal molecule L when added to the liquid crystal, and with respect to linearly polarized light parallel to the alignment direction of the liquid crystal molecule L. Is a so-called P-type dichroic dye that exhibits the maximum absorbance and exhibits the minimum absorbance for linearly polarized light perpendicular to the alignment direction of the liquid crystal molecules L.

On the inner surface side of the lower substrate 13 made of a translucent material such as glass or plastic, a semi-transmissive reflection layer 18 made of a metal film having a high reflectance such as aluminum, silver or an alloy thereof is formed. There is. The semi-transmissive reflective layer 18 is provided with an opening 18a for transmitting the light emitted from the backlight 12 for each pixel, and in the formation region of the semi-transmissive reflective layer 18, a metal film is actually formed. The existing portion constitutes the reflective display area R, and the portion of the opening 18a constitutes the transmissive display area T.

A pixel electrode 23 made of a transparent conductive film such as ITO (Indium Tin Oxide) is formed on the semi-transmissive reflective layer 18 including the opening 18a.
An alignment film 24 made of polyimide or the like is laminated so as to cover the. In the case of the present embodiment, the lower substrate 13 is composed of an element substrate having pixel switching elements such as TFTs, data lines, scanning lines, etc., but in FIG. 1, the pixel switching elements, data lines, scanning lines are formed. Illustrations of the like are omitted. Further, a lower polarizing plate 28 is provided on the outer surface side of the lower substrate 13.

On the other hand, on the inner surface side of the upper substrate 14 made of a transparent material such as glass or plastic, a common electrode 32 made of a transparent conductive film such as ITO and an alignment film 33 made of polyimide are sequentially laminated. . An upper polarizing plate 36 is provided on the outer surface side of the upper substrate 14. Although illustration is omitted, R (red), G (green),
A color filter having each B (blue) dye layer is provided.

Alignment film 3 on the upper substrate 14 side and the lower substrate 13 side
Horizontal alignment treatments such as rubbing treatments are applied to the reference numerals 3 and 24.
Of the alignment film 24 on the lower substrate 13 side in the direction parallel to the paper surface of FIG.
The orientation directions of are set in the directions perpendicular to the paper surface of FIG. The liquid crystal molecules L and the dichroic dye molecules S of the liquid crystal layer 16 are applied to the upper substrate 14 when a non-selective voltage is applied (voltage off).
Between the lower substrate 13 and the lower substrate 13 in a plane parallel to the substrate surface.
It is in a 0 ° twisted state. The transmission axis direction of the upper polarizing plate 36 and the transmission axis direction of the lower polarizing plate 28 are both set in the direction parallel to the paper surface of FIG. That is, the transmission axis direction of the upper polarizing plate 36 and the alignment direction of the liquid crystal molecules L in contact with the inner surface of the upper substrate 14 are substantially parallel to each other, and the transmission axis direction of the lower polarizing plate 28 and the liquid crystal molecules L in contact with the inner surface of the lower substrate 13. Is almost perpendicular to the orientation direction of.

The backlight 12 has a light source 37, a reflection plate 38, and a light guide plate 39, and the lower surface of the light guide plate 39 (the side opposite to the liquid crystal panel 1) transmits through the light guide plate 39. A reflection plate 40 for emitting light toward the liquid crystal cell 11 side is provided.

The display principle of the liquid crystal display device 10 of the present embodiment will be described below with reference to FIG. First, when dark display is performed in the reflective mode (see the left side of FIG. 2), the liquid crystal layer 16
Voltage is not applied to (non-selection voltage applied state),
The liquid crystal molecule L and the dichroic dye molecule S are approximately 9 between the upper and lower substrates.
The state is 0 ° twist orientation. Since the transmission axis of the upper polarizing plate 36 is parallel to the paper surface, the light incident from above the upper polarizing plate 36 becomes linearly polarized light parallel to the paper surface after passing through the upper polarizing plate 36. This linearly polarized light is rotated while being absorbed by the dichroic dye molecule S along the twist of the liquid crystal molecule L, reaches the semi-transmissive reflection layer 18, is reflected, and then further passes through the same path to pass through the dichroic dye. While being absorbed by the molecule S, it rotates and returns. In this case, since the light passes through the liquid crystal layer 16 twice, the light is sufficiently absorbed by the dichroic dye. Even if there is light that could not be fully absorbed by the dichroic dye, when the reflected light returns to the upper polarizing plate 36, it becomes linearly polarized light that is perpendicular to the paper surface, so it is absorbed by the upper polarizing plate 36. To be done. Therefore, a sufficiently dark dark display is provided, which leads to an improvement in contrast.

Next, when a bright display is performed in the reflection mode (see the right side of FIG. 2), the liquid crystal layer 16 and the dichroic dye molecule are brought into a state in which a voltage is applied to the liquid crystal layer 16 (a selection voltage applied state). It is assumed that S stands up in a direction substantially normal to the substrate surface. In this case, the linearly polarized light which is incident from above the upper polarizing plate 36 and which is parallel to the paper surface is hardly absorbed by the dichroic dye molecules S while reciprocating in the liquid crystal layer 16 and is not rotated, and the upper polarizing plate is kept as it is. Return to 36. Therefore, this light passes through the upper polarizing plate 36 and is exposed to the outside (observer side).
Since it returns to, it becomes a bright display.

On the other hand, when the dark display is performed in the transmissive mode (see the left side of FIG. 2), the orientations of the liquid crystal molecules L and the dichroic dye molecules S are the same as those in the reflective mode and the dark display. The light incident from the backlight 12 is the lower polarizing plate 28.
When the transmission axis of is parallel to the paper surface, it becomes a linearly polarized light parallel to the paper surface after passing through the lower polarizing plate 28. This linearly polarized light is
Since the polarization direction is orthogonal to the alignment direction of the dichroic dye molecule S on the side in contact with the lower substrate 13, it is hardly absorbed by the dichroic dye molecule S, and the polarization direction is substantially due to the optical activity of the liquid crystal. It becomes a linearly polarized light which is perpendicular to the paper surface rotated by 90 ° and reaches the upper substrate 14 side. Since the polarization direction of this linearly polarized light is orthogonal to the transmission axis direction of the upper polarizing plate 36, it is absorbed by the upper polarizing plate 36 and cannot be transmitted, resulting in a dark display. Further, since the dichroic dye absorbs the component of the light that cannot be fully rotated, the dark display becomes darker and the contrast is improved.

Next, when bright display is performed in the transmission mode (see the right side of FIG. 2), the orientation of the liquid crystal molecules L and the dichroic dye molecules S is on the substrate surface as in the reflection mode and the bright display. On the other hand, the state of substantially vertical alignment is set. In this alignment state, there is almost no absorption of light by the dye,
Since the optical rotatory power of the liquid crystal has also disappeared, the light incident from the backlight 12 passes through the liquid crystal layer 16 and reaches the upper polarizing plate 36 as linearly polarized light parallel to the paper surface. Since the polarization direction of this linearly polarized light is parallel to the transmission axis direction of the upper polarizing plate 36, the linearly polarized light is transmitted through the upper polarizing plate 36 and returns to the outside (observer side) to provide a bright display. Particularly in the transmissive mode, since light passes through the liquid crystal layer 16 only once, the liquid crystal layer 16 in which the dye concentration is set for reflective display is less affected by the decrease in brightness in transmissive display.

In the transmission mode, the lower polarizing plate 28
Of the linearly polarized light that is transmitted through the sheet and is reflected on the back surface of the semi-transmissive reflective layer 18, the light is transmitted through the lower polarizing plate 28 as it is to the backlight 12, and is reflected by the reflection plate 40 on the lower surface of the backlight 12. Then, since the light is emitted toward the liquid crystal cell 11 again, the light reflected on the back surface of the semi-transmissive reflective layer 18 can be reused to contribute to the transmissive display.

In the liquid crystal display device 10 of the present embodiment, both the optical rotatory power of the liquid crystal and the optical absorption of the dichroic dye are used in the reflective display, and only the optical rotatory power of the liquid crystal is used in the transmissive display. By using it, the display characteristics of both reflective display and transmissive display can be set independently. That is, the reflective display uses the guest host mode,
The contrast is adjusted by the addition amount of the dichroic dye, etc., while the transmissive display uses the TN mode that utilizes the optical rotatory power due to the twist of the liquid crystal alignment, regardless of the dichroic dye. A high contrast can be easily obtained independently of the contrast.

It should be noted that the addition amount of the dichroic dye is preferably smaller than in the usual guest-host mode. The reason is that, in the case of the present embodiment, not only the absorption by the dye is used in the reflective display but also the optical rotatory power of the liquid crystal is also used, so that the dye does not have to be so much, This is because when the amount of dye is large, the amount of absorption in bright display increases even if the molecules are vertically aligned, and the brightness becomes dark.

Further, since circularly polarized light is not used for transmissive display,
There is no component absorbed by the upper polarizing plate 36 during bright display, and there is no component absorbed by the lower polarizing plate 28 on the back surface side of the semi-transmissive reflective layer 18 in the reflective display region R. It becomes available, and the transparent display can be brightened. Furthermore, in the liquid crystal display device of the present embodiment, the alignment state of the liquid crystal molecules at the same time in the transmissive display region T and the reflective display region R may be basically the same, and a complicated structure is not required, and therefore, the manufacturing is possible. It's easy.

[Electronic Equipment] Examples of electronic equipment equipped with the liquid crystal display device of the above-described embodiment will be described. FIG. 3 is a perspective view showing an example of a mobile phone. In FIG. 3, reference numeral 1000 indicates a mobile phone main body, and reference numeral 1001 indicates a liquid crystal display unit using the above liquid crystal display device.

FIG. 4 is a perspective view showing an example of a wrist watch type electronic device. In FIG. 4, reference numeral 1100 indicates a watch body, and reference numeral 1101 indicates a liquid crystal display unit using the above liquid crystal display device.

FIG. 5 is a perspective view showing an example of a portable information processing device such as a word processor and a personal computer. In FIG. 5, reference numeral 1200 is an information processing apparatus, reference numeral 1202 is an input unit such as a keyboard, reference numeral 1204 is an information processing apparatus main body, and reference numeral 1206 is a liquid crystal display unit using the above liquid crystal display device.

Since the electronic equipment shown in FIGS. 3 to 5 is provided with the liquid crystal display unit using the liquid crystal display device of the above-mentioned embodiment, a display unit capable of obtaining a bright display regardless of the reflection mode or the transmission mode is provided. It is possible to realize an electronic device that the user has.

The technical scope of the present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, the present invention is not limited to the active matrix type transflective color liquid crystal display device as in the above embodiment, but can be applied to a passive matrix type liquid crystal display device of monochrome display.

[0037]

EXAMPLES In order to demonstrate the effect of the present invention, the present inventors actually manufactured a liquid crystal display device having the constitution according to the present invention, and measured the transmittance, the reflectance and the contrast. The results are reported below.

As a liquid crystal composition having a positive dielectric anisotropy, MJ
A small amount of chiral substance was added to 96411 (trade name, manufactured by Merck & Co., Inc.). As the dichroic dye, four types of dyes shown in Table 1 below were mixed to give a black dye. Table 1
A guest-host liquid crystal was prepared by mixing with the above liquid crystal at the concentration shown in.

[0039]

[Table 1]

The guest-host liquid crystal was injected into a 90 ° twisted TN cell and its characteristics were evaluated. The liquid crystal layer thickness was 11 μm. SEG1425DU is used for the upper and lower polarizing plates.
(Product name, manufactured by Nitto Denko Corporation, polarization degree: 99.9%) was used. In order to examine the reflection characteristics and the transmission characteristics independently, two types of cells, a cell having a full-surface reflection layer and a cell having no reflection layer, were prepared and the characteristics were evaluated.

(Reflection characteristics) Using a cell having a reflection layer, the spectral reflectance and the contrast were measured when no voltage was applied and when a rectangular wave voltage of 5 V having a frequency of 64 Hz was applied.
As a result, as shown in FIG. 6, the contrast was about 10 or more and the reflectance was 31% in the visible light region. As a comparative example, a normal TN cell in which a liquid crystal not mixed with a dichroic dye was injected into a cell having the same cell thickness, and an upper polarizing plate was placed to measure only the reflectance, the reflectance was 38%. there were. Of course, since the structure of this comparative example does not contain a dichroic dye, it is not possible to obtain a dark display even if a voltage is applied to the cell. In the liquid crystal display device having the structure according to the present invention, since the dichroic dye is mixed in the liquid crystal, the reflectance in the bright display is slightly decreased, but it is not so much decreased and is within the allowable range. It was The contrast was sufficiently satisfactory for reflective display.

(Transmission Characteristics) Using a cell without a reflective layer,
The applied voltage-transmittance characteristic (VT characteristic) was measured. As a result, as shown in FIG. 7, the transmittance when applying 5 V was 30.
%, And the maximum contrast was 490. As a comparative example, when a normal TN cell in which a liquid crystal not mixed with a dichroic dye was injected into a cell having the same cell thickness, the transmittance was 3
The contrast was 6% and 230. In the liquid crystal display device having the configuration according to the present invention, the transmissivity in the bright display is slightly lowered because the dichroic dye is mixed in the liquid crystal,
It was within a permissible range, not a significant decrease.
On the other hand, in the case of the conventional transflective liquid crystal display device using circularly polarized light as shown in FIG. 8, even if the entire pixel is made into a transmissive part without the reflective part, a normal TN cell (comparative example) is used. It can be said that the transmittance is significantly increased from 18% to 30% as compared with the case where only about half of the transmittance (about 18%) is obtained. It was also confirmed that the contrast was significantly improved compared to the comparative example. The reason for this is
It is considered that in the dark display, the dichroic dye absorbs a component of the light that cannot be absorbed by the upper polarizing plate in the configuration of the comparative example, and thus the brightness of the dark display is further reduced.

[0043]

As described above in detail, according to the structure of the present invention, the optical rotation of the liquid crystal and the absorption of the light by the dichroic dye are used in the reflective display, and only the optical rotation of the liquid crystal is used in the transmissive display. By using, it is possible to improve the display characteristics of both reflective display and transmissive display. In addition, the alignment states of the liquid crystal at the same time of the transmissive display section and the reflective display section may be basically the same, and a complicated structure is not required, so that the manufacturing can be facilitated.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a schematic configuration of a liquid crystal display device according to an embodiment of the present invention.

FIG. 2 is a diagram for explaining the display principle of the liquid crystal display device, showing only the components necessary for explaining the display principle.

FIG. 3 is a perspective view showing an example of an electronic device according to the present invention.

FIG. 4 is a perspective view showing another example of an electronic device according to the present invention.

FIG. 5 is a perspective view showing still another example of an electronic device according to the present invention.

FIG. 6 is a diagram showing spectral reflectance and contrast in a liquid crystal display device according to an example of the present invention.

FIG. 7 is a diagram showing the transmittance of a liquid crystal display device according to an example of the present invention.

FIG. 8 is a cross-sectional view showing a schematic configuration of an example of a conventional liquid crystal display device.

FIG. 9 is a diagram for explaining the display principle of the liquid crystal display device, showing only the components necessary for explaining the display principle.

[Explanation of symbols]

10 Liquid crystal display device 11 Liquid crystal cell 12 backlight 13 Lower substrate 14 Upper substrate 16 Liquid crystal layer 18 Semi-transmissive reflective layer 18a opening 24,33 Alignment film 28 Lower polarizing plate 36 Upper polarizing plate R reflective display area T transparent display area S dichroic dye molecule L liquid crystal molecule

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G02F 1/13357 G02F 1/13357 1/137 1/137 F term (reference) 2H049 BA02 BA08 BA22 BA42 BB03 BB05 BC22 2H088 GA13 HA03 HA12 HA18 HA21 JA05 KA11 KA26 MA02 MA04 2H090 KA05 KA06 LA07 LA08 LA09 LA16 MA02 MA06 2H091 FA02Y FA08X FA08Z FA11X FA14Y FA41Z FD09 GA06 HA07 HA08 KA03 LA15 LA17 LA18

Claims (3)

[Claims] 1. A transflective liquid crystal display device having a liquid crystal layer sandwiched between an upper substrate and a lower substrate facing each other and having a transmissive display region and a reflective display region in one dot region. An upper polarizing plate is provided on the outer surface side of the upper substrate and a lower polarizing plate is provided on the outer surface side of the lower substrate, and the liquid crystal layer is a liquid crystal having a positive dielectric anisotropy mixed with a dichroic dye. The liquid crystal molecules of the liquid crystal layer containing the composition are twisted by about 90 ° in a plane parallel to the substrate surface between the upper substrate and the lower substrate when a non-selective voltage is applied, and The axial direction and the alignment direction of the liquid crystal molecules in contact with the inner surface of the upper substrate are substantially parallel, and the transmission axis direction of the lower polarizing plate and the alignment direction of the liquid crystal molecules in contact with the inner surface of the lower substrate are substantially vertical. Liquid crystal display device characterized by. 2. The liquid crystal display device according to claim 1, further comprising a color filter provided between the upper substrate and the lower substrate. 3. An electronic apparatus comprising the liquid crystal display device according to claim 1.