JP3603923B2 - Reflective liquid crystal display - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a reflection type liquid crystal display device which performs display using external light by using liquid crystal.
[0002]
[Prior art]
The reflection type 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. Therefore, the reflection type liquid crystal display device has been attracting attention as a display device for small information devices and portable information terminals.
[0003]
As a reflection type liquid crystal display device capable of monochrome display such as monochrome display, a TN (twisted nematic) type is known. In a TN type reflection type liquid crystal display device, 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 the alignment film. A TN cell twisted continuously by 90 ° is formed between the substrates, a polarizing plate orthogonal to each other is arranged outside the upper and lower substrates, and a reflecting plate is arranged outside the lower polarizing plate.
[0004]
In the reflection type liquid crystal display device of the TN mode, when no voltage is applied to the TN cell, the light vertically incident on the upper substrate rotates the polarization plane by 90 ° along the twist of the liquid crystal molecules while passing through the cell. The light passes through the lower polarizer and is reflected by the outer reflector to enter the eyes of the observer, and the TN cell exhibits white.
[0005]
On the other hand, when a voltage equal to or higher than the threshold is applied to the TN cell, the liquid crystal molecules except for the liquid crystal molecules near the electrode surface are arranged parallel to the direction of the electric field, so that the rotation of the polarization plane does not occur. The incident light does not pass through the lower polarizing plate, and the TN cell exhibits black. Therefore, characters and the like can be displayed by turning on and off the voltage.
[0006]
However, since the reflection type liquid crystal display device of the TN mode uses a polarizing plate to limit the polarization direction of incident light to one direction, more than half of the incident light is lost, the reflected light becomes weak, and white display is performed. In this case, there is a disadvantage that the white color becomes very dark and the contrast becomes low.
[0007]
Therefore, as a reflection-type liquid crystal display device capable of performing monochromatic display without using a polarizing plate, for example, a reflection type liquid crystal display device using NCAP (Nematic Curvilinear Aligned Phase: nematic curve type alignment phase) liquid crystal is considered.
[0008]
The reflection type liquid crystal display device using the NCAP liquid crystal forms an NCAP liquid crystal layer in which fine liquid crystal capsules are dispersed in a polymer matrix between two transparent substrates each having a transparent electrode formed thereon, and receives external light. A black film is formed on the outside of the substrate on the opposite side.
[0009]
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 incident light is generated by the birefringence of the liquid crystal molecule. Since the light is scattered on the surface and inside of the liquid crystal capsule, a white color is displayed, and when a voltage higher than a threshold is applied between the pair of electrodes, the liquid crystal molecules are aligned in the direction of the electric field, and the incident light is NCAP liquid crystal. Since the light passes through the layer and is absorbed by the black film, a black color is displayed.
[0010]
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.
[0011]
Therefore, there have been proposed some reflection-type liquid crystal display devices capable of multicolor display without using a color filter.
[0012]
For example, JP-A-3-209425 discloses that, as shown in FIG. 9, a transparent electrode 22a is provided on one surface of a transparent substrate 21a, transparent electrodes 23a and 22b are provided on one surface and another surface of the transparent substrate 21b, and one surface of the transparent substrate 21c. Transparent electrodes 23b and 22c are formed on the other surface, and a transparent electrode 23c is formed on one surface of the transparent substrate 21d. The reflection layers 24a and 22c are formed between the transparent electrodes 22a and 23a, 22b and 23b, and 22c and 23c, respectively. 24b and 24c, cholesteric liquid crystals are dispersed in a polymer to form selective reflection layers for selectively reflecting red, green and blue color lights, respectively. The reflection layers 24a, 24b and 24c are respectively formed by driving circuits 25a and 24c. 25b and 25c are driven separately to display an arbitrary color according to the principle of additive color mixing. It is.
[0013]
In Japanese Patent Application Laid-Open No. 4-178623, two types of layers having different refractive indices are alternately laminated as the reflective layers 24a, 24b and 24c in FIG. 9, and at least one of the layers has a refractive index that changes with a voltage. Forming an interference filter that reflects red, green, and blue color light, forming a black film on the back surface of the transparent substrate 21d on the side opposite to the incident side of external light, and driving the reflection layers 24a, 24b, and 24c, respectively. It is shown that the circuits 25a, 25b and 25c are separately driven to display an arbitrary color according to the principle of additive color mixture.
[0014]
Further, in Optical Engineering, 23 (1984) and p247, guest host cells containing dichroic dyes of yellow, cyan and magenta, respectively, are used as the reflection layers 24a, 24b and 24c in FIG. It is shown that the display is realized.
[0015]
[Problems to be solved by the invention]
However, the reflection type liquid crystal display device using NCAP liquid crystal, which enables monochromatic display without using a polarizing plate, also has a low reflectance of about 20% when incident light is scattered, and white color in white display. There is a disadvantage that the image becomes very dark and the contrast is low.
[0016]
Further, the reflection type liquid crystal display device shown in FIG. 9 and capable of performing multi-color display without using a color filter requires a drive electrode and a drive circuit for three colors. The transparent electrode and the transparent substrate are provided between the reflective layers 24a, 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 is increased.
[0017]
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.
[0018]
A second object of the present invention is to provide a reflection type liquid crystal display device capable of multicolor display while obtaining sufficient contrast, reducing manufacturing costs, and reducing parallax.
[0019]
[Means for Solving the Problems]
The invention of claim 1 Reflective liquid crystal display device Each has an electrode, and selectively reflects light of different wavelengths in visible light between a pair of substrates, at least one of which is transparent. And the threshold voltage of the change from the planar phase to the focal conic phase and the threshold voltage of the change from the focal conic phase to the homeotropic phase are the same. Multiple selective reflection layers with cholesteric liquid crystal dispersed in polymer Are stacked without interposing an electrode and a substrate between the respective layers. .
[0020]
The invention of claim 2 Reflective liquid crystal display device Is Each having an electrode, at least one of which is transparent between a pair of transparent substrates, selectively reflects light of different wavelengths in visible light, and has a threshold voltage of change from each planar phase to a focal conic phase. Threshold voltages for the transition from the focal conic phase to the homeotropic phase are different from each other Multiple selective reflection layers with cholesteric liquid crystal dispersed in polymer Are stacked without interposing an electrode and a substrate between the respective layers. .
[0021]
[Action]
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 the circularly polarized light component that matches the helix direction of the helical light. Selective reflection that transmits light. When the helical pitch is p, the average refractive index in a plane perpendicular 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. -Represented by p, the light reflected by the cholesteric liquid crystal exhibits a vivid color depending on the helical pitch.
[0022]
That is, the cholesteric liquid crystal having a positive dielectric anisotropy has (A) a planar phase in which the helical axis is perpendicular to the cell surface to cause selective reflection as the applied electric field increases, and (B) a helical axis having a random helical axis. There are three states: a focal conic phase oriented in the direction, and (C) a homeotropic phase in which the liquid crystal director is oriented in the electric field direction 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 the ground state without electric field.
[0023]
However, in a polymer-dispersed cholesteric liquid crystal in which cholesteric liquid crystal is dispersed in a polymer, a phase transition from a focal conic phase to a planar phase due to thermal fluctuation does not occur due to interaction with a polymer interface, and these two states Exist stably without an electric field.
[0024]
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 to a homeotropic phase with an increase in voltage as described above during pulse application. However, after the voltage is removed, the homeotropic phase changes to the planar phase, and one of the planar phase and the focal conic phase is held by the above memory effect.
[0025]
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, the voltage before voltage removal is Vth2. In the above case, the state becomes a selective reflection state by the planar phase, when between Vth1 and Vth2, the state becomes a transmission state by the focal conic phase, and when the voltage is Vth1 or less, the state before voltage application is continued, that is, the state of the selective reflection by the planar phase or the focal conic state. It becomes a transmission state by the phase.
[0026]
In the present invention, by utilizing the bistability phenomenon of the polymer-dispersed cholesteric liquid crystal, switching between (A) a selective reflection state by a planar phase and (B) a transmission state by a focal conic phase with small backscattering is performed. , Display.
[0027]
That is, in the reflection type liquid crystal display device according to the first aspect of the invention, a cholesteric liquid crystal that has electrodes, and at least one of which is a pair of transparent substrates, for example, selectively reflects red, green, and blue light, respectively, is provided. Three layers of selective reflection layer dispersed in polymer are laminated And each Since the phase change threshold voltages Vth1 and Vth2 of the cholesteric liquid crystal of the selective reflection layer are the same voltages Vrgb1 and Vrgb2, respectively, a voltage of Vrgb2 or more is applied between a pair of electrodes to form the three selective reflection layers. When all are in the selective reflection state, white is displayed. By applying a voltage between Vrgb1 and Vrgb2 between a pair of electrodes, and all the three selective reflection layers are in the transmission state, three layers are selected. Light transmitted through the reflective layer is absorbed by the black film provided on the side opposite to the side on which external light is incident, and black is displayed. Therefore, monochrome display is possible.
[0028]
Then, since the reflectance of the selective reflection by the cholesteric liquid crystal is 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 the driving electrode and the driving circuit are shared, so that the parallax is reduced and the manufacturing cost is reduced.
[0029]
In the reflection type liquid crystal display device according to the second aspect of the invention, a cholesteric liquid crystal, which has electrodes and at least one of which is transparent between at least one pair of substrates, for example, selectively reflects red, green, and blue light, respectively, is a polymer. The three selective reflection layers dispersed therein are laminated, and the phase change threshold voltages Vth1 and Vth2 of the cholesteric liquid crystal of each selective reflection layer are set to different voltages Vr1, Vg1, Vb1 and Vr2, Vg2, Vb2, respectively. Therefore, according to the voltage applied between the pair of electrodes, any one of the three selective reflection layers or specific two or all three layers can be selectively reflected, and All layers can be in a transmissive state.
[0030]
Therefore, white is displayed by setting all the three selective reflection layers to the selective reflection state, and red, green, and white are displayed by setting only one of the three selective reflection layers to the selective reflection state. Blue is displayed, and black is displayed by setting all three selective reflection layers in the transmission state.
[0031]
Further, two of the three selective reflection layers are selectively reflected according to 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. Thus, yellow and cyan, or cyan and magenta, or magenta and yellow are displayed. Therefore, multi-color display is possible.
[0032]
Then, 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. Since the electrodes and the driving circuit are common, the parallax is reduced and the manufacturing cost is reduced.
[0033]
BEST MODE FOR CARRYING OUT THE INVENTION
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 between polymers 3R, 6G and 6B, respectively. The selective reflection layers 5R, 5G, and 5B having a polymer dispersed cholesteric liquid crystal (PDCLC: Polymer Dispersed Cholesteric Liquid Crystal) structure are stacked, and the electrodes 3 and 4 are connected to the drive circuit 8.
[0034]
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.
[0035]
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 incident side. Specifically, a black resin, for example, BKR-105 manufactured by Nippon Kayaku Co., Ltd. is applied.
[0036]
The selective reflection layers 5R, 5G, 5B are formed by, for example, a PIPS (Polymerization Induced Phase Separation) method.
[0037]
That is, a photopolymer precursor, such as NOA65 manufactured by Norland Co., which has a refractive index substantially the same as that of the liquid crystal after polymerization, is added to the cholesteric liquid crystal 7B, and is applied onto the substrate 2 on which the electrodes 4 are formed. For example, 10 mW / cm ² Irradiation with ultraviolet light having a strength of 3 forms the skeleton of the polymer 6B by the photopolymerization reaction, and obtains the selective reflection layer 5B in which the cholesteric liquid crystal 7B is dispersed as fine droplets. 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 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 polymerization with ultraviolet light.
[0038]
The cholesteric liquid crystals 7R, 7G, and 7B are used as nematic liquid crystals having positive dielectric anisotropy as optically active 2-methylbutyl, 2-methylbutoxy, or 4-methylhexyl as terminal groups called chiral agents. It can be obtained by adding a liquid crystal having a group or the like bonded thereto. The helical pitch p is determined by the amount of the chiral agent added.
[0039]
As an example, as the cholesteric liquid crystals 7B, 7G, and 7R, a cyanobiphenyl-based nematic liquid crystal such as E8 manufactured by Merck and a dextrorotatory chiral agent such as CB15 manufactured by Merck are used in a weight ratio of 50%, 42%, and 33%, respectively. By adding, the central wavelength λb of the selective reflection of the selective reflection layer 7B is in the range of 380 to 530 nm including the blue region, and the central wavelength λg of the selective reflection of the selective reflection layer 7G is 480 to 630 nm including the green region. The respective spiral pitches pb, pg, and pr are adjusted so that the central wavelength λr of the selective reflection of the selective reflection layer 7R is in the range of 570 to 780 nm including the red region.
[0040]
As shown in FIG. 2, the cholesteric liquid crystal 7 having a positive dielectric anisotropy loaded between the electrodes 3 and 4 increases with the increase in the electric field applied between the electrodes 3 and 4 (A). (B), a planar phase in which the helical axis is perpendicular to the cell surface to cause selective reflection, a focal conic phase in which the helical axis is oriented in a random direction as shown in FIG. (B), and a spiral as shown in FIG. It shows three states, a homeotropic phase, in which the structure is unraveled and the liquid crystal director faces the electric field direction. Then, when there is no anchoring effect at the interface, the planar phase having the minimum free energy is in the ground state without electric field.
[0041]
However, 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 in the selective reflection layers 5R, 5G, and 5B, the heat is generated due to the interaction with the polymer interface. No phase transition from the focal conic phase to the planar phase occurs due to the oscillation, and these two states are stably present without an electric field.
[0042]
That is, the selective reflection layers 5R, 5G, and 5B made of the polymer dispersed cholesteric liquid crystal having positive dielectric anisotropy respectively change from the planar conic to the focal conic as the voltage increases as described above during the pulse application. The phase changes from the focal conic phase to the homeotropic phase. After the voltage is removed, the homeotropic phase changes to the planar state as shown in FIG. 3 showing the relationship between the voltage value of the applied pulse and the reflectance after the pulse is applied. The phase changes to a phase, and one of the planar phase and the focal conic phase is held by the above-described memory effect.
[0043]
Therefore, when the threshold voltage of the change from the planar phase to the focal conic phase of each selective reflection layer 5R, 5G, 5B is Vth1, and the threshold voltage of the change from the focal conic phase to the homeotropic phase is Vth2. After the voltage is removed, the selective reflection layers 5R, 5G, and 5B are in a selective reflection state by the planar phase when the voltage before the removal is equal to or higher than Vth2, and are in a transmission state by the focal conic phase when between Vth1 and Vth2. When the voltage is equal to or lower than Vth1, the state before voltage application is continued, that is, a selective reflection state by a planar phase or a transmission state by a focal conic phase.
[0044]
In the reflection type liquid crystal display device of the embodiment of FIG. 1, utilizing the bistability phenomenon of the polymer dispersed cholesteric liquid crystal, each of the selective reflection layers 5R, 5G, 5B is planarized as shown in FIG. The display is performed by switching between a selective reflection state by a phase and a transmission state by a focal conic phase with small backscattering as shown in FIG.
[0045]
(Example 1)
In the first embodiment for performing the monochromatic 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, the cholesteric liquid crystal 7R of each of the selective reflection layers 5R, 5G, and 5B. , 7G, 7B have the same voltage Vrgb1 and Vrgb2, respectively.
[0046]
Assuming that the dielectric anisotropy of the cholesteric liquid crystal is Δε, the twist elastic modulus is K22, and the bend elastic modulus is K33, the threshold voltage Vth1 is p ^-1 , Δε ^-1/2 , K22 and K33 ^-1/2 The threshold voltage Vth2 is expressed as ^-1 , Δε ^-1/2 And K22 ^1/2 Is represented by the function
[0047]
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 center wavelengths λr, When 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. 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.
[0048]
As described above, 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, and when a voltage higher than Vrgb2 is applied between the electrodes 3 and 4, the selective reflection layer is formed. 5R, 5G, and 5B are all in the selective reflection state, and white is displayed.
[0049]
When a voltage between Vrgb1 and Vrgb2 is applied between the electrodes 3 and 4, the selective reflection layers 5R, 5G and 5B are all in a transmitting state, and the light transmitted through the selective reflecting layers 5R, 5G and 5B is black. It is absorbed by the film 9 and a black color is displayed. Therefore, monochrome display is possible.
[0050]
Since the reflectance of the selective reflection by the cholesteric liquid crystals 7R, 7G, and 7B is 50% in principle, the white color in 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.
[0051]
(Example 2)
In the second embodiment for performing multi-color display, as shown in FIG. 6 showing the relationship between the voltage value of the applied pulse and the reflectance after the pulse application, the cholesteric liquid crystal 7R of each of the selective reflection layers 5R, 5G, and 5B. The phase change threshold voltages Vth1 and Vth2 of 7G and 7B are respectively different voltages Vr1, Vg1, Vb1 and Vr2, Vg2, Vb2. The example of FIG. 6 is a case where Vr1 <Vg1 <Vb1 and Vr2 <Vg2 <Vb2.
[0052]
As described above, the threshold voltage Vth1 is p ^-1 , Δε ^-1/2 , K22 and K33 ^-1/2 The threshold voltage Vth2 is expressed as ^-1 , Δε ^-1/2 And K22 ^1/2 Is represented by the function
[0053]
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 center wavelengths λr, When λg and λb satisfy the relationship of λr>λg> λb, and when the cholesteric liquid crystals 7R, 7G and 7B are formed of the same nematic liquid crystal, Vr1 <Vg1 <Vb1 and Vr1 <Vg1 <Vb1 depending on the helical pitches pr, pg and pb. Vr2 <Vg2 <Vb2.
[0054]
However, in order to obtain a larger driving margin, it is desirable that each of the cholesteric liquid crystals 7R, 7G, 7B is formed of a nematic liquid crystal having a different dielectric anisotropy Δε or a twist elastic modulus K22 or a bend elastic modulus K33.
[0055]
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. The refresh voltage Vr and 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.
[0056]
FIG. 8 shows a state of a phase change of each selective reflection layer 5R, 5G, 5B by a combination of the refresh voltage Vr and the select voltage Vs in this case, and is “0 ??” “00?” “000”. The top (left side) of the numerical value such as “100” indicates the phase state of the selective reflection layer 5R, the middle (center) indicates the selective reflection layer 5G, and the bottom (right side) indicates the selective reflection layer 5B. “1” indicates a selective reflection state by the planar phase, “0” indicates a transmission state by the focal conic phase, and “?” Indicates an undetermined state depending on a state before application of the drive signal. However, only the case of significant Vr> Vs is shown.
[0057]
As is clear from this, when a drive signal that 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, and white is displayed. When 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 a transmission state, and light transmitted through the selective reflection layers 5R, 5G, and 5B is transmitted to the black film. 9 and a black color is displayed.
[0058]
When a drive signal that 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 a drive signal that changes in the order of Vf → Vb → 0V is applied. When the voltage 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, only the selective reflection layer 5B is in the selective reflection state. Is displayed in blue.
[0059]
Further, when a drive signal that changes in the order of Vg → Vf → 0V is applied, the selective reflection layers 5R and 5G enter the selective reflection state, yellow is displayed, and the drive signal changes in the order of Vg → Vb → 0V. Is applied, the selective reflection layers 5G and 5B enter the selective reflection state, and cyan is displayed.
[0060]
Therefore, any one of seven colors of white, black, red, green, blue, yellow, and cyan can be displayed in one pixel, and multicolor display can be performed.
[0061]
Then, since the reflectance of the selective reflection by the cholesteric liquid crystals 7R, 7G, and 7B is 50% in principle, the contrast is increased. Moreover, the selective reflection layers 5R, 5G, and 5B are directly laminated 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.
[0062]
In the above example, the colors displayed by the additive color mixture of the reflected lights from the two selective reflection layers are yellow and cyan, but the phase change threshold of each of the cholesteric liquid crystals 7R, 7G, and 7B. By changing the magnitude relationship between the value voltages Vr1, Vg1, Vb1 and Vr2, Vg2, Vb2 from the above example, the colors displayed by the additive color mixture of the reflected lights from the two selective reflection layers are changed to cyan and magenta, or Can be magenta and yellow.
[0066]
[Other embodiments]
In the embodiment of FIG. 1, three selective reflection layers 5R, 5G, and 5B are stacked between the electrodes 3 and 4. For example, two selective reflection layers may be stacked. For example, when only the selective reflection layers 5R and 5G are stacked, yellow is displayed by setting the selective reflection layers 5R and 5G to the selective reflection state, and by setting the selective reflection layers 5R and 5G to the transmission state. Black is displayed, and a monochrome display is possible.
[0067]
Further, by setting the phase change threshold voltages Vth1 and Vth2 of the cholesteric liquid crystals 7R and 7G of the selective reflection layers 5R and 5G to voltages Vr1, Vg1 and Vr2, Vg2 different from each other, a multi-color display is possible.
[0068]
【The invention's effect】
As described above, according to the first aspect of the invention, it is possible to obtain a sufficient contrast in the reflection type liquid crystal display device capable of monochrome display such as monochrome display. At the same time, the manufacturing cost can be reduced and the parallax can be reduced. .
[0069]
According to the second aspect of the present invention, in the reflective liquid crystal display device capable of multicolor display, 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 illustrating a switching operation of a cholesteric liquid crystal having a positive dielectric anisotropy.
FIG. 4 is a view 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 illustrating an example of a relationship between a cholesteric liquid crystal phase change threshold voltage of each selective reflection layer in the second embodiment.
FIG. 7 is a diagram illustrating 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 electrodes
5R, 5G, 5B selective reflection layer
6R, 6G, 6B polymer
7R, 7G, 7B Cholesteric liquid crystal
8 Drive circuit
9 Black film

Claims (2)

Each having an electrode, at least one of which is transparent between a pair of transparent substrates, selectively reflects light of different wavelengths in visible light , and has a threshold voltage of change from each planar phase to a focal conic phase. And a plurality of selective reflection layers in which the same cholesteric liquid crystal is dispersed in a polymer with the same threshold voltage for the change from the focal conic phase to the homeotropic phase are stacked without interposing an electrode and a substrate between each layer. reflection type liquid crystal display device, characterized in that there. Each having an electrode, at least one of which is transparent between a pair of transparent substrates, selectively reflects light of different wavelengths in visible light, and has a threshold voltage of change from each planar phase to a focal conic phase. A plurality of selective reflection layers in which cholesteric liquid crystals having different threshold voltages for changing from the focal conic phase to the homeotropic phase are dispersed in a polymer are stacked without interposing an electrode and a substrate between the respective layers. reflection type liquid crystal display device, characterized in that there.

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