JPH0784231A - Recording medium - Google Patents

Abstract

PURPOSE:To provide a recording medium with which stable recording and erasing characteristics and memory characteristics are obtd., the display part can be solidified, excellent mechanical strength such as wear resistance is obtd., and fast recording and erasing rate can be obtd. CONSTITUTION:A composite layer 13 produced by dispersing a cholesteric polymer liquid crystal and a low mol.wt. liquid crystal in a polymer matrix, and a pyroelectric layer 14 are interposed between a pair of electrodes facing to each other. For erasing, a high frequency electric field is applied to orient the low mol.wt. liquid crystal in the composite layer 13 so that the layer is changed into transparent. For recording, a low frequency electric field caused by the pyroelectric effect produced by rapid temp. change is applied to disturb the orientation in the cholesteric polymer liquid crystal in the composite layer 13 so that the layer is changed into white.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rewritable recording medium, and more particularly to a rewritable OHP film, a display which does not require record holding energy, a card having a rewritable display portion, and the like.

[0002]

2. Description of the Related Art In recent years, the amount of various types of information has expanded remarkably as office automation has progressed. With this increase in the amount of information, the number of opportunities to output information is also increasing. Generally, the output of information includes a hard copy display on paper by a printer and a display display.
The hard copy display will use a large amount of paper as a recording medium when the output of information increases, and thus will become a problem in the future from the viewpoint of resource protection. On the other hand, the display display has a problem in view of portability and cost because a large-scale circuit board is required for the display portion. Therefore, a rewritable recording medium without such a problem is expected as the third recording medium.

At present, a rewritable recording medium which is becoming widespread is, for example, JP-A-55-154198.
JP-A-57-82086 and resins made of low-molecular and high-molecular organic compounds capable of recording and erasing with a thermal printer head (hereinafter abbreviated as TPH). It is a matrix type. This type of recording medium has a relatively good balance of required characteristics as a rewritable recording medium, and is partially used as a prepaid card.

However, since this recording medium uses binary recording of heat, it is weak against thermal noise, has a narrow environmental temperature range in which recording / erasing can be performed in a short time by TPH, and has a repetition count of 150. ~ 500 times, which is relatively small. This is a very limited field of application, and cannot be applied to, for example, a station service IO card having a wide operating environment temperature.

To solve this problem, for example, a liquid crystal display element, an electrochromic element, an electrophoretic element,
It has been proposed to use a non-emissive device having a memory characteristic using a photochromic element or a thermochromic element. Among these elements, the electrochromic element requires a current application time of several tens to several hundreds of milliseconds, so that the recording and erasing speed is slow and it is difficult to increase the speed. Further, it is difficult to solidify the entire electrophoretic element, the photochromic element has insufficient light resistance, and the thermochromic element has a narrow environmental temperature range. For this reason,
At present, the liquid crystal display element is the only device that can practically obtain rewritable recording characteristics superior to those of the resin matrix recording medium.

When the liquid crystal display element is used as a rewritable recording medium, the first requirement is that stable recording / erasing characteristics and memory characteristics are obtained, and secondly the display section required when making a card. Can be solidified, and thirdly, it has excellent mechanical strength such as wear resistance,
Fourth, it is necessary to satisfy all four conditions that the recording / erasing speed can be increased.

The liquid crystal display element generally has stable recording / erasing characteristics but does not have memory characteristics. Therefore, when the application of the electric field for holding the display is stopped, the recording disappears. Therefore, it is conceivable to use a ferroelectric liquid crystal that can obtain a memory characteristic by causing spontaneous polarization, but the ferroelectric liquid crystal has a problem in stability because it is weak against vibration. Although polymer liquid crystals also have memory characteristics, it is difficult to achieve high recording / erasing speed when polymer liquid crystals are used. Furthermore, recently, regarding the liquid crystal in the resin matrix, an optical memory phenomenon peculiar to this system has been reported (Yamaguchi et al., IEICE Technical Report EID 91-27 (1991) p.81). Since it has excellent mechanical strength, it is expected to be applied to recording media. However, when this type of liquid crystal is used as a recording medium, the change in light transmittance is small without operating the temperature of the liquid crystal, and it takes several tens of milliseconds to apply an electric field.
Erase speed is slow. In addition, in the liquid crystal of this system, by using a high-molecular liquid crystal / low-molecular liquid crystal composite as a liquid crystal material, the memory phenomenon and the transparency at the writing frequency of the applied electric field
There is also a report that achieved cloudiness (Kikuchi et al., IEICE Tech.
-11 (1992) p.13). However, even in this configuration, the recording / erasing speed is slow because the electric field application time requires several hundred milliseconds.

Therefore, the currently practical liquid crystal display element uses the liquid crystal of the smectic C layer, and the S
A phase change of m (smectic) -N (nematic) -I (isotropic liquid) is caused to make the nematic phase opaque in the nematic phase at the time of temperature decrease and to be transparent by applying an electric field (for example, JP-A-58-125247,
JP-A-60-114323, Kubota et al., TV Society Technical Report OPT 191 (1984) p. 19, Hato et al., TV Society Technical Report IPD 91-1
5 (1984) p.37). When this liquid crystal display element is used as a recording medium, matrix wiring and a driving means for individually applying an electric field are arranged to each pixel of the recording medium, and the heat of the laser is used as a heating source to give recording energy. To be On the other hand, when the matrix wiring and the driving means cannot be individually arranged in each pixel, the electric field is collectively controlled by the sandwich electrode formed on the entire surface of the substrate, and the recording and erasing are individually performed by using heat. .

Further, in Japanese Patent Application Laid-Open No. 3-22532, a recording in which a smectic liquid crystal is made transparent by using a laminated body with a ferroelectric substance subjected to a poling treatment and by an electric field generated by heating the ferroelectric substance A medium has been proposed.
However, any recording medium using these liquid crystal display elements has a problem that mechanical strength such as abrasion resistance is insufficient as compared with the resin matrix system.

[0010]

As described above, it has been difficult for a liquid crystal display device expected to be used as a recording medium to satisfy all of the above four conditions required for a rewritable recording medium.

The present invention has been made in view of the above points. Stable recording / erasing characteristics and memory characteristics are obtained, the display portion can be solidified, and mechanical strength such as abrasion resistance is excellent. Moreover, it is an object of the present invention to provide a recording medium capable of increasing the recording / erasing speed.

[0012]

The present invention is a rewritable recording medium which can be repeatedly recorded and erased several thousand times, and in particular, a liquid crystal display device comprising a cholesteric polymer liquid crystal, a low molecular liquid crystal and a polymer matrix. , And a pyroelectric material, the recording medium satisfies the above four conditions at the same time.

That is, the present invention is characterized in that a pyroelectric layer and a composite layer in which a cholesteric polymer liquid crystal and a low molecular weight liquid crystal are dispersed in a polymer matrix are sandwiched between a pair of electrodes facing each other. A recording medium is provided.

[0014]

In the recording medium of the present invention as described above,
By applying a low-frequency electric field due to the pyroelectric effect of the pyroelectric layer to the composite layer, the composite layer becomes clouded and recording is performed,
By applying a high frequency electric field, the composite layer is made transparent and erased.

As described above, since recording / erasing is performed by applying an electric field to the composite layer, the stability of recording / erasing is superior to the binary recording of heat. Moreover, since the cholesteric polymer liquid crystal and the low molecular liquid crystal are used together as the liquid crystal, the memory characteristic can be secured.

Further, since the composite layer has a structure in which liquid crystal is dispersed in a polymer matrix, it has excellent mechanical strength and can solidify the entire display portion. Furthermore, by utilizing the electric field maintenance effect of the pyroelectric material when the composite layer becomes cloudy, high-speed recording and erasing can be performed even if the electric field application time required for clouding is several hundred milliseconds. It becomes possible.

[0017]

Embodiments of the present invention will be specifically described below with reference to the drawings. FIG. 1 is a sectional view showing an example of a display portion of a recording medium of the present invention. In the figure, 11 indicates a support substrate. A counter electrode 12 having a light reflection characteristic is formed on the support substrate 11. Formed on the counter electrode 12 is a composite layer 13 in which a cholesteric polymer liquid crystal and a low molecular liquid crystal are dispersed in a polymer matrix. Composite layer 1
A transparent pyroelectric layer 14 is formed on the surface 3. Furthermore, a transparent electrode 15 is formed on the pyroelectric layer 14.

As the supporting substrate 11, a glass substrate, a metal substrate, a ceramic substrate, a Si wafer, a substrate made of resin such as polyethylene terephthalate (PET), or the like can be used. The thickness of the support substrate 11 is 0.1 to 2.0.
It is preferably about mm.

As a material of the counter electrode 12, a metal such as aluminum, chromium, titanium or the like can be used. Further, the thickness of the counter electrode 12 is preferably 0.1 to 2.0 μm.

As the polymer matrix of the composite layer 13, an ultraviolet curable resin or the like can be used. Also,
As the liquid crystal, a cholesteric polymer liquid crystal as shown in Chemical formulas 1 and 2 and a low molecular liquid crystal as shown in Chemical formulas 3, 4 and 5 are used in combination. The thickness of the composite layer 13 is 5 to 20 μm.
It is preferably m. This is because when the thickness of the composite layer 13 is less than 5 μm, the light transmittance does not decrease sufficiently when it becomes cloudy, and when the thickness exceeds 20 μm, it is necessary to increase the applied electric field and the composite layer 13 Is complicated.

[0021]

[Chemical 1]

[0022]

[Chemical 2]

[0023]

[Chemical 3]

[0024]

[Chemical 4]

[0025]

[Chemical 5]

As the material of the pyroelectric layer 14, TGS can be used for an organic substance and LiTaO ₃ or the like can be used for a single crystal. Further, the thickness of the pyroelectric layer 14 is such that the maximum electric field strength due to the pyroelectric voltage is about 1 to 50 × 10 ⁵ V / cm in consideration of the pyroelectric constant, the dielectric constant, and the reached temperature of the pyroelectric body. Is set as appropriate. Specifically, the thickness of the pyroelectric layer 14 is 0.5 to
It is preferably 50 μm. This is the pyroelectric layer 14
If the thickness is less than 0.5 μm, the electrostatic capacity tends to increase and the electric field due to the pyroelectric effect tends to decrease.
This is because if it exceeds 0 μm, it becomes difficult to make a recording medium into a card. When reading information from the transparent electrode 15 side, the pyroelectric layer 14 needs to be transparent.

The material of the transparent electrode 15 is ITO, S
nO ₂ or the like can be used. In addition, the transparent electrode 15
Is preferably 2 to 200 nm, and when the thickness is reduced to about 5 nm or less, a metal such as Au can be widely used as the material of the transparent electrode 15.

Next, a method of manufacturing the recording medium having the above structure will be described. FIG. 2 is a sectional view showing a manufacturing process of the recording medium of the present invention, and FIG. 3 is a plan view and a sectional view of the recording medium obtained at this time.

First, as shown in FIG. 2A, the support substrate 11 is subjected to ozone treatment to increase the adhesion strength on the surface. Next, as shown in FIG. 2B, a metal is deposited on the surface of the support substrate 11 by a DC sputtering method, a vacuum deposition method or the like to form the counter electrode 12 and the extraction electrode 16. In this case, patterning is performed using a metal mask. Alternatively, the support substrate 11 may be electrolessly plated with aluminum or the like to form a metal film, and then patterned by etching.

Next, as shown in FIG. 2C, for example, a UV-curable resin as a polymer matrix is mixed with a cholesteric polymer liquid crystal and a low-molecular liquid crystal, and the mixture is applied on the counter electrode 12 and dried. After the resin film is formed by, the resin film is irradiated with ultraviolet rays to cure the ultraviolet curable resin to form the composite layer 13 (Yamaguchi et al., IEICE Tech.
D 91-27 (1991) p.81). In addition to this, as a method for forming the composite layer 13, a method in which a resin, a cholesteric polymer liquid crystal and a low molecular liquid crystal are dispersed in a solvent, which is applied onto the counter electrode 12 and dried (for example, Kikuchi, Kajiyama) , IEICE Technical Report OME 92-11 (1992) p.13), fine particles that can be dissolved in a solvent such as chloroform are dispersed in a solvent together with a resin, and then the fine particles are applied onto the counter electrode 12 and dried. A method in which a cholesteric polymer liquid crystal and a low molecular weight liquid crystal are dissolved in a solvent and the space is filled (for example, Hasegawa et al., IEICE Technical Report ONE 92-39 (1992) p.37) can be mentioned. At this time, as a coating method on the counter electrode 12, there are several methods such as a bar coating method, a spin coating method, a gravure coating method, and a casting method.

Next, as shown in FIG. 2D, a connection portion 17 with the transparent electrode 15 is formed on the extraction electrode 16.
The connection part 17 is formed of a flexible conductor, a conductive paste, or the like.

On the other hand, as shown in FIG. 2F, ITO or the like is deposited by RF sputtering, for example, on the protective film 18 necessary for forming a card as shown in FIG. 2E. The transparent electrode 15 is formed. Here, by providing the protective film 18, the wear resistance of the display portion of the recording medium can be improved. Next, as shown in FIG. 2G, the pyroelectric layer 14 is formed on the transparent electrode 15. The pyroelectric layer 14 is formed by forming a pyroelectric film on the transparent electrode 15, heating the transparent electrode 15 to an appropriate temperature, and applying an electric field from the outside to align the polarization directions (polling treatment). 2) or a method of forming a pyroelectric body such as a LiTaO ₃ single crystal produced by a pulling method in the form of a wafer and adhering it to the transparent electrode 15.
The poling process is performed by sandwiching the pyroelectric body with electrodes and applying an electric field exceeding the coercive electric field, or by providing an electrode on only one side of the pyroelectric body as shown in FIG. It is carried out by a method such as generating an electric field exceeding the above. These methods are appropriately selected in consideration of other processes.

Thereafter, the support substrate 11 having the connecting portion 17 formed thereon and the protective film 18 having the pyroelectric layer 14 formed thereon are brought into contact with each other while the composite layer 13 and the pyroelectric layer 14 are in contact with each other while the temperature is raised. And glue. In the case of the pyroelectric layer 13 in which a single crystal is formed in a wafer shape, the transparent electrode 15 and the protective film 18 such as AlN _x are laminated on one main surface of the single crystal, and then the other is formed. The main surface may be bonded to the composite layer 13.

The recording medium thus obtained is shown in FIG.
The configuration is as shown in (A) to (D). 3A is a plan view of the obtained recording medium, FIG. 3B is a sectional view taken along the line AA, and FIG. 3C is a line BB thereof. FIG. 3D is a sectional view taken along the line C-C.

Next, recording / recording of the recording medium having the above configuration
Erasing will be described with reference to FIGS. 4 and 5. The visibility of the recording medium is obtained by the electro-optical effect of the composite layer 13. That is, the modulation of the light transmittance by making the composite layer 13 cloudy and transparent by applying an electric field as described above is used. For example, the thickness of the composite layer 13 is 10 μm
In this case, the light transmittance is about 2 to 5% in the cloudy mode and about 95 to 99% in the transmission mode.

As shown in FIG. 4A, the transparency is mainly obtained by utilizing the alignment of the low molecular weight liquid crystal under a high frequency electric field. First, a high frequency electric field as shown in FIG. 4B is applied between the counter electrode 12 and the transparent electrode 15. The side chains of the low molecular weight liquid crystal and the cholesteric polymer liquid crystal in the composite layer 13 are aligned in the direction perpendicular to the electrode surface by the high frequency electric field, and as a result, as shown in FIG. Becomes transparent in several hundreds of milliseconds (300 milliseconds in FIG. 4). At this time, the maximum electric field strength applied to the composite layer 13 is set in the range of 1 to 50 × 10 ⁵ V / cm in consideration of the response speed and the breakdown voltage.

On the other hand, the white turbidity utilizes the disorder of the alignment of the cholesteric polymer liquid crystal under a low frequency electric field, as shown in FIG. 5 (A). That is, the orientation of the main chain of the cholesteric polymer liquid crystal is disturbed by the low-frequency electrolysis, and as a result, the side chains of the cholesteric polymer liquid crystal and the low-molecular liquid crystal are disturbed, and the entire surface of the composite layer 13 becomes clouded. To do. Here, the low-frequency electric field is generated by the pyroelectric effect due to the temperature difference caused by the heat supplied to the pyroelectric layer 14 from the outside using TPH, for example. In general, when the temperature changes slowly, the current caused by the pyroelectric effect is proportional to the time derivative of the temperature with the pyroelectric rate as a coefficient.
Therefore, the generated electric field is proportional to the time integral of the pyroelectric current, and is therefore almost proportional to the value of the temperature change. On the other hand, as shown in FIG. 5 (B), when a heat pulse of about 1 millisecond is used from the outside, the temperature change is abrupt, so the temperature fall time is about several tens of milliseconds. However, in this case, the electric field generated by the pyroelectric effect falls more slowly than the temperature rises due to the relaxation time of the polarization of the pyroelectric body, etc. The electric field due to the electric effect is maintained. This is effectively several Hz
To a low-frequency electric field for clouding with a comma frequency of several Hz.
In this way, high-speed recording of about 1 millisecond per line becomes possible.

In the transparent / whitening system as described above, the overwrite characteristic is as shown in FIG. 6, where the contribution of the high frequency electric field and the contribution of the low frequency electric field due to the pyroelectric effect It becomes possible when the contribution becomes overwhelmingly dominant. Generally, in the recording medium of the present invention, the effect of the low frequency electric field becomes dominant when the electric field strengths of the high frequency electric field and the low frequency electric field are similar. It is the pyroelectric layer 14 from the outside.
This is because the composite layer 13 is also locally heated by the heat supplied to the cholesteric polymer liquid crystal, and the movement of the cholesteric polymer liquid crystal in the composite layer 13 becomes active. Therefore, for example, by applying heat with TPH while applying a high-frequency electric field between the counter electrode 12 and the transparent electrode 15, overwrite recording becomes possible.

Next, another example of the display portion of the recording medium of the present invention will be described with reference to FIGS. The same parts as those of the display section of the recording medium shown in FIG. 1 are designated by the same reference numerals, and the description thereof will be omitted. Only the characteristic parts will be described.

In the recording medium shown in FIG. 7, a transparent electrode 15 is used in place of the counter electrode 12, and the support substrate 11 is colored black, for example. With such a configuration, the contrast with the background can be improved. Alternatively, as shown in FIG.
A colored sheet member 20 may be interposed between the support substrate 11 and the transparent transparent electrode 15.

In the recording medium shown in FIG. 9, a transparent glass substrate or a substrate made of a resin such as PET is used as the supporting substrate 11, a transparent electrode 15 is formed on the supporting substrate 11, and the pyroelectric layer 14 is formed. The counter electrode 12 is formed on the. With such a configuration, it is not necessary to make the pyroelectric layer 14 transparent, and the range of selection of the material of the pyroelectric layer 14 is widened. In this configuration, for example, a single crystal pyroelectric material is cut out, the counter electrode 12 is formed thereon, and then assembled on the composite layer 13 by a method such as thermocompression bonding.

In the recording medium shown in FIG. 10, the light absorbing layer 21 is formed on the counter electrode 12 of the recording medium shown in FIG.
The protective film 18 is formed thereon. As the light absorption layer 21, TeOx, SnTeSe, CdTe /
A thin film made of Al, Cr or the like is used. With such a structure, it is possible to cope with an optical recording system by heat of a laser. In the recording medium shown in FIG. 10, recording is performed by irradiating a laser beam from the protective film 18 side, and information is read from the supporting substrate 11 side.

On the other hand, the recording medium shown in FIG. 11 is one in which a light absorption layer 21, a counter electrode 12, a pyroelectric layer 14, a composite layer 13 and a transparent electrode 15 are sequentially laminated on a transparent support substrate 11. The information is read from the transparent electrode 15 side by recording with the laser beam from the supporting substrate 11 side. In this case, the light absorbing layer 21 can be omitted by using a light absorbing material as the material of the counter electrode 12. With the recording medium shown in FIGS. 10 and 11, recording can be performed on the display unit without contact.

In the recording medium shown in FIG. 12, a metal material having conductivity such as a stainless plate is used as the material of the support substrate 11. With this structure, the counter electrode 12 can be omitted. In addition, the mechanical strength of the recording medium itself is improved. Further, the supporting substrate 1
Electrical continuity can be taken from the 1 side.

In the recording medium shown in FIGS. 13A and 13B, the auxiliary electrode 22 is formed on the counter electrode 12 and the transparent electrode 15 around the display portion, and the transparent electrode 15 is protected. The film 18 is formed. Further, the extraction electrode 16 is provided on the surface of the display section. Since this recording medium is a recording medium for OHP, it is necessary that all of the supporting substrate 11, the counter electrode 12, and the pyroelectric layer 14 are made of a transparent material.

In such a structure, the composite layer 13
The white turbid image recorded in 1 hinders the passage of light in the composite layer 13 by scattering the light incident from the support substrate 11 side. As a result, an OHP image is displayed.

It should be noted that, in the present invention, various other structural modifications can be considered without departing from the spirit of the present invention. For example, a heat storage layer may be provided to reduce heat power.

As described above, the recording medium of the present invention satisfies all the four conditions that are the subject. In particular,
The recording medium of the present invention has excellent wear resistance in a recording medium using a liquid crystal display element. Here, regarding the recording medium having the display unit having the configuration shown in FIG.
When the abrasion resistance was evaluated by the rewritable recording characteristics in the running test of the O card with TPH, it was about the same as that of the resin matrix recording medium. On the other hand, the abrasion resistance was similarly evaluated for a recording medium using a layer containing smectic liquid crystal instead of the composite layer 13 in which a cholesteric polymer liquid crystal and a low molecular liquid crystal are dispersed in a polymer matrix. However, it is 1 more than the resin matrix system
It was found that the resistance was lower than the order of magnitude.

[0049]

As described above, according to the recording medium of the present invention, stable recording / erasing characteristics and stable memory characteristics can be obtained, and it is possible to solidify the entire display portion and to provide a machine having abrasion resistance and the like. In addition, it is possible to realize high-speed recording and erasing, and it is possible to realize high-visibility image recording and erasing without requiring energy to hold the display. It becomes possible to realize a recording medium.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an example of a display unit of a recording medium of the present invention.

2A to 2H are sectional views showing a manufacturing process of the recording medium of the present invention.

3A is a plan view of the recording medium of the present invention obtained by the manufacturing process shown in FIG. 2, FIG. 3B is a sectional view taken along the line AA of FIG. 3A, and FIG. ) Is a cross-sectional view taken along line BB of FIG.
(D) is sectional drawing which follows CC line of (A).

FIG. 4A is a schematic diagram showing a transparent state of a composite layer,
FIG. 6B is a characteristic diagram showing an applied signal and a light transmittance in the transparent mode.

FIG. 5 (A) is a schematic view showing a opaque state of the composite layer,
(B) is a characteristic diagram showing an applied signal and a light transmittance in the clouding mode.

FIG. 6 is a characteristic diagram for explaining overwrite characteristics.

FIG. 7 is a sectional view showing another embodiment of the recording medium of the present invention.

FIG. 8 is a sectional view showing another embodiment of the recording medium of the present invention.

FIG. 9 is a sectional view showing another embodiment of the recording medium of the present invention.

FIG. 10 is a sectional view showing another embodiment of the recording medium of the present invention.

FIG. 11 is a sectional view showing another embodiment of the recording medium of the present invention.

FIG. 12 is a sectional view showing another embodiment of the recording medium of the present invention.

13A is a plan view showing another embodiment of the recording medium of the present invention, and FIG. 13B is a sectional view taken along the line D-D of FIG. 13A.

[Explanation of symbols]

11 ... Support substrate, 12 ... Counter electrode, 13 ... Composite layer, 1
4 ... Pyroelectric layer, 15, 19 ... Transparent electrode, 16 ... Extraction electrode, 17 ... Connection part, 18 ... Protective film, 20 ... Sheet member,
21 ... Light absorption layer, 22 ... Auxiliary electrode.

Claims (1)

[Claims] 1. A recording medium comprising a pyroelectric layer and a composite layer in which a cholesteric polymer liquid crystal and a low-molecular liquid crystal are dispersed in a polymer matrix between a pair of opposing electrodes. .