PRIORITY

[0001] This application claims priority from U.S. Ser. No. 63/177,544 filed on April 21, 2021, the entire contents of which are incorporated herein by reference.

FIELD

[0002] This application relates to methods and systems for reducing the porosity proximate the surface of a paperboard substrate and, more particularly, to the use of Bronsted acids, such as zinc chloride, for reducing surface porosity of paperboard substrates.

BACKGROUND

[0003] Automated systems for manufacturing packaging containers and moving packaging containers typically rely on moving the packaging containers pneumatically. Challenges arise with paperboard and cellulose packaging containers due to the porosity of standard paperboard materials. If the porosity is too high, the suctioning strength may not be sufficient to properly adhere to and move the packaging container. If the porosity is too low, pneumatically adhering to the packaging containers may be challenging due to the lack of air flow through the packaging container material.

[0004] Accordingly, those skilled in the art continue with research and development efforts in the field of reducing porosity on paperboard surfaces.

SUMMARY

[0005] Disclosed are various methods for reducing a porosity of a surface of a paperboard substrate.

[0006] In one example, the disclosed method includes applying a solution including a Bronsted acid to the surface of the paperboard substrate. [0007] In another example, the disclosed method includes applying a solution including zinc chloride to the surface of the paperboard substrate.

[0008] In another example, the disclosed method includes steps of (1) applying a solution including a Bronsted acid to the surface of the paperboard substrate; and (2) subjecting the paperboard substrate to a) pressure and/or b) mild mechanical action (e.g., contact with a roll, press nip, etc.).

[0009] In yet another example, the disclosed method includes steps of (1) applying a solution including a Bronsted acid, such as zinc chloride, to the surface of the paperboard substrate; (2) heating the paperboard substrate; (3) subjecting the paperboard substrate to a) pressure and/or b) mild mechanical action (e.g., contact with a roll, press nip, etc.); and (4) rinsing the paperboard substrate. The step of heating the paperboard substrate can be performed before, during or after the step of applying the solution including the Bronsted acid to the surface of the paperboard substrate.

[0010] Also disclosed are paperboard substrates.

[0011] In one example, the disclosed paperboard substrate includes a first surface and a second surface opposed from the first surface. At least one of the first surface and the second surface includes a surface treatment with a solution having at least 60 percent by weight a Bronsted acid, such as zinc chloride.

[0012] Also disclosed are various systems for reducing a porosity of a surface of a paperboard substrate.

[0013] In one example, the disclosed system includes a first processing section. The first processing section includes a spraying apparatus configured to selectively spray a solution including a Bronsted acid, such as zinc chloride, on a surface of the paperboard substrate. The system further includes a second processing section. The second processing section includes a rinsing apparatus for removing the solution including the Bronsted acid from the surface of the paperboard substrate. BRIEF DE S CRIPTION OF THE DRAWINGS

[0014] Fig. 1 is flow chart depicting one example of the disclosed method for reducing a porosity of a surface of a paperboard substrate;

[0015] Fig. 2 is a cross-sectional view of a paperboard substrate of a paperboard substrate produced according to the method shown in Fig. 1;

[0016] Fig. 3 is a block diagram of a system for reducing a porosity of a surface of a paperboard substrate;

[0017] Fig. 4 is a schematic illustration of a paper making process into which the system of Fig. 3 may be incorporated; and

[0018] Fig. 5 is a micrograph depicting an example paperboard substrate having a denser, less porous portion achieved in accordance with the present disclosure.

DETAILED DE S CRIPTION

[0019] The following detailed description refers to the accompanying drawings, which illustrate specific examples of the disclosed methods and systems for reducing the porosity proximate the surface of a paperboard substrate. It will be understood that the disclosed examples are merely exemplary embodiments of the way in which certain aspects of the invention can be implemented and do not represent an exhaustive list of all of the ways the invention may be embodied. Other examples having different structures and operations do not depart from the scope of the present disclosure. Like reference numerals may refer to the same feature, element, or component in the different drawings. The figures are not necessarily to scale and some features may be exaggerated or minimized to show details of particular components. Throughout the present disclosure, any one of a plurality of items may be referred to individually as the item and a plurality of items may be referred to collectively as the items. Moreover, as used herein, a feature, element, component, or step preceded with the word “a” or “an” should be understood as not excluding a plurality of features, elements, components, or steps, unless such exclusion is explicitly recited. [0020] Illustrative, non-exhaustive examples, which may be, but are not necessarily, claimed, of the subject matter according to the present disclosure are provided below. Reference herein to “example” means that one or more feature, structure, element, component, characteristic, and/or operational step described in connection with the example is included in at least one aspect, embodiment, and/or implementation of the subject matter according to the present disclosure. Thus, the phrases “an example,” “another example,” “one or more examples,” and similar language throughout the present disclosure may, but do not necessarily, refer to the same example. Further, the subject matter characterizing any one example may, but does not necessarily, include the subject matter characterizing any other example. Moreover, the subject matter characterizing any one example may be, but is not necessarily, combined with the subject matter characterizing any other example.

[0021] Zinc chloride, and many Bronsted acids, are known to dissolve cellulose when applied at high concentrations. Dissolving cellulose is beneficial in reducing porosity of paperboard products. Thus, to reduce porosity of paperboard products, it is beneficial to subject paperboard product in concentrated solutions of zinc chloride or other Bronsted acids.

[0022] Exposing too much of a paperboard product in concentrated solutions of zinc chloride or other Bronsted acids may result in densification and brittleness of the product. Another disadvantage to current practices includes the inability to selectively treat portions of paperboard products.

[0023] The following disclosure is directed to a method 100, paperboard substrate 200, and system 400 for localized treatment of a paperboard substrate with a Bronsted acid to reduce the porosity proximate (at or near) the surface of the paperboard substrate. The disclosed method may also advantageously increase surface smoothness and maintain flexibility of the untreated portion of the paperboard substrate. The method 100 further improves the Gurley porosity of a paperboard substrate from approximately 5-15 s/lOOcc to, for example, approximately 25-50 s/lOOcc.

[0024] Referring to Fig. 1, disclosed is a method 100 for reducing a porosity of a surface 210 of a paperboard substrate 200. The method 100 includes applying 110 a solution 300 to the surface 210 of the paperboard substrate 200. The solution 300 includes a Bronsted acid. In one specific, non-limiting example, the Bronsted acid is zinc chloride. In another specific, non limiting example, the Bronsted acid is a combination of Bronsted acids that includes zinc chloride.

[0025] The solution 300 includes water and a concentration of at least 50 percent by weight of the Bronsted acid. In one example, the concentration of the Bronsted acid in the solution 300 is at least 55 percent by weight. In another example, the concentration of the Bronsted acid in the solution 300 is at least 60 percent by weight. In another example, the concentration of the Bronsted acid in the solution 300 is at least 65 percent by weight. In another example, the concentration of the Bronsted acid in the solution 300 is at least 70 percent by weight. In yet another example, the solution 300 is essentially 100 percent Bronsted acid. It is contemplated that the solution 300 includes other additives, such as surfactant, defoaming agents, or any other additive.

[0026] In one example, the applying 110 the solution 300 to the surface 210 of the paperboard substrate 200 comprises spraying the solution 300 on the surface 210, see FIG. 2, of the paperboard substrate 200. The applying 110 may be achieved with a spraying apparatus 405, see Fig. 3. In another example, the applying 110 the solution 300 to the surface 210 of the paperboard substrate 200 comprises rolling the solution 300 on the surface 210. In yet another example, the applying 110 the solution 300 to the surface 210 of the paperboard substrate 200 comprises brushing the solution 300 on the surface 210. In another example, the solution 300 is printed via a flexo tint sleeve or selectively applied to specific regions of the paperboard substrate 200. Other means of applying 110 the solution 300 to the surface 210 may be implemented as well.

[0027] The applying 110 may be performed such that the solution 300 is localized proximate (at or near) the surface 210 of the paperboard substrate 200. In one example, the applying 110 is performed such that the solution 300 penetrates at most 80 percent of the total cross-sectional thickness T (Fig. 2) of the paperboard substrate 200. In another example, the applying 110 is performed such that the solution 300 penetrates at most 75 percent of the total cross-sectional thickness T of the paperboard substrate 200. In another example, the applying 110 is performed such that the solution 300 penetrates at most 60 percent of the total cross-sectional thickness T of the paperboard substrate 200. In another example, the applying 110 is performed such that the solution 300 penetrates at most 50 percent of the total cross-sectional thickness T of the paperboard substrate 200. In another example, the applying 110 is performed such that the solution 300 penetrates at most 40 percent of the total cross-sectional thickness T of the paperboard substrate 200. In another example, the applying 110 is performed such that the solution 300 penetrates at most 30 percent of the total cross-sectional thickness T of the paperboard substrate 200. In another example, the applying 110 is performed such that the solution 300 penetrates at most 20 percent of the total cross-sectional thickness T of the paperboard substrate 200. In another example, the applying 110 is performed such that the solution 300 penetrates at most 10 percent of the total cross-sectional thickness T of the paperboard substrate 200.

[0028] Still referring to Fig. 1, the method 100 may further include heating 120 the surface 210 of the paperboard substrate 200. The heating 120 step, while optional, may be achieved with a heater 415, see Fig. 3, and may be particularly advantageous when the paperboard substrate 200 is cold. The heating 120 is configured to promptly remove excess water from the solution 300 to yield a concentration of at least 60 percent by weight of Bronsted acid on the surface 210 of the paperboard substrate 200. The resulting concentration of Bronsted acid on the surface 210 is configured to soften cellulose fibers on the surface 210 such that any holes located between the cellulose fibers are effectively plugged, therefore reducing porosity on the surface 210 of the paperboard substrate 200. Furthermore, the optional heating 120 step may raise the temperature of the paperboard substrate 200 to a temperature at which the Bronsted acid more quickly dissolves cellulose.

[0029] Referring to Fig. 1, the method 100 further includes subjecting 130 the paperboard substrate 200 to pressure. Subjecting 130 the paperboard substrate 200 to pressure further improves the reduction in porosity. In one example, the subjecting 130 comprises passing the paperboard substrate 200 through two rollers that define a nip, such as a low intensity nip. A drive roll 430, for example, may include two rollers configured to form a low intensity nip. The subjecting 130 may further include subjecting to mild mechanical action, such as contact with a roll, press nip, etc. [0030] Still referring to Fig. 1, the 100 further includes rinsing 140 the surface 210 of the paperboard substrate 200 with water. Rinsing 140 the surface 210 with the paperboard substrate 200 with water removes the solution 300 and thus stops dissolution of cellulose fibers, therefore maintaining the solution 300 localized proximate the surface 210. The rinsing 140 is achieved with a rinsing apparatus 425, see Fig. 3. In one example, the rinsing 140 includes spraying water on the surface 210 of the paperboard substrate 200. In another example, the rinsing 140 includes passing the paperboard substrate 200 over a water spray bar 440. In another example, the rinsing 140 includes passing the paperboard substrate 200 over a wet calendar 441. In yet another example, the rinsing 140 includes passing the paperboard substrate 200 over a size press 443.

[0031] The method 100 may be performed during the manufacturing of paperboard substrate 200 on a paper making machine. In one example, a paperboard substrate 200 may be manufactured by a paper making process 500 by discharging a fiber slurry from a head box 510 onto a Fourdrinier 520 to form a web. The web may pass through one or more wet presses 525 and, optionally, through one or more dryers. The method 100 includes applying a Bronsted acid, such as zinc chloride, at a concentration of at least 60 percent by weight on a surface of the web, or paperboard substrate, for example, a drying sheet, on the paper making machine.

Alternatively, a relatively lower concentration of a Bronsted acid solution may be used in conjunction with an evaporation step such that it results in a concentration of at least 60 percent by weight on the surface of the paperboard substrate 200 after the water has evaporated.

[0032] One prior, commercially accepted method for generating porosity is through added refining. While it is useful to reduce porosity, thus yielding desirable Gurley porosity and less air flow per a measured amount of time, it can disadvantageously increase water retention values. An increase in fourdrinier drainage time ultimately slows down production to accommodate any refining side effects. Refining further reduces sheet bulk for paperboard sold on caliper point. Contrarily, the disclosed method 100 to achieve porosity in a desired working range avoids refining "side effects" of prior methods and targets the surface or % based on penetration depth.

[0033] The method 100 may be performed during the manufacturing of paperboard substrate 200 outside of a paper making machine. In one example, the Bronsted acid is applied outside of a paper making machine, including on an off-line coater / applicator, printer etc. Printers have inking stations that are designed to apply liquid, such as a B runs ted acid solution, followed by rollers that provide mechanical action (touch, pressure etc.), a wash water application, and finally a heating mechanism for drying the paperboard substrate 200. In another example, the B runs ted acid solution is applied just ahead of a breaker stack, such that a nip can uniformly drive the Bronsted acid solution into the surface from a spray mechanism. Right after the nip, the surface can be sprayed with a water washing spray to remove any excess Bronsted acid solution prior to passing through remaining dryer sections. In yet another example, the Bronsted acid solution is applied as part of a water nip gradient-based hot calendar stack promoting surface densification.

[0034] The resulting surface 210 of the paperboard substrate 200 exhibits softened fibers that result in localized fiber densification, effectively plugging any holes located between the fibers. To further improve the plugging of any holes located within the fibers of the surface, the method 100 may further include passing the web through a calendar and applying low pressure on the web, or paperboard substrate 200, between two rolls in contact with each other. Once the holes between the fibers are plugged, the surface 210 of the paperboard substrate 200 may then be rinsed with water to remove essentially all, or at least some of the Bronsted acid, to stop dissolving the cellulose fibers.

[0035] The selective, localized treatment disclosed herein differs from prior methods of treating more than the surface 210, or even the whole sheet of the paperboard substrate 200. Treating the whole sheet, as opposed to selective treatment proximate the surface 210 of the sheet, results in sheet densification and brittleness. The disclosed method 100 selectively treats the surface 210 such that the rest of the sheet maintains a low density and does not become brittle. The disclosed method 100 further achieves a Gurley porosity of approximately 25 s/lOOcc to approximately 30 s/lOOcc for the paperboard substrate. The resulting paperboard substrate may be useful, for example, in food packaging and liner board for corrugated box construction.

[0036] Referring to FIG. 2, disclosed is a paperboard substrate 200. Various cellulosic substrates may be used as the disclosed paperboard substrate 200 without departing from the scope of the present disclosure. Examples of appropriate materials useful as the paperboard substrate 200 include, but are not limited to, corrugated medium, liner board, solid bleached sulfate (SBS), unbleached kraft, and folding boxboard (FBB). In one example, the paperboard substrate 200 is packaging for food. In another example, the paperboard substrate 200 is linerboard for corrugated box construction.

[0037] The paperboard substrate 200 may have an uncoated basis weight of at least about 40 pounds per 3000 ft ² . In one example, the paperboard substrate 200 may have an uncoated basis weight ranging from about 40 pounds per 3000 ft ² to about 300 pounds per 3000 ft ² . In another example, the paperboard substrate 2002 may have an uncoated basis weight ranging from about 85 pounds per 3000 ft ² to about 300 pounds per 3000 ft ² . In another example, the paperboard substrate 200 may have an uncoated basis weight ranging from about 85 pounds per 3000 ft ² to about 250 pounds per 3000 ft ² . In yet another example, the paperboard substrate 200 may have an uncoated basis weight ranging from about 100 pounds per 3000 ft ² to about 250 pounds per 3000 ft ² .

[0038] Furthermore, the paperboard substrate 200 may have a caliper (thickness) ranging, for example, from about 4 points to about 30 points (0.004 inch to 0.030 inch). In one example, the caliper range is from about 8 points to about 16 points. In another example, the caliper range is from about 10 points to about 13 points.

[0039] Still referring to Fig. 2, paperboard substrate 200 has a first surface 212 and an opposing second surface 214. A midsection 216 is disposed between the first surface 212 and the second surface 214. At least one of the first surface 212 and the second surface 214 includes a surface treatment 310 of a solution 300 having at least 60 percent by weight a Bronsted acid. In one example, the Bronsted acid is zinc chloride. The surface treatment 310 may include spraying 115 the solution 300 onto either the first surface 212 or the second surface 214 of the paperboard substrate 200.

[0040] As illustrated in Fig. 2, the surface treatment 310 yields a denser, less porous portion 215 of the paperboard substrate 200 proximate the surface 210 of the paperboard substrate 200. The denser, less porous portion 215 of the paperboard substrate 200 has a cross-sectional thickness t that is substantially less than the total cross-sectional thickness T of the paperboard substrate 200. In one example, the cross-sectional thickness t of the denser, less porous portion 215 of the paperboard substrate 200 is at most 80 percent of the total cross-sectional thickness T of the paperboard substrate 200. In another example, the cross-sectional thickness t of the denser, less porous portion 215 of the paperboard substrate 200 is at most 75 percent of the total cross- sectional thickness T of the paperboard substrate 200. In another example, the cross-sectional thickness t of the denser, less porous portion 215 of the paperboard substrate 200 is at most 60 percent of the total cross-sectional thickness T of the paperboard substrate 200. In another example, the cross-sectional thickness t of the denser, less porous portion 215 of the paperboard substrate 200 is at most 50 percent of the total cross-sectional thickness T of the paperboard substrate 200. In another example, the cross-sectional thickness t of the denser, less porous portion 215 of the paperboard substrate 200 is at most 40 percent of the total cross-sectional thickness T of the paperboard substrate 200. In another example, the cross-sectional thickness t of the denser, less porous portion 215 of the paperboard substrate 200 is at most 30 percent of the total cross-sectional thickness T of the paperboard substrate 200. In another example, the cross- sectional thickness t of the denser, less porous portion 215 of the paperboard substrate 200 is at most 20 percent of the total cross-sectional thickness T of the paperboard substrate 200. In another example, the cross-sectional thickness t of the denser, less porous portion 215 of the paperboard substrate 200 is at most 10 percent of the total cross-sectional thickness T of the paperboard substrate 200.

[0041] Prior to receiving the surface treatment 310, the paperboard substrate 200 exhibits a Gurley porosity of approximately 10 s/lOOcc to approximately 15 s/lOOcc. After receiving the surface treatment 310, the resulting Gurley porosity of the paperboard substrate 200 is approximately 20 s/lOOcc to approximately 40 s/lOOcc. In another example, the resulting Gurley porosity of the paperboard substrate 200 is approximately 25 s/lOOcc to approximately 35 s/lOOcc. In yet another example, the resulting Gurley porosity of the paperboard substrate 200 is approximately 25 s/lOOcc to approximately 30 s/lOOcc.

[0042] Referring to Fig. 3, disclosed is a system 400 for reducing a porosity of a surface of a paperboard substrate. The system 400 may be incorporated into a paper making process 500, as shown in Fig. 4. The system 400 includes a first processing section 410. In one example, the first processing section 410 is a dryer section of the system 400. The first processing section 410 includes an application apparatus 407. In one example, the application apparatus 407 comprises a spraying apparatus 405. The spraying apparatus 405 is configured to selectively spray a solution 300 on a surface 210 of the paperboard substrate 200. [0043] The solution 300 includes water and a concentration of at least 50 percent by weight of the Bronsted acid. In one example, the concentration of the Bronsted acid in the solution (300) is at least 55 percent by weight. In another example, the concentration of the Bronsted acid in the solution 300 is at least 60 percent by weight. In another example, the concentration of the Bronsted acid in the solution 300 is at least 65 percent by weight. In yet another example, the concentration of the Bronsted acid in the solution 300 is at least 70 percent by weight.

[0044] Referring to Fig. 3, the first processing section 410 may further include a heater 415. The heater 415 is configured to heat the paperboard substrate 200, if needed, such that it flashes the water out of the surface 210, leaving a concentrated Bronsted acid on the surface 210 of the paperboard substrate 200.

[0045] Still referring to Fig. 3, the first processing section 410 further comprises a drive roll 430. The drive roll 430 may include two rollers that are configured to receive the paperboard substrate 200 such that the paperboard substrate 200 passes through a low intensity nip resulting from the two rollers contacting and pressing against the first surface 212 and opposing second surface 214 of the paperboard substrate 200.

[0046] Referring to Fig. 3, the system 400 includes a second processing section 420. The second processing section 420 comprises a rinsing apparatus 425. The rinsing apparatus 425 is configured to rinse the surface 210 of the paperboard substrate 200. In one example, the rinsing apparatus 425 comprises a water spray bar 440. In another example, the rinsing apparatus 425 comprises a wet calendar 441. In yet another example, the rinsing apparatus 425 comprises a size press 443. The second processing section 420 may be a drying section having a heater 415 such that it is configured to further dry the paperboard substrate 200.

EXAMPLE

[0047] A paperboard substrate having a denser, less porous portion localized proximate one surface of the paperboard substrate was prepared in accordance with the present disclosure. Specifically, a paperboard substrate was prepared using an aqueous zinc chloride solution (62 percent by weight zinc chloride (ZnCb) in water (FhO)). The aqueous zinc chloride solution was applied to one surface of a 13 point uncoated solid bleached sulfate (SBS) paperboard having a basis weight of 160 pounds per 3000 square feet. The application of the aqueous zinc chloride solution was performed using a paint brush and occurred at room temperature under atmospheric conditions. Promptly after application of the aqueous zinc chloride solution, the sample was passed through a standard couch roll (TAPPI standard T205), which applied pressure to the sample. After the couch roll, the sample was rinsed with water to remove the aqueous zinc chloride solution. Then, the sample was allowed to dry.

[0048] The result is shown in Fig. 5. As can be seen, a denser, less porous portion was formed proximate one (the upper in Fig. 5) surface of the paperboard substrate. The cross-sectional thickness t of the denser, less porous portion of the paperboard substrate is about 30 percent of the total cross-sectional thickness T of the paperboard substrate. The sample exhibited a Gurley porosity between about 25 and 50 s/lOOcc.

[0049] Although various examples of the disclosed methods and systems for reducing the porosity proximate the surface of a paperboard substrate have been shown and described, modifications may occur to those skilled in the art upon reading the specification. The present application includes such modifications and is limited only by the scope of the claims.