CN110366747B

CN110366747B - Driving method for color display device

Info

Publication number: CN110366747B
Application number: CN201880014602.9A
Authority: CN
Inventors: C·林; J-C·黄; H-c·陈; P·B·雷克斯顿; 王铭; P-Y·程; 臧宏玫
Original assignee: E Ink California LLC
Current assignee: E Ink Corp
Priority date: 2017-04-25
Filing date: 2018-04-17
Publication date: 2022-10-18
Anticipated expiration: 2038-04-17
Also published as: KR102373217B1; TW202201099A; TWI700679B; KR20190101488A; CA3051003A1; TWI734572B; JP6967082B2; JP2020513114A; EP3616188A1; TWI807370B; TW202117691A; CN110366747A; TW201843669A; CA3051003C; WO2018200252A1; JP2021107936A; EP3616188A4

Abstract

The invention relates to a driving method for a color display device capable of displaying high-quality color states. The display device utilizes an electrophoretic fluid that includes three types of pigment particles, each having different optical characteristics, and displays on a viewing surface not only the colors of the three types of particles, but also the color of a binary mixture thereof.

Description

Driving method for color display device

Cross Reference to Related Applications

This application claims priority from U.S. patent application No. 15/496,604, filed on 25/4/2017 and disclosed as U.S. patent publication No. 2017/0263176. The entire contents of which are hereby incorporated by reference. The contents of all other U.S. patents and published applications mentioned below are hereby incorporated by reference.

Technical Field

The present invention relates to a driving method for a color display device to display high quality color states.

Background

In order to realize color display, a color filter is often used. The most common approach is to add color filters over the black/white sub-pixels of the pixelated display to display the colors red, green, and blue. When red is desired, the green and blue subpixels become black, so that the only color displayed is red. When blue is desired, the green and red sub-pixels become black, so that the only displayed color is blue. When green is desired, the red and blue subpixels become black, so that the only color displayed is green. When a black state is desired, all three subpixels become in the black state. When a white state is desired, the three sub-pixels become red, green, and blue, respectively, and as a result, the viewer sees a white state.

The biggest disadvantage of such a technique is that the white state is rather dim, since the reflectivity of each sub-pixel is about one third (1/3) of the desired white state. To compensate for this, a fourth sub-pixel capable of displaying only black and white states may be added, such that the white level is doubled at the expense of the red, green or blue levels (where each sub-pixel has only one-fourth of the pixel area). Brighter colors can be obtained by adding light from white pixels, but this is done at the expense of color gamut, so that the colors become very bright and unsaturated. A similar result can be achieved by reducing the color saturation of the three sub-pixels. Even with these methods, the white level is typically approximately less than half of that of a black and white display, making it an unacceptable choice for display devices (e.g., e-readers or displays requiring black and white brightness and contrast for good readability).

Disclosure of Invention

The first part of the invention relates to a driving method for an electrophoretic display comprising a first surface on a viewing side, a second surface on a non-viewing side and an electrophoretic fluid comprising a first type of pigment particles, a second type of pigment particles and a third type of pigment particles, all types of pigment particles being dispersed in a liquid, wherein

a) The three types of pigment particles have optical characteristics different from each other;

b) The first type of pigment particles and the second type of pigment particles carry opposite charge polarities; and

c) The third type of pigment particles have a charge polarity identical to that of the second type of pigment particles, but a lower zeta potential,

the method comprises the following steps:

(i) Applying a first drive voltage to a pixel in the electrophoretic display for a first period of time, the first drive voltage having a polarity that drives the first type of pigment particles toward the first surface, thereby causing the pixel to display optical characteristics of the first type of pigment particles on the first surface;

(ii) Applying a second drive voltage to the pixel for a second period of time, the second drive voltage having a polarity that drives the third type of pigment particles toward the first surface, thereby driving the pixel on the first surface to the optical properties of the third type of pigment particles; and

(iii) repeating steps (i) and (ii).

In one embodiment, the first type of pigment particles is negatively charged and the second type of pigment particles is positively charged. In one embodiment, the amplitude of the second driving voltage is less than 50% of the amplitude of the first driving voltage. In one embodiment, steps (i) and (ii) are repeated at least four times. In one embodiment, the method further comprises a shaking waveform prior to step (i). In an embodiment, the method further comprises driving the pixel to all-optical properties of the first type of pigment particles after the shaking waveform, but before step (i). In one embodiment, the first period of time is 40 to 140 milliseconds, the second period of time is greater than or equal to 460 milliseconds, and steps (i) and (ii) are repeated at least seven times.

A second part of the invention relates to a driving method for an electrophoretic display as described above, but comprising the additional steps of: (iii) after step (ii), but before repeating steps (i) and (ii), applying no drive voltage to the pixel for a third period of time; and repeating steps (i), (ii) and (iii).

In one embodiment, the first type of pigment particles is negatively charged and the second type of pigment particles is positively charged. In one embodiment, the amplitude of the second driving voltage is less than 50% of the amplitude of the first driving voltage. In one embodiment, steps (i), (ii), and (iii) are repeated at least four times. In one embodiment, the method further comprises a vibration waveform prior to step (i). In one embodiment, the method further comprises a driving step of reaching a full color state of the first type of pigment particles after the shaking waveform, but before step (i).

A third aspect of the present invention is directed to a driving method for an electrophoretic display comprising a first surface on a viewing side, a second surface on a non-viewing side and an electrophoretic fluid comprising a first type of pigment particles, a second type of pigment particles and a third type of pigment particles, all types of pigment particles being dispersed in a liquid, wherein

c) The third type of pigment particles having a charge polarity that is the same as the second type of pigment particles, having a lower zeta potential,

and the method has a voltage insensitive range of at least 0.7V.

A fourth aspect of the invention relates to a driving method for an electrophoretic display according to the first aspect of the invention, but comprising the additional steps of:

(iii) (iii) after step (i) but before step (ii), not applying a drive voltage to the pixel for a third period of time;

(iv) (iii) after step (ii), but before repeating the steps, not applying a drive voltage to the pixel for a fourth period of time; and

(iii) repeating steps (i) - (iv).

In one embodiment, the first type of pigment particles can be negatively charged and the second type of pigment particles positively charged. In one embodiment, the amplitude of the second driving voltage is less than 50% of the amplitude of the first driving voltage. In one embodiment, steps (i) - (iv) are repeated at least three times. In one embodiment, the method further comprises a vibration waveform prior to step (i). In one embodiment, the method further comprises driving the pixel to the full color state of the first type of pigment particles after the shaking waveform but before step (i).

A fifth aspect of the present invention is directed to a driving method for an electrophoretic display comprising a first surface on a viewing side, a second surface on a non-viewing side and an electrophoretic fluid sandwiched between a common electrode and a pixel electrode layer and comprising a first type of pigment particles, a second type of pigment particles and a third type of pigment particles, all types of pigment particles being dispersed in a solvent or solvent mixture, wherein

c) The third type of pigment particles have the same charge polarity as the second type of pigment particles, but at a lower intensity,

the method comprises the following steps:

(i) Applying a first drive voltage to a pixel in the electrophoretic display for a first period of time, wherein the first drive voltage has a polarity that is the same as the first type of pigment particles to drive the pixel to a color state of the first type of pigment particles at the viewing side;

(ii) Applying a second drive voltage to the pixel for a second period of time, wherein the second drive voltage has a polarity that is the same as the second type of pigment particles to drive the pixel to the color state of the second type of pigment particles at the viewing side; and

(iii) repeating steps (i) and (ii).

In an embodiment, the method further comprises a waiting time during which no driving voltage is applied. In one embodiment, the first type of pigment particles is negatively charged and the second type of pigment particles is positively charged. In one embodiment, the second period of time is at least twice as long as the first period of time. In one embodiment, steps (i) and (ii) are repeated at least three times. In one embodiment, the method further comprises a vibration waveform prior to step (i). In one embodiment, the method further comprises driving the pixel to the full color state of the second type of pigment particles after the shaking waveform but before step (i).

A sixth aspect of the present invention is directed to a driving method for an electrophoretic display comprising a first surface on a viewing side, a second surface on a non-viewing side and an electrophoretic fluid sandwiched between a common electrode and a pixel electrode layer and comprising a first type of pigment particles, a second type of pigment particles and a third type of pigment particles, all types of pigment particles being dispersed in a solvent or solvent mixture, wherein

c) The third type of pigment particles have a charge polarity identical to that of the second type of pigment particles, but at a lower intensity,

the method comprises the following steps:

(i) Applying a first drive voltage to a pixel in the electrophoretic display for a first period of time, wherein the first drive voltage has a polarity that is the same as the second type of pigment particles to drive the pixel to a color state of the second type of pigment particles at the viewing side;

(ii) Applying a second drive voltage to the pixel for a second period of time, wherein the second drive voltage has a polarity that is the same as the first type of pigment particles to drive the pixel to the color state of the first type of pigment particles at the viewing side;

(iii) Applying no driving voltage to the pixel for a third period; and

(iv) repeating steps (i), (ii) and (iii).

In one embodiment, the first type of pigment particles is negatively charged and the second type of pigment particles is positively charged. In one embodiment, steps (i), (ii), and (iii) are repeated at least three times. In an embodiment, the magnitude of the second drive voltage is the same as the magnitude of the drive voltage required to drive the pixel from the color state of the first type of pigment particles to the color state of the second type of pigment particles, and vice versa. In an embodiment, the magnitude of the second drive voltage is higher than the magnitude of the drive voltage required to drive the pixel from the color state of the first type of pigment particles to the color state of the second type of pigment particles, and vice versa. In one embodiment, the method further comprises a vibration waveform. In one embodiment, the method further comprises driving the pixel to the full color state of the first type of pigment particles after the shaking waveform but before step (i).

A seventh aspect of the present invention is directed to a driving method for an electrophoretic display comprising a first surface on a viewing side, a second surface on a non-viewing side and an electrophoretic fluid sandwiched between a common electrode and a pixel electrode layer and comprising a first type of pigment particles, a second type of pigment particles and a third type of pigment particles, all types of pigment particles being dispersed in a solvent or solvent mixture, wherein

the method comprises the following steps:

(i) Applying a first drive voltage to a pixel in the electrophoretic display for a first period of time, the first drive voltage having a polarity that is the same as the second type of pigment particles to drive the pixel to the color state of the second type of pigment particles, wherein the first period of time is insufficient to drive the pixel to the full color state of the second type of pigment particles at the viewing side;

(ii) Applying a second drive voltage to the pixel for a second period of time, the second drive voltage having a polarity that is the same as the first type of pigment particles to drive the pixel at the viewing side to a mixed state of the first and second types of pigment particles; and

(iii) repeating steps (i) and (ii).

In one embodiment, the first type of pigment particles is negatively charged and the second type of pigment particles is positively charged. In one embodiment, the amplitude of the second driving voltage is less than 50% of the amplitude of the first driving voltage. In one embodiment, steps (i) and (ii) are repeated at least four times. In one embodiment, the method further comprises a vibration waveform prior to step (i). In one embodiment, the method further comprises driving the pixel to the full color state of the first type of pigment particles after the shaking waveform but before step (i).

The fourth driving method of the present invention may be applied to a pixel in a color state of the first type of pigment particles, or may be applied to a pixel in a color state other than the color state of the first type of pigment particles.

The invention also provides a driving method for displaying the optical characteristic mixture of two of the three particles in the electrophoretic display fluid. A first such "hybrid feature" method comprises the steps of:

(iii) Applying a third drive voltage having the same polarity as the first drive voltage for a third period of time, the third period of time being shorter than the first period of time, thereby producing a mixture of the optical properties of the first and third types of particles on the viewing surface.

In the first mixing characteristics method, the duration of the third period of time may be about 20% to 80%, and preferably about 20% to 40%, of the duration of the first period of time. A vibration waveform may be applied prior to step (i), and a drive voltage to drive the first type of pigment particles towards the first surface may be applied prior to the vibration waveform.

A second "hybrid feature" method includes the steps of:

(i) Applying a first drive voltage to a pixel in the electrophoretic display for a first period of time, the first drive voltage having a polarity that drives the second type of pigment particles towards the first surface, thereby causing the pixel to display optical characteristics of the second type of pigment particles on the first surface;

(ii) Applying a second drive voltage to the pixel for a second period of time, the second drive voltage having the same polarity as the first drive voltage but having a smaller amplitude than the first drive voltage, thereby driving the third type of pigment particles on the first surface and producing a mixture of the optical properties of the second and third types of particles on the first surface.

In the second method of mixing characteristics, the duration of the second period of time may be about 100% to 150% of the duration of the first period of time. A vibration waveform may be applied prior to step (i), and a drive voltage to drive the first type of pigment particles towards the first surface may be applied prior to the vibration waveform.

A third "hybrid feature" method includes the steps of:

(ii) Applying a second drive voltage to the pixel for a second period of time, the second drive voltage having a polarity that drives the third type of pigment particles toward the first surface; and

(iii) repeating steps (i) and (ii),

wherein the durations of steps (i) and (ii) and the magnitudes of the voltages applied therein are adjusted to produce a mixture of the optical properties of the third type of particles and one of the first and second types of particles on the first surface.

In the third mixing characteristic method, a vibration waveform may be applied before step (i), and a driving voltage that drives the first type of pigment particles toward the first surface may be applied before the vibration waveform.

Drawings

FIG. 1 is a schematic cross-sectional view of an electrophoretic display fluid that may be used in the driving method of the present invention.

Fig. 2A, 2B and 2C are schematic cross-sectional views similar to fig. 1 showing the position of the particles in black, white and red (colored) states, respectively, of the display fluid.

Fig. 3 is a typical waveform for driving a pixel from the white state of fig. 2B to the red state of fig. 2C.

Fig. 4 is a waveform that can be used to implement the first driving method of the present invention instead of the portion of the waveform of fig. 3 during period t3.

Fig. 5 and 6 depict waveforms generated by modifying the waveforms of fig. 3 with partial waveforms of fig. 4 in order to implement the first driving method of the present invention.

Fig. 7 is a second waveform that can be used to implement the second driving method of the present invention in place of the portion of the waveform of fig. 3 during period t3.

Fig. 8 and 9 depict waveforms generated by modifying the waveforms of fig. 3 with partial waveforms of fig. 7 in order to implement a second driving method of the present invention.

Fig. 10A and 10B are optical results produced by the third driving method of the present invention. Fig. 10A is a relationship of a driving voltage applied based on the waveform of fig. 3 to an optical state property (a), and fig. 10B is a relationship of a driving voltage applied based on the waveform of fig. 3 modified based on a partial waveform of fig. 4 to an optical state property (a).

Fig. 11 is a waveform that can be used to implement the fourth driving method of the present invention instead of the portion in the period t3 in the waveform of fig. 3.

Fig. 12 and 13 depict waveforms generated by modifying the waveforms of fig. 3 with partial waveforms of fig. 11 in order to implement a fourth driving method of the present invention.

Fig. 14 depicts typical waveforms for driving a pixel from the white state of fig. 2B to the black state of fig. 2A.

Fig. 15 is a waveform that can be added at the end of the waveform of fig. 14 to implement a fifth driving method of the present invention.

Fig. 16 is a composite waveform combining the waveforms of fig. 14 and 15 to implement a fifth driving method of the present invention.

Fig. 17 depicts typical waveforms for driving a pixel to the white state of fig. 2B.

Fig. 18A and 18B are two waveforms that can be used to implement the sixth driving method of the present invention instead of the portion of the waveform of fig. 17 in the period t17.

Fig. 19A and 19B depict waveforms resulting from modifying the waveforms of fig. 17 with partial waveforms of fig. 18A or 18B, respectively, in order to implement a sixth driving method of the present invention.

Fig. 20A and 20B are schematic cross-sectional views similar to fig. 1 showing the positions of particles in black and gray states, respectively, of a display fluid.

Fig. 21 is a typical waveform for driving a pixel to the gray state of fig. 20B.

Fig. 22 is a waveform that can be used to implement the seventh driving method of the present invention in place of the portion of the waveform of fig. 21 in the period t23.

Fig. 23 is a composite waveform combining the waveforms of fig. 21 and 22 to implement a seventh driving method of the present invention.

Fig. 24 is a waveform used in the eighth driving method of the present invention.

Fig. 25 is a composite waveform combining the waveforms of fig. 14 and 24 to implement an eighth driving method of the present invention.

Fig. 26A and 26B are the generation of a gray state of a pixel starting from the white state of the pixel.

Fig. 26C and 26D are the generation of a gray state of a pixel starting from the black state of the pixel.

Fig. 27 is a waveform that may be used to drive a display via a white state to a reddish state in a first hybrid characteristic driving method of the present invention.

Fig. 28 is a waveform that can be used to drive a display to a deep red state in the second hybrid characteristic driving method of the present invention.

Fig. 29 is a second waveform useful for driving a display to a deep red state in a third hybrid characteristics driving method of the present invention.

Detailed Description

The present invention relates to a driving method for a color display device.

The device uses an electrophoretic fluid as shown in figure 1. The fluid includes three types of pigment particles dispersed in a liquid, typically a dielectric solvent or solvent mixture. For convenience of explanation, the three types of pigment particles may be referred to as white particles (11), black particles (12), and colored particles (13). The colored particles are non-white and non-black.

However, it is understood that the scope of the present invention broadly encompasses pigment particles of any color, so long as the three types of pigment particles have distinguishable optical characteristics. Thus, the three types of pigment particles may also be referred to as a first type of pigment particle, a second type of pigment particle, and a third type of pigment particle.

The white particles (11) may be made of, for example, tiO ₂ 、ZrO ₂ 、ZnO、Al ₂ O ₃ 、Sb ₂ O ₃ 、BaSO ₄ 、PbS O ₄ And the like.

The black particles (12) may be Cl pigment black 26 (Cl pigment black 26) or 28, etc. (e.g., iron manganese black (mangenese ferrite black) or copper chromium black (copper chromium black) or carbon black).

The third type of particles may have a color like red, green, blue, magenta, cyan or yellow. Pigments for this type of particle may include, but are not limited to, CI pigment PR254, PR122, PR149, PG36, PG58, PG7, PB15: 3. PY138, PY150, PY155, or PY20. Those are the commonly used organic pigments described in the Pigment 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, hostape rm Green GNX, BASF Irgazine Red L3630, cinqasia Red L4100 HD, and Irgazine Red L3660 HD; sun Chemical phthalocyanines blue, phthalocyanines green, diarylide yellow or diarylide AAOT yellow.

In addition to the colors, the first, second and third types of particles may also have other different optical properties, such as light transmission, reflectivity and light emission brightness, or, in the case of displays intended for machine reading, false colors (p-colors) in the sense of variations in the reflectivity of electromagnetic wave wavelengths outside the visible range.

The liquid in which the three types of pigment particles are dispersed may be clear and colorless. It preferably has a low viscosity and a dielectric constant in the range of about 2 to 30, preferably about 2 to 15, for high particle mobility. Examples of suitable dielectric fluids include hydrocarbons (e.g., isoparaffinic solvents (Iso par), DECALIN (decahydronaphthalene, decaalin), 5-ethylidene-2-norbornene- (5-ethyl idene-2-norbomene), fatty Oils (fatty Oils), paraffin Oils (paraffin Oils), silicon fluids (silicon n fluids), aromatic hydrocarbons (e.g., toluene (toluene), xylene (xylene), phenyl dimethylethane (phenylxylene)), dodecylbenzene (docylcyanine) or alkylnaphthalenes (alkylnaphthalene)), halogenated solvents (halogenated solvents) (e.g., perfluorodecalin (perfluorodecalin), octafluorotoluene (perfluorotoluene), perfluoroxylene (perfluoroxylene), dichlorotrifluorotoluene (dichlorobenzotrifluoride), 3,4, 5-trichlorotrifluorotoluene (3, 4, 5-trichlorotrifluorotoluene), chloropentafluorobenzene (chloropentafluorobenezene), dichlorononane (dichlorononane) or pentachlorobenzene (pentachlorobenezene)) and perfluorosolvents (perfluorinated solvents) (for example, FC-43, FC-70 or FC-5060 from 3m company, st. Paul MN), low molecular weight halogen-containing polymers (e.g., homopolymers of hexafluoropropylene oxide (pol y) from TCI America, portland, oregon), poly (chlorotrifluoroethylene) (poly (chlorotrifluoroethylene)) (e.g., halocarbon Oils (Halocarbon Oils) from Halocarbon Product corp., river Edge, NJ), perfluoropolyalkyl ethers (perfluoropolyalkyl ethers) (e.g., galden from Ausimont or Krytox Oils and Greases K-Fluid Series from DuPont, delaware), silicone oil based on polydimethylsiloxane (polydimethylsiloxane) from Dow-burning (DC-200).

The display layer using the display fluid of the invention has two surfaces, a first surface (16) on the viewing side and a second surface (17) on the opposite side of the display fluid layer from the first surface (16). Thus, the second surface is located on the non-viewing side. The term "viewing side" means the side from which the image is viewed.

The fluid is shown sandwiched between these two surfaces. On the first surface (16) side, there is a shared electrode (14), which is a transparent electrode layer (e.g., ITO), distributed over the entire top of the display layer. On the second surface (17) side, an electrode layer (15) including a plurality of pixel electrodes (15 a) is provided. However, since the various particles (11, 12, 13) react only to an electric field applied within the display fluid layer, as will be apparent to those skilled in the art of electrophoretic displays, other electrode configurations may be used; for example, the shared electrode may be replaced by a series of stripe electrodes or a matrix of electrodes similar to the pixel electrodes 15 a.

The display fluid is filled in the display unit. The display element may be aligned or misaligned with the pixel electrode. The term "display cell" means a micro-container filled with an electrophoretic fluid. Examples of "display cells" may include cup-shaped microcells as described in U.S. Pat. No. 6,930,818 and microcapsules as described in U.S. Pat. No. 5,930,026. The micro-containers may have any shape or size, all of which are within the scope of the present application.

One region corresponding to one pixel electrode may be referred to as one pixel (or one sub-pixel). The driving of an area corresponding to a pixel electrode is realized by applying a potential difference (or referred to as a driving voltage or an electric field) between the common electrode and the pixel electrode.

The pixel electrode is described in U.S. Pat. No. 7,046,228. The entire contents of which are hereby incorporated by reference. It is noted that although reference is made to active matrix driving using a Thin Film Transistor (TFT) backplane for the pixel electrode layer, the scope of the invention includes other types of electrode addressing as long as the electrodes provide the desired functionality.

The space between two vertical dashed lines represents a pixel (or sub-pixel). For the sake of brevity, when referring to a "pixel" in the driving method, this term also includes "sub-pixels".

Two of the three types of pigment particles carry opposite charge polarities, while the third type of pigment particles are slightly charged. The term "slightly charged" or "lower charge intensity" is intended to refer to a charge level of particles that is less than about 50% (preferably, about 5% to 30%) of the charge intensity of the more strongly charged particles. In one embodiment, the charge strength can be measured in terms of zeta potential. In one embodiment, zeta potential is measured by a colloidal dynamics Acoustosizer IIM using a CSPU-100 signal processing unit, an ESA EN # Att n flow through cell (K: 127). Before the test, instrument constants such as the density of the solvent used for the sample at the test temperature (25 ℃), the dielectric constant of the solvent, the sound velocity in the solvent, and the viscosity of the solvent were input. The pigment sample is dispersed in a solvent (which is typically a hydrocarbon fluid having less than 12 carbon atoms) and diluted to 5-10 weight percent. The sample also contained a charge control agent (Solsperse 17000, available from Lubrizol Corporation, berkshire hathawaway company, "Solsperse" is a registered trademark) at a 1:10. the mass of the diluted sample was measured and then the sample was loaded into the flow channel to measure the zeta potential.

For example, if the black particles are positively charged and the white particles are negatively charged, the colored pigment particles may be slightly charged. In other words, in this example, the charges carried by the black and white particles are much stronger than the charges carried by the colored particles.

Furthermore, the colored particles carrying a slight charge have the same charge polarity as the charge polarity carried by either of the other two types of more strongly charged particles. In the following it will be assumed that the colored particles (13) carry charges of the same polarity as the second (black) particles (12).

It is noted that of the three types of pigment particles, the slightly charged type of particles preferably have a larger size.

Further, in the context of the present application, a high drive voltage (V) _H1 Or V _H2 ) Is defined as a drive voltage sufficient to drive the pixel from one extreme color state to the other extreme color state. High drive voltage (V) if the first and second types of pigment particles are higher charged particles _H1 Or V _H2 ) Meaning that the drive voltage is sufficient to drive the pixel from the color state of the first type of pigment particles to the color state of the second type of pigment particles and vice versa. For example, a high driving voltage V _H1 Means a drive voltage sufficient to drive the pixel from the color state of the first type of pigment particles to the color state of the second type of pigment particles, and V _H2 Meaning a drive voltage sufficient to drive the pixel from the color state of the second type of pigment particles to the color state of the first type of pigment particles. In this case as stated, a low driving voltage (V) _L ) Is defined as may be sufficient to resemble an imageThe pixel is driven from the color state of the first type of pigment particle to a drive voltage of the color state of a third type of pigment particle (which has less charge and may be larger in size). For example, a low drive voltage may be sufficient to drive to the color state of the colored particles, while black and white particles are not visible on the viewing side.

In general, V _L Less than V _H (e.g., V) _H1 Or V _H2 ) The amplitude is 50%, or preferably less than 40%.

The following is an example of a driving method illustrating how different color states can be displayed by the above-described electrophoretic fluid.

Example 1

This example is shown in fig. 2A-2C. The white pigment particles (21) are negatively charged and the black pigment particles (22) are positively charged, and both types of pigment particles are smaller than the colored particles (23).

The colored particles (23) have the same charge polarity as the black particles, but are slightly charged. As a result, at certain driving voltages, the black particles move faster than the colored particles (23).

In FIG. 2A, the applied drive voltage is +15V (i.e., V) _H1 I.e., the pixel electrode is +15V with respect to the common electrode). In this case, the negative white particles (21) move to the vicinity of the relatively positive pixel electrode (25) or at the relatively positive pixel electrode (25), while the positive black particles (22) and the positive charged particles (23) move to the vicinity of the relatively negative shared electrode (24) or at the relatively negative shared electrode (24). As a result, black is seen on the viewing side. The colored particles (23) move toward the viewing-side shared electrode (24); however, they move slower than black particles due to their lower charge density and larger size.

In FIG. 2B, when-15V (i.e., V) is applied _H2 ) The negative white particles (21) move to the vicinity of the relatively positive shared electrode (24) or to the relatively positive shared electrode (24) on the viewing side, and the positive black particles and the positive charged particles move to the vicinity of the relatively negative pixel electrode (25) or to the relatively negative pixel electrode (25). As a result, white is seen on the viewing side.

Is worthy ofNote that V is _H1 And V _H2 Of opposite polarity and of the same amplitude or of different amplitudes. In the example shown in FIG. 2, V _H1 Is positive (same polarity as the black particles), and V _H2 Is negative (same polarity as the white particles).

The driving from the white state of fig. 2B to the colored state of fig. 2C can be summarized as follows:

a driving method for an electrophoretic display comprising a first surface on a viewing side, a second surface on a non-viewing side and an electrophoretic fluid, the fluid being sandwiched between a shared electrode and a pixel electrode layer and comprising a first type of pigment particles (i.e. white), a second type of pigment particles (i.e. black) and a third type of pigment particles (i.e. coloured), all types of pigment particles being dispersed in a solvent or solvent mixture, wherein

c) The third type of pigment particles has the same charge polarity as the second type of pigment particles, but at a lower intensity,

the method comprises driving a pixel in an electrophoretic display from a color state of a first type of pigment particles towards a color state of a third type of pigment particles by applying a low drive voltage sufficient to drive the third type of pigment particles to a viewing side while leaving the first and second types of pigment particles at a non-viewing side, and the polarity of the applied low drive voltage is the same as the polarity of the third type of pigment particles.

To drive the pixel to the color state of the third type of pigment particles, i.e. red (see fig. 2C), the method starts with the color state of the first type of pigment particles, i.e. white (see fig. 2B).

When the color of the third type of particles is seen at the viewing side, the other two types of particles may mix at the non-viewing side (opposite 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 type of particles are black and white and the third type of particles is red, then in fig. 2C, when the red color is seen on the viewing side, the gray color is on the non-viewing side.

In the case of fig. 2C, the driving method will ideally ensure color brightness (i.e., prevent black particles from being seen) and color purity (i.e., prevent white particles from being seen). In practice, however, it is difficult to achieve this desired result for a variety of reasons, including particle size distribution and particle charge distribution.

One solution to this is to use a vibration waveform before 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 vibration waveform consists of repeating a pair of opposing drive pulses for a number of cycles. For example, the vibration waveform may consist of a +15V pulse of 20msec and a-15V pulse of 20msec, and such a pair of pulses is repeated 50 times. The total time of this vibration waveform was 2000msec. The symbol "msec" represents milliseconds.

Whatever the optical state (black, white or red) before the drive voltage is applied, a shaking waveform can be applied to the pixel. After applying the vibration waveform, the optical state will not be pure white, pure black or pure red. Instead, the color state will consist of a mixture of three types of pigment particles.

With the above method, the vibration waveform is applied before the pixel is driven to the color state of the first type of pigment particles (i.e., white). With this added vibration waveform, even though the white state is measurably the same as the white state without the vibration waveform, the color state (i.e., red) of the third type of pigment particles will be significantly better than the color state without the vibration waveform in terms of color brightness and color purity. This indicates a better separation of white particles from red particles and a better separation of black particles from red particles.

The application time of each drive pulse in the vibration waveform is not more than half of the drive time required to drive from the full black state to the full white state, and vice versa. For example, if 300msec is required to drive a pixel from a fully black state to a fully white state, or vice versa, the shaking waveform can be composed of positive and negative pulses, each applied for no more than 150msec. In practice, it is preferable that the shaking waveform pulses be short.

It is noted that the vibration waveform is truncated (i.e., the number of pulses is less than the actual number) throughout all of the drawings of the entire application.

The waveforms for driving the display to the colored (red) state of fig. 2C are shown in fig. 3. In this waveform, after the vibration waveform, a high negative drive voltage (V) is applied _H2 E.g., -15V) for a period of t2 to drive the pixel towards the white state. From the white state, a low positive voltage (V) may be applied _L E.g., + 5V) for t3, the pixel is driven toward the colored state (i.e., red) (i.e., the pixel is driven from fig. 2B to fig. 2C).

The driving period "t2" is when V is applied _H2 Is sufficient to drive the pixel to the white state, and the drive period "t3" is when V is applied _L Is sufficient to drive the pixel from the white state to the red state. The drive voltage is preferably applied for a period of time t1 before the vibration waveform to ensure dc balance. Throughout this application, the term "dc-balanced" is intended to mean that the drive voltage applied to a pixel is substantially zero when integrated over a period of time (e.g., the duration of the entire waveform).

The first driving method:

fig. 4 is a waveform that can be used in the first driving method of the present invention; this waveform may be used instead of the driving period t3 in fig. 3.

In an initial step, a high negative drive voltage (V) is applied _H2 E.g., -15V), followed by application of a positive drive voltage (+ V') to drive the pixel towards the red state. The amplitude of + V' is less than V _H (e.g., V) _H1 Or V _H2 ) 50% of the amplitude.

In this drive waveform, a high negative drive voltage (c) is appliedV _H2 ) For a period t4 to push the white particles to the viewing side, and then a positive driving voltage of + V' is applied for a period t5 to pull down the white particles and push the red particles to the viewing side.

In one embodiment, t4 may be in the range of 20-400msec, and t5 may be greater than or equal to 200msec.

The waveform of FIG. 4 is repeated for at least four cycles (N.gtoreq.4), preferably at least eight cycles. The red color becomes more intense after each drive cycle.

The driving method of fig. 4 can be summarized as follows:

a driving method for an electrophoretic display comprising a first surface on a viewing side, a second surface on a non-viewing side and an electrophoretic fluid, the electrophoretic fluid being sandwiched between a shared electrode and a pixel electrode layer and comprising a first type of pigment particles, a second type of pigment particles and a third type of pigment particles, all types of pigment particles being dispersed in a solvent or solvent mixture, wherein

the method comprises the following steps:

(i) Applying a first drive voltage to the pixels in the electrophoretic display for a first period of time, the first drive voltage having a polarity that is the same as the first type of pigment particles to drive the pixels to a color state of the first type of pigment particles on the viewing side;

(ii) Applying a second drive voltage to the pixel for a second period of time, the second drive voltage having a polarity that is the same as the third type of pigment particles to drive the pixel to the color state of the third type of pigment particles on the viewing side; and

(iii) repeating steps (i) and (ii).

In an embodiment, the first type of pigment particles is negatively charged and the second type of pigment particles is positively charged.

In one embodiment, the amplitude of the second driving voltage is less than 50% of the amplitude of the first driving voltage.

As described above, the drive waveform shown in fig. 4 may be used in place of the drive period t3 in fig. 3, and fig. 5 is a combined waveform after the replacement. In other words, the driving sequence may be: the vibration waveform is then driven toward the white state for a period t2, and then the waveform of fig. 4 is applied.

In another embodiment, the step of driving to the white state for the period t2 may be deleted, and in this case, the vibration waveform is applied immediately before the waveform of fig. 4 is applied (see fig. 6).

In one embodiment, the drive sequence of fig. 5 or 6 is dc balanced.

The second driving method includes:

fig. 7 shows waveforms that can be used in the second driving method of the present invention. This waveform is an alternative to the driving waveform of fig. 4, and can also be used to replace the driving period t3 in fig. 3.

In this alternative waveform, a waiting time "t6" is added after the red-going pulse (red-going pulse) in the period t5 and before the white-going pulse (white-going pulse) in the period t4, and the red-going pulse is repeated in the period t 5. During the waiting time, no driving voltage is applied. The entire waveform of FIG. 7 is also repeated for a number of cycles (e.g., N ≧ 4).

The waveform of fig. 7 is designed to discharge charge imbalance stored in the dielectric layer in an electrophoretic display device, particularly when the resistance value of the dielectric layer is high, such as at low temperatures.

In the context of the present application, the term "low temperature" means a temperature below about 10 ℃.

The latency presumably eliminates the unwanted charge stored in the dielectric layer and makes the short pulse ("t 4") for driving the pixel to the white state and the longer pulse ("t 5") for driving the pixel to the red state more efficient. As a result, this alternative driving method allows for better separation of the low charged pigment particles from the higher charged pigment particles. The latency ("t 6") may be in the range of 5-5,000msec depending on the resistance value of the dielectric layer.

The driving method of fig. 7 can be summarized as follows:

the method comprises the following steps:

(i) Applying a first drive voltage to the pixel in the electrophoretic display for a first period of time, the first drive voltage having the same polarity as the first type of pigment particles to drive the pixel to a color state of the first type of pigment particles at the viewing side;

(ii) Applying a second drive voltage to the pixel for a second period of time, the second drive voltage having the same polarity as the third type of pigment particles to drive the pixel at the viewing side to the color state of the third type of pigment particles;

(iii) Applying no driving voltage to the pixel for a third period; and

(iv) repeating steps (i), (ii) and (iii).

In one embodiment, the first type of pigment particles is negatively charged and the second type of pigment particles is positively charged.

As described above, the driving waveforms shown in fig. 7 can also be used to replace the driving period t3 (see fig. 8) in fig. 3. In other words, the driving sequence may be: the vibration waveform is then driven toward the white state for a period t2, and then the waveform of fig. 7 is applied.

In another embodiment, the step of driving to the white state for the period t2 may be deleted, and in this case, the vibration waveform is applied before the waveform of fig. 7 is applied (see fig. 9).

In another embodiment, the drive sequence of fig. 8 or 9 is dc balanced.

It should be noted that the length of any drive period mentioned in the present application may depend on the temperature.

The third driving method:

fig. 10A shows the relationship between the applied drive voltage (V') and the optical performance based on the waveform of fig. 3. As shown, the applied positive drive voltage V' may affect the red state performance of the color display device described above. The red state performance of the display device is represented as a value by means of a color system.

The maximum a in fig. 10A occurs at the applied drive voltage V' (about 3.8V) in fig. 3. However, if the applied drive voltage produces a variation of ± 0.5V, the resulting a value will be about 37, which is about 90% of the maximum a, and thus still acceptable. This tolerance is advantageous for accommodating changes in drive voltage caused by, for example, variations in the electronic components of the display device, a drop in battery voltage over time, batch variations in the TFT backplane, batch variations in the display device, or temperature and humidity fluctuations.

Based on the data presented in fig. 10A, a study was conducted to find the range of driving voltage V' that can be driven to the red state with more than 90% of the maximum a value. In other words, the optical performance is not significantly affected when any driving voltage within this range is applied. This range may therefore be referred to as a "voltage insensitive" range. The wider the "voltage insensitive" range, the more tolerant the driving method is to batch variations and environmental variations.

In fig. 4, three parameters t4, t5 and N need to be considered for the present study. The effect of the three parameters on the voltage insensitive range is interactive and non-linear.

From the model of fig. 10A, the best set of values for the three parameters can be found to achieve the widest voltage insensitive range of the fig. 4 waveform. The results are summarized in fig. 10B.

When t4 is between 40-140msec, t5 is greater than or equal to 460msec, and N is greater than or equal to 7, the voltage insensitive range according to fig. 10B (i.e., 3.7V to 6.5V) is twice as wide as the voltage insensitive range according to fig. 10A (i.e., 3.3V-4.7V).

The optimal parameters discussed above may also be applied to any of the driving methods of the present invention.

Therefore, the third driving method can be summarized as follows:

a driving method for an electrophoretic display comprising a first surface on a viewing side, a second surface on a non-viewing side and an electrophoretic fluid sandwiched between a shared electrode and a pixel electrode layer and comprising a first type of pigment particles, a second type of pigment particles and a third type of pigment particles, all types of pigment particles being dispersed in a solvent or solvent mixture, wherein

and the method has a voltage insensitive range of at least 0.7V.

In such a method, the optical quality of the achievable color state is at least 90% of the maximum acceptable "a" value when a drive voltage in such a range is applied.

It is also noted that the data shown in fig. 10A and 10B was collected at ambient temperature.

The fourth driving method includes:

fig. 11 shows waveforms that can be used in the fourth driving method of the present invention. This drive waveform may be used instead of the drive period t3 in fig. 3.

In an initial step, a high negative drive voltage (V) is applied _H2 E.g., -15V) to the pixel for a period t7 (see the corresponding pulse in period t4 of fig. 4). This pulse is followed by a waiting time t8 during which no voltage is applied. After the waiting time, a positive driving voltage (V', e.g., less than V) is applied _H1 Or V _H2 50%) to the pixel for a period t9 (see the corresponding pulse in period t5 in fig. 4). After the pulse at t9, but before repeating the steps of the waveform, there is a second waiting time t10 during which no voltage is applied. The waveform of fig. 11 is repeated N times. The term "waiting time" as described above means a period of time during which no driving voltage is applied.

This driving method is not only particularly effective at low temperatures, but also provides better tolerance to structural variations caused by the display device during its manufacture. Therefore, its utility is not limited to low temperature driving.

In the waveform of fig. 11, the first waiting time t8 is very short, and the second waiting time t10 is long. The period t7 is also shorter than the period t 9. For example, t7 may be in the range of 20-200 msec; t8 may be less than 100msec; t9 may be in the range of 100-200 msec; and t10 may be less than 1000msec.

Fig. 12 shows a waveform generated by inserting the waveform of fig. 11 instead of the period t3 of fig. 3. In fig. 3, a white state is displayed during t 2. As a general rule, the better the white state during this period, the better the red state displayed at the end of the waveform.

In the shaking waveform, the positive/negative pulse pairs are preferably repeated 50-1500 times, and each pulse is preferably applied for 10msec.

In an embodiment, the step of driving to the white state for the period t2 may be deleted, and in this case, the vibration waveform is applied before the waveform of fig. 11 is applied (see fig. 13).

The fourth driving method of fig. 11 can be summarized as follows:

the method comprises the following steps:

(i) Applying a first drive voltage to the pixel in the electrophoretic display for a first period of time, wherein the first drive voltage has a polarity that is the same as the first type of pigment particles to drive the pixel to a color state of the first type of pigment particles on the viewing side;

(ii) Not applying a driving voltage to the pixel for a second period of time;

(iii) Applying a second driving voltage to the pixel for a third period of time, wherein the second driving voltage has the same polarity as the third type of pigment particles to drive the pixel to the color state of the third type of pigment particles at the viewing side;

(iv) Not applying the driving voltage to the pixel for a fourth period of time; and

(iii) repeating steps (i) - (iv).

In one embodiment, steps (i) - (iv) are repeated at least three times.

In an embodiment, the second drive voltage is less than 50% of the drive voltage sufficient to drive the pixel from the color state of the first type of pigment particles to the color state of the second type of pigment particles, and vice versa.

In another embodiment, the drive sequence of fig. 12 or 13 is dc balanced.

The fifth driving method:

as shown in fig. 2 (a), since the black particles and the red particles carry the same charge polarity, they tend to move in the same direction. Even though the black particles move faster than the red particles at certain drive voltages due to their higher charge and possibly also due to their smaller size, some of the red particles may still be driven to the viewing side with the black particles, thus resulting in a reduced black state quality.

Fig. 14 depicts typical waveforms for driving a pixel to the black state. A shaking waveform (as described above) is included to ensure color brightness and purity. As shown, a high positive drive voltage (V) is applied after the vibration waveform _H1 E.g., + 15V) for a period t12 to drive the pixel toward the black state. The drive voltage is applied for a period t11 before the vibration waveform to ensure dc balance.

Fig. 15 is a waveform that may be added at the end of the waveform of fig. 14 for driving a pixel to a black state. The combined waveform may further allow for better separation of black particles from red particles, making the black state more saturated and the red less colored.

In FIG. 15, V is applied _H2 A (negative) short pulse "t13", followed by V _H1 The longer pulse "t14" of (positive) and the waiting time (0V) of t 15. Such a sequence is applied at least once, preferably at least three times (i.e., N.gtoreq.3), more preferably at least five to seven times.

Pulse "t14" is typically at least twice as long as pulse "t 13".

V _H2 Pushes the black and red particles towards the pixel electrode, and V _H1 The longer pulses "t14" push them towards the shared electrode side (i.e., the viewing side). This asymmetric drive sequence is more favorable for black particles than for red particles, because the velocities of the two types of pigment particles are different at the same drive voltage. As a result, the black particles can be better separated from the red particles.

The waiting time "t15" is optional, depending on the dielectric layer in the display device. In general, the resistance value of the dielectric layer is more pronounced at lower temperatures, and in this case, a waiting time may be required to release the charge trapped in the dielectric layer.

The fifth driving method of fig. 15 can be summarized as follows:

the method comprises the following steps:

(i) Applying a first drive voltage to a pixel in the electrophoretic display for a first period of time, wherein the first drive voltage has a polarity that is the same as the first type of pigment particles to drive the pixel to a color state of the first type of pigment particles on a viewing side;

(ii) Applying a second drive voltage to the pixel for a second period of time, wherein the second drive voltage has the same polarity as the second type of pigment particles to drive the pixel to the color state of the second type of pigment particles at the viewing side;

(iii) Optionally, applying no drive voltage to the pixel for a third period of time; and

(iv) repeating steps (i), (ii) and (iii) (if present).

Fig. 16 shows a composite waveform that combines the waveforms of fig. 14 with the waveforms of fig. 15. However, it is also worth noting that "t12" can be shortened depending on the particle velocity and the number of cycles (N) in the sequence. In other words, at the end of "t12", the pixel does not have to be in a full black state. Instead, the waveforms of fig. 15 may start at any state from black to white (including gray) as long as the number of sequences (N) is sufficient to drive the pixel to the black state at the end.

The methods described in fig. 14-16 can also be used to drive pixels to the black state at low temperatures. In this case, the period t14 should be longer than t13, and the waiting time t15 should be at least 50msec.

In one embodiment, the drive sequence of FIG. 16 is DC balanced.

The sixth driving method:

fig. 17 depicts typical waveforms for driving a pixel to the white state. A shaking waveform (as described above) is included to ensure color brightness and purity. Applying V after the vibration waveform _H2 For a period t17. Applying V before the vibration waveform _H1 For a period t16 to ensure dc balance.

Fig. 18A and 18B show waveforms that can be used in place of the pulse t17 in the waveform of fig. 17.

This driving method is particularly suitable for low temperature driving, but is not limited to low temperature driving.

In FIG. 18A, V is applied _H1 A short (positive) pulse "t18", followed by V _H2 The longer pulse "t19" of (negative) and the waiting time (0V) of t 20. As shown in FIG. 18B, the amplitude of the negative drive voltage (V') applied during t19 may be higher than V _H2 Is measured (e.g., -30V instead of-15V).

Such a sequence is applied at least once, preferably at least three times (i.e., in FIGS. 18A and 18B, N.gtoreq.3, more preferably at least five to seven times).

t19 should be longer than t 18. For example, t18 may be in the range of 20-200msec, while t19 may be less than 1000msec. The waiting time t20 should be at least 50msec.

The sixth driving method shown in fig. 18A and 18B may be summarized as follows:

the method comprises the following steps:

(i) Applying a first drive voltage to the pixels in the electrophoretic display for a first period of time, wherein the first drive voltage has the same polarity as the second type of pigment particles to drive the pixels to the color state of the second type of pigment particles at the viewing side;

(ii) Applying a second drive voltage to the pixel for a second period of time, wherein the second drive voltage has the same polarity as the first type of pigment particles to drive the pixel at the viewing side to the color state of the first type of pigment particles;

(iii) Applying no driving voltage to the pixel for a third period of time; and

(iii) repeating steps (i) and (ii).

In the embodiment shown in fig. 18A, the second voltage is the drive voltage required to drive the pixel from the color state of the first type of pigment particles towards the color state of the second type of pigment particles, and vice versa.

In another embodiment shown in fig. 18B, the second voltage has a higher amplitude than the drive voltage required to drive the pixel from the color state of the first type of pigment particles toward the color state of the second type of pigment particles, and vice versa.

Fig. 19A and 19B show composite waveforms that combine the waveform of fig. 17 with the waveform of fig. 18A or 18B, respectively.

In the shaking waveform, the positive/negative pulses are preferably repeated 50-1500 times, and each pulse is preferably applied for 10msec.

In one embodiment, the drive sequence of fig. 19A or 19B is dc balanced.

The seventh driving method:

a seventh driving method of the invention is to drive the pixels towards an intermediate color state (e.g. grey).

Fig. 20A and 20B are directed to particle motion. As shown, when a low negative drive voltage (V) is applied _L E.g., -5V), the pixel in the black state (see fig. 20A) is driven toward the gray state. In this process, the red particles are pushed by the low driving voltage towards the pixel electrode and a mixture of black and white particles is seen on the viewing side.

Waveforms for this driving method are shown in fig. 21. After the vibration waveform, a high positive drive voltage (V) is applied _H1 E.g., + 15V) for a period t22 to drive the pixel toward the black state. From the black state, a low negative drive voltage (V) can be applied _L E.g., -5V) for a period t23, the pixel is driven toward the gray state, i.e., from fig. 20A to fig. 20B.

The driving period t22 is when V is applied _H1 Is sufficient to drive the pixel to the black state, and t23 is when V is applied _L Is sufficient to drive the pixel from the black state to the grey state. Before the vibration waveform, V is preferably applied _H1 For a period t21 to ensure dc balance.

Fig. 22 is a drive waveform that can be used in place of the pulse t23 in fig. 21. In an initial step, a high positive drive voltage (V) is applied _H1 E.g. + 15V) for a short period t24 to push the black particles towards viewingSide, but t24 is not sufficient to drive the pixel to the full black state, and then a low negative drive voltage (V) is applied _L E.g., -5V) for a period t25 to drive the pixel towards the gray state. V _L Is less than V _H (e.g., V) _H1 Or V _H2 ) 50% of the total weight of the steel.

The waveform of FIG. 22 is repeated for at least four cycles (N ≧ 4), preferably at least eight cycles.

At ambient temperature, the period t24 is less than about 100msec, while t25 is typically greater than 100msec.

The seventh driving method shown in fig. 22 can be summarized as follows:

the method comprises the following steps:

(i) Applying a first drive voltage to the pixel in the electrophoretic display for a first period of time, the first drive voltage having the same polarity as the second type of pigment particles to drive the pixel to the color state of the second type of pigment particles, wherein the first period of time is insufficient to drive the pixel to the full color state of the second type of pigment particles on the viewing side;

(ii) Applying a second drive voltage to the pixel for a second period of time, the second drive voltage having a polarity that is the same as the first type of pigment particles to drive the pixel on the viewing side to a mixed state of the first and second types of pigment particles; and

(iii) repeating steps (i) and (ii).

As described above, in this method, the second driving voltage is about 50% of the first driving voltage.

Fig. 23 shows a composite waveform combining the waveform of fig. 21 and the waveform of fig. 22, in which the driving period t23 in fig. 21 is replaced with the waveform of fig. 22. This composite waveform is composed of four phases. The first stage is a dc balancing stage (t 21); the second stage is a vibration step; and the third stage drives the pixel to the black state (t 22). The waveform used in the third stage may be any waveform that drives the pixel to a good black state. The fourth phase comprises a short period t24 with a high positive drive voltage followed by a longer period with a low negative drive voltage. Repeating the fourth stage several times.

Note that t22 may be optional in fig. 23.

Can be controlled by changing the low negative voltage (V) _L ) The grey state is turned to brighter or darker. In other words, the waveform sequence and shape may remain unchanged; but V _L May vary (e.g., -4V, -5V, -6V, or-7V) to cause different gray levels to be displayed. This feature can potentially reduce the space required for look-up tables in the drive circuitry, thus reducing cost. The driving method can produce high quality intermediate states (of the first type of pigment particles and the second type of pigment particles) with very little color interference from the third type of pigment particles.

In one embodiment, the drive sequence of FIG. 23 is DC balanced.

The eighth driving method:

fig. 24 is a waveform used in the eighth driving method of the present invention. This waveform is intended to be applied to pixels that are not in the white state (i.e., the color state of the first type of pigment particles).

In an initial step, a high negative drive voltage (V) is applied _H2 E.g., -15V) for a period t26, followed by a wait time t27. After the waiting time, a positive driving voltage (V', e.g., less thanV _H1 Or V _H2 50%) for a period t28 followed by a second waiting period t29. The waveform of fig. 24 is repeated N times. The term "waiting time" as described above means a period of time during which no driving voltage is applied.

This driving method is particularly effective at low temperatures and also reduces the overall driving time to the red state.

It is noted that the period t26 is rather short, typically in the range of about 50% of the time required to drive from the fully black state to the fully white state, and is therefore insufficient to drive the pixel to the fully white state. The period t27 may be less than 100msec; the period t28 may be in the range of 100-200 msec; and the period t29 may be less than 1000msec.

The waveforms of fig. 24 are similar to those of fig. 11, except that the waveforms of fig. 11 would be applied to pixels that are in a white state (i.e., the color of the first type of pigment particles), while the waveforms of fig. 24 are intended to be applied to pixels that are not in a white state.

Fig. 25 is an example in which the waveform of fig. 24 is applied to a pixel in a black state (i.e., a color state of a second type of pigment particle).

Like the driving method of fig. 11, the eighth driving method of fig. 24 can be summarized as follows:

the method comprises the following steps:

(ii) Not applying the driving voltage to the pixel for a second period of time;

(iii) Applying a second drive voltage to the pixel for a third period of time, wherein the second drive voltage has the same polarity as the third type of pigment particles to drive the pixel to the color state of the third type of pigment particles at the viewing side;

(iii) repeating steps (i) - (iv).

In one embodiment, steps (i) - (iv) are repeated at least three times.

In one embodiment, the drive sequence of FIG. 25 is DC balanced.

Generation of intermediate colors:

advantageously, the driving method of the present invention is capable of displaying intermediate colors (i.e., a mixture of two particle colors) in addition to the colors of a single particle. In many cases, the display using the present method is required to display gray scale images, which requires area modulation (area modulation) of the display. Such area modulation increases the number of colors that can be displayed, but at the cost of reducing the resolution of the display because multiple pixels of the display are area modulated to form a gray scale "super-pixel". Providing each pixel of the display with the ability to display intermediate colors and increasing the number of intermediate colors that each pixel can display can reduce the number of pixels that must be used in each super-pixel and thus increase the resolution of the gray scale display.

One generation method for intermediate gray (i.e., a mixture of black and white particle colors) has been discussed above with reference to fig. 20A and 20B. Gray can also be produced by driving the pixels to a black or white state (fig. 2A or fig. 2B, respectively) and then applying a high driving voltage of ± 15V to drive the pixels to a white or black state, respectively, but terminating the driving voltage before the white or black state is reached, thereby producing a gray state. It should be noted, however, that in the three particle system used in the present method, it is advantageous to use a method that starts from the white state instead of the black state to produce the gray state for the reasons that will be explained with reference to fig. 26A-26D.

Fig. 26A and 26B are diagrams for generating a gray state from a white state. Fig. 26A (which is substantially the same as fig. 2B) is a graph of the voltage drop across the cell by applying a high negative drive voltage (-15v _H2 ) To produce a white state, a high negative drive voltage drives the white particles 21 to the viewing side, while the black particles 22 and the red particles 23 are driven towards the pixel electrode. Starting from the white state of fig. 26A, a high positive voltage (+ 15v _H1 ) The short drive pulse drives the white particles towards the pixel electrode and the black and red particles towards the viewing side. The brief drive pulse is terminated when the white and black particles mix near the viewing side. Because the red particles have a lower electrophoretic mobility than the black particles, the red particles move relatively slowly away from the pixel electrode and are therefore shielded from the viewer in the grey state by the black and white particles, which are located between the red particles and the viewing surface. Thus, fig. 26B appears "bright" gray, consisting of only a color mixture of black and white particles and not contaminated by the color of the red particles.

In contrast, fig. 26C and 26D generate a gray state starting from a black state. FIG. 26C (which is essentially the same as FIG. 2A) is generated by applying a high positive drive voltage (+ 15V _H1 ) To produce a black state, a high positive drive voltage drives the black 22 and red 23 particles towards the viewing side, and the white particles 21 adjacent to the pixel electrode. Starting from the black state of fig. 26C, a negative voltage (-15v _H2 ) The short drive pulse drives the white particles towards the viewing side and the black and red particles towards the pixel electrode. The brief drive pulse is terminated when the white and black particles mix near the viewing side. However, because the red particles have a lower electrophoretic mobility than the black particles, the red particles move relatively slowly away from the viewing side and thus mix with the black and white particles in the gray state; in practice, the red particles may tend to be closer to the viewing side than the black particles. Thus, fig. 26D appears "dull" gray, where the color mixture of the black and white particles is significantly contaminated by the color of the red particles.

As described above, the gray state of a pixel can be generated starting from either the black state or the white state. Likewise, a light red state (color mixing of white and red particles) can be produced starting from a red state or a white state. In the former case, the full red state is driven first (see FIG. 2C), and then a high negative drive voltage (-15V _H2 ) For a brief period of time insufficient to reach the white state of fig. 2B. A high negative drive voltage causes the white particles 21 to move quickly towards the viewing side, the black particles 22 to move quickly towards the pixel electrode, and the red particles 23 to move relatively slowly towards the pixel electrode. When the white and red particles mix, the drive voltage is terminated, thus leaving a visible light red color on the viewing side. The black particles are located near the pixel electrode and are thus shielded from the viewer by the white and red particles. In the latter case, the cell is first driven to the full white state (see FIG. 2B), and a low positive drive voltage (+ 5V _L ) For a period of time insufficient to reach the red state of fig. 2C. The low negative drive voltage causes the white particles 21 to move towards the pixel electrode and the red particles to move towards the viewing side, thus again producing a mixture of red and white particles and a display of light red. Substitute and makeWith a continuous low negative drive voltage, the transition from the white state to the light red state can be achieved using a push-pull waveform (pus h-pull waveform) as shown in fig. 5, 6, 8 or 9.

It has been empirically found that the light red state resulting from the red state is less uniform than the light red state resulting from the white state. Although the cause of this difference in uniformity is not fully understood, it is believed to be related to the variation in the position of the various particles within the microcapsules (if present) as well as the electrophoretic mobility of the individual particles and the variation of the various components of the electrophoretic display. Also, it seems that the low driving voltage for driving from the red state is more affected by power supply variation than the high driving voltage.

FIG. 27 is a waveform for driving a display via a white state to a light red state. In the waveform of fig. 27, a high negative drive voltage (V) is applied _H2 E.g., -15V) for a period t31 to drive the pixel towards the white state. Starting from the white state, by applying a low positive voltage (V) _L E.g., + 5V) for a period t32, the pixel is driven toward the red state, thereby driving the pixel from the state of fig. 2B to the state of fig. 2C. Finally, by applying a high negative drive voltage (V) _H2 E.g., -15V) for a period t33, driving the pixel from the red state to the light red state, wherein the period t33 is shorter than the period t31 and is insufficient to drive the pixel to the fully white state. It is desirable to apply the vibration waveform before the white-oriented pulse in the period t31, and preferably, to apply a negative drive voltage (e.g., V) before the vibration waveform _H2 E.g., -15V) for a period t30 to ensure dc balance. It will be seen that the waveform of fig. 27 is substantially the waveform of fig. 3, but with the addition of a white inversion pulse in period t 33. The exact chromaticity of the light red color obtained can be varied by adjusting the duration of the period t33, which period t33 is typically in the range of about 20-300msec (typically 20-100 msec). The duration of the period t33 is typically about 10% to 60% of the duration of the period t 31.

Achieving a deep red state (i.e., color mixing of black and red particles) is much more difficult than achieving a light red state because the black and red particles carry charges of the same polarity andand thus tend to react in a similar manner to an applied electric field. For example, if the pixel is first driven to the red state of FIG. 2C, then by applying a high positive drive voltage (+ 15V, V) to drive the pixel to the black state of FIG. 2A _H1 ) To try to create a mixture of red and black particles, the red particles (already adjacent to the front electrode as shown in fig. 2C) will remain adjacent to the front electrode and will not move aside to accommodate the arriving black particles. The result is that even after a high positive drive voltage has been applied for a long time, which is longer than the time required to drive the pixel from the white state of fig. 2B to the black state of fig. 2A, the resulting "dark red" state will actually be only slightly darker than the previous red state.

Two approaches have been found to achieve a satisfactory deep red state. The first method uses the waveform shown in fig. 28 and essentially starts from a dark gray state. As shown, this waveform is preceded by a high positive drive voltage (+ 15V _H1 ) To drive the pixel to a dark grey state (not a fully black state). After this high positive drive voltage, a low positive drive voltage (V) is applied _L E.g., + 5V) for a period t36, the period t36 is typically much longer than t35 to drive the pixel to a deep red state. For the reasons described above, the high positive drive pulse in period t35 may optionally be preceded by a shaking waveform and/or a high negative drive voltage pulse (V) of period t34 _H2 For example. -15V). the duration of t36 may vary widely, but may typically be about 300-2000msec, more typically 500-1000msec; the darkness of the deep red color produced can be varied by varying the duration of t36, with longer durations tending to increase the redness of the color produced.

A second approach to achieving a satisfactory deep red state uses waveforms as shown in fig. 29, fig. 29 being essentially the same as fig. 5, but the duration of the various drive pulses shown in fig. 29 will be different from those of the drive pulses of fig. 5 for reasons discussed below. It will be recalled from the discussion of FIG. 5 above that the main portion of the relevant waveform includes a low positive drive voltage (V) represented as time duration t39 in FIG. 29 _L E.g., + 5V) with a high negative drive voltage (V40) of duration t in fig. 29 _H2 E.g., -15V) to pulse. This sequence of alternating pulses may be preceded by one or more of the following: (a) High negative drive voltage (V) of duration t37 intended for DC balancing _H2 E.g., -15V) white going pulses; (b) a vibration waveform; and (c) a high negative drive voltage (V) of duration t38 _H2 E.g., -15V), which may be different from or the same as the duration t40 of the latter white going pulse already mentioned.

The waveforms of fig. 5 are described above as producing a pure red state. However, it has been found empirically that by adjusting the durations t39 and t40 in fig. 29 and/or by adjusting the drive voltages V' and V applied during these periods _H2 This type of waveform can produce not only a pure red state, but also deep red and light red states. If the size of V 'is increased, the red color becomes darker, whereas if the size of V' is decreased, the red color becomes lighter. Likewise, if the duration of t40 is increased relative to t39, a lighter red color will be produced, whereas if the duration of t39 is increased relative to t40, a darker red color will be produced. Obviously, a combination of drive voltage and duration variation may be used. the duration of t39 and t40 may vary within wide limits; for example, at 25 ℃, t40 may drop from 60msec to 20msec, while t39 may rise from 300msec to 600msec. At low temperatures like 0 ℃, even wider ranges may be desired; for example, at this temperature, t40 may be 60msec and t39 3000msec.

Example 2

An electrophoretic medium substantially as described above with reference to fig. 1 was prepared by mixing 30 weight percent polymer-coated titanium dioxide particles (white), 8 weight percent polymer-coated mixed metal oxide particles (black), and 7 weight percent red pigment particles in an isoalkane solvent (isoparaffin solvent) and adding a charge control agent (Solsperse 19000). The white particles are negatively charged and the black and red particles are positively charged, but the red particles have a lower charge density than the black particles. The resulting electrophoretic medium was loaded into a standard test cell with a substantially transparent front electrode and driven to the white, black, red and gray states described above with reference to fig. 2A, 2B, 2C and 26B, respectively. Values of L, a and b were measured for all four color states using standard techniques, and the results are as follows:

TABLE 1

Colour(s)	L*	a*	b*
				White colour	60.2	-1.0	-1.4
Black color (black)	12.6	7.7	-0.8
				Red colour	27.0	37.9	17.6
Grey colour	38.4	-1.0	-4.0

The reflectance Y in the gray state was 10.3%. From these results, it can be seen that the experimental medium of the present invention can display good white, black and red states, and can also display a gray state.

While the invention has been described with reference to specific embodiments thereof, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the true spirit and scope of the invention. In addition, many modifications may be made to adapt a particular situation, material, composition, process step or steps, to the objective and scope of the present invention. All such modifications are intended to be within the scope of the appended claims.

Claims

1. A driving method for an electrophoretic display comprising a first surface on a viewing side, a second surface on a non-viewing side and an electrophoretic fluid comprising particles of a first type, particles of a second type and particles of a third type, all types of particles being dispersed in a liquid, wherein

c) The third type of pigment particles have a charge polarity that is the same as the second type of pigment particles, but a lower zeta potential,

the method comprises the following steps:

(ii) Applying a second drive voltage to the pixel for a second period of time, the second drive voltage having a polarity that drives the third type of pigment particles towards the first surface, thereby driving the pixel on the first surface to the optical properties of the third type of pigment particles; and

(iii) Applying a third drive voltage for a third period of time, the third drive voltage having the same polarity as the first drive voltage and the third period of time being shorter than the first period of time, to produce a mixture of the optical properties of the first and third types of particles on the viewing surface;

wherein the duration of the third period of time is 20% to 80% of the duration of the first period of time.

2. The method according to claim 1, wherein the duration of the third period of time is 20% to 40% of the duration of the first period of time.

3. The method of claim 1, further comprising applying a vibration waveform prior to step (i).

4. The method of claim 3, further comprising applying a drive voltage that drives the first type of pigment particles toward the first surface prior to the vibration waveform.