JP4882496B2 - Optical address type display medium writing method, external light blocking member used therefor, and optical address type display medium writing apparatus - Google Patents

Description

The present invention relates to an optical address type display medium writing method and an apparatus for writing an image by irradiating an optical address type display medium with address light from a light source.
Specifically, the present invention relates to a writing method and a writing apparatus for an optical address type display medium suitable for writing an image by irradiating address light in the presence of external light. The present invention also relates to an external light blocking member used for the writing method of the optical address type display medium.

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 on various rewritable marking technologies that are even more convenient has been made, but as one of the directions, the technology using a photoaddressable display medium in which a display layer (particularly a liquid crystal layer) and a photoconductive layer are laminated, Attention has been paid to the fact that repeated recording / erasing can be performed and other excellent characteristics can be realized.

  In order to write an image on such an optical address type display medium, in general, the back side of the display side surface is set as the writing side surface, and the surface is positioned in a dark room space, and then an exposure device such as a projector is used. It is exposed (see Patent Document 1). FIG. 12 is a schematic diagram showing a state in which an image is written on the optical address type display medium by the exposure apparatus in this way.

  In the example illustrated in FIG. 12, the optical writing device includes a projector 501, a light control layer 504, and a voltage application unit 502. The light control layer 504 is reversibly switched between light scattering and light transmission in accordance with the characteristic switching voltage signal, so that the projected image can be viewed visually.

As shown in FIG. 12, a predetermined voltage is applied to the display medium 503 by the voltage application unit 502, and light from the projector 501 is converted into address light by the dimming layer 504, which is displayed on the display medium 503. The image is written by being irradiated. At this time, the writing side surface irradiated with the address light is the back side of the display side of the display medium 503.
Thus, by projecting from the back side of the display side of the display medium 503, the contrast of the address light is ensured without being affected by external light.

  In recent years, small-sized projectors that can be carried and carried have been developed. This is mainly intended to irradiate a desktop or wall surface with a projected image, but it goes without saying that it would be convenient if such a projector could write an image on an optical address type display medium. .

However, it is considered that the projection image irradiation by such a small-sized projector is normally performed from the display side of the optical address type display medium, and it is difficult to eliminate the presence of external light. Of course, in writing an image on the optical address type display medium by the projector whose purpose is to expose a simple projection image, it is only a large scale to put a dark room between the projector and the optical address type display medium. If the image cannot be written by irradiating the projected image in the presence of external light, the practicality is questioned.
If image writing is performed in the presence of external light, the contrast of address light becomes difficult to obtain due to the influence of external light, and there is a concern that the contrast of a display image formed after writing cannot be obtained.

JP 2003-75865 A

  Accordingly, an object of the present invention is to provide a writing method and a writing apparatus for an optical address type display medium capable of obtaining a good contrast in a formed display image without being affected by the presence of external light. It is to provide. Moreover, this invention is providing the member suitable for using for the writing method of the optical address type display medium which can achieve the said objective.

The above object is achieved by the present invention described below. That is, the optical address type display medium writing method of the present invention (hereinafter sometimes simply referred to as “the writing method of the present invention”) writes an image by irradiating the optical address type display medium with address light from a light source. A method of writing an optical address type display medium,
A louver-shaped external light blocking member formed by arranging a plurality of elongated plate-like bodies arranged so that the inclination of the short side thereof is substantially parallel to the traveling direction of the address light, the optical address type display The address light is emitted from the light source in a state of being arranged on the writing side of the medium.

  Address light (writing light) by exposure means such as a projector has high straightness, whereas external light is scattered light and has low straightness. Therefore, a louver-shaped external light blocking member formed by arranging a plurality of elongated plate-like bodies arranged so that the inclination of the short side thereof is substantially parallel to the traveling direction of the address light includes the light. Since the address light is arranged on the writing side surface of the address type display medium, the address light passes through the gap of the external light blocking member parallel to the traveling direction, and the external light which is scattered light whose traveling direction is not constant is Almost no light can pass through the gap between the external light blocking members, and the external light blocking member is shielded. As a result, an image having a bright and dark contrast can be formed on the optical address type display medium without being affected by external light.

The writing method of the present invention is particularly effective when the writing side surface of the optical address type display medium also serves as the display side surface. When performing from the display side of the optical address type display medium, such as irradiation of a projection image by a small size projector, it is difficult to eliminate the presence of external light. An image having a bright and dark contrast can be formed on the optical address type display medium without being affected.
The plate-like body constituting the external light blocking member preferably has a black surface. By setting it as black, the external light which is scattered light is absorbed without reflecting on the surface of the plate-like body, and the external light is efficiently shielded by the external light blocking member.

In the writing method of the present invention, as the above-mentioned optical address type display medium to be written, as a suitable material, at least according to the phase state of the liquid crystal contained between a pair of electrode layers whose display side is transparent. A display layer that reflects light and a photoconductive layer that absorbs light in a specific wavelength region and changes a resistance value according to the amount of the absorbed light are stacked, and in this case, When irradiating the address light, a predetermined voltage is applied between the pair of electrode layers. The liquid crystal contained in the display layer is preferably a cholesteric liquid crystal, and the display layer is preferably formed by dispersing the cholesteric liquid crystal in a polymer. The photoconductive layer is preferably made of an organic photoconductor.
In the writing method of the present invention, the light source may be a point light source such as a projector or a surface light source.

The external light blocking member of the present invention is an external light blocking member used in the writing method of the optical address type display medium of the present invention as described above, and the elongated plates are inclined at substantially the same angle, and the surface thereof A plurality of arrays are arranged so as to be substantially parallel to each other, and are configured in a louver shape. When the light source is a point light source, the external light blocking member is such that the traveling direction of the address light emitted from the point light source is radial, so that the plate-like body in which a plurality of short sides are arranged substantially in parallel thereto Inevitably has a shape curved in its longitudinal direction. Thus, in the present invention, the “plate-like body” is not limited to a flat plate shape, but includes a concept that includes a curved body as a whole.
As the external light blocking member of the present invention, the surface is preferably black for the reasons already described.

On the other hand, the optical address type display medium writing device of the present invention (hereinafter sometimes simply referred to as “the writing device of the present invention”) writes the optical address type display medium for writing an image on the optical address type display medium. A device,
Exposure means for irradiating address light onto a writing side surface of the optical address type display medium;
A louver formed by arranging a plurality of elongated plate-like bodies arranged so that the inclination of the short side thereof is substantially parallel to the traveling direction of the address light, on the writing side of the optical address type display medium. An external light blocking member detachably attached to the surface;
It is characterized by providing.

  According to the writing apparatus of the present invention, when the external light blocking unit is mounted on the writing side surface of the optical address type display medium and the addressing light is irradiated by the exposure unit, the addressing light travels in the traveling direction. The external light, which is scattered light whose traveling direction is not constant, passes through the gap between the external light blocking members that is parallel to the external light blocking member, and hardly passes through the gap between the external light blocking members. As a result, an image having a bright and dark contrast can be formed on the optical address type display medium without being affected by external light.

The writing device of the present invention is particularly effective when the writing side surface of the optical address type display medium to which an image is to be written also serves as the display side surface. When performing from the display side of the optical address type display medium, such as irradiation of a projection image by a small size projector, it is difficult to eliminate the presence of external light. An image having a bright and dark contrast can be formed on the optical address type display medium without being affected.
The plate-like body constituting the external light blocking member preferably has a black surface. By setting it as black, the external light which is scattered light is absorbed without reflecting on the surface of the plate-like body, and the external light is efficiently shielded by the external light blocking member.

In the writing apparatus of the present invention, as the optical address type display medium to be written, as a suitable material, at least according to the phase state of the liquid crystal contained between a pair of electrode layers whose display side is transparent. In this case, a display layer that reflects light and a photoconductive layer that absorbs light in a specific wavelength region and changes a resistance value according to the amount of the absorbed light are stacked. It is desirable that the writing device of the invention further includes voltage applying means for applying a voltage between the pair of electrode layers. The liquid crystal contained in the display layer is preferably a cholesteric liquid crystal, and the display layer is preferably formed by dispersing the cholesteric liquid crystal in a polymer. The photoconductive layer is preferably made of an organic photoconductor.
In the writing apparatus of the present invention, the light source may be a point light source such as a projector or a surface light source.

According to the present invention, by using the external light blocking member characteristic of the present invention that can block scattered light, even in the presence of external light, the display image that is formed is favorable without being affected by it. It is possible to provide a writing method and a writing apparatus for an optical address type display medium capable of obtaining a high contrast.
In addition, the present invention can provide an external light blocking member suitable for use in a writing method of an optical address type display medium capable of forming a display image with good contrast.

Hereinafter, the present invention will be specifically described with reference to preferred embodiments.
FIG. 1 is a schematic configuration diagram of an embodiment which is an exemplary aspect of a system to which a writing method of an optical address type display medium of the present invention is applied. The system of this embodiment is roughly divided into a display medium (optical address type display medium) 1, a power supply device (voltage applying means) 17, a projector (exposure means) 18, and an external light blocking sheet (external light blocking member). 2 is composed of two components of a writing device (a writing device for an optical address type display medium). Both of these components will be described in detail before the operation thereof will be described.

<Display medium>
In the present embodiment, as the display medium (optical address type display medium) 1, a display side and a writing side are illustrated on the same surface. The display medium 1 is formed by laminating a transparent substrate 3, an electrode layer 5, a display layer 7, a laminate layer 8, an OPC layer (photoconductive layer) 10, an electrode layer 6 and a substrate 4 in this order from the display surface side. is there.

(substrate)
The transparent substrate 3 and the substrate 4 are members for the purpose of holding each functional layer on the inner surface and maintaining the structure of the display medium. The transparent substrate 3 and the substrate 4 are sheet-shaped objects having strength that can withstand external forces, and the transparent substrate 3 on the display surface side has a function of transmitting at least incident light and address 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.

(Electrode layer)
The electrode layers 5 and 6 are members for the purpose of uniformly applying the bias voltage applied from the power supply device 17 to each functional layer in the display medium. The electrode layers 5 and 6 have surface-uniform conductivity, and the display-side electrode layer 5 has a function of transmitting at least incident light and 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 invention, address light can be incident from the display side. In this case, the non-display side electrode (the electrode layer 6 in this embodiment) may not be transparent.

(Display layer)
In the present invention, the display layer has a function of modulating a reflection / transmission state of specific color light 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, the display layer is not particularly limited as long as it has a function of reflecting light. For example, if a phase change of liquid crystal is used, a vertically aligned nematic liquid crystal, a parallel aligned nematic liquid crystal, a twisted nematic liquid crystal, Super twisted nematic liquid crystal, surface-stabilized ferroelectric liquid crystal, etc., which uses a change in polarization state, such as a polymer dispersion type liquid crystal, etc., which uses a change in light scattering state, light from guest host liquid crystal, etc. Various liquid crystal elements having different optical effects can be used, such as those using a change in absorption state and those using a change in optical interference state such as cholesteric (chiral nematic) liquid crystal. In the present embodiment, the last one is illustrated.

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 crystal, and display methods other than liquid crystal may be used. It does not matter.

  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, an optically active material (for example, 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. 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.

  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 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.

  The polymer matrix has a function of holding cholesteric liquid crystal and suppressing the flow of liquid crystal (change in image) due to deformation of the display medium, and does not dissolve in the liquid crystal material and does not dissolve in the liquid crystal. The polymer material is preferably used. In addition, the polymer matrix is desirably a material that has strength to withstand external force and exhibits high transparency to at least reflected light and 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. An alternating current (AC) operation is possible, and it is desirable to drive symmetrically with respect to the address light. The charge generation layer (CGL) is formed in a three-layer structure in which a charge transport layer (CTL) is stacked above and below. In this embodiment, as the OPC layer 10, an upper charge generation layer 13, a charge transport layer 14, and a lower charge generation layer 15 are laminated in order from the upper layer in FIG. 1.

  The charge generation layers 13 and 15 are layers having a function of absorbing address light and generating optical carriers. The charge generation layer 13 mainly uses the amount of light carriers flowing in the direction from the electrode layer 5 on the display surface side to the electrode layer 6 on the writing surface side, and the charge generation layer 15 generates the electrode on the display surface side from the electrode layer 6 on the writing surface side. The amount of optical carriers flowing in the direction of the layer 5 influences each. 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 include 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, Condensed aromatic pigments such as dibromoanthanthrone, cyanine dyes, xanthene pigments, charge transfer complexes such as polyvinylcarbazole and nitrofluorene, kyosho complexes consisting of pyrylium salt dyes and polycarbonate resins) 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 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.

(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 adhere the display layer 7 and the OPC layer 10 (charge generation layer 13) 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.

<Writing device>
In this embodiment, the writing device (drive device for the optical address type display medium) is a device for writing an image on the display medium 1, a projector (exposure means) 18 that irradiates the display medium 1 with address light, and a display. A power supply device (voltage applying means) 17 for applying a voltage to the medium 1 and an external light blocking sheet (external light blocking member) 2 are main components, and a control circuit (not shown) for controlling this operation is arranged. .

(projector)
The projector (exposure means) 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 (specifically, on the OPC layer) based on an input signal from the control circuit. If it can irradiate a desired optical image pattern (spectrum, intensity, spatial frequency), it will not be restrict | limited.

The address light irradiated by the projector 18 is preferably selected under the following conditions.
Spectrum: It is preferable that the energy in the absorption wavelength region of the OPC layer 10 is 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 emitted by the projector 18 is desirably light having a peak intensity in the absorption wavelength region of the OPC layer 10 and a bandwidth as narrow as possible.

  The projector 18 in the present embodiment has a laser diode (LD) as a light source and is a small size that can be carried and carried, and includes a light control element (light control layer) that converts uniform light into an image. Built-in and configured to project an image directly.

In the writing apparatus of the present invention, the exposure means is not limited to the projector type. Specifically, including the projector type, the following may be mentioned.
(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)

  In the case of using an exposure means that does not incorporate a light control member, there is no problem with a configuration that converts light from the projector 501 into address light in the light control layer 504 as described with reference to FIG. Can be used. In this case, specific examples of the light control layer that can be used include “um film” manufactured by Nippon Sheet Glass Um Products.

(Power supply)
The power supply device (voltage applying means) 17 has a function of applying a predetermined bias voltage to the display medium 1, and a desired voltage is applied to the display medium (between each electrode) based on an input signal from a control circuit (not shown). Any device capable of applying a waveform may be used. However, AC output is possible and a high slew rate is required. As the power supply device 17, for example, a bipolar high voltage amplifier or the like can be used.

Application of a voltage to the display medium 1 by the power supply device 17 is performed between the electrode layer 5 and the electrode layer 6 via the contact terminals 19 and 20.
Here, the contact terminals 19 and 20 are members that contact the power supply device 17 and the display medium 1 (electrode layers 5 and 6) and conduct both of them, have high conductivity, and have electrode layers 5 and 6. And a thing with small contact resistance with the power supply device 17 is selected. It is preferable that the display medium 1 and the power supply device 17 have a structure that can be separated from either or both of the electrode layers 5 and 6 and the power supply device 17 so that the display medium 1 and the power supply device 17 can be separated.

  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.

(Control circuit)
A control circuit (not shown) includes a power supply device 17 and a projector 18 in accordance with 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). This is a member having a function of appropriately controlling the operation. 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.

(External light blocking sheet)
An external light blocking sheet (external light blocking member) 2 that is characteristic of the present invention and is arranged on the display side surface of the display medium 1 is a louver-like object in which a plurality of elongated plates are arranged. In FIG. 2, the typical perspective view of the external light shielding sheet 2 used for this embodiment is shown. As shown in FIG. 2, in the external light blocking sheet 2, a plurality of plate-like bodies 12a are arranged.

  Note that the size and density of the plate-like bodies 12a, the distance between the plate-like bodies 12a, and the like are greatly changed as compared with actual objects for easy explanation. In other words, the plate-like body 12a is more slender and the long part is overwhelmingly longer than the short side, but for the sake of easy explanation, the length of the short side is drawn longer and the density is also overwhelmingly smaller. In addition, the distance between the plate-like bodies 12a is increased. Hereinafter, the same applies to the drawings for explaining the external light blocking sheet (external light blocking member).

  FIG. 3 shows only the plate-like body 12a. 4 is a cross-sectional view taken along the line AA in FIG. As can be seen from FIGS. 3 and 4, the external light blocking sheet 2 is formed by arranging a plurality of slanted plate-like bodies 12 a inclined in a louver shape (blind shape) in parallel. As shown in FIG. 4, the inclination of the plate-like body 12a is such that the short side of the plate-like body 12a is parallel to the traveling direction of the address light (light irradiated by the projector 18 in FIG. 1). It has become an angle.

  In the present embodiment, as shown in FIG. 1, the address light is emitted not diagonally above the display medium 1 but obliquely from a slightly shifted position, so that the plate-like body 12a is inclined obliquely. However, in the present invention, as the external light blocking member, the plate-like body does not always have to be inclined obliquely.

  FIG. 5 is an illustration of another external light blocking sheet (external light blocking member), and shows a cross-sectional view seen from the same direction as FIG. As described above, when the address light is applied to the external light blocking sheet from the vertical direction, the short side of the plate-like body 12b is also parallel to this, so that it is arranged perpendicular to the surface of the external light blocking sheet. It will be in the state.

  By the way, when the addressing light is parallel light, such as when the light source of the exposure means is a surface light source, or when the light source of the exposure means is sufficiently away from the external light blocking sheet, the address light is considered to be substantially parallel light. In the case of thinning, there is no problem when the plate-like bodies 12a and 12b are arranged in parallel as shown in FIGS. 4 and 5, but the light source of the exposure means is a point light source and external light When the distance from the blocking sheet (and the optical address type display medium) is short, the address light diffuses radially and is not parallel light, so the plate-like body arranged along the traveling direction of the address light The inclination is not constant and the plate-like bodies are not arranged in parallel.

  FIG. 6 illustrates an external light blocking sheet (external light blocking member) when the light source of the exposure unit is a point light source and the distance from the external light blocking sheet is short. FIG. 6 is a cross-sectional view of only the plate-like body 12c extracted from the same direction as FIG. 4, and the light source is included in the drawing in order to explain the positional relationship with the light source.

  As shown in FIG. 6, when the light source 9 is a point light source and the distance from the external light blocking sheet is short, the address light travels radially, and the address is increased as the irradiated position is farther from the light source 9. The inclination of light increases. Therefore, the inclination of the plate-like body 12c whose short side is substantially parallel to the traveling direction of the address light is increased as the distance from the light source 9 increases.

  In this case, the external light blocking sheet exhibits an array state in which the plate-like bodies are characteristic even in a plan view. FIG. 7 is a perspective view of an external light blocking sheet (external light blocking member) 2 ′ illustrated by extracting only the plate-like body 12 c in FIG. 6. As shown in FIG. 7, the plate-like body 12 c is curved in the longitudinal direction (long side) and has an annual ring shape as a whole. This is because the inclination of the address light is determined in accordance with the distance from the light source 9 on the surface of the external light blocking sheet 2 ′. Therefore, when the plate-like body 12c is formed at the same inclination at the same distance, the plate inevitably becomes a plate. This is because the shape of the cylindrical body 12c is curved.

  However, in the external light blocking sheet (external light blocking member), it is necessary to bend the plate-shaped body when the light source of the exposure means is a point light source and the distance from the external light blocking sheet is short Moreover, it is not required so much depending on the density of the plate-like body, the length of the short side, the shielding performance of the external light to be obtained, and the like. Therefore, in the present invention, the short side of the plate-like body is not required to be completely parallel to the traveling direction of the address light, and allows a certain width. In the present invention, the relation between the traveling direction of the address light and the short side of the plate-like body is expressed as “substantially parallel” instead of “parallel”.

  In the relationship between the traveling direction of the address light and the short side of the plate-like body, how much width is allowed from the parallel state depends on the density of the plate-like body, the length of the short side, the shielding performance of the external light to be obtained, and the address Since it varies greatly depending on the intensity of light, it cannot be generally stated. More specifically, it is desired that the address light does not hinder the progress of the address light, and it does not matter if the writing of the optical address type display medium is not hindered.

  The material of the plate-like body 12 is not particularly limited, and any material can be used, but various plastics and paper are preferable from the viewpoint of moldability. Further, in order to prevent scattering / transmission due to reflection of external light, the surface of the plate-like body 12 is desirably black. As a method of making the surface of the plate-like body 12 black, the material constituting the plate-like body 12 itself may be black, or the surface may be covered with a black layer. The black layer can be formed by applying a black paint or dye.

The external light blocking sheet (external light blocking member) 2 may be molded by filling a gap between the plate-like bodies 12 with a transparent filler. By filling with a filler, shape retainability can be imparted and it can be handled as a sheet.
Moreover, the surface and / or the back surface of the external light shielding sheet 2 can be covered with a transparent cover material regardless of whether or not the gap between the plate-like bodies 12 is filled with a transparent filler. By covering with a transparent cover material, shape retention can be imparted, as well as damage, scratches, and the like due to external impacts can be prevented.
The material that can be used as the filler or cover material as described above is not particularly limited as long as it has transparency, and various plastic materials and glass can be used without problems, but from the viewpoint of moldability and transparency. Polyethylene terephthalate is most preferable.

  In the present embodiment, only one sheet of external light blocking sheet 2 is used, but two or more sheets may be used on condition that the inclined direction of the plate-like body 12 is aligned. When two or more external light shielding sheets 2 are used in an overlapping manner, the shielding property of the external light is improved, but the transmission property of the address light inevitably decreases. Therefore, it may be selected as appropriate according to the desired degree of shielding of external light and the degree of transparency of address light.

  In the case of the inclination of the plate-like body 12b as shown in FIG. 5, that is, the address light applied to the external light blocking sheet (and the optical address type display medium) travels perpendicularly to these. As the external light blocking sheet, a commercially available viewing angle adjusting film (for example, “(trade name) light control film” manufactured by Sumitomo 3M Limited) can be used as it is.

<Operation>
In this embodiment, as described above, a liquid crystal layer of a self-holding type liquid crystal composite made of cholesteric liquid crystal and transparent resin is formed as the display layer 7.
The planar phase exhibited 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. 8A, 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. 8B, 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 is unwound as shown in FIG. 8C. 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 pulse signal is applied exhibits a switching behavior as shown in FIG. 9, and when the voltage of the applied pulse signal is equal to or higher than Vfh, the selective reflection 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 application is continued, that is, a selective reflection state due to the planar phase or a transmission state due to the focal conic phase. Become.

  In the figure, the vertical axis represents the normalized reflectance, and the reflectance is normalized with the maximum reflectance being 100 and the minimum 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, the case where the normalized reflectance is 50 or more is the selective reflection state, and the case where the normalized reflectance is less than 50. The transmission state is defined, and the phase change threshold voltage between the planar phase and the focal conic phase is Vpf, and the phase change threshold voltage 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.

  In the display medium 1 according to the present embodiment, by using the bistable phenomenon of the cholesteric liquid crystal, the power supply device 17 determines (A) the selective reflection state by the planar phase and (B) the transmission state by the focal conic phase by the power supply device 17. By switching with the projector 18 while applying a voltage, an image having memory characteristics without an electric field is written and displayed.

  The voltage applied by the power supply device 17 is, for example, a partial pressure between Vpf and Vfh applied to the display layer 7, and the partial pressure applied to the display layer 7 when the projector 18 is irradiated with address light having a predetermined wavelength and intensity. The voltage is set to Vfh or higher. 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.

As shown in FIG. 1, the position of the projector 18 is not directly above the center of the display medium 1 but is shifted laterally. Therefore, the address light is applied to the external light blocking sheet 2 and the display medium 1 slightly obliquely.
However, although not shown because FIG. 1 is a schematic configuration diagram, the position of the projector 18 is sufficiently away from the external light blocking sheet 2 and the display medium 1. Is considered to be parallel (address light is parallel light) and there is no problem.

  In this state, when the address light is selectively irradiated by the projector 18, only the irradiated portion is applied with a partial pressure of Vfh or more, and the phase changes from the focal conic (F) state to the homeotropic (H) state. . Thereafter, when the applied voltage is released, the portion that has been irradiated with the address light and phase-changed 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 present embodiment, for example, by applying a voltage of Vfh or higher and releasing the voltage, the entire surface is set in a planar (P) state in advance, and then writing light having a predetermined wavelength and intensity is irradiated below Vpf. While applying a voltage that is sometimes Vpf or higher to the display layer 7, a phase change that selectively irradiates writing light and changes the phase of the irradiated portion to the focal conic (F) state may be used. . 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.

  Even when the above writing operation is performed in the presence of outside light such as indoors where a fluorescent lamp is lit, the outside light blocking sheet 2 covers the writing side (= display side) surface of the display medium 1, The outside light which is scattered light is shielded by this. On the other hand, the address light from the projector 18 can pass through the gap between the plate-like bodies 12 without difficulty because the short sides of the plate-like bodies 12 in the external light blocking sheet 2 are parallel to the address light.

  As described above, in this embodiment, the external light that inhibits the ON / OFF contrast of the address light is effectively shielded by the external light blocking sheet 2, and the address light basically passes through the external light blocking sheet 2 as it is. Even in the presence of external light, a good contrast can be obtained in the formed display image without being affected by it.

<Functional evaluation test of external light blocking sheet>
Hereinafter, it is confirmed by evaluating the functions of two external light blocking sheets, which are specific examples of the external light blocking member, that the external light blocking member used in the present invention can produce the effect of expressing the effects of the present invention. did. The characteristics of the addressing light intensity of the optical address type display medium were measured, and the conditions of the writing method of the present invention were examined from the function of the external light blocking sheet.

(Evaluation Test 1)
FIG. 10 is an explanatory diagram showing an outline of a set subjected to evaluation test 1. FIG.
The light source of the projector that irradiates address light was set at a position 40 cm above the work table in the laboratory. The light source was set at a position 80 cm away from the nearest indoor fluorescent lamp in plan view. The ceiling height in which the indoor fluorescent lamp is embedded is 180 cm from the work table. The indoor fluorescent lamps are arranged in parallel at a pitch of 200 cm and are also present on the upper right side of the projector in FIG. 10, but are not shown in FIG.

The measurement point A was set on the work table directly under the indoor fluorescent lamp, and the measurement point B was set on the work table just below the light source of the projector. The address light from the light source of the projector was irradiated toward the measurement point A when measuring at the measurement point A and toward the bottom (measurement point B) when measuring at the measurement point B. That is, at the measurement point A, the address light irradiates the measurement point at an angle of 60 ° with respect to the perpendicular from the work table, and at the measurement point B, the address light irradiates the measurement point from a completely vertical direction.
In any measurement point, illumination light (scattered light) from the indoor fluorescent lamp is always irradiated.

  When the sensor unit of the light meter is placed flat on the measurement points A and B, and the external light blocking sheet (external light blocking member) is placed on the measuring point A and B (2), it is left as it is without placing anything. In case (1), the light source of the projector was turned on / off (bright / dark), and the amount of light (measurement frequency: 550 nm) under each condition was measured.

Note that a viewing angle adjusting film (trade name: light control film, visible angle 60 °) manufactured by Sumitomo 3M Limited was used as the external light blocking sheet. In this viewing angle adjusting film, as shown in FIG. 5, the plate-like bodies 12b are arranged perpendicularly to the film surface, and the viewing angle is 60 ° from the length of the short side and the gap between the plate-like bodies 12b. It is the thing adjusted so that it cannot visually recognize from the above direction.
In other words, this means that the external light blocking sheet used has a function of blocking address light and other light in the traveling direction at an angle of 30 ° or more with respect to the perpendicular from the surface.

When the external light blocking sheet is placed (2), the test is performed under two conditions: when the viewing angle adjusting film is one (2-1) and when the two are stacked (2-2). Went.
Table 1 below shows the results of this evaluation test.

  From the result of the measurement point B shown in Table 1, the outside light blocking sheet was not affected enough by the outside light even in the dark, resulting in a considerable amount of light. It can be seen that the influence of external light in the dark can be suppressed by passing the sheet, and the contrast of light and dark is increased. At this time, using two sheets as compared with one outside light blocking sheet increases the contrast of light and darkness, but it is understood that the address light is also lost correspondingly and the amount of light at the time of light is low. .

  On the other hand, from the result of the measurement point A shown in Table 1, even the indoor fluorescent lamp located directly above can be blocked by the external light blocking sheet, and the external light blocking sheet is more than one sheet. It can be seen that a higher effect can be obtained with two sheets. In addition, almost all address light emitted from an oblique angle of 60 ° with respect to the normal of the work table (and the external light blocking sheet) is cut through the external light blocking sheet, and the ON / OFF is changed to the light amount. You can see that it has no effect.

As described above, from the result of the evaluation test 1, the external light shielding sheet in which the plate-like bodies are arranged perpendicular to the sheet surface is effective in shielding the external light, and the address light is effectively transmitted. It was confirmed that high contrast of address light can be realized.
Further, it was confirmed that by overlapping two sheets of external light shielding sheets, the effect of shielding external light is enhanced and high contrast of address light can be ensured, but the amount of address light is reduced. This means that when considering the specifications of the external light blocking member in the present invention, the one with the optimum conditions is selected in consideration of the characteristics of the optical address type display medium to be written, the intensity of address light, the writing environment, etc. It can be said that this contributes to high contrast of the display image.

(Evaluation test 2)
In the set used in the evaluation test 1, the light source of the projector that irradiates the address light is kept at the same angle as the irradiation angle of the address light to the measurement point A (that is, the address light at an angle of 60 ° with respect to the perpendicular from the work table). Was moved to a position where the spatial distance from the measurement point A was 30 cm, and was set for this evaluation test. In addition, the sensor unit of the light meter was placed flat only at the measurement point A.

  The external light blocking sheet (external light blocking member) has the same configuration as the viewing angle adjusting film used in Evaluation Test 1, and only the internal plate-like body is inclined at an angle of 60 ° (the angle, presence or absence of a cover material, etc.) Although different, the product similar to that shown in FIG. 2, FIG. 3 and FIG. When there is an external light blocking sheet (2), the direction of inclination of the plate-like body inside the external light blocking sheet and the direction of the address light from the projector light source coincide with each other on the sensor unit of the light meter. The external light blocking sheet was placed in close contact with the substrate. Only one external light blocking sheet was used.

As in Evaluation Test 1, the projector light source was switched between the case where the external light blocking sheet was placed in close contact with the sensor unit of the light meter (2) and the case where nothing was placed (1). The light amount (measurement frequency: 550 nm) under each condition was measured with ON / OFF (light / dark).
Table 2 below shows the results of this evaluation test.

  From the results shown in Table 2, it was found that there was a considerable amount of light even in the dark without the external light blocking sheet, resulting in a considerable amount of light, and the contrast of light and darkness was not sufficient through the external light blocking sheet. Thus, it can be seen that the influence of external light in the dark can be suppressed, and the contrast of light and dark is as extremely high as about 200/10.

(Evaluation Test 3)
A monochrome display optical address type display medium for this evaluation test was prepared. The display medium has the same configuration as that of the display medium 1 shown in FIG. 1 (hereinafter described using the reference numerals of the constituent members in FIG. 1). Specifically, the display medium has a thickness of 125 μm obtained by sputtering the transparent electrode 5. A paper-like black-and-white display medium was prototyped using the polyethylene terephthalate film as the transparent substrate 3 and similarly the substrate 4. Light-green and pink cholesteric liquid crystal microcapsules (average particle size 8μm) with polyurethane / urea shells made by interfacial polymerization of polyisocyanate monomer are prepared and mixed in equal amounts to a thickness of about 35μm with a water-soluble polymer binder. The black and white display layer 7 was produced by coating. On the other hand, as an organic photoconductive layer, a charge generation layer (upper CGL13, lower CGL15) of about 0.2 μm thick phthalocyanine pigment, and an 8 μm thick charge transport layer in which a benzidine hole transport material is dispersed in a polycarbonate binder ( CTL14) was laminated. The laminate layer 8 was applied thereon and bonded to the display layer, whereby the display medium 1 was obtained.

  For this display medium 1, while changing the exposure intensity (light quantity) while applying a voltage (a voltage of Vpf or more and Vfp or less in FIG. 9) such that the cholesteric liquid crystal in the display layer 7 is aligned in the focal conic phase, The normalized reflectance of the display image finally obtained was measured using an integrating sphere spectrometer (CM 2002, manufactured by Konica Minolta). 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%.

When the voltage applied to the display layer 7 is over a threshold voltage (Vfp in FIG. 9), the cholesteric liquid crystal in the display layer 7 changes to the homeotropic phase, and when the voltage application is canceled, the planar Since the phase changes to the phase, the reflectance is improved.
The measurement results are shown in a graph in FIG.

If exposure intensity is 10 .mu.W / cm ² or less, around but the surface of the display side of the display medium 1 remained black, beyond which gradually improves the reflectance, in excess of 100 .mu.W / cm ² Almost saturated. From this, the display medium 1 subjected to this evaluation test has an exposure intensity exceeding 100 μW / cm ² when address light is irradiated (bright) and when address light is not irradiated (dark). It has been found that a display image with good contrast can be obtained when the light and dark contrast state is such that the exposure intensity is 10 μW / cm ² or less. Since the brightness is 100 to 300 μW / cm ² under a normal office environment, if the display medium 1 is written as it is without shielding external light under the office environment, a black float appears in the display image. Presumed to be.

(Write to display media)
Based on the results of the evaluation test 3, the results of the above-described evaluation tests 1 and 2 (Tables 1 and 2) show that the external light shielding sheet is overlapped at the measurement point B in the evaluation test 1 and the evaluation test. It can be seen that, in the case where there is an external light blocking sheet in No. 2, the conditions can be written as it is without blocking external light.

  Under both conditions, the external light blocking sheet is disposed in close contact with the display-side surface of the display medium 1, and the light source of the projector is turned on / off while applying a predetermined voltage, thereby irradiating / non-irradiating address light. When a display image was obtained by selecting, an image with good contrast was obtained under any conditions.

It is a schematic block diagram of embodiment which is an exemplary aspect of the system to which the writing method of the optical address type display medium of this invention is applied. It is a typical perspective view of the external light blocking sheet (external light blocking member) in FIG. It is the perspective view which extracted and represented only the plate-shaped object from the external light shielding sheet typically shown in FIG. It is AA arrow sectional drawing in FIG. FIG. 5 is an illustration of another external light blocking sheet (external light blocking member), and is a cross-sectional view taken out from the same direction as in FIG. Furthermore, it is an illustration of the other external light shielding sheet (external light shielding member), Comprising: Only the plate-shaped object was extracted and it is sectional drawing seen from the same direction as FIG. FIG. 7 is a perspective view of an external light blocking sheet (external light blocking member) illustrated in FIG. 6. 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 explanatory drawing which shows the outline | summary of the set used for the evaluation test 1. FIG. 7 is a graph showing the results of evaluation test 3. It is a schematic diagram showing a mode that the image is written in the optical address type display medium by the exposure apparatus by the conventional technique of writing from the back side on the display side.

Explanation of symbols

  1: display medium (optical address type display medium), 2: external light blocking sheet (external light blocking member), 3: transparent substrate, 4: substrate, 5, 6: electrode layer, 7: display layer, 8: laminate layer 9: light source (exposure means), 10: OPC layer (photoconductive layer), 12: plate-like body, 13, 15: charge generation layer, 14: charge transport layer, 17: power supply device (voltage application means), 18 : Projector (light source / exposure means) 19, 20: Contact terminal, 501: Projector, 502: Voltage application unit, 503: Display medium, 504: Light control layer

Claims (9)

An optical address type display medium writing device for writing an image by irradiating an optical address type display medium with address light from a light source,
Exposure means for irradiating address light onto a writing side surface of the optical address type display medium;
The traveling direction of the address light, the plate-like body elongated inclined short side was arranged substantially in parallel is at louvered formed by arraying a plurality of write side of the optical address type display medium An external light blocking member detachably attached to the surface ,
The light source is a point light source, and the external light blocking member is formed in an annual ring shape along the irradiation light from the point light source, and a gap between adjacent external light blocking members is A writing device for an optical address type display medium, which is filled with a transparent filler . 2. The optical address display medium writing device according to claim 1 , wherein a writing side surface of the optical address display medium to which an image is to be written also serves as a display side surface. Surface of the plate body constituting the external light shielding member is writing device optically addressable display medium according to claim 1 or 2, characterized in that it is black. The optical address type display medium to which an image is to be written includes at least a display layer that reflects light in accordance with a phase state of liquid crystal contained between a pair of electrode layers that are transparent at least on the display side, and a specific wavelength range And a photoconductive layer that changes the resistance value according to the amount of the absorbed light and is sandwiched and laminated,
Moreover, the writing apparatus optical address type display medium according to any one of claims 1 to 3, characterized in that it comprises a voltage applying means for applying a voltage to the pair of electrode layers. 5. The optical address type display medium writing device according to claim 4 , wherein the liquid crystal contained in the display layer is cholesteric liquid crystal. 6. The optical address type display medium writing device according to claim 5 , wherein the display layer is formed by dispersing the cholesteric liquid crystal in a polymer. Writing device optically addressable display medium according to any one of claims 1 to 6, wherein said photoconductive layer is characterized by comprising an organic photoconductor. The exposure means, the writing device optically addressable display medium according to any one of claims 1 to 7, characterized in that a point light source. The exposure means, the writing device optically addressable display medium according to any one of claims 1 to 8, characterized in that a surface light source.

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