JPH11237600A - Information storing medium and information writer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to rewritably record unvisible information in one information storing medium with the same device, and to display and rewritably record visible information. SOLUTION: A non-display storing layer 8A consisting of a cholesteric liquid crystal(LC) layer for selectively reflecting ultraviolet rays and a display storing layer 8B consisting of a cholesteric LC layer for selectively reflecting light of specific wavelength out of visible light are laminated through a separation board 4 between two substrates 2, 3 and a light absorbing layer 6 is formed on the rear face of the substrate 3 arranged on the opposite side of an external light incident side. The phase changing threshold electric field intensity of the cholesteric LC forming the layer 8A is made different from that of the cholesteric LC forming the layer 8B. An information writer 20 is formed independently of an information storing medium 1 and constituted of writing electrodes 21, 22 for holding the medium 1 and a driving circuit 23 for impressing a write signal between the electrodes 21, 22. Consequently unvisible information can be recorded in the layer 8A and visible information can be displayed and recorded in the layer 8B.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an information storage medium capable of rewritably recording invisible information or invisible information and visible information.

[0002]

2. Description of the Related Art As an information storage medium on which invisible information such as various data can be recorded in a rewritable manner, a magnetic card and an IC card are considered.

Various types of display recording media capable of rewriting and displaying visible information such as images have been considered, but in many cases, reversible display elements are printed or pasted on a substrate such as a card. To form a display recording unit.

For example, Japanese Patent Application Laid-Open No. 61-25885 discloses a display composed of a high-molecular and low-molecular composite resin that switches between a transparent mode and a cloudy mode by heating with a thermal head. A recording medium is shown, and in addition, a display recording medium using a leuco dye, which develops color by heating with a thermal head and decolorizes with a heat roll, similarly becomes cloudy with a thermal head and becomes transparent with a heat roll, Display recording media made of molecular liquid crystals and the like have been considered.

[0005] Further, as those requiring heat and electric field,
JP-A-8-272297 discloses a display recording medium comprising a composite film of a liquid crystal and a polymer.
No. 1 discloses a display recording medium made of a magnetic powder that records a difference in brightness between vertical and horizontal magnetism.

[0006]

However, a conventional information storage medium, such as a magnetic card or an IC card, which records invisible information in a rewritable manner, is a medium on which information is recorded although the information itself cannot be viewed. And the part where the information was recorded is clearly apparent at first glance,
There is a disadvantage that the risk of information falsification and unauthorized use of the medium is great.

Further, any of the above-described conventional display recording media for rewriting and displaying visible information cannot record rewritable invisible information, or even if it can record, it is difficult to record visible information and invisible information. Since recording is based on another principle and means, recording or rewriting of visible information and invisible information must be performed by another device or method, and it takes time to record or rewrite information, and the medium and the writing device are expensive. There is a disadvantage.

Accordingly, a first object of the present invention is to provide a medium on which information is recorded, and a part in which the information is recorded,
It is an object of the present invention to provide an information storage medium capable of recording invisible information in a rewritable manner, which is less obvious at first glance and reduces the risk of information tampering and unauthorized use of the medium.

A second object of the present invention is to record invisible information in a rewritable manner, and for the invisible information, as in the first object, to be a medium on which information is recorded, The recorded part is not apparent at first glance, reducing the risk of information tampering and unauthorized use of the medium, and also allows the visible information to be rewritten and displayed on the same medium, and also records the invisible information and the visible information Or rewriting can be performed collectively and at high speed by the same principle and means, using the same device or method,
An object of the present invention is to reduce the cost of a medium and a writing device.

[0010]

According to a first aspect of the present invention, there is provided an information storage medium comprising a transparent cholesteric liquid crystal layer which selectively reflects light having a wavelength other than visible light and stores invisible information between a pair of substrates. Is formed.

In this case, it is preferable that the cholesteric liquid crystal layer forming the non-display storage layer contains a polymer, and the cholesteric liquid crystal forming the non-display storage layer has a selective reflection wavelength in an ultraviolet region. desirable.

According to a fifth aspect of the present invention, there is provided an information storage medium comprising: a non-display storage layer made of a transparent cholesteric liquid crystal layer for selectively reflecting light having a wavelength other than visible light and storing invisible information between a pair of substrates; And a display storage layer composed of a cholesteric liquid crystal layer that selectively reflects light of a specific wavelength in visible light and stores visible information.

In this case, it is desirable that the cholesteric liquid crystal layer forming the non-display storage layer and the cholesteric liquid crystal layer forming the display storage layer each contain a polymer. Further, it is desirable that the selective reflection wavelength of the cholesteric liquid crystal forming the non-display storage layer be in the ultraviolet region.

It is desirable that the cholesteric liquid crystal forming the non-display storage layer and the cholesteric liquid crystal forming the display storage layer have different phase-change threshold electric field intensities.

[0015]

The cholesteric liquid crystal having a helical structure of liquid crystal molecules divides light incident parallel to the helical axis into right-handed and left-handed light, and Bragg-reflects a circularly polarized light component that matches the helix direction of the helical light. Causes a selective reflection phenomenon that transmits light.
The center wavelength λ of the reflected light is represented by λ = n · p, where p is a helical pitch and n is an average refractive index in a plane perpendicular to the helical axis.

By setting the reflection center wavelength λ outside the visible light region, the cholesteric liquid crystal layer can be made transparent to human eyes, but can selectively reflect infrared rays or ultraviolet rays.

A cholesteric liquid crystal having a positive dielectric anisotropy has a helical axis perpendicular to the cell surface as shown in FIG. As shown in FIG. 4B, the helical axis is substantially parallel to the cell surface, and the focal conic phase transmits the incident light while slightly scattering the light forward, and as shown in FIG. The liquid crystal director faces the direction of the electric field when released, and shows a homeotropic phase in which incident light is transmitted almost completely.

Of the above three phases, the planar phase and the focal conic phase can exist bistable without an electric field. Therefore, the phase state of the cholesteric liquid crystal is not uniquely determined with respect to the electric field intensity applied to the liquid crystal layer. When the planar phase is in the initial state, the planar state and the focal conic phase are increased with the electric field intensity. ,
It changes in the order of the homeotropic phase, and when the focal conic phase is in the initial state, changes in the order of the focal conic phase and the homeotropic phase as the electric field intensity increases.

On the other hand, when the electric field intensity is suddenly reduced to zero, the planar phase and the focal conic phase are maintained as they are, and the homeotropic phase changes to the planar phase.

Therefore, the cholesteric liquid crystal layer immediately after the application of the pulse signal shows a switching behavior as shown in FIG. 14, and the electric field intensity of the applied pulse signal becomes
When Efh is 90 or more, the selective reflection state changes from the homeotropic phase to the planar phase, and Ep
When between f, 10 and Efh, 10, the transmission state is caused by the focal conic phase, and when Epf, 90 or less, the state before application of the pulse signal is continued, that is, the state is selectively reflected by the planar phase or is caused by the focal conic phase. It becomes a transmission state.

In the drawing, the vertical axis represents the normalized reflectance. The reflectance is normalized with the maximum reflectance being 100 and the minimum reflectance being 0. In addition, between the states of the planar phase, the focal conic phase and the homeotropic phase,
Since the transition region exists, the case where the normalized reflectance is 90 or more is defined as the selective reflection state, and the case where the normalized reflectance is 10 or less is defined as the transmission state, and the threshold electric field of the phase change between the planar phase and the focal conic phase is defined. The intensities are set to Epf, 90 and Epf, 10, respectively, before and after the transition region, and the threshold electric field intensities of the phase change between the focal conic phase and the homeotropic phase are set to Ef, respectively, before and after the transition region.
h, 10, and Efh, 90.

In particular, PNCLC (Polymer Network Ch) obtained by adding a polymer to cholesteric liquid crystal.
olesteric Liquid Crystal)
Structure or PDCLC (Polymer Disper)
sed Cholesteric Liquid Cr
In the liquid crystal layer having a ystal) structure, the bistability of the planar phase and the focal conic phase in an electric field-free state is improved by interference at the interface between the cholesteric liquid crystal and the polymer.
The state immediately after the application of the pulse signal can be maintained for a long time, and the memory effect is significantly increased.

According to the first aspect of the present invention, a cholesteric liquid crystal layer that selectively reflects light having a wavelength other than visible light is formed as a non-display storage layer by utilizing the bistable phenomenon of the cholesteric liquid crystal. By switching between the selective reflection state by the planar phase and the transmission state by the focal conic phase,
Invisible information is written in the cholesteric liquid crystal layer.

Therefore, the invisible information can be recorded and rewritten so as to have a memory property without an electric field.

Further, since the cholesteric liquid crystal layer as the non-display storage layer is transparent, the non-display storage layer can be seen only as a mere transparent film, and is a medium on which information is recorded. At first glance, the risk of information tampering and unauthorized use of the medium is reduced.

However, when the cholesteric liquid crystal is observed from a direction oblique to the helical axis, the spectrum of the selectively reflected light changes to the shorter wavelength side according to the inclination angle. When the selective reflection wavelength of the cholesteric liquid crystal layer is in the infrared region, the invisible information recorded on the medium may be seen as red color light having a shorter wavelength than the infrared light, depending on the direction in which the medium is viewed. There is.

On the other hand, when the selective reflection wavelength of the cholesteric liquid crystal layer as the non-display storage layer is in the ultraviolet region as described above, since visible light does not exist on the shorter wavelength side than ultraviolet light, the medium No matter what direction is observed, the invisible information recorded in the image will not be seen.

According to the fifth aspect of the present invention, a cholesteric liquid crystal layer that selectively reflects light having a wavelength other than visible light is used as a non-display storage layer by utilizing the bistable phenomenon of cholesteric liquid crystal. A cholesteric liquid crystal layer that selectively reflects light is stacked and formed as a display storage layer, and for each cholesteric liquid crystal layer, switching between a selective reflection state by a planar phase and a transmission state by a focal conic phase is performed. Invisible information is written in the cholesteric liquid crystal layer as the non-display storage layer, and visible information is displayed and written in the cholesteric liquid crystal layer as the display storage layer.

Therefore, in the cholesteric liquid crystal layer as a non-display storage layer, invisible information can be recorded and rewritten so as to have a memory property without an electric field, and the cholesteric liquid crystal layer as a display storage layer can be rewritten. It can display and display visible information, and can be recorded and rewritten so as to have a memory property without an electric field.

In this case, the cholesteric liquid crystal forming the non-display storage layer and the cholesteric liquid crystal forming the display storage layer have different phase change threshold electric field intensities.
By applying a write signal having an electric field intensity selected from a plurality of electric field intensities having a boundary between the phase change threshold electric field intensities of the respective cholesteric liquid crystals to the stacked body of the non-display storage layer and the display storage layer, (1) The non-display storage layer and the display storage layer are both in a selective reflection state by the planar phase, (2) both the non-display storage layer and the display storage layer are in the transmission state by the focal conic phase, and (3) the non-display storage layer is Four states are obtained: a selective reflection state by the planar phase, a display storage layer in a transmission state by the focal conic phase, (4) a non-display storage layer by a transmission state by the focal conic phase, and a display storage layer by a selective reflection state in the planar phase. The writing of invisible information to the non-display storage layer and the display and writing of visible information to the display storage layer are independent within one pixel. One can be carried out at the same time.

Therefore, in this case, without providing a drive electrode or a drive circuit for each of the non-display storage layer and the display storage layer, the non-display storage layer and the display storage layer may be provided between the electrodes on both sides of the stacked body of the non-display storage layer and the display storage layer. By applying a common signal from a common driving circuit between an electrode on one side of the body and an external electrode, or between a pair of external electrodes, writing of invisible information to a non-display storage layer and display storage The display and writing of the visible information on the layer can be collectively performed at high speed, and the cost of the medium and the writing device can be reduced.

[0032]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an example of an information storage medium according to the first aspect of the present invention.

In this example, the information storage medium 1
A non-display storage layer 8A made of a cholesteric liquid crystal layer that selectively reflects ultraviolet light is formed between the three by inserting a spacer 9A, and a light absorption layer 6 is formed on the back surface of the substrate 3 on the side opposite to the outside light incident side. It is provided.

The substrates 2 and 3 can be made of glass, silicon, or a polymer film such as polyethylene, polystyrene, polyethylene terephthalate, polyvinyl alcohol, polycarbonate, polyvinyl chloride, polyimide, polyamide, and polysulfone. The substrate 2 on the side is formed of a material that transmits at least ultraviolet light.

The thickness of the substrates 2 and 3 ranges from several tens μm to several tens
When the thickness is 0 μm, it is preferable to have both self-supporting property and flexibility. In order to increase the partial pressure ratio to the non-display storage layer 8A, it is preferable that the dielectric constant is as large as possible. If necessary, a known functional film such as a liquid crystal alignment layer, a wear-resistant layer, or a barrier layer for preventing gas from entering the information storage medium 1 may be formed on the surface.

As the spacer 9A, a ball type or a cylindrical type made of glass, plastic, or the like can be used, and the thickness of the non-display storage layer 8A is set to several μm to several tens.
Control to 0 μm. In particular, when a flexible material is used for the substrates 2 and 3, the spacer 9A coated with an adhesive component is provided around the substrate 2 and 3 so that the thickness of the non-display storage layer 8A does not greatly change due to deformation of the substrates 2 and 3. It is preferable to bond between the substrates 2 and 3 by using.

In place of the spacer 9A, the substrate 2
Alternatively, a protrusion or the like that can control the thickness of the non-display storage layer 8A may be formed on the surface of No. 3.

The light absorbing layer 6 is not particularly limited as long as it absorbs ultraviolet light transmitted through the non-display storage layer 8A. For example, a polymer film containing a dye such as carbon black may be used. Can be used.

Instead of forming the light absorbing layer 6 on the back surface of the substrate 3 on the side opposite to the external light incident side, the light absorbing layer 6 is formed between the substrate 3 and the non-display storage layer 8A. 3 can be colored with a black dye or the like to give the substrate 3 an ultraviolet absorbing property, and the light absorbing layer 6 can be omitted.

The cholesteric liquid crystal constituting the non-display storage layer 8A includes Schiff base, azo, azoxy, biphenyl, terphenyl, benzoate, tolan, pyrimidine, cyclohexanecarboxylate, phenyl Use a nematic liquid crystal having a positive dielectric anisotropy such as a cyclohexane-based or dioxane-based material, or a material obtained by adding a chiral agent having an asymmetric carbon such as an ester derivative, a cyanobiphenyl derivative, or a bis-annealed derivative to a mixture thereof. be able to.

The helical pitch of the cholesteric liquid crystal is adjusted by the amount of the chiral agent added to the nematic liquid crystal so that the central wavelength of selective reflection is in the range of 300 to 400 nm.

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 dependences may be used.

The information writing device 20 includes the information storage medium 1
In this example, the write electrodes 21 and 22 sandwich the information storage medium 1 and the drive circuit 23 that applies a write signal between the electrodes 21 and 22. Although not shown in the figure, the drive circuit 23 is provided with electrodes 21 and 22 based on a drive power supply and input invisible information.
And a control unit for controlling a signal to be applied therebetween.

The information writing device 20 includes, for example, the electrode 2
A gap corresponding to the thickness of the information storage medium 1 is provided between the information storage medium 1 and the information storage medium 1 at the time of writing the invisible information. Or the electrode 21 side can be opened and closed with respect to the electrode 22 side. After the electrode 21 side is opened and the information storage medium 1 is inserted into a predetermined position, the electrode 21 side is closed and the information storage medium 1 is inserted into the information storage medium 1. It is possible to write invisible information.

Note that the information writing device 20 of this example
Any device capable of externally applying a write signal to the information storage medium 1 of this example may be used. For example, a pen writing type writing device having a pixel-sized electrode, a line scanning writing device having one-dimensionally arranged electrodes There is no particular limitation on a writing device of a type, a writing device of a surface writing type having two-dimensionally arranged electrodes, or a writing device of generating an ion current in these forms.

FIG. 1 shows an example in which the information storage medium 1 has no internal electrodes or wirings for applying an electric field at all.
The common electrode 7 may be provided on one substrate side of the information storage medium 1 as in the example shown in FIG.

In order to increase the voltage division ratio to the non-display storage layer 8A, the common electrode 7 is provided inside one of the substrates, for example, inside the substrate 3 on the side opposite to the external light incidence side, that is, when the substrate 3 is not displayed. It is desirable to form it between the storage layer 8A and the thickness thereof is preferably about several μm.

In this case, the information writing device 20 is provided with a contact which is in contact with and electrically connected to the common electrode 7 of the information storage medium 1 when writing invisible information. A write signal is applied between the write electrode 21 of the writing device 20 and the common electrode 7 of the information storage medium 1.

In this case, the information storage medium 1 may be attached to a surface of the printed material 10 opposite to the printing surface 11.

FIGS. 1 and 2 show the non-display storage layer 8A.
The cholesteric liquid crystal layer forming the non-display storage layer 8A is a cholesteric liquid crystal layer forming only the cholesteric liquid crystal.
(Polymer Network Liquid C
cholesteric liquid crystal dispersed in a droplet structure in a polymer (skeleton) or polymer skeleton.
lymer Dispersed LiquidCry
sta) structure.

The non-display storage layer 8A has a PNLC structure or a PDL.
With the C structure, an anchoring effect is generated at the interface between the cholesteric liquid crystal and the polymer, and the holding state of the planar phase or the focal conic phase without an electric field can be further stabilized.

In the information storage medium 1 of the example of FIG. 1 or FIG. 2, the threshold of the phase change between the planar phase and the focal conic phase as shown in FIG. 14 of the cholesteric liquid crystal layer forming the non-display storage layer 8A. Electric field strength Epf, 10
And a first electric field intensity Ea between the threshold electric field intensity Efh, 10 of the phase change between the focal conic phase and the homeotropic phase, and a threshold electric field intensity of the phase change between the focal conic phase and the homeotropic phase. Efh, an electric field strength of 90 or more is defined as a second electric field strength Eb.

Then, the external information writing device 20 generates an AC pulse as shown in FIG. 8A (the refresh period Tr is also shown in FIG. 8A, but the refresh period Tr is unnecessary in this example). Select period Ts
And a write signal in which the electric field strength Es in the select period Ts is the electric field strength selected from the electric field strengths Ea and Eb based on the invisible information. Or the same figure (B)
(Similarly, in this example, the refresh period T
r is unnecessary), the select period Ts of the DC pulse,
And a write signal in which the electric field strength Es in the select period Ts becomes the electric field strength selected from the electric field strengths Ea and Eb based on the invisible information. To the information storage medium 1.

As a result, the cholesteric liquid crystal layer as the non-display storage layer 8A has a state of (1) a state of selectively reflecting ultraviolet light of the planar phase and a state of (2) of transmitting ultraviolet light of the focal conic phase. The invisible information is written to the non-display storage layer 8A.

In order to read the invisible information recorded in this manner, as shown in FIG. 3, the information storage medium 1 is made of ultraviolet light from an ultraviolet lamp such as a black light fluorescent lamp or the like from the substrate 2 side. Or an incident light 31 which sufficiently contains ultraviolet light.

As a result, reflected light 32 of ultraviolet light is obtained from the pixels which are selectively reflected by the planar phase. The invisible information recorded on the information storage medium 1 can be read by detecting the reflected light 32 with a photodetector such as a CCD sensor that senses ultraviolet light.

The ultraviolet reflected light 32 may be converted into visible light by a wavelength conversion element, and the converted light may be detected by a photodetector such as a CCD sensor.

[Fifth Embodiment of the Invention] FIG. 4 shows an example of the information storage medium of the fifth invention.

In this example, the information storage medium 1
3, a non-display storage layer 8A made of a cholesteric liquid crystal layer that selectively reflects ultraviolet light and a display storage layer 8B made of a cholesteric liquid crystal layer that selectively reflects light of a specific wavelength in visible light, In addition, spacers 9A and 9B are inserted into the display storage layer 8B, and the non-display storage layer 8B is inserted.
A and the display storage layer 8B are laminated with a separation substrate 4 interposed therebetween, and the light absorption layer 6
Is provided.

The substrates 2 and 3 described above can be used. At least the substrate 2 on the external light incident side is formed of a material that transmits ultraviolet light and visible light.

Also in this case, the thickness of the substrates 2 and 3 is
It is preferably from μm to several hundred μm, having both self-supporting property and flexibility. In order to increase the voltage division ratio to the non-display storage layer 8A and the display storage layer 8B, it is preferable that the dielectric constant is as large as possible. If necessary, a known functional film such as a liquid crystal alignment layer, a wear-resistant layer, or a barrier layer for preventing gas from entering the information storage medium 1 may be formed on the surface.

The separation substrate 4 can use the same polymer film as the substrates 2 and 3 and is formed of a material having light transmittance. It preferably has a thickness of several μm to several tens μm and has flexibility. Similarly to the substrates 2 and 3, it is preferable that the dielectric constant be as large as possible in order to increase the partial pressure ratio to the non-display storage layer 8A and the display storage layer 8B. If necessary, a known functional film such as a liquid crystal alignment layer may be formed on the surface.

The spacers 9A and 9B are respectively shown in FIG.
Or, it is the same as the spacer 9A in the example of FIG. Also,
Instead of the spacers 9A and 9B, protrusions or the like that can control the thickness of the non-display storage layer 8A and the display storage layer 8B may be formed on the surfaces of the substrates 2 and 3 and the separation substrate 4.

The light absorbing layer 6 is not particularly limited as long as it absorbs ultraviolet light and visible light transmitted through the non-display storage layer 8A and the display storage layer 8B.
A polymer film containing a dye such as the above-described carbon black can be used.

Instead of forming the light absorbing layer 6 on the back surface of the substrate 3 on the side opposite to the external light incident side, the light absorbing layer 6 is placed between the substrate 3 and the display storage layer 8B formed on the substrate 3. Or by coloring the substrate 3 with a black dye or the like.
The light absorbing layer 6 may be omitted, and the light absorbing layer 6 may be omitted.

The cholesteric liquid crystal constituting the non-display storage layer 8A and the display storage layer 8B can use the same material as the non-display storage layer 8A in the example of FIG. The helical pitch of the cholesteric liquid crystal is adjusted by the amount of the chiral agent added to the nematic liquid crystal. For the non-display storage layer 8A, the central wavelength of selective reflection is in the range of 300 nm to 400 nm. The center wavelength is, for example, in the range of 500 nm to 600 nm. Further, in order to compensate for the temperature dependence of the helical pitch of the cholesteric liquid crystal, the method shown in the example of FIG. 1 may be used.

Also in this example, the information writing device 20 is formed separately from the information storage medium 1 and applies write signals between the write electrodes 21 and 22 sandwiching the information storage medium 1 and between the electrodes 21 and 22. And a driving circuit 23 that performs the driving. In addition, the information writing device 20 can be configured similarly to the example of FIG.

The example of FIG. 4 is a case where the information storage medium 1 does not have any electrodes or wirings for applying an electric field inside, as in the example of FIG. 1. However, as shown in FIG. The common electrode 7 may be provided on one substrate side of the medium 1. Common electrode 7
Is configured similarly to the example of FIG.

FIG. 4 or FIG. 5 shows an example of the non-display storage layer 8A.
And the cholesteric liquid crystal layer forming the display storage layer 8B has an LC structure composed of only cholesteric liquid crystal. However, the cholesteric liquid crystal layer forming the non-display storage layer 8A and the display storage layer 8B has the above-described PNLC structure or PDLC. It can also be structured.

When the non-display storage layer 8A and the display storage layer 8B 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 planar or focal conic phase in the absence of an electric field. The holding state can be made more stable. Further, with respect to the display storage layer 8B, it is possible to prevent a display defect of the Grand Jean texture caused by uneven thickness of the cholesteric liquid crystal layer.

The PNLC structure and the PDLC structure are formed by a known method for separating a polymer and a liquid crystal, for example, an acrylic type,
PIPS (Polymerizat) that mixes a liquid crystal with a polymer precursor such as a thiol-based or epoxy-based polymer that is polymerized by heat or light, and polymerizes from a uniform phase to separate phases.
ion Induced Phase Separat
Ion) method, Emulsion method in which liquid crystal is mixed with a polymer having low solubility in liquid crystal such as polyvinyl alcohol, and the liquid crystal is droplet-dispersed in the polymer by stirring and suspending, and liquid crystal is mixed with thermoplastic polymer. , TIPS (Therma) which is cooled from a state heated to a uniform phase and separated into phases.
lly Induced Phase Separat
ion) method, a polymer and liquid crystal are dissolved in a solvent such as chloroform, and the solvent is evaporated to separate the polymer and the liquid crystal.
(Se Separation) method or the like, but the manufacturing method is not particularly limited.

In particular, when the non-display storage layer 8A and the display storage layer 8B have the PDLC structure, the cholesteric liquid crystal of each cholesteric liquid crystal layer is covered by the polymer, and even if the separation substrate 4 is not provided, Since the cholesteric liquid crystal of the cholesteric liquid crystal layer does not mix with each other, the separation substrate 4 can be omitted.
When the PDLC structure is formed using a coating method capable of regulating the film thickness, such as a bar coating method, a spin coating method, and a roll coating method, the spacers 9A, 9
One or both of B can be omitted.

FIG. 6 shows an example of an information storage medium when the non-display storage layer 8A and the display storage layer 8B have a PDLC structure, and the non-display storage layer 8A and the display storage layer 8 are shown.
B represents polymer matrices 31A and 31B, respectively.
The cholesteric liquid crystals 32A and 32B are droplet-dispersed therein. No spacer is inserted between the non-display storage layer 8A and the display storage layer 8B, and there is no space between the non-display storage layer 8A and the display storage layer 8B. This is a case where the layers are formed without interposing the separation substrate.

FIG. 7 shows the non-display storage layer 8A and the display storage layer 8 of the information storage medium of the examples of FIGS. 4 to 6 with respect to the electric field intensity applied by the external information writing device 20.
4 shows the switching behavior of B.

The information storage medium of these examples includes a transition area between the planar phase and the focal conic phase and a transition between the focal conic phase and the homeotropic phase in the non-display storage layer 8A and the display storage layer 8B. The non-display storage layer 8A and the display storage layer 8B are configured so that the regions do not exist with the same electric field strength, and the layer having the larger phase change threshold electric field strength of the non-display storage layer 8A and the display storage layer 8B is the L layer. , The electric field strength of 90 or less is Ea,
The electric field strength between Epf, 10 of the L layer and Epf, 90 of the H layer is represented by Eb, and Epf, 10 of the H layer and Efh, 10 of the L layer.
Is the electric field strength between Efh, 90 of the L layer and Efh, 90 of the H layer.
An electric field strength of 90 or more is defined as Ee.

As shown in FIG. 8A, the external information writing device 20 includes at least a refresh period Tr and a select period Ts of an AC pulse, and a subsequent display period Td without an electric field. , Its refresh period Tr and select period T
a write signal in which the electric field strengths Er and Es at s have an electric field strength selected from the above five levels of electric field strengths Ea to Ee based on the invisible information and the visible information in a relationship of Er> Es, or As shown in FIG.
At least the DC pulse refresh period T
r, a select period Ts, and a subsequent display period Td in which no electric field is applied.
And electric field strengths Er and Es in the select period Ts
Applies a write signal having an electric field strength selected from the above five levels of electric field strengths Ea to Ee based on the invisible information and the visible information in a relationship of Er> Es to the information storage medium.

FIG. 9 shows the relationship between the refresh electric field intensity Er and the select electric field intensity Es in this case.
Shows the state of phase change of the layer and the L layer, where “p” is a selective reflection state by a planar phase, “f” is a transmission state by a focal conic phase, and “?” Depends on a state before application of a write signal. To be determined, respectively,
The L layer and the H layer are shown in this order.

As is clear from the above, according to the information storage medium and the information writing method described above, (1) both the H layer and the L layer are in a focal conic phase, and
Both the layer and the L layer are in a planar phase, (3) the H layer is in a focal conic phase, the L layer is in a planar phase, and (4) the H layer is in a planar phase and the L layer is in a focal conic phase. Four types of phase change states are obtained.

Therefore, for example, when the non-display storage layer 8A for selectively reflecting ultraviolet light is configured as an H layer and the display storage layer 8B for selectively reflecting green light is configured as an L layer, as shown in FIG. (“T” in the figure indicates that the corresponding layer is in a transmission state by the focal conic phase). (1) Black is displayed by a write signal of Er = Ec and Es = Ea, and ultraviolet light is displayed. No reflection,
(2) For example, green is displayed by a write signal of Er = Ee, Es = Ea, and a state in which ultraviolet light is reflected. (3) Green is displayed by a write signal of Er = Ed, Es = Ea. (4) Black state is displayed by the write signal of Er = Ee, Es = Eb, but the ultraviolet light is reflected.
In one state, invisible information can be recorded and visible information can be displayed and recorded within one pixel.

The reading of the invisible information recorded in the non-display storage layer 8A may be performed according to the method described above with reference to FIG.

The examples of FIGS. 4 to 6 show the case where the non-display storage layer 8A is on the outside light incident side. Conversely, the display storage layer 8B may be on the outside light incidence side. Further, the display storage layer 8B may be a cholesteric liquid crystal layer that selectively reflects red or blue color light. Further, the display storage layer may be formed by laminating three cholesteric liquid crystal layers that selectively reflect red, green, and blue color light, respectively.

Example An information storage medium according to the present invention was prototyped and its characteristics were measured.

(Example 1) In Example 1, an information storage medium having only a non-display storage layer having a PNLC structure was manufactured, and recording characteristics were measured.

50. A nematic liquid crystal BL012 (manufactured by Merck) having a positive dielectric anisotropy as a mixed solution of a cholesteric liquid crystal and a polymer precursor to form a cholesteric liquid crystal layer having a PNLC structure that selectively reflects ultraviolet light. 0w
25%, dextrorotatory chiral agent CB15 (Merck) 25.
0 wt% and dextrorotatory chiral agent CE2 (Merck)
To a solution obtained by mixing 25.0 wt%, 15 wt% of a thiol-based UV polymer precursor NOA65 (manufactured by Norland)
% Was added.

On a 75 μm-thick PET film lumirror (manufactured by Toray Industries, Inc.) forming the substrate 3, a 5 μm-diameter spherical spacer hayabeads L-25 (manufactured by Hayakawa Rubber Co., Ltd.) with an adhesive.
Was wet-sprayed, and the above-mentioned mixed solution was dropped, and a 75 μm-thick PET film mirror (manufactured by Toray Industries, Inc.) forming the substrate 2 was brought into close contact therewith.

After performing the above steps at 60 ° C., the film is heated to 110 ° C. to bond the spacer and the film.
Hold for 0 minutes. Returning to the environment of 60 ° C. again, the high-pressure mercury lamp was filtered to 50 mW / cm ² (365 mW / cm ² ).
nm) of UV light for 60 seconds. P forming the substrate 3
Forming a light absorbing layer 6 on the back surface of the ET film mirror,
An information storage medium having a non-display storage layer having a PNLC structure that selectively reflects ultraviolet light was obtained.

The obtained information storage medium is sandwiched between a pair of aluminum electrodes connected to a pulse generator and a high-voltage power supply, and an AC select signal of 50 Hz and 250 ms and a write signal consisting of a display period of no electric field are transmitted. The light was applied, taken out from between the electrodes, irradiated with light from an ultraviolet lamp in a dark room, and the fluorescent printed matter was placed on the reflection surface, and the presence or absence of ultraviolet light reflection was observed. Electric field strength E of select signal applied between aluminum electrodes
FIG. 11 shows s and the presence or absence of ultraviolet light reflection.

Example 2 In Example 2, an information storage medium having a non-display storage layer and a display storage layer, each having a PNLC structure, was manufactured.

As a cholesteric liquid crystal forming a cholesteric liquid crystal layer for selectively reflecting ultraviolet light, a nematic liquid crystal ZLI4389 having a positive dielectric anisotropy (manufactured by Merck) 65.0 wt%, a dextrorotatory chiral agent CB15 (merck company) 17.5 wt% and dextrorotatory chiral agent CE2
As a cholesteric liquid crystal for forming a cholesteric liquid crystal layer for selectively reflecting green light, a nematic liquid crystal E186 having a positive dielectric anisotropy (manufactured by Merck) 72.2 wt%. 13.9 wt% of dextrorotatory chiral agent CB15 (manufactured by Merck) and 13.9 w of dextrorotatory chiral agent CE2 (manufactured by Merck)
Then, 15% by weight of each of the thiol-based UV-polymerized polymer precursors NOA65 (manufactured by Netherlands) was added.

On a 75 μm-thick PET film lumirror (manufactured by Toray Industries, Inc.) forming the substrate 3, a 5 μm diameter spherical spacer hayabeads L-25 (manufactured by Hayakawa Rubber Co., Ltd.)
Was wet-sprayed, and the above mixed solution for green light was dropped, and a spherical spacer hayabeads L-25 (manufactured by Hayakawa Rubber Co., Ltd.) having a diameter of 5 μm and having an adhesive on one surface was wet-sprayed.
A μ-thick PET film mirror (manufactured by Toray Industries, Inc.) was brought into close contact with the non-scattering surface of the spacer.

Further, the above-mentioned mixed solution for ultraviolet light was dropped thereon, and a 75 μm-thick PET film mirror (manufactured by Toray Industries, Inc.) for forming the substrate 2 was adhered thereto.

After performing the above steps at 70 ° C., the film is heated to 110 ° C. in order to bond the spacer and each film.
Hold for 30 minutes. After returning to the environment of 70 ° C. again, the high-pressure mercury lamp was filtered to 50 mW / cm ² (36
5 nm) for 60 seconds. A light absorbing layer 6 is formed on the back surface of the PET film mirror forming the substrate 3, and a non-display storage layer 8A having a PNLC structure, which selectively reflects ultraviolet light, and a display for displaying green from the external light incident side. An information storage medium on which the storage layer 8B was laminated was obtained.

The obtained information storage medium is sandwiched between a pair of aluminum electrodes connected to a pulse generator and a high-voltage power supply, and an AC refresh signal for 50 Hz and 250 ms, an AC select signal for 50 Hz and 250 ms, and Apply a write signal consisting of a display period with no electric field,
It was taken out from between the electrodes, and the display color was observed. At the same time, the light of an ultraviolet lamp was applied in a dark room, the fluorescent printed matter was placed on the reflection surface, and the presence or absence of ultraviolet light reflection was observed. The electric field strengths Er and Es of the refresh signal and the select signal applied between the aluminum electrodes, and the display color and the presence or absence of ultraviolet light reflection are determined.
As shown in FIG.

Even when these writing operations were repeated 1,000 times or more, no change was observed in the display color and the presence or absence of reflection of ultraviolet light, and the electric field strength of the refresh signal and select signal required for display and reflection of ultraviolet light. The recording of the invisible information and the visible information both had sufficient memory properties, and no change was observed even after 30 days or more. Further, the information storage medium had flexibility at a thickness of 200 μm or less.

[0095]

As described above, according to the first aspect of the present invention, the fact that the medium is a medium on which information is recorded, the part on which the information is recorded is not apparent at a glance, It is possible to realize an information storage medium in which the danger of use is reduced and invisible information can be recorded in a rewritable manner.

According to the fifth aspect of the present invention, the invisible information can be recorded in a rewritable manner, and the invisible information is the same as the above, and the visible information can be rewritten and displayed on the same medium. Recording and rewriting of invisible information and visible information can be performed collectively and at high speed by the same principle and means, using the same device or method, and the cost of the medium and the writing device can be reduced. .

[Brief description of the drawings]

FIG. 1 is a diagram showing a first example of an information storage medium and an example of an information writing device according to the present invention.

FIG. 2 is a diagram showing a second example of the information storage medium of the invention of claim 1 and an example of an information writing device.

FIG. 3 is a diagram illustrating a method of reading invisible information recorded on the information storage medium of FIG. 1;

FIG. 4 is a diagram showing a first example of an information storage medium and an example of an information writing device according to the invention of claim 2;

FIG. 5 is a diagram showing a second example of the information storage medium and an example of the information writing device according to the second aspect of the present invention.

FIG. 6 is a diagram showing a third example of the information storage medium and an example of the information writing device according to the second aspect of the present invention.

FIG. 7 is a diagram showing a switching behavior of the information storage medium of FIGS.

FIG. 8 is a diagram showing an example of a write signal to the information storage medium of the present invention.

9 is a diagram showing a phase state of each layer of the information storage medium performing the switching behavior shown in FIG.

10 is a diagram illustrating a reflection state of the information storage medium that performs the switching behavior illustrated in FIG. 7;

FIG. 11 is a diagram showing the electric field intensity and the presence or absence of ultraviolet light reflection when information is written to the information storage medium of Example 1.

FIG. 12 is a diagram showing electric field strength, display colors, and the presence or absence of ultraviolet light reflection when information is written to the information storage medium of Example 2.

FIG. 13 is a diagram showing a phase change of a cholesteric liquid crystal having a positive dielectric anisotropy.

FIG. 14 is a diagram illustrating an example of a switching behavior of a cholesteric liquid crystal having a positive dielectric anisotropy with respect to a pulse signal.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Information storage medium 2, 3 Substrate 4 Separation substrate 6 Light absorption layer 7 Common electrode 8A Non-display storage layer 8B Display storage layer 9A, 9B Spacer 20 Information writing device 21, 22, Writing electrode 23 Drive circuit 31A, 31B Polymer matrix 32A , 32B cholesteric liquid crystal

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Haruo Harada 430 Border, Nakai-cho, Ashigarakami-gun, Kanagawa Prefecture Inside Green Tech Nakai Fuji Xerox Co., Ltd.

Claims (12)

[Claims] 1. An information storage medium having a non-display storage layer made of a transparent cholesteric liquid crystal layer for selectively reflecting light having a wavelength other than visible light and storing invisible information between a pair of substrates. 2. The information storage medium according to claim 1, wherein the cholesteric liquid crystal layer forming the non-display storage layer comprises:
An information storage medium comprising a polymer. 3. The information storage medium according to claim 1, wherein said non-display storage layer is for writing invisible information by applying an electric field from an external information writing device. Storage medium. 4. The information storage medium according to claim 3, wherein a common electrode is provided on one of the substrates. 5. A non-display storage layer composed of a transparent cholesteric liquid crystal layer for selectively reflecting light having a wavelength other than visible light and storing invisible information between a pair of substrates, and a light of a specific wavelength in visible light. And a display storage layer composed of a cholesteric liquid crystal layer that selectively reflects light and stores visible information. 6. The information storage medium according to claim 5, wherein the cholesteric liquid crystal layer forming the non-display storage layer and the cholesteric liquid crystal layer forming the display storage layer each include a polymer. Storage medium. 7. The information storage medium according to claim 5, wherein a cholesteric liquid crystal forming the non-display storage layer and a cholesteric liquid crystal forming the display storage layer have different phase change threshold electric field intensities. Information storage medium. 8. The information storage medium according to claim 5, wherein the invisible information and the visible information are written to the non-display storage layer and the display storage layer by applying an electric field from an external information writing device. An information storage medium characterized by being stored. 9. The information storage medium according to claim 8, wherein a common electrode is provided on one substrate side. 10. The information storage medium according to claim 1, wherein the cholesteric liquid crystal forming the non-display storage layer has a selective reflection wavelength in an ultraviolet region. 11. The apparatus for writing information to an information storage medium according to claim 7, wherein a boundary between the non-display storage layer and the display storage layer is a phase change threshold electric field strength of each of the cholesteric liquid crystals. An information writing apparatus, wherein an invisible information is written to the non-display storage layer and a visible information is written to the display storage layer by applying a write signal having an electric field intensity selected from a plurality of levels of electric field intensity. 12. The information writing method according to claim 5, wherein digital information related to the visible information is written as the invisible information.