CROSS-REFERENCE TO RELATED APPLICATIONS [0001] Not Applicable

STATEMENT RE: FEDERALLY SPONSORED RESEARCH/DEVELOPMENT [0002] Not Applicable

BACKGROUND

[0003] In various environments where one uses protective eyewear such as goggles, visors, and face shields, it is important to maintain visibility as debris accumulates on the eyewear. For example, participants in off-road sports like motocross racing need to maintain visibility of the course as mud, bugs, and other debris accumulate on their goggles or helmet visor. Similarly, in an operating room environment, splatter can impair the view of surgeons or other operating personnel during a procedure. In response to these needs, tearoff films are commonly employed, either individually or in laminated stacks, which are applied to the goggle lens, visor, or face shield. As debris accumulates on the outermost tearoff film or the outermost tearoff film becomes damaged, the wearer simply tears it off to reveal the next pristine film underneath.

[0004] In order to ensure visual acuity through such stacked lenses, it is desirable to minimize internal reflection. One promising technology for reducing reflection is so- called moth-eye (ME) coatings, which simulate the anti-reflective properties of a moth’s eye by providing a pattern of microscopic bumps that effectively eliminate the index of refraction interface between the lens and the air. Unfortunately, in the case of a stack of lenses, the adhesives used between the layers have a tendency to fill in around the bumps of the ME coating, drastically increasing the peel strength of each layer (making it 650 to 1,070 grams/inch, for example) and thus making the stack unusable as the layers cannot easily be tom off and the force to remove a layer may be greater than the tensile strength of the lens material. BRIEF SUMMARY

[0005] The present disclosure contemplates various devices and methods for overcoming the drawbacks accompanying the related art. One aspect of the embodiments of the present disclosure is a removable lens stack. The removable lens stack may comprise a base layer including a substrate having a first side and a second side opposite the first side, the base layer further including a moth eye coating on the first side of the substrate. The removable lens stack may further comprise one or more removable lens layers, each removable lens layer including a substrate having a first side and a second side opposite the first side, a moth eye coating on the first side of the substrate, and a fluoropolymer coating on the second side of the substrate. The one or more removable lens layers may be stacked on top of the base layer such that the second side of the substrate of each removable lens layer faces the first side of the substrate of an immediately preceding layer from among the base layer and the one or more removable lens layers. Each of the fluoropolymer coatings may be molded to fit the moth eye coating of the immediately preceding layer.

[0006] In each of the one or more removable lens layers and the base layer, the moth eye coating may comprise a polymer.

[0007] In each of the one or more removable lens layers and the base layer, the moth eye coating may define a pattern of bumps with half-wave pitch.

[0008] In each of the one or more removable lens layers and the base layer, the moth eye coating may define a pattern of bumps with half-wave height.

[0009] In each of the one or more removable lens layers and the base layer, the moth eye coating may define a pattern of cones.

[0010] The base layer may further include a moth eye coating on the second side of the substrate.

[0011] In each of the one or more removable lens layers and the base layer, the substrate may comprise polyethylene terephthalate (PET).

[0012] The removable lens stack may comprise, in each of the one or more removable lens layers and the base layer, an adhesion treatment between the substrate and the moth eye coating. The adhesion treatment may comprise a pressure sensitive adhesive. [0013] The removable lens stack may comprise, in each of the one or more removable lens layers, an adhesion treatment between the substrate and the fluoropolymer coating. The adhesion treatment may comprise a pressure sensitive adhesive.

[0014] A peel strength of each of the one or more removable lens layers may be less than 100 grams per inch. A peel strength of each of the one or more removable lens layers may be between 15 and 50 grams per inch and may, more particularly, be between 15 and 30 grams per inch.

[0015] A visible light transmission (VLT) of the removable lens stack may be greater than 95% and may, more particularly, be greater than 98%.

[0016] Another aspect of the embodiments of the present disclosure is a method of manufacturing a removable lens stack. The method may comprise providing a base layer including a substrate having a first side and a second side opposite the first side, the base layer further including a moth eye coating on the first side of the substrate. The method may further comprise stacking one or more removable lens layers on top of the base layer, each removable lens layer including a substrate having a first side and a second side opposite the first side, a moth eye coating on the first side of the substrate, and a fluoropolymer coating on the second side of the substrate. The one or more removable lens layers may be stacked on top of the base layer such that the second side of the substrate of each removable lens layer faces the first side of the substrate of an immediately preceding layer from among the base layer and the one or more removable lens layers. The method may further comprise laminating the stacked one or more removable lens layers to the base layer, each of the fluoropolymer coatings being molded to fit the moth eye coating of the immediately preceding layer. [0017] The laminating may comprise laminating the stacked one or more removable lens layers to the base layer under pressure at a temperature less than 40 °C.

[0018] The method may comprise, in each of the one or more removable lens layers, applying a corona treatment between the substrate and the moth eye coating. [0019] The method may comprise, in each of the one or more removable lens layers, applying a corona treatment between the substrate and the fluoropolymer coating. BRIEF DESCRIPTION OF THE DRAWINGS [0020] These and other features and advantages of the various embodiments disclosed herein will be better understood with respect to the following description and drawings, in which like numbers refer to like parts throughout, and in which: [0021] Figure 1 is a cross-sectional view of a base layer and two removable lens layers of a removable lens stack according to an embodiment of the present disclosure; and

[0022] Figure 2 is a cross-sectional view of the removable lens stack.

DET AIDED DESCRIPTION

[0023] The present disclosure encompasses various embodiments of removable lens stacks and manufacturing methods thereof. The detailed description set forth below in connection with the appended drawings is intended as a description of several currently contemplated embodiments and is not intended to represent the only form in which the disclosed invention may be developed or utilized. The description sets forth the functions and features in connection with the illustrated embodiments. It is to be understood, however, that the same or equivalent functions may be accomplished by different embodiments that are also intended to be encompassed within the scope of the present disclosure. It is further understood that the use of relational terms such as first and second and the like are used solely to distinguish one from another entity without necessarily requiring or implying any actual such relationship or order between such entities.

[0024] Figure 1 is a cross-sectional view of a base layer 100 and two removable lens layers 200, which may be stacked together to form a removable lens stack 10 as shown in cross-section in Figure 2. The base layer 100 of the removable lens stack 10 may be affixed to a surface such as a goggle lens or visor or a transparent window of a surgical helmet, hood, or gown, for example, or alternatively may be attached at a perimeter thereof to a frame such that the removable lens stack 10 itself serves as the lens, visor, face shield, etc. (i.e. without being affixed to a surface). In the example of Figures 1 and 2, two removable lens layers 200 are shown, which are stacked on the base layer 100 to form the removable lens stack 10. However, it is contemplated that there may be more than two removable lens layers 200 or that there may be only a single removable lens layer 200. As shown, each of the removable lens layers 200 may comprise a substrate 210 and a moth eye coating 220 on a first side 212 thereof. The base layer 100 may likewise comprise a substrate 110 and a moth eye coating 120a on a first side 112 thereof, as well as an optional moth eye coating 120b on a second side 114 opposite the first side 112. Owing to the moth eye coatings 120a, 120b, 220, the removable lens stack 10 may have very low reflectance and, accordingly, may exhibit a visible light transmission (VLT) of greater than 95% or in some cases greater than 98% (e.g. >99% with reflections sub 1%).

[0025] Unlike conventional removable lenses, each removable lens layer 200 may additionally comprise a fluoropolymer coating 230 on a second side 214 of the substrate 210 opposite the first side 212. As such, when the removable lens layer(s) 200 are stacked on top of the base layer 100 with the second side 214 of each substrate 210 facing the first side 112, 212 of the immediately preceding substrate 110, 210 (which may be the substrate 210 of an immediately preceding removable lens layer 200 or the substrate 110 of the base layer 100 as the case may be), the fluoropolymer coating(s) 230 may abut the moth eye coatings 120a, 220. Upon laminating the stacked removable lens layer(s) 200 to the base layer 100, each fluoropolymer coating 230 may thus be molded to fit the moth eye coating 120a, 220 of the immediately preceding layer 100, 200. The resulting mechanical interlocking of the moth eye coatings 120a, 220 with the molded female patterns corresponding thereto formed in the adjacent fluoropolymer coatings 230 may function similarly to a zipper to fix the adjacent layers together. Owing to this mechanical interlocking, the use of an acrylic or other tacky adhesive on the moth eye coating 120a, 220 may be entirely avoided, preventing the increased peel strength associated with such conventional adhesives collecting around the bumps of the moth eye coating 120a, 220. Thus, the removable lens layer(s) 200 may advantageously have a much lower peel strength, which may be less than 100 grams per inch and may, for example, be between 15 and 50 grams per inch or more particularly between 15 and 30 grams per inch (e.g. 25 grams per inch), making it possible for the wearer to remove each layer 200 as desired with a reasonable amount of pulling force. (It is noted that the use of a tacky adhesive to affix the base layer 100 to a surface may not present a problem since the base layer 100 need not be removable and thus an increased peel strength caused by buildup of adhesive around the bumps of the optional moth eye coating 120b may be acceptable.)

[0026] The substrate 110, 210 of each layer 100, 200 may comprise a transparent polymer such as polyethylene terephthalate (PET) and may be 1 to 10 mil thick, for example, around 2 mil thick for the substrate 210 of each removable lens layer 200 with the substrate 110 of the base layer 100 being the same thickness or typically thicker (e.g. 7 mil). The moth eye coating 220 of each of the removable lens layers 200, as well as the moth eye coating(s) 120a, 120b of the base layer 100, may comprise a polymer and may typically be made of a hard polymer such as glassy carbon having a Mohs hardness of 7, for example. The moth eye coating 120a, 120b, 220 may define a pattern of nano sized micro-projections or bumps (e.g. transparent cones) on the surface of the substrate 110, 210 with dimensions on the order of the wavelength of light (e.g. visible light), such as half-wave pitch and/or half-wave height, to produce the antireflective effect. For example, the pitch and/or height of the bumps may be 200-375 nm. Various shapes are possible for the bumps of the moth eye coating 120a, 120b, 220, including rounded or rectangular raised surfaces instead of cones, for example.

[0027] The moth eye coating 120a, 120b, 220 may be refractive index matched (e.g. to within 0.2) with the substrates 110, 210 and with the fluoropolymer coating(s) 230, as well as with any adhesives that may be used (as described below), such that the entire removable lens stack 10 may have a consistent index of refraction (e.g. within 0.2). However, because the refractive index interface between the air and the removable lens stack 10 may be effectively eliminated by the outermost moth eye coating 220 (as the interface appears like a gradient rather than a sudden change in material from the perspective of incident light), it is not necessary to index match the removable lens stack 10 to air (n = 1). Therefore, it is contemplated that a wide variety of materials may be used for the substrates 110, 210 and other components of the removable lens stack 10.

[0028] In general, when building a conventional removable lens stack, a removable bonding material is used to wet each pair of adjacent surfaces together. The term “wetting,” in this context, may refer to when two surfaces come in such close contact with each other that the contact displaces all of the air in between the two surfaces, allowing for good bonding. Whereas simply laying one lens on top of another lens does not disperse the air trapped between the lenses, an acrylic removable adhesive may be used to wet the surfaces together and promote bonding. By matching the refractive index of the adhesive with the refractive index(es) of the lenses (e.g. to within 0.2), visible light may stay at a constant speed at the interfaces, minimizing reflections. An example of such a system may be found in U.S. Patent No. 9,295,297, entitled “Adhesive Mountable Stack of Removable Layers,” the entire contents of which is expressly incorporated by reference herein. However, because adhesive is tacky to the touch, issues arise when bonding two surfaces together where one or both surfaces have a moth eye coating. In particular, as described above, the adhesive fills in around the micro-projections of the moth eye coating, drastically increasing the peel strength beyond what is functionally suitable for a removable lens stack.

[0029] Therefore, in order to wet the surfaces of the substrates 110, 210 together and achieve the preferred peel strength in the disclosed removable lens stack 10, the fluoropolymer coating(s) 230 may be provided on the second side 214 of each substrate 210. The fluoropolymer coating 230 may be an index-matched (e.g. to within 0.2) soft fluoropolymer such as fluorinated ethylene-propylene copolymer (FEP), perfluoroalkoxy alkane (PFA), or tetrafluoroethylene perfluoro(methyl vinyl ether) (MFA) that is not tacky to the touch but is moldable under laminating pressure to produce a debossed (female) pattern corresponding to the bumps of the abutting moth eye coating 120a, 220.

[0030] In some cases, an adhesion treatment 140a, 240 may be provided between the substrate 110 and moth eye coating 120a of the base layer 100 and/or between the substrate 210 and moth eye coating 220 of each removable lens layer 200. Likewise, if the substrate 110 of the base layer 100 further includes a moth eye coating 120b on the second side 114 thereof, an adhesion treatment 140b may be provided between the substrate 110 and the moth eye coating 120b. In each removable lens layer 200, an adhesion treatment 250 may similarly be provided between the substrate 210 and the fluoropolymer coating 230. The adhesion treatments 140a, 140b, 240, 250 may comprise a pressure sensitive adhesive such as a silicone adhesive (e.g. a polydimethyl/methylvinyl siloxane polymer and resin dispersed in toluene/isopropyl alcohol such as an adhesive sold under the name DOWSIL™ 7655 Adhesive or DOWSIL™ 7656 Adhesive by the Dow Chemical Company). The adhesive may be index matched (e.g. to within 0.2) with the substrates 110, 210 and other elements of the removable lens stack 10 as noted above.

[0031] The base layer 100 and one or more removable lens layers 200 may be manufactured by coating each substrate 110, 210 with the moth eye coating(s) 120a, 120b, 220 and fluoropolymer coating 230, which may in some cases be adhered to the substrates 110, 210 by adhesion treatments 140a, 140b, 240, 250 as described above. In order to improve adhesion, it is also contemplated that a corona treatment may be applied between the substrate 110, 210 and the moth eye coating 120a, 120b, 220, and/or between the substrate 210 and the fluoropolymer coating 220. This may ensure that the fluoropolymer coating 220 remains with the outermost removable lens layer 200 as it is pulled off the removable lens stack 10, for example. The corona treatment may be applied instead of or in addition to the above-described adhesion treatments 140a, 140b, 240, 250. The removable lens layer(s) 200 may then be stacked on top of the base layer 100 such that the second side 214 of the substrate 210 of each removable lens layer 200 faces the first side 112, 212 of the substrate 110, 210 of an immediately preceding layer from among the base layer 100 and the one or more removable lens layers 200 (as the case may be). In the illustrated example shown in Figures 1 and 2, a first removable lens layer 200 (shown in the center of each figure) is stacked on the base layer 100 and a second removable lens layer 200 (shown in the left-hand side of each figure) is stacked on the first removable lens layer 200. Additional removable lens layers 200 may similarly be provided and added to the stack.

[0032] The removable lens layer(s) 200 may then be laminated to the base layer 100 under pressure with or without heat, for example, under pressure at a temperature less than 40 °C. It should be noted that the base layer 100 and removable lens layer(s) 200 may be laminated together in a single lamination process or in multiple lamination processes, for example, with each removable lens layer 200 added to the stack in a separate lamination process (or with multiple removable lens layers 200 being laminated together before being laminated to the base layer 100). As a result of the lamination, each fluoropolymer coating 230 may be molded to fit the moth eye coating 120a, 220 of the immediately preceding layer. In particular, the hard bumps of the moth eye coating 120a, 220 may press into the soft fluoropolymer coating 230 to produce the corresponding debossed (female) pattern in the fluoropolymer coating 230. In this way, the above-described mechanical interlocking between the layers 100, 200 may be achieved to produce the desired peel strength (e.g. 25 grams per inch) without the use of tacky adhesives between the layers 100, 200 that might otherwise fill in between the bumps and increase the peel strength too much. At the same time, the air between the layers 100, 200 may be expelled during the laminating process, allowing for wetting of the opposing layers 100, 200 (and slight adhesion as a result), while the refractive index interface may be effectively eliminated due to the index gradient created by the architecture of the moth eye coatings 120a, 220. The resulting visible light transmission (VLT) of the removable lens stack 10 may be greater than 95% (e.g. 96% with 4% reflection), as opposed to 92% with 8% reflection that might be found in an uncoated lens. In some cases, the VLT may be greater than 98% (e.g. >99%), especially when the moth eye coating 120b is provided so that there are moth eye coatings 120a, 120b, 220 on both sides of the stack 10.

[0033] When the removable lens stack 10 is incorporated into eyewear and being worn, the wearer may easily peel off the outermost removable lens layer 200 to reveal an unblemished removable lens layer 200 (or the base layer 100) underneath. In the case of a removable lens stack 10 having multiple removable lens layers 200, the pulling force used to remove the outermost removable lens layer 200 may generally involve an initial outward force (perpendicular to the stack 10) as the wearer lifts the outermost removable lens layer 200 off the stack 10 on one side to separate it from the other removable lens layers 200 (e.g. by grasping an easily accessible tab on one side of the stack 10), followed by a continuous sideways force (with a component parallel to the stack 10) as the wearer peels the outermost removable lens layer 200 off. It is contemplated that the continuous sideways force that is responsible for the majority of the separation of the removable lens layers 200 may have more of a tendency to lift off the outermost removable lens layer 200 than to separate subsequent layers 200 underneath. Therefore, the wearer can readily peel off one layer 200 at a time without accidentally tearing off additional layers 200 of the removable lens stack 10.

[0034] The above description is given by way of example, and not limitation. Given the above disclosure, one skilled in the art could devise variations that are within the scope and spirit of the invention disclosed herein. Further, the various features of the embodiments disclosed herein can be used alone, or in varying combinations with each other and are not intended to be limited to the specific combination described herein. Thus, the scope of the claims is not to be limited by the illustrated embodiments.