Electrically driven variable transmittance film with very low haze and visible grid in transparent state

Abstract

A light attenuator providing a transparent light state and an absorptive dark state is used to selectively control light, particularly for smart glass applications. The light attenuator includes attenuating and transparent contiguous regions forming a repeating or quasi-repeating pattern. When the light attenuator is in the light state, the attenuated regions are visible, but the repeating pattern is large enough that an observer looks through the attenuator and does not see haze.

Description

[0001] Related Applications

[0002] This application claims priority to UK Patent Application No. 1914105.0 filed on September 30, 2019 and UK Patent Application No. 1914933.5 filed on October 16, 2019. All references, patents and patent applications disclosed herein are incorporated herein by reference in their entirety. Technical Field

[0003] The present invention relates to an electrophoretic device having a configuration providing a transparent optical state for selectively controlling light, particularly for smart glass applications. Background Art

[0004] There is a need for an electrically switchable electrophoretic device that is transparent to visible light and provides glass-like qualities in one or more light states, while strongly attenuating light in other light states. Glass-like qualities include providing very good clarity and light transmittance, very low haze, minimal tint perception in the transparent state, and minimal diffraction. In the prior art, available electrophoretic solutions have limitations on their functionality in some cases and inherent technical barriers in other cases.

[0005] In the applicant's EP2976676, the sizes of the apertures (transparent areas) and obstacles (light blocking areas) have their maximum sizes and pitches determined by the resolution of the typical observer's eye, so that the apertures and obstacles are small enough that their geometric shapes are not obvious in the front view. In the examples in the literature of its transparent state, its black charged particles are gathered and surrounded by discrete transparent apertures, and at the required viewing distance, the maximum angle of the aperture to the observer is 1 arc minute (corresponding to 290 microns at a viewing distance of 1 meter), and preferably 0.6 arc minutes (corresponding to 174.5 microns at 1 meter). The angle between the aperture pitch (i.e., the aperture and the area where the charged particles are gathered) can be twice these limits, but only to the extent that the geometry is not obvious in the front view.

[0006] Similarly, in the applicant's EP3281055 it is noted that the device (including smart windows) has a solid polymer structure embedded in its viewing area, which is at the scale of a microstructure and is invisible to the naked eye. An example of a smart glass device with a cavity pitch of 250 microns is given. If only viewed from a distance, the document theoretically allows cavities to reach 1,000 microns, however, the document limits the microstructure to being invisible in use. This restrictive constraint is similar to the earlier EP2976676 and is described as a maximum angle of 1 arc minute, preferably 0.6 arc minutes, to the observer at the desired viewing distance of the microfastener portion.

[0007] In US8183757, it is pointed out that when the colorant particles are gathered in the reservoir area, the colorant particles can color the visible area. The coloration caused by the colorant particles may hinder the neutral white or transparent optical state of the display. The device uses an opaque layer on the second electrode in each groove area. The black opaque layer in the groove (or reservoir) covers the colored aggregated particles. In the related patent US8384659, a hexagonal reservoir with a radius of 67.5 microns is shown in Figure 2E.

[0008] In the transparent light state of the prior art device, there is a perceptible hue corresponding to the color of the charged particles in the electrophoretic ink. Due to the micron-scale, discrete and dense distribution of holes or obstacles similar to halftone printing on paper or color displays, the observer's perception of the hue (including the black hue) is one of uniform hue. The pixel density of the latter is high enough to ensure that individual pixels cannot be distinguished even at close observation, and the light from adjacent pixels is seamlessly blended by the observer's eye. Summary of the invention

[0009] In an embodiment, a light attenuator (200, 203, 204) comprises a unit (300, 303, 304) having a first transparent substrate (190) and a second transparent substrate (190), the first transparent substrate (190) and the second transparent substrate (190) defining respective viewing surfaces (150, 153, 154) and having opposing major surfaces (i.e. parallel juxtaposed) with transparent electrodes (160) and being spaced apart (dimension 5) to provide a volume therebetween, the volume comprising a transparent polymer structure (100, 103, 104) and an electrophoretic ink (1, 2, 3), the ink comprising charged particles (10, 11, 12) dispersed in a transparent fluid (15, 16, 17), the charged particles moving between a first extreme light state and a second extreme light state in response to an electric field applied to the electrodes, in the first extreme light state the particles are most The particles are dispersed to a maximum extent within the cell to be located in a sunlight path for attenuating sunlight through the cell, and in a second extreme light state, the particles are maximally aggregated in locations (130, 133, 134) within the cell defined by the polymer structure to remove the particles from a sunlight path for transmitting sunlight through the cell and provide visual access, and in the second light state, the viewing surface of the light attenuator has a visible pattern of attenuation regions (20, 24) adjacent to transparent regions (30, 34), the attenuation regions and transparent regions being defined by the presence and absence of the aggregated particles, respectively, wherein each of the adjacent regions has a size (50, 55, 60, 65) of 0.3 mm or greater, and a center-to-center distance (40, 41) of adjacent attenuation regions or a center-to-center distance (45, 46) of adjacent transparent regions of 0.6 mm or greater.

[0010] Each of the regions in the pattern subtends an angle (80, 90) of more than two arc minutes at a distance of 0.5 M from the viewing surface (150), and a pair of adjacent regions subtends an angle (70) of more than four arc minutes.

[0011] In some embodiments, the pattern is a repeating pattern and the center-to-center distance is the same as the pitch. The repeating pattern is a switchable grid that is visible in the second light state and unrecognizable in the first light state. In some embodiments, the shortest distance or width (61) of the transparent area is 75% or more of the pitch, and the shortest distance (51) of the attenuation area is 25% or less. Preferably, the limits of the aforementioned rules are 80% and 20%, respectively, and more preferably 85% and 15%.

[0012] The transparent area in the front view of the embodiment is 60% or more, preferably 62% or more, more preferably 65% ​​or more, and most preferably 70% or more of the total effective (i.e., switchable) area, and the visible pattern includes discontinuous and / or continuous areas and can be perceived as a pattern of attenuation areas. The visible pattern is superimposed on the visual access. The color of the pattern or grid is the color of the charged particles. Preferably, the superimposed visible pattern or grid is designed to be aesthetically acceptable (or pleasing) by selecting the design of the positions of the aggregated charged particles in the polymer structure.

[0013] One of the regions is either: monodisperse or having a distribution of size and / or shape, and preferably the shape of the region is selected to minimize the chance of moiré fringes appearing in the visual access and includes selecting a shape whose boundaries are defined by applying a modulation function to a geometric shape.

[0014] In some embodiments, the center-to-center distance of adjacent attenuation regions and the center-to-center distance of adjacent transparent regions are 0.6 mm or greater.

[0015] In some embodiments, the center-to-center distance is, in order of preference: 0.62 mm or more, 0.65 mm or more, 0.7 mm or more, 0.8 mm or more, 1.0 mm or more, and most preferably 1.25 mm or more. Corresponding to the foregoing, the adjacent attenuation region and transparent region each have one or more dimensions, which are, in order of preference: 0.31 mm or more, 0.325 mm or more, 0.35 mm or more, 0.4 mm or more, 0.5 mm or more, and most preferably 0.625 mm or more.

[0016] The colorant of the charged particles includes one or more of the following: dye colorants, pigment colorants, strong light scattering materials, strong reflective materials, or strong absorbing materials, and the particles can be any color, including black or white.

[0017] A polymer structure separates the substrates and divides the volume into single-layer discrete cavities having polymer walls and filled with the electrophoretic ink, and preferably the polymer structure includes a sealing layer that seals the ink within the cavities.

[0018] In some embodiments, a color layer is selectively applied to the polymer wall so that in the viewing plane, the color of the wall region matches the color of the charged particles.

[0019] In an embodiment, the location of the aggregated charged particles is at the polymer wall, or the location of the aggregated charged particles is in a discrete liquid reservoir in the polymer structure and the location does not coincide with the wall, or the location of the aggregated charged particles is in a depression or channel between protrusions in the polymer structure, and the location may or may not coincide with the wall.

[0020] Electrophoretic inks have two or more charged particle types, including: positively charged, negatively charged, different electrophoretic mobilities, and / or different colors.

[0021] The electrophoretic ink has two charged particle types, each type having a different electrophoretic mobility and color from the other but the same charge polarity, and in the second optical state the two types separate when they are concentrated at the location with one type obscuring the other relative to one of the viewing surfaces.

[0022] Preferably, the optical attenuator provides at least one optical state between the first and second states by moving the charged particles between a collection site in the polymer structure and an opposing electrode to vary the degree of collection or dispersion, respectively.

[0023] A device, comprising one of the following: a window, a mirror, a light shutter, a light modulator, a variable light transmittance sheet, a variable light absorptance sheet, a variable light reflectance sheet, an electrophoretic visor for a vehicle, or a transparent display, contains a light attenuator. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, in which:

[0025] Figure 1a The embodiment 200 is shown in a first light state. The figure shows a front view thereof.

[0026] Figure 1b The embodiment 200 is shown in a second light state and is a three-dimensional view of the front side thereof.

[0027] Figure 1c A polymer structure 100 is shown and is a three-dimensional view of the front side thereof.

[0028] Figure 2a The embodiment 200 is shown in a second light state and is a front view.

[0029] Figure 2b The embodiment 200 is shown in a second light state and is a front view.

[0030] Figure 3 Embodiment 203 is shown in a second light state and is a cross-sectional view.

[0031] Figure 4 The embodiment 204 is shown in a second light state and is a front view. DETAILED DESCRIPTION

[0032] The embodiment achieves improved optical quality in its electrophoretic light attenuator by making its particles visible as a pattern or grid-like structure or array in its transparent light state. In this state, the colored charged particles are gathered in a limited area by a transparent polymer structure, so that the area between them transmits light. In the prior art, both the area of ​​aggregated particles and the transparent area are indistinguishable, but in the embodiment, both areas can be distinguished as different by the naked eye from a distance of at least 1M. The embodiment minimizes the fusion of the two areas by the observer, so that the scene observed through the attenuator is significantly less contaminated by the color or haze of the charged particles. The observer's perception of the front of the embodiment is a transparent glass with a colored grid (or array) structure. The colored grid (or array) structure can be selected to be aesthetically pleasing. In addition, by selecting the scale of the visible pattern or grid-like structure (or array), the light attenuator made of white particles does not appear blurry, but looks like a foreground white grid superimposed on the background scene. In addition, by using visible scales to design the transparent light state, the diffraction of light is greatly reduced.

[0033] The embodiments are described with reference to the accompanying drawings. Figures 1a to 1c as well as Figure 2a and 2b , different features of the same optical attenuator (200) are shown in a front view. Figure 1a shows the first light state with strong light decay, while Figure 1b , 2a and 2b show the transparent second optical state. Figure 1c The polymer structure of Example (200) is shown. Figure 3 Embodiment (203) is shown in cross section and is similar to embodiment (200). In these embodiments, the second optical state is caused by charged particles (10, 11) of electrophoretic ink being concentrated in channels (130, 133) between protrusions (110, 113) in the polymer structure (100, 103) by an applied electric field. Figure 4 A front view of an alternative embodiment (204) is shown having a different layout of the polymer structure (104) such that its charged particles (12) move across the polymer surface (117) to collect in discrete reservoirs or pits (134) in the second optical state.

[0034] In the figure, the optical attenuator (200, 203, 204) of the embodiment includes an electrophoretic cell (300, 303, 304) having two transparent substrates (190), each of which is coated with a transparent electrode (160) on one side. Figure 3 As shown, the major surfaces of the electrodes face each other and are parallel and juxtaposed. The opposing surfaces of the substrates form the viewing surfaces (150, 153, 154) of the cell. The substrates are spaced apart and the volume between them is the electro-optical layer of the device. The dimension indicating the spacing is (5) and is Figure 3 . In some embodiments, dimension (5) defines a cell gap. The electro-optic layer (or volume) includes a transparent polymer structure (100, 103, 104) and an electrophoretic ink (1, 2, 3). The electrophoretic ink includes charged particles (10, 11, 12) dispersed in an otherwise transparent fluid (15, 16, 17). The charged particles can be any color, including black (11), white (12), or red (13). The particles move between optical states defined by two extremes in response to an electric field applied to the electrodes. Figure 1a In the first extreme light state shown, the particles are maximally dispersed within the cell to lie in the path of sunlight passing through the cell so that the sunlight is attenuated and the viewing surface is the color of the particles. The first extreme light state corresponds to a dispersed state or maximum attenuation or an obscured or hidden state.

[0035] In the second extreme light state (such as Figure 1b , 2a , 2b, 3 and 4), the particles are maximally aggregated in the positions (130, 133, 134) defined by the polymer structure (100, 103, 104) within the unit. Figure 1c A three-dimensional view of the polymer structure (100) is shown. The channels (130) form interconnected depressions or spaces between the discrete protrusions (110) to confine the aggregated particles (10) in the second light state. The aggregated particles can fill the channels to a level shown as (115). This removes the particles from the path of sunlight passing through the cell so that the sunlight is transmitted without tinting (i.e., transmitted without encountering the colored particles), and the cell is transparent, providing visual access through the opening of the combined embodiment.

[0036] Figure 3 The second light state of the cell (303) shown in shows that light (1200) from the external environment passes through the protrusion (113) corresponding to the transparent area (shown in shading) and is emitted from the cell as light (1201) to illuminate the internal environment. In embodiment (203), light incident on the aggregated particle area is diffusely reflected by the white particles (11) in the channel (133), as shown by the incident light (1205) and the reflected light (1206), respectively. Figure 2aIn the illustrated cell (300), light incident on the aggregated particle region (20) is strongly absorbed by the black charged particles (10). Figure 4 In the illustrated cell (304), light incident on the aggregated particle region (24) is absorbed and diffusely reflected in the visible spectrum by the red charged particles (12). Regardless of the color of the charged particles, light incident on the aggregated particle region is not significantly transmitted, so the region is described herein as attenuated.

[0037] Figure 1b The invention shows that in a second extreme light state, the viewing surface (150) of the light attenuator has a visible pattern of attenuation regions (20) adjacent to (i.e., juxtaposed or parallel to) transparent regions (30), the attenuation regions (20) and the transparent regions (30) being defined by the presence or absence of aggregated particles, respectively, which in turn are defined by channels (130) and protrusions (110) of the polymer structure (the latter two being as shown in FIG. Figure 1c shown).

[0038] exist Figure 2a In the embodiment of the present invention, these attenuating (20) and transparent (30) adjacent areas are arranged so that each area has one or more dimensions of 0.3 mm or more (see (50) and (60)), and therefore, is visible or discernible or distinguishable as a part (or element) to the naked eye. In addition, the center-to-center distance (40) of adjacent attenuating areas or the center-to-center distance (45) of adjacent transparent areas is 0.6 mm or more. The viewing surface (150) has multiple adjacent areas and center-to-center distances and they form a visible pattern on its area.

[0039] Similarly, in Figure 4 In the embodiment of the present invention, the attenuating (24) and transparent (34) adjacent regions are arranged so that each region has one or more dimensions of 0.3 mm or greater (see (55) and (65)) and is therefore visible to the naked eye. In addition, the center-to-center distance (41) of adjacent attenuating regions or the center-to-center distance (46) of adjacent transparent regions is 0.6 mm or greater. The viewing surface (154) has multiple adjacent regions and center-to-center distances and they form a visible pattern on its area.

[0040] The center-to-center dimension of 0.6 mm is large enough to be visible to an observer with a visual acuity of 1.0 or greater at 1.0 M because the viewing distance results in an angular resolution of two arc minutes. The pattern is visible because the attenuation regions corresponding to the aggregated particles form distinguishable portions (or features) in the second light state when the attenuation regions have a center-to-center distance of 0.6 mm or greater and the transparent regions are in the spaces between adjacent attenuation regions. A visual analogy can be made with the graduation pattern on a steel ruler; graduations with a center-to-center distance of 0.5 mm (i.e., 0.5 millimeter divisions) are visible.

[0041] Although the size of each area of ​​the attenuation (20) and transparent (30) adjacent areas should be at least 0.3 mm or larger to be discernible by an observer at 1.0 M and have a center-to-center dimension of at least 0.6 mm, it is also desirable that the size of each area of ​​the attenuation (20) and transparent (30) adjacent areas should not be so large that the pigment load of the transparent area cannot be filled into the attenuation area. This is because, in most configurations, the area above the transparent area increases with the square of the size, while the surface area of ​​the attenuation area that will be filled with particles increases roughly linearly with size. If the size grows too large, the particles cannot be effectively filled into the attenuation area, resulting in a darker transparent state. It has also been found that larger sizes require higher voltages to achieve good clearing. Experience with various size sizes shows that the area of ​​the attenuation (20) and transparent (30) adjacent areas should not exceed 3 cm. The corresponding maximum center-to-center dimension is approximately 6 cm. Therefore, each repetition of attenuation (20) and transparent (30) adjacent areas should have dimensions (50, 55 and 60, 65) between 0.3 mm and 3 cm, while the center-to-center distance (40, 41) of adjacent attenuation areas or the center-to-center distance (45, 46) of adjacent transparent areas is between 0.6 mm and 6 cm.

[0042] In an embodiment, in the second light state, and for multiple instances, the center-to-center distance of adjacent attenuation areas, or the center-to-center distance of adjacent transparent areas, is preferably in the order of: 0.62mm to 5.8cm, 0.65mm to 5.5cm, 0.7mm to 5.14cm, 0.8mm to 4.5cm, 1.0mm to 3.6cm, and most preferably 1.25mm to 3cm. Corresponding to the foregoing, adjacent attenuation areas and transparent areas each have one or more sizes, in the preferred order of: 0.31mm to 2.9cm, 0.325mm to 2.75cm, 0.35mm to 2.57cm, 0.4mm to 2.25cm, 0.5mm to 1.8cm, and most preferably 0.625mm to 1.5cm.

[0043] In an embodiment, the transparent area in the front view is 60% or more, preferably 62% or more, more preferably 65% ​​or more, and most preferably 70% or more of the total active (i.e., switchable) area. The attenuation area is the remainder in each case. The transparent area, the attenuation area, and the distinguishable parts and patterns in the corresponding second light state are defined by the polymer structure of the device.

[0044] exist Figure 2bIn the example shown, the vehicle is equipped with an embodiment for its side windows and sunroof. The charged particles (10) are not drawn, but the corresponding attenuation areas (20) are shown. Through these openings in the second light state, the occupants of the vehicle typically have a viewing distance of 0.5M (or less). The angle subtended by the attenuation area (20) is represented by (80), while the angle of the transparent area (30) is represented by the number (90). The adjacent attenuation area (20) and transparent area (30) are shown as subtending an angle (70). When the distance (edge ​​to edge) of the adjacent areas is 0.6mm or greater, at a viewing distance of 0.5M, the adjacent area pair (20) + (30) subtends more than 4.1 arc minutes or 4.1 times the minimum angular resolution of an observer with 1.0 vision. The angle is calculated as follows:

[0045] Subtended angle = tan(0.6 / 500)

[0046] =0.0012 (radians)

[0047] =4.125 (arc minutes)

[0048] The corresponding calculation for the subtended angles (80) and (90) at the smallest dimension of 0.3 mm in the visible pattern in the example is 2.06 arc minutes:

[0049] Subtended angle = tan(0.3 / 500)

[0050] =0.0006 (radians)

[0051] =2.063 (arc minutes)

[0052] Since the subtending angles of (70), (80) and (90) are multiples of the minimum resolution of an observer (having 1.0 visual acuity), the embodiment (200) has a distinct visible pattern when viewed at 0.5 M. The attenuation region (20) (comprising the black aggregated particles (10)) can be viewed as a black grid (or array) with transparent openings, similar to a metal mesh with similar openings and walls. The perception of the black hue by an object viewed through this embodiment is negligible because the observer's eye does not blend the black grid region with the view through the transparent region.

[0053] In contrast, the motivation for prior art electrophoretic, optical attenuator devices having polymer structures throughout their electro-optical layers is to arrange their structures so that the structures (or the associated patterns in the light states defined by the structures) are small enough that an observer cannot perceive them. In applicant's EP2976676, the dimensions of the apertures (transparent areas) and obstacles (light blocking areas) have their maximum dimensions and pitches (similar to the repeated center-to-center distances) determined by the resolution of a typical observer's eye, so that at a viewing distance of 0.5M, their areas subtend an angle of less than 1 arc minute, which is equivalent to less than 0.145mm, to avoid the pattern being noticeable to the observer.

[0054] In embodiments, in the second light state, the center-to-center distance of the attenuated regions or transparent regions (defined by the presence or absence of aggregated particles, respectively, which in turn are defined by the polymer structure) can be random or have more than one value. In other embodiments, the center-to-center distance repeats uniformly in one direction and is the same as the pitch of the repeating pattern visible to the naked eye.

[0055] Figure 2a The pitch (1040) of adjacent attenuation and transparent regions in the top to bottom direction is shown. It is longer than the pitch (1041) in the left to right direction. In an embodiment (200), the shortest distance or width (61) of the transparent region can be 75% or more of the pitch (1041), and the shortest distance (51) of the attenuation region can be 25% or less. Preferably, the limits of the aforementioned rules are 80% and 20%, respectively, and more preferably 85% and 15%. Figure 4 The pitch (1045) of adjacent attenuation and transparent regions of an alternative embodiment (204) is shown.

[0056] In the embodiment (200), the transparent region (30) is discrete and the attenuation region (20) is continuous, see Figure 2a . Figure 4 The embodiment (204) in shows the opposite relationship: the attenuation region (24) is discrete and the transparent region (34) is continuous. In both embodiments, the center-to-center distances of adjacent discrete regions are easily identified (see (45) and (41) respectively). Figure 2a Medium size (40) and Figure 4 As shown in the dimension (46) in , the corresponding center-to-center distance of the continuous area is related to the area between the discrete areas. In this regard, an embodiment can be defined by the center-to-center distance of both its attenuation area and its transparent area.

[0057] In the second light state, a visible pattern formed by attenuation and transparent areas in the front face of the embodiment is superimposed on the view through the front face. The visible pattern is in the foreground and the view is in the background. The eye resolves the visible pattern as a grid (or array) and sees it as a grid of opaque areas that are the color of the particles. In an embodiment, the grid can be made unrecognizable on the front face when switched to the first light state. The charged particles in the first light state are evenly dispersed and opposite to the location where the particles are received when the particles are aggregated in the second light state. Preferably, the superimposed visible pattern or grid (or array) is designed to be aesthetically acceptable (or pleasing) by selecting the design of the locations where the charged particles are aggregated in the polymer structure.

[0058] The polymer structure of one embodiment, including locations for aggregating charged particles, is formed at least in part in an imprinting, molding or replication step. Examples of molding techniques are described in the applicant's EP2976676 entitled "An Electrophoretic Device Having a Transparent Light State". To minimize haze in an embodiment, the refractive index of the polymer structure (100, 103, 104) matches that of the suspending fluid (15, 16, 17) of the ink, preferably within 0.005, more preferably 0.002, and most preferably 0.001.

[0059] The replicated polymer structure has depressions, channels, pits, grooves or reservoirs corresponding to the attenuation regions and protrusions, funnel-shaped inclined surfaces or intermediate convex surfaces corresponding to the transparent regions. The shapes of the two regions in the front view and the center-to-center distance are defined by the polymer structure. Any type of region (i.e. attenuation or transparency) can be monodisperse or have a distribution of size and / or shape. Examples of devices with channels and protrusions can be found in the applicant's EP2976676; devices with reservoirs and funnel-shaped inclined surfaces in HP's US8184357; and devices with grooves and convex surfaces in HP's US7,957,054. The latter refers to a dielectric layer with grooves, but the dielectric layer is a polymer structure, and in its transparent light state, its aggregated particles are located at the grooves (or pits, pores or holes) in the layer. In an alternative embodiment, the polymer structure provides a wall, and in the second light state, the charged particles are gathered on the wall. These devices are called dielectrophoresis, and an example is shown in US2018 / 0364542A1 by E Ink.

[0060] In some embodiments, the shape of the regions is selected to minimize the chance of moiré fringes, which would otherwise appear if the opaque grid of embodiments (i.e., strongly attenuating regions arranged in an array) were overlaid on a similar pattern in the background viewed through the front. To avoid or minimize moiré fringes, the attenuation regions preferably avoid patterns of consecutive parallel lines. In this regard, as Figure 2a The honeycomb structure shown is preferred because it is less likely to resemble a grid structure encountered in background scenes. However, in a more preferred embodiment, a modulation function is applied to a geometric shape. For example, in an alternative embodiment, Figure 1c The boundaries of the hexagonal protrusions (110) of the polymer structure (110) shown are modulated with sine waves to have wavy sides rather than flat surfaces. The visible pattern of this alternative embodiment features wavy segments rather than straight segments and is therefore less likely to cause moire fringes when viewing a scene.

[0061] In some embodiments, two or more devices are stacked and to avoid moiré fringes, each device has a different grid (or array) pattern. In one embodiment example, a visor in a vehicle includes a stack of two devices to achieve very low transmittance when both devices are operating in their respective maximum attenuation light states. This embodiment achieves the corresponding maximum light transmittance state when both devices are in their light transmittance states. In some embodiments, to avoid moiré fringes, the attenuation regions (and transparent regions) of both devices are precisely aligned, however, in a preferred embodiment, the shape of the light attenuation regions is selected to be different between the devices. For example, the attenuation region of one device has a honeycomb structure, while the other device has a monodisperse shape, such as a sphere, or the boundaries of one device are modulated by a sine wave.

[0062] exist Figure 3 In the embodiment shown (203), the polymer structure (103) uses integrated pillars (123) to separate the substrates of the optical attenuator. The pillars (123) define the cell gap, and the vertical distance between the substrates is shown as dimension (5). The cell is sealed on all sides with a polymer seal (not shown). Figure 1c The pillars (120) on the polymer structure (100) shown have similar functions. In other embodiments, the polymer structure uses polymer walls to separate the substrates of the light attenuator and divide the volume between them into a single layer of discrete cavities filled with electrophoretic ink. In this case, the walls define the cell gap.

[0063] In an embodiment, the cell gap ( Figure 3 The size (5) in the nanostructured carbon nanotubes is 7.5 to 300 microns, preferably 13.5 to 200 microns, more preferably 16.5 to 150 microns, and most preferably 18 to 125 microns.

[0064] Preferably, a color layer is selectively applied to the top of the polymer wall and / or pillars so that in the viewing plane, the color of the wall area matches the color and transmittance of the attenuated area in the second light state. Preferably, the polymer structure includes a sealing layer or sealing mechanism to seal the fluid in each cavity. The sealing layer is preferably combined with (or includes) the color layer on the polymer wall. In some embodiments, the sealed cavities are independent of each other and can be described as a unit, and the light attenuator comprises a single layer of units.

[0065] In some embodiments, in the second light state, the polymer structure will position the aggregated charged particles against or adjacent to its polymer wall, including in a channel adjacent to its wall. In such an embodiment, there are aggregated particles on each side of the polymer wall portion for the corresponding cavity on each side. Preferably, the polymer wall has an attenuation layer and is colored to match the particles; the attenuation area of ​​the aggregated particles will then appear continuous on the front of the device, while the transparent area will be discrete. Optionally, the polymer wall can be transparent, and if so, preferably as narrow as possible, and preferably with a width in the range of 15 microns to 75 microns. In the latter case, the attenuation area in the second light state is discontinuous.

[0066] In other embodiments, in the second light state, the polymer structure positions the aggregated charged particles in discrete reservoirs that do not coincide with the walls. The attenuation regions are discrete and surrounded by continuous transparent regions. Preferably, the walls are as narrow as possible and remain transparent so that the attenuation regions in the second light state appear continuous. Alternatively, the walls may have a colored layer.

[0067] In a more preferred embodiment, the aggregated charged particles are located in depressions or channels between protrusions in the polymer structure, and this location may or may not coincide with the wall. The transparent region is discrete, while the attenuation region is continuous. Preferably, the wall has an attenuation layer in embodiments where the wall coincides with the location of the aggregated particles, or the wall is transparent in the case where they do not coincide.

[0068] The cavity may contain a single transparent region and a single attenuation region or multiple or a portion of either. The cavity may be uniform and may be repeated or have differences in pitch. The center-to-center distance between adjacent cavities may be greater than, equal to, or less than the center-to-center distance of the transparent or attenuation region defined by the aggregated charged particles in the second light state. The polymer walls of the cavity may also form a visible grid on the front of the embodiment, but the grid is not switchable. It should be understood that it is advantageous to arrange the polymer wall with the attenuation layer as close as possible to the location of the aggregated particles. Alternatively, it is advantageous to arrange the transparent wall primarily in the transparent region of the second light state.

[0069] In some units, a color mask (i.e., a color layer) different from the color of the charged particles is selectively applied to the surface of the polymer structure at the location where the particles are gathered (i.e., the attenuation area) in the second light state. The color mask area corresponds to the attenuation area and thus forms a visible pattern or grid in an embodiment. In the observation surface on the same side as the color mask, in the second light state, the color of the location obscures the color of the gathered charged particles. An embodiment with white charged particles can avoid diffuse reflection from its attenuation area (i.e., the area of ​​gathered charged particles) in the second light state by covering these areas with a black mask printed on the polymer structure or on the surface of the substrate on the same side. Alternatively, a color mask can be applied to an opposite area on the polymer structure or to an opposite substrate to cover another observation surface. Similarly, both sides can be selectively printed to cover or minimize diffuse reflection or transmission from the area of ​​gathered particles in the second light state. In an embodiment, the color mask is defined by locations (130, 133, 134) in the polymer structure (100, 103, 104) that define aggregated charged particles (10, 11) in a second optical state and are therefore visible to the naked eye when viewed from a face adjacent thereto.

[0070] In an embodiment, the electrophoretic ink may have one, two or more types of charged particles, including: positively charged, negatively charged, different electrophoretic mobilities, and / or different colors, or any combination of these. The colorant that the charged particles have includes one or more of the following: dye colorants, pigment colorants, strong light scattering materials, strong reflective materials, or strong absorbing materials. In some embodiments, the electrophoretic ink has two types of charged particles, each type of electrophoretic mobility and color is different from each other, but the charge polarity is the same. In the second light state, the two types separate when they are gathered at this position in the polymer structure, with one type covering the other type relative to the viewing surface on the same side. This is an alternative to applying a color mask to the position described in the previous paragraph. A small number of black charged particles with higher electrophoretic mobility can be used to cover charged particles of different colors, such as a majority of white particles with lower electrophoretic mobility.

[0071] Preferably, the light attenuator provides at least one light state between the first and second states by moving the charged particles between the aggregation location in the polymer structure and the relative electrode to change the degree of aggregation or dispersion, respectively. Once the particles begin to aggregate at the provided location, a visible pattern will become apparent in the intermediate light state. In embodiments where the charged particles are a color other than black (e.g., white), the haze will be minimal in the second light state and increase as the intermediate light state approaches the first light state. In some embodiments, the first light state is very hazy to provide a privacy function.

Claims

1. An optical attenuator (200, 203, 204) comprising a unit (300, 303, 304) having a first transparent substrate (190) and a second transparent substrate (190), the first transparent substrate (190) and the second transparent substrate (190) defining respective viewing surfaces (150, 153, 154) and having opposing major surfaces with transparent electrodes (160), and being spaced apart (5) to provide a volume therebetween, the volume containing a transparent polymer structure (100, 103, 104) and an electrophoretic ink (1, 2, 3), the ink comprising charged particles (10, 11, 12) dispersed in a transparent fluid (15, 16, 17), The charged particles move in response to an electric field applied to the electrodes between a first extreme light state in which the particles are maximally dispersed within the cell to lie in a sunlight path that attenuates sunlight passing through the cell and a second extreme light state in which the particles are maximally concentrated within the cell in locations (130, 133, 134) defined by the polymer structure to remove the particles from a sunlight path that transmits sunlight through the cell and provide visual access, and In the second extreme light state, the viewing surface of the light attenuator has a visible pattern of attenuated regions (20, 24) adjacent to transparent regions (30, 34), the attenuated regions and transparent regions being defined by the presence and absence, respectively, of aggregated particles, in, The repeating unit of the visible pattern consists of attenuation areas and transparent areas, and the dimensions (50, 55 and 60, 65) used therein are between 0.3 mm and 3 cm, while the center-to-center distance (40, 41) of adjacent attenuation areas or the center-to-center distance (45, 46) of adjacent transparent areas is between 0.6 mm and 6 cm.

2. The optical attenuator of claim 1, wherein each of said regions in said pattern subtends an angle (80, 90) exceeding two arc minutes at a distance of 0.5 M from said viewing surface, and an adjacent region subtends an angle (70) exceeding four arc minutes.

3. The optical attenuator according to claim 1, wherein: The pattern is a repeating pattern and the center to center distance (40, 45) is the same as the pitch (1041).

4. The optical attenuator according to claim 1, wherein: The transparent area in front view is at least 60% of the total effective switchable area and the visible pattern can be perceived as a pattern of attenuated areas.

5. The optical attenuator according to claim 4, wherein: The visible pattern is superimposed on the visual access.

6. The optical attenuator according to claim 3, wherein: The repeating pattern is a switchable grid visible in the second extreme light state and unrecognizable in the first extreme light state, and the grid is the color of the charged particles.

7. The optical attenuator according to claim 1, wherein: The shape of the regions is chosen to minimize the probability and size distribution of moiré fringes.

8. The optical attenuator according to claim 1, wherein: The center-to-center distance of the adjacent attenuation areas and the center-to-center distance of the adjacent transparent areas are 0.6 mm or greater.

9. The optical attenuator according to claim 1, wherein: The center-to-center distance is 0.62 mm to 5.8 cm, and the adjacent attenuation areas and transparent areas each have a size of 0.31 mm to 2.9 cm.

10. The optical attenuator according to claim 3, wherein: The distance of the transparent area (61) is 75% or more of the pitch (1041), and the distance of the attenuation area (51) is 25% or less.

11. The optical attenuator according to claim 1, wherein: The polymer structure separates the substrates and divides the volume into single-layer discrete cavities having polymer walls and filled with the electrophoretic ink.

12. The optical attenuator according to claim 11, wherein: A color layer is selectively applied to the polymer wall so that in the viewing plane the color of the wall region matches the color of the attenuation region.

13. The optical attenuator according to claim 11, wherein: The location where the charged particles are concentrated is at the polymer wall.

14. The optical attenuator according to claim 11, wherein: The locations where the charged particles are aggregated are in discrete reservoirs in the polymer structure and the locations do not coincide with the walls.

15. The optical attenuator according to claim 11, wherein: The locations where the charged particles are accumulated are in the depressions or channels between the protrusions in the polymer structure, and the locations may or may not coincide with the walls.

16. The optical attenuator according to claim 1, wherein: A color mask is selectively applied to the surface of the substrate or electrode defined by the positions, and in the observation surface on the same side as the color mask, the color of the positions is different from the color of the charged particles, and in the second extreme light state, the color mask covers the aggregated charged particles and forms an area corresponding to the attenuation area.

17. The optical attenuator according to claim 1, wherein: The electrophoretic ink has two or more types of charged particles, including: positively charged, negatively charged, different electrophoretic mobilities, and / or different colors.

18. The optical attenuator according to claim 17, wherein: The electrophoretic ink has two charged particle types, each type having a different electrophoretic mobility and color from the other but the same charge polarity, and in a second extreme light state, the two types separate when they are concentrated at the location with one type obscuring the other relative to one of the viewing surfaces.

19. The optical attenuator according to claim 1, wherein: The charged particles move between the first extreme light state and the second extreme light state to provide at least one light state between the first extreme light state and the second extreme light state.

20. The optical attenuator according to claim 4, wherein: The transparent area in the front view is at least 62% of the total effective switchable area.

21. The optical attenuator according to claim 4, wherein: The transparent area in front view is at least 65% of the total effective switchable area.

22. The optical attenuator according to claim 4, wherein: The transparent area in front view is at least 70% of the total active switchable area.

23. The optical attenuator according to claim 1, wherein: The center-to-center distance is 0.65 mm to 5.5 cm, and the adjacent attenuation areas and transparent areas each have a size of 0.325 mm to 2.75 cm.

24. The optical attenuator according to claim 1, wherein The center-to-center distance is 0.7 mm to 5.14 cm, and the adjacent attenuation areas and transparent areas each have a size of 0.35 mm to 2.57 cm.

25. The optical attenuator according to claim 1, wherein The center-to-center distance is 0.8 mm to 4.5 cm, and the adjacent attenuation areas and transparent areas each have a size of 0.4 mm to 2.25 cm.

26. The optical attenuator according to claim 1, wherein The center-to-center distance is 1.0 mm to 3.6 cm, and the adjacent attenuation areas and transparent areas each have a size of 0.5 mm to 1.8 cm.

27. The optical attenuator according to claim 1, wherein: The center-to-center distance is 1.25 mm to 3 cm, and the adjacent attenuation areas and transparent areas each have a size of 0.625 mm to 1.5 cm.

28. The optical attenuator according to claim 11, wherein: And the polymer structure includes a sealing layer that seals the ink within the cavity.

29. Use of the light attenuator in the following devices: a window, a mirror, a light shutter, a light modulator, a variable light transmittance sheet, a variable light absorption sheet, a variable light reflectance sheet, an electrophoretic visor of a vehicle, or a transparent display, which comprises the light attenuator according to any one of claims 1 to 28.

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