Switchable light-collimating layer with reflectors

Abstract

A light collimating film comprises an elongated chamber of a bistable electrophoretic fluid. The light collimating film is suitable for controlling the amount and / or direction of light incident on a transmissive substrate. Such a film can be integrated into a device such as an LCD display to provide a privacy zone for a user viewing the LCD display. Because the light collimating film is switchable, it allows the user to change the collimation of the emitted light as desired. Since the films are bistable, no additional power source is required after they have been switched to the display state.

Description

[0001] Related Applications

[0002] This application claims priority to U.S. Provisional Patent Application No. 62 / 717,104, filed on August 10, 2018. The entire contents of any patent, published application, or other published work cited herein are incorporated herein by reference. Background Art

[0003] The present invention relates to switchable light collimating films, which 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 sold 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. Typically, when a user wishes to limit the image on the display to a "privacy cone" visible only to the user, a privacy filter is applied to the front surface of a video display. Privacy films typically use micro-machined plastic channels that are backfilled with a material having a different refractive index from 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 incorrect direction will be back-reflected and / or absorbed. The same technology can also be used as window treatments to modify the directionality of sunlight passing through, for example, an exterior window.

[0004] Several groups have attempted to make active media that can be switched between a privacy state and a non-privacy state. For example, U.S. Patent Publication 2016 / 0179231 ('231 Application) describes an electrically active 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 electric field, collimating the light and providing a privacy zone for the user. However, it is necessary to provide a constant potential to the privacy layer to keep the material aligned to maintain the privacy state. Because the privacy device requires a constant electric field to maintain the privacy state, the device consumes additional energy beyond the typical energy required by the monitor. When used with a battery-powered device (such as a laptop), the additional energy required to power the privacy layer will shorten the battery's operating time. PCT Publication WO2013 / 048846 also describes an alternative switchable privacy film that also uses anisotropic particles that are held in a position aligned with the electric field. Similar to the '231 application, the device disclosed in '846 also requires a constant supply of energy in a privacy-protected state.

[0005] Other active switching anti-peeping devices have been described, which rely on blocking the movement of particles in the channel rather than the alignment of anisotropic particles. For example, U.S. Patent Publication No. 2016 / 0011441 ('441 application) describes an electrically switchable electrochromic material arranged in a microstructured rib extending along the length of the anti-peeping layer. In the '441 application, when current is supplied to the electrochromic material, the absorption spectrum of the electrochromic material changes. Although the actual switching process requires considerable energy (about 5 minutes of direct current), once the transition is completed, the anti-peeping layer of the '441 application is able to maintain its state for a period of time. Another alternative method is described in U.S. Patent Publication No. 2017 / 0097554, in which a long light control channel is formed between transparent conductive films, and the channel is filled with an electrophoretic member including a transmissive dispersant and light-shielding particles. By using a set of three shaping electrodes to control the dispersion of light-shielding particles in the air gap, the electrophoretic member can be switched between a narrow field of view mode and a wide field of view mode. The manufacture 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] Although switchable privacy filters can be obtained, for example, using anisotropic particle alignment, there is still a need for inexpensive privacy films with low energy consumption. Therefore, the present invention describes a light-collimating film comprising a plurality of elongated chambers of a bistable electrophoretic fluid, the bistable electrophoretic fluid comprising 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 2 (or more). Importantly, because the light-collimating film comprises a bistable electrophoretic fluid, the light-collimating film is stable in either a wide or narrow state for a long time and only requires energy to change from one state to another. In addition, because the bistable electrophoretic fluid is separated into a plurality of elongated chambers, the electrophoretic material is less likely to settle when the same light-collimating film is applied in different directions relative to gravity. In addition, when the bistable electrophoretic fluid is separated into many 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] In addition, since the light-collimating film includes a plurality of small chambers, it is easy to cut the film into a desired shape / size after manufacturing without losing a large amount of electrophoretic fluid. This allows the same equipment to be used to create light-collimating films of large and small areas. For example, a section sheet of a square meter of light-collimating film or a roll of light-collimating film can be cut into fragments of the desired size without significant loss of 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 small. In some cases, hundreds of small pieces (e.g., for mobile phones) can be cut from a single section or roll. In some embodiments, elongated chambers can be manufactured in a predetermined pattern so that sheet cutting does not result in the loss of electrophoretic fluid. The design disclosed herein also benefits from including a light-reflecting surface so that light that might otherwise be absorbed by the pigment particles is recycled in a device including a light-collimating film.

[0008] Thus, in one aspect, the present invention includes 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 chambers, and a second light-transmitting electrode layer, wherein the first light-transmitting layer and the second light-transmitting layer are arranged on both sides of the collimating layer. Each elongated chamber has an opening, and a bistable electrophoretic fluid containing pigment particles is arranged in each elongated chamber. There is a portion of the collimating layer between the elongated chambers, thereby defining a valley in the material constituting the collimating layer. The elongated chambers are sealed with a sealing layer, which seals the bistable electrophoretic fluid therein by spanning the opening of the elongated chamber. The light collimating film also includes a light reflecting surface aligned with the opening of each elongated chamber, wherein the light reflecting surface does not substantially overlap with the portion of the collimating layer between the elongated chambers. The switchable light collimating film typically has a thickness of less than 500 μm, and the height of the elongated chamber is equal to or less than the thickness of the collimating layer. Typically, the elongated chamber has a width between 5 μm and 150 μm and a length between 200 μm and 5 mm. For example, the elongated chamber may have a width between 5 μm and 50 μm and a length 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. Typically, the light-reflecting surface comprises a metal or a light-reflecting metal oxide. In some embodiments, the light-reflecting surface contacts a bistable electrophoretic fluid. In some embodiments, the sealing layer forms the light-reflecting surface. In some embodiments, the switchable light-collimating film comprises a substrate contacting a first light-transmitting electrode or a second light-transmitting electrode and a light-reflecting surface contacting the substrate. The first light-transmitting electrode layer or the second light-transmitting electrode layer can be made of indium tin oxide.

[0010] Bistable electrophoretic fluids are generally comprised of pigment particles and free polymers functionalized by polymers in nonpolar solvents.Usually, pigments are functionalized by polyacrylate, polystyrene, polynaphthalene or polydimethylsiloxane.Free polymers may include polyisobutylene or a copolymer including ethylene, propylene or styrene monomers, and sealing layer may include water-soluble polymers or water-dispersible polymers, for example naturally occurring water-soluble polymers, for example cellulose or gelatin, or synthetic polymers, for example polyacrylate, polyvinyl alcohol, polyethylene, poly(vinyl)acetic acid, poly(vinyl)pyrrolidone, polyurethane or its copolymer.

[0011] In one embodiment, when the collimation layer is viewed from above, the elongated chambers are arranged in rows and columns, 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, when the collimation layer is viewed from above, the elongated chambers are arranged in rows and columns, 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. The light reflecting surface does not cover a majority of the light collimating film between the elongated chambers. In some cases, the light reflecting surface is formed at the bottom of the elongated chambers before the elongated chambers are filled with a bistable electrophoretic fluid.

[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 switchable light collimating film including a first light-transmitting electrode layer, a collimating layer having a thickness of at least 20 μm and including a plurality of elongated chambers, and a second light-transmitting electrode layer, wherein the first light-transmitting layer and the second light-transmitting layer are arranged on both sides of the collimating layer. Each elongated chamber has an opening, and a bistable electrophoretic fluid containing pigment particles is arranged in each elongated chamber. There is a portion of the collimating layer between the elongated chambers, thereby defining a valley in the material constituting the collimating layer. The elongated chambers are sealed by a sealing layer, which seals the bistable electrophoretic fluid therein by spanning the opening of the elongated chamber. The light collimating film also includes a light reflecting surface aligned with the opening of each elongated chamber, wherein the light reflecting surface does not substantially overlap with the portion of the collimating layer between the elongated chambers. The light reflecting surface reduces the amount of light directly absorbed by the pigment particles from the light source. Instead, this light is back-reflected and increases the total illumination that passes through the switchable light-collimating film and ultimately enters the liquid crystal layer.

[0013] In some embodiments, the light collimating film or the 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 diffusion 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 a switchable light-collimating film is shown, wherein 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 supply.

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

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

[0017] Figure 1D A return to a state in which the chamber has electrophoretic particles distributed throughout the collimating layer is shown.

[0018] Figure 1E The fourth state of the switchable light-collimating film is shown, wherein upon application of Figure 1B Under the condition of a potential of opposite polarity, the electrophoretic particles are driven toward the second light-transmitting electrode.

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

[0020] Figure 2A It is shown that when the electrophoretic particles are distributed throughout the cavities of the collimating layer, the light emitted from the source is confined to an angle θ1. Some of the light emitted from the light source is directly absorbed by the pigment particles.

[0021] Figure 2B It is shown that when the electrophoretic particles are distributed throughout the cavities of the collimating layer, the light emitted from the source is confined to an angle θ1. Due to the light reflecting surfaces, some of the light that would be absorbed by the pigment particles is reflected back.

[0022] Figure 2C It is shown that when the electrophoretic particles are gathered on the light-transmitting electrode closest to the light source, the light emitted from the source is at an angle θ2, where θ2>>θ1.

[0023] Figure 2D It is shown that when the electrophoretic particles are concentrated on the light transmissive electrode farthest from the light source, the light emitted from the source is at an angle θ3, where θ3 >> θ1. It is observed that light loss is minimized due to the presence of the pigment particles on the emission side of the light collimating film.

[0024] Figure 3 Active layers of a liquid crystal display assembly including a switchable light-collimating film are shown. The layers are not drawn to scale.

[0025] Figure 4 The active layers of a liquid crystal display assembly including a switchable light collimating film and a touch screen are shown. The layers are not drawn to scale. There is no limitation on the location of the light reflecting surfaces. As discussed in the text, they can be placed in a variety of locations.

[0026] Figure 5 Active layers of a liquid crystal display assembly including a switchable light-collimating film and a prismatic film are shown. The layers are not drawn to scale.

[0027] Fig. 6A An embodiment of a switchable light-collimating film disposed on a lower substrate is shown. The switchable light-collimating film also includes an edge seal. An exploded view details the sealing layer on top of an elongated chamber filled with a bistable electrophoretic fluid. Fig. 6A In the embodiment, a light reflecting surface is fabricated above the opening of an elongated chamber.

[0028] Figure 6B An embodiment of a switchable light-collimating film disposed on a lower substrate is shown. The switchable light-collimating film also includes an edge seal. An exploded view details the sealing layer on top of an elongated chamber filled with a bistable electrophoretic fluid. Figure 6B In the embodiment, the sealing layer also provides a light reflecting surface.

[0029] Figure 6C An embodiment of a switchable light-collimating film disposed on a lower substrate is shown. The switchable light-collimating film also includes an edge seal. An exploded view details the sealing layer on top of an elongated chamber filled with a bistable electrophoretic fluid. Figure 6C In the embodiment of the present invention, a light reflecting surface is created at the bottom of the elongated chamber before the elongated chamber is filled with a bistable electrophoretic fluid.

[0030] Fig. 7A is a top view of an embodiment of a switchable light-collimating film, wherein the elongated chambers are arranged in a row-column format. Fig. 7A The light reflecting surface in the elongated chamber is located above the opening (see Fig. 6A ) such that the light reflecting surface does not substantially overlap with portions of the collimating layer between the elongated chambers.

[0031] Figure 7Bis a top view of an embodiment of a switchable light-collimating film, wherein the elongated chambers are arranged in a row-column format. Fig. 7A The light reflecting surface in the can be incorporated into the sealing layer (see Figure 6B ) or arranged at the bottom of the elongated chamber (see Figure 6C ) such that the light reflecting surface does not substantially overlap with portions of the collimating layer between the elongated chambers.

[0032] 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.

[0033] Fig. 9A and 9B A simplified embossing process is shown.

[0034] Fig.10 Methods for forming an imprint tool to create the collimation layer of the present invention are described in detail.

[0035] Fig.11 A method for forming a shim for use in an imprint tool is described.

[0036] Fig.12 An alternative method for forming a shim for use in an imprint tool is detailed.

[0037] Fig.13 A method of forming a light-collimating layer by using a light-reflecting surface as a mask during photolithography is shown.

[0038] Fig.14 A method of forming a light collimating layer by contact printing a light reflective material at the bottom of an elongated cavity is shown. DETAILED DESCRIPTION

[0039] As described above, the present invention provides a light-collimating film comprising an elongated chamber 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 a device such as an LCD display to provide useful features, such as providing a peep-proof area 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. In addition, because the medium is bistable, the collimated state will be stable for a period of time, such as minutes, hours, days, or months, without providing additional energy to the light-collimating film. The light-collimating film of the present invention also includes a light-reflecting surface that back-reflects incident light that would otherwise be directly absorbed by the pigment particles in the bistable electrophoretic fluid.

[0040] Using the design of the present invention, a switchable light-collimating film can be cheaply manufactured using a roll-to-roll process. Therefore, it is feasible to produce large pieces of switchable light-collimating film, which can be incorporated into the device during other assembly processes (such as the manufacture of LCD displays). Such a film may include an auxiliary optically transparent adhesive layer and a release sheet, allowing the light-collimating film to be transported and distributed as a finished product. The light-collimating film can also be used for after-market light control, such as for conference room windows, exterior windows of buildings, and sunshade skylights and skylights. In some embodiments, the light-reflecting surface will reduce the amount of light absorbed by the film, thereby keeping the film (and associated substrate materials, such as windows) cool.

[0041] Electrophoretic displays typically include 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 an elongated row electrode, while the other may be patterned as an elongated column electrode extending at right angles to the row electrode, with the pixel being defined by the intersection of the row electrode and the column electrode. 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 "bistable" are used herein in their conventional sense in the art to refer to a display including a display element having first and second display states that differ in at least one optical property such that after any given element is driven to assume its first or second display state with an addressing pulse of finite duration, that state will persist after termination of the addressing pulse for a time that is at least several times (e.g., at least 4 times) the minimum duration of the addressing pulse required to change the state of the display element. It is shown in U.S. Pat. No. 7,170,670 that some particle-based electrophoretic displays supporting gray scales can be stable not only in their extreme black and white states, but also in intermediate gray states, as well as some other types of electro-optical displays. This type of display is 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 a resin) or glass. In the case of producing the film (10) using a roll-to-roll process, the first substrate (16) and the second substrate (18) are flexible. The light-transmitting electrode and the substrate 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 fragments, 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 transmissive polymer (20) which has been processed to produce a plurality of elongated chambers (22) to contain a bistable electrophoretic fluid (24) comprising electrophoretic particles (26). The switchable light collimating film (10) further comprises a light reflecting layer (27) associated with each elongated chamber (22). The light reflecting layer (27) is used to back-reflect incident light that would otherwise be directly absorbed by the electrophoretic particles (26) within the elongated chamber (22). In one 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 transmissive electrode layer (12) and the second light transmissive electrode layer (14)). The thickness of the light collimating layer may 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 chamber, for example 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 collimation 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 an electrode, a wire or a trace (31). In some embodiments, the trace (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 Ink listed herein, but is primarily due to having a specific mixture of distributed polymers (e.g., polyisobutylene or polylauryl acrylate) in the bistable electrophoretic fluid (24) such that the electrophoretic particles (26) are stabilized by depletion flocculation. Thus, in Figure 1A In the first state shown, the electrophoretic particles (26) are stabilized 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, days, etc. Figure 1C shown.

[0047] The state of the light collimating film (10) can be reversed by driving the collected 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 (substantially) 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 1BThe electrophoretic particles (26) can be driven through the distribution state and toward the second light-transmitting electrode (14) by applying a reverse polarity voltage. 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 the state. Figure 1C and Figure 1F The state leads to wide-angle transmission, so it can be Figure 1A , 1C , 1D, and 1F while maintaining the overall DC balance of the drive electronics. DC balanced drive electronics reduce charge accumulation and extend the life of system components.

[0048] The internal phase of the electrophoretic medium comprises charged pigment particles in a suspension 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 (Exxon Mobil) or (Total); terpenes, such as limonene, such as 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 the ELISA® available from Cargille-Sacher Laboratories Inc. (Cedar Grove, NJ). Refractive index matching fluid. In the encapsulation medium of the present invention, preferably, the refractive index of the particle dispersion matches the refractive index of the encapsulating material as closely as possible to reduce haze. This refractive index match is best achieved when the refractive index of the solvent is close to the refractive index of the encapsulating material (when using conventional polymer encapsulating materials). In most cases, it is advantageous that the refractive index of the internal phase at 550nm is between 1.51 and 1.57, preferably the refractive index at 550nm is about 1.54.

[0049] Charged pigment particles can have a variety of colors and components. 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 by 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 show white, or composite particles designed and manufactured to have a desired refractive index. Black charged particles can be formed by CI Pigment Black 26 or 28, etc. (such as iron manganese black or copper chrome black) or carbon black. Other colors (non-white and non-black) can be formed by organic pigments, such as CI pigments PR254, PR122, PR149, PG36, PG58, PG7, PB28, PB15:3, PY83, PY138, PY150, PY155 or PY20. Other examples include Hostaperm Red D3G 70-EDS, Hostaperm Pink E-EDS, PV fast red D3G, Hostaperm RedD3G 70, Hostaperm Blue B2G-EDS, Hostaperm Yellow H4G-EDS, Novoperm Yellow HR-70-EDS, Hostaperm Green GNX from Clariant, Irgazine Red L 3630, Cinquasia Red L4100 HD and Irgazin Red L 3660HD from BASF; Phthalocyanine Blue, Phthalocyanine Green, Aniline Yellow or Benzidine Yellow from Sun Chemical. Colored particles may also be formed from inorganic pigments, such as CI Pigment Blue 28, CI Pigment Green 50, CI Pigment Yellow 227, and the like. The surface of the charged particles can be modified by known techniques based on the desired charge polarity and charge level of the particles, as described in U.S. Patent Nos. 6,822,782, 7,002,728, 9,366,935, and 9,372,380 and U.S. Publication No. 2014-0011913, the entire contents of which are incorporated herein by reference.

[0050] The particles may exhibit a natural charge, or may be explicitly charged using a charge control agent, or may acquire a charge when suspended in a solvent or solvent mixture. Suitable charge control agents are well known in the art; they may be polymeric or non-polymeric in nature, or may be ionic or non-ionic. Examples of charge control agents may include, but are not limited to, Solsperse 17000 (active polymer dispersant), Solsperse 9000 (active polymer 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, the stabilizing material can be adsorbed on the charged pigment particles. Such stabilizing material keeps the particles separated from each other so that when the particles are in their dispersed state, the variable transmission medium is substantially non-transmissive. As known in the art, charged particles (usually carbon black, as described above) can be dispersed in a solvent of low dielectric constant by the use of a surfactant. Such surfactants typically contain a polar "head group" and a non-polar "tail group" that is compatible with or soluble in the solvent. In the present invention, preferably, the non-polar tail group is a saturated or unsaturated hydrocarbon portion, or another group that is soluble in a hydrocarbon solvent (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 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 size of the charge on the electrophoretic particles. CCA is typically a molecule containing ions or other polar groups (hereinafter referred to as head groups). At least one of the positive or negative ion head groups is preferably attached to a non-polar chain (usually a hydrocarbon chain), which is hereinafter referred to as a tail group. It is believed that CCA forms reverse micelles in the internal phase, and is a minority of charged reverse micelles, which leads to conductivity in non-polar fluids that are typically used as electrophoretic fluids.

[0052] Reverse micelles contain a highly polar core (usually containing water) surrounded by the non-polar tails of 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, especially 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 an electrophoretic medium, 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 containing a fluid. When an electric field is applied, both charged particles and charged reverse micelles can move through the fluid, so there are two parallel paths for electrical conduction through the fluid (which itself usually has a very small conductivity).

[0053] The polar core of the CCA is believed to affect the charge on the surface by adsorbing onto the surface. In an electrophoretic display, this adsorption can be on the surface of the electrophoretic particle or on the inner wall of the microcapsule (or other solid phase, such as the wall of the microunit) to form structures similar to reverse micelles, which are referred to as hemi-micelles hereinafter. When one ion in an ion pair is more firmly attached to the surface than the other ion (e.g., by covalent bonding), ion exchange between the hemi-micelle and the unbound reverse micelle can result in charge separation, wherein the more firmly bound ion remains associated with the particle, while the less firmly bound ion will bind to the core of the free reverse micelle.

[0054] The ionic material forming the head group of the CCA can also induce ion pair formation at the surface of the electrophoretic particle (or other). Therefore, CCA can perform two basic functions: generating charge at the surface and separating charge from the surface. Charge generation can be caused by acid-base or ion exchange reactions between certain parts of the CCA molecules present in or otherwise bound to the reverse micelle core or fluid and the particle surface. Therefore, useful CCA materials are those that can participate in such reactions or any other charging reaction known in the art. When the particles are irradiated with light, the CCA molecules can additionally act as receptors for photoexcitons generated by the electrophoretic particles.

[0055] Non-limiting types 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 (barium petronate), calcium petroleum sulfonate, cobalt, calcium, copper, manganese, magnesium, nickel, zinc, aluminum, and iron salts of carboxylic acids (e.g., cyclohexane acid, octanoic acid, oleic acid, palmitic acid, stearic acid, and myristic acid, etc.). 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 graft copolymers of molecular weight about 1800 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 an 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 attachment to capsules 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 the electrophoretic medium can be improved by including in the fluid a polymer having a number average molecular weight in excess of about 20,000 which is substantially nonadsorbed onto the electrophoretic particles; poly(isobutylene) is a preferred polymer for this purpose.

[0059] In addition, for example, as described in U.S. Patent No. 6,693,620, particles with a fixed charge on their surface establish an oppositely charged double layer in the surrounding fluid. The ionic head groups of CCA can ion pair with charged groups on the surface of the electrophoretic particles to form a layer of fixed or partially fixed charged species. Outside of this layer is a diffusion layer, which includes 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 opposite force on the movable countercharges, causing slip to occur within the diffusion layer and the particles to move relative to the fluid. The potential at the slip plane is called the ζ (zeta) potential.

[0060] like Figure 2B , 2C As shown in FIG. 2D and FIG. 3D , the resulting light collimating film (10) can be used to narrow (collimate) light (33). To better explain the benefits of the light reflecting surface (27), Figure 2A A first embodiment without a light reflecting surface (27) is shown in FIG. Figure 2A In the embodiment, 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 of the substrate (18), the transmission angle θ1 is defined by the distance from the substrate (18). Figure 2A As can be seen, 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] As in Figure 2AAs can be seen in Figure 2, a portion of the light emitted from points X and Y (and all points between them) will enter the elongated chamber (22) where it will be immediately absorbed. This direct absorption leads to at least two complications. First, in the case of incorporating a light collimating film into an LCD display (or other type of backlit display), a portion of the energy used to illuminate the light source is wasted. This results in, for example, a shortened battery life of the device. A second disadvantage is that the additional light captured by the bistable electrophoretic medium ultimately becomes heat, which increases the temperature of the device and associated substrate. Since the viscosity of an electrophoretic medium generally decreases with increasing temperature, this heat load may also make the electrophoretic medium less stable. This may result in some drift in the state of the electrophoretic medium when no voltage is applied.

[0062] Therefore, if Figure 2B As shown, the present invention includes a plurality of light reflecting surfaces (27). Although the light reflecting surfaces do not significantly change the transmission angle θ1 of the device, including the light reflecting surfaces (27) does improve the performance of the device, especially as Figure 3-5 As shown when paired with a backlit display medium. The light reflective surface can include any light reflective material, such as a metal, such as silver, gold, aluminum, chromium or an alloy thereof. The light reflective surface can alternatively contain a metal oxide of high reflectivity, such as titanium dioxide, zinc oxide and bismuth oxide. The light reflective surface can also include a thin film layered material (e.g., a dielectric mirror) designed to reflect visible light and / or infrared light, such as those made of silicon dioxide, zinc sulfide and / or titanium dioxide. In an alternative embodiment, the sealing layer can be doped with reflective particles, such as metal fragments or titanium dioxide. Once the sealing layer is cured, the reflective particles are essentially locked in the opening of the elongated chamber and increase the amount of backscattered light.

[0063] As described above, the light collimating layer can achieve the change of the transmission angle by switching the state of the bistable electrophoretic medium (24). Figure 1C In the first wide-angle state, the electrophoretic particles (26) are driven to a closer substrate (16), and as Figure 2C As shown, a new transmission angle θ2 is established by light rays X-X' and Y-Y'. Figure 2C As 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 chambers (22), the width (W) of each elongated chamber (22), and the height (H) of the light collimating film (10).

[0064] 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 2D As shown, a new transmission angle θ3 is established by light rays X-X' and Y-Y'. Figure 2D As shown, the new transmission angle θ3 will be much wider than θ1, that is, θ3>>θ1. Figure 2C Similarly, 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). In addition, although it seems that the electrophoretic particles (26) accumulated adjacent to the second substrate (18) may cast a shadow, this was not observed. It is speculated that there is sufficient scattered light passing through the light collimating film (10) to eliminate this effect.

[0065] It is expected that in most configurations, the 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 relative to 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 glass panels (such as interior office windows), 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.

[0066] 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 a display stack including an 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 a viewer ( Figure 3 The light then propagates in the direction of the eye at the top of the eye and then encounters a light collimating film (10) of the type described above. Figure 3In the state shown, the light collimating film (10) will allow light to pass through the active layer only when the light propagates within a narrow transmission angle (see Figure 2). The light that passes 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 passes 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 is transmitted 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. Various additional layers of optical adhesive (47) may be included in the stack as needed. 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 is a protective cover layer (49) and a capacitive touch sensing layer (48).

[0067] include Figure 3 The net effect of the LCD stack of light collimating films (10) shown is that the transmission angle of light emitted from an LCD display (e.g., a computer monitor, smart phone, 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 can be switched between privacy and non-privacy modes without having to be powered off.

[0068] In other embodiments, in order 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, for example, in mobile devices such as laptops or phones.

[0069] exist Figures 6A-6C Various positions for the light reflecting surface (27) are shown in FIG. Fig. 6A In the embodiment of the present invention, the light reflecting surface is arranged on top of a first substrate (16) directly above the opening of the elongated chamber (22). Figure 6B In the embodiment, the sealing layer (28) has been modified to incorporate a light reflective material such as titanium dioxide (not shown), and after curing, the sealing layer (28) serves as both the sealing layer (28) and the light reflective surface (27). In an alternative embodiment, a redox reaction between the sealing material and the light reflective electrophoretic particles can be initiated. One substance for the redox reaction is added to the seal, while the other substance is incorporated into the bistable electrophoretic medium (24). In Figure 6C In the embodiment of the present invention, the light reflecting surface (27) is arranged at the bottom of the elongated chamber (22) before the bistable electrophoretic fluid (24) is filled into the elongated chamber. Of course, other locations may also be suitable, such as being arranged below the second substrate (18) [not shown]. In all cases, the light reflecting surface does not substantially overlap with the portion of the collimating layer between the elongated chambers. This feature allows as much light as possible to pass through the light collimating layer (10).

[0070] In all three graphs ( Figures 6A-6C ) shows an exploded view of the sealing layer (28). Fig. 6A As shown in the exploded view of FIG. 1 , the sealing layer (28) seals the top of the elongated chamber (22) to contain the bistable electrophoretic fluid (24). The seal can be achieved by under-filling the elongated chamber (22) with the bistable electrophoretic fluid (24) and then overcoating the fully filled elongated chamber (22) with the sealing agent (see FIG. Figure 6B In other embodiments, the sealing composition may be dispersed in the bistable electrophoretic fluid (24) when filled, but designed to have the correct hydrophilicity and density so that the sealing formulation 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 ( Figures 6A-6C (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.

[0071] Examples of basic components in the sealing composition for 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, etc. Additives such as polymer binders or thickeners, photoinitiators, catalysts, vulcanizers, fillers, colorants, or surfactants may be added to the sealing composition to improve physical and mechanical properties and the light-collimating film.

[0072] 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 may include, but are not limited to, polyvinyl alcohol; polyethylene glycol, its copolymers with polypropylene glycol and their derivatives, 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(propylene glycol); The sealing material may also include a water-dispersible polymer with water as the formulation solvent. Examples of suitable polymer aqueous dispersions may include polyurethane aqueous dispersions and latex aqueous 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 / acrylates.

[0073] 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, polyurethane, polyamide, ethylene-vinyl acetate copolymer, epoxide, multifunctional acrylate, vinyl, vinyl ether and oligomers, polymers and copolymers thereof. The adhesive layer may also include 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 form and its copolymers; poly(methacrylic acid), its salt form and its copolymers; 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.

[0074] like Figures 6A-6C As shown, an entire stack, for example including a substrate (53), can be sealed with an edge seal (51). The edge seal (51) can include any of the above-mentioned sealing compositions. 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 edge 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 sealing material that provides moisture or gas barrier properties. In one embodiment, the edge seal is sandwiched between two protective substrates.

[0075] 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 can be provided by flexible ribbon connectors.

[0076] In addition to showing the details of the sealing layer (28), Figures 6A-6CAlso shown is how the light-collimating layer (10) is laminated to a substrate (53) such as glass or another transparent durable material. Although not shown in FIG. 6 , note that the light-collimating layer (10) can be protected on the top and bottom by substrates. 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) (e.g., available from Delo Adhesives) is used to bond the light-collimating layer (10) to the substrate (53). Alternatively, the light-collimating layer (10) can be coated with a combination of an 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 is cut to size. Prior to unrolling, the release sheet (54) can be removed and the light-collimating layer (10) can be attached directly to the substrate (53) (not shown). 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.

[0077] Fig. 7A and 7B Two geometries of light collimating layers produced by the above-described manufacturing method are shown (viewed from above). These geometries show a general trend in the aspect ratio 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 Fig. 7A and 7B ] Typically, the width of each elongated cavity is between 5 μm and 150 μm. Typically, the length of each elongated cavity is between 200 μm and 5 mm.

[0078] As discussed previously, the spacing (A) between rows (also known as "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" decreases. However, reducing "A" means that the light passes through more of the bistable electrophoretic fluid (24) with pigment particles, and the overall transmittance of the light collimating film decreases. In a similar manner, the gap width "G" between adjacent elongated chambers in 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, Fig. 7A Total transmittance Figure 7B The total transmission is low. However, Fig. 7A In the EM-based approach, there is less “leakage” of non-collimated light because the incident light has fewer off-axis paths to propagate through the elongated chamber.

[0079] In some embodiments, when creating the elongated chambers, for example using a rolling embossing tool as described above, the elongated chambers are formed into rows and columns (as viewed from above). Fig. 7A and Figure 7B In 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 7B 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.

[0080] The light reflecting surface (27) does not substantially overlap the light collimating material between the elongated chambers (22). Fig. 7A As shown, the light reflective surface (27) applied to the substrate may just extend beyond the edge of the elongated chamber (22). In some cases, when the light reflective material is incorporated into the sealing layer and the edge of the sealing layer extends beyond the boundary of the elongated chamber (22), when Fig. 7A When viewed from above, for example, the edge of the light reflecting surface may extend beyond the elongated surface by less than 5 mm, such as less than 3 mm, such as less than 1 mm. In other embodiments, for example, when the sealing material and the light reflecting material are combined into a sealing layer, the light reflecting surface does not extend beyond the elongated cavity (22), such as Figure 7B In addition, in the case where the light reflecting surface is arranged at the bottom of the elongated chamber (22), the light reflecting surface does not exceed the range of the elongated chamber (22), as shown in FIG. Figure 7B shown.

[0081] Because the spacing between the elongated chambers is on the order of the wavelength of visible light, e.g. Fig. 7A and 7BThe 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, the position of the gap between adjacent elongated chambers (22) can be "walked" laterally for each consecutive row. Alternatively or in addition, the gap width (G) can be changed between adjacent elongated chambers (22) for different rows. In addition, the gap width (G) can be changed between elongated chambers (22) in the same row. Alternatively or in addition, 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, the width (W) of each elongated chamber (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 destroy the symmetry by making most of the features on the roller asymmetric. The repeating pattern caused by the rolling stamping tool is typically on the order of 20 cm, so no interference effects occur.

[0082] Fabrication of light-collimating layers

[0083] 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 thermosetting plastic, 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 is easily volatile). 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 the 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 the 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 chamber (63) is 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 an embodiment, the sealing composition will rise to the top of the elongated chamber (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 transparent adhesive layer (67), which may be a pressure sensitive adhesive, a hot melt adhesive, a heat, moisture or radiation curable adhesive. [Preferred materials for optically transparent adhesives include acrylic, 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 their oligomers, polymers and copolymers. In a final step, the finished switchable light-collimating film sheet can be cut, for example, with a knife edge (69) or with a laser cutter. In some embodiments, an eighth step can be performed on the finished switchable light-collimating film, which includes laminating another optically clear adhesive and a release sheet so that the film can be shipped in slices or rolls and cut to size when used, for example for incorporation into a display, window or other device / substrate.

[0084] 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 cleaning with an appropriate organic solvent or aqueous solution. The remaining photoresist is dried and sputtered again with a thin layer of seed metal. Then, the master is ready for electroforming. Typical materials for electroforming are nickel cobalt. Alternatively, the master can be made of nickel by nickel sulfamate electroforming or electroless nickel deposition. The bottom 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 interference, as described in "Replication techniques for micro-optics", SPIE Proc. Vol. 3099, pp 76-82 (1997). Alternatively, the imprint tool can be made by using light processing of plastics, ceramics or metals. Several methods for embossing tool production are described in more detail below.

[0085] Fig. 9A and 9B An embossing process with an embossing tool (111) having a three-dimensional microstructure (circles) on its surface is shown. Fig. 9A and 9B As shown, after applying the embossing tool (111) to the embossing composition (112) which is at least 20 μm thick, such as at least 40 μm thick, such as at least 50 μm thick, such as at least 60 μm thick, such as at least 80 μm thick, such as at least 100 μm thick, such as at least 150 μm thick, such as at least 200 μm thick, such as at least 250 μm thick. 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 Fig. 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 (imprinting 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.

[0086] Using conventional imprint tools, the cured or hot imprint material is sometimes not completely released from the tool due to undesirably strong adhesion between the cured or hot imprint material and the surface of the imprint tool. In such cases, some of the cured or hot imprint material may transfer to or stick to the surface of the imprint tool, leaving an uneven surface on the object formed by the process.

[0087] This problem is more 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.

[0088] In some cases, the object may be formed on a stack of layers and, in such cases, the release process of the cured or hot embossing material from the embossing tool may result in rupture between the two layers 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.

[0089] The above 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, in the case where one of the polymer layer and the cured or hot embossed embossing composition is hydrophilic and the other is hydrophobic, the adhesion between the polymer layer and the cured or hot embossed embossing composition is very weak. Therefore, preferably, the embossing composition and the support layer are both hydrophobic or both hydrophilic.

[0090] Suitable hydrophilic compositions for forming the imprint layer or support layer may include polar oligomers or polymer materials. As described in U.S. Pat. No. 7,880,958, such polar oligomers or polymer materials may be selected from the group consisting of oligomers or polymers having at least one of the following groups, such as nitro (-NO2), hydroxyl (-OH), carboxyl (-COO), alkoxy (-OR, wherein R is an alkyl), halogen (e.g., fluorine, chlorine, bromine or iodine), cyano (-CN), sulfonic acid (-SO3), etc. 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 may include, but are not limited to, polyvinyl alcohol, polyacrylic acid, poly(2-dimethylaminoethyl methacrylate), polyhydroxy-functional 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).

[0091] The embossing tool (111) can be used directly to emboss the composition (112). More typically, the embossing tool (111) is mounted on a flat cylinder to allow an embossing sleeve to rotate on the embossing composition (112). The embossing cylinder or sleeve (121) is usually 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 cylinder or sleeve. For example, the center of the cylinder or sleeve can be formed of stainless steel, and a nickel layer is sandwiched between the stainless steel and the outermost layer, which can be a copper layer.

[0092] Method A: Fig.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. Fig.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. Then, the photosensitive material (122), such as a photoresist, can 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 by dip coating, spray coating, or ring coating. After drying and / or baking, the photosensitive material can be subjected to exposure, such as Fig.10 As shown in step C of , 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.

[0093] exist Fig.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). Fig.10 The thickness of the patterned photosensitive material is preferably greater than the depth or height of the three-dimensional microstructure to be formed.

[0094] The metal or alloy (e.g., nickel, cobalt, chromium, copper, zinc, or alloys derived from any of the above metals) may be electroplated and / or electrolessly plated on the roller or sleeve. The plated 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, such as Fig.10 As shown in step E. 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 be less than 1%.

[0095] Alternatively, where electroplating is used to deposit the plating material (126), the thickness variation of the deposit across the surface of the roller or sleeve can be controlled by inserting a non-conductive thickness uniformer between the cathode (i.e., roller 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.

[0096] After plating, the patterned photosensitive material (125) can be stripped by a stripper (eg, 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 is acceptable. Fig.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.

[0097] Method B: Alternatively, Fig.11 As shown, three-dimensional microstructures can be formed on a flat substrate. Fig.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, slit extrusion 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 a light source.

[0098] exist Fig.11In step B, after exposure, depending on the characteristics of the photosensitive material, the exposed or unexposed areas of the photosensitive material will be removed by using a developer. After development, before step C, the substrate layer (141) with the remaining photosensitive material (142) can be baked or fully exposed. 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 may also be used.

[0099] In step D, a metal or alloy (144) (e.g., nickel, cobalt, chromium, copper, zinc, or an alloy 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. Fig.11 The thickness (h) in step D is preferably 25 to 5000 micrometers, and more preferably 25 to 1000 micrometers.

[0100] 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) with a three-dimensional structure on one side and a flat metal sheet on the other side. Precision polishing can be applied to the metal sheet (144), after which the flat shim sheet can be used directly for embossing, or it can be mounted (i.e., wound on) a roller with a three-dimensional microstructure on the outer surface to form an embossing tool. As described above, the precious metal or its alloy is finally coated on the entire surface of the embossing tool. As described above, gold or its alloy lacks reactivity and is therefore more preferred than other precious metals and alloys.

[0101] Method C: Fig.12 Another alternative method is shown in . This method is similar to Fig.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 noble metal or its alloy layer (153) is simply coated on the photosensitive material (152). As mentioned above, gold or its alloy is preferred. Therefore, in step E, after the plating material (154) is separated from the substrate (151), only the photosensitive material (152) is removed, and the gold or alloy coating (153) is retained together with the metal sheet (154) having a three-dimensional structure on one side and being flat on the other side.

[0102] Examples of components in the composition for forming the collimating layer may include, but are not limited to, thermoplastic or thermosetting materials or precursors thereof, such as multifunctional vinyls, including but not limited to acrylates, methacrylates, allyls, vinylbenzenes, vinyl ethers, multifunctional epoxides and oligomers or polymers thereof, etc. Multifunctional acrylates and oligomers thereof are often used. Combinations of multifunctional epoxides and multifunctional acrylates are also used to obtain the desired physical and mechanical properties of the collimating layer. A low Tg (glass transition temperature) binder or a cross-linkable oligomer imparting flexibility, such as polyurethane acrylates or polyester acrylates, may also be added to improve the bending resistance of the embossed anti-peeping layer.

[0103] Other examples of compositions for the alignment layer may include polar oligomers or polymer materials. Such polar oligomers or polymer materials may be selected from the group consisting of oligomers or polymers having at least one of the following groups, such as nitro (-NO2), hydroxyl (-OH), carboxyl (-COO), alkoxy (-OR, wherein R is an alkyl), halogen (e.g., fluorine, chlorine, bromine or iodine), cyano (-CN), sulfonic acid (-SO3), etc. 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 may include, but are not limited to, polyhydroxy-functional polyester acrylates (e.g., BDE1025, Bomar Specialties Co, Winsted, CT) or alkoxylated acrylates, such as ethoxylated nonylphenol acrylate (e.g., SR504, Sartomer, USA), ethoxylated trimethylolpropane triacrylate (e.g., SR9035, Sartomer, USA), or ethoxylated pentaerythritol tetraacrylate (e.g., SR494, from Sartomer, USA).

[0104] Alternatively, the collimating 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.

[0105] Creating light-reflecting surfaces

[0106] In some embodiments, the light reflecting surface is created by simply depositing a metal (e.g., aluminum, gold, silver, chromium, or alloys thereof) over the openings of the elongated cavities (22). Alternatively, a metal film may be deposited over the entire light collimating film (10), and the areas above the interstitial material between the elongated cavities (22) may be cut away, for example, using laser cutting. In advanced embodiments, as Fig.13 As shown, the light reflective surface (27) can be deposited on the substrate (16), for example, by printing onto the substrate (16) followed by dry film resist lamination or resist coating. A photoresist is then coated on the opposite side of the substrate (16), which is exposed to light through the metal reflector side. Subsequent resist development gives the desired elongated chamber (22) pattern, with the light reflective surface (27) on the bottom of the substrate (16) opposite the bottom of the elongated chamber (22).

[0107] Another embodiment includes as in Figure 8 During the stamping process, a light reflecting surface is deposited on the bottom of the elongated chamber (20) by stamp transfer from the second shim sheet (200). Fig.14 As shown, before the shim (200) enters the elongated chamber (22), the shim tip is coated with a light reflective material, which may be a curable composition. Due to the better adhesion of the light reflective material to the bottom of the elongated chamber (22), the light reflective material will be transferred from the second shim (200) to the bottom of the elongated chamber (22). Once the bottom of the elongated chamber (22) is coated with the light reflective material and optionally cured, the elongated chamber (22) is filled with a bistable electrophoretic medium (24).

[0108] Another alternative is to use the finished light collimating film (10) as a mask for in-situ photolithography. The light reflecting film on the resist is first laminated onto the substrate (16), and then exposed from the other side. Because the elongated chamber (20) is filled with absorptive electrophoretic particles (26), the shadow of the electrophoretic medium becomes a mask for the size of the elongated chamber (20). After exposure, the light reflecting material on the substrate above the interstitial material can be easily removed. The method can be used to create a light reflecting surface (27) on a first substrate (16) or a second substrate (18).

[0109] Numerous patents and applications assigned to or in the name of the Massachusetts Institute of Technology (MIT), Ink Corp., Ink California LLC, and related companies describe various techniques for encapsulated and microcell electrophoretic and other electro-optical media. Encapsulated electrophoretic media include a plurality of small capsules, each of which itself includes an inner phase containing electrophoretically movable particles in a fluid medium and a capsule wall surrounding the inner phase. Typically, the capsules themselves are held in a polymer binder to form a coherent layer between two electrodes. In a microcell electrophoretic display, the charged particles and fluid are not encapsulated in microcapsules, but are held in a plurality of cavities formed in a carrier medium (usually a polymer film).

[0110] The technologies described in these patents and applications include: (a) electrophoretic particles, fluids, and fluid additives; see, for example, U.S. Patent Nos. 7,002,728 and 7,679,814; and U.S. Patent Application Publication No. 2016 / 0170106; (b) capsules, binders, and encapsulation processes; see, for example, U.S. Patent Nos. 6,922,276 and 7,411,719; and U.S. Patent Application Publication No. 2011 / 0286081; (c) microcell structures, wall materials, and methods of forming microcells; see, for example, U.S. Patent Nos. 6,672,921 and 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; 8,891, 156; 9,279,906; 9,291,872; and 9,388,307; 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; (d) methods for filling and sealing microlocations; see, e.g., U.S. Patent No.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; 7,564,614; 7,572,491; 7,616,374; 7,684,108; 7,715,087; 7,715,088; 8,179,589; 8,361,356; 8,520,292; 8,625,188; 8,830,561; 9,081,250; and 9,346,987; 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; (e) films and subassemblies containing 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; 8,482,835; 8,786,929; 8,830,553; 8,854,721; 9,075,280; and 9,238,340; and U.S. Patent Application Publication Nos. 2007 / 0237962; 2009 / 0109519; 2009 / 0168067; 2011 / 0164301; 2014 / 0115884; and 2014 / 0340738; (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 No.2016 / 0103380 and 2016 / 0187759; (g) a method for driving a display; see, for example, U.S. Pat. No.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; 7,4 08,699; 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; 8,174,4 90; 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; and 9,412,314; and U.S. Patent Application Publication No.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 / 0322 721; 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 / 0 063333; 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; 201 4 / 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 generally involves at least one lamination operation. For example, in several patents and applications of MIT and Iinke mentioned above, a process for manufacturing an encapsulated electrophoretic display is described, wherein an encapsulated electrophoretic medium including capsules in a binder is coated on a flexible substrate, the flexible substrate includes an indium tin oxide (ITO) or similar conductive coating (which is used as one electrode of the final display) on a plastic film, and the capsule / binder coating is dried to form a coherent layer of the electrophoretic medium firmly adhered to the substrate. Separately, a backplane is prepared, which contains an array of pixel electrodes and an appropriate arrangement of conductors connecting the pixel electrodes to the drive circuit. In order to form the final display, a substrate with a capsule / binder layer thereon is laminated to the backplane using a laminating adhesive. In one embodiment, the backplane itself is flexible and is prepared by printing pixel electrodes and conductors on a plastic film or other flexible substrate. In other embodiments, both electrodes are flexible, thereby allowing the constructed electrophoretic display to be flexible. The obvious lamination technology for mass production of displays by this process is roller lamination using a laminating adhesive. Similar fabrication techniques can be used with other types of electro-optical displays. For example, microcell electrophoretic media can be laminated to a backplane or flexible electrode in much the same manner as encapsulated electrophoretic media.

[0112] U.S. Patent No. 6,982,178 describes a method of assembling solid electro-optical displays (including encapsulated electrophoretic displays) that is well suited for mass production. In essence, the patent describes a so-called "front plane laminate" ("FPL") that includes, 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 the substrate can be manually wound onto a roller of (for example) 10 inches (254 mm) diameter without permanent deformation. The term "light-transmitting" is used in the patent and refers herein to a layer so designated that transmits sufficient light to enable an observer to observe through the layer a change in the display state of the electro-optic medium, which will typically be observed through the conductive layer and the adjacent substrate (if present); in the case where the electro-optic medium displays a change in reflectivity of non-visible wavelengths, the term "light-transmitting" should of course be interpreted as referring to the transmission of the relevant non-visible wavelengths. The substrate is typically a polymer film and will typically have a thickness ranging from about 1 to about 25 mils (25 to 634 microns), preferably from 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, such as "aluminized Mylar" ("Mylar" is a registered trademark) from DuPont of 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 herein in its conventional sense, namely the integral of voltage with respect to time. However, some bistable electro-optical media act 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 acts as a voltage-to-time impulse converter or as a charge-to-impulse converter, the appropriate definition of impulse should be used.

[0115] Another complication in driving an electrophoretic display is the need for so-called "DC balance." U.S. Patent Nos. 6,531,997 and 6,504,524 discuss the problems that may 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 result in 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 include electrophoretic capsules arranged in a polymer binder that is used to form discrete capsules into a coherent layer. The continuous phase in the polymer-dispersed electrophoretic medium plays a similar role to the cell walls of the microcell medium. The Iink researchers found that the specific material used as a binder in the electrophoretic medium affects the electro-optical properties of the medium. Among the electro-optical properties of the electrophoretic medium that are affected by the choice of binder, there is the so-called "residence time dependence". As discussed in U.S. Patent No. 7,119,772 (see especially FIG. 34 and related description), in some cases, the impulse required for the transition between two specific optical states of a bistable electrophoretic display varies with the residence time of the pixel in its initial optical state, a phenomenon known as "residence time dependence" or "DTD". Obviously, it is desirable to make the DTD as small as possible because the DTD affects the difficulty of driving the display and may affect the quality of the image produced; for example, the DTD may cause the gray levels of pixels that should form a uniform gray area to be slightly different from each other, and the human eye is very sensitive to such changes. Although it is known that the choice of binder affects the DTD, heretofore the selection of an appropriate binder for any particular electrophoretic medium has been based on trial and error, with little understanding of the relationship between the DTD and the chemistry of the binder.

[0117] U.S. Patent Application Publication No. 2005 / 0107564 describes an aqueous polyurethane dispersion comprising a polyurethane polymer comprising the following reaction products: (a) an isocyanate-terminated prepolymer comprising the following reaction products: (i) at least one polyisocyanate comprising a,a,a,a-tetramethylxylene diisocyanate [scientific name 1,3-bis(1-isocyanato-1-methylethyl)benzene; hereinafter the material is 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, primary amino, secondary amino, 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; (e) water. It has been found that this polyurethane dispersion (which may be referred to hereinafter as a "TMXDI / PPO" dispersion) is 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 can maintain 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 limiting sense.

Claims

1. 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 chambers with a portion of the collimating layer between the elongated chambers, each elongated chamber having an opening; a bistable electrophoretic fluid comprising pigment particles disposed in each elongated chamber; a sealing layer comprising a light reflective material, which seals a top of at least one of the plurality of elongated chambers by spanning an opening of the elongated chamber so as to contain the bistable electrophoretic fluid within the elongated chamber; as well as a second light-transmitting electrode layer, wherein the first light-transmitting layer and the second light-transmitting layer are arranged on both sides of the collimating layer; Wherein the sealing layer provides a light reflecting surface that is aligned with the opening of each elongated chamber, and wherein the light reflecting surface does not substantially overlap with portions of the collimating layer between elongated chambers.

2. The switchable light-collimating film of claim 1, wherein: The thickness of the alignment layer is less than 500 μm.

3. The switchable light-collimating film of claim 1, wherein: The height of the elongated cavity is equal to or less than the thickness of the collimating layer, the width of the elongated cavity is between 5 μm and 150 μm, and the length of the cavity is between 200 μm and 5 mm.

4. The switchable light-collimating film of 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 thioacetylene monomer, or a vinyl ether monomer.

5. The switchable light-collimating film of claim 1, wherein: The light reflective surface includes a metal or a light reflective metal oxide.

6. The switchable light-collimating film of claim 1, wherein: The first light-transmitting electrode layer or the second light-transmitting electrode layer includes indium tin oxide.

7. The switchable light-collimating film of claim 1, wherein: The bistable electrophoretic fluid includes polymer-functionalized pigment particles and free polymer in a non-polar solvent.

8. The switchable light-collimating film of claim 7, wherein: The pigments are functionalized with polyacrylates, polystyrenes, polynaphthalenes or polydimethylsiloxanes.

9. The switchable light-collimating film of claim 7, wherein: The free polymer comprises polyisobutylene or a copolymer comprising ethylene, propylene or styrene monomers.

10. The switchable light-collimating film of claim 1, wherein: The sealing layer comprises cellulose, gelatin, polyacrylate, polyvinyl alcohol, polyethylene, poly(vinyl)acetic acid, poly(vinyl)pyrrolidone, polyurethane or copolymers of any of the above polymers.

11. The switchable light-collimating film of claim 1 , wherein: The light reflecting surface contacts the bistable electrophoretic fluid.

12. The switchable light-collimating film of claim 1, further comprising a substrate contacting the first light-transmitting electrode or the second light-transmitting electrode, wherein: The light reflecting surface contacts the substrate.

13. The switchable light-collimating film of claim 12, wherein: The substrate includes a first surface contacting the first light-transmitting electrode or the second light-transmitting electrode and an opposite surface contacting the light reflecting surface.

14. The switchable light-collimating film of claim 1 further comprising an optically clear adhesive layer.

15. The switchable light-collimating film of claim 14, further comprising a release layer adjacent to the optically clear adhesive layer.

16. The switchable light-collimating film of claim 1, wherein: The sealing layer forms the light reflecting surface.

17. A display comprising a switchable light collimating film according to any one of claims 1-16.

18. A display comprising: light source; Switchable light-collimating films, including: a first light-transmitting electrode layer, a collimating layer having a thickness of at least 20 μm and comprising a plurality of elongated chambers with a portion of the collimating layer between the elongated chambers, each elongated chamber having an opening, a bistable electrophoretic fluid comprising pigment particles disposed in each elongated chamber, a sealing layer comprising a light reflective material, which seals a top of at least one of the plurality of elongated chambers by spanning the opening so as to contain the bistable electrophoretic fluid within the elongated chamber, and A second light-transmitting electrode layer, wherein the first light-transmitting layer and the second light-transmitting layer are arranged on both sides of the collimating layer, wherein the sealing layer provides a light reflecting surface that is aligned with the opening of each elongated chamber, and wherein the light reflecting surface does not substantially overlap with portions of the collimating layer between the elongated chambers; Active matrix of thin film transistors; a liquid crystal layer; and Color filter array.

19. The display of claim 18, further comprising 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.

20. The display of claim 18, further comprising a prismatic film disposed between the light source and the switchable light-collimating film.

21. The display of claim 20 further comprising a diffuser layer between the prismatic film and the light source.

22. The display of claim 18, further comprising a touch screen layer.

23. The display according to claim 18, wherein: The light reflecting surface is arranged between the light source and the active matrix of the thin film transistors.

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