JPH10177191A - Reflection type liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to obtain sufficient contrast in a reflection type liquid crystal, display device capable of multicolor display, to reduce its production cost, and to make a parallax smaller. SOLUTION: Electrodes 3, 4 are respectively formed on the one-side surfaces of substrates 1, 2 and selective reflection layers 5R, 5G, 5B respectively dispersed with cholesteric liquid crystals 7R, 7G, 7B in high polymers 6R, 6G, 6B are laminated between these electrodes 3 and 4. The electrodes 3, 4 are connected to a driving circuit 8. The threshold voltages of the change of the cholesteric liquid crystals 7R, 7G, 7B of the selective reflection layers 5R, 5G, 5B from a planar phase to a focal conic phase and the threshold voltages of the change thereof from the focal conic phase to a homeotropic phase are set respectively at the voltages different from each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a reflection type liquid crystal display device which uses a liquid crystal and performs display using external light.

[0002]

2. Description of the Related Art A reflective liquid crystal display device does not require a dedicated light source such as a backlight, consumes less power, and can be configured to be flat and small. Attention has been paid.

As a reflection type liquid crystal display device capable of monochrome display such as black and white display, there is known a device of a TN (twisted nematic) type. In a reflection type liquid crystal display device of the TN mode, a nematic liquid crystal having a positive dielectric anisotropy is loaded between two transparent substrates each having a transparent electrode formed thereon, and the long axis of the liquid crystal molecules is controlled by controlling an alignment film. 90 between substrates
° A continuously twisted TN cell is formed, polarizing plates orthogonal to each other are arranged outside the upper and lower substrates, and a reflecting plate is arranged outside the lower polarizing plate.

In this TN type reflection type liquid crystal display device,
When no voltage is applied to the TN cell, the light vertically incident on the upper substrate is transmitted through the lower polarizer by rotating the polarization plane by 90 ° along the twist of the liquid crystal molecules while passing through the cell,
The light is reflected by the outer reflector and enters the observer's eyes, and TN
The cell has a white color.

On the other hand, when a voltage higher than the threshold value is applied to the TN cell, the liquid crystal molecules except for the liquid crystal molecules near the electrode surface are arranged in parallel to the direction of the electric field, so that the rotation of the polarization plane occurs. The incident light does not pass through the lower polarizer, and the TN cell turns black. Therefore, characters and the like can be displayed by turning on and off the voltage.

However, in the reflection type liquid crystal display device of the TN mode, the polarization direction of the incident light is limited to one direction by using a polarizing plate, so that more than half of the incident light is lost and the reflected light becomes weak. , The white color in the white display becomes very dark,
There is a disadvantage that the contrast is reduced.

Therefore, as a reflection type liquid crystal display device which enables a monochromatic display without using a polarizing plate, for example, NC
AP (Nematic Curvilinear Al
(igned Phase: nematic curve type alignment phase) A liquid crystal using liquid crystal has been considered.

A reflection type liquid crystal display device using an NCAP liquid crystal is provided between two transparent substrates each having a transparent electrode formed thereon.
An NCAP liquid crystal layer in which fine liquid crystal capsules are dispersed in a polymer matrix is formed, and a black film is formed on the outside of the substrate on the side opposite to the outside light incident side.

In the reflection type liquid crystal display device using the NCAP liquid crystal, when no voltage is applied between the pair of electrodes, the liquid crystal molecules in the liquid crystal capsule are arranged along the outer wall of the liquid crystal capsule, and the liquid crystal molecules are birefringent. Since the incident light is scattered on the surface or inside the liquid crystal capsule, white is displayed, and when a voltage higher than the threshold is applied between the pair of electrodes, the liquid crystal molecules are aligned along the direction of the electric field, and the incident light is Is transmitted through the NCAP liquid crystal layer and absorbed by the black film,
Black color is displayed.

As a reflection type liquid crystal display device capable of multicolor display, a device using a color filter is known. However, when a color filter is used, light is lost, so that a reflective liquid crystal display device that cannot amplify the light amount, such as a transmissive liquid crystal display device using a backlight, cannot provide sufficient contrast. There is.

Therefore, there have been proposed some reflection type liquid crystal display devices capable of multicolor display without using a color filter.

For example, JP-A-3-209425 discloses that
As shown in FIG. 9, a transparent electrode 2 is formed on one surface of a transparent substrate 21a.
2a is provided with a transparent electrode 2 on one side and the other side of the transparent substrate 21b.
3a and 22b, transparent electrodes 23b and 22c on one surface and the other surface of the transparent substrate 21c, and a transparent electrode 23c on one surface of the transparent substrate 21d.
a, 23a, 22b, 23b, and 22c, 23
c, reflection layers 24a, 24b, and 24c are formed by selectively reflecting red, green, and blue light, respectively, in which a cholesteric liquid crystal is dispersed in a polymer.
1b and 2c are separately driven by driving circuits 25a, 25b and 25c, respectively, to display an arbitrary color according to the principle of additive color mixture.

In Japanese Patent Application Laid-Open No. 4-178623, two layers having different refractive indices are alternately laminated as the reflective layers 24a, 24b and 24c in FIG. Are formed, each of which forms an interference filter that reflects red, green, and blue color light, and the transparent substrate 21d on the opposite side to the incident side of external light.
A black film is formed on the back surface of the drive circuit, and the reflection layers 24a, 24b and 24c are respectively connected to the drive circuits 25a, 25b and 25c.
3C, each of which is independently driven to display an arbitrary color by the principle of additive color mixture.

[0014] Further, Optical Engineer
Ring, 23 (1984), p247, full color display is realized by using guest host cells containing yellow, cyan and magenta dichroic dyes as the reflection layers 24a, 24b and 24c in FIG. It is shown to be.

[0015]

However, the reflection type liquid crystal display device using NCAP liquid crystal, which enables monochromatic display without using a polarizing plate, has a reflectance of about 20% when incident light is scattered. There is a drawback that the white is very dark when displaying white and the contrast is low.

Further, the reflection type liquid crystal display device shown in FIG. 9 and capable of multi-color display without using a color filter requires driving electrodes and driving circuits for three colors, which increases the manufacturing cost. In addition, the reflection layer 24 of each color
A transparent electrode and a transparent substrate are provided between a, 24b, and 24c, and the distance between the reflective layers 24a, 24b, and 24c of each color is increased, so that there is a disadvantage that the parallax increases.

Therefore, a first object of the present invention is to provide a reflection type liquid crystal display device capable of monochrome display such as monochrome display so as to obtain sufficient contrast.

A second object of the present invention is to provide a reflection type liquid crystal display device capable of multi-color display, in which sufficient contrast can be obtained, manufacturing costs are reduced, and parallax is reduced. .

[0019]

According to the first aspect of the present invention, a cholesteric liquid crystal which has electrodes, and at least one of which is transparent, selectively reflects light having different wavelengths in visible light between a pair of transparent substrates. A plurality of selective reflection layers dispersed in a polymer are laminated.

According to a second aspect of the present invention, in the reflective liquid crystal display device of the first aspect, a phase change threshold voltage of each cholesteric liquid crystal differs between the plurality of selective reflection layers.

[0021]

The cholesteric liquid crystal, in which the liquid crystal molecules have a helical structure, separates light incident parallel to the helical axis into right-handed and left-handed light, and reflects a circularly polarized light component that matches the helix direction of the helix. Selective reflection that transmits the circularly polarized light component occurs.
When the helical pitch is p, the average refractive index in a plane orthogonal to the helical axis is n, and the birefringence is Δn, the reflection center wavelength λ and the reflection wavelength width Δλ are λ = n · p and Δλ = Δn, respectively. The light reflected by the cholesteric liquid crystal exhibits a bright color depending on the helical pitch.

That is, the cholesteric liquid crystal having a positive dielectric anisotropy has the following characteristics: (A) a planar phase in which the helical axis becomes perpendicular to the cell surface to cause selective reflection as the applied electric field increases, and (B) a helical axis. Show three states: a focal conic phase in which the liquid crystal director is oriented in a random direction, and a homeotropic phase in which the liquid crystal director is oriented in the direction of the electric field by unwinding the helical structure. Then, when there is no anchoring effect at the interface, the planar phase having the minimum free energy is in a ground state without an electric field.

However, in a polymer-dispersed cholesteric liquid crystal in which a cholesteric liquid crystal is dispersed in a polymer,
Due to the interaction with the polymer interface, a phase transition from the focal conic phase to the planar phase due to thermal fluctuation does not occur, and these two states are stably present without an electric field.

That is, the polymer-dispersed cholesteric liquid crystal having a positive dielectric anisotropy changes from a planar phase to a focal conic phase and increases from a focal conic phase with an increase in voltage during pulse application as described above. Although the phase changes to the homeotropic phase, after the voltage is removed, the homeotropic phase changes to the planar phase, and either the planar phase or the focal conic phase is held by the above-described memory effect.

Therefore, assuming that the threshold voltage of the change from the planar phase to the focal conic phase is Vth1 and the threshold voltage of the change from the focal conic phase to the homeotropic phase is Vth2, When the voltage is equal to or higher than Vth2, the state becomes a selective reflection state by the planar phase. When the voltage is between Vth1 and Vth2, the state becomes a transmission state by the focal conic phase. When the voltage is Vth1 or lower, the state before application of the voltage is continued. Or, it becomes a transmission state by the focal conic phase.

In the present invention, utilizing the bistability phenomenon of the polymer-dispersed cholesteric liquid crystal, switching between (A) the selective reflection state by the planar phase and (B) the transmission state by the focal conic phase with small backscattering is performed. By doing so, display is performed.

That is, the reflection type liquid crystal display device according to the first aspect of the present invention has electrodes respectively, at least one of which is transparent between a pair of substrates.
Three selective reflection layers in which cholesteric liquid crystals that selectively reflect green and blue color lights are dispersed in a polymer are laminated. For example, the phase change threshold voltages Vth1 and Vth2 of the cholesteric liquid crystal of each selective reflection layer are set. Since the voltages Vrgb1 and Vrgb2 are the same, a voltage of Vrgb2 or more is applied between a pair of electrodes,
By setting all three selective reflection layers to the selective reflection state, white is displayed, and Vrgb1 and Vrg are displayed between a pair of electrodes.
gb2 is applied to make all three selective reflection layers transmissive, so that the light transmitted through the three selective reflection layers is provided on the black film provided on the side opposite to the outside light incident side. And is displayed in black. Therefore, monochrome display is possible.

Since the reflectance of the selective reflection by the cholesteric liquid crystal becomes 50% in principle, the white color in white display becomes bright and the contrast becomes high. Further, the three selective reflection layers are directly laminated without interposing a transparent electrode and a transparent substrate therebetween, and have a common drive electrode and drive circuit. Therefore, parallax is reduced and manufacturing cost is reduced.

According to a second aspect of the present invention, there is provided a reflection type liquid crystal display device having electrodes, at least one of which is provided between a pair of transparent substrates.
Three layers of selective reflection layers in which cholesteric liquid crystals that selectively reflect blue color light are dispersed in a polymer are laminated, and the phase change threshold voltages Vth1 and Vth2 of the cholesteric liquid crystals of the respective selective reflection layers are different from each other. Voltages Vr1, Vg1, Vb1 and Vr2, Vg2, Vb
2, so that according to the voltage applied between the pair of electrodes,
Any one of the three selective reflection layers or a specific two
Layers or all three layers can be in a selective reflection state,
In addition, all three layers can be in a transmission state.

Accordingly, white is displayed by setting all the three selective reflection layers to the selective reflection state, and red by setting only one of the three selective reflection layers to the selective reflection state. , Green and blue are displayed, and black is displayed by setting all three selective reflection layers in the transmission state.

Further, two of the three selective reflection layers are changed in accordance with the order of the phase change threshold voltages Vr1, Vg1, Vb1 and Vr2, Vg2, Vb2 of the cholesteric liquid crystal of the three selective reflection layers. By setting the selective reflection state, yellow and cyan, or cyan and magenta, or magenta and yellow are displayed. Therefore, multi-color display is possible.

Since the reflectance of the selective reflection by the cholesteric liquid crystal is 50% in principle, the contrast is increased, and the three selective reflection layers are directly laminated without a transparent electrode and a transparent substrate therebetween. In addition, since the driving electrode and the driving circuit are shared, the parallax is reduced and the manufacturing cost is reduced.

[0033]

FIG. 1 shows an embodiment of the reflection type liquid crystal display device of the present invention. In this embodiment, electrodes 3 and 4 are formed on one surface of substrates 1 and 2 respectively, and cholesteric liquid crystals 7R, 7G and 7B are dispersed in polymers 6R, 6G and 6B between electrodes 3 and 4, respectively. Polymer-dispersed cholesteric liquid crystal (PDCLC: Polymer)
Dispersed Cholesteric Liq
Uid Crystal) structure selective reflection layer 5R, 5
G and 5B are stacked, and the electrodes 3 and 4 are connected to the drive circuit 8.

The substrates 1 and 2 are formed of an insulating and light-transmitting material such as glass and plastic, and the electrodes 3 and 4 are formed of a conductive and light-transmitting material such as ITO. Specifically, as the substrates 1 and 2 and the electrodes 3 and 4, a glass substrate with an ITO electrode, for example, 7059 manufactured by Corning Incorporated can be used.

A black film 9 for absorbing visible light components transmitted through the selective reflection layers 5R, 5G and 5B is formed on the back surface of the substrate 2 on the side opposite to the outside light incidence side. Specifically, a black resin, for example, BKR-10 manufactured by Nippon Kayaku Co., Ltd.
5 is applied.

The selective reflection layers 5R, 5G, 5B are, for example,
PIPS (Polymerization Induc)
(ed Phase Separation) method.

That is, a photopolymerizable polymer precursor, for example, NOA65 manufactured by Norland Co., which can obtain a refractive index substantially the same as that of the liquid crystal after polymerization, is added to the cholesteric liquid crystal 7B and coated on the substrate 2 on which the electrode 4 is formed. . By irradiating this with ultraviolet light having an intensity of, for example, 10 mW / cm ² , the skeleton of the polymer 6B is formed by a photopolymerization reaction, and the selective reflection layer 5B in which the cholesteric liquid crystal 7B is dispersed as fine droplets is obtained. In the same manner, the selective reflection layer 5G is formed on the selective reflection layer 5B, a material for the selective reflection layer 5R is further applied on the selective reflection layer 5G, and the substrate 1 on which the electrodes 3 are formed is superposed. The selective reflection layer 5R is formed by polymerizing with ultraviolet light.

The cholesteric liquid crystals 7R, 7G, 7B are:
Each nematic liquid crystal with positive dielectric anisotropy,
It can be obtained by adding a liquid crystal to which an optically active 2-methylbutyl group, 2-methylbutoxy group, 4-methylhexyl group or the like is bound as a terminal group called a chiral agent. The helical pitch p is determined by the amount of the chiral agent added.

As an example, the cholesteric liquid crystal 7B, 7
G and 7R as cyanobiphenyl nematic liquid crystal;
For example, a dextrorotatory chiral agent, for example, CB15 manufactured by Merck, is added to E8 manufactured by Merck, 50% by weight, 42% by weight, respectively.
% Or 33%, the central wavelength λb of the selective reflection of the selective reflection layer 7B becomes 380 to 5 including the blue region.
The central wavelength λg of the selective reflection of the selective reflection layer 7G is 480 to 630 nm including the green region.
And the central wavelength λ of the selective reflection of the selective reflection layer 7R.
The respective spiral pitches pb, pg, and pr are adjusted so that r is in the range of 570 to 780 nm including the red region.

As shown in FIG. 2, the cholesteric liquid crystal 7 having a positive dielectric anisotropy and loaded between the electrodes 3 and 4 has:
As the electric field applied between the electrodes 3 and 4 increases, the helical axis becomes perpendicular to the cell surface as shown in FIG. 3A to cause selective reflection, and the helical axis as shown in FIG. There are three states, a focal conic phase in which the axis is oriented in a random direction, and a homeotropic phase in which the liquid crystal director is oriented in the direction of the electric field by unwinding the helical structure as shown in FIG. Then, when there is no anchoring effect at the interface, the planar phase having the minimum free energy is in a ground state without an electric field.

However, the selective reflection layers 5R, 5G, 5
In the polymer-dispersed cholesteric liquid crystal in which the cholesteric liquid crystals 7R, 7G, and 7B are dispersed in the polymers 6R, 6G, and 6B, as shown in B, the interaction with the polymer interface causes the focal conic phase due to thermal fluctuation to change from the planar phase to the planar phase. These two states exist stably without an electric field without causing a phase transition to.

That is, the selective reflection layers 5R, 5 made of a polymer dispersed cholesteric liquid crystal having a positive dielectric anisotropy.
G and 5B respectively change from the planar phase to the focal conic phase and change from the focal conic phase to the homeotropic phase as the voltage increases as described above during the pulse application, but after the voltage is removed, As shown in FIG. 3, the relationship between the voltage value of the applied pulse and the reflectivity after the pulse is applied, the homeotropic phase changes to the planar phase, and either the planar phase or the focal conic phase is held by the above memory effect. You.

Therefore, each selective reflection layer 5R,
For 5G and 5B, the threshold voltage for the change from the planar phase to the focal conic phase is Vth1, and the threshold voltage for the change from the focal conic phase to the homeotropic phase is V.
If it is assumed that th2, the respective selective reflection layers 5R, 5G, 5
B indicates that after the voltage is removed, if the voltage before removal is equal to or higher than Vth2, the state becomes a selective reflection state by the planar phase, and Vth1
When the voltage is between Vth2 and Vth2, the transmission state is caused by the focal conic phase. When the voltage is equal to or lower than Vth1, the state before application of the voltage is continued, that is, the state is selectively reflected by the planar phase or transmitted by the focal conic phase.

In the reflection type liquid crystal display device of the embodiment shown in FIG. 1, each of the selective reflection layers 5R, 5G and 5B is shown in FIG. 4A by utilizing the bistable phenomenon of the polymer dispersed cholesteric liquid crystal. Display is performed by switching between such a selective reflection state by the planar phase and a transmission state by the focal conic phase with small back scattering as shown in FIG.

(Embodiment 1) In the first embodiment for performing monochrome display, as shown in FIG. 5, for example, as shown by the relationship between the voltage value of the applied pulse and the reflectance after the pulse application, each selective reflection layer 5R , 5G, 5B cholesteric liquid crystal 7R, 7G,
7B, the phase change threshold voltages Vth1 and Vth2 are
It is assumed that the voltages Vrgb1 and Vrgb2 are the same.

The dielectric anisotropy of the cholesteric liquid crystal is Δε,
Assuming that the twist elastic modulus is K22 and the bend elastic modulus is K33, the threshold voltage Vth1 is p ⁻¹ , Δε ^−1/2 ,
The threshold voltage Vth2 is expressed by a function of K22 and K33-1 ^{/ 2} , and the threshold voltage Vth2 is represented by p- ¹ , Δ? ^-1/2 and K22.
It is represented by a function of ^1/2 .

Therefore, as described above with reference to FIG. 1, the helical pitches pr, pg, and pb of the cholesteric liquid crystals 7R, 7G, and 7B are set so that pr>pg> pb, and the reflection centers of the cholesteric liquid crystals 7R, 7G, and 7B are set. When the wavelengths λr, λg, and λb satisfy the relationship of λr>λg> λb, the phase change threshold voltages Vth1 and Vth2 of the cholesteric liquid crystals 7R, 7G, and 7B are set to the same voltages Vrgb1 and Vrgb2, respectively. The cholesteric liquid crystals 7R, 7G, and 7B may be formed of nematic liquid crystals having different dielectric anisotropy Δε or twist elastic modulus K22 or bend elastic modulus K33.

As described above, the cholesteric liquid crystal 7R, 7R
G, 7B phase change threshold voltages Vth1 and Vth2
Are respectively the same voltage Vrgb1 and Vrgb2, and when a voltage of Vrgb2 or more is applied between the electrodes 3 and 4, the selective reflection layers 5R, 5G and 5B are all in the selective reflection state, and white is displayed.

Further, Vrgb1 and Vrg
When the voltage between b2 is applied, the selective reflection layer 5R,
5G and 5B are all in a transmission state, and the selective reflection layer 5
The light transmitted through R, 5G and 5B is absorbed by the black film 9, and black is displayed. Therefore, monochrome display is possible.

Then, the cholesteric liquid crystals 7R, 7G,
Since the reflectance of the selective reflection by 7B is 50% in principle, the white color in the white display becomes bright and the contrast becomes high. In addition, the selective reflection layers 5R, 5G, and 5B are directly stacked without interposing a transparent electrode and a transparent substrate therebetween, and have a common drive electrode and drive circuit, so that parallax is reduced and manufacturing cost is reduced.

(Embodiment 2) In the second embodiment for performing multi-color display, as shown in FIG. 6, as shown by the relationship between the voltage value of the applied pulse and the reflectance after application of the pulse, each of the selective reflection layers 5R, 5R,
The phase change threshold voltages Vth1 and Vth2 of the cholesteric liquid crystals 7R, 7G and 7B of 5G and 5B are respectively changed to voltages Vr1, Vg1, Vb1 and Vr different from each other.
2, Vg2 and Vb2. In the example of FIG. 6, Vr1 <Vg
This is a case where 1 <Vb1 and Vr2 <Vg2 <Vb2.

As described above, the threshold voltage Vth1 is
p ^-1, Δε ^-1/2, expressed in function of the K22 and ^{K33 -1/2,} the threshold voltage Vth2 ^{is, p -1, Δε
−1/2} and K22 ^1/2 .

Therefore, as described above with reference to FIG. 1, the helical pitches pr, pg, and pb of the cholesteric liquid crystals 7R, 7G, and 7B are set so that pr>pg> pb, and the reflection centers of the cholesteric liquid crystals 7R, 7G, and 7B are determined. When the wavelengths λr, λg, λb satisfy the relationship of λr>λg> λb, and the cholesteric liquid crystals 7R, 7G, 7B are formed of the same nematic liquid crystal, Vr1 <Vg1 depending on the helical pitches pr, pg, pb. <Vb1
And Vr2 <Vg2 <Vb2.

However, in order to obtain a larger driving margin, each of the cholesteric liquid crystals 7R, 7G, 7
B is desirably formed of a nematic liquid crystal having different dielectric anisotropy Δε or twist elastic modulus K22 or bend elastic modulus K33.

As shown in FIG. 7, a signal composed of a 1 kHz pulse voltage refresh period and a select period, and a subsequent non-voltage display period are applied between the electrodes 3 and 4 as drive signals. Apply and
The refresh voltage Vr and the select voltage Vs of the drive signal are changed between seven levels of voltages Va to Vg shown in FIG. 6 based on the input data in a relationship of Vr> Vs.

FIG. 8 shows the refresh voltage Vr in this case.
It shows the state of the phase change of each selective reflection layer 5R, 5G, 5B by the combination of the select voltage Vs and the highest value of numerical values such as “0 ??” “00?” “000” “100” The left side shows the phase state of the selective reflection layer 5R, the middle (center) shows the phase state of the selective reflection layer 5G, and the lowermost (right side) shows the phase state of the selective reflection layer 5B. , “0” indicates a transmission state by the focal conic phase, and “?” Indicates an undetermined state depending on a state before the application of the drive signal. Where V is significant
Only the case where r> Vs is shown.

As is clear from this, when a drive signal which changes in the order of Vg → Va → 0V is applied between the electrodes 3 and 4, the selective reflection layers 5R, 5G and 5B are all in the selective reflection state. When a white color is displayed and a drive signal that changes in the order of Vg → Vd → 0 V is applied, all of the selective reflection layers 5R, 5G, and 5B are in the transmission state, and the light transmitted through the selective reflection layers 5R, 5G, and 5B is transmitted. Is absorbed by the black film 9 and black is displayed.

When a drive signal which changes in the order of Vg → Ve → 0V is applied, only the selective reflection layer 5R is in the selective reflection state, red is displayed, and Vf → Vb → 0.
When a drive signal that changes in the order of V is applied, only the selective reflection layer 5G is in the selective reflection state, and green is displayed. When a drive signal that changes in the order of Vg → Vc → 0V is applied, the selective reflection is performed. Only the layer 5B is in the selective reflection state, and blue is displayed.

Further, when applying a drive signal that changes in the order of Vg → Vf → 0V, the selective reflection layers 5R and 5R
G is in the selective reflection state, yellow is displayed, and Vg
When a drive signal that changes in the order of → Vb → 0V is applied, the selective reflection layers 5G and 5B enter the selective reflection state, and cyan is displayed.

Therefore, any one of the seven colors of white, black, red, green, blue, yellow and cyan can be displayed in one pixel, and a multi-color display is possible.

The cholesteric liquid crystals 7R, 7G,
Since the reflectance of the selective reflection by 7B is 50% in principle, the contrast is increased. Moreover, the selective reflection layer 5
R, 5G, and 5B are directly stacked without interposing a transparent electrode and a transparent substrate therebetween, and have a common drive electrode and drive circuit, so that parallax is reduced and manufacturing cost is reduced.

In the above example, the colors displayed by the additive color mixture of the reflected light from the two selective reflection layers are yellow and cyan, but the colors of the cholesteric liquid crystals 7R, 7G, and 7B are different. Change threshold voltage Vr1,
By changing the magnitude relationship between Vg1, Vb1 and Vr2, Vg2, Vb2 from the above example, the color displayed by the additive color mixture of the reflected light from the two selective reflection layers is changed to cyan and magenta or magenta and yellow. can do.

(Other Embodiments) In the first embodiment for displaying a single color, the cholesteric liquid crystals 7R, 7G, 7
This is a case where the phase change threshold voltages Vth1 and Vth2 of B are the same voltages Vrgb1 and Vrgb2, respectively.
The phase change threshold voltages Vth1 and Vth2 of each of the cholesteric liquid crystals 7R, 7G and 7B are set to different voltages Vr1, Vg1, Vb1 and Vr2, respectively.
Vg2 and Vb2 may be used.

In this case, Vg → Va → 0 between the electrodes 3 and 4
When a drive signal that changes in the order of V is applied, the selective reflection layers 5R, 5G, and 5B all enter the selective reflection state,
When white is displayed and a drive signal that changes in the order of Vg → Vd → 0V is applied, the selective reflection layers 5R, 5G, 5B
Are all in a transparent state, black is displayed, and black and white display is possible.

That is, when a single color display is performed, the phase change threshold voltages Vth1 and Vth2 of the cholesteric liquid crystals 7R, 7G and 7B may be the same voltages Vrgb1 and Vrgb2, respectively, or different voltages. Vr1, Vg1, Vb1 and V
r2, Vg2, and Vb2 may be used.

[Other Embodiments] In the embodiment shown in FIG. 1, three selective reflection layers 5R, 5G and 5B are laminated between the electrodes 3 and 4. For example, two selective reflection layers are laminated. You may make it. For example, when only the selective reflection layers 5R and 5G are stacked, the selective reflection layers 5R and 5G are stacked.
By setting G to the selective reflection state, yellow is displayed, and by setting the selective reflection layers 5R and 5G to the transmissive state, black is displayed, so that monochrome display is possible.

Further, the phase change threshold voltages Vth1 and Vth2 of the cholesteric liquid crystals 7R and 7G of the selective reflection layers 5R and 5G are set to different voltages Vr1 and Vg, respectively.
By setting 1 and Vr2, Vg2, multi-color display becomes possible.

[0068]

As described above, according to the first aspect of the present invention, it is possible to obtain a sufficient contrast in a reflective liquid crystal display device capable of monochrome display such as monochrome display.

According to the second aspect of the present invention, in a reflective liquid crystal display device capable of multicolor display, a sufficient contrast can be obtained, the manufacturing cost can be reduced, and the parallax can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing one embodiment of a reflection type liquid crystal display device of the present invention.

FIG. 2 is a diagram showing a phase change of a cholesteric liquid crystal having a positive dielectric anisotropy.

FIG. 3 is a diagram showing a switching operation of a cholesteric liquid crystal having a positive dielectric anisotropy.

FIG. 4 is a diagram showing a bistable state of each selective reflection layer of the reflection type liquid crystal display device of FIG. 1;

FIG. 5 is a diagram showing an example of a relationship between a cholesteric liquid crystal phase change threshold voltage of each selective reflection layer in the first embodiment.

FIG. 6 is a diagram showing an example of a relationship between phase change threshold voltages of cholesteric liquid crystals of each selective reflection layer in the second embodiment.

FIG. 7 is a diagram showing a form of a drive signal applied between a pair of electrodes of the reflective liquid crystal display device of FIG.

FIG. 8 is a diagram showing a state of a phase change of each selective reflection layer due to a combination of a refresh voltage and a select voltage in the second embodiment.

FIG. 9 is a diagram showing an example of a conventional reflective liquid crystal display device capable of multicolor display.

[Explanation of symbols]

 1, 2 substrate 3, 4 electrode 5R, 5G, 5B selective reflection layer 6R, 6G, 6B polymer 7R, 7G, 7B cholesteric liquid crystal 8 drive circuit 9 black film

Claims (2)

[Claims] 1. A plurality of selective reflections in which a cholesteric liquid crystal which selectively reflects light of different wavelengths in visible light is dispersed in a polymer between a pair of substrates each having an electrode and at least one of which is transparent. A reflective liquid crystal display device, wherein layers are stacked. 2. The reflection type liquid crystal display device according to claim 1, wherein a phase change threshold voltage of each cholesteric liquid crystal is different between the plurality of selective reflection layers.