JP3080122B2 - Display / recording medium, display / recording method and display / recording 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 display / recording medium using a liquid crystal, a display / recording method, and a display / recording apparatus.

[0002]

2. Description of the Related Art Hitherto, a display / recording apparatus has been developed in which a smectic liquid crystal is sandwiched between glass substrates on which electrodes are formed, and display data is formed using an electric field and heat.
FIG. 7 shows the principle of forming display data by using a smectic liquid crystal and using both heat and an electric field. The homeotropic alignment state in which the liquid crystal molecules are arranged vertically on the substrate is heated to bring the liquid crystal molecules into an isotropic state that does not exhibit liquid crystallinity. Cooling in this state results in a focal conic state in which the orientation of the liquid crystal is disturbed. The homeotropic alignment state is transparent, while the focal conic state becomes a cloudy state that scatters light. To change the focal conic state to the original homeotropic alignment state, a strong electric field may be applied, or an electric field may be applied during cooling after heating. Since the homeotropic alignment state and the focal conic state have an external state holding mechanism unnecessary and have a memory property that is held for a long time,
A display can be formed by locally forming a focal conic scattering region and a homeotropically oriented transparent region on the display surface (Liquid Crysta1s App1icatio).
ns and Uses, Vo1.1, Edited by Birendra Bahadur, Wor
1d Scientific, 1990, see Chapter 12).

However, this method has a disadvantage that only monochrome display can be obtained because the display is formed by switching between the two states of scattering and transmission.

On the other hand, the polymer dispersed liquid crystal PDLC is a composition obtained by dispersing a nematic liquid crystal in a polymer (P olyme
r D ispersed L iquid C rystal), the Japanese Patent Application No. 3-6613
As shown in FIG. 3, a writing method using both heat and an electric field can form and maintain a transmission state or a scattering state. This situation is similar to the case of the smectic liquid crystal described above, and has a drawback that only monochrome display can be obtained because transmission and scattering are used.

On the other hand, as a method of easily obtaining a color display, a display medium in which a cholesteric liquid crystal is dispersed in a polymer has been reported (PP Crooker and DKYan).
g, "Polymer-dispersed chiral liquid cryatal color
display ", Appl. Phys. Lett., Vol.57, p.2529-2531,
1991).

This display medium has a structure in which a cholesteric liquid crystal obtained by adding a chiral agent to a nematic liquid crystal having a negative dielectric anisotropy is spherically dispersed in a polymer. The dispersed liquid crystal is called a droplet from the shape. When an electric field is applied, the long axis of the liquid crystal in the droplet is oriented in a direction perpendicular to the electric field, and at the same time, because of the cholesteric liquid crystal, a helical axis is oriented in the direction of the electric field. Therefore, a specific wavelength determined by the helical pitch is reflected. On the other hand, when the electric field is removed, the orientation of the liquid crystal returns to the initial state, and the liquid crystal is scattered due to the difference in the refractive index at the interface between the polymer and the liquid crystal. This method has an advantage that a color display is obtained because light having a wavelength determined by the helical structure of the cholesteric liquid crystal is reflected, but the color display state needs to be maintained by applying an electric field,
There are drawbacks such as the necessity of a complicated drive circuit configuration such as a method of maintaining a voltage for each pixel using a thin film transistor and the like, and the extremely low operation speed of the order of seconds.

[0007]

An object of the present invention is to provide a display / recording medium, a display / recording method and a display / recording apparatus which do not have the above-mentioned disadvantages.

[0008]

In the present invention, a display / recording medium is used in which a composition layer in which a cholesteric liquid crystal is dispersed in a polymer is sandwiched between substrates on which a transparent conductor is formed.
By cooling the display / recording medium in a state of applying a high electric field after heating, the dispersed state of the liquid crystal becomes uniform and a mode in which light of a specific wavelength is reflected can be obtained. By cooling the liquid crystal, the alignment state of the liquid crystal becomes random and a mode in which light in the visible region is transmitted uniformly can be obtained, and both the modes can be reversibly changed.

According to the present invention, in the above-mentioned display / recording medium, in a mode in which the alignment state is uniform and light of a specific wavelength is reflected, a plurality of display / recording media reflecting different wavelengths, polarizations or different wavelengths and polarizations are provided. Are laminated.

Further, by cooling the above-mentioned display / recording medium under a high electric field applied state after heating, the dispersed state of the liquid crystal becomes uniform and a mode in which light in the visible region is transmitted can be obtained. A composition in which a nematic liquid crystal is dispersed in a polymer, in which the alignment state of the liquid crystal becomes random by applying an electric field or cooling in the absence of an electric field, and the mode becomes a mode in which light in the visible region is scattered. A display / recording medium in which layers are stacked may be used.

The method of writing the display / recording is based on the control of the electric field applied to each display / recording medium at the time of heating and cooling an arbitrary position of the display / recording medium or the laminated display / recording medium.

At this time, the heating of an arbitrary position of the display / recording medium is performed by condensing light or electromagnetic waves.

Further, the display / recording apparatus comprises at least means for heating an arbitrary position of the display / recording medium and means for controlling an applied electric field in accordance with the heating position of the display / recording medium.

[0014]

The structure in which a liquid crystal is dispersed in a polymer is generally called a polymer dispersed liquid crystal PDLC, but a polymer dispersed liquid crystal in which a cholesteric liquid crystal is dispersed is particularly PDCLC.
Called (P olymer D ispersed C horesteric L iquid C rystal). The present invention provides a PDCLC having a uniform orientation and a randomized state by a state writing method using both heat and an electric field, and has a memory property in which the above state is maintained without a state maintaining mechanism such as electric field application. It was made with a focus on having.

FIG. 1 shows the principle of the state writing method using both heat and electric field for PDCLC in which cholesteric liquid crystal having negative dielectric anisotropy is dispersed.

The state of the PDCLC 1 in which the cholesteric liquid crystal is dispersed in the polymer 3 is (a), and the liquid crystal orientation in the cholesteric liquid crystal droplet 2 is random. However, the refractive index difference Δn of the liquid crystal is small, and the average refractive index n of the liquid crystal is
If is approximately equal to the refractive index of the polymer, a transmission state in which light in the visible light region can be transmitted uniformly is obtained. Here, the transparent electrode 4 is a transparent conductive film such as indium tin oxide (ITO). Next, as shown in (b), a part of the PDCLC 1 is heated (heating area 5), and an electric field is applied from a power source 6,
As shown in (c), when cooling is performed while applying an electric field, the liquid crystal molecules in the droplet are oriented in a direction perpendicular to the electric field, that is, in a direction parallel to the electrodes only in the heated region.
The structure is unique to cholesteric with the helical axis as the direction of the electric field. As shown in (d), even if the electric field is removed, the orientation of the liquid crystal in the droplet is maintained. It is in a state of reflecting the wavelength λ of light. on the other hand,
As shown in (e), when the region where the orientation is uniform is heated again and cooled without applying an electric field, the orientation becomes random again and the original transmission state is obtained. That is, the transmission and reflection states are reversible.

FIG. 2 is a schematic diagram for explaining a display / recording medium and a color display / recording method according to the present invention. In the figure, a display / recording medium 25 is a red reflective PDC that selectively reflects light in a red area sandwiched by transparent electrodes 20.
The display / recording medium 25 has a configuration in which an LC 21, a green reflective PDCLC 22 which also selectively reflects light in a green region, a blue reflective PDCLC 23 which also selectively reflects light in a blue region, and a black light absorber 24 are stacked. 1 by controlling the application of an electric field from the power supply 29 by the electric field control Sw 30 in accordance with the display color of the heated portion.
The reflection area 27 and the transmission area 28 are formed in accordance with the principle described above. As a result, display / recording composed of each reflection area is obtained. A reflection region for a specific wavelength transmits another wavelength in principle, and a region having a random orientation is a transmission region. Therefore, a color display can be performed without canceling out reflected colors. Note that the region where all layers are transparent looks black with the black light absorber 26 placed on the lowermost layer, and becomes white in principle if all layers are reflective regions.

In this method, PDCLC having different reflection wavelengths
By preparing the layers, all layers can be written at once, so that the writing time can be shortened and there is an advantage that color shift does not occur at each data point. Since the reflection wavelength is determined by the material, it can be easily adjusted as in the embodiments described below.

As a means for heating the display / recording medium 25, it is sufficient that the display / recording medium, which is a laminated body, is uniformly heated in a short time, and contact of a heater or irradiation of an electromagnetic wave such as a laser beam can be applied.

The black light absorber 24 is unnecessary at the time of writing, and may be laminated at the time of display. Further, the transparent electrode 20 may be formed directly on the PDCLC, or may be formed on a glass substrate or a polyethylene terephthalate (PET) sheet.

However, the above configuration has a drawback that the light utilization efficiency is 50% at the maximum. That is, reflected light from a cholesteric liquid crystal having a helical structure is limited to circularly polarized light having a rotation direction that matches the rotation direction of the helix. Therefore, FIG. 3 shows an example of a display / recording medium which improves the light use efficiency without such a defect. This is a structure in which PDCLC that reflects clockwise circularly polarized light and PDCLC that reflects counterclockwise circularly polarized light are simultaneously laminated. That is, a structure is obtained in which a total of six PDCLC layers are stacked. However, a PDC that reflects clockwise and counterclockwise circularly polarized light
Write LC to same state.

In the display / recording medium described above, white is obtained by combining reflected light of the three primary colors of red, green and blue. However, this white has a problem that the white is inferior due to restrictions such as that the reflection wavelength width cannot completely cover the visible light region. An example of a display / recording medium that solves this problem is shown in FIGS.

In this case, similarly to the PDCLC, a PLDLC capable of writing with the aid of heat and an electric field is laminated. FIG.
FIG. 5 shows the medium with poor light use efficiency shown in FIG. 2, and FIG. 5 shows the medium with improved light use efficiency shown in FIG. The PDLC is written so that only a portion where all of the PDCLC is a reflection region is a scattering region. In this way, the area to be white is the backscattering of the PDLC and each PDC
Clear white can be secured by the synergistic effect of the forward scattering of the reflected light from the LC.

FIG. 6 is a conceptual diagram showing a configuration example of a display / recording device according to the present invention. (A) shows a case in which condensed light from a laser or the like or an electromagnetic wave is used as the display / recording medium heating means 62, and the irradiation angle is set so that the light can be condensed at an arbitrary position on the display / recording medium. Change. Applied or not applied so that a state corresponding to the display data is formed by means 63 for controlling the applied electric field together with the light collection.
(B) and (c) show the case where a heating head or a laser head is used as the heating means 62. The heating means 62 may be moved as shown in (b) to heat an arbitrary position of the display / recording medium. , (C), the display / recording medium 61 may be moved. In both cases, the application of the electric field is controlled by the means 63 for controlling the applied electric field in accordance with the display data together with the heating.

As described above, the use of the display / recording medium according to the present invention in which PDCLCs having different reflection wavelength regions are stacked has an advantage that color display / recording can be performed extremely easily.

[0026]

The features of the present invention will become more apparent in the following description of the embodiments.

Example 1 A nematic liquid crystal having a negative dielectric anisotropy, ZLI-3381 (manufactured by Merck) to which 26% of a chiral agent was added, and a photocurable resin NOA65 (manufactured by Norland) were mixed at a weight ratio of 1: 1. Then, after injecting between two glass substrates on which ITO electrodes are formed (gap 10 μm),
PDC by irradiating ultraviolet light that causes polymerization of photocurable resin
LC was made. This PDCLC is heated to 100 ° C.
Cooling was performed while applying a voltage of 100 V at 60 Hz. After the removal of the electric field, a state in which red with a peak near 650 nm was reflected was obtained. This state did not change even after being left for a long time. When heated again to 100 ° C. and cooled without applying an electric field, it was possible to make it almost transparent. These states could be repeated alternately many times. On the other hand, after it became transparent,
Although 0 V was applied, the state did not change. That is,
With the help of heat, the liquid crystal can be brought into a uniform alignment state, and the state can be maintained even when the electric field is removed.

Example 2 A PDCLC was prepared using the liquid crystal and the photocurable resin of Example 1 while changing the concentration of the chiral agent to 28% and 30%.

As a result, as the concentration of the chiral agent increased, the reflection wavelength shifted to the shorter wavelength side, and PDCLC of green reflection having a peak around 520 nm and blue reflection having a peak near 480 nm was obtained. The red reflection PDCLC obtained in Example 1 and the green reflection and blue reflection PDCLC were laminated. As in Example 1, reflection and transmission of each color were observed by the combined use of heat and electric field.

Example 3 Dye (vanadium phthalocyanine oxide) having an absorption peak in the infrared region in each PDCLC used in Example 2
Was added, and a display / recording medium was manufactured using a PET sheet on which ITO was formed as a substrate. The film thickness was about 10 μm. Sheets corresponding to three colors of RGB were laminated, and each sheet was connected to a power source via a computer control relay unit. Light from a semiconductor infrared laser having a wavelength of 822 nm was guided by an optical fiber, and an arbitrary position on the sheet was irradiated. A voltage of 50 Hz and 100 V was turned on / off by a computer. Since the laser light was used, the stacked display / recording media were uniformly heated, and turned on in a reflection state in an On portion and in a transmission state in an Off portion. There is an effect that a color display can be obtained in a laminated state.

Example 4 A PDLC produced by the following method was laminated on the laminated display / recording medium used in Example 3. That is, the nematic liquid crystal E7 (manufactured by Merck) was mixed with the photocurable resin MultiCure 628 (manufactured by Daimax), sandwiched between PET sheets on which ITO was formed, and then irradiated with UV light to produce PDLC. . The thickness of the PDLC was about 20 μm. This PDLC also contained a trace amount of the dye used in Example 3.

By stacking PDLC and three kinds of PDCLC,
In the same manner as in Example 3, the laser beam was irradiated, and the electric field was turned on / off. At this time, PDLC has PDCL
In the portion of C where all the RGB were in the reflection state, no electric field was applied, and the portion was in a cloudy state. In the portion where any of the RGB was reflected or completely transmitted, the electric field was applied to make the transmission state. As a result, there was an effect that white which was slightly unclear in Example 3 could be made clear.

As described above, the gist of the present invention is to use heat and an electric field together to uniformly fix the orientation of the cholesteric liquid crystal in the polymer so as to reflect light of a specific wavelength, or to make it random. Is to form a display by uniformly transmitting light in the visible light region, and furthermore, P which reflects RGB, which are the three primary colors of light, respectively.
An object of the present invention is to realize a color display by stacking DCLCs and writing necessary states at the same time.

Therefore, it is clear that the types of liquid crystals and polymers used for PDCLC fabrication are not limited to those described in the above embodiments. It is clear that other types of substrates and transparent electrodes can be used according to the conditions of use.

[0035]

As described above, when the present invention is used, there is an effect that a color display sheet can be easily obtained. Moreover, this color display sheet can be rewritten and reused. Therefore, by replacing and repeatedly using various posters and the like, there is an effect that the consumption of paper discarded in a short period of time is suppressed and the environment is protected.

[Brief description of the drawings]

FIG. 1 is a schematic view showing the principle of a state writing method using both heat and an electric field for a PDCLC according to the present invention.

FIG. 2 is a schematic diagram illustrating a display / recording medium and a color display / recording method according to the present invention.

FIG. 3 is a schematic diagram illustrating an example of a display / recording medium with improved light use efficiency.

FIG. 4 is a schematic diagram showing an example of a display / recording medium with improved white display characteristics.

FIG. 5 is a schematic diagram showing another example of a display / recording medium with improved white display characteristics.

6A and 6B are conceptual diagrams illustrating a configuration example of a display / recording device according to the present invention, wherein FIG. 6A illustrates an example using a laser or the like as a heating unit, FIG. 6B illustrates an example in which a heating unit such as a thermal head is moved,
(C) shows an example in which a heating means such as a thermal head is fixed and the display / recording medium is moved.

FIG. 7 is a diagram illustrating the principle of display using a conventional smectic liquid crystal.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 PDCLC 2 Droplet 3 Polymer 4 Transparent electrode 5 Heating area 6 Power supply 20 Transparent electrode 21 Red reflection PDCLC 22 Green reflection PDCLC 23 Blue reflection PDCLC 24 Black absorber 25 Display / recording medium 26 Heating area 27 Reflection area 28 Transmission area 29 Power supply 30 Electric Field Control Sw 31 Clockwise Circularly Polarized Red Reflection PDCLC 32 Clockwise Circularly Polarized Green Reflection PDCLC 33 Clockwise Circularly Polarized Blue Reflection PDCLC 34 Counterclockwise Circularly Polarized Red Reflection PDCLC 35 Counterclockwise Circularly Polarized Green Reflection PDCLC 36 Counterclockwise Circularly Polarized Blue Reflective PDCLC 37 black light absorber

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-61-59496 (JP, A) JP-A-4-163520 (JP, A) JP-A-4-301618 (JP, A) JP-A-6-59 18831 (JP, A) JP-A-6-250615 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02F 1/1334 G02F 1/13 102 G02F 1/13 505

Claims (6)

(57) [Claims] 1. A display / recording medium in which a composition layer in which a cholesteric liquid crystal is dispersed in a polymer is sandwiched between substrates on which a transparent conductor is formed, and the composition is dispersed by cooling in a state of applying a high electric field after heating. The alignment state of the liquid crystal becomes uniform, and it can be set to a mode that reflects light of a specific wavelength. A display / recording medium characterized in that the mode can be set to be transparent to light, and both modes can be changed reversibly. 2. The display / recording medium according to claim 1, wherein in a mode in which the alignment state is uniform and light of a specific wavelength is reflected, a plurality of display / recording media having different reflected wavelengths, polarizations, or different wavelengths and polarizations. A display / recording medium characterized by laminating. 3. The display / recording medium according to claim 2, wherein the liquid crystal dispersed in the display / recording medium is cooled in a state of applying a high electric field after heating, so that the dispersed state of the liquid crystal becomes uniform and a mode in which light in a visible region is transmitted can be obtained. Later, by applying a low electric field or cooling with no electric field, the alignment state of the liquid crystal becomes random and it becomes a mode that scatters light in the visible region, and both modes are reversibly changed, and a nematic liquid crystal is dispersed in a polymer. A display / recording medium characterized by laminating a composition layer. 4. A method for writing display / recording on the display / recording medium according to claim 1, 2 or 3, wherein the display / recording medium or the stacked display / recording medium is heated and cooled at an arbitrary position. A display / recording method characterized by controlling an electric field applied to each display / recording medium at the time. 5. A display / recording method according to claim 4, wherein the heating of an arbitrary position on the display / recording medium is performed by condensing light or electromagnetic waves. 6. A means for heating at least an arbitrary position of the display / recording medium according to claim 1, 2 or 3, and means for controlling an applied electric field according to the heating position of the display / recording medium. Display / recording device characterized by the above-mentioned.