HK1167465B - Electro-optic displays with color filters - Google Patents

Description

Electro-optic display with color filter

The present application relates to:

(a) U.S. patent publication numbers 2004/0190114;

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

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

Technical Field

The present application relates to electro-optic displays and color filters for use in such displays.

Background

Background terminology and the state of the art with respect to electro-optic displays are discussed in detail in U.S. patent No. 7,012,600, to which the reader is referred for further information. Accordingly, the following is a brief summary of the terminology and state of the art.

As applied to materials or displays, the term "electro-optic" is used herein in its conventional sense in the imaging arts 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 display state to its second display state by application of an electric field to the material. Although optical properties generally refer to colors that are perceivable by the human eye, they may also refer to other optical properties, such as transmission of light, reflectivity, luminescence, or pseudo-color in the sense of a change in reflectivity of electromagnetic wavelengths outside the visible range when the display is used for machine reading.

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 means of an addressing pulse having a finite duration, that state will continue for a time at least several times (e.g. at least 4 times) the minimum duration of the addressing pulse required to change the state of that display element after the addressing pulse has terminated.

Several types of electro-optic displays are known, for example:

(a) rotating two-color element displays (see, e.g., U.S. Pat. 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, e.g., Nature1991, 353,737 to O' Regan, b. et al; information display, 18(3), 24 (3/2002), Bach, u. et al, adv. mater, 2002, 14(11), 845 to Bach, u. et al, and U.S. patent nos. 6,301,038, 6,870,657, and 6,950,220);

(c) electrowetting displays (see, e.g., Hayes, r.a. et al, Nature, 425, 383-;

(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. 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 and 6,130,774; U.S. patent application 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 patent application publication No. WO 00/38000; WO 00/36560; WO00/67110 and WO 01/07961; and European patent Nos. 1,099,207B1 and 1,145,072B 1; and other patents and applications for EInk discussed in the aforementioned U.S. Pat. No. 7,012,600).

There are several different variations of electrophoretic media. The electrophoretic medium may use a liquid or gaseous fluid; for gaseous fluids see, for example, "Electrical energy for electronic paper-like display" published by Kitamura, T.et al in IDWJapan, PaperHCS1-1 in 2001 and "Tonerdplayinginsulating particulate Schargentry" published by Yamaguchi et al in IDWJapan, PaperAMD4-4) in 2001; U.S. patent publication numbers 2005/0001810; european patent application 1,462,847; 1,482,354, respectively; 1,484,635, respectively; 1,500,971, respectively; 1,501,194, respectively; 1,536,271, respectively; 1,542,067, respectively; 1,577,702, respectively; 1,577,703 and 1,598,694; and international application WO 2004/090626; WO2004/079442 and WO 2004/001498. The medium may be encapsulated, comprising a plurality of capsules, each capsule itself comprising an internal phase comprising electrophoretically mobile particles suspended in a fluid suspension medium, and a capsule wall surrounding the internal phase. Typically, the capsules themselves are held within a polymeric binder to form an adhesive layer (coherentlayer) located between two electrodes; see the MIT and EInk patents and applications mentioned above. Alternatively, the walls surrounding the discrete microcapsules in the 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 polymeric material; see, for example, U.S. patent No. 6,866,760. For the purposes of this application, such polymer-dispersed electrophoretic media are considered to be a subclass of encapsulated electrophoretic media. Another variation is the so-called "microcell electrophoretic display", in which charged particles and a fluid are retained 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.

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

Although electrophoretic media are typically opaque (e.g., because in many electrophoretic media the particles substantially block transmission of visible light through the display) and operate in a reflective mode, many electrophoretic displays can be operated in a so-called "shutter mode" in which one display state is substantially opaque and one display state is light-transmissive. See, e.g., the aforementioned U.S. patent nos. 6,130,774 and 6,172,798, and U.S. patent No. 5,872,552; 6,144,361, respectively; 6,271,823, respectively; 6,225,971, respectively; and number 6,184,856. A dielectrophoretic display similar to the electrophoretic display but relying on variations in electric field strength may operate in a similar mode; see U.S. patent No. 4,418,346.

Other types of electrophoretic media may also be used in the present invention.

Many types of electro-optic media are substantially monochromatic (monochrome), meaning that any medium is provided that has two extreme optical states and a gray scale ranging between the two extreme optical states. As already explained, the two extreme optical states need not be black and white. For example, one extreme optical state is white and the other is dark blue, making the intermediate grey scale blue at a different shade, or one extreme optical state is red and the other is blue, making the intermediate grey scale violet at a different shade.

There is an increasing demand for full-color displays, even those of small portable size, such as those found on most cell phones today, are full-color. To provide a full color display using a single color medium, it is necessary to place the color filter array in a position where the display can be viewed through the color filter array, or to place areas of different electro-optic media capable of displaying different colors in close proximity to each other.

However, attaching the color filter to the electro-optic display in the correct position is a difficult operation. A number of color filter arrays are formed on a glass plate or similar rigid material to allow the color filters to maintain a stable size (even if the size of the color filter array is slightly distorted, this may result in at least a portion of the color filter array being misaligned with respect to the pixels of the display, thereby causing a deviation in the color displayed to the viewer). For similar reasons, most backplanes used in color electro-optic displays are made of rigid materials. The electro-optic medium is secured to one of the rigid plates, which are then laminated together, typically with a layer of polyurethane, or other laminating adhesive, positioned between the two rigid plates to form the final display. The thickness of the laminate adhesive layer may be about 25 μm. Laminating adhesives are tacky at room temperature and, therefore, it is difficult to laminate two rigid plates together without trapping air pockets between them, especially when the size of the plates is particularly small. Although special alignment tools are used to keep the rigid plate flat and a comparable pressure on the order of 100psig (about 0.8MPa) is applied at room temperature, it has been found that it is difficult to avoid trapping large bubbles. The number of air bubbles can be reduced or eliminated by passing the laminated display between rollers under sufficient temperature and pressure conditions, or by autoclaving (autoclaving) the display again under sufficient temperature and pressure conditions. This emergency method of bubble removal can significantly increase the cost and cycle time of manufacturing the display assembly, resulting in time and effort consuming and not necessarily resulting in a high quality color display. Furthermore, this method for laminating rigid panels, typically glass panels, is not a good manufacturing method because it introduces many additional limitations on electrical and rheological properties, making lamination very difficult.

Disclosure of Invention

Accordingly, there is a need for a method of laminating a color filter array to a backplane to form an electro-optic display that eliminates or at least alleviates the foregoing problems, and the present invention is providing such a method.

The present invention provides a method of assembling an electro-optic display that separates lamination of an electro-optic layer to a backplane from lamination and alignment of a color filter array to the backplane.

Accordingly, one aspect of the present invention provides a method for manufacturing a colour electro-optic display, the method comprising:

providing an electro-optic subassembly comprising an electro-optic layer and a light-transmissive electrically-conductive layer;

laminating the electro-optic subassembly to a backplane comprising a plurality of electrodes such that the electro-optic layer is disposed between the backplane and the electrically conductive layer;

placing a flowable material on the conductive layer; and

a color filter array is placed on the conductive layer and aligned with the electrodes of the backplane to form a color electro-optic display.

In this method, an adhesive layer is typically provided between the electro-optic layer and the backplane. However, if the electro-optic layer is sufficiently tacky to the backplane, it is not always necessary to provide such a separate electro-optic layer, for example, as is known from U.S. patent No. 7,110,164, in some cases, the polymeric binder component within the electro-optic layer can act as an adhesive, thus eliminating the need for a separate adhesive layer.

In one implementation of the method, the electro-optic subassembly is in the form of a front plane laminate comprising an electrically conductive layer, an electro-optic layer, and an adhesive layer disposed on an opposite side of the electro-optic layer from the electrically conductive layer, and lamination is achieved by contacting the adhesive layer to a backplane. The front plane laminate may further comprise a release sheet overlying the surface of the adhesive layer remote from the electro-optic layer and removed prior to laminating the front plane laminate to the backplane. As discussed in U.S. patent No. 6,982,178, the release sheet may include an electro-optic layer to facilitate testing of the electro-optic performance of the front plane laminate; the conductive layer may typically be provided by the same metallized polymer film as the release sheet. In another implementation of the method, the electro-optic subassembly is in the form of an inverted front plane laminate comprising, in order, a conductive layer, a first adhesive layer, an electro-optic layer, and a second adhesive layer, and the lamination is achieved by contacting the second adhesive layer to the backplane. The inverted front plane laminate may further comprise a release sheet overlying the surface of the second adhesive layer remote from the electro-optic layer and removed prior to laminating the inverted front plane laminate to the backsheet.

Another variation of this method employs a so-called "double release membrane" as described in U.S. patent No. 7,561,324. This "dual release film" is essentially a simplified version of the front plane laminate of the aforementioned U.S. patent No. 6,982,178. One form of dual release sheet comprises a layer of solid electro-optic medium sandwiched between two layers of adhesive, one or both (typically two) of which are covered by a release sheet. To use such a dual release film in the present method, one of the release sheets is removed from the dual release film and the remaining layer is laminated to a backing sheet with the exposed adhesive layer in contact with the backing sheet. The second release sheet is then removed and the conductive layer is laminated in a second lamination to the backplane/electro-optic layer subassembly formed at the first lamination. Alternatively, but generally less desirably, the lamination can be performed in the reverse order, with a first lamination securing the electro-optic layer to the conductive layer to form an inverted front plane laminate and a second lamination securing the inverted FPL to the backplane, as described above. A variant of these two methods using a double release film allows the conductive layer and the electro-optical layer to be selected independently of each other, which is very useful from a manufacturing point of view; different customers of the manufacturer may require different types of conductive layers but the same electro-optic layer, and to meet the customer's needs, the manufacturer may manufacture a dual release film that employs a common electro-optic layer and then laminate the dual release film to the selected conductive layer upon specific instructions from the customer.

Another variation of this approach is to employ a so-called "inverted front plane laminate" described in U.S. patent publication No. 2007/0109219, which is essentially a variation of the front plane laminate described in U.S. patent No. 6,982,178. The inverted front plane laminate sequentially comprises: at least one of the light-transmitting protective layer and the light-transmitting conductive layer, an adhesive layer, a solid electro-optic medium layer, and a release sheet. The inverted front plane laminate is used to form an electro-optic display having a layer of laminating adhesive between the electro-optic layer and a 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 definition and low temperature performance.

In the method of the present invention, the electro-optic subassembly may further comprise a front substrate disposed on the opposite side of the electrically conductive layer from the electro-optic layer, the front substrate providing mechanical support and protection to the electrically conductive layer. In some cases, it is desirable to have such a front substrate because the conductive layer is not self-supporting; for example, when the conductive layer is made of sputtered ITO, the thickness of the ITO is typically on the order of 1 μm and it is not self-supporting. The thickness of the front substrate may be no greater than 50 μm, desirably no greater than 25 μm; the front substrate remains in the final display and if it is too thick, it can cause parallax problems between the electro-optic layer and the color filter array. Whether or not there is a front substrate, the electro-optic layer assembly may include a mask that may be used to significantly increase the thickness of the subassembly, thereby facilitating handling of the subassembly, and which may also be used to prevent mechanical damage to the conductive layer and/or the front substrate (if any). The mask is removed prior to laminating the color filter array. The thickness of the mask may be 100-200 μm, although thicker masks may be used if desired, for example to protect the integrated circuits on the backplate.

The method allows for the use of various flowable materials and various methods of introducing the flowable material between the conductive layer and the color filter array. In one variation of the method, disposing the flowable material and the color filter array on the conductive layer is accomplished by: the method includes the steps of disposing a plurality of spacers on an exposed surface of an electro-optic subassembly laminated to a backplane, disposing a color filter array on the plurality of spacers, introducing a curable polymer between the exposed surface and the color filter array, and curing the curable polymer. The method can also include placing a curable edge sealing polymer around a perimeter of the electro-optic layer but leaving a plurality of voids within the edge sealing polymer, curing the edge sealing polymer to form an edge seal, wherein the edge seal has a plurality of apertures extending therethrough, drawing a vacuum to at least one aperture while connecting at least one of the other apertures to a supply of curable polymer, thereby drawing the curable polymer between the conductive layer and the color filter array.

In another variation of the method, the flowable material is a curable polymer dispersed on the conductive layer, and after the color filter array is placed on the curable polymer and aligned, the curable polymer is cured to secure the color filter array to the conductive layer. In this variant of the method, curing the polymer is advantageously achieved by two steps: after the color filter array is placed on and aligned with the curable polymer, the plurality of discrete portions of curable polymer are cured, the curable polymer is treated to remove air bubbles therefrom, and the remaining portions of uncured polymer are cured to form the final display.

In yet another variation of the method, the flowable material is a room temperature (about 21 ℃) non-tacky adhesive layer. Alternatively, the flowable material is a non-curable material that remains unchanged in the final display, such as a grease, preferably a silicone grease. When such a non-curable material is employed, the method may further comprise, after alignment of the color filter array, dispensing a curable polymer around the perimeter of the electro-optic layer and the color filter array, and curing the polymer to form an edge seal that secures the electro-optic layer and the color filter array to each other.

In any of the methods of the present invention that require removal of air bubbles from the flowable material by autoclaving or other means, it is desirable to ensure that the color filter array does not move relative to the backplane during the air bubble removal process. Although mechanical clamping means may be used to hold the color filter array, it is more convenient to spot cure the flowable material itself, or (if a non-curable material is used) the curable edge encapsulating material to hold the color filter in place relative to the backplane.

The electro-optical layer used in this method may be of any of the types discussed above. For example, the electro-optic layer may include a rotating bichromal member or an 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 charged particles and the fluid may be confined within a plurality of capsules or microcells. Alternatively, the charged particles and fluid may appear as a plurality of discrete droplets surrounded by a continuous phase comprising a polymeric material. The fluid may be in a liquid or gaseous state.

The invention also provides an electro-optic display comprising, in order:

a back plate comprising a plurality of electrodes;

an electro-optic layer;

a light-transmitting conductive layer;

a layer of non-cured, flowable material; and

a color filter array.

In this display, the flowable material may be a grease, such as silicone grease.

Drawings

FIG. 1 is a schematic cross-sectional view through a front plane laminate for use in the method of the present invention;

FIG. 2 is a schematic cross-sectional view, similar to FIG. 1, of an inverted front plane laminate for use through the method of the present invention;

FIG. 3 is a schematic cross-sectional view, similar to FIGS. 1 and 2, through the deformed inverted front plane laminate of FIG. 2;

FIG. 4 is a top view of an electro-optic display assembled using the method of the present invention, taken at an intermediate point in the method, i.e., after lamination of the front plane laminate to the backplane but before lamination of the color filter array;

FIG. 5 is a flow chart showing the manner in which the method of the present invention conveniently produces both monochrome and color electro-optic displays using the same front plane laminate and backplane.

Detailed Description

As already mentioned, the present invention provides a method for forming an electro-optic display in which an electro-optic layer and an electrically conductive layer (typically in the form of a front plane laminate) are first laminated to a backplane. A flowable material is then deposited over the conductive layer and a Color Filter Array (CFA) is placed over the conductive layer, which can be performed in either order. In some implementations of the method, the flowable material is cured after the CFA is in place; in other implementations, a non-curing material may be used such that the material remains unchanged throughout the final display.

In the present method, it is desirable that the electro-optic layer take the form of a front plane laminate. The FPL may be a "classical" FPL as described in U.S. Pat. No. 6,982,178 or an inverted FPL as described in U.S. patent application publication No. 2007/0109219. In either case, it is desirable to make the substrate of the FPL near the CFA thin in order to minimize parallax and color deviations caused by the gap between the CFA and the electro-optic layer. Figure 1 schematically illustrates a generic classical FPL (shown generally at 100) suitable for use in the present method. The FPL100 includes a thin front substrate 102, which is typically a transparent polymer film formed from, for example, poly (ethylene terephthalate) (PET). The front substrate 102 may have a thickness of about 6 to about 50 μm; commercially available films having a thickness of about 13 μm are well suited for use in this process. The use of a thin front substrate is important because the color filter array (described below) is spaced from the electro-optic layer by the thickness of the front substrate (and by the thickness of the conductive layer described below, but the conductive layer is typically much thinner than the front substrate) and if the front substrate is too thick, parallax problems are encountered, resulting in a reduction in the quality of the image on the color display. The FPL100 also includes a light-transmissive conductive layer 104, which can be made of, for example, Indium Tin Oxide (ITO), carbon nanotubes, or organic conductors. The requirements on the properties of the conductive layer are not of primary importance as long as the conductive layer is sufficiently conductive to switch the electro-optical layer, and a resistance below 104 ohm/square is generally sufficient. ITO-coated PET films are commercially available and can be used to form layers 102 and 104 of FPL 100.

The next layer of the FPL100 is an electro-optic layer 106, where the electro-optic layer 106 is an encapsulated electrophoretic layer comprising capsules in a polymer binder. The electro-optic layer may be coated directly onto the conductive layer 104 as described in the aforementioned U.S. patent No. 6,982,178. Disposing a laminating adhesive layer 108 on a side of the electrophoretic layer 106 opposite the substrate 102; suitable adhesives are discussed, for example, in U.S. Pat. nos. 7,012,735 and 7,477,444. Finally, the FPL100 includes a release plate 110.

Fig. 2 illustrates an inverted front plane laminate 200 that can be used in the present method. The inverted FPL200 differs from the classical FPL100 shown in FIG. 1 by including a second adhesive layer 208 between the conductive layer 104 and the electro-optic layer 106. The reason for including the second adhesive layer 208 is discussed in detail in the aforementioned 2007/0109219.

Fig. 3 illustrates a second inverted front plane laminate 300 that differs from the inverted FPL200 shown in fig. 2 by the addition of a mask 312 covering the substrate 102. As explained in U.S. patent application publication No. 2008/0174853, it is useful to include a mask in a thin FPL or similar multilayer film to facilitate handling of the film and/or to provide mechanical protection to the substrate during manufacture or operation of the display assembly.

The FPL100 shown in FIG. 1 can also be modified by adding a mask similar to that shown in FIG. 3.

As already mentioned, the first step of the process of the present invention is to laminate the FPL to the backplane; the backplane may be of the direct drive type (in which each electrode is provided with a separate conductor such that the voltage on each electrode is independently controllable) or of the active matrix type (in which pixel electrodes are arranged in a two-dimensional matrix of rows and columns, in which a non-linear device, typically a thin film transistor, is associated with each pixel, and in which all electrodes in each row are connected to a row electrode and all electrodes in each column are connected to a column electrode). Some types of electro-optic media also allow the use of passive matrix backplanes.

Figure 4 is a top view of a preferred method of the present invention after a FPL402 (which may be of any of the types described above) is laminated to a backplane, shown generally at 404. As shown in fig. 4, the backplane 404 comprises a substrate 406, the central portion of which is occupied by an active matrix backplane 408; the FPL402 is laminated to the active matrix backplane 408 such that a small perimeter portion of the FPL402 extends beyond the edge of the backplane 408. An alignment mark 410 is provided on the substrate 402 near the footprint of the FPL 402. A die attach area 412 is also provided on substrate 406 at a location spaced from backplane 408.

The FPL402 may be laminated to the backplane 408 using any of the methods described in the aforementioned EInk patents and applications. Basically, the release sheet 110 (see fig. 1 to 3) is peeled off the FPL, and the FPL is laminated to the back sheet, typically under elevated temperature and pressure. Once the FPL is laminated, which results in the intermediate structure shown in fig. 4, the color filter array is attached using the first method of the present invention.

As already mentioned, this method requires the introduction of a flowable liquid material between the FPL and the color filter array. Within the scope of the present invention, various methods may be used to introduce the flowable liquid material. One method is similar to the method used to assemble a liquid crystal display. A mixture of spacers (typically spheres) having a precisely controllable diameter and a curable polymer is dispensed around the perimeter of the FPL to form a perimeter seal, but leaves a plurality of voids when sealed. The CFA is then placed on the mixture of spacer and polymer. Accurate positioning of the CFA relative to the backplane is typically achieved by aligning alignment marks on the CFA with similar marks on the backplane; the uncured polymer allows the CFA to move relative to the backing plate. The polymer is then cured to fix the CFA relative to the backplane. One or more of the apertures in the perimeter seal formed by the above-described voids are connected to a vacuum system, while the other apertures are connected to a source of a low viscosity curable polymer that is attracted by the vacuum system located between the FPL and the CFA. Finally, the low viscosity curable polymer is cured to form the final display. In some cases it may be beneficial to form a narrow peripheral edge of (typically) a different curable polymer at the perimeter of the FPL after lamination of the FPL to the backplane, such different curable polymer being selected to avoid switching performance issues at the display edges. The narrow peripheral edge of the polymer also seals the FPL, thereby preventing loss of moisture and/or ingress of environmental contaminants when the FPL is exposed to vacuum during the filling process. Similar perimeter sealing of the FPL may also be used in other variations of the method of the present invention described below.

In one variation of the method, a curable polymer is dispensed on top of the FPL after the FPL is laminated to the backplane. Selecting a pattern of curable polymer dispersion that minimizes air entrapment between the FPL and the CFA to be placed on the FPL; for example, the pattern may be a single pit (dummy) located at the center of the FPL, a line pattern radiating outward from the center of the FPL, or an "X" shape. The CFA is then applied down to the curable polymer and pressed gently down, causing the curable polymer to spread and form the entire area of the face-to-face FPL and CFA surfaces. The volume of curable polymer on the FPL is carefully controlled so that the entire area of the facing FPL and CFA surfaces can be covered, but no excess curable polymer leaks out of the CFA edges. At this point, the CFA may be aligned with alignment marks such as those shown in FIG. 4, and a large amount of the small area of curable polymer near the perimeter of the FPL is cured to lock the CFA in place relative to the backplane. The polymer is then autoclaved or other known techniques to remove residual bubbles. After the bubbles are removed, the uncured polymer on the remaining area is cured to form the final display.

In another variation of the method, the CFA is bonded to the FPL with a "solid-state," non-tacky adhesive ("non-tacky" means non-tacky at room temperature or about 21 ℃). The adhesive is placed on the FPL or CFA, conveniently coated onto a release sheet, and other components attached immediately after lamination to the FPL or CFA. It may be desirable to form a rough pattern or some rough pattern in the adhesive, which allows air to escape when laminating the FPL to the CFA. The non-tacky adhesive allows sufficient relative movement of the FPL and CFA with respect to each other to bring the FPL and CFA into overall alignment prior to laminating them to the CFA using any one or more of elevated temperature, pressure and vacuum. In some cases, the post-lamination CFA/FPL combination may be reheated sufficiently after lamination to achieve final alignment of the two portions.

In another variant of the method, a pressure-sensitive adhesive (PSA) that is tacky at room temperature may be used as the flowable material. The use of such a PSA avoids the risk of deformation of certain display components that may result from operation at elevated temperatures, but has the disadvantage that limited movement of the color filter array relative to the backplane is possible once these parts are in contact with each other.

In another variation of the present method, a grease film may be used to attach the FPL to the CFA. Suitable greases include the silicone greases described in U.S. patent nos. 5,275,680 and 5,371,619. These greases are chemically stable, perform stably over a wide temperature range, have a long working life at room temperature and form fewer voids during lamination. The grease film may be coated directly on the FPL or CFA or a pre-formed (e.g. coated on a release sheet) grease film may be laminated to one or the other of these parts. The parts are then brought together and accurately aligned. The air bubbles remaining in the grease can be removed by autoclaving, which is particularly effective for grease films due to the viscosity and fluidity of the grease. Because grease can flow even in the finished display, it is desirable to disperse a curable polymer around the perimeter of the FPL and CFA and cure the polymer to form an edge seal in the final step of assembling the display to secure the FPL and CFA in the correct position relative to each other. As already noted, such a curable polymer edge seal may be spot cured to keep the color filter array stationary relative to the backplane during the operation of removing air bubbles from the grease.

As already mentioned, the present invention separates the lamination of the electro-optic layer (typically in the form of an FPL) to the backplane from the lamination of the CFA to the electro-optic layer. A further advantage is that it provides a convenient process for manufacturing both monochrome and colour displays on a single production line, as illustrated in figure 5. As shown, the production line may be operated to take a supply of FPL502 and a backplane 504 and laminate them together (as shown at 506) to form a backplane/FPL laminate. The laminate is then laminated to a CFA to form a color display, as shown at 508, or a protective layer is laminated over the FPL to form a monochrome display, as shown at 510.

In summary, the present invention provides an improved white state of a color display, wherein only the saturation of the basic color is less affected, providing a balanced color reproduction and better transparent saturation, and saving energy when front or back lighting is used.

Claims (7)

1. A method for manufacturing a colour electro-optic display, the method comprising:

providing an electro-optic subassembly comprising an electro-optic layer and a light-transmissive electrically-conductive layer;

laminating the electro-optic subassembly to a backplane comprising a plurality of electrodes such that the electro-optic layer is disposed between the backplane and the electrically conductive layer; and

a color filter array is placed on the conductive layer and aligned to the electrodes of the backplane to form a color electro-optic display,

the method is characterized by, after laminating the electro-optic subassembly to the backplane but before disposing the color filter array on the conductive layer, disposing a flowable material on the conductive layer,

wherein the placement of the flowable material and the color filter array on the conductive layer is accomplished by: the method includes disposing a plurality of spacers on a conductive layer, disposing a color filter array on the plurality of spacers, introducing a curable polymer between the conductive layer and the color filter array, and then curing the curable polymer.

2. A method according to claim 1 further comprising placing a curable edge sealing polymer around the perimeter of the electro-optic layer but leaving a plurality of voids in the edge sealing polymer, curing the edge sealing polymer to form an edge seal, wherein the edge seal has a plurality of holes extending therethrough, drawing a vacuum to at least one hole while connecting at least one of the other holes to the supply of curable polymer, thereby drawing the curable polymer between the conductive layer and the color filter array.

3. A method for manufacturing a colour electro-optic display, the method comprising:

providing an electro-optic subassembly comprising an electro-optic layer and a light-transmissive electrically-conductive layer;

laminating the electro-optic subassembly to a backplane comprising a plurality of electrodes such that the electro-optic layer is disposed between the backplane and the electrically conductive layer; and

a color filter array is placed on the conductive layer and aligned to the electrodes of the backplane to form a color electro-optic display,

the method is characterized by, after laminating the electro-optic subassembly to the backplane but before disposing the color filter array on the conductive layer, disposing a flowable material on the conductive layer,

wherein the flowable material is a curable polymer dispersed on the conductive layer and, after the color filter array is placed on the curable polymer and aligned, the curable polymer is cured to secure the color filter array to the conductive layer.

4. A method according to claim 3 wherein after the color filter array is placed on and aligned with the curable polymer, the plurality of separate portions of curable polymer are cured, the curable polymer is treated to remove air bubbles therefrom, and the remaining portions of uncured polymer are cured to form the final display.

5. A method according to claim 3, wherein the electro-optic layer comprises a rotating bichromal member or an electrochromic material.

6. A method according to claim 3, wherein the electro-optical layer 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.

7. The method of claim 6, wherein the fluid is gaseous.