Light modulator with bonding structure embedded in viewing area

Abstract

Providing a switchable light modulator device SOLUTION: A switchable light modulator device (201, 202, 203, 204, 205) comprising a first substrate (101, 102, 103) with opposing major surfaces spaced apart by one or more polymer structures and a second substrate (141, 142, 143, 144), wherein each of the one or more polymer structures comprises two or more portions and defines wall features (21b, 22b, 23b) for a plurality of cavities (111, 112, 113, 114); The cavities seal the fluids (71, 72, 73, 74) or gels in separate volumes. Each of the one or more polymeric structures comprises a mold portion (21, 22, 23) bonded to the first substrate and defining a recess (31, 32, 33), and a cast portion, wherein the cast portion fills the recess and is bonded to the second substrate and a surface of the recess, and wherein the cast portion is defined by the surface of the recess and the second substrate and replicates both surfaces.SELECTED DRAWING: None

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This application claims the benefit of and priority to UK Patent Application No. 2003224.9 filed March 5, 2020, the contents of which are incorporated herein by reference in their entirety.

[0002] FIELD OF THE INVENTION The present invention relates to optically switchable light modulator devices comprising a fluid or gel layer, particularly devices with flexible substrates. Such devices preferably have polymer structures in the viewing area to maintain the gap between the substrates and to aid in handling during use, including bending and lamination to glass or another substrate. Example product applications include switchable smart windows, outdoor information displays, and flexible display devices. [Background technology]

[0003] The present invention relates to light modulators, also referred to as variable transmission windows, mirrors, and similar devices, designed to modulate the amount of light or other electromagnetic radiation passing through them. For convenience, the term "light" may be generally used herein, but this term should be understood in a broad sense to include electromagnetic radiation at non-visible wavelengths. For example, the present invention may be applied to provide windows that can modulate infrared radiation to control the temperature within a building. More specifically, the present invention relates to light modulators that use particle-based electrophoretic media to control light modulation. Examples of electrophoretic media that can be incorporated into various embodiments of the present invention include those described, for example, in U.S. Pat. No. 10,809,590 and U.S. Patent Publication No. 2018 / 0366069 (the contents of both of which are incorporated herein by reference in their entireties).

[0004] Prior art solutions that have polymer structures within a fluid or gel layer and are suitable for use with the present invention include U.S. Pat. No. 8,508,695 (Vlyte Innovations Ltd.), which discloses dispersing fluid droplets (1-5 microns in diameter) within a continuous polymer matrix that is cured in place on both substrates to contain liquid crystals. Additionally, U.S. Pat. No. 10,809,590 (E Ink Corporation) discloses microencapsulating fluid droplets and deforming them to form a monolayer of tightly packed polymer shells within a polymer matrix on one substrate, followed by applying an adhesive layer to bond the encapsulation layer to the substrate. European Patent No. 1,264,210 (E Ink California) also discloses embossing a microcup structure on one substrate, filling the cups with a fluid having a polymerizable component, polymerizing the component to form a sealing layer on the fluid / cup surface, and then applying an adhesive layer to bond to a second substrate. Additionally, EP 2976676 (Vlyte Innovations Ltd.) discloses forming a wall structure on one substrate, coating the top of the walls with an adhesive, filling the cavities defined by the walls with a fluid, and polymerizing the adhesive to bond the top of the walls to an opposing substrate.

[0005] Many of these prior art solutions impose limitations in order to provide a viable solution for isolating one specific fluid (e.g., liquid crystal (LC)) for one specific application (e.g., switchable LC films). To do this, all of the above solutions expose the electro-optical fluid to a pre-polymer component and a polymerization step. This forces compromises and adds complexity. For example, the electro-optical fluid component must neither participate in nor interfere with the polymerization, and the pre-polymer component must phase separate from the fluid upon polymerization and somehow form a solid polymer structure in a defined area (e.g., only on the fluid surface of the microcups). In addition, generating strong chemical bonds between the surface and the substrate in the presence of the fluid can be difficult because the fluid preferentially wets the surface and can impair peel adhesion. Furthermore, residual components, including unused monomers, low-molecular-weight polymers, and nanoparticles, from the polymerization step performed in contact with the fluid may exist, which can contaminate or otherwise impair the switching of the electro-optical fluid. All of these conditions can lead to failure of the final product due to lack of optical activity, delamination, or leakage of internal fluids.

[0006] In EP 3281055 (Vlyte Innovations Ltd.), the electro-optical fluid is not subjected to a polymerization step. EP 3281055 describes a flexible device comprising solid polymer microstructures embedded in its viewing area, the microstructures being on both substrates. The microstructures join (i.e., fasten) the device's substrates together by engaging with each other along lengths perpendicular to the substrates. The joined microstructures incorporate wall structures that divide the device's fluid layer into separate, volumetric monolayers contained within corresponding cavities. This provides the device with considerable structural strength. In the described method, mating microstructures (i.e., male and female portions) are formed on each substrate, then precisely aligned with each other and joined with an interference fit that seals the fluid layer within the cavity. As previously described, the electro-optical fluid is not subjected to a polymerization step. A limitation of the method is that it requires precise alignment and dimensional stability in the X and Y axes of the surfaces to be joined over large distances (typically over a meter in smart glass applications).

[0007] Particle-based electrophoretic displays, in which a plurality of charged particles migrate through a suspending fluid under the influence of an electric field, have been the subject of intensive research and development over the past few years. Compared to liquid crystal displays, such displays can have attributes of good brightness and contrast, wide viewing angles, state bistability, and low power consumption. The terms "bistable" and "bistable" are used herein in their conventional sense in the art to refer to displays comprising display elements having first and second display states that differ in at least one optical property, such that any given element can be driven into either its first or second display state with a finite-duration address pulse and then persists in that state for at least several times, e.g., at least four times, the minimum duration of the address pulse required to change the state of the display element after the address pulse has terminated. Published U.S. Patent Application No. 2002 / 0180687 shows that some particle-based electrophoretic displays capable of gray scale are stable not only in their extreme black and white states but also in their intermediate gray states, and the same is true for several other types of electro-optic displays. Displays of this type are properly called "multistable" rather than bistable, although for convenience the term "bistable" may be used herein to encompass both bistable and multistable displays.

[0008] As mentioned above, electrophoretic media require the presence of a suspending fluid. In most prior art electrophoretic media, this suspending fluid is liquid, but electrophoretic media can also be produced using a gaseous suspending fluid. See, for example, Kitamura, T., et al., "Electrical toner movement for electronic paper-like display," IDW Japan, 2001, Paper HCS1-1, and Yamaguchi, Y., et al., "Toner display using insulative particles charged triboelectrically," IDW Japan, 2001, Paper AMD4-4. See also European Patent Applications Nos. 1,429,178, 1,462,847, 1,482,354, International Applications Nos. WO2004 / 090626, WO2004 / 079442, WO2004 / 077140, WO2004 / 059379, WO2004 / 055586, WO2004 / 008239, WO2004 / 006006, WO2004 / 001498, WO03 / 091799, and WO03 / 088495. Such gas-based electrophoretic media are believed to be susceptible to the same types of problems as liquid-based electrophoretic media due to particle settling when used in an orientation that allows for such settling, for example, in signs where the medium is placed on a vertical surface. Indeed, particle settling is believed to be a more severe problem in gas-based electrophoretic media than in liquid-based ones, because the lower viscosity of gaseous suspending fluids compared to liquid ones allows for more rapid settling of electrophoretic particles.

[0009] Numerous patents and applications assigned to or in the name of Massachusetts Institute of Technology (MIT), E Ink Corporation, E Ink California, LLC, and related companies describe various techniques used in encapsulated and microcell electrophoretic and other electro-optic media. Encapsulated electrophoretic media comprise a multitude of small capsules, each of which itself comprises an internal phase containing electrophoretically movable particles in a fluid medium and a capsule wall surrounding the internal phase. Typically, the capsules are themselves held within a polymer binder to form a coherent layer positioned between two electrodes. In microcell electrophoretic displays, the charged particles and fluid are not encapsulated within microcapsules, but instead are held within 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, e.g., U.S. Pat. Nos. 7,002,728 and 7,679,814). (b) Capsules, binders, and encapsulation processes (see, e.g., U.S. Patent Nos. 6,922,276 and 7,411,719) (c) Microcell structures, wall materials, and methods of forming the microcells (see, e.g., U.S. Patent Nos. 7,072,095 and 9,279,906) (d) Methods for filling and sealing microcells (see, e.g., U.S. Patent Nos. 7,144,942 and 7,715,088) (e) Films and subassemblies containing electro-optical materials (see, e.g., U.S. Patent Nos. 6,982,178 and 7,839,564) (f) Backplanes, adhesive layers, and other auxiliary layers and methods used in displays (see, e.g., U.S. Pat. Nos. 7,116,318 and 7,535,624) (g) Color formation and color control (see, e.g., U.S. Patent Nos. 7,075,502 and 7,839,564) (h) Methods of driving displays (see, e.g., U.S. Patent Nos. 7,012,600 and 7,453,445) (i) Display applications (see, e.g., U.S. Patent Nos. 7,312,784 and 8,009,348) (j) Non-electrophoretic displays (see, e.g., U.S. Pat. No. 6,241,921 and U.S. Patent Application Publication No. 2015 / 0277160), and non-display applications of encapsulation and microcell technology (see, e.g., U.S. Patent Application Publication Nos. 2015 / 0005720 and 2016 / 0012710).

[0010] Many of the aforementioned patents and applications recognize that the walls surrounding the separate microcapsules in an encapsulated electrophoretic medium may be replaced with a continuous phase, thus producing a so-called polymer-dispersed electrophoretic display, in which the electrophoretic medium comprises a plurality of separate droplets of electrophoretic fluid and a continuous phase of polymer material, and the separate droplets of electrophoretic fluid in such a polymer-dispersed electrophoretic display may be considered capsules or microcapsules even though no separate capsule membrane is associated with each individual droplet. See, for example, the aforementioned 2002 / 0131147. Therefore, for purposes of this application, such polymer-dispersed electrophoretic media are considered a subspecies of encapsulated electrophoretic media.

[0011] A related type of electrophoretic display is the so-called "microcell electrophoretic display." In a microcell electrophoretic display, the charged particles and suspending fluid are not encapsulated in microcapsules, but instead are held within a plurality of 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 No. 2002 / 0075556, both assigned to SiPix Imaging, Inc.

[0012] Electrophoretic media are often opaque (e.g., because in many electrophoretic media, the particles substantially block the transmission of visible light through the display) and operate in a reflective mode. This functionality is illustrated in FIG. 5A, where the reflectance of light striking the surface is modulated by using a suitable voltage to move black or white charged particles toward the viewing surface. However, electrophoretic devices can be made to operate in a so-called "shutter mode," where one display state is substantially opaque and one is light-transmitting. See, for example, the aforementioned U.S. Patents 6,130,774 and 6,172,798, and U.S. Patents 5,872,552, 6,144,361, 6,271,823, 6,225,971, and 6,184,856. Dielectrophoretic displays, which are similar to electrophoretic displays but rely on variations in electric field strength, can operate in a similar mode (see U.S. Pat. No. 4,418,346). Other types of electro-optic displays may also be capable of operating in shutter mode. In particular, when this "shutter-mode" electrophoretic device is constructed on a transparent substrate, it is possible to modulate the transmission of light through the device.

[0013] Encapsulated or microcell electrophoretic displays typically do not suffer from the clustering and settling failure modes of conventional electrophoretic devices and offer additional advantages, such as the ability to print or coat the display on a variety of flexible and rigid substrates. (The use of the word "printing" is intended to include all forms of printing and coating, including, but not limited to, pre-metered coating, e.g., patch die coating, slot or extrusion coating, slide or cascade coating, curtain coating, roll coating, e.g., knife-over-roll coating, forward and reverse roll coating, gravure coating, dip coating, spray coating, meniscus coating, spin coating, brush coating, air knife coating, silk screen printing processes, electrostatic printing processes, thermal printing processes, inkjet printing processes, electrophoretic deposition, and other similar techniques.) Thus, the resulting display can be flexible. Furthermore, because the display medium can be printed (using a variety of methods), the display itself can be made inexpensively.

[0014] One potentially important market for electrophoretic media is windows with variable light transmission. As energy performance of buildings and vehicles becomes increasingly important, electrophoretic media could be used as a coating on windows, allowing a percentage of incident radiation to be transmitted through an electronically controlled window by varying the optical state of the electrophoretic media. Effective implementation of such "variable transmittance" ("VT") technology in buildings is expected to provide increased occupant comfort by: (1) reducing unwanted heating effects during high outdoor temperatures (thus reducing the amount of energy required for cooling, the size of air conditioning equipment, and peak electrical demand); (2) increasing the use of natural daylight (thus reducing the energy used for lighting and peak electrical demand); and (3) increasing both thermal and visual comfort. Further benefits would be expected to accrue in automobiles, where the ratio of glossy surface to enclosed volume is significantly greater than in typical buildings. Specifically, effective implementation of VT technology in automobiles is expected to provide not only the aforementioned benefits, but also (1) increased driving safety, (2) reduced glare, (3) enhanced mirror performance (by using electro-optical coatings on the mirrors), and (4) increased ability to use head-up displays. Other potential applications of VT technology include privacy glass and glare protection in electronic devices. Other potential applications of VT technology include privacy glass and glare protection in electronic devices. [Prior art documents] [Patent documents]

[0015] [Patent Document 1] U.S. Patent No. 8,508,695 [Patent Document 2] U.S. Patent No. 10,809,590 [Patent Document 3] European Patent No. 3281055 Summary of the Invention [Means for solving the problem]

[0016] Described herein are improved architectures for switchable light modulators that can be used for windows, mirrors, displays, sunshades, or signs, among many other applications. In particular, the described designs are more robust than variable transmission devices such as electrochromic films and provide a better viewing experience due to improved clear (open state) with reduced haze.

[0017] In a first aspect, a switchable light modulator includes a first substrate having a first major surface, a second substrate having a second major surface, and a polymer wall structure having a top and a bottom. The polymer wall structure is disposed between the first and second major surfaces, thereby creating a plurality of cavities containing a modulating fluid or modulating gel in separate volumes within the cavities. The polymer wall structure includes a molded portion defining recesses along the top of the polymer wall structure, the molded portion being formed by disposing a fluid precursor in the recesses, filling the recesses, and subsequently curing the fluid precursor to bond a second substrate to the surface of the recesses. In one embodiment, the bottom of the polymer wall structure is bonded to the first substrate. In one embodiment, the fluid precursor does not contact the modulating fluid or modulating gel. In one embodiment, the fluid precursor extends beyond the sidewalls defining the recesses and into the cavities. In one embodiment, the molded portion is optically transparent, and the molded portion obscures light and includes a colorant, filler material, or light-scattering material. In one embodiment, the molded article includes a colorant that matches the color of the particles disposed within the modulating fluid or modulating gel. In one embodiment, the fluid precursor comprises an elastomeric polymer having a glass transition temperature (Tg) of less than 20°C. In one embodiment, the elastomeric polymer is polyurethane. In one embodiment, the recesses have a maximum depth of 5% or more of the orthogonal distance between the first and second major surfaces. In one embodiment, the cavities have a longest dimension of 0.3 mm to 3 cm, and the center-to-center distance between adjacent cavities is 0.6 mm to 10 cm. In one embodiment, the molded article has variations in the shape of each of its recesses, including variations in the depth and width of the recesses. In one embodiment, the polymer wall structure additionally includes brace features. In one embodiment, the first substrate or the second substrate comprises a flexible, transmissive material. In one embodiment, the switchable light modulator has a first state that strongly attenuates light and a second state that is substantially transparent to visible light. In one embodiment, the modulating fluid or modulating gel comprises electrophoretic particles, liquid crystals, a combination of polar and non-polar liquids, electrochromic fluids, thermochromic fluids, or photochromic fluids.

[0018] In another aspect, a method for fabricating a switchable light modulator is provided. The method includes providing a first substrate including a first major surface, providing a second substrate including a second major surface, providing a polymer wall structure having a top and a bottom, the polymer wall structure including a molded portion defining a recess along the top of the polymer wall structure, filling the recess with a fluid precursor, providing a modulating fluid or modulating gel in separate volumes within the plurality of cavities, disposing the polymer wall structure between the first and second major surfaces, and curing the fluid precursor to bond the surfaces of the second substrate and the recess together. In one embodiment, the wall structure is bonded to the first substrate before providing the modulating fluid or modulating gel in separate volumes within the plurality of cavities. In one embodiment, curing the fluid precursor to bond the surfaces of the second substrate and the recess together includes heating the fluid precursor or exposing the fluid precursor to UV light. In one embodiment, disposing the polymer wall structure between the first and second major surfaces further comprises compressing the polymer wall structure between the first and second substrates with a roller.

[0019] In another aspect, a switchable light modulator device has a first substrate with opposing major surfaces spaced apart by one or more polymer structures and a second substrate, each comprising two or more portions defining a plurality of wall features for cavities, the plurality of cavities sealing a fluid or gel within separate volumes, each of the one or more polymer structures bonded to the first substrate and comprising a molded portion defining a recess and a cast portion thereof, the cast portion filling the recess and bonded to the second substrate and a surface of the recess, the cast portion encapsulating the surface of the recess and the second substrate, replicating both surfaces.

[0020] In a further aspect, a switchable light modulator device is provided. In some embodiments, the molded portion is optically transparent (i.e., comprises only optically transparent polymer), and the cast portion obscures light. Light is obscured by the molded portion by dispersing or solubilizing one or more of a colorant, a filler material, or a light-scattering material in its polymer structure. Preferably, the color of the colorant is selected to match the color or hue of one or more switchable light states of such embodiments.

[0021] A particular advantage of keeping the molded part optically transparent is that UV absorption is minimized when it is formed by an embossing process that relies on rapid ultraviolet (UV)-initiated polymerization. In contrast, if the molded part has a light-absorbing material, polymerization of deep wall sections (e.g., 20 microns or more) will be at least slowed and most likely not possible. In a roll-to-roll process using an embossing drum, the molded precursor will have several seconds to harden before being released / peeled from the drum surface. With such a manufacturing process for the molded part, it is important to use an optically transparent precursor. Advantageously, in embodiments, the molded part is cast in place within the device, so the molded part with the light-absorbing material can be thermally cured for an appropriately long period of time.

[0022] These and other aspects of the present invention will become apparent in light of the following description. The present invention provides, for example, the following items. (Item 1) A switchable optical modulator (201, 202, 203, 204, 205), comprising: a first substrate (101, 102, 103) having a first main surface; a second substrate (141, 142, 143, 144) having a second main surface; a polymeric wall structure (21, 22, 23) having a top and a bottom, said polymeric wall structure being disposed between said first major surface and said second major surface, thereby creating a plurality of cavities (111, 112, 113, 114), said plurality of cavities containing a modulating fluid (71, 72, 73, 74) or modulating gel in separate volumes within said cavities (111, 112, 113, 114), said polymeric wall structure (21, 22, 23) including molded portions (31, 32, 33) defining recesses along said tops of said polymeric wall structures (21, 22, 23); Casting parts (81, 82, 83, 84) Including, The switchable light modulator, wherein the molded portion is formed by depositing a fluid precursor into the recess, filling the recess, and subsequently curing the fluid precursor to bond the second substrate to a surface of the recess. (Item 2) Item 1 . The switchable light modulator of item 1 , wherein the bottom of the polymer wall structure is bonded to the first substrate. (Item 3) Item 1 . The switchable light modulator of item 1 , wherein the fluid precursor does not contact the modulating fluid or the modulating gel. (Item 4) 2. A switchable light modulator according to item 1, wherein the fluid precursor extends beyond the side walls (21a, 22a, 23a) defining the recess and into the cavity. (Item 5) Item 10. The switchable light modulator of item 1, wherein the molded portion is optically transparent and the cast portion obscures light and comprises a colorant, a filler material, or a light scattering material. (Item 6) 6. The switchable light modulator of item 5, wherein the molded object includes a colorant that matches the color of particles disposed within the modulating fluid or modulating gel. (Item 7) Item 14. The switchable light modulator of item 1, wherein the fluid precursor comprises an elastomeric polymer having a glass transition temperature (Tg) of less than 20°C. (Item 8) 8. The switchable light modulator of item 7, wherein the elastomeric polymer is polyurethane. (Item 9) Item 2. The switchable light modulator of item 1, wherein the recess has a maximum depth (1031, 1032) of 5% or more of the orthogonal distance (121, 122) between the first and second main surfaces. (Item 10) Item 2. The switchable light modulator of item 1, wherein the cavities have a longest dimension of 0.3 mm to 3 cm and the center-to-center distance between adjacent cavities is 0.6 mm to 10 cm. (Item 11) Item 2. A switchable light modulator according to item 1, wherein the molded portions have differences in the shape of each of their recesses, including variations in the depth (1031, 1032) and width (1041, 1042) of the recesses. (Item 12) Item 2. The switchable light modulator of item 1, wherein the polymer wall structure further comprises a brace feature (23c). (Item 13) Item 10. The switchable light modulator of item 1, wherein the first substrate or the second substrate comprises a flexible transmissive material (90). (Item 14) Item 1. A switchable light modulator according to item 1, wherein the switchable light modulator has a first state that strongly attenuates light and a second state that is substantially transparent to visible light. (Item 15) Item 2. The switchable light modulator of item 1, wherein the modulating fluid or modulating gel comprises electrophoretic particles, liquid crystals, a combination of polar and non-polar liquids, electrochromic fluids, thermochromic fluids, or photochromic fluids. (Item 16) 2. A display, window, mirror, shade, or sign comprising the switchable light modulator of item 1. (Item 17) A method for making a switchable light modulator (201, 202, 203, 204, 205), said method comprising the steps of: providing a first substrate (101, 102, 103) including a first major surface; providing a second substrate (141, 142, 143, 144) including a second major surface; providing a polymeric wall structure (21, 22, 23) having a top and a bottom, said polymeric wall structure (21, 22, 23) including a molded portion (31, 32, 33) defining a recess along said top of said polymeric wall structure (21, 22, 23); filling the recess with a fluid precursor; providing a modulating fluid (71, 72, 73, 74) or modulating gel in separate volumes within said plurality of cavities (111, 112, 113, 114); disposing the polymer wall structure (21, 22, 23) between the first major surface and the second major surface; curing the fluid precursor to bond the second substrate and the surface of the recess together; and A method comprising: (Item 18) 18. A method for making a switchable light modulator according to item 17, wherein the wall structure is bonded to the first substrate prior to the step of providing a modulating fluid (71, 72, 73, 74) or modulating gel in separate volumes within the plurality of cavities (111, 112, 113, 114). (Item 19) Item 18. A method of making a switchable light modulator according to item 17, wherein curing the fluid precursor and bonding the second substrate and the surface of the recess together comprises heating the fluid precursor or exposing the fluid precursor to UV light. (Item 20) 20. A method for making a switchable light modulator according to item 19, wherein arranging the polymer wall structure (21, 22, 23) between the first and second main surfaces further comprises compressing the polymer wall structure between the first and second substrates using a roller. (Item 21) a switchable light modulator device (201, 202, 203, 204, 205) having a first substrate (101, 102, 103) and a second substrate (141, 142, 143, 144), the first substrate and the second substrate having opposing major surfaces spaced apart by one or more polymer structures, each of the one or more polymer structures comprising two or more portions and defining wall features (21b, 22b, 23b) for the plurality of cavities (111, 112, 113, 114), the cavities sealing the fluids (71, 72, 73, 74) or gels within separate volumes; a switchable light modulator device, wherein each of the one or more polymer structures comprises a molded portion (21, 22, 23) bonded to the first substrate and defining a recess (31, 32, 33), and a cast portion (81, 82, 83, 84) thereof, the cast portion filling the recess and bonded to the second substrate and a surface of the recess, the cast portion being encapsulated by the surface of the recess and the second substrate and replicating both surfaces; [Brief explanation of the drawings]

[0023] Embodiments of the present invention will now be described, by way of example, with reference to the accompanying three-dimensional drawings.

[0024] [Figure 1A] FIG. 1A shows a first substrate 101 including its molded microstructures 21 and recesses 31 .

[0025] [Figure 1B] FIG. 1B shows a first substrate 101 with recesses 31 filled with a prepolymer 41 .

[0026] [Figure 1C] FIG. 1C shows an embodiment 201 that includes a molded microstructure 21 and a cast microstructure 81 .

[0027] [Figure 2A] FIG. 2A shows the first substrate 102 with its molded microstructures 22 and recesses 32 .

[0028] [Figure 2B] FIG. 2B shows an embodiment 202 that includes a molded microstructure 22 and a cast microstructure 82 .

[0029] [Figure 3A] FIG. 3A shows the first substrate 103 with its molded microstructures 23 and recesses 33 .

[0030] [Figure 3B] FIG. 3B shows an embodiment 203 that includes molded microstructures 23 and cast microstructures 83 .

[0031] [Figure 4] FIG. 4 shows an embodiment 204 that includes a molded microstructure 21 , a cast microstructure 84 , and a thin second substrate 144 .

[0032] [Figure 5] FIG. 5 shows embodiment 205, which comprises embodiment 204 secured to active matrix backplane 165.

[0033] The drawings depict one or more implementations in accordance with the present concepts, by way of example only, and not by way of limitation. DETAILED DESCRIPTION OF THE INVENTION

[0034] An embodiment of the present invention provides a switchable light modulator device with a fluid layer. The device has a solid polymer structure embedded in the fluid layer, the structure having a height and width (orthogonal to the juxtaposed major surfaces of the substrate) on the micron scale. The polymer structure is referred to herein as a microstructure. The polymer microstructure is arranged in two parts: a first part bonded to a first substrate and a second part bonded to a second substrate. The two parts are also bonded to each other, thereby bonding or securing the substrates of the device to each other. The first part incorporates wall features that divide the fluid layer of the device into single layers of separate volumes corresponding to cavities, and the second part incorporates sealant features that seal the volumes, thereby isolating the cavities from each other. Although the second part seals, the polymer structure is almost completely isolated from contact with the fluid layer of the device by the polymer of the first part.

[0035] In embodiments, the first parts of the two-part polymer structure are referred to as molded microstructures, which are covalently bonded to the inner major surface of the first substrate. The molded microstructures are created by microreplicating the surface of a tool onto the first substrate in an embossing or molding step. The molded microstructures are patterned with recessed features (recessed features may also be referred to as channels, notches, or depressions). In embodiments, the recesses are filled with the second part of the two-part polymer structure. This second part is referred to as the molded microstructure, which is covalently bonded to the inner surface of the second substrate. The molded microstructures replicate the recesses by being molded from them, but are not separated from the molded microstructures after casting.

[0036] The prepolymer used for molding is printed or otherwise coated to fill the recesses in the molded microstructure. The device is then assembled with its fluid layer, which is placed between the spaced-apart opposite major surfaces of the first and second substrates. The molded microstructure extends from the major surface of the first substrate into the fluid layer and contacts the opposite major surface of the second substrate. In this way, the molded microstructure defines the cell gaps of the fluid layer. At this stage, the recesses are filled with the prepolymer of the molded microstructure and the cavities are filled with fluid. The prepolymer is then polymerized in a molding step to form the molded microstructure, covalently bonding the molded microstructure to the molded microstructure and the inner major surface of the second substrate. As a result, the molding step occurs with the fluid layer in place between the substrates following the molding step. During polymerization (i.e., casting), the prepolymer bulk within the recess does not come into contact with the fluid, and after polymerization, the casting is encapsulated and isolated from the fluid by the molded microstructure. Embodiments are characterized by a two-part polymer structure comprising a molded microstructure portion and a cast microstructure portion.

[0037] The light modulators of the embodiments selectively change one or more of light attenuation, color, specular transmittance, or diffuse reflectance in response to electrical, optical, or thermal changes to provide two or more optical states. Preferably, the optical states include one extreme state that is transparent to visible light and another extreme state that strongly attenuates light. An important application for the embodiments is in smart windows. Some embodiments incorporate the device into a window as a layer within a glass laminate. In other embodiments, the device is flexible and bonded to a glass pane. In both smart window embodiments, the film device has considerable structural strength, compartmentalizing the fluid layer with each separate, self-sealed fluid volume. The structural strength of the embodiments comes from the design of their molded and cast microstructures and the selection of their polymer materials. Structural strength includes the need to withstand the glass lamination or bonding process, the loads encountered when handling and installing large smart windows, and the loads imposed on the device over its lifetime by environmental shocks such as extreme wind and temperature. Additionally, for transport applications, the polymer structure of the device is selected to be vibration resistant.

[0038] Other embodiments for the device include use as a light shutter, a light attenuator, a variable light transmission sheet, a variable light absorption sheet, a variable light reflectance sheet, a mirror, a sunshade for a vehicle, an electronic skin, a monochrome display, a color display, or a see-through display. 2 ~5m 2 Furthermore, the device, which is a roll of film, can be mounted on a surface of up to 1,000m². 2 or may have a larger area.

[0039] The embodiments will be described with reference to the three-dimensional projections shown in the figures. Figures 1a-1c are used to describe embodiment 201. Figures 2A and 2B describe embodiment 202, Figures 3A and 3B describe embodiment 203, Figure 4 describes embodiment 204, and Figure 5 describes embodiment 205. In the figures, the embodiments comprise fluid or gel layers (71, 72, 73, 74) held between first substrates (101, 102, 103) and second substrates (141, 142, 143, 143). In some embodiments, the fluid layers (71, 72, 73, 74) can be described as electro-optic layers, for example, as described above.

[0040] The substrates are spaced apart by polymer microstructures (21, 22, 23) to define cell gaps (121, 122, 123, 124) for the fluidic layer. The microstructures also divide the fluidic layer into separate sealed cavities (111, 112, 113, 114) or compartments. The microstructures are in two parts: one part is a molded microstructure (21, 22, 23) that replicates the surface of a tool and is formed in an embossing or molding step on the first substrate prior to device assembly, and the other is a cast microstructure (81, 82, 83, 84) that is formed in recesses (31, 32, 33) in the molded microstructure and on the second substrate after device assembly. As a result, the cast microstructure arises directly from its interface (or intimate contact or shared surface) with the recesses in the microstructure of the casting and its interface (or intimate contact or shared surface) with the second substrate.

[0041] In some embodiments, one or both of the substrates is a transparent flexible film (90) that is coated on the fluid side with a transparent electrode (60). The major surfaces of the electrodes face each other and are juxtaposed parallel. The opposing surfaces of the substrates form the viewing surfaces of the embodiment. In alternative embodiments involving photochromic or thermochromic light modulators, the substrates (and device) do not have an electrode coating on the viewing surface (or switchable area).

[0042] Herein, the molded microstructures (21, 22, 23) have features described as (or corresponding to) cavity walls (21a, 22a, 23a), recesses (31, 32, 33), recess walls (31a, 32a, 33a), and wall braces (23c). These features are considered separate from the wholes (21, 22, 23) of which they are a part, but are formed in a single embossing step. In contrast, the cast microstructures (81, 82, 83, 84) are formed in separate steps and, in some embodiments, have a different material than the molded microstructures.

[0043] In Figures 1C, 2B, 3B, 4, and 5, just seven complete fluid cavities (111, 112, 113, 114) are shown with cross sections cut through adjacent cavities and the fluid within those cavities (71, 72, 73, 74). The cross sections through the fluid are not shown with hatching, but the presence of fluid is generally indicated. The illustrations of the embodiments correspond to localized areas (or cross sections) of a much larger device, and the illustrations are not drawn to scale. In embodiments, the pitch of the cavities (or fluid volumes defined thereby) is between 50 microns and 3,000 microns. The longest dimension (LD in Figure 1A) for the hexagonal cavities can be, for example, 0.3 mm to 3 cm, as shown in Figure 1A. The corresponding center-to-center distance (C.-C. in Figure 1A) can be between 0.6 mm and 10 cm. The relationship between the longest dimension of the cavities and the center-to-center distance can vary depending on the geometry of the cavities relative to one another. In some cases, the cavities can be a collection of irregular polygons, which can reduce moiré or other optical interference effects. In one embodiment, a smart glass device with a 250-micron pitch will typically have 2,000 to 6,000 separate fluid cavities across its face, 2,000 to 20,000 along its face, or a total number of cavities of 4 million to 120 million. In other embodiments, a larger pitch can be used to improve the viewing experience (i.e., with reduced haze and moiré). When a larger pitch is used, the eye resolves the visible pattern as a grid (or array) and perceives the cast as a grid of opaque areas that are the color of the light-attenuating particles. In many cases, the cast is indistinguishable on the face of the light modulator when the light modulator is switched to the first (opaque / dark) light state. When the light modulator is switched to an open, light-transmitting (second) state, the colored particles aggregate adjacent to the visible cast portion, giving the overall appearance of insect screen. However, the larger size of the cavities significantly improves haze. Case studies suggest that for larger applications (e.g., vehicle or building windows), the presence of visible cell walls is less objectionable than the higher haze that can be present in smaller pitch designs.

[0044] FIG. 1a shows a first substrate 101 of embodiment 201 (the latter is shown in FIG. 1c). Molded microstructure 21 is a wall structure that defines a hexagonal-shaped cavity 111, and the wall structure is bonded to the inner surface of substrate 101. The latter is shown in FIG. 1A as microstructure 21 bonded to the surface of optional electrode 60 on flexible film 90. The cavity wall feature (or formation) of microstructure 21 is designated by 21b, its height perpendicular to the substrate plane is designated by dimension 1021, and its width is designated by 1051. On the opposite side of substrate 101, microstructure 21 has a recess 31. The wall (or side) of microstructure 21 that defines recess 31 is designated by 21a and is shown in enlarged view 1001. The width of recess 31 is designated by 1041, and its height is designated by 1031.

[0045] The width 1051 of the majority of the wall sections embedded in the viewing area is between 7.5 microns and 175 microns, more preferably between 12 microns and 125 microns, and most preferably between 15 microns and 90 microns. The width 1041 of the majority of the recesses is between 2.5 microns and 100 microns, more preferably between 7.5 microns and 85 microns, and most preferably between 10 microns and 75 microns. The height (or depth) 1031 of the majority of the recesses perpendicular to the surface of the second substrate is between 2.5% and 99% of the cell gap 121, more preferably between 5% and 66%, and most preferably between 6.25% and 46%.

[0046] FIG. 1B shows first substrate 101 after prepolymer 41 has been printed or coated into recesses 31 in molded microstructure 21. Examples of suitable printing processes for this step in device assembly (or preparation or manufacturing) include screen printing or inkjet printing. The preferred printing direction is indicated by arrow 1010. This avoids printing into the recessed areas parallel to the printing squeegee. Prepolymer 41 is a precursor to molding 81. Preferably, it is a high-viscosity (1,000 cst or greater) resin curable by free-radical polymerization (suitable materials are described later). In FIG. 1B, the top surface of prepolymer 41 is indicated by 41a. This surface preferably coincides with or exceeds wall surface 21a. In some embodiments, an excess of prepolymer 41 can coat upper wall surface 21a after the printing step and before the fluid deposition step.

[0047] In FIG. 1C , the fluid layer of embodiment 201 is shown as 71, which occupies a portion of the volume defined between optional electrodes 60 of substrates 101 and 141. Cell gap 121 corresponds to the orthogonal distance between the respective interfaces of fluid layer 71 with the first and second substrates. Fluid 71 is then divided into separate fluid volumes by walls 21b that are part of molded microstructure 21, with each fluid volume defined by a cavity 111. The fluid cavities 111 are arranged side-by-side in a hexagonal grid and are in a single layer. In some embodiments, the cavities have an irregular shape that results in a side-by-side arrangement with some degree of irregularity or randomness.

[0048] The embodiment 201 is assembled in the lamination step using a pair of horizontally oriented NIP rollers with a vertical feed direction (relative to the path between the NIP rollers). In some embodiments, during lamination, the substrates are held under tension by an unwinding and / or rewinding station or module as part of a roll-to-roll system. The fluid 71 of the device is introduced between the substrates 101 and 141, forming a reservoir, before passing vertically through the NIP rollers. The preferred direction of lamination relative to the orientation of the hexagonal cavities is indicated by arrow 1010 in FIG. 1B (previously described in connection with printing prepolymer 41). In this orientation, the fluid 71 does not encounter cavity walls parallel to the NIP point of the lamination rollers (i.e., parallel to the rollers), making it easier to push excess fluid out of the cavities as the device passes the NIP point. The prepolymer 41 within the recesses 31 (within the molded microstructures 21) is cast during the curing stage, resulting in the cast microstructures 81 from the microstructures 21. Preferably, curing is by free radical polymerization, the latter preferably being carried out in a high intensity ultraviolet radiation module as part of a roll-to-roll process. Alternative curing methods include thermal curing, and alternative types of chain growth polymerization include ionic, cationic, and coordination polymerization.

[0049] Once curing is complete, the cast microstructure 81 is firmly bonded to the second substrate 141 and the molded microstructure 21. Because the cast microstructure 81 is cast within the volume between the mold recess 31 and the inner surface of the second substrate 141, it is surrounded and encapsulated by both, and derived and defined by both. The cast 81 replicates both interface surfaces and is a 3D transcription of those surfaces and the volume between them. By selecting the prepolymer 41 to be chemically compatible with both surfaces, the cured cast 81 is firmly bonded to both. The cast 81 is a child of the parent molded microstructure 21, and the two parts (or pair) are described as the mold 21 and its cast 81.

[0050] In another embodiment, a thermoplastic polymer is applied in liquid form as a prepolymer 41 and allowed to solidify before the fluid lamination step. After laminating the fluid 71 between the substrates, the casting step is completed by exposing the device to a temperature high enough to reflow the thermoplastic polymer 41. Upon cooling, the thermoplastic polymer 41 bonds to the molded microstructure 21 and the second substrate 141 as it solidifies into the molded object 81. Examples of thermoplastics include poly(methyl methacrylate) (PMMA) (known by trade names such as Lucite®, Perspex®, and Plexiglas®) and polycarbonate. Grades suitable for use in outdoor settings (particularly automotive applications) are preferred. Soft thermoplastics with a Shore A hardness of 30 to 100, including grades of low-density polyethylene (LDPE), are most preferred.

[0051] In embodiment 201, casting 81 is continuous with cavity 111 and, together with molding 21, encloses fluid 71 of the cavity. The fluid is sealed and isolated from adjacent cavities 111. In FIG. 1C , the top surface of casting 81 is designated as 81a, and the top surface of molding 21 is designated as 21a. Casting 81 continuously seals cavity 111 by chemically bonding to second substrate 141 and molded microstructure 21, which in turn is continuously sealed by chemically bonding to first substrate 101. Thus, in embodiment 201, molded microstructure 21 defines the enclosing walls of the cavity, and cast microstructure 81 defines the fluid sealant of the cavity.

[0052] The fluid lamination step (described previously) substantially forces the fluid out of the contact area between the cast prepolymer 41 and the second substrate 141. Applying a compressive force during lamination forces the prepolymer 41 into intimate contact with the second substrate 141, and excess prepolymer is squeezed out of the recess 31 in a thin layer onto the top of the recess wall 21a. In some embodiments, the casting step seals the cavity by polymerizing a thin layer of excess prepolymer between the top of the molded microstructure 21 and the second substrate 141. The cured thin layer is also known as flashing. Preferably, the cured thin layer has a thickness of less than 5 microns, more preferably less than 3 microns, and most preferably less than 2 microns. In some embodiments, the excess polymer from the cast microstructure extends beyond the molded top surface 21a into the cavity side of the recess wall.

[0053] Advantageously, in embodiment 201, fluid 70 is barely exposed to the prepolymer 41 of the mold because the prepolymer 41 of the mold is contained within the recess 31. Lamination squeezes the fluid 70 out of the contact area of ​​the prepolymer 41 with the second substrate 141, leaving the prepolymer 41 largely unexposed to the fluid during the lamination step, substantially isolating the prepolymer 41 (a high-viscosity fluid) from the optical fluid 71. The lamination step non-permanently seals the prepolymer 41 between the recess 31 and the top substrate 141. Immediately following lamination, a polymerization step hardens the prepolymer and makes the seal permanent (i.e., by forming the mold 81). During polymerization, the prepolymer bulk within the recess 31 does not come into contact with fluid 70. Contact is only possible with any excess prepolymer squeezed into the cavity during lamination. By selecting and controlling the amount of prepolymer 41 printed into the recess 31, excess prepolymer can be minimized or avoided, as desired.

[0054] In some embodiments, the juxtaposed, parallel, spaced-apart (from the first substrate) major surface of the second substrate 141 has a polymer insulating and / or adhesive layer on its electrode layer 60 (not shown in FIG. 1C ). In some embodiments, the polymer layer is polymerized simultaneously with the polymerization of the prepolymer 41 of the casting 41. In this manner, the adhesive layer improves the peel adhesion of the casting 41 to the second substrate.

[0055] In device 201, cell gaps 121 are less than or equal to wall height 1021 of molded microstructure 21 (see FIG. 1A). Advantageously, in some embodiments, fluid 71 is under suction within cavity 111 because walls 21b are under compression or load from the fluid deposition step, which compression or load results in a reduced wall height within the device corresponding to cell gaps 121. As used herein, a fluid under suction refers to a fluid that is at a lower pressure relative to the surrounding atmospheric pressure. In embodiment 201, wall height 121 is less than the outside height of device 1021, and preferably the wall height within the device is less than or equal to 0.99 times the outside height of the device.

[0056] 2A shows the first substrate 102 of embodiment 202. The latter is shown in FIG. 2B. Embodiment 202 is similar to embodiment 201 described previously. The walls (or sides) of the microstructure 22 that define the recess 32 are indicated by 22a and are shown in enlarged view 1002. The wall height is 1022 and its width is 1052. The width of the recess 32 is indicated by 1042 and its height is indicated by 1032. The recess 32 has outwardly sloping curved (or rounded) walls, as indicated by 22a in enlarged view 1002. In FIG. 2A, the walls 22a of the recess 32 become thinner towards the edge opposite the first substrate.

[0057] In FIG. 2B , the cavity is 112 and is filled with fluid 72. The cell gap is 122. The walls 22 a of the recess 32 taper toward the edges that contact (or are close to or adjacent to) the second substrate 142. As a result, the top surface 82 a of the casting 82 overlaps substantially all of the top surface 22 a of the molding 22, as shown in FIG. 2B . Advantageously, when the casting 82 has a colorant and the molding 22 is transparent, a viewer viewing the viewing surface of the embodiment perceives both microstructures as colored.

[0058] In some embodiments, the materials of the molded and cast microstructures are the same; in others, they are different. In preferred embodiments, the molded portion is optically clear, and the cast portion obscures light and includes one or more of a colorant (pigment or dye), a filler material, or a light-scattering material. Preferably, the color of the colorant is selected to match the color or hue of one or more switchable light states of the switchable light modulator device. For example, one embodiment with black, clear, and neutral-tone states has an optically clear molded microstructure comprising a polymer that includes a carbon black-loaded polymer and a black cast microstructure. In another example, one embodiment with white, clear, and neutral-tone states has an optically clear molded microstructure comprising a polymer that includes a titanium dioxide-loaded polymer and a white cast microstructure. In some embodiments with colored extreme light states, the cast microstructure is black to minimize haze and color perception in the clear light state.

[0059] A particular advantage of keeping the molded part optically transparent is that UV absorption is minimized when it is formed by an embossing process that relies on rapid ultraviolet (UV)-initiated polymerization. In contrast, if the molded part has a light-absorbing material, polymerization of deep wall sections (e.g., 20 microns or more) will be at least slowed and most likely not possible. In a roll-to-roll process using an embossing drum, the molded precursor will have several seconds to harden before being released / peeled from the drum surface. With such a manufacturing process for the molded part, it is important to use an optically transparent precursor. Advantageously, in embodiments, the molded part is cast in place within the device, so the molded part with the light-absorbing material can be thermally cured for an appropriate long period of time.

[0060] FIG. 3A shows the first substrate 103 of embodiment 203, the latter of which is shown in FIG. 3B. Embodiment 203 is similar to previously described embodiments 201 and 202. The walls (or sides) of the microstructure 23 defining the recess 33 are indicated by 23a and are shown in enlarged view 1003. The cavity walls are indicated by 23b, and their height is 1023 and their width is 1053. The recess 33 has outwardly sloping walls, as indicated by 23a in enlarged view 1003. In FIG. 3A, the walls 23a of the recess 33 taper towards the step on the side opposite the first substrate. The width of the recess 33 is indicated by 1043 within the recess and as 1063 between the step areas where the recess is at its widest point. The height (or depth) of the recess is indicated by 1033. The recess 33 has a "V" shaped cross section. In some embodiments, the moldings have variations in the shape of the recesses, or the shape of their recesses, including variations in depth or width.

[0061] In FIG. 3B, the cavity is 113 and is filled with liquid crystal fluid 73. The cell gap is 123. The wall 23a of the recess 33 tapers toward the step that contacts (or is close to or adjacent to) the second substrate 143. As a result, the upper surface 83a of the molding 83 overlaps substantially all of the upper surface 23a of the molded article 23, as shown in FIG. 3B. The second substrate 143 comprises the substrate 142 (shown in FIG. 2B) and a liquid crystal matching layer 193. Advantageously, the matching layer 193 can be coated on the electrode surface of the substrate 142 before the liquid crystal fluid is laminated thereon. The cavity 113 is then sealed by curing the molding 83. The seal does not interfere with the matching layer 193, which contacts the liquid crystal 73.

[0062] 3A and 3B, wall feature 23b of molded microstructure 23 has brace feature 23c. Brace feature 23c is included to provide additional strength to the wall. This is beneficial when releasing the molded microstructure on an embossing tool (described previously) and subsequently when the embodiment is laminated between glass sheets. The width of brace feature 23c is shown as 1073 in close-up 1003, and its height as 1083. In some embodiments, the height is the same as wall height 1023; preferably, in such devices, the brace feature has a recess that is bonded to the cavity wall recess. In this way, the brace feature has an associated molded portion and adds to the peel adhesion of the device (peel adhesion refers to the adhesive strength between a first substrate and a second substrate).

[0063] Device 204 is shown in FIG. 4 and shares many elements with device 201 (shown in FIG. 1C). Common elements are designated by the same numerals in both figures. Second substrate 144 of device 204 differs from second substrate 141 of device 201. In FIG. 4, second substrate 144 is shown affixed to optional release liner 154. As implied by its name, release liner 154 is a sacrificial layer intended to be removed when the device is in use (or prior to a manufacturing step). Second substrate 144 is continuous, and its thickness (or the dimension orthogonal to its major surface) is between 0.5 microns and 50 microns, preferably between 1 micron and 35 microns, and most preferably between 1.25 microns and 25 microns.

[0064] In some embodiments, this thin sheet (i.e., second substrate 144) is a thin solid polymer and can function as one or more of a cavity, an insulating layer, a barrier layer, or a cover layer for a hard coat. In some embodiments, second substrate 144 is optically clear, in other embodiments has a colorant, and in still other embodiments, is solar reflective. With respect to second substrate 141 (device 201), a distinguishing feature of second substrate 144 (device 204) is the absence of electrode layer 60 on second substrate 141 (device 201).

[0065] In embodiment 204, the cast microstructure 84 resembles the casting 81 in embodiment 201. The casting 84 is rigidly bonded to the second substrate 144 and to the molded microstructure 21. Because the cast microstructure 84 is cast within the volume between the molded recess 31 and the inner surface of the second substrate 144, it is surrounded and encapsulated by both, and derived and defined by both. The casting 84 replicates both interface surfaces and is a 3D transcription of those surfaces and the volume between them.

[0066] 4, the fluid layer of embodiment 204 is shown as 74 and occupies a portion of the volume defined between electrode 60 of substrate 101 and the interior surface (or interface) of second substrate 144. Cell gap 124 corresponds to the orthogonal distance between the respective interfaces of fluid layer 74 with the first and second substrates. Fluid 74 is then divided into separate fluid volumes by walls 21b that are part of molded microstructure 21, with each fluid volume being defined by a cavity 114. In embodiment 204, casting 84 is continuous with cavity 114 and, together with molding 21, surrounds and seals fluid 74 in the cavity, isolating the fluid from adjacent cavities 114.

[0067] In some embodiments of device 204, the electrodes 60 on the first substrate 101 are patterned into segments, and in use, the fluid 74 is subjected to an electric field by applying different voltage polarities and / or levels to adjacent segments. In such devices, the second substrate may not have an electrode layer associated with it (i.e., the device uses a single electrode layer to form optical states and may be said to use in-plane switching).

[0068] Embodiment 205 is shown in FIG. 5 and includes embodiment 204, as shown secured to an active matrix backplane 165 (with release liner 154 removed). Securing can be by any suitable means, including by adhesive (not shown in FIG. 5). If an adhesive / polymer layer is used, its thickness is preferably kept to the minimum necessary (i.e., 0.5 microns to 15 microns) to uniformly secure device 204 to backplane 165 and achieve adequate peel adhesion between portions. Active matrix backplane 165 has electrodes patterned to form pixels, which, together with active matrix transistors, allow device 205 to operate as a matrix of pixel areas on which arbitrary images can be displayed. Examples of products (205) include electronic book readers and electronic shelf labels.

[0069] In some embodiments, the switchable light modulator device comprises one of the following types or hybrid versions thereof: an electrophoretic device, a liquid crystal device, an electrowetting device, an electrokinetic device, an electrochromic device incorporating an electrolyte / gel, a thermochromic device, or a photochromic device. Advantageously, in some embodiments, the fluid layer is in contact with a portion of the juxtaposed, parallel, spaced-apart major surfaces of a substrate, the substrate including a substrate surface, the substrate surface comprising an electrode layer (60), an inorganic dielectric layer, an organic dielectric layer, a matching layer (193), an electrochromic layer, an ion storage layer, or an active matrix layer. In electrochromic embodiments, the fluid is an electrolytic gel, and the fluid is in contact with an electrochromic layer overlaid on an electrode on one substrate and an ion storage layer overlaid on another electrode on the other substrate. Examples of electrochromic devices are described in U.S. Pat. No. 6,934,067 (Gentex). In hybrid electrochromic / photochromic embodiments, the switchable material is a liquid or a gel. Switchable liquids or gels are described in U.S. Patent No. 8,837,032, Switch Material. In liquid crystal devices, the fluid is preferably chiral nematic liquid crystal, and a suitable device is described by the applicant in UK Patent Application No. 1416385.1, entitled "A Chiral Nematic Liquid Crystal Light Shutter." Electrokinetic devices are a hybrid of electrophoretic devices and comprise an ink containing charged particles suspended in a fluid. See, for example, U.S. Patent No. 2019 / 0256625 (Crown Electrokinetics). In electrowetting embodiments, the fluid layer can comprise a fluid described in U.S. Patent No. 8,854,714 (Sun Chemical Corp.).

[0070] To improve peel adhesion, in some embodiments, isolated molded and cast parts can be located within a cavity. For example, a cavity can have a centrally located post with a recess (molded microstructure) and be bonded to the opposing substrate through a molded microstructure that is hardened into the recess. This provides peel adhesion within the cavity that complements the peel adhesion provided by the cavity walls. The centrally located microstructure also serves as additional space within the fluid layer, making the device more resistant to externally applied point pressure.

[0071] In some embodiments, a peripheral edge seal around the viewing area uses a molded and cast polymer portion. The molded portion of the edge seal is replicated on the substrate in a molding or embossing step at the same time that the molded microstructure is replicated. Devices made with such a peripheral edge seal are suitable for mass production of identical devices, such as automobile sunroofs or visors. The device can be produced as a repeating device on a continuous roll of film and then die-cut or laser-cut from the roll of film.

[0072] In some embodiments, the added peel adhesion of the peripheral edge seal is better suited for more extreme conditions, such as when the edge of the device is exposed. For example, a smart window embodiment can be bonded to a glass plate on only one side, leaving the other substrate and edge area exposed.

[0073] The substrates (101, 102, 103, 141, 142, 143) can be any suitable transparent sheet material, such as polymer or glass, and can be flexible or rigid. Flexible substrates include polymers such as PET (i.e., polyethylene terephthalate), PEN (i.e., polyethylene naphthalate), PES (i.e., polyethersulfone), PC (i.e., polycarbonate), PI (i.e., polyimide), or FRP (i.e., fiber reinforced plastic), or flexible glass (e.g., 50 micron or 100 micron glass (Nippon Electric Glass Co. Ltd.)). Rigid substrates can be float glass, heat-treated float glass, polished glass, tinted / colored glass, heat-absorbing / reflective glass, or active matrix glass.

[0074] The electrodes (60) can be any suitable transparent conductor, for example, ITO (i.e., indium tin oxide), carbon nanotubes, silver nanowires, or a conductive polymer such as PEDOT (i.e., poly(ethylenedioxythiophene)). The top electrode is one type, such as ITO, and the bottom electrode is another type, such as PEDOT. PEDOT-coated PET substrates are available from Kodak (USA), and ITO-coated PET substrates are available from Sheldahl (USA).

[0075] In flexible embodiments, the microstructure and substrate are sufficiently flexible to allow the device to conform to the curvature of a cylinder with a radius of 300 mm, preferably a radius of 100 mm, and most preferably a radius of 50 mm.

[0076] As previously described with respect to some embodiments, the polymer used in the molded microstructure is cured by light or thermal means to covalently bond to the inner surface of its surrounding molded microstructure and its bounding substrate. Preferably, the prepolymer of the mold is not soluble in the fluid of the fluid layer and has a majority, by weight ratio, of high molecular weight components and high viscosity. In some embodiments, the molded and cast microstructures are at least as flexible as the device substrate.

[0077] Preferably, suitable flexible (or deformable) polymers for use in the molded (21, 22, 23) and cast (81, 82, 83) microstructures of the embodiments include thermosetting polymers, more specifically, elastomeric solid polymers. The elastomers are characterized by a glass transition temperature (i.e., Tg) below 20 degrees Celsius (i.e., 293 K) and possess cross-linking. In some embodiments, the Tg is below the minimum operating temperature required for the application. In some embodiments, the stiffness of the elastomeric polymer of the microstructure can be selected using the level of cross-linking. In some embodiments, the elastomer can be filled with dispersed hard materials (i.e., fillers) to increase its stiffness, tear strength, and durability under load. Examples of filler materials include precipitated silica, fused silica, quartz powder, black pigment nanoparticles, carbon fiber or nanoparticles, or ceramic fiber or nanoparticles. In embodiments, the modulus of elasticity of the solid polymer is selected to provide suitable elastic deformation of the molded and cast microstructures, the modulus being in the range of 2 MPa to 200 MPa, more preferably 3 MPa to 100 MPa. In embodiments, the tear strength of the solid polymer used in the microstructures is selected to be in the range of 7.5 kN / m to 75 kN / m at 20 degrees Celsius, more preferably 9 kN / m to 50 kN / m. The minimum tear strength at the maximum operating temperature (e.g., 90 degrees Celsius) is selected to be ≥ 7.5 kN / m. In embodiments, the linear thermal expansion coefficients of the polymers used in the molded and cast microstructures are matched.

[0078] In preferred embodiments, the elastomer for one or both of the microstructured portions (i.e., molded and cast portions) is polyurethane (i.e., contains polyurethane linkages). Preferred polyurethanes have acrylate / methacrylate groups that are cured to form crosslinks. In some embodiments, the polymer precursor formulation has difunctional polyurethane chains in solution using monofunctional monomers. Both of these components can be fluorinated to improve chemical resistance to swelling by fluids (71, 72, 73, 74) in certain embodiments. Commercially available examples of optical-grade prepolymers suitable for use as elastomeric polymers in embodiments include the following (Norland Products (www.norlandprod.com)): NOA78, NOA75, NOA68, NOA68T, and fluorinated grades NOA142, NOA139, NOA138, and NOA13825.

[0079] To minimize haze, some embodiments match the refractive index of the molded and cast microstructures relative to the fluid, preferably to within 0.02, more preferably 0.005, and most preferably 0.002 of each other. Other embodiments include a colorant within the polymer of the cast microstructure to absorb and / or reflect light. Preferably, a solar pigment that reflects the solar infrared spectrum is used for the colorant. Preferably, the colorant is black to avoid light scattering (and therefore haze). A black colorant within the solid polymer of the cast microstructure allows for mismatched refractive indices for the fluid and the black solid polymer. Furthermore, embodiments using a black colorant within the solid polymer of the cast microstructure can use polymers that are not optically transparent. For example, as previously described, the solid polymer can incorporate dispersed hard filler materials. In another example, the polymer can have a semi-crystalline structure.

[0080] In some embodiments, to provide in-plane (i.e., within the electro-optic layer) switching, the polymer of the cast microstructure is a conductive cast microstructure that also functions as a cast electrode within the device.

[0081] Next, molding techniques are described for creating molded microstructures within the embodiments. Molding techniques may also be described as replication techniques. These and other suitable replication techniques are described in European Patent No. 3396446 (Vlyte Innovations), entitled "An Electrophoretic Device Having a Transparent Light State."

[0082] In molding techniques, a hard or soft tool surface is used as a negative mold master in the molding step, and the inverse of the three-dimensional (3D) shape of the master's surface is transferred (i.e., replicated) onto a substrate to form the molded microstructure. An example of a hard tool surface is electroformed nickel, which is suitable for producing up to 100,000 replicas on a substrate. An example of a soft tool surface is cross-linked polydimethylsiloxane, which can produce up to 1,000 replicas. The molding step involves coating the surface of the master with a prepolymer, laminating the substrate (optionally, the coating is performed as part of the lamination), curing the coating so that the shape of the master's surface is inversely replicated in the polymer bonded to the substrate, and peeling it off, leaving the replicated microstructure on the substrate.

[0083] The molded microstructure of a device can be continuously repeated (by replication) on a roll of film in a roll-to-roll process. In this case, the surface of the drum is the hard tool. Alternatively, a continuous roll of film can be cut into sheets corresponding to the device, and then the molded microstructure can be replicated on each substrate in a sheet process. In this case, an electroformed sheet is a suitable hard tool, or P(DMS) on PET is a suitable soft tool.

[0084] A hard, negative mold master can be created from a polymer template by electroforming nickel onto the surface of the template, thereby transferring the shape of the polymer template to the surface of the hard mold master. The surface of the polymer template is directly formed by optically writing microstructures into a photosensitive polymer known as photoresist and developing the resist. Direct writing of the surface of the template in a photosensitive polymer includes techniques described as direct-write lithography, single-point laser writing, laser interferometry, and electron-beam lithography. Any suitable photoresist can be used, including the SU8 series available from www.microchem.com. Direct-write microstructures expose a photosensitive polymer, and the exposed structures are developed in a solution in a separate step. Preferably, a computer-controlled system uses a laser beam or an electron beam (e-beam) to expose the photosensitive polymer and form molded microstructures with wall and recess features. Prior to electroforming the negative mold master onto the surface of the polymer template, the template is made more compatible (for electroforming) by depositing a thin (<250 nm) metal or ceramic conformal coating (or coatings) on its polymer surface.

[0085] In other techniques, three-dimensional surfaces are formed directly in a hard master (e.g., stainless steel, copper, electroformed nickel, silicon, fused silica, or calcium fluoride) by material removal. Hard surfaces can be formed by mechanical cutting (e.g., single-point diamond turning), chemical etching, ion beam cutting, reactive ion etching, or laser ablation to directly form (or write) a replica surface. Typically, a reverse (i.e., negative) image is directly formed in a small area, called a tile, and a metal foil copy of this area (called a shim) is used to coat a tool surface, such as the surface of an embossing drum. It will be apparent to those skilled in the art that numerous changes and modifications can be made in the specific embodiments of the invention described above without departing from the scope of the invention. Therefore, the entire foregoing description should be interpreted in an illustrative, and not a limiting, sense.

[0086] All of the foregoing published patents, publications, and pending applications are incorporated herein by reference in their entirety.

Claims

[Claim 1] Devices, systems, methods, etc.

Images