TWI901325B - Piezo-electrophoretic films and displays, and methods for manufacturing the same - Google Patents

Abstract

Low voltage piezo-electrophoretic films and display films including low profile piezo-electrophoretic films and displays. In some embodiments, the piezoelectric material of the piezo-electrophoretic films can be selectively patterned with high-voltage electric fields during or after fabrication of the piezo-electrophoretic films. Such films have high contrast ratio and are useful as security markers, authentication films, or sensors. The films are generally flexible. Some films are less than 100 µm in thickness. Some films are less than 50 µm in thickness. Displays formed from the films do not require an external power source.

Description

Piezoelectric electrophoretic film, display and manufacturing method thereof Cross-references to related applications:

This application is a continuation-in-part of U.S. application No. 18/171,719 (Publication No. 2023-0273495), filed on February 21, 2023, which claims priority to U.S. Provisional Patent Application No. 63/314,584, filed on February 28, 2022. This application also claims priority to U.S. Provisional Application No. 63/579,375, filed on August 29, 2023, and U.S. Provisional Application No. 63/579,377, filed on August 29, 2023.

The entire disclosure of the above-mentioned application and all other applications or publications referred to below are incorporated herein by reference in their entirety.

The subject matter disclosed herein relates to electrophoretic displays, and more particularly, to thin piezoelectric electrophoretic displays with improved contrast and methods for manufacturing the same. The subject matter disclosed herein also relates to low-profile piezoelectric electrophoretic displays that can be activated or driven without a power source and methods for manufacturing the same.

An electrophoretic display (EPD) is a non-emissive device based on the electrophoresis of charged pigment particles dispersed in a solvent or solvent mixture. The display typically comprises two opposing electrodes that provide an electric field to drive the charged pigment particles into motion. One of these electrodes is typically transparent. When a voltage difference is applied between the two electrodes, the pigment particles move to one side or the other, resulting in the color of the pigment particles or the solvent (if any) being visible from the viewing side.

Many electrophoretic displays incorporate an electrophoretic fluid consisting of a nonpolar solvent and one or more charged pigment particles. These particles can have different optical properties (color), different charges (positive or negative), different charge magnitudes (zeta potentials), and/or different absorption properties (widely absorb light, widely reflect light, or selectively absorb or reflect light). In the case of multiple groups of particles with opposite charges, applying an electric field causes one pigment particle in one group to appear on the viewing surface, while another pigment particle in the other group moves away from the viewing surface.

Many electrophoretic displays are bi-stable, meaning that the display's optical state persists even after the activating electric field is removed. Bistability is primarily due to the formation of an induced dipole charge layer near the charged pigment, resulting from a complex interaction between the pigment, the charge control agent, and the free polymer dispersed in the solvent. Bistable displays can persist in their last addressed optical state for years before switching again with the application of a new driving field.

Driving an electrophoretic display requires a power source, such as a battery, to provide power to the display and/or its driver circuitry. For example, a battery can be used to power a driver IC, which in turn generates an electric field to power the display's electrodes. Alternatively, the power source can be a photovoltaic cell, a fuel cell, or a source that draws power from a wall outlet. Alternatively, the power source can be a piezoelectric element that generates an electrical 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 of these cases, some type of driver circuit is required to provide an electrical path between the power source and the electrodes. Typically, this circuit also includes a control element (e.g., a switch, transistor, etc.) and several separate components (e.g., resistors, capacitors, etc.).

In most cases, the circuitry used in traditional displays is complex but well-known to those skilled in the display technology field. However, incorporating such circuitry can limit the display's resistance to mechanical stresses, such as bending and/or twisting. Furthermore, the presence of additional components often increases the overall physical size of the fully assembled display.

Because the physical limitations imposed on displays by adding power and drive circuitry can make such displays unsuitable, there is an increasing demand for applications that reduce the overall thickness of the display. Therefore, to reduce display thickness, some electrophoretic displays utilize low-profile piezoelectric elements that generate charge in response to mechanical strain or thermal cycling. However, the thickness of the piezoelectric material layer is generally directly related to the magnitude of the voltage that the piezoelectric material can generate in response to mechanical stress. In other words, 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, to generate a voltage potential large enough to cause the charged pigment particles to move an amount sufficient to achieve acceptable contrast, conventional piezoelectric electrophoretic displays typically incorporate a layer of piezoelectric material that is too thick, making such displays unusable for applications that require them to be durable and largely unnoticeable when incorporated into thin, low-profile end display products such as paper or bank notes.

Therefore, there is a need for electrophoretic displays (EPDs) that are structurally simple, flexible, durable, and thin for applications such as security markings, sensors, and indicators. There is also a need for piezoelectric EPDs that are thin and durable enough for applications that require a thin end product while also providing high contrast.

According to one aspect of the subject matter disclosed herein, an electro-optical display may include a layer of electrophoretic material; a first conductive layer; and a piezoelectric material located between the electrophoretic material layer and the first conductive layer, the piezoelectric material overlapping a portion of the electrophoretic material layer, and a portion of the first conductive layer overlapping the remainder of the electrophoretic material.

In a first aspect, the present invention includes an electrophoretic display film less than 100 microns thick, comprising (from top to bottom) a first adhesive layer, an electrophoretic medium layer, a patterned piezoelectric layer comprising differentially polarized regions, and a flexible, light-transmitting electrode layer. In some embodiments, the electrophoretic medium layer comprises a plurality of microcapsules containing a nonpolar fluid and charged pigment particles that move toward or away from the piezoelectric layer when the piezoelectric layer is deflected, wherein the microcapsules are interconnected by a polymer adhesive. In some embodiments, the electrophoretic medium layer comprises a plurality of microcells containing a nonpolar fluid and charged pigment particles that move toward or away from the piezoelectric layer when the piezoelectric layer is deflected, wherein the nonpolar fluid and charged pigment particles are sealed within the microcells by a sealing layer. In some embodiments, the membrane is less than 50 microns thick. In some embodiments, the patterned piezoelectric layer comprises polyvinylidene fluoride (PVDF). In some embodiments, the PVDF is polarized to produce differentially polarized regions. In some embodiments, the flexible, light-transmitting electrode layer comprises a metal oxide including tin or zinc. In some embodiments, the flexible, light-transmitting electrode layer comprises poly(3,4-ethylenedioxythiophene) (PEDOT). In some embodiments, the present invention includes an electrophoretic display film assembly comprising a release sheet attached to the electrophoretic display film, wherein the release sheet is attached to a first adhesive layer. In some embodiments, there is a second adhesive layer attached to the flexible light-transmitting electrode layer, and a second release sheet attached to the second adhesive layer.

In a second aspect, the present invention includes a method for manufacturing an electrophoretic display film. The method comprises bonding a polyvinylidene fluoride (PVDF) film to a polymer film comprising acrylate, vinyl ether, or epoxy to produce a piezoelectric microcell front-driver film, bonding the piezoelectric microcell front-driver film to a flexible, light-transmitting electrode layer, bonding the light-transmitting electrode layer to a first release film via a first adhesive layer, embossing the piezoelectric microcell front-driver film to produce a microcell array, wherein the microcells have a bottom, a wall, and an upper opening, filling the microcells with an electrophoretic medium through the upper opening, and sealing the upper opening of the filled microcells with a water-soluble polymer. In some embodiments, the method further comprises applying a primer to a polymer film comprising an acrylate, vinyl ether, or epoxy, and then bonding the polymer film to the polyvinylidene fluoride (PVDF) film. In some embodiments, the method further comprises bonding the water-soluble polymer to a second release film via a second adhesive layer. In some embodiments, the method further comprises removing the first release film to produce an electrophoretic display film less than 100 microns thick. In some embodiments, the electrophoretic medium layer comprises a plurality of micelles containing a nonpolar fluid and charged pigment particles (which move toward or away from the piezoelectric layer when the piezoelectric layer is deflected), wherein the nonpolar fluid and charged pigment particles are sealed within the micelles by a sealing layer. In some embodiments, the PVDF is polarized to create differentially polarized regions. In some embodiments, the flexible, light-transmitting electrode layer comprises a metal oxide including tin or zinc. In some embodiments, the flexible, light-transmitting electrode layer comprises poly(3,4-ethylenedioxythiophene) (PEDOT). In some embodiments, the polyvinylidene fluoride film is patterned using an electric field to create differentially polarized regions. In some embodiments, the method further comprises patterning the completed electrophoretic display film using an electric field to create differentially polarized regions in the polyvinylidene fluoride film.

In a third aspect, the present invention includes a method for manufacturing an electrophoretic display film. The method includes dispersing a polyvinylidene fluoride (PVDF) solution on a first release film to produce a PVDF film having a thickness of less than 10 microns, bonding the PVDF film to a second release film with a conductive adhesive, removing the first release film, bonding a polymer film comprising acrylate, vinyl ether, or epoxy to produce a piezoelectric-micelle pre-driver film, bonding the piezoelectric-micelle pre-driver film to a flexible, light-transmitting electrode layer, bonding the light-transmitting electrode layer to the first release film with a first adhesive layer, embossing the polymer film comprising acrylate, vinyl ether, or epoxy to produce a micelle array, wherein the micelles have a bottom, a wall, and an upper opening, filling the micelles with an electrophoretic medium through the upper opening, and sealing the upper opening of the filled micelles with a water-soluble polymer. In some embodiments, the method further comprises applying a primer to a polymer film comprising an acrylate, vinyl ether, or epoxy, and then bonding the polymer film to the PVDF membrane. In some embodiments, the method further comprises bonding the water-soluble polymer to a second release film via a second adhesive layer. In some embodiments, the method further comprises removing the first release film to produce an electrophoretic display film less than 100 microns thick. In some embodiments, the electrophoretic medium layer comprises a plurality of micelles containing a nonpolar fluid and charged pigment particles (which move toward or away from the piezoelectric layer when the piezoelectric layer is deflected), wherein the nonpolar fluid and charged pigment particles are sealed within the micelles by a sealing layer. In some embodiments, the PVDF is polarized to produce differentially polarized regions. In some embodiments, the flexible, light-transmitting electrode layer comprises a metal oxide including tin or zinc. In some embodiments, the flexible, light-transmitting electrode layer comprises poly(3,4-ethylenedioxythiophene) (PEDOT). In some embodiments, the PVDF film is patterned using an electric field to create differential polarization regions. In some embodiments, the method further comprises patterning the completed electrophoretic display film using an electric field to create differential polarization regions in the PVDF film.

In a fourth aspect, an electrophoretic display film less than 100 microns thick comprises (from top to bottom) a first adhesive layer, a patterned piezoelectric layer comprising differentially polarized regions, an electrophoretic medium layer, and a flexible, light-transmitting electrode layer. In some embodiments, the electrophoretic medium layer comprises a plurality of microcapsules containing a nonpolar fluid and charged pigment particles that move toward or away from the piezoelectric layer when the piezoelectric layer is deflected, wherein the microcapsules are interconnected with a polymer adhesive. In some embodiments, the electrophoretic medium layer comprises a plurality of microcells containing a nonpolar fluid and charged pigment particles that move toward or away from the piezoelectric layer when the piezoelectric layer is deflected, wherein the nonpolar fluid and charged pigment particles are sealed within the microcells by a sealing layer. In some embodiments, the sealing layer is conductive. In some embodiments, the membrane is less than 50 microns thick. In some embodiments, the patterned piezoelectric layer comprises polyvinylidene fluoride (PVDF). In some embodiments, the PVDF is polarized to produce differentially polarized regions. In some embodiments, the flexible, light-transmitting electrode layer comprises a metal oxide including tin or zinc. In some embodiments, the flexible, light-transmitting electrode layer comprises poly(3,4-ethylenedioxythiophene) (PEDOT). In some embodiments, the present invention includes an electrophoretic display film assembly comprising a release sheet bonded to the electrophoretic display film, wherein the release sheet is bonded to a first adhesive layer. In some embodiments, the electrophoretic display film further comprises a second adhesive layer bonded to the flexible, light-transmitting electrode layer, and a second release sheet bonded to the second adhesive layer.

In a fifth aspect, the present invention includes a method for patterning a piezoelectric electrophoretic dielectric film. The method includes forming a piezoelectric electrophoretic dielectric film by bonding a film of polyvinylidene fluoride (PVDF) to a layer of electrophoretic dielectric, and patterning the piezoelectric electrophoretic dielectric film with an electric field. In some embodiments, the electric field is provided by a coma discharge. In some embodiments, the method further includes placing a conductive shield adjacent to the piezoelectric electrophoretic dielectric film before patterning the piezoelectric electrophoretic dielectric film with the coma discharge. In some embodiments, the electric field is provided by a high-voltage writing head. In some embodiments, the patterning includes forming regions of differing polarity within the PVDF. In some embodiments, the patterning produces a security mark. In some embodiments, the electrophoretic medium layer comprises a plurality of microcapsules containing a nonpolar fluid and charged pigment particles (which move toward or away from the piezoelectric layer when the piezoelectric layer is deflected), wherein the microcapsules are bonded to each other with a polymer binder. In some embodiments, the electrophoretic medium layer comprises a plurality of micelles containing a nonpolar fluid and charged pigment particles (which move toward or away from the piezoelectric layer when the piezoelectric layer is deflected), wherein the nonpolar fluid and charged pigment particles are sealed within the micelles with a sealing layer.

In a sixth aspect, the present invention includes an electrophoretic display film less than 100 microns thick, comprising (from top to bottom) an adhesive layer, an electrophoretic medium layer, a patterned piezoelectric layer comprising differentially polarized regions, and a conductive adhesive layer. In some embodiments, the electrophoretic medium layer comprises a plurality of microcapsules containing a nonpolar fluid and charged pigment particles that move toward or away from the piezoelectric layer when the piezoelectric layer is deflected, wherein the microcapsules are interconnected with a polymer adhesive. In some embodiments, the electrophoretic medium layer comprises a plurality of microcells containing a nonpolar fluid and charged pigment particles that move toward or away from the piezoelectric layer when the piezoelectric layer is deflected, wherein the nonpolar fluid and charged pigment particles are sealed within the microcells by a sealing layer. In some embodiments, the sealing layer is conductive. In some embodiments, the film is less than 50 microns thick. In some embodiments, the patterned piezoelectric layer comprises polyvinylidene fluoride (PVDF). In some embodiments, the PVDF is polarized to produce differentially polarized regions. In some embodiments, the present invention includes an electrophoretic display film assembly comprising a release sheet coupled to the electrophoretic display film, wherein the release sheet is coupled to a first adhesive layer. In some embodiments, the present invention includes an electrophoretic display film assembly comprising a release sheet coupled to an electrophoretic display film including a conductive adhesive layer, wherein the release sheet is coupled to the conductive adhesive layer.

In a seventh aspect, the present invention includes an electrophoretic display film less than 100 microns thick, which comprises (from top to bottom) an adhesive layer, a patterned piezoelectric layer comprising differentially polarized regions, an electrophoretic dielectric layer, and a conductive adhesive layer.

In an eighth aspect, the present invention includes a method for fabricating a piezoelectric electrophoretic display. The method comprises depositing a first conductive adhesive on a first substrate and depositing a piezoelectric material comprising a polyvinylidene fluoride (PVDF) solution on the first conductive adhesive to produce a piezoelectric layer having a thickness of less than 5 microns. The method also comprises applying a mask to the piezoelectric layer, wherein the mask comprises a plurality of shielding portions that shield a plurality of first regions of the piezoelectric layer and a plurality of non-shielding portions that expose a plurality of second regions of the piezoelectric layer. The method also includes polarizing the piezoelectric layer to produce a plurality of polarized portions of the piezoelectric material corresponding to the second regions of the piezoelectric layer and a plurality of unpolarized portions of the piezoelectric material corresponding to the first regions of the piezoelectric layer. The method also includes removing the mask from the piezoelectric layer and bonding the piezoelectric layer to a micelle precursor material. The method also includes embossing the micelle precursor material to produce a layer of a plurality of micelles, wherein the micelles have a bottom, a plurality of walls, and a top opening. The method also includes filling the micelles with an electrophoretic medium through the top opening, and sealing the top opening of the filled micelles with a water-soluble polymer to form a sealing layer. The method also includes depositing a second conductive adhesive on the second substrate and bonding the sealing layer to the second conductive adhesive.

In some embodiments, the method also includes coupling a polymer film comprising an acrylate, vinyl ether, or epoxide to produce the micelle precursor material. In some embodiments, the method also includes applying a primer to the micelle precursor material before bonding the piezoelectric layer to the micelle precursor material. In some embodiments, the primer comprises a thermoplastic or thermosetting material or a precursor thereof, such as polyurethane, multifunctional acrylate or methacrylate, vinylbenzene, vinyl ether, epoxide, or oligomers or polymers thereof.

In some embodiments, the method also includes activating the micelles using a vapor plasma treatment before filling the micelles with the electrophoretic medium. In some embodiments, the electrophoretic medium layer comprises a nonpolar fluid and charged pigment particles. When the piezoelectric layer is subjected to mechanical stress, the nonpolar fluid and the charged pigment particles migrate toward or away from the piezoelectric layer, wherein the nonpolar fluid and the charged pigment particles are encapsulated within the micelles having the encapsulating layer. In some embodiments, the piezoelectric layer is polarized using an electric field. In some embodiments, the electric field is provided by a coma discharge.

In some embodiments, the first substrate and the second substrate are release films.

In some embodiments, the method also includes peeling the second substrate from the second conductive adhesive and bonding the second conductive adhesive to a target object. In some embodiments, bonding the second conductive adhesive to the target object includes heat stamping the second conductive adhesive onto the target object.

In some embodiments, the method also includes peeling the first substrate from the first conductive adhesive and applying a protective coating to the remaining layers of the piezo-electrophoretic display and the target object. In some embodiments, the protective coating includes a lacquer. In some embodiments, the target object includes one of a paper, a bank note, and a money order.

In a ninth aspect, the present invention includes a method for fabricating a piezoelectric electrophoretic display. The method comprises depositing a piezoelectric material comprising a polyvinylidene fluoride (PVDF) solution onto a temporary substrate to produce a piezoelectric layer having a thickness of less than 5 microns. The method also comprises bonding the piezoelectric layer to a first substrate using a first conductive adhesive, wherein the temporary substrate is removed from the piezoelectric layer during the bonding process. The method also comprises applying a mask to the piezoelectric layer, the mask comprising a plurality of shielding portions that shield a plurality of first regions of the piezoelectric layer and a plurality of non-shielding portions that expose a plurality of second regions of the piezoelectric layer. The method also includes polarizing the piezoelectric layer to produce a plurality of polarized portions of the piezoelectric material corresponding to the second regions of the piezoelectric layer and a plurality of unpolarized portions of the piezoelectric material corresponding to the first regions of the piezoelectric layer. The method also includes removing the mask from the piezoelectric layer and depositing a second conductive adhesive onto a second substrate. The method also includes combining the second conductive adhesive with a micelle precursor material and embossing the micelle precursor material to produce a layer of a plurality of micelles, wherein the micelles have a bottom, a plurality of walls, and a top opening. The method also includes filling the micelles with an electrophoretic medium through the top opening and sealing the top openings of the filled micelles with a water-soluble polymer to form a sealing layer. The method also includes bonding the sealing layer to the piezoelectric layer.

In some embodiments, the method also includes coupling a polymer film comprising an acrylate, vinyl ether, or epoxide to produce the micelle precursor material. In some embodiments, the method also includes applying a primer to the micelle precursor material before bonding the second conductive adhesive to the micelle precursor material. In some embodiments, the method also includes activating the micelles using a vapor plasma treatment before filling the micelles with the electrophoretic medium.

In some embodiments, the electrophoretic medium layer includes a nonpolar fluid and charged pigment particles. When the piezoelectric layer is subjected to mechanical stress, the nonpolar fluid and the charged pigment particles migrate toward or away from the piezoelectric layer, wherein the nonpolar fluid and the charged pigment particles are encapsulated within the microcells encapsulated by the encapsulating layer. In some embodiments, the piezoelectric layer is polarized using an electric field. In some embodiments, the electric field is provided by a coma discharge.

In some embodiments, the first substrate and the second substrate are release films.

In some embodiments, the method also includes peeling the second substrate from the second conductive adhesive and bonding the second conductive adhesive to a target object. In some embodiments, bonding the second conductive adhesive to the target object includes heat stamping the second conductive adhesive onto the target object.

In some embodiments, the method also includes stripping the first substrate from the first conductive adhesive and applying a protective coating to the remaining layers of the piezo-electrophoretic display and the target object. In some embodiments, the protective coating includes a lacquer. In some embodiments, the target object includes one of paper, banknotes, and money orders.

According to a tenth aspect of the subject matter disclosed herein, an electro-optical display may include an electrophoretic material layer; a first conductive layer; and a piezoelectric material located between the electrophoretic material layer and the first conductive layer, the piezoelectric material overlapping a portion of the electrophoretic material layer, and a portion of the first conductive layer overlapping a remaining portion of the electrophoretic material.

In an eleventh aspect, the present invention is characterized by a method for manufacturing a piezoelectric electrophoretic display. The method includes depositing a first conductive material on a first substrate to form a first electrode, and bonding the first electrode to a first surface of the electrophoretic material layer. The method also includes depositing a piezoelectric material on a second surface of the electrophoretic material layer, wherein the piezoelectric material overlaps with a first surface region of the second surface of the electrophoretic material layer. The method also includes depositing a second conductive material to form a second electrode, wherein the second electrode is formed to overlap with all of the piezoelectric material and a second surface region of the second surface of the electrophoretic material layer.

In some embodiments, the electrophoretic material layer includes a first portion of the electrophoretic material overlapping the first surface region and a second portion of the electrophoretic material overlapping the second surface region. In some embodiments, the first portion of the electrophoretic material has a first resistance and the second portion of the electrophoretic material has a second resistance.

In some embodiments, the layer of electrophoretic material includes a first portion of the electrophoretic material having a first resistance corresponding to a first volume of the electrophoretic material overlapping the first surface area, and a second portion of the electrophoretic material having a first volume of the electrophoretic material overlapping the first surface area. In some embodiments, the value of the first resistance and the value of the second resistance are based on a ratio of the first surface area to the second surface area.

In some embodiments, applying a mechanical stress to the piezoelectric material generates a first voltage across a first portion of the electrophoretic material and a second voltage across a second portion of the electrophoretic material, wherein the first voltage and the second voltage have opposite polarities.

In some embodiments, the combining comprises: coating the first electrode with a micelle precursor material; embossing the micelle precursor material to produce a micelle layer, wherein the micelles have a bottom, walls, and a top opening; filling the micelles with an electrophoretic medium through the top opening; and sealing the top opening of the filled micelles with a water-soluble polymer to form a sealing layer.

In some embodiments, the method further includes applying a primer to the micelle precursor material before imprinting the micelle precursor material. In some embodiments, the method further includes activating the micelles by treating with a vapor plasma before filling the micelles with an electrophoretic medium. In some embodiments, the electrophoretic medium includes a nonpolar fluid and charged pigment particles that migrate toward or away from the piezoelectric material when the piezoelectric material is subjected to mechanical stress, wherein the nonpolar fluid and charged pigment particles are sealed within the micelles by a sealing layer.

In some embodiments, the method further includes applying a layer of adhesive material between the piezoelectric material and the first surface region of the second surface of the electrophoretic material layer, wherein the adhesive material layer has a resistivity between 10 ² ohm*cm and 10 ¹² ohm*cm. In some embodiments, the method further includes applying a layer of adhesive material between the piezoelectric material and the first surface region of the second surface of the electrophoretic material layer, wherein the adhesive material layer has a resistivity that is at least one order of magnitude greater than that of the first and second electrodes.

In some embodiments, the method further includes depositing a dielectric layer before depositing the second conductive material, wherein the dielectric layer is formed to overlap all of the piezoelectric material and a second surface region of the second surface of the electrophoretic layer. The second electrode is formed to overlap the entire dielectric layer. In some embodiments, the dielectric layer has a resistivity between 10 ² ohm*cm and 10 ¹² ohm*cm. In some embodiments, the resistivity of the dielectric layer is at least one order of magnitude greater than that of the first electrode and the second electrode.

In some embodiments, the method further includes printing one or more images onto at least one of the first electrode and the second electrode. In some embodiments, the method further includes attaching the piezoelectric display to an object selected from the group consisting of paper, banknotes, and money orders.

100: Piezoelectric electrophoretic display

110: First region of piezoelectric material

120: Second region of piezoelectric material

210: Piezoelectric materials

220: Base material

230: High voltage coma discharge

240: Conductive shield

260: Differential polarization zone

270: Differential polarization zone

320: Base material

340: Conductive shield

360: Single piezoelectric material film area

370: Second region of piezoelectric material film

405: Thin piezoelectric electrophoretic dielectric film

410: Piezoelectric materials

420: Electrophoresis micelles

423: Electrophoretic particles

425: Electrophoresis medium

427: Electrophoretic particles

430: Sealing layer

460: Differential Polarization Zone

470: Differential Polarization Zone

501: Piezoelectric electrophoretic film

502: Piezoelectric electrophoretic film

503: Piezoelectric electrophoretic film

504: Piezoelectric electrophoretic film

510: Release

520: Release adhesive

530: Micelles

535: Primer

540: Sealing layer

550: Adhesive

560: Piezoelectric layer

570: Conductive adhesive

580: Flexible electrode

601: Piezoelectric electrophoretic display

602: Piezoelectric electrophoretic display

670: Second conductive adhesive

680: Second flexible electrode

710, 720, 730, 740, 750, 760, 770: Steps

801: Piezoelectric electrophoretic film

901: Piezoelectric electrophoretic film

910: Release

920: Adhesive

930: Micelles

935: Primer layer

940: Piezoelectric material, sealing layer

960: Piezoelectric film

980:Electrode layer

990: Electrophoresis medium, microcapsule layer

995: Adhesive

1001: Piezoelectric electrophoretic display

1002: Piezoelectric electrophoretic display

1003: Piezoelectric electrophoretic display

1080: Second electrode layer

1110, 1120, 1130, 1140, 1145, 1150, 1160: Steps

1201: Piezoelectric electrophoretic film

1202: Piezoelectric electrophoretic display

1210: Release

1220: Adhesive

1235: Primer

1240: Sealing layer

1250: Adhesive

1255: Carrier substrate

1260: Piezoelectric film

1280: Electrode

1285: Second electrode

1301: Piezoelectric electrophoretic film

1302: Piezoelectric electrophoretic display

1400: Methods

1410, 1420, 1430, 1440, 1450, 1460, 1470, 1480: Steps

1501, 1502, 1503, 1504, 1505, 1506: Cross-sections

1530: Micelles

1533: High-voltage coma discharge

1535: Sealing layer

1540: Mask

1542: Shelter

1544: Non-shielded area

1550: Electrode

1555: Base Material

1560: Piezoelectric layer

1562: Unpolarized Division

1564: Polarization Division

1585: Electrode

1586: Base Material

1588: Target

1589: Protective coating

1600: Enlarged image

1601: Piezoelectric electrophoretic display

1602: Dashed Line

1631: Electrophoretic layer

1632: Part 1

1634: Part 2

1700: Equivalent circuit

1701: Current

1800: Methods

1810, 1820, 1830, 1840, 1850, 1860, 1870, 1880: Steps

1901, 1902, 1903, 1904, 1905, 1906, 1907: Cross-sections

1930: Micelles

1933: High-voltage coma discharge

1935: Sealing layer

1940: Mask

1942: Shelter

1944: Unsheltered Division

1950: Electrode

1955: Base Material

1960: Piezoelectric layer

1962: Unpolarized Ministry

1964: Ministry of Polarization

1965: Temporary substrate

1985: Electrode

1986: Base Material

1988: Target

2000: Piezoelectric electrophoretic display

2002: Piezoelectric Materials

2004: Electrophoretic material layer

2006, 2008: Electrode

2122: Dashed Line

2132: Part 1

2134: Part 2

2200: Equivalent circuit

2201: Current

2300: Piezoelectric electrophoretic display

2302: Piezoelectric Materials

2304: Electrophoretic material layer

2308: Electrode

2320: Piezoelectric Materials

2321: Surface area

2330: Dielectric layer

A, B, C: nodes or points

R ₁ ,R ₂ :Resistors

V _PZ : Voltage

Figure 1A shows a side view of a piezoelectric electrophoretic display film according to the present invention, which includes a star-shaped differentially polarized region. It shows three exemplary positions from the side: a convex portion, a neutral portion, and a concave portion. The total thickness of the piezoelectric electrophoretic display film can be less than 100 microns, for example, less than 50 microns, or even less than 25 microns. Figure 1B shows a top view of a piezoelectric electrophoretic display film according to the present invention, which includes a star-shaped differentially polarized region. It shows three exemplary positions from the top: a convex portion, a neutral portion, and a concave portion. When the piezoelectric electrophoretic display film is deflected, the differentially polarized regions cause oppositely charged particles to appear on the viewing surface. Figure 2A shows an exemplary piezoelectric material layer on a substrate. Figure 2B illustrates a method for creating differentially polarized regions within a piezoelectric material layer using a strong electric field from a coma discharge. Moving the piezoelectric material closer to or farther from the discharge allows spatial control of the polarization amount. Figure 2C illustrates another method for creating differentially polarized regions within a piezoelectric material layer using a strong electric field from a coma discharge. The piezoelectric material is patterned using a conductive mask to produce differential polarization regions; Figure 2D describes the polarization (poling) pattern that can be obtained using the method of Figures 2B and 2C; Figure 3A describes a side view of a piezoelectric film polarized in the A direction; Figure 3B describes a top view of a piezoelectric film polarized in the A direction; Figure 3C describes a side view of a piezoelectric film polarized in the G direction using a conductive mask; Figure 3D describes a top view of a piezoelectric film polarized in the G direction using a conductive mask; Figure 4A shows a sample piezoelectric-microcell pre-driver film layer on a substrate; Figure 4B illustrates a method of using a strong electric field of coma discharge to produce differential polarization regions in a piezoelectric material layer of a piezoelectric-microcell pre-driver film. Moving the piezoelectric-microcell pre-driver film closer to or farther from the discharge can spatially vary the polarization. Figure 4C illustrates a method for creating differentially polarized regions within the piezoelectric material layer of the piezoelectric-microcell pre-driver film using the high electric field of a coma discharge. The piezoelectric material of the piezoelectric-microcell front driver film is patterned using a conductive mask to produce differential polarization regions; FIG4D describes the polarization (poling) pattern that can be obtained in the piezoelectric-microcell front driver film using the method of FIG3B and FIG3C; FIG5A is a schematic cross-sectional view of an embodiment of a piezoelectric electrophoretic film; FIG5B is a schematic cross-sectional view of an embodiment of a piezoelectric electrophoretic film; FIG5C is a schematic cross-sectional view of an embodiment of a piezoelectric electrophoretic film; FIG5D is a schematic cross-sectional view of an embodiment of a piezoelectric electrophoretic film FIG6A is a schematic cross-sectional view of an embodiment of a piezoelectric electrophoretic display; FIG6B is a schematic cross-sectional view of an embodiment of a piezoelectric electrophoretic display; FIG7 details a method for manufacturing a piezoelectric electrophoretic film or (optionally) a display; FIG8A is a schematic cross-sectional view of an embodiment of a piezoelectric electrophoretic film; FIG8B is a schematic cross-sectional view of an embodiment of a piezoelectric electrophoretic film; FIG9A is a schematic cross-sectional view of an embodiment of a piezoelectric electrophoretic film; FIG9B is a schematic cross-sectional view of an embodiment of a piezoelectric electrophoretic film. FIG10A is a schematic cross-sectional view of an embodiment of a piezoelectric electrophoretic display; FIG10B is a schematic cross-sectional view of an embodiment of a piezoelectric electrophoretic display; FIG10C is a schematic cross-sectional view of an embodiment of a piezoelectric electrophoretic display; FIG11 details a method for manufacturing a low-profile piezoelectric electrophoretic film; FIG12A is a schematic cross-sectional view of a piezoelectric electrophoretic film manufactured by the method shown in FIG11; FIG12B is a schematic cross-sectional view of a piezoelectric electrophoretic display manufactured by the method shown in FIG11. FIG13A is a schematic cross-sectional view of an alternative piezoelectric electrophoretic film manufactured by the method shown in FIG11; FIG13B is a schematic cross-sectional view of an alternative piezoelectric electrophoretic display manufactured by the method shown in FIG11; FIG14 is a flow chart detailing the steps of a method for manufacturing a high-contrast piezoelectric electrophoretic film and display; FIG15A is a schematic cross-sectional view of the piezoelectric electrophoretic film at step 1440 of the method shown in FIG14; FIG15B is a schematic cross-sectional view of the piezoelectric electrophoretic film after completing step 1440 of the method shown in FIG14. FIG15C is a schematic cross-sectional view of the piezoelectric electrophoretic film after completing step 1450 of the method shown in FIG14; FIG15D is a schematic cross-sectional view of the piezoelectric electrophoretic film after completing step 1470 of the method shown in FIG14; FIG15E is a cross-sectional view of the piezoelectric electrophoretic film combined with a target after completing step 1480 of the method shown in FIG14; FIG15F is a cross-sectional view of the piezoelectric electrophoretic film combined with a target and coated with a protective coating after completing step 1480 of the method shown in FIG14; FIG16 shows FIG17 shows an example equivalent circuit of the enlarged cross section of FIG16 ; FIG18 is a flow chart detailing the steps of a method for creating a high contrast piezoelectric electrophoretic film and a display; FIG19A is a schematic cross-sectional view of the piezoelectric electrophoretic film at step 1810 of the method shown in FIG18 ; FIG19B is a schematic cross-sectional view of the piezoelectric electrophoretic film at step 1830 of the method shown in FIG18 ; FIG19C is a schematic cross-sectional view of the piezoelectric electrophoretic film after completing step 1840 of the method shown in FIG18 Schematic cross-sectional view of a piezoelectric electrophoretic film; Figure 19D is a schematic cross-sectional view of the piezoelectric electrophoretic film after completing steps 1850 and 1860 of the method shown in Figure 18; Figure 19E is a schematic cross-sectional view of the piezoelectric electrophoretic film after completing step 1870 of the method shown in Figure 18; Figure 19F is a cross-sectional view of the piezoelectric electrophoretic film bonded to a target according to the method shown in Figure 18; Figure 19G is a cross-sectional view of the piezoelectric electrophoretic film bonded to a target and coated with a protective coating after completing step 1880 of the method shown in Figure 18; FIG20 is a schematic cross-sectional view of an exemplary piezoelectric electrophoretic display according to the subject matter disclosed herein; FIG21A is a schematic cross-sectional view illustrating additional features of a piezoelectric electrophoretic display according to the subject matter disclosed herein; FIG21B is a perspective view illustrating additional features of a piezoelectric electrophoretic display according to the subject matter disclosed herein; FIG22 illustrates an exemplary equivalent circuit of a piezoelectric electrophoretic display according to the subject matter disclosed herein; and FIG23 is a schematic cross-sectional view of an exemplary piezoelectric electrophoretic display according to the subject matter disclosed herein.

The present invention discloses low-profile piezoelectric electrophoretic films and displays and methods for making such films and displays. 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 at the point of production, such as with a corona discharge, which can include a barcode or serial number that is only visible when the piezoelectric electrophoretic film is manipulated. The low-profile piezoelectric electrophoretic films and displays described below can also achieve a high contrast ratio. The films and displays described herein are generally flexible and can be used as security markers, authentication films, or sensors. The films are typically flexible. Some films have a thickness of less than 100 microns. In some embodiments, the piezoelectric electrophoretic film is less than 50 microns and can be folded without breaking. Displays formed according to the subject matter disclosed herein do not require an external power source.

The term "electro-optic," as applied to materials or displays, is used herein in its conventional sense in the imaging arts to refer to a material having first and second display states with at least one optical property that differs, the material changing from the first to the second state in response to the application of an electric field. While this optical property is typically color perceptible to the human eye, it may also be other optical properties such as optical transmittance, reflectance, brightness, or, in the case of displays intended for machine reading, pseudo-color such as variations in reflectance at electromagnetic wavelengths outside the visible range.

The terms "bi-state" and "bi-stable" are used herein in their commonly understood sense in the art to refer to a display comprising display elements having first and second display states differing in at least one optical property, such that after any particular element has been driven to assume its first or second display state by an address pulse of finite duration, that state persists after termination of the address pulse for at least several times, for example, at least four times, the shortest address pulse duration required to change the state of the display element. U.S. Patent No. 7,170,670 demonstrates that some particle-based electrophoretic displays capable of grayscale are stable not only in their extreme black and white states but also in intermediate gray states, as are some other types of electro-optical displays. This type of display is more properly called "multi-stable" rather than bi-stable, although for convenience the term "bi-stable" will be used here to cover both bi-stable and multi-stable displays.

The term "gray state" is used herein in its conventional sense in imaging technology to refer to a state intermediate between the two extreme optical states of a pixel, and does not necessarily imply a black-to-white transition between the two extreme states. For example, many of the E Ink patents and published applications referenced below describe electrophoretic displays whose extreme states are white and dark blue, making the intermediate "gray state" actually pale blue. In fact, as mentioned, a change in optical state need not necessarily be a change in color. The terms "black" and "white" may be used below to refer to the two extreme optical states of a display, and it should be understood that these terms generally include extreme optical states that are not strictly black and white, such as the white and dark blue states mentioned above. The term "monochrome" may be used below to refer to displays or driving schemes in which pixels are driven only to their two extreme optical states, with no intermediate gray states.

The term "pixel" is used here in its conventional sense in display technology, referring to the smallest unit of a display capable of producing all the colors the display itself can display. In a full-color display, each pixel is generally composed of multiple sub-pixels, each of which can display fewer than the full range of colors the display itself can display. For example, in most conventional full-color displays, each pixel is composed of a red sub-pixel, a green sub-pixel, a blue sub-pixel, and optionally a white sub-pixel, and each sub-pixel can display a range of colors from black to the brightest version of its specific color.

Various types of electro-optical displays are known. One type of electro-optical display uses an electrochromic medium, such as an electrochromic medium in the form of a nanochromic film, which includes an electrode formed at least in part of a semiconducting metal oxide and a plurality of reversibly color-changing dye molecules 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 in, for example, U.S. Patents Nos. 6,301,038, 6,870,657, and 6,950,220. This type of medium is also generally bi-stable.

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

One type of electro-optical display is the particle-based electrophoretic display (EPD), which has been the subject of intensive research and development for many years. In this method, multiple charged particles are moved through a fluid under the influence of an electric field. Compared to liquid crystal displays (LCDs), EPDs offer excellent brightness and contrast, wide viewing angles, bi-stability, and low power consumption.

Electrophoretic displays typically comprise a layer of electrophoretic material and at least two other layers arranged on opposite sides of the electrophoretic material, one of 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 the display's pixels. For example, one electrode layer may be patterned into elongated column electrodes, and the other into elongated row electrodes arranged at right angles to the column electrodes, with the pixels being defined by the intersection of the row and column electrodes. Alternatively, and more commonly, one electrode layer may be in the form of a single continuous electrode, and the other electrode layer may be patterned into a matrix of pixel electrodes, each of which defines a pixel of the display. In another type of electrophoretic display intended for use with a stylus, a print head or similar movable electrode is separate from the display. Only one of the layers adjacent to the electrophoretic layer contains the electrode. The layer on the opposite side of the electrophoretic layer is typically a protective layer intended to prevent the movable electrode from damaging the electrophoretic layer.

Numerous patents and applications assigned to or in the name of the Massachusetts Institute of Technology (MIT) and E Ink Corporation describe various technologies for encapsulating electrophoretic and other electro-optical media. These encapsulated media comprise numerous small capsules, each of which contains an inner phase containing electrophoretically mobile particles in a fluid medium and a capsule wall surrounding the inner phase. Typically, the capsules are held in a polymeric binder, forming a coherent layer between two electrodes. 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; (b) capsules, adhesives, and packaging methods; see, for example, U.S. Patent Nos. 6,922,276 and 7,411,719; (c) films and subassemblies containing electro-optical materials; see, for example, U.S. Patent Nos. 6,982,178 and 7,839,564; (d) backplanes, adhesive layers, and other auxiliary layers and methods for displays; see, for example, U.S. Patent Nos. 7,116,318 and 7,535,624; (e) color formation and color adjustment; see, for example, U.S. Patent Nos. 7,075,502 and 7,839,564; (f) driving (g) Display methods; see, for example, U.S. Patent Nos. 7,012,600 and 7,453,445; (h) Non-electrophoretic displays, such as those disclosed in U.S. Patent Nos. 6,241,921, 6,950,220, 7,420,549, and 8,319,348; ,759, and described in U.S. Patent Application Publication No. 2012/0293858; (i) micelle structures, wall materials, and methods for forming micelles; see, for example, U.S. Patent Nos. 7,072,095 and 9,279,906; and (j) methods for filling and sealing micelles; see, for example, U.S. Patent Nos. 7,144,942 and 7,715,088.

Many of the aforementioned patents and applications consider that the walls surrounding isolated microcapsules in an encapsulated electrophoretic medium can be replaced by a continuous phase, thereby producing a so-called polymer-dispersed electrophoretic display (PDED). The electrophoretic medium comprises a plurality of isolated droplets of electrophoretic fluid and a continuous phase of polymeric material. The isolated droplets of electrophoretic fluid within such a PDED can be considered capsules or microcapsules, even though there are no separate capsule membranes binding the individual droplets; see, for example, the aforementioned U.S. Patent No. 6,866,760. Therefore, for the purposes of this application, such PDED media are considered a subspecies of encapsulated electrophoretic media.

A related type of electrophoretic display is the so-called "microcellular electrophoretic display," also known as MICROCUP®. In a microcellular electrophoretic display, charged particles and fluids are not encapsulated within microcapsules but rather retained within a plurality of cavities formed within a carrier medium (typically a polymer film). See, for example, U.S. Patent Nos. 6,672,921 and 6,788,449, both of which are incorporated herein by reference in their entirety.

Although electrophoretic media are often opaque (for example, because in many electrophoretic media, the particles substantially block visible light from passing through the display) and operate in a reflective mode, many types of electrophoretic displays can be operated in a so-called "shutter mode," in which one display state is substantially opaque and the other is transmissive. 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. Dielectrophoretic displays, which are similar to electrophoretic displays but rely on variations in electric field strength, can operate in a similar mode; see U.S. Patent 4,418,346. Other types of electro-optical displays can also operate in a shutter mode. Electro-optical media operating in shutter mode can be used in multi-layer structures for full-color displays; in this structure, at least one layer adjacent to the display's viewing surface is operated in shutter mode, while a second layer further from the viewing surface is exposed or concealed.

Packaged EPDs generally do not suffer from the clustering and sedimentation failure modes of conventional EPDs and offer further advantages, such as the ability to print or coat the displays onto a wide variety of flexible and rigid substrates. (The use of the word "printing" is intended to include all forms of printing and coating, including but not limited to: front-metered coating, such as sheet die coating, slot or extrusion coating, slide or string coating, curtain coating; roll coating, such as doctor blade roll coating, reverse roll coating; gravure coating; dip coating; spray coating; bend coating; rotary coating; brush coating; air knife coating; screen printing; electrostatic printing; thermal printing; inkjet printing; electrophoretic deposition (see U.S. Patent No. 7,339,715); and other similar technologies.) Therefore, the resulting display can be flexible. Furthermore, because display media can be printed using a variety of methods, the display itself can be manufactured inexpensively.

The aforementioned U.S. Patent No. 6,982,178 describes a method for assembling solid-state electro-optical displays (including packaged electrophoretic displays) that is highly suitable for mass production. Essentially, the patent describes a so-called "front plate layer" ("FPL") that comprises, in sequence, a light-transmitting electrically conductive layer, a solid electro-optic medium electrically contacting the conductive layer, an adhesive layer, and a release sheet. Typically, the light-transmitting electrically conductive layer is supported by a light-transmitting substrate, which is preferably flexible, such as one that can be manually wound around a roll having a diameter of, for example, 10 inches (254 mm) without permanent deformation. The term "light-transmissive" is used in this patent and means that the layer is so designed as to transmit light sufficient to enable an observer to see through the layer and observe the change in the displayed state of the electro-optical medium, which is usually through the electrically conductive layer and the adjacent substrate (if any); in the case where the electro-optical medium displays a change in reflectivity at non-visible wavelengths, the term "light-transmissive" should of course be interpreted as referring to transmission of the relevant non-visible wavelengths. The substrate is typically a polymeric film and typically has a thickness ranging from about 1 to about 25 mils (25 to 634 microns), preferably about 2 to about 10 mils (51 to 254 microns). The electrically conductive layer is conveniently a thin metal or metal oxide layer such as aluminum or ITO, or can be a conductive polymer. Poly(ethylene terephthalate) (PET) films coated with aluminum or ITO are commercially available, for example, from E.I. du Pont de Nemours & Company of Wilmington, Delaware, as "Aluminized Mylar" ("Mylar" is a registered trademark), and this commercial material can be used in the front laminate with good results.

Electro-optical displays assembled using this front-panel laminate are assembled by removing the release sheet from the front-panel laminate and contacting the adhesive layer with the backplane under conditions effective to cause the adhesive layer to adhere to the backplane, thereby securing the adhesive layer, electro-optical dielectric layer, and conductive layer to the backplane. This method is highly suitable for high-volume production because the front-panel laminate can be manufactured in large quantities (typically using roll-to-roll coating technology) and then cut into sheets of any size required for a given backplane.

U.S. Patent No. 7,561,324 describes so-called "double-sided release sheets," which are essentially simplified versions of the front-panel laminates described in the aforementioned U.S. Patent No. 6,982,178. One form of double-sided release sheet comprises a layer of a solid electro-optical medium sandwiched between two adhesive layers, one or both of which are covered by the release sheet. Another form of double-sided release sheet comprises a layer of a solid electro-optical medium sandwiched between two release sheets. Both forms of double-sided release film are intended for use in methods generally similar to those described for assembling electro-optical displays from front-panel laminates, but involving two separate laminations. Typically, a double-sided release sheet is laminated to the front electrode in a first lamination pass to form the front assembly, and then the front assembly is laminated to the backplane in a second lamination pass to form the final display, although the order of these two laminations can be reversed if desired.

The subject matter presented herein relates to the structural design and manufacturing process of piezoelectric electrophoretic films and displays that do not require a power source (e.g., a battery, wired power source, photovoltaic power source, etc.) to operate the display. Consequently, the assembly process is simplified, and the thickness of such displays is significantly thinner than that of conventional piezoelectric electrophoretic displays.

Piezoelectricity is the accumulation of electrical charge in a solid material in response to applied mechanical stress. Materials suitable for the subject matter disclosed herein may include polyvinylidene fluoride (PVDF), quartz (SiO ₂ ), aluminum phosphate (AlPO ₄ ), gallium orthophosphate (GaPO ₄ ), calcite, barium titanium oxide (BaTiO ₃ ), lead zirconate titanium oxide (PZT), zinc oxide (ZnO), aluminum nitride (AlN), lithium tantalum, gallium vanadium silicate, potassium sodium tartrate, and any other known piezoelectric materials.

The piezoelectric electrophoretic films and piezoelectric electrophoretic displays described herein use piezoelectricity to drive charged pigment particles of an electrophoretic medium toward one of the display electrodes. Thus, when an electrophoretic medium layer is attached, manipulation or physical strain of the piezoelectric material can cause the color of the electrophoretic material at the viewing surface to change. For example, by bending or introducing mechanical stress into a sheet of piezoelectric material, a voltage can be generated across the electrophoretic medium, and this voltage can be used to cause the color pigment particles of the electrophoretic medium to move. If only portions of an electrophoretic medium layer are attached to a piezoelectric material, or if differentially polarized regions are created in the piezoelectric material, high-contrast patterns can be produced using an electrophoretic medium with two types of oppositely charged pigments, as shown in Figures 1A and 1B. The term "contrast ratio" or "CR" as used herein for electro-optical displays (e.g., electrophoretic displays) is defined as the ratio of the brightness of the brightest color (white) to the darkest color (black) that the display can produce. High contrast is generally a desirable characteristic of electro-optical displays.

Figures 1A and 1B illustrate side and top views of an exemplary piezoelectric electrophoretic display 100 in accordance with the subject matter disclosed herein. In this embodiment, a piezoelectric material is layered onto an electrophoretic medium layer (discussed below) and includes one or more electrodes to provide an appropriate electric field to cause electrophoretic particles to travel toward (or away from) a viewing surface. In the embodiment shown in Figures 1A and 1B, a second region 120 of the piezoelectric material of the piezoelectric electrophoretic display 100 is polarized in an opposite direction from the first region 110. Thus, when the piezoelectric electrophoretic display 100 is manipulated from a neutral state (position 2) to a first (position 1) or second (position 3) optical state, the first and second regions (110, 120) exhibit different colors in the two regions. When the electrophoretic medium has black and white oppositely charged particle groups, a high-contrast image is formed, as shown, for example, in FIG1B . Because the first and second regions (110, 120) of the piezoelectric material can be polarized to provide good resolution (as discussed below), a variety of images/information can be encoded and "appear" when the piezoelectric electrophoretic display 100 is operated. For example, a security ribbon in a neutral state can be made to appear as a gray stripe, but when the security ribbon is bent, it displays a security symbol, such as the star shown in FIG1B . Of course, the security symbol may include a barcode, numbers, text, a phone number and URL, a QR code, a photo, a halftone image, or a logo.

In principle, a piezoelectric material (and optionally an adjacent electrophoretic material) can be polarized with a local strong electric field, as shown in Figures 2A-3D. It is known that piezoelectric materials (especially films) can be stimulated to move between polarization states with various external stresses, such as mechanical stretching, heat, electromagnetic fields, and applied forces. The piezoelectric effect is related to the generation of electric dipole moments in solids. The dipole density or polarization (P) is equivalent to the dipole moment per volume unit cell, usually measured in C/m². The generated dipole density P is a specific vector field (i.e., differential polarization) for a particular region of the material. Similar to magnets, dipoles that are close to each other tend to align in the region (Weiss domains). When first generated, the domains are usually randomly oriented. However, using various multi-step methods, the domains can be aligned to produce locally differentially polarized regions. Methods for aligning these regions are known as polarization.

While many piezoelectric materials are crystalline, several flexible piezoelectrically active polymers are known, such as polyvinylidene fluoride (PVDF) and its copolymers, polyamides, and parylene-C. Non-crystalline polymers, such as polyimides and polyvinylidene chloride (PVDC), are amorphous bulk polymers. The standard procedure for fabricating piezoelectrically active films such as polyvinylidene fluoride (PVDF) is to form the polymer film and stretch it to induce stress and align the polar dipoles. Stretching transforms the unpolarized α-phase regions of PVDF into the polarized β-phase. A subsequent stimulant, such as a strong electric field, is introduced into the polar regions of the β-phase. Other methods for aligning the β-phase have been described in the literature, such as laser irradiation and strong magnetic fields. See, for example, U.S. Patent No. 9,831,417. If the stimuli can achieve sufficiently high resolution, the poles can be used to generate visible patterns, as depicted, for example, in Figures 1A and 1B. In some embodiments, the electric field is applied at elevated temperatures, although this is not always necessary. In particular, for very thin piezoelectric films, for example, less than 20 microns, such as less than 10 microns or less than 5 microns, high temperatures are not required to polarize the film, provided the electric field is sufficiently strong. In the case of PVDF, an additional benefit is that the film is also optically transparent, so it can be coupled between the viewing surface and the electrophoretic medium, or the electrophoretic medium can be layered between the piezoelectric film and the viewing surface.

An exemplary method for polarizing a thin film of piezoelectric material is described in Figures 2A-2D. A thin film of piezoelectric material 210 (such as PVDF) can be melted and spin-coated on a substrate 220 to form a thin film. The film can be optionally heat-conditioned or stretched before polarization. Suitable monolithic PVDF is available from, for example, Sigma-Aldrich as a monolithic powder or as a film. Pre-stretched piezoelectric active PVDF membranes are also available from, for example, PolyK Technologies (State College, Pennsylvania). This membrane can also be obtained from a coating with a metallized electrode on one side, which can also be used in piezoelectric electrophoretic films and displays, however, it is difficult to polarize piezoelectric electrophoretic films with supporting metal layers using an electric field. PVDF copolymers, such as polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE), are also available from Sigma-Aldrich and PolyK. In some embodiments, thin 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 seam-coating the concentrated solution onto a suitable transfer substrate or release sheet (e.g., using a roll-to-roll process). The PVDF-coated substrate is then heated to drive off the DMF, yielding a thin PVDF film (e.g., less than 20 microns, such as less than 10 microns, less than 5 microns). Careful control of the thermal cycle can pre-condition the resulting film to have a greater number of polarizable β-phase domains.

As shown in Figures 2B and 2C, a thin film of piezoelectric material 210 can be polarized with a spatially focused high-voltage coma discharge 230. Suitable coma discharge equipment is available, for example, from Simco-Ion (Alameda, California). This device can generate local 10-50 kV fields, such as 30 kV fields, such as 20 kV fields, which can be brought within a few microns of the piezoelectric material to be polarized. Spatial focusing can be achieved by manipulating the electric field and/or gas flow, which focuses/manipulates the flow of ions emitted from the coma discharge. As shown in Figure 2B, the high-voltage coma discharge 230 can be moved in three dimensions to create differential polarization regions, that is, to pattern the piezoelectric material 210. Alternatively, the piezoelectric material 210 can be mounted on an XYZ stage and the film wafer brought into controlled proximity with the high-voltage corona discharge 230. In an alternative embodiment, a conductive shield 240 can be used to protect areas of the piezoelectric material 210 from the high-voltage corona discharge 230, as shown in FIG2C . The conductive shield can be made of, for example, conductive stainless steel or other conductive materials that can withstand proximity to a corona discharge. Alternative shields made of charge-absorbing or charge-blocking materials (such as glass, plastic, or rubber) can also be used. When a high-voltage corona discharge 230 is moved over the thin film of piezoelectric material 210, the thin film of piezoelectric material 210 is polarized only in the areas of the piezoelectric material 210 that are not covered by the conductive cover 240. Furthermore, the polarity of the high-voltage corona discharge 230 can be reversed, so that some areas are polarized in a first direction, some areas are polarized in a second direction, and some areas are randomly polarized or unpolarized. See also Figures 3A-3D.

Using the techniques shown in Figures 2B and 2C, a thin film of piezoelectric material 210 having differentially polarized regions P1 _and P2 is directly fabricated, with P1 and P2 being shown as 260 and 270 in Figure _2D . The differentially polarized regions 260 and 270 do not necessarily have opposite polarities of the same magnitude, however, this arrangement often provides better contrast when using _a two _- particle electrophoretic medium in conjunction with a thin film of piezoelectric material 210. For example, as shown in Figure 2D, a first region 260 can be polarized toward the viewer, while a second region 270 can be polarized away from the viewer. This technique is further described in Figures 3A-3D, which show how a single thin film region 360 of piezoelectric material deposited on a substrate 320 can be polarized to have an out-of-page polarization vector, as shown in Figure 3B. Therefore, when the piezoelectric material film is manipulated (flexed), it preferentially drives one polarity of the electrophoretic particles toward the viewing surface. As shown in Figure 3C, the second region 370 of the piezoelectric material film can be polarized in different directions, with or without the addition of a conductive shield 340, to generate some patterned combinations of polarities and magnitudes as required by the application. As shown in Figure 3D, some parts of the region 370 are polarized toward the viewing surface, but there is a shadow created by the conductive shield 340. Therefore, when the piezoelectric material is manipulated (flexed), it preferentially drives one polarity of the electrophoretic particles toward the viewing surface, except for the areas where the polarization has been shielded, which will remain in the neutral color stage, thereby generating a pattern, such as a security mark.

Figures 2A-3D describe various techniques that can be used to create differential polarization regions in a thin film of piezoelectric material 210. These same techniques can also be used to create differential polarization regions in a thin piezoelectric electrophoretic dielectric film 405, as described in Figures 4A-4D. As shown in Figure 4A, a thin film of piezoelectric material 410 can be bonded to a layer of electrophoretic microcells 420 to create the piezoelectric electrophoretic dielectric film 405. The thin film of piezoelectric material 410 can be bonded to a layer of electrophoretic microcells 420 with an adhesive layer (not shown), or the thin film of piezoelectric material 410 can be spin-coated directly onto a layer of electrophoretic microcells 420, as discussed above with respect to Figure 2A. Electrophoretic micelles 420 are typically formed from polymers, such as acrylates, vinyl ethers, or epoxies, as described in detail in, for example, U.S. Patent Nos. 6,930,818, 7,052,571, 7,616,374, 8,361,356, and 8,830,561, all of which are incorporated herein by reference. In some embodiments, the layer of electrophoretic micelles 420 can be filled with an electrophoretic medium 425, which includes two or more electrophoretic particles 423 and 427, typically having different electrophoretic mobilities and optical properties. The electrophoretic medium 425 can be sealed with a sealing layer 430, preferably a water-soluble sealing layer such as described in U.S. Patent Nos. 7,560,004, 7,572,491, 9,759,978, or 10,087,344, all of which are incorporated herein by reference. In some embodiments, a layer of electrophoretic micelles 420 is fabricated on a release sheet, filled with the electrophoretic medium 425, and sealed with a sealing layer 430. The filled and sealed electrophoretic micelles 420 are then used as a substrate for fabricating a thin film of piezoelectric material 410. The resulting structure is a thin piezoelectric electrophoretic medium film 405. In other embodiments, a thin film of piezoelectric material 410 is laminated onto an acrylate, vinyl ether, or epoxy film, which serves as a front driver for electrophoretic micelles 420. The combined thin film of piezoelectric material 410 and front driver material is then embossed onto the front driver side (discussed below), followed by filling with electrophoretic medium 425 and sealing with sealing layer 430, thereby fabricating a thin piezoelectric electrophoretic dielectric film 405. In still other embodiments (not shown in Figures 4A-4D), a complex microcell front plate laminate of the type described in U.S. Patent No. 7,158,282 and commercially available from E Ink Corporation can be used as a substrate for the thin film of piezoelectric material 410 (which can be polarized as described below). Obviously, when using a front-panel laminate material, the final structure also includes a conductive layer, which is generally light-transmissive. The front-panel laminate can be oriented so that the light-transmissive electrode layer contacts the thin film of piezoelectric material 410, or the front-panel laminate can be flipped so that the sealing layer contacts the thin film of piezoelectric material 410.

Once the thin piezoelectric electrophoretic dielectric film 405 has been fabricated, the thin film of piezoelectric material 410 can be addressed, as described above with respect to Figures 2A-3D . That is, the thin film of piezoelectric material 410 can be polarized by a spatially focused high-voltage coma discharge 230, as shown in Figure 4B , for example, by mounting the thin piezoelectric electrophoretic dielectric film 405 on an XYZ stage and bringing the film wafer into controlled proximity with the high-voltage coma discharge 230. In an alternative embodiment, a conductive shield 240 can be used to protect areas of the thin piezoelectric electrophoretic dielectric film 405 from the high-voltage coma discharge 230, as shown in Figure 4C . As discussed with respect to Figures 2A-3D, the polarity of the high-voltage corona discharge 230 can be reversed so that some regions are polarized in a first direction, some regions are polarized in a _second direction, and some regions are randomly polarized or unpolarized. As shown in Figure 2D above, polarizing _the thin film of piezoelectric material 410 in the thin piezoelectric electrophoretic dielectric film 405 creates differentially polarized regions P1 and P2 , as shown by 460 and 470 in Figure 4D. The key point is that because the thin piezoelectric electrophoretic dielectric film 405 can be manufactured before polarization, it is possible for the end customer to control the final step of manufacturing the desired polarization design in the thin piezoelectric electrophoretic dielectric film 405. Therefore, if the final product includes a security mark or serial number, it can be applied after the final product has been completed and authenticated. For example, a U.S. Treasury Department $100 bill could be printed with a serial number in metallic ink, while a security ribbon containing a thin piezoelectric electrophoretic dielectric film 405 could be polarized to produce an authentication code corresponding to the serial number. This feature eliminates many logistical issues and associated costs, as it eliminates the need to match specific products with pre-made security marks further down the supply chain.

The above technology can be used to obtain a wide variety of thin piezoelectric electrophoretic films as described in the figure below.

As shown in Figures 5A-6B, 8A-10C, and 12A-13B, a piezoelectric electrophoretic film or piezoelectric electrophoretic display comprises a layered stack of components (including a thin piezoelectric film) and a layer of an electrophoretic medium. The piezoelectric material can be any of the materials listed above, but polymers (such as PVDF and its copolymers) are preferred because they can be made into very thin films. The electrophoretic medium generally comprises a group of one or more charged particles that move through a non-polar solvent in the presence of an electric field. The electrophoretic medium is generally contained in, for example, microcapsules, micelles, or dispersed droplets. The electrophoretic medium can also be contained in an open tank or well, which is sealed in a larger flexible container. The piezoelectric electrophoretic films and piezoelectric electrophoretic displays exemplified herein can be made quite thin, e.g., 100 microns thick or less, e.g., 70 microns thick or less, e.g., 50 microns thick or less, e.g., 35 microns thick or less, e.g., 20 microns thick or less, e.g., 10 microns thick or less. Such thin materials can bend without cracking or leaking and are unnoticeable when incorporated into a final product, such as paper or banknotes. Furthermore, many piezoelectric electrophoretic films or piezoelectric electrophoretic displays include layers that are both light-transmissive and/or sufficiently thin to be light-transmissive, thus allowing the piezoelectric electrophoretic response to be visible from both above and below. In such piezoelectric electrophoretic films or piezoelectric electrophoretic displays, while a first image is visible from the top surface, e.g., position 1 in FIG. 1B , the bottom surface typically displays a negative image, e.g., position 3 in FIG. 1B . However, when the electrophoretic medium incorporates more than two types of particles, the top and bottom portions may not show a reverse image due to the mixed particle state on one of the two surfaces.

Piezoelectric electrophoretic films or piezoelectric electrophoretic displays often include at least one electrode layer, which may be light-transmitting and which may be flexible. Suitable materials include commercially available ITO-coated PET, which may be used as a substrate for fabrication. In some other embodiments, flexible and transparent conductive coatings including other transparent conductive oxides (TCOs) may 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 fluorine-doped tin oxide. Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) is used in many of the embodiments described herein because it has excellent bending properties and is optically transparent. Although the overall conductivity is not as high as, for example, PET/ITO, PEDOT:PSS is sufficient to provide the electric field required to drive the electrophoretic particles in the electrophoretic medium. Other materials include polymers doped with conductive materials (such as carbon black, metal chips, metal whiskers, carbon nanotubes, silicon nitride nanotubes, or graphene), generally light-transmitting polymers. In some cases, the electrode layer is a metal film, such as copper, silver, gold, or aluminum film or foil. Metal-coated polymer films are also suitable as electrode layers. The resistance of the electrode layer can be 500 ohm-meters (ohm-m) or less, such as 100 ohm-meters or less, such as 1 ohm-meter or less, such as 0.1 ohm-meter or less, such as 0.01 ohm-meter or less. (For comparison, the resistance of electrophoretic dielectric layers is typically around ^10⁷ to ^10⁸ ohm-meters, and the resistance of piezoelectric materials is ^10⁻¹¹ to ^10⁻¹４ ohm-meters.)

Piezoelectric electrophoretic films or piezoelectric electrophoretic displays often include at least one adhesive layer formed of a polymer, such as acrylic or polyurethane, 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, polyvinyl pyrrolidone, poly(2-ethyl-2- The adhesive may also include one or more low-k dielectric polymers or oligomers, ionic liquids, or conductive fillers (e.g., carbon black, metal shavings, metal whiskers, carbon nanotubes, silicon nitride nanotubes, or graphene). Adhesives that include such charged and/or conductive materials are considered conductive adhesives. The polymers and oligomers used in the adhesive layer may have functional groups for chain extension or crosslinking during or after the deposition process. The resistivity of the adhesive layer is approximately 10 ⁶ ohm*cm to 10 ⁸ ohm*cm, preferably less than 10 ¹² ohm*cm.

Among the aforementioned polymers and oligomers, polyurethanes, polyureas, polycarbonates, polyesters, and polyamides are particularly preferred due to their excellent adhesion, optical properties, and high environmental resistance, especially those containing functional groups. Examples of such functional groups include, but are not limited to, -OH, -SH, -NCO, -NCS, -NHR, -NRCONHR, -NRCSNHR, vinyl groups, or epoxides and their derivatives, including cyclic derivatives. "R" in these functional groups can be hydrogen, or an alkyl, aryl, alkylaryl, or arylalkyl group having up to 20 carbon atoms. Such alkyl, aryl, alkylaryl, or arylalkyl groups may be optionally substituted or interrupted by N, S, O, or a halogen. "R" is preferably hydrogen, methyl, ethyl, phenyl, hydroxymethyl, hydroxyethyl, or hydroxybutyl. Particularly preferred are 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.

In many embodiments, a piezoelectric electrophoretic film or display often includes a release sheet. The release sheet can be used temporarily to facilitate handling of the piezoelectric electrophoretic film or display, such as during embossing, filling, cutting, etc. In other embodiments, the release sheet can be used to transport the final piezoelectric electrophoretic film or display to be adhered to the final product. In some cases, the release sheet is used to manipulate the functional adhesive layer of the piezoelectric electrophoretic film or display before the piezoelectric electrophoretic film or display is deployed in the final product. The release sheet can be formed from a material selected from the group consisting of polyethylene terephthalate (PET), polycarbonate, polyethylene (PE), polypropylene (PP), paper, and laminates or overlays thereof. The release sheet can also be metallized to facilitate quality control measurements and/or to control static charges during handling, shipping, and downstream incorporation into the product. In some embodiments, a silicone release coating can be applied to the release sheet to improve release properties.

Although not shown in Figures 5A-6B, 8A-10C, and 12A-13B, the piezoelectric electrophoretic film or display may also include additional edge sealants and/or barrier materials to maintain a desired humidity level within the piezoelectric electrophoretic film or display and to prevent leakage of, for example, non-polar solvents or adhesives, and to prevent the ingress of water, dust, or gases. The barrier material can be any flexible material, typically a polymer with a negligible water vapor transmission rate (WVTR). Suitable materials include polyethylene terephthalate, polyethylene naphthalate, polycarbonate, polyimide, cyclic olefins, and combinations thereof. If the piezoelectric electrophoretic film or piezoelectric electrophoretic display will be exposed to particularly harsh conditions, a flexible glass such as WILLOW® Glass (Corning, Inc.) can be used as a barrier layer. The edge sealant can be a metallized foil or other barrier foil adhered to the edge of the piezoelectric electrophoretic film or piezoelectric electrophoretic display. The edge sealant can also be formed from a dispensed sealant (thermal, chemical, and/or radiation-cured), polyisobutylene, or an acrylate-based sealant, which can be crosslinked. In some embodiments, the edge sealant can be a sputter-coated ceramic such as aluminum oxide or indium tin oxide, or advanced ceramics such as those available from Vitex Systems, Inc. (San Jose, California).

The layers of the piezoelectric electrophoretic film 501-504 are typically arranged/laminated in an order that produces optimal performance for the final application. As shown, for example, in FIG5A , the piezoelectric electrophoretic film 501 can be prepared by disposing a micelle precursor material on a release film 510 including a release adhesive 520. The micelle precursor is then embossed or lithographically processed to produce an array of micelles 530. The micelles 530 can be cured thermally or with electromagnetic radiation, such as UV light. The micelles 530 can then be filled with an electrophoretic medium and sealed with a sealing layer 540, as discussed above with respect to FIG4A . (It should be understood that the cells 530 adjacent to the sealing layer 540 are filled with an electrophoretic medium consisting of charged particles in a nonpolar solvent, even though the electrophoretic medium is not shown in subsequent figures.) The piezoelectric layer 560 is laminated to the sealing layer 540 using an adhesive 550 (typically an optically transparent adhesive formed from one of the materials listed above). Finally, the flexible electrode 580 is bonded to the piezoelectric electrophoretic film using a conductive adhesive 570. This piezoelectric electrophoretic film 501 can subsequently be manipulated by processing the release die 510 until the stack outside of the release die 510 is secured to the final product. In a piezoelectric electrophoretic film 501, the piezoelectric layer 560 is typically polarized before the flexible electrode 580 is attached to the piezoelectric electrophoretic film to create differentially polarized regions. In some embodiments, the flexible electrode 580 and the conductive adhesive 570 can be replaced with a thin layer of transparent conductive oxide, such as ITO. The ITO can be sputter-coated directly onto the piezoelectric layer 560.

A closely related but alternative stack is shown in Figures 5B-5D. In Figure 5B, a piezoelectric electrophoretic film 502 is fabricated, wherein a piezoelectric layer 560 is formed on a separate release film 510 prior to fabrication. For example, the piezoelectric layer 560 can be a pre-stretched PVDF film that has been polarized to produce a security pattern. The piezoelectric layer 560 is then attached to a sealed microcell layer 530, which is already attached to a flexible electrode 580. Notably, in the piezoelectric electrophoretic film 502, the opening of the microcell layer 530 faces away from the piezoelectric layer 560, which facilitates good bonding between the microcell layer 530 and the piezoelectric layer 560. This bonding can be improved by introducing a primer 535 to improve the adhesion of the piezoelectric layer 560 to the micelle material (typically a polymer comprising an acrylate, vinyl ether, or epoxy). Primer 535 can be a polar oligomeric or polymeric material, such as a polyhydroxy-functional polyester acrylate (e.g., BOMAR® BDE 1025 from Dymax), or an alkoxylated acrylate, such as ethoxylated nonylphenol acrylate (e.g., SR504 from Sartomer), ethoxylated trihydroxymethylpropane triacrylate (e.g., SR9035 from Sartomer), or ethoxylated pentaerythritol tetraacrylate (e.g., SR494 from Sartomer). Examples of polar polymers suitable for primer 535 include solvent urethane polymers, such as Irostic® polymers.

Of course, the stack can also be constructed so that the openings of the microcell layer 530 face the piezoelectric layer 560, as in the piezoelectric electrophoretic film 504 depicted in FIG5D . As shown in FIG5C , another alternative is to arrange the piezoelectric electrophoretic film 503 so that the openings of the microcell layer 530 face away from the piezoelectric layer 560, but the piezoelectric layer 560 is directly connected to the flexible electrode 580.

By adding a second flexible electrode 680 in place of the release layer in Figures 5A-5D, the piezoelectric electrophoretic films (501, 502, 503, 504) shown in Figures 5A-5D can be transformed into piezoelectric electrophoretic displays (601, 602). Piezoelectric electrophoretic displays (601, 602) generally also include a second conductive adhesive 670. However, it should be noted that in some cases, the conductive adhesive 670 alone may be sufficient to provide the electric field required to switch the electrophoretic material. Alternatively, the second electrode can be fabricated by directly coating the bottom of the microcell layer 530 (Figure 6A) or the sealing layer 540 (Figure 6B) with a thin layer of transparent conductive oxide. If it is not necessary to see through the top and bottom of the piezoelectric electrophoretic display (601, 602), a conductive metal foil can be used as the second flexible electrode 680. As shown in Figures 6A and 6B, a release mold 510 is typically added to the completed piezoelectric electrophoretic display (601, 602) to improve processing and provide a ready-made adhesive to fix the piezoelectric electrophoretic display (601, 602). In some embodiments, the piezoelectric electrophoretic display 601 can be formed by simply bonding the piezoelectric layer 560 to a commercially available front laminate including the second flexible electrode 680 and the sealed microcell layer 530 (which already includes the electrophoretic medium). In this case, the piezoelectric layer 560 is typically polarized before the front laminate is connected to the piezoelectric layer 560 to create differential polarization regions. Although the piezoelectric layer 560 of Figures 6A and 6B is shown as being above the sealed microcell layer 530, it should be understood that the piezoelectric layer 560 can also be placed below the sealed microcell layer 530 to create a piezoelectric display similar to Figures 5B and 5D.

Prototype performance:

A series of piezoelectric electrophoretic films of the type illustrated in Figure 5A were fabricated using PEDOT:PSS film as the flexible electrode 580. The piezoelectric layer 560 was varied (composition and thickness) as shown in Table 1. The piezoelectric films were sourced from TE Connectivity (Norwood, MA), Fishman (Andover, MA), or cast in-house and cured using PVDF powder from Sigma-Aldrich. The patterns were fabricated by varying the polarization direction using the described polarization techniques. The electrophoretic medium consisted of a low-voltage combination of black and white particles, black and red particles, or red and black particles, designed to switch color states at +/- 3 volts. As shown in Table 1, all variants provided adequate switching.

Table 1 suggests that polymorphic electrophoretic media respond appropriately to the small electric fields generated by bending thin piezoelectric films. In particular, spin-coated polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE) films thinner than 3 microns were found to possess sufficient charge injection to cause DV electrophoretic media switching. See Experiment 7. This piezoelectric electrophoretic film 801 (see Figure 8A) can be formed using the method described in Figure 7. First, a concentrated PVDF/DMF solution is cast onto a suitable substrate (seam-dye coating) and heated to drive off the solvent, producing a thin film of piezoelectric material 940, as shown in step 710 of Figure 7. The piezoelectric film 960 is then removed from the substrate in step 720. The cast piezoelectric film 960 can be 10 microns thick or less, such as 5 microns thick or less, for example 3 microns thick or less. The piezoelectric film 960 can also be stretched to increase the number of β-phase domains and/or polarized with an appropriate electric field, as discussed above. In step 730, a release die 910 with an adhesive 920 is provided. Then, in step 740, the release die 910 and adhesive 920 are laminated onto the cast piezoelectric film 960. The piezoelectric film 960 is then coated/bonded with an electrophoretic layer in step 750. The electrophoretic layer can be a sealed microcell layer comprising filled microcells 930 and a sealing layer 940, or the electrophoretic layer can comprise an electrophoretic medium 990 encapsulated in a polymer adhesive 995, as shown in Figures 9A and 9B. It is advantageous to bond the piezoelectric film 960 to the electrophoretic layer via an intermediate primer layer 935, for example, using one of the primer materials discussed above. If the electrophoretic layer is a sealed microcell layer, the microcells 930 can be arranged such that the sealing layer 940 is adjacent to the piezoelectric film 960, as shown in Figure 8A, or the microcells 930 can be arranged such that the sealing layer 940 is disposed on the opposite side of the piezoelectric film 960, as shown in Figure 8B. The final step 760 is to fabricate an electrode layer 980 and bond/deposit it onto any of the microcells 930 as shown in FIG8A , or bond/deposit it onto the sealing layer 940 as shown in FIG8B . As described above, the electrode layer 980 may comprise a flexible conductive material such as PEDOT:PSS, or it may comprise a transparent conductive oxide (TCO) that is directly deposited (e.g., by sputtering or vapor deposition). In some embodiments, the electrode 980 may comprise a prefabricated ITO film on a polymer substrate (e.g., PET). The piezoelectric electrophoretic film 801, comprising a directly deposited TCO electrode layer 980, a thin piezoelectric layer 960, and a thin layer of microcapsules 930 (approximately 10 microns thick), is extremely thin (i.e., less than 25 microns thick excluding the release film 910). This allows the piezoelectric electrophoretic film 801 to be bent without failure and remain inconspicuous when affixed to an object (e.g., a bank note). A corresponding piezoelectric electrophoretic film 901 including microcapsules can also be manufactured with a total thickness of less than 25 microns. Of course, alternative configurations of the thin piezoelectric film 960 can also be used, such as placing the piezoelectric film 960 between the electrode 980 and the electrophoretic layer (i.e., microcapsule layer 990), as shown in FIG9B . An alternative is to replace the electrode 980 in Figures 8A-9B with a conductive adhesive (not shown) or a conductive adhesive combined with an additional release layer (not shown).

Similar to Figures 6A and 6B , the piezoelectric electrophoretic film of Figures 8A-9B may include a second electrode layer to form a corresponding display ( 1001 , 1002 , 1003 ), as shown in Figures 10A-10C . Both the electrode layer 980 and the second electrode layer 1080 may comprise a flexible conductive material, such as PEDOT:PSS, or both the electrode layer 980 and the second electrode layer 1080 may comprise a transparent conductive oxide (TCO) directly deposited (e.g., by sputtering or vapor deposition), or a combination thereof. Again, using thin TCO films for electrode layer 980 and second electrode layer 1080 allows the resulting piezoelectric electrophoretic display (1001, 1002, 1003) to be very thin, i.e., less than 25 microns thick, excluding release film 910. In some embodiments, electrode layer 980 is fabricated as shown in FIG10A and bonded/deposited on micelles 930. In other embodiments, electrode layer 980 is bonded/deposited on sealing layer 940 as shown in FIG10B. Alternatively, piezoelectric electrophoretic display 1003 can be fabricated using an assembly of piezoelectric electrophoretic displays 1001 and 1002 and microcapsules 990 containing an electrophoretic medium held together by adhesive 995, as shown in FIG10C. An alternative is to replace the electrodes 980/1080 in Figures 10A-10C with a conductive adhesive (not shown) or a conductive adhesive combined with an additional release layer (not shown).

The flow chart of Figure 11 describes an alternative method for forming a piezoelectric electrophoretic film and a piezoelectric electrophoretic display. A piezoelectric film 1260 is obtained, which can be a commercially available film or the cast film described above. In step 1110, the piezoelectric film 1260 is laminated onto the micelle precursor material. The piezoelectric film 1260 is stretched and/or polarized before lamination. The precursor material is typically an acrylate polymer, but any suitable embossable material can be used, such as a vinyl ether polymer or epoxy polymer film. Generally, the precursor film is 30 microns thick or less, for example 20 microns thick or less. The precursor film can be treated with a primer 1235 before lamination step 1110. Once the piezoelectric film 1260 and the microcell pre-driver material are bonded, the side of the piezoelectric film 1260 opposite the microcell pre-driver material is coated with a transparent conductive material, such as one selected from the aforementioned materials, typically indium tin oxide. (Alternatively, depending on the application, the side of the piezoelectric film 1260 opposite the microcell pre-driver material can be coated with a conductive adhesive that can be supported by a release layer.) This coating step produces the electrodes 1280 shown in the piezoelectric electrophoretic film 1201 and the piezoelectric electrophoretic display 1202, as shown in Figures 12A and 12B, respectively. (Although not shown in FIG. 11 , an alternative configuration is to obtain the piezoelectric film 1260 pre-coated with a transparent conductive material, and then laminate the pre-coated piezoelectric film 1260 with the micelle pre-driver material, including an optional primer 1235.) After fabricating the stack of electrodes 1280, piezoelectric film 1260, and micelle pre-driver, the stack is laminated to a carrier substrate 1255 using an adhesive layer 1250, as shown in step 1130. The carrier substrate 1255 can be any of the materials described above as a release film, and the adhesive 1250 can be any of the adhesives described above. In practice, carrier substrate 1255 is typically PET because PET sheets are easy to handle during embossing step 1140. In step 1140, the stack comprising carrier substrate 1255, adhesive 1250, piezoelectric film 1260, and micelle precursor is micro-embossed using the techniques described in U.S. Patents Nos. 6,930,818, 7,052,571, 7,616,374, 8,361,356, and 8,830,561. When this step is performed using thin piezoelectric films and thin micelle precursors, the final stack thickness (excluding the carrier substrate) can be 30 microns or less, for example, 20 microns or less. This creates an open-cell structure, which is then filled with the desired electrophoretic medium in step 1150 and sealed with a water-soluble sealing layer 1240. Sealing layer 1240 can be conductive by including a conductive species. Sealing layer 1240 is typically light-transmissive or transparent. Before filling the cells with the desired electrophoretic medium, the open cells can be cleaned/activated by a vapor plasma treatment 1145. Finally, in step 1160, a release sheet 1210 is attached to sealing layer 1240 using an adhesive 1220, facilitating transport of the piezoelectric electrophoretic film 1201 and placement on the final product. Adhesive 1220 can also be conductive. The resulting structure is shown in FIG. 12A . Importantly, the steps of FIG. 11 can be completed without polarizing the piezoelectric film 1260 , thereby allowing the end customer to pattern the piezoelectric electrophoretic film 1201 at the final assembly location, for example by creating differentially polarized regions using coma discharge, as described above.

As shown in Figure 12B , the method of Figure 11 can be expanded to fabricate a piezoelectric electrophoretic display 1202 by adding a second electrode 1285. Second electrode 1285 can also comprise a transparent conductive material, incorporated directly into sealing layer 1240 in place of release film 1210 and adhesive 1220. However, in other embodiments, release film 1210 is eliminated, and second electrode 1285 is laminated to sealing layer 1240 with adhesive 1220. If piezoelectric electrophoretic display 1202 does not require the electrophoretic medium to be visible from both sides, second electrode 1285 can be a metal film. Alternatively, second electrode 1285 can be a conductive polymer, such as PEDOT:PSS. In some other embodiments, adhesive 1220 may be a conductive adhesive that provides sufficient conductivity to serve as the second electrode 1285.

Finally, it should be understood that before embossing the stack comprising the piezoelectric film 1260 and the microcell precursor material, the electrode need not be connected to the piezoelectric film 1260. Instead, a stack comprising the release sheet 1210, adhesive 1220, piezoelectric film 1260, and microcell precursor material can be prepared, followed by embossing the microcell precursor material, filling, and sealing as described above. Alternatively, a stack comprising the release sheet 1210, adhesive 1220, electrode 1285, piezoelectric film 1260, and microcell precursor material can be prepared, followed by embossing the microcell precursor material, filling, and sealing as described above, as shown in FIG13B. The resulting piezoelectric electrophoretic film 1301 and piezoelectric electrophoretic display 1302 are shown in Figures 13A and 13B, respectively. Piezoelectric electrophoretic film 1301 and piezoelectric electrophoretic display 1302 can be useful in applications where it is desirable to place piezoelectric film 1260 as close as possible to the attachment surface on the final product, i.e., when using piezoelectric electrophoretic film 1301 as a strain sensor, and it is important that the intermediate electrophoretic dielectric layer does not dissipate the force away from the surface.

FIG14 is a flow chart detailing the steps of a method 1400 for manufacturing a high-contrast piezoelectric electrophoretic film and a piezoelectric electrophoretic display. The method 1400 has been optimized for manufacturing the piezoelectric electrophoretic film using a roll-to-roll process.

Method 1400 is described with reference to Figures 15A-15F. Method 1400 begins at step 1410, where a first electrode (electrode 1550) is formed on a first substrate (substrate 1555) by depositing a conductive material, such as one selected from the materials described above, onto the substrate. For example, a thin layer of the conductive material can be deposited directly (e.g., by sputtering or vapor deposition) onto a suitable substrate, such as a polymer substrate (e.g., PET). In some embodiments, substrate 1555 can be any of the materials described above as a temporary release sheet to facilitate the fabrication of piezoelectric electrophoretic films. In some embodiments, the conductive material used to form electrode 1550 is an adhesive or connecting layer comprising a transparent conductive material (e.g., a first conductive adhesive) comprising a conductive metal oxide, a conductive polymer, and/or other suitable conductive material coated onto substrate 1555. In some embodiments, to form electrode 1550, the adhesive or connecting layer is deposited onto substrate 1555, and a conductive polymer, such as PEDOT, is deposited onto the connecting layer. In some cases, electrode 1550 is a metal film, such as a film or foil of copper, silver, gold, or aluminum, bonded to a flexible, optically transparent substrate, such as a polymer film. In some embodiments, electrode 1550 has a thickness of less than 5 microns. In some embodiments, the thickness of electrode 1550 is between 1 micron and 3 microns.

Next, in step 1420, a piezoelectric layer 1560 is formed on the conductive material (e.g., electrode 1550) by depositing the piezoelectric material onto the conductive material. For example, the electrode 1550 can be coated with a thin film of piezoelectric material, such as a film selected from the above-mentioned materials, such as PVDF, using a spin-on process as described above or casting (e.g., seam dye coating). In some embodiments, the piezoelectric layer 1560 is formed on the electrode 1550 using a film deposition process such as printing, spraying, or gravure coating. In some embodiments, the resulting piezoelectric layer 1560 has a thickness of less than 10 microns. In some embodiments, the resulting piezoelectric layer 1560 has a thickness of approximately 3 microns.

As shown in step 1430, after forming the piezoelectric layer 1560 on the electrode 1550, a mask 1540 is applied to the piezoelectric material of the piezoelectric layer 1560. In the above-described embodiment, the mask 1540 can be used to shield or isolate the plurality of first regions of the piezoelectric layer 1560 from the high-voltage corona discharge 1533 used to polarize the piezoelectric layer 1560. This allows the piezoelectric layer 1560 to be patterned with images, text, and other information (e.g., machine-readable code). The mask 1540 can be made of a material having a dielectric strength sufficient to withstand at least a localized 5 kilovolt (kV) field. In some embodiments, the mask 1540 is formed of a disposable material that can be applied in a roll-to-roll process. For example, mask 1540 can be formed from a paper such as electrically insulating paper having a pressure-sensitive adhesive applied to one surface to bond to piezoelectric layer 1560. Alternatively, mask 1540 can be a reusable fixture made of a charge-absorbing or charge-blocking material that is integrated into a roll-to-roll translation stage, such as a screen printing process or a rotary roll.

FIG15A is a schematic cross-sectional view 1501 of a piezoelectric electrophoretic film in step 1440 of the method shown in FIG14 . As shown in FIG15A , the mask 1540 includes a shielding portion 1542 that shields or isolates corresponding areas of the piezoelectric layer 1560 from high-voltage corona discharge 1533, and an unshielded portion 1544 that allows polarization in areas of the piezoelectric layer 1560 not covered by the mask 1540. The piezoelectric material is then polarized in step 1440. For example, a high-voltage coma discharge (e.g., high-voltage coma discharge 1533) or other suitable electric field discussed above can be used to polarize the non-shielded portion of the piezoelectric layer 1560 in a first direction while leaving the shielded portion unpolarized. If a disposable material such as paper is used as a mask, the mask is then removed from the piezoelectric layer 1560.

In some embodiments, the piezoelectric material patterning process can begin with a sheet or roll of polarized PVDF film. The film can be patterned by laser cutting, laser ablation (e.g., laser photoablation), die cutting, or other cutting methods, and then laminated onto an electrode layer, or the aforementioned microcapsule- or microcell-based planar laminate or FPL.

FIG15B is a schematic cross-sectional view 1502 of the piezoelectric electrophoretic film after completing step 1440 of the method shown in FIG14 . As shown in FIG15B , the piezoelectric layer 1560 now includes an unpolarized portion 1562 corresponding to the location of the shielding portion 1542 of the mask 1540 and a polarized portion 1564 corresponding to the location of the non-shielding portion 1544 of the mask 1540 .

In step 1450, the piezoelectric material is then bonded to the electrophoretic material. For example, the piezoelectric layer 1560 can be coated with an electrophoretic dielectric layer comprising a plurality of microcapsules containing a non-polar fluid and charged pigment particles (not shown in FIG. 15B ). Alternatively, an electrophoretic dielectric layer comprising microcell units 1530 can be formed on the piezoelectric layer 1560 using a process similar to that shown in the flow chart of FIG. 11 . For example, an imprintable microcell precursor material can be layered onto the piezoelectric layer 1560. Prior to lamination, the precursor material can be treated or coated with a microcell primer, one of the primer materials discussed above. In some examples, the microporous primer includes a thermoplastic or thermosetting material such as polyurethane or a precursor thereof, such as a multifunctional acrylate or methacrylate of lauryl methacrylate, vinylbenzene, vinyl ether, epoxide, or an oligomer or polymer thereof.

The micelle precursor is microembossed using the aforementioned technique to produce an open micelle structure. This structure is then filled with the desired electrophoretic medium and sealed with a sealing layer 1535 as shown in FIG15C , which is a schematic cross-sectional view 1503 of a piezoelectric electrophoretic film after step 1450 of the method shown in FIG14 . Prior to filling the micelles 1530 with the desired electrophoretic medium, a vapor plasma treatment is optionally used to clean/activate the open micelles.

In some embodiments, the thickness of the microcell layer 1530 is between 8 and 20 microns, and the thickness of the sealing layer 1535 is between 3 and 10 microns. In some embodiments, the thickness of the microcell layer 1530 is about 10 microns, and the thickness of the sealing layer 1535 is about 5 microns.

In another embodiment, instead of forming micelles on the piezoelectric layer 1560, one of the piezoelectric layers 1560 shown in FIG15B is bonded or laminated to the aforementioned microcapsule- or micelle-based planar laminate or FPL.

In step 1460, a second electrode (electrode 1585) is formed on a second substrate (substrate 1586). Electrode 1585 can be formed on substrate 1586 using one of the processes described above for electrode 1550 and substrate 1555. As an example, substrate 1586 can be a release sheet used temporarily to facilitate the fabrication of the piezoelectric electrophoretic film, and electrode 1585 can be formed from an adhesive or connecting layer comprising a transparent conductive material deposited onto substrate 1586. In some embodiments, electrode 1585 has a thickness of less than 5 microns. In some embodiments, electrode 1585 has a thickness between 1 and 3 microns.

Then, in step 1470, the conductive material deposited on the second substrate is bonded to the electrophoretic material. For example, substrate 1586, electrode 1585, and sealing layer 1535, which can be laminated to micelles 1530, form the structure shown in FIG15D . FIG15D is a schematic cross-sectional view 1504 of the piezoelectric electrophoretic film after completing step 1470 of the method shown in FIG14 . Electrode 1585 (and substrate 1586) are added to the piezoelectric electrophoretic film to form a piezoelectric electrophoretic display that can be bonded to a target object. For example, the structure shown in FIG15D can be a piezoelectric electrophoretic display sandwiched between two release sheets (e.g., substrates 1555 and 1586).

In another embodiment not shown in FIG. 14 , steps 1460-1470 are replaced by the following process. The sealing layer 1535 of the microcell 1530 can be coated with a conductive material such as PEDOT or one of the materials discussed above to form an electrode 1585. Subsequently, in step 1480 described below, the electrode 1585 can be coated with an adhesive material (e.g., heat seal adhesive "HSA" or one of the materials described above for bonding piezoelectric electrophoretic displays to a target).

Returning to Figure 14 , in step 1480 , the piezoelectric electrophoretic display can be bonded to a target object. For example, the image displayed by the piezoelectric electrophoretic display shown in Figure 15D can be processed and attached to a target object 1588 such as a piece of paper or a bank note, as shown in Figure 15E . Figure 15E is a cross-sectional view 1505 of the piezoelectric electrophoretic film bonded to the target object after completing step 1480 of the method shown in Figure 14 .

In some embodiments, substrate 1586 is a release sheet that is peeled or removed from electrode 1585, and a hot stamping process is used to bond electrode 1585 to the surface of target 1588. For example, heat and pressure can be applied to the PIE display and/or target 1588 during a roll-to-roll hot stamping process in which the PIE display is pressed against target 1588. Adhesive (not shown) remaining on electrode 1585 after substrate 1586 is peeled off is activated by the heat and pressure, bonding the PIE display to target 1588.

In some embodiments, the electrode 1585 is formed from an adhesive or connecting layer that is activated during the bonding process to bond the PIEZO display to the target 1588. In some embodiments, a roll-to-roll lamination process is used to bond the PIEZO display to the target 1588.

In some embodiments, substrate 1555 and substrate 1586 are release sheets, and the force required to remove each release sheet is adjusted individually to ensure that substrate 1586 is removed before substrate 1555 during the bonding process. For example, the adhesives used to temporarily adhere substrates 1555 and 1586 to electrodes 1550 and 1585, respectively, can be formulated or selected so that the force required to peel substrate 1586 from the piezoelectric electrophoretic display is less than the force required to peel substrate 1555 from the piezoelectric electrophoretic display.

FIG15F is a cross-sectional view 1506 of the piezoelectric electrophoretic film bonded to a target and coated with a protective coating after completing step 1480 of the method shown in FIG14. As illustrated in FIG15F, after the piezoelectric electrophoretic display is bonded to the target 1588, the substrate 1555 can be peeled from the electrode 1550, and a protective coating 1589 can be applied to the surface of the piezoelectric electrophoretic display and the target 1588 to which the piezoelectric electrophoretic display is bonded. In some embodiments, the protective coating 1589 is a lacquer layer applied to the surface of the piezoelectric electrophoretic display and the target 1588 using a printing process. Suitable materials for the protective coating 1589 may include UV-cured polyester acrylates, polyurethane acrylates, UV-cured epoxies, and thermally cured epoxies, or any material that adequately seals the piezoelectric electrophoretic display and target 1588 to repel dirt and prevent excessive contact.

Thus, the process associated with FIG. 14 can be used to manufacture piezoelectric electrophoretic displays having a thickness significantly less than conventional displays, and thus can be incorporated into objects such as bank notes or currency bills without significantly or generally unnoticeably increasing the overall thickness. In some embodiments, the total thickness of the piezoelectric electrophoretic display can be between 50 microns and 100 microns. In some embodiments, the total thickness of the piezoelectric electrophoretic display can be between 25 microns and 50 microns. In some embodiments, the total thickness of the piezoelectric electrophoretic display can be less than 25 microns.

FIG16 shows an enlarged view 1600 of a partial cross-sectional view of a piezoelectric electrophoretic display 1601 fabricated according to the subject matter disclosed herein. For purposes of describing the operation of the display, only a subset of the layers of the piezoelectric electrophoretic display 1601 are shown: the electrode 1550, the piezoelectric layer 1560 including an unpolarized portion 1562 and a polarized portion 1564, the microcells 1530, the sealing layer 1535, and the second electrode 1585. In the enlarged view 1600, the microcells 1530 and the sealing layer 1535 are represented by the electrophoretic layer 1631.

Enlarged view 1600 includes one of the unpolarized portions 1562 and one of the polarized portions 1564. A first portion 1632 of the electrophoretic layer 1631 is located above the unpolarized portion 1562, while a second portion 1634 is located above the polarized portion 1564, as depicted by dashed line 1602. Each of the first portion 1632 and the second portion 1634 has a resistance based on the volume of the electrophoretic layer 1631 they enclose. Furthermore, the unpolarized portion 1562 also has a resistance based on the volume of the piezoelectric layer 1560 it encloses. As indicated by the "+" and "-" symbols, a voltage is generated in the polarized portion 1564 of the piezoelectric layer 1560, for example, in response to bending or mechanical stress on the piezoelectric material.

FIG17 illustrates an exemplary equivalent circuit 1700 of the enlarged cross-sectional view shown in FIG16 . The three nodes or points shown in FIG16 , "A" at the polarized portion 1564, "B" at the electrode 1585, and "C" at the electrode 1550, correspond to the same points shown in the equivalent circuit 1700 of FIG17 . Resistor _R1 corresponds to the sum of the resistances of the first portion 1632 of the electrophoretic layer 1631 and the unpolarized portion 1562 of the piezoelectric layer 1560. Resistor R2 corresponds to the resistance of the second portion 1634 of the electrophoretic layer 1631.

Polarized portion 1564 of piezoelectric layer 1560 is shown as a battery, and voltage V _PZ is the voltage generated by polarized portion 1564 between points A and C. Resistors _R1 and _R2 are shown in series because the presence of a voltage source beneath a portion of electrophoretic layer 1631 effectively divides the layer into separate sections with different electrical characteristics (as depicted by dashed line 1602). For example, when voltage V _PZ is generated, the potential at point A is higher than the potential at points B or C. Using a traditional current flow paradigm, current 1701 flows from point A through resistor _R1 to point B, and from point B through resistor _R2 to point C. As can be seen, the voltage developed across resistor _R1 is of opposite polarity to the voltage developed across resistor _R2 . In effect, two opposite voltages are generated in series on different parts of the electrophoretic layer.

Thus, fabricating a piezoelectric electrophoretic display as described with respect to method 1400 offers advantages over conventional piezoelectric electrophoretic displays. For example, selectively polarizing the piezoelectric layer advantageously provides an improved way to drive oppositely charged pigment particles in an electrophoretic medium in opposite directions without the presence of a matrix of individually addressable pixel electrodes. Consequently, piezoelectric electrophoretic displays produced according to method 1400 can be made thin enough for use in applications requiring them to be durable and unobtrusive, while still providing a high contrast between polarized and unpolarized regions when incorporated into thin, low-profile end products such as paper or banknotes due to the aforementioned effects. Furthermore, in this embodiment, the piezoelectric layer only requires a single polarization operation.

FIG18 is a flow chart detailing the steps of a method 1800 for manufacturing a high-contrast piezoelectric electrophoretic film and a piezoelectric electrophoretic display. The method 1800 is optimized for manufacturing the piezoelectric electrophoretic film using a roll-to-roll manufacturing process.

Method 1800 is described with reference to Figures 19A-19G . To facilitate understanding, where possible, the same or similar reference numerals and names are used in Figures 19A-19G to reference elements corresponding to or functionally similar to those shown in Figures 15A-15F . However, a person skilled in the art will understand, based on the description herein, that the elements of each embodiment need not be identical in composition and structure, and that elements disclosed with reference to one embodiment may be beneficially employed in other embodiments without specific recitation.

Method 1800 begins at step 1810, where a piezoelectric layer 1960 is formed on a temporary substrate 1965 by depositing a piezoelectric material onto the temporary substrate 1965. For example, the temporary substrate 1965 can be coated with a thin film of a piezoelectric material selected from the aforementioned materials, such as PVDF, using a spin-on process as described above or by casting (e.g., seam dye coating). The temporary substrate 1965 can be a release sheet used temporarily to facilitate the fabrication of the piezoelectric electrophoretic film. In some embodiments, the temporary substrate 1965 is a release sheet formed from a material selected from the group consisting of polyethylene terephthalate (PET), polycarbonate, polyethylene (PE), polypropylene (PP), paper, and a laminate or a coating thereof. An organosilicon release coating may also be applied to the temporary substrate 1965 to improve release characteristics. FIG19A is a schematic cross-sectional view 1901 of a piezoelectric electrophoretic film at step 1810 of method 1800.

In some embodiments, a film deposition process such as printing, spraying, or gravure coating is used to form the piezoelectric layer 1960 on the temporary substrate 1965. In some embodiments, the resulting piezoelectric layer 1960 has a thickness of less than 10 microns. In some embodiments, the resulting piezoelectric layer 1960 has a thickness of approximately 3 microns.

In step 1820, the piezoelectric material is combined with the conductive material coated on the first substrate. For example, the temporary substrate 1965 can be peeled from the piezoelectric layer 1960, and the piezoelectric layer 1960 can be laminated onto the first electrode (i.e., electrode 1950) formed on the first substrate (i.e., substrate 1955). Electrode 1950 can be formed on substrate 1955 using one of the processes described above with respect to electrode 1550 and substrate 1555. As an example, substrate 1955 can be a release sheet used temporarily to facilitate the fabrication of the piezoelectric electrophoretic film, and electrode 1950 can be formed from an adhesive or connecting layer including a transparent conductive material deposited onto substrate 1955. In some embodiments, the thickness of electrode 1950 is less than 5 microns. In some embodiments, the thickness of electrode 1950 is between 1 micron and 3 microns.

In an alternative embodiment not shown in FIG. 18 , steps 1810 and 1820 are replaced by the following process. Instead of using a temporary substrate 1965, substrate 1955 can be coated with a conductive material (e.g., one of the materials discussed above) to form electrode 1950. In some embodiments, to form electrode 1950, an adhesive or connecting layer is deposited on substrate 1955, and a conductive polymer such as PEDOT is deposited on the connecting layer. After electrode 1950 is formed, a piezoelectric material is bonded to electrode 1950 to form piezoelectric layer 1960. For example, the piezoelectric material can be applied to electrode 1950 as described above.

Returning to FIG. 18 , after the piezoelectric layer 1960 is bonded to the electrode 1950 , a mask 1940 is applied to the piezoelectric layer 1960 as shown in step 1830 . As in the embodiments described above, the mask 1940 can be used to shield or isolate areas of the piezoelectric layer 1960 from the high voltage corona discharge 1933 used to polarize the piezoelectric layer 1960 . This allows the piezoelectric layer 1960 to be patterned with images, text, and other information (e.g., a machine-readable code). The mask 1940 can be made of a material having a dielectric strength sufficient to withstand at least a localized 5 kV field. In some embodiments, the mask 1940 is formed of a disposable material that can be applied in a roll-to-roll process. For example, mask 1940 can be formed from a paper such as electrically insulating paper having a pressure-sensitive adhesive applied to one surface for adhesion to piezoelectric layer 1960. Alternatively, mask 1940 can be a reusable fixture made of a charge-absorbing or charge-blocking material that is integrated into a roll-to-roll translation platform similar to a screen printing process or a rotary roll.

FIG19B is a schematic cross-sectional view 1902 of the piezoelectric electrophoretic film at step 1830 of the method shown in FIG18 . As shown in FIG19B , the mask 1940 includes a shielding portion 1942 and a non-shielding portion 1944. The shielding portion 1942 shields or isolates corresponding regions of the piezoelectric layer 1960 from the effects of high-voltage coma discharge 1933, while the non-shielding portion 1944 allows the piezoelectric layer 1960 to be polarized in corresponding regions not covered by the mask 1940.

The piezoelectric material is then polarized or poled in step 1840. For example, a high-voltage coma discharge (e.g., high-voltage coma discharge 1933) or other suitable electric field discussed above can be used to polarize the non-shielded portion of the piezoelectric layer 1960 in a first direction while leaving the shielded portion unpolarized. If a disposable material such as paper is used as the mask, the mask is then removed from the piezoelectric layer 1960.

FIG19C is a schematic cross-sectional view 1903 of the piezoelectric electrophoretic film after completing step 1840 of the method shown in FIG18 . As shown in FIG19C , the piezoelectric layer 1960 now includes an unpolarized portion 1962 located relative to the shielding portion 1942 of the mask 1940 and a polarized portion 1964 located relative to the non-shielding portion 1944 of the mask 1940 .

In step 1850, a second electrode (electrode 1985) is formed on a second substrate (substrate 1986) by depositing a conductive material, such as one selected from the materials described above, onto the substrate. Electrode 1985 can be formed on substrate 1986 using one of the processes described above for electrode 1550 and substrate 1555. In one example, to form electrode 1985, an adhesive or connecting layer is deposited on substrate 1986, and a conductive polymer, such as PEDOT, is deposited on the connecting layer. In some embodiments, electrode 1985 has a thickness of less than 5 microns. In some embodiments, electrode 1985 has a thickness between 1 micron and 3 microns.

The electrophoretic material is then bonded to the conductive material in step 1860. For example, the electrode 1985 can be coated with an electrophoretic medium layer comprising a plurality of microcapsules containing a non-polar fluid and charged pigment particles (not shown in FIG. 19D ). Alternatively, an electrophoretic medium layer comprising microcells 1930 can be formed on the electrode 1985 using a process similar to that shown in the flow chart of FIG. 11 . For example, a precursor material capable of imprinting microcells is layered onto the electrode 1985. Prior to layering, the precursor material can be primed, such as with one of the primer materials discussed above. Using the above-described techniques, the micelle precursor is microembossed to produce an open micelle structure, which is then filled with the desired electrophoretic medium and sealed with a sealing layer 1935, as shown in FIG19D , which is a schematic cross-sectional view 1904 of a piezoelectric electrophoretic film after completing steps 1850 and 1860 of the method shown in FIG18 . Prior to filling the micelles 1930 with the desired electrophoretic medium, the open micelles can optionally be cleaned/activated using a vapor plasma treatment.

In some embodiments, the thickness of the microcell layer 1930 is between 8 and 20 microns, and the thickness of the sealing layer 1935 is between 3 and 10 microns. In some embodiments, the thickness of the microcell layer 1930 is about 10 microns, and the thickness of the sealing layer 1935 is about 5 microns.

In other embodiments, rather than forming micelles on electrode 1985, electrode 1985 is bonded or laminated to the aforementioned microcapsule- or micelle-based front planar layer or "FPL," as shown in FIG. 19D .

Then, in step 1870, the piezoelectric material deposited on the first electrode is combined with the electrophoretic material. For example, the piezoelectric layer 1960 can be laminated onto the sealing layer 1935 of the microcell 1930 to form the structure shown in FIG19E , which is a schematic cross-sectional view 1905 of the piezoelectric electrophoretic film after completing step 1870 of the method shown in FIG18 . In some embodiments, the piezoelectric layer 1960 can be coupled to the sealing layer 1935 using an adhesive layer (not shown in FIG19E ).

Adding a piezoelectric layer 1960 with electrodes 1550 (and substrate 1555) to the piezoelectric electrophoretic film forms a piezoelectric electrophoretic display that can be bonded to a target. For example, the structure shown in FIG19E can be a piezoelectric electrophoretic display sandwiched between two release sheets (e.g., substrates 1955 and 1986).

In step 1880, the piezoelectric electrophoretic display can be bonded to a target. For example, the piezoelectric electrophoretic display shown in FIG19E can be processed and attached to a target 1988 such as a paper or banknote, as shown in FIG19F , which is a cross-sectional view 1906 of the piezoelectric electrophoretic film bonded to the target according to the method shown in FIG18 .

In some embodiments, substrate 1986 is a release sheet that is peeled or removed from electrode 1985 and bonded to the surface of target 1988 using a hot stamping process as described above.

In some embodiments, the electrode 1985 is formed from an adhesive or connecting layer that is activated during the bonding process to bond the piezoelectric electrophoretic display to the target 1988. In some embodiments, a roll-to-roll lamination process is used to bond the piezoelectric electrophoretic display to the target 1988.

In some embodiments, substrate 1955 and substrate 1986 are release sheets, and the force required to remove each release sheet is individually adjusted to ensure that substrate 1986 is removed before substrate 1955 during the bonding process. For example, the adhesives used to temporarily adhere substrate 1955 and substrate 1986 to electrode 1950 and electrode 1985, respectively, can be formulated or selected so that the force required to peel substrate 1986 from the piezoelectric electrophoretic display is less than the force required to peel substrate 1955 from the piezoelectric electrophoretic display.

FIG19G is a cross-sectional view 1907 of a piezoelectric electrophoretic display film bonded to a target and coated with a protective coating after completing step 1880 of the method shown in FIG18 . As illustrated in FIG19G , after bonding the piezoelectric electrophoretic display to a target 1988 , the substrate 1955 can be peeled from the electrode 1950 , and a protective coating 1989 can be applied to the surfaces of the piezoelectric electrophoretic display and the target 1988 , and the piezoelectric electrophoretic display can be bonded as described above.

Thus, the process described in conjunction with FIG. 18 can be used to produce a piezoelectric electrophoretic display that is significantly thinner than conventional displays and, therefore, can be bonded to objects such as banknotes or money orders without significantly or substantially increasing the overall thickness. In some embodiments, the overall thickness of the piezoelectric electrophoretic display can be between 50 microns and 100 microns. In some embodiments, the overall thickness of the piezoelectric electrophoretic display can be between 25 microns and 50 microns. In some embodiments, the overall thickness of the piezoelectric electrophoretic display can be less than 25 microns. Thus, the resulting piezoelectric electrophoretic display produced using method 1800 provides substantially similar benefits and advantages as the piezoelectric electrophoretic display produced using method 1400 described above.

A person of ordinary skill in the art will appreciate that the steps of method 1400 and method 1800 do not need to be performed in the exact order in which they are presented. As an example, steps 1810-1840 of method 1800 do not necessarily need to occur before steps 1850 and 1860.

It should be understood that the piezoelectric electrophoretic films and displays described herein can be combined with other known technologies for producing security or authentication labels. For example, the piezoelectric electrophoretic films and displays can additionally include a semi-transparent overlay that does not change its optical properties when the piezoelectric film is manipulated. For example, a smiley face overlay can include eyes formed from the piezoelectric electrophoretic display, such that when the layered material is bent, the eyes appear to blink. In some embodiments, an image or shape can be printed or laminated onto a solid color (e.g., white) background, and the pre-arranged pattern must be viewed through the piezoelectric electrophoretic film. Thus, when not in use, the viewer sees only the solid color, i.e., the printed image or shape is hidden. However, the printed image or shape will be displayed when the device is operated. It is also possible to adhere the piezoelectric electrophoretic film or piezoelectric electrophoretic display to a separate light-transmitting polymer film included in the target product (such as a banknote) so that the pattern in the piezoelectric layer can only be seen when the target product is held under a light source and operated.

FIG20 illustrates a cross-sectional view of another exemplary piezoelectric electrophoretic display 2000 according to the subject matter disclosed herein. Display 2000 utilizes piezoelectric material 2002 to generate a voltage potential sufficient to drive charged pigment particles within an electrophoretic material layer 2004. Display 2000 includes a first electrode, namely, electrode 2006, superimposed on or covering a first surface of electrophoretic material layer 2004. Display 2000 also includes piezoelectric material 2002 superimposed on or covering a first portion of a second surface of electrophoretic material layer 2004, as indicated by surface region 2120 in FIG20 . The second electrode, electrode 2008, overlaps all of the piezoelectric material 2002 and a second portion of the second surface of the electrophoretic material layer 2004, as shown as surface region 2121 in FIG. 20 .

The piezoelectric material 2002 can be a piezoelectric film coupled to the surface region 2120 of the electrophoretic material layer 2004 using a lamination process. In some embodiments, the piezoelectric material 2002 is formed by depositing the piezoelectric material onto the electrophoretic material layer 2004. For example, the surface region 2120 of the electrophoretic material layer 2004 can be coated with a thin film of piezoelectric material, such as PVDF, using a spin-on process or casting (e.g., slot dye coating). In some embodiments, the piezoelectric material 2002 is formed on the electrophoretic material layer 2004 using a film deposition process such as printing, spraying, or gravure coating. In some embodiments, the resulting piezoelectric material 2002 has a thickness of less than 10 microns. In some embodiments, the resulting piezoelectric material 2002 has a thickness of approximately 3 microns.

Electrode 2008 overlies or covers surface region 2121 of piezoelectric material 2002 and electrophoretic material layer 2004. Electrode 2008 can be a conductive adhesive material (e.g., copper tape) applied to surface region 2121 of piezoelectric material 2002 and electrophoretic material layer 2004. In some embodiments, electrode 2008 is a metal film, such as a copper, silver, gold, or aluminum film or foil, bonded to a flexible, optically transparent substrate (not shown), such as a polymer film. In some embodiments, electrode 2008 is an adhesive or connecting layer comprising a transparent conductive material (e.g., a first conductive adhesive) including a conductive metal oxide, a conductive polymer, and/or other suitable conductive agent applied to a substrate (not shown). For example, a thin layer of conductive material can be deposited (e.g., sputtering, vapor deposition) directly onto a suitable substrate, such as a polymer substrate (e.g., PET). In some embodiments, the thickness of electrode 2008 is less than 5 microns. In some embodiments, the thickness of electrode 2008 is between 1 micron and 3 microns. In some embodiments, the thickness of electrode 2008 is less than 1 micron.

The first electrode, electrode 2006, is bonded to the electrophoretic material layer 2004 on a surface opposite the piezoelectric material 2002 and the electrode 2008. For example, the electrode 2006 can be laminated to the electrophoretic material layer 2004 to form a microcapsule or microcell-based planar laminate or FPL as described in the aforementioned U.S. Patent No. 6,982,178.

Electrode 2006 can be pre-formed on a substrate (not shown) using the process described above for electrode 2008. In some embodiments, electrode 2006 can be formed from an adhesive or connecting layer comprising a transparent conductive material deposited on the substrate. The substrate can be a temporary release sheet to facilitate the fabrication of the piezoelectric electrophoretic film. In some embodiments, electrode 2006 has a thickness of less than 5 microns. In some embodiments, electrode 2006 has a thickness between 1 and 3 microns.

In some embodiments, the electrophoretic material layer 2004 is fabricated onto the electrode 2006 prior to being combined with the piezoelectric material 2002 and the electrode 2008. For example, the electrode 2006 can be coated with an electrophoretic medium layer comprising a plurality of microcapsules containing a non-polar fluid and charged pigment particles (not shown in FIG. 20 ). Alternatively, an electrophoretic medium layer comprising a plurality of microcellular structures can be formed on the electrode 2006. For example, an imprintable microcellular precursor material can be layered onto the electrode 2006. Prior to lamination, the precursor material can be treated or coated with a microporous primer containing, for example, acrylates, vinyl ethers, or epoxides, as described in U.S. Patent Nos. 6,930,818, 7,052,571, 7,616,374, 8,361,356, and 8,830,561, which are incorporated herein by reference. The micelle precursor is micro-embossed or lithographically formed into an open microcell structure, which is then filled with the desired electrophoretic medium and sealed with a sealing layer. Before filling the microcells with the desired electrophoretic medium, the open micelles can optionally be cleaned/activated using a vapor plasma treatment.

In some embodiments, the thickness of the electrophoretic material layer 2004 is between 10 microns and 30 microns. In some embodiments, the thickness of the electrophoretic material layer 2004 is approximately 15 microns.

In some embodiments, electrode 2006 can be segmented (not shown). As a result, the grayscale changes caused by the movement of charged pigment particles in electrophoretic material layer 2004 will also appear segmented. Alternatively, electrode 2006 can comprise a single, continuous sheet or film of conductive material, and the grayscale changes will appear continuous. It should be understood that all layers of display 2000 (e.g., layers 2002, 2004, 2006, 2008) can be made transparent, allowing display 2000 to be viewed from any orientation or direction.

In practice, the contrast ratio (CR) of the piezoelectric electrophoretic display 2000 can vary depending on the ratio of surface area 2120 (i.e., the surface area of the electrophoretic material layer 2004 overlapped or covered by the piezoelectric material 2002) to surface area 2121 (i.e., the surface area of the electrophoretic material layer 2004 overlapped or covered by the electrode 2008). Experimental results of CR are shown in Table 2 below.

As shown in Table 2, increasing the ratio of surface area 2121 to surface area 2120 can improve the contrast ratio (CR) of the display. For example, the display shows that the contrast ratio (CR) improves from a value of 2 when the ratio of surface area 2120 to surface area 2121 is 1:2 to a value of 7 when the ratio is 2:1.

In some embodiments, an adhesive layer (not shown) is present between the piezoelectric material 2002 and the electrophoretic material layer 2004. In some embodiments, the adhesive layer has a resistivity between 10 ² ohm*cm and 10 ⁸ ohm*cm, preferably less than 10 ¹² ohm*cm. In some embodiments, the adhesive layer has a resistivity that is at least one order of magnitude greater than the resistivity of the electrode. Thus, the adhesive layer can have the resistivity characteristics of a semiconductor material or a high-resistance insulating material. In this configuration, the adhesive layer can act as a dielectric to prevent the rapid dissipation of charge generated locally in the piezoelectric material 2002, resulting in an improvement in the display's contrast ratio (CR). Furthermore, it was determined that reducing the width of electrode 2006 or electrode 2008 and applying physical stress vertically to the longer side of electrode 2008 can further improve the contrast ratio (CR) of the display.

FIG21A is a schematic cross-sectional view illustrating additional characteristics of the piezoelectric electrophoretic display 2000 of FIG20 according to the presently disclosed subject matter. A first portion 2132 of the electrophoretic material layer 2004 overlaps or is adjacent to the piezoelectric material 2002, and a second portion 2134 of the electrophoretic material layer 2004 overlaps or is adjacent to the electrode 2008, as depicted by dashed line 2122. The first portion 2132 and the second portion 2134 each have a resistance based on the volume of the electrophoretic material they enclose. As indicated by the "+" and "-" symbols, a voltage is generated within the piezoelectric material 2002 through charge separation in response to bending or mechanical stress on the piezoelectric material 2002.

FIG21B is a perspective view illustrating additional features of the piezoelectric electrophoretic display 2000 shown in FIG20 according to the subject matter disclosed herein. For ease of viewing, the electrode 2006 is not shown in FIG21B . As shown in FIG21B , a first portion 2132 of the electrophoretic material layer 2004 overlaps the piezoelectric material 2002 at or near the first surface region 2120 (shown as a dashed line), and a second portion 2134 of the electrophoretic material layer 2004 overlaps the second electrode 2008 at or near the second surface region 2121 (shown as a dashed line).

FIG22 illustrates an exemplary equivalent circuit 2200 of the piezoelectric electrophoretic display 2000 shown in FIG21A and FIG21B according to the presently disclosed subject matter. As shown in FIG21A , three nodes or points: point "A" near the piezoelectric material 2002 and portion 2132, point "B" at 2106 of electrode 1, and point "C" at 2108 of electrode 2 correspond to the same three points A, B, and C shown in the equivalent circuit 2200 of FIG22 . Resistor _R1 corresponds to the resistance of the first portion 2132 of the electrophoretic material layer 2004, and resistor _R2 corresponds to the resistance of the second portion 2134 of the electrophoretic material layer 2004.

In Figure 22, the piezoelectric material layer 2002 is represented as a battery, and the voltage V _PZ is the voltage generated by the piezoelectric material between points A and C. Resistors _R1 and _R2 are shown in series because the voltage source is only present under a portion of the electrophoretic material layer 2004, effectively dividing the layer into separate sections with different electrical characteristics (as depicted by the dashed line 2122). For example, when the voltage V _PZ is generated, the potential at point A is higher than the potential at points B or C. Using the traditional current flow example, current 2201 flows from point A through resistor _R1 to point B, and from point B to point C through resistor _R2 . As can be seen, the voltage generated across resistor _R1 is of opposite polarity to the voltage generated across resistor _R2 . In effect, two opposite voltages are generated in series on different portions of the electrophoretic material layer 2004.

FIG23 is a schematic cross-sectional view of an exemplary piezoelectric electrophoretic display 2300 according to the subject matter disclosed herein. The configuration of display 2300 is similar to the configuration of display 2000 shown in FIG20 , 21A , and 21B . For example, display 2300 includes piezoelectric material 2302 overlapping or covering a first portion of a surface area of an electrophoretic material layer 2304 , as shown in FIG23 as surface area 2320 . However, display 2300 includes a dielectric layer 2330 overlapping all of piezoelectric material 2302 and a second portion of the surface area of electrophoretic material layer 2304 , as shown in FIG23 as surface area 2321 . Electrodes 2308 of display 2300 overlap all of dielectric layer 2330 .

Dielectric layer 2330 can be similar to the adhesive layer described in conjunction with display 2000 in FIG. For example, dielectric layer 2330 can be formed from a material having the resistivity characteristics of a semiconductor material or a high-resistance insulating material. In some embodiments, dielectric layer 2330 has a resistivity between 10 ² ohm*cm and 10 ⁸ ohm*cm, and preferably less than 10 ¹² ohm*cm.

The dielectric layer 2330 prevents the charges generated by the piezoelectric material 2320 from dissipating as quickly as they would if the piezoelectric material 2320 were in direct contact with the electrode 2308. This allows these charges to be applied more effectively and efficiently to the electrophoretic material layer 2304, thereby maximizing the movement of the charged pigment particles, which in turn improves the display contrast ratio (CR).

Table 3 below shows a comparison of the contrast ratios (CRs) achieved between various display designs. The first display, in which the piezoelectric material at least partially overlaps or contacts both electrodes, achieved a contrast ratio (CR) of 1.7. As described above, when the ratio of surface area 2120 to surface area 2121 is 2:1, display 2000 achieves a contrast ratio (CR) of 7. Among the various configurations, display 2300 shown in FIG23 includes: FIG23 shows the best contrast ratio (CR) performance at 18 when the resistivity value of dielectric layer 2330 is approximately 10 ⁸ ohm*cm.

It should be understood that all layers of display 2300 can be made transparent, allowing for viewing from any orientation or direction. Also note that, with reference to the display configurations shown in Figures 20 through 23, the conductive paths between the electrodes, piezoelectric material, and electrophoretic material layers are complete, without requiring any additional conductors or contacts for display operation. This advantageously reduces the overall thickness of the final piezoelectric/electrophoretic display device while also improving the display's CR ratio.

Latent Images:

Displays made in accordance with the present subject matter can be used to display hidden or so-called "latent" images. In particular, an image (e.g., a shape, text, a barcode, etc.) can be layered or printed onto either electrode of the display, such that the image becomes visible only when the charged pigment particles move in response to a voltage generated by bending or other mechanical stress introduced into the piezoelectric material.

In some embodiments, an image is printed or laminated onto one of the electrodes on a white background, and the display is viewed from the opposite electrode. When the display appears white (e.g., white pigment particles are located closest to the electrode without the image printed on it), the printed image is blurred or hidden. However, when the position of the pigment particles shifts in response to the mechanical stress of the piezoelectric material, the white pigment particles move away from the viewing surface, while pigment particles of another color (typically a darker color) move toward the viewing surface, allowing the image to be displayed.

In another embodiment, a dark image is printed or laminated onto one of the electrodes without a background color, and the display is again viewed from the opposite electrode. In this embodiment, when the display is held in front of a dark or black background, the image remains essentially blurred or hidden, regardless of whether the display is displaying white or another color. However, when the display is placed in front of a light or white background, the image becomes visible. For this embodiment, the image becomes visible when the display is displaying white, but is more clearly visible when the display is displaying a darker color.

The piezoelectric electrophoretic display produced as described above can be attached to low-profile objects such as money orders or bank notes. Thus, an image can be integrated into the banknote, allowing users to easily distinguish genuine banknotes from counterfeit ones based on how the display's optical state changes (or does not change) when the banknote is bent or curved.

The display configuration described herein enables the fabrication of fully functional piezoelectrically driven display devices with thicknesses less than 50 microns. Furthermore, the structure of the display described herein is significantly simplified, making the resulting display more sensitive to smaller applied physical stresses.

Thus, fabricating piezoelectric electrophoretic displays having the structures described herein offers advantages over conventional piezoelectric electrophoretic displays. For example, the piezoelectric electrophoretic displays described herein provide an improved means for driving oppositely charged pigment particles in an electrophoretic medium in directions different from one another, without requiring a matrix of individually addressable pixel electrodes. Consequently, piezoelectric electrophoretic displays produced as described herein can be made thin enough to be used in applications requiring them to be durable and largely unobtrusive when incorporated into thin, low-profile end products (such as paper or banknotes) while still providing high contrast between different portions of the electrophoretic material layer due to the effects described above.

In the specific embodiments of the present invention described above, many changes and modifications can be made without departing from the scope of the present invention, as will be apparent to those skilled in the art. Therefore, the above description is to be interpreted in all respects as illustrative rather than restrictive.

This disclosure provides aspects and embodiments as described in the following clauses:

Article 1: An electrophoretic display film having a thickness of less than 100 microns, comprising (from top to bottom) the following: a first adhesive layer; an electrophoretic dielectric layer; a patterned piezoelectric layer comprising differentially polarized regions; and a flexible, light-transmitting electrode layer.

Article 2: An electrophoretic display film as described in Article 1, wherein the electrophoretic medium layer comprises a plurality of microcapsules containing a non-polar fluid and charged pigment particles, and when the patterned piezoelectric layer is deflected, the charged pigment particles move toward or away from the patterned piezoelectric layer, wherein the microcapsules are connected to each other by a polymer binder.

Article 3: An electrophoretic display film as described in Article 1, wherein the electrophoretic medium layer comprises a plurality of micelles containing a non-polar fluid and charged pigment particles, and when the patterned piezoelectric layer is deflected, the charged pigment particles move toward or away from the patterned piezoelectric layer, wherein the non-polar fluid and charged pigment particles are sealed in the micelles by a sealing layer.

Article 4: An electrophoretic display film as described in any one of Articles 1 to 3, wherein the electrophoretic display film is less than 50 microns thick.

Article 5: An electrophoretic display film as described in any one of Articles 1 to 4, wherein the patterned piezoelectric layer comprises polyvinylidene fluoride (PVDF).

Item 6: An electrophoretic display film as described in Item 5, wherein the PVDF is polarized to produce differentially polarized regions.

Article 7: The electrophoretic display film according to any one of Articles 1 to 6, wherein the flexible light-transmitting electrode layer comprises a metal oxide, and the metal oxide comprises tin or zinc.

Item 8: An electrophoretic display film as described in any one of Items 1 to 6, wherein the flexible light-transmitting electrode layer comprises poly(3,4-ethylenedioxythiophene) (PEDOT).

Item 9: An electrophoretic display film assembly comprising a release sheet bonded to the electrophoretic display film according to any one of Items 1 to 8, wherein the release sheet is bonded to the first adhesive layer.

Article 10: The electrophoretic display film assembly according to Article 9 further comprises a second adhesive layer connected to the flexible light-transmitting electrode layer, and a second release sheet connected to the second adhesive layer.

Article 11: A method for manufacturing an electrophoretic display film, comprising: bonding a polyvinylidene fluoride (PVDF) film to a polymer film comprising acrylate, vinyl ether, or epoxy to produce a piezoelectric microcell front-driver film; bonding the piezoelectric microcell front-driver film to a flexible light-transmitting electrode layer, bonding the light-transmitting electrode layer to a first release film via a first adhesive layer; embossing the piezoelectric microcell front-driver film to produce an array of microcells, wherein the microcells have a bottom, a wall, and an upper opening; filling the microcells with an electrophoretic medium through the upper opening; and sealing the upper opening of the filled microcells with a water-soluble polymer to produce an electrophoretic medium layer.

Item 12: The method of Item 11 further comprises applying a primer to the polymer film comprising acrylate, vinyl ether, or epoxy, and then bonding the polymer film to the polyvinylidene fluoride (PVDF) film.

Item 13: The method of Item 11 or 12, further comprising bonding the water-soluble polymer to a second release film via a second adhesive layer.

Article 14: The method according to any one of Articles 11-13, further comprising removing the first release film to produce an electrophoretic display film having a thickness of less than 100 microns.

Article 15: The method of any one of Articles 11-14, wherein the electrophoretic medium layer comprises a plurality of micelles containing a non-polar fluid and charged pigment particles, wherein when the piezoelectric layer is deflected, the charged pigment particles move toward or away from the piezoelectric layer of the driver film in front of the piezoelectric micelles.

Article 16: The method of any one of Articles 11-15, wherein the PVDF is polarized to produce differentially polarized regions.

Article 17: The method of any one of Articles 11-16, wherein the flexible light-transmitting electrode layer comprises a metal oxide, and the metal oxide comprises tin or zinc.

Item 18: The method of any one of Items 11-16, wherein the flexible light-transmitting electrode layer comprises poly(3,4-ethylenedioxythiophene) (PEDOT).

Article 19: The method of any one of Articles 11-18, wherein the polyvinylidene fluoride film is patterned using an electric field to produce regions of different polarizations.

Article 20: The method of any one of Articles 11-18, further comprising patterning the completed electrophoretic display film with an electric field to create regions of different polarization in the polyvinylidene fluoride film.

Article 21: A method for fabricating a piezoelectric electrophoretic display, the method comprising depositing a first conductive adhesive on a first substrate, and depositing a piezoelectric material comprising a polyvinylidene fluoride (PVDF) solution on the first conductive adhesive to produce a piezoelectric layer having a thickness of less than 5 microns. The method also comprises applying a mask to the piezoelectric layer, wherein the mask comprises a plurality of shielding portions that shield a plurality of first regions of the piezoelectric layer and a plurality of non-shielding portions that expose a plurality of second regions of the piezoelectric layer. The method also includes polarizing the piezoelectric layer to produce a plurality of polarized portions of the piezoelectric material corresponding to the second regions of the piezoelectric layer and a plurality of unpolarized portions of the piezoelectric material corresponding to the first regions of the piezoelectric layer. The method also includes removing the mask from the piezoelectric layer and bonding the piezoelectric layer to a micelle precursor material. The method also includes embossing the micelle precursor material to produce a layer of a plurality of micelles, wherein the micelles have a bottom, a plurality of walls, and a top opening. The method also includes filling the micelles with an electrophoretic medium through the top opening, and sealing the top opening of the filled micelles with a water-soluble polymer to form a sealing layer. The method also includes depositing a second conductive adhesive on the second substrate and bonding the sealing layer to the second conductive adhesive.

Article 22: The method of Article 21 further comprises coupling a polymer film comprising an acrylate, vinyl ether, or epoxide to produce the micelle precursor material.

Article 23: The method of Article 21 or 22 further comprises applying a primer to the micelle precursor material before bonding the piezoelectric layer to the micelle precursor material.

Article 24: The method of any one of Articles 21-23 further comprises activating the micelles using a vapor plasma treatment before filling the micelles with the electrophoretic medium.

Article 25: The method of any one of Articles 21-24, wherein the electrophoretic medium layer comprises a non-polar fluid and charged pigment particles, and when the piezoelectric layer is subjected to mechanical stress, the non-polar fluid and the charged pigment particles move toward or away from the piezoelectric layer, wherein the non-polar fluid and the charged pigment particles are encapsulated within the microcells having the encapsulation layer.

Article 26: A method as described in any one of Articles 21-25, wherein the piezoelectric layer is polarized using an electric field.

Article 27: The method of Article 26, wherein the electric field is provided by a coma discharge.

Article 28: In the method according to any one of Articles 21-27, the first substrate and the second substrate are release films.

Article 29: The method of Article 28 further includes peeling the second substrate from the second conductive adhesive and bonding the second conductive adhesive to a target object.

Article 30: The method of Article 29, wherein bonding the second conductive adhesive to the target object comprises heat embossing the second conductive adhesive onto the target object.

Article 31: The method of Article 29 further includes peeling the first substrate from the first conductive adhesive and applying a protective coating on the remaining layers of the piezoelectric electrophoretic display and the target object.

Article 32: In the method of Article 31, the protective coating comprises a paint.

Article 33: A method as described in any of Articles 29 to 32, wherein the object comprises one of a paper, a bank note, and a bill of exchange.

Article 34: A method for manufacturing a piezoelectric electrophoretic display, the method comprising depositing a piezoelectric material comprising a polyvinylidene fluoride (PVDF) solution on a temporary substrate to produce a piezoelectric layer having a thickness of less than 5 microns; bonding the piezoelectric layer to a first substrate using a first conductive adhesive, wherein the temporary substrate is removed from the piezoelectric layer during the bonding process; applying a mask to the piezoelectric layer, the mask comprising a plurality of shielding portions shielding a plurality of first regions of the piezoelectric layer and a plurality of non-shielding portions exposing a plurality of second regions of the piezoelectric layer; and polarizing the piezoelectric layer to produce piezoelectric polarization corresponding to the second regions of the piezoelectric layer. The method further comprises forming a plurality of polarized portions of a piezoelectric material and a plurality of unpolarized portions of the piezoelectric material corresponding to the first regions of the piezoelectric layer; removing the mask from the piezoelectric layer and depositing a second conductive adhesive on a second substrate; combining the second conductive adhesive with a micelle precursor material and embossing the micelle precursor material to produce a layer of a plurality of micelles, wherein the micelles have a bottom, a plurality of walls, and a top opening; filling the micelles with an electrophoretic medium through the top opening, and sealing the top opening of the filled micelles with a water-soluble polymer to form a sealing layer; and bonding the sealing layer to the piezoelectric layer.

Article 35: The method of Article 34 further comprises coupling a polymer film comprising an acrylate, vinyl ether, or epoxide to produce the micelle precursor material.

Article 36: The method of Article 35 further includes applying a primer to the micelle precursor material before bonding the second conductive adhesive to the micelle precursor material.

Article 37: The method of any one of Articles 34-36 further comprises activating the micelles using a vapor plasma treatment before filling the micelles with the electrophoretic medium.

Article 38: The method of any one of Articles 34-37, wherein the electrophoretic medium layer comprises a non-polar fluid and charged pigment particles, and when the piezoelectric layer is subjected to mechanical stress, the non-polar fluid and the charged pigment particles move toward or away from the piezoelectric layer, wherein the non-polar fluid and the charged pigment particles are sealed within the microcells having the sealing layer.

Article 39: A method as described in any one of Articles 34-38, wherein the piezoelectric layer is polarized using an electric field.

Article 40: The method of Article 39, wherein the electric field is provided by a coma discharge.

Article 41: The method of any one of Articles 34-40, wherein the first substrate and the second substrate are release films.

Article 42: The method of Article 41 further includes peeling the second substrate from the second conductive adhesive and bonding the second conductive adhesive to a target object.

Article 43: The method of Article 42, wherein bonding the second conductive adhesive to the target object comprises heat embossing the second conductive adhesive onto the target object.

Article 44: The method of Article 42 further includes peeling the first substrate from the first conductive adhesive and applying a protective coating on the remaining layers of the piezoelectric electrophoretic display and the target object.

Article 45: The method of Article 44, wherein the protective coating comprises a paint

Article 46: The method of any of Articles 42-45, wherein the object comprises one of a paper, a bank note, and a money order.

Article 47: A method for manufacturing a piezoelectric electrophoretic display, comprising depositing a first conductive material on a first substrate to form a first electrode; bonding the first electrode to a first surface of the electrophoretic material layer; depositing a piezoelectric material on a second surface of the electrophoretic material layer, wherein the piezoelectric material overlaps with a first surface region of the second surface of the electrophoretic material layer; and depositing a second conductive material to form a second electrode, wherein the second electrode is formed to overlap with all of the piezoelectric material and a second surface region of the second surface of the electrophoretic material layer.

Article 48: The method of Article 47, wherein the electrophoretic material layer comprises: a first portion of the electrophoretic material overlapping the first surface area; and a second portion of the electrophoretic material overlapping the second surface area.

Article 49: The method of Article 48, wherein the first portion of the electrophoretic material has a first resistance and the second portion of the electrophoretic material has a second resistance.

Article 50: The method of Article 49, wherein the value of the first resistor and the value of the second resistor are based on a ratio of the first surface area to the second surface area.

Article 51: The method of Article 49 or 50, wherein applying a mechanical stress to the piezoelectric material generates a first voltage across a first portion of the electrophoretic material and generates a second voltage across a second portion of the electrophoretic material, wherein the first voltage and the second voltage have opposite polarities.

Article 52: The method of Article 47, wherein the layer of electrophoretic material comprises: a first portion of electrophoretic material having a first resistance corresponding to a first volume of electrophoretic material overlapping the first surface region; and a second portion of electrophoretic material having a second resistance corresponding to a second volume of electrophoretic material overlapping the second surface region.

Article 53: The method of Article 52, wherein the value of the first resistor and the value of the second resistor are based on the ratio of the first surface area to the second surface area.

Article 54: The method of Article 52 or 53, wherein applying a mechanical stress to the piezoelectric material generates a first voltage across a first portion of the electrophoretic material and generates a second voltage across a second portion of the electrophoretic material, wherein the first voltage and the second voltage have opposite polarities.

Article 55: The method of any one of Articles 52-54, wherein the combining comprises: coating the first electrode with a micelle precursor material; embossing the micelle precursor material to produce a micelle layer, wherein the micelles have a bottom, a plurality of walls, and a top opening; filling the micelles with an electrophoretic medium through the top opening; and sealing the top opening of the filled micelles with a water-soluble polymer to form a sealing layer.

Article 56: The method of Article 55 further comprises applying a primer to the micellar precursor material before imprinting the micellar precursor material.

Article 57: The method of Article 56 further comprises activating the micelles by treating them with steam plasma before filling the micelles with the electrophoresis medium.

Article 58: A method as described in any of Articles 55-57, wherein the electrophoretic medium comprises a non-polar fluid and charged pigment particles, and when the piezoelectric material is subjected to mechanical stress, they move toward or away from the piezoelectric material, wherein the non-polar fluid and charged pigment particles are sealed in micelles using a sealing layer.

Item 59: The method of any of Items 55-58 further comprising applying a layer of adhesive material between the piezoelectric material and the first surface region of the second surface of the electrophoretic material layer, wherein the layer of adhesive material has a resistivity between 10 ² ohm*cm and 10 ¹² ohm*cm.

Article 60: The method of any one of Articles 55-59 further comprises applying an adhesive material layer between the piezoelectric material and the first surface region of the second surface of the electrophoretic material layer, wherein the adhesive material layer has a resistivity that is at least one order of magnitude greater than that of the first and second electrodes.

Article 61: The method of any one of Articles 55-60 further includes depositing a dielectric layer before depositing the second conductive material, wherein the dielectric layer is formed to overlap with all of the piezoelectric material and the second surface region of the second surface of the electrophoretic layer, and wherein the second electrode is formed to overlap with the entire dielectric layer.

Clause 62: The method of Clause 61, wherein the dielectric layer has a resistivity between 10 ² ohm*cm and 10 ¹² ohm*cm.

Article 63: The method of Article 61, wherein the resistivity of the dielectric layer is at least one order of magnitude greater than that of the first electrode and the second electrode.

Article 64: The method of any one of Articles 55-63 further comprises printing one or more images onto at least one of the first electrode and the second electrode.

Article 65: The method of any one of Articles 55-64 further comprises securing the piezoelectric display to an object selected from the group consisting of paper, bank notes, and money orders.

1400: Methods

1410, 1420, 1430, 1440, 1450, 1460, 1470, 1480: Steps

Claims (26)

A method for manufacturing a piezoelectric electrophoretic display comprises: depositing a first conductive adhesive on a first substrate; depositing a piezoelectric material comprising a polyvinylidene fluoride (PVDF) solution on the first conductive adhesive to produce a piezoelectric layer having a thickness of less than 5 microns; applying a mask to the piezoelectric layer, the mask comprising a plurality of shielding portions shielding a plurality of first regions of the piezoelectric layer and a plurality of non-shielding portions exposing a plurality of second regions of the piezoelectric layer; polarizing the piezoelectric layer to produce a plurality of polarized portions of the piezoelectric material corresponding to the second regions of the piezoelectric layer; and The invention relates to a method for forming a piezoelectric layer having a plurality of unpolarized portions of the piezoelectric material corresponding to the first regions of the piezoelectric layer; removing the mask from the piezoelectric layer; bonding the piezoelectric layer with a micelle precursor material; embossing the micelle precursor material to produce a layer of a plurality of micelles, wherein the micelles have a bottom, a plurality of walls, and a top opening; filling the micelles with an electrophoretic medium through the top opening; sealing the top opening of the filled micelles with a water-soluble polymer to form a sealing layer; depositing a second conductive adhesive on a second substrate; and bonding the sealing layer and the second conductive adhesive. The method of claim 1, further comprising coupling a polymer film comprising an acrylate, a vinyl ether, or an epoxide to produce the micelle precursor material. The method of claim 2, further comprising applying a primer to the micelle precursor material before bonding the piezoelectric layer to the micelle precursor material. The method of claim 1, further comprising activating the micelles using a vapor plasma treatment before filling the micelles with the electrophoretic medium. The method of claim 1, wherein the electrophoretic medium layer comprises a non-polar fluid and charged pigment particles, and when the piezoelectric layer is subjected to mechanical stress, the non-polar fluid and the charged pigment particles move toward or away from the piezoelectric layer, wherein the non-polar fluid and the charged pigment particles are sealed in the microcells having the sealing layer. The method of claim 1, wherein the piezoelectric layer is polarized using an electric field. The method of claim 6, wherein the electric field is provided by a coma discharge. The method of claim 1, wherein the first substrate and the second substrate are release films. The method of claim 8, further comprising: peeling the second substrate from the second conductive adhesive; and bonding the second conductive adhesive to a target object. The method of claim 9, wherein bonding the second conductive adhesive to the target object comprises heat stamping the second conductive adhesive onto the target object. The method of claim 9, further comprising: peeling the first substrate from the first conductive adhesive; and applying a protective coating on the remaining layer of the piezoelectric electrophoretic display and the target object. The method of claim 11, wherein the protective coating comprises a paint. The method of claim 9, wherein the object comprises one of a paper, a bank note, and a money order. A method for manufacturing a piezoelectric electrophoretic display comprises: depositing a piezoelectric material containing a polyvinylidene fluoride (PVDF) solution on a temporary substrate to produce a piezoelectric layer having a thickness of less than 5 microns; bonding the piezoelectric layer to a first substrate using a first conductive adhesive, wherein the temporary substrate is removed from the piezoelectric layer during the bonding process; applying a mask to the piezoelectric layer, the mask comprising a plurality of shielding portions shielding a plurality of first regions of the piezoelectric layer and a plurality of non-shielding portions exposing a plurality of second regions of the piezoelectric layer; polarizing the piezoelectric layer to produce polarizations corresponding to the second regions of the piezoelectric layer; The invention relates to a method for forming a piezoelectric layer having a plurality of polarized portions of a piezoelectric material and a plurality of unpolarized portions of the piezoelectric material corresponding to the first regions of the piezoelectric layer; removing the mask from the piezoelectric layer; depositing a second conductive adhesive on a second substrate; combining the second conductive adhesive with a micelle precursor material; embossing the micelle precursor material to produce a layer of a plurality of micelles, wherein the micelles have a bottom, a plurality of walls and a top opening; filling the micelles with an electrophoretic medium through the top opening; sealing the top opening of the filled micelles with a water-soluble polymer to form a sealing layer; and combining the sealing layer with the piezoelectric layer. The method of claim 14, further comprising coupling a polymer film comprising an acrylate, vinyl ether, or epoxide to produce the micelle precursor material. The method of claim 15, further comprising applying a primer to the micelle precursor material before bonding the second conductive adhesive to the micelle precursor material. The method of claim 14, further comprising activating the micelles using a vapor plasma treatment before filling the micelles with the electrophoretic medium. The method of claim 14, wherein the electrophoretic medium layer comprises a non-polar fluid and charged pigment particles, and when the piezoelectric layer is subjected to mechanical stress, the non-polar fluid and the charged pigment particles move toward or away from the piezoelectric layer, wherein the non-polar fluid and the charged pigment particles are sealed in the microcells having the sealing layer. The method of claim 14, wherein the piezoelectric layer is polarized using an electric field. The method of claim 19, wherein the electric field is provided by a coma discharge. The method of claim 14, wherein the first substrate and the second substrate are release films. The method of claim 21, further comprising: peeling the second substrate from the second conductive adhesive; and bonding the second conductive adhesive to a target object. The method of claim 22, wherein bonding the second conductive adhesive to the target object comprises heat stamping the second conductive adhesive onto the target object. The method of claim 22, further comprising: peeling the first substrate from the first conductive adhesive; and applying a protective coating on the remaining layer of the piezoelectric electrophoretic display and the target object. The method of claim 24, wherein the protective coating comprises a paint. The method of claim 22, wherein the object comprises one of a paper, a bank note, and a money order.