CN101393369B - Electrophoretic medium - Google Patents

Abstract

A first electrophoretic medium comprises an electrically charged particle suspended in a suspending fluid, the particle having a polymeric shell having repeating units derived from at least one monomer the homopolymer of which is incompatible with the suspending fluid. A second, similar electrophoretic medium comprises a suspending fluid, and first and second types of electrically charged particle suspended in the suspending fluid, the two types of particle having differing optical characteristics but both having polymeric shells. The polymeric shells are arranged such that homoaggregation of the two types of particles is thermodynamically favored over heteroaggregation.

Description

Electrophoretic medium

The application is dividing an application of an application for a patent for invention, and the applying date of its female case is that October 8, application number in 2004 are that 200480036461.9 (PCT/US2004/033188), denomination of invention are " electrophoretic medium ".

Technical field

The present invention relates to electrophoretic medium.Although do not get rid of other situation, this electrophoretic medium is specially adapted in the electrophoretic display device (EPD) of encapsulation and micro unit.The invention still further relates to the electrophoretic particles that is used in this medium, and comprise the display of this medium.Except electrophoretic display device (EPD), some aspect of the present invention also can expand in the electro-optic displays.Electrophoretic particles of the present invention has adopted polymer modification.Electro-optic displays of the present invention has adopted the electro-optical medium with threshold voltage.

In display of the present invention, electro-optical medium (when for non-electrophoretype electro-optical medium) typically is a kind of solid (this display is known as " solid electro-optic displays " hereinafter for simplicity), its meaning is that this electro-optical medium has solid-state outside surface, although this medium can have, and usually have the space that liquid or gas have been filled in inside, and relate to the method that has adopted the display of this electro-optical medium for assembling.Therefore, term " solid electro-optic displays " comprises the electrophoretic display device (EPD) of encapsulation, the liquid crystal display of encapsulation, and the display of other type discussed below.

Background technology

The term " electric light " that is applied in material or the display is that it is in the conventional sense of imaging field as used herein, refer to a kind of material with first and second show states, this two states has a kind of difference of optical property at least, makes this material be converted to its second show state from its first show state by apply electric field to described material.Although optical property is the appreciable color of human eye normally, but it also can be another kind of optical characteristics, such as light transmission, reflectivity, luminous, perhaps be used in the situation of machine-readable formula display the false colour on the meaning that the electromagnetic wavelength reflectivity aspect beyond the visible-range changes.

Term " grey attitude " be as used herein its in the conventional sense of imaging field, refer to the state between two kinds of extreme optical state of pixel, and between these two kinds of extremities, needn't comprise black-to-white transition.For example, put down in writing extremity in some patents that the below mentions and the open application and be white and dark blue electrophoretic display device (EPD), middle " grey attitude " in fact will be for light blue like this.Really, as mentioned above, perhaps the transition between two kinds of extremities is not a kind of variable color.

Term " bistable " and " bistable state " are that it is in the conventional sense of imaging field as used herein, refer to contain the display of display element, described display element has the first and second show states, this two states has a kind of difference of optical property at least, so that after the addressing pulse by finite duration drives any given element, present its first or second show state, after addressing pulse stops, this state will continue several times at least, for example at least four times, this is to change the required addressing pulse minimum duration of status display module.In disclosed U.S. Patent application No.2002/0180687, put down in writing, some electrophoretic display device (EPD)s based on particle with gray level are stable at its extreme black and white state not only, and grey attitude therebetween also is stable, and the electro-optic displays of some other types also is like this.Such display should be called " multistable " rather than bistable rightly, but term used herein " bistable " comprises bistable state and multistable display simultaneously for simplicity.

The electro-optic displays of more known types.One class electro-optic displays is the double-colored component type of rotation, for example U.S. Patent No. 5808783,5777782,5760761,6054071,6055091, put down in writing (although such display is commonly called " rotation twin color ball " display in 6097531,6128124,6137467 and 6147791, more accurate and more preferred but term " rotates double-colored element ", because rotating element is also aspheric in more above-mentioned patents).This display has adopted the wisp (with often for spherical or columniform) of the part that contains in a large number two or more tool different optical character, and a kind of internal dipole.These wisps suspend and are filled with in the substrate in the vacuole of liquid, and this vacuole is filled with liquid so that described object can rotate freely.Apply electric field to display, also change the object part of seeing by observing the surface thereby make described object rotate to various positions, thereby change presenting of display.This class electro-optical medium is generally bistable.

Another kind of electro-optic displays has adopted electrochromic media, the electrochromic media of nanometer color form membrane for example, it comprises at least part of electrode that is made of metal oxide semiconductor and is connected to the multiple dye molecule that can reversibly change color on this electrode; Referring to for example O ' Regan, the people such as B, Nature1991,353,737; And Wood, D., Information Display, 18 (3), 24 (in March, 2002).Also can be referring to Bach, U. waits the people, Adv.Mater., 2002,14 (11), 845.This class nanometer color film is to some extent record in the international application of WO01/27690 and the U.S. Patent application 2003/0214695 at for example U.S. Patent No. 6301038, publication number also.This class medium also is bistable usually.

Another kind of electro-optic displays is based on the electrophoretic display device (EPD) of particle, and people have carried out further investigation and exploitation for many years to it, and wherein a large amount of charged particles move through the fluid of suspension under the impact of electric field.Compare with liquid crystal display, electrophoretic display device (EPD) can have good brightness and contrast, visual angle widely, the advantage of bistable state and low power consumption.Yet the problem that this class display exists aspect long-term image quality has hindered it to use widely.For example, form the easy sedimentation of particle of electrophoretic display device (EPD), so that these displays are not long serviceable life.

A large amount of patents and the application of assigning to or belonging to Massachusetts Institute of Technology (MIT) and E InkCorporation are disclosed recently, have wherein put down in writing the electrophoretic medium of encapsulation.The medium of this encapsulation comprises a large amount of Caplets, and each Caplet itself comprises the disperse phase that contains the electrophoresis moving particles that is suspended in the liquid suspension medium and the capsule wall that surrounds this disperse phase.Typically, thus described capsule self is fixed on and has formed coherent layer in a kind of polymer adhesive between two electrodes.This class encapsulation medium is for example, U.S. Patent No. 5930026,5961804,6017584,6067185,6118426,6120588,6120839,6124851,6130773,6130774,6172798,6177921,6232950,6249721,6252564,6262706,6262833,6300932,6312304,6312971,6323989,6327072,6376828,6377387,6392785,6392786,6413790,6422687,6445374,6445489,6459418,6473702,6480182,6498114,6504524,6506438,6512354,6515649,6518949,6521489,6531997,6535197,6538801,6545291,6580545,6639578,6652075,6657772,6664944,6680725,6683333,6704133,6710540,6721083,6727881,6738050,6750473, and 6753999; And publication number is 2002/0019081,2002/0021270,2002/0060321,2002/0060321,2002/0063661,2002/0090980,2002/0113770,2002/0130832,2002/0131147,2002/0171910,2002/0180687,2002/0180688,2002/0185378,2003/0011560,2003/0020844,2003/0025855,2003/0038755,2003/0053189,2003/0102858,2003/0132908,2003/0137521,2003/0137717,2003/0151702,2003/0214695,2003/0214697,2003/0222315,2004/0008398,2004/0012839,2004/0014625,2004/0027327,2004/0075634,2004/0094422,2004/0105036,2004/0112750, and 2004/0119681 U.S. Patent application; And publication number is WO99/67678, WO00/05704, WO00/38000, WO00/38001, WO00/36560, WO00/67110, WO00/67327, WO01/07961, WO01/08241, WO03/107315, WO2004/023195, and to some extent record in the international application of WO2004/049045.

Known electrophoretic medium, encapsulation and unpackaged all can be divided into two kinds of main Types, hereinafter is called for simplicity " individual particle " and " two particle ".The individual particle medium only has separately a kind of electrophoretic particles that is suspended in the suspending medium, and this medium has at least a kind of optical property to be different from described particle.(for an independent class particle, and do not mean that all these class particles all are absolute identical.For example, establish all these class particles with the electric charge of identical polar, can allow has a lot of differences on the parameter, for example grain color, size and electrophoretic mobility, and can not affect the effectiveness of medium.For example, two kinds of different colours but can be mixed together in a capsule with a kind of pigment (or multiple pigment) of opposite charges with the particle of identical charges, the color by suitable these pigment of selection one of provide in two kinds of optical states or whole any medium tone of wanting.) when this medium is between pair of electrodes, wherein at least one is transparent, relative electromotive force according to these two electrodes, this medium can demonstrate described particle (when particle is positioned near near observer's the electrode time, hereinafter be called " front " electrode) optical property or near the optical property of suspending medium (particle is positioned at away from observer's electrode time, hereinafter be called " afterwards " electrode (this particle is covered by described suspending medium like this)).

Two granule mediums have two kinds of dissimilar particles, and their at least a optical properties are different, and a kind of suspension that can be colourless or coloured, but are generally colourless.The electrophoretic mobility of this particle of two types is different, and the difference on this mobility can be for the cause of polarity (this type can hereinafter referred to as " the two particles of opposite charges " medium) and/or size.When this pair of granule medium is between above-mentioned electrode pair, relative electromotive force by these two electrodes, described medium just can demonstrate the optical property of arbitrary group of particle, although realize its really the butt formula come from according to mobility difference that polarity only comes from size and be different.In order to be easy to explanation, imagination class particle in electrophoretic medium is the another kind of situation for white of black.If two types particle on polarity different (for example, if black particle positively charged, the electronegative words of white particle), then described particle will be subject to the attraction of two Different electrodes, if like this, when for example front electrode is negative pole with respect to rear electrode, black particle will be subject to the attraction of front electrode, and white particle is subject to the attraction of rear electrode, thereby described medium will present black to the observer.Otherwise if when front electrode is anodal with respect to rear electrode, white particle will be subject to the attraction of front electrode, and black particle is subject to the attraction of rear electrode, thereby described medium will present white to the observer.

If the electric charge of two types particle band identical polar, but the words that electrophoretic mobility is different (this class medium is hereinafter referred to as " the two particles of identical polar " medium), two types particle all will be subject to the attraction of same electrode, but a kind ofly will before another kind, arrive described electrode, thus according to the electrode that attracts particle different make in the face of observer's type different.For example, suppose above-mentioned explanation is become, the black and white particle is positively charged all, but black particle has higher electrophoretic mobility.If current front electrode is negative pole with respect to rear electrode, the black and white particle all will be subject to the attraction of front electrode, but because black particle has higher mobility, it will at first arrive, thereby the black particle layer will cover front electrode, and described medium will present black to the observer.Otherwise, if front electrode is anodal with respect to rear electrode, the black and white particle all will be subject to the attraction of rear electrode, but because black particle has higher mobility, it will at first arrive, thereby the black particle layer will cover rear electrode, so that the white particle layer is away from rear electrode and in the face of the observer, described like this medium will present white to the observer: notice that the two granule mediums of this class need that suspension is enough transparent to be seen so that be easy to the person of being observed away from the white particle layer of rear electrode.Typically, the suspension in this display is fully colourless, but can see through any bad color that white particle is seen in order to proofread and correct, and perhaps in order to generate desirable color colourity in grey attitude, can add some colors.

Grey attitude in the middle of individual particle and two particle electrophoresis display can present, it has the optical property between aforementioned two kinds of extreme optical state.

Some above-mentioned patents and open application have disclosed the packaged type electrophoretic medium that has three kinds or more kinds of dissimilar particles in each capsule.For purposes of this application, this many granule mediums are considered to be the subclass of two granule mediums.

Equally, mention in many above-mentioned patents and the application, the wall that surrounds discrete microcapsules in the packaged type electrophoretic medium can be replaced by a kind of external phase, thereby produce the electrophoretic display device (EPD) of so-called dispersed polymeres, wherein electrophoretic medium comprises a large amount of discrete electrophoretic fluid drops and the external phase of polymeric material, and the electrophoretic fluid discrete droplets in this dispersed polymeres electrophoretic display device (EPD) can be regarded as capsule or microcapsules, although there is not discrete capsule membrane to link to each other with each independent drop; Referring to for example, above-mentioned 2002/0131147.Therefore, for purposes of this application, the electrophoretic medium of this dispersed polymeres is considered to be the subclass of packaged type electrophoretic medium.

The electrophoretic display device (EPD) that one class is relevant is called as " microcell electrophoretic display ".In microcell electrophoretic display, charged particle and suspension are not encapsulated in the microcapsules, replace to stay in a large amount of chambers that form in the mounting medium (being generally polymer film).Referring to, for example publication number is the international application of WO02/01281, and disclosed U. S. application No.2002/0075556, the two is all assigned to Sipix Imaging, Inc..

That although electrophoretic medium is generally is opaque (because; for example in many electrophoretic mediums; particle has been blocked visible light transmission display device basically) and move with reflective-mode; many electrophoretic display device (EPD)s can be made in the mode of a kind of being called as " shutter mode " and move; wherein a kind of show state is opaque basically, and a kind of be light transmission.Referring to, for example above-mentioned U.S. Patent No. 6130774 and 6172798, and U.S. Patent No. 5872552,6144361,6271823,6225971 and 6184856.Dielectrophoretic displays, itself and electrophoretic display device (EPD) are similar but depend on the variation of electric field intensity, can be with similar mode operation, referring to U.S. Patent No. 4418346.

Encapsulationization or microcell electrophoretic display usually no longer have aggegation and the sedimentation failure mode of conventional electrophoretic device, and have other advantage, for example can in the flexibility of numerous species and rigid substrate be printed or the coating display.(use word " printing " to be intended to comprise printing and the coating of form of ownership, include but not limited to: measure in advance coating, such as square mould (patch die) coating, slit or extrusion coated, slope or cascade coating, curtain coating; Roller coating is such as scraper roller coating (knifeover roll coating), front and back roller coating; The intaglio plate coating; Dip coated; Spraying; The liquid level coating; Spin coating; Brush; Airblade coating; Silk-screen printing technique; Electrostatic printing process; The temperature-sensitive typography; Inkjet printing technique; And other similar technology.) therefore, resulting display can be flexible.In addition, owing to can print display medium (utilizing several different methods), just can make at an easy rate display itself.

Yet, still be lower than overall expection the serviceable life of the packaged type electrophoretic display device (EPD) of single and two grain types.Look that (although the present invention never is subject to the restriction of any theory of relevant this class material) is subject to the impact of some factors this serviceable life, for example electrophoretic particles is to the capsule wall adhesiveness, and the particle agglomerating trend of condensing, it has hindered particle to be implemented in to show between its optical states and has switched necessary motion.In this respect, two particle electrophoresis displays of opposite charges have caused particularly serious problem because the particle of oppositely charged own each other extremely near the time will be subject to each other electrostatic attraction, and will show and form the strong trend of stablizing agglutination body.By experiment, it is found that if attempt utilizing undressed titanium dioxide and the carbon black pigment buied on the market to make such black/white packaged type display, to such an extent as to then this display not only switches but also very short can not be used for commercial purpose serviceable life.

People know that for a long time the physical property of electrophoretic particles and surface nature can be by adsorbing various materials at this particle surface, perhaps on these surfaces, connect various materials and in addition modification by chemical bond, detailed discussion reader for the prior art history of utilizing this method can be referring to International Application No. WO 02/093246, special paragraph referring to 7 page of the 26th row of its 6th page of the 3rd row to the.

Above-mentioned WO02/093246 has put down in writing the advantage of using granules of pigments in electrophoretic medium, and described granules of pigments has with chemical bond connection or crosslinked polymkeric substance on this granules of pigments.This application has also been put down in writing the various improvement to the particle of this coated polymkeric substance, comprise that control is deposited on the amount of the polymkeric substance on this particle, the structure of polymkeric substance, form the technology of polymer coating at electrophoretic particles, and form the technology that polymer coating is used for this electrophoretic particles of pre-service before thereon.Also put down in writing the method for the granules of pigments of making this coated polymkeric substance in this application, the method comprises: granules of pigments and a kind of reaction reagent are reacted, this reaction reagent has and can and be connected to functional group on this particle with this particle reaction, but also have the group of polymerisable or initiated polymerization, thereby this functional group is reacted with described particle surface and described polymerisable group is connected thereon; But and (b) under the condition that reacts between the group that effectively causes the above polymerizable of particle or initiated polymerization and described at least a monomer or the oligomer, the product of step (a) and at least a monomer or oligomer are reacted, thereby form the polymkeric substance that is connected on the described granules of pigments.

Put down in writing a kind of electrophoretic medium in above-mentioned 2002/0180687, comprise the particle that is suspended in a large number in the hydrocarbon suspension, described particle can move through described fluid when applying electric field to medium, this fluid has the polyisobutylene that is dissolved or dispersed in wherein, its viscosity-average molecular weight is about 400000 to 1200000g/mol, and described polyisobutylene accounts for about 0.25 to about 2.5% of suspension weight.Also put down in writing in the same application and comprised the electrophoretic medium that is suspended in a large number the particle in the suspension, described particle can move through described fluid when applying electric field to medium, this fluid has the polymkeric substance that is dissolved or dispersed in wherein, its intrinsic viscosity in this suspension is η, and there is no ion or ionizable group in the suspension, the polymer concentration that is present in this suspension is about 0.5[η] ^-1To about 2.0[η] ^-1The existence of polyisobutylene in the suspension (PIB) or other polymkeric substance has improved the bistable state of display greatly.

The above points out that electrophoretic display device (EPD) only needs very low electric power to come to switch to another kind of state from a kind of state.For bistable display, this lower powered needs that are used for switching are converted into the low general power needs for the display operation.Yet electrophoretic display device (EPD) does not have unlimited picture steadiness.The Blang of granules of pigments diffusion and sedimentation, and owing to apply the motion that little residual voltage that switch pulse and other factor cause drives, all may decay and switch the optical states that obtains by display.There is not mechanism to prevent that described optical states must carry out regular update in the situation of this optical states decay.The refresh display consumed power, thus the practicality of this display reduced.In addition, in some applications (especially active matrix driving display), be difficult to or can having blanking pulse (namely, before being driven to final desired optical states, order about the pulse of pixel under the one extreme optical state, more above-mentioned document 2003/0137521) situation under finish the renewal of single pixel.For this reason, still extremely need to improve the picture steadiness of electrophoretic medium.

Equally point out, put down in writing in above-mentioned 2002/0180687 by adding the polymkeric substance of high molecular, such as PIB, and reach the electrophoretic medium of good picture steadiness, described polymkeric substance (is generally aliphatic hydrocarbon in suspending medium, such as isoalkane (Isopar) G) have good dissolubility, but be not adsorbed on the electrophoretic particles.The existence of this polymkeric substance in solution it is believed that (although the present invention never is subject to the restriction of this theory) caused the weak flocculating of pigment by known in the colloid ambit " vacancy flocculation " mechanism.For identical purpose, also can adopt the polymkeric substance except PIB.The another kind of examples of polymer of having found to be useful on this is Kraton G, and a kind of segmented copolymer is included in the polystyrene block and the Parleam block that form agglutinate structure in the suspending medium.In this case, agglutination body is the material that causes the vacancy flocculation, rather than the segmented copolymer of monomer itself.

No matter what polymkeric substance to cause vacancy with, the material adding suspending medium of soluble high-molecular amount all will be increased the viscosity of this medium.Because response time of display (under the fixed working voltage, or its any given pixel, show the needed time at two extreme optical state Transforms) be directly proportional with the viscosity of medium, concerning picture steadiness, will reduce by this method the switch speed of display.And, (it can be defined as practically because the vacancy Flocculating mechanism only is higher than stack concentration at polymer concentration, polymer concentration when causing dielectric viscosity to be increased to twice) work the time, all polymkeric substance that work by this mechanism are estimated all can produce similar switch speed and are reduced.In the practice, enough when stable when producing with enough polymkeric substance, switch speed reduces to about 1/2nd to 1/3rd.People wish to have other mode to realize picture steadiness, and can not diminish like this response time.

As discussed above, PIB and other polymkeric substance have improved picture steadiness by the colloidal stability of control granules of pigments.The particle that is recorded among the above-mentioned WO02/093246 preferred coated polymkeric substance has colloidal stability in suspending medium because in its preparation process the grown polymer shell of (being generally) poly-(dodecyl methyl acrylate) of particle surface.Composition by suitable control polymer shell, particle is had with PIB, Kraton and other be dispersed in the identical colloidal stability that polymkeric substance provides in the suspending medium (and thereby show identical picture steadiness), but not need that condiment such as PIB are arranged in the suspending medium.This display should be greatly faster than the display that contains PIB or equivalent, and should be in the lower speed operation to equate under the voltage that applies.

Summary of the invention

On the one hand, the present invention tries hard to provide the method for the electrophoretic particles of the polymer shell with modification, and it can be produced fast and the display of image stabilization.

On the other hand, the present invention tries hard to provide a kind of improved two-step approach form, for the preparation of this electrophoretic particles that is coated with polymkeric substance, described in top the 21st section.In the preferred form of the method, titania (or similar metal oxide pigment) is at first used silicon dioxide coated, and then this is coated with the titania of silicon dioxide with the silane treatment that contains thiazolinyl.Then exist in the situation of radical polymerization initiator, titania and various unsaturated monomer that the silane treatment that obtains is crossed react, such as 2-ethylhexyl acrylate or dodecyl methyl acrylate, thereby form the titania that is coated with polymkeric substance of expecting.Process carbon black with the diazo reagent that contains thiazolinyl, the reaction product of 4-ethene aniline and nitrous acid for example is connected to the surface of carbon black with thiazolinyl, makes afterwards it to react with various unsaturated monomer with mode substantially the same described in the titania.

In the ad hoc approach shown in the embodiment of above-mentioned WO02/093246, last polymerization procedure (being called as " graft polymerization step ") carries out in toluene, mainly is because known this solvent has good performance to be used for this type free base polymerization process in polymer industry.Yet in the process of the electrophoretic pigment particles for preparing polymer coating, it works as inconvenient as solvent phase.Because the many reasons that discusses in detail in the patent of aforementioned E Ink and MIT and the application, in practice, the suspension that uses in the electrophoretic display device (EPD) is aliphatic hydrocarbon (combining separately or with halocarbon).Therefore, because the granules of pigments of polymer coating is dispersed in the aliphatic hydrocarbon the most at last, and need to avoid this aliphatic hydrocarbon of toluene concentration (because the character of electrophoretic medium is responsive to the very little change in elevation of suspension component easily in some cases), in toluene, finish polyreaction and with pigment after separating from toluene of polymer coating, must be suspended at the granules of pigments of polymer coating the toluene of removing all traces before the final suspension.In practice, must contain toluene granules of pigments one or many with what tetrahydrofuran (THF) washing came from the graft polymerization step, centrifugal so that pigment is separated from THF after the washing, last in baking oven dried pigment to remove the THF of last trace.All these processes must be implemented two kinds of pigment that use in two particle electrophoresis media respectively.

These washings, centrifugal and drying steps be labour intensive and cost very high.Owing to dry pigment is dispersed in the final suspension again, has just caused further cost.In addition, owing to have toluene and THF, washing, centrifugal and the drying steps often pigment of danger and commercial size ground production polymer coating need to use explosion-proof baking oven, mixer and hydro-extractor, and explosion-proof electric-control board, and this has increased the cost of production equipment greatly.Simultaneously, although used the method for protective device or anti-exposure, the operator still can be exposed in the steam significantly in process.At last, drying steps may be harmful in the performance of pigment in final electrophoretic medium.Therefore people wish to find a kind of substituting solvent, wherein can carry out polyreaction, and can exempt if possible dry needs with disperseing again dried pigment.

At last, the present invention tries hard to provide the electro-optic displays that can drive with a kind of simplified way.No matter display is reflective or transmission-type, and whether bistable the electro-optical medium that no matter uses is, and for obtaining a kind of high-resolution display, the single pixel of display must be addressable and be not subjected to the interference of neighbor.A kind of method that realizes this target is, a kind of nonlinear element array is provided, for example transistor or diode, and wherein at least one nonlinear element all links to each other with each pixel, thereby produces a kind of " active matrix " display.A kind of addressing that is addressed to a pixel or pixel electrode are connected with suitable voltage source by relevant nonlinear element.Usually, when nonlinear element was transistor, pixel electrode linked to each other with this transistorized drain electrode, and this set can be supposed as follows, although its basically be arbitrarily and pixel electrode can link to each other with transistorized source electrode.Usually, in high-resolution array, pixel is arranged to the two-dimensional array of row and column, so that any specific pixel is limited uniquely by the intersection point of a particular row and a particular column.The source electrode of every row all crystals pipe links to each other with single row electrode, and the gate pole of every row all crystals pipe links to each other with single column electrode; Equally, source electrode is conventional to row and gate pole to the setting that is listed as, but is arbitrarily basically, and can be inverted if desired.Column electrode links to each other with line driver, this has guaranteed only to select delegation in any given moment basically, namely, voltage is applied on the selected column electrode, to guarantee that transistors all in select row has electric conductivity, and voltage is applied to all other row, keeps not having electric conductivity to guarantee transistors all in these non-selected row.The row electrode links to each other with row driver, and it is arranged on a plurality of row electrode voltages, selects this voltage to arrive its predetermined optical states with the pixel that drives in the select row.(above-mentioned voltage is relevant with conventional front electrode, and this electrode usually is arranged on one side opposite with non-linear array in the electro-optical medium and extends in the whole display).After the pre-selected interval that is called " row addressing time ", cancel selected row, selected next line, the voltage on the row driver changes over the next line that writes display.Repeat this process so that whole display writes in line by line mode.Therefore, in the capable display of N, any given pixel is the time of addressing mark 1/N only.

Successfully set up the method for making Active Matrix Display.For example, thin film transistor (TFT) can utilize various depositions and photoetching technique to make.Transistor comprises gate pole, insulation dielectric layer, semiconductor layer and source electrode and drain electrode.Apply voltage so that the electric field of striding dielectric layer to be provided to gate pole, this will significantly increase, and source electrode arrives the electric conductivity of drain electrode in the semiconductor layer.This variation has allowed the conductivity between source electrode and the drain electrode.Usually, composition is carried out in gate pole, source electrode and drain electrode.In general, semiconductor layer is also carried out composition in order to reduce stray electrical conduction (namely disturb) between the adjacent circuit element.

Liquid crystal display adopts the thin film transistor (TFT) (" TFT ") of amorphous silicon (" a-Si ") as the switching device shifter of display pixel usually.This TFT has lower gate configuration usually.In a pixel, thin-film capacitor is keeping being switched and the electric charge of transmission by TFT usually.Electrophoretic display device (EPD) can adopt the TFT that similarly has electric capacity, although this electric capacity is different from the liquid crystal display some on function; Referring to WO00/67327, and above-mentioned 2002/0106847 and 2002/0060321.Thin film transistor (TFT) can manufacture has very high performance.Yet the manufacture process meeting so that cost significantly increase.

In the TFT addressing array, pixel electrode is expert in the addressing time by TFT and charged.In the addressing time course of being expert at, the gate voltage that applies by change makes TFT switch to conduction state.For example, for n-type TFT, gate voltage switches to " high pressure " state so that TFT switches to conduction state.

What do not wish to see is that when the capable voltage of selecting changed to cause that the TFT passage exhausts, the pixel electrode typical earth surface revealed variation.Pixel electrode generation variation is because have electric capacity between pixel electrode and the TFT gate pole.This variation model can be:

ΔV _p＝G _gpΔ/(C _gp+C _p+C _s)

C wherein _GpBe gate pole pixel capacitance, C _pBe pixel capacitance, C _sBe memory capacitance, and Δ is the skew of the gate voltage when TFT effectively exhausts mark.This variation is commonly referred to " gate pole feedthrough ".

The gate pole feedthrough can be by upper plane voltage (being applied to the voltage on the conventional front electrode) offset Δ V _pRemedy.Yet this can complicate the issue because between pixel and the pixel because C _GpDifference and make Δ V between pixel and the pixel _pDifferent.Therefore, bias voltage possibility sustainable existence, in addition also like this when the upper plane of change remedies the mean pixel variation.Bias voltage can cause the error of pixel optics state, and the degraded of electro-optical medium.

C _GpVariation be because, for example be used to form misalignment between two conductive layers of the gate pole of TFT and source electrode-drain electrode level; The variation of gate pole dielectric thickness; And the etched variation of row, width error is caused at once.

The tolerance of the conductive layer of depositing for mistake can obtain by utilizing the gate pole that is superimposed on fully on the drain electrode.Yet this technology can cause very large gate pole pixel capacitance.Large gate pole pixel capacitance is undesirable, because it may carry out a large amount of remedying at a selected capable voltage levvl.And existing addressing structure can produce undesirable bias voltage, for example, and owing to different the causing between pixel in the gate pole pixel capacitance and the pixel.This voltage can produce damage effect to specific electro-optical medium, particularly when having the long period.

The problems referred to above are so that use a kind of electro-optical medium that does not have a threshold voltage to design the task that a kind of bistable electro-optic displays is difficulty.Because some pixels on the display can seldom be upgraded, even do not need, people must guarantee that the optical states of this pixel keeps interference-free as far as possible.In the practice, this mode has reduced to be applied to quantity and the amplitude at the stray voltage peak on this pixel.

For example, the voltage that is added on source electrode (data) row of Active Matrix Display of facility scans in the mode of above-mentioned routine.In the electrophoretic display device (EPD) of encapsulation, these row switch between+15V and the-15V with respect to conventional electrodes, and are frequent as each row addressing time (selecting the time of the given row of Active Matrix Display) of this display.These voltages on electric capacity directly and the pixel electrode coupling of display, and may be very firm in this Pixel Design that is coupled at field shield.Even be forced to for a long time in the situation of DC balance at the voltage peak of these couplings, apply continuously the change that these Voltage Peaks also may cause the pixel optics state.

Known these voltage peaks, and the problem that causes thus can reduce by the pixel storage capacitor that is coupled to each pixel electrode is provided; Referring to for example above-mentioned 2002/0106847.In the prior art, but reduce or the basically unique implementation of eliminating the impact of these voltage peaks is, increase the size of pixel storage capacitor, can greatly increase like this power consumption of display.In addition, the large scale of memory capacitance has limited maximum accessible resolution, and because the increase of metal-metal stack area may cause the reduction of screen board output.

Now clear, problem discussed above can be by using the electro-optical medium can show threshold voltage in the active matrix electro-optic displays, that is, and and the medium that when being subject to the voltage of low and non-zero, basically can not switch and being reduced or eliminated.

On the one hand, the invention provides a kind of electrophoretic medium, comprise the charged particle that is suspended in the suspension, this particle has the polymer shell that comprises repetitive, described repetitive is from least a monomer, and the homopolymer of this monomer is incompatible with described suspension.

This aspect of the present invention will be called " incompatible monomer medium " hereinafter for simplicity.In this medium, polymer shell preferably further comprises repetitive, and it comes from least a monomer, and the homopolymer of this monomer is compatible with described suspension.Described one or more monomers (these monomers will be called " compatible monomer " hereinafter for simplicity) that form compatible homopolymer can account for described polymer shell weight about 15% to about 99%, preferably approximately 50% to 99%.Described suspension typically is hydrocarbon, but also can adopt hydrocarbon and other compatible solvent, such as the potpourri of halocarbon.Perhaps, can adopt silicone fluid or fluorocarbon as suspension

Form the monomer (this monomer will be called " incompatible monomer " hereinafter for the purpose of degeneracy) of incompatible homopolymer.Should be appreciated that whether the particle monomer can be counted as incompatible monomer and depend on employed specific suspension, and specific monomer can be incompatible monomer in a kind of suspension, and be compatible monomer in different suspensions.For example, the dodecyl methyl acrylate is compatible monomer in the aliphatic hydrocarbon suspension, then is generally incompatible monomer in the silicones suspension.

For the medium that only or mainly contains hydrocarbon, incompatible monomer can for, by any or multiple acrylate or the methacrylate that contain the alcohols that is not more than about eight carbon atoms and form, described alcohols optionally contains hydroxyl or halogen or other polar substituent, for example carboxyl, cyano group, ketone or aldehyde radical; Acrylamide and Methacrylamide; N, N-dialkyl group acrylamide; The N-vinylpyrrolidone; Styrene and its derivatives; Vinyl esters; And ethene halogenide.The particular instance of incompatible monomer comprises methyl methacrylate, β-dimethyl-aminoethylmethacrylate, butyl methacrylate, isobutyl methacrylate, Tert-butyl Methacrylate, 2-Propenoic acid, 2-methyl-, octyl ester, 2-Ethylhexyl Methacrylate, HEMA, acrylamide, acrylic acid, vinyl cyanide, methyl vinyl ketone, Methacrylamide, N-vinylpyrrolidone, styrene, vinyl acetate, vinyl chloride and vinylidene chloride.Other example of incompatible monomer comprises fluorine-containing acrylate and methacrylate, such as the fluorinated monomer of trifluoroethyl methacrylate, acrylic acid hexafluoro butyl ester or other kind, such as pentafluorostyrene or contain other polyfluoro aryl molecule of polymerizable functional group.The incompatible monomer of other kind in the hydrocarbon medium comprises the molecule of containing silicone resin, comprises polymerisable vinyl in its structure.In the particular hydrocarbon medium of the present invention of in following examples, describing, compatible monomer comprises the dodecyl methyl acrylate, and incompatible monomer comprises any or multiple in trifluoroethyl methacrylate, acrylic acid hexafluoro butyl ester, styrene, Tert-butyl Methacrylate and the N-vinylpyrrolidone.

For the suspension of other type, fluorocarbon medium for example, the many incompatible monomer in the above-mentioned type can use with the fluorocarbon monomer of the compatible monomer of conduct of vast scale.Similarly, for the silicones suspension, compatible monomer can comprise a large amount of silicones groups, and incompatible monomer can comprise any monomer listed above, except those comprise a large amount of silicones functionality.

Inconsistent monomer medium can further comprise the charged particle of the second type, and it has at least a optical property different from other (the first) one or more charged particles, and this second charged particle has polymer shell.In a kind of form of this pair of particle system, the first charged particle comprises titania, and the second charged particle comprises carbon black or copper chromite.

The present invention also provides a kind of electrophoretic particles for incompatible monomer medium of the present invention.In adopting hydrocarbon or the electrophoretic medium of halocarbon as suspension, this electrophoretic particles (hereinafter being called for simplicity " incompatible monomer particle ") comprises the granules of pigments with repetitive polymer shell, described repetitive is from least a monomer, and homopolymer and the normal hexane of this monomer are incompatible.(obvious for the electrophoretic medium those skilled in the art, be generally used for the potpourri that hydrocarbon suspension in this medium comprises various low-molecular-weight aliphatic hydrocarbons, not clear for fear of implication, available normal hexane is as the compatibility of single test compounds in order to test and this hydrocarbon mixture).

In incompatible monomer particle of the present invention, polymer shell can further comprise the repetitive from least a monomer, and homopolymer and the normal hexane of wherein said monomer are compatible.Compatible monomer can account for polymer shell weight about 15% to about 99%, preferably approximately 50% to about 99%.Incompatible monomer can comprise any or multiple in those materials of listing in top the 56th section.In the of the present invention specific particle of describing in following examples, compatible monomer comprises the dodecyl methyl acrylate, and incompatible monomer comprises any or multiple in styrene, Tert-butyl Methacrylate and the N-vinylpyrrolidone.The pigment that is used to form particle of the present invention can be, any or multiple in titania, carbon black and the copper chromite for example.

On the other hand, the invention provides for fluoridizing and based on the similar electrophoretic particles of silicones suspension.Therefore, the invention provides a kind of electrophoretic particles, it comprises the granules of pigments with repetitive polymer shell, and described repetitive is from least a monomer, and homopolymer and the perfluorodecalin of this monomer are incompatible.The present invention also provides a kind of electrophoretic particles, and it comprises the granules of pigments with repetitive polymer shell, and described repetitive is from least a monomer, and the homopolymer of this monomer and viscosity are that the dimethyl silicone polymer 200 of 0.65 centistoke is incompatible.

On the other hand, the invention provides a kind of electrophoretic medium, comprising:

Suspension;

Be suspended in the first kind charged particle in the suspension, described first kind particle has the first optical property and polymer shell; And

The Equations of The Second Kind particle, it has the second optical property that is different from described the first optical property, and polymer shell;

Wherein said polymer shell is arranged to, and makes the even aggegation of the first and second class particles be better than inhomogeneous aggegation at thermodynamics.

This medium is called as hereinafter for simplicity " evenly agglutination medium " of the present invention.Should be appreciated that at the of the present invention pair of incompatible monomer medium of particle and evenly have considerable overlappingly between the agglutination medium that it means that many media all can satisfy the definition of these two simultaneously.

In even agglutination medium of the present invention, the polymer shell of the first and second class particles can comprise respectively the repetitive from least a monomer, and homopolymer and the suspension of described monomer are incompatible.Every kind of polymer shell can further comprise the repetitive from least a monomer, and homopolymer and the suspension of described monomer are compatible.Compatible monomer can account for polymer shell weight about 15% to about 99%, preferably approximately 50% to 99%.This suspension can have the specific inductive capacity less than about 5, and can comprise hydrocarbon, is preferably aliphatic hydrocarbon.Perhaps, described suspension can comprise aryl-alkane or dodecyl benzene.

Equally, incompatible monomer can be included in one or more in top the 46th section those materials of listing.In the preferred form of even agglutination medium, compatible monomer comprises the dodecyl methyl acrylate, and incompatible monomer comprises any or multiple in styrene, Tert-butyl Methacrylate and the N-vinylpyrrolidone.

For the reason of following detailed explanation, even agglutination medium of the present invention can have the operating threshold threshold voltage.This medium can be for what encapsulate, that is, suspension and particle can be kept in a plurality of capsules or the unit.

The present invention also provides a kind of electrophoretic display device (EPD), comprises any electrophoretic medium among the present invention, and at least one is arranged near the electrode this electrophoretic medium and is arranged to apply electric field to it.

The present invention also provides a kind of active matrix electro-optic displays, comprises one deck electro-optical medium; And be arranged near a large amount of pixel electrode of electro-optical medium layer, and be arranged to apply electric field to it, wherein said electro-optical medium shows threshold voltage.

This electro-optic displays will be called " threshold voltage display " of the present invention hereinafter for simplicity.In this display, electric capacity can be linked to each other with each pixel electrode.Described electro-optical medium can comprise a large amount of charged particles that are suspended in the suspension, and it can move through wherein when applying electric field to this electro-optical medium.These charged particles can have the polymer shell from the repetitive of at least a monomer, and the homopolymer of this monomer is incompatible with described suspension.This electro-optical medium can also be even agglutination medium of the present invention.

At last, the invention provides a kind of method of making the granules of pigments of polymer coating, the method comprises:

(a) make the reaction of granules of pigments and reaction reagent, this reaction reagent has and can and be connected in functional group on this particle with this particle reaction, but also have the group of polymerisable or initiated polymerization, thereby this functional group is reacted with described particle surface and described polymerisable group is connected thereon; And

(b) but under the condition that reacts between the group of the polymerizable that can effectively cause described particle or initiated polymerization and described at least a monomer or the oligomer, the product of step (a) and at least a monomer or oligomer are reacted, thereby form the polymkeric substance that is connected on the described granules of pigments.

Wherein step (b) is carried out in aliphatic hydrocarbon.

The method can be called as " aliphatics polymerization reaction method " of the present invention hereinafter for simplicity.

Description of drawings

Fig. 1 is the method response diagram that schematically shows for the production of incompatible monomer electrophoretic particles of the present invention.

Fig. 2 is that the dynamic range of expression even aggegation electrophoretic medium of the present invention changes as the alive functional arrangement of executing of various pulse lengths, described in following examples.

Embodiment

The above points out, the present invention relates to adopt the electrophoretic medium of the particle with polymer shell, is used for the electrophoretic particles of this medium, contains this medium or the similar electrophoretic display device (EPD) of electro-optical medium, and for the preparation of the method for above-mentioned polymer shell.Relate to electrophoretic particles, thereon form polymer shell method, comprise the electrophoretic medium of this particle and the background technical information of display, the reader can be referring to above-mentioned WO02/093246, particularly its 12nd to 41 page.Can also be referring to above-mentioned 2002/0185378, the [0124] to [0165] section.Because this information is easy to obtain in these open applications, will no longer repeat at this, unless need to explain what kind of difference is the similar solid described in electrophoretic particles of the present invention, medium, display and method and these international applications have.

The polymer shell that exists at electrophoretic particles of the present invention can not exclusively cover the surface of particle, and this is just can be with regard to this polymer surfaces forms without other polymkeric substance; Certainly, discuss as following, often find that second polymerization procedure will form on the surface of particle other polymkeric substance usually.Therefore, term " polymer " shell used herein " and do not mean that a kind of polymer coating layer only and get rid of the possibility that forms other polymkeric substance by further polymerization procedure at particle.

Be used for connecting many ceramic oxide pigment, especially the preferred kind of the functional group of the coated titania of silicon dioxide and/or aluminium oxide and similar silicon dioxide coated granules of pigments has, silane coupled group, the especially group of trialkoxy silane coupling.A kind of preferred reagent that is used for polymerisable group is connected on titania and the similar pigment is above-mentioned 3-(trimethoxysilyl) propyl methyl acid esters:

H ₂C＝C(CH ₃)CO ₂(CH ₂) ₃Si(OCH ₃) ₃ (I)

This material can be from Dow Chemical Company, Wilmington, and Delaware buys, and commodity are called Z6030.Also can use corresponding acrylate.Another kind of practical reagent is the amino silicyl derivant of following general formula:

H ₂C＝CHC ₆H ₄CH ₂NHCH ₂CH ₂NH(CH ₂) ₃Si(OCH ₃) ₃.HCl (II)

Except providing " anchor " to polymer shell so that forming around the electrophoretic particles afterwards, these silicyl methyl (acrylate) also contain the group of controlling electric charge, and it has given final electrophoretic particles obtains the expection electric charge in the situation that one or more suitable charged reagent exist ability.When needing the particle of positively charged, can use the reagent of general formula (II), and the reagent of general formula (I) provides electronegative particle.Certainly, two kinds of reagent all comprise polymerisable vinyl, and it can allow to produce in the solution grafting process of polymeric groups.

In practice, the suspension in the electrophoretic medium is generally the liquid with low-k, for example hydrocarbon, halocarbon (especially fluorocarbons) or silicones.Incompatible monomer medium of the present invention can use the suspension of any these kinds.The medium that the present invention contains main reference the hydrocarbon suspension below describes, and is apparent with the suspension that utilizes other type for the technician in the colloidal chemistry field of this suspension but change medium.Polymer shell itself generally includes the hydrocarbon chain (that is, the chain of the homopolymer of formation and suspending medium highly compatible) of vast scale; The group that provides except for charged purpose and for the compatibility of adjusting with suspension, as described below, then do not need a large amount of strong polarity or ionic group.Equally, at least when the medium that will use particle comprises the aliphatic hydrocarbon suspension (as conventional situation), advantageously polymkeric substance has side chain or " comb shape " structure, and it has a main chain and a plurality of side chain away from this main chain extension.Each of these side chains should have about at least four, preferably about at least six carbon atom.In fact long side chain will be favourable; For example, dodecyl (C ₁₂) side chain.Side chain itself can be branch; For example, each side chain can be branched alkyl, such as the 2-ethylhexyl.It is believed that (although the present invention never is subject to the restriction of this theory) is owing to the high affinity of hydrocarbon chain to the alkyl suspension, the side chain of polymkeric substance is expanded with scopiform or tree structure by a large amount of liquid each other, thereby prevented close ties with other similar particle, and so that this particle has colloidal stability in suspended particle.

Described in above-mentioned WO02/093246, having found has an optimum range for the amount that will be formed at the polymkeric substance on the electrophoretic particles, and can reduce its electrophoretic property at particle formation polymkeric substance excessive or in shortage.Optimum range will change along with some factors, comprise the density of coated particle and size, wherein will use the character of suspending medium of particle and the character that is formed at the polymkeric substance on the particle, for any specific particle, polymkeric substance and suspending medium, optimum range preferably rule of thumb comes to determine.Yet, by general guidance, should be noted that particle is more intensive, the optimal proportion that polymkeric substance accounts for particle weight is lower, and more segmentation (particle size is less) of particle, and the optimal proportion of polymkeric substance is higher.Put down in writing among the above-mentioned WO02/093246, particle should be coated with at least 2%, the polymkeric substance of preferred at least 4% weight, and in most of the cases, the optimal proportion scope of polymkeric substance is 4% to 15% of particle weight, is generally 6% to 15% of particle weight, most preferably is 8% to 12% of weight.In more detail, in the situation of titanium dioxide granule, put down in writing among the above-mentioned WO02/093246, the preferred polymers scope is 8% to 12% of titania weight.

Yet, in order to help the application of the present invention in the particle of in a big way particle size and density, can be advantageously with the form of polymer surfaces density (namely, the polymer weight of per unit area particle surface) amount of polymkeric substance is described, for example the polymkeric substance milligram number of every square metre of particle surface.The superficial density of polymkeric substance can be calculated by following general formula:

Γ＝WρD/6

Wherein Γ is the superficial density of polymkeric substance, and W is the polymer weight (deriving from thermogravimetry) of every gram sample, and ρ is the density of base particle, and D is the diameter of base particle.For copper chromite, the useful scope of having found superficial density is 2 to 40mg/g, and preferable range is 14 to 24mg/g, and particularly preferred scope is 18 to 22mg/g.

Except electrophoretic display device (EPD), the particle of polymer coating of the present invention can also be used for other application.For example, the controlled affinity to the hydrocarbon material that is provided by the polymkeric substance that is coated on the pigment of the present invention will make pigment have advantage for polymkeric substance and rubber mass, and wherein said pigment will be than similar but without the coated easier dispersion of pigment.The chemical property dirigibility of polymer coating layer so that should coated layer " adaptation " in any particular substrate controlled dispersiveness.Therefore, but pigment of the present invention can be used as dispersed color or reactive extrusion compound.In addition, the trend that between particle and host material, cut-out occurs or break at the interface by reducing this potpourri, this polymer coating layer on the particle can be used for improving the mechanical property of this pigment/polymkeric substance or rubber composition.If produce polymer coating particle (as discussed above) by the method for in the potpourri with " dissociating " polymkeric substance that is not connected on the particle, producing the polymer coating particle, then in many cases, needn't be in that particle is separated coated particle before being dispersed in polymkeric substance or rubber mass from free copolymer, because free polymer dispersed will not have harm in matrix.

In medium of the present invention, can be based on relevant chemical inertness, and the density that is complementary of electrophoretic particles or and electrophoretic particles and capsule or the micro unit wall chemical compatibility (in the situation of encapsulationization electrophoretic display device (EPD)) between the two to the selection of suspension.When the needs particle moving, fluid viscosity should be low.The refractive index of suspension also can be basically and being complementary of particle.Here " the basically coupling " of the refractive index of employed suspension and particle refers to that their specific refractivities separately are between about 0 to about 0.3, preferably between about 0.05 to about 0.2.Yet, by the electrophoretic display device (EPD) that scattered power determines, need the refractive index between scatterer and the medium that big-difference is arranged for the optical states part.Titanium dioxide granule usually as scattering particles in order in two particle electrophoresis displays, to produce white states, this material has high index of refraction (about 2.7), so just needs to have low-refraction in the suspending medium.

Practical organic solvent includes but not limited to that epoxide is such as decane epoxide and dodecane epoxide; The ethene ethers is such as cyclohexyl vinethene and Decave (International Flavors﹠amp; Fragrances, Inc., New York, the registered trademark of NY); And aromatic hydrocarbons, such as toluene and other benzene derivative, such as dodecyl benzene and naphthalene and alkyl naphthalene derivant.Practical halogenated organic solvent includes but not limited to tetrafluoro dibromoethane, zellon, chlorotrifluoroethylene, 1,2,4-trichloro-benzenes and phenixin.These materials have high density.Practical hydro carbons includes but not limited to, dodecane, the tetradecane, Isopar (registered trademark) series (Exxon, Houston, TX), Norpar (registered trademark) (a series of n-paraffin), Shell-Sol (registered trademark) (Shell, Houston, TX) and aliphatic hydrocarbon, naphtha and other the white spirit of Sol-Trol (registered trademark) in (Shell).These materials have low-density usually.The practical example of silicone oil includes but not limited to, the annular siloxane of prestox cyclosiloxane and higher molecular weight, poly-(methyl phenyl siloxane), HMDO and dimethyl silicone polymer.These materials have low-density usually.Practical low-molecular-weight polymer containing halogen includes but not limited to, poly-(chlorotrifluoroethylene) polymkeric substance (Halogenated Hydrocarbon Inc., River Edge, NJ), Galden (registered trademark) (from Ausimont, Morristown, the perfluorinated ethers of NJ), perhaps from the Krytox (registered trademark) of du Pont (Wilmington, DE).Many above-mentioned substances are available in a series of viscosity, density and boiling point.

Electrophoretic particles, medium and display with controlled particle/suspension compatibility

Up to now, people think that natch the polymkeric substance that needs to have highly compatible with circumgranular suspension in a kind of and the electrophoresis matrix (being generally aliphatic hydrocarbon, such as isoalkane G) forms a kind of polymer coating layer or shell around electrophoretic particles.It is believed that needs to use the polymer shell of this highly compatible so that good spatial stability to be provided.Therefore, in most of embodiment of above-mentioned WO02/093426, only need single monomer, and single polymerization procedure comes to provide polymer shell stable on the space at the functionality pigment of colloidal stability.The monomer that is used to form this polymer shell is the dodecyl methyl acrylate normally, but also uses other monomer in above-mentioned WO02/093426.

Have realized that by polymer-modified shell to make the compatibility of itself and suspension few, that is, make the some parts of this polymer shell and suspension incompatible, can obtain some important advantage, especially improve picture steadiness.

What term " compatible " and " incompatible " were used here is that it is in the implication of polymer arts.In the simplest level, the compatibility of polymkeric substance and the suspension meaning is that polymkeric substance (when not when relevant basic electrophoretic particles links to each other) dissolves in the solvent.Whether polymkeric substance is solvable can determine by simple visual examination usually; Solution is optically clear normally, but not solution (potpourri or dispersion) is opaque or has obvious two phases.

Yet compatibility is not dimorphism, that is to say, polymkeric substance does not need with given suspension perhaps fully incompatible fully mutually.But an inclusive ranges is arranged, it depends between fluid and the polymer segment (roughly being to form the monomer of polymkeric substance) and the interactional relative intensity between the polymer segment itself.When the polymkeric substance height was dissolved in the fluid, polymkeric substance-fluid interaction more was better than Polymer-polymer Thermodynamic Interaction on energy.In this case, polymkeric substance is easy to form twister, and the described polymkeric substance twister in the solution is longer than the twister of polymkeric substance in the polymer melts.This prolongation can utilize capillary viscosity agent or light scattering technique to record.For example, if measure a series of characteristic viscosities [η] with polymer samples of different molecular weight (M), usually find between these two amounts, to have power law relation:

[η]＝KM ^α

The scope of index α is between 0.5 to about 0.8 (for flexible polymer), and it depends on the quality of solvent, and it is better to be worth larger expression solvent.When α=0.5, fluid is called as " theta solvent ", similar (that is, only being surrounded by other polymer segment) in the conformation of polymkeric substance and the polymer melts, and so in fact this polymkeric substance and fluid have moderate compatibility.The conformation of polymer chain moves at random under this class condition.

For homopolymer and copolymer systems the two, the Huggins coefficient can be used as the index of solvent quality (that is, the compatibility of polymkeric substance and solvent).The Huggins constant is the item [η] in the expression formula of relative viscosity of following polymkeric substance dilute solution ²κ ':

$\frac{\mathrm{\η}}{{\mathrm{\η}}_s}=1+\left[\mathrm{\η}\right]c+\mathrm{\κ}\′{\left[\mathrm{\η}\right]}^2{c}^2+...$

η in this expression formula _sBe the viscosity of solvent, [η] is characteristic viscosity, and c is the concentration of polymkeric substance in the fluid.For compatible fluid, the scope of κ ' is 0.30 to 0.40, and for more inconsistent fluid, κ ' is large (0.50 to 0.80).(referring to C.W.Macosko, RheologyPrinciples, Methods, and Applications, VCH Publishers, 1994, p.481).

Similarly the second virial coefficient value of the given fluid-polymer solution that can measure by static light scattering or osmometery of information is collected and is obtained.In general, large second virial coefficient means comparatively compatible fluid.In situation about combining between the polymkeric substance of dissolving, for incompatible polymers-solvent phase interaction basically, second virial coefficient even can become negative value (referring to C.Tanford, Physical Chemistry of Macromolecules, JohnWiley and Sons, New York, 1961, pp.293-296).

When polymkeric substance is insoluble in the fluid, be inconsistent, this polymkeric substance sometimes still can be by described fluid institute swelling.Under this situation, swellbility (at the ratio of the volume that has polymer samples in the situation of fluid with the dry polymer volume) can be used as measuring of fluid and polymer-compatible degree.Swellbility is larger, and compatibility is higher.

Can make the compatibility of polymer shell and suspension less by certain methods.At first, polymer shell can have the repetitive from least a monomer, and homopolymer and the suspension of this monomer are incompatible, and is consistent with the aspect of incompatible monomer electrophoretic medium among the present invention.Typically, this polymer shell also can comprise a kind of compatibility monomer, a kind of its homopolymer monomer compatible with suspension namely, and the compatibility of polymer shell and suspension can be adjusted by the ratio that changes two kinds of monomers.

The polymer shell (obviously, every kind exist type may be incessantly a kind of) that comprises simultaneously incompatible and compatible monomer can be that (perhaps it is unique polymerization procedure) adopts polymerizable monomer mixture and the randomcopolymer shell that forms in last polymerization procedure.If wherein a kind of monomer is compatible and a kind of with suspension incompatible, then can set up a series of colloidal stability in this particle according to the ratio of monomer in shell.And, because different monomeric species can be given incompatibility in various degree, can further adjust inconsistent degree by changing this incompatible monomer.For example, now observe, when as the only monomer in the polymer shell, the acrylate (for example butyl methacrylate) with the short-side chain that is not more than about eight carbon atoms is created in the particle that does not have colloidal stability in the isoalkane G suspension.On the other hand, the dodecyl methyl acrylate is created in the electrophoretic particles that has splendid colloidal stability among the isoalkane G.Therefore, certain mol proportion with butyl methacrylate and dodecyl methyl acrylate in polyblend is routine, the multipolymer of this dodecyl methyl acrylate and butyl methacrylate will produce the polymer shell with isoalkane G edge compatibility, and the particle of a kind of edge colloidal stability.

Modification is polyreaction by subordinate phase around the another kind of method of the polymer shell of electrophoretic particles.Experiment shows above-mentioned general formula (I) and the surface functionality that (II) provides does not have full consumption and falls in single graft polymerization step process.For example, if the titania of functionalisation of surfaces and polymer coating only is resuspended in the polymerisation medium (generally include toluene, dodecyl methyl acrylate and as the azoisobutyronitrile (AIBN) of initiators for polymerization) simply, heat and after 16 hours the pigment that separates is done thermogravimetry show from reaction mixture, the amount of conjugated polymer increases to some extent (to be measured by thermogravimetry (TGA): after first time polyreaction: 7.3%; For the second time after the polyreaction: twice different in service be 8.9% and 9.9%).In this dual graft polymerization process, the monomer that uses in the polyreaction for the second time can from the first time in use different, thereby make it can in final polymer shell, add polymer chain by the different monomers structure.In addition, by changing the condition of the first polymerization procedure, can adjust the initial grafting density of chain, and the existence of the surperficial ethylene functionality of subordinate phase polyreaction (and attainability).Therefore, this Dual polymerization method provides the second flexibility ratio in the electrophoretic particles of polymer stabilising makes up.In first or second polymerization stage by in polymeric blends, adding chain-transferring agent, thereby the molecular weight of perhaps adjusting the concentration telomerized polymer chain of monomer or radical initiator by the known method of polymer arts may be very useful.

Because at present preferred aliphatic hydrocarbon suspension is considered to all very low with the compatibility of many homopolymer usually, the monomer that therefore is easy in a large number to obtain can be used for by the incompatible monomer in the polymer shell of any manufacturing in above-mentioned two kinds of methods.This incompatible monomer comprises the acrylate with alkyl, its chain length and branched structure are different, but (for example usually have eight or carbon atom still less, methyl methacrylate, β-dimethyl-aminoethylmethacrylate, butyl methacrylate, isobutyl methacrylate, Tert-butyl Methacrylate, 2-Propenoic acid, 2-methyl-, octyl ester, 2-Ethylhexyl Methacrylate), and corresponding acrylate, acrylate with fluorocarbons ester side chain, the acrylate of functionality alcohols, HEMA for example, acrylic amide, acrylamide for example, Methacrylamide, N-monoalkyl acrylamide and methacryl amine, N, N-dialkyl group acrylic amide, N-vinylpyrrolidone, and functionality acrylamide derivative, styrene, the styrene derivative that replaces, vinyl acetate and other vinyl esters, vinyl halides derivant (vinyl chloride, vinylidene chloride etc.) and other polymerisable monomer material.

Although the present invention never only limits to consider in theory, can provide rational explanation to the electrophoretic medium characteristic that improves, wherein circumgranular polymer shell contains incompatible monomer.The polymer shell that all is made of compatible monomer provides the spatial stability of electrophoretic particles, because it is surrounded by suspension rather than other polymer segment at the polymer chain that thermodynamics is conducive to form shell.Therefore, the polymer shell that all is made of the compatibility monomer for example is dispersed in the pure polymer shell that gathers (dodecyl methyl acrylate) in the aliphatic hydrocarbon, has the swellability of height.Because near the infiltration of the shell particle has increased the number of polymkeric substance-polymkeric substance contact with respect to more favourable polymkeric substance-solvent contact, thereby had effective repulsive force between the particle, thereby thereby it keeps the interval to be dispersed in the suspension easily each other.The polymer shell that is made of complete inconsistent monomer does not provide this spatial stability, because the polymer chain that forms shell on thermodynamics easily by other polymer segment but not suspension surround, so that polymer shell is disintegrated, arrange suspension, thus and easily each other easily aggegation of attraction of electrophoretic particles.In other words, the polymer shell of highly compatible easily makes electrophoretic particles be dispersed in the suspension, and the incompatible polymers shell easily makes the electrophoretic particles aggegation.The picture steadiness of electrophoretic medium is subject to the support of electrophoretic particles aggegation trend, because in the electrophoretic medium of every type shown in Fig. 1 to 3, in a single day image writes, and its stability depends on that the similar electrophoretic particles in the even aggegation (layer) of particle of electrophoretic particles and responsible image keeps the ability of aggegation.(notice that Fig. 1 to 3 simplifies, in fact, the stratum granulosum of more than one deck is arranged usually in the particle agglutination body that forms in imaging process).By in polymer shell, adding the compatibility that compatible and inconsistent monomer comes telomerized polymer shell and suspension, can the telomerized polymer shell and the overall compatibility of suspension, and the stability of this particle aggregate, and the picture steadiness of regulating thus resulting display.

Another advantage of the preferred embodiments of the invention is to have introduced the threshold value that electrophoretic medium switches.If electrophoretic particles attract each other with and thereby the trend of the stable and uniform agglutination body that keeps enough strong, will need significantly so that particle is released this even agglutination body, they just can move in this like this.Exist the obvious voltage threshold that is used for the switching electrophoretic medium that many benefits are arranged.If this threshold value is enough large, just can adopt the passive matrix addressing process of high resolution display.Less threshold value can be used for reducing Active Matrix Display to the sensitivity of voltage leak between stray voltage and pixel.

The present invention also provides the method for picture steadiness in the two particle electrophoresis media of another kind of raising.In two particle electrophoresis media, two types electrophoretic particles all must work to whole picture steadiness.If only a kind of particle is that " image stabilization " (that is, remaining in the even agglutination body in the position that is switched to) and Equations of The Second Kind particle free setting or diffusion in suspension are inadequate.If so, a kind of extreme optical state of medium may reasonably show good picture steadiness, but another kind will show very poor stability.Can spread such as fruit granule equally, a kind of bad picture steadiness of particle is also impelled the optical deterioration of the second extreme optical state easily.Therefore wish that two class particles all have spatial stability, it is suitably regulated to give good picture steadiness.If someone attempts to adopt the method for " vacancy flocculation " to comprise in the suspension that by making polymkeric substance obtains good picture steadiness (referring to above-mentioned 2002/0180687), the degree that then is applied to the vacancy mechanism on this two classes particle is according to the geometric configuration of the size of particle and particle and different, and can not regulate independently, also be used for giving two class particle images stability in the suspension because only have a kind of polymkeric substance to add.Yet in incompatible monomer electrophoretic medium of the present invention, the colloidal stability of every type particle can be regulated independently.And, add particle that polymkeric substance may make two independent types in the suspension relative to each other and himself do not have colloidal stability according to the vacancy flucculation process, therefore impelled two different particle types that inhomogeneous aggegation occurs.Inhomogeneous aggegation may cause many results of occuring of not wishing in two particle electrophoresis displays, comprise that slow down response time and needs use the higher voltage (owing to the higher electric field intensity of needs is separated this inhomogeneous agglutination body) that applies, and bad optical states (owing to charged inhomogeneous agglutination body may not separate by applied field fully, if wherein a class particle exists in a large number).

According to the feature of even agglutination medium of the present invention, by two particle electrophoresis media are provided, wherein the even agglutination of two class particles is better than inhomogeneous agglutination at thermodynamics, and these problems can be eliminated, and perhaps reduce at least.Reaching this effect can pass through, and two types of particles with polymer shell are provided, and regulates the compatibility of itself and suspension so that be easy to occur even aggegation, regulates simultaneously the compatibility of these two kinds of polymer shells so that be difficult for occuring inhomogeneous aggegation.In the polymer shell of two class particles, use different incompatible monomers can relatively easily realize this effect; Usually, identical compatibility monomer can be used for the polymer shell on the two class particles.If two kinds of incompatible monomers are mutually not compatible, then the trend of the inhomogeneous aggegation of this two classes particle will reach minimum, and only promote even aggegation, thereby faster response time and the purer optical states of electrophoretic medium are provided.

The above mentions, and the present invention is not limited to use aliphatic hydrocarbon as suspension.Fluorine and halocarbon oils, silicone oils, aralkyl solvent are (for example, toluene, dodecyl benzene etc.) or its potpourri also can be used for the present invention, because they can be with respect to the solvation of polymer shell and the character of modified suspending fluid further, and are as described above.

The present invention can be used in all types of electrophoretic mediums, but may be particularly useful for adopting the encapsulated electrophoretic medium of preformed capsule or micro unit.The present invention also can be applicable to have in the display of various switching geometric configuratioies, comprises forward and formula backward, and the switching of side direction and shutter mode.

In the accompanying drawing, Fig. 1 has schematically shown a kind of for the preparation of the method for optimizing according to electrophoretic particles of the present invention, such as among the following embodiment use, the method is substantially similar to the method described in the above-mentioned WO02/093246.In the phase one of the method, with silicon dioxide coated basic pigment particle 700 to produce the pigment 702 that silicifies; This step has been carried out comprehensive description in above-mentioned WO02/093246.Then, this pigment 702 that silicifies with the difunctionality agent treated, described difunctionality reagent have a kind of can with the functional group of silica surface reaction, and another kind of electric charge control group, thus produce functionalisation of surfaces pigment 704 with electric charge control group on its surface.This difunctionality reagent also provides the site that is used for forming at granules of pigments polymkeric substance.At last, as shown in Figure 1, effectively forming under the condition that is connected to the polymkeric substance on the electric charge control group, the pigment 704 of functionalisation of surfaces is contacted with one or more monomers or oligomer, thereby generate the functionality pigment 706 that is coated with polymkeric substance, it is used for electrophoretic medium.

Provide now following examples; it is the mode by illustrating only; describe the synthetic of some different electrophoretic particles with polymer shell of the present invention, described polymer shell has the controlled compatibility with suspension, and in order to the advantage of explanation by this electrophoretic particles acquisition.

Test among these embodiment will adopt the mode of contracted notation to describe, and will be as follows.These tests have been adopted based on the white TiO 2 pigment of du Pont Ti-Pure R960 with based on the black copper chromite pigment of Shepherd Black 1G.These particles have carried out the functionalisation of surfaces processing according to the reaction scheme of Fig. 7, and it adopts for the Z6030 of Chinese white and is used for the reagent of the above-mentioned general formula (I) of black pigment, then forms polymer shell thereon according to the following mode of putting down in writing.When adding contain Solsperse17K and as the isoalkane G suspension of the Span of charged reagent in the time, the white particle that generates thus is electronegative, and the black particle positively charged.Particle with the preparation of dodecyl methyl Voncoat R 3310 shell is tested in contrast, and white particle and black particle are called alphabetical J and D.Modification concerning polymer shell is described as follows: for the particle that utilizes random copolymers, one-step polymerization process to make, comonomer is labeled as, after suitable pigment indicant, alphanumeric codes shown in the lower Table I are arranged in bracket, and the numeral of the comonomer mole fraction of using in the expression polyreaction.Residue all is the dodecyl methyl acrylate in all cases.Therefore, the Chinese white made by the polyblend of the dodecyl methyl acrylate that comprises 15 % by mole Tert-butyl Methacrylate and 85 % by mole of symbol J (BMA15) expression.The two-stage polymerization process is represented by a plus sige; In general, the molar ratio of polymkeric substance that is used for these particles is very not known, does not therefore indicate component roughly.Thereby the J (+St) Chinese white made by the two-stage polymerization process of expression.Parent material has employed dodecyl methyl acrylate in 100 % by mole the first step polymerization process for contrast pigment in the case; The second step polymerization process only utilizes styrene to implement as polymerisable monomer.

Table 1

Monomer	Shorthand notation
		Styrene	St
Tert-butyl Methacrylate	TBMA
		Vinylpyrrolidone	VP

Be used to form polymer shell and particle adding electrophoretic medium and the step in the display of resulting polymer coating is as follows.All centrifugal processes of mentioning are all implemented in Beckman GS-6 or Allegra6 hydro-extractor (available from Beckman Coulter, Inc., Fullerton, CA92834).

1. standard dodecyl methyl acrylic ester polymerization reaction

The round-bottomed flask of single neck 250mL is equipped with magnetic stirring bar, reflux condenser and argon/or nitrogen inlet, and is placed in the silicone oil bath.Add 60g in the flask and grind to form the pigment of the silane package quilt of fine powder with mortar and pestle, then add 60mL dodecyl methyl acrylate (LMA, Aldrich) and 60mL toluene.Then rapid stirred reaction mixture and with argon gas or this flask of purging with nitrogen gas one hour.During this period of time silicon is bathed and be heated to 50 ℃.In the purge process, (2,2 ' azoisobutyronitrile Aldrich) is dissolved in the 13mL toluene with 0.6g AIBN.In the latter stage of one hour purge, add the AIBN/ toluene solution with glass pipet rapidly.Sealed reaction vessel is heated to 65 ℃ and its stirring is spent the night.In the latter stage of polyreaction, add 100mL ethyl acetate in the reaction mixture of thickness and stirred the mixture again 10 minutes.Potpourri is poured in the plastic bottle under the 3600rpm centrifugal 15-20 minute and incline and supernatant.Add fresh ethyl acetate in the pigment after centrifugal, stir and processed 10 minutes with ultrasound wave with the stainless steel spatula.After above-mentioned steps, wash again described pigment twice with ethyl acetate.Make the pigment air dried overnight, then under high vacuum dry 24 hours.Polymkeric substance free in the bulk solution is precipitated also dry in a vacuum in methyl alcohol.The molecular weight of free polymkeric substance is measured by vapor-phase chromatography (GPC) in the solution.The polymkeric substance that is combined on the pigment is measured by TGA.

2. the copolymerization on the titania

The round-bottomed flask of single neck 250mL is equipped with magnetic stirring bar, reflux condenser and argon/or nitrogen inlet, and is placed in the silicone oil bath.In flask, add 60ml toluene, 60g titania (the Dupont R960 that Z6030 is coated), dodecyl methyl acrylate (LMA) and the second monomer, such as styrene, Tert-butyl Methacrylate, 1-ethene-2-Pyrrolidone, acrylic acid hexafluoro butyl ester and methacrylate, NIPA or vinyl cyanide (Aldrich), the amount of LMA and the second monomer is decided according to predetermined monomer ratio.The ratio of LMA/ the second monomer is generally 95/5,85/15,75/25.Then rapid stirred reaction mixture and with argon gas or this flask of purging with nitrogen gas one hour.During this period of time silicon is bathed and be heated to 50 ℃.In the purge process, with 0.6gAIBN dissolving or be partially dissolved in the 13mL toluene.In the latter stage of one hour purge, add the AIBN/ toluene solution with glass pipet rapidly.Sealed reaction vessel is heated to 65 ℃ and its stirring is spent the night.In the reaction mixture of thickness, add 100mL ethyl acetate and stirred again the gained potpourri 10 minutes.Potpourri is poured in the plastic bottle under the 3600rpm centrifugal 15-20 minute and incline and supernatant.Add fresh ethyl acetate in the pigment after centrifugal, stir resulting potpourri and with ultrasound wave processing 10 minutes with the stainless steel spatula.Wash again described pigment twice with ethyl acetate, the centrifugal and supernatant that inclines.Make the pigment air dried overnight, then under high vacuum dry 24 hours.Polymkeric substance free in the bulk solution is precipitated also dry in a vacuum in methyl alcohol.The molecular weight of free polymkeric substance is measured by GPC in the solution.The polymkeric substance that is combined on the pigment is measured by TGA.

2.1 copolymerization LMA and 1-ethene-2-Pyrrolidone on titania

The round-bottomed flask of single neck 250mL is equipped with magnetic stirring bar, reflux condenser and argon/or nitrogen inlet, and is placed in the silicone oil bath.In flask, add 60ml toluene, 60g titania (the Dupont R960 that Z6030 is coated), 51ml dodecyl methyl acrylate (LMA) and 3.3mL1-ethene-2-Pyrrolidone.The ratio of LMA/1-ethene-2-Pyrrolidone is generally 85/15.Then rapid stirred reaction mixture and with argon gas or this flask of purging with nitrogen gas one hour.During this period of time silicon is bathed and be heated to 50 ℃.In the purge process, with 0.6g AIBN dissolving or be partially dissolved in the 13mL toluene.In the latter stage of one hour purge, add the AIBN/ toluene solution with glass pipet rapidly.Sealed reaction vessel is heated to 65 ℃ and its stirring is spent the night.Add 100mL ethyl acetate in the reaction mixture of thickness and stirred the mixture again 10 minutes.Potpourri is poured in the plastic bottle under the 3600rpm centrifugal 15-20 minute and incline and supernatant.Add fresh ethyl acetate in the pigment after centrifugal, stir resulting potpourri and with ultrasound wave processing 10 minutes with the stainless steel spatula.Wash again described pigment twice with ethyl acetate, the centrifugal and supernatant that inclines.Make the pigment air dried overnight, then under high vacuum dry 24 hours.Polymkeric substance free in the bulk solution is precipitated also dry in a vacuum in methyl alcohol.The molecular weight of free polymkeric substance is measured by GPC in the solution.The polymkeric substance that is combined on the pigment is measured by TGA.

3. adopt the two-stage polymerization reaction of the coated Chinese white of LMA

The round-bottomed flask of single neck 250mL is equipped with magnetic stirring bar, reflux condenser and argon/or nitrogen inlet, and is placed in the silicone oil bath.Add 60g in the flask and grind to form the pigment of the silane package quilt of fine powder with mortar and pestle, then add 60mL dodecyl methyl acrylate and 60mL toluene.Then rapid stirred reaction mixture and with argon gas or this flask of purging with nitrogen gas one hour.During this period of time silicon is bathed and be heated to 50 ℃.In the purge process, 0.6g AIBN is dissolved in the 13mL toluene.In the latter stage of one hour purge, add the AIBN/ toluene solution with glass pipet rapidly.Sealed reaction vessel is heated to 65 ℃ and its stirring is spent the night.In polyreaction latter stage, in the reaction mixture of thickness, add 100mL ethyl acetate and stirred again resulting potpourri 10 minutes.Potpourri is poured in the plastic bottle under the 3600rpm centrifugal 15-20 minute and incline and supernatant.Add fresh ethyl acetate in the pigment after centrifugal, stir resulting potpourri with the stainless steel spatula.After the above-mentioned steps, wash again described pigment twice with ethyl acetate.Make the pigment air dried overnight, then under high vacuum dry 24 hours.Polymkeric substance free in the bulk solution is precipitated also dry in a vacuum in methyl alcohol.The molecular weight of free polymkeric substance is measured by GPC in the solution.The polymkeric substance that is combined on the pigment is measured by TGA.

Attention has been omitted the front and has been described employed ultrasound wave processing procedure in the step in above-mentioned steps, is for fear of cause any possible infringement to remaining in the surface of pigments vinyl after the first step polyreaction that has been illustrated.

In order to realize the polyreaction of second step, adopt the round-bottomed flask of another single neck 250mL, magnetic stirring bar, reflux condenser and argon/or nitrogen inlet is housed, and is placed in the silicone oil bath.Add the coated pigment of LMA of 50g preparation as described above in the flask, grind to form fine powder with mortar and pestle, then add 85mL toluene and 16g styrene.Then rapid stirred reaction mixture and with argon gas or this flask of purging with nitrogen gas one hour.During this period of time silicon is bathed and be heated to 50 ℃.In the purge process, 0.4g AIBN is dissolved in the 10mL toluene.In the latter stage of one hour purge, add the AIBN/ toluene solution with glass pipet rapidly.Sealed reaction vessel is heated to 65 ℃ and its stirring is spent the night.In polyreaction latter stage, in the reaction mixture of thickness, add 100mL ethyl acetate and stirred again resulting potpourri 10 minutes.Potpourri is poured in the plastic bottle under the 3600rpm centrifugal 15-20 minute and incline and supernatant.Add fresh ethyl acetate in the pigment after centrifugal, stir resulting potpourri and with ultrasound wave processing 10 minutes with the stainless steel spatula.After above-mentioned steps, wash again described pigment twice with ethyl acetate.Make the pigment air dried overnight, then under high vacuum dry 24 hours.Polymkeric substance free in the bulk solution is precipitated also dry in a vacuum in methyl alcohol.The molecular weight of free polymkeric substance is measured by GPC in the solution.The polymkeric substance that is combined on the pigment is measured by TGA.

4. the copolyreaction of carrying out at coated copper chromite

The round-bottomed flask of single neck 250mL is equipped with magnetic stirring bar, reflux condenser and argon gas entrance, and is placed in the silicone oil bath.In flask, add 60g grinds to form the silane of the above-mentioned general formula of being coated with of fine powder (I) with mortar and pestle copper chromite (CuCr ₂O ₄, Shepherd Black 1G), then add 1.2mL styrene, 57mL dodecyl methyl acrylate and 60mL toluene.Then rapid stirred reaction mixture and with argon gas or this flask of purging with nitrogen gas one hour, and silicon bathed be heated to 50 ℃.In the purge process, with 0.6g AIBN dissolving or be partially dissolved in the 13mL toluene.In the latter stage of one hour purge, add rapidly the AIBN/ toluene solution with glass pipet.Sealed reaction vessel is heated to 65 ℃ and its stirring is spent the night.In the reaction mixture of thickness, add 100mL ethyl acetate and stirred again resulting potpourri 10 minutes.Potpourri is poured in the plastic bottle under the 3600rpm centrifugal 15-20 minute and incline and supernatant.Add fresh ethyl acetate in the pigment after centrifugal, stir resulting potpourri and with ultrasound wave processing 10 minutes with the stainless steel spatula.Wash again described pigment twice with ethyl acetate, the centrifugal and supernatant that inclines.Make the pigment air dried overnight, then under high vacuum dry 24 hours.Polymkeric substance free in the bulk solution is precipitated also dry in a vacuum in methyl alcohol.The molecular weight of free polymkeric substance is measured by GPC in the solution.The polymkeric substance that is combined on the pigment is measured by TGA.

Preparation disperse phase reference substance (electrophoretic particles adds suspension)

The prescription of disperse phase reference substance is as follows: (a) 85g contains the J pigment stock solution of the coated titania of the LMA of 60% weight in isoalkane G; (b) 42.5g contains the D pigment stock solution of the coated copper chromite of the LMA of 60% weight in isoalkane G; (c) 10.71g contains the stock solution of the Solsperse17000 of 10% weight in isoalkane G; (d) 31.03g isoalkane G; And (e) 0.77g Span85 (a kind of non-ionics).

In the plastic bottle of 250ml, add J and D stock solution, then add Solsperse17000 solution and Span85, add at last remaining solvent.The disperse phase that obtains was firmly rocked about 5 minutes, then be placed on the kibbler roll spend the night (at least 12 hours).

Utilize the black pigment of Chinese white of the present invention and prior art to prepare disperse phase

The prescription of disperse phase is as follows: (a) 40g contains the modification J pigment stock solution of the coated titania (mol ratio is 85/15) of the LMA/TBMA of 60% weight in isoalkane G; (b) 20g contains the D pigment stock solution of the coated copper chromite of the LMA of 60% weight in isoalkane G; (c) 5.04g contains the stock solution of the Solsperse17000 of 10% weight in isoalkane G; (d) 14.60g isoalkane G; And (e) 0.36g Span85 (a kind of non-ionics).

Mix and deposit this disperse phase with the method identical with above-mentioned disperse phase.

Utilize Chinese white and the black pigment of the present invention of prior art to prepare disperse phase

The prescription of disperse phase is as follows: (a) identical J pigment stock solution in 40g and the disperse phase reference substance, and this stock solution contains the coated titania of LMA of 60% weight in isoalkane G; (b) 20g contains the D pigment stock solution of the coated copper chromite (the monomer ratio is 85/15 or 95/5) of the LMA/St of 60% weight in isoalkane G; (c) 5.04g contains the stock solution of the Solsperse17000 of 10% weight in isoalkane G; (d) 14.60g isoalkane G; And (e) 0.36g Span85 (a kind of non-ionics).

Mix and deposit this disperse phase with the method identical with above-mentioned disperse phase.

The disperse phase (respectively) of like this preparation is encapsulated in gel/Arabic gum microcapsules, basic as above-mentioned 2002/0180687 [0069] to described in [0074] section.The microcapsules that obtain are separated according to size, and average particle size particle size is that the capsule of about 35 μ m is used for following test.Microcapsules are sneaked in the slurry with polyurethane adhesive and by the coating of roller type process, (PET) be coated with 18gm in the film surface at 7mil (177 μ m) poly-(ethylene glycol terephthalate) ^-2The dry coating of weight, described PET film with tin indium oxide (ITO) layer, are deposited on microcapsules on the surface of ITO covering on a surface, basically described in above-mentioned 2002/0180687 [0075] and [0076].Then will make front flat laminated by the polyurethane laminated bonding agent that it is laminated into one deck and is carried on the releasing piece with the film of capsule, this is stacked under the 65psig (0.51mPa) and utilizes the two roll laminating machines of Western Magnum to make with the speed of 6 inch per minutes (2.5mm/sec), and wherein two rollers all remain on 120 ℃.For providing experimental and be applicable to single pixel display of these tests, the releasing piece of resulting front plate stack synusia is removed, then be pressed into the PET film that is coated with carbon black layer that 5cm takes advantage of 5cm 75 ℃ of lower floors, as the rear electrode of single pixel display.

Picture steadiness is measured

Utilize 500 milliseconds of square-wave pulses to switch being applied under the upper 10V AC signal with respect to the ground connection rear electrode of upper flat plate (ITO layer) single pixel display of making like this.Switch for vibration 2 seconds stand-down between the pulse.By making pixel switch to suitable optical states (white or black), with upper flat plate ground connection, and the continuous coverage optical reflectivity was measured the stability of image in 10 minutes.Suppose that the optics recoil (kickback) that is caused by residual voltage in bonding agent and the stack adhesive layer decays in second at 5-10.Optical states is (with L between 5 seconds and 10 minutes ^*The unit meter) difference can be regarded the measured value to picture steadiness as.Result shown in the following table 2 is from selected pixel.

Table 2

Pigment	The embodiment numbering	White states IS (dL *)	Black state IS (dL *)
				J/D (reference substance)	1	-6.3	2.7
J(TBMA5)/D	2	-2.2	2.1
				J(TBMA15)/D	3	-4.2	1.1
J/D(St5)	4	-4.7	2.0
				J/D(St15)	5	-4.7	1.6
J(TBMA5)/D(St15)	6	-3.3	1.7
				J(TBMA15)/D(St5)	7	-1.6	3.0
J(+St)/D	8	-2.2	0.3

The reference substance pixel demonstrates relatively preferably black state stability, (similarly display adopts carbon black to replace copper chromite as black pigment yet white states stability is on duty mutually, and there is not PIB in the suspension, it all shows very different state stability under white and dark state, the order of magnitude is at 10-15L ^*).Any electrodeposition paint pigments of the present invention all increases with respect to the picture steadiness of reference substance, under white states or under black state or the two all.Only have the picture steadiness of pixel of the present invention in a kind of situation to be inferior to reference substance (J (TBMA15)/D (St5)), and its difference may be within the deviation between the experimental pixel here.The display that best general image stability is made by the Chinese white that utilizes two-step approach, adopts styrene to synthesize as the second monomer is provided.This display has good picture steadiness in white states, and has splendid picture steadiness at black state.

Response time

The response time of the electrophoretic display device (EPD) shown in the table 2 records by the electro-optic response as the function of pulse length under the operating voltage of measuring 10V.All mensuration adopts 2000 milliseconds the length of stopping.Discovery is by the difference L between white states and the dark state ^*The electro-optic response that records is issued to saturated in certain pulse length, then slightly descend under long pulse length.Control sample is a kind of prescription pixel identical with reference substance in the table 2, and is the similar pixel of the high molecular PIB that contains 0.3 and 0.9% weight of the conduct method that reaches good picture steadiness.Table 3 represented electro-optic response reach display with table 2 under 1 pulse per second (PPS) length this value 90% the time pulse length.

Table 3

Pigment	The embodiment numbering	Reached for 90% saturated time (msec)
			J/D (reference substance-without PIB)	1	294
J(TBMA5)/D	2	173
			J(TBMA15)/D	3	281
J/D(St5)	4	325
			J/D(St15)	5	375
J(+St)/D	8	380
			J/D+0.9%PIB (reference substance)	9	740
J/D+0.3%PIB (reference substance)	10	575

The response time of containing the control sample of PIB is longer than the response time according to sample of the present invention basically.At least need 0.3% PIB to obtain enough picture steadinesses, preferred 0.9% PIB in this system.Therefore method of the present invention has obtained good picture steadiness, its response time contrast sample reach soon 1.5 to 4 times.

Threshold voltage

Above-mentioned pixel has adopted Chinese white and 15 % by mole of cinnamic black pigments with 5 % by mole of TBMA in its polymer shell, except having preferably picture steadiness, also show large work threshold value.Voltage threshold as shown in Figure 2, it shows that the dynamic range of pixel for many pulse lengths is to execute alive function.Very little (order of magnitude is at 1L for dynamic range when applying voltage and lying prostrate less than 4-5 ^*), it is independent of pulse length, but has shown good dynamic range (greater than 30L under the pulse greater than 600 milliseconds and 10V ^*).

As can be seen from the above, incompatible monomer of the present invention, particle, medium and display and even agglutination medium have good picture steadiness, and compare with the similar mediums that contains polymeric additive in the suspension and to have many advantages, especially because the present invention and need not sacrifice the response time and obtain good picture steadiness.This advantage on response time is used in operation display under the lower voltage.The display of reporting in the table 2 has mostly switched to the lower 300 milliseconds state of saturation of 7.5V, and has been issued to best contrast ratio at 10V and 250-300 millisecond.Under 15 volts, can reach the switching time about 100 milliseconds.

Aliphatics polymerization process

The above once mentioned, and found among the above-mentioned WO02/09326 and graft polymerization step described above can at aliphatic hydrocarbon, especially be implemented in the isoparaffic solvent; A kind of preferred solvent is isoalkane G for this reason, Exxon Mobil Corporation, and Houston TX sells.Because this aliphatic hydrocarbon is identical with the material that is typically used as the electrophoretic medium suspension, coated pigment plays the final display of its adding from the graft polymerization step and can remain in the substantially the same environment.

When the graft polymerization step finished, aliphatic hydrocarbon solvent can contain any or multiple excessive initiators for polymerization, excessive monomer or oligomer, and be not connected to free copolymer on the granules of pigments.These material demands were removed from granules of pigments before granules of pigments adds final electrophoretic medium basically, because these materials can and/or cause adverse influence serviceable life to the electro-optical characteristic of medium.Therefore, usually still need to isolate the pigment of polymer coating from the graft polymerization reaction solvent, for example by centrifugal mode, and the washing granules of pigments is to remove the above-mentioned substance of last trace.Yet, needn't carry out to the pigment of this polymer coating dry hydrocarbon solvent (can eliminate like this pollution control problem that solvent vapour causes) therefrom to remove last trace, will again not be dispersed in the aliphatic hydrocarbon solvent by dry granules of pigments yet; Because when washing step finished, pigment was soaked by aliphatic hydrocarbon solvent, final required pigment is dispersed in the relatively large solvent again of electrophoretic medium do not have difficulties.Obviously, if polyreaction is carried out by this way: so that after finishing polyreaction, only stay the minimum above-mentioned substance that is present in the graft polymerization reaction solvent, can exempt in theory separation and the washing of the pigment of polymer coating.

The pigment of the polymer coating that in aliphatic hydrocarbon solvent, prepares according to the present invention and method according to prior art in toluene, prepare between look that not have any essence significantly different, as if but some tests show that the pigment for preparing in the aliphatic hydrocarbon solvent has higher polymer content easily.

Before mentioned, the suspension in the electrophoretic medium is generally separately or the aliphatic hydrocarbon that combines with halocarbon.If suspension is the potpourri of aliphatic hydrocarbon and halocarbon, then at present preferably in independent aliphatic hydrocarbon, implement graft polymerization reaction, not so difficult because the pigment that after the washing aliphatic hydrocarbon is soaked is dispersed in the potpourri of aliphatic hydrocarbon and halocarbon again.Yet we do not get rid of the possibility that graft polymerization reaction itself can carry out in the potpourri of aliphatic hydrocarbon and halocarbon.

When the two particle electrophoresis medium of preparation (for example, containing the medium of adularescent titanium dioxide granule and carbon black granules), method of the present invention can be applied to respectively in this two classes particle.Yet, supposing that two class particles have the polymer coating layer of similar type, the present invention can also implement like this: mix two kinds of pigment after polymerisable group at first is provided on it, then carry out the graft polymerization reaction step at this pigment composition.Therefore, two kinds of pigment gather together by forming the required remaining step of electrophoretic medium.In fact, the polymer coating pigment of the mixing that obtains by this process can be regarded the stock solution of pigment as, and it seldom or no longer need may need further process after residual impurity is removed in washing.This variation of the inventive method thereby further reduced in order to original pigment is changed into the quantity of the discontinuous step of the required enforcement of final electrophoretic medium.

Method of the present invention has reduced the potential safety hazard of being correlated with in the art methods, because the aliphatic hydrocarbon solvent that uses in the inventive method is less than the harm of toluene and THF.The above mentions, method of the present invention has reduced the use of solvent, also reduced whole for the manufacture of the number of steps in the method for electrophoretic medium, because it has removed again dispersion steps of original drying and pigment from, therefore reduced the time of dispersion treatment and might improve the overall quality of the final dispersion of pigment in the aliphatic hydrocarbon solvent.

Another aspect of the present invention relates to relative size and the quality of particle in the control electrophoretic medium, in order to reduce the trend of electrophoretic particles aggegation.

Known in electrophoretic medium, in especially two particle electrophoresis media, particle performance goes out a kind of trend of aggegation.This trend especially bothers in two particle electrophoresis media of two class particle band opposite polarity electric charges, because a kind of coherent natural tendency is arranged concerning the particle of any oppositely charged.The aggegation of this particle has reduced the contrast of display; For example, if the black and white particle aggregation forms indissociable grizzled particle, when applying electric field when changing the optical states of display, according to supposition, the ater of display or white optical state will be subject to the pollution of grey agglutination body, thereby reduce contrast ratio.In addition, the function that serious and lasting aggegationization can finally hinder display realizes, thus the serviceable life of minimizing display.

Have recognized that now the relative motion of two class particles can be used for breaking agglutination body in two particle electrophoresis media, and therefore reduce the problem relevant with this agglutination body.Under the given electric field the second particle of oppositely moving relative to the first particle being introduced in the electrophoretic medium, will cause the motion of two class particles to pass through mutually, cluster of grains and subtract less granular aggegation by physics mode minute splits.

In preferred embodiments, electrophoretic medium contains at least one class particle, its mean diameter be oppositely charged the second average diameter of particles about 0.25 to about 4 times; Preferably, the average grain mass ratio between the two class particles is between about 0.25 to about 4.00.

Equally in preferred embodiments, electrophoretic medium contains the particle of at least two class band opposite polarity electric charges, its size be F apply that separating distance is spacing (G) under the electric field, can obtain respectively speed V1 and V2:

V1+V2>f(F，G)

Wherein f is a function, and wherein when satisfying this inequality, particle agglutination reduces or eliminates.

The threshold voltage display

The above points out, the invention provides a kind of active matrix electro-optic displays, and it has adopted the electro-optical medium with threshold voltage.Utilize such electro-optical medium to reduce design limitations on the electro-optic displays backboard.

For example, establish a kind of electro-optical medium and under 5V, show strong threshold voltage.Term " strong voltage threshold value " is used in reference to that medium does not switch fully under less than the voltage of this threshold value, and no matter pulse is how long.Under the voltage on the threshold value, medium normally switches.Utilize this medium to alleviate by data line and be coupled to the data peaks problem (referring to top 42-52 section) that causes on the pixel electrode, if to the amplitude of the voltage peak of pixel less than 5V, this strong threshold voltage medium will not respond.The pixel storage capacitor of using in this display only need to be made the size that the voltage peak that keeps electro-optical medium to stand is lower than threshold voltage, do not have electric capacity required in the prior art electro-optic displays of threshold voltage to compare with the electro-optical medium display, this will reduce the size of this memory capacitance greatly.

The present invention is not limited only to use the electro-optical medium of the strong threshold voltage of performance, also can expand to the electro-optical medium that employing only has " weak threshold voltage ", this term used herein refers to the medium to the voltage responsive that is applied for a long time that is lower than threshold value, but its very short this voltage that need to apply can not work to electro-optic displays the time responds.For example, the time that needs can be single sweep frame (about 20 milliseconds usually), or the renewal of whole image (about 1000 milliseconds usually).

The present invention can utilize the electro-optical medium of any type discussed above, as long as this electro-optical medium can show strong or weak threshold voltage.Usually preferably have the incompatible monomer electrophoretic medium of threshold voltage, as described above.

The invention enables active matrix array, the design rule that is generally thin film transistor (TFT) (TFT) array is relaxed.More particularly, the invention enables the pixel electrode area of per unit can utilize less memory capacitance, thereby can utilize the technology of low resolution, make the TFT backboard such as printing technology.In addition, by reducing the size of memory capacitance, can reduce transistorized size simultaneously.The size that reduces these two kinds of elements is incited somebody to action so that line capacitance reduces greatly, thereby has reduced the power consumption of backboard.Therefore, electro-optic displays Billy of the present invention has improved performance with the conventional design of the amorphous silicon structure of prior art.

Claims (13)

1. electrophoretic medium, comprise at least a charged particle that is suspended in the fluid and when applying electric field to fluid, can in fluid, moves, wherein said at least a charged particle contains copper chromite, described copper chromite has polymer shell, described polymer shell comprises the repetitive from least a its homopolymer and the inconsistent monomer of described suspension, and further comprises the repetitive from least a its homopolymer monomer compatible with described suspension.

2. according to claim 1 electrophoretic medium, wherein said polymkeric substance is formed by methacrylate.

3. according to claim 1 electrophoretic medium; also comprise having at least a at least a Equations of The Second Kind particle that is different from the optical property of described copper chromite particle, wherein said at least a Equations of The Second Kind particle also has the electrophoresis that is different from described copper chromite particle and moves character.

4. according to claim 3 electrophoretic medium, wherein said copper chromite particle and Equations of The Second Kind particle carry opposite polarity electric charge.

5. according to claim 3 electrophoretic medium, wherein said Equations of The Second Kind particle are white substantially.

6. according to claim 5 electrophoretic medium, wherein said Equations of The Second Kind particle comprises titania.

7. according to claim 1 electrophoretic medium, wherein said fluid comprises hydrocarbon.

8. according to claim 1 electrophoretic medium comprises that also described fluid and described at least a particle are stored in capsule wall wherein.

9. according to claim 8 electrophoretic medium comprises a plurality of capsules, and wherein each capsule comprises that capsule wall and described fluid and described at least a particle are stored in the capsule wall, and described medium also comprises the polymer adhesive around described capsule.

10. electrophoretic display device (EPD), comprise according to claim 1 electrophoretic medium and at least one be arranged on and be used for applying to electrophoretic medium the electrode of electric field near this electrophoretic medium.

11. electrophoretic display device (EPD) according to claim 10, wherein said electrophoretic medium comprises a plurality of capsules.

12. copper chromite particle, it has polymer shell, described polymer shell comprises the repetitive from the inconsistent monomer of suspension at least a its homopolymer and the electrophoretic medium, and further comprise the repetitive from least a its homopolymer monomer compatible with described suspension, wherein said suspension is the liquid that has less than 5 specific inductive capacity.

13. copper chromite particle according to claim 12, wherein said polymkeric substance is formed by methacrylate.

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