JP2000111942A - Display memory medium, image writing method and image writing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a full color displayable display memory medium which is capable of rapidly rewriting images by an external device, decreasing the voltage necessary for writing of the images and preventing the deterioration in display characteristics by the adhesion of dust, etc. SOLUTION: The display memory medium 1 is formed by laminating display layers 8A, 8B and 8C consisting of cholesteric liquid crystals which selectively reflect respective color light rays of blue, green and red, a light absorption layer 6 and a photoconductive layer 7 between substrates 2 and 3 formed with bias electrodes 10 and 11 on their inside surfaces. The threshold voltage of the respective cholesteric liquid crystals for the voltage to be impressed over the entire part of the display layers 8A, 8B and 8C is changed. An image writing device 12 is formed as a separate body from the display memory medium 1 and impresses bias voltage between the electrodes 10 and 11 for a voltage impression section 13 in a refreshing period and a selecting period and irradiate the photoconductive layer 7 with writing light 17 from a photoirradiation section 14. The voltage impressed over the entire part of the display layers 8A, 8B and 8C in the refreshing period and the selecting period is selected from plural stages of the voltage bordering at the threshold voltage described above.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a display storage medium for displaying an image (including information such as characters and figures) and storing the display state, and a method and an apparatus for writing an image on the display storage medium. .

[0002]

2. Description of the Related Art Mass consumption of paper, especially in offices, has become a problem due to the destruction of forest resources, which are the raw materials of paper pulp, the disposal of waste, and environmental pollution caused by incineration. However, due to the spread of personal computers and the development of the information society including the Internet, the consumption of paper as a so-called short-lived document for the purpose of temporarily browsing electronic information tends to increase. There is a need for a rewritable display storage medium that can replace paper.

[0003]

Therefore, the applicant has previously filed Japanese Patent Application No. 9-317049 (November 18, 1997).
Date, application), has a memory without power supply, and can rewrite the image in a short time by an external device,
A display storage medium capable of full color display, an image writing method thereof, and an image writing device have been proposed.

In the prior invention, as shown in FIG. 17, as a display storage medium 27, blue, green and red color lights are selectively reflected between substrates 16 and 17, respectively.
The display layers 21A, 21B and 21C made of cholesteric liquid crystal having different threshold voltages from each other
1A, 21B and 21C have spacers 22 respectively.
A, 22B, and 22C are inserted and stacked between the display layers 21A and 21B via a separation substrate 18, and between the display layers 21B and 21C via a separation substrate 19, and the light absorption layer 20 is provided on the back surface of the substrate 17. Is provided.

[0005] The image writing device 26 includes a display storage medium 2.
7 are formed separately from each other, and write electrodes 23 and 24 for sandwiching the display storage medium 27 and a drive circuit 25 are provided. The cholesteric liquid crystal of the display layers 21A, 21B, and 21C includes a refresh period and a select period, and a subsequent non-voltage display period. The applied voltages Vr and Vs in the refresh period and the select period have a relationship of Vr> Vs. A write signal having a voltage selected from seven levels of voltages with the threshold voltage of
Apply between four.

However, in the display storage medium, the image writing method and the image writing apparatus according to the invention of the prior application, the substrates 16 and 1 having a thickness of several tens μm to several hundreds μm are provided.
7, a write signal is applied from outside the display layer 21.
The voltage actually applied to A, 21B, and 21C is considerably smaller than the voltage of the write signal. Therefore, in order to switch the display layers 21A, 21B and 21C, there is a disadvantage that a very large voltage must be applied between the write electrodes 23 and 24.

Further, the substrates 16, 17 and the write electrode 2
If foreign matter such as dust is present between the display layers 21A, 21B, and 21C due to a change in the distance between the electrodes 23 and 24 and a voltage drop due to a gap between the air layers. Is not the desired value, the switching of the cholesteric liquid crystal is not performed properly, and the display characteristics are degraded.

Accordingly, the present invention reduces the voltage required for writing an image in a display storage medium capable of full-color display in which an image can be rewritten in a short time by an external device, and an image writing method and an image writing apparatus. It is another object of the present invention to reduce deterioration of display characteristics due to adhesion of dust and the like.

[0009]

According to the first aspect of the present invention, as a display storage medium, at least a mutually different color light in visible light is selectively reflected between a pair of transparent substrates on which a bias electrode having a solid structure is formed. A plurality of display layers made of cholesteric liquid crystal and a photoconductive layer are stacked, and a voltage is applied between the bias electrodes from an external writing device, and the photoconductive layer is irradiated with light to form an image. Is written.

According to a second aspect of the present invention, in the display storage medium of the first aspect, the plurality of display layers include, among voltages applied between the bias electrodes from an external writing device,
It is assumed that the threshold voltage of each cholesteric liquid crystal is different from the voltage applied to the entire display layers.

According to a third aspect of the present invention, in the display storage medium of the first or second aspect, each of the plurality of display layers is made of a cholesteric liquid crystal that selectively reflects the same color light and has a helical twist direction opposite to each other. It is assumed that it consists of two display layers.

According to a fourth aspect of the present invention, in the method for writing an image on a display storage medium according to the first or second aspect, a voltage is applied from at least a voltage between the bias electrodes from an external image writing device to the photoconductive layer. A select period for irradiating light of an arbitrary intensity and a display period in which no voltage is applied between the bias electrodes, and a write signal for changing all the cholesteric liquid crystals of the plurality of display layers to the same alignment state. I do.

According to a fifth aspect of the present invention, in the method for writing an image on the display storage medium according to the second aspect, a voltage is applied between at least the bias electrodes from an external image writing device, and an arbitrary intensity is applied to the photoconductive layer. And a select period in which a voltage smaller than the voltage applied in the refresh period is applied between the bias electrodes, and a select period in which the photoconductive layer is irradiated with light of an arbitrary intensity. And a display period in which no voltage is applied, and the voltage applied to the entirety of the plurality of display layers is selected from a plurality of voltages having a threshold voltage of the cholesteric liquid crystal of the plurality of display layers as a boundary. It is assumed that a voltage write signal is applied.

According to a sixth aspect of the present invention, in the device for writing an image on the display storage medium according to the first or second aspect, a voltage is applied from at least between the bias electrodes from outside the display storage medium to the photoconductive layer. A select period for irradiating light of an arbitrary intensity and a display period in which no voltage is applied between the bias electrodes, and a write signal for changing all the cholesteric liquid crystals of the plurality of display layers to the same alignment state. I do.

According to a seventh aspect of the present invention, in the device for writing an image on the display storage medium according to the second aspect, at least a voltage is applied between the bias electrodes from outside the display storage medium, and an arbitrary intensity is applied to the photoconductive layer. And a select period in which a voltage smaller than the voltage applied in the refresh period is applied between the bias electrodes, and a select period in which the photoconductive layer is irradiated with light of an arbitrary intensity. And a display period in which no voltage is applied, and the voltage applied to the entirety of the plurality of display layers is selected from a plurality of voltages having a threshold voltage of the cholesteric liquid crystal of the plurality of display layers as a boundary. It is assumed that a voltage write signal is applied.

[0016]

In the display storage medium of the present invention, a voltage is applied to a plurality of display layers by a bias electrode having a solid structure formed on the inner surfaces of the upper and lower substrates of the display storage medium, and light applied to the photoconductive layer is applied. The image is addressed externally by the signal. Therefore, there is no voltage drop between the upper and lower substrates of the voltage applied from the external writing device, and the voltage required for writing an image can be reduced.

Further, even when a foreign substance is present between the display storage medium and the image writing device, the distance between the bias electrodes for applying a voltage to the display layer does not change, and almost no optical signal for addressing an image can be obtained. Since no influence is exerted, deterioration of display characteristics can be prevented.

[0018]

FIG. 1 shows an embodiment of a display storage medium and an image writing apparatus according to the present invention.

In this embodiment, the display storage medium 1 selectively reflects different colors of visible light from the display surface side between the substrates 2 and 3 having the bias electrodes 10 and 11 formed on the inner surface, respectively. The three display layers 8A, 8B, 8C made of cholesteric liquid crystal, the light absorbing layer 6, and the photoconductive layer 7 are inserted, and the display layers 8A, 8B, 8C are inserted with spacers 9A, 9B, 9C, respectively. A separation substrate 4 is provided between the display layers 8B and 8C, and a separation substrate 5 is provided between the display layers 8B and 8C.
It is assumed that they are stacked through

The substrates 2 and 3 can be made of glass, silicon, or a polymer film such as polyester (polyethylene terephthalate), polysulfone, polyethersulfone, or polycarbonate, and are formed of a material having an insulating property and a light transmitting property. .

The bias electrodes 10 and 11 are made of ITO or Sn.
It is formed on the substrates 2 and 3 by a vapor deposition method, a sputtering method, or the like using a conductive and light-transmitting material such as O ₂ .
If necessary, a known functional film such as a liquid crystal alignment film may be formed on the surface.

The separation substrates 4 and 5 can be made of the same polymer film as the substrates 2 and 3 and are formed of a light-transmitting material. Its thickness is several μm to several tens μm
In order to increase the partial pressure ratio to the display layers 8A, 8B and 8C, it is preferable that the dielectric constant is as large as possible. Also,
If necessary, a known functional film such as a liquid crystal alignment film may be formed on the surface.

As the spacers 9A, 9B and 9C, a ball type or a cylinder type made of glass or plastic can be used.
The thickness of B and 8C is controlled to several μm to several tens μm. In particular, when a flexible material is used for the substrates 2 and 3, the display layers 8A, 8B and 8C
It is preferable to bond between the substrates using spacers 9A, 9B, 9C around which an adhesive component is applied so that the thickness of the substrate does not greatly change.

In place of the spacers 9A, 9B and 9C, projections or the like which can control the thickness of the display layers 8A, 8B and 8C are formed on the surfaces of the bias electrodes 10 and 11 or the separation substrates 4 and 5. Is also good.

The light absorbing layer 6 is not particularly limited as long as it absorbs incident light transmitted through the display layers 8A, 8B, and 8C. The light absorbing layer 6 may be made of a high-level material containing an inorganic substance such as CdTe or a black dye. An insulating material such as molecules can be used, and the dielectric constant is preferably as large as possible in order to increase the partial pressure ratio to the display layers 8A, 8B, and 8C.

The cholesteric liquid crystal constituting the display layers 8A, 8B and 8C is composed of a steroid cholesterol derivative,
Alternatively, a chiral nematic liquid crystal in which an optically active group is introduced into a part of a nematic liquid crystal such as a Schiff base type, an azo type, an ester type or a biphenyl type, or a Schiff base type, an azo type, an azoxy type, an ethane type or a biphenyl type. ,
Terphenyl, cyclohexyl carboxylate, phenylcyclohexane, benzoate,
A nematic liquid crystal having a positive dielectric anisotropy such as a pyrimidine-based, dioxane-based, tolan-based, cyclohexylcyclohexane-ester-based, or alkenyl-based liquid crystal, or a material added as a chiral agent to a mixed liquid crystal thereof can be used.

A cholesteric liquid crystal in which liquid crystal molecules have a helical structure divides light incident on a helical axis into right-handed circularly polarized light and left-handed circularly polarized light, and Bragg-reflects a circularly-polarized light component that matches the twisting direction of the helical light. A selective reflection phenomenon that causes transmission occurs.
The center wavelength λ of the reflected light and the reflection wavelength width Δλ are: helical pitch: p; average refractive index in a plane perpendicular to the helical axis: n;
Assuming that the birefringence is Δn, λ = n · p and Δλ =
The light reflected by the cholesteric liquid crystal layer exhibits a bright color depending on the helical pitch.

As shown in FIG. 15A, a cholesteric liquid crystal having a positive dielectric anisotropy has a planar structure 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, the helical axis is substantially parallel to the cell surface, and the focal conic tissue that transmits the incident light while slightly scattering the light forward, and as shown in FIG. It shows three states: a homeotropic structure in which the liquid crystal director is oriented in the direction of the electric field when unraveled and the incident light is transmitted almost completely.

Of the above three tissues, the planar tissue and the focal conic tissue can exist bistable at no voltage. Therefore, the alignment state of the cholesteric liquid crystal is not uniquely determined with respect to the voltage applied to the liquid crystal layer. When the planar structure is in the initial state, the planar structure, the focal conic structure, When the focal conic tissue is in the initial state, it changes in the order of the focal conic tissue and the homeotropic tissue as the applied voltage increases.

On the other hand, when the voltage applied to the liquid crystal layer is rapidly reduced to zero, the planar structure and the focal conic structure are maintained as they are, and the homeotropic structure changes to the planar structure.

Therefore, the cholesteric liquid crystal layer immediately after the application of the pulse signal exhibits an electro-optical response as shown in FIG. 16, and the voltage of the applied pulse signal is Vfh,
When it is 90 or more, it becomes a selective reflection state changed from a homeotropic tissue to a planar tissue. When it is between Vpf, 10 and Vfh, 10, it becomes a transmission state by a focal conic tissue.
The state before application of the pulse signal is continued, that is, a selective reflection state by a planar tissue or a transmission state by a focal conic tissue.

In the figure, the vertical axis represents the normalized reflectance, which is normalized with the maximum reflectance being 100 and the minimum reflectance being 0. In addition, since there is a transition region between each state of the planar tissue, the focal conic tissue, and the homeotropic tissue, the case where the normalized reflectance is 90 or more is the selective reflection state, and the case where the normalized reflectance is 10 or less. The threshold voltage of the planar tissue and the focal conic tissue is defined as Vpf, 90 and Vpf, 10, respectively, before and after the transition region, and the threshold voltages of the focal conic tissue and the homeotropic tissue are defined as the transmission state. , Vfh, 10, Vfh,
90.

The helical pitch of the cholesteric liquid crystal is adjusted by the amount of the chiral agent added to the nematic liquid crystal. For example, the central wavelengths of the selectively reflected light of the display layers 8A, 8B and 8C are 400 to 500 nm and 500 to 600 n, respectively.
m, within the range of 600 to 700 nm. If the solubility of the chiral agent in the nematic liquid crystal is low and a selective reflection wavelength within the above range cannot be obtained, a known method of adding a plurality of chiral agents may be used.

In order to compensate for the temperature dependence of the helical pitch of the cholesteric liquid crystal, a known method of adding a plurality of chiral agents having different twist directions or exhibiting opposite temperature dependence may be used.

The photoconductive layer 7 only needs to change its impedance according to the amount of light to be irradiated. The charge generating substance can be formed by a vapor deposition method, a sputtering method, an ion plating method, or the like.
Films formed by CVD, etc., charge generating substances dispersed in a resin binder and applied by bar coating, spin coating, roll coating, dipping, casting, etc., or these charge generating layers And a layer in which a charge transport layer is laminated.

As the charge generating material, a-Si, ZnS,
Inorganic materials such as ZnO, CdS, CdSe, Se, SeTe, and TiO; phthalocyanine, azo, polycyclic quinone, indigo, quinacridone, perylene, squarium, azurenium, cyanine, pyrylium Organic materials can be used. As the resin binder, polycarbonate, polyarylate, polyethylene, polypropylene, polyester, polyvinyl acetate, polyvinyl butyral, acryl, methacryl, vinyl chloride, vinyl acetate, and copolymers thereof can be used. As a charge transport material, carbazole, triazole, oxadiazole, imidazole, pyrazoline, hydrazone, stilbene,
Organic materials such as amine-based and nitrofluorenone-based materials can be used.

The image writing device 12 includes the display storage medium 1
And in this embodiment, the display storage medium 1
And a voltage application unit 13 for applying a bias voltage between the bias electrodes 10 and 11 of the display storage medium 1 via the contact 16. A light irradiating unit 14 for irradiating the non-display surface side of the display storage medium 1 with the writing light 17 and a voltage applying unit 13 based on the input image data.
And a control unit 15 that controls the light amount of the writing light 17 that the light irradiation unit 14 irradiates the non-display surface side of the display storage medium 1 with the bias voltage applied between the bias electrodes 10 and 11.

The light irradiator 14 may be any as long as it can irradiate the display storage medium 1 with an arbitrary amount of writing light 17.
Self-luminous elements such as laser beam scanning devices, LED arrays, CRT displays, plasma displays, and EL displays; and combinations of dimming elements such as liquid crystal shutters with light sources such as fluorescent tubes, xenon lamps, halogen lamps, and mercury lamps. There is no particular limitation.

In the embodiment shown in FIG. 1, the display layers 8A, 8B, 8
In the case where C has a structure composed of only cholesteric liquid crystal, the display layers 8A, 8B, and 8C are made of PNLC (Pol) containing a network polymer in a continuous phase of cholesteric liquid crystal.
ymer NetworkLiquid Crysta
1) PDLC (Polymer) in which a cholesteric liquid crystal is dispersed in a droplet shape in a structure or a polymer skeleton.
Dispersed Liquid Crysta
l) A structure may be adopted.

When the display layers 8A, 8B, and 8C have the PNLC structure or the PDLC structure, an anchoring effect occurs at the interface between the cholesteric liquid crystal and the polymer, and the state of maintaining the planar structure or the focal conic structure without voltage is maintained. The switching speed can be improved while stabilizing. Furthermore, the viewing angle is improved by the fluctuation of the helical axis, and a solid display texture can be obtained.

FIG. 3 shows an equivalent circuit of the display storage medium 1 of the present invention described above with reference to FIG.

[0042] In the figure, C _E and R _E is the equivalent capacitance and equivalent resistance components other than the display layer and the photoconductive layer, FIG. 1
In the embodiment shown in FIG. 7, the serial sum of the capacitance and the resistance of the separation substrates 4 and 5, the light absorbing layer 6 and the bias electrodes 10 and 11 is shown, and V _E is an external image writing device 12.
3 shows a voltage drop occurring in components other than the display layer and the photoconductive layer when a bias voltage V is applied between the bias electrodes 10 and 11 of the display storage medium 1. Usually, the equivalent resistance R _E of the components other than the display layer and the photoconductive layer is sufficiently large, it can be regarded as insulators.

In the figure, C _A , C _B , C _C and R _A , R _B , R _C
Each display layer 8A, 8B, indicates the capacitance and the resistance value of 8C, V _A, V _B, V _C, the voltage V from the image writing device 12 between the bias electrodes 10 and 11 of the display storage medium 1 When applied, the voltage actually applied to each of the display layers 8A, 8B, and 8C is shown. Normally, display layer 8
The resistance values R _A , R _B , and R _C of A, 8B, and 8C are sufficiently large, and the capacitances C _A , C _B , and C _C of the liquid crystal have dielectric anisotropy. It changes depending on the orientation state.

Here, C _D is the equivalent capacitance of the entire display layer and indicates the series sum of the capacitances of the display layers 8A, 8B and 8C, and V _D is the display storage from the external image writing device 12. When the voltage V is applied between the bias electrodes 10 and 11 of the medium 1, the voltage actually applied to the entire display layer is shown.

In the drawing, C _O and R _O represent the capacitance and resistance of the photoconductive layer 7, and V _O is the bias electrodes 10, 11 of the display storage medium 1 from an external image writing device 12.
It shows a voltage drop that occurs in the photoconductive layer 7 when the voltage V is applied therebetween.

The resistance value R _O of the photoconductive layer 7 changes in accordance with the amount of writing light 17 applied to the display storage medium 1 from the light irradiation section 14 of the image writing device 12. When the light amount of the writing light 17 is small, the resistance R
_O is sufficiently large, and the voltage V _D actually applied to the entire display layer is as follows depending on the capacitance partial pressures of C _E , C _D , and C _O.

V _D = (C / C _D ) V {(1) where C = C _E C _D C _O / (C _E C _D + C _E C _O + C _D C _O )} (2)

On the other hand, when the light quantity of the writing light 17 increases, the resistance value R _O of the photoconductive layer 7 decreases due to the internal photoelectric effect, and the voltage V _D actually applied to the entire display layer increases.

That is, in the display storage medium 1 and the image writing device 12 of the present invention, the amount of the writing light 17 emitted from the light irradiation section 14 of the image writing device 12 to the display storage medium 1 is controlled, so that the image From the writing device 12 to the bias electrode 10 of the display storage medium 1,
When a voltage V is applied between 11 can control the voltage V _D to be actually applied to the entire display layer.

On the other hand, when the voltage V _D is applied to the entire display layer, the display layers 8A, 8B, a voltage V _A which is actually applied to 8C, V _B, V _C is as follows.

V _A = (C _D / C _A ) V _D ‥‥ (3) V _B = (C _D / C _B ) V _D ‥‥ (4) V _C = (C _D / C _C ) V _D ‥ ‥ (5) where C _D = C _A · C _B · C _C / (C _A · C _B + C _A · C _C + C _B ·
C _C ) ‥ (6).

As described above, the bias voltage V is applied from the external image writing device 12 to the display storage medium 1 of the present invention, and the writing light 17 of an arbitrary amount is irradiated.
When an arbitrary voltage V _D is applied to the entire display layer, a voltage due to the above-described capacitance division is applied to each of the display layers 8A, 8B, and 8C. The alignment state of the cholesteric liquid crystal of the display layers 8A, 8B, 8C changes.

[0053] Thus, in the display storage medium 1 of the present invention, the voltage V _D applied to the entire display layer, and the distribution ratio of the display layers 8A, 8B, to 8C, the display for the voltage actually applied layers 8A, 8B, the electro-optical response of 8C, by controlling the two, the display layers 8A for the voltage V _D applied to the entire display layer, 8B, 8C the electro-optical response of the desired configuration can do.

More specifically, the former display layers 8A, 8
B, 8C, as described above, the distribution ratio of each display layer 8A, 8C.
B, 8C, the latter, each display layer 8
A, 8B, and 8C show the electro-optical response of each display layer 8A, 8A.
The dielectric anisotropy, elastic modulus, and helical pitch of the cholesteric liquid crystal constituting B and 8C, and when a polymer is added, the interface between the polymer and the liquid crystal is affected by the structure of the polymer and the phase separation process. Can be controlled depending on the degree of the anchoring effect in the above.

[0055] Figure 4, an example of a display storage medium 1 of the present invention, for the pulse voltage V _D applied to the entire display layer,
The electro-optical response of each display layer 8A, 8B, 8C is shown.

The display storage medium of this example has three display layers 8
A, 8B, and 8C, the largest value Vth1 of the threshold voltages Vpf, 10 of the planar structure and the focal conic structure, and the three display layers 8A, 8B, 8
C, the threshold value Vth2 of each of the focal conic tissue and the homeotropic tissue is set so that the smallest value Vth2 has a relationship of Vth1 <Vth2, and a voltage between Vth1 and Vth2. To V
a, the threshold voltage Vf3 of the three display layers 8A, 8B, and 8C, which is the highest value Vth3 or more, of the threshold voltages Vfh and 90 of the focal conic tissue and the homeotropic tissue is Vb.

Then, between the bias electrodes 10 and 11 of the display storage medium 1 by an external image writing device 12.
The select period T of the AC pulse as shown in FIG.
s and a subsequent bias voltage composed of a non-voltage display period Td, and at least the selection period T
The writing light 17 is irradiated from the light irradiation unit 14 so as to include the end of s. Alternatively, at least the display storage medium 1
In the case where the photoconductive layer 7 is unipolar, between the bias electrodes 10 and 11 of the display storage medium 1 as shown in FIG.
A bias voltage constituted by a DC pulse select period Ts and a subsequent no-voltage display period Td is applied, and the writing light 17 is irradiated from the light irradiation unit 14 so as to include at least the end of the select period Ts.

FIG. 6 shows a change in the reflectance of each of the display layers 8A, 8B and 8C with respect to the transmittance T of the light control element when the light control section and the light source are combined as the light irradiation section 14. FIG. 3A shows the relationship between the transmittance T of the light control element and the logarithmic light amount of the writing light 17, and FIG.
7 and the pulse voltage V _D applied to the entire display layer
Relationship with, FIG (c) is described above is shown in FIG. 4, in the display storage medium of this embodiment, for the pulse voltage V _D applied to the entire display layer, the display layers 8A, 8B, 8C reflection FIG. 4D shows the respective display layers 8A, 8B, and 8C with respect to the transmittance T of the light control element of the light irradiation unit 14.
Shows the change in reflectance.

[0059] Figure 7, the pulse voltage V _D applied to the entire display layer, Va, respectively, in FIG 4, so as to Vb, the bias voltage Vs of the select period Ts V1, amount of writing light 17, i.e. the In the example, the transmittance T of the light control element is
Are selected as Ta and Tb, three display layers 8A and 8
The orientation states of B and 8C are shown, “p” represents a selective reflection state by a planar structure, and “f” represents a transmission state by a focal conic structure, respectively.
8B and 8C are shown in this order.

As is apparent from the above, according to the display storage medium and the image writing method described above, there are two types: (1) all three layers have a planar structure, and (2) all three layers have a focal conic structure. Is obtained.

Therefore, for example, when the display layer 8A is configured to selectively reflect blue color light, the display layer 8B is configured to reflect green color light, and the display layer 8C is configured to selectively reflect red color light, as shown in FIG. “T” in the figure indicates that the corresponding layer is in a transmission state by the focal conic tissue), (1) a state in which white (W) is displayed by a write signal of Vs = V1, T = Tb, (2) Vs =
A write signal of V1, T = Ta causes black (B
k) can be displayed, and two colors of black and white can be displayed within one pixel.

Further, by performing an area gradation such as a dither method or an error diffusion method, a multi-value monochrome display can be performed.

The order of stacking the display layers for selectively reflecting the blue, green and red color lights is not limited to the above example, but may be arbitrarily configured.

[0064] Figure 9 shows another example of the display storage medium 1 of the present invention, for the pulse voltage V _D applied to the entire display layer, the display layers 8A, 8B, 8C the electro-optical response of.

The display storage medium of this example has three display layers 8
The transition regions A, 8B, and 8C between the states of the planar tissue and the focal conic tissue and the transition regions between the states of the focal conic tissue and the homeotropic tissue do not exist at the same voltage. Three display layers 8
When the display layer having the largest threshold voltage among A, 8B, and 8C is the H layer, the middle display layer is the M layer, and the smallest display layer is the L layer, the voltages Va, Vb, Vc, Vd, Ve,
Vf, Vg, V: Vpf of the L layer, a voltage of 90 or less,
Vb: voltage between Vpf, 10 of the L layer and Vpf, 90 of the M layer, Vc: Vpf, 10 of the M layer and Vpf, 9 of the H layer
0, Vd: Vpf of H layer, 10 and V of L layer
fh, 10; Ve: Vfh, 90 of L layer and Vfh, 10 of M layer; Vf: Vf of M layer
h, 90 and Vfh, 10 of the H layer, Vg: H
Vfh of the layer, a voltage of 90 or more.

Then, as shown in FIG. 10A, at least the refresh period Tr and the select period Ts of the AC pulse are applied between the bias electrodes 10 and 11 of the display storage medium 1 by the external writing device 12.
And a subsequent non-voltage display period Td, and the refresh period Tr and the select period Ts.
Apply a bias voltage having a relationship of Vr> Vs, and at least the refresh period Tr
The first writing light is emitted from the light irradiating unit 14 so as to include the end, and the second writing light is irradiated from the light irradiating unit 14 so as to include at least the end of the select period Ts.

Alternatively, when at least the photoconductive layer 7 of the display storage medium 1 is unipolar, a DC pulse refresh between the bias electrodes 10 and 11 of the display storage medium 1 as shown in FIG. Period Tr and select period T
s and a subsequent no-voltage display period Td, and the refresh period Tr and the select period Ts
Apply a bias voltage having a relationship of Vr> Vs, and at least the refresh period Tr
The first writing light is emitted from the light irradiating unit 14 so as to include the end, and the second writing light is irradiated from the light irradiating unit 14 so as to include at least the end of the select period Ts.

FIG. 11 shows a change in the reflectance of the H layer, the M layer, and the L layer with respect to the transmittance Trt of the light control element during the refresh period Tr when the light control element and the light source are combined as the light irradiation unit 14. As shown in FIG.
The relationship between the transmittance Trt a first writing light logarithmic quantity of light control device, FIG. (B) shows the relationship between the pulse voltage V _D applied to the entire display layer and the first writing light logarithmic quantity FIG. 9C shows the pulse voltage V _D applied to the entire display layer in the display storage medium of this example described above with reference to FIG.
FIG. 4D shows the reflectance of the H layer, the M layer, and the L layer with respect to the transmittance Trt of the light control element of the light irradiation unit 14 with respect to the reflectance. The change is shown.

FIG. 12 shows the light irradiation unit 14 as
Select period T when a light control element and a light source are combined
H, M with respect to the transmittance Tst of the light control element at s
FIG. 6A shows the change in the reflectivity of the L layer and the L layer.
FIG. 4B shows the relationship between the transmittance Tst of the light control element and the logarithmic light amount of the second writing light, and FIG. 4B shows the relationship between the logarithmic light amount of the second writing light and the pulse voltage V _D applied to the entire display layer. FIG. 9C shows the reflectance of the H layer, the M layer, and the L layer with respect to the pulse voltage V _D applied to the entire display layer in the display storage medium of this example described above with reference to FIG. (D) shows a change in the reflectance of the H layer, the M layer, and the L layer with respect to the transmittance Tst of the light control element of the light irradiation unit 14.

[0070] Figure 13, in the refresh period Tr, an as pulse voltage V _D applied to the entire display layer becomes Ve, respectively, in FIG 9, Vf, the Vg, bias voltage Vr V1, the first writing light the light amount, i.e., selects the transmittance Trt dimming device in the above example Te, Tf, the Tg, in the select period Ts, the pulse voltage V _D applied to the entire display layer, Va, respectively, in FIG 9, Vb , V
The bias voltage Vs is set to V2, and the light amount of the second writing light, that is, in the above example, the transmittance Tst of the dimming element is set to Ta, Tb, and Tc so that H is equal to H in each combination. And "p" represents a selective reflection state by a planar structure, and "f" represents a transmission state by a focal conic structure, respectively, and the L layer, the M layer, and the H layer. Are shown in this order.

As is clear from the above, according to the display storage medium and the image writing method described above, (1) H layer, M layer
All three layers, the layer and the L layer, are in the state of a planar structure,
(2) H layer, M layer and L layer are all in the state of focal conic organization, (3) H layer is planar organization and M layer
Layer and L layer have a focal conic structure, (4) M layer has a planar structure, H layer and L layer have a focal conic structure, (5) L layer has a planar structure, H layer and M layer.
The layer is in a focal conic organization state, (6) the H and M layers are in a planar organization, the L layer is in a focal conic organization, (7) the M and L layers are in a planar organization, and the H layer is in a focal conic organization. State).

Therefore, for example, the display layer 8A is an H layer that selectively reflects blue color light, the display layer 8B is an M layer that selectively reflects green color light, and the display layer 8C is an L layer that selectively reflects red color light. In such a case, FIG.
("T" in the figure indicates that the corresponding layer is in a permeation state by the focal conic tissue) as shown in FIG.
(1) Vr = V1, Tr = Tg, Vs = V2, Ts = T
A state where white (W) is displayed by the write signal a, (2) For example, Vr = V1, Tr = Te, Vs
= V2, Ts = Tc, black (Bk) is displayed by the write signal, (3) Vr = V1, Tr =
A state in which blue (B) is displayed by a write signal of Tg, Vs = V2, Ts = Tc, (4) Vr = V
1, green (G) is displayed by a write signal of Tr = Tf, Vs = V2, Ts = Tb, (5)
A state where red (R) is displayed by a write signal of Vr = V1, Tr = Te, Vs = V2, and Ts = Ta;
(6) Vr = V1, Tr = Tg, Vs = V2, Ts = T
state where cyan (C) is displayed by the write signal b, (7) Vr = V1, Tr = Tf, Vs = V2, T
With the write signal of s = Ta, seven display states of yellow (Y) can be obtained. In one pixel, five colors of white, black, blue, green and red, and cyan are displayed. And a total of seven colors, i.e., two colors, yellow and yellow.

Further, at least white, black,
A full-color display can be performed by performing an area gradation such as a dither method or an error diffusion method using five colors of blue, green, and red.

In the above-described example, cyan and yellow are displayed as two of the three colors cyan, magenta and yellow with the display layer selectively reflecting green light as the M layer. When the display layer selectively reflecting M is made of M layers, cyan and magenta can be displayed as two of the three colors of cyan, magenta and yellow, and the display layer that selectively reflects red color light is M. In the case of a layer, magenta and yellow can be displayed as two of the three colors cyan, magenta and yellow.

The order of lamination of the display layers for selectively reflecting the blue, green and red color lights or the magnitude of the threshold voltage is not limited to the above example, but may be arbitrarily configured.

The embodiment shown in FIG. 1 has three display layers 8.
A, 8B, and 8C selectively reflect circularly polarized light components in any one of the turning directions that match the helical twist direction of each cholesteric liquid crystal. FIG. 2 shows the display storage medium 1 of the present invention. As in other embodiments, the display layer 8
A, 8B, and 8C are each formed of a cholesteric liquid crystal having a helical twist direction to the right so as to selectively reflect the same color light and show the same electro-optical response to a voltage applied to the entire display layer. Layer 8A (R), 8
B (R), 8C (R) and display layers 8A (L), 8B made of cholesteric liquid crystal with a helical twist direction leftward
(L) and 8C (L). In this case, monochrome display or color display with higher reflectance can be performed by using the above-described writing method.

The display layers 8A (R), 8B (R),
The stacking order of 8C (R), 8A (L), 8B (L), and 8C (L) is not limited to the example of FIG. 2 and can be arbitrarily configured.

(Example 1) In Example 1, a display storage medium of a monochrome display having a PNLC structure using an inorganic material for a photoconductive layer was manufactured, and write characteristics were measured.

As a mixed solution of a cholesteric liquid crystal and a polymer precursor of a display layer that selectively reflects red color light, a nematic liquid crystal BL012 having a positive dielectric anisotropy (manufactured by Merck) 69.0 wt%, dextrorotatory Chiral agent CB15
A solution obtained by mixing 15.5 wt% (manufactured by Merck) and 15.5 wt% of a dextrorotatory chiral agent CE2 (manufactured by Merck) was mixed with 15 wt% of a thiol-based UV polymer precursor NOA65 (manufactured by Norland). Was added.

As a mixed solution of a cholesteric liquid crystal and a polymer precursor of a display layer which selectively reflects green color light, a nematic liquid crystal BL012 having a positive dielectric anisotropy (manufactured by Merck) 60.0 wt%, dextrorotatory Chiral agent CB1
5 (manufactured by Merck) and 20.0 wt% of a dextrorotatory chiral agent CE2 (manufactured by Merck) were mixed with a solution containing a thiol-based UV polymer precursor NOA65.
(Norland) was added in an amount of 15 wt%.

As a mixed solution of a cholesteric liquid crystal and a polymer precursor of a display layer that selectively reflects blue color light, a nematic liquid crystal BL012 having a positive dielectric anisotropy (manufactured by Merck) at 54.6 wt%, dextrorotatory Chiral agent CB15
A solution obtained by mixing 22.7 wt% (manufactured by Merck) and 22.7 wt% of the dextrorotatory chiral agent CE2 (manufactured by Merck) was mixed with 15 wt% of a thiol-based UV polymer precursor NOA65 (manufactured by Norland). Was added.

The ITO transparent electrode was sputter-deposited,
A 5 μm-thick hydrogenated amorphous silicon film was formed as a photoconductive layer on a 7059 glass substrate (Corning) having an inch square of 0.7 mm thickness by using a plasma CVD method.

Further, a black resin BKR-105 (manufactured by Nippon Kayaku Co., Ltd.) was spin-coated thereon as a light absorbing layer, and dried at 100 ° C. for 2 minutes.

A 5 μm-diameter spherical spacer Micropearl SP-205 (manufactured by Sekisui Fine Chemical Co., Ltd.) was wet-sprayed on the obtained light-absorbing layer, and the above red mixed solution heated to 60 ° C. was added dropwise. A 4.5 μm-thick PET film mirror (manufactured by Toray Industries Co., Ltd.) on which a 5 μm-diameter spherical spacer Micropearl SP-205 (manufactured by Sekisui Fine Chemical Co., Ltd.) was wet-sprayed on one side was brought into close contact with the non-sprayed surface of the spacer. .

Further, the above green mixed solution heated to 60 ° C. was added dropwise thereto, and a spherical spacer Micropearl SP-205 (manufactured by Sekisui Fine Chemical Co., Ltd.) having a diameter of 5 μm was wet-sprayed on one side to 4.5 μm. A thick PET film mirror (manufactured by Toray Industries, Inc.) was brought into close contact with the non-scattering surface of the spacer. Furthermore, on top of this, 60
The above blue mixed solution heated to ℃ is dropped, and IT
O transparent electrode sputter-deposited, 1 inch square 0.7
A 7059 mm thick glass substrate (manufactured by Corning) was
The TO transparent electrode surface was brought into close contact with the liquid crystal.

After applying pressure with a smoothing device using air pressure, 50 mW / cm on a hot plate at 60 ° C.
² (365 nm) UV light is irradiated for 60 seconds from the external light incident surface side, and from the external light incident side, display storage of a monochrome display in which a blue display layer, a green display layer, and a red display layer of a PNLC structure are respectively laminated. I got the medium.

Example 2 In Example 2, a display storage medium of a color display having a PNLC structure using an organic material in which a polymer was dispersed was used for a photoconductive layer.

As a cholesteric liquid crystal for a display layer that selectively reflects red color light, a nematic liquid crystal ZLI4520 (manufactured by Merck) having a positive dielectric anisotropy of 68.6 wt.
%, Dextrorotatory chiral agent CB15 (Merck) 15.
7 wt% and a dextrorotatory chiral agent CE2 (manufactured by Merck) 15.7 wt% mixed with a thiol UV
15% of the polymer precursor NOA65 (Norland)
wt% was added.

As a cholesteric liquid crystal of a display layer that selectively reflects green color light, 72.2 wt% of a nematic liquid crystal E186 having a positive dielectric anisotropy (manufactured by Merck),
Right-handed chiral agent CB15 (Merck) 13.9w
t% and dextrorotatory chiral agent CE2 (Merck)
To a solution obtained by mixing 13.9 wt%, 15 wt% of a thiol UV polymer precursor NOA65 (manufactured by Norland) was added.
% Was added.

As a cholesteric liquid crystal of a display layer for selectively reflecting blue color light, a nematic liquid crystal ZLI4389 (manufactured by Merck) having a positive dielectric anisotropy of 64.9 wt.
%, Dextrorotatory chiral agent CB15 (Merck) 17.
5% by weight and a mixture of 17.5% by weight of a dextrorotatory chiral agent CE2 (manufactured by Merck) were mixed with a thiol UV.
15% of the polymer precursor NOA65 (Norland)
wt% was added.

The ITO transparent electrode was sputter deposited and 1
As a charge generation layer, 2.1 wt% of chlorogallium phthalocyanine, 1.8 wt% of a polyvinyl chloride / vinyl acetate copolymer resin, and n-butyl acetate 31 were placed on a 125 μm-inch square PET film high beam (manufactured by Toray Industries, Inc.). 0.75% by weight, a solution dispersed in xylene 64.4% by weight
Thick dip coating was applied.

Further, on this, as a charge transport layer,
3,3′-dimethyl-N, N, N ′, N′-tetrakis
(4-methylphenyl) -1,1′-biphenyl-4,
4′-diamine 7.2 wt%, poly (4,4′-cyclohexylidene diphenylene carbonate) 10.8 wt
%, Monochlorobenzene 82 wt% mixed solution,
After diluting it twice with monochlorobenzene, it was spin-coated to a thickness of 3 μm.

Further, a black resin BKR-105 (manufactured by Nippon Kayaku Co., Ltd.) was spin-coated as a light absorbing layer, and dried at 100 ° C. for 2 minutes.

On the obtained light absorbing layer, 5 μm
m-diameter spherical spacer hair beads L-21S (manufactured by Hayakawa Rubber Co., Ltd.) are wet-sprayed, the above-mentioned red mixed solution heated to 70 ° C. is added dropwise, and a 5-μm-diameter spherical spacer hair beads with an adhesive on one surface. A 4.5 μm-thick PET film mirror (manufactured by Toray Industries Co., Ltd.) onto which L-21S (manufactured by Hayakawa Rubber Co., Ltd.) was wet-sprayed was brought into close contact with the non-spraying surface of the spacer.

Further, the above green mixed solution heated to 70 ° C. was added dropwise thereto, and one surface of an adhesive
A 4.5 μm-thick PET film mirror (manufactured by Toray Industries Co., Ltd.) wet-sprayed with spherical spacer hayabeads L-21S (manufactured by Hayakawa Rubber Co., Ltd.) having a diameter of μm was adhered so that the non-scattering surface of the spacer was in contact with the mirror. Further, the above-mentioned blue mixed solution heated to 70 ° C. was dropped thereon, and a 1-inch square 125 μm-thick PET film high beam (manufactured by Toray Industries Co., Ltd.) on which an ITO transparent electrode was sputter-deposited, was deposited on the ITO transparent electrode. The electrode was brought into close contact with the liquid crystal.

After applying heat and pressure with a laminator, 70
50 mW / cm ² (365 n
m) is irradiated with UV light for 60 seconds from the external light incident side, and a color display storage medium in which a blue display layer, a green display layer, and a red display layer each having a PNLC structure are stacked from the external light incident side. Obtained.

(Comparative Example) In a comparative example, a display storage medium of a monochrome display in which external electrodes were written using the same display layer as in Example 1 was manufactured, and write characteristics were measured.

[0098] One-inch square 75 colored in black
On a μm-thick PET film Lumirror (Toray),
5 μm diameter spherical spacer hayabeads L-2 with adhesive
1S (manufactured by Hayakawa Rubber Co., Ltd.) was wet-sprayed, and a red mixed solution similar to that in Example 1 heated to 60 ° C. was dropped, and a spherical spacer haze beads L-2 having a diameter of 5 μm and having an adhesive on one surface.
4.5 μm thick P wet-sprayed with 1S (Hayakawa Rubber Co., Ltd.)
An ET film mirror (manufactured by Toray Industries, Inc.) was brought into close contact with the non-scattering surface of the spacer.

Further, a green mixed solution similar to that of Example 1 heated to 60 ° C. was dropped thereon, and spherical spacer hair beads L-21 having a diameter of 5 μm and having an adhesive on one surface were added.
4.5 µm thick PE wet-sprayed with S (Hayakawa Rubber Co., Ltd.)
A T film mirror (manufactured by Toray Industries, Inc.) was brought into close contact with the non-scattering surface of the spacer. In addition,
A blue mixed solution similar to that of Example 1 heated to 60 ° C. was dropped, and a 1-inch square 75 μm-thick PET film mirror (manufactured by Toray Industries, Inc.) was adhered.

After applying heat and pressure with a laminator, 60
50 mW / cm ² (365 n
m) is irradiated for 60 seconds from the external light incident surface side, and a monochrome display display storage medium in which a blue display layer, a green display layer, and a red display layer each having a PNLC structure are stacked from the external light incident side. Obtained.

(Writing Characteristics of Example 1 and Comparative Example) The bias electrode of the display storage medium of Example 1 was brought into contact with a pair of aluminum electrodes connected to a pulse generator and a high-voltage power supply, and an alternating current of 50 Hz and 250 ms was applied. A bias voltage consisting of a select period and a non-voltage display period was applied, a mask was brought into close contact with the substrate on the non-display surface side, and writing light from a halogen lamp was irradiated to observe a display color. When the bias voltage during the select period was 620 V and the light amount of the writing light was 5 mW / cm ² , white display was obtained in the irradiation part of the writing light and black display was obtained in the non-irradiation part of the writing light.

The display storage medium of the comparative example was sandwiched between a pair of aluminum electrodes connected to a pulse generator and a high-voltage power supply, and a write signal consisting of an AC select period of 50 Hz and 250 ms and a display period of no voltage was applied. Then, it was taken out from between the electrodes, and the display color was observed. In order to perform white display, a writing voltage of 3.3 kV, which is about five times that of the first embodiment, was required.

To observe the influence of dust, 30 μm
In the display storage medium of Example 1, a spacer having a diameter is interposed between the substrate and the mask on the non-display surface side, and in the display storage medium of the comparative example, between the upper and lower substrates and the aluminum electrode. , Writing. With the display storage medium of Example 1, under the same conditions as above, white display was obtained in the writing light irradiation part and black display was obtained in the writing light non-irradiation part. However, in the display storage medium of the comparative example, the display did not change from the state before writing under the same conditions as described above.

[0104]

As described above, according to the present invention, a display storage medium capable of full-color display, having a memory function without power supply and capable of rewriting an image in a short time by an external device, and the image storage medium In the writing method and the image writing device, a voltage required for writing an image can be reduced, and display characteristics can be prevented from deteriorating due to adhesion of dust or the like.

[Brief description of the drawings]

FIG. 1 is a diagram showing one embodiment of a display storage medium and an image writing device of the present invention.

FIG. 2 is a diagram showing another embodiment of the display storage medium of the present invention.

FIG. 3 is a diagram showing an equivalent circuit of the display storage medium of the present invention.

FIG. 4 is a diagram showing an electro-optical response of an example of the display storage medium of the present invention.

FIG. 5 is a diagram showing a write signal in an embodiment of the image writing method of the present invention.

FIG. 6 is a diagram showing a change in the reflectance of each display layer with respect to the transmittance of the light control element constituting the light irradiation unit in one embodiment of the image writing method of the present invention.

FIG. 7 is a diagram showing an orientation state of each display layer of the display storage medium showing the electro-optical response of FIG. 4 in the case of the method of FIGS. 5 and 6;

8 is a diagram showing a display state of a display storage medium showing the electro-optical response of FIG. 4 in the case of using the methods of FIGS. 5 and 6. FIG.

FIG. 9 is a diagram showing an electro-optical response of another example of the display storage medium of the present invention.

FIG. 10 is a diagram showing a write signal in another embodiment of the image writing method of the present invention.

FIG. 11 is a diagram illustrating a change in the reflectance of each display layer with respect to the transmittance of a light control element constituting a light irradiation unit during a refresh period in another embodiment of the image writing method of the present invention.

FIG. 12 is a diagram illustrating a change in the reflectance of each display layer with respect to the transmittance of a light control element constituting a light irradiation unit during a select period according to another embodiment of the image writing method of the present invention.

FIG. 13 is a diagram showing an orientation state of each display layer of the display storage medium showing the electro-optical response of FIG. 9 in the case of the method of FIGS. 10 to 12;

FIG. 14 is a diagram showing a display state of a display storage medium showing the electro-optical response of FIG. 9 in the case of the method of FIGS. 10 to 12;

FIG. 15 is a diagram showing a change in alignment of a cholesteric liquid crystal having a positive dielectric anisotropy.

FIG. 16 is a diagram illustrating an example of an electro-optical response to a pulse signal of a cholesteric liquid crystal having a positive dielectric anisotropy.

FIG. 17 is a diagram showing an embodiment of a display storage medium according to the invention of the prior application.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Display storage medium 2, 3 ... Substrate 4, 5 ... Separation substrate 6 ... Light absorption layer 7 ... Photoconductive layer 8A, 8B, 8C ... Display layer 9A, 9B, 9C ... Spacer 10, 11 ... Bias electrode 12 ... Image Writing device 13 ... Voltage application unit 14 ... Light irradiation unit 15 ... Control unit 16 ... Contact 17 ... Writing light

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hideo Kobayashi 430 Nakai-cho, Nakai-machi, Ashigara-kami, Kanagawa Prefecture Inside Green Tech Nakai Fuji Xerox Co., Ltd. (72) Inventor Minoru Koshimizu 430 Border, Nakai-cho, Ashigami-gun, Kanagawa Prefecture Green Tech Nakai Fuji Xerox Co., Ltd.F-term (reference)

Claims (7)

[Claims] 1. A plurality of display layers each comprising at least a cholesteric liquid crystal selectively reflecting different colors of visible light among a pair of transparent substrates on which a bias electrode having a solid structure is formed, and a photoconductive layer. A display storage medium, wherein an image is written by applying a voltage between the bias electrodes from an external writing device and irradiating the photoconductive layer with light. 2. The display storage medium according to claim 1, wherein the plurality of display layers are applied to the entirety of the plurality of display layers among voltages applied between the bias electrodes from an external writing device. A display storage medium, wherein a threshold voltage of each cholesteric liquid crystal is different from a voltage. 3. The display storage medium according to claim 1, wherein each of the plurality of display layers selectively reflects the same color light, and includes two cholesteric liquid crystal layers having helical twist directions opposite to each other. A display storage medium, comprising: 4. A method for writing an image on a display storage medium according to claim 1 or 2, wherein a voltage is applied at least between said bias electrodes from an external image writing device, and light of an arbitrary intensity is applied to said photoconductive layer. Image writing, comprising a select period for irradiation and a display period in which no voltage is applied between the bias electrodes, and applying a write signal for changing all the cholesteric liquid crystals of the plurality of display layers to the same alignment state. Method. 5. A method for writing an image on a display storage medium according to claim 2, wherein a voltage is applied at least between said bias electrodes from an external image writing device to irradiate said photoconductive layer with light of an arbitrary intensity. A refresh period, a select period in which a voltage lower than the voltage applied in the refresh period is applied between the bias electrodes, and a light of arbitrary intensity is applied to the photoconductive layer; and a display in which no voltage is applied between the bias electrodes. A write signal, wherein the voltage is applied to the plurality of display layers as a whole, and is a voltage selected from a plurality of levels of voltages with a threshold voltage of the cholesteric liquid crystal of the plurality of display layers as a boundary. Image writing method. 6. An apparatus for writing an image on a display storage medium according to claim 1, wherein a voltage is applied from at least a portion between said bias electrodes from outside the display storage medium, and light having an arbitrary intensity is applied to said photoconductive layer. Image writing, comprising a select period for irradiation and a display period in which no voltage is applied between the bias electrodes, and applying a write signal for changing all the cholesteric liquid crystals of the plurality of display layers to the same alignment state. apparatus. 7. The apparatus for writing an image on a display storage medium according to claim 2, wherein a voltage is applied from at least between the bias electrodes from outside the display storage medium to irradiate the photoconductive layer with light of an arbitrary intensity. A refresh period, a select period in which a voltage lower than the voltage applied in the refresh period is applied between the bias electrodes, and a light of arbitrary intensity is applied to the photoconductive layer; and a display in which no voltage is applied between the bias electrodes. A write signal, wherein the voltage is applied to the plurality of display layers as a whole, and is a voltage selected from a plurality of levels of voltages with a threshold voltage of the cholesteric liquid crystal of the plurality of display layers as a boundary. And an image writing device.