Background

An optical device can include a microlens array and a mask including an array of pinholes.

Summary

The present disclosure relates generally to optical constructions and methods of making optical constructions. An optical construction can include a lens film and a solvent-deposited mask layer disposed on the lens film that includes a plurality of laser-ablated through openings therein.

In some aspects of the present disclosure, an optical construction is provided. The optical construction includes a lens film including an outermost structured first major surface and an opposing outermost substantially planar second major surface. The structured first major surface includes a plurality of microlenses arranged along orthogonal first and second directions. The optical construction includes a solvent-deposited optically opaque mask layer applied over the second major surface of the lens film. The mask layer has an average thickness of less than about 10 microns and defines a plurality of laser-ablated through openings therein arranged along the first and second directions. The through openings are aligned to the microlenses in a one-to-one correspondence, such that for a substantially collimated light incident on the structured first major surface side of the optical construction along an incident direction forming an incident angle with the second major surface, an optical transmittance of the optical construction as a function of a transmitted angle includes a first transmitted peak having a first peak transmittance T1 and a corresponding full width at half maximum Wl. The first transmitted peak is within about 10 degrees of the incident angle. In some embodiments, T1 > 50% and Tl/Wl > 4%/degree.

In some aspects of the present disclosure, an optical construction is provided. The optical construction includes a lens film including an outermost structured first major surface and an opposing outermost substantially planar second major surface. The structured first major surface includes a plurality of microlenses arranged along orthogonal first and second directions. The optical construction includes a solvent-deposited optically opaque mask layer applied over the second major surface of the lens film. The mask layer has a third major surface facing the lens film and an opposing fourth major surface. An average separation between the third and fourth major surfaces can be less than about 10 microns. The mask layer defines a plurality of laser-ablated through openings therein arranged along the first and second directions. The through openings are aligned to the microlenses in a one-to-one correspondence, such that for a substantially collimated light incident on the structured first major surface side of the optical construction along an incident direction forming an incident angle with the second major surface, an optical transmittance of the optical construction as a funchon of a transmitted angle includes a first transmitted peak having a first peak transmittance T1 > 40%. For at least one of the third and fourth major surfaces, each through opening has an open end at the major surface having a shape having a circularity being 4p times an area of the shape divided by a square of a perimeter of the shape, the circularities of the shapes of the open ends of at least about 20% of the through openings being at least about 0.75, the areas of the shapes of the open ends of the through openings having an average A and a standard deviahon of less than about 12% of A.

In some aspects of the present disclosure, an optical construction is provided. The ophcal construction includes a lens film including an outermost structured first major surface and an opposing outermost substantially planar second major surface. The structured first major surface includes a plurality of microlenses arranged along orthogonal first and second direchons. The optical construction includes a solvent-deposited optically opaque mask layer applied over the second major surface of the lens film. The mask layer has an average thickness of less than about 10 microns and defines a plurality of laser-ablated through openings therein arranged along the first and second directions. The through openings are aligned to the microlenses in a one-to-one correspondence, such that for a substantially collimated light incident on the structured first major surface side of the optical construction along an incident direction forming an incident angle with the second major surface, an optical transmittance of the ophcal construction as a function of a transmitted angle includes a first transmitted peak having a first peak transmittance T1 > 40%. In at least a first cross-sechon of the ophcal construction along a thickness direchon of the ophcal construction and substantially bisecting a first opening in the plurality of through openings, the first opening includes opposing first and second sidewalls. A best linear fit to at least one of the first and second sidewalls has an r-squared value of greater than about 0 8

In some aspects of the present disclosure, a method of making an optical construction is provided. The method includes providing a lens film including an outermost structured first major surface and an opposing outermost substantially planar second major surface, where the structured first major surface includes a plurality of microlenses arranged along orthogonal first and second directions; coahng the second major surface of the lens film with a mixture of solvent, polymer, and optically absorptive material; drying the coated mixture to form a mask layer having an average thickness of less than about 10 microns and a substantially uniform optical density of greater than about 1.5; and ablating a plurality of through openings in the mask layer using a laser emitting infrared light incident on the structured first major surface of the lens film such that the through openings are arranged along the first and second directions and are aligned to the microlenses in a one-to-one correspondence. Each through opening in at least a majority of the through openings has an optical density less than about 0.3. For at least one major surface of the mask layer, each through opening has an open end at the major surface having a shape having a circularity being 4p times an area of the shape divided by a square of a perimeter of the shape. The circularities of the shapes of the open ends of at least 20% of the through openings is at least about 0.75. The areas of the shapes of the open ends of the through openings having an average A and a standard deviation of less than about 15% of A.

These and other aspects will be apparent from the following detailed description. In no event, however, should this brief summary be construed to limit the claimable subject matter.

Brief Description of the Drawings

FIG. 1 is a schematic cross-sectional view of an illustrative optical construction.

FIGS. 2A-2B are schematic cross-sectional views of illustrative optical constructions, according to some embodiments.

FIG. 3 is a top perspective view of an illustrative lens film.

FIG. 4 is a bottom view image of an illustrative mask layer.

FIG. 5 is a schematic plot of an optical transmittance through an optical construction.

FIG. 6 is a schematic view of an illustrative open end of a through opening.

FIG. 7 is a schematic view of a cross-section of a portion of an optical construction.

FIGS. 8A-8C are schematic illustrations of steps in a method of making an optical construction.

FIGS. 9-10 are plots of optical transmittance through exemplary optical constructions versus angle in cross-web and down-web directions, respectively.

FIG. 11 is an image of a cross-section through an exemplary optical construction.

FIG. 12 is a plot of optical transmittance through a comparative optical construction.

FIG. 13 is a bottom view image of the optical construction of FIG. 12.

FIG. 14 is an image of a cross-section through the optical construction of FIG. 12.

FIG. 15 is a plot of optical transmittance through comparative optical constructions.

Detailed Description

In the following description, reference is made to the accompanying drawings that form a part hereof and in which various embodiments are shown by way of illustration. The drawings are not necessarily to scale. It is to be understood that other embodiments are contemplated and may be made without departing from the scope or spirit of the present description. The following detailed description, therefore, is not to be taken in a limiting sense. An optical construction can include a microlens array and a metal mask having an array of through openings (e.g., pinholes) corresponding to the microlenses. However, it has been found that using a metal mask can result in unwanted specular reflection from regions of the mask between through openings. A polymeric layer including optically absorptive material in place of a metal mask can be used. However, previous optical constructions using such polymeric layers have had through openings with poor shape definition which can result in undesirably broad peaks in optical transmittance through the through openings and/or can result in undesired cross-talk (e.g., light incident on one microlens may be transmitted through an adjacent through hole) and/or can result in undesirably low peak transmittance (unless large diameter through openings are used which would result in undesired cross-talk). For example, the resulting through openings can have open ends with low circularity and/or sidewalls that are jagged or irregular and/or the mask layer can have a low uniformity of area of the open ends. According to some embodiments, optically opaque mask layers are provided which provide a sharp peak in optical transmittance through the optical construction and/or provide through openings with substantially linear sidewalls and/or provide through openings having open ends with high circularity and/or provide through openings having a high uniformity of area of the open ends. The mask layer can be solvent-deposited. As used herein, a “solvent-deposited” mask layer is a mask layer formed by depositing (e.g., coating) materials (e.g., polymer and light absorbing materials) of the layer in a solvent and then evaporating the solvent. The through-holes can then be formed by laser ablation. It has been found that solvent-deposited mask layers provide improved through hole shape definition compared to polymeric mask layers formed by coating and curing, for example. Further, it has been found that the mask layer can be made at a sufficient thickness (e.g., about 2 microns to about 7 microns) to provide a high optical density (e.g., an optical density of at least about 1.5) while still providing good through hole shape definition.

In some embodiments, the optical constructions are useful as angular optical filters which can be used in a variety of applications such as fingerprint sensing applications, for example. The optical construction may be disposed between a fingerprint sensing area and a sensor in a device (e.g., cell phone) and can be adapted to transmit light reflected from a finger in the fingerprint sensing area to the sensor while rejecting light incident on the optical construction from different angles.

FIG. 1 is a schematic cross-sectional view of an optical construction 200 including a lens film 110 and a mask layer 120, according to some embodiments. FIGS. 2A-2B are schematic cross-sectional views of optical construction 200’, 200” including a lens film 110 and a mask layer 120 and one or more optional additional layers or films, according to some embodiments. Optical construction 200’ includes optional additional layer 138 and optical construction 200” further includes optional additional layer or film 197 and optional additional layer 199. The lens film 110 has an outermost major surface 102 including a plurality of microlenses 103. The microlenses can be arranged in any suitable pattern. For example, the microlenses can be arranged in a regular two-dimensional array such as a square or hexagonal array. FIG. 3 is a top perspective view of a lens fdm 110 including microlenses 103, according to some embodiments. The microlens film 110 can be formed by any suitable process such as casting and curing a resin between a substrate and a tool, for example. FIG. 4 is a bottom view of a mask layer 120 defining through openings 123 therein, according to some embodiments. The through openings 123 can be aligned to the microlenses 103 in a one-to-one correspondence, such that the optical construction has a desired optical transmittance for light incident on the microlenses, for example. FIG. 5 is a schematic plot of an optical transmittance 267 through an optical construction 200, 200’, 200” as a function of a transmitted angle, according to some embodiments. The optical construction may be adapted to primarily transmit light along an incident direction (e.g., direction 134 in FIG. 1 or the minus z-direction in FIG. 2).

In some embodiments, an optical construction 200, 200’, 200” includes a lens film 110 including an outermost structured first major surface 102 and an opposing outermost substantially planar (e.g., planar or nominally planar or planar up to variations or curvature small compared to that of the structured first major surface) second major surface 104. The structured first major surface 102 includes a plurality of microlenses 103 arranged along orthogonal first and second directions (x- and y-directions referring to the illustrated x-y-z coordinate system). The optical construction 200, 200’ includes a solvent-deposited optically opaque mask layer 120 applied over the second major surface 104 of the lens film 110. The mask layer 120 has an average thickness t of less than about 10 microns and defines a plurality of laser-ablated through openings 123 therein arranged along the first and second directions. The mask layer 120 has opposing third and fourth major surfaces 143 and 144, where the third major surface 143 faces the lens film 110. The average thickness t may alternatively be described as the average separation between the third and fourth major surfaces 143 and 144. The average refers to the unweighted mean unless indicated differently. The average thickness t can be less than about 8 microns, or less than about 7 microns, or less than about 6 microns, or less than about 5 microns, for example. The average thickness t can be greater than about 1 micron, or greater than about 2 microns, or greater than about 2.5 microns, for example. The average thickness t can be in a range of about 2 microns to about 7 microns or about 2.5 microns to about 6 microns, for example. In some embodiments, a total thickness T of the lens film 110 and the mask layer 120 is no greater than about 100 microns (e.g., in a range of about 30 microns to about 100 microns). The lens film 110 can include a lens layer cast and cured on a substrate layer, for example, so that the thickness of the lens film is the thickness of the lens layer and the substrate layer.

A microlens is generally a lens with at least two orthogonal dimensions (e.g., a height and a diameter, or a diameter along two axes) less than about 1 mm and greater than about 100 nm.

The microlenses can have an average diameter in a range of about 0.5 microns to about 500 microns, or about 5 microns to about 100 microns, for example. The microlenses can have an average radius of curvature in a range of 5 microns to 50 microns, for example. The microlenses can have any suitable shape. The microlenses can be spherical or aspherical microlenses, for example. In some embodiments, the microlenses are pillow lenses which can allow for a higher fraction of the area covered by the lenses to be optically active, for example. A pillow lens may be substantially symmetric under reflection about two orthogonal planes (e.g., planes passing through a center of the lens and parallel to the x-z plane and the y-z plane, respectively), or about three planes parallel to the thickness direction of the lens film where each plane makes an angle of about 60 degrees with each other plane, without being rotationally symmetric about any axis. The optical construction 200, 200’, 200” can have a total thickness in a range of about 10 microns to about 200 microns or about 30 microns to about 100 microns, for example.

A mask layer can be described as optically opaque when the transmittance of unpolarized visible light (e.g., wavelengths from about 400 nm to about 700 nm) normally incident on the layer in a region between openings is less than 20%, or less than 15%, or less than 10%, or less than 5%, or less than 3%, or less than 2%, or less than 1%. The mask layer can alternatively be characterized by its optical density (minus base 10 logarithm of [transmittance/ 100%], where the transmittance is for unpolarized normally incident visible light unless indicated differently). In some embodiments, between adjacent through openings, the mask layer has an optical density of greater than about 1.5, or greater than about 1.6, or greater than about 1.7. The mask layer can be optically absorptive so that most light incident on the mask layer between adjacent through openings is absorbed rather than reflected.

The through openings 123 are aligned to the microlenses 103 in a one-to-one correspondence, such that for a substantially collimated light 133, 133 ’ incident on the structured first major surface side of the optical construction 200, 200’, 200” along an incident direction (e.g., direction 134 in FIG. 1 or minus z-direction in FIG. 2A) forming an incident angle (e.g., cp in FIG. 1 or about zero degrees in FIG. 2A) with the second major surface 104 (incident angle is the angle relative to the surface normal), an optical transmittance 267 of the optical construction 200, 200’, 200” as a function of a transmitted angle Q includes a first transmitted peak 268 having a first peak transmittance T1 and a corresponding full width at half maximum Wl. The substantially collimated light 133, 133 ’ can be collimated or nominally collimated or can have a divergence angle or convergence angle less than about 20 degrees, or less than about 10 degrees, or less than about 5 degrees, for example. The substantially collimated light 133, 133’ can fill or substantially fill at least one microlens or can fill or substantially fill a plurality of the microlenses. The incident direction can be substantially orthogonal to the first and second directions. For example, the angle cp can be less than about 20 degrees, or less than about 10 degrees, or less than about 5 degrees. In some embodiments, the first transmitted peak 268 is within about 10 degrees of the incident angle (e.g., the first transmitted peak 268 can be at a first transmitted angle q 1 which can be within 10 degrees of the angle cp). In some such embodiments or in other embodiments, T1 > 40% or T1 > 50%. In some such embodiments or in other embodiments, Tl/Wl > 2%/degree, or Tl/Wl > 4%/degree, or Tl/Wl > 6%/degree, or Tl/Wl > 8%/degree. For example, in some embodiments, T1 > 50% and Tl/Wl > 4%/degree. Typically, a sharp peak (e.g., Tl/Wl of 4%/degree or higher) is preferred. In some embodiments, W1 is less than about 20, or 15, or 12, or 10 degrees. In some embodiments, T1 is greater than about 50% or greater than about 55%. In some embodiments,

70% > T1 > 50%. For example, optical constructions with 70% > T1 may be preferred in some cases since the cross-talk is typically smaller for such optical constructions than for optical constructions having a higher Tl, while optical constructions with T1 > 50% may be preferred in some cases to provide a desired throughput of incident light.

The substantially collimated light 133, 133’ can be visible light (e.g., wavelengths from about 400 nm to about 700 nm) or can have at least one wavelength in a visible wavelength range. In some embodiments, the optical transmittance 267 is an average optical transmittance over a wavelength range extending from at least about 450 nm to about 650 nm. In some embodiments, the optical transmittance 267 is an optical transmittance for at least one wavelength in a wavelength range extending from about 450 nm to about 650 nm (e.g., the optical transmittance can be for a wavelength of about 530 nm).

In some embodiments, the optical construction is adapted to transmit light incident along the incident direction and to substantially not transmit light incident along a direction making an angle greater than about 15 degrees with the incident direction. The incident angle cp can be about zero degrees or can be greater than zero degrees depending on the incident angles which are desired to be transmitted.

In some embodiments, the optical transmittance 267 of the optical construction 200, 200’, 200” further includes a second transmitted peak 269 having a second peak transmittance T2 at a transmitted angle Q2 greater than the incident angle (e.g., cp) by at least about 30 degrees. In some embodiments, T2 < 3%, or T2 < 2.5%, or T2 < 2%, or T2 < 1.5%, or T2 < 1%, or T2 < 0.5%, or T2 < 0.3%. In some embodiments, T2/T1 is less than about 0.07, or less than about 0.05. In some embodiments, 0.3% < T2 < 3% or 0.5% < T2 < 2.5%. A second peak transmittance T2 > 3% is typically undesired as this can result in undesired cross-talk. In some embodiments, the second peak is not present or is too small to be discerned in a plot of the optical transmittance versus transmitted angle. The second peak may be present for angles along a first direction (e.g., a down- web direction) but not along an orthogonal second direction (e.g., a cross-web direction). This may result from shape variations in the microlenses arising the process (e.g., a cast and cure process) used to form the microlens film.

In some embodiments, the mask layer 120 is formed by coating the second major surface 104 of the lens film 110 with a mixture of solvent, polymer, and optically absorptive material; drying the coated mixture to form a mask layer; and then laser ablating holes through the mask layer. In some embodiments, the mask layer is substantially free of polymerization initiators such as photoinitiators or thermal initiators. Substantially free in this context means that if any polymerization initiators are included, they are included at less than an amount needed to cause polymerization under normal processing conditions. In some embodiments, the mask layer 120 includes no or less than about 0.1%, 0.05%, 0.03%, 0.02%, or 0.01% by weight of a polymerization initiator. In some embodiments, the mask layer 120 includes no or less than about 0.1%, 0.05%, 0.03%, 0.02%, or 0.01% by weight of a photoinitiator. In some embodiments, the mask layer 120 include no or less than about 0.1%, 0.05%, 0.03%, 0.02%, or 0.01% by weight of a thermal initiator. In some embodiments, the mask layer 120 includes a non-crosslinked polymer. For example, the mask layer 120 can include optically absorptive material, such as carbon black particles, dispersed in a thermoplastic polymer. In some embodiments, the mask layer can be described as a polymeric layer (i.e., a layer having a continuous phase of organic polymer). For example, the mask layer can be a solvent-deposited non-crosslinked polymeric optically opaque mask layer.

Various polymer systems can act as carrier resins (the resin that is to be solvent-deposited) in solvent systems. Nitrocellulose and cellulose esters, for example, are a useful class of polymers. Medium to high molecular weight hydroxyl-functional, partially hydrolyzed, vinyl-chloride vinylacetate copolymer can also be used as carrier resins. For alcohol rich solvent systems, polyvinylbutyral may be useful or preferred. Polyamides, ethylcellulose, cellulose acetate propionate, cellulose acetate butyrate, polyurethane, maleic resins, epoxy resins, acrylic, vinyl acrylic may also be useful or preferred based on the solvent mix, substrate choice, degree of adhesion desired, etc. Suitable cellulose esters are available from Eastman Chemical company, for example. Suitable polyurethanes are available under the VERS AMID PUR tradename, for example. Suitable polyvinylbutyral polymers are available under the tradename MOWITAL from Kuraray America, for example. Suitable acrylate co-polymers are available under the tradename PARALOID from Dow Chemical company, for example. Some other polymers that may be useful in some cases include polyurethanes with silanes or silsesquioxanes. Other polymers which can be dissolved or dispersed in a solvent system and can form a film post-drying may also be used.

Suitable solvents include alcohols, ketones, esters, hydrocarbons, glycols, glycol ethers, and glycol esters. Some of these solvents can be high boiling and may be present in small amounts in the coating solution. High boiling hydrocarbons and petroleum naptha and aromatics can optionally also be present in small amounts. Though typically not intentionally added, small amounts of water or moisture can be present in some polar solvents. Nitriles, aminoethanols, amines can also be used as a co-solvent. The preferred solvent may be determined by resin choice as well as process type and conditions (e.g., temperature). Typical preferred solvents include ketones and low boiling alcohols.

The optically absorptive material can be a pigment. The pigment can be or include an organic pigment, an inorganic pigment, a metal organic pigment, or a combination thereof. The pigment preferably absorbs both visible and infrared (IR) light (e.g., in a wavelength range from 1000 nm - 1100 nm or in other near infrared ranges described elsewhere herein). The absorption strength of the pigment may be similar or different in the visible and infrared part of the light spectrum. It is typically preferred to have a pigment which has stronger light absorption in the visible than in the IR to achieve sufficient visible light blocking but also have adequate absorption in the IR for laser ablation. A suitable organic pigment is carbon black, for example. Suitable inorganic pigments are metal oxides, for example. The pigment is preferably a broad band absorber (e.g., carbon black). For making a stable coating solution, carbon black may be generally uniformly dispersed with the aid of a dispersant. A dispersant can be a surfactant molecule in simple form or a polymer which has affinity both for the pigment particle as well as for the polymer resin and is also soluble in the solvent. In some embodiments, the average particle size of the pigment (e.g., carbon black) is less than 1 micron, or less than 500 nm, or less than 250 nm, or less than 100 nm. For example, the average particle size can be in a range of 5 nm or 10 nm or 20 nm to 250 nm. It is possible to have a distribution of pigment particles with various sizes. The average particle size can be understood to be the Dv50 value (median particle size in a volume distribution). In some embodiments, pigment is included in the mask layer at about 10 to about 35 weight percent or at about 15 to about 30 weight percent.

Polymer, solvent and pigment can be combined to make a coating mixture. Suitable coating mixtures include solvent-based printing inks. Sun Chemicals, Dainichiseika Color and chemicals Mfg Co, ltd, Huber group, for example, make useful inks containing carbon black. These printing inks can have different viscosities based on polymer choice, molecular weight of polymers as well as the solid content. Various inks can be chosen based on the coating or printing methods. Thinner solvent can be used to adjust the viscosity prior to coating or printing. In some embodiments, the printing ink is applied via die coating. Other coating or printing methods such as gravure, flexographic printing can alternatively be used. The choice of coating or printing method may also depend on the desired thickness of the layer to be printed or coated.

In some embodiments, in at least a first cross-section of the outermost structured first major surface in a direction substantially orthogonal to the first and second directions and substantially bisecting a first opening 123a in the plurality of through openings 123, the first opening 123a has a larger first width dl on a side of the mask layer 120 facing the lens film 110 and a smaller second width d2 on a side of the mask layer 120 facing away from the lens film 110 (see, e.g., FIG. 1). In other embodiments, the first width dl is smaller than the second width d2. In some embodiments, dl and d2 are about equal. The relative widths of dl and d2 may depend on material choice for the mask layer and on laser ablation processing conditions. Adjusting shapes of through holes via laser processing conditions is generally described in in U.S. Pat. No. 7,864,450 (Segawa et ak), for example. In some embodiments, a ratio (dl/d2) of the first width dl to the second width d2 is in a range of about 1.1 to about 2.

In some embodiments, the microlenses 103 are arranged in a hexagonal pattern (see, e.g., FIG. 3). In some embodiments, the microlenses fill a large fraction (at least about 85%) of a total area of the structured first major surface 102 so that a large fraction of the total area is optically active (e.g., changes a divergence angle of incident light). In some embodiments, at least about 85%, or at least about 90%, or least about 95%, or at least about 98% of a total area of the structured first major surface 102 is optically active.

In some embodiments (see, e.g., FIGS. 2A-2B), a layer 138 is disposed on the mask layer 120 opposite the lens film 100. In some such embodiments, material 139 (e.g., polymeric material and/or a low index optical adhesive material) from the layer 138 at least partially fills some or all of the through openings 123 (e.g., the layer 138 can cover substantially the entire mask layer so that all of the through openings are at least partially filled or the layer 138 can be disposed over only a portion of the mask layer so that only some of the through openings are at least partially filled). In some embodiments, the mask layer 120 has a first refractive index (the refractive index of the material forming the mask layer) and at least some of the through openings are at least partially filled with a polymeric material 139 having a second refractive index. In some embodiments, a real part of the second refractive index is less than a real part of the first refractive index. For example, in some embodiments, the real part of the first refractive index minus the real part of the second refractive index is at least about 0.05. Refractive indices can be understood to be determined at a wavelength of 532 nm except where indicated differently.

In some embodiments (see, e.g., FIG. 2B), a layer or film 197 is disposed between the lens film 110 and the mask layer 120. The layer or film 197 can be a wavelength selective layer or film. For example, the layer or film 197 can include dye(s) and/or pigment(s) that absorb in some wavelength range(s) and not others. As another example, the layer of film 197 can be a multilayer optical film reflecting in some wavelength range(s) and not others. As is known in the art, multilayer optical films including alternating polymeric layers can be used to provide desired reflection and transmission in desired wavelength ranges by suitable selection of layer thicknesses. Multilayer optical films and methods of making multilayer optical films are described in U.S. Pat. Nos. 5,882,774 (Jonza et al ); 6,179,948 (Merrill et al ); 6,783,349 (Neavin et al ); 6,967,778 (Wheatley et al.); and 9,162,406 (Neavin et al.), for example. Preferably, the layer or film 197 is substantially transmissive for a visible wavelength range (e.g., about 450 to about 650 nm) and a near infrared wavelength range (e.g., 900 to 1000 nm). In some embodiments, the layer or film 197 absorbs or reflects in at least a portion of a wavelength range from about 650 nm to about 900 nm, for example.

In some embodiments (see, e.g., FIG. 2B), a layer 199 is disposed on the structured first major surface 102 of the lens film 110. The layer 199 can have a major surface 196 substantially conforming to the structured major surface 102 and an opposite substantially planar major surface 198. In other words, the layer 199 can substantially planarize the structured first major surface 102. The layer 199 can be a low index layer. In some embodiments, the layer 199 has a refractive index less than about 1.4, or less than about 1.35, or less than about 1.3, or in a range of about 1.1 to about 1.35 or to about 1.3, for example. In some embodiments, the layer 199 can have a refractive index at least 0.1, or at least 0.2, or at least 0.3 lower than that of the lens layer 110. The low index layer may be a nanovoided layer as described in U.S. Pat. Appl. Publ. Nos. 2013/0011608 (Wolk et al.) and 2013/0235614 (Wolk et al.), for example.

In some embodiments, any one, two or all three of elements 138, 197 and 199 can be omitted. In some embodiments, layer or film 197 is omitted and layer 138 includes dye(s) and/or pigment(s) that absorb in some wavelength range(s) and not others.

In some embodiments, the material in the through openings 123 is air or an optically transparent material. In some embodiments, each through opening in at least a majority of the through openings has an optical density less than about 0.3, or less than about 0.2, or less than about 0.15, or less than about 0.1. In some such embodiments, or in other embodiments, between adjacent through openings, the mask layer 120 has a substantially uniform optical density of greater than about 1.5. Substantially uniform optical density refers to optical density that is uniform to a good approximation on a length scale of about 1 micron. For example, each cylindrical region through the mask layer 120 between through openings having a diameter of about 1 micron can have an optical density within about 15% or within about 10% or within about 5% of an average optical density of such regions. In some embodiments, a mask layer having a substantially uniform optical density is obtained by using optically absorptive particles (e.g., carbon black particles) having an average diameter substantially smaller than 1 micron (e.g., less than about 250 nm) and substantially uniformly dispersed in the layer at a loading sufficiently high that an average center to center spacing between the particles is less than about 1 micron.

In some embodiments, the through openings 123 have an average diameter in a range of about 1 micron to about 10 microns, or about 2 microns to about 8 microns. The diameter dO of a through opening can be understood to be the diameter of a cylinder having a length equal to the thickness t and having a volume equal to the volume of the through opening (e.g., the diameter dO may be about equal to (dl+d2)/2 in FIG. 1). The average diameter is the diameter dO averaged (unweighted mean) over the through openings. The average of dl or the average of d2 may also or alternatively be specified. In some embodiments, for at least one of the third and fourth major surfaces 143 and 144, the open ends at the major surface (e.g., open ends 121 at major surface 143 or open ends 122 at major surface 144) have an average diameter in a range of about 1 micron to about 10 microns, or about 2 microns to about 8 microns. The diameter of an open end can be understood to be the diameter of a circle having a same area as the open end. The average diameter of the open ends is diameter averaged (unweighted mean) over the open ends. In some embodiments, 0.5 < d/t < 2, where d is the average dO, dl, or d2 and t is the average thickness of the mask layer.

In some embodiments, each opening in at least a substantial fraction (e.g., at least about 20%) of the through openings has at least one open end having a high circularity (e.g., at least about 0.75, or at least about 0.8, or at least about 0.85). The circularity (C) of a shape is 4p times an area Ai of the shape divided by a square of a perimeter Pi of the shape (i.e., C = 4pAi/ Pi ² ). The circularity, which is also referred to as the isoperimetric ratio, is 1 for a circle and less than 1 for any other shape (by a mathematical result known as the isoperimetric inequality). Circularity is a commonly used parameter to describe how close to a circle an object is and is often determined automatically by software in a digital camera, for example. FIG. 6 is a schematic view of a shape 125 of an open end (e.g., open end 121 at major surface 143 or open end 122 at major surface 144) of a through opening. The shape 125 has an area Ai and a perimeter Pi (length around the area Ai). The geometry of the open ends at the major surface 144 can be determined from a microscope image of the major surface 144. The geometry of the open ends at the major surface 143 can be determined by first coating the microlenses 103 with an index matching coating to substantially planarize the major surface 102. The open ends at the major surface 143 can then be determined from a microscope image of the major surface 143 viewed through the planarizing layer and the lens film 110. In some embodiments, for at least one major surface of the mask layer 120 (e.g., for at least one of the third and fourth major surfaces 143 and 144), each through opening 123 has an open end at the major surface (open end 121 at major surface 143 and/or open end 122 at major surface 144). In some embodiments, the circularities of the shapes 125 of the open ends of at least about 20% of the through openings 123 is at least about 0.75. In some such embodiments or in other embodiments, the areas of the shapes 125 of the open ends of the through openings 123 having an average A (e.g., the unweighted mean of the areas Ai can be A) and a standard deviation (e.g., standard deviation of the areas Ai) of less than about 15% of A. In some embodiments, the standard deviation is less than about 12% of A, or less than about 10% of A, or less than about 8% of A.

In some embodiments, the at least about 20% of the through openings include at least about 50%, or at least about 60%, or at least about 70%, or at least about 80%, or at least about 90% of the through openings. In some embodiments, the circularities of the shapes of the open ends of the at least about 20% of the through openings is at least about 0.8, or at least about 0.85, or at least about 0.9. In some embodiments, the circularities of the shapes of the open ends of at least about 50% of the through openings is at least about 0.75, or at least about 0.8, or at least about 0.85. In some embodiments, the circularities of the shapes of the open ends of at least about 70% of the through openings is at least about 0.75, or at least about 0.8, or at least about 0.85. In some embodiments, the circularities of the shapes 125 of the open ends of the through openings 123 have an average of at least about 0.75, or at least about 0.8, or at least about 0.85 and a standard deviation of less than about 0.2. In some embodiments, the standard deviation is less than about 0.18 or less than about 0.16 or less than about 0.14.

FIG. 7 is a schematic view of a cross-section of a portion of an optical construction. In some embodiments, in at least a first cross-section of the optical construction in a direction (e.g., a thickness direction of the optical construction) substantially orthogonal to the first and second directions (i.e., the first cross-section contains the direction substantially orthogonal to the first and second direction) and substantially bisecting (e.g., bisecting into two substantially equal parts having volumes within about 20% or within about 10% or within about 5% of one another) a first opening 123a in the plurality of through openings 123, the first opening 123a includes opposing first and second sidewalls 161 and 162, where a best linear fit to at least one of the first and second sidewalls (e.g., linear fit 163 to first sidewall 161 and/or linear fit 164 to second sidewall 162) has an r-squared value of greater than about 0.7, or greater than about 0.8, or greater than about 0.85, or greater than about 0.9, or greater than about 0.95. In some such embodiments or in other embodiments, in the first cross-section, the first opening has a larger width dl on a side of the mask layer 120 facing the lens film 110 and a smaller width d2 on a side of the mask layer 120 facing away from the lens film 110 (see, e.g., FIG. 1). In some embodiments, the best linear fit to each of the first and second sidewalls has an r-squared value of greater than about 0.7, or greater than about 0.8, or greater than about 0.85, or greater than about 0.9, or greater than about 0.95. The r-squared value, which is sometimes referred to as the coefficient of determination, can be determined from a linear least squares fit, as is known in the art. The best linear fit to a sidewall is determined for the position of the sidewall along the direction (e.g., z-direction) substantially orthogonal to the first and second directions of the optical construction as a function of distance along an orthogonal direction (e.g., x-direction) in the first cross-section, unless indicated differently. For example, a sidewall may be described in terms of the z-coordinate of the sidewall as a function of x-coordinate and the best linear fit may be expressed as z = a x + b for constants a andb.

FIGS. 8A-8C are schematic illustrations of steps in a method of making an optical constmction (e.g., 200 or 200’ or 200”). The method includes providing a lens film 110 (see, e.g., FIG. 8A) including an outermost structured first major surface 102 and an opposing outermost substantially planar second major surface 104, where the structured first major surface 102 includes a plurality of microlenses 103 arranged along orthogonal first and second directions; coating (see, e.g., FIG. 8B) the second major surface of the lens film with a mixture 150 of solvent 151, polymer 152, and optically absorptive material 153; drying (see, e.g., FIGS. 8B-8C) the coated mixture to form a mask layer 120 having an average thickness t of less than about 10 microns and a substantially uniform optical density of greater than about 1.5; and ablating (see, e.g., FIGS. 8C, 1, and 2A-2B) a plurality of through openings 123 in the mask layer 120 using a laser 177 emitting infrared light 178 incident on the structured first major surface 102 of the lens film 110 such that the through openings 123 are arranged along the first and second directions and are aligned to the microlenses 103 in a one-to-one correspondence. The infrared light 178 can have wavelengths in a range described elsewhere herein (e.g., 1020 nm to 1100 nm). The infrared light 178 can have a wavelength at a peak intensity of about 1064 nm, for example. The infrared light 178 can have a beam diameter that fills or substantially fills at least one microlens. The optically absorptive material 153 is preferably optically absorptive for the wavelength range of the infrared light 178 as well as for a visible wavelength range (e.g., at least from about 450 nm to about 650 nm). The optically absorptive material 153 can be optically absorptive for visible wavelengths and for the infrared light 178 so that the optically absorptive material 153 absorbs the infrared light 178 for ablation to occur and provides the desired optical density for the resulting mask layer 120. Suitable optically absorptive material 153 includes carbon black. In some embodiments, each through opening 123 in at least a majority of the through openings has an optical density less than about 0.3 or an optical density in any of the ranges described elsewhere herein for a through opening. The resulting optical construction can have an optical transmittance as described elsewhere and/or can have through openings having open ends having a circularity and/or area distribution (e.g., average area and standard deviation of the area) as described further elsewhere.

The through holes can be created using a coherent, pulsed light source (e.g., laser) with wavelengths from 400 nm - 1200 nm, or from 500 nm - 1100 nm, or from 1000 nm - 1100 nm, or from 1020 nm to 1100 nm. For example, the light source can be a doped fiber laser that produces a near infrared (NIR) band having wavelengths from about 1020 nm to about 1100 nm. A wide range of lasers can be used for the light source. Suitable lasers include Nd:YAG lasers, fiber lasers, and diode lasers, for example. 1 ^st , 2 ^nd or 3 ^rd harmonics may be used, for example. The desired wavelength range of the laser may depend on the polymer and optically absorptive material used in the mask layer.

Examples

All parts and percentages in the Examples are by weight unless indicated otherwise.

Coating Solution 1

350 grams of REXTABlack (RX-P005 REXTA R92 BLACK US) printing ink from Toyo Ink America, Wooddale, IL was mixed under stirring with 200 grams of 2-butanone and 125 grams of isopropyl alcohol to make a diluted coating solution.

Examples 1-4

For Examples 1-4, the Coating Solution 1 was delivered at flow rates of 63 cc/min, 55.2 cc/min, 47.3 cc/min, 39.4 cc/min, respectively, through a Zenith BPB pump with a pump rate of 1.168 cc/rev to a slot coating die for 6” wide coating on the backside of a 9” wide 0.92 mil thick clear polyethylene terephthalate (PET) film with 20 micron microlens features. The dry coating thickness at the line speed of 30ft/min based on the above flow rates was estimated to be around 4.8 microns, 4.2 microns, 3.6 microns and 3 microns, respectively. After the solution was coated, the coated web first passed through a 10 ft long 2-zone gap dryer to minimize the airflow induced mottle defect. Both gap dryer zones were left at ambient temperature. A 3-zone air flotation oven equipped with top and bottom air bars was followed immediately after the gap dryer to dry off all the volatile solvent and cool down the coating temperature in the last zone. Each dryer zone was about 2 meter long. The temperature of zone 1, zone 2 and zone 3 were set at 150, 175 and 200 °F, respectively.

An array of through openings (pinholes) was created in the resulting mask layer by laser ablation though the microlens array. The process used a doped fiber that produced a near infrared (NIR) band from 900nm - 1 lOOnm wavelength. A range of average laser power from 20 watts - 100 watts and laser pulse energy density from 1 pj - 200 pj was explored. The laser energy and laser pulse energy density were adjusted to provide through holes with average diameter from about 1 to about 6 microns, while providing a desired shape and quality without causing thermal surface damage. The beam was rastered across the sample while maintaining a center to center pulse separation of about 50 microns to 100 microns.

The samples were measured on a customized goniometer system that included a collimated light source and a silicon detector. The light source was a green LED with 530 nm emission wavelength attached to a collimation lens, both from Thorlabs. The light source was stationary and had a fixed illumination angle. The silicon detector had a light-sensitive area of 20mm X 20mm and was also obtained from Thorlabs. After the microlens sample was clamped to the silicon detector, it rotated with the silicon detector along two orthogonal axes, and the optical transmittance of the sample was calculated based on the measured power transmission. FIGS. 9-10 are plots of the optical transmittance of the optical constructions of Examples 1-4 as a function of a transmitted angle along cross-web and down-web direchons, respectively, for a substantially collimated light substantially normally incident on the structured major surface side of the optical construction. FIG. 4 is an image of through holes in the mask layer of Example 4. FIG. 11 is an image of a cross-section through a through hole in the mask layer of Example 4.

The area and circularity of the through holes on the side of the mask layer facing away from the microlenses were determined using a microscope. The average (mean) and standard deviation of the area and the circularity are reported in the table below.

Comparative Example Cl

An ultraviolet (UV) curable formulation containing 11 parts carbon black, 54 parts isobomyl acrylate, 35 parts EBECRYL 4396 (isocyanate aliphatic functional urethane acrylate available from Allnex USA, Alpharetta, GA) and 3 parts IRGACURE 819 (photoinitiator available from BASF, Florham Park, NJ) was used. This UV curable 100% solids formulation was coated on the planar side of 9” wide 0.92 mil thick clear PET film with 20 micron microlens features on one side. The conditions were designed so that the thickness of the coating was around 5 microns. The coating was cured using medium pressure mercury UV “D type” light source. Through holes were laser ablated through the resulting mask layer as described for Examples 1-4 and transmission through the sample was measured as described for Examples 1-4. FIG. 12 is a plot of the optical transmittance of the optical construction of Comparative Example Cl as a function of a transmitted angle along cross-web and down-web directions for a substantially collimated light substantially normally incident on the structured major surface side of the optical construction. The transmittance had peaks at greater than about 30 degrees with peak intensities greater than 3.2%. FIG. 13 is an image of through holes in the mask layer of Comparative Example Cl. FIG. 14 is an image of a cross-section through two through holes in the mask layer of Comparative Example Cl. The through holes exhibited poor shape definition as shown in FIGS. 13-14.

Comparative Example C2

Comparative Example C2 was prepared as described for Comparative Example Cl except that the UV curable formulation contained 13 parts carbon black, 52 parts isobomyl acrylate, 35 parts EBECRYL 4396 (isocyanate aliphatic functional urethane acrylate available from Allnex USA, Alpharetta, GA) and 3 parts IRGACURE 819 (photoinitiator available from BASF, Florham Park, NJ).

Comparative Example C3

Comparative Example C3 was prepared as described for Comparative Example Cl except that the UV curable formulation contained 15 parts carbon black, 60 parts isobomyl acrylate, 25 parts EBECRYL 4396 (isocyanate aliphatic functional urethane acrylate available from Allnex USA, Alpharetta, GA) and 3 parts IRGACURE 819 (photoinitiator available from BASF, Florham Park, NJ) was used.

FIG. 15 is a plot of the optical transmittance of the optical constructions of Comparative Examples C2-C3 as a function of a transmitted angle along cross-web (CW) and down-web (DW) directions for a substantially collimated light substantially normally incident on the structured major surface side of the optical construction.

The ratio of the standard deviation of the areas of the through openings visible in a microscope image of the mask layer to the mean area of the through openings were determined from analysis of microscope images of Comparative Examples Cl to C3 to be 0.13, 0.18, and 0.17, respectively. Terms such as “about” will be understood in the context in which they are used and described in the present description by one of ordinary skill in the art. If the use of “about” as applied to quantities expressing feature sizes, amounts, and physical properties is not otherwise clear to one of ordinary skill in the art in the context in which it is used and described in the present description, “about” will be understood to mean within 5 percent of the specified value. A quantity given as about a specified value can be precisely the specified value. For example, if it is not otherwise clear to one of ordinary skill in the art in the context in which it is used and described in the present description, a quantity having a value of about 1, means that the quantity has a value between 0.95 and 1.05, and that the value could be 1.

All references, patents, and patent applications referenced in the foregoing are hereby incorporated herein by reference in their entirety in a consistent manner. In the event of inconsistencies or contradictions between portions of the incorporated references and this application, the information in the preceding description shall control.

Descriptions for elements in figures should be understood to apply equally to corresponding elements in other figures, unless indicated otherwise. Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations can be substituted for 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, or combinations of the specific embodiments discussed herein. Therefore, it is intended that this disclosure be limited only by the claims and the equivalents thereof.