HK1227112B - Electro-optic display with a two-phase electrode layer - Google Patents

Description

Electro-optical display with dual-phase electrode layer

Citation of Related Applications

This application relates to:

(a) U.S. Patent No. 7,012,735, filed on March 26, 2004;

(b) U.S. Patent No. 7,349,148, filed December 20, 2006, which is a divisional of U.S. Patent No. 7,173,752, filed November 5, 2004;

(c) U.S. Patent No. 8,446,664, filed on April 4, 2011; and

(b) Co-pending U.S. Patent Publication No. 2009/0122389A1.

Technical Field

The present invention relates to electro-optical displays, and more particularly, to electro-optical components comprising a dual-phase, light-transmitting, conductive layer comprising a first phase formed from a highly conductive substrate and a second phase formed from a polymeric material composition having controlled volume resistivity. In another aspect, the present invention provides a dual-phase electrode layer wherein the polymeric material composition of the second phase is formed from a conductive polymer. In another aspect, the present invention provides a dual-phase electrode layer wherein the polymeric material composition of the second phase is formed from a polymer and an additive. The polymeric material compositions disclosed herein can be used in applications other than electro-optical displays.

Background Art

An electro-optic display includes a layer of electro-optic material, a term used herein in the conventional sense of the art to refer to a material having first and second display states that differ in at least one optical property, the material being changed from the first display state to the second display state by application of an electric field to the material. The optical property is typically color perceptible to the human eye, but may be another optical property such as optical transmission, reflectivity, luminescence, or, in the case of a display intended for machine reading, false color in the sense of a change in reflectivity of electromagnetic wavelengths outside the visible range.

Several types of electro-optic displays are known. One type of electro-optic display is the rotating dichromatic member type, as described, for example, 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 (although this type of display is often referred to as a "rotating dichromatic sphere" display, the term "rotating dichromatic member" is preferred and more accurate because in some of the above-mentioned patents, the rotating members are not spherical). Such displays use a large number of small bodies (usually spherical or cylindrical) that include two or more segments with different optical properties and an internal dipole. These bodies are suspended within a liquid-filled vacuole within a matrix, and the vacuole is filled with liquid to allow the bodies to rotate freely. The appearance of the display is changed by applying an electric field to the display, thereby rotating the body to various positions and changing which segment of the body is seen through the viewing surface. This type of electro-optic medium is typically bistable.

Another type of electro-optical display uses an electrochromic medium, such as an electrochromic medium in the form of a nanochromic film, which includes an electrode formed at least in part from a semiconducting metal oxide and a plurality of dye molecules attached to the electrode that are capable of undergoing a reversible color change; see, for example, O'Regan, B. et al., Nature 1991, 353, 737; and Wood, D., Information Display, 18(3), 24 (March 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. Patent Nos. 6,301,038; 6,870,657; and 6,950,220. This type of medium is also generally bistable.

Another type of electro-optical display is the electrowetting display, developed by Philips and described in Hayes, R.A. et al., "Video-Speed Electronic Paper Based on Electrowetting", Nature, 425, 383-385 (2003). It is shown in U.S. Patent No. 7,420,549 that such an electrowetting display can be made bi-stable.

One type of electro-optical display that has been the subject of intensive research and development for many years is the particle-based electrophoretic display (EPD), in which a plurality of charged particles are moved through a fluid under the influence of an electric field. Compared to liquid crystal displays (LCDs), EPDs can have the following attributes: good brightness and contrast, wide viewing angles, state bistability, and low power consumption. However, issues with the long-term image quality of these displays have prevented their widespread use. For example, the particles that make up EPDs tend to settle, resulting in a short service life for these displays.

As mentioned above, electrophoretic media require the presence of a fluid. In most prior art electrophoretic media, the fluid is liquid, but electrophoretic media can be produced using gaseous fluids; see, for example, Kitamura, T. et al., "Electrical toner movement for electronic paper-like display", IDW Japan, 2001, Paper HCS1-1, and Yamaguchi, Y. et al., "Toner display using insulative particles charged triboelectrically", IDW Japan, 2001, Paper AMD4-4. See also U.S. Patents No. 7,321,459 and 7,236,291. Such gas-based electrophoretic media, when used in an orientation that allows particle sedimentation (e.g., in a signboard where the medium is arranged in a vertical plane), appear to experience the same type of problems as liquid-based electrophoretic media due to particle sedimentation. In fact, particle sedimentation presents a more serious problem in gas-based electrophoretic media than in liquid-based electrophoretic media due to the lower viscosity of the gaseous suspending fluid compared to the liquid suspending fluid, which allows for faster sedimentation of the electrophoretic particles.

Numerous patents and applications issued to or in the names of the Massachusetts Institute of Technology (MIT) and Ink Corp. describe various techniques used in encapsulating electrophoretic and other electro-optical media. Such encapsulated media comprise a plurality of small capsules, each of which itself comprises an inner phase containing electrophoretically mobile particles in a fluid medium, and a capsule wall surrounding the inner phase. Typically, the capsules themselves are held within a polymeric binder to form a coherent layer positioned between two electrodes. The techniques described in these patents and applications include:

(a) electrophoretic particles, fluids, and fluid additives; see, for example, U.S. Patent Nos. 7,002,728 and 7,679,814;

(b) Encapsulation, adhesives, and encapsulation processes; see, e.g., U.S. Patent Nos. 5,930,026; 6,067,185; 6,130,774; 6,172,798; 6,249,271; 6,327,072; 6,392,785; 6,392,786; 6,459,418; 6,839,158; 6,866,760; 6,922,276; 6,958,848; 6,987,603; 7,061,663; 7,071,913; 7,079,305; 7,109,968; 7,110,164; 7,202,991; and U.S. Patent Application Publication Nos. 2005/0156340; 2007/0091417; 2008/0130092; 2009/0122389; 2010/0044894; 2011/0286080; and 2011/0286081;

(c) Films and subassemblies containing electro-optical materials; see, e.g., U.S. Patent Nos. 6,825,829; 6,982,178; 7,236,292; 7,443,571; 7,513,813; 7,561,324; 7,636,191; 7,649,666; 7,728,811; 7,729,039; 7,791,782; 7,839,564; 7,843,621; 7,843,624; 8 ,034,209; 8,068,272; 8,077,381 and 8,177,942; and U.S. Patent Application Publication Nos. 2008/0309350; 2009/0034057; 2009/0109519; 2009/0168067; 2011/0032595; 2011/0032396; 2011/0075248; 2011/0164301 and 2012/0176664;

(d) Backplanes, adhesive layers and other auxiliary layers and methods used in displays; see, e.g., U.S. Patent Nos. 7,116,318 and 7,535,624;

(e) color formation and color adjustment; see, e.g., U.S. Patent No. 7,075,502 and U.S. Patent Application Publication No. 2007/0109219;

(f) Methods for driving displays; see, for example, U.S. Patent Nos. 7,012,600 and 7,453,445;

(g) Display applications; see, for example, U.S. Patent Nos. 7,312,784 and 8,009,348; and

(h) Non-electrophoretic displays, such as described in U.S. Patent Nos. 6,241,921; 6,950,220; 7,420,549; and 8,319,759; and U.S. Patent Application Publication No. 2012/0293858.

A number of patents and applications have recently been published, issued to or in the names of the Massachusetts Institute of Technology (MIT) and Ink Corp., describing encapsulated electrophoretic media. Such encapsulated media comprise a plurality of small capsules, each of which itself comprises an inner phase containing electrophoretically mobile particles suspended in a liquid suspending medium, and a capsule wall surrounding the inner phase. Typically, the capsules themselves are held within a polymeric binder to form a coherent layer positioned between two electrodes. This type of packaging medium is described, for example, in U.S. Patent 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; 6,2 49,271; 6,252,564; 6,262,706; 6,262,833; 6,300,932; 6,312,304; 6,312,971; 6,323,989; 6,327,072; 6,376,828; 6,377,387; 6,392,785; 6,392,786; 6,413,790; 6,422,687; 6,445,374; 6, 445,489; 6,459,418; 6,473,072; 6,480,182; 6,498,114; 6,504,524; 6,506,438; 6,512,354; 6,515,649; 6,518,949; 6,521,489; 6,531,997; 6,535,197; 6,538,801; 6,545,291; 6,580,545; ,639,578;6,652,075;6,657,772;6,664,944;6,680,725;6,683,333;6,693,620;6,704,133;6,710,540;6,721,083;6,724,519;6,727,881;6,738,050;6,750,473;6,753,999;6,816,147; 6,819,471; 6,822,782; 6,825,068; 6,825,829; 6,825,970; 6,831,769; 6,839,158; 6,842,167; 6,842,279; 6,842,657; 6,864,875; 6,865,010; 6,866,760; 6,870,661; 6,900,851; 6,922,276 ; 6,950,220; 6,958,848; 6,967,640; 6,980,196; 6,982,178; 6,987,603; 6,995,550; 7,002,728; 7,012,600; 7,012,735; 7,023,420; 7,030,412; 7,030,854; 7,034,783; 7,038,655; 7,061,66 3; 7,071,913; 7,075,502; 7,075,703; 7,079,305; 7,106,296; 7,109,968; 7,110,163; 7,110,164; 7,116,318; 7,116,466; 7,119,759; 7,119,772; 7,148,128; 7,167,155; 7,170,670; 7,173,7 52; 7,176,880; 7,180,649; 7,190,008; 7,193,625; 7,202,847; 7,202,991; 7,206,119; 7,223,672; 7,230,750; 7,230,751; 7,236,290; 7,236,292; 7,242,513; 7,247,379; 7,256,766; 7,259, 744; 7,280,094; 7,304,634; 7,304,787; 7,312,784; 7,312,794; 7,312,916; 7,327,511; 7,339,715; 7,349,148; 7,352,353; 7,365,394; and 7,365,733; and U.S. Patent Application Publication Nos. 2002/0060321; 2002/00 90980; 2003/0102858; 2003/0151702; 2003/0222315; 2004/0105036; 2004/0112750; 2004/0119681; 2004/0155857; 2004/0180476; 2004/0190114; 2004/0257635; 2004/0263947; 2005/00008 13;2005/0007336;2005/0012980;2005/0018273;2005/0024353;2005/0062714;2005/0099672;2005/0122284;2005/0122306;2005/0122563;2005/0134554;2005/0151709;2005/0152018; 2005/0156340; 2005/0179642; 2005/0190137; 2005/0212747; 2005/0253777; 2005/0280626; 2006/0007527; 2006/0038772; 2006/0139308; 2006/0139310; 2006/0139311; 2006/0176267; 200 6/0181492; 2006/0181504; 2006/0194619; 2006/0197737; 2006/0197738; 2006/0202949; 2006/0223282; 2006/0232531; 2006/0245038; 2006/0262060; 2006/0279527; 2006/0291034; 2007/0 035532; 2007/0035808; 2007/0052757; 2007/0057908; 2007/0069247; 2007/0085818; 2007/0091417; 2007/0091418; 2007/0109219; 2007/0128352; 2007/0146310; 2007/0152956; 2007/0153 361; 2007/0200795; 2007/0200874; 2007/0201124; 2007/0207560; 2007/0211002; 2007/0211331; 2007/0223079; 2007/0247697; 2007/0285385; 2007/0286975; 2007/0286975; 2008/0013155 ; 2008/0013156; 2008/0023332; 2008/0024429; 2008/0024482; 2008/0030832; 2008/0043318; 2008/0048969; 2008/0048970; 2008/0054879; 2008/0057252; and 2008/0074730; and International Application Publication Nos. WO 00/38000; WO 00/36560; WO 00/67110; and WO 01/07961; and European Patent Nos. 1,099,207 Bl; and 1,145,072 Bl.

Many of the aforementioned patents and applications recognize that the walls surrounding discrete microcapsules in an encapsulated electrophoretic medium can be replaced by a continuous phase, thereby creating a so-called polymer-dispersed electrophoretic display, wherein the electrophoretic medium comprises a plurality of discrete droplets of an electrophoretic fluid and a continuous phase of a polymer material, and wherein the discrete droplets of electrophoretic fluid within such a polymer-dispersed electrophoretic display can be considered to be capsules or microcapsules, even though there is no discrete capsule membrane associated with each individual droplet; see, for example, the aforementioned U.S. Patent No. 6,866,760. Therefore, 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 a microcell electrophoretic display, charged particles and fluids are not encapsulated in microcapsules, but rather 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 issued to Sipix Imaging. Hereinafter, the term "microcavity electrophoretic display" may be used to cover both encapsulated and microcell electrophoretic displays.

U.S. Patent No. 6,982,178, filed May 22, 2003, describes a "front plane laminate" (FPL) for use in electro-optic displays that includes, in sequence, a light-transmitting conductive layer or electrode layer, a solid electro-optic medium layer in electrical contact with the conductive layer, an adhesive layer, and a release sheet.

Most electro-optical displays require a light-transmitting conductive layer to serve as one electrode of the display, through which an observer can observe changes in the optical state of the electro-optical medium. In some cases, such as variable transmission windows, both electrodes must be light-transmitting. Traditionally, the light-transmitting conductive layer has been formed from indium tin oxide (ITO) on some type of mechanical support, such as a polymer film or a glass plate. More recently, films made of thin metal mesh materials, such as carbon nanotubes and silver wire, have replaced ITO films as light-transmitting conductive layers. Such films include areas of high conductivity surrounded by areas of significantly lower conductivity, which can accumulate charge and interfere with the performance of the electro-optical display. Therefore, there is a need for electrode layers based on metal mesh that do not suffer from these disadvantages.

Summary of the Invention

The present invention provides an electro-optical display comprising a dual-phase electrode layer, wherein a first phase is formed from a highly conductive substrate, and a second phase is formed from a polymer material composition having a controlled volume resistivity. In one form of the invention, the polymer material of the second phase can be inherently conductive or can be a polymer blended with additives such that the polymer material has a resistivity of no greater than 1 x 10 ¹² Ohm-cm. The polymer can be selected, for example, from polyurethane, vinyl acetate, ethylene vinyl acetate, epoxy resin, or polyacrylic acid, or combinations thereof.

In another form, the invention provides a two-phase electrode layer in which the second phase is an ionically conductive polymer in which one ion can migrate through the polymer material but another ion cannot, such as an ionic salt of a polymeric carboxylate.

In another form of the invention, the polymer material of the second phase may comprise one or more conductive polymers selected from PEDOT-PSS, polyacetylene, polyphenylene sulfide, polyphenylene vinylene, and combinations thereof.

In another form of the invention, the additive in the second phase may be selected from, for example, salts, polyelectrolytes, polymer electrolytes, solid electrolytes, or combinations thereof.

In one embodiment, the additive in the polymeric material is a salt; for example, an inorganic salt, an organic salt, or a combination thereof. In one specific embodiment, the salt comprises potassium acetate. In an alternative embodiment, the salt may comprise a quaternary ammonium salt, for example, a tetraalkylammonium salt such as tetrabutylammonium chloride or hexafluorophosphate. In another embodiment, the additive may be a salt having an anion containing at least three fluorine atoms; for example, the additive may have a hexafluorophosphate anion, such as 1-butyl-3-methylimidazolium hexafluorophosphate.

In another form of the invention, the additive in the second phase is a polyelectrolyte and may include a salt of a polyacid such as, but not limited to, an alkali metal salt of polyacrylic acid.

In another form of the invention, the additive to the polymer material of the second phase may be selected from a non-reactive solvent, a conductive organic compound, and combinations thereof.

In another form of the invention, the additive in the second phase may be a low number average molecular weight hydroxyl group containing polymer such as poly(ethylene glycol) (PEG) in which protons rather than electrons migrate.

The polymer material containing additives can provide areas of different colors and act as a color filter. Alternatively, the polymer material can include optical biasing elements.

In one aspect, an electro-optical assembly is provided, comprising first and second substrates, an adhesive layer, and an electro-optic material layer disposed between the first and second substrates. In the electro-optical assembly, at least one of the first and second substrates may comprise a dual-phase electrode layer, wherein the first phase is a highly conductive matrix and the second phase is a polymer material having controlled resistivity, the second substrate may comprise a release sheet, and the electro-optic medium may be a solid electro-optic medium; thereby, the entire electro-optical assembly has the form of a front plane laminate as described in the aforementioned U.S. Patent No. 6,982,178.

In another aspect of the present invention, an electro-optical component is provided, comprising first and second substrates, an adhesive layer and an electro-optical material layer disposed between the first and second substrates, and a dual-phase electrode layer, wherein the first phase is a highly conductive matrix and the second phase is a polymer material having controlled resistivity.

DETAILED DESCRIPTION

Thus, the present invention provides an electro-optical display comprising a dual-phase light-transmitting conductive layer comprising a first phase made of a highly conductive matrix and a second phase made of a polymeric material composition having a controlled volume resistivity. The electro-optical display typically comprises a layer of electro-optical material and at least two other layers disposed on opposite sides of the electro-optical material, at least one of which is a light-transmitting conductive layer. The term "light-transmitting" is used herein to mean that the layer designated thereby transmits sufficient light to enable an observer, when looking towards the layer, to observe a change in the display state of the electro-optical medium, which is typically observed through the conductive layer and the adjacent substrate (if present).

The first phase can be a conductive matrix. The term "conductive matrix" is used herein to describe the first phase array of highly conductive regions of the electrode layer. The matrix can be constructed from carbon nanotubes, silver nanowires, metal-coated open foam structures, printed screens, or any such material that does not completely cover the viewing surface. The first phase can be light-transmitting or light-absorbing, with diameters ranging from a few nanometers to a few millimeters. The matrix can be arranged regularly (i.e., in a grid, hexagonally, reticularly, etc.) or irregularly (i.e., randomly). The matrix can be arranged very thinly or sparsely filled so that the electrode layer is light-transmitting.

The second phase can be made of a polymer that is conductive in nature or a polymer mixed with a conductive additive. Although the second phase is significantly less conductive than the first phase, it has conductive properties (i.e., a resistivity of no more than 1×10 ¹² Ohm-cm). Preferably, the second phase has a resistivity of approximately 1x10 ⁷ to 1x10 ¹² Ohm-cm. The second phase can be ionically or electronically conductive. Typically, the second phase surrounds or coats the first phase to create a less conductive area surrounding the conductive substrate. This provides mechanical integrity and protection for the first phase, which may be fragile due to its structure. If the first phase is light absorbing and the second phase is light transmissive, a high ratio of less conductive areas to highly conductive areas is desired. More preferably, the first phase constitutes less than 10% of the observation area, and the second phase constitutes the remaining observation area.

The polymeric material can be any polymeric material that meets the specific needs of the end-use application. Examples of suitable polymeric materials include polyurethanes, vinyl acetate, ethylene-vinyl acetate, epoxy resins, polyacrylic acid-based adhesives, or combinations thereof. These adhesive materials can be solvent-based or water-based. Examples of specific polyurethanes that can be used are described in U.S. Patent No. 7,342,068.

The accompanying drawing is a schematic cross-section of a base front plane laminate (10) of an electro-optical display of the present invention having a conductive layer. Typically, a light-transmitting conductive layer (14) will be carried on a light-transmitting substrate (12), which is preferably flexible in the sense that the substrate can be manually wrapped around a barrel (for example) having a diameter of 10 inches (254 mm) without permanent deformation. The substrate is typically a polymer film and generally 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). The substrate (12) forms the viewing surface of the final display and may have one or more additional layers, for example, a protective layer to absorb ultraviolet radiation, a barrier layer to prevent the ingress of moisture, or an anti-reflective coating.

The conductive layer (14) includes a biphasic electrode layer. An electro-optic medium layer (16) is in electrical contact with the conductive layer (14). The electro-optic medium shown in the figure is an oppositely charged dual-particle encapsulated electrophoretic medium having a plurality of microcapsules, each of which includes a capsule wall (18) comprising a hydrocarbon-based liquid in which negatively charged white particles (22) and positively charged black particles (24) are suspended. The microcapsules are held within a binder (25). When an electric field is applied to the electro-optic layer (16), the white particles (22) move to the positive electrode and the black particles (24) move to the negative electrode, so that to an observer viewing the display through the substrate (12), the layer (16) appears white or black depending on whether the layer (14) is positive or negative relative to the backplane at any point in the final display.

The front plane laminate (10) shown in the figure also includes a layer of laminating adhesive (26) adjacent to the electro-optic medium layer (16) and a release sheet (28) covering the adhesive layer (26). The release layer (28) is peeled from the adhesive layer (26), and the adhesive layer is laminated to the backplane to form the final electro-optic display.

The dual-phase conductive layer of the present invention can be the front electrode of an electro-optical display, which is the electrode located on the side closest to the viewing surface. In an electro-optical display that is completely transparent or has two viewing surfaces, the dual-phase conductive layer of the present invention can be the front electrode and the back electrode.

For electro-optical displays, it is critical to control the electrical properties of the polymer material; otherwise, the display may experience diminished optical performance. Optical performance can be enhanced when the bulk resistance of the polymer material is no greater than 1 x 10 ¹² Ohm-cm.

Conductive polymers

In another form, the present invention provides a two-phase electrode layer in which the second phase is an ionically conductive polymer, wherein one ion can migrate through the polymer material while another cannot. This type of ionic material prevents ions from diffusing out of the polymer material and potentially damaging other layers (e.g., organic semiconductor layers) into which the ions diffuse.

Ionic conduction is shown to occur by " jumping " mechanism, wherein, the free ion of dissociation is transferred between ion aggregate (ion pair and higher aggregate), and most of these aggregates are neutral in fact.According to the present invention, only one of the negatively charged ion and the positively charged ion of ionic material can move.Fixed ion is constrained to single position, and mobile ion still freely migrates.The example of suitable ionic material is polymer salt, for example, the ionic salt of polymeric carboxylate.In this case, carboxylate ion is effectively fixed, because it is attached to polymer chain, and only can whole body move along with polymer.On the other hand, cationic counter ion can freely participate in jumping motion, and its speed that can move depends on the intensity of electrostatic interaction with anionic carboxylate, the concentration of carboxylate-counter ion aggregate in the adhesive medium, the viscosity of medium and the free energy of dissolving of the counter ion by medium.

As described in U.S. Patent Publication No. 2009/0122389, large cations are advantageous because they have relatively low electrostatic energy of attraction to ionic aggregates and therefore readily dissociate from ionic aggregates. As an example, quaternary ammonium bases can be used to neutralize carboxyl functionality on polyurethanes, resulting in quaternary ammonium carboxylate polymers that can support ion conduction as described above.

It is desirable that the ionic material be selected so that the conductivity of the final polymer material after drying can be modified and adjusted by varying the carboxylic acid content of the polyurethane and also by the cation used. For example, in the aforementioned system where the carboxyl groups on the polyurethane are neutralized with a quaternary ammonium base, at a given carboxylic acid content, the conductivity can be expected to increase in the following order:

Tetramethylammonium <tetraethylammonium <tetrabutylammonium, etc.

Phosphate salts can also be used and, due to the larger size of the central atom, should be more conductive than nitrogen containing analogs. Other cationically active species (e.g., complex ions of metals) can also be used for this purpose. The solubility of ionic materials in polymeric materials is not a problem in this method because the ions are an intrinsic part of the medium and therefore cannot phase separate into separate crystalline phases.

The acidic components of the polymeric material can also be made more acidic by replacing the carboxylic acid component with a group with a higher dissociation constant (e.g., sulfate, sulfonic acid, sulfinic acid, phosphonic acid, phosphinic acid, or phosphate), as long as there is at least one dissociable proton. Quaternary salts and other large cations will still be desirable as counterions due to their large size and relatively high ionic dissociation in the low-polarity dry binder medium. Nitrogen-based acids can also be used if attached to a sufficiently electron-withdrawing function (e.g., _RSO2 -NH- _SO2R ). In this case, almost any mobile ion can be used, including tertiary amines, since mobile ions are present in the dry binder even in protonated form. However, mobile ions based on larger amines (i.e., amines with longer alkyl tails) may still be preferred because they are actually larger in size and therefore ion pairs including them will be more dissociable. Alternatively, the carboxylic acid groups on the polymer can be used with mobile ions that are not strong Bronsted acids (i.e., do not have acidic protons, such as the quaternary cations mentioned above).

Can be by using quaternary ammonium group in polymer backbone or as side chain, and preferably use large negatively charged ion (for example, hexafluorophosphate, tetrabutylammonium, tetraphenylborate etc.) as movable ion to construct the polymer material in which cation is fixed ion.Quaternary ammonium group can be replaced by phosphorus, sulphur or other cationic radicals without dissociable hydrogen, including the cationic radical formed by the complexation with metal cation.The latter's example includes polyether/comprising the complex of lithium ion, particularly macrocyclic polyether (for example, 18-crown ether-6) or the polyamine complex with transition metal ion.In this case, the movable ion of negatively charged ion can include the ion of those types listed above, plus the material of the stronger basis such as carboxylate or even phenolate.

Alternative fixed cationic polymer materials include polymers containing repeating units derived from base monomers, such as poly(vinylpyridine), poly(β-dimethylaminoethyl acrylate), and the like, as well as copolymers containing such groups, along with mobile anions that are not good Bronsted acceptors (e.g., sulfonates, sulfates, hexafluorophosphates, tetrafluoroborates, bis(methylsulfonyl)imide esters, phosphates, phosphonates, etc.). Quaternary salts derived from such amino monomers can also be used, such as poly(N-methyl or phenyl(vinylpyridine)), poly(N-alkyl (or aryl)-N'-vinylimidazole), and poly(β-trimethylaminoethyl) acrylic or methacrylic acid salts, as well as vinyl copolymers containing these ionic groups. As before, larger mobile ions are preferred.

These chemical modification techniques are not limited to polyurethanes, but can be applied to any polymer of suitable structure. For example, vinyl polymers can contain fixed ions that are either anionic or cationic.

In another form of the invention, the polymeric material may comprise one or more conductive polymers selected from PEDOT-PSS, polyacetylene, polyphenylene sulfide, polyphenylene ethylene and combinations thereof. The thickness of the polymeric material may range from about 0.1 μm to 20 μm. The polymeric material may be (a) water-soluble or water-dispersible and coated with water, (b) soluble or dispersible in an organic solvent and coated with an organic solvent, or (c) coated in monomeric or oligomeric form and then polymerized by UV, irradiation, heating or other methods known in the art. The additive incorporated into the polymeric material may be formed in situ; in other words, one or more precursor materials may be incorporated into the polymeric material, wherein the precursor materials may react with each other or with the polymeric material, or may be changed to form the final additive by exposing the polymeric material to conditions that cause changes in the precursor material (e.g., exposure to heat, light, or a magnetic or electric field).

Diffusible ionic additives

The second phase may comprise one or more ionic additives, for example, (a) salts, polyelectrolytes, polymer electrolytes, solid electrolytes, and combinations thereof; or (b) non-reactive solvents, conductive organic compounds, and combinations thereof.

In one form, the additive can be a salt, such as an inorganic salt, an organic salt, or a combination thereof, as described in U.S. Patent No. 7,012,735. Exemplary salts include potassium acetate and tetraalkylammonium salts, particularly tetrabutylammonium salts, such as chlorides. Additional examples of salts include salts such as _RCF3SOF3 , _RClO4 , _LiPF6 , _RBF4 , _RAsF6 , RB(Ar) ₄ , _{and RN(CF3SO2)3 , where R} can be any cation, such as Li ⁺ , Na ⁺ , H ⁺ , or K ⁺ . Alternatively, R can include an ammonium group of the form N ⁺ R1R2R3R4. A preferred salt is tetrabutylammonium hexafluorophosphate.

In another form, the additive can be a salt having an anion containing at least three fluorine atoms, as described in U.S. Patent No. 8,446,664. The salt can, for example, have a hexafluorophosphate anion. The salt can also have an imidazolium cation. Exemplary salts include 1-butyl-3-methylimidazolium hexafluorophosphate (hereinafter "BMIHFP"), 1-butyl-3-methylpiperidinium hexafluorophosphate, 1-butyl-3-methylpyridinium hexafluorophosphate, 1-ethyl-3-methylpyridinium hexafluorophosphate, sodium hexafluorophosphate, 1-butyl-3-methylimidazolium trifluoromethanesulfonate, and 1-butyl-3-methylimidazolium boron tetrafluoride. The preferred salt is BMIHFP. The preferred salt is liquid at 25°C and can be dispersed directly in an aqueous polymer dispersion or emulsion without using any solvent. Alternatively, since the preferred salt is soluble in water at about one percent at 25°C, the salt can be added in the form of a dilute aqueous solution. The addition of the salt as an aqueous solution avoids the introduction of any undesirable organic solvent into the adhesive.

Alternatively, the fluorine-containing salt can have a tetrafluoroborate anion, a tetraphenylborate anion, a bis(trifluoromethane)sulfonamide anion ("triflimide"), a tetrakis(pentafluorophenyl)borate anion, a tetrakis(3,5-bis(trifluoromethyl)phenyl)borate anion, or a trifluoromethanesulfonate ("triflate"), for example, 1-butyl-3-methylimidazolium boron tetrafluoride or 1-butyl-3-methylimidazolium trifluoromethanesulfonate. The fluorine-containing salt can be present in an amount of from about 50 to about 10,000 ppm, and typically from about 100 to about 1,000 ppm, based on the solids content of the polymeric material.

In other embodiments, the polymer electrolyte is a polyelectrolyte. A polyelectrolyte is typically a polymer in which about 10% or more of the molecules are composed of functional groups that can ionize to form charged species. Examples of specific functional groups within a polyelectrolyte include, but are not limited to, carboxylic acids, sulfonic acids, phosphoric acids, and quaternary ammonium compounds. These polymers can be combined with organic or inorganic salts or alternatively used alone. Examples of polyelectrolytes include, but are not limited to, polyacrylic acid, polystyrene sulfonate, poly(2-vinylpyridine), poly(4-vinylpyridine), poly(dimethylammonium chloride), poly(dimethylaminoethyl methacrylate), poly(diethylaminoethyl methacrylate), and may include salts of polyacids such as, but not limited to, alkali metal salts of polyacrylic acid. A preferred polyelectrolyte is the sodium salt of polyacrylic acid.

In another form of the invention, the additive is a polymer electrolyte. The term "polymer electrolyte" as used herein describes a polymer that is capable of dissolving salts. The solubility of salts in these polymers can be enhanced by the presence of oxygen and/or nitrogen atoms in the polymer that form ethers, carbonyls, carboxylates, primary, secondary, tertiary, quaternary amino groups, sulfonic acid groups, acids. Examples of polymer electrolytes include polyether compounds such as polyethylene oxide, polypropylene oxide, polytetrahydrofuran; polyamines such as polyethyleneimine, polyvinylpyrrolidone; polymers containing quaternary ammonium groups such as N ⁺ R1R2R3R4, wherein R1, R2, R3 and R4 are each independently H or straight, branched, or cycloalkyl groups having 1-25 carbon atoms, wherein the counterion can be selected from any organic or inorganic anion.

Other additives may still include non-reactive solvents that can improve or alternatively hinder the mobility of ions in the solution. Examples of suitable non-reactive solvents include water, ethyl ether, propyl ether, diethylene glycol, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, N-methylpyrrolidone, etc. In another embodiment, conductive organic compounds can be used as additives. Some non-limiting examples of these compounds include polyaniline, polythiophene, polypyrrole, poly-3,4-dioxyethylenethiophene, and derivatives of these materials in their n-type or p-type doped states.

As disclosed in U.S. Patent No. 7,256,766, it is also known that an "optical biasing element" can be provided in a layer of an encapsulated electrophoretic display to adjust the display's appearance. Such an optical biasing element can be added to a polymer material. The electrical properties of a polymer material containing such an optical biasing element can be optimized by using the additives described herein.

The optimal amount of additive will, of course, vary widely with the exact polymer material and exact additive used, as well as the desired volume resistivity of the final mixture. However, as a general guide, it can be noted that concentrations of about 10 ^{^-5} to about 10^{^-4} moles of additive per gram of polymer material have been found to give useful results. When the additive is a salt, this range applies to 1:1 salts such as tetrabutylammonium chloride, tetrabutylammonium hexafluorophosphate, and potassium acetate; if a 1:2 salt such as sodium carbonate or calcium chloride is used, a lower concentration of salt on the order of 10 ^{^-6} moles per gram of polymer material may be sufficient. The volume resistivity of a polymer material generally varies in a predictable manner with the concentration of the additive, so the ultimate choice of how much additive should be added to achieve the desired volume resistivity can be readily determined empirically.

Although small amounts of salts have been added to polymers used as binders and laminating adhesives in prior art electro-optical displays, for example as bactericides, to protect the polymers from biodegradation during extended storage, such salts are generally used up during storage (where they perform their bactericidal or similar functions). In contrast, the additives used in the present invention are intended to be permanent components of the polymer material, as they are intended to achieve a permanent adjustment of its electrical conductivity. Furthermore, the optimal amount of additive used is generally significantly greater than the amount of salt used as a bactericide, etc.

Low molecular weight polymer/glycol additives containing hydroxyl groups

Another form of the invention relates to an electro-optical display having an electrode layer comprising a first phase made of a conductive matrix and a second phase made of a polymer mixed with an additive, wherein the additive is a hydroxyl-containing polymer of low number average molecular weight (Mn not greater than about 5000). As described in U.S. Patent No. 7,349,148, a preferred polymer for this purpose is poly(ethylene glycol) (PEG), which desirably has an Mn not greater than about 2000. In this additive, protons migrate rather than electrons. The optimum concentration of the hydroxyl-containing polymer additive for any particular system is best determined empirically, but as a general guide, it can be said that an optimum concentration of about ^10-6 to ^10-5 moles per gram of polymer material is generally an optimum concentration.

Typically, if the electrode layer is formed by coating a thin film of a solution of the second phase onto a substrate comprising the first phase and drying to form the electrode layer, the additive is typically simply dissolved or dispersed in a solution of the polymer material prior to coating. The additive may be added to the neat solution, or may be dissolved in an aqueous solution, a non-aqueous solution, or a combination thereof. It is of course necessary to ensure that the additive is evenly distributed throughout the polymer material to prevent variations in conductivity within the final conductive layer, but those skilled in the art of coating will be familiar with conventional techniques, such as extended stirring on a roller mill, for ensuring such even distribution. The two-phase electrode layer may be used with a substrate as appropriate. Alternatively, once set, the second phase may add sufficient structure to the first phase to enable the substrate to be removed.

The choice of the specific additive to be used is largely determined by considering the compatibility with the electrodes and the solubility in the polymer material to which the additive is to be added. Typically, if the additive is to be added to an aqueous polymer material, the additive should be selected to have good water solubility, so that among salts, alkaline metals and alternative ammonium salts are generally preferred. Care should be taken to ensure that the additive does not cause aggregation of the polymer particles. Furthermore, the additive should desirably not cause a significant change in the pH of the polymer material and should not chemically react with the electrodes or polymer material or other components (e.g., backplane) of the final display with which it ultimately contacts.

The addition of one or more additives significantly expands the range of polymeric materials that can be used in electro-optical displays. In particular, the addition of one or more additives enables the use of polymeric materials that possess highly desirable mechanical properties in electro-optical displays but have a volume resistivity that is too high to be useful in their pure form. Furthermore, because some electro-optical displays, particularly encapsulated electrophoretic and electrochromic displays, are moisture-sensitive, the addition of one or more additives can be used to replace the water-based polyurethane dispersions previously used in such displays with non-hygroscopic and/or hydrophobic polymeric materials.

The polymer material may contain ingredients other than the additives used to adjust its volume resistivity; for example, the polymer material may also contain a dye or other colorant.

It will be appreciated that the improved polymeric materials disclosed herein may be used in applications other than electro-optical displays.

Claims (16)

1. An electro-optic display, comprising an electro-optic material layer and an electrode layer configured to apply an electric field to the electro-optic material layer, the electrode layer comprising: The first phase is made of a highly conductive substrate, and The second phase is made of a transparent polymer material component with controlled volume resistivity. 2. The electro-optic display according to claim 1, wherein the matrix of the first phase is carbon nanotubes, silver nanowires, an open foam structure coated with metal, or a printed screen, or a combination thereof. 3. The electro-optic display according to claim 1, wherein the substrate of the first phase is regularly arranged. 4. The electro-optic display according to claim 1, wherein the substrate of the first phase is irregularly arranged. 5. The electro-optic display according to claim 1, wherein the first phase constitutes less than 10% of the observation area. 6. The electro-optic display according to claim 1, wherein the controlled volume resistivity of the second phase is not greater than 1 x ^10¹² Ohm-cm. 7. The electro-optic display according to claim 1, wherein the light-transmitting polymer material component of the second phase is made of a conductive polymer. 8. The electro-optic display according to claim 7, wherein the conductive polymer is PEDOT-PSS, polyacetylene, polyphenylene sulfide, or polyphenylene ethylene, or a combination thereof. 9. The electro-optic display according to claim 7, wherein the conductive polymer is an ion-conducting polymer. 10. The electro-optic display according to claim 9, wherein the ion-conducting polymer is a polymer salt. 11. The electro-optic display according to claim 1, wherein the light-transmitting polymer material component of the second phase is made of polymer and additives. 12. The electro-optic display according to claim 11, wherein the additive is one or more ionic additives. 13. The electro-optic display according to claim 12, wherein the ionic additive is a salt, a polyelectrolyte, a polymeric electrolyte, or a solid electrolyte, or a combination thereof. 14. The electro-optic display according to claim 13, wherein the ionic additive is a salt, and the salt is a fluorine-containing salt. 15. The electro-optic display of claim 11, wherein the additive is a hydroxyl-containing polymer with a low numerical average molecular weight. 16. The electro-optic display according to claim 15, wherein the additive is polyethylene glycol.