JP2011002654A - Optical writing device, optical writing type display device, and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical writing device, optical writing type display device, and program for suppressing image quality deterioration caused by application of an AC voltage where a unit pulse waveform of one polarity is asymmetrical with a unit pulse waveform of the other side to a cholesteric liquid crystal layer.SOLUTION: A voltage application section 26 is controlled so that the area ratio is larger than 1 and AC voltage within a predetermined range whose area ratio is less than an area ratio corresponding to the optical reflectance difference when the area ratio is 1 is applied between an electrode 15 and an electrode 22.

Description

  The present invention relates to an optical writing device, an optical writing display device, and a program.

  In Patent Document 1, a scanning signal is applied to a scanning electrode in an active matrix type liquid crystal display device using a non-linear resistance element having a current-voltage characteristic asymmetric depending on the polarity of an applied voltage as a switching element for driving a liquid crystal pixel. A driving method of a liquid crystal ideographic device is started in which a data signal is applied to a signal electrode during a scanning signal selection period to write display data to each pixel. In this liquid crystal display device driving method, when a positive voltage is applied to a liquid crystal pixel, the scanning signal selection period is the same when a negative voltage is applied, and the width of one data signal is the scanning signal selection period. It is characterized by being smaller than.

  Also, in Cited Document 2, an organic photoreceptor having a charge generation layer, a liquid crystal layer mainly composed of liquid crystal forming a cholesteric phase, and a pair of first and second layers arranged with the organic photoreceptor and the liquid crystal layer interposed therebetween. An optical recording driving method for driving an optical recording element including a second electrode is disclosed. In this optical recording driving method, a first pulse is applied between the first and second electrodes, and then the polarity is opposite to that of the first pulse and the absolute value of the amplitude is smaller than that of the first pulse. A second pulse is applied.

JP-A-8-5988 Japanese Patent Application Laid-Open No. 2004-12469

  An object of the present invention is to provide a pair of electrodes of a display medium in which an alternating voltage within a range in which the ratio of the area of one unit pulse waveform of the other polarity to the area of one unit pulse waveform of the other polarity contributing to image writing is within a predetermined range. The present invention provides an optical writing device, an optical writing display device, and a program that can suppress deterioration in image quality as compared with a case where the voltage is not applied to the optical device.

  To achieve the above object, in the optical writing device according to claim 1, the reflectance is changed between a pair of electrodes, at least one of which has translucency, according to the magnitude of the applied voltage. A display medium provided with a cholesteric liquid crystal layer in which an image is written and a photoconductive layer that changes a voltage applied to the cholesteric liquid crystal layer by changing an electric resistance according to the intensity of illumination light irradiated Voltage applying means for applying a voltage between the pair of electrodes, irradiating means for irradiating the photoconductive layer to the photoconductive layer from the translucent electrode side, and the illumination light irradiating the photoconductive layer The alternating current voltage is generated so that the first unit pulse waveform having one polarity and the second unit pulse waveform having a polarity different from the one polarity are alternately generated. Reflection when an area ratio indicating the ratio of the area of the second unit pulse waveform to the area of the displacement pulse waveform is larger than 1 and a voltage for image writing is applied to the cholesteric liquid crystal layer in the initial stage with respect to the area ratio The reflectance difference when the area ratio is 1 in the optical characteristics showing the relationship between the reflectance and the reflectance difference when the voltage for image writing is applied to the cholesteric liquid crystal layer a plurality of times. Control means for controlling the voltage application means so that an alternating voltage within a predetermined range less than the area ratio corresponding to is applied between the pair of electrodes.

  Further, in the optical writing device according to claim 2, in the invention according to claim 1, the control means corresponds to the area where the area ratio is irradiated with the illumination light of the photoconductive layer. The cholesteric liquid crystal layer corresponds to a region where the illumination light of the photoconductive layer is not irradiated with respect to the magnitude of a voltage applied between the pair of electrodes at a boundary point at which the cholesteric liquid crystal layer changes from a focal conic state to a homeotropic state. The voltage application means is controlled so that an alternating voltage, which is a ratio of the magnitude of the voltage applied between the pair of electrodes at the boundary point of the cholesteric liquid crystal layer, is applied between the pair of electrodes.

  An optical writing device according to a third aspect of the present invention is the optical writing device according to the first or second aspect, wherein the photoconductive layer includes a first charge generation layer having an absorption wavelength range of the illumination light, It comprises a second charge generation layer having an absorption wavelength region other than the absorption wavelength region, and a charge transport layer sandwiched between the first charge generation layer and the second charge generation layer.

  According to a fourth aspect of the present invention, there is provided the optical writing device according to the first or second aspect, wherein the photoconductive layer is a charge generation layer having an absorption wavelength range of the illumination light, and a charge transport layer is formed. The control unit is configured to irradiate the photoconductive layer with the illumination light when a voltage having a polarity that does not contribute to writing of the AC voltage image is applied between the pair of electrodes by the voltage application unit. The illuminating means is controlled so as not to occur.

  On the other hand, in order to achieve the above object, an optical writing type display device according to claim 5 includes an optical writing device according to any one of claims 1 to 4 and writing light from the irradiation unit. And the display medium on which an image is written by being irradiated.

  On the other hand, in order to achieve the above object, the program according to claim 6 changes the reflectivity according to the magnitude of the applied voltage between a pair of electrodes, at least one of which has translucency. A cholesteric liquid crystal layer on which an image is written, and a photoconductive layer that changes a voltage applied to the cholesteric liquid crystal layer by changing an electric resistance according to the intensity of illumination light applied. The illumination means for irradiating the photoconductive layer to the photoconductive layer from the electrode side having translucency is controlled so that the photoconductive layer of the display medium is irradiated with illumination light. An alternating voltage in which a unit pulse waveform and a second unit pulse waveform having a polarity different from the one polarity are alternately generated, wherein the second unit pulse with respect to the area of the first unit pulse waveform The area ratio indicating the area ratio of the waveform is larger than 1, and the reflectance when the voltage for image writing is applied to the cholesteric liquid crystal layer in the initial stage with respect to the area ratio and the image writing ratio to the cholesteric liquid crystal layer. A predetermined ratio less than the area ratio corresponding to the reflectance difference when the area ratio in the optical characteristics indicating the relationship of the reflectance difference expressed by the difference from the reflectance when the voltage is applied a plurality of times is 1. A program for functioning as a control means for controlling a voltage applying means for applying a voltage between the pair of electrodes so that an alternating voltage within a range is applied between the pair of electrodes.

  According to the first, fifth, and sixth aspects of the invention, the ratio of the area of the unit pulse waveform of the other polarity to the area of the unit pulse waveform of the other polarity that contributes to image writing is predetermined. As compared with a case where an AC voltage within the range is not applied to the pair of electrodes of the display medium, an effect of suppressing deterioration in image quality is obtained.

  According to the invention of claim 2, the area ratio is between the pair of electrodes at the boundary point where the cholesteric liquid crystal layer corresponding to the region irradiated with the illumination light of the photoconductive layer changes from the focal conic state to the homeotropic state. An AC voltage that is a ratio of the magnitude of the voltage applied between the pair of electrodes at the boundary point of the cholesteric liquid crystal layer corresponding to the region where the illumination light of the photoconductive layer is not irradiated with respect to the magnitude of the voltage applied to As compared with the case where the voltage is not applied between the pair of electrodes, an effect of suppressing the image quality deterioration can be obtained.

  According to the inventions according to claim 3 and claim 4, the horizontal diffusion of charges in the photoconductive layer is suppressed as compared with the case where the photoconductive layer has a two-layer structure of a charge transport layer and a charge generation layer. As a result, an effect of obtaining a high-resolution image quality can be obtained.

It is sectional drawing which shows an example of a structure of the display medium contained in the optical writable display apparatus which concerns on embodiment. It is a circuit diagram which shows the equivalent circuit of the display medium shown in FIG. It is a schematic diagram which shows the relationship between the molecular orientation of a cholesteric liquid crystal, and an optical characteristic, (A) shows a planar state, (B) shows a focal conic state, (C) shows a homeotropic state, respectively. It is a graph for demonstrating the electro-optical response characteristic of a cholesteric liquid crystal layer. It is a block diagram which shows an example of a structure of the optical writing type display apparatus which concerns on embodiment. It is a figure which shows an example of the waveform which shows the electric field in the exposure part when the drive voltage is applied between electrodes, and an example of the waveform which shows the electric field in the non-exposure part when the drive voltage is applied between electrodes. . It is a flowchart which shows the flow of a process of the voltage application process program which concerns on embodiment. It is a figure where it uses for description of the adjustment method of the ratio of the negative electrode pulse with respect to the positive electrode pulse of the alternating voltage applied between electrodes. It is a graph which shows the comparative example of the electro-optic response characteristic of a cholesteric liquid crystal layer when illumination light is irradiated to a display medium, and when illumination light is not irradiated to a display medium. The positive side waveform of the divided voltage applied to the exposed portion when the drive voltage is applied between the electrodes, and the divided voltage applied to the non-exposed portion when the drive voltage is applied between the electrodes It is a figure which shows the comparative example of a positive electrode side waveform. Relationship between the ratio of the negative electrode pulse to the positive electrode pulse and the difference in light reflectance at the exposed portion when an AC voltage for a plurality of cycles is applied between the electrodes at each of a plurality of predetermined ratios of the negative electrode pulse to the positive electrode pulse It is a graph which shows an example. The relationship between the ratio of the negative electrode pulse to the positive electrode pulse and the light reflectance difference at the exposed portion when an AC voltage for a plurality of cycles is applied between the electrodes at each of a plurality of predetermined ratios of the negative electrode pulse to the positive electrode pulse, And the ratio of the negative electrode pulse to the positive electrode pulse and the difference in light reflectance at the non-exposed portion when an AC voltage for a plurality of cycles is applied between the electrodes at each of a plurality of predetermined ratios of the negative electrode pulse to the positive electrode pulse. It is a graph which shows the comparative example of a relationship. The relationship between the ratio of the negative pulse to the positive pulse and the difference in the light reflectance at the exposed area when the ratio of the negative pulse to the positive pulse of the AC voltage applied between the electrodes is adjusted by changing the applied voltage, and between the electrodes Comparative example of the relationship between the ratio of the negative electrode pulse to the positive electrode pulse and the difference in the light reflectance at the exposed portion when the ratio of the negative electrode pulse to the positive electrode pulse of the alternating voltage applied to is adjusted by changing the voltage application time It is a graph to show. It is sectional drawing which shows the other structural example of a display medium.

  Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a cross-sectional view illustrating an example of a configuration of a display medium included in the optical writing display device according to the present embodiment. As shown in the figure, the display medium 12 includes a substrate 24, an electrode 22, a photoconductive layer 20, a laminate layer 18, a light absorbing layer 19, and a cholesteric liquid crystal layer 17 in order from the non-display surface side (the lower side in the figure). The electrode 15 and the substrate 13 are laminated, and an image is written by irradiating writing light and applying a voltage according to the image, and holds the written image.

  The substrates 13 and 24 are members for holding the electrode 15, the cholesteric liquid crystal layer 17, the light absorption layer 19, the laminate layer 18, the photoconductive layer 20, and the electrode 22 between the substrates and maintaining the structure of the display medium 12. It is. The substrate 13 and the substrate 24 are sheet-shaped objects having a strength that can withstand external force. The substrate 13 provided on the display surface side is at least incident light, and the substrate 24 provided on the side opposite to the display surface is described later. Write light and initialization preparation light (hereinafter collectively referred to as “illumination light” when used without distinction) are transmitted. Further, the substrate 13 and the substrate 24 may have flexibility. In the present embodiment, since an organic material is used for the photoconductive layer (charge generation layer and charge transport layer), a flexible substrate can be obtained, molding is easy, cost, etc., for example, polyethylene terephthalate, A substrate formed of a light-transmitting polymer film such as polysulfone, polyethersulfone, polycarbonate, or polyethylene naphthalate is preferably used. Further, a known functional film such as an antifouling film, an anti-abrasion film, an antireflection film, or a gas barrier film may be formed on the surface.

  In addition, although the board | substrate 13 and the board | substrate 24 have transparency over visible light whole region in this embodiment, you may have transparency in the wavelength range to display.

  The electrode 15 and the electrode 22 are members for applying a voltage applied from the optical writing device 14, which will be described in detail later, to each functional layer in the display medium 12. For this reason, the electrode 15 and the electrode 22 have conductivity, the electrode 15 provided on the display surface side transmits at least incident light, and the electrode 22 provided on the opposite side to the display surface transmits at least illumination light. Specific examples of the electrode 15 and the electrode 22 include a metal (for example, gold or aluminum), a metal oxide (for example, indium oxide, tin oxide, or indium tin oxide (ITO)), a conductive organic polymer (for example, polythiophene). A conductive film formed of, for example, a system or a polyaniline system). In addition, a known functional film such as an adhesion improving film, a light reflection preventing film, or a gas barrier film may be formed on the surface. In this embodiment, “conductive” and “conductive” indicate, for example, those having a sheet resistance of 500Ω or less.

  In addition, although the electrode 15 and the electrode 22 have transparency over the entire visible light range in this embodiment, they may have transparency in the wavelength range to be displayed.

  The photoconductive layer 20 is provided in a region sandwiched between the electrode 15 and the electrode 22, has an internal photoelectric effect, and changes the impedance characteristic according to the irradiation intensity of the illumination light, thereby changing the intensity distribution of the irradiated light. It is a layer showing the corresponding electrical characteristic distribution. In the present embodiment, as shown in FIG. 1, the photoconductive layer 20 includes, in order from the non-display surface side (electrode 22 side), a charge generation layer (Carrier Generation Layer; CGL) 20B, a charge transport layer (Carrier Transport Layer). CTL) 20A is a two-layer structure in which the layers are sequentially stacked.

  The charge generation layer 20B is a layer having a function of generating charges by absorbing the irradiated light. Accordingly, the writing light applied to the display medium 12 when an image is written on the display medium 12 and the initialization preparation light applied to the display medium 12 during the preparation period for initialization of the display medium 12 are included in the charge generation layer 20B. The light in the absorption wavelength range that is absorbed by is applied. As the charge generation layer 20B, the irradiated light is absorbed to generate excitons (a pair of carriers of −charge and + charge), and the inside of the charge generation layer 20B or the charge generation layer 20B and the charge transport layer 20A. In particular, a charge generating material (for example, a metal or metal-free phthalocyanine, a squalium compound, an azurenium compound, a perylene pigment, an indigo pigment, an azo compound such as bis or tris) is preferable. Pigments, quinacridone pigments, pyrrolopyrrole dyes, polycyclic quinone pigments, condensed aromatic pigments such as dibromoanthanthrone, cyanine dyes, xanthene pigments, charge transfer complexes such as polyvinylcarbazole and nitrofluorene, or pyrylium salt dyes and polycarbonate resins The dry method of directly forming a film (e.g. The generated material is 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, acrylic resin, vinyl chloride resin, styrene resin. , Vinyl acetate resin, vinyl acetate resin, or silicone resin, etc.) in a suitable solvent to prepare a coating solution, which is applied and dried to form a film. Layer.

  The charge transport layer 20A is a layer having a function of drifting in the direction of an applied electric field when charges generated in the charge generation layer 20B are injected. In general, the charge transport layer 20A has a thickness several tens of times that of the charge generation layer 20B. For this reason, the capacitance of the charge transport layer 20A, the dark current of the charge transport layer 20A, and the current flowing inside the charge transport layer 20A determine the light-dark impedance of the entire photoconductive layer 20.

  The charge transport layer 20A preferably includes a charge transport material, efficiently injects + charges from the charge generation layer 20B, and hops and moves the injected holes.

  The charge transport layer 20A is composed of a low molecular 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, or benzidine compounds), or low-molecular electron transport materials (eg, quinone compounds, tetracyanoquinodimethane compounds, furfreon compounds, xanthone compounds, or benzophenones) Compound) with a polymer binder (for example, polycarbonate resin, polyarylate resin, polyester resin, polyimide resin, polyamide resin, polystyrene resin, or silicon-containing crosslinked resin) in an appropriate solvent Those were stone dissolved, or the hole transport material and electron transport material were prepared are dispersed or dissolved in a suitable solvent polymerized material may be formed by which was coated and dried.

  The cholesteric liquid crystal layer 17 is provided on the display surface side from the photoconductive layer 20 via a laminate layer 18 and a light absorption layer 19 described later. The cholesteric liquid crystal layer 17 has a function of selecting either a reflection state or a transmission state of incident light according to an applied voltage by using a change in the light interference state of the cholesteric (chiral nematic) liquid crystal. Even if the application of is canceled, the selected property is maintained. Further, the cholesteric liquid crystal layer 17 preferably has a structure that is not deformed by an external force such as bending or pressure.

  As the cholesteric liquid crystal layer 17 of the present embodiment, a liquid crystal layer of a self-holding type liquid crystal composite including a polymer matrix (transparent resin) 17A and a cholesteric liquid crystal 17B is used. In the present embodiment, the cholesteric liquid crystal layer 17 is a liquid crystal layer that does not require a spacer or the like because it has a self-holding property as a composite, and the cholesteric liquid crystal 17B is dispersed in the polymer matrix 17A. Has been.

  Examples of forming a self-holding type liquid crystal composite including a polymer matrix 17A and a cholesteric liquid crystal 17B include a PNLC (Polymer Network Liquid Crystal) structure including a network-like resin in the continuous phase of cholesteric liquid crystal. And a PDLC (Polymer Dispersed Liquid Crystal) structure (including microencapsulated) in which a cholesteric liquid crystal is dispersed in a droplet shape in a polymer skeleton.

  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. A PIPS (Polymerization Induced Phase Separation) method in which they are mixed, polymerized from a predetermined phase state and phase separated, a polymer such as polyvinyl alcohol and liquid crystal are mixed, suspended and stirred, and the liquid crystal is mixed into the polymer. Droplet-dispersed emulsion method, thermoplastic polymer and liquid crystal are mixed, TIPS (Thermally Induced Phase Separation) method to cool and phase-separate from a heated state to a predetermined phase, polymer and liquid crystal to chloroform It is formed by the SIPS (Solvent Induced Phase Separation) method, etc., in which the polymer and liquid crystal are phase separated by dissolving in a solvent such as State examples include, but not particularly limited.

  The polymer matrix 17A holds the cholesteric liquid crystal 17B and has a function of suppressing liquid crystal flow (image change) due to deformation of the display medium 12. For example, the polymer matrix 17A does not dissolve in the liquid crystal material and is compatible with the liquid crystal. A polymer material using an insoluble liquid as a solvent is used. The polymer matrix 17A is preferably a material that has strength to withstand external force and transmits at least reflected light and illumination light.

  Specific examples of the polymer matrix 17A include water-soluble polymer materials (for example, gelatin, polyvinyl alcohol, cellulose derivatives, polyacrylic acid polymers, ethyleneimine, polyethylene oxide, polyacrylamide, polystyrene sulfonate, polyamidine, or isoprene). Sulfonic acid polymer), or a material to be emulsified in water (for example, fluororesin, silicone resin, acrylic resin, urethane resin, or epoxy resin).

  The cholesteric liquid crystal 17B has a function of selecting one of the reflected and transmitted states of specific color light from incident light, and liquid crystal molecules are twisted and aligned in a spiral shape, and light incident from the direction of the spiral axis. Among them, specific light depending on the helical pitch is interference-reflected. The alignment of the liquid crystal molecules is changed by the electric field, and the reflection state is changed. The cholesteric liquid crystal 17B is effective for the display medium 12 of the present embodiment because it has higher reflectivity with respect to the applied voltage and better display performance than other liquid crystals, and has memory characteristics.

  Specific examples of the cholesteric liquid crystal 17B include nematic liquid crystals and smectic liquid crystals (for example, Schiff base type, azo type, azoxy type, benzoate type, biphenyl type, terphenyl type, cyclohexyl carboxylic acid ester type, phenylcyclohexane type, biphenyl type). Cyclohexane, pyrimidine, dioxane, cyclohexyl cyclohexane ester, cyclohexyl ethane, cyclohexane, tolan, alkenyl, stilbene, or condensed polycyclic), or mixtures thereof, and chiral agents (eg, steroids) Cholesterol derivatives, Schiff bases, azos, esters, or biphenyls) are added.

  The helical pitch of the cholesteric liquid crystal 17B is adjusted by the amount of chiral agent added to the nematic liquid crystal. For example, when the display colors are blue, green, and red, the center wavelength of selective reflection is set in the range of, for example, 400 nm to 500 nm, 500 nm to 600 nm, and 600 nm to 700 nm. Further, in order to compensate 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.

  In a region sandwiched between the cholesteric liquid crystal layer 17 and the photoconductive layer 20, a laminate layer 18 and a light absorption layer 19 are laminated in order from the side of the photoconductive layer 20 in contact with the charge transport layer 20 </ b> A. The laminate layer 18 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 are bonded together.

The laminate layer 18 is made of a polymer material, and a material that adheres and adheres to a layer to be bonded by heat or pressure (in this embodiment, the cholesteric liquid crystal layer 17 and the photoconductive layer 20) is selected. Examples of the material of the laminate layer 18 include an adhesive polymer material (for example, urethane resin, epoxy resin, acrylic resin, or silicone resin). In the present embodiment, the laminate layer 18 is configured as an insulating layer. In the present embodiment, “insulation” and “insulation” are those having a sheet resistance of 10 ¹⁰ Ω or more.

  The light absorption layer (light-shielding layer) 19 optically separates illumination light and incident light, prevents malfunction due to mutual interference, and displays external light incident from the non-display surface side of the display medium 12 when displaying images. This layer is provided for the purpose of optically separating images and preventing deterioration of image quality. However, for this purpose, the light absorption layer 19 is required to have a function of absorbing at least light in the absorption wavelength region of the charge generation layer 20B and light in the reflection wavelength region of the cholesteric liquid crystal layer 17.

  Specific examples of the light absorption layer 19 include inorganic pigments (for example, cadmium-based, chromium-based, cobalt-based, manganese-based, or carbon-based), or organic dyes and organic pigments (for example, azo-based, anthraquinone-based, indigo-based, Triphenylmethane, nitro, phthalocyanine, perylene, pyrrolopyrrole, quinacridone, polycyclic quinone, squalium, azurenium, cyanine, pyrylium, or anthrone) of the photoconductor layer 10 A dry method in which a film is formed directly on the surface on the charge generation layer 13 side, or these are dispersed or dissolved in a suitable solvent together with a polymer binder (for example, polyvinyl alcohol resin or polyacrylic resin) to prepare a coating solution, Examples thereof include those formed by a wet coating method in which this is applied and dried to form a film.

  In the display medium 12 of the present embodiment, the light absorption layer 19 is stacked on the charge transport layer 20A via the laminate layer 18, but the light absorption layer 19 is formed on the charge transport layer 20A. May be directly stacked. In this case, the light absorption layer 19 is preferably configured as an insulating layer. Further, depending on the material of the laminate layer 18 or the method of forming the laminate layer 18, some may damage the photoconductive layer 20, and in that case, an insulating isolation is provided in a region sandwiched between the laminate layer 18 and the charge transport layer 20 A. A layer may be provided.

  Next, an image writing operation of the display medium 12 according to the present embodiment will be described.

  In the display medium 12 configured as described above, when a voltage is applied between the electrode 15 and the electrode 22, each layer stacked in a region sandwiched between the electrode 15 and the electrode 22 has a partial pressure in each layer. The divided voltage thus applied is applied. In this state, when the photoconductive layer 20 is irradiated with writing light, the resistance distribution of the photoconductive layer 20 changes according to the irradiated writing light, so that the photoconductive layer 20 is applied to the cholesteric liquid crystal layer 17 according to the writing light. The divided voltage also changes. When the voltage distribution applied to the cholesteric liquid crystal layer 17 changes, the orientation of the liquid crystal molecules changes, so that information corresponding to the writing light is displayed on the cholesteric liquid crystal layer 17.

Specifically, this will be described with reference to FIG. FIG. 2 is a circuit diagram showing an equivalent circuit of the display medium 12 having the structure shown in FIG. In FIG. 2, C _lc , C _opc and R _lc , R _opc are the capacitance and resistance values of the cholesteric liquid crystal layer 17 and the photoconductive layer 20, respectively. C _e and R _e are equivalent capacitance and equivalent resistance values of components other than the cholesteric liquid crystal layer 17 and the photoconductive layer 20.

When the voltage applied between the electrode 15 and the electrode 22 of the display medium 12 is V, the divided voltages V _lc , V _opc and V _e determined by the impedance ratio between the components are applied to each component. . Further, when the writing light is irradiated, the resistance value R _opc of the photoconductive layer 20 changes according to the intensity of the writing light. Therefore, the _divided voltage applied to the cholesteric liquid crystal layer 17 by exposure or non-exposure with the writing light is reduced. Be controlled. Specifically, in the exposure region exposed by the writing light in a state where a voltage is applied between the electrode 15 and the electrode 22, the resistance value R _opc of the photoconductive layer 20 becomes small and is applied to the cholesteric liquid crystal layer 17. The voltage is higher than that in the non-exposed area.

  Here, the light modulation function of the cholesteric liquid crystal 17B will be described in more detail. 3A to 3C are schematic explanatory views showing the relationship between the molecular orientation of the cholesteric liquid crystal 17B and the optical characteristics. As described above, the amount of light reflected from the cholesteric liquid crystal 17B is controlled by the alignment state of the liquid crystal molecules twisted in a spiral. Specifically, as shown in FIG. 3A, the cholesteric liquid crystal 17B has a planar reflection phenomenon in which the helical axis is substantially perpendicular to the cell surface and reflects light of a specific wavelength with respect to incident light. As shown in FIG. 3 (B), the focal axis is such that the helical axis is substantially parallel to the cell surface and the incident light is transmitted while being slightly scattered forward, and the helical structure as shown in FIG. 3 (C). The liquid crystal molecules show three phase states: homeotropic that allows liquid crystal molecules to face the electric field direction and transmit incident light. In the present embodiment, “substantially vertical” means a predetermined angle range in which the angle of the helical axis with respect to the cell surface assumed to be a horizontal plane when the phase state of the cholesteric liquid crystal 17B is planar is 90 degrees. (For example, a range larger than 89 degrees and smaller than 91 degrees), and “substantially parallel” refers to a cell surface assumed to be a horizontal plane when the phase state of the cholesteric liquid crystal 17B is focal conic. It means a predetermined angle range in which the angle of the spiral axis of the cholesteric liquid crystal 17B includes 0 degrees (for example, a range larger than -1 degree and smaller than 1 degree).

Among the above three phase states, the planar and focal conic exist bistable at no voltage. Therefore, the alignment state of the cholesteric liquid crystal 17B is not uniquely determined with respect to the voltage ( _divided voltage V _lc ) applied to the cholesteric liquid crystal layer 17, and when the planar is in the initial state, the applied voltage increases. Change in the order of planar, focal conic, and homeotropic. When the focal conic is in the initial state, the focal conic state changes in the order of homeotropic as the applied voltage increases. On the other hand, when the voltage applied to the cholesteric liquid crystal layer 17 is steeply 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. In the present embodiment, “the voltage is sharply reduced to zero” varies depending on the constituent material of the cholesteric liquid crystal 17B, the configuration of the display medium 12, and the like. For example, the application of the voltage to the cholesteric liquid crystal layer 17 is canceled. This means that the voltage becomes zero after 0.5 ms from the start of operation. Further, the present invention is not limited to this, and a voltage is applied when the phase state of the cholesteric liquid crystal 17B is homeotropic by an experiment with an actual device of the optical writing display device 10 or a computer simulation based on a design specification of the optical writing display device 10. After the start of the release operation, the phase state of the cholesteric liquid crystal 17B is changed from homeotropic to planar, but the voltage is set to zero when a predetermined time has passed as a limit time that does not change to focal conic. It ’s fine.

FIG. 4 is a graph for explaining the electro-optic response of the cholesteric liquid crystal layer 17. In FIG. 4, the vertical axis represents the normalized light reflectance, the light reflectance is normalized with the maximum light reflectance being 100% and the minimum light reflectance being 0%, and the horizontal axis is the cholesteric liquid crystal layer. 17 is a pulse voltage to be applied. In addition, there is a transition region between the planar, focal conic, and homeotropic phase states. Therefore, when the normalized light reflectance is 50% or more, the selective reflection state is less than 50%. The case is defined as the transmission state, the threshold voltage for the phase change of focal conic and homeotropic is the upper threshold voltage V _fh, and the threshold voltage for the phase change of planar and focal conic is the lower threshold voltage V _pf .

As an example, the cholesteric liquid crystal layer 17 when the application of the pulse voltage is canceled and the voltage value is steeply reduced to zero shows the switching behavior shown in FIG. That is, when the _divided voltage V _lc applied to the cholesteric liquid crystal layer 17 is equal to or higher than the upper threshold voltage V _fh , a selective reflection state is changed from homeotropic to planar. When the divided voltage V _lc applied to the cholesteric liquid crystal layer 17 is larger than the lower threshold voltage V _pf and lower than the upper threshold voltage V _fh , a transmissive state by focal conic is established. When the divided voltage V _lc applied to the cholesteric liquid crystal layer 17 is equal to or lower than the lower threshold voltage V _pf , the state before the voltage application is continued, that is, the selective reflection state by the planar or the transmission state by the focal conic It becomes.

For example, in a monochrome type optically writable display medium, when focal conic is in an initial state, in an exposure region where a _divided voltage applied to the cholesteric liquid crystal layer 17 is large (V _fh or more), the application of the voltage cancels the homeotropic. The selective reflection state changed from planar to planar is achieved, and white pixels are displayed. On the other hand, in the non-exposure region where the _divided voltage applied to the cholesteric liquid crystal layer 17 is small (less than V _fh ), the application of the voltage is canceled and a transmissive state is formed by focal conic and black pixels are displayed. Thus, a white image is displayed on a black background.

  FIG. 5 is a configuration diagram showing an example of the configuration of the optical writing display device according to the present embodiment. As shown in FIG. 5, the display medium 12 is attached to the optical writing device 14 according to the present embodiment, and the optical writing display device 10 is configured by the display medium 12 and the optical writing device 14. . In the present embodiment, an example in which the display medium 12 and the optical writing device 14 are separated will be described. However, the display medium 12 and the optical writing device 14 are integrated so as not to be separated. An optical writing type display device may be used.

  The optical writing device 14 is a device that writes an image on the display medium 12, and has a function of exposing the display medium 12 with writing light and a function of exposing initialization preparation light to an area to be initialized of the display medium 12. And an exposure device 32 as an irradiating unit, a voltage applying unit 26 as a voltage applying unit for applying a voltage between the electrode 15 and the electrode 22 of the display medium 12, and an exposure device 32 and the voltage applying unit 26 electrically. The controller 28 is connected and is configured to include a controller 28 as a control means for controlling them.

  The exposure device 32 has a plurality of light sources (not shown) arranged on the display medium 12 to irradiate the display medium 12 with writing light as light in an absorption wavelength region absorbed by the photoconductive layer 20 of the display medium 12. ). In the present embodiment, the irradiation area of the cholesteric liquid crystal layer 17 of the writing light irradiated from the light source of the exposure device 32 is set to be smaller than the area corresponding to each pixel of the image displayed on the cholesteric liquid crystal layer 17. In addition, the exposure and non-exposure of the writing light from each of the plurality of light sources are adjusted, so that the exposure and non-exposure of the writing light are adjusted according to each pixel of the image displayed on the cholesteric liquid crystal layer 17.

  In addition, as a plurality of light sources constituting the exposure device 32, an address for specifying the position of the light source to emit light and an address for specifying the position of other light sources are specified based on an input signal from the control unit 28. As long as it irradiates the photoconductive layer 20 of the display medium 12 with the write light, there is no particular limitation.

  As a specific example of the plurality of light sources constituting the exposure apparatus 32, there is an exposure apparatus configured to include an LCD (Liquid Crystal Display) panel and a backlight for irradiating the LCD panel with illumination light. In addition, a cold cathode tube, a xenon lamp, a halogen lamp, a light emitting diode (LED), an EL, or a laser is arranged in a two-dimensional array. Note that the exposure device 32 may further include various optical elements (for example, a microlens array, a cell hook lens array, a prism array, or a viewing angle adjustment sheet).

  In this embodiment, an example in which exposure with “writing light” and exposure with “initialization preparation light” is performed with one exposure apparatus is described. However, the present invention is not limited to this. On the other hand, an exposure apparatus that scans and exposes writing light and an exposure apparatus that performs batch exposure of initialization preparation light on the entire surface of the display medium 12 may be provided separately.

  The voltage application unit 26 applies an AC voltage corresponding to the input signal between the electrode 15 and the electrode 22 of the display medium 12 based on an input signal from the control unit 28. For example, a bipolar high voltage amplifier or the like is used. Used. In the present embodiment, a pulsed voltage in which a pulsed positive electrode component (first unit pulse waveform) and a pulsed negative electrode component (second unit pulse waveform) alternately and periodically change is used as an AC voltage. .

  Specifically, the voltage application to the display medium 12 by the voltage application unit 26 is performed between the electrode 15 and the electrode 22 via the contact terminal 25. Here, the contact terminal 25 is a member that contacts the electrode 15 and the electrode 22 of the voltage application unit 26 and the display medium 12 and conducts both of them, and is connected to the electrode 15, the electrode 22, and the voltage application unit 26. One with a low contact resistance is selected.

  Examples of the contact terminal 25 include metal (for example, gold, silver, copper, aluminum, or iron), carbon, a composite in which these are dispersed in a polymer, a conductive polymer (for example, polythiophene or polyaniline), and the like. A clip-shaped terminal sandwiching an electrode may be mentioned.

  The control unit 28 includes a CPU (Central Processing Unit) 28A, a ROM (Read Only Memory) 28B that is a read-only storage medium, and a RAM (Random Access Memory) 28C.

  The CPU 28A controls the entire operation of the optical writing device 14. The ROM 28B as a storage medium functions as a storage medium that stores in advance a control program for controlling the operation of the optical writing device 14, an image writing processing program to be described later, various parameters, and the like. The RAM 28C is a storage medium used as a work area or the like when executing various programs. The CPU 28A is connected to each of the ROM 28B and the RAM 28C. Therefore, the CPU 28A accesses the ROM 28B and the RAM 28C.

  The optical writing device 14 includes an NVM (Non Volatile Memory) 29 that is a non-volatile storage medium. The NVM 29 stores various types of information that must be retained even when the power switch of the apparatus is turned off, and stores image information indicating an image to be displayed on the display medium 12. The NVM 29 is connected to the CPU 28A of the control unit 28. Accordingly, the CPU 28A reads the image information from the NVM 29 according to the program stored in the ROM 28B, and controls the voltage application unit 26 and the exposure device 32 so that the image indicated by the image information is displayed on the display medium 12.

  In FIG. 6, a region of the cholesteric liquid crystal layer 17 (hereinafter referred to as an “exposure portion”) corresponding to a region irradiated with illumination light in the display medium 12 when a drive voltage is applied between the electrode 15 and the electrode 22. )) And an area of the cholesteric liquid crystal layer 17 corresponding to an area not irradiated with illumination light in the display medium 12 when a drive voltage is applied between the electrode 15 and the electrode 22 (hereinafter referred to as a waveform). , An example of a waveform indicating an electric field in “non-exposed portion”). Here, “driving voltage” means a voltage to be applied between the electrode 15 and the electrode 22 when an image is written on the display medium 12. As shown in the figure, the waveform indicating the electric field in the exposure portion when a drive voltage is applied between the electrode 15 and the electrode 22 is a positive voltage (a positive electrode component of the AC voltage) between the electrode 15 and the electrode 22. When applied, the electrical resistance of the photoconductive layer 20 corresponding to the exposed portion is lower than that when a negative voltage (a negative electrode component of an AC voltage) is applied between the electrode 15 and the electrode 22, and the exposed portion is reduced by the reduced amount. Since the electric field on the positive electrode side increases, the positive electrode side and the negative electrode side are asymmetric.

  On the other hand, in the non-exposed portion, the electrical resistance of the photoconductive layer 20 does not change depending on the polarity of the voltage applied between the electrode 15 and the electrode 22, so that the drive voltage is applied between the electrode 15 and the electrode 22. The waveform indicating the electric field in the non-exposed portion is symmetrical on the positive electrode side and the negative electrode side.

  In this way, in the exposed portion, an alternating voltage in which the positive electrode component and the negative electrode component are asymmetric is applied, which causes uneven distribution of ion impurities in the cholesteric liquid crystal layer 17. This is a factor that causes a reduction in the quality of the image displayed on the display medium 12.

  Therefore, in the optical writable display device 10 according to the present embodiment, the voltage applied between the electrode 15 and the electrode 22 is controlled in order to suppress deterioration in image quality due to application of an alternating voltage in which the positive electrode component and the negative electrode component are asymmetric. A voltage application process is executed.

  Next, as an operation of the optical writing display device 10 according to the present embodiment, a voltage application process executed by the optical writing display device 10 will be described with reference to FIG. FIG. 7 is a flowchart showing the flow of processing of the voltage application processing program executed by the CPU 28A when writing the image indicated by the input image information to the display medium 12 in the initialized state. In the optical writable display device 10 according to the present embodiment, the voltage application processing program is stored in the ROM 28B in advance. However, the present invention is not limited to this, and the image writing processing program is not limited to the CD-ROM, DVD-ROM, USB ( (Universal Serial Bus) A form provided in a state of being stored in a recording medium readable by a computer such as a memory may be applied, or a form distributed via wired or wireless communication means may be applied. Further, in the present embodiment, the above-mentioned “initialization” means that the phase state of the cholesteric liquid crystal 17B included in the cholesteric liquid crystal layer 17 in the region to be initialized of the display medium 12 is set to a focal conic.

  In step 100 of the figure, the negative electrode with respect to the area of the unit pulse waveform of the positive component contributing to the writing of the image on the display medium 12 so that the effective voltage waveform applied to the cholesteric liquid crystal layer 17 is symmetrical between the positive and negative electrodes. An instruction signal for instructing application of an AC voltage between the electrodes 15 and 22 within a predetermined range in which the area ratio of the unit pulse waveform of the component is described later is output to the voltage application unit 26, and this voltage application processing program Exit.

  By the processing of step 100, the voltage application unit 26 writes the area of the unit pulse waveform of the positive component as the first unit pulse waveform (so that the image indicated by the image information input to the CPU 28A is written on the display medium 12). Hereinafter, the ratio (hereinafter also referred to as “area ratio”) of the area (hereinafter referred to as “negative electrode pulse”) of the unit pulse waveform of the negative electrode component as the second unit pulse waveform relative to “positive electrode pulse”) in advance. An alternating voltage within a predetermined range is applied between the electrode 15 and the electrode 22.

  In this embodiment, as shown in FIG. 8 as an example, when the negative pulse is represented by “negative pulse = voltage V1 × time t1,” and the positive pulse is represented by “positive pulse = voltage V2 × time t2,” The area ratio of the AC voltage applied between the electrode 15 and the electrode 22 is adjusted by fixing the time t1 and the time t2 and changing the voltage V1 and the voltage V2.

  Next, the “predetermined range” will be described.

  FIG. 9 is a graph showing a comparative example of the electro-optic response characteristics of the cholesteric liquid crystal layer 17 when the display medium 12 is irradiated with illumination light and when the display medium 12 is not irradiated with illumination light. In the figure, the vertical axis represents the light reflectance of the cholesteric liquid crystal layer 17, and the horizontal axis represents the voltage applied between the electrode 15 and the electrode 22. In the figure, the solid line graph shows the behavior of the cholesteric liquid crystal layer 17 when the display medium 12 is illuminated, and the dotted line graph is when the display medium 12 is not illuminated. The behavior of the cholesteric liquid crystal layer 17 is shown.

As shown in the drawing, when the display medium 12 is not irradiated with illumination light, the upper threshold voltage (hereinafter referred to as “non-exposure threshold voltage V _thd ”) in which the phase state of the cholesteric liquid crystal layer 17 changes from focal conic to homeotropic. Is an upper threshold voltage (hereinafter referred to as “threshold voltage V _thp during exposure”) in which the phase state of the cholesteric liquid crystal layer 17 changes from focal conic to homeotropic when the display medium 12 is irradiated with illumination light. Larger than.) Therefore, in a state where a voltage (hereinafter referred to as “driving voltage”) that is larger than the exposure threshold voltage V _thp and smaller than the non-exposure threshold voltage V _thd is applied between the electrode 15 and the electrode 22, for example, When the display medium 12 is irradiated with writing light, an image corresponding to the writing light is written on the display medium 12.

  FIG. 10 shows the waveform on the positive side of the divided voltage applied to the exposure portion when the drive voltage is applied between the electrode 15 and the electrode 22, and when the drive voltage is applied between the electrode 15 and the electrode 22. It is a figure which shows the comparative example of the positive electrode side waveform of the divided voltage applied to the non-exposure part.

As shown in the figure, the divided voltage applied to the exposed portion is larger than the divided voltage applied to the non-exposed portion, and is applied to the exposed portion with respect to the divided voltage applied to the non-exposed portion. The ratio of the _divided voltage substantially matches the ratio of the non-exposure threshold voltage V _{thd to} the exposure threshold voltage V _thp .

  FIG. 11 shows the area ratio when an AC voltage for a plurality of cycles is applied between the electrode 15 and the electrode 22 at each of a plurality of predetermined ratios of the negative electrode pulse to the positive electrode pulse, and the light reflectance difference at the exposure portion. It is a graph which shows an example of the relationship with ((DELTA) light reflectance). The “light reflectance difference” means the cholesteric state when a writing voltage is initially applied to the cholesteric liquid crystal layer 17 (for example, when the writing voltage is first applied to the cholesteric liquid crystal layer 17). A value indicating the absolute value of the difference between the light reflectivity (initial light reflectivity) of the liquid crystal layer 17 and the light reflectivity of the cholesteric liquid crystal layer 17 when an AC voltage for a plurality of cycles is applied between the electrodes 15 and 22. Yes, the closer this value is to “0”, the better. The above-mentioned plurality of cycles means a case where driving is performed 100 times continuously.

  As shown in the figure, in the range where the area ratio of the AC voltage applied between the electrode 15 and the electrode 22 is larger than “1” and less than “4.3”, the range in which the difference in light reflectance can be considered good. In other cases, the light reflectance difference is beyond the range that can be regarded as good.

  In the present embodiment, the above-mentioned “range that can be considered good” is 0 or more and less than the light reflectance difference (for example, 1.6) of the exposed portion when the ratio of the negative pulse to the positive pulse is 1. The range is as follows.

  FIG. 12 shows an area ratio when a plurality of cycles of AC voltage is applied between the electrode 15 and the electrode 22 at each of a plurality of predetermined ratios of the negative electrode pulse to the positive electrode pulse, and a difference in light reflectance at the exposure portion. Of the negative electrode pulse with respect to the positive electrode pulse and the ratio of the area when the AC voltage for a plurality of cycles is applied between the electrode 15 and the electrode 22 and the difference in the light reflectance at the non-exposed portion. It is a graph which shows the comparative example of the relationship. Table 1 below shows data constituting the graph shown in FIG.

  As shown in the figure, in the area where the area ratio of the AC voltage applied between the electrode 15 and the electrode 22 is less than “3.3” in the non-exposed part, the difference in light reflectance is within a range that can be considered good. However, in other cases, the light reflectance difference exceeds the range that can be regarded as good. On the other hand, as described above, the exposure portion falls within a range in which the difference in light reflectance can be considered good when the ratio of the negative electrode pulse to the positive electrode pulse is greater than “1” and less than “4.3”. ing.

  Therefore, when an image is written on the display medium 12, the ratio of the negative electrode pulse to the positive electrode pulse should be within a range where the difference in light reflectance can be considered good regardless of whether it is an exposed part or a non-exposed part. Therefore, the voltage application unit 26 is configured so that the AC voltage within the range where the ratio of the negative electrode pulse to the positive electrode pulse of the AC voltage is greater than “1” and less than “3.3” is applied between the electrode 15 and the electrode 22. To control. That is, as shown in Table 1 above, the light reflectivity when a writing voltage is applied to the cholesteric liquid crystal layer 17 in the first period and the writing voltage to the cholesteric liquid crystal layer 17 in the 100th period. An alternating voltage between the electrode 15 and the electrode 22 that makes the difference between the exposed part and the non-exposed part of the value indicating the absolute value of the difference from the light reflectance when applied (light reflectance difference) 1.6% or less. The voltage application unit 26 is controlled so as to be applied to.

  In addition, as shown in FIG. 12, the area ratio of the alternating voltage applied between the electrode 15 and the electrode 22 in the exposure part, and the area ratio of the alternating voltage applied between the electrode 15 and the electrode 22 in the non-exposure part. In the range from “2” to “3”, the difference between the light reflectance difference of the exposed portion and the light reflectance difference of the non-exposed portion is most reduced. It is better to control the voltage application unit 26 so that an AC voltage within the range of “2” or more and “3” or less is applied between the electrode 15 and the electrode 22.

Further, as shown in FIG. 12, the area ratio of the AC voltage applied between the electrode 15 and the electrode 22 in the exposed part and the area ratio of the AC voltage applied between the electrode 15 and the electrode 22 in the non-exposed part. Is “2” (= non-exposure threshold voltage V _thd / exposure threshold voltage V _thp ), the difference between the light reflectance difference in the exposed portion and the light reflectance difference in the non-exposed portion is minimized, and exposure is performed. The average value of the light reflectance difference of the non-exposed portion and the average value of the light reflectance difference of the non-exposed portion is closer to “0” than the average value of the light reflectance difference of the exposed portion and the non-exposed portion Therefore, when writing an image on the display medium 12, it is better to control the voltage application unit 26 so that an AC voltage having an area ratio of “2” is applied between the electrode 15 and the electrode 22. That is, as shown in Table 1 above, the light reflectance when a writing voltage is applied to the cholesteric liquid crystal layer 17 in the first period and the writing voltage to the cholesteric liquid crystal layer 17 in the 100th period. An alternating voltage between the electrode 15 and the electrode 22 is set so that the difference between the exposed part and the non-exposed part of the value indicating the absolute value of the difference from the light reflectance when applied (light reflectance difference) is 0.1% or less. The voltage application unit 26 is controlled so as to be applied to.

  Therefore, the above-mentioned “predetermined range” is an area ratio corresponding to the light reflectance difference when the area ratio in the optical characteristics is greater than 1 and indicates the relationship of the light reflectance difference with respect to the area ratio. Means less than.

  As described above, when an image is written on the display medium 12, an AC voltage having an area ratio larger than 1 and an area ratio of 1 is applied, whereby the light reflectance difference (for example, positive pulse) of the exposed portion is applied. In advance, it does not exceed a value (for example, 3.3) when the non-exposed portion shows a light reflectance difference corresponding to a light reflectance difference of “1.6” of the exposed portion when the ratio of the negative pulse to 1 is 1. The voltage application unit 26 is controlled so that an AC voltage within a predetermined range (for example, a range greater than “1” and less than “3.3”) is applied between the electrode 15 and the electrode 22. As a result, the effective voltage waveform applied to the cholesteric liquid crystal layer 17 is symmetric between the positive and negative electrodes.

  In the above embodiment, the area ratio of the AC voltage applied between the electrode 15 and the electrode 22 is adjusted by changing the applied voltage while fixing the voltage application time between the electrode 15 and the electrode 22. However, by fixing the voltage application time between the electrode 15 and the electrode 22 and changing the voltage applied between the electrode 15 and the electrode 22, the area ratio of the AC voltage applied between the electrode 15 and the electrode 22 is adjusted. Even if it does, the area of the alternating voltage applied between the electrode 15 and the electrode 22 by fixing the applied voltage between the electrode 15 and the electrode 22 and changing the voltage application time between the electrode 15 and the electrode 22 Even in the case of adjusting the ratio, as shown in FIG. 13 as an example, it contributes almost equally to the difference in light reflectivity. In the area ratio of the AC voltage applied may be adjusted by varying the application time of a voltage to between the electrodes 15 and the electrode 22 to fix the voltage applied to between the electrodes 15 and the electrode 22.

  In the above embodiment, the display medium 12 to which the photoconductive layer 20 having the two-layer structure is applied has been described as an example. However, the present invention is not limited thereto. Further, a display medium to which a so-called dual CGL photoconductive layer in which a charge generation layer (lower CGL) is sequentially stacked may be used. FIG. 15 is a cross-sectional view showing the configuration of a display medium to which a dual CGL photoconductive layer is applied. As shown in the figure, the display medium 12B is different from the display medium 12 in that a photoconductive layer 20 'is applied instead of the photoconductive layer 20. The photoconductive layer 20 ′ is different from the photoconductive layer 20 in that a charge generation layer 20 C is further provided. The charge generation layer 20C is disposed in a region sandwiched between the laminate layer 18 and the charge transport layer 20A. The charge generation layer 20C, like the charge generation layer 20B, is a layer having a function of generating a charge by absorbing irradiated light, but has an absorption wavelength region other than the absorption wavelength region of the initialization preparation light and the writing light. Have Note that both the charge generation layer 20B and the charge generation layer 20C in the same drawing may have absorption wavelength ranges for initialization preparation light and writing light. In this case, the CPU 28 </ b> A is photoconductive when a voltage having a polarity that does not contribute to writing of an AC voltage image (in the above embodiment, the negative electrode component of the AC voltage) is applied between the electrode 15 and the electrode 22 by the voltage application unit 26. The exposure device 32 is controlled not to irradiate the layer 20 'with illumination light.

  Although the mechanism is not necessarily clear, it is assumed that the charge is temporarily trapped by the presence of the charge generation layer 20C, thereby suppressing the horizontal diffusion of the charge and providing a higher resolution image quality. .

In the above embodiment, the polarity component of the alternating voltage that contributes to the writing of the image on the display medium 12 is the positive electrode component. However, the present invention is not limited to this, and may be a negative electrode component. In this case, the ratio of the positive pulse to the negative pulse of the AC voltage applied between the electrode 15 and the electrode 22 falls within a predetermined range including the ratio of the non-exposure threshold voltage V _{thd to} the exposure threshold voltage V _thp . Thus, the voltage application unit 26 is controlled.

  In the above embodiment, the display medium 12 and the light source 30A are relatively moved by moving the light source 30A while the display medium 12 is fixed. However, the display medium 12 is fixed with the light source unit 30A fixed. It may be configured to move the two or both.

DESCRIPTION OF SYMBOLS 10 Optical writing type display apparatus 12 Display medium 14 Optical writing apparatus 17 Cholesteric liquid crystal layer 20, 20 'Photoconductive layer 20A Charge transport layer 20B, 20C Charge generation layer 15, 22 Electrode 26 Voltage application part 28 Control part 32 Exposure apparatus

Claims (6)

A cholesteric liquid crystal layer in which an image is written by changing the reflectance according to the magnitude of an applied voltage between a pair of electrodes having at least one of translucency, and depending on the intensity of illumination light to be irradiated Voltage applying means for applying a voltage between the pair of electrodes of the display medium provided with the photoconductive layer that changes the voltage applied to the cholesteric liquid crystal layer by changing the electrical resistance;
An irradiation means for irradiating the photoconductive layer with the illumination light from the electrode side having translucency;
The illumination means is controlled so that the illumination light is applied to the photoconductive layer, and a first unit pulse waveform having one polarity and a second unit pulse waveform having a polarity different from the one polarity are alternately generated. And an area ratio indicating the ratio of the area of the second unit pulse waveform to the area of the first unit pulse waveform is greater than 1, and an image is written to the cholesteric liquid crystal layer at an initial stage relative to the area ratio. The optical characteristics showing the relationship between the reflectance when the voltage for application is applied and the reflectance difference expressed by the difference between the reflectance when the voltage for image writing is applied to the cholesteric liquid crystal layer a plurality of times. The voltage application means is controlled so that an AC voltage within a predetermined range less than the area ratio corresponding to the reflectance difference when the area ratio is 1 is applied between the pair of electrodes. And control means,
An optical writing device.   The control means is configured such that the area ratio is between the pair of electrodes at a boundary point where the cholesteric liquid crystal layer corresponding to the region irradiated with the illumination light of the photoconductive layer changes from a focal conic state to a homeotropic state. The ratio of the magnitude of the voltage applied between the pair of electrodes at the boundary point of the cholesteric liquid crystal layer corresponding to the area of the photoconductive layer not irradiated with the illumination light with respect to the magnitude of the voltage applied to The optical writing device according to claim 1, wherein the voltage applying unit is controlled such that an alternating voltage is applied between the pair of electrodes.   The photoconductive layer includes a first charge generation layer having an absorption wavelength range of the illumination light, a second charge generation layer having an absorption wavelength range other than the absorption wavelength range, the first charge generation layer, and the second charge generation layer. The optical writing device according to claim 1, further comprising: a charge transport layer sandwiched between the charge generation layers. The photoconductive layer is configured by sandwiching a charge transport layer with a charge generation layer having an absorption wavelength range of the illumination light,
The control means is configured to prevent the illumination light from being applied to the photoconductive layer when a voltage having a polarity that does not contribute to writing of the AC voltage image is applied between the pair of electrodes by the voltage application means. 3. The optical writing device according to claim 1, wherein the optical writing device controls the means. An optical writing device according to any one of claims 1 to 4,
The display medium on which an image is written by being irradiated with writing light from the irradiation means;
An optical writable display device. Computer
A cholesteric liquid crystal layer in which an image is written by changing the reflectance according to the magnitude of an applied voltage between a pair of electrodes having at least one of translucency, and depending on the intensity of illumination light irradiated And having a translucency so that illumination light is irradiated to the photoconductive layer of the display medium provided with the photoconductive layer that changes the voltage applied to the cholesteric liquid crystal layer by changing the electrical resistance. The illumination means for irradiating the illumination light to the photoconductive layer from the electrode side is controlled, and a first unit pulse waveform having one polarity and a second unit pulse waveform having a polarity different from the one polarity are alternately generated. And an area ratio indicating a ratio of the area of the second unit pulse waveform to the area of the first unit pulse waveform is greater than 1, and an initial value with respect to the area ratio A reflectance difference expressed by a difference between a reflectance when an image writing voltage is applied to the cholesteric liquid crystal layer and a reflectance when an image writing voltage is applied to the cholesteric liquid crystal layer a plurality of times. The pair of electrodes so that an alternating voltage within a predetermined range less than an area ratio corresponding to a reflectance difference when the area ratio in the optical characteristic indicating the relationship is 1 is applied between the pair of electrodes. A program for functioning as control means for controlling voltage application means for applying a voltage therebetween.

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