WO2024145324A1 - Dispositif de transmission de lumière variable et son procédé de fabrication - Google Patents

Dispositif de transmission de lumière variable et son procédé de fabrication Download PDF

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Publication number
WO2024145324A1
WO2024145324A1 PCT/US2023/085977 US2023085977W WO2024145324A1 WO 2024145324 A1 WO2024145324 A1 WO 2024145324A1 US 2023085977 W US2023085977 W US 2023085977W WO 2024145324 A1 WO2024145324 A1 WO 2024145324A1
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WIPO (PCT)
Prior art keywords
microcell
protrusion
layer
base
pigment particles
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PCT/US2023/085977
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English (en)
Inventor
Yu Xia
Dirk Hertel
Dan Luo
Stephen J. Telfer
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E Ink Corporation
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Application filed by E Ink Corporation filed Critical E Ink Corporation
Priority claimed from US18/396,994 external-priority patent/US20240219798A1/en
Publication of WO2024145324A1 publication Critical patent/WO2024145324A1/fr

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Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/165—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on translational movement of particles in a fluid under the influence of an applied field
    • G02F1/166—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on translational movement of particles in a fluid under the influence of an applied field characterised by the electro-optical or magneto-optical effect
    • G02F1/167—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on translational movement of particles in a fluid under the influence of an applied field characterised by the electro-optical or magneto-optical effect by electrophoresis
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/165—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on translational movement of particles in a fluid under the influence of an applied field
    • G02F1/1675—Constructional details
    • G02F1/1679—Gaskets; Spacers; Sealing of cells; Filling or closing of cells
    • G02F1/1681—Gaskets; Spacers; Sealing of cells; Filling or closing of cells having two or more microcells partitioned by walls, e.g. of microcup type
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/165—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on translational movement of particles in a fluid under the influence of an applied field
    • G02F1/1685—Operation of cells; Circuit arrangements affecting the entire cell

Definitions

  • this invention relates to variable light transmission devices that use particle-based electrophoretic media to control light modulation.
  • electrophoretic media that may be incorporated into various embodiments of the present invention include, for example, the electrophoretic media described in U.S. Patent Nos. 7,116,466, 7,327,511, 8,576,476, 10,319,314, 10,809,590, 10,067,398, 10,067,398, and 11,143,930, and U.S. Patent Application Publication Nos. 2014/0055841, 2017/0351155, 2017/0235206, 2011/0199671, 2020/0355979, 2020/0272017, 2021/0096439, and U.S. Patent Application Ser. No. 17/935,386, filed on September 27, 2022, the contents of which are incorporated by reference herein in their entireties.
  • Particle-based electrophoretic displays in which a plurality of electrically charged pigment particles move through a suspending fluid under the influence of an electric field, have been the subject of intense research and development for a number of years. Such displays can have attributes of good brightness and contrast, wide viewing angles, state bistability, and low power consumption when compared with liquid crystal displays.
  • bistable and “bistability” are used herein in their conventional meaning in the art to refer to displays comprising display elements having first and second display states differing in at least one optical property, and such that after any given element has been driven by means of an addressing pulse of finite duration, to assume either its first or second display state, after the addressing pulse has terminated, that state will persist for at least several times, for example at least four times, the minimum duration of the addressing pulse required to change the state of the display element. It is shown in published U.S. Patent Application Ser. No.
  • electrophoretic media require the presence of a suspending fluid.
  • this suspending fluid is a liquid, but electrophoretic media can be produced using gaseous suspending fluids.
  • gas-based electrophoretic media appear to be susceptible to the same types of problems due to particle settling as liquid-based electrophoretic media, when the media are used in an orientation which permits such settling, for example in a sign where the medium is disposed in a vertical plane.
  • particle settling appears to be a more serious problem in gas-based electrophoretic media than in liquid-based ones, since the lower viscosity of gaseous suspending fluids as compared with liquid ones allows more rapid settling of the electrically charged pigment particles.
  • Encapsulated electrophoretic media comprise numerous small capsules, each of which itself comprises an internal phase containing electrophoretically- mobile particles in a liquid medium, and a capsule wall surrounding the internal phase.
  • the capsules are themselves held within a polymeric binder to form a coherent layer positioned between two electrodes.
  • a related type of electrophoretic display is a so-called "microcell electrophoretic display”.
  • the electrically charged pigment particles and the suspending liquid are not encapsulated within microcapsules but instead are retained within a plurality of cavities formed within a carrier medium, typically a polymeric film.
  • a carrier medium typically a polymeric film.
  • An encapsulated or microcell electrophoretic display typically does not suffer from the clustering and settling failure mode of traditional electrophoretic devices and provides further advantages, such as the ability to print or coat the display on a wide variety of flexible and rigid substrates.
  • Use of the word "printing” is intended to include all forms of printing and coating, including, but without limitation: pre-metered coatings such as patch die coating, slot or extrusion coating, slide or cascade coating, curtain coating; roll coating such as knife over roll coating, forward and reverse roll coating; gravure coating; dip coating; spray coating; meniscus coating; spin coating; brush coating; air knife coating; silk screen printing processes; electrostatic printing processes; thermal printing processes; ink jet printing processes; electrophoretic deposition; and other similar techniques.
  • the resulting display can be flexible.
  • the display medium can be printed (using a variety of methods), the display itself can be made inexpensively.
  • electrophoretic media One potentially important market for electrophoretic media is windows with variable light transmission. As the energy performance of buildings and vehicles becomes increasingly important, electrophoretic media could be used as coatings on windows to enable the proportion of incident radiation transmitted through the windows to be electronically controlled by varying the optical state of the electrophoretic media.
  • Effective implementation of such "variable transmissivity" (“VT") technology in buildings is expected to provide (1) reduction of unwanted heating effects during hot weather, thus reducing the amount of energy needed for cooling, the size of air conditioning plants, and peak electricity demand; (2) increased use of natural daylight, thus reducing energy used for lighting and peak electricity demand; and (3) increased occupant comfort by increasing both thermal and visual comfort. Even greater benefits would be expected to accrue in an automobile, where the ratio of glazed surface to enclosed volume is significantly larger than in a typical building.
  • VT technology in automobiles is expected to provide not only the aforementioned benefits but also (1) increased motoring safety, (2) reduced glare, (3) enhanced mirror performance (by using an electro-optic coating on the mirror), and (4) increased ability to use heads-up displays.
  • Other potential applications include of VT technology include privacy glass and glare-guards in electronic devices.
  • Application of a second electric field between the first light transmissive electrode layer and the second light transmissive electrode layer via a second waveform may cause a movement of the electrically charged pigment particles towards the first light transmissive electrode layer with a velocity, the velocity having a lateral component, leading to a closed optical state.
  • the second waveform may be DC-imbalanced.
  • the second waveform may comprise at least one positive voltage and at least one negative voltage, the second waveform having a net positive or a net negative impulse.
  • the closed optical state has lower percent light transmission than the open optical state.
  • the protrusion structure may be a geometric solid of a pyramid having a base with n sides, the base with n sides being the protrusion base of the protrusion structure, wherein n is an integer from 7 to 12, (m) an pyramid having a base with n sides on a prism having a base with n sides, the base of the prism having n sides being the protrusion base of the protrusion structure, wherein n is from 7 to 12.
  • FIG. 1 is an illustration of a cylindrical particle in a liquid under the influence of an applied electric field and resulting forces on the particle.
  • FIG. 10 provides graphs of light reflection, transmission, and absorption versus layer thickness of a layer comprising a light reflecting pigment particles.
  • FIG. 14 shows a plan view of a microcell of the variable transmission device that was used in the examples.
  • FIG. 15 shows a cross sectional view of a microcell of the variable transmission device that was used in the examples.
  • FIG. 19 is a micrograph of a microcell array of the variable light transmission device from Example 5, wherein the black pigment particles of the light blocking composition are driven into the channel of the microcells (closed optical state).
  • FIG. 21 is a micrograph of an open optical state of a microcell array of the variable light transmission device of Example 6; the white electrically charged pigment particles of the light blocking composition are driven in the channel (open optical state).
  • FIG. 22 is a micrograph of an open optical state of a microcell array of the variable light transmission device of Example 7, the electrophoretic medium of the device comprising white and black pigment particles.
  • the distance of a point from a plane is the shortest perpendicular distance from the point to the plane.
  • the shortest distance from a point to a plane is the length of the perpendicular parallel to the normal vector dropped from the given point to the given plane.
  • Slope of a cone is defined as the angle that has (a) vertex (A) on the circumference of the base of the cone, (b) first arm the line that connects point A (vertex) and the center of the base of the cone, and (c) second arm the line that connects point A (vertex) and the apex of the cone.
  • DC-balanced waveform or “DC-balanced driving waveform” applied to a pixel is a driving waveform where the driving voltage applied to the pixel is substantially zero when integrated over the period of the application of the entire waveform.
  • the DC bal nce can be achieved by having each stage of the waveform balanced, that is, a first positive voltage will be chosen such that integrating over the subsequent negative voltage results in zero or substantially zero. If the waveform is not DC-balanced, it is referred to as “DC-imbalanced waveform” or “DC-imbalanced driving waveform”.
  • the driving waveform applied to a pixel may have a portion that is DC-imbalanced and at least one additional pulse of the opposite impulse to ensure that the overall waveform applied to a pixel is DC-balanced.
  • This additional pulse may be applied before the DC-imbalanced portion of the waveform (pre-pulse).
  • Typical examples of DC-imbalanced waveforms include (a) a square or sinusoidal AC waveform having a duty cycle of less (or more) than 50%, and (b) square or sinusoidal AC waveform that has a DC offset.
  • the term “lateral component of velocity” in relation to the movement of electrically charged pigment particles in a microcell of the variable light transmission device of the present invention is the velocity in the horizontal direction.
  • the velocity of the electrically charged particles is a vector resulting from the vector addition of the velocity in the horizontal direction (Vh), and the velocity in the vertical direction (Vv), and that the vertical direction in the case of the movement of the electrically charged pigment particles inside an electrophoretic microcell is the direction from the first light transmissive electrode layer to the second light transmissive electrode layer or form the second light transmissive electrode layer to the first light transmissive electrode layer.
  • the phenomenon of Induce-Charge-Electro-Osmosis can be utilized to move polarizable particles, such as pigment particles, that are present in an electrophoretic medium, laterally. That is, the polarizable particles can move parallelly to the electrode layers that sandwich the electrophoretic medium.
  • a particle may experience a force, which is caused by polarization of the particle (or by polarization of an adsorbed conductive coating on the particle surface, or of the electrical double layer around the particle). This force may result in a perturbation in the flow of mobile charge, such as ions or charged micelles, in the electrophoretic medium, as shown in FIG.
  • Equation (1) E is the field strength, s is the dielectric constant of the solvent, r
  • the time scale T is given by Equation (2).
  • the geometries of the induced flows are affected by the shape of the particular microcell used. For example, in the simplest case of two parallel electrodes, it was shown that, using an appropriate electric field strength and AC frequency, the flow can adopt a roll structure with periodic spacing that corresponds to the width of the gap between the electrodes.
  • FIGS. 2A, 2B, and 2C illustrate a cross-section (not to scale) of a portion of a variable light transmission device that shows only one microcell of the plurality of microcells of the device. All three FIGS. 2A, 2B, 2C are identical in terms of the device structure that is illustrated, but different parts of the device are identified on each of the figures.
  • Each microcell of the plurality of microcells 204 comprises an electrophoretic medium 209 including electrically charged pigment particles and a charge control agent in a non-polar liquid.
  • the components of the electrophoretic medium are not shown in FIGS. 2A, 2B, and 2C.
  • Each microcell of the plurality of microcells 204 has a microcell opening 205, the sealing layer 206 spanning the microcell openings 205 of the plurality of microcells 204.
  • Each microcell of the plurality of microcells 204 comprises microcell bottom layer 210, protrusion structure 217, microcell walls 212, and channel 215.
  • Microcell bottom layer 210 has microcell bottom inside surface 211, the microcell bottom inside surface 211 that comprises exposed microcell bottom inside surface 211a and unexposed microcell bottom inside surface 211b. Unexposed microcell bottom surface 211b is in contact with the protrusion base 218.
  • Each microcell of the plurality of microcells (204) comprises a first light blocking layer (232), the first light blocking layer (232) being in contact with the exposed microcell bottom inside surface (211a) and with the electrophoretic medium (209),
  • the protrusion structure 217 is a cone on a cylinder.
  • the protrusion structure 217 has a protrusion base 218, a protrusion surface 221, a protrusion apex 219, and a protrusion height 220.
  • the protrusion apex 219 is a point or a set of points of the protrusion structure 217 having shorter distance from microcell opening 205 than all other points of the protrusion structure 217.
  • the protrusion apex 219 is the apex of the cone of the protrusion structure.
  • the protrusion height 220 is the distance between the protrusion base 218 and the protrusion apex 219. If the protrusion structure 217 has a protrusion apex 219 that comprises more than one points, such as a planar surface, the protrusion height 220 is the distance between the planar surface and the protrusion base 218 of the protrusion structure 217.
  • a microcell layer comprising a plurality of microcells 204 having a protrusion structure 217 may be manufactured by embossing thermoplastic or thermoset precursor layer using a pre-patterned male mold, followed by releasing the mold. The precursor layer may be hardened by radiation, cooling, solvent evaporation, or oilier means during or after the embossing step.
  • Each microcell of the plurality of microcells comprises an electrophoretic medium including electrically charged pigment particles 222 and a charge control agent in a non-polar liquid.
  • Each microcell of the plurality of microcells 204 has a microcell opening, the sealing layer 206 spanning the microcell openings of the plurality of microcells.
  • Each microcell of the plurality of microcells comprises microcell bottom layer 210, protrusion structure 217, microcell walls 212, and channel 215.
  • the variable light transmission device illustrated in FIG. 2D is in the closed optical state.
  • the second waveform comprises an AC waveform, having a duty cycle different from 50%.
  • An example of the second waveform of the first embodiment is illustrated in FIG. 4.
  • FIG. 7b The closed optical state of this example of variable light transmission device is illustrated in FIG. 7b.
  • first light transmissive electrode layer 202 and second light transmissive electrode layer 207 both types of electrically charged pigment particles 222a and 222b will move towards the first light transmissive electrode layer to achieve a closed optical state.
  • second type of electrically charged pigment particles 222b (light absorbing) will be positioned closer to sealing layer 206 than the first type of electrically charged pigment particles 222a (light reflecting), because first type of electrically charged pigment particles 222a have lower charge (and larger size).
  • the amount of second type of electrically charged pigment particles which can have a black color, will be chosen to be sufficient to hide the white pigment in the channel (open optical state), when viewed from below, but not so high as to lead to too much light absorption in the closed state. “Viewed from below” means that the observer is located on the side of the variable light transmission device which is closer to the second light transmissive electrode layer 207, as opposed to the side that is closer to first light transmissive electrode layer 202.
  • FIG. 10 provides graphs of light reflection, transmission, and absorption versus layer thickness of a layer comprising a white pigment (light reflecting). That is, for each layer thickness, the graphs provide the amount of light that is reflected, transmitted, and absorbed as a ratio of the incident light.
  • the white pigment can be switched into the channel by a negative DC offset to the AC waveform.
  • Both white and black particles are present in the channel (as shown in FIG. 7a.
  • the electric field of the second step may drive a portion of the black pigment particles out of the channel, it will not move the black pigment laterally.
  • the black particles that may move out of the channel will undergo a vertical motion to provide the open optical state similar to that illustrated in FIG. 8a.
  • FIG. 12 illustrate a side view of an inventive variable light transmission device comprising a first light transmissive electrode layer 202, a second light transmissive electrode layer, and an electrophoretic medium including electrically charged pigment particles 222, the electrically charged pigment particles being light reflective.
  • the variable light transmission device also comprises a first light blocking layer 232 on the exposed microcell bottom inside surface of the microcell.
  • the first light blocking layer 232 may comprise black pigment particles that are light absorbing.
  • the electrically charged pigment particles of the electrophoretic medium are included in the channel of the microcell (FIG. 12a).
  • a method of manufacture of the variable light transmission device shown in FIG. 12 comprises the steps of (a) providing an assembly comprising a third electrode layer, a second light transmissive electrode layer, a layer comprising a plurality of microcells, the layer comprising a plurality of microcells being disposed between the third electrode layer and the second light transmissive electrode layer, each microcell of the plurality of microcells including a light blocking composition comprising (i) light absorbing electrically charged pigment particles, (ii) a polymer, oligomer, or monomer and, (iii) optionally, a solvent, each microcell of the plurality of microcells having a microcell opening, the third electrode layer spanning the microcell openings of the plurality of microcells, each microcell of the plurality of microcells comprising a microcell bottom layer, a protrusion structure, microcell walls, and a channel, the microcell bottom layer having a microcell bottom inside surface , the microcell bottom inside surface comprising an exposed microcell bottom
  • the light blocking composition comprises a solvent
  • the solvent is evaporated during the curing of the first dispersion composition.
  • the curing of the light blocking composition may be achieved by UV irradiation, thermally, or by solvent evaporation.
  • the light blocking composition comprises a solvent
  • the solvent is evaporated during the curing of the second dispersion composition.
  • the curing of the light blocking composition may be achieved by UV irradiation, thermally, or by solvent evaporation.
  • Examples 5 and 6 describe experiments towards the formation of a blocking layers using blocking compositions.
  • the blocking composition comprises black electrically charged pigment particles
  • the blocking composition comprises white electrically charged pigment particles.
  • a variable light transmission device with improved performance of the closed optical state can also be achieved by using the device illustrated in FIG. 13.
  • the variable light transmission device illustrated in FIG. 13 comprises a first light transmissive electrode layer (202); a second light transmissive electrode layer (207); and a microcell layer (203).
  • the first light blocking layer 232 mitigates the haze when the device is viewed from below.
  • the second light blocking layer 233 contributes to an improved closed state by increasing the opacity of the device that may be caused by a partially light transmissive wall material.
  • the second light blocking layer 233 may be black, white, or any other color.
  • the second light blocking layer 233 may electrically conductive, which may facilitate the switching of the device.
  • the second light blocking layer (233) can be formed by coating a pigment dispersion on the microcell wall upper surface and curing the coating via UV irradiation, thermally, or by solvent evaporation.
  • the pigment dispersion may comprise pigment particles, a polymer, oligomer or monomer, and, optionally, a solvent.
  • the variable light transmission device of FIG. 13 may further comprise an auxiliary layer 234, which is disposed between the sealing layer and the second light blocking layer 233.
  • the auxiliary layer 234 may comprise an adhesive material.
  • the auxiliary layer 234 may comprise a light reflecting pigment to further improve the opacity of the closed optical state.
  • the auxiliary layer 234 may also comprise an encapsulated electrophoretic layer comprising an electrophoretic medium including electrically charged pigment particles. Application of an electric field across the encapsulated electrophoretic layer of the auxiliary layer 234 may switch the color (or the image) of the auxiliary layer 234, which can also affect the appearance of the variable light transmission device of FIG. 13.
  • Charge control agents are typically oligomeric or polymer materials that are soluble in the non-polar liquid of the electrophoretic medium.
  • Charge control agents are surfactanttype molecules having one or more polar functional group (head) and a non-polar part (tail).
  • the electrophoretic medium may comprise a charge control agent in a concentration of from 0.1 weight percent to 10 weight percent by weight of the electrophoretic medium.
  • the electrophoretic medium may comprise a charge control agent in a concentration of from 0.5 weight percent to 9 weight percent, from 0.7 weight percent to 8 weight percent, from 1 weight percent to 7 weight percent, or from 1 weight percent to 6 weight percent by weight of the electrophoretic medium.
  • the non-polar liquid of the electrophoretic medium may comprise an aliphatic hydrocarbon, a cycloaliphatic hydrocarbon, an aromatic hydrocarbon, a halogenated aliphatic hydrocarbon, a polydimethylsiloxane, or mixture thereof.
  • the electrophoretic medium may also comprise a flocculating agent, also called depletor.
  • the depletor induces an osmotic pressure difference between pigment-pigment particle and pigment particle depletor molecules. As a result, bistability of the optical states (open and closed) of the device is enhanced.
  • Depletors are typically polymeric material such as polyisobutylene and polydimethylsiloxane.
  • Example 1 A device was prepared by laminating together a sheet of polyethylene terephthalate (PET) coated with an Indium Tin Oxide (ITO) transparent conductor to an embossed microcell array on a second sheet of PET/ITO containing and electrophoretic medium.
  • PET polyethylene terephthalate
  • ITO Indium Tin Oxide
  • FIG. 14 is a plan view of a microcell of the device.
  • FIG. 15 shows the corresponding cross-sectional view of one microcell of the device. Table 1 shows the dimensions of the microcell.
  • Example 2 In Example 2, the effect of the concentration of the charge control agent (CCA) on the motion of white pigments in an embossed microcell device was studied.
  • CCA charge control agent
  • the device having electrophoretic medium comprising 1 wt% CCA could be switched from the open optical state to the closed optical state using (a) a simple square wave AC of +/-100V at 0.5 Hz, or (b) a +/-50V square wave AC with 50 Hz frequency with superimposed DC voltage of -50V.
  • the open optical state was reached by a +/-50V square wave AC with 5% duty cycle, whereas the closed optical state required +/-50V square wave AC with 95% duty cycle.
  • the switching time in each case was approximately 1 second.
  • Example 3 The effect of the charge of the white pigment on switching performance of a variable light transmission device was studied.
  • a variable light transmission device was prepared having an electrophoretic medium comprising 10 wt% positively charged white pigment particles in Isopar E.
  • the white pigment was functionalized with 1.6% wt of silane Z6030 and grafted with polylauryl methacrylate (PLMA).
  • the zeta potential of the treated pigment was +35 mV titrated with the CCA (cationic polymer disclosed in Example 1-CCA111 of US2020/0355978CCA111).
  • the electrophoretic medium also comprised 1 wt% of CCA (cationic polymer disclosed in Example 1-CCA111 of US2020/035597811).
  • the waveform that was used to switch the device from the open optical state to the closed optical state was DC superimposing AC, i.e., square wave waveform, +/-50V AC with 500 Hz frequency.
  • the waveform to switch the device from the closed optical state to the open optical state was +/-50V AC with offset of +50V DC.
  • the behavior of the device of Example 3 was thus very similar to that of the device with electrophoretic medium comprising 1 wt% of CCA of Example 2, except that the DC offset required to achieve the open optical state was of opposite polarity.
  • Example 4 In this example, the solvent of the electrophoretic medium matched the polymer that formed the embossed microcells.
  • “Haze” refers to the percentage of diffuse transmitted light compared to the total transmitted light. Diffuse transmitted light is light that is scattered as it is transmitted. In order to make a variable light transmission device with low haze, it was necessary to match the refractive index of the solvent of the electrophoretic medium liquid and the polymeric material that was used to make the embossed microcells, as described in U.S. Patent No. 7,327,511.
  • solvents used in electrophoretic media have low dielectric constant (preferably less than 10 and desirably less than 3), low viscosity, low vapor pressure, and relatively high refractive index.
  • solvents include, but are not limited to, aliphatic hydrocarbons such as heptane, octane, and petroleum distillates such as Isopar® (ExxonMobil) or Isane® (Total), terpenes, such as limonene, e.g., 1 -limonene, and aromatic hydrocarbons, such as toluene.
  • the refractive index of the encapsulated electrophoretic medium closely matches that of the encapsulating material. In most instances, it is beneficial to use an electrophoretic medium having a refractive index between 1.51 and 1.57 at 550 nm, preferably about 1.54 at 550 nm.
  • a variable transmission device was prepared by laminating together a sheet of PET coated with an ITO transparent conductor to an embossed microcell array on a second sheet of PET/ITO, the embossed microcell array containing an electrophoretic medium.
  • the structure of the embossed microcell array is illustrated in FIGS. 2A to 2D, although the microcell of this example does not comprise a sealing layer.
  • the light blocking composition that was used for the light blocking layer comprised a black pigment, a solvent, a charge control agent, and depletor.
  • the light blocking composition was prepared by mixing 10 wt % black pigment, 1 wt% CCA (Cationic Charge Control Agent from Example 1 - CCA111 of US2020/0355978111), and 0.5 wt% polyisobutylene in a solvent mixture of a partially hydrogenated terphenyl, available commercially as Cargille® 5040 from Cargille-Sacher Laboratories, 55 Commerce Rd, Cedar Grove N.J. 07009, Limonene, Isopar M and Isopar E.
  • the black pigment particle has a core comprising black iron oxide (Pigment Black 11) and a polymeric shell.
  • a variable transmission device was prepared by laminating together of a sheet of PET coated and an ITO transparent conductor to an embossed microcell array, containing and electrophoretic medium, on a second sheet of PET/ITO.
  • the structure of the microcell corresponded to the illustration in FIG. 2A to 2D, except that the device does not comprise a sealing layer.
  • the structure of the embossed microcell array is illustrated in FIGS. 14 and 15.
  • an electrophoretic composition comprising a black pigment was prepared and switched into the open optical state (black pigment included in the channel). The first light transmissive electrode layer was then removed and the solvent was evaporated.
  • an electrophoretic medium containing a white pigment, solvent, and charge control agent (CCA) was prepared.
  • the electrophoretic medium was prepared by mixing 10 wt% white pigment and 1 wt% CCA111 in a solvent mixture of a partially hydrogenated terphenyl, available commercially as Cargille® 5040 from Cargille- Sacher Laboratories, 55 Commerce Rd, Cedar Grove N.J. 07009, Limonene, Isopar M and Isopar E.
  • the white pigment particles were prepared with a titanium dioxide pigment core, which comprises a polymer coating, as described in Example 1 of United States Patent No. 8,582,196.
  • a waveform of 10 Hz, 50V square waveform 50% duty cycle and +2V offset was applied to the first light transmissive electrode layer 202 while the second light transmissive electrode layer was kept at 0V.
  • the electric field between the electrodes induced electrophoresis with superimposed induced-charge electro-osmosis and drove the positive black pigment into the channel.
  • a waveform of 500 Hz / 50V square waveform 50% duty cycle and alternating +2V and -2V offset was applied to the first electrode, while the second electrode was kept at 0V.
  • the white pigment was driven into the channel during the phases of the waveform with a negative DC offset.
  • the result was that both the white and the black pigments were switched into the channels of the microcells.

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  • Physics & Mathematics (AREA)
  • Nonlinear Science (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Molecular Biology (AREA)
  • Electrochromic Elements, Electrophoresis, Or Variable Reflection Or Absorption Elements (AREA)

Abstract

Un dispositif de transmission de lumière variable est divulgué et son procédé de fabrication. Le dispositif de transmission de lumière variable comprend deux électrodes transmettant la lumière et une couche de microcellules ayant une pluralité de microcellules, chaque microcellule comprenant une structure en saillie et un canal, et comprenant un milieu électrophorétique. L'opacité du dispositif est commandée par un champ électrique appliqué.
PCT/US2023/085977 2022-12-30 2023-12-27 Dispositif de transmission de lumière variable et son procédé de fabrication WO2024145324A1 (fr)

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US202263436119P 2022-12-30 2022-12-30
US63/436,119 2022-12-30
US18/396,994 US20240219798A1 (en) 2022-12-30 2023-12-27 Variable light transmission device comprising electrophoretic medium having light reflective pigment particles
US18/396,994 2023-12-27

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WO2024145324A1 true WO2024145324A1 (fr) 2024-07-04

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