(19)
(11)EP 3 388 891 B1

(12)EUROPEAN PATENT SPECIFICATION

(45)Mention of the grant of the patent:
04.12.2019 Bulletin 2019/49

(21)Application number: 18020193.1

(22)Date of filing:  01.10.2013
(51)International Patent Classification (IPC): 
G02F 1/167(2019.01)
G09F 9/00(2006.01)
G09G 3/34(2006.01)
G09F 9/30(2006.01)

(54)

COLOR DISPLAY DEVICE

FARBANZEIGEVORRICHTUNG

DISPOSITIF D'AFFICHAGE EN COULEURS


(84)Designated Contracting States:
AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR

(30)Priority: 02.10.2012 US 201213633788
01.05.2013 US 201313875145

(43)Date of publication of application:
17.10.2018 Bulletin 2018/42

(62)Application number of the earlier application in accordance with Art. 76 EPC:
13844148.0 / 2904602

(73)Proprietor: E Ink California, LLC
Fremont, CA 94538 (US)

(72)Inventors:
  • WANG, Ming
    Fremont, California 94536 (US)
  • LI, Yu
    Fremont, California 94538 (US)
  • DU, Hui
    Milpitas, California 95935 (US)
  • ZHANG, Xiaojia
    Fremont, California 94539 (US)
  • LIN, Craig
    San Jose, California 95131 (US)

(74)Representative: Cole, David John 
46 Kirkhill Gardens West Greenlees Estate
Cambuslang Glasgow G72 8EZ
Cambuslang Glasgow G72 8EZ (GB)


(56)References cited: : 
JP-A- 2007 140 129
US-A1- 2012 194 899
JP-A- 2009 116 041
  
      
    Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention).


    Description


    [0001] The present invention is directed to a color display device in which each display cell can display high quality color states, and an electrophoretic fluid for such an electrophoretic display.

    [0002] In order to achieve a color display, color filters are often used. The most common approach is to add color filters on top of black/white sub-pixels of a pixellated display to display the red, green and blue colors. When a red color is desired, the green and blue sub-pixels are turned to the black state so that the only color displayed is red. When the black state is desired, all three-sub-pixels are turned to the black state. When the white state is desired, the three sub-pixels are turned to red, green and blue, respectively, and as a result, a white state is seen by the viewer.

    [0003] The disadvantage of such a technique is that since each of the sub-pixels has a reflectance of about one third (1/3) of the desired white state, the white state is fairly dim. To compensate this, a fourth sub-pixel may be added which can display only the black and white states, so that the white level is doubled at the expense of the red, green or blue color level (where each sub-pixel is only one fourth of the area of the pixel). Brighter colors can be achieved by adding light from the white pixel, but this is achieved at the expense of color gamut to cause the colors to be very light and unsaturated. A similar result can be achieved by reducing the color saturation of the three sub-pixels. Even with these approaches, the white level is normally substantially less than half of that of a black and white display, rendering it an unacceptable choice for display devices, such as e-readers or displays that need well readable black-white brightness and contrast.

    [0004] JP 2009-116041A describes an electrophoretic display device including a liquid dispersion containing first and second particles which are negatively charged and third particles which are positively charged. The first particles are higher in electrophoretic mobility but smaller in charge density than the second particles. The device has a first state in which the first particles are located closer to a transparent electrode than the second particles by using the difference in electrophoretic mobility by applying a positive voltage to the transparent electrode and a negative voltage to a counter electrode. The device has a second state in which the positional relation between the first and second particles is reversed by applying an alternating voltage between the electrodes.

    [0005] US 2012/0194899 A1 describes an electrophoretic display device including a liquid dispersion containing first and second particles which bear charges of opposite polarity and non-charged or slightly charged colored third particles. Each pixel of the display has a front electrode (which forms the viewing surface) and two separate rear electrodes. Each pixel has three color states: (a) a first state in which the first particles lie adjacent the viewing surface; (b) a second state in which the second particles lie adjacent the viewing surface; and (c) a third state in which the first particles lie adjacent one rear electrode, the second particles lie adjacent the other rear electrode and the color of the third particles is displayed.

    [0006] JP 2007-140129A describes an electrophoretic display device in which at least three different types of particles having different colors, and different threshold voltages for movement between electrodes, are sealed in a plurality of cells. The device displays information by selectively transferring between its electrodes the various particles using varying voltages such that only the particles having thresholds below the applied voltage are transferred. Throughout the description, "charge density" corresponds to the "intensity" or to the "charge intensity" recited in the claims.

    [0007] The present invention not only provides a realistic solution for a color display device in which each display cell can display highly saturated color states, but also eliminates the need of color filters.

    [0008] More specifically, the present invention is directed to an electrophoretic fluid which is generally similar to that described in the aforementioned JP 2009-116041A in comprising a first type of pigment particles, a second type of pigment particles and third type of pigment particles, all of which are dispersed in a solvent or solvent mixture, wherein
    1. (a) the first type of pigment particles and the second type of pigment particles carry opposite charge polarities; and
    2. (b) the third type of pigment particles has the same charge polarity as the second type of pigment particles but at a lower charge density.; and


    [0009] The electrophoretic fluid of the invention is characterized in that:
    (c) the second type of pigment particles has a threshold voltage.

    [0010] The first type of pigment particles and the second type of pigment particles may be black and white respectively, with the third type of pigment particles being non-white and non-black; the third type of pigment particles may be of a color selected from the group consisting red, green and blue, yellow, cyan and magenta.

    [0011] The third type of particles may be larger in size than the first or the second type of particles. The third type of particles may be about 2 to about 50 times larger than the first or second type of particles. The third type of particles may have a charge density less than about 50% the charge intensity of the first type or second type of particles.

    [0012] In one embodiment, the three types of pigment particles have different levels of mobility. The charge density of the first type of pigment particles may be at least about 2 times the charge density of the second type of pigment particles and the charge density of the third type of particles may be about 50% less than the charge density of the second type of particles. The third type of particles may be larger than the first or the second type of particles. The third type of particles may be about 2 to about 50 times larger than the first or second type of particles.

    [0013] The display cells of the display device may be microcups or microcapsules.

    [0014] In one embodiment, the display cells are aligned with the pixel electrodes. In another embodiment, the display cells are not aligned with the pixel electrodes.

    [0015] In one embodiment, the third type of pigment particles is of the same color in all display cells. In another embodiment, the third type of pigment particles is of different colors in display cells.

    [0016] In one embodiment, the fluid of the present invention is driven by a voltage potential difference between the common electrode and a pixel electrode. In another embodiment, there are at least three different levels of voltage potential difference applied to the common electrode layer and the pixel electrode.

    [0017] The electrophoretic display of the invention may be driven by from a color state of the first type of pigment particles to a color state of the third type of pigment particles by applying a voltage which is the same or lower than the threshold voltage of the second type of pigment particles.

    [0018] This driving method may further comprise applying a shaking waveform before the display is driven to the color state of the first type of pigment particles.

    [0019] When the color of the third type of particles is seen at a viewing side, the first and second types of particles gather at the side opposite of the viewing side resulting in an intermediate color between the colors of the first and second types of particles.

    Figure 1 depicts an electrophoretic display device which can be driven by the method of the present invention.

    Figures 2-4 depict various driving methods of the present invention.

    Figure 5 depicts an alternative driving method of the present invention.

    Figure 6 shows two options where the display cells are aligned or unaligned, respectively, with the pixel electrodes.

    Figure 7 shows how a full color display of the present invention is realized.

    Figure 8 shows an example of shaking waveform.



    [0020] The electrophoretic fluid of the present invention comprises three types of pigment particles dispersed in a dielectric solvent or solvent mixture. For ease of illustration, the three types of pigment particles may be referred to as white particles (11), black particles (12) and colored particles (13), as shown in Figure 1. However, it is understood that the scope of the invention broadly encompasses pigment particles of any colors as long as the three types of pigment particles have visually contrasting colors.

    [0021] The display fluid is sandwiched between two electrode layers. One of the electrode layers is a common electrode (14) which is a transparent electrode layer (e.g., ITO), spreading over the entire top of the display device. The other electrode layer (15) is a layer of pixel electrodes (15a). The color state displayed by the fluid is determined by the applied voltages between the common electrode and a pixel electrode.

    [0022] The pixel electrodes are described in US Patent No. 7,046,228. It is noted that while active matrix driving with a thin film transistor (TFT) backplane is mentioned for the layer of pixel electrodes, the scope of the present invention encompasses other types of electrode addressing as long as the electrodes serve the desired functions.

    [0023] The white particles (11) may be formed from an inorganic pigment, such as TiO2, ZrO2, ZnO, Al2O3, Sb2O3, BaSO4, PbSO4 or the like.

    [0024] The black particles (12) may be formed from CI pigment black 26 or 28 or the like (e.g., manganese ferrite black spinel or copper chromite black spinel) or carbon black.

    [0025] The third type of pigment particles may be of a color such as red, green, blue, magenta, cyan or yellow. The pigments for this type of particles may include, but are not limited to, CI pigment PR 254, PR122, PR149, PG36, PG58, PG7, PB28, PB15:3, PY138, PY150, PY155 or PY20. Those are commonly used organic pigments described in color index handbook "New Pigment Application Technology" (CMC Publishing Co, Ltd, 1986) and "Printing Ink Technology" (CMC Publishing Co, Ltd, 1984). Specific examples include Clariant Hostaperm Red D3G 70-EDS, Hostaperm Pink E-EDS, PV fast red D3G, Hostaperm red D3G 70, Hostaperm Blue B2G-EDS, Hostaperm Yellow H4G-EDS, Hostaperm Green GNX, BASF Irgazine red L 3630, Cinquasia Red L 4100 HD, and Irgazin Red L 3660 HD; Sun Chemical phthalocyanine blue, phthalocyanine green, diarylide yellow or diarylide AAOT yellow.

    [0026] The percentages of the three types of pigment particles in the fluid may vary. For example, the black particle may take up about 0.1% to 10%, preferably 0.5% to 5% by volume of the electrophoretic fluid; the white particle may take up about 1% to 50%, preferably 5% to 15% by volume of the fluid; and the colored particle may take up about 2% to 20%, preferably 4% to 10% by volume of the fluid.

    [0027] There may be other particulate matters in the fluid which are included as additives to enhance performance of the display device, such as switching speed, imaging bistability and reliability.

    [0028] The solvent in which the three types of pigment particles are dispersed is clear and colorless. It preferably has a low viscosity and a dielectric constant in the range of about 2 to about 30, preferably about 2 to about 15 for high particle mobility. Examples of suitable dielectric solvent include hydrocarbons such as isopar, decahydronaphthalene (DECALIN), 5-ethylidene-2-norbornene, fatty oils, paraffin oil, silicon fluids, aromatic hydrocarbons such as toluene, xylene, phenylxylylethane, dodecylbenzene or alkylnaphthalene, halogenated solvents such as perfluorodecalin, perfluorotoluene, perfluoroxylene, dichlorobenzotrifluoride, 3,4,5 -trichlorobenzotri fluoride, chloropentafluoro-benzene, dichlorononane or pentachlorobenzene, and perfluorinated solvents such as FC-43, FC-70 or FC-5060 from 3M Company, St. Paul MN, low molecular weight halogen containing polymers such as poly(perfluoropropylene oxide) from TCI America, Portland, Oregon, poly(chlorotrifluoro-ethylene) such as Halocarbon Oils from Halocarbon Product Corp., River Edge, NJ, perfluoropolyalkylether such as Galden from Ausimont or Krytox Oils and Greases K-Fluid Series from DuPont, Delaware, polydimethylsiloxane based silicone oil from Dow-corning (DC -200).

    [0029] The first and second types of pigment particles carry opposite charge polarities and the third type of pigment particles has the same charge polarity as the second type of pigment particles but at a lower charge density.

    [0030] For example, if the (first) black particles are positively charged and the (second) white particles are negatively charged, then the (third) colored pigment particles have a lower charge density. In other words, in this example, the charge carried by the black and the white particles is much more dense than the charge carried by the colored particles.

    [0031] The three types of pigment particles may have varying sizes. In one embodiment, one of the three types of pigment particles is larger than the other two types. Among the three types of pigment particles, the one type of particles which has a lower charge density preferably has a larger size.

    [0032] For example, both the black and the white particles are relatively small and their sizes (tested through dynamic light scattering) may range from about 50 nm to about 800 nm and more preferably from about 200 nm to about 700 nm, and in this example, the colored particles preferably are about 2 to about 50 times and more preferably about 2 to about 10 times larger than the black particles and the white particles.

    [0033] The term "threshold voltage", in the context of the present invention, is defined as the maximum bias voltage that may be applied to a group of pigment particles, without causing the pigment particles to appear at the viewing side of the display device. The term "viewing side" refers to a side of a display device where images are seen by the viewers.

    [0034] In the present invention, the second of pigment particles demonstrates a threshold voltage under triangle voltage driving testing.

    [0035] The threshold voltage is either an inherent characteristic of the charged pigment particles or an additive-induced property.

    [0036] In the former case, the threshold is generated, relying on certain attraction force between particles or between particles and certain substrate surfaces. A threshold may also be generated via interaction of two types of oppositely charged particles.

    [0037] In the latter case referred to above, to achieve a threshold voltage, a threshold agent which induces or enhances the threshold characteristics of an electrophoretic fluid may be added. The threshold agent may be any material which is soluble or dispersible in the solvent or solvent mixture of the electrophoretic fluid and carries or induces a charge opposite to that of the charged pigment particles. The threshold agent may be sensitive or insensitive to the change of applied voltage. The term "threshold agent" may broadly include dyes or pigments, electrolytes or polyelectrolytes, polymers, oligomers, surfactants, charge controlling agents and the like.

    [0038] Additional information relating to the threshold agent may be found in US Patent No. 8,115,729.

    [0039] The following are a few examples illustrating the present invention.

    Examples


    Example 1(a)



    [0040] This example is demonstrated in Figure 2. The black particles (22) are assumed to have a threshold voltage of 5V. Therefore, the black particles (22) would not move to the viewing side if an applied voltage potential difference is 5V or lower.

    [0041] The white pigment particles (21) are negatively charged while the black pigment particles (22) are positively charged, and both types of the pigment particles are smaller than the colored particles (23).

    [0042] The colored particles (23) carry the same charge polarity as the black particles which have the threshold voltage, but have a lower charge density, preferably being less than about 50%, preferably about 5% to about 30%, the charge density of the black or the white particles. As a result, the black particles move faster than the colored particles (23), when an applied voltage potential is higher than the threshold voltage of the black particles because of the stronger charge density they carry.

    [0043] In Figure 2a, the applied voltage potential is +15V. In this case, the white particles (21) move to be near or at the pixel electrode (25) and the black particles (22) and the colored particles (23) move to be near or at the common electrode (24). As a result, the black color is seen at the viewing side. The colored particles (23) move towards the common electrode (24); however because their lower charge density and larger size, they move slower than the black particles.

    [0044] In Figure 2b, when a voltage potential difference of -15V is applied, the white particles (21) move to be near or at the common electrode (24) and the black particles and the colored particles move to be near or at the pixel electrode (25). As a result, the white color is seen at the viewing side.

    [0045] The colored particles (23) move towards the pixel electrode because they are also positively charged. However, because of their lower charge density and larger size, they move slower than the black particles.

    [0046] In Figure 2c, the applied voltage potential difference has changed to +5V. In this case, the negatively charged white particles (21) move towards the pixel electrode (25). The black particles (22) move little because of their threshold voltage being 5V. Due to the fact that the colored particles (23) do not have a significant threshold voltage, they move to be near or at the common electrode (24) and as a result, the color of the colored particles is seen at the viewing side.

    [0047] In order to drive the display to the color state of the third type of pigment particles, i.e., red (see Figure 2c), the method starts from the color state of the first type of pigment particles, i.e., white (see Figure 2b).

    [0048] In Figure 2b, the first type of pigment particles (i.e., white) are at or near the common electrode (24) and the second and third types of pigment particles (i.e., black and red) are at or near the pixel electrode (25). When a voltage which is the same or lower than the threshold voltage of the second type of pigment particles (i.e., black) is applied, the first type of pigment particles (i.e., white) are pushed downwards; the third type of pigment particles (i.e., red) move up towards the common electrode (24) to reach the viewing side; and the second type of pigment particles (i.e., black) barely move because of their threshold voltage.

    [0049] In this scenario, when the color of the third type of particles is seen at the viewing side, the other two types of the particles may be mixed at the non-viewing side (side opposite of the viewing side), resulting in an intermediate color state between the colors of the first and second types of particles. If the first and second types of particles are black and white and the third type of particles is red, then in Figure 2(c), when the red color is seen at the viewing side, a grey color is seen at the non-viewing side.

    [0050] The driving method ideally would ensure both color brightness (i.e., preventing the black particles from being seen) and color purity (i.e., preventing the white particles from being seen) in the scenario of Figure 2c. However, in practice, this desired result is difficult to control for various reasons, including particle size distribution, particle charge distributions and other factors.

    [0051] One solution to this is the use of a shaking waveform prior to driving from the color state of the first type of pigment particles (i.e., white) to the color state of the third type of pigment particles (i.e., red). The shaking waveform consists of repeating a pair of opposite driving pulses for many cycles. For example, the shaking waveform may consist of a +15V pulse for 20 msec and a -15V pulse for 20 msec and such a pair of pulses is repeated for 50 times. The total time of such a shaking waveform would be 2000 msec (see Figure 8).

    [0052] In practice, there may be at least 10 repetitions (i.e., ten pairs of positive and negative pulses).

    [0053] The shaking waveform may be applied to the display regardless of the optical state (black, white or red) prior to a driving voltage is applied. After the shaking waveform is applied, the optical state would not be a pure white, pure black or pure red. Instead, the color state would be from a mixture of the three types of pigment particles.

    [0054] For the method as described above, a shaking waveform is applied prior to the display being driven to the color state (i.e., white) of the first type of pigment particles. With this added shaking waveform, even though the white state is measurably the same as that without the shaking waveform, the color state (i.e., red) of the third type of pigment particles would be significantly better than that without the shaking waveform, on both color brightness and color purity. This is an indication of better separation of the white particles from the red particles as well as the black particles from the red particles.

    [0055] Each of the driving pulse in the shaking waveform is applied for not exceeding 50% (or not exceeding 30%, 10% or 5%) of the driving time required from the full black state to the full white state. For example, if it takes 300 msec to drive a display device from a full black state to a full white state or vice versa, the shaking waveform may consist of positive and negative pulses, each applied for not more than150 msec. In practice, it is preferred that the pulses to be shorter.

    Example 1(b)



    [0056] In an alternative design as illustrated in Figure 3, the white particles (31) are assumed to have a threshold voltage of 5V. Therefore, the white particles (31) would not move to the viewing side if an applied voltage potential difference is 5V or lower.

    [0057] The white pigment particles (31) are negatively charged while the black pigment particles (32) are positively charged, and both types of the pigment particles are smaller than the colored particles (33).

    [0058] The colored particles (33) carry the same charge polarity as the white particles which have the threshold voltage, but have a lower charge density. As a result, the white particles move faster than the colored particles (33), when an applied voltage potential is higher than the threshold voltage of the white particles because of the stronger charge density they carry.

    [0059] In Figure 3a, the applied voltage potential is -15V. In this case, the black particles (32) move to be near or at the pixel electrode (35) and the white particles (31) and the colored particles (33) move to be near or at the common electrode (34). As a result, the white color is seen at the viewing side. The colored particles (33) move towards the common electrode (34); however because of their lower charge density and larger size, they move slower than the white particles.

    [0060] In Figure 3b, when a voltage potential difference of +15V is applied, the white particles (31) move to be near or at the pixel electrode (35) and the black particles move to be near or at the common electrode (34). As a result, the black color is seen at the viewing side.

    [0061] The colored particles (33) move towards the pixel electrode as they are also negatively charged. However, because of their lower charge density and larger size, they move slower than the white particles.

    [0062] In Figure 3c, the applied voltage potential difference has changed to -5V. In this case, the positively charged black particles (32) move towards the pixel electrode (35). The white particles (32) move little because of their threshold voltage being 5V. Due to the fact that the colored particles (33) do not have a significant threshold voltage, they move to be near or at the common electrode (34) and as a result, the color of the colored particles is seen at the viewing side.

    Example 1(c)



    [0063] It is also possible to have the colored particles to have a threshold voltage, as shown in Figure 4. In this case, the colored particles (43) would not move to the viewing side if an applied voltage potential difference is 5V or lower.

    [0064] The black pigment particles (42) are negatively charged while the colored pigment particles (43) are positively charged, and both types of the pigment particles are smaller than the white particles (41).

    [0065] The white particles (41) carry the same charge polarity as the colored particles which have the threshold voltage, but at a lower charge density. As a result, the colored particles move faster than the white particles (41), when an applied voltage potential is higher than the threshold voltage of the colored particles because of the stronger charge density they carry.

    [0066] In Figure 4a, the applied voltage potential is +15V. In this case, the black particles (42) move to be near or at the pixel electrode (45) and the colored particles (43) and the white particles (41) move to be near or at the common electrode (44). As a result, the color of the colored particles is seen at the viewing side. The white particles (41) move towards the common electrode (44); however because of their lower charge density and larger size, they move slower than the colored particles.

    [0067] In Figure 4b, when a voltage potential difference of -15V is applied, the colored particles (43) move to be near or at the pixel electrode (45) and the black particles move to be near or at the common electrode (44). As a result, the black color is seen at the viewing side.

    [0068] The white particles (41) move towards the pixel electrode as they are also positively charged. However, because of their lower charge density and larger size, they move slower than the colored particles.

    [0069] In Figure 4c, the applied voltage potential difference has changed to +5V. In this case, the negatively charged black particles (42) move towards the pixel electrode (45). The colored particles (43) move little because of their threshold voltage being 5V. Due to the fact that the white particles (41) do not have a significant threshold voltage, they move to be near or at the common electrode (44) and as a result, the white color is seen at the viewing side.

    [0070] In an alternative embodiment of the present invention, all three types of pigment particles have different levels of charge density, thus different levels of mobility.

    [0071] For example, the first and second types of particles carry opposite charge polarities and the charge density of the first type of particles is at least about 2 times, preferably about 3 to about 15 times, the charge density of the second type of particles, or vice versa. The charge density of the third type of particles is less than about 50%, preferably about 5% to about 30%, the charge density of the first or second type of particles, whichever has a lower charge density. In a specific example, if black particles have twice the charge density of the white particles, then the colored particles may have less than 50% the charge density of the white particles.

    [0072] The particles that carry the least charge density are preferably larger than the other two types of particles.

    [0073] Due to different levels of charge density, the three types of pigment particles would have different levels of mobility. The higher the charge density, the faster the particles move. The following example illustrates this embodiment of the invention.

    Example 2



    [0074] This example is shown in Figure 5. It is assumed that the charge density of the black particles (52) is twice the charge density of the white particles (51) and therefore the black particles move twice as fast as the white particles. The colored particles (53) have a charge density which is less than 50% the charge density of the white particles.

    [0075] Therefore if it takes a driving time, t, for the black particles to travel the distance between the common electrode and a pixel electrode ("d"), it would then take 2t for the white particles and at least 4t for the colored particles, to travel the same distance, d.

    [0076] In addition, the black particles are positively charged and the white particles are negatively charged. The colored particles carry the same charge polarity as the particles having the highest charge density, that is, the black particles in this case.

    [0077] In Figure 5a, when a negative voltage potential is applied to the common electrode (54) and the pixel electrode (55), after a driving time of 2t, the white pigment particles (51) would be near or at the common electrode (i.e., the viewing side) and the black pigment particles (52) would be near or at the pixel electrode. As a result, the white color state is seen. The colored particles (53), due to their larger size and lower charge density/lower mobility, they would move a little. In addition, because they are positively charged, they would move towards the pixel electrode (55).

    [0078] In Figure 5b, when a positive voltage potential is applied to the common electrode (54) and the pixel electrode (55), after a driving time of 2t, the black pigment particles (52) would be near or at the common electrode and the white pigment particles (51) would be near or at the pixel electrode. As a result, the black color state is seen.

    [0079] Because of their low charge density and low mobility, the colored particles barely move. While the black and colored particles carry the same charge polarity, the black particles would move to be closer to the common electrode because of their higher charge density and smaller size.

    [0080] Before the step of Figure 5c, it is preferred that the white particles are at or near the pixel electrode (55) and the black and colored particles are at or near the common electrode (54). In Figure 5c, when a negative voltage potential is applied between the common electrode (54) and the pixel electrode (55), after a driving time of t, the white particles (51) at the bottom would move to an area between the common electrode and the pixel electrode, about at the mid-level, while the black particles (52) would travel the full distance, d, to be at or near the pixel electrode. The colored particles would travel a short distance downward; but remain closer to the common electrode. As a result, the color of the colored particles (53) is seen at the viewing side.

    [0081] As shown in this example, the switching among three optical states therefore could be achieved by controlling the driving time frame, driving amplitude or both.

    [0082] The larger and slower moving particles in this example are the colored particles. However, the designs may vary depending on the needs. It is also possible to make the black or white particles the larger and slower moving particles.

    [0083] The electrophoretic fluid in an electrophoretic display device of the invention is filled in display cells. The display cells may be microcups as described in US Patent No. 6,930,818. The display cells may also be other types of micro-containers, such as microcapsules, microchannels or equivalents, regardless of their shapes or sizes. All of these are within the scope of the present application.

    [0084] In one embodiment of the present invention, the display device is a high-light display device and in this embodiment, the colored particles are of the same color in all display cells. Each display cell would be a pixel in such a highlight display device. In addition, as shown in Figure 6, the display cells may be aligned with the pixel electrodes (see Figure 6a) or not aligned with the pixel electrodes (see Figure 6b).

    [0085] In another embodiment, the display device may be a multi-color display device. In this embodiment, the colored particles are of different colors in the display cells. In this embodiment, the display cells and the pixel electrodes are aligned.

    [0086] Figure 7 illustrates how multiple colors are displayed with a display device of the present invention. Each display cell represents a sub-pixel and each pixel has three sub-pixels. The three display cells, each representing a sub-pixel, are filled with an electrophoretic fluid in which the third type of pigment particles is red, green and blue, respectively.

    [0087] In Figure 7a, when a white pixel is desired, all three sub-pixels are turned to the white color state. In Figure 7b, when a black pixel is desired, all three sub-pixels are turned to the black color state. In Figure 7c, when a red color is desired, one of the sub-pixels is turned to red and the remaining two sub-pixels are turned to the black state for maximum color saturation. Similarly, Figure 7d and Figure 7e display the green and blue colors respectively. Alternatively, in Figures 7c, 7d and 7e, one of the sub-pixels is driven to the color state while the remaining two sub-pixels are driven to the white state for maximum brightness (at the expense of the color saturation). Further alternatively, in Figures 7c, 7d and 7e, one of the sub-pixel is driven to the color state while the remaining two sub-pixels are driven to the black and white states respectively.


    Claims

    1. An electrophoretic fluid comprising a first type (11; 21; 31; 41; 51) of pigment particles, a second type (12; 22; 32; 42; 52) of pigment particles and a third type (13; 23; 33; 43; 53) of pigment particles, all of which are dispersed in a solvent or solvent mixture, wherein

    (a) the first type (11; 21; 31; 41; 51) of pigment particles and the second type (12; 22; 32; 42; 52) of pigment particles carry opposite charge polarities; and

    (b) the third type (13; 23; 33; 43; 53) of pigment particles has the same charge polarity as the second type (12; 22; 32; 42; 52) of pigment particles but at a lower intensity; the electrophoretic fluid being characterized in that:

    (c) the second type (12; 22; 32; 42; 52) of pigment particles has a threshold voltage.


     
    2. The fluid of Claim 1, wherein the first type (11; 21; 31; 41; 51) of pigment particles and the second type (12; 22; 32; 42; 52) of pigment particles are of the black and white colors, respectively.
     
    3. The fluid of Claim 1, wherein the third type (13; 23; 33; 43; 53) of pigment particles is non-white and non-black.
     
    4. The fluid of Claim 3, wherein the third type (13; 23; 33; 43; 53) of pigment particles is of a color selected from the group consisting red, green and blue.
     
    5. The fluid of Claim 1, wherein the third type (13; 23; 33; 43; 53) of particles is larger in size than the first (11; 21; 31; 41; 51) or the second type (12; 22; 32; 42; 52) of particles.
     
    6. The fluid of Claim 1, wherein the third type (13; 23; 33; 43; 53) of particles has a charge level less than about 50% of the charge intensity of the first type (11; 21; 31; 41; 51) or the second type (12; 22; 32; 42; 52) of particles.
     
    7. A display device comprising display cells filled with the fluid of Claim 1, wherein the display cells are sandwiched between a common electrode layer (14; 24; 34; 44; 54) and a layer of pixel electrodes (15, 15a; 25; 35; 45; 55).
     
    8. The display device of Claim 7, wherein the display cells are aligned with the pixel electrodes (15, 15a; 25; 35; 45; 55).
     
    9. The display device of claim 7 wherein the display cells are not aligned with the pixel electrodes.
     
    10. The display device of Claim 7, wherein the third type (13; 23; 33; 43; 53) of pigment particles is of the same color in all display cells.
     
    11. The display device of claim 7 wherein the third type (13; 23; 33; 43; 53) of pigment particles are of different colors in different display cells.
     


    Ansprüche

    1. Elektrophoretisches Fluid, umfassend einen ersten Typ (11; 21; 31; 41; 51) von Pigmentpartikeln, einen zweiten Typ (12; 22; 32; 42; 52) von Pigmentpartikeln, und einen dritten Typ (13; 23; 33; 43; 53) von Pigmentpartikeln, von denen alle in einem Lösungsmittel oder einer Lösungsmittelmischung dispergiert sind, wobei

    (a) der erste Typ (11; 21; 31; 41; 51) von Pigmentpartikeln und der zweite Typ (12; 22; 32; 42; 52) von Pigmentpartikeln entgegengesetzte Ladungspolaritäten tragen; und

    (b) der dritte Typ (13; 23; 33; 43; 53) von Pigmentpartikeln dieselbe Ladungspolarität wie der zweite Typ (12; 22; 32; 42; 52) von Pigmentpartikeln hat, jedoch mit niedrigerer Intensität,
    wobei das elektrophoretische Fluid dadurch gekennzeichnet ist, dass:

    (c) der zweite Typ (12; 22; 32; 42; 52) von Pigmentpartikeln eine Schwellenwertspannung aufweist.


     
    2. Fluid nach Anspruch 1, wobei der erste Typ (11; 21; 31; 41; 51) von Pigmentpartikeln und der zweite Typ (12; 22; 32; 42; 52) von Pigmentpartikeln von schwarzer beziehungsweise weißer Farbe ist.
     
    3. Fluid nach Anspruch 1, wobei der dritte Typ (13; 23; 33; 43; 53) von Pigmentpartikeln weder weiß noch schwarz ist.
     
    4. Fluid nach Anspruch 3, wobei der dritte Typ (13; 23; 33; 43; 53) von Pigmentpartikeln eine Farbe ausgewählt aus der Gruppe bestehend aus rot, grün und blau aufweist.
     
    5. Fluid nach Anspruch 1, wobei der dritte Typ (13; 23; 33; 43; 53) von Partikeln größer bemessen als der erste Typ (11; 21; 31; 41; 51) oder der zweite Typ (12; 22; 32; 42; 52) von Partikeln ist.
     
    6. Fluid nach Anspruch 1, wobei der dritte Typ (13; 23; 33; 43; 53) von Partikeln ein Ladungsniveau von weniger als etwa 50 % der Ladungsintensität des ersten Typs (11; 21; 31; 41; 51) oder des zweiten Typs (12; 22; 32; 42; 52) von Partikeln aufweist.
     
    7. Anzeigevorrichtung, die Anzeigezellen umfasst, die mit dem Fluid gemäß Anspruch 1 gefüllt sind, wobei die Anzeigezellen sandwichartig zwischen einer gemeinsamen Elektrodenschicht (14; 24; 34; 44; 54) und einer Schicht von Pixelelektroden (15, 15a; 25; 35; 45; 55) angeordnet sind.
     
    8. Anzeigevorrichtung nach Anspruch 7, wobei die Anzeigezellen mit den Pixelelektroden (15, 15a; 25; 35; 45; 55) ausgerichtet sind.
     
    9. Anzeigevorrichtung nach Anspruch 7, wobei die Anzeigezellen nicht mit den Pixelelektroden ausgerichtet sind.
     
    10. Anzeigevorrichtung nach Anspruch 7, wobei der dritte Typ (13; 23; 33; 43; 53) von Pigmentpartikeln in allen Anzeigezellen dieselbe Farbe aufweist.
     
    11. Anzeigevorrichtung nach Anspruch 7, wobei der dritte Typ (13; 23; 33; 43; 53) von Pigmentpartikeln in unterschiedlichen Anzeigezellen unterschiedliche Farben aufweist.
     


    Revendications

    1. Fluide électrophorétique comprenant un premier type (11 ; 21 ; 31 ; 41 ; 51) de particules de pigment, un deuxième type (12 ; 22 ; 32 ; 42 ; 52) de particules de pigment et un troisième type (13 ; 23 ; 33 ; 43 ; 53) de particules de pigment, toutes étant dispersées dans un solvant ou mélange de solvants, dans lequel

    (a) le premier type (11 ; 21 ; 31 ; 41 ; 51) de particules de pigment et le deuxième type (12 ; 22 ; 32 ; 42 ; 52) de particules de pigment portent des polarités de charge opposées ; et

    (b) le troisième type (13 ; 23 ; 33 ; 43 ; 53) de particules de pigment a la même polarité de charge que le deuxième type (12 ; 22 ; 32 ; 42 ; 52) de particules de pigment, mais à une intensité inférieure ;
    le fluide électrophorétique étant caractérisé en ce que :

    (c) le deuxième type (12 ; 22 ; 32 ; 42 ; 52) de particules de pigment a une tension seuil.


     
    2. Fluide de la revendication 1, dans lequel le premier type (11 ; 21 ; 31 ; 41 ; 51) de particules de pigment et le deuxième type (12 ; 22 ; 32 ; 42 ; 52) de particules de pigment sont respectivement de couleur noire et blanche.
     
    3. Fluide de la revendication 1, dans lequel le troisième type (13 ; 23 ; 33 ; 43 ; 53) de particules de pigment n'est ni blanc, ni noir.
     
    4. Fluide de la revendication 3, dans lequel le troisième type (13 ; 23 ; 33 ; 43 ; 53) de particules de pigment est d'une couleur choisie dans le groupe constitué par le rouge, le vert et le bleu.
     
    5. Fluide de la revendication 1, dans lequel le troisième type (13 ; 23 ; 33 ; 43 ; 53) de particules est de plus grande taille que le premier (11 ; 21 ; 31 ; 41 ; 51) ou le deuxième type (12 ; 22 ; 32 ; 42 ; 52) de particules.
     
    6. Fluide de la revendication 1, dans lequel le troisième type (13 ; 23 ; 33 ; 43 ; 53) de particules a un niveau de charge inférieur à environ 50 % de l'intensité de charge du premier type (11 ; 21 ; 31 ; 41 ; 51) ou du deuxième type (12 ; 22 ; 32 ; 42 ; 52) de particules.
     
    7. Dispositif d'affichage comprenant des cellules d'affichage remplies avec le fluide de la revendication 1, les cellules d'affichage étant intercalées entre une couche d'électrode commune (14 ; 24 ; 34 ; 44 ; 54) et une couche d'électrodes de pixel (15, 15a ; 25 ; 35 ; 45 ; 55).
     
    8. Dispositif d'affichage de la revendication 7, dans lequel les cellules d'affichage sont alignées avec les électrodes de pixel (15, 15a ; 25 ; 35 ; 45 ; 55).
     
    9. Dispositif d'affichage de la revendication 7 dans lequel les cellules d'affichage ne sont pas alignées avec les électrodes de pixel.
     
    10. Dispositif d'affichage de la revendication 7, dans lequel le troisième type (13 ; 23 ; 33 ; 43 ; 53) de particules de pigment est de la même couleur dans toutes les cellules d'affichage.
     
    11. Dispositif d'affichage de la revendication 7 dans lequel le troisième type (13 ; 23 ; 33 ; 43 ; 53) de particules de pigment est d'une couleur différente dans différentes cellules d'affichage.
     




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    Cited references

    REFERENCES CITED IN THE DESCRIPTION



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    Patent documents cited in the description




    Non-patent literature cited in the description