Apparatus and process for producing electrophoretic device

A system (apparatus and process) for producing an electrophoretic (display) device is provided for allowing production of such a device wherein electrophoretic particles in the dispersion liquid are easily and evenly distributed to respective cells (pixels) between two substrates of the device even in the case of a very small gap between the two substrates or the case of using a flexible substrate. The system includes a storage unit for a dispersion liquid containing the charged phoretic particles dispersed therein, a stirrer for stirring the dispersion liquid, a substrate-holder for holding the substrate in the dispersion liquid, and a voltage source for applying a voltage to the electrodes formed on the substrate thereby depositing the electrophoretic particles on the electrodes.

FIELD OF THE INVENTION AND RELATED ART

The present invention relates to an apparatus for producing an electrophoretic (display) device wherein electrophoretic particles are moved between electrodes to effect a display, and also a process for producing such an electrophoretic (display) device including a step of filling an electrophoretic device with an electrophoretic dispersion liquid containing charged (electro-)phoretic particles. More specifically, the present invention relates to a process for producing an electrophoretic device including a step of filling with charged phoretic particles a very small gap or spacing between a pair of substrates, of which at least one is provided with an electrode, of the electrophoretic device.

In recent years, accompanying the progress of data processing apparatus, there has been an increasing demand for a display device requiring a small power consumption and a small thickness, and extensive study and development have been made on devices satisfying such a demand. Among these, a liquid crystal display device wherein an alignment of liquid crystal molecules is electrically controlled to change optical characteristics has been extensively developed and commercialized as a display device satisfying the demand described above.

However, such liquid crystal display devices are still accompanied with problems of visual load on human eyes, such as difficulty of recognizing characters on display depending on a viewing angle or due to reflection light, and flickering and low luminance of light sources. Accordingly, extensive study is still made for new-types of display devices causing less visual load on human eyes.

Reflection-type display devices are expected from the viewpoints of lower power consumption and less visual load on human eyes. As a type thereof, an electrophoretic display device has been proposed by Harold D. Lees, et al. (U.S. Pat. No. 3,612,758). Electrophoretic display devices are also disclosed in, e.g., Japanese Laid-Open Patent Application (JP-A) 9-185087.

A structure and an operation of an electrophoretic display device are described with reference toFIGS. 1A and 1B. Referring to these figures, a display device125includes a dispersion layer comprising an insulating liquid124containing a colorant dissolved therein and charged electrophoretic or electrophoretically migrating particles123dispersed in the insulating liquid124, and a pair of oppositely disposed electrodes121and122sandwiching the dispersion layer. When a voltage is applied across the dispersion layer via the electrodes121and122, the colored electrophoretic particles123are attracted to an electrode of a polarity opposite to that of the charge of the particles123. A display is performed by a combination of the color of the electrophoretic particles123and the color of the insulating liquid124having a different color from the electrophoretic particles123due to the colorant dissolved therein.

More specifically, when the first electrode121is made a negative electrode and the second electrode122is made a positive electrode, positively charged colored electrophoretic particles123are moved or migrated and attached to the surface of the first electrode121disposed closer to a viewer, thereby displaying the color of the particles123(FIG.1B).

On the other hand, when the first electrode121is made a positive electrode and the second electrode122is made a negative electrode, the positively charged electrophoretic particles123are moved and attached to the surface of the second electrode farther from the viewer to display the color of colorant contained in the insulating layer124(FIG.1A).

Recently, a new type of electrophoretic display device has been reported (JP-A 11-202804). In this electrophoretic display device, unlike a conventional one, charged phoretic particles are moved horizontally relative to the substrates to effect a display, and a pair of electrodes for driving the charged phoretic particles are formed in lamination on one substrate, so as to display a bright state or a dark state depending on a degree of spreading of phoretic particles corresponding to different areas of electrodes as viewed from a display surface. This system utilizes a degree of spreading of charged phoretic particles for display, so that a transparent dispersion liquid medium can be used. As a result, it becomes possible to relatively easily realize a color display by utilizing a color filter layer, etc. Further, the pair of electrodes are formed on one substrate, the positional alignment of the two electrodes and wiring thereto become easier.

The display quality of an electrophoretic display device substantially depends on the density of charged phoretic particles dispersed in the dispersion liquid, it is necessary to dispose the charged phoretic particles in dispersion uniformly over the entire display surface. As methods for dispersing charged phoretic particles in a conventional type electrophoretic display device, two methods as follows are known.

In a first one, a structure of two substrates being applied to each other with a certain gap therebetween is evacuated to a vacuum and is dipped in a dispersion liquid containing charged phoretic particles, followed by restoration to a normal pressure to inject the dispersion liquid into the gap (JP-A 11-38898).

In a second method, one substrate provided with one electrode is placed on a liquid container provided with a counter electrode, a suspension liquid containing charged phoretic particles dispersed therein is injected thereto, and the charged phoretic particles are attached onto the one electrode on the one substrate under application of an electric field. An apparatus therefor is illustrated inFIG. 2(JP-A (Tokuhyo) 8-502599).

The method of JP-A 11-38898 may be satisfactory in the case of a large gap between the substrates, but at a smaller gap, the flow of charged phoretic particles is retarded compared with that of the dispersion liquid medium, so that the density of charged phoretic particles is liable to be higher at the injection port, and a uniform dispersion becomes difficult.

On the other hand, the method of JP-A 8-502599 uses an apparatus231as illustrated inFIG. 2to allow attachment of charged phoretic particles contained in a dispersion, liquid234over an entire area of a substrate232. In this method, the attached amount of charged phoretic particles substantially depends on a gap size between the electrode on the substrate232and an electrode233on the apparatus231, the concentration distribution of charged phoretic particles becomes nonuniform if a flexible substrate232is used. Further, in this method, it is necessary to provide the apparatus with an electrode233having an area identical to that of the substrate232, thus leaving problems regarding mass productivity and production cost.

An organization and an operation principle of another electrophoretic display device are described with reference toFIGS. 3A and 3Billustrating a cell structure thereof. The device includes a pair of electrodes302and304disposed opposite to each other so as to sandwich an electrophoretic dispersion liquid308colored with a colorant and containing charged phoretic particles309dispersed therein. At least one of the electrodes302and304is made transparent. The device also includes spacers302for keeping constant the gap between a pair of substrates301and303and dividing the gap into small sections (cells, only one being shown).

For driving, a voltage is applied across the dispersion liquid308between the electrodes302and304from a voltage application circuit340, thereby attracting the charged phoretic particles309toward an electrode of a polarity opposite to that of the particles309per se. More specifically, as shown inFIGS. 3A and 3B, the display is performed based on a difference between the color of the charged phoretic particles309and the color of the dispersion liquid308containing a colorant having a color different from the charged phoretic particles309and dissolved therein. In the state shown inFIG. 3A, the color of the dispersion liquid308is seen to the viewer, and in the state ofFIG. 3B, the color of the charged phoretic particles309is seen to the viewer.

The electrophoretic display device is prepared by first providing a first electrode-forming substrate305comprising a first substrate301and a first electrode302thereon, forming spacers307thereon, filling the dispersion liquid308containing the colorant dispersed therein, and applying thereonto a second electrode-forming substrate306comprising a second substrate302and a second electrode304formed thereon to seal the dispersion system.

FIG. 4illustrates a method of filling a known electrophoretic display device, wherein prior to assembling a first electrode-forming substrate435and a second electrode-forming substrate (not shown) onto an electrophoretic display device, a first electrode-forming substrate435(or a second electrode forming substrate) is coated with charged phoretic particles and then the coated substrate305is assembled into a display device, and an electrophoretic dispersion liquid is filled into the device (JP-A 8-502599).

According to an embodiment, the application of the charged phoretic particles436onto the first electrode-forming substrate is performed in the following manner. On an affixing substrate433provided with an electrode434and a polyethylene terephthalate (PET)438, a first electrode-forming substrate435is affixed so as to leave an opening430, and a dispersion liquid437containing the charged phoretic particles436is injected through the opening430. Simultaneously therewith, a voltage is applied between the electrode434on the affixing substrate433and the first electrode432of the first electrode-forming substrate435from a voltage supply440to move the charged phoretic particles436toward the first electrode-forming substrate435, thereby coating the first electrode-forming substrate435with the charged phoretic particles436. After the sufficient coating, the voltage is removed. Then, the coated first electrode-forming substrate435is assembled with a second electrode-forming substrate and then a dispersion liquid437is filled in the assembled device.

The above-mentioned method of filling the charged phoretic particles436and the dispersion liquid437is effective in the case where a very small gap is retained between a pair of substrates, and for the coating of one substrate with the charged phoretic particles436, a precise control of the concentration thereof within the dispersion liquid437is not required.

However, in the step of coating the first (or second) electrode-forming electrode with the charged phoretic particles436, the charged phoretic particles436are simply attracted to the first (or second) electrode-forming substrate by electrophoresis under application of a DC voltage, so that the charged phoretic particles436of the same polarity are gathered to proximity of the electrodes, and the charge distribution of the charged phoretic particles is not controlled.

In the case where the charge distribution of the charged phoretic particles436is not controlled, the charged phoretic particles436coating the first (or second) electrode forming substrate are in the form of a mixture of particles having large a charge and particles having a small charge. For driving such particles having a small charge, a high drive voltage is required because at a low voltage application, only a low display contrast can be attained. Thus, for allowing a lower voltage drive, a method of selectively using charged phoretic particles436having a high charge is required, and for attaining a high contrast, a method of selecting particles having a uniform change is required.

Further, the amount of the attached charged phoretic particles remarkably depends on a gap width between the electrode432formed on the first electrode-forming substrate435and the electrode434formed on the affixing substrate433, the concentration distribution of charged phoretic particles becomes ununiform if a flexible substrate is used for the first (or second) electrode-forming substrate wherein it is difficult to maintain the gap between the electrodes432and434at constant over the extension of the first (or second) electrode-forming substrate435.

An organization and an operation principle of another electrophoretic display device are described with reference to FIG.5. Referring toFIG. 5, the device includes a first substrate501, a first electrode502, a second substrate503, a second electrode504, spacers507, a liquid dispersion medium508, electrophoretic particles509and a voltage application circuit540.

More specifically, the device includes a dispersion system comprising a liquid dispersion medium508with a colorant dissolved therein and electrophoretic particles509, a pair of a first substrate501and a second substrate503disposed opposite to each other so as to sandwich the dispersion system, and spacers507for retaining a prescribed gap between the substrates501and503and functioning as partitioning walls for dividing and confining the dispersion systems into small sections or cells (only two of which are illustrated). At least one of the first and second substrates501and503is made transparent.

For a display, a voltage is applied across the dispersion system between the first and second electrodes502and504, whereby the electrophoretic particles509are attached toward either one of the electrodes502and504depending on the charged polarity of the electrophoretic particles509. The display is performed based on a difference between the color of the electrophoretic particles509observed when the particles509are attracted to the second substrate503and the color of the dispersion liquid medium observed when the electrophoretic particles509are attracted to the first substrate501.

For the production of the device, spacers507are formed on a first substrate501provided with a first electrode502, a mixture of the colored liquid dispersion medium508and electrophoretic particles509are filled in the respective cells, and a second substrate503provided with a second electrode504is applied thereon to seal up the dispersion.

For the preparation of the above device, the method of JP-A 8-502599 may be again adopted. Thus, electrophoretic particles are first attained onto a first (or a second) substrate under application of a DC voltage as described. Then, the first (or a second) substrate to which the electrophoretic particles are attached, is assembled into an electrophoretic display device, followed by filling of the liquid dispersion medium. Thereafter, the attached electrophoretic particles on the first (or second) electrode are caused to diffuse between the first and second by electrophoresis under application of a voltage between the electrodes to form a uniform dispersion system.

The diffusion of attached electrophoretic particles relying on only the electrophoretic effect is accompanied with several problems.

The diffusion by the electrophoretic effect alone may require application of a large-voltage between the electrodes, which is liable to cause an electric insulation breakdown of the electrophoretic apparatus. In case where a TFT is adopted as a drive element, the applicable voltage is restricted by the withstand voltage of the TFT.

Another difficulty is that the electrophoretic particles are liable to cause agglomeration with each other in a step of attachment thereof onto one substrate prior to the diffusion step, so that the electrophoretic diffusion can cause separation of the electrophoretic particles from one substrate but the full disintegration of the agglomerated particles is difficult to be performed thereby.

As a result, the resultant electrophoretic display device is liable to be accompanied with difficulties, such as a lower resolution and a lower display contrast, attributable to localization of electrophoretic particles.

SUMMARY OF THE INVENTION

A generic object of the present invention is to provide a solution to the above-mentioned problems of the prior art methods of producing electrophoretic display devices.

A more specific object of the present invention is to provide an apparatus and a process for producing a high-quality electrophoretic (display) device wherein charged phoretic particles in a dispersion liquid are easily and evenly distributed to respective cells or pixels even in the case of a very small gap between two substrates or the case of using a flexible substrate.

Another object of the present invention is to provide an apparatus and a process for producing an electrophoretic (display) device wherein an electrophoretic dispersion liquid containing charged phoretic particles having an appropriate charge distribution is filled at an appropriate concentration distribution regardless of a gap size between a pair of substrates or a flexibility of a substrate.

A further object of the present invention is to provide an apparatus and a process for producing an electrophoretic (display) device wherein electrophoretic are distributed in a good diffusion state in the electrophoretic dispersion system.

According to the present invention, there is provided an apparatus for producing an electrophoretic (display) device comprising at least: charged phoretic particles, a dispersion liquid medium for dispersing the charged phoretic particles therein, and a pair of substrates including a substrate with electrodes formed thereon; said apparatus comprising: storage means for storing a dispersion liquid containing the charged phoretic particles dispersed therein, stirring means for stirring the dispersion liquid, substrate-holding means for holding the substrate in the dispersion liquid, and means for applying a voltage to the electrodes formed on the substrate thereby depositing the charged phoretic particles on the electrodes.

According to another aspect of the present invention, there is provided an apparatus for producing an electrophoretic (display) device comprising at least: charged phoretic particles, a dispersion liquid medium for dispersing the charged phoretic particles therein, and a pair of substrates including a substrate with electrodes formed thereon; said apparatus comprising: substrate-holding means for holding the substrate, means for applying a voltage to the electrodes formed on the substrate, and ejection means for ejecting a dispersion liquid containing the charged phoretic particles dispersed therein onto the electrodes on the substrate thereby depositing the charged phoretic particles on the substrate.

The present invention further provides a process for producing an electrophoretic (display) device comprising a pair of a first substrate and a second substrate, of which at least the first substrate is provided with a first electrode and a second electrode between which a voltage can be applied, and a dispersion liquid disposed between the first and second electrodes and comprising a dispersion liquid medium and charged phoretic particles dispersion therein; said process comprising:

a first step of depositing the charged phoretic particles on the first substrate,

a second step of pouring the dispersion liquid medium over the charged phoretic particles on the first substrate to form the dispersion liquid, and

a third step of sealing the dispersion liquid between the first substrate and the second substrate.

The present invention further provides a process for producing an electrophoretic (display) device comprising a pair of a first substrate and a second substrate, of which at least the first substrate is provided with first and second electrodes and a dispersion liquid disposed between the first and second electrodes and comprising a dispersion liquid medium and charged phoretic particles dispersion therein; said process comprising:

a first step of depositing the charged phoretic particles on an electrode-provided surface of the first substrate,

a second step of washing the electrode-provided surface of the first substrate carrying the deposited charged phoretic particles thereon with the dispersion liquid medium alone or in mixture with the charged phoretic particles,

a third step of pouring the dispersion liquid medium over the electrode-provided surface of the first substrate to form the dispersion liquid on the first substrate, and

a fourth step of sealing the dispersion liquid between the first substrate and the second substrate.

There is also provided a process for producing a display device comprising a pair of substrates including at least one transparent substrate, a spacer for defining a gap between the substrates, a dispersion liquid comprising a dispersion liquid medium and charged phoretic particles dispersed therein and disposed between the substrates so as to fill the gap, and a pair of electrodes for applying a voltage to the dispersion liquid, so as to move the charged phoretic particles in the dispersion liquid to effect a display, said process including: a sealing step of sealing the dispersion liquid between the substrates to form a filled device, and a vibration step of applying a vibration from outside to the filled device so as to diffuse the charged phoretic particles in the dispersion liquid sealed between the substrates.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 6is a schematic illustration (partly in section) of an embodiment of the apparatus for producing an electrophoretic display device according to the present invention. Referring toFIG. 6, an apparatus1011includes a first vessel1014as a storage means for holding a dispersion liquid1013containing charged phoretic particles1012dispersed therein; a second vessel for holding a dispersion liquid medium1015not containing such charged phoretic particles1012; stirring means1017for stirring the dispersion liquid (medium)1013and1015; a substrate-holding means1019for holding a substrate1018; and a voltage application means10110for applying a voltage to an electrode formed on the substrate1018.

It is further preferred for the substrate-holding means1019to have functions of conveying and vibrating the substrate1018. The apparatus1011further includes a first concentration detection means10111for detecting the concentration of charged phoretic particles1012collected on the electrode, a second concentration detection means10112for detecting the concentration of the charged phoretic particles in the dispersion liquid1013, and a control means10113for controlling these means inclusively.

The first and second vessels1014and1016may be formed of any materials inclusive of glass, various resins and metals, as far as they are free from liberation of impurities adversely affecting the charged phoretic particles1012and the dispersion liquid1013.

The stirring means1017may be of any type as far as it is suitable for stirring of liquids. An internal stirring means, such as a stirring blade or a magnetic stirrer, may be used, but circulation by a liquid feed pump can also be used.

The substrate-holding means1019is used for surely holding the substrate1018and may preferably have a function of conveying the substrate1018. It is further preferred that the substrate-holding means1019also has a function of vibrating or repetitively moving the substrate1018relative to the dispersion liquid1013. The repetitive movement (vibration) may be performed in various directions, such as back and forth (perpendicularly to the drawing), laterally, up and down (vertically) and in rotation or swing. A sheet or plural sheets of the substrate1018may be held at a time by the substrate-holding means1019.

The substrate1018may be formed of glass or a thick plastic sheet, or also a thin film of plastic materials, such as polyethylene terephthalate, polyimide, polycarbonate or polyphenylene sulfide, of at most several tens μm in thickness. Such a thin and flexible film substrate can be used since the application of the charged phoretic particle onto the substrate does not require a counter electrode, thus without being substantially affected by a gap between the substrates.

The voltage application means10110is used to apply a voltage of, e.g., up to 200 volts, to electrodes formed on the substrate1018. An AC voltage or a DC voltage may be applied between each pair of electrodes, but an AC voltage is preferred. A frequency of ca. 0.1-10 Hz may be used while it is not particularly restrictive. Any voltage waveform may be used, and voltage application conditions inclusive of a voltage amplitude, a frequency and a voltage waveform, may be varied so as to facilitate the control of deposition rate of charged phoretic particles on the substrate.

The density of the charged phoretic particles on the electrodes on the substrate1018may be detected by the optical density detection means10111in the manner of detecting an optical density while driving the charged phoretic particles1012by applying an AC voltage to the electrodes on the substrate1018. Any detection method capable of measuring an optical density may be used.

The density detection means10112for detecting the density of charged phoretic particles1012in the dispersion liquid1013is provided to the first vessel1014, thereby detecting the density of charged phoretic particles in the dispersion liquid1013lowered by deposition thereof onto the substrate1012. The detection may be performed according to any method capable of detecting a density. The detection means can also be provided to the second vessel1016.

As the control means10113for inclusively controlling the above-mentioned means, a personal computer, etc., may be used, so as to control the holding, conveyance and vibration (movement) of the substrate, the control of the voltage application conditions, the detection and correction of the concentration of charged phoretic particles, etc., for accomplishing desired deposition of charged phoretic particles on the electrodes.

An electrophoretic display device may be prepared by using the above-mentioned production apparatus in the following manner.

The first vessel1014is filled with a dispersion liquid1013containing charged phoretic particles dispersed therein. The second vessel1016is filled with a dispersion liquid medium containing no charged phoretic particles. A substrate1018prepared according to, e.g., the method of JP-A 11-202804 is caused to be held by the substrate-holding means1019. The substrate1018is provided with pairs of electrodes disposed in lamination for each pair and is dipped in the dispersion liquid1013in the first vessel after connecting the electrodes to the voltage application circuit10110. (Regarding a process for a detailed process for producing an electrode plate or sheet3010having a superposed structure including two types of electrodes3011and3012disposed in lamination, the disclosure of JP-A 11-202804 is incorporated herein by reference.) Then, a voltage, preferably an AC voltage, is applied between each pair of the electrodes. During the voltage application, the dispersion liquid1013in the first vessel1014is moved relative to the substrate1018by the substrate-holding means1019or the solution stirring means1017, so as to continuously supply a fresh portion of the dispersion liquid1013to the electrodes on the substrate. After deposition of a sufficient amount of charged phoretic particles1012on the electrodes of the substrate1018, the substrate1018while being continually supplied with the voltage is conveyed and dipped in the dispersion liquid medium1015in the second vessel1016(with continued application of the AC voltage) to remove an excessive or an insufficiently charged portion of the charged phoretic particles. As a result to of this operation, the charged phoretic particles having uniform properties can be uniformly distributed over the electrodes (and to respective cells each having the pair of electrodes). Then, the substrate1018is dipped out of the dispersion liquid1015to measure a density contrast (given by a state of spreading and a state of localization of charged phoretic particles giving two display states) on the electrodes by the first density detection means10111. If the measured density contrast is sufficient, the treatment operation for the substrate is finished, and the above-mentioned operation is started for a subsequent (batch of) substrate(s), and the treated substrate is subjected to a subsequent step of display device preparation, such as application of a second substrate. More specifically, the treated substrate may be subjected to the addition of the dispersion liquid medium, the application of and sealing with the second or display surface-side substrate, and the disposition of and connection with an electrical circuit for completing an electrophoretic display device.

If the density contrast or uniformity thereof is judge to be insufficient for the above-treated substrate, the above-mentioned steps of attachment of charged phoretic particles and removal of non-uniformly attached charged phoretic particles can be repeated several times.

A specific production example is described hereinbelow.

An electrophoretic display device was prepared by using an apparatus according to the present invention as shown in FIG.1.

A dispersion liquid1013was prepared by dispersing ca. 1-2 μm-dia. black charged phoretic particles and a charge control agent in a dispersion liquid medium comprising principally aliphatic hydrocarbons (“ISOPER” (trade name), made by Exxon Co.) and placed in a first vessel1014. As positive charge control agents, it is possible to use a naphthenic acid salt of a metal, such as cobalt, manganese or iron, zirconium octenate, etc. and as negative control agents, it is possible to use lecithin, calcium petroleum-sulfonate, calcium alkylbenzene-sulfonate, sodium dioctylsulfonate, alkylalanine, etc. Such a charge control agent can also be incorporated in (charged) phoretic particles.

Then, a dispersion liquid medium1015(identical to the above) not containing charged phoretic particles was placed in a second vessel1016. The liquids within the first and second vessels1014and1016were respectively stirred gently by magnetic stirrers1017. A substrate1018of PET (polyethylene terephthalate film) with sizes of 300 mm-L, 200 mm-W and 120 μm-T provided with pairs of electrodes and also provided with 30 μm-high and 15 μm-wide spacers (not shown) formed by photolithography, was held by a substrate-holding means1019and the electrodes were connected to a voltage application circuit10110so as to apply a rectangular AC voltage of ±80 volts at a frequency of 1 Hz between the electrodes in each pair. The substrate1018was then dipped in the dispersion liquid1013in the first vessel1014, and was held therein for 10 min. while being swung back and forth by the substrate-holding means119, thereby depositing charged phoretic particles1012on the electrodes. During the deposition step, the concentrations of charged phoretic particles in the first vessel1014was continually measured by a second concentration detection means10112. After the deposition of the charged phoretic particles1012, the substrate1018was transferred onto the second vessel1016while continuing the voltage supply to the electrodes. The voltage application was continued for 5 min. within the second vessel1016for smoothing the charged phoretic particles1012on the electrodes of the substrate1018.

Then, the substrate1018was pulled up from the second vessel1016to check the concentration of the charged phoretic particles1012on the electrodes. As a result, the charged phoretic particles on the electrodes exhibited a sufficient contrast, so that the step of deposition of charged phoretic particles was finished.

The above steps were all performed under a control of the control means10113. After the charged phoretic particle-deposition step, post treatments were performed, such as the supplement of the dispersion liquid medium, the application of another transparent substrate of also PET onto the above-treated substrate to seal up the dispersion liquid within a gap of 30 μm given by the spacers, and the connection of the electrodes to an electrical circuit, to complete an electrophoretic device. The thus-prepared electrophoretic display device comprised a matrix of rectangular cells of 30 mm×20 mm each defined by a surrounding wall of spacer and comprising 30 μm-side (and 30 mm-long) stripes of 160 first electrodes (black) arranged at a pitch of 125 μm and a 30 mm×20 mm-second electrode (white) disposed below the first electrodes, over an entire display area of 300 mm×200 mm.

As a result of drive of the thus-prepared electrophoretic display device by applying voltages of ±40 volts alternately to the first and second electrodes, the device exhibited a very uniform contrast distribution over the entire display area extension regardless of a very small gap of 30 μm.

As described above, by using a production apparatus of the present invention, it is possible to uniformly distribute charged phoretic particles of a display dispersion liquid to respective display cells easily and evenly even in the case of a small gap between two substrates or the case of using flexible substrate, thereby allowing the production of a high-quality electrophoretic display device. Further, as the production apparatus does not include a counter electrode, the apparatus is advantageous than the conventional apparatus in respects of mass productivity and production cost.

FIG. 7is a schematic illustration (partly in section) of an embodiment of the apparatus for producing an electrophoretic display device of the present invention. Referring toFIG. 7, an apparatus2011includes a substrate-holding means2013for holding a substrate2012with electrodes formed thereon, a voltage application means2014for applying a voltage to the electrodes formed on the substrate2012, a nozzle2017as a means for ejecting a dispersion liquid2016containing charged phoretic particles2015dispersed therein, and a pump2018for supplying the dispersion liquid2016to the nozzle2017. The apparatus2011further includes a first vessel2019for storing the dispersion liquid2016to be ejected and receiving an excess of the ejected dispersion liquid2016, an optical density detection means20110for detecting the density of the charged phoretic particles2015deposited on the electrodes, a density detection means20111for measuring the concentration of charged phoretic particles2015in the dispersion liquid2016in the first vessel2019, and control means20112for inclusively controlling the above means. The substrate-holding means2013also has functions of conveying the substrate2012to the position above the first vessel2019and causing a repetitive movement (vibration, swinging, reciprocation, rotation, etc.) of the substrate2012above the first vessel2019. The apparatus2011can further include a nozzle20114for spraying or ejecting a dispersion liquid20113not containing or containing only a low concentration of charged phoretic particles and a pump20115therefor, a second vessel20116for supplying the dispersion liquid20113to be sprayed or recovering the ejected dispersion liquid20113. The first and second vessels2019and20116can be equipped with a stirring means20117.

The first and second vessels2019and20116may be formed of any materials inclusive of glass, various resins and metals, as far as they are free from liberation of impurities adversely affecting the charged phoretic particles2015and the dispersion liquid2016and20113.

The substrate-holding means2013is used for surely holding the substrate2012and may preferably have a function of conveying the substrate2012. It is further preferred that the substrate-holding means2013also has a function of vibrating or repetitively moving the substrate2012above the first vessel2019. The repetitive movement (vibration) may be performed in various directions, such as back and forth (perpendicularly to the drawing), laterally, up and down (vertically) and in rotation or swing. A sheet or plural sheets of the substrate2012may be held at a time by the substrate-holding means2013. During the ejection of the dispersion liquid2016, the substrate2012may be held horizontally (as shown), vertically or obliquely.

The substrate2012may be formed of glass or a thick plastic sheet, or also a thin film of plastic materials, such as polyethylene terephthalate, polyimide, polycarbonate or polyphenylene sulfide, of at most several tens μm in thickness. Such a thin and flexible film substrate can be used since the application of the charged phoretic particle onto the substrate does not require a counter electrode, thus without being substantially affected by a gap between the substrates.

The voltage application means2014is used to apply a voltage of, e.g., up to 300 volts, to electrodes formed on the substrate2012. An AC voltage or a DC voltage may be applied between each pair of electrodes, but an AC voltage is preferred. A frequency of ca. 0.01-50 Hz may be used while it is not particularly restrictive. Any voltage waveform may be used, and voltage application conditions inclusive of a voltage amplitude, a frequency and a voltage waveform, may be varied so as to facilitate the control of deposition rate of charged phoretic particles on the substrate.

The density of the charged phoretic particles2015on the electrodes on the substrate2012may be detected by the optical density detection means20110in the manner of detecting an optical density while driving the charged phoretic particles2015by applying an AC voltage to the electrodes on the substrate2012. Any detection method capable of measuring an optical density may be used.

The density detection means20111for detecting the density of charged phoretic particles2015in the dispersion liquid2016is provided to the first vessel2019, thereby detecting the density of charged phoretic particles in the dispersion liquid2016lowered by deposition thereof onto the substrate2012. The detection may be performed according to any method capable of detecting a density. The detection means can also be provided to the second vessel20116.

The stirring means1017may be of any type as far as it is suitable for stirring of liquids. An internal stirring means, such as a stirring blade or a magnetic stirrer, may be used, but circulation by a liquid feed pump can also be used.

The second vessel20116may preferably be provided with a filter20118for removing charged phoretic particles.

As the control means20112for inclusively controlling the above-mentioned means, a personal computer, etc., may be used, so as to control the holding, conveyance and vibration (repetitive movement) of the substrate, the control of the voltage application conditions, the detection and correction of the concentration of charged phoretic particles, etc., for accomplishing desired deposition of charged phoretic particles on the electrodes.

An electrophoretic display device may be prepared by using the above-mentioned production apparatus in the following manner.

The first vessel2019is filled with a dispersion liquid2016containing charged phoretic particles dispersed therein. The second vessel20116may be filled with a dispersion liquid medium containing no charged phoretic particles. A substrate2012prepared according to, e.g., the method of JP-A 11-202804 is caused to be held by the substrate-holding means2013. The substrate2012is provided with pairs of electrodes disposed in lamination for each pair and is disposed above the first vessel2019after connecting the electrodes to the voltage application circuit2014. Then, a voltage, preferably an AC voltage, is applied between each pair of the electrodes.

Then, the dispersion liquid2016containing charged phoretic particles dispersed therein is ejected out of the nozzle2017while scanningly move the nozzle2017relative to the substrate2012, so as to have the dispersion liquid always flow over the electrodes on the substrate2012and always supply a fresh portion of the dispersion liquid2016.

After deposition of a sufficient amount charged phoretic particles2015on the electrodes of the substrate2012, the substrate2012while being continually supplied with the voltage is conveyed to above the second vessel20116, and a dispersion liquid20113not containing charged phoretic particles or containing a sufficiently low concentration of charged phoretic particles is ejected out of the nozzle20114while scanningly move the nozzle20114relative to the substrate2012. As a result of this operation, an excessive amount of charged phoretic particles and/or an insufficiently charged portion of charged phoretic particles on the substrate are removed to realize a uniform distribution of charged phoretic particles having uniformized properties over the electrodes (and to respective cells each having a pair of electrodes). Alternatively, this smoothing treatment can also be performed by directly dipping the substrate2012after the charged phoretic particle-deposition treatment above the first vessel2019into the dispersion liquid20113in the second vessel20116. In this case, it is preferred to effect an appropriate degree of stirring of the dispersion liquid20113in the second vessel by a stirring means20117provided to the second vessel20116, as illustrated in FIG.8.

Then, the substrate2012is subjected to measurement of the density contrast on the electrodes by the optical density measurement means20110. If the measured density contrast is sufficient, the treatment operation for the substrate is finished, and the above-mentioned operated is started for a subsequent (batch of) substrate(s), and the treated substrate is subjected to a subsequent step of display device preparation, such as application of a second substrate. More specifically, the treated substrate may be subjected to the addition of the dispersion liquid medium, the application of and sealing with the second or display surface-side substrate, and the disposition of and connection with an electrical circuit for completing an electrophoretic display device.

If the density contrast or uniformity thereof is judge to be insufficient for the above-treated substrate, the above-mentioned steps of attachment of charged phoretic particles and removal of non-uniformly attached charged phoretic particles can be repeated several times.

Some specific production examples are described hereinbelow.

An electrophoretic display device was prepared by using an apparatus according to the present invention as shown in FIG.7.

A dispersion liquid2016was prepared by dispersing ca. 1-2 μm-dia. black charged phoretic particles and a charge control agent in a dispersion liquid medium comprising principally aliphatic hydrocarbons (“ISOPER” (trade name), made by Exxon Co.) and placed in a first vessel2019.

Then, a dispersion liquid medium20113(identical to the above) not containing charged phoretic particles was placed in a second vessel20116. The liquids within the first and second vessels2019and20116were respectively stirred by magnetic stirrers. A PET-substrate2012of 300 mm-L, 200 m-W and 120 μm-T provided with pairs of electrodes was held by a substrate-holding means2013and the electrodes were connected to a voltage application circuit2014so as to apply a rectangular AC voltage of ±8 volts at a frequency of 1 Hz between the electrodes in each pair.

Onto the substrate2012thus disposed above the first vessel2019, the dispersion liquid2016containing charged phoretic particles dispersed therein were ejected for 2 min. out of the nozzle2017while scanningly move the nozzle2017relative to the substrate2012, thereby depositing charged phoretic particles2015on the substrate2012.

During the deposition step, the concentration of charged phoretic particles in the first vessel2019was continually measured by a concentration detection means20111. After the deposition of the charged phoretic particles2015, the substrate2012was moved to above the second vessel20116while continuing the voltage supply to the electrodes. In this state, the dispersion liquid medium20113containing no charged phoretic particles was ejected out of the nozzle20114for 3 min. while scanningly move the nozzle20114relative to the substrate2012, thereby removing an excessive portion and/or an insufficiently charged portion of the charged phoretic particles2015on the substrate2012to uniformly distribute the charged phoretic particles having uniform properties over the electrodes (and thus to respective cells for display). During the ejection through the nozzle, the charged phoretic particles in the dispersion liquid20113in the second vessel20116were removed by passing through the filter20118.

Then, the density of the charged phoretic particles deposited on the substrates was detected by the optical detection means20110. As a result, the charged phoretic particles on the electrodes exhibited a sufficient contrast, so that the step of deposition of charged phoretic particles was finished.

The above steps were all performed under a control of the control means20112. After the charged phoretic particle-deposition step, as post treatments, the dispersion liquid medium was supplementary added, the dispersion liquid was sealed up by application of a display-side substrate while leaving a gap of 30 μm, and the electrodes were connected to an electrical circuit to complete an electrophoretic display device.

As a result of drive of the thus-prepared electrophoretic display device, the device exhibited a very uniform contrast distribution over the planar extension regardless of a very small gap of 30 μm.

An electrophoretic display device was prepared by again using an apparatus according to the present invention as shown in FIG.7.

A dispersion liquid2016was prepared by dispersing ca. 1-2 μm-dia. black charged phoretic particles and a charge control agent in a dispersion liquid medium comprising principally aliphatic hydrocarbons (“ISOPER” (trade name), made by Exxon Co.) and placed in a first vessel2019.

Then, a dispersion liquid medium20113(identical to the above) not containing charged phoretic particles was placed in a second vessel20116. The liquids within the first and second vessels2019and20116were respectively stirred by magnetic stirrers. A PET-substrate identical to the one used in Example 2-1 and provided with pairs of electrodes was held by a substrate-holding means2013and the electrodes were connected to a voltage application circuit2014so as to apply a rectangular AC voltage of ±80 volts at a frequency of 1 Hz between the electrodes in each pair.

Onto the substrate2012thus disposed above the first vessel2019, the dispersion liquid2016containing charged phoretic particles dispersed therein were ejected for 1 min. out of the nozzle2017while scanningly move the nozzle2017relative to the substrate2012, thereby depositing charged phoretic particles2015on the substrate2012.

During the deposition step, the concentration of charged phoretic particles in the first vessel2019was continually measured by a concentration detection means20111. After the deposition of the charged phoretic particles2015, the substrate2012was moved to above the second vessel20116while continuing the voltage supply to the electrodes. In this state, the dispersion liquid medium20113containing no charged phoretic particles was ejected to of the nozzle20114for 2 min. while scanningly move the nozzle20114relative to the substrate2012, thereby removing an excessive portion and/or an insufficiently charged portion of the charged phoretic particles2015on the substrate2012to uniformly distribute the charged phoretic particles having uniform properties over the electrodes (and thus to respective cells for display). During the ejection through the nozzle, the charged phoretic particles in the dispersion liquid20113in the second vessel20116was removed by passing through the filter20118.

Then, the density of the charged phoretic particles deposited on the substrates was detected by the optical detection means20110. As a result, the charged phoretic particles on the electrodes exhibited a sufficient contrast, so that the step of deposition of charged phoretic particles was finished.

The above steps were all performed under a control of the control means20112. After the charged phoretic particle-deposition step, another transparent substrate was applied onto the above-treated substrate so as to sandwich the charged phoretic particles and the dispersion liquid medium therebetween while leaving a gap of 30 μm between the substrates as in Example 2-1 to complete an electrophoretic display device.

As a result of drive of the thus-prepared electrophoretic display device, the device exhibited a very uniform contrast distribution over the planar extension regardless of a very small gap.

An electrophoretic display device was prepared by using an apparatus as shown in FIG.8.

The deposition of charged phoretic particles2015onto a substrate2012was performed above a first vessel2019in the same manner as in Example 2-1.

Then, the substrate2012was then transferred to a second vessel20116and dipped into a dispersion liquid20113contained therein under mild stirring while continuing the voltage application to the electrodes on the substrate2012. The dipping was continued for 3 min. under continued voltage application, thereby removing an excessive portion and/or an insufficiently charged portion of the charged phoretic particles2015on the substrate2012to uniformly distribute the charged phoretic particles having uniform properties over the electrodes (and thus to respective cells for display).

Then, the substrate2012was pulled up from the second vessel20116and the density of the charged phoretic particles deposited on the substrates was detected by the optical detection means20110. As a result, the charged phoretic particles2015on the electrodes. As a result, the charged phoretic particles on the electrodes exhibited a sufficient contrast, so that the step of deposition of charged phoretic particles was finished.

The above steps were all performed under a control of the control means20112. After the charged phoretic particle-deposition step, as post treatments, the dispersion liquid medium was supplementary added, the dispersion liquid was sealed up by application of a display-side substrate while leaving a gap of 30 μm, and the electrodes were connected to an electrical circuit to complete an electrophoretic display device.

As a result of drive of the thus-prepared electrophoretic display device, the device exhibited a very uniform contrast distribution over the planar extension regardless of the very small gap.

As described above, according to Second embodiment of the production apparatus of the present invention, it is possible to uniformly distribute charged phoretic particles of a display dispersion liquid to respective display cells easily and evenly even in the case of a small gap between two substrates or the case of using flexible substrate, thereby allowing the production of a high-quality electrophoretic display device. Further, as the production apparatus does not include a counter electrode, the apparatus is advantageous than the conventional apparatus in respects of mass productivity and production cost.

According to an embodiment, the process for producing an electrophoretic display device comprises sequential steps including a first step of exposing a substrate equipped with electrodes formed thereon to a dispersion liquid containing charged phoretic particles dispersed therein while applying a voltage to the electrodes to coat the electrodes with the charged phoretic particles, a second step of disposing a dispersion liquid medium over the coated electrodes on the substrate, and a third step of assembling the substrate with another substrate to seal up a dispersion liquid comprising the charged phoretic particles and the dispersion liquid medium.

The respective steps are described in more details with reference toFIGS. 9-18, wherein only one cell section (display section) is shown for convenience of illustration, but such a cell may generally be arranged two-dimensionally to form an entire display device. In the process, a substrate (an electrode sheet) provided with first electrodes and a second electrode as formed by the method of JP-A 11-202804 may be used for preparing an electrophoretic display device. A functionally equivalent electrode sheet may also be used.

Such an electrode sheet can be formed from a substrate of a flexible material, such as polyethylene terephthalate (PET) or polyether sulfone (PES).

FIGS. 9 and 10illustrate the above-mentioned first step. Referring to these figures, an electrode sheet3010provided with first electrodes3012and a second electrode3014is exposed to a dispersion liquid comprising a dispersion liquid medium3017and charged phoretic particles3018dispersed therein, and in this state, a periodically varying voltage is applied between the first electrodes3012and the second electrodes3014from a voltage application circuit4013, whereby the charged phoretic particles3018disposed in the dispersion liquid medium3017are moved toward the first electrodes3012or the second electrode3014. When the voltage application is continued for a certain period, the charged phoretic particles3018collected on the first electrodes3012or the second electrodes3014reach a prescribed concentration. By appropriately controlling the period, a desired concentration of the charged phoretic particles3018can be obtained. Further, by appropriately regulating the applied voltage, the charged phoretic particles3018may be provided with a desired charge distribution.

Finally, as shown inFIG. 11, a dispersion liquid comprising a dispersion liquid medium3017and charged phoretic particles3018contained therein at appropriate concentration and charge distribution is disposed on the electrode sheet3010provided with a spacer3016. In this instance, it is preferred that the dispersion liquid medium3017also contains a charge control agent (not specifically shown).

The charge control agent may be a positive charge control agent or a negative charge control agent. As positive charge control agents, it is possible to use a naphthenic acid salt of a metal, such as cobalt, manganese or iron, zirconium octenate, etc. and as negative control agents, it is possible to use lecithin, calcium petroleum-sulfonate, calcium alkylbenzene-sulfonate, sodium dioctylsulfonate, alkylalanine, etc. Such a charge control agent can also be incorporated in phoretic particles.

When a structure shown inFIG. 11is subjected to application of a periodically varying voltage between the first electrodes3012and the second electrode3014from the voltage application circuit3041, the charged phoretic particles3018are moved periodically between a state shown inFIG. 11 and astate shown inFIG. 12according to electrophoresis, i.e., a state where the charged phoretic particles3018are collected above the first electrodes (FIG. 11) or a state where the charged phoretic particles3018are moved to a place above the second electrode3014not covered with the first electrodes3012(FIG.12). The application voltage may have an amplitude up to 300 volts and a frequency of 0.01-50 Hz. Further, any voltage waveform may be used.

The charged phoretic particles3018in the dispersion liquid medium3017are generally charged to an identical polarity. However, in a case where some portion of phoretic particles are charged to an opposite polarity, such an oppositely charged portion of charged phoretic particles may preferably be removed, e.g., by electrophoresis, in advance of the first step of deposition of the charged phoretic particles3018described with reference toFIGS. 9 and 10.

FIG. 13illustrates the above-mentioned second step. Usually, the electrode sheet3010after the first step is short of the dispersion liquid medium3017. In such a case or a case where an excess of dispersion liquid medium3017is preferred, the dispersion liquid medium3017may be gradually disposed or supplemented over the electrodes on the electrode sheet3010while applying an AC voltage (or a DC voltage).

FIGS. 14 and 15respectively illustrate a third step (assembling step). Referring toFIG. 14, for example, in opposition to the electrode sheet3010carrying the dispersion liquid, a second substrate3013is applied, and simultaneously, an excess of the dispersion liquid medium3017is squeezed out, followed by bonding between the first and second substrates3011and3013. As a result, the dispersion liquid comprising the medium3017and the charged phoretic particles3018is sealed up in the device. Until substantially completing the third step, it is preferred to continually apply some AC or DC voltage between the electrodes so as to prevent the movement of the charged phoretic particles3018as by convection of the dispersion liquid.

FIG. 15illustrates the application of a second electrode sheet identical to the electrode sheet3015instead of the second substrate3013shown in FIG.14.

The thus-prepared display device is driven in such a manner that the charged phoretic particles3018are moved in parallel with the substrate surfaces depending on potential differences between the first electrodes3012and the second electrode3014to a position above the first electrodes3012or a position above the second electrode3014not covered with the first electrodes3012. For example, as shown inFIGS. 16A and 16B, if the first electrodes3012are supplied with a negative voltage (FIG. 16A) or a positive voltage (FIG. 16B) relative to the second electrode3014grounded, positively charged phoretic particles are moved to one electrode of a relatively low potential (i.e., the first electrodes3012in FIG.16A and the second electrode3014in FIG.16B).

In this instance, in case where the charged phoretic particles3018and the first electrodes3012are colored in black and the second electrode3014is colored in white, a white display state is exhibited when the charged phoretic particles3018are collected above the first electrodes3012(FIG. 16A) and a black display state is exhibited when the charged phoretic particles3018are collected at a position above the second electrode3014not covered with the first electrodes3012(FIG.16B).

Some specific examples of the above-described process will be described hereinbelow.

Referring toFIG. 9, a dispersion liquid medium3017was formed by dispersing a charge control agent (not specifically shown) in a principally aliphatic hydrocarbon liquid “ISOPER” (trade name), made by Exxon Co.), and black polystyrene particles having an average particle size of 1-2 μm as charged phoretic particles3018were dispersed therein to form a dispersion liquid3017A, which was charged in a vessel3050as shown in FIG.9. The concentration of charged phoretic particles3018in the dispersion liquid3017A was set to be lower than that in the objective electrophoretic display device finally produced.

As shown inFIG. 9, a separately prepared electrode sheet3010comprising a 10 cm-square PET film substrate3011of 100 μm in thickness and provided with first electrodes3012and the second electrode3014was dipped in the dispersion liquid3017A with its electrode-provided surface directed downwards. Immediately thereafter, a rectangular AC voltage of ±60 volts and 1 Hz was started to be applied between the first electrodes3012and the second electrode3014. The voltage application was continued for 30 min.

Then, the level of the dispersion liquid3017A in the vessel3050was gradually lowered to take the electrode sheet3010out of the dispersion liquid3017.

Then, as a second step, the electrode sheet3010carrying the charged phoretic particles3018was inverted upside-down as shown inFIG. 13, while applying a DC voltage of 200 volts between the first electrodes3012(as positive electrode) and the second electrode3014(as negative electrode), and under the continued voltage application, a dispersion liquid medium3017containing a charge control agent dispersed therein was poured over the electrodes.

Then, as a third step, as shown inFIG. 14, while the DC voltage application was continued, a second substrate3013was disposed opposite to and gradually pressed against the electrode sheet3010to squeeze out an excessive portion of the dispersion liquid medium3017.

Thereafter, the periphery and other bonding portions of the electrode sheet3010and the second substrate3013were bonded under heating to seal up a dispersion liquid3017B comprising the dispersion liquid medium3017and the charged phoretic particles3018within a gap of 20 μm retained between the substrates to form an electrophoretic device comprising a matrix of rectangular cells each measuring 10 mm×5 mm and comprising 30 μm-wide stripe-form first electrodes (black) arranged at a pitch of 125 μm and a 10 mm×5 mm-second electrode (white).

The thus-formed electrophoretic display device exhibited a contrast of 8 at a response speed of ca. 10 msec when supplied with a drive voltage of ±40 volts.

Referring toFIG. 9, the process of Example 3-1 was repeated until the dipping of an electrode sheet3010within a dispersion liquid3017A.

Immediately thereafter, a rectangular AC voltage of ±60 volts and 1 Hz was started to be applied between the first electrodes3012and the second electrode3014. The voltage application was continued for 25 min. while horizontally vibrating the electrode sheet3010within the dispersion liquid3017A.

Then, as a second step, as shown inFIG. 13, under a continual application of a DC voltage of 200 volts between the first electrodes3012(as positive electrode) and the second electrode3014(as negative electrode), a dispersion liquid medium3017containing a charge control agent dispersed therein was poured over the electrodes on the electrode sheet3010.

Thereafter, the third step was repeated similarly as in Example 3-1 to complete an electrophoretic display device.

The thus-formed electrophoretic display device exhibited a contrast of 8 at a response speed of ca. 10 msec when supplied with a drive voltage of ±40 volts.

A dispersion liquid medium3017, charged phoretic particles3018, a dispersion liquid3017A and an electrode sheet3010, were prepared in the same manner as in Example 3-1. Then, as shown inFIG. 10, the electrode sheet3010was held obliquely, and under application of a rectangular AC voltage of ±60 volts and 1 Hz between the first electrodes3012and the second electrode3014, the dispersion liquid3017A comprising the dispersion liquid medium3017and the charged phoretic particles3018dispersed therein was sprayed several times onto the electrode-provided surface of the electrode sheet3010. The above operation was continued for 25 min. while slowly rotating the electrode sheet3010about a vertical line passing through a center of the electrode sheet3010as a rotation axis.

The thus-treated electrode sheet3010carrying the charged phoretic particles3018thereon was thereafter subjected to the second and third steps similarly as in Example 3-1 to complete an electrophoretic display device.

The electrophoretic display device thus prepared exhibited a display contrast of 8 at a response speed of ca. 10 msec when supplied with a drive voltage of ±40 volts.

A dispersion liquid medium3017and charged phoretic particles3018were prepared in the same manner as in Example 3-1.

Then, a mixture of the dispersion liquid medium and the charged phoretic particles was placed between a pair of electrode plates in a vessel (not shown), and by applying a DC voltage of 100 volts between the electrode plates, thereby selectively recovering a majority of the charged phoretic particles charged to a positive polarity. Then, the thus selected charged phoretic particles were dispersed in a fresh dispersion liquid medium3017to prepare a dispersion liquid3017A at a concentration lower than that in an objective electrophoretic display device finally produced.

Then, as shown inFIG. 9, the dispersion liquid3017A was filled in a vessel3050, and an electrode sheet3010prepared similarly as in Example 3-1 was dipped in the dispersion liquid3017A with its electrode-provided surface directed downwards. Immediately thereafter, a rectangular AC voltage of ±60 volts and 1 Hz was applied for 10 min. between the first electrodes3012and the second electrode3014.

The thus-treated electrode sheet3010carrying the charged phoretic particles318thereon was thereafter subjected to the second and third steps similarly as in Example 3-1 to complete an electrophoretic display device.

The electrophoretic display device thus prepared exhibited a display contrast of 8 at a response speed of ca. 10 msec when supplied with a drive voltage of ±40 volts.

An electrophoretic display device as illustrated inFIG. 15including two electrode sheets (i.e., a first electrode sheet3045farther from a viewer and a second electrode sheet3046closer to the viewer) was produced in the following manner.

Each of the first and second electrode sheets3045and3046was prepared in the same manner as the electrode sheet3010in Example 3-1 except that the first electrodes3042and the second electrode3044on the second electrode sheet3046were formed of transparent indium tin oxide (ITO). Moreover, a dispersion liquid medium3017, charged phoretic particles3018and a dispersion liquid3017A were prepared in the same manner as in Example 3-1.

Each of the first and second electrode sheets3045and3046was obliquely held in the place of an electrode sheet3010inFIG. 11, and the dispersion liquid3017A was sprayed several times onto the electrode-provided surface of the electrode sheet while applying a rectangular AC voltage of ±30 volts and 1 Hz between the first electrodes3012and the second electrode3014. The above operation was continued for 20 min. while slowly rotating the electrode sheet about a vertical line passing through a center of the electrode sheet.

Then, the first electrode sheet3045carrying the charged phoretic particles3018was set in the place of the electrode sheet3010inFIG. 13, and the dispersion liquid medium3017containing a charge control agent was poured over the electrodes3012and3014while applying a DC voltage of 100 volts between the first electrodes3012(as positive electrodes) and the second electrode3014(as negative electrode). The same operation was applied to the second electrode sheet3046.

Then, as a third step, as shown inFIG. 15, while the DC voltage was continually applied between the first electrodes3012and the second electrode3014and between the first electrodes3042and the second electrode3044, the second electrode sheet3046was disposed opposite to and slowly pressed against the first electrode sheet3045to squeeze out an excessive portion of the dispersion liquid medium3017.

Thereafter, the periphery and other bonding portions of the first electrode sheet3045and the second electrode sheet3046were bonded under heating to seal up a dispersion liquid3017B comprising the dispersion liquid medium3017and the charged phoretic particles3018within a gap of 15 μm retained between the substrates to form an electrophoretic display device.

An AC drive voltage of ±25 volts was applied synchronously between the first electrodes3012and the second electrode3014on the first electrode sheet3045and between the first electrodes3042and the second electrode3044on the second electrode sheet3045, whereby the electrophoretic display device exhibited a contrast of 8 at a response time of ca. 7 msec.

As described above, according to Third Embodiment of the present invention as a process for producing an electrophoretic display device including a step of filling an electrophoretic dispersion liquid containing charged phoretic particles, it is possible to fill the dispersion liquid at an appropriate concentration distribution of the charged phoretic particles even in the case of a very small gap between a pair of substrates or the case of using a flexible substrate. As a result, it becomes possible to produce an electrophoretic display device having a very small gap between the substrates, which can exhibit a high contrast at a lower drive voltage than in the known devices.

According to an embodiment, the process for producing an electrophoretic display device comprises sequential steps including a first step of depositing charged phoretic particles on electrodes formed on a substrate surface; a second step of causing the charged phoretic particle-deposited substrate surface to contact a dispersion liquid medium, thereby leaving a reduced amount of the charged phoretic particles deposited on the substrate surface; a third step of disposing a dispersion liquid medium over the charged phoretic particles on the substrate; and assembling the substrate with another substrate to seal up a dispersion liquid comprising the charged phoretic particles and the dispersion liquid medium.

The respective steps are described in more details with reference toFIGS. 19-27, wherein only one cell section (display section) is shown for convenience of illustration, but such a cell may generally be arranged two-dimensionally to form an entire display device. In the process, a substrate (an electrode sheet) provided with first electrodes and a second electrode as formed by the method of JP-A 11-202804 may be used for preparing an electrophoretic display device. A functionally equivalent electrode sheet may also be used.

Such an electrode sheet can be formed from a substrate of a flexible material, such as polyethylene terephthalate (PET) or polyether sulfone (PES).

The above-mentioned first step of this process embodiment may be performed, e.g., by two methods as illustrated in FIG.19andFIGS. 20A-20B.

FIG. 19illustrate one method wherein a surface of an electrode sheet4010provided with electrodes is covered with charged phoretic particles4018.FIGS. 20A and 20Billustrate another method wherein charged phoretic particles4018dispersed in a dispersion liquid medium4017to form a dispersion liquid4017A are selectively deposited on first electrodes4012or a position above a second electrode4014not covered with the first electrodes4021by applying a voltage between the first electrodes4012and the second electrode4014.

In any case, it is preferred that the dispersion liquid medium4017also contains a charge control agent (not specifically shown).

The charge control agent may be a positive charge control agent or a negative charge control agent. As positive charge control agents, it is possible to use a naphthenic acid salt of a metal, such as cobalt, manganese or iron, zirconium octenate, etc. and as negative control agents, it is possible to use lecithin, calcium petroleum-sulfonate, calcium alkylbenzene-sulfonate, sodium dioctylsulfonate, alkylalanine, etc. Such a charger control agent can also be incorporated in phoretic particles.

The charged phoretic particles4018in the dispersion liquid medium4017are generally charged to an identical polarity. However, in a case where some portion of phoretic particles are charged to an opposite polarity, such an oppositely charged portion of charged phoretic particles may preferably be removed, e.g., by electrophoresis, in advance of the first step of deposition of the charged phoretic particles4018described with reference toFIGS. 19 and 20.

The above-mentioned two methods are described in further detail.

Referring toFIG. 19, the first step may be performed by dipping an electrode sheet4010in a dispersion liquid4017A as a mixture of a dispersion liquid medium4017and charged phoretic particles4018; or by ejecting, pouring or printing such a dispersion liquid4017A onto the electrode sheet4010to cover the surface of the electrode sheet4010provided with the electrodes.

According to the latter method illustrated inFIGS. 20A and 20B, the charged phoretic particle4018are selectively deposited on first electrodes4012or a position above a second electrode4014not covered with the first electrodes4012. For this purpose, the following steps are taken.

In a state where the electrode-provided surface of the electrode sheet4010is exposed to the dispersion liquid4017A containing the charged phoretic particles4018, if a periodically varying voltage is applied between the first electrodes4012and the second electrode4014from the voltage application circuit4041, the charged phoretic particles43018are moved periodically between a state shown inFIG. 20A and astate shown inFIG. 20Baccording to electrophoresis, i.e., a state where the charged phoretic particles3018are collected above the first electrodes4012(FIG. 20A) or a state where the charged phoretic particles4018are moved to a place above the second electrode4014not covered with the first electrodes4012(FIG.20B). If the voltage application is continued for a certain period, a certain amount of the charged phoretic particles are collected to the selected places shown inFIG. 20Aor20B.

The application voltage may have an amplitude up to 300 volts and a frequency of 0.01-50 Hz. Further, any voltage waveform may be used.

In the first step, the concentration of the charged phoretic particles4018in the dispersion liquid4017A need not be appropriately adjusted. As a result, an excessive amount of the charged phoretic particles4018can be present on or above the first electrodes4012and/or the second electrode4014, and also the charged phoretic particles4018can be present at a non-uniform charge distribution.

After the first step is completed according to the method ofFIG. 19or20, the following steps are taken.

FIGS. 21A and 21Billustrate a second step wherein an excessive portion of the charged phoretic particles4018are removed by washing with a dispersion liquid medium4017alone (or in mixture with a relatively small amount of charged phoretic particles4018as shown in FIGS.22A and22B).

The excessive portion of the charged phoretic particles4018herein means a portion having a lower charge of the charged phoretic particles4018in the dispersion liquid4017A and a portion of the charged phoretic particles4018having a nonuniform property thus possibly adversely affecting the electrophoretic performance of the charged phoretic particles4018.

In the washing step shown in FIGS.21A and21B, an AC voltage is applied between the first electrodes4012and the second electrode4014, and simultaneously the charged phoretic particles4018deposited on the electrode sheet4010possibly together with a minor proportion of the dispersion liquid4017are caused to contact freshly poured dispersion liquid4017. As a result, a portion of the charged phoretic particles4018relatively weakly constrained by electrophoretic power acting between the first electrodes4012and the second electrode4014are washed out of the electrode sheet4010.

The contacting with the dispersion liquid4017in the washing step may preferably be performed by dipping the electrode sheet4010after the first step within a bath of dispersion liquid medium4017alone or in mixture with charged phoretic particles4018or by ejecting or pouring a dispersion liquid medium4017alone or in mixture with charged phoretic particles4018onto the electrode sheet4010after the first step carrying the charged phoretic particles4018. The ejection or pouring of the dispersion liquid medium4017may preferably be performed from plural directions. In any case, the washing step may preferably be performed under a repetitive movement, such as rotation or vibration.

The voltage applied in the second step may preferably be smaller than in the first step within a range of up to 300 volts and may preferably have a frequency of 0.01-50 Hz. The voltage waveform is not particularly restricted.

FIG. 23illustrates a state of the electrode sheet4010after the second step wherein an excessive portion of charged phoretic particles4018have been removed (and also illustrates an optional third step). In this state, the charged phoretic particles418are disposed on the electrode sheet4018in an amount and a charge distribution appropriate for electrophoretic display. However, in order to adjust the concentration of the charged phoretic particles4018and supplement the dispersion liquid medium4017, a fresh portion of dispersion liquid medium4017may preferably be slowly added to over the electrode sheet4010to provide a dispersion liquid4017B suitable for electrophoretic display. The dispersion liquid medium4017may preferably contain a charge control agent dispersed therein, and the addition thereof may preferably be performed while applying an AC or DC voltage between the first electrodes4012and the second electrode4014.

FIG. 24illustrates a fourth step (assembling step). Referring toFIG. 24, in opposition to the electrode sheet4010carrying the dispersion liquid, a second substrate4013is applied, and simultaneously, an excess of the dispersion liquid medium4017is squeezed out, followed by bonding between the first and second substrates4011and4013. As a result, the dispersion liquid4017B comprising the medium4017and the charged phoretic particles4018is sealed up in the device. Until substantially completing the fourth step, it is preferred to continually apply some AC or DC voltage between the electrodes so as to prevent the movement of the charged phoretic particles4018as by connection of the dispersion liquid.

FIG. 25illustrate the application of a second electrode sheet identical to the electrode sheet4015instead of the second substrate4013shown in FIG.24.

The thus-prepared display device is driven in such a manner that the charged phoretic particles4018are moved in parallel with the substrate surfaces depending on potential differences between the first electrodes4012and the second electrode4014to a position above the first electrodes4012or a position above the second electrode4014not covered with the first electrodes4012. For example, as shown inFIGS. 26A and 26B, if the first electrodes4012are supplied with a negative voltage (FIG. 26A) or a positive voltage (FIG. 26B) relative to the second electrode4014grounded, positively charged phoretic particles are moved to one electrode of a relatively low potential (i.e., the first electrodes4012in FIG.16A and the second electrode4014in FIG.26B).

In this instance, in case where the charged phoretic particles4018and the first electrodes4012are colored in black and the second electrode4014is colored in white, a white display state is exhibited when the charged phoretic particles4018are collected above the first electrodes4012(FIG. 26A) and a black display state is exhibited when the charged phoretic particles4018are collected at a position above the second electrode4014not covered with the first electrodes4012(FIG.26B).

Some specific examples of the above-described process will be described hereinbelow.

Referring toFIG. 18, a dispersion liquid medium4017was formed by dispersing a charge control agent (not specifically shown) in a principally aliphatic hydrocarbon liquid “ISOPER” (trade name), made by Exxon Co.), and black polystyrene particles having an average particle size of 1-2 μm as charged phoretic particles4018were dispersed therein to form a dispersion liquid4017A. The concentration of charged phoretic particles4018in the dispersion liquid4017A was set to be lower than that in the objective electrophoretic display device finally produced.

A separately prepared electrode sheet4010comprising a 10 cm-square PET film substrate4011of 100 μm in thickness and provided with first electrodes4012and the second electrode4014was dipped in the dispersion liquid4017A contained in a vessel (not shown) with its electrode-provided surface directed upwards. Then, the electrode sheet4010was slowly pulled out of the bath of dispersion liquid4017A. As a result, a state as shown inFIG. 19where the electrode sheet4010was covered with the dispersion liquid4017A was formed but with a less amount of the charged phoretic particles4018than shown in FIG.19.

Then, as a second step as shown inFIGS. 21A and 21B, the electrode sheet4010was held in a slightly oblique state with application of a rectangular AC voltage of ±40 volts and 1 Hz, and a fresh dispersion liquid medium4017containing a charge control agent was slowly poured over the electrode-provided surface covered with the charged phoretic particles4018of the electrode sheet4010.

The above operation was performed by slowly rotating the electrode sheet4010about a vertical line passing through a center of the electrode sheet4010as a rotation axis.

The above-mentioned first and second step operations were repeated 5 times.

Then, as a third step, while applying a DC voltage of 200 volts between the first electrodes4012(as positive electrode) and the second electrode4014(as negative electrode), a dispersion liquid medium4017containing a charge control agent dispersed therein was poured over the electrodes on the electrode sheet4016shown in FIG.23.

Then, as a fourth step, as shown inFIG. 24, while the DC voltage application was continued, a second substrate4013was disposed opposite to and gradually pressed against the electrode sheet4010to squeeze out an excessive portion of the dispersion liquid medium4017.

Thereafter, the periphery and other bonding portions of the electrode sheet4010and the second substrate4013were bonded under heating to seal up a dispersion liquid4017B comprising the dispersion liquid medium4017and the charged phoretic particles4018within a gap of 20 μm retained between the substrates.

The thus-formed electrophoretic display device exhibited a contrast of 8 at a response speed of ca. 10 msec when supplied with a drive voltage of ±40 volts between the first electrodes4012and the second electrode4014.

A dispersion liquid medium4017, charged phoretic particles4018, a dispersion liquid4017A and an electrode sheet4010were prepared in the same manner as in Example 4-1.

Then, as a first step, while holding the electrode sheet4010obliquely at an angle of ca. 30 deg. from the horizon and slowly vibrating the electrode sheet4010, the dispersion liquid4017A was ejected against the electrode-provided surface of the electrode sheet4010, to provide a state of the electrode sheet4010carrying the charged phoretic particles as shown inFIG. 19but with less charged phoretic particles than shown therein.

Then, as a second step as shown inFIGS. 21A and 21B, the electrode sheet4010was held in a slightly oblique state with application of a rectangular AC voltage of ±40 volts and 1 Hz, and a fresh dispersion liquid medium4017containing a charge control agent was slowly poured over the electrode-provided surface covered with the charged phoretic particles4018of the electrode sheet4010.

The above operation was performed while slowly rotating the electrode sheet4010about a vertical line passing through a center of the electrode sheet4010as a rotation axis.

The above-mentioned first and second step operations were repeated 4 times.

By using the electrode sheet4010thus treated, the third and following steps were performed in the same manner as in Example 4-1 to obtain an electrophoretic display device.

The thus-formed electrophoretic display device exhibited a contrast of 8 at a response speed of ca. 10 msec when supplied with a drive voltage of ±40 volts between the first electrodes4012and the second electrode4014.

A dispersion liquid medium4017, charged phoretic particles4018, a dispersion liquid4017A and an electrode sheet4010were prepared in the same manner as in Example 4-1.

Then, as a first step, the dispersion liquid4017A was uniformly printed on the electrode-provided surface of the electrode sheet4010.

Then, as a second step as shown inFIGS. 21A and 21B, the electrode sheet4010was held in a slightly oblique state with application of a rectangular AC voltage of ±40 volts and 1 Hz, and a fresh dispersion liquid medium4017containing a charge control agent was slowly poured over the electrode-provided surface covered with the charged phoretic particles4018of the electrode sheet4010.

The above operation was performed while slowly rotating the electrode sheet4010about a vertical line passing through a center of the electrode sheet4010as a rotation axis.

The above-mentioned first and second step operations were repeated 4 times.

By using the electrode sheet4010thus treated, the third and following steps were performed in the same manner as in Example 4-1 to obtain an electrophoretic display device.

The thus-formed electrophoretic display device exhibited a contrast of 8 at a response speed of ca. 10 msec when supplied with a drive voltage of ±40 volts between the first electrodes4012and the second electrode4014.

A dispersion liquid medium4017, charged phoretic particles4018, a dispersion liquid4017A and an electrode sheet4010were prepared in the same manner as in Example 401.

Then, as a first step, the electrode sheet4010was dipped in the dispersion liquid4017A with its electrode-provided surface directed downwards while slowly stirring the dispersion liquid4017A. Immediately thereafter, a rectangular AC voltage of ±60 volts and 1 Hz was started to be applied between the first electrodes4012and the second electrode4014. The voltage application was continued for 3 min.

Then, the level of the dispersion liquid4017A in the vessel was gradually lowered to take the electrode sheet4010out of the dispersion liquid4017A.

Then, as a second step as shown inFIGS. 21A and 21B, the electrode sheet4010was held in a slightly oblique state with application of a rectangular AC voltage of ±40 volts and 1 Hz, and a fresh dispersion liquid medium4017containing a charge control agent was slowly poured over the electrode-provided surface covered with the charged phoretic particles4018of the electrode sheet4010.

The above operation was performed while slowly rotating the electrode sheet4010about a vertical line passing through a center of the electrode sheet4010as a rotation axis.

The above-mentioned first and second step operations were repeated 3 times.

By using the electrode sheet4010thus treated, the third and following steps were performed in the same manner as in Example 4-1 to obtain an electrophoretic display device.

The thus-formed electrophoretic display device exhibited a contrast of 8 at a response speed of ca. 10 msec when supplied with a drive voltage of ±40 volts between the first electrodes4012and the second electrode4014.

A dispersion liquid medium4017, charged phoretic particles4018, a dispersion liquid4017A and an electrode sheet4010were prepared in the same manner as in Example 4-1.

Then, as a first step, the dispersion liquid4017A was poured onto the electrode-provided surface of the electrode sheet4010, followed immediately by 3 minutes of application of a rectangular AC voltage of ±60 volts and 1 Hz.

Then, as a second step, while continuing the AC voltage application, the electrode sheet4010was dipped in a bath of the dispersion liquid4017A under slow stirring with its electrode-provided surface directed downwards and slowly rotated therein for 3 min.

The above-mentioned first and second steps were repeated 4 times.

Then, as a third step, while continuing the AC voltage application, the dispersion liquid4017A was poured onto the electrode sheet4010which was held obliquely and slowly rotated about a vertical line passing through the center of the electrode sheet4010as a rotation axis.

By using the electrode sheet4010thus treated, the fourth and following steps were performed in the same manner as in Example 4-1 to obtain an electrophoretic display device.

The thus-formed electrophoretic display device exhibited a contrast of 8 at a response speed of ca. 10 msec when supplied with a drive voltage of ±40 volts between the first electrodes4012and the second electrode4014.

A dispersion liquid medium4017and charged phoretic particles4018were prepared in the same manner as in Example 4-1.

Then, a mixture of the dispersion liquid medium and the charged phoretic particles was placed between a pair of electrode plates in a vessel (not shown), and by applying a DC voltage of 200 volts between the electrode plates, thereby selectively recovering a majority of the charged phoretic particles charged to a positive polarity. Then, the thus selected charged phoretic particles were dispersed in a fresh dispersion liquid medium4017to prepare a dispersion liquid4017A at a concentration lower than that in an objective electrophoretic display device finally produced.

Then, as a first step, the dispersion liquid4017A was filled in a vessel (not shown), and an electrode sheet4010prepared similarly as in Example 4-1 was dipped in the dispersion liquid4017A with its electrode-provided surface directed downwards. Immediately thereafter, a rectangular AC voltage of ±60 volts and 1 Hz was applied for 6 min. between the first electrodes4012and the second electrode4014.

Then, as a second step as shown inFIGS. 21A and 21B, the electrode sheet4010was held in a slightly oblique state with application of a rectangular AC voltage of ±40 volts (lower than in the first step) and 1 Hz, and a fresh dispersion liquid medium4017containing a charge control agent was slowly poured over the electrode-provided surface covered with the charged phoretic particles4018of the electrode sheet4010.

The above operation was performed while slowly rotating the electrode sheet4010about a vertical line passing through a center of the electrode sheet4010as a rotation axis.

The above-mentioned first and second step operations were repeated 2 times.

By using the electrode sheet4010thus treated, the third and following steps were performed in the same manner as in Example 4-1 to obtain an electrophoretic display device.

The thus-formed electrophoretic display device exhibited a contrast of 8 at a response speed of ca. 10 msec when supplied with a drive voltage of ±40 volts between the first electrodes4012and the second electrode4014.

A dispersion liquid medium4017, charged phoretic particles4018, a dispersion liquid4017A and an electrode sheet4010were prepared in the same manner as in Example 401.

Then, as a first step, the electrode sheet4010was dipped in a bath of the dispersion liquid4017A with its electrode-provided surface directed upwards.

Then, the electrode sheet4010was slowly pulled out of the bath of dispersion liquid4017A. As a result, a state as shown inFIG. 19where the electrode sheet4010was covered with the dispersion liquid4017A was formed but with a less amount of the charged phoretic particles4018than shown in FIG.19.

Then, as a second step as shown inFIGS. 22A and 22B, the electrode sheet4010was held in a slightly oblique state with application of a rectangular AC voltage of ±40 volts and 1 Hz, and a fresh dispersion liquid4017A containing a charge control agent and charged phoretic particles4018was slowly poured over the electrode-provided surface covered with the charged phoretic particles4018of the electrode sheet4010.

The above operation was performed while slowly rotating the electrode sheet4010about a vertical line passing through a center of the electrode sheet4010as a rotation axis.

The above-mentioned first and second step operations were repeated 3 times.

By using the electrode sheet4010thus treated, the third and following steps were performed in the same manner as in Example 4-1 to obtain an electrophoretic display device.

The thus-formed electrophoretic display device exhibited a contrast of 8 at a response speed of ca. 10 msec when supplied with a drive voltage of ±40 volts between the first electrodes4012and the second electrode4014.

An electrophoretic display device as illustrated inFIG. 25including two electrode sheets (i.e., a first electrode sheet4045farther from a viewer and a second electrode sheet4046closer to the viewer) was produced in the following manner.

Each of the first and second electrode sheets4045and4046was prepared in the same manner as the electrode sheet4010in Example 4-1 except that the first electrodes4042and the second electrode4044on the second electrode sheet4046were formed of transparent indium tin oxide (ITO). Moreover, a dispersion liquid medium4017, charged phoretic particles4018and a dispersion liquid4017A were prepared in the same manner as in Example 4-1.

The first electrode sheet4045was dipped in the dispersion liquid4017A with its electrode-provided surface directed downwards while slowly stirring the dispersion liquid4017A. Immediately thereafter, a rectangular AC voltage of ±60 volts and 1 Hz was started to be applied between the first electrodes4012and the second electrode4014. The voltage application was continued for 3 min.

Then, the level of the dispersion liquid4017A in the vessel was gradually lowered to take the electrode sheet4010out of the dispersion liquid4017A.

Then, as a second step as shown inFIGS. 21A and 21B, the electrode sheet4010was held in a slightly oblique state with application of a rectangular AC voltage of ±40 volts (lower than in the first step) and 1 Hz, and a fresh dispersion liquid medium4017containing a charge control agent was slowly poured over the electrode-provided surface covered with the charged phoretic particles4018of the electrode sheet4010.

The above operation was performed while slowly rotating the electrode sheet4010about a vertical line passing through a center of the electrode sheet4010as a rotation axis.

The above-mentioned first and second step operations were repeated 3 times.

The second electrode sheet4046was treated in the same manner as the first electrode sheet4045described above.

Then, as a third step, as shown inFIG. 25, while the DC voltage was continually applied between the first electrodes4012and the second electrode4014and between the first electrodes4042and the second electrode4044, the second electrode sheet4046was disposed opposite to and slowly pressed against the first electrode sheet4045to squeeze out an excessive portion of the dispersion liquid medium4017.

Thereafter, the periphery and other bonding portions of the first electrode sheet4045and the second electrode sheet4046were bonded under heating to seal up a dispersion liquid4017B comprising the dispersion liquid medium4017and the charged phoretic particles4018within a gap of 15 μm retained between the substrates to form an electrophoretic display device.

An AC drive voltage of ±25 volts was applied synchronously between the first electrodes4012and the second electrode4014on the first electrode sheet4045and between the first electrodes4042and the second electrode4044on the second electrode sheet4045, whereby the electrophoretic display device exhibited a contrast of 8 at a response time of ca. 7 msec.

As described above, according to Fourth Embodiment of the present invention as a process for producing an electrophoretic display device including a step of filling an electrophoretic dispersion liquid containing charged phoretic particles, it is possible to remove a portion of charged phoretic particles having a lower charge and a desired concentration distribution of charged phoretic particles by including a washing step using a dispersion liquid medium even in the case of a very small gap between a pair of substrates or the case of using a flexible substrate. As a result, it becomes possible to produce an electrophoretic display device having a very small gap between the substrates, which can exhibit a high contrast at a lower drive voltage than in the known devices.

FIGS. 28-35illustrate various steps involved in this embodiment of process for producing an electrophoretic (display) device, andFIGS. 36-37illustrate the organization and operation of the resultant devices. In most figures, only two cell sections (display cells or pixels), are shown for convenience of illustration but actual devices include larger number of such cells two-dimensionally arranged. In these figures, common numerals or symbols are used for representing identical members. More specifically, these figures commonly show member, such as a first substrate5001, a first electrode5002, a second substrate5003, a second electrode5004, a spacer5007also functioning as a partitioning wall for partitioning the device and the dispersion liquid (system) contained thereinto small cell sections as mentioned above, a dispersion liquid medium5008, charged phoretic particles5009, a voltage application circuit5040, a nozzle5050, a fluorine-containing resin layer5060, a closed vessel5065, an ultrasonic wave applicator5070, and an electrophoretic device (panel)50100.

In most figures, there is shown a device example wherein first electrodes5002and second electrodes5004are formed on an identical substrate, particularly on a first substrate5001for convenience of convenience of described, which can be prepared by a process, e.g., as disclosed in JP-A 11-202804. This is however just an example, and the present invention is not restricted thereto. For example, the pair of first and second electrodes can be formed on the second substrate5003, and the present invention also allows the disposition of the first electrodes5002and the second electrodes5004on one and the other substrate, respectively.

Incidentally, in a display device having the above-mentioned pair of first electrode and second electrode are disposed on one substrate, unlike in a conventional device as illustrated inFIGS. 1A and 1B, charged phoretic particle5009are moved between first electrode and second electrode horizontally, i.e., in parallel to the substrate extension, within the dispersion liquid medium, to either a position above the first electrode5002or a position above the second electrode5004not covered by the first electrode5002depending on a potential difference between these electrodes, thereby effecting a display.

For example, for positively charged phoretic particles5009, when a positive or a negative voltage is applied to the first electrodes5002while the second electrode5004is grounded as shown inFIGS. 36A and 36B, the positively charged phoretic particle5009are moved to an electrode of a lower potential (i.e., the first electrode5002inFIG. 36Aor the second electrode5004in FIG.3B). Then, in the case where the charged phoretic particle5009and the first electrodes5002are colored in black, and the second electrode5004is colored in white, a white state is displayed when the charged phoretic particles5009are collected above the first electrodes5002, and a black state is displayed when the charged phoretic particles5009are collected at a position above the second electrode5004not covered by the first electrodes5002.

The process of the present invention is classified into two modes, i.e., a first mode wherein charged phoretic particles are attached to at least one of two substrates, then the two substrates are applied to each other to form a non-filled device (panel), and then a dispersion liquid medium is injected into the device, and a second mode wherein a dispersion liquid is disposed on a substrate prior to application of the two substrate. The following Embodiments 5-1 and 5-2 are embodiment according to the first mode, and Embodiment 5-3 is an embodiment according to the second mode.

According to this embodiment, the process for producing an electrophoretic (display) device comprises sequential steps including a first step of causing an electrode sheet provided with a pair of electrodes to contact a dispersion liquid while applying a voltage between the electrodes; a second step of vaporizing a portion of the dispersion liquid medium in the dispersion liquid on the electrode sheet; a third step of applying two substrates including the electrode sheet to each other; a fourth step of filling the dispersion liquid medium between the substrates to form a dispersion liquid; a fifth step of sealing up the dispersion liquid within the device (panel); and a sixth step of imparting vibration to the charged phoretic particles to cause a diffusion of the charged phoretic particles in the dispersion liquid medium. The respective steps will be described in further detail below.

A dispersion liquid is caused to contact an electrode-provided surface of an electrode sheet while applying a voltage between a pair of electrodes provided to the electrode sheet.

The contact of the first substrate (as electrode sheet) with a dispersion liquid may be performed in various ways, e.g., by dipping the first substrate5001within a dispersion liquid5008A comprising a mixture of a dispersion liquid medium5008and charged phoretic particles5009(FIGS.28A-28C); pouring of the dispersion liquid5008A over the first substrate5001(FIGS.29A-29C), etc. In this instance, by applying a voltage of alternating polarities (i.e., an AC voltage) between the first electrodes5002and the second electrode5004as shown inFIGS. 28A and 28B, etc. it becomes easy to control the amount of charged phoretic particles5009attracted to the first substrate5001.

In the case of dipping within the dispersion liquid5008A, it is possible to dip the first substrate5001with its electrode-provided surface directed downward, and then pull the first substrate5001out of the dispersion liquid while continually applying a voltage between the electrodes (FIG.28C). In this instance, it is also possible to incline the first substrate at an appropriate angle between 1 deg. to 179 deg. at the time of pulling the first substrate out of the dispersion liquid5008A. Any manner allowing removal of an excess of the dispersion liquid medium5008may be adopted.

In the case of pouring the dispersion liquid5008A onto the first substrate, it is preferred to hold the first substrate5001at an appropriately inclined state and apply a voltage between the electrodes thereby removing an excess of the dispersion liquid5008A, particularly the dispersion liquid medium5008(FIG.29C). In this instance, the first substrate5001can be vibrated or rotated so as to effectively remove the excessive dispersion liquid5008A. The inclination angle may be any angle within 1 to 177 deg., but preferably 30 to 150 deg.

The voltage applied between the electrodes may be controlled depending on the cell size (pixel size) so as to retain an amount of charged phoretic particles5009attracted to the first electrode5002or second electrode5004sufficient for providing a dispersion liquid for electrophoretic display and obtain a desired charge distribution of the charged phoretic particles5009. The voltage applied for these purposes may have an amplitude of 1 to 300 volts and a frequency of 0.01 to 50 Hz, and may preferably be applied for ca. 5 to 10 min. The voltage waveform is not particularly restricted.

The substrate may comprise a film of a heat-resistant resin, such as PET (polyethylene terephthalate) or PES (polyether sulfone), or an inorganic material, such as glass or quartz. However, in view of the application of vibration, it is preferred to use a breakage-resistant material, e.g., a resin such as PET, than an inorganic material, such as glass. The thickness may appropriately selected depending on the usage.

The electrodes5002and5004may be formed of a metal or a metal oxide, e.g., Al, Au, Pt, Ag, Ni, Ti, Cr, ITO (indium tin oxide), ZnO, SnO2, etc. The electrodes on the viewer's side substrate may preferably be composed of a transparent electrode material, such as ITO.

The electrophoretic particles (charged phoretic particles) may representatively comprise titanium oxide (titanium white), but may also be formed from appropriately selected other materials, such as well-known colloid particles, various organic and inorganic pigments, dyes, metal powders, fine powders of glass and resins, these materials further containing a colorant, and a mixture of polystyrene and carbon black. The particle size may ordinarily range from 0.1 to 50 μm. For allowing a high-resolution display, a particle size of ca. 0.1 to 5 μm is preferred. If the process of the present invention is adopted, a dispersion liquid containing such minute electrophoretic particles at an appropriate concentration can be sealed up within the display device at a good dispersion state.

Electrophoretic particles of identical species of material are ordinarily charged to an identical polarity, but in case where a dispersion liquid contains a portion of charged phoretic particles having a different polarity, such a portion may preferably be removed by electrophoresis, etc. to select charged phoretic particles of an identical polarity, prior to deposition of the charged phoretic particles on the substrate.

The dispersion liquid medium may comprise any insulating liquid, examples of which may include: silicone oil, toluene, xylene, high-purity petroleum, and isoparaffinic hydrocarbons. The dispersion liquid medium can be used in mixture with a colorant as far as the insulating property is not impaired thereby.

The dispersion liquid may preferably contain a charge control agent. This is also effective for controlling the charge of the charged phoretic particles to provide a designed adsorption force for adsorbing the charged phoretic particles5009onto the electrodes in the state of voltage application for electrophoretic display of the product display device.

By controlling the charge of the charged phoretic particles, it is possible to provide a good compromise between display memory characteristic and degradation of display quality. More specifically, a larger charge of charged phoretic particles provides a better display memory characteristic due to stronger adsorption of charged phoretic particles onto the electrodes at a stronger inter-molecular force, but too large a charge is liable to gradually result in sticking of the charged phoretic particles onto the electrodes, thus resulting in an inferior contrast. The appropriate charge control can obviate such a difficulty.

The charge control agent may be a positive charge control agent or a negative charge control agent. As positive charge control agents, it is possible to use a naphthenic acid salt of a metal, such as cobalt, manganese or iron, zirconium octenate, etc. and as negative control agents, it is possible to use lecithin, calcium petroleum-sulfonate, calcium alkylbenzene-sulfonate, sodium dioctylsulfonate, alkylalanine, etc. Such a charge control agent may be contained in either a dispersion liquid medium or disposed phoretic particles, or in both of them.

An appropriate portion of the dispersion liquid medium5008is evaporated off. The degree of vaporization may preferably be such as to provide a state where the charged phoretic particles are just wetted with the dispersion liquid medium5008(FIG.30).

By including this step, a good bonding state can be obtained in the subsequent step of bonding the two substrates as substantially no dispersion liquid medium remains at the bonding surfaces, and the charged phoretic particles are well retained on the substrate due to a surface tension of the remaining dispersion liquid medium5008, thus obviating the separation or floating of the charged phoretic particles5009until a later step of injection of the dispersion liquid medium5008into a non-filled device.

The evaporation of the dispersion liquid medium5008can also be effected by natural cooling in the atmosphere, but a drying in a closed atmosphere, such as in a desiccator may be preferred. It is also possible to apply heat, as desired, for promoting the evaporation.

The first substrate5001and the second substrate5003are bonded to each other to form a non-filled device while leaving an injection port for injecting an additional portion of dispersion liquid medium in a later step.

The bonding agent may for example be a hot melt adhesive or an ultraviolet-curable adhesive (inclusive of a commercially available UV-curable adhesive of “Luxtrak LCR 0634”, made by Toa Gosei K.K.

The non-filled device is placed at a gaseous phase in a closed vessel5065containing a prescribed volume of dispersion liquid medium5008, and the gaseous phase is evacuated to a reduced pressure below the atmospheric pressure. Then, the non-filled device is immersed in the bath of dispersion liquid medium5008, and the gaseous phase is restored to the atmospheric pressure, thereby injecting the dispersion liquid medium5008through the injection port to fill the device50100(FIG.33).

In this instance, it is preferred to apply an appropriate strength of DC voltage in the range of 1 to 300 volts between the electrodes502and5004so as to attract the charged phoretic particles5009to the electrodes thereby obviating the disturbance or movement of the charged phoretic particles into adjacent cells due to flow of the injected dispersion liquid medium5008.

The filled device50100is taken out of the closed vessel5065, and the injection port is plugged with an adhesive to seal up the dispersion liquid5008B within the device50100. Also in this plugging operation, it is preferred to apply a voltage between the first electrodes5002and the second electrode5004so as to attract the charged phoretic particles toward the electrodes (FIG.34).

A vibration is imparted to the charged phoretic particles5009localized at the electrodes to diffuse the charged phoretic particles5009in respective cells.FIG. 35illustrates an example of this step performed by applying ultrasonic wave to the device50100from an ultrasonic applicator5070via a vibration-transmission medium5170in which the device50100is immersed. Alternatively, it is also possible to apply a mechanical imparting force by impingement of liquid droplets, a solid member, such as a hammer in a strength not adversely affecting the device per se. It is also possible to apply external electromagnetic force without via the electrodes5002are5004. In this instance, it is preferred to simultaneously apply a DC voltage of, e.g., +15 volts, to both electrodes, of a polarity identical to the charge polarity of the charged phoretic particles5009in the dispersion liquid medium5008so as to promote the diffusion of the charged phoretic particles in the dispersion liquid medium5008. It is also possible to apply an AC voltage for promoting the diffusion of the charged phoretic particles.

The vibration-transmission medium5170may comprise a gas, a liquid or a solid capable of transmitting vibration, but it is preferred to use a liquid medium identical to the dispersion liquid medium5008contained in the device50100, such as silicone oil, toluene, xylene, high-purity petroleum, or isoparaffinic hydrocarbon.

The strength of the vibration may be appropriately selected depending on the strength of the substrates and also the strength of agglomeration of the charged phoretic particles, and the frequency may be selected from a range of 10 Hz to 100 kHz. For example, in the case of using a PET substrate and charged phoretic particles comprising a polystyrene-carbon mixture, a frequency of 1 to 50 kHz may suitably be used.

Incidentally, the above process can also be performed by using an electrode sheet provided with a pair of electrodes also as a second substrate. In this case, the above-described first and second steps are applied to both the first and second substrates and the thus-processed first and second substrates are subjected to the subsequent steps starting from the third step of bonding the first and second substrates to each other. In this case, either one of the first and second substrate5001and5003is provided with electrodes of transparent conductor materials.

According to this embodiment, the process for producing an electrophoretic (display) device comprises sequential steps including a first step of printing an ink containing charged phoretic particles onto a substrate; a second step of applying two substrates to each other; a third step of filling the dispersion liquid medium between the substrates to form a dispersion liquid; a fourth step of sealing up the dispersion liquid within the device (panel); and a fifth step of imparting vibration to the charged phoretic particles to cause a diffusion of the charged phoretic particles in the dispersion liquid medium. The respective steps will be described in further detail below.

An ink containing charged phoretic particles is printed on a substrate (either a first substrate or a second substrate). According to this method, it is possible to easily control the deposition amount of the charged phoretic particles per unit area on the substrate, thereby later providing a dispersion liquid for electrophoretic display having an appropriate concentration and its distribution. In this instance, it preferred to pre-coat the surface to be printed of the substrate with a fluorine-containing resin so as to promote the separation and diffusion of the charged phoretic particles in a later step.FIG. 32illustrates a case of printing on a second substrate5003.

Any fluorine-containing resin promoting releasability may be used inclusive of “FLUORADO FC-722” (made by Sumitomo 3M K.K.). In this case of printing on a viewer's side substrate, it is necessary to use a transparent fluorine-containing resin inclusive of “CYTOP” (made by Asahi Garasu K.K.).

The substrate printed with charged phoretic particles5009is bonded with its printed side directed inwards to another substrate while leaving an injection port for injecting a dispersion liquid medium5008in a later step (not shown).

These steps are substantially identical to Fourth to Sixth steps of Embodiment 5-1.

According to this embodiment, the process for producing an electrophoretic (display) device comprises sequential steps including a first step of distributing a dispersion liquid through a nozzle onto a substrate provided with a spacer, a second step of bonding another substrate to seal up the dispersion liquid within the device (panel); and a third step of imparting a vibration to the charged phoretic particles to cause a diffusion of the charged phoretic particles in the dispersion liquid medium. The respective steps will be described in further detail below.

Onto a first substrate5001provided with a spacer5007, a dispersion liquid comprising a mixture of a dispersion liquid medium and charged phoretic particles5009is distributed to cells defined by the spacer5007on the first substrate5001. As a result, it is possible to easily control the amount of the dispersion liquid per unit area on the first substrate, thereby providing a dispersion liquid for electrophoretic display having an appropriate concentration of charged phoretic particles (FIG.34).

While retaining the distributed state of the dispersion liquid on the first substrate5001, another substrate is bonded thereto to seal up the dispersion liquid in the resultant device.

In the above first and second steps, it is preferred to apply a DC voltage of, e.g., 10 to 100 volts between the first electrodes5002and the second substrate5004, thereby preventing the flowing of the charged phoretic particles5009out of the cells.

This step is substantially identical to Sixth step of Embodiment 5-1.

Some specific examples of the above-described Examples will be described below.

This is an example of Embodiment 5-1.

In this example, on a ca. 200 μm-thick PET film, an ITO electrode was formed as a second electrode5004which could be observed in white by reflection, first electrodes5002having a lower metal layer coated with a dark black-color resist layer were formed, and a spacer5007was formed of a photoresist, to provide a first substrate5001(as an electrode sheet). Ca. 1 to 2 μm-dia. black electrophoretic particles5009were formed of a polystyrene-carbon mixture, and mixed with a dispersion liquid medium5008comprising a principally hydrocarbon liquid (“ISOPER” made by Exxon K.K.) containing rosin ester as a charge control agent to provide a dispersion liquid5008A; wherein the charged phoretic particles5009were positively charged. The concentration of the charged phoretic particles5009was set to be lower than that in the objective electrophoretic display device finally produced.

Into a bath of the above-prepared dispersion liquid5008under mild stirring, the above prepared first substrate5001was dipped with its electrode-provided surface directed downwards. Immediately thereafter, a rectangular AC voltage of ±60 volts and 1 Hz was started to be applied between the first electrodes5002and the second electrode5004. The voltage application was continued for 8 min. (FIG.28A).

Then, a DC voltage of 120 volts was applied between the first electrodes5002(negative) and the second electrode5004(positive) so as to attract the positively charged phoretic particles5009to the first electrodes5002, and in this state, the level of the dispersion liquid5008A in the vessel was gradually lowered to take the first substrate5001out of the dispersion liquid5008A (FIG.28C).

Then, the first substrate5001carrying the charged phoretic particles5009together with a substantial amount of the dispersion liquid medium5008was placed in a dessiccator to evaporate off the dispersion liquid medium5008to a state of just wetting the charged phoretic particles5009(FIG.30).

The peripheries and other bonding parts of the above-treated first substrate5001and a second substrate5003(of also a ca. 200 m-thick PET film) were heat-bonded with an adhesive (“STAFIX”, made by Fuji Film K.K.) while leaving an injection port for injecting an additional dispersion liquid medium in a later step to form a non-filled device.

The non-filled device was placed at a gaseous phase of a closed vessel5065containing a prescribed volume of dispersion liquid medium5008, and the gaseous phase was evacuated to a reduced pressure below the atmospheric pressure. Then, the non-filled device was immersed in the dispersion liquid medium5008while applying a DC voltage of 200 volts between the first electrodes5002(negative) and the second electrode5004(positive), so as to attract the positively charged phoretic particles5009at the first electrodes5002.

Then, the pressure of the gaseous phase in the closed vessel5065was restored to the atmospheric pressure to inject the dispersion liquid medium5008through the injection port into the device50110(FIG.33).

Then, the device50100was quickly taken out of the closed vessel5065, and the injection port was plugged with an adhesive (FIG.34).

The filled device50100was then immersed in a vibration-transmission fluid5170(“ISOPER”, made by Exxon Co.; identical to the dispersion liquid medium5008except for not containing a charge control agent) contained in an ultrasonic wave applicator5070, wherein the device50100was supplied with a vibration at a frequency of 50 kHz so as to diffuse the charged phoretic particles localized in the dispersion liquid5008B, while supplying a DC voltage of +15 volts to both the first electrodes5002and the second electrode5004, i.e., the sample polarity of voltage as the charged potential of the charged phoretic particles5009(FIG.35).

Through the above steps, an electrophoretic display device having a cell size of 100 μm-square was formed by using small particle-sized charged phoretic particles5009. The electrophoretic display device50110thus-prepared exhibited a display contrast of 8 at a response speed of ca. 10 msec when supplied with a drive voltage of ±40 volts between the first electrodes5002and the second electrode5004from the voltage application circuit5040.

This is also an example of Embodiment 5-1.

The materials used were identical to those in FIG. 5-1.

The dispersion liquid5008A was ejected at a rate of 10 ml/sec for 6 min. out of a 100 μm-dia. nozzle onto the electrode-provided surface of the first substrate5001held obliquely at an angle of ca. 30 deg. from the horizon while a rectangular AC voltage of ±60 volts and 1 Hz was applied between the first electrodes5002and the second electrode5004(FIGS.29A-29C).

The above-treated first substrate5001was subjected to substantially identical treatments as in Second and Sixth steps of Example 5-1. The resultant electrophoretic display device exhibited similar performances as in Example 5-1.

This is an example of Embodiment 5-3.

The materials used were identical to those in Example 5-1 except for the bonding agent.

A dispersion liquid5008B (having a charged phoretic particle concentration identical to that for electrophoretic display) was distributed to cells defined by the spacer5007while applying a DC voltage of 50 volts between the first electrodes5002(negative) and the second electrode5004(positive) so as to attract the charged phoretic particles5009to the first electrodes5002(FIG.31).

The peripheries and other bonding portions of the above-treated first substrate5001and the second substrate5002were bonded to each other with a UV-curable adhesive (“LUXTRAK LCR0634”, made by Toa Gosei K.K.) while applying a DC voltage of 100 volts between the first electrodes5002(negative) and the second electrode5004(positive) so as to attract the charged phoretic particles5009to the first electrodes5002to form a display device50100(FIG.34).

Liquid droplets were ejected at a rate of 10 ml/sec from a 100 μm-dia. nozzle onto the display device50100so as to apply a vibration to the charged phoretic particles5009in the dispersion liquid5008B while applying a DC voltage of +15 volts (of an identical polarity to the charge of the phoretic particles5009) to both the first electrodes5002and the second electrode5004.

The thus-produced electrophoretic display device exhibited similar performances as in Example 5-1.

This is an example of Embodiment 5-2.

The materials used were identical to those used in Example 5-1 except for the use of a second substrate coated with a fluorine-containing resin.

Electrophoretic particles5009were provided by means of copying apparatus (not shown) onto a second substrate5003coated with a layer5060of a fluorine-containing resin (“CYTOP”, made by Asahi Garasu K.K.)

Except for the use of the thus-treated second substrate and the untreated first substrate, the operations of Third to Sixth steps of Example 5-1 were repeated.

The thus-produced electrophoretic display device exhibited similar performances as in Example 5-1.

This is an example of Embodiment 5-2.

The materials used were identical to those used in Example 5-1 except for the use of a first substrate coated with a fluorine-containing resin.

Electrophoretic particles5009were provided by means of copying apparatus (not shown) onto a first substrate5001coated with a layer5060of a fluorine-containing resin (“FLUORADO”, made by Sumitomo 3M K.K.)

Except for the use of the thus-treated first substrates, the operations of Third to Sixth steps of Example 5-1 were repeated.

The thus-produced electrophoretic display device exhibited similar performances as in Example 5-1.

An electrophoretic display device as illustrated inFIGS. 37A and 37Bincluding two electrode sheets (i.e., a first electrode sheet5001farther from a viewer and a second electrode sheet5003closer to the viewer) was produced in the following manner.

Each of the first and second electrode sheets5001and5003was prepared in the same manner as the electrode sheet5010in Example 5-1 except that the first electrodes5002and the second electrode5004on the second electrode sheet5003were formed of transparent indium tin oxide (ITO). Moreover, a dispersion liquid medium5008, charged phoretic particles5009and a dispersion liquid5008A were prepared in the same manner as in Example 5-1.

The first substrate5001was dipped in the dispersion liquid5008A with its electrode-provided surface directed downwards. Immediately thereafter, a rectangular AC voltage of ±60 volts and 1 Hz was started to be applied between the first electrodes5002and the second electrode5004. The voltage application was continued for 8 min. (FIG.28A).

Then, the level of the dispersion liquid5008A in the vessel was gradually lowered to take the first substrate5001out of the dispersion liquid5008A while applying a DC voltage of 120 volts between the first electrodes5002(as positive electrode) and the second substrate5004(as negative electrode) (FIG.28C).

Then, as a second step, the electrode sheet5010carrying the charged phoretic particles5009was inverted upside-down, and the voltage was released.

Then, the first substrate5001carrying the charged phoretic particles5009together with a substantial amount of the dispersion liquid medium5008was placed in a desiccator to evaporate off the dispersion liquid medium5008to a state of just wetting the charged phoretic particles5009(FIG.30).

The second substrate5003was also subjected to First and Second steps similarly as above.

The peripheries and other bonding parts of the above-treated first substrate5001and a second substrate5003were heat-bonded with an adhesive (“STAFIX”, made by Fuji Film K.K.) while leaving an injection port for injecting an additional dispersion liquid medium in a later step to form a non-filled device.

The non-filled device was placed at a gaseous phase of a closed vessel5065containing a prescribed volume of dispersion liquid medium5008, and the gaseous phase was evacuated to a reduced pressure below the atmospheric pressure. Then, the non-filled device was immersed in the dispersion liquid medium5008while applying a DC voltage of 200 volts between the first electrodes5002(negative) and the second electrode5004(positive), so as to attract the positively charged phoretic particles5009at the first electrodes5002.

Then, the pressure of the gaseous phase in the closed vessel5065was restored to the atmospheric pressure to inject the dispersion liquid medium5008through the injection port into the device50110(FIG.33).

Then, the device50100was quickly taken out of the closed vessel5065, and the injection port was plugged with an adhesive (FIG.34).

The filled device50100was then immersed in a vibration-transmission fluid5170(“ISOPER”, made by Exxon Co.; identical to the dispersion liquid medium5008except for not containing a charge control agent) contained in an ultrasonic wave applicator5070, wherein the device50100was supplied with a vibration at a frequency of 50 kHz so as to diffuse the charged phoretic particles localized in the dispersion liquid5008B, while supplying a DC voltage of +15 volts to both the first electrodes5002and the second electrode5004, i.e., the sample polarity of voltage as the charged potential of the charged phoretic particles5009(FIG.35).

Thereafter, the device50100was taken out of the ultrasonic applicator5070to obtain an electrophoretic display device.

The thus-obtained electrophoretic display device exhibited a contrast of 8 at a response time of ca. 7 msec when a drive voltage of ±50 volts was synchronously applied between the first electrodes5002and the second electrodes5004on the first and second electrodes respectively.

As described above, according to Fifth embodiment of the present invention, it becomes possible to realize a good distribution state of charged phoretic particles, thereby providing an electrophoretic display device having improved resolution and contrast.

Hereinabove, the present invention has been described with reference to the production of an electrophoretic display device, but the device produced by the present invention is also applicable as another device also utilizing electrophoresis, such as a dimmer device and a photo-indicator.