HK1142415A - Methods for production of electro-optic displays - Google Patents

Description

Method for manufacturing electro-optic display

This application is a divisional application of the chinese patent application entitled "method for manufacturing an electro-optic display" filed on 8/3/2007 under application number 200780001181.

Technical Field

The present invention relates to international application publication nos. WO2003/104884, WO 2004/023195, WO2005/041160 and WO2005/073777, and international application nos. PCT/US2006/60049 and PCT/US 2006/62399. The reader of these international applications is referred to for background information on the present invention.

Background

The present invention relates to methods for manufacturing electro-optic displays, to components used in the methods, and to displays manufactured using these methods and components. The invention is particularly, but not exclusively, intended for use with displays comprising encapsulated electrophoretic media. However, the invention can also be used with other different types of solid electro-optic media, solid in the sense that it has a solid outer surface, although the media can and typically does have an interior space containing a fluid (liquid or gas). Accordingly, the term "solid state electro-optic display" includes encapsulated electrophoretic displays, encapsulated liquid crystal displays, and other types of displays described below.

An electro-optic display comprises a layer of electro-optic material, the term electro-optic material being taken in its conventional sense in the art of imaging and referring to a material having first and second display states which differ in at least one optical property, the material being caused to transition from the first to the second display state by the application of an electric field to the material. Although this optical property is typically a color that is perceptible to the human eye, other optical properties are possible, such as optical transmission, reflectance, luminescence, or, in the case of displays for machine reading, pseudo-color in the sense of a change in reflectance of electromagnetic wavelengths outside the visible range.

The terms "bistable" and "bistability" are used herein in their conventional sense in the art to refer to displays comprising display elements having first and second display states differing in at least one optical property such that, after any given element is driven to assume its first or second display state by an addressing pulse of finite duration, that state will last for at least several times, for example at least four times, the minimum duration of the addressing pulse required to change the state of that display element after the addressing pulse has terminated. Shown in international application publication No. wo 02/079869: some particle-based electrophoretic displays capable of displaying gray levels are stable not only in their extreme black and white states, but also in their intermediate gray states, as are some other types of electro-optic displays. This type of display is properly referred to as "multi-stable" rather than bi-stable, but the term "bi-stable" as used herein covers both bi-and multi-stable displays for convenience.

Various types of electro-optic displays are known. One type of electro-optic display is the rotating bichromal member type (although this type of display is often referred to as a "rotating bichromal ball" display, the term "rotating bichromal member" is more accurate since the rotating member is not spherical in some of the above patents), such as disclosed in U.S. patent 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. Such displays use a large number of small bodies (typically spherical or cylindrical) having two or more portions with different optical properties and an internal dipole. These bodies are suspended in liquid-filled vacuoles in a matrix, which vacuoles are filled with liquid so that the bodies can rotate freely. An electric field is applied to the display, thereby rotating the bodies to various positions and changing the location of those bodies as seen through the viewing surface, thereby changing the appearance of the display. This type of electro-optic medium is typically bistable.

Another type of electro-optic display uses an electrochromic medium, such as in the form of a color-changing film (nanochromic film), which includes an electrode formed at least in part of a semiconducting metal oxide and a plurality of reversibly color-changeable dye molecules attached to the electrode. See, e.g., O' Regan, b. et al, Nature, 1991, 353, 737; wood, d., in InformationDisplay, 18, (3), 24 (3.2002), and see Bach, u.et al, in adv.mater.2002, 14(11), 845. Color-changing films of this type are also described, for example, in U.S. patent nos. 6,301,038 and 6,870,657 and 6,950,220. This type of media is also typically bistable.

Another type of electro-optic display was developed by Philips and is described in Hayes, r.a. et al, "Video-Speed Electronic Paper Based on electrowetting", Nature, 425, 383-385 (2003). It is shown in international application publication No.2005/038764 that the electrowetting display can be made bistable.

Another type of electro-optic display that has been extensively studied and developed over the years is a particle-based electrophoretic display, in which a plurality of charged particles are passed through a fluid under the influence of an electric field. Electrophoretic displays have the advantages of good brightness and contrast, wide viewing angles, state bistability, and low power consumption compared to liquid crystal displays. However, long-term image quality issues of these displays have prevented their widespread use. For example, the particles that make up electrophoretic displays tend to settle, resulting in inadequate service life for these displays.

As indicated above, the presence of a fluid is required in electrophoretic media. In most prior art electrophoretic media this fluid is referred to as a liquid, but the electrophoretic medium may be made of a gaseous fluid; see, for example, "movement of electronic toner in electronic Paper-like display" by Kitamura, t. et al, "toner display using electrostatically charged insulating particles" by IDW japan, 2001, Paper HCS1-1 and Yamaguchi, y. et al, "toner display using electrostatically charged insulating particles", IDW japan, 2001, Paper AMD 4-4. See also U.S. patent application 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, 1,598,694; and international application publications WO 2004/090626, WO2004/079442, WO 2004/001498. Such gas-based electrophoretic media are susceptible to the same types of problems associated with particle settling as liquid-based electrophoretic media when the media is used in an orientation that allows such settling, for example for signage, in which the media is positioned on a vertical flat panel. In fact, the problem of particle settling is more severe in gas-based electrophoretic media than in liquid-based electrophoretic media, because the lower viscosity of gaseous suspending fluids compared to liquid fluids causes the electrophoretic particles to settle more quickly.

A number of patents and applications, assigned to the institute of technology and technology (MIT) and the eink corporation, or both, have recently been published which describe encapsulated electrophoretic media. Such encapsulated media comprise a plurality of capsules, each of which itself comprises an internal phase containing electrophoretically-mobile particles suspended in a liquid suspension medium, and a capsule wall surrounding the internal phase. Typically, the capsules themselves are held in a polymeric binder to form an adhesive layer between two electrodes. For example, in U.S. Pat. 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, 6,130,774, 6,172,798, 6,177,921, 6,232,950, 6,262,833, 6,232,950; and U.S. patent application publication 2002/0060321; 2002/0090980, 2003/0011560, 2003/0102858, 2003/0151702, 2003/0222315, 2004/0014265, 2004/0075634, 2004/0094422, 2004/0105036, 2004/0112750, 2004/0119681, 2004/0136048, 2004/0155857, 2004/0180476, 2004/0190114, 2004/0196215, 2004/0226820, 2004/0239614, 2004/0257635, 2004/0263947, 2005/0000813, 2005/0007336, 2005/0012980, 2005/0017944, 2005/0018273, 2005/0024353, 2005/0062714, 2005/0067656, 2005/0078099, 2005/0099672, 2005/0122284, 2005/0122306, 2005/0122563, 2005/0134554, 2005/0146774, 2005/0151709, 2005/0152018, 2005/0152022, 2005/0156340, 2005/0168799, 2005/0179642, 2005/0190137, 2005/0212747, 2005/0213191, 2005/0219184, 2005/0253777, 2005/0270261, 2005/0280626, 2006/0007527, 2006/0024437, 2006/0038772, 2006/0139308, 2006/0139310, 2006/0139311, 2006/0176267, 2006/0181492, 2006/0181504, 2006/0194619, 2006/0197736, 2006/0197737, 2006/0197738, 2006/0198014, 2006/0202949, and 2006/0209388; and international application publications nos. WO 00/38000, WO 00/36560, WO00/67110 and WO 01/07961, and european patents nos. 1,099,207B 1 and 1,145,072B1 all describe encapsulated media of this type.

Many of the above patents and applications recognize that the walls surrounding the discrete microcapsules in an encapsulated electrophoretic medium can be replaced with a continuous phase, thus producing a so-called polymer-dispersed (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 the electrophoretic fluid within such a polymer-dispersed electrophoretic display can be considered as capsules or microcapsules, even if no discrete capsule membrane is associated with each individual droplet; see, for example, the aforementioned U.S. patent No.6,866,760. Thus, for the purposes of this application, such polymer-dispersed electrophoretic media are considered to be a subclass of encapsulated electrophoretic media.

A related type of electrophoretic display is the so-called "microcell electrophoretic display". In microcell electrophoretic displays, the charged particles and the fluid are not encapsulated in microcapsules but are held within a plurality of cavities formed within a carrier medium, typically a polymer film. See, for example, U.S. patent nos. 6,672,921 and 6,788,449, both assigned to Sipix Imaging, inc.

Although electrophoretic media are typically opaque (because, for example, in many electrophoretic media, the particles substantially block the transmission of visible light through the display) and operate in a reflective mode, many electrophoretic displays may operate in a so-called "shutter mode" having a substantially opaque display state and a light transmissive display state. See, for example, the aforementioned U.S. Pat. Nos. 6,130,774 and 6,172,798, and U.S. Pat. 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 on changes in electric field strength, can also operate in a similar mode; see U.S. patent No.4,418,346.

Encapsulated or microcell electrophoretic displays typically do not suffer from the aggregation and settling failure modes of conventional electrophoretic display devices and have additional advantages such as the ability to print or coat the display on a variety of flexible and rigid substrates. (use of the word "printing" is intended to include, but is not limited to, various forms of printing and coating such as pre-metered coating such as patch die coating, slot or die 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 (meniscus) coating, spin coating, brush coating, air knife coating, screen printing processes, electrostatic printing processes, thermal printing processes, ink jet printing processes, electrophoretic deposition, and other similar techniques). Thus, the manufactured display may be flexible. In addition, since the display medium can be printed (using various methods), the display itself can be manufactured inexpensively.

Other types of electro-optic media may also be used in the displays of the present invention.

Typically, an electro-optic display comprises a layer of electro-optic material and at least two other layers, one of which is an electrode layer, disposed on opposite sides of the electro-optic material. In most such displays both layers are electrode layers, either or both of which are patterned to define the pixels of the display. For example, where one electrode layer is patterned as elongate row electrodes and the other electrode layer is patterned as elongate column electrodes extending at right angles to the row electrodes, the pixels are defined by the intersections of the row and column electrodes. Alternatively, and more commonly, one electrode layer is in the form of a single continuous electrode, while the other electrode layer is patterned as a matrix of pixel electrodes, each defining a pixel of the display. In another type of electro-optic display, which employs a stylus, print head or similar movable electrode separate from the display, only one of the layers adjacent to the electro-optic layer includes an electrode, the layer on the opposite side of the electro-optic layer generally acting as a protective layer to prevent the movable electrode from damaging the electro-optic layer.

The manufacture of a three-layer electro-optic display typically involves at least one lamination operation. For example, in several of the MIT and E Ink incorporated patents and applications mentioned above, a process is described for manufacturing an encapsulated electrophoretic display in which an encapsulated electrophoretic medium comprising capsules in an adhesive is coated on a flexible substrate comprising Indium Tin Oxide (ITO) or similar conductive coating coated on a plastic film, which serves as one electrode of the final display, and the capsules/adhesive coating is dried to form an adhesive layer of the electrophoretic medium which adheres strongly to the substrate. A backplane is separately prepared, which includes an array of pixel electrodes and an appropriate arrangement of conductors to connect the pixel electrodes to the drive circuitry. To form the final display, the substrate with the bladder/adhesive layer on top is laminated to a backplane using a laminating adhesive (electrophoretic displays using contact pins or similar movable electrodes can be prepared using a very similar process, i.e., by replacing the backplane with a simple protective layer such as a plastic film over which the contact pins or other movable electrodes can slide). In a preferred form of the process, the backplane is itself flexible and it can be prepared by printing the pixel electrodes and conductors on a plastic film or other flexible substrate. One obvious lamination technique for mass production of displays by this process is roll lamination using a lamination adhesive. Other types of electro-optic displays may also use similar manufacturing techniques. For example, a microcell electrophoretic medium or a rotating bichromal element medium may be laminated to the backplane in substantially the same manner as the encapsulated electrophoretic medium.

In the above-described process, it is beneficial to laminate the substrate carrying the electro-optic layer to the backplane using vacuum lamination. Vacuum lamination can effectively evacuate air between the two materials to be laminated, thus avoiding air bubbles that are not desirable in the final display, as such air bubbles may cause artifacts in the picture generated by the display. However, vacuum lamination of two parts of an electro-optic display in this manner requires the use of an adhesive such as that used in the aforementioned U.S. patents 6,657,772 and 6,831,769, particularly for displays using encapsulated electrophoretic media. The adhesive must have sufficient adhesive strength to be able to bond the electro-optical layer to the layer (typically the electrode layer) to which it is to be laminated, and in the case of encapsulated electrophoretic media, must have sufficient adhesive strength to be able to mechanically secure the capsules together. If the electro-optic display is of a flexible type (and an important advantage of the two-colour rotating member and the encapsulated electrophoretic display is that they can be made flexible), the adhesive must be sufficiently flexible so as not to introduce flaws in the display when the display is bent. At lamination temperatures, the lamination adhesive must also have sufficient flow properties to ensure high quality lamination, and in this regard, the requirement for lamination of encapsulated electrophoretic and some other types of electro-optic media is very difficult; lamination needs to be carried out at temperatures no higher than about 130 c because exposing the media to higher temperatures would damage it, but the fluidity of the adhesive must be able to accommodate the relatively uneven surface of the layer comprising the capsules, which is irregular due to the capsules beneath it. The laminating adhesive must be chemically compatible with all other materials in the display.

In considering the selection of a lamination adhesive for use in an electro-optic display, attention must be paid to the process of assembling the display. Most prior art methods for final lamination of electro-optic displays are essentially batch methods in which the electro-optic medium, lamination adhesive and backplane are only combined together just prior to final assembly, and thus there is a need for methods that are better suited for high volume production.

As described in the aforementioned WO2003/104884, many of the components used in solid state electro-optic displays, and the methods for making such displays, have been derived from the technology used in Liquid Crystal Displays (LCDs), which are obviously also electro-optic displays, although they employ liquid rather than solid media. For example, solid state electro-optic displays may employ an active matrix backplane comprising an array of transistors or diodes and a corresponding array of pixel electrodes, substantially as in an LCD, and a "continuous" front electrode (in the sense of an electrode that extends over a plurality of pixels and typically over the entire display) on a transparent substrate. The methods used to assemble LCDs cannot be used with solid state electro-optic displays. Generally, assembling an LCD requires the following process: the back plate and the front electrode are fabricated on separate glass substrates, the components are then adhesively secured together with small voids between them, and the resulting assembly is then placed under vacuum and immersed in a bath of liquid crystal, thereby causing the liquid crystal to flow through the voids between the back plate and the front electrode. Finally, the aperture is sealed as the liquid crystal flows into place, thereby obtaining the final display.

This LCD assembly process cannot be easily transferred to a solid state electro-optic display. Since the electro-optical material is solid, it must be present between the back plate and the electrode before the two whole are fixed to each other. In addition, the liquid crystal material may simply be interposed between the front electrode and the backplane without being attached to either the front electrode or the backplane, in contrast to solid electro-optic media which typically need to be secured to both the front electrode and the backplane. In most cases the solid electro-optic medium is formed on the front electrode because this is generally easier to achieve than forming the medium on a backplane containing the circuitry, and then laminating the front electrode/electro-optic medium assembly to the backplane. Typically this lamination is performed by covering the entire surface of the electro-optic medium with an adhesive and then laminating under conditions of temperature, pressure and possibly vacuum.

The price of electro-optic displays is often expensive, and the cost of color LCDs found in portable computers, for example, typically accounts for a significant portion of the overall cost of the computer. With the widespread use of electro-optic displays in devices such as cell phones and Personal Digital Assistants (PDAs) that are much cheaper than portable computers, there is significant pressure to reduce the cost of these displays. As described above, the ability to form layers of some solid electro-optic media on flexible substrates by printing techniques makes it possible to reduce the cost of the electro-optic components of displays by mass production of displays using, for example, roll-to-roll coating techniques using commercial equipment used to produce coated paper, polymer films, and similar media. However, such devices are expensive and the area of electro-optic medium currently on the market is not sufficient to allow the use of dedicated devices, and so it is often necessary to transfer the coated medium from a commercial coating apparatus to an apparatus for final assembly of an electro-optic display without damage to the relatively fragile layer of electro-optic medium.

The aforementioned WO2003/104884 describes a method of assembling a solid state electro-optic display, including a particle-based electrophoretic display, which is well suited for high volume production. This patent essentially describes a so-called "front plane laminate" (FPL) comprising, in order, a light-transmissive electrically conductive layer, a layer of solid electro-optic medium in electrical contact with the electrically conductive layer, an adhesive layer, and a release sheet (releasesheet). Typically, the light-transmissive electrically conductive layer is carried by a light-transmissive substrate, which is preferably flexible in the sense that the substrate can be manually wound into, for example, a 10 inch (254 mm) diameter cylinder without permanent deformation. The term "light transmissive" as used herein and in this patent means that the layer so designated is capable of passing sufficient light to enable a viewer to see through the layer to observe changes in the display state of the electro-optic medium, typically as viewed through the electrically conductive layer and the adjacent substrate, if any. Typically, the substrate is a polymer film, and typically has a thickness in the range of about 1 to about 25 mils (25 to 634 μm), preferably about 2 to about 10 mils (51 to 254 μm). Suitably, the electrically conductive layer may be a thin metal or metal oxide layer, such as aluminium or ITO, or a conductive polymer. Polyethylene terephthalate (PET) films coated with aluminum or ITO are commercialized, such as "aluminized Mylar" ("Mylar" is a registered trademark) from dupont DE & Company, Wilmington DE, Wilmington, a commercial material that can be used for front plane lamination and has good results.

The combination of electro-optic displays with such front plane lamination can be achieved by: the release sheet is removed from the front plane lamination and the adhesive layer is contacted with the backplane under conditions effective to promote adhesion of the adhesive layer to the backplane, thereby securing the adhesive layer, the layer of electro-optic medium, and the electrically conductive layer to the backplane. The process is well suited for mass production, as front plane lamination is typically mass produced using roll-to-roll coating techniques and then cut into blocks of any size required for use with a particular backplane.

The aforementioned WO2003/104884 also describes a method for testing the electro-optic medium in a front plane laminate before the front plane laminate is introduced into a display. In this test method a release plate is provided with an electrically conductive layer and a voltage sufficient to change the optical state of the electro-optical medium is applied between the electrically conductive layer and an electrically conductive layer on the other side of the electro-optical medium. Since observation of the electro-optic medium reveals any imperfections in the medium, this avoids laminating imperfect electro-optic medium into the display, at the ultimate cost of otherwise discarding the entire display rather than just imperfect front plane lamination.

The aforementioned WO2003/104884 also describes a second method of testing electro-optic media in front plane lamination by placing an electrostatic charge on a discharge plate, thereby forming an image on the electro-optic medium. The image is then viewed in the same manner as before to detect any imperfections in the electro-optic medium.

The aforementioned WO 2004/023195 describes a so-called "double release film" which is essentially a simplified version of the front plane lamination of the aforementioned WO 2003/104884. One form of dual release sheet comprises a layer of solid electro-optic medium sandwiched between two adhesive layers, one or both of which are covered by a release sheet. Another form of dual release layer comprises a layer of solid electro-optic medium sandwiched between two release plates. Both forms of the dual release film are intended for use in a process substantially similar to that already described for assembling an electro-optic display from a front plane laminate, but which includes two separate laminates. Typically, the dual release sheet is laminated to the front electrode in a first lamination to form a front sub-assembly, and then the front sub-assembly is laminated to the backplane in a second lamination to form the final display, although the order of the two laminations can be reversed if desired.

The aforementioned PCT/US2006/60049 describes a so-called "inverted front plane laminate", which is a variation of the front plane laminate described in the aforementioned WO 2003/104884. The inverted front plane lamination sequentially comprises: at least one of a light-transmissive protective layer and a light-transmissive electrically conductive layer, an adhesive layer, a layer of solid electro-optic medium, and a release sheet. The use of this inverted front plane lamination is for forming an electro-optic display having a lamination adhesive layer between the electro-optic layer and the front electrode or front substrate; there may or may not be a second, typically very thin, adhesive layer between the electro-optic layer and the backplane. The electro-optic display has both good resolution and low temperature performance.

The aforementioned PCT/US2006/62399 describes a number of different methods designed for the mass production of electro-optic displays using inverted front plane lamination. A preferred approach among these is the "multiple-up" approach designed to allow component lamination of multiple electro-optic displays simultaneously.

The aforementioned WO2003/104884 also describes a method of forming an electrical connection between a backplane to which the front plane laminate is laminated and a light-transmissive electrically conductive layer in the front plane laminate. As shown in figures 21 and 22 of the international application, the formation of the layer of electro-optic medium in the front plane lamination may be controlled so as to leave uncoated areas ("slots") in which no electro-optic medium is present, and a portion of these uncoated areas may thereafter be used to form the required electrical connections. However, this method of forming connections is undesirable from a manufacturing standpoint because the arrangement of the connections obviously varies with backplane design, so that FPLs coated with slots in a particular arrangement can only be used with one backplane or a limited range of backplanes, while for cost reasons it is desirable to manufacture only one form of FPL that can be used with any backplane.

Thus, the aforementioned WO2003/104884 also describes a method of forming the required electrical connection by: the electro-optic medium is applied over the entire area of the FPL and then removed where electrical connections are desired. But removal of the electro-optic medium has its own problems. Typically, the electro-optic medium must be removed by means of a solvent or mechanical clean-up, either of which may result in damage to or removal of the electrically conductive layer of the FPL (which is typically a layer of metal oxide such as indium tin oxide, less than 1 μm thick) so that an electrical connection cannot be made. In extreme cases, it is also possible to cause damage to the front substrate (usually a polymer film) used to support and mechanically protect the electrically conductive layer. In some cases, the materials used to form the electro-optic medium do not dissolve readily and therefore cannot be removed without the use of corrosive solvents and/or high mechanical pressures, both of which can exacerbate the aforementioned problems.

Similar methods employing selective coating of the electro-optic medium and/or selective removal of the electro-optic medium may also be applied to the aforementioned dual release film and inverted front plane lamination.

It is common practice to use laser cutting to separate appropriately sized pieces from a continuous web of FPL for lamination to individual backplanes. Such laser cutting can also be used to prepare the areas for electrically connecting the back plates by: the FPL is "kiss cut" (kiss cutting) from the side of the lamination adhesive using a laser to remove the lamination adhesive and the electro-optic medium from the connection area, but not the electrically conductive layer. Precise control of laser power and cutting speed by kiss cutting is desirable if the thin, relatively fragile electrically conductive layer is not removed or damaged. Also, depending on the location of the connection, the curvature of the electrically conductive layer and the associated front substrate may cause the electrically conductive layer to break, resulting in failure to achieve a proper connection between the backplane and the electrically conductive layer, and ultimately failure to form a display.

There is therefore a need for an improved method of making electrical connections to a front plane laminated electrically conductive layer, and it is to such an improved method that the present invention seeks to provide.

Another aspect of the invention relates to the production of flexible displays. Coating operations, lamination, and assembly of displays using thin, flexible substrates are difficult due to the lack of stiffness of the thin substrate materials typically used. These difficulties can be eliminated to some extent by performing some processing steps on a continuous web, but the final assembly of flexible displays typically requires lamination of a thin front plane laminate or similar subassembly of the display to a thin backplane, and the lamination of such two thin subassemblies creates considerable mechanical difficulties. One aspect of the present invention relates to an improved lamination process that can reduce or eliminate these difficulties.

Another aspect of the invention relates to improved laminate adhesive layers for use in electro-optic displays. The backplates used in such displays typically have a substantial surface roughness, especially if the backplates are of the direct drive type (having a plurality of electrodes of substantial size and a separate conductor associated with each electrode for controlling the voltage thereon) as opposed to active matrix displays. To avoid the formation of voids in the lamination adhesive due to the roughness of the backsheet, it is desirable to use a relatively soft lamination adhesive (at 70 ℃ and 10 ℃)^-4Under Hz, G' < 1000 Pa). However, the use of such soft adhesives can adversely affect the high temperature performance of the display. The invention provides an adhesive layer which can avoid the formation of gaps and can provide better high-temperature performance.

Another aspect of the invention relates to replacing front plane lamination used in the assembly of electro-optic displays where close tolerances or other desired parameters are difficult to achieve.

Disclosure of Invention

Accordingly, one aspect of the present invention provides a process for producing a front plane laminate for use in an electro-optic display, the process comprising:

forming a subassembly comprising a lamination adhesive layer and a layer of electro-optic medium;

forming an aperture through the subassembly; and

a light-transmissive electrode layer is then secured to the exposed surface of the laminate adhesive layer of the subassembly, the electrode layer extending over the aperture.

For convenience, this process of the invention will be referred to hereinafter as the "preformed connecting porosity" or "PFCA" process of the invention.

In such a PFCA process, the aperture may extend to the edges of the lamination adhesive and electro-optic medium layers so that the "aperture" is present as a cut at the edge of these layers, rather than a true aperture being completely surrounded by the lamination adhesive and electro-optic medium layers. Typically, at least one exposed surface of the subassembly is covered by a release plate; the aperture may or may not pass through this release plate, but it is generally most convenient for the aperture to extend through at least one of the release plates. The light-transmissive electrode may be carried by a support layer, typically an electrode layer being part of the front substrate which, in addition to the electrode layer, comprises a support layer, typically a polymer film, which may provide mechanical support and protection for the typically relatively fragile electrode layer. The sub-assembly comprises two lamination adhesive layers on opposite sides of a layer of electro-optic medium, typically in such sub-assemblies apertures will extend through both lamination adhesive layers. The light-transmissive electrode may be larger than the layer of electro-optic medium in both dimensions for reasons described below.

The apertured front plane laminate produced by the process of the present invention can be used in a manner very similar to the apertured FPL produced by mechanical or solvent removal of the electro-optic medium and the laminating adhesive described in the aforementioned WO 2003/104884. For example, after securing the light-transmissive electrode layer to the laminate adhesive layer, the subassembly may be laminated to a backplane comprising at least one electrode, during which lamination electrically conductive material is introduced into the apertures to provide an electrical connection between the light-transmissive electrode layer and contacts disposed on the backplane. For example, an FPL produced by a PFCA process may be laminated to a backplane with a drop of conductive ink previously deposited thereon, such that the conductive ink enters the pores of the FPL and forms the required electrical connection between the backplane and the conductive layer of the FPL which forms the front electrode of the electro-optic display after the lamination operation.

The electro-optic medium used in the PFCA process may be any of the types of solid electro-optic medium described above. The electro-optical medium may thus be a rotating bichromal member or an electrochromic medium. The electro-optic medium may also be an electrophoretic material comprising a plurality of electrically charged particles distributed in a fluid and capable of passing through the fluid under the influence of an electric field. The electrically charged particles and the fluid may be confined in a plurality of capsules or microcells. Alternatively, the electrophoretic material may be a polymer dispersed type, in which the electrically charged particles and the fluid are present in the form of a plurality of discrete droplets surrounded by a continuous phase comprising a polymeric material. The fluid used may be liquid or gaseous.

The present invention also provides a second related process for forming a front plane laminate for use in an electro-optic display. In this second process, a subassembly is still formed comprising a layer of lamination adhesive and a layer of electro-optic medium. However, there is no need to form apertures through the subassembly; instead, a light-transmissive electrode layer is secured to the exposed surface of the laminate adhesive layer of the subassembly, the electrode layer having a tab portion extending beyond the periphery of the laminate adhesive layer and the electro-optic medium layer. Accordingly, the present invention provides a process for producing a front plane laminate for use in an electro-optic display, the process comprising: forming a subassembly comprising a lamination adhesive layer and a layer of electro-optic medium; and subsequently securing a light-transmissive electrode layer to the exposed surface of the laminate adhesive layer of the subassembly, the electrode layer having a tab portion extending beyond the periphery of the laminate adhesive layer and the layer of electro-optic medium.

For convenience, the second process of the present invention will be referred to hereinafter as the "extended tab" process of the present invention. In this extended tab process, the electrode layer is larger than the electro-optic medium layer in both dimensions for reasons described below. The subassembly may further comprise at least one release sheet covering at least one exposed surface of the lamination adhesive layer and the layer of electro-optic medium. As described in the PFCA process described above, in the extended tab process, the light-transmissive electrodes may be carried by a support layer. The subassembly may include first and second layers of laminating adhesive disposed on opposite sides of a layer of electro-optic medium. After fixing the light-transmissive electrode layer to the first lamination adhesive layer, a second lamination adhesive layer may be laminated onto the back sheet including at least one electrode, wherein the tab portion is in contact with a contact disposed on the back sheet.

The electro-optic medium used in the extended tab process may be any of the types of solid electro-optic media described above. The electro-optical medium may thus be a rotating bichromal member or an electrochromic medium. An electro-optic medium may also be an electrophoretic material comprising a plurality of electrically charged particles distributed in a fluid and capable of passing through the fluid under the influence of an electric field. The electrically charged particles and the fluid may be confined in a plurality of capsules or microcells. Alternatively, the electrophoretic material may be of the polymer dispersed type, in which the electrically charged particles and the fluid are present in the form of a plurality of discrete droplets surrounded by a continuous phase comprising the polymeric material. The fluid used may be liquid or gaseous.

In another aspect, the invention provides a process for forming a flexible electro-optic display, the process comprising: providing a backing plate comprising at least one electrode; providing a front plane laminate comprising a light transmissive electrically conductive layer, a layer of solid electro-optic medium, an adhesive layer and a release sheet; removing the release sheet from the front plane laminate; and laminating the front plane laminate to the backplane to form the electro-optic display, wherein prior to the laminating, a stiffening layer is affixed to at least one of the front plane laminate and the backplane, the stiffening layer for increasing the stiffness of the front plane laminate and/or the backplane. After lamination, the hardened layer is typically removed.

For convenience, this process of the present invention will be referred to hereinafter as the "hardened layer" process of the present invention.

The present invention also provides a hardened front plane laminate comprising, in order: a hardened layer, a light-transmitting electrically conductive layer; a layer of solid electro-optic medium in electrical connection with the electrically conductive layer; an adhesive layer and a release sheet, the hardened layer being removable from the electrically conductive layer.

The hardened layer process and hardened front plane lamination of the present invention may utilize any known type of solid electro-optic medium as previously described.

The present invention also provides an electro-optic display comprising: a backing plate having at least one electrode; a first layer of non-crosslinked adhesive in contact with the backing sheet; a second layer of cross-linked adhesive on the other side of the first layer opposite the backing sheet; and a layer of electro-optic medium opposite the first layer on the other side of the second layer. For convenience, the electro-optic display may be referred to hereinafter as the "dual adhesive layer" display of the present invention.

The present invention also provides a front plane laminate comprising, in order: a light-transmissive electrically conductive layer, a layer of electro-optic medium, a layer of cross-linked adhesive, a layer of non-cross-linked adhesive, and a release sheet. For convenience, this front plane lamination may be referred to hereinafter as the "dual adhesive layer front plane lamination" or "DALFPL" of the present invention.

The present invention also provides a dual release film comprising: a layer of solid electro-optic medium having first and second surfaces on opposite sides; a first adhesive layer on a first surface of the layer of solid electro-optic medium; a second adhesive layer on a second surface of the layer of solid electro-optic medium; and a release sheet arranged on the other side of the first adhesive layer, opposite the layer of solid electro-optic medium, wherein one of the first and second adhesive layers comprises a first sub-layer of cross-linked adhesive adjacent a surface of the solid electro-optic medium layer and a second sub-layer of non-cross-linked adhesive. Such a double release film may be referred to hereinafter as "double adhesive layer double release film" or "DALDRF" of the present invention.

The electro-optic displays produced using the methods and components of the present invention may be used in any application where electro-optic displays were previously used. The invention thus extends to an electronic book reader, portable computer, tablet computer, mobile telephone, smart card, sign, watch, shelf label or flash drive comprising a display of the invention or produced using a method or component of the invention.

Finally, the present invention provides various processes for assembling electro-optic displays without the use of front plane lamination.

Drawings

FIGS. 1A to 1D are schematic cross-sectional views of various stages of a first preformed connecting aperture process of the present invention;

FIGS. 2A to 2E are schematic cross-sectional views of stages of a second preformed connecting aperture process of the present invention;

FIGS. 3A through 3D are schematic cross-sectional views of various stages of an extended tab process of the present invention, and FIG. 3E is a top view of the same process stage as FIG. 3C;

FIG. 4 is a schematic cross-sectional view through a hardened front plane laminate of the present invention;

FIG. 5 is a schematic cross-sectional view through a dual adhesive layer electro-optic display of the present invention;

figures 6A to 6E are schematic cross-sectional views of stages in a process of the invention for forming an electro-optic display without the use of front plane lamination.

It should be emphasized that all of the figures are schematic and not to scale. In particular, the thicknesses of the various layers in the figures do not correspond to their actual thicknesses for ease of illustration. And the thickness of the various layers is exaggerated relative to their lateral dimensions throughout the drawings.

Detailed Description

From the foregoing summary, it will be apparent that the invention has many different aspects, which will be described primarily in the following. It will be understood, however, that a single electro-optic display or component thereof may utilize aspects of the invention, such as incorporating the subassemblies used in the PFCA process of the invention into the dual adhesive layers of the invention.

Before describing in detail the various aspects of the present invention, it is necessary to set forth some of the definitions. The term "backplane" as used herein is its conventional meaning in the field of electro-optic displays and in the aforementioned patents and published applications, and refers to a rigid or flexible material provided with one or more electrodes. The backplane may also be provided with electronic components for addressing the display, or such electronic components may be provided in a unit separate from the backplane. In flexible displays, it is highly desirable that the backplane have sufficient barrier properties to prevent ingress of moisture and other contaminants through the non-viewing side of the display (the display is typically viewed from a side remote from the backplane). If one or more additional layers are desired to be added to the backplane to reduce the ingress of moisture or other contaminants, the barrier layer should be located as close to the electro-optic layer as possible so that there is little or no edge profile (edgeprofile) of the low barrier material between the front (discussed below) and back barrier layers.

The term "front substrate" as used herein is its conventional meaning in the field of electro-optic displays and in the aforementioned patents and published applications, and refers to a light-transmissive (and preferably transparent) material that is rigid or flexible. The front substrate comprises at least one electrode layer, most commonly a single continuous front electrode extending across the entire display. Typically, the exposed surface of the front substrate forms a viewing surface through which an observer views the display, although additional layers may be interposed between the front substrate and the viewing surface. Like the backplane, the front substrate should provide sufficient barrier properties to prevent the ingress of moisture and other contaminants through the viewing side of the display. If one or more additional layers are desired to be added to the front substrate to reduce the ingress of moisture or other contaminants, the barrier layer should be located as close to the electro-optic layer as possible so that there is little or no edge profile of the low barrier material between the front and back barrier layers.

Part A: PFCA and extended tabbing process

These aspects of the invention are combined with the common goal of reducing or eliminating the need to remove the electrode layer with a mechanical or solvent, thereby forming an electrical connection between the layer and the backsheet, and reducing the risk of breaking or damaging the electrode layer (especially fragile metal oxide layers such as indium tin oxide layers) when using thin substrates.

Fig. 1A to 1D are schematic cross-sectional views of a subassembly and front plane laminate formed by a first PFCA process of the present invention. As shown in fig. 1A, the process begins by first coating (deposition techniques other than coating may be used depending on the particular type of electro-optic medium used) a layer 102 of electro-optic medium on a first release sheet 100. In a subsequent step of the process, a layer 104 of laminating adhesive is coated on a second release sheet 106 and the resulting subassembly is laminated to a layer 102 of electro-optic medium on a first release sheet 100 to secure the laminating adhesive layer 104 to the layer 102 of electro-optic medium to produce a subassembly as shown in figure 1B. Then, through the cut aperture 108 of the subassembly as shown in fig. 1C. Finally, the second release sheet 106 is removed and the electrode layer 110 is laminated to the adhesive layer 104 such that the electrode layer 110 extends over the apertures 108, as shown in FIG. 1D (in practice, the electrode layer 110 is typically supported by a support sheet, but the support sheet is omitted from FIG. 1D for simplicity).

As can be seen from fig. 1D, the electrode layer 110 is shown to be larger than the adhesive layer 104 and the layer of electro-optic medium 104, which is intended because the final front plane lamination shown in fig. 1D is intended for use in the manufacture of displays having a so-called "underfill" edge seal, as described in the aforementioned WO 2003/104884. To produce such an unfilled closure, the backplane, electrode layer and front support layer (when present) are made larger in both dimensions than the intervening adhesive and electro-optic medium layers so that after lamination of the front plane laminate to the backplane, a sealing material can be injected between the backplane and the electrode or front support and cured to form an edge seal completely around the adhesive and electro-optic medium layers.

It is apparent that there may be many variations in the basic PFCA process shown in figures 1A to 1D. For example, the aperture 108 may be formed using a variety of techniques, including mechanical punching, drilling, or laser cutting. The aperture 108 may extend to the periphery of the layer of electro-optic medium 102 and the adhesive layer 104 to form a cut at the edge of these layers rather than a true aperture. It is not strictly necessary to apply the adhesive layer 104 to the second release sheet and the adhesive layer may be applied directly to the layer of electro-optic medium, depending on the particular adhesive and electro-optic medium used.

The process illustrated in fig. 1A to 1D has considerable flexibility with respect to operating on a continuous web of material and with respect to operating on a sliced material of suitable dimensions for each display (or possibly a fraction of the displays produced in a single lamination operation). The steps shown in fig. 1A and 1B may generally be performed on a continuous web of material. The pores 108 may be formed on either a continuous web of material or a cut sheet. The final lamination of the "oversized" electrode layer 110 can typically be achieved on a slice of the material.

As shown in fig. 1A to 1D, it will be appreciated that this process does not provide an adhesion layer that is typically present between the layer of electro-optic medium 102 and its associated release sheet 100. In the form shown in fig. 1A to 1D, the final front plane lamination may be used in a process where a laminating adhesive is placed on the backplane, or in a process where a laminating adhesive is not required, since, for example, in an electro-optic medium being an encapsulated electrophoretic medium, the capsules are embedded in a polymeric binder that is itself useful as a laminating adhesive, as described in some of the aforementioned patents and applications by the company yingk (E ink). If it is desired to provide the FPL produced in the process shown in figures 1A to 1D with a second layer of laminating adhesive on the side of the electro-optic medium layer opposite the adhesive layer 104, this can be readily achieved by a process modification in which the release layer 100 is removed from the subassembly as shown in figure 1B and the second layer of laminating adhesive attached to a third release sheet (to be described below with reference to figures 2A to 2E) is laminated to the electro-optic medium layer 102. Of course, the aperture 108 may extend through both adhesive layers in this modified process.

Fig. 2A to 2E show a second preferred PFCA process of the present invention. As shown in fig. 2A and 2B, the first two steps of the process, which are carried out using the first release sheet 200, the layer of electro-optic medium 202, the adhesive layer 204 and the second release sheet 206, are the same as the corresponding steps shown in fig. 1A and 1B. However, the next step in the second preferred PFCA process involves removing the first release sheet 200 and laminating a second laminating adhesive layer 212 attached to a third release sheet 214 on the surface of the layer of electro-optic medium 202 thus exposed, as shown in figure 2C. The remaining process step of the process is to form the aperture 208 through all five layers of the structure shown in fig. 2C, thereby forming the apertured structure shown in fig. 2D. Removal of the second release sheet 206 and lamination of the electrode layer 210 extending over the apertures 208 will result in a finished front plane lamination as shown in fig. 2E. It should be noted that in this second process, the second lamination adhesive layer 212 and the electrode layer 210 are each made larger than the intervening electro-optic medium layer 202 and adhesive layer 204. Although not apparent in fig. 2E, this difference in size exists in two dimensions, and this arrangement in the final lamination process is to form a front plane lamination as shown in fig. 2E, with the perimeter of the second lamination adhesive layer 212 bonded to the electrode layer, thereby forming an edge seal (the thickness of the layers in fig. 2A-2E is clearly exaggerated relative to their lateral dimensions) around the layer 202 of electro-optic medium.

In the second PFCA process shown in fig. 2A to 2E, the first two steps (to create the structure shown in fig. 2B) are typically performed on a continuous web of material, while the remaining steps are performed on slices of material that are cut to fit individual displays.

Fig. 3A to 3E illustrate a preferred extended tab process of the present invention. As shown in fig. 3A and 3B, the first two steps of the process, which are carried out using the first release sheet 300, the layer of electro-optic medium 302, the adhesive layer 304 and the second release sheet 306, are the same as the corresponding steps shown in fig. 1A and 1B. The next step in the process, removal of the second release sheet 306 and lamination of the electrode layer 310, is also substantially similar to the first PFCA process except that no apertures are formed and, as shown in figures 3C to 3E, the electrode layer 310 is slightly larger in both dimensions than the electro-optic medium layer 302 and is provided with protruding tabs 316 which will ultimately be used to connect the electrode layer 310 to the backplane.

The final step of the extended tab process is substantially similar to the second PFCA process described above. As shown in fig. 3D, the first release sheet 300 is removed and the surface of the layer of electro-optic medium 302 thus exposed is laminated to a second laminating adhesive layer 312 attached to a third release sheet 314. Again, the relative dimensions of the various layers of the final front plane laminate are designed to ensure that during the final lamination the second adhesive layer 312 adheres to the electrode layer 310 to form an edge seal around the electro-optic medium layer 302.

As described above, in the PFCA process of the present invention, the "aperture" may be a real aperture or a cut from the edge of the electro-optic medium and adhesive layer, whereas the extended tab process of the present invention does not require the formation of any aperture. Each of these methods for providing electrical connections has its advantages and disadvantages. Placing the aperture inside the electro-optic medium and the adhesive layer (i.e. using a PFCA process with a real aperture instead of a cut) allows a compact design but does not allow the entire active area of the electro-optic medium to be used for the display, since the connection area has to be hidden. Because the connection area is spaced from the edge seal, the strain (strain) at the front electrode is small and there is no risk of damaging the edge of the display. The use of a PFCA process with a notch may improve the use of the active area of the electro-optic medium while keeping the strain at the connection small. However, there is a risk of damaging the edge seal at the incision. The use of external tab processes allows the entire active area of the electro-optic medium to be utilized, but does require additional space on the backplane to accommodate such external tabs. The strain on the external tab connection tends to be greater than in the PFCA process, but there is little or no risk of damaging the edge seal of the display. In any event, it is desirable to employ multiple connections to minimize the probability of display failure due to poor electrical connection or strain at these connections.

The PFCA and extended tab displays of the present invention may include additional layers for enhanced protection of the electro-optic medium from materials, particularly moisture present in the environment. One preferred form of front substrate for electro-optic displays comprises a thin layer of ITO on polyethylene terephthalate (PET), such coated films being readily commercially available, as discussed in the aforementioned WO2003/104884, WO 2004/023195 and WO2005/041160, and in the aforementioned PCT/US 2006/62399. In such a front substrate the ITO material acts as a barrier material, but is inevitably physically damaged by pinholes or cracks, allowing moisture or other contaminants to penetrate through the pinholes or cracks to the electro-optic medium. To enhance the sealing properties of such PET/ITO or similar front substrates, it is desirable to laminate an additional barrier layer onto the front substrate, the additional barrier layer being formed from a homopolymer (e.g. polychlorotrifluoroethylene (polychlorotrifluoroethylene) sold under the trade mark "ACLAR" under the hounwell Corporation) or a sputtered ceramic (e.g. AlO under the trade name "Toppan GX film" under the relief Printing Company (Toppan Printing Company))_X) And (4) forming. If a flexible display is desired, the additional barrier layer should be thin, ideally about 12 μm, but thicknesses of up to 5 mils (127 μm) are possible if sufficient flexibility can also be achieved. In case it is desired to adhere an additional barrier layer to the front substrate by means of an adhesive layer, the adhesive layer should be transparent, colorless, thin, flexible and have a low creep (when it appears to be)When the display is bent or rolled up) and is stable at any temperature within the operating range of the display. Certain crosslinked polyurethanes and polyacrylates may also be used as the adhesive.

Alternatively, the barrier properties of the PET/ITO or similar front substrate may be improved by coating an additional metal oxide layer (e.g. an aluminium oxide layer) either on the surface of the front substrate opposite the ITO layer or underneath the ITO layer. The combination of the ITO layer and the additional metal oxide layer improves the barrier properties of the front substrate (e.g. by reducing the transfer of water vapour through unavoidable pinholes or cracks in the ITO layer) without causing undue yellowing of the substrate, which may occur, for example, in attempts to improve the barrier properties by increasing the thickness of the ITO layer. Instead of a simple metal oxide layer, a more complex structure comprising a ceramic material may be used, for example a sealing material such as Barix (registered trademark) from Vitex Systems, inc., 3047 Orchard park, San Jose, CA95134, San Jose, San 95134, San Jose, San may be located in the front substrate at a surface remote from the. The Vitex Systems company currently sells a polymer film with a layer of Barix and ITO, under the trade name Flexglass200, but the polymer film is 5 mils (127 μm) of polyethylene naphthalate (PEN).

The barrier properties and properties of the front substrate, such as flexibility, cost, and other properties, can also be controlled by careful selection of the polymers and conductive materials used in the front substrate. In principle almost any flexible, light-transmitting polymer can be used; suitable polymers include: PET, PEN, polycarbonate, polyvinylidene chloride (sold under the registered trademark "SARAN"), polychlorotrifluoroethylene (sold under the registered trademarks "ACLAR" and "CLARIS"), cellulose triacetate (sold under the registered trademark "ARTON" by JSR corporation), Polyethersulfone (PES), and laminates of two or more of these materials. Suitable transparent conductive materials include ITO, organic conductive polymers such as Baytron P (registered trademark), carbon nanotubes, and other suitable conductive transparent (T > 60%) materials having a resistivity of less than about 10⁴Ohm meterConductor per square.

In the PFCA and extended display of the present invention, the electro-optic layer may be an encapsulated electrophoretic layer, a polymer dispersed electrophoretic layer, or any other type of electro-optic layer discussed above. The display may comprise one or two laminated adhesive layers for adhering the electro-optic material to the front substrate and/or the backplane. The display may be viewed through any of the laminated adhesive layers and may be assembled using direct coating and lamination, or using front plane lamination, inverted front plane lamination, or dual release films, as described in the application mentioned in the first paragraph of this application. Although the display is typically viewed through the front substrate, as described above, in some cases a light transmissive backplane may be utilized to provide a two-sided display, or to provide one of the operations in the shutter mode described above. The display may employ an edge seal of the type described in the aforementioned PCT/US2006/62399 or the following description.

From the foregoing, it can be seen that the PFCA and extended tab process of the present invention reduces or eliminates many of the problems previously encountered in providing electrical connections to conventional electrodes in electro-optic displays, and avoids the need to mechanically clear the electro-optic medium from the front electrode layer.

And part B: hardened front plane lamination and process therefor

As already stated, another aspect of the present invention provides an improvement in the process of forming an electro-optic display using front plane lamination as described in the aforementioned WO 2003/104884. According to the present invention, an improvement in the process is achieved by affixing a stiffening layer to at least one of the front plane laminate and the backplane before laminating the front plane laminate to the backplane to form the display. After lamination, the hardened layer is typically removed. By referring to the stiffening layer being fixable to the front plane laminate prior to lamination to the backplane we do not exclude the possibility of manufacturing the FPL with the stiffening layer already deployed and indeed this is often the most convenient method since the stiffening effect provided by the stiffening layer may be useful in manufacturing the FPL itself and also in laminating it to the backplane. For example, when it is desired to prepare an FPL starting from a thin, flexible substrate comprising, say, ITO on PET, it is advantageous to first fix the substrate to the rigidifying layer, then prepare the FPL by applying the electro-optic medium to the substrate, then applying the adhesive layer, and finally covering the adhesive with a release sheet. In this process, if the coating process is carried out on a web (as is often the case), the increase in hardness of the substrate provided by the hardened layer may result in a beneficial increase in tension and uniformity. The resulting FPL can then be laminated to a backplane in the usual manner to form an electro-optic display, and the stiffening layer removed from the final display.

Fig. 4 is a schematic cross-sectional view through a hardened front plane laminate (generally 400) of the present invention. The front plane laminate 400 comprises a stiffening layer 402, a polymeric support layer 404, a light-transmissive electrically conductive layer 406, a layer of electro-optic medium 408, a laminate adhesive layer 410 and a release sheet 414, with a conductive layer 412 on the surface of the release sheet 414 facing the laminate adhesive layer; this conductive layer 412 is used to test the electro-optic medium prior to introducing the FPL into the display, as described in the aforementioned U.S. patent 6,982,178 and brief description above.

In the hardened FPL of the invention, the electro-optic medium and the adhesion layer may be of any of the types described in the above-mentioned WO2003/104884, WO 2004/023195, WO2005/041160, WO2005/073777, PCT/US2006/60049 and PCT/US 2006/62399. The electro-optic medium may be, for example, an encapsulated electrophoretic medium, a polymer dispersed electrophoretic medium, a rotating bichromal medium, a microcell electrophoretic medium, or any other type of electrophoretic medium described above. The FPL may be of the conventional type with a laminated adhesive layer adjacent to the release sheet as described in WO2003/104884, or of the inverted type as described in the aforementioned PCT/US2006/60049, in which the order of the layer of electro-optic medium and the adhesive layer is inverted so that the layer of electro-optic medium is brought closer to the release sheet. The "FPL" may also be in the form of a dual release sheet comprising a single layer of the electro-optic medium sandwiched between two separate adhesive layers.

Whether a stiffening layer is present on the anterior planar laminate or on the posterior plate, or both, it may be made of a number of different materials. Typically, the stiffening layer is a polymer film and may be formed from, for example, polyethylene, polypropylene, polyethylene terephthalate, or other polymers. The hardened layer may be affixed to the front plane laminate or back plate by a releasable adhesive or electrostatic sticker.

As described above, the assembly sequence for an electro-optic display employing the hardened front plane laminate of the present invention is typically that the release sheet is removed and the FPL is laminated to the backplane (which may or may not be hardened with an additional hardened layer). If the edge seal material is to be dispensed around the perimeter of the display and cured to form the edge seal, this is typically done at a later stage in the process. Finally, the hardened layer is removed.

The stiffening layer may also be used at other stages in the assembly of the electro-optic display to assist in the processing of the thin layer. For example, if it is desired to assemble a composite front plane laminate of an electro-optic display from separate layers, such as a 0.5 mil (13 μm) ITO/PET film and a 0.5 mil (13 μm) AlOx/PET film, a stiffening layer may be applied to one of the layers so that an adhesive can be applied to the layer before laminating the two layers together. The hardened layer may be left in place for assisting downstream processing.

As discussed in section a above, an electro-optic display produced using a rigidizer according to the present invention may incorporate additional sealing layers or edge seals of any known type to isolate the electro-optic medium from the environment.

Part C: dual adhesion layer display and front plane lamination

As mentioned above, in prior art electro-optic displays and front plane lamination, the choice of lamination adhesive brings a compromise between the need for good lamination quality and the need for high temperature performance of the display in order to avoid the formation of voids in the adhesive layer. In order to provide good laminationIn amounts desired to use a soft adhesive (at 70 ℃ and 10 ℃)^-4Hz, G' < 1000Pa), but because of the low cohesive strength of such adhesives, they do not provide good high temperature performance for the final electro-optic display formed, and therefore, stiffer, more elastic adhesives are needed to enhance their high temperature performance.

According to the invention the aforementioned compromise can be avoided by using a two-layer adhesive, a non-crosslinked adhesive layer adjacent the backplane and a crosslinked adhesive layer adjacent the electro-optical medium. The former is for good fit with the backing plate, i.e. the soft adhesive provides the fluidity needed for good adhesion to the relatively rough backing plate; the latter prevents void formation by preventing outgassing of the volatile components of the electro-optic layer. The crosslinked adhesive may also act as a moisture barrier to maintain a constant level of moisture in the electro-optic medium; this is important because the properties of many types of electro-optic media vary with the amount of moisture in the medium.

The relative thicknesses of the two adhesive layers may vary and the optimum thickness for any particular combination of adhesive, cross-linking agent and electro-optic medium is preferably determined empirically. However, it has been found in accordance with general teachings that good results are generally obtained by making the two adhesive layers to substantially the same thickness. For example, the thickness of each adhesion layer may be about 25 μm.

Figure 5 of the accompanying drawings is a schematic cross-sectional view through a dual adhesive layer electro-optic display of the present invention, generally designated 500. Display 500 includes a front substrate 502, a light-transmissive electrode layer 504, an electro-optic layer 506, a crosslinked adhesive layer 508 (which may be formed, for example, from a polyurethane adhesive crosslinked with diglycidyl aniline), a non-crosslinked adhesive layer 510 (which may be formed from non-crosslinked polyurethane), and a backplane 512 with pixel electrodes (not shown).

It can be readily seen that the display 500 is readily formed using the dual adhesive layer front plane lamination of the present invention, which is similar to the FPL 400 shown in fig. 4, except that the single adhesive layer in the FPL 400 is replaced by the dual adhesive layers 508, 510 in fig. 5.

To illustrate the advantages of the present invention, experimental single pixel displays were prepared. The backplane of this display comprises a single gold electrode disposed on an insulating backplane that is larger than the gold electrode so as to leave a peripheral portion of the insulating backplane exposed entirely around the gold electrode, but otherwise is substantially the same as the display shown in figure 5. A protective sheet is provided covering the exposed surface of the front substrate and a perimeter portion of the sheet extends outwardly beyond the edge of the front substrate. A sealing material is injected between the back plate and the peripheral portion of the protective plate to form an edge seal, thereby forming a sealed display substantially similar to the display shown in figure 20 of the aforementioned WO 2003/104884.

The electro-optic medium used in the display is an encapsulated electrophoretic medium comprising an internal phase of polymer-coated titanium dioxide and an internal phase of polymer-coated carbon black in a hydrocarbon fluid, encapsulated in capsules of gelatin/gum arabic (acacia) and prepared substantially as described in the aforementioned WO 02/079869, line 17 from page 20 to page 22, line 17. The two-layer adhesive layer used comprised 25 μm of a crosslinked and non-crosslinked custom polyurethane adhesive; a control display can be made using a single layer of the same non-crosslinked adhesive of 50 μm.

Both the test and control displays were stored at 75 ℃ and in a dry environment and their switching ability was tested at intervals. The dual adhesive layer display of the present invention showed no void generation after 664 hours at 75 c, whereas the control display using a single adhesive layer generated voids in less than 24 hours. The display of the invention showed no voids at 348 hours at 60 c and 80% relative humidity and at 348 hours at 40 c and 90% relative humidity, while in each case the control display showed voids after a much shorter storage time.

As described in section a above, the dual adhesive layer electro-optic displays of the present invention may incorporate additional sealing layers or edge seals of any known type to isolate the electro-optic medium from the surrounding environment.

And part D: forming electro-optic displays without front plane lamination

Assembling a composite electro-optic display with an integral barrier layer and/or edge seal is a complex process. It is possible to deliver to the manufacturer a front plane laminate with all the layers required for the final display, but forming the front plane laminate requires aligning the individual layers in multiple lamination steps. Depending on the allowed alignment tolerances, it may not be possible to form the FPL using either a web-based or a plate-based process. Typically, it is still necessary for the edge seal to be formed by the manufacturer for each display individually. For manufacturing or inventory reasons, it is desirable to avoid as much as possible assembling the entire FPL structure before sending it to the manufacturer of the final display.

Accordingly, layer-by-layer formation of an electro-optic display is advantageous over providing an entire FPL, based on the requirement for positional accuracy of lamination. Such a layer-by-layer approach also has manufacturing advantages in that each layer can be coated, transformed or inspected individually, which is required to achieve cost-effectiveness for each layer. The method allows the layers to be cut to size as required by the individual manufacturers, and thus provides flexibility in transferring the different layers to different manufacturers of the display, thereby eliminating the need to manufacture fully assembled FPLs for each manufacturer.

A number of techniques for assembling electro-optic displays layer by layer are described in the aforementioned WO2005/041160 and will not be repeated here. Instead, the process for making an electro-optic display, generally designated 600, as shown in figure 6E of the drawings, will be discussed herein by way of example, although it is contemplated that any structure may be employed that is compatible with the requirements of the edge seal and the front substrate. An electro-optic display 600 (which is equivalent to that shown in figure 9 of the aforementioned PCT/US 2006/62399) comprises a front substrate 602, the front substrate 602 having barrier properties and being provided with a thin, transparent electrically conductive layer (not separately shown in figure 6E) on its lower surface (as shown in figure 6E). The display 600 also includes an upper laminated adhesive layer 604, an electro-optic layer 606, a lower laminated adhesive layer 608, and a backplane 610, the backplane 610 having similar barrier properties as the front substrate 602. The front substrate 602 and the back-plate 610 are made larger in both dimensions than the intermediate layers 604, 606 and 608, so that the peripheral portions 602P and 610P of the front substrate 602 and the back-plate 610, respectively, extend outwardly beyond the edges of these intermediate layers. An edge seal 612 extends between the peripheral portions 602P and 610P, thus forming a complete seal around the electro-optic layer 606.

Fig. 6A-6D illustrate successive stages in the manufacture of an electro-optic display 500. One preferred process for forming an electro-optic display begins with a web of a lower laminate adhesive layer 608 sandwiched between first and second release sheets; the web can obviously be prepared by coating an adhesive layer on one release sheet and covering the coated layer with another release sheet. A piece is cut from the web, sized to provide the lower laminated adhesive layer 608 shown in fig. 6E, the first release sheet is removed, and the adhesive layer 608 and second release sheet 614 are laminated to the backing sheet 610 to form the structure shown in fig. 6A.

In the next step of the process, a web of electro-optic layer 606 is formed intermediate the third and fourth release sheets; the web can obviously be prepared by coating an electro-optic layer on one release sheet and covering the coated layer with another release sheet. A piece is cut from the web, sized to provide the electro-optic layer 606 shown in fig. 6E, and the third release sheet is removed. The second release plate 614 is also removed from the configuration shown in fig. 6A. The electro-optic layer/fourth release sheet is then laminated to the underlying adhesive layer to form the structure shown in FIG. 6B, in which the electro-optic layer 606 is covered by a fourth release sheet 616.

The third stage of the process is very similar to the first stage. A web of the upper laminate adhesive layer 604 sandwiched between the fifth and sixth release sheets is prepared and a piece is cut from the web to the size required to provide the upper adhesive layer 604 as shown in figure 6E. The fifth release sheet is removed, the fourth release sheet is removed from the structure shown in FIG. 6B, and the upper adhesive layer 604 is laminated to the electro-optic layer 606 to form the structure shown in FIG. 6C, wherein the adhesive layer 604 is covered by the sixth release sheet 618.

In the next step of the process, a web of the anterior substrate 602 is secured to a web of stiffening layer 620, the resulting composite web is cut to form blocks having the desired dimensions of the anterior substrate 602 as shown in FIG. 6E, the sixth release sheet 618 is removed from the structure shown in FIG. 6C, and the anterior substrate 602 is laminated to the adhesive layer 604 to form the structure shown in FIG. 6D. Here, the material needed to form edge seal 612 may be interspersed between perimeter portions 602P and 610P and cured to form edge seal 612 as shown in fig. 6E. The stiffening layer 620 may then be removed to form the final electro-optic display 600.

Obviously, many different variations on the above process are possible. For example, in the above process, each layer is added individually to the stack of layers formed on the backplane 610. Also, it is possible to assemble a set of layers having the same dimensions separately and then add this set of layers to the stack in a single lamination operation. For example, in the process shown in FIGS. 6A through 6E, the lower adhesive layer 608, electro-optic layer 606, and upper adhesive layer 604 can all be prepared in the form of webs as described above, with separate webs being laminated together after one release sheet is removed from each web, and cut into sized pieces only after all three layers have been laminated together.

It will be appreciated that in the above process, a single layer of the final display is prepared in the form of a web sandwiched between two release sheets which are later removed from the central layer at different times, thus requiring the two release sheets to have an asymmetric character, i.e. different degrees of adhesion to the central layer, so that one of the release sheets can be removed without disturbing the other. It is well within the ability of the person skilled in the art to provide such a release sheet with asymmetric properties, as described in the aforementioned example of WO 2004/023195.

The display of the present invention may incorporate any known type of edge seal, including any of the types described in the aforementioned PCT/US 2006/62399. The display of the present invention may also incorporate an additional sealing layer of any known type to isolate the electro-optic medium from the environment, as discussed in section a above.

The above-described process allows the manufacture of electro-optic displays using a tight tolerance (light tolerance) laminate, which is desirable for many active matrix applications. In some cases, the process may also facilitate the formation of an edge seal.

In the displays of all aspects of the present invention, the configuration of the electrodes may be of any type as described in the aforementioned E Ink and MIT patents and applications. For example, the display may be of the direct drive type, in which the backplate is provided with a plurality of electrodes, and each electrode is provided with a separate connector through which the controller controls the voltage applied to a particular electrode. In such direct drive displays, the entire display is typically covered with a single continuous front electrode, although other configurations of front electrodes are also possible. Depending on the type of electro-optic material used, it is also possible to use a passive matrix drive arrangement, typically in which the backplane carries a plurality of elongate parallel electrodes ("column electrodes") and on the other side of the electro-optic material a plurality of elongate parallel electrodes ("row electrodes") are arranged, extending at right angles to the column electrodes, the overlap of a particular row electrode and a particular column electrode defining a pixel of the display. The display may also be of the active matrix type, typically with a single continuous front electrode covering the entire display and a matrix of pixel electrodes on a backplane, each pixel electrode defining a pixel of the display and having a transistor or other non-linear element associated therewith, the active matrix display being scanned and written in a row-by-row fashion in a conventional manner. Finally, the present display may also be of the stylus-driven type (typically) with a single electrode on the back plate and no permanent front electrode, writing of the display being achieved by moving the stylus over the front surface of the display.

Claims (12)

1. A process for producing a front plane laminate for an electro-optic display, the process comprising;

forming a subassembly comprising a lamination adhesive layer (304) and a layer of electro-optic medium (302); and

a light transmissive electrode layer (310) is then secured to the exposed surface of the laminate adhesive layer (304) of the sub-assembly, the electrode layer (310) having a tab portion (316) extending beyond the periphery of the laminate adhesive layer and the electro-optic medium layer (304, 302).

2. A process according to claim 1 wherein the electrode layer (310) is larger in both dimensions than the layer of electro-optic medium (302).

3. A process according to claim 1, wherein the subassembly further comprises at least one release sheet (300, 306) covering at least one exposed surface of the lamination adhesive layer (304) and the layer of electro-optic medium (302).

4. The process of claim 1, wherein the light-transmissive electrode layer is carried by a support layer.

5. A process according to claim 1 wherein the sub-assembly comprises first and second layers of laminating adhesive (304, 312) disposed on opposite sides of the layer of electro-optic medium (302).

6. The process of claim 1, wherein after securing the light-transmissive electrode layer to the lamination adhesive layer, the subassembly is laminated to a backplane comprising at least one electrode, wherein the tab portion is in contact with a contact disposed on the backplane.

7. A process for forming a flexible electro-optic display, the process comprising;

providing a backing plate comprising at least one electrode;

providing a front plane laminate (400), the front plane laminate (400) comprising a light-transmissive electrically conductive layer (406), a layer of solid electro-optic medium (408), an adhesive layer (410) and a release sheet (412, 414);

removing the release sheet (412, 414) from the front plane laminate (400); and

laminating (400) the front plane laminate to the backplane to form an electro-optic display,

the process is characterized in that prior to said laminating, a stiffening layer (402) is fixed on at least one of said anterior planar laminate (400) and said back-plate, said stiffening layer (402) being used to increase the stiffness of said anterior planar laminate and/or back-plate.

8. A hardened front plane laminate (400) comprising, in order: a hardened layer (402), a light-transmissive electrically-conductive layer (406); a layer (408) of solid electro-optic medium in electrical contact with the electrically conductive layer (406); an adhesive layer (410) and a release sheet (412, 414), the stiffening layer (402) being removable from the electrically conductive layer (406).

9. An electro-optic display comprising: a backing plate having at least one electrode; a first layer of non-crosslinked adhesive in contact with the backing sheet; a second layer of cross-linked adhesive on the other side of the first layer opposite the backing sheet; and a layer of electro-optic medium opposite the first layer on the other side of the second layer.

10. An electronic book reader, portable computer, tablet computer, mobile phone, smart card, sign, watch, shelf label or flash drive comprising a display according to claim 9.

11. A front plane laminate (500) comprising, in order: a light-transmissive electrically-conductive layer (504), a layer of electro-optic medium (506), a layer of cross-linked adhesive (508), a layer of non-cross-linked adhesive (510), and a release sheet (512).

12. A dual release film comprising:

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

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

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

a release sheet, opposite the layer of solid electro-optic medium, arranged on the other side of the first adhesive layer,

wherein one of the first and second adhesive layers comprises a first sub-layer of cross-linked adhesive adjacent to the surface of the layer of solid electro-optic medium and a second sub-layer of non-cross-linked adhesive.