WO2009151675A2

WO2009151675A2 - Electro-optic displays

Info

Publication number: WO2009151675A2
Application number: PCT/US2009/036756
Authority: WO
Inventors: Jr. Richard J. Paolini; Michael D. Mccreary
Original assignee: E Ink Corporation
Priority date: 2008-03-11
Filing date: 2009-03-11
Publication date: 2009-12-17
Also published as: US20150338717A1; CN101981496A; WO2009151675A3; US9152004B2; US20120182599A1; HK1149959A1; KR20100121659A; KR101304027B1; CN101981496B; US20080218839A1; US8177942B2

Abstract

An electro-optic display, intended for writing with a stylus or similar instrument, is produced by forming a layer of an electro-optic material on an electrode; depositing a substantially solvent-free polymerizable liquid material over the electro-optic material; and polymerizing the polymerizable liquid material.

Description

ELECTRO-OPTIC DISPLAYS

[Para 1 ] This application is related to:

(a) U.S. Patent No. 7,349,148;

(b) U.S. Patent No. 7,173,752;

(c) U.S. Patent No. 6,831,769;

(d) U.S. Patent Application Publication No. 2005/0122563;

(e) U.S. Patent No. 7,012,735; and

(f) U.S. Patent No. 7,110,164.

[Para 2] The entire contents of the aforementioned applications are herein incorporated by reference. The entire contents of all United States Patents and published and copending Applications mentioned below are also herein incorporated by reference.

[Para 3] The present invention relates to electro-optic displays. More specifically, this invention relates to processes for the production of stylus-based and similar electro-optic displays. The present invention is especially, though not exclusively, intended for use in displays containing encapsulated electrophoretic media.

[Para 4] 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 5] 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. Some electro-optic materials are solid in the sense that the materials have solid external surfaces, although the materials may, and often do, have internal liquid- or gas-filled spaces. Such displays using solid electro-optic materials may hereinafter for convenience be referred to as "solid electro-optic displays". Thus, the term "solid electro-optic displays" includes rotating bichromal member displays, encapsulated electrophoretic displays, microcell electrophoretic displays and encapsulated liquid crystal displays.

Page l of 16 [Para 6] 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 7] 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 Electro wetting", 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 8] 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 9] 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; electrophoretic deposition (See U.S. Patent No. 7,339,715); 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 1 0] The manufacture of a three-layer electro-optic display normally involves at least one lamination operation. For example, in several of the aforementioned MIT and E Ink patents and applications, there is described a process for manufacturing an encapsulated electrophoretic display in which an encapsulated electrophoretic medium comprising capsules in a binder is coated on to a flexible substrate comprising indium-tin-oxide (ITO) or a similar conductive coating (which acts as an one electrode of the final display) on a plastic film, the capsules/binder coating being dried to form a coherent layer of the electrophoretic medium firmly adhered to the substrate. Separately, a backplane, containing an array of pixel electrodes and an appropriate arrangement of conductors to connect the pixel electrodes to drive circuitry, is prepared. To form the final display, the substrate having the capsule/binder layer thereon is laminated to the backplane using a lamination adhesive. A very similar process can be used to prepare an electrophoretic display usable with a stylus or similar movable electrode by replacing the backplane with a simple protective layer, such as a plastic film, over which the stylus or other movable electrode can slide. In one preferred form of such a process, the backplane is itself flexible and is prepared by printing the pixel electrodes and conductors on a plastic film or other flexible substrate. The obvious lamination technique for mass production of displays by this process is roll lamination using a lamination adhesive. Similar manufacturing techniques can be used with other types of electro-optic displays. For example, a microcell electrophoretic medium or a rotating bichromal member medium may be laminated to a backplane in substantially the same manner as an encapsulated electrophoretic medium.

[Para 1 1 ] The present invention relates to so-called "stylus-based displays". As discussed above, most electro-optic displays are constructed with fixed electrodes on both sides of the electro-optic medium. However, it is known (see, for example, the aforementioned U.S. Patent No. 6,473,072) that electro-optic displays can be constructed with a fixed electrode on only one side of the electro-optic medium, typically on the side opposite the viewing surface of the display. The other electrode needed to provide an electric field across the electro-optic medium has the form of a stylus, printhead or similar movable device which can be moved, either manually or mechanically, relative to the electro-optic medium. (The term "stylus-based displays" is used herein in a broad sense to cover all displays having such a movable electrode regardless of the exact nature of the movable electrode, and the term "stylus" is used to refer to all such movable electrodes.) Such stylus-based displays are useful, inter alia, for capturing hand-written material, including signatures, since a user can manipulate a movable electrode in a manner similar to a pen and "write" on the viewing surface of the display. [Para 1 2] One problem in producing stylus-based displays is providing a suitable layer between the electro-optic medium and the stylus. Many electro-optic media are susceptible to mechanical damage, and given the heavy-handed manner in which some users tend to handle a stylus when writing on an electro-optic display, it is necessary to provide, between the electro-optic medium and the stylus, a protective layer sufficiently thick and robust to protect the electro-optic medium from mechanical damage. However, since such a protective layer lies between the electrodes of the display, there is a voltage drop across the protective layer which, for any given operating voltage applied between the electrodes, reduces the voltage across the electro-optic medium itself, and hence reduces the electro-optic performance of this medium. Although it might appear that the voltage drop across the protective layer could be minimized by using a highly conductive protective layer, the resistance of the protective layer needs to be large enough to prevent lateral flow of current (i.e., flow of current in the plane of the protective layer) through the protective layer, since such lateral flow of current causes changes in the optical state of the electro-optic medium over areas substantially wider than the width of the stylus, and thus in effect "smears" the line produced by moving the stylus over the protective layer.

[Para 1 3] The voltage drop across the protective layer can require a substantial increase in the operating voltage of the display to provide satisfactory electro-optic performance. For example, encapsulated electrophoretic media sold commercially by E Ink Corporation operate at 15 V, when used in displays with two set of fixed electrodes such that only the electro-optic medium and a (relatively thin) lamination adhesive layer is present between the electrodes. To use such electrophoretic media in stylus-based displays, it has hitherto been deemed necessary to use polymer sheets such as Pomalux SD-A (a static-dissipative acetal copolymer manufactured by Westlake Plastics Co., P.O. Box 127, Lenni PA 19052-0127) in thicknesses of 5-10 mil (127-254 μm). These polymer sheets are stiff, and increase the required operating voltage of the display to 100-200 V. Such high operating voltages are disadvantageous in that they are often perceived by users as unsafe (although in fact, the very low currents required by electrophoretic displays allow such voltages to be used with complete safety). More importantly, one major application for stylus-based displays is electronic notebooks, which need to be highly portable and battery powered. Producing an operating voltage of 100-200 V from batteries requires complex and relatively expensive power supply circuitry, and the high voltages uses so much power that battery life is undesirably short. Also, the thickness of the protective layer reduces the maximum resolution of the display, because there is inevitably some lateral flow of current within the protective layer, so that lines written by a stylus are inevitably widened by some fraction of the thickness of the protective layer.

[Para 1 4] Accordingly, there is a need for a protective sheet for stylus-based electro-optic displays which can provide adequate protection to the electro-optic medium while reducing the operating voltage needed, and the present invention seeks to provide such a protective layer.

[Para 1 5] SUMMARY OF THE INVENTION

[Para 1 6] This invention provides a process for the preparation of an electro-optic display, the process comprising: forming a layer of an electro-optic material on an electrode; depositing a layer of a substantially solvent-free polymerizable liquid material over the layer of electro-optic material; and exposing the polymerizable liquid material to conditions effective to cause polymerization of the material, thereby forming a polymeric layer overlying the layer of electro- optic material.

[Para 1 7] The display thus produced is intended to be written with a stylus (as that term is broadly defined above). In such a process, the polymerizable liquid material may be thermally curable and the conditions effective to cause polymerization of the material may comprise heating the liquid material to a temperature high enough to cure the material. Alternatively, the polymerizable liquid material may be radiation curable and the conditions effective to cause polymerization of the material may comprise exposing the liquid material to radiation of a wavelength effective to cure the material; those skilled in the technology of solvent-free polymerizable liquid materials will be aware that typically the polymerizing radiation is in the ultra-violet. The polymerizable liquid material may comprise an acrylate or a urethane acrylate blend or a silicone.

[Para 1 8] The process may comprise controlling the thickness of the layer of polymerizable liquid material deposited on the layer of electro-optic material. The thickness of the layer of polymerizable liquid material may be controlled by doctor blade or die coating. Alternatively, the thickness of the layer of polymerizable liquid material may be controlled by contacting the layer of liquid material with a release sheet and passing a nip roller over the release sheet prior to polymerizing the liquid material.

[Para 1 9] For reasons already explained, it is desirable to keep the thickness of the final polymeric layer as small as possible, consistent with good protection for the electro-optic material. Accordingly, the thickness of the polymeric layer may be from about 6 to about 250 μm, and preferably from about 8 to about 50 μm. In some cases, the layer of electro-optic material formed on the electrode has a non-planar exposed surface and the final polymeric layer planarizes the layer of electro-optic material so that the exposed surface of the final polymeric layer is substantially planar.

[Para 20] The electro-optic material used in the present process may be of any of the types discussed above. Thus, for example, the electro-optic material 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 electrophoretic material may be of the polymer- dispersed type, with the electrically charged particles and the fluid present as a plurality of discrete droplets surrounded by a continuous phase comprising a polymeric material. The fluid may be liquid or gaseous.

[Para 21 ] This invention also provides an electro-optic display capable of being imaged by a stylus, the display comprising: an electrode; a layer of an electro-optic material disposed on the electrode; and a polymeric layer overlying the layer of electro-optic material, the polymeric layer comprising the polymerization product of a substantially solvent-free polymerizable liquid material.

[Para 22] BRIEF DESCRIPTION OF THE DRAWINGS

[Para 23] Figure 1 of the accompanying drawings is a schematic side elevation showing application of a polymerizable liquid material to an electro-optic material in a process for forming an electro-optic display of the present invention.

[Para 24] Figure 2 is a schematic side elevation similar to Figure 1 but showing the use of release sheet and a roller to form a uniform layer of the polymerizable liquid material. [Para 25] DETAILED DESCRIPTION

[Para 26] As discussed above, the present invention relates to the use of substantially solvent- free polymerizable liquid materials (so-called "100% solids" monomers or oligomers) to form a protective layer over a layer of electro-optic material, this protective layer serving to prevent mechanical damage to the electro-optic material when a stylus or similar instrument is used to write on the display. It has been found that the use of substantially solvent-free polymerizable liquid materials to form such protective layers alleviates or eliminates the problems discussed above with regard to stylus-based displays; in particular, the use of these polymerizable liquid materials allows for the formation of thin but tough protective layers which provide adequate mechanical protection to commercial electro-optic materials but are sufficiently thin that the operating voltage of the display can be substantially reduced as compared with prior art stylus- based displays using conventional protective layers. In practice, it has been found that the operating voltage of displays of the present invention can be 80-90 per cent lower than those of prior art displays. The thinner protective layers also allow higher resolution addressing of the display and enable the manufacture of stylus-based flexible displays.

[Para 27] The stylus-based displays of the present invention can be formed by coating or laminating a layer of an electro-optic material directly on to a conductive electrode. (In many cases, especially where the electrode needs to be light-transmissive, the electrode typically needs to be mechanically supported on a substrate, typically a polymeric film; however, such substrates will not be discussed in detail herein since appropriate substrates are well known to those skilled in the technology of electro-optic displays, and are discussed in, for example, the aforementioned U.S. Patent No. 6,982,178.) The polymerizable liquid material may be used to form either the viewing or the non- viewing surface of the display, more commonly the former. Obviously, if the polymerizable liquid material is to form the viewing surface of the display, the polymeric layer formed by polymerization of the liquid material must be light-transmissive, and in this case the electrode on which the layer of electro-optic material is formed may be opaque and can be formed from an inexpensive conductor such as metallized poly(ethylene terephthalate) (PET) or an aluminum or other metal foil. However, if the electrode on which the layer of electro-optic material is formed will comprise the viewing surface of the display, this electrode needs to be light-transmissive, and may be formed for example of indium tin oxide (ITO), CNT, or a conductive polymer such as polythiophene. [Para 28] The polymerizable liquid materials used in this process of the present invention are known in several industries as "hard coat materials" and are used, for example, as optical adhesives, to provide hard surfaces on wooden flooring, and as scratch resistant coatings on spectacles and other optical devices. The polymerizable liquid materials comprise a radiation or thermally curable monomer or oligomer, typically an acrylate, urethane acrylate blend or a silicone. The presently preferred liquid materials are optical adhesives manufactured by Norland Products, 2540 Route 130, Suite 100, P.O. Box 637, Cranbury NJ 08512, especially those sold under the trade names NOA 63, NOA 71, and NOA 81. The polymerizable liquid materials are relatively low viscosity liquids which can flow to produce thin layers of liquid overlying the electro-optic material. Typically, the polymeric layer which is produced after polymerization of the liquid will have a thickness in the range of from about 6 to 250 μm, desirably in the range of from 8 to 50 μm.

[Para 29] One important property of the polymerizable liquid material is the conductivity of the layer formed after polymerization; the polymerized layer should not be too conductive or display resolution will be lost. Empirically, it has been found that loss of resolution seems to become significant in the range of surface conductivity 5 x 10⁵ ohm/sq.

[Para 30] The thickness of the layer of polymerizable liquid material, and hence of the final polymeric layer can be controlled by several techniques which are familiar to those skilled in liquid coating. For example, Figure 1 of the accompanying drawings illustrates, in a highly schematic manner, a conductive electrode 102 on which has been deposited an electrophoretic layer comprising capsules 104 disposed in a binder 106. A polymerizable liquid material 108 is being dispensed (for example, by means of a die or slot coater) over the electrophoretic layer, and the thickness of the liquid material 108 is controlled by a doctor blade 110. It should be noted that, since the capsules 104 protrude upwardly from the binder 106, the upper surface (as illustrated in Figure 1) of the electrophoretic layer is non-planar, but that the provision of the liquid material 108 enables the final surface of the polymeric protective layer to be planar. (Although Figure 1 suggests that the thickness of the layer of polymerizable liquid material may approach zero over the centers of the capsules 104, in practice this is undesirable and at least a minimal thickness of protective layer should be present over the entire electrophoretic layer.) [Para 31 ] Figure 2 illustrates, in a highly schematic manner, an alternative process of the invention. The conductive electrode 102, the capsules 104 and the binder 106 in this second process are identical to those shown in Figure 1. Again a polymerizable liquid material 108 is being dispensed over the electrophoretic layer. However, no doctor blade is employed; instead, a release sheet 212 is applied over the liquid material 108 and the entire assembly is passed between nip rollers 214 and 216 to control the thickness of the liquid material 108. [Para 32] Although Figure 2 suggests that the assembly passes horizontally through the nip rollers, in large scale roll-to-roll production it may be more convenient for the assembly to travel vertically downwardly through the nip rollers, with the polymerizable liquid material being dispensed continuously between the electrophoretic medium and the release sheet 212. [Para 33] When a release sheet is employed to control the thickness of the liquid material 108, the release sheet may be removed immediately after curing of the liquid material, or it may be left in place until a later time to provide mechanical protection to the polymeric layer formed by curing the liquid material.

[Para 34] In the present process, it is not essential that the sheet used to control the thickness of the liquid layer be a release sheet, nor is it necessary that this sheet be flexible. Furthermore, it is not essential that the sheet be removed from the polymeric layer formed by curing the liquid material. For example, the sheet, whether rigid or flexible, could comprise a transparent sheet which acts as a protective layer in the final display. Alternatively, the sheet could comprise an electrically-conductive layer, which can remain permanently attached to the final display by the polymer layer. Typically, such an electrically-conductive layer will form the common front electrode of the final display, and in such a case, the electrically-conductive layer should be light-transmissive so that the change in optical state of the electro-optic medium can be seen through the electrically-conductive layer.

[Para 35] The sheet used to control the thickness of the liquid layer can also have the form of a color filter array (typically with an electrically-conductive layer to form the common front electrode of the final display), which can be flexible or rigid. Such a color filter array needs to be aligned with the pixels of the electrode on the opposed side of the electro-optic medium. If the color filter array is rigid (for example, a glass color filter array), the color filter array may be placed on the polymerizable liquid material and coarsely aligned with the pixels. The color filter array may then be pressed or rolled, and one portion of the color filter array finely aligned with the pixels using a color filter array alignment tool or fixture. Following the fine alignment, a small area of the polymerizable liquid material is spot cured to fix the color filter array in position relative to the other components of the display. The display may be treated to remove any trapped gas (see below) before the remaining parts of the polymerizable liquid material are cured.

[Para 36] A flexible color filter array may be attached in a very similar manner except that to avoid misalignments due to distortion of the flexible color filter array, the steps of fine alignment of the color filter array and subsequent spot curing will typically need to be repeated multiple times on different areas of the display until all areas of the display are properly finely aligned. [Para 37] In most cases where the sheet used to control the thickness of the liquid layer is to remain as a permanent part of the display, it is difficult to avoid trapping some air bubbles underneath the sheet. Techniques for removing such trapped air bubbles are known in the art (for example autoclaving the display, or placing the display under vacuum) and any of the known techniques may be used in the present process. As noted above, if the sheet is a color filter array or similar sheet which needs to be aligned with the remaining parts of the display, spot curing of the polymerizable liquid material should be effected before the bubble removal process in order to ensure that the alignment of the sheet is preserved during bubble removal. In other cases, for example when the sheet simply comprises an electrically-conductive layer and (optionally) a support for the electrically-conductive layer, no fine alignment is required, and bubble removal can be carried out without previous spot curing of the polymerizable liquid material. [Para 38] The following Example is now given, though by way of illustration only, to show details of a presently preferred process of the invention. [Para 39] Example

[Para 40] A capsule/binder slurry was slot coated on to the ITO-covered surface of a poly(ethylene terephthalate)/ITO film substantially as described in the aforementioned U.S. Patent No. 6,982,178, and the resultant coated film dried to produce a coherent layer of capsules in binder on the PET/ITO film. Separately, a thin metal sheet approximately 24 inches (61 cm) square was covered with a plastic release sheet, arranged to that the release layer was exposed. A 12 inch (30 cm) square of the dried capsule-coated film was placed centrally on top of the release sheet, with the capsule layer exposed. A bead of Norland optical adhesive (NOA 63, NOA 71, or NOA 81) was placed 13 mm from one edge of the capsule-coated film, this bead extending to within about 13 mm of each side edge of the film to minimize the amount of the optical adhesive squeezing from the display during later steps of the process. A second release sheet was then placed over the capsule-coated film bearing the optical adhesive, the second release sheet being placed with its release layer facing the capsule-coated film, and being of a size such that it extended at least 2 inches (51 mm) beyond the edge of the capsule-coated film all around the periphery of the film to minimize contamination of laminator rollers during the subsequent lamination.

[Para 41 ] The entire stack of metal plate, capsule-coated film and two release sheets was then positioned in a roll laminator with the rolls open, the stack being positioned such that the rolls would close on the release sheet clear of the capsule-coated film. The stack was then passed through the roll laminator at room temperature and 50 psig (about 0.48 MPa) at a speed of 0.5 ft/min (about 2.5 mm/sec) using 6 inch (152 mm) rollers medium durometer silicone rollers. This pass through the laminator caused the optical adhesive to spread out in a thin layer over the who of the capsule-coated film, in the process planarizing the original rough surface of the film. The stack was then passed twice at a speed of 20 feet/min (about 100 cm/sec) under a 150 W/inch (6 W/mm) ultraviolet lamp to partially cure the optical adhesive. The top release sheet was then removed, and the remaining layers passed twice under the same conditions beneath the ultraviolet lamp to complete the curing of the optical adhesive. Thereafter, the complete PET/ITO/capsule-binder layer/optical adhesive display can be removed from the metal plate and adjacent release sheet and cut to the size needed. It will be appreciated that the process as described in this Example is a small-scale laboratory method and that other techniques, especially roll-to-roll techniques may be more appropriate for mass production. [Para 42] The use of polymerizable liquid materials which can be cured to a hard, tough finish, in accordance with preferred embodiments of the present invention, allows for the use of a very thin, non-conductive protective layer having a smooth finish and giving good mechanical protection to an electro-optic layer. Radiation curing allows for fast line speeds and economical roll-to-roll production methods.

Claims

1. A process for the preparation of an electro-optic display, the process comprising: forming a layer of an electro-optic material (104, 106) on an electrode (102); depositing a layer of a substantially solvent-free polymerizable liquid material (108) over the layer of electro-optic material (104, 106); and exposing the polymerizable liquid material (108) to conditions effective to cause polymerization of the material, thereby forming a polymeric layer overlying the layer of electro- optic material (104, 106).

2. A process according to claim 1 wherein the polymerizable liquid material (108) is thermally curable and the conditions effective to cause polymerization of the material comprise heating the liquid material to a temperature high enough to cure the material.

3. A process according to claim 1 wherein the polymerizable liquid material (108) is radiation curable and the conditions effective to cause polymerization of the material comprise exposing the liquid material to radiation of a wavelength effective to cure the material.

4. A process according to claim 1 wherein the polymerizable liquid material (108) comprises an acrylate or a urethane acrylate blend or a silicone.

5. A process according to claim 1 further comprising controlling the thickness of the layer of polymerizable liquid material (108) deposited on the layer of electro- optic material (104, 106).

6. A process according to claim 5 wherein the thickness of the layer of polymerizable liquid material is controlled by a doctor blade (110) or die coating.

7. A process according to claim 5 wherein the thickness of the layer of polymerizable liquid material is controlled by contacting the layer of liquid material (108) with a sheet (212) and passing a nip roller (214) over the release sheet (212) prior to polymerizing the liquid material (108).

8. A process according to claim 7 wherein the sheet is a release sheet which is removed from the final display.

9. A process according to claim 7 wherein the sheet comprises an electrically-conductive layer which remains as a permanent part of the final display.

10. A process according to claim 7 wherein the sheet comprises a color filter array which remains as a permanent part of the final display.

11. A process according to claim 1 wherein the thickness of the final polymeric layer is from 6 to 250 μm.

12. A process according to claim 11 wherein the thickness of the final polymeric layer is from 8 to 50 μm.

13. A process according to claim 1 wherein the layer of electro-optic material (104, 106) formed on the electrode (102) has a non-planar exposed surface and the final polymeric layer planarizes the layer of electro-optic material (104, 106) so that the exposed surface of the final polymeric layer is substantially planar.

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

15. 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.

16. A process according to claim 15 wherein the electrically charged particles and the fluid are confined within a plurality of capsules or microcells.

17. A process according to claim 15 wherein the electrically charged particles and the fluid are present as a plurality of discrete droplets surrounded by a continuous phase comprising a polymeric material.

18. A process according to claim 15 wherein the fluid is gaseous.

19. An electro-optic display capable of being imaged by a stylus, the display comprising: an electrode (102); a layer of an electro-optic material (104, 106) disposed on the electrode (102); and a polymeric layer overlying the layer of electro-optic material (104, 106), the polymeric layer comprising the polymerization product of a substantially solvent-free polymerizable liquid material (108).