Continuous photolithographic manufacturing process for generating seamless microstructures used in electro-optical displays and light modulation films

Abstract

A roll-to-roll method for manufacturing a seamless microstructure includes the steps of: (a) continuously forming a laminated structure including a photomask film superimposed on a substrate, with a layer of photosensitive material between the substrate and the photomask film, wherein the photomask film includes a pattern of light-transmitting regions and light-shielding regions; (b) irradiating the photomask film of the laminated structure formed in step (a) so that light passes through the light-transmitting regions of the photomask film, curing the portion of the photosensitive material exposed by the light-transmitting regions while leaving the remaining portion of the photosensitive material covered by the light-shielding regions uncured; (c) peeling the photomask film from the photosensitive material selectively cured in step (b); and (d) removing the uncured portion of the photosensitive material and forming a layer of microstructure on the substrate from the cured portion of the photosensitive material.

Description

Technical Field

[0001] (Cross-Reference to Related Applications) This application claims priority from U.S. Provisional Patent Application No. 63 / 547,747, filed on November 8, 2023, entitled CONTINUOUS PHOTOLITHOGRAPHIC FABRICATION PROCESS FOR PRODUCING SEAMLESS MICROSTRUCTURES USED IN ELECTRO-OPTIC DISPLAYS AND LIGHT MODULATING FILMS, which is hereby incorporated by reference in its entirety into the present specification.

Background Art

[0002] (Background) The present application relates generally to electrophoretic displays and other electro-optic displays as well as light modulating films, and more specifically to a continuous photolithographic fabrication process for producing seamless microstructures for use in such displays and films.

[0003] Electrophoretic light-modulated films modulate the amount of light or other electromagnetic radiation passing through an electrophoretic medium. In some cases, light will pass through the film completely (i.e., from top to bottom). In other cases, light may pass through the electrophoretic medium, be reflected / scattered at the surface, and pass through the medium a second time to return (i.e., from top to bottom and then back to top). In other cases, light will be absorbed by pigment particles present on the viewing surface. In other cases, the selective absorption of light by the pigment particles will result in a rendered image, such as text or a picture. Such films can be incorporated into displays, labels, variable transparency windows, mirrors, and similar devices. Typically, a film has an "open" state (in which one or more sets of pigment particles are isolated on the sides or in wells, etc., and as a result, most of the incident light can pass through the medium) and a "closed" state (in which one or more sets of pigment particles are distributed through the medium and absorb some or all of the incident light).

[0004] For example, U.S. Patent No. 10,067,398 discloses an electrophoretic light attenuator comprising a cell including a first substrate, a second substrate spaced apart from the first substrate, a layer disposed between the substrate and an electrophoretic ink, and a monolayer of densely packed microstructured protrusions protruding into the electrophoretic ink and positioned adjacent to the surface of the second substrate. The protrusions have surfaces that define a plurality of recesses between adjacent protrusions. The electrophoretic medium layer (ink layer) contains at least one type of charged particles, which move in response to an electric field applied to the cell between a first extreme light state (in which the particles are maximally diffused within the cell, resulting in them being located in the path of light passing through the cell, thereby strongly attenuating light transmitted from one substrate to the opposite substrate) and a second extreme light state (in which the particles are maximally concentrated within the recesses, resulting in light transmission). The total area corresponding to the particles concentrated in the recesses is a portion of the total area.

[0005] This type of device relies at least in part on the shape of their non-planar polymer structures to concentrate absorbent charged particles (e.g., black particles) in an electrophoretic ink in a transparent light state, thereby forming (or exposing) light apertures (i.e., transmission areas) and light shielding areas (i.e., strongly absorption areas). The present application further relates to a more conventional electrophoretic display that modulates light reflected on a viewing surface by the presence of charged pigment particles, as described in U.S. Patents No. 9,921,451 and No. 9,812,073.

[0006] Prior art solutions having polymer structures in fluid or gel layers include U.S. Patent No. 8,508,695 to Vlyte Innovations Ltd, which discloses dispersing fluid droplets (1-5 microns in diameter) in a continuous polymer matrix cured in place on both substrates to include liquid crystals. Furthermore, U.S. Patent No. 10,809,590 to E Ink Corporation discloses microencapsulating fluid droplets, deforming them to form a monolayer of densely packed polymer shells in a polymer matrix on one substrate, followed by applying an adhesive layer to bond the capsule layer to the substrate. Additionally, European Patent Application Publication EP1264210 to E Ink California discloses embossing a microcell structure (including multiple cavities or cups) on one substrate, filling the cups with a fluid containing polymerizable components to polymerize the components, forming a seal layer on the fluid / cup surface, followed by applying an adhesive layer to bond to a second substrate. Furthermore, EP2976676 to Vlyte Innovations Ltd. discloses forming a wall structure on one substrate, coating the top surface of the wall with an adhesive, filling the cavity defined by the wall with fluid, polymerizing the adhesive, and bonding the top surface of the wall to the opposing substrate. EP3281055 describes a flexible device including a solid polymer microstructure embedded in its visible area, the microstructure being on both substrates. The microstructures bond (i.e., fix) the substrates of the device to each other by engaging with each other over lengths perpendicular to the substrates. The bonded microstructures incorporate wall structures that divide the fluid layer of the device into individual volumes of single layers housed within the corresponding cavities. This provides the device with significant structural strength. In the described method, mating microstructures (i.e., male and female parts) are formed on each substrate, then precisely aligned with each other and bonded by press-fit, which also seals the fluid layer in the cavity.

[0007] Particle-based electrophoretic displays, in which multiple charged particles move through a suspension fluid under the influence of an electric field, have been the subject of vigorous research and development for many years. Compared to liquid crystal displays, such displays may have advantages such as good brightness and contrast, wide viewing angles, state bistable, and low power consumption. The terms “bistable” and “bistable” are used herein in their conventional sense in the art and refer to a display having a display element having a first and second display state that differs in at least one optical property, so that any given element will be driven to take either its first or second display state by a finite-duration addressing pulse, and after the addressing pulse has terminated, that state will persist for at least several times, e.g., at least four times, the minimum duration of the addressing pulse required to change the state of the display element. U.S. Patent No. 7,170,670 shows that several particle-based electrophoretic displays capable of grayscale are stable not only in their extreme black and white states but also in their intermediate gray states, and that the same is true for several other types of electro-optic displays. While this type of display is more appropriately called "multistable" rather than "bistable," for convenience, the term "bistable" may be used herein to cover both bistable and multistable displays.

[0008] As mentioned above, electrophoretic media require the presence of a suspension fluid. In most conventional electrophoretic media, this suspension fluid is liquid, but electrophoretic media can also be produced using a gaseous suspension 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 and 1,482,354; and International Patent Applications 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 likely to be susceptible to the same type of problems caused by particle sedimentation as liquid-based electrophoretic media, when the medium is used in orientations that allow such sedimentation, such as in labels placed in a vertical plane. In fact, particle sedimentation is considered a more serious problem in gas-based electrophoretic media than in liquid-based ones, because the lower viscosity of gaseous suspensions compared to liquids allows for faster sedimentation of electrophoretic particles.

[0009] Numerous patents and applications assigned to or in the names of the Massachusetts Institute of Technology (MIT) and E Ink Corporation, E Ink California, LLC, and their affiliates describe various techniques used in encapsulation and microcell electrophoresis and other electro-optical media. Encapsulated electrophoretic media comprise numerous small capsules, each of which comprises an internal phase containing electrophoretic particles in a fluid medium, and a capsule wall surrounding the internal phase. Typically, the capsules themselves form a coherent layer held within a polymer binder and positioned between two electrodes. In microcell electrophoretic displays, charged particles and fluids are not encapsulated within microcapsules, but rather retained in multiple cavities formed within a carrier medium, typically a polymer film. The techniques described in these patents and applications include: (a) Electrophoretic particles, fluids, and fluid additives; see, for example, U.S. Patent Nos. 7,002,728 and 7,679,814. (b) Capsules, binders, and encapsulation processes; see, for example, U.S. Patent Nos. 6,922,276 and 7,411,719. (c) Microcell structures, wall materials, and methods for forming microcells; see, for example, U.S. Patent Nos. 7,072,095 and 9,279,906. (d) Methods for filling and sealing microcells; see, for example, U.S. Patent Nos. 7,144,942 and 7,715,088. (e) Films and subassemblies containing electrophoretic materials; see, for example, 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, for example, U.S. Patents No. 7,116,318 and No. 7,535,624. (g) Color formation and color adjustment; see, for example, U.S. Patent Nos. 7,075,502 and 7,839,564. (h) A method for driving a display; see, for example, U.S. Patent Nos. 7,012,600 and 7,453,445. (i) Uses of the display; see, for example, U.S. Patent Nos. 7,312,784 and 8,009,348. (j) Non-electrophoretic displays as described in U.S. Patent No. 6,241,921 and U.S. Patent Application Publication No. 2015 / 0277160; as well as applications of encapsulation and microcell technologies other than displays; see, for example, U.S. Patent Applications No. 2015 / 0005720 and 2016 / 0012710.

[0010] Many of the aforementioned patents and applications recognize that the walls surrounding individual microcapsules in encapsulated electrophoretic media can be replaced by a continuous phase, thereby generating so-called polymer-dispersed electrophoretic displays in which the electrophoretic medium comprises a plurality of individual droplets of electrophoretic fluid and a continuous phase of polymer material, and that individual droplets of electrophoretic fluid in such polymer-dispersed electrophoretic displays can be considered capsules or microcapsules even if individual capsule membranes are not associated with each individual droplet; see, for example, U.S. Patent Application Publication No. 2002 / 0131147. For the purposes of this application, such polymer-dispersed electrophoretic media are considered a variant of encapsulated electrophoretic media.

[0011] Electrophoretic media are often opaque (for example, in many electrophoretic media, particles substantially block the transmission of visible light through the display) and operate in either light absorption mode or light reflection mode. However, electrophoretic devices can also be designed to operate in so-called “shutter mode,” in which one display state is substantially opaque and the other is substantially light-transmitting. See, for example, 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 mentioned above. Dielectric displays, which are similar to electrophoretic displays but rely on variations in electric field intensity, can operate in similar modes. See U.S. Patent 4,418,346. Other types of electrophoretic displays may also be capable of operating in shutter mode. In particular, when this "shutter mode" electrophoresis device is built on a transparent substrate, it is possible to adjust the transmission of light through the device.

[0012] Encapsulated or microcell electrophoretic displays typically do not suffer from the clustering and sedimentation failure modes of conventional electrophoretic devices and offer further advantages such as the ability to print or coat displays on a wide variety of flexible and rigid substrates. (The use of the term "printing" is intended to include all forms of printing and coating, including but not limited to: pre-metered coatings such as patch die coating, slot or extrusion coating, slide or cascade coating, curtain coating; roll coatings such as knife-over roll coating, forward and reverse roll coating; gravure coating; dip coating; spray coating; meniscus coating; spin coating; brush coating; air knife coating; silkscreen printing processes; electrostatic printing processes; thermal printing processes; inkjet printing processes; electrophoretic deposition; and other similar techniques. Thus, the resulting displays may be flexible. Furthermore, since the display medium can be printed (using a wide variety of methods), the displays themselves can be manufactured inexpensively.)

[0013] One potentially significant market for electrophoretic media is visible light-transmitting windows. As the energy performance of buildings becomes increasingly important, electrophoretic media can be used as coatings on windows to allow the rate of incident radiation transmitted through the window to be electronically controlled by varying the optical state of the electrophoretic media. The effective implementation of such “Visible Transmittance” ("VT") technology in buildings is expected to provide (1) a reduction in unwanted heating effects during hot weather, thereby reducing the amount of energy required for cooling, the size of air conditioning equipment, and peak power demand; (2) increased use of natural lighting, thereby reducing the energy used for lighting and peak power demand; and (3) increased occupant comfort by enhancing both thermal and visual comfort. Further advantages may be expected in automobiles or other vehicles where the ratio of glass surface to enclosed volume is significantly larger than in typical buildings. Specifically, the effective implementation of VT technology in automobiles is expected to provide not only the aforementioned benefits, but also (1) increased motoring safety, (2) reduced glare, (3) improved mirror performance (by using electro-optic coatings on the mirrors), and (4) increased usability of head-up displays. Other potential applications of VT technology include privacy glass and glare guards in electronic devices.

[0014] Many applications for switchable electrophoretic photomodulators and displays require covering large areas. For example, a photomodulator may be used in an office building window with an area of ​​several meters by several meters, or an electrophoretic display may be a wide-format label with diagonal measurements exceeding one meter. One factor limiting the fabrication of such large modulators and displays is the difficulty in fabricating seamless patterns of the large-area polymer structures used in the devices.

[0015] Polymer structures containing high-resolution 3D microstructures can be manufactured by photolithography using photomasks or by embossing processes using negative-type structural shims. While photolithography offers high resolution, it is typically a slow, sheet-to-sheet process. Roll-to-roll embossing processes facilitate continuous, high-throughput production, but the roll width is limited by the shim size, and creating seamless patterns is difficult due to the connection areas where the shims are mounted on the drum. Lithography processes using cylindrical masks also present challenges in achieving seamless patterns. There is a demand for processes to produce seamless patterns of microstructures on rolls with widths exceeding 1 m, preferably at process speeds exceeding 10 feet / min. There is also a demand for processes to manufacture polymer structures having multiple layers of microstructures potentially containing different materials. [Prior art documents] [Patent Documents]

[0016] [Patent Document 1] U.S. Patent No. 10,067,398 [Non-patent literature]

[0017] [Non-Patent Document 1] Kitamura, T., et al., “Electrical toner movement for electronic paper-like display”, IDW Japan, 2001, Paper HCS1-1 [Overview of the Initiative] [Means for solving the problem]

[0018] (overview) A roll-to-roll method for producing a seamless microstructure is provided, the method comprising: (a) continuously forming a laminated structure including a photomask film overlaid on a substrate, with a layer of photosensitive material between the substrate and the photomask film, wherein the photomask film comprises a pattern of light-transmissive regions and light-shielding regions; (b) irradiating the photomask film of the laminated structure formed in step (a), such that light passes through the light-transmissive regions of the photomask film to cure portions of the photosensitive material exposed by the light-transmissive regions, while leaving the remaining portions of the photosensitive material covered by the light-shielding regions uncured; (c) peeling the photomask film from the photosensitive material selectively cured in step (b); and (d) removing the uncured portions of the photosensitive material to form a layer of microstructure on the substrate from the cured portions of the photosensitive material.

[0019] According to one or more embodiments, step (a) of the method comprises advancing the photomask film, the substrate, and the layer of photosensitive material between a pair of pinch rollers to form the laminated structure.

[0020] According to one or more embodiments, the light comprises ultraviolet (UV) light.

[0021] According to one or more embodiments, the photosensitive material comprises a negative-type UV-sensitive material.

[0022] According to one or more embodiments, the microstructure comprises a crosslinked UV light-cured structure.

[0023] According to one or more embodiments, the method further comprises reusing the photomask film peeled off in step (c) of the method in a subsequent microstructure manufacturing process.

[0024] According to one or more embodiments, steps (a) and (b) of the method are performed on a multi-coating head production line.

[0025] According to one or more embodiments, step (b) of the method is performed while the laminated structure is being transported.

[0026] According to one or more embodiments, a layer of photosensitive material is coated onto the substrate prior to step (a), preferably using a rod, bar, blade, or slot die coating process.

[0027] According to one or more embodiments, the substrate to be laminated in step (a) includes an existing set of microstructures formed thereon.

[0028] According to one or more embodiments, the existing set of microstructures is formed by a pre-embossing process carried out on the substrate.

[0029] According to one or more embodiments, an existing set of microstructures is formed by a prior microstructure manufacturing process involving a substrate, which includes steps (a), (b), (c), and (d).

[0030] According to one or more embodiments, the method further includes, prior to step (a), drawing out the photomask film and the substrate from their respective rolls.

[0031] According to one or more embodiments, the width of each roll exceeds 1 meter.

[0032] According to one or more embodiments, the microstructure includes feature regions having an X / Y dimensional resolution of 200 μm to 2000 μm and a Z dimensional resolution of 1 μm to 500 μm.

[0033] According to one or more embodiments, a substrate on which a microstructure layer is formed has a width of more than 1 m.

[0034] According to one or more embodiments, the substrate on which the microstructure layer is formed has a length of more than 1 m.

[0035] According to one or more embodiments, the microstructure manufacturing process has a speed of more than 3 meters / minute.

[0036] According to one or more embodiments, step (d) of the method includes introducing a photosensitive material and a substrate into a solvent bath to dissolve any uncured portions of the photosensitive material and forming a layer of microstructures on the substrate.

[0037] According to one or more embodiments, a microstructure manufacturing method produces a seamless roll of substrate having layers of microstructures thereon.

[0038] According to one or more embodiments, the photomask film includes a photomask pattern printed on a release liner.

[0039] According to one or more embodiments, the photomask pattern faces and is adjacent to the photosensitive material.

[0040] According to one or more embodiments, the release liner faces and is adjacent to the photosensitive material.

[0041] According to one or more embodiments, a layer of microstructures on a substrate is used in constructing an electrophoretic device.

[0042] According to one or more embodiments, the photomask film includes grayscale feature areas for varying the intensity of light incident on the photosensitive material and for varying the height of the microstructure.

[0043] These and other aspects of the present invention will become clear when considered in the following description. [Brief explanation of the drawing]

[0044] (Brief explanation of the drawing) Embodiments of the present invention will be described here by reference to the accompanying drawings.

[0045] [Figure 1] Figures 1A to 1D are simplified cross-sectional views illustrating exemplary continuous lithography manufacturing processes for producing microstructures used in electrophoresis and other electro-optical devices, according to one or more embodiments.

[0046] [Figure 2] Figure 2 is a simplified cross-sectional view illustrating an exemplary continuous photolithography manufacturing process in which the photomask film is inverted, according to one or more embodiments.

[0047] [Figure 3] Figure 3 is a simplified cross-sectional view illustrating an exemplary continuous photolithography manufacturing process for generating multiple layers of microstructures on a substrate, according to one or more embodiments.

[0048] [Figure 4] Figure 4 is a simplified cross-sectional view illustrating a continuous lithography manufacturing process for generating a microstructure on a substrate having a photomask element, according to one or more embodiments.

[0049] [Figure 5] Figure 5 is a simplified cross-sectional view illustrating an exemplary continuous photolithography manufacturing process for generating microstructures on a substrate using two photomask films, according to one or more embodiments.

[0050] [Figure 6] Figure 6 is a plan view of an exemplary thin-film photomask having an emulsion photolithographic pattern according to one or more embodiments.

[0051] [Figure 7] Figure 7 shows the measured topography of the formed microstructure according to one or more embodiments.

[0052] [Figure 8] Figure 8 shows the measured topography of another set of formed microstructures according to one or more embodiments.

[0053] Similar or identical reference numbers are used to indicate common or similar elements.

[0054] The drawings depict one or more implementations of this concept, not as limitations, but as examples only. [Modes for carrying out the invention]

[0055] (Detailed explanation) Various embodiments disclosed herein relate to continuous photolithography manufacturing processes for generating microstructures used in large-area electrophoretic displays and optically modulated films. In one or more embodiments, a continuous lithography process is disclosed that uses a thin-film photomask which may have the same length as the substrate on which the microstructures are formed. This process enables seamless roll-to-roll lithography patterning of microstructures, such as microcell walls and non-planar polymer structures used in electrophoretic devices, on a roll having a width of more than 1 m, preferably at a process speed of more than 10 feet / min. Furthermore, this process enables improved control of the thickness of the microstructures and allows patterning of multiple layers of potentially different materials to form more complex microstructures. For example, this process can generate microstructures of transparent cones and wells overlaid with black walls for transmittance control in optically modulated films.

[0056] Figures 1A–1D are simplified cross-sectional views illustrating exemplary continuous photolithography manufacturing processes for generating microstructures used in electrophoretic devices, according to one or more embodiments. The process utilizes a thin-film photomask 100, shown in Figure 1A, which includes a printed light-shielding layer 105 on a release liner 104 (which may be, for example, a plastic substrate). The light-shielding layer 105 can be formed by applying a printing black or reflective material onto the release liner 104 to define a pattern of light-shielding regions 106 and light-transmitting regions 108. Various printing processes, including but not limited to screen printing, lithography, flexography, inkjet printing, aerosol jet printing, and gravure printing, can be used to apply the printing black or reflective material onto the release liner 104. Some of the known printing methods include continuous roll-to-roll printing of seamless high-resolution photomasks (see, for example, U.S. Patent No. 10,479,905).

[0057] As shown in Figure 1B, a laminated structure 110 comprising a thin-film photomask 100, a photosensitive material 102, and a substrate 101 is formed in a continuous manner. The photosensitive material 102 is nip-coated between the thin-film photomask 100 and the substrate 101 as the material is supplied between a pair of pinch rollers 112.

[0058] The photosensitive material 102 may be a positive or negative photoresist comprising various types of photosensitive polymers such as polyimide, acrylic resin, or epoxy resin. For example, the photosensitive material 102 may be a diazonaphthoquinone (DNQ)-novolac resin, which is a common type of positive photoresist. The photosensitive material 102 may also comprise dual-cure, thiolene, and other cross-linked chemical compositions commonly used as negative photoresists. In one or more preferred embodiments, the photosensitive material 102 comprises a negative ultraviolet (UV) photosensitive material.

[0059] The substrate 101 may comprise a variety of materials depending on its intended use in an electrophoretic device. For example, the substrate may comprise an indium tin oxide (ITO) coated polyethylene terephthalate (PET) film for forming a microcell cavity layer in an electrophoretic display device, or the substrate may comprise a polymer film for forming a non-planar polymer structure for concentrating absorbent charged particles in a light attenuator. In other examples, the substrate may comprise a flexible material such as transparent plastic or glass, which may be coated with a conductive layer (e.g., ITO). Suitable plastics include, for example, polycarbonate (PC), polycarbonate and copolymer blends, polyethersulfone (PES), cellulose triacetate (TAC), polyamide, p-nitrophenyl butyrate (PNB), polyetheretherketone (PEEK), polyethylene naphthalate (PEN), polyetherimide (PEI), polyarylate (PAR), or other similar plastics known in the art. Flexible glass may include materials such as Corning® Willow® Glass.

[0060] As shown in Figure 1C, the laminated structure 110 is then irradiated while it is moving forward and being transported through a light source 114 (e.g., a UV light source). If the photosensitive material 102 is a negative-type photosensitive material, the light from the light source 114 passes through the light-transmitting region 108 of the photomask film 100, curing the portion of the photosensitive material 102 exposed by the light-transmitting region 108, while leaving the remaining portion of the photosensitive material 102 covered by the light-shielding region 106 uncured.

[0061] Next, the photomask film 100 is peeled off from the selectively cured photosensitive material 102. This step can be carried out continuously using a release roller.

[0062] Next, as shown in Figure 1D, the uncured portion of the photosensitive material 102 is removed, leaving a desired pattern of UV-crosslinked microstructures 103 on the substrate 101. This developing step can be carried out, for example, by immersing the photosensitive material 102 in a solvent bath that dissolves the uncured portion of the photosensitive material 102. This step can be carried out continuously during material transport.

[0063] If the photosensitive material 102 is a positive-type photosensitive material, the light from the light source 114 makes the exposed portion of the photosensitive material 102 more easily soluble in the solvent, and as a result the exposed portion is removed, and a microstructure 103 can be formed from the remaining unexposed portion of the photosensitive material.

[0064] This generates a seamless roll of microstructure 103 (e.g., UV-crosslinked microstructure) as shown in Figure 1D.

[0065] The thin-film photomask 100 can generally be made to any desired length. For example, the thin-film photomask 100 may have the same length as the substrate 101 on which the microstructure 103 is formed. Furthermore, the microstructure 103 may be formed on a roll having a width of more than 1 m. As a result, large-area seamless patterns of microstructure 103 for large-area electrophoretic optical modulators and displays can be generated.

[0066] In one or more embodiments, the process is a roll-to-roll process having a process speed of more than 10 feet / minute.

[0067] In one or more embodiments, surface energy modification is performed on the substrate 101 and the release liner 104 in order to reduce residue from the removal of the photomask 100 and to provide a robust microstructure 103 with good adhesion to the substrate 101.

[0068] In one or more embodiments, the thin-film photomask 100 can be reused multiple times in additional microstructure fabrication processes.

[0069] In one or more embodiments, the thin-film photomask manufacturing step and microstructure photolithography may be performed sequentially in a single multi-coating head production line.

[0070] In one or more alternative embodiments, the laminated structure 110 is formed by applying a photosensitive material 102 onto a substrate 101 and then laminating a photomask film 100 onto the photosensitive material 102. The photosensitive material 102 may be applied onto the substrate 101 using rods, bars, blades, slot dies, and various other coating methods to allow control over a wider thickness range.

[0071] In one or more alternative embodiments, as shown in Figure 2, the photosensitive material 102, the substrate 101, and the photomask film 100 form a laminated structure 110' in which the photomask film 100 is inverted, i.e., the light-shielding layer 105 of the photomask film 100 faces and is in contact with the photosensitive material 102. The use of such a laminated structure 110' can reduce light scattering and enable the formation of a microstructure 103 with higher resolution, for example, a microstructure having feature parts smaller than 20 μm.

[0072] The continuous photolithography microstructure manufacturing process can be adapted to manufacture multiple layers of microstructures of the same or different materials. As illustrated in Figure 3, a substrate 101 having a set of microstructures 120 on it may be used to form a laminated structure 110'' with a photosensitive material 102 and a photomask film 100. Different sets of microstructures 103 may then be patterned on the substrate 101 using the photolithography process described above. In this way, multiple sets of microstructures 103, 120 containing the same or different materials may be formed on the substrate 101.

[0073] The initial microstructures 120 on the substrate 101 may be manufactured using the same continuous photolithography process as described above, or using other processes, such as embossing through shims. The microstructures 103 and 120 may perform the same or different functions in the device into which they are incorporated.

[0074] In one or more embodiments, the thin-film photomask 100 may include grayscale feature areas for varying the exposure intensity level of the UV light source 114 to create a 3D microstructure 103 having controllable height variation.

[0075] In one or more further alternative embodiments, a laminated structure 110'' is formed, as shown in Figure 4, in which a thin-film photomask 124 forms a lower substrate beneath the photosensitive material 102. The thin-film photomask 124 is intended to form part of the final structure and is not sacrificial. A printed light-shielding layer 105 of the thin-film photomask 124 is provided on the substrate 101. The release liner 104 is removed prior to the development of the photosensitive material 102 for forming the microstructure 103. The printed light-shielding layer 105' is transparent to visible light for use but is shielding against the transmission of g-line (436 nm) and h-line (405 nm) for photopatterning. As part of the final structure, the light-shielding layer 105' has the additional advantage of shielding certain types of harmful light during use.

[0076] In one or more further embodiments, a laminated structure 110'''' is formed, as shown in Figure 5, comprising a first thin-film photomask 100, a second thin-film photomask 124, and a photosensitive material 102 between them. The second thin-film photomask 124 includes a printed light-shielding layer 105' having grayscale features similar to those of the printed light-shielding layer 105' in Figure 4. The first thin-film photomask 100 includes light-shielding features similar to those of the printed light-shielding layer 105 in Figure 2. The photomasks 100, 124 form a pattern of microstructures 103', 103. Either one of the photomasks 100, 124 may remain as part of the final structure, while the other photomask is removed after the photopatterning step.

[0077] (Examples) The following process was used to form the microstructure pattern. Small droplets of a blue UV resin called Creative Materials' 127-24PB were cast onto an ITO-coated PET sheet. A 5×5 cm photomask 130 with the emulsion photolithographic pattern shown in Figure 6 was manually laminated onto the top of the resin on the PET-ITO sheet.

[0078] Next, a photomask 130 was used, and the UV polymer was patterned onto the microcell walls by curing the laminate with a DECO Delolux 03S curing lamp for 30 seconds. The photomask 130 was peeled off, and the raw resin, cured resin, and PET-ITO sheet were immersed in isopropyl alcohol (IPA) for 1 minute, and the uncured resin was wiped off using a cloth. Figure 7 shows the measured topography of the microstructure wall formed using this process.

[0079] Next, the above procedure was repeated, but with a PET-ITO sheet having an existing microstructure on top, similar to the process described in Figure 3. Figure 8 shows the measured topography of the microstructure wall formed using this process.

[0080] It will be apparent to those skilled in the art that numerous changes and modifications can be made in the specific embodiments of the present invention described above without departing from the scope of the invention. Therefore, the entire above description should be interpreted as illustrative rather than restrictive.

Claims

1. A method for manufacturing a roll-to-roll seamless microstructure, (a) A step of continuously forming a laminated structure including a photomask film superimposed on a substrate, with a layer of photosensitive material between the substrate and the photomask film, wherein the photomask film includes patterns of light-transmitting regions and light-shielding regions, (b) The photomask film of the laminated structure formed in step (a) is irradiated with light from a light source, exposing the portion of the photosensitive material covered by the light-transmitting region to the light, while leaving the remaining portion of the photosensitive material covered by the light-shielding region unexposed to the light, (c) A step of peeling the photomask film from the photosensitive material that was selectively irradiated in step (b), (d) the step of selectively removing the portion of the photosensitive material that has been exposed to the light, or the portion of the photosensitive material that has not been exposed to the light, and forming a microstructure layer on the substrate. Methods that include...

2. The method according to claim 1, wherein step (d) comprises selectively removing the portion of the photosensitive material exposed to the light to form a layer of microstructures on the substrate.

3. The method according to claim 1, wherein step (d) comprises selectively removing the portion of the photosensitive material that has not been exposed to the light to form a layer of microstructures on the substrate.

4. The method according to claim 1, wherein in step (b), the portion of the photosensitive material exposed to the light is cured by the light, while the remaining portion of the photosensitive material remains uncured, and in step (d), the uncured portion of the photosensitive material is removed, and a layer of the microstructure is formed on the substrate from the cured portion of the photosensitive material.

5. The method according to claim 1, wherein the light includes ultraviolet light.

6. The method according to claim 1 or claim 5, wherein the photosensitive material includes a negative-type ultraviolet-sensitive material.

7. The method according to claim 1, claim 5, or claim 6, wherein the microstructure includes a crosslinked ultraviolet photocurable structure.

8. The method according to any one of the claims, wherein step (a) is to advance the layers of the photomask film, the substrate, and the photosensitive material between a pair of pinch rollers to form the laminated structure.

9. The method according to any one of the claims, further comprising reusing the photomask film peeled off in step (c) in a subsequent microstructure manufacturing process.

10. Steps (a) and (b) are performed in a multi-coating head production line, according to any one of the claims.

11. Step (b) is the method according to any one of the claims, performed while the laminated structure is being transported.

12. The method according to any one of the claims, wherein the layer of photosensitive material is coated onto the substrate prior to step (a).

13. The method according to any one of the claims, wherein the layer of photosensitive material is coated onto the substrate prior to step (a) using a rod, bar, blade, or slot die coating process.

14. The method according to any one of the claims, wherein the substrate to be stacked in step (a) includes an existing set of microstructures formed thereon.

15. The method according to claim 14, wherein the existing set of microstructures is formed by a pre-embossing process performed on the substrate.

16. The method according to claim 14, wherein the existing set of microstructures is formed by a prior microstructure manufacturing process involving the substrate, comprising steps (a), (b), (c), and (d).

17. The method according to any one of the claims, further comprising drawing the photomask film and the substrate from the roll prior to step (a).

18. The method according to claim 17, wherein the width of each roll is greater than 1 meter.

19. The method according to any one of the claims, wherein the microstructure includes a feature portion having an X / Y dimensional resolution of 20 μm to 2000 μm and a Z dimensional resolution of 1 μm to 500 μm.

20. The method according to any one of the claims, wherein the substrate on which the microstructure layer is formed has a width of more than 1 m.

21. The method according to any one of the claims, wherein the substrate on which the microstructure layer is formed has a length of more than 1 m.

22. The method according to any one of the claims, wherein the microstructure manufacturing process has a speed of more than 3 meters / minute.

23. The method according to any one of the claims, wherein step (d) includes introducing the photosensitive material and the substrate into a solvent bath to dissolve the portion of the photosensitive material to be removed.

24. The method for manufacturing the microstructure, comprising generating a seamless roll of the substrate having a layer of the microstructure thereon, according to any one of the claims.

25. The method according to any one of the claims, wherein the photomask film includes a photomask pattern printed on a release liner.

26. The method according to claim 25, wherein the photomask pattern faces and is adjacent to the photosensitive material.

27. The method according to claim 25, wherein the release liner faces and is adjacent to the photosensitive material.

28. The method according to any one of the claims, wherein the layer of the microstructure on the substrate is used in constructing an electrophoretic device.

29. The method according to any one of the claims, wherein the photomask film includes a grayscale feature portion for changing the intensity of the light incident on the photosensitive material and for varying the height of the microstructure.

30. A layer of microstructure on a substrate generated by the method described in any of the above claims.

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