JP2007322756A - Optical modulation element and its driving method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance chroma of a coloring image, especially chroma of a coloring image from a middle wavelength region to a long wavelength region in a visible light region in spite of a comparatively simple structure in an optical modulation element and to provide a driving method of the optical modulation element. <P>SOLUTION: In the optical modulation element 1 including at least one pair of optical modulation units 2 in which at least a display layer 7 selectively reflecting light having a specified wavelength region and constituted of a cholesteric liquid crystal and a light conductive layer 10 absorbing writing light and changing a resistance value according to an absorbed light quantity are layered and which is interposed between a pair of electrode layers 5 and 6 at least one of which on a display side is transparent, the light conductive layer 10 has a property absorbing light having any wavelength region except the specified wavelength region and the light conductive layer 10 and the display layer 7 are layered so as to be positioned on the display side and on a non-display side, respectively, in at least the one pair of optical modulation units 2. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention is a light modulation in which a display layer composed of a cholesteric liquid crystal that selectively reflects light in a specific wavelength range and a photoconductive layer having photoresponsiveness are sandwiched and an image can be written by light. The present invention relates to an element and a driving method thereof.

There are high expectations for rewritable marking technology as a hard copy technology that replaces paper, for reasons such as the preservation of the global environment such as forest resource protection and the improvement of the office environment such as space saving.
Research into various rewritable marking technologies that are even more convenient has been made, but as one direction, the technology using a liquid crystal device in which a liquid crystal and a photoconductor are laminated enables repeated recording / erasing. In addition, it attracts attention because it can realize other excellent characteristics.

  In particular, a liquid crystal display element using cholesteric liquid crystal (chiral nematic liquid crystal) can be appropriately written and erased by utilizing the phase change, and can form a full color image by laminating liquid crystal layers. It is attracting attention because it has various excellent properties.

  The planar phase shown by cholesteric liquid crystal (chiral nematic liquid crystal) divides light incident parallel to the helical axis into right-handed rotation and left-handed rotation, Bragg-reflects circularly polarized light components that match the twist direction of the helix, and reflects the remaining light. Causes a selective reflection phenomenon to be transmitted. 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 cholesteric liquid crystal layer in the planar phase expressed by Δn · p exhibits a bright color depending on the helical pitch.

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

  Among the above three states, the planar phase and the focal conic phase can exist bistable without an electric field. Therefore, the phase 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 phase is in the initial state, the planar phase and the focal conic phase are increased as the electric field strength increases. When the focal conic phase is in the initial state, the focal conic phase and the homeotropic phase change in this order as the electric field strength increases.

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

  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, since there are transition regions between the states of the planar phase, the focal conic phase, and the homeotropic phase, when the normalized light reflectance is 50 or more, the selective reflection state, and the normalized light reflectance is less than 50. The case is defined as a transmission state, the threshold voltage of the phase change between the planar phase and the focal conic phase is Vpf, and the threshold voltage of the phase change between the focal conic phase and the homeotropic phase is Vfh.

  In particular, a PNLC (Polymer Network Liquid Crystal) structure including a network-like resin in a continuous phase of cholesteric liquid crystal, or a PDLC (Polymer Dispersed Liquid Crystal) structure in which cholesteric liquid crystal is dispersed in a droplet form in a polymer skeleton ( In the liquid crystal layer (including those encapsulated), the bistability of the planar phase and the focal conic phase in the absence of an electric field is improved due to interference at the interface between the cholesteric liquid crystal and the polymer (anchoring effect). It is possible to maintain the state immediately after the pulse signal is applied.

Conventionally, many light modulation elements using the technology have been proposed (see, for example, Patent Document 1 and Non-Patent Document 1).
The optically addressed spatial light modulator according to this technology uses this cholesteric liquid crystal bistable phenomenon to switch between (A) the selective reflection state by the planar phase and (B) the transmission state by the focal conic phase. Accordingly, monochrome display of various hues having memory characteristics without an electric field or color display having memory characteristics without an electric field is performed.

  FIG. 12 is a schematic diagram schematically showing a state in which an exposure apparatus performs image writing on a general light modulation element according to the technology. As shown in FIG. 12, the light modulation element according to the technique has a display layer that is a liquid crystal layer and an OPC 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 of the OPC layer sidewise with an exposure device while applying a predetermined bias voltage to both transparent electrodes.

  The light modulation element according to this technique can form a full-color image by laminating three units of RGB, each of which has a display layer and a photoconductive layer sandwiched between electrode layers. At this time, in order to obtain a clear full-color image, it is important to increase the saturation of each color. Of course, it is needless to say that saturation of a desired hue is required in order to obtain a clear image in any display element, not limited to a light modulation element capable of forming a full-color image.

  FIG. 13 is a graph showing the relationship between the wavelength of external light and the reflectance when a certain display layer is in a reflective state or a transmissive state, which is made of cholesteric liquid crystal that enables red display. In the display layer, red light is reflected and displayed in red in the reflection state, and the wavelengths of all regions are transmitted in the transmission state. Therefore, if the back surface is black, black is displayed.

  Looking at the graph when the display layer is in the reflective state, a peak of reflectance is seen in the vicinity of 600 to 650 nm, which is the wavelength region of red light, but an arrow appears in the vicinity of 400 to 500 nm on the shorter wavelength side. As can be seen, a gentle peak occurs. This is presumed to be a scattering component due to the variation in the orientation of the cholesteric liquid crystal domain, and if a light scattering component is generated at a wavelength other than the wavelength region of such red light, the saturation is lowered.

  Such a scattering component is likely to occur in a region shorter than the target reflection wavelength. For this reason, the hue of a medium wavelength region, for example, a display layer that enables green display, may cause a decrease in saturation due to a scattering component on the shorter wavelength side than the display wavelength (green light wavelength) region.

JP 11-237644 A Reflective Display with Photoconductive Layer and Bistable, Reflective Cholesteric Mixture: SID 96 APPLICATION DIGEST p. 59-62

  Therefore, the present invention improves the saturation of the color image, particularly the color image in the medium wavelength region to the long wavelength region in the visible light region, while having a relatively simple structure for the light modulation element. And it aims at providing the drive method of this light modulation element.

The above object is achieved by the present invention described below. That is, the light modulation element of the present invention absorbs at least a display layer composed of a cholesteric liquid crystal that selectively reflects light in a specific wavelength region between a pair of electrode layers that are transparent at least on the display side. A light modulation element including at least one set of light modulation units formed by sandwiching and sandwiching a photoconductive layer whose resistance value is changed according to the amount of absorbed light, wherein at least one set of the light modulation units In
The photoconductive layer has a property of absorbing light in any wavelength region other than the specific wavelength region; and
The photoconductive layer is laminated on the display side, and the display layer is laminated on the non-display side.

  In the light modulation element of the present invention, a photoconductive layer having a property of absorbing light in any wavelength region other than the specific wavelength region (hereinafter referred to as “specific absorption wavelength region”) is positioned on the display side. Therefore, since external light in the specific absorption wavelength region can be effectively absorbed, light in the specific absorption wavelength region does not reach the display layer, and light scattering in the display layer can be suppressed. Accordingly, a reflected image having a desired hue consisting only of the specific wavelength region can be obtained without being affected by light in the specific absorption wavelength region, so that the saturation of the image is increased. In addition, the arrangement of the photoconductive layer included in a general light modulation element is merely changed, and another member such as a filter layer is not newly provided. Therefore, the element is increased in size and the cost is increased. It is easy to manufacture without fear of dripping.

  The specific absorption wavelength region absorbed by the photoconductive layer is preferably a wavelength region on a shorter wavelength side than the specific wavelength region. Scattering in the display layer is likely to occur on the shorter wavelength side than the specific wavelength region. Therefore, if the photoconductive layer absorbs this, the scattering of light with a short wavelength can be particularly effectively suppressed. Since a reflected image of a desired hue consisting only of a specific wavelength region is obtained, the saturation of the image is increased.

  In the light modulation element of the present invention, the light modulation unit may have a single color display configuration or a multicolor display configuration in which two or more sets are stacked. The present invention is also preferably applied to a full-color display configuration in which the light modulation units of three colors of R (red), G (green), and B (blue) are superimposed. When two or more sets of the light modulation units are stacked, at least one of the light modulation units only needs to have a configuration characteristic of the present invention.

  In many cases, the photoconductive layer is designed to have a hue that is complementary to the light in a specific wavelength range that is selectively reflected by the cholesteric liquid crystal in the paired display layers. At this time, there may be a property of absorbing an inherent absorption wavelength region (and a wavelength region on the shorter wavelength side than the specific wavelength region), and in that case, in particular, absorption is performed for the present invention. There is no need to control the wavelength. Of course, in order to further enhance such properties, it is also preferable to appropriately control the composition of the photoconductive layer.

  In the light modulation element of the present invention, an invisible member that absorbs at least light in the specific wavelength region may be provided outside the non-display-side electrode layer. By providing such an invisible member on the non-display side, it is possible to avoid visual recognition from the non-display side that is not the intended color image.

  Examples of the invisibility member include a substrate shape, a case shape, containers of various shapes, a chassis of an electric device, etc., and any configuration as long as it is configured so as not to be visible from the non-display side. The substrate may be of a structure or shape, but among them, a substrate that is in surface contact with the electrode layer on the non-display side is preferable.

  In the light modulation element of the present invention, a filter layer that transmits light in the specific wavelength region and absorbs light of other wavelengths may be disposed on the display side of the display layer. By disposing the filter layer, the saturation improvement effect of the present invention may be supplemented. The filter layer may be disposed adjacent to the display layer (that is, between the display layer and the photoconductive layer) or through one or more layers. (In other words, it may be disposed between the display layer and the electrode layer, between the layers including other layers to be laminated, or outside the electrode layer).

  In the light modulation element of the present invention, the specific wavelength region selectively reflected by the cholesteric liquid crystal in the display layer is a wavelength region of red light, a wavelength region of green light, or a wavelength region of blue light. Is the case. According to the present invention, when the specific wavelength region is the wavelength region of red light, scattering around the purple to green wavelength region is suppressed. Further, when the specific wavelength region is the wavelength region of green light, scattering around the purple to blue wavelength region can be suppressed. Furthermore, when the specific wavelength region is a wavelength region of blue light, scattering around the purple wavelength region (about 380 to 420 nm) on the shorter wavelength side than blue is suppressed. As a result, the saturation of each color image can be improved.

The display layer is preferably one in which the cholesteric liquid crystal is dispersed in a polymer. The photoconductor layer is preferably made of an organic photoconductor.
Since the cholesteric liquid crystal having the PDLC structure tends to have a particularly unnecessary peak in a short wavelength region with respect to the specific wavelength region to be selectively reflected, the present invention is particularly effective when the cholesteric liquid crystal has the PDLC structure.

On the other hand, the light modulation element driving method of the present invention (hereinafter sometimes simply referred to as “the driving method of the present invention”) is a driving method for writing an image on the light modulation element of the present invention.
A step of selecting a portion exceeding the threshold value of the cholesteric liquid crystal in the display layer and a portion not exceeding the threshold value by appropriately selecting and exposing the light modulation element while applying a voltage between the electrode layers. To do.

  When the light modulation element is selectively exposed, it can be exposed from the display side. Of course, if the invisibility member is not provided outside the electrode layer on the non-display side, or if it has the property of transmitting the writing light even if it is provided, selective exposure may be performed from the non-display side. Is possible.

  According to the present invention, the saturation of a color image in a light modulation element, in particular, color development from a middle wavelength region to a long wavelength region in a visible light region, while being a relatively simple structural change that does not require a new component. The saturation of the image can be improved. Further, according to the present invention, it is possible to provide an excellent light modulation element driving method having such an effect.

Hereinafter, the present invention will be described in detail with reference to the drawings with preferred embodiments.
[First Embodiment]
FIG. 1 is a schematic cross-sectional view of a light modulation element according to a first embodiment which is an exemplary aspect of the present invention. In the present embodiment, an example of a light modulation element capable of displaying a red single color image is given.

<Light modulation element>
In this embodiment, the display medium 1 that is a light modulation element is a light in which an electrode layer 5, an OPC layer (photoconductive layer) 10, a laminate layer 8, a display layer 7, and an electrode layer 6 are laminated in order from the display side. The modulation unit 2 is sandwiched between a display-side substrate 3 and a non-display-side substrate 4.

(substrate)
The substrate 3 is a member for holding each functional layer on the inner surface and maintaining the structure of the display medium. The substrate 3 is a sheet-shaped object having a strength that can withstand external force, and has a function of transmitting at least incident light and address light (writing light). Depending on the purpose of use, it is preferable to 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). A known functional film such as an antifouling film, an anti-abrasion film, a light antireflection film, or a gas barrier film may be formed on the outer surface.

  On the other hand, the substrate (invisible member) 4 disposed on the non-display side is a member for maintaining each functional layer on the inner surface and maintaining the structure of the display medium in the same manner as the substrate 3, and has a strength to withstand external force. It is a sheet-shaped object. However, when this substrate 4 is transparent, there is a concern that an unintended image that is inferior in saturation due to inversion of the front and back is visually recognized from the non-display side, causing the viewer to make a mistake in the front and back. Therefore, it is preferable to have a light shielding property. In view of the purpose, the light shielding property is sufficient as long as it absorbs light in a specific wavelength region (red light in the present embodiment) selectively reflected by a cholesteric liquid crystal in the display layer described later. Of course, any substrate material generally having a light shielding property can be used without any problem. Specific examples of the substrate material include materials obtained by mixing a colorant such as a pigment with various substrates exemplified in the description of the substrate 3, and substrates having a known light-shielding film formed on one side or both sides.

In addition, in this embodiment, although the board | substrate 4 is used as an invisible member in this way, the invisible member in this invention may not be the shape of a board | substrate. Specifically, the housing and the container that are attached to the casing and containers of various shapes so that the display side of the light modulation element is exposed to the outside and the non-display side faces the inside also function as an invisible member. In addition, when the light modulation element of the present invention is attached to various electric devices and other devices and members and the non-display side is in an invisible state, these all function as invisible members.
Of course, in the present invention, these invisible members are not essential components.

(Electrode layer)
The electrode layers 5 and 6 are intended members for uniformly applying the applied bias voltage to the respective functional layers in the light modulation element. The electrode layers 5 and 6 have surface-uniform conductivity, and the display-side electrode layer 5 has a function of transmitting at least light of a specific wavelength. At least one of the electrode layer 5 and the electrode layer 6 has a function of transmitting address light.

Specifically, it is formed of metal (for example, gold, aluminum), metal oxide (for example, indium oxide, tin oxide, indium tin oxide (ITO)), conductive organic polymer (for example, polythiophene-based / polyaniline-based), etc. An electroconductive thin film can be mentioned. A known functional film such as an adhesion improving film, an antireflection film, or a gas barrier film may be formed on the surface.
In the present embodiment, when address light is incident from the display side, the electrode layer 6 on the non-display side may not be transparent. However, when address light is incident from the non-display side, non-display is performed. The side electrode layer 6 is preferably transparent to address light.

(Display layer)
In the present invention, the display layer has a function of modulating the reflection / transmission state of colored light in a specific wavelength region of incident light by an electric field, and has a property that the selected state can be maintained with no electric field. A structure that is not deformed by an external force such as bending or pressure is preferable.

In the present invention, as the display layer, a display layer using a change in optical interference state of cholesteric (chiral nematic) liquid crystal is used.
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 this embodiment, although not shown, cholesteric liquid crystal is dispersed in a polymer matrix (transparent resin).
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 nematic liquid crystals and smectic liquid crystals (for example, Schiff base, azo, azoxy, benzoate, biphenyl, terphenyl, cyclohexylcarboxylate, phenylcyclohexane). System, biphenylcyclohexane system, pyrimidine system, dioxane system, cyclohexylcyclohexane ester system, cyclohexylethane system, cyclohexane system, tolan system, alkenyl system, stilbene system, condensed polycyclic system), or a mixture thereof. And steroidal cholesterol derivatives, Schiff bases, azos, esters, and biphenyls).

  The helical pitch of the cholesteric liquid crystal is adjusted by the amount of chiral agent added to the nematic liquid crystal. 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 this embodiment, since red display is performed, the center wavelength of selective reflection is adjusted to be in the range of 600 nm to 700 nm. In order to compensate for the temperature dependence of the helical pitch of the cholesteric liquid crystal, a known method of adding a plurality of chiral agents having different twisting directions or opposite temperature dependences may be used.

  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 in which cholesteric liquid crystal is dispersed in a droplet shape in a polymer skeleton can be used. By using a PNLC structure or a PDLC structure, an interface between the cholesteric liquid crystal and the polymer can be used. An anchoring effect is produced, and the planar state or the focal conic phase 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 cooled and phase-separated, and the polymer and liquid crystal are mixed with chloroform. Evaporate the solvent Allowed can be formed by a polymer and liquid crystal and SIPS for phase separation (Solvent Induced Phase Separation) method, and is not particularly limited.
In the present embodiment, a cholesteric liquid crystal having a PDLC structure in which an unnecessary peak is likely to appear particularly in a region on the short wavelength side with respect to a specific wavelength region that selectively reflects is used.

  The polymer matrix holds the cholesteric liquid crystal and has the function of suppressing the flow of the liquid crystal (change in the image) due to deformation of the light modulation element. The polymer matrix does not dissolve in the liquid crystal material and does not dissolve in the liquid crystal. A polymer material used as a solvent is preferably used. In addition, the polymer matrix has strength to withstand external force and at least reflected light (in this embodiment, there is only one set of light modulation unit, but when there are two or more sets and writing from the display side, the upper layer The display layer in the light modulation unit located at is preferably a material exhibiting high transparency to “address 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).

(OPC layer)
The OPC layer (photoconductive layer) 10 is a layer having an internal photoelectric effect and a characteristic that impedance characteristics change according to the irradiation intensity of address light (writing light). In the present invention, a property of absorbing a wavelength region of light in any wavelength region (specific absorption wavelength region) other than the specific wavelength region selectively reflected by the cholesteric liquid crystal in the display layer is required. In the present embodiment, the OPC layer 10 has a property of absorbing a violet to green peripheral region on a shorter wavelength side than the wavelength region of red light selectively reflected by the cholesteric liquid crystal in the display layer.

In the cholesteric liquid crystal, scattering is likely to occur in a wavelength region shorter than the specific wavelength region. Therefore, in the present embodiment, this is absorbed by the OPC layer 10 positioned above the display layer 7 to generate red light. The saturation of the red image is improved so that only the image can be visually recognized.
In the present embodiment, attention is focused only on the wavelength region on the shorter wavelength side than the specific wavelength region. However, the wavelength region on the longer wavelength side also has the property that the photoconductive layer absorbs the wavelength region on the longer wavelength side. This is preferable from the viewpoint of improving the saturation.

  The OPC layer 10 is capable of alternating current (AC) operation and is preferably driven symmetrically with respect to the address light. In the OPC, generally, a charge generation layer (CGL) is formed in a three-layer structure in which a charge transport layer (CTL) is stacked above and below. In the present embodiment, the OPC layer 10 is formed by laminating an upper charge generation layer 13, a charge transport layer 14, and a lower charge generation layer 15 in order from the upper layer in FIG.

  The charge generation layers 13 and 15 are layers having a function of absorbing address light and generating optical carriers. Mainly, the amount of light carriers that the charge generation layer 13 flows in the direction from the display-side electrode layer 5 to the non-display-side electrode layer 6, and the charge generation layer 15 from the non-display-side electrode layer 6 to the display-side electrode layer 5. The amount of light carriers flowing in the direction of the The charge generation layers 13 and 15 are preferably ones that absorb address light to generate excitons and can be efficiently separated into free carriers inside the CGL or at the CGL / CTL interface.

  The charge generation layers 13 and 15 are charge generation materials (for example, metal or metal-free phthalocyanine, squalium compound, azurenium compound, perylene pigment, indigo pigment, azo pigment such as bis and tris, quinacridone pigment, pyrrolopyrrole dye, polycyclic quinone pigment, A dry method of directly forming a film of a condensed ring aromatic pigment such as dibromoanthanthrone, a cyanine dye, a xanthene pigment, a charge transfer complex such as polyvinylcarbazole and nitrofluorene, or a symbiotic complex composed of a pyrylium salt dye and a polycarbonate resin) The charge generating material may be a polymer binder (eg, polyvinyl butyral resin, polyarylate resin, polyester resin, phenol resin, vinyl carbazole resin, vinyl formal resin, partially modified vinyl acetal resin, carbonate resin, Resin), vinyl chloride resin, styrene resin, vinyl acetate resin, vinyl acetate resin, silicone resin, etc.) and dispersion or dissolution in an appropriate solvent to prepare a coating solution, which is applied and dried to form a film. It can be formed by a method or the like.

  The charge transport layer 14 is a layer having a function of drifting in the direction of the electric field applied by the bias signal when the photocarriers generated in the charge generation layers 13 and 15 are injected. In general, since CTL has a thickness several tens of times that of CGL, the capacitance of the charge transport layer 14, the dark current of the charge transport layer 14, and the photocarrier current inside the charge transport layer 14 cause the light / dark impedance of the entire OPC layer 10. I have decided.

  The charge transport layer 14 efficiently injects free carriers from the charge generation layers 13 and 15 (preferably close to the ionization potential of the charge generation layers 13 and 15), and the injected free carriers hop as fast as possible. Those that move are preferred. In order to increase the dark impedance, it is preferable that the dark current due to the heat carrier is low.

  The charge transport layer 14 is composed of a low molecular weight hole transport material (for example, trinitrofluorene compound, polyvinylcarbazole compound, oxadiazole compound, hydrazone compound such as benzylamino hydrazone or quinoline hydrazone, stilbene compound, Triphenylamine compounds, triphenylmethane compounds, benzidine compounds), or low molecular electron transport materials (for example, quinone compounds, tetracyanoquinodimethane compounds, furfreon compounds, xanthone compounds, benzophenone compounds) , Dispersed or dissolved in an appropriate solvent together with a polymer binder (for example, polycarbonate resin, polyarylate resin, polyester resin, polyimide resin, polyamide resin, polystyrene resin, silicon-containing crosslinked resin, etc.) Were prepared, it may be formed by which was coated and dried.

  In order to give the OPC layer (photoconductive layer) a characteristic having an absorption wavelength region as described above (a wavelength region shorter than a specific wavelength region = “400 to 500 nm” in this embodiment), The absorption wavelength in the charge generation layer or the charge transport layer may be controlled by the material and composition. However, since there is a concern that the charge transporting layer may affect the charge transporting ability when the charge transporting layer absorbs light, the charge generating layer generally has the absorbing ability.

  In addition, the charge generation layer is desired to have a hue that is in a complementary color relationship with light in a specific wavelength range that is selectively reflected by the cholesteric liquid crystal in the paired display layers. At this time, there is a case where it originally has a property of absorbing a wavelength region shorter than the specific wavelength region, and in that case, it is not necessary to control the absorption wavelength particularly for the present invention.

  Of course, it is also preferable to appropriately control the material and composition of the charge generation layer in order to appropriately control the actual absorption wavelength and enhance the desired properties. As a specific control method, the type and amount of the charge generation material to be used, the mixing ratio, the thickness of the charge generation layer, and the like may be appropriately adjusted. In addition, a method of appropriately blending a pigment that does not have charge generation ability is also included.

(Laminate layer)
The laminate layer 8 is made of a polymer material having a low glass transition point, and a material that can adhere and bond the display layer 7 and the OPC layer 10 (charge generation layer 15) by heat or pressure is selected. . Further, it is necessary to have transparency to at least incident light and address light.
Examples of suitable materials for the laminate layer 8 include adhesive polymer materials (for example, urethane resin, epoxy resin, acrylic resin, silicone resin).
The laminate layer 8 is not an essential component in the present invention.

<Driving method of light modulation element>
Next, a method of driving the light modulation element that writes an image on the display medium 1 that is the light modulation element of the present embodiment will be described. FIG. 2 is a schematic configuration diagram showing a state in which an image is written on the display medium 1.

As shown in FIG. 2, the display medium 1 is driven by a light irradiation unit (exposure device) 18 that irradiates the display medium 1 with address light and a voltage application unit (power source) that applies a voltage to the display medium 1. Device) 17 is required. The light irradiation unit 18 and the voltage application unit 17 constitute a writing device. The writing device further includes a control circuit (not shown) that controls the operations of the light irradiation unit 18 and the voltage application unit 17.
First, an outline of these writing devices will be described, and then a specific driving method will be described.

(Writing device)
The light irradiation unit (exposure device) 18 has a function of irradiating the display medium 1 with a predetermined address light pattern that becomes an image, and on the display medium 1 (in detail, an OPC layer based on an input signal from the control circuit). The above is not particularly limited as long as it can irradiate a desired optical image pattern (spectrum, intensity, spatial frequency).

The address light irradiated by the light irradiation unit 18 is preferably selected under the following conditions.
Spectrum: the absorption wavelength range of the OPC layer 10 (the wavelength range as writing light, and does not refer to the “specific absorption wavelength range” in the present invention. However, this is not limited to the region where the two overlap. ) Is preferably as much as possible.
Irradiation intensity: The voltage applied to the display layer 7 at the time of light becomes equal to or higher than the upper and lower threshold voltage due to the partial pressure with the OPC layer 10, causing the liquid crystal in the display layer 7 to change phase, and lower in the dark. Strength.
The address light irradiated by the light irradiation unit 18 is preferably light having a peak intensity in the absorption wavelength region of the OPC layer 10 and a narrow bandwidth as much as possible.

Specific examples of the light irradiation unit 18 include the following.
(1-1) A uniform light source (1 such as a light source (for example, a cold cathode tube, a xenon lamp, a halogen lamp, an LED, an EL) arranged in an array or a combination of a light source and a light guide plate) -2) Combination of light control elements (for example, LCD, photomask, etc.) for creating a light pattern (2) Surface-emitting display (for example, CRT, PDP, EL, LED, 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)

  The voltage application unit 17 has a function of applying a predetermined bias voltage to the display medium 1 and can apply a desired voltage waveform to the display medium (between each electrode) based on an input signal from the control circuit. Good. However, AC output is possible and a high slew rate is required. 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 display medium 1 between the electrode layer 5 and the electrode layer 6 through the contact terminals 19 and 20.
Here, the contact terminals 19 and 20 are members that contact the voltage application unit 17 and the display medium 1 (electrode layers 5 and 6) and conduct both of them, and have high conductivity. 6 and the one having a small contact resistance with the voltage application unit 17 are selected. It is preferable that the display medium 1 and the writing device have a structure that can be separated from either the electrode layers 5 and 6 and the voltage application unit 17 or both.

  Contact terminals 19 and 20 are made of metal (for example, gold, silver, copper, aluminum, iron), carbon, a composite in which these are dispersed in a polymer, or a conductive polymer (for example, polythiophene-based or polyaniline-based). Examples of the terminals that can be used include clips and connectors that sandwich the electrodes.

  A control circuit (not shown) is connected to the voltage application unit 17 and the light 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). It is a member having a function of appropriately controlling the operation of the irradiation unit 18. The specific control content by the control circuit is such that the cholesteric liquid crystal in the display layer 7 is finally selected in an image-like manner by reflection by the planar phase and transmission by the focal conic phase. Specific examples of control contents will be described in the following driving method section.

(Driving method)
In order to write an image on the display medium 1 which is the light modulation element of the present embodiment, the light irradiation unit 18 applies the display medium while applying a predetermined voltage between the pair of electrode layers 5 and 6 by the voltage application unit 17. 1 is appropriately exposed from the display side (in this embodiment, it is from the display side, but in the present invention, it is not limited to this, and exposure from the non-display side may be used). A part of the layer 7 that exceeds the threshold of the cholesteric liquid crystal is selected (hereinafter referred to as “selection step”). In some cases, the process includes at least a process for preparing the selection process or a process for holding before and after the process.
A more specific example will be described below. The description will be made using the graph of FIG. 11 used in the background art section.

  The voltage applied by the voltage application unit 17 is applied to the display layer 7 when, for example, a partial pressure between Vpf and Vfh is applied to the display layer 7 and writing light having a predetermined wavelength and intensity is applied by the light irradiation unit 18. The voltage is set such that the partial pressure is equal to or higher than Vfh. In a state where such a voltage is applied, the planar (P) state portion changes phase to the focal conic (F) state, the focal conic (F) state portion remains unchanged, and all the portions are focal conic ( F) State.

  In this state, when the writing light is selectively irradiated by the light irradiation unit 18 (selection step), only the irradiated portion is applied with a partial pressure of Vfh or more, and the homeotropic (H) is generated from the focal conic (F) state. ) Phase change to the state. Then, when the applied voltage is released, the portion that has been irradiated with the writing light and has undergone a phase change to the homeotropic (H) state becomes the planar (P) phase in the selective reflection state. On the other hand, the portion not irradiated with the writing light remains in the transmissive state of the focal conic (F) phase. In this way, a phase change is selectively made and an image is written.

  In the present invention, there is no particular limitation on which phase state change is used, and a phase change occurs by selectively irradiating write light having a predetermined wavelength and intensity, and reflection / transmission is selected. If the image can be written, there is no problem. Also in the display medium 1 of the present embodiment, for example, by applying a voltage of Vfh or higher and releasing the voltage, the entire surface is previously set in a planar (P) state, and then writing light having a predetermined wavelength and intensity of Vpf or lower is used. Is applied between the electrode layers 5 and 6 so that a voltage equal to or higher than Vpf is applied when irradiating the film, and the writing light is selectively irradiated to change the irradiated part into a focal conic (F) state. You may use the phase change to make. In this case, the portion irradiated with the writing light becomes a focal conic (F) phase in a transmission state, and the portion not irradiated with the writing light becomes a planar (P) phase in a selective reflection state. In this way, a phase change is selectively made and an image is written.

  The image written as described above is viewed by the viewer as a reflected image based on the planar phase of the cholesteric liquid crystal when viewed from the display side. At this time, in the color image of the display layer 7 itself, as described with reference to FIG. 13 in the background art section, the wavelength on the shorter wavelength side than the reflectance peak near 600 to 650 nm which is the wavelength region of red light. A gentle peak occurs in the vicinity of 400 to 500 nm as indicated by arrows.

However, in the present embodiment, since the OPC layer 10 having a characteristic of absorbing a wavelength region in the vicinity of 400 to 500 nm is disposed on the display side closer to the viewer than the display layer 7, the color image is turbid. There will be no saturation.
As described above, according to the present embodiment, no special member is newly provided as compared with, for example, the conventional light modulation element as shown in FIG. 12, and therefore, the manufacturing is complicated and the cost is increased. In addition, the saturation of the color image can be effectively improved.

[Second Embodiment]
FIG. 3 is a schematic cross-sectional view of the light modulation element of the second embodiment, which is another exemplary aspect of the present invention. In this embodiment as well, as in the first embodiment, an example of a light modulation element capable of displaying a red single color image will be given. However, in the light modulation element of the present embodiment, a colored layer (filter layer) 9 is disposed between the OPC layer (photoconductive layer) 10 and the laminate layer 8 in the first embodiment. Since the other points are basically the same as those of the first embodiment and the constituent members are also common, members having the same functions are denoted by the same reference numerals, and detailed description thereof is omitted. To do.
The colored layer 9 characteristic of this embodiment will be described below.

  The colored layer (filter layer) 9 is a wavelength region shorter than a specific wavelength region (600 nm to 700 nm = a wavelength region of red light) selectively reflected by the cholesteric liquid crystal in the display layer 7 that the OPC layer 10 carries. It is a layer provided for the purpose of supplementing the function of absorbing (around 400 to 500 nm). Of course, it is a member which is not necessary when the function can be sufficiently expected only by the OPC layer 10, and is not an essential component in the present invention.

Specifically, the colored 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) on the OPC layer 10 side of the charge generation layer 13 Or by coating or drying these with a polymer binder (for example, polyvinyl alcohol resin, polyacrylic resin, etc.) in an appropriate solvent. can do.
Since other configurations and driving methods in the light modulation element of the present embodiment are the same as those of the first embodiment, description thereof is omitted.

  The image written in the light modulation element of this embodiment is viewed by the viewer as a reflection image based on the planar phase of the cholesteric liquid crystal when viewed from the display side. At this time, a gentle peak (near 400 to 500 nm) on the shorter wavelength side than the red light generated in the color image of the display layer 7 itself is an OPC arranged on the display side of the display layer 7 in this embodiment. It is effectively absorbed by the layer 10 and the colored layer 9 so that the color image has no turbidity and has very high saturation.

As described above, according to the present embodiment, even if only the OPC layer 10 is expected to have a sufficient saturation improvement effect, a further saturation improvement effect can be expected by providing the colored layer 9. .
Further, for example, as compared with the case where a colored layer having the same function as that of the present embodiment is provided as an upper layer of the display layer of the conventional light modulation element as shown in FIG. 12, the OPC layer 10 shares the function. Therefore, the level of performance required for the colored layer 9 in the present embodiment is lowered, and effects such as reduction in manufacturing cost and improvement in freedom of material selection can be obtained.

  In the present embodiment, the colored layer (filter layer) 9 is disposed between the OPC layer (photoconductive layer) 10 and the laminate layer 8. However, the display layer 7 may be disposed at any position as long as it is on the display side. In the example of FIG. 3, for example, various locations such as between the display layer 7 and the laminate layer 8, between the OPC layer 10 and the electrode layer 5, between the electrode layer 5 and the substrate 3, and the upper layer (surface on the display side) of the substrate 3. Even if a colored layer (filter layer) is provided, the function as a filter layer can be exhibited.

[Third Embodiment]
FIG. 4 is a schematic cross-sectional view of the light modulation element of the third embodiment which is still another exemplary aspect of the present invention. In the present embodiment, an example of a light modulation element capable of displaying a full-color image composed of RGB three-color stacked images will be described.

<Light modulation element>
In the present embodiment, the display medium 1 that is a light modulation element includes, in order from the display surface side, an external substrate 23, a light modulation unit 22B, an internal substrate 31, a light modulation unit 22G, an internal substrate 32, a light modulation unit 22R, and an external substrate. 24 is a laminated product.
The external substrate 23 is a member having the same function as the substrate 3 in the first embodiment, and the external substrate 24 is a member having the same function as the substrate 4 in the first embodiment. Therefore, the detailed description is abbreviate | omitted.

  The three light modulation units 22B, 22G, and 22R include electrode layers 25B, 25G, and 25R, OPC layers (photoconductive layers) 30B, 30G, and 30R, laminate layers 28B, 28G, and 28R, display layers 27B, 27G, and 27R, and electrodes. The points where the layers 26B, 26G, and 26R are laminated are common. However, the order of stacking differs between the light modulation units 22B and 22G and the light modulation unit 22R.

  Specifically, the light modulation unit 22R is stacked from the display side in the order described above, whereas the light modulation units 22B and 22G have OPC layers (photoconductive layers) 30B and 30G in the order described above. The order of the laminate layers 28B and 28G and the display layers 27B and 27G is reversed. That is, the light modulation units 22B and 22G have the same stacking order of the conventional light modulation elements, and the light modulation unit 22R has the same stacking order of the light modulation elements of the first embodiment. That is, only the light modulation unit 22R is a light modulation unit having a configuration characteristic of the present invention.

  For the three light modulation units 22B, 22G, and 22R, each material is appropriately selected so that the display color (the color reflected by the liquid crystal) or the drive color (the color absorbed by the OPC layer) becomes the respective set value. Etc. are adjusted. However, although the stacking order is different, the specific configurations of the individual members are the same, and the electrode layer 5, OPC layer (photoconductive layer) 10, laminate layer 8, display layer 7, and display layer in the first embodiment Since it is substantially the same as the electrode layer 6, the detailed description is abbreviate | omitted.

The display-side external substrate 23 and the non-display-side external substrate 24 are also substantially the same as the display-side substrate 3 and the non-display-side substrate 4 in the first embodiment, and thus detailed description thereof is omitted. To do.
Since the internal substrate 31 and the internal substrate 32 are not exposed to the outside, it is not necessary to provide a functional film therefor. However, since some degree of independence is desired during manufacturing, the same properties as the external substrate 23 are required. -Materials are preferably used.

<Driving method of light modulation element>
Next, a method of driving the light modulation element that writes an image on the display medium 21 that is the light modulation element of the present embodiment will be described. FIG. 5 is a schematic configuration diagram showing a state in which an image is written on the display medium 1.

  As shown in FIG. 5, the display medium 21 is driven by a light irradiation unit (exposure device) 38 that irradiates the display medium 21 with address light and a voltage application unit (power source) that applies a voltage to the display medium 21. Equipment) 37B, 37G, 37R are required. The light irradiation unit 38 and the voltage application units 37B, 37G, and 37R constitute a writing device. The writing device further includes a control circuit (not shown) that controls the operations of the light irradiation unit 38 and the voltage application units 37B, 37G, and 37R.

  The light irradiation unit 38 is configured so that light having a wavelength absorbed by the three OPC layers (photoconductive layers) 30B, 30G, and 30R can be exposed from the display side as writing light (in the present invention, writing light is used). The exposure is not limited to from the display side, and may be configured to allow exposure from the non-display side. Other than that, it is substantially the same as the light irradiation part 38 in 1st Embodiment.

  On the other hand, the voltage application units 37B, 37G, and 37R are connected to the pair of electrode layers 25B, 25G, and 25R and the electrode layers 26B, 26G, and 26R in the three light modulation units 22B, 22G, and 22R. A voltage is applied via 39G, 39R and contact terminals 40B, 40G, 40R, respectively. The individual voltage application units 37B, 37G, and 37R are substantially the same as the voltage application unit 17 in the first embodiment.

  A control circuit (not shown) is connected to voltage application units 37B and 37G 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). , 37R and a member having a function of appropriately controlling the operation of the light irradiation unit 38. With this control circuit, voltage application units 37B, 37G are applied so that the light modulation units 22B, 22G, 22R are imagewise exposed with the appropriate wavelength and light amount while applying the voltages of the appropriate wavelength and magnitude. , 37R and the light irradiation unit 38 are controlled.

In order to write an image on the display medium 21 that is the light modulation element of the present embodiment, a pair of electrode layers 25B, 25G, and 25R and electrode layers 26B, 26G, and 26R for each of the light modulation units 22B, 22G, and 22R. The light irradiation unit 18 appropriately selects and exposes the display medium 21 from the display side while applying a predetermined voltage by the voltage application units 37B, 37G, and 37R during the period, so that the cholesteric liquid crystal in the display layers 27B, 27G, and 27R A part that exceeds the threshold and a part that does not exceed the threshold are selected (selection step). In some cases, the process includes at least a process for preparing the selection process or a process for holding before and after the process.
Since driving in each of the light modulation units 22B, 22G, and 22R is the same as that in the first embodiment, a detailed description thereof is omitted.

  By driving the three light modulation units 22B, 22G, and 22R, three color images of BGR (RGB) are formed on the display layers 27B, 27G, and 27R to form a laminated image. The laminated image is viewed by the viewer as a full color image by reflection based on the planar phase of the cholesteric liquid crystal when viewed from the display side.

  Also in this embodiment, as in the first embodiment, in the color image of the display layer 27R itself in the light modulation unit 22R, a gradual peak occurs in the vicinity of 400 to 500 nm on the shorter wavelength side than the red light. The peak is effectively absorbed by the OPC layer 30 disposed on the display side of the layer 27R. That is, the color image of red is not turbid and has very high saturation.

  In a full-color image, even if the saturation of any of the three primary colors is slightly inferior, the color is greatly affected, and it becomes difficult to obtain a high-definition image. In this regard, according to the present embodiment, particularly in the red light modulation unit 22R that is easily affected by scattering in the short wavelength region, such influence can be eliminated and the saturation is improved, so that the entire full-color image is extremely difficult. It will be highly detailed. In addition, no special member is newly provided, and therefore the manufacturing complexity and cost increase are not caused.

  Although the present invention has been described in detail with reference to three preferred embodiments, the present invention is not limited to the above embodiments. For example, in the above embodiment, only one light modulation unit having a configuration of one set and three sets of configurations is described as a specific example. However, in the present invention, the display layer is not limited to these, There may be two sets or four or more sets.

Further, in the configuration of two or more sets of light modulation units, the number of light modulation units having a configuration characteristic to the present invention (a configuration in which the photoconductive layer is disposed on the display side and the display layer is disposed on the non-display side) In the third embodiment, only one example has been described. However, two or more sets may be provided on the assumption that the absorption wavelength of the photoconductive layer is appropriately controlled in relation to other layers.
In addition, those skilled in the art can appropriately modify the present invention according to conventionally known knowledge. Of course, such modifications are included in the scope of the present invention as long as they still have the configuration of the present invention.

The present invention will be described more specifically with reference to the following examples. However, the present invention is not limited to the examples.
In the example, a light modulation element having the configuration shown in FIG. 1 was manufactured and driven as shown in FIG. Hereinafter, description will be given with reference to these drawings.

  A 125 μm-thick polyethylene terephthalate (PET) film (manufactured by Toray Industries, Inc., high beam) with ITO (surface resistance 300Ω / □) formed on one side is cut into 50.8 mm (2 inch) squares, and the substrate 3 and the electrode layer 5 did.

  Further, on the surface on the ITO (electrode layer 5) side, a paint in which a charge generating material (dibromoanthanthrone) is dispersed with a paint shaker in a solution in which polyvinyl butyral resin is dissolved in butanol, a dry film thickness is 0 by spin coating. The charge generation layer 13 was formed by coating and drying to a thickness of 2 μm.

  Next, a paint in which a polycarbonate resin and a charge transporting material (benzidine N, N′-bis (3-methylphenyl) -1,1′-biphenyl-4,4′-diamine) are dissolved in monochlorobenzene is formed thereon. The charge transport layer 14 was formed by applying and drying so as to have a dry film thickness of 6 μm by a gap coating method. Furthermore, a coating material in which a charge generating material (dibromoanthanthrone) is dispersed with a paint shaker is applied to a solution obtained by dissolving polyvinyl butyral resin in butanol so that the dry film thickness becomes 0.35 μm by a spin coating method. Drying was performed to form the charge generation layer 15, and the OPC layer 10 including the charge generation layer 13, the charge transport layer 14, and the charge generation layer 15 was formed.

  Similarly, an OPC layer 10 is separately formed, and the transmittance in the visible light region is measured by a measurement system (MCPD-3000) manufactured by Otsuka Electronics through a PET film on which an ITO film is formed. did. A result is as the graph shown in FIG. As can be seen from the graph of FIG. 6, it is confirmed that the transmittance around 450 to 550 nm on the short wavelength side is lower than the wavelength range of 600 nm to 650 nm of red light, and has a characteristic of absorbing this wavelength region. It was done.

  As the cholesteric liquid crystal, nematic liquid crystal (Merck, E7) 80.5% by mass, dextrorotatory chiral agent (Merck, CB15) 15.6% by mass, and dextrorotatory chiral agent (Merck, R1011) 3 .9% by mass was mixed to prepare a material A that reflects red.

Using a membrane emulsification apparatus (manufactured by SPG Techno Co., Microkit) on which a ceramic porous membrane having a diameter of 4.2 μm is set, the material A is reduced to a concentration of 0.1 under a condition of a nitrogen pressure of 11.8 kPa (0.12 kgf / cm ² ). The emulsion was emulsified in 25% by weight aqueous sodium dodecylbenzenesulfonate. The obtained emulsion had a cholesteric liquid crystal drop particle size average of 14.9 μm and was almost monodispersed.

  Next, the emulsion was allowed to stand to settle the cholesteric liquid crystal drop, and the supernatant was removed to obtain a concentrated emulsion. By adding 4 parts by mass of a 7.7% by mass aqueous solution of acidic bone gelatin (manufactured by Nippi Co., Ltd., jelly strength 314) to 1 part by mass of this concentrated emulsion, the non-volatile content volume ratio in the coating liquid for the display layer Was about 0.15, and the volume ratio of cholesteric liquid crystal in the nonvolatile content was about 0.70.

  On the other hand, a 125 μm thick polyethylene terephthalate (PET) film with ITO (surface resistance 300Ω / □) formed on one side was cut into 50.8 mm (2 inch) squares to form a substrate 4 and an electrode layer 6.

  Next, the gap on the ITO (electrode layer 6) side surface is adjusted so that the wet film thickness after application of the display layer coating solution in which gelatin is sol-heated by heating to 50 ° C. is 90 μm. It was applied with an applicator with a micrometer.

  A shape in which a monodisperse cholesteric liquid crystal drop having a mean particle diameter of 14.9 μm is slightly flattened as the display layer 7 after being kept in a high temperature and high humidity chamber of 50 ° C./RH 90% for 15 minutes and then dried at room temperature for 12 hours. Thus, a PDLC layer having a thickness of about 12 μm dispersed in a single layer in a polymer binder was formed.

  On the OPC layer 10 already formed on the other substrate, a two-component urethane laminating agent diluted with butyl acetate (A-315 / A50, manufactured by Mitsui Takeda Chemical Co., Ltd.) is applied to the dried film by spin coating. The laminate layer 8 was formed by applying and drying to a thickness of 1.2 μm.

Two substrates manufactured as described above (the substrate 3 on which the electrode layer 5, the OPC layer 10 and the laminate layer 8 are formed, and the substrate 4 on which the electrode layer 6 and the display layer 7 are formed) are displayed. The layer 7 and the laminate layer 8 face each other, and were overlapped so that a part of the end face was slightly shifted and adhered through a laminator at 100 ° C. to obtain the display medium 1 which is a light modulation element of this example.
In addition, each functional film on the shifted end face was removed to expose the ITO electrode so that the electrode layers 5 and 6 can be conducted from the outside of the display medium 1.

The obtained display medium 1 is a transparent substrate and electrode layer on the non-display side for the example, and is not provided with any invisibility member. Therefore, if it is turned upside down, it can be used as a comparative light modulation element. . Therefore, this was used as a light modulation element of a comparative example.
A commercially available worm clip (contact terminals 19, 20) with a lead wire is connected to the electrode layers 5, 6 of the obtained display medium 1, and the other end of the lead wire is connected to the high speed / voltage application unit 17. This was connected to a high voltage amplifier (manufactured by Matsusada Precision Co., Ltd., HEOPT1B-60 type).

  On the other hand, a color light-emitting diode light source (manufactured by CCS, HLV-3M-RGB type) was used as a light source, and the light-irradiating unit 18 was fabricated by being configured to irradiate the display side surface of the display medium 1. The light irradiation unit 18 can irradiate Blue light having a peak wavelength of 470 nm and a band half width of 25 nm.

  In addition, a multi-channel analog power output board (National Instruments 6713 type) and control software (National Instruments LabVIEW) are used as a control circuit (not shown), and the voltage application unit 17 is based on image data from a personal computer. In addition, wiring is performed so that the operation of the light irradiation unit 18 can be appropriately controlled.

In this state, while applying a voltage of 130 V at 50 Hz by the voltage application unit 17, the light irradiation unit 18 irradiated the address light having an intensity of 0.5 mW / cm ² from the surface side of the display medium 1 to the entire surface. The voltage application and address light irradiation were performed simultaneously for 200 mS.

  For the display image formed on the display medium 1, first, the normalized reflectance on the non-display side was measured using an integrating sphere spectrometer (CM 2002, manufactured by Konica Minolta). This corresponds to a comparative example. Here, the normalized reflectivity is obtained by standardizing the reflection intensity measured under the SCE (regular reflection light removal) condition according to the diffuse illumination vertical light receiving method of JIS Z8772 with the complete diffuse surface as 100%. The results are as shown in the graph of FIG. Similarly, the normalized reflectance was measured on the display side. The results are as shown in the graph of FIG.

As can be seen from the graph of FIG. 7, in the comparative example, a reflectance peak is observed in the vicinity of 600 to 650 nm of the red light wavelength region, but a gentle peak is generated in the vicinity of 450 nm on the shorter wavelength side. Yes. On the other hand, in the example, as can be seen from the graph of FIG. 8, it is understood that the component on the shorter wavelength side than the red light is cut, and the reflectance in the vicinity of 400 to 550 nm is greatly reduced.
The chromaticity coordinates x and y were determined for the display images of these examples and comparative examples. The results are shown in Table 1 below. Moreover, the chromaticity diagram which plotted this result is shown in FIG.

  In the comparative example, the chromaticity coordinates were (0.339, 0.334), but in the example, the chromaticity coordinates were (0.495, 0.344), and the hue saturation was improved. It was confirmed that

1 is a schematic cross-sectional view of a light modulation element according to a first embodiment which is an exemplary aspect of the present invention. It is a schematic block diagram which shows a mode that the image is written with respect to the light modulation element of FIG. It is a schematic cross section of the light modulation element of the second embodiment which is another exemplary aspect of the present invention. It is a schematic cross section of the light modulation element of the third embodiment which is still another exemplary aspect of the present invention. It is a schematic block diagram which shows a mode that the image is written with respect to the light modulation element of FIG. It is a graph which shows the transmittance | permeability in the area | region of the visible ray of the photoconductive layer used in the Example, and plots the measured value of the transmittance | permeability on the horizontal axis | shaft on the horizontal axis. It is a graph showing the measurement result of the normalized reflectance of the display image in the light modulation element of the comparative example in which the stacking order of the photoconductive layer and the display layer is different from the embodiment, the horizontal axis represents the wavelength of the reflected light, and the vertical axis represents The measurement results of normalized reflectance are plotted. It is a graph showing the measurement result of the normalized reflectance of the display image in the light modulation element of an Example, the wavelength of reflected light is plotted on the horizontal axis, and the measurement result of light reflectance is plotted on the vertical axis. It is a chromaticity diagram of a display image in the light modulation element of an example and a comparative example. It is a schematic explanatory view showing the relationship between the molecular orientation and optical characteristics of cholesteric liquid crystal, wherein (A) is in the planar phase, (B) is in the focal conic phase, and (C) is in the homeotropic phase. 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 image writing is performed with the exposure apparatus with respect to the conventional general light modulation element. It is a graph showing the relationship between the wavelength of external light and reflectance when a display layer capable of displaying red is in a reflective state or a transmissive state.

Explanation of symbols

  1, 2: 1: Display medium (light modulation element), 2, 22B, 22G, 22R: Light modulation unit, 3: Substrate, 4: Substrate (invisible member), 5, 6, 25B, 25G, 25R, 26B, 26G , 26R: electrode layer, 7, 27B, 27G, 27R: display layer, 8, 28B, 28G, 28R: laminate layer, 9: colored layer (filter layer), 10, 30: OPC layer (photoconductive layer), 13 , 15, 33B, 33G, 33R, 35B, 35G, 35R: charge generation layer, 14, 34B, 34G, 34R: charge transport layer, 17, 37B, 37G, 37R: voltage application unit, 18, 38: light irradiation unit 19, 20, 39B, 39G, 39R, 40B, 40G, 40R: contact terminals, 23: external substrate, 24: external substrate (invisible member), 31, 32: internal substrate

Claims (12)

At least between a pair of electrode layers whose display side is transparent, at least a display layer composed of cholesteric liquid crystal that selectively reflects light in a specific wavelength range, and depending on the amount of absorbed light by absorbing writing light A light modulation element including at least one light modulation unit in which a photoconductive layer for changing a resistance value is sandwiched and sandwiched, and in at least one set of the light modulation units,
The photoconductive layer has a property of absorbing light in any wavelength region other than the specific wavelength region; and
A light modulation element, wherein the photoconductive layer is laminated on the display side, and the display layer is laminated on the non-display side. The light modulation element according to claim 1, wherein the photoconductive layer has a property of absorbing light in a wavelength region shorter than the specific wavelength region. The light modulation element according to claim 1, wherein an invisible member that absorbs at least light in the specific wavelength region is provided outside the electrode layer on the non-display side. 4. The light modulation element according to claim 3, wherein the invisible member is a substrate that is in surface contact with the electrode layer on the non-display side. The display side of the display layer is adjacent to the display layer or through one or more layers, and transmits light in the specific wavelength range and absorbs light of other wavelengths. The light modulation element according to claim 1, wherein a filter layer is provided. The light modulation element according to claim 1, wherein the specific wavelength region is a wavelength region of red light. The light modulation element according to claim 1, wherein the specific wavelength region is a wavelength region of green light. The light modulation element according to claim 1, wherein the specific wavelength region is a wavelength region of blue light. The light modulation element according to claim 1, wherein the display layer is formed by dispersing the cholesteric liquid crystal in a polymer. The light modulation element according to claim 1, wherein the photoconductor layer is made of an organic photoconductor. The light modulation element according to claim 1, wherein the cholesteric liquid crystal has a PDLC structure. A driving method for writing an image to the light modulation element according to claim 1,
A step of selecting a portion exceeding the threshold value of the cholesteric liquid crystal in the display layer and a portion not exceeding the threshold value by appropriately selecting and exposing the light modulation element while applying a voltage between the electrode layers. Driving method of the light modulation element.

Images