JP2000352611A - Color filter for reflection transmission type liquid crystal display device and display device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a color liquid crystal display device which does not cause negative-positive reversal of an image for both of the reflection display mode and transmission display mode by constituting the color filter of a patterned reflection type cholesteric color filter and of a light absorption type color filter which transmits light in the same color as the color of the respective reflected light. SOLUTION: The liquid crystal display device has transparent substrates 11, 12 disposed at an equal gap, and a color filer layer is formed on the transparent substrate 12 on the back light 91 side and facing a liquid crystal layer 4. The color filter layer is formed by laminating reflection type cholesteric color filters 5R, 5G, 5B patterned into respective colors of R, G, B, and light absorption type color filters 6R, 6G, 6B which transmit light of the same colors as those of the respective reflected light. Below the substrate, the device is also equipped with a diffusion plate 8 to homogenize the light emitted from the back light system consisting of the back light 91 and a light guide plate 92 which guides the light from the back light 91, and with a condenser plate 7 to collimate the diffused light.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflection-transmission type liquid crystal display device, and more particularly to a reflection-type cholesteric color filter using a guest-host type liquid crystal layer.

[0002]

2. Description of the Related Art A transflective liquid crystal display device can freely select a transmissive display mode or a reflective display mode according to the surrounding environment, so that visibility in a dark environment is improved as in the front light system. So excellent. The transflective monochrome liquid crystal display element has a characteristic feature in that a transflective plate is provided between the backlight and the lower polarizer. As described above, the transflective monochrome liquid crystal display device has been put to practical use, but only a part of the color liquid crystal display device has been developed and has not been put to practical use yet.

FIG. 6 is a cross-sectional view of a recently proposed transflective color liquid crystal display device. In the figure, 6
1 is a polarizing plate, 62 is a retardation film, 63 is a color liquid crystal display element, 64 is a diffusing plate, 65 is a reflective polarizing plate, 66 is a light absorber, and 67 is a backlight system. As shown in FIG. 6, the reflective / transmissive color liquid crystal display element uses a reflective polarizing plate 65 having a function of reflecting a specific polarized light component on the outer surface of the liquid crystal panel and transmitting the remaining polarized light components. This method has an excellent feature that a bright display can be obtained in any of the transmission display mode and the reflection display mode, and is considered to be ideal from the viewpoint of light use efficiency. However, the problem with this method is that the display is inverted in the reflective display mode (a) and the transmissive display mode (b), so that the same display must be realized by converting the data signal. The effect of the reversal is that the contrast characteristics of the transmissive display mode depend on the surrounding environmental conditions.

[0004]

SUMMARY OF THE INVENTION The object of the present invention is to provide a transflective color liquid crystal display element in which an image is not negatively or positively inverted in either a reflective display mode or a transmissive display mode.

[0005]

According to a first aspect of the present invention, there is provided a color filter for use in a transflective type liquid crystal display device, comprising: a patterned reflective cholesteric color filter; And a light absorption type color filter which transmits light of the same color as the reflected light color. With the above configuration, it is possible to easily manufacture a color filter for a reflection-transmission type liquid crystal display element in which an image is not negatively or positively inverted in the reflection display mode or the transmission display mode. According to a second aspect of the present invention, a guest-host type liquid crystal layer, a color filter for a transmissive liquid crystal display element according to the first aspect, and a backlight are formed in this order. It is characterized by. With the above configuration, a transflective liquid crystal display element in which an image is not negative-positive inverted in the transflective display mode or the transmissive display mode can be obtained.

[0006]

Next, an embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a sectional view of a transflective liquid crystal display device according to the present invention. In FIG. 1, 11 is an upper transparent substrate, 12 is a lower transparent substrate disposed in parallel with the upper substrate, 21 is an upper ITO (transparent electrode), 22 is a lower ITO, 31 is an upper alignment film,
Reference numeral 32 denotes a lower alignment film. 4 is a guest-host type liquid crystal layer, 5 is a cholesteric color filter, and R (red)
・ G (green) ・ B (blue)
Reference numeral 6 denotes a normal color filter, which is similarly patterned for each of R, G, and B colors. Reference numeral 7 denotes a light collector, 8 denotes a diffusion plate, 91 denotes a backlight, and 92 denotes a light guide plate.

As can be seen from FIG. 1, the liquid crystal display device of the present invention has transparent substrates 11, 12 arranged at equal intervals.
In the meantime, a guest-host type liquid crystal layer 4 capable of controlling light transmittance over a visible light region, and transparent electrodes 21 and 22 and alignment films 31 and 32 are formed so as to hold the liquid crystal layer 4, respectively. . The transparent substrate 12 on the side of the backlight 91 of the liquid crystal layer 4 has reflective cholesteric color filters 5R, 5G, and 5B patterned for each of R, G, and B, and light absorption that transmits light of the same color as the reflected light color of each of them. A color filter layer is formed by laminating the mold color filters 6R, 6G, and 6B. Further thereunder, a backlight 91 and a light guide plate 92 for guiding light from the backlight 91 are provided.
And a light collecting plate 7 (or a condensing film) for collimating the light emitted from the backlight system comprising

The guest-host liquid crystal layer 4 itself is known.
That is, a dichroic dye is added to a normal liquid crystal, and when no electric field is applied, the dichroic dye is oriented in the horizontal direction, so that light does not pass through and looks dark. Since the coloring pigment is oriented vertically and vertically, it has the property of transmitting light and appearing bright.

A cholesteric color filter is a filter utilizing cholesteric selective reflection, and is well known per se. 1) For example, for a method of producing a cholesteric color filter, see R.S. Mauer, FH. Kreuzer, and
J. Strohrer, SID94 DIgest,
399 (1994). P. Wite, M .; Brehmer, and J
oh Lub, IDW98, 303 (1998). And so on. 2) A liquid crystal display using a cholesteric color filter is disclosed in Japanese Patent Application Laid-Open No. Hei 10-177167. JP-A-8-320480. And so on.

That is, the cholesteric color filter 5 is composed of a cholesteric liquid crystal layer, and its liquid crystal molecules are oriented parallel to the layer, but the molecules have a helical structure in the vertical direction of the layer. If the layer is formed by controlling the physical property values of the cholesteric liquid crystal layer, that is, the ordinary light refractive index, the extraordinary light refractive index, and the helical pitch, an optical filter having an arbitrary selective reflection center wavelength and a selective reflection wavelength width can be formed. The adjustment of the helical pitch can be performed by, for example, a manufacturing method in which two or more materials having different helical pitches are mixed and adjusted. When the spiral is right-handed, the cholesteric color filter reflects right circularly polarized light and transmits left circularly polarized light along the spiral. When the helix has a left-handed twist, it reflects the left-handed circularly polarized light component and transmits the right-handed circularly polarized light component.

FIG. 4 shows the optical characteristics of the cholesteric color filter 5. In FIG. 4B, reference numeral 1 denotes a center wavelength of 450 nm (nanometers) and 400 to 50 nm.
A cholesteric color filter for light in the 0 nm region (blue), a cholesteric color filter for light having a center wavelength of 550 nm and light in the range of 500 to 600 nm (green), and a cholesteric color filter for light having a center wavelength of 650 nm and light in the range of 600 to 700 nm (red). In the case of a cholesteric color filter, the ratio of transmitted light to wavelength (a) and the ratio of reflected light to wavelength (b) are shown. 1, that is, according to 1) a and b in FIG. 4 (B), 50% (blue light left circularly polarized light) is transmitted for light (blue) in the region of 400 to 500 nm having a center wavelength of 450 nm,
50% (blue light right circularly polarized light) is reflected. Light other than the above-mentioned region of 400 to 500 nm is all transmitted and is not reflected. I can understand.

2. Similarly, according to 2) a and b in FIG. 4 (B), 50% (green light left circularly polarized light) is transmitted for light (green) in the region of 500 to 600 nm having a center wavelength of 550 nm. ,
50% (green light right circularly polarized light) is reflected. Light other than the above region 500 to 600 nm is all transmitted, and is not reflected. I can understand.

3, and similarly, 3) a in FIG.
According to b, for light (red) in the region of 600 to 700 nm with a center wavelength of 650 nm, 50% (red light left circularly polarized light) is transmitted,
50% (red light right circularly polarized light) is reflected. Light other than the above-mentioned region of 600 to 700 nm is all transmitted and is not reflected. I can understand.

FIG. 4A illustrates the operation of the cholesteric color filter of the red-light right circularly polarized light reflection type according to 3) a and b in FIG. 4B. In the figure, for each color of red, green, and blue, the dotted line indicates left circularly polarized light, and the solid line indicates right circularly polarized light. As can be seen from the figure, the red light right circularly polarized reflection type cholesteric color filter reflects only red light right circularly polarized light,
Other colors (ie, left circularly polarized red light,
The right circularly polarized green / blue light) has the function of transmitting. In FIG. 4A, a red light right circularly polarized light reflection type cholesteric color filter is described as an example, but the same applies to other green light and blue light.

A reflection type cholesteric color filter as shown in FIG. 4 is used as the cholesteric color filter 5 in FIG. 1 and is patterned into red, green and blue pixels, respectively. In FIG. 1, in order from the left, a red light right circularly polarized reflection type cholesteric color filter (ie,
All other light is transmitted), green light right circularly polarized cholesteric color filter (ie, all other light is transmitted), blue light right circularly polarized cholesteric color filter (ie, all other light is transmitted) ).

FIG. 5 is a view for explaining the optical characteristics of the ordinary color filter 6 shown in FIG. 1 using a red pigment dispersion type color filter as an example. In FIG. 5B, reference numeral 1 denotes a center wavelength of 45.
Light in the 400 to 500 nm region at 0 nm (blue pigment dispersion type)
Color filter 2, 500 with center wavelength of 550 nm
A light (green pigment dispersion type) color filter in a 600 nm region,
Reference numeral 3 denotes a light (red pigment dispersion type) color filter having a center wavelength of 650 nm and a wavelength range of 600 to 700 nm, and indicates the ratio of wavelength to transmitted light. 1. According to 1) of FIG. 5B, all light (blue) in the region of 400 to 500 nm having a center wavelength of 450 nm is transmitted. All the light in the region other than 400 to 500 nm is absorbed. I can understand. 2. Similarly, according to 2) in FIG. 5B, all light (green) in the 500-600 nm region having a center wavelength of 550 nm is transmitted. All the light in the region other than 500 to 600 nm is absorbed. I can understand. 3, and similarly, according to 3) in FIG. 5B, all light (red) in the region of 600 to 700 nm having a center wavelength of 650 nm is transmitted. All light in the region other than the above-mentioned region of 600 to 700 nm is absorbed. I can understand.

FIG. 5A illustrates the operation of the red pigment-dispersed color filter according to 3) of FIG. 5B. In the figure, for each color of red, green, and blue, the dotted line indicates left circularly polarized light, and the solid line indicates right circularly polarized light. As can be seen from the figure, red light transmits both right circularly polarized light and left circularly polarized light, and absorbs other colors (ie, left and right circularly polarized green and blue lights). are doing. FIG. 5A illustrates a red pigment dispersion type color filter as an example, but the same applies to other color pigment dispersion type color filters.

A pigment-dispersed color filter as shown in FIG. 5 is used as the ordinary color filter 6 in FIG. 1, and is patterned into red, green and blue pixels.
In FIG. 1, in order from the left, a red pigment dispersion type color filter (that is, red transmission and absorption of all light other than red) is provided below a red light right circular polarization reflection type cholesteric color filter 5, and green light right circular polarization reflection. Below the cholesteric color filter 5, a green pigment dispersion type color filter (that is, green transmission and absorption of all light except for green) is provided under a blue light right circular polarization reflection type cholesteric color filter 5, and a blue pigment dispersion type filter is provided. Color filters (that is, blue transmission and absorption of all light other than blue) are provided, respectively.

FIGS. 2 and 3 are schematic diagrams showing the display principle of the display device shown in FIG. 1. FIG.
Indicates that the liquid crystal is in the light shielding mode. 2 and 3, the cholesteric color filter 5 shown in FIG.
The cholesteric color filter shown in FIG. 4 is a red-light right circularly polarized light reflection type, and the ordinary color filter 6 shown in FIG.
The following shows an example using a red pigment dispersion type color filter. According to the present invention having the above configuration, the reason why the image is not negative-positive inverted in the reflective display mode or the transmissive display mode will be described with reference to FIGS.

A: When the liquid crystal is in the light transmitting state: In FIG. 2 where the liquid crystal 4 is in the light transmitting state, the case of the reflective display mode and the case of the transmissive display mode will be described first. 1. When external light is used (that is, in the case of the reflection display mode): The red light right circularly polarized reflection type cholesteric color filter 5 reflects only red light right circularly polarized light, and other colors (that is, left circularly polarized red light, And the left and right circularly polarized green and blue lights) have the function of transmitting the red and right circularly polarized light reflection type cholesteric color filters 5,
Only the right circularly polarized light of red light is reflected, and the other colors are transmitted and reach the red pigment dispersion type color filter 6. Since the red pigment dispersion type color filter 6 has a function of transmitting red light but absorbing other colors (that is, left and right circularly polarized lights of green and blue light), the red pigment dispersion type color filter 6 has a function of absorbing red light. The left and right circularly polarized lights of green and blue light are absorbed by the action of the filter 6, and these colors do not return to the liquid crystal 4 again. As a result, red light right circularly polarized light that is reflected light, that is, 50% of red light comes into the eyes. 2. When backlight light is used (that is, in the case of the transmissive display mode): light from the backlight light is transmitted only by red light by the action of the red pigment dispersion type color filter 6;
Other colors (green and blue light) are absorbed. The red light transmitted through the red pigment dispersion type color filter 6 reaches the red light right circular polarization reflection type cholesteric color filter 5. The red light that has arrived transmits red light left circularly polarized light and reflects red light right circularly polarized light by the action of the red light right circularly polarized light reflection type cholesteric color filter 5. Accordingly, red light left circularly polarized light, that is, transmitted light, that is, 50% of red light enters the eyes. As described above, in the case of the reflective display mode using external light, red light of right-handed circularly polarized light, which is reflected light, enters the eyes, and in the case of the transmissive display mode using backlight light, The transmitted light, red light, left circularly polarized red light enters the eyes, and in each case, the red light is visible. Thus, according to the present invention,
There is no negative / positive reversal.

B: When the liquid crystal is in the light-shielded state: The case of the reflective display mode in FIG. 3 in which the liquid crystal 4 is in the light-shielded state and the case of the transmissive display mode will now be described. 1. When using external light (that is, in the case of the reflective display mode): Since external light (red, green, and blue light) is absorbed by the liquid crystal 4 in a light-shielded state, it cannot reach the cholesteric color filter 5. Therefore, there is no reflected light. 2. When backlight light is used (that is, in the case of the transmissive display mode): light from the backlight light is transmitted only by red light by the action of the red pigment dispersion type color filter 6;
Other colors (green and blue light) are absorbed. The red light transmitted through the red pigment dispersion type color filter 6 reaches the red light right circular polarization reflection type cholesteric color filter 5. The red light that has arrived transmits red light left circularly polarized light and reflects red light right circularly polarized light by the action of the red light right circularly polarized light reflection type cholesteric color filter 5. The red left circularly polarized light transmitted through the red right circularly polarized reflection type cholesteric color filter 5 is absorbed by the liquid crystal 4 in a light shielding state. Therefore, there is no transmitted light. As described above, in the reflective display mode using external light and in the transmissive display mode using backlight, red light is not seen by the liquid crystal 4 in the light-shielded state. in this way,
According to the present invention, of course, no light is visible when the liquid crystal is shielded. In summary, according to the transflective liquid crystal display device of the present invention, the liquid crystal is completely dark when the liquid crystal is in a light-shielding state, and is red-light when the liquid crystal is in a light-transmitting state in both the reflective display mode and the transmissive display mode. And no negative / positive inversion occurs.

A specific embodiment of the present invention is as follows. First, a method for manufacturing this element will be described. As the transparent substrate 11, a glass plate having a patterned ITO electrode and having a thickness of 1.1 mm was used. As the transparent substrate 12, a glass plate having a thickness of 1.1 mm was used. Next, a color filter was formed and patterned on the transparent substrate 12 by using a transfer resist film (transser) for forming a pigment dispersion type color filter manufactured by Fuji Photo Film Co., Ltd. Cholesteric Color Filter is Wacker Chemie Gmb
Liquid crystal silicone composition TC3951L manufactured by Company H was mixed with Irgocur 907 manufactured by Ciba-Geigy, which is a polymerization initiator, and the mixture was mixed with an organic solvent, followed by spin coating.
Then, after evaporating the solvent by heating, the film was formed by performing mask exposure while changing the temperature. Further, after a flattening layer was formed thereon, an ITO film was formed by a sputtering method. The patterning of the ITO film was performed by a known method. Before a pigment dispersion type color filter is formed by a driving method, a thin film transistor or a thin film diode may be formed as a switching element by a known method. On these substrates, a polyimide alignment film LX-1400 manufactured by Hitachi Chemical DuPont Microsystems was formed by spin coating, and after heating and firing, an alignment treatment was performed by rubbing. Next, these substrates were bonded together with a 7 μm diameter silica spacer interposed therebetween. As liquid crystals, 3 wt% of NKX-1366 (manufactured by Nippon Kogaku Dye Co., Ltd.), which is a dichroic dye mixture, was added to ZLI- manufactured by Merck, and S-811 manufactured by Merck was used as a chiral agent so that the helical pitch became about 8 μm. And made adjustments. When a voltage was applied to this element and the response was visually confirmed, switching of display could be clearly recognized regardless of the intensity of ambient light.

[0023]

As described above, according to the present invention,
The reflection-transmission type liquid crystal display element is connected to a guest-host type liquid crystal layer 4.
And a patterned reflection type cholesteric color filter 5, a light absorption type color filter 6 that transmits light of the same color as the respective reflected light colors, and a backlight and light guide plates 91 and 92. For example, when using a red light right circularly polarized reflection type cholesteric color filter and a red pigment dispersion type color filter, the pixel reflects, for example, red light right circularly polarized light in the reflection display mode, and, for example, red light left circularly polarized light in the transmission display mode. Is transmitted, so that red light enters the eyes in both cases, and there is an effect that a transflective liquid crystal display element in which an image is not negative-positive inverted in both the reflective display mode and the transmissive display mode is obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view of a transflective liquid crystal display device according to the present invention.

FIG. 2 is a schematic diagram showing a display principle of the display element (when liquid crystal transmits light) of FIG.

FIG. 3 is a schematic diagram illustrating a display principle of the display element (when liquid crystal is shielded from light) of FIG. 1;

FIG. 4 is a diagram illustrating optical characteristics of the cholesteric color filter of FIG. 1 in which a red light right circularly polarized light reflection type cholesteric color filter is used as an example.

FIG. 5 is a diagram illustrating optical characteristics of the ordinary color filter of FIG. 1 using a red pigment dispersion type color filter as an example.

FIG. 6 is a cross-sectional view of a conventionally known transflective liquid crystal display element.

[Explanation of symbols]

 Reference Signs List 11 upper transparent substrate 12 lower transparent substrate 21 upper ITO (transparent electrode) 22 lower ITO 31 upper alignment film 32 lower alignment film 4 guest host type liquid crystal layer 5 cholesteric color filter 6 ordinary color filter 7 light collector 8 light diffusion Board 91 Backlight 92 Light guide plate

Claims (2)

[Claims] 1. A color for a transflective liquid crystal display, comprising: a patterned reflective cholesteric color filter; and a light absorption type color filter that transmits light of the same color as the reflected light. Filter. 2. A transflective liquid crystal display device comprising: a guest-host type liquid crystal layer; a color filter for a transflective liquid crystal display according to claim 1; and a backlight.