JP2008535005A - Brightness improvement of TIR modulation electrophoretic reflection image display - Google Patents

Abstract

  The reflective display has a plurality of transparent half beads (60), each having a reflective region (80) surrounding a non-reflective region (82). The light-absorbing particles (26) are suspended in the half-bead (60) and move toward or away from the half-bead (60) and enter the half-bead (60). Selectably frustrate or facilitate total internal reflection of light rays. By selectively reflecting light rays through a non-reflective region (82) of a half bead, for example, a patterned electrode (48) having a conductive region (104) and a plurality of reflective regions (108) is formed. Forming and aligning the reflective region (108) of the electrode with the non-reflective region (82) of the half bead and applying a voltage across the medium (20) via the electrode (48) to produce particles (26) Between the position where the particle substantially covers the half bead (60) and another position where the particle (26) covers the conductive region (104) of the electrode without covering the reflective region (108) of the electrode. ) Is electrophoretically moved to improve display reflectivity.

Description

(Refer to related applications)
This application claims the benefit of US Provisional Patent Application No. 60 / 671,538 filed on Apr. 15, 2005 and claims the benefit of US Patent Provisional Application No. 60 / 759,772 filed on January 17, 2006. .

  The present invention relates to US Pat. No. 5,999,307, US Pat. No. 6,604,784, US Pat. No. 6,215,920, US Pat. No. 6,865,511, US Pat. No. 6,885,496, US Pat. No. 6,891,658. The entire disclosure of which is hereby incorporated by reference in its entirety.

FIG. 1A illustrates a prior art reflective (ie front illumination) electrophoretically frustrated total reflection adjustment of the type described in US Pat. No. 6,885,496, US Pat. No. 6,891,658. Internal reflection (TIR) modulated) A part of the display 10 is shown. In the inner surface of the high refractive index (eg, η ₂ > ˜1.75) polymer material, the display 10 has a flat outer display surface 17 that the viewer V observes through the angular range of the display direction Y, It includes a transparent outer sheet 12 formed by partially embedding a spherical or substantially spherical bead 14 having a large number of high refractive indexes (for example, η ₁ > ˜1.90). “Inside” and “outward” are indicated by double-headed arrows Z. The bead 14 is closely packed to form an inwardly projecting single layer 18 having a thickness approximately equal to one diameter of the bead 14. Ideally, each bead 14 is in contact with all the beads immediately adjacent to that bead. A minimal interstitial gap remains between adjacent beads (ideally no gap).

The electrophoretic medium 20 is maintained adjacent to a portion of the bead 14 that protrudes inwardly from the material 16 by the containment of the medium 20 within the reservoir 22 defined by the lower sheet 24. Inert, low refractive index (eg, less than about 1.35) and low viscosity insulation, such as Fluorinert® perfluorinated hydrocarbon liquid (η ₃ -1.27) available from 3M, St. Paul, Minnesota Liquid is a suitable electrophoretic medium. Other liquids or water can also be used as the electrophoretic medium 20. In this way, a bead-liquid TIR contact surface is formed. The medium 20 includes, for example, a suspension in a finely dispersed state of light-scattering or absorbing particles 26 such as pigments or silica or latex particles that are made scattering / absorbing by dyeing or the like. The optical properties of the sheet 24 are not so important, and the sheet 24 only needs to form a reservoir that contains the electrophoretic medium 20 and the particles 26 and serve as a support for the back electrode 48.

As is well known, the TIR interface between two media having different refractive indices is characterized by a critical angle θ _c . rays incident on said contact surface at an angle less than theta _c is transmitted through the contact surface. rays incident on the contact surface at an angle greater than theta _c, the TIR at the contact surface. A small critical angle is preferred at the TIR interface because it provides a large range of angles where TIR can occur.

  In the absence of electrophoresis, as shown on the right side of the dotted line 28 in FIG. 1A, most of the light rays passing through the sheet 12 and the bead 14 undergo TIR on the inner surface of the bead 14. For example, incident rays 30, 32 are reflected by material 16 and bead 14. The light beam TIRs twice or more at the TIR contact surface of the bead and liquid, as shown at points 34 and 36 in the case of light beam 30 and at points 38 and 40 in the case of light beam 32. Thereafter, the totally reflected light beam is refracted through the bead 14 and the material and emitted as light beams 42 and 44, respectively, resulting in a “white” appearance in each reflective region or pixel.

  A voltage can be applied to the entire surface of the medium 20 via the electrodes 46 and 48 (shown as dotted lines) that can be applied, for example, by vapor deposition to the inwardly protruding surface portion of the bead 14 and the outer surface of the sheet 24. . The electrode 46 is transparent and fairly thin to minimize interference with the light beam at the bead-liquid TIR interface. The back electrode 48 may not be transparent. As shown on the left side of the dotted line 28, when the electrophoretic medium 20 is driven by operating the voltage source 50 so that a voltage is applied between the electrodes 46 and 48, the suspended particles 26 are regions where the evanescent wave is relatively strong. (Ie, within 0.25 microns or closer to the inner surface of the inwardly projecting bead 14). When moving electrophoretically as described above, particles 26 scatter or absorb light, thereby altering the imaginary component, possibly the real component, of the effective refractive index at the bead-liquid TIR interface. By doing so, the TIR is frustrated or modulated. This is indicated by rays 52 and 54. Light rays 52 and 54 are scattered and absorbed when they strike the particle 26 inside the thin (˜0.5 μm) evanescent wave region at the TIR contact surface of the bead and liquid, as indicated by 56 and 58, respectively. Or scattered or absorbed, thereby creating a “dark” appearance in each TIR frustrated non-reflective absorbing region or pixel. Particles 26 properly operate voltage source 50 to restore the TIR capability of the bead-liquid TIR interface to convert each “dark” non-reflective absorbing region or pixel to a “white” reflective region or pixel. By doing so, it is only necessary to move the thin evanescent wave region outside.

  As described above, the net optical characteristics of the outer sheet 12 can be controlled by controlling the voltage applied across the medium 20 via the electrodes 46 and 48. The electrodes can be segmented so as to control the electrophoretic drive of the medium 20 to form an image over individual areas or entire pixels of the sheet 12.

FIG. 2 shows one inner hemisphere or “half bead” portion 60 of the spherical bead 14 in an enlarged cross section. The half bead 60 has a normalized radius r = 1 and a refractive index η ₁ . A light ray 62 incident on the half bead 60 perpendicularly (via the material 16) at a radial distance a from the center C of the half bead 60 is inward of the half bead 60 at an angle θ1 with respect to the radiation axis 66. Hit the surface. To theoretically discuss this theoretically, material 16 has the same index of refraction as half-bead 60 (ie, η ₁ = η ₂ ), and ray 62 passes from material 16 into half-bead 60 without refraction. Assume that it goes. The light beam 62 is refracted on the inner surface of the half bead 60 and travels into the electrophoretic medium 20 as a light beam 64 at an angle θ 2 with respect to the radiation axis 66.

  Here, the distance of the following formula from the center C of the half bead 60

にて半ビード６０に垂直方向に（材料１６を介して）入射する光線６８を検討する。光線６８は、（放射軸７０に対する）臨界角θ_ｃつまりＴＩＲが起こる最小所要角度にて半ビード６０の内方表面に当たる。光線６８は、したがって、光線７２として全反射され、光線７２は、再び、臨界角θ_ｃにて半ビード６０の内方表面に当たる。光線７２は光線７４として内方表面に全反射し、臨界角θ_ｃにて半ビード６０の内方表面に当たる。光線７４は光線７６として全反射され、光線７６は半ビード６０を垂直方向に通過してビード１４の埋設部分と材料１６に入る。したがって光線６８は入射光線６８とほぼ反対の方向に光線７６として反射される。

Consider a light ray 68 incident on the half bead 60 perpendicularly (via material 16). Ray 68 strikes the inner surface of half bead 60 at a critical angle θ _c (relative to radial axis 70), ie, the minimum required angle at which TIR occurs. Beam 68, thus, is totally reflected as ray 72, ray 72 is again strikes the inner surface of the half bead 60 at the critical angle theta _c. Beam 72 is totally reflected on the inner surface as a light 74 strikes the inward surface of the half bead 60 at the critical angle theta _c. Ray 74 is totally reflected as ray 76, which passes vertically through half bead 60 and enters the buried portion of material 14 and material 16. Therefore, the light beam 68 is reflected as a light beam 76 in a direction substantially opposite to the incident light beam 68.

All light rays incident on hemi at a distance a ≧ a _c from the center C of the half bead 60 is reflected toward the light source (but not the exact inverse reflection). This means that the reflection is enhanced when the light source is slightly behind the viewer's head, the reflected light has a dispersive characteristic, and a white appearance desirable in reflective display applications is obtained. 3A, 3B, and 3C show three of the reflection modes of the half bead 60. FIG. Although these and other modes coexist, it is useful to discuss each mode separately.

In FIG. 3A, a light ray incident within a distance of a _c <a ≦ a ₁ undergoes TIR twice (twice TIR mode), and the reflected light is compared with the center in the direction opposite to the incident light direction. branches off target wide arc φ within _1. In FIG. 3B, the light ray incident within the distance range of a ₁ <a ≦ a ₂ undergoes TIR three times (three times TIR mode), and the reflected light is also centered in the direction opposite to the direction of the incident light ray. Branches within a narrower φ ₂ <φ ₁ . In FIG. 3C, a light ray incident within a distance range of a ₂ <a ≦ a ₃ undergoes TIR four times (four times TIR mode), and the reflected light is also centered in a direction opposite to the direction of the incident light ray. Further, the branching is performed within a narrow φ ₃ <φ ₂ . Thus, the half bead 60 has a “semi-retro-reflective”, partially distributed reflection characteristic, and the display 10 has a distributed appearance similar to paper.

  The display 10 has a relatively high apparent brightness compared to paper when the dominant illumination source is within a small angular range behind the viewer. This is shown in FIG. 1B. FIG. 1B shows a wide angle range α in which the viewer can see the display 10 and an angle β that is a deviation angle of the illumination source S with respect to the position of the viewer V. The high apparent brightness of the display 10 is maintained unless β is too large. The reflection R of the half bead 60 at the normal incidence (that is, the portion reflected by TIR among the light rays incident on the half bead 60) is obtained by the equation (1).

η_１は、半ビード６０の屈折率であり、η_３は、ＴＩＲが起こる半ビード６０の表面近傍にある媒質の屈折率である。したがって、半ビード６０がポリカーボネート（η_１〜１．５９）などのより低い屈折率の材料で形成される場合、また、隣接する媒質がＦｌｕｒｏｒｉｎｅｒｔ（η_３〜１．２７）である場合、約３６％の反射率Ｒが得られ、一方、半ビード６０が屈折率の高いナノ複合材料（η_１〜１．９２）で形成された場合、約５６％の反射率Ｒが得られる。照明源Ｓ（図１Ｂ）が視聴者Ｖの頭の背後にあるとき、ディスプレイ１０の見かけの輝度は、上述した半再帰反射特性によって更に向上する。

η ₁ is the refractive index of the half bead 60, and η ₃ is the refractive index of the medium in the vicinity of the surface of the half bead 60 where TIR occurs. Therefore, when the half bead 60 is formed of a material of lower refractive index such as polycarbonate (η ₁ ~1.59), also if the adjacent medium is Flurorinert (η ₃ ~1.27), about 36 % Reflectivity R is obtained, whereas when the half bead 60 is formed of a nanocomposite material (η ₁ -1.92) with a high refractive index, a reflectivity R of approximately 56% is obtained. When the illumination source S (FIG. 1B) is behind the viewer V's head, the apparent brightness of the display 10 is further improved by the semi-retroreflective characteristics described above.

As shown in FIGS. 4A to 4G, the reflectivity of the half-bead 60 is maintained over a wide range of incident angles, thereby improving the display characteristics at the wide angle of the display 10 and its apparent brightness. For example, FIG. 4A shows the half bead 60 as viewed from normal incidence, ie, from an angle of incidence that is 0 degrees away from the normal. In this case, the portion 80 of the half beads 60 a ≧ _{a c} appears as an annulus. The annulus is shown as white and corresponds to the fact that, as described above, this is the region of the half bead 60 that reflects incident light by TIR. The annulus surrounds a circular region 82, shown as dark, which corresponds to the fact that the incident light is absorbed and is a non-reflective region of the half bead 60 that does not TIR. 4B to 4G show the half beads 60 when viewed from an incident angle deviated by 15 degrees, 30 degrees, 45 degrees, 60 degrees, 75 degrees, and 90 degrees, respectively, from the perpendicular. When the Figure 4G compared with FIG. 4A from Figure 4B, the observation area of the reflection part 80 of the half beads 60 for a ≧ a _c it can be seen that not reduced only gradually as the incident angle increases. Even at myopia incidence angles (eg, FIG. 4F), the observer is still looking at a significant portion of the reflective portion 80, so that the display 10 has a wide angle at which high apparent brightness is maintained. A display range is obtained.

  An estimate of the reflectivity of the array of hemispheres corresponding to the inner “half-bead” portion of each one of the beads 14 shown in FIG. 1A multiplies the reflectivity of the individual half-beads by the fill efficiency factor f of the half-bead. Obtained by. In the calculation of the filling efficiency factor f of the densely packed structure, various direct geometric methods well known to those skilled in the art are applied. In the hexagonal close-packed (HCP) structure shown in FIG. 5, assuming that the beads 14 have a uniform size, a filling efficiency of f 充填 π / (6 · tan 30 degrees) to 90.7% is obtained.

Although the HCP structure provides the highest packing density for the hemisphere, the half beads may not be filled in a regular arrangement, and the half beads may not be of uniform size. For an irregular dispersion of non-uniform half beads having a diameter in the range of about 1 μm to 50 μm, the packing density is 80% and its optical appearance is similar to the HCP arrangement of uniform size half beads. It is. For some reflective display applications, such an irregularly distributed arrangement may be more practical to manufacture, and for this reason, some of the reflectivity due to poor packing density It seems that there is no problem with the decrease in However, for the sake of brevity, the following description focuses on the uniform size half-bead HCP arrangement of FIG. 5 and uses a material having a refractive index η ₁ / η ₃ = 1.5. Is assumed. These factors should not be considered as limiting the scope of the present disclosure.

As described with respect to FIG. 2, a significant portion of light rays vertically incident on the flat outer surfaces of the half bead 60 at a distance a <a _c from the center C of the half bead 60 is not TIR, therefore, half It is not reflected by the bead 60. Instead, a significant portion of such rays are scattered and absorbed or scattered or absorbed by the prior art display 10 resulting in a dark non-reflective circular region 82 (FIGS. 4A-4G) in the half bead 60. FIG. 5 shows a plurality of dark non-reflective regions 82, each surrounded by a reflective annular region 80, as described above.

The average surface reflectance R of the half bead 60 is determined by the ratio of the reflective annular zone 80 area: the total area including the reflective annular zone 80 and the dark circular region 82. The ratio is determined by the ratio of the refractive index η _{1 of the} half bead 60 to the refractive index η ₃ of the medium adjacent to the surface of the half bead 60 where TIR occurs according to the equation (1). Therefore, it is clear that the average surface reflectance R increases with the ratio of the refractive index η ₁ of the half bead 60 to the refractive index η ₃ of the adjacent medium. For example, the average surface reflectance R of the hemispherical water droplets (η _{1 to} 1.33) in the air (η _{3 to} 1.0) is about 43%, and the glass hemisphere in the air (η _{1 to} 1.5) The average surface reflectance R is about 55%, and the average surface reflectance R of the diamond hemisphere (η _{1 to} 2.4) in the air exceeds 82%.

  As described above, it may be convenient to make the display 10 using spherical (or hemispherical) shaped beads, even if the spherical (or hemispherical) beads 14 are contained within a single layer 18 (FIG. 1A). Even if it is packed as densely as possible, it is inevitable that the intervening gap 84 (FIG. 5) remains between adjacent beads. Light rays that enter any of the gaps 84 are “lost” in the sense that they travel directly into the electrophoretic medium 20, creating an undesirable dark spot on the display surface 17. Since these points are so small that they cannot be seen, the appearance of the display 10 is not impaired, but the net average surface reflectance R of the display surface 17 is surely impaired.

  The “semi-retroreflective” characteristics described above are important in reflective displays, because in a general viewing condition where the light source S is above the viewer V and behind the viewer V, a significant portion of the reflected light. Is returned to the viewer V. As a result, as a result, the apparent reflectance is about 1.5 "semi-recursive reflection improvement coefficient".

の値を超えてしまう（モスマン、Ｍ．Ａ他共著 「Ａ Ｈｉｇｈ Ｒｅｆｌｅｃｔａｎｃｅ， Ｗｉｄｅ Ｖｉｅｗｉｎｇ Ａｎｇｌｅ Ｒｅｆｌｅｃｔｉｖｅ Ｄｉｓｐｌａｙ Ｕｓｉｎｇ Ｔｏｔａｌ Ｉｎｔｅｒｎａｌ Ｒｅｆｌｅｃｔｉｏｎ ｉｎ Ｍｉｃｒｏ−Ｈｅｍｉｓｐｈｅｒｅｓ」 ２２３〜２３６ページ、Ｓｏｃｉｅｔｙ ｆｏｒ Ｉｎｆｏｒｍａｔｉｏｎ Ｄｉｓｐｌａｙ、 第２３回国際表示装置研究会議 ２００３年９月１５日〜１８日アリゾナ州フェニックスにて開催を参照）。例えば、屈折率η_１／η_３＝１．５のシステムにおいては、式（１）に従って求めた５５％の平均表面反射率Ｒは、上述した半再帰反射観察条件では、約８５％まで向上する。

(Mossman, M.A, et al., “A High Reflection, Wide Viewing Angle Reflective Display Using Total Internal Reflection in Micro-Respired in Micro-Hemis 36”, page 22) (See Meeting 15-15 September 2003 in Phoenix, Arizona). For example, in a system having a refractive index η ₁ / η ₃ = 1.5, the average surface reflectance R of 55% obtained according to the equation (1) is improved to about 85% under the above-described semi-retroreflection observation conditions. .

Individual half beads 60 can be so small that they are not visible in the range of 2 to 50 μm in diameter, and as shown in FIG. 5, when filled into the array, a large number of small, adjacent, reflective annular regions 80. Because of this, it is possible to create a display surface that appears to be very reflective. In those regions 80 where TIR can occur, the particles 26 (FIG. 1A) do not impair the reflection of incident light when not in contact with the inner hemispherical portion of the bead 14. However, in regions 82 and 84 where TIR does not occur, for example, even if the particle 26 moves outside the evanescent wave region so that it does not optically contact the inner hemispherical portion of the bead 14, the particle 26 is not incident. May absorb light. The refractive index ratio η ₁ / η ₃ can be increased to increase the size of each reflective region 80 and reduce such absorption losses. The non-reflective regions 82 and 84 cumulatively reduce the overall surface reflectivity R of the display 10. Since display 10 is a reflective display, it is clearly desirable to minimize such reduction.

Neglecting the semi-recursive reflection enhancement factor described above, a system having a refractive index ratio η ₁ / η ₃ = 1.5 has an average surface reflectivity R of 55%, as described above. Considering the above-described filling efficiency for an HCP configuration of about 91%, the overall average surface reflectivity of the system is 91% of 55%, or about 50%, implying a loss of about 50%. . 41% of this loss is due to light absorption in the circular non-reflective region 82 and the remaining 9% of this loss is due to light absorption in the non-reflective interstitial gap 84. The reflectivity of the display 10 is such that using a specific selected index value, optical microstructure, or material having a patterned surface placed on the outside or inside of the single layer 18 (FIG. 1A). This can be increased by reducing the absorption loss.

  For example, since the maximum surface reflectivity of the display 10 is determined by the ratio of the refractive index values of the half bead 60 and the electrophoretic medium 20, the reflectivity can be substituted for a low refractive index liquid (refractive index less than 1.35) This can be increased by substituting air (refractive index = 1.0) as the electrophoretic medium 20.

As described below, the surface reflectance of the display 10 can be increased, thereby improving the appearance of the display.
The various examples described above of the related art and various limitations related thereto are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those skilled in the art upon reading this specification and reviewing the drawings.

  Exemplary embodiments are shown in the reference figures of the drawings. It is intended that the various embodiments and figures disclosed herein are to be considered illustrative rather than restrictive.

  Throughout the following description, specific details are set forth so that those skilled in the art may more thoroughly understand. However, well-known elements have not been shown or described in detail to avoid unnecessarily obscuring the disclosure. Accordingly, the description and drawings are to be regarded in an illustrative sense rather than a restrictive sense.

  The back electrode 48 can be formed on the sheet 24 using either the pattern 100 or 102 shown in FIG. 6A or 6B, respectively. The black areas 104, 106 are conductive areas and can be reflective or non-reflective. The white areas 108, 110, 112 are reflective areas and are made conductive or non-conductive, provided that there is no conductivity between the areas 108, 110, 112 on the one hand and the areas 104, 106 on the other hand. be able to.

  The reflective regions 108, 110 are preferably circular in shape, and have a diameter that is greater than or equal to (preferably equal to) one diameter of one non-reflective circular region 82 of the half bead 60. Region 104 of pattern 100 has an overall size and shape that is substantially similar to the overall size and shape of regions 80 and 84 of half-bead 60.

  The optical properties of the regions 104, 106 are not as important as the optical properties of the sheet 24. However, a reflective outer surface is placed on the sheet 24, with the rest of the area 108 (or 110, 112) that constitutes the reflective outer surface of the sheet 24, with the area 104 (or 106) thereon. It is desirable to form.

  In the following description, the patterned back electrode 100 reduces the absorption loss due to light absorption in the region 82, but does not reduce the absorption loss due to light absorption in the gap region 84. In contrast, when used in the following description, the patterned back electrode 102 reduces absorption losses due to light absorption in both regions 82, 84. This is because each one of the reflective regions 112 has a size and shape that is substantially similar to the size and shape of one of the gaps 84, and each one of the reflective regions 112 has a gap 84 relative to an adjacent region 82 of the gap. It is obtained by forming the pattern 102 in one corresponding location and in the same location relative to its adjacent reflective region 110.

  The patterned back electrode 100 (or 102) is positioned on the single layer 18 to align each circular reflective region 108 (or 110) with a corresponding one of the non-reflective circular regions 82, thereby The conductive region 104 (or 106) is also aligned with the reflective region 80.

  When the electrophoretic medium 20 is driven by actuating the voltage source 50 to apply a voltage between the electrodes 46 and 48, the particles 26 are non-reflective utilizing the patterned back electrode 100 (FIG. 7A). The inner surface of the half-bead 60 of the single layer 18 is substantially covered, as shown in FIG. Particles 26 absorb light rays (eg, light beam 114) incident on the reflective annular region by frustrating or modulating TIR, as described above, and light rays that pass through beads 14 without TIR (eg, light beam 114). , Absorbs light rays 116). Because the particles 26, as described above in connection with FIG. 2, many incident rays interact with the half bead 60 several times, so that they substantially cover and result in a problem-free level of absorption. The inner surface of the half bead 60 may not be completely covered.

  In the reflective state shown in FIG. 7B, the particles 26 are attracted to the conductive region 104 of the patterned back electrode 100 (or the conductive region 106 of the patterned back electrode 102). Since region 104 is aligned with reflective annular region 80, particle 26 is invisible and hidden (ie, light beam 114 that would otherwise illuminate particle 26 is caused by region 80. Because it is reflected). Ray 116 that does not TIR but instead passes through half-bead 60 strikes one of the reflective regions 108 and is thereby reflected.

  When the half-bead monolayer 18 is positioned at an appropriate distance above the reflective region 108, the transmitted light is collected toward the reflective annular region 80 so that the light is returned almost in the direction it came. . This improves the semi-retroreflective properties of the display and can result in perceptual reflectance values exceeding 100%. Even with the absorption loss associated with red-green-blue (RGB) color filter arrays, the patterned back electrodes 100, 102 allow for the production of a reflective image display having a brightness comparable to the color ink on the white paper.

  FIG. 8 illustrates an alternative display brightness (ie, reflectance) enhancement method in which the absorbent particles 26 are intermingled in the electrophoretic medium 20 with the finely dispersed suspension or particles 118 of the reflective beads. . The average diameter of the reflective beads 118 is significantly larger (eg, about 10 times) than the average diameter of the absorbent particles 26. The reflective bead 118 can be electrophoretically neutral so that it is not affected by the applied electric field. Alternatively, the reflective bead 118 can have an opposite charge to the absorbent particles 26 such that the bead 118 moves away from the particle 26 when affected by the applied electric field. While maintaining a suspension of oppositely charged stable particles may seem counterintuitive, this can be obtained by using appropriate stabilizing dispersants (Amandson, K et al. Co-authored “Microencapsulated Electrophoretic Materials for Electronic Paper Displays”, 20th International Display Research Conference Proceedings, pages 84-87, Society for Information Display from Palm Beach, Florida, September 25, 2000 ). The reflective bead 118 can be a substantially reflective (eg, white) granular material with a suitable granular size distribution, but a high refractive index material such as titanium dioxide (η˜2.4) is preferred. .

  When there is no electrophoresis, as shown to the left of the dotted line 28 in FIG. 8, the smaller the absorbent particles 26, the more likely to be fixed under the large reflective beads 118 toward the lower sheet 24. Accordingly, the incident light (eg, light 120) absorbed by the non-reflective circular region 82 otherwise is reflected by the bead 118 (eg, light 122) instead, resulting in a high reflectivity. Become. A light ray (eg, light ray 124) incident on reflective annular region 80 is totally internally reflected (eg, light ray 126) as described above.

  When a voltage is applied across the entire medium 20, as shown to the right of the dotted line 28 in FIG. 8, the smaller the absorbent particle 26, the more electrophoretically passing through the gap between the beads 118, the inside of the half bead 60. To the surface. When so moved to this absorptive state, the particles 26 absorb light rays (eg, light rays 128) incident on the reflective annular region 80 by frustrating or modulating the TIR, as described above. In addition, it absorbs light (eg, 130) passing through the bead 14 without TIR. Thus, the reflective bead 118 forms a porous filter, and the absorbent particles 26 move outward to contact the half bead 60 in the absorbent state, and move inward from the half bead 60 in the reflective state. So that the absorbent particles 26 are obscured without being directly visible in the reflective state. Although the reflective bead 118 is shown as a spherical shape in FIG. 8, those skilled in the art will appreciate that such a shape is not essential and that the bead 118 can be of any shape. .

  In the method of FIG. 8, various advantages other than the improvement in luminance can be obtained. For example, if the beads 118 are supplied at a sufficiently high density, they tend to impair long-term lateral movement of the absorbent particles 26, thereby slowing the agglomeration action of the absorbent particles 26. Such an aggregating action may cause image degradation of the electrophoretic image display.

  It is possible to estimate the brightness enhancement (i.e. reflectivity) achievable by the method of FIG. For example, assuming that the reflective bead 118 has a diffuse reflectance of about 40%, and assuming that the bead 118 affects the integrity of the 50% absorption loss area described above, about 20% ( That is, a luminance improvement of 40% (50%) is obtained.

  FIG. 9 shows a further alternative display brightness (ie, reflectivity) enhancement method in which a reflective porous membrane 140 is installed between the inner surface of the half bead 60 and the outer sheet 24. The average diameter of the pores in the membrane 140 is significantly larger (eg, about 10 times) than the average diameter of the absorbent particles 26. The pores in membrane 140 constitute a sufficiently large proportion (eg, at least 120%) of the total surface area of membrane 140 to allow substantially unimpeded passage of absorbent particles 26 through membrane 140. To do. The membrane 40 can be formed of a porous membrane material such as polycarbonate or a fiber woven membrane. The outer surface 142 of the membrane 140 is highly reflective and can be diffuse or specular. Suitable reflective films 140 are materials that are intrinsically reflective, such as multilayer band reflectors (eg, multilayer optical films sold by 3M, St. Paul, Minn.) Or aluminized Mylar® flexible films. Or by coating the outer surface 142 with a reflective (eg, aluminum) film using standard vapor deposition techniques.

  In the absence of electrophoresis, as shown to the left of the dotted line 28 in FIG. 9, the smaller the absorbent particles 26, the more likely they are fixed toward the lower sheet 24 through the holes of the film 140. Accordingly, incident light that is otherwise absorbed by the non-reflective circular region 82 (eg, light ray 144) is instead reflected by the reflective outer surface 142 of the membrane 140 (eg, light ray 146). As a result, the reflectance increases. A light ray (eg, light ray 148) incident on the reflective annular region 80 is totally internally reflected (eg, light ray 150) as described above.

  When a voltage is applied to the entire medium 20, as shown to the right of the dotted line 28 in FIG. 9, the absorbent particles 26 move electrophoretically through the holes of the membrane 140 and the inner surface of the half bead 60 To. When moved in this absorptive state, the particles 26 absorb light rays (eg, light rays 152) incident on the reflective annular region 80 by frustrating or modulating the TIR, as described above. In addition, it absorbs light (eg, 154) that passes through the bead 14 without TIR. The pores in the membrane 140 allow the absorbent particles 26 to move outward, contact the half bead 60 in an absorbent state, and move inward from the half bead 60 in a reflective state, thereby absorbing the particles. The particles 26 are obscured without being directly visible in the reflective state.

  It is possible to estimate the brightness enhancement (i.e. reflectivity) achievable by the method of FIG. For example, assuming that the outer surface 142 of the membrane 140 has an overall reflectivity of about 60% and assumes that it affects the integrity of the 50% absorption loss area described above, then about 30% (ie , 60% of the brightness is improved by 50%).

  FIG. 10 illustrates another alternative display brightness (ie, reflectivity) enhancement method in which the intervening area 160 of the outer sheet 12 between the half beads 60 is modified to increase reflectivity. This is because the reflective polymeric material used to form the sheet 12 has a generally hemispherical shape between the half bead portions 60 of the spherical bead 14 via the intervening region 160, as shown at 162. The spherical beads 14 are partially embedded in the outer sheet 12 so as to protrude in the direction.

  When the reflective polymer structures 162 each have a “perfect” hemispherical shape (theoretically ideal, but not practically achievable), the light reflection absorption characteristics of the polymer structure 162 are as described above. As such, it is exactly the same as the half bead 60. The polymer structure 162 is preferably hemispherical in order to obtain desired reflectance characteristics, but may not be completely hemispherical. The polymeric structure 162 need only be substantially hemispherical in that its inner surface should have a sufficiently high curvature to cause TIR of incident light. The TIR occurring within the polymeric structure 162 can be frustrated by the absorbent particles 26 in the same manner as described above with respect to the half bead 60.

  TIR typically does not occur in the intervening region 160, thereby reducing the overall reflectivity of the sheet 12. If the half bead 60 has a hexagonal close packed arrangement, the overall average surface reflectivity is 91%, as described above, and the remaining 9% is lost due to light absorption in the intervening region 160. The By facilitating TIR within the intervening region 160, the brightness enhancement method of FIG. 10 increases this percentage by theoretically increasing the percentage of the sheet 12 carrying useful light reflecting structures to nearly 100%. % Loss.

  Instead of partially embedding the spherical beads 14 in the outer sheet 12, the brightness can be improved by minimizing the size of the intervening region 160. For example, by adopting a polymer material such as polycarbonate with plastic deformation properties so that the uncured or softened resin material essentially forms a hemispherical structure, both the half bead 60 and the polymeric structure 162 are It can be produced as a single integrated array, eliminating the need for a high precision casting mold.

The brightness enhancement method of FIG. 10 can be used in combination with the brightness enhancement method of FIG. 7A, FIG. 7B, FIG. 8 or FIG. 9 in order to further improve the display brightness.
While several exemplary aspects and embodiments have been discussed above, those skilled in the art will recognize certain modifications, substitutions, additions, sub-combinations thereof. Accordingly, the following appended claims and the claims introduced hereinafter are to be construed as including all such modifications, substitutions, additions and sub-combinations that are within the true spirit and scope. I intend to.

A is a partial longitudinal cross-sectional view of an electrophoretic frustrated or modulated prior art reflective image display, not to scale, but greatly enlarged, and B is a wide-angle display range α of the display of FIG. It is the schematic which shows angle range (beta) of a source. 1B is a greatly enlarged longitudinal section of one hemisphere (“half bead”) portion of the spherical bead of the apparatus of FIG. 1A. A, B, and C are diagrams showing semi-recursive reflections of light incident perpendicularly to the half-bead of FIG. 2 at increasing off-axis distances where the incident light is TIR twice, three times, and four times, respectively. A, B, C, D, E, F, and G are shown in FIG. 2 when viewed from observation angles that are deviated from the perpendicular by 0, 15, 30, 45, 60, 75, and 90 degrees, respectively. It is a figure which shows a half bead. 2 is a cross-sectional view of a portion of the display of FIG. 1 (i.e., viewed from an observation angle offset by 0 degrees from the normal) showing a spherical bead disposed within a hexagonal close-packed (HCP) structure. FIG. FIGS. 6A and 6B are plan views greatly enlarging two alternative back electrode patterns used with the structure of FIG. FIGS. 6A and 6B are greatly enlarged partial cross-sectional views of a portion of an electrophoretic frustrated (ie, modulated) reflection image display incorporating the back electrode pattern of FIG. 6A. FIG. 2 is a cross-sectional view, greatly enlarged but not to scale, of a portion of an electrophoretic frustrated or modulated reflective image display incorporating electrophoretic suspension absorbing reflective particles. FIG. 2 is a cross-sectional view of an electrophoretic frustrated or modulated reflected image display incorporating a reflective porous membrane, but not greatly to scale, but greatly enlarged. FIG. 2 is a cross-sectional view, not to scale, but greatly enlarged of a portion of an electrophoretic frustrated or modulated reflection image display that incorporates excess polymeric material in the gap between adjacent half beads.

Claims (47)

In reflective display,
(A) A plurality of transparent half beads (60) projecting inward from the inner surface of the transparent sheet (12) having the outer display surface (17), each surrounding the non-reflective region (82). The plurality of transparent half beads (60) having a reflective region (80);
(B) a second sheet (24) that is spaced inwardly from the transparent sheet (12) and defines a reservoir between the transparent sheet (12);
(C) an electrophoretic medium (20) in the reservoir;
(D) a plurality of light-absorbing particles (26) suspended in the medium;
(E) means for selectively reflecting light rays from the second sheet (24) through the non-reflective region (82) of the half-bead (60);
Including reflective display. Said means for selectively reflecting light rays;
(I) a conductive region (104 or 106);
(B) a first plurality of reflective regions (108 or 110);
And an electrode formed on the outer side of the second sheet (24) in a pattern (100 or 102) including the first plurality of reflective regions (108) of the second sheet (24). Or 110) is associated with a corresponding one of the non-reflective areas (82) of the half-bead (60) and of the non-reflective areas (82) of the half-bead (60). The reflective display of claim 1, wherein the reflective display is aligned with a corresponding one. Each one of the first plurality of reflective regions (108 or 110) of the second sheet (24) is the corresponding one size of the non-reflective region (82) of the half-bead (60). The reflective display of claim 2, having a size and shape substantially similar to the shape. The conductive region (104 or 106) according to claim 3, wherein the conductive region (104 or 106) has an overall size and shape substantially similar to the overall size and shape of the reflective region (80) of the half-bead (60). Reflective display as described. Each one of the half beads (60) is adjacent to one or more other half beads (60) and the display is a non-reflective gap between each adjacent one or more half beads (60) ( 84),
The pattern (100 or 102) further comprises a second plurality of reflective regions (112) on an outer side of the second sheet (24);
Each one of the second plurality of reflective regions (112) corresponds to a corresponding one of the gaps (84) and is aligned with a corresponding one of the gaps (84). Reflective display according to. The reflective display according to claim 5, wherein each one of the second plurality of reflective regions (112) has a size and shape substantially similar to a corresponding size and shape of the gap (84). . Each one of the non-reflective regions (82) of the half-bead (60) has a circular shape having a first diameter, and the first plurality of reflective regions (108) of the pattern (100 or 102). Or each of 110) has a circular shape having a second diameter substantially equal to the first diameter. The reflective display according to claim 7, wherein each one of the reflective regions (80) of the half-bead (60) has an annular shape. A reflective display according to claim 1, wherein the means for selectively reflecting light rays further comprises a plurality of reflective particles (118) suspended in the medium (20). The reflective display of claim 9, wherein the reflective particles (118) have an average diameter substantially greater than an average diameter of the absorbent particles (26). A reflective display according to claim 10, wherein the reflective particles (118) have an average diameter of about 10 times the average diameter of the absorbent particles (26). A reflective display according to claim 10, wherein the reflective particles (118) are electrophoretically neutral. A reflective display according to claim 10, wherein the reflective particles (118) have an electrostatic charge opposite to the electrostatic charge of the absorbent particles (26). A reflective display according to claim 10, wherein the reflective particles (118) are white particulates. A reflective display according to claim 10, wherein the reflective particles (118) are titanium dioxide particles. The reflective display according to claim 1, wherein the means for selectively reflecting light further comprises a reflective porous membrane (140) between the half-bead (60) and the second sheet (24). . 17. A reflective display according to claim 16, wherein each membrane (140) further comprises pores having an average diameter substantially greater than the average diameter of the absorbent particles (26). 18. A reflective display according to claim 17, wherein the holes have an average diameter of about 10 times the average diameter of the absorbent particles (26). The membrane (140) has a surface area and the pores are sufficient to allow a substantially unimpeded passage of the absorbent particles (26) through the membrane (140) of the surface area. The reflective display according to claim 17, comprising a large percentage. The reflective display of claim 16, wherein the film (140) further comprises a diffusely reflective outer surface (142). The reflective display according to claim 16, wherein the membrane (140) further comprises a specularly reflective outer surface (142). Each one of the half beads (60) is adjacent to the one or more other half beads (60), and the means for selectively reflecting light rays is adjacent to each one of the half beads (60). The reflective display of claim 1, further comprising between one or more reflective structures (162). A reflective display according to claim 22, wherein each one of the reflective structures (162) protrudes inwardly from the inner surface of the transparent sheet (16). 24. A reflective display according to claim 23, wherein each one of the reflective structures (162) has a substantially hemispherical shape. 24. A reflective display according to claim 23, wherein each one of the reflective structures (162) has a curvature that is sufficiently high to cause total reflection of a substantial portion of light rays incident on the reflective structure (162). . (A) A plurality of transparent half beads (60) projecting inward from the inner surface of the transparent sheet (16) having the outer display surface (17), each surrounding the non-reflective region (82). A plurality of transparent half beads (60) having a reflective region (80), and (b) spaced inward from the transparent sheet (16), and defining a reservoir between the transparent sheet (16). Reflection of a reflective display having a second sheet (24), (c) an electrophoretic medium (20) in the reservoir, and (d) a plurality of light absorbing particles (26) suspended in the medium. A method to increase the rate,
The method comprising the step of selectively reflecting light rays through the non-reflective region (82) of the half-bead (60). The step of selectively reflecting light through the non-reflective region of the half-bead (60);
(I) a non-reflective region (104 or 106);
(Ii) forming an electrode (48) on the outer side of the second sheet (24) with a pattern (100 or 102) comprising a first plurality of reflective regions (108 or 110);
Aligning each one of the first plurality of reflective regions (108 or 110) with a corresponding one of the non-reflective regions (82) of the half-bead (60);
A voltage is applied across the medium (20) such that the absorbent particles (26) substantially cover the inner surface of the half-bead (60), and the absorbent particles (26) The absorptivity between a second position of the electrode (48) substantially covering the non-reflective region (104 or 106) without covering the first plurality of reflective regions (108 or 110). 27. The method of claim 26, comprising selectively moving the particles (26) electrophoretically. The method further includes the step of separating the transparent sheet (12) from the second sheet (24) by a distance, the distance being the first plurality of reflective regions (108 or 110) of the electrode (48). 28) is selected such that the incident light beam reflected by one of the two is reflected in a direction substantially opposite to the direction of incidence of the incident light beam. Each one of the first plurality of reflective regions (108 or 110) having a size and shape substantially similar to the size and shape of the non-reflective region (82) of the half-bead (60). 28. The method of claim 27, further comprising the step of: Forming the non-reflective region (104 or 106) with an overall size and shape substantially similar to the overall size and shape of the reflective region (80) of the half-bead (60). 28. The method of claim 27, further comprising: Each one of said half beads (60) is adjacent to said one or more other half beads (60);
There is a non-reflective gap (84) between each adjacent one or more of the half beads (60);
The pattern further includes a second plurality of reflective regions (112), each one of the second plurality of reflective regions (112) being substantially the same as one size and shape of the gap (84). 32. The method of claim 30, having a similar size and shape. Each one of the non-reflective regions (82) of the half-bead (60) is a circular shape having a first diameter, and the method has a second diameter substantially equal to the first diameter. 31. The method of claim 30, further comprising forming each one of the first plurality of reflective regions (108 or 110) in a circular shape. The step of selectively reflecting light rays through the non-reflective region (82) of the half-bead (60);
Suspending a plurality of reflective particles (118) in the medium (20);
A voltage is applied across the medium (20) so that the absorbent particles (26) substantially cover the inner surface of the half-bead (60), and the reflective particles (118) are The absorbent particles (26) can be selected electrophoretically via the reflective particles (118) between a half bead (60) and a second position between the absorbent particles (26). 27. The method of claim 26, further comprising the step of moving. 34. The method of claim 33, wherein the reflective particles (118) have an average diameter that is substantially greater than the average diameter of the absorbent particles (26). The method of claim 34, wherein the reflective particles (118) have an average diameter of about 10 times the average diameter of the absorbent particles (26). 34. The method of claim 33, further comprising electrophoretically neutrally charging the reflective particles (118). 34. The method of claim 33, further comprising charging the reflective particles (118) with an electrostatic charge opposite to the electrostatic charge of the absorbent particles (26). The step of selectively reflecting light rays through the non-reflective region (82) of the half-bead (60);
Installing a reflective porous membrane (140) in the medium (20) between the half bead (60) and the second sheet (24);
A voltage is applied across the medium (20) such that the absorbent particles (26) substantially cover the inner surface of the half bead (60), and the membrane (140) is the half (60). The absorptive particles (26) are selectively moved electrophoretically through the membrane (140) between a bead (60) and a second position between the absorptive particles (26). 27. The method of claim 26, further comprising: 39. The method of claim 38, wherein the membrane (140) further comprises pores having an average diameter substantially greater than the average diameter of the absorbent particles (26). 40. The method of claim 39, wherein the pores have an average diameter of about 10 times the average diameter of the absorbent particles (26). The membrane (140) has a surface area and the pores are sufficient to allow a substantially unimpeded passage of the absorbent particles (26) through the membrane (140) of the surface area. 40. The method of claim 38, wherein the method comprises a large percentage. Each one of said half beads (60) is adjacent to said one or more other half beads (60);
The means for selectively reflecting light rays through the non-reflective region (82) of the half-bead;
Installing a reflective structure (162) between each adjacent one or more of the half beads (60);
Applying a voltage across the medium (20) so that the absorbent particles (26) substantially cover the inner surface of the half-bead (60) and the reflective structure (162); The absorbent particles (26) are selectably electrophoretically moved to and from a second position where the absorbent particles (26) do not cover the half beads (60) or the reflective structure (162). The method of claim 26, further comprising: 43. The method of claim 42, further comprising forming the reflective structure (162) to project inwardly from the inward surface of the transparent sheet (12). 44. The method of claim 43, further comprising forming the reflective structure (162) in a generally hemispherical shape. 44. The method of claim 43, further comprising forming the reflective structure (162) having a sufficiently high curvature to cause a total reflection of a substantial portion of incident light on the reflective structure (162). Method. The semi-bead (60) and the reflective structure (162) are formed by the step of softening the transparent sheet (12) and the step of partially embedding the densely arranged spherical beads in the transparent sheet (12). 44. The method of claim 43, further comprising the step of: Installing a mesh with a circular aperture;
Softening the transparent sheet (12);
Applying pressure to the transparent sheet (12);
44. The method of claim 43, further comprising forming the half-bead (60) and the reflective structure (162) by press-fitting the mesh into the transparent sheet (12).

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