JP5151022B2 - Light modulation element and driving method thereof - Google Patents

Description

  The present invention relates to a light modulation element including a display layer containing liquid crystal and capable of displaying and recording images on both sides, and a driving method thereof.

There are high expectations for rewritable marking technology as a hard copy technology that replaces paper, for reasons such as the preservation of the global environment such as forest resource protection and the improvement of the office environment such as space saving.
Hard copies of paper are (1) bright, high-contrast, reflective full-color display, easy to read, high information display density, (2) light and thin, flexible structure, easy to use (3) The display has memory characteristics, can display and store information without power, and is flickerless. It has excellent convenience not found in conventional electronic displays, such as low fatigue, (4) low cost, easy to obtain a list by simultaneous display of multiple images, and easy comparison and browsing of information. .

  For this reason, the paperless office has not been promoted as expected, resulting in the act of viewing the information displayed on the electronic display after printing it again on paper as a hard copy. Therefore, in addition to the rewritability for realizing resource saving and waste saving, it is necessary to reproduce various conveniences unique to the paper document as described above in the display medium instead of paper.

  Research into various rewritable marking technologies that are even more convenient has been made, but as one direction, the technology using a liquid crystal device in which a liquid crystal and a photoconductor are laminated enables repeated recording / erasing. In addition, it attracts attention because it can realize other excellent characteristics.

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

  The planar phase of cholesteric liquid crystal is a selective reflection phenomenon that splits light incident parallel to the helical axis into right-handed and left-handed light, Bragg-reflects circularly polarized light components that match the twisted direction of the spiral, and transmits the remaining light. Wake up. 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. 4A, 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. 4B, a focal conic phase in which the helical axis is substantially parallel to the cell surface and transmits incident light while being slightly scattered forward, and the helical structure is unwound as shown in FIG. The director shows three states: a homeotropic phase in which the director is directed in the direction of the electric field and almost completely transmits the incident light.

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

On the other hand, when the electric field strength applied to the liquid crystal layer is suddenly reduced to zero, the planar phase and the focal conic phase are maintained as they are, and the homeotropic phase is changed to the planar phase.
Therefore, the cholesteric liquid crystal layer immediately after the pulse signal is applied exhibits a switching behavior as shown in FIG. 5, and when the applied pulse signal voltage is equal to or higher than Vfh, the selective reflection is changed from the homeotropic phase to the planar phase. When it is between Vpf and Vfh, it becomes a transmission state due to the focal conic phase, and when it is equal to or lower than Vpf, the state before the pulse signal 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 FIG. 5, the vertical axis represents the normalized reflectance, and the reflectance is normalized with the maximum reflectance being 100 and the minimum reflectance being 0. Further, when the normalized reflectance is 50 or more, the selective reflection state is defined, and when the normalized reflectance is less than 50, the transmission state is defined. The threshold voltage of the phase change between the planar phase and the focal conic phase is defined as Vpf, and the focal Let Vfh be the threshold voltage of the phase change between the conic phase and the homeotropic phase.

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

Conventionally, many light modulation elements using the technology have been proposed (see, for example, Patent Document 1 and Non-Patent Document 1).
In the light modulation element according to the technology, by utilizing the bistable phenomenon of the cholesteric liquid crystal, (A) a selective reflection state by the planar phase and (B) a transmission state by the focal conic phase are switched to thereby generate an electric field. Black / white monochrome display having a memory property in a color display, or a color display having a memory property without an electric field.

  FIG. 6 is a schematic diagram schematically showing a state in which an image is written by an exposure apparatus with respect to a general light modulation element according to the technique. As shown in FIG. 6, in the light modulation element according to the technique, a display layer that is a liquid crystal layer and an OPC layer that is a photoconductor layer are provided between a pair of transparent electrodes (a light shielding layer (not shown) if necessary). Are stacked) and are sandwiched between a pair of substrates. A desired recorded image can be written by exposing the surface of the OPC layer sidewise with an exposure device while applying a predetermined bias voltage to both transparent electrodes.

In light of the viewpoint of a rewritable marking technology as a hard copy technology that replaces paper, a light modulation element that can record on both the front and back sides is desired.
In order to configure a light modulation element that can be recorded on both the front and back surfaces by the above-described technique described with reference to FIG. 6, a structure in which the basic structure of the light modulation element shown in FIG.

  FIG. 7 is a schematic diagram schematically showing a light modulation element capable of double-sided recording having a structure in which a basic structure of a general light modulation element is bonded vertically. As shown in FIG. 7, in the configuration in which the basic structures A and B are symmetrically bonded with the intermediate substrate interposed therebetween, the light modulation elements are arranged back and forth with the intermediate substrate as a boundary. Images can be recorded on both sides.

However, such a structure is not practical because the structure of the light modulation element itself is complicated, the suitability for manufacture is reduced, and the manufacturing cost is increased.
Further, in the case of the light modulation element, it is necessary to perform exposure by writing from both surfaces, and a dedicated writing device having two upper and lower exposure devices is used, or writing is performed on one surface of the light modulation element. After that, it was necessary to turn over and write again, which was cumbersome and lacked versatility.

  By the way, with respect to the rewritable marking technique, various techniques using a reflective liquid crystal display element have been proposed. Above all, the image writing and display by the threshold shift method using the laminated light modulation element by the present inventors can control the two display layers independently by one drive signal, so that the structure of the medium is simplified. There is a great merit that the manufacturing cost can be reduced (see Patent Document 2 and Patent Document 3). That is, the threshold shift method has an excellent effect that it is possible to display and record an image of two or more colors including a full color easily and at low cost.

The principle of image writing and display by the threshold shift method will be described.
FIG. 8 is a schematic explanatory diagram for explaining a state of image writing by the threshold shift method. The laminated light modulation element 501 includes two display layers 507a and 507b made of cholesteric liquid crystal between a pair of transparent electrodes 505 and 506, and an OPC layer (organic photoconductor layer) 510 that is a photoconductor layer. Are mainly laminated. In FIG. 8, a colored layer 509 is disposed between these two layers.

  In the multilayer light modulation element 501 used for image writing by the threshold shift method, the operating threshold voltage of the cholesteric liquid crystal is made different between the display layer 507a and the display layer 507b, thereby applying voltages to the transparent electrode 505 and the transparent electrode 506. Accordingly, any one or both of the display layers can be in a reflective state, or both can be in a transmissive state.

  FIG. 9 shows a graph showing the switching behavior of the cholesteric liquid crystal in the display layer 507a and the display layer 507b. As shown in FIG. 9, in any of the cholesteric liquid crystals of the display layer 507a and the display layer 507b, when the externally applied voltage by the power supply device 517 increases, the planar phase selective reflection state or the focal conic phase transmission state From the focal conic phase to the transmission state, and when the phase is further increased, the phase changes from the focal conic phase to the homeotropic phase, and when the applied voltage is released, the phase changes to the planar phase to enter the selective reflection state.

However, the threshold value causing this phase change is shifted between the display layer 507a and the display layer 507b, as can be seen from the graph shown in FIG. That is, regarding the threshold voltage of the phase change from the planar phase to the focal conic phase (in the present invention, this is referred to as “lower threshold”), the display layer 507a is Vpfa and the display layer 507b is Vpfb. The cholesteric liquid crystal of the display layer 507b has a higher value. On the other hand, for the threshold voltage for phase change from the focal conic phase or the planar phase to the homeotropic phase (in the present invention, this is referred to as the “upper threshold value”), the display layer 507a displays the display layer with respect to Vfpa. 507b is Vfpb, which is also higher for the cholesteric liquid crystal of the display layer 507b.
Strictly speaking, the threshold voltage differs between the phase change from the focal conic phase to the homeotropic phase and the phase change from the planar phase to the homeotropic phase.

The threshold shift method is configured to control the display layer 507a and the display layer 507b independently by utilizing the difference in threshold value.
Specifically, first, the power supply device 517 applies a bias voltage that is lower than the upper threshold value Vfpb of the display layer 507b and higher than the upper threshold value Vfpa of the display layer 507a so that the voltage between Vc (reset voltage) is applied to the entire display layer.

At the same time, selective exposure is performed by the exposure apparatus 512, and the partial pressure of the display layer 507a and the display layer 507b is increased by changing (decreasing) the resistance value of the photoconductor layer 510 in the exposed portion. Thereby, in the exposure part, the voltage applied to the display layer 507a and the display layer 507b exceeds the upper threshold value V fpb , and the display layer 507b changes to the homeotropic phase. Further, since the voltage applied to the non-exposed portion is Vc, the display layer 507b becomes a focal conic phase.

  On the other hand, the display layer 507a becomes a homeotropic phase regardless of the exposed portion and the non-exposed portion. When the voltage application is rapidly released in this state, the homeotropic phase changes to the planar phase, and the focal conic phase maintains that state. In this way, the phase is selected for each part of the display layer 507b.

Thereafter, a bias voltage (select voltage) is applied so that the voltage applied to the entire display layer is lower than the lower threshold value Vpfa of the display layer 507a, and at the same time, the exposure device 512 selectively exposes the voltage. Similarly, the partial pressure of the display layer 507a and the display layer 507b in the exposure part is increased. Thereby, in the exposure part, the voltage applied to the display layer 507a and the display layer 507b exceeds the lower threshold value Vpfa, and the display layer 507a changes to the focal conic phase. Since the voltage applied to the non-exposed portion is Va, the display layer 507a maintains the planar state.
On the other hand, the display layer 507b maintains the state of the planar phase or the focal conic phase regardless of the exposed and non-exposed portions. In this manner, a phase is selected and writing is performed for each portion of the display layer 507a.

  That is, any one or both of the display layer 507a and the display layer 507b can be in a reflective state, or both can be in a transmissive state, and a reflected image is displayed from the display side (the upper surface side in FIG. 8). Therefore, since the two display layers can be controlled independently by one drive signal, the structure of the medium can be simplified and the manufacturing cost can be reduced.

  As described above, the technique of the threshold shift method has been described. In the technique, a stacked light modulation element in which a plurality of display layers are stacked is controlled by one drive signal, and an image having a different hue is formed for each layer. The object is to form a color image by superimposing the images, and there is no conventional contact with the problem of recording an image on the front and back surfaces of the light modulation element.

JP 11-237644 A Japanese Patent Laid-Open No. 10-177191 JP 2000-111942 A Reflective Display with Photoconductive Layer and Bistable, Reflective Cholesteric Mixture: SID 96 APPLICATION DIGEST p. 59-62

  Therefore, the present invention provides a light modulation element capable of recording an image on both the front and back surfaces by only exposure from one of the front and back surfaces while having a relatively simple structure, and a driving method thereof. For the purpose.

As a result of diligent research, the present inventors have conceived the present invention that can achieve the above-mentioned object by arranging image writing and display techniques by the threshold shift method.
That is, the light modulation element of the present invention operates with a lower threshold as an operation threshold for an externally applied voltage for a change from a planar phase to a focal conic phase, and an operation for an externally applied voltage for a change from a focal conic phase or a planar phase to a homeotropic phase. A pair of display layers made of at least cholesteric liquid crystals having different upper thresholds as thresholds; a photoconductor layer disposed between the pair of display layers; and the photoconductor layer side of the pair of display layers; Includes at least one set of light modulation units each including a pair of electrode layers disposed on opposite surfaces.

  The light modulation element of the present invention has moved the position of the OPC layer (photoconductor layer) 510 between the display layers 507a and 507b in the conventional stacked light modulation element used for the threshold shift method having the configuration shown in FIG. (However, the colored layer 509 is further removed.) Accordingly, the structure is greatly simplified as compared with a light modulation element capable of double-sided recording in which a basic structure of a general light modulation element as shown in FIG. .

  Thus, even if the position of the OPC layer 510 is changed and the order of “display layer—photoconductor layer—display layer” of the present invention is changed from the order of “display layer—display layer—photoconductor layer” in the past, The same effect as the threshold shift method is obtained, and the display layers arranged on both sides of the photoconductor layer can be driven independently. That is, according to the light modulation element of the present invention, by applying image writing similar to the conventional threshold shift method, image recording can be performed on both the front and back surfaces only by exposure from one of the front and back surfaces. It becomes possible.

  In the light modulation unit, the pair of display layers are preferably made of cholesteric liquid crystal that reflects visible light in a specific wavelength range, and the photoconductor layer is the same as the specific wavelength range. It is preferable to be configured to absorb visible light in the wavelength range.

In the light modulation element of the present invention, it is preferable that two or more sets of the light modulation units are laminated, and the display layer in each of the light modulation units is made of cholesteric liquid crystals that reflect different wavelength ranges.
In the light modulation element of the present invention, the photoconductor layer is preferably made of an organic photoconductor, and the display layer is preferably formed by dispersing the cholesteric liquid crystal in a polymer.

On the other hand, the driving method of the light modulation element of the present invention is a driving method for writing an image on the light modulation element of the present invention,
A first writing step of selecting a portion that exceeds the upper threshold and a portion that does not exceed the upper threshold in each display layer by appropriately exposing the light modulation element while applying a voltage between the electrodes;
A second writing step of selecting a portion exceeding the lower threshold and a portion not exceeding the lower threshold in each display layer by appropriately selectively exposing the light modulation element while applying a voltage between the electrodes;
The operation consisting of is performed on all the light modulation units included.

The light modulation element of the present invention can record images on both the front and back surfaces by the light modulation element drive method of the present invention to which the drive method similar to the conventional threshold shift method is applied.
In the driving method of the light modulation element of the present invention, the exposure in the first writing step and the exposure in the second writing step can be performed from the same surface side in the light modulation element, which is a preferable mode.

According to the present invention, it is possible to provide an optical modulation element that has a relatively simple structure and can be recorded on both front and back surfaces only by exposure from either one of the front and back surfaces. In addition, the light modulation element of the present invention can be exposed not only on one of the front and back sides, but also on both sides, and recording can be performed on both the front and back sides, as in a conventional exposure apparatus for a light modulation element. The present invention can be applied as it is to a writing apparatus configured to write from both front and back sides, and its versatility is high.
On the other hand, according to the driving method of the light modulation element of the present invention, it is possible to record images on both sides of the light modulation element of the present invention having the above-mentioned excellent characteristics. Images can be recorded on both the front and back surfaces of the light modulation element only by exposure from the surface.

  Hereinafter, the present invention will be described in detail with reference to the drawings with preferred embodiments. Note that the technique of the present invention also applies the same principle and operation as the conventional threshold shift method as described above, and therefore will be described using the term “threshold shift method” in the following description. .

[First Embodiment]
FIG. 1 is a schematic configuration diagram of a first embodiment which is an exemplary aspect of a system to which a light modulation element and a driving method thereof according to the present invention are applied. The system of this embodiment includes a display medium (light modulation element) 1 and a writing device 2 which are light modulation elements of the present invention. Both of these components will be described in detail before the driving method thereof will be described.

<Display medium>
In the present embodiment, a display medium (light modulation element of the present invention) 1 includes a transparent substrate 3, a transparent electrode (electrode) 5, a display layer 7, an OPC layer (photoconductor layer) 10, in order from the upper surface side in FIG. The display layer 8, the transparent electrode (electrode) 6, and the transparent substrate 4 are laminated.

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

(Transparent electrode)
The transparent electrodes 5 and 6 are members for the purpose of uniformly applying the bias voltage applied from the writing device 2 to each functional layer in the optical address element. The transparent electrodes 5 and 6 have uniform surface conductivity and transmit incident light and address light, respectively. 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.

(Display layer)
In the present invention, the display layer is a liquid crystal layer having a function of modulating the reflection / transmission state of specific color light of incident light by an electric field, and maintaining the selected state with no electric field. A structure that is not deformed by an external force such as bending or pressure is preferable.

In the present embodiment, the display layer is formed by forming a liquid crystal layer of a self-holding liquid crystal composite made of cholesteric liquid crystal and transparent resin. 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, and the display layer may be composed of only liquid crystals.

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

  Specific liquid crystals that can be used as cholesteric liquid crystals include nematic liquid crystals and smectic liquid crystals (for example, Schiff base, azo, azoxy, benzoate, biphenyl, terphenyl, cyclohexylcarboxylate, phenylcyclohexane). System, biphenylcyclohexane system, pyrimidine system, dioxane system, cyclohexylcyclohexane ester system, cyclohexylethane system, cyclohexane system, tolan system, alkenyl system, stilbene system, condensed polycyclic system), or a mixture thereof, 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 colors are blue, green, and red, the center wavelengths of selective reflection are in the range of 400 nm to 500 nm, 500 nm to 600 nm, and 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 layers 7 and 8 form a self-holding type liquid crystal composite composed of a cholesteric liquid crystal and a polymer matrix (transparent resin), a PNLC (Polymer Network Liquid Crystal) containing a network-like resin in the continuous phase of the cholesteric liquid crystal. ) Structure or a PDLC (Polymer Dispersed Liquid Crystal) structure in which cholesteric liquid crystal is dispersed in the form of droplets in a polymer skeleton. By using a PNLC structure or a PDLC structure, a cholesteric liquid crystal and a polymer can be used. An anchoring effect is produced at the interface, 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).

In the display medium 1 as a light modulation element used for the threshold shift method, it is desired that the upper and lower thresholds are appropriately separated between the display layer 8 and the display layer 7 and an operation margin is ensured by the threshold shift method.
FIG. 2 shows a graph showing the switching behavior of the cholesteric liquid crystal of the display layer 7 and the display layer 8. In the present embodiment, as shown in the graph of FIG. 2, the upper threshold value Vfp8 of the display layer 8 is smaller than the upper threshold value Vfp7 of the display layer 7, and the lower threshold value Vpf8 of the display layer 8 is also lower than that of the display layer 7. It is adjusted to be smaller than the lower threshold value Vpf7.

In the present invention, the capacitance ratio and the resistance ratio of the display layer are appropriately adjusted by appropriately adjusting the liquid crystal material and the thickness of each layer.
The specific resistance of the liquid crystal material can be controlled by, for example, mixing a high-resistance fluorine-based material and a low-resistance cyano-based material, or adding an ionic impurity to the liquid crystal material. At this time, it is preferable to give a slight difference in capacitance between the display layers. The difference in capacitance between the display layers can be controlled by changing the dielectric constant of the liquid crystal material and the thickness of the display layer.

  In addition, the switching behavior of the display layers 7 and 8 is the dielectric anisotropy, elastic modulus, helical pitch, polymer skeleton structure and side chain of the cholesteric liquid crystal constituting the display layers 7 and 8, the phase separation process, the polymer It can also be controlled by the morphology of the interface between the matrix and the display layers 7 and 8, the degree of anchoring effect at the interface between the polymer matrix and the display layers 7 and 8 determined by these factors, and the like.

  More specifically, the types and composition ratios of nematic liquid crystals, the types of chiral agents, the types of resins, the types and composition ratios of monomers, oligomers, initiators, crosslinking agents, etc., which are starting materials for polymer resins, the polymerization temperature, Exposure light source for photopolymerization, exposure intensity, exposure time, ambient temperature, electron beam intensity for electron beam polymerization, exposure time, atmospheric temperature, solvent type and composition ratio during coating, solution concentration, wet film thickness, Examples include, but are not limited to, the drying temperature, the starting temperature when the temperature drops, and the temperature drop rate.

(OPC layer)
The OPC layer (photoconductor 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. Alternating current (AC) operation is possible and must be driven 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 stacked 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. Mainly, the amount of light carriers that the charge generation layer 13 flows in the direction from the transparent electrode 5 on the side opposite to the writing surface to the transparent electrode 6 on the writing surface side, and the charge generation layer 15 on the opposite side from the transparent electrode 6 on the writing surface side. The amount of light carriers flowing in the direction of the transparent electrode 5 on the side 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 address light (light exposed for writing) is basically the same color as the reflected light of the display layers 7 and 8, that is, the display color. In order to absorb it, the charge generation layers 13 and 15 It is preferable to adjust so as to exhibit a hue that is complementary to the color. For example, when the display colors of the display layers 7 and 8 are green, the charge generation layers 13 and 15 exhibiting a magenta color having a complementary color relationship are used. However, the display color and the address light are not necessarily the same color, and the display color and the color of the charge generation layer do not necessarily have a complementary color relationship. The reflected light of the display layers 7 and 8 may have a different hue, and the charge generation layers 13 and 15 may have different hues.

  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. Since the charge transport layer generally has a thickness several tens of times that of the charge generation layer, the capacity 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 are The overall light / dark impedance of 10 is determined.

  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.

<Writing device>
In the present embodiment, the writing device (light modulation element driving device) 2 is a device that writes an image on the display medium 1, and includes a light irradiation unit (exposure device) 18 that irradiates the display medium 1 with address light, and A voltage application unit (power supply device) 17 that applies a voltage to the display medium 1 is a main component, and a control circuit 16 that controls this operation is arranged.

(Light irradiation part)
The light irradiation unit (exposure device) 18 has a function of irradiating the display medium 1 with a predetermined address light pattern that becomes an image. On the display medium 1 (in detail, OPC is based on an input signal from the control circuit 16. The layer is not particularly limited as long as it can irradiate a desired optical image pattern (spectrum, intensity, spatial frequency).

The address light irradiated by the light irradiation unit 18 is preferably selected under the following conditions.
Spectrum: 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 layers 7 and 8 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, and the liquid crystal in the display layers 7 and 8 changes in phase, and in the dark Strength to be as follows.
The address light irradiated by the light irradiation unit 18 is preferably light having a peak intensity in the absorption wavelength region of the OPC layer 10 and a narrow bandwidth as much as possible.

Specific examples of the light irradiation unit 18 include the following.
(1-1) A uniform light source (1 such as a light source (for example, a cold cathode tube, a xenon lamp, a halogen lamp, an LED, an EL) arranged in an array or a combination of a light source and a light guide plate) -2) Combination of light control elements (for example, LCD, photomask, etc.) for creating a light pattern (2) Surface-emitting display (for example, CRT, PDP, EL, LED, FED, SED)
(3) A combination of the above (1-1), (1-2) or (2) and an optical element (for example, a microlens array, a cell hook lens array, a prism array, a viewing angle adjustment sheet)

(Voltage application part)
The voltage application unit 17 has a function of applying a predetermined bias voltage to the display medium 1 and can apply a desired voltage waveform to the display medium (between each electrode) based on an input signal from the control circuit 16. That's fine. However, AC output is possible and a high slew rate is required. For the voltage application unit 17, for example, a bipolar high voltage amplifier can be used.

The voltage application unit 17 applies a voltage to the display medium 1 between the transparent electrode 5 and the transparent electrode 6 via the contact terminals 19 and 20.
Here, the contact terminals 19 and 20 are members that contact the voltage application unit 17 and the display medium 1 (transparent electrodes 5 and 6) and conduct both of them, and have high conductivity. 6 and the one having a small contact resistance with the voltage application unit 17 are selected. It is preferable that the display medium 1 and the writing device 2 have a structure that can be separated from either or both of the transparent electrodes 5 and 6 and the voltage application unit 17 so as to 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)
The control circuit 16 includes a voltage application unit 17 and a light irradiation unit according to image data from the outside (an image capturing device, an image receiving device, an image processing device, an image reproducing device, or a device having a plurality of these functions). This is a member having a function of appropriately controlling the operation of 18. The specific contents of control by the control circuit 16 are composed of two steps, a “first writing step” and a “second writing step”, and details thereof are described in detail in the section <Driving method> below. I decided to.

<Driving method>
The method for driving the light modulation element of this embodiment will be described in detail below.
As described above, the display layer 7 and the display layer 8 of the light modulation element of this embodiment show the switching behavior shown in the graph of FIG. Based on this assumption, each process will be described.

(First writing step)
First, a bias voltage (reset voltage) is applied with a predetermined pulse waveform such that the voltage applied to the display layers 7 and 8 is lower than the upper threshold value Vfp7 of the display layer 7 and higher than the upper threshold value Vfp8 of the display layer 8. While being applied by the application unit 17, at the same time, it is selectively exposed by the light irradiation unit 18, and the partial pressure of the display layer 7 and the display layer 8 is changed by changing (decreasing) the resistance value of the OPC layer 10 in the exposure unit. To raise. As a result, the voltage applied to the display layer 7 and the display layer 8 exceeds the upper threshold voltage Vfp7 in the exposure portion, and the display layer 7 changes to the homeotropic phase.
In the non-exposed portion, the applied voltage is Vc, so that the display layer 7 is in a focal conic phase.

On the other hand, the display layer 8 becomes a homeotropic phase regardless of the exposed part and the non-exposed part. When the voltage application is rapidly released in this state, the homeotropic phase changes to the planar phase, and the focal conic phase maintains that state.
In this way, the phase is selected for each part of the display layer 7. That is, an image is recorded on one surface (upper surface in FIG. 1) of the display medium 1 by the operation of the first writing process.

(Second writing step)
After the operation of the first writing process is performed, a bias voltage (select voltage) is set to a predetermined pulse waveform so that the voltage applied to the display layers 7 and 8 is between Va lower than the lower threshold value Vpf8 of the display layer 8. At the same time as the voltage application unit 17 applies, the light irradiation unit 18 selectively exposes to increase the partial pressure of the display layer 7 and the display layer 8 in the exposure unit as in the first writing step. Thereby, in the exposure part, the voltage applied to the display layer 7 and the display layer 8 exceeds the lower threshold value Vpf8, and the display layer 8 changes to the focal conic phase. Further, since the voltage applied to the non-exposed part is Va, the display layer 8 maintains the planar state.

On the other hand, the display layer 7 maintains a planar or focal conic state regardless of the exposed portion and the non-exposed portion. That is,
In this way, the phase is selected for each part of the display layer 8. That is, by the operation of the second writing process, an image is recorded on the back surface (the lower surface in FIG. 1) of the display medium 1 on the side recorded by the operation of the first writing process.

  When the operation of the writing process described above is sequentially performed and exposure / non-exposure is selected depending on the site while applying a voltage, any one of the display layer 7 and the display layer 8 or the combination is selected depending on the combination. Both are in a reflective state or both are in a transmissive state. Thus, the phases are selected, and writing (driving) is performed on both the front and back surfaces of the light modulation element.

  The display medium 1 on which images are recorded on both the front and back sides in this manner can be freely carried and handled by being removed from the contact terminals 19 and 20. Each recorded image can be viewed visually when viewed from either the front or back side. At this time, the OPC layer 10 (more precisely, the charge generation layers 13 and 15) has a hue (this embodiment) that is complementary to the reflected light (display color; green in this embodiment) of the display layers 7 and 8. In this case, the recorded image on the back side as viewed from the viewer side is absorbed by the OPC layer 10 and is not visible to the viewer. That is, it is possible to visually recognize a clear image with no show-back of the image.

  As described above, the display medium 1 of the present embodiment, which is the light modulation element of the present invention, can easily record images on both the front and back surfaces by exposure from one surface by the above driving method in which the threshold shift method is arranged. be able to. In addition, while it is possible to record images on both the front and back sides in a simple manner, the structure is relatively simple, the cost of manufacturing the display medium can be reduced, and the number of layers to be stacked is small, so that the display medium It is possible to reduce the thickness.

[Second Embodiment]
FIG. 3 is a schematic configuration diagram of a second embodiment which is another exemplary aspect of a system to which the light modulation element of the present invention and the driving method thereof are applied. The system according to this embodiment includes a display medium (light modulation element) 101 that is a light modulation element of the present invention capable of recording a full-color image, and a writing device 102. Both of these components will be described in detail before the driving method thereof will be described.

<Display medium>
In the present embodiment, a display medium (light modulation element of the present invention) 101 includes a transparent substrate 103, a light modulation unit 200B, an internal substrate 111, a light modulation unit 200G, an internal substrate 112, and a light modulation unit in order from the upper surface side in FIG. 200R and transparent substrate 104 are laminated.

  In addition, the three sets of light modulation units 200B, 200G, and 200R are respectively, in order from the upper surface side in FIG. 3, transparent electrodes (electrodes) 105B, 105G, and 105R, display layers 107B, 107G, and 107R, and OPC layers (photoconductor layers). ) 110B, 110G, 110R, display layers 108B, 108G, 108R and transparent electrodes (electrodes) 106B, 106G, 106R are laminated.

  Also, the three OPC layers (photoconductor layers) 110B, 110G, and 110R are arranged in order from the upper surface side in FIG. 3, respectively, the upper charge generation layers 113B, 113G, and 113R, the charge transport layers 114B, 114G, and 114R, and the lower side, respectively. The charge generation layers 115B, 115G, and 115R are stacked.

  Each of the light modulation units 200B, 200G, and 200R constitutes the basic configuration of the light modulation element of the first embodiment. Therefore, the light modulation element of this embodiment is substantially the same as that obtained by superposing three sets of the light modulation elements of the first embodiment. These light modulation units 200B, 200G, and 200R have basically the same configuration between the units except that the conditions regarding colors are different.

  In the following description, the light modulation unit and its constituent members may be described by removing the alphabet at the end from the reference numeral, but this does not indicate a specific color, but three-color light modulation. It is meant to be applied to each unit or its constituent members.

  The transparent substrates 103 and 104 are equivalent to the transparent substrates 3 and 4 in the first embodiment, and have the same configuration and characteristics. The internal substrates 111 and 112 are basically similar to the transparent substrates 103 and 104 except that the thickness can be changed from that of the transparent substrates 103 and 104, and have the same configuration and characteristics. Is used.

On the other hand, the members constituting the light modulation unit 200 also correspond to the corresponding members in the first embodiment (transparent electrodes 5 and 6 for the transparent electrodes 105 and 106, and display for the display layers 107 and 108, respectively), except for the color-related conditions. It is equivalent to the OPC layer 10) for the layers 7 and 8 and the OPC layer 110, and has the same configuration and characteristics.
Therefore, the detailed description about each structural member of the display medium 101 in this embodiment is omitted. And the light modulation unit 200 peculiar to a present Example is demonstrated below.

  The light modulation unit 200R is a unit that can display a red (R) color. Therefore, the cholesteric liquid crystal included is selected so that the display layers 107R and 108R in the light modulation unit 200R reflect the R color. On the other hand, the address light for the light modulation unit 200R also becomes R color, and in order to absorb it, the charge generation layers 113R and 115R are adjusted to exhibit a cyan (C) color that is complementary to the address light. .

  The light modulation unit 200G is a unit that can display a green (G) color. Therefore, the cholesteric liquid crystal contained is selected so that the display layers 107G and 108G in the light modulation unit 200G reflect the G color. On the other hand, the address light for the light modulation unit 200G also becomes G color, and in order to absorb it, the charge generation layers 113G and 115G are adjusted to exhibit a magenta (M) color that is complementary to the address light. .

  The light modulation unit 200B is a unit that can display a blue (B) color. Therefore, the cholesteric liquid crystal contained is selected so that the display layers 107B and 108B in the light modulation unit 200B reflect the B color. On the other hand, the address light for the light modulation unit 200B also becomes B color, and in order to absorb it, the charge generation layers 113B and 115B are adjusted to exhibit a yellow (Y) color that is complementary to the address light. .

<Writing device>
In this embodiment, the writing device (light modulation element driving device) 102 is a device that writes an image on the display medium 101, and includes a light irradiation unit (exposure device) 118 that irradiates the display medium 101 with address light, and A voltage application unit (power supply device) 117 that applies a voltage to the display medium 101 is a main component, and a control circuit 116 that controls this operation is arranged.

(Light irradiation part)
The light irradiation unit 118 is configured to be able to irradiate the exposure surface side (lower side in FIG. 3) of the display medium with three address lights of red (R), green (G), and blue (B). ing. The address light may be emitted simultaneously for the three colors or separately. From the viewpoint of shortening the writing time, it is preferable to irradiate three colors simultaneously. Except for the fact that the address light has three colors in this way, the other configurations, functions, and the like are the same as those of the light irradiation unit 18 in the first embodiment, so a more detailed description is omitted.

(Voltage application part)
The voltage application unit 117 has a function of applying a predetermined bias voltage to the display medium 101. In this embodiment, three voltage application units 109B, 109G, which correspond to the voltage application unit 17 in the first embodiment are used. 109R.

The voltage application unit 117 applies the voltage to the display medium 101 through the three voltage application units 109B, 109G, and 109R in order through the contact terminals 119B and 120B, the contact terminals 119G and 120G, and the contact terminals 119R and 120R, respectively. , Between the transparent electrode 105B and the transparent electrode 106B, between the transparent electrode 105G and the transparent electrode 106G, and between the transparent electrode 105R and the transparent electrode 106R. Then, the respective voltage application units 109B, 109G, 109R have the same or different conditions (voltage, frequency, pulse waveform, application time, application time, etc.) and the corresponding light modulation units 200B, 200G, 200R of the display medium 101. A voltage can be applied to the.
Note that the individual voltage application units 109B, 109G, and 109R are similar in configuration and function to the voltage application unit 17 in the first embodiment, and will not be described in more detail.

  The control circuit 116 includes a voltage application unit 17 and a light irradiation unit according to image data from the outside (an image capturing device, an image receiving device, an image processing device, an image reproducing device, or a device having a plurality of these functions). This is a member having a function of appropriately controlling the operation of 18. The specific control contents by the control circuit 116 will be described in the following <Driving method> section.

<Driving method>
The method for driving the light modulation element of this embodiment will be described in detail below.
As described above, the display medium 101 that is the light modulation element of the present embodiment is formed by superposing three sets of light modulation units 200B, 200G, and 200R. As a method for driving the display medium 101, the operations of the two steps “first writing step” and “second writing step” described in the first embodiment are performed for each of the light modulation units 200. The The details of the operations and their actions in each step, as well as the meaning and mode, are basically the same as in the case of the first embodiment, so the description of the individual light modulation units 200 is omitted, and the overall The operation will be described.

  In the driving method of the present embodiment, in response to the operations of the “first writing process” and the “second writing process” described in the first embodiment, the voltage application unit 117 of the writing device 102 respectively emits each light. While applying a voltage between the transparent electrode 105 and the transparent electrode 106 of the modulation unit 200, image light addressing light of three colors of R, G and B is simultaneously applied from the light irradiation unit 118 to the exposure surface side of the display medium ( Irradiation is performed from the lower side in FIG. That is, “voltage application” + “address light irradiation” corresponding to each process is performed. Irradiation of address light in each step may be performed simultaneously for three colors or separately.

  The B-color address light is transmitted through the light modulation units 200R and 200G that are not in a complementary color relationship, is also transmitted through the display layer 108B of the light modulation unit 200B, and is a charge generation layer 113B that exhibits a Y color that is in a complementary color relationship with the B color. 115B is absorbed. The operation of the “first writing process” or the “second writing process” in the light modulation unit 200B is realized.

  The G-color address light is transmitted through the light modulation unit 200R that is not in a complementary color relationship, is also transmitted through the display layer 108G of the light modulation unit 200G, and enters the charge generation layers 113G and 115G that exhibit M color in a complementary color relationship with the G color. Absorbed. The operation of the “first writing process” or the “second writing process” in the light modulation unit 200G is realized. The G-color address light is absorbed by the charge generation layers 113G and 115G, and thus does not reach the upper light modulation unit 200B of the light modulation unit 200G.

  The R-color address light passes through the display layer 108R of the light modulation unit 200R and is absorbed by the charge generation layers 113R and 115R exhibiting the C color that is complementary to the R color. Then, the operation of the “first writing process” or the “second writing process” in the light modulation unit 200R is realized. The R-color address light is absorbed by the charge generation layers 113R and 115R, and thus does not reach the upper light modulation unit 200G and the light modulation unit 200B of the light modulation unit 200R.

  As described above, when the operations of the “first writing process” and the “second writing process” are performed for each light modulation unit 200, exposure / non-exposure is selected depending on the part while applying a voltage, and the combination Accordingly, any one or both of the display layer 107 and the display layer 108 are in a reflection state or both are in a transmission state. Thus, the phases are selected, and writing (driving) is performed on both the front and back surfaces of each light modulation unit 200.

  The display medium 101 on which images are recorded on both the front and back surfaces of each light modulation unit 200 in this manner can be freely carried and handled by being removed from the contact terminals 119 and 120. Each recorded image can be viewed visually when viewed from either the front or back side. At this time, the OPC layer 110 (more accurately, the charge generation layers 113 and 115) in each light modulation unit 200 exhibits a hue that is complementary to the reflected light (display color) of the display layers 107 and 108. Therefore, the recorded image on the back side of each light modulation unit 200 as viewed from the viewer side is absorbed by the OPC layer 10 and is not visually recognized by the viewer. That is, there is no show-back of the image for each color. That is, a clear image can be visually recognized.

  Further, when the reflected images from the display layers 107 and 108 in each light modulation unit 200 are visually recognized, even if there are one or two sets of light modulation units 200 in front of the viewer as viewed from the viewer side, Since there is no complementary color relationship, the light is transmitted as it is, and the original color image drawn by each light modulation unit 200 can be visually recognized. That is, a full color image with high color reproducibility by color superposition of the color images of each light modulation unit 200 can be viewed.

  As described above, the display medium 101 of the present embodiment, which is the light modulation element of the present invention, is a full-color on both the front and back sides by exposure of three colors of address light from one surface by the driving method arranged with the threshold shift method. Images can be recorded easily. In addition, full-color image recording on both the front and back surfaces is possible in this way, but the structure is relatively simple, the cost of manufacturing the display medium can be reduced, and the number of layers stacked is relatively small. Further, it is possible to reduce the thickness as a full-color display medium.

Although the present invention has been described in detail with reference to two preferred embodiments, the present invention is not limited to the above embodiments. For example, in the above embodiment, only the light modulation unit having one set and three sets is described as a specific example. However, in the present invention, the display layer is not limited to these, It may be a two-layer structure or a four-layer or more structure.
In addition, those skilled in the art can appropriately modify the present invention according to conventionally known knowledge. Of course, such modifications are included in the scope of the present invention as long as they still have the configuration of the present invention.

It is a schematic block diagram of 1st Embodiment which is an exemplary aspect of the system to which the light modulation element of this invention and its drive method are applied. 2 is a graph showing the switching behavior of cholesteric liquid crystal in each display layer in the light modulation element of FIG. 1. It is a schematic block diagram of 2nd Embodiment which is another exemplary aspect of the system to which the light modulation element of this invention and its drive method are applied. It is a schematic explanatory view showing the relationship between the molecular orientation and optical characteristics of cholesteric liquid crystal, wherein (A) is in the planar phase, (B) is in the focal conic phase, and (C) is in the homeotropic phase. It is a graph for demonstrating the switching behavior of a cholesteric liquid crystal. It is a schematic diagram which represents typically a mode that image writing is performed with the exposure apparatus with respect to the conventional general light modulation element. It is a schematic diagram schematically showing a light modulation element capable of double-sided recording having a structure in which a basic structure of a general light modulation element is bonded to an upper and lower object. It is a schematic explanatory drawing for demonstrating the mode of the image writing by the threshold value shift method of a prior art. It is a graph which shows the switching behavior of the cholesteric liquid crystal of each display layer in the laminated | stacked light modulation element provided to a threshold value shift method.

Explanation of symbols

  1, 101: Display medium (light modulation element), 2, 102: Writing device, 3, 4, 103, 104: Transparent substrate, 5, 6, 105, 106, 505, 506: Transparent electrode (electrode), 7, 8, 107, 108, 507: display layer, 10, 110, 510: OPC layer (photoconductor layer), 13, 15, 113, 115: charge generation layer, 14, 114: charge transport layer, 16, 116: Control circuit 17, 117: Voltage application unit 18, 118: Light irradiation unit 19, 20, 119, 120: Contact terminal 109: Voltage application unit 111, 112: Internal substrate 200: Light modulation unit 501 : Laminated light modulation element, 509: colored layer, 512: exposure device, 517: power supply device

Claims (1)

The lower threshold that is the operation threshold for the externally applied voltage for the change from the planar phase to the focal conic phase, and the upper threshold that is the operation threshold for the externally applied voltage for the change from the focal conic phase or the planar phase to the homeotropic phase are different from each other, at least A pair of display layers each made of cholesteric liquid crystal and reflecting visible light in a specific wavelength range having different hues,
A photoconductor layer disposed between the pair of display layers,
A pair of electrode layers respectively disposed on a surface opposite to the photoconductor layer side in the pair of display layers;
It is configured by stacking multiple light modulation units consisting of
The photoconductor layer in each of the light modulation units is formed in a three-layer structure in which charge generation layers are stacked above and below a charge transport layer, respectively.
And, the two charge generation layer in each of the photoconductor layer, a specific wavelength range and the same wavelength of the visible light in which the display layer in the charge generation layer side of each of the pair of display layers is reflected A light modulation element configured to absorb visible light in a region .

Images