Patent Publication Number: US-10310353-B2

Title: Aligned particle layer

Description:
BACKGROUND 
     Electronic paper (“e-paper”) is a display technology designed to recreate the appearance of ink on ordinary paper. Some examples of e-paper reflect light like ordinary paper and may be capable of displaying text and images. Some e-paper is implemented as a flexible, thin sheet, like paper. One familiar e-paper implementation includes e-readers. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a sectional view schematically representing a charge-receiving layer, according to an example of the present disclosure. 
         FIG. 1B  is a sectional view schematically representing a charge-receiving layer, according to an example of the present disclosure. 
         FIG. 2A  is a sectional view schematically representing a charge receiving layer, according to an example of the present disclosure. 
         FIG. 2B  is a sectional view schematically representing a charge-receiving layer, according to an example of the present disclosure. 
         FIG. 3A  is a sectional view schematically representing an e-paper assembly, according to an example of the present disclosure. 
         FIG. 3B  is an enlarged sectional view of a portion of  FIG. 3A  that schematically represents a portion of an e-paper assembly, according to an example of the present disclosure. 
         FIG. 3C  is an enlarged sectional view schematically representing a portion of an e-paper assembly, according to an example of the present disclosure. 
         FIG. 3D  is a perspective view schematically representing a coating layer, according to an example of the present disclosure. 
         FIG. 4A  is a top elevational view schematically representing a display media, according to an example of the present disclosure. 
         FIG. 4B  is a top view schematically representing a dot-by-dot portion of an image, according to an example of the present disclosure. 
         FIG. 5  is a diagram including a sectional side view schematically representing an e-paper assembly, according to an example of the present disclosure. 
         FIG. 6  is a diagram including a sectional side view schematically representing an e-paper assembly and a side view of an imaging head, according to an example of the present disclosure. 
         FIG. 7  is a diagram including a sectional side view schematically representing an e-paper assembly and a side view of an imaging head, according to an example of the present disclosure. 
         FIG. 8  is a diagram including a sectional side view schematically representing an e-paper assembly and a side view of an imaging head, according to an example of the present disclosure. 
         FIG. 9  is a diagram including a flow diagram schematically representing a method of forming a coating layer, according to an example of the present disclosure. 
         FIG. 10  is a diagram including schematically representing a portion of a method of forming a coating layer, according to an example of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration specific examples in which the disclosure may be practiced. It is to be understood that other examples may be utilized and structural or logical changes may be made without departing from the scope of the present disclosure. The following detailed description, therefore, is not to be taken in a limiting sense. 
     At least some examples of the present disclosure are directed to a coating layer that protects an e-paper structure while also acting as a charge-receiving layer to receive airborne charges from a non-contact, external image-writing module and facilitate passage of those charges to a charge-responsive layer of the e-paper structure. In one aspect, the coating layer exhibits anisotropic conductivity to facilitate passage of the airborne charges in a first orientation through a thickness of the coating layer while inhibiting migration of those charges in a second orientation generally perpendicular to first orientation. In one aspect, the second orientation is generally parallel to a plane through which the coating layer extends. The coating layer also has a thickness and/or composition that provides scratch resistance, strength, and toughness to protect the e-paper structure from mechanical insults. In some examples, other aspects of the coating layer provide protection from electrical insults, as further described later. 
     In some examples, a charge-receiving layer for an electronic paper assembly includes a plurality of conductive paths spaced apart throughout an electrically insulative matrix (e.g. a conductive-resistant medium). Each conductive path includes at least one elongate pattern of separate conductive particles. In one aspect, each conductive path extends in a first orientation generally perpendicular to a plane through which the charge-receiving layer extends and a plane through which the charge-responsive layer extends. In some examples, the conductivity of any single elongate pattern of conductive particles is at least two orders of magnitude greater than a conductivity of the insulative matrix. In some examples, a combined conductivity of all the conductive paths is about one order of magnitude greater than a conductivity of the insulative matrix. 
     It will be understood that the term “insulative matrix” does not indicate that the matrix is an absolute electrical insulator, but rather that the matrix is electrically insulative at least relative to the conductivity of the conductive paths (of elongate patterns of conductive particles). Further examples of the insulative matrix are described throughout the present disclosure. 
     With such arrangements provided via at least some example of the present disclosure, charges deposited on a surface of the charge-receiving layer can travel in generally direct alignment with a targeted area of the charge-responsive layer (of an e-paper structure) to be imaged. 
     In sharp contrast, unprotected e-paper will not survive the rigors of use in practical consumer and business applications. In further sharp contrast to at least some examples of the present disclosure, other types of protective coatings which exhibit nearly perfect dielectric behavior (e.g. glass, some polymers) tend to produce “dot blooming” because any charges deposited on the surface of the protective layer tend to build up at the surface of the protective coating and spread laterally far beyond the targeted area. This surface spreading, in turn, results in lateral spreading of the imaged area in the charge-responsive layer of the e-paper structure, thereby reducing the clarity and resolution of the image. 
     In further sharp contrast to at least some examples of the present disclosure, other types of protective coatings exhibit semi-conductive behaviors and therefore permit passage of charges through a thickness of the protective coating to a charge-responsive layer. However, the isotropic nature of the semi-conductive protective coatings still results in a “dot blooming” effect because as the charges travel through the semi-conductive material, the charges spread laterally so that by the time the charges reach the targeted image area, the charges affect an much larger than intended area of the charge-responsive layer. This behavior can result in poor image quality. 
     However, with at least some examples of the present disclosure, some of which are introduced above, even with relatively thick protective coatings (e.g. 150 μm), an anisotropic conductive configuration in the charge-receiving layer prevents lateral migration of deposited charges. Accordingly, high quality imaging is achieved while providing the desired protection for the e-paper structures. 
     In at least some examples of the present disclosure, a method of manufacturing an outer coating for an e-paper structure includes forming a first layer from a mixture of conductive particles dispersed within an insulative matrix. A field is applied to cause the conductive particles to align in generally parallel, spaced apart elongate patterns that are generally perpendicular to a plane through which the layer extends. In some examples, the applied field is a magnetic field and the particles are magnetically-responsive particles. In some examples, the applied field is an electric field. 
     In some examples, the method further includes curing, at ambient temperatures and without applied pressure, the first layer via radiation energy while maintaining the applied field. 
     In one aspect, at least an outer surface of the protective outer coating (for the e-paper structure) that is exposed to the ambient environment is non-adhesive or non-sticky. 
     In sharp contrast to at least some examples of the present disclosure, at least some types of anisotropic conductive films (ACF) act as adhesive interconnects for circuitry components and therefore do not serve well as outer protective coatings generally, and particularly for a charge-responsive layer of an e-paper structure. Moreover, deployment of such types of anisotropic conductive films (ACF) typically involves the application of high heat and/or pressure, which would be destructive to the delicate nature of passive e-paper structures. 
     In addition, such types of anisotropic conductive films typically rely on a monolayer of metal spheres which define the thickness of the film. Accordingly, attempts to create relatively thick protective films (e.g. 150 μm) would involve films with large diameter spheres, and typically result in large spacing (e.g. 150 μm) between the conductive spheres. This arrangement, in turn, would result in a poor mismatch between the large spaces between adjacent conductive spheres relative to the closely adjacent microcapsules of the passive e-paper structure, leading to poor image quality. In another aspect, traditional anisotropic conductive films typically used as circuitry interconnects also exhibit impedances on the order of Ohms. 
     In sharp contrast, in at least some examples of the present disclosure the insulative matrix exhibit impedances in hundreds of kiloOhms (e.g. 10 5  to 10 9  Ohms) while each preferential conductive path exhibits impedances about two orders of magnitude less than the insulative matrix. In this environment, in at least some examples of the present disclosure, a current density associated with deposited air-borne charges and the above-described preferential conductive charge-receiving layer falls within a range of 10 to 100 μA/cm 2 . 
     In at least some further examples of the present disclosure, the conductive particles have a maximum dimension no greater than 5 μm. In some examples, the generally parallel elongate patterns (of conductive particles) are spaced apart from each other by about 10 μm. In some examples, the conductive particles have a maximum dimension no greater than 100 nanometers. In some examples, the conductive particles have a maximum dimension no greater than 10 nanometers. Other examples are described later. 
     In some examples, the conductive particles are sized such that each elongate pattern of aligned particles comprises a mono-layer in which a width of a respective elongate pattern corresponds to a maximum dimension of a respective one of the conductive particles. In some examples, the conductive particles have a relatively smaller size such that each elongate pattern of aligned particles comprises a multi-layer in which a width of each elongate pattern corresponds to multiple layers of the conductive particles. 
     Moreover, an e-paper structure (according to at least some examples of the present disclosure) forms at least a portion of a passive e-paper display media. The passive e-paper display media is relatively thin and light because it omits a power supply and omits internal circuitry, thereby giving the passive e-paper display media a look and feel more like traditional paper. The passive e-paper display media in at least some examples of the present disclosure relies on a charge-responsive layer that is imageable via an external writing module and that does not require a power supply to be imaged or to retain an image. 
     In sharp contrast, traditional e-paper implementations include active e-paper structures having internal circuitry and/or an on-board power supply, making them relatively heavy and not feeling like traditional paper. 
     These examples, and additional examples, are described and illustrated below in association with at least  FIGS. 1A-10 . 
       FIG. 1A  is a side sectional view schematically representing a coating layer  20 , according to an example of the present disclosure. In one example, the coating layer  20  provides protection for an e-paper structure (shown later in at least  FIGS. 3A, 5-8 ). 
     As shown in  FIG. 1A , coating layer  20  includes a first side  22 A and an opposite second side  22 B, as well as opposite ends  26 A,  26 B. In one example, coating layer  20  includes a body  30  in which is formed a plurality of conductive pathways  32 . In one aspect a longitudinal axis (A 1 ) of the conductive paths  32  extends generally perpendicular to a longitudinal axis (A 2 ) the body  30 . In one example, in contrast to conductive paths  32 , body  30  includes an insulative matrix  33  (e.g. conductive-resistant medium). 
     In one example, the conductivity (σ path ) of a single conductive path  32  is at least two orders of magnitude greater than the conductivity (σ body ) of body  30 . In some examples, a combined conductivity of all the conductive paths  32  in coating layer  20  is at least one order of magnitude greater than the conductivity (σ body ) of body  30 . 
     As further shown in  FIG. 1A , coating layer  20  is adapted to receive air-borne charges  39  from an external imaging head (not shown) that is spaced apart from and not in contact with the coating layer  20 . In one aspect, due to the relatively low conductivity of body  30 , charges that are generally received on body  30  are conducted laterally through the outer surface of body  30  until they reach a conductive pathway  35  while charges received at a conductive pathway  35  travel straight (i.e. directly) through a thickness of the coating layer  20 . In particular, the relatively high conductivity of conductive paths  32  facilitates passage of the charges (through layer  20 ) from the first side  22 A to the second side  22 B. 
     In some examples, when coating layer  20  forms part of a larger e-paper assembly, coating layer  20  acts as a charge-receiving layer to facilitate receiving charges from an external location/source and conveying those charges to a charge-responsive layer of the e-paper assembly. This configuration is illustrated later in association with at least  FIGS. 3A and 5-8 . 
     In one example, for illustrative purposes,  FIG. 1A  does not depict a particular density of conductive paths  32  relative to body  30 . Rather, the coating layer  20  in  FIG. 1A  is merely illustrative for describing general principles in at least some examples of the present disclosure, such as the orientation and/or conductivity of the paths  32  relative to body  30 . 
       FIG. 1B  is a side sectional view of a coating layer  40 , according to one example of the present disclosure. In some examples, coating layer  40  is at least consistent with, and/or includes at least some of substantially the same features and attributes as, coating layer  20  in  FIG. 1A . In coating layer  40 , a plurality of conductive paths extend from first side  22 A to second side  22 B with each conductive path being defined by at least one elongate pattern  56  of conductive particles  58 . Each conductive path facilitates the passage of charges from first side  22 A to second side  22 B. 
     In some examples, as shown in  FIG. 1B , a conductive path  53  corresponds to a single elongate pattern  56  of conductive particles  58  while in some examples, a conductive path  52  corresponds to at least two adjacent elongate patterns  56  of conductive particles  58 . 
     In one example, the conductivity (σ path ) of a single elongate pattern  56  of conductive particles  58  is at least two orders of magnitude greater than the conductivity (σ body ) of body  30  of insulative matrix  33  at the relevant electrical fields used for imaging. 
     In some examples, the number of adjacent elongate patterns  56  of conductive particles  58  that defines a conductive path  52  corresponds to a size of an imageable dot in dot-based imaging scheme. For instance, in one example implementation involving an image with 300 dots-per-inch density on a media, a dot is about 80 to 100 microns in diameter with the dots spaced apart by 84 microns. In such an implementation, as further described below in association with at least  FIGS. 4A-4B , several elongate patterns  56  of conductive particles  58  define the conductive path  52  to cause imaging of a single dot on a charge-responsive layer of an e-paper assembly. 
     In one example, particles  58  are at least partially made of a field-responsive material that is alignable into the elongate patterns  56  during formation of the coating layer  40 . With this in mind,  FIG. 2A  provides a brief introduction into the process of forming the elongate patterns  56  of separate conductive particles  58  within body  30 . In particular, as shown in  FIG. 2A , a fluid mixture of at least insulative matrix  33  (e.g. conductive-resistant medium) and conductive particles  58  is formed as a layer  80  on a substrate, such as but not limited to, an e-paper assembly. Upon initial deposit, the particles  58  within the layer  80  are randomly and generally dispersed throughout the insulative matrix  33 . Prior to curing of the layer  80 , a field (AF) is applied to the layer  80  with an orientation to cause the conductive particles  58  to become aligned with the field lines (F) of the applied field (AF), to result in the arrangement shown in  FIG. 1B , in which the particles  58  remain separate particles but become aligned into elongate patterns  56  that are generally parallel to each other and spaced apart from each other, as shown in  FIG. 1B . In some examples, once aligned into an elongate pattern  56 , some particles  58  (of a particular elongate pattern  56 ) contact each other while some particles (of that same elongate pattern  56 ) are spaced apart from each other. Once in the arrangement shown in  FIG. 1B , at least layer  80  is cured in a manner such that the particles  58  will remain in the arrangement shown in  FIG. 1B . 
     In one example, the conductive particles  58  include a magnetically-responsive material and the applied field is a magnetic field. 
     Further details regarding the type of material comprising the particles and regarding a process of arranging the particles  58  into elongate patterns  56  are described later in association with at least  FIGS. 9-10 . 
       FIG. 2B  is a sectional view schematically representing a charge-receiving layer  90 , according to one example of the present disclosure. In some examples, charge-receiving layer  90  is at least consistent with and/or includes at least substantially the same features and attributes as charge-receiving layer  40  (as previously described in association with  FIG. 1B ), except for providing elongate patterns  102  of conductive particles  58  (forming conductive paths  100 ) in which the conductive particles  58  are not aligned in a strictly linear pattern. Instead, the particles  58  vary in their position along the X plane (represented by directional arrow X) by a small distance, but with substantially all of the particles  58  (of one elongate pattern  102 ) falling between boundaries B 1  and B 2  (for one conductive path  100 ), and between B 3  and B 4  (for another conductive path  100 ), respectively. In addition, despite the variable spacing along the X plane, the conductive particles  58  still form elongate patterns  102  that have a longitudinal axis (A 1 ) that extends generally perpendicular to a longitudinal axis (A 2 ) of the charge-receiving layer  90 . 
     In some examples, some conductive paths  100  include an end particle  61  directly exposed at first side  22 A, while in some examples, some conductive paths  100  include an end particle  59  recessed from (i.e. spaced apart) first side  22 A by a gap G 1 , as shown in  FIG. 26 . As further demonstrated via  FIG. 2B , in some examples at least some of the conductive particles, such as  63 ,  64  are spaced apart from each other (represented by gap G 2 ) along a first orientation generally parallel to the longitudinal axis (A 1 ) of the elongate pattern  102 . In this latter aspect, in some examples the particles  58  (such as  63 ,  64 ) do not form a contiguous structure or monolithic structure, but instead define an elongate band or elongate pattern of separate particles adapted to provide a conductive path to convey (i.e. facilitate migration) of charges. In some examples, the spacing (e.g. G 2 ) along the Y orientation or in the X plane is non-uniform. 
       FIG. 3A  is a diagram  130  including a side sectional view schematically representing an e-paper structure  132  and an associated e-paper writing module  160 , according to one example of the present disclosure. In some examples, e-paper structure  132  is consistent with, and/or includes at least some of substantially the same features and attributes as e-paper display media previously described in association with at least  FIGS. 1A-2 . Meanwhile, writing module  160  is provided in  FIG. 3A  to generally illustrate a response of the e-paper structure  132  to air-borne charges emitted from an erasing unit  166  and/or a writing unit  164 . 
     As shown in  FIG. 3A , the writing module  160  includes writing unit  164  and an erasing unit  166 . The writing unit  164  and erasing unit  166  both face a charge receiving surface  192  of the media, with the writing module  160  spaced apart from the surface  192 . In some examples, this external writing module  160  is spaced apart (at least during erasing and/or writing) from the charge-receiving layer  138  by a distance of 125 μm to 2 millimeters. 
     In some examples, one or both of the writing unit  164  and erasing unit  166  comprises an ion-based head. In one example, the ion-based head is provided via a corona-based charge ejecting device. In some examples, an ion-based erasing unit  166  is replaced with an electrode that comes into close contact with, or that is dragged along, the surface  192  in front of the writing unit  164 . As represented by arrow R, erasing and writing is performed upon relative movement between the writing module  160  and the e-paper structure  132 . 
     In some examples, a surface  192  is sometimes referred to as an imaging side of the e-paper structure  132  and an opposite surface  190  is sometimes referred to as a non-imaging side of the e-paper structure  132 . 
     In general terms, as shown in  FIG. 3A , e-paper structure  132  includes a protective layer  138 , a charge-responsive layer  139 , and a base  140 . The protective layer  138  is sometimes referred to as charge-receiving layer  138 . The base  140  defines or includes a counter electrode, as further described below, which serves as a ground plane. In some examples, it will be understood that, even in the absence of layer  138 , charge-responsive layer  139  is imageable by charges  39  and that layer  138  primarily is provided for protection of unintentional and/or malicious mechanical and electrical insults to charge-responsive layer  139 . Nevertheless, in at least some examples of the present disclosure, the presence of the protective layer  138  facilitates producing and retaining quality images at charge-responsive layer  139  in the manner described herein. 
     In some examples, charge-receiving layer  138  is consistent with, and/or includes at least some of substantially the same features and attributes as layers  20 ,  40  ( FIGS. 1A-2 ). In particular, as shown in  FIG. 3A , charge-receiving layer  138  includes a plurality of generally parallel, spaced apart conductive paths  185 , with each conductive path formed from an elongate pattern of separate conductive particles  188 . As shown in the enlarged portion A of  FIG. 3A , the conductive particles  188  are generally arranged in series. 
     Furthermore, it will be understood that particles  188  are not limited to the shapes shown in portion A of  FIG. 3A  and the shape of the particles  188  can vary depending on the type of material forming particles  188  and/or depending on the processing of the materials forming particles  188 . 
     With further reference to at least  FIG. 3A  and consistent with at least  FIG. 2B , in some examples, each conductive path  185  has a width or diameter (D 3 ) with adjacent conductive paths  185  being spaced apart by a distance D 2 . In some examples, the spacing (D 2 ) between adjacent conductive paths  185  is about 10 μm and can fall within range between 5 to 15 μm. Meanwhile, the width (D 3 ) of the conductive paths  185  generally falls within a range between 2 and 6 μm, with the width (D 3 ) depending on the viscosity of the insulative matrix  33  in which the conductive paths  185  are dispersed. 
     In some examples, the protective or charge-receiving layer  138  has a thickness of about 10 μm to about 200 μm. In some examples, the charge-receiving layer  138  has a thickness of about 50 μm to about 175 μm. In some examples, the charge-receiving layer  138  has a thickness of about 150 μm. 
     In some examples, the charge-receiving layer  138  has a thickness that is a multiple (e.g. 2×, 3×, 4×) of a thickness of a charge-responsive layer  139  to ensure robust mechanical protection of the charge-responsive layer  139 . In one aspect of such examples, a thickness of the charge-responsive layer  139  generally corresponds to a diameter of microcapsules  145  (forming a monolayer). 
     In one aspect, the thickness and type of materials forming charge-receiving layer  138  are selected to mechanically protect the charge-responsive layer  139  (including microcapsules  145 ) from punctures, abrasion, bending, scratching, liquid hazards, crushing, and other impacts. Moreover, as further described later, in some examples the layer  138  also protects the charge-responsive layer  139  from tribo charges. 
     In addition, by providing preferential conductivity, charge-receiving layer  138  reduces unintentional increases in image dot size that might otherwise occur due to a blooming effect, as previously described. 
     In the example shown in  FIG. 3A , the charge-responsive layer  139  includes a plurality of microcapsules  145  arranged in a monolayer. Each microcapsule  145  encapsulates some charged black particles  154  and some charged white particles  150  dispersed within a matrix  141 , such as a dielectric liquid (e.g. an oil). In one example, as shown in at least  FIGS. 3A and 5-8 , the black particles  154  are positively charged and the white particles  150  are negatively charged while the erasing unit  166  produces negative charges and the writing unit  164  produces positive charges. 
     In some examples, the erasing unit  166  erases any information stored via the microcapsules  145  prior to writing information with the writing unit  164 . In the example shown in  FIG. 3A , upon relative motion between the e-paper structure  132  and the writing module  160 , the negatively charged erasing unit  166  emits a stream of air-borne charges  41 , which will result in removal of positively charged ions that are attached to the surface  147  of charge-responsive layer  139 , as further illustrated in the enlarged view of  FIG. 3B . The negatively charged erasing unit  166  also creates electrostatic forces that drive negatively charged white particles  150  away from the charge receiving layer  138  and attracts positively charged black particles  154  toward the charge receiving layer  138 . By passing the erasing unit  166  over the charge receiving layer  138 , any information previously written to the e-paper structure  132  is erased by positioning the positively charged black particles  154  near the top of the microcapsules  145  and pushing the negatively charged white particles  150  to the bottom of the microcapsules  145 . 
     It will be understood that depending on whether a particular side  192  or  190  of e-paper structure  132  is opaque or transparent, a respective side  192  or  190  can be a viewing side or non-viewing side of the e-paper structure, as will be further noted later. However, regardless of which side  192  or  190  is a viewing side, side  192  will remain an imaging side of the e-paper structure  132 . 
     Microcapsules  145  exhibit image stability using adhesion between particles and/or between the particles and the microcapsule surface. For example, microcapsules  145  can hold text, graphics, and images indefinitely without using electricity, while allowing the text, graphics, or images to be changed later. 
     In some examples, the diameter (D 1 ) of each microcapsule  145  is substantially constant within charge-responsive layer  139  of e-paper structure  132  and, in some examples, the thickness (H 1 ) of charge-responsive layer  139  is between about 20 μm and about 100 μm, such as 50 μm. In some examples, the charge-responsive layer  139  is arranged as a monolayer and has a thickness of generally corresponding to a diameter (D 1 ) of the microcapsules, which in some examples, is about 30 to 40 μm. 
     In some examples, base  140  has a thickness between about 20 μm and about 1 mm, or larger depending on how e-paper structure  132  is to be used. 
     In one aspect, base  140  is structured to provide enough conductivity to enable counter charges to flow during printing. As such, in general terms, base  140  comprises a member including at least some conductive properties. In some examples, base  140  comprises a non-conductive material that is impregnated with conductive additive materials, such as carbon nanofibers or other conductive elements. In some examples, base  140  comprises a conductive polymer, such as a urethane material or a carbonite material. In further examples, base  140  is made from a conductive polymer with carbon nanofibers, to provide flexibility with adequate strength. 
     In some examples, base  140  is primarily comprised of a conductive material, such as an aluminum material and therefore is impregnated or coated with additional conductive materials. 
     In some examples, whether conductivity is provided via coating, impregnation or other mechanisms, the body of base  140  is formed from a generally electrically insulative, biaxially-oriented polyethylene terephthalate (BOPET), commonly sold under the trade name MYLAR to provide flexibility and strength in a relatively thin layer. 
     As noted elsewhere throughout the present disclosure, the base  140  is opaque or is transparent, depending on the particular implementation of the e-paper display media. In some examples, the base  140  comprises a generally resilient material, exhibiting flexibility and in some implementations, semi-rigid behavior. In some examples, the base  140  comprises a rigid material. 
       FIG. 3A  also shows one example of a writing operation performed by the writing module  160  in which the deposition of charges within target zone Z (between dashed lines Z 1 , Z 2 ) influences the distribution of charged pigments/particles within affected microcapsules  145 . In one aspect, in order to form an image on e-paper structure  132 , the writing unit  164  is designed and operated to selectively eject positive charges  39  toward the surface  192  of charge-receiving layer  138 , when a region of the e-paper structure  132  (located beneath the writing unit  164 ) is to be changed from white to black (or vice versa in some examples). As noted above, conductive paths  185  extending through the charge-receiving layer  138  (between opposite sides  172 A,  172 B) facilitate passage of the deposited charges to the charge-responsive layer  139 . It will be understood that the passage of charges  39  through charge-receiving layer  138  is limited to those locations (e.g. within target zone Z) at which charges were intentionally deposited by writing module  160 . 
     In this example, as a resulting effect from the deposit of the positive charges  39  at charge-receiving layer  138 , the positively charged black particles  154  (within the nearby microcapsules  145 ) are repelled and driven away from the surface  147  of charge-responsive layer  139 , while the negatively charged white particles  150  (within nearby microcapsules  145 ) are attracted to the positive charges  39  and pulled toward the charge receiving surface  147 , as further illustrated in the enlarged view of  FIG. 3B . 
     In some examples, when at least a portion of base  140  is transparent and surface  190  comprises a viewing side of the e-paper structure  132 , the areas of surface  147  having a positive charge will result in the microcapsules  145  (or portions of a microcapsule  145 ) producing a black appearance at surface  190  while the areas of surface  147  having negative charge will result in corresponding microcapsules  145  or portions of a microcapsule  145 ) producing a white appearance at surface  190 . In some instances of this example, the charge-receiving layer  138  is opaque to facilitate clarity in viewing through transparent base  140  at surface  190 . Accordingly, in this implementation, the charge-receiving layer  138  serves as an imaging side, but is a non-viewing side of the e-paper structure  132 . 
     On the other hand, in some examples, when at least a portion of charge-receiving layer  138  is transparent and surface  192  comprises a viewing side of the e-paper structure  132 , the areas of surface  147  having a positive charge will result in the microcapsules  145  (or portions of a microcapsule  145 ) producing a white appearance at surface  192  while the areas of surface  147  having negative charge will result in corresponding microcapsules  145  (or portions of a microcapsule  145 ) producing a black appearance at surface  192 . In some instances of this example, the base  140  is opaque to facilitate clarity in viewing through transparent charge-receiving layer  138  at surface  192 . Accordingly, in this implementation, the charge-receiving layer  138  serves as both an imaging side and a viewing side of the e-paper structure  132 . 
     In some examples, as shown in  FIG. 3A , during writing and erasing electrical contact is made by a ground resource (GND), associated with writing module  160 , with exposed portions of base  140  to allow biasing of the writing module  160  while it directs charges to charge receiving layer  138  during the writing process. 
     The e-paper writing module  160 , as shown in  FIG. 3A , is not limited to implementations in which the writing unit  164  produces positive charges and the erasing unit  166  erases information with negative charges. Instead, in some examples, the microcapsules  145  in matrix material  141  of the charge-responsive layer  139  of e-paper structure  132  are composed of negatively charged black particles  154  and positively charged white particles  150 . In such examples, the writing unit  164  is designed to produce negative charges (e.g. negatively charged ions), while the erasing unit  166  uses positive charges to erase information stored in the microcapsules  145  of the charge-responsive layer  139  of the e-caper structure  132 . 
     In one aspect, it will be understood that in at least some examples of the present disclosure, the e-paper structure  132  operates without an applied voltage at surface  192  (e.g. side  172 A of layer  138 ) and without an electrically-active conductive element in contact with surface  192 . Instead, via the presence of the counter electrode  140  (e.g. base) and the established ground path, air-borne charges produced via writing module  160  arrive at surface  192  and flow to charge-responsive layer  139  through targeted preferential conductive paths in charge-receiving layer  138 . 
     With reference to the enlarged view of  FIG. 3C  as taken from  FIG. 3A  (represented by marker C), in some examples in which conductive particles  188  are magnetically responsive, an insulative matrix  243  of a charge-receiving layer further includes a plurality  245  of non-magnetically-responsive conductive elements  247  dispersed throughout the insulative matrix  243 , such as between the conductive paths  185  (made of magnetically-responsive particles  188 ). It will be understood that for illustrative purposes, conductive elements  247  are not necessarily shown to scale in  FIG. 3C . In some examples, the conductive elements  247  slightly augment the conductivity of the insulative matrix  243  to provide anti-static, protective qualities without otherwise disrupting the anisotropic conductivity provided via the conductive paths. In other words, while the conductive paths  185  facilitate passage of intentionally deposited charges from writing module  160  ( FIG. 3A ), the non-magnetic conductive elements  247  act as a secondary charge dissipation mechanism for residual and/or tribo charges on surface  192  of the e-paper structure. In this way, the non-magnetic conductive elements help to prevent inadvertent disturbance of an image formed at charge-responsive layer  139  of e-paper structure  132  ( FIG. 3A ), and their presence contributes to the stability and clarity of an image written to charge-responsive layer  139  of e-paper structure  132 . In one aspect, because the conductive elements  247  are non-magnetically-responsive, their location is unaffected during formation of the charge-receiving layer  138  when particles  188  are subjected to a magnetic field to cause their alignment into conductive paths  185 . 
       FIG. 3D  is a diagram  250  including a perspective view schematically representing a portion of a charge-receiving layer  260  of an e-paper structure, according to an example of the present disclosure. In one example, the charge-receiving layer  260  is consistent with, and/or includes at least some of substantially the same features and attributes, as charge-receiving layer  138  as previously described in association with at least  FIGS. 3A-30 . As shown in  FIG. 3D , the example portion of the charge-receiving layer  260  includes a plurality  280  of conductive paths  285  with each conductive path  285  formed via magnetically-alignable conductive particles. The example portion exhibits a height (H 2 ) in the z-direction and in the x-y direction, has a width (D 4 ) and length (D 5 ). Among other attributes,  FIG. 3D  illustrates a relative density of the conductive paths  285  within a given portion of the charge-receiving layer  138 . In some examples, the density of conductive paths  285  is at least partly controllable based on a viscosity of the insulative matrix  287 . 
     It will be understood that the conductive paths  285  are shown in  FIG. 3D  resembling columnar structures solely for illustrative simplicity to depict geometric and spatial relationships for a charge-receiving layer, and that the conductive paths  285  would actually be implemented via elongate patterns of separate conductive particles, as previously described in at least  FIGS. 1B, 2B, 3A , etc. 
       FIG. 4A  is top plan view schematically representing a portion of an e-paper display media  300 , according to an example of the present disclosure. As shown in  FIG. 1A , display media  300  includes image-bearing face  330 . 
     As further described below in more detail, e-paper display media  300  incorporates e-paper structure like e-paper structure  132  as previously described in association with at least  FIG. 3A . Accordingly, in some examples, the image-viewable surface (i.e. image-bearing surface)  330  corresponds to the image-writing surface (e.g. surface  192  in  FIG. 3A ) of the e-paper display media  300  while in some examples, the image-viewable surface (i.e. image-bearing surface) corresponds to a non-image-writable surface (e.g. surface  190  in  FIG. 3A ) of the e-paper display media  300 . 
     As shown in  FIG. 4A , in some examples e-paper display media  300  bears an image  340 , in some examples, image  340  includes text  344  and/or graphics  348  positioned among the remaining blank portion  350 . It will be understood that in this context, in some examples, graphics also refers to an image, such as specific picture of a person, object, place, etc. Moreover, the particular content of the information in image  340  is not fixed, but is changeable by virtue of the rewritable nature of the e-paper structure  132  incorporated within display media  300 . In one example, a location, shape, and/or size of text  344  and/or graphics  348  of an image  340  is also not fixed, but is changeable by virtue of the rewritable nature of the e-paper display media  300 . 
     In at least some examples of the present disclosure, an e-paper structure (e.g. e-paper structure  132  in  FIG. 3A ) forming at least a portion of display media  300  is a passive e-paper display. In one aspect, the e-paper display  300  is passive in the sense that it is re-writable and holds an image without being connected to an active power source during the writing process and/or after the writing is completed. Instead, as previously described, the passive e-paper structure  132  is imaged in a non-contact manner in which the e-paper display  300  receives charges (emitted by a on head) that travel through the air and then forms the image  340  via a response by charged particles within the charge-responsive layer  139  of the e-paper structure  132 . After the imaging process is completed, the passive e-paper display  300  retains the image generally indefinitely and without a power supply until image  340  is selectively changed at a later time. 
     In some examples, an e-paper structure forming display media  300  and that includes a charge-receiving layer (such as charge-receiving layer  138  in  FIG. 3A  or in later  FIGS. 5-8 ) is not strictly limited to the particular type of charge-responsive layer  139  previously described in association with at least  FIG. 3A . Rather, in some examples, the charge-responsive layer forming an e-paper assembly (onto which a charge-receiving layer according to at least some examples of the present disclosure) operates at least consistent with general electrophoretic principles. With this in mind, in some examples, such charge-responsive layers include charged color particles (other than microcapsules  145 ) that switch color when charges are selectively applied a non-contact manner by an external writing module. In some examples, the charged color particles comprise pigment/dye components. 
     In some examples, an e-paper structure incorporated within display media  300  is constructed via placing celled structures between two containing walls. In some examples, an e-paper structure incorporated within display media  300  includes air borne particles insides capsules, such as a “quick response liquid powder display” formerly available from Bridgestone Corporation of Tokyo, Japan. 
     With further reference to  FIG. 4A , in some examples, the image  340  appearing on face  330  of display media  300  results from writing the image at resolution of 300 dots-per-inch. In some examples, image  340  is written at greater or less resolutions than 300 dots-per-inch. 
     With this in mind,  FIG. 4B  is a diagram  375  including a top plan view of a portion  378  of image  340 , according to one example of the present disclosure. As shown in  FIG. 4B , diagram  375  includes a layout  380  of dots  382 , each of which can be written as black dots or white dots based on a response of the underlying e-paper structure  132  to deposited charges selectively targeted in a manner corresponding to the pattern of image  340 . As shown in  FIG. 4B , the portion  378  of image  340  includes some white dots  382 A and some black dots  382 B. The white dots  382 A appear as blank portion  350  in image  340  shown in  FIG. 4A , while the black dots  382 B appear as a portion of text  344 , graphic  348 , etc. A center-to-center spacing between dots  382  is represented by distance D 6  while a diameter of each dot  382  is represented by distance D 7 . In one example, to achieve a 300 dpi image, the distance D 6  is 84 microns and the diameter (D 7 ) of each dot  382  is about 80 to 100 microns. 
     With this in mind, in some examples, a black dot  382 B typically corresponds to several (e.g. 3-4) microcapsules  145  in charge-responsive layer  139  of e-paper structure  132 , as represented in at least  FIGS. 3A-3B . In one aspect, the deposited charges  39  (that correspond to formation of one black dot  382 B ( FIG. 4B )) correspond to at least the microcapsules  145  (or portions of microcapsules) within target zone Z in  FIG. 3A . 
       FIG. 5  is a diagram  400  including a side sectional view schematically representing an e-paper structure  402 , according to an example of the present disclosure. In one example, the e-paper structure  402  is consistent with, and/or includes at least some of substantially the same features and attributes as e-paper structure  132 , as previously described in association with at least  FIG. 3A . However, in diagram  400  the conductive paths  185  within charge-receiving layer  138  extend at an angle (α) relative to a vertical plane V, which is also represented by the line segment A-B. Plane V extends generally perpendicular to a longitudinal axis A 3  of charge-receiving layer  139  and A 2  of charge-receiving layer  138 . In one aspect, line segment A-C generally corresponds to a length of an angled conductive path  185  while line segment A-B corresponds to a height (H 2 ) of the charge-receiving layer  138 . In another aspect,  FIG. 5  shows line segment B-C, which corresponds to a lateral distance from the vertical plane V to an end  405 B of an angled conductive path  185 . 
     The distance of line segment B-C corresponds to a lateral deviation in the placement of a charge at the charge-responsive layer  139  that occurs due to the conductive paths  185  being formed at the angle (α) instead of generally parallel to the plane V. 
     As further described below, at least an adequate resolution is maintained in the resolution of an image despite a small lateral deviation (as represented by line segment B-C) in charge placement when the conductive paths  185  are formed with a slight non-vertical angle. In one example, assuming a configuration including a thickness (H 2  or line segment A-B) of charge-receiving layer  138  of 150 μm and an angle (α) of 5 degrees from plane V, a lateral deviation (line segment B-C) of about 13 μm would occur. Given a dot-to-dot spacing of 84 μm between imageable “dots” (having a diameter of about 80 to 100 μm) provided via writing module  160  ( FIG. 3A ), a lateral deviation of about 13 μm at the charge-responsive layer  139  is generally acceptable for 300 dpi imaging. 
     In some examples, as previously described in association with at least  FIG. 1A , a combined conductivity of all the conductive paths  32  in charge-receiving layer  138  is at least one order of magnitude greater than the conductivity (σ body ) of insulative matrix  33 . Moreover, in some examples, a first ratio of this combined conductivity of all the conductive paths  32 ) relative to the conductivity of the insulative matrix  33  is proportional to a second ratio of a thickness of the charge-receiving layer  138  relative to a maximum allowable lateral travel (e.g. lateral deviation represented by line segment B-C in  FIG. 5 ) of a charge in the insulative matrix  33 . 
     In some examples, these relationships exhibited within a charge-receiving layer  138  are further represented by the equation:
 
 d   Z   /d   XY   ˜vd   Z   /vd   XY ˜σ Z /σ XY ˜ρ XY /ρ Z ,
         where XY represents an XY plane, Z represents a Z axis orthogonal to the XY plane, where d represents a traveled distance, vd represents a drift velocity of charges, σ represents conductivity, and ρ represents resistivity.       

     Accordingly, in some examples, to achieve a lateral deviation less than 10 μm then the charge-receiving layer  138  will exhibit a resistivity ratio (ρ XY /ρ Z ) larger than 15. 
       FIG. 6  is diagram  420  including a side sectional view of an e-paper structure  432 , according to one example of the present disclosure. In one example, the e-paper structure  432  is consistent with, and/or includes at least some of substantially the same features and attributes as, e-paper structure  132  (as previously described in association with at least  FIG. 3A ), except with e-paper structure  432  having conductive paths  441  formed from spaced apart segments  442 A,  442 B,  442 C instead of a conductive path  185  formed as a single elongate pattern that extends the full thickness (H 2 ) of the charge-receiving layer  138 , as in at least  FIG. 3A . 
     In particular, for comparison purposes, in the example of charge-receiving layer  138  of  FIG. 3A , a single conductive path  185  generally provides a single elongate pattern of conductive particles  58  to convey (i.e. facilitate passage) of charges through the entire thickness of the charge-receiving layer  138 . However, in the example of e-paper structure  432  shown in  FIG. 6 , charge-receiving layer  438  includes a plurality of generally parallel, spaced apart elongate conductive paths  441 , with each path  441  including a series of two or three (or more) conductive segments of field-aligned conductive particles. As shown in  FIG. 6 , some elongate conductive paths  441  include three separate or distinct segments  442 A,  442 B,  442 C aligned in generally end-to-end configuration (with some lateral spacing) and that, in some examples, function as a single elongate conductive path  441  to facilitate passage of charges through charge-receiving layer  138 .  FIG. 6  illustrates that, in some examples, a first segment  442 A has a height H 4  and that a second segment (or a combination of a second segment  442 B and third segment  442 C) has a height H 3 , with a sum of H 3  and H 4  generally corresponding to the total height (H 2 ) of charge-receiving layer  438 . 
     As further shown in the enlargement portion (labeled E) in  FIG. 6 , in some examples, an end  443  of one segment  442 B is vertically spaced apart from (i.e. forms a gap relative to) an end  443  of an adjacent segment  442 C by a distance (D 9 ) while the end  443  of one segment  442 B is horizontally spaced apart from (i.e. forms a gap relative to) the end of adjacent segment  442 C. In one aspect, enlargement portion E further illustrates that each segment is formed from an elongate pattern of conductive particles  188 . In some examples, the distance D 8  and distance D 9  is no greater than 10 percent of a length of one of the respective segments  442 B,  442 B. Given a reasonably small spacing, charges are able to travel through charge-receiving layer  438  by jumping such vertical gaps and/or horizontal gaps. In one aspect, the arrangement of a conductive path  441  (as a series of separate segments  442 A,  442 B,  442 C) demonstrates that elongate patterns of conductive particles for conveying charges need not be formed into homogeneous conductive paths each having a uniform shape, length, position in order for conveying charges. Nevertheless, the arrangement of elongate conductive paths  441  in e-paper structure  432  ( FIG. 6 ) does maintain generally parallel, spaced apart paths of preferential conductivity within an insulative matrix  433 . 
     In some examples, the multiple, spaced apart segments forming elongate conductive paths  441  in  FIG. 6  aids in preventing attempted tampering with a written image on the charge-responsive layer  139 , such as might be attempted via a charged stylus of pointed electrode, because any unwanted electrical charges from these contact-based electrical sources would be limited to traveling just the first segment (e.g.  442 A) nearest the surface  192 . However, in some examples, the free charges deposited by the external writing module  160 , in at least some examples of the present disclosure, would be free to jump along the segments  442 A,  442 B, and  442 C to reach the charge-responsive layer  139 . 
       FIG. 7  is a diagram  460  including a side sectional view of an e-paper structure  462 , according to one example of the present disclosure. In one example, the e-paper structure  462  is consistent with, and/or includes at least some of substantially the same features and attributes as, e-paper structure  432  ( FIG. 6 ), except with e-paper structure  462  having elongate conductive paths  481  provided via spaced apart, separate segments  482 A,  482 B that, when combined in series, do not extend the full height H 2  of the charge-receiving layer  488 . In particular, the elongate conductive paths  481  are formed from one segment  482  or from two generally end-to-end segments  482 A,  482 B with each elongate conductive path  481  having a height H 5  that is less than the full height H 2  of charge-receiving layer  488 . In this configuration, a top portion  485  of charge-receiving layer  488  generally does not include any preferential conductive segments and has a height H 6 . In one aspect, in this configuration the deposited charges  39  are not subject to preferential conductive pathways within charge-receiving layer  488  until the charges  39  have traveled through top portion  485 , and then the charges  39  are conveyed through one of the generally parallel, spaced apart elongate conductive paths  481 . 
     In one aspect, this configuration achieves preferential conductive passage of charges  39  while consuming a lower volume of particles than configurations having full height conductive paths, such as conductive paths  185  in  FIG. 3A . In addition, the top portion  485  inhibits image disruptions from unintentional or malicious electrical insults because the end  484  of the elongate conductive paths  481  is not directly accessible at surface  192 . Moreover, despite the generally insulative nature of the matrix  433  forming top portion  485 , enough conductivity is present for charges deposited at surface  192  to migrate to top end  484  of segments  482 A. 
       FIG. 8  is a diagram  490  including a side sectional view of an e-paper structure  492 , according to one example of the present disclosure. In one example, the e-paper structure  492  is consistent with, and/or includes at least some of substantially the same features and attributes as, e-paper structure  482  (as previously described in association with at least  FIG. 7 ), except with a separate top portion  494  that omits preferentially conductive segments  481 . In one aspect, charge-receiving layer  491  has a height H 5 , which is less than the full height H 2  with top portion  494  having a height H 6 . In some examples, charge-receiving layer  491  includes at least substantially the same features and attributes as charge-receiving layers  138  ( FIG. 3A ) or charge-receiving layer  438  of  FIG. 6 . 
     In one aspect, the top portion  494  is made of a material different than the insulating matrix  433  (i.e. conductive-resistant medium) of charge-receiving layer  491 . This different material in top portion  494  provides scratch resistance, toughness, and strength while still permitting deposited charges to pass through top portion  494 , while still on target, to be conveyed via the elongate conductive paths  481  extending through insulative matrix  433  of charge-receiving layer  491 . 
     In some examples, the material forming top portion  494  exhibits greater strength, toughness, etc, than the material forming insulative matrix  433 . In some examples, the material forming top portion  494  has a greater degree of conductivity than insulative matrix  433  to facilitate passage of deposited charges until the charges reach end  484  of an upper segment  482 A of the elongate conductive paths  481 . 
       FIG. 9  is a flow diagram schematically representing a method  600  of manufacturing a coating for an e-paper structure, according to an example of the present disclosure, in some examples, the method  600  is consistent with, and/or includes at least some of the components, materials, configurations, as previously described in association with  FIGS. 1A-8 , and/or method  600  can be applied to manufacture at least some of the components, materials, and configurations provided in association with  FIGS. 1A-8 . 
     As shown in  FIG. 9 , method  600  includes (at  602 ) forming a first layer as coating of conductive particles dispersed within an insulative matrix and at  604 , applying a field to cause the conductive particles to align in generally parallel, spaced apart elongate patterns that are generally perpendicular to a plane through which the first layer extends. At  606 , method  600  includes curing, at ambient temperatures and without applied pressure, the first layer via radiation energy while maintaining the applied field. 
     In some examples, the particles are magnetically responsive and the field is a magnetic field. 
     In some examples, the method  600  further includes providing a substrate as an e-paper assembly having a first side comprising an electrically passive, charge-responsive layer and an opposite second side comprising a counter electrode layer, as shown at  620  in  FIG. 10 . In one aspect, the first layer is formed onto, or transferred onto, the first side of the e-paper assembly. 
     In some examples, other forms of substrates are used prior to formation of the final e-paper structure including a charge-receiving layer. 
     Further details regarding the manufacture of a protective coating layer according to at least some examples of the present disclosure are provided below. 
     In some examples, during preparation of the first layer, such as a charge-receiving layer (e.g.  40  in  FIG. 1B, 138  in  FIG. 3A ), an insulative matrix ( 33  in  FIG. 1B ) is selected to provide an electrical resistance &gt;10 12  Ω-cm. In some examples, the electrical resistance of the insulative matrix is at least 10 6  to 10 9  Ohms. In some examples, the electrical resistance of the insulative matrix is 10 9  to 10 12  Ohms. 
     In some examples, the insulative matrix and conductive particles ( FIG. 3A ) are selected such that the resistance ratio (ρ metal /ρ matrix ) between the conductive particles (such as particles  58  that form elongate patterns  56  in at least  FIG. 1B ) and the insulating matrix (e.g.  33  in  FIG. 1B ) is greater than 10 2 . At least some examples of appropriate insulative matrix materials include, but are not limited to, any organic and inorganic forms of mono-, co-, cyclic, block, star and random polymers composed of urethanes, acrylates, methacrylates, silicone, epoxies, carbonates, amides, imine, lactones, saturated linear and/or branched hydrocarbons, unsaturated and/or branched olefins, and aromatics. In some examples, these examples include epoxies and silicone rubbers. 
     With this in mind, in at least some examples, the insulative matrix is made at least partially from a semi-conductive material and/or materials having charge-dissipative qualities. Accordingly, the insulative matrix is considered to be substantially insulative and is not, strictly speaking, an absolute electrical insulator. Rather, the insulative matrix of the charge-receiving layer is considered substantially insulative because it is insulative relative to the conductive paths (of elongate patterns of conductive particles), but is otherwise not a strict insulator. 
     In one aspect, such polymers are curable from liquid (viscosity ranging from 10 cP-10,000 P) to solid (hardness range from shore A-D), with or without color, using radiation energy in any wavelengths at ambient temperatures and without pressure. In one example, the polymers are UV-curable and the applied radiation energy falls within the UVA-UVB range. 
     In some examples, the conductive particles (e.g. particles  58  in  FIG. 1B, 188  in  FIG. 3A ) include any materials that respond to a magnetic field. In some examples, these magnetically-responsive materials are diamagnetic, paramagnetic, ferromagnetic, ferromagnetic, or antiferromagnetic. In some examples, the material(s) forming the particles  58 ,  188  are electrically conductive or semi-conductive provided that the particles  58 ,  188  exhibit conductivity that is significantly greater than the conductivity of the insulative matrix (i.e. conductive-resistant medium). In one example, the particles  58 ,  188  exhibit conductivity that is at least two orders of magnitude (e.g. 10 2 ) greater than the conductivity of the insulative matrix. In some examples, materials suitable to serve as conductive particles (e.g.  58 , 188 , etc.) generally include, but are not limited to, pure transition metals, pure lanthanides, transition metal oxides, lanthanide oxides, and complexes of metals from the transition metals and lanthanides. In some examples, the conductive particles are made from pure forms of metals selected from the group including Nickel, Neodymium, Iron, Cobalt, and magnetite (Fe 3 O 4 ), or made from oxides or complexes of Nickel, Neodymium, Iron, Cobalt, and magnetite. 
     In some examples, the conductive particles have a maximum dimension no greater than 10 μm. In some examples, the conductive particles have a maximum dimension no greater than 5 μm. In some examples, the conductive particles have a maximum dimension no greater than 1 μm. In some examples, the conductive particles have a maximum dimension no greater than 100 nanometers. It will be understood that, in this context, maximum dimension refers to a maximum dimension in any orientation (e.g. length, width, depth, height, diameter, etc.). In some examples, the particles vary in size within a given elongate pattern, which in some instances, facilitates formation of the elongate patterns. In some examples, at least some of the particles have an aspect ratio of 1, which in some instances, facilitates their alignment into elongate patterns, unlike other types of conductive elements such as rods having a high aspect ratio (length/width), which can hinder alignment when subjected to a field at least due to physical interference of the rods with each other. 
     Once the appropriate materials are gathered as described above, an anisotropic conductive coating is prepared according to one of several non-limiting examples described below. In some examples, the conductive particles are dispersed directly within the insulative matrix. In some examples, the conductive particles are dispersed (e.g. in a solvent) prior to mixing with the insulative matrix. These examples are further described below. 
     In one example of preparation including direct dispersion, magnetite particles (Fe 3 O 4 ) are obtained and Polymer 3010 (P3010) from Conductive Compounds, Inc. of Hudson, N.H. is obtained and used without further preparation. In one example, the magnetite particles are obtained from a vendor, such as Sigma-Aldrich of St. Louis, Mo. and used without further preparation. 
     To a clean container, 0.28 g of magnetite (i.e. Fe 3 O 4 ) and 2.5 g of the P3010 polymer are combined into a mixture. In some examples, 15 g of 3 mm zirconia beads are then introduced to the mixture to facilitate dispersion of the magnetite during milling. The charged container was then subjected to centrifugal milling in a tool such as Speed mixer for increments of 30 seconds until the resulting mixture was homogenous, such as when the mixture produces a reading of greater than 7 on a Hegman gauge. 
     In one example of preparation, Nickel particles are obtained and Polymer P15-7SP4 from MasterBond of Hackensack, N.J. is obtained and used without further preparation. In one example, the Nickel particles are obtained from a vendor, such as Sigma-Aldrich of St. Louis, Mo. 
     To a clean container, 0.5 g of Nickel and 3.5 g of the P15-7SP4 polymer are combined into a mixture. The charged container was then subjected to centrifugal milling in a tool such as Speed mixer for increments of 30 seconds until the resulting mixture was homogenous, such as when the mixture produces a reading of greater than 7 on a Hegman gauge. 
     In one example of preparing an anisotropic conductivity coating, particles are pre-dispersed in a compatible solvent via sonication, milling, speed mixing, or micro-fluidization. In some examples, non-impact dispersion methods are used to reduce additional steps to remove milling media. In some examples, a typical procedure includes charging a container with isopropanol with 15-50% particles by weight. After this dispersion, the liquid/slurry is then incorporated into a polymer matrix. The resulting mixture is then subject to rotary evaporation to remove the isopropanol. 
     In some examples, further preparation of the anisotropic conductivity solution includes evacuating the mixture to remove any air that is incorporated during processing. In some examples, the prepared mixture is subjected to vacuum (&lt;0.05 mBar) until completely out-gassed. The resulting mixture is then ready for deposition as a film. 
     Using the out-gassed, prepared solution, in some examples a film is prepared on any substrate directly. In some examples, releasing substrates are used to produce free films on glass or glass-coated substrate. In some examples, prior to receiving a film, a substrate is prepared with a releasing agent such as silicone grease. 
     With this in mind, in some examples the anisotropic conductive film is prepared onto a substrate and then transferred onto a charge-responsive layer of an e-paper structure. In some example, the anisotropic conductive film is deposited directly onto a charge-responsive layer (e.g. an electrically passive, imageable layer) of an e-paper structure. 
     In some examples, an anisotropic conductivity film is deposited onto a substrate via one of several different deposition methods. In some examples, such deposition methods include, but are not limited to, drawn-down coating, spin-coating, guided spreading, or roll coating. Once the desired thickness is achieved, the film is carefully brought to a magnetic field with the appropriate field alignment to cause alignment of the magnetically-responsive particles to form the previously-described elongate patterns, which serve as conductive pathways. 
     Once the desired “elongate conductive path” configuration is established, this configuration (while still being subject to the magnetic field) is then further subjected to curing with the appropriate energy wavelengths (i.e. infrared (IR), e-beam, or ultra-violet (UV)) to solidify the matrix with the elongate conductive path arrangement. 
     In some examples, the width or diameter of the elongate conductive paths (e.g.  56  in  FIG. 1B, 185  in  FIG. 3A, 441  in  FIG. 6  etc.) and/or spacing between such elongate conductive paths is controllable via varying the viscosity of the insulative matrix (e.g.  33  in  FIG. 1B, 3A or 433  in  FIG. 6 ), the materials used, and/or the size of the conductive particles (e.g.  58  in  FIG. 1B, 188  in  FIG. 3A , etc.). 
     In some examples, instead of the above-described examples of providing magnetically-responsive conductive particles and aligning them with a magnetic field, the conductive particles are provided with a dielectric constant that differs greatly from a dielectric constant of the insulative matrix and an electric field is used to align the conductive particles into elongate patterns to provide elongate conductive paths similar to those previously described in association with at least  FIGS. 1A-8 . In some examples, an electric field is applied to a system including a dielectric matrix (polymer in uncured state) and conducting particles, in which the conducting particles would tend to arrange in vertical paths to reduce local fields. 
     At least some examples of the present disclosure provide for a protective coating for an electrically passive, e-paper structure with the protective coating providing preferential conductive paths to facilitate passage of air-borne charges to the imageable layer of the e-paper structure. 
     Although specific examples have been illustrated and described herein, a variety of alternate and/or equivalent implementations may be substituted for the specific examples shown and described without departing from the scope of the present disclosure. This application is intended to cover any adaptations or variations of the specific examples discussed herein. Therefore, it is intended that this disclosure be limited only by the claims and the equivalents thereof.