WO2010101981A2

WO2010101981A2 - Electro-optic displays with color filters

Info

Publication number: WO2010101981A2
Application number: PCT/US2010/026019
Authority: WO
Inventors: Jr. Richard J. Paolini; Steven Joseph Battista; Jonathan D. Albert
Original assignee: E Ink Corporation
Priority date: 2009-03-03
Filing date: 2010-03-03
Publication date: 2010-09-10
Also published as: KR20110132433A; US8098418B2; JP2012519883A; US20130242378A1; WO2010101981A3; TWI425288B; CN102439518A; HK1167465A1; US20100225995A1; TWI554812B; KR101303512B1; CN102439518B; TW201415150A; US20120081779A1; US8441716B2; TW201042346A

Abstract

A process for producing a color electro-optic display uses a sub-assembly (100; 200; 300; 402) comprising an electro-optic layer (106) and a light-transmissive electrically-conductive layer (104). This sub-assembly is laminated to a backplane (404, 408) bearing electrodes with the electro-optic layer (106) disposed between the backplane (404, 408) and the electrically-conductive layer (106). A flowable material is placed over the sub-assembly (100; 200; 300; 402) and a color filter array is placed over the electrically-conductive layer (106) and aligned with the electrodes of the backplane (404, 408) to form the color display.

Description

ELECTRO-OPTIC DISPLAYS WITH COLOR FILTERS

[Para 1 ] This application is related to:

(a) U.S. Patent Publication No. 2004/0190114;

(b) U.S. Patent No. 6,864,875; and

(c) U.S. Patent No. 7,075,502.

[Para 2] This invention relates to electro-optic displays and color filters for use in such displays.

[Para 3] The background nomenclature and state of the art regarding electro-optic displays is discussed at length in U.S. Patent No. 7,012,600 to which the reader is referred for further information. Accordingly, this nomenclature and state of the art will be briefly summarized below.

[Para 4] The term "electro-optic", as applied to a material or a display, is used herein in its conventional meaning in the imaging art to refer to a material having first and second display states differing in at least one optical property, the material being changed from its first to its second display state by application of an electric field to the material. Although the optical property is typically color perceptible to the human eye, it may be another optical property, such as optical transmission, reflectance, luminescence or, in the case of displays intended for machine reading, pseudo-color in the sense of a change in reflectance of electromagnetic wavelengths outside the visible range.

[Para 5] The terms "bistable" and "bistability" are used herein in their conventional meaning in the art to refer to displays comprising display elements having first and second display states differing in at least one optical property, and such that after any given element has been driven, by means of an addressing pulse of finite duration, to assume either its first or second display state, after the addressing pulse has terminated, that state will persist for at least several times, for example at least four times, the minimum duration of the addressing pulse required to change the state of the display element.

[Para 6] Several types of electro-optic displays are known, for example:

(a) rotating bichromal member displays (see, for example, U.S. Patents Nos. 5,808,783; 5,777,782; 5,760,761; 6,054,071 6,055,091; 6,097,531; 6,128,124; 6,137,467; and 6,147,791); (b) electrochromic displays (see, for example, O'Regan, B., et al., Nature 1991, 353, 737; Wood, D., Information Display, 18(3), 24 (March 2002); Bach, U., et al., Adv. Mater., 2002, 14(11), 845; and U.S. Patents Nos. 6,301,038; 6,870.657; and 6,950,220);

(c) electro-wetting displays (see Hayes, R.A., et al., "Video-Speed Electronic Paper Based on Electrowetting", Nature, 425, 383-385 (25 September 2003) and U.S. Patent Publication No. 2005/0151709);

(d) particle-based electrophoretic displays, in which a plurality of charged particles move through a fluid under the influence of an electric field (see U.S. Patents Nos. 5,930,026; 5,961,804; 6,017,584; 6,067,185; 6,118,426; 6,120,588; 6,120,839; 6,124,851; 6,130,773; and 6,130,774; U.S. Patent Applications Publication Nos. 2002/0060321; 2002/0090980; 2003/0011560; 2003/0102858; 2003/0151702; 2003/0222315; 2004/0014265; 2004/0075634; 2004/0094422; 2004/0105036; 2005/0062714; and 2005/0270261; and International Applications Publication Nos. WO 00/38000; WO 00/36560; WO 00/67110; and WO 01/07961; and European Patents Nos. 1,099,207 Bl; and 1,145,072 Bl; and the other MIT and E Ink patents and applications discussed in the aforementioned U.S. Patent No. 7,012,600).

[Para 7] There are several different variants of electrophoretic media. Electrophoretic media can use liquid or gaseous fluids; for gaseous fluids see, for example, Kitamura, T., et al., "Electrical toner movement for electronic paper-like display", IDW Japan, 2001, Paper HCSl-I, and Yamaguchi, Y., et al., "Toner display using insulative particles charged triboelectrically", IDW Japan, 2001, Paper AMD4-4); U.S. Patent Publication No. 2005/0001810; European Patent Applications 1,462,847; 1,482,354; 1,484,635; 1,500,971; 1,501,194; 1,536,271; 1,542,067; 1,577,702; 1,577,703; and 1,598,694; and International Applications WO 2004/090626; WO 2004/079442; and WO 2004/001498. The media may be encapsulated, comprising numerous small capsules, each of which itself comprises an internal phase containing electrophoretically-mobile particles suspended in a liquid suspending medium, and a capsule wall surrounding the internal phase. Typically, the capsules are themselves held within a polymeric binder to form a coherent layer positioned between two electrodes; see the aforementioned MIT and E Ink patents and applications. Alternatively, the walls surrounding the discrete microcapsules in an encapsulated electrophoretic medium may be replaced by a continuous phase, thus producing a so-called polymer-dispersed electrophoretic display, in which the electrophoretic medium comprises a plurality of discrete droplets of an electrophoretic fluid and a continuous phase of a polymeric material; see for example, U.S. Patent No. 6,866,760. For purposes of the present application, such polymer- dispersed electrophoretic media are regarded as sub-species of encapsulated electrophoretic media. Another variant is a so-called "microcell electrophoretic display" in which the charged particles and the fluid are retained within a plurality of cavities formed within a carrier medium, typically a polymeric film; see, for example, U.S. Patents Nos. 6,672,921 and 6,788,449.

[Para 8] An encapsulated electrophoretic display typically does not suffer from the clustering and settling failure mode of traditional electrophoretic devices and provides further advantages, such as the ability to print or coat the display on a wide variety of flexible and rigid substrates. (Use of the word "printing" is intended to include all forms of printing and coating, including, but without limitation: pre-metered coatings such as patch 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; silk screen printing processes; electrostatic printing processes; thermal printing processes; ink jet printing processes; and other similar techniques.) Thus, the resulting display can be flexible. Further, because the display medium can be printed (using a variety of methods), the display itself can be made inexpensively.

[Para 9] Although electrophoretic media are often opaque (since, for example, in many electrophoretic media, the particles substantially block transmission of visible light through the display) and operate in a reflective mode, many electrophoretic displays can be made to operate in a so-called "shutter mode" in which one display state is substantially opaque and one is light-transmissive. See, for example, the aforementioned U.S. Patents Nos. 6,130,774 and 6,172,798, and U.S. Patents Nos. 5,872,552; 6,144,361; 6,271,823; 6,225,971; and 6,184,856. Dielectrophoretic displays, which are similar to electrophoretic displays but rely upon variations in electric field strength, can operate in a similar mode; see U.S. Patent No. 4,418,346.

[Para 1 0] Other types of electro-optic media may also be useful in the present invention. [Para 1 1 ] Many types of electro-optic media are essentially monochrome, in the sense that any given medium has two extreme optical states and a range of gray levels lying between the two extreme optical states. As already indicated, the two extreme optical states need not be black and white. For example, one extreme optical state can be white and the other dark blue, so that the intermediate gray levels will be varying shades of blue, or one extreme optical state can be red and the other blue, so that the intermediate gray levels will be varying shades of purple.

[Para 1 2] There is today an increasing demand for full color displays, even for small, portable displays; for example, most displays on cellular telephones are today full color. To provide a full color display using monochrome media, it is either necessary to place a color filter array where the display can be viewed through the color filter array, or to place areas of different electro-optic media capable of displaying different colors adjacent one another. [Para 1 3] However, attaching a color filter to an electro-optic display in the correction position is a difficult operation. Many color filter arrays are formed on sheets of glass or similar rigid material in order that the color filter will maintain stable dimensions (even slight distortions of the dimensions of a color filter array can lead to at least part of the color filter array being misaligned with the pixels of the display, with consequent errors in the colors displayed to an observer). For similar reasons, most backplanes used in color electro-optic displays are formed of rigid materials. The electro-optic medium is secured to one of the rigid sheets, and then the two rigid sheets are laminated together, typically with a layer of a polyurethane or other lamination adhesive between them, to form the final display. The lamination adhesive layer may have a thickness of about 25 μm. The lamination adhesive is tacky at room temperature , which makes is extremely difficult to laminate the two rigid sheets together without trapping pockets of air between them, especially if the sheets are of substantial size. Despite the use of special alignment tools to keep the rigid sheet flat, and application of substantial pressure, of the order of 100 psig (about 0.8 MPa) at room temperature, it has been found that in practice it is difficult to avoid trapping significant numbers of air bubbles. The air bubbles can be reduced in number or eliminated by passing the laminated display between rolls under conditions of substantial temperature and pressure, or by autoclaving the displays, again under conditions of substantial temperature and pressure. Such expedients for bubble removal substantially increase the cost and duration of the display assembly process, rendering it very time and labor intensive, and do not consistently result in high quality color displays. Furthermore, it appears that this process for lamination of rigid, typically glass, sheets will not allow for a good manufacturing process, because it imposes a large additional set of electrical and rheological constraints that make the lamination very difficult. [Para 1 4] Accordingly, there is a need for a process for the lamination of color filter arrays to backplanes to form electro-optic displays which eliminates, or at least reduces, the aforementioned problems, and the present invention seeks to provide such a process. [Para 1 5] This invention provides a process for assembling an electro-optic display which decouples lamination of the electro-optic layer to the backplane from the lamination and alignment of the color filter array to the backplane

[Para 1 6] Accordingly, in one aspect this invention provides a process for producing a color electro-optic display, the process comprising: providing an electro-optic sub-assembly comprising an electro-optic layer and a light-transmissive electrically-conductive layer; laminating the electro-optic sub-assembly to a backplane comprising a plurality of electrodes such that the electro-optic layer is disposed between the backplane and the electrically-conductive layer; disposing a flowable material over the electrically-conductive layer; and disposing a color filter array over the electrically-conductive layer and aligning the color filter array with the electrodes of the backplane to form the color electro- optic display.

[Para 1 7] In this process, typically an adhesive layer will be provided between the electro- optic layer and the backplane. However, provided sufficient adhesion of the electro-optic layer to the backplane can be achieved, it is not always necessary to provide such a discrete electro-optic layer; for example, it is known from U.S. Patent No. 7,110,164 that in some cases a polymeric binder component within an electro-optic layer can serve as an adhesive, thus eliminating the need for a discrete adhesive layer.

[Para 1 8] In one form of this process, the electro-optic sub-assembly has the form of a front plane laminate comprising the electrically-conductive layer, the electro-optic layer and an adhesive layer disposed on the opposed side of the electro-optic layer from the electrically- conductive layer, and the lamination is effected by contacting the adhesive layer with the backplane. The front plane laminate may further comprise a release sheet covering the surface of the adhesive layer remote from the electro-optic layer, and this release sheet is removed before the lamination of the front plane laminate to the backplane. As discussed in U.S. Patent No. 6,982,178, the release sheet may comprise an electrically-conductive layer to permit testing of the electro-optic properties of the front plane laminate; such an electrically- conductive layer is conveniently provided by using a metalized polymeric film as the release sheet. In another form of the process of the present invention, the electro-optic sub-assembly has the form of an inverted front plane laminate comprising, in this order, the electrically- conductive layer, a first adhesive layer, the electro-optic layer, and a second adhesive layer, and the lamination is effected by contacting the second adhesive layer with the backplane. The inverted front plane laminate may further comprise a release sheet covering the surface of the second adhesive layer remote from the electro-optic layer, and this release sheet is removed before the lamination of the inverted front plane laminate to the backplane. [Para 1 9] A further variant of this process uses a so-called "double release film" as described in U.S. Patent No. 7,561,324. This double release film is essentially a simplified version of the front plane laminate of U.S. Patent No. 6,982,178. One form of the double release sheet comprises a layer of a solid electro-optic medium sandwiched between two adhesive layers, one or both (typically both) of the adhesive layers being covered by a release sheet. To use such a double release film in the present process, one of the release sheets is removed from the double release film and the remaining layers are laminated to the backplane with the exposed adhesive layer in contact with the backplane. The second release sheet is then removed and in a second lamination an electrically-conductive layer is laminated to backplane/electro-optic layer sub-assembly produced in the first lamination. Alternatively, but generally less desirably, the laminations could be performed in the reverse order, with the first lamination securing the electro-optic layer to the electrically-conductive layer to form an inverted front plane laminate, and the second lamination securing this inverted FPL to the backplane, as described above. Both variants of the process using a double release film allow the electrically-conductive layer and the electro-optic layer to be chosen independently of one another, and this can be very useful from a manufacturing standpoint; a manufacturer may have various customers requiring differing types of electrically-conductive layer but the same electro-optic layer, and to meet customer demands may manufacture a double release film in bulk using the common electro-optic layer, and then laminate the double release film to the chosen electrically-conductive layer when a particular order is received from a customer.

[Para 20] Another variant of this process uses a so-called "inverted front plane laminate", as described in U.S. Patent Publication No. 2007/0109219, which is essentially a variant of the front plane laminate described in U.S. Patent No. 6,982,178. An inverted front plane laminate comprises, in order, at least one of a light-transmissive protective layer and a light- transmissive electrically-conductive layer; an adhesive layer; a layer of a solid electro-optic medium; and a release sheet. This inverted front plane laminate is used to form an electro- optic display having a layer of lamination adhesive between the electro-optic layer and the front electrode or front substrate; a second, typically thin layer of adhesive may or may not be present between the electro-optic layer and a backplane. Such electro-optic displays can combine good resolution with good low temperature performance.

[Para 21 ] In the process of the present invention, the electro-optic sub-assembly may further comprise a front substrate disposed on the opposed side of the electrically-conductive layer from the electro-optic layer, the front substrate providing mechanical support and protection to the electrically-conductive layer. In some cases the presence of such a front substrate is necessary because the electrically-conductive layer is not self-supporting; for example, when the electrically-conductive layer is formed of sputtered ITO, the ITO is typically of the order of 1 μm thick and is not self-supporting. This front substrate may have a thickness not greater than 50 μm, and desirably not greater than 25 μm; the front substrate remains in the final display and if it is too thick, it may give rise to parallax problems between the color filter array of the electro-optic layer. Whether or not a front substrate is present, the electro-optic sub-assembly may comprise a masking film; such a masking film can serve to substantially increase the thickness of the sub-assembly, thus facilitating handling of the sub-assembly, and may also serve to prevent mechanical damage to the electrically-conductive layer and/or front substrate (if present). The masking film is removed before lamination of the color filter array. The masking film may have a thickness of 100-200 μm, although thicker films can be used if desired, for example to protect integrated circuits present on the backplane.. [Para 22] The present process allows a variety of flowable materials to be used, as well as a variety of methods of introducing the flowable material between the electrically-conductive layer and the color filter array. In one variant of the present process, the dispositions of the flowable material and the color filter array over the electrically-conductive layer are effected by disposing a plurality of spacers on the exposed surface of the electro-optic sub-assembly laminated to the backplane, disposing the color filter array on the plurality of spacers, introducing a curable polymer between the exposed surface and the color filter array, and curing the curable polymer. Such a process may further comprise disposing a curable edge seal polymer around the periphery of the electro-optic layer but leaving a plurality of gaps in the edge seal polymer, curing the edge seal polymer to form an edge seal having a plurality of apertures extending therethrough, applying a vacuum to at least one of the apertures while connecting at least one other aperture to a supply of the curable polymer, thereby drawing the curable polymer between the electrically-conductive layer and the color filter array. [Para 23] In another variant of the present process, the flowable material is a curable polymer dispensed on to the electrically-conductive layer, and after the color filter array has been disposed over the curable polymer and aligned, the curable polymer is cured to secure the color filter array to the electrically-conductive layer. In this variant of the process, the curing of the polymer may advantageously be effected in two stages; after the color filter array has been disposed over the curable polymer and aligned, a plurality of discrete portions of the curable polymer are cured, the curable polymer is treated to remove air bubbles therefrom, and the remaining portions of the uncured polymer are cured to produce the final display.

[Para 24] In yet another variant of the present process, the flowable material is an adhesive layer which is non-tacky at room temperature (about 21⁰C). Alternatively, the flowable material may be a non-curable material which remains unchanged in the final display, for example a grease, desirably a silicone grease. When such a non-curable material is used, the process may further comprise, after alignment of the color filter array, dispensing a curable polymer around the periphery of the electro-optic layer and color filter array, and curing this polymer to form an edge seal which secures the electro-optic layer and color filter array to each other.

[Para 25] In any process of the present invention which requires removal of gas bubbles from the flowable material, by autoclaving or any other process, it is necessary to ensure that the color filter array does not move relative to the backplane during the bubble removal process. While mechanical clamping devices could be used to secure the color filter array, in practice it is more convenient to spot cure either the flowable material itself or, if a non- curable flowable material is employed, to spot cure a curable edge seal material to fix the color filter array in position relative to the backplane.

[Para 26] The electro-optic layer used in the present process may be of any of the types discussed above. Thus, for example, the electro-optic layer may comprise a rotating bichromal member or electrochromic material. Alternatively, the electro-optic material may comprise an electrophoretic material comprising a plurality of electrically charged particles disposed in a fluid and capable of moving through the fluid under the influence of an electric field. The electrically charged particles and the fluid may be confined within a plurality of capsules or microcells. Alternatively, the electrically charged particles and the fluid may be present as a plurality of discrete droplets surrounded by a continuous phase comprising a polymeric material. The fluid may be liquid or gaseous.

[Para 27] This invention also provides an electro-optic display comprising, in this order: a backplane comprising a plurality of electrodes; an electro-optic layer; a light-transmissive electrically-conductive layer; a layer of a non-curable, flowable material; and a color filter array.

[Para 28] In such a display, the flowable material may be a grease, for example a silicone grease.

[Para 29] Figure 1 of the accompanying drawings is a schematic cross-section through a front plane laminate useful in the process of the present invention.

[Para 30] Figure 2 is a schematic cross-section, similar to that of Figure 1, through an inverted front plane laminate useful in the process of the present invention. [Para 31 ] Figure 3 is a schematic cross-section, similar to those of Figures 1 and 2, through a modified form of the inverted front plane laminate of Figure 2.

[Para 32] Figure 4 is a top plan view of an electro-optic display being assembled by a process of the present invention, the top plan view being taken at an intermediate point in the process after lamination of a front plane laminate to the backplane but before lamination of a color filter array.

[Para 33] Figure 5 is a flow diagram showing the manner in which the process of the present invention facilitates the manufacture of monochrome and color electro-optic displays using the same front plane laminate and backplane.

[Para 34] As already mentioned, the present invention provides a process for forming an electro-optic display in which a electro-optic layer and an electrically-conductive layer (typically in the form of a front plane laminate) are first laminated to a backplane. Thereafter, a flowable material is deposited over the electrically-conductive layer, and a color filter array (CFA) is placed over the electrically-conductive, these two steps being performed in either order. In some forms of the present process, the flowable material is cured after the CFA is in place; in others, a non-curable material is employed so that the material remains unchanged in the final display. [Para 35] In the present process, the electro-optic layer is desirably provided in the form of a front plant laminate. This FPL may be a "classic" FPL as described in U.S. Patent No. 6,982,178 or an inverted FPL as described in U.S. Patent Application Publication No. 2007/0109219. In either case, it is desirable to make the substrate of the FPL adjacent the CFA thin, in order to minimize parallax and color errors due to the spacing between the CFA and the electro-optic layer. A typical classic FPL (generally designated 100) suitable for use in the present process is shown schematically in Figure 1 of the accompanying drawings. The FPL 100 comprises a thin front substrate 102, which is typically a transparent polymeric film formed, for example of poly(ethylene terephthalate) (PET). This front substrate 102 may have a thickness of about 6 to about 50 μm; films having thickness of about 13 μm are available commercially and are very suitable for use in the present process. The use of a thin front substrate is important since the color filter array (described below) is separated from the electro-optic layer by the thickness of the front substrate (and by the thickness of the electrically-conductive layer described below, but the electrically-conductive layer is typically much thinner than the front substrate), and if the thickness of the front substrate is too large, parallax problems may be encountered, with consequent degradation of the quality of the image on the color display. The FPL 100 further comprises a light-transmissive, electrically-conductive layer 104, which may be formed of, for example, indium tin oxide (ITO), carbon nanotubes, or an organic conductor. The exact nature of the conductive layer is not of primary importance so long as it is sufficiently conductive to switch the electro-optic layer; usually a resistivity of less than 10⁴ ohms/square suffices. ITO-coated PET films are available commercially and may be used to form the layer 102 and 104 of the FPL 100. [Para 36] The next layer of the FPL 100 is the electro-optic layer 106, which in this case is an encapsulated electrophoretic layer comprising capsules in a polymeric binder. As described in the aforementioned U.S. Patent No. 6,982,178, this electro-optic layer may be coated directly on to the conductive layer 104. A layer of lamination adhesive 108 is disposed on the opposed side of the electrophoretic layer 106 from the substrate 102; suitable adhesives are discussed, for example, in U.S. Patents Nos. 7,012,735 and 7,477,444. Finally, the FPL 100 comprises a release sheet 110.

[Para 37] Figure 2 illustrates an inverted front plane laminate 200 which can be used in the present process. The inverted FPL 200 differs from the classic FPL 100 shown in Figure 1 by the inclusion of a second adhesive layer 208 interposed between the conductive layer 104 and the electro-optic layer 106. The reasons for inclusion of this second adhesive layer 208 are discussed in detail in the aforementioned 2007/0109219.

[Para 38] Figure 3 illustrates a second inverted front plane laminate 300 which differs from the inverted FPL 200 shown in Figure 2 by the addition of a masking film 312 covering the substrate 102. As explained in U.S. Patent Application Publication No. 2008/0174853, a masking film can usefully be included in a thin FPL or similar multi-layer film to facilitate handling of the thin film and/or to provide mechanical protection to a substrate during manufacturing or display assembly operations.

[Para 39] The FPL 100 shown in Figure 1 can also be modified by the addition of a masking film similar to that shown in Figure 3.

[Para 40] As already mentioned, the first step in the process of the present invention is lamination of an FPL to a backplane; this backplane may be of the direct drive type (in which each electrode is provided with a separate conductor so that the voltage on each electrode can be controlled independently) or of an active matrix type (in which pixel electrodes are arranged in a two-dimensional matrix of rows and columns, with a non-linear device, typically a thin film transistor, associated with each pixel, and with all of the electrodes in each row being connected to a row electrode and all of the electrodes in each column being connected to a column electrode). Some forms of electro-optic medium may also permit the use of a passive matrix backplane.

[Para 41 ] Figure 4 is a top plan view of a preferred process of the present invention after lamination of an FPL 402 (which may be of any of the types described above) to a backplane (generally designated 404). As shown in Figure 4, the backplane 404 comprises a substrate 406, the central part of which is occupied by an active matrix backplane 408; the FPL 402 is laminated on to this active matrix backplane 408 so that a small peripheral portion of the FPL 402 extends beyond the edges of the backplane 408. Alignment marks 410 are provided on the substrate 406 adjacent the area occupied by the FPL 402. Chip bonding areas 412 are also provided on the substrate 406 at points spaced from the backplane 408. [Para 42] The lamination of the FPL 402 to the backplane 408 may be effected by any of the methods described in the aforementioned E Ink patents and applications. Basically, the release sheet 110 (see Figures 1-3) is peeled from the FPL, and the FPL is laminated to the backplane, typically at elevated temperature and pressure. Once the FPL has been so laminated to produce an intermediate structure as shown in Figure 4, a color filter array is attached using the first process of the present invention. [Para 43] As already mentioned, this process requires introduction of a flowable liquid material between the FPL and a color filter array. Within the scope of the present invention, various methods may be used to introduce the flowable liquid material. One method is similar to that used to assembly liquid crystal displays. A mixture of spacers (typically spheres of closely controlled diameter) and a curable polymer is dispensed around the periphery of the FPL to form a peripheral seal, but multiple gaps are left in this seal. The CFA is then placed on to the mixture of spacers and polymer. Typically, accurate location of the CFA relative to the backplane is effected by aligning alignment marks on the CFA with similar marks on the backplane; the uncured polymer permits movement of the CFA relative to the backplane. The polymer is then cured to fix the CFA relative to the backplane. One or more of the apertures in the peripheral seal produced by the aforementioned gaps is connected to a vacuum, while the other apertures are connected to a supply of low viscosity curable polymer, which is drawn by the vacuum between the FPL and the CFA. Finally, the low viscosity curable polymer is cured to form the final display. In some cases, it may be advantageous to lay down a narrow perimeter of a (typically) different curable polymer around the periphery of the FPL after the FPL has been laminated to the backplane, this different curable polymer being chosen to avoid switching performance issues at the edges of the display. The narrow perimeter of polymer also seals the FPL, thus preventing loss of moisture and/or entry of environmental contaminants when the FPL is exposed to vacuum during the filling process. A similar peripheral seal of the FPL can be used in other variants of the present process described below.

[Para 44] In one such variant of the present process, a curable polymer is dispensed on top of the FPL after the FPL has been laminated to the backplane. The pattern in which the curable polymer is dispensed should be chosen to minimize trapping of air between the FPL and the CFA to be placed over the FPL; for example, this pattern could take the form of a single puddle in the center of the FPL, a pattern of lines radiating from the center of the FPL, or a "X" shape. The CFA is then brought down on to the curable polymer and pressed lightly downwards to cause the curable polymer to spread and set the entire area of the facing FPL and CFA surfaces. The volume of curable polymer placed on the FPL should be carefully controlled so that the entire area of the facing FPL and CFA surfaces is covered, but there is no excessive leaking of curable polymer past the edges of the CFA. At this point, the CFA can be aligned using alignment marks such as those shown in Figure 4, and a number of small areas of the curable polymer adjacent the periphery of the FPL are cured to lock the CFA in place relative to the backplane. Any gas bubbles remaining in the polymer can then be removed by autoclaving or any other known technique. After elimination of the gas bubbles, the remaining areas of uncured polymer are cured to produce the final display. [Para 45] In another variant of the present process, a "solid", non-tacky adhesive is used to adhere the CFA to the FPL (by "non-tacky" is meant non-tacky at room temperature, or about 21⁰C. This adhesive may be placed on the FPL or on the CFA, and the adhesive layer may conveniently be coated on to a release sheet and laminated to the FPL or CFA immediately prior to attachment of the other part. It is desirable that a pattern or some form of roughness be formed into the adhesive to allow air to escape during the lamination of the FPL to the CFA. The non-tacky adhesive allows for relative movement between the FPL and the CFA sufficient for alignment of the two integers prior to lamination of the two using any one or more of elevated temperature, pressure and vacuum. In some cases, the laminated CFA/FPL combination may be reheated after lamination sufficiently to enable final alignment of the two parts to be effected.

[Para 46] In another variant of the present process, a pressure sensitive adhesive (PSA) that is tacky at room temperature may be used as the flowable material. The use of such a PSA avoids the need for processing at elevated temperatures with consequent risk of distortion of certain display components but does have the disadvantage of providing only limited movement of the color filter array relative to the backplane once these parts come into contact with each other.

[Para 47] In another variant of the present process, a film of grease is used to couple the FPL to the CFA. Appropriate greases include the silicone greases described in U.S. Patents Nos. 5,275,680 and 5,371,619. Such greases are chemically inert, have stable properties over a wide temperature range, have a long working life at room temperature and show low void formation during the lamination process. The grease film may be coated directed on to either the FPL or the CFA, or a pre-formed grease film (for example, coated on a release sheet) may be laminated to one or other of these parts. The parts can then be brought together and aligned accurately. Any air bubbles trapped in the grease can be eliminated by autoclaving, which is especially effective with a grease film because of the viscosity and flowability of the grease. Since the grease remains flowable even in the completed display, it is desirable, as a final step in the assembly of the display, to dispense a curable polymer around the periphery of the FPL and CFA and cure this polymer to form an edge seal which secures the FPL and CFA in the correct positions relative to each other. As already noted, such a curable polymer edge seal may usefully be spot cured to hold the color filter array fixed relative to the backplane during operations for removing bubbles from the grease.

[Para 48] As already mentioned, the present invention decouples the lamination of the electro-optic layer (typically in the form of an FPL) to the backplane from the lamination of the CFA to the electro-optic layer. This has the further advantage of providing a convenient route to manufacture of both monochrome and color displays on a single production line, as illustrated in Figure 5. As shown in that Figure, such a production line may be operated to take a supply of FPL 502 and a supplies of backplanes 504, and laminate them together (as represented at 506) to produce backplane/FPL laminates. These laminates can then be laminated to CFA to form color displays, as represented at 508, or a protective layer can be laminated over the FPL to form monochrome displays, as indicated at 510. [Para 49] In summary, the present invention provides an improved white state of a color display with only minor impact on the saturation of basic colors, provides balanced rendering of color and better apparent saturation, and can provide energy savings when front or back lighting is used.

Claims

1. A process for producing a color electro-optic display, the process comprising: providing an electro-optic sub-assembly (100; 200; 300; 402) comprising an electro-optic layer (106) and a light-transmissive electrically-conductive layer (104); laminating the electro-optic sub-assembly (100; 200; 300; 402) to a backplane (404, 408) comprising a plurality of electrodes such that the electro-optic layer (106) is disposed between the backplane (404, 408) and the electrically-conductive layer (104); and disposing a color filter array over the electrically-conductive layer (104) and aligning the color filter array with the electrodes of the backplane (404, 408) to form the color electro-optic display, the process being characterized in that, after the lamination of the electro-optic sub-assembly (100; 200; 300; 402) to the backplane (404, 408) but before disposition of the color filter array over the electrically -conductive layer (104), a flowable material is disposed over the electrically-conductive layer (106).

2. A process according to claim 1 wherein the electro-optic sub-assembly (402) has the form of a front plane laminate (100) comprising the electrically -conductive layer (104), the electro-optic layer (106) and an adhesive layer (108) disposed on the opposed side of the electro-optic layer (106) from the electrically-conductive layer (104), and the lamination is effected by contacting the adhesive layer (108) with the backplane (404, 408).

3. A process according to claim 2 wherein the front plane laminate (100) further comprises a release sheet (110) covering the surface of the adhesive layer (108) remote from the electro-optic layer (106), and this release sheet (110) is removed before the lamination of the front plane laminate (100) to the backplane(404,408).

4. A process according to claim 1 wherein the electro-optic sub-assembly (402) has the form of an inverted front plane laminate (200) comprising, in this order, the electrically-conductive layer (104), a first adhesive layer (208), the electro-optic layer (106), and a second adhesive layer (108), and the lamination is effected by contacting the second adhesive layer (108) with the backplane (404, 408).

5. A process according to claim 4 wherein the inverted front plane laminate (200) further comprises a release sheet (110) covering the surface of the second adhesive layer (108) remote from the electro-optic layer (106), and this release sheet (110) is removed before the lamination of the inverted front plane laminate (200) to the backplane (404, 408).

6. A process according to claim 1 wherein the electro-optic sub-assembly (100; 200; 300; 402) further comprises a front substrate (102) disposed on the opposed side of the electrically-conductive layer (104) from the electro-optic layer (106), the front substrate (102) providing mechanical support and protection to the electrically-conductive layer (104).

7. A process according to claim 1 wherein the electro-optic sub-assembly (300) further comprises a masking film (312) disposed on the opposed side of the electrically- conductive layer (104) from the electro-optic layer (106), the masking film (312) being removed from the sub-assembly (300) before the color filter array is laminated thereto.

8. A process according to claim 1 wherein the dispositions of the flowable material and the color filter array over the electrically-conductive layer (104) are effected by disposing a plurality of spacers on the electrically -conductive layer (104), disposing the color filter array on the plurality of spacers, introducing a curable polymer between the electrically-conductive layer (104) and the color filter array, and curing the curable polymer.

9. A process according to claim 8 further comprising disposing a curable edge seal polymer around the periphery of the electro-optic layer but leaving a plurality of gaps in the edge seal polymer, curing the edge seal polymer to form an edge seal having a plurality of apertures extending therethrough, applying a vacuum to at least one of the apertures while connecting at least one other aperture to a supply of the curable polymer, thereby drawing the curable polymer between the electrically-conductive layer (104) and the color filter array.

10. A process according to claim 1 wherein the flowable material is a curable polymer dispensed on to the electrically -conductive layer (104) and, after the color filter array has been disposed over the curable polymer and aligned, the curable polymer is cured to secure the color filter array to the electrically-conductive layer (104).

11. A process according to claim 10 wherein, after the color filter array has been disposed over the curable polymer and aligned, a plurality of discrete portions of the curable polymer are cured, the curable polymer is treated to remove air bubbles therefrom, and the remaining portions of the uncured polymer are cured to produce the final display.

12. A process according to claim 1 wherein the flowable material is a non- curable material which remains unchanged in the final display.

13. A process according to claim 12 wherein the non-curable material is a grease.

14. A process according to claim 13 wherein the grease is a silicone grease.

15. A process according to claim 12 further comprising, after alignment of the color filter array, dispensing a curable polymer around the periphery of the electro-optic layer (106) and color filter array, and curing this polymer to form an edge seal which secures the electro-optic layer (106) and color filter array to each other.

16. A process according to claim 1 wherein the electro-optic material comprises a rotating bichromal member or electrochromic material.

17. A process according to claim 1 wherein the electro-optic material comprises an electrophoretic material comprising a plurality of electrically charged particles disposed in a fluid and capable of moving through the fluid under the influence of an electric field.

18. A process according to claim 17 wherein the fluid is gaseous.

19. An electro-optic display comprising, in this order: a backplane (404, 408) comprising a plurality of electrodes; an electro-optic layer (106); a light-transmissive electrically-conductive layer (104); a layer of a non-curable, flowable material; and a color filter array.