Coextruded polymer film with sequential peel forces

Abstract

The present disclosure describes multilayer polymeric films configured so that successive constituent layer packets can be delaminated from the remainder of the film in continuous sheet form. The present disclosure further describes compositions, materials, and methods for minimizing the likelihood of removing multiple layer packets together, including by increasing the peel force between the layer packets. In some embodiments, the peel force increases sequentially from the interface between the first and second layer packets to the interface between the next-to-last ((n-1)th layer packet) and the last (nth layer packet).

Description

Summary of the Invention

[0001] The present disclosure describes multilayer polymeric films configured such that successive constituent layer packets can be delaminated from the remainder of the film in continuous sheet form. The sequential peel forces between layer packets can minimize the chance of removing multiple layer packets together (instead of a single layer packet at a time).

[0002] In one aspect, the present disclosure describes a film comprising a coextruded stack of polymer layers. The polymer layers are organized into layer packets, each layer packet comprising a first layer A, a second layer B, and a third layer C. Layer B is disposed between layer A and layer C. The film further comprises a packet interface between adjacent layer packets, the packet interface exhibiting a first peel force of 1 gram / inch or greater; a layer interface between adjacent layer A and layer B, the layer interface exhibiting a second peel force greater than the first peel force; and a layer interface between adjacent layer B and layer C, the layer interface exhibiting a third peel force greater than the first peel force. The layer packets are irreversibly peelable separately from the remainder of the stack. The coextruded stack of polymer layers comprises at least a first layer packet and a second layer packet.

[0003] In some embodiments, each layer packet includes a conformable layer including layer B and layer C, and the thickness of the conformable layer of the second layer packet is greater than the thickness of the conformable layer of the first layer packet.

[0004] In some embodiments, the thickness of Layer A of the second layer packet is less than the thickness of Layer A of the first layer packet.

[0005] In another aspect, the present disclosure describes a film comprising a coextruded stack of polymer layers. The polymer layers are organized into layer packets, each layer packet comprising a first layer A, a second layer B, and a third layer C. Layer B is disposed between layer A and layer C. Layer A of the film comprises a first polymer composition A, layer B of the film comprises a second polymer composition B, and layer C of the film comprises a third polymer composition C.

[0006] Polymer composition A includes polyester, copolyester, polyolefin, poly-alpha-olefin, polymethacrylate, polycarbonate, polycarbonate alloy, polyurethane, aliphatic polyester, polyhydroxybutyrate, polyhydroxysuccinate, styrenic copolymer, silicone, silicone thermoplastic, acrylic, or copolymer or blend thereof. Polymer composition B includes polyester, polyolefin, poly-alpha-olefin, polymethacrylate, polycarbonate, polycarbonate alloy, aliphatic polyester, polyethylene succinate, polylactic acid, styrenic block copolymer, silicone, or copolymer or blend thereof. Polymer composition C includes polyester, polyolefin, poly-alpha-olefin, polymethacrylate, polycarbonate, polycarbonate alloy, aliphatic polyester, polyethylene succinate, polylactic acid, styrenic block copolymer, silicone, or copolymer or blend thereof.

[0007] The layer packets are irreversibly peelable separately from the remainder of the stack.The coextruded stack of polymer layers includes at least a first layer packet and a second layer packet.

[0008] In some embodiments, each layer packet includes a conformable layer including layer B and layer C, and the thickness of the conformable layer of the second layer packet is greater than the thickness of the conformable layer of the first layer packet.

[0009] In some embodiments, the thickness of Layer A of the second layer packet is less than the thickness of Layer A of the first layer packet.

[0010] In another aspect, the present disclosure describes a face shield comprising the multilayer polymeric film described herein.

[0011] The words "preferred" and "preferably" refer to embodiments of the invention that may offer certain benefits, under certain circumstances, although other embodiments may also be preferred, under the same or other circumstances. Furthermore, the description of one or more preferred embodiments does not imply that other embodiments are not useful, or is intended to exclude other embodiments from the scope of the invention.

[0012] The terms "comprises" and variations thereof do not have a limiting meaning where these terms appear in the specification and claims. Such terms are understood to imply the inclusion of a described step or element or group of steps or elements, but not the exclusion of any other step or element or group of steps or elements.

[0013] By "consisting of," it is meant to include and be limited to everything that precedes the phrase "consisting of." Thus, the phrase "consisting of" indicates that the listed elements are required or essential, and that no other elements may be present. "Consisting essentially of" means to include all elements listed before the phrase, and is limited to other elements that do not interfere with or contribute to the action or function specified in this disclosure for those listed elements. Thus, the phrase "consisting essentially of" indicates that the listed elements are required or essential, but that other elements are optional and may or may not be present depending on whether they materially affect the action or function of the listed elements.

[0014] Unless otherwise specified, "a," "an," "the," and "at least one" are used interchangeably and mean one or more.

[0015] As used herein, the term "or" is generally used in its ordinary sense including "and / or" unless the content clearly dictates otherwise.

[0016] The term "and / or" means one or all of the listed elements or a combination of any two or more of the listed elements.

[0017] Also herein, the recitations of numerical ranges by endpoints include all numbers subsumed within that range (eg, 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, 5, etc.).

[0018] As used herein, a "up to" number (eg, up to 50) is inclusive of that number (eg, 50).

[0019] The terms "in the range" or "within a range" (and similar descriptions) include the endpoints of the stated range.

[0020] For any method disclosed herein that includes distinct steps, the steps can be performed in any practicable order, and, where appropriate, any combination of two or more steps can be performed simultaneously.

[0021] All headings are for the convenience of the reader and should not be used to limit the meaning of the text that follows the heading, unless so specified.

[0022] References throughout this specification to "one embodiment," "an embodiment," "particular embodiments," or "some embodiments" mean that the particular feature, configuration, composition, or characteristic described in connection with an embodiment is included in at least one embodiment of the present disclosure. Thus, the appearances of such phrases in various places throughout this specification are not necessarily all referring to the same embodiment of the present disclosure. Furthermore, the particular features, configurations, compositions, or characteristics may be combined in any suitable manner in one or more embodiments.

[0023] Unless otherwise indicated, all numbers expressing amounts of components, molecular weights, and the like used in the specification and claims are to be understood as being modified in all instances by the term "about." As used herein, in connection with a measured quantity, the term "about" refers to a variation in that measured quantity that would be expected by one of ordinary skill in the art making the measurement and exercising a level of care commensurate with the purpose of the measurement and the precision of the measuring equipment used. Accordingly, unless otherwise indicated to the contrary, the numerical parameters set forth in the specification and claims are approximations that may vary depending upon the desired properties sought to be obtained by the present application. At the very least, each numerical parameter should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques, although this is not intended to limit the doctrine of equivalents to the scope of the claims.

[0024] Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible, however, all numerical values inherently contain ranges necessarily resulting from the standard deviations found in their respective testing measurements.

[0025] The above summary of the present invention is not intended to describe each disclosed embodiment or every implementation of the present invention. The following description more particularly exemplifies exemplary embodiments. In several places throughout this application, guidance is provided through lists of examples, which examples can be used in various combinations. In each instance, the recited items serve only as a representative group and should not be interpreted as an exclusive list. [Brief explanation of the drawings]

[0026] [Figure 1A] 1 is a schematic side or cross-sectional view of a layer packet of polymeric film. [Figure 1B] 1 is a schematic side or cross-sectional view of an exemplary polymeric film including a layer packet and configured for sequential irreversible delamination. [Figure 1C] 1 is a schematic side or cross-sectional view of an exemplary polymeric film including a layer packet and configured for sequential irreversible delamination. [Figure 1D] 1 is a schematic side or cross-sectional view of an exemplary polymeric film including a layer packet and configured for sequential irreversible delamination. [Figure 1E] 1 is a schematic side or cross-sectional view of an exemplary polymeric film including a layer packet and configured for sequential irreversible delamination. [Figure 2A] 1 is a schematic side or cross-sectional view of a polymer film configured for sequential, irreversible delamination. [Figure 2B] 2B is a schematic side or cross-sectional view of the polymer film of FIG. 2A as successive layer packets are delaminated and peeled from the film. [Figure 2C] 2B is a schematic side or cross-sectional view of the polymer film of FIG. 2A as successive layer packets are delaminated and peeled from the film. [Figure 2D] 2B is a schematic side or cross-sectional view of the polymer film of FIG. 2A as successive layer packets are delaminated and peeled from the film. [Figure 3A]1 is a schematic side or cross-sectional view of a polymeric film including a base layer and configured for sequential irreversible delamination. [Figure 3B] 3B is a schematic side or cross-sectional view of the polymer film of FIG. 3A as successive layer packets are delaminated and peeled from the film. [Figure 3C] 3B is a schematic side or cross-sectional view of the polymer film of FIG. 3A as successive layer packets are delaminated and peeled from the film. [Figure 3D] 3B is a schematic side or cross-sectional view of the polymer film of FIG. 3A as successive layer packets are delaminated and peeled from the film. [Figure 3E] 3B is a schematic side or cross-sectional view of the polymer film of FIG. 3A as successive layer packets are delaminated and peeled from the film. [Figure 4] FIG. 1 is a schematic diagram of a manufacturing system in which three polymeric materials are coextruded to form a multilayer polymeric film. [Figure 5] FIG. 1 is a schematic diagram of film processing equipment that can be used to stretch a cast multilayer polymeric film. [Figure 6] FIG. 1 is a schematic front view of a face shield including a polymer film including a layer packet configured for sequential, irreversible delamination. [Figure 7] 1 is a chart of peel force in grams per inch (g / in) of layers of a polymer film undergoing sequential irreversible delamination in grams per inch (g / in), prepared and measured as described in Example 1. [Figure 8] 1 is a chart of peel force in grams per inch (g / in) of layers of a polymer film undergoing sequential irreversible delamination in grams per inch (g / in), prepared and measured as described in Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0027] The present disclosure describes combinations of polymeric materials that, when incorporated into a coextrusion stack of polymer layers, can be used to produce multilayer polymeric films containing multiple layer packets that can be delaminated or peeled one layer packet at a time from the rest of the film. The stack of polymer layers is arranged or organized to form layer packets, with each layer packet having at least two of the polymer layers. In contrast to the films of U.S. Patent Application Publications 2015 / 0183178(A1), 2019 / 0248117(A1), and 2019 / 0248118(A1), the films disclosed herein exhibit gradient peel forces between layer packets throughout the stack of polymer layers. The gradient can increase such that the peel force is successively greater from the interface between the first and second layer packets to the interface between the next-to-last (the (n-1)th layer packet) and the last (the nth layer packet). The gradient peel force reduces the likelihood of multiple layer packets being removed together, rather than a single layer packet being removed from a stack of polymer layers.

[0028] These films may be made by coextruding all of the polymer layers in the stack, eliminating the need to laminate separately manufactured films or layers to build the stack. This construction allows the individual layer packets (which can be peeled sequentially) to be much thinner than would otherwise be possible, allowing for more separately peelable sheets to be included in a film of a given total thickness. Coextruded layers are also less susceptible to contamination during manufacturing than layers that are made separately and then laminated together.

[0029] The film can also be made without the need for any pressure-sensitive adhesives, or other types of adhesives, in the stack of polymer layers. The absence of adhesives simplifies manufacturing and creates a film surface that is internal to the initial final product film, but also an external surface from which the layer packet is peeled off during use, which is cleaner than can be achieved with films made using separate lamination steps.

[0030] For example, some of the features of peelable polymer films, including the composition of the polymers of the polymer layers within the layer packets, or the methods of making the polymer stacks, described in commonly assigned U.S. Patent Application Publication Nos. 2015 / 0183178(A1), 2019 / 0248117(A1), and 2019 / 0248118(A1), and WO 2019 / 032635, may be suitable for use with the films disclosed herein that exhibit gradient peel forces between layer packets throughout the stack of polymer layers.

[0031] Specific embodiments of the present invention will be described with reference to the accompanying drawings, in which like numbers represent like elements, and in which: Figure 1 is a schematic diagram of a system for implementing a method of manufacturing a semiconductor device according to the present invention;

[0032] Exemplary polymer layers of a layer packet are shown in Figure 1A. As shown in Figure 1A, each layer packet includes a first layer A, a second layer B, and a third layer C, labeled 142, 144, and 146, respectively. Layer B 144 is disposed between layer A 142 and layer C 146. Layers B 144 and C 146 may together form conformable layer 132. In some embodiments, layer B 144 and layer C 146 may have the same composition, and in those embodiments, the layer packet may be considered to include two layers: layer A 142 and the conformable layer.

[0033] 1A, conformable layer 132 may include layers B 144 and C 146 having the same thickness. However, in some embodiments, as described further below, if the coextruded stack of polymer layers exhibits a gradient in the thickness of the conformable layers, the thickness of layer B may increase while the thickness of layer C remains constant, or the thickness of layer C may increase while the thickness of layer B remains constant, or the thickness of both layers B and C may increase such that the ratio of the thickness of layer B to the thickness of layer C remains constant throughout the depth of the stack of polymer layers.

[0034] Layer A, Layer B, and Layer C may each be formed of any suitable polymer composition. In some embodiments, Layer A may comprise a first polymer composition A, Layer B may comprise a second polymer composition B, and Layer C may comprise a third polymer composition C. In some embodiments, polymer composition B may be different from polymer composition A, and polymer composition C may be different from polymer composition A. In other embodiments, polymer composition C may be different from polymer composition A and polymer composition B. In some embodiments, polymer composition B may be different from polymer composition A, and polymer composition C may be different from polymer composition A, but polymer composition B may be the same as polymer composition C.

[0035] In some embodiments, polymer composition A, polymer composition B, and polymer composition C are preferably melt processable at a temperature of at least 204°C (400°F).

[0036] In some embodiments, polymer composition A, B, or C, or a combination thereof, may be a polyester-based material, although other suitable materials may also be used. For example, polymer composition A may be or may include polyester, copolyester, polyolefin, poly-alpha-olefin, polymethacrylate, polycarbonate, polycarbonate alloy, polyurethane, aliphatic polyester (e.g., polylactic acid, polyhydroxybutyrate, polyhydroxysuccinate, styrenic copolymer, silicone, silicone thermoplastic, acrylic, or copolymers and / or blends thereof. In an exemplary embodiment, polymer composition A may be or may include polyethylene terephthalate (PET). In some embodiments, polymer composition B or polymer composition C, or both, may be or may include polyester, polyolefin, poly-alpha-olefin, polymethacrylate, polycarbonate, polycarbonate alloy, aliphatic polyester (e.g., polyhydroxybutyrate, polyethylene succinate, polylactic acid, styrenic block copolymer, silicone, or copolymers and / or blends thereof. Exemplary polyolefins include polypropylene and polyethylene. In exemplary embodiments, polymer composition B or polymer composition C, or both, may be or include a copolymer based on styrene and ethylene / butylene. For example, polymer composition B or polymer composition C, or both, may be or include KRATON G1645 (Kraton Corporation, Houston, TX), a linear triblock copolymer based on styrene and ethylene / butylene. The copolymer may be block or random, or a combination thereof.

[0037] In some embodiments, polymer composition B, and either polymer composition A or polymer composition C, are preferably polyester-based materials. As further described in U.S. Patent Application Publication No. 2019 / 0248117, appropriate incorporation of a combination of polyester and non-polyester-based materials into Layer B or Layer A or Layer C of a layer packet can cause the layer packet to preferentially delaminate along interfaces between adjacent layer packets (e.g., between Layer C and Layer A), instead of within the layer packet (e.g., between Layer A and Layer B or between Layer B and Layer C).

[0038] 1A, delamination between Layer C and Layer A can be achieved by making Layer C less strongly attached to Layer A than Layer C is to Layer B, and Layer B less strongly attached to Layer A. In some embodiments, preferential delamination between layer packets (e.g., between adjacent Layers C and A) can be achieved by using a blend of a polypropylene copolymer and a suitable amount of another resin for polymer composition C. For example, polymer composition C can be a miscible blend of a propylene copolymer and a styrenic block copolymer, or a miscible blend of a propylene copolymer and an ethylene-alpha-olefin copolymer, or a miscible blend of a propylene copolymer and an olefin block copolymer. When polymer composition C is a miscible blend of a propylene copolymer and a styrenic block copolymer, polymer composition B may be an immiscible blend of a copolyester and an olefin, and polymer composition A may be a semi-crystalline polyester optionally blended with an amorphous copolyester, or polymer composition B may be an amorphous copolyester and polymer composition A may be a semi-crystalline polyester. When polymer composition A is a blend of a semi-crystalline polyester and an amorphous copolyester, the composition may contain up to 50% amorphous copolyester, although in some embodiments, including when cost is a consideration, up to 20% amorphous copolyester may be preferred.

[0039] In some cases, polymer composition C may be at least partially miscible with polymer composition B, which may be at least partially miscible with polymer composition A, but polymer composition C may not be miscible with polymer composition A. As used herein, a given polymer composition that is an immiscible blend of polymers, such as any of polymer compositions A, B, or C, may be said to be at least partially miscible with another polymer composition if at least one component of the immiscible blend is miscible with the other polymer composition (or, if the other polymer composition is also an immiscible blend or a block copolymer, with at least one component of the other polymer composition (in which case "component" refers to the individual block domains of the block copolymer)). As already mentioned above, adhesion between the polymer A layer and the polymer C layer may be weakest, but such adhesion can still be greater than zero. For example, the peel force at the packet interface (between adjacent layers A and C) may be at least 1 gram / inch, or at least 2 grams / inch. The unit of peel force is grams per inch (or grams per inch width), abbreviated as g / in, which is sometimes referred to as grams per linear inch (abbreviated as gli). 1 g / in is equal to 0.3860886 N / m.

[0040] For purposes of this disclosure, the terms "miscible," "miscibility," and the like are not meant in the absolute sense of requiring the two or more polymers in question to form one homogeneous phase of spatially constant composition, but rather in the relative sense that there is sufficient interdiffusion of the two or more polymers to provide significant inter-phase interaction across the interface between the phases and / or entanglement across what is sometimes referred to in the literature as the "interphase" between the layers. Miscibility in this relative sense is also sometimes referred to in the polymer science literature as "compatibility" or "partial miscibility." Furthermore, a homopolymer or random copolymer may be said to exhibit miscibility in this sense with a block copolymer if it possesses such an ability to interact with the domains of only one block of the block copolymer, even if, for example, the homopolymer or copolymer is completely immiscible with the domains of the other block of the block copolymer.

[0041] In addition to miscibility differences, the presence of polymer orientation or crystallinity, or both, in at least one component of adjacent layers (e.g., adjacent Layer A or Layer B, or both) can affect the peel force of adjacent layers due to reduced intermolecular entanglement across the interface between the two layers. Intermolecular entanglement can be caused by reduced mobility of polymer molecules that are molecularly oriented (rather than in a random coil configuration), involved in structured crystallites (rather than in an amorphous state), or both. In other words, morphology (e.g., crystallinity) and composition can be used to affect the relative peel force between pairs of layers.

[0042] For example, the peel force between adjacent layers can be increased by increasing molecular orientation or crystallinity, or both. In some embodiments, at least one of Layer A, Layer B, or Layer C comprises a crystalline or semi-crystalline polymer. In one embodiment, Layer A comprises a crystalline or semi-crystalline polymer.

[0043] In some embodiments, polymer composition A, polymer composition B, and polymer composition C may independently comprise one or more polymers selected from polyesters, polyolefins, poly-alpha-olefins, polymethacrylates, polycarbonates, polycarbonate alloys, polyurethanes, polylactic acids, polyhydroxybutyrates, polyhydroxysuccinates, styrenic copolymers, silicones, or copolymers or blends thereof.

[0044] In some embodiments, polymer composition A comprises a polyester, copolyester, acrylic, or silicone thermoplastic resin, or a combination thereof (e.g., including a blend). In some embodiments, polymer composition A may be selected from polyester, copolyester, acrylic, and silicone thermoplastic resins. In some embodiments, polymer composition A comprises a semi-crystalline polyester. In an exemplary embodiment, polymer composition A comprises polyethylene terephthalate (PET).

[0045] In some embodiments, polymer composition B comprises a copolyester, PMMA, co-PMMA, styrenic block copolymer, polypropylene, or silicone polyoxamide, or a combination thereof (e.g., including blends). In some embodiments, polymer composition B may be selected from various polymers and polymer blends, including, but not limited to, copolyester, PMMA, co-PMMA, styrenic block copolymer, polypropylene, and silicone polyoxamide, and in some embodiments, polymer composition B comprises a copolyester, or a styrenic block copolymer, or a combination thereof (e.g., including blends). In an exemplary embodiment, polymer composition B comprises a copolymer based on styrene and ethylene / butylene, including, for example, KRATON G1645 (Kraton Corporation, Houston, TX), a linear triblock copolymer based on styrene and ethylene / butylene.

[0046] In some embodiments, polymer composition C may be selected from a blend of olefins, such as polypropylene or polyethylene, blended with a suitable amount of a styrenic block copolymer, or an ethylene-alpha-olefin copolymer, or an olefin block copolymer. In some embodiments, polymer composition C comprises an olefin, or a styrenic block copolymer, or a combination (e.g., including a blend) thereof. In an exemplary embodiment, polymer composition C comprises a copolymer based on styrene and ethylene / butylene, including, for example, KRATON G1645 (Kraton Corporation, Houston, TX), a linear triblock copolymer based on styrene and ethylene / butylene.

[0047] It should be noted that not all combinations of the aforementioned suitable compositions for different polymer compositions will produce the desired results, and judgment must be used to identify appropriate combinations of polymeric materials for use in different layer types to achieve the desired functionality and delamination characteristics. For example, polymer composition A may be or include a semi-crystalline polyester, polymer composition C may be or include a styrenic block copolymer, an ethylene-alpha-olefin copolymer, or a polypropylene blended with an olefin block copolymer, and polymer composition B may be or include a copolyester. In another example, polymer composition A may be or include polymethyl methacrylate (PMMA) or co-PMMA, polymer composition C may be or include a blend of polypropylene and a styrenic block copolymer, and polymer composition B may be a blend of PMMA or co-PMMA with a styrenic block copolymer or polypropylene. In yet another example, polymer composition A may be or include a silicone polyoxamide, polymer composition C may be or include a polypropylene and a styrenic block copolymer, and polymer composition B may be a styrenic block copolymer.

[0048] In some embodiments, polymer composition C is at least partially miscible with polymer composition B. In some embodiments, polymer composition B is at least partially miscible with polymer composition A. In some embodiments, polymer composition C is not miscible with polymer composition A. In some embodiments, polymer composition C is at least partially miscible with polymer composition B, polymer composition B is at least partially miscible with polymer composition A, and polymer composition C is not miscible with polymer composition A.

[0049] One or more optional additives may also be included in some or all of the layers. Optional additives may include, for example, UV light stabilizers, antimicrobial agents, beads or other particles of a suitable size, and / or other desired additives. In some embodiments, the additive may be dispersed in Layer A of each layer packet but may not be present in any of the other polymer layers. In some embodiments, the additive may be present as a continuous or co-continuous phase material. In some embodiments, the additive may also be soluble in one, some, or all of the layers of the layer stack.

[0050] In some embodiments, Layer A, Layer B, or Layer C, or a combination thereof, comprises one or more ultraviolet (UV) light stabilizers. In some embodiments, Layer A, Layer B, or Layer C, or a combination thereof, does not comprise a UV light stabilizer.

[0051] In some embodiments, Layer A, Layer B, or Layer C, or a combination thereof, comprises one or more organic antimicrobial agents. In some embodiments, Layer A, Layer B, or Layer C, or a combination thereof, does not comprise an antimicrobial agent.

[0052] In some embodiments, Layer A and Layer B, or Layer A and Layer C, or Layer B and Layer C, or some combination thereof, can be oriented. Such oriented layers may have a minimum level of birefringence, including, for example, a birefringence of 0.03 or greater, 0.04 or greater, 0.05 or greater, 0.07 or greater, or 0.10 or greater. In this regard, a given material or material layer is said to be birefringent if it has a refractive index for light polarized along one direction that is different from the refractive index for light polarized along a different direction. In that case, the "birefringence" of a material or material layer is the maximum difference between such refractive indices. In some cases, such a maximum difference may occur between two orthogonal axes that are both in the plane of the film (e.g., the x- and y-axes in Figures 1B-1E, 2, and 3), and in other cases, it may occur between two orthogonal axes, one of which is in the plane of the film and the other of which is perpendicular to the plane of the film (e.g., the x- and z-axes in Figures 1B-1E, 2, and 3).

[0053] FIG. 1A illustrates a three-layer (ABC) layer packet. The layers may be organized differently, or other layer types (e.g., polymer layer D, polymer layer E, etc.) may be added to the stack, resulting in a layer packet containing more than three individual polymer layers. For example, layers A, B, and C may be arranged in an arrangement of A, B, A, B, C, A, B, A, B, C, etc., resulting in each layer packet being a five-layer group of polymer layers (ABABC). In this case, the adhesion of layer C to layer A is again substantially weaker than the adhesion of layer C to layer B, which is weaker than the adhesion of layer B to layer A, so that a delamination surface forms at the packet interface between layer C and layer A. However, to ensure that the film does not easily fall apart, the adhesion of layer C to layer A is characterized by a peel force greater than zero. For example, the peel force between adjacent layers C and A may be 0.8 grams / inch or greater, 1 gram / inch or greater, 1.5 grams / inch or greater, or 2 grams / inch or greater.

[0054] In one example, a polymer layer D made of a polymer composition D different from compositions A, B, and C may be added to the layer stack. According to one embodiment, the polymer compositions are co-extrudable with one another, such that the entire layer stack can be co-extruded in a single operation. In some embodiments, polymer composition D is preferably melt-processable at a temperature of at least 204°C (400°F). In some cases, none of compositions A, B, C, or D is a pressure sensitive adhesive (PSA) or other type of adhesive.

[0055] Preferably, any additional polymer layers are added such that the modified stack can be made by a single coextrusion process, and the sheets or layer packets can be sequentially and irreversibly delaminated from the remainder of the layer stack of the multilayer polymer film. The modified stack including the additional polymer layers can remain adhesive or PSA-free.

[0056] In some embodiments, any or all of the polymer layers A, B, C, D, etc. may be oriented. Such orientation layers may have a minimum level of birefringence, including, for example, a birefringence of 0.03 or more, 0.04 or more, 0.05 or more, 0.07 or more, or 0.10 or more.

[0057] As shown in Figures 1B-1E, layer packets 122b, 122c, 122d, 122e, 124b, 124c, 124d, 124e, 126b, 126c, 128b, and 128c may be organized into a coextrusion stack of polymer layers. The coextrusion stack of polymer layers may include as few as two layer packets, although, as shown in Figures 1B-1E, the stack may include any suitable number (n) of layer packets. The number of layer packets may be selected by one skilled in the art based on the ease of manufacturing or intended use of the coextrusion stack of polymer layers. In some embodiments, the coextrusion stack of polymer layers includes n layer packets. In some embodiments, the nth layer packet is the 2nd, 3rd, 4th, 5th, 6th, 7th, 8th, 9th, 10th, 11th, 12th, 13th, 14th, 15th, 16th, 17th, 18th, 19th, 20th, or 21st layer packet. One advantage of creating polymer layers in a single coextrusion operation is that up to 20 or more very thin layer packets can be incorporated into the polymer film, which can be removed sequentially in continuous sheet form.

[0058] In some embodiments, the peel force between adjacent layer packets (i.e., at the packet interfaces) increases from one packet interface to the next. Such increased peel force can help prevent more than one layer packet from peeling at once. However, even at the final packet interface, the peel force is less than the peel force within a given packet (i.e., at the layer interfaces within the packet).

[0059] In some embodiments, a coextruded stack of polymer layers may exhibit a peel force gradient from the first layer packet to the nth layer packet. For example, the peel force at the packet interface between layer A of the second layer packet and layer C of the first layer packet may be less than the peel force between layer A of the third layer packet and layer C of the second layer packet. The peel force at the packet interface between layer A of the second layer packet and layer C of the first layer packet may be less than the peel force between layer A of the nth layer packet and layer C of the (n-1)th layer packet. The peel force at each successive packet interface may be greater than the peel force at the previous packet interface.

[0060] In some embodiments, the peel force at the packet interface between layer A of the second layer packet and layer C of the first layer packet is at least 5, at least 10, at least 100, or at least 250 times less than the peel force between layer A of the nth layer packet and layer C of the (n-1)th layer packet. In some embodiments, the peel force at the packet interface between layer A of the second layer packet and layer C of the first layer packet is up to 500, up to 250, up to 100, or up to 10 times less than the peel force between layer A of the nth layer packet and layer C of the (n-1)th layer packet. For example, in an exemplary embodiment, the peel force at the packet interface between layer A of the second layer packet and layer C of the first layer packet is 500 times less than the peel force between layer A of the nth layer packet and layer C of the (n-1)th layer packet.

[0061] In some embodiments, the peel force at each successive packet interface increases from the previous packet interface by at least 0.5 percent, at least 1 percent, at least 5 percent, at least 10 percent, at least 20 percent, at least 50 percent, or at least 100 percent. In some embodiments, the peel force at each successive packet interface can increase from the previous packet interface by up to 1 percent, up to 5 percent, up to 10 percent, up to 20 percent, up to 50 percent, up to 100 percent, up to 1000 percent, up to 10,000 percent, or up to 50,000 percent.

[0062] In some embodiments, a coextruded stack of polymer layers may exhibit a gradient in the thickness of layer A, layer B, or layer C, or a combination thereof, from the first layer packet to the nth layer packet. In one embodiment, a coextruded stack of polymer layers exhibits a gradient in the thickness of layer A. The gradient can be a decrease in the thickness of layer A in the stack from the first layer packet to the nth layer packet. In one embodiment, a coextruded stack of polymer layers exhibits a gradient in the thickness of layer B or layer C, or the combined thickness of layers B and C. The gradient can be an increase in the thickness of layer B or layer C, or the combined thickness of layers B and C in the stack from the first layer packet to the nth layer packet.

[0063] In exemplary embodiments, as shown in Figure 1B, the coextruded stack of polymer layers exhibits a gradient in the thickness of the conformable layers (including layers B and C) from the first layer packet to the nth layer packet. In some embodiments, as shown in Figure 1B, the thickness of the conformable layers of the first layer packet 122b is less than the thickness of the conformable layers of the nth layer packet 128b. The thickness of the conformable layers (e.g., layers B and C combined) may increase sequentially throughout the stack from the first layer packet to the nth layer packet.

[0064] In some embodiments, the thickness of the conformable layer of the first layer packet may be at least 1.1 times, at least 1.2 times, at least 1.5 times, or at least 2 times less than the thickness of the conformable layer of the nth layer packet. In some embodiments, the thickness of the conformable layer of the first layer packet may be up to 2 times, up to 5 times, or up to 10 times less than the thickness of the conformable layer of the nth layer packet. According to one embodiment, as described in Example 1, the peel force from one packet interface to the next packet interface increases as the thickness of each conformable layer (relative to the previous conformable layer) increases. In an exemplary embodiment, the thickness of the conformable layer of the first layer packet may be 3 times less than the thickness of the conformable layer of the nth layer packet.

[0065] In some embodiments, the thickness of the conformable layer of each successive layer packet increases by at least 5 percent, at least 10 percent, at least 15 percent, at least 20 percent, at least 25 percent, or at least 30 percent. In some embodiments, the thickness of the conformable layer of each layer packet increases by up to 50 percent, up to 100 percent, up to 200 percent, up to 500 percent, or up to 1000 percent. In some embodiments, the thickness of the conformable layer of each successive layer packet increases by 5 percent to 500 percent, 10 percent to 200 percent, or 15 percent to 100 percent. As described in Example 1, a 20 percent change in conformable layer thickness from one layer to the next can, in some embodiments, provide a difference in peel force of approximately 0.5 g / in.

[0066] In some embodiments, the total thickness of all conformable layers in a stack of polymer layers may be at least 10 micrometers, at least 15 micrometers, at least 20 micrometers, at least 25 micrometers (about 1.0 mil), at least 30 micrometers, at least 35 micrometers, at least 40 micrometers (about 1.6 mil), at least 45 micrometers, at least 50 micrometers (about 2.0 mil), at least 55 micrometers, at least 60 micrometers, at least 65 micrometers (about 2.5 mil), at least 70 micrometers, at least 80 micrometers, at least 90 micrometers, or at least 100 micrometers. In some embodiments, the total thickness of all conformable layers in a stack of polymer layers can be up to 300 micrometers, up to 200 micrometers, up to 100 micrometers, up to 90 micrometers, up to 80 micrometers, up to 70 micrometers, up to 65 micrometers (about 2.5 mils), up to 60 micrometers, up to 55 micrometers, up to 50 micrometers (about 2.0 mils), up to 45 micrometers, up to 40 micrometers (about 1.6 mils), up to 35 micrometers, up to 30 micrometers, or up to 25 micrometers (about 1.0 mil). In some embodiments, the total thickness of all conformable layers in a stack of polymer layers can be between 20 micrometers and 200 micrometers, or between 25 micrometers and 100 micrometers.

[0067] As described in Example 1, the thickness of each of the conformable layers in a stack of polymer layers may be added together to form the "total conformable layer thickness." As the total conformable layer thickness increases, the difference in peel force from layer packet to layer packet increases. In some embodiments, the upper limit of the total conformable layer thickness may be determined by extrusion and / or film orientation capabilities.

[0068] In some embodiments, a coextruded stack of polymer layers may exhibit both a peel force gradient and a thickness gradient. In some embodiments, a peel force gradient between layer packets throughout the stack of polymer layers is achieved by varying the ratio of the thickness of the conformable layer to the thickness of Layer A throughout the stack. In some embodiments, either the thickness of Layer A, the thickness of Layer B, the thickness of Layer C, or a combination thereof is varied.

[0069] In exemplary embodiments, as shown in Figure 1C, the coextruded stack of polymer layers exhibits a gradient in the thickness of layer A from the first layer packet to the nth layer packet. In some embodiments, as shown in Figure 1C, the thickness of layer A in the first layer packet 122c is less than the thickness of layer A in the nth layer packet 128c. The thickness of layer A sequentially decreases in adjacent layer packets.

[0070] In some embodiments, the thickness of Layer A of the first layer packet may be at least 1.1 times, at least 1.2 times, at least 1.5 times, or at least 2 times greater than the thickness of Layer A of the nth layer packet. In some embodiments, the thickness of Layer A of the first layer packet may be up to 2 times, up to 5 times, or up to 10 times greater than the thickness of Layer A of the nth layer packet. In an exemplary embodiment, the thickness of Layer A of the first layer packet may be 3 times greater than the thickness of Layer A of the nth layer packet.

[0071] In some embodiments, the thickness of Layer A in each layer packet decreases by at least 5 percent, at least 10 percent, at least 15 percent, at least 20 percent, at least 25 percent, or at least 30 percent from one layer packet to the next, hi some embodiments, the thickness of Layer A in each layer packet decreases by up to 50 percent, up to 100 percent, up to 200 percent, up to 500 percent, or up to 1000 percent from one layer packet to the next.

[0072] In some embodiments, both the thickness of the conformable layer and the thickness of Layer A may vary throughout the stack. For example, as shown in FIG. 1D, the thickness of Layer A may decrease from the first layer to the nth layer as the thickness of the conformable layer increases from the first layer to the nth layer. Alternatively, as shown in FIG. 1E, the thickness of the conformable layer and the thickness of Layer A may both increase from the first layer to the nth layer. As a result, the ratio of the thickness of Layer A to the thickness of the conformable layer remains constant throughout the depth of the stack. Without wishing to be bound by theory, it is believed that thicker A layers, which are semi-crystalline or mostly semi-crystalline, are harder and more easily initiate peeling.

[0073] The front and rear major surfaces of adjacent layer packets are in intimate contact with each other, forming a packet interface. Each layer packet has at least two polymer layers disposed between the front and rear major surfaces: one polymer layer A and one conformable layer (which may be a single layer or may include layers B and C). As shown in the figure, layer A of a given packet is the forward-most polymer layer in the packet, and layer B is the rear-most polymer layer in the packet. The stack of layer packets may be constructed such that the forward-most polymer layer is intended to be peeled first. The rear-most polymer layer may form a workpiece or may be attached to a workpiece. For example, the rear-most polymer layer may be attached to a mask such as a face shield, a set of safety glasses, sunglasses, safety goggles, ski goggles, or another application where removal of contamination on a surface may be beneficial. In one embodiment, the stack of layer packets is coextruded with a workpiece or portion of a workpiece, such as a shield or lens of a face shield, safety glasses, sunglasses, safety goggles, ski goggles, etc.

[0074] In some embodiments, the thickness of a single layer packet in a coextruded stack of polymer layers is at most 10 micrometers, at most 25 micrometers, at most 50 micrometers, at most 75 micrometers, at most 100 micrometers, at most 125 micrometers, or at most 150 micrometers. In some embodiments, the thickness of a single layer packet in a coextruded stack of polymer layers is at least 1 micrometer, at least 5 micrometers, at least 10 micrometers, at least 25 micrometers, at least 50 micrometers, at least 75 micrometers, at least 100 micrometers, or at least 125 micrometers.

[0075] An exemplary multilayer polymer film is shown schematically in FIG. 2A. In this exemplary embodiment, film 210a is composed of a stack of polymer layers 220a. Film 210a is typically relatively thin and flexible so that it can be applied to and conform to a non-flat, contoured workpiece. For example, film 210a may have a total thickness of up to 510 micrometers (approximately 20 mils), up to 380 micrometers (approximately 15 mils), up to 300 micrometers, up to 200 micrometers, up to 100 micrometers, or up to 50 micrometers. In some embodiments, film 210a may have a total thickness of at least 25 micrometers, at least 50 micrometers, at least 100 micrometers, at least 200 micrometers, at least 300 micrometers, or at least 380 micrometers.

[0076] Alternatively, in some cases, it may be desirable for film 210a to be relatively thick and inflexible or rigid. For example, a stiffer film may be preferred when the film is used in applications such as face shields where at least a portion of the film is unsupported. In some embodiments, the Young's modulus of the film may be at least 1 GPa, at least 2 GPa, or at least 3 GPa. In some embodiments, the Young's modulus of the film may be up to 3 GPa, up to 4 GPa, up to 5 GPa, or up to 10 GPa. (For reference, the Young's modulus of steel is approximately 200 GPa.)

[0077] 2A includes layer packets 222, 224, 226, and 228. Four layer packets are shown. However, polymer film 210a may include more than four layer packets, such as up to 10, up to 15, up to 20, up to 25, or up to 30 layer packets. The layer packets are irreversibly peelable separately from the remainder of the stack.

[0078] Each layer packet (222, 224, 226, and 228) includes a layer A (242a, 242b, 242c, and 242d for layer packets 222, 224, 226, and 228, respectively) and a compatible layer (232a, 232b, 232c, and 232d for layer packets 222, 224, 226, and 228, respectively). Each layer packet is characterized by a front major surface and a rear major surface. Layer packet 222 has a front major surface 222a and a rear major surface 222b. Layer packet 224 has a front major surface 224a (in intimate contact with rear major surface 222b) and a rear major surface 224b. Layer packet 226 has a front major surface 226a (in intimate contact with rear major surface 224b) and a rear major surface 226b. Layer packet 228 has a front major surface 228a (in intimate contact with rear major surface 226b) and a rear major surface 228b.

[0079] As used in the context of this discussion, the terms "front," "rear," and the like (e.g., forward-most, rear-most) are used for convenience to designate the order of layers relative to the outer major surfaces of a film or stack and should not be construed in a limiting manner. Thus, even if a film or packet is intended for use with one outer major surface facing outward (forward) and the other outer major surface facing inward (rearward), either of these outer major surfaces can be considered the "front," and the other outer major surface would then be considered the "rear." In some embodiments, the first layer packet can be the forward-most layer packet of a coextruded stack of polymer layers.

[0080] The polymer composition of each layer of the layer packet is adjusted so that the rearmost polymer layer (e.g., layer C) is less adherent to the forward-most polymer layer (e.g., layer A) than to the inner polymer layer (e.g., layer B). Thus, the first layer packet will tend to irreversibly delaminate from the second layer packet along a delamination surface corresponding to the interface between the layer packets.

[0081] For example, in some embodiments, the packet interface between adjacent layer A and layer C of the layer packet exhibits a first peel force, the layer interface between adjacent layer A and layer B exhibits a second peel force that is greater than the first peel force, and the layer interface between adjacent layer B and layer C exhibits a third peel force that is greater than the first peel force. In some embodiments, the third peel force is greater than the second peel force.

[0082] In some embodiments, the first peel force is 0.8 grams / inch or greater, 1 gram / inch or greater, 1.5 grams / inch or greater, 2 grams / inch or greater, or 5 grams / inch or greater. In some embodiments, the first peel force is up to 500 g / in.

[0083] In some embodiments, the second peel force is at least 1.02, at least 1.04, at least 1.07, at least 1.1, at least 2, or at least 3 times the first second peel force, hi some embodiments, the second peel force is up to 500 times the second peel force.

[0084] In some embodiments, the third peel force is at least 1.02 times, at least 1.04 times, at least 1.07 times, at least 1.1 times, at least 2 times, or at least 3 times the first peel force, hi some embodiments, the third peel force is up to 500 times the first peel force.

[0085] The film of Figure 2A is configured so that successive layer packets can be delaminated from the remainder of the film in a continuous sheet form. The film of Figure 2A is configured so that the first peel force increases from the first packet interface (between the first layer packet 222 and the second layer packet 224) to the last packet interface (between the third layer packet 226 and the fourth layer packet 228). However, even as the first peel force at the packet interfaces increases, the second and third peel forces are greater than the first peel force to facilitate delamination at the packet interfaces.

[0086] This delamination is illustrated in the sequence shown in Figures 2B-2D. In Figure 2B, film 210a of Figure 2A becomes film 210b modified by removal of top or frontmost layer packet 222. Delamination of each layer packet can be initiated by pulling on the top layer packet. Delamination may be assisted by applying a knife or other sharp instrument to the edges of film 210a, by applying adhesive tape (including, for example, Scotch brand tape (3M Company, St. Paul, MN)) to the top layer packet, or by using tabs or tab-like features, as discussed further below.

[0087] Layer packet 222 is delaminated from the remainder of stack 220a in continuous sheet form, such that the peeled-away layer stack 220b remains in place as part of modified film 210b, as shown in FIG. 2B. Delamination occurs preferentially along a delamination surface corresponding to the packet interface between layer packet 222 and layer packet 224. After removal of layer packet 222, layer packet 224 becomes the outermost layer packet of film 210b, and forward major surface 224a of layer packet 224 becomes the forward major surface of film 210b. Surface 224a is then typically exposed to air or other ambient environment. Removal of layer packet 222 can expose an uncontaminated (or potentially sterile) surface.

[0088] As shown in FIG. 2C , outermost layer packet 224 can then be removed from film 210b to form a new, modified film 210c. Layer packet 224 is delaminated from the remainder of stack 220b in continuous sheet form, such that the peeled-away, reduced layer stack 220c remains in place as part of modified film 210c. Delamination occurs preferentially along a delamination surface corresponding to the packet interface between layer packet 224 and layer packet 226. After removal of layer packet 224, layer packet 226 becomes the outermost layer packet of film 210c, and forward major surface 226a of layer packet 226 becomes the forward major surface of film 210c. Surface 226a is then typically exposed to air or other ambient environment. Removal of layer packet 224 can expose an uncontaminated (or potentially sterile) surface.

[0089] After removal of layer packet 224, outermost layer packet 226 can be removed from film 210c to form a new modified film 210d, as shown in FIG. 2D . Layer packet 226 is delaminated from the remainder of stack 220c in continuous sheet form, such that the peeled-away reduced layer stack 220d remains in place as part of modified film 210d. Delamination occurs preferentially along a delamination surface corresponding to the packet interface between layer packet 226 and layer packet 228. After removal of layer packet 226, layer packet 228 becomes the outermost layer packet of film 210d, and forward major surface 228a of layer packet 228 becomes the forward major surface of film 210d. Surface 228a is then typically exposed to air. Removal of layer packet 226 can expose an uncontaminated (or potentially sterile) surface.

[0090] Although the original film 210a in FIG. 2A is shown as having four layer packets, in other cases the original film may include more than four layer packets, or, if desired, fewer than four (but at least two) layer packets.

[0091] The film of Figure 3A, like the film of Figure 2A, is constructed so that successive layer packets can be delaminated from the remaining film in continuous sheet form. This delamination is shown in sequence in Figures 3B-3E, with like numbers in Figure 3 referring to like elements in Figure 2. For example, Figure 2A includes layer packets 222, 224, 226, and 228, while Figure 3 includes layer packets 322, 324, 326, and 328. Each layer packet (322, 324, 326, and 328) includes layer A (342a, 342b, 342c, and 342d for layer packets 322, 324, 326, and 328, respectively) and a conformable layer (332a, 332b, 332c, 332d for layer packets 322, 324, 326, and 328, respectively). Each layer packet includes a front major surface (322a, 324a, 326a, 328a for layer packets 322, 324, 326, and 328, respectively) and a rear major surface (322b, 324b, 326b, 328b for layer packets 322, 324, 326, and 328, respectively).

[0092] 3A, in some embodiments, a film, such as original film 310a in FIG. 3A, may be in intimate contact with base layer 312. For example, rear major surface 328b of layer packet 328 may be in contact with base layer 312.

[0093] In Figure 3B, film 310a of Figure 3A becomes film 310b modified by the removal of top or frontmost layer packet 322. In Figure 3C, film 310b of Figure 3B becomes film 310c modified by the removal of layer packet 324. In Figure 3D, film 310c of Figure 3C becomes film 310d modified by the removal of layer packet 326.

[0094] 3E, the depicted film 310e is the same as film 310d after complete removal of third layer packet 326. Layer stack 320d therefore includes only fourth layer packet 328, which remains attached to base layer 312. Base layer 312 may optionally be attached to a workpiece via an adhesive backing layer.

[0095] The fourth layer packet 328 can also be removed, with the front major surface of the base layer 312 becoming the front major surface of the film 310d.

[0096] In some embodiments, the base layer may comprise the same polymer composition as Layer A. In some embodiments, the base layer may further comprise an amorphous polymer composition that is miscible with the polymer composition of Layer A. In exemplary embodiments, the base layer may be or comprise polyethylene terephthalate (PET). In some embodiments, the base layer may further comprise an amorphous polyester (e.g., PETg) at a level sufficient to eliminate any haze that may result from crystallization of PET. For example, in exemplary embodiments, the base layer may further comprise at least 5% amorphous polyester (PETg).

[0097] Because the polymer composition of each layer of the layer packet is adjusted so that the rearmost polymer layer (e.g., Layer C) is less adherent to the forward-most polymer layer (e.g., Layer A) than the inner polymer layer (e.g., Layer B), forming the base layer from the same polymer composition as Layer A means that the final layer packet can be irreversibly delaminated from the base layer along a delamination surface corresponding to the interface between the rearmost surface of the final layer packet and the base layer.

[0098] In some embodiments, the base layer may be thicker than an individual Layer A, Layer B, or Layer C. In some embodiments, the base layer may have a thickness of at least 100 micrometers, at least 150 micrometers, at least 200 micrometers, at least 250 micrometers (about 10 mils), or at least 300 micrometers. In some embodiments, the base layer may have a thickness of up to 150 micrometers, up to 200 micrometers, up to 250 micrometers (about 10 mils), up to 300 micrometers, up to 500 micrometers, or up to 1000 micrometers.

[0099] In some embodiments, the base layer may be coextruded with the layer packet in one film structure.

[0100] To facilitate the sequential removal of only one layer packet at a time, film 210a or 310a, as well as other multilayer polymer films described herein, may be fabricated with tabs on the edges of the film. For example, the polymer film may have kiss-cut tab-like features of varying depths on the edges of the film. In this regard, Wu et al. (WO 2012 / 092478) illustrates a method for using laser radiation to cut and subdivide a polymer multilayer film body without substantial delamination at the laser cut edge line, which may be useful for forming desired tab-like features. The laser radiation may be selected to have a wavelength at which at least some of the material of the film has substantial absorption, so that the absorbed electromagnetic radiation can effectively vaporize or ablate the film body along the cut line. The laser radiation may also be shaped with suitable focusing optics and controlled to a suitable power level to achieve vaporization along a narrow cut line. The laser radiation may also be rapidly scanned across the workpiece according to preprogrammed instructions and rapidly switched on and off to trace a cut line of any shape.

[0101] In some cases, it may be desirable for the layer stack to be compatible with sterilization, for example, by ethylene oxide or by radiation. In some embodiments, the coextruded polymer film is sterilized, for example, by ethylene oxide or by radiation.

[0102] Ethylene oxide has the ability to penetrate paper, many plastics, and rubber. It is currently used to sterilize disposable syringes, hypodermic needles, packaged materials, Petri dishes, pipettes, etc. Advantages of ethylene oxide sterilization include that it can be carried out at room temperature or slightly above room temperature, making it suitable for non-heat-resistant materials; it requires only low humidity, so it does not damage moisture-sensitive materials and equipment; ethylene oxide's excellent penetration ability allows it to be used on packaged items; and although ethylene oxide is a highly reactive compound, relatively few materials are damaged by the process.

[0103] In certain embodiments, it may be desirable to sterilize the film by ionizing radiation, such as gamma radiation or electron beam radiation. In such cases, the material composition of the film is selected to withstand this treatment. One or more antioxidants, such as hindered phenols, phosphites, and hindered amines, can be added to the polymer composition used in the film to enhance polymer stability during sterilization. In some embodiments, the coextruded polymer film contains one or more antioxidants and is sterilized by ionizing radiation.

[0104] In addition to gradients in peel forces between layer packets throughout the stack of polymer layers, the stack may be configured to promote otherwise irreversible delamination at the packet interfaces. Examples of such delamination-promoting physical structures are described in U.S. Patent Application Publication No. 2019 / 0248118 A1 and include sets of nested kiss-cut holes formed by mechanical blades, laser radiation, or any other suitable means.

[0105] The coextruded polymer film may include a label, indicia, or other visual or textured marking or feature. For example, a label, indicia, or other marking or feature may be provided on or within one or more layers of the stack.

[0106] Additionally or alternatively, the markings may include holes of different depths through the stack, which may all open at the exposed surface of the forward-most layer and terminate in different layer packets, with the shallowest hole terminating in the forward-most layer packet, the next deepest hole terminating in the next layer packet, the next deepest hole terminating in the next layer packet, and so on.

[0107] In some embodiments, various layers may be made to have different colors by incorporating dyes, pigments, or other coloring or coloring agents, for example, so that every other layer packet (or one or more layers thereof) is a different color, or the last layer packet or last few layer packets in the stack may be colored with such dyes, pigments, etc. to visually indicate to the user that there are no more layer packets (or only one or a few layer packets) available for delamination.

[0108] Production method As shown in FIG. 1A, individual layers A, B, and C form layer packet 122, and as shown in FIGS. 2A and 3A, layer packets may be coextruded together to form stack 220a or 320a, which may form all or part of multilayer polymer film 210a or 310a. In the embodiment shown in FIG. 1A, layer packet 122 is composed of three types of layers: layer A 142, layer B 144, and layer C 146, which may be composed of different polymer compositions A, B, and C, respectively. These three different layer types are organized into repeating groups such as layer A, B, C, A, B, C, where the minimum repeating unit (A, B, C) defines a single layer packet. In some cases, a layer packet may include only two types of layers.

[0109] In some embodiments, it is preferred that none of polymer composition A, polymer composition B, or polymer composition C is a pressure-sensitive adhesive (PSA) or other type of adhesive. In this regard, "adhesive" refers to a material or layer that, when applied to or onto the surfaces of different components, bonds the surfaces together, resists separation, and is tacky at room temperature. Furthermore, polymer composition A, polymer composition B, and polymer composition C are preferably coextrudable with each other, such that the entire layer stack 220a or 320a, including repeating layers of polymer composition A, polymer composition B, and polymer composition C, may be coextruded in a single operation and then laminated together with an adhesive, rather than being made in separate operations.

[0110] In some cases, the multilayer polymer film may be made by coextrusion, which may include melt processing at a temperature of at least 190°C, at least 195°C, at least 200°C, at least 200°C, at least 204°C, at least 206°C, at least 208°C, or at least 210°C.

[0111] In some cases, preparing a multilayer polymer film may also include one or more stretching or orientation steps. In some embodiments, Layer A and Layer B, or Layer A and Layer C, or Layer B and Layer C, or some combination thereof, may be oriented. Such oriented layers may have a minimum level of birefringence, including, for example, a birefringence of at least 0.05. As noted above, the polymer orientation or crystallinity, or both, of at least one component of Layer A or Layer B, or both, can affect the peel force of the AB pair. One or more uniaxial stretching steps or more biaxial stretching steps in the film preparation process can be used to promote polymer orientation, crystallization, or both.

[0112] Stretching, sometimes referred to as drawing, can be uniaxial or biaxial, and if biaxial, can be simultaneous or sequential. The act or process of stretching a multilayer film may orient all, some, or none of the constituent polymer layers, depending on the materials used and process conditions such as the temperature of the film during stretching. For a further discussion of known stretching or drawing techniques, see U.S. Pat. No. 6,179,948 (Merrill et al.). For example, a two-step drawing process can be performed in which one set of layers (e.g., layers A) is substantially oriented during both drawing steps, while the other set of layers (e.g., layers B) is substantially oriented during only one drawing step. The result is a multilayer film having one set of material layers that is substantially biaxially oriented after drawing, and another set of material layers that is substantially uniaxially oriented after drawing.

[0113] 4 and 5 are schematic diagrams of manufacturing systems that can be used to produce the disclosed multilayer polymer films. FIG. 4 schematically illustrates the coextrusion of polymer composition A, polymer composition B, and polymer composition C to form a multilayer polymer film 410. Here, the polymer compositions may be fed via a twin-screw extruder or other suitable means to a feedblock 430 with alternating molten polymer flow paths to form a multilayer extrudate 409 in which polymer layers A, B, and C are arranged in a repeating pattern desired in the finished film. In some cases, the extrudate 409 may be fed to one or more layer multiplier units to form an output extrudate having a multiple (e.g., 2x, 3x, or 4x) of the number of layers in the original extrudate 409. Regardless of whether a layer multiplier is used, the multilayer extrudate may then be fed to a film die 432, the output of which may be quenched on a casting wheel to form a cast multilayer polymer film. In some cases, the cast film, in the absence of additional components, may become the finished multilayer polymer film 410. In other cases, additional layers and coatings may be applied to the cast film for additional functionality. For example, a release liner may be applied to one or both exposed major surfaces of the cast film. Also, an adhesive backing layer may be coated on one of the exposed major surfaces of the cast film to facilitate application to a workpiece. Regardless of how many additional layers and coatings are applied, the finished multilayer polymer film 410 includes a stack of polymer layers formed by coextrusion using the feedblock 430, optional layer multiplier, and die 432, with the layers in the stack organized into layer packets that are adapted to irreversibly delaminate from one another as discussed elsewhere herein.

[0114] In some cases, it may be desirable to stretch or orient the multilayer cast film, whether to impart birefringence to some or all of the individual layers within the film or to change other material properties of some or all of the individual polymer layers. Such stretching or orientation is shown schematically in FIG. 5. A multilayer cast film 508, which may be the same as or similar to cast film 410 of FIG. 4 and include at least three different polymer layer types arranged in a repeating pattern desired in the finished film, may be fed to one or more known film handling devices that stretch the film in the downweb and / or crossweb directions, whether sequentially, simultaneously, or a combination thereof, to provide an oriented multilayer polymer film 510 having the delamination characteristics described herein. In FIG. 5, the multilayer cast film 508 is shown first fed to a length orienter (LO) 534 to stretch the film in the downweb direction to provide a pre-oriented film 509, followed by a tenter 536 to stretch the film in the crossweb direction to obtain the finished oriented multilayer polymer film 510. In alternative embodiments, the length orienter 534 may be omitted, or the tenter 536 may be omitted, or additional length orienters and / or tenters may be added. A tenter (not shown) designed to be capable of simultaneously stretching a film in both the downweb and crossweb directions may also be used, alone or in combination with the aforementioned stretching devices. Specially designed tenters, such as so-called parabolic tenters, may also be used, alone or in combination with other stretching units. In other embodiments (not shown), the cast film may be formed into a tubular rather than flat film configuration, and the tubular cast film may then be stretched using a blown film process, or the like. The methods that can be used to stretch / orient the cast film into a stretched film are not limited.

[0115] Similar to the discussion above in connection with Figure 4, the finished oriented film 510 may have no additional components, but may be a finished multilayer polymer film with delamination properties as discussed herein. In other cases, additional layers and coatings, such as release liners and adhesive backing layers, may be applied to the oriented film for additional functionality. Regardless of how many additional layers and coatings are applied, the finished multilayer polymer film comprises a stack of polymer layers originally formed by coextrusion and then optionally oriented by stretching, with the layers in the stack organized into layer packets that are adapted to irreversibly delaminate from one another as discussed elsewhere herein.

[0116] As shown in Figure 4, because the polymer layers in the layer stack are preferably compatible with simultaneous formation by coextrusion, individually peelable layer packets can be made thinner than if they were manufactured separately and then laminated together. Preferably, each layer packet in the stack may have a thickness of about 2 mils (about 50 micrometers) or less. Furthermore, the layer stack may include a total of n layer packets, where n may be at least 5 or at least 10, and the film may have a total thickness of about 15 or 20 mils (about 380 or 510 micrometers, respectively) or less. At least n-1 layer packets may have the same number m of polymer layers, where m may be at least 3. The m polymer layers may be arranged in the same order for n-1 layer packets or for all n layer packets.

[0117] In one approach to tailoring the adhesion strength of one polymer layer to other polymer layers in a layer stack, a polymer composition comprised of a blend of polypropylene and one of several copolymer resins exhibits adhesion strength to other polypropylene layers that is a function of the proportions of the blended components. This approach is discussed in more detail in U.S. Patent Application Publication No. 2019 / 0248817.

[0118] How to use The multilayer polymeric films described herein may be tailored for a variety of purposes and end uses. In some cases, the film may be an anti-graffiti film. In some cases, the film may be used as a cover for a mask, such as a face shield, a set of safety glasses, sunglasses, safety goggles, ski goggles, or another application where removal of the film to remove contamination on the surface of the mask, glasses, or goggles may be beneficial. In some embodiments, the film may be used as a cover for a high-touch surface in a hospital, laboratory, school, hotel, restaurant, or other setting where the ability to remove a contaminated surface to expose a sterile surface is beneficial.

[0119] In some embodiments, the film, and, if included, the base layer, may be substantially transparent, such that the workpiece to which it is applied does not change in appearance or functionality, regardless of how much of the original film is present on the workpiece at any given time. In some embodiments, the film, and, if included, the base layer, may have a haze of at most 2 percent, at most 3 percent, at most 4 percent, or at most 5 percent. In some embodiments, the film, and, if included, the base layer, may have a transmittance of at least 70 percent, at least 75 percent, at least 80 percent, at least 85 percent, or at least 90 percent. In some embodiments, the film, and, if included, the base layer, may have a transparency of at least 80 percent, at least 85 percent, at least 90 percent, at least 95 percent, or at least 99 percent. In some embodiments, haze and transmittance are measured using ASTM D1003-13. In some embodiments, transparency is measured using ASTM D3430-95(2016).

[0120] In other embodiments, for example, where clarity is not important, the transmittance may be as low as 0%, the haze may be as high as 100%, and the clarity may be as low as 0%.

[0121] In some embodiments, the multilayer polymeric films described herein can be used to provide a sterile, substantially aseptic environment. In this regard, an advantage of producing the individual polymer layers and layer packets in a single coextrusion operation, rather than separate manufacturing operations involving handling, aligning, and laminating separately manufactured films, is that the forward major surface of a given layer packet can be much more easily maintained in an uncontaminated (e.g., sterile) state until exposed by peeling of the layer packet preceding it.

[0122] In some embodiments, the multilayer polymeric films described herein can be used to provide a workpiece with a controlled surface topography. For example, it may be desirable to effectively provide a workpiece with a high-quality, smooth (low roughness) surface finish. Rather than polishing the surface of the workpiece itself, the film may be applied to the workpiece to provide the desired smooth surface. During use, when the outer surface of the film wears down or otherwise becomes uneven, the layer packet can be peeled off to restore the desired smooth surface.

[0123] In other embodiments, a controlled degree of roughness may be desired on the workpiece. In such cases, a controlled amount of beads or other particles of a suitable size may be provided in the forward-most polymeric layer of each layer packet, so that the forward-most (exposed) surface of the film has the desired amount of surface roughness. When the exposed surface becomes worn, abraded, contaminated with other materials, etc., the desired surface roughness can be restored simply by peeling off the outermost layer packet to expose the clean surface of the immediately adjacent layer packet (which also has the desired surface roughness).

[0124] face shield An exemplary embodiment in which a film is used as a cover for a face shield 790 is shown in Figure 6. Base layer 712 may be coextruded with layer packets 722 and 724 in a single film structure. Alternatively, the film may include layer packets 722 and 724 attached to a workpiece via an adhesive backing layer. While Figure 6 shows face shield 790 including two layer packets, the face shield may include a stack of polymer layers including any suitable number of layer packets.

[0125] In some embodiments, as shown in FIG. 6 , layer packets 722 and 724 include tabs 782 and 784 to facilitate sequential removal of only one layer packet at a time. Tabs 782, 784 may vary in depth at the edges of each layer packet. Tabs 782, 784 may be formed by any suitable process, such as a kiss-cut process. In this regard, Wu et al., International Publication No. 2012 / 092478, illustrates a method using laser radiation to cut and subdivide a polymeric multilayer film body without substantial delamination at the laser cut edge lines, which may be useful for forming desired tabs.

[0126] In some embodiments, the face shield 790 is compatible with sterilization, for example, by ethylene oxide or by radiation. In some embodiments, the face shield 790 is sterilized, for example, by ethylene oxide or by radiation.

[0127] In some embodiments, as shown in FIG. 6, the base layer 712 includes strap, tab, or pin patterns 772, 774 to allow the face shield to be connected to a mounting assembly such as a crown.

[0128] In some embodiments, base layer 712 comprises the same polymer composition as Layer A. In some embodiments, the base layer may further comprise an amorphous polymer composition that is miscible with the polymer composition of Layer A. In exemplary embodiments, base layer 712 may be or comprise polyethylene terephthalate (PET). In some embodiments, base layer 712 may further comprise amorphous polyester (PETg) at a level sufficient to eliminate any haze that may result from crystallization of PET. For example, in exemplary embodiments, base layer 712 may further comprise at least 5% amorphous polyester (PETg).

[0129] In an exemplary embodiment, the thicknesses of at least some of the layers of the layer packets in face shield 790 vary sequentially from the forward-most layer packet to the rear-most layer packet. For example, the thickness of a conformable layer (e.g., combined layers B and C) may increase sequentially from the first layer packet (e.g., layer packet 722) to the second layer packet (e.g., layer packet 724) and in subsequent layer packets. The thickness of layer A may decrease sequentially from the first layer packet (e.g., layer packet 722) to the second layer packet (e.g., layer packet 724) and in subsequent layer packets.

[0130] In an exemplary embodiment, Layer A comprises polymer composition A including a polyester, copolyester, acrylic, or silicone thermoplastic resin, or a combination thereof; Layer B comprises polymer composition B including a copolyester, PMMA, co-PMMA, styrenic block copolymer, polypropylene, or silicone polyoxamide, or a combination thereof; and Layer C comprises polymer composition C including an olefin or styrenic block copolymer, or a combination thereof. For example, polymer composition A may comprise polyethylene terephthalate (PET), and polymer composition B and polymer composition C may comprise a copolymer based on styrene and ethylene / butylene, including, for example, KRATON G1645 (Kraton Corporation, Houston, TX), a linear triblock copolymer based on styrene and ethylene / butylene.

[0131] In an exemplary embodiment, a face shield including the base layer exhibits a maximum haze of 5%, a transmittance of at least 85%, and a transparency of at least 95%, as measured using ASTM D1003-13 (for transmittance and haze) and ASTM D3430-95(2016) (for transparency).

[0132] Exemplary Film Embodiments Including Variable Thickness of Conformable Layer 1. a coextruded stack of polymer layers, the polymer layers being organized into layer packets, each layer packet including a first layer A, a second layer B, and a third layer C, with layer B disposed between layer A and layer C; a packet interface between Layer A and Layer C of adjacent layer packets, the packet interface exhibiting a first peel force of 1 gram / inch or greater; a layer interface between adjacent layers A and B, the layer interface exhibiting a second peel force greater than the first peel force; a layer interface between adjacent layers B and C, the layer interface exhibiting a third peel force greater than the first peel force; the layer packets are irreversibly peelable separately from the remainder of the stack; The coextruded stack of polymer layers includes at least a first layer packet and a second layer packet, each layer packet comprising a conformable layer including a layer B and a layer C, and the thickness of the conformable layer of the second layer packet is greater than the thickness of the conformable layer of the first layer packet. 2. The film of embodiment 1, wherein the coextruded stack of polymer layers comprises n layer packets, and the coextruded stack of polymer layers exhibits a peel force gradient from the first layer packet to the nth layer packet, or a gradient in conformable layer thickness from the first layer packet to the nth layer packet, or both a peel force gradient and a thickness gradient. 3. The film of embodiment 2, wherein the peel force at the packet interface between layer A of the second layer packet and layer C of the first layer packet is less than the peel force between layer A of the nth layer packet and layer C of the (n-1)th layer packet. 4. The film of embodiment 3, wherein the peel force at the packet interface between layer A of the second layer packet and layer C of the first layer packet is at least 5, at least 10, at least 100, or at least 250 times less than the peel force between layer A of the nth layer packet and layer C of the (n-1)th layer packet. 5. The film of embodiment 3 or 4, wherein the peel force at the packet interface between layer A of the second layer packet and layer C of the first layer packet is at most 500, at most 250, at most 100, or at most 10 times less than the peel force between layer A of the nth layer packet and layer C of the (n-1)th layer packet. 6. The film of any one of aspects 3-5, wherein the peel force at each successive packet interface increases by at least 0.5 percent, at least 1 percent, at least 5 percent, at least 10 percent, at least 20 percent, at least 50 percent, or at least 100 percent. 7. The film of any one of aspects 3-6, wherein the peel force at each successive packet interface increases by up to 1 percent, up to 5 percent, up to 10 percent, up to 20 percent, up to 50 percent, up to 100 percent, up to 1000 percent, up to 10,000 percent, or up to 50,000 percent. 8. The film of any one of aspects 2-7, wherein the thickness of the conformable layer of the first layer packet is at least 1.1 times, at least 1.2 times, at least 1.5 times, or at least 2 times less than the thickness of the conformable layer of the nth layer packet. 9. The film of any one of aspects 2-8, wherein the thickness of the conformable layer of the first layer packet is at most 2 times, at most 5 times, or at most 10 times less than the thickness of the conformable layer of the nth layer packet. 10. The film of any one of aspects 2-9, wherein the thickness of the conformable layers of each successive layer packet increases by at least 15 percent, at least 20 percent, at least 25 percent, or at least 30 percent. 11. The film of any one of aspects 2-10, wherein the thickness of the compatible layers of each successive layer packet increases by up to 50 percent, up to 100 percent, up to 200 percent, up to 500 percent, or up to 1000 percent. 12. The film of any one of embodiments 1-11, wherein the peel force at the packet interface between layer C of the first layer packet and layer A of the second layer packet is less than the peel force between layer C of the nth layer packet and the base layer. 13. The film of any one of aspects 2-12, wherein the nth layer packet is the 2nd, 3rd, 4th, 5th, 6th, 7th, 8th, 9th, 10th, 11th, 12th, 13th, 14th, 15th, 16th, 17th, 18th, 19th, 20th, or 21st layer packet. 14. The film of any one of aspects 1-13, wherein Layer A comprises a first polymer composition A, Layer B comprises a second polymer composition B, and Layer C comprises a third polymer composition C. 15. The film of embodiment 14, wherein polymer composition B is different from polymer composition A, and polymer composition C is different from polymer composition A. 16. The film of embodiment 15, wherein polymer composition C is different from polymer composition B. 17. The film of any one of aspects 14-16, wherein polymer composition A, polymer composition B, and polymer composition C independently comprise one or more polymers selected from polyester, polyolefin, poly-alpha-olefin, polymethacrylate, polycarbonate, polycarbonate alloy, polyurethane, polylactic acid, polyhydroxybutyrate, polyhydroxysuccinate, styrenic copolymer, silicone, or copolymer or blend thereof. 18. The film of any one of aspects 14-17, wherein polymer composition A comprises a semicrystalline polyester. 19. The film of any one of aspects 14-18, wherein polymer composition B comprises a copolyester, or a styrenic block copolymer, or a combination thereof. 20. The film of any one of aspects 14-19, wherein polymer composition C comprises an olefin, or a styrenic block copolymer, or a combination thereof. 21. The film of any one of aspects 14-20, wherein polymer composition C is at least partially miscible with polymer composition B, polymer composition B is at least partially miscible with polymer composition A, and polymer composition C is not miscible with the first polymer composition. 22. The film of any one of aspects 14-21, wherein the film further comprises a base layer, the base layer comprising the same polymer composition as layer A. 23. The film of embodiment 22, wherein the base layer further comprises an amorphous polymer composition that is miscible with the polymer composition of layer A. 24. The film of any one of aspects 1-23, wherein Layer A, Layer B, or Layer C, or a combination thereof, comprises one or more additives. 25. The film of any one of aspects 1-24, wherein Layer A, Layer B, or Layer C, or a combination thereof, comprises one or more ultraviolet (UV) light stabilizers. 26. The film of any one of aspects 1-25, wherein Layer A, Layer B, or Layer C, or a combination thereof, comprises one or more organic antimicrobial agents. 27. The film of any one of aspects 1-26, wherein Layer A and Layer B, or Layer A and Layer C, or Layer B and Layer C, or combinations thereof, are oriented and have a birefringence of at least 0.5. 28. The film of any one of aspects 1-27, wherein each of the layer packets in the coextruded stack of polymer layers has a thickness of at most 10 micrometers, at most 25 micrometers, or at most 50 micrometers. 29. The film of any one of aspects 1-28, wherein each of the layer packets in the coextruded stack of polymer layers has a thickness of at least 1 micrometer, at least 5 micrometers, or at least 10 micrometers. 30. The film of any one of embodiments 1-29, wherein the second peel force is at least 1.04 times the first peel force. 31. The film of any one of aspects 1-30, wherein the second peel force is up to 500 times greater than the first peel force. 32. The film of any one of aspects 1-31, wherein the third peel force is at least 1.1 times the first peel force. 33. The film of any one of aspects 1-32, wherein the third peel force is up to 500 times greater than the first peel force. 34. The film of any one of aspects 1-33, wherein the third peel force is at least 1.04 times the second peel force. 35. The film of any one of aspects 1-34, wherein the third peel force is up to 500 times greater than the second peel force. 36. The film of any one of aspects 1-35, wherein the first peel force is up to 500 grams / inch. 37. The film of any one of aspects 1-36, wherein the film has a total thickness of at most 510 micrometers, at most 380 micrometers, at most 300 micrometers, at most 200 micrometers, at most 100 micrometers, or at most 50 micrometers. 38. The film of any one of the preceding aspects, wherein the film has a total thickness of at least 25 micrometers, at least 50 micrometers, at least 100 micrometers, at least 200 micrometers, at least 300 micrometers, or at least 380 micrometers. 39. The film of any one of embodiments 2-38, wherein the thickness of layer A is held constant from the first layer packet to the nth layer packet. 40. The film of any one of embodiments 2-38, wherein the coextruded stack of polymer layers comprises a gradient in thickness of layer A from the first layer packet to the nth layer packet. 41. The film of embodiment 40, wherein the thickness of layer A of the first layer packet is greater than the thickness of layer A of the nth layer packet. 42. The film of embodiment 40, wherein the thickness of layer A of the first layer packet is less than the thickness of layer A of the nth layer packet. 43. The film of embodiment 42, wherein the ratio of the thickness of layer A to the thickness of the conformable layer remains constant throughout the depth of the stack.

[0133] Exemplary Film Embodiments Including Variable Thickness of Layer A 1. a coextruded stack of polymer layers, the polymer layers being organized into layer packets, each layer packet including a first layer A, a second layer B, and a third layer C, with layer B disposed between layer A and layer C; a packet interface between Layer A and Layer C of adjacent layer packets, the packet interface exhibiting a first peel force of 1 gram / inch or greater; a layer interface between adjacent layers A and B, the layer interface exhibiting a second peel force greater than the first peel force; a layer interface between adjacent layers B and C, the layer interface exhibiting a third peel force greater than the first peel force; the layer packets are irreversibly peelable separately from the remainder of the stack; The coextruded stack of polymer layers includes at least a first layer packet and a second layer packet, wherein the thickness of Layer A of the second layer packet is less than the thickness of Layer A of the first layer packet. 2. The film of embodiment 1, wherein the coextruded stack of polymer layers comprises n layer packets, and the coextruded stack of polymer layers exhibits a peel force gradient from the first layer packet to the nth layer packet, or a gradient in thickness of layer A from the first layer packet to the nth layer packet, or both a peel force gradient and a thickness gradient. 3. The film of embodiment 2, wherein the peel force at the packet interface between layer A of the second layer packet and layer C of the first layer packet is less than the peel force between layer A of the nth layer packet and layer C of the (n-1)th layer packet. 4. The film of embodiment 3, wherein the peel force at the packet interface between layer A of the second layer packet and layer C of the first layer packet is at least 5, at least 10, at least 100, or at least 250 times less than the peel force between layer A of the nth layer packet and layer C of the (n-1)th layer packet. 5. The film of embodiment 3 or 4, wherein the peel force at the packet interface between layer A of the second layer packet and layer C of the first layer packet is at most 500, at most 250, at most 100, or at most 10 times less than the peel force between layer A of the nth layer packet and layer C of the (n-1)th layer packet. 6. The film of any one of aspects 3-5, wherein the peel force at each successive packet interface increases by at least 0.5 percent, at least 1 percent, at least 5 percent, at least 10 percent, at least 20 percent, at least 50 percent, or at least 100 percent. 7. The film of any one of aspects 3-6, wherein the peel force at each successive packet interface increases by up to 1 percent, up to 5 percent, up to 10 percent, up to 20 percent, up to 50 percent, up to 100 percent, up to 1000 percent, up to 10,000 percent, or up to 50,000 percent. 8. The film of any one of aspects 2-7, wherein the thickness of Layer A of the first layer packet is at least 1.1 times, at least 1.2 times, at least 1.5 times, or at least 2 times greater than the thickness of Layer A of the nth layer packet. 9. The film of any one of aspects 2-8, wherein the thickness of Layer A of the first layer packet is at most 2 times, at most 5 times, or at most 10 times greater than the thickness of Layer A of the nth layer packet. 10. The film of any one of aspects 2-9, wherein the thickness of Layer A in each successive layer packet decreases by at least 15 percent, at least 20 percent, at least 25 percent, or at least 30 percent. 11. The film of any one of aspects 2-10, wherein the thickness of Layer A in each successive layer packet decreases by up to 50 percent, up to 100 percent, up to 200 percent, up to 500 percent, or up to 1000 percent. 12. The film of any one of embodiments 1-11, wherein the peel force at the packet interface between layer C of the first layer packet and layer A of the second layer packet is less than the peel force between layer C of the nth layer packet and the base layer. 13. The film of any one of aspects 2-12, wherein the nth layer packet is the 2nd, 3rd, 4th, 5th, 6th, 7th, 8th, 9th, 10th, 11th, 12th, 13th, 14th, 15th, 16th, 17th, 18th, 19th, 20th, or 21st layer packet. 14. The film of any one of aspects 1-13, wherein Layer A comprises a first polymer composition A, Layer B comprises a second polymer composition B, and Layer C comprises a third polymer composition C. 15. The film of embodiment 14, wherein polymer composition B is different from polymer composition A, and polymer composition C is different from polymer composition A. 16. The film of embodiment 15, wherein polymer composition C is different from polymer composition B. 17. The film of any one of aspects 14-16, wherein polymer composition A, polymer composition B, and polymer composition C independently comprise one or more polymers selected from polyester, polyolefin, poly-alpha-olefin, polymethacrylate, polycarbonate, polycarbonate alloy, polyurethane, polylactic acid, polyhydroxybutyrate, polyhydroxysuccinate, styrenic copolymer, silicone, or copolymer or blend thereof. 18. The film of any one of aspects 14-17, wherein polymer composition A comprises a semicrystalline polyester. 19. The film of any one of aspects 14-18, wherein polymer composition B comprises a copolyester, or a styrenic block copolymer, or a combination thereof. 20. The film of any one of aspects 14-19, wherein polymer composition C comprises an olefin, or a styrenic block copolymer, or a combination thereof. 21. The film of any one of aspects 14-20, wherein polymer composition C is at least partially miscible with polymer composition B, polymer composition B is at least partially miscible with polymer composition A, and polymer composition C is not miscible with the first polymer composition. 22. The film of any one of aspects 14-21, wherein the film further comprises a base layer, the base layer comprising the same polymer composition as layer A. 23. The film of embodiment 22, wherein the base layer further comprises an amorphous polymer composition that is miscible with the polymer composition of layer A. 24. The film of any one of aspects 1-23, wherein Layer A, Layer B, or Layer C, or a combination thereof, comprises one or more additives. 25. The film of any one of aspects 1-24, wherein Layer A, Layer B, or Layer C, or a combination thereof, comprises one or more ultraviolet (UV) light stabilizers. 26. The film of any one of aspects 1-25, wherein Layer A, Layer B, or Layer C, or a combination thereof, comprises one or more organic antimicrobial agents. 27. The film of any one of aspects 1-26, wherein Layer A and Layer B, or Layer A and Layer C, or Layer B and Layer C, or combinations thereof, are oriented and have a birefringence of at least 0.5. 28. The film of any one of aspects 1-27, wherein each of the layer packets in the coextruded stack of polymer layers has a thickness of at most 10 micrometers, at most 25 micrometers, or at most 50 micrometers. 29. The film of any one of aspects 1-28, wherein each of the layer packets in the coextruded stack of polymer layers has a thickness of at least 1 micrometer, at least 5 micrometers, or at least 10 micrometers. 30. The film of any one of embodiments 1-29, wherein the second peel force is at least 1.04 times the first peel force. 31. The film of any one of aspects 1-30, wherein the second peel force is up to 500 times greater than the first peel force. 32. The film of any one of aspects 1-31, wherein the third peel force is at least 1.1 times the first peel force. 33. The film of any one of aspects 1-32, wherein the third peel force is up to 500 times greater than the first peel force. 34. The film of any one of aspects 1-33, wherein the third peel force is at least 1.04 times the second peel force. 35. The film of any one of aspects 1-34, wherein the third peel force is up to 500 times greater than the second peel force. 36. The film of any one of aspects 1-35, wherein the first peel force is up to 500 grams / inch. 37. The film of any one of aspects 1-36, wherein the film has a total thickness of at most 510 micrometers, at most 380 micrometers, at most 300 micrometers, at most 200 micrometers, at most 100 micrometers, or at most 50 micrometers. 38. The film of any one of the preceding aspects, wherein the film has a total thickness of at least 25 micrometers, at least 50 micrometers, at least 100 micrometers, at least 200 micrometers, at least 300 micrometers, or at least 380 micrometers. 39. The film of any one of aspects 2-38, wherein each layer packet comprises a conformable layer including Layer B and Layer C, and the thickness of the conformable layer is held constant from the first layer packet to the nth layer packet. 40. The film of any one of embodiments 2-38, wherein each layer packet comprises a conformable layer including layer B and layer C, and wherein the coextruded stack of polymer layers comprises a gradient in conformable layer thickness from the first layer packet to the nth layer packet. 41. The film of embodiment 40, wherein the thickness of the conformable layer of the first layer packet is less than the thickness of layer A of the nth layer packet. 42. The film of embodiment 41, wherein the ratio of the thickness of layer A to the thickness of the conformable layer remains constant throughout the depth of the stack.

[0134] Exemplary Film Embodiments Comprising Polymer Compositions 1. a coextruded stack of polymer layers, the polymer layers being organized into layer packets, each layer packet including a first layer A, a second layer B, and a third layer C, with layer B disposed between layer A and layer C; Layer A of the film comprises a first polymer composition A, Layer B of the film comprises a second polymer composition B, and Layer C of the film comprises a third polymer composition C; polymer composition A comprises a polyester, a copolyester, a polyolefin, a poly-alpha-olefin, a polymethacrylate, a polycarbonate, a polycarbonate alloy, a polyurethane, an aliphatic polyester, a polyhydroxybutyrate, a polyhydroxysuccinate, a styrenic copolymer, a silicone, a silicone thermoplastic, an acrylic, or a copolymer or blend thereof; polymer composition B comprises a polyester, a polyolefin, a poly-alpha-olefin, a polymethacrylate, a polycarbonate, a polycarbonate alloy, an aliphatic polyester, a polyethylene succinate, a polylactic acid, a styrenic block copolymer, a silicone, or a copolymer or blend thereof; polymer composition C comprises a polyester, a polyolefin, a poly-alpha-olefin, a polymethacrylate, a polycarbonate, a polycarbonate alloy, an aliphatic polyester, a polyethylene succinate, a polylactic acid, a styrenic block copolymer, a silicone, or a copolymer or blend thereof; the layer packets are irreversibly peelable separately from the remainder of the stack; The coextruded stack of polymer layers includes at least a first layer packet and a second layer packet, each layer packet including a conformable layer including layer B and layer C, and the thickness of the conformable layer of the second layer packet is greater than the thickness of the conformable layer of the first layer packet, forming a film. 2. a coextruded stack of polymer layers, the polymer layers being organized into layer packets, each layer packet including a first layer A, a second layer B, and a third layer C, with layer B disposed between layer A and layer C; Layer A of the film comprises a first polymer composition A, Layer B of the film comprises a second polymer composition B, and Layer C of the film comprises a third polymer composition C; polymer composition A comprises a polyester, a copolyester, a polyolefin, a poly-alpha-olefin, a polymethacrylate, a polycarbonate, a polycarbonate alloy, a polyurethane, an aliphatic polyester, a polyhydroxybutyrate, a polyhydroxysuccinate, a styrenic copolymer, a silicone, a silicone thermoplastic, an acrylic, or a copolymer or blend thereof; polymer composition B comprises a polyester, a polyolefin, a poly-alpha-olefin, a polymethacrylate, a polycarbonate, a polycarbonate alloy, an aliphatic polyester, a polyethylene succinate, a polylactic acid, a styrenic block copolymer, a silicone, or a copolymer or blend thereof; polymer composition C comprises a polyester, a polyolefin, a poly-alpha-olefin, a polymethacrylate, a polycarbonate, a polycarbonate alloy, an aliphatic polyester, a polyethylene succinate, a polylactic acid, a styrenic block copolymer, a silicone, or a copolymer or blend thereof; the layer packets are irreversibly peelable separately from the remainder of the stack; The coextruded stack of polymer layers includes at least a first layer packet and a second layer packet, wherein the thickness of Layer A of the second layer packet is less than the thickness of Layer A of the first layer packet. 3. Polymer composition A comprises a polyester, copolyester, acrylic, or silicone thermoplastic resin, or a combination thereof; Polymer composition B comprises a copolyester, PMMA, co-PMMA, a styrenic block copolymer, polypropylene, or a silicone polyoxamide, or a combination thereof; 3. The film of any one of the preceding claims, wherein polymer composition C comprises an olefin or a styrenic block copolymer, or a combination thereof. 4. The film a packet interface between Layer A and Layer C of adjacent layer packets, the packet interface exhibiting a first peel force of 1 gram / inch or greater; a layer interface between adjacent layers A and B, the layer interface exhibiting a second peel force greater than the first peel force; The film of any one of Aspects 1-3, further comprising a layer interface between adjacent Layers B and C, the layer interface exhibiting a third peel force greater than the first peel force. 5. The film of any one of aspects 1-4, wherein polymer composition A comprises a semi-crystalline polyester. 6. The film of any one of aspects 1-5, wherein polymer composition A comprises polyethylene terephthalate (PET). 7. The film of any one of aspects 1-6, wherein polymer composition B comprises a copolyester, or a styrenic block copolymer, or a combination thereof. 8. The film of any one of aspects 1-7, wherein polymer composition B comprises a copolymer based on styrene and ethylene / butylene. 9. The film of any one of aspects 1-8, wherein polymer composition C comprises a copolymer based on styrene and ethylene / butylene. 10. The film of any one of embodiments 1-9, wherein the peel force at the packet interface between layer A of the second layer packet and layer C of the first layer packet is less than the peel force between layer A of the nth layer packet and layer C of the (n-1)th layer packet. 11. The film of embodiment 10, wherein the peel force at the packet interface between layer A of the second layer packet and layer C of the first layer packet is at least 5, at least 10, at least 100, or at least 250 times less than the peel force between layer A of the nth layer packet and layer C of the (n-1)th layer packet. 12. The film of aspect 10 or 11, wherein the peel force at the packet interface between layer A of the second layer packet and layer C of the first layer packet is at most 500, at most 250, at most 100, or at most 10 times less than the peel force between layer A of the nth layer packet and layer C of the (n-1)th layer packet. 13. The film of any one of aspects 1-12, wherein the peel force at each successive packet interface increases by at least 0.5 percent, at least 1 percent, at least 5 percent, at least 10 percent, at least 20 percent, at least 50 percent, or at least 100 percent. 14. The film of any one of aspects 1-13, wherein the peel force at each successive packet interface increases by up to 1 percent, up to 5 percent, up to 10 percent, up to 20 percent, up to 50 percent, up to 100 percent, up to 1000 percent, up to 10,000 percent, or up to 50,000 percent. 15. The film of any one of embodiments 1-14, wherein the peel force at the packet interface between layer C of the first layer packet and layer A of the second layer packet is less than the peel force between layer C of the nth layer packet and the base layer. 16. The film of any one of aspects 10-15, wherein the nth layer packet is the 2nd, 3rd, 4th, 5th, 6th, 7th, 8th, 9th, 10th, 11th, 12th, 13th, 14th, 15th, 16th, 17th, 18th, 19th, 20th, or 21st layer packet. 17. The film of any one of embodiments 1-16, wherein polymer composition C is at least partially miscible with polymer composition B, polymer composition B is at least partially miscible with polymer composition A, and polymer composition C is not miscible with the first polymer composition. 18. The film of any one of the preceding aspects, wherein the film further comprises a base layer, the base layer comprising the same polymer composition as layer A. 19. The film of embodiment 18, wherein the base layer further comprises an amorphous polymer composition that is miscible with the polymer composition of layer A. 20. The film of any one of aspects 1-19, wherein Layer A, Layer B, or Layer C, or a combination thereof, comprises one or more additives. 21. The film of any one of aspects 1-20, wherein Layer A, Layer B, or Layer C, or a combination thereof, comprises one or more ultraviolet (UV) light stabilizers. 22. The film of any one of the preceding aspects, wherein Layer A, Layer B, or Layer C, or a combination thereof, comprises one or more organic antimicrobial agents. 23. The film of any one of aspects 1-22, wherein Layer A and Layer B, or Layer A and Layer C, or Layer B and Layer C, or combinations thereof, are oriented and have a birefringence of at least 0.5. 24. The film of any one of aspects 1-23, wherein each of the layer packets in the coextruded stack of polymer layers has a thickness of at most 10 micrometers, at most 25 micrometers, or at most 50 micrometers. 25. The film of any one of aspects 1-24, wherein each of the layer packets in the coextruded stack of polymer layers has a thickness of at least 1 micrometer, at least 5 micrometers, or at least 10 micrometers. 26. The film of any one of aspects 1-25, wherein the second peel force is at least 1.04 times the first peel force. 27. The film of any one of aspects 1-26, wherein the second peel force is up to 500 times greater than the first peel force. 28. The film of any one of aspects 1-27, wherein the third peel force is at least 1.1 times the first peel force. 29. The film of any one of aspects 1-28, wherein the third peel force is up to 500 times greater than the first peel force. 30. The film of any one of aspects 1-29, wherein the third peel force is at least 1.04 times the second peel force. 31. The film of any one of aspects 1-30, wherein the third peel force is up to 500 times greater than the second peel force. 32. The film of any one of aspects 1-31, wherein the first peel force is up to 500 grams / inch. 33. The film of any one of aspects 1-32, wherein the film has a total thickness of at most 510 micrometers, at most 380 micrometers, at most 300 micrometers, at most 200 micrometers, at most 100 micrometers, or at most 50 micrometers. 34. The film of any one of aspects 1-33, wherein the film has a total thickness of at least 25 micrometers, at least 50 micrometers, at least 100 micrometers, at least 200 micrometers, at least 300 micrometers, or at least 380 micrometers. 35. The film of any one of aspects 1 or 3-34, wherein the thickness of layer A is held constant from the first layer packet to the nth layer packet. 36. The film of any one of aspects 1 or 3-34, wherein the coextruded stack of polymer layers comprises a gradient in thickness of layer A from the first layer packet to the nth layer packet. 37. The film of embodiment 36, wherein the thickness of layer A of the first layer packet is greater than the thickness of layer A of the nth layer packet. 38. The film of embodiment 36, wherein the thickness of layer A of the first layer packet is less than the thickness of layer A of the nth layer packet. 39. The film of embodiment 38, wherein the ratio of the thickness of layer A to the thickness of the conformable layer remains constant throughout the depth of the stack. 40. The film of any one of aspects 2-34, wherein each layer packet comprises a conformable layer including Layer B and Layer C, and the thickness of the conformable layer is held constant from the first layer packet to the nth layer packet.

[0135] Face shield type 1. A face shield comprising a film according to any one of the film claims. 2. The face shield of aspect 1, further comprising a face shield base. 3. The face shield of embodiment 2, wherein the face shield base and film are coextruded. 4. The face shield of any one of embodiments 1-3, wherein layer A of the film comprises a first polymer composition A, layer B of the film comprises a second polymer composition B, layer C of the film comprises a third polymer composition C, and the face shield base comprises polymer composition A. 5. The face shield of embodiment 4, wherein the face shield comprises a face shield base, the face shield base further comprising an amorphous polymer composition that is miscible with the polymer composition of layer A. 6. The face shield of embodiment 4 or embodiment 5, wherein polymer composition B and polymer composition C are the same. 7. The face shield of any one of aspects 4-6, wherein polymer composition A comprises polyethylene terephthalate (PET). 8. The face shield of embodiment 7, wherein the face shield base further comprises amorphous polyethylene terephthalate (PET). 9. The face shield of any one of aspects 2-8, wherein the face shield base has a thickness of at least 100 micrometers, at least 150 micrometers, at least 200 micrometers, at least 250 micrometers, or at least 300 micrometers. 10. The face shield of any one of aspects 2-9, wherein the face shield base has a thickness of at most 150 micrometers, at most 200 micrometers, at most 250 micrometers, at most 300 micrometers, at most 500 micrometers, or at most 1000 micrometers. 11. The face shield of any one of aspects 1-10, wherein the layer packet comprises a tab. 12. The face shield of any one of aspects 1-11, wherein the face shield further comprises crown protection. 13. The face shield of any one of aspects 2-12, wherein the face shield and face shield base exhibit a maximum haze of 5%, a transmittance of at least 85%, and a transparency of at least 95%. 14. The face shield of any one of aspects 2-12, wherein the layer packet of the face shield comprises a kiss-cut tab. 15. Layer A of the film comprises a first polymer composition A, layer B of the film comprises a second polymer composition B, and layer C of the film comprises a third polymer composition C; polymer composition A comprises a polyester, a copolyester, a polyolefin, a poly-alpha-olefin, a polymethacrylate, a polycarbonate, a polycarbonate alloy, a polyurethane, an aliphatic polyester, a polyhydroxybutyrate, a polyhydroxysuccinate, a styrenic copolymer, a silicone, a silicone thermoplastic, an acrylic, or a copolymer or blend thereof; polymer composition B comprises a polyester, a polyolefin, a poly-alpha-olefin, a polymethacrylate, a polycarbonate, a polycarbonate alloy, an aliphatic polyester, a polyethylene succinate, a polylactic acid, a styrenic block copolymer, a silicone, or a copolymer or blend thereof; 15. The face shield of any one of the preceding aspects, wherein polymer composition C comprises a polyester, a polyolefin, a poly-alpha-olefin, a polymethacrylate, a polycarbonate, a polycarbonate alloy, an aliphatic polyester, a polyethylene succinate, a polylactic acid, a styrenic block copolymer, a silicone, or a copolymer or blend thereof. 16. Polymer composition A comprises a polyester, copolyester, acrylic, or silicone thermoplastic resin, or a combination thereof; Polymer composition B comprises a copolyester, PMMA, co-PMMA, a styrenic block copolymer, polypropylene, or a silicone polyoxamide, or a combination thereof; 16. The face shield of any one of the preceding embodiments, wherein polymer composition C comprises an olefin, or a styrenic block copolymer, or a combination thereof. 17. The face shield of any one of aspects 1-16, wherein composition A comprises polyethylene terephthalate (PET). 18. The face shield of any one of the preceding aspects, wherein polymer composition B comprises a copolyester, or a styrenic block copolymer, or a combination thereof. 19. The face shield of any one of the preceding aspects, wherein polymer composition B comprises a copolymer based on styrene and ethylene / butylene. 20. The face shield of any one of the preceding aspects, wherein polymer composition C comprises a copolymer based on styrene and ethylene / butylene.

[0136] The present invention is further illustrated by the following examples, with the understanding that the specific examples, materials, amounts, and procedures are to be interpreted broadly in accordance with the scope and spirit of the invention described herein. [Example]

[0137] All reagents, starting materials, and solvents used in the following examples were purchased from commercial sources (e.g., Sigma Aldrich, St. Louis, MO) and used without further purification unless otherwise indicated.

[0138] Example 1 The film stack was prepared using three extruders feeding a single 16-layer feedblock attached to a 13-inch-wide die. One extruder supplied polyester (PET) resin to provide six PET layers (A layers). Another extruder supplied five layers of "tie layer" (B layers) material (Kraton G1645 (Kraton Corporation, Houston, TX), a linear triblock copolymer based on styrene and ethylene / butylene). Another extruder supplied five layers of "release layer" (C layers) material (a blend of polypropylene (PP) and KRATON G1645 (Kraton Corporation, Houston, TX), a linear triblock copolymer based on styrene and ethylene / butylene, used in a 9:1 (PP:KRATON) ratio).

[0139] The feedblock was designed to deliver six PET layers at a uniform thickness. However, the feedblock was designed to increase the thickness of the combined "tie" and "release" layers (i.e., Layers B and C or "conformable layers") throughout the stack, so that the thickest conformable layer was three times thicker than the thinnest conformable layer.

[0140] The results are shown in Figure 7. The predicted layer thickness of each conformable layer for the sample is shown in Table 1. The measured layer thickness of each conformable layer for the sample is shown in Table 2. Layer A was designed to maintain a thickness of 9.5 micrometers throughout the entire depth of the stack.

[0141] A clear increase or decrease in peel force was observed depending on the direction of the gradient: lower peel forces correlated with thinner end gradients and higher peel forces correlated with thicker end gradients.

[0142] As shown in Figure 7, with increasing conformable layer thickness, an increase in packet-to-packet peel force was observed as the thickness of each conformable layer increased. Additionally, as the total thickness of the conformable layers (i.e., the sum of all conformable layers in each film sample) increased, the difference in packet-to-packet peel force became more apparent.

[0143] Using the data in the table, the combination of layer thickness and peel force suggests that a 20% change in conformable layer thickness is sufficient to provide about a 0.5 g / in (i.e., approximately 0.5 percent) difference in peel force.

[0144] A gradient where the thickest conformable layer is more than three times the thickness of the thinnest conformable layer can provide an even greater difference in peel force from "ABC" layer packet to "ABC" layer packet.

[0145] [Table 1]

[0146] [Table 2]

[0147] Comparative Example 1 Film stacks were prepared as described in Example 1, except that a different feedblock was used. As in Example 1, the feedblock was designed to feed six PET layers at a uniform thickness. In contrast to Example 1, the feedblock was designed to extrude five tie layers at a uniform thickness throughout the stack and five release layers at a uniform thickness throughout the stack.

[0148] The nominal thickness of each PET layer was approximately 10 μm thick. The nominal thickness of each tie layer plus release layer (i.e., Layers B and C or "compatible layers") was approximately 11 μm.

[0149] The results are shown in Figure 8.

[0150] The entire disclosures of all patents, patent applications, and publications, as well as electronically available materials, mentioned herein are incorporated by reference. In the event of any inconsistency between the disclosure of this application and the disclosure of any document incorporated by reference herein, the disclosure of this application shall control. The foregoing detailed description and examples have been given for clarity of understanding only. No unnecessary limitations are to be construed thereby. The invention is not limited to the exact details shown and described; variations obvious to those skilled in the art are within the scope of the invention as defined by the claims.

Claims

1. a coextruded stack of polymer layers, the polymer layers being organized into layer packets, each layer packet including a first layer A, a second layer B, and a third layer C, with layer B disposed between layer A and layer C; a packet interface between Layer A and Layer C of adjacent layer packets, the packet interface exhibiting a first peel force of 1 gram / inch or greater; a layer interface between adjacent layers A and B, the layer interface exhibiting a second peel force greater than the first peel force; a layer interface between adjacent layers B and C, the layer interface exhibiting a third peel force greater than the first peel force; the layer packets are irreversibly peelable separately from the remainder of the stack; said coextruded stack of polymer layers comprising an n-layer packet; The thickness of layer A from the first layer packet to the nth layer packet is the same; said coextruded stack of polymer layers exhibiting both a peel force gradient from the first layer packet to the nth layer packet and a gradient in thickness of Layers B and C from the first layer packet to the nth layer packet; A film in which the peel force at each successive packet interface increases by at least 0.5 percent and the thickness of Layers B and C of each successive layer packet increases by at least 20 percent.

2. a coextruded stack of polymer layers, the polymer layers being organized into layer packets, each layer packet including a first layer A, a second layer B, and a third layer C, with layer B disposed between layer A and layer C; Layer A of the film comprises a first polymer composition A, Layer B of the film comprises a second polymer composition B, and Layer C of the film comprises a third polymer composition C; polymer composition A comprises a polyester, a copolyester, a polyolefin, a poly-alpha-olefin, a polymethacrylate, a polycarbonate, a polycarbonate alloy, a polyurethane, an aliphatic polyester, a polyhydroxybutyrate, a polyhydroxysuccinate, a styrenic copolymer, a silicone, a silicone thermoplastic, an acrylic, or a copolymer or blend thereof; polymer composition B comprises a polyester, a polyolefin, a poly-alpha-olefin, a polymethacrylate, a polycarbonate, a polycarbonate alloy, an aliphatic polyester, a polyethylene succinate, a polylactic acid, a styrenic block copolymer, a silicone, or a copolymer or blend thereof; polymer composition C comprises a polyester, a polyolefin, a poly-alpha-olefin, a polymethacrylate, a polycarbonate, a polycarbonate alloy, an aliphatic polyester, a polyethylene succinate, a polylactic acid, a styrenic block copolymer, a silicone, or a copolymer or blend thereof; the layer packets are irreversibly peelable separately from the remainder of the stack; said coextruded stack of polymer layers comprising an n-layer packet; The thickness of layer A from the first layer packet to the nth layer packet is the same; said coextruded stack of polymer layers exhibiting both a peel force gradient from the first layer packet to the nth layer packet and a gradient in thickness of Layers B and C from the first layer packet to the nth layer packet; A film in which the peel force at each successive packet interface increases by at least 0.5 percent and the thickness of Layers B and C of each successive layer packet increases by at least 20 percent.

3. A face shield comprising the film of claim 1 or 2.

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