HK1115767B - Electro-optic displays - Google Patents

Description

Electro-optic display

This application is a divisional application filed on the application date of 2003, 9/2, with application number 03820879.2, entitled "electro-optic display".

Technical Field

The present invention relates to electro-optic displays. More particularly, the invention relates to components for use in electro-optic displays, novel color filters for use in such displays, and methods of making such color filters. The invention also relates to a novel method for controlling the color of an electrophoretic display.

Background

An electro-optic display comprises a layer of electro-optic material, the term used herein in its conventional sense referring to a material having first and second display states which differ in at least one optical property, the change from the first to the second display state being brought about by the application of an electric field to the material. The optical property is typically a color that is readily visible to the human eye, but may also be another optical property, such as light transmission, reflection, luminescence, or pseudo-color in the sense that electromagnetic wavelength reflection outside the visible range changes in the case of a display for machine reading.

Most aspects of the invention are for electro-optic displays comprising an electro-optic medium which is solid (hereinafter such displays will be referred to as "solid electro-optic displays" for convenience), meaning that the electro-optic medium has a solid outer surface, although the medium may, and often does, have a space filled with a liquid or gas therein, and to methods of assembling displays using such electro-optic media. Thus, the term "solid electro-optic display" includes encapsulated electrophoretic displays, rotating bichromal element displays, electrochromic displays, microcell displays, and other types of displays described below.

One type of electro-optic display is, for example, U.S. patent No. 5,808,783; 5,777,782, respectively; 5,760,761, respectively; 6,054,071, respectively; 6,055,091; 6,097,531, respectively; 6,128,124, respectively; 6,137,467, respectively; and the rotating bichromal element type described in 6,147,791 (although such displays are often referred to as "rotating bichromal ball" displays, in some of the above patents the term "rotating bichromal element" is more accurate and preferred since it is not spherical) such displays use a large number of small objects (typically spherical or cylindrical) having two or more portions of different optical properties and an internal dipole. These objects are suspended in vacuoles filled with liquid in a matrix, the vacuoles being filled with liquid, so that the objects are free to rotate. The display of the display is changed by applying an electric field to the display, rotating the object to different positions, and viewing through the viewing surface which parts of the object are changed.

Another electro-optic medium is an electrochromic medium, such as in the form of a nanochromic (nanochromic) film that includes an electrode formed at least in part of a semiconducting metal oxide and a plurality of dye molecules capable of reversing the color change associated with the electrode; see, for example, 0' Regan, b. et al, Na tur e 1991, 353, 737; and Wood, d., Information Display, 18(3), 24 (3 months 2002). See also Bach, u, et al, adv.ma t er., 2002, 14(11), 845. Such nanochrome films are also described, for example, in U.S. patent No.6,301,038, international application publication No. wo 01/27690, and co-pending U.S. application serial No.10/249,128 (filed 3/18/2003).

Another electro-optic display that has been the subject of intense research and development for many years is a particle-based electrophoretic display in which a plurality of charged particles move through a suspension under the influence of an electric field. Electrophoretic displays have attributes of good brightness and contrast, wide viewing angles, state bistability, and low power consumption compared to liquid crystal displays. Of course, the long-standing image quality problems of these displays have prevented widespread use of such displays. For example, the particles that make up electrophoretic displays tend to deposit, resulting in an insufficiently long useful life of these displays.

A number of patents and applications assigned to Massachusetts Institute of techno logy (MIT) and EInk companies or under the MIT and EInk names have recently been published which describe encapsulated electrophoretic media. Such encapsulation media comprise a plurality of small capsules, each capsule itself comprising an internal phase containing electrophoretically-mobile particles suspended in a fluid suspension medium, and a capsule wall surrounding the internal phase. The capsules themselves are typically held in a polymeric binder to form a coherent layer between the two electrodes. For example, in U.S. Pat. nos. 5,930,026; 5,961,804; 6,017,584; 6,067,185, respectively; 6,118,426, respectively; 6,120,588; 6,120,839, respectively; 6,124,851, respectively; 6,130,773, respectively; 6,130,774, respectively; 6,172,798; 6,177,921, respectively; 6,232,950, respectively; 6,249,721, respectively; 6,252,564, respectively; 6,262,706, respectively; 6,262,833; 6,300,932, respectively; 6,312,304, respectively; 6,312,971, respectively; 6,323,989, respectively; 6,327,072, respectively; 6,376,828, respectively; 6,377,387, respectively; 6,392,785, respectively; 6,392,786, respectively; 6,413,790, respectively; 6,422,687, respectively; 6,445,374, respectively; 6,445,489, respectively; 6,459,418, respectively; 6,473,072, respectively; 6,480,182, respectively; 6,498,114, respectively; 6,504,524; 6,506,438, respectively; 6,512,354, respectively; 6,515,649, respectively; 6,518,949, respectively; 6,521,489, respectively; 6,531,997, respectively; 6,535,197, respectively; 6,538,801, respectively; 6,545,291, respectively; and No.6,580,545; and U.S. patent application publication No. 2002/0019081; 2002/0021270, respectively; 2002/0053900, respectively; 2002/0060321, respectively; 2002/0063661, respectively; 2002/0063677, respectively; 2002/0090980, respectively; 2002/0106847, respectively; 2002/0113770, respectively; 2002/0130832, respectively; 2002/0131147, respectively; 2002/0145792, respectively; 2002/0171910, respectively; 2002/0180687, respectively; 2002/0180688, respectively; 2002/0185378, respectively; 2003/0011560, respectively; 2003/0011867, respectively; 2003/0011868, respectively; 2003/0020844, respectively; 2003/0025855, respectively; 2003/0034949, respectively; 2003/0038755, respectively; 2003/0053189, respectively; 2003/0076573, respectively; 2003/0096113, respectively; 2003/0102858, respectively; 2003/0132908, respectively; 2003/0137521, respectively; and No. 2003/0137717; and international application publication No. WO 99/67678; WO 00/05704; WO 00/38000; WO 00/38001; WO 00/36560; WO 00/67110; WO 00/67327; WO 01/07961; and WO 01/08241.

Many of the above patents and applications recognize that: the walls surrounding the discrete microcapsules in the encapsulated electrophoretic medium may be replaced by a continuous phase, resulting in a so-called polymer dispersed electrophoretic display, wherein the electrophoretic medium comprises a plurality of discrete droplets of an electrophoretic fluid and a continuous phase of a polymeric material; and the discrete droplets of electrophoretic fluid in such polymer dispersed electrophoretic displays can be viewed as capsules or microcapsules even when no discrete capsule film is associated with each individual droplet; see, for example, 2002/0131147 above. Thus, for the purposes of this application, such polymer dispersed electrophoretic media are considered to be a subdivided variety of encapsulated electrophoretic media.

Encapsulated electrophoretic displays are generally unaffected by the aggregation and settling failure modes of conventional electrophoretic devices and offer other advantages, such as the ability to print or coat the display on a variety of flexible and rigid substrates. (the use of the word "printing" is intended to encompass all forms of printing and coating including, but not limited to, premetered coating such as sheet die coating, slot or extrusion coating, slide or cascade coating, curtain coating, roll coating such as knife-over-roll coating, forward and reverse roll coating, gravure coating, dip coating, spray coating, meniscus coating, spin coating, brush coating, air knife coating, screen printing processes, electrostatic printing processes, thermal printing processes, ink jet printing processes, and other similar techniques.) thus, the resulting display may be flexible. Further, since the display medium can be printed (by various methods), the display itself can be made inexpensive.

One related type of electrophoretic display is the so-called "microcell electrophoretic display". In microcell electrophoretic displays, the charged particles and the suspension are not encapsulated within microcapsules, but are held within a plurality of cavities formed within a carrier medium, which is typically a polymer film. See, for example, International application publication No. WO02/01281, and published U.S. patent application No. 2002/0075556, both assigned to Sipix Imaging, Inc.

Most types of electro-optic media have only a limited number of optical states, such as a dark (black) state, a bright (white) state, and in some cases, one or more intermediate gray scale states. Thus, in order to construct a full-color display using such a medium, it is common to place an electro-optic medium in the vicinity of a color filter having, for example, a plurality of red, green and blue regions, and to provide a driving device for the electro-optic medium which is capable of independently controlling the medium in the vicinity of each red, green or blue region. Some applications of color filters in electrophoretic displays are described in the above-mentioned application serial No. 09/289,507. 2003/0011560 above describes a method of changing the optical properties of an electrophoretic display by employing a light biasing element in any of the various components of the display.

Disclosure of Invention

The present invention seeks to improve upon the color filters used in electro-optic displays, and the methods of producing color in such displays.

In one aspect, the present invention provides an electrophoretic medium comprising a plurality of charged particles dispersed in a suspension; the medium is characterized in that the particles comprise at least two types of particles having substantially the same electrophoretic mobility but different colors. This aspect of the invention is hereinafter referred to as a "custom color" electrophoretic medium.

In such custom color electrophoretic media, it is desirable to form the charged particles from inorganic pigments, which may be coated with a coating selected from silica and silica/alumina. The charged particles may be coated with a polymer. The charged particles and the suspension may be held within at least one capsule.

The present invention also provides a method for forming the custom color electrophoretic medium of the present invention. The method comprises the following steps:

mixing at least two pigments having different colors to form a mixed pigment;

subjecting the mixed pigment to at least one surface treatment; and is

The surface-treated mixed pigment is dispersed in a suspension to form at least two types of particles having substantially the same electrophoretic mobility but different colors.

In the method, the surface treatment may include treating the mixed pigment with a silane coupling agent to form a site where a polymer may be attached to the mixed pigment, followed by treating the silanized mixed pigment with at least one of a monomer and an oligomer under conditions effective to cause the polymer to form a surface of the mixed pigment.

In another aspect, the invention provides an electro-optic display element comprising:

an electro-optic display medium;

a light deflecting element for altering the optical properties of the electro-optic display element; and

address electrodes for addressing the electro-optic display medium. The electro-optical display element is characterized in that the color of the light biasing element is different in different parts of the electro-optical display element, whereby the light biasing element forms a color filter.

This aspect of the invention will be referred to hereinafter as an "internal color filter" display element.

In such an internal color filter display element, the electro-optic display medium may be an electrophoretic medium comprising a suspension, and a plurality of charged particles suspended in the suspension and movable through the suspension by application of an electric field to the suspension; the electrophoretic medium further comprises at least one capsule having a capsule wall enclosing the suspension and the charged particles, the display element optionally comprises a binder surrounding the capsule, and/or a lamination binder disposed adjacent to the electrophoretic medium, and/or a front electrode disposed between the electrophoretic medium and the viewing surface of the display, and the light deflecting element may be disposed in at least one of the capsule wall, the binder, the lamination binder, and the front electrode.

Another related aspect of the invention provides an electro-optic display comprising a solid layer of electro-optic medium, at least one electrode disposed adjacent the layer of electro-optic medium for applying an electric field thereto, and a color filter array disposed between the electro-optic medium and the electrode, the display being characterized in that the resistance of the color filter array is not substantially greater than the resistance of the layer of electro-optic medium.

In such electro-optic displays, the color filter array typically has a thickness of no greater than about 10¹⁰Volume resistivity in ohm-centimeters.

In another aspect, the present invention provides an electrophoretic medium comprising a plurality of capsules, each capsule comprising a suspension, a plurality of charged particles suspended in the suspension and movable through the suspension by application of an electric field to the suspension; and a capsule wall surrounding the suspension and the charged particles, the medium further comprising a color filter array; the electrophoretic medium is characterized in that the color filter array has a plurality of non-rectangular pixels. In a preferred form of the electrophoretic display, the pixels of the color filter array are hexagonal, square or triangular, preferably equilateral triangular.

In another aspect, the present invention provides an article comprising:

a solid electro-optic medium layer having a first surface and a second surface on opposite sides;

a first adhesive layer on the first surface of the solid electro-optic medium layer;

a (first) release sheet disposed on a side of the first adhesive layer opposite the solid electro-optic medium layer; and

and a second adhesive layer on a second surface of the solid electro-optic medium layer.

Preferred versions of the article also include a second release sheet disposed on the opposite side of the second adhesive layer from the solid electro-optic medium layer.

In the article, the electro-optic medium may be an electrophoretic medium comprising a plurality of capsules, each capsule containing a suspension, a plurality of charged particles suspended in the suspension and capable of moving through the suspension by application of an electric field to the suspension, and a capsule wall surrounding the suspension and the charged particles. In addition, the first and second adhesive layers may extend beyond the edges of the electro-optic medium layer; this provides a convenient way of forming an edge seal for a display, as described in more detail below.

In another aspect, the present invention provides an article comprising:

a solid electro-optic medium layer having a first surface and a second surface on opposite sides;

a first separator sheet covering the first surface of the solid electro-optic medium layer; and

a second separator sheet covering the second surface of the solid electro-optic medium layer.

The above-mentioned article may be hereinafter referred to as "double separation membrane" of the present invention.

The invention also provides a method of forming an electro-optic display using the inventive double separation film. The method comprises the following steps:

providing an article comprising: a solid electro-optic medium layer having a first surface and a second surface on opposite sides; a first adhesive layer on the first surface of the solid electro-optic medium layer; the separating sheet is arranged on one side, opposite to the solid electro-optic medium layer, of the first bonding layer; and a second adhesive layer on a second surface of the solid electro-optic medium layer;

laminating the article to a front substrate via a second adhesive layer to form a front assembly;

removing the separator from the front assembly; and

the front assembly is laminated to a backplane comprising at least one electrode by a first adhesive layer to form an electro-optic display.

In such a method, the front substrate may include electrodes and/or a color filter array. The article may include a second release sheet overlying the second adhesive layer, the method including removing the second release sheet from the second adhesive layer prior to laminating the article to the front substrate.

In another aspect, the present invention provides a method for forming a color filter array, the method comprising:

imaging the photosensitive film to form a color filter array pattern thereon; and is

Thereafter, a conductive layer is deposited on the photosensitive film.

In another aspect, the present invention provides a method for forming an electrophoretic display, the method comprising:

providing a color filter array;

providing an electrophoretic medium comprising a plurality of capsules, each capsule comprising a suspension, a plurality of charged particles suspended in the suspension and movable through the suspension by application of an electric field to the suspension, and a capsule wall surrounding the suspension and the charged particles;

depositing an electrophoretic medium on the color filter array to form a coated color filter array; and

the coated color filter array is then laminated to a backplane comprising at least one pixel electrode.

In this method, the surface of the color filter array may be surface treated prior to depositing to create regions of varying surface energy on the surface.

In another aspect, the invention provides a method for depositing an electrophoretic medium on an electrode, the method comprising:

providing an electrode;

providing an electrophoretic medium comprising a plurality of capsules, each capsule comprising a suspension, a plurality of charged particles suspended in the suspension and capable of moving through the suspension by applying an electric field to the suspension, and a capsule wall surrounding the suspension and the charged particles;

subjecting the electrode to a surface treatment to produce regions of varying surface energy thereon; and

an electrophoretic medium is deposited on the surface-treated electrode.

Finally, the present invention provides a method for forming an electrophoretic display, the method comprising:

providing a front substrate;

providing a bottom plate;

providing an electrophoretic medium comprising a plurality of capsules, each capsule comprising a suspension, a plurality of charged particles suspended in the suspension and capable of moving through the suspension by applying an electric field to the suspension, and a capsule wall surrounding the suspension and the charged particles;

surface treating the surface of the front substrate to facilitate wetting thereof by the capsules;

surface treating the surface of the bottom plate to facilitate dewetting thereof by the capsules;

assembling the front substrate and the base plate together with their treated surfaces facing each other with a gap between the treated surfaces; and

an electrophoretic medium is placed in the gap so that the capsules of electrophoretic medium fill against the treated surface of the front substrate.

Drawings

Fig. 1 is a schematic cross-sectional view of an encapsulated electrophoretic display unit with a color filter array disposed in the capsule wall;

FIGS. 2A, 2B and 2C illustrate three different arrangements of pixels in a color filter array of the present invention;

FIG. 3 is a schematic cross-sectional view of a double separation membrane of the present invention; and

FIG. 4 is a schematic cross-sectional view, similar to FIG. 3, of a second separation membrane of the present invention having an edge seal.

Detailed Description

The present invention proposes a number of different improvements in other aspects of colour filters and electro-optic displays, and in methods of producing colour in such displays. The various improvements can be utilized alone or in various combinations (e.g., a single display can use a color filter array with non-rectangular pixels produced by the imaging method of the present invention). For convenience, various aspects of the invention will be described separately below, although it will be recalled that various aspects of the invention may be used in a single electro-optic display, or in a component thereof.

Custom colors in partial A-electrophoretic displays

As described in the above-mentioned E Ink and MIT patents and published applications, an alternative to using color filters in electrophoretic displays is to use multiple types of capsules that can display different colors. For example, 2002/0180688 is shown in FIG. 3I as encapsulating a pixel of an electrophoretic display, the pixel comprising three sub-pixels, each sub-pixel comprising a single capsule capable of displaying three colors. Although it is not actually a color as described with reference to fig. 3I, it will be readily understood by those skilled in the art of electro-optic displays that full color RGB displays can be fabricated using capsules capable of producing white/black/red, white/black/green and white/black/blue optical states.

One of the primary commercial uses of electro-optic displays is advertising where it is desirable to customize the color displayed for a particular customer. For example, many large companies have established corporate businesses that require certain color logos and/or trademarks to be displayed in a completely consistent manner, with the appropriate color of each part of the associated logo or trademark being specified in terms of Pantone ("Pantone" is a registered trademark) or similar color system. Thus, such companies require (say) accurately tailoring the blue color state of an RGB electrophoretic display to display the blue portion of their company's logo, even at the expense of some reduction in the display color gamut (the range of colors that the display can display).

This customization of colors in electrophoretic displays seems to have formidable obstacles to the first eye. Determining the type of particles used in an electrophoretic display is a complex process that requires consideration not only of the color of the particles, but also, in particular, their ability to maintain a consistent charge (and thus consistent electrophoretic mobility), their tendency to aggregate, their color fastness to light, and their compatibility with other components of the electrophoretic medium, such as the suspension in which the electrophoretic particles are suspended and the capsule walls. Furthermore, it has been found in practice that organic pigments are not intended for use in electrophoretic displays because of their rapid degradation, so that commercial displays use metal oxides or similar inorganic pigments, and that changing the exact color of such inorganic pigments is far less easy than organic pigments.

It has now been realized, however, that in an electrophoretic display, all electrophoretic particles of a particular type (e.g. the blue particles shown in fig. 3I above) used to generate a particular color need not have the same color, as long as all particles of the same type have similar electrophoretic mobilities, so that they do not separate during operation of the display. Typically individual electrophoretic particles, which are in the order of 1 μm in diameter, are too small to be visible to a viewer of the display. Thus, the viewer can only see the average color of all particles of a particular type as long as the particles do not separate during operation of the display. For example, it is well known to those skilled in the art of toning that the apparent saturation of many blues can be improved by adding a small portion of magenta to the blue. Thus, if, for example, a particular consumer requires that the blue state of the white/black/blue subpixel have a saturation that is greater than that achievable with available blue particles, the subpixel may contain a mixture of a majority of the blue particles and a small fraction (say about 10%) of the magenta particles.

Such ability to use a mixture of particles with different colors as a single kind of electrophoretic particles greatly simplifies the problem of custom colors in electrophoretic displays. If a set of three or four electrophoretic particles having different colors (assumed to be RGB, RGBK, CMY or CMYK) but substantially the same electrophoretic mobility is prepared, a pixel having any desired color contained within a color gamut obtainable from the combination can be prepared by simply mixing and encapsulating appropriate amounts of the respective particles to form the desired color.

Thus, as already mentioned in one aspect of the present invention, there is provided an electrophoretic medium comprising a plurality of charged particles dispersed in a suspension, the particles comprising at least two types of particles having substantially the same electrophoretic mobility but different colours.

Although this aspect of the invention is described herein primarily in terms of full color displays, it is of course not limited to such displays. For example, the invention may be used in a simple blinking display in which a layer of electrophoretic medium is confined between two electrodes, drive pulses of alternating polarity are applied to the electrodes, and the electrophoretic medium layer comprises different kinds of capsules deposited in different areas, each capsule having (say) a black optical state and a second optical state of another color. Such a display may be used to flash a company logo or other symbol.

There is a technique that can greatly reduce the difficulty of ensuring that electrophoretic particles formed of different pigments have approximately the same electrophoretic mobility. 2002/0185378 as defined above and corresponding WO

02/093246 describes a method for forming electrophoretic particles in which a pigment is first coated with a layer of silica (other oxides may be used) and then a polymer is formed that is chemically bonded to the silica; the polymer may contain charged groups to enhance the electrophoretic mobility of the particles. In such silica/polymer coated particles, the surface charge responsible for the electrophoretic migration of the particles must be localized in the silica layer and/or the polymer, so that the nature of the underlying pigment must be independent of the electrophoretic mobility of the particles. Thus, as long as the particle size of the pigment is controlled, a plurality of pigments can be coated in this manner to produce electrophoretic particles having approximately the same electrophoretic mobility.

Furthermore, if the required production scale ensures that the mixing of the different pigments required for manufacturing a display with a customized color can be achieved at an early stage of the multi-step process required for manufacturing a display, the resulting pigment mixture is thereafter treated as one single component in a subsequent step of the process. The method comprises (a) forming a silica or silica/alumina shell around a raw pigment; (b) treating the silica-coated pigment with a silane coupling agent to provide sites at which the polymer can attach to the pigment; and (c) treating the silanized pigment with at least one monomer or oligomer under conditions effective to result in the formation of a polymer on the surface of the pigment (some preferred forms of the method require multiple polymerization steps and/or further processing in order to alter the chemistry of the initially formed polymer). In this method, two or more pigments are mixed to produce a custom color in the final display, and the mixing of the dyes can be achieved at various stages as described below:

1. mixing raw material pigments:

the original untreated pigment may be mixed to obtain the desired color before the surface is first modified. The mixed pigment mixture is then coated with silica or silica/alumina, followed by silane treatment and polymer formation steps.

At first glance, this appears to be the most preferred method of ensuring that the mixed pigment is treated in the same manner under the same conditions, so that the mixed pigment has the same surface chemistry. On the other hand, it is difficult to judge the color obtained by mixing the original pigments with the color in the final display due to changes in color caused by inorganic coatings, pigment wetting in suspension (silica coated pigments are used in paint applications to prevent this wetting effect from occurring, although wetting must still be considered), and pigment color when placed behind the capsule walls, conductors, adhesives, binders, color filters and other layers conventionally used in electrophoretic displays, as described in the above mentioned E Ink and MIT patents and applications. These color changes require repeated mixing processes and the manufacture of displays from mixed pigments, which can substantially increase the cost and development time of custom color displays.

2. Mixing pigments after forming the inorganic shell

In this method, the raw pigment is first modified with silica or silica/alumina shell separately and then mixed to obtain the desired color, after which the mixed pigment is subjected to silane treatment and polymer formation process.

3. Mixing pigments after inorganic shell formation and silane treatment

In this process, the starting pigment is first modified separately with a silica or silica/alumina shell and subjected to a silane treatment. The pigments are then mixed to obtain the desired color, and the mixed pigment is subjected to a polymer formation process.

4. Mixing pigments after inorganic shell formation, silane treatment, and polymer formation

In this method, the raw pigment is first modified with a silica or silica/alumina shell separately, and then subjected to silane treatment and polymer formation processes. The pigments are thereafter mixed to obtain the desired color.

This method ensures that the surface modification of the pigment does not change the color of the pigment, since the pigment is mixed after all chemical modifications are completed. Needless to say, the color of the mixed pigments may still change after inclusion in the internal phase and placement in the capsule wall, binder and other layers as described above. However, this method has problems in ensuring that the pigments in the final mixture are treated in the same manner under the same conditions to produce the same surface chemistry, such as thickness/coverage of the silica or silica/alumina layer, coverage/mass/density of the silane deposit, and thickness/molecular weight/density of the polymer.

Part B- "internal" color filter

Conventional Color Filter Arrays (CFAs) used in electro-optic displays comprise a layer of material that is colored in a suitable manner and disposed adjacent to the viewing surface of the display "outside" the front electrode, i.e., between the front electrode and the viewer. Such a conventional CFA must be spaced apart from the electro-optic layer by at least the thickness of the front electrode and possibly other layers, such as the substrate on which the front electrode is mounted, and/or the adhesive holding the electrophoretic capsules, and/or the polymer matrix in a rotating two-color element display. This separation between the CFA and the electro-optic layer can cause parallax problems, and the wide viewing angle of many electro-optic displays can exacerbate these problems. This parallax problem adversely affects the image quality of the display, particularly when the display is viewed at a large angle relative to the normal to the viewing surface of the display.

Another problem with conventional CFAs is the alignment of the CFA with the pixel electrodes used to drive the display; it will be appreciated that any misalignment between the CFA and the pixel electrodes will cause cross-talk between the colour channels of the image on the display. Alignment of the CFA to the pixel electrode is more difficult in many electro-optic displays than in liquid crystal displays, because in liquid crystal displays the CFA can be aligned to the pixel electrode before the liquid crystal itself is injected into the display, whereas in electrophoretic or rotating bichromal cell displays, for example, this is not feasible because the conventional method of manufacturing such displays is to deposit the electro-optic layer on the CFA and then to laminate the combined electro-optic layer/CFA onto the backplane containing the pixel electrode. Since the electro-optic layer of the electrophoretic or rotating bichromal element must be opaque, the pixel electrode cannot be seen through the electro-optic layer during lamination, thereby preventing optical alignment of the CFA with the pixel electrode.

As already described, the above 2003/0011560 describes a method of changing the optical properties of an electrophoretic display by including a light deflecting element in any of a number of components of the display. It has now been realized that such a light deflecting element may be used as a color filter of a display, as long as the light deflecting element has different colors in different areas of the display to provide the necessary color filtering elements.

The possible positions of such light deflecting elements/filters may vary depending on the type of electro-optical display. For example, in an encapsulated electrophoretic display, color filters may be disposed (a) in the capsule walls; (b) in the adhesive surrounding the capsule; (c) a laminating adhesive for securing the electrophoretic medium to a substrate constituting a viewing surface of the display; or (d) in the front electrode of the display. (Note that while 2003/0011560 above describes the light-deflecting element as being located "behind" the electrophoretic medium, i.e., on the side of the medium opposite the viewing surface of the display, since the electrophoretic medium is largely opaque, light-deflecting elements that serve as color filters must be disposed within the electrophoretic medium itself or between the electrophoretic medium and the viewing surface of the display.) in a microcell electrophoretic display, color filters may be disposed in the front plate that seals the microcells, or in locations corresponding to (c) or (d) above. In a rotating bichromal element display, the light deflecting element/colour filter may be provided in a polymer matrix surrounding the rotating element (which matrix must correspond to the adhesive encapsulating the electrophoretic display) or in the above mentioned positions (c) or (d).

Fig. 1 is a schematic cross-sectional view of a preferred embodiment of the present invention in which a color filter is disposed in the capsule wall of an encapsulated electrophoretic display, generally designated 100. The display 100 includes an encapsulated electrophoretic medium, generally indicated at 102, comprising a plurality of capsules 104, 104', 104 ", each capsule containing a suspension 106 and a plurality of positively charged black particles 108 and a plurality of negatively charged white particles 116 dispersed therein. (the triangular shape of particle 108 and the circular shape of particle 116 are for illustration only to ease differentiation of the particles in the figures, and do not correspond to the physical shape of an actual particle, which is typically roughly spherical.)

The display 100 further comprises a common transparent front electrode 110, the front electrode 110 constituting a viewing surface through which a viewer can view the display 100; the display 100 also includes a plurality of separate rear electrodes 112, 112', 112 ", each defining a pixel of the display 100. For ease of illustration and understanding, fig. 1 shows only one individual microcapsule constituting a pixel defined by each rear electrode, although in practice a large number (20 or more) of microcapsules are typically used per pixel. The back electrodes 112, 112', 112 "are mounted on a substrate 114.

Display 100 is an RGB display having red, green, and blue pixels arranged in cyclically repeating columns; it will be appreciated that although only one electrode is shown in each column in figure 1, in practice each column may contain a large number of electrodes, the potential at each electrode being independently controlled by conventional active matrix drive circuitry (not shown). No external color filter is present; instead, an "internal" color filter is formed by coloring the walls of the capsule 104, 104', 104 ". As indicated by the shading differences in fig. 1, the walls of the capsule 104 are colored to transmit red light, the walls of the capsule 104' are colored to transmit green light, and the walls of the capsule 104 "are colored to transmit blue light.

Fig. 1 shows a display 100 having rear electrodes 112 and 112 "that remain negative with respect to a common front electrode 110, and a rear electrode 112' that remains positive with respect to the common front electrode 110. Thus, in the capsules 104 and 104 ", the white particles 116 are located near the viewing surface of the display so that the pixels appear red and blue, respectively. However, in the capsule 104', the black particles 108 are located near the viewing surface of the display, so that the pixel appears black.

It will be appreciated that displays of the type shown in fig. 1 need not use an RGB color scheme, but may use a CMY color scheme, for example. In practice, the latter is preferred for reflective electro-optic media, such as the electrophoretic media shown in fig. 1, since CMY color schemes typically absorb less incident light, resulting in brighter colors.

By forming the CFA by dyeing the microcapsule walls in an electrophoretic display in the manner described above with reference to fig. 1, the parallax problem described above is substantially eliminated, since there is no longer any space between the color filter array and the electro-optic layer of the display. Similar advantages with respect to parallax problems can also be obtained by disposing the CFA in the adhesive of the electrophoretic layer or in the polymer matrix of the rotating bichromal element layer.

Displays with the internal CFA of the present invention can be fabricated using a variety of techniques. These techniques fall into two main groups: "pre-fabricated" CFAs, wherein color is introduced into the display components prior to forming the display components in the display; and "in-situ" CFAs, where the CFAs are formed in situ in the final display or in some subcomponent thereof. One example of a prefabricated CFA is to dye (or possibly treat with pigments) the capsules to form red, green and blue light-transmissive capsule walls as described above with reference to fig. 1, and then place three strips of microcapsules in alignment with the pixel electrodes to form the display shown in fig. 1. However, in general, in-situ CFAs are more readily suited for high volume manufacturing of displays. It will be appreciated that in the display of fig. 1, for example, all the capsules are the same except for the colouring of the capsule walls, so that the display can be made by applying a uniform layer of capsules, then colouring the capsule walls, and optionally surrounding an adhesive to make the internal CFA. Note that although this approach may result in a single capsule extending over two adjacent electrodes, it has little or no effect on the properties of the display, since it has been found empirically that adjacent portions of the same capsule may have different optical states when exposed to different electric fields.

In situ methods for forming CFAs can be divided into two main types. In the first type, an external colorant (e.g., a dye or pigment, or an agent that reacts in a color-forming reaction with the components of the display in which the CFA is to be formed) is applied imagewise to the display. For example, the capsule walls may be colored with pigments or dyes deposited using coating or printing techniques such as registered slot coating of a ribbon, by mask jet, ink jet, offset, letterpress-gravure or intaglio printing. In the second type, a technique based on a photolithographic method is used to form colors in the components of the display in which the CFA is to be constructed. For example, chemical additives may be coated onto the capsule wall to make it resemble a color film. However, by projecting an image of the desired CFA onto the capsule coating, the capsule can be stained to obtain the appropriate coloration. While the term "photolithographic method" is used, it is not intended to limit the color formation method used to silver halide based photosensitivity methods, it is not generally desirable to actually use silver based color formation because of the considerable difficulty in actually removing silver and silver halide from the CFA after exposure. However, certain color-forming reactions are known to be extremely sensitive to wavelength, see U.S. Pat. No. 4,602,263, and can be used to form CFAs. For example, capsules can be prepared having a wall containing a mixture of red, green and blue dye-forming compounds that are sensitive to three different wavelengths of radiation (typically different infrared wavelengths). After the capsule is incorporated into the display, the relevant areas of the display are exposed to radiation of different wavelengths, preferably emitted by a laser, to turn these areas red, green and blue, thereby forming a CFA. Alternatively, the nanoparticle color formation techniques described in U.S. Pat. Nos. 6,323,989 and 6,538,801 and co-pending application Ser. No. 10/065,617 (publication No. 2003/0096113) may be used to produce the desired color change. For example, the patent and application disclose tethered nanoparticles that change color when the tether is broken by, for example, ultraviolet or other radiation. By including the bound nanoparticles in the capsule wall, and then exposing the relevant area of the display to radiation that breaks the binding, the color change required to form the CFA can be achieved.

The in situ method described above for forming a CFA can be performed on an electro-optic layer on a dual separation membrane (see section E below), rather than on an assembled display.

The in-situ formation of the CFA can be used to reduce or eliminate the CFA alignment problem described above by using the display itself to provide the alignment marks needed to precisely align the CFA with the pixel electrodes. For example, consider the above-described display comprising capsules containing in the walls of which are mixtures of red, green and blue dye-forming compounds that are sensitive to three different wavelengths of radiation. Once such a display is assembled with an active matrix backplane, a portion of the backplane may be activated to form an image on the display. For example, the backplane may be activated so that areas intended to be red and green are black in color and areas intended to be blue are white in the final CFA. The resulting image can be used as an alignment mark to expose the white areas of the display to the radiation required to turn the capsules in these areas to transmit blue light. The blue and intended green areas may then be blackened, while the intended red areas are whited, for example. It is clear that by this method the complete CFA can be manufactured in correct alignment with the pixel electrodes.

In addition to the internal CFA, the display of the present invention may include any one or more of an anti-reflective coating, a microlens array, a holographic filter, and a brightness enhancement film. It is also desirable that the front side of the display stack comprises a shielding film.

Part C-color filter with non-rectangular pixels

Conventional CFAs used in liquid crystal displays are not best suited for encapsulating electrophoretic displays. The encapsulated electrophoretic medium exhibits a slightly degraded optical state at the boundary between the capsules (i.e. at the capsule wall) compared to the optical state exhibited near the centre of the capsules.

It has now been recognized that the effect of the capsule wall can be minimized by careful selection of the shape of the pixels in the CFA; the pixel electrodes used to control the display must of course match the shape of the CFA pixels. Designs that increase this likelihood are preferred over (elongated, non-square) rectangular pixels typically used in liquid crystal displays, where the capsule walls are located in the gaps between adjacent pixels-CFA pixels may have a hexagonal (see fig. 2A), square (fig. 2B) or triangular shape, preferably an equilateral triangle (fig. 2C). In the accompanying single color drawings, the color of each pixel is represented by R, G and B for red, green, and blue, respectively. While pentagonal pixels could theoretically be used, these and similar shapes, such as octagonal pixels, are disfavored because there is no close packing on the surface. Hexagonal pixels are particularly preferred because the capsules are ideally tightly packed in a hexagonal grid; square pixels are also preferred.

Conductive color filter between partial D-electrodes

As described above, the conventional CFA developed for use in the liquid crystal display includes: a layer is colored in a suitable manner and is arranged "outside" the front electrode, i.e. the material between the front electrode and the viewer, near the viewing surface of the display. Such conventional CFAs are fabricated on a glass substrate and are composed of a plurality of thin films (commonly referred to as "stacks"), typically including a black mask (typically formed of chromium), red, green and blue photoresist layers, and a conductive layer, typically formed of Indium Tin Oxide (ITO), constituting the front electrode of the display.

As has also been noted, certain types of electro-optic displays, particularly encapsulated electrophoretic displays, microcell displays, and rotating bichromal element displays, have the advantage that they can be formed on flexible substrates such as plastic films made of poly (ethylene terephthalate) or poly (ethylene naphthalate). Although conventional CFAs of the type described in the preceding paragraph may be used technically in electro-optic displays formed on plastic films, such conventional CFAs are not particularly well suited for such use. Black chrome masks can be troublesome on plastic substrates because such metals are typically patterned using etchants that tend to damage the plastic; thus, it is desirable to remove the black mask.

It is also desirable that if the "internal" CFA described in section B of the present invention is not employed, the present inventors recognize that the order of the colored layers and conductive layers is swapped. This exchange facilitates manufacturing because plastic films coated with conductive materials (such as ITO) are readily available on the market and can be used as starting materials in the CFA manufacturing process.

However, this exchange must place the colored layer between the electrodes of the display and, at any given operating voltage between the electrodes, reduce the voltage on the electro-optic medium itself, since the voltage on the electro-optic medium is equal to the operating voltage minus the voltage drop across the colored layer. The reduced voltage across the electro-optic medium typically slows the switching speed of the medium. Although the reduced voltage across the electro-optic medium can be compensated for by increasing the operating voltage, this is undesirable because it increases the power consumption of the display and may require changes in circuitry to generate and/or control the increased voltage. Furthermore, the resistivity of many commercial photoresists is so high that to compensate for the colored layer present between the electrodes, the increase in the required operating voltage is very large and often unacceptable.

Thus, it is desirable to increase the conductivity of the material used to form the colored layer so that the resistance of the colored layer does not greatly exceed the resistance of the electro-optic layer, and in fact is desirably less than the resistance of the electro-optic layer. Suppose is largeMost types of electro-optic media are low conductivity, then the colored layer should have a conductivity no greater than about 10¹⁰Preferably no greater than about 10⁹Volume resistivity in ohm-centimeters. The colored layer can be made more conductive by incorporating conductive nanoparticles such as silver, gold, aluminum, platinum, or carbon nanoparticles; although these materials are opaque in bulk, making them small enough nanoparticles (typically less than 10nm in diameter) they do not substantially scatter light and thus do not interfere with the optical problems of the colored layer. Other organic or inorganic pigments having good electrical and optical properties may also be used, as may conductive polymers and other materials, although of course the overall optical properties of the display after addition of these materials must be considered. The conductivity of the colored layer can be controlled using the techniques described in 2003/0011867 above. Furthermore, because the coloured layer is placed between the electrodes of an electro-optic display, the electrical properties, and changes in these properties with environmental parameters (such as temperature), will necessarily affect the operating properties of the display in the same way as any other layer (e.g. laminating adhesive) placed between the electrodes of the display. The reader is referred to 2003/0025855 above, which summarizes in detail the desirable properties of laminating adhesives used in electro-optic displays; most of these properties are directly applicable to the colored layer used as the internal color filter array according to the present invention.

Partial E-double separation membrane

As already indicated, the method of incorporating CFAs used in liquid crystal displays is not particularly applicable to other types of electro-optic media. In particular, as already indicated, the techniques used for assembling liquid crystal displays are not well suited for other types of electro-optic media. In a conventional method for assembling a liquid crystal display, a front assembly including a substrate, a color filter layer, and a conductive layer is formed and aligned and fixed with a rear assembly including a pixel electrode and associated circuitry, and a narrow cell gap is maintained between the two assemblies using a spacer. The cell gap is then evacuated and filled with liquid crystal material by dipping the assembled assembly into a pool of liquid crystal material.

Although encapsulated electrophoretic displays can theoretically be formed in a similar manner, in practice this assembly technique is highly undesirable because when injected into narrow cell gaps, the capsules are not as tightly packed as is required for the resulting display to obtain optimal optical properties. Instead, it is desirable to form the final electrophoretic medium layer by coating or printing the encapsulated electrophoretic material with the paste-like polymeric binder on the substrate, and then drying and/or curing the coated or printed layer. While the coating or printing step may be performed directly on the CFA, some CFAs may be problematic when the capsules are properly filled and/or when the capsules are sufficiently adhered to the CFA.

In one aspect of the invention, electrophoretic display material or other solid electro-optic material is coated, printed or otherwise deposited onto a separator sheet for later transfer to a CFA or other substrate, such as a backplane (see also co-pending patent application serial No.10/249,957 and corresponding international application PCT/US 03/16433). It is desirable to coat the display material so that a thin adhesive layer exists between the display material and the separator; a second adhesive layer may be disposed on an opposite side of the display material capsule. In order to protect the coated composite during processing, it is desirable to apply a second release sheet over the second adhesive layer.

A preferred dual separator sheet of the present invention is shown in fig. 3 (generally designated 300). The release sheet 300 comprises a central layer 302 of electro-optic material, in particular a layer comprising capsules 304 in a polymer binder 306 in figure 3. The capsule 304 may be similar to that described above with reference to fig. 1. The sheet 300 also includes a first adhesive layer 308, a first release sheet 310 covering the first adhesive layer 308, a second adhesive layer 312 disposed on the opposite side of the layer 302 from the first adhesive layer 308, and a second release sheet 314 covering the second adhesive layer 312.

The first adhesive layer 308 may be formed by first coating the release sheet 310 with an adhesive layer and then drying or curing it. The mixture of capsules 304 and binder 306 is then printed or otherwise deposited on the first adhesive layer 308, and the mixture is then dried or cured to form the adherent layer 302. Finally, an adhesive layer is deposited on layer 302, dried or cured to form a second adhesive layer 312, and covered with a second release sheet 314 to form the dual release sheet 300.

It will be apparent to those skilled in the coating art that this sequence of operations for forming the sheet 300 is well suited for continuous production and, by careful selection of materials and process conditions, the entire sequence of operations can be carried out at once by conventional roll-to-roll coating equipment.

To assemble a display using a dual release film, such as film 300, one release sheet (typically having an electro-optic material coated thereon) is peeled off and the remaining layers of the dual release film are attached to the CFA or another front substrate using, for example, a thermal, radiation or chemical-based lamination process. Typically, the CFA or front substrate includes a conductive layer that will constitute the front electrode of the final display. The CFA and the conductive layer may be in any order, but for reasons already discussed, the CFA is preferably located between the conductive layer and the electro-optic layer. The front substrate may comprise additional layers such as UV filters or protective layers intended to protect the CFA and/or the conductive layer from mechanical damage. Thereafter, the other release sheet is peeled away, thereby exposing the second adhesive layer, which is used to attach the CFA/electro-optic material coating assembly to the backplane. Also, thermal, radiation, or chemical based lamination processes may be used. It will be appreciated that the order of the two laminations is virtually arbitrary and can be reversed, although in practice it will generally be more convenient to first laminate the dual separation membrane to the CFA or another front substrate and then laminate the resulting front assembly to the backplane.

As described above, in all CFA-based electro-optic displays, it is desirable to make the distance from the bottom surface of the color filter to the optically active layer as small as possible. This minimizes light loss and reduces parallax problems. Therefore, the lamination adhesive on both the display front and the capsule wall should be as thin as possible. It is conceivable that the thickness of these layers can be reduced to approximately 1 μm. Furthermore, it is desirable that the capsules deform during the coating and drying process so that they present a substantially flat surface against the color filter array. This will help to minimize the chance that light incident through one pixel will exit through an adjacent (different color) pixel after being diffusely reflected from the optically active display material. In addition, it is desirable to match the refractive indices of all the films used in constructing the display stack.

A variety of display assembly techniques may be employed including, but not limited to, wet bonding or hot melt lamination methods. In some applications, it is preferred to use a repositionable adhesive or an aerosol adhesive. In other applications, it is preferred to use radiation, heat or chemically curing adhesives. However, in each assembly technique, the CFA sub-pixels must be aligned with the TFT array electronics on the backplane. To obtain high resolution alignment (assuming better alignment within 10-20 μm), a standard optical alignment system that aligns the fiducial marks on the backplane with the fiducial marks on the CFA may be used. Once the fiducials on the two substrates are aligned, they are bonded together without introducing misalignment and a lamination process is performed. The lamination process may be based on: 1. mechanical contact (i.e., pressure sensitive adhesive that may or may not be repositionable), 2 thermal effects (e.g., hot melt, wet adhesion, vacuum lamination, etc.), or 3 radiation-based methods (e.g., UV curing).

It will be apparent to those skilled in the art of electro-optic displays that many changes and modifications can be made to the described method of forming an electro-optic display from a dual-separation film. For example, in each of the two laminations, only one of the two parts laminated together needs to be provided with an adhesive layer, and which part is provided with an adhesive layer is an essential issue of the processing. Thus, in some cases, it may be convenient to omit one or both of adhesive layers 308 and 312 from sheet 300, and instead place a similar adhesive layer on the CFA, backplane, or another substrate used in the lamination. Furthermore, in some cases, a separate sheet may be omitted without causing the adhesive layer to be exposed to contaminants for a long time. For example, if a double release sheet, such as sheet 300, is formed on a continuous production line and laminated to a color filter array or another substrate in a short time after the second adhesive layer 312 is formed, the use of the second release sheet 314 may be omitted and the second adhesive layer used to laminate the sheet 300 to the color filter array.

It will be apparent to those skilled in the art of electro-optic displays that the double separator sheet of the present invention can be considered a variant of the front plane laminate described in the above-mentioned co-pending application serial No.10/249,957 and the corresponding international application PCT/US 03/16433. Such a front plane laminate comprises, in order, a light-transmissive electrically conductive layer (typically on a polymer film substrate), a solid electro-optic medium layer in electrical contact with the conductive layer, an adhesive layer and a separator sheet. The inventive double separator sheet is essentially a variant of such a front plane laminate obtained by replacing its conductive layer with a second separator sheet, optionally with an associated second adhesive layer. Thus, a dual separator sheet of the present invention may include any of the optional features of the front plane laminate described in the above-mentioned co-pending application Ser. No.10/249,957 and the corresponding International application PCT/US 03/16433. For example, the double separator sheet may have one or more of the following: (a) a conductive layer on one or both of its separate sheets to enable detection of the electro-optic medium (see FIGS. 2-7 and related description of application Ser. No.10/249,957); (b) a conductor extending through the layer of electro-optic medium (see FIGS. 9 and 10 and related description of application Ser. No.10/249,957); (c) a hole extending through the layer of electro-optic medium, which hole can be later filled with a conductive material to form the conductor described in (b) (see FIGS. 8 and 18 and related description of application Ser. No.10/249,957); (d) edge seals (see FIGS. 11-17, 19 and 20 and associated description of application Ser. No.10/249,957); and (e) a label in which the separator sheet extends beyond the layer of electro-optic material to facilitate removal of the separator sheet (see fig. 21 and 22 and related description of application serial No.10/249, 957).

For reasons of display lifetime and robustness, a seal around the edge of the display is required. The edge sealing material may comprise a UV, heat or chemically curable adhesive that is compatible with the encapsulating electrophoretic display material. The adhesive may be deposited around the edges of the display using printing methods, automated pipette dispensing techniques, or other similar techniques known to those skilled in the art. In a conventional liquid crystal manufacturing method, such a sealing material is cured before liquid crystal is filled into a cell gap. This approach is unacceptable for encapsulating displays because the edge seal can lock voids (e.g., air gaps) into the stacked display. There are several ways to eliminate this problem. First, the edge banding material can be filled into the narrow gap around the edge of the display after lamination is complete. Second, edge banding material may be provided around only a portion of the display edge, laminated, and then filled with the remainder of the edge banding material. These and other edge sealing techniques are described in the above-mentioned co-pending application serial No.10/249,957. The dual release film of the present invention, however, provides an alternative method of forming the edge seal by having the adhesive layers on opposite sides of the electro-optic layer extend beyond the edges of the electro-optic layer, but not beyond the edges of the display. Figure 4 illustrates a seal formed in this manner. Figure 4 shows a display (generally designated 400) formed from a double-separated film similar to the film 300 shown in figure 3 by the double lamination method already described. The final display 400 includes the electro-optic layer 302, the backplane 316, and the CFA 318. The two adhesive layers 308 'and 310' extend beyond the edges of the electro-optic layer, but not beyond the edges of the display, so that after two laminations, the two adhesive layers adhere together to form the edge seal 320. Edge seals are often necessary in forming robust electro-optic displays, which can make the display withstand large changes in environmental conditions and make it easier to form the required seal in this way using existing adhesive layers, rather than introducing a separate sealing material around the outer edges of the display.

Partial F-fabrication of color filter arrays by photolithographic imaging

In another aspect of the invention, a method is provided for making a color filter for use in an electro-optic display. The method includes imaging a color filter pattern on a photosensitive film, processing the film (if necessary) to reveal the image, and then depositing a conductive layer on the photosensitive film as an electrode. The term "photosensitive film" as used herein is not limited to films based on silver halide chemistry, nor to films sensitive to visible wavelengths, but includes films sensitive to electromagnetic radiation outside the visible range. If the photosensitive film used is a conventional silver halide film comprising a substrate silver halide emulsion, a conductive layer is typically deposited on the emulsion side of the film. The result is a flexible color filter that can be used as the top surface of an electro-optic display.

The requirements in preparing CFAs on flexible substrates have been discussed above, as well as the problems encountered in attempting to change the conventional methods of forming CFAs on glass, originally developed for use in liquid crystal displays. As already described, this method is not well suited for flexible substrates and the manufacturing costs are also high compared to the cost of amorphous silicon TFT backplanes on quartz.

In one embodiment of the invention, the image is transferred to the photographic film by contact printing an existing color filter array onto glass. The film is then placed on a flat, non-reflective surface with the emulsion side up. The dye side of the color filter is then placed down on top of the film. The film is exposed through a color filter using a light source. This method requires an existing color filter as a master.

Another embodiment of the present invention for making color filters uses a camera to image a pattern onto a thin film. The pattern may be an existing color filter, in which case the pattern is backlit. In this case, the camera is set to reproduce a 1: 1 image on the film. Alternatively, the master may be a large (poster-sized) reflective object, such as a high quality picture on paper. In this case, the master should be illuminated from the front and the camera set to reduce the image on the film to the appropriate size. This method has the advantage of enabling the rapid construction of CFAs from microscopic patterns, thereby enabling parameters such as color filter density, black mask size, etc. to be varied.

Yet another embodiment of the present invention uses a linear array of emissive elements translated across the film in a direction perpendicular to the long axis of the linear array to create a fringe pattern on the film. If a black mask is required in this embodiment, the emissive elements are turned on or off in place to create dark regions on the film.

In any of the above embodiments, the overall color cast of the color filter may be reduced (or enhanced) by applying an appropriate color filter to the illumination source, or (when used) by placing the color filter over the lens of the camera. The density of the color filters can be adjusted by increasing or decreasing the film exposure. If the film (possibly) does not reproduce exactly one or more colors in the color filter, the color in the master must be adjusted. For any film, there is an inverse transformation controlled by the spectral response function of the photosensitive emulsion, which determines the appropriate color to use in the master in order to obtain the desired color in the final display.

To complete the construction of the CFA, the film may be treated using appropriate chemistry after one of the processes described above. A thin film of Indium Tin Oxide (ITO) or other conductive material may then be evaporated onto the latex side of the film. Alternatively, a transparent conductive polymer such as Baytron (registered trademark) may be applied to the surface.

The present invention enables the fabrication of CFAs on flexible substrates at low cost. Furthermore, using the simplified method described above, CFAs of arbitrary geometry and color can be manufactured using very simple and readily available tools, enabling rapid prototyping of color filter variations.

Multiple methods of partial G-fabrication of color filter arrays

The present invention relates to various methods for integrating electrophoretic display materials into CFA-based electrophoretic displays. The manufacturing method of the present invention is significantly different from the method used in the manufacture of liquid crystal displays.

In a first aspect of the invention, an encapsulating electrophoretic display material is applied directly onto a CFA, and the coated CFA is subsequently laminated to a backplane containing pixel electrodes.

The encapsulating electrophoretic display material (i.e., capsules) may be deposited directly onto the color filter array by crafting, meniscus, curtain coating, or other coating methods. The color filter array may be composed of a glass or other optically transparent substrate (including polymer substrates and thin "flexible" glass), a plurality of red, green, and blue stripes, and a transparent conductor. In certain embodiments, the color filter array includes a "black mask," which is an opaque wire grid used to implicitly select unwanted locations on the assembled electronic display. In other embodiments, the color filter array is comprised of a plurality of red, green, and blue pixels, rather than stripes. The black mask can be located above or below the color bars or pixels. In another embodiment, the color filters may comprise optically transparent rather than colored stripes or pixels.

It is important to ensure that the encapsulating electrophoretic display material is in intimate contact with the CFA to ensure adequate optical coupling between the display material and the color filter. At least the distance between the surface of the color filter and the front surface of the optically active material in the encapsulated electrophoretic display material is required to be much smaller than the minimum size of a pixel of the display. For example, for a 100 μm wide pixel, it should be ensured that the distance from the surface of the color filter stripe to the front surface of the optically active material is less than 10 μm. The gap can be filled with a laminating adhesive, a polymer adhesive, a capsule wall material, a film over the colored area of the color filter, and the color filter can be surface treated.

Another aspect of the invention relates to a method for generating a regular surface energy pattern on a CFA to influence the fill density of capsules on the CFA. According to this aspect of the invention, the CFA may be surface treated to affect the filling of capsules that are subsequently coated directly on the surface treated CFA. In general, it is desirable to design the color filter so that a regular pattern of surface energy exists on the surface of the color filter that is in contact with the encapsulated electrophoretic display material. This helps to ensure that the capsules are filled in a way that improves the optical performance of the display.

Alternatively or in addition to such creation of a regular surface energy pattern, the surface may be prepared in such a way as to uniformly increase or decrease the wettability of the surface. This may be accomplished by applying an adhesion promoter or appropriate surface chemistry such as 1-propanamine, 3- (trimethicone) (more commonly known as 3-aminopropyltrimethoxysilane), 3-aminopropyldimethylethoxysilane, hexamethyldisilazane or other such materials. Similar surface treatments may also be applied to the surface of the backplane (or other surfaces requiring wettability modification, as described below) in order to enhance display properties.

In a particular embodiment of the invention, the CFA may be constructed as follows: 1. patterning red, green and blue stripes on a substrate, 2. patterning a black mask over the color stripes (the black mask typically underlies the color stripes), and 3. surface treating the black mask to make it non-wetting to the encapsulating electrophoretic display material and the color stripes wetting to the encapsulating electrophoretic display material. Representative surface treatments include the spectrum of octadecyltrichlorosilane, other silanes and thiol based chemicals, various polytetrafluoroethylene reagents and other materials known to those skilled in the art. The black mask can be made receptive to these agents by including a surface treatment receptive film on the topmost surface of the black mask. For example, a thin gold film may be deposited as the topmost layer of the black mask, and alkanethiol deposited on the gold. The thiol material can be configured to have a significantly different surface energy than the colored stripes to achieve the desired effect.

Another aspect of the invention relates to a method of using a patterned surface treatment to affect the fill density of a coated capsule on a continuous electrode. In this aspect, a patterned surface treatment is deposited on the continuous electrode to affect the filling of subsequently deposited capsules. The patterned surface treatment may be applied to the continuous electrode on top of the color filter by printing techniques including microcontact, offset, intaglio, letterpress-intaglio or other printing techniques known to those skilled in the art. This is an ideal use of printing, since perfect manufacturing is not required on a local scale; local defects are not catastrophic, as proper filling of the capsules over long distances tends to properly organize the capsules, regardless of the local defect.

In another aspect, the present invention relates to the use of monodisperse capsules (substantially uniformly sized capsules, e.g., where at least about 95% of the capsules have a diameter that does not differ from the average diameter by more than about 20%, and preferably by no more than about 10%) in an electrophoretic display. It is particularly desirable to use such monodisperse capsules in conjunction with the surface treatment aspects of the invention that have been described, because for polydisperse capsules, surface treatment agents with regular patterns become less effective when the deposited film is rearranged into a regular pattern, whether they are deposited on a color filter black mask or on a continuous electrode.

These aspects of the present invention are used to improve the optical performance of an encapsulated electrophoretic display by affecting the filling of capsules applied to the front electrode. The surface treatment for this purpose is either added to the black mask of the color filter or printed directly on the continuous electrode in contact with the display material.

Another aspect of the present invention relates to a novel surface treatment agent capable of filling a cell gap between a CFA and a backplane with an encapsulating electrophoretic display material. The novel surface treatment technique of the present invention enables the use of more traditional liquid crystal display manufacturing techniques. In this aspect of the invention, a surface agent that promotes wetting of the capsules is applied to the CFA and a surface agent that promotes dewetting of the capsules is applied to the floor. The color filter array and backplane are assembled with precise spacers between them and edge sealed with epoxy or other edge sealant, as in conventional liquid crystal manufacturing processes. The encapsulated electrophoretic display material is then pumped into the space between the color filter array and the backplane using a pump, vacuum, or other similar techniques known to those skilled in the art. However, due to the presence of the surface treatment on the CFA and the backplane, the capsules fill preferentially against the front surface of the display (the color filter surface) and tend to dewet and move away from the backplane surface. The present invention ensures that the encapsulated electrophoretic display material fills against the front viewing surface, significantly improving optical performance compared to techniques where the material fills against the backplane or techniques that do not preferentially fill against the CFA or backplane surface. Surface stress is used to attract the capsule to the front electrode, although other forces, including gravity, electrophoresis, and magnetism, may be used for this purpose.

This aspect of the invention improves the optical performance of the display by affecting the filling of the capsules injected into the cell gap formed between the front electrode and the backplane. Conventional display filling techniques can be used in encapsulated electrophoretic displays.

The electrophoretic medium used in various aspects of the present invention may be of any of the types described in the above-mentioned E Ink and MIT patents and applications to which the reader is referred for further information.

Claims (9)

1. An article for use as a component in an electro-optic display, comprising:

a solid electro-optic medium layer (302) having a first surface and a second surface on opposite sides;

a first adhesive layer (308) on a first surface of the solid electro-optic medium layer (302);

the article is characterized by providing a release sheet (310) on the side of the first adhesive layer (308) opposite the solid electro-optic dielectric layer (302); and

a second adhesive layer (312) on a second surface of the solid electro-optic medium layer (302),

wherein the release sheet (310) is removable from the first adhesive layer (308) to leave the first adhesive layer (308) adhered to the first surface of the solid electro-optic medium layer (302).

2. The article of claim 1, further comprising a second release sheet (314) disposed on a side of the second adhesive layer (312) opposite the solid electro-optic medium layer (302).

3. An article of manufacture as claimed in claim 1 or 2, wherein the electro-optic medium (302) is an electrophoretic medium comprising a plurality of capsules (304), each capsule containing a suspension, a plurality of charged particles suspended in the suspension and movable through the suspension by application of an electric field to the suspension, and a capsule wall surrounding the suspension and the charged particles.

4. The article of claim 1, wherein the first and second adhesive layers (308, 312) extend beyond the edges of the electro-optic medium layer (302).

5. A method for forming an electro-optic display, the method characterized by:

providing an article comprising: a solid electro-optic medium layer having a first surface and a second surface on opposite sides; a first adhesive layer on the first surface of the solid electro-optic medium layer; a separator disposed on a side of the first adhesive layer opposite the solid electro-optic medium layer; and a second adhesive layer on a second surface of the solid electro-optic medium layer;

laminating the article to a front substrate via a second adhesive layer to form a front assembly;

removing a separator sheet from the front assembly; and

the front assembly is laminated to a backplane comprising at least one electrode by a first adhesive layer to form an electro-optic display.

6. The method of claim 5, wherein the front substrate includes an electrode.

7. The method of claim 5 or 6, wherein the front substrate comprises a color filter array.

8. The method of claim 5, wherein the article comprises a second release sheet overlying the second adhesive layer, the method comprising removing the second release sheet from the second adhesive layer prior to laminating the article to the front substrate.

9. The method of claim 5, wherein the first and second adhesive layers of the article extend beyond the edges of the electro-optic medium layer, and in which method edge portions of the first and second adhesive layers are adhered to one another to form an edge seal around the electro-optic medium.