Cushioning film including protruding cushioning structures

Abstract

A cushioning film includes a plurality of structures disposed on a base layer of the cushioning film. The structures are arranged along a width of the cushioning film and extend along a length of the cushioning film. Each structure includes opposing first and second sidewalls extending along a thickness direction of the cushioning film from the base layer to a curved top portion of the structure. In a first cross-section orthogonal to the length of the cushioning film, the structures include a curved top portion concave toward the base layer and are tilted toward a same first direction along the width of the cushioning film.

Description

[0001] CUSHIONING FILM INCLUDING PROTRUDING CUSHIONING STRUCTURES

[0002] TECHNICAL FIELD

[0003] The present description relates generally to cushioning films.

[0004] BACKGROUND

[0005] A film can include an array of hollow polymeric tubes to allow compression of the film.

[0006] SUMMARY

[0007] In some aspects, the present description provides a cushioning film including a plurality of structures disposed on a base layer of the cushioning film. The structures are arranged along a width of the cushioning film and extend along a length of the cushioning film. Each structure includes opposing first and second sidewalls extending along a thickness direction of the cushioning film from the base layer to a curved top portion of the structure. In a first cross-section orthogonal to the length of the cushioning film, the structures include a curved top portion concave toward the base layer and are tilted toward a same first direction along the width of the cushioning film.

[0008] In some aspects, the present description provides a cushioning film including a plurality of structures disposed on a base layer of the cushioning film. The structures are arranged along a width of the cushioning film and extend along a length of the cushioning film. Each structure includes opposing first and second sidewalls extending along a thickness direction of the cushioning film from the base layer to a curved top portion of the structure. The curved top portion can be concave towards the base layer and extends between and connects the first and second sidewalls. The second sidewall includes first and second portions, where the first portion is between the base layer and the second portion, and the second portion is between the first portion and the curved top portion. In a first cross-section orthogonal to the length of the cushioning film, the first and second sidewalls make respective first and second angles with a same first direction along the width of the cushioning film, where the first angle is greater than 40 degrees and less than 90 degrees along substantially an entire length of the first side wall, and the second angle is in a range of 90 to 150 degrees along substantially an entire length of the first portion and is in a range of 70 to 89.5 degrees along substantially an entire length of the second portion. The length of the second portion can be at least 2 times the length of the first portion. A total length of the first and second portions can be at least 80% of a total length of the second sidewall.

[0009] In some aspects, the present description provides a cushioning film including a plurality of structures disposed on a base layer of the cushioning film. The structures are arranged along a width of the cushioning film and extend along a length of the cushioning film. The structures have an average height H from the base layer to a top of the structures and are arranged at an average pitch P along a first direction along the width of the cushioning film. An average of a maximum width of the structures along the first direction is W. In some embodiments, 7 H > P > H / 2 and 4 > H / W > 1. In a first cross-section orthogonal to the length of the cushioning film, the structures include a curved top portion concave toward the base layer and can be tilted toward the first direction such that when the cushioning film is compressed along a thickness direction of the cushioning film, the structures further tilt along the first direction. A plot of compressive stress on the cushioning film versus percent compression of the cushioning film includes a first portion extending at least from 15 percent compression to 35 percent compression. A largest compressive stress in the first portion is no greater than 2 times a smallest compressive stress in the first portion.

[0010] These and other aspects will be apparent from the following detailed description. In no event, however, should this brief summary be construed to limit the claimable subject matter.

[0011] BRIEF DESCRIPTION OF THE DRAWINGS

[0012] FIG. 1 is a schematic cross-sectional view of a portion of a cushioning film, according to some embodiments.

[0013] FIG. 2 is a schematic top perspective view of a portion of a cushioning film, according to some embodiments.

[0014] FIG. 3 is a schematic cross-sectional view of a portion of a cushioning film including spaced apart structures on a base layer, according to some embodiments.

[0015] FIG. 4 is a schematic cross-sectional view of a multilayer stack of cushioning films, according to some embodiments.

[0016] FIG. 5 is a schematic illustration of the compression of a multilayer stack of cushioning films, according to some embodiments.

[0017] FIG. 6 is a schematic cross-sectional view of an assembly including a multilayer stack of cushioning films disposed between electrochemical cells, according to some embodiments.

[0018] FIG. 7 is a schematic cross-sectional view of an assembly including a multilayer stack of cushioning films disposed between a structural element and electrochemical cells, according to some embodiments.

[0019] FIGS. 8-11 are exemplary stress-strain plots for multilayer stacks of cushioning films, according to some embodiments.

[0020] DETAILED DESCRIPTION

[0021] In the following description, reference is made to the accompanying drawings that form a part hereof and in which various embodiments are shown by way of illustration. The drawings are not necessarily to scale. It is to be understood that other embodiments are contemplated and may be made without departing from the scope or spirit of the present description. The following detailed description, therefore, is not to be taken in a limiting sense.

[0022] Cushioning films may be used in many applications. For example, a cushioning film may be used to support fragile elements in packaging applications, may be used for personal padding, or may be used to provide an approximately constant pressure on an element as that element changes size or shape. One exemplary application for cushioning films is a replacement for foam that is conventionally used with flexographic printing plates to control the pressure that the plate exerts when pressed on a paper or film. Another exemplary application for cushioning films is in battery packs for electric vehicles or energy storage for mini-grid or home storage, for example, where a cushioning film can be utilized to provide an appropriate pressure to electrochemical cells as their volumes change during their charging and discharging cycles.

[0023] To improve the range and efficiency of electric vehicle, the current industry trend is to increase battery pack-level energy density through consolidated cell formats and higher energy-density lithium battery cell chemistries. Maintaining battery cell pressure and pressure uniformity for pouch and prismatic cells during the volume change of charge-discharge cycles is desired for battery life and failure mode avoidance. Foams have been used in past attempts to provide the desired pressure profiles. Longer- term, there is a general trend toward all solid-state battery cells, which have even higher energy density (e.g., 500 Wh / kg) than conventional lithium (Li) ion batteries and are safer. However, stack pressure uniformity beyond what conventional foam materials can provide is desired for maintaining the integrity of the Li-solid-state electrolyte interfaces for low contact resistance during cell cycling. This presents a significant challenge to the successful implementation of long-life solid-state battery cells in electric vehicles. As a result, there is a need for cushioning materials that provide an expanded Compression Force Deflection (CFD) plateau, where the force (stress) that the cushioning material exerts on the battery cell is relatively uniform over a wide range of compression levels (strain) for the expected 10-year life of the battery. For example, a CFD plateau stress of at least 100 kPa (e.g., 100 to 5000 kPa) may be desired in solid state battery cells to maintain contact between the solid electrolyte and electrodes. A CFD plateau stress of at least 150, 200, 250, 300, 400, 500, 600, 800, 1000, 1200 kPa may be desired for some solid- state battery cells. In addition, there is a desire for a CFD plateau range of extending at least from 15 to 35% strain to improve reliability and give a larger working range. A CFD plateau can have a stress that varies somewhat with compression, but the variation with compression is at a substantially lower rate than that of regions of the stress-compression curve on each side of the CFD plateau.

[0024] Films can include an array of hollow polymeric tubes as generally described in U.S. Pat. Appl. Pub. Nos. 2023 / 0226733 (Ausen et al.) and 2022 / 0266495 (Ausen et al.), for example. Such films may be useful as cushioning films. However, it has been found that such films often provide a limited CFD plateau width and / or limited CFD plateau stress and / or that such films are often slower and more expensive to manufacture than films including structures protruding from a base layer.

[0025] According to some embodiments of the present description, it has been found that a cushioning film including suitable structures extending from a base layer along a thickness direction of the cushioning film can provide desired cushioning performance (e.g., a desired CFD plateau stress and width). The suitable structures are typically generally tilted with a curved top portion in order to facilitate further tilt and bend over of the structures when the film is compressed. In some embodiments, the structures of cushioning film provide a cushioning effect primarily by bending rather than compression. That is, there may be little volume change of the structures as they bend, and the bending of the structures provides most or substantially all of the cushioning provided by the film. The structures may also have a side wall with a hinge region where the slope of the side wall changes relatively rapidly to further facilitate the bending of the structures. The precise shapes of the structures (e.g., widths of the structures, or slopes of the sidewalls of the structures, versus height above base layer) may be fine-tuned using predictive modeling (e.g., finite element analysis) to tailor the resulting stress-strain curve. The structures extending from the base layer along the thickness direction can be described as protruding from the base layer.

[0026] Suitable materials for the structures and base layer include elastic or hyperelastic polymers. Useful materials include polyolefin elastomers, polyethylenes such as low-density polyethylene (LDPE), polypropylenes, polyurethanes, ethylene-acrylic elastomers, styrene-butadiene-styrene rubber, styrene- isoprene-styrene rubber, styrenic block copolymers, acrylic polymers, acrylate polymers, acrylate copolymers, polyethers, polyether copolymers, polyester, polyester copolymers, polyamide, polyamide copolymers, silicones, polysiloxanes, and blends thereof. The cushioning film may be made, for example, via extrusion replication using thermoplastic polymers. Extrusion replication processes are known in the art. In brief summary, an extrusion replication process for making the structures and base layer can include extruding a molten stream of polymeric material in the form of a melt curtain against a structured surface of a tool (or between the structured surface and a nip roll), cooling the polymeric material and removing the resulting film from the tool. Extrusion replication processes and suitable materials for such processes are described in U.S. Pat. Appl. Pub. No. 2010 / 0252961 (Bay et al.). Other suitable extrudable materials and related extrusion processes are described in U.S. Pat. Appl. Pub. Nos. 2023 / 0226733 (Ausen et al.) and 2022 / 0266495 (Ausen et al.), for example.

[0027] FIG. 1 is a schematic cross-sectional view of a portion of a cushioning film 100 including a structure 110 on a base layer 120, according to some embodiments. FIG. 2 is a schematic top perspective view of a portion of a cushioning film 100, according to some embodiments. FIG. 3 is a schematic cross- sectional view of a portion of a cushioning film 100 including spaced apart structures 110 on a base layer 120, according to some embodiments.

[0028] In some embodiments, a cushioning film 100 includes a plurality of structures 110 disposed on a base layer 120 of the cushioning film 100 where the structures 110 are arranged along a width of the cushioning film and extend along a length of the cushioning film 100. The cushioning film 100 can define a length direction (y-direction) along the length of the film, a width direction (x-direction) along the width of the film, and a thickness direction (z -direction) along the thickness of the film where the width, length and thickness directions are mutually orthogonal. In some embodiments, each structure 110 includes opposing first and second sidewalls 111 and 112 extending along a thickness direction (z- direction) of the cushioning film 100 from the base layer 120 to a curved top portion 125 of the structure 110, where the curved top portion 125 is concave towards the base layer 120 and extends between and connects the first and second sidewalls 111 and 112. The second sidewall 112 includes first and second portions 113 and 114, where the first portion 113 is between the base layer 120 and the second portion 114, and the second portion 114 is between the first portion 113 and the curved top portion 125. In some embodiments, in a first cross-section (xz-cross section) that is orthogonal to the length of the cushioning film and / or parallel to the width of the cushioning film: the first and second sidewalls 111 and 112 make respective first and second angles al and a2 with a same first direction (x-direction) along the width of the cushioning film 100. In some embodiments, the first sidewall 111 and each of the first and second portions 113 and 114 of the second sidewall 112 slope toward one another in a direction from the base layer to the top portion 125 of the structure 110. Slopes of the sidewalls can be measured from optical images, or scanning electron micrography (SEM) images, of the structures 110 in the first cross-section.

[0029] In some embodiments, a monolithic film comprises the plurality of structures 110 and the base layer 120. For example, the structures 110 can be formed in an extrusion replication process and the base layer 120 may be a land layer integrally formed with the structures 110 in that process.

[0030] The aspect ratio (ratio of height H to width W) may be adjusted to adjust the CFD plateau, for example. A lower aspect ratio H / W in may be useful for increasing the CFD plateau stress, but a greater number of cushioning films may be needed to give a desired total deflection when a lower aspect ratio is utilized. In some embodiments, the structures 110 have an average height H from the base layer 120 to a top 128 of the structures 110 and an average of a maximum width of the structures 110 (e.g., unweighted mean of the widths of the structures 110 at the base layer 120) along the first direction is W, where 4 > H / W > 1. In some such embodiments, or in other embodiments, H / W is less than or equal to 3.5, 3, or 2.5. In some such embodiments, or in other embodiments, H / W is greater than or equal to 1.25, 1.5, 1.75, or 2. For example, in some embodiments, 3.5 > H / W > 1.25, or 3 > H / W > 1.5, or 2.5 > H / W > 1.75, or 2.5 > H / W > 2. In some such embodiments, or in other embodiments, the average height H is in a range of 50 micrometers to 2 mm. In some such embodiments, or in other embodiments, the average height H is at least 75, 100, 125, 150, 200, 250, 300, or 350 micrometers. In some such embodiments, or in other embodiments, the average height H is no more than 1.75, 1.5, 1.25, 1, 0.9, 0.8, 0.7, or 0.6 mm. For example, in some embodiments, the average height H is in a range of 100 micrometers to 1 mm.

[0031] The first angle al can be greater than 40 degrees and less than 90 degrees along substantially an entire length of the first side wall 111. The second angle a2 can change from a2-a in the first portion 113 to a2b in the second portion 114. The second angle a2 can be in a range of 90 to 150 degrees along substantially an entire length of the first portion 113 and can be in a range of 70 to 89.5 degrees along substantially an entire length of the second portion 114. In some embodiments, the first angle al is at least 45, 50, 55, 60, 65, 70 degrees along substantially an entire length of the first sidewall 111. In some such embodiments, or in other embodiments, the first angle al is no more than 85, 80, 78, 76, 75 degrees along substantially an entire length of the first sidewall 111. In some such embodiments, or in other embodiments, the second angle a2 (or a2a) is at least 95, 100, 102, 104, 106, or 108 degrees along substantially an entire length of the first portion 113. In some such embodiments, or in other embodiments, the second angle a2 (or a2a) is no more than 145, 140, 135, 130, 125, 120, 115, 112, or 111 degrees along substantially an entire length of the first portion 113. In some such embodiments, or in other embodiments, the second angle a2 (or a2b) is at least 75, 80, 85, or 86 degrees along substantially an entire length of the second portion 114. In some such embodiments, or in other embodiments, the second angle a2 (or a2b) is no more than 89.4, 89.3, 89.2, 89.1, 89, 88.9, 88.8, 88.7, 88.6, 88.5, or 88.4 degrees along substantially an entire length of the second portion 114.

[0032] Substantially an entire length (e.g., of a sidewall or a portion of a sidewall) can be the entire length or the entire length except possibly for small portions where a slope has shifted due to manufacturing variations or due to other variations. Substantially an entire length generally includes at least 75% of the entire length. In some embodiments, substantially an entire length can be at least 80, 85, 90, 95, 96, 97, 98, or 99 percent of the entire length.

[0033] In some embodiments, for each structure of the plurality of structures 110 and for each distance Z1 above the base layer 120 between the base layer 120 and the curved top portion 125, the second angle a2 is greater than the first angle al. In some embodiments, for each structure of the plurality of structures 110, a minimum value of the second angle a2 is greater than a maximum value of the first angle al .

[0034] In some embodiments, the length L2 of the second portion 114 is at least 2, 3, 4, 5, 6, 7 or 8 times the length LI of the first portion 113. In some such embodiments, or in other embodiments, the length L2 is up to 50, 40, 30, 20, 15, 12, 11, or 10 times the length LI. For example, in some embodiments, the length L2 is in a range of 2 to 50, 3 to 40, 4 to 30, 5 to 20, 6 to 15, or 8 to 11 times the length LI.

[0035] In some embodiments, for each structure of the plurality of structures 110, the second angle a2 changes between the first and second portions 113 to 114 of the second sidewall 112 to define a hinge region 140. The hinge region 140 may be radiused to provide a gradual change in slope, for example. In some embodiments, the second angle changes by at least 10 degrees over a distance along the thickness direction (z-direction) of less than 5 percent of the average height H of the structures 110. In some embodiments, for each structure of the plurality of structures 110, the first portion 113 of the second side wall 112 extends from the base layer 120 to the hinge region 140 and the second portion 114 of the second sidewall 112 extends from the hinge region 140 to the curved top portion 125. In some embodiments, a total length (L1+L2) of the first and second portions 113 and 114 is at least 80, 85, 90, 95,96, 97, 98, 98.5, 99, or 99.5% of a total length Lt of the second sidewall 112. Lt may be greater than LI + L2 due to the (e.g., radiused) hinge region 140 contributing to a portion of the length Lt.

[0036] The structures 110 may be arranged at a pitch P selected to be sufficiently large that the structures can bend to a desired degree without contacting one another and sufficiently small to provide a desired CFD plateau stress. In some embodiments, the structures 110 have an average height H from the base layer 120 to a top 128 of the structures 110 and are arranged at an average pitch P along the first direction. In some embodiments, 7 H > P > H / 2. In some such embodiments, or in other embodiments, 6.5, 6, 5.5, 5, 4.5, 4, 3.5, 3, 2.5 times H is greater than or equal to P. In some such embodiments, or in other embodiments, P is greater than or equal to 0.55, 0.6, 0.65, 0.7, or 0.75 times H. For example, in some embodiments, 6 H > P > 0.55 H, or 5 H > P > 0.6 H, or 4 H > P > 0.65 H, or 3 H > P > 0.7 H, or 2.5 H > P > 0.75 H.

[0037] In some embodiments, the first portions 113 of the second side walls 112 have an average height hl along the thickness direction (z -direction). In some embodiments, hl / H is less than or equal to 0.25, 0.22, 0.20, 0.18, or 0.16. In some such embodiments, or in other embodiments, hl / H is greater than or equal to 0.02, 0.03, 0.04, or 0.05. For example, in some embodiments, 0.25 > hl / H > 0.02, or 0.22 > hl / H > 0.03, or 0.2 > hl / H > 0.04, or 0.16 > hl / H > 0.05.

[0038] In some embodiments, the second portions 114 of the second sidewalls 112 have an average height h2 along the thickness direction. In some embodiments, h2 / H is less than or equal to 0.98, 0.97, 0.96, or 0.95. In some such embodiments, or in other embodiments, h2 / H is greater than or equal to 0.75, 0.78, 0.8. 0.82, or 0.84. For example, in some embodiments, 0.98 > h2 / H > 0.75, or 0.97 > h2 / H > 0.8, or 0.96 > h2 / H > 0.82, or 0.95 > h2 / H > 0.84.

[0039] In some embodiments, for each structure 110, the length LI of the first portion 113 of the second sidewall 112 is in a range of 0.02 to 0.5 times the total length Lt of the second sidewall 112 and the length L2 of the second portion 114 of the second sidewall 112 is in a range of 0.5 to 0.98 times the total length Lt of the second sidewall 112. In some such embodiments, or in other embodiments, LI is at least 0.025, 0.03, 0.04, or 0.05 times Lt. In some such embodiments, or in other embodiments, LI is no more than 0.45, 0.4, 0.3, 0.25, or 0.2 times Lt. In some such embodiments, or in other embodiments, L2 is at least 0.55, 0.6, 0.7, 0.75, or 0.8 times Lt. In some such embodiments, or in other embodiments, L2 is no more than 0.975, 0.97, 0.96, or 0.95 times Lt. For example, in some embodiments, for each structure 110, the length LI of the first portion 113 of the second sidewall 112 is in a range of 0.04 to 0.3 times the total length Lt of the second sidewall 112 and the length L2 of the second portion 114 of the second sidewall 112 is in a range of 0.7 to 0.96 times the total length Lt of the second sidewall 112.

[0040] FIG. 4 is a schematic cross-sectional view of a multilayer stack 150 of cushioning films 100, according to some embodiments. In some embodiments, a multilayer stack 150 includes a plurality of films 100 stacked on one another along a same thickness direction (z-direction) of the films 100, where each film of the plurality of films can be any cushioning film of the present description, and where the films 100 are oriented such that the structures 110 of the films 100 face a same direction (+z -direction). In some embodiments, the films 100 are oriented such that the structures 110 extend along a same length direction (y-direction) of the films 100. Alternatively, at least some of the films may be rotated (e.g., about the z-axis) relative to one another so that the structures 110 of two different films 100 extend in two-different in-plane (xy-plane) directions. The multilayer stack may include 2 to 100, 3 to 50, 4 to 30, or 4 to 20 films 100 in total, for example. FIG. 5 is a schematic cross-sectional view of the compression of a multilayer stack 150' of cushioning films 100a and 100b, according to some embodiments. Each of the cushioning films 100a and 100b can correspond to cushioning film 100. A cover layer 173 is included in the multilayer stack 150' over the cushioning films 100a and 100b. A sequence of increasing compression is represented by the arrows in the figure.

[0041] As described further in the Examples, FIGS. 8-11 are exemplary plots of stress-strain curves for multilayer stacks of cushioning films 100, according to some embodiments. The stress-stain curves for a single layer of the corresponding cushioning film 100 appears substantially the same as that of the multilayer stack, but a single cushioning film provides less deflection distance that a multilayer stack of the cushioning films. The structures of the exemplary cushioning films were arranged at a large pitch which can be reduced to increase the overall scale of the stress in the stress-strain curved. The stress scale may be further increased by using higher modulus materials for the structures 110, for example, and / or increasing the width W of the structures 110, for example. In some embodiments, a plot of compressive stress on the cushioning film when the cushioning film is compressed along the thickness direction of the cushioning film versus percent compression of the cushioning film includes a first portion 401 of the plot extending at least from 15 percent compression to 35 percent compression, where a largest compressive stress in the first portion 401 of the plot is no greater than 2 (or in a range described elsewhere herein) times a smallest compressive stress in the first portion 401 of the plot.

[0042] In some embodiments, a cushioning film 100 includes a plurality of structures 110 disposed on a base layer 120 of the cushioning film 100, where the structures 110 are arranged along a width of the cushioning film 100 and extend along a length of the cushioning film 100. The structures have an average height H from the base layer 120 to a top 128 of the structures 110 and are arranged at an average pitch P along a first direction (x-direction) along the width of the cushioning film 100. An average of a maximum width W of the structures along the first direction is W. In some embodiments, 7 H > P > H / 2 and 4 > H / W > 1. P / H and / or H / W can alternatively be an any of the respective ranges described elsewhere herein. In some embodiments, in a first cross-section orthogonal to the length of the cushioning film 100 and / or parallel to the width of the cushioning film 100, the structures 110 include a curved top portion 125 concave toward the base layer 120 and are tilted toward the first direction (e.g., the structures 110 can tilt in the +x-direction so that a center or centroid of the curved top portion 125 is at a larger x-value than an x-value of a center or centroid of a base of the structure 110 along the base layer 120 as schematically illustrated in FIG. 1, for example) such that when the film is compressed along a thickness direction (z-direction) of the cushioning film 100, the structures 110 further tilt along the first direction (e.g., as schematically illustrated in FIG. 5). When the cushioning film is compressed along the thickness direction of the cushioning film, a plot of compressive stress versus percent compression can be generated. In some embodiments, a plot (see, e.g., plot 301 in FIGS. 8-10 and plots 301a and 301b in FIG. 11) of compressive stress on the cushioning film 100 versus percent compression of the cushioning film 100 includes a first portion 401 extending at least from 15 percent compression to 35 percent compression, where a largest compressive stress in the first portion 401 is no greater than 2 times a smallest compressive stress in the first portion 401. In some such embodiments, or in other embodiments, the first portion 401 extends (e.g., starts from) at least from 14, 13, 12, 11, or 10 percent compression. In some such embodiments, or in other embodiments, the first portion 401 extends at least to 40, 45, 50, 60, 70, 80 percent compression. In some such embodiments, or in other embodiments, the largest compressive stress in the first portion 401 is no greater than 1.9, 1.8, 1.7, 1.6, or 1.5 times the smallest compressive stress in the first portion 401. In some such embodiments, or in other embodiments, the smallest compressive stress in the first portion 401 is at least 100, 150, 200, 250, 300, 400, 500, 600, 800, 1000, or 1200 kPa. In some such embodiments, or in other embodiments, the smallest compressive stress in the first portion 401 is no more than 12, 10, 8, 6, or 5 MPa. For example, in some embodiments, the first portion 401 extends at least from 12 percent compression to 50 percent compression, the largest compressive stress in the first portion 401 is no greater than 1.6 times the smallest compressive stress in the first portion 401, and the smallest compressive stress in the first portion 401 is in a range of 200 kPa to 5 MPa. The compressive stress versus percent compression can be determined, for example, according to the ASTM D3574-17 test standard.

[0043] In some embodiments, when the cushioning film is further compressed along the thickness direction of the cushioning film, the structures curve while further tilting along the first direction so that the curved structures are concave toward the base layer (see, e.g., FIG. 5).

[0044] In some embodiments, after the cushioning film is compressed a first time with a compressive force along the thickness direction to at least 35, 40, 45, 50, 60, 70, 80 percent compression and then the compressive force is removed, when the cushioning film is then compressed a second time along the thickness direction, a second plot 302 (see, e.g., FIGS. 8-10) of compressive stress on the cushioning film versus percent compression of the cushioning film includes a second portion 402 extending at least from 15 percent compression to 35 percent compression, where a largest compressive stress in the second portion 402 is no greater than 2 times a smallest compressive stress in the second portion. In some such embodiments, or in other embodiments, the second portion 402 extends (e.g., starts from) at least from 14, 13, 12, 11, or 10 percent compression. In some such embodiments, or in other embodiments, the second portion 402 extends at least to 40, 45, 50, 60, 70, 80 percent compression. In some such embodiments, or in other embodiments, the largest compressive stress in the second portion 402 is no greater than 1.9, 1.8, 1.7, 1.6, or 1.5 times the smallest compressive stress in the second portion 402. In some such embodiments, or in other embodiments, the smallest compressive stress in the second portion 402 is at least 100, 150, 200, 250, 300, 400, 500, 600, 800, 1000, or 1200 kPa. In some such embodiments, or in other embodiments, the smallest compressive stress in the second portion 402 is no more than 12, 10, 8, 6, or 5 MPa. For example, in some embodiments, the second portion 402 extends at least from 14 percent compression to 45 percent compression, the largest compressive stress in the second portion 402 is no greater than 1.7 times the smallest compressive stress in the second portion 402, and the smallest compressive stress in the second portion 402 is in a range of 150 kPa to 5 MPa. FIG. 6 is a schematic cross-sectional view of an assembly 501 including a multilayer stack 150 of cushioning films disposed between electrochemical cells 211 and 212, according to some embodiments. In some embodiments, an assembly 501 includes first and second electrochemical cells 211 and 212 and any multilayer stack 150 of cushioning films 100 of the present description disposed therebetween. In some embodiments, an assembly 501 includes first and second electrochemical cells 211 and 212, and a plurality of films disposed therebetween, where the films stacked on one another along a same thickness direction (z -direction) of the films, and where each film of the plurality of films is a cushioning film 100 of the present description. In some embodiments, the films are oriented such that the structures 110 of the films face a same direction (e.g., z-direction of FIG. 4).

[0045] FIG. 7 is a schematic cross-sectional view of an assembly 502 including a multilayer stack 150 of cushioning films disposed between a structural element 280 and electrochemical cells 211 and 212, according to some embodiments. In some embodiments, an assembly 502 includes an electrochemical cell (211 and / or 212), a structural element 280 (e.g., of a battery pack), and any multilayer stack 150 of cushioning films 100 of the present description disposed therebetween. In some embodiments, an assembly 502 includes an electrochemical cell (211, and / or 212), a structural element 280 of a battery pack, and a plurality of films disposed therebetween, where the films stacked on one another along a same thickness direction (z-direction) of the films, and where each film of the plurality of films is a cushioning film 100 of the present description. In some embodiments, the films are oriented such that the structures 110 of the films face a same direction (e.g., z-direction of FIG. 4). In some embodiments, the stack of films is disposed between a plurality of electrochemical cells 211 and 212 and the structural element 280. In some embodiments, each of the cushioning films is oriented with the structures of the cushioning film facing the electrochemical cells 211, 212. In other embodiments, each of the cushioning films is oriented with the structures of the cushioning film facing the structural elements 280.

[0046] In some embodiments, the multilayer stack 150 is substantially coextensive with the structural element 280. In other embodiments, separate first and second multilayer stacks that are substantially coextensive with the respective first and second electrochemical cells 211 and 213 are disposed between the respective first and second electrochemical cells 211 and 213 and the structural element 280.

[0047] A structural element is generally any element that provides or supports a structure of an article. The assemblies 501, 502 may be battery packs or portions of battery packs. The structural element 280 may be any structural element of a battery pack. The structural element 280 may be one or more of a cooling plate, a frame, a lid, a cross beam, or another electrochemical cell, for example.

[0048] EXAMPLES

[0049] Cushioning films having a geometry as generally depicted in FIGS. 1-3 were made. The designed geometry was as follows: the width W was 236 micrometers; the width at a height of the hinge 140 was 213 micrometers; the height hl was 45 micrometers; the height h2 was 427 micrometers; and the pitch P was 1181 micrometers. Multilayer stacks as generally depicted in FIG. 4 were tested to determine stress- strain curves as follows: Two inch diameter circles were punched out of the sample fdms to make consistent size samples that fit into the compression testing fixture. Multiple layers were stacked together with all layers were oriented with rails parallel to each other. An Instron Model 5969 load frame with a 50 kN load cell was used to measure the stress-strain curves. A 3-cycle compression test procedure was setup to go to 50% compression strain then decompress to 0% strain and repeat for 3 compression / decompression cycles. All cycles had a rate of 1 mm / min.

[0050] Examples 1-3 used blends of polyolefin elastomer (available from Dow Chemical, Midlands, MI under the tradename ENGAGE 8842) and low density polyethylene (LDPE - available from LyondellBasell, Houston, TX under the tradename PETROTHENE NA217000). Example 1 used 75% polyolefin and 25% LDPE. Examples 2 and 3 used 25% polyolefin and 75% LDPE. All proportions in the Examples are by weight unless otherwise indicated. Example 4 used a blend of 75% styrene block copolymer (available from Kraton Corporation, Houston, TX, USA under the tradename KRATON DI 161), and 25% polypropylene (available from ExxonMobil, Spring, TX, USA under the tradename PP1024E4). The cushioning films were generally made as follows: Dry blended pellets of the materials described above were fed into a 2.5" single screw extruder feeding a 16" wide extrusion die. The melt curtain was fed vertically into a nip including a smooth steel nip roll and a cast roll with a tool pattern to make structures having the geometry described above. The process conditions were as follow: 20 cc gear pump at 8.5 revolutions per minute, line speed of 12 feet per minute, extrudate temperature of 475 deg. F, nip roll temperature of 155 deg. F, cast roll temperature of 135 deg. F, and nip pressure of 300 pounds per linear inch.

[0051] In Example 1, a multilayer stack of 10 films was tested. The total thickness of the multilayer stack was about 6 mm. In Examples 2-3, multilayer stacks of 9 and 10 films, respectively, were tested. The total thicknesses of the multilayer stacks were about 6.45 mm and 6.66 mm, respectively. In Example 4, multilayer stacks of 5 and 10 films were tested. The total thickness of the multilayer stacks were about 3.62 mm and 7.37 mm, respectively. Stress-strain results for Examples 1-4 are shown in FIGS. 8 to 11, respectively. Stress strain plots for first and second compression cycles are labeled 301 and 302, respectively, in FIGS. 8-10 and are labeled 301a, 301b and 302a, 302b, respectively in FIG. 11 for the respective 5 and 10 film samples. Stress-strain regions 401 and 402 of the first and second compression cycles are indicated in FIGS. 8-10 and a stress-strain region 401 of the first compression cycle is indicated in FIG. 11. Examples 1-3 showed good recovery while Example 4 exhibited relatively poor recovery.

[0052] Terms such as “about” will be understood in the context in which they are used and described in the present description by one of ordinary skill in the art. If the use of “about” as applied to quantities expressing feature sizes, amounts, and physical properties is not otherwise clear to one of ordinary skill in the art in the context in which it is used and described in the present description, “about” will be understood to mean within 10 percent of the specified value. A quantity given as about a specified value can be precisely the specified value. For example, if it is not otherwise clear to one of ordinary skill in the art in the context in which it is used and described in the present description, a quantity having a value of about 1, means that the quantity has a value between 0.9 and 1. 1, and that the value could be 1.

[0053] Terms such as “substantially” will be understood in the context in which they are used and described in the present description by one of ordinary skill in the art. If the use of “substantially” with reference to a property or characteristic is not otherwise clear to one of ordinary skill in the art in the context in which it is used and described in the present description and when it would be clear to one of ordinary skill in the art what is meant by an opposite of that property or characteristic, the term “substantially” will be understood to mean that the property or characteristic is exhibited to a greater extent than the opposite of that property or characteristic is exhibited.

[0054] All references, patents, and patent applications referenced in the foregoing are hereby incorporated herein by reference in their entirety in a consistent manner. In the event of inconsistencies or contradictions between portions of the incorporated references and this application, the information in the preceding description shall control.

[0055] Descriptions for elements in figures should be understood to apply equally to corresponding elements in other figures, unless indicated otherwise. Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and / or equivalent implementations can be substituted for the specific embodiments shown and described without departing from the scope of the present disclosure. This application is intended to cover any adaptations, or variations, or combinations of the specific embodiments discussed herein. Therefore, it is intended that this disclosure be limited only by the claims and the equivalents thereof.

Claims

What is claimed is:

1. A cushioning film comprising a plurality of structures disposed on a base layer of the cushioning film, the structures arranged along a width of the cushioning film and extending along a length of the cushioning film, each structure comprising: opposing first and second side walls extending along a thickness direction of the cushioning film from the base layer to a curved top portion of the structure, the curved top portion being concave towards the base layer and extending between and connecting the first and second sidewalls, the second sidewall comprising first and second portions, the first portion between the base layer and the second portion, the second portion between the first portion and the curved top portion, wherein in a first cross-section orthogonal to the length of the cushioning film: the first and second sidewalls make respective first and second angles with a same first direction along the width of the cushioning film, the first angle being greater than 40 degrees and less than 90 degrees along substantially an entire length of the first sidewall, the second angle being in a range of 90 to 150 degrees along substantially an entire length of the first portion and being in a range of 70 to 89.5 degrees along substantially an entire length of the second portion, the length of the second portion being at least 2 times the length of the first portion, a total length of the first and second portions being at least 80% of a total length of the second sidewall.

2. The cushioning film of claim 1, wherein the structures have an average height H from the base layer to a top of the structures and are arranged at an average pitch P along the first direction, 7 H > P > H / 2.

3. The cushioning film of claim 1, wherein the structures have an average height H from the base layer to a top of the structures, an average of a maximum width of the structures along the first direction being W, 4 > H / W > 1.

4. The cushioning film of claim 2 or 3, wherein the average height H is in a range of 50 micrometers to 2 mm.

5. The cushioning film of claim 1, wherein for each structure of the plurality of structures, the second angle changes between the first and second portions of the second sidewall to define a hinge region, the first portion of the second sidewall extending from the base layer to the hinge region and the second portion of the second sidewall extending from the hinge region to the curved top portion.

6. The cushioning film of claim 1, wherein for each structure of the plurality of structures and for each distance above the base layer between the base layer and the curved top portion, the second angle is greater than the first angle.

7. The cushioning film of claim 1, wherein for each structure of the plurality of structures, a minimum value of the second angle is greater than a maximum value of the first angle.

8. The cushioning film of claim 1, wherein a plot of compressive stress on the cushioning film when the cushioning film is compressed along the thickness direction of the cushioning film versus percent compression of the cushioning film comprises a first portion of the plot extending at least from 15 percent compression to 35 percent compression, a largest compressive stress in the first portion of the plot being no greater than 2 times a smallest compressive stress in the first portion of the plot.

9. A multilayer stack comprising a plurality of films stacked on one another along a same thickness direction of the films, each film of the plurality of films being a cushioning film according to claim 1, wherein the films are oriented such that the structures of the films face a same direction.

10. An assembly comprising first and second electrochemical cells and the multilayer stack of claim 9 disposed therebetween.

11. An assembly comprising an electrochemical cell, a structural element, and the multilayer stack of claim 9 disposed therebetween.

12. A cushioning film comprising a plurality of structures disposed on a base layer of the cushioning film, the structures arranged along a width of the cushioning film and extending along a length of the cushioning film, the structures having an average height H from the base layer to a top of the structures and being arranged at an average pitch P along a first direction along the width of the cushioning film, an average of a maximum width of the structures along the first direction being W, 7 H > P > H / 2, 4 > H / W > 1, wherein in a first cross-section orthogonal to the length of the cushioning film, the structures comprise a curved top portion concave toward the base layer and are tilted toward the first direction such that when the cushioning film is compressed along a thickness direction of the cushioning film, the structures further tilt along the first direction, wherein a plot of compressive stress on the cushioning film versus percent compression of the cushioning film comprises a first portion extending at least from 15 percent compression to 35 percent compression, a largest compressive stress in the first portion being no greater than 2 times a smallest compressive stress in the first portion.

13. The cushioning film of claim 12, wherein the smallest compressive stress in the first portion is at least100 kPa.

14. The cushioning film of claim 12, when the cushioning film is further compressed along the thickness direction of the film, the structures curve while further tilting along the first direction so that the curved structures are concave toward the base layer.

15. The cushioning film of claim 12, wherein after the cushioning film is compressed a first time with a compressive force along the thickness direction to at least 35 percent compression and then the compressive force is removed, when the cushioning film is then compressed a second time along the thickness direction, a second plot of compressive stress on the cushioning film versus percent compression of the cushioning film comprises a second portion extending at least from 15 percent compression to 35 percent compression, a largest compressive stress in the second portion being no greater than 2 times a smallest compressive stress in the second portion.

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