TW202201099A - Driving methods for color display device - Google Patents

Abstract

The present invention is directed to driving methods for a color display device which can display high quality color states. The display device utilizes an electrophoretic fluid which comprises three types of pigment particles having different optical characteristics, and provides for displaying at a viewing surface not only the colors of the three types of particles but also the colors of binary mixtures thereof.

Description

Driving method for color display device

[References for related applications]

This application claims priority to US Patent Application Serial No. 15/496,604 filed on April 25, 2017 and published as US Patent Publication No. 2017/0263176. It is hereby incorporated by reference in its entirety. The contents of all other US patents and published applications mentioned below are incorporated herein by reference.

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

To achieve color display, color filters are often used. The most common method is to add color filters on top of the black/white sub-pixels of a pixelated display to display red, green, and blue. When red is desired, the green and blue sub-pixels become black, so that the only displayed color 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 change to a black state, so that the only displayed color is green. When a black state is desired, all three subpixels become black. 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 because 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 can be added, doubling the white level at the expense of the red, green, or blue level (where each sub-pixel is only a quarter of the pixel area) . Brighter colors can be achieved by adding light from white pixels, but this is achieved at the expense of color gamut, resulting in very bright and unsaturated colors. Similar results can be achieved by reducing the color saturation of the three sub-pixels. Even with these methods, the white level is typically roughly half the white level of a black and white display, making it an unacceptable choice for display devices such as e-readers or displays that require good readability of black and white brightness and contrast.

A first aspect of the present invention relates to a driving method for an electrophoretic display including a first surface on a viewing side, a second surface on a non-viewing side, and an electrophoretic fluid, the electrophoretic fluid comprising a first type Pigment particles of the second type, pigment particles of the second type and pigment particles of the third type, all types of pigment particles dispersed in a liquid, where a) the three types of pigment particles have different optical properties 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 the same charge polarity as the second type of pigment particles, but with a lower zeta potential, The method includes 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 to drive the first type of pigment particles toward the first surface, thereby urging the pixel to operate at the first surface the optical properties of the first type of pigment particles displayed on the first surface; (ii) applying a second driving voltage to the pixel for a second period of time, the second driving voltage having a polarity to drive the third type of pigment particles towards the first surface, thereby driving the pixel on the first surface towards the optical properties of the third type of pigment particles; and Repeat steps (i) and (ii).

In one embodiment, the first type of pigment particles are negatively charged and the second type of pigment particles are 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 applying a vibration waveform prior to step (i). In one embodiment, the method further includes driving the pixel to full optical properties of the first type of pigment particles after the vibrational 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 aspect of the present invention relates to a driving method for an electrophoretic display like the above, but the method includes additional steps as follows: (iii) after step (ii), but after repeating steps (i) and (ii) ), no driving voltage is applied to the pixel for a third period of time; and steps (i), (ii) and (iii) are repeated.

In one embodiment, the first type of pigment particles are negatively charged and the second type of pigment particles are 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 applying a vibration waveform prior to step (i). In one embodiment, the method further includes a driving step to achieve a full color state of the first type of pigment particles after the vibrational waveform, but before step (i).

A third aspect of the present invention relates to a driving method for an electrophoretic display including a first surface on a viewing side, a second surface on a non-viewing side, and an electrophoretic fluid, the electrophoretic fluid comprising a first type Pigment particles of the second type, pigment particles of the second type and pigment particles of the third type, all types of pigment particles dispersed in a liquid, where a) the three types of pigment particles have different optical properties 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 the same charge polarity as the second type of pigment particles, but with a lower zeta potential, And the method has a voltage insensitive range of at least 0.7V.

A fourth aspect of the present invention relates to a driving method for an electrophoretic display according to the first aspect of the present invention, but includes additional steps as follows: (iii) after step (i), but before step (ii), no driving voltage is applied to the pixel for a third period of time; (iv) after step (ii), but before repeating the steps, no driving voltage is applied to the pixel for a fourth period of time; and Repeat steps (i)-(iv).

In one embodiment, the first type of pigment particles may be negatively charged, while the second type of pigment particles are 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 applying a vibration waveform prior to step (i). In one embodiment, the method further includes driving the pixel to a full color state of the first type of pigment particles after the vibration waveform, but before step (i).

A fifth aspect of the present invention relates to a driving method for an electrophoretic display, the electrophoretic display including a first surface on a viewing side, a second surface on a non-viewing side, and an electrophoretic fluid sandwiched in a common Between the electrode and a pixel electrode layer and including the first type of pigment particles, the second type of pigment particles and the third type of pigment particles, all types of pigment particles are dispersed in a solvent or solvent mixture, wherein a) the three types of pigment particles have different optical properties 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 the same charge polarity as the second type of pigment particles, but at a lower intensity, The method includes the following steps: (i) applying a first driving voltage to a pixel in the electrophoretic display for a first period of time, wherein the first driving voltage has the same polarity as the first type of pigment particles to drive the pixel toward the viewing side the colour state of the first type of pigment particles; (ii) applying a second driving voltage to the pixel for a second period of time, wherein the second driving voltage has the same polarity as the second type of pigment particles to drive the pixel towards the second type on the viewing side the color state of the pigment particles; and Repeat steps (i) and (ii).

In one embodiment, the method further includes a wait time in which the driving voltage is not applied. In one embodiment, the first type of pigment particles are negatively charged and the second type of pigment particles are 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 applying a vibration waveform prior to step (i). In one embodiment, the method further includes driving the pixel to a full color state of the second type of pigment particles after the vibration waveform, but before step (i).

A sixth aspect of the present invention relates to a driving method for an electrophoretic display, the electrophoretic display including a first surface on a viewing side, a second surface on a non-viewing side, and an electrophoretic fluid sandwiched in a common Between the electrode and a pixel electrode layer and including the first type of pigment particles, the second type of pigment particles and the third type of pigment particles, all types of pigment particles are dispersed in a solvent or solvent mixture, wherein a) the three types of pigment particles have different optical properties 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 the same charge polarity as the second type of pigment particles, but at a lower intensity, The method includes the following steps: (i) applying a first driving voltage to a pixel in the electrophoretic display for a first period of time, wherein the first driving voltage has the same polarity as the second type of pigment particles to drive the pixel toward the viewing side the color state of the second type of pigment particles; (ii) applying a second driving voltage to the pixel for a second period of time, wherein the second driving voltage has the same polarity as the first type of pigment particles to drive the pixel towards the first type on the viewing side the color state of the pigment particles; (iii) no driving voltage is applied to the pixel for the third period; and Repeat steps (i), (ii) and (iii).

In one embodiment, the first type of pigment particles are negatively charged and the second type of pigment particles are positively charged. In one embodiment, steps (i), (ii) and (iii) are repeated at least three times. In one 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 The same is true. In one embodiment, the magnitude of the second driving voltage is higher than the magnitude of the driving 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 The same is true. In one embodiment, the method further includes applying a vibration waveform. In one embodiment, the method further includes driving the pixel to a full color state of the first type of pigment particles after the vibration waveform, but before step (i).

A seventh aspect of the present invention relates to a driving method for an electrophoretic display, the electrophoretic display including a first surface on a viewing side, a second surface on a non-viewing side, and an electrophoretic fluid sandwiched in a common Between the electrode and a pixel electrode layer and including the first type of pigment particles, the second type of pigment particles and the third type of pigment particles, all types of pigment particles are dispersed in a solvent or solvent mixture, wherein a) the three types of pigment particles have different optical properties 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 the same charge polarity as the second type of pigment particles, but at a lower intensity, The method includes the following steps: (i) applying a first driving voltage to a pixel in the electrophoretic display for a first period of time, the first driving voltage having the same polarity as the second type of pigment particles, to drive the pixel towards the second type of pigment the color state of the particles, wherein the first period of time is insufficient to drive the pixel on the viewing side to the full color state of the second type of pigment particles; (ii) applying a second driving voltage to the pixel for a second period of time, the second driving voltage having the same polarity as the first type of pigment particles, to drive the pixel towards the first and second on the viewing side the mixed state of the types of pigment particles; and Repeat steps (i) and (ii).

In one embodiment, the first type of pigment particles are negatively charged and the second type of pigment particles are 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 applying a vibration waveform prior to step (i). In one embodiment, the method further includes driving the pixel to a full color state of the first type of pigment particles after the vibration waveform, but before step (i).

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

The present invention also provides a driving method for displaying the mixing of optical properties of two of the three particles in the aforementioned electrophoretic display fluid. The first such "mixed properties" method involved 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 to drive the first type of pigment particles toward the first surface, thereby urging the pixel to operate at the first surface the optical properties of the first type of pigment particles displayed on the first surface; (ii) applying a second driving voltage to the pixel for a second period of time, the second driving voltage having a polarity to drive the third type of pigment particles towards the first surface, thereby driving the pixel on the first surface towards the optical properties of the third type of pigment particles; and (iii) applying a third driving voltage for a third period of time, the third driving voltage having the same polarity as the first driving voltage, and the third period of time being shorter than the first period of time, whereby in the viewing A mixture of the optical properties of the first and third types of particles is produced on the surface.

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

A second "mixed property" method includes 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 to drive the second type of pigment particles towards the first surface, thereby urging the pixel to operate at the first surface the optical properties of the second type of pigment particles displayed on the first surface; (ii) applying a second driving voltage to the pixel for a second period of time, the second driving voltage having the same polarity as the first driving voltage, but having a smaller amplitude than the first driving voltage, whereby in the first driving voltage The third type of pigment particles are driven on a surface and a mixture of the optical properties of the second and third types of particles is produced on the first surface.

In the second hybrid property method, the duration of the second period of time may be about 100% to about 150% of the duration of the first period of time. A vibrational waveform may be applied prior to step (i), and a driving voltage for driving the first type of pigment particles towards the first surface may be applied prior to the vibrational waveform.

A third "mixed property" method includes 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 to drive the first type of pigment particles toward the first surface, thereby urging the pixel to operate at the first surface the optical properties of the first type of pigment particles displayed 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 to drive the third type of pigment particles toward the first surface; and Repeat steps (i) and (ii), wherein the duration of steps (i) and (ii) and the magnitude of the voltage applied therein are adjusted to generate one of the third type of particles and the first and second types of particles on the first surface A mixture of optical properties of types of particles.

In the third hybrid property method, a vibrational waveform may be applied prior to step (i), and a driving voltage for driving the first type of pigment particles toward the first surface may be applied prior to the vibrational waveform.

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

The device uses the electrophoretic fluid shown in Figure 1. The fluid includes three types of pigment particles dispersed in a liquid (usually a dielectric solvent or solvent mixture). For convenience of illustration, the three types of pigment particles may be referred to as white particles (11), black particles (12), and colored particles (13). 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 as long as the three types of pigment particles have distinguishable optical properties. Therefore, the three types of pigment particles may also be referred to as the first type of pigment particles, the second type of pigment particles and the third type of pigment particles.

The white particles ( 11 ) may be formed of inorganic pigments like TiO ₂ , ZrO ₂ , ZnO, Al ₂ O ₃ , Sb ₂ O ₃ , BaSO ₄ , PbSO ₄ , and the like.

The black particles (12) may be CI pigment black 26 or 28, etc. (eg, manganese ferrite black spinel or copper chromite black spinel) 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 pigments PR254, PR122, PR149, PG36, PG58, PG7, PB15:3, PY138, PY150, PY155 or PY20. Those are commonly used organic pigments described in the Pigment Index Handbooks "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 Irgazine Red L 3660 HD; Sun Chemical phthalocyanine blue, phthalocyanine green, diarylide yellow or diarylide AAOT yellow.

In addition to color, the first, second and third types of particles may also have other different optical properties, such as light transmission, reflectivity and luminous brightness, or in the case of displays intended for machine reading, Pseudo-color in the sense of a change in reflectivity of electromagnetic wave wavelengths outside the visible range.

The liquid in which the three types of pigment particles are dispersed can be clear and colorless. For high particle mobility, 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). Examples of suitable dielectric fluids include hydrocarbons (eg, Isopar, decahydronaphthalene (DECALIN), 5-ethylidene-2-norbornene ), fatty oils, paraffin oils, silicone fluids, aromatic hydrocarbons (for example, toluene, xylene, phenyldimethylethane ( phenylxylylethane), dodecylbenzene or alkylnaphthalene), halogenated solvents (for example, perfluorodecalin, perfluorotoluene, perfluoroxylene) ), dichlorobenzotrifluoride, 3,4,5-trichlorobenzotrifluoride, chloropentafluorobenzene, dichlorononane or pentachloro pentachlorobenzene) and perfluorinated solvents (eg, FC-43, FC-70, or FC-5060 from 3M Company, St. Paul MN), low molecular weight halogen-containing polymers (eg, from TCI Poly(perfluoropropylene oxide), poly(chlorotrifluoroethylene)) from America, Portland, Oregon (eg, from Halocarbon Product Corp., River Edge, NJ Halocarbon Oils), perfluoropolyalkylethers (eg, Galden from Ausimont or Krytox Oils and Greases K-Fluid Series from DuPont, Delaware), polydimethyl ethers from Dow-corning Silicone oil based on polydimethylsiloxane (DC-200).

The display layer using the display fluid of the present 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 away from the first surface (16). Therefore, the second surface is on the non-viewing side. The term "viewing side" means the side from which the image is viewed.

Shows fluid sandwiched between these two surfaces. On the side of the first surface (16), there is a common electrode (14), which is a transparent electrode layer (eg ITO) distributed over the whole of the display layer. On the side of the second surface (17), there is an electrode layer (15) including a plurality of pixel electrodes (15a). However, since the various particles (11, 12, 13) are only responsive to the 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 common electrode may consist of a series of strips electrodes or a matrix of electrodes similar to the pixel electrodes (15a).

The display fluid is filled in the display cells. The display cells may or may not be aligned with the pixel electrodes. The term "display unit" means a microvessel filled with an electrophoretic fluid. Examples of "display cells" may include cup-shaped microcells as described in US Pat. No. 6,930,818 and microcapsules as described in US Pat. No. 5,930,026. Microcontainers can be of any shape or size, all of which are within the scope of this application.

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

Pixel electrodes are described in US Patent No. 7,046,228. It is hereby incorporated by reference in its entirety. Note that while active matrix drive using a thin film transistor (TFT) backplane is mentioned for the pixel electrode layer, the scope of the present invention includes other types of electrode addressing as long as the electrodes provide the desired function.

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

Two of the three types of pigment particles carry opposite charge polarities, while the third type of pigment particles is slightly charged. The terms "slightly charged" or "lower charge strength" are intended to refer to the charge level of a particle that is about 50% (preferably, about 5% to about 30%) less than the charge strength of the more strongly charged particle. In one embodiment, the charge strength can be measured in terms of zeta potential. In one embodiment, the zeta potential was determined by a Colloidal Dynamics AcoustoSizer IIM using a CSPU-100 signal processing unit, ESA EN# Attn flow through cell (K: 127). Before testing, enter instrument constants like the density of the solvent used in the sample at the test temperature (25 ^o C), the dielectric constant of the solvent, the speed of sound in the solvent, and the viscosity of the solvent. Pigment samples are dispersed in a solvent (which is usually a hydrocarbon fluid with less than 12 carbon atoms) and diluted to 5-10 weight percent. The samples also contained a charge control agent (Solsperse 17000, available from Lubrizol Corporation, Berkshire Hathaway company, "Solsperse" is a registered trademark) in a 1:10 weight ratio of charge control agent to particles. The mass of the diluted sample was determined and then loaded into the flow cell for zeta potential determination.

For example, if the black particles are positively charged and the white particles are negatively charged, then 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 those carried by the colored particles.

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

Notably, of the three types of pigment particles, the slightly charged type preferably has a larger size.

Furthermore, in the context of this application, a high drive voltage (V _H1 or V _H2 ) is defined as a drive voltage sufficient to drive a pixel from one extreme color state to the other extreme color state. If the first and second types of pigment particles are higher charged particles, a high drive voltage (V _H1 or V _H2 ) means that the drive voltage is sufficient to drive the pixel from the color state of the first type of pigment particles to the second type of The color state of the pigment particles and vice versa. For example, a high drive voltage V _H1 means a drive voltage sufficient to drive a pixel from a color state of a first type of pigment particles to a color state of a second type of pigment particle, and V _H2 means a drive voltage sufficient to drive a pixel from a second type of pigment particle The driving voltage at which the color state of the pigment particles is driven to the color state of the first type of pigment particles. In the case described, a low drive voltage ( _VL ) is defined as being sufficient to drive a pixel from a color state of a first type of pigment particle to a third type of pigment particle (which has less electrical charge and which size can be larger) the driving voltage of the color state. For example, a low drive voltage may be sufficient to drive to the color state of fire-colored particles without black and white particles being visible on the viewing side.

Typically, _VL is less than 50%, or preferably, less than 40% of the amplitude of _VH (eg, _VH1 or _VH2 ).

The following is an example of a driving method illustrating how different color states can be displayed by the above electrophoretic fluid. Example 1

This example is shown in Figures 2A-2C. The white pigment particles (21) are negatively charged, while 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 Figure 2A, the applied driving voltage is +15V (ie, V _H1 , that is, 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 colored particles (23) move to the vicinity of the relatively negative common electrode (24) or at the relatively negative common electrode (24). As a result, black is seen on the viewing side. The colored particles (23) move towards the common electrode (24) on the viewing side; however, due to their lower charge density and larger size, they move slower than the black particles.

In Figure 2B, when a driving voltage of -15V (ie, _VH2 ) is applied, the negative white particles (21) move to the vicinity of the relatively positive common electrode (24) on the viewing side or to the relatively positive common electrode ( 24), and the positive black particles and the positive colored particles move to the vicinity of the relatively negative pixel electrode (25) or at the relatively negative pixel electrode (25). As a result, white is seen on the viewing side.

Notably, V _H1 and V _H2 have opposite polarities and have the same amplitude or different amplitudes. In the example shown in Figure 2, _VH1 is positive (same polarity as black particles) and _VH2 is negative (same polarity as white particles).

The driving from the white state of Figure 2B to the colored state of Figure 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 sandwiched between a common electrode and a pixel electrode layer and comprising a first type of pigment Particles (ie, white), pigment particles of a second type (ie, black), and pigment particles of a third type (ie, colored), all types of pigment particles dispersed in a solvent or solvent mixture, wherein a) the three types of pigment particles have different optical properties from each other; b) the first type of pigment particles and the second type of pigment particles carry opposite charge polarities; and c) the pigment particles of the third type have the same charge polarity as the pigment particles of the second type, but at a lower intensity, The method includes switching pixels in an electrophoretic display from the first type of display by applying a low drive voltage sufficient to drive the third type of pigment particles to the viewing side while keeping the first and second types of pigment particles on the non-viewing side. The color state of the pigment particles is driven toward the color state of the third type of pigment particles, and the polarity of the applied low driving voltage is the same as that of the third type of pigment particles.

In order to drive the pixel to the color state of the third type of pigment particles, ie, red (see Figure 2C), the method starts from the color state of the first type of pigment particles (ie, white (see Figure 2B) )Start.

When the color of the third type of particles is seen on the viewing side, the other two types of particles may mix on the non-viewing side (opposite the viewing side), resulting in a difference between the colors of the first and second types of particles Intermediate color state. If the particles of the first and second types are black and white, and the particles of the third type are red, then in Figure 2C, when red is seen on the viewing side, grey is on the non-viewing side.

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

One solution to this is to use a vibrational waveform before driving from the color state of the first type of pigment particles (ie, white) to the color state of the third type of pigment particles (ie, red). The vibration waveform consists of repeating a pair of opposing drive pulses for multiple cycles. For example, the vibration waveform may consist of a 20msec +15V pulse and a 20msec -15V pulse, and such a pair of pulses is repeated 50 times. The total time of this vibration waveform was 2000 msec. The symbol "msec" stands for milliseconds.

Regardless of the optical state (black, white, or red) prior to applying the drive voltage, a vibrational waveform can be applied to the pixel. After applying the vibrational 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.

For the above method, the vibration waveform is applied prior to driving the pixel to the color state (ie, white) of the first type of pigment particles. With this added vibrational waveform, the color state of the third type of pigment particle (ie, red) will be apparent in terms of color brightness and color purity, even though the white state is measurably the same as the white state without the vibrational waveform. Better than color states without vibration waveforms. This means that white particles are better separated from red particles, and black particles are better separated from red particles.

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

Notably, in all figures throughout the application, the vibration waveform is truncated (ie, the number of pulses is less than the actual number).

The waveform used to drive the display to the colored (red) state of Figure 2C is shown in Figure 3. In this waveform, after the vibration waveform, a high negative drive voltage (V _H2 , eg, -15V) is applied for a period of t2 to drive the pixel toward the white state. From the white state, the pixel can be driven toward the colored state (ie, red) by applying a low positive voltage ( _VL , eg, +5V) for a period of t3 (ie, driving the pixel from 2B Figure drive to Figure 2C).

The drive period "t2" is a period sufficient to drive the pixel to the white state when V _H2 is applied, and the drive period "t3" is a period sufficient to drive the pixel from the white state to the red state when _VL is applied. The driving voltage is preferably applied for a period of t1 before the vibration waveform to ensure DC-DC balance. Throughout this application, the term "DC balanced" is intended to mean that the drive voltage applied to the pixel is approximately zero when integrated over a period of time (eg, the duration of the entire waveform). The first drive method:

A waveform that can be used in the first driving method of the present invention is illustrated in FIG. 4; this waveform can be used in place of the driving period t3 in FIG. 3. FIG.

In an initial step, a high negative drive voltage ( _VH2 , eg, -15V) is applied, followed by a positive drive voltage (+V') to drive the pixel toward the red state. The amplitude of +V' is less than 50% of the amplitude of _VH (eg, _VH1 or _VH2 ).

In this drive waveform, a high negative drive voltage (V _H2 ) is applied for period t4 to push the white particles to the viewing side, and then a positive drive voltage of +V' is applied for period t5 to pull the white particles down and Red particles are pushed towards the viewing side.

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

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

The driving method in Figure 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 sandwiched between a common electrode and a pixel electrode layer and comprising a first type of Pigment particles, pigment particles of the second type and pigment particles of the third type, all types of pigment particles dispersed in a solvent or solvent mixture, wherein a) the three types of pigment particles have different optical properties from each other; b) the first type of pigment particles and the second type of pigment particles carry opposite charge polarities; and c) the pigment particles of the third type have the same charge polarity as the pigment particles of the second type, but at a lower intensity, The method includes the following steps: (i) applying a first driving voltage to the pixels in the electrophoretic display for a first period of time, the first driving voltage having the same polarity as that of the first type of pigment particles, to drive the pixels toward the first type of pigment particles on the viewing side color status; (ii) applying a second driving voltage to the pixel for a second period of time, the second driving voltage having the same polarity as the third type of pigment particles, to drive the pixel towards the color state of the third type of pigment particles on the viewing side; and Repeat steps (i) and (ii).

In one embodiment, the first type of pigment particles are negatively charged and the second type of pigment particles are 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 driving waveform shown in FIG. 4 can be used to replace the driving period t3 in FIG. 3 , and the combined waveform after the replacement is illustrated in FIG. 5 . In other words, the drive sequence may be a vibration waveform, then drive toward the white state for a period t2, and then apply the waveform of FIG. 4 .

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

In one embodiment, the drive sequence of Figure 5 or Figure 6 is DC balanced. Second drive method:

Waveforms that can be used in the second driving method of the present invention are illustrated in FIG. 7 . This waveform is a substitute for the driving waveform in FIG. 4, and can also be used in place of the driving period t3 in FIG. 3. FIG.

In this alternate waveform, a waiting time "t6" is added after the red-going pulse in period t5 and before the white-going pulse in period t4, and repeated in period t5 Pulse in red. During the waiting time, no driving voltage is applied. The entire waveform of Figure 7 is also repeated for multiple cycles (eg, N > 4).

The waveform of FIG. 7 is designed to relieve charge imbalances stored in the dielectric layer in an electrophoretic display device, especially when the resistance value of the dielectric layer is high, eg, at low temperatures.

In the context of this application, the term "low temperature" means a temperature below about 10°C.

The latency presumably eliminates unwanted charges stored in the dielectric layer and results in a short pulse ("t4") for driving the pixel toward the white state and a longer pulse ("t5") for driving the pixel toward the red state ")more efficient. As a result, this alternative actuation method results in better separation of low-charged pigment particles from higher-charged pigment particles. The waiting time ("t6") can be in the range of 5-5,000 msec, depending on the resistance value of the dielectric layer.

The driving method in Figure 7 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 common electrode and a pixel electrode layer and comprising a first type of Pigment particles, pigment particles of the second type and pigment particles of the third type, all types of pigment particles dispersed in a solvent or solvent mixture, wherein a) the three types of pigment particles have different optical properties from each other; b) the first type of pigment particles and the second type of pigment particles carry opposite charge polarities; and c) the pigment particles of the third type have the same charge polarity as the pigment particles of the second type, but at a lower intensity, The method includes the following steps: (i) applying a first driving voltage to the pixels in the electrophoretic display for a first period of time, the first driving voltage having the same polarity as that of the first type of pigment particles, to drive the pixels toward the first type of pigment particles on the viewing side color status; (ii) applying a second driving voltage to the pixel for a second period of time, the second driving voltage having the same polarity as the third type of pigment particles, to drive the pixel towards the color state of the third type of pigment particles on the viewing side; (iii) no driving voltage is applied to the pixel for the third period; and Repeat steps (i), (ii) and (iii).

In one embodiment, the first type of pigment particles are negatively charged and the second type of pigment particles are 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 driving waveform shown in FIG. 7 can also be used instead of the driving period t3 in FIG. 3 (see FIG. 8 ). In other words, the drive sequence may be a vibration waveform, then drive toward the white state for a period t2, and then apply the waveform of FIG. 7 .

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

In another embodiment, the drive sequence of Figure 8 or Figure 9 is DC balanced.

It should be noted that the length of any drive period mentioned in this application may be temperature dependent. The third driving method:

FIG. 10A shows the relationship between applied drive voltage (V') and optical performance according to the waveforms 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 expressed as a* value using the L*a*b* color system.

The maximum a* in Figure 10A occurs at the applied drive voltage V' (about 3.8V) in Figure 3. However, if the applied drive voltage varies by ±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 beneficial for accommodating changes in driving voltage caused by, for example, variations in electronic components of the display device, drop in battery voltage over time, batch variation in TFT backplanes, batch variation in display devices, or fluctuations in temperature and humidity of.

Based on the data presented in Figure 10A, a study was conducted to find a range of drive voltages V' that could 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. Therefore, this range can be called the "voltage insensitive" range. The wider the "voltage insensitive" range, the more tolerant the drive method is to batch variations and environmental changes.

In Figure 4, three parameters t4, t5 and N need to be considered for this study. The effects of the three parameters on the voltage-insensitive range are interactive and nonlinear.

From the model of Figure 10A, an optimal set of values for the three parameters can be found to achieve the widest voltage insensitivity range of the waveform of Figure 4. The results are summarized in Figure 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 insensitivity range according to Figure 10B (ie 3.7V to 6.5V) is the voltage insensitivity range according to Figure 10A (ie, twice as wide as 3.3V-4.7V).

The optimal parameters discussed above are also applicable to any driving method 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 common electrode and a pixel electrode layer and comprising a first type of Pigment particles, pigment particles of the second type and pigment particles of the third type, all types of pigment particles dispersed in a solvent or solvent mixture, wherein a) the three types of pigment particles have different optical properties from each other; b) the first type of pigment particles and the second type of pigment particles carry opposite charge polarities; and c) the pigment particles of the third type have the same charge polarity as the pigment particles of the second type, but at a lower intensity, And the method has a voltage insensitivity 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 driving voltages within such ranges are applied.

It is also worth noting that the data shown in Figures 10A and 10B were collected at ambient temperature. Fourth driving method:

Waveforms that can be used in the fourth driving method of the present invention are illustrated in FIG. 11 . This driving waveform can be used in place of the driving period t3 in FIG. 3 .

In an initial step, a high negative drive voltage ( _VH2 , eg, -15V) is applied to the pixel for period t7 (see corresponding pulse in period t4 of Figure 4). This pulse is followed by a waiting time t8 during which no voltage is applied. After the waiting time, a positive drive voltage (V', eg, less than 50% of _VH1 or _VH2 ) is applied to the pixel for period t9 (see corresponding pulse in period t5 of FIG. 4). After the pulse of t9, but before repeating the various steps of the waveform, there is a second waiting time t10 during which no voltage is applied. Repeat the waveform in Figure 11 N times. The above term "waiting time" means a period of time during which no driving voltage is applied.

This driving method is not only particularly efficient at low temperatures, but can also provide better tolerance for structural variations of 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 t9. For example, t7 may be in the range of 20-200 msec; t8 may be less than 100 msec; t9 may be in the range of 100-200 msec; and t10 may be less than 1000 msec.

FIG. 12 shows the waveform generated by inserting the waveform of FIG. 11 in place of the period t3 of FIG. 3 . In FIG. 3, the white state is displayed during the period t2. As a general rule, the better the white state during this period, the better the red state will be displayed at the end of the waveform.

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

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

The fourth driving method of Fig. 11 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 common electrode and a pixel electrode layer and comprising a first type of Pigment particles, pigment particles of the second type and pigment particles of the third type, all types of pigment particles dispersed in a solvent or solvent mixture, wherein a) the three types of pigment particles have different optical properties from each other; b) the first type of pigment particles and the second type of pigment particles carry opposite charge polarities; and c) the pigment particles of the third type have the same charge polarity as the pigment particles of the second type, but at a lower intensity, The method includes the following steps: (i) applying a first driving voltage to the pixels in the electrophoretic display for a first period of time, wherein the first driving voltage has the same polarity as the first type of pigment particles to drive the pixels towards the first type of pigment on the viewing side the color state of the particle; (ii) not applying the 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 towards the color state of the third type of pigment particles on the viewing side ; (iv) not applying the driving voltage to the pixel for a fourth period of time; and Repeat steps (i)-(iv).

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

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

In one 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 Figure 12 or Figure 13 is DC balanced. Fifth drive method:

As shown in Figure 2A, because the black and red particles carry the same charge polarity, they tend to move in the same direction. Even though black particles move faster than red particles at certain driving voltages due to their higher charge and possibly also due to their smaller size, some red particles may still be driven to the viewing side along with the black particles, so Causes the black state to decrease.

Figure 14 depicts typical waveforms for driving a pixel towards a black state. Vibration waveforms (described above) are included to ensure color brightness and purity. As shown, a high positive drive voltage (V _H1 , eg, +15V) is applied for period t12 following the vibration waveform to drive the pixel toward the black state. The driving voltage is applied for a period t11 before the vibration waveform to ensure DC balance.

Figure 15 illustrates a waveform that may be added to the end of the waveforms of Figure 14 for driving the pixel towards the black state. Combining waveforms can further provide better separation of black particles from red particles, resulting in more saturated black states and less red tinting.

In Fig. 15, a short pulse "t13" of V _H2 (negative) is applied, followed by a long pulse "t14" of V _H1 (positive) and a waiting time (0V) of t15. Such a sequence is applied at least once, preferably, at least three times (ie, N≧3), and more preferably, at least five to seven times.

Pulse "t14" is usually at least twice as long as pulse "t13".

The short pulse "t13" of _VH2 pushes the black and red particles toward the pixel electrodes, while the longer pulse "t14" of _VH1 pushes them toward the common electrode side (ie, the viewing side). Because the velocities of the two types of pigment particles are different at the same drive voltage, this asymmetric drive sequence is more favorable for black particles than for red particles. As a result, black particles can be better separated from red particles.

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

The fifth driving method of Fig. 15 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 common electrode and a pixel electrode layer and comprising a first type of Pigment particles, pigment particles of the second type and pigment particles of the third type, all types of pigment particles dispersed in a solvent or solvent mixture, wherein a) the three types of pigment particles have different optical properties from each other; b) the first type of pigment particles and the second type of pigment particles carry opposite charge polarities; and c) the pigment particles of the third type have the same charge polarity as the pigment particles of the second type, but at a lower intensity, The method includes the following steps: (i) applying a first driving voltage to the pixels in the electrophoretic display for a first period of time, wherein the first driving voltage has the same polarity as the first type of pigment particles to drive the pixels towards the first type of pigment on the viewing side the color state of the particle; (ii) applying a second driving voltage to the pixel for a second period of time, wherein the second driving voltage has the same polarity as the second type of pigment particles to drive the pixel towards the color state of the second type of pigment particles on the viewing side ; (iii) optionally, no drive voltage is applied to the pixel for a third period of time; and Repeat steps (i), (ii) and (iii) (if present).

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

Figure 16 shows a composite waveform combining the waveform of Figure 14 with the waveform of Figure 15. However, it is also worth noting that depending on the particle velocity and the number of cycles (N) of the sequence, "t12" can be shortened. In other words, at the end of "t12", the pixel does not have to be completely black. Instead, the waveform of Figure 15 can 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 Figures 14-16 can also be used to drive pixels to a 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 Figure 16 is DC balanced. Sixth drive method:

Figure 17 depicts typical waveforms for driving a pixel to a white state. Vibration waveforms (described above) are included to ensure color brightness and purity. The driving voltage of V _H2 is applied for a period t17 after the vibration waveform. The driving voltage of V _H1 is applied for a period t16 before the vibration waveform to ensure DC balance.

Figures 18A and 18B show waveforms that can be used to replace pulse t17 in the waveform of Figure 17.

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

In Fig. 18A, a short pulse "t18" of V _H1 (positive) is applied, followed by a longer pulse "t19" of V _H2 (negative) and a waiting time (0V) of t20. As shown in Figure 18B, the amplitude of the negative drive voltage (V") applied during _t19 may be higher than the amplitude of VH2 (eg, -30V instead of -15V).

Such a sequence is applied at least once, preferably, at least three times (ie, in Figures 18A and 18B, N > 3, more preferably, at least five to seven times).

t19 should be longer than t18. 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 FIGS. 18A and 18B 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 common electrode and a pixel electrode layer and comprising a first type of Pigment particles, pigment particles of the second type and pigment particles of the third type, all types of pigment particles dispersed in a solvent or solvent mixture, wherein a) the three types of pigment particles have different optical properties from each other; b) the first type of pigment particles and the second type of pigment particles carry opposite charge polarities; and c) the pigment particles of the third type have the same charge polarity as the pigment particles of the second type, but at a lower intensity, The method includes the following steps: (i) applying a first driving voltage to the pixels in the electrophoretic display for a first period of time, wherein the first driving voltage has the same polarity as the second type of pigment particles to drive the pixels towards the second type of pigment on the viewing side the color state of the particle; (ii) applying a second driving voltage to the pixel for a second period of time, wherein the second driving voltage has the same polarity as the first type of pigment particles to drive the pixel towards the color state of the first type of pigment particles on the viewing side ; (iii) no driving voltage is applied to the pixel for a third period of time; and Repeat steps (i) and (ii).

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

In the embodiment shown in Figure 18A, the second voltage is the driving 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 another embodiment shown in Figure 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 to the color state of the second type of pigment particles ,vice versa.

Figures 19A and 19B show composite waveforms combining the waveforms of Figure 17 with the waveforms of Figures 18A or 18B, respectively.

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

In one embodiment, the driving sequence of FIG. 19A or FIG. 19B is DC balanced. Seventh drive method:

The seventh driving method of the present invention drives the pixel toward an intermediate color state (eg, gray).

Figures 20A and 20B illustrate the particle motion involved. As shown, when a low negative drive voltage ( _VL , eg, -5V) is applied, the pixels in the black state (see Figure 20A) are driven toward the gray state. During this process, the low drive voltage pushes the red particles towards the pixel electrodes, and a mixture of black and white particles is seen on the viewing side.

The waveforms used for this driving method are shown in Figure 21. After the vibration waveform, a high positive drive voltage (V _H1 , eg, +15V) is applied for period t22 to drive the pixel towards the black state. From the black state, the pixel can be driven toward the gray state, ie, from Figure 20A to Figure 20B, by applying a low negative drive voltage ( _VL , eg, -5V) for period t23.

The drive period t22 is a period sufficient to drive the pixel to the black state when V _H1 is applied, and t23 is a period sufficient to drive the pixel from the black state to the gray state when _VL is applied. Before the vibration waveform, a pulse of V _H2 is preferably applied for a period t21 to ensure DC balance.

Fig. 22 illustrates 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 _H1 , eg, +15V) is applied for a short period of t24 to push the black particles to the viewing side, but t24 is not enough to drive the pixel to full black, then a low A negative drive voltage ( _VL , eg, -5V) is applied for period t25 to drive the pixel toward the gray state. The amplitude of _VL is less than 50% of _VH (eg, _VH1 or _VH2 ).

The waveform of Figure 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 100 msec, while t25 is typically greater than 100 msec.

The seventh driving method shown in FIG. 22 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 common electrode and a pixel electrode layer and comprising a first type of Pigment particles, pigment particles of the second type and pigment particles of the third type, all types of pigment particles dispersed in a solvent or solvent mixture, wherein a) the three types of pigment particles have different optical properties from each other; b) the first type of pigment particles and the second type of pigment particles carry opposite charge polarities; and c) the pigment particles of the third type have the same charge polarity as the pigment particles of the second type, but at a lower intensity, The method includes the following steps: (i) applying a first driving voltage to the pixels in the electrophoretic display for a first period of time, the first driving voltage having the same polarity as the second type of pigment particles to drive the pixels towards 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 driving voltage to the pixel for a second period of time, the second driving voltage having the same polarity as the first type of pigment particles to drive the pixel towards the mixture of the first and second type of pigment particles on the viewing side status; and Repeat steps (i) and (ii).

As mentioned 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 , wherein the driving period t23 of FIG. 21 is replaced by the waveform of FIG. 22 . This composite waveform consists of four stages. The first stage is the DC balance stage (t21); the second stage is the vibration step; and the third stage drives the pixel to the black state (t22). The waveform used in the third stage can be any waveform that drives the pixel to a good black state. The fourth phase includes a short period of t24 with a high positive drive voltage followed by a longer period of t25 with a low negative drive voltage. Repeat the fourth stage several times.

Notably, in Figure 23 t22 may be optional.

The gray state can be tuned brighter or darker by changing the low negative voltage (V _L ). In other words, the waveform sequence and shape can remain the same; but the amplitude of _VL can be varied (eg, -4V, -5V, -6V, or -7V) to cause different grayscales to be displayed. This feature can potentially reduce the space required for look-up tables in the driver circuit, thereby reducing cost. The actuation method as exemplified can produce a high quality intermediate state (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 Figure 23 is DC balanced. Eighth driving method:

FIG. 24 illustrates waveforms 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 (ie, the color state of the first type of pigment particles).

In an initial step, a high negative drive voltage ( _VH2 , eg, -15V) is applied for a period of t26, followed by a waiting period of t27. After the waiting time, a positive drive voltage (V', eg, less than 50% of _VH1 or VH2) is applied for a period of _t28 , followed by a second waiting time t29. Repeat the 24th waveform N times. The above term "waiting time" means a period of time during which no driving voltage is applied.

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

Notably, the period t26 is rather short, typically in the range of about 50% of the time required to drive from the full black state to the full white state, so it is not sufficient to drive the pixel to the full white state. Period t27 may be less than 100 msec; period t28 may be in the range of 100-200 msec; and period t29 may be less than 1000 msec.

Except that the waveform of Figure 11 is to be applied to pixels that are in the white state (ie, the color of the pigment particles of the first type), and the waveform of Figure 24 is intended to be applied to pixels that are not in the white state, the 24 The waveform of the figure is similar to that of Figure 11.

Figure 25 is an example in which the waveform of Figure 24 is applied to a pixel in the black state (ie, the color state of the second type of pigment particles).

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

Like the driving method of Fig. 11, the eighth driving method of Fig. 24 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 common electrode and a pixel electrode layer and comprising a first type of Pigment particles, pigment particles of the second type and pigment particles of the third type, all types of pigment particles dispersed in a solvent or solvent mixture, wherein a) the three types of pigment particles have different optical properties from each other; b) the first type of pigment particles and the second type of pigment particles carry opposite charge polarities; and c) the pigment particles of the third type have the same charge polarity as the pigment particles of the second type, but at a lower intensity, The method includes the following steps: (i) applying a first driving voltage to the pixels in the electrophoretic display for a first period of time, wherein the first driving voltage has the same polarity as the first type of pigment particles to drive the pixels towards the first type of pigment on the viewing side the color state of the particle; (ii) not applying the 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 towards the color state of the third type of pigment particles on the viewing side ; (iv) not applying the driving voltage to the pixel for a fourth period of time; and Repeat steps (i)-(iv).

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

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

In one 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 one embodiment, the drive sequence of Figure 25 is DC balanced. Generation of intermediate colors:

Advantageously, the driving method of the present invention is capable of displaying intermediate colors (ie, a mixture of the colors of two particles) in addition to the color of a single particle. In many cases, a display using this method is required to display a grayscale image that requires area modulation of the display. Such regional 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 regionally modulated to form a grayscale "superpixel". 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 superpixel, and thus increase the resolution of grayscale displays.

A method for the generation of mid-grey (ie, a mixture of the colors of black and white particles) has been discussed above with reference to Figures 20A and 20B. By first driving the pixel to a black or white state (Figure 2A or 2B, respectively), then applying a high drive voltage of ±15V to drive the pixel towards the white or black state, respectively, but before reaching the white or black state Terminating this drive voltage produces a gray state, which also produces gray. It should be noted, however, that of the three particle systems used in this method, it is advantageous to use a method starting from the white state rather than the black state to produce the grey state for reasons that will be explained with reference to Figures 26A-26D of.

Figures 26A and 26B illustrate starting from a white state to produce a gray state. Figure 26A (which is substantially the same as Figure 2B) illustrates the creation of the white state by applying a high negative drive voltage (-15V, _VH2 ) that drives the white particles 21 to the viewing side, while the The black particles 22 and the red particles 23 are driven toward the pixel electrodes. Starting from the white state of Figure 26A, a brief drive pulse of a high positive voltage (+15V, _VH1 ) 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 away from the pixel electrode relatively slowly, so they are hidden from the viewer in the gray state by the black and white particles, where the black and white The particle is located between the red particle and the viewing surface. As a result, Figure 26B presents a "bright" gray, which consists only of a mixture of the colors of black and white particles and is not contaminated by the color of the red particles.

Conversely, Figures 26C and 26D illustrate starting from a black state to produce a gray state. Figure 26C (which is substantially the same as Figure 2A) illustrates the creation of the black state by applying a high positive drive voltage (+15V, _VH1 ) which directs black particles 22 and red particles 23 to the viewing side drive, and the white particles 21 are driven to be adjacent to the pixel electrodes. Starting from the black state of Figure 26C, a brief drive pulse of negative voltage (-15V, _VH2 ) drives the white particles towards the viewing side and the black and red particles towards the pixel electrodes. The brief drive pulse is terminated when the white and black particles mix near the viewing side. However, because red particles have a lower electrophoretic mobility than black particles, red particles move more slowly away from the viewing side and thus mix with black and white particles in the gray state; in fact, red particles may tend to be more closer to the viewing side. As a result, Figure 26D presents a "dull" gray, where the mixture of colors 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 a black state or a white state. Likewise, the reddish state (a mixture of the colors of the white and red particles) can be produced starting from the red state or the white state. In the former case, drive to the full red state (see Figure 2C) and then apply a high negative drive voltage (-15V, _VH2 ) for a brief period of time that is insufficient to reach the white state of Figure 2B. A high negative drive voltage causes the white particles 21 to move rapidly toward the viewing side, the black particles 22 to move rapidly toward the pixel electrode, and the red particles 23 to move more slowly toward 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 electrodes, so they are hidden from the viewer by the white and red particles. In the latter case, first drive to the full white state (see Figure 2B), and apply a low positive drive voltage (+5V, _VL ) for a period of time insufficient to reach the red state of Figure 2C. The low positive drive voltage moves the white particles 21 towards the pixel electrode and the red particles towards the viewing side, thus again producing a mixture of red and white particles and a reddish display. Instead of using a continuous low positive drive voltage, the transition from the white state to the light red state can be achieved using a push-pull waveform as illustrated in Figures 5, 6, 8 or 9.

It has been empirically found that the reddish state produced from the red state is more heterogeneous than the reddish state produced from the white state. Although the reasons for this uniformity difference are not fully understood, it is believed to be related to variations in the positions of the various particles within the microcapsules (if any) as well as variations in the electrophoretic mobility of individual particles and various components of the electrophoretic display. Also, it seems that the low drive voltage used for driving from the red state is more affected than the high drive voltage by power supply fluctuations.

Figure 27 illustrates the waveform for driving the display to the reddish state via the white state. In the waveform of Figure 27, a high negative drive voltage ( _VH2 , eg, -15V) is applied for period t31 to drive the pixel toward the white state. Starting from the white state, the pixel is driven toward the red state by applying a low positive voltage ( _VL , eg, +5V) for period t32, thereby driving the pixel from the state of Figure 2B to the state of Figure 2C. Finally, the pixel is driven from the red state to the reddish state by applying a high negative drive voltage (V _H2 , eg, -15V) for a period t33 , which is shorter than period t31 and insufficient to drive the pixel to All white state. It is desirable to apply a vibration waveform before the white pulse in period t31, and preferably, a negative drive voltage (eg, _VH2 , eg, -15V) is applied for period t30 before the vibration waveform to ensure DC balance. It will be seen that the waveform of Fig. 27 is basically the waveform of Fig. 3, but with the addition of a white directional pulse in the period t33. The exact hue of reddish obtained can be varied by adjusting the duration of period t33, which is typically in the range of about 20-300 msec (typically 20-100 msec). The duration of period t33 is typically about 10% to about 60% of the duration of period t31.

Achieving a deep red state (i.e., a mixture of the colors of black and red particles) is much more difficult than reaching a light red state, because black and red particles carry charges of the same polarity and therefore tend to react in similar ways to an applied electric field. reaction. For example, if the pixel is first driven to the red state of Figure 2C, then an attempt is made to produce a mix of red and black particles by applying the high positive drive voltage (+15V, _VH1 ) used to drive the pixel to the black state of Figure 2A , the red particles (already adjacent to the front electrode as shown in Figure 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 an extended period of 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 "deep" The "red" state will actually be only slightly darker than the previous red state.

It has been found that there are two ways to achieve a satisfactory deep red state. The first method uses a waveform as illustrated in Figure 28 and essentially starts from a dark grey state. As shown, this waveform first applies a high positive drive voltage (+15V, V _H1 ) to drive the pixel to a dark gray state (not a full black state). Following this high positive drive voltage, a low positive drive voltage ( _VL , eg, +5V) is applied for a period t36, which is typically much longer than t35, to drive the pixel to the deep red state. For the above reasons, the high positive drive pulse in period t35 may optionally be preceded by a vibration waveform and/or a high negative drive voltage pulse (V _H2 , eg -15V) in period t34 . The duration of t36 can vary widely, but can typically be around 300-2000msec, more typically 500-1000msec; the resulting dark red shade can be altered by varying the duration of t36, longer durations tend to Increases the redness of the resulting color.

A second method of achieving a satisfactory deep red state uses waveforms as illustrated in Figure 29, which is substantially the same as Figure 5, but for reasons discussed below, the various drives shown in Figure 29 The durations of the pulses will be different from those of the drive pulses of FIG. 5 . Recalling from the discussion of Figure 5 above, the major portion of the relevant waveform consists of a red-going pulse of a low positive drive voltage ( _VL , eg, +5V) of duration t39 represented in Figure 29, which is associated with the White-going pulses of high negative drive voltage (V _H2 , eg, -15V) of duration t40 in FIG. 29 alternate. This sequence of alternating pulses may be preceded by one or more of the following: (a) a white-going pulse of a high negative drive voltage (V _H2 , eg, -15V) of duration t37 intended for DC balancing; (b) vibration waveform; and (c) a white-going pulse of high negative drive voltage ( _VH2 , eg, -15V) of duration t38, which may be different or the same as the duration t40 of the later-faced white-going pulse already mentioned.

The waveform of Figure 5 was described above as producing a pure red state. However, it has been found empirically that by adjusting the durations _t39 and t40 in Figure 29 and/or by adjusting the driving voltages V' and VH2 applied during these periods, this type of waveform can not only produce pure red state, and can produce dark red and light red states. If the size of V' is increased, the red becomes darker, whereas if the size of V' is decreased, the red becomes lighter. Likewise, if the duration of t40 is increased relative to t39, a lighter red will be produced, whereas if the duration of t39 is increased relative to t40, a darker red will be produced. Obviously, a combination of driving voltage and duration changes can be used. The durations of t39 and t40 can vary widely; for example, at 25°C, t40 can decrease from 60msec to 20msec, and t39 can increase from 300msec to 600msec. At low temperatures like 0°C, even wider ranges may be desired; for example, at this temperature, t40 may be 60msec, while t39 is 3000msec. Example 2

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 in isoparaffin solvent percent red pigment particles and adding a charge control agent (Solsperse 19000) to prepare an electrophoretic medium substantially as described above with reference to Figure 1. White particles are negatively charged, while black and red particles are positively charged, but red particles have a lower charge density than 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 grey states described above with reference to Figures 2A, 2B, 2C and 26B, respectively. The L*, a*, and b* values for all four colored states were measured using standard techniques and the results were as follows:

surface 1 color L* a* b* White 60.2 -1.0 -1.4 black 12.6 7.7 -0.8 Red 27.0 37.9 17.6 grey 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 the object and scope of the invention to a particular situation, material, composition, process, process step. All such modifications are intended to be within the scope of the appended claims.

10: Electrophoretic display fluid 11: White particles 12: Black particles 13: Colored particles 14: Common electrode 15: Electrode layer 15a: Pixel electrode 16: First Surface 17: Second Surface 21: White Pigment Particles 22: Black Pigment Particles 23: Colored particles 24: Common electrode 25: Pixel electrode

Figure 1 is a schematic cross-section of a display fluid through electrophoresis that can be used in the driving method of the present invention.

Figures 2A, 2B and 2C are schematic cross-sections similar to Figure 1 showing the positions of particles in the black, white and red (colored) states of the display fluid, respectively.

Figure 3 illustrates a typical waveform for driving a pixel from the white state of Figure 2B to the red state of Figure 2C.

FIG. 4 illustrates a waveform that can be used to replace the portion of the waveform of FIG. 3 in the period t3 to implement the first driving method of the present invention.

FIGS. 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 illustrates a second waveform that can be used to replace the portion of the waveform of FIG. 3 in the period t3 to implement the second driving method of the present invention.

FIGS. 8 and 9 depict waveforms generated by modifying the waveforms of FIG. 3 with some of the waveforms of FIG. 7 in order to implement the second driving method of the present invention.

Figures 10A and 10B illustrate the optical results produced by the third driving method of the present invention. Fig. 10A shows the applied drive voltage versus optical state performance (a*) based on the waveforms of Fig. 3, and Fig. 10B shows the applied drive voltages based on the waveforms of Fig. 3 modified with some of the waveforms of Fig. 4 Relationship to Optical State Performance (a*).

FIG. 11 illustrates a waveform that can be used to replace the portion of the waveform of FIG. 3 in the period t3 to implement the fourth driving method of the present invention.

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

Figure 14 depicts a typical waveform for driving a pixel from the white state of Figure 2B to the black state of Figure 2A.

FIG. 15 illustrates waveforms that can be added to the end of the waveforms of FIG. 14 to implement the fifth driving method of the present invention.

FIG. 16 illustrates a composite waveform combining the waveforms of FIGS. 14 and 15 to implement the fifth driving method of the present invention.

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

Figures 18A and 18B illustrate two waveforms that can be used to replace the part of the waveform of Figure 17 in the period t17 to implement the sixth driving method of the present invention.

FIGS. 19A and 19B depict waveforms generated by modifying the waveforms of FIG. 17 with partial waveforms of FIGS. 18A or 18B, respectively, in order to implement the sixth driving method of the present invention.

20A and 20B are schematic cross-sections similar to Figure 1 showing the positions of particles in the black and grey states of the display fluid, respectively.

Figure 21 illustrates a typical waveform for driving a pixel to the gray state of Figure 20B.

FIG. 22 illustrates a waveform that can be used to replace the portion of the waveform of FIG. 21 in the period t23 to implement the seventh driving method of the present invention.

Fig. 23 illustrates a composite waveform of combining the waveforms of Figs. 21 and 22 to realize the seventh driving method of the present invention.

FIG. 24 illustrates waveforms used in the eighth driving method of the present invention.

Fig. 25 illustrates a composite waveform of combining the waveforms of Figs. 14 and 24 to realize the eighth driving method of the present invention.

Figures 26A and 26B illustrate the generation of the gray state of a pixel starting from the white state of the pixel.

Figures 26C and 26D illustrate the generation of the gray state of a pixel starting from the black state of the pixel.

Figure 27 illustrates waveforms that can be used to drive a display to a reddish state via a white state in the first hybrid characteristic driving method of the present invention.

Figure 28 illustrates waveforms that can be used to drive a display to a deep red state in the second hybrid characteristic driving method of the present invention.

Figure 29 illustrates a second waveform that can be used to drive the display to the deep red state in the third hybrid characteristic driving method of the present invention.

10: Electrophoretic display fluid

11: White particles

12: Black particles

13: Colored particles

14: Common electrode

15: Electrode layer

15a: Pixel electrode

16: First Surface

17: Second Surface

Claims (7)

A driving method for an electrophoretic display, the 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 comprising particles of a first type, particles of a second type, and a first Three types of particles, all types of particles dispersed in a liquid, wherein a) the three types of pigment particles have different optical properties 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 the same charge polarity as the second type of pigment particles, but with a lower zeta potential, The method includes 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 to drive the second type of pigment particles towards the first surface, thereby urging the pixel to operate at the first surface the optical properties of the second type of pigment particles displayed on the first surface; and (ii) applying a second driving voltage to the pixel for a second period of time, the second driving voltage having the same polarity as the first driving voltage, but having a smaller amplitude than the first driving voltage, whereby in the first driving voltage The third type of pigment particles are driven on a surface and a mixture of the optical properties of the second and third types of particles is produced on the first surface. The method of claim 1, further comprising applying a vibration waveform prior to step (i). The method of claim 1, wherein the amplitude of the second driving voltage is less than half of the amplitude of the first driving voltage. The method of claim 1, wherein the first type of pigment particles are negatively charged and the second type of pigment particles are positively charged. A driving method for an electrophoretic display, the 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 dispersed in a liquid, wherein a) the three types of pigment particles have different optical properties 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 the same charge polarity as the second type of pigment particles, but with a lower zeta potential, The method includes 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 to drive the first type of pigment particles toward the first surface, thereby urging the pixel to operate at the first surface the optical properties of the first type of pigment particles displayed on the first surface; and (ii) applying a second drive voltage to the pixel for a second period of time, the second drive voltage having a polarity to drive the third type of pigment particles toward the first surface; and Repeat steps (i) and (ii), wherein the duration of steps (i) and (ii) and the amplitude of the voltage applied therein are adjusted to produce on the first surface the third type of particles and one of the first and second types of particles a mixture of the optical properties of the particles. The method of claim 5, further comprising applying a vibration waveform prior to step (i). The method of claim 5, wherein the first type of pigment particles are negatively charged and the second type of pigment particles are positively charged.

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