Fluid pouch with inner microstructure

Disclosed is a pouch (also called a flexible container) for holding fluid, the pouch including: (a) a first polymeric sheet including a first inner body and a first outer surface, the first inner body including a first inner surface and inner microstructure extending from the first inner surface, the first inner body defining an aerial microstructure surface area density (AMSAD) between 5% and 15%; (b) a second polymeric sheet including a second inner surface and a second outer surface. The second polymeric sheet may be joined with the first polymeric sheet such that the first inner body and the second inner surface form an air-tight fluid chamber therebetween. The second polymeric sheet may lack microstructure extending from the second inner surface. The first inner surface, the first outer surface, the second inner surface, and the second outer surface may be smooth and non-recessed.

TECHNICAL FIELD

This application relates to pouches for storing fluids.

BACKGROUND

Sealed plastic pouches are used to store a range of liquids, fluids, or semi-fluids (referred to as “fluids”) such as syrup for soft drinks, laundry detergent, orange juice, paint, soap, glue etc. These sealed pouches may include a port. A user opens the port and connects a tube to the opened port (or if no port exists, then the user may puncture the pouch with the tube). The other end of the tube links to a pump. The pump extracts the fluid from the pouch and directs the fluid to a dispenser (e.g., a soda-fountain, a nozzle, etc.). A pump is not necessary. The fluid may be squeezed out of the pouch by air pressure on the exterior of the pouch or by gravity.

Pouches typically include a top flexible sheet joined with a bottom flexible sheet. Fluid occupies space between the top and bottom sheets. The pump and/or the port prevents ambient air from replacing pumped fluid. Thus, as the pump extracts fluid from the pouch, the top and bottom sheets wrinkle and the space between the top and bottom sheets shrinks.

Once the space between the top and bottom sheets has shrunk to a certain extent and a sufficient number of wrinkles have been introduced, the pump can no longer extract fluid from the pouch. The pouch is now obsolete. The user discards the obsolete pouch and attaches a fresh pouch. Fluid remaining in the obsolete pouch is wasted. Many existing pouches become obsolete with 20% or more of the original mass of fluid remaining.

Accordingly, there is a need for new pouches with properties that delay obsolescence until a greater amount of the original fluid has been extracted.

SUMMARY

Various embodiments of the present disclosure solve the above problems by providing a pouch for holding fluid, the pouch including: (a) a first polymeric sheet including a first inner body and a first outer surface, the first inner body including a first inner surface and inner microstructure extending from the first inner surface, the first inner body defining an aerial microstructure surface area density (AMSAD) between 1% and 15%; (b) a second polymeric sheet including a second inner surface and a second outer surface.

The second polymeric sheet may be joined with the first polymeric sheet such that the first inner body and the second inner surface form an air-tight fluid chamber therebetween. The second polymeric sheet may lack microstructure extending from the second inner surface. The first inner surface, the first outer surface, the second inner surface, and the second outer surface may be smooth and non-recessed.

Some embodiments of the disclosed pouch enable 99% mass extraction of stored fluid via some or all of the above-described techniques including extraction via a pump, via air pressure on the exterior of the pouch, or via gravity.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

In this application, the use of the disjunctive is intended to include the conjunctive. The use of definite or indefinite articles is not intended to indicate cardinality. In particular, a reference to “the” object or “a” and “an” object is intended to denote also one of a possible plurality of such objects. Further, the conjunction “or” may be used to convey features that are simultaneously present, as one option, and mutually exclusive alternatives as another option. In other words, the conjunction “or” should be understood to include “and/or” as one option and “either/or” as another option. The claims may include dimensions and numeric values. It should be appreciated that such dimensions and numeric values are approximate unless otherwise stated. Approximate includes a tolerance of ±10%.

FIGS. 1, 2, and 4are schematic top plan views of a pouch1(also called a flexible container) consistent with the present disclosure. Pouch1may be configured to intake, store, and expel a gas, liquid, fluid, or semi-fluid (referred to as “fluid”). Pouch1may include a first or top sheet2, a second or bottom sheet3, a port4, and microstructure11. As with all features disclosed herein, port4is optional. Pouch1can be polymeric, laminated, or coated. Pouch1can be organic (e.g., paper) with polymeric microstructure coated onto the organic material (i.e., the sheets). Any features discussed with reference to pouch1can be applied to a bag, sachet, or tote liner.

First or top sheet2may be heat sealed to second or bottom sheet3about an outer perimeter5of pouch1. Top sheet2and bottom sheet3may be rectangular or any other geometric shape (e.g., circular, oval-shaped, etc.). InFIGS. 1, 2 and 4, top sheet2and bottom sheet3are rectangular. Thus, outer perimeter5includes a right side51, a front side52, a left side53, and a back side54. Top sheet and bottom sheet3may have the same or different lengths, widths, and thicknesses. Pouch1can be made from a single sheet of material, folded onto itself and sealed along its outer edges. In this case, the single sheet could be thought of as including a top sheet2and a bottom sheet3. Pouch1can include 2, 4, or 6 sides/sheets. As such, outer perimeter5, instead of being an interface between top sheet2and bottom sheet3, may include separate sheets. For example, right side51, front side52, left side53, and back side54may all be separate individual sheets, each joined with top sheet2and bottom sheet3.

Port4may include a base41and a conduit42. Base41may have a greater outer diameter than conduit42. Port4may be connected to top sheet2, bottom sheet3, or both sheets.FIG. 1shows port4being connected to top sheet2.FIG. 2shows port4being connected to both of top sheet2and bottom sheet3.FIG. 4shows port4being connected to bottom sheet3. Port4may be connected to top and/or bottom sheets2,3in any suitable manner. As one example, a hole may be cut in top sheet2. An outer diameter of base41may be sealed, via heat treatment, to the portions of sheet2defining the hole. Although not shown, conduit42may include an on-off valve.

FIG. 3is a schematic cross sectional view taken along line3-3ofFIG. 1. As shown inFIG. 3, bottom sheet3may include microstructure11(also called micropattern11). Top sheet2may not include microstructure. Fluid F may occupy an inner void defined between top sheet2and bottom sheet3.

With continued reference toFIG. 3, top sheet2may include an inner surface21and an outer surface22. Bottom sheet3may include an inner surface31, an outer surface32, and microstructure11inwardly protruding from inner surface31. Inner surfaces21,31may be smooth. Similarly, outer surface22,32may be smooth. Back side54of perimeter51may be visible in cross section. A combination of inner surface31and microstructure11is referred to as a bottom inner body (not labeled). A combination of inner surface21and microstructure11is referred to as a top inner body (not labeled).

AlthoughFIG. 3shows microstructure11extending from inner surface31of bottom sheet3, it should be appreciated that microstructure11may extend alternatively or in addition from inner surface21of top sheet2. According a preferred embodiment, microstructure11only extends from one of top sheet2and bottom sheet3. It was surprisingly found that when only one of top sheet2and bottom sheet3include microstructure11, fluid extraction from pouch1is improved for reasons discussed below. Put differently, when only one of top sheet2and bottom sheet3include microstructure11, a greater amount of fluid in pouch1may be extracted before pouch1becomes obsolete.

As shown inFIG. 4, pouch1may include a top protective layer7and a bottom protective layer8. The top protective layer7may be a sheet with an inner surface71and an outer surface72. Similarly, the bottom protective layer8may be a sheet with an inner surface81and an outer surface82. Inner surface71of top protective layer7may be affixed to outer surface22of top sheet2via any suitable method (e.g., glue, heat treatment, etc.) to form a top interface1a. Similarly, inner surface81of bottom protective layer8may be affixed to outer surface32of bottom sheet3via the above methods to form a bottom interface1b. According to other embodiments (not shown), top protective layer7may be only affixed to top sheet2along perimeter5and bottom protective layer8may only be affixed to bottom sheet3along perimeter5. Pouch1may include any number of protective layers. Some of these layers may be rigid (e.g., cardboard). Some may be organic (e.g., cotton).

With reference toFIG. 5, a large amount of fluid has been pumped or extracted from pouch1. Because pouch1is sealed, ambient air cannot replace extracted fluid. As a result, top sheet2and bottom sheet3now include wrinkles13. Wrinkles13may include contact wrinkles13awhere top sheet2touches bottom sheet3. Wrinkles13may include non-contact wrinkles13b, where top sheet2and bottom sheet3are close together, but not in contact.

FIG. 6is a schematic cross sectional view taken along line6-6ofFIG. 4after a first amount of fluid (e.g., 90%) has been pumped from pouch1. As shown inFIG. 5, microstructure11discourages contact wrinkles13ain favor of non-contact wrinkles13b. More specifically, microstructure11serve as pillars separating top sheet2from bottom sheet3. Fluid flow paths12are defined in between adjacent microstructure11.

FIG. 7is a schematic cross sectional view taken along line6-6ofFIG. 4after a greater second amount of fluid (e.g, 92%) has been pumped from pouch1. Although some contact wrinkles13ahave formed, microstructure11has reduced their width. As a result, fluid flow paths12are defined between contact wrinkles13aand microstructure11.

The disclosed embodiments do not guarantee 100% fluid extraction from pouch1before obsolescence. The disclosed embodiments, however, enable a greater percentage of fluid to be extracted before obsolescence, compared with existing pouches. As an illustrative example, one embodiment of pouch1may enable a certain capacity pump to extract 99% of fluid (e.g., soft-drink syrup) before obsolescence while an existing pouch may only allow the same capacity pump to only extract 70% of the same fluid before obsolescence.

FIG. 8is a top plan view of inner surface31of bottom sheet3. Inner surface31includes microstructure11. As previously discussed, top sheet2may include microstructure11alternatively or in addition to bottom sheet3. As previously discussed, port4may be affixed to either top sheet2or bottom sheet3. It should thus be understood that any description related to microstructure11may apply to top sheet2and/or bottom sheet3. Similarly, any description of bottom sheet may additionally or alternatively apply to top sheet2.

With reference toFIG. 8, bottom sheet3may include a length L, a width W, and a thickness T. Microstructure11may be arranged in a array with rows and columns. According to preferred embodiments, the array of microstructure11may extend across all of inner surface31. Alternatively, and as shown inFIG. 12, the array of microstructure11may be confined to a central section31aof inner surface31.

Returning toFIG. 8, a first pitch X separates centers of adjacent microstructure11in the width dimension. A second pitch Y separates centers of adjacent microstructure11in the length dimension. First pitch X may be equal to second pitch Y. Inner surface31may include a smooth surface area, representing the total surface area of inner surface31without microstructure11and a microstructure surface area, representing the total surface area of microstructure11.

With reference toFIGS. 9 and 10, microstructure11may be semicircular with a radius R and diameter D=2*R. Microstructure11may form a contact angle A with respect to inner surface31. If the array extends across all of the inner body, the surface area of inner surface31is: W*L−(total number of microstructure11)*(pi*R2). The total number of microstructure11is approximately: W/X*L/Y. If first pitch X and second pitch Y are equal, then the total number of microstructure11is approximately: (W*L)/X2.

Bottom sheet3includes an aerial microstructure surface area density (AMSAD), which is: [(total surface area of microstructure, when viewed from a top plan perspective)/(total surface area of the inner body, when viewed from a top plan perspective)]. An example top plan perspective is shown inFIG. 8.

Thus, the AMSAD of bottom sheet3is approximately: [(R2*pi)*(the total number of microstructure11)]/[W*L]=[R2*pi*W*L]/[X2*W*L]=[R2*pi]/[X2]. It was surprisingly discovered that a smaller AMSAD improves fluid evacuation from pouch1. More specifically, an AMSAD between the range of 1% to 21% counter-intuitively performs better than an AMSAD of less than 1% or greater than 21%. Thus, according to preferred embodiments, bottom sheet3has an AMSAD of between 5% and 15% or 5% to 9%.

According to preferred embodiments, bottom sheet3has a thickness T of 0.057 to 0.1 mm, and microstructure11has a radius of 0.10 to 0.20 mm, a first pitch X of 0.8 mm to 1.2 mm, a second pitch Y of 0.8 mm to 1.2 mm and a contact angle A of 88 to 107 degrees. According to one of these preferred embodiments, microstructure11has a radius of 0.15 mm, a first pitch of 1 mm, a second pitch of 1 mm, and a contact angle of 90 degrees. According to the same embodiment, bottom sheet3has an AMSAD of approximately 7%. According to these preferred embodiments, the total volume of microstructure11is 5 to 21% of the total volume of bottom sheet3excluding microstructure11.

In some examples, a change in contact angle may alter the effectiveness of the microstructure. An experiment was run using four microstructures having different contact angles. Bags including microstructures with each respective contact angle were filled with liquid and evacuated. Then a percent evacuated based on weight before and after was measured for each bag/contact angle. The results are shown in Table 1. As can be seen, a relationship between contact angle and percent evacuated can be used to select an appropriate microstructure.

According to some embodiments, bottom sheet3and/or top sheet2have a thickness T of 12 microns to 600 microns or 2.5 mm.

Although AMSAD was described with reference to the length and width of bottom sheet3, it should be appreciated that in cases where microstructure11only occupies a central portion31aof bottom sheet3, the relevant length and width in the AMSAD calculation are the length and width of central portion31a(assuming central portion31ais rectangular, which need not be the case) or the multiple central portions31a(if multiple central portions31aexist).

The especially preferred embodiment of bottom sheet3was tested with a stable Newtonian syrup having a resting viscosity ranging from 20 centipoise to 65 centipoise at 21 degrees Celsius. A pouch1was formed from bottom sheet3, including microstructure11, and a smooth top sheet2. Both bottom sheet2and top sheet3had a length and width of 10.16 cm. Half of the volume of pouch1was filled with the stable Newtonian syrup. A rigid tube was inserted 2.54 cm into pouch1and the interface between pouch1and the rigid tube was sealed. Via the rigid tube, pouch1was subject to a vacuum of 84.66 kilo-Pascals. After sixty seconds of vacuum, only 0.70% of the original mass of the stable Newtonian syrup remained in pouch1. The same test was performed with a pouch without microstructure. After sixty seconds of vacuum, 37.97% of the original mass of the stable Newtonian syrup remained in the pouch.

It should thus be appreciated that disclosed embodiments of pouch1enable at least 95, 96, 97, 98, and 99% mass extraction of a stable Newtonian syrup having a resting viscosity ranging from 20 centipoise to 65 centipoise at 21 degrees Celsius when subject to a vacuum pressure of at least 84 kilo-Pascals for sixty seconds.

For improved structural integrity and fluid extraction performance, bottom sheet3may be manufactured via a hot re-flow molding process instead of an embossing process. The process may be a cured fluid process, where curing happens via heat, solvent loss, light, or other chemical reactions.

More specifically, and with reference toFIGS. 13 to 16, a mold100includes an inner perimeter wall105and a bottom walls103,104. Bottom walls103,104include a flat and smooth base wall103and interspersed smooth well walls104. The combination of inner perimeter wall105and bottom walls103,104defines an inner recessed area102. Inner recessed area102has a length and width equal to the desired length L and width W of bottom sheet3. Inner perimeter wall105has a thickness106. Well walls104define semi-circular recesses107having geometry identical to microstructure11. As with all features disclosed herein, inner perimeter wall105is unnecessary. No perimeter wall may be present and the film, post-curing, may be trimmed to the desired size.

With reference toFIG. 15, a mass of polymer106is placed in recessed area102, which may be box-shaped with a thickness107less than thickness106of inner perimeter wall105. Mass of polymer106is heated until mass of polymer106readily flows. To achieve this effect, mass of polymer106may be heated to a temperature slightly below its melting point (e.g., 80 to 99% of its melting point). With reference toFIG. 16, mass of polymer106flows into semi-circular recesses107. Optionally, a flat press may compress mass of polymer106to (a) encourage flow into semi-circular recesses107and (b) ensure that a top surface of mass of polymer106(which will eventually correspond to outer surface32) is flat and smooth. Alternatively or in addition to the press, each recess107may be in fluid communication with a small vacuum port or tube. When activated, a compressor, via the vacuum ports or tube, generates vacuum pressure in the recesses107, thus drawing the polymer106into the recesses107. When mass of polymer106cools, bottom sheet3is formed. Although polymer106has been used as an example, other materials may be used such as inks, coatings, adhesive, epoxies, or other curable materials.

Recessed area102need not cover the entire surface area of mold100. As stated above, pouch1may be formed from a folded unity sheet. When such a sheet is desired, less than 50% of the surface area of mold100may be a recessed area102and the remaining surface area of mold100may be simply flat (e.g., identical to bottom wall103).

Because bottom sheet3is formed via a molding process instead of via an embossing process (e.g., stretch embossing), bottom sheet3, including microstructure11, is integral. As a result, the non-microstructured portion of bottom sheet3(i.e., inner surface21) is less likely to flex or deform with respect to microstructure11, thus enabling bottom sheet3to resist wrinkling. If bottom sheet3were formed via embossing, bottom sheet3could include indentations or recesses along outer surface32corresponding to microstructure11. Due to these indentations or recesses, the structural integrity of bottom sheet3would be impaired and bottom sheet3would more readily wrinkle.

Embossing, however, may be necessary in some cases and thus presents a less-preferred, but still advantageous embodiment of manufacturing pouch1. During the embossing process, two rollers are used. The first roller is smooth and cylindrical. The second roller is cylindrical, but defines recesses107corresponding to microstructure (similar to mold100ofFIG. 14if mold100was arced as in a cylinder. Hot molten polymer or heated film106is placed into the nip between the embossed roller (which defines the microstructure) and the other smooth roller. The smooth roller applies pressure against the heated film or polymeric material106, which forces the same into the recesses107. Both rollers are rotated to draw unembossed polymer or film106toward the nip. After being deformed in the nip, the embossed film106bears tightly against the embossed roller. The embossed film106is continuously removed from the embossed roller such that no film is located on the portion of the embossed roller disposed directly before the nip. At least the embossed roller is chilled while rotating. This may be accomplished by circulating water or refrigerant through the embossed roller, returning the heated water or refrigerant from the embossed roller to a heat exchanger, cooling the heated water or refrigerant at the heat exchanger, and returning the cooled water or refrigerant to the embossed roller.

As an alternative to the above processes, an additive manufacturing system such as a 3D printer may be applied. A smooth and flat sheet may be placed before the 3D printer, which may then apply or deposit heated and at least semi-liquid material onto the smooth and flat sheet. Upon curing, the smooth and flat sheet is microstructured. Some 3D printers include curing features (e.g., UV lights or hot air blows) to accelerate curing.

FIGS. 17 to 34, and 39-41present alternative microstructure1701,1901,2101,2301,2501,2701,2901,3101, and3901. Any of the alternative microstructure may replace microstructure11. Put differently, (a) features of pouch1discussed above or below with reference to microstructure11may apply to any or all of the alternative microstructure, (b) the above-discussed AMSAD ranges may apply to any or all of the alternative microstructure, and (c) the above or below discussed method of manufacturing pouch1may apply to any or all of the alternative microstructure. AlthoughFIGS. 17 to 35refer to bottom sheet3, these Figures may, alternatively or in addition, apply to top sheet2.

With reference toFIGS. 17 and 18, microstructure1701includes a base1702and a top1703. Base1702is cylindrical. Top1703is conical. Top forms a tip angle1704of 130 degrees. A vertical height of microstructure (in the direction out of the page) is half the diameter of base1702. Microstructure1701are separated by equal first and second pitches.

With reference toFIGS. 19 and 20, microstructure1901are vertically swept ovals and are thus oval-shaped. Microstructure1901includes longitudinal microstructure1901aand transverse microstructure1901b, which have identical structure but perpendicular orientations such that major axes of longitudinal microstructure1901extend in a direction perpendicular to major axes of transverse microstructure1901b. Microstructure1901include a rectangular box middle1902and semicylindrical ends1903,1904. Semicylindrical ends1903,1904are each half a cylinder with identical radii of curvature.

Microstructure1901are arrayed as shown inFIG. 19. Each row of microstructure1901includes longitudinal microstructure1901aalternating with transverse microstructure1901b. Each column of microstructure1901includes longitudinal microstructure1901balternating with transverse microstructure1901b. Each transverse microstructure1901bis equally spaced from the four nearest longitudinal microstructure1901a(edge conditions excluded). Each longitudinal microstructure1901ais equidistant from the four nearest transverse microstructure1901b(edge conditions excluded).

With reference toFIGS. 21 and 22, microstructure2101are truncated cones. A diameter of a flat upper surface2102is equal to a height. Contact angle A (explained with reference toFIG. 10) is 135 degrees. Microstructure2101are separated by equal first and second pitches.

With reference toFIGS. 23 and 24, microstructure2301are cones with a vertical height2302between 25 and 28% of a base diameter2303. A tip angle2304is 120 degrees. The first and second pitches are equal.

With reference toFIGS. 25 and 26, generic microstructure2501, representing any microstructure described in this application, are shown. Paths2502intersect at a field2503, which is disposed directly below base41and/or conduit42of port4(i.e., a line perpendicular to the Z-axis inFIG. 1and extending through any portion of base41and/or conduit42intersects field2503). Field2503is shown as being rectangular (e.g., squared) but may be circular. In one example, field2503is positioned at an edge of the first inner surface as shown inFIGS. 25 and 26, aligned with the port4coupled to the outer surface. When pouch1includes paths2502and field2503, port4may be disposed in a center of top sheet2or bottom sheet3and paths2502may extend, at regular intervals, from the complete outer perimeter of field2503.

Advantageously, neither paths2502nor field2503are recessed into inner surface31. Put differently, paths2502and field2503are non-microstructured portions of inner surface31that exclude a portion of at least one microfeature of the inner microstructure as shown inFIGS. 25 and 26. Paths2502are straight and may radially extend at equal intervals from field2503.

Advantageously, neither paths2502nor field2503are recessed into inner surface31. Put differently, paths2502and field2503are non-microstructured portions of inner surface31. Paths2502are straight and may radially extend at equal intervals from field2503.

With reference toFIGS. 27 and 28, microstructure2701are cones with compressed bases. As such, corner microstructure2701ainclude two compressed base edges2702, side microstructure2701binclude three compressed base edges2702, and central microstructure2701cinclude four compressed base edges2702. Compressed base arcs2703are formed between consecutive compressed base edges. Each compressed base arc2703has a compressed radius of curvature. Arced diamonds2704with four arced sides are defined between four compressed base arcs2703. Arced diamonds2704are portions of inner surface31. A vertical height2705of microstructure2701is fifteen percent of the first pitch, which is equal to the second pitch.

With reference toFIGS. 29 and 30, microstructure2901include a cylindrical base2902and a semispherical tip2903. A maximum radius of semispherical tip2903is equal to a radius of cylindrical base2902. A vertical height of cylindrical base2902is equal to twice the radius of semispherical tip2903. The first pitch is equal to the second pitch, which are both more than five, ten, and fifteen times greater than the radius of spherical tip2903.

With reference toFIGS. 31 to 34, sinusoidal microstructure3101is conical and triangularly arrayed such that a group of three adjacent microstructure3101a,3101b,3101cdefine an equilateral triangle3106through their respective centers. Microstructure3101include sinusoidal peaks3102and are separated by sinusoidal valleys3103. Outer surfaces of adjacent microstructure define arced triangles3105having three arced sides. Arced triangles3105are portions of flat inner surface31.

With reference toFIGS. 39-41, microstructure3901is generally circular with protruding members on a top side. Microstructure3901include a main body3902, having protruding members3903. In some examples, a substrate on which microstructure3901is structures may include protruding members3903as well.

As shown inFIG. 35, bottom sheet3may include a plurality of different concentric microstructure3501,3502,3503, which may be circular, rectangular, etc. First or outer microstructure3501may be any of the above-discussed microstructure11,1701,1901,2101,2301,2501,2701,2901,3101. Second or intermediate microstructure3502may be any of the above-discussed microstructure11,1701,1901,2101,2301,2501,2701,2901,3101. Third or inner microstructure3503may be any of the above-discussed microstructure11,1701,1901,2101,2301,2501,2701,2901,3101. First, second, and third microstructure11are non-overlapping.

As shown inFIG. 36, top sheet2and bottom sheet3may both include microstructure, arranged in complementing arrays such that when top sheet2and bottom sheet3lie flat against each other (e.g., when pouch1is fully evacuated), microstructure of top sheet2does not contact microstructure of bottom sheet3. When top sheet2and bottom sheet3lie flat against each other, microstructure may span the entire surface area of pouch11or only a portion thereof. Manufacturing of complementary top and bottom sheets2,3may be accomplished by applying above-discussed manufacturing techniques to both top and bottom sheets2,3. The microstructure may be one or more of the above-discussed microstructure11,1701,1901,2101,2301,2501,2701,2901,3101,3901.

For example, outer area3601of bottom sheet3may be microstructured (with any of the above-discussed microstructure) while inner area3602is non-microstructured. At the same time, outer area3603of top sheet2may be non-microstructured, while inner area3604is microstructured (with any of the above-discussed microstructure). The outer area3601and inner area3604may have different microstructure shapes (e.g., any of the above discussed microstructure shapes), as well as densities (e.g., any of the above discussed microstructure dimensions, spacing, etc.) This arrangement of microstructured areas is only one example, and it should be appreciated that the opposite may be present instead (where only inner area3602of bottom sheet3is microstructured and only outer area3603of top sheet2is microstructured).FIG. 36shows the first inner surface31with an outer microstructured area3601that extends around the perimeter of the first inner surface31, and an inner rectangular non-microstructured area3602. The second inner surface21has an outer non-microstructured area3604that extends around the perimeter of the second inner surface21, and an inner rectangular microstructured area3604. The arrays are not limited to the rectangular shapes shown below and may be any suitable shape (e.g., circular). The arrays may include random or scattered placements microstructure such that within the microstructured area of the sheet, the locations of the microstructure do not observe any discernible pattern. A schematic of randomized microstructure placement is shown inFIG. 38.

As a similar example, only one of outer area3601and inner area3602of bottom sheet3includes microstructure11, and only one of outer area3603and inner area3604of top sheet2includes microstructure, bottom sheet3and top sheet2being arranged and/or configured to complement each other (as previously discussed, to prevent overlap between microstructure11of bottom sheet3with microstructure11of top sheet2).

Although the above examples show top and bottom sheets2,3only being segmented into two different areas (an inner or outer microstructured area and an outer or inner nonmicrostructured area), top and bottom sheets2,3may be segmented into any number of different areas (e.g., 3, 4, 5 different areas).

For example, with reference toFIG. 37, outer areas3701,3705of both top and bottom sheets2,3may be nonmicrostructured or only one of outer areas3701,3705may be microstructured. First intermediate area3702and inner area3704of bottom sheet3may be microstructured while second intermediate area3703is nonmicrostructured. Top sheet2may complement bottom sheet3. Thus, some or all of top sheet2may be nonmicrostructured. As one example, first intermediate area3706and inner area3708may be nonmicrostructured while second intermediate area3707is microstructured. Thus, pouch1is configured such that when bottom sheet3lies against top sheet2, microstructure will not overlap or contact.

A flexible container (e.g., a pouch) for holding fluid is thus disclosed. The flexible container may comprise, consistent essentially of, or consist of: (a) a first sheet defining a first inner body and a first outer surface, the first inner body defining a first inner surface and inner microstructure extending from the first inner surface, the first inner body defining an aerial microstructure surface area density (AMSAD) between 5% and 15%, the AMSAD being defined as a total surface area of the microstructure, when viewed from a top plan perspective, divided by a total surface area of the inner body, when viewed from a top plan perspective; (b) a second sheet defining a second inner surface and a second outer surface, the second sheet being joined with the first sheet such that the first inner body and the second inner surface at least partially define an air-tight fluid chamber therebetween, the second sheet lacking microstructure extending from the second inner surface. The first inner surface, the first outer surface, the second inner surface, and the second outer surface are smooth and non-recessed.

A method of manufacturing a fluid pouch (i.e., a flexible container) is thus disclosed, the method comprising: (a) producing a first polymeric sheet comprising a first inner body and a flat and smooth first outer surface, the first inner body comprising a flat and smooth first inner surface and semi-spherical microstructure, (b) heating a perimeter of the first polymeric sheet to join the perimeter of the first polymeric sheet with a second polymeric sheet, the second polymeric sheet comprising a flat and smooth second inner surface and a flat and smooth second outer surface.

The step of producing the first polymeric sheet may comprise: (i) placing a mass of polymeric material into a mold, the mold defining a plurality of semi-spherical recesses arranged in an array; (ii) heating the mass of polymeric material, in the mold, at least until the mass of polymeric material flows into the semi-spherical recesses; (iii) cooling the mass polymeric material and removing the cooled mass of polymeric material from the mold. During the step of heating the perimeter of the first polymeric sheet, the semi-spherical microstructure of the first polymeric sheet may face the second inner surface of the second polymeric sheet. The second polymeric sheet may be non-microstructured. The mold may not include side-walls and thus the cooled polymeric sheet may be trimmed to the desired shape.