Piezoelectrophoretic film containing patterned piezoelectric polarity for generating images via electrophoretic medium

Abstract

Thin piezoelectric films and display films comprising the thin piezoelectric films. In some embodiments, the piezoelectric material of the piezoelectric films can be patterned with a high-voltage electric field after fabrication of the piezoelectric films. Such films are useful as security markers, authentication films, or sensors. The films are generally flexible. Some films are less than 100 μm thick. Displays formed from the films do not require an external power source.

Description

Background Art

[0001] (Reference to Related Applications) This application claims the priority of U.S. Patent Application No. 63 / 314,584, filed on February 28, 2022. All patents and publications disclosed herein are incorporated by reference in their entirety.

[0002] 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 includes two electrodes placed facing each other, which provide an electric field and drive the movement of the charged pigment particles. One of the electrodes is usually transparent. When a voltage difference is applied between the two electrodes, the pigment particles migrate to one side or the other, making either the color of the pigment particles or the color of the solvent (if colored) visible from the viewing side. The electrophoretic fluid typically includes a non-polar solvent and one or more sets of charged particles. The particles can have different optical properties (color), different charges (positive or negative), different magnitudes of charge (zeta potential), and / or different absorptive properties (broadly, light absorptivity, broadly, light reflectivity, or selective absorptivity or selective reflectivity). In cases where there are multiple sets of particles with opposite charge polarities, the application of an electric field can cause one set of particles to appear on the viewing surface while the other particles are driven away from the viewing surface.

[0003] Many electrophoretic displays are bistable, and their optical states persist even after the activating electric field is removed. The bistability mainly results from an induced dipole charge layer formed around the charged pigment due to the complex interactions among the pigment, charge control agent, and free polymer dispersed in the solvent. Bistable displays can persist for several years in their last addressed optical state before being switched again using the application of a new driving field.

[0004] Driving an electrophoretic display requires a power source to provide an electric field between electrodes. The power source is typically a battery, which provides power to the electrodes via a drive network. One or more electrodes may be incorporated within an active matrix backplane. The power source could be, for example, a photovoltaic cell, a fuel cell, or a wall current-operated power source. The power source could also be a piezoelectric element, which generates charge through physical motion or thermal expansion, as described in U.S. Patent No. 5,930,026 (integrated as a whole by reference). In all these examples, several types of drive networks are required to provide an electrical path between the power source and the electrodes, and typically, the network includes control elements such as switches and transistors. In most cases, the network is fairly commonplace, however, it typically adds bulk and structural limitations to the final display (i.e., it is not flexible or torsionable). There is a need for extremely simple, flexible, durable, and thin electrophoretic displays for applications such as security markers, sensors, and indicators. [Overview of the Initiative] [Means for solving the problem]

[0005] 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 positioned between the layer of electrophoretic material and the first conductive layer, wherein the piezoelectric material overlaps with a portion of the layer of electrophoretic material, and a portion of the first conductive layer overlaps with the remainder of the electrophoretic material.

[0006] In a first aspect, the present invention includes an electrophoretic display film having a thickness (from top to bottom) less than 100 μm, comprising a first adhesive layer and an electrophoretic medium layer, differentialThe electrophoretic medium layer comprises a patterned piezoelectric layer with polarization zones 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, the charged pigment particles moving toward or away from the piezoelectric layer when the piezoelectric layer is bent, and the microcapsules are bonded to each other using a polymer binder. In some embodiments, the electrophoretic medium layer comprises a plurality of microcells containing a nonpolar fluid and charged pigment particles, the charged pigment particles moving toward or away from the piezoelectric layer when the piezoelectric layer is bent, and the nonpolar fluid and charged pigment particles are sealed within the microcells using a seal layer. In some embodiments, the film is less than 50 μm thick. In some embodiments, the patterned piezoelectric layer comprises polyvinylidene fluoride (PVDF). In some embodiments, the PVDF is differential Polarization is performed to generate a polarization zone. In some embodiments, the flexible light-transmitting electrode layer comprises a metal oxide comprising tin or zinc. In some embodiments, the flexible light-transmitting electrode layer comprises poly(3,4-ethyleneoxythiophene) (PEDOT). In some embodiments, the present invention includes an electrophoretic display film assembly comprising a release sheet bonded to an electrophoretic display film as described above, the release sheet being bonded to a first adhesive layer. In some embodiments, a second adhesive layer is bonded to the flexible light-transmitting electrode layer, and the second release sheet is bonded to the second adhesive layer.

[0007] In a second aspect, the present invention includes a method for producing an electrophoretic display film. The method includes: bonding a polyvinylidene fluoride (PVDF) film to a polymer film comprising an acrylate, vinyl ether, or epoxide to produce a piezoelectric microcell precursor film; bonding the piezoelectric microcell precursor film to a flexible light-transmitting electrode layer; bonding the light-transmitting electrode layer to a first release film using a first adhesive layer; embossing the piezoelectric microcell precursor film to produce an array of microcells, wherein the microcells have a bottom, walls, 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 includes coating the polymer film comprising an acrylate, vinyl ether, or epoxide with a primer before bonding the polymer film to the polyvinylidene fluoride (PVDF) film. In some embodiments, the method further includes bonding a water-soluble polymer to a second release film using a second adhesive layer. In some embodiments, the method further includes removing a first release film to yield an electrophoretic display film having a thickness less than 100 μm. In some embodiments, the electrophoretic medium layer comprises a plurality of microcells containing a nonpolar fluid and charged pigment particles, the charged pigment particles moving toward or away from the piezoelectric layer when the piezoelectric layer is bent, and the nonpolar fluid and charged pigment particles are sealed within the microcells using a seal layer. In some embodiments, the PVDF is polarized differentialPolarization is performed to generate zones. In some embodiments, the flexible light-transmitting electrode layer comprises a metal oxide comprising tin or zinc. In some embodiments, the flexible light-transmitting electrode layer comprises poly(3,4-ethyleneoxythiophene) (PEDOT). In some embodiments, a polyvinylidene fluoride film is patterned using an electric field to generate areas of different polarization. In some embodiments, the method further comprises patterning a completed electrophoretic display film using an electric field to generate areas of different polarization within a polyvinylidene fluoride film.

[0008] In a third aspect, the present invention includes a method for producing an electrophoretic display film. The method includes: dispersing a polyvinylidene fluoride (PVDF) solution on a first release agent to produce a PVDF film less than 10 μm thick; bonding the PVDF film to a second release agent using a conductive adhesive; removing the first release agent; bonding a polymer film comprising acrylate, vinyl ether, or epoxide to produce a piezoelectric microcell precursor film; bonding the piezoelectric microcell precursor film to a flexible light-transmitting electrode layer; bonding the light-transmitting electrode layer to a first release film using a first adhesive layer; and embossing a polymer film comprising acrylate, vinyl ether, or epoxide to produce an array of microcells, wherein the microcells have a bottom, walls, 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 the polymer film comprising an acrylate, vinyl ether, or epoxide before bonding the polymer film to a PVDF film. In some embodiments, the method further comprises bonding a water-soluble polymer to a second release film using a second adhesive layer. In some embodiments, the method further comprises removing the first release film to produce an electrophoretic display film having a thickness of less than 100 μm. In some embodiments, the electrophoretic medium layer comprises a plurality of microcells containing a nonpolar fluid and charged pigment particles, the charged pigment particles moving toward or away from the piezoelectric layer when the piezoelectric layer is bent, and the nonpolar fluid and charged pigment particles are sealed within the microcells using a seal layer. In some embodiments, the PVDF is differentialPolarized to generate a polarization zone. In some embodiments, the flexible light-transmitting electrode layer comprises a metal oxide comprising tin or zinc. In some embodiments, the flexible light-transmitting electrode layer comprises poly(3,4-ethyleneoxythiophene) (PEDOT). In some embodiments, the PVDF film is patterned using an electric field. differential To generate a polarized area. In some embodiments, the method uses an electric field to pattern the completed electrophoretic display film. differential The method further includes generating a polarized area within the PVDF film.

[0009] In the fourth aspect, an electrophoretic display film with a thickness less than 100 μm (from top to bottom) has a first adhesive layer and, differential The material comprises a patterned piezoelectric layer with polarization zones, 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, the charged pigment particles moving toward or away from the piezoelectric layer when the piezoelectric layer is bent, and the microcapsules are bonded to each other using a polymer binder. In some embodiments, the electrophoretic medium layer comprises a plurality of microcells containing a nonpolar fluid and charged pigment particles, the charged pigment particles moving toward or away from the piezoelectric layer when the piezoelectric layer is bent, and the nonpolar fluid and charged pigment particles are sealed within the microcells using a seal layer. In some embodiments, the seal layer is conductive. In some embodiments, the film is less than 50 μm thick. In some embodiments, the patterned piezoelectric layer comprises polyvinylidene fluoride (PVDF). In some embodiments, the PVDF is polarized differentialPolarized to generate zones. In some embodiments, the flexible light-transmitting electrode layer comprises a metal oxide comprising tin or zinc. In some embodiments, the flexible light-transmitting electrode layer comprises poly(3,4-ethyleneoxythiophene) (PEDOT). In some embodiments, the present invention includes an electrophoretic display film assembly comprising a release sheet bonded to an electrophoretic display film as described above, the release sheet being bonded to a first adhesive layer. In some embodiments, the electrophoretic display film is further comprising a flexible light-transmitting It includes a second adhesive layer bonded to the electrode layer and a second release sheet bonded to the second adhesive layer.

[0010] In a fifth aspect, the present invention includes a method for patterning a piezoelectric medium film. The method includes bonding a polyvinylidene fluoride (PVDF) film to a layer of electrophoretic medium to produce a piezoelectric medium film, and patterning the piezoelectric medium film using an electric field. In some embodiments, the electric field is provided by corona discharge. In some embodiments, the method further includes placing a conductive mask adjacent to the piezoelectric medium film before patterning the piezoelectric medium film using corona discharge. In some embodiments, the electric field is provided by a high-voltage writing head. In some embodiments, patterning includes forming regions of different polarities within the PVDF. In some embodiments, patterning generates security markers. In some embodiments, the layer of electrophoretic medium comprises a non-polar fluid and a plurality of microcapsules containing charged pigment particles, the charged pigment particles moving toward or away from the piezoelectric layer when the piezoelectric layer is bent, and the microcapsules are bonded to each other using a polymer binder. In some embodiments, the electrophoretic medium layer comprises a plurality of microcells containing a nonpolar fluid and charged pigment particles, the charged pigment particles moving toward or away from the piezoelectric layer when the piezoelectric layer is bent, and the nonpolar fluid and charged pigment particles are sealed within the microcells using a sealing layer.

[0011] In a sixth aspect, the present invention comprises an adhesive layer and an electrophoretic medium layer, differentialThe electrophoretic display film comprises a patterned piezoelectric layer having polarization zones and a conductive adhesive layer, with a thickness of less than 100 μm (top to bottom). In some embodiments, the electrophoretic medium layer comprises a plurality of microcapsules containing a nonpolar fluid and charged pigment particles, the charged pigment particles moving toward or away from the piezoelectric layer when the piezoelectric layer is bent, and the microcapsules are bonded to each other using a polymer binder. In some embodiments, the electrophoretic medium layer comprises a plurality of microcells containing a nonpolar fluid and charged pigment particles, the charged pigment particles moving toward or away from the piezoelectric layer when the piezoelectric layer is bent, and the nonpolar fluid and charged pigment particles are sealed within the microcells using a seal layer. In some embodiments, the seal layer is conductive. In some embodiments, the film is less than 50 μm thick. In some embodiments, the patterned piezoelectric layer comprises polyvinylidene fluoride (PVDF). In some embodiments, PVDF is differential Polarization is performed to generate a polarization zone. In some embodiments, the present invention includes an electrophoretic display film assembly comprising a release sheet bonded to an electrophoretic display film as described above, wherein the release sheet is bonded to a first adhesive layer. In some embodiments, the present invention includes an electrophoretic display film assembly comprising a release sheet bonded to an electrophoretic display film comprising a conductive adhesive layer, wherein the release sheet is bonded to the conductive adhesive layer.

[0012] In a seventh aspect, the present invention relates to an adhesive layer and differential The present invention includes an electrophoretic display film with a thickness of less than 100 μm (top to bottom) comprising a patterned piezoelectric layer having polarization zones, an electrophoretic medium layer, and a conductive adhesive layer. The present invention provides, for example, the following items: (Item 1) An electrophoretic display film having a thickness of less than 100 μm (from top to bottom), wherein the electrophoretic display film is, in order, The first adhesive layer (520) and, Electrophoretic media layer (405, 530), differential A patterned piezoelectric layer (410, 560, 960) with polarization zones, Flexible light-transmitting electrode layer (580) and An electrophoretic display film equipped with this feature. (Item 2) The electrophoretic medium layer (405, 530) comprises a plurality of microcapsules (990) containing a nonpolar fluid (425) and charged pigment particles (423, 427), wherein the charged pigment particles (423, 427) move toward or away from the patterned piezoelectric layer (410, 560, 960) when the patterned piezoelectric layer (410, 560, 960) is bent, and the microcapsules (990) are bound together with a polymer binder (995), or The electrophoretic display film according to item 1, wherein the electrophoretic medium layer (405, 530) comprises a plurality of microcells (420, 530) containing a nonpolar fluid (425) and charged pigment particles (423, 427), the charged pigment particles (423, 427) move toward or away from the patterned piezoelectric layer (410, 560, 960) when the patterned piezoelectric layer (410, 560, 960) is bent, and the nonpolar fluid (425) and charged pigment particles (423, 427) are sealed within the microcells (420, 530) using a seal layer (430). (Item 3) The electrophoretic display film is the electrophoretic display film described in item 1, having a thickness less than 50 μm. (Item 4) The patterned piezoelectric layers (410, 560, 960) comprise polyvinylidene fluoride (PVDF), and the PVDF may optionally be, differentialThe electrophoretic display film according to item 1, which is polarized to generate polarization zones (460, 470). (Item 5) The electrophoretic display film according to item 1, wherein the flexible light-transmissive electrode layer (580) comprises a metal oxide containing tin or zinc, or poly(3,4-ethylenedioxythiophene) (PEDOT). (Item 6) An electrophoretic display film assembly comprising a release sheet (510) bonded to the electrophoretic display film according to item 1, wherein the release sheet (510) is bonded to the first adhesive layer (520). (Item 7) The electrophoretic display film assembly according to item 6, further comprising a second adhesive layer bonded to the flexible light-transmissive electrode layer (580) and a second release sheet bonded to the second adhesive layer. (Item 8) A method of manufacturing an electrophoretic display film, the method comprising: Bonding a film (1260) of polyvinylidene fluoride (PVDF) to a polymer film (1230) comprising an acrylate, a vinyl ether, or an epoxide to produce a piezoelectric microcell precursor film; Bonding the piezoelectric microcell precursor film to a flexible light-transmissive electrode layer (1280); Using a first adhesive layer (1250) to bond the flexible light-transmissive electrode layer (1280) to a first release film (1255); Embossing the piezoelectric microcell precursor film to produce an array of microcells (1230), the microcells having a bottom, a wall, and an upper opening; Filling the microcells with an electrophoretic medium (405, 530) through the upper opening; The upper opening of the filled microcell is sealed with a water-soluble polymer (1240) to create an electrophoresis medium layer (405, 530). Methods that include... (Item 9) The method according to item 8, further comprising coating the polymer film (1230), which comprises an acrylate, vinyl ether, or epoxide, with a primer (1235) before bonding the polymer film (1230) to the polyvinylidene fluoride (PVDF) film (1260). (Item 10) The method according to item 8, further comprising bonding the water-soluble polymer (1240) to the second release film (1210) using a second adhesive layer (1220). (Item 11) The method according to item 8, further comprising removing the first release film (1255) to produce an electrophoretic display film having a thickness of less than 100 μm. (Item 12) The electrophoretic medium layer (405, 530) comprises a nonpolar fluid (425) and charged pigment particles (423, 427), wherein the charged pigment particles (423, 427) move toward or away from the polyvinylidene fluoride (PVDF) film (1260) when the film (1260) is bent, according to the method of item 8. (Item 13) The polyvinylidene fluoride (PVDF) film (1260) is polarized differential The method described in item 8, which is polarized to generate zones (460, 470). (Item 14) The method according to item 8, wherein the flexible light-transmitting electrode layer (1280) comprises a metal oxide comprising tin or zinc, or poly(3,4-ethyleneoxythiophene) (PEDOT). (Item 15) The method according to item 8, wherein the polyvinylidene fluoride (PVDF) film (1260) is patterned using an electric field to generate areas of different polarization (460, 470). [Brief explanation of the drawing]

[0013] [Figure 1A] Figure 1A shows a side view of the piezoelectric display film of the present invention, which includes a star-shaped area of ​​differential polarization. Three exemplary positions, namely convex, neutral, and concave, are shown from the side. The total thickness of the piezoelectric display film can be less than 100 μm, for example less than 50 μm, for example less than 25 μm.

[0014] [Figure 1B] Figure 1B shows a top view of the piezoelectric display film of the present invention, which includes a star-shaped area of ​​differential polarization. Three exemplary positions, namely convex, neutral, and concave, are shown from above. When the piezoelectric display film is bent, the differential polarization area results in oppositely charged particles appearing on the visible surface.

[0015] [Figure 2A] Figure 2A shows an exemplary thin layer of piezoelectric material on a substrate.

[0016] [Figure 2B] Figure 2B illustrates a method for generating an area of ​​differential polarization within a thin layer of piezoelectric material by using the strong electric field of a corona discharge. By moving the piezoelectric material closer to and further away from the discharge, the amount of polarization can be spatially controlled.

[0017] [Figure 2C] Figure 2C illustrates a method for generating areas of differential polarization within a thin layer of piezoelectric material by using a strong electric field from a corona discharge. A conductive mask is used to pattern the piezoelectric material and generate the areas of differential polarization.

[0018] [Figure 2D]Figure 2D illustrates the polarization patterns that can be achieved using the methods shown in Figures 2B and 2C.

[0019] [Figure 3A] Figure 3A shows a side view of a piezoelectric film that is polarized in direction A.

[0020] [Figure 3B] Figure 3B shows a top view of a piezoelectric film that is polarized in direction A.

[0021] [Figure 3C] Figure 3C shows a side view of a piezoelectric film polarized in the G direction using a conductive mask.

[0022] [Figure 3D] Figure 3D illustrates a top view of a piezoelectric film polarized in the G direction using a conductive mask.

[0023] [Figure 4A] Figure 4A shows an exemplary thin layer of piezoelectric microcell precursor film on a substrate.

[0024] [Figure 4B] Figure 4B illustrates a method for generating an area of ​​differential polarization within a thin layer of piezoelectric material in a piezoelectric microcell precursor film by using a strong electric field from a corona discharge. By moving the piezoelectric microcell precursor film closer to and further away from the discharge, the amount of polarization can be spatially controlled.

[0025] [Figure 4C] Figure 4C illustrates a method for generating areas of differential polarization within a thin layer of piezoelectric material in a piezoelectric microcell precursor film by using a strong electric field from a corona discharge. A conductive mask is used to pattern the piezoelectric material of the piezoelectric microcell precursor film and generate areas of differential polarization.

[0026] [Figure 4D] Figure 4D illustrates the polarization (polarization) pattern within a piezoelectric microcell precursor film that can be achieved using the methods shown in Figures 3B and 3C.

[0027] [Figure 5A] Figure 5A is a schematic cross-sectional view of an embodiment of a piezoelectric film.

[0028] [Figure 5B] Figure 5B is a schematic cross-sectional view of an embodiment of a piezoelectric film.

[0029] [Figure 5C] Figure 5C is a schematic cross-sectional view of an embodiment of a piezoelectric film.

[0030] [Figure 5D] Figure 5D is a schematic cross-sectional view of an embodiment of a piezoelectric film.

[0031] [Figure 6A] Figure 6A is a schematic cross-sectional view of an embodiment of a piezoelectric display.

[0032] [Figure 6B] Figure 6B is a schematic cross-sectional view of an embodiment of a piezoelectric display.

[0033] [Figure 7] Figure 7 details a method for producing a piezoelectric film or (optionally) a display.

[0034] [Figure 8A] Figure 8A is a schematic cross-sectional view of an embodiment of a piezoelectric film.

[0035] [Figure 8B] Figure 8B is a schematic cross-sectional view of an embodiment of a piezoelectric film.

[0036] [Figure 9A]Figure 9A is a schematic cross-sectional view of an embodiment of a piezoelectric film.

[0037] [Figure 9B] Figure 9B is a schematic cross-sectional view of an embodiment of a piezoelectric film.

[0038] [Figure 10A] Figure 10A is a schematic cross-sectional view of an embodiment of a piezoelectric display.

[0039] [Figure 10B] Figure 10B is a schematic cross-sectional view of an embodiment of a piezoelectric display.

[0040] [Figure 10C] Figure 10C is a schematic cross-sectional view of an embodiment of a piezoelectric display.

[0041] [Figure 11] Figure 11 details a method for producing a thin piezoelectric film.

[0042] [Figure 12A] Figure 12A is a schematic cross-sectional view of a piezoelectric film produced using the method shown in Figure 11.

[0043] [Figure 12B] Figure 12B is a schematic cross-sectional view of a piezoelectric display produced using the method shown in Figure 11.

[0044] [Figure 13A] Figure 13A is a schematic cross-sectional view of an alternative piezoelectric film produced using the method shown in Figure 11.

[0045] [Figure 13B] Figure 13B is a schematic cross-sectional view of an alternative piezoelectric display produced using the method shown in Figure 11. [Modes for carrying out the invention]

[0046] Thin piezoelectric films and display films including thin piezoelectric films are disclosed herein. In some embodiments, the piezoelectric material of the piezoelectric film can be patterned using a high-voltage electric field after the piezoelectric film has been fabricated. This feature allows the end user to handle the piezoelectric material, for example, using corona discharge during production, and it may include, for example, a barcode or serial number that is only visible when the piezoelectric film is being manipulated. Such films are useful as security markers, authentication films, indicators, or sensors. The films are generally flexible. Some films have a thickness of less than 100 μm. In some embodiments, the piezoelectric film is less than 50 μm and is foldable without damage. Displays formed using the films do not require an external power supply.

[0047] The term “electro-optics” is used herein to refer to a material having first and second display states having at least one different optical property, as applied to materials or displays, in its conventional sense in the field of imaging technology, and which can be changed from its first display state to its second display state by the application of an electric field to the material. The optical property is typically color, which is perceptible to the human eye, but may be other optical properties such as optical transmittance, reflectance, luminescence, or, in the case of displays intended for machine reading, pseudocolor in the sense of changes in reflectance at electromagnetic wavelengths outside the visible range.

[0048] The terms “bistable” and “bistable” are used herein to refer to a display having a display element having a first and second display state that differs in at least one optical property, after any given element is driven with a finite-duration address pulse to exhibit either the first or second display state, and after the address pulse has terminated, that state will persist for at least several times, e.g., at least four times, the minimum duration of the address pulse required to change the state of the display element. U.S. Patent No. 7,170,670 shows that several grayscale-enabled particle-based electrophoretic displays are stable not only in their extreme black and white states but also in their intermediate gray states, and that the same is true for several other types of electro-optic displays. This type of display is appropriately called “multistable” rather than bistable, but for convenience, the term “bistable” may be used herein to encompass both bistable and multistable displays.

[0049] The term “gray state” is used herein in its conventional sense in the field of imaging technology, referring to an intermediate state between two extreme optical states of a pixel, and not necessarily meaning a black-white transition between these two extreme states. For example, some of E INK’s patents and published applications, referenced below, describe electrophoretic displays where the extreme states are white and dark blue, with the intermediate “gray state” actually being light blue. In fact, as already described, a change in optical state may not be a change in color at all. The terms “black” and “white” may be used hereafter to refer to two extreme optical states of a display, and should generally be understood to include extreme optical states that are not strictly black and white, e.g., the aforementioned white and dark blue states. The term “monochrome” may be used hereafter to refer to a display or driving scheme that drives pixels to only its two extreme optical states without an intervening gray state.

[0050] The term "pixel" is used herein in its conventional sense in the field of display technology to mean the smallest unit of a display capable of producing all the colors that the display itself can produce. In a full-color display, typically each pixel consists of several subpixels, each of which can display less than all the colors that the display itself can produce. For example, in most conventional full-color displays, each pixel consists of a red subpixel, a green subpixel, a blue subpixel, and optionally, a white subpixel, each of which can display a range of colors from black to the brightest version of its defined color.

[0051] Several types of electro-optic displays are known. One type of electro-optic display uses an electrochromic medium in the form of a nanochromic film, which consists of electrodes formed from at least partially semiconductor metal oxides and a plurality of dyeing molecules attached to the electrodes that can reverse the color change. See, for example, O'Regan, B., et al., Nature 1991, 353, 737 and Wood, D., Information Display, 18(3), 24 (March 2002). Also see Bach, U., et al., Adv. Mater., 2002, 14(11), 845. This type of nanochromic film is also described, for example, in U.S. Patents 6,301,038, 6,870,657, and 6,950,220. This type of medium is also typically bistable.

[0052] Another type of electro-optical display is the electrowetting display, developed by Philips and described in Hayes, RA, et al., "Video-Speed ​​Electronic Paper Based on Electrowetting," Nature, 425, 383-385 (2003). U.S. Patent No. 7,420,549 demonstrates that such electrowetting displays can be bistable.

[0053] Another type of electro-optical display that has been the subject of focused research and development for many years is the particle-based electrophoretic display, in which multiple charged particles move through a suspension fluid under the influence of an electric field. Compared to liquid crystal displays, electrophoretic displays can have attributes such as good brightness and contrast, wide viewing angle, state bistability, and low power consumption.

[0054] Electro-optical devices typically comprise an electrophoretic material layer and at least two other layers positioned opposite the electrophoretic material, one of which is an electrode layer. In most such displays, both layers are electrode layers, and one or both of the electrode layers are patterned to define pixels on the display. For example, one electrode layer may be patterned into elongated row electrodes, and the other into elongated column electrodes extending perpendicular to the row electrodes, with pixels defined by the intersections of the row and column electrodes. Alternatively, and more commonly, one electrode layer may have the form of a single continuous electrode, and the other electrode layer may be patterned into a matrix of pixel electrodes, each of which defines one pixel on the display. In another type of electrophoretic display intended for use with a separate stylus, print head, or similar movable electrode, only one of the layers adjacent to the electrophoretic layer contains the electrode, while the layer opposite the electrophoretic layer is typically a protective layer intended to prevent the movable electrode from damaging the electrophoretic layer.

[0055] Numerous patents and applications, assigned to or filed in the name of the Massachusetts Institute of Technology (MIT) and E Ink Corporation, describe various techniques used in encapsulated electrophoretic media and other electro-optical media. Such encapsulated media comprise numerous small capsules, each of which comprises an inner phase containing particles movable by electrophoresis in a fluid medium, and a capsule wall surrounding the inner phase. Typically, the capsules are held within a polymer binder to form a coherent layer positioned between two electrodes. The techniques 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, binders, and encapsulation processes (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. Patents No. 6,982,178 and 7,839,564); (d) backplanes, adhesive layers, and other auxiliary layers, and methods used in displays (see, for example, U.S. Patents 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) A method for driving a display (see, for example, U.S. Patent Nos. 7,012,600 and 7,453,445); (g) Application of displays (see, for example, U.S. Patent Nos. 7,312,784 and 8,009,348); (h) Non-electrophoretic displays (see U.S. Patent Nos. 6,241,921, 6,950,220, 7,420,549, and 8,319,759, and U.S. Patent Application Publication No. 2012 / 0293858); (i) Microcell structures, wall materials, and methods for forming microcells (see, for example, U.S. Patents 7,072,095 and 9,279,906); (j) Methods for filling and sealing microcells (see, for example, U.S. Patent Nos. 7,144,942 and 7,715,088).

[0056] Many of the aforementioned patents and applications recognize that the walls surrounding individual microcapsules in an encapsulated electrophoretic medium may be replaced by a continuous phase, thus producing a so-called "polymer-dispersed electrophoretic display," in which the electrophoretic medium consists of multiple individual droplets of electrophoretic fluid and a continuous phase of polymer material, and that individual droplets of electrophoretic fluid within such a polymer-dispersed electrophoretic display may be considered capsules or microcapsules even if no separate capsule membrane is associated with each individual droplet. See, for example, U.S. Patent No. 6,866,760. For the purposes of this application, such polymer-dispersed electrophoretic media are considered a variant of encapsulated electrophoretic media.

[0057] A related type of electrophoretic display is the microcell electrophoretic display, also known as MICROCUP®. In microcell electrophoretic displays, charged particles and fluids are not encapsulated within microcapsules, but instead are held within multiple cavities formed within a carrier medium, typically a polymer film. See, for example, U.S. Patents 6,672,921 and 6,788,449 (both incorporated by referring to them as a whole).

[0058] Electrophoretic media are often impermeable (for example, in many electrophoretic media, the particles substantially block the transmission of visible light through the display) and can operate in reflective mode. However, many electrophoretic displays can be manufactured to operate in a so-called "shielding mode," where one display state is substantially impermeable and the other is light-transmitting. See, for example, U.S. Patents 5,872,552, 6,130,774, 6,144,361, 6,172,798, 6,271,823, 6,225,971, and 6,184,856. Dielectric displays, which are similar to electrophoretic displays but rely on variations in electric field strength, can operate in a similar mode. See, for example, U.S. Patent 4,418,346. Other types of electro-optical displays may also be capable of operating in shielding mode. Electro-optical media operating in occlusion mode may be useful in multilayer structures for full-color displays. In such a structure, at least one layer adjacent to the viewing surface of the display operates in occlusion mode, exposing or concealing a second layer located further away from the viewing surface.

[0059] Encapsulated electrophoretic displays typically do not suffer from the clustering and sedimentation failure modes of conventional electrophoretic devices and offer further advantages such as the ability to print or coat displays on a wide variety of flexible and rigid substrates. (The use of the word “printing” is intended to include, but is not limited to, all forms of printing and coating, including, pre-metering coatings such as patch-die coating, slot or extrusion coating, slide or cascade coating, curtain coating; roll coatings such as knife-over-roll coating, forward and reverse roll coating; gravure coating; immersion coating; spray coating; meniscus coating; spin coating; brush coating; air-knife coating; silkscreen printing processes; electrostatic printing processes; thermal printing processes; inkjet printing processes; electrophoretic deposition (see U.S. Patent No. 7,339,715); and other similar techniques.) Therefore, the resulting displays can be flexible. Furthermore, since the display medium can be printed using a variety of methods, the displays themselves can be manufactured inexpensively.

[0060] The aforementioned U.S. Patent No. 6,982,178 describes a method for assembling a solid-state electro-optic display (including a particle-based electrophoretic display) that is well-suited for mass production. Essentially, the patent describes a so-called “front-plane lamination” (“FPL”), which comprises, in order, a light-transmitting conductive layer, a layer of a solid-state electro-optic medium in electrical contact with the conductive layer, an adhesive layer, and a release sheet. Typically, the light-transmitting conductive layer may be supported on a light-transmitting substrate, which is preferably flexible in the sense that the substrate can be manually wound around a drum with a diameter of (for example) 10 inches (254 mm) without permanent deformation. The term “light transmittance” as used in this patent and herein means that a layer so designated transmits enough light to enable an observer looking through that layer to observe changes in the display state of an electro-optic medium, and is usually visible through the conductive layer and adjacent substrates (if any). If the electro-optic medium exhibits changes in reflectance at invisible wavelengths, the term “light transmittance” should naturally be interpreted as referring to the transmission of the relevant invisible wavelengths. The substrate is typically a polymer film, usually having a thickness in the range of about 1 to about 25 mils (25 to 634 μm), preferably about 2 to about 10 mils (51 to 254 μm). The conductive layer may conveniently be, for example, a thin metal or metal oxide layer of aluminum or ITO, or a conductive polymer. Poly(ethylene terephthalate) (PET) films coated with aluminum or ITO are commercially available, for example, as "aluminum-coated Mylar" ("Mylar" is a registered trademark) from EIdu Pont de Nemours & Company (Wilmington DE), and such commercial materials can be used with favorable results in front-plane lamination.

[0061] The assembly of an electro-optical display using such a front-plane lamination can be achieved by removing the release sheet from the front-plane lamination and bringing the adhesive layer into contact with the backplane under conditions effective for bonding the adhesive layer to the backplane, thereby fixing the adhesive layer, the electro-optical medium layer, and the conductive layer to the backplane. This process is very suitable for mass production because the front-plane lamination is typically mass-produced using roll-to-roll coating techniques and can then be cut into pieces of any size required for use with a particular backplane.

[0062] U.S. Patent No. 7,561,324 describes a so-called “double release sheet,” which is essentially a simplified version of the front-plane lamination described in U.S. Patent No. 6,982,178. One form of the double release sheet comprises a layer of solid electro-optic medium sandwiched between two adhesive layers, one or both of which are covered by a release sheet. Another form of the double release sheet comprises a layer of solid electro-optic medium sandwiched between two release sheets. Both forms of the double release film are intended for use in a process generally similar to the process for assembling an electro-optic display from the front-plane lamination already described, but involving two separate laminations, typically in the first lamination in which the double release sheet is laminated onto the front-plane electrodes to form the front-plane assembly, and then in the second lamination in which the front-plane assembly is laminated onto the back-plane to form the final display, although the order of these two laminations may be reversed as desired.

[0063] The subject matter presented herein relates, in particular, to the design of piezoelectric display structures, which do not require a power source (e.g., battery or wired power source, photovoltaic power source, etc.) for the electrophoretic display to operate. The assembly of such an electrophoretic display is therefore simplified. In some embodiments, the piezoelectric material and the electrophoretic medium are directly laminated together. The electrophoretic medium may be contained in microcells, microcapsules, as described above, or the electrophoretic medium may be dispersed in a polymer matrix. In some embodiments, the piezoelectric material is polarized (i.e., written) using a high-voltage electric field after the piezoelectric film or piezoelectric display has been generated, as discussed below.

[0064] Pneumatic charge is the electric charge that accumulates in a solid material in response to applied mechanical stress. Suitable materials for the subject disclosed herein may include polyvinylidene fluoride (PVDF), quartz (SiO2), berinite (AlPO4), gallium phosphate (GaPO4), tourmaline, barium titanate (BaTiO3), lead zirconate titanate (PZT), zinc oxide (ZNO), aluminum nitride (AlN), lithium tantalate, gallium silicate lanthanum, sodium potassium tartrate, and any other known piezoelectric materials. In piezoelectric materials,

[0065] The piezoelectric films and piezoelectric displays described herein use voltage to drive the charged pigments of the electrophoretic medium. Therefore, when the piezoelectric material bonded to the electrophoretic medium layer is manipulated, the color of the electrophoretic material on the viewing surface changes. For example, a voltage can be generated by bending a segment of the piezoelectric material or by introducing stress into a segment, and this voltage can be used to cause the migration of the color pigments of the electrophoretic material. When segments of the piezoelectric material with different polarizations are used, or, differentialWhen areas of polarization are generated within a piezoelectric film, an electrophoretic medium having two types of oppositely charged pigments can be used to generate patterns with a high contrast ratio, as shown in Figures 1A and 1B. As used herein, the term “contrast ratio” (CR) in reference to 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 is capable of producing. Typically, a high contrast ratio, or CR, is a desired aspect of a display.

[0066] Figures 1A and 1B illustrate side and top views of an exemplary piezoelectric display 100 according to the subject disclosed herein. In this embodiment, the piezoelectric material is laminated on an electrophoretic medium layer (discussed below), and one or more electrodes are included to provide a suitable electric field and propagate the electrophoretic particles toward (or away from) the viewing surface. In the embodiments shown in Figures 1A and 1B, a second area 120 of the piezoelectric material of the piezoelectric display 100 is polarized in the opposite direction to the first area 110, so that when the piezoelectric display 100 is operated from a neutral state (position 2) to either a first (position 1) or second (position 3) optical state, the first and second areas (110, 120) will achieve different colors within the two areas. In the case of an electrophoretic medium having a set of black and white oppositely charged particles, a high-contrast image will be formed, for example, as shown in Figure 1B. Since the first and second areas (110, 120) of the piezoelectric material can be polarized with good resolution (as discussed below), various images / information can be encoded so that they "appear" when the piezoelectric display 100 is operated. For example, a security ribbon may be generated to exist in a neutral state as a gray fragment, but when the security ribbon is bent, the ribbon will display a security seal such as the star shape shown in Figure 1B. Naturally, the security seal may, as an alternative, include barcodes, numbers, words, telephone numbers and internet addresses, QR codes (registered trademarks), photographs, halftone images, or logos.

[0067] In principle, piezoelectric materials (and optionally adjacent electrophoretic materials) can be polarized using a localized strong electric field, as shown in Figures 2A-3D. It is known that piezoelectric materials (especially films) can be stimulated to move between polarized states using various external stresses such as mechanical stretching, heat, electromagnetic fields, and applied forces. The piezoelectric effect is closely related to the generation of electric dipole moments in solids. Dipole density or polarization (P) corresponds to the dipole moment / volume of a crystallographic unit cell, typically C / m 2It is measured at [location]. The resulting dipole density P is a vector field specific to a particular region of the material (i.e., differential polarization transformation ) Similar to magnets, dipoles in each other's vicinity tend to align within a region (Weiss domain). When initially generated, domains are usually oriented randomly. However, using various multi-step processes, domains can be reoriented. differential They can be aligned to produce localized areas of polarization. The process in these aligned regions is known as polarization.

[0068] While many piezoelectric materials are crystalline, several flexible piezoelectric polymers such as polyvinylidene fluoride (PVDF) and its copolymers, polyamides, and parylene-C are known. Amorphous polymers such as polyimide and polyvinylidene chloride (PVDC) are classified as amorphous bulk polymers. The standard procedure for fabricating piezoelectric films such as polyvinylidene fluoride (PVDF) involves generating a polymer film, stretching it to generate stress, and aligning dipoles. Stretching converts the unpolarized alpha phase region of the PVDF into a polarized beta phase. Subsequent stimulation is added to the polar region of the beta phase, for example, using a strong electric field. Other methods for aligning the beta phase, such as laser irradiation and concentrated magnetic fields, are also described in the literature. See, for example, U.S. Patent No. 9,831,417. If the stimulation can be performed with sufficiently high resolution, the poles can be used to generate a visible pattern, for example, as shown in Figures 1A and 1B. In some embodiments, the electric field is applied at high temperatures, however, this is not always necessary. In particular, with respect to very thin piezoelectric films, e.g., less than 20 μm, e.g., less than 10 μm, less than 5 μm, it is feasible to polarize the film without high temperatures, provided that the electric field is sufficiently strong. In the case of PVDF, an additional benefit is that such films are also optically transparent, and therefore they can be bonded to an electrophoretic medium between the viewing surface and the electrophoretic medium, or the electrophoretic medium can be layered between the piezoelectric film and the viewing surface.

[0069] Exemplary methods for polarizing thin films of piezoelectric materials are illustrated in Figures 2A-2D. A thin film of a piezoelectric material 210, such as PVDF, can be melted and spin-coated onto a substrate 220 to form a thin film. The thin film can optionally be thermally adjusted or stretched prior to polarization. Suitable bulk PVDF is available, for example, as bulk powder or film from Sigma-Aldrich. Pre-stretched piezoelectrically active PVDF films are also available, for example, from PolyK Technologies (State College, PA). Such films can also be fabricated with a metallized electrode coating on one side, which can be used for piezoelectric films and displays; however, polarization of piezoelectric electrophoresis with a backing metal layer using an electric field is difficult. Copolymers of PVDF, such as polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE), are also available from both 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 suitable volatile solvent such as dimethylformamide (DMF), and then slot-coating the concentrated solution onto a suitable transport substrate or release agent, for example, using a roll-to-roll process. The PVDF-coated substrate is then heated to remove the DMF, resulting in a thin film of PVDF (e.g., less than 20 μm, e.g., less than 10 μm, less than 5 μm). By carefully controlling the thermal cycling, the resulting film can be pre-conditioned to have a larger number of beta-phase domains suitable for polarization.

[0070] As shown in Figures 2B and 2C, a thin film of piezoelectric material 210 can be polarized using a high-voltage corona discharge 230 with spatial focus. Suitable corona discharge equipment is available, for example, from Simco-Ion (Alameda, CA). Such equipment can generate localized 10-50 kV fields, e.g., 30 kV fields, e.g., 20 kV fields, which can be introduced into a piezoelectric material of several micrometers in thickness that will be polarized. Spatial focus can be achieved using a steerable electric field and / or gas flow, which focuses / steers the flow of ions emitted from the corona discharge. As shown in Figure 2B, the high-voltage corona discharge 230 is moved in three dimensions. differential Areas of polarization can be generated, i.e., the piezoelectric material 210 can be patterned. Alternatively, the piezoelectric material 210 can be mounted on an XYZ stage, which in a controlled manner allows the film workpiece to approach the high-voltage corona discharge 230. In an alternative embodiment, a conductive mask 240 can be used to protect areas of the piezoelectric material 210 from the high-voltage corona discharge 230, as shown in Figure 2C. The conductive mask may be made from, for example, conductive stainless steel, or another conductive material that can withstand proximity to the corona discharge. Alternative masks made from charge-absorbing or charge-blocking materials such as glass, plastic, or rubber would also function. As the high-voltage corona discharge 230 moves over the thin film of the piezoelectric material 210, the thin film of the piezoelectric material 210 is polarized only in areas where the conductive mask 240 does not cover the thin film of the piezoelectric material 210. In addition, the polarity of the high-voltage corona discharge 230 can be reversed such that some areas are polarized in a first direction, some areas are polarized in a second direction, and some areas are randomly polarized or depolarized. See also Figures 3A-3D.

[0071] Using the techniques shown in Figures 2B and 2C, the results are shown as 260 and 270 in Figure 2D. differential It is straightforward to produce a thin film of piezoelectric material 210 with polarized areas P1 and P2. differential The polarized areas 260 and 270 do not necessarily have opposite polarities of equal magnitude; however, such an arrangement generally provides a better contrast ratio when a two-particle electrophoretic medium is used with a thin film of piezoelectric material 210. For example, as shown in 2D, the first area 260 may be polarized toward the viewer, while the second area 270 may be polarized toward the viewer. This technique is further illustrated in Figures 3A-3D, which show how a single area 360 of a thin film of piezoelectric material deposited on a substrate 320 can be polarized to have a polarization vector toward the outward side of the page, as shown in Figure 3B. Thus, when the thin film of piezoelectric material is manipulated (bent), it will preferentially drive one polarity of the electrophoretic particles toward the viewing surface. As shown in Figure 3C, a second area 370 of the piezoelectric material thin film can be polarized in different directions, with or without the addition of a conductive mask 340, depending on the application, resulting in several patterned combinations of polarity and size. As shown in Figure 3D, some portions of 370 are polarized to the visible surface, while shading is generated by the conductive mask 340. Therefore, when the piezoelectric material is manipulated (bent), it will preferentially drive one polarity of the electrophoretic particles toward the visible surface, except in the areas where the polarization is masked, and the areas where the polarization is masked will remain in a neutral color stage, thereby producing a certain pattern, such as a security seal.

[0072] Figure 2A-3D shows, differential Various techniques that may be used to generate a polarization area within a thin film of piezoelectric material 210 are illustrated. As shown in Figures 4A-4D, these same techniques are similar, differentialIt can also be used to generate a polarization area within a thin piezoelectric medium film 405. As shown in Figure 4A, a thin film of piezoelectric material 410 can be bonded to a layer of electrophoretic microcell 420 to produce a piezoelectric medium film 405. The thin film of piezoelectric material 410 can be bonded to a layer of electrophoretic microcell 420 using an adhesive layer (not shown), or the thin film of piezoelectric material 410 can be spin-coated directly to a layer of electrophoretic microcell 420, i.e., as discussed above with respect to Figure 2A. The electrophoretic microcell 420 is typically formed from polymers such as acrylates, vinyl ethers, or epoxides, as described in detail, for example, in U.S. Patents 6,930,818, 7,052,571, 7,616,374, 8,361,356, and 8,830,561 (all incorporated within by reference to them as a whole). In some embodiments, the layers of the electrophoretic microcell 420 may be filled with an electrophoretic medium 425 containing two or more electrophoretic particles 423 and 427 having different electrophoretic mobilities and optical properties. The electrophoretic medium 425 may be sealed with a seal layer 430, preferably a water-soluble seal layer, as described in U.S. Patents 7,560,004, 7,572,491, 9,759,978, or 10,087,344 (all of which are incorporated within by referring to them as a whole). In some embodiments, the layers of the electrophoretic microcell 420 are formed on a release agent, filled with the electrophoretic medium 425, sealed with a seal layer 430, and then the filled and sealed electrophoretic microcell 420 is used as a substrate for the formation of a thin film of piezoelectric material 410. The resulting structure is a thin piezoelectric medium film 405. In other embodiments, a thin film of the piezoelectric material 410 is laminated onto an acrylate, vinyl ether, or epoxide film that is a precursor for the layer of the electrophoretic microcell 420.A thin film of the piezoelectric material 410 and a precursor material is then embossed on the precursor side (discussed below), subsequently filled with electrophoretic medium 425 to produce a thin piezoelectric medium film 405, and sealed with a seal layer 430. In yet another embodiment (not shown in Figures 4A-4D), a complete microcell front-plane laminate of the type described in U.S. Patent No. 7,158,282, which is commercially available from E Ink Corporation, can be used as a substrate for a thin film of the piezoelectric material 410, and the thin film of the piezoelectric material 410 can be polarized as described below. It is worth noting that when the front-plane laminate material is used, the final structure also includes a conductive layer, which is typically light-transmitting. The front-plane laminate can be oriented so that the light-transmitting electrode layer is in contact with the thin film of the piezoelectric material 410, or the front-plane laminate can be flipped so that the seal layer is in contact with the thin film of the piezoelectric material 410.

[0073] Once the thin piezoelectric medium film 405 is produced, the thin film of piezoelectric material 410 can be dealt with as described with respect to Figures 2A-3D above. That is, the thin film of piezoelectric material 410 can be polarized using a high-voltage corona discharge 230 with spatial focus, as shown in Figure 4B, by mounting the thin piezoelectric medium film 405 on an XYZ stage that allows the film workpiece to approach the high-voltage corona discharge 230 in a controlled manner. In an alternative embodiment, a conductive mask 240 can be used to protect areas of the thin piezoelectric medium film 405 from the high-voltage corona 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 areas are polarized in a first direction and some areas are polarized in a second direction. Therefore, some areas may be randomly polarized or depolarized. Polarization of a thin film of piezoelectric material 410 within a thin piezoelectric medium film 405, as shown in Figure 2D above, is shown as 460 and 470 in Figure 4D. differential polarization transformation This brings about areas P1 and P2. Importantly, since the thin piezoelectric medium film 405 can be manufactured before polarization, it is feasible for the end customer to control the final step of generating the desired polarization design within the thin piezoelectric medium film 405. Thus, if the final product will include a security seal or serial number, the security seal or serial number can be installed after the final product is completed and verified, etc. For example, a US $100 bill, printed with metallic ink and a serial number at the US Treasury Department, can simultaneously have a thin piezoelectric medium film 405 equipped with a security ribbon that generates a verification code corresponding to the serial number. This feature eliminates many logistical problems and associated costs, for example, since it is not necessary to match a pre-fabricated security marker with a specific product further downstream in the supply chain.

[0074] The techniques described above can be used to produce a wide variety of thin piezoelectric films, as illustrated in the following diagram.

[0075] As shown in Figures 5A-6B, 8A-10C, and 12A-13B, a piezoelectric film or piezoelectric display comprises a layered stack of a number of components, including thin piezoelectric films and layers of electrophoretic media. The piezoelectric material can be any of the materials listed above, however polymers such as PVDF and their copolymers are also preferred because they can be fabricated into very thin films. The electrophoretic media typically comprises one or more sets of charged particles that move through a nonpolar solvent in the presence of an electric field. The electrophoretic media is typically contained within microcapsules, microcells, or dispersed droplets. The electrophoretic media can also be contained within open valleys or wells sealed within a larger flexible container. The piezoelectric films and piezoelectric displays illustrated herein can be made very thin, for example, 100 μm or less in thickness, 70 μm or less, 50 μm or less, 35 μm or less, 20 μm or less, or 10 μm or less. Such thin materials are bendable without breaking or leaking and are inconspicuous when incorporated into final products such as paper or banknotes. In addition, many piezoelectric films or piezoelectric displays include layers, all of which are light-transmitting and / or thin enough to be light-transmitting, thus allowing the piezoelectric response to be visible from above and below. In such piezoelectric films or piezoelectric displays, when the first image is visible from the top surface, for example, position 1 in Figure 1B, the bottom surface will typically show an inverted image, for example, at position 3 in Figure 1B. However, when incorporating three or more types of particles into an electrophoretic medium, the top and bottom may not show opposite images due to the mixed particle state on one of the two surfaces.

[0076] Piezoelectrophoretic films or piezoelectric displays often include at least one electrode layer, which may be light-transmitting and flexible. Suitable materials include PET coated with commercial ITO, which can be used as a substrate for manufacturing. In some other embodiments, flexible and transparent conductive coatings containing other transparent conductive oxides (TCOs) may be used, such as fluorinated variations of these oxides, e.g., zinc oxide, zinc-tin oxide, indium zinc oxide, aluminum zinc oxide, indium tin zirconium oxide, indium gallium oxide, indium gallium zinc oxide, or fluorinated tin oxides doped with fluorine. In many of the embodiments described herein, poly(3,4-ethyleneoxythiophene) polystyrene sulfonate (PEDOT:PSS) is used because it has excellent flexural properties and is optically transparent. While its overall conductivity is not as high as, for example, PET / ITO, PEDOT:PSS is sufficient to provide the electric field necessary to drive electrophoretic particles in the electrophoretic medium. Other materials include polymers, typically light-transmitting polymers doped with conductive materials such as carbon black, metal flakes, metal whisker crystals, carbon nanotubes, silicon nitride nanotubes, or graphene. In some cases, the electrode layer is a metal film such as copper, silver, gold, or aluminum film or foil. Metal-coated polymer films may also be suitable for use as electrode layers. The resistance of the electrode layer may be 500 ohms or less, e.g., 100 ohms or less, e.g., 1 ohm or less, e.g., 0.1 ohms or less, e.g., 0.01 ohms or less. (For comparison, the electrophoretic medium layer is typically about 10 7 ~10 8 Having an ohmmeter resistance, the piezoelectric material is 10 11 ~10 14 It has a resistance of ohms per meter.

[0077] Piezoelectrophoretic films or piezoelectric displays often include at least one adhesive layer formed from polymers such as acrylic or polyurethane, polyurethane, polyurea, polycarbonate, polyamide, polyester, polycaprolactone, polyvinyl alcohol, polyether, polyvinyl acetate derivatives, e.g., poly(ethylene-co-vinylacetic acid), polyvinyl fluoride, polyvinylidene fluoride, polyvinyl butyral, polyvinylpyrrolidone, poly(2-ethyl-2-oxazoline), acrylic or methacrylic copolymers, maleic anhydride copolymers, vinyl ether copolymers, styrene copolymers, diene copolymers, siloxane copolymers, cellulose derivatives, gum arabic, alginic acid, lecithin, and polymers derived from amino acids. The adhesive may also include one or more low-dielectric polymers or oligomers, ionic liquids, or conductive fillers, e.g., carbon black, metal flakes, metal whisker crystals, carbon nanotubes, silicon nitride nanotubes, or graphene. Adhesives containing such charged and / or conductive materials are conductive adhesives. Polymers and oligomers used in the adhesive layer may have functional groups for chain extension or crosslinking during or after lamination. The adhesive layer is generally 10 6 Ohm * cm ~ 10 8 Ohms * cm, preferably 10 12 It may have a resistivity value of less than ohms * cm.

[0078] Of the polymers and oligomers described above, polyurethanes, polyureas, polycarbonates, polyesters, and polyamides, in particular those equipped with functional groups, are preferred due to their superior adhesive strength, optical properties, and high environmental resistance. Examples of functional groups, but not limited to, include -OH, -SH, -NCO, -NCS, -NHR, -NRCONHR, -NRCSNHR, vinyl or epoxide, and cyclic derivatives, and their derivatives. In the functional groups described above, "R" may be hydrogen, or an alkyl, aryl, alkylaryl, or arylalkyl with up to 20 carbon atoms, and the alkyl, aryl, alkylaryl, or arylalkyl may optionally be substituted or interrupted by N, S, O, or halogens. "R" is preferably hydrogen, methyl, ethyl, phenyl, hydroxymethyl, hydroxyethyl, hydroxybutyl, etc. Functionalized polyurethanes, such as hydroxyl-terminated polyester polyurethanes or polyether polyurethanes, isocyanate-terminated polyester polyurethanes or polyether polyurethanes, or acrylate-terminated polyester polyurethanes or polyether polyurethanes, are particularly preferred.

[0079] In many embodiments, the piezoelectric film or piezoelectric display will often include a release sheet. The release agent may be used to temporarily facilitate the processing of the piezoelectric film or piezoelectric display, for example, when embossing, filling, cutting, etc. In other embodiments, the release agent may be used to deliver the final piezoelectric film or piezoelectric display that will be bonded to the final product. In some cases, the release agent will protect a functional adhesive layer that will be used to manipulate the piezoelectric film or piezoelectric display prior to its placement in the final product. The release agent may be formed from a material selected from the group consisting of polyethylene terephthalate (PET), polycarbonate, polyethylene (PE), polypropylene (PP), paper, and their laminates or cladding films. The release agent may be metallized to facilitate quality control measurements and / or to control static electricity during handling, shipping, and downstream incorporation into the product. In some embodiments, a silicone release coating may be applied on the release agent to improve its release properties.

[0080] Although not shown in Figures 5A-6B, 8A-10C, and 12A-13B, the piezoelectric film or piezoelectric display may include additional edge seal and / or barrier material, which may enable the piezoelectric film or piezoelectric display to maintain a desired humidity level, prevent leakage of, for example, nonpolar solvents or adhesives, and prevent the ingress of water, dust, or gases. The barrier material can be any flexible material, typically a polymer with low to negligible WVTR (water vapor transmission rate). Suitable materials include polyethylene terephthalate, polyethylene naphthalate, polycarbonate, polyimide, cyclic olefins, and combinations thereof. Flexible glass such as WILLOW® glass (Corning, Inc.) may be used for the barrier layer, especially if the piezoelectric film or piezoelectric display will be exposed to harsh conditions. The edge seal can be a metallized foil or other barrier foil that covers and adheres to the edge of a piezoelectric film or piezoelectric display. The edge seal can also be formed from dispensed sealants (cured by heat, chemical, and / or radiation), polyisobutylene, or acrylate-based sealants, which can be crosslinked. In some embodiments, the edge seal can be a sputtered ceramic such as alumina or indium tin oxide, or a high-grade ceramic available from Vitex Systems, Inc. (San Jose, CA), etc.

[0081] Generally, the layers of the piezoelectric films 501-504 can be arranged / laminated in an order that produces the best performance for the end application. For example, as shown in Figure 5A, the piezoelectric film 501 can be prepared by placing a microcell precursor material on a release agent 510 containing a release agent adhesive 520. The microcell precursor can then be embossed or photolithographed to produce an array of microcells 530. The microcells 530 can be cured thermally or using electromagnetic radiation such as UV light. The microcells 530 can then be filled with an electrophoretic medium and sealed with a seal layer 540, as discussed above with respect to Figure 4A. (It should be understood that the microcell 530 adjacent to the seal layer 540 is filled with an electrophoretic medium containing charged particles in a nonpolar solvent, although the electrophoretic medium is not shown in the subsequent figures.) The piezoelectric layer 560 can be laminated to the seal layer 540 using an adhesive 550, which would typically be an optically transparent adhesive formed from one of the materials listed above. Finally, the flexible electrode 580 will be bonded to the piezoelectric film using a conductive adhesive 570. Such a piezoelectric film 501 can then be manipulated by handling the release agent 510 until a stack without the release agent 510 is attached to the final product. In the piezoelectric film 501, the piezoelectric layer 560 is typically bonded to the piezoelectric film before the flexible electrode 580 is bonded to the piezoelectric film. differential The electrodes are polarized to generate areas of polarization. In some embodiments, the flexible electrodes 580 and conductive adhesive 570 can be replaced with a thin layer of transparent conductive oxide such as ITO. The ITO can be sputtered directly onto the piezoelectric layer 560.

[0082] A closely related but alternative stack is shown in Figures 5B-5D. In Figure 5B, a piezoelectric film 502 is produced, and in the piezoelectric film 502, the piezoelectric layer 560 is prepared prior to its fabrication on a separate release agent 510. For example, the piezoelectric layer 560 may be a pre-stretched PVDF film that has already been polarized to generate a security pattern. The piezoelectric layer 560 is then bonded to a sealed microcell layer 530, which is already bonded to a flexible electrode 580. It is worth noting that in the piezoelectric film 502, the openings of the microcell layer 530 face away from the piezoelectric layer 560, which can facilitate 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 microcell material, typically a polymer comprising acrylate, vinyl ether, or epoxide. Primer 535 may be a polar oligomer or polymer material, such as polyhydroxy-functionalized polyester acrylate (e.g., Dymax BOMAR® BDE1025) or alkoxylated acrylate, such as ethoxylated nonylphenol acrylate (e.g., Sartomer SR504), ethoxylated trimethylolpropane triacrylate (e.g., Sartomer SR9035), or ethoxylated pentaerythritol tetraacrylate (e.g., Sartomer SR494). Examples of polar polymers suitable for use with Primer 535 include solvent urethane polymers such as Irostic® polymers.

[0083] Naturally, it is also possible to construct the stack such that the openings of the microcell layer 530 face toward the piezoelectric layer 560, as shown in the piezoelectric film 504 illustrated in Figure 5D. As a further alternative shown in Figure 5C, the piezoelectric film 503 has the openings of the microcell layer 530 facing toward the away from the piezoelectric layer 560, however, the piezoelectric layer 560 is positioned to be directly bonded to the flexible electrode 580.

[0084] The piezoelectric films (501, 502, 503, 504) shown in Figures 5A-5D can be converted into piezoelectric displays (601, 602) with the addition of a second flexible electrode 680 instead of the release layer in Figures 5A-5D. The piezoelectric displays (601, 602) will typically 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 necessary to switch the electrophoretic material. In addition, it is also possible to generate a second electrode by directly coating the bottom of the microcell layer 530 (Figure 6A) or the seal layer 540 (Figure 6B) with a thin layer of transparent conductive oxide. Furthermore, if it is not necessary to see through both the top and bottom of the piezoelectric displays (601, 602), a conductive metal foil can be used as the second flexible electrode 680. As shown in Figures 6A and 6B, it is typical to add a release agent 510 to the completed piezoelectric displays (601, 602) to improve handling and to provide an easy-to-use adhesive for mounting the piezoelectric displays (601, 602). In some embodiments, the piezoelectric display 601 can be formed simply by bonding a piezoelectric layer 560 to a commercial front-plane laminate, the commercial front-plane laminate comprising a sealed microcell layer 530 containing a second flexible electrode 680 and an electrophoretic medium. In such cases, the piezoelectric layer 560 is typically bonded to the piezoelectric layer 560 before the front-plane laminate is bonded to the piezoelectric layer 560. differential Polarization is performed to generate areas of polarization. The piezoelectric displays (601, 602) in Figures 6A and 6B are shown with the piezoelectric layer 560 above the sealed microcell layer 530, but it should be understood that the piezoelectric layer 560 can also be placed below the sealed microcell layer 530 to generate a piezoelectric display similar to those in Figures 5B and 5D.

[0085] (Prototype performance) A series of piezoelectric films of the type illustrated in Figure 5A were produced using PEDOT:PSS film as the flexible electrode 580. The piezoelectric layer 560 was varied as shown in Table 1 (composition and thickness). The piezoelectric films were obtained from TE Connectivity (Norwood, MA), Fishman (and over, MA), or cast and cured in-house using PVDF powder from Sigma-Aldrich. The polarization direction was modified to generate a pattern using the polarization technique described. The electrophoretic medium contained low-voltage formulations of black and white particles, or black and red particles, or red and black particles, designed to switch color states using + / -3V. As shown in Table 1, all variations provided suitable switching. [Table 1]

[0086] Table 1 suggests that several types of electrophoretic media would respond well to the small electric field generated by bending a thin piezoelectric film. In particular, spin-coated polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE) films less than 3 μm thick were found to have sufficient charge injection to switch DV electrophoretic media. See Experiment No. 7. Such piezoelectric films 801 (see Figure 8A) can be formed using the method described in Figure 7. First, a thin film of piezoelectric material 940 is produced by casting (slot die coating) a concentrated PVDF / DMF solution onto a suitable substrate, heating, and removing the solvent, as in step 710 of Figure 7. In step 720, the piezoelectric film 960 is removed from the substrate. The cast piezoelectric film 960 may be 10 μm or less in thickness, e.g., 5 μm or less, e.g., 3 μm or less. Furthermore, the piezoelectric film 960 may be stretched to increase the number of beta-phase domains and / or polarized using a suitable electric field, as discussed above. In step 730, a release agent 910 is provided together with an adhesive 920, and the release agent 910 and adhesive 920 are subsequently laminated onto the cast piezoelectric film 960 in step 740. The piezoelectric film 960 is then coated with / bonded to an electrophoretic layer in step 750. The electrophoretic layer may be a sealed microcell layer comprising filled microcells 930 and a seal layer 940, as shown in Figures 9A and 9B, or alternatively, the electrophoretic layer may contain encapsulated electrophoretic medium 990 within a polymer binder 995. Bonding the piezoelectric film 960 to the electrophoretic layer may be facilitated using an intervening primer layer 935, for example, one of the primer materials discussed above. If the electrophoretic layer is a sealed microcell layer, the microcell 930 can be positioned such that the sealing layer 940 is adjacent to the piezoelectric film 960 (as shown in Figure 8A), or the microcell 930 can be positioned such that the sealing layer 940 is on the opposite side from the piezoelectric film 960 (i.e., as shown in Figure 8B).As the final step 760, the electrode layer 980 is produced either by being bonded to / deposited on the microcell 930 as shown in Figure 8A, or by being bonded to / deposited on the seal layer 940 as shown in Figure 8B. As described above, the electrode layer 980 may include a flexible conductive material such as PEDOT:PSS, or it may include a directly deposited (e.g., sputtered or vapor-deposited) transparent conductive oxide (TCO). In some embodiments, the electrode 980 may include a pre-fabricated film of ITO on a polymer substrate such as PET. The piezoelectric film 801, including the directly deposited TCO electrode layer 980, the thin piezoelectric layer 960, and the thin layer of microcell 930 (approximately 10 μm thick), is remarkably thin (i.e., less than 25 μm thick excluding the release agent 910), which allows the piezoelectric film 801 to be bent without damage and to be inconspicuous when attached to an object such as a banknote. The corresponding piezoelectric film 901 containing the microcapsules can also be fabricated with a total thickness of less than 25 μm. Naturally, alternative structures using a thin piezoelectric film 960 are also possible, such as positioning the piezoelectric film 960 between the electrode 980 and the electrophoretic layer, i.e., the layer of microcapsules 990, as shown in Figure 9B. Alternatively, the electrode 980 in Figures 8A-9B may be replaced with a conductive adhesive (not shown) or a conductive adhesive, along with an additional release layer (not shown).

[0087] Similar to Figures 6A and 6B, the piezoelectric films of Figures 8A-9B can include a second electrode layer, as shown in Figures 10A-10C, to form the corresponding displays (1001, 1002, 1003). Both electrode layer 980 and the second electrode layer 1080 may comprise a flexible conductive material such as PEDOT:PSS, or both electrode layer 980 and the second electrode layer 1080 may comprise a transparent conductive oxide (TCO) that is directly deposited (e.g., by sputtering or vapor deposition), or a combination thereof. Again, in the case where both electrode layer 980 and the second electrode layer 1080 use a thin TCO film, the resulting piezoelectric displays (1001, 1002, 1003) can be made very thin, i.e., less than 25 μm thick, excluding the release agent 910. In some embodiments, the electrode layer 980 is produced by bonding to / depositing onto a microcell 930, as shown in Figure 10A. In other embodiments, the electrode layer 980 is bonded to / deposited onto a seal layer 940, as shown in Figure 10B. The assemblies of the piezoelectric displays 1001 and 1002 are also used with microcapsules 990 containing an electrophoretic medium held together with a binder 995, and thus a piezoelectric display 1003 can be produced, as shown in Figure 10C. Alternatively, the electrodes 980 / 1080 in Figures 10A-10C may be replaced with a conductive adhesive (not shown) or a conductive adhesive in conjunction with an additional release layer (not shown).

[0088] An alternative method for constructing piezoelectric films and piezoelectric displays is described with respect to the flowchart in Figure 11. The piezoelectric film 1260 is procured, and it may be a commercial film or a cast film, as described above. The piezoelectric film 1260 is laminated onto a microcell precursor material in step 1110. Prior to lamination, the piezoelectric film 1260 may be stretched and / or polarized. The precursor material is typically an acrylate polymer, however, any suitable embossable material such as a vinyl ether polymer or an epoxide polymer film may be used. Typically, the precursor film is 30 μm thick or less, for example, The thickness is 20 μm or less. The precursor film may be treated with a primer 1235 prior to the lamination step 1110. Once the piezoelectric film 1260 and the microcell precursor material are bonded, the side of the piezoelectric film 1260 opposite to the microcell precursor material is coated with a transparent conductive material, typically indium tin oxide, selected from, for example, those described above. (Alternatively, depending on the application, the side of the piezoelectric film 1260 opposite to the microcell precursor material may be coated with a conductive adhesive, which may be supported by a release layer.) This coating step produces electrodes 1280, shown in the piezoelectric film 1201 and piezoelectric display 1202, respectively, shown in Figures 12A and 12B. (Although not shown in Figure 11, an alternative construct is to obtain a piezoelectric film 1260 pre-coated with a transparent conductive material, and then laminate the pre-coated piezoelectric film 1260 and the microcell precursor material together (including the optional use of primer 1235).) After the stack of electrode 1280, piezoelectric film 1260, and microcell precursor is generated, the stack is laminated onto a carrier substrate 1255 using an adhesive layer 1250, as shown in step 1130. The carrier substrate 1255 may be any of the materials described above for use as a release agent, and the adhesive 1250 may be any of the adhesives described above. In practice, the carrier substrate 1255 is typically PET, as PET sheets are easy to handle during the embossing step 1140. In step 1140, a stack comprising a carrier substrate 1255, an adhesive 1250, a piezoelectric film 1260, and a microcell precursor is microembossed using the techniques described above with respect to U.S. Patents 6,930,818, 7,052,571, 7,616,374, 8,361,356, and 8,830,561. Once this procedure is completed using a thin piezoelectric film and a thin microcell precursor, the final stack thickness (excluding the carrier substrate) may be 30 μm or less, for example, 20 μm or less.This results in an open microcell structure, which is subsequently filled with the desired electrophoretic medium in step 1150 and sealed with a water-soluble seal layer 1240. The seal layer 1240 can be made conductive by containing conductive species. The seal layer 1240 is typically light-transmitting or transparent. The open microcell can be cleaned / activated using a water vapor plasma treatment 1145 before the microcell is filled with the desired electrophoretic medium. Finally, the release sheet 1210 is bonded to the seal layer 1240 using an adhesive 1220 in step 1160 to facilitate the transfer of the piezoelectric film 1201 and to facilitate the placement of the electrophoretic film 1201 onto the final product. The adhesive 1220 can also be conductive. The resulting structure is shown in Figure 12A. Importantly, it is possible to complete the steps in Figure 11 without polarization of the piezoelectric film 1260, thereby allowing the end customer to, for example, use corona discharge as described above. differential By generating polar areas, it becomes possible to pattern the piezoelectric film 1201 at the final assembly site.

[0089] As shown in Figure 12B, the method of Figure 11 can be extended to produce a piezoelectric display 1202 with the addition of a second electrode 1285. The second electrode 1285 may also include a transparent conductive material that is added directly to the seal layer 1240 instead of the release agent 1210 and adhesive 1220. However, in other embodiments, the release agent 1210 would be removed, and the second electrode 1285 would be laminated to the seal layer 1240 using the adhesive 1220. If the piezoelectric display 1202 does not require the electrophoretic medium to be visible from both sides, the second electrode 1285 can be a metal film. Alternatively, the second electrode 1285 may be a conductive polymer such as PEDOT:PSS. In some other embodiments, the adhesive 1220 may be a conductive adhesive that provides sufficient conductivity to function as the second electrode 1285.

[0090] Finally, it should be understood that the electrodes do not need to be bonded to the piezoelectric film 1260 prior to embossing the stack comprising the piezoelectric film 1260 and the microcell precursor material. Rather, a stack comprising the release agent 1210, the adhesive 1220, the piezoelectric film 1260, and the microcell precursor can be prepared, and the microcell precursor can subsequently be embossed, filled, and sealed as described above. Alternatively, a stack comprising the release agent 1210, the adhesive 1220, the electrode 1285, the piezoelectric film 1260, and the microcell precursor can also be prepared, as shown in Figure 13B, and the microcell precursor can subsequently be embossed, filled, and sealed as described above. The resulting piezoelectric film 1301 and piezoelectric display 1302 are shown in Figures 13A and 13B, respectively. The piezoelectric film 1301 and the piezoelectric display 1302 may be preferred for applications where it is desirable to have the piezoelectric film 1260 as close as possible to the mounting surface on the final product, i.e., when the piezoelectric film 1301 is used as a strain sensor and it is important that the intervening electrophoretic medium layer does not dissipate the force from the surface.

[0091] It should be understood that the piezoelectric films and piezoelectric displays described herein can be combined with other known techniques for generating security markers or authenticity indicators. For example, the piezoelectric film or piezoelectric display may also include a translucent upper layer that does not change the optical properties when the piezoelectric film is manipulated. For example, a smiley face upper layer may include eyes constructed from a piezoelectric display so that the eyes appear to blink when the layered material is bent. In some embodiments, an image or shape may be printed or laminated on a monochromatic (e.g., white) background and must be visible through the piezoelectric film to see a pre-arranged pattern. Thus, when not in use, only the monochromatic color will be visible to the viewer, i.e., the printed image or shape will be hidden. However, the printed image or shape will be revealed when the device is manipulated. It is also feasible to adhere a piezoelectric film or piezoelectric display to a separate light-transmitting polymer film contained within a target product (e.g., banknotes), thereby making the pattern within the piezoelectric layer visible only when the target product is held and manipulated upwards relative to a light source.

[0092] It will be apparent to those skilled in the art that numerous changes and modifications can be made without departing from the scope of the invention, in the specific embodiments of the invention described above. Therefore, the entire preceding description should be interpreted as illustrative, not restrictive.

Claims

1. An electrophoretic display film having a thickness of less than 100 μm (from top to bottom), wherein the electrophoretic display film is, in order, A first adhesive layer (520) and Electrophoretic media layer (405, 530), A piezoelectric layer (410, 560, 960), wherein the piezoelectric layer (410, 560, 960) includes a plurality of differential polarization areas, each area having a different polarity from the adjacent area, and the piezoelectric layer (410, 560, 960) comprises Flexible light-transmitting electrode layer (580) and Equipped with, The electrophoretic medium layer and the piezoelectric layer together form a single layer that is a piezoelectric electrophoretic medium film. The piezoelectric electrophoretic medium film comprises a polyvinylidene fluoride (PVDF) layer bonded to the electrophoretic medium layer, wherein the PVDF layer has a polarization pattern including multiple areas of differential polarization, thereby forming an electrophoretic display film.

2. The electrophoretic media layer (405, 530) comprises a plurality of microcapsules (990) containing a nonpolar fluid (425) and charged pigment particles (423, 427), wherein the charged pigment particles (423, 427) move toward or away from the piezoelectric layer (410, 560, 960) when the piezoelectric layer (410, 560, 960) is bent, and the plurality of microcapsules (990) are bound together with a polymer binder (995), or The electrophoretic display film according to claim 1, wherein the electrophoretic medium layer (405, 530) comprises a plurality of microcells (420, 530) containing a nonpolar fluid (425) and charged pigment particles (423, 427), the charged pigment particles (423, 427) move toward or away from the piezoelectric layer (410, 560, 960) when the piezoelectric layer (410, 560, 960) is bent, and the nonpolar fluid (425) and the charged pigment particles (423, 427) are sealed within the plurality of microcells (420, 530) using a sealing layer (430).

3. The electrophoretic display film according to claim 1, wherein the electrophoretic display film has a thickness less than 50 μm.

4. The electrophoretic display film according to claim 1, wherein the flexible light-transmitting electrode layer (580) comprises a metal oxide containing tin or zinc, or poly(3,4-ethyleneoxythiophene) (PEDOT).

5. An electrophoretic display film assembly comprising a release sheet (510) bonded to the electrophoretic display film described in claim 1, wherein the release sheet (510) is bonded to the first adhesive layer (520).

6. The electrophoretic display film assembly according to claim 5, further comprising a second adhesive layer bonded to the flexible light-transmitting electrode layer (580) and a second release sheet bonded to the second adhesive layer.

7. A method for producing an electrophoretic display film, wherein the method is: A piezoelectric microcell precursor film is produced by bonding a polyvinylidene fluoride (PVDF) film (1260) to a polymer film (1230) containing acrylate, vinyl ether, or epoxide, and The piezoelectric microcell precursor film is bonded to a flexible light-transmitting electrode layer (1280), The flexible light-transmitting electrode layer (1280) is bonded to the first release film (1255) using the first adhesive layer (1250), The piezoelectric microcell precursor film is embossed to generate an array of multiple microcells (1230), wherein each of the multiple microcells has a bottom, a wall, and an upper opening. The plurality of microcells are filled with electrophoretic media (405, 530) through the upper opening, By sealing the upper openings of the multiple filled microcells with a water-soluble polymer (1240), an electrophoresis medium layer (405, 530) is prepared. Methods that include...

8. The method according to claim 7, further comprising applying a primer (1235) to the polymer film (1230) containing an acrylate, vinyl ether, or epoxide before bonding the polymer film (1230) to the polyvinylidene fluoride (PVDF) film (1260).

9. The method according to claim 7, further comprising bonding the water-soluble polymer (1240) to the second release film (1210) using a second adhesive layer (1220).

10. The method according to claim 7, further comprising removing the first release film (1255) to produce an electrophoretic display film having a thickness of less than 100 μm.

11. The method according to claim 7, wherein the electrophoretic medium layer (405, 530) comprises a nonpolar fluid (425) and charged pigment particles (423, 427), and the charged pigment particles (423, 427) move toward or away from the polyvinylidene fluoride (PVDF) film (1260) when the polyvinylidene fluoride (PVDF) film (1260) is bent.

12. The method according to claim 7, wherein the polyvinylidene fluoride (PVDF) film (1260) is polarized to generate a plurality of differential polarization areas (460, 470).

13. The method according to claim 7, wherein the flexible light-transmitting electrode layer (1280) comprises a metal oxide containing tin or zinc, or poly(3,4-ethyleneoxythiophene) (PEDOT).

14. The method according to claim 7, wherein the polyvinylidene fluoride (PVDF) film (1260) is patterned using an electric field to generate a plurality of differential polarization areas (460, 470).

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