CA2176483A1 - Formulations for improved electrophoretic display suspensions and related methods - Google Patents
Formulations for improved electrophoretic display suspensions and related methodsInfo
- Publication number
- CA2176483A1 CA2176483A1 CA002176483A CA2176483A CA2176483A1 CA 2176483 A1 CA2176483 A1 CA 2176483A1 CA 002176483 A CA002176483 A CA 002176483A CA 2176483 A CA2176483 A CA 2176483A CA 2176483 A1 CA2176483 A1 CA 2176483A1
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- Canada
- Prior art keywords
- suspension
- electrophoretic
- process according
- pigment particles
- percent
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
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Classifications
-
- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/165—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on translational movement of particles in a fluid under the influence of an applied field
- G02F1/166—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on translational movement of particles in a fluid under the influence of an applied field characterised by the electro-optical or magneto-optical effect
- G02F1/167—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on translational movement of particles in a fluid under the influence of an applied field characterised by the electro-optical or magneto-optical effect by electrophoresis
Abstract
The invention provides an electrophoretic suspension comprising a suspension medium including tetrachloroethylene, 5tthylidene-2-norbornene and an aromatic solvent including either a mixture of phenyl xylyl ethanes or a mixture of mono and dibenzyl toluene. The suspension further comprises a plurality of pigment particles dispersed in the suspension medium; a fluid dye dissolved in the suspension medium for providing a contrast with the pigment particles; and a charge control agent adsorbed on the pigment particles for preventing the pigment particles from agglomerating.
Description
WO 9511S363 ~17 6 ~ 8 3 PCT/US94113S17 FORMUL~TIONS FOR IMPROVED ELECIROPHORETIC DISPI~Y
SUSPENSIONS AND REI~TED METHODS
~ELATED APPLICATIONS
The acci~ee~ Copytele, Inc. is the record owner of U.S. Patent application entitled "SUSPENSION FOR USE IN ELECI~ROPHORETIC IMAGE DISPLAY
S SYSTEMS", Serial No. 08/092,749, filed on July 6, 1993 for Frederic E. Schubert and ~c~igne~l to Copytele, Inc.
TECHNICAL F~ELD OF THE INVENTION
This invention relates to electro-optical devices in general and, more particularly, to dielectric fluid suspension compositio~ for electrophoretic displays and related methods of m~mlf~ct~lre.
BACKGROUND ART
The electrophoretic effect is well known as the prior art is replete with p~tent~ and articles describing the effect. As described and discussed in the prior, the electrophoretic effect operates on the principle that certain particles, when suspended in a medium, can be electrically charged and thereby caused to migrate through the medium to an electrode of opposite charge. Electrophoretic image displays (EPIDs) implement the electrophoretic effect to produce desired im~f~es In prior art EPIDs, colored particles, which are charged either positively or negatively, are suspended in a dielectric fluid medium that is either clear or of a color which optically contrasts with the particles. ~he suspension is injected into a cell COlllplisi~g two parallel screen electrodes, at least one of which is tral~are.lt. The colored particles are caused to migrate to, and impinge upon, WO 9S/lS363 ,~ 1 7 6 ~ PCT/US94/13517 one of the screen electrodes under the application of an electric field, therebydisplacing the fluid me~ 1m at that electrode creating the desired image. When the polarity of the ~leld is reversed, the colored particles migrate to the opposite screen electrode.
For suitable example of such devices using the electrophoretic effect, rererel,ce is made to U.S. Pat. No. 4,732,830 entitled ELECI'ROPHORETIC
DISPL,AY PANELS AND ASSOCLATED METHODS and issued to Frank J.
DiSanto et al. on Mar. 22, 1988. In this patent, there is ~lis~losed an electrophoretic display apparatus which in~ des a planar ~ palell~ member having disposed thereon a plurality of vertically extending, electrically con(lllçtiye lines defining a grid. A plurality of hori7nnt~11y to-~tentlin~ electrically conductive cathode lines are disposed on top of the vertical lines but are ins111~ted thererro by a thin in~ ting layer, thereby forming an XY matrix of electrodes. A
conc1uctive plate or anode is spaced above the line pattern and disposed therebetween in an electrophoretic dispersion of yellow pigment particles in a dark colored suspension medium. The particles are transportable within the medium.
The performance of the res111ting display is strongly dependent upon the suspension stability. Colloid particles owe their suitability against instability to the fact that their surfaces are charged and, hence, repel each other. When the particles are uncharged, the dispersion is unstable. The fact that a colloidal particle bears a net surface charge is not a sufficient con(litinn for stability because electroneutrality demands that the particle plus its immediate surrounding bear no net charge. In other words, the surface charge must be compens~ted by an equal but opposite counter charge, so that surface charge and counterchal~e together form an electrical double layer. P. Murau and B Singer, in an article wo ss/ls363 ~ 1 7 6 4 8 3 PCT/US94113517 appearing in Vol. 49, No. 9 of the Journal of Applied Physics (1978) and entitled 'The Underst~n~lin~ and F.limin~tio~ of Some Suspension Instabilities in an Electrophoretic Display", indicated that when the double layer is co-l-pressed, the particles can approach each other to within a few hundred an~l.o..~s before S repulsion is felt and the van der Waals attraction becomes so strong that aggregation occurs.
The interactions of particle s l~ces and charge control agents in colloidal suspensions has been the subject of con~i~erable research. Reference is made to an article entitled "Meçh~ni~m of Electric Charging of Particles in Nonaqueous Liquids" appearing in Vol. 15 of the Journal of the American (~hemic~l Society (1982), F.M. Fowkes et al discuss the mech~ni~m of electrostatic charging of suspended acidic particles by basic dispersants in solvents of low dielectric consla~l. Reference is also made to an article entitled "Steric and Electrostatic C~ontributions to the Colloidal Properties of Nonaqueous Dispersions" appearing in Vol. 21 of the Journal of the American Chemical Society (1984) wherein F.M.
Fowkes and R.J. Pugh discuss the importance of anchoring sites for steric stabilizers in minimi7ing particle flocc~ tion. The essential point developed bythese references is that particle surface interactions are acid-base in character.
Acidic pigment surface sites and basic charge control agents yield negative pigment surface charge. On the other hand, basic pigment surface sites and acidic charge control agents yield positive pigment surface charge.
Since electrophoretic devices utilize low polarity liquids in which ioni7~tion of or.lillaly organic acids and salts is negligible the charge of the particle is governed by trace impurities unless otherwise controlled by adsorbing on the pigment surface a suitable charge control agent. This amount of charge, althoughsuf~lcient for electrophoretic activity may still be inadequate for electrostatic WO 9SIlS363 2 1 7 ~ q 8 3 ! PCT/US94/13S17--, st~hili7~tion of the suspension. If the charge control agent is also polymeric, or a polymeric dispersant is present in addition, the colloid stability can be further enhanced. See for example, an article by P. Murau and B singer appearing in Vol 49, No. 9 of the Journal of Applied Physics (1978) and entitled '~he S Underst~ntling and F.limin~ion of some suspension instabilities in an Electrophoretic Display". Over recent years, ~tte~tion has therefore been directed to dispersion stabilization by way of adsorbed polymers on particle surfaces. Iftwo colloidal particles coated with adsorbed layers of polymers approach each other, steric repulsion can occur as soon as the polymer layers start to penetrate.
Acco~dil-g to Murau and Singer, the polyrner molecules adsorbed on a colloidal particle never lie flat on the surface. Rather, parts of the long chains (loose-ends, side br~nch~, and loops) are free from the surface and ~ulroullded by liquid.
As will be recognized by a person skilled in the art, the selection of the electrophoretic particles used in the EPID is very important in dele---~illin~ the performance of the EPID and the qualify of the viewed image produced. Ideally, electrophoretic particles should have an OpLilllulll charge/mass ratio, which isdependent upon the particle size and surface charge, in order to obtain good electrostatic deposition at high velocity as well as rapid re~ al of particle motion when voltages change. Additionally, it is desirable to utilize electrophoretic palticles that have essentially the same density as the fluid medium in which they are suspended. By using electrophoretic particles through the medium remains independent of both the orient~tion of the EPID and the forces of gravity.
To effect the greatest optical contrast between electrophoretic particles and the suspension medium, it is desirable to have either light-colored particles suspended in a dark medium or black particles suspended in a b~kli~ ted clear merljllm In the prior art, it has been proven r~ lt to produce black WO 95/lS363 ~ 1 7 6 ~ 8 3 PCT/US94/13517 ~^ electrophoretic particles that are dielectric, of ullirwlll size and have a density m~t~.hing that of a common susperlsion m~ lm As a result, EPIDs, commQnly use readily m~nllf~rt~lred light colored electrophoretic particles suspended in dark media. Such EPIDs are exemplified in U.S. Patent Nos: 4,655,897 to DiSanto et al., 4,093,534 to Carter et al., 4,298,448 to Muller et al., and 4,285,801 to ~h~ing Another parameter of display pelforlllance which is of critical importance is writing speed. Writing speed is the speed at which the colored particles, resting initially on one screen electrode move through a medium and rest on an oppositely charged screen electrode when an electric field is applied. The actual writing time or speed required to produce an image on the display is very dependent upon 1) the speed at which the colored particles separate from the screen electrode and 2)the speed at which the colored particles pack at the oppositely charged screen electrode. In the quest to increase the writing speed of the display, prior art suspension formulations have been made which exhibit extremely fast speeds of sep~ration from the screen electrode but which exhibit slow and unusable packing speeds at the oppositely charged screen electrode.
AccoldiL~gly, it is an object of the present invention to provide an electrophoretic suspension composition and method of m~king, which eYhibit~ an increased writing speed via an increased speed of colored particle separation from the screen electrode while m~int~ining an acceptable speed of colored particle packing at the oppositely charged screen electrode.
DlSCLOSURE OF THE lNVENTlON
In accordance with the present invention, an electrophoretic suspension form~ tion comprising a suspension medium in~ lin~ tetrachloroethylene, 5-WO 95/lS363 ` ' ' ' ` PCT/US94/13517 ~1 76~83 ethylidene 2-norbornene, and an ~rolllaLic solvent inrhl(ling either a ~ ure of phenyl sylyl ethanes or a rnixture of mono and di-ben2yl tolllenes; a plurali~r of pigrnent particles dispersed in the suspension medium; a fluid dye dissolved in the suspension medium for providing a contrast with the pigrnent particles; and a S charge control agent adsorbed on the pigrnent particles for yr~v~ g the pigrnent particles from agglomerating. The electrophoretic suspension of the present invention is m~nnf~ctnred by combining tetrachloroethylene with 5-ethylident 2-norbornene and either a mixture of phenyl xylyl ethanes or a mixture of mono anddi-ben~yl tolllenes to form a suspension medium; adding pigment particles of a first color to said suspension medium; adding a charge control agent to ~rcv~"l ~lomeration of the pigment particles; dissolving a fluid dye of a second color in the suspension medium; and ball milling the suspension me~ lm to thoroughly disperse the pigment particles therein. The specific gravity of the suspension medium is adjusted to be slightly greater than the specific gravity of the pigment particles by adding 5-ethylidene-2-norbornene. The suspension medium is celllliruged to remove unwanted particulate matter and then homogenized by ultrasound.
A more complete appreciation of the invention and many of the ~tten.1~nt adv~nt~es thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when con~idered inconnection with the accolllyanying drawing wherein:
Fig. 1 is a simplified perspective view of an electrophoretic display device with portions partially cut away.
WO 95/153G3 ~ 1 7 6 4 8 3 PCT/US94/13517 . ~ f BEST MODE FOR CARRY~NG OUT THE INVENTION
In its broadest aspects, the present invention is directed toward illlpl`OVil~g the speed, usable lifetime and usable tempel~lu,e range of suspensions in electrophoretic display devices. Referring to the sole figure, there is shown a simplffled perspective view of an electrophoretic display device. Apart from theprocess of m~king the suspension, the display 10 can be fabricated in a manner as known in the art. The construction of such displays are well known and refere~ce may be had to the aforementioned U.S. Pat. No. 4,732,830 to DiSanto et al., the disclosure of which is incorporated herein by reference, for details of the same. As shown in FIG. 1, a cell 10 in~lucles a back panel 12, a front panel14 and side panels 16 to define an enclosed space 18. The endosed space is bounded by interior surfaces 20, with the cell exterior having exterior surfaces 22.
A layer of conductive material is deposited on an interior side of back panel 12 to serve as the anode 24. Subst~nti~lly parallel strips 26 of a condllctive material are deposited an interior side of front panel 14 to serve as a set of cathodes. Each strip cathode is electrically isolated from adjacent strip cathodes.
On top of cathodes 26 is deposited a layer of electrically inclll~ting material 28.
On top of layer 28 are deposited substantial parallel strips 30 of conductive material to serve as the control or grid electrodes. Adjacent grid electrodes 30 are also electrically isolated from one another.
The portions of insulator 28 exposed in between the grid electrodes are etched away in a conventional manner to expose small sections of the cathodes between the column~ of grid electrodes. When cell 10 is viewed through back panel 12, the grid electrodes 30 overlap cathodes 26 in square or rect~n~ r sections. Within each such section a number of walls 32 are etched into the grid Wo 9S/lS363 2~ 7 6 4 8 3 PCI~/US94/13517 ` - ` 8 electrodes and into the inc~ tor layer underneath to expose portions of the cathode at the bottom of the wells. ~tllodes 26, in~ ting material 28, and control electrodes 30 form X-Y matrix structure 33. o Back panel 12 is typically composed of glass or Llal~arellt plastic. Anode 24 is colll~lised of an electrically conductive metal or metal oxide, such as a n~ Luic of in~ lm oxide and tin oxide ("ITO") and may be applied to front panel 12 by means such as vacuum sputtering. Front panel 14 is also typically coll~ised of glass or transparent plastic and is coated with a layer of ITO, which, based on its thickn~c~, is transparent. The cathode strip pattern is etched on the surface of the lrrO layer on front panel 14 using conventional etchants as used in the integrated circuit art. The grid electrodes 30 may be colll~lised of chrome or some other electrically conductive material and may be applied to the inc~ tin~
m~teri~l 28 by vacuum sputtering or some other technique. Front panel 14 may extend beyond back panel 12 and carry means thereon (not shown) for conducting voltages to the anodes 24, control electrodes 30, and cathodes 26.
A dielectric, or suspending, liquid 34 is disposed within the enclosed space 18. The liquid t,vpically fills the volume between the front and back panels andside panels of the cell and wells 32. Pigment particles 36 are disposed in the suspension and function as a diffuse reflector when the particles are packed on the cathode. When a sufficient electrical bias is applied between the anode 24 and cathode 26, the electrophoretic particles 36 migrate in respollse thereto to either the cathode 26 or anode 24 depending on polarity and displace the dark color me~ m 24 at the viewing surface, thereby creating a white pixel. Reversing the voltage produces a dark pixel.
As briefly discussed earlier, the operation of an electrophoretic cell involves movement of particles, initially resting on one electrode, through space under the WO 9S/15363 ~ 1 7 6 ~ $ 3 PCT/US94113517 A inflllence of an electric field, to rest finally on an electrode of opposite charge.
~f a simple electrophoretic cell is pictured, with particles initially on one electrode, attracted there by their charge, which is opposite to the applied voltage, r~.,elsal of the sign of the applied voltage will lead to motion.
S The motion of the particles from cathode to anode across the cell, upon electrode voltage sign reversal, can be viewed as taking place in four steps:
1) Separation of particles from the starting electrode.
SUSPENSIONS AND REI~TED METHODS
~ELATED APPLICATIONS
The acci~ee~ Copytele, Inc. is the record owner of U.S. Patent application entitled "SUSPENSION FOR USE IN ELECI~ROPHORETIC IMAGE DISPLAY
S SYSTEMS", Serial No. 08/092,749, filed on July 6, 1993 for Frederic E. Schubert and ~c~igne~l to Copytele, Inc.
TECHNICAL F~ELD OF THE INVENTION
This invention relates to electro-optical devices in general and, more particularly, to dielectric fluid suspension compositio~ for electrophoretic displays and related methods of m~mlf~ct~lre.
BACKGROUND ART
The electrophoretic effect is well known as the prior art is replete with p~tent~ and articles describing the effect. As described and discussed in the prior, the electrophoretic effect operates on the principle that certain particles, when suspended in a medium, can be electrically charged and thereby caused to migrate through the medium to an electrode of opposite charge. Electrophoretic image displays (EPIDs) implement the electrophoretic effect to produce desired im~f~es In prior art EPIDs, colored particles, which are charged either positively or negatively, are suspended in a dielectric fluid medium that is either clear or of a color which optically contrasts with the particles. ~he suspension is injected into a cell COlllplisi~g two parallel screen electrodes, at least one of which is tral~are.lt. The colored particles are caused to migrate to, and impinge upon, WO 9S/lS363 ,~ 1 7 6 ~ PCT/US94/13517 one of the screen electrodes under the application of an electric field, therebydisplacing the fluid me~ 1m at that electrode creating the desired image. When the polarity of the ~leld is reversed, the colored particles migrate to the opposite screen electrode.
For suitable example of such devices using the electrophoretic effect, rererel,ce is made to U.S. Pat. No. 4,732,830 entitled ELECI'ROPHORETIC
DISPL,AY PANELS AND ASSOCLATED METHODS and issued to Frank J.
DiSanto et al. on Mar. 22, 1988. In this patent, there is ~lis~losed an electrophoretic display apparatus which in~ des a planar ~ palell~ member having disposed thereon a plurality of vertically extending, electrically con(lllçtiye lines defining a grid. A plurality of hori7nnt~11y to-~tentlin~ electrically conductive cathode lines are disposed on top of the vertical lines but are ins111~ted thererro by a thin in~ ting layer, thereby forming an XY matrix of electrodes. A
conc1uctive plate or anode is spaced above the line pattern and disposed therebetween in an electrophoretic dispersion of yellow pigment particles in a dark colored suspension medium. The particles are transportable within the medium.
The performance of the res111ting display is strongly dependent upon the suspension stability. Colloid particles owe their suitability against instability to the fact that their surfaces are charged and, hence, repel each other. When the particles are uncharged, the dispersion is unstable. The fact that a colloidal particle bears a net surface charge is not a sufficient con(litinn for stability because electroneutrality demands that the particle plus its immediate surrounding bear no net charge. In other words, the surface charge must be compens~ted by an equal but opposite counter charge, so that surface charge and counterchal~e together form an electrical double layer. P. Murau and B Singer, in an article wo ss/ls363 ~ 1 7 6 4 8 3 PCT/US94113517 appearing in Vol. 49, No. 9 of the Journal of Applied Physics (1978) and entitled 'The Underst~n~lin~ and F.limin~tio~ of Some Suspension Instabilities in an Electrophoretic Display", indicated that when the double layer is co-l-pressed, the particles can approach each other to within a few hundred an~l.o..~s before S repulsion is felt and the van der Waals attraction becomes so strong that aggregation occurs.
The interactions of particle s l~ces and charge control agents in colloidal suspensions has been the subject of con~i~erable research. Reference is made to an article entitled "Meçh~ni~m of Electric Charging of Particles in Nonaqueous Liquids" appearing in Vol. 15 of the Journal of the American (~hemic~l Society (1982), F.M. Fowkes et al discuss the mech~ni~m of electrostatic charging of suspended acidic particles by basic dispersants in solvents of low dielectric consla~l. Reference is also made to an article entitled "Steric and Electrostatic C~ontributions to the Colloidal Properties of Nonaqueous Dispersions" appearing in Vol. 21 of the Journal of the American Chemical Society (1984) wherein F.M.
Fowkes and R.J. Pugh discuss the importance of anchoring sites for steric stabilizers in minimi7ing particle flocc~ tion. The essential point developed bythese references is that particle surface interactions are acid-base in character.
Acidic pigment surface sites and basic charge control agents yield negative pigment surface charge. On the other hand, basic pigment surface sites and acidic charge control agents yield positive pigment surface charge.
Since electrophoretic devices utilize low polarity liquids in which ioni7~tion of or.lillaly organic acids and salts is negligible the charge of the particle is governed by trace impurities unless otherwise controlled by adsorbing on the pigment surface a suitable charge control agent. This amount of charge, althoughsuf~lcient for electrophoretic activity may still be inadequate for electrostatic WO 9SIlS363 2 1 7 ~ q 8 3 ! PCT/US94/13S17--, st~hili7~tion of the suspension. If the charge control agent is also polymeric, or a polymeric dispersant is present in addition, the colloid stability can be further enhanced. See for example, an article by P. Murau and B singer appearing in Vol 49, No. 9 of the Journal of Applied Physics (1978) and entitled '~he S Underst~ntling and F.limin~ion of some suspension instabilities in an Electrophoretic Display". Over recent years, ~tte~tion has therefore been directed to dispersion stabilization by way of adsorbed polymers on particle surfaces. Iftwo colloidal particles coated with adsorbed layers of polymers approach each other, steric repulsion can occur as soon as the polymer layers start to penetrate.
Acco~dil-g to Murau and Singer, the polyrner molecules adsorbed on a colloidal particle never lie flat on the surface. Rather, parts of the long chains (loose-ends, side br~nch~, and loops) are free from the surface and ~ulroullded by liquid.
As will be recognized by a person skilled in the art, the selection of the electrophoretic particles used in the EPID is very important in dele---~illin~ the performance of the EPID and the qualify of the viewed image produced. Ideally, electrophoretic particles should have an OpLilllulll charge/mass ratio, which isdependent upon the particle size and surface charge, in order to obtain good electrostatic deposition at high velocity as well as rapid re~ al of particle motion when voltages change. Additionally, it is desirable to utilize electrophoretic palticles that have essentially the same density as the fluid medium in which they are suspended. By using electrophoretic particles through the medium remains independent of both the orient~tion of the EPID and the forces of gravity.
To effect the greatest optical contrast between electrophoretic particles and the suspension medium, it is desirable to have either light-colored particles suspended in a dark medium or black particles suspended in a b~kli~ ted clear merljllm In the prior art, it has been proven r~ lt to produce black WO 95/lS363 ~ 1 7 6 ~ 8 3 PCT/US94/13517 ~^ electrophoretic particles that are dielectric, of ullirwlll size and have a density m~t~.hing that of a common susperlsion m~ lm As a result, EPIDs, commQnly use readily m~nllf~rt~lred light colored electrophoretic particles suspended in dark media. Such EPIDs are exemplified in U.S. Patent Nos: 4,655,897 to DiSanto et al., 4,093,534 to Carter et al., 4,298,448 to Muller et al., and 4,285,801 to ~h~ing Another parameter of display pelforlllance which is of critical importance is writing speed. Writing speed is the speed at which the colored particles, resting initially on one screen electrode move through a medium and rest on an oppositely charged screen electrode when an electric field is applied. The actual writing time or speed required to produce an image on the display is very dependent upon 1) the speed at which the colored particles separate from the screen electrode and 2)the speed at which the colored particles pack at the oppositely charged screen electrode. In the quest to increase the writing speed of the display, prior art suspension formulations have been made which exhibit extremely fast speeds of sep~ration from the screen electrode but which exhibit slow and unusable packing speeds at the oppositely charged screen electrode.
AccoldiL~gly, it is an object of the present invention to provide an electrophoretic suspension composition and method of m~king, which eYhibit~ an increased writing speed via an increased speed of colored particle separation from the screen electrode while m~int~ining an acceptable speed of colored particle packing at the oppositely charged screen electrode.
DlSCLOSURE OF THE lNVENTlON
In accordance with the present invention, an electrophoretic suspension form~ tion comprising a suspension medium in~ lin~ tetrachloroethylene, 5-WO 95/lS363 ` ' ' ' ` PCT/US94/13517 ~1 76~83 ethylidene 2-norbornene, and an ~rolllaLic solvent inrhl(ling either a ~ ure of phenyl sylyl ethanes or a rnixture of mono and di-ben2yl tolllenes; a plurali~r of pigrnent particles dispersed in the suspension medium; a fluid dye dissolved in the suspension medium for providing a contrast with the pigrnent particles; and a S charge control agent adsorbed on the pigrnent particles for yr~v~ g the pigrnent particles from agglomerating. The electrophoretic suspension of the present invention is m~nnf~ctnred by combining tetrachloroethylene with 5-ethylident 2-norbornene and either a mixture of phenyl xylyl ethanes or a mixture of mono anddi-ben~yl tolllenes to form a suspension medium; adding pigment particles of a first color to said suspension medium; adding a charge control agent to ~rcv~"l ~lomeration of the pigment particles; dissolving a fluid dye of a second color in the suspension medium; and ball milling the suspension me~ lm to thoroughly disperse the pigment particles therein. The specific gravity of the suspension medium is adjusted to be slightly greater than the specific gravity of the pigment particles by adding 5-ethylidene-2-norbornene. The suspension medium is celllliruged to remove unwanted particulate matter and then homogenized by ultrasound.
A more complete appreciation of the invention and many of the ~tten.1~nt adv~nt~es thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when con~idered inconnection with the accolllyanying drawing wherein:
Fig. 1 is a simplified perspective view of an electrophoretic display device with portions partially cut away.
WO 95/153G3 ~ 1 7 6 4 8 3 PCT/US94/13517 . ~ f BEST MODE FOR CARRY~NG OUT THE INVENTION
In its broadest aspects, the present invention is directed toward illlpl`OVil~g the speed, usable lifetime and usable tempel~lu,e range of suspensions in electrophoretic display devices. Referring to the sole figure, there is shown a simplffled perspective view of an electrophoretic display device. Apart from theprocess of m~king the suspension, the display 10 can be fabricated in a manner as known in the art. The construction of such displays are well known and refere~ce may be had to the aforementioned U.S. Pat. No. 4,732,830 to DiSanto et al., the disclosure of which is incorporated herein by reference, for details of the same. As shown in FIG. 1, a cell 10 in~lucles a back panel 12, a front panel14 and side panels 16 to define an enclosed space 18. The endosed space is bounded by interior surfaces 20, with the cell exterior having exterior surfaces 22.
A layer of conductive material is deposited on an interior side of back panel 12 to serve as the anode 24. Subst~nti~lly parallel strips 26 of a condllctive material are deposited an interior side of front panel 14 to serve as a set of cathodes. Each strip cathode is electrically isolated from adjacent strip cathodes.
On top of cathodes 26 is deposited a layer of electrically inclll~ting material 28.
On top of layer 28 are deposited substantial parallel strips 30 of conductive material to serve as the control or grid electrodes. Adjacent grid electrodes 30 are also electrically isolated from one another.
The portions of insulator 28 exposed in between the grid electrodes are etched away in a conventional manner to expose small sections of the cathodes between the column~ of grid electrodes. When cell 10 is viewed through back panel 12, the grid electrodes 30 overlap cathodes 26 in square or rect~n~ r sections. Within each such section a number of walls 32 are etched into the grid Wo 9S/lS363 2~ 7 6 4 8 3 PCI~/US94/13517 ` - ` 8 electrodes and into the inc~ tor layer underneath to expose portions of the cathode at the bottom of the wells. ~tllodes 26, in~ ting material 28, and control electrodes 30 form X-Y matrix structure 33. o Back panel 12 is typically composed of glass or Llal~arellt plastic. Anode 24 is colll~lised of an electrically conductive metal or metal oxide, such as a n~ Luic of in~ lm oxide and tin oxide ("ITO") and may be applied to front panel 12 by means such as vacuum sputtering. Front panel 14 is also typically coll~ised of glass or transparent plastic and is coated with a layer of ITO, which, based on its thickn~c~, is transparent. The cathode strip pattern is etched on the surface of the lrrO layer on front panel 14 using conventional etchants as used in the integrated circuit art. The grid electrodes 30 may be colll~lised of chrome or some other electrically conductive material and may be applied to the inc~ tin~
m~teri~l 28 by vacuum sputtering or some other technique. Front panel 14 may extend beyond back panel 12 and carry means thereon (not shown) for conducting voltages to the anodes 24, control electrodes 30, and cathodes 26.
A dielectric, or suspending, liquid 34 is disposed within the enclosed space 18. The liquid t,vpically fills the volume between the front and back panels andside panels of the cell and wells 32. Pigment particles 36 are disposed in the suspension and function as a diffuse reflector when the particles are packed on the cathode. When a sufficient electrical bias is applied between the anode 24 and cathode 26, the electrophoretic particles 36 migrate in respollse thereto to either the cathode 26 or anode 24 depending on polarity and displace the dark color me~ m 24 at the viewing surface, thereby creating a white pixel. Reversing the voltage produces a dark pixel.
As briefly discussed earlier, the operation of an electrophoretic cell involves movement of particles, initially resting on one electrode, through space under the WO 9S/15363 ~ 1 7 6 ~ $ 3 PCT/US94113517 A inflllence of an electric field, to rest finally on an electrode of opposite charge.
~f a simple electrophoretic cell is pictured, with particles initially on one electrode, attracted there by their charge, which is opposite to the applied voltage, r~.,elsal of the sign of the applied voltage will lead to motion.
S The motion of the particles from cathode to anode across the cell, upon electrode voltage sign reversal, can be viewed as taking place in four steps:
1) Separation of particles from the starting electrode.
2) Acceleration of particles to terminal velocity in the electric field.
3) Movement of particles at terminal velocity to the neighborhood of the anode.
4) Deceleration and packing of particles at the anode.
This motion becomes complicated by the fact that a wave of space charge, and not a single particle in involved. Step 1 is extremely important because theactual writing time to produce an image on the display is determined by what occurs during the first few microns of movement. This is the distance involved in moving from the cathode on the front panel 14 to beyond the grid 30, an inc~ tor thickness away. Mixes with otherwise acceptable electrophoretic properties are not useful if ap~uarenL stickiness lengthe~ the time for Step 1.
Step 2 is quite brief. For particles about one micron in diameter with about 100 electron charges in a field of about one megavolt per meter, a terminal velocity of around 3 microns per millisecond is reached in about one microsecond.
Given the terminal velocity, Step 3 is dependent on the thickness of the cell. Step 4 is irnportant since settling of the pigment on the back electrodes insures complete writing of the cell. That is, the next voltage adjustment in the cell will not lead to ghosting or crosstalk if no loose pigment sits between electrodes.
Complete settling involves times varying significantly with suspension composition WO 95/lS3~3 ~ 2 17 6 ~ 8 3 PCT/US94/13517--and cell thi~ness. For a cell with cathode to anode ~i~t~n~e of about 14 mils this time is typically of the order of a second. Suspensions have been made with extremely fast Step 1 times which were unusable because Step 4 was too long L.l~love-.lents in speed from the standpoint of sl-~p~n~ion co~ osiLion must S address both Steps 1 and 4. Resi(les involving varying times for different suspen~ion~, Step 4 does not always produce a smooth layer of pigment on the anode. Cell thickness, pigment concentration and field strength interact to determine coating layer smoothness. The pigment concenLl~lions employed in the h.ll)r(~vc~d suspension were chosen a~ter testing to ~Lillli~e ul~irolll-,less of electrode coating and acceptable Step 4 times for a cell with a cathode-anode sp~n~ of about 100 microns and a field strength of about one megavolt per meter.
The suspension composition of the present invention increases the speed of Step 1 significantly while keeping the time for Step 4 at an acceptable level.
~ltlition~l improvements associated with this suspension are: enhanced lifetime by absorption of reactive impurities; enhanced lifetime by reducing solvent attack on the pigment particle surface; and a broader range of temperature stability.
To hllplove the overall speed of operation of the electrophoretic display, ~ttentiQn was focused on increasing the speed of Step 1, the freeing of the pigment particles form the electrode and from their neighbors. It is well known that xylene will attack the surface of pigment particles made from Yellow 14. As such, the solvent, secondary-butyl benzene, has been utilized in the past because it is a somewhat weaker solvent, due to its alkyl chain. It is still an aromatic and is chemically sirnilar to xylene and thus capable of aiding in wetting the pigment surface in suspension preparation. Tests showing growth of pigment particle size W095/lS363 - ~ ~ 7 6 ~ 8 3 PCT/US94/13517 with suspension heating, suggest a strong pigment solvent interaction.
The present invention employs tetrachloroethylene (a high density - component), in combination with two other solvents. One of the other two solvents comprises an aliphatic solvent which does not interact strongly with the S pi~ment s-lrf~ce The other of the two solvents col-,ylises an aromatic liquid added in sufficient quantity to insure that the pigrnent surface is wetted. Thism~in~in.c good interaction between the OLOA sllrf~ct~nt and pi~ment, while stillredll~n~ the total amount of aromatic solvent in the system. OLOA is a preferredst~hili7er and charging agent and is adsorbed by the pigrnent partides to .~ e particle agglomeration.
The aromatic liquid chosen in the present invention comprises SAS 40 from Nisseki Chemical Co. This mixture of substituted phenyl xylyl ethanes was developed for use in the electronics industry as a dielectric. In ~d~lition to its dielectric properties it tends to chemically absorb hydrogen formed from electrochemical reactions arising from i~ urilies, like water. Water is both present initially in the cell and is also introduced over time by diffusion through the chamber walls. The gas absorbing character of SAS 40 extends the life of industrial electronic components and is a positive factor in electrophoretic displays.
Other aromatic liquids like Jarylec C-101 made by Prodelec Co., a ll~i~lul of mono and di-benzyl toluenes can also be used. Both SAS40 and Jarylec C-101 are characterized by a high C/H ratio produced by multiple aromatic rings. They are also liquids over a practically useful temperature range. These aromatic liquids were chosen as an aid in pigment-surfactant interaction and to help in absorption of possible hydrogen gas generated by i~ ulilies.
- The preferred non-aromatic hydrocarbon in the present invention is 5-WO 95/lS363 PCT/US94113517--2i7~483 12 ethylidene-2-norbornene. Other choices are possible, but this material poc~esse a few positive characteristics. First, it is a liquid over a broad temperature range.
Second, its viscosity is not high. Low viscosity is inlpollant because speed of pigrnent movement through the cell is inversely proportional to solvent viscosity.
l~us as viscosity is lowered, speed of pigment movement increases. Third, its density is about 25% higher than that of comparable straight chain hydrocarbons.This leads to less tetrachloroethylene being needed in the suspension to match pigment density. ~ourth, mixes made with this bicyclic hydrocarbon do not display as much pigment adhesion to the electrode in cell operation. This produces a quicker release from the electrode in Step 1.
A typical solvent suspension which may be utilized contains a non-polar solvent merlillm which has been density matched to the particles so that the particles remain randomly dispersed therein, unaffected by the orientation of the EPID or the effects of gravity. For example, in U.S. Pat. No. 4,732,830 to DiSanto et al., the solvent comprised a mixture consisting mainly of tetrachloroethylenewith a small amount of an aromatic hydrocarbon added thereto. In U.S. Pat No.
4,203,106, entitled X-Y ADDRESSABLE ELECI ROPHORETIC DISPLAY
DEVICE WITH CONTROL ELECTRODE and issued to Dalis et al. on May 13, 1980, there is disclosed an electrophoretic suspension lltili7ing xylene and perchloroethylene as the dielectric fluid. In contrast, the ill,pruved suspension of the present invention still employs tetrachloroethylene, however, the single ~romatic low density component of the prior art form~ tion is replace by a combination of an aromatic liquid and an aliphatic liquid.
Pigment motion in the suspension is not sufficient by itself to produce an image. A contrasting dye must be used to "hide" the pigment in dark areas of theimage while the WO 9511S363 ~ 17 6 ~ 8 3 PCT/US94/13517 pigment itself produces the bright or yellow portion of the image. Solvent Blue 35 dye solution is used in the suspension of the present invention, and producesa very strong blue-black contrast to the yellow pjgment EX~ PLE 1 Any known manner may be utilized to prepare the pigment particles of the electrophoretic suspension in which the form~ tion of the present invention is employed. In preparation of the suspension in accordallce with this example, a yellow pigment was selected designated as AAOT yellow which is a pigment ... ~.".r~ct~lred by Sun Chemical Company.
The charge control agent and stabilizing agent employed with this pigment is OLOA 1200, a product of Chevron Corporation. OLOA 1200 is a polybutene suc~nimi~le with a basic anchoring group and an extended polyisobutylene chain.
The particles were prepared by ball milling all components for about eight hours.
This was done to increase the surface area of the pigment powder by breaking up the dry agglomerated pigment powder into individual particles, thereby increasing the reactivity between the pigment po-vder and the stabilizer. During milling the temperature of the suspension rises to a ]ittle over 40~1C.
The media used in the milling procedure are 2.0 mm ~hconiulll beads having a densi~ of 6.0 g/ml. During the milling procedure, some of the OLOA-1200 is adsorbed in to the surface of the beads, forrning a coating thereon. After millin~, the suspension is strained from the beads. At this point, the specific gravity of the mix is measured. If necessary, the rnix is adjusted by adding 5-ethylidene-2-norborene to make sure the mix is slightly more dense than the pigment The suspension is then divided into centrifuge tubes and spun at 5000 RPM for 30 minutes. The suspension is transferred to fresh test tubes by carefully WO 95/lS363 ! i PCTIUS94/13S17 2 ~76~83 drawillg out the pigment and most of the liquid. A small amount of liquid and grey-white dense solid, which has settled out, are left behind. The ~lhn~y source of the residue is the zirconium oxide. The process of Ir~re~ g to fresh tubes is repeated three times to ensure adequate removal of unw~u~led parti~ te matter. In order to produce the EPID suspension, the resllltin,~ lure was homogenized for about 8 sec using ultrasound (Model UP150, hlsLlulllent of Sonicor, Inc.) and filled as the suspension into an EPID cell (test cell in accold~nce with FIG. 1) . The suspension composition is presented in Table 1.
wo 9S/15363 21 7 6 ~ 8 3 PcrJuss4/l3sl7 Concentration Yellow pigment, AAOT, S product of Sun Chemical Co.
Solvent Blue 35 (SB35) 0.32~o blue dye, ~30,643-6, product of Aldrich Co. 1,4-Bis (butylamino~ -9,10-anthracenedione OLOA 1200 stabilker and 0.8%
charging agent, product of Chevron Chemicals Co.
SAS 40 product of Nisseki 6%
Chemical Co. (nlixLule of phenyl xylyl ethanes) Tetrachloroethylene and 91.9~o S-ethylidene - 2-norbornene bac~.oulld solvent adjusted to a density of 1.43g/ml WO 9S/15363 PCT/US94113Sl~
~176483 The suspension of example 1 manifested si~nific~nt i~ ovement in Step 1 speed while m~int~ining acceptable Step 4 speed. Thus, it was significantly faster in writing images than prior art suspensions.
EXAl~IPLE 2 E ample 2 was prepared in the same manner as in FY~mrle 1 except that Jarylec C 101, a mixture of mono and di-ben~yl toluenes was s~lbstihlterl for SAS
40. The suspension of example 2 displayed properties like those of Example 1, inthat it provided significantly faster writing speed via increased step 1 speed than previous suspension formulations.
This motion becomes complicated by the fact that a wave of space charge, and not a single particle in involved. Step 1 is extremely important because theactual writing time to produce an image on the display is determined by what occurs during the first few microns of movement. This is the distance involved in moving from the cathode on the front panel 14 to beyond the grid 30, an inc~ tor thickness away. Mixes with otherwise acceptable electrophoretic properties are not useful if ap~uarenL stickiness lengthe~ the time for Step 1.
Step 2 is quite brief. For particles about one micron in diameter with about 100 electron charges in a field of about one megavolt per meter, a terminal velocity of around 3 microns per millisecond is reached in about one microsecond.
Given the terminal velocity, Step 3 is dependent on the thickness of the cell. Step 4 is irnportant since settling of the pigment on the back electrodes insures complete writing of the cell. That is, the next voltage adjustment in the cell will not lead to ghosting or crosstalk if no loose pigment sits between electrodes.
Complete settling involves times varying significantly with suspension composition WO 95/lS3~3 ~ 2 17 6 ~ 8 3 PCT/US94/13517--and cell thi~ness. For a cell with cathode to anode ~i~t~n~e of about 14 mils this time is typically of the order of a second. Suspensions have been made with extremely fast Step 1 times which were unusable because Step 4 was too long L.l~love-.lents in speed from the standpoint of sl-~p~n~ion co~ osiLion must S address both Steps 1 and 4. Resi(les involving varying times for different suspen~ion~, Step 4 does not always produce a smooth layer of pigment on the anode. Cell thickness, pigment concentration and field strength interact to determine coating layer smoothness. The pigment concenLl~lions employed in the h.ll)r(~vc~d suspension were chosen a~ter testing to ~Lillli~e ul~irolll-,less of electrode coating and acceptable Step 4 times for a cell with a cathode-anode sp~n~ of about 100 microns and a field strength of about one megavolt per meter.
The suspension composition of the present invention increases the speed of Step 1 significantly while keeping the time for Step 4 at an acceptable level.
~ltlition~l improvements associated with this suspension are: enhanced lifetime by absorption of reactive impurities; enhanced lifetime by reducing solvent attack on the pigment particle surface; and a broader range of temperature stability.
To hllplove the overall speed of operation of the electrophoretic display, ~ttentiQn was focused on increasing the speed of Step 1, the freeing of the pigment particles form the electrode and from their neighbors. It is well known that xylene will attack the surface of pigment particles made from Yellow 14. As such, the solvent, secondary-butyl benzene, has been utilized in the past because it is a somewhat weaker solvent, due to its alkyl chain. It is still an aromatic and is chemically sirnilar to xylene and thus capable of aiding in wetting the pigment surface in suspension preparation. Tests showing growth of pigment particle size W095/lS363 - ~ ~ 7 6 ~ 8 3 PCT/US94/13517 with suspension heating, suggest a strong pigment solvent interaction.
The present invention employs tetrachloroethylene (a high density - component), in combination with two other solvents. One of the other two solvents comprises an aliphatic solvent which does not interact strongly with the S pi~ment s-lrf~ce The other of the two solvents col-,ylises an aromatic liquid added in sufficient quantity to insure that the pigrnent surface is wetted. Thism~in~in.c good interaction between the OLOA sllrf~ct~nt and pi~ment, while stillredll~n~ the total amount of aromatic solvent in the system. OLOA is a preferredst~hili7er and charging agent and is adsorbed by the pigrnent partides to .~ e particle agglomeration.
The aromatic liquid chosen in the present invention comprises SAS 40 from Nisseki Chemical Co. This mixture of substituted phenyl xylyl ethanes was developed for use in the electronics industry as a dielectric. In ~d~lition to its dielectric properties it tends to chemically absorb hydrogen formed from electrochemical reactions arising from i~ urilies, like water. Water is both present initially in the cell and is also introduced over time by diffusion through the chamber walls. The gas absorbing character of SAS 40 extends the life of industrial electronic components and is a positive factor in electrophoretic displays.
Other aromatic liquids like Jarylec C-101 made by Prodelec Co., a ll~i~lul of mono and di-benzyl toluenes can also be used. Both SAS40 and Jarylec C-101 are characterized by a high C/H ratio produced by multiple aromatic rings. They are also liquids over a practically useful temperature range. These aromatic liquids were chosen as an aid in pigment-surfactant interaction and to help in absorption of possible hydrogen gas generated by i~ ulilies.
- The preferred non-aromatic hydrocarbon in the present invention is 5-WO 95/lS363 PCT/US94113517--2i7~483 12 ethylidene-2-norbornene. Other choices are possible, but this material poc~esse a few positive characteristics. First, it is a liquid over a broad temperature range.
Second, its viscosity is not high. Low viscosity is inlpollant because speed of pigrnent movement through the cell is inversely proportional to solvent viscosity.
l~us as viscosity is lowered, speed of pigment movement increases. Third, its density is about 25% higher than that of comparable straight chain hydrocarbons.This leads to less tetrachloroethylene being needed in the suspension to match pigment density. ~ourth, mixes made with this bicyclic hydrocarbon do not display as much pigment adhesion to the electrode in cell operation. This produces a quicker release from the electrode in Step 1.
A typical solvent suspension which may be utilized contains a non-polar solvent merlillm which has been density matched to the particles so that the particles remain randomly dispersed therein, unaffected by the orientation of the EPID or the effects of gravity. For example, in U.S. Pat. No. 4,732,830 to DiSanto et al., the solvent comprised a mixture consisting mainly of tetrachloroethylenewith a small amount of an aromatic hydrocarbon added thereto. In U.S. Pat No.
4,203,106, entitled X-Y ADDRESSABLE ELECI ROPHORETIC DISPLAY
DEVICE WITH CONTROL ELECTRODE and issued to Dalis et al. on May 13, 1980, there is disclosed an electrophoretic suspension lltili7ing xylene and perchloroethylene as the dielectric fluid. In contrast, the ill,pruved suspension of the present invention still employs tetrachloroethylene, however, the single ~romatic low density component of the prior art form~ tion is replace by a combination of an aromatic liquid and an aliphatic liquid.
Pigment motion in the suspension is not sufficient by itself to produce an image. A contrasting dye must be used to "hide" the pigment in dark areas of theimage while the WO 9511S363 ~ 17 6 ~ 8 3 PCT/US94/13517 pigment itself produces the bright or yellow portion of the image. Solvent Blue 35 dye solution is used in the suspension of the present invention, and producesa very strong blue-black contrast to the yellow pjgment EX~ PLE 1 Any known manner may be utilized to prepare the pigment particles of the electrophoretic suspension in which the form~ tion of the present invention is employed. In preparation of the suspension in accordallce with this example, a yellow pigment was selected designated as AAOT yellow which is a pigment ... ~.".r~ct~lred by Sun Chemical Company.
The charge control agent and stabilizing agent employed with this pigment is OLOA 1200, a product of Chevron Corporation. OLOA 1200 is a polybutene suc~nimi~le with a basic anchoring group and an extended polyisobutylene chain.
The particles were prepared by ball milling all components for about eight hours.
This was done to increase the surface area of the pigment powder by breaking up the dry agglomerated pigment powder into individual particles, thereby increasing the reactivity between the pigment po-vder and the stabilizer. During milling the temperature of the suspension rises to a ]ittle over 40~1C.
The media used in the milling procedure are 2.0 mm ~hconiulll beads having a densi~ of 6.0 g/ml. During the milling procedure, some of the OLOA-1200 is adsorbed in to the surface of the beads, forrning a coating thereon. After millin~, the suspension is strained from the beads. At this point, the specific gravity of the mix is measured. If necessary, the rnix is adjusted by adding 5-ethylidene-2-norborene to make sure the mix is slightly more dense than the pigment The suspension is then divided into centrifuge tubes and spun at 5000 RPM for 30 minutes. The suspension is transferred to fresh test tubes by carefully WO 95/lS363 ! i PCTIUS94/13S17 2 ~76~83 drawillg out the pigment and most of the liquid. A small amount of liquid and grey-white dense solid, which has settled out, are left behind. The ~lhn~y source of the residue is the zirconium oxide. The process of Ir~re~ g to fresh tubes is repeated three times to ensure adequate removal of unw~u~led parti~ te matter. In order to produce the EPID suspension, the resllltin,~ lure was homogenized for about 8 sec using ultrasound (Model UP150, hlsLlulllent of Sonicor, Inc.) and filled as the suspension into an EPID cell (test cell in accold~nce with FIG. 1) . The suspension composition is presented in Table 1.
wo 9S/15363 21 7 6 ~ 8 3 PcrJuss4/l3sl7 Concentration Yellow pigment, AAOT, S product of Sun Chemical Co.
Solvent Blue 35 (SB35) 0.32~o blue dye, ~30,643-6, product of Aldrich Co. 1,4-Bis (butylamino~ -9,10-anthracenedione OLOA 1200 stabilker and 0.8%
charging agent, product of Chevron Chemicals Co.
SAS 40 product of Nisseki 6%
Chemical Co. (nlixLule of phenyl xylyl ethanes) Tetrachloroethylene and 91.9~o S-ethylidene - 2-norbornene bac~.oulld solvent adjusted to a density of 1.43g/ml WO 9S/15363 PCT/US94113Sl~
~176483 The suspension of example 1 manifested si~nific~nt i~ ovement in Step 1 speed while m~int~ining acceptable Step 4 speed. Thus, it was significantly faster in writing images than prior art suspensions.
EXAl~IPLE 2 E ample 2 was prepared in the same manner as in FY~mrle 1 except that Jarylec C 101, a mixture of mono and di-ben~yl toluenes was s~lbstihlterl for SAS
40. The suspension of example 2 displayed properties like those of Example 1, inthat it provided significantly faster writing speed via increased step 1 speed than previous suspension formulations.
Claims (23)
1. An electrophoretic suspension comprising:
a suspension medium comprising tetrachloroethylene. 5-ethylidene norbornene and an aromatic solvent;
a plurality of pigment particles dispersed in said suspension medium;
a fluid dye dissolved in said suspension medium for providing a contrast with said pigment particles; and a charge control agent adsorbed on said pigment particles for preventing said pigment particles from agglomerating.
a suspension medium comprising tetrachloroethylene. 5-ethylidene norbornene and an aromatic solvent;
a plurality of pigment particles dispersed in said suspension medium;
a fluid dye dissolved in said suspension medium for providing a contrast with said pigment particles; and a charge control agent adsorbed on said pigment particles for preventing said pigment particles from agglomerating.
2. The electrophoretic suspension according to claim 1, wherein said aromatic solvent is a mixture of phenyl xylyl ethanes.
3. The electrophoretic suspension according to claim 1, wherein said aromatic solvent is a mixture of mono and di-benzyl toluenes.
4. The electrophoretic suspension according to claim 1, wherein said tetrachloroethylene and said 5-ethylidene-2-norbornene are present in said suspension at a concentration of 91.9 percent by weight.
5. The electrophoretic suspension according to claim 1, wherein said aromatic solvent is present in said suspension at a concentration of 6.0 percent by weight.
6. The electrophoretic suspension according to claim 1, wherein said charge control agent is present in said suspension at a concentration of 0.8 percent by weight.
7. The electrophoretic suspension according to claim 1, wherein said fluid dye is present in said suspension at a concentration of 0.32 percent by weight.
8. The electrophoretic suspension according to claim 1, wherein said plurality of pigment particles are present in said suspension at a concentration of 1.0 percent by weight.
9. The electrophoretic suspension according to claim 1, wherein said suspension has a specific gravity of 1.43 grams/milliliter.
10. A process for making a suspension for an electrophoretic display, comprising the steps of:
combining tetrachloroethylene with 5-ethylidene-2-norbornene and an aromatic solvent to form a suspension medium;
adding pigment particles of a first color to said suspension medium;
adding a charge control agent to said suspension medium to prevent agglomeration of said plurality of pigment particles;
dissolving a fluid dye of a second color in said suspension medium; and ball milling said suspension medium to thoroughly disperse said pigment particles therein.
combining tetrachloroethylene with 5-ethylidene-2-norbornene and an aromatic solvent to form a suspension medium;
adding pigment particles of a first color to said suspension medium;
adding a charge control agent to said suspension medium to prevent agglomeration of said plurality of pigment particles;
dissolving a fluid dye of a second color in said suspension medium; and ball milling said suspension medium to thoroughly disperse said pigment particles therein.
11. The process according to claim 10, wherein said ball milling is substantially eight hours in duration.
12. The process according to claim 10, further comprising the step of adjusting the specific gravity of said suspension to be slightly greater than the specific gravity of said pigment particles by adding said 5-ethylidene-2-norbornene.
13. The process according to claim 12 further comprising the step of centrifuging said suspension to remove unwanted particulate matter.
14. The process according to claim 13, wherein said centrifuging of said suspension is for 30 minutes at 5000 rpm.
15. The process according to claim 12, further comprising, the step of homogenizing said suspension using ultrasound.
16. The process according to claim 15, where said step for homogenizing is approximately 8 seconds in duration.
17. The process according to claim 10, wherein said first color contrasts with said second color.
18. The process according to claim 10, wherein said tetrachloroethylene and said 5-ethylidene-2-norbornene are present in said suspension at a concentration of 91.9 percent.
19. The process according to claim 10, wherein said aromatic solvent is a mixture of phenyl xylylethanes present in said suspension at a concentration of 6.0 percent by weight.
20. The process according to claim 10, wherein said aromatic solvent is a mixture of mono and di-benzyl toluenes present in said suspension at a concentration of 6.0 percent by weight.
21. The process according to claim 10. wherein said charge control agent is present in said suspension at a concentration of 0.8 percent by weight.
22. The process according to claim 10, wherein said fluid dye is present in said suspension at a concentration of 0.32 percent by weight.
23. The process according to claim 10, wherein said pigment particles are present in said suspension at a concentration of 1.0 percent by weight.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US161,315 | 1993-12-02 | ||
| US08/161,315 US5403518A (en) | 1993-12-02 | 1993-12-02 | Formulations for improved electrophoretic display suspensions and related methods |
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| Publication Number | Publication Date |
|---|---|
| CA2176483A1 true CA2176483A1 (en) | 1995-06-08 |
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ID=22580686
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002176483A Abandoned CA2176483A1 (en) | 1993-12-02 | 1994-11-21 | Formulations for improved electrophoretic display suspensions and related methods |
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| Country | Link |
|---|---|
| US (1) | US5403518A (en) |
| EP (1) | EP0740693A4 (en) |
| JP (1) | JP3192150B2 (en) |
| CA (1) | CA2176483A1 (en) |
| WO (1) | WO1995015363A1 (en) |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| US3612758A (en) * | 1969-10-03 | 1971-10-12 | Xerox Corp | Color display device |
| US3742076A (en) * | 1970-03-06 | 1973-06-26 | H Imai | Process for the production of 5-ethylidene norbornene-2 |
| DE2906652A1 (en) * | 1979-02-02 | 1980-08-14 | Bbc Brown Boveri & Cie | METHOD FOR PRODUCING AN ELECTROPHORETIC DISPLAY WITH WAX-COVERED PIGMENT PARTICLES |
| US4309081A (en) * | 1979-05-29 | 1982-01-05 | Bell Telephone Laboratories, Incorporated | Display devices |
| US4285801A (en) * | 1979-09-20 | 1981-08-25 | Xerox Corporation | Electrophoretic display composition |
| US4655897A (en) * | 1984-11-13 | 1987-04-07 | Copytele, Inc. | Electrophoretic display panels and associated methods |
| US4732830A (en) * | 1984-11-13 | 1988-03-22 | Copytele, Inc. | Electrophoretic display panels and associated methods |
| US4680103A (en) * | 1986-01-24 | 1987-07-14 | Epid. Inc. | Positive particles in electrophoretic display device composition |
-
1993
- 1993-12-02 US US08/161,315 patent/US5403518A/en not_active Expired - Fee Related
-
1994
- 1994-11-21 WO PCT/US1994/013517 patent/WO1995015363A1/en not_active Application Discontinuation
- 1994-11-21 EP EP95903148A patent/EP0740693A4/en not_active Ceased
- 1994-11-21 JP JP51567695A patent/JP3192150B2/en not_active Expired - Fee Related
- 1994-11-21 CA CA002176483A patent/CA2176483A1/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| JPH09507881A (en) | 1997-08-12 |
| JP3192150B2 (en) | 2001-07-23 |
| EP0740693A1 (en) | 1996-11-06 |
| WO1995015363A1 (en) | 1995-06-08 |
| US5403518A (en) | 1995-04-04 |
| EP0740693A4 (en) | 1997-04-02 |
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| Date | Code | Title | Description |
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| FZDE | Discontinued |