This application is based on and claims priority under 35 U.S.C. 119 from Japanese Patent Application No. 2009-285050, which was filed on Dec. 16, 2009.
1. Technical Field
The present invention relates to a writing device.
2. Related Art
A writing device writes an image to a display medium having a display layer and a photoconductive layer disposed between a pair of electrodes. The display layer typically contains a cholesteric liquid crystal.
In one aspect of the present invention, there is provided a writing device for writing an image to a display medium, the display medium containing (a) a display layer unit that includes a first display layer, the first display layer having a liquid crystal that undergoes transition to a light-transmissive state when a voltage equal to or larger than a first threshold voltage and smaller than a second threshold voltage is applied to the display layer unit at least for a predetermined first time period, and that undergoes transition to a light-reflecting state when a voltage equal to or larger than the second threshold voltage is applied to the display layer unit at least for a predetermined second time period that is shorter than the first time period, after which the voltage is decreased to a predetermined voltage smaller than the first threshold voltage, (b) a pair of electroconductive layers between which a voltage is applied, the pair of electroconductive layers sandwiching the display layer unit therebetween, and (c) a photosensitive layer interposed between the pair of electroconductive layers, wherein when light is irradiated onto a portion of the photosensitive layer, an electric resistance of the light-irradiated portion of the photosensitive layer decreases in accordance with an intensity of the light, the writing device including: a voltage-applying unit that applies a voltage between the pair of electroconductive layers; and a light-irradiating unit that irradiates light onto the photosensitive layer, wherein the light-irradiating unit irradiates light onto a region of the photosensitive layer that overlaps a region of the display layer unit where the liquid crystal of the first display layer is to undergo transition to the light-reflecting state, and the voltage-applying unit applies a voltage between the pair of electroconductive layers for a time period equal to or longer than the second time period and shorter than the first time period, such that a voltage equal to or larger than the second threshold voltage is applied to the region of the display layer unit where the liquid crystal of the first display layer is to undergo transition to the light-reflecting state, and a voltage smaller than the second threshold voltage is applied to a region of the display layer unit overlapped by a region of the photosensitive layer to which no light is irradiated.
Exemplary embodiments of the present invention will be described in detail based on the following figures, wherein:
Writing device 1 is a device for writing an image to display medium 21. Writing device 1 has slot 11 into which display device 2 is inserted. Writing device 1 writes an image to display device 2 inserted into an inside of writing device 1 through slot 11. Glass plate 110 is a transparent glass plate. Through glass plate 11, a user of writing device 1 can view display medium 21 of display device 2 placed inside of writing device 1. Further, writing device 1 is provided with terminals for electric connection with the electroconductive layers of display device 2 and a unit for irradiating light onto the photosensitive layer of display device 2. Writing device 1 irradiates light onto display device 2 while applying a voltage to the electroconductive layers of display device 2 via the terminals, to cause display device 2 to display an image.
Substrate layers 201A, 201B are layers for protecting an image-displaying portion of display medium 21 and supporting a shape of the same. Each substrate layer 201A, 201B is exposed to a corresponding surface of display device 2. In this exemplary embodiment, each substrate layer is made of polyethylene terephthalate, but the material constituting each substrate layer is not limited to polyethylene terephthalate, and can be another material having a light-transmitting property and an electrically insulating property.
In this exemplary embodiment, electroconductive layers 202A, 202B are made of indium tin oxide. Each electroconductive layer 202A, 202B is transparent and has electric conductivity. The material for constituting electroconductive layers 202A, 202B is not limited to indium tin oxide, and can be another material having a light-transmitting property and electric conductivity. In
Display layer 204R contacting a surface of electroconductive layer 202A facing toward the light-irradiated side, and display layer 204G contacting a surface of display layer 204R facing toward the light-irradiated side are layers constituted of plural materials such as a cholesteric liquid crystal, light-transmissive resin, etc. Each display layer has a structure such that the cholesteric liquid crystal is dispersed in the resin. Molecules of a cholesteric liquid crystal are helically aligned and the alignment state changes depending on an applied voltage. Thus, in response to an applied voltage, a cholesteric liquid crystal undergoes transition to a state for reflecting light of a specific wavelength or to a state for allowing light to pass therethrough. In this exemplary embodiment, the cholesteric liquid crystal of display layer 204G is adjusted to reflect green light (light having a wavelength in a range from 500 nm to 600 nm), and the cholesteric liquid crystal of display layer 204R is adjusted to reflect red light (light having a wavelength in a range from 600 nm to 700 nm). It is to be noted that green light and red light are mere examples, and the light reflected from each display layer is not limited thereto. The material of the cholesteric liquid crystal of each display layer may be selected such that different display layers reflect light of predetermined different wavelength ranges. The resin used in each display layer functions to hold the cholesteric liquid crystal in position to suppress any change in an image. The resin used in each display layer is strong enough to withstand an external force and is transmissive to light.
In this exemplary embodiment, a stack of display layer 204R and display layer 204G constitutes a display layer unit.
Photosensitive layer 205 is in contact with a surface of electroconductive layer 202B facing toward the viewer side and, in this exemplary embodiment, includes electric charge generation layers 2051, 2053 that generate electric charge and electric charge transportation layer 2052 that transports electric charge. Photosensitive layer 205 is constituted of electric charge generation layer 2051, electric charge transportation layer 2052, and electric charge generation layer 2053 stacked in this order from the viewer side. When light is irradiated onto photosensitive layer 205, an electric resistance of the portion of photosensitive layer 205 irradiated with light is reduced. A voltage applied to the pair of electroconductive layers, between which the display layer unit and the photosensitive layer are sandwiched, is divided between display layer unit and the photosensitive layer, and thus, if an electric resistance of a portion of the photosensitive layer is decreased, the ratio of voltage applied to the photosensitive layer to the voltage applied to the display layer unit changes such that the voltage applied to the display layer unit is increased.
Colored layer 206 is positioned to contact a surface of photosensitive layer 205 facing toward the viewer side and absorbs light. Colored layer 206 is colored with an inorganic pigment, an organic dye or an organic pigment. Laminate layer 207 is disposed between colored layer 206 and display layer 204G to serve to adhere the display layer to the colored layer and absorbs surface irregularities of these layers. As a material of laminate layer 207, a high polymer is selected that has a low glass transition temperature and is able to cause adherence between the display layer and the photosensitive layer in a close contact state when a heat and/or a pressure is applied. Also, laminate layer 207 is transmissive at least to incident light. The material used for laminate layer 207 may be an adhesive high polymer such as urethane resin, epoxy resin, acrylic resin, or silicone resin.
In display medium 21 constituted of the above-explained layers, the cholesteric liquid crystal in the display layers undergoes transition from a planar state to a focal-conic state and from a focal-conic state to a homeotropic state as an applied voltage increases, in a case where the initial state before application of a voltage is a planar state.
If the initial state before application of a voltage is the focal-conic state, the cholesteric liquid crystal changes to the homeotropic state with an increase in an applied voltage. If the voltage application is stopped when the cholesteric liquid crystal is in the focal-conic state, the cholesteric liquid crystal remains in the focal-conic state. Also, if the voltage application is stopped when the cholesteric liquid crystal is in the homeotropic state, the alignment state changes from the homeotropic state to the planar state, and the cholesteric liquid crystal stays in the planar state.
Provided that Vg1 represents a threshold voltage for a transition of cholesteric liquid crystal of display layer 204G from the planar state to the focal-conic state and Vg2 represents a threshold voltage for a transition of the same from the focal-conic state to the homeotropic state, in a case where the voltage applied to the display layer unit via the electroconductive layers and the photosensitive layer is equal to or larger than Vg2 before termination of the voltage application, the cholesteric liquid crystal of display layer 204G will be in the planar state after the voltage application is terminated, to reflect green light contained in external light. On the other hand, in a case where the voltage applied to the display layer unit via the electroconductive layers and the photosensitive layer is equal to or larger than Vg1 and smaller than Vg2 before termination of the voltage application, the cholesteric liquid crystal of display layer 204G will be in the focal-conic state after the voltage application is terminated, to allow external light to pass therethrough.
Also, provided that Vr1 represents a threshold voltage for a transition of cholesteric liquid crystal of display layer 204R from the planar state to the focal-conic state and Vr2 represents a threshold voltage for a transition of the same from the focal-conic state to the homeotropic state, in a case where the voltage applied to the display layer unit via the electroconductive layers and the photosensitive layer is equal to or larger than Vr2 before termination of the voltage application, the cholesteric liquid crystal of display layer 204R will be in the planar state after the voltage application is terminated, to reflect red light contained in external light. On the other hand, in a case where the voltage applied to the display layer unit via the electroconductive layers and the photosensitive layer is equal to or larger than Vr1 and smaller than Vr2 before termination of the voltage application, the cholesteric liquid crystal of display layer 204R will be in the focal-conic state after the voltage application is terminated, to allow external light to pass therethrough.
As described in the foregoing, the cholesteric liquid crystal in each display layer undergoes transition to the focal-conic state when an applied voltage becomes equal to or greater than a threshold voltage for a transition from the planar state to the focal-conic state (Vr1, Vg1; hereinafter referred to as a lower threshold voltage). Also, the cholesteric liquid crystal in each display layer undergoes transition to the homeotropic state when an applied voltage becomes equal to or greater than a threshold voltage for a transition from the focal-conic state to the homeotropic state (Vr2, Vg2; hereinafter referred to as an upper threshold voltage), and further undergoes transition to the planar state when the voltage application is terminated.
It is to be noted that in this exemplary embodiment, the lower threshold voltage for display layer 204R is smaller than the lower threshold voltage for display layer 204G, and the upper threshold voltage for display layer 204R is smaller than the upper threshold voltage for display layer 204G. In the present specification, a display layer having a smaller value of lower threshold voltage is referred to as a first display layer, and a display layer having a larger value of lower threshold voltage is referred to as a second display layer. Further, the lower threshold voltage of the first display layer is referred to as a first threshold voltage, the upper threshold voltage of the first display layer is referred to as a second threshold voltage, the lower threshold voltage of the second display layer is referred to as a third threshold voltage, and the upper threshold voltage of the second display layer is referred to as a fourth threshold voltage.
The time period required to cause alignment-state transition of the cholesteric liquid crystal is different between the transition from the planar state to the focal-conic state and the transition from the focal-conic state to the homeotropic state. In the exemplary embodiment, to cause transition of the cholesteric liquid crystal from the planar state to the focal-conic state, it is necessary to apply a voltage between the lower threshold value and the upper threshold value for 100 ms or more. On the other hand, to cause transition of the cholesteric liquid crystal from the focal-conic state to the homeotropic state, it is necessary to apply a voltage equal to or larger than the upper threshold value for 10 ms or more. It is noted, however, that the time period required for alignment-state transition is not limited to the above time periods, and can be another time period depending on a kind of cholesteric liquid crystal or other factors.
Control unit 101 has a so-called microcomputer having a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), an input port, an output port, etc. The ROM stores a control program for controlling various units. Upon execution of the control program by the CPU, Control unit 101 controls various units of writing device 1 in accordance with an operation input through operation unit 106. Also, by executing the control program, control unit 101 achieves a function of overwriting an additional image to display medium 21.
Voltage-applying unit 103 has a terminal for connection with terminal 203A and a terminal for connection with terminal 203B. Further, voltage-applying unit 103 is equipped with a voltage generator. Voltage-applying unit 103 applies the voltage generated by the voltage generator to electroconductive layers 202A, 202B via terminals 203A, 203B, respectively. The voltage applied to electroconductive layers 202A, 202B from voltage-applying unit 103 is controlled by control unit 101.
Interface unit 105 serves as an interface for communication with a computer device such as a personal computer. Interface unit 105 is connected to a personal computer by means of a communications cable, and receives image data representing an image from the personal computer. The image data received from the personal computer is stored in the RAM.
Operation unit 106 includes display device 106A that displays an image, and touch panel 106B, which is transparent and is disposed on a surface of display device 106A. Display device 106A is constituted of a liquid crystal display device, for example, and displays a screen for allowing a user to operate writing device 1. Touch panel 106B provides control unit 101 with a signal that indicates a location selected by the user.
First, display device 2 is inserted into slot 11 of writing device 1 by a user. As a result, voltage-applying unit 103 of writing device 1 is electrically connected to terminals 203A, 203B of display device 2. Then, when the user inputs an instruction through operation unit 106 for writing an image represented by image data stored in the RAM to an entire part of display medium 21, the process described below is executed.
Control unit 101 controls light output unit 102 and voltage-applying unit 103 to cause display medium 21 to display the image represented by the image data. Concretely, in a state that light output unit 102 is not irradiating light onto display medium 21, control unit 101 controls voltage-applying unit 103 to apply a voltage between terminals 203A, 203B such that an effective value of a divisional voltage applied to the display layer unit constituted of a stack of display layer 204R and display layer 204G becomes a certain value between Vr2 and Vg2 (V2 in
Next, control unit 101 controls light output unit 102 in accordance with the image represented by the image data, such that light is irradiated onto portions of display medium 21 that are to exhibit green and onto portions of display medium 21 that are to exhibit yellow. The light output from light output unit 102 reaches photosensitive layer 205. At portions of photosensitive layer 205 where light reaches, the electric resistance decreases, and this changes a ratio of the divisional voltage applied to the display layer unit to the divisional voltage applied to photosensitive layer 205, and as a result, the effective value of the divisional voltage applied to the display layer unit is increased to be equal to or larger than Vg2. In portions of display layer 204G where the effective value of the applied voltage is increased, the cholesteric liquid crystal undergoes transition to the homeotropic state. Thereafter, control unit 101 controls voltage-applying unit 102 to terminate the voltage application to the electroconductive layers. Further, control unit 101 controls light output unit 102 to terminate the irradiation of light onto photosensitive layer 205. Upon termination of voltage application to the electroconductive layers and irradiation of light onto photosensitive layer 205, the portions of the cholesteric liquid crystal of each display layer that have been brought into the homeotropic state undergo transition to the planar state.
Subsequently, control unit 101 controls voltage-applying unit 103 to apply a voltage between terminals 203A, 203B such that the effective value of the divisional voltage applied to the display layer unit becomes equal to a specific value smaller than Vr1 (Va in
Thereafter, when the user inputs an instruction through operation unit 106 for overwriting an additional image represented by image data stored in the RAM to display medium 21, the process described below is executed.
Explanation will now be made of a case where sub-region A12 exhibiting yellow, sub-region A13 exhibiting red, and sub-region A14 exhibiting green are overwritten on black color region A1, as shown in
Next, in the second step, control unit 101 controls light output unit 102 such that light of a first luminous intensity is irradiated onto sub-region A13, light of a second luminous intensity, which is larger than the first luminous intensity, is irradiated onto sub-region A14 and sub-region A12, and no light is irradiated onto sub-region A11. Then, control unit 101 controls voltage-applying unit 103 to apply a voltage between terminals 203A, 203B (or between electroconductive layers 202A, 202B) such that a divisional voltage is applied to the display layer unit. The voltage applied between terminals 203A, 203B is selected such that a voltage between Vg1 and Vr2 (V1 in
Upon application of voltage from voltage-applying unit 103, a voltage between Vr2 and Vg2 (V2 of
It is to be noted that in the second step, the time period of voltage application from voltage-applying unit 103 is shorter than the time period required for causing the cholesteric liquid crystal in the planar state to undergo transition to the focal-conic state. Therefore, though a voltage is applied to electroconductive layers 202A, 202B such that voltage V1, which is larger than Vr1 and Vg1, is applied to the display layer unit in portions where no light is irradiated, the cholesteric liquid crystal that is in the planar state (such as the cholesteric liquid crystal of each display layer in region A2) and is contained in such portions (and thus is applied with voltage V1) does not undergo transition to the focal-conic state and remains in the planar state.
Subsequently, in the third step, control unit 101 controls light output unit 102 to irradiate light of the first luminous intensity onto sub-region A14. At the same time, control unit 101 controls light output unit 102 such that no light is irradiated onto sub-regions A11, A12, and A13.
Then, control unit 101 controls voltage-applying unit 103 such that a divisional voltage is applied to the display layer unit via terminals 203A, 203B. At this time, the voltage applied between terminals 203A, 203B is selected such that voltage Va is applied to the display layer unit in portions where no light is irradiated (such as in sub-regions A11, A12, and A13). Thus, when the voltage is applied from voltage-applying unit 103, the cholesteric liquid crystal in sub-regions A11, A12, and A13 remains in the same alignment state as that prior to the voltage application (i.e., either in the planar state or in the focal-conic state), as shown in
In the state after completion of the third step, in sub-region A11, the cholesteric liquid crystal of each display layer is still in the focal-conic state, and thus, sub-region A11 appears black to a user. In sub-region A12, the cholesteric liquid crystal in each display layer 204R, 204G has been brought into the planar state, and thus, sub-region A12 appears yellow to a user. In sub-region A13, the cholesteric liquid crystal of display layer 204G has remained in the focal-conic state and the cholesteric liquid crystal of display layer 204R has been brought into the planar state, and thus, sub-region A13 appears red to a user. Further, in sub-region A14, the cholesteric liquid crystal of display layer 204G has been brought into the planar state and the cholesteric liquid crystal of display layer 204R has been eventually brought into the focal-conic state, and thus, sub-region A14 appears green to a user.
Explanation will now be made of a case where sub-region A21 exhibiting black, sub-region A23 exhibiting red, and sub-region A24 exhibiting green are overwritten on yellow color region A2, as shown in
In this state, the divisional voltage applied to the display layer unit in sub-region A22 remains at voltage Va. Thus, the cholesteric liquid crystal of each display layer remains in the planar state in sub-region A22, as shown in
Next, in the second step, control unit 101 controls light output unit 102 such that light of the first luminous intensity is irradiated onto sub-region A23, and no light is irradiated onto sub-regions A21, A22, and A24. Then, control unit 101 controls voltage-applying unit 103 to apply a voltage between terminals 203A, 203B such that voltage V1 shown in
Upon application of voltage from voltage-applying unit 103, voltage V2 shown in
As mentioned above, in the second step, the time period of voltage application from voltage-applying unit 103 is shorter than the time period required for causing the cholesteric liquid crystal in the planar state to undergo transition to the focal-conic state. Therefore, though a voltage is applied to electroconductive layers 202A, 202B such that voltage V1, which is larger than Vr1 and Vg1, is applied to the display layer unit in portions where no light is irradiated, the cholesteric liquid crystal that is in the planar state (such as the cholesteric liquid crystal of each display layer in sub-region A22 or the cholesteric liquid crystal of display layer 204G in sub-region A24) and is contained in those portions (and thus is applied with voltage V1), does not undergo transition to the focal-conic state and remains in the planar state.
Subsequently, in the third step, control unit 101 controls light output unit 102 such that no light is irradiated onto sub-regions A21-A24. Then, control unit 101 controls voltage-applying unit 103 such that a divisional voltage is applied to the display layer unit via terminals 203A, 203B. At this time, the voltage applied between terminals 203A, 203B is selected such that voltage Va is applied to the display layer unit in portions where no light is irradiated. Thus, when the voltage is applied from voltage-applying unit 103, voltage Va is applied to the display layer unit in sub-regions A21-A24, and the cholesteric liquid crystal in sub-regions A21-A24 remains in the same alignment state as that prior to the voltage application (i.e., either in the planar state or in the focal-conic state), as shown in
In the state after completion of the third step, in sub-region A21, the cholesteric liquid crystal of each display layer has been brought into the focal-conic state, and thus, sub-region A21 appears black to a user. In sub-region A22, the cholesteric liquid crystal in each display layer 204R, 204G has remained in the planar state, and thus, sub-region A22 appears yellow to a user. In sub-region A23, the cholesteric liquid crystal of display layer 204G has been brought into the focal-conic state and the cholesteric liquid crystal of display layer 204R has been eventually brought into the planar state, and thus, sub-region A23 appears red to a user. Further, in sub-region A24, the cholesteric liquid crystal of display layer 204G has remained in the planar state and the cholesteric liquid crystal of display layer 204R has been brought into the focal-conic state, and thus, sub-region A24 appears green to a user.
Explanation will now be made of a case where sub-region A31 exhibiting black, sub-region A32 exhibiting yellow, and sub-region A34 exhibiting green are overwritten on red color region A3, as shown in
In this state, the divisional voltage applied to the display layer unit in sub-region A33 remains at voltage Va. Thus, the cholesteric liquid crystal of each display layer in sub-region A33 remains in the same alignment state as that prior to the voltage application, as shown in
Next, in the second step, control unit 101 controls light output unit 102 such that light of the second luminous intensity is irradiated onto sub-regions A32 and A34 and no light is irradiated onto sub-regions A31 and A33. Then, control unit 101 controls voltage-applying unit 103 to apply a voltage between terminals 203A, 203B (or between electroconductive layers 202A, 202B) such that voltage V1 shown in
Upon application of voltage from voltage-applying unit 103, voltage V3 shown in
As mentioned above, in the second step, the time period of voltage application from voltage-applying unit 103 is shorter than the time period required for causing the cholesteric liquid crystal in the planar state to undergo transition to the focal-conic state. Therefore, though a voltage is applied to electroconductive layers 202A, 202B such that voltage V1, which is larger than Vr1 and Vg1, is applied to the display layer unit in portions where no light is irradiated, the cholesteric liquid crystal that is in the planar state (such as the cholesteric liquid crystal of display layer 204R in sub-region A33) and is contained in such portions (and thus is applied with voltage V1) does not undergo transition to the focal-conic state and remains in the planar state.
Subsequently, in the third step, control unit 101 controls light output unit 102 such that light of the first luminous intensity is irradiated onto sub-region A34 and no light is irradiated onto sub-regions A31-A33. Then, control unit 101 controls voltage-applying unit 103 such that a divisional voltage is applied to the display layer unit via terminals 203A, 203B. At this time, the voltage applied between terminals 203A, 203B is selected such that voltage Va is applied to the display layer unit in portions where no light is irradiated. Thus, when the voltage is applied from voltage-applying unit 103, voltage Va is applied to the display layer unit in sub-regions A31-A33, and the cholesteric liquid crystal in sub-regions A31-A33 remains in the same alignment state as that prior to the voltage application (i.e., either in the planar state or in the focal-conic state), as shown in
In the state after completion of the third step, in sub-region A31, the cholesteric liquid crystal of display layer 204R has been brought into the focal-conic state and the cholesteric liquid crystal of display layer 204G remains in the focal-conic state, and thus, sub-region A31 appears black to a user. In sub-region A32, the cholesteric liquid crystal in each display layer 204R, 204G has been brought into the planar state, and thus, sub-region A32 appears yellow to a user. In sub-region A33, the cholesteric liquid crystal of display layer 204R has remained in the planar state and the cholesteric liquid crystal of display layer 204G has remained in the focal-conic state, and thus, sub-region A33 appears red to a user. Further, in sub-region A34, the cholesteric liquid crystal of display layer 204G has been brought into the planar state and the cholesteric liquid crystal of display layer 204R has been brought into the focal-conic state, and thus, sub-region A34 appears green to a user.
Explanation will now be made of a case where sub-region A41 exhibiting black, sub-region A42 exhibiting yellow, and sub-region A43 exhibiting red are overwritten on green color region A4, as shown in
In this state, the divisional voltage applied to the display layer unit in sub-region A44 remains at voltage Va. Thus, the cholesteric liquid crystal of each display layer in sub-region A44 remains in the same alignment state as that prior to the voltage application, as shown in
Next, in the second step, control unit 101 controls light output unit 102 such that light of the first luminous intensity is irradiated onto sub-region A43, light of the second luminous intensity is irradiated onto sub-region A42, and no light is irradiated onto sub-regions A41 and A44. Then, control unit 101 controls voltage-applying unit 103 to apply a voltage between terminals 203A, 203B (or between electroconductive layers 202A, 202B) such that voltage V1 shown in
Upon application of voltage from voltage-applying unit 103, voltage V2 shown in
As mentioned above, in the second step, the time period of voltage application from voltage-applying unit 103 is shorter than the time period required for causing the cholesteric liquid crystal in the planar state to undergo transition to the focal-conic state. Therefore, though a voltage is applied to electroconductive layers 202A, 202B such that voltage V1, which is larger than Vr1 and Vg1, is applied to the display layer unit in portions where no light is irradiated, the cholesteric liquid crystal that is in the planar state (such as the cholesteric liquid crystal of display layer 204G in sub-region A44) does not undergo transition to the focal-conic state and remains in the planar state.
Subsequently, in the third step, control unit 101 controls light output unit 102 such that no light is irradiated onto sub-regions A41-A44. Then, control unit 101 controls voltage-applying unit 103 such that a divisional voltage is applied to the display layer unit via terminals 203A, 203B. At this time, the voltage applied between terminals 203A, 203B is selected such that voltage Va is applied to the display layer unit in portions where no light is irradiated. Thus, when the voltage is applied from voltage-applying unit 103, voltage Va is applied to the display layer unit in sub-regions A41-A44, and the cholesteric liquid crystal in sub-regions A41-A44 remains in the same alignment state as that prior to the voltage application (i.e., either in the planar state or in the focal-conic state), as shown in
In the state after completion of the third step, in sub-region A41, the cholesteric liquid crystal of display layer 204G has been brought into the focal-conic state and the cholesteric liquid crystal of display layer 204R remains in the focal-conic state, and thus, sub-region A41 appears black to a user. In sub-region A42, the cholesteric liquid crystal in each display layer 204R, 204G has been brought into the planar state, and thus, sub-region A42 appears yellow to a user. In sub-region A43, the cholesteric liquid crystal of display layer 204R has been brought into the planar state and the cholesteric liquid crystal of display layer 204G has been brought into the focal-conic state, and thus, sub-region A43 appears red to a user. Further, in sub-region A44, the cholesteric liquid crystal of display layer 204G has remained in the planar state and the cholesteric liquid crystal of display layer 204R has remained in the focal-conic state, and thus, sub-region A44 appears green to a user.
In the foregoing, explanation is made of the exemplary embodiment of the present invention, but the present invention is not limited to the exemplary embodiment and can be practiced in a variety of other embodiments. For example, the above-described exemplary embodiment may be modified as described below to practice the invention. Also, the exemplary embodiment and the following modified embodiments may be combined, as necessary.
In the foregoing exemplary embodiment, the display layer unit of display medium 21 includes two display layers, i.e., display layer 204R and display layer 204G, but the display layer unit may include only a single display layer. As an example of a single display layer structure, display medium 21 may include only display layer 204G, for example. In such a structure, to locally change an alignment state of the cholesteric liquid crystal to the planar state, writing device 1 applies a voltage to the electroconductive layers such that an effective value of the divisional voltage applied to display layer 204G in portions where no light is irradiated becomes equal to voltage V2, and controls light output unit 102 to irradiate light onto the photosensitive layer such that voltage V3 is applied to a portion(s) of the cholesteric liquid crystal where the alignment state should be changed to the planar state. In this case also, a time period during which the voltage is applied from voltage-applying unit 103 is set shorter than the first time period and longer than the second time period. It is to be noted that the single display layer structure may be constituted of a structure that includes display layer 204R only. Further, in a single display layer structure, the wavelength of light reflected from the display layer may be different from the wavelength of light reflected by display layer 204R or 204G.
In the foregoing exemplary embodiment, display medium 21 includes two display layers, i.e., display layer 204R and display layer 204G, but display medium 21 may include three display layers.
Each electroconductive layer 202A, 202B, 202C, 202D is a layer that is transparent and has electric conductivity. Electroconductive layer 202A is in contact with a surface of substrate layer 201A facing toward the light-irradiated side. Electroconductive layer 202B is in contact with a surface of substrate layer 201B facing toward the viewer side. Electroconductive layer 202C is in contact with a surface of substrate layer 201B facing toward the light-irradiated side. Electroconductive layer 202D is in contact with a surface of substrate layer 201C facing toward the viewer side. Further, electroconductive layer 202A is connected to terminal 203A, electroconductive layer 202B to terminal 203B, electroconductive layer 202C to terminal 203C, and electroconductive layer 202D to terminal 203D. Terminals 203A-203D are supplied with a voltage from writing device 1, and are arranged to be exposed to a surface(s) of display device 2.
Each display layer 204B, 204G, 204R is a layer constituted of plural materials such as a cholesteric liquid crystal, light-transmissive resin, etc., and has such a structure that the cholesteric liquid crystal is dispersed in the resin. Display layer 204B is in contact with a surface of electroconductive layer 202A facing toward the light-irradiated side, display layer 204G is in contact with a surface of display layer 204B facing toward the light-irradiated side, and display layer 204R is in contact with a surface of electroconductive layer 202C facing toward the light-irradiated side. In this modified embodiment, display layer 204R and display layer 204G have the same structure as described in the foregoing with respect to the exemplary embodiment. The cholesteric liquid crystal of display layer 204B is adjusted to reflect blue light (light having a wavelength in a range of 400 nm-500 nm).
Like photosensitive layer 205 of the above-described exemplary embodiment, each photosensitive layer 205R, 205BG is constituted of electric charge generation layer 2051, electric charge transportation layer 2052, and electric charge generation layer 2053 stacked in this order from the viewer side. Photosensitive layer 205R is in contact with a surface of electroconductive layer 202B facing toward the viewer side, and photosensitive layer 205R is in contact with a surface of electroconductive layer 202D facing toward the viewer side.
Colored layer 206R is a layer that absorbs light having the same wavelength as the light absorbed by the charge generation layer of photosensitive layer 205R. Colored layer 206R is colored with an inorganic pigment, an organic dye or an organic pigment, to assume a color complementary to the color of light reflected by display layers 204B, 204G Colored layer 206R is in contact with a surface of photosensitive layer 205R facing toward the viewer side. Colored layer 206BG is a layer that absorbs light having the same wavelength as the light absorbed by the charge generation layer of photosensitive layer 205BG, and is colored with an inorganic pigment, an organic dye or an organic pigment, to assume a color complementary to the color of light reflected by display layers 204R. Colored layer 206BG is in contact with a surface of photosensitive layer 205BG facing toward the viewer side.
Laminate layer 207 is made of the same material as laminate layer 207 of the above-described exemplary embodiment. In this modified embodiment, two laminate layers 207 are disposed; one between colored layer 206R and display layer 204G and the other between colored layer 206BG and display layer 204R.
Provided that Vb1 represents a threshold voltage for a transition of cholesteric liquid crystal of display layer 204B from the planar state to the focal-conic state and Vb2 represents a threshold voltage for a transition of the same from the focal-conic state to the homeotropic state, in a case where the voltage applied to a display layer unit constituted of a stack of display layer 204B and display layer 204G via the electroconductive layers and the photosensitive layer is equal to or larger than Vb2 before termination of the voltage application, the cholesteric liquid crystal of display layer 204B will be in the planar state after the voltage application is terminated, to reflect green light contained in external light. On the other hand, in a case where the voltage applied to display layer unit via the electroconductive layers and the photosensitive layer is between Vb1 and Vb2 before termination of the voltage application, the cholesteric liquid crystal of display layer 204B will be in the focal-conic state after the voltage application is terminated, to allow external light to pass therethrough.
Compared with the exemplary embodiment, in the configuration shown in
In the foregoing exemplary embodiment, two display layers are disposed between electroconductive layers 202A and 202B to constitute a display layer unit. However, it is possible that display layers 204R, 204G, 204B are disposed between electroconductive layers 202A and 202B to form a display layer unit. In such a case, a voltage applied to the stack of display layers (or the display layer unit) and a normalized light reflectivity of each display layer may have a relationship as shown in
In this modified embodiment, display layer 204B having the smallest lower threshold voltage corresponds to the first display layer, display layer 204R having the second smallest lower threshold voltage corresponds to the second display layer, and display layer 204G having the largest lower threshold voltage corresponds to the third display layer. Also, in the present specification, the lower threshold voltage of the third display layer is referred to as a fifth threshold voltage, and an upper threshold voltage of the third display layer is referred to as a sixth threshold voltage.
In writing device 1, means for irradiating light onto the light-irradiated side of display medium 21 is not limited to a liquid crystal display. It is possible to arrange light emitting diodes in a plane, and selectively turn on the light emitting diodes in accordance with a position signal to thereby irradiate light onto a desired portion(s) on the light-irradiated side of display medium 21. Further, instead of the liquid crystal display, an EL (electroluminescent) display or any other display device using a material that emits light in response to a voltage application may be utilized. Also, the liquid crystal display may be any of a variety of types. For example, the liquid crystal display may be a monochromatic type having a backlight unit that can selectively emit one of three colors of light (red light, green light, blue light) and that is capable of setting a state of each pixel to either of a light-transmitting state or a light non-transmitting state. Furthermore, another plane-type display device, such as a CRT (Cathode Ray Tube), PDP (Plasma Display Panel), FED (Field Emission Display), SED (Surface-conduction Electron-emitter Display), may be used to irradiate light onto display medium 21.
The foregoing description of the embodiments of the present invention is provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.
Number | Date | Country | Kind |
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2009-285050 | Dec 2009 | JP | national |