JP4903541B2 - Display medium and display element - Google Patents

Description

  The present invention relates to an image display medium capable of reversibly changing a display state using particles that are electrophoresed by the action of an electric field.

  In an image display device using the principle of electrophoresis, two substrates, at least one of which is transparent, are arranged to face each other with a predetermined gap through a spacer, and a sealed space is formed between the substrates. Is done. In this sealed space, a display liquid in which electrophoretic particles are dispersed in a dispersion medium having a color tone different from that of the particles is filled to form a display panel. By applying an electric field to the display panel and moving the electrophoretic particles in the direction of the electric field, display is performed by changing the color of the panel surface, and the transparent substrate side becomes the display surface. There has also been proposed a microcapsule type electrophoretic display device in which a display liquid is microcapsulated and a plurality of microcapsules filled with the display liquid are sandwiched between two substrates without using a spacer.

In a display device using these electrophoretic principles, long-term display retention characteristics, that is, once a voltage is applied to display an image, the application of the voltage is stopped, and the displayed image is However, if a liquid dispersion medium is used at room temperature, the image may be lost due to the influence of external force or static electricity, and sufficient image retention characteristics may be obtained. There wasn't. As a method for improving image retention characteristics, according to the method disclosed in Patent Document 1, as a dispersion medium in which particles of two colors having different charge polarities are dispersed, it exhibits solidity at room temperature and softens when heated. The material that becomes liquid is used. For example, there are wax, resin, rubber, wax and the like. When these materials are used, when the dispersed particles are subjected to electrophoresis, the display state can be changed by heating and melting the dispersion medium, and the display content is retained by cooling and returning the dispersion medium to a solid state. be able to.
When using a dispersion medium for improving the image retention characteristics, that is, a dispersion medium that shows solidity at room temperature and becomes liquid when heated, the image retention is significantly higher than when a dispersion medium that is liquid at room temperature is used. To improve.

It is important that the material used for the dispersion medium has a low melting temperature, a sharp melt, and a property that is difficult to thermally expand.
However, conventional waxes and the like have not been sufficiently provided with such properties.
For example, natural waxes (carnauba, rice, etc.) have a low melting temperature and are sharp melts. However, thermal expansion tends to occur during heating to melt the wax. For this reason, irregularities occur on the surface of the media such as the display panel after cooling, and this has to be smoothed with a roller or the like.
On the other hand, synthetic waxes (paraffin, polypropylene, etc.) hardly undergo thermal expansion but have a low melting temperature and no sharp melt. For this reason, there is a problem that the image is easily sticky at room temperature and the image is easily disturbed (image retention is poor).

Japanese Patent Publication No. 50-15115

  The present invention has been made in view of the problems as described above, and the object of the present invention is to perform at least electrophoresis performed by a dispersion medium that changes to a solid state at room temperature and a liquid state when heated, and an electric field. An object of the present invention is to provide a display medium and a display element, each of which includes one type of electrophoretic particles in a dispersion medium, which has high image retention and has no irregularities on the surface.

  The present invention has solved the above problems by the following technical configuration.

(1) A display medium that includes a dispersion medium that is in a solid state at normal temperature and changes to a liquid state when heated, and in which the dispersion medium includes at least one type of electrophoretic particles that are electrophoresed by an electric field. Special solid ester (special solid ester is transparent melting point (° C) 60 or less, penetration 7 or less (measuring condition: JIS K 2207, load 150g, temperature 23 ° C, humidity 50%), 70 ° C A display medium comprising a melt viscosity (mPa · s) of 4 or less and an ester whose probe displacement rate (%) has a maximum point of 1.0 or less as an expansion characteristic .
(2) The display medium as described in (1) above, which contains at least one of quaternary ammonium salt ethyl sulfate, fatty acid ester, and sulfosuccinic acid surfactant.
(3) is disposed opposite to, the first and second electrodes at least one of which is transparent electroconductive, the filled between the first and second electrodes (1) to (2) A display element comprising: the display medium according to any one of the above; a heating unit that heats the display medium; and an electric field applying unit that applies an electric field to the first and second electrodes and the display medium.
(4) Any one of (1) to (2) filled between the first and second substrates disposed opposite to each other and at least one of which is transparent, and the first and second substrates. A display element comprising: the display medium according to 1), a heating unit for heating the display medium, an electric field applying unit for applying an electric field to the display medium, and an electrode.

  According to the present invention, there is provided a display medium including a dispersion medium that changes to a solid state at normal temperature and a liquid state upon heating, and at least one type of electrophoretic particles that undergo electrophoresis by an electric field. It is possible to provide a display medium and a display element that are high in size and have no irregularities on the surface.

The electrophoretic particles in the present invention exhibit electrophoretic properties by being charged positively or negatively when a special solid ester of a heat-fusible substance that is a dispersion material is in a molten state, specifically, Inorganic powders (or pigments) such as TiO ₂ and BaSO ₄ , organic pigments, and the like can be used. The color of the electrophoretic particles is not particularly limited, and each color can be used. As a suitable material constituting the electrophoretic particles, the following inorganic oxide pigments can be mentioned. As white materials, inorganic oxides such as TiO ₂ , ZnO ₂ , Al ₂ O ₃ , SiO ₂ , Cd—Se oxides as red materials, and Ti—Ba—Ni oxides as yellow materials As materials, blue materials, Co—Al-based oxides, phthalocyanine blue, etc., as green materials, Ti—Zn—Ni—Co-based oxides, phthalocyanine green, etc., as black materials, Cu— Examples thereof include Fe-Mn oxides and carbon black. The particle diameter of the electrophoretic particles is preferably within a range of 0.01 to 5 μm, and if the size is within this range, good electrophoretic characteristics can be obtained. The amount of the electrophoretic fine particles dispersed in the special solid ester which is a hot-melt material can be appropriately set so as to obtain good electrophoretic properties and visibility, preferably in the range of 1 to 90% by weight. Is suitably in the range of 5 to 50% by weight.

The special solid ester of the present invention has a transparent melting point (° C.) of 60 or less and a penetration of 7 or less (measurement conditions: conforming to JIS K 2207, load 150 g, temperature 23 ° C., humidity 50%, the same applies hereinafter), 70 ° C. An ester having a melt viscosity (mPa · s) of 4 or less and a maximum point of probe displacement rate (%) of 1.0 or less as an expansion characteristic. The measurement conditions for the probe displacement rate (%) are measuring device TMA100 (Seiko Instruments Inc.), temperature rising condition 2.0 ° C./min, sample thickness 2.5 mm, probe load 100 g, probe diameter 1.0 mm, The nitrogen flow rate is 80 ml / min (the same applies hereinafter).
Therefore, it has a transparent melting point (° C.) of 60 or less and a low melting point.
In addition, the penetration is as low as 7 or less near room temperature and sufficient hardness, and the melt viscosity at 70 ° C. is extremely low as 4 or less, which is a sharp melt.
Furthermore, the maximum point of the probe displacement rate (%) is 1.0 or less, and there is almost no thermal expansion. The maximum point of the probe displacement rate (%) is more preferably 0.5 or less, and most preferably 0.1 or less.
The melting point of the special solid ester is preferably 50 ° C. or less. When the melting point exceeds 60 ° C., it is necessary to increase the heating temperature, and energy consumption increases.

It is preferable that a surfactant is allowed to coexist in the dispersion medium constituting the display medium of the present invention. The reason is that the display speed can be increased by adjusting the type and amount of the surfactant.
The surfactant of the present invention may be ionic or nonionic. Examples of nonionic surfactants include fatty acid esters such as sorbitan fatty acid esters and polyoxyethylene sorbitan fatty acid esters, polyoxyethylene alkyl ethers, fluoroalkylethylene oxide adducts, and polyethylene glycols. Examples of the ionic surfactant include a compound obtained by combining a carboxylic acid or a salt thereof, a sulfonic acid or a salt thereof, sulfuric acid or a salt thereof, an amine or a salt thereof, and the like. Among these, quaternary ammonium salt ethyl sulfate, fatty acid ester, and sulfosuccinic acid are preferably used alone or in combination. The surfactant is blended in an amount of 0.1 to 2 parts by weight with respect to 100 parts by weight of the special solid ester.

FIG. 1 shows an embodiment of a display element 1 using the display medium of the present invention. The display medium 2 is sandwiched between a substrate 4 provided with an electrode 3 and a substrate 6 provided with an electrode 5 and further fills a sealed space surrounded by spacers 7. Of these two sets of substrate-electrode combinations, at least one set, that is, the substrate 4-electrode 3 needs to be transparent, and a transparent electrode needs to be formed on the transparent substrate. A heating means 8 such as a surface heater for heating the display medium 2 is provided outside the substrate 6. The display medium 2 is heated by the heating means 8 and the special solid ester becomes liquid. At this time, when a voltage is applied between the electrodes 3 and 5 by the electric field applying means 9 including a power source and a switch, an image is displayed by the physical movement of the electrophoretic particles in the display medium 2. When the heating unit 8 is turned off and the display medium 2 returns to normal temperature, the special solid ester becomes solid. At this time, since the special solid ester becomes a solid and immobilizes the electrophoretic particles, the display is maintained even when the application of the voltage to the display element is released.
If the electrodes 3 and 5 have sufficient strength and the electrode 5 has heat resistance, the substrates 4 and 6 can be omitted.
Still further, it is sufficient that at least one of the electrode and the heating means can selectively act on an arbitrary place.
That is, it may be selectively heated and melted by a heating means while a voltage is applied to the entire surface by an electrode, or a voltage may be selectively applied while the entire surface is heated and dissolved. Of course, it may be selectively heated and melted while a voltage is selectively applied. As a result, free display is possible.
Moreover, it is preferable to include the case of the entire surface with an arbitrary portion.
For example, at the time of writing, it is selectively heated and dissolved while a voltage is applied to the entire surface. At the time of erasing, the entire surface can be heated while a voltage having a polarity opposite to that at the time of writing is applied, so that the initial state before writing can be restored.

FIG. 2 shows another embodiment of the display element 1a using the display medium of the present invention. The display medium 2 is sandwiched between the substrate 4 and the substrate 6 and further fills a sealed space surrounded by the spacers 7. At least the substrate 4 needs to be transparent. Heating means 8 a such as a heating head for heating the display medium 2 is provided on the outside of the substrate 6. The display medium 2 is heated by the heating means 8a, and the special solid ester becomes liquid. At this time, when a voltage is applied by the electric field applying means 9 and the electrodes 5a and 5b, the electrophoretic particles in the display medium 2 are physically moved to display an image. Further, when the heating means 8a is turned off and the display medium 2 returns to normal temperature, the special solid ester becomes solid. At this time, since the special solid ester becomes a solid and immobilizes the electrophoretic particles, the display is maintained even when the application of the voltage to the display element is released.
As in the case of FIG. 1, it is sufficient that at least one of the electrode and the heating means can selectively act on an arbitrary place.
Moreover, it is preferable to include the case of the entire surface with an arbitrary portion.
Still further, the electrodes 5a and 5b, the heating means 8a, and the electric field applying means 9 are integrally configured as a rewritable printer, the display medium 2, the substrates 4 and 6, and the spacer 7 are configured as rewritable paper, and the rewritable paper in the rewritable printer. It is also possible to form an image by passing.

  Although the heating temperature of the display medium depends on the melting point of the special solid ester, it is preferable that melting and solidification of the display medium can be switched in a heating temperature range of 50 to 90 ° C. When a heating temperature higher than this range is required, energy consumption due to heating increases, which is not preferable. On the other hand, when operating at a heating temperature lower than the above range, for example, it melts with a small amount of heat energy flowing in from other devices used together, which is not preferable because it causes erroneous display. The applied voltage is preferably 3 to 200V. When the voltage is lower than this, the movement of particles becomes slow or does not move. When the applied voltage is high, the power supply unit becomes large and it is difficult to use it for space-saving purposes. The spacer thickness is preferably 10 to 500 μm.

  As the substrates 4 and 6, various resins other than glass can be used. Specifically, a homopolymer such as ethylene, polypropylene, butene or a polyolefin (PO) resin such as a copolymer or a copolymer, an amorphous polyolefin resin (APO) such as a cyclic polyolefin, polyethylene terephthalate (PET), Polyester resins such as polyethylene 2,6-naphthalate (PEN), polyamide (PA) resins such as nylon 6, nylon 12, copolymer nylon, polyvinyl alcohol (PVA) resin, ethylene-vinyl alcohol copolymer (EVOH) Polyvinyl alcohol resins such as polyimide (PI) resin, polyetherimide (PEI) resin, polysulfone (PS) resin, polyethersulfone (PES) resin, polyetheretherketone (PEEK) resin, polycarbonate (PC) resin , Polyvini Butyrate (PVB) resin, polyarylate (PAR) resin, can be used a fluorine-based resin or the like. The thickness of the substrate is about 25 μm to several mm. The transparent substrate 4 is preferably polyethylene terephthalate (PET) or polycarbonate (PC) resin.

  As the first transparent electrode 3 and the second electrode 5, a conductive metal oxide such as tin oxide, zinc oxide, indium oxide, indium tin oxide (ITO), indium zinc oxide (IZO), or the like can be used. . A method for producing the transparent anode may be appropriately selected from the vacuum deposition method, the sputtering method, the ion plating method, the CVD method, the plasma CVD method, and the like in consideration of suitability for the material. The patterning of the transparent anode can be performed by a chemical etching method using photolithography, a physical etching method using a laser, a vacuum evaporation method using a mask, a sputtering method, a lift-off method, a printing method, or the like. Metals such as gold, silver, and aluminum can also be used as the material of the second electrode 5 that does not have transparency.

Example 1
(Sample preparation)
Special solid ester A (trade name: Nissan Electol WE-40, transparent melting point (° C) 36.8, penetration 3, melt viscosity at 70 ° C (mPa · s) 3 or less, probe displacement rate (%) (Maximum point of 0.05, manufactured by NOF Corporation)
100 wt%
・ Black dye (trade name: OILBLACK HBB, manufactured by Orient Chemical Co.) 1wt%
・ Titanium oxide (trade name: JR-603, manufactured by Teica) 5 wt%
・ Surfactant (quaternary ammonium salt ethyl sulfate, trade name: SAT-60, manufactured by Nippon Pure Chemical Co., Ltd.)
0.5wt%
The raw materials of the above-mentioned prescription were weighed and put into a 500 cm ³ polyethylene bottle, and the zirconia beads having a diameter of 1 mm were put in the same amount as the total amount of the raw materials weighed. The polyethylene bottle containing this sample was left in a high temperature bath set at 120 ° C. for 30 minutes. After 30 minutes, it was taken out, quickly set on a stirrer (Red Devil), and stirred for 15 minutes. After stirring, it was again left in a constant temperature bath at 120 ° C. for 30 minutes, taken out, and stirred with a stirrer for 15 minutes. After stirring, the mixture was again left at 120 ° C. and stirred for 15 minutes. This completes the dispersion. The sample that had been stirred for 15 minutes × 3 times was again left in a 120 ° C. environment for 30 minutes, removed, and filtered using a mesh having an opening of 500 μm or less to separate the sample and beads.
The display element of Example 1 was produced by injecting the sample prepared above between ITO glasses with a 200 μm film (spacer) interposed therebetween.

(Test method)
<Image retention>
The display element was subjected to finger pressure from above the ITO glass at room temperature (25 ° C.), the image was visually confirmed, and the results are shown in Table 1. In Table 1, “◯” is given if there is no disturbance in the image, and “X” is given if the image is disturbed.
<Surface unevenness>
The display element was left in a constant temperature bath at 60 ° C. for 15 minutes or longer to dissolve the wax. A voltage of 100 V was applied to the upper and lower ITO at 60 ° C. to move the titanium oxide. Next, +-was reversed and the titanium oxide was moved to the opposite side.
This operation was repeated 10 times, the ITO surface was visually confirmed, and the results are shown in Table 1. In Table 1, if there was no unevenness, it was rated as ◯, and if there was unevenness, it was marked as x.

  As is clear from Table 1, the image retention of the display element of Example 1 was good, and surface irregularities did not occur.

Example 2
Special solid ester B instead of special solid ester A (trade name: Nissan Electol WE-60, transparent melting point (° C) 41.5, penetration 3 and melt viscosity at 70 ° C (mPa · s) 3, probe A sample was prepared and evaluated in the same manner as in Example 1 except that the maximum point of displacement rate (%) 0.05, manufactured by NOF Corporation was used. The results are shown in Table 1.

  As is clear from Table 1, the image retention of the display element of Example 2 was good, and surface irregularities did not occur.

Comparative Example 1
A sample was prepared in the same manner as in Example 1 except that rice wax (trade name: HC-35, maximum point of probe displacement (%) 2.35, manufactured by NS Chemical Co., Ltd.) was used in place of the special solid ester A. evaluated. The results are shown in Table 1.

  As is clear from Table 1, the image retention of the display element of Comparative Example 1 was good, but surface irregularities occurred.

Comparative Example 2
Example 1 except that paraffin wax (trade name: EMW-0003, penetration depth of 10 or more, maximum point of probe displacement (%) 0.20, manufactured by Nippon Seiki Co., Ltd.) was used in place of the special solid ester A A sample was prepared and evaluated in the same manner as above. The results are shown in Table 1.

  As is clear from Table 1, the image retention of the display element of Comparative Example 2 was x, and the image was disturbed when pressed softly at room temperature. However, the unevenness on the surface was ○, and the unevenness due to rewriting did not occur.

(Evaluation results)
As shown in Table 1, the display elements of Example 1 and Example 2 were excellent in image retention, and surface irregularities were not generated.
On the other hand, the display element of Comparative Example 1 has a problem in practical use in the unevenness of the surface although it has excellent image retention.
Further, the display element of Comparative Example 2 had a practical problem in image retention although the surface unevenness did not occur.

It is a schematic cross section of the display element of the present invention. It is a schematic cross section of the display element of the present invention.

Explanation of symbols

1, 1a Display element 2 Display medium 3 Electrode (transparent electrode)
4 Substrate (transparent substrate)
5, 5a, 5b Electrode 6 Substrate 7 Spacer 8, 8a Heating means 9 Electric field applying means

Claims (4)

A display medium comprising a dispersion medium that is in a solid state at room temperature and changes to a liquid state when heated, and in which the dispersion medium includes at least one type of electrophoretic particles that are electrophoresed by an electric field. Ester (special solid ester has a transparent melting point (° C) of 60 or less, a penetration of 7 or less (measurement conditions: conforming to JIS K 2207, load 150 g, temperature 23 ° C, humidity 50%), melt viscosity at 70 ° C ( mPa · s) 4 or less, and an expansion characteristic, which is an ester having a probe displacement rate (%) maximum point of 1.0 or less) . The display medium according to claim 1 , comprising at least one of a quaternary ammonium salt, ethyl sulfate, a fatty acid ester, and a sulfosuccinic acid surfactant. The display according to any one of claims 1 to 2 , wherein the display is filled between the first and second electrodes arranged opposite to each other and at least one of which is transparent conductive, and the first and second electrodes. A display element comprising: a medium; heating means for heating the display medium; and electric field applying means for applying an electric field to the first and second electrodes and the display medium. The display medium according to claim 1 , wherein the display medium is filled between the first and second substrates disposed opposite to each other and at least one of which is transparent. A display element comprising heating means for heating the display medium, electric field applying means for applying an electric field to the display medium, and electrodes.

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