JPH086508A - Display medium and its display method - Google Patents

Abstract

PURPOSE:To make it possible to hold images even if the number of repetitive use times is large and there is no supply of energy by providing a display medium with a container of which at least one surface consist of a transparent material and a specific image forming medium. CONSTITUTION:This display medium is composed of the container which includes transparent electrodes 9 and a counter electrode 2 formed on a supporting base body 1, the image forming medium 5 which is arranged between the respective electrodes 2 and 9 and consists of columnar materials 6 for separating the container to respective cells, an insulating hot meltable material 3 separated by these columnar materials 6 and electrifiable particulates 4 as migration particles dispersed in these hot meltable material 3 and a transparent coating film 7 which is formed on the transparent electrodes 9. The electrophoresis of the electrifiable particulates 4 to, for example, the transparent electrode 9 side is effected in the hot meltable material 3 melted by impressing voltage to the electrodes 2, 9 by which the hue occurring in the electrifiable particulates 4 is displayed from the transparent electrode 9 side. The electrophoresis to the counter electrode 2 side is effected, by which the hue occurring in the hot meltable material 3 is displayed from the transparent electrode 9 side.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rewritable display medium exhibiting electrophoretic characteristics by applying an electric field at the time of temperature rise, particularly a card having a rewritable display section, and a portable recording medium which does not require record holding energy The present invention relates to a display medium suitable for a display (display paper) and a display method thereof.

[0002]

2. Description of the Related Art Due to the spread of OA in recent years, the amount of data of various kinds of information is increasing and the output of information is also increasing accordingly. The output of information is represented by a hard copy display on paper and a display display by a printer.
However, in recent years, as a third recording medium, a rewritable recording medium (an all-solid or semi-solid recording medium capable of performing a large number of highly visible image recording / erasing cycles and not requiring energy to hold a display) ) Is expected in various fields from the viewpoint of resource protection from the former that uses a large amount of paper, and from the viewpoint of cost reduction and portability of recording media from the latter that requires a large-scale electric circuit in the display section. ing.

At present, a rewritable recording medium which is becoming popular is a thermal printer head (abbreviated as T).
PH) is an organic low molecular weight / polymer resin matrix system (for example, JP-A-55-154198, JP-A-57-82086). This system has a relatively well-balanced requirement of characteristics as a rewritable recording medium, and is partially used as a prepaid card. However, this organic low molecular weight / polymer resin matrix system has some problems, and the fact that the number of repetitions is relatively small, about 150 to 500 times, significantly limits the field of application of this rewritable recording medium. However, for example, it could not be applied to a station service IO card having a wide operating environment temperature.

On the other hand, research on an electrophoretic device using particles exhibiting electrophoresis is under way (eg, I.0t).
a et.al., Proceedings. of the IEEE, 61,832 (1973)),
FIG. 12 shows a schematic sectional view of the electrophoretic element. As shown in the figure, the basic structure of the electrophoretic element is an image composed of a transparent electrode 9 formed on a transparent substrate 12 (for example, glass) and a suspension 13 in which charged fine particles 4 as electrophoretic particles are dispersed. It depends on the forming medium, the counter electrode 2 formed on the support base 1, the spacer 14 which holds the space between the transparent electrode 9 and the counter electrode 2. Here, at least one of the counter electrode 2 and the transparent electrode 9 is separated corresponding to the individual pixel. The image signal is electrically scanned for each individual pixel,
A desired image is formed by controlling the movement of the electrophoretic particles by an image signal sent for each pixel.

However, since the image forming medium of the electrophoretic element is basically a liquid, when the supply of electric energy from the outside is stopped, the formed image is time-lapsed (for example, pigment sedimentation). Since the density changes, it was not suitable for carrying cards and the like.

[0006]

As described above, the number of repetitions is small in the conventional method. Alternatively, there is a problem that the image density changes over time. The present invention has been made in view of the above problems, and an object of the present invention is to provide a display medium that can be repeatedly used and that can hold an image without supplying energy.

[0007]

According to the first invention of the present application, a container having at least one surface made of a transparent material, a heat-meltable material arranged in the container, and a charging dispersed in the heat-meltable material. An image forming medium made of organic fine particles is provided.

The second invention of the present application is the display medium according to the first invention of the present application, wherein the container comprises a counter electrode and a transparent electrode as the transparent material.

A third invention of the present application is the display medium according to the first invention of the present application, wherein the container is element-separated by a pillar material.

A fourth invention of the present application is a step of controlling the electrophoresis of the charging fine particles by heating a display medium having an image forming medium composed of the charging fine particles and a heat-melting material and applying an electric field. And a step of cooling the image forming medium after the heating is completed.

A fifth aspect of the present invention is characterized in that the image forming medium is heated at a desired position and the electrophoresis of only the charged fine particles in the heat-meltable material melted by the heating is controlled. It is a display method of a display medium according to a fourth invention.

According to a sixth aspect of the present invention, there is provided a container having at least one surface made of a transparent material, an image forming medium made of a heat fusible material disposed in the container, and chargeable fine particles dispersed in the heat fusible material. The display medium is characterized by comprising: forming a image on the image forming medium by applying heat and an electric field for forming an image to the container, and then solidifying the image.

FIG. 1 is a schematic partial sectional view showing an example of the display medium of the present invention. Hereinafter, the present invention will be described in more detail with reference to FIG. As shown in the drawing, a container provided with a transparent electrode 9 and a counter electrode 2 formed on a supporting substrate 1, and a pillar material 6 arranged between the counter electrode 2 and the transparent electrode 9 to separate the container into cells. Formed on the transparent electrode, and an image forming medium 5 composed of an insulating heat-meltable material 3 separated by the pillar material and chargeable fine particles 4 as electrophoretic particles dispersed in the heat-meltable material 3. It is composed of a transparent coating film 7.

In the display medium display method of the present invention, the heat-melting material 3 is melted by heating the display medium, and the heat-melting material is melted by applying a voltage to the electrodes 2 and 9. In FIG. 3, the chargeable fine particles 4 are electrophoresed on the transparent electrode side 9 to display the hue caused by the chargeable fine particles 4 from the transparent electrode 9 side, and the transparent electrode 9 is electrophoresed on the counter electrode 2 side. From the side, it is possible to display the hue caused by the heat-meltable material 3.
Further, by stopping the heat supply to the displayed display medium (natural cooling) and solidifying the heat-meltable material 3,
It becomes possible to fix the chargeable fine particles 4 and maintain the displayed image even in a state where electric energy is not supplied. The recording method and mechanism will be described below.

First, a theoretical formula (1) (AL Dariga. I) that approximates the migration time of electrophoretic charged fine particles is used.
EEE Transaction on Electro
nDevices, vol. ED-24 (7), 827
(1977)).

[Equation 1] Here, t is the migration time of the chargeable fine particles 4, η is the viscosity of the heat-meltable material 3, L is the distance between the electrodes 2 and 9, ε is the dielectric constant of the heat-meltable material 3, and E is applied. Electric field strength, ζ
Indicates the zeta potential (several to several hundred tens mV), and V indicates the applied voltage.

The case of inputting an image signal by heating will be described more specifically. First, prior to the image signal, a voltage is applied to the transparent electrode 9 and the counter electrode 2 to apply a uniform DC electric field to the image forming medium 5. Thereafter, an image signal is applied in the form of heat by TPH, for example, at a recording speed of 1 ms per line. The heat applied from TPH is applied to the transparent coating film 7
The temperature of the image forming medium 5 is raised via the, and the heat-meltable material 3 is phase-changed into a fluid state. In the heat-meltable material 3 that has become a migration medium by being melted, the chargeable fine particles 4 migrate by the Coulomb force and reach the transparent electrode 9 before the heat-meltable material 3 in a molten state solidifies and reach the transparent electrode 9. The particles adhere to the transparent electrode 9 and, as a result, the color of that portion viewed from the transparent electrode 9 side becomes the color of the chargeable fine particles 4. Since the chargeable fine particles 4 in the heat-meltable material 3 in the non-melted state (non-heated portion) are fixed / held in the solid regardless of whether or not they are charged, they do not show electrophoresis.
The color viewed from the transparent electrode 9 side is the background color, that is, the color caused by the heat-meltable material 3. As a result, the chargeable fine particles 4
An image is formed of a hue caused by the above and a hue caused by the heat-meltable material 3. Further, the heat-meltable material 3 is cooled (may be naturally cooled) to be solidified while holding the image. Since the present invention uses the heat-meltable material 3 as the migration medium as described above, the chargeable fine particles 4 in the image forming medium 5 are fixed by the solidified heat-meltable material 3.
That is, the image density is retained and there is no change in image density over time.

Although the electric field is applied through the electrodes here, it is also possible to apply the electric field to the display medium by installing an electrostatic body instead of the electrodes and charging the surface thereof.

Here, the more excellent point of the method of recognizing the portion to which heat is applied as a pattern on the display medium to which the DC electric field is uniformly applied as described above is that the display is performed by the conventional electrophoretic element. In contrast, it is necessary to apply an electric field applied to each pixel, whereas it is sufficient to apply an electric field to the entire display medium, so that the manufacturing of the display medium can be simplified. That is, in order to perform display with a conventional electrophoretic element, it is necessary to apply an electric field to each pixel, whereas in the present invention, an electric field may be applied to the entire display medium. There is no need to form.

The method of inputting an image signal by heat as described above is particularly advantageous in that the speed of the image input signal can be increased when the display medium is moved and recording is performed in a short time, such as an automatic ticket gate. It is suitable. This point will be described with reference to FIG. FIG. 2 is an example of a drive timing chart when an image signal is input by heating to the display medium of the present invention using an appropriate heat-fusible material. As shown in the figure, an electric field is continuously applied to the entire display medium. , TPH, etc.
It is possible to heat the heat-meltable material above the melting point by heating for about 1 ms, and the melting state of the heat-meltable material once heated is 30 m due to the heat storage effect and the supercooling property of the image forming medium.
The melting time after heating can be maintained for at least s, and the voltage can be applied by a simple device even when the display medium is moving at high speed.

Further, as will be described in detail in Examples to be described later, by introducing screen printing or thermal transfer printing to the formation of the image forming medium, there is a feature that the colorizing element can be easily manufactured.

When re-recording an arbitrary image on this display medium, a reverse bias is first applied to heat the entire display medium,
It is necessary to record the image after resetting the image, that is, causing the charged fine particles to electrophorese on the counter electrode side.
Heating at the time of image reset may be carried out by heating with a heat roller or surface heating with an infrared lamp.By arranging the writing system directly for resetting, preheating before writing can be performed and higher speed recording can be performed. preferable.
The method of inputting an image signal is not limited to heating, and for example, a method of providing an electric field such as an electrode for each pixel in a display medium or the like and controlling the electric field applied to each electrode is also possible. The entire display medium can be heated to bring the heat-meltable material into a molten state.

Next, the materials constituting the display medium of the present invention will be described. Since the thermofusible material according to the present invention serves as an electrophoretic medium for charged fine particles, the viscosity of the molten state is important. This can be seen from the above theoretical formula (1),
This is because when the viscosity of the heat-meltable material that serves as the migration medium is reduced, the migration time of the chargeable fine particles can be shortened, that is, the display speed can be increased. The viscosity of the heat-meltable material in the molten state is 5 × at a kinematic viscosity of 120 ° C.
It is preferably 10 ^-5 m ² s ^-1 or less. Further, in the case of a kinematic viscosity at 100 ° C., it is preferably 1 × 10 ⁻⁴ m ² s ⁻¹ or less, more preferably 0.2 × 10 ⁻⁴ m ² s ⁻¹ or less.

On the other hand, the melting point of the heat fusible material is 40 ° C. or higher, preferably 50 ° C., depending on the environmental temperature conditions in which the display medium is used.
More preferably, it is 60 ° C or higher. These are because the display medium of the present invention may be used in a high temperature atmosphere such as in a closed car. It is desirable to use a material whose viscoelastic modulus (kinematic viscosity) decreases by 4 digits or more in the temperature range of 20 ° C across the melting point.

The heat-fusible material is a carboxyl group in the molecule (-COOH) or an alcoholic a hydroxyl group (-OH), a an amino group (-NH _2), an organic material containing groups such as carbonyl groups (> CO) desirable. In addition, for example, a melting organic material such as paraffin may contain an additive such as a surface active agent in an amount of about several percent, so that the migration characteristics of the chargeable fine particles can be improved. As a matter of course, it is necessary to use an insulating substance as the heat-meltable material.

Examples of such a heat-meltable material include various waxes, saturated fatty acids and higher alcohols listed below.

Higher monohydric alcohols such as stearyl alcohol, 1-eicosanol, 1-docosanol, 1-tetracosanol, 1-hexacosanol, 1-octacosanol, 1,8-octanediol, 1,10-decanediol ,
Linear higher polyhydric alcohols such as 1,12-dodecanediol, 1,12-octadecanediol, 1,2-dodecanediol, 1,2-tetradecanediol and 1,2-hexadecanediol, palmitic acid, stearic acid, 1-octadecanoic acid, behenic acid, 1-docosanoic acid, 1-tetracosanoic acid, 1-
Higher fatty acids such as hexacosanoic acid and 1-octacosanoic acid, sebacic acid, dodecane diacid, straight chain higher polyvalent fatty acids such as 1,12-dodecanedicarboxylic acid, cyclododecanol, 1,2-cyclohexanediol, 1 Aliphatic alcohols such as 1,4-cyclohexanediol, steroids such as cholesterol, stigmasterol and lanosterol, plant waxes such as carnauba wax and candelilla wax, animal waxes such as beeswax and lanolin, montan wax, etc. Mineral waxes,
There are petroleum-based synthetic waxes such as alcohol type wax and urethane type wax.

The chargeable fine particles are those having electrophoretic properties when a heat-meltable material is charged positively or negatively in a molten state, and specifically, inorganic powders such as TiO ₂ and BaSO ₄ ( Or pigments), organic pigments, etc. are used. Inorganic oxide pigments shown below are suitable materials. White materials include TiO ₂ and Al
Inorganic oxides such as ₂ O ₃ and SiO ₂ , red materials include Cd—Se oxides, and yellow materials include Ti—
As Ba—Ni-based oxides and blue materials, Co—Al
Ti-Zn-Ni-C as oxides and green materials
Examples of the o-based oxides and black materials include Cu-Fe-Mn-based oxides. Further, the inorganic powder such as TiO ₂ can be used after being coated with a different material.

The particle size of the chargeable fine particles used is 0.01 μm.
It is desirable to use those having a thickness of m to 5 μm. If the particle size is
If it is less than 0.01 μm, the viscous resistance in the image forming medium increases and the electrophoretic speed decreases, which may decrease the display speed. Further, when the particle diameter is 5 μm or more, the dispersibility of the chargeable fine particles is deteriorated and the image accuracy is lowered.

The amount of the chargeable fine particles contained in the image forming medium is usually 5 to 50% by weight, but the amount of the chargeable fine particles contained is such that the color can be visually recognized. The content is not particularly limited as long as it is 1 to 90% by weight.

Further, in order to improve the visibility, it is possible to disperse the coloring dye / pigment in the heat-melting material or the charging fine particles. However, the coloring dye / pigment is selected in consideration of charging characteristics, Further, when selecting a dye, it is necessary to consider diffusion of the dye by heat. Suitable materials include dyes having a benzene ring and an —NR ₂ or —NHR group (where R represents an organic group), such as anthraquinone dyes (waxerines) and triphenylmethane dyes (rhodamine). And the like), and mordant azo dyes (such as nigrosine).

When the heat resistance of the portion heated in the heating step according to the present invention is not sufficient, a heat resistant coating film may be provided. As a thermal requirement of this coating film, one having a heat resistance of 120 ° C. or higher at a continuous use temperature, more preferably 150 ° C. or higher is preferable, and it is more flexible to use a polymer sheet because of its flexibility. preferable. Generally, a transparent material is heated, but it is necessary to use a transparent substance for the coating film used at this time. For example, polyester films such as PET film and PBT film, and PES film are used.

If the applied heat is transferred in the lateral direction, a clear image may not be obtained. Therefore, it is desirable to separate the display medium into elements by using a pillar material or the like. As the columnar material, a material having a melting point of 60 ° C. or more and a melt index at 120 ° C. of 50 or less, or a melting point of 150 ° C. or more is preferable. However, it is necessary to avoid a material system that is completely compatible with the heat-fusible material during melting or softening. As a material used as a concrete pillar material, an acrylic polymer, a silicone polymer, a polyethylene polymer (for example, EEA, E
AA, EMAA, PE, EVA, etc.), polyimide-based polymer, polyamide-based polymer, polyolefin-based polymer,
Examples include polyester-based polymers, polystyrene-based polymers, polycarbonate-based polymers, and polyvinyl alcohol-based polymers. As the method for forming the pillar material, the pillar material dispersion solution is mixed with the image forming medium solution to form a coating solution and simultaneously applied to form the image forming medium, and the fine particles are melted and removed from the pillar material film in which the fusible particles are dispersed. how to,
Screen printing and heat transfer printing are available. Furthermore, by providing such a pillar material, the mechanical strength of the display medium can be increased.

When the pillar material is formed, the average diameter of each element of the image forming medium, which is separated by the pillar material, as viewed from a plan view is such that the viscous resistance of the pillar material is not increased.
The thickness is preferably not less than μm, and is preferably not more than 5 mm in order to prevent a change in composition distribution of the image forming medium due to repeated use. Furthermore, when the volume change of the heat-fusible material is 2% or more during melting and solidification (to prevent short circuit between electrodes due to defects in the film of the image forming medium) 1
It is preferable that the thickness is less than or equal to mm.

As described above, when the electrode is coated with a coating film, the sheet resistance is 500 Ω / cm.
² or less is preferable. The strength of the electric field used is 1 ×
Range of 10 ⁵ to 1 × 10 ⁷ V / m (more preferably 5 × 10 ⁵
Up to 5 × 10 ⁶ V / m) is sufficient.

The thickness range of the image forming medium is preferably 1 μm or more from the permissible limit of the contrast ratio of the image and 100 μm or less from the permissible limit of the migration time. If further limited, a short circuit between electrodes due to a defect in the film of the image forming medium. It is more preferable that the thickness is 3 μm or more in order to prevent the above, and 15 μm or less in order to supply heat to the image forming medium at high speed using TPH or the like. The thickness range of the coating film is 0.3 from the viewpoint of wear resistance.
It is preferably not less than 10 μm in order to supply heat to the image forming medium at high speed using TPH or the like.

[0036]

Example First, uncoated TiO ₂ (average particle size 0.3 μm) was used as chargeable fine particles (electrophoretic particles),
Table 1 shows the experimental results of the charge polarity when various waxes were used as the heat-meltable material. Anthraquinone dye (WAXOLINE RED MP-FW) is used for coloring heat-meltable materials.
Was dispersed by 10% by weight.

[0037]

[Table 1] According to the experimental results shown in Table 1, the charge polarity of uncoated TiO ₂ for the hot-melt material was positively charged for the material having —OH and —COOH groups. In the material which does not contribute to electron transfer, such as paraffin (C _n H _{2n + 2)} hardly charged without the addition of surface active material. Among the waxes in Table 1, the materials having good reproducibility of charge and relatively fast response were alcohol type wax, fatty acid glycol ester, carnauba wax and candelilla wax. The trend is uncoated Ti
With respect to O ₂ , a heat-meltable material having a hydroxyl group and a carboxylic acid group has favorable positive charging characteristics. On the contrary, a thermofusible material having an amino group is preferable for the negative charging property.

As the image forming medium material of the display device, there are a huge combination of selections of types and compositions such as heat-melting material, chargeable fine particles, and additives in some cases. Among them, in order to select the material suitable for this element, it is necessary to select the material from the approximate expression of electrophoresis, but in addition to that, the electrophoretic characteristics of the image forming medium at the time of temperature rise are evaluated. , It is necessary to extract a combination with excellent characteristics. Table 2
And 3 show the electrophoretic characteristics of the specific combinations. The measurement conditions in Tables 2 and 3 are: sample temperature 120 ° C, applied voltage ± 100 V, spacer thickness 5
The size is 0 μm and the window size is 2 mm × 5 mm. The composition of the sample is such that the weight ratio of the heat-fusible material is 10, the chargeable fine particles are 5, and the dye is 1. The dye used in Table 2 is Waxoline Red MP-FW (manufactured by Japan ICI), the red and green pigments are Waxoline Blue MP-FW (manufactured by Japan ICI), and the dye used in Table 3 is Waxoline Red MP-FW. (Manufactured by Japan ICI).

[0039]

[Table 2]

[Table 3] FIG. 3A shows a schematic sectional view of the electrophoretic property evaluation cell, and FIG. 3B shows a plan view from above. The numbers in the figure are the same as the numbers shown in FIG. a, b, t are
The long side, the short side, and the thickness of the rectangular parallelepiped cell, respectively. As a result of trial and error, the present inventors have found that a × b is 2 mm × 2 mm, and t is
It was set to 50 μm. Increasing a and b (or decreasing t) causes a problem that lateral electrophoresis causes composition deviation and a problem that the image forming medium material disappears from the edge of the cell due to surface tension during melting. As described above, the surface area of the cell is 4 m when the ratio of t to a × b is, for example, about 50 μm, because a crack occurs due to volume change during recrystallization and an interlayer short circuit occurs.
It has been found that it is desirable to hold it within m ² . The suitable diameter of the cell in which the elements are separated and the suitable thickness range of the image forming medium are based on the evaluation experiment of the electrophoretic characteristics. The cell temperature is fixed at 120 ℃ ± 10 ℃, and the applied voltage is 0V-10.
A square wave of 0V was used. This experiment measures the response frequency and number of repetitions and the contrast ratio of the square wave, the response frequency is 10 Hz or higher, number of repetitions is 10 ⁴ or more, the contrast ratio was selected composition over 1:15. An example of the selected composition is shown by weight ratio.

Alcohol wax NPS9210
59% (Nippon Seiren Co., Ltd.) Titanium dioxide particles TA-100 32% (Fuji Titanium Industry Co., Ltd.) CCA TNS-2 3% (Hodogaya Chemical Co., Ltd.) Dye WAXOLINE RED 6% (Japan I
CI) In order to improve the photostability of the background color, a colored pigment having different migration characteristics (for example, polarity and mobility) (for example, the chargeable fine particles are titanium dioxide particles and phthalocyanine green) is used instead of the dye. The pigment system shows almost no thermal diffusion and the dyeing of transparent surface coatings with heat is negligible. On the other hand, the pigment type tends to have a higher viscosity at the time of melting than the dye type, and therefore, the fast response characteristic does not reach that of the dye type.

FIG. 4A is a vertical sectional view of a display medium showing another example of the present invention, and FIG. 4B is a plan view from above of FIG. 4A. The display medium shown in FIG. 4 is different from the electrophoretic characteristic evaluation cell of FIG. 3 in that the image forming medium 5 is element-separated by the pillar material 6 made of acrylic resin, and the thickness is 10 μm or less. Since 1 uses flexible PET and the transparent coating film 7 is intended for thermal recording by TPH or thermal stamping, ITO is formed as the transparent electrode 9 on the PET film having a thickness of 4.5 μm. That is the case.
Further, when the present invention is made into a card, the extraction electrode 8 is formed outside the display portion. In addition, 14 is a spacer. (The magnetic recording portion and the non-rewritable display portion are omitted from the drawing because they were not formed in the writing life test sample.) A writing life test by TPH was performed on this card-shaped display medium. Writing speed 1 line 1m
s, maximum power is 0.45 mj / dot (image density is 8 dp
m × 15.41 pm) and erasing was performed with a heat roller. The applied voltage was ± 30 V, respectively. The test results of the number of repetitions and the contrast are shown in FIG. As shown in the figure, about 2500 operations were confirmed before the contrast dropped to half of the initial state. The cause of the decrease in contrast is that the PET film became translucent due to heat change and abrasion, and it is considered that the operation can be performed up to 3000 times by selecting a transparent medium that is resistant to heat change and abrasion.

FIGS. 6A to 6G show an example of a method of manufacturing the display medium of the present invention. As shown in FIG. 6 (A), the support 1 is made of a flexible PET film, and the counter electrode 2 is formed on one surface of the support 1 by, for example, vacuum deposition, sputtering, electroless plating, screen printing, gravure printing, or the like. An Al thin film with a thickness of 1 μm or less is formed. For electrode patterning, mask vapor deposition (sputtering, plating), photoetching, or the like is used. Alternatively, a film having a solid electrode may be attached to a support. In addition, the step of forming a conductive paste or resin by gravure printing and heating and curing is good in productivity and practical. The counter electrode 2 and the extraction electrode 8 are formed by patterning. Next, as shown in FIG. 6 (B), a film-shaped spacer 14 is adhered if necessary. Then, as shown in FIG. 6C, a solvent (for example, toluene)
Alcohol wax as a heat-melting material, titanium dioxide particles as the chargeable fine particles 4, an additive, a dispersion solvent A liquid in which a dye is dispersed, and a resin which is not compatible with the alcohol wax in a solvent (for example, methyl ethyl ketone) The pillar material dispersion solution 15 obtained by mixing (for example, polyester resin) and the dispersion solvent B liquid in which the dye is dispersed is shown in FIG.
Apply and dry as shown in (D). As a result of the drying process, the image forming medium area containing alcohol wax, titanium dioxide particles, additives, and dye as main components and the column material area containing resin and dye as main components as shown in FIG. 6E are separated. A state called "Umishima structure" is completed. Although this structure has a large diameter distribution of the image forming medium cells, it has an advantage that the image forming medium 5 and the pillar material 6 can be formed by a single forming process. Further, as shown in FIG. 6 (F), after the image forming medium and the pillar material are formed, the surface of the pillar material resin is dissolved with a solvent, and ITO is formed as the transparent electrode 9 to form the PET film (4.5 μm) as the coating film 7. Thickness) I
The TO side is used as the surface of the pillar material resin and bonded so that air does not enter. After the bonding, the ITO and the image forming medium 5 are heated to a temperature equal to or higher than the melting point of the image forming medium as shown in FIG.
Ensure the electrical connection of. The transparent electrode 9 and the take-out electrode 8 are connected by a flexible conductor or a conductive paste, if necessary. Finally, cut out the card according to the size and finish.

FIGS. 7A to 7D show an example of a method of manufacturing the image forming medium and the pillar material. As shown in FIG. 7 (A),
On the counter electrode 2 formed on the surface of the supporting substrate 1, a polyvinyl alcohol (PVA) 5% aqueous solution, for example, unpolymerized polymethylmethacrylate (PMMA) fine particles 10 (20
The solution 6a in which
It is applied by the gravure coating method. After the pillar material 6 is formed by drying the solution 6a formed on the counter electrode 2 as shown in FIG. 7 (B), it is placed in a solvent (for example, methyl ethyl ketone) as shown in FIG. 7 (C). And ultrasonic waves are applied to elute PMMA10 fine particles. Finally, the image forming medium 5 in a molten state is injected into the space where the PMMA particles 10 of the pillar material film are missing, so that a display medium as shown in FIG. 7D can be obtained.

FIGS. 8A to 8D show another example of the method of manufacturing the image forming medium and the pillar material. As shown in FIG. 8 (A), a solution 6a in which, for example, unpolymerized PMMA fine particles 10 (20 μm diameter) are dispersed in an ultraviolet curable acrylic monomer
Is coated on the counter electrode 2 formed on the support base 1 to a thickness of about 10 μm by, for example, a bar coating method. Next, as shown in FIG. 8 (B), the solution is irradiated with ultraviolet rays to be cured to form a pillar material 6, and then ultrasonic waves are applied in a solvent (for example, methyl ethyl ketone) as shown in FIG. 8 (C). In addition, the PMMA fine particles 10 are eluted. As shown in FIG. 8D, a display medium can be obtained by injecting the image forming medium 5 in a molten state into the space where the PMMA particles of the pillar material 6 are finally missing.

The titanium dioxide particles as the chargeable fine particles in this embodiment are white, but the present invention allows any combination of colors regardless of the white pigment. Therefore, a pattern is formed in an arbitrary multicolor image by selecting a combination of colored dyes. That is, for example, by allocating pigments of each color to a plurality of heat-melting materials having different melting points in each space partitioned by a pillar material and repeating the process of writing from the color to which the high-melting-point heat melting material is distributed, It is also possible to form a multicolor image.

FIGS. 9A to 9E show an example of a manufacturing process of an image forming medium and a pillar material suitable for multicoloring of the image forming medium (screen printing application). This method is shown in FIG.
As shown in (A), a dam 6a, which is a pillar material, is transferred to the base material 1 by screen printing with a thermosetting epoxy resin by about 10 μm. Next, as shown in FIG. 9B, the dam is cured by heating to form the pillar-shaped material 6 for element isolation. After that, as shown in FIG. 9C, one of the background colors of the image forming medium 5 is formed at a predetermined position by screen printing or the like, and as shown in FIG. 9D, the image forming medium 5 is subjected to heat treatment. To dry. After the steps shown in FIGS. 9C and 9D are repeated for the required number of colors, the image forming material 5 is further heat-melted so that the image forming medium and the pillar material as shown in FIG. It is formed.

The thermal transfer recording method can be used as part of the manufacturing process of the image forming medium and the pillar material (transferring process of the image forming medium) shown in FIGS. 9 (A) to 9 (E). This method is characterized in that an image forming medium having chargeable fine particles of each color is transferred and moved by a thermal transfer recording system. The merit of this method is that the manufacturing yield is increased especially in the case of forming a film thickness of 5 μm or less, and that the process does not require an organic solvent. Further, there is an advantage in forming a high-definition image because of easy alignment. The extraction electrode realizes electrical connection with a conductive roller or the like. As a method of applying an electric field, in addition to a method of realizing electrical connection by contact, for example, a method of supplying ions by a corona charger to an electrode in a non-contact manner.

FIG. 10 is a schematic cross section showing another example of the display medium of the present invention. This structure is a structure to which an overwrite characteristic, which was impossible in the embodiment of FIG. 1, is added. In order to enable overwriting, the constitution of the present invention is an image forming medium in which the film is laminated on the transparent coating film 7 with the transparent electrode 9 inside and the pillar material 6 separates the elements and contains the chargeable fine particles 4. 5, the display unit has a structure in which the pyroelectric film 11 and the counter electrode 2 are laminated on the supporting substrate 1. Here, the pyroelectric film 11 is formed by controlling the crystal state so as to generate an electric field in a direction opposite to the applied electric field by increasing the temperature.

FIG. 11 shows another example of the drive timing chart of the present invention, and the operation principle of the overwrite image display will be described. First, prior to the image signal, a voltage is applied to the transparent electrode 9 and the counter electrode 2 to apply a uniform electric field to the image forming medium 5. The image signal is then applied in the form of heat, for example by TPH. The heat applied from TPH causes the image forming medium 5 to undergo a phase change to a flowable state, whereby the chargeable fine particles 4 are moved in the heat-meltable material 3 by Coulomb force.
The pyroelectric film 11 generates an electric field in the opposite direction to the applied electric field due to temperature rise, but under the erasing (recording) condition, the strength of the applied electric field is superior, and the chargeable fine particles 4 are the heat-melting material 3 of the melting material. Reaches the transparent electrode 9 before it solidifies and adheres to it, resulting in the color of the charging fine particles 4. On the other hand, under the recording (erasing) condition, a heat amount sufficiently larger than that under the erasing (recording) condition is applied from TPH. The sufficiently heated pyroelectric film 11 generates a pyroelectric electric field exceeding the applied electric field strength, and the chargeable fine particles 4 are separated from the transparent electrode 9 before the molten heat-meltable material 3 is solidified, The result is a background color. What is particularly important here is that the signal pulse applied to the TPH is within 1 ms, while the molten state of the thermofusible material is maintained for several tens of ms, and the pyroelectric field has a slower falling characteristic of several hundred ms. ms is to be kept. Due to this effect, an image can be displayed at a high-speed image signal input that cannot be followed by the original electrophoretic element, and an overwrite image display operation, which was impossible in the basic embodiment of FIG. 1, is made possible.

However, since overwrite recording separates recording and erasing only by the threshold value of thermal energy, the stability margin with respect to environmental temperature is smaller than that of 2-pass recording, and overwrite recording and 2-pass recording have advantages and disadvantages. is there. In addition, the embodiment has been mainly described in which the image forming medium is sandwiched between two conductive media as the display medium. However, as the basic configuration of the present invention,
There is no need to form a conductive medium inside the display medium. Therefore, there is an application in which a conductive medium (as a recording / erasing process system) is provided outside the display medium. As described above, the present invention has various material and composition selection ranges other than the examples described in the examples, and has a wide range of applications.

As a specific application example of the present invention, for example, as a rewritable recording medium, a prepaid card in the transportation field, a commuter pass, a number of tickets, a prepaid card in the traffic field and the distribution field, an admission ticket, a price display card, etc. Cards and PP that can be used many times in the OA field
Examples include recording papers such as C paper and thermal paper that can be used many times.

[0052]

As described above, when the display medium and the display method according to the present invention according to claims 1 to 6 are used, the number of times of repeated use is increased, and the image is retained even if energy is not supplied. Is possible.

[Brief description of drawings]

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

FIG. 2 is an example of a drive timing chart according to the present invention.

FIG. 3A is a schematic cross-sectional view of an electrophoretic property evaluation cell according to the present invention. FIG. 3B is a schematic plan view of the electrophoretic property evaluation cell according to the present invention.

FIG. 4A is a vertical cross-sectional view of a display medium showing another example of the present invention. FIG. 4B is a plan view of a display medium showing another example of the present invention.

FIG. 5 is a diagram showing test results of the number of repetitions and contrast of the display medium of the present invention.

FIG. 6 (A) is a process chart showing the method of manufacturing the display medium of the present invention. (B) is a step following (A).
(C) is a process following (B). (D) is a step following (C). (E) is a step following (D).
(F) is a step following (E). (G) is a step following (F).

FIG. 7 (A) is a process chart showing a method for manufacturing an image forming medium and a pillar material according to the present invention. (B) is a step following (A). (C) is a process following (B).
(D) is a step following (C).

FIG. 8 (A) is a process drawing showing another method for producing an image forming medium and a pillar material according to the present invention. (B) is a step following (A). (C) is a process following (B). (D) is a step following (C).

FIG. 9A is a process chart showing a method for manufacturing an image forming medium and a pillar material suitable for multicoloring the image forming medium.
(B) is a step following (A). (C) is a process following (B). (D) is a step following (C).
(E) is a step following (D).

FIG. 10 is a schematic cross-sectional view showing another example of the display medium of the present invention.

FIG. 11 is another example of a drive timing chart according to the present invention.

FIG. 12 is a schematic cross-sectional view of an electrophoretic element.

[Explanation of symbols]

1 ... Support substrate, 2 counter electrode, 3 heat melting material, 4 charged particles, 5 image forming medium,
6 ... Pillar material, 7 ... Transparent surface coating film, 8 ... Extraction electrode, 9 ... Transparent electrode, 10 ... PMMA fine particles, 11 ... Pyroelectric film, 12 ... ... Transparent substrate, 13
……… Suspension 14 ……… Spacer.

Claims (6)

[Claims] 1. A container comprising at least one surface made of a transparent material, and an image-forming medium made of a heat-meltable material and chargeable fine particles dispersed in the heat-meltable material. Characteristic display medium. 2. The display medium according to claim 1, wherein the container comprises a counter electrode and a transparent electrode as the transparent material. 3. The display medium according to claim 1, wherein the container is element-separated by a pillar material. 4. A step of heating a display medium having an image forming medium composed of chargeable fine particles and a heat-fusible material and controlling the electrophoresis of the chargeable fine particles by applying an electric field, and the heating is completed. And a step of solidifying the image forming medium afterwards. 5. The image forming medium according to claim 4, wherein the image forming medium is heated at a desired position, and the electrophoresis of only the chargeable fine particles in the heat melting material melted by the heating is controlled. Display method of display medium. 6. A container comprising at least one surface made of a transparent material, an image-forming medium made of a heat-meltable material disposed in the container, and chargeable fine particles dispersed in the heat-meltable material. A display medium characterized by solidifying after forming an image on the image forming medium by applying heat and an electric field for forming an image to the container.