Optical control film and method for producing the same

Abstract

The present disclosure provides a light control film and a method for manufacturing the same. The method includes providing a microstructured film. The microstructured film includes a plurality of light-transmitting regions alternating with channels. The microstructured film is defined by a top surface and a pair of side surfaces of each light-transmitting region and a bottom surface of each channel. The method further includes coating the pair of side surfaces of each light-transmitting region and the bottom surface of each channel with a coating. The coating includes light-absorbing particles dispersed in a liquid. The method further includes drying the coating to selectively deposit the light-absorbing particles on the pair of side surfaces of each light-transmitting region.

Description

Technical Field

[0001] The present invention relates to a light control film and a method for manufacturing the same.

Background Art

[0002] A light control film (LCF), also known as a "privacy film," is an optical film that adjusts the light transmittance. Various LCFs are known and typically include a light transmissive film having a plurality of parallel louvers. The louvers are formed of a light absorbing material.

[0003] The LCF can be placed close to a display surface, an image surface, or any other surface to be viewed. At normal incidence (i.e., a viewing angle of 0 degrees) where an observer views an image through the LCF in a direction perpendicular to the film surface, the image is visible. As the viewing angle increases, the amount of light transmitted through the LCF decreases until the viewing cut-off angle is reached, at which point substantially all of the light is blocked by the light absorbing material and the image becomes invisible. This can provide privacy to the observer by blocking the view of others outside the typical range of the viewing angle.

[0004] The LCF can have a low on-axis transmittance due to the absorption of light by the light absorbing material. Some efforts have been made to improve the on-axis transmittance of the LCF. For example, the aspect ratio of the LCF can be increased to reduce the thickness of the light absorbing material. However, it has not been possible to provide an LCF with a high aspect ratio using conventional microfabrication methods.

Summary of the Invention

[0005] The present invention relates to a light control film and a method for manufacturing the same. The present invention also relates to a light control film for use with optical applications.

[0006] In one embodiment of the present disclosure, a method of manufacturing a light control film is provided. The method includes providing a microstructured film. The microstructured film includes a plurality of light transmission regions alternating with channels. The microstructured film is defined by the upper surface and a pair of side surfaces of each light transmission region and the bottom surface of each channel. The method further includes coating the pair of side surfaces of each light transmission region and the bottom surface of each channel. The coating includes light absorbing particles dispersed in a liquid. The method further includes drying the coating to selectively deposit the light absorbing particles on the pair of side surfaces of each light transmission region.

[0007] In some embodiments, the coating is an aqueous coating and the liquid is water.

[0008] In some embodiments, the upper surface of each light transmission region and the bottom surface of each channel do not contain light absorbing particles.

[0009] In some embodiments, the light absorbing particles have an average particle size of at least 20 nm.

[0010] In some embodiments, the light absorbing particles have an average particle size of at least 1 micrometer.

[0011] In some embodiments, drying of the coating is achieved by at least one of air drying, infrared heating, and oven drying.

[0012] In some embodiments, drying of the coating is achieved at a temperature of at least 50 °C.

[0013] In some embodiments, the method further includes performing a surface treatment on the surface of the microstructured film. Further, in some embodiments, the surface treatment includes at least one of oxygen plasma treatment, corona treatment, and fluorocarbon plasma treatment.

[0014] In some embodiments, the microstructured film is not surface-treated.

[0015] In some embodiments, the method further includes filling the channels of the microstructured film with a material similar to that of the light-transmitting region.

[0016] In some embodiments, the coating includes additives.

[0017] In some embodiments, the additives include at least one of a binder, a surfactant, and a crosslinking agent.

[0018] In some embodiments, the binder includes at least one of an anionic binder, a cationic binder, and an amphoteric ion binder.

[0019] In some embodiments, the light-absorbing particles include carbon black particles.

[0020] In some embodiments, the light-absorbing particles are present at a concentration of at least 1% by weight based on the total weight of the coating.

[0021] In some embodiments, the microstructured film further includes a base layer. The light-transmitting region extends from the base layer.

[0022] In some embodiments, the microstructured film includes a polymerizable resin.

[0023] In another embodiment, a method for manufacturing a light control film is provided. The method includes providing a microstructured film. The microstructured film includes a plurality of light transmissive regions alternating with channels. The microstructured film is defined by the upper surface and a pair of side surfaces of each light transmissive region, and the bottom surface of each channel. The method further includes performing a first surface treatment and then selectively performing a second surface treatment on the upper surface of each light transmissive region and the bottom surface of each channel. The method further includes coating the pair of side surfaces of each light transmissive region and the bottom surface of each channel. The coating includes light absorbing particles dispersed in a liquid. The method further includes drying the coating to selectively deposit the light absorbing particles on the pair of side surfaces of each light transmissive region.

[0024] In some embodiments, the first surface treatment includes an oxygen plasma treatment or a corona treatment.

[0025] In some embodiments, the second surface treatment includes a fluorocarbon plasma treatment.

[0026] In some embodiments, the coating is an aqueous coating and the liquid is water.

Brief Description of the Drawings

[0027] By considering the following "Modes for Carrying Out the Invention" in relation to the following figures, the exemplary embodiments disclosed herein can be more fully understood. The figures are not necessarily to scale. Like numbers used in the figures refer to like components. When there are multiple like elements, a single reference number can be assigned to each of the multiple like elements using a lowercase designation to refer to a particular element. When referring to elements collectively or to one or more unspecified elements, the lowercase designation can be omitted. However, it should be understood that using a certain number to refer to a component in a given figure is not intended to limit that component to being labeled with the same number in another figure.

Figure 1A

Figure 1B

Figure 2

Figure 3A

Figure 3B

Figure 3C

Figure 3D

Figure 3E

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Figure 6A

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Figure 7

DETAILED DESCRIPTION OF THE INVENTION

[0028] In the following description, reference is made to the accompanying drawings, which form a part hereof and in which various embodiments are shown by way of example. It should be understood that other embodiments may be contemplated and practiced without departing from the scope or spirit of the present disclosure. Therefore, the following detailed description of the invention is not to be construed in a limiting sense.

[0029] In the context of the present disclosure, the terms "first" and "second" are used as identifiers. Thus, such terms should not be construed as limiting the present disclosure. When used in conjunction with a feature or element, the terms "first" and "second" may be exchanged throughout the embodiments of the present disclosure.

[0030] As used herein, when a first material is said to be "similar" to a second material, at least 90% by weight of the first material and the second material is the same, and if there is a variation between the first material and the second material, the variation is less than about 10% by weight of each of the first material and the second material.

[0031] The present disclosure is directed to a light control film and a method of manufacturing the same. The microstructured film includes a plurality of light transmission regions alternating with channels. The microstructured film is defined by the upper surface and a pair of side surfaces of each light transmission region, and the bottom surface of each channel. The method further includes coating the pair of side surfaces of each light transmission region and the bottom surface of each channel. The coating includes light absorbing particles dispersed in a liquid. In some embodiments, the coating is an aqueous coating and the liquid is water. The method further includes drying the coating to selectively deposit the light absorbing particles on the pair of side surfaces of each light transmission region. The light control film has various applications such as displays, windows, and the like.

[0032] FIG. 1A is a perspective view of an exemplary light control film ("LCF"). In one embodiment, the LCF 100 has a high aspect ratio. The LCF includes a light input surface 110 and a light output surface 120 on the opposite side of the light input surface 110. The light output surface 120 is typically parallel to the light input surface 110. The LCF 100 includes alternating light transmission regions 130 (alternatively referred to as "transmission regions 130") and light absorption regions 140 (alternatively referred to as "absorption regions 140") disposed between the light output surface 120 and the light input surface 110.

[0033] As shown in FIG. 1A, the transmission region 130 is typically integral with the land region L, which means that there is no interface between the land region and the base portion 131 of the transmission region 130. Alternatively, the LCF may lack such a land region L, or there may be an interface between the land region L and the transmission region 130. Typically, the land region L is disposed between the alternating transmission regions 130 and absorption regions 140 and the light input surface 110.

[0034] Alternatively, in some embodiments, the surface 120 may be the light input surface and the surface 110 may be the light output surface. In such a case, the land region is disposed between the alternating transmission regions 130 and absorption regions 140 and the light output surface.

[0035] The transmission region 130 can be defined by a width W T . Excluding the land region L, the transmission region 130 typically has the same height as the absorption region 140 nominally. In this embodiment, the height H A of the absorption region is at least 30, 40, 50, 60, 70, 80, 90 or 100 micrometers. In some cases, the height H A is 200, 190, 180, 170, 160 or 150 micrometers or less. In some cases, the height H A is 140, 130, 120, 110, or 100 micrometers or less. The LCF 100 typically includes a plurality of transmission regions 130 having nominally the same height and width. In some cases, the transmission region 130 has a height H T , a maximum width W T at the widest part of the transmission region 130, and an aspect ratio of at least 1.75 H T / W T . In some embodiments, H T / W Tis at least 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, or 5.0. In other embodiments, the aspect ratio of the transmissive region 130 is at least 6, 7, 8, 9, 10. In other embodiments, the aspect ratio of the transmissive region 130 is at least 15, 20, 25, 30, 35, 40, 45, or 50.

[0036] The absorption region 140 has a height H defined by the distance between the bottom surface 155 and the top surface 145 A and such top surface 145 and bottom surface 155 are typically parallel to the light output surface 120 and the light input surface 110, respectively. The absorption region 140 has a maximum width W A and is spaced apart by a pitch P along the light output surface 120 A only.

[0037] The width W of the absorption region at the base (i.e., adjacent to the bottom surface 155) A is typically nominally the same as the width of the absorption region 140 adjacent to the top surface 145. However, if the width of the absorption region at the base is different from the width adjacent to the top surface, the width is defined by the maximum width. The maximum widths of the plurality of absorption regions can be averaged with respect to the area of interest, such as the area where the transmittance (e.g., luminance) is measured. The absorption regions 140 of the LCF100 typically have nominally the same height and width. The absorption region 140 typically has a width of 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 micrometer or less. The absorption region 140 typically has a width of 900, 800, 700, 600, or 500 nanometers or less and has a width of at least 50, 60, 70, 80, 90, or 100 micrometers.

[0038] The absorption region 140 has an aspect ratio (H A / W A) can be defined by. Typically, the aspect ratio of the absorption region is at least 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10. In some embodiments, the height and width of the absorption region(s) are selected such that the absorption region(s) 140 has a higher aspect ratio. In some cases, the aspect ratio of the absorption region is at least 25, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or 100. In other cases, the aspect ratio of the absorption region is at least 200, 300, 400, or 500. The aspect ratio can be up to 10,000 or more. In some cases, the aspect ratio is 9,000, 8,000, 7,000, 6,000, 5,000, 4,000, 3000, 2,000, or 1,000 or less.

[0039] As shown in FIG. 1B, the LCF 100 includes alternating transmission regions 130 and absorption regions 140, and an interface 150 between the transmission region 130 and the absorption region 140. The interface 150 forms a wall angle θ with a line 160 perpendicular to the light output surface 120. The larger the wall angle θ, the lower the transmittance at normal incidence, that is, at a viewing angle of 0 degrees. A smaller wall angle is preferred so that the transmittance of light at normal incidence can be made as large as possible. Typically, the wall angle θ is less than 10, 35 9, 8, 7, 6, or 5 degrees. More specifically, the wall angle θ is 2.5, 2.0, 1.5, 1.0, 0.5, or 0.1 degrees or less. In the illustrated embodiment, the wall angle θ is zero or close to zero. When the wall angle θ is zero, the angle between the absorption region 140 and the light output surface 120 is 90 degrees. The transmission region 130 can have a rectangular or trapezoidal cross-section depending on the wall angle θ.

[0040] When the incident light undergoes total internal reflection (TIR) from the interface between the absorption region 140 and the transmission region 130, the transmittance (e.g., the luminance of visible light) can be increased. Whether the light ray will undergo TIR can be determined from the incident angle with respect to the interface and the difference in refractive indices of the materials of the transmission region 130 and the absorption region 140.

[0041] As shown in FIG. 1B, the transmission region 130 between the absorption regions 140 has an interface angle θI defined by the geometry of the alternating transmission regions 130 and absorption regions 140. As shown in FIGS. 1A and 1B, the interface angle θI can be defined by the intersection of two lines. The first line extends from a first point defined by the bottom and sidewall surfaces of the first absorption region 140 and a second point defined by the top and sidewall surfaces of the nearest second absorption region 140. The second line extends from a first point defined by the top and sidewall surfaces of the first absorption region 140 and a second point defined by the bottom and sidewall surfaces of the second absorption region 140.

[0042] In some cases, the polar cutoff field of view angle θP is equal to the sum of the polar cutoff field of view half-angle θ1 and the polar cutoff field of view half-angle θ2, each of which is measured from the normal to the light input surface 110. In some cases, the polar cutoff field of view angle θP is symmetric, and the polar cutoff field of view half-angle θ1 is equal to the polar field of view half-angle θ2. Alternatively, the polar cutoff field of view angle θP may be asymmetric, and the polar cutoff field of view half-angle θ1 is not equal to the polar cutoff field of view half-angle θ2.

[0043] The light control film 100 described herein can have any desired polar field of view cutoff angle θP. In one aspect, the polar field of view cutoff angle θP is in the range of 40° to 90° or even a larger range. The polar field of view cutoff angle θP can be determined by various parameters, namely H A 、W A 、W T 、P A 、and the refractive index of the material of the light control film 100.

[0044] Figure 2 shows a microstructured film 200 according to an embodiment of the present disclosure. The microstructured film 200 is coated to fabricate an LCF. As shown in FIG. 2, the microstructured film 200 includes a microstructured surface including a plurality of channels 201a to 201d (collectively referred to as "channel 201") on a base layer 260. The microstructured surface is disposed on the upper surface 210 of the base layer 260. Further, a continuous land layer L1 may exist between the bottom surface 205 of the channel 201 and the upper surface 210 of the base layer 260. Alternatively, the channel 201 may extend completely through the microstructured film 200. In another aspect (not shown), the bottom surface 205 of the groove or channel 201 may coincide with the upper surface 210 of the base layer 260. The microstructured film 200 further includes a plurality of light transmission regions 230 extending from the continuous land layer L1. In some cases, the base layer 260 is a pre-formed film including an organic polymer material different from the transmission region 230, as will be described later.

[0045] In the illustrated embodiment, the light transmission region 230 is a protrusion. The height and width of the transmission region 230 are defined by adjacent channels (e.g., 201a and 201b). The transmission region 230 may be defined by an upper surface 220, a bottom surface 231, and a pair of side surfaces 232 and 233 that connect the upper surface 220 to the bottom surface 231. The microstructured film 200 has a surface defined by the upper surface 220 and the pair of side surfaces 232, 233 of each light transmission region 230 and the bottom surface 205 of each channel 201.

[0046] In some cases, the side surfaces 232, 233 may be parallel to each other. Alternatively, each of the side surfaces 232, 233 may have a tapered profile. Further, the tapered profile of each of the side surfaces 232, 233 tapers towards the upper surface 220 of the microstructured film 200. Alternatively, the side surfaces 232, 233 may have a vertical profile. Further, the cross-section of each of the plurality of light transmission regions 230 includes at least one of a square shape, a rectangular shape, a curved shape, a trapezoidal shape, and a polygonal shape. In the illustrated embodiment, the light transmission region 230 has a rectangular shape. The light transmission regions 230 may be equally spaced from each other.

[0047] In some embodiments, the light transmission region 230 is formed with a high-definition surface on the base layer 260. An exemplary high-definition surface process is described in U.S. Patent No. 8,503,122 (B2) (Liu et al.). A typical high-definition surface process includes depositing a sufficient amount of a polymerizable composition on the microstructured forming surface of the master negative to fill the cavities of the master. The cavities are then filled by moving the beads of the polymerizable composition between a preformed base and the master. The composition is then cured. The light transmission region 230 may be formed on the base layer 260 by various methods such as extrusion, casting and curing, coating, or some other method.

[0048] In some embodiments, the protrusions (e.g., the light transmission regions 230) have a pitch P of at least 10 micrometers T The pitch P T is, as shown in FIG. 2, the distance between the start of the first protrusion (e.g., the transmission region) and the start of the second protrusion (e.g., the transmission region). The pitch P T may be at least 15, 20, 25, 30, 35, 40, 45, or 50 micrometers. The pitch P T is typically 1 mm or less. The pitch P T is typically 900, 800, 700, 600, or 500 micrometers or less. In some cases, the pitch P Tis typically 550, 500, 450, 400, 350, 300, 250, or 200 micrometers or less. In some embodiments, the pitch P T is 175, 150, 100 micrometers or less. In some cases, the protrusions are evenly spaced at a single pitch. Alternatively, the protrusions may be spaced so that the pitch between adjacent protrusions is not the same.

[0049] In some cases, the light transmission region 230 is made of a polymerizable resin. In some cases, the polymerizable resin may be optically transparent with a substantially high transmittance in the wavelength range of about 300 nanometers (nm) to about 800 nm. The polymerizable resin may include a combination of a first polymerizable component and a second polymerizable component selected from (meth)acrylate monomers, (meth)acrylate oligomers, and mixtures thereof. As used herein, "monomer" or "oligomer" is any substance that can be converted into a polymer. The term "(meth)acrylate" refers to both acrylate compounds and methacrylate compounds. In some cases, the polymerizable composition may include (meth)acrylated urethane oligomers, (meth)acrylated epoxy oligomers, (meth)acrylated polyester oligomers, (meth)acrylated phenolic oligomers, (meth)acrylated acrylic oligomers, and mixtures thereof. The polymerizable resin may be a radiation-curable polymer resin such as a UV-curable resin. More specifically, a casting and curing process by UV crosslinking of an acrylate resin for a custom tool was used. The tool was made in a "square wave" design, which means that the pitch is approximately equal to the width of the channel.

[0050] An article having a microstructure (e.g., the microstructured film 200 shown in FIG. 2) can be prepared by any suitable method. In one aspect, an article having a microstructure (e.g., the microstructured film 200 shown in FIG. 2) can be prepared by a method including: (a) preparing a polymerizable composition; (b) depositing an amount of the polymerizable composition sufficient to barely fill the cavities of the master onto a master negative microstructured surface (e.g., a tool); (c) filling the cavities by moving beads of the polymerizable composition between a base layer (e.g., a preformed film) at least one of which is flexible and the master; and (d) curing the composition. The deposition temperature can range from ambient temperature to about 180°F (82°C). The master can be made of a metal such as nickel, chromium-plated or nickel-plated copper or brass, or a thermoplastic material that is stable under polymerization conditions and has a surface energy that allows for clean removal of the polymerized material from the master. When the base layer is a preformed film, one or more of the surfaces of the film can optionally be primed or otherwise treated to promote adhesion to the organic material in the light transmissive regions.

[0051] The polymerizable composition may include a combination of a first polymerizable component and a second polymerizable component selected from (meth)acrylate monomers, (meth)acrylate oligomers, and mixtures thereof. As used herein, "monomer" or "oligomer" is any substance that can be converted into a polymer. The term "(meth)acrylate" means both acrylate compounds and methacrylate compounds. Optionally, the polymerizable composition can include (meth)acrylated urethane oligomers, (meth)acrylated epoxy oligomers, (meth)acrylated polyester oligomers, (meth)acrylated phenolic oligomers, (meth)acrylated acrylic oligomers, and mixtures thereof.

[0052] Examples of base layer materials include, for example, styrene-acrylonitrile, cellulose acetate butyrate, cellulose acetate propionate, cellulose triacetate, polyethersulfone, polymethyl methacrylate, polyurethane, polyester, polycarbonate, polyvinyl chloride, polystyrene, polyethylene naphthalate, copolymers or blends based on naphthalenedicarboxylic acid, polyethylene, polypropylene, and polycyclo-olefins, polyimides, and polyolefin-based materials such as cast films or oriented films of glass. Optionally, the base layer 260 can contain a mixture or combination of these materials. In some embodiments, the base layer may be multilayered or can contain a dispersed component suspended or dispersed in a continuous phase.

[0053] Examples of base layer materials include polyethylene terephthalate (PET) and polycarbonate (PC). Examples of useful PET films include a photograde polyethylene terephthalate available under the trade name "Melinex 618" from DuPont Films, Wilmington, Delaware. Examples of optically graded polycarbonate films include LEXAN.RTM polycarbonate film 8010 available from GE Polymershapes, Seattle, Washington, and Panlite 1151 available from Teijin Kasei, Alpharetta, Georgia.

[0054] Figures 3A-3E illustrate a method of manufacturing a light control film. Figure 3A shows a microstructured film 500. The microstructured film 500 includes a light transmission region 501. Channels 502 are defined between adjacent light transmission regions 501. Each light transmission region 501 has an upper surface 503 and a pair of side surfaces 504. Each channel 502 has a bottom surface 505. The bottom surface 505 of each channel 502 coincides with the base layer 506 of the microstructured film 500.

[0055] Figure 3B shows the coating of side 504 of channel 502. Each channel 502 is coated with a coating containing light-absorbing particles 507 dispersed in a liquid. In some embodiments, the coating is an aqueous coating and the liquid is water. Specifically, the light-absorbing particles 507 are disposed in water.

[0056] In some cases, the aqueous coating contains additives. The additives may be a binder, a surfactant, a crosslinking agent, or a combination thereof. In some cases, the binder may be an anionic binder, a cationic binder, and an amphoteric ion binder. Suitable examples of the binder include polyurethane, poly(vinyl alcohol), polyester, polyester-melamine, sulfonated polyester, fluoropolymer, polyacrylate, styrene-acrylic acid copolymer, styrene-acrylic acid-alkyl acrylate copolymer, styrene-maleic acid copolymer, styrene-maleic acid-alkyl acrylate copolymer, styrene-methacrylic acid copolymer, styrene-methacrylic acid-alkyl acrylate copolymer, styrene-maleic acid half ester copolymer, vinyl naphthalene-acrylic acid copolymer, vinyl naphthalene-maleic acid copolymer, and salts thereof.

[0057] In combination with the light-absorbing particles 507, various surfactants can be used. Suitable nonionic or amphoteric surfactants include fluorinated alkyl polyoxyethylene ethanol; fluorinated alkyl alkoxylate; fluorinated alkyl ester; alkyl polyethylene oxide; alkyl phenyl polyethylene oxide; acetylene polyethylene oxide; polyethylene oxide block copolymer; diesters of amine, amide, ester (such as fatty acid ester) and polyethylene oxide; sorbitan fatty acid ester; glycerin fatty acid ester; fluorinated alkyl amphoteric mixture; polyether siloxane copolymer; organo-modified polysiloxane; dimethyl-polysiloxane blend. Suitable ionic surfactants include anionic surfactants selected from ammonium perfluoroalkyl sulfonate; lithium perfluoroalkyl sulfonate; potassium perfluoroalkyl sulfonate; fatty acid salt; alkyl sulfate ester salt; alkyl allyl sulfonate salt, dialkyl sulfosuccinate salt, alkyl phosphate ester salt, and polyoxyethylene alkyl sulfate ester salt. Suitable cationic surfactants include fluorinated alkyl quaternary ammonium iodide.

[0058] In some cases, the light-absorbing particles 507 can be provided in combination with a cross-linking agent. The choice of cross-linking agent will depend on the surface functionality of the light-absorbing particles and can therefore be selected from materials generally known for such applications. Examples of materials that can be used are aziridine, carbodiimide, isocyanate, melamine, epichlorohydrin, polycation, polyanion.

[0059] The light-absorbing material useful for forming the light-absorbing particles 507 may be any suitable material that functions to absorb or block light in at least a portion of the visible spectrum. Preferably, the light-absorbing material is coated on the side surface 504 of the light-transmitting region 501 or otherwise provided on the side surface 504 of the light-transmitting region 501 to form a light-absorbing region within the LCF. Exemplary light-absorbing materials include black or other light-absorbing colorants (such as carbon black or other pigments or dyes, or combinations thereof). Other light-absorbing materials can include particles or other scattering elements that function to prevent light from passing through the light-absorbing region.

[0060] A variety of commercially available pigments can be used as the material for the light-absorbing particles 507. For example, suitable pigments can be obtained commercially as colloidal stable aqueous dispersions from manufacturers such as Cabot, Clariant, DuPont, Dainippon, and Degussa. Particularly suitable pigments include pigments available under the name CAB-O-JET® from Cabot Corporation, such as 250C (blue-green), 260M (red-violet), 270Y (yellow), or 352K (black). In some cases, the light-absorbing (e.g., pigment) particles 507 are surface-treated to impart an ionic functional group. Examples of ionic functional groups suitable for the light-absorbing particles 507 include sulfonate functional groups, carboxylate functional groups, and phosphate or bisphosphonate functional groups. In some embodiments, surface-treated light-absorbing (e.g., pigment) particles having an ionic functional group are commercially available. For example, the CAB-O-JET® pigments sold under the trade names 250C (blue-green), 260M (red-violet), 270Y (yellow), and 200 (black) and available commercially from Cabot Corporation contain sulfonate functional groups. The CABO-O-JET® pigments available commercially from Cabot Corporation under the trade names 352K (black) and 300 (black) contain carboxylate functional groups.

[0061] In some cases, multiple light-absorbing materials (e.g., pigments) can be utilized to achieve a specific hue, shade, or color in the final product. When multiple light-absorbing materials (e.g., pigments) are used, the materials are selected to ensure both the affinity and performance between the materials themselves and the affinity and performance with the optical product components.

[0062] In some embodiments, the median particle size of the light-absorbing particles 507 is generally less than 1 micrometer. In some cases, the median particle size is 900, 800, 700, 600, or 500 nm or less. In some cases, the median particle size is 450, 400, 350, 300, 250, 200, or 100 nm or less. In some cases, the median particle size is 90, 85, 80, 75, 70, 65, 60, 55, or 50 nm or less. In some cases, the median particle size is 30, 25, 20, or 15 nm or less. The median particle size is typically at least 1, 2, 3, 4, or 5 nanometers. In some embodiments, the light-absorbing particles 507 can be nanoparticles. The particle size of the nanoparticles in the absorption region can be measured using transmission electron microscopy or scanning electron microscopy. In some embodiments, the light-absorbing particles 507 have an average particle size of at least 20 nm. In some embodiments, the light-absorbing particles 507 have an average particle size of less than 1 micrometer.

[0063] In some embodiments, the light-absorbing particles 507 are present at a concentration of at least 1 wt% based on the total weight of the aqueous coating. In some other embodiments, the concentration of the light-absorbing particles 507 is at least 2, 3, 4, 6, 8, 10, 15, 20, 25, 30, 35, 40, 45, or 50 wt% of the total weight of the aqueous coating. In some other embodiments, the concentration of the light-absorbing particles 507 is less than 50, 40, 30, 20, 10, or 5 wt% of the total weight of the aqueous coating. The concentration of the light-absorbing particles 507 in the aqueous coating can be determined by any method known in the art, such as thermogravimetric analysis.

[0064] In some embodiments, the coating method may include, for example, spin coating, bar coating, screen printing, inkjet printing, slit die coating, flood coating, and the like. Alternatively, each channel 502 of the microstructured film 500 can be filled with an aqueous coating solution.

[0065] Furthermore, as shown in FIG. 3C, the aqueous coating further includes a drying step that results in a selective coating of the side surfaces 504 of each light transmission region 501. The upper surface 503 of the light transmission region 501 and the bottom surface 505 of the channel 502 do not contain light absorbing particles. Typically, the drying step can be achieved by any conventional drying technique known in the art. More specifically, drying can be achieved by at least one of air drying, infrared drying, and oven drying. In some cases, the drying step can be achieved at room temperature. In some cases, drying is achieved at a temperature of at least 40, 50, 60, 70, 80, 90, or 100 °C or higher. Alternatively, drying can be achieved by using an infrared heater. In some cases, during the step of drying the aqueous coating, an air flow 509 may be supplied substantially parallel to the channels 502 of the microstructured film 500 so that the air flow does not interfere with the liquid. Due to drying, a coating of light absorbing particles 507 can be formed on the side surfaces 504. The coating can proceed downward along the side surfaces 504.

[0066] Referring to FIG. 3D, a selectively coated microstructured film 500 is shown. More specifically, a coating 508 is formed on the side surfaces 504 of each light transmission region 501. The coating 508 can be formed by drying an aqueous coating that results in the deposition of light absorbing particles 507 on the side surfaces 504, as shown in FIG. 3C. The thickness of the coating 508 on the side surfaces 504 of the light transmission region 501 is at least 0.1 μm. Furthermore, the upper surface 503 of each light transmission region 501 and the bottom surface 505 of each channel 502 do not contain a coating of light absorbing particles 507.

[0067] As shown in FIG. 3E, the microstructured film 500 includes a plurality of light transmission regions 501 and light absorption regions formed by a coating 508. Each channel 502 (shown in FIG. 3D) is filled with a material similar to that of the light transmission region 501. Specifically, each channel 502 is filled back with a material similar to that of the light transmission region 501 to form a light transmission region 510. In some cases, the material includes an organic polymer material such as a curable polymeric resin. Each light transmission region 510 is disposed between two light absorption regions formed by the coating 508. Therefore, the microstructured film 500 may include alternative light transmission regions 501, 510 and light absorption regions formed by the coating 508. Therefore, the microstructured film 500 is a light control film as shown in FIG. 3E.

[0068] Referring to FIG. 4, there is a method 300 for manufacturing a light control film. The method 300 will be described with reference to FIGS. 3A to 3E.

[0069] In step 302, the method includes providing a microstructured film 500. The microstructured film 500 includes a plurality of light transmission regions 501 alternating with a plurality of channels 502. Each of the light transmission regions 501 includes an upper surface 503 and a pair of side surfaces 504 extending from the upper surface 503. Each channel 502 includes a bottom surface 505. The surface of the microstructured film 500 is defined by the upper surface 503, the side surfaces 504, and the bottom surface 505.

[0070] In some cases, the method further includes performing a surface treatment on the surface of the microstructured film 500. More preferably, the surface treatment includes at least one of an oxygen plasma treatment, a corona treatment, and a fluorocarbon plasma treatment. In some cases, the microstructured film 500 is not surface plasma treated.

[0071] In step 304, method 300 further includes coating the side surfaces 504 of each light transmission region 501 and the bottom surface 505 of each channel 502. In some embodiments, the coating is an aqueous coating. The aqueous coating includes light absorbing particles 507 dispersed in water.

[0072] In some cases, the coating further includes an additive. In some cases, the additive includes at least one of a binder, a surfactant, and a crosslinking agent. In some cases, the light absorbing particles are present at a concentration of at least 1 wt% based on the total weight of the coating.

[0073] In step 306, method 300 further includes drying the coating to selectively deposit the light absorbing particles 507 on a pair of side surfaces 504 of each light transmission region 501.

[0074] In some cases, the drying of the coating includes at least one of air drying, infrared heating, and oven drying. In some cases, the drying is achieved at a temperature of at least 50 °C.

[0075] Referring to FIG. 5, there is a method 700 for manufacturing a light control film. Method 700 will be described with reference to FIGS. 3A - 3E.

[0076] In step 702, method 700 includes providing a microstructured film 500. The microstructured film 500 includes a plurality of light transmission regions 501 alternating with a plurality of channels 502. Each of the light transmission regions 501 includes an upper surface 503 and a pair of side surfaces 504 extending from the upper surface 503. Each channel 502 includes a bottom surface 505. The surface of the microstructured film 500 is defined by the upper surface 503, the side surfaces 504, and the bottom surface 505.

[0077] In step 704, method 700 includes performing a first surface treatment on the surface of the microstructured film 500. In some embodiments, the first surface treatment includes a plasma treatment method. In some embodiments, the first surface treatment includes at least one of an oxygen plasma treatment or a corona treatment.

[0078] In step 706, method 700 includes selectively performing a second surface treatment on the upper surface 503 of each light transmission region 501 and the bottom surface 505 of each channel 501. In some embodiments, the second surface plasma treatment includes a fluorocarbon plasma treatment.

[0079] In step 708, method 700 further includes coating the surface-treated microstructured film 500 with an aqueous coating containing light-absorbing particles 507.

[0080] In some cases, the light-absorbing particles 507 are present at a concentration of at least 1 wt% based on the total weight of the aqueous coating.

[0081] In some embodiments, the aqueous coating may include additives. In some cases, the additives include at least one of a binder, a surfactant, and a crosslinking agent. In some cases, the binder may include at least one of an anionic binder, a cationic binder, and an amphoteric binder.

[0082] In step 710, method 700 includes drying the aqueous coating to selectively deposit the light-absorbing particles 507 on a pair of side surfaces 504 of each light transmission region 501.

[0083] In some cases, the aqueous coating is achieved at a temperature of at least 50 °C. In some cases, drying the aqueous coating includes at least one of air drying, infrared heating, and oven drying.

[0084] Referring to FIGS. 6A and 6B, a method of performing a surface treatment on the surface of a structured film 800 is shown. Referring to FIG. 6A, this method includes manufacturing a microstructured film 800 that includes a plurality of light-transmissive regions 802. Channels 803 are defined between adjacent light-transmissive regions 802. Each light-transmissive region 802 has an upper surface 806 and a pair of side surfaces 801. Each channel 803 has a bottom surface 807. A surface treatment is performed on the microstructured film 800. The surface of the microstructured film 800 is defined by the upper surface 806 and the pair of side surfaces 801 of each light-transmissive region 802 and the bottom surface 807 of each channel 803. The surface of the microstructured film 800 is treated by a first surface treatment. In some embodiments, the optical film 800 is treated by an oxygen plasma. Due to the oxygen plasma treatment, the hydrophilicity of the surface of the microstructured film 800 is increased, and this surface is represented by a high-energy surface 804. In some other embodiments, the first surface treatment can be a corona treatment.

[0085] Referring to FIG. 6B, the microstructured film 800 is selectively treated by a second surface treatment. In some embodiments, the microstructured film 800 is selectively treated by a fluorocarbon (FC) plasma treatment. The FC plasma treatment is selectively applied onto the upper surface 806 of each light-transmissive region 802 and onto the bottom surface 807 of each channel 803. Due to the FC plasma treatment, the hydrophobicity of the upper surface 806 and the bottom surface 807 of the channel becomes higher, and this surface is represented by a low-energy surface 805. Due to the selective treatment, the side surfaces 801 continue to have a high-energy surface 804.

[0086] Furthermore, in some embodiments, this method includes coating the light-transmissive regions 802 with an aqueous coating. This method further includes drying the aqueous coating. In some cases, drying the aqueous coating includes at least one of air drying, infrared heating, and oven drying. In some cases, the aqueous coating is achieved at a temperature of at least 50°C.

[0087] The present disclosure is further illustrated by the following examples, but the specific materials and their amounts listed in these examples should not be construed as unduly limiting the present disclosure, any more than the other conditions and details.

[0088] Examples Unless otherwise specified, all parts, percentages, ratios, etc. in the examples and the rest of this specification are by weight. The following is a list of the materials used throughout the examples, along with brief descriptions and sources thereof.

[0089] The components of Resin A used in the casting and curing high-precision surface process are listed in Table 1 below. Resin A can be used in the manufacture of the microstructured films 100, 200, 500.

[0090] [Table 1]

[0091] Example 1 Preparation of "Square Wave" Microstructured Film This example can be used in the manufacture of the microstructured films 100, 200, 500.

[0092] A tool with a plurality of parallel linear grooves was cut using a diamond (tip width 29.0 μm, included angle 3°, depth 87 μm). The grooves were spaced at a pitch of 62.6 micrometers.

[0093] Resin A was prepared by mixing the materials in Table 2 below.

[0094] [Table 2]

[0095] Using the resin A and tool described above, a "casting and curing" high-definition surface process was carried out. A resin A mixture described in Table 1 was molded on a 0.007-inch (0.178 mm) polycarbonate (PC) film and ultraviolet (UV) light-cured to produce a microstructured film.

[0096] The line conditions were a resin temperature of 150°F, a die temperature of 150°F, a coater IR of 120°F at the edges / 130°F at the center, a tool temperature of 100°F, and a line speed of 70 fpm. A Fusion D lamp with a peak wavelength of 385 nm was used for curing and operated at 100% power. For these structured films, a cylindrical metal roll with exquisitely precise channels machined on the outer surface serves as the mold. First, the resin mixture was coated on the PC substrate film and then firmly pressed against the metal roll to completely fill the mold. After polymerization, the structured film was removed from the mold.

[0097] The obtained microstructured film included a plurality of protrusions (e.g., light transmission regions 230) separated by channels (e.g., channel 201 shown in FIG. 2). The protrusions of the microstructured film are a negative replica of the grooves of the tool. The protrusions have a wall angle of 1.5 degrees, and thus the protrusions are slightly tapered (wider at the light input surface and narrower at the light output surface). The channels of the microstructured film are a negative replica of the non-cut portions of the tool between the grooves.

[0098] Example 2 Method for manufacturing a surface-treated light control film and a non-surface-treated light control film Microstructured films similar to the microstructured films 100, 200, 500 are provided.

[0099] [Table 3]

[0100] The microstructured film has a 3:1 structure (width 30 μm, depth 90 μm) made of Resin B. The composition of Resin B is provided in Table 3 above. Resin B was prepared by blending the monomers in the ratios specified in Table 3 above. The diluent contained one or more (meth)acrylate diluents.

[0101] The coating solution was about 1% Cabojet-200 carbon black, 0.06% Tomadol 25-9 surfactant, and 0.04% Neocryl A639a aqueous acrylic dispersion. This solution was applied to the microstructured film by airbrush until gloss was observed on the film (indicating that the channels were filled). The sample was then dried in an 80 °C batch oven. Data for the in-axis and out-of-axis % transmittance (%T) at 0 degrees and about 35 degrees were obtained using a Hazegard Plus transparency meter. Table 4 provides the percent transmittance of the plasma-treated and non-plasma-treated microstructured films.

[0102]

Table 4

[0103] Example 3: Transmittance of a light control film with an aqueous coating. Microstructured films (e.g., microstructured films 100, 200, 500, and 800) are coated with an aqueous coating solution. The various compositions of the aqueous coating solution are shown in Table 5.

[0104]

Table 5

[0105] Referring to Figure 7, a plot of the transmittance (%) versus the viewing angle for the various coating compositions of Table 5 is provided. As shown in Figure 7, at normal incidence, Sample 1 has the highest transmittance, followed by Sample 3 and Sample 2.

[0106] Unless otherwise indicated, all numbers expressing feature sizes, amounts, and physical properties used in this specification and the claims are to be understood as being modified by the term "about." Accordingly, unless specifically indicated to the contrary, the numerical parameters set forth in the foregoing specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by those skilled in the art utilizing the teachings disclosed herein.

[0107] Although the invention has been described in connection with certain specific embodiments, it will be understood by those skilled in the art that various alternatives and / or equivalent implementations may replace the specific embodiments shown and described without departing from the scope of the present disclosure. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein. Accordingly, the present disclosure is intended to be limited only by the claims and their equivalents. Exemplary embodiments are shown below. [Item 1] A method for manufacturing a light control film, providing a microstructured film comprising a plurality of light transmission regions alternating with channels, the microstructured film having a surface defined by the upper surface and a pair of side surfaces of each light transmission region and the bottom surface of each channel; coating the pair of side surfaces of each light transmission region and the bottom surface of each channel with a coating containing light absorbing particles dispersed in a liquid; drying the coating to selectively deposit the light absorbing particles on the pair of side surfaces of each light transmission region; A method comprising: [Item 2] The method according to Item 1, wherein the coating is an aqueous coating and the liquid is water. [Item 3] The method according to Item 1, wherein the upper surface of each light transmission region and the bottom surface of each channel do not contain the light absorbing particles. [Item 4] The method according to Item 1, wherein the light absorbing particles have an average particle size of at least 20 nm. [Item 5] The method according to Item 1, wherein the light absorbing particles have an average particle size of less than 1 micrometer. [Item 6] The method according to Item 1, wherein the drying of the coating includes at least one of air drying, infrared heating, and oven drying. [Item 7] The method according to Item 1, wherein the drying of the coating is achieved at a temperature of at least 50°C. [Item 8] The method according to Item 1, further comprising performing a surface treatment on the surface of the microstructured film. [Item 9] The method according to Item 8, wherein the surface treatment includes at least one of oxygen plasma treatment, corona treatment, and fluorocarbon plasma treatment. [Item 10] The method according to Item 1, wherein the microstructured film is not surface-treated. [Item 11] The method according to Item 1, further comprising filling the channels with a material similar to the material of the light transmission regions. [Item 12] The method according to Item 1, wherein the coating further includes an additive. [Item 13] The method according to Item 12, wherein the additive includes at least one of a binder, a surfactant, and a crosslinking agent. [Item 14] The method according to Item 13, wherein the binder includes at least one of an anionic binder, a cationic binder, and an amphoteric ion binder. [Item 15] The method according to item 1, wherein the light-absorbing particles include carbon black particles. [Item 16] The method according to item 1, wherein the light-absorbing particles are present at a concentration of at least 1% by weight based on the total weight of the coating. [Item 17] The method according to item 1, wherein the microstructured film further includes a base layer, and the light transmission region extends from the base layer. [Item 18] The method according to item 1, wherein the microstructured film includes a polymerizable resin. [Item 19] A method for manufacturing a light control film, providing a microstructured film having a plurality of light transmission regions alternating with channels, the microstructured film having a surface defined by the upper surface and a pair of side surfaces of each light transmission region and the bottom surface of each channel; performing a first surface treatment on the surface of the microstructured film; selectively performing a second surface treatment on the upper surface of each light transmission region and the bottom surface of each channel; coating the pair of side surfaces of each light transmission region and the bottom surface of each channel with a coating containing light-absorbing particles dispersed in a liquid; drying the coating to selectively deposit the light-absorbing particles on the pair of side surfaces of each light transmission region; The method including the above steps. [Item 20] The method according to item 19, wherein the first surface treatment includes an oxygen plasma treatment or a corona treatment. [Item 21] The method according to item 19, wherein the second surface treatment includes a fluorocarbon plasma treatment. [Item 22] The method according to item 19, wherein the light-absorbing particles have an average particle size of at least 20 nm. [Item 23] The method according to item 19, wherein drying the coating includes at least one of air drying, infrared heating, and oven drying. [Item 24] The method according to item 19, wherein the coating is an aqueous coating and the liquid is water.

Claims

1. A method for manufacturing a light control film, comprising: providing a microstructured film having a plurality of light transmission regions alternating with channels, the microstructured film having a surface defined by an upper surface and a pair of side surfaces of each light transmission region and a bottom surface of each channel; coating the pair of side surfaces of each light transmission region and the bottom surface of each channel with a coating containing light absorbing particles dispersed in a liquid; selectively performing a surface treatment on the upper surface of each light transmission region and the bottom surface of each channel; drying the coating to selectively deposit the light absorbing particles on the pair of side surfaces of each light transmission region; wherein the coating on the bottom surface is removed by the drying.

2. The method according to claim 1, wherein the coating is an aqueous coating and the liquid is water.

3. The method according to claim 1, wherein the upper surface of each light transmission region and the bottom surface of each channel do not contain the light absorbing particles.

4. The method according to claim 1, wherein the light absorbing particles have an average particle size of at least 20 nm.

5. The method according to claim 1, wherein the light absorbing particles have an average particle size of less than 1 micrometer.

6. The method according to claim 1, wherein the drying of the coating includes at least one of air drying, infrared heating, and oven drying.

7. The method according to claim 1, wherein the drying of the coating is achieved at a temperature of at least 50°C.

8. The method according to claim 1, further comprising performing a surface treatment on the surface of the microstructured film.

9. The method according to claim 8, wherein the surface treatment includes at least one of oxygen plasma treatment, corona treatment, and fluorocarbon plasma treatment.

10. A method for manufacturing a light control film, comprising: providing a microstructured film having a plurality of light transmission regions alternating with channels, the microstructured film having a surface defined by an upper surface and a pair of side surfaces of each light transmission region and a bottom surface of each channel; performing a first surface treatment on the surface of the microstructured film; selectively performing a second surface treatment on the upper surface of each light transmission region and the bottom surface of each channel; Coating the pair of side surfaces of each light transmission region and the bottom surface of each channel with a coating containing light-absorbing particles dispersed in a liquid; Drying the coating to selectively deposit the light-absorbing particles on the pair of side surfaces of each light transmission region; A method for manufacturing a light control film, including the above steps, wherein the coating on the bottom surface is removed by the drying.

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