JP2000089208A - Reflection type liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device which is high in resolution, display luminance and image quality by providing the device with a specific image display means and a color display means which is formed on the image display means and is capable of successively selectively switching three primary colors of colors in synchronization with black and white images. SOLUTION: This liquid crystal display device is provided with the image display means which impresses display voltage from pixel electrodes to liquid crystals and successively displays the black and white images corresponding to the three primary colors of colors from the image display surface by modulating the reflected light intensity of the light entering from outside at every pixel electrodes and the color display means which is capable of formed on the image display means and is capable of successively selectively switching the three primary colors of colors in synchronization with the black and white images. With this device, incident light 114 is any of the three primary colors R, G and B by transmitting a liquid crystal color shutter 102 twice. The light is reflected by Al reflection electrodes 105 of respective pixels according to the monochromatic display images meeting the display colors of the liquid crystal color shutter in a monochromatic reflection type liquid crystal display section 101 and is then transmitted through or absorbed by a polarizing plate 108, by which the light is subjected to modulation of brightness and darkness and as the result, the images of the selected display colors are displayed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a reflection type liquid crystal display device.

[0002]

2. Description of the Related Art In recent years, a reflection type liquid crystal display device has been actively developed in recent years as a reflection type display device which does not have a light source in the display device and uses reflected light of external light for display because of its low power consumption. . When a color display is performed by a reflective liquid crystal display device, RG is used similarly to a transmissive liquid crystal display device having a backlight on the back.
Additive color display is performed in which B color filters are arranged in parallel and display is performed by a combination of light and dark of each pixel. In addition, in order to ensure the reflectance, a single polarizing plate is provided, and a reflector provided below the liquid crystal layer is provided with a gain to increase the front luminance. In a reflection type liquid crystal display device, it is important to increase the reflection luminance. At the same time, if an attempt is made to increase the definition by reducing the pixel size, a pixel area ratio effective for display per pixel (an aperture in a transmission type liquid crystal display device). Rate) is reduced, and it becomes difficult to secure a necessary reflection luminance. Further, since a color filter is required to perform color display, display luminance is significantly reduced.

[0003]

In the conventional reflection type liquid crystal display device, if an attempt is made to achieve higher definition by reducing the pixel size, the effective pixel area ratio for display per pixel is reduced, and the necessary reflection luminance is secured. In addition, there has been a problem that the display brightness is significantly reduced due to the necessity of a color filter and the like, because the same color display principle as that of the transmissive liquid crystal display device is used by the additive color mixture display.

The present invention has been made in view of the above problems, and does not reduce the effective pixel area ratio for display per pixel even if the pixel size is reduced, and does not require a color filter. It is an object of the present invention to provide a reflection type liquid crystal display device in which the display brightness is improved by the above method.

[0005]

According to a first aspect of the present invention, there is provided a reflective liquid crystal display device comprising: a pair of first light-transmitting substrates facing each other; A set of pixel electrodes and a counter electrode formed on the surface, and a switching element having a function of holding a voltage applied to each of the pixel electrodes, and the liquid crystal sandwiched between the first light-transmissive substrates includes Image display means for sequentially displaying a monochrome image corresponding to three primary colors from an image display surface by applying a display voltage from a pixel electrode to modulate the intensity of reflected light of light incident from the outside for each of the pixel electrodes. And color display means formed on the image display surface and capable of sequentially selecting and switching three primary colors in synchronization with the monochrome image.

According to a second aspect of the present invention, in the first aspect, the color display means can apply a voltage to the liquid crystal sandwiched between a pair of second light transmissive substrates facing each other. A liquid crystal color shutter comprising a plurality of liquid crystal cells.

According to a third aspect of the present invention, in the reflective liquid crystal display device according to the second aspect, the liquid crystal color shutter has a plurality of chromatic polarizing plates. According to a fourth aspect of the present invention, in the reflective liquid crystal display device according to the second aspect, the image display means includes a liquid crystal having spontaneous polarization.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In a reflection type liquid crystal display device of the present invention, a high-speed response liquid crystal mode can be used as an image display means for displaying a monochrome image in a time-division manner. For example, a ferroelectric or antiferroelectric liquid crystal in which liquid crystal molecules have spontaneous polarization, OCB (Optically Controlled Birefringingenc).
e), π twist cell, homogeneous alignment cell, BTN
(BistableTwisted Nematic) modes can be used. In particular, thresholdless antiferroelectric liquid crystal, DHF (Deformed H
The elix-ferroelectric mode, OCB, and the like are suitable for displaying halftones because the voltage-reflectance curve changes gently, and are most suitable as monochrome image display means.

These image display means have a structure in which an achromatic polarizing plate having substantially the same polarization characteristics over the entire wavelength range is provided on the incident side and a reflective electrode is provided below the liquid crystal layer.
The light transmitted through the polarizing plate undergoes the modulation of the polarization component when passing through the liquid crystal layer, is reflected by the reflective electrode, and is analyzed by the same polarizing plate to perform monochrome display. A retardation film may be provided between the polarizing plate and the liquid crystal layer in order to perform viewing angle compensation. The operation mode of the liquid crystal without using the polarizing plate, for example, G
Even when H (guest host) or cholesteric liquid crystal layer uses circularly polarized light selective reflection, the response speed of the liquid crystal is sufficiently fast, and if it is about several ms, it can be used as a display element.

It is desirable to provide a means for diffusing light in order to use illumination light from the surroundings efficiently for display and to have an appropriate reflection gain. This is realized by providing a transmission type light scattering element having appropriate scattering characteristics, or by using both of them.

In order to display a good image, it is desirable to provide a thin film transistor (TFT) in each pixel as a switching means for applying and holding a voltage to a liquid crystal layer in each pixel portion. The thin film transistor is formed of amorphous Si or poly Si. Since a light leakage current is generated, a light-shielding film is provided on the TFT layer, and a reflection electrode layer is formed on the light-shielding film through a through-hole to suppress the light leakage current due to incident light and reduce the effective display area ratio (opening ratio). ) Can be increased.

The color display means of the present invention comprises a liquid crystal color shutter. Conventionally proposed liquid crystal cell 2
The principle of a liquid crystal color shutter composed of one sheet and a plurality of chromatic polarizing plates is described in, for example, Japanese Patent Publication No. 4-49928. As for the liquid crystal operation mode, a high-speed response liquid crystal mode, that is, a ferroelectric or antiferroelectric liquid crystal in which liquid crystal molecules have spontaneous polarization, OCB, π twist cell, BTN, DHF mode, etc. can be used as in the monochrome image display means. is there. These liquid crystal operation modes are different from the liquid crystal operation modes used for the image display means, and basically only need to be capable of binary switching.

In the liquid crystal layer of the color display means, by switching the voltage application state, it is possible to provide two states of retardation per liquid crystal cell and four states of two liquid crystal cells. The color display method is to perform RGB primary color display using three of the four states. The principle is that when the polarization plane of light passes through the liquid crystal cell, the polarization state changes due to the retardation of the liquid crystal cell, thereby selectively switching the visible light component absorbed by the chromatic polarizer provided in the optical path. . The polarization axes of the chromatic polarizers are combined in an orthogonal relationship, but the retardation of the liquid crystal cell is such that, under certain voltage application conditions, the fast axis or the slow axis is at 45 ° to one of the polarization axes of the polarizer, and the other is the other. In the application condition, the parallel direction or the birefringence is set to disappear. The center wavelength of the retardation is 450 to 580
It is desirable to set to nm. In addition, 1 /
Optical compensation can be performed at a wavelength that deviates from the center wavelength of retardation by a combination of two-wavelength films. By adopting this optical arrangement, in the former state, the polarization plane rotates by 90 ° with respect to the incident polarized light transmitted through the incident-side polarizing plate, and in the latter, the light is transmitted through the liquid crystal layer without being modulated. By controlling the rotation angle of the polarization plane and selecting the transmission / absorption wavelength range of the chromatic polarizing plate, RGB colors can be displayed. It is also possible to provide a plurality of GH mode liquid crystal layers using chromatic dichroic dyes as color display means without using a chromatic polarizing plate. In the case of the GH mode, three layers of dichroic dyes exhibiting the three primary colors of red, green, and blue are stacked, one layer is colored, and the other layer is in a decolored state, so that the RGB display can be switched. Alternatively, three layers of dichroic dyes exhibiting three primary colors of cyan, yellow and magenta may be laminated, two layers may be colored, and one layer may be in a decolored state.

The switching of the RGB display colors in the color display means is performed in synchronization with the display switching of the RGB images in the image display means. It is desirable to switch the display, instead of switching the entire screen at once, to divide the color display means into a plurality of upper and lower areas and to perform scroll switching from the upper part of the screen to the lower part.

Further, in order to avoid display degradation of the image, it is desirable that the color display means perform black display during a transitional period of switching when the display image is updated. This is for example
Since four states of color can be displayed by two liquid crystal cells, the fourth display color may be set to black display in addition to the three primary colors of RGB. In many cases, the chromatic polarizing plate completely transmits light with a wavelength of 700 nm or more, and may exhibit reddish brown instead of black. In this case, it is effective if any one of the glass substrates of the liquid crystal cell or a new optical filter is provided to absorb light of 700 nm or more. It can be said that as the filter characteristics, for example, characteristics similar to those of HOYA C-500 are desirable. In particular, in a liquid crystal having spontaneous polarization such as a ferroelectric or antiferroelectric liquid crystal, it is necessary to display all four display colors in order to avoid DC voltage application within one field period. The display period is divided into three equal intervals and inserted between each of the RGB display periods, so that deterioration of the image and the liquid crystal can be prevented, which is convenient.

In the reflection type liquid crystal display device of the present invention, by making the image display means and the color display means separable, it is possible to realize a monochrome reflection type liquid crystal display apparatus which is low in power consumption and bright and easy to see when the color display means is separated. It becomes possible. In the case of a liquid crystal operation mode in which a polarizing plate is used for the image display unit and a system in which a color polarizing plate is used for the color display unit, the achromatic polarizing plate on the image display unit side and the image display unit side polarizing plate of the color display unit are shared. You can do it. When the entire screen is to be displayed in monochrome, the color display means may be separated, and luminance information obtained from the RGB image may be displayed on each pixel of the image display means. By removing the color display means, it is possible to prevent a decrease in transmittance caused by color separation, so that the brightness of the screen is increased to three times that in color display. Further, in this configuration, it is not necessary to sequentially display each RGB image, and it is sufficient to display an image composed of luminance information once in the same field period. Therefore, the field frequency is reduced to one third as compared with the color image display. And power consumption can be reduced to 1/3.

In the reflection type liquid crystal display of the present invention,
When there is no illumination by external light, a front illumination device can be attached and used in front of the display screen as an auxiliary light source. As the light source light, besides a three-wavelength light-emitting cold cathode fluorescent tube conventionally used as a backlight light source, an LED can be used. In particular, since LEDs can be driven at low voltage and direct current, they do not require a circuit such as an inverter, and are desirable as auxiliary light sources for reflective LCDs that are required to be thin and lightweight. Further, the absorption in the polarizing plate is reduced, or
More preferably, the auxiliary illumination light is polarized light to improve the color ratio. For this reason, it is possible to improve the light use efficiency by selectively polarizing the light source light using a polarization separation sheet such as DBEF (Sumitomo 3M).

[0018]

Embodiments of the present invention will be described below. However, the configuration of the present invention is not limited to the embodiments described in the examples, and it goes without saying that various combinations of the components of the configurations described in the embodiments and examples of the invention can be adopted. Absent.

(Embodiment 1) Embodiment 1 of the present invention will be described. FIG. 1 is a diagram schematically showing a reflective color liquid crystal display device of the present invention from a side. Although each member is installed in close contact with each other, they are arranged separately for convenience of explanation. A monochrome reflective liquid crystal display unit 101 is provided at the lowermost surface as a monochrome image display means, and a liquid crystal color shutter 102 is provided as a color display means above the monochrome reflective liquid crystal display unit 101.

In this embodiment, the monochrome reflection type liquid crystal display section 101 has a structure using a polarizing plate and a reflection electrode, and a thresholdless antiferroelectric liquid crystal 1 is provided between upper and lower glass substrates 103.
In addition, an Al reflective electrode 105 also serving as a pixel electrode is formed below the liquid crystal layer 104. A forward scattering film 107 for giving a good reflection gain and a so-called achromatic polarizer 108 having a polarization separation effect over the entire visible region are provided on the upper glass substrate 103.

On the other hand, a liquid crystal color shutter 102 serving as a color display means is provided with antiferroelectric liquid crystal cells 109 and 111 for switching the phase of incident light, a half-wave retardation film 113 made of stretched PVA for phase compensation, and different wavelengths. Color polarizing plates 110 and 112 in which two of the characteristics are combined,
The monochrome reflection type liquid crystal display unit 101 is constituted by an achromatic polarizing plate 108 which is shared.

The incident light 114 is applied to the liquid crystal color shutter 102.
Is transmitted twice, and becomes one of the three primary colors of RGB. After being reflected by the Al reflective electrode 105 of each pixel in the monochrome reflective liquid crystal display unit 101 according to the monochrome display image corresponding to the display color of the liquid crystal color shutter, the polarizing plate The light or dark is transmitted or absorbed by the light 108 so that an image of the selected display color is displayed. By switching the three primary color images displayed in time series in this manner at high speed, a color image is displayed.

FIG. 2 is an enlarged view of a partial area 106 of the monochrome reflective liquid crystal display section in FIG. An amorphous Si thin-film transistor (TFT) 201 is formed on the lower glass substrate 103, and a light-shielding insulating film 202 is formed thereon to prevent a light leakage current in the TFT 201 due to incident light. Al reflective electrode 105
Although not shown in the figure, the projections and depressions are formed on the light-shielding film 202 provided with through holes for conducting with the TFT 201 by a sputtering method, thereby having an optimum gain for visual recognition from the front. . An ITO transparent conductive layer 203 is formed as a common electrode on the upper portion of the glass substrate. Although not shown, an alignment film is formed on the upper and lower liquid crystal surface interfaces.

FIG. 3 is a diagram schematically showing an orientation state of the antiferroelectric liquid crystal. When no voltage is applied (FIG. 3B), the liquid crystal molecules have a structure in which the polarization directions are opposite to each other, and thus have no macroscopic birefringence. On the other hand, when either positive or negative voltage is applied (FIGS. 3A and 3C), the polarization direction of the liquid crystal molecules is aligned in one direction, so that birefringence occurs. Generally, the direction perpendicular to the liquid crystal molecules is the ordinary ray refractive index direction, so that it is the fast axis. When the polarity of the applied voltage is reversed, the arrangement direction is reversed, so that the fast axis direction is also reversed.

FIG. 4 is a diagram schematically showing the optical arrangement (left figure) and the voltage-reflectance characteristic (right figure) in the monochrome reflection type liquid crystal display unit 101. Here, the thresholdless antiferroelectric liquid crystal layer 104 has a quarter-wave retardation when a voltage is applied, and the switching angle of the liquid crystal molecules is 90 °. Light incident from the polarizing plate 108 is incident on the liquid crystal layer 104 as linearly polarized light with the polarization transmission axis P. When no voltage is applied, the polarization component is not modulated in the liquid crystal layer.
05, the incident polarized light is reflected while maintaining the polarization state, so that a bright display is obtained. When a voltage is applied, the linearly polarized light is converted into circularly polarized light by arranging the fast axis F in the 45 ° azimuth, and the phase is inverted on the reflection surface 105.
At the time of re-incidence, the circularly polarized light is converted into linearly polarized light orthogonal to the polarization axis P, so that it is absorbed by the polarizing plate 108 to be in a dark state. Since the thresholdless antiferroelectric liquid crystal does not have a hysteresis characteristic and the alignment state of the liquid crystal changes continuously, the voltage (V) -reflectance (R) characteristic is as shown in the right diagram of FIG. Can be displayed.

FIG. 5 is a diagram schematically showing the optical arrangement (left diagram) and the voltage-transmittance characteristic (right diagram) in the liquid crystal color shutter 102. FIG. 6 is a diagram showing the fast axis of the liquid crystal cell 109 or 111 and 1 /. FIG. 3 is a diagram illustrating the orientation of a two-wavelength film 113. Since a binary display is acceptable for the liquid crystal color shutter,
It may have a hysteresis characteristic at an intermediate applied voltage.
5 and 6, for simplicity, the antiferroelectric liquid crystal cell 109 or 11 is placed between the achromatic polarizing plates 108 in the crossed Nicols state.
Consider a case where the 1 and 1/2 wavelength films 113 are arranged. The liquid crystal cell 109 or 111 has a switching angle of 45 ° of 17.5 ° when the positive voltage is applied, and 112.5 ° when the negative voltage is applied.
It has retardation of two wavelengths. The fast axis F of the half-wave film 113 is 22.5 ° (FIG. 6). Considering the case where light enters from the side where the polarization transmission axis P is in the horizontal direction (0 °), the incident light is linearly polarized light having an azimuth of 0 °. Generally, when the light passes through a half-wave plate that forms an angle of θ with respect to the oscillation axis of the linearly polarized light, the transmitted light is converted into 2θ linearly polarized light. Therefore, the linearly polarized light having the azimuth of 0 ° passes through the liquid crystal cell 109 or 111 having the fast axis of 67.5 ° (FIG. 6A) when the positive polarity voltage is applied, and 67.5 × 2 =
It becomes 135 ° linearly polarized light. Since the linearly polarized light having an azimuth of 135 ° is incident on the half-wave film 113 having an azimuth of 22.5 °, it is rotated by (22.5-135) × 2 = −225 °, and a linear line having an azimuth of 135-225 = −90 °. The light is transmitted because it becomes polarized light and coincides with the polarization plate polarization transmission axis. On the other hand, when a negative voltage is applied, the liquid crystal cell 109 or 111 has a fast axis of 112.5 °. Accordingly, the linearly incident polarized light of the 0 ° azimuth becomes linearly polarized light of 112.5 × 2 = 225 ° = −135 °, and − (180−135−22.5 °) for the half-wave film 113 having the azimuth of 22.5 °. ) .Times.2 = -45.degree., So that the light becomes linearly polarized light of 180.degree. (0.degree.) And is absorbed. Even when light reverses, 90 ° → (−135 ° rotation) → -4 when a positive polarity voltage is applied.
5 ° → (225 ° rotation) → 180 ° (transmission), and even when a negative voltage is applied, 90 ° → −45 ° → (−45
(Rotation) → −90 ° (absorption), so that the relationship between voltage and transmittance does not change. Accordingly, the voltage (V) -transmittance (T) characteristic is as shown in the right diagram of FIG.

FIG. 7 is a diagram showing the optical arrangement of each optical element in the liquid crystal color shutter 102. On the light incident side, the transmission axis direction is full wavelength transmission, and the absorption axis direction is a yellow (Y) polarizing plate that absorbs the wavelength range of B, and a blue polarizer (B) that absorbs the GR wavelength range in the direction of the absorption axis that is a complementary color thereof. Are arranged with their polarization transmission axes orthogonal to each other (Y: 0 °, B: 90 °) (112). Hereinafter, a cyan polarizing plate and a red polarizing plate are similarly orthogonally arranged (110) via the liquid crystal cell 111 and the half-wave film 113 having the optical arrangement shown in FIGS.
On the side facing the monochrome reflective liquid crystal display section, an achromatic polarizing plate 108 is arranged in common with a transmission axis azimuth of 0 °. Thus, a color shutter operation can be performed by arranging two sets of polarizers having a complementary color relationship between the liquid crystal cells in an optical arrangement orthogonal to each other. Here, in this embodiment, it is desirable that the achromatic polarizing plate is arranged on the monochrome reflective liquid crystal display side in order to reduce the number of members by commonization, but even if the arrangement order of the two sets of color polarizing plates 112 and 113 is exchanged. There is no problem even if the polarization axis is rotated by 90 °. FIG. 8 shows the optical arrangement of each polarizing plate.

FIG. 9 shows the transmission axes of the color polarizing plates 110 and 112,
FIG. 4 is a diagram illustrating transmittance wavelength characteristics in an absorption axis direction. The case where linearly polarized light is incident and no absorption occurs is shown as 1. The present invention is characterized in that the optical density in the direction of the absorption axis is lower than that of a normal color polarizing plate and that the light loss in the direction of the transmission axis is smaller than that of a normal color polarizing plate because it is used for reflection, that is, transmission twice.

FIG. 10 shows the liquid crystal color shutter in the optical arrangement of FIG.
een), blue (Blue), and black (Black). Natural light incident,
The results are shown under the condition that the reflection gain is 1. It can be seen that each RGB reflectance characteristic was obtained favorably, and even in black display, almost no reflection occurred over 400 to 700 nm, which is almost the entire visible region, indicating that good black display was obtained.

FIG. 11 shows the optical arrangement shown in FIGS.
FIG. 7 is a diagram showing the correspondence between the polarity of the voltage applied to the liquid crystal cells 109 and 111 and the display colors obtained. FIG. 12 is a diagram showing a color gamut obtained from the reflectance characteristics of FIG. FIG.
The chromaticity when the vertices of a triangle surrounded by a straight line on the CIE1931xy chromaticity diagram of No. 2 indicate B, G, and R clockwise from the left, and the inside of the triangle is the color display of the reflective liquid crystal display device of the present invention. Indicates a possible area. According to this example, it was found that a very good RGB chromaticity value was obtained, and that vivid color reproducibility was obtained.

FIG. 13 is a diagram for explaining the sequence of switching the display color of the liquid crystal color shutter and rewriting the screen of the monochrome reflective liquid crystal display unit during one field period in the reflective color liquid crystal display device of this embodiment. According to the present invention, the R, G, and B images of monochrome display are displayed at least once within one field period on the monochrome reflection type liquid crystal display unit, and the liquid crystal color shutters are used to perform R, G, B display in synchronization with this. It is necessary to Since the display of the image is sequentially updated from the upper side to the lower side of the screen, in this embodiment, the display unit of the liquid crystal color shutter is provided in six areas (1301, 1301).
1302, 1303, 1304, 1305, 1306)
The scroll display is performed by shifting the displayed phase. Further, in order to avoid direct current application to the liquid crystal cell of the liquid crystal color shutter, four colors of RGBK are displayed for an equal period within one field period. At this time, the black (K) display period is divided into three equal periods and inserted at the time of switching each RGB display, thereby suppressing flickering caused by performing K display.
Further, the TFT is turned on in the monochrome reflection type liquid crystal display section,
The image is updated (written) by accumulating the electric charge in each pixel, and the image is held by turning off the TFT and holding the electric charge until the next writing period. The display is prevented from being disturbed by setting the display area of the liquid crystal color shutter corresponding to the area to be K display, and the synchronization period between the RGB display period of the liquid crystal color shutter and the RGB image display period of the monochrome reflective liquid crystal display unit is set. It is possible to maximize it. Reference numeral 1308 denotes a holding period.

FIG. 14 is a diagram schematically showing a screen display state at each time in FIG. (A) to (d) show FIG.
3 shows a display state of the time shown in FIG. FIG.
In (a), the display areas 1301 and 1302 of the liquid crystal color shutter display K (black), and in synchronization with this, 13 of the areas 1401 in the monochrome reflection type liquid crystal display section.
One line near the boundary between 01 and 1302 is selected, and the G image to be displayed next is written. Display area 1304-1
Reference numeral 306 denotes an R display, and 14 corresponding to this area is displayed.
In the case of 02, the R image is held and the display is being performed. In FIG. 14B, the area 1 in which writing of the G image has been completed
The liquid crystal color shutter 403 displays G, and the line for writing is near the center of the area 1401. As described above, in the liquid crystal color shutter, the RGB color shutter
Scroll display is performed, one line included in the K display area is selected in the monochrome reflective liquid crystal display unit, and an image of a color to be displayed next is written and held, thereby enabling color moving image display.

FIG. 15 is a block diagram of a circuit for generating a drive signal according to the present embodiment. RGB signal 150 as an original signal
When a control synchronization signal 1502 including a vertical synchronization signal and a horizontal synchronization signal is input, the control signal is converted to n-times speed by the double-speed conversion circuit 1505, and the monochrome reflection type liquid crystal display unit 101 is adjusted to the n-fold field period.
Are input to the X driver 1507 and the Y driver 1508. The RGB parallel signal 1501 is input to the X driver 1507 as an RGB serial signal whose frequency is multiplied by n by the parallel-serial double speed conversion circuit 1504, and sequentially displays a desired RGB image at high speed.

On the other hand, a double-speed control signal is input from the double-speed conversion circuit 1505 to the control circuit 1506, and a six-phase drive signal for operating the liquid crystal color shutter is supplied to the liquid crystal cell 10.
9 and 111 are input.

According to this embodiment, it is not necessary to divide the entire screen into three RGB pixels as compared with a conventional reflection type liquid crystal display device having a structure in which RGB pixels are arranged in a plane. Can be provided. Furthermore, since a color filter or the like is not required, a high-quality reflective color liquid crystal display device with high display luminance can be provided.

(Embodiment 2) FIG. 16 is a diagram schematically illustrating the configuration of Embodiment 2 of the present invention. The feature of this embodiment lies in that the reflection type liquid crystal display unit 101 and the liquid crystal color shutter 102 can be separated, and switching between color and monochrome display is possible. When performing color display, as in the first embodiment,
The combination of the reflection type liquid crystal display unit 101 and the liquid crystal color shutter 102 synchronizes each RGB display color and the RGB display image to perform high-speed scroll display. On the other hand, when performing monochrome display, the achromatic polarizing plate 108, which is a common member, is left on the reflective liquid crystal display unit 101 side, and the color shutter 102 is removed from the display surface, so that the reflectance does not decrease due to color display and is bright. Display becomes possible. Further, it is possible to display an image three times higher in definition with the same number of pixels as compared with a conventional liquid crystal display device in which color filters are juxtaposed. Furthermore, in the case of monochrome display, it is not necessary to perform high-speed display, and the drive frequency can be set in the same manner as usual, so that an increase in power consumption can be prevented.

FIG. 17 is a block diagram of a circuit for generating a drive signal according to the present embodiment. By generating the color / monochrome switching signal 1701 in response to the removal of the liquid crystal color shutter, an out enable signal or a double speed switching signal is generated by the control circuit 1702 to control the double speed switching of the frequency and the switching of the high speed serial / parallel output of the RGB signal. I do.

The second embodiment has the same effects as the first embodiment, and further reduces power consumption by turning off the power of an extra circuit such as a parallel-serial conversion circuit during monochrome display. It is possible to do.

(Embodiment 3) FIG. 18 is a diagram schematically showing the configuration of Embodiment 3 of the present invention. The feature of this embodiment is that three guest host (GH) type liquid crystal layers (1802 to 1804) are provided as the liquid crystal color shutter 102. In order to reduce an increase in weight due to an increase in the number of liquid crystal layers, the transparent substrate 1801 has a common intermediate layer.

FIG. 19 shows the principle of operation of a liquid crystal color shutter using a GH type liquid crystal layer. Liquid crystal layer 180
2, 1803 and 1804 are mixed with cyan (C), magenta (M) and yellow (Y) p-type dyes as dichroic dyes, respectively, so that voltage can be applied to each layer independently. For example, when a voltage is applied to the M liquid crystal layer 1803, the p-type liquid crystal molecules are vertically aligned with respect to the substrate, so that the color is erased. On the other hand, when the C liquid crystal layer 1802 and the Y liquid crystal layer 1804 are colored,
Therefore, since the R component and the B component are absorbed by the Y liquid crystal layer 1804, only the G component can be transmitted and green display can be performed. Here, the monochromatic reflective liquid crystal display unit arranged on the lower side has an achromatic polarizing plate, so that the liquid crystal molecules are aligned in parallel, and the so-called Heilmeier type GH cell structure in which the absorption axis during coloring matches the transmission axis of the polarizing plate. By taking the value, it is possible to obtain the best selection ratio.

FIG. 20 shows the transmittance-wavelength characteristics of each GH liquid crystal layer during coloring / erasing. Each CMY spectrum has an overlapping portion so that there is no wavelength component that is always transmitted in the visible wavelength range.

FIG. 21 is a diagram showing the correspondence between combinations of voltage application in each CMY liquid crystal layer and displayed colors. The black display state can be obtained by turning off all the layers. However, in the GH liquid crystal, since there is no restriction between the application of the AC voltage and the display color, the black display period is set in the display sequence as in the first embodiment. It may be added or omitted.

FIG. 22 shows the RGB values obtained by this embodiment.
This is a reflectance wavelength characteristic at the time of display. The natural light incidence and reflection gain are set to 1. In the third embodiment, in addition to the effects of the first embodiment, since no polarizing plate is provided, a higher reflectance can be realized. Therefore, there is an effect that a brighter display can be obtained than the display obtained by the first embodiment.

(Embodiment 4) FIG. 23 is a view showing Embodiment 4 of the present invention. This embodiment is characterized in that the liquid crystal layer 2301 in the monochrome reflection type liquid crystal display unit 101 is made of GH liquid crystal using a black dichroic dye, and the polarizing plate is completely removed. By using this embodiment, light is not absorbed by the polarizing plate, so that a reflective color liquid crystal display device which is bright and easy to see can be realized. Further, since an optical member such as a polarizing plate is not required for the intermediate layer, the substrate 2302 can be used in common with the liquid crystal color shutter 102, and there is an advantage that the weight can be reduced accordingly. In this embodiment, each GH
In order to optimize the selection ratio (contrast) of the liquid crystal layers 2301 and 1802 to 1804, it is desirable that the liquid crystal molecules have an orientation such that the liquid crystal molecules take a helical structure during coloring.

(Embodiment 5) FIG. 24 is a view showing Embodiment 5 of the present invention. This embodiment is characterized in that an auxiliary lighting device is attached to the first embodiment. The auxiliary lighting device of this embodiment includes a white LED 2401, a reflector 2402, a polarization separation sheet 2403, and a light guide plate 2404.
The illumination light emitted from the white LED 2401 is polarized light separating sheet 2
Only one polarized light component is transmitted by 403, and the undesired polarized light component 2407 is converted by the retroreflection with the reflector 2402 to be a transmissible polarized light component. The light incident on the light guide plate 2404 is reflected by the reflection surface 2405, but is reflected by the minute reflection surface 2406 provided on the observer side of the light guide plate.
(Refer to the enlarged view in the figure), the reflection direction and the amount of reflected light are controlled, and the reflected light enters the reflection type LCD as illumination light. The reflected light 114 having the display information is emitted in a substantially vertical direction from the gap between the minute reflecting surfaces 2406.

Here, since the white LED can emit light by a low-voltage constant-current DC circuit of about 5 V, an inverter and the like necessary for lighting the fluorescent tube are not required. Therefore, the structure of the light source can be simplified, and the weight can be reduced. In addition, the polarization axis of the polarization separation sheet 2403 is set in the paper surface direction or in the direction perpendicular to the paper surface, that is, in the longitudinal direction or short direction of the screen of the reflection type LCD so that the polarization component does not change during reflection in the light guide plate at the subsequent stage. Must match. In this way, it is necessary to make the transmission axis of the incident-side polarizing plate of the liquid crystal color shutter 102 coincide with the polarization axis of the illuminating light. When the liquid crystal color shutter 102 is in an oblique direction, it is possible to provide a retardation film between the exit surface of the light guide plate 2404 and the liquid crystal color shutter 102 so that the polarization component of the illumination light coincides with a desired polarization axis. In addition, the auxiliary lighting device according to the present embodiment can be combined not only with the first embodiment but also with the second, third, and fourth embodiments. In the case of the combination with the second and third embodiments, the auxiliary lighting device is detachable and color display is performed.
It is important that the polarization axis directions of the entrance-side polarizing plate of the liquid crystal color shutter and the monochromatic polarizing plate 108 coincide with each other so that the monochromatic display can function effectively. In the case of the combination with the third and fourth embodiments, if the polarization axis of the illumination light of the auxiliary illumination device is made to coincide with the direction of the absorption axis at the time of coloring of the dichroic dye, the dichroic ratio can be maximized and the display contrast can be improved.

As described above, by combining the auxiliary lighting device as described in this embodiment with the first to fourth embodiments, the image information can be clearly displayed even in an environment where the outside light is small and the reflection type display device is not suitable for visual recognition. It becomes possible to visually recognize.

[0048]

As described above, according to the present invention, it is possible to provide a reflection type liquid crystal display device capable of high-definition and high-quality color display with high display luminance as compared with the conventional embodiment.

[Brief description of the drawings]

FIG. 1 is a diagram schematically illustrating a reflective color liquid crystal display device according to a first embodiment of the present invention from a side.

FIG. 2 is a structural diagram of a monochrome reflective liquid crystal display unit according to the first embodiment of the present invention.

FIG. 3 is a schematic view showing an orientation state of an antiferroelectric liquid crystal in Example 1 of the present invention.

FIG. 4 is a diagram illustrating a monochrome reflective liquid crystal display unit according to the first embodiment of the present invention.

FIG. 5 is a diagram schematically illustrating an optical arrangement and a voltage-transmittance characteristic in a liquid crystal color shutter according to the first embodiment of the present invention.

FIG. 6 is a diagram showing a fast axis of a liquid crystal cell and an orientation of a half-wave film in Example 1 of the present invention.

FIG. 7 is a diagram showing an optical arrangement of each optical element in a liquid crystal color shutter according to the first embodiment of the present invention.

FIG. 8 is a diagram illustrating an optical arrangement of a polarizing plate according to the first embodiment of the present invention.

FIG. 9 shows a transmission axis of a color polarizing plate according to the first embodiment of the present invention;
Diagram illustrating transmittance wavelength characteristics in the absorption axis direction

FIG. 10 is a diagram showing a reflectance-wavelength characteristic when each of RGBK is displayed in the first embodiment of the present invention.

FIG. 11 is a diagram showing the correspondence between the polarity of the voltage applied to the liquid crystal cell and the display color obtained in the first embodiment of the present invention.

FIG. 12 is a diagram showing a color gamut obtained in Embodiment 1 of the present invention.

FIG. 13 is a view for explaining a drive sequence in the first embodiment of the present invention.

FIG. 14 is a diagram schematically showing a screen display state at each time according to the first embodiment of the present invention.

FIG. 15 is a diagram showing a drive circuit according to the first embodiment of the present invention.

FIG. 16 is a diagram schematically illustrating the configuration of a second embodiment of the present invention.

FIG. 17 is a diagram illustrating a drive circuit according to a second embodiment of the present invention.

FIG. 18 is a diagram schematically illustrating a configuration of a third embodiment of the present invention.

FIG. 19 is a diagram showing an operation principle of a liquid crystal color shutter according to a third embodiment of the present invention.

FIG. 20 is a graph showing transmittance / wavelength characteristics of each GH liquid crystal layer when colored / decolored in Example 3 of the present invention.

FIG. 21 is a diagram showing a correspondence relationship between a combination of voltage application to each CMY liquid crystal layer and a displayed color according to a third embodiment of the present invention.

FIG. 22 is a diagram illustrating a reflectance-wavelength characteristic during RGB display according to the third embodiment of the present invention.

FIG. 23 is a cross-sectional view schematically illustrating a configuration of a fourth embodiment of the present invention.

FIG. 24 is a cross-sectional view schematically illustrating a configuration of a fifth embodiment of the present invention.

[Explanation of symbols]

101: Monochrome reflective liquid crystal display unit 102: Liquid crystal color shutter 103, 1801, 2302 ... Substrate 104, 1802-1804, 2301: Liquid crystal layer 105 ... Reflective electrode 106: Monochrome reflection -Type liquid crystal display pixel portion 107: forward scattering element 108: achromatic polarizing plate 109, 111: liquid crystal color shutter portion liquid crystal cell 110, 112: color polarizing plate 113: 1/2 wavelength film 114 ... Light 201 ... TFT 202 ... Light shielding layer 203 ... Transparent electrode layer 1301-1306, 1401-1403 ... Display screen area 1307 ... Voltage writing period 1308 ... Voltage holding period 1501 ... RGB signal 1502 ... Synchronous signal 1504 ... Parallel-serial conversion circuit 150 ··· Double speed conversion circuit 1506 ··· Liquid crystal color shutter signal generation circuit 1507 ··· X driver 1508 ··· Y driver 1701 ··· Display switching signal 1702 ··· Control circuit 1703 ··· Buffer 2401 ··· LED 2402 Reflector 2403 Polarization separation sheet 2404 Light guide plate 2405 2406 Reflection surface 2407 Undesired polarized light

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) 2H091 FA09X FA11Z FA14Y FA16Z FA23Z FA31Y FA34Y FA42Z FA45Z FD06 GA13 HA07 HA08 HA12 2H092 JA24 JB07 JB51 KB13 MA05 NA26 PA06 PA09 PA11 PA13 QA08 QA13 QA14 2H093 NA16 ND25 NF06 NF19 NF20

Claims (4)

[Claims] 1. A set of opposing first light-transmitting substrates, a set of pixel electrodes and opposing electrodes formed on opposing surfaces of the first light-transmitting substrate, and a voltage applied to each of the pixel electrodes A switching element having a holding function of applying a display voltage from the pixel electrode to the liquid crystal sandwiched between the first light-transmitting substrates, thereby reducing the intensity of reflected light of light incident from the outside. Image display means for sequentially displaying a black-and-white image corresponding to the three primary colors by modulating each pixel electrode from the image display surface; and forming the three primary colors in synchronization with the black-and-white image formed on the image display surface. A reflection type liquid crystal display device provided with color display means capable of sequentially selecting and switching. 2. A liquid crystal color shutter comprising a plurality of liquid crystal cells capable of applying a voltage to liquid crystals sandwiched between a pair of opposing second light-transmitting substrates. The reflective liquid crystal display device according to claim 1, wherein: 3. The reflection type liquid crystal display device according to claim 2, wherein said liquid crystal color shutter has a plurality of chromatic polarizing plates. 4. The reflection type liquid crystal display device according to claim 2, wherein said image display means comprises a liquid crystal having spontaneous polarization.