JP3016108B2 - Reflective liquid crystal electro-optical device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflection type liquid crystal electro-optical device, and more particularly to a color reflection type liquid crystal electro-optical device which is used for a timepiece and a small portable device and which displays a color excellent in brightness and aesthetic appearance.

[0002]

2. Description of the Related Art Conventionally, in a reflection type color liquid crystal electro-optical device, a color filter is generally provided in front of a reflection plate of a normal reflection type TN liquid crystal display device. As the color filter, those obtained by coating the surface of a transparent resin film with a dye or those produced by dissolving a dye in a transparent resin are used. Furthermore, a method that enables color display by using a color polarizing plate for at least one of the polarizing plates without using a color filter, or coating or printing a dye on a metal surface of a reflecting plate, There is a method that enables color display as a colored reflector, or a method that enables color display as a dichroic mirror by coating several layers of a dielectric on the substrate surface of the reflector. Further, a method has been proposed in which a cholesteric liquid crystal cell that exhibits selective reflectivity at a specific wavelength in the visible light region is used instead of the reflector, and has the function of a color reflector.

[0003]

However, the color display system in which a color filter and a reflection plate made of aluminum or the like, which have been frequently used, are combined with each other, the transmittance of a dye used in the color filter and the reflection ratio of a metal reflection plate made of aluminum or the like are reduced. Poor reflectivity makes clear color display impossible. In the method using two polarizing plates, the reflected light is emitted through the color filter layer twice and through the polarizing plate four times, so that a bright display cannot be realized. Also,
The color display method using a dichroic mirror with a dielectric coating has a high linear reflectance after reflection and a low diffuse reflectance, so that the contrast between the display unit and the non-display unit is low and the display is difficult to distinguish, Also, a vacuum process is required for the dielectric coating, which increases the manufacturing cost.

Using only one polarizing plate shown in FIG. 2,
In a system using a cholesteric liquid crystal cell having a feature of being bright as a color reflector, a change in a reflection wavelength accompanying a temperature change of a cholesteric pitch is large, and a temperature region showing selective reflection is narrow. In addition, since the cholesteric liquid crystal is a low-molecular liquid crystal, it is necessary to have a structure in which it is injected into a gap between two glass substrates, so that the distance between the liquid crystal optical element and the reflection plate becomes large, and a shadow is generated, resulting in visibility. Deteriorates.
Furthermore, it has drawbacks that it cannot be manufactured inexpensively due to its structure,
There has been a problem that it is difficult to obtain a reflective liquid crystal electro-optical device that is practical, has a clear appearance, and is capable of displaying a color with excellent appearance.

Accordingly, an object of the present invention is to provide a cholesteric liquid crystal polymer film which exhibits selective reflectivity in the visible light region to provide a practical, bright, clear and aesthetically pleasing color. An object of the present invention is to provide a reflective liquid crystal electro-optical device capable of displaying.

[0006]

Means for Solving the Problems In order to solve the above-mentioned problems, a twist orientation of about 90 ° is provided between two transparent substrates having a transparent electrode and having been subjected to an alignment treatment on the transparent electrode. A liquid crystal cell in which liquid crystal is sealed, a polarizing plate disposed on the front surface of the liquid crystal cell so that the alignment direction and absorption axis of the liquid crystal in contact with the substrate on the front surface of the liquid crystal cell are parallel or perpendicular, and the back surface of the liquid crystal cell A quarter-wave plate disposed so that an optical axis thereof is approximately 45 ° with respect to an alignment direction of liquid crystal in contact with a substrate on a back surface of the liquid crystal cell, and a cholesteric liquid crystal polymer film disposed on the back surface of the quarter-wave plate And a reflective liquid crystal electro-optical device comprising a light absorbing plate disposed on the back of the cholesteric liquid crystal polymer film.

[0007]

The operation principle of the reflection type liquid crystal electro-optical device configured as described above will be described with reference to FIG. FIG. 1 is an explanatory view showing an embodiment of the reflection type liquid crystal electro-optical element of the present invention. FIG.
1A and 1B, reference numeral 1 denotes a liquid crystal cell having a 90 ° TN alignment. A transparent electrode 4 made of patterned ITO is formed inside the transparent upper substrate 2 and lower substrate 3, and an alignment film 5 such as polyimide is applied, and the alignment direction between the upper substrate 2 and the lower substrate 3 becomes substantially perpendicular. As described above, a parallel alignment treatment was performed by rubbing. The effect is the same even if this alignment film is formed by oblique evaporation of silicon oxide. The gap was filled with a nematic liquid crystal 6 having a positive dielectric anisotropy. A polarizing plate 7 was provided outside the upper substrate 2 so that the optical axis coincided with the alignment direction of the alignment film 5 on the upper substrate 2. A 波長 wavelength plate 8 is provided outside the lower substrate 3 so that the optical axis forms an angle of 45 ° with the alignment direction of the alignment film 5 on the lower substrate 3. Further on the outside, a cholesteric liquid crystal polymer film 9 and a light absorbing plate 10 for absorbing visible light were provided. The cholesteric liquid crystal polymer film 9 is a polymer having a cholesteric liquid crystal structure of a polypeptide such as polyglutamate. In the present invention, the cholesteric liquid crystal polymer film may be constituted singly or may be constituted so as to be sandwiched between two transparent plastic films.

FIG. 1A shows the state when no electric field is applied.
When no electric field is applied, the liquid crystal 6 in the liquid crystal cell 1 is twisted by 90 ° between the upper and lower substrates by the above-described alignment treatment. After passing through the polarizing plate 7, the incident light 11 becomes linearly polarized light and enters the liquid crystal cell 1.
The light enters the four-wavelength plate 8. The light that has passed through the quarter-wave plate 8 becomes right (or left) circularly polarized light, and light in a specific wavelength range of this polarized light is reflected by the cholesteric liquid crystal polymer film 9, and light outside this range falls in the visible light range. The light reaches the absorbing light absorbing plate 10.

Here, when the light absorbing plate is a black plate, all the light that has arrived is absorbed. If the light absorbing plate has a characteristic of reflecting only light of a specific wavelength, the light of the specific wavelength is reflected by the light absorbing plate and transmitted through the cholesteric liquid crystal polymer film again. The circularly polarized light reflected by the cholesteric liquid crystal polymer film and the circularly polarized light reflected by the light absorbing plate are
The light passes through the quarter-wave plate 8 again to be linearly polarized, the polarization direction is rotated by 90 ° in the liquid crystal cell 1, and passes through the polarizing plate 7 to become the output light 12. Therefore, when the light absorbing plate is a black plate, it shows vivid coloring of the selective reflection wavelength reflected by the cholesteric liquid crystal polymer film, and when the light absorbing plate reflects light of a specific wavelength, the light is reflected by the light absorbing plate. The light having the specific wavelength and the light having the selective reflection wavelength reflected by the cholesteric liquid crystal polymer film are combined, emitted, and colored.

FIG. 1B shows a state when an electric field is applied. When an electric field is applied, the liquid crystal 6 in the liquid crystal cell 1 rearranges vertically with respect to the upper and lower substrates due to its dielectric anisotropy. Incident light 11
Is a linearly polarized light after passing through the polarizing plate 7,
, But is incident on the 波長 wavelength plate 8 without changing the polarization direction. The light that has passed through the quarter-wave plate 8 becomes circularly polarized light whose rotation direction is opposite to that when voltage is applied, and light in the entire wavelength range of this polarized light passes through the cholesteric liquid crystal polymer film 9 and reaches the light absorbing plate 10. I do.

When the light absorbing plate is a black plate, all the light that has arrived is absorbed. When the light absorbing plate reflects light of a specific wavelength, a cholesteric liquid crystal polymer film, １ ／
The light passes through a wave plate, a liquid crystal cell, and a polarizing plate and is emitted. Therefore, when the light absorbing plate is a black plate, a black display can be realized on a colored background by vivid selective reflection light, and when the light absorbing plate reflects a specific wavelength, the background is selected by a cholesteric liquid crystal polymer film. The color of the light is a mixture of the reflected light and the light reflected by the light absorbing plate, and the display unit exhibits the color of the light reflected by the light absorbing plate. That is, the color tone can be slightly changed by slightly changing the reflection characteristics of the light absorbing plate.

In the reflection type liquid crystal electro-optical device configured as described above, the color tone of the display hardly changes even when the temperature of the surrounding atmosphere is changed within the temperature range in which the liquid crystal exhibits a liquid crystal state. . This is because the helical pitch of the cholesteric liquid crystal is fixed in the polymer, so that the temperature dependence of the helical pitch is extremely small.

Further, the reflection type liquid crystal electro-optical device having the above-described structure can realize a bright display because of one polarizing plate. However, when a polarizing plate having a high transmittance is used, the color tone of the display becomes brighter and more beautiful. Become. A polarizing plate with high transmittance means that the degree of polarization is small.For example, when a black plate is used as the light absorbing plate, the degree of black in the ON portion of the display hardly changes, and selective reflection This is because the light transmittance increases. In the case of a normal TN type liquid crystal display device, a polarizing plate having a transmittance of about 40% is often used.
When the transmittance of the polarizing plate is 45% or more, the display becomes remarkably bright and beautiful.

The cholesteric liquid crystal polymer film is a thin film having a thickness of about 0.1 mm, and can be laminated and integrated with a quarter-wave plate and a light absorbing plate by thermocompression bonding. It can also be formed to the same thickness. By stacking and integrating in this way, not only can it be made thinner, but also the Fresnel reflection at each interface, which occurs when an air layer is interposed, is reduced, and a bright and highly visible display becomes possible.

As compared with the case where the cholesteric liquid crystal cell as shown in FIG. 2 is used as the selective reflection plate, the thickness up to the selective reflection layer can be reduced by the thickness of one substrate of the cholesteric liquid crystal cell. The cholesteric liquid crystal cell's substrate interface eliminates Fresnel reflection, which reduces the display brightness,
The sharpness of the color has made it possible to make a marked improvement.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. (Embodiment 1) In FIG. 1, the transparent substrates 2 and 3 are smooth glass plates, but a transparent polymer film may be used. The transparent electrode 4 provided on the transparent substrates 2 and 3 is
A transparent conductive film made of an ITO film was divided and formed by photolithography. Then, on the transparent electrode 4, for example, polyimide or polyvinyl alcohol having a film thickness of several tens of nm is applied and processed so that the rubbing direction is about 90 degrees to form an alignment film 5, and then the cell gap is formed. About 6
A nematic liquid crystal having a positive dielectric anisotropy was injected to a thickness of μm. The polarizing plate 7 was installed such that the absorption axis was aligned with the alignment direction of the alignment film 5 on the upper substrate 2.

A quarter-wave plate 8 was attached to the back surface of the lower substrate 3 with an ester-based optical adhesive or an adhesive made of a copolymer of butyl acrylate and an acrylic monomer mainly composed of 2-ethylhexyl acrylate. The direction of the optical axis at the time of bonding is 45 degrees with respect to the alignment direction of the alignment film 5 on the lower substrate 3 so that the incident light 11 is converted from the linearly polarized light emitted from the liquid crystal cell 1 into the circularly polarized light.゜. As the quarter-wave plate 8, a polycarbonate film obtained by uniaxially stretching a polycarbonate film and having a phase difference Δnd of 133 nm was used. The quarter-wave plate 8 can be made of a polymer film such as polystyrene or an optical crystal such as a quartz flake or calcite, in addition to polycarbonate.

Further, a cholesteric liquid crystal polymer film 9 was formed on the light absorbing plate 10 and then laminated via an adhesive. The light absorbing plate 10 was a black plate obtained by dyeing a methacrylic resin having a thickness of 0.5 mm into a black color so as to absorb light in the visible light region. The cholesteric liquid crystal polymer film 9 is a film in which a polymer having a cholesteric liquid crystal structure of a polypeptide such as polyglutamate is sandwiched between polyethylene terephthalate films, rapidly cooled from a heating state at a specific temperature after sealing, and has a thickness of about 0.1 mm. Those having a wavelength λ0 of 530 nm, a wavelength band Δλ of 70 nm, and a maximum reflectance of 48% (non-polarization measurement conditions) were used. Here, the black plate 10 may be a polymer film, a substrate, or a metal plate dyed black, other than methacrylic resin. Further, as the cholesteric liquid crystal polymer film 9, a film in which a cholesteric structure is formed by forming a cholesteric structure from a lyotropic cholesteric liquid crystal by using a photopolymerizable unsaturated monomer as a solvent and then photopolymerizing the cholesteric liquid crystal can be used. Further, the light absorbing plate 10 and the cholesteric liquid crystal polymer film 9 may be laminated and integrated by press heating.

When the reflection-type liquid crystal electro-optical device manufactured in this manner is observed under the condition of vertical incidence of white light, as shown in FIG. 1A, in the region where no driving voltage is applied,
The incident light 11 was observed as reflected light 12 being colored in a vivid green color. On the other hand, drive voltage is applied (B)
In this case, the incident light 11 can hardly be observed as the reflected light 12 and exhibits a black display.

Next, when this reflection type liquid crystal electro-optical device is mounted on a wristwatch and observed, a deep black display is obtained on a clear green background, which is much brighter and more visible than a color display using a color filter. Was good. Temperature -20
Observation in the range of ° C. to 90 ° C. showed little change in the green display, satisfying the actual use environment conditions of the wristwatch.

The polarizing plate 7 or the quarter-wave plate 8 is
When rotated by 0 °, a clear green display was obtained on a deep black background. Here, if the black plate is replaced with a dark red light absorbing plate, the color tone when viewed from the front changes to yellow-green,
Beautiful yellow-green display on a dark red background.

In addition, when the set angles of the polarizing plate and the quarter-wave plate were shifted with the above-described configuration using a black plate as the light absorbing plate, the color tone slightly changed. At the time, the sharpness of the color was the best. Further, in addition to the liquid crystal cell having a twist angle of 90 °, a cell having a twist angle of 70 μm, 80 °, 100 °, and 110 ° and a cell gap of 6 μm is manufactured, and the same configuration is used to change the display state. Observed. The twist angle of the liquid crystal is 80 °,
The reflection type liquid crystal electro-optical device incorporating the 100 ° cell provided a beautiful display having almost the same color tone as that of the 90 ° cell. Was.

(Example 2) A polarizing plate 7 having a single transmittance of 45 was used.
%, A reflection type liquid crystal electro-optical device having the same configuration as that of Example 1 except for using a polarizing plate of not less than%. As the polarizing plate 7, a polarizing plate NPF-G1228DU manufactured by Nitto Denko Corporation (single transmittance 4)
6.5%). Since the incident light and the selectively reflected light pass through such a polarizing plate having a high transmittance, a very bright and highly visible display was obtained.

Example 3 A reflective liquid crystal electro-optical device having the same structure as in Example 1 except that a low refractive index polymer was applied to the surface of the polarizing plate 7 was prepared. This is because, by applying a polymer having a low refractive index, the surface reflection on the polarizing plate surface is reduced, the amount of substantially transmitted light to the liquid crystal cell 1 is increased, and the selective reflection efficiency of the cholesteric liquid crystal polymer is increased. In the reflection type liquid crystal electro-optical device thus obtained,
There was little reflection of ambient light, and the color tone of the selective reflection light became vivid. Similar effects can be expected from other anti-reflection films using a method of depositing a thin film.

(Example 4) A reflection type liquid crystal electro-optical device having the same structure as that of Example 1 except that a quarter wavelength plate 8, a cholesteric liquid crystal polymer film 9 and a light absorbing plate 10 were laminated and integrated. . By bringing the films into close contact, the surface reflection between the films could be reduced, so that a high contrast and bright display could be realized.

Example 5 A reflective liquid crystal electro-optical device similar to that of Example 1 was prepared except that the polarizing plate 7 was changed to a color polarizing plate. As the polarizing plate 7, a polarizing plate NPF-Q manufactured by Nitto Denko Corporation
-10R (display color is red) was used. In the reflection-type liquid crystal electro-optical device thus obtained, two-color display, namely, red display produced by a color polarizing plate on a background of a vivid selective reflection color was realized.

Example 6 A reflective liquid crystal electro-optical device similar to that of Example 1 was formed except that a cholesteric liquid crystal polymer film 9 was formed on a polyethylene terephthalate film having irregularities. Since the cholesteric surface of the cholesteric liquid crystal polymer is uneven, the dependency of the selectively reflected light on the incident angle is reduced, and the change in color tone due to the viewing angle is suppressed.

[0028]

As described above, according to the present invention, the color change of the colored portion does not occur even when the environment is changed, and the color of the selective reflection light is clear, the visibility is high, and the reflection type is high. Since the liquid crystal electro-optical device can be realized at low cost, there is an effect that it can be used outdoors where the environment changes drastically.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an embodiment of a reflection type liquid crystal electro-optical device according to the present invention.

FIG. 2 is an explanatory view showing a conventional reflection type liquid crystal electro-optical device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Liquid crystal cell 2 Upper substrate 3 Lower substrate 4 Transparent electrode 5 Alignment film 6 Liquid crystal 7 Polarizer 8 1/4 wavelength plate 9 Cholesteric liquid crystal polymer film 10 Light absorption plate 11 Incident light 12 Outgoing light 13 Cholesteric liquid crystal cell

────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-60-147720 (JP, A) JP-A-56-139506 (JP, A) JP-A-1-18831 (JP, A) JP-A-3- 274022 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G02F 1/1335

Claims (6)

(57) [Claims] As well as have a 1. A transparent electrode, an alignment process is
The upper substrate and the lower substrate, and the twisted neat sealed between the upper substrate and the lower substrate.
A liquid crystal layer of amatic type, a polarizing plate provided on the front surface of the upper substrate, and a linear polarization
A quarter-wave plate for converting light into circularly polarized light and passing therethrough, and a quarter-wave plate provided behind the quarter-wave plate and having a specific rotation direction.
Cholesteric liquid that reflects light in a specific wavelength range of circularly polarized light
And crystallized polymeric film, provided behind the cholesteric liquid crystal polymer film
A light absorbing plate , wherein when a voltage is applied to the liquid crystal layer, the
The direction of rotation of the circularly polarized light emitted is the voltage applied to the liquid crystal layer.
The circularly polarized light emitted from the 1/4 wavelength plate when no light is applied.
A reflection type liquid crystal electro-optical device, wherein the direction is opposite to the turning direction . 2. The method according to claim 1, wherein said quarter wavelength plate is provided on said lower substrate.
With an optical axis that makes an angle of approximately 45 ° with the direction of the alignment process
2. The reflection type liquid crystal electro-optical device according to claim 1, wherein
Place. 3. The light absorbing plate according to claim 1, wherein said light absorbing plate has all wavelengths in a visible light region.
2. A black plate which absorbs the light of claim 1.
Or the reflective liquid crystal electro-optical device according to 2. 4. The light absorbing plate according to claim 1, wherein said light absorbing plate has a specific wavelength in a visible light region.
2. The light-emitting device according to claim 1, wherein the light-reflecting characteristic is provided.
Or the reflective liquid crystal electro-optical device according to 2. 5. A reflection type liquid crystal electro-optical device according to any of claims 1-4, characterized by comprising the light absorbing plate wherein a quarter wavelength plate and the cholesteric liquid crystal polymer film integrally laminated . 6. A reflection type liquid crystal electro-optical device according to any one of claims 1-5, characterized in that said cholesteric liquid crystal polymer film and the quarter wavelength plate are laminated with an uneven surface.