Switchable light-collimating layer comprising a bistable electrophoretic fluid

Abstract

This invention discloses a method for manufacturing a switchable light-collimating film. The switchable light-collimating film can be used as a privacy filter for computer monitors or other display devices. The film comprises multiple elongated cavities containing pigment particles, the position of which can be controlled by applying an electric field. Instead of the pigment particles concentrating on one side of the cavities, the pigment particles are distributed throughout the elongated cavities, narrowing the viewing angle of light passing through the film and providing privacy protection for users viewing images.

Description

[0001] This application is a divisional application of the patent application with application number 201980048552.0 filed on January 20, 2021, and invention name “Switchable light-collimating layer comprising bistable electrophoretic fluid”.

[0002] This application claims priority to U.S. Provisional Application No. 62 / 717,124, filed on August 10, 2018, which is hereby incorporated by reference in its entirety. Background Art

[0003] The present invention relates to switchable light-collimating films that can be used, for example, to control the directionality of incident light passing through a transparent or translucent substrate. Passive films with this capability have been commercially available for some time and are widely marketed as "privacy filters" for computer monitors. See, for example, products from 3M Company of St. Paul, MN, and various U.S. patents, such as US 8,213,082. Privacy filters are typically applied to the front surface of a video display when the user wishes to restrict the image on the display to a "privacy cone" visible only to the user. Privacy films typically utilize micromachined plastic channels backfilled with a material having a different refractive index than the plastic substrate. The interface between the materials creates a refractive surface, and only light directed in the correct direction can pass through the filter, while other incident light directed in the wrong direction is backreflected and / or absorbed. The same technology can also be used as window treatments to modify the directionality of sunlight, for example, passing through exterior windows.

[0004] Several groups have attempted to create active media that can switch between a privacy-protected state and a non-privacy-protected state. For example, U.S. Patent Publication 2016 / 0179231 (the '231 application) describes an electroactive privacy layer that can be used in conjunction with a display device. The '231 application teaches the use of electrically anisotropic materials, such as dielectric polymers. When an electric field is applied, the anisotropic material aligns with the field, collimating light and providing a privacy-protected area for the user. However, a constant potential must be applied to the privacy layer to maintain the material's alignment and maintain the privacy state. Because the privacy device requires a constant electric field to maintain the privacy state, it consumes additional energy beyond the typical power required by a monitor. When used with battery-powered devices, such as laptops, the additional energy required to power the privacy layer can shorten the battery's operating time. PCT Publication WO2013 / 048846 also describes an alternative switchable privacy film that also employs anisotropic particles that are held in alignment with the electric field. Similar to the '231 application, the device disclosed in '846 also requires constant power to be provided in a privacy-protected state.

[0005] Other actively switchable privacy protection devices have been described that rely on blocking the movement of particles within a channel rather than the alignment of anisotropic particles. For example, U.S. Patent Publication No. 2016 / 0011441 (the '441 application) describes an electrically switchable electrochromic material arranged in microstructured ribs extending along the length of a privacy layer. In the '441 application, when an electric current is supplied to the electrochromic material, its absorption spectrum changes. While the actual switching process requires considerable energy (approximately 5 minutes of DC current), once the transition is complete, the privacy layer of the '441 application is able to maintain its state for a period of time. Another alternative approach is described in U.S. Patent Publication No. 2017 / 0097554, in which a long light-control channel is formed between transparent conductive films and filled with an electrophoretic structure comprising a transmissive dispersant and light-blocking particles. By using a set of three shaping electrodes to control the dispersion of the light-blocking particles in the air gap, the electrophoretic structure can be switched between a narrow field of view mode and a wide field of view mode. The fabrication of shaped electrodes can be technically challenging (and expensive) because of the need to create so many closely spaced, individually addressable electrodes. Summary of the Invention

[0006] While switchable privacy filters can be achieved, for example, using anisotropic particle alignment, there remains a need for inexpensive privacy films with low energy consumption. Therefore, the present invention describes a light-collimating film comprising multiple elongated chambers of a bistable electrophoretic fluid containing a light-scattering pigment. By appropriately arranging the elongated chambers, the film can narrow the viewing angle of light passing through the film by a factor of two (or more). Importantly, because the light-collimating film comprises a bi-stable electrophoretic fluid, it is stable in either the wide or narrow state for extended periods of time, requiring only a small amount of energy to change from one state to the other. Furthermore, because the bi-stable electrophoretic fluid is partitioned into multiple elongated chambers, the electrophoretic material is less susceptible to sedimentation when the same light-collimating film is applied in different orientations relative to gravity. Furthermore, when the bi-stable electrophoretic fluid is partitioned into numerous elongated chambers, the transition speed between the wide and narrow states is improved, and the overall effect is more consistent across the entire device.

[0007] Furthermore, because the light-collimating film comprises multiple small chambers, it is easy to cut the film into the desired shape / size after manufacturing without losing significant amounts of the electrophoretic fluid. This allows the same equipment to be used to create both large and small area light-collimating films. For example, a one-square-meter section sheet or a roll of light-collimating film can be cut into pieces of the desired size without significant loss of the electrophoretic fluid. Although some chambers are opened during the cutting process, each chamber only holds a small amount of fluid, so the overall loss is minimal. In some cases, hundreds of small pieces can be cut from a single section or roll (e.g., for mobile phones). In some embodiments, the elongated chambers can be manufactured in a predetermined pattern so that sheet cutting does not result in loss of the electrophoretic fluid.

[0008] Thus, in one aspect, the present invention comprises a switchable light-collimating film comprising a first light-transmitting electrode layer, a collimating layer having a thickness of at least 20 μm and comprising a plurality of elongated cavities, and a second light-transmitting electrode layer, wherein the first light-transmitting layer and the second light-transmitting layer are arranged on either side of the collimating layer. Each elongated cavity has an opening, and a bistable electrophoretic fluid comprising pigment particles is arranged in each elongated cavity. The elongated cavities are sealed with a sealing layer that seals the bistable electrophoretic fluid therein by spanning the opening of the elongated cavity. The switchable light-collimating film typically has a thickness of less than 500 μm, and the height of the elongated cavities is equal to or less than the thickness of the collimating layer. Typically, the width of the elongated cavities is between 5 μm and 150 μm, and the length is between 200 μm and 5 mm. For example, the width of the elongated cavities can be between 5 μm and 50 μm, and the length is between 50 μm and 5 mm.

[0009] The switchable light-collimating film is typically made of a polymer, such as a polymer made of an acrylate monomer, a urethane monomer, a styrene monomer, an epoxide monomer, a silane monomer, a thioolefin monomer, a thioalkyne monomer, or a vinyl ether monomer. The first light-transmitting electrode layer or the second light-transmitting electrode layer can be made of indium tin oxide.

[0010] Bistable electrophoretic fluid is generally included in the pigment particles and the free polymer of polymer functionalization in non-polar solvent.Usually, pigment is by polyacrylate, polystyrene, polynaphthalene or polydimethylsiloxane functionalization.Free polymer can comprise polyisobutylene or comprise the copolymer of ethylene, propylene or styrene monomer.Sealing layer can comprise water-soluble polymer or water-dispersible polymer, for example naturally occurring water-soluble polymer, for example cellulose or gelatin, or synthetic polymer, for example polyacrylate, polyvinyl alcohol, polyethylene, poly (vinyl) acetic acid, poly (vinyl) pyrrolidone, polyurethane or its copolymer.

[0011] In one embodiment, the elongated chambers are arranged in rows and columns when the collimation layer is viewed from above, wherein the longer dimension of the elongated chambers extends along the rows, and wherein the rows are spaced apart from each other by at least three times the width of the elongated chambers. Typically, the elongated chambers are arranged in rows and columns when the collimation layer is viewed from above, and the gaps between adjacent elongated chambers in the same row are less than 30 μm. In some embodiments, the gaps between adjacent elongated chambers in a first row are horizontally offset relative to the gaps between adjacent elongated chambers in a second row. In some embodiments, the symmetry of the elongated chambers is disrupted by changing the length of the elongated chambers, the width of the elongated chambers, the pitch of the elongated chambers, or the width or position of the gaps between the elongated chambers.

[0012] In another aspect, the present invention includes a display having a light source, a switchable light-collimating film, an active matrix of thin-film transistors, a liquid crystal layer, and a color filter array. The switchable light-collimating film includes a first light-transmitting electrode layer, a collimating layer having a thickness of at least 20 μm and including a plurality of elongated cavities, and a second light-transmitting electrode layer, wherein the first and second light-transmitting layers are disposed on either side of the collimating layer. The elongated cavities contain a bistable electrophoretic fluid containing pigment particles, and the elongated cavities are sealed with a sealing layer that spans the openings of the elongated cavities.

[0013] In some embodiments, the light-collimating film or display additionally includes a voltage source and a controller to provide a voltage impulse between the first light-transmitting electrode layer and the second light-transmitting electrode layer. In some embodiments, the display includes a prismatic film disposed between the light source and the switchable light-collimating film. In some embodiments, the display includes a diffuser layer between the prismatic film and the light source. In some embodiments, the display includes a touch screen layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1A A first state of the switchable light-collimating film is shown, in which the electrophoretic particles are distributed throughout the cavities of the collimating layer. The electrophoretic particles are stable in this state without the need for an applied power source.

[0015] Figure 1B shows a second state of the switchable light-collimating film, wherein, under application of an electric potential, the electrophoretic particles are driven towards the first light-transmitting electrode;

[0016] Figure 1C A third state of the switchable light-collimating film is shown, in which electrophoretic particles are concentrated near the first light-transmitting electrode. The particles remain stable in this position even after the potential is removed.

[0017] Figure 1D shows a return to a state in which the chamber has electrophoretic particles distributed throughout the collimating layer;

[0018] Figure 1EThe fourth state of the switchable light-collimating film is shown, wherein upon application of Figure 1B When the potential of the opposite polarity is applied, the electrophoretic particles are driven toward the second light-transmitting electrode;

[0019] Figure 1F A fifth state of the switchable light-collimating film is shown, in which electrophoretic particles are concentrated near the second light-transmitting electrode. The particles remain stable in this position even after the potential is removed.

[0020] Figure 2A shows that when the electrophoretic particles are distributed throughout the cavity of the collimating layer, the light emitted from the source is confined to an angle θ1;

[0021] Figure 2B It shows that when the electrophoretic particles are gathered close to the light-transmitting electrode closest to the light source, the light emitted from the source is at an angle θ2, where θ2>>θ1;

[0022] Figure 2C It shows that when the electrophoretic particles are concentrated close to the light-transmitting electrode farthest from the light source, the light emitted from the source is at an angle θ3, where θ3 >> θ1. It is observed that the light loss is minimized due to the presence of the pigment particles on the emission side of the light-collimating film;

[0023] Figure 3 Shown are the active layers of a liquid crystal display assembly including a switchable light-collimating film. The layers are not to scale;

[0024] Figure 4 Shown are the active layers of a liquid crystal display assembly, including a switchable light-collimating film and a touch screen. Layers are not to scale;

[0025] Figure 5 Shown are the active layers of a liquid crystal display assembly including a switchable light-collimating film and a prismatic film. The layers are not to scale;

[0026] Figure 6 An embodiment of a switchable light-collimating film disposed on a lower substrate is shown. The switchable light-collimating film additionally includes an edge seal. An exploded view details the seal layer on top of an elongated chamber filled with a bistable electrophoretic fluid;

[0027] Figure 7 A switchable light-collimating film is shown with an optically clear adhesive and release sheet on one side. Such a film can be used, for example, to provide collimating features on existing surfaces, such as glass windows.

[0028] Figure 8 A roll-to-roll process is shown that can be used to form an alignment layer having a plurality of elongated chambers and then fill the elongated chambers with a bistable electrophoretic fluid and seal the filled elongated chambers;

[0029] Figure 9A and 9B A simplified embossing process is shown;

[0030] Figure 10 A method for forming an imprint tool to create the collimation layer of the present invention is detailed;

[0031] Figure 11 A method for forming a shim for use in an imprint tool is detailed;

[0032] Figure 12 An alternative method for forming a shim for use in an imprint tool is detailed;

[0033] Figure 13 is a top view of an embodiment of a switchable light-collimating film in which elongated chambers are arranged in a row-column format;

[0034] Figure 14 is a top view of an embodiment of a switchable light-collimating film in which elongated chambers are arranged in a row-column format;

[0035] Figure 15 is a top view of an embodiment of a switchable light-collimating film in which the position of gaps between elongated chambers in the same row advances in one direction between consecutive rows, thereby breaking the symmetry of the columns;

[0036] Figure 16 is a top view of an embodiment of a switchable light-collimating film in which the size of the gaps between elongated chambers in the same row is different between consecutive rows, thereby breaking the symmetry of the columns;

[0037] Figure 17 is a top view of an embodiment of a switchable light-collimating film in which the pitch between consecutive rows varies, thereby breaking the symmetry of the rows;

[0038] Figure 18 is a top view of an embodiment of a switchable light-collimating film in which the length and / or width of the chambers vary between consecutive rows, breaking the symmetry of the rows and columns. DETAILED DESCRIPTION

[0039] As described above, the present invention provides a light-collimating film comprising elongated chambers of a bistable electrophoretic fluid. Such a film itself can be used to control the amount and / or direction of light incident on a transmissive substrate. Such a film can also be integrated into devices such as LCD displays to provide useful features, such as providing a privacy barrier for users viewing the LCD display. Because the light-collimating film is switchable, it allows the user to change the collimation of the emitted light as needed. Furthermore, because the medium is bi-stable, the collimated state remains stable for a period of time, such as minutes, hours, days, or months, without requiring additional energy to be supplied to the light-collimating film.

[0040] The present invention enables the inexpensive manufacture of switchable light-collimating films using a roll-to-roll process. This makes it feasible to produce large sheets of switchable light-collimating film that can be incorporated into devices during other assembly processes, such as the manufacture of LCD displays. Such films can include a supplementary optically clear adhesive layer and release sheet, allowing the light-collimating film to be shipped and distributed as a finished product. The light-collimating film can also be used for after-market light control, such as in conference room windows, exterior windows of buildings, and sunroofs and skylights.

[0041] Electrophoretic displays typically comprise a layer of electrophoretic material and at least two other layers arranged on opposite sides of the electrophoretic material, one of the two layers being an electrode layer. In most such displays, both layers are electrode layers, and one or both of the electrode layers are patterned to define the pixels of the display. For example, one electrode layer may be patterned as elongated row electrodes, while the other may be patterned as elongated column electrodes extending at right angles to the row electrodes, the pixels being defined by the intersections of the row and column electrodes. Alternatively, and more typically, one electrode layer has the form of a single continuous electrode, while the other electrode layer is patterned into a matrix of pixel electrodes, each pixel electrode defining a pixel of the display. In some embodiments, two light-transmitting electrode layers are used, thereby allowing light to pass through the electrophoretic display.

[0042] 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.

[0043] The general function of the switchable light-collimating film (10) is Figures 1A-1FAs shown in . The film (10) includes a first light-transmitting electrode layer (12) and a second light-transmitting electrode layer (14). Typically, each electrode layer is associated with a first substrate (16) and a second substrate (18), respectively. The first substrate (16) and the second substrate (18) can be a light-transmitting polymer (e.g., a film or resin) or glass. In the case where the film (10) is produced using a roll-to-roll process, the first substrate (16) and the second substrate (18) are flexible. The light-transmitting electrodes and substrates can also be integrated into a single layer, such as a PET-ITO film, PEDOT, or another light-transmitting polymer doped with a conductive material (e.g., graphene, nanotubes, metal flakes, conductive metal oxide particles, or metal fibers) and / or doped with a conductive monomer or polymer and / or doped with an ionic material (e.g., a salt).

[0044] The light collimating layer (21) comprises a light-transmitting polymer (20) that has been processed to produce a plurality of elongated chambers (22) to contain a bistable electrophoretic fluid (24) comprising electrophoretic particles (26). In an embodiment, the bistable electrophoretic fluid (24) comprises a hydrocarbon solvent and the electrophoretic particles (26) comprise carbon black (optionally functionalized as described below). The light collimating layer is at least 20 μm thick (i.e., the distance between the first light-transmitting electrode layer (12) and the second light-transmitting electrode layer (14)). The thickness of the light collimating layer can be greater than 20 μm, such as greater than 30 μm, such as greater than 50 μm, such as greater than 70 μm, such as greater than 100 μm, such as greater than 150 μm, such as greater than 200 μm. The fabrication of the elongated chambers, such as by embossing a thermoplastic, will be described in more detail below. After or during the process of filling the elongated chamber (22), the elongated chamber (22) is sealed with a sealing layer (28), which may be, for example, a hydrophilic polymer that is incompatible with the bistable electrophoretic fluid (24).

[0045] In order to change the collimating characteristics of the film (10), the first light-transmitting electrode layer (12) and the second light-transmitting electrode layer (14) can be coupled to a potential source (30). The source can be, for example, a battery, a power supply, photovoltaic or some other potential source. The source can provide a simple direct current (DC) potential, or can be configured to provide a voltage that varies with time, for example, a "waveform" as described below. The first light-transmitting electrode layer (12) and the second light-transmitting electrode layer (14) can be coupled to the source (30) via electrodes, wires or traces (31). In some embodiments, the traces (31) can be interrupted by a switch (32), which can be, for example, a transistor switch. The potential between the first light-transmitting electrode layer (12) and the second light-transmitting electrode layer (14) is typically at least 1 volt, for example at least 2 volts, for example at least 5 volts, for example at least 10 volts, for example at least 15 volts, for example at least 18 volts, for example at least 25 volts, for example at least 30 volts, for example at least 30 volts, for example at least 50 volts.

[0046] Because the bistable electrophoretic fluid (24) is bistable, the electrophoretic particles (26) will maintain their distribution without the need for an applied electric field. This feature is well described in the patents of Iink listed herein, but is primarily due to having a specific mixture of distributed polymers (e.g., polyisobutylene or polylauryl methacrylate) in the bistable electrophoretic fluid (24), which stabilizes the electrophoretic particles (26) by depletion flocculation. Thus, in Figure 1A In the first state shown, the electrophoretic particles (26) are stable in a dispersed state, although no potential is applied between the first light-transmitting electrode layer (12) and the second light-transmitting electrode layer (14). By applying an appropriate potential, for example, Figure 1B As shown, the electrophoretic particles (26) move toward the appropriately biased electrode layer, thereby creating a light transmission gradient along the height of the elongated chamber (22). Once the electrophoretic particles (26) are driven to the desired electrode layer, the source (30) can be decoupled from the electrode layer, thereby turning off the potential. However, due to the bistability of the bistable electrophoretic fluid (24), the electrophoretic particles (26) will remain in the second state for a long time, such as minutes, hours, or days. Figure 1C shown.

[0047] The state of the light collimating film (10) can be reversed by driving the aggregated electrophoretic particles (26) away from the electrode with a reverse polarity voltage (not shown) to achieve Figure 1D When returning to the initial state (equivalent to 1A), only (roughly) collimated light will be able to pass through the light-collimating film, as described in more detail below. Figure 1D The state is also stable. Figure 1B The electrophoretic particles (26) can be driven through the distribution state and toward the second light-transmitting electrode (14) by applying a voltage of opposite polarity. Figure 1E As a result, as discussed below, the electrophoretic particles (26) will be concentrated adjacent to the second light-transmitting electrode (14), which also results in a wide viewing angle. Figure 1F The wide-angle transmissive state shown is also bistable, that is, no power is required to maintain this state. Figure 1C and Figure 1F The state results in wide-angle transmission, so it can be Figure 1A 、 1C The system switches between the states shown in 1D, 1F, and 1F while maintaining the overall DC balance of the drive electronics. DC balanced drive electronics reduce charge buildup and extend the life of system components.

[0048] The internal phase of the electrophoretic medium comprises charged pigment particles suspended in a fluid. 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). Particularly preferred solvents include aliphatic hydrocarbons, such as heptane, octane, and petroleum distillates, such as Isopar® (Exxon Mobil) or Isane® (Total); terpenes, such as limonene, e.g., 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, such as Cargille® refractive index matching fluid available from Cargille-Sacher Laboratories Inc. (Cedar Grove, NJ). In the encapsulated medium of the present invention, the refractive index of the particle dispersion is preferably matched as closely as possible to that of the encapsulating material to reduce haze. This refractive index match is best achieved when the solvent has a refractive index close to that of the sealant (when using common polymer sealants). In most cases, it is advantageous for the internal phase to have a refractive index at 550 nm between 1.51 and 1.57, preferably about 1.54 at 550 nm.

[0049] 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, the entire contents of which are incorporated herein by reference. 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 (>100nm) to appear white, or composite particles designed to have a desired refractive index. Black charged particles can be formed from CI Pigment Black 26 or 28 (for example, iron manganese black or copper chrome black) or carbon black. Other colors (non-white and non-black) can be formed from organic pigments, such as CI pigments PR254, PR122, PR149, PG36, PG58, PG7, PB28, PB15:3, PY83, PY138, PY150, PY155 or PY20. Other examples include Clariant's 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, and Hostaperm Green GNX; BASF's Irgazine Red L 3630, Cinquasia Red L4100 HD, and Irgazin Red L 3660 HD; and Sun Chemical's Phthalocyanine Blue, Phthalocyanine Green, Aniline Yellow, and Benzidine Yellow. Colored particles can also be formed from inorganic pigments, such as CI Pigment Blue 28, CI Pigment Green 50, and CI Pigment Yellow 227. 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.

[0050] The particles may exhibit a natural charge, or they may be explicitly charged using a charge control agent, or they 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, and the like. In addition to the suspending fluid and the charged pigment particles, the internal phase may include stabilizers, surfactants, and charge control agents. When the charged pigment particles are dispersed in a solvent, a stabilizing material can be adsorbed onto the charged pigment particles. This stabilizing material keeps the particles separated from one another, rendering the variable transmission medium substantially opaque when the particles are in their dispersed state. As is known in the art, the dispersion of the charged particles (typically carbon black, as described above) in a low dielectric constant solvent can be aided by the use of a surfactant. Such surfactants typically comprise a polar "head group" and a non-polar "tail group" that is 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 hydrocarbon solvents (e.g., 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 preferably, the head group is a carboxylic acid or carboxylate salt group. Stabilizers suitable for use in the present invention include polyisobutylene and polystyrene. In some embodiments, a dispersant is added, such as polyisobutylene succinimide and / or sorbitan trioleate and / or 2-hexyldecanoic acid.

[0051] The electrophoretic medium of the present invention will typically contain a charge control agent (CCA) and may contain a charge director. These electrophoretic medium components typically contain a low molecular weight surfactant, a polymerizing agent, or a mixture of one or more components and are used to stabilize or otherwise modify the sign and / or magnitude of the charge on the electrophoretic particles. CCAs are typically molecules containing ionic or other polar groups (hereinafter referred to as head groups). At least one of the positive or negative ionic head groups is preferably attached to a non-polar chain (typically a hydrocarbon chain), which is hereinafter referred to as a tail group. It is believed that CCAs form reverse micelles in the internal phase and are the minority of charged reverse micelles that contribute to the conductivity in the non-polar fluids typically used as electrophoretic fluids.

[0052] Reverse micelles comprise a highly polar core (usually containing water) surrounded by the non-polar tails of the CCA molecules, and their size can vary from 1 nm to tens of nanometers (and can have spherical, cylindrical or other geometric shapes). Reverse micelles have been widely studied, particularly in ternary mixtures such as oil / water / surfactant mixtures. An example is an isooctane / water / AOT mixture, such as described in Fayer et al., J. Chem. Phys., 131, 14704 (2009). In electrophoretic media, three phases can generally be distinguished: solid particles with a surface, a highly polar phase distributed in the form of extremely small droplets (reverse micelles), and a continuous phase comprising a fluid. When an electric field is applied, both the charged particles and the charged reverse micelles can move through the fluid, so there are two parallel paths for electrical conduction through the fluid (which itself generally has very low electrical conductivity).

[0053] The polar core of a CCA is believed to influence the charge on a surface by adsorbing onto it. In electrophoretic displays, this adsorption can occur on the surface of electrophoretic particles or on the inner walls of microcapsules (or other solid phases, such as the walls of microcells), forming structures similar to reverse micelles, hereinafter referred to as hemi-micelles. When one ion in an ion pair is more strongly attached to a surface than the other (e.g., by covalent bonding), ion exchange between the hemi-micelle and the unbound reverse micelle can result in charge separation, with the more strongly bound ion remaining associated with the particle, while the less strongly bound ion will bind to the core of the free reverse micelle.

[0054] The ionic materials that form the head groups of CCAs can also induce ion pair formation at the surface of the electrophoretic particle (or other) surface. Thus, CCAs can perform two basic functions: generating charge at the surface and separating charge from the surface. Charge generation can result from acid-base or ion exchange reactions between certain moieties present in the CCA molecule or otherwise incorporated into the reverse micelle core or fluid, and the particle surface. Therefore, useful CCA materials are those that are capable of participating in such reactions or any other charging reactions known in the art. CCA molecules can additionally act as acceptors for photoexcitons generated by the electrophoretic particle when the particle is illuminated with light.

[0055] Non-limiting examples of charge control agents useful in the media of the present invention include organic sulfates or sulfonates, metal soaps, block or comb copolymers, organic amides, organic zwitterions, and organic phosphates and phosphonates. Useful organic sulfates and sulfonates include, but are not limited to, sodium bis(2-ethylhexyl)sulfosuccinate, calcium dodecylbenzenesulfonate, calcium petroleum sulfonate, neutral or basic barium dinonylnaphthalenesulfonate, neutral or basic calcium dinonylnaphthalenesulfonate, sodium dodecylbenzenesulfonate, and ammonium lauryl sulfate. Useful metal soaps include, but are not limited to, basic or neutral barium petroleum sulfonate, calcium petroleum sulfonate, cobalt, calcium, copper, manganese, magnesium, nickel, zinc, aluminum, and iron salts of carboxylic acids (e.g., naphthenic acid, octanoic acid, oleic acid, palmitic acid, stearic acid, and myristic acid). Useful block or comb copolymers include, but are not limited to, AB diblock copolymers of (A) polymers of 2-(N,N-dimethylamino)ethyl methacrylate quaternized with methyl p-toluenesulfonate and (B) poly(2-ethylhexyl methacrylate), and comb-type graft copolymers of about 1800 molecular weight having oil-soluble tails of poly(12-hydroxystearic acid) pendant to oil-soluble anchoring groups of poly(methyl methacrylate-methacrylic acid). Useful organic amides / amines include, but are not limited to, polyisobutylene succinimides such as OLOA 371 or 1200 (available from Chevron Oronite Company LLC, Houston, Tex.) or Solsperse 17000 (available from Lubrizol, Wickliffe, OH: Solsperse is a registered trademark) and N-vinyl pyrrolidone polymers. Useful organic zwitterions include, but are not limited to, lecithin. Useful organic phosphates and phosphonates include, but are not limited to, sodium salts of mono- and diglycerides of phosphate with saturated and unsaturated acid substituents. Useful tail groups for CCA include polymers of olefins, such as poly(isobutylene) with a molecular weight in the range of 200-10,000. The head group can be a sulfonic acid, phosphoric acid, or carboxylic acid or amide, or alternatively, an amino group, such as a primary, secondary, tertiary, or quaternary ammonium group.

[0056] The charge adjuvant used in the media of the present invention can bias the charge on the surface of the electrophoretic particles, as described in more detail below.Such a charge adjuvant can be a Bronsted or Lewis acid or base.

[0057] Particle dispersion stabilizers may be added to prevent particle flocculation or adhesion to the capsule or other walls or surfaces. For typical high-resistivity liquids used as fluids in electrophoretic displays, anhydrous surfactants may be used. These include, but are not limited to, glycol ethers, acetylenic glycols, alkanolamides, sorbitol derivatives, alkylamines, quaternary amines, imidazolines, dialkyl oxides, and sulfosuccinates.

[0058] As described in US Pat. No. 7,170,670, the bistability of electrophoretic media can be improved by including in the fluid a polymer having a number average molecular weight exceeding about 20,000 that does not substantially adsorb onto the electrophoretic particles; poly(isobutylene) is a preferred polymer for this purpose.

[0059] Furthermore, as described, for example, in U.S. Patent No. 6,693,620, particles with fixed charges on their surfaces establish an oppositely charged double layer in the surrounding fluid. The ionic head groups of CCA can ionically pair with charged groups on the surface of the electrophoretic particles, forming a layer of fixed or partially fixed charged species. Outside this layer, there is a diffusion layer consisting of charged (reverse) micelles containing CCA molecules in the fluid. In conventional DC electrophoresis, the applied electric field exerts a force on the fixed surface charges and an opposing force on the mobile countercharges, causing slip within the diffusion layer and the particle to move relative to the fluid. The potential at the slip plane is called the zeta potential.

[0060] like Figure 2A 、 2B As shown in FIG2C , the resulting light collimating film ( 10 ) can be used to narrow (collimate) light ( 33 ). Figure 2A In the first narrowed state shown, the electrophoretic particles (26) are distributed throughout the elongated chambers (22), resulting in a pitch (A) between the elongated chambers (22), a width (W) of each elongated chamber (22), a height (H) of the light collimating film (10), and a distance from the light source (33) to the exit substrate (at Figure 2A In the example, the distance from the substrate (18) defines the transmission angle θ1. Figure 2A As can be seen in FIG, angle θ1 is roughly defined by rays X-X' and Y-Y', which define the maximum angle with the normal that light can leave the source (33) and pass through the top and bottom of the elongated chamber (22) throughout which the electrophoretic particles (26) are distributed.

[0061] In the equivalent of the above Figure 1C In the first wide-angle state, the electrophoretic particles (26) are driven closer to the substrate (16), and as Figure 2B As shown, a new transmission angle θ2 is established by the light rays X-X' and Y-Y'. Figure 2BAs shown, the new transmission angle θ2 will be much wider than θ1, that is, θ2 >> θ1. Again, the effective narrowing of the transmission angle θ2 will be a function of the pitch (A) between the elongated cavities (22), the width (W) of each elongated cavity (22), and the height (H) of the light collimating film (10).

[0062] In the equivalent of the above Figure 1F In the second wide-angle state, the electrophoretic particles (26) are driven to the substrate (16) away from the light source (33), and as Figure 2C As shown, a new transmission angle θ3 is established by the light rays X-X' and Y-Y'. Figure 2C As shown in , the new transmission angle θ3 will be much wider than θ1, that is, θ3>>θ1. Figure 2B , the effective narrowing of the transmission angle θ3 will be a function of the pitch (A) between the elongated chambers (22), the width (W) of each elongated chamber (22), and the height (H) of the light-collimating film (10). Furthermore, while it appears that electrophoretic particles (26) accumulated adjacent to the second substrate (18) might cast a shadow, this was not observed. It is presumed that there is sufficient scattered light passing through the light-collimating film (10) to eliminate this effect.

[0063] It is expected that in most configurations, at wide transmission angles ( Figure 2B and 2C ) to a narrow transmission angle ( Figure 2A ), the light collimating film (10) of the present invention will provide at least a two-fold reduction in effective viewing area (defined by a relative transmission of less than 50% as a function of the angle from the normal). In some embodiments, the reduction in viewing area will be greater than two-fold, such as three-fold, such as four-fold. Due to this functionality, the light collimating film (10) may be useful when simply applied to a glass sheet (e.g., an interior office window), thereby greatly reducing the transmission angle of the glass, thereby increasing privacy for office users, while still allowing a good amount of light to be transmitted through the window.

[0064] like Figure 3 As shown, a light collimating film (10) can be incorporated into a liquid crystal display (LCD) stack. Figure 3 is exemplary, as LCD stacks have many different configurations. Figure 3 As shown, light (33), typically from one or more light emitting diodes (LEDs), is guided through the display stack including the active layer by a combination of a light guide plate (34) and a diffuser plate (35). The light leaving the diffuser plate (35) travels along the path of the viewer ( Figure 3 The light then propagates in the direction of the eye (top of the eye) and encounters a light collimating film (10) of the type described above. Figure 3 In the state shown, the light collimating film (10) will only collimate light when the light is at a narrow transmission angle (see Figure 2A 、 Figure 2B and Figure 2C ) is allowed to pass through the active layer. The light that has passed through the light collimating film (10) will then continue to pass through the first polarizing film (36), an active matrix thin film transistor (AM-TFT) array (40) including a plurality of pixel electrodes (42). The polarized light that has passed through the AM-TFT (40) and the pixel electrodes (42) will then encounter the liquid crystal layer (44), whereby the polarization of the light can be manipulated by the liquid crystal so that the light will be transmitted through the second polarizing film (37) or rejected. Specifically, as is known in the art of LCD displays, the optical state of the liquid crystal layer (44) is changed by providing an electric field between the pixel electrode and the front electrode (45). The light that has passed through the light collimating film (10), the AM-TFT (40), the pixel electrode (42), the liquid crystal layer (44) and the front electrode (45) will then be transmitted through the color filter array (46), which will only pass the color spectrum associated with the pixel electrode (42) below. Finally, a certain amount of light with the correct color and the correct polarization (determined by the liquid crystal layer) will pass through the second polarizing film (37) and be viewed by the viewer. If desired, various additional layers of optical adhesive (47) may be included in the stack. The stack may also include a protective cover layer (49), which may be, for example, glass or plastic. Additional elements such as a capacitive touch sensing layer (48) or a digitizer layer (not shown) may also be added to the stack to enable touch screen capabilities or write capabilities, etc. Figure 4 Shown are a protective cover layer (49) and a capacitive touch sensing layer (48).

[0065] include Figure 3 The net effect of the illustrated LCD stack of light collimating films (10) is that the transmission angle of light emitted from an LCD display (e.g., a computer monitor, smartphone, data terminal, or other LCD display) can be independently controlled. Furthermore, because the switching medium is bi-stable, the device can be maintained in either the "wide" or "narrow" state almost indefinitely. In advanced embodiments, the amount of narrowing can be adjusted by controlling the relative amount of pigment driven toward the viewing side of the elongated chamber. The transmission angle can be adjusted completely independently of the state of the LCD. That is, the monitor does not have to be powered down to switch between privacy and non-privacy modes.

[0066] In other embodiments, to increase the amount of incident light that is directed toward the light collimating film (10) in the correct orientation to pass through the light collimating film (10), additional prismatic films (50) may be added to the stack of optical elements, such as Figure 5 As shown. Incorporating a prismatic film (50) will result in a display with a slight angular dependence of brightness, but the overall efficiency of the display stack is improved and results in less power consumption. This feature may be particularly desirable in mobile devices such as laptops or phones, for example.

[0067] exist Figure 6 An exploded view of the sealing layer (28) is shown in FIG. In some embodiments, as shown in the exploded view, the sealing layer (28) seals the top of the elongated chamber (22) to contain the bistable electrophoretic fluid (24). This can be achieved by under-filling the elongated chamber (22) with the bistable electrophoretic fluid (24) and then overcoating the very full elongated chamber (22) with the sealing composition (discussed below). In other embodiments, the sealing composition can be dispersed in the bistable electrophoretic fluid (24) at the time of filling, but designed to have the correct hydrophilicity and density so that the sealing composition rises to the top of the elongated chamber (22) so that it can be hardened, for example, using light, heat, or exposure to a chemical activator. In alternative embodiments ( Figure 6 (not shown), the elongated chamber (22) may be filled to the top and a sealing layer spread over the entire top of the light-transmitting polymer (20), thereby sealing the bistable electrophoretic fluid (24) within the elongated chamber.

[0068] Examples of essential components of the sealing composition used in the sealing layer may include, but are not limited to, thermoplastics or thermosetting plastics and their precursors. Specific examples may include materials such as monofunctional acrylates, monofunctional methacrylates, multifunctional acrylates, multifunctional methacrylates, polyvinyl alcohol, polyacrylic acid, cellulose, gelatin, and the like. Additives such as polymer binders or thickeners, photoinitiators, catalysts, vulcanizing agents, fillers, colorants, or surfactants may be added to the sealing composition to improve physical and mechanical properties and the light-collimating film.

[0069] The sealing composition may be a water-soluble polymer with water as the sealing solvent. Examples of suitable water-soluble polymers or water-soluble polymer precursors can include, but are not limited to, polyvinyl alcohol; polyethylene glycol, its copolymers with polypropylene glycol and derivatives thereof, such as PEG-PPG-PEG, PPG-PEG, PPG-PEG-PPG; poly(vinyl pyrrolidone) and its copolymers, such as poly(vinyl pyrrolidone) / vinyl acetate (PVP / VA); polysaccharides, such as cellulose and its derivatives, poly(glucosamine), dextran, guar gum and starch; gelatin; melamine formaldehyde; poly(acrylic acid), its salt forms and copolymers thereof; poly(methacrylic acid), its salt forms and copolymers thereof; poly(maleic acid), its salt forms and copolymers thereof; poly(2-dimethylaminoethyl methacrylate); poly(2-ethyl-2-oxazoline); poly(2-vinylpyridine); poly(allylamine); polyacrylamide; polyethyleneimine; polymethacrylamide; poly(sodium styrene sulfonate); cationic polymers functionalized with quaternary ammonium groups, such as poly(2-methacryloyloxyethyltrimethylammonium bromide), poly(allylamine hydrochloride). The sealing material may also include a water-dispersible polymer formulated with water as the solvent. Examples of suitable aqueous polymer dispersions may include aqueous polyurethane dispersions and aqueous latex dispersions. Suitable latexes in aqueous dispersions include polyacrylates, polyvinyl acetates and copolymers thereof, such as ethylene vinyl acetate, and polystyrene copolymers, such as polystyrene butadiene and polystyrene / acrylate.

[0070] Examples of additional components that may be present in, for example, the adhesive composition may include, but are not limited to, acrylic acid, styrene-butadiene copolymers, styrene-butadiene-styrene block copolymers, styrene-isoprene-styrene block copolymers, polyvinyl butyral, cellulose acetate butyrate, polyvinyl pyrrolidone, polyurethanes, polyamides, ethylene-vinyl acetate copolymers, epoxides, multifunctional acrylates, vinyls, vinyl ethers, and oligomers, polymers, and copolymers thereof. The adhesive layer may also comprise a polyurethane dispersion and a water-soluble polymer selected from the group consisting of: polyvinyl alcohol; polyethylene glycol and its copolymers with polypropylene glycol; poly(vinyl pyrrolidone) and its copolymers; polysaccharides; gelatin; poly(acrylic acid), its salt forms and copolymers thereof; poly(methacrylic acid), its salt forms and copolymers thereof; poly(2-dimethylaminoethyl methacrylate); poly(2-ethyl-2-oxazoline); poly(2-vinyl pyridine); poly(allylamine); polyacrylamide; polymethacrylamide; and cationic polymers functionalized with quaternary ammonium groups. The adhesive layer may be post-cured after lamination, for example by heat or radiation, such as ultraviolet (UV) light.

[0071] like Figure 6As shown, the entire stack, for example including the substrate (53), can be sealed with an edge seal (51). The edge seal (51) can include any of the sealing compositions described above. The edge seal (51) can be continuous around the light collimating layer (10) and the substrate (53), or the edge seal (51) can cover only a portion of the stack, for example only the outer edges of the light collimating layer (10). In some embodiments, the edge seal (51) can include an additional protective layer, such as an impermeable layer, such as transparent polyethylene. The protective layer can provide moisture or gas barrier properties. The edges of the protective layer and / or edge seal can be sealed with a heat or UV curable or heat activated edge seal material that provides moisture or gas barrier properties. In one embodiment, the edge seal is sandwiched between two protective substrates.

[0072] In some embodiments, the edge seal (51) will actually surround the entire stack, thereby creating a sealed assembly. Although not shown, it should be understood that one or more electrical connections may have to traverse the edge seal (51) to provide electrical connections to the first electrode (12) and the second electrode (14). Such connections may be provided by flexible ribbon connectors.

[0073] In addition to showing details of the sealing layer (28), Figure 6 It is also shown how the light collimating layer (10) can be laminated to a substrate (53) such as glass or another transparent durable material. Figure 6 Not shown, but note that the light collimating layer (10) can be protected by substrates on the top and bottom. The two substrates can be different or the same, for example, the first substrate can be glass and the second substrate can be polyethylene. An edge seal (51) can extend around the top and bottom substrates and the light collimating layer (10) between the substrates. Typically, an optical adhesive (52) (such as available from Delo Adhesives) is used to bond the light collimating layer (10) to the substrates (53). Alternatively, the light collimating layer (10) can be coated with a combination of optical adhesive (52) and a release sheet (54) so that the light collimating layer (10) with the release sheet (54) can be rolled up and shipped to an assembly plant where it can be cut to size. As Figure 7 As shown, before deployment, the release sheet (54) can be removed and the light collimating layer (10) can be attached directly to the substrate (53). The substrate can be any transparent surface where light collimation is desired, such as a conference room window, automotive glass, or a diffuser in an LCD stack.

[0074] Fabrication of light-collimating layers

[0075] You can use Figure 8 The light-collimating film is produced by a roll-to-roll process as shown in FIG. 1 and described in detail in US 9,081,250. Figure 8As shown, the process involves multiple steps: in a first step, a layer (60) of an imprint composition (e.g., a thermoplastic, a thermoset, or a precursor thereof), optionally together with a solvent, is deposited on a conductive transparent film (61), such as a polyethylene terephthalate (PET) (PET-ITO) film including an indium tin oxide layer. (If a solvent is present, the solvent evaporates readily.) A primer layer (i.e., an electrode protection layer) can be used to increase the adhesion between the imprint composition layer and the support layer (which can be PET). In addition, an adhesion promoter can be used in the primer layer to improve adhesion to the support layer. In a second step, the layer (60) is imprinted at a temperature above the glass transition temperature of the layer material by a pre-patterned imprint tool (62), the manufacture of which is described below. (The primer and / or adhesion promoter can be adjusted to reduce adhesion to the imprint tool (62).) In a third step, the patterned layer (60) is preferably released from the imprint tool (62) during or after hardening, such as by cooling. The characteristic pattern of elongated chambers is now established (as described above). In step four, the elongated chambers (63) are filled with the bistable electrophoretic fluid (64) described above. In some embodiments, the bistable electrophoretic fluid will include a sealing composition that is incompatible with the electrophoretic fluid (64) and has a specific gravity less than the solvent and pigment particles in the electrophoretic fluid (64). In such embodiments, the sealing composition will rise to the top of the elongated chambers (63) so that it can harden in a subsequent step. As an alternative ( Figure 8 (not shown), a sealing composition may be applied after the elongated chamber (63) is filled with the electrophoretic fluid (64). In a next step, the elongated chamber (63) filled with the electrophoretic fluid (64) is sealed by hardening the sealing composition with, for example, UV radiation (65), or by heat or moisture. In a sixth step, the sealed elongated chamber is laminated to a second transparent conductive film (66), which may be pre-coated with an optically clear adhesive layer (67), which may be a pressure sensitive adhesive, a hot melt adhesive, a heat, moisture or radiation curable adhesive. [Preferred materials for the optically clear adhesive include acrylic, styrene-butadiene copolymer, styrene-butadiene-styrene block copolymer, styrene-isoprene-styrene block copolymer, polyvinyl butyral, cellulose acetate butyrate, polyvinyl pyrrolidone, polyurethane, polyamide, ethylene-vinyl acetate copolymer, epoxide, multifunctional acrylate, vinyl, vinyl ether and oligomers, polymers and copolymers thereof.] In a final step, the completed switchable light-collimating film may be cut, for example, with a knife edge (69) or with a laser cutter. In some embodiments, an eighth step may be performed on the completed switchable light-collimating film, comprising laminating another optically clear adhesive and a release sheet so that the film can be shipped in sheets or rolls and cut to size at the time of use, for example for incorporation into a display, window, or other device / substrate.

[0076] The imprint tool (62) can be prepared by a photoresist process followed by etching or electroplating. It is then coated with a layer of photoresist and exposed to UV. A mask is placed between the UV and photoresist layers. In some embodiments, the unexposed or exposed areas are then removed by washing with an appropriate organic solvent or aqueous solution. The remaining photoresist is dried and sputtered again with a thin layer of seed metal. The master is then ready for electroforming. Typical materials used for electroforming are nickel cobalt. Alternatively, the master can be made of nickel by electroforming of nickel sulfamate or electroless nickel deposition. The base plate of the imprint tool is typically 50 to 5000 microns thick. The master can also be made using other microengineering techniques, including electron beam (e-beam) writing, dry etching, chemical etching, laser writing, or laser interferometry, as described in "Replication techniques for micro-optics", SPIE Proc. Vol. 3099, pp 76-82 (1997). Alternatively, the imprint tool can be made by photoprocessing using plastics, ceramics, or metals. Several methods for embossing tool production are described in more detail below.

[0077] Figure 9A and 9B An embossing process is shown with an embossing tool (111) having a three-dimensional microstructure (circles) on its surface. Figure 9A and 9B As shown, after applying the embossing tool (111) to the embossing composition (112) of at least 20 μm thickness, such as at least 40 μm thickness, such as at least 50 μm thickness, such as at least 60 μm thickness, such as at least 80 μm thickness, such as at least 100 μm thickness, such as at least 150 μm thickness, such as at least 200 μm thickness, such as at least 250 μm thickness. After the embossing composition is cured (e.g., by radiation) or the hot embossing material is embossed by heat and pressure, the embossing material is released from the embossing tool (see Figure 9B ), leaving an elongated cavity of desired dimensions, for example, wherein the height of the elongated cavity is equal to or less than the thickness of the alignment layer (imprint composition), and wherein the width of the elongated cavity is between 9 μm and 150 μm, and the length of the cavity is between 200 μm and 5 mm.

[0078] With conventional embossing tools, the cured or hot embossing material sometimes cannot be fully released from the tool due to undesirably strong adhesion between the cured or hot embossing material and the surface of the embossing tool. In such cases, some of the cured or hot embossing material may transfer to or stick to the surface of the embossing tool, leaving an uneven surface on the object formed by the process.

[0079] This problem is particularly pronounced if the object is formed on a support layer, such as a transparent conductive layer or a polymer layer. If the adhesion between the cured or hot embossing material and the support layer is weaker than the adhesion between the cured or hot embossing material and the surface of the embossing tool, the release process of the cured or hot embossing material from the embossing tool may cause the object to separate from the support layer.

[0080] In some cases, the object may be formed from a stack of layers. In such cases, if the adhesion between any two adjacent layers is weaker than the adhesion between the cured or hot embossing material and the surface of the embossing tool, the release of the cured or hot embossing material from the embossing tool may result in a rupture between the two layers.

[0081] This problem is particularly concerning when the cured embossing composition or hot embossing material does not adhere well to certain support layers. For example, if the support layer is a polymer layer, if one of the polymer layer and the cured or hot embossing composition is hydrophilic and the other is hydrophobic, the adhesion between the polymer layer and the cured or hot embossing composition is very weak. Therefore, preferably, the embossing composition and the support layer are both hydrophobic or both hydrophilic.

[0082] Suitable hydrophilic compositions for forming the imprinting layer or support layer may include polar oligomeric or polymeric materials. As described in U.S. Patent No. 7,880,958, such polar oligomeric or polymeric materials may be selected from the group consisting of oligomers or polymers having at least one of the following groups: nitro (-NO2), hydroxyl (-OH), carboxyl (-COO), alkoxy (-OR, where R is an alkyl group), halogen (e.g., fluorine, chlorine, bromine, or iodine), cyano (-CN), sulfonic acid (-SO3), and the like. The glass transition temperature of the polar polymeric material is preferably less than about 100°C, and more preferably less than about 60°C. Specific examples of suitable polar oligomeric or polymeric materials can include, but are not limited to, polyvinyl alcohol, polyacrylic acid, poly(2-dimethylaminoethyl methacrylate), polyhydroxy-functionalized polyester acrylates (e.g., BDE 1025, Bomar Specialties Co., Winsted, CT), or alkoxylated acrylates, such as ethoxylated nonylphenol acrylate (e.g., SR504, Sartomer Company, USA), ethoxylated trimethylolpropane triacrylate (e.g., SR9035, Sartomer Company, USA), or ethoxylated pentaerythritol tetraacrylate (e.g., SR494, from Sartomer Company, USA).

[0083] The embossing tool (111) can be used to emboss the composition (112) directly. More typically, the embossing tool (111) is mounted on a flat roller to allow the embossing sleeve to rotate on the embossing composition (112). The embossing roller or sleeve (121) is typically formed of a conductive material, such as a metal (e.g., aluminum, copper, zinc, nickel, chromium, iron, titanium, cobalt, etc.), an alloy derived from any of the above metals, or stainless steel. Different materials can be used to form the roller or sleeve. For example, the center of the roller or sleeve can be formed of stainless steel, and a nickel layer is sandwiched between the stainless steel and an outermost layer, which can be a copper layer.

[0084] Method A: If Figure 10 As shown, the impression cylinder or sleeve (121) may be formed of a non-conductive material having a conductive coating or conductive seed layer on its outer surface. Figure 10 As shown in step B, before the photosensitive material (122) is applied to the outer surface of the roller or sleeve (21), precision grinding and polishing can be used to ensure the smoothness of the outer surface of the roller or sleeve. The photosensitive material (122), such as a photoresist, can then be applied to the outer surface of the roller or sleeve (121). The photosensitive material can be positive, negative, or bi-sexual. The photosensitive material can also be a chemically amplified photoresist. Coating can be performed using dip coating, spray coating, or ring coating. After drying and / or baking, the photosensitive material can be subjected to exposure, such as Figure 10 As shown in step C, for example, by exposing the photosensitive material to a light source. Alternatively, the photosensitive material (122) can be a dry film photoresist laminated to the outer surface of the roller or sleeve (121). When a dry film is used, it is also exposed to a light source as described above.

[0085] exist Figure 10 In step C, a suitable light source (123), such as infrared (IR), UV, electron beam or laser, is used to expose the photosensitive material coated on the roller or sleeve (121) or the laminated dry film photoresist (122). The light source can be continuous light or pulsed light. A photomask (124) is optionally used to define the three-dimensional microstructure to be formed. Depending on the microstructure, the exposure can be step-by-step, continuous or a combination thereof. After exposure, the photosensitive material (122) can be subjected to post-exposure treatment, such as baking, before development. Depending on the characteristics of the photosensitive material, the exposed or unexposed areas will be removed by using a developer. After development, the roller or sleeve (such as) having the patterned photosensitive material (125) on its outer surface can be subjected to a post-exposure treatment, such as baking, before deposition (such as electroplating, electroless plating, physical vapor deposition, chemical vapor deposition or sputtering deposition). Figure 10 The thickness of the patterned photosensitive material is preferably greater than the depth or height of the three-dimensional microstructure to be formed.

[0086] A metal or alloy (e.g., nickel, cobalt, chromium, copper, zinc, or alloys derived from any of the foregoing) may be electroplated and / or electrolessly plated onto the roller or sleeve. The plating material (126) is deposited on the outer surface of the roller or sleeve in areas not covered by the patterned photosensitive material. The thickness of the deposit is preferably less than the thickness of the photosensitive material, e.g., Figure 10 By adjusting the plating conditions, for example, the distance between the anode and cathode (i.e., the drum or sleeve) (if electroplating is used), the rotation speed of the drum or sleeve, and / or the circulation of the plating solution, the thickness variation of the deposit over the entire drum or sleeve area can be controlled to less than 1%.

[0087] Alternatively, where electroplating is used to deposit the plating material (126), the thickness variation of the deposit across the surface of the drum or sleeve can be controlled by inserting a non-conductive thickness uniformer between the cathode (i.e., drum or sleeve) and the anode, as described in U.S. Patent No. 8,114,262, the entire contents of which are incorporated herein by reference.

[0088] After plating, the patterned photosensitive material (125) can be stripped by a stripper (e.g., an organic solvent or aqueous solution). Precision polishing can optionally be used to ensure that the thickness variation and roughness of the deposit (126) across the drum or sleeve are acceptable. Figure 10 Step F of FIG. 1 shows a cross-sectional view of an impression cylinder or sleeve having a three-dimensional patterned microstructure formed thereon.

[0089] Method B: Alternatively, as Figure 11 As shown, three-dimensional microstructures can be formed on flat substrates. Figure 11 In step A, a photosensitive material (142) is coated on a substrate layer (141) (e.g., a glass substrate). As described above, the photosensitive material (142) can be positive, negative, or bisexual. The photosensitive material (142) can also be a chemically amplified photoresist. Coating can be performed using dip coating, spray coating, slot die coating, or spin coating. After drying and / or baking, the photosensitive material is exposed to a suitable light source (not shown) through a photomask (not shown). Alternatively, the photosensitive material (142) can be a dry film photoresist (which is typically commercially available) laminated to the substrate (141). As described above, the dry film is also exposed to the light source.

[0090] exist Figure 11In step B, after exposure, the exposed or unexposed areas of the photosensitive material are removed by using a developer, depending on the characteristics of the photosensitive material. After development, the substrate layer (141) with the remaining photosensitive material (142) can be baked or fully exposed before step C. The thickness of the remaining photosensitive material should be the same as the depth or height of the three-dimensional microstructure to be formed. In step C, a conductive seed layer (143) is coated on the remaining photosensitive material (142) and the areas of the substrate (141) not occupied by the photosensitive material. The conductive seed layer is typically formed of silver; however, other conductive materials, such as gold or nickel, can also be used.

[0091] In step D, a metal or alloy (144) (e.g., nickel, cobalt, chromium, copper, zinc, or alloys derived from any of the foregoing metals) is electroplated and / or electrolessly plated on the surface covered by the conductive seed layer, and the plating process is not stopped until there is a sufficient thickness (h) of the plated material on the patterned photosensitive material. Figure 11 The thickness (h) in step D is preferably 25 to 5000 μm, and more preferably 25 to 1000 μm.

[0092] After plating, the plating material (144) is separated from the stripped substrate layer (141). The photosensitive material (142) and the conductive seed layer (143) are removed. The photosensitive material can be removed by a stripper (e.g., an organic solvent or an aqueous solution). The conductive seed layer (143) can be removed by an acidic solution (e.g., a sulfuric acid / nitric acid mixture) or a commercially available chemical stripper, leaving only a metal sheet (144) having a three-dimensional structure on one side and a flat side on the other side. The metal sheet (144) can be precision polished, and after precision polishing, the flat sheet can be used directly for stamping, or it can be mounted (i.e., wound) on a roller having a three-dimensional microstructure on its outer surface to form an imprinting tool. As described above, the precious metal or its alloy is finally coated on the entire surface of the imprinting tool. As described above, gold or its alloy is preferred over other precious metals and alloys due to its lack of reactivity.

[0093] Method C: Figure 12 An alternative approach is shown in . This approach is similar to Figure 11 The method is similar to the method of the present invention, but is simplified. Instead of a conductive seed layer such as silver, a layer of a noble metal or its alloy (153) is simply coated on the photosensitive material (152). As mentioned above, gold or its alloy is preferred. Therefore, in step E, after the plated material (154) is separated from the substrate (151), only the photosensitive material (152) is removed, and the gold or alloy coating (153) remains together with the metal sheet (154) having a three-dimensional structure on one side and a flat surface on the other side.

[0094] Examples of components in the composition used to form the alignment layer include, but are not limited to, thermoplastic or thermosetting materials or their precursors, such as multifunctional vinyls, including but not limited to acrylates, methacrylates, allyl groups, vinylbenzenes, vinyl ethers, multifunctional epoxides, and their oligomers or polymers. Multifunctional acrylates and their oligomers are often used. Combinations of multifunctional epoxides and multifunctional acrylates are also used to achieve the desired physical and mechanical properties of the alignment layer. Low-Tg (glass transition temperature) binders or crosslinkable oligomers that impart flexibility, such as polyurethane acrylates or polyester acrylates, may also be added to improve the bending resistance of the embossed privacy layer.

[0095] Other examples of compositions for the alignment layer may include polar oligomers or polymers. Such polar oligomers or polymers may be selected from the group consisting of oligomers or polymers having at least one of the following groups: nitro (-NO2), hydroxyl (-OH), carboxyl (-COO), alkoxy (-OR, where R is an alkyl group), halogen (e.g., fluorine, chlorine, bromine, or iodine), cyano (-CN), sulfonic acid (-SO3), and the like. The glass transition temperature of the polar polymer material is preferably less than about 100°C, and more preferably less than about 60°C. Specific examples of suitable polar oligomeric or polymeric materials can include, but are not limited to, polyhydroxy-functionalized polyester acrylates (e.g., BDE 1025, Bomar Specialties Co., Winsted, CT) or alkoxylated acrylates, such as ethoxylated nonylphenol acrylate (e.g., SR504, Sartomer, Inc., USA), ethoxylated trimethylolpropane triacrylate (e.g., SR9035, Sartomer, Inc., USA), or ethoxylated pentaerythritol tetraacrylate (e.g., SR494, from Sartomer, Inc., USA).

[0096] Alternatively, the alignment layer composition may include (a) at least one bifunctional UV curable component, (b) at least one photoinitiator, and (c) at least one release agent. Suitable bifunctional components may have a molecular weight greater than about 200. Bifunctional acrylates are preferred, and bifunctional acrylates having a urethane or ethoxy backbone are particularly preferred. More specifically, suitable bifunctional components may include, but are not limited to, diethylene glycol diacrylate (e.g., SR230 from Sartomer), triethylene glycol diacrylate (e.g., SR272 from Sartomer), tetraethylene glycol diacrylate (e.g., SR268 from Sartomer), polyethylene glycol diacrylate (e.g., SR295, SR344, or SR610 from Sartomer), polyethylene glycol dimethacrylate (e.g., SR603, SR644, SR252, or SR740 from Sartomer), ethoxylated dimethacrylates. Phenol A diacrylate (e.g., CD9038, SR349, SR601, or SR602 from Sartomer), ethoxylated bisphenol A dimethacrylate (e.g., CD540, CD542, SR101, SR150, SR348, SR480, or SR541 from Sartomer), and urethane diacrylate (e.g., CN959, CN961, CN964, CN965, CN980, or CN981 from Sartomer; Ebecryl 230, Ebecryl 270, Ebecryl 8402, Ebecryl 8804, Ebecryl 8807, or Ebecryl 8808 from Cytec, USA). Suitable photoinitiators may include, but are not limited to, bisacylphosphine oxide, 2-benzyl-2-(dimethylamino)-1-[4-(4-morpholinyl)phenyl]-1-butanone, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, 2-isopropyl-9H-thioxanthen-9-one, 4-benzoyl-4'-methyldiphenyl sulfide, and 1-hydroxy-cyclohexyl-phenyl ketone, 2-hydroxy-2-methyl-1-phenyl-propane-1-one, 1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propane-1-one, 2,2-dimethoxy-1,2-diphenylethane-1-one, or 2-methyl-1[4-(methylthio)phenyl]-2-morpholinopropane-1-one. Suitable release agents may include, but are not limited to, organically modified silicone copolymers such as silicone acrylates (e.g., Ebercryl 1360 or Ebercyl 350 from Cytec), silicone polyethers (e.g., Silwet 7200, Silwet 7210, Silwet 7220, Silwet 7230, Silwet 7500, Silwet 7600, or Silwet 7607 from Momentive).The composition may further optionally comprise one or more of the following components: a co-initiator, a monofunctional UV curable component, a multifunctional UV curable component, or a stabilizer.

[0097] Setting up the elongated chamber

[0098] Figure 13 and 14 Two geometries of light collimating layers produced by the above-described fabrication method are shown (as viewed from above). These geometries show a general trend in the aspect ratios of the elongated chambers (22) being that they are longer in one direction (L) than in another direction (W). That is, the length (L) of the elongated chamber is typically at least twice the width (W) of the elongated chamber, such as at least three times the width of the elongated chamber, such as at least four times the width of the elongated chamber, such as at least five times the width of the elongated chamber, such as at least ten times the width of the elongated chamber. [As discussed above, the height (H) of the elongated chamber (in Figure 13 and 14 Typically, the width of each elongated cavity is between 9µm and 150µm. Typically, the length of each elongated cavity is between 200µm and 5mm.

[0099] As previously discussed, the spacing (A) between rows (also known as the "pitch") plays a major role in determining how much the viewing angle is reduced when the electrophoretic pigment (26) is fully distributed in the elongated chambers (22). If the height of the elongated chambers (22) remains constant, the viewing angle becomes narrower as the spacing "A" is reduced. However, reducing "A" means that the light passes through more of the bistable electrophoretic fluid (24) with pigment particles, and the total light transmittance of the light collimating film is reduced. In a similar manner, the gap width "G" between adjacent elongated chambers within the same row also affects the total transmission of the light collimating layer due to the number of scattering particles between the light source and the viewer. Therefore, Figure 13 Total transmittance Figure 14 The total transmission is low. However, Figure 13 In the CMOS process, there is less “leakage” of non-collimated light because the incident light has fewer off-axis paths to travel through the elongated cavity.

[0100] In some embodiments, when creating the elongated chambers, for example using a roller stamping tool as described above, the elongated chambers are formed into rows and columns (as viewed from above). Figure 13 and Figure 14In the embodiment, the gaps between adjacent elongated chambers in a first row are horizontally offset relative to the gaps between adjacent elongated chambers in a second row. Typically, the gap width "G" between adjacent elongated chambers in the same row is less than 30 μm, such as less than 25 μm, such as less than 20 μm, such as less than 15 μm, such as less than 10 μm. The gaps between adjacent elongated chambers in consecutive rows may be offset by at least 1 μm, such as at least 2 μm, such as at least 3 μm, such as at least 5 μm. In some embodiments, as Figure 14 As shown, the entire gap of the first row is spanned by the elongated chambers of the second row. In most embodiments, L>G. In many embodiments, L>>G. In most embodiments, A>W. In many embodiments, A>>W.

[0101] Because the spacing between the elongated chambers is on the order of the wavelength of visible light, e.g. Figure 13 and 14 The repetitive pattern may produce undesirable interference effects on viewing, which may appear as spots, moire fringes, color spots or other visible defects. Various changes can be made to the design of the light collimating layer (10) to overcome these interference effects. For example, Figure 15 As shown, the position of the gaps between adjacent elongated chambers (22) may be "walked" laterally for each successive row. Alternatively or additionally, as Figure 16 As shown, the gap width (G) can be varied between adjacent elongated chambers (22) for different rows. In addition, the gap width (G) can be varied between elongated chambers (22) within the same row. Alternatively or additionally, as Figure 17 As shown, the pitch (A) between rows can be modified across the light collimating film. Alternatively or in addition, the length (L) of each elongated chamber (22) can be modified within a single row and / or between rows. In addition, as Figure 18 As shown, the width (W) of each elongated cavity (22) can be modified within a single row and / or between rows. Although the embossing process described herein is repetitive because it is performed with a rolling tool, it is possible to disrupt symmetry by making most features on the roller asymmetrical. The repeating pattern caused by the rolling embossing tool is typically on the order of 20 cm, so no interference effects will occur.

[0102] 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).

[0103] The technologies described in these patents and applications include:

[0104] (a) Electrophoretic particles, fluids, and fluid additives; see, for example, U.S. Patent Nos. 7,002,728 and 7,679,814; and U.S. Patent Application Publication No. 2016 / 0170106;

[0105] (b) Capsules, binders, and encapsulation processes; see, eg, US Patent Nos. 6,922,276 and 7,411,719; and US Patent Application Publication No. 2011 / 0286081.

[0106] (c) Microcell structures, wall materials, and methods of forming microcells; see, e.g., U.S. Patent Nos. 6,672,921; 6,751,007; 6,753,067; 6,781,745; 6,788,452; 6,795,229; 6,806,995; 6,829,078; 6,833,177; 6,850,355; 6,865,012; 6,870,662; 6,885,495; 6,906,779; 6,930,818; 6,933,098; 6,947,202; 6,987,605; 7,046,228; 7,072,095; 7,079,303; 7,141,279;7,156,945; 7,205,355; 7,233,429; 7,261,920; 7,271,947; 7,304,780; 7,307,778;7,327,346; 7,347,957; 7,470,386; 7,504,050; 7,580,180; 7,715,087; 7,767,126;7,880,958; 8,002,948; 8,154,790; 8,169,690; 8,441,432; 8,582,197; and U.S. Patent Application Publication Nos. 2003 / 0175480; 2003 / 0175481; 2003 / 0179437; 2003 / 0203101; 2013 / 0321744; 2014 / 0050814; 2015 / 0085345; 2016 / 0059442; 2016 / 0004136; and 2016 / 0059617;

[0107] (d) Methods for filling and sealing microlocations; see, e.g., U.S. Patent Nos. 6,545,797; 6,751,008; 6,788,449; 6,831,770; 6,833,943; 6,859,302; 6,867,898; 6,914,714; 6,972,893; 7,005,468; 7,046,228; 7,052,571; 7,144,942; 7,166,182; 7,374,634; 7,385,751; 7,408,696; 7,522,332; 7,557,981; 7,560,004; and U.S. Patent Application Publication Nos. 2002 / 0188053; 2004 / 0120024; 2004 / 0219306; 2006 / 0132897; 2006 / 0164715; 2006 / 0238489; 2007 / 0035497; 2007 / 0036919; 2007 / 0243332; 2015 / 0098124; and 2016 / 0109780;

[0108] (e) Films and subassemblies comprising electro-optical materials; see, e.g., U.S. Patent Nos. 6,825,829; 6,982,178; 7,112,114; 7,158,282; 7,236,292; 7,443,571; 7,513,813; 7,561,324; 7,636,191; 7,649,666; 7,728,811; 7,729,039; 7,791,782; 7,839,564; 7,843,621; 7,843,624; 8,034,209; 8,068,272; 8,077,381; 8,177,942; 8,390,301; and U.S. Patent Application Publication Nos. 2007 / 0237962; 2009 / 0109519; 2009 / 0168067; 2011 / 0164301; 2014 / 0115884; and 2014 / 0340738;

[0109] (f) Backplanes, adhesive layers, and other auxiliary layers and methods for use in displays; see, e.g., U.S. Patent Nos. 7,116,318; 7,535,624; and 9,310,661; and U.S. Patent Application Publication Nos. 2016 / 0103380 and 2016 / 0187759.

[0110] (g) Methods for driving displays; see, e.g., U.S. Patent Nos. 5,930,026; 6,445,489; 6,504,524; 6,512,354; 6,531,997; 6,753,999; 6,825,970; 6,900,851; 6,995,550; 7,012,600; 7,023,420; 7,034,783; 7,061,166; 7,061,662; 7,116,466; 7,119,772; 7,177,066; 7,193,625; 7,202,847; 7,242,514; 7,259,744; 7,304,787; 7,312,794; 7,327,511; 7,408,699; 7,453,445; 7,492,339; 7,528,822; 7,545,358; 7,583,251; 7,602,374; 7,612,760; 7,679,599; 7,679,813; 7,683,606; 7,688,297; 7,729,039; 7,733,311; 7,733,335; 7,787,169; 7,859,742; 7,952,557; 7,956,841; 7,982,479; 7,999,787; 8,077,141; 8,125,501; 8,139,050; 8,174,490; 8,243,013; 8,274,472; 8,289,250; 8,300,006; 8,305,341; 8,314,784; 8,373,649; 8,384,658; 8,456,414; 8,462,102; 8,514,168; 8,537,105; 8,558,783; 8,558,785; 8,558,786; 8,558,855; 8,576,164; 8,576,259; 8,593,396; 8,605,032; 8,643,595; 8,665,206; 8,681,191; 8,730,153; 8,810,525; 8,928,562; 8,928,641; 8,976,444; 9,013,394; 9,019,197; 9,019,198; 9,019,318; 9,082,352; 9,171,508; 9,218,773; 9,224,338; 9,224,342; 9,224,344; 9,230,492;and U.S. Patent Application Publication Nos. 2003 / 0102858; 2004 / 0246562; 2005 / 0253777; 2007 / 0091418; 2007 / 0103427; 2007 / 0176912; 2008 / 0024429; 2008 / 0024482; 2008 / 0136774; 2008 / 0291129; 2008 / 0303780; 2009 / 0174651; 2009 / 0195568; 2009 / 0322721; 2010 / 0194733; 2010 / 0194789; 2010 / 0220121; 2010 / 0265561; 2010 / 0283804; 2011 / 0063314; 2011 / 0175875; 2011 / 0193840; 2011 / 0193841; 2011 / 0199671; 2011 / 0221740; 2012 / 0001957; 2012 / 0098740; 2013 / 0063333; 2013 / 0194250; 2013 / 0249782; 2013 / 0321278; 2014 / 0009817; 2014 / 0085355; 2014 / 0204012; 2014 / 0218277; 2014 / 0240210; 2014 / 0240373; 2014 / 0253425; 2014 / 0292830; 2014 / 0293398; 2014 / 0333685; 2014 / 0340734; 2015 / 0070744; 2015 / 0097877; 2015 / 0109283; 2015 / 0213749; 2015 / 0213765; 2015 / 0221257; 2015 / 0262255; 2015 / 0262551; 2016 / 0071465; 2016 / 0078820; 2016 / 0093253; 2016 / 0140910 and 2016 / 0180777. ;

[0111] The manufacture of three-layer electro-optical displays typically involves at least one lamination operation. For example, the aforementioned MIT and Iink patents and applications describe a process for manufacturing encapsulated electrophoretic displays (EPDs), in which an encapsulated electrophoretic medium, comprising capsules in a binder, is applied to a flexible substrate comprising an indium tin oxide (ITO) or similar conductive coating on a plastic film (which serves as one electrode in the final display). The capsule / binder coating is dried to form a coherent layer of electrophoretic medium firmly adhered to the substrate. Separately, a backplane is prepared, containing an array of pixel electrodes and an appropriate arrangement of conductors connecting the pixel electrodes to the drive circuitry. To form the final display, the substrate with the capsule / binder layer is laminated to the backplane using a laminating adhesive. In one embodiment, the backplane itself is flexible and is prepared by printing the pixel electrodes and conductors on a plastic film or other flexible substrate. In other embodiments, both electrodes are flexible, allowing the constructed EPD to be flexible. The obvious lamination technique for mass-producing displays using this process is roll lamination using a laminating adhesive. Similar fabrication techniques can be used with other types of electro-optic displays. For example, microcell electrophoretic media can be laminated to a backplane or flexible electrode in much the same way as encapsulated electrophoretic media.

[0112] U.S. Patent No. 6,982,178 describes a method for assembling solid-state electro-optic displays (including encapsulated electrophoretic displays) that is well-suited for mass production. Essentially, the patent describes a so-called "front plane laminate" ("FPL") comprising, in sequence, a light-transmitting conductive layer, a solid electro-optic medium layer in electrical contact with the conductive layer, an adhesive layer, and a release sheet. Typically, the light-transmitting conductive layer will be carried on a light-transmitting substrate, which is preferably flexible, in the sense that it can be manually wound onto a roll (for example) 10 inches (254 mm) in diameter without permanent deformation. The term "light-transmitting" is used in the patent and, in this context, means that the designated layer transmits sufficient light to enable an observer to observe changes in the display state of the electro-optic medium through the layer, which would typically be observed through the conductive layer and the adjacent substrate (if present); in the case of an electro-optic medium displaying changes in reflectivity at non-visible wavelengths, the term "light-transmitting" should of course be interpreted as referring to transmission of the relevant non-visible wavelengths. The substrate is typically a polymer film and will typically have a thickness in the range of about 1 to about 25 mils (25 to 634 microns), preferably about 2 to about 10 mils (51 to 254 microns). The conductive layer is conveniently a thin metal or metal oxide layer such as aluminum or ITO, or may be a conductive polymer. Poly(ethylene terephthalate) (PET) films coated with aluminum or ITO are commercially available, for example as "aluminized Mylar" ("Mylar" is a registered trademark) from E.I. DuPont de Nemours and Company, Wilmington, Delaware, and such commercial materials may be used to good effect in the front plane laminate.

[0113] Assembly of an electrophoretic display using such a front plane laminate can be achieved by removing a release sheet from the front plane laminate and contacting the adhesive layer with the backplane under conditions that effectively adhere the adhesive layer to the backplane, thereby securing the adhesive layer, the electrophoretic medium layer, and the conductive layer to the backplane. This process is well suited for mass production because the front plane laminate can typically be mass-produced using roll-to-roll coating technology and then cut into pieces of any size for a particular backplane.

[0114] The term "impulse" is used here in its conventional sense, namely, the integral of voltage with respect to time. However, some bistable electro-optical media function as charge converters, and for such media, an alternative definition of impulse may be used, namely, the integral of current with respect to time (which is equal to the total applied charge). Depending on whether the medium functions as a voltage-to-time impulse converter or a charge-to-impulse converter, the appropriate definition of impulse should be used.

[0115] Another complication in driving electrophoretic displays is the need for so-called "DC balance." U.S. Patent Nos. 6,531,997 and 6,504,524 discuss the problems that can be encountered and the reduced operating life of the display if the method used to drive the display does not result in a zero or near-zero net time-averaged applied electric field across the electrophoretic medium. Driving methods that do achieve a zero net time-averaged applied electric field across the electrophoretic medium are conveniently referred to as "direct current balance" or "DC balance."

[0116] As already noted, encapsulated electrophoretic media typically consist of electrophoretic capsules arranged in a polymer binder that serves to form the discrete capsules into a coherent layer. The continuous phase in polymer-dispersed electrophoretic media plays a similar role to the cell walls of microcellular media. Yiink researchers have discovered that the specific binder material used in electrophoretic media can influence the electro-optical properties of the media. Among the electro-optical properties of electrophoretic media affected by binder selection is the so-called "dwelling time dependence." As discussed in U.S. Patent No. 7,119,772 (see, in particular, FIG. 34 and the related description), in certain circumstances, the impulse required to transition between two specific optical states of a bistable electrophoretic display varies with the dwell time of the pixel in its initial optical state, a phenomenon known as "dwelling time dependence" or "DTD." Minimizing the DTD is obviously desirable because it affects the difficulty of driving the display and can affect the quality of the resulting image; for example, DTD can cause pixels that should form a uniform gray area to have slightly different gray levels from one another, and the human eye is very sensitive to such variations. Although it is known that the choice of binder affects the DTD, the selection of an appropriate binder for any particular electrophoretic medium has heretofore been based on trial and error, with little understanding of the relationship between the DTD and the binder chemistry.

[0117] U.S. Patent Application Publication No. 2005 / 0107564 describes an aqueous polyurethane dispersion comprising a polyurethane polymer comprising the reaction product of: (a) an isocyanate-terminated prepolymer comprising the reaction product of: (i) at least one polyisocyanate comprising a,a,a,a-tetramethylxylene diisocyanate [scientific name 1,3-bis(1-isocyanato-1-methylethyl)benzene; hereinafter referred to as "TMXDI"]; (ii) at least one difunctional polyol comprising polypropylene glycol; and (iii) an isocyanate-reactive compound comprising an acidic functional group and at least two isocyanate-reactive groups selected from hydroxyl groups, primary amino groups, secondary amino groups, and combinations thereof; (b) a neutralizing agent comprising a tertiary amino group; (c) a monofunctional chain terminator; (d) a chain extender comprising an organic diamine; and (e) water. This polyurethane dispersion (hereinafter referred to as a "TMXDI / PPO" dispersion) has been found to be useful as a laminating adhesive in electrophoretic displays.

[0118] From the above, it can be seen that the present invention can provide a switchable light-collimating film and a device including a switchable light-collimating film. In particular, the present invention provides a bistable light-collimating film and is capable of maintaining wide and narrow viewing conditions without additional energy input.

[0119] 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. A method for manufacturing a switchable light-collimating film, comprising the following steps: providing a first light-transmitting electrode layer; depositing an imprint composition on the surface of the first light-transmitting electrode layer to form an imprint composition layer; imprinting the imprint composition using a pre-patterned imprint tool at a temperature above the glass transition temperature of the material of the imprint composition layer, thereby forming a patterned layer; releasing the patterned layer from the imprint tool to form an alignment layer, the alignment layer having a thickness of at least 20 μm and comprising a plurality of elongated cavities, each elongated cavity having an opening, a height, a length (L), and a width (W), the plurality of elongated cavities being arranged in rows and columns when the alignment layer is viewed from above, wherein the lengths (L) of the plurality of elongated cavities extend along the rows, and wherein gaps between adjacent elongated cavities within the same row are less than 30 μm, wherein a first row of elongated cavities comprises gaps between elongated cavities in a first column and a second column, wherein a second row of elongated cavities comprises gaps between elongated cavities in the first column and a second column, and wherein the gaps between the elongated cavities in the first column and the second column in the first row are horizontally offset relative to the gaps between the elongated cavities in the first column and the second column in the second row; filling each of the plurality of elongated chambers with a bistable electrophoretic fluid including pigment particles through openings of the plurality of elongated chambers; sealing the filled openings of the plurality of elongated chambers with a sealing composition, thereby forming a sealing layer spanning the opening of each elongated chamber of the plurality of elongated chambers; The sealed elongated cavity is laminated to a second light-transmitting electrode layer, wherein the first light-transmitting electrode layer and the second light-transmitting electrode layer are arranged on either side of the collimating layer.

2. The method for manufacturing a switchable light-collimating film according to claim 1, wherein: The third row of elongated chambers includes a gap between the first and second columns of elongated chambers; wherein the gap between the first and second columns of elongated chambers in the second row is horizontally offset relative to the gap between the first and second columns of elongated chambers in the third row, and wherein the gap between the first and second columns of elongated chambers in the first row is horizontally offset relative to the gap between the first and second columns of elongated chambers in the third row.

3. The method for manufacturing a switchable light-collimating film according to claim 1, wherein: The alignment layer includes a polymer including an acrylate monomer, a urethane monomer, a styrene monomer, an epoxide monomer, a silane monomer, a thioolefin monomer, a thioalkyne monomer, or a vinyl ether monomer.

4. The method for manufacturing a switchable light-collimating film according to claim 1, wherein: The collimating layer includes polyacrylate.

5. The method for manufacturing a switchable light-collimating film according to claim 1, wherein: The bistable electrophoretic fluid comprises polymer-functionalized pigment particles and free polymer in a non-polar solvent.

6. The method for manufacturing a switchable light-collimating film according to claim 5, wherein: The polymer-functionalized pigment particles are functionalized with polyacrylate, polystyrene, polynaphthalene, or polydimethylsiloxane.

7. The method for manufacturing a switchable light-collimating film according to claim 5, wherein: The free polymer comprises polyisobutylene or a copolymer comprising ethylene, propylene or styrene monomers.

8. The method for manufacturing a switchable light-collimating film according to claim 1, wherein: The rows of the plurality of elongated chambers are spaced apart from one another by at least three times the width of the elongated chambers.

9. The method for manufacturing a switchable light-collimating film according to claim 1, wherein: The thickness of the alignment layer is less than 500 μm.

10. The method for manufacturing a switchable light-collimating film according to claim 1, wherein: The width of the elongated chamber is between 5 μm and 150 μm.

11. The method for manufacturing a switchable light-collimating film according to claim 1, wherein: The height of the elongated chamber is equal to or less than the thickness of the collimating layer.

12. The method for manufacturing a switchable light-collimating film according to claim 1, wherein: The length of the elongated chamber is between 200µm and 5mm.

13. The method for manufacturing a switchable light-collimating film according to claim 1, wherein: The first light-transmitting electrode layer or the second light-transmitting electrode layer includes indium tin oxide.

14. The method for manufacturing a switchable light-collimating film according to claim 1, wherein: The sealing layer comprises cellulose, gelatin, polyacrylate, polyvinyl alcohol, polyethylene, poly(vinyl)acetic acid, poly(vinyl)pyrrolidone, polyurethane or a copolymer of any of the above polymers.

15. A method for manufacturing a switchable light-collimating film, comprising the following steps: providing a first light-transmitting electrode layer; depositing an imprint composition on the surface of the first light-transmitting electrode layer to form an imprint composition layer; imprinting the imprint composition using a pre-patterned imprint tool at a temperature above the glass transition temperature of the material of the imprint composition layer, thereby forming a patterned layer; releasing the patterned layer from the imprint tool to form an alignment layer, the alignment layer having a thickness of at least 20 μm and comprising a plurality of elongated cavities, each elongated cavity having an opening, a height, a length (L), and a width (W), the plurality of elongated cavities being arranged in rows and columns when the alignment layer is viewed from above, wherein the lengths (L) of the plurality of elongated cavities extend along the rows, and wherein gaps between adjacent elongated cavities within the same row are less than 30 μm, wherein a first row of elongated cavities comprises gaps between elongated cavities in a first column and a second column, wherein a second row of elongated cavities comprises gaps between elongated cavities in the first column and a second column, and wherein the gaps between the elongated cavities in the first column and the second column in the first row are horizontally offset relative to the gaps between the elongated cavities in the first column and the second column in the second row; filling each of the plurality of elongated chambers with a bistable electrophoretic fluid including pigment particles through openings of the plurality of elongated chambers; sealing the filled openings of the plurality of elongated chambers with a sealing composition, thereby forming a sealing layer spanning the opening of each elongated chamber of the plurality of elongated chambers; An optically clear adhesive layer and a release layer are attached to the sealing layer, wherein the optically clear adhesive layer is disposed between the sealing layer and the release layer.

Images