Piezoelectric electrophoretic film and display and manufacturing method thereof

Abstract

Low-voltage piezoelectric electrophoretic displays, including low-profile piezoelectric electrophoretic displays. In some embodiments, the piezoelectric material of the piezoelectric electrophoretic film can be selectively patterned with an insulating material during manufacturing. In some embodiments, the piezoelectric material of the piezoelectric electrophoretic film can be selectively patterned with cutouts, or partially coated with a conductive material on the surface opposite the electrodes. Such films have high contrast and can be used as security markers, anti-counterfeiting films, or sensors. The films are typically flexible. Some films have a thickness of less than 100 μm. Some films have a thickness of less than 50 μm. Displays formed from said films do not require an external power supply.

Description

[0001] Cross-references to related applications

[0002] This application claims priority to U.S. Provisional Application No. 63 / 616,721, filed December 31, 2023, the entire contents of which are incorporated herein by reference. Furthermore, the entire contents of any patent, published application, or other published work cited herein are incorporated herein by reference in their entirety. Invention Field

[0003] This invention relates to electrophoretic displays, and more particularly to thin piezoelectric electrophoretic displays with improved contrast and methods for manufacturing the same. Background of the Invention

[0005] An electrophoretic display (EPD) is a non-emission device based on the electrophoresis of charged pigment particles dispersed in a solvent or solvent mixture. The display typically includes two electrodes placed opposite each other, which provide an electric field to drive the movement of the charged pigment particles. One of the electrodes is usually transparent. When a voltage difference is applied between the two electrodes, the pigment particles migrate to one side or the other, resulting in the color of the pigment particles or the solvent (if colored) as seen from the viewing side. The electrophoretic fluid typically comprises a nonpolar solvent and one or more groups of charged particles. The particles may have different optical properties (color), different charges (positive or negative), different charge amounts (zeta potential), and / or different absorption properties (broad light absorption, broad light reflection, or selective absorption or selective reflection). In the presence of multiple groups of particles with opposite charge polarities, the application of an electric field can cause one group of particles to appear on the viewing surface, while other particles are driven away from the viewing surface.

[0006] Many electrophoretic displays are bistable, meaning their optical state persists even after the activation electric field is removed. Bistableness is primarily due to an induced dipole charge layer formed around the charged pigment by complex interactions between the pigment, charge control agent, and free polymer dispersed in the solvent. Bistable displays can persist in their last addressed optical state for years before being switched again by applying a new driving field.

[0007] Driving an electrophoretic display requires a power source to provide an electric field between the electrodes. The power source is typically a battery that supplies power to the electrodes via a driving circuit. One or more electrodes may be integrated into an active matrix backplane. The power source can also be, for example, a photovoltaic cell, a fuel cell, or a power source that operates using wall current. The power source can also be a piezoelectric element that generates charge through physical motion or thermal expansion, as described in U.S. Patent No. 5,930,026, which is incorporated herein by reference in its entirety. In all these examples, some type of driving circuitry is required to provide an electrical path between the power source and the electrodes, and typically, this circuitry includes control elements such as switches or transistors. In most cases, the circuitry is fairly conventional; however, it often adds size and structural constraints to the final display (i.e., it is not flexible or non-twistable).

[0008] Furthermore, for many applications, reducing the overall thickness of the display is desirable. However, the thickness of the piezoelectric material layer is typically directly related to the voltage amplitude that the piezoelectric material can generate in response to mechanical stress. That is, reducing the thickness of the piezoelectric material also reduces the magnitude of the voltage generated by the piezoelectric material under stress (and vice versa). Therefore, in order to generate a sufficiently large voltage to induce adequate movement of the charged pigment particles required to achieve acceptable contrast, conventional piezoelectric electrophoretic displays often incorporate piezoelectric material layers that are too thick, making such displays unsuitable for applications requiring durability and which are essentially unobtrusive when incorporated into thin, low-profile end products such as paper or banknotes.

[0009] Furthermore, conventional piezoelectric electrophoretic displays are typically constructed using continuous layers of piezoelectric material that generate charge outside the desired area when subjected to mechanical stress. For example, if mechanical stress is applied to an area of ​​the piezoelectric layer that is larger than the portion containing the security seal or image, the piezoelectric material in the portion outside the security seal or image will generate charge, causing charged pigment to move near those portions.

[0010] The aforementioned effects can create color gradients in the displayed image by bending a portion of the piezoelectric electrophoretic display. Therefore, the image may lack sharp edges due to lateral charge overflow or diffusion into the unbent portion of the piezoelectric electrophoretic display. These effects are similar to the blurring or crosstalk artifacts observed in electrophoretic displays with actively driven pixel arrays and can lead to blurring and other distracting visual artifacts, or make it difficult to reliably view security seals or images. Invention Overview

[0012] Therefore, applications such as safety markers, sensors, and indicators require very simple, flexible, durable, and thin electrophoretic displays. Piezoelectric electrophoretic displays that are thin enough and durable for such applications also need to provide high contrast.

[0013] Therefore, in one aspect, the subject matter disclosed herein includes a method for fabricating a piezoelectric electrophoretic display comprising a first electrode and a second electrode. The method includes forming a microcell layer. The microcell has a bottom, walls, and a top opening. The method further includes filling the microcell with an electrophoretic medium through the top opening and sealing the top opening of the filled microcell with a water-soluble polymer to form a sealing layer. The method further includes bonding a second electrode to the sealing layer. The method further includes treating a piezoelectric material film to form a piezoelectric layer comprising one or more voids in the piezoelectric material. The method further includes bonding the piezoelectric layer to the microcell layer on a surface opposite to the sealing layer and forming the first electrode by depositing a conductive material on the piezoelectric layer. The conductive material fills one or more voids in the piezoelectric material and coats the surface of the piezoelectric layer.

[0014] In some embodiments, the conductive material of the first electrode comprises poly(3,4-ethylenedioxythiophene)polystyrene sulfonate (PEDOT-PSS). In some embodiments, the conductive material of the first electrode, which fills one or more voids in the piezoelectric material, is in contact with the microcell layer. In some embodiments, the second electrode comprises a conductive material coupled to the substrate.

[0015] In some implementations, the method further includes attaching a piezoelectric electrophoretic display to a target object, which includes one of paper, banknotes, and circulating banknotes.

[0016] In some embodiments, the electrophoretic medium comprises a nonpolar fluid and charged pigment particles, which move toward or away from the piezoelectric layer when subjected to mechanical stress, and the nonpolar fluid and charged pigment particles are sealed within the microcell by a sealing layer. In some embodiments, the method of claim 1 is used, wherein the piezoelectric layer is polarized by an electric field.

[0017] On the other hand, the subject matter disclosed herein includes a method for manufacturing a piezoelectric electrophoretic display. The method includes processing a piezoelectric material film on a release film to form a piezoelectric layer comprising one or more voids in the piezoelectric material, and forming a first electrode by depositing a conductive material onto the piezoelectric layer. The conductive material fills one or more voids in the piezoelectric material and coats the surface of the piezoelectric layer. The method further includes forming a microcell layer, wherein the microcells have bottom, wall, and top openings, and filling the microcells with an electrophoretic medium through the top openings. The method further includes sealing the top openings of the filled microcells with a water-soluble polymer to form a sealing layer, and bonding a second electrode to the sealing layer. The method further includes removing the release film from the piezoelectric layer and bonding the piezoelectric layer to the microcell layer on the surface opposite the sealing layer.

[0018] In some implementations, the conductive material of the first electrode, which fills one or more voids in the piezoelectric material, is in contact with the microcell layer.

[0019] In some embodiments, the second electrode includes a conductive material coupled to the substrate. In some embodiments, the conductive material of the first electrode includes poly(3,4-ethylenedioxythiophene)polystyrene sulfonate (PEDOT-PSS).

[0020] In some implementations, the method further includes attaching a piezoelectric electrophoretic display to a target object, which includes one of paper, banknotes, and circulating banknotes.

[0021] In some embodiments, the electrophoretic medium comprises a nonpolar fluid and charged pigment particles. When the piezoelectric layer is subjected to mechanical stress, the charged pigment particles move toward or away from the piezoelectric layer, and the nonpolar fluid and charged pigment particles are sealed within the microcell by a sealing layer. In some embodiments, the piezoelectric layer is polarized by an electric field.

[0022] On the other hand, the subject matter disclosed herein includes a method for manufacturing a piezoelectric electrophoretic display. The method includes bonding a first electrode to a piezoelectric layer comprising polyvinylidene fluoride (PVDF). The method further includes forming one or more conductive segments on the surface of the piezoelectric layer opposite the first electrode. The method also includes forming a microcell layer having bottom, wall, and top openings, filling the microcells with an electrophoretic medium through the top openings, and sealing the top openings of the filled microcells with a water-soluble polymer to form a sealing layer. The method further includes bonding a second electrode to the sealing layer and bonding the piezoelectric layer and one or more conductive segments to the microcell layer on the surface opposite the sealing layer.

[0023] In some implementations, the first electrode includes a conductive material coupled to the substrate.

[0024] In some embodiments, the conductive material of the second electrode includes poly(3,4-ethylenedioxythiophene)polystyrene sulfonate (PEDOT-PSS).

[0025] In some embodiments, the method further includes attaching a piezoelectric electrophoretic display to a target object, said target object being one of paper, banknotes, and circulating banknotes. In some embodiments, the piezoelectric layer is polarized by an electric field.

[0026] In some embodiments, the thickness of one or more conductive segments is about 50-100 nm. In some embodiments, one or more conductive segments comprise poly(3,4-ethylenedioxythiophene)polystyrene sulfonate (PEDOT-PSS).

[0027] In some embodiments, the electrophoretic medium comprises a nonpolar fluid and charged pigment particles. When the piezoelectric layer is subjected to mechanical stress, the charged pigment particles move toward or away from the piezoelectric layer, and the nonpolar fluid and charged pigment particles are sealed in the microcell by a sealing layer. Brief description of the attached diagram

[0029] Further details of one or more embodiments of the subject matter described herein are set forth in the accompanying drawings and the following description. Other features, aspects, and advantages of the subject matter will become apparent from the description and drawings contained herein. The drawings are not necessarily drawn to scale, and in all drawings, elements of similar structures are generally labeled with similar reference numerals for illustrative purposes. However, the specific nature and function of elements in different embodiments may differ. Furthermore, the drawings are intended only to facilitate the description of the subject matter. The drawings do not illustrate every aspect of the described embodiments and do not limit the scope of this disclosure or the claims.

[0030] Figure 1A This is a schematic cross-sectional view of an exemplary conventional piezoelectric electrophoresis display.

[0031] Figure 1B This is a schematic cross-sectional view of another exemplary conventional piezoelectric electrophoresis display.

[0032] Figure 2 This is a schematic cross-sectional view of an exemplary conventional piezoelectric electrophoresis display under applied mechanical stress.

[0033] Figure 3 An enlarged view of a portion of a cross-section of a piezoelectric electrophoresis display according to the subject matter disclosed herein is shown.

[0034] Figure 4 Illustration Figure 3 An exemplary equivalent circuit with an enlarged cross-section is shown.

[0035] Figure 5 An enlarged view of a portion of a cross-section of a piezoelectric electrophoresis display according to the subject matter disclosed herein is shown.

[0036] Figure 6 Illustration Figure 5 An exemplary equivalent circuit with an enlarged cross-section is shown.

[0037] Figure 7A A cross-section of a piezoelectric electrophoretic display according to the subject matter disclosed herein is shown.

[0038] Figure 7B A top view of a piezoelectric electrophoresis display with a first electrode not shown is shown.

[0039] Figure 7C A top view of a piezoelectric electrophoresis display with a first electrode not shown is shown.

[0040] Figure 8A A cross-section of a piezoelectric electrophoretic display formed according to the subject matter disclosed herein is shown.

[0041] Figure 8B A cross-section of a piezoelectric electrophoretic display according to the subject matter disclosed herein is shown. Invention Details

[0043] This document discloses low-profile piezoelectric electrophoretic films and display films including low-profile piezoelectric electrophoretic films. In some embodiments, the piezoelectric material of the piezoelectric electrophoretic film can be patterned with a high-voltage electric field after the piezoelectric electrophoretic film is manufactured. This feature allows the end user to address the piezoelectric material during production using, for example, corona discharge, which can include, for example, barcodes or serial numbers, visible only when the piezoelectric electrophoretic film is operated. Other piezoelectric electrophoretic displays and films described herein include features that improve display contrast without increasing the overall thickness of the display. Such films can be used as security markers, anti-counterfeiting films, or sensors. The films are typically flexible. Some films are less than 100 μm thick. In some embodiments, the piezoelectric electrophoretic film is less than 50 μm and can be folded without breaking. Displays formed with this film do not require an external power supply.

[0044] When applied to materials or displays, the term "electro-optic" here takes its conventional meaning in the imaging field to refer to a material having a first display state and a second display state that differ in at least one optical property, which changes from its first display state to its second display state by applying an electric field to the material. While this optical property is typically color perceptible to the human eye, it can be another optical property such as transmittance, reflectivity, luminescence, or, in the case of a display intended for machine reading, pseudocolor, meaning a change in reflectivity at electromagnetic wavelengths outside the visible light range.

[0045] The terms “bistable” and “bistable” are used herein in their conventional sense to refer to a display comprising display elements having a first display state and a second display state that are different in at least one optical property, such that after either given element is driven to present its first or second display state by an addressing pulse of finite duration, the state persists for at least several times, for example, at least four times, the shortest duration of the addressing pulse required to change the state of the display element. U.S. Patent No. 7,170,670 shows that some particle-based electrophoretic displays capable of displaying grayscale are stable not only in their extreme black and white states but also in their intermediate gray states, and this is also true for some other types of electro-optical displays. This type of display is precisely called “multistable” rather than bistable, but for convenience, the term “bistable” as used herein can be used to encompass both bistable and multistable displays.

[0046] The term "grayscale" is used herein in its conventional sense within the imaging field to refer to an intermediate state between two extreme optical states of a pixel, and does not necessarily imply a black-and-white transition between these two extreme states. For example, several E Ink patents and published applications mentioned below describe electrophoretic displays where the extreme states are white and dark blue, making the intermediate "grayscale" actually a pale blue. In fact, as already mentioned, a change in optical state may not be a change in color at all. The terms "black" and "white" can be used below to refer to the two extreme optical states of a display and should be understood to generally include extreme optical states that are not strictly black and white, such as the aforementioned white and dark blue states. The term "monochrome" can be used below to refer to a driving scheme that drives pixels only to their two extreme optical states without an intermediate grayscale state.

[0047] The term "pixel" is used here in its conventional sense within the field of displays, referring to the smallest unit of a display capable of producing all the colors that the display itself can display. In full-color displays, each pixel typically consists of multiple subpixels, each capable of displaying fewer colors than the display itself can. For example, in most conventional full-color displays, each pixel consists of a red subpixel, a green subpixel, a blue subpixel, and an optional white subpixel, each capable of displaying a range of colors from black to the brightest version of its designated color.

[0048] Several types of electro-optic displays are known. One type of electro-optic display uses an electrochromic medium, such as an electrochromic medium in the form of a nanochromic film, which comprises an electrode formed at least partially of a semiconductor metal oxide and a plurality of dye molecules reversibly capable of changing color attached to the electrode; see, for example, O'Regan, B., et al., Nature 1991,353, 737; and Wood, D., Information Display, 18(3), 24 (March 2002). See also Bach, U., et al., Adv. Mater., 2002, 14(11), 845. This type of nanochromic film is also described, for example, in U.S. Patents 6,301,038; 6,870,657; and 6,950,220; this type of medium is generally also bistable.

[0049] Another type of electro-optic display is the electrowetting display developed by Philips and described in Hayes, RA, et al., “Video-Speed ​​Electronic Paper Based on Electrowetting”, Nature, 425,383-385 (2003). U.S. Patent No. 7,420,549 shows that such an electrowetting display can be fabricated to be bistable.

[0050] Electro-optic displays, a type of display that has been the subject of in-depth research and development for many years, are particle-based electrophoretic displays, in which multiple charged particles move through a fluid under the influence of an electric field. Compared with liquid crystal displays, electrophoretic displays can have attributes such as good brightness and contrast, wide viewing angle, bistable state, and low power consumption.

[0051] Electrophoretic displays typically comprise an electrophoretic material layer and at least two other layers disposed on opposite sides of the electrophoretic material, one of which is an electrode layer. In most such displays, both layers are electrode layers, and one or both of the electrode layers are patterned to define pixels of the display. For example, one electrode layer may be patterned as elongated row electrodes, and the other as elongated column electrodes extending perpendicularly to the row electrodes, with pixels defined by the intersections of the row and column electrodes. Alternatively and more commonly, one electrode layer may have the form of a single continuous electrode, and the other electrode layer may be patterned as a matrix of pixel electrodes, where each pixel electrode defines a pixel of the display. In another type of electro-optical display, intended for use with a stylus, printhead, or similar removable electrodes separate from the display, only one layer adjacent to the electrophoretic layer includes electrodes, and the layers on opposite sides of the electrophoretic layer are typically protective layers designed to prevent damage to the electrophoretic layer by the removable electrodes.

[0052] Numerous patents and applications assigned to or attributed to MIT and E Ink describe various techniques for encapsulating electrophoretic and other electro-optic media. Such encapsulated media comprise a plurality of small capsules, each containing an inner phase with particles capable of electrophoretic movement in a fluid medium, and a capsule wall surrounding the inner phase. Typically, the capsule itself is held in a polymer binder to form a coherent layer between two electrodes. The techniques described in these patents and applications include:

[0053] (a) Electrophoretic particles, fluids, and fluid additives; see, for example, U.S. Patents 7,002,728 and 7,679,814;

[0054] (b) Encapsulation, adhesives, and encapsulation methods; see, for example, U.S. Patents 6,922,276 and 7,411,719;

[0055] (c) Films and subassemblies containing electro-optic materials; see, for example, U.S. Patents 6,982,178 and 7,839,564;

[0056] (d) Backplates, adhesive layers and other auxiliary layers used in displays and methods thereof; see, for example, U.S. Patents 7,116,318 and 7,535,624;

[0057] (e) Color formation and color adjustment; see, for example, U.S. Patents 7,075,502 and 7,839,564;

[0058] (f) A method for driving a display; see, for example, U.S. Patents 7,012,600 and 7,453,445;

[0059] (g) Applications of displays; see, for example, U.S. Patents 7,312,784 and 8,009,348;

[0060] (h) Non-electrophoretic displays, as described in U.S. Patent Nos. 6,241,921; 6,950,220; 7,420,549 and 8,319,759; and U.S. Patent Application Publication No. 2012 / 0293858;

[0061] (i) Microunit structures, wall materials, and methods of forming microunits; see, for example, U.S. Patents 7,072,095 and 9,279,906; and

[0062] (j) A method for filling and sealing microcells; see, for example, U.S. Patents 7,144,942 and 7,715,088.

[0063] Many of the aforementioned patents and applications recognize that the walls surrounding discrete microcapsules in an encapsulated electrophoretic medium can be replaced by a continuous phase, thereby producing a so-called polymer-dispersed electrophoretic display, wherein the electrophoretic medium comprises a plurality of discrete droplets of electrophoretic fluid and a continuous phase of polymeric material, and the discrete droplets of electrophoretic fluid in such a polymer-dispersed electrophoretic display can be considered as capsules or microcapsules, even without a discrete membrane associated with each individual droplet; see, for example, U.S. Patent No. 6,866,760 mentioned above. Therefore, for the purposes of this application, such polymer-dispersed electrophoretic media are considered a subclass of encapsulated electrophoretic media.

[0064] A related type of electrophoretic display is the microcell electrophoresis display, also known as MICROCUP®. In a microcell electrophoresis display, charged particles and fluid are not encapsulated in microcapsules, but rather retained in multiple cavities formed within a carrier medium (typically a polymer membrane). See, for example, U.S. Patents 6,672,921 and 6,788,449, the entire contents of which are incorporated herein by reference.

[0065] Although electrophoretic media are often opaque (e.g., because in many electrophoretic media, particles essentially block visible light from passing through the display) and operate in a reflective mode, many electrophoretic displays can be made to operate in a so-called "shutter mode," where one display state is substantially opaque and the other is transparent. See, for example, U.S. Patents 5,872,552; 6,130,774; 6,144,361; 6,172,798; 6,271,823; 6,225,971; and 6,184,856. Dielectric electrophoretic displays, similar to electrophoretic displays but dependent on changes in electric field strength, can operate in a similar mode; see U.S. Patent 4,418,346. Other types of electro-optic displays may also be able to operate in a shutter mode. Electro-optic media operating in shutter mode can be used in multilayer structures for full-color displays; in such structures, at least one layer adjacent to the viewing surface of the display operates in shutter mode to expose or hide a second layer further away from the viewing surface.

[0066] Encapsulated electrophoretic displays are generally not affected by the aggregation and sedimentation failure modes of conventional electrophoretic devices and offer further advantages, such as the ability to print or coat the display on a wide variety of flexible and rigid substrates. (The term "printing" is used to include all forms of printing and coating, including but not limited to: volumetric coating, such as patch die coating, slot or extrusion coating, cascade coating, curtain coating; roll coating, such as doctor blade roll coating, forward and reverse roll coating; gravure coating; dip coating; spray coating; meniscus coating; spin coating; brush coating; air knife coating; screen printing; electrostatic printing; thermal transfer printing; inkjet printing; electrophoretic deposition (see U.S. Patent No. 7,339,715); and other similar techniques.) Therefore, the resulting display can be flexible. Furthermore, since the display medium can be printed using a variety of methods, the display can be manufactured at low cost.

[0067] The aforementioned U.S. Patent No. 6,982,178 describes a method for assembling a solid-state electro-optic display (including an encapsulated electrophoretic display) that is well-suited for mass production. Essentially, the patent describes a so-called “front panel laminate” (“FPL”) comprising, in sequence: a light-transmitting conductive layer; a solid electro-optic dielectric layer electrically in contact with the conductive layer; an adhesive layer; and a release liner. Typically, the light-transmitting conductive layer is carried on a light-transmitting substrate, which is preferably flexible, meaning that the substrate can be manually wrapped around a roller with a diameter of approximately 10 inches (254 mm) without permanent deformation. In this patent and herein, the term “light-transmitting” means that the layer so specified transmits sufficient light that an observer can observe changes in the display state of the electro-optic dielectric through the layer, changes in which would typically be viewed through the conductive layer and an adjacent substrate (if present); where the electro-optic dielectric exhibits a change in reflectivity at non-visible wavelengths, the term “light-transmitting” should, of course, be interpreted as transmission at the corresponding non-visible wavelength. The substrate is typically a polymer film and is generally in the range of about 1 to about 25 mils (25 to 634 μm) thick, preferably about 2 to about 10 mils (51 to 254 μm). The conductive layer is suitably a thin metal or metal oxide layer, such as aluminum or ITO, or it may be a conductive polymer. Poly(ethylene terephthalate) (PET) films coated with aluminum or ITO are commercially available, for example, from EI du Pont de Nemours & Company in Wilmington, Delaware, under the name "aluminized Mylar" ("Mylar" is a registered trademark), and such commercial materials can be used in front panel laminates with good results.

[0068] Assembling an electro-optic display using such a front-panel laminate can be achieved by removing the release liner from the front-panel laminate and bringing the adhesive layer into contact with the backplate while effectively adhering the adhesive layer to the backplate, thereby securing the adhesive layer, electro-optic dielectric layer, and conductive layer to the backplate. This process is well-suited for mass production because the front-panel laminate can be mass-produced, typically using roll-to-roll coating technology, and then cut into sheets of any size required for use with a specific backplate.

[0069] U.S. Patent No. 7,561,324 describes a so-called "dual release sheet," which is essentially a simplified version of the front panel laminate of the aforementioned U.S. Patent No. 6,982,178. One form of the dual release sheet includes a solid electro-optic dielectric layer sandwiched between two adhesive layers, wherein one or both adhesive layers are covered by the release sheet. Another form of the dual release sheet includes a solid electro-optic dielectric layer sandwiched between two release sheets. Both forms of dual release sheets are intended for processes generally similar to those used for assembling electro-optic displays from the described front panel laminate, but involving two separate laminations; typically, in the first lamination, the dual release sheet is laminated to the front electrode to form a front sub-assembly, and then in the second lamination, the front sub-assembly is laminated to the back panel to form the final display, although the order of these two laminations can be reversed if desired.

[0070] The subject matter presented herein relates particularly to the design of piezoelectric electrophoretic films and display structures that enable electrophoretic displays to operate without a power source (e.g., battery or wired power, photovoltaic power, etc.). This simplifies the assembly of such electrophoretic displays. In some embodiments, the piezoelectric material and the electrophoretic medium are directly laminated together. As mentioned above, the electrophoretic medium can be contained in microcells, microcapsules, or dispersed in a polymer matrix. In some embodiments, the piezoelectric material is polarized (i.e., written) with a high-voltage electric field after the piezoelectric electrophoretic film or piezoelectric electrophoretic display is generated.

[0071] Piezoelectricity is the response of the electric charge accumulated in a solid material to applied mechanical stress. Suitable materials for the subject matter disclosed herein may include polyvinylidene fluoride (PVDF), quartz (SiO2), berlinite (AlPO4), gallium orthophosphate (GaPO4), tourmaline, barium titanate (BaTiO3), lead zirconate titanate (PZT), zinc oxide (ZnO), aluminum nitride (AlN), lithium tantalate, lanthanum gallium silicate, potassium sodium tartrate, and any other known piezoelectric materials.

[0072] The piezoelectric electrophoretic membranes and piezoelectric electrophoretic displays described herein utilize piezoelectricity to drive charged pigments in the electrophoretic medium. Therefore, when the piezoelectric material coupled to the electrophoretic medium layer is manipulated or stressed (e.g., flexed, bent), a color change in the electrophoretic material at the surface is observed. For example, a voltage can be generated by bending or introducing mechanical stress onto a piece of piezoelectric material, and this voltage can be used to induce movement of the colored pigments in the electrophoretic material.

[0073] While many piezoelectric materials are crystalline, many flexible piezoelectric active polymers are known, such as polyvinylidene fluoride (PVDF) and its copolymers, polyamides, and parylene-C. Amorphous polymers, such as polyimide and polyvinylidene chloride (PVDC), belong to the category of amorphous bulk polymers. The standard procedure for manufacturing piezoelectric active films such as PVDF is to fabricate a polymer film and stretch it to generate stress and align dipoles. Stretching transforms the unpolarized α-phase region of PVDF into a polarized β-phase. For example, a strong electric field is subsequently applied to the polar regions of the β-phase. Other methods for aligning the β-phase, such as laser irradiation and strong magnetic fields, have been described in the literature. See, for example, U.S. Patent No. 9,831,417.

[0074] Piezoelectric material films such as PVDF can be melted and spin-coated onto a substrate to form a film. The film can optionally be thermally tempered or stretched prior to polarization. Suitable bulk PVDF is available from, for example, Sigma-Aldrich in bulk powder or film form. Pre-stretched piezoelectric active PVDF films are also available from, for example, PolyK Technologies (State College, PA). Such films can also have a metallized electrode coating on one side, which can also be used for piezoelectric electrophoretic films and displays, but it is difficult to use an electric field to polarize piezoelectric electrophoretic materials with a backing metal layer. Copolymers of PVDF, such as polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE), are also available from Sigma-Aldrich and PolyK. In some embodiments, films of PVDF and PVDF copolymers can be produced by preparing a concentrated solution of bulk PVDF in a compatible volatile solvent, such as dimethylformamide (DMF), and slit-coating the concentrated solution onto a suitable transfer substrate or release agent, for example, using a roll-to-roll method. The PVDF-coated substrate is then heated to remove the DMF, producing a PVDF film (e.g., less than 20 μm, less than 10 μm, less than 5 μm). By carefully controlling the thermal cycling, the resulting film can be pre-tuned to have a greater number of β-phase domains suitable for polarization.

[0075] The electrophoretic microunits discussed herein are typically formed of polymers such as acrylates, vinyl ethers, or epoxides, as detailed in, for example, U.S. Patents 6,930,818, 7,052,571, 7,616,374, 8,361,356, and 8,830,561, the entire contents of which are incorporated herein by reference. In some embodiments, the electrophoretic microunit layer may be filled with an electrophoretic medium comprising two or more types of electrophoretic particles, which typically have different electrophoretic mobilities and optical properties. The electrophoretic medium may be sealed with a sealing layer 430, preferably a water-soluble sealing layer as described in U.S. Patents 7,560,004, 7,572,491, 9,759,978, or 10,087,344, the entire contents of which are incorporated herein by reference. In some embodiments, an electrophoretic microcell layer is formed on a release liner, filled with an electrophoretic medium and sealed with a sealing layer. The filled and sealed electrophoretic microcells are then used as a substrate for producing a piezoelectric material film. The resulting structure is a thin piezoelectric electrophoretic film.

[0076] Figure 1A This is a schematic cross-sectional view of an exemplary conventional piezoelectric electrophoresis display 100a. Figure 1A As shown, the piezoelectric electrophoretic display 100a includes a layered stacked assembly, which includes a first electrode layer (e.g., electrode 181), a piezoelectric material layer (e.g., piezoelectric layer 160), an electrophoretic dielectric layer (e.g., electrophoretic layer 130), a sealing layer (e.g., sealing layer 140), and a second electrode layer (e.g., electrode 182).

[0077] Electrode layers 181 and 182 can be transparent or flexible. Suitable materials include commercially available ITO-coated PET, which can be used as a substrate for fabricating the electrode layers. In some embodiments, flexible and transparent conductive coatings including other transparent conductive oxides (TCOs) can be used, such as zinc oxide, zinc tin oxide, indium zinc oxide, aluminum zinc oxide, indium tin zirconium oxide, indium gallium oxide, indium gallium zinc oxide, or fluorinated variants of these oxides, such as fluorinated tin oxide. In some embodiments, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) is used because of its excellent flexibility and optical transparency. Although the overall conductivity is not as high as, for example, PET / ITO, PEDOT:PSS is sufficient to provide the necessary electric field to drive electrophoretic particles in the electrophoretic medium of electrophoretic layer 130.

[0078] Other materials include polymers, typically translucent polymers, doped with conductive materials such as carbon black, metal flakes, metal whiskers, carbon nanotubes, silicon nitride nanotubes, or graphene. In some cases, one or both of electrodes 181 and 182 are metal films, such as copper, silver, gold, or aluminum films or foils. Metal-coated polymer films are also suitable as electrode layers. The resistivity of the electrode layer can be 500 ohm-m or less, for example 100 ohm-m or less, for example 1 ohm-m or less, for example 0.1 ohm-m or less, for example 0.01 ohm-m or less. (For comparison, electrophoretic dielectric layers typically have a resistivity of approximately 10...) 7 Up to 10 8 The resistivity of piezoelectric materials is 10 ohm-m. 11 Up to 10 14 (The resistivity of ohm-m.)

[0079] The piezoelectric material constituting the piezoelectric layer 160 can be any of the materials listed above; however, polymers such as PVDF and its copolymers are preferred because they can be made into very thin films. The electrophoretic medium of the electrophoretic layer 130 typically comprises one or more groups of charged particles that move through a nonpolar solvent in the presence of an electric field. Figure 1A The electrophoretic medium shown comprises microunits. However, the electrophoretic medium can be contained in other structures, such as microcapsules or dispersed droplets. The electrophoretic medium can also be contained in open grooves or pores sealed within a larger flexible container.

[0080] The sealing layer 140 of the microunits in the electrophoretic layer 130 may be coated with a conductive material, such as PEDOT or one of the aforementioned materials, to form an electrode 182.

[0081] The sealing layer 140 may be a water-soluble sealing layer, which is applied to the open micro-unit structure of the electrophoretic layer 130 after filling with the desired electrophoretic medium. The sealing layer 140 may become conductive by containing a conductive material. The sealing layer 140 is typically light-transmitting or transparent.

[0082] Despite Figure 1ANot shown, but piezoelectric electrophoretic displays will often include at least one adhesive layer to bond the individual layers together when they are not formed directly on each other. As an example, ITO can be directly sputtered onto the piezoelectric layer 160 to form electrode 181. The adhesive used can be formed from polymers such as acrylic or polyurethane. In some embodiments, at least one adhesive layer is formed from polyurethane, polyurea, polycarbonate, polyamide, polyester, polycaprolactone, polyvinyl alcohol, polyether, polyvinyl acetate derivatives such as poly(ethylene-co-vinyl acetate), polyvinyl fluoride, polyvinylidene fluoride, polyvinyl butyral, polyvinylpyrrolidone, poly(2-ethyl-2-oxazoline), acrylic or methacrylic acid copolymers, maleic anhydride copolymers, vinyl ether copolymers, styrene copolymers, diene copolymers, siloxane copolymers, cellulose derivatives, gum arabic, alginate, lecithin, polymers derived from amino acids, etc. The adhesive may further include one or more low-dielectric polymers or oligomers, ionic liquids, or conductive fillers such as carbon black, metal flakes, metal whiskers, carbon nanotubes, silicon nitride nanotubes, or graphene. Adhesives that include such charged and / or conductive materials are conductive adhesives. The polymers and oligomers used in the adhesive layers may have multiple functional groups for chain extension or crosslinking during or after lamination. The adhesive layers may have approximately 10 6 ohm*cm to 10 8 ohm*cm, preferably less than 10 12 The resistivity value in ohm*cm.

[0083] Among the aforementioned polymers and oligomers, polyurethanes, polyureas, polycarbonates, polyesters, and polyamides, especially those containing functional groups, are particularly preferred because they exhibit excellent adhesive and optical properties as well as high environmental resistance. Examples of functional groups may include, but are not limited to, -OH, -SH, -NCO, -NCS, -NHR, -NRCONHR, -NRCSNHR, vinyl or epoxides and their derivatives, including cyclic derivatives. The "R" in the aforementioned functional groups can be hydrogen or an alkyl, aryl, alkylaryl, or aralkyl group with up to 20 carbon atoms, which may optionally be substituted or interrupted by N, S, O, or a halogen. "R" is preferably hydrogen, methyl, ethyl, phenyl, hydroxymethyl, hydroxyethyl, hydroxybutyl, etc. Functionalized polyurethanes, such as hydroxyl-terminated polyester polyurethanes or polyether polyurethanes, isocyanate-terminated polyester polyurethanes or polyether polyurethanes, or acrylate-terminated polyester polyurethanes or polyether polyurethanes, are particularly preferred.

[0084] In some implementations, the piezoelectric electrophoretic membrane or display includes a release liner ( Figure 1A(Not shown in the image). For example, release agents can be temporarily used to facilitate the processing of piezoelectric electrophoretic films or displays during embossing, filling, cutting, etc. In other embodiments, release agents can be used to deliver the final piezoelectric electrophoretic film or display to be adhered to the final product. In some cases, the release agent protects the functional adhesive layer that will be used to manipulate the piezoelectric electrophoretic film or display before it is placed in or on the final product. Release agents can be formed from materials selected from polyethylene terephthalate (PET), polycarbonate, polyethylene (PE), polypropylene (PP), paper, and their laminates or overlays. Release agents can also be metallized to facilitate quality control measurements and / or control static electricity during handling, transportation, and downstream bonding to the product. In some embodiments, a siloxane release coating can be applied to the release agent to improve its properties.

[0085] Although Figure 1A Not shown, but piezoelectric electrophoretic displays may also include additional edge seals and / or barrier materials to maintain a desired humidity level inside the piezoelectric electrophoretic display and to prevent leakage of, for example, nonpolar solvents or adhesives, as well as to prevent the ingress of water, dust, or gases. The barrier material can be any flexible material, typically a polymer with a negligible WVTR (water vapor transmission rate). Suitable materials include polyethylene terephthalate, polyethylene naphthalate, polycarbonate, polyimide, cycloolefins, and combinations thereof. If the piezoelectric electrophoretic membrane or piezoelectric electrophoretic display will be exposed to particularly harsh conditions, flexible glass such as WILLOW® glass (Corning, Inc.) can be used as a barrier layer. The edge seal can be a metallized foil or other barrier foil adhered to the edge of the piezoelectric electrophoretic membrane or piezoelectric electrophoretic display. The edge seal can also be formed from dispersed sealants (thermally cured, chemically cured, and / or radiation cured), polyisobutylene, or acrylate-based sealants, which may be cross-linked. In some implementations, the edge seal may be sputtered ceramic, such as alumina or indium tin oxide (ITO), or advanced ceramics such as those available from Vitex Systems, Inc. (San Jose, CA).

[0086] Figure 1B This is a schematic cross-sectional view of another exemplary conventional piezoelectric electrophoresis display 100b. The piezoelectric electrophoresis display 100b and... Figure 1A It is closely related to the piezoelectric electrophoretic display 100a, but has an alternative stack of layered components.

[0087] like Figure 1BAs shown, the piezoelectric electrophoretic display 100b includes a first electrode layer (e.g., electrode 181), an electrophoretic dielectric layer (e.g., electrophoretic layer 130), a sealing layer (e.g., sealing layer 140), a piezoelectric material layer (e.g., piezoelectric layer 160), and a second electrode layer (e.g., electrode 182).

[0088] Of course, other arrangements of stacked layered components can also be used to fabricate piezoelectric electrophoretic displays. For example, a piezoelectric electrophoretic display similar to piezoelectric electrophoretic display 100a can be configured such that the openings of the microcells in the electrophoretic layer 130 face the piezoelectric layer 160. As a further alternative, a piezoelectric electrophoretic display similar to piezoelectric electrophoretic display 100b can be configured such that the openings of the microcells in the electrophoretic layer 130 face away from the piezoelectric layer 160. Finally, as described above, piezoelectric electrophoretic displays can be constructed using electrophoretic media other than microcells such as microcapsules.

[0089] Figure 2 This is a schematic cross-sectional view of an exemplary conventional piezoelectric electrophoretic display 200 under applied mechanical stress. The piezoelectric electrophoretic display 200 has a configuration similar to that of the piezoelectric electrophoretic display 100a (…). Figure 1A Similar stacked layers, and including a first electrode layer (e.g., electrode 281), a piezoelectric material layer (e.g., piezoelectric layer 260), an electrophoretic dielectric layer, and a sealing layer (in Figure 2 Together they are depicted as a micro-unit layer 231, and a second electrode layer (e.g., electrode 282).

[0090] like Figure 2 As depicted, mechanical stress is applied to the piezoelectric electrophoretic display 200. Specifically, bending force is applied to the middle portion of the piezoelectric electrophoretic display 200. Figure 2 The left portion of the piezoelectric electrophoretic display 200, represented by part 291, and the right portion of the piezoelectric electrophoretic display 200, represented by part 292, are not subjected to mechanical stress and remain unbent.

[0091] The force applied to the piezoelectric layer 260 causes charge separation within the piezoelectric material. As indicated by the "+" and "-" symbols, charge is generated in portion 290 of the piezoelectric layer 260 in response to bending force. Because the piezoelectric material generates charge proportional to the magnitude of the mechanical stress applied per unit area, a higher charge concentration is generated near the center of portion 290, and a more dispersed amount of charge is generated towards the edges of portions 290 adjacent to portions 291 and 292.

[0092] The layer stack of the piezoelectric electrophoretic display 200 provides a conductive path between electrodes 281 and 282 for the flow of charge generated by the piezoelectric layer 260. Therefore, a voltage can be generated across the layers of the piezoelectric electrophoretic display 200, and the electric field formed between electrodes 281 and 282 passes through the microcell layer 231, causing charged pigment particles within the microcells to move according to their charge polarity. This can be used to generate a security strip with an image that remains neutral or hidden when no mechanical stress is applied to the display, but displays a security seal or image when the security strip bends and the charged ink particles move in the bent or stressed portion.

[0093] Because of the higher charge concentration near the center of portion 290, the micro-units in the center of portion 290 may be subjected to a stronger electric field. Therefore, charged pigment particles within those central micro-units may move farther and / or faster than charged pigment particles located at or near the edges of portions 290 adjacent to portions 291 and 292. Furthermore, because the layers of the electrophoretic display are continuous material layers, some of the charge generated in portion 290 flows through portions 291 and 292, potentially causing some movement of charged pigment particles in those portions. For example, if mechanical stress is applied to a region or portion of the piezoelectric layer 260 that is larger than the portion including the security seal or image, the piezoelectric material in the portion outside the security seal or image will generate a charge, which will cause the charged pigment near those portions to move.

[0094] The aforementioned effects can lead to a transitional gradient of charged pigment particles within the micro-unit layer 231. For example, an image displayed by bending a portion of the piezoelectric electrophoretic display 200 may lack sharp edges due to lateral charge overflow or diffusion into the unbent portion of the piezoelectric electrophoretic display 200. These effects are similar to the blurring or crosstalk artifacts observed in electrophoretic displays with actively driven pixel arrays.

[0095] The lower contrast provided by piezoelectric electrophoretic displays, such as conventional displays described above, may be unacceptable or undesirable for some applications. For example, some anti-counterfeiting applications require displays capable of showing images with sharp edges, so the fidelity of images displayed by security ribbons must not be blurred.

[0096] Figure 3 An enlarged view 300 of a partial cross-section of a piezoelectric electrophoretic display 301 according to the subject matter disclosed herein is shown. The stacking of the piezoelectric electrophoretic display 301 is similar to... Figure 1BThe piezoelectric electrophoretic display 100b is shown. However, for the purpose of describing the characteristics of the display, only a subset of the layers of the piezoelectric electrophoretic display 301 is shown: electrode 381, piezoelectric layer 360, electrophoretic dielectric layer (e.g., microcell 330), sealing layer 340, and second electrode 382. In the magnified view 300, the electrophoretic dielectric layer and sealing layer 340 are represented by electrophoretic layer 331.

[0097] The piezoelectric layer 360 of the piezoelectric electrophoretic display 301 is not a continuous layer or film of piezoelectric material, but rather has an electrically insulating material 361 dispersed therein. The electrically insulating material 361 has a resistivity that prevents the rapid dissipation of charge generated by any adjacent piezoelectric electrophoretic material across the layers of the piezoelectric electrophoretic display 301. In some embodiments, the electrically insulating material 361 has a resistivity of approximately 10. 8 The resistivity is approximately 10 ohms*cm. In some embodiments, the electrical insulating material 361 has a resistivity of approximately 10 ohms*cm. 2 ohm*cm to 10 14 The resistivity is measured in ohms per centimeter. Depending on the material used, electrical insulating material 361 can act as a true insulator, but it can also act as a dielectric.

[0098] Electrical insulating material 361 can be formed from, for example, silicone resin, epoxy resin, or acrylic resin. In some embodiments, electrical insulating material 361 is an insulating polymer material comprising polymethyl methacrylate as a major component. In some embodiments, electrical insulating material 361 is made of polycarbonate, polyester, polystyrene, polyimide, epoxy resin, polyisocyanate, polyamide, polyvinyl alcohol, polybutadiene, polymethyl methacrylate, copolynylon, UV-curable acrylic resin, fluoropolymer, etc.

[0099] In some embodiments, the electrically insulating material 361 is formed from the unpolarized portion of the piezoelectric material of the piezoelectric layer 360. In some embodiments, the electrically insulating material 361 is formed from the same material as the piezoelectric material of the piezoelectric layer 360 (e.g., polyvinylidene fluoride or "PVDF"), but a portion of the electrically insulating material 361 is an α phase with a zero dipole moment chain, and is therefore essentially non-piezoelectric, while the charge-generating portion of the piezoelectric material is a β phase and has significant piezoelectric properties.

[0100] In some embodiments, the electrically insulating material 361 is formed of a piezoelectric material that is thicker than the charge-generating piezoelectric material of the piezoelectric layer 360. In this case, the two piezoelectric materials will generate different charges depending on their thicknesses.

[0101] like Figure 3As shown, the piezoelectric layer 360 can be patterned alternately with the electrically insulating material 361. This allows images, shapes, and / or text to be embedded in the piezoelectric electrophoretic display 301. This can also increase the contrast of the piezoelectric electrophoretic display 301 because the potential generated near the charge-generating portion of the piezoelectric material is different from the potential generated near the electrically insulating material 361.

[0102] The enlarged view 300 includes a portion of an electrically insulating material 361 (denoted as insulating portion 362) and a portion of a charge-generating piezoelectric material of the piezoelectric layer 360 (denoted as charge-generating piezoelectric material 364). A first portion 332 of the electrophoretic layer 331 lies above the insulating portion 362, and a second portion 334 lies above the charge-generating piezoelectric material 364, as shown by dashed line 302. The first portion 332 and the second portion 334 each have a resistance based on the volume of the electrophoretic layer 331 they surround. Furthermore, the insulating portion 362 also has a resistance based on the volume and properties of the electrically insulating material 361 it surrounds. As indicated by the "+" and "-" symbols, for example, a voltage has been generated in the charge-generating piezoelectric material 364 of the piezoelectric layer 360 in response to bending or mechanical stress of the piezoelectric material.

[0103] Figure 4 Illustration Figure 3 An exemplary equivalent circuit 400 with an enlarged cross-section is shown. Figure 3 The three nodes or points shown correspond to 'A' at piezoelectric material 364, 'B' at electrode 381, and 'C' at electrode 382, ​​where charge is generated. Figure 4 The equivalent circuit 400 shows the same points. Resistor R1 corresponds to the sum of the resistances of the first portion 332 of the electrophoretic layer 331 and the insulating portion 362 of the piezoelectric layer 360. Resistor R2 corresponds to the resistance of the second portion 334 of the electrophoretic layer 331.

[0104] The piezoelectric material 364 that generates charge in the piezoelectric layer 360 is represented as a battery with voltage V. PZ This is the voltage generated by the piezoelectric material 364 that produces charge across points A and C. Resistors R1 and R2 are represented in series because the presence of a voltage source beneath a portion of the electrophoretic layer 331 effectively divides the layer into independent sections with different electrical properties (as shown by dashed line 302). For example, when a voltage V has been generated... PZ At this point, the voltage potential at point A is higher than the voltage potential at points B or C. Using a conventional current flow example, current 401 flows from point A through resistor R1 to point B, and from point B through resistor R2 to point C. Therefore, the voltage across resistor R1 is opposite in polarity to the voltage across resistor R2. In fact, the series connection of the separated portions across the electrophoretic layer produces two opposite voltages.

[0105] Therefore, manufacturing the piezoelectric electrophoretic display 300 as described above, in which the piezoelectric layer 360 and the electrically insulating material 361 are alternately patterned, provides advantages over conventional piezoelectric electrophoretic displays. For example, the electrically insulating material 361 can prevent the flow of large amounts of charge in its vicinity, thereby generating a smaller voltage potential across the piezoelectric electrophoretic display 300. This can improve the sharpness of the edges of lines and shapes that the piezoelectric electrophoretic display 300 can produce. Furthermore, the potential difference generated near the insulating portion 362 of the piezoelectric layer 360 and the charge-generating piezoelectric material 364 advantageously provides an improved means of driving pigment particles with opposite charges in opposite directions in the electrophoretic medium without the need for individually addressable pixel electrode matrices. Thus, piezoelectric electrophoretic displays can be made thin enough for applications requiring durability and to be substantially inconspicuous when incorporated into thin, low-profile end products such as paper or banknotes, while still providing high contrast between the insulating portion 362 and the charge-generating piezoelectric material 364 of the piezoelectric layer 360 due to the aforementioned effects.

[0106] Figure 5 An enlarged view 500 of a partial cross-section of a piezoelectric electrophoretic display 501 according to the subject matter disclosed herein is shown. The stacking of the piezoelectric electrophoretic display 501 is similar to... Figure 1A The piezoelectric electrophoretic display 100a is shown. However, for the purpose of describing the characteristics of the display, only a subset of the layers of the piezoelectric electrophoretic display 501 is shown: the first electrode 581, the piezoelectric layer 560, the electrophoretic dielectric layer (e.g., microcell 530), the sealing layer 540, and the second electrode 582. In the magnified view 500, the electrophoretic dielectric layer and the sealing layer 540 are represented by the electrophoretic layer 531.

[0107] The piezoelectric layer 560 of the piezoelectric electrophoretic display 501 is not a continuous layer or film of piezoelectric material, but rather has one or more voids or cutouts 562 dispersed therein, where the piezoelectric material has been cut away or otherwise removed. In some embodiments, instead of removing material from the piezoelectric layer 560, the piezoelectric layer 560 is selectively deposited onto the microcells 530, leaving gaps between portions of the piezoelectric material display cutouts 562. The deposition of the piezoelectric material can be performed using one of many methods known in the art.

[0108] like Figure 5 As shown, when electrode 581 is laminated onto piezoelectric layer 560, some portions of electrode 581 contact the piezoelectric material of piezoelectric layer 560, while other portions contact microcell 530. Depending on the thickness of the piezoelectric material, bubbles or air gaps 565 may form at the edges of the piezoelectric material wherever the conductive material of electrode 581 transitions from different surface heights. Using a thinner piezoelectric material can prevent the formation of such air gaps 565.

[0109] Similar to Figure 3 In the illustrated embodiment, the piezoelectric layer 560 can be patterned alternately with several gaps or cutouts 562. This allows images, shapes, and / or text to be embedded in the piezoelectric electrophoretic display 501. This can also increase the contrast of the piezoelectric electrophoretic display 501 because the potential generated near the piezoelectric material is different from the potential generated near the cutouts 562, as described below.

[0110] Enlarged view 500 includes a portion of the piezoelectric material of piezoelectric layer 560 and a cutout 562. A first portion 532 of electrophoretic layer 331 lies below cutout 562, and a second portion 534 lies below the piezoelectric material of piezoelectric layer 560, as shown by dashed line 502. The first portion 532 and the second portion 534 each have a resistance based on the volume of the electrophoretic layer 531 they enclose. In this embodiment, since cutout 562 removes any material from piezoelectric layer 560, there is no additional resistance. As indicated by the "+" and "-" symbols, for example, a voltage is generated in the piezoelectric material of piezoelectric layer 360 in response to bending or mechanical stress of the piezoelectric material.

[0111] Figure 6 Illustration Figure 5 An exemplary equivalent circuit 600 with an enlarged cross-section is shown. Figure 5 The three nodes or points shown, 'A' at piezoelectric layer 560, 'B' at electrode 582, and 'C' at electrode 581, correspond to... Figure 6 The equivalent circuit 600 shows the same points. Resistor R1 corresponds to the resistance of the first portion 532 of the electrophoretic layer 531. Resistor R2 corresponds to the resistance of the second portion 534 of the electrophoretic layer 531.

[0112] Piezoelectric layer 560 is represented as a battery with a voltage V. PZ This is the voltage generated by the piezoelectric material that produces charge across points A and C. Resistors R1 and R2 are represented in series because the presence of a voltage source beneath a portion of the electrophoretic layer 531 effectively divides the layer into independent sections with different electrical properties (as shown by dashed line 502). For example, when a voltage V has been generated... PZ At this point, the voltage potential at point A is higher than the voltage potential at points B or C. Using a conventional current flow example, current 601 flows from point A through resistor R2 to point B, and from point B through resistor R1 to point C. Therefore, the voltage across resistor R1 is opposite in polarity to the voltage across resistor R2. In fact, the series connection across the separated portions of electrophoretic layer 531 produces two opposite voltages.

[0113] Therefore, manufacturing the piezoelectric electrophoretic display 500 as described above, in which the piezoelectric layer 560 is patterned alternately with one or more notches 562, provides advantages over conventional piezoelectric electrophoretic displays. For example, the potential difference generated near the charge-generating piezoelectric material of the notches 562 and the piezoelectric layer 360 advantageously provides an improved means of driving pigment particles with opposite charges in opposite directions in the electrophoretic medium without the need for individually addressable pixel electrode matrices. Thus, piezoelectric electrophoretic displays can be made thin enough for applications requiring durability and to be substantially inconspicuous when incorporated into thin, low-profile end products such as paper or banknotes, while still providing high contrast and improved sharpness of lines and shape edges that the piezoelectric electrophoretic display 500 can produce due to the aforementioned effects.

[0114] Figure 7A A cross-section of a piezoelectric electrophoretic display 700 according to the subject matter disclosed herein is shown. The stacking of the piezoelectric electrophoretic display 700 is similar to... Figure 1A The piezoelectric electrophoresis display 100a shown includes a first electrode 781, a piezoelectric layer 760, an electrophoretic dielectric layer (e.g., microcell 730), a sealing layer 740, and a second electrode 782.

[0115] The piezoelectric layer 760 of the piezoelectric electrophoretic display 700 is not a continuous layer or thin film of piezoelectric material, but rather has one or more cuts 763 distributed thereon, in which the piezoelectric material has been cut away or otherwise removed. This embodiment is similar to Figure 5 The piezoelectric electrophoretic display 501 is shown, but the notches 763 can be formed on the piezoelectric layer 760 before it is laminated or otherwise adhered to the microcell 730. For example, a piezoelectric material film can be pretreated to create one or more voids or notches 763. The pretreated piezoelectric material film can then be laminated to the microcell 730. Subsequently, the pretreated piezoelectric material film can be coated with a conductive material that fills the notches 763 and creates an electrode layer 781. Alternatively, the conductive material can be deposited on the pretreated piezoelectric material film on a release liner before lamination to the microcell 730.

[0116] An exemplary process for manufacturing a piezoelectric electrophoretic display 700 will now be described. Figure 7A As shown, the piezoelectric electrophoretic display 700 includes a first electrode (e.g., first electrode 781) and a second electrode (e.g., second electrode 782). The method includes forming a layer of microcells (e.g., microcell 730), wherein the microcells have a bottom, walls, and a top opening. The method further includes filling the microcells with an electrophoretic medium through the top openings and sealing the top openings of the filled microcells with a water-soluble polymer to form a sealing layer (e.g., sealing layer 740). For example, as described above, the electrophoretic microcells can be formed from polymers such as acrylates, vinyl ethers, or epoxides.

[0117] In some embodiments, the electrophoretic microcell layer may be filled with an electrophoretic medium comprising two or more types of electrophoretic particles, which typically have different electrophoretic mobilities and optical properties. For example, the electrophoretic medium may include a nonpolar fluid and charged pigment particles, which move toward or away from the piezoelectric layer (e.g., piezoelectric layer 760) when the piezoelectric layer is subjected to mechanical stress. The electrophoretic medium may be sealed with a sealing layer (e.g., sealing layer 740), preferably a water-soluble sealing layer as described above. The nonpolar fluid and charged pigment particles are sealed within the microcell using the sealing layer.

[0118] The second electrode can be bonded to the sealing layer. For example, the sealing layer of the microcell can be coated with a conductive material, such as PEDOT or one of the aforementioned materials. In some embodiments, as described above, the second electrode includes a conductive material coupled to a suitable substrate material.

[0119] Furthermore, as described above, the method may include processing a piezoelectric material film to form a piezoelectric layer (e.g., piezoelectric layer 760), which includes one or more voids (e.g., voids or cutouts 763) in the piezoelectric material. The method may then include bonding the piezoelectric layer to a microcell layer on a surface opposite to the sealing layer. For example, a roll-to-roll process such as lamination may be used to bond the piezoelectric layer to the microcell layer. In some embodiments, the piezoelectric layer may be a layer of adhesive ( Figure 7A (Not shown in the image) is coupled to a micro-unit.

[0120] The first electrode can be formed by depositing a conductive material on a piezoelectric layer. The conductive material used to form the first electrode fills one or more voids in the piezoelectric material and coats the surface of the piezoelectric layer. Thus, the conductive material of the first electrode, which fills one or more voids in the piezoelectric material, is in contact with the microcell layer because the voids penetrate the piezoelectric material.

[0121] Piezoelectric electrophoretic displays can be integrated with target objects. For example, such as Figure 7A The piezoelectric electrophoretic display shown can be processed and adhered to a target object such as paper, banknotes, or circulating currency. In some embodiments, a hot stamping process is used to bond the piezoelectric electrophoretic display to the target object. In some embodiments, the piezoelectric layer is polarized by an electric field. In some embodiments, the electric field is provided by corona discharge.

[0122] As described above, an alternative method can be used to manufacture the piezoelectric electrophoretic display 700, wherein a piezoelectric layer is formed on a suitable release liner and processed as described above to include one or more voids in the piezoelectric material. Alternatively, a first electrode can be formed by depositing a conductive material onto the piezoelectric layer, with the conductive material filling one or more voids in the piezoelectric material and coating the surface of the piezoelectric layer. In an alternative embodiment of the method, the release liner is then removed from the piezoelectric layer, which is then bonded to a microcell layer on the surface opposite the sealing layer. In some embodiments, a roll-to-roll process is used to bond the piezoelectric layer to the microcell layer.

[0123] Figure 7B A top view of a piezoelectric electrophoresis display 700 is shown, where electrodes 781 are not shown. Figure 7B In the middle, the cut 763b is formed as a slit that extends completely from one edge of the piezoelectric layer 760 to the opposite edge. Figure 7C A top view of a piezoelectric electrophoresis display 700 is shown, where electrodes 781 are not shown. Figure 7C In the middle, the cut 763c is formed into a small hole or through hole that can be dispersed throughout the piezoelectric layer 760.

[0124] Similar to Figure 5 In the illustrated embodiment, the piezoelectric layer 760 can be patterned alternately with several notches 763. This allows images, shapes, and / or text to be embedded in the piezoelectric electrophoretic display 700. This can also increase the contrast of the piezoelectric electrophoretic display 700 because the potential generated near the piezoelectric material differs from the potential generated near the notches 763, as described below. Figures 7A-7C The described implementation scheme demonstrates the relationship with Figure 5 The same implementation scheme has the same effect, but can also prevent any problems that may occur, such as the formation of pinholes, bubbles or air gaps due to the lamination process.

[0125] Figure 8A A cross-section 801a of a piezoelectric electrophoretic display formed according to the subject matter disclosed herein is shown. Figure 8A The electrophoretic dielectric layer (e.g., microcell 830), sealing layer 840, and second electrode 882 are shown bonded together. Figure 8A A first electrode 881 is also shown applied to the piezoelectric layer 860. In this embodiment, a conductive segment 883 has been formed on the surface of the piezoelectric layer 860 opposite to the first electrode 881. For example, the conductive segment 883 may be formed from a thin layer of a conductive material such as PEDOT. In some embodiments, the thickness of the conductive segment 883 is about 50-100 nm.

[0126] like Figure 8AAs indicated by the arrows, a structure including a first electrode 881, a piezoelectric layer 860, and a conductive segment 883 is applied to the surface of the microcell 830 to form... Figure 8B The piezoelectric electrophoretic display 800 is shown. For example, a roll-to-roll lamination process can be used to form the piezoelectric electrophoretic display 800.

[0127] An exemplary process for manufacturing a piezoelectric electrophoretic display 800 is now described. The method includes bonding a first electrode (e.g., first electrode 881) to a piezoelectric layer (e.g., piezoelectric layer 860) comprising polyvinylidene fluoride (PVDF). For example, as described above, the first electrode may be formed of a conductive material deposited on a piezoelectric material film. Next, as described above, one or more conductive segments (e.g., conductive segment 883) may be formed on the surface of the piezoelectric layer opposite the first electrode. In some embodiments, the conductive segments are formed of a thin layer of a conductive material such as PEDOT and have a thickness of approximately 50-100 nm.

[0128] The method includes forming a layer of microunits (e.g., microunit 830), wherein the microunits have a bottom, walls, and a top opening. The method also includes filling the microunits with an electrophoretic medium through the top openings and sealing the top openings of the filled microunits with a water-soluble polymer to form a sealing layer (e.g., sealing layer 840). For example, as described above, the electrophoretic microunits may be formed from polymers such as acrylates, vinyl ethers, or epoxides.

[0129] In some embodiments, the electrophoretic microcell layer may be filled with an electrophoretic medium comprising two or more types of electrophoretic particles, which typically have different electrophoretic mobilities and optical properties. For example, the electrophoretic medium may include a nonpolar fluid and charged pigment particles, which move toward or away from the piezoelectric layer (e.g., piezoelectric layer 860) when the piezoelectric layer is subjected to mechanical stress. The electrophoretic medium may be sealed with a sealing layer (e.g., sealing layer 840), preferably a water-soluble sealing layer as described above. The nonpolar fluid and charged pigment particles are sealed within the microcell using the sealing layer.

[0130] A second electrode (e.g., second electrode 882) may be bonded to a sealing layer. For example, the sealing layer of the microcell may be coated with a conductive material, such as PEDOT or one of the other conductive materials described above. In some embodiments, as described above, the second electrode comprises a conductive material coupled to a suitable substrate material. The method may then include bonding a piezoelectric layer to the microcell layer on a surface opposite the sealing layer. For example, a roll-to-roll process such as lamination may be used to bond the piezoelectric layer to the microcell layer. In some embodiments, the piezoelectric layer may be an adhesive layer ( Figure 8B (Not shown in the image) is coupled to a micro-unit.

[0131] Therefore, a piezoelectric layer having conductive segments (e.g., conductive segment 883) is combined with a microcell layer such that the conductive segments are in contact with the microcell layer. Advantageously, the conductive segment 883 in the piezoelectric electrophoretic display 800 exhibits the same effect as in the piezoelectric electrophoretic displays 500 and 700, requiring no cutting or post-processing of the piezoelectric layer 860 once it is adhered to the microcell 830 (or optionally formed on a release liner). For example, in response to the charge generated by the piezoelectric material when mechanical stress is applied, the conductive segment 883 is driven to the same potential as the first electrode 881. Thus, the conductive segment 883 effectively acts as a short circuit between the first electrode 881 and the surface of the microcell 830, thereby achieving the same beneficial effects as in the piezoelectric electrophoretic displays 500 and 700. Furthermore, the thickness of the conductive segment 883 is small enough to achieve the same roughness level as the surface of the piezoelectric layer 860. Therefore, no special processing or machining is required to manufacture the piezoelectric electrophoretic display 800.

[0132] Piezoelectric electrophoretic displays can be bonded to target objects. For example, a piezoelectric electrophoretic display such as piezoelectric electrophoretic display 800 can be processed and adhered to a target object such as paper, banknotes, or circulating currency. In some embodiments, a hot stamping process is used to bond the piezoelectric electrophoretic display to the target object. In some embodiments, the piezoelectric layer is polarized by an electric field. In some embodiments, the electric field is provided by corona discharge.

[0133] Those skilled in the art will understand that the methods described herein are exemplary and not limiting. Other methods or other sequences of method steps can be used to manufacture displays having the structure and features of the piezoelectric electrophoretic displays described herein.

[0134] It will be apparent to those skilled in the art that various changes and modifications can be made to the specific embodiments of the present invention described above without departing from the scope of the invention. Therefore, the entire foregoing description should be interpreted as illustrative rather than restrictive.

[0135] This disclosure provides aspects and implementation methods as set forth in the following terms:

[0136] Clause 1: A method for manufacturing a piezoelectric electrophoretic display including a first electrode and a second electrode, the method comprising: forming a microcell layer, wherein the microcell has a bottom, a wall, and a top opening; filling the microcell with an electrophoretic medium through the top opening; sealing the top opening of the filled microcell with a water-soluble polymer to form a sealing layer; bonding the second electrode to the sealing layer; processing a piezoelectric material film to form a piezoelectric layer, the piezoelectric layer including one or more voids in the piezoelectric material; bonding the piezoelectric layer to the microcell layer on a surface opposite to the sealing layer; and forming the first electrode by depositing a conductive material onto the piezoelectric layer, wherein the conductive material fills one or more voids in the piezoelectric material and coats the surface of the piezoelectric layer.

[0137] Clause 2: A method for manufacturing a piezoelectric electrophoretic display, the method comprising: processing a piezoelectric material film on a release film to form a piezoelectric layer, the piezoelectric layer including one or more voids in the piezoelectric material; forming a first electrode by depositing a conductive material onto the piezoelectric layer, wherein the conductive material fills one or more voids in the piezoelectric material and coats a surface of the piezoelectric layer; forming a microcell layer, wherein the microcell has a bottom, a wall, and a top opening; filling the microcell with an electrophoretic medium through the top opening; sealing the top opening of the filled microcell with a water-soluble polymer to form a sealing layer; bonding a second electrode to the sealing layer; removing the release film from the piezoelectric layer; and bonding the piezoelectric layer to the microcell layer on a surface opposite to the sealing layer.

[0138] Clause 3: A method for manufacturing a piezoelectric electrophoretic display, the method comprising: bonding a first electrode to a piezoelectric layer comprising polyvinylidene fluoride (PVDF); forming one or more conductive segments on a surface of the piezoelectric layer opposite to the first electrode; forming a microcell layer, wherein the microcell has a bottom, a wall, and a top opening; filling the microcell through the top opening with an electrophoretic medium; sealing the top opening of the filled microcell with a water-soluble polymer to form a sealing layer; bonding a second electrode to the sealing layer; and bonding the piezoelectric layer and one or more conductive segments to the microcell layer on the surface opposite to the sealing layer.

[0139] Clause 4: The method of any one of Clauses 1-3, wherein the conductive material of the first electrode comprises poly(3,4-ethylenedioxythiophene)polystyrene sulfonate (PEDOT-PSS).

[0140] Clause 5: The method of any one of Clauses 1-4, wherein the second electrode comprises a conductive material coupled to the substrate.

[0141] Clause 6: The method of any one of Clauses 1-5 further includes incorporating a piezoelectric electrophoretic display to a target object, said target object being one of paper, banknotes, and circulating banknotes.

[0142] Clause 7: The method of any one of Clauses 1-6, wherein the piezoelectric layer is polarized by an electric field.

[0143] Clause 8: The method of any one of Clauses 1-7, wherein the electrophoretic medium comprises a nonpolar fluid and charged pigment particles, wherein the charged pigment particles move toward or away from the piezoelectric layer when the piezoelectric layer is subjected to mechanical stress, wherein the nonpolar fluid and charged pigment particles are sealed in a microcell by a sealing layer.

[0144] Clause 9: The method described in Clause 1 or 2, wherein the conductive material of the first electrode, which fills one or more voids in the piezoelectric material, is in contact with the microcell layer.

Claims

1. A method for manufacturing a piezoelectric electrophoretic display including a first electrode and a second electrode, the method comprising: A layer of micro-units is formed, wherein the micro-units have bottom, wall and top openings; The micro-units are filled with an electrophoretic medium through the top opening; The top opening of the filled micro-unit is sealed with a water-soluble polymer to form a sealing layer; The second electrode is bonded to the sealing layer; A piezoelectric material film is processed to form a piezoelectric layer, the piezoelectric layer comprising one or more voids in the piezoelectric material; The piezoelectric layer is bonded to the micro-unit layer on the surface opposite to the sealing layer; and A first electrode is formed by depositing a conductive material onto the piezoelectric layer, wherein the conductive material fills one or more voids in the piezoelectric material and coats the surface of the piezoelectric layer.

2. The method of claim 1, wherein the conductive material of the first electrode comprises poly(3,4-ethylenedioxythiophene)polystyrene sulfonate (PEDOT-PSS).

3. The method of claim 1, wherein the conductive material of the first electrode filling one or more voids in the piezoelectric material is in contact with the microcell layer.

4. The method of claim 1, wherein the second electrode comprises a conductive material coupled to the substrate.

5. The method of claim 1, further comprising attaching the piezoelectric electrophoretic display to a target object, the target object being one of paper, banknotes, and circulating banknotes.

6. The method of claim 1, wherein the electrophoretic medium comprises a nonpolar fluid and charged pigment particles, wherein the charged pigment particles move toward or away from the piezoelectric layer when the piezoelectric layer is subjected to mechanical stress, wherein the nonpolar fluid and charged pigment particles are sealed in the microcell by a sealing layer.

7. The method of claim 1, wherein the piezoelectric layer is polarized by an electric field.

8. A method for manufacturing a piezoelectric electrophoretic display, the method comprising: A piezoelectric material film on a release film is processed to form a piezoelectric layer, the piezoelectric layer comprising one or more voids in the piezoelectric material; A first electrode is formed by depositing a conductive material onto the piezoelectric layer, wherein the conductive material fills one or more voids in the piezoelectric material and coats the surface of the piezoelectric layer. A layer of micro-units is formed, wherein the micro-units have bottom, wall and top openings; The micro-units are filled with an electrophoretic medium through the top opening; The top opening of the filled micro-unit is sealed with a water-soluble polymer to form a sealing layer; The second electrode is bonded to the sealing layer; Remove the release film from the piezoelectric layer; and The piezoelectric layer is bonded to the microcell layer on the surface opposite to the sealing layer.

9. The method of claim 8, wherein the conductive material of the first electrode comprises poly(3,4-ethylenedioxythiophene)polystyrene sulfonate (PEDOT-PSS).

10. The method of claim 8, wherein the conductive material of the first electrode filling one or more voids in the piezoelectric material is in contact with the microcell layer.

11. The method of claim 8, wherein the second electrode comprises a conductive material coupled to the substrate.

12. The method of claim 8, further comprising incorporating a piezoelectric electrophoretic display to a target object, said target object comprising one of paper, banknotes, and circulating banknotes.

13. The method of claim 8, wherein the electrophoretic medium comprises a nonpolar fluid and charged pigment particles, wherein the charged pigment particles move toward or away from the piezoelectric layer when the piezoelectric layer is subjected to mechanical stress, wherein the nonpolar fluid and charged pigment particles are sealed in the microcell by the sealing layer.

14. The method of claim 8, wherein the piezoelectric layer is polarized by an electric field.

15. A method for manufacturing a piezoelectric electrophoretic display, the method comprising: The first electrode is bonded to a piezoelectric layer containing polyvinylidene fluoride (PVDF); One or more conductive segments are formed on the surface of the piezoelectric layer opposite to the first electrode; A layer of micro-units is formed, wherein the micro-units have bottom, wall and top openings; The micro-units are filled with an electrophoretic medium through the top opening; The top opening of the filled micro-unit is sealed with a water-soluble polymer to form a sealing layer; The second electrode is bonded to the sealing layer; and The piezoelectric layer and one or more conductive segments are bonded to a micro-unit layer on the opposite surface of the sealing layer.

16. The method of claim 15, wherein the conductive material of the first electrode comprises poly(3,4-ethylenedioxythiophene)polystyrene sulfonate (PEDOT-PSS).

17. The method of claim 15, wherein the second electrode comprises a conductive material coupled to the substrate.

18. The method of claim 15, further comprising attaching a piezoelectric electrophoretic display to a target object, said target object comprising one of paper, banknotes, and circulating banknotes.

19. The method of claim 15, wherein the piezoelectric layer is polarized by an electric field.

20. The method of claim 15, wherein the thickness of the one or more conductive segments is about 50-100 nm.

21. The method of claim 15, wherein the one or more conductive segments comprise poly(3,4-ethylenedioxythiophene)polystyrene sulfonate (PEDOT-PSS).

22. The method of claim 15, wherein the electrophoretic medium comprises a nonpolar fluid and charged pigment particles, wherein the charged pigment particles move toward or away from the piezoelectric layer when the piezoelectric layer is subjected to mechanical stress, wherein the nonpolar fluid and charged pigment particles are sealed in the microcell by the sealing layer.

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