HK1098542B - Process for sealing electro-optic display - Google Patents

Description

Process for sealing electro-optic displays

The present invention relates to U.S. patent applications serial No. 10/249,957, publication No. 2004/0027327 (see also corresponding international application PCT/US03/16433, publication No. WO 03/104884), filed on day 22/5/2003, and to U.S. patent applications serial No. 10/605,024, publication No. 2004/0155857 (see also corresponding international application PCT/US 03/27686, publication No. WO2004/023195), filed on day 2/9/2003, to which the reader is referred for background information.

The present invention relates to a process for encapsulating electro-optic displays, which is designed particularly, although not exclusively, for encapsulating such displays using an encapsulated electrophoretic medium. The invention is also applicable to various other types of electro-optic displays using a solid electro-optic medium, meaning that it has a solid outer surface, although the medium may, and often does, have internal cavities containing a fluid (either liquid or gas). Accordingly, the term "solid state electro-optic display" includes encapsulated electrophoretic displays, encapsulated liquid crystal displays, and other types of displays discussed below.

An electro-optic display comprises a layer of electro-optic material, which term is used herein in its conventional sense of imaging technology to refer to a material having first and second display states differing in at least one optical property, the material changing from its first state to its second state by application of an electric field across the material. While the optical characteristic is typically a color that is perceived by the human eye, it may be another optical characteristic, such as transmission, reflection, fluorescence of light, or in the case of designs intended for machine reading, a false color, meaning a change in reflection of electromagnetic wavelengths outside the visible range.

The terms "bistable" and "bistable" are used herein in their conventional sense in the art to refer to displays which comprise display elements having first and second display states which differ in at least one optical characteristic, and which thus either assume the first or assume the second display state after any given element has been actuated by means of an addressing pulse of finite duration which, after the termination of the addressing pulse, will last for at least several times (e.g. at least four times) the minimum duration of the addressing pulse required to change the state of the display element. It is shown in published U.S. patent application No.2002/0180687 that some particle-based electrophoretic displays that allow gray scale are stable not only in the extreme black and white states, but also in their intermediate gray states, as are some other types of electro-optic displays. Such displays are more appropriately referred to as "multi-stable" than bistable, although for convenience herein the term "bistable" may be used to encompass both bistable and multi-stable displays.

Several types of electro-optic displays are known. One type of electro-optic display is a rotating bichromal member type, such as described in U.S. patent nos. 5,808,783; 5,777,782, respectively; 5,760,761, respectively; 6,054,0716,055,091, respectively; 6,097,531, respectively; 6,128,124, respectively; 6,137,467, respectively; (ii) a And 6,147,791 (although this type of display is often referred to as a "rotating bicolor ball" display, the term "rotating bicolor member" is preferred for greater accuracy because the rotating members are not spherical in some of the above patents). Such displays use a large number of small objects (usually spherical or cylindrical) having two or more portions of different optical properties and an internal dipole. These small objects are suspended in liquid-filled cavities in the matrix, which cavities are filled with liquid so that the objects can rotate freely. The appearance of the display can be changed by applying an electric field across the display, thereby rotating the object to various positions and changing the portions of the object that are seen through the viewing surface. 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 nanochromic (nanochromic) thin film, which includes electrodes formed at least in part of a semiconducting metal oxide and a plurality of dye molecules attached to the electrodes that are reversibly color-changeable; see, for example, O' Regan et al, Nature 1991, 353, 737; and Wood, d., Information Display, 18(3), 24 (3 months 2002). See also Bach, u., et al, adv.mater., 2002, 14(11), 845. Nanochromic films of this type are also described, for example, in U.S. Pat. No.6,301,038, International application publication No. WO 01/27690, and U.S. patent application 2003/0214695. This type of media is also generally bistable.

Another type of electro-optic display, which has been the subject of intense research and development for many years, is a particle-based electrophoretic display in which a plurality of charged particles are moved in a suspending fluid under the influence of an electric field. Electrophoretic displays have attributes of good brightness and contrast, wide viewing angles, state bistability, and low power consumption, as compared to liquid crystal displays. The long-term image quality issues of these displays have prevented their widespread use. For example, particles that make up electrophoretic displays tend to settle, resulting in insufficient lifetime of these displays.

As noted above, electrophoretic media require the presence of a suspending fluid. In most prior art electrophoretic media, the suspending fluid is a liquid, but the electrophoretic medium can be produced using a gaseous suspending fluid, see, for example, Kitamura et al, "Electrical inside movement for electronic paper-like Display", Asia Display/IDW' 01(Proceedings of the 21^st International Display ResearchConference in conjunction with The 8^thInternational displayWorkshops, October 16-19, 2001, Nagoya, Japan), page 1517, PaperHCS1-1, AND Yamaguchi, Y., et al, "inside Display using insulating charged triboelectric", Asia Display/IDW' 01, page 1729, page AND 4-4. See also european patent application 1,429,178; 1,462,847, respectively; 1,482,354, respectively; and 1,484,625; and international application WO 2004/090626; WO 2004/079442; WO 2004/077140; WO 2004/059379; WO 2004/055586; WO 2004/008239; WO 2004/006006; WO 2004/001498; WO 03/091799; and WO 03/088495. These gas-based electrophoretic media are used in the orientation of the medium to allow such deposition, e.g. when the medium is arranged in a vertical planeThe same problems as in the liquid-based electrophoretic medium tend to occur due to particle precipitation. Indeed, particle settling appears to be a more serious problem in gas-based electrophoretic media than in liquid-based media, because the lower viscosity of gaseous suspending fluids allows for faster settling of the electrophoretic particles compared to liquid suspending fluids.

Recently, many patents to or applications in the name of the institute of technology, Massachusetts (MIT) and E Ink Corporation have been issued, which describe encapsulated electrophoretic media. Such a sealing medium comprises a number of small capsules, each of which itself comprises an internal phase containing electrophoretically mobile particles suspended in a liquid suspending medium, and a capsule wall surrounding the internal phase. The capsules themselves are typically held in a polymeric binder, forming an adhesive layer between the two electrodes. Such sealing media are described, for example, in the following U.S. patent nos.: 5,930,026; 5,961,804; 6,017,584; 6,067,185, respectively; 6,118,426, respectively; 6,120,588; 6,120,839, respectively; 6,124,851, respectively; 6,130,773, respectively; 6,130,774, respectively; 6,172,798; 6,177,921, respectively; 6,232,950, respectively; 6,249,721, respectively; 6,252,564, respectively; 6,262,706, respectively; 6,262,833; 6,300,932, respectively; 6,312,304, respectively; 6,312,971, respectively; 6,323,989, respectively; 6,327,072, respectively; 6,376,828, respectively; 6,377,387, respectively; 6,392,785, respectively; 6,392,786, respectively; 6,413,790, respectively; 6,422,687, respectively; 6,445,374, respectively; 6,445,489, respectively; 6,459,418, respectively; 6,473,072, respectively; 6,480,182, respectively; 6,498,114, respectively; 6,504,524; 6,506,438, respectively; 6,512,354, respectively; 6,515,649, respectively; 6,518,949, respectively; 6,521,489, respectively; 6,531,997, respectively; 6,535,197, respectively; 6,538,801, respectively; 6,545,291, respectively; 6,580,545, respectively; 6,639,578, respectively; 6,652,075, respectively; 6,657,772, respectively; 6,664,944, respectively; 6,680,725, respectively; 6,683,333, respectively; 6,704,133, respectively; 6,710,540, respectively; 6,721,083, respectively; 6,727,881, respectively; 6,738,050, respectively; 6,750,473, respectively; 6,753,999, respectively; 6,816,147, respectively; 6,819,471, respectively; and U.S. patent application publication nos.: 2002/0060321, respectively; 2002/0060321, respectively; 2002/0063661, respectively; 2002/0090980, respectively; 2002/0113770, respectively; 2002/0130832, respectively; 2002/0131147, respectively; 2002/0171910, respectively; 2002/0180687, respectively; 2002/0180688, respectively; 2003/0011560, respectively; 2003/0020844, respectively; 2003/0025855, respectively; 2003/0102858, respectively; 2003/0132908, respectively; 2003/0137521, respectively; 2003/0151702, respectively; 2003/0214695, respectively; 2003/0214697, respectively; 2003/0222315, respectively; 2004/0008398, respectively; 2004/0012839, respectively; 2004/0014265, respectively; 2004/0027327, respectively; 2004/0075634, respectively; 2004/0094422, respectively; 2004/0105036, respectively; 2004/0112750, respectively; and international application publication No.:

WO 99/67678；WO 00/05704；WO 00/38000；WO 00/38001；WO00/36560；WO00/67110；WO 00/67327；WO 01/07961；WO 01/05241；WO 03/107,315；WO2004/023195；WO 2004/049045；WO 2004/059378；WO 2004/088002；WO2004/088395；WO 2004/090857；and WO 2004/099862.

many of the above patents and applications recognize that the walls surrounding discrete microcapsules in an encapsulated electrophoretic medium may be replaced with a continuous phase, thus resulting in a so-called polymer dispersed electrophoretic display in which the electrophoretic medium comprises a plurality of discrete droplets of an electrophoretic fluid and a polymeric material of the continuous phase, in which discrete droplets of the electrophoretic fluid may be considered as being encapsulated or microencapsulated, even if no discrete encapsulation film is associated with each droplet, see, for example, 2002/0131147 above. Accordingly, in the present invention, 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 suspending fluid are not encapsulated within microcapsules, but are held within a plurality of cavities formed in a carrier medium (typically a polymer film). See, for example, international application publication No. WO 02/01281, and published U.S. application No.2002/0075556, both to Sipix Imaging, inc.

Another type of electro-optic display is the electro-wetting display developed by Philips, entitled "Performing Pixels" in the journal "Nature" during 9/25 th 2003: this is described in the article by Moving Images on Electronic Paper. It is described in international application PCT/US04/32828 that such electrowetting displays can be made bistable.

Other types of electro-optic displays may also be used in the present invention. Of particular interest, bistable ferroelectric liquid crystal displays (FLCs) are known in the art.

Although electrophoretic media are often opaque (e.g., because in many electrophoretic media the particles actually block visible light from transmitting through the display) and operate in a reflective mode, many electrophoretic displays can be made to operate in a so-called "shutter mode" in which one display state is substantially opaque and the other is light-transmissive. See, for example, the above-mentioned U.S. Pat. Nos. 6,130,774 and 6,172,798; and U.S. patent nos. 5,872,552; 6,144,361, respectively; 6,271,823, respectively; 6,225,971, respectively; and 6,184,856. Dielectrophoretic displays, similar to electrophoretic displays, but which rely on changes in electric field strength, can operate in a similar manner; see U.S. patent No.4,418,356. Other types of electro-optic displays may also operate in a shutter mode.

Encapsulated or microcell electrophoretic displays generally do not suffer from the clustering and settling failure modes of conventional electrophoretic devices and can provide further advantages such as the ability to print or coat the display on a wide variety of flexible and rigid substrates. ("print" is intended to include all forms of printing and coating including, but not limited to, pre-metered coating such as patch die coating, slot or extrusion coating, slide or cascade coating, curtain coating, roller coating such as knifeover roller coating, forward and reverse roller 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, electrophoretic deposition, and other similar techniques). Thus, the result display may be flexible. Further, since the display medium can be printed (using various methods), the display itself can be manufactured at low cost.

In addition to the layer of electro-optic material, electro-optic displays typically include at least two other layers disposed on opposite sides of the electrophoretic material, one of the two layers being an electrode layer. In most such displays, both layers are electrode layers, and one or both electrode layers are patterned to define the pixels of the display. For example, one electrode layer is patterned into elongate row electrodes and the other layer is patterned into elongate column electrodes extending at right angles to the row electrodes, with pixels being defined by the intersections of the row and column electrodes. Alternatively, it is more common for one electrode layer to be in the form of a single continuous electrode, while the other electrode layer is patterned with a matrix of pixel electrodes, each defining a pixel of the display. In another type of electro-optic display, which is designed for use with 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 typically being 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 aforementioned MIT and E Ink patents and applications, a process for manufacturing an encapsulated electrophoretic display is described in which an encapsulated electrophoretic medium comprising capsules in an adhesive is applied to a flexible substrate comprising Indium Tin Oxide (ITO) or similar conductive coating on a plastic film (serving as one electrode of the final display), and the capsules/adhesive coating is dried to form an electrophoretic medium adhesion layer that adheres strongly to the substrate. A backplane is separately prepared containing an array of pixel electrodes and appropriate conductor layouts for connecting the pixel electrodes to the drive circuitry. To form the final display, the substrate with the encapsulation/adhesive layer thereon is laminated to the backplane using a lamination adhesive. (very similar procedures can be used to prepare electrophoretic displays that can be used with a stylus or similar movable electrode, i.e. replacing the backplane with a simple protective layer (e.g. a plastic film) over which the stylus or other movable electrode can slide). In a preferred form of this process the backplane is itself flexible and is prepared by printing the pixel electrodes and conductors on a plastic film or other flexible substrate. An obvious lamination technique for mass production of displays using this process is roller lamination using lamination adhesive. Similar manufacturing techniques may be used for other types of electro-optic displays. For example, a microcell electrophoretic medium or a rotating bichromal member medium may be laminated to the backplane in substantially the same manner as the encapsulated electrophoretic medium.

In the above process, the lamination of the substrate carrying the electro-optical layer onto the backplane may advantageously be carried out using a vacuum lamination process. The vacuum lamination process effectively removes air from between the two layers of material being laminated, thus avoiding undesirable air bubbles in the final display that could introduce undesirable distortions in the image produced on the display. However, vacuum lamination of two parts of an electro-optic display in this manner places stringent requirements on the lamination adhesive used, as described above in 2003/0011867 and 2003/0025855, particularly in the case of displays using encapsulated electrophoretic media. The laminating adhesive must have sufficient adhesive strength to bond the electro-optic layer to the layer (typically the electrode layer) it is intended to laminate, and in the case of an encapsulated electrophoretic medium, must also have sufficient adhesive strength to mechanically hold the capsules together. If the electro-optic display is of the flexible type (an important advantage of the rotating bichromal member and the encapsulated electrophoretic display is that they can be made flexible), the adhesive must be sufficiently flexible not to introduce defects into the display when it is bent. The adhesive must have sufficient flow characteristics at lamination temperatures to ensure high quality lamination, and in this regard, the requirements for laminate seal electrophoresis and other types of electro-optic media are unusually stringent: lamination must be carried out at temperatures no higher than about 130 c because the media cannot be exposed to higher temperatures than this, otherwise it will be damaged, but the flow of the adhesive must be able to cope with the relatively uneven surface of the layer containing the capsules, the surface of the layer becoming irregular due to the capsules below. The lamination adhesive must be chemically compatible with all other materials in the display.

Attention must be paid to the assembly process of the display in considering the choice of laminating adhesive for an electro-optic 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 bonded together only prior to final assembly, and thus it is desirable to provide methods that are more suitable for mass production. However, 2004/0027327 above describes a method of assembling solid state electro-optic displays, including particle-based electrophoretic displays, that are well suited for mass production. The published application describes primarily a so-called "front plane laminate" (FPL) which comprises, in order: a light-transmitting conductive layer; a solid electro-optic medium layer in electrical contact with the conductive layer; an adhesive layer; and separating (release) the slices. Typically, the light-transmissive conductive layer is mounted on a light-transmissive substrate, which is preferably flexible, meaning that the substrate can be manually wound around a 10 inch (254mm) diameter (say) cylinder without permanent deformation. The term "light transmissive" as used in the copending applications and herein means that the layer so defined transmits sufficient light to enable a viewer to observe a change in the display state of the electro-optic medium when viewed through the layer, typically through the conductive layer and adjacent substrate (if any). The substrate is typically a thin polymer film, typically having a thickness in the range of about 1 to about 25 mils (25 to 634 μm), and preferably about 2 to about 10 mils (51 to 254 μm). The conductive layer is typically a thin metal layer, such as aluminum or Indium Tin Oxide (ITO), or may be a conductive polymer. Polyethylene terephthalate (PET) films coated with aluminum or ITO are commercially available, for example, "aluminized Mylar" ("Mylar" is a registered trademark) produced by e.i.du pont Nemour & Company, Wilmington DE, which are well suited for use in front sheet laminates.

The assembly of an electro-optic display using such a front plane laminate can be achieved by: the release sheet is removed from the front plane laminate and the adhesive layer is brought into contact with the backplane under conditions such that the adhesive layer adheres to the backplane, thereby securing the adhesive layer, the electro-optic medium layer and the conductive layer to the backplane. This process is well suited for mass production, as the front plane stack can be mass produced, typically using roll-to-roll coating techniques, and then cut into pieces of any desired size for a particular backplane.

2004/0027327 above also describes a method of testing the electro-optic medium in the front plane laminate before the front plane laminate is incorporated into a display. In this test method, the separator is provided with an electrically conductive layer, and a voltage sufficient to change the optical state of the electro-optic medium is applied between the conductive layer and the conductive layer on the opposite side of the electro-optic medium. Observation of the electro-optic medium reveals any defects in the medium, thereby avoiding lamination of the defective electro-optic medium into the display, at the expense of not only a defective front plane laminate, but discarding the entire display.

2004/0027327 above also describes a second method of testing the electro-optic medium in the front plane laminate, namely: an electrostatic charge is placed on the separator sheet to form an image on the electro-optic medium. This image is then viewed in the same manner as described above to detect any defects in the electro-optic medium.

2004/0155857 describes a so-called "double release film" which is essentially a simplified version of the front sheet stack described above. One form of a double release sheet comprises a layer of solid electro-optic medium sandwiched between two adhesive layers, the release sheet covering one or both of the adhesive layers. Another form of dual separator sheet comprises a layer of a solid electro-optic medium sandwiched between two separator sheets. Both forms of the dual release film are intended for use in a process generally similar to that described above for assembling an electro-optic display from a front plane laminate, but involving two separate laminae, typically a first lamination in which a dual release sheet is laminated to a front electrode to form a front sub-assembly, and a second lamination in which the front sub-assembly is laminated to a back plane to form the final display.

2004/0027327 above also illustrates the importance of protecting electro-optic media from environmental contamination because some electro-optic media are sensitive to humidity and ultraviolet radiation, and most such media are susceptible to mechanical damage. The published application shows in fig. 10 a process in which a protective film is laminated onto a front-plate laminate in the same laminating operation of the front-plate laminate; this protective film protects the electro-optic medium from moisture, other liquids, and some gases. However, even with such protective films, the edges of the electro-optic medium are still exposed to the environment, and the co-pending application teaches that the display preferably includes an edge seal to prevent ingress of moisture and gaseous contaminants around the outer edges of the display. Various types of edge seals are shown in fig. 11-17 of the published application. The edge seal may be comprised of a metallized foil or other barrier foil attached to the FPL edge, an applied sealant (thermally, chemically, and/or radiation cured), a polyisobutylene or acrylate based sealant, and the like. It has been found that a mixed radiation and thermal cure sealant (i.e., UV curable plus thermal post bake) can provide some advantages to display system performance. The Threebond 30Y-491 material (manufactured by Threebond corporation, Cincinnati, OH) is particularly preferred because of its favorable water vapor barrier properties, low viscosity at high temperatures, easy dispensing of the edge sealing material, good wetting characteristics, and manageable curing characteristics. Those skilled in the art and familiar with advanced sealants will be able to identify other sealants that provide comparable performance.

FIG. 20 of 2004/0027327 above (which is intended to be the only figure herein in modified form) shows a preferred form of electro-optic display having a front protective layer and an edge seal. As can be seen from this figure, the preferred display, generally designated 100, comprises a Thin Film Transistor (TFT) backplane 102, the Thin Film Transistor (TFT) backplane 102 being generally similar to those used in liquid crystal displays and having a matrix of pixel electrodes and associated thin film transistors and conductors for independently controlling the voltages applied to the pixel electrodes, which are omitted from the figure for clarity. The ribbon bond package 104 is attached to a peripheral portion of the backplane 102 and is provided with a driver integrated circuit 106 (which controls the operation of the display 100); the ribbon bond package 104 is also connected to a printed circuit board 108 that contains additional circuitry for controlling the operation of the display 100.

On the upper surface (as shown) of the base plate 102 are provided: laminating an adhesive layer 110, an electro-optic medium layer 112 (shown as encapsulating electrophoretic medium as described in the above-mentioned E Ink and MIT patents, although other types of electro-optic media may be used), a front electrode 114, and a front substrate 116; the front electrode 114 and the front substrate 116 are both conventionally formed from indium tin oxide coated polymer films, which are commercially available and readily available. The layers 110 and 112, the front electrode 114 and the front substrate 116 are all derived from a front stack that has been laminated to the backplane 102. As can be seen in the figure, a portion (shown as the left-hand end) of the front electrode 114 and the front substrate 116 extends beyond the electro-optic layer 112, in the extended portion of the front electrode 114 and the front substrate 116, a conductive via 118 formed from silver ink electrically connects the front electrode 114 to circuitry provided on the backplane 102, and an adhesive layer 120 secures the extended portion of the front electrode 114 to the backplane 102.

A first layer 122 of optically clear adhesive, a barrier film 124, a second layer 126 of optically clear adhesive, and another relatively thick protective film 128 having a glare-resistant coating (not shown) are provided in that order on the front substrate 116. The protective film 128 serves to block ultraviolet radiation from reaching the electro-optic layer 112 and also prevents atmospheric moisture or other contaminants from reaching the layer.

To form a complete seal around the electro-optic layer 112, the barrier film 124, the second layer 126 of optically clear adhesive, and the protective film 128 are all sized larger on both sides than the front substrate 116, such that the layers 124, 126, and 128 all have a perimeter that extends or "overhangs" the outer edge of the front substrate 106. To complete the sealing of the electro-optic layer 112, a curable edge sealing material is injected into the suspension area, typically by a dispensing needle, and allowed to cure to form an edge seal 130 that completely surrounds the electro-optic layer 112.

Only a limited number of commercially available edge sealing materials have all the characteristics required for use in such electro-optic displays, and most of these materials are cured with ultraviolet radiation. However, in the preferred display shown in the figure, and in similar displays in which the electro-optic medium is coated with a UV protective layer, the presence of a protective layer that is substantially opaque to ultraviolet radiation makes curing of the sealing material difficult. In the preferred display shown in the figure, the sealing material actually needs to be cured by irradiation from the side, which requires expensive basic equipment and requires a large penetration depth of the radiation (in the typical case several millimeters). In addition, the basic device needs to be custom designed for a particular display size, and therefore new devices need to be purchased as long as there is a non-trivial change in size in the product.

There is therefore a need for a process for curing sealing materials in displays having UV absorbing protective layers that does not require side irradiation of the sealing material nor does it require expensive equipment to perform such side irradiation, and the present invention seeks to provide such a process.

Accordingly, the present invention provides a process for curing an edge sealing material in an electro-optic display, the display comprising: a base plate; a layer of electro-optic material disposed adjacent the backplane; and a protective layer capable of absorbing ultraviolet radiation and disposed on a side of the layer of electro-optic material opposite the backplane, the protective layer extending beyond the layer of electro-optic material to form a peripheral region, wherein a gap exists between the protective layer and the backplane. The process includes placing an uncured edge sealing material in the gap and applying appropriate radiation to cure the material. In this process, the edge sealing material may be cured by radiation transmitted by the protective layer; and curing is effected by transmitting said curing radiation, thereby curing the edge sealing material and forming an edge seal in the gap.

In this process, the radiation used to cure the edge sealing material has a wavelength greater than 385nm, desirably greater than 395nm, and preferably greater than 405 nm. The edge sealing material may include 5, 7-diiodo-3-butoxy-6-fluorone (5, 7-diiodo-3-butoxy-6-fluorone) as a curing initiator. The edge sealing material may comprise a curable acrylate and may also comprise a filler, such as silica. Typically, the cured edge sealing material has a width in the plane of the layer of electro-optic material that is greater than its thickness perpendicular to the plane. Disposing the uncured edge sealing material into the gap may be performed by: an uncured bead of edge sealing material is dropped adjacent the gap, causing the edge sealing material to be pulled into the gap by capillary forces. In this process, at least one of the uncured edge sealing material and the display may be heated during dropping of the edge sealing material to accelerate movement of the uncured edge sealing material into the gap.

In the process of the invention, the layer of electro-optic material may use any of the types of electro-optic material described above. For example, the electro-optic material may be a rotating bichromal member material, or an electrochromic material. Alternatively, the electro-optic material may be a particle-based electrophoretic material comprising a plurality of electrically charged particles disposed in a suspending fluid in which they are capable of moving upon application of an electric field to the suspending fluid. In such electrophoretic materials, the suspending fluid may be a liquid or a gas. Furthermore, such electrophoretic material may be encapsulated, i.e. may hold the suspending fluid and the charged particles within a plurality of capsules or microcells.

As mentioned above, the sole figure of the present invention shows a schematic cross-sectional view of an edge-sealed electro-optic display that can be produced using the process of the present invention.

As described above, the present invention provides a process for edge sealing of electro-optic displays. The display includes: a base plate; a layer of electro-optic material disposed adjacent the backplane; and a protective layer capable of absorbing ultraviolet radiation and disposed on a side of the layer of electro-optic material opposite the backplane. The protective layer extends beyond the edges of the layer of electro-optic material to form a peripheral region in which a gap exists between the protective layer and the backplane. To form the edge seal, an uncured edge sealing material is placed within the gap in an arrangement that is curable by radiation transmitted through the protective layer and that is effective to cure the edge sealing material is transmitted through the protective layer, thereby curing the edge sealing material and forming an edge seal in the gap.

Thus, according to the invention, the edge seal is formed by an edge sealing material which is cured with radiation having a wavelength which is greater than the UV radiation absorbed by the protective layer, so that the radiation can be transmitted through the protective layer, instead of having to be applied from the side, as in the above-mentioned prior art process. In practice this usually means that the edge sealing material will contain photoinitiators sensitive to these longer wavelengths of light. The UV absorbing protective layer can be tailored for the application at hand, but typically transmits less than 25% for 385nm incident light, less than 60% for 395nm incident light, and less than 75% for 405nm incident light.

It will be apparent to those skilled in the construction of electro-optic displays that the "protective layer" of the display formed using the process of the present invention may be a composite of several individual layers. For example, in the illustrated display, the barrier film 124, the optically clear adhesive layer 126, and the protective film 128 can all be considered part of a "protective layer". It is clear that the exact number and type of layers present in the "protective layer" is essentially irrelevant for the purposes of the present invention, as long as the radiation energy used to cure the edge sealing material is transmitted through all of these layers. Moreover, of course, the protective layer is not required to be completely transparent to the radiation required to cure the edge sealing material; the protective layer is allowed to absorb radiation to some extent if sufficient radiation is transmitted to effect curing within an acceptable processing time. The exact form of "protective layer" used in the present process may therefore vary depending on the exact type of protection required for the particular electro-optic material used.

To minimize the total exposure (curing) time required, the edge sealing material should preferably react at a wavelength above 385nm, more preferably above 395nm, and most preferably above 405 nm. Photoinitiators sensitive at these wavelengths include, for example, 5, 7-diiodo-3-butoxy-6-fluorone (5, 7-diiodo-3-butoxy-6-fluorone) (available under the trade name "H-Nu 470" from Spectra Group Limited, Maumee, Ohio, United states of America), which has a peak absorption between about 380nm and 520 nm. Other chemicals known to those skilled in the art of formulating such adhesives can be readily identified.

Edge sealing materials made with visible light initiators are commercially available as model # LC-1210, 1211, 1212, 1213 and 1214 from 3M corporation (Minneapolis MN); Ultra-Light Weld material of Dymax (Torrington, connected, Unit States of America) (Ultra-Light Weld is a registered trademark); model #1771E, 1772E and 1776E from Threbond Corporation (Cincinnati, Ohio, United States of America), and other such manufacturers. These materials are often based on acrylate chemistry (Threebond materials are this type), but other materials of basic chemistry may also be used. Moreover, it should be noted that these sealing materials may be filled with filler materials (e.g., silica particles) to enhance one or more performance attributes (e.g., mechanical properties, permeation properties, opacity, etc.).

With such a sealing material, the sealing material can be cured simply from the front side of the display through the UV-absorbing protective layer. This eliminates the need for highly customized expensive UV curing systems. Moreover, the present process allows a single curing system to cure edge seals across varying display sizes. Furthermore, the process reduces the risk of exposing any UV sensitive material used in the electro-optic display, which would occur if radiation was applied to the edge sealing material from the side (which makes it possible for a small proportion of the radiation to pass through the sealing material into the electro-optic material itself).

Furthermore, the present invention can improve both throughput and sealing material cure uniformity, since edge sealing can be most effective when the edge sealing ports are made wide and thin (i.e., such sealing ports typically have dimensions substantially larger in planes parallel to the backplane and the layer of electro-optic material than in planes perpendicular to those planes). The curing time can be significantly reduced by curing the front protective layer of the display rather than from the side (i.e. through the width of the sealing material). This increase in yield is very beneficial in reducing the manufacturing cost of electro-optic displays.

In order to achieve further improvements in manufacturing yield during the sealant dispensing process, it is advantageous to use advanced dispensing systems. In general, simpler systems slowly deposit a bead of edge seal material around the periphery of the electro-optic material and rely on capillary forces to pull the seal material into the edge seal cavity (gap). It is helpful to heat the sealant and display, which can reduce the viscosity of the sealant during this dispensing process for increased dispensing speed. More complex dispensing systems can be used in order to obtain higher yields than with this capillary approach. In a preferred embodiment, a dispenser with five degrees of freedom (x-y-z cartesian degrees of freedom, rotation angle β about an axis perpendicular to the plane of the backplane, and angle α in the plane of the backplane) may be used. This multiple degree of freedom arrangement allows the dispensing needle to always be positioned at a fixed angle (measured above the plane of the cliche) above a normal drawn outward from the edge seal cavity (gap) in the plane of the cliche. This multiple degree of freedom configuration enables true "injection" of the sealing material into the gap at the edge of the display at high speed, thereby enabling improved throughput.

Claims (15)

1. A process for curing an edge sealing material in an electro-optic display (100), the display (100) comprising:

a base plate (102);

a layer (112) of solid electro-optic material disposed adjacent the backplane (102); and

a protective layer (128) capable of absorbing ultraviolet radiation and disposed on a side of the layer of solid electro-optic material (112) opposite the backplane (102), the protective layer (128) extending beyond edges of the layer of solid electro-optic material (112) forming a peripheral region, wherein a gap exists between the protective layer (128) and the backplane (102);

the process includes placing an uncured edge sealing material within the gap; and applying radiation to the edge sealing material effective to cure the edge sealing material to form an edge seal (130) in the gap,

the technical process is characterized in that: the edge sealing material may be cured by radiation transmitted through the protective layer; and the radiation used to cure the edge sealing material is transmitted through the protective layer.

2. The process of claim 1, wherein the radiation used to cure the edge sealing material has a wavelength greater than 385 nm.

3. The process of claim 2, wherein the radiation used to cure the edge sealing material has a wavelength greater than 395 nm.

4. The process of claim 3, wherein the radiation used to cure the edge sealing material has a wavelength greater than 405 nm.

5. The process of claim 1, wherein the edge sealing material comprises 5, 7-diiodo-3-butoxy-6-fluorone.

6. The process of claim 1, wherein the edge sealing material comprises a curable acrylate.

7. The process of claim 1, wherein the edge sealing material includes a filler.

8. The process of claim 7 wherein said filler comprises silica.

9. The process of claim 1 wherein the cured edge sealing material has a width in the plane of the layer of solid electro-optic material (112) that is greater than its thickness perpendicular to the plane.

10. The process of claim 1, wherein the uncured edge sealing material is placed in the gap using the following method: dispensing a bead of the uncured edge sealing material adjacent the gap such that the edge sealing material is pulled into the gap by capillary forces.

11. The process of claim 10, wherein at least one of the uncured edge sealing material and the display is heated during dispensing of the edge sealing material.

12. The process of claim 1 wherein the solid electro-optic material is a rotating bichromal member material or an electrochromic material.

13. The process of claim 1 wherein said solid electro-optic material is a particle-based electrophoretic material comprising a plurality of electrically charged particles disposed in a suspending fluid in which they are capable of moving upon application of an electric field to said suspending fluid.

14. The process of claim 13 wherein the suspending fluid is a gas.

15. The process of claim 13, wherein the suspending fluid and the charged particles are held in a plurality of capsules or microcells.