JP5109612B2 - Method and apparatus for driving liquid crystal display medium, and liquid crystal display medium - Google Patents

Description

  The present invention relates to a method and apparatus for driving a liquid crystal display medium, and a liquid crystal display medium.

  Research on various rewritable marking technologies with high convenience has been made, but as one direction, display media using cholesteric liquid crystals have a memory property that can hold display without power supply, and use polarizing plates In recent years, it has attracted attention because it has features such as being able to obtain a bright display and enabling color display without using a color filter.

  The planar cholesteric liquid crystal (chiral nematic liquid crystal) shows that light incident in parallel to the spiral axis is divided into right-handed and left-handed light, Bragg-reflects circularly polarized components that coincide with the twisted direction of the helix, and transmits the remaining light. Cause selective reflection phenomenon. The central wavelength λ and the reflection wavelength width Δλ of the reflected light are λ = n · p and Δλ =, where p is the helical pitch, n is the average refractive index in the plane orthogonal to the helical axis, and Δn is the birefringence. The light reflected by the planar cholesteric liquid crystal layer expressed by Δn · p exhibits a bright color depending on the helical pitch.

  As shown in FIG. 10A, a cholesteric liquid crystal having positive dielectric anisotropy has a planar structure in which the spiral axis is perpendicular to the cell surface and causes the selective reflection phenomenon described above with respect to incident light. As shown in FIG. 10B, a focal conic in which the spiral axis is substantially parallel to the cell surface and transmits the incident light while being slightly scattered forward, and as shown in FIG. Three states are shown: homeotropic, which faces the electric field direction and transmits the incident light almost completely.

  Of the above three states, the planar and the focal conic can exist bistable without an electric field. Therefore, the state of the cholesteric liquid crystal is not uniquely determined with respect to the electric field strength applied to the liquid crystal layer. When the planar is in the initial state, the planar, focal conic, and homeotropic states are increased as the electric field strength increases. When the focal conic is in the initial state, it changes in the order of focal conic and homeotropic as the electric field strength increases.

On the other hand, when the electric field strength applied to the liquid crystal layer is rapidly reduced to zero, the planar state and the focal conic state are maintained as they are, and the homeotropic state is changed to the planar state.
Therefore, the cholesteric liquid crystal layer immediately after the pulse signal is applied exhibits a switching behavior as shown in FIG. 11, and when the voltage of the applied pulse signal is equal to or higher than Vfh, a selective reflection state is changed from homeotropic to planar. When Vpf is between Vpf and Vfh, the transmission state is caused by focal conic, and when it is equal to or lower than Vpf, the state before application of the pulse signal is continued, that is, the selective reflection state by the planar or the transmission state by focal conic.

  In FIG. 11, the vertical axis represents the normalized light reflectance, and the light reflectance is normalized with the maximum light reflectance being 100 and the minimum light reflectance being 0. In addition, there is a transition region between the planar, focal conic, and homeotropic states. Therefore, the normalized reflection rate is 50 or more when the normalized reflection rate is less than 50, and the normalized reflection rate is less than 50. The state is defined as a state, and the threshold voltage of the planar and focal conic state change is Vpf, and the threshold voltage of the focal conic and homeotropic state change is Vfh.

  In addition to a structure in which liquid crystal is sealed as a continuous phase between a pair of display substrates, a display medium using cholesteric liquid crystal has a PDLC (Polymer Dispersed Liquid Crystal) structure in which cholesteric liquid crystal is dispersed in a polymer binder in a drop shape, or a polymer. A PDMLC (Polymer Dispersed Liquid Crystal Crystal) structure in which microencapsulated cholesteric liquid crystal is dispersed in a binder can be formed (see, for example, Patent Documents 1 to 3).

  When the PDLC structure or the PDMLC structure is used, the fluidity of the liquid crystal is suppressed, so that the image disturbance due to bending and pressure is reduced, and a flexible medium can be realized. Further, a color display can be performed by directly laminating a plurality of cholesteric liquid crystal layers, or a display medium in which an image is addressed by an optical signal by laminating with a photoconductive layer can be obtained. Further, since the display layer can be formed using a thick film printing technique, there is an advantage that the manufacturing method is simplified and the cost is reduced.

Conventionally, many display media using the technology have been proposed (see, for example, Patent Document 4).
The optical writing type (optical address type) display medium according to the technology uses the bistable phenomenon of the cholesteric liquid crystal to switch between (A) the selective reflection state by the planar and (B) the transmission state by the focal conic. By doing so, monochrome display of various hues having a memory property without an electric field or a color display having a memory property without an electric field is performed.

  FIG. 12 is a schematic diagram schematically showing a state in which an image is written by a light irradiation device on a general display medium according to the technology. As shown in FIG. 12, the display medium according to the technique has a display layer that is a liquid crystal layer and an organic photosensitive layer that is a photoconductor layer between a pair of transparent electrodes (a light shielding layer (not shown) if necessary). Are stacked) and are sandwiched between a pair of substrates. A desired recorded image can be written by exposing the surface on the side of the organic photosensitive layer imagewise with an exposure device in a state where a predetermined voltage is applied to both transparent electrodes.

As described above, in the photo-writing type display medium, the photoconductive layer is laminated on the display layer in order to selectively control the state of the cholesteric liquid crystal between the exposed portion and the non-exposed portion.
By simplifying the layer structure of the display medium, it is possible to reduce the manufacturing cost and improve the flexibility by reducing the film thickness. In addition, the drive voltage can be kept lower as the number of layers arranged between the pair of electrode layers is smaller (thinner is thinner).
Therefore, it is desired to simplify the layer structure in the optical writing type liquid crystal display medium.

Japanese Patent Publication No. 7-009512 Japanese Patent Laid-Open No. 9-236791 Japanese Patent No. 3178530 JP 11-237644 A

  The present invention provides a driving method and a driving apparatus for writing an image on an optical writing type liquid crystal display medium with a simplified layer structure, and an optical writing type liquid crystal display medium with a simplified layer structure. Let it be an issue.

The above-mentioned subject is achieved by the following present invention. That is, the liquid crystal display medium driving method of the present invention (hereinafter sometimes simply referred to as “driving method of the present invention”) does not include a photoconductive layer between a pair of electrode layers, and cholesteric liquid crystal and photoisomerization. With respect to a liquid crystal display medium in which a display layer containing a chiral agent is at least sandwiched and the state of the cholesteric liquid crystal is selectively controlled between a planar and a focal conic to form an image in which light reflection or transmission is selected. A writing step of imagewise irradiating light that isomerizes the photoisomerizable chiral agent;
The cholesteric liquid crystal in the part irradiated with light in the writing process exceeds a threshold value of state change from focal conic to homeotropic, and the part not irradiated with light has a voltage not exceeding the threshold value. A voltage application step to be applied to the pair of electrode layers in the display medium;
A fixing step for performing an operation for reverse isomerization of the photoisomerized chiral agent isomerized in the writing step;
Are sequentially performed.

  According to the driving method of the present invention, optical writing can be performed on a liquid crystal display medium whose layer structure is greatly simplified by not including a photoconductive layer. At this time, since the liquid crystal display medium is a thin film, the driving voltage can be reduced as compared with the case of writing to the liquid crystal display medium including the photoconductive layer. The drive voltage reduction effect enables power saving and driver IC load reduction, enables the use of small and / or general-purpose driver ICs, and reduces the cost of the drive device. can do.

  The liquid crystal display medium to be driven can be restored to its original state by irradiating light (for example, visible light) having a wavelength different from that of light (for example, ultraviolet light) that can be used for photoisomerization. When a material containing a photoisomerizable chiral agent (which can be reverse isomerized) is used, the operation in the fixing step is an operation of irradiating light having a wavelength different from the wavelength of light irradiated in the writing step. Can do. If light with a wavelength different from that available for isomerization can be used to restore the isomerized chiral agent (reverse isomerization), reverse isomerization can be reliably performed (controlled) in the fixing process. Is preferable. Further, depending on the apparatus, the same apparatus as that used to irradiate light used for isomerization can be used for reverse isomerization.

On the other hand, the driving device for the liquid crystal display medium of the present invention (hereinafter sometimes simply referred to as “driving device of the present invention”) does not include a photoconductive layer between at least a pair of electrode layers. A liquid crystal display medium in which at least a display layer containing a photoisomerization chiral agent is sandwiched and the state of the cholesteric liquid crystal is selectively controlled between a planar and a focal conic to form an image in which light reflection or transmission is selected. Voltage applying means for applying a voltage to the pair of electrode layers, light irradiating means for irradiating the liquid crystal display medium with image light, and an operation for returning the isomerized photoisomerization chiral agent A fixing means capable of
A writing operation of irradiating the light isomerized with the light irradiating means in an imagewise manner by the light irradiating means;
In the writing operation, the cholesteric liquid crystal in the portion irradiated with light exceeds the threshold of state change from focal conic to homeotropic, and the portion not irradiated with light has a voltage not exceeding the threshold. Voltage application operation applied by an application means;
A fixing operation for performing an operation for reverse isomerizing the photoisomerized chiral agent isomerized in the writing operation by a fixing unit;
Are configured to be sequentially performed.

  According to the driving device of the present invention, it is possible to perform optical writing on a liquid crystal display medium whose layer structure is greatly simplified by not including a photoconductive layer. At this time, since the liquid crystal display medium is a thin film, the driving voltage can be reduced as compared with the case of writing to the liquid crystal display medium including the photoconductive layer. The drive voltage reduction effect enables power saving and driver IC load reduction, enables the use of small and / or general-purpose driver ICs, and reduces the cost of the drive device. can do.

  The liquid crystal display medium to be driven can be restored to its original state by irradiating light (for example, visible light) having a wavelength different from that of light (for example, ultraviolet light) that can be used for photoisomerization. In the case of using a photoisomerization chiral agent (which can be reverse isomerized), the fixing performed by irradiating the light having the wavelength different from the wavelength of the light irradiated as the writing operation as the operation performed by the fixing means. It can be an action. If light having a wavelength different from that used for isomerization can be used to restore the isomerized chiral agent (reverse isomerization), reverse isomerization can be reliably performed (controllable) by the fixing means. This is preferable. Further, depending on the apparatus, the same apparatus as that used to irradiate light used for isomerization can be used for reverse isomerization.

In the liquid crystal display medium of the present invention, at least a display layer containing cholesteric liquid crystal is sandwiched between a pair of electrode layers, and the state of the cholesteric liquid crystal is selectively controlled between the planar and the focal conic to transmit light. An optically writable liquid crystal display medium that forms an image selected for reflection or transmission,
The display layer includes a photoisomerization chiral agent, and no photoconductive layer is disposed between the pair of electrode layers.

  According to the liquid crystal display medium of the present invention, since a photo-writing type display medium can be configured without using a photoconductive layer, the layer configuration can be greatly simplified. By simplifying the layer structure, the manufacturing process can be simplified and the material cost can be reduced. Therefore, the manufacturing cost of the display medium can be reduced. Further, since the number of layers is small, the thickness of the display medium can be further reduced, and the effect of improving the flexibility of the display medium itself can be expected. Furthermore, there is no partial pressure on the photoconductive layer between the pair of electrode layers, the driving voltage for driving the liquid crystal of the display layer is reduced, and power saving and load reduction of the driver IC can be realized. it can. In addition, by reducing the load, a small-sized and / or general-purpose driver IC can be used, and the cost of the driving device can be reduced.

  As the photoisomerization chiral agent in the present invention, a chiral agent that undergoes reverse isomerization by irradiating light having a wavelength different from that of light that can be subjected to isomerization can be mentioned as a preferable example. If light with a wavelength different from that available for isomerization can be used to restore the isomerized chiral agent (reverse isomerization), reverse isomerization can be reliably performed (controlled) in the fixing process. Is preferable. Further, depending on the apparatus, the same apparatus as that used to irradiate light used for isomerization can be used for reverse isomerization.

Preferable specific examples of the photoisomerization chiral agent include those containing azobenzenes in their structure (chiral azobenzene).
In the present invention, the display layer is preferably one in which the cholesteric liquid crystal is dispersed in a polymer.

According to the present invention, a driving method and a driving apparatus for writing an image on a liquid crystal display medium that is a photo-writing type but has no photoconductive layer and a simplified layer configuration, and a layer configuration are simplified. An optical writing type liquid crystal display medium can be provided.
By simplifying the layer structure, the manufacturing cost of the liquid crystal display medium can be reduced, the flexibility can be improved, and the driving voltage can be reduced. The reduction effect of the driving voltage can realize power saving and cost reduction of the driving device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a liquid crystal display medium, a driving method and a driving apparatus thereof according to the present invention will be described in detail with reference to the drawings with preferred embodiments.
FIG. 1 is a schematic configuration diagram of an embodiment which is an exemplary aspect of a system including a liquid crystal display medium and an entire driving device of the present invention. The system according to this embodiment includes a liquid crystal display medium 1 and a driving device 2. Both of these components will be described in detail before the operation (driving method) will be described.

<Liquid crystal display medium>
In this embodiment, the liquid crystal display medium 1 includes a substrate 3, an electrode 5, a display layer 7, a laminate layer 8, an electrode (electrode layer) 6, a substrate 4 and a light shielding layer (colored layer) 9 in order from the display surface side. It is a thing made.

(substrate)
The substrates 3 and 4 are members for holding the functional layers on the inner surface and maintaining the structure of the display medium. The substrates 3 and 4 are sheet-shaped objects having strength that can withstand external forces, and preferably have flexibility. Specific examples of the material include inorganic sheets (for example, glass / silicon), polymer films (for example, polyethylene terephthalate, polysulfone, polyethersulfone, polycarbonate, and polyethylene naphthalate). At least the substrate 3 on the display surface side has a function of transmitting display light and isomerization light (writing light). A known functional film such as an antifouling film, an anti-abrasion film, a light reflection preventing film, or a gas barrier film may be formed on the outer surface. In the present embodiment, a light shielding layer 9 is provided on the outer surface of the substrate 4. The light shielding layer 9 will be described later.

(electrode)
The electrodes (electrode layers) 5 and 6 are intended members for applying the voltage applied from the voltage application unit 17 in the driving device 2 to the display layer 7 in the liquid crystal display medium 1. Specifically, metal (for example, gold, silver, copper, iron, aluminum), metal oxide (for example, indium oxide, tin oxide, indium tin oxide (ITO)), carbon, and a composite in which these are dispersed in a polymer And conductive thin films formed of conductive organic polymers (for example, polythiophene-based or polyaniline-based). A known functional film such as an adhesion improving film, an antireflection film, or a gas barrier film may be formed on the surface.

(Display layer)
In the present invention, the display layer has a function of modulating the reflection / transmission state of incident light by an electric field by utilizing the change in the light interference state of the cholesteric (chiral nematic) liquid crystal, and the selected state is maintained without an electric field. It is of a nature that can be done. The display layer preferably has a structure that is not deformed by an external force such as bending or pressure.

In this embodiment, as the display layer, a liquid crystal layer of a self-holding type liquid crystal composite made of cholesteric liquid crystal and transparent resin is formed. That is, it is a liquid crystal layer that does not require a spacer or the like because it has a self-holding property as a composite. In the present embodiment, the cholesteric liquid crystal 12 is dispersed in the polymer matrix (transparent resin) 11.
In the present invention, it is not essential that the display layer is a liquid crystal layer of a self-holding type liquid crystal composite. Of course, the display layer may be composed of only liquid crystals.

  Cholesteric liquid crystals have the function of modulating the reflection / transmission state of specific color light in incident light, and liquid crystal molecules are twisted and aligned in a spiral shape. Interfering and reflecting the specific light depending. The orientation is changed by the electric field, and the reflection state can be changed. When the display layer is a self-holding liquid crystal composite, it is preferable that the drop size is uniform and the single layer is densely arranged.

  Specific liquid crystals that can be used as cholesteric liquid crystals include steroidal cholesterol derivatives, nematic liquid crystals and smectic liquid crystals (for example, Schiff base series, azo series, azoxy series, benzoate series, biphenyl series, terphenyl series, cyclohexyl carboxyl series). Acid ester, phenylcyclohexane, biphenylcyclohexane, pyrimidine, dioxane, cyclohexylcyclohexane ester, cyclohexylethane, cyclohexane, tolan, alkenyl, stilbene, condensed polycyclic), or mixtures thereof And those to which chiral agents (for example, steroidal cholesterol derivatives, Schiff bases, azos, esters, and biphenyls) are added.

  The spiral pitch of the cholesteric liquid crystal is such that, for example, when the display color is blue, green, or red, the center wavelength of selective reflection is in the range of 400 nm to 500 nm, 500 nm to 600 nm, or 600 nm to 700 nm, respectively. . In order to control the helical pitch of the cholesteric liquid crystal, the liquid crystal molecules have a suitable chemical structure and are generally adjusted by the type and amount of chiral agent added to the nematic liquid crystal.

In the present invention, a photoisomerization chiral agent (also referred to as a photochromic chiral agent, a chiral agent having photochromic properties, a chiral photochromic material, or the like) is used as the chiral agent.
A photoisomerization chiral agent is a chiral agent whose torsional force HTP (Herical Twisting Power) is changed by light irradiation, and it is structurally composed of a photochromic site (site showing photoisomerization) and an optically active site. It is a compound that is bound using various synthetic techniques.
In addition, as a chiral agent used in this invention, you may mix with the general chiral agent which does not show photoisomerization only with the said photoisomerization chiral agent. What is necessary is just to adjust suitably and to use so that the characteristic of the desired chiral agent may be expressed in the mixed state.

In the present invention, the photochromic moiety undergoes reversible isomerization reaction or ring-opening-ring-closing reaction by light or heat, and has various physical properties (refractive index, dielectric constant, absorption spectrum, etc.) due to changes in geometric structure and electronic structure. A structural site that causes a change. Representative photochromic sites include azobenzenes, spiropyrans, diarylethenes, fulgides, etc. Specific examples of reversible reactions in the respective structures are shown below.

  In the present invention, the optically active site refers to a structural site that has a three-dimensional structure having an enantiomer and exhibits a basic function as a chiral agent that induces a helical structure in a liquid crystal. Specific examples of the structure of the optically active site include those having an asymmetric center as an asymmetric source, cholesteric derivatives having an asymmetric carbon, branched alkyl groups, and the like, and those having an asymmetric axis as an asymmetric source. Examples include allene derivatives, biphenyl derivatives, naphthalene derivatives, and the like, and those having an asymmetric surface as an asymmetric source include cyclophane. In addition, there are those in which the molecule itself has a helical structure, such as helicene.

  Specific examples of the optically active site are listed below. In the following structural formula, an atom marked with * is an asymmetric carbon.

(A) Cholesteric derivative having asymmetric carbon

(B) a branched alkyl group having an asymmetric carbon

(C) Allene derivative

(D) Biphenyl derivative

(E) Naphthalene derivatives

  Representative photoisomerizable chiral agents include azobenzenes at the photochromic site, and chiral azobenzenes with the optically active site as a branched alkyl group having an asymmetric carbon. Specific chemical structures thereof are listed in the following structural formulas (1) to (3).

  The light that can be used for the photoisomerization of the photoisomerization chiral agent needs to have a wavelength that can be efficiently absorbed by the molecule before isomerization and sufficient energy to change the molecular structure. In general, light having a relatively short wavelength is suitable, and it is selected from the range of ultraviolet light to visible light, depending on its structure.

  On the other hand, when the isomerized chiral agent can be returned to its original state by irradiating the photoisomerized chiral agent with light having a wavelength longer than the wavelength of light that can be subjected to photoisomerization. There are many. In addition, there is a chiral agent that restores the isomerized state by heating or leaving it at room temperature.

  In azobenzenes, the double bond isomerizes from the trans isomer to the cis isomer by absorption of ultraviolet light, and reverse isomerization from the cis isomer to the trans isomer by absorption of visible light. Since the trans isomer has a lower energy and is more stable than the cis isomer, the cis isomer may return to the trans isomer by a thermal reaction.

Spiropyrans are ring-opened by absorption of ultraviolet light to isomerize into merocyanine, and ring-closed by absorption of visible light or thermal reaction to return to the original state.
In diarylethenes and fulgides, the hetero 5-membered ring is closed by absorption of ultraviolet light, and the ring is opened and restored by absorption of visible light. Diarylethenes and fulgides have high thermal stability.

  The wavelength of light necessary for isomerization or reverse isomerization depends on an absorption spectrum in each state (more specifically, an energy gap between each ground state and an excited state). Also, the thermal stability depends on the activation energy (ground state potential energy) for the reverse isomerization reaction. These can be controlled by the chemical structure of the whole molecule and the interaction between molecules.

Photoisomerized chiral agents generally have a strong tendency to return to a stable state prior to isomerization due to absorption of visible light. Therefore, by controlling the helical pitch of cholesteric liquid crystals depending on the presence or absence of photoisomerization of chiral agents. When a display image is obtained, reverse isomerization proceeds due to external light during observation and the image disappears. In addition, since the photoisomerization chiral agent has a strong tendency to return to a stable state before isomerization even by heat, the image disappears with time even if the visible light is not strongly applied.
That is, if an image is formed using the planar helical pitch change (that is, change in selective reflection wavelength) as it is due to the photoisomerization of the chiral agent as it is, the memory performance of the image is extremely low.

  In the liquid crystal display medium of the present invention, the state is selectively controlled between the planar and the focal conic by changing the threshold of the state change of the cholesteric liquid crystal by the photoisomerization of the chiral agent, thereby reflecting or transmitting light. Form a selected image. A specific image writing method (driving method) will be described later.

  As a form in which the display layer 7 forms a self-supporting liquid crystal composite composed of a cholesteric liquid crystal and a polymer matrix (transparent resin), a PNLC (Polymer Network Liquid Crystal) structure including a network-like resin in the continuous phase of the cholesteric liquid crystal. Alternatively, a PDLC (Polymer Dispersed Liquid Crystal) structure (including microencapsulated structures) in which cholesteric liquid crystal is dispersed in a droplet shape in a polymer skeleton can be used. As a result, an anchoring effect is produced at the interface between the cholesteric liquid crystal and the polymer, and the planar or focal conic holding state without an electric field can be made more stable.

  The PNLC structure or PDLC structure is a known method for phase-separating a polymer and a liquid crystal, for example, an acrylic, thiol, or epoxy-based polymer precursor that is polymerized by heat, light, electron beam, or the like. Polymers having low liquid crystal solubility such as PIPS (Polymerization Induced Phase Separation) method, polyvinyl alcohol, and the like, which are mixed, polymerized from a homogeneous phase, and phase-separated, are mixed, and suspended by stirring to increase the liquid crystal. Emulsion method in which droplets are dispersed in a molecule, TIPS (Thermally Induced Phase Separation) method in which a thermoplastic polymer and liquid crystal are mixed, cooled to a homogeneous phase, and then phase-separated, and the polymer and liquid crystal are mixed with chloroform. Dissolve in a solvent such as Although it can be formed by a SIPS (Solvent Induced Phase Separation) method in which the polymer and the liquid crystal are phase-separated to generate, it is not particularly limited.

  The polymer matrix has a function of holding cholesteric liquid crystal and suppressing the flow of liquid crystal (change in image) due to deformation of the display medium, and does not dissolve in the liquid crystal material and does not dissolve in the liquid crystal. The polymer material is preferably used. In addition, the polymer matrix is desirably a material having strength to withstand external force and high transparency to at least reflected light and isomerized light (writing light).

  Examples of materials that can be used as the polymer matrix include water-soluble polymer materials (eg, gelatin, polyvinyl alcohol, cellulose derivatives, polyacrylic acid polymers, ethyleneimine, polyethylene oxide, polyacrylamide, polystyrene sulfonate, polyamidine, isoprene-based materials). Sulfonic acid polymer), or a material that can be emulsified in water (for example, fluororesin, silicone resin, acrylic resin, urethane resin, epoxy resin).

  The switching (hysteresis) behavior of the display layer 7 depends on the type and amount of the photoisomerization chiral agent used, the dielectric anisotropy and elastic modulus of the cholesteric liquid crystal 12 constituting the display layer 7, the skeleton structure and side chain of the polymer, It can be controlled by the phase separation process, the morphology of the interface between the polymer matrix 11 and the display layer 7, the degree of anchoring effect at the interface between the polymer matrix 11 and the display layer 7, and the like.

  More specifically, the types and composition ratios of nematic liquid crystals, the types and amounts of photoisomerization chiral agents used, the types of resins, the types of monomers, oligomers, initiators, crosslinking agents, etc. that are starting materials for polymer resins, Composition ratio, polymerization temperature, exposure light source for photopolymerization, exposure intensity, exposure time, atmosphere temperature, electron beam intensity for electron beam polymerization, exposure time, atmosphere temperature, solvent type and composition ratio during coating, solution The density, the wet film thickness, the drying temperature, the start temperature at the time of temperature drop, the temperature drop speed, and the like are not limited thereto.

(Light shielding layer)
The light-shielding layer (colored layer) 9 is a layer provided for the purpose of optically separating external light incident from the non-display surface side of the display medium and a display image at the time of display and preventing deterioration of image quality, and is essential in the present invention. It is not a component. However, in order to improve the performance of the liquid crystal display medium 1, it is a layer desired to be provided. For this purpose, the light shielding layer 9 is required to have a function of absorbing at least light in the reflection wavelength region of the display layer 7.

  Specifically, the light shielding layer 9 is an inorganic pigment (for example, cadmium-based, chromium-based, cobalt-based, manganese-based, or carbon-based), or an organic dye or organic pigment (azo-based, anthraquinone-based, indigo-based, or triphenylmethane-based). , Nitro, phthalocyanine, perylene, pyrrolopyrrole, quinacridone, polycyclic quinone, squalium, azurenium, cyanine, pyrylium, anthrone) polymer binders (eg polyvinyl alcohol resin, polyacrylic) It can be formed by a wet coating method in which a coating solution is prepared by dispersing or dissolving in a suitable solvent together with a resin or the like, and this is applied to the outer surface of the substrate 4 and dried to form a film.

(Laminate layer)
The laminate layer 8 is a layer provided for the purpose of absorbing unevenness and bonding when the functional layers formed on the inner surfaces of the upper and lower substrates 3 and 4 are bonded, and is an essential component in the present invention. Absent. The laminate layer 8 is made of thermoplastic, thermosetting, or a mixed organic material thereof, and a material that can adhere and bond the display layer 7 and the light shielding layer 9 by heat or pressure is selected. The In addition, it is necessary to have transparency to at least incident light.
Examples of suitable materials for the laminate layer 8 include adhesive / adhesive polymer materials (for example, polyethylene, polypropylene, polyurethane, epoxy, acrylic, rubber, and silicone).

(Contact terminal)
The contact terminal 19 is a member that contacts the voltage application unit 17 and the liquid crystal display medium 1 (electrode layers 5 and 6) and conducts both of them, and has high conductivity. A thing with small contact resistance with the application part 17 is selected. It is preferable that the structure be separable from the electrodes 5 and 6 so that the liquid crystal display medium 1 and the driving device 2 can be separated.

  As the contact terminal 19, metal (for example, gold, silver, copper, iron, aluminum), carbon, a composite in which these are dispersed in a polymer, metal oxide (for example, indium oxide, tin oxide, indium tin oxide (ITO) )), Carbon, composites in which these are dispersed in a polymer, terminals made of a conductive organic polymer (for example, polythiophene-based or polyaniline-based), and a clip / connector shape that sandwiches an electrode. .

<Drive device>
In the present invention, the driving device (driving device for the liquid crystal display medium) 2 is a device for writing an image on the liquid crystal display medium 1, and a light irradiation unit (irradiation light (writing light) is irradiated to the liquid crystal display medium 1 A light application means) 18 and a voltage application section (voltage application means) 17 for applying a voltage to the liquid crystal display medium 1 are the main constituent elements, and a control circuit 16 for controlling these operations is arranged.

(Light irradiation part)
The light irradiation unit (light irradiation means) 18 has a function of irradiating the liquid crystal display medium 1 with a predetermined isomerized light pattern that becomes an image, and is based on the input signal from the control circuit 16 (on the liquid crystal display medium 1 ( Specifically, there is no particular limitation as long as a desired light image pattern (spectrum / intensity / spatial frequency) can be irradiated onto the display layer 7). The area to be irradiated with light does not have to be the entire writing surface of the liquid crystal display medium 1 and is not limited to the area in which the display layer is formed, but the area to be written (writing area). It is enough if it is within.

The isomerization light irradiated by the light irradiation unit 18 is preferably selected under the following conditions, but is not limited to this in the present invention.
Spectrum: It is desirable that the photoisomerization chiral agent contained in the display layer 7 has as much energy as possible in the wavelength region where photoisomerization occurs. When a photoisomerizable chiral agent that can be isomerized by irradiating with ultraviolet light is used, it is desirable that the light has a peak wavelength of the ultraviolet light.
Irradiation intensity: An intensity at which the photoisomerization chiral agent contained in the display layer 7 shows light isomerization during light and lower than that during darkness.

  In addition, the photoisomerization chiral agent is a chiral agent that can return the isomerized product to the original (can be reverse isomerized) by irradiating light having a wavelength different from the wavelength of light that can be subjected to photoisomerization. In this case, it is preferable that the light irradiation unit 18 has a function capable of irradiating light of such “different wavelengths”. Thereby, the operation of the writing process (writing operation) and the operation of the fixing process (fixing operation) in the driving method described later can be performed by one light irradiation unit 18. In this case, the light of “different wavelengths” irradiated by the light irradiation unit 18 (hereinafter sometimes referred to as “fixing light”) also has the spectrum and irradiation intensity as described above, similar to the isomerized light. Is preferred.

Specific examples of the light irradiation unit 18 include the following.
(1-1) A light source (for example, a cold cathode tube, a xenon lamp, a halogen lamp, a light emitting diode (LED), an EL, a laser, etc.) arranged in a one-dimensional array, a combination with a polygon mirror, etc. A device capable of forming an arbitrary two-dimensional light emission pattern by a scanning operation (1-2) A uniform light source such as an array of light sources arranged in an array or a combination with a light guide plate, and a light control element for producing an optical pattern (for example, (2) A self-luminous display such as a light source arranged in a plane (for example, CRT, PDP, EL, light emitting diode, FED, SED)
(3) A combination of the above (1-1), (1-2) or (2) and an optical element (for example, a microlens array, a cell hook lens array, a prism array, a viewing angle adjustment sheet)

(Voltage application part)
The voltage application unit (voltage application means) 17 has a function of applying a predetermined application voltage (drive voltage; hereinafter simply referred to as “bias voltage”) to the liquid crystal display medium 1 at the time of writing, and a control circuit. Any desired voltage waveform may be applied to the display medium (between each electrode) based on the input signal from 16. However, a high slew rate is preferable. For the voltage application unit 17, for example, a bipolar high voltage amplifier can be used.
The voltage application unit 17 applies a voltage to the liquid crystal display medium 1 between the electrode 5 and the electrode 6 through the contact terminal 19.

(Control circuit)
The control circuit 16 includes a voltage application unit 17 and a light irradiation unit according to image data from the outside (an image capturing device, an image receiving device, an image processing device, an image reproducing device, or a device having a plurality of these functions). 18 is a member such as a driver IC having a function of appropriately controlling the operation of 18. The specific control content by the control circuit 16 is such that the operation of each step by the driving method of the present invention is executed as the operation of each component member in the driving device. The method is as described in detail.

<Driving method>
As described above, in the liquid crystal display medium 1, a liquid crystal layer of a self-holding type liquid crystal composite composed of a cholesteric liquid crystal 12 and a polymer matrix 11 is formed as a display layer 7, and the display layer 7 is subjected to photoisomerization as described above. It comprises a chiral agent. In the liquid crystal display medium 1 of the present embodiment, by using the bistable phenomenon of the cholesteric liquid crystal, (A) the selective reflection state by the planar and (B) the transmission state by the focal conic are converted into the photoisomerization chiral agent. By controlling using an isomerization reaction, a display image having a memory property without an electric field is written.

In this embodiment,
(A) a writing step of irradiating the liquid crystal display medium 1 imagewise with ultraviolet light as light (isomerization light) isomerized by the photoisomerization chiral agent contained in the display layer 7;
(B) The part irradiated with ultraviolet light in the writing process exceeds the threshold of state change from focal conic to homeotropic, and the part not irradiated with ultraviolet light has a voltage not exceeding the threshold. A voltage application step to be applied between the electrodes 5 and 6;
(C) a fixing step of irradiating the entire surface of the liquid crystal display medium 1 with visible light (fixing light) as an operation for returning the photoisomerized chiral agent isomerized in the writing step;
The basic operations are performed sequentially.
The basic principle of the present invention will be described.

First, the change in switching behavior of the display layer 7 will be described using the graph of FIG.
The state of the cholesteric liquid crystal changes according to the magnitude of the externally applied voltage: planar, focal conic, homeotropic when the planar or homeotropic state is the initial state, and focal conic when the focal conic state is the initial state. , Homeotropic and change. In the final state planar and focal conic, the state is maintained even after the applied voltage is removed, but in the homeotropic state, as shown in FIG. 11, the state changes to the planar state. Therefore, the planar or focal conic is selected as the final state depending on the magnitude of the applied voltage. As shown in FIG. 10, the planar state is light reflection, and the focal conic state is light transmission.

  In the graph of FIG. 11, as the externally applied voltage on the horizontal axis increases, the state of the display layer (liquid crystal layer) changes to planar, focal conic, homeotropic (finally homeotropic → planar), or focal conic, homeo. It changes to tropic (finally homeotropic → planar), and the reflectance on the display surface (reflectance with respect to incident light from the substrate 3 side in FIG. 1) changes accordingly. Yes. The voltage at which each state change occurs is called a threshold value. In particular, the threshold value for the state change from planar to focal conic is the “threshold value on the low voltage side”, and the state change from focal conic to homeotropic. The threshold value is called “high voltage side threshold value”. In the graph of FIG. 11, the former is represented by Vpf and the latter is represented by Vfh.

In this embodiment, the threshold value on the high voltage side is used as the threshold value for state change used for image writing.
The threshold electric field E _c on the high voltage side (focal conic → homeotropic) of the cholesteric liquid crystal is expressed by the following equation.

(E _c: threshold electric field, P _0: helical pitch, k _22: twist elastic modulus, epsilon _0: dielectric constant of vacuum, [Delta] [epsilon]: dielectric anisotropy)

  As can be seen from the above equation, the state change threshold of the cholesteric liquid crystal is inversely proportional to the helical pitch (proportional to the energy required to unwind the helical structure). Therefore, if the function of the chiral agent for inducing the helical structure is lowered, the helical pitch becomes longer, and the state change threshold value is lowered.

On the other hand, the isomerization reaction of the photoisomerizable chiral agent will be described by taking typical chiral azobenzene as an example. The isomerization reaction of chiral azobenzene can be represented by the chemical reaction formula shown in FIG.
Trans-form chiral azobenzene functions as a normal chiral agent. When this is irradiated with ultraviolet light or the like (light that isomerizes the photoisomerizable chiral agent), it is isomerized into a cis form as shown in the chemical reaction formula of FIG. A cis-type chiral agent does not function as a chiral agent (induction of the helical structure of cholesteric liquid crystal). This is presumed to be due to a decrease in compatibility with the liquid crystal due to the bending of the molecular structure.

  In the present invention, a desired image is written by the photoisomerization reaction of the photoisomerization chiral agent by utilizing the properties of the photoisomerization chiral agent and the cholesteric liquid crystal. That is, for a portion where an image is to be written (a portion where a liquid crystal is to be driven), the photoisomerization chiral agent is isomerized as shown in FIG. Reduce functionality. Then, at that location, the helix of the cholesteric liquid crystal is extended, the helix pitch is increased, and the state change threshold value is reduced (the writing process).

  About the said location, a threshold value is exceeded with small energy compared with another location, for example, a small applied voltage, and it changes from a focal conic to a homeotropic. Therefore, there is a voltage whose magnitude exceeds the threshold only at the location and does not exceed the threshold at the location not irradiated with ultraviolet light. Therefore, when such a voltage is applied to the display layer 7, the light irradiation part becomes homeotropic and the light non-irradiation part becomes focal conic. Thereafter, when the applied voltage is removed, the state changes from homeotropic to planar.

  Furthermore, as an operation for returning the photoisomerized chiral agent that has been isomerized into a cis form to a trans form, visible light that is fixing light (having a wavelength longer than the wavelength of light irradiated for image writing). Light). Then, the photoisomerization chiral agent is reversely isomerized into a trans form, and the original function as the chiral agent is restored, the helical pitch of the cholesteric liquid crystal is reduced, the hue is changed, and the display image having a desired hue is fixed. (Fixing process).

  As described above, the driving method of the present invention partially deactivates the function of the image portion by photoisomerization of the photoisomerization chiral agent, lowers the threshold value, and generates a latent image depending on the magnitude of the threshold value. An image is written by uniformly applying a bias voltage between the two threshold values after the formation. Thus, since the photoisomerization chiral agent contained in the display layer has a function of reflecting the irradiation pattern of writing light (isomerization light in the present invention) in the change in orientation of the liquid crystal, the liquid crystal provided for the present invention The display medium does not need to use the photoelectric effect of the photoconductive layer for reflecting the writing light irradiation pattern on the change in the orientation of the liquid crystal. By omitting the photoconductive layer, the layer structure can be greatly simplified, and the following excellent effects can be obtained (including the effect as a liquid crystal display medium and the effect of the driving device used in the driving method). .

a) The manufacturing process of the liquid crystal display medium can be simplified.
b) Photoconductive layer material can be saved during the manufacture of liquid crystal display media.
c) From the above a) and b), the manufacturing cost of the liquid crystal display medium can be reduced.
d) Since the number of layers is small, the thickness of the display medium can be reduced, and the effect of improving the flexibility of the display medium itself can be desired.
e) There is no partial pressure on the photoconductive layer between the pair of electrode layers, and the driving voltage for driving the liquid crystal in the display layer is reduced.
f) From e) above, power saving can be achieved.
g) From the above e), it is possible to reduce the load on the driver IC, and it is possible to use a small-sized and / or general-purpose driver IC, and it is possible to reduce the cost of the driving device. .

  By the way, similarly to the present invention, by utilizing the above-mentioned characteristics of the photoisomerization chiral agent, a low voltage drive is performed even in a liquid crystal display medium of a writing method (voltage writing type) by applying an image-like voltage instead of light. It is possible to expect the effects of f) and g). In other words, if the electrodes 5 and 6 have the same layer structure as that of the liquid crystal display medium 1 in FIG. 1 and the display layers 7 divided for each predetermined cell can be individually driven, the photoisomerism can be obtained. Voltage writing can be performed in a state where the threshold of the cholesteric liquid crystal is lowered by isomerizing the chiral agent and low voltage driving is realized. The display layer 7 may be fractionated into cells, although the display layer 7 itself may be physically fractionated for each cell, but the display layer 7 is not particularly changed, and the electrodes 5 and 6 are appropriately configured. It's enough. That is, the electrodes 5 and 6 may have a segment structure, a simple matrix structure, or an active matrix structure using TFTs or the like.

Specifically, an image can be written on the liquid crystal display medium having the above structure by the following driving method.
First, the entire surface of the liquid crystal display medium is irradiated with predetermined ultraviolet light to isomerize the photoisomerized chiral agent as shown in FIG. 2 to form a cis form, thereby reducing the function as the chiral agent. Then, on the entire surface of the display layer, the helix of the cholesteric liquid crystal extends to increase the helix pitch, and the alignment change threshold value (high voltage side) decreases.

  Next, by selectively applying a voltage that exceeds or does not exceed the threshold value on the high voltage side of the cholesteric liquid crystal in the display layer, a cell that has applied a voltage exceeding the threshold value is focal conic. A cell that changes from a homeotropic to a homeotropic and applies a voltage that does not exceed the threshold value maintains a focal conic state or changes from a planar to a focal conic. The write voltage to be applied at this time can be kept low because the threshold value of the cholesteric liquid crystal on the entire display layer is lowered as described above.

Thereafter, when the applied voltage is removed, the state changes from homeotropic to planar.
Further, similarly to the driving method of the present invention, a display image having a desired hue can be obtained by performing the fixing process.
In addition, about the said drive method of the liquid crystal display medium of such a structure, specific drive verification is performed by the below-mentioned reference experiment.

  Further, by utilizing the above characteristics of the photoisomerizable chiral agent, it is possible to drive at a low voltage even in a liquid crystal display medium having a photoconductive layer such as an organic photosensitive layer (OPC). ) Can be expected. That is, in a liquid crystal display medium having a photoconductive layer, if a photoisomerizable chiral agent is used for the cholesteric liquid crystal of the display layer, the photoisomerizable chiral agent is isomerized to lower the threshold value of the cholesteric liquid crystal. In this state, optical writing can be performed, and low voltage driving is realized. Specifically, an image can be written by the following driving method.

  First, the entire surface of the liquid crystal display medium is irradiated with predetermined ultraviolet light to isomerize the photoisomerized chiral agent as shown in FIG. 2 to form a cis form, thereby reducing the function as the chiral agent. Then, on the entire surface of the display layer, the helix of the cholesteric liquid crystal extends to increase the helix pitch, and the alignment change threshold value (high voltage side) decreases.

  Next, by applying a predetermined bias voltage and irradiating image-like writing light (in this case, the writing light having a wavelength and intensity with which the photoconductive layer to be arranged has sensitivity) is irradiated, The irradiation site of light changes from the focal conic to the homeotropic beyond the threshold value, and the non-irradiation site changes from the planar to the focal conic without exceeding the threshold value. The bias voltage to be applied at this time can be kept low because the threshold value of the cholesteric liquid crystal on the entire display layer is lowered as described above.

Thereafter, when the applied voltage is removed, the homeotropic changes to a planar.
Further, similarly to the driving method of the present invention, a display image having a desired hue can be obtained by performing the fixing process.

  Next, the driving method of the liquid crystal display medium of the present invention will be described in detail for each step with reference to FIG. Here, FIG. 3 is a process explanatory view showing the state of the cholesteric liquid crystal transitioned by the liquid crystal display medium driving method of the present invention for each process.

(A: writing process)
In the writing process, the light irradiation unit 18 irradiates the liquid crystal display medium 1 with isomerization light (writing light) imagewise. The isomerization light is irradiated with ultraviolet light in this embodiment. However, in the present invention, the isomerized light may be light in a wavelength region sufficient for the photoisomerizable chiral agent contained in the display layer 7 to isomerize, and is not limited to ultraviolet light.

As shown in the column “(a) Writing process” in FIG. 3, a part of the photoisomerization chiral agent is isomerized from the trans isomer to the cis isomer at the site irradiated with isomerization light by the operation of this step. As a result, the function as a chiral agent is lowered, the helix of the cholesteric liquid crystal is elongated, and the helix pitch is increased. In this state, the threshold value for changing the state of the cholesteric liquid crystal from focal conic to homeotropic is small.
Note that the wavelength and intensity of the isomerization light irradiated in this step and the light irradiation time vary depending on the type of photoisomerization chiral agent used, and may be set as appropriate.

(B: Voltage application process)
In the voltage application step, a bias voltage having an appropriate voltage value is applied between the electrodes 5 and 6. As described above, the cholesteric liquid crystal in the display layer 7 has a lower threshold of state change from the focal conic to the homeotropic (threshold on the high voltage side) only at the portion irradiated with light in the writing process. There is no change in the part that was not irradiated. That is, there is a difference in threshold value between the light irradiation portion and the non-irradiation portion. Therefore, the bias voltage applied in this step is a voltage value such that the portion irradiated with light in the writing step exceeds the threshold on the high voltage side, and the portion not irradiated with light does not exceed the threshold. It is.

As shown in the column “(b) During voltage application process” in FIG. 3, by the operation of this process, the irradiation site of light changes from the focal conic to the homeotropic beyond the threshold value, and the non-irradiation site Remains focal conic without changing the threshold or changes from planar to focal conic.
Note that the waveform, magnitude, and application time of the voltage applied in this step vary depending on the type of cholesteric liquid crystal or photoisomerization chiral agent to be used, and may be set as appropriate.

In the present invention, the operation of the voltage application process is performed following the operation of the writing process in principle. However, the operations of both processes may be performed simultaneously or overlappingly. For example, even if the irradiation of the isomerization light in the writing process and the application of the bias voltage in the voltage application process are started simultaneously or with a certain time difference, the photoisomerization reaction of the photoisomerization chiral agent in the writing process is started. Then, there is no problem as long as the operations in both steps are continued for a time sufficient to cause a change to the homeotropic region where the photoisomerization reaction has occurred. That is, both the writing process and the voltage application process are not performed independently over time, but the state change in the display layer by both operations, more specifically, the photoisomerization of the photoisomerization chiral agent and the cholesteric The operations in both steps may be performed so that the change of the liquid crystal to the homeotropic state appears in this order.
Thereafter, when the applied voltage is removed, as shown in the column “(b ′) after completion of voltage application process” in FIG. 3, the light irradiation section in the writing process changes from homeotropic to planar.

  When the cholesteric liquid crystal state of the liquid crystal display medium 1 used for writing is not aligned in a focal conic state, a voltage for aligning the cholesteric liquid crystal state in the display layer 7 is applied between the electrodes 5 and 6 before the writing process. May be. The voltage applied for this initialization is a voltage that exceeds the threshold for changing orientation from the planar to the focal conic in the cholesteric liquid crystal of the display layer 7 (threshold on the low voltage side). The entire layer 7 is aligned to the focal conic state.

(C: fixing process)
In the fixing step, an operation for returning the photoisomerized chiral agent isomerized in the writing step to a cis form into a trans form is performed. In the present embodiment, the operation is an operation in which the light irradiation unit 18 irradiates the entire surface of the liquid crystal display medium 1 with visible light as fixing light. However, in the present invention, the operation of this step is not limited to irradiation with visible light, and may be appropriately selected depending on the properties of the chiral agent, such as heating or leaving at room temperature. it can.
Also, when fixing light is irradiated, it is not limited to binding with visible light, and depending on the nature of the chiral agent, an operation of irradiating light of a wavelength different from the wavelength of light irradiated in the writing process; can do.

At the site where the photoisomerizable chiral agent is isomerized in the writing process, the helical pitch of the cholesteric liquid crystal is long, but the state is maintained even after the voltage application process. Therefore, after the voltage application process is completed, the chiral agent cannot exhibit its function and does not have the intended hue in the selective reflection by the planar. Also, cis-type chiral agents are relatively unstable and gradually shift to the trans form, and the hue changes with time.
However, the chiral agent that has been isomerized to the cis form is actively returned to the trans form (reverse isomerization) to restore its function as a chiral agent by the operation of the fixing process, and is fixed as a display image of the desired hue. Is done.

  The liquid crystal display medium of the present invention, the driving method and the driving apparatus thereof have been described in detail above with reference to preferred embodiments, but the present invention is not limited to the above embodiments. For example, in the above embodiment, the display medium for forming a monochromatic image having only one display layer has been described as an example. However, a multicolor image can be formed by using a plurality of display layers and other layers as necessary. A display medium may be used, and at this time, a display medium capable of forming a full-color image by stacking display layers capable of displaying at least three primary colors of blue, green, and red may be used.

  In addition, those skilled in the art can appropriately modify the liquid crystal display medium of the present invention, the driving method of the present invention, or the driving apparatus of the present invention in accordance with conventionally known knowledge. Of course, such modifications are also included in the scope of the present invention as long as the liquid crystal display medium of the present invention, the driving method of the present invention, or the configuration of the driving apparatus of the present invention are provided.

EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated more concretely, this invention is not limited to a following example.
[Example]
A liquid crystal display medium 101 and a driving device 102 shown in FIG. 4 are prototyped as liquid crystal display media used in the examples, and the verification (verification test) of the operation of the present invention (examples) and image writing (driving test) are performed. Went. This will be described with reference to FIG.

<Production of Liquid Crystal Display Medium 101>
As the cholesteric liquid crystal, nematic liquid crystal (Merck, E7) 77.0% by mass, levorotatory chiral agent (Merck, S811) 11.5% by mass and levorotatory photoisomerization chiral agent (the structural formula (3)) The compound which selectively reflects orange was prepared by mixing 11.5% by mass of the above compound).

  On the other hand, two 1.1 mm-thick glass substrates (7059, manufactured by Corning) with ITO (surface resistance 300Ω / □) sputtered on one side were prepared. A liquid crystal vertical alignment film (manufactured by Nissan Chemical Co., Ltd., trade name SE7511L) was applied to the surface on which these ITO films were formed by spin coating so that the dry film thickness was 10 nm. A polyvinyl alcohol aqueous solution in which a carbon black pigment is dispersed is formed on one of the outer surfaces (the surface on which ITO is not formed) by spin coating so that the dry film thickness is 2 μm. The light shielding layer 109 was used. In the glass substrate, the glass portion corresponds to the substrate 104 in FIG. 4, and the ITO film corresponds to the electrode 106.

  On the other glass substrate, spherical spacers having a diameter of 10 μm (product name SP210, manufactured by Sekisui Fine Chemical Co., Ltd.) were wet-sprayed on the surface on which the ITO film was formed. Note that in the glass substrate, the glass portion corresponds to the substrate 103 in FIG. 4 and the ITO film corresponds to the electrode 105.

The surface of the glass substrate (substrate 103) on which the spherical spacers are dispersed is drawn with a dispenser on the peripheral portion of the surface on which the spherical spacers are dispersed. The other glass substrate (substrate 104) was bonded so that the surface on the ITO film (electrode 106) side faced, and was optically bonded with the optical adhesive to form an empty cell.
Into the obtained empty cell, the obtained orange cholesteric liquid crystal was capillary injected to form the display layer 107 between the ITO films (electrodes 105 and 106).
The liquid crystal display medium 101 was produced as described above.

<Production of drive device>
As the voltage application unit 117, a high-voltage power supply device (manufactured by Matsusada Precision Co., Ltd., HEOPT-1B60) was used, and this was connected to the electrodes 105 and 106 of the liquid crystal display medium 101 via the contact terminals 119.

  A UV light emitting diode (manufactured by Nichia Corporation, trade name NCSU033A type) is used as an isomerizing light source 118a for irradiating isomerizing light (writing light), and a fixing light source 118b for irradiating fixing light (reverse isomer light). As a light emitting unit 118, a blue light emitting diode (manufactured by Citizen Electronics Co., Ltd., trade name CL-191HB1 type) was used, and the display surface of the liquid crystal display medium 101 could be irradiated. The light irradiation unit 118 can irradiate ultraviolet (UV) isomerized light having a peak wavelength of 365 nm and visible light (BLUE) fixing light having a peak wavelength of 470 nm.

  As shown in FIG. 4, the light irradiation unit 118 is provided with an OHP sheet on which a desired image pattern is printed as a dimming member 118c between the isomerization light source 118a and the liquid crystal display medium 101. Inserted. The light control member 118c is inserted into the spot when the isomerization light source 118a is turned on to irradiate the image pattern, and is removed in advance when the fixing light source 118b is turned on.

  As the control circuit 116, a multi-channel DAQ board (National Instruments 6713 type) and control software (National Instruments LabVIEW) can be used so that the operation of the voltage application unit 117 and the light irradiation unit 118 can be appropriately controlled by a personal computer. Wired.

Although not shown, an integrating sphere spectrometer (manufactured by Konica Minolta, Inc.) for measuring the light reflectance of the display image of the display layer 107 on the surface of the liquid crystal display medium 101 on the display surface side (substrate 103 side). CM2002 type) was attached.
As described above, a drive evaluation system including a liquid crystal display medium and a drive device used in the examples was manufactured.

<Verification test>
The isomerization behavior was measured as follows using the produced drive evaluation system.
First, the entire surface of the liquid crystal display medium 101 was irradiated with isomerization light (UV) by the isomerization light source 118a while changing the amount of irradiation light. In this operation, the light control member 118c was removed.

  Thereafter, the reflection spectrum of the display surface of the liquid crystal display medium 101 was measured. The results are shown in the graph of FIG. The graph of FIG. 5 shows the relationship between the irradiation amount of isomerized light and the normalized reflection spectrum immediately after the irradiation. From the graph, it can be seen that the reflection spectrum shifts to a longer wavelength as the irradiation amount of isomerized light increases.

The irradiation amount of isomerization light of each curve in the graph of FIG. 5 is plotted logarithmically on the horizontal axis, and with respect to the peak wavelength λ ₀ when isomerization light is not irradiated (isomerization light irradiation amount 0 mJ / cm ² ). each curve change in peak wavelength lambda _x of the dose x Te (increase in peak wavelength: lambda _x 1-? ₀₎ is shown a graph plotting on the vertical axis in FIG. 6. As shown in FIG. 6, the peak reflectance changes from orange to red to infrared as the amount of isomerized light irradiation increases, and the photoisomerized chiral agent changes from trans to cis by irradiation with isomerized light. It can be seen that the spiral pitch of the cholesteric liquid crystal has been extended.
Next, the entire surface of the sample irradiated with isomerization light with an irradiation amount of 1000 mJ / cm ² was solidly irradiated with fixing light (BLUE) by the fixing light source 118b while changing the irradiation light amount. During this operation, the light control member 118c was removed.

Thereafter, the reflection spectrum of the display surface of the liquid crystal display medium 101 was measured. From the measurement result of the obtained reflection spectrum, the ratio (hereinafter referred to as “reverse isomerization rate”) of how much the peak wavelength before irradiation with isomerization light was returned was obtained. The reverse isomerization rate F (y) [%] when irradiated with the fixing light having the irradiation light amount ymJ / cm ² can be obtained by the following equation.

(In the formula, lambda ₀ is the peak wavelength in the isomerization of light irradiation amount 0mJ / cm ^2, λ ₁₀₀₀ is the peak wavelength in the isomerization of light irradiation amount 1000mJ / cm ^2, λ _y fixing light quantity ymJ / cm ² Represents the peak wavelength after irradiation with fluorinated light.)

  FIG. 7 shows a graph plotting the obtained results with the fixing light irradiation amount on the horizontal axis and the reverse isomerization rate F (y) on the vertical axis. It can be seen that by irradiating the fixing light of 50 to 100% of the isomerization light irradiation amount, the photoisomerization chiral agent is changed from the cis type to the trans type, and the cholesteric liquid crystal is returned to the original state.

For each sample was irradiated with isomerization of light irradiation amount 300 mJ / cm ² with a sample not irradiated with isomerization of light (isomerization light irradiation amount 0mJ / cm ^2), the voltage value of the pulse voltage by the voltage application unit 117 Was applied between the electrodes 105 and 106 for 0.2 seconds, and the fixing light (BLUE) was irradiated on the entire surface with an irradiation amount of 300 mJ / cm ² . The light control member 118c was removed at the time of irradiation with isomerization light and fixing light.

About each obtained sample, the reflectance of the display surface was measured. The result is shown in the graph of FIG. The graph of FIG. 8 shows the relationship between the voltage value of the applied pulse voltage and the reflectance, and these are plotted on the horizontal axis and the vertical axis in order. In addition, as the reflectance on the vertical axis, the value of the obtained luminous reflectance Y is indicated by a value (normalized Y value) normalized with the maximum value being 1 and the minimum value being 0. In addition, a sample that was not irradiated with isomerized light was expressed as “non-irradiated portion” and indicated by a black dot, and a sample that was irradiated with isomerized light with an irradiation amount of 300 mJ / cm ² was expressed as “irradiated portion” and plotted as a white point. ing.

  It can be seen from the graph of FIG. 8 that the threshold voltage for the state change of the cholesteric liquid crystal is lowered by isomerizing the photoisomerizable chiral agent from trans to cis. In this example, by applying a bias voltage of 42.5 V indicated by the broken line in the graph of FIG. 8, the isomerized light irradiation part is set to the bright state by the planar, and the non-irradiation part is set to the dark state by the focal conic. It can be seen that the selection can be controlled.

<Driving test>
The image was actually written according to the conditions obtained in the above verification test.
First, with the light control member 118c inserted, the surface of the liquid crystal display medium 101 was irradiated with isomerization light (UV) with an irradiation amount of 300 mJ / cm ^{2 from} the isomerization light source 118a (writing process). Then, the light transmission part of the light control member 118c became a light brown state.

Next, a bias voltage of 42.5 V was applied between the electrodes 105 and 106 by the voltage application unit 117 for 0.2 seconds (voltage application step). Then, the irradiated portion of the isomerized light remained almost the same light brown color as before application, and the non-irradiated portion of the isomerized light became dark.
Further, with the light adjusting member 118c removed, the fixing light source 118b was irradiated with fixing light (BLUE) having a dose of 300 mJ / cm ^{2 on} the entire surface of the liquid crystal display medium 101 (fixing step). Then, the non-irradiated part of the isomerized light was not changed and kept in a dark state, and the irradiated part of the isomerized light was bright orange and an image was displayed.
Since the image finally obtained as described above is formed by a planar with a memory property and a focal conic, it changes even after several months (discoloration, image change) in a state exposed to external light. There was no blur or bleeding.

[Reference experiment]
Next, as a reference experiment, a configuration for driving a voltage writing type liquid crystal display medium at a low voltage using the characteristics of a photoisomerization chiral agent as in the case of the present invention of an optical address type (optical writing type). Verification was performed. A drive evaluation system including a liquid crystal display medium and a drive device used in this reference experiment is shown in FIG.

<Production of Liquid Crystal Display Medium 201>
The liquid crystal display medium 201 used for the reference experiment is different from the optical address type liquid crystal display medium 101 used in the embodiment in that ITO electrodes are patterned in a pixel shape. Specifically, it is as follows.

  Two 1.1 mm-thick glass substrates (Corning Corp., 7059) were prepared by sputtering ITO (surface resistance 300Ω / □) into four lines on one side. A liquid crystal vertical alignment film (manufactured by Nissan Chemical Co., Ltd., trade name SE7511L) was applied to the surface on which these ITO films were formed by spin coating so that the dry film thickness was 10 nm. A polyvinyl alcohol aqueous solution in which a carbon black pigment is dispersed is formed on one of the outer surfaces (the surface on which ITO is not formed) by spin coating so that the dry film thickness is 2 μm. The light shielding layer 209 was used. In the glass substrate, the glass portion corresponds to the substrate 204 in FIG. 9 and the ITO film corresponds to the electrode 206.

  On the other glass substrate, spherical spacers (SP210 manufactured by Sekisui Fine Chemical Co., Ltd.) having a diameter of 10 μm were wet-sprayed on the surface on which the ITO film was formed. Note that in the glass substrate, the glass portion corresponds to the substrate 203 in FIG. 9, and the ITO film corresponds to the electrode 205.

  The surface of the glass substrate (substrate 203) on which the spherical spacers are dispersed is drawn with a dispenser on the peripheral edge of the surface on which the spherical spacers are dispersed. The other glass substrate (substrate 204) is bonded so that the ITO film (electrode 206) side faces each other and the ITO line patterns of both substrates are orthogonal to each other, and optically bonded with the optical adhesive. Empty cell.

An orange cholesteric liquid crystal similar to that of the example was capillary injected into the obtained empty cell to form a display layer 207 between the ITO films (electrodes 205 and 206).
As described above, a liquid crystal display medium 101 having a display unit composed of 4 × 4 16 pixels was manufactured.
In FIG. 9, only the electrode 206 is illustrated as being divided into four lines, but the electrode 205 orthogonal thereto is similarly divided into four lines.

<Production of drive device>
The driving device 202 used for the reference experiment is different from the optical addressing type driving device 102 used in the embodiment in that the light irradiation unit 218 has no dimming member, isomerized light from the isomerized light source 218a, and fixing. An image selection unit 220 including a switch for selecting a line of electrodes 205 and 206 to which a voltage is applied from the voltage application unit 217 and a point that the fixing light from the light source 218b is solid irradiation is displayed. The difference is that the application of an electric field to the layer 207 can be selected for each pixel.

  In FIG. 9, the switch of the image selection unit 220 is arranged only for conduction between the voltage application unit 217 and the electrode 206, but conduction from the voltage application unit 217 to the electrode 205 is performed for each line. Can be selected. In actual image writing, the electrode 205 is made conductive for each line, and the conduction to the corresponding electrode 206 is selected for each line by the switch of the image selection unit 220 at the time of each conduction. Can be granted.

Specifically, the driving device 202 is manufactured as follows.
A high voltage power supply device (manufactured by Matsusada Precision Co., HEOPT-1B60) is used as the voltage application unit 217, and a photo MOS relay (manufactured by Matsushita Electric Co., Ltd., AQV257 type) is used as the image selection unit 220. The electrodes 205 and 206, which are electrodes, were connected.

  A UV light emitting diode (manufactured by Nichia Corporation, trade name NCSU033A type) is used as an isomerizing light source 218a for irradiating isomerizing light (writing light), and a fixing light source 218b for irradiating fixing light (reverse isomer light). As a light emitting unit 218, a blue light emitting diode (manufactured by Citizen Electronics Co., Ltd., trade name CL-191HB1 type) was used, and the display surface of the liquid crystal display medium 201 could be irradiated. The light irradiation unit 218 can irradiate ultraviolet (UV) isomerized light having a peak wavelength of 365 nm and visible light (BLUE) fixing light having a peak wavelength of 470 nm.

  As the control circuit 216, a multi-channel DAQ board (National Instruments 6713 type) and control software (National Instruments LabVIEW) are used. Based on image data from a personal computer, a voltage application unit 217, an image selection unit 220, and Wiring was performed so that the operation of the light irradiation unit 218 could be appropriately controlled.

  Although not shown, an integrating sphere spectrometer (manufactured by Konica Minolta Co., Ltd.) for measuring the light reflectance of the display image of the display layer 207 on the surface of the liquid crystal display medium 201 on the display surface side (substrate 203 side). CM2002 type) was attached.

As described above, a drive evaluation system including a liquid crystal display medium and a drive device used for a reference experiment was produced.
For the obtained drive evaluation system, an image was actually written.
First, the surface of the liquid crystal display medium 201 was irradiated with isomerization light (UV) having an irradiation amount of 300 mJ / cm ^{2 from} the isomerization light source 218a. The whole surface became light brown.

  Next, a voltage of 42.5 V or 35 V is applied between the electrodes 205 and 206 for 0.2 seconds while controlling the voltage application unit 217 and the image selection unit 220 to apply an electric field to a specific pixel in the display layer 207. Applied. Then, the pixel to which the voltage of 42.5 V was applied remained almost the same light brown as before the application, and the pixel to which the voltage of 35 V was applied was in a dark state.

Further, the entire surface of the liquid crystal display medium 201 was fixedly irradiated with fixing light (BLUE) by the fixing light source 218b. Then, the pixels to which the voltage of 35 V was applied remained unchanged and the pixels to which the voltage of 42.5 V was applied exhibited a bright orange color and displayed an image.
Since the image finally obtained as described above is formed by a planar with a memory property and a focal conic, it changes even after several months (discoloration, image change) in a state exposed to external light. There was no blur or bleeding.

  On the other hand, a voltage of 42.5 V is applied while controlling so that an electric field is applied to a specific pixel, except that irradiation with isomerization light (UV) is not performed, and fixing is performed. When irradiated with light, the entire surface was dark and an image could not be written.

It is a schematic block diagram which shows the exemplary one aspect | mode of the system containing the liquid crystal display medium of this invention, and the whole drive device. It is a chemical reaction formula showing an isomerization reaction of chiral azobenzene which is a typical photoisomerization chiral agent. It is process explanatory drawing which shows the state of the cholesteric liquid crystal which changes with the drive method of the liquid crystal display medium of this invention for every process. It is a schematic block diagram of the drive evaluation system containing the liquid crystal display medium and drive device which were provided to the Example. It is a result of the verification test of an Example, Comprising: It is a graph which shows the relationship between the irradiation light quantity of isomerization light, and the reflection spectrum immediately after the irradiation. It is a result of the verification test of an Example, Comprising: The irradiation amount of the isomerization light of each curve in the graph of FIG. 5 is plotted on the horizontal axis logarithmically, and each with respect to the peak wavelength when not irradiated with isomerization light. It is the graph which plotted the change (increase amount) of the peak wavelength of the curve in the irradiation amount of this to the vertical axis | shaft. It is a result of the verification test of an Example, Comprising: It is a graph showing the relationship between the irradiation amount of fixing light, and a reverse isomerization rate. It is a result of the verification test of an Example, Comprising: About the liquid crystal display medium when not irradiating with isomerization light, it is a graph which shows the relationship between the voltage value of the applied pulse voltage, and a reflectance. . It is a schematic block diagram of the drive evaluation system containing the liquid crystal display medium and drive device which were used for the reference experiment. It is a schematic explanatory view showing the relationship between molecular orientation and optical characteristics of cholesteric liquid crystal, (A) is planar, (B) is focal conic, and (C) is homeotropic. It is a graph for demonstrating the switching behavior of a cholesteric liquid crystal. It is a schematic diagram which represents typically a mode that the image is written in with the exposure apparatus with respect to the conventional general display medium.

Explanation of symbols

  1, 101, 201: Liquid crystal display medium, 2, 102, 202: Drive device, 3, 4, 103, 104, 203, 204: Substrate, 5, 6, 105, 106, 205, 206: Electrode (electrode layer) 7, 107, 207: display layer, 8: laminate layer, 9, 109, 209: light shielding layer, 11: polymer matrix, 12: cholesteric liquid crystal, 16, 116, 216: control circuit, 17, 117, 217: Voltage application unit (voltage application unit) 18, 118, 218: Light irradiation unit (light irradiation unit) 19, 119: Contact terminal, 118a, 218a: Isomerization light source, 118b, 218b: Fixation light source, 118c : Light control member, 220: Image selection unit

Claims (9)

A photoconductive layer is not disposed between the pair of electrode layers, a display layer containing at least a cholesteric liquid crystal and a photoisomerization chiral agent is sandwiched, and the state of the cholesteric liquid crystal is selectively controlled between the planar and the focal conic. A writing step of imagewise irradiating light isomerized by the photoisomerization chiral agent with respect to a liquid crystal display medium that forms an image selected to reflect or transmit light;
The cholesteric liquid crystal in the part irradiated with light in the writing process exceeds a threshold value of state change from focal conic to homeotropic, and the part not irradiated with light has a voltage not exceeding the threshold value. A voltage application step to be applied to the pair of electrode layers in the display medium;
A fixing step for performing an operation for reverse isomerization of the photoisomerized chiral agent isomerized in the writing step;
Are sequentially performed. A method for driving a liquid crystal display medium. The photoisomerization chiral agent contained in the display layer of the liquid crystal display medium is a chiral agent that undergoes reverse isomerization by irradiating light having a wavelength different from that of light that can be subjected to isomerization,
2. The method for driving a liquid crystal display medium according to claim 1, wherein the operation in the fixing step is an operation of irradiating light having a wavelength different from the wavelength of light irradiated in the writing step. At least a photoconductive layer is not disposed between the pair of electrode layers, and at least a display layer including a cholesteric liquid crystal and a photoisomerization chiral agent is sandwiched, and the state of the cholesteric liquid crystal is selectively selected between the planar and the focal conic. Voltage applying means for applying a voltage to the pair of electrode layers of the liquid crystal display medium for controlling and forming an image of which light reflection or transmission is selected, light irradiation means for irradiating the liquid crystal display medium with image light, And a fixing means capable of performing an operation for returning the isomerized photoisomerizable chiral agent to the original,
A writing operation of irradiating the light isomerized with the light irradiating means in an imagewise manner by the light irradiating means;
In the writing operation, the cholesteric liquid crystal in the portion irradiated with light exceeds the threshold of state change from focal conic to homeotropic, and the portion not irradiated with light has a voltage not exceeding the threshold. Voltage application operation applied by an application means;
A fixing operation for performing an operation for reverse isomerizing the photoisomerized chiral agent isomerized in the writing operation by a fixing unit;
A liquid crystal display medium driving device, wherein the liquid crystal display medium is configured to be sequentially performed. The photoisomerization chiral agent contained in the display layer of the liquid crystal display medium is a chiral agent that undergoes reverse isomerization by irradiating light having a wavelength different from that of light that can be subjected to isomerization,
4. The liquid crystal display medium driving device according to claim 3 , wherein the operation performed by the fixing means is a fixing operation in which light having a wavelength different from the wavelength of light irradiated as a writing operation is irradiated.   5. The liquid crystal display medium driving device according to claim 4, wherein the light irradiating means can selectively irradiate light having different wavelengths and also serves as the fixing means. At least a display layer containing a cholesteric liquid crystal and a photoisomerization chiral agent is sandwiched between a pair of electrode layers, and the state of the cholesteric liquid crystal is selectively controlled between the planar and the focal conic so that light can be reflected or transmitted. forming a selected image, a liquid crystal display medium of the optical writing type which is not photoconductive layer is disposed between the pair of electrode layers,
The liquid crystal display medium was irradiated with light in a writing operation in which the light isomerizing chiral agent of the display layer irradiates in an imagewise manner, and in the writing operation of the light irradiation unit . The portion of the cholesteric liquid crystal exceeds a threshold of state change from focal conic to homeotropic, and a portion not irradiated with light has a voltage not exceeding the threshold, and the pair of electrode layers of the liquid crystal display medium Voltage applying means for applying a voltage applied to the light source, and fixing means for performing a fixing operation for reverse isomerizing the photoisomerization chiral agent of the display layer isomerized in the writing operation of the light irradiation means. Including drive and
With
The liquid crystal display device according to claim 1, wherein the driving device is configured to sequentially perform a writing operation of the light irradiation unit, a voltage application operation of the voltage application unit, and a fixing operation of the fixing unit . The photoisomerization chiral agent contained in the display layer in a liquid crystal display medium, Ri chiral agent der inversely isomerization by irradiation with light of a wavelength different from the light that may be subjected to isomerization,
The liquid crystal display device according to claim 6 , wherein the reverse isomerization operation of the fixing unit in the driving device irradiates light having a wavelength different from the wavelength of light irradiated as the writing operation of the light irradiation unit . The liquid crystal display device according to claim 6, wherein the photoisomerization chiral agent contained in the display layer of the liquid crystal display medium contains azobenzenes in its structure. The liquid crystal display device according to claim 6, wherein the cholesteric liquid crystal is dispersed in a polymer in the display layer of the liquid crystal display medium .

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