JP2008209742A - Optical writing display medium, optical writing device, and optical writing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent degradation in display image quality based on degradation in a photoconductive layer with time caused by irradiation with reading light for browsing, in an optical writing display medium in which information is written from the browsing face side. <P>SOLUTION: The optical writing display medium 10 includes a display layer 18, the optical characteristics of which selectively vary according to applied voltage and which selectively transmits or reflects incident visible light; a photoconductive layer 26, the electrical resistance of which varies according to the irradiation of visible light, in a first wavelength region in the visible light having a predetermined wavelength range passed through the display layer 18; and a selective transmissive layer 20 which transmits a visible light, having a wavelength contained in the first wavelength region passed through the display layer 18 and which absorbs visible light in a second wavelength region, having a wavelength at least other than the first wavelength region. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical writing type display medium, an optical writing device, and an optical writing method.

  In recent years, electronic paper for the purpose of temporarily browsing electronic information has attracted attention as a display medium. One of the electronic papers is an optical writing type. Optical writing type electronic paper is configured by laminating a display layer made of, for example, liquid crystal and a photoconductive layer whose electrical resistance is changed by light, in which a display state is maintained even in a non-powered state. Such optically writable electronic paper includes one that forms an image by irradiating light from the viewing surface side and one that forms an image by irradiating light from the opposite side (back side) of the viewing surface. is there. In Patent Documents 1 and 2, as electronic paper for color, when writing light is irradiated from the back side, the absorption wavelength region of the photoconductive layer corresponding to each color and transmission of reading light incident from the viewing surface side are disclosed. The relationship with the wavelength region is disclosed.

JP 2003-140184 A JP 2004-198949 A

  An object of the present invention is to prevent deterioration of display image quality due to deterioration of a photoconductive layer over time due to reading light irradiation for viewing in an optical writing display medium written from the viewing surface side. is there.

According to the first aspect of the present invention, the optical characteristics selectively change according to the applied voltage, and a display layer that selectively transmits or reflects incident visible light, and a predetermined range of light transmitted through the display layer. Of visible light having a wavelength, a photoconductive layer whose electrical resistance changes in response to irradiation of visible light in the first wavelength region, and visible light having a wavelength included in the first wavelength region transmitted through the display layer And a selective transmission layer that absorbs visible light in a second wavelength region having a wavelength other than at least the first wavelength region.
Here, “transmission” means that 50% or more of the incident light is transmitted, and “absorption” means that 50% or more of the incident light is absorbed.

  The present invention according to claim 2 is the optically writable display medium according to claim 1, wherein the display layer is composed of cholesteric liquid crystal.

  The present invention according to claim 3 is the optically writable display medium according to claim 1 or 2, wherein the color of the first wavelength region and the color of the second wavelength region are in a complementary color relationship.

  The present invention according to claim 4 is the photo-writing display medium according to claim 3, wherein the photoconductive layer uses a phthalocyanine pigment as a charge generating material, and the selective transmission layer transmits a red component as a first component. is there.

  According to a fifth aspect of the present invention, the photoconductive layer uses a dibromoanthanthrone pigment as a charge generating substance, and the selective transmission layer transmits a blue component as a first component. It is a medium.

  The present invention according to claim 6 further comprises a light absorption layer that is disposed on the opposite side of the photoconductive layer from the display layer and absorbs light transmitted through the photoconductive layer. This is an optical writable display medium.

  The present invention according to claim 7 is the optically writable display medium according to any one of claims 1 to 6, wherein the selective transmission layer is formed by bonding the display layer and the photoconductive layer. .

  The present invention according to claim 8 further includes an adhesive layer for bonding the display layer and the selective transmission layer, and the selective transmission layer prevents isolation of components of the adhesive layer to the photoconductive layer. The optically writable display medium according to claim 1, comprising performance.

  The present invention according to claim 9 further includes a pair of electrode layers disposed so as to sandwich at least the display layer and the photoconductive layer, and at least the electrode layer on the display layer side is visible among the pair of electrode layers. The optically writable display medium according to any one of claims 1 to 8, which transmits light.

  According to a tenth aspect of the present invention, there is provided a voltage applying means for applying a voltage to the display layer and the photoconductive layer of the optically writable display medium according to the first aspect, and light in the first wavelength region as a component. An optical writing device having a light emitting device that generates visible light.

  According to an eleventh aspect of the present invention, the optically writable display medium further includes a pair of electrode layers disposed so as to sandwich at least the display layer and the photoconductive layer, and the voltage applying unit includes the pair of voltage layers. 11. The optical writing device according to claim 10, wherein a voltage is applied to the electrode layer, and at least the electrode layer on the notation layer side of the pair of electrode layers transmits visible light.

  The present invention according to claim 12 has a display layer whose optical characteristics are selectively changed according to an applied voltage, selectively transmitting or reflecting incident visible light, and a predetermined range of light transmitted through the display layer. Of visible light having a wavelength, a photoconductive layer whose electrical resistance changes in response to irradiation of visible light in the first wavelength region, and visible light having a wavelength included in the first wavelength region transmitted through the display layer And a selective transmission layer that absorbs visible light in a second wavelength region having a wavelength other than at least the first wavelength region, and prepares an optical writable display medium of the optical writable display medium. In this optical writing method, visible light including a first wavelength region as a component is applied while a voltage is applied to the display layer and the photoconductive layer.

  According to the first aspect of the present invention, it is possible to prevent display image quality from being deteriorated due to deterioration of the photoconductive layer over time due to irradiation of reading light for viewing.

  According to the second aspect of the present invention, in addition to the effect of the first aspect of the present invention, an image can be stored without applying a voltage to the display layer.

  According to the third aspect of the present invention, in addition to the effect of the present invention according to the first or second aspect, the color of the portion that has passed through the display layer can be adjusted to approach black.

  According to the present invention according to claim 4, in the present invention according to claim 3, when the phthalocyanine pigment is used for the photoconductive layer, the color of the portion that has passed through the display layer is adjusted to be closer to black. Can do.

  According to the present invention according to claim 5, in the present invention according to claim 3, when the dibromoanthanthrone pigment is used for the photoconductive layer, the color of the portion transmitted through the display layer is adjusted so as to be closer to black. can do.

  According to the sixth aspect of the present invention, in addition to the effect of the present invention according to any one of the first to fourth aspects, the transmitted light is transmitted to the back side as compared with the case where the light absorbing layer that absorbs light is not provided. An optically writable display medium having a large white / black contrast ratio can be easily obtained without providing a separate absorbing member.

  According to the present invention of claim 7, in addition to the effects of the present invention of any of claims 1 to 6, the structure is simplified compared to the case where the selective transmission layer and the adhesive layer are formed separately. can do.

  According to the eighth aspect of the present invention, in addition to the effect of the present invention according to any one of the first to sixth aspects, the structure is simplified as compared with the case where the selective transmission layer and the isolation layer are formed separately. can do.

  According to the ninth aspect of the present invention, in addition to the effect of the present invention according to any one of the first to eighth aspects, the optical writing type display medium can be used for optical writing as compared with the case where no electrode layer is provided. Need not be sandwiched between the electrodes, and image formation can be simplified.

  According to the tenth aspect of the present invention, there is provided an optical writable display medium capable of preventing display image quality deterioration due to deterioration of a photoconductive layer over time due to reading light irradiation for viewing. An optical writing device capable of forming an image can be provided.

  According to the eleventh aspect of the present invention, in addition to the effect of the present invention according to the tenth aspect, an electrode for applying a voltage is separately provided compared to the case where the optically writable display medium does not have an electrode layer. Since it is not necessary to provide the optical writing device, the configuration can be simplified.

  According to the present invention of claim 12, there is provided an optical writable display medium capable of preventing display image quality deterioration due to deterioration of a photoconductive layer over time due to reading light irradiation for viewing. An optical writing method capable of forming an image can be provided.

Next, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic view showing an optical writing type display medium 10 and an optical writing device 12 according to the first embodiment of the present invention.
The optical writing type display medium 10 is, for example, flexible electronic paper, and an image is displayed on one surface and writing light corresponding to the displayed image is incident. One surface is referred to as a viewing surface, and the other surface is referred to as a back surface.

  In this embodiment, the optical writable display medium 10 includes the first substrate 14, the first electrode layer 16, the display layer 18, the selective transmission layer 20, the adhesive layer 22, the isolation layer 24, the light from the viewing surface side. The conductive layer 26, the light absorption layer 28, the second electrode layer 30, and the second substrate 32 are configured.

  The first substrate 14 and the second substrate 32 are made of an insulating material, and are made of, for example, glass, silicon, or a polymer film such as polyethylene terephthalate, polysulfone, polyethersulfone, or polycarbonate. The first substrate 14 is transmissive to writing light and reading light. The second substrate 22 may be formed from the same material as the first substrate 14, but may be formed from another material and does not necessarily have transparency to the writing light and the reading light.

The first electrode layer 16 and the second electrode layer 30 are made of a conductive material so as to sandwich the display layer 18 and the photoconductive layer 26 and apply a voltage to the display layer 18 and the photoconductive layer 26. . That is, the first electrode layer 16 and the second electrode layer 30 are made of a metal thin film such as gold or aluminum, a metal oxide such as indium oxide or tin oxide, or a conductive organic polymer such as polypyrrole, polyacetylene, or polyaniline. Become. The first electrode layer 16 is transmissive to writing light and reading light. The second electrode layer 30 may be formed of the same material as the first electrode layer 16, but may be formed of other materials and is not necessarily transparent to the writing light and the reading light. Absent.
A pulse voltage is applied between the first electrode layer 16 and the second electrode layer 30 from a voltage application unit 34 of the optical writing device 12 described later.
As another embodiment, the first electrode layer 16 and the second electrode layer 30 can be provided on the optical writing device 12 side instead of being provided on the optical writing display medium 10. In addition, either the first electrode layer 16 or the second electrode layer 30 can be provided on the optical writing type display medium 10 and the other can be provided on the optical writing device 12 side.

  The display layer 18 selectively changes its optical characteristics in accordance with an applied voltage and selectively transmits or reflects incident visible light. For example, a liquid crystal is used. Liquid crystals include vertical alignment nematic liquid crystal, parallel alignment nematic liquid crystal, twist nematic liquid crystal, super twist nematic liquid crystal, surface-stabilized ferroelectric liquid crystal, etc. Various liquid crystals with different optical effects, such as a method using a change in state, a method using a change in the light absorption state of a guest-host liquid crystal, or a method using a change in the light interference state of a cholesteric (chiral nematic) liquid crystal An element can be used.

  In this embodiment, the display layer 18 uses cholesteric liquid crystal. However, in addition to the structure consisting only of cholesteric liquid crystals, a structure containing a network polymer in the continuous phase of the liquid crystal, a structure in which the liquid crystal is dispersed in the form of droplets in a polymer binder skeleton, and the liquid crystal is wrapped in a polymer shell. A microencapsulated structure or a structure in which microencapsulated liquid crystal is dispersed in a polymer binder skeleton can be employed.

  Cholesteric liquid crystals include steroidal cholesterol derivatives or chiral components made of optically active materials such as Schiff bases, azos, esters or biphenyls, and Schiff bases, azos, azoxys, benzoates, biphenyls. Terphenyl, cyclohexylcarboxylic acid ester, phenylcyclohexane, biphenylcyclohexane, pyrimidine, dioxane, cyclohexylcyclohexane ester, cyclohexylethane, cyclohexane, tolan, alkenyl, stilbene, condensed polycycle A material added to a nematic liquid crystal, a smectic liquid crystal, or a mixed liquid crystal thereof can be used, and the dielectric anisotropy is configured to be positive.

  Cholesteric liquid crystal with positive dielectric anisotropy is a planar crystal whose spiral axis is almost perpendicular to the cell surface and causes the above-mentioned selective reflection phenomenon with respect to incident light. The spiral axis is almost parallel to the cell surface and incident. Three states are shown: a focal conic that transmits light while being slightly scattered forward, and a homeotropic structure in which a helical structure is unwound and the liquid crystal director is directed in the direction of the electric field and transmits incident light almost completely.

  Of these three states, the planar and focal conic can exist bistable with no voltage. Therefore, the alignment state of the cholesteric liquid crystal is not uniquely determined with respect to the applied voltage, and when the initial state is planar, it changes in the order of planar, focal conic, and homeotropic as the applied voltage increases. When the initial state is focal conic, it changes in the order of focal conic and homeotropic as the applied voltage increases. On the other hand, when the applied voltage is suddenly reduced to zero, the planar and focal conic remain as they are, and the homeotropic changes to the planar.

FIG. 2 is a schematic diagram showing the optical characteristics of the cholesteric liquid crystal immediately after the pulse voltage is applied.
In FIG. 2, the vertical axis represents the normalized reflectance normalized with the maximum reflectance being 100 and the minimum reflectance being 0, and the horizontal axis is the applied pulse voltage. The curve indicated by the solid line in the figure represents the optical characteristics of the cholesteric liquid crystal immediately after the pulse voltage is applied. When the applied pulse voltage is equal to or higher than the threshold voltage Vfh, the selective reflection state changes from homeotropic to planar. When the voltage is between the voltage Vpf and the voltage Vfh, the transmission state is caused by focal conic. When the voltage is equal to or lower than the voltage Vpf, the state before the pulse voltage is applied, that is, the selective reflection state by the planar or the transmission state by the focal conic is continued. .

  The selective transmission layer 20 is made of an insulating material, and a wavelength included in a wavelength region (hereinafter sometimes referred to as a predetermined range) in which a photoconductive layer described later exhibits a change in electrical resistance due to light irradiation. The visible light component in the first wavelength region is transmitted, and at least the visible light in the second wavelength region having a wavelength other than the first wavelength region is absorbed. The color of the first wavelength region and the color of the second wavelength region are in a complementary color relationship. This selective transmission layer 20 is made of an inorganic pigment such as cadmium, chromium, cobalt or manganese, or azo, anthraquinone, indigo, triphenylmethane, nitro, phthalocyanine, perylene, pyrrolopyrrole. , Quinacridone-based, polycyclic quinone-based, squalium-based, azurenium-based, cyanine-based, pyrylium-based or anthrone-based organic dyes or organic pigments, or a material in which these are dispersed in a polymer binder.

  The adhesive layer 22 is at least transparent to writing light and is made of an adhesive material such as polyurethane or polyester.

  The isolation layer 24 is at least transparent to writing light, and prevents the photoconductive layer 26 described later from being eluted by the material of the adhesive layer 22. The isolation layer 24 is formed using a water-soluble resin such as a carboxyl group, a sulfonic acid group, an amino group, a hydroxyl group, a polyethylene glycol skeleton, an amide group, or a methylolamine group.

  The photoconductive layer 26 includes, for example, three layers, and has a configuration in which a charge transport layer 266 is provided between the upper charge generation layer 262 and the lower charge shipping layer 264. In the upper charge generation layer 262 and the lower charge generation layer 264, a charge shipping substance is dispersed in a polymer binder. In the charge transport layer 266, a charge transport material is dispersed in a polymer binder.

  As the charge generation material, inorganic materials such as a-Si, ZnS, ZnO, CdS, CdSe, Se, SeTe, or TiO, or phthalocyanine, azo, polycyclic quinone, indigo, quinacridone, perylene, Organic materials such as squalium, azulenium, cyanine, pyrylium, and anthrone can be used.

  As the charge transport material, organic materials such as carbazole, triazole, oxadiazole, imidazole, pyrazoline, hydrazone, stilbene, amine, or nitrofluorenone can be used.

  As the polymer binder, polycarbonate, polyarylate, polyvinyl alcohol (PVA), polyethylene, polypropylene, polyester, polyvinyl acetate, polyvinyl butyral, acrylic, methacryl, vinyl chloride, vinyl acetate, or a copolymer thereof can be used. .

The light absorption layer 28 absorbs light transmitted through the photoconductive layer 26, and is formed of, for example, black and is made of an insulating material. For example, the light absorption layer 28 is formed by dispersing carbon black in a polymer binder.
The light absorbing layer 28 is not necessarily laminated in the optical writable display medium 10, and a background portion that is separate from the optical writable display medium 10 is prepared at the time of reading, and this background portion is optically writable. What is necessary is just to arrange | position to the back surface side of the display medium 10.

  The optical writing device 12 includes a voltage application unit 34, a control unit 36, and a light emitting device 38. The voltage application unit 34 is connected to the first electrode layer 16 and the second electrode layer 30 of the optical writable display medium 10 and applies a pulse voltage to the first electrode layer 16 and the second electrode layer 30.

  The control unit 36 controls the application of the pulse voltage of the voltage application unit 34 and the light emission of the light emitting device 38.

The light emitting device 38 may be any device that can irradiate the optical writing type display medium 10 with arbitrary writing light, such as a laser beam scanning device, a LED array, a CRT display, a plasma display or an EL display, or a liquid crystal shutter. A combination of the light control element and a light source such as a fluorescent tube, a xenon lamp, a halogen lamp, a mercury lamp, or an LED lamp is not particularly limited.
However, in this embodiment, it is configured to emit visible light in the first wavelength region out of visible light having a predetermined range of wavelengths through a filter or the like.

FIG. 3 shows an equivalent circuit diagram of the optical writable display medium 10.
In FIG. 3, the optical writable display medium 10 includes a parallel circuit composed of a resistance R1 of electrode layers 16 and 30, a resistance R2 of a display layer 18 and a capacitance C2, and a resistance R3 and a capacitance C3 of other layers. The parallel circuit and the parallel circuit composed of the resistor R3 and the capacitance C3 of the photoconductive layer 26 are connected in series. The voltage V applied between the electrode layers 16 and 30 from the voltage application unit 34 is divided by the impedance of each circuit. Here, when write light is irradiated from the light emitting device 38 to the photoconductive layer 26, the resistance value R4 of the photoconductive layer 26 decreases, so that the partial pressure V2 applied to the portion of the display layer 18 irradiated with the write light. Becomes higher than the portion not irradiated with the writing light. Accordingly, the voltage distribution of the display layer 18 changes according to the light amount of the writing light, and the optical state of the display layer also changes according to the voltage distribution. Therefore, the light amount distribution of the writing light is reflected in the reflectance distribution of the reading light. Can be made.

Next, a method for writing an image on the optical writing type display medium 10 using the optical writing device 12 will be described.
First, the optical writing type display medium 10 is set in the optical writing device 12 arranged in a dark room or the like. When the setting of the optical writing medium 10 is completed, the control unit 36 instructs the voltage application unit 34 to apply a pulse voltage between the electrode layers 16 and 30. The pulse voltage applied by the voltage application unit 34 is set so that the partial pressure of the display layer 18 is between Vpf and Vfh. For this reason, the liquid crystal of the display layer 18 becomes a transmissive state by focal conic. Next, the control unit 36 instructs the light emitting device 38 to irradiate the optical writing type display medium 10 with the writing light corresponding to the image. The optical writing light irradiated from the viewing surface side reaches the photoconductive layer 26 through the first substrate 14, the first electrode layer 16, the display layer 18, the selective transmission layer 20, the adhesive layer 22 and the isolation layer 24. When the optical writing light reaches the photoconductive layer 26, the resistance value R4 of the photoconductive layer 26 decreases, so that the partial pressure V2 applied to the portion irradiated with the writing light in the display layer 18 becomes higher than Vfh. , That part changes homeotropic. Next, the control unit 36 instructs the pulse voltage between the electrode layers 16 and 30 to be rapidly reduced to zero. When the pulse voltage between the electrode layers 16 and 30 is abruptly reduced to zero, the portion of the display layer 18 corresponding to the portion irradiated with the writing light changes to a planar portion, and the portion not irradiated with the writing light remains as a focal conic. In this state, image formation is completed. Even if the optical writing type display medium 10 is separated from the optical writing device 12, the liquid crystal state of the display layer 18 is maintained as it is, and an image is stored in the optical writing type display medium 10.

  When the optically writable display medium 10 on which the image is thus formed is irradiated with reading light which is external light, the portion of the display layer 18 in the focal conic state is the first substrate 14 and the first electrode layer 16. The light passes through the display layer 18 and reaches the selective transmission layer 20. The selective transmission layer 20 transmits only the first component, absorbs the second component other than the first component, and reduces the amount of light reaching the photoconductive layer 26. The readout light transmitted through the selective transmission layer 20 further reaches the light absorption layer 28 via the adhesive layer 22, the isolation layer 24, and the photoconductive layer 26, and the readout light is absorbed and appears as black. On the other hand, in the planar state portion of the display layer 18, the readout light is reflected by the display layer 18 and appears white.

  The component of the writing light irradiated from the viewing side of the medium and transmitted through the display layer 18 is subsequently absorbed by the photoconductive layer 26 and further absorbed by the light absorbing layer 28 provided on the back surface thereof, or the light absorbing layer If it does not transmit, the region that was not selectively reflected by the display layer should be displayed in black. However, since a difference in refractive index occurs between the photoconductive layer 26 and the previous layer (isolation layer 24 in this embodiment), part of the readout light is reflected toward the viewing-side substrate. It becomes. If the selective transmission layer 20 is not provided at this time, among the light components transmitted through the display layer 18, the light component having a wavelength that is absorbed by the selective transmission layer 20 is not absorbed and is in front of the photoconductive layer 26. Since the light is reflected by a difference in refractive index between the layers, this color component is a color to the black portion of the readout light. However, by providing the selective transmission layer 20, the light transmitted through the display layer 18 and transmitted through the selective transmission layer 20 includes only the light component having the transmission wavelength of the selective transmission layer 20. For this reason, it is possible to prevent the black portion of the readout light from being tinted.

Further, the operation of the selective transmission layer 20 will be described in detail.
FIG. 4 shows the relationship between the absorption spectrum of the selective transmission layer 20 and the photoconductive layer 26 and the external light spectrum. The selective transmission layer 20 has a low absorptance with respect to the first wavelength region which is a wavelength region near the writing light wavelength (for example, 640 nm), and absorbs with respect to the second wavelength region which is the other wavelength region. The rate is high. On the contrary, the photoconductive layer 26 has a high absorption rate for the first component and a low absorption rate for the second component. The entire optical writable display medium 10 has a high absorptance (low reflectance) for light of any wavelength.
In this embodiment, the selective transmission layer 20 has a high transmittance only with respect to the first component in the wavelength region near 640 nm. Reaching the conductive layer 26 can be prevented.

  FIG. 5 shows an example in which a layer that transmits red is used as the selective transmission layer 20 and a phthalocyanine pigment is used as the charge generation material of the photoconductive layer 26. The wavelength of the writing light is, for example, 640 nm, the selective transmission layer 20 has the writing light absorptance of 0.2 or less, and the photoconductive layer 26 has the writing light absorptance of 0.8 or more.

  FIG. 6 shows an example in which a layer that transmits blue is used as the selective transmission layer 20 and a dibromoanthanthrone (DBA) pigment is used as a charge dispatching material of the photoconductive layer 26. The wavelength of the writing light is, for example, 480 nm, the selective transmission layer 20 has an absorption factor of writing light of 0.5 or less, and the photoconductive layer 26 has an absorption factor of 0.6 or more.

  FIG. 7 shows an optical writable display medium 10 according to the second embodiment. Compared to the first embodiment described above, the selective transmission layer 20 is provided as a layer different from the adhesive layer 22 in the first embodiment. However, in the second embodiment, the selective transmission layer 20 is provided. Is added with an adhesive function, and no single adhesive layer is provided. The permselective layer 22 is made of an adhesive material such as polyurethane or polyester, an inorganic pigment such as cadmium, chromium, cobalt or manganese, or azo, anthraquinone, indigo, triphenylmethane, or nitro. In addition, organic dyes or organic pigments such as phthalocyanine, perylene, pyrrolopyrrole, quinacridone, polycyclic quinone, squalium, azurenium, cyanine, pyrylium, or anthrone are dispersed.

  FIG. 8 shows an optical writable display medium 10 according to the third embodiment. Compared to the second embodiment described above, in the second embodiment, an adhesive function is added to the selective transmission layer 20, whereas in the third embodiment, the selective transmission layer 20 has an isolation function. It is added. The selectively permeable layer 20 is made of a water-soluble resin such as a carboxyl group, a sulfonic acid group, an amino group, a hydroxyl group, a polyethylene glycol skeleton, an amide group or a methylolamine group, and an inorganic pigment such as a cadmium type, chromium type, cobalt type or manganese type. Or azo, anthraquinone, indigo, triphenylmethane, nitro, phthalocyanine, perylene, pyrrolopyrrole, quinacridone, polycyclic quinone, squalium, azurenium, cyanine, pyrylium or An anthrone-based organic dye or organic pigment is dispersed.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples. In the following, “%” means “mass%” and “parts” means “mass parts”.

Example 1:
(Light absorption layer, photoconductive layer and isolation layer)
As the light absorbing layer, an aqueous solution (solid content concentration of 10%) using PVA as a binder, carbon black as a pigment, and a weight ratio of 3: 1 is prepared so that the dry film thickness becomes 2 μm. Formed on the upper charge generation layer and dried at 100 ° C. for 30 minutes.
As a dispersion for the lower charge generation layer, chlorogallium phthalocyanine is used as a charge generation material, polyvinyl butyral is used as a binder resin, the mass ratio of both is 6: 4, and this is dispersed in butanol (concentration 4%) Was prepared. This dispersion was applied onto the charge transport layer by spin coating and then dried to form an upper charge generation layer having a thickness of 0.8 μm.
As a solution for the charge transport layer, a benzidine charge transport material and a binder resin PolyCarbonate bisphenol-Z (poly (4,4′-cyclohexylidene diphenylene carbonate)) are mixed at a mass ratio of 6: 4, respectively. Was dissolved in monochlorobenzene to prepare a 10% solution. A 20% solution was prepared. A charge transport layer having a thickness of 8 μm was formed on the lower charge generation layer using an applicator having a Gap width of 80 μm.

As a dispersion for the upper charge generation layer, chlorogallium phthalocyanine is used as a charge generation material, polyvinyl butyral is used as a binder resin, and the mass ratio of both is 6: 4, which is dispersed in butanol (concentration 2%) Was prepared. This dispersion was applied onto the charge transport layer by spin coating and then dried to form an upper charge generation layer having a thickness of 0.2 μm. Thus, a light absorption layer and a photoconductive layer having a light absorption layer comprising a substrate, a lower charge generation layer, a charge transport layer, and an upper charge generation layer were produced.
Further, an aqueous solution in which 6% of PVA was dissolved was prepared as an isolation layer, which was formed on the upper charge generation layer so as to have a dry film thickness of 1 μm, and dried at 100 ° C. for 30 minutes.

(Substrate, electrode layer and display layer)
The cholesteric liquid crystal was obtained by adding 12.8% of the chiral agent R811 (made by Merck) and 3.2% of the chiral agent R1011 (made by Merck) to the nematic liquid crystal E7 (made by Merck).
To 10 parts of this cholesteric liquid crystal, 1.2 parts of polyisocyanate compound Takenate D-110N (manufactured by Takeda Pharmaceutical Co., Ltd.) and 100 parts of ethyl acetate are added to prepare an oil phase composition, which is made of 1% polyvinyl alcohol. (Poval 217EE: manufactured by Kuraray) It was put into 1000 parts of an aqueous solution, stirred and emulsified to prepare an o / w emulsion having a diameter of about 10 μm. This was heated at 60 ° C. for 3 hours to obtain a microcapsule using polyurethane as a wall material. After the microcapsules were collected by centrifugation, a 12% polyvinyl alcohol (Poval 217C: manufactured by Kuraray) aqueous solution was added to obtain a microcapsule liquid crystal paint.
As a substrate and an electrode layer, the above-mentioned microcapsule liquid crystal paint was applied using a commercially available ITO vapor-deposited PET resin film (Hibeam: manufactured by Toray) to a dry film thickness of 30 μm and dried at 100 ° C. for 30 minutes. Layer and display layer.

(Red selective transmission layer)
As a PVA binder, a red pigment (dioketopyrrolopyrrole) was dispersed and an aqueous solution was prepared so that the weight ratio thereof was 1: 1 (solid content concentration 10%). This red ink was applied on the display layer with an applicator so that the thickness after drying was 2 μm, and dried at 90 ° C. for 30 minutes.

(Adhesive layer)
Next, spin coating is applied to the isolation layer of the substrate on which the photoconductive layer was prepared using the laminating ink in which butyl acetate was used as a solvent and 2-pack urethane adhesive Takelac A50 / A315 (made by Mitsui Chemical Polyurethane) was dissolved. This was applied to form an adhesive layer having a thickness of 5 μm.
Finally, the layers prepared in this manner were stacked and bonded through a laminator heated to 90 ° C. to complete an electronic paper.

Example 2:
(Light absorption layer, photoconductive layer and isolation layer)
As an optical absorption layer, an aqueous solution (solid content concentration 10%) using PVA as a binder, carbon black as a pigment, and a weight ratio of 3: 1 is prepared so that the dry film thickness becomes 2 μm. Formed on the upper charge generation layer and dried at 100 ° C. for 30 minutes.
As a dispersion for the lower charge generation layer, chlorogallium phthalocyanine is used as a charge generation material, polyvinyl butyral is used as a binder resin, the mass ratio of both is 6: 4, and this is dispersed in butanol (concentration 4%) Was prepared. This dispersion was applied onto the charge transport layer by spin coating and then dried to form an upper charge generation layer having a thickness of 0.8 μm.
As a solution for the charge transport layer, a benzidine charge transport material and a binder resin PolyCarbonate bisphenol-Z (poly (4,4′-cyclohexylidene diphenylene carbonate)) are mixed at a mass ratio of 6: 4, respectively. Was dissolved in monochlorobenzene to prepare a 10% solution. A 20% solution was prepared from this solution by dip coating. A charge transport layer having a thickness of 8 μm was formed on the lower charge generation layer using an applicator having a Gap width of 80 μm.

As a dispersion for the upper charge generation layer, chlorogallium phthalocyanine is used as a charge generation material, polyvinyl butyral is used as a binder resin, and the mass ratio of both is 6: 4, which is dispersed in butanol (concentration 2%) Was prepared. This dispersion was applied onto the charge transport layer by spin coating and then dried to form an upper charge generation layer having a thickness of 0.2 μm. Thus, a photoconductive layer comprising a substrate, a lower charge generation layer, a charge transport layer, and an upper charge generation layer was produced.
Further, an aqueous solution in which 6% of PVA was dissolved was prepared as an isolation layer, which was formed on the upper charge generation layer so as to have a dry film thickness of 1 μm, and dried at 100 ° C. for 30 minutes.

(Substrate, electrode layer and display layer)
The cholesteric liquid crystal was obtained by adding 12.8% of the chiral agent R811 (made by Merck) and 3.2% of the chiral agent R1011 (made by Merck) to the nematic liquid crystal E7 (made by Merck).
To 10 parts of this cholesteric liquid crystal, 1.2 parts of polyisocyanate compound Takenate D-110N (manufactured by Takeda Pharmaceutical Co., Ltd.) and 100 parts of ethyl acetate are added to prepare an oil phase composition, which is made of 1% polyvinyl alcohol. (Poval 217EE: manufactured by Kuraray) It was put into 1000 parts of an aqueous solution, stirred and emulsified to prepare an o / w emulsion having a diameter of about 10 μm. This was heated at 60 ° C. for 3 hours to obtain a microcapsule using polyurethane as a wall material. After the microcapsules were collected by centrifugation, a 12% polyvinyl alcohol (Poval 217C: manufactured by Kuraray) aqueous solution was added to obtain a microcapsule liquid crystal paint.
As a substrate and an electrode layer, the above-mentioned microcapsule liquid crystal paint was applied using a commercially available ITO vapor-deposited PET resin film (Hibeam: manufactured by Toray) to a dry film thickness of 30 μm and dried at 100 ° C. for 30 minutes. Layer and display layer.

(Red selective transmission layer and adhesive layer)
Next, using a laminate ink in which diketopyrrolopyrrole is dispersed as a red pigment in a thermoplastic resin using butyl acetate as a solvent, the photoconductive layer is formed on the isolation layer of the substrate by spin coating, and the film thickness is 5 μm. It was set as the adhesive layer.
Finally, the layers prepared in this manner were stacked and bonded through a laminator heated to 90 ° C. to complete an electronic paper.

Example 3:
(Light absorption layer, photoconductive layer and isolation layer)
As an optical absorption layer, an aqueous solution (solid content concentration 10%) using PVA as a binder, carbon black as a pigment, and a weight ratio of 3: 1 is prepared so that the dry film thickness becomes 2 μm. Formed on the upper charge generation layer and dried at 1100 ° C. for 30 minutes.
As a dispersion for the lower charge generation layer, chlorogallium phthalocyanine is used as a charge generation material, polyvinyl butyral is used as a binder resin, the mass ratio of both is 6: 4, and this is dispersed in butanol (concentration 4%) Was prepared. This dispersion was applied onto the charge transport layer by spin coating and then dried to form an upper charge generation layer having a thickness of 0.8 μm.
As a solution for the charge transport layer, a benzidine charge transport material and a binder resin PolyCarbonate bisphenol-Z (poly (4,4′-cyclohexylidene diphenylene carbonate)) are mixed at a mass ratio of 6: 4, respectively. Was dissolved in monochlorobenzene to prepare a 10% solution. A 20% solution was prepared from this solution by dip coating. A charge transport layer having a thickness of 8 μm was formed on the lower charge generation layer using an applicator having a Gap width of 80 μm.

As a dispersion for the upper charge generation layer, chlorogallium phthalocyanine is used as a charge generation material, polyvinyl butyral is used as a binder resin, and the mass ratio of both is 6: 4, which is dispersed in butanol (concentration 2%) Was prepared. This dispersion was applied onto the charge transport layer by spin coating and then dried to form an upper charge generation layer having a thickness of 0.2 μm. Thus, a photoconductive layer comprising a substrate, a lower charge generation layer, a charge transport layer, and an upper charge generation layer was produced.
Further, an aqueous solution in which 6% of PVA was dissolved was prepared as an isolation layer, which was formed on the upper charge generation layer so as to have a dry film thickness of 1 μm, and dried at 100 ° C. for 30 minutes.

(Substrate, electrode layer and display layer)
The cholesteric liquid crystal was obtained by adding 12.8% of the chiral agent R811 (made by Merck) and 3.2% of the chiral agent R1011 (made by Merck) to the nematic liquid crystal E7 (made by Merck).
To 10 parts of this cholesteric liquid crystal, 1.2 parts of polyisocyanate compound Takenate D-110N (manufactured by Takeda Pharmaceutical Co., Ltd.) and 100 parts of ethyl acetate are added to prepare an oil phase composition, which is made of 1% polyvinyl alcohol. (Poval 217EE: manufactured by Kuraray) It was put into 1000 parts of an aqueous solution, stirred and emulsified to prepare an o / w emulsion having a diameter of about 10 μm. This was heated at 60 ° C. for 3 hours to obtain a microcapsule using polyurethane as a wall material. After the microcapsules were collected by centrifugation, a 12% polyvinyl alcohol (Poval 217C: manufactured by Kuraray) aqueous solution was added to obtain a microcapsule liquid crystal paint.
Using the commercially available ITO vapor-deposited PET resin film (High Beam: manufactured by Toray) as the substrate and electrode layer, the microcapsule liquid crystal paint was applied to a dry film thickness of 30 μm and dried at 100 ° C. for 30 minutes, did.

(Red selective transmission layer)
As a PVA binder, a red pigment (dioketopyrrolopyrrole) was dispersed and an aqueous solution was prepared so that the weight ratio thereof was 1: 1 (solid content concentration 10%). This red ink was applied onto the upper charge generation layer by spin coating so that the thickness after drying was 2 μm, and dried at 90 ° C. for 30 minutes.

(Adhesive layer)
Next, spin coating is applied to the isolation layer of the substrate on which the photoconductive layer was prepared using the laminating ink in which butyl acetate was used as a solvent and 2-pack urethane adhesive Takelac A50 / A315 (made by Mitsui Chemical Polyurethane) was dissolved. This was applied to form an adhesive layer having a thickness of 5 μm.
Finally, the layers prepared in this manner were stacked and bonded through a laminator heated to 90 ° C. to complete an electronic paper.

Example 4:
(Light absorption layer, photoconductive layer and isolation layer)
As an optical absorption layer, an aqueous solution (solid content concentration 10%) using PVA as a binder, carbon black as a pigment, and a weight ratio of 3: 1 is prepared so that the dry film thickness becomes 2 μm. Formed on the upper charge generation layer and dried at 100 ° C. for 30 minutes.
As a dispersion for the lower charge generation layer, dibromoanthanthrone is used as a charge generation material, polyvinyl butyral is used as a binder resin, and the mass ratio of both is 8: 1. This is dispersed in butanol (concentration 4%). Was prepared. This dispersion was applied onto the charge transport layer by spin coating and then dried to form an upper charge generation layer having a thickness of 0.8 μm.
As a solution for the charge transport layer, a benzidine charge transport material and a binder resin PolyCarbonate bisphenol-Z (poly (4,4′-cyclohexylidene diphenylene carbonate)) are mixed at a mass ratio of 6: 4, respectively. Was dissolved in monochlorobenzene to prepare a 10% solution. A 20% solution was prepared from this solution by dip coating. A charge transport layer having a thickness of 8 μm was formed on the lower charge generation layer using an applicator having a Gap width of 80 μm.

As a dispersion for the upper charge generation layer, dibromoanthanthrone is used as a charge generation material, polyvinyl butyral is used as a binder resin, and the mass ratio of both is 8: 1. This is dispersed in butanol (concentration 2%). Was prepared. This dispersion was applied onto the charge transport layer by spin coating and then dried to form an upper charge generation layer having a thickness of 0.2 μm. In this way, a light absorption layer and a photoconductive layer comprising a substrate, a lower charge generation layer, a charge transport layer, and an upper charge generation layer were produced.
Further, an aqueous solution in which 6% of PVA was dissolved was prepared as an isolation layer, which was formed on the upper charge generation layer so as to have a dry film thickness of 1 μm, and dried at 100 ° C. for 30 minutes.

(Substrate, electrode layer and display layer)
The cholesteric liquid crystal was obtained by adding 12.8% of the chiral agent R811 (made by Merck) and 3.2% of the chiral agent R1011 (made by Merck) to the nematic liquid crystal E7 (made by Merck).
To 10 parts of this cholesteric liquid crystal, 1.2 parts of polyisocyanate compound Takenate D-110N (manufactured by Takeda Pharmaceutical Co., Ltd.) and 100 parts of ethyl acetate are added to prepare an oil phase composition, which is made of 1% polyvinyl alcohol. (Poval 217EE: manufactured by Kuraray) It was put into 1000 parts of an aqueous solution, stirred and emulsified to prepare an o / w emulsion having a diameter of about 10 μm. This was heated at 60 ° C. for 3 hours to obtain a microcapsule using polyurethane as a wall material. After the microcapsules were collected by centrifugation, a 12% polyvinyl alcohol (Poval 217C: Kuraray) aqueous solution was added to obtain a microcapsule liquid crystal paint.
Using the commercially available ITO vapor-deposited PET resin film (High Beam: manufactured by Toray) as the substrate and electrode layer, the microcapsule liquid crystal paint was applied to a dry film thickness of 30 μm and dried at 100 ° C. for 30 minutes, did.

(Blue selective transmission layer)
A blue ink was prepared using a vinyl chloride vinegar copolymer resin as a binder, a blue pigment (copper phthalocyanine) dispersed therein, and a solvent of butyl acetate so that the weight ratio thereof was 1: 2. This blue ink was applied on the display layer with an applicator so that the thickness after drying was 2 μm, and dried at 100 ° C. for 30 minutes.

(Adhesive layer)
Next, spin coating is applied to the isolation layer of the substrate on which the photoconductive layer was prepared using the laminating ink in which butyl acetate was used as a solvent and 2-pack urethane adhesive Takelac A50 / A315 (made by Mitsui Chemical Polyurethane) was dissolved. This was applied to form an adhesive layer having a thickness of 5 μm.
Finally, the layers prepared in this manner were stacked and bonded through a laminator heated to 90 ° C. to complete an electronic paper.

Comparative example:
(Light absorption layer, photoconductive layer and isolation layer)
As an optical absorption layer, an aqueous solution (solid content concentration 10%) using PVA as a binder, carbon black as a pigment, and a weight ratio of 3: 1 is prepared so that the dry film thickness becomes 2 μm. Formed on the upper charge generation layer and dried at 100 ° C. for 30 minutes.
As a dispersion for the lower charge generation layer, chlorogallium phthalocyanine is used as a charge generation material, polyvinyl butyral is used as a binder resin, the mass ratio of both is 6: 4, and this is dispersed in butanol (concentration 4%) Was prepared. This dispersion was applied onto the charge transport layer by spin coating and then dried to form an upper charge generation layer having a thickness of 0.8 μm.
As a solution for the charge transport layer, a benzidine charge transport material and a binder resin PolyCarbonate bisphenol-Z (poly (4,4′-cyclohexylidene diphenylene carbonate)) are mixed at a mass ratio of 6: 4, respectively. Was dissolved in monochlorobenzene to prepare a 110% solution. A 20% solution was prepared from this solution by dip coating. A charge transport layer having a thickness of 8 μm was formed on the lower charge generation layer using an applicator having a Gap width of 80 μm.

As a dispersion for the upper charge generation layer, chlorogallium phthalocyanine is used as a charge generation material, polyvinyl butyral is used as a binder resin, and the mass ratio of both is 6: 4, which is dispersed in butanol (concentration 2%) Was prepared. This dispersion was applied onto the charge transport layer by spin coating and then dried to form an upper charge generation layer having a thickness of 0.2 μm. Thus, a photoconductive layer comprising a substrate, a lower charge generation layer, a charge transport layer, and an upper charge generation layer was produced.
Further, an aqueous solution in which 6% of PVA was dissolved was prepared as an isolation layer, which was formed on the upper charge generation layer so as to have a dry film thickness of 1 μm, and dried at 100 ° C. for 30 minutes.

(Substrate, electrode layer and display layer)
The cholesteric liquid crystal was obtained by adding 12.8% of the chiral agent R811 (made by Merck) and 3.2% of the chiral agent R1011 (made by Merck) to the nematic liquid crystal E7 (made by Merck).
To 10 parts of this cholesteric liquid crystal, 1.2 parts of polyisocyanate compound Takenate D-110N (manufactured by Takeda Pharmaceutical Co., Ltd.) and 100 parts of ethyl acetate are added to prepare an oil phase composition, which is made of 1% polyvinyl alcohol. (Poval 217EE: manufactured by Kuraray) It was put into 1000 parts of an aqueous solution, stirred and emulsified to prepare an o / w emulsion having a diameter of about 10 μm. This was heated at 60 ° C. for 3 hours to obtain a microcapsule using polyurethane as a wall material. After the microcapsules were collected by centrifugation, a 12% polyvinyl alcohol (Poval 217C: manufactured by Kuraray) aqueous solution was added to obtain a microcapsule liquid crystal paint.
Using the commercially available ITO vapor-deposited PET resin film (High Beam: manufactured by Toray) as the substrate and electrode layer, the above microcapsule liquid crystal paint was applied to a dry film thickness of 30 micrometers, dried at 100 ° C. for 30 minutes, and displayed. Layered.

(Adhesive layer)
Next, spin coating is applied to the isolation layer of the substrate on which the photoconductive layer has been prepared using lami ink in which butyl acetate is used as a solvent and 2-pack urethane adhesive Takelac A50 / A315 (Mitsui Chemical Polyurethane) is dissolved. Thus, an adhesive layer having a thickness of 5 μm was obtained.
Finally, the layers prepared in this manner were stacked and bonded through a laminator heated to 90 ° C. to complete an electronic paper.

Rating:
(1) Light resistance evaluation The light resistance of Examples and Comparative Examples was examined. Using the fluorescent lamp as a light source, the aforementioned evaluation medium was placed in the vicinity of 2 cm and irradiated for a predetermined time. Prior to the exposure, the writing reflectance in the white state was measured in advance as an initial characteristic. The writing waveform was about 400 VOp, and a rectangular pulse was applied at 10 Hz for 200 ms. The amount of light was about 120 to 200 uw. As for the wavelength of the writing light source, a 640 nm LED (light emitting diode) was used in Examples 1, 2, and 3, and a 500 nm LED was used in Example 4. Next, a fluorescent lamp light source for light resistance test was irradiated. In the measurement, the reflectance was measured again after 3 hours and after 5 hours, and it was examined whether or not the degree of deterioration was compared with the initial value. Minolta spectrocolorimeter CM-2002 was used for the measurement of the reflectance.

  As a result, as shown in FIG. 9, the reflectance dropped to about 20% of the initial value after the comparative example was irradiated for 5 hours, whereas Examples 1 and 2 had almost no deterioration. In addition, the same experiment was performed for Examples 3 and 4, but the deterioration after exposure for 5 hours was 10% or less. This showed an improvement in light resistance.

(2) Evaluation of blackness In order to examine the black color, it was measured using the above-described Minolta spectrophotometer CM-2002. The evaluation was performed using the L * a * b * color system while observing the spectral spectra of Examples and Comparative Examples. That is, after measuring L * a * b * with a spectrophotometer, the root mean square of a * and b * was calculated and evaluated. The smaller the calculated value, the more achromatic, i.e., the better the color is not black. FIG. 10 shows the spectrum. For comparison, the reflectance is normalized with the minimum reflectance being 1. As shown in FIG. 10, in the comparative example, it can be seen that the gain in the blue region having a short wavelength is particularly high and bluish. On the other hand, in Examples 1, 2, and 3, the blue gain is lower than the other wavelengths and is uniform with respect to the wavelength. FIG. 11 shows the evaluation result of blackness by L * a * b *. As shown in FIG. 11, it was confirmed that Examples 1, 2, and 3 were smaller and better than the comparative example. When similar evaluation was made for Example 4, the mean square was 10 or less, and good results were obtained.

1 is a schematic diagram illustrating an optical writing display medium and an optical writing device according to a first embodiment of the present invention. It is a schematic diagram which shows the optical characteristic at the time of a pulse voltage being applied to the cholesteric liquid crystal used for the display layer of the 1st Embodiment of this invention. It is a circuit diagram which shows the equivalent circuit schematic of the optical writable display medium in the 1st Embodiment of this invention. It is the schematic which shows the relationship between the absorption spectrum and external light spectrum of the selective transmission layer and photoconductive layer which were used for the 1st Embodiment of this invention. In the 1st Embodiment of this invention, it is a diagram which shows each absorption spectrum at the time of using the thing which permeate | transmits a red component as a selective transmission layer, and using a phthalocyanine pigment as a charge generation substance of a photoconductive layer. In the first embodiment of the present invention, a line showing respective absorption spectra when a layer that transmits blue is used as the selective transmission layer and a dibromoanthanthrone (DBA) pigment is used as the charge shipping substance of the photoconductive layer 26. FIG. It is sectional drawing which shows the optical writable display medium which concerns on the 2nd Embodiment of this invention. It is sectional drawing which shows the optical writing type display medium which concerns on the 3rd Embodiment of this invention. It is a diagram which shows the light resistance evaluation result of Example 1, 2 and a comparative example. It is a diagram which shows Example 1, 2, 3 and the black spectrum of a comparative example. It is a graph which shows the black color evaluation result of Example 1, 2, 3 and a comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Optical writing type display medium 12 Optical writing apparatus 14 1st board | substrate 16 1st electrode layer 18 Display layer 20 Selective transmission layer 22 Adhesion layer 24 Isolation layer 26 Photoconductive layer 28 Light absorption layer 30 2nd electrode layer 32 1st 2 substrate 34 voltage application unit 36 control unit 38 light emitting device

Claims (12)

A display layer that selectively changes optical characteristics according to an applied voltage and selectively transmits or reflects incident visible light;
Of the visible light having a predetermined range of wavelengths transmitted through the display layer, a photoconductive layer whose electrical resistance changes in response to irradiation with visible light in the first wavelength region;
A selectively transmissive layer that transmits visible light having a wavelength included in the first wavelength region transmitted through the display layer and absorbs visible light in a second wavelength region having a wavelength other than at least the first wavelength region; and
An optically writable display medium.   The optically writable display medium according to claim 1, wherein the display layer is made of cholesteric liquid crystal.   3. The optically writable display medium according to claim 1, wherein the color of the first wavelength region and the color of the second wavelength region are in a complementary color relationship.   4. The photo-writing display medium according to claim 3, wherein the photoconductive layer uses a phthalocyanine pigment as a charge generation material, and the selective transmission layer transmits a red component as a first component.   4. The photo-writing display medium according to claim 3, wherein the photoconductive layer uses a dibromoanthanthrone pigment as a charge generating material, and the selective transmission layer transmits a blue component as a first component.   6. The photo-writing display medium according to claim 1, further comprising a light absorption layer that is disposed on a side opposite to the display layer of the photoconductive layer and absorbs light transmitted through the photoconductive layer.   The optically writable display medium according to claim 1, wherein the selective transmission layer is formed by bonding the display layer and the photoconductive layer.   7. The device according to claim 1, further comprising an adhesive layer that adheres the display layer and the selective transmission layer, wherein the selective transmission layer has a separating performance that prevents elution of components of the adhesive layer into the photoconductive layer. Or an optically writable display medium.   9. The apparatus according to claim 1, further comprising a pair of electrode layers disposed so as to sandwich at least the display layer and the photoconductive layer, wherein at least the electrode layer on the display layer side of the pair of electrode layers transmits visible light. Any one of the optical writing type display media. A voltage applying unit that applies a voltage to the display layer and the photoconductive layer of the optically writable display medium according to claim 1,
An optical writing device comprising: a light emitting device that generates visible light containing light in the first wavelength region as a component.   The optically writable display medium further includes a pair of electrode layers disposed so as to sandwich at least the display layer and the photoconductive layer, and the voltage applying unit applies a voltage to the pair of electrode layers. The optical writing apparatus according to claim 10, wherein at least the electrode layer on the notation layer side of the pair of electrode layers transmits visible light. A display layer that selectively changes optical characteristics according to an applied voltage and selectively transmits or reflects incident visible light;
Of the visible light having a predetermined range of wavelengths transmitted through the display layer, a photoconductive layer whose electrical resistance changes in response to irradiation with visible light in the first wavelength region;
A selectively transmissive layer that transmits visible light having a wavelength included in the first wavelength region transmitted through the display layer and absorbs visible light in a second wavelength region having a wavelength other than at least the first wavelength region; and
An optical writable display medium having
An optical writing method of irradiating visible light containing a first wavelength region as a component while applying a voltage to the display layer and the photoconductive layer of the optical writing type display medium.

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