HK40121451A - A variable light transmission device and a method of operation of the same - Google Patents

Description

Variable light transmission device and its operation method

Related applications

This application claims priority to U.S. Provisional Patent Application No. 63/436,127, filed December 30, 2022, the entire contents of which, as well as all other patents and patent applications disclosed herein, are incorporated herein by reference.

Background Technology

This invention relates to a variable light transmission device and its operating method. Specifically, the invention relates to a micro-unit electro-optic device comprising an electrophoretic medium including charged pigment particles and a charge control agent. The content of the charge control agent in the electrophoretic medium is expressed as a weight percentage of the charge control agent relative to the weight of the electrophoretic medium. The electrophoretic medium is capable of switching between optical states using an electric field. The invention also relates to a driving method for switching between optical states. Variable light transmission devices regulate the amount of light and other electromagnetic radiation passing through them. They can be used in mirrors, windows, skylights, and similar items. For example, the invention can be applied to windows capable of regulating infrared radiation to control the temperature inside buildings and vehicles. Examples of 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, as well as U.S. Patent Application Publications Nos. 2014/0055841, 2017/0351155, 2017/0235206, 2011/0199671, 2020/0355979, 2020/0272017, 2021/0096439 and U.S. Patent Application Serial No. 17/935,386, filed September 27, 2022, the entire contents of which are incorporated herein by reference.

Particle-based electrophoretic displays, in which multiple charged pigment particles move through a suspended fluid under the influence of an electric field, have been a subject of in-depth research and development for many years. Compared with liquid crystal displays, these displays offer advantages such as superior brightness and contrast, wide viewing angles, state-stability, and low power consumption.

As used herein, the terms “bistable” and “bistable” in their conventional sense in the art refer to a display comprising display elements having a first display state and a second display state that differ in at least one optical characteristic, such that after any given element is driven to present its first or second display state by means of an addressing pulse of finite duration, the state will persist for at least several times (e.g., at least four times) the minimum duration of the addressing pulse required to change the state of the display element after the addressing pulse terminates. Published U.S. Patent Application Serial No. 2002/0180687 shows that some particle-based grayscale electrophoretic displays are stable not only in their extreme black and extreme white states but also in their intermediate grayscale states, as are some other types of electro-optical displays. Such types of displays are more appropriately called “multistable” than “bistable,” but for convenience, the term “bistable” may be used herein to encompass both bistable and multistable displays.

As mentioned above, electrophoretic media require the presence of a suspending fluid. In most prior art electrophoretic media, this suspending fluid is a liquid, but gaseous suspending fluids can be used to generate electrophoretic media. When the medium is used in a direction that allows particle sedimentation (e.g., in the case of a medium located in a vertical plane), such gas-based electrophoretic media appear to be susceptible to the same type of particle sedimentation problem as liquid-based electrophoretic media. In fact, particle sedimentation appears to be a more severe problem in gas-based electrophoretic media than in liquid-based electrophoretic media because the lower viscosity of the gaseous suspending fluid compared to liquid electrophoretic media allows charged pigment particles to settle more quickly.

Numerous patents and applications assigned to MIT, Einkel Corporation, Einkel California, LLC, and their affiliates, or filed in their names, describe various techniques for encapsulating and encapsulating micro-unit electrophoresis and other electro-optic media. Encapsulating electrophoretic media comprises numerous small capsules, each capsule itself comprising an inner phase consisting of electrophoretically moving particles in a liquid medium, and a capsule wall surrounding the inner phase. Typically, the capsules themselves are held in a polymer binder to form a continuous layer between two electrodes. In micro-unit electrophoretic displays, charged pigment particles and liquid are not encapsulated in microcapsules, but rather retained in multiple cavities formed within a carrier medium (typically a polymer film). The techniques described in these patents and applications include:

(a) Electrophoretic particles, fluids, and fluid additives; see, for example, U.S. Patent Nos. 7,002,728 and 7,679,814.

(b) Encapsulation, adhesives and encapsulation processes; see, for example, U.S. Patent Nos. 6,922,276 and 7,411,719.

(c) Microunit structures, wall materials, and methods of forming microunits; see, for example, U.S. Patent Nos. 7,072,095 and 9,279,906.

(d) Methods for filling and sealing microcells; see, for example, U.S. Patent Nos. 7,144,942 and 7,715,088.

(e) Thin films and sub-assemblies containing electro-optic materials; see, for example, U.S. Patent Nos. 6,982,178 and 7,839,564.

(f) Backplanes, adhesive layers and other auxiliary layers used in displays and methods; see, for example, U.S. Patent Nos. 7,116,318 and 7,535,624.

(g) Color formation and color adjustment; see, for example, U.S. Patent Nos. 7,075,502 and 7,839,564.

(h) A method for driving a display; see, for example, U.S. Patent Nos. 7,012,600 and 7,453,445.

(i) Applications of displays; see, for example, U.S. Patent Nos. 7,312,784 and 8,009,348.

(j) Non-electrophoretic displays, as described in U.S. Patent No. 6,241,921 and U.S. Patent Application Publication No. 2015/0277160; and applications of packaging and microcell technologies other than displays; see, for example, U.S. Patent Application Publication Nos. 2015/0005720 and 2016/0012710.

Many of the aforementioned patents and applications recognize that the walls surrounding discrete microcapsules in an encapsulated electrophoretic medium can be replaced by a continuous phase, thereby producing a so-called polymer dispersion electrophoretic display, wherein the electrophoretic medium comprises a plurality of discrete droplets of nonpolar liquid and a continuous phase of polymeric material, and the discrete droplets of the electrophoretic medium within such a polymer dispersion electrophoretic display can be considered as capsules or microcapsules, even if each individual droplet does not have an associated independent capsule membrane; see, for example, 2002/0131147 above. Therefore, for the purposes of this application, such polymer dispersion electrophoretic media are considered a subclass of encapsulated electrophoretic media.

One related type of electrophoretic display is the so-called "micro-unit electrophoretic display." In a micro-unit electrophoretic display, charged pigment particles and suspended liquid are not encapsulated in microcapsules, but rather retained in multiple cavities formed within a carrier medium (typically a polymer film). See, for example, International Application Publication No. WO 02/01281 and published U.S. Application Serial No. 2002/0075556, both assigned to Sipix Imaging, Inc.

Although electrophoretic media are typically opaque (because, for example, in many electrophoretic media, particles essentially block visible light transmission through the display) and operate in reflective mode, many electrophoretic displays can be configured to operate in so-called “shutter modes,” where one display state is substantially opaque and the other is translucent. See, for example, U.S. Patent Nos. 6,130,774 and 6,172,798, and U.S. Patent Nos. 5,872,552, 6,144,361, 6,271,823, 6,225,971, and 6,184,856. Dielectrophoretic displays, similar to electrophoretic displays but dependent on changes in electric field strength, can operate in a similar mode; see U.S. Patent No. 4,418,346. Other types of electro-optic displays may also be able to operate in shutter mode.

Encapsulated electrophoretic displays or microcell electrophoretic displays generally do not suffer from the aggregation and sedimentation failure modes of conventional electrophoretic apparatus and offer further advantages, such as the ability to print or coat displays on a variety of flexible and rigid substrates. The term "printing" is used to encompass all forms of printing and coating, including but not limited to: pre-quantity coating, such as block die coating, slot coating or extrusion coating, slide coating or cascade coating, curtain coating; roll coating, such as doctor blade roll coating, forward and reverse roll coating; gravure coating; dip coating; spray coating; meniscus coating; spin coating; brush coating; air knife coating; screen printing processes; electrostatic printing processes; thermal printing processes; inkjet printing processes; electrophoretic deposition; and other similar techniques. Therefore, the resulting displays can be flexible. Furthermore, because the display medium can be printed (using various methods), the displays themselves can be manufactured inexpensively.

One potentially significant market for electrophoretic media is windows with variable transmittance. As energy performance becomes increasingly important for buildings and vehicles, electrophoretic media can be used in windows to electronically control the proportion of incident radiation transmitted through the window by altering its optical state. Effective implementation of this “variable transmittance” (“VT”) technology in buildings is expected to provide the following benefits: (1) reduced unwanted thermal effects during hot weather, lowering the energy required for cooling, the size of air conditioning equipment, and peak power demand; (2) increased use of natural daylight, thereby reducing lighting energy consumption and peak power demand; and (3) improved occupant comfort by enhancing thermal and visual comfort. Since the ratio of glass surface area to enclosed volume is significantly larger in automobiles than in conventional buildings, automobiles are expected to benefit even more. Specifically, effective implementation of variable transmittance technology in automobiles is expected to provide not only the aforementioned benefits but also the following: (1) improved driving safety; (2) reduced glare; (3) enhanced mirror performance (through the use of electro-optic coatings on mirrors); and (4) improved ability to use head-up displays. Other potential applications of variable transmittance technology include privacy glass and anti-glare glass in electronic devices.

Examples of existing devices exist that include an electrophoretic medium sandwiched within an electrode layer, enabling switching between an optically closed (opaque) state and an optically open (transparent) state, achieved by applying an electric field to the electrophoretic medium. However, conventional electrophoresis devices employing conventional structures and waveforms require long switching times, making them less than ideal. The inventors of this invention have unexpectedly discovered that a specific device with a micro-unit layer and a specific waveform can achieve efficient switching between the open and closed optical states.

Summary of the Invention

On one hand, the present invention provides a method of operating a variable light transmission device, comprising the following steps: (a) providing a variable light transmission device; (b) applying a first electric field to switch the variable light transmission device to an open optical state; and (c) applying a second electric field to switch the variable light transmission device to a closed optical state.

The variable light transmission device includes a first light-transmitting electrode layer, a second light-transmitting electrode layer, and a micro-unit layer. The micro-unit layer includes multiple micro-units and a sealing layer. The micro-unit layer is disposed between the first and second light-transmitting electrode layers. Each micro-unit includes an electrophoretic medium comprising charged pigment particles and a charge control agent in a fluid. The content of the charge control agent in the electrophoretic medium is expressed as a weight percentage of the charge control agent relative to the weight of the electrophoretic medium. Each of the multiple micro-units has a micro-unit opening. The sealing layer spans the micro-unit openings of the multiple micro-units. Each of the multiple micro-units includes a micro-unit bottom layer, a raised structure, a micro-unit wall, and a channel. The micro-unit bottom layer has an inner surface of the micro-unit bottom, which includes an exposed inner surface and an unexposed inner surface. The raised structure has a raised base, a raised surface, a raised apex, and a raised height. A protrusion apex is a point or set of points on a protruding structure whose distance from the micro-unit opening is shorter than the distances from all other points on the protruding structure to the micro-unit opening. The protrusion height is the distance between the protrusion base and the protrusion apex. A protrusion surface is the surface of the protrusion structure excluding the protrusion apex which contacts the electrophoretic medium. A micro-unit wall has an inner wall surface and an upper wall surface. The inner wall surface is the surface of the micro-unit wall of the micro-unit that contacts the electrophoretic medium. The upper wall surface is the surface of the micro-unit wall of the micro-unit that contacts the sealing layer. The channel has a channel height that is 50% of the protrusion height. The unexposed inner surface of the micro-unit bottom contacts the protrusion base. The channel is the volume between the exposed inner surface of the micro-unit bottom, the protrusion surface, and the inner wall surface of the micro-unit. The weight percentage of the charge control agent in the electrophoretic medium of the variable light transmission device can be from 1% to 8% of the electrophoretic medium weight.

The operation method of the variable light transmission device includes the following steps: applying a first electric field between a first and a second light-transmitting electrode layer via a first waveform to cause charged pigment particles to move toward the channel, thereby switching the variable light transmission device to an open optical state. The charged pigment particles in the open optical state are located within the channel.

The operation of the variable light transmission device includes the following steps: applying a second electric field between a first and a second light-transmitting electrode layer via a second waveform, causing charged pigment particles to move toward the first light-transmitting electrode layer at a certain velocity having a transverse component, thereby resulting in a closed optical state. The second waveform may be DC unbalanced. The second waveform may include at least one positive voltage and at least one negative voltage, and the second waveform has a net positive impulse or a net negative impulse. The closed optical state has a lower percentage of light transmission than the open optical state.

In one embodiment, the second waveform of the operation method of the variable light transmission device may include an alternating current (AC) waveform having a frequency and a duty cycle from 5% to 45%. The duty cycle of the AC waveform may be higher than 50%, higher than 55%, higher than 60%, or higher than 65%. The duty cycle of the AC waveform may be 55% to 95%, 58% to 90%, 60% to 88%, 65% to 85%, or 70% to 80%. The duty cycle of the AC waveform may be lower than 50%, lower than 45%, lower than 40%, or lower than 35%. The duty cycle of the AC waveform may be 5% to 45%, 8% to 40%, 10% to 38%, 10% to 40%, 15% to 35%, or 20% to 30%. The AC waveform may be a square wave, a sine wave, a triangle wave, or a sawtooth wave. The ratio of the frequency of the alternating current waveform, expressed in Hertz, to the content of the charge control agent in the electrophoretic medium, expressed as a weight percentage of the charge control agent to the weight of the electrophoretic medium, can range from 400 to 2000 Hz.

The AC waveform can be a square wave with two or more cycles. In this case, the positive and negative voltages of the AC waveform have the same amplitude; the amplitude of the AC waveform can be from 10V to 200V; the frequency of the AC waveform can be from 0.1Hz to 6000Hz or from 100Hz to 3000Hz; the amplitude of the AC waveform can be from 10V to 200V or from 20V to 180V, and the frequency of the AC waveform can be from 0.1Hz to 6000Hz or from 100Hz to 3000Hz. The ratio of the frequency of the AC waveform, expressed in Hertz, to the content of the charge control agent in the electrophoretic medium, expressed as a weight percentage of the charge control agent to the electrophoretic medium, can be from 400 to 2000Hz.

In another embodiment, the second waveform of the operation method of the variable light transmission device may include a waveform formed by superimposing a DC voltage component and an AC waveform having a frequency and an amplitude. The frequency of the AC waveform may be 0.1 Hz to 6000 Hz, 100 Hz to 3000 Hz, or 400 Hz to 2000 Hz. The amplitude of the AC waveform may be 10 V to 200 V or 20 V to 180 V. The DC voltage component has an amplitude of 0.1 V to 500 V. The ratio of the frequency of the AC waveform, expressed in Hertz, to the content of the charge control agent in the electrophoretic medium, expressed as a weight percentage of the charge control agent to the electrophoretic medium, may be from 400 to 2000 Hz. The second waveform may include an AC waveform with a DC offset. The AC waveform may be selected from the group consisting of square waves, sine waves, triangle waves, and sawtooth waves.

The convex structure can be a geometry selected from the group consisting of: (a) a cone; (b) a cone on a cylinder, the cylinder having a base, the base of the cylinder being the convex base of the convex structure; (c) a tetrahedron; (d) a tetrahedron on a triangular prism, the triangular prism having a triangular base, the triangular base being the convex base of the convex structure; (e) a triangular prism, the triangular prism having a square base, the square base being the convex base of the convex structure; (f) a square pyramid having a square base, the square base being the convex base of the convex structure; (h) a square pyramid on a cube, the cube having a base, the cube base being the convex base of the convex structure. The raised base of the structure; (i) a square pyramid on a regular parallelepiped, the regular parallelepiped having a regular parallelogram base, the regular parallelogram base being the raised base of the raised structure; (j) a pentagonal pyramid, the pentagonal pyramid having a pentagonal base; the pentagonal base being the raised base of the raised structure; (k) a pentagonal pyramid on a pentagonal prism, the pentagonal prism having a pentagonal base, the pentagonal base being the raised base of the raised structure; (l) a hexagonal pyramid, the hexagonal pyramid having a hexagonal base, the pentagonal base being the raised base of the raised structure; (m) a hexagonal pyramid on a hexagonal prism, the hexagonal prism having a hexagonal base, the hexagonal base being the raised base of the raised structure. The raised structure can be a cone, the slope of the cone can be 5 degrees to 10 degrees. The raised structure can be a cone on a cylinder. A cylinder may have a base, the base of which is a raised base of a convex structure; the slope of a cone may be 10 degrees or less. A convex structure may be a pyramidal geometry with a base of n sides, where n is an integer from 7 to 12; (m) a pyramid with a base of n sides, the pyramid situated on a prism with a base of n sides, where n is a raised base of a convex structure.

The electrophoretic medium may include a first type of charged pigment particles and a second type of charged pigment particles. The first type of charged pigment particles can reflect light, and the second type of charged pigment particles can absorb light. The first type of charged pigment particles may be white, and the second type of charged pigment particles may be black. The first type of charged pigment particles may have the same polarity as the second type of charged pigment particles, or they may have opposite polarities.

The upper surface of the microcell wall may have a light-blocking layer located between the upper surface of the microcell and the sealing layer. This light-blocking layer may include a light-absorbing pigment. The light-blocking layer may include a black pigment.

On the other hand, the present invention provides a variable light transmission device. The variable light transmission device includes a first light-transmitting electrode layer, a second light-transmitting electrode layer, and a micro-unit layer. The micro-unit layer includes a plurality of micro-units and a sealing layer. The micro-unit layer is disposed between the first and second light-transmitting electrode layers. Each micro-unit includes an electrophoretic medium comprising charged pigment particles and a charge control agent in a fluid. Each of the plurality of micro-units has a micro-unit opening. The sealing layer spans the micro-unit openings of the plurality of micro-units. Each of the plurality of micro-units includes a micro-unit bottom layer, a raised structure, a micro-unit wall, and a channel. The micro-unit bottom layer has a micro-unit bottom inner surface, which includes an exposed micro-unit bottom inner surface and an unexposed micro-unit bottom inner surface. The raised structure has a raised base, a raised surface, a raised apex, and a raised height. The raised apex is a point or set of points on the raised structure whose distance from the micro-unit opening is shorter than the distances from all other points on the raised structure to the micro-unit opening. The protrusion height is the distance between the protrusion base and the protrusion apex. The protrusion surface is the surface of the protrusion structure excluding the apex which contacts the electrophoretic medium. The micro-unit wall has an inner wall surface and an upper wall surface. The inner wall surface is the surface of the micro-unit wall of the micro-unit that contacts the electrophoretic medium. The upper wall surface is the surface of the micro-unit wall of the micro-unit that contacts the sealing layer. The channel has a channel height that is 50% of the protrusion height. The unexposed inner surface of the micro-unit bottom contacts the protrusion base. The channel is the volume between the exposed inner surface of the micro-unit bottom, the protrusion surface, and the inner wall surface of the micro-unit.

A first electric field is applied between the first and second light-transmitting electrode layers via a first waveform, causing charged pigment particles to move into the channel, thereby switching the variable light transmission device to an open optical state. The charged pigment particles in the open optical state are located within the channel.

A second electric field is applied between the first and second light-transmitting electrode layers via a second waveform, causing charged pigment particles to move towards the first light-transmitting electrode layer at a certain velocity with a transverse component, thereby resulting in a closed optical state. The second waveform may be DC unbalanced. The second waveform may include at least one positive voltage and at least one negative voltage, and the second waveform has a net positive impulse or a net negative impulse. The closed optical state has a lower percentage of light transmission than the open optical state.

The second waveform may include an AC waveform having a frequency and a duty cycle from 5% to 45%. The AC waveform may be a square wave, a sine wave, a triangle wave, or a sawtooth wave.

The AC waveform can be a square wave with two or more cycles, wherein the positive and negative voltages of the AC waveform have the same amplitude. The amplitude of the square wave can be from 10V to 200V, and the frequency can be from 0.1Hz to 6000Hz or from 100Hz to 3000Hz. Alternatively, the amplitude of the square wave can be from 10V to 200V or from 20V to 180V, and the frequency can be from 0.1Hz to 6000Hz or from 100Hz to 3000Hz. The ratio of the frequency of the AC waveform, expressed in Hertz, to the content of the charge control agent in the electrophoretic medium, expressed as a weight percentage of the charge control agent to the electrophoretic medium, can be from 400 to 2000Hz.

Alternatively, the second waveform may include a waveform formed by superimposing a DC voltage component and an AC waveform, wherein the AC waveform has an amplitude and a frequency, and the DC voltage component has an amplitude. The frequency of the AC waveform may be from 0.1 Hz to 6000 Hz, 100 Hz to 3000 Hz, or 400 Hz to 2000 Hz, and the amplitude of the AC waveform may be from 10 V to 200 V or 20 V to 180 V. The amplitude of the DC voltage component may be from 0.1 V to 500 V. The ratio of the frequency of the AC waveform, expressed in Hertz, to the content of the charge control agent in the electrophoretic medium, expressed as a weight percentage of the charge control agent by weight, may be from 400 to 2000 Hz. The second waveform may include an AC waveform with a DC offset. The AC waveform may be selected from the group consisting of square waves, sine waves, triangle waves, and sawtooth waves.

Attached Figure Description

Figure 1 shows a cylindrical particle in a liquid under the influence of an electric field and the force generated on the particle.

Figures 2A, 2B, 2C and 2D show side views of an example of a portion of the variable light transmission device of the present invention.

Figure 3 shows a side view of a microcell in the optically open state and a side view of a microcell in the optically closed state.

Figure 4 is an example of the first embodiment of the present invention; the example is a DC unbalanced waveform that can be applied to a variable transmittance device to achieve a closed state; the waveform includes an AC waveform with a duty cycle of more than 50%.

Figure 5 is an example of the second embodiment of the present invention. The example is a DC unbalanced waveform that can be applied to a variable transmittance device to achieve a closed state. The waveform is a superposition of a DC voltage component and an AC waveform.

Figure 6 illustrates the force exerted by charged pigment particles on the conical protrusion surface of the variable light transmission device of the present invention.

Figure 7 shows a portion of a variable light transmission device with an electrophoretic medium comprising a first type of charged pigment particles and a second type of charged pigment particles having the same polarity.

Figure 8 shows a portion of a variable light transmission device with an electrophoretic medium comprising a first type of charged pigment particles and a second type of charged pigment particles having opposite polarities.

Figure 9 shows the variation of light reflection, transmission, and absorption of a layer containing light-absorbing pigment particles with layer thickness.

Figure 10 shows the variation of light reflection, transmission, and absorption of a layer containing light-reflecting pigment particles with layer thickness.

Figure 11 shows the effect of layer thickness on the reflection, transmission, and absorption of a closed optical state layer, which includes a combination of light-reflecting pigment particles and light-absorbing pigment particles.

Figure 12 shows a portion of a variable light transmission device, which includes a light-blocking layer on the exposed inner surface of the bottom of a microcell.

Figure 13 shows a portion of a variable light transmission device, which includes a light-blocking layer on the upper surface of a micro-unit wall.

Figure 14 shows a plan view of the micro-unit of the variable transmission device used in the example.

Figure 15 shows a cross-sectional view of the micro-unit of the variable transmission device used in the example.

Figure 16 provides photomicrographs of the open and closed optical states of the variable light transmission device of Example 1, which are generated by various waveforms.

Figure 17 provides micrographs of the on and off optical states of the variable light transmission device of Example 2, the electrophoretic medium of which includes charge control agents of different concentrations.

Figure 18 is a photomicrograph of the micro-unit array of the variable light transmission device of Example 5; the light blocking composition includes black pigment particles distributed throughout the micro-units (optical off state).

Figure 19 is a photomicrograph of the micro-unit array of the variable light transmission device of Example 5, in which black pigment particles of the light-blocking composition are driven into the channels of the micro-units (optical closed state).

Figure 20 is a photomicrograph of the micro-unit array of the variable light transmission device of Example 6 in the optical-off state; white charged pigment particles of the light-blocking composition are distributed throughout the micro-units (optical-off state).

Figure 21 is a photomicrograph of the micro-unit array of the variable light transmission device of Example 6 in the open optical state; white charged pigment particles of the light-blocking composition are driven into the channel (open optical state).

Figure 22 is a micrograph of the microarray of the variable light transmission device of Example 7 in the open optical state, the electrophoretic medium of which consists of white and black pigment particles.

Detailed Implementation

The distance from a point to a plane is the shortest perpendicular distance from that point to the plane. The shortest distance from a point to a plane is the length of the perpendicular line parallel to the normal vector of the given plane from that point.

The distance between two planes in three-dimensional space is the shortest distance between the planes, that is, the shortest distance from any point on one plane to any point on another plane.

The slope of a cone is defined as an angle having: (a) a vertex (A) located on the circumference of the base of the cone, (b) a first arm which is a line connecting point A (vertex) and the center of the base of the cone, and (c) a second arm which is a line connecting point A (vertex) and the vertex of the cone.

The term "charged pigment particle" can refer to a pigment particle whose surface does not have any polymer material. Alternatively, it can refer to a pigment particle whose surface has polymer material.

"Micro-unit inner wall surface" refers to the surface of the micro-unit wall that is in contact with the electrophoretic medium of the micro-unit.

The "upper surface of the micro-unit wall" is the surface of the micro-unit wall that is in contact with the sealing layer of the micro-unit. When a light-blocking layer is present on the upper surface of the micro-unit wall, the light-blocking layer is located between the upper surface of the micro-unit wall and the sealing layer.

A “DC-balanced waveform” or “DC-balanced drive waveform” applied to a pixel refers to a drive waveform in which the integrated drive voltage applied to the pixel is essentially zero over the entire waveform application period. DC balance can be achieved by balancing each phase of the waveform, that is, by selecting a first positive voltage such that the integrated result with respect to subsequent negative voltages is zero or essentially zero. If the waveform is not DC-balanced, it is called a “DC-unbalanced waveform” or “DC-unbalanced drive waveform.” The drive waveform applied to a pixel may have a portion of DC-unbalanced waveform, plus at least one additional pulse of reverse impulse to ensure that the overall waveform applied to the pixel is DC-balanced. This additional pulse may be applied before the DC-unbalanced portion of the waveform (pre-pulse). Typical examples of DC-unbalanced waveforms include: (a) a square or sinusoidal AC waveform with a duty cycle less than (or greater than) 50%, and (b) a square or sinusoidal AC waveform with a DC offset.

The term "impulse" refers to the integral of voltage over time. That is, for a waveform pulse of voltage V with an applied time t, its impulse is V × t. If the polarity of voltage V is positive, the impulse is positive; if the polarity of voltage V is negative, the impulse is negative.

The term “net positive impulse” for waveform means that during the application of waveform, negatively charged pigment particles will be attracted to and move toward the first transparent electrode layer.

In the microcells of the variable light transmission device of this invention, the term "lateral component of velocity" related to the motion of charged pigment particles refers to the velocity in the horizontal direction. In this definition, we assume that the velocity of a charged particle is a vector sum of its horizontal velocity (Vh) and its vertical velocity (Vv), and that, in the case of charged pigment particles moving within the electrophoretic microcell, the vertical direction is either from the first phototransmitting electrode layer to the second phototransmitting electrode layer, or from the second phototransmitting electrode layer to the first phototransmitting electrode layer. In the same system, the horizontal direction of the charged pigment particle's motion within the electrophoretic microcell is from one side of the microcell wall to the other, parallel to the first phototransmitting electrode layer. Therefore, the statement "the velocity of the charged pigment particle has a lateral component" means that the magnitude of the horizontal velocity is greater than zero.

Induced charge electroosmosis (ICEO) can be used to laterally move polarizable particles, such as pigment particles, present in an electrophoretic medium. That is, polarizable particles can move parallel to the electrode layer sandwiching the electrophoretic medium. Under the influence of an electric field, the particles may experience forces caused by particle polarization (or polarization by a conductive coating adsorbed on the particle surface, or polarization by the electric double layer surrounding the particle). This force can cause disturbances in the flow of mobile charges (such as ions or charged micelles) in the electrophoretic medium, as shown in Figure 1, where cylindrical particles 101 are surrounded by the liquid of the electrophoretic medium under the influence of an applied electric field. This figure is reproduced from the following article: Bazant and Squires, J. Fluid Mech., 2004, 509, 217-252.

A perfectly symmetrical spherical particle experiences no net force, but a less symmetrical particle experiences a force with a component perpendicular to the applied field direction. The cooperative flow resulting from this force acting on a group of particles can lead to a “vortex” in an electrophoretic medium containing multiple particles. According to the theory proposed by Bazant and Squires in their paper, the maximum velocity u of such a vortex for a particular particle is approximately given by expression (1).

Expression (1)

In expression (1), E is the field strength, ε is the dielectric constant of the solvent, η is the viscosity of the electrophoretic solution, ν is the frequency of the applied sinusoidal alternating current, and τ is the time scale for the solvent charge to move around the charge to form a shielding charge layer. This time scale τ is given by formula (2).

Formula (2)

In formula (2), _λD is the Debye shielding length, R is the particle radius, and D is the diffusion constant of the charge carrier in the fluid.

According to expression (1), as the frequency increases, the value of increases, and the maximum velocity of the induced charge flow decreases. Furthermore, for a value much greater than 1, the maximum rotational velocity is proportional to the square of the ratio. Regardless of the polarity of the applied electric field, the induced charge flow occurs in the same direction and can therefore be driven by an alternating field.

When the electrophoretic medium is contained within microcells (which is preferred in electrophoretic displays), the geometry of the induced flow is influenced by the shape of the specific microcells used. For example, in the simplest case of two parallel electrodes, results show that, with appropriate electric field strength and AC frequency, the flow can adopt a coiled structure with periodic spacing corresponding to the gap width between the electrodes.

The inventors of this invention utilize a complex micro-unit structure formed by an imprinting process to fabricate a switchable device. In one example, the imprinted structure includes a conical protrusion at the bottom of each micro-unit. Figures 2A, 2B, and 2C illustrate examples of a variable light transmission device according to the invention, wherein the protrusion structure of the variable light transmission device is a cone on a cylinder. As shown in Figures 2A, 2B, and 2C, the cone of the protrusion structure can guide the flow of electrophoretic particles into a channel. If the electric field applied to the electrophoretic medium has a suitable polarity related to the polarity of the charged pigment particles, the charged pigment particles will move toward the channel. For example, if the charged pigment particles are positively charged, and the voltage applied via the light-transmitting electrode causes the second light-transmitting electrode to be negatively charged, the charged pigment particles will move toward the channel. The same movement occurs if the charged pigment particles are negatively charged, and the voltage applied via the light-transmitting electrode causes the second light-transmitting electrode to be positively charged. Figures 2A, 2B, and 2C show a cross-section (not drawn to scale) of a portion of the variable light transmission device, showing only one of the multiple micro-units of the device. Figures 2A, 2B, and 2C show the same device structure, but each figure marks different parts of the device.

The variable light transmission device 200 shown in Figures 2A, 2B, and 2C includes a micro-unit layer comprising multiple micro-units and a sealing layer. Although only one micro-unit is shown in Figures 2A, 2B, and 2C, an entire variable light transmission device comprising multiple micro-units is conceivable. This variable light transmission device may include a first transparent substrate 201, a first light-transmitting electrode layer 202, a micro-unit layer 203 comprising multiple micro-units 204 and a sealing layer 206, a second light-transmitting electrode layer 207, and a second transparent substrate 208. Each of the multiple micro-units 204 includes an electrophoretic medium 209 comprising charged pigment particles and a charge control agent in a fluid. The composition of the electrophoretic medium is not shown in Figures 2A, 2B, and 2C. Each of the multiple micro-units 204 has a micro-unit opening 205, and the sealing layer 206 spans the micro-unit openings 205 of the multiple micro-units 204. Each of the plurality of micro-units 204 includes a micro-unit bottom layer 210, a protrusion structure 217, a micro-unit wall 212, and a channel 215. The micro-unit bottom layer 210 has a micro-unit bottom inner surface 211, which includes an exposed micro-unit bottom inner surface 211a and an unexposed micro-unit bottom inner surface 211b. The unexposed micro-unit bottom inner surface 211b contacts the protrusion base 218. The exposed micro-unit bottom inner surface 211a is highlighted in thicker lines in Figure 2A.

In this example, the protrusion 217 is a cone on a cylinder. The protrusion 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 set of points on the protrusion 217 that is closer to the micro-unit opening 205 than all other points of the protrusion 217 are closer to the micro-unit opening 205. In the example of the variable light transmission device shown in Figures 2A, 2B, and 2C, the protrusion apex 219 is the apex of the protrusion cone. The protrusion height 220 is the distance between the protrusion base 218 and the protrusion apex 219. If the protrusion 217 has protrusion apexes 219 comprising more than one point, such as a plane, then the protrusion height 220 is the distance between the plane of the protrusion 217 and the protrusion base 218. A micro-unit layer comprising multiple micro-units 204 with raised structures 217 can be manufactured by imprinting a thermoplastic or thermosetting precursor layer using a pre-patterned male mold, followed by demolding. The precursor layer can be hardened during or after the imprinting step by radiation, cooling, solvent evaporation, or other means.

The micro-unit wall 212 has an inner wall surface 213 and an upper wall surface 214. The inner wall surface 213 is in contact with the electrophoretic medium 209. The upper wall surface 214 is the surface of the micro-unit wall 212 of the micro-unit that is in contact with the sealing layer 206. The inner wall surface 213 is highlighted with a thicker line in Figure 2B.

Channel 215 is the volume between the exposed microcell bottom inner surface 211a, the microcell inner wall surface 213, and the raised surface 221. Channel 215 is the volume location where most charged particles reside when the device is in the optically open state. The channel height 216 of channel 215 is 50% of the raised height 220. Therefore, the channel height, along with the exposed microcell bottom inner surface 211a, microcell inner wall surface 213, and raised surface 221, further define the channel. In Figure 2C, the raised surface 221 is highlighted with a thicker line.

Figure 2D illustrates an example of a variable light transmission device according to the present invention, wherein the protruding structure of the variable light transmission device is a cone on a cylinder. The variable light transmission device shown in Figure 2D is similar to the devices shown in Figures 2A, 2B, and 2C, but shows a larger portion of the device comprising four micro-units. The variable light transmission device 200 includes a first transparent substrate 201, a first light-transmitting electrode layer 202, a micro-unit layer 203 comprising a plurality of micro-units 204 and a sealing layer 206, a second light-transmitting electrode layer 207, and a second transparent substrate 208. Each of the plurality of micro-units includes an electrophoretic medium comprising charged pigment particles 222 in a fluid and a charge control agent. Each of the plurality of micro-units 204 has a micro-unit opening, and the sealing layer 206 spans the micro-unit openings of the plurality of micro-units. Each of the plurality of micro-units includes a micro-unit bottom layer 210, a protruding structure 217, a micro-unit wall 212, and a channel 215. The variable light transmission device shown in Figure 2D is in a closed optical state.

When a first electric field is applied between the first and second transparent electrode layers 202 and 207 via a first waveform, if the polarity of the charged pigment particles 222 is opposite to the voltage polarity of the second transparent electrode layer, the charged pigment particles 222 will move towards the channel. If the polarity of the charged pigment particles 222 is opposite to the voltage polarity of the second transparent electrode layer, the charged pigment particles 222 will be attracted by the second transparent electrode, and the variable light transmission device will switch to an open optical state, which has a higher light transmission percentage than the closed optical state. The open optical state is shown in Figure 3a, where the charged pigment particles 222 are represented by solid black circles. In this example, the electrophoretic medium includes one type of charged pigment particles 222.

A second electric field is applied between the first and second light-transmitting electrode layers 202 via a second waveform, causing charged pigment particles 222 to move towards the first light-transmitting electrode layer 202 at a certain velocity. This results in a closed optical state, as shown in Figure 3b. This velocity has a lateral component. If no lateral component of the velocity exists, the closed optical state will not occur because the charged pigment particles 222 will move from the open channel towards the first light-transmitting electrode layer 202, but these charged pigment particles 222 will occupy the area near the micro-units around the sealing layer 206. That is, the charged pigment particles 222 will not be distributed across the entire surface of the first light-transmitting electrode layer 202. Therefore, the closed optical state cannot be effectively formed because the light transmittance of the closed optical state is relatively high.

The above indicates that the transition from the closed optical state to the open optical state is easier to achieve because when charged pigment particles collide with the raised surface of the raised structure during their movement toward the second transparent electrode layer, the slope of the raised structure (e.g., the cone in Figures 3a and 3b) will introduce a lateral component to the velocity of the charged pigment particles.

By making the electrical conductivity of the electrophoretic medium and the cone significantly different from each other, it is possible to create an electric field within a variable light transmission device. For example, if the conductivity of the cone is much lower than that of the electrophoretic medium, the field lines will tend to guide charged pigment particles into the channel. However, even in this case, it may still be necessary to provide a larger horizontal force component to redisperse the charged pigment particles from the channel. Furthermore, at the current level of technology, it is easier to assemble and operate the device when the resistivity of the cone material and the electrophoretic medium are approximately equal (approximately ^10¹⁰ Ω*cm). In this case, the electric field lines will pass through the unit approximately perpendicularly. Therefore, it is preferable to use a waveform that induces lateral movement of the charged pigment particles.

The operation of the variable light transmission device includes the following steps: applying a first electric field between a first and a second light-transmitting electrode layer via a first waveform to cause charged pigment particles to move toward a channel, thereby switching the variable light transmission device to an open optical state, wherein the charged pigment particles in the open optical state are located within the channel. The operation of the variable light transmission device further includes the following step: applying a second electric field between the first and second light-transmitting electrode layers via a second waveform to cause the charged pigment particles to move toward the first light-transmitting electrode layer at a certain velocity having a transverse component, resulting in a closed optical state. The second waveform includes a series of at least two positive and negative pulses with a net positive impulse or a net negative impulse, wherein the closed optical state has a lower percentage of light transmission than the open optical state.

The second waveform can be DC unbalanced. The second waveform can include at least one positive voltage and at least one negative voltage, and the second waveform has a net positive impulse or a net negative impulse. The choice of net positive impulse or net negative impulse depends on the polarity of the charged pigment particles. Specifically, if the charged pigment particles are negatively charged, a net positive impulse is needed to move the charged pigment particles from the channel towards the first phototransparent electrode layer. In other words, this movement requires that the applied voltage ultimately attracts the negatively charged particles with a positive voltage between the first phototransparent electrode layer and the second phototransparent electrode layer. Conversely, if the charged pigment particles are positively charged, a net negative impulse is needed to move the charged pigment particles from the channel near the second phototransparent electrode layer 207 towards the first phototransparent electrode layer.

The optical state was turned off by a second electric field applied between the two transparent electrode layers via a second waveform.

In the first embodiment, the second waveform includes an AC waveform having a duty cycle different from 50%. An example of the second waveform of the first embodiment is shown in Figure 4.

AC waveforms can have positive or negative DC bias. DC bias can be achieved by controlling the waveform's duty cycle. A positive DC bias waveform has a duty cycle higher than 50%. The duty cycle of a positive DC bias waveform can be higher than 55%, higher than 60%, or higher than 65%. The duty cycle of a positive DC bias waveform can range from 55% to 95%, from 58% to 90%, from 60% to 88%, from 65% to 85%, or from 70% to 80%. Similarly, a negative DC bias waveform has a duty cycle lower than 50%. The duty cycle of a negative DC bias waveform can be lower than 45%, lower than 40%, or lower than 35%. The duty cycle of a negative DC bias waveform can range from 5% to 45%, from 8% to 40%, from 10% to 38%, from 15% to 35%, or from 20% to 30%.

The waveform shown in the example of Figure 4 includes an AC square wave with two or more cycles. Each cycle may include a first pulse of amplitude V1 applied to time period t1 and a second pulse of amplitude V2 applied to time period t2, where V1 is positive, V2 is negative, and t1 is greater than t2. DC bias is achieved by the difference in time periods when the amplitude of V1 is equal to the amplitude of V2 (|V1|=|V2|). In the case of the example of Figure 4, there is a positive DC bias because the application time period (t1) of the positive voltage V1 is longer than the application time period (t2) of the negative voltage V2. Positive DC bias means that if the charged pigment particles of the variable light transmission device are negatively charged, the charged pigment particles will move toward the first light-transmitting electrode layer of the device. The duty cycle of the waveform can be calculated by formula (3).

Duty cycle = 100 × (V1 · t1) / [(V1 · t2) + ((V2 · t2)] Formula (3)

In the waveform example in Figure 4, the amplitude of V1 can be equal to the amplitude of V2 (|V1|=|V2|), but in general, the amplitudes V1 and V2 can be different from each other.

The example drive waveform shown in Figure 4 is DC unbalanced. However, the waveform shown in Figure 4 can include one or more additional pulses of reverse impulse, which ensures that the overall waveform applied to the pixel is DC balanced. This additional pulse (or multiple additional pulses) can be applied before the DC unbalanced waveform (pre-pulse). Furthermore, the waveform example shown in Figure 4 is a square wave AC waveform. Other examples of AC waveforms that can be used include sine waves, triangle waves, and sawtooth waves.

The AC waveform in the first embodiment can have an amplitude from 10V to 200V and a frequency from 0.1 to 6000Hz. The AC waveform can have an amplitude from 15V to 180V, from 20V to 160V, from 25V to 150V, or from 30V to 140V. The AC waveform can have a frequency from 0.5Hz to 5000Hz, from 1Hz to 4000Hz, from 5Hz to 3000Hz, from 10Hz to 2000Hz, from 15Hz to 1000Hz, from 20Hz to 800Hz, or from 25Hz to 600Hz. The ratio of the AC waveform frequency to the weight percentage of the charge control agent in the electrophoretic medium can range from 400Hz to 2000Hz.

In the second embodiment, the second waveform may include a waveform formed by superimposing a DC voltage component and an AC waveform. An example of the second waveform in the second embodiment is shown in Figure 5.

The waveform in Figure 5 has a net negative impulse due to the DC offset (Vd). Although the application time of the positive pulse (t3) is equal to the application time of the negative pulse (t4), a DC offset is generated due to the difference in pulse amplitude. Specifically, the amplitude of the positive pulse V3 is less than the amplitude of the negative pulse V4. This is caused by the DC voltage component Vd of the waveform. In other words, the waveform shown in Figure 5 has a DC offset.

The example drive waveform shown in Figure 5 is DC unbalanced. However, the waveform shown in Figure 5 can include one or more additional pulses of reverse impulse, which ensures that the overall waveform applied to the pixel is DC balanced. This additional pulse (or multiple additional pulses) can be applied before the DC unbalanced waveform (pre-pulse). Furthermore, the waveform example shown in Figure 5 is a square wave AC waveform. Other examples of AC waveforms that can be used include sine waves, triangle waves, and sawtooth waves.

The AC waveform can have an amplitude from 10V to 200V and a frequency from 0.1 to 6000Hz. The AC waveform can have an amplitude from 15V to 180V, from 20V to 160V, from 25V to 150V, or from 30V to 140V. The AC waveform can have a frequency from 0.5Hz to 5000Hz, from 1Hz to 4000Hz, from 5Hz to 3000Hz, from 10Hz to 2000Hz, from 15Hz to 1000Hz, from 20Hz to 800Hz, or from 25Hz to 600Hz. The ratio of the AC waveform frequency to the weight percentage of the charge control agent in the electrophoretic medium can range from 400Hz to 2000Hz.

Even with relatively low ICEO induced motion of charged pigment particles, the protruding structure of the microcell contributes to the efficient operation of the variable transmission device, even when using a DC-balanced AC waveform drive. In the example where the protruding structure is a cone, any charged pigment particle located on the surface of the cone will be subjected to a net force that will cause them to move towards the apex of the cone. As shown in Figure 6, charged pigment particles 222 are in contact with the protruding structure 617 (cone) in an electric field 602. In this case, the ICEO flow direction is indicated by the curved arrows, with the “uphill” side of the cone experiencing greater constraint than the “downhill” side. This exerts a force on the particles, as indicated by the dashed horizontal arrows. There will be a reaction force perpendicular to the cone, forcing the particles to move towards the apex of the cone. By appropriately selecting the AC field and frequency, particles can thus be moved out of the channel region and upwards to the side of the cone.

The electrophoretic medium of the variable light transmission device of the present invention includes charged pigment particles, charge control agent and fluid.

Electrophoretic media can include two types of charged pigment particles: Type I charged pigment particles and Type II charged pigment particles. Type I charged pigment particles can reflect light, while Type II charged pigment particles can absorb light. A typical example of light-reflecting pigment particles is titanium dioxide, which is white in color. Typical examples of light-absorbing pigment particles include organic and inorganic pigment particles in black, blue, cyan, magenta, red, green, yellow, and other colors. Type I charged pigment particles can have the same polarity as Type II charged pigment particles. Type I charged pigment particles can also have opposite polarities to Type II charged pigment particles.

In an electrophoretic medium containing first-type and second-type charged pigment particles (which have the same charge polarity), the Zeta potential of the first-type charged pigment particles can be lower than that of the second-type charged pigment particles. Furthermore, the average particle size of the first-type charged pigment particles can be larger than that of the second-type charged pigment particles, the particle size being determined by the average diameter of the pigment particles. Figure 7a illustrates the open optical state of an example of a variable light transmission device. In this example, after applying an appropriate electric field between the first transparent electrode layer 202 and the second transparent electrode layer 207, both types of charged pigment particles 222a (first type) and 222b (second type) move into the channels of the microcells to form an open state. However, because the first-type charged pigment particles 222a have a lower charge (and a larger size), the second-type charged pigment particles 222b (light absorption) will be located below the first-type charged pigment particles 222a (light reflection). In other words, the second type of charged pigment particles 222b will be closer to the exposed bottom inner surface of the microcell (bottom of the channel) than the first type of charged pigment particles 222a. Figure 7b illustrates the closed optical state of this example of a variable light transmission device. After applying an appropriate electric field between the first light-transmitting electrode layer 202 and the second light-transmitting electrode layer 207, both types of charged pigment particles 222a and 222b will move towards the first light-transmitting electrode layer, thereby achieving the closed optical state. However, the second type of charged pigment particles 222b (light absorption) will be closer to the sealing layer 206 than the first type of charged pigment particles 222a (light reflection) because the first type of charged pigment particles 222a has a lower charge (and a larger size).

In another example, the variable light transmission device has an electrophoretic medium comprising a first type of charged pigment particles (light reflection) and a second type of charged pigment particles (light absorption), wherein the first type of charged pigment particles and the second type of charged pigment particles have opposite charge polarities. Figures 8a and 8b illustrate two possible open optical states of this example, respectively. After applying an appropriate electric field between the first light-transmitting electrode layer 202 and the second light-transmitting electrode layer 207, the first charged pigment particles 223a (light reflection) or the second charged pigment particles 223b (light absorption) will move toward the channel (open optical state) depending on the polarity of the applied electric field. A closed optical state can be formed by applying an appropriate electric field (second electric field) between the first light-transmitting electrode layer 202 and the second light-transmitting electrode layer 207, which causes one type of charged pigment particles to move toward the first light-transmitting electrode layer 202 at a certain velocity having a transverse component. Depending on the applied electric field, the first type of charged pigment particles 223a or the second type of charged pigment particles 223b will diffuse in the micro-unit region (micro-unit opening) near the sealing layer 206.

The number of black, second-type charged pigment particles will be selected to be sufficient to cover the white pigment in the channel when viewed from below (optical state open), but not too high to avoid excessive light absorption when the optical state is closed. "Viewed from below" means that the observer is located on the side of the variable light transmission device closer to the second light-transmitting electrode layer 207, opposite to the side closer to the first light-transmitting electrode layer 202.

High transmittance and low haze are desirable in the open optical state of variable transmittance devices. Furthermore, in some applications, such as building windows or vehicle sunroofs, it is desirable to manage the temperature rise of the building or vehicle. Thermal management is challenging when variable transmittance devices incorporate electrophoretic media (including light-absorbing charged pigment particles). In the closed optical state of such devices, incident light may be absorbed, causing them to heat up. Incident light can include wavelengths within the solar spectrum, namely ultraviolet, visible, and infrared light. Another issue may be that the closed optical state is not completely opaque. That is, some incident light may penetrate the building or vehicle, warming its interior.

Figure 9 shows the light reflection, transmission, and absorption of a layer including black pigment (light absorber) as a function of layer thickness. That is, for each layer thickness, these figures provide the ratio of reflected, transmitted, and absorbed light to incident light.

Figure 10 provides graphs showing the light reflection, transmission, and absorption of a layer including white pigment (light reflection) as a function of layer thickness. In other words, for each layer thickness, these graphs provide the ratio of reflected, transmitted, and absorbed light to incident light.

Figures 9 and 10 show that white pigment reflects significantly more light than black pigment, but does not absorb incident light. In fact, white pigment provides opacity through light reflection/scattering. As the layer thickness increases, more incident light is reflected, and less incident light is transmitted. However, a variable light transmission device comprising a medium with white pigment particles (reflection) was observed to exhibit noticeable haze in the optically open state.

The inventors of this invention have discovered that a variable light transmission device comprising an electrophoretic medium provides significant benefits, such as reduced haze. The electrophoretic medium has charged particles comprising a reflective pigment (a first type) and charged particles comprising an absorbing pigment (a second type), the reflective pigment being titanium dioxide and the absorbing pigment being an inorganic black pigment, such as iron oxide black.

Figure 11 illustrates the effect of layer thickness on the reflection, transmission, and absorptivity of a composition comprising a white pigment (light reflection) and a black pigment (light absorption) in a closed optical state. The weight ratio of black pigment to white pigment is 0.1. That is, for each layer thickness, these figures provide the ratio of reflected, transmitted, and absorbed light to incident light.

As the layer thickness increases, the rate of decrease in transmission remains almost constant, but the upper limit of reflectivity for white pigment is 30%. Absorption increases with increasing layer thickness, but is only about half that of the pure black pigment layer shown in Figure 9. Placing the white pigment layer before the black pigment layer, rather than mixing the two, reduces absorption and its unwanted thermal effects.

In an example of a variable transmission device with an electrophoretic medium, the electrophoretic medium comprises a first type of charged pigment particles (white or reflective, with a negative charge polarity) and a second type of charged pigment particles (black or absorptive, with a positive charge polarity). The relative positions of the two types of charged pigment particles in the on and off optical states can be controlled by an applied electric field. For each type of charged pigment particle, the polarizability and size of the particle determine the frequency required to achieve optimal movement. The maximum ICEO velocity of the two types of pigment particles with opposite charges can be achieved by using an electric field comprising AC waveforms of different frequencies. In Example 7 below, which is relevant to this scenario, the characteristic AC waveform frequency of the white pigment is much higher than that of the black pigment. Therefore, a relatively low AC frequency can be used to switch the black pigment into the channel, and an appropriate DC offset can be superimposed to move the black pigment in the microcell channel, as shown in the figure. Because the black pigment is positively charged, applying an AC voltage and a positive offset voltage to the first transparent electrode layer while grounding the second transparent electrode layer will cause the black pigment to move into the channel. The alternating current frequency is relatively low (10 Hz); at this frequency, both white and black pigments exhibit strong ICEO-induced lateral movement. Once the black pigment is in the channel, the alternating current frequency increases to a higher value. At higher frequencies, the ICEO-induced movement of the black pigment is weakened, but the movement of the white pigment is maintained. Therefore, the white pigment can be switched into the channel by applying a negative DC offset to the alternating current waveform. Both white and black particles are present in the channel simultaneously (as shown in Figure 7a). Although under certain conditions, the electric field in the second step can drive some black pigment particles out of the channel, it does not cause the black pigment to move laterally. Therefore, the black particles that can be removed from the channel will undergo vertical movement, thus providing an open optical state similar to that shown in Figure 8a.

Figure 12 illustrates another method for reducing haze in a variable light transmission device caused by light scattering effects from charged pigment particles. Figure 12 shows a side view of an innovative variable light transmission device comprising a first light-transmitting electrode layer 202, a second light-transmitting electrode layer, and an electrophoretic medium comprising charged pigment particles 222, which are light-reflective. The variable light transmission device also includes a first light-blocking layer 1202 located on the exposed bottom inner surface of the microcell. The first light-blocking layer 1202 may include light-absorbing black pigment particles. In the open optical state of the device, the charged pigment particles of the electrophoretic medium are included in the channels of the microcell (Figure 12a). When the device is viewed from the bottom, the first light-blocking layer 1202 can block haze. Viewing from the bottom refers to the observer viewing the device from the side closest to the second light-transmitting electrode layer 207. However, when the device is viewed from the top, haze is still noticeable. Viewing from the top refers to the observer viewing the device from the side closest to the first light-transmitting electrode layer 202. Figure 12b shows the device in the closed optical state. The variable light transmission device shown in Figure 12 can be used in applications where the observer is typically located on one side of the variable light transmission device, such as, for example, a skylight.

The method of manufacturing the variable light transmission device shown in Figure 12 includes the following steps: (a) providing an assembly comprising a third electrode layer, a second light-transmitting electrode layer, and a layer comprising a plurality of micro-units, wherein the layer comprising a plurality of micro-units is disposed between the third electrode layer and the second light-transmitting electrode layer, each of the plurality of micro-units comprising a light-blocking composition comprising (i) light-absorbing charged pigment particles, (ii) a polymer, oligomer or monomer, and (iii) an optional solvent, each of the plurality of micro-units having a micro-unit opening, the third electrode layer spanning the micro-unit openings of the plurality of micro-units, each of the plurality of micro-units comprising a micro-unit bottom layer, a protruding structure, a micro-unit wall and a channel, the micro-unit bottom layer having a micro-unit base (a) The inner surface of the microcell includes an exposed inner surface of the microcell bottom and an unexposed inner surface of the microcell bottom; (b) applying an electric field between the third electrode layer and the second transparent electrode layer via a waveform that causes the light-absorbing charged pigment particles of the light-blocking composition to move toward the channel, thereby placing the light-absorbing charged pigment particles in the channel; (c) curing the light-blocking composition to form a light-blocking layer on the exposed inner surface of the microcell bottom; (d) removing the third electrode layer; (e) filling each of the plurality of microcells with an electrophoretic medium comprising charged pigment particles, a charge control agent and a fluid; (f) sealing each of the plurality of microcells with a sealing layer; and (g) attaching the first transparent electrode layer to the sealing layer.

If the light-blocking composition includes a solvent, the solvent evaporates during the curing process. Curing of the light-blocking composition can be achieved by ultraviolet irradiation, heat treatment, or solvent evaporation.

Another method of manufacturing the device in Figure 12 includes the following steps: (a) providing an assembly comprising, in sequence, a second light-transmitting electrode layer, a second light-transmitting electrode layer, and a layer comprising a plurality of micro-units disposed on the second light-transmitting electrode layer, each of the plurality of micro-units having a micro-unit opening, each of the plurality of micro-units including a micro-unit bottom layer, a protrusion structure, a micro-unit wall, and a channel, the micro-unit bottom layer having a micro-unit bottom inner surface, the micro-unit bottom inner surface including an exposed micro-unit bottom inner surface and an unexposed micro-unit bottom inner surface, the protrusion structure having a protrusion base, a protrusion surface, a protrusion apex, and a protrusion height, the protrusion apex being a point or a set of points of the protrusion structure, the distance of the point or set of points to the micro-unit opening being shorter than the distances of all other points of the protrusion structure to the micro-unit opening, the protrusion height being the distance between the protrusion base and the protrusion apex, and the protrusion surface being the protrusion structure excluding the protrusion apex and the protrusion. The base surface, the micro-unit wall having a micro-unit inner wall surface and a micro-unit upper surface, the channel having a channel height of 50% of the protrusion height, the unexposed micro-unit bottom inner surface in contact with the protruding base, the channel being the volume between the exposed micro-unit bottom inner surface, the protruding surface and the micro-unit inner wall surface; (b) dispersing a light-blocking composition onto the exposed micro-unit bottom inner surface of each micro-unit, the light-blocking composition comprising (i) light-absorbing pigment particles, (ii) a polymer, oligomer or monomer, and (iii) an optional solvent; (c) curing the light-blocking composition to form a light-blocking layer on the exposed micro-unit bottom inner surface; (d) filling each of the plurality of micro-units with an electrophoretic medium comprising charged pigment particles, a charge control agent and a fluid; (e) sealing each of the plurality of micro-units with a sealing layer; and (f) attaching a first light-transmitting electrode layer to the sealing layer.

If the light-blocking composition includes a solvent, the solvent evaporates during the curing process. Curing of the light-blocking composition can be achieved by ultraviolet irradiation, heat treatment, or solvent evaporation.

Examples 5 and 6 describe experiments using light-blocking compositions to form blocking layers. In Example 5, the light-blocking composition comprises black charged pigment particles; however, in Example 6, the light-blocking composition comprises white charged pigment particles.

A variable light transmission device with improved closed optical state performance can also be realized by using the device shown in Figure 13. The variable light transmission device shown in Figure 13 includes a first transparent electrode layer (202), a second transparent electrode layer (207), and a micro-unit layer (203). The micro-unit layer is disposed between the first transparent electrode layer (202) and the second transparent electrode layer (207). The micro-unit layer includes multiple micro-units and a sealing layer. Each of the multiple micro-units includes an electrophoretic medium comprising charged pigment particles and a charge control agent in a fluid. Each of the multiple micro-units has a micro-unit opening, and the sealing layer spans the micro-unit openings of the multiple micro-units. Each of the multiple micro-units includes a micro-unit bottom layer, a raised structure, a micro-unit wall, and a channel. The micro-unit bottom layer has a micro-unit bottom inner surface, which includes an exposed micro-unit bottom inner surface and an unexposed micro-unit bottom inner surface. The raised structure has a raised base, a raised surface, a raised apex, and a raised height. A protrusion apex is a point or set of points in the protrusion structure whose distance from the micro-unit opening is less than that of all other points in the protrusion structure. The protrusion height is the distance between the protrusion base and the protrusion apex. A protrusion surface is the surface of the protrusion structure excluding the protrusion apex that contacts the electrophoretic medium. The micro-unit wall has an inner wall surface, an upper surface, and a second light-blocking layer 1311. The inner wall surface is the surface of the micro-unit wall of the micro-unit that contacts the electrophoretic medium. The second light-blocking layer 1311 is located between the upper surface of the micro-unit wall and the sealing layer. The channel has a channel height that is 50% of the protrusion height. The unexposed inner surface of the micro-unit bottom contacts the protrusion base. The channel is the volume between the exposed inner surface of the micro-unit bottom, the protrusion surface, and the inner wall surface of the micro-unit. The variable light transmission device in FIG13 may further include a first light-blocking layer 1202 disposed on the exposed inner surface layer of the micro-unit bottom. As described above, the first light-blocking layer 1202 can reduce haze when observing the device from below. The second light-blocking layer 1311 facilitates improved opacity in the closed state by increasing the opacity of the device, which may be caused by a partially translucent wall material. The second light-blocking layer 1311 may be black, white, or any other color. The second light-blocking layer 1311 may be conductive, thereby facilitating switching of the device. The variable light transmission device shown in FIG13 may further include an auxiliary layer 1312 disposed between the sealing layer and the second light-blocking layer 1311. The auxiliary layer 1312 may include an adhesive material. The auxiliary layer 1312 may include light-reflecting pigments to further improve opacity in the closed optical state. The auxiliary layer 1312 may also include an encapsulation electrophoretic layer comprising an electrophoretic medium of charged pigment particles. Applying an electric field to the encapsulation electrophoretic layer of the auxiliary layer 1312 can switch the color (or image) of the auxiliary layer 1312, which may also affect the appearance of the variable light transmission device shown in FIG13.

Charge control agents are typically oligomers or polymers soluble in the electrophoretic medium. They are surfactant-type molecules having one or more polar functional groups (heads) and nonpolar moieties (tails). The electrophoretic medium may contain charge control agents at concentrations ranging from 0.1% to 10% by weight of the electrophoretic medium. Specifically, the electrophoretic medium may contain charge control agents at concentrations ranging from 0.5% to 9%, 0.7% to 8%, 1% to 7%, or 1% to 6% by weight of the electrophoretic medium.

The fluid used in electrophoresis can include aliphatic hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons, halogenated aliphatic hydrocarbons, polydimethylsiloxanes, or mixtures thereof.

Electrophoretic media may also include flocculants, also known as dissipants. Dissipants create osmotic pressure differences between pigment particles and between pigment-dissipant molecules. This enhances the bistable state of the device's optical states (on and off). Dissipants are typically polymeric materials such as polyisobutylene and polydimethylsiloxane.

Example

Example 1 : A device is fabricated by laminating a polyethylene terephthalate (PET) sheet coated with an indium tin oxide (ITO) transparent conductor onto a second sheet containing PET/ITO and an electrophoretic dielectric. The structure of this device corresponds to the illustrations in Figures 2A to 2D, but without the sealing layer 212. The structure of the imprinted microcell array is shown in Figure 14, which is a plan view of the microcells in the device. Figure 15 shows a corresponding cross-sectional view of one microcell in the device. Table 1 shows the external dimensions of the microcells.

Table 1: Device Structure

element Distance (micrometers) Cavity spacing: from center to center of microunit 500 The height of the cylinder (base) below the cone protrusion 15.2 Maximum height of particle filling level (above the base) 15.2 Minimum wall width at the first substrate 15 Draft angle of the wall and base of the cone 8 wall height 50 Width of the wall notch/groove at the first substrate 10 Wall notch/groove draft angle 26.6 Wall notch/groove depth 5 The gap between the apex of the protrusion and the top of the wall 9 Cone inclination (degrees) 7.3

The electrophoretic medium comprises a white pigment, a hydrocarbon solvent, a charge control agent (CCA), and a dissipative agent. In this example, the electrophoretic medium sample was prepared by mixing 10 wt% of white pigment and 5 wt% of charge control agent (a cationic charge control agent from Example 1-CCA111 of US2020/0355978) in Isopar E solvent. The apparatus was switched using a 50V square wave AC waveform with a 50% duty cycle. As shown in Figure 16, three different pigment movement patterns were observed by increasing the AC frequency from 0 Hz to 5000 Hz. The white pigment particles were prepared with a titanium dioxide pigment core and a polymer shell, as described in Example 1 of US Patent No. 8,582,196.

At a low frequency of 10 Hz, and after several switching, the white pigment moves towards the edge (near the periphery) of the microunit (Figure 16(a)), likely due to a slight downward push along the slope of the cone. Once in the channel, the pigment switches vertically up and down. At the low frequency of 10 Hz, the movement is predominantly normal electrophoresis. By increasing the frequency to 100 Hz, the pigment tends to diffuse laterally into the region above the cone in the imprinted microunit structure (Figure 16(b)). At a frequency of 1000 Hz, the white pigment diffuses completely into the circle of the imprinted microunit structure, as shown in Figure 16(c). At a frequency of 1000 Hz, the behavior of the pigment is considered to be predominantly lateral movement of induced charges, likely a result of ICEO. At a frequency of 5000 Hz, the white pigment particles tend to converge towards the center of the near-cone region of the imprinted microunit structure, as shown in Figure 16(d).

Example 2 : In Example 2, the effect of charge control agent (CCA) concentration on the movement of white pigment in an imprinted microcell device was investigated.

As previously mentioned, it is anticipated that increasing the concentration of the charge control agent in the electrophoretic medium will reduce the Debye length associated with the surface of the charged pigment particles, thereby increasing the frequency required for a specific ICEO flow. To verify this hypothesis, three variable light transmission devices with similar electrophoretic media but using different concentrations of charge control agent were prepared. The charge control agent used in this example is the cationic polymer disclosed in Example 1-CCA111 of US2020/0355978. Three different electrophoretic media were prepared with charge control agent concentrations of 0.1 wt%, 1 wt%, and 5 wt% of the electrophoretic medium weight, respectively. Each electrophoretic medium also includes 10 wt% of white pigment and Isopar E solvent. The white pigment particles were prepared using a titanium dioxide pigment core comprising a polymer coating, as described in Example 1 of US Patent No. 8,582,196.

The switching performance of three samples was evaluated in an imprinted microcell device (shown in Figures 14 and 15). The waveform was a square wave AC current of +/- 50V with a 50% duty cycle. As shown in Figure 17, the frequency required to achieve the optical shutdown state increased with increasing charge control agent concentration. Specifically, for an electrophoretic medium containing 0.1 wt% CCA, a frequency of 50 Hz was required to achieve the optical shutdown state; for an electrophoretic medium containing 1 wt% CCA, a frequency of 100 Hz was required; and for an electrophoretic medium containing 5 wt% CCA, a frequency of 1000 Hz was required. In these three experiments, the frequency-to-CCA concentration ratios were 500 Hz, 1000 Hz, and 1000 Hz, respectively.

The electrophoretic medium of the device comprises 1 wt% CCA, which can switch from an on-optical state to an off-optical state using either (a) a simple square wave AC current of +/-100V, 0.5Hz, or (b) a square wave AC current of +/-50V, 50Hz superimposed on a -50V DC voltage. The on-optical state is achieved by a +/-50V square wave AC current with a duty cycle of 5%, while the off-optical state requires a +/-50V square wave AC current with a duty cycle of 95%. The switching time in each case is approximately 1 second.

Example 3 : The effect of the charge of white pigment on the switching performance of a variable light transmission device was studied.

A variable light transmission device was prepared, the electrophoretic medium of which comprised 10 wt% positively charged white pigment particles in Isopar E. The white pigment was functionalized with 1.6 wt% silane Z6030 and grafted with polymethyl methacrylate (PLMA). Titration with CCA (the cationic polymer disclosed in Example 1-CCA111 of US Patent No. 2020/0355978) was performed to achieve a zeta potential of +35 mV for the treated pigment. The electrophoretic medium also comprised 1 wt% CCA (the cationic polymer disclosed in Example 1-CCA111 of US Patent No. 2020/0355978). The waveform used to switch the device from an on-optical state to an off-optical state was a DC superimposed AC, i.e., a square wave waveform with a frequency of +/-50 V AC at 500 Hz. The waveform used to switch the device from an off-optical state to an on-optical state was a +/-50 V AC offset from a DC. Therefore, the device in Example 3 behaves very similarly to the device in Example 2 that uses an electrophoretic medium comprising 1 wt% CCA, except that the polarity of the DC offset required to achieve the optical state is reversed.

Example 4 : In this example, the solvent of the electrophoretic medium is matched with the polymer that forms the imprinted microunits.

"Haze" refers to the percentage of diffuse transmitted light out of the total transmitted light. Diffuse transmitted light is light that is scattered during transmission. In order to manufacture variable light transmission devices with low haze, it is necessary to match the refractive index of the liquid solvent of the electrophoretic medium with the refractive index of the polymer material used to manufacture the imprinted microunits, as described in U.S. Patent No. 7,327,511.

Typically, solvents used in electrophoretic media have low dielectric constants (preferably less than 10, ideally less than 3), low viscosity, low vapor pressure, and relatively high refractive indices. Examples of solvents include, but are not limited to, aliphatic hydrocarbons such as heptane and octane, petroleum fractions such as Isopar® (ExxonMobil) or Isane® (Total), terpenes such as limonene (e.g., 1-limonene), and aromatic hydrocarbons such as toluene. Limonene is a particularly preferred solvent because it combines a low dielectric constant (2.3) with a relatively high refractive index (1.47). The refractive index of the electrophoretic media can be altered by adding refractive index matching agents. For example, an electrophoretic medium suitable for a variable light transmission device, as described in the aforementioned U.S. Patent No. 7,679,814, wherein the nonpolar liquid of the electrophoretic medium comprises a mixture of partially hydrogenated aromatic hydrocarbons and terpenes, preferably a mixture of d-limonene and partially hydrogenated terphenyl, which is commercially available as Cargille® 5040 from Cargille-Sacher Laboratories, 55 Commerce Rd, Cedar Grove N.J. 07009.

To reduce haze, the refractive index of the encapsulating electrophoretic medium should ideally be closely matched to the refractive index of the encapsulating material. In most cases, it is beneficial to use an electrophoretic medium with a refractive index between 1.51 and 1.57 at 550 nm, preferably around 1.54 at 550 nm.

Example 4A : A variable light transmission device comprising microunits was prepared, the electrophoretic medium comprising 5 wt% white pigment and 1 wt% CCA (the cationic polymer disclosed in Example 1-CCA111 of US2020/035597811), the solvents being Cargille® 5040 and Isopar E. A square wave AC current with a frequency of 10 Hz and an amplitude of +/- 50 V was used. A 5% duty cycle was used to achieve the optically off state. To achieve the optically on state, a 95% duty cycle was initially used, and then the duty cycle was changed to 50%.

Example 4B : Another variable light transmission device comprising microunits was prepared using an electrophoretic medium with a composition similar to that of Example 4A, further comprising polyisobutylene (PIB) as a dissipant. The dissipant is used to improve the bistableness of the device, i.e., to ensure that the device remains in an on-optical state and an off-optical state when no electric field is applied. The electrophoretic medium comprises 10 wt% white pigment, 1 wt% CCA (the cationic polymer disclosed in Example 1-CCA111 of US2020/035597811), 0.5 wt% Cargille® 5040 polyisobutylene, and Isopar E solvent. A square wave AC current of +/- 50 V and 10 Hz was used. To achieve the off-optical state, an alternating mode of 5% and 50% duty cycles was used. To achieve the on-optical state, a 95% duty cycle was used, followed by a 50% duty cycle. The time required for a complete switchover was approximately 20 seconds. This takes much longer than the time required to switch to a non-refractive index-matched solvent without dissipatives (Example 4A).

Example 5 : Light-blocking layer including black particles.

A variable transmission device was fabricated by laminating a PET sheet coated with an ITO transparent conductor onto an imprinted microcell array on another PET/ITO sheet. The imprinted microcell array includes an electrophoretic medium. The structure of the imprinted microcell array is shown in Figures 2A to 2D, but the microcells in this example do not include a sealing layer.

The light-blocking composition used for the light-blocking layer comprises a black pigment, a solvent, a charge control agent, and a dissipative agent. In this example, the light-blocking composition is prepared by mixing 10 wt% black pigment, 1 wt% CCA (a cationic charge control agent from Example 1-CCA111 of US2020/0355978111), and 0.5 wt% polyisobutylene in a solvent mixture of partially hydrogenated terphenyl, which is commercially available as Cargille® 5040 from Cargille-Sacher Laboratories, 55 Commerce Rd, Cedar Grove N.J.07009, and also includes limonene, Isopar M, and Isopar E. The black pigment particles have a core comprising black iron oxide (pigment black 11) and a polymer shell. As shown in Figure 18, during device fabrication, the black pigment particles are dispersed throughout the electrophoretic medium. A 0.5Hz, 50V square wave with a +50V offset (i.e., switching between +100V and 0V) and a 50% duty cycle is applied to the first transparent electrode layer, while the second transparent electrode layer is held at 0V. Electrophoresis is performed between the two electrodes induction, driving positive black pigment to the unexposed microcell bottom surface (inside the channel), as shown in Figure 19. After voltage release, the black pigment remains on the unexposed microcell bottom surface. The PET/ITO first electrode is then peeled off the device to allow film evaporation.

Example 6 : The preparation of the variable light transmission device is the same as that of the variable light transmission device in Example 5, except that the light blocking composition is formulated by mixing 10 wt% white pigment and 5 wt% CCA (the cationic charge control agent of Example 1-CCA111 from US2020/0355978111) in Isopar E solvent. The device can be easily switched between an optically off state (0V offset, Figure 20) and an optically on state (-50V offset, Figure 21) at a 50Hz/50V square wave.

Example 7 : Switch black and white pigments with opposite charges into the channels of the imprinted microcell.

A variable transmission device is fabricated by laminating a PET coating and an ITO transparent conductor together onto an imprinted microcell array including an electrophoretic medium on another PET/ITO sheet. Except for the absence of a sealing layer, the structure of this microcell corresponds to the illustrations in Figures 2A to 2D. The structure of the imprinted microcell array is shown in Figures 14 and 15.

First, an electrophoretic composition comprising a black pigment is prepared and switched to an open optical state (the black pigment is included in the channel). Then, the first transparent electrode layer is removed and the solvent is evaporated. After solvent evaporation, an electrophoretic medium comprising a white pigment, solvent, and charge control agent (CCA) is prepared. In this example, the electrophoretic medium is prepared by mixing 10 wt% white pigment and 1 wt% CCA111 in a solvent mixture of partially hydrogenated terphenyl, commercially available as Cargille® 5040 from Cargille-Sacher Laboratories, 55 Commerce Rd, Cedar Grove N.J. 07009, and also includes limonene, Isopar M, and Isopar E. The white pigment particles are prepared using a titanium dioxide pigment core comprising a polymer coating, as described in Example 1 of U.S. Patent No. 8,582,196.

An electrophoretic medium is assembled into a micro-unit device in which black pigment is switched into a channel while the solvent evaporates. Therefore, the device comprises white and black pigment particles with opposite charges. Both pigments can be switched electrophoretically. To switch the two pigments into the channel, the black pigment is first switched into the channel using a positive DC offset on a relatively low-frequency AC voltage, and then the white pigment is switched into the channel using a negative DC offset on a relatively high-frequency AC voltage.

In the first step, a 10Hz, 50V square wave with a 50% duty cycle and a +2V offset is applied to the first transparent electrode layer 202, while the second transparent electrode layer is held at 0V. The electric field between the electrodes induces electrophoresis through superimposed induced charge electroosmosis, driving the positive black pigment into the channel. In the second step, a 500Hz/50V square wave with a 50% duty cycle and alternating +2V and -2V offsets is applied to the first electrode, while the second electrode is held at 0V. At higher frequencies (500Hz, compared to 10Hz in the first step), the lateral movement of the black pigment is less than that of the white pigment. That is, during the phase of the waveform with a negative DC offset, the white pigment is driven into the channel. As shown in Figure 22, the result is that both white and black pigments are switched into the channels of the microcell.

Partial structure shown in the figure: 200 Variable transmission device; 201 First transparent substrate; 202 First light-transmitting electrode layer; 203 Micro-unit layer; 204 Multiple micro-units; 205 Micro-unit opening; 206 Sealing layer; 207 Second light-transmitting electrode layer; 208 Second transparent substrate; 209 Electrophoretic medium; 210 Micro-unit bottom layer; 211 Micro-unit bottom inner surface; 211a Exposed micro-unit bottom inner surface; 211b Unexposed micro-unit bottom inner surface; 212 Micro-unit wall; 213 Micro-unit inner wall surface; 214 Micro-unit wall upper surface; 125 Channel; 216 Through 217 Protrusion height; 218 Protrusion base; 219 Protrusion apex; 220 Protrusion height; 221 Protrusion surface; 222 Charged pigment particles; 222a First type charged pigment particles; 222b Second type charged pigment particles; 223a First type charged pigment particles with the opposite charge polarity to the second type charged pigment particles 223b; 223b Second type charged pigment particles with the opposite charge polarity to the first type charged pigment particles 223a; 1202 First light-blocking layer; 1311 Second light-blocking layer; 1312 Auxiliary layer.

Claims (20)

1. A method for operating a variable light transmission device, comprising the following steps: A variable light transmission device (200) is provided, the variable light transmission device (200) comprising: First light-transmitting electrode layer (202); The second transparent electrode layer (207); and A micro-unit layer (203) is disposed between the first light-transmitting electrode layer (202) and the second light-transmitting electrode layer (207). The micro-unit layer (203) includes a plurality of micro-units (204) and a sealing layer (206). Each of the plurality of microunits (204) includes an electrophoretic medium (209), the electrophoretic medium (209) comprising charged pigment particles and a charge control agent in a nonpolar liquid. Each of the plurality of micro-units (204) has a micro-unit opening (205), and the sealing layer (206) spans the micro-unit openings (205) of the plurality of micro-units (204). Each of the plurality of micro-units (204) includes a micro-unit bottom layer (210), a protrusion structure (217), a micro-unit wall (212), and a channel (215). The micro-unit bottom layer (210) has a micro-unit bottom inner surface (211), which includes an exposed micro-unit bottom inner surface (211a) and an unexposed micro-unit bottom inner surface (211b). The protruding structure (217) has a protruding base (218), a protruding surface (221), a protruding vertex (219), and a protruding height (220). The protruding vertex (219) is a point or a group of points of the protruding structure (217) that is closer to the micro-unit opening (205) than all other points of the protruding structure (217) are closer to the micro-unit opening (205). The protruding height (220) is the distance between the protruding base (218) and the protruding vertex (219). The protruding surface (221) is the surface of the protruding structure (217) excluding the part of the protruding vertex that is in contact with the electrophoretic medium (209). The micro-unit wall (212) has an inner wall surface (213) and an upper wall surface (214) of the micro-unit. The inner wall surface (213) is the surface of the micro-unit wall (212) of the micro-unit that is in contact with the electrophoretic medium (209), and the upper wall surface (214) is the surface of the micro-unit wall (212) of the micro-unit that is in contact with the sealing layer (206). The channel (215) has a channel height (216), which is 50% of the protrusion height (220). The unexposed micro-unit bottom inner surface (211b) contacts the raised base (218). The channel (215) is the volume between the exposed bottom inner surface (211a) of the microcell, the raised surface (221), and the inner wall surface (213) of the microcell. A first electric field is applied between the first light-transmitting electrode layer (202) and the second light-transmitting electrode layer (207) via a first waveform, causing the charged pigment particles to move toward the channel (215), thereby switching the variable light transmission device (200) to an open optical state. The charged pigment particles in the open optical state are located within the channel (215). A second electric field is applied between the first light-transmitting electrode layer (202) and the second light-transmitting electrode layer (207) via a second waveform to cause the charged pigment particles (222) to move toward the first light-transmitting electrode layer (202) at a certain speed, the speed having a lateral component and resulting in a closed optical state, the second waveform including at least one positive voltage and at least one negative voltage, the second waveform having a net positive impulse or a net negative impulse, wherein the closed optical state has a lower percentage of light transmission than the open optical state. 2. The method of operating the variable light transmission device according to claim 1, wherein the content of the charge control agent in the electrophoretic medium is 1% to 8% of the weight of the electrophoretic medium. 3. The method of operating the variable light transmission device according to claim 1 or 2, wherein the second waveform comprises an AC waveform having a frequency and the AC waveform having a duty cycle from 5% to 45%. 4. The method of operating the variable light transmission device according to claim 3, wherein the AC waveform is a square wave, a sine wave, a triangular wave, or a sawtooth wave. 5. The method of operating the variable light transmission device according to claim 3 or 4, wherein the AC waveform is a square wave having two or more cycles, wherein the positive voltage and negative voltage of the AC waveform have the same amplitude, the amplitude being 10V to 200V, and wherein the frequency of the AC waveform is from 0.1Hz to 6000Hz. 6. The method of operating the variable light transmission device according to claim 5, wherein the frequency of the AC waveform is from 100Hz to 3000Hz, and the amplitude of the AC waveform is from 20V to 180V. 7. A method of operating the variable light transmission device according to any one of claims 3 to 6, wherein the ratio of the frequency of the alternating waveform, expressed in Hertz, to the content of the charge control agent in the electrophoretic medium, expressed as a weight percentage of the charge control agent to the weight of the electrophoretic medium, is from 400 to 2000 Hz. 8. The method of operating the variable light transmission device according to claim 1 or 2, wherein the second waveform comprises a waveform formed by superimposing a DC voltage component and an AC waveform, the AC waveform having a frequency and an amplitude, the frequency being 0.1 Hz to 6000 Hz and the amplitude being 10 V to 200 V, the DC voltage component having an amplitude, the amplitude of the DC voltage component being 0.1 V to 500 V. 9. The method of operating the variable light transmission device according to claim 8, wherein the AC waveform is a square wave, a sine wave, a triangular wave, or a sawtooth wave. 10. The method of operating the variable light transmission device according to claim 8 or 9, wherein the ratio of the frequency of the alternating waveform, expressed in Hertz, to the content of the charge control agent in the electrophoretic medium, expressed as a weight percentage of the charge control agent to the weight of the electrophoretic medium, is from 400 to 2000 Hz. 11. A method of operating the variable light transmission device according to any one of claims 1 to 10, wherein the protruding structure is a geometry selected from the group consisting of: (a) a cone, (b) a cone on a cylinder having a base, the base of the cylinder being the protruding base of the protruding structure, (c) a tetrahedron, (d) a tetrahedron on a triangular prism having a triangular base, the triangular base being the protruding base of the protruding structure, (e) a triangular prism having a square base, the square base being the protruding base of the protruding structure, (f) a square pyramid having a square base, the square base being the protruding base of the protruding structure, (h) a square pyramid on a cube, the square pyramid having a square base being the protruding base of the protruding structure, the square pyramid having a square base being the protruding base of the protruding structure, and (h) a square pyramid on a cube, the square pyramid having a square base being the protruding base of the protruding structure ... A cube has a base, the cube base being the protruding base of the protruding structure; (i) a square pyramid on a regular parallelepiped, the regular parallelepiped having a regular parallelogram base, the regular parallelogram being the protruding base of the protruding structure; (j) a pentagonal pyramid, the pentagonal pyramid having a pentagonal base, the pentagonal base being the protruding base of the protruding structure; (k) a pentagonal pyramid on a pentagonal prism, the pentagonal prism having a pentagonal base, the pentagonal base being the protruding base of the protruding structure; (l) a hexagonal pyramid, the hexagonal pyramid having a hexagonal base, the hexagonal base being the protruding base of the protruding structure; (m) a hexagonal pyramid on a hexagonal prism, the hexagonal prism having a hexagonal base, the hexagonal base being the protruding base of the protruding structure. 12. The method of operating the variable light transmission device according to claim 11, wherein the protruding structure is a cone, and the inclination of the cone is 5 to 10 degrees. 13. The method of operating the variable light transmission device according to claim 11, wherein the protrusion structure is a cone on a cylinder, the cylinder having a base, the base of the cylinder being the protrusion base of the protrusion structure, wherein the slope of the cone is 10 degrees or less. 14. The method of operating the variable light transmission device according to claim 1, wherein the protruding structure is a geometric body of a pyramid with a base having n sides, the base having n sides being the protruding base of the protruding structure, where n is an integer from 7 to 12, (m) a pyramid with a base having n sides, the pyramid being located on a prism with a base having n sides, the base of the prism having n sides being the protruding base of the protruding structure, where n is from 7 to 12. 15. A method of operating the variable light transmission device according to any one of claims 1 to 14, wherein the electrophoretic medium comprises a first type of charged pigment particles and a second type of charged pigment particles, the first type of charged pigment particles being light-reflective and the second type of charged pigment particles being light-absorbent. 16. The method of operating the variable light transmission device according to claim 15, wherein the first type of charged pigment particles are white. 17. The method of operating the variable light transmission device according to claim 15, wherein the second type of charged pigment particles are black. 18. The method of operating the variable light transmission device according to claim 15, wherein the first type of charged pigment particles and the second type of charged pigment particles have the same polarity. 19. The method of operating the variable light transmission device according to claim 15, wherein the first type of charged pigment particles and the second type of charged pigment particles have opposite polarities. 20. A variable light transmission device (200), comprising: First light-transmitting electrode layer (202); The second transparent electrode layer (207); and A micro-unit layer (203) is disposed between the first light-transmitting electrode layer (202) and the second light-transmitting electrode layer (207). The micro-unit layer (203) includes a plurality of micro-units (204) and a sealing layer (206). Each of the plurality of microunits (204) includes an electrophoretic medium (209), the electrophoretic medium (209) comprising charged pigment particles and a charge control agent in a nonpolar liquid. Each of the plurality of micro-units (204) has a micro-unit opening (205), and the sealing layer (206) spans the micro-unit openings of the plurality of micro-units (204). Each of the plurality of micro-units (204) includes a micro-unit bottom layer (210), a protrusion structure (217), a micro-unit wall (212), and a channel (215). The micro-unit bottom layer (210) has a micro-unit bottom inner surface (211), which includes an exposed micro-unit bottom inner surface (211a) and an unexposed micro-unit bottom inner surface (211b). The protruding structure (217) has a protruding base (218), a protruding surface (221), a protruding vertex (219), and a protruding height (220). The protruding vertex (219) is a point or a set of points of the protruding structure (217) that is closer to the micro-unit opening (205) than all other points of the protruding structure (217) are closer to the micro-unit opening (205). The protruding height (220) is the distance between the protruding base (218) and the protruding vertex (219). The protruding surface (221) is the surface of the protruding structure (217) excluding the protruding vertex (219) that is in contact with the electrophoretic medium (209). The micro-unit wall (212) has an inner wall surface (213) and an upper wall surface (214) of the micro-unit. The inner wall surface (213) is the surface of the micro-unit wall (212) of the micro-unit that is in contact with the electrophoretic medium (209), and the upper wall surface (214) is the surface of the micro-unit wall (212) of the micro-unit that is in contact with the sealing layer (206). The channel (215) has a channel height (216), which is 50% of the protrusion height (220). The unexposed micro-unit bottom inner surface (211b) contacts the raised base (218). The channel (215) is the volume between the exposed bottom inner surface (211a) of the microcell, the raised surface (221), and the inner wall surface (213) of the microcell. Specifically, a first electric field is applied between the first light-transmitting electrode layer (202) and the second light-transmitting electrode layer (207) via a first waveform, causing the charged pigment particles to move toward the channel (215), thereby causing the variable light transmission device (200) to switch to an open optical state. The charged pigment particles in the open optical state are located within the channel (215), and A second electric field is applied between the first light-transmitting electrode layer (202) and the second light-transmitting electrode layer (207) via a second waveform to cause the charged pigment particles (222) to move toward the first light-transmitting electrode layer (202) at a certain speed, the speed having a lateral component and resulting in a closed optical state, the second waveform including at least one positive voltage and at least one negative voltage, the second waveform having a net positive impulse or a net negative impulse, wherein the closed optical state has a lower percentage of light transmission than the open optical state.