Variable transmission electrophoresis device

Abstract

A variable transmission film may include an electrophoretic medium having a plurality of capsules and a binder, each capsule containing a plurality of charged particles and a fluid, the charged particles being movable by application of an electric field and being switchable between an open state and a closed state. The film may include at least one of: a binder comprising fish gelatin and a polyanion; a binder containing one or more colorants; a capsule containing a charge control agent, such as an oligoamine-terminated polyolefin and a branched fatty acid comprising at least 8 carbon atoms; selection of capsules wherein at least 60% of the diameter is between 50 [mu] m and 90 [mu] m and at least 15% of the diameter is between 20 [mu] m and 49 [mu] m; a colored adhesive layer; and a fluid selected from one or more non-conjugated olefins.

Description

[0001] This application is a divisional application of the divisional application with application number 202211272902.1, filed on June 14, 2018, with application number 201880039519.7 and invention name “Variable Transmission Electrophoresis Device”.

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This application claims the benefit of and priority to U.S. Provisional Patent Application Serial No. 62 / 520,629 (filed June 16, 2017), U.S. Provisional Patent Application Serial No. 62 / 520,600 (filed June 16, 2017), U.S. Provisional Patent Application Serial No. 62 / 520,731 (filed June 16, 2017), U.S. Provisional Patent Application Serial No. 62 / 520,699 (filed June 16, 2017), U.S. Provisional Patent Application Serial No. 62 / 563,137 (filed September 26, 2017), and U.S. Provisional Patent Application Serial No. 62 / 673,743 (filed May 18, 2018). This application is also related to U.S. Patent Nos. 7,256,766; 7,327,511; 7,679,814; and 7,999,787.

[0004] The entire contents of these applications, patents, and all other U.S. patents and published and co-pending applications referenced below are incorporated herein by reference. Technical Field

[0005] The present invention relates to a variable transmission device and more particularly to a variable transmission device comprising an electrophoretic medium comprising a plurality of capsules in a binder and adhesive layer, the electrophoretic medium being capable of improving the optical performance of the variable transmission device. Background Art

[0006] Light modulators represent a potentially significant market for electro-optical media. As energy performance in buildings and vehicles becomes increasingly important, electro-optical media can be used as coatings on windows (including skylights and skylights) to enable the proportion of incident radiation transmitted through the window to be electronically controlled by varying the optical state of the electro-optical media. Effective implementation of such "variable transmittance" ("VT") technology in buildings is expected to provide (1) reduced unwanted heating during hot weather, thereby reducing the energy required for cooling, the size of air conditioning equipment, and peak power demand; (2) increased utilization of natural light, thereby reducing the energy used for lighting and peak power demand; and (3) increased occupant comfort by increasing thermal and visual comfort. Even greater benefits are expected in automobiles, where the ratio of glass surface to enclosed volume is much greater than in typical buildings. Specifically, effective implementation of VT technology in automobiles is expected to provide not only the benefits mentioned above, but also (1) enhanced driving safety, (2) reduced glare, (3) enhanced rearview mirror performance (through the use of electro-optical coatings on rearview mirrors), and (4) enhanced ability to use head-up displays. Other potential applications of VT technology include privacy glass and anti-glare covers in electronic devices.

[0007] U.S. Patent No. 7,327,511 describes variable transmission devices comprising encapsulated charged pigment particles dispersed in a nonpolar solvent. These devices can be driven to an open state using an AC drive voltage, thereby driving the charged pigment particles to the capsule wall. Consequently, these variable transmission devices can be used for viewing surfaces requiring variable transmittance, such as privacy glass, skylights, and windows on buildings.

[0008] U.S. Patent No. 7,327,511 also describes various factors important for optimizing electrophoretic media for optimal performance in light modulators. One important factor is minimizing haze. In this application, "haze" refers to the percentage of diffusely transmitted light (light scattered during transmission) to the total transmitted light. When designing a light modulator that can be electrically switched from an open, transparent state to a closed, opaque state, it is desirable to have a haze of less than 10% in the open state, and more preferably less than 2%. Another important factor is contrast. Another issue with variable transmission devices including capsules is grain. In this application, "grain" refers to visual non-uniformity caused by various factors, such as clusters of colored binder or clumps / layers of capsules, variability in capsule packaging, voids, thickness variations, and coating defects including pinholes. These non-uniformities reduce visibility when a user views the device in the open state. The term "grain" originates from film photography, where clumps of silver were known in early silver film, giving developed photos a "grainy" appearance. Efforts to reduce particulate matter in variable transmission devices have generally focused on reducing variations in capsule packing density.

[0009] One approach to reducing the amount of particles in encapsulated electrophoretic media is to use more capsules, these capsules being smaller in size, for example, between 20 and 50 μm in diameter. This small size allows for tighter packing of the capsules, and due to their microscopic size, individual capsules are less likely to be discerned. As a result, a user viewing the device will see fewer particles. However, it has been observed that variable transmission devices comprising a single layer of "small" capsules (i.e., with diameters in the range of 20 μm to 50 μm) exhibit less contrast between the open and closed states due to the thinner electro-optical layer. This means that less pigment interferes with transmission through the layer, resulting in higher transmission in the closed state. Furthermore, the presence of many similarly sized capsules in a tightly packed single layer can result in "halos" or "starbursts" due to interference when viewing a light source through the variable transmission device. These interfering patterns can be distracting to the viewer and diminish the viewing experience in the open state.

[0010] Another drawback of the variable transmission device described in U.S. Patent No. 7,327,511 is "recoil," or self-erasure of the optical display state due to an impedance mismatch between the electrophoretic inner phase and the binder surrounding the electrophoretic inner phase. The impedance mismatch causes charge regions to accumulate between the various materials and affect the position of the electrophoretic particles in the inner phase, resulting in a decay of the optical state. Obviously, self-erasure is highly undesirable because it can reverse the desired optical state of the display (or otherwise distort it in the case of a grayscale display) or cause the transmission device to change from open to closed. Self-erasure has been found to be a particular problem in polymer-dispersed electrophoretic media and displays, in which the capsules are substantially removed from the electro-optical medium, leaving only bubbles of the inner phase in the polymer binder.

[0011] Efforts to reduce the impedance mismatch between the electrophoretic internal phase and the binder introduce new challenges. For example, a binder formulation that matches the resistance of the electrophoretic internal phase (and encapsulation layer, if present) can produce undesirable color or introduce "haze." In this case, when the variable transmission film is in its highest transmission (i.e., "on") state, the viewer perceives the film as having "tint" and / or "spotting," which is undesirable. While objectionable in most applications, tint and speckling can present safety issues when used in automotive or aircraft glazing.

[0012] Therefore, there is a need for improved electro-optical media that can be incorporated into variable transmission devices. Summary of the Invention

[0013] In one aspect, the present invention provides a variable transmission electrophoretic medium comprising a plurality of capsules in a binder, each capsule having an internal phase comprising a plurality of charged particles in a fluid, the charged particles being movable between an open state and a closed state by application of an electric field, wherein in the open state, the capsules have a low absorbance for light passing through the medium, and in the closed state, the capsules have a high absorbance for light passing through the medium, and wherein the absorbance of the binder in the closed state is 0.5 to 2.0 times the absorbance of the capsules. For example, the absorbance of the binder in the closed state may be 0.75 to 1.25 times, or 0.9 to 1.1 times, the absorbance of the capsules. Since the binder used is typically polymeric and essentially transparent, at least in thicknesses of at least 50 μm, typically used in electrophoretic media, to produce the necessary absorbance in the binder, it is often necessary to color the binder using a dye or pigment. The latter is often preferred when the variable transmission medium is to be used in locations subject to significant UV radiation (e.g., in the sunroof or windows of a variable transmission vehicle or in the windows of a house), as dyes tend to fade with prolonged exposure to UV radiation. A preferred pigment for this purpose is carbon black, which should have a very small particle size (primary aggregates less than 100 nm) to minimize undesirable light scattering. In other embodiments, color can be achieved using multiple pigments (e.g., a combination of cyan, yellow, and magenta pigments), which can provide a medium with relatively low haze.

[0014] For reasons discussed below, it is desirable that the proportion of binder in the electrophoretic medium be higher than that of most prior art packaged electrophoretic media; there should be at least 1 part by weight of binder for every 15 parts by weight of capsules, and optionally, at least 1 part by weight of binder for every 4 parts by weight of capsules.

[0015] In another aspect, the present invention provides an electrophoretic medium comprising a plurality of charged particles, a liquid in which the particles are dispersed, and a charge control agent ("CCA") comprising an oligoamine-terminated polyolefin and a branched fatty acid containing at least about 8 carbon atoms.

[0016] The polyolefin used as part of the charge control agent in the electrophoretic medium of the present invention can be an oligoamine-terminated polyisobutylene. This type of copolymer is commercially available as OLOA® 11000 (manufactured by ChevronOronite Company LLC, located in San Ramon, California). The branched fatty acid used is desirably a 2-alkyl fatty acid, which may contain 12 or more carbon atoms, with 2-hexyldecanoic acid ("2-HDA") being a particularly preferred acid. The fatty acid used should be readily soluble in the liquid used to disperse the particles and resistant to crystallization.

[0017] In another aspect, the present invention provides an electro-optic medium comprising a plurality of capsules in a binder comprising a mixture of fish gelatin and a polyanion. The capsules are typically formed from a coacervate of gelatin and gum arabic, and they encapsulate an internal phase comprising a mixture of a non-polar solvent and charged pigment particles. The gelatin formulations according to various embodiments of the present invention, particularly the fish gelatin and gum arabic mixtures, are suitable as binders for encapsulated electro-optic media. Furthermore, when used with porcine gelatin / gum arabic coacervates to encapsulate the internal phase, these gelatin binders provide excellent refractive index matching, and thus low haze, when incorporated into a transmissive device, for example. Additionally, electro-optic media incorporating the fish gelatin and polyanion mixture as a binder do not suffer from the recoil observed in binder compositions containing only gelatin.

[0018] In some embodiments, the binder comprises fish gelatin and polyanion in a weight ratio of 0.5 to 2.0, or more preferably, approximately equal parts by weight. In some embodiments, the capsules additionally encapsulate second charged pigment particles. The second charged pigment particles can be oppositely charged to the first charged pigment particles and have a different color. In some embodiments, the binder additionally comprises a pigment or dye. The mixture of the non-polar solvent and the first charged pigment particles can additionally comprise a charge control agent, and the non-polar solvent can be a mixture of hydrocarbons or limonene (e.g., 1-limonene). The binder of the present invention can have a refractive index of 1.47 to 1.57 at 550 nm and 50% relative humidity (RH).

[0019] In another aspect, an electro-optic medium is provided, comprising a plurality of capsules in a polymer binder, each capsule encapsulating charged pigment particles in a non-polar solvent, wherein the plurality of capsules comprises at least 60% within a size range of 50 μm to 90 μm in diameter and at least 15% within a size range of 20 μm to 49 μm in diameter. In another aspect, an electro-optic medium is provided, comprising a plurality of capsules and a binder, each capsule encapsulating charged pigment particles in a non-polar solvent, wherein the plurality of capsules comprises at least 90% within a size range of 5 μm to 50 μm in diameter, and the average number diameter of the plurality of capsules is 20 μm to 30 μm. In another aspect, an electro-optic medium is provided, comprising a plurality of capsules and a binder, each capsule encapsulating charged pigment particles in a non-polar solvent, wherein the plurality of capsules comprises less than 90% within a size range of 5 μm to 50 μm in diameter, and the average number diameter of the plurality of capsules is 25 μm to 35 μm.

[0020] In another aspect, a method of forming an electro-optic medium may include providing an internal phase mixture of a non-polar solvent and charged pigment particles, encapsulating a portion of the internal phase mixture in a plurality of capsules, screening the plurality of capsules by size to separate at least two size distributions, a first size distribution having a diameter between 50 µm and 90 µm and a second size distribution having a diameter between 20 µm and 49, and mixing 2 to 5 parts by weight of the first size distribution with 1 part by weight of the second size distribution along with a polymeric binder.

[0021] In another aspect, a binder formulation for a variable transmittance film is provided that may include a blend of colored particles to achieve a colorless variable transmittance film (i.e., a neutral density film). Generally, the variable transmittance film of the present invention includes a first light-transmitting electrode and a second light-transmitting electrode, with an electrophoretic layer and a polyurethane acrylate-based adhesive disposed between the first and second light-transmitting electrodes. The electrophoretic layer may include an encapsulated internal phase comprising a charged pigment in a non-polar liquid and a binder comprising a blend of colored particles. The blend of colored particles includes black, cyan, and magenta particles. In most embodiments, the average particle diameter of the blend of colored particles is between 20 and 100 nm. In some embodiments, the ratio of black to cyan particles may be between 10:1 and 3:2 (black:cyan). In some embodiments, the ratio of black to magenta particles may be between 10:1 and 3:2 (black:magenta). In some embodiments, the blend of colored particles may be between 0.1% and 3% (based on the weight of the binder).

[0022] In another aspect, the present invention provides a variable transmission electrophoretic medium comprising a plurality of capsules in a binder, each capsule having an internal phase comprising a plurality of charged particles in a fluid, the charged particles being movable between an open state and a closed state by application of an electric field, wherein the fluid comprises one or more non-conjugated olefins.

[0023] On the other hand, the present invention provides a variable transmission electrophoretic device, which includes the above-mentioned variable transmission electrophoretic medium layer arranged between two light-transmitting electrodes. Such a variable transmission electrophoretic device may also include at least one light-transmitting substrate on the opposite side of one of the light-transmitting electrodes to the electro-optical medium; obviously, such a substrate may be provided for each light-transmitting electrode. The electro-optical medium according to various embodiments of the present invention may also be incorporated into other types of electro-optical devices. For example, a front plane laminate (FPL) may include a light-transmitting electrode layer, an adhesive layer and the electro-optical medium of the present invention. In some embodiments, the front plane laminate will also include a release sheet or an adhesive layer or both. The electro-optical medium of the present invention may also be incorporated into an electro-optical display, which includes a light-transmitting electrode layer, an adhesive layer, the electro-optical medium of the present invention and an array of pixel electrodes.

[0024] These and other aspects of the invention will be apparent from the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The accompanying drawings depict one or more embodiments according to the present concepts by way of example only and not limitation.In the accompanying drawings, like reference numerals refer to the same or similar elements.

[0026] Attached Figures 1A-1F are schematic cross-sectional views of: (i) a prior art variable transmission display without a colorant in the binder ( Figure 1A The closed state is schematically shown. Figure 1B (ii) using a highly pigmented, very thin adhesive to Figure 1A and 1B Modification of the prior art display ( Figure 1C and 1D ); and (iii) a variable transmission display of the present invention having a relatively thick colored binder ( Figure 1E and 1F ).

[0027] Figure 2 Yes Figure 1A A micrograph of a prior art display in the off state is shown and illustrates the poor contrast of such a display.

[0028] Figure 3 Yes Figure 1D A micrograph of the display in the open state is shown, illustrating the presence of dark multilayers and the resulting particles.

[0029] Figure 4 is similar to Figure 3 The micrographs, however, show that Figure 1F The display is shown in the on state.

[0030] Figures 5A-5C is shown for a colorless binder (such as Figure 1A / 1B) and colored adhesive ( Figure 1E / 1F) of the display in the off state ( Figure 5A ), the amount of light transmitted in the open state ( Figure 5B ) and the resulting contrast ( Figure 5C ) diagram.

[0031] Figure 6A and 6B It shows that according to Figure 1C / 1D( Figure 6A )and Figure 1E / 1F( Figure 6B) in the closed and open states of a single pixel display and illustrates the improvements provided by the particles of the present invention.

[0032] Attached Figure 7 is a graph showing the contrast achieved with packaged electrophoretic media using combinations of OLOA and various other charging agents.

[0033] Figure 8 is similar to Figure 7 However, plots showing the contrast obtained using OLOA and different ratios of 2-HDA or control CCA are shown.

[0034] Figure 9 is similar to Figure 8 However, instead of a graph of contrast, a minimum haze value is shown.

[0035] Figures 10A-10D are graphs showing the minimum on-state transmittance, minimum off-state transmittance, minimum on-state haze, and contrast ratio of encapsulated electrophoretic media using OLOA / 2-HDA and OLOA / Span 85 charge control agents under varying drive voltages, respectively.

[0036] Figure 11 is similar to Figure 10D However, graphs showing the contrast ratios obtained by encapsulating electrophoretic media using OLOA / 2-HDA and OLOA / oleic acid charge control agents at variable ratios and at various driving voltages are shown.

[0037] Figure 12A Illustration of an electro-optical display consisting of two types of charged particles. The particles can be moved toward (or away from) an observer by applying an electric field.

[0038] Figure 12B is an illustration of a variable transmission device comprising first and second light-transmitting electrode layers and an electro-optical medium disposed between the layers. Applying an electric field can cause particles to move closer to the capsule wall, thereby allowing light to pass through the medium.

[0039] Figure 13A Shown are haze measurements of variable transmission samples of various fish gelatin binder compositions. The left panel sample contains a binder without gum arabic, the middle panel sample contains a binder with 33% (wt. / wt.) gum arabic, and the right panel sample contains a binder with equal parts fish gelatin and gum arabic.

[0040] Figure 13BShown are contrast measurements of variable transmission samples of various fish gelatin binder compositions. The left panel sample contains a binder without gum arabic, the middle panel sample contains a binder with 33% (wt. / wt.) gum arabic, and the right panel sample contains a binder with equal parts fish gelatin and gum arabic.

[0041] Figure 13C Recoil measurements of variable transmission samples of various fish gelatin binder compositions are shown. The left panel sample contains a binder without gum arabic, the middle panel sample contains a binder with 33% (wt. / wt.) gum arabic, and the right panel sample contains a binder with equal parts fish gelatin and gum arabic.

[0042] Figure 14 The decay of the closed state of a sample with only fish gelatin as a binder is shown compared to a sample with equal parts fish gelatin and gum arabic. In the test, the 1:1 mixture of fish gelatin and gum arabic had significantly reduced recoil, resulting in stable open and closed states for several weeks.

[0043] Figure 15 is a flow chart describing a method for producing an electro-optic medium having a predetermined distribution of capsule sizes.

[0044] Figure 16A Shown are the differences in open-state transmittance for a sample of a variable transmission device having only small capsules (left) and for a variable transmission device having a blend of large and small capsules (right).

[0045] Figure 16B Shown are the differences in off-state transmittance for a sample of a variable transmission device having only small capsules (left) and for a variable transmission device having a blend of large and small capsules (right).

[0046] Figure 16C Shown are the differences in open-state haze for a sample of a variable transmission device having only small capsules (left) and for a variable transmission device having a blend of large and small capsules (right).

[0047] Figure 16D The contrast ratio (on transmission / off transmission) is shown for a sample of a variable transmission device with only small capsules (left) and for a variable transmission device with a blend of large and small capsules (right). The blend of large and small capsules has a much greater contrast ratio between the on and closed states.

[0048] Figure 17 Images of a variable transmission device comprising only small capsules (left) and a blend of large and small capsules (right) are shown. Figure 17 It shows that there is little variation in the particles between the two different capsule size distributions.

[0049] Figure 18 The visible absorption spectra of various binder-pigment formulations are shown. Figure 18 As shown, the combination of 3 parts cyan, 3 parts magenta, and 14 parts black produces a relatively uniform visible light absorption spectrum.

[0050] Figure 19 Contrast measurements are shown for a binder with 3 parts cyan, 3 parts magenta, and 14 parts black (left) and a binder with only carbon black colorant (right). Although the contrast is better for the black-only binder, the contrast with the colored blend binder is sufficient for most variable transmission applications.

[0051] Figure 20 Haze measurements are shown for a binder with 3 parts cyan, 3 parts magenta, 13 parts black (left) and a binder with only carbon black colorant (right). The haze for both formulations is very low.

[0052] Figure 21 is a cross-sectional side view of a variable transmission film having a transparent adhesive layer.

[0053] Figure 22A and 22B Cross-sectional side views of an electrophoretic medium combined with a transparent adhesive in the closed and open states, respectively.

[0054] Figure 23A and 23B Cross-sectional side views of an electrophoretic medium combined with a pigmented adhesive in the closed and open states, respectively.

[0055] Figure 24A is a photograph of the variable transmission assembly including the transparent adhesive layer in an open state.

[0056] Figure 24B is a photograph of a variable transmission assembly including a colored adhesive layer in an open state according to an embodiment of the present invention.

[0057] Figures 25A to 25D are graphs respectively illustrating minimum off-state transmittance, minimum on-state transmittance, contrast ratio, and minimum on-state haze of encapsulated electrophoretic media according to various embodiments of the present invention.

[0058] Figures 26A to 26L is a graph illustrating minimum off-state transmittance, minimum on-state transmittance, contrast ratio, and minimum on-state haze for encapsulated electrophoretic media containing capsules of various sizes according to various embodiments of the present invention. DETAILED DESCRIPTION

[0059] Electrophoretic displays (e.g. e-readers) are typically opaque and operate in reflective mode. Figure 12A In the example shown in FIG, the reflectivity of light striking the surface is modulated by moving black or white charged particles towards the viewing surface at a suitable voltage. However, it is also possible to make an electrophoretic device with Figure 12B The device is shown to operate in a so-called "shutter mode," where one operating state is substantially opaque and the other operating state is light-transmissive. When this "shutter mode" electrophoretic device is constructed on a transparent substrate, the transmission of light through the device can be adjusted. One potential use for shutter mode electrophoretic media is as a window with variable light transmission.

[0060] Figure 12A and 12B The device comprises an electro-optic medium consisting of capsules in a polymer binder. The capsules contain charged pigment particles that move in response to an electric field. The capsules are typically formed from a gelatin material, described in more detail below. The electro-optic medium is distributed between first and second electrode layers, which can be made of known materials, such as indium tin oxide (ITO)-coated polyethylene terephthalate (PET). Alternatively, the electrode layers can include metal electrodes arranged as pixels. The pixels can be controllable as an active matrix, allowing the display of text and images. An additional adhesive layer is typically present between the electro-optic medium and one of the electrode layers. The adhesive layer can be UV-curable and typically improves the planarity of the final device by "filling in" deviations created by the capsules. Suitable adhesive formulations are described in U.S. Patent No. 2017 / 0022403, which is incorporated herein by reference.

[0061] When a DC field is applied to Figure 12A When the device is turned on, the dark or light particles move towards the viewing surface, changing the optical state from dark to light. Figure 12B In both embodiments, when an alternating electric field is applied to one of the electrodes, the charged pigment particles are driven to the capsule walls, forming pores through the capsule for light transmission, i.e., the open state. In both embodiments, because the solvent is nonpolar and contains a charge control agent and / or stabilizer, the optical state (black / white; on / off) can be maintained for extended periods (weeks) without the need for an electric field. As a result, the device can be "switched" only a few times a day, consuming very little power.

[0062] The term "gray state" is used herein in its conventional meaning in the imaging field, referring to a state between the two extreme optical states of a pixel, but not necessarily implying a black-white transition between these two extreme states. For example, several of the Iink patents and published applications referenced above describe electrophoretic displays in which the extreme states are white and dark blue, such that the intermediate "gray state" is actually light blue. In fact, as already mentioned, the change in optical state may not be a color change at all. The terms "black" and "white" or "off" and "on" will be used hereinafter to refer to the two extreme optical states of a display and should be understood to generally include extreme optical states that are not strictly black and white, such as the white and dark blue states mentioned above. The term "monochromatic" may be used hereinafter to refer to a drive scheme that drives a pixel only to its two extreme optical states, without an intermediate gray state. (In the case of shutter-mode displays discussed below, the two extreme optical states may be referred to as "dark" and "clear" or "on" and "off.")

[0063] The terms "bistable" and "bistability" are used herein in their conventional sense in the art to refer to a display comprising a display element having first and second display states, wherein the first and second display states differ in at least one optical property such that after any given element is driven to assume its first or second display state by an addressing pulse of finite duration, that state persists after termination of the addressing pulse for a time that is 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. As shown in U.S. Patent No. 7,170,670, some particle-based electrophoretic displays that support grayscale can be stable not only in their extreme black and white states but also in intermediate gray states, as can some other types of electro-optical displays. Such displays are properly referred to as "multistable" rather than bistable, but for convenience, the term "bistable" will be used herein to cover both bistable and multistable displays.

[0064] 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 multiple charged particles move through a fluid under the influence of an electric field. Compared to liquid crystal displays (LCDs), EPDs can offer 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 lifespan for these displays.

[0065] As mentioned above, electrophoretic media require the presence of a fluid. In most prior art electrophoretic media, the fluid is a liquid, but electrophoretic media can be generated using a gaseous fluid; see, for example, Kitamura, T. et al., “Electronic toner movement for electronic paper-like display,” IDW Japan, 2001, Paper HCS 1-1, 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. When such gas-based electrophoretic media are used in an orientation that allows particle sedimentation, such as in signs where the media is arranged in a vertical plane, such gas-based electrophoretic media are susceptible to the same problems as liquid-based electrophoretic media due to particle sedimentation. In fact, the particle sedimentation problem is more severe in gas-based electrophoretic media than in liquid-based electrophoretic media because the viscosity of the gaseous suspending fluid is lower than that of the liquid, thus causing the electrophoretic particles to sediment more quickly.

[0066] Numerous patents and applications assigned to or in the names of the Massachusetts Institute of Technology (MIT), Iink Corporation, Iink California LLC, and related companies describe various technologies for encapsulated and microcell electrophoretic and other electro-optical media. Encapsulated electrophoretic 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. The capsules themselves are typically held in a polymer binder to form a coherent layer positioned between two electrodes. In microcell electrophoretic displays, the charged particles and fluid are not encapsulated within microcapsules, but rather within a plurality of cavities formed within a carrier medium (usually a polymer film). The technologies described in these patents and applications include:

[0067] (a) Electrophoretic particles, fluids, and fluid additives; see, e.g., U.S. Patent Nos. 5,961,804; 6,017,584; 6,120,588; 6,120,839; 6,262,706; 6,262,833; 6,300,932; 6,323,989; 6,377,387; 6,515,649; 6,538,801; 6,580,545; 6,652,075; 6,693,620; 6,721,083; 6,727,881; 6,822,782; 6,831,771; 6,870,661; 6,927,892; 6,956,690; 6,958,849; 7,002,728; 7,038,655; 7,052,766; 7,110,162; 7,113,323; 7,141,688; 7,142,351; 7,170,670; 7,180,649; 7,226,550; 7,230,750; 7,230,751; 7,236,290; 7,247,379; 7,277,218; 7,286,279; 7,312,916; 7,375,875; 7,382,514; 7,390,901; 7,411,720; 7,473,782; 7,532,388; 7,532,389; 7,572,394; 7,576,904; 7,580,180; 7,679,814; 7,746,544; 7,767,112; 7,848,006; 7,903,319; 7,951,938; 8,018,640; 8,115,729; 8,119,802; 8,199,395; 8,257,614; 8,270,064; 8,305,341; 8,361,620; 8,363,306; and U.S. Patent Application Publication No.2003 / 0048522; 2003 / 0151029; 2003 / 0164480; 2003 / 0169227; 2003 / 0197916; 2004 / 0030125; 2005 / 0012980; 2005 / 0136347; 2006 / 0132896; 2006 / 0281924; 2007 / 0268567; 2009 / 0009852; 2009 / 0206499; 2009 / 0225398; 2010 / 0148385; 2011 / 0217639; 2012 / 0049125; 2012 / 0112131; 2013 / 0161565; 2013 / 0193385; 2013 / 0244149; 2014 / 0011913; 2014 / 0078024; 2014 / 0078573; 2014 / 0078576; 2014 / 0078857; 2014 / 0104674; 2014 / 0231728; 2014 / 0339481; 2014 / 0347718; 2015 / 0015932; 2015 / 0177589; 2015 / 0177590; 2015 / 0185509; 2015 / 0218384; 2015 / 0241754; 2015 / 0248045; 2015 / 0301425; 2015 / 0378236; 2016 / 0139483; and 2016 / 0170106.

[0068] (b) capsules, 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; 7,184,197; and U.S. Patent Application Publication Nos. 2005 / 0156340; 2007 / 0091417; 2008 / 0130092; 2009 / 0122389; and 2011 / 0286081;

[0069] (c) microcell structures, wall materials, and methods of forming microcells; see, for example, U.S. Patent Nos. 7,072,095 and 9,279,906;

[0070] (d) Methods for filling and sealing microlocations; see, e.g., U.S. Patent Nos. 7,144,942 and 7,715,088;

[0071] (e) Films and subassemblies containing electro-optical materials; see, for example, U.S. Patent Nos. 6,982,178 and 7,839,564;

[0072] (f) Backsheets, adhesive layers, and other auxiliary layers and methods for use in displays; see, e.g., U.S. Patent Nos. 7,116,318 and 7,535,624;

[0073] (g) color formation and color adjustment; see, e.g., U.S. Patent Nos. 7,075,502 and 7,839,564;

[0074] (h) Methods for driving displays; see, for example, U.S. Patent Nos. 7,012,600 and 7,453,445; and

[0075] (i) Display applications; see, for example, US Pat. Nos. 7,312,784 and 8,009,348.

[0076] 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 electrophoretic fluid and a continuous phase of polymer material, and 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, aforementioned U.S. Patent Nos. 6,866,760 and 7,079,305. Therefore, for the purposes of this application, such polymer-dispersed electrophoretic media are considered to be a subclass of encapsulated electrophoretic media.

[0077] While electrophoretic media are typically opaque (because, for example, in many electrophoretic media, the particles substantially block visible light from being transmitted 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 one display state is light-transmissive. See, for example, U.S. Patents Nos. 5,872,552, 6,130,774, 6,144,361, 6,172,798, 6,271,823, 6,225,971, and 6,184,856. Dielectrophoretic displays, which are similar to electrophoretic displays but rely on variations in electric field strength, can operate in a similar mode; see U.S. Patent No. 4,418,346. Other types of electro-optical displays can also operate in a shutter mode. Electro-optical media operating in shutter mode can be used in multilayer structures for full-color displays; in this structure, at least one layer adjacent to the viewing surface of the display is operated in shutter mode to expose or hide a second layer further away from the viewing surface.

[0078] Charged pigment particles can have a variety of colors and compositions. In addition, charged pigment particles can be functionalized with surface polymers to improve state stability. Such pigments are described in U.S. Patent Publication No. 2016 / 0085132, which is incorporated herein by reference in its entirety. For example, if the charged particles are white, they can be formed from inorganic pigments such as TiO2, ZrO2, ZnO, Al2O3, Sb2O3, BaSO4, PbSO4, etc. They can also be polymer particles with a high refractive index (>1.5) and a certain size (>100 nm) to appear white, or composite particles engineered to have a desired refractive index. Black charged particles can be formed from CI Pigment Black 26 or 28 or similar (such as iron manganese black or copper chrome black) or carbon black. Other colors (non-white and non-black) can be formed by organic pigments, such as CI pigments PR 254, PR122, PR149, PG36, PG58, PG7, PB28, PB15:3, PY83, PY138, PY150, PY155 or PY20. Other examples include Clariant Hostaperm Red D3G 70-EDS, Hostaperm Pink E-EDS, PV fast red D3G, Hostaperm red D3G 70, Hostaperm Blue B2G-EDS, Hostaperm Yellow H4G-EDS, Novoperm Yellow HR-70-EDS, Hostaperm Green GNX, BASF Irgazine Red L 3630, Cinquasia Red L 4100 HD, and Irgazin Red L 3660 HD; Sun Chemical Phthalocyanine Blue, Phthalocyanine Green, Aniline Yellow, or AAOT Aniline Yellow. Colored particles can also be formed from inorganic pigments, such as CI Pigment Blue 28, CI Pigment Green 50, CI Pigment Yellow 227, and the like. The surface of the charged particles can be modified by known techniques based on the desired charge polarity and charge level of the particles, as described in U.S. Patent Nos. 6,822,782, 7,002,728, 9,366,935, and 9,372,380, and U.S. Publication No. 2014-0011913, the entire contents of which are incorporated herein by reference in their entireties.

[0079] The particles may exhibit a natural charge, or may be explicitly charged using a charge control agent, or may acquire a charge when suspended in a solvent or solvent mixture. Suitable charge control agents are well known in the art; they may be polymeric or non-polymeric in nature, or ionic or non-ionic. Examples of charge control agents may include, but are not limited to, Solsperse 17000 (reactive polymeric dispersant), Solsperse 9000 (reactive polymeric dispersant), OLOA® 11000 (succinimide ashless dispersant), Unithox 750 (ethoxylate), Span 85 (sorbitan trioleate), Petronate L (sodium sulfonate), Alcolec LV30 (soy lecithin), Petrostep B100 (petroleum sulfonate) or B70 (barium sulfonate), Aerosol OT, polyisobutylene derivatives, or poly(ethylene-co-butylene) derivatives, among others. In addition to the suspension and charged pigment particles, the internal phase may also include stabilizers, surfactants, and charge control agents. When the charged pigment particles are dispersed in the solvent, the stabilizing material may be adsorbed onto the charged pigment particles. The stabilizing material separates the particles from one another so that the variable transmission medium is substantially non-transmissive when the particles are in their dispersed state.

[0080] As is known in the art, charged particles (typically carbon black, as described above) can be dispersed in a low dielectric constant solvent using a surfactant. Such surfactants typically comprise a polar "head group" and a non-polar "tail group" that are compatible with or soluble in the solvent. In the present invention, the non-polar tail group is preferably a saturated or unsaturated hydrocarbon moiety, or another group soluble in a hydrocarbon solvent, such as a poly(dialkylsiloxane). The polar group can be any polar organic functional group, including ionic materials such as ammonium salts, sulfonates, or phosphonates, or acidic or basic groups. Particularly preferred head groups are carboxylic acid or carboxylate groups. Stabilizers suitable for use in the present invention include polyisobutylene and polystyrene. In some embodiments, a dispersant such as polyisobutylene succinimide and / or sorbitan trioleate and / or 2-hexyldecanoic acid is added.

[0081] The fluid used in the variable transmission medium of the present invention will generally have a low dielectric constant (preferably less than 10, and desirably less than 3). The fluid is preferably a solvent with low viscosity, a relatively high refractive index, low cost, low reactivity, and a low vapor pressure / high boiling point. Examples of solvents include, but are not limited to, aliphatic hydrocarbons such as heptane, octane, and petroleum distillates such as Isopar® (Exxon Mobil) or Isane® (Total); terpenes such as limonene, for example, 1-limonene; and aromatic hydrocarbons such as toluene. A particularly preferred solvent is limonene because it combines a low dielectric constant (2.3) with a relatively high refractive index (1.47). The refractive index of the internal phase can be modified by adding a refractive index matching agent. For example, the aforementioned U.S. Patent No. 7,679,814 describes an electrophoretic medium suitable for use in a variable transmission device, wherein the fluid surrounding the electrophoretic particles comprises a mixture of partially hydrogenated aromatic hydrocarbons and terpenes, preferably a mixture of d-limonene and partially hydrogenated terphenyls, available commercially as Cargille® 5040 from Cargille-Sacher Laboratories, 55 Commerce Rd, Cedar Grove, NJ 07009. In encapsulation media prepared according to various embodiments of the present invention, it is preferred that the refractive index of the encapsulated dispersion be matched as closely as possible to that of the encapsulating material to reduce haze. In most cases, it is advantageous to have an internal phase having a refractive index at 550 nm between 1.51 and 1.57, preferably about 1.54 at 550 nm.

[0082] In preferred embodiments of the present invention, the encapsulated fluid may comprise one or more non-conjugated olefins, preferably cyclic hydrocarbons. Examples of non-conjugated olefins include, but are not limited to, terpenes such as limonene; phenylcyclohexane; hexyl benzoate; cyclododecatriene; 1,5-dimethyltetralin; partially hydrogenated terphenyls such as Cargille® 5040; phenylmethylsiloxane oligomers; and combinations thereof. The most preferred composition for encapsulating fluids according to embodiments of the present invention comprises cyclododecatriene and partially hydrogenated terphenyls.

[0083] It has been previously proposed that the optimal approach for variable transmission electrophoretic media would be polymer-dispersed electrophoretic media with a broad droplet size distribution; such a broad size distribution should result in low particle size due to the excellent uniformity of the electrophoretic medium layer and the presence of very small droplets (often referred to as "fines") filling the gaps between larger droplets. Previous attempts to use microencapsulated media in variable transmission devices have suffered from excessive particle size (localized variations in optical density) and high minimum transmission values (i.e., a relatively leaky closed state), rendering such media useless in certain commercial applications, such as automotive sunroofs. However, polymer-dispersed electrophoretic media present their own challenges, including unpredictable gelation of the continuous phase with parameters such as shear and temperature (which significantly complicates the media's production process) and the need for a skimcoat to reduce the likelihood of droplet breakage. Capsules are more resistant to breakage than droplets in polymer-dispersed media, enabling the use of certain coating techniques (such as spray coating) for capsule-based media that are not possible with polymer-dispersed media. Capsule-based media do not require descaling to prevent capsule rupture, and the capsules can be size-separated by techniques such as sieving, allowing media with a restricted range of capsule sizes to be produced in a manner that is difficult or impossible with polymer-dispersed media.

[0084] However, as previously discussed, capsule-based electrophoretic media tend to suffer from undesirably high transmittance in the off state and / or excessive particle content. For example, at low coat weights, capsule-based media exhibit high transmittance through pinholes or interstices (gaps between adjacent capsules), while at higher coat weights, excessive particle content and poor contrast can become significant issues. Even when using capsules of all sizes, the capsule walls (especially those of small capsules) can increase transmittance in the off state and reduce the contrast possible in a capsule-based variable transmission device. Even at high operating voltages (e.g., 120 V), capsule-based media can suffer from insufficient contrast (the ratio of maximum on transmission to minimum off transmission). It has now been discovered that the aforementioned disadvantages of capsule-based variable transmission devices can be reduced or even substantially eliminated by utilizing variable transmission electrophoretic media made according to various embodiments of the present invention.

[0085] According to a first embodiment of the present invention, undesirably high light transmittance and / or excessive particles can be reduced or substantially eliminated by providing a variable-transmission electrophoretic medium comprising a plurality of capsules and a binder, wherein the absorbance of the binder (continuous phase) is approximately equal to the absorbance of the internal phase within the capsules in the closed state. The binder used in capsule-based electrophoretic media is typically polymeric and substantially transparent, with a thickness of at least 50 μm typically used in such media. To create the necessary absorbance in the binder, color can be added to the binder using dyes or pigments (collectively referred to as "colorants"). To minimize haze, dyes or finely dispersed pigments should be used as colorants. However, because variable-transmission devices such as windows and automotive sunroofs are exposed to sunlight with a significant proportion of near-UV radiation for extended periods of time, pigments are generally preferred as colorants because they are susceptible to photo- or thermal bleaching. Carbon black is currently the preferred pigment due to its desirable neutral hue and excellent light stability. However, carbon black does have a strong tendency to aggregate (almost all commercial carbon black is an aggregate of small particles), making it necessary to add a dispersant or surfactant to the carbon black to maintain a particle size that does not excessively scatter light. Furthermore, maintaining good dispersion of the carbon black in the electrophoretic medium is crucial because carbon black is highly conductive, and the formation of particle aggregates or filaments could create electrical shorts between the electrodes or at least increase the conductivity of the binder to an undesirable level. Finally, the concentration of carbon black in the binder must be kept low to prevent a significant portion of the electric field between the electrodes from passing through the binder and around the capsules, thereby degrading the electro-optical performance of the capsules. Although low-molecular-weight surfactants can be used to aid in the dispersion of carbon black, such surfactants tend to migrate to interfaces other than the one between the carbon black and the surrounding phase, and this surfactant migration can cause various problems. Thus, polymeric surfactants are preferably used, for example, poloxamer dispersants such as Kolliphor P188 (available from BASF) have been found to work well with preferred carbon blacks sold commercially as Emperor 2000 carbon black by Cabot Corporation in liquid gelatin (such as Hipure liquid gelatin sold by Norland Products) or blends of liquid gelatin and gum arabic.

[0086] In preferred embodiments of the present invention, the colorant may comprise a blend of colored particles. The blend of colored particles may include black, cyan, and magenta particles. In most embodiments, the average particle diameter of the blend of colored particles may be between 20 and 100 nm. In some embodiments, the ratio of black to cyan particles may be between 10:1 and 3:2 (black:cyan). In some embodiments, the ratio of black to magenta particles may be between 10:1 and 3:2 (black:magenta). In some embodiments, the blend of colored particles may be present in an amount of 0.1% to 3% (based on the weight of the binder). In some embodiments, the binder comprises approximately 3 parts cyan, 3 parts magenta, and 14 parts carbon black, with the total color mixture comprising approximately 2% of the binder mass. This binder blend has been found to be particularly suitable when the internal phase is encapsulated in a coacervate of (porcine) gelatin and gum arabic. The resulting electro-optical medium exhibits low haze and reduced recoil when used in a transmissive device, resulting in improved long-term state stability.

[0087] For reasons explained below with reference to the accompanying drawings, it is undesirable for the variable transmission media of the present invention to contain a thin layer of a relatively heavily pigmented binder; a relatively thicker layer of a lighter pigmented binder achieves the best results. In fact, it has been found desirable for the media of the present invention to contain a higher proportion of binder than most prior art encapsulated electrophoretic media; at least 1 part by weight of binder should be present for every 15 parts by weight of capsules, and optionally up to 1 part by weight of binder should be present for every 4 parts by weight of capsules. This relatively high proportion of binder minimizes the transmission of light through pinholes and voids in the capsule layer. Furthermore, the coating weight used should be such that at least a monolayer of capsules, or slightly more, is deposited on the substrate for coating.

[0088] Figure 1A and 1B Schematic cross-sections through a prior art capsule-based electrophoretic medium in the closed and open states, respectively, where the binder is not colored. It can be seen that the transmittance of the medium in the closed state is increased due to the presence of pinholes (as shown) or voids, where there is essentially no obstruction to the transmission of light through the medium even in the closed state. The resulting "leakage" of light through the closed state of the medium can significantly reduce its contrast. In practice, even if the coating weight is increased from the standard 20 g / m 2 Increased to about 24 g / m 2 The presence of such gaps and holes is also problematic because they limit the minimum transmittance in the closed state to above 3%, which is too high for a car sunroof.

[0089] Figure 1C and 1D is a schematic cross section of a capsule-based electrophoretic medium, similar to Figure 1A and1B The capsule-based electrophoretic medium includes a small amount of a heavily pigmented binder. The presence of this pigmented binder greatly reduces the effects of pinholes and voids in the closed state ( Figure 1C ), so with Figure 1A and 1B Compared with the medium with the same color, the contrast of the medium is improved. However, in the open state ( Figure 1D ), heavy pigmented binders can lead to undesirably high particles because heavy pigmented binders tend to overemphasize the capsule walls in multilayered portions of the display, see Figure 1D .

[0090] Figure 1E and 1F is a schematic cross-sectional view of a preferred capsule-based electrophoretic medium of the present invention, which is similar to Figure 1A and 1B The capsule-based electrophoretic medium uses Figure 1C and 1D The binder in the closed state is lighter colored but present in greater amounts, so that the absorbance of the binder in the closed state essentially matches the absorbance of the internal phase. It can be seen that the presence of this lighter colored binder has essentially the same effect in reducing the effects of pinholes and voids in the closed state ( Figure 1E ), thus with Figure 1A and Figure 1B The contrast of the medium is improved compared to the medium, such as Figure 1C However, unlike the heavily pigmented but thinner binder in Figure 1D In contrast, particles in the open state ( Figure 1F ) is greatly reduced because in the reference Figure 1F The capsule walls are not overly emphasized in the multi-layered portion of the display.

[0091] According to a second embodiment of the present invention, the contrast deficiency of variable transmission electrophoretic media can be improved by including a charge control agent comprising a branched fatty acid having at least about 8 carbon atoms and an oligoamine-terminated polyolefin, such as OLOA® 11000. Encapsulating the electrophoretic media containing the charge control agent produces an encapsulated medium that exhibits significantly improved contrast, even at reduced operating voltages (and thus reduced power consumption), and low haze in the open state, which is important for variable transmission devices such as windows and automotive sunroofs. The fatty acid used is preferably an oil-soluble acid that is insoluble in water.

[0092] According to a third embodiment of the present invention, an improved electro-optic medium is provided, comprising encapsulated pigment particles and a binder. In particular, a mixture of fish gelatin and a polyanion (e.g., gum arabic) has been found to be an excellent binder for use with capsules formed from coacervates of (porcine) gelatin and gum arabic. Polyanions that can be included in the binder with fish gelatin include, but are not limited to, carbohydrate polymers such as starch and cellulose derivatives, plant extracts (e.g., gum arabic), and polysaccharides (e.g., alginates); proteins such as gelatin or whey protein; lipids such as waxes or phospholipids; and combinations thereof. This result is surprising, as neither fish gelatin nor polyanions (e.g., gum arabic) can be used alone as binder materials for electro-optical media. As described below, fish gelatin alone exhibits unacceptable recoil, while polyanions (e.g., gum arabic) alone can shrink and crack during conditioning after coating. The resulting electro-optic medium exhibits low haze and reduced recoil when used in a transmissive device, resulting in improved long-term state stability. Electro-optical media can be coated onto large surfaces and laminated with electrodes, etc., to create a variety of electro-optical devices, including sunlight-readable displays and smart windows.

[0093] Gelatin-based capsule walls used in variable transmission devices have been described in many of the aforementioned E Ink and MIT patents and applications. Gelatin is available from various commercial suppliers, such as Sigma Aldrich or Gelitia USA. It can be obtained in various grades and purities depending on the application requirements. Gelatin primarily consists of collagen that has been harvested and hydrolyzed from animal products (cattle, pigs, poultry, fish). It contains a mixture of peptides and proteins. In many of the embodiments described herein, gelatin is combined with gum arabic (gum arabic), which is derived from the hardened sap of the acacia tree. Gum arabic is a complex mixture of glycoproteins and polysaccharides and is often used as a stabilizer in food products. The pH of aqueous solutions of gum arabic and gelatin can be adjusted to form a polymer-rich coacervate phase that can encapsulate droplets of a nonpolar internal phase, as described below.

[0094] Capsules containing gelatin / gum arabic can be prepared as follows; see, for example, U.S. Patent No. 7,170,670, which is incorporated by reference in its entirety. In this process, a water-soluble mixture of gelatin and / or gum arabic is emulsified with a hydrocarbon internal phase (or other water-immiscible phase to be encapsulated) to encapsulate the internal phase. The solution may be heated to 40°C prior to emulsification to dissolve the gelatin. After achieving the desired droplet size distribution, the pH is typically lowered to form coacervates. Capsules are formed by controlled cooling and mixing of the emulsion (typically to room temperature or lower). If the wetting and spreading conditions are correct (which largely depend on the internal phase composition), proper mixing and certain encapsulation recipes (e.g., gelatin and gum arabic concentrations and pH) can be achieved to uniformly and discretely gel the coacervates around the internal phase droplets. This process produces capsules ranging in size from 20 to 100 µm, typically incorporating more than 50% of the starting material into usable capsules. The resulting capsules are then separated by size by sieving or other size exclusion sorting. Capsules larger than 100 µm are generally excluded because they are visible to the naked eye and larger capsules increase the gap between electrodes, thereby increasing the necessary drive voltage.

[0095] Surprisingly, according to a fourth embodiment of the present invention, it has been discovered that the addition of larger capsules can improve the viewing experience through the open state in a variable transmission device. This result was unexpected because traditionally, variable transmission devices with a predominance of capsules with diameters in the range of 50 μm and 90 μm are "grainy" due to inconsistent capsule packaging. It has been discovered that by intentionally sorting the capsules by size during the manufacture of the electro-optical medium and then intentionally combining the selected size distributions to obtain a specific size distribution ratio, a variable transmission device with good contrast and low grain can be obtained. When a light source is viewed through the device, the resulting variable transmission device has low grain, good contrast, and a reduced diffraction pattern.

[0096] The process for preparing the electro-optical medium of the present invention according to the fourth embodiment of the present invention can be found in Figure 15 , wherein the process begins with the preparation of capsules comprising charged pigment particles, as described above. A two-screen process (typically Figure 15 The encapsulated electrophoretic medium is then size-screened using sieves A and B in Figure 1 . While three different size exclusions are shown, it should be understood that additional size exclusions can be performed, but it may only be necessary to separate the capsules into two size distributions. The size distributions are then recombined in the desired proportions (by weight) with a polymer binder (e.g., gelatin) to form an electro-optical medium that can be coated onto a light-transmitting electrode layer. For every part by weight of smaller capsules, the device of the present invention can include between two and five parts by weight of larger capsules. In some embodiments, there can be approximately three parts by weight of larger capsules for every part by weight of smaller capsules.

[0097] After size sorting, the capsules are mixed with a binder to produce a slurry for coating (e.g., using slot coating, blade coating, spin coating, etc.). In embodiments of the present invention, the binder comprises gelatin, typically fish gelatin. In preferred embodiments, the gelatin is mixed with gum arabic, but it has been found that the mixture should not be complexed into a coacervate because maintaining slurry homogeneity is more difficult. In addition, it has been found that the haze of the transmissive medium can be improved by varying the amount of gum arabic added to the binder mixture.

[0098] According to various embodiments of the present invention, to improve the off-axis transparency of a display including an electro-optical medium layer, it may be advantageous to keep the layer as thin as possible, thereby reducing the size of any particle structures that extend through the thickness of the electrophoretic layer; however, as described above, a thin electrophoretic layer requires a corresponding increase in the volume fraction of the electrophoretic particles to achieve sufficient opacity in the off state of the display. Therefore, for any given choice of material for the light modulator, the electrophoretic layer may have an optimal thickness. Off-axis transparency can also be improved by controlling the particle structure so that it does not occupy the entire sidewall of the droplet. In particular, it may be advantageous to concentrate the particles so that the particle structure occupies only a portion of the sidewall adjacent to one major surface of the electrophoretic medium layer. Such a particle structure can be generated according to the DC / AC drive method of the present invention by first placing all particles within the droplet adjacent to one major surface of the electrophoretic layer by applying a DC field to the electrophoretic layer, and then driving the particles to the sidewall using an AC field of an appropriate frequency.

[0099] As mentioned above, the variable transmission film of the present invention may include a first light-transmitting electrode and a second light-transmitting electrode, wherein the electrophoretic layer and the UV curable adhesive (eg, polyurethane acrylate blend) are disposed between the first light-transmitting electrode and the second light-transmitting electrode, such as Figure 21 . According to another embodiment of the present invention, the adhesive layer of the variable transmission film may include a non-scattering colorant. Coloring the film's adhesive can further reduce particles and pinholes. Adding a non-scattering colorant (such as a dye or a very small (<100 nm) well-dispersed pigment) to a UV-curable adhesive may fill the pinholes in the capsule layer, resulting in reduced light transmission through the pinholes. Colored UV adhesives can also significantly improve the particle size of the variable transmission film. Examples of colorants include, but are not limited to, Macrolex Black 2B, Keyplast Black AN, Macrolex Violet 3R, Macrolex Blue 3R, Orasol Black X51, and Orasol Black X55.

[0100] The adhesive composition according to various embodiments of the present invention preferably includes 0.25 to 0.5 phr of one or more colorants. The adhesive is not limited to being colored with a single material. Blends of pigments and / or dyes can be used to improve light fastness and high temperature resistance. Depending on the application of the variable transmission film, the color of the adhesive can be adjusted by selecting a colored dye / pigment without having to change the underlying capsule layer.

[0101] While not wishing to be bound by theory, it is possible that due to the varying thickness of the capsule layer and the use of a 100% solids UV-curable adhesive that is effective for planarization, which results in some graining, the variable thickness of the pigmented adhesive layer can effectively complement the shape of the capsule layer. For example, the thickest portion of the pigmented adhesive will be located near the location of the pinhole in the capsule layer, thereby providing maximum coloration where it is most needed (see Figure 22A 、 22B , 23A, and 23B). For example, the addition of a black dye soluble in the adhesive, such as Keyplast Black AN, can reduce open-state particulates (cqi score) and closed-state pinholes without increasing open-state haze. Because the UV-curable adhesive layer cannot change its transmittance during device switching, the colorant loading is preferably selected so that the transmittance of the adhesive layer is between the open- and closed-state transmittances of the capsule layer. For example, if a device with an approximately 1 mil capsule layer has an off-state transmittance of approximately 1% and an open-state transmittance of approximately 30%, an adhesive layer with a thickness of approximately 1 mil should be tinted to achieve a transmittance between 1 and 30% to complement the active capsule layer.

[0102] Example

[0103] Examples will now be given, albeit by way of illustration only, to illustrate details of electrophoretic media prepared according to various embodiments of the present invention.

[0104] I. Variable Transmission Media Containing a Pigmented Binder

[0105] Example 1

[0106] A non-aqueous internal phase is prepared by combining OLOA® 11000, 1-limonene, Cargille® 5040 infusion solution, carbon black, polystyrene, and sorbitan trioleate. The resulting mixture is encapsulated by adding it to an aqueous gelatin / gum arabic solution under stirring. After the internal phase is added, the mixture is emulsified. After a period of mixing, heating, and pH adjustment, the mixture is cooled, and the resulting capsules are sieved to a size range of 20-60 μm, with an average size of 30-40 μm.

[0107] The resulting capsules were then mixed with an aqueous binder made from fish gelatin (Norland HiPure liquid gelatin) at a ratio of 1 part binder to 7 parts capsules by weight, and an aqueous colorant dispersion comprising 10% by weight of Emperor 2000 carbon black and 5% by weight of Kolliphor P188 at a ratio of 1 part colorant dispersion to 49 parts binder. The resulting mixture was rod-coated onto a 125 mm thick indium tin oxide-coated polyester film (with the capsules deposited on the ITO-coated surface), and the coated film was dried to produce an electrophoretic medium approximately 25 μm thick, comprising essentially a single layer of capsules.

[0108] The exposed surface of the electrophoretic medium was then coated with a radiation-curable polyurethane acrylate-based adhesive. While the adhesive layer was being applied, a 125 mm thick screen-printed sheet of indium tin oxide-coated polyester film was applied. The resulting assembly was then cured by exposure to ultraviolet light.

[0109] A second capsule-based electrophoretic display was prepared in a similar manner, except that the colorant dispersion was omitted.

[0110] Figure 2 is similar to Figure 1A and 1B Micrograph of a capsule-based electrophoretic medium shown with the unpigmented binder in its closed state (actually, Figure 2 yes Figure 1A It can be seen that in various areas of the medium (see Figure 2 There are numerous pinholes and voids in the circled area (in the middle and left of center), and even in the off state, these areas are much lighter in color than the rest of the image, resulting in high minimum transmission and poor contrast.

[0111] Figure 3 is similar to Figure 1C and 1D Micrograph of capsule-based electrophoretic medium shown in open state with heavily pigmented binder (actually, Figure 3 yes Figure 1D ). It can be seen that multilamellar capsules are present in various areas of the medium (especially the circled areas), and these areas appear darker than the surrounding monolamellar areas, resulting in an excess of particles.

[0112] Figure 4 is similar to Figure 3 But it is similar to Figure 1E and 1F Micrographs of capsule-based electrophoretic media with increasing ratios of binder to Figure 3 The coloring shown is minimal, and the medium is shown in its open state (actually, Figure 3 yes Figure 1F It can be seen that there are multilayer capsules in various areas of the medium (especially the circled areas), but these areas do not have much contrast with the surrounding monolayer areas, resulting in a larger particle size. Figure 3 The medium is much lower.

[0113] Figure 5A 、 5B 5C and 5D respectively show the minimum transmittance in the closed state, the minimum transmittance in the open state, and the minimum transmittance using a capsule-based electrophoretic medium with an unpigmented binder (e.g. Figure 1A and 1B shown) and similar media with optimal pigmented binders (e.g. Figure 1E and 1F The contrast ratio of the single pixel display prepared by Figures 5A-5C As can be seen in Figure 5, the coloring of the adhesive reduces the minimum transmittance in the closed state from about 7.5% to about 2%, while the transmittance in the open state only decreases from about 21% to about 19%, so the contrast ratio increases from about 9 to about 23.

[0114] Figure 6A and 6B is shown to have highly pigmented binders (e.g. Figure 1C and 1D — Figure 6A as shown) and the binder with the best coloration (as Figure 1E and 1F — Figure 6B ) are photographs of the open and closed states of the capsule-based electrophoretic medium. It can be seen that the highly pigmented binder medium has more particles than the optimally pigmented binder medium.

[0115] Example 2

[0116] A non-aqueous internal phase is prepared by combining OLOA® 11000, 1-limonene, Cargille® 5040 impregnation solution, carbon black, polystyrene, and 2-hexyldecanoic acid. This internal phase is then encapsulated by adding the mixture to an aqueous solution of porcine gelatin and gum arabic, followed by the addition of Emperor 2000 carbon black with 5 wt% Kolliphor P188. After heating, mixing, and pH adjustment, the resulting capsules are cooled and then sorted to form a capsule mixture with a size distribution ranging from 20 to 90 µm in diameter, with an average diameter of 50-70 µm.

[0117] The capsule slurry was centrifuged and then mixed with an aqueous binder of 50:50 fish gelatin (Norland HiPure Liquid Gelatin): gum arabic (AEP colloid) at a ratio of 1 part binder to 4 parts capsules. A solution of colorant (7 wt% Emperor 2000 carbon black with 3.5 wt% Kolliphor P188 (Sigma-Aldrich 15759), 1.5 wt% Cab-o-jet 265M (Cabot Corp), and 1.5 wt% Cab-o-jet 250C (Cabot Corp)) was prepared in water and added to the aqueous binder at a ratio of 1 part colorant to 52.3 parts binder. The resulting mixture of binder and encapsulated internal phase was rod-coated onto a 125 μm thick indium tin oxide-coated polyester film. The coated film was dried to produce an electrophoretic medium approximately 33 μm thick, consisting essentially of a single layer of capsules.

[0118] The capsule-coated surface of the coated film was then coated with a polyurethane acrylate-based adhesive. While the adhesive layer was being applied, a 125 mm thick screen-printed sheet of indium tin oxide-coated polyester film was applied. The resulting assembly was then cured by exposure to UV light from a CSun UV lamp.

[0119] Using the above techniques, a neutral density window pixel (i.e., top and bottom light-transmitting electrodes) was created with a binder colored with a mixture of Emperor 2000 carbon black, Cab-o-jet 265M magenta pigment, and Cab-o-jet 250C cyan pigment. As a control, a similar window pixel was constructed using the same techniques, except that an equal weight of the colored pigment mixture was replaced with Emperor 2000 carbon black. The samples were evaluated for contrast and haze using an optical evaluation test bench. Figure 19 and 20 As shown, the contrast and haze of the color mixture are almost as good as the control.

[0120] While the optical performance is nearly equivalent, the color difference between the two samples in the open state is noticeable to the naked eye. To quantify the color difference, reflectance measurements were performed on a dual-transmissive electrode test cell against a white printer paper background. As shown in Table 1, the sample with the pigment blend in its binder exhibits a more neutral color (a* and b* values closer to zero) and a greater total reflectance.

[0121] Table 1. Reflectance measurements of a dual window test pixel through the same internal phase, where the binder included: A) Emperor 2000 carbon black alone, approximately 2% colorant by weight; and B) a mixture of colorants (14 parts Emperor 2000 carbon black, 3 parts Cab-o-jet 265M magenta, and 3 parts Cab-o-jet 250C cyan) at approximately 2% colorant by weight.

[0122]

[0123] II. Variable Transmission Media Containing CCA Blends

[0124] A non-aqueous internal phase is prepared by combining OLOA® 11000, 1-limonene, Cargille® 5040 impregnation solution, carbon black, polystyrene, and 2-hexyldecanoic acid. This mixture is then emulsified by adding it to an aqueous gelatin / gum arabic solution and encapsulated by adding a dispersion of Emperor 2000 carbon black and 5 weight percent Kolliphor P 188. After mixing, heating, and pH adjustment, the resulting capsules are cooled and sieved to a size range of 20-60 μm, with an average size of 30-40 μm.

[0125] The capsules were centrifuged and then mixed with an aqueous binder of fish gelatin (Norland HiPure liquid gelatin) at a ratio of 1 part binder to 7 parts capsules by weight, and an aqueous colorant dispersion comprising 10% by weight of Emperor 2000 carbon black and 5% by weight of Kolliphor P188 at a ratio of 1 part colorant dispersion to 49 parts binder. The resulting mixture was rod-coated onto a 125 mm thick indium tin oxide-coated polyester film (with the capsules deposited on the ITO-coated surface). The coated film was dried to produce an electrophoretic medium approximately 25 μm thick, comprising essentially a single layer of capsules.

[0126] The exposed surface of the electrophoretic medium was then coated with a radiation-curable polyurethane acrylate-based adhesive. While the adhesive layer was being applied, a 125 mm thick screen-printed sheet of indium tin oxide-coated polyester film was applied. The resulting assembly was then cured by exposure to ultraviolet light.

[0127] The electro-optical performance of capsule-based electrophoretic media produced as described above was compared to other similar capsule-based electrophoretic media, except that the charge control agent used in the comparative samples was OLOA® 11000 alone or in combination with Pluronic L31 (two samples), Span 65, and Span 85 (two samples). For each medium, coating weight, internal phase conductivity and viscosity, as well as contrast ratio at drive voltages of 72, 90, and 120 volts and relative humidity of 50% and 60% were measured. The results are shown in Figure 2. Figure 7 shown.

[0128] from Figure 7 As can be seen in the figures, the media containing only OLOA® 11000 has an undesirably low contrast ratio, and the addition of Pluronic L31 produces essentially no change. The addition of Span 65 produces some improvement in contrast, especially at 120 V, although the measured contrast ratio is very susceptible to humidity variations. The addition of Span 85 produces better results than Span 65, although the measured contrast ratio is still very susceptible to humidity variations, and a high drive voltage of 120 V is required to achieve a consistently high contrast ratio above 30. The results achieved with the addition of 2-HAD are the best of the tested compositions, achieving high contrast ratios even at 72 V while reducing humidity dependence.

[0129] Example 2

[0130] Various experimental displays were prepared in the same manner as described in Example 1 above, except that the weight ratios of 2-HDA:OLOA® 11000 were 0.025:1, 0.05:1, 0.1:1, and 0.2:1, respectively. To provide a control, a similar display was prepared using Span 85 and OLOA® 11000 at a weight ratio of 0.825:1 (the larger molecular weight of Span 85 makes this ratio approximately equivalent to the 0.2:1 2-HDA:OLOA® ratio on a molar basis). Coating weight, internal phase conductivity, contrast ratio, and minimum haze values were measured at the same driving voltage and relative humidity as in Example 1 above, and the results are shown in Table 1. Figure 8 and 9 shown.

[0131] from Figure 8 and 9As can be seen, the contrast ratio of the 2-HDA display increases monotonically with the 2-HDA ratio and drive voltage, reaching values well over 30 at a 2-HAD ratio of 0.2:1 and a drive voltage of 90 V, which is substantially greater than the corresponding value for the Span 85 display. The minimum haze value does not vary significantly with the 2-HAD ratio, but does decrease with increasing drive voltage. Therefore, the display with a 2-HAD:OLOA® 11000 weight ratio of 0.2:1 exhibits the best overall performance.

[0132] Example 3

[0133] The display prepared in Example 2 above was further tested at driving voltages of 45, 60, 90, and 120 V, which contained 2-HDA and OLOA® in a weight ratio of 0.2:1 and Span 85 and OLOA® in a weight ratio of 0.825:1. Figures 10A-10D The maximum on transmittance, minimum off transmittance, minimum on haze, and contrast ratio determined in these tests are shown, respectively.

[0134] from Figures 10A-10D As can be seen in the graph, under the same conditions as the display containing Span 85, the display containing 2-HDA exhibits higher maximum on transmittance, lower minimum off transmittance, lower on haze, and substantially higher contrast. In particular, the Span 85 display failed to achieve the ideal contrast ratio of 30 under any test conditions, while the 2-HDA display consistently achieved this contrast ratio at a drive voltage of at least 60 V.

[0135] Example 4

[0136] Displays containing 2-HDA and OLOA® in a weight ratio of 0.2:1 and oleic acid and OLOA® in a weight ratio of 0.4:1 were prepared as described in Example 1 above. These displays were tested at drive voltages of 72, 90, and 120 V. FIG5 shows the contrast ratios determined in these tests.

[0137] from Figure 11 As can be seen in Figure 5, displays containing 2-HDA consistently exhibit significantly higher contrast ratios under the same conditions as displays containing oleic acid.

[0138] III. Variable Transmission Medium Comprising Fish Gelatin: Gum Arabic Binder

[0139] A non-aqueous internal phase was prepared by combining OLOA® 11000, 1-limonene, Cargille® 5040 impregnation solution, carbon black, polystyrene, and 2-hexyldecanoic acid. This mixture was then emulsified by adding it to an aqueous gelatin / gum arabic solution and encapsulated by adding a dispersion of 10% by weight Emperor 2000 carbon black and 5% by weight Kolliphor P188. After mixing, heating, and pH adjustment, the resulting capsules were cooled and sorted using sieving to produce a capsule mixture with a size range of 15-50 μm, with an average size of approximately 30 μm.

[0140] The resulting aqueous capsule slurry was centrifuged and then mixed into three different fish gelatin-based aqueous binders: A) no gum arabic, B) a 1:2 mixture of gum arabic and fish gelatin, and C) a 1:1 mixture of gum arabic and fish gelatin. The fish gelatin was HiPure liquid gelatin purchased from Norland, while the gum arabic was obtained from AEP Colloids. Each gelatin binder was mixed at a ratio of 1 part binder to 7 parts capsules by weight, and a colorant solution consisting of 10% by weight Emperor 2000 carbon black and 5% by weight Kolliphor P188 (Aldrich 15759) in water, at a ratio of 1 part carbon black colorant to 49 parts binder. The resulting mixture was rod-coated onto 125 mm thick indium tin oxide-coated polyester film. The coated film was dried to produce an electrophoretic medium approximately 25 μm thick, which essentially contained a single layer of capsules.

[0141] The capsule-coated surface of the coated film was then coated with a polyurethane acrylate-based adhesive. While the adhesive layer was being applied, a 125 mm thick screen-printed sheet of indium tin oxide-coated polyester film was applied. The resulting assembly was then cured by exposure to UV light from a CSun UV lamp.

[0142] Several samples of variable transmission test film were prepared for each adhesive formulation. The samples were then evaluated for on and off transmittance, as well as haze, using the optical evaluation apparatus described in U.S. Patent No. 7,679,814. Briefly, each sample was placed in front of a calibrated light source with an integrated detector on the other side of the sample. Each sample was driven into the on and off states, and its transmittance was evaluated. In addition, a calibrated chopper wheel was used to measure the relationship between diffuse and transmitted light to evaluate haze. Recoil was also evaluated by comparing the decay over time in the on state (see Figure 14 The data obtained are Figures 13A-13C Shown in.

[0143] By evaluating the differences between the three binder formulations, it was evident that a 1:1 mixture of fish gelatin and gum arabic produced a binder with good contrast (difference between open and closed states; Figure 13B ) and low haze ( Figure 13A ) electro-optical medium. In addition, the two binder mixtures containing gum arabic showed almost no recoil, resulting in very long stability in both the on and off states. Figure 14 .

[0144] IV. Variable Transmission Medium Containing Capsules

[0145] Example 1

[0146] A non-aqueous internal phase was prepared by combining OLOA® 11000, 1-limonene, Cargille® 5040 impregnation solution, carbon black, polystyrene, and 2-hexyldecanoic acid. The internal phase mixture was then encapsulated by adding the mixture to an aqueous gelatin / gum arabic solution, emulsifying the mixture, and adding a dispersion of 10 wt% Emperor 2000 carbon black and 5 wt% Kolliphor P 188.

[0147] After mixing, heating, and pH adjustment, the resulting capsules were cooled and sorted into two size distributions, one ranging from about 20 μm to about 50 μm with an average size of about 35 μm, and another ranging from about 50 μm to about 90 μm with an average size of about 60 μm. For some experiments detailed below, three parts by weight of the second part were combined with one part by weight of the first part.

[0148] The resulting capsule slurry was centrifuged and then mixed with an aqueous binder of 50:50 fish gelatin (Norland HiPure liquid gelatin): gum arabic (AEP colloid) at a ratio of 1 part binder to 7 parts capsules, along with a colorant solution consisting of 10% by weight Emperor 2000 carbon black and 5% by weight Kolliphor P188 in water, at a ratio of 1 part carbon black colorant to 49 parts binder. The resulting mixture was rod-coated onto 125 mm thick indium tin oxide-coated polyester film. The coated film was oven-dried to produce an electrophoretic medium approximately 25 μm thick, comprising essentially a single layer of capsules.

[0149] The capsule-coated surface of the coated film was then coated with a polyurethane acrylate-based adhesive. While the adhesive layer was being applied, a 125 mm thick screen-printed sheet of indium tin oxide-coated polyester film was applied. The resulting assembly was then cured by exposure to UV light from a CSun UV lamp.

[0150] Two sets of samples were prepared. The first set of samples was prepared by using only capsules of about 20 μm to about 50 μm ( Figures 16A-16D A second set of samples ( ) was prepared by mixing three parts by weight of capsules of about 50 μm to about 90 μm with one part by weight of capsules of 20 μm to about 50 μm. Figures 16A-16D Mixed in [ ].

[0151] The samples were then evaluated for open and closed transmittance and haze using an optical evaluation setup described in U.S. Patent No. 7,679,814. Briefly, each sample was placed in front of a calibrated light source with an integrated detector on the other side of the sample. Each sample was driven to the open and closed states, and its transmittance was evaluated. Additionally, a calibrated chopper wheel was used to measure the relationship between diffuse and transmitted light to evaluate haze. The resulting data was then analyzed in Figures 16A-16D Shown in. Figure 17 Side-by-side images of the sample showing only the small sample and the mixed capsule sample in the open state are shown. Figure 17 As can be seen, there is almost no change in the particles between the small capsule only formulation and the mixed capsule formulation.

[0152] By evaluating the differences between the small sample alone and the mixed sample, it became clear that the mixture of large and small capsules produced an electro-optical medium with excellent contrast (the difference between the on and off states) and low haze. Significantly less haloing (interference patterns) was also observed in the mixed sample compared to the small sample alone.

[0153] Example 2

[0154] Capsules were prepared similarly to the procedure in Example 1 above, except that the capsules were sieved into three size categories and two blends were prepared. The blends included a small group with a size distribution of approximately 5 μm to approximately 50 μm and a mean diameter of approximately 20 μm; a medium group with a size distribution of approximately 20 μm to approximately 90 μm and a mean diameter of approximately 35 μm; and a large group with a size distribution of approximately 20 μm to approximately 90 μm and a mean diameter of approximately 40 μm. The two blends included a medium blend with a weight ratio of medium-sized capsules to small-sized capsules of 2:1, resulting in a mean diameter of approximately 25 μm, and a large blend with a weight ratio of large-sized capsules to small-sized capsules of 7:1, resulting in a mean diameter of approximately 30 μm.

[0155] The electro-optical properties of small, medium, large, medium blend, and large blend capsules were tested to determine the particle appearance, haze, and transmittance. Figures 26A to 26LThe results are provided in [ 1 ]. As can be seen from the results, the addition of small capsules reduces particles in the closed state, while large capsules better reduce particles in the open state and reduce haze. Therefore, the data shows that the electro-optical properties can be tuned based on which properties are most important for a specific application.

[0156] V. Variable Transmission Films Containing Pigmented Adhesives

[0157] Sample 1: A non-aqueous internal phase was prepared by combining OLOA® 11000, 1-limonene, Cargille® 5040 impregnation solution, carbon black, polystyrene, and 2-hexyldecanoic acid. This mixture was emulsified by adding it to an aqueous gelatin / gum arabic solution and encapsulated by adding a 10 wt% dispersion of Emperor 2000 carbon black and 5 wt% of Kolliphor P188. After mixing, heating, and pH adjustment, the resulting capsules were cooled and sieved to a size range of 20-60 μm, with an average size of 30-40 μm.

[0158] The resulting capsules were centrifuged and then mixed with an aqueous binder consisting of 50:50 fish gelatin (Norland HiPure liquid gelatin): gum arabic at a ratio of 1 part binder to 7 parts capsules, along with an aqueous colorant dispersion comprising 10% by weight of Emperor 2000 carbon black and 5% by weight of Kolliphor P188 at a ratio of 1 part colorant dispersion to 54 parts binder. The resulting mixture was rod-coated onto a 125 μm thick indium tin oxide-coated polyester film (with the capsules deposited on the ITO-coated surface), and the coated film was oven-dried to produce an electrophoretic medium approximately 27 μm thick, comprising essentially a single layer of capsules.

[0159] The exposed surface of the electrophoretic medium was then coated with a radiation-curable polyurethane acrylate-based adhesive composition. While applying the adhesive layer, a 125 μm thick screen-printed sheet of indium tin oxide-coated polyester film was applied. The resulting assembly was then cured by exposure to ultraviolet light.

[0160] Sample 2: The same procedure as Sample 1 was followed, but the UV-curable adhesive also contained 0.5 phr of Keyplast Black AN. The cured 1 mil unit with the pigmented adhesive blend had a transmittance of 21.5% and a haze of 0.7%. Table 2 provides the electro-optical properties of Samples 1 and 2.

[0161] Table 2. EO properties of electrophoretic media with and without pigmented binder.

[0162]

[0163] Based on the comparison results of Sample 1 and Sample 2, the variable transmission film containing the pigmented UV curable adhesive provided less particles and reduced pinholes, and the use of a dye soluble in the adhesive did not increase haze. Figure 24A A photo of Sample 1 in the open state is provided in Figure 24B A photo of Sample 2 in the opened state is provided in .

[0164] VI. Variable Transmission Films Containing Encapsulated Non-Conjugated Olefins

[0165] Example 1

[0166] A non-aqueous internal phase is prepared by combining OLOA® 11000, Cargille® 5040 impregnation solution, trans, trans, cis-1,5,9-cyclododecatriene (CDT), carbon black, polystyrene, and 2-hexyldecanoic acid. This mixture is then emulsified by adding it to an aqueous gelatin / gum arabic solution and encapsulated by adding a dispersion of 10% by weight Emperor 2000 carbon black and 5% by weight Kolliphor P188. After mixing, heating, and pH adjustment, the resulting capsules are cooled and sieved to a size range of 20-60 μm, with an average size of 30-40 μm.

[0167] The resulting capsules were centrifuged and then mixed with an aqueous binder made from fish gelatin (Norland HiPure liquid gelatin) at a ratio of 1 part binder to 7 parts capsules by weight, along with an aqueous colorant dispersion consisting of 10% by weight Emperor 2000 carbon black and 5% by weight Kolliphor P188 at a ratio of 1 part colorant dispersion to 49 parts binder. The resulting mixture was rod-coated onto a 125 μm thick indium tin oxide-coated polyester film (with the capsules deposited on the ITO-coated surface). The coated film was dried to produce an electrophoretic medium approximately 22 μm thick, comprising essentially a single layer of capsules.

[0168] The exposed surface of the electrophoretic medium was then coated with a radiation-curable polyurethane acrylate-based adhesive. While the adhesive layer was being applied, a 125 mm thick screen-printed sheet of indium tin oxide-coated polyester film was applied. The resulting assembly was then cured by exposure to ultraviolet light.

[0169] Example 2

[0170] A comparative assembly containing encapsulated 1-limonene and Cargille® 5040 was prepared according to the procedure provided in Part III of the above example. Figures 25A to 25D The electro-optical performance of the components of Example 1 and Example 2 is provided in .

[0171] As described above, the present invention provides an improved variable transmission electrophoretic medium that is well suited for use in, for example, variable transmission windows and vehicle sunroofs. The medium of the present invention can be readily produced using conventional processes and can be deposited onto glass or other rigid substrates more easily than slot die coating.

[0172] It will be apparent to those skilled in the art that many changes and modifications may be made to the specific embodiments of the invention described above without departing from the scope of the invention. Therefore, the entire foregoing description is to be interpreted in an illustrative rather than a restrictive sense.

Claims

1. An electro-optical medium comprising a plurality of capsules and a binder, each capsule encapsulating charged pigment particles in a non-polar solvent, wherein less than 90% of the plurality of capsules are within a size range of 5 μm to 50 μm in diameter.

2. The electro-optical medium according to claim 1, wherein The average diameter of the plurality of capsules is 25 μm to 35 μm.

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